EXHAUST GAS PURIFICATION APPARATUS FOR AN INTERNAL COMBUSTION ENGINE

Abstract

First processing and second processing are carried out, wherein in the first processing, the electric power to be supplied to the heat generation element is set to a first electric power in a first period of time such that a temperature inside the heat generation element falls within an allowable temperature range, and in the second processing, at least one of setting the electric power to be supplied to said heat generation element from said power supply to a second electric power smaller than said first electric power, and/or setting the electric power to be supplied to said heat generation element from said power supply to zero, is performed in a second period of time such that the temperature difference inside the heat generation element falls within an allowable temperature difference range.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No, 2016-238483 filed on Dec. 8, 2016 the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to an exhaust gas purification apparatus for an internal combustion engine.

BACKGROUND ART

In the past, it has been known that an electrically heated catalyst is provided in which a catalyst is heated by electrical energization, and that activation of the catalyst is attained by electrically energizing the electrically heated catalyst before starting of an internal combustion engine. Then, there has also been known a technique in which an energizing period of time required of the electrically heated catalyst is calculated based on the temperature of the electrically heated catalyst detected before the starting of the internal combustion engine, and when the energizing period of time thus calculated has elapsed from the point in time of starting the electrical energization of the electrically heated catalyst, the electrical energization thereof is stopped (for example, refer to patent literature 1).

CITATION LIST

Patent Literature

Patent Literature 1: Japanese patent application laid-open No. H05-321645

Patent Literature 2: Japanese patent laid-open publication No. 2014-084759

Patent Literature 3: Japanese patent laid-open publication No. 2012-215145

SUMMARY

Technical Problem

Here, when an amount of electric energy to be supplied is the same, a mean temperature of the electrically heated catalyst will be substantially the same, even if the energizing period of time and the electric power to be supplied vary. Accordingly, the mean temperature of the electrically heated catalyst becomes a temperature according to the amount of electric energy supplied. However, when the electrically heated catalyst is electrically energized, i.e., when an electric current is supplied to the electrically heated catalyst, it passes through those locations in the electrically heated catalyst in which the electric resistance is small, such that heat is generated in the locations where the electric current has passed. For this reason, in locations where the electric resistance is large and the electric current is hard to pass through, heat is hard to be generated. Accordingly, when the electric resistance in the catalyst is not uniform, the temperature inside the electrically heated catalyst becomes nonuniform. As a result, even if an amount of electric energy is supplied with which it is assumed that the mean temperature of the electrically heated catalyst will reach an activation temperature of the catalyst, a part of the catalyst may not reach its activation temperature. In that case, there is a fear that the exhaust gas purifying ability of the electrically heated catalyst as a whole may not increase to an expected level.

For example, by making small the electric power to be supplied to the electrically heated catalyst, a difference between a temperature rise by the generation of heat in the locations where the electric resistance is small, and a temperature rise in the locations where the electric resistance is large by the transfer of heat from the locations where the electric resistance is small to the locations where the electric resistance is large becomes small, as a result of which the temperature difference inside the electrically heated catalyst becomes small. However, if the electric power to be supplied to the electrically heated catalyst is made small, the temperature rise of the electrically heated catalyst as a whole will take a longer period of time. In cases where the internal combustion engine should be started quickly, it is preferable to raise the temperature of the entire electrically heated catalyst quickly.

On the other hand, if the temperature in locations where the temperature is low is intended to be raised by increasing the amount of electric energy to be supplied to the electrically heated catalyst, the temperature in the locations where the electric resistance is small will become higher than necessary, so the electric power will be supplied uselessly. Moreover, there will also be a fear that in the locations where the electric resistance is small, the temperature becomes too high, thus causing thermal degradation due to overheating. In addition, in the electrically heated catalyst in which SiC is used as a base material, for example, the higher the temperature, the smaller the electric resistance becomes, and hence, even if the electric power or electric energy is increased, it becomes further easy for the electric current to flow through the locations where the electric resistance is small and the electric current is apt to flow at the beginning. That is, the electric current flows through the high temperature locations, so the temperature there further goes up, but instead, in the low temperature locations, the electric current remains hard to flow, so the temperature becomes hard to go up. In this manner, the temperature difference inside the electrically heated catalyst is enlarged with the lapse of time.

The present disclosure has been made in view of the problems as mentioned above, and the object of the disclosure is to enhance the purification ability of an electrically heated catalyst as a whole, by making small a temperature difference inside the electrically heated catalyst at the time of starting an internal combustion engine after a required amount of electric energy has been supplied to the electrically heated catalyst.

Solution to Problem

In order to solve the above-mentioned problem, according to the present disclosure, there is provided an exhaust gas purification apparatus for an internal combustion engine comprising: an electrically heated catalyst that includes a heat generation element arranged in an exhaust passage of the internal combustion engine for generating heat by receiving supply of electric power, and a catalyst supported by said heat generation element; a power supply that supplies electric power to said heat generation element; and a controller configured to adjust the electric power to be supplied to said heat generation element from said power supply; wherein in a first period of time and a second period of time in which said internal combustion engine is stopped and which are before starting said internal combustion engine, said second period of time being after said first period of time, said controller is configured to supply electric power such that a total amount of electric energy to be supplied to said heat generation element from said power supply becomes a required amount of electric energy; and said controller is further configured to carry out first processing, in which the electric power to be supplied to said heat generation element from said power supply is set to a first electric power in said first period of time such that a temperature inside said heat generation element falls within an allowable temperature range, and second processing, in which at least one of setting the electric power to be supplied to said heat generation element from said power supply to a second electric power smaller than said first electric power, and/or setting the electric power to be supplied to said heat generation element from said power supply to zero, is performed in said second period of time such that a difference in temperature inside said heat generation element falls within an allowable temperature difference range.

The first processing can be said to be as processing for quickly raising a mean temperature of the electrically heated catalyst. The first electric power and the first period of time are set in such a manner that the mean temperature of the electrically heated catalyst can be raised quickly, and at the same time, the electrically heated catalyst can not be overheated in a portion of the electrically heated catalyst where the temperature thereof becomes the highest. Here, note that the allowable temperature range may also be a range in which the electrically heated catalyst is not overheated in its portion where the temperature is the highest (e.g., a range in which thermal degradation does not occur in the catalyst). When the temperature inside the electrically heated catalyst is within the allowable temperature range, the mean temperature of the electrically heated catalyst can be raised more quickly as the electric power is made larger. That is, if a large electric power is supplied for a long period of time, the electrically heated catalyst may be overheated. On the other hand, if the first electric power is too small, it will take a long period of time to raise the temperature of the electrically heated catalyst. Thus, the first electric power and the first period of time are appropriately set in consideration of these facts.

The second processing can be said to be as processing for diminishing the temperature difference inside the electrically heated catalyst, or processing for suppressing an enlargement of the temperature difference inside the electrically heated catalyst. That is, the second period of time is a period of time until the temperature difference inside the electrically heated catalyst falls into the allowable temperature difference range. This allowable temperature difference range may be set such that the purification rate of the exhaust gas in the electrically heated catalyst falls within an allowable range. Here, note that in cases where electric power is supplied in the second period of time, the electric power to be supplied may be set so as to diminish the temperature difference inside the electrically heated catalyst more than at the end of the first period of time, or may be set so as to suppress the temperature difference inside the electrically heated catalyst from being enlarged from the end of the first period of time.

Here, the mean temperature of the electrically heated catalyst can be quickly raised by supplying the first electric power, which is a relatively large electric power, in the first period of time. However, when the relatively large first electric power is supplied to the electrically heated catalyst, the temperature difference inside the electrically heated catalyst is enlarged. On the other hand, in the second period of time, by supplying a relatively small second electric power, or by supplying no electric power, it is possible to suppress the temperature difference inside the electrically heated catalyst from being enlarged. That is, the second electric power is smaller than the first electric power, and so, when the second electric power is supplied, it is possible to decrease the amount of heat generation in the portion of the electrically heated catalyst where the electric resistance is small. On the other hand, in cases where the electric power to be supplied is set to 0 in the second period of time, the generation of heat does not occur inside the electrically heated catalyst. Then, because heat is transmitted from locations where the temperature inside the electrically heated catalyst is high to locations where the temperature is low, it is possible to suppress the temperature difference inside the electrically heated catalyst from being enlarged. Here, note that the required amount of electric energy may also be an amount of electric energy which is required to raise the mean temperature of the electrically heated catalyst up to the activation temperature of the catalyst.

In addition, in the present disclosure, said controller can set the electric power to be supplied to said heat generation element from said power supply to 0 in a stop period of time before supply of the second electric power, which is included in said second period of time, and can also set the electric power to be supplied to said heat generation element from said power supply to said second electric power in a second electric power supply period of time, which is included in said second period of time and which is after said stop period of time before supply of the second electric power.

Thus, by providing, after the first period of time, a period of time in which electric power is not supplied to the electrically heated catalyst, the amount of heat transfer from locations where the temperature is high to locations where the temperature is low in the electrically heated catalyst can be made to increase without raising the mean temperature of the electrically heated catalyst. Accordingly, the supply of the second electric power can be started in a state where the temperature difference inside the electrically heated catalyst has been diminished. For that reason, it is possible to suppress the temperature difference inside the electrically heated catalyst from being enlarged, in a more reliable manner.

Moreover, in the present disclosure, said controller can set the electric power to be supplied to said heat generation element from said power supply to said second electric power in a second electric power supply period of time which is included in said second period of time, and can also set the electric power to be supplied to said heat generation element from said power supply to 0 in a stop period of time after the second electric power supply period of time, which is included in said second period of time and which is after said second electric power supply period of time.

Even if there are locations in which the activation temperature has not been reached at the time when the supply of the first electric power and the second electric power is terminated, heat can be transferred from the locations where the temperature is high to the locations where the temperature is low, by providing a period of time in which electric power is not supplied until a start point in time of starting of the internal combustion engine. Accordingly, the temperature of the locations where the temperature is low can be raised, even if electric power is not supplied after the supply of the second electric power is terminated. That is, the temperature of the locations, in which the activation temperature has not been reached at the time when the supply of the second electric power is terminated, can be raised up to the activation temperature. Thus, the temperature difference inside the electrically heated catalyst can be diminished, after the point in time at which the supply of the second electric power has been terminated and before the start point in time of starting of the internal combustion engine.

Further, in the present disclosure, said controller can set said first electric power, said first period of time, said second electric power and said second period of time in such a manner that the amount of electric energy at an end point in time of said second period of time becomes the required amount of electric energy, and can start said internal combustion engine at a point in time at which said second period of time expires.

The amount of electric energy in the first period of time is decided by the length of the first period of time, and the magnitude of the first electric power. Also, the amount of electric energy in the second period of time is decided by the length of a period of time in which electric power is supplied during the first period of time, and the magnitude of the second electric power. If a sum total of the amount of electric energy in the first period of time and the amount of electric energy in the second period of time becomes the required amount of electric energy, the mean temperature inside the electrically heated catalyst will become the activation temperature of the catalyst, for example. Then, at the point in time at which the second period of time expires, the temperature difference inside the electrically heated catalyst becomes small, and hence, if the internal combustion engine is started at the point in time at which the second period of time expires, the exhaust gas can be purified in a suitable manner.

Advantageous Effects

According to the present disclosure, the purification ability of an electrically heated catalyst as a whole can be enhanced, by making small a temperature difference inside the electrically heated catalyst at the time of starting an internal combustion engine after a required amount of electric energy has been supplied to the electrically heated catalyst.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing the schematic construction of a hybrid vehicle according to embodiments of the present disclosure.

FIG. 2 is a time chart showing the changes over time of electric energy and electric power supplied to an electrically heated catalyst in temperature rise control according to a first embodiment of the present disclosure.

FIG. 3 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst in the case where the electric power to be supplied until it reaches a required amount of electric energy is set constant at 3 kW.

FIG. 4 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst in the case where the electric power to be supplied until it reaches the required amount of electric energy is initially set constant at 4 kW and is thereafter set constant at 2 kW.

FIG. 5 is a view showing the temperature distribution of the electrically heated catalyst after the end of electrical energization in the case where the electric power is set constant at 2 kW, and the required amount of electric energy is set to 120 kJ.

FIG. 6 is a view showing the temperature distribution of the electrically heated catalyst after the end of electrical energization in the case where the electric power is set constant at 3 kW, and the required amount of electric energy is set to 120 kJ.

FIG. 7 is a view showing the temperature distribution of the electrically heated catalyst after the end of electrical energization in the case where the electric power is set constant at 4 kW, and the required amount of electric energy is set to 120 kJ.

FIG. 8 is a view showing the temperature distribution of the electrically heated catalyst after the end of electrical energization in the case where the electric power is set constant at 5 kW, and the required amount of electric energy is set to 120 kJ.

FIG. 9 is a view in which the temperature distributions of FIG. 5 through FIG. 8 are summarized.

FIG. 10 is a view showing the temperature distribution of the electrically heated catalyst in the case where the electric power is initially set constant at 4 kW and supplied for 20 seconds, and thereafter is set to 2 kW and supplied for another 20 seconds.

FIG. 11 is a view similar to FIG. 9, showing the temperature distribution related to FIG. 10.

FIG. 12 is a flow chart showing a flow for temperature rise control according to the first embodiment.

FIG. 13 is a flow chart showing a flow for setting an electrical energization permission flag and an engine starting flag which are used in the flow chart of FIG. 12.

FIG. 14 is a time chart showing the changes over time of electric energy supplied to an electrically heated catalyst, a completion counter, an engine state, and electric power supplied to the electrically heated catalyst in temperature rise control according to a second embodiment of the present disclosure.

FIG. 15 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst in the case where the electric power to be supplied until it reaches the required amount of electric energy is set constant at 4 kW, and thereafter the supply of the electric power is stopped.

FIG. 16 is a flow chart showing a flow for the temperature rise control according to the second embodiment.

FIG. 17 is a time chart showing the changes over time of electric energy supplied to an electrically heated catalyst, a stop counter, an engine state, and electric power supplied to the electrically heated catalyst in temperature rise control according to a third embodiment of the present disclosure.

FIG. 18 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst in the case where the electric power to be supplied until it reaches the required amount of electric energy is initially set constant at 4 kW, then is set to 0 kW, and thereafter is further set constant at 2 kW.

FIG. 19 is a view showing the temperature distribution of the electrically heated catalyst in the case where electric power is initially set constant at 4 kW and supplied for 20 seconds, then is not supplied for 10 seconds, and thereafter is further set to 2 kW and supplied for another 20 seconds.

FIG. 20 is a view similar to FIG. 9 and FIG. 11, showing the temperature distribution related to FIG. 19,

FIG. 21 is a flow chart showing a flow for temperature rise control according to the third embodiment.

FIG. 22 is a time chart showing the changes over time of electric energy supplied to an electrically heated catalyst, a stop counter, a completion counter, an engine state, and electric power supplied to the electrically heated catalyst in temperature rise control according to a fourth embodiment of the present disclosure.

FIG. 23 is a flow chart showing a flow for temperature rise control according to the fourth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the modes for carrying out the present disclosure will be exemplarily described in detail based on embodiments with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements and so on of component parts described in the embodiments are not intended to limit the scope of the present disclosure to these alone in particular as long as there are no specific statements.

First Embodiment

FIG. 1 is a view showing the schematic construction of a hybrid vehicle 100 according to a first embodiment of the present disclosure. On the hybrid vehicle 100, there is mounted an internal combustion engine 1. Here, note that the internal combustion engine 1 may be either a gasoline engine or a diesel engine. In addition, an electric motor 2 is mounted on the hybrid vehicle 100. The hybrid vehicle 100 according to this embodiment can be driven by the internal combustion engine 1 or the electric motor 2. Moreover, electricity can be generated by means of the electric motor 2 using the internal combustion engine 1 as a power source. A battery 20 is connected to the electric motor 2 through electrical wiring.

An exhaust passage 3 is connected to the internal combustion engine 1. An electrically heated catalyst 4 is arranged in the middle of the exhaust passage 3. The electrically heated catalyst 4 according to this embodiment has a catalyst 4B supported on a catalyst carrier 4A. For the catalyst carrier 4A, there is used a material such as for example SiC, which has electric resistance and is electrically energized to generate heat. The catalyst carrier 4A has a plurality of passages extending in the direction of flow of exhaust gas. The exhaust gas flows through these passages. The catalyst carrier 4A has an outer shape which is a cylindrical shape around the central axis of the exhaust passage 3, for example. Here, note that in this embodiment, the catalyst carrier 4A corresponds to a heat generation element in the present disclosure. Also, an additional SCR catalyst can be further provided at the downstream side of the electrically heated catalyst 4.

For the catalyst 4B, there can be mentioned, for example, an oxidation catalyst, a three-way catalyst, an NOx storage reduction catalyst, an NOx selective catalytic reduction catalyst, etc. When the temperatures of these catalysts become equal to or higher than their activation temperatures, respectively, they will exhibit exhaust gas purifying ability. Two pieces of electrodes 4C are connected to the catalyst carrier 4A, so that the catalyst carrier 4A is energized by applying a voltage between these electrodes 4C. The catalyst layer 4A generates heat due to the electric resistance thereof. The electrodes 4C are also electrically connected to a battery 20 through a voltage controller 21. Here, note that in this embodiment, the battery 20 correspond to a power supply in the present disclosure. The voltage controller 21 is operated by an ECU 10 to be described later, and adjusts a voltage to be applied from the battery 20 to the electrodes 4C.

Then, in the internal combustion engine 1, there is arranged in combination therewith the ECU 10 which is an electronic control unit for controlling the internal combustion engine 1 and the electric motor 2. This ECU 10 is provided with a CPU and other elements such as a ROM, a RAM and so on, for storing a variety of kinds of programs and maps, and controls the internal combustion engine 1, the electric motor 2 and so on in accordance with the operating conditions of the internal combustion engine 1 and/or driver's requirements. Here, note that in this embodiment, the ECU 10 corresponds to a controller in the present disclosure.

Besides the above-mentioned sensors, an accelerator opening sensor 12, which serves to detect an engine load by outputting an electrical signal corresponding to an amount by which a driver depressed an accelerator pedal 11, and a crank position sensor 13, which serves to detect the rotational speed of the engine, are connected to the ECU 10 through electrical wiring, and the output signals of these variety of kinds of sensors are inputted to the ECU 10. In addition, the voltage controller 21 is connected to the ECU 10 through electrical wiring, so that the ECU 10 controls the supply of current (electrical energization) to the electrically heated catalyst 4 through the voltage controller 21.

In addition, the battery 20 is connected to the ECU 10, so that the ECU 10 calculates a residual amount of charge (hereinafter, referred to as an amount of SOC) of the battery 20. Further, the electric motor 2 is connected to the ECU 10 through electrical wiring, so that the ECU 10 controls the supply of electric power (electrical energization) to the electric motor 2 and the generation of electrical energy (power generation) in the electric motor 2. When the amount of SOC is large, the ECU 10 drives the hybrid vehicle 100 by means of the electric motor 2, whereas when the amount of SOC becomes small, the ECU 10 starts the internal combustion engine 1 so that the amount of SOC is recovered, and at the same time, the hybrid vehicle 100 is driven to operate by the internal combustion engine 1.

Then, before starting of the internal combustion engine 1, the ECU 10 carries out temperature rise control which is to raise the temperature of the electrically heated catalyst 4. In the temperature rise control, the ECU 10 adjusts the electric power to be supplied to the electrically heated catalyst 4 from the battery 20. The ECU 10 calculates, based on the temperature of the electrically heated catalyst 4, an amount of electric energy required for a mean temperature of the electrically heated catalyst 4 to go up to a target temperature (hereinafter, also referred to as a required amount of electric energy). The temperature of the electrically heated catalyst 4 is estimated by the ECU 10. Here, note that the relation between the temperature of the electrically heated catalyst 4 and the required amount of electric energy can have been obtained in advance by experiments, simulations or the like, so it can have been stored in the ECU 10 in advance. In addition, the required amount of electric energy may also be set to a fixed value, instead of being calculated based on the temperature of the electrically heated catalyst 4. This fixed value has also been obtained in advance through experiments, simulations or the like. The ECU 10 continues to supply electric power to the electrically heated catalyst 4 until the amount of electric energy supplied to the electrically heated catalyst 4 becomes the required amount of electric energy. In that case, from a start point in time of the supply of electric power to an end point in time of the first period of time, first processing is carried out in which a first electric power, being relatively large, is supplied, and from the end point in time of the first period of time to an end point in time of the second period of time, a second processing is carried out in which a second electric power, being smaller than the first electric power, is supplied. The ECU 10 sets the first electric power, the first period of time, the second electric power and the second period of time, in such a manner that the amount of electric energy at the end point in time of the second period of time becomes the required amount of electric energy. Then, when the second period of time ends, the internal combustion engine 1 is driven to start.

FIG. 2 is a time chart showing the changes over time of electric energy and electric power which are supplied to the electrically heated catalyst 4 in the temperature rise control according to this embodiment. In FIG. 2, T1 is a start point in time of the first period of time; T2 is the end point in time of the first period of time and a start point in time of the second period of time; and T3 is the end point in time of the second period of time and a point in time of starting of the internal combustion engine 1. In FIG. 2, Q1 is the required amount of electric energy, and Q2 is an amount of electric energy at the point in time of T2. In addition, in FIG. 2, E1 is an electric power to be supplied in the first period of time, and E2 is an electric power to be supplied in the second period of time. The electric power to be supplied in the first period of time is fixed at E1, and the electric power to be supplied in the second period of time is fixed at E2.

In this manner, in the temperature rise control according to this embodiment, first of all, a relatively large first electric power is supplied, and after that, a relatively small second electric power is supplied. Here, it is difficult from the point of view of manufacture to make uniform the electric resistance between the electrodes 4C of the electrically heated catalyst 4, so there exist a location where the electric resistance is large, and a location where the electric resistance is small. Because electric current tends to flow through the location where the electric resistance is small, the temperature of the location where the electric resistance is small becomes apt to go up easily. In addition, electric current will necessarily flow through the contact portions of the electrodes 4C and the catalyst carrier 4A, and the electric resistance in the contact portions is large, so the temperature in the vicinity of the electrodes 4C is apt to go up during electrical energization. Accordingly, when electric power is supplied to the electrically heated catalyst 4, there may occur a temperature difference inside the electrically heated catalyst 4. Here, note that in cases where SIC is adopted as the catalyst carrier 4A, the higher the temperature thereof, the smaller the electric resistance thereof becomes due to an NTC (Negative Temperature Coefficient) characteristic of SiC, and hence, through the location where the electric resistance is first small and electric current has first flowed, the electric current is also apt to flow after that. For that reason, the temperature of the same location continues to rise, so that the temperature difference inside the electrically heated catalyst 4 is further enlarged.

Here, the first electric power and the first period of time are set in such a manner that the mean temperature of the electrically heated catalyst 4 can be raised quickly, and at the same time, the electrically heated catalyst 4 can not be overheated in its location where the temperature thereof is high. That is, the first electric power is set in such a manner that the temperature inside the electrically heated catalyst 4 falls within an allowable temperature range in the first period of time. For example, in cases where the same amount of electric energy is supplied, when the first electric power is made large and the first period of time is made short, there is a fear that the electrically heated catalyst 4 may be overheated in its locations where the temperature thereof is high. Then, thermal degradation will occur due to such overheating, and the purification performance of the electrically heated catalyst 4 will drop. On the other hand, in cases where the same amount of electric energy is supplied, when the first electric power is made small and the first period of time is made long, it will take time to raise the mean temperature of the electrically heated catalyst 4. Accordingly, in consideration of these, the first electric power E1 and the first period of time are set so as to fall in ranges where these can be both permitted. Thus, in the first period of time, by supplying the first electric power E1, a temperature difference between a location where the temperature is high (e.g., in the vicinity of the ends of the electrodes 4C), and a location where the temperature is low (e.g., in the vicinity of the central axis of the catalyst carrier 4A) will become relatively large. At the end point in time T2 of the first period of time, the amount of electric energy Q has not reached the required amount of electric energy Q1, so the mean temperature of the electrically heated catalyst 4 is equal to or less than its activation temperature, so a wide range of the electrically heated catalyst 4 has not reached the activation temperature, though a part thereof may have reached the activation temperature.

Then, the second period of time is provided after the end of the first period of time, and the second electric power E2 is supplied in this second period of time. Here, the second electric power E2 and the second period of time are set in such a manner that the temperature difference inside the electrically heated catalyst 4 falls within the allowable temperature difference range at the end point in time of the second period of time. This allowable temperature difference range may be set in such a manner that the purification rate of the exhaust gas in the electrically heated catalyst 4 falls within an allowable range. Moreover, the second electric power E2 and the second period of time are set in such a manner that the amount of electric energy Q supplied in the first period of time and the second period of time reaches the required amount of electric energy Q1 at the end point in time of the second period of time. Here, when the second electric power is too large, the temperature difference inside the electrically heated catalyst 4 will be enlarged, whereas when the second electric power is too small, it will take time until the amount of electric energy reaches the required amount of electric energy Q1. Thus, in consideration of these factors, the second electric power E2 and the second period of time are appropriately set so that these factors fall in allowable ranges.

In the second period of time, the relatively small second electric power E2 is supplied, so a temperature rise in a location of the electrically heated catalyst 4 through which electric current flows becomes slower as compared with that in the first period of time. In addition, in the second period of time, heat is transmitted from locations of the electrically heated catalyst 4 where the temperature was high in the first period of time to locations thereof where the temperature is low. That is, when a comparison is made between the first period of time and the second period of time, the temperature rise in locations where the electric resistance is small (i.e., locations where the temperature is high) is smaller in the second period of time than in the first period of time, but the temperature rise due to the heat transfer in locations where the electric resistance is large (i.e., locations where the temperature is low) also occurs in the second period of time, continuously from the first period of time, as a consequence of which it is possible to suppress the temperature difference inside the electrically heated catalyst 4 from being enlarged in the second period of time. Then, at the end point in time T3 of the second period of time, the amount of electric energy Q has reached the required amount of electric energy Q1, so the mean temperature of the electrically heated catalyst 4 has reached the activation temperature. In the second period of time, the enlargement of the temperature difference inside the electrically heated catalyst 4 has been suppressed, so that at the end point in time T3 of the second period of time, the activation temperature has been reached in a wider range of the inside of the electrically heated catalyst 4. Accordingly, at the end point in time T3 of the second period of time, the internal combustion engine 1 can be started in a state where the exhaust gas purifying ability of the electrically heated catalyst 4 is high.

Here, FIG. 3 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst 4 in the case where the electric power to be supplied until it reaches the required amount of electric energy is fixed at 3 kW. In addition, FIG. 4 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst 4 in the case where the electric power to be supplied until it reaches the required amount of electric energy is initially set constant at 4 kW and is thereafter set constant at 2 kW. In FIG. 3 and FIG. 4, a solid line indicates the electric power to be supplied; an alternate long and short dash line indicates the lowest temperature inside the electrically heated catalyst 4; and a broken line indicates the highest temperature inside the electrically heated catalyst 4. In addition, TA indicates a point in time at which the amount of electric energy reaches the required amount of electric energy. The required amounts of electric energy in FIG. 3 and FIG. 4 are the same with each other at 120 kJ. TA indicates a point in time at which the amount of electric energy reaches the required amount of electric energy. In FIG. 3 and FIG. 4, the periods of time in each of which the electric power is supplied are the same with each other.

When a comparison is made between FIG. 3 and FIG. 4, a temperature difference between the highest temperature and the lowest temperature inside the electrically heated catalyst 4 at the point in time TA at which the amount of electric energy reaches the required amount of electric energy is smaller in FIG. 4 than in FIG. 3. Also, when a comparison is also made between FIG. 3 and FIG. 4, the highest temperature is higher in FIG. 3 than in FIG. 4. That is, in cases where the electric power to be supplied is made constant as shown in FIG. 3, there is a fear that the temperature may become too high in the location of the highest temperature. If the electric power to be supplied is made constant or fixed at a small electric power so as to suppress the temperature in the location of the highest temperature from becoming too high, it will take time to raise the location of the lowest temperature to the temperature requested. In contrast to this, by supplying a relatively large electric power in the first period of time, and then supplying a relatively small electric power in the second period of time, as shown in FIG. 4, it becomes possible to attain a prompt temperature rise, while making small the temperature difference inside the electrically heated catalyst 4. That is, in cases where the required amount of electric energy is the same, and in cases where electric power is supplied only for the same period of time, the temperature difference inside the electrically heated catalyst 4 can be made small more quickly in the case where a relatively large electric power is first supplied and a relatively small electric power is then supplied, than in the case where a fixed or constant electric power is supplied.

Next, FIG. 5 is a view showing the temperature distribution of the electrically heated catalyst 4 after the end of electrical energization in the case where the electric power is set constant at 2 kW, and the required amount of electric energy is set to 120 kJ. FIG. 6 is a view showing the temperature distribution of the electrically heated catalyst 4 after the end of electrical energization in the case where the electric power is set constant at 3 kW, and the required amount of electric energy is set to 120 kJ. FIG. 7 is a view showing the temperature distribution of the electrically heated catalyst 4 after the end of electrical energization in the case where the electric power is set constant at 4 kW, and the required amount of electric energy is set to 120 kJ. FIG. 8 is a view showing the temperature distribution of the electrically heated catalyst 4 after the end of electrical energization in the case where the electric power is set constant at 5 kW, and the required amount of electric energy is set to 120 kJ. FIG. 5 through FIG. 8 shows the temperature distributions on a cross section which is orthogonal to the central axis of the electrically heated catalyst 4, As shown in FIG. 5 through FIG. 8, the electrodes 4C are formed along the outer peripheral surface of the catalyst carrier 4A. In these figures, “TEMPERATURE: HIGH” indicates a location where the temperature is relatively high, and “TEMPERATURE: LOW” indicates a location where the temperature is relatively low. In FIG. 5 through FIG. 8, the temperature distributions are shown by isothermal lines, each of which is a line connecting points or locations having the same temperature. Also, in FIG. 5 through FIG. 8, the required amount of electric energy is the same, so the mean temperature of the electrically heated catalyst 4 is substantially equal or the same. However, the larger the electric power, the shorter the period of time to supply the electric power becomes. As shown in FIG. 5 through FIG. 8, in any of these figures, the temperature in the vicinity of the ends of the electrodes 4C is high, and the temperature in the vicinity of the central axis of the catalyst carrier 4A is low. As can be seen from the comparison among FIG. 5 through FIG. 8, the larger the electric power, the narrower the intervals of the isothermal lines become, and the larger the temperature differences become, even if the required amount of electric energy is the same.

FIG. 9 is a view in which the temperature distributions of FIG. 5 through FIG. 8 are summarized. In FIG. 9, a solid line indicates the mean temperature of the electrically heated catalyst 4; an alternate long and short dash line indicates the lowest temperature inside the electrically heated catalyst 4; and a broken line indicates the highest temperature inside the electrically heated catalyst 4. In cases where the amount of electric energy is the same, the smaller the electric power, and the longer the period of supply of electric power, the smaller becomes the difference between the highest temperature and the lowest temperature (i.e., the more uniform become the temperature distributions), and besides, the higher becomes the lowest temperature. However, the smaller the electric power, the longer becomes a period of time until the amount of electric energy reaches the required amount of electric energy, and hence, the longer becomes a period of time until the exhaust gas of the internal combustion engine 1 becomes able to be purified. Accordingly, in cases where the electric power is made small so as to make small the temperature difference inside the electrically heated catalyst 4, it will take time until the catalyst 4B becomes able to purify the exhaust gas. Then, in cases where the exhaust gas can not be purified and the starting of the internal combustion engine 1 is inhibited, it will take time until the internal combustion engine 1 is started. Accordingly, it is not preferable to decrease the temperature difference inside the electrically heated catalyst 4 by supplying a fixed or constant small electric power.

Here, FIG. 10 is a view showing the temperature distribution of the electrically heated catalyst 4 in the case where the electric power is initially set constant at 4 kW and supplied for 20 seconds, and then is set to 2 kW and supplied for another 20 seconds. The required amount of electric energy in FIG. 10 is 120 kJ. In addition, FIG. 11 is a view similar to FIG. 9, showing the temperature distribution related to FIG. 10. In the electric power in FIG. 11, “4-2” indicates a case where the electric power is initially set constant at 4 kW and supplied for 20 seconds, and is then set to 2 kW and supplied for another 20 seconds (i.e., in the case of supply of the electric power related to FIG. 10). Note that FIG. 10 can be said to be a view in the case of carrying out the temperature rise control according to this embodiment. Here, as shown in FIG. 11, in the case where the electric power is “4-2”, the temperature difference becomes a little larger than in the case where it is set constant at 2 kW. However, the period of time until the amount of electric energy reaches the required amount of electric energy can be more shortened by first setting the electric power to 4 kW than in the case where the electric power is set constant at 2 kW. On the other hand, in the case where the electric power is “4-2”, the temperature difference can be made smaller as compared with the case where the electric power is fixed at 3 kW, even though the period of time until the amount of electric energy reaches the required amount of electric energy is the same. Thus, according to the temperature rise control according to this embodiment, a period of time to carry out the temperature rise control can be shortened by supplying the first electric power in the first period of time. Further, it is possible to suppress the temperature difference inside the electrically heated catalyst 4 from being enlarged, by supplying the second electric power in the second period of time.

FIG. 12 is a flow chart showing a flow or routine for the temperature rise control according to this embodiment. The routine in this flow chart is carried out by means of the ECU 10 at each predetermined time interval. In addition, FIG. 13 is a flow chart showing a flow for setting an electrical energization permission flag and an engine starting flag which are used in the flow chart of FIG. 12. The routine in the flow chart shown in FIG. 13 is also carried out by means of the ECU 10 at each predetermined time interval. The routine in the flow chart shown in FIG. 13 has been carried out in advance before the flow chart shown in FIG. 12 is carried out. Here, note that the routines in the flow charts shown in FIG. 12 and FIG. 13 are carried out only for a period of time until the internal combustion engine 1 is started for the first time after an ignition switch (IG-SW) (illustration omitted) has been turned on. The hybrid vehicle 100 is driven by the electric motor 2 until the internal combustion engine 1 is started for the first time. The ignition switch (IG-SW) is a switch which is turned on by the driver of the hybrid vehicle 100 when the hybrid vehicle 100 is activated. In this embodiment, a process to start the internal combustion engine 1 will be explained, in cases where the amount of SOC (state of charge) of the battery 20 becomes small while the hybrid vehicle 100 is driven by the electric motor 2.

First, reference will be made to the flow chart shown in FIG. 13. In step S121, it is determined whether the IG-SW is on. That is, it is determined whether the hybrid vehicle 100 is in a state where it can be driven by the electric motor 2 or the internal combustion engine 1. In cases where an affirmative determination is made in step S121, the routine of the flow chart in FIG. 13 goes to step S122, whereas in cases where a negative determination is made, this routine is ended.

In step S122, it is determined whether the amount of SOC of the battery 20 is equal to or less than a first predetermined amount SOC1. The amount of SOC is separately calculated by the ECU 10. A well-known technique can be used for the calculation of this amount of SOC. Here, in cases where the amount of SOC is sufficiently large, the hybrid vehicle 100 is driven by the electric motor 2. In this case, it is not necessary to operate the internal combustion engine 1, so it is also not necessary to electrically energize the electrically heated catalyst 4. Accordingly, in cases where the amount of SOC is more than the first predetermined amount SOC1, the electrically heated catalyst 4 is not electrically energized. The first amount of SOC1 has been obtained in advance through experiments, simulations or the like, as an amount of SOC in which it is not necessary to start the internal combustion engine 1. In cases where an affirmative determination is made in step S122, the routine goes to step S123, whereas in cases where a negative determination is made, the routine goes to step S126.

In step S123, it is determined whether the amount of SOC of the battery 20 is equal to or less than a second predetermined amount SOC2. The second predetermined amount SOC2 is a value smaller than the first predetermined amount SOC1, and is an amount of SOC used as a threshold value for starting the internal combustion engine 1. That is, in cases where the amount of SOC is more than the second predetermined amount SOC2, the hybrid vehicle 100 can be driven by the electric motor 2, so the internal combustion engine 1 is stopped. On the other hand, in cases where the amount of SOC is smaller than the second predetermined amount SOC2, the internal combustion engine 1 is started in order to increase the amount of SOC. In cases where an affirmative determination is made in step S123, the routine goes to step S124, whereas in cases where a negative determination is made, the routine goes to step S125.

In step S124, the electrical energization permission flag is set to off, and the engine starting flag is set to on. The electrical energization permission flag is set to on in a state where electrical energization to the electrically heated catalyst 4 can be permitted, and it is set to off in a state where electrical energization to the electrically heated catalyst 4 can not be permitted. In addition, the engine starting flag is set to on in a state where the starting of the internal combustion engine 1 can be permitted, and it is set to off in a state where the starting of the internal combustion engine 1 can not be permitted. In step S124, the amount of SOC of the battery 20 is equal to or less than the second predetermined amount SOC2, and hence, when the amount of SOC decreases any further, there is a fear that the starting of the internal combustion engine 1 will become difficult, as a result of which the electrical energization permission flag is set to off. In addition, it is necessary to start the internal combustion engine 1 in order to recover or restore the amount of SOC, the engine starting flag is set to on.

In step S125, the electrical energization permission flag is set to on, and the engine starting flag is set to off. In step S125, the amount of SOC is sufficient, so the electric power can be supplied to the electrically heated catalyst 4. Accordingly, the electrical energization permission flag is set to on. In addition, due to the sufficient amount of SOC, it is not necessary to start the internal combustion engine 1 in order to restore the amount of SOC, so the engine starting flag is set to off.

In step S126, the electrical energization permission flag is set to off, and the engine starting flag is set to off. In step S126, the amount of SOC is larger than the first predetermined amount SOC1, so the hybrid vehicle 100 can be driven by the electric motor 2 for a relatively long period of time. Because it is not necessary to start the internal combustion engine 1 while driving the hybrid vehicle 100 by means of the electric motor 2, it is also not necessary to raise the temperature of the catalyst 4B. Accordingly, the electrical energization permission flag is set to off, and the engine starting flag is set to off.

Next, reference will be made to the flow chart shown in FIG. 12. In step S101, it is determined whether the IG-SW is on. That is, it is determined whether the hybrid vehicle 100 is in the state where it can be driven by the electric motor 2 or the internal combustion engine 1. In cases where an affirmative determination is made in step S101, the routine of the flow chart in FIG. 12 goes to step S102, whereas in cases where a negative determination is made, this routine is ended.

In step S102, it is determined whether the electrical energization permission flag is on. In cases where an affirmative determination is made in step S102, the routine goes to step S103, whereas in cases where a negative determination is made, the routine goes to step S107.

In step S103, it is determined whether the amount of electric energy Q supplied before is equal to or less than the required amount of electric energy Q1. In this step S103, it is determined whether it is necessary to supply the electric power to the electrically heated catalyst 4. In cases where an affirmative determination is made in step S103, the routine goes to step S104, whereas in cases where a negative determination is made, the routine goes to step S107.

In step S104, it is determined whether the amount of electric energy Q is equal to or less than a switch amount of electric energy Q2. The switch amount of electric energy Q2 is an amount of electric energy which is used as a threshold value for switching from the first electric power E1 to the second electric power E2, as mentioned above. The switch amount of electric energy Q2 has been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of overheating of the electrically heated catalyst 4 compatible with each other. In cases where an affirmative determination is made in step S104, the routine goes to step S105, whereas in cases where a negative determination is made, the routine goes to step S106.

In step S105, the electric power to be supplied to the electrically heated catalyst 4 is set to the relatively large first electric power E1. On the other hand, in step S106, the electric power to be supplied to the electrically heated catalyst 4 is set to the relatively small second electric power E2. The first electric power E1 has been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of overheating of the electrically heated catalyst 4 compatible with each other. Also, the second electric power E2 has been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of enlargement of the temperature difference inside the electrically heated catalyst 4 compatible with each other.

Here, note that in this embodiment, a period of time from a start point in time of electrical energization until a point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 corresponds to a first period of time in the present disclosure, and a period of time from a point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 until a point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 corresponds to a second period of time in the present disclosure. In addition, in this second embodiment, the processing in which the ECU 10 sets the electric power to be supplied to the first electric power in the first period of time corresponds to first processing in the present disclosure, and the processing in which the ECU 10 sets the electric power to be supplied to the second electric power in the second period of time corresponds to second processing in the present disclosure.

On the other hand, in step S107, the electrical energization to the electrically heated catalyst 4 is inhibited. That is, in cases where a negative determination is made in step S102, it is not necessary to start the internal combustion engine 1, or the electrical energization to the electrically heated catalyst 4 is inhibited because the amount of SOC is too small. In addition, in cases where a negative determination is made in step S103 after the affirmative determination was made in step S102, a sufficient amount of electric energy is supplied to the electrically heated catalyst 4, so the electrical energization to the electrically heated catalyst 4 is inhibited.

In step S108, it is determined whether the engine starting flag is on. In cases where, an affirmative determination is made in step S108, the routine goes to step S109, whereas in cases where a negative determination is made, this routine is ended. Here, note that in cases where a negative determination is made in step S108, the hybrid vehicle 100 is driven by the electric motor 2.

In step S109, the internal combustion engine 1 is started. With this, the hybrid vehicle 100 is driven by the internal combustion engine 1. After that, the routine goes to step S110, where various parameters are reset. A parameter to be reset in step S110 is, for example, the amount of electric energy Q. Then, when the processing of step S110 is terminated, the repeated execution of the flow charts shown in FIG. 12 and FIG. 13 is terminated.

As described above, in this embodiment, the temperature of the electrically heated catalyst 4 is raised until the amount of electric energy Q becomes larger than the required amount of electric energy Q1, while changing the electric power in two steps. Then, when the amount of electric energy Q is equal to or less than the switch amount of electric energy Q2, a larger amount of heat can be supplied to the electrically heated catalyst 4 in a short time, by setting the electric power to the relatively large first electric power E1, so that the mean temperature of the electrically heated catalyst 4 can be caused to rise more quickly. Moreover, when the amount of electric energy Q becomes larger than the switch amount of electric energy Q2, a local temperature rise can be suppressed by setting the electric power to the relatively small second electric power E2, and at the same time, an enlargement of the temperature difference inside the electrically heated catalyst 4 can be suppressed due to the transfer of heat from high temperature locations to low temperature locations. With this, it is possible to activate a wide range of the catalyst 4B, so that the purification rate of the exhaust gas in the electrically heated catalyst 4 can be enhanced.

Here, note that, in this embodiment; when the amount of electric energy Q exceeds the switch amount of electric energy Q2, the electric power is changed from the first electric power E1 to the second electric power E2, but instead of this, the timing to change the electric power may be decided based on an elapsed period of time from the start of electrical energization to the electrically heated catalyst 4.

In addition, in this embodiment, the explanation has been made by taking the hybrid vehicle 100 as an example. In this case, the electrically heated catalyst 4 can be heated when the hybrid vehicle 100 is driven by the electric motor 2. On the other hand, even in the case of vehicles other than the hybrid vehicle 100, the electrically heated catalyst 4 may be heated before starting of the internal combustion engine 1, by delaying the starting of the internal combustion engine 1, for example.

In addition, in this embodiment, SiC is exemplified as the catalyst carrier 4A, but instead of this, metal may be adopted as the catalyst carrier 4A. However, the heat conductivity of SiC is relatively large, so heat moves quickly from the high temperature locations to the low temperature locations. Accordingly, by using SiC, the effect related to the second period of time becomes larger.

Second Embodiment

In the temperature rise control according to the first embodiment, at the time when the amount of electric energy Q reaches the switch amount of electric energy Q2, the electric power is changed from the first electric power E1 to the second electric power E2. On the other hand, in temperature rise control according to this second embodiment, an electric power E is set to a first electric power E3 until an amount of electric energy Q reaches a required amount of electric energy Q1, and after that, a period in time in which electric power is not supplied is set until the time of starting the internal combustion engine 1. The other components and so on in this second embodiment are the same as those in the first embodiment, so the explanation thereof is omitted.

FIG. 14 is a time chart showing the changes over time of electric energy supplied to the electrically heated catalyst 4, a completion counter, an engine state, and electric power supplied to the electrically heated catalyst 4 in the temperature rise control according to the second embodiment of the present disclosure. In FIG. 14, in the engine state, “on” indicates that the internal combustion engine 1 is operated, and “off” indicates that the internal combustion engine 1 is stopped. The completion counter indicates an elapsed period of time from a point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1. In FIG. 14, T1 is a start point in time of the first period of time; T2 is an end point in time of the first period of time and a start point in time of the second period of time; and T3 is an end point in time of the second period of time and a point in time of starting of the internal combustion engine 1. In FIG. 14, Q1 is the required amount of electric energy, and E3 is the electric power to be supplied in the first period of time. In the second period of time, the electric power is 0, and the electric power is not supplied. Here, note that the first electric power E3 according to this second embodiment does not necessarily need to be the same as the first electric power E1 according to the first embodiment. The first electric power E3 and the first period of time according to this second embodiment have been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of overheating of the electrically heated catalyst 4 compatible with each other. The second period of time has been obtained in advance by experiments, simulations or the like, so that the temperature difference inside the electrically heated catalyst 4 falls within the allowable temperature difference range in a shorter period of time.

In this manner, in the temperature rise control according to this second embodiment, the first period of time in which the first electric power E3 is supplied is first provided, and thereafter, the second period of time in which the electric power to be supplied is set to 0 is provided. In that case, the temperature difference inside the electrically heated catalyst 4 is diminished in the second period of time.

That is, in the first period of time, the temperature of locations where the electric resistance is small goes up quickly, by supplying the first electric power. Then, by providing the second period of time after the first period of time, and stopping the supply of electric power in the second period of time, heat is transmitted from the high temperature locations of the electrically heated catalyst 4 to the low temperature locations thereof, so the temperature difference is diminished.

FIG. 15 is a time chart showing the change over time of the temperature of each portion or location of the electrically heated catalyst 4 in the case where the electric power to be supplied until it reaches the required amount of electric energy is set constant at 4 kW, and thereafter the supply of the electric power is stopped. In FIG. 15, TA indicates a point in time at which the amount of electric energy reaches the required amount of electric energy. FIG. 15 can be said to be a view in the case of carrying out the temperature rise control according to this second embodiment. The required amount of electric energy in FIG. 15 is 120 kJ. Although a difference in temperature between a location of the highest temperature and a location of the lowest temperature at the point in time TA at which the amount of electric energy reaches the required amount of electric energy is relatively large, this temperature difference is diminished with the lapse of time after the end of electrical energization.

FIG. 16 is a flow chart showing a flow or routine for the temperature rise control according to this second embodiment. The routine in this flow chart is carried out by means of the ECU 10 at each predetermined time interval. In FIG. 16, for those steps in which the same processings as in the flow chart shown in FIG. 12 are carried out, the same reference numerals and characters are attached and the explanation thereof is omitted. The routine in the flow chart shown in FIG. 13 has been carried out in advance before the flow chart shown in FIG. 16 is carried out. Here, note that the routine in the flow chart shown in FIG. 16 is carried out only for a period of time until the internal combustion engine 1 is started for the first time after an ignition switch (IG-SW) has been turned on.

In the flow chart shown in FIG. 16, in cases where an affirmative determination is made in step S103, the routine goes to step S201. In step S201, the electric power to be supplied to the electrically heated catalyst 4 is set to the first electric power E3.

On the other hand, in the flow chart shown in FIG. 16, when a negative determination is made in step S103, the routine goes to step S202. In step S202, the electrical energization to the electrically heated catalyst 4 is inhibited. That is, in cases where a negative determination is made in step S103, a sufficient amount of electric energy is supplied to the electrically heated catalyst 4, so the electrical energization to the electrically heated catalyst 4 is inhibited.

In step S203, the completion counter is counted up. The completion counter indicates the elapsed period of time from the point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1, as explained in FIG. 14.

In step S204, it is determined whether the completion counter exceeds a starting threshold value. The starting threshold value is set based on a period of time from the point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 until the temperature difference in the electrically heated catalyst 4 diminishes into the allowable temperature difference range. The starting threshold value has been obtained in advance, together with the first electric power E3 and the first period of time, through experiments, simulations or the like. In cases where an affirmative determination is made in step S204, the routine goes to step S109, whereas in cases where a negative determination is made, the routine goes to step S108.

In addition, in the flow chart shown in FIG. 16, various parameters are reset in step S205. The parameters to be reset in step S205 are, for example, the amount of electric energy Q and the completion counter. That is, in step S205, the amount of electric energy Q and the completion counter are reset to 0. Then, when the processing of step S205 is terminated, the repeated execution of the flow charts shown in FIG. 16 and FIG. 13 is terminated.

Here, note that in this second embodiment, a period of time from a start point in time of electrical energization until a point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 corresponds to the first period of time in the present disclosure, and a period of time from the point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 until a point in time at which the completion counter reaches the starting threshold value corresponds to the second period of time in the present disclosure. In addition, in this second embodiment, the processing in which the ECU 10 sets the electric power to be supplied to the first electric power E3 in the first period of time corresponds to the first processing in the present disclosure, and the processing in which the ECU 10 sets the electric power to be supplied to 0 in the second period of time corresponds to the second processing in the present disclosure.

As described above, in this second embodiment, the first electric power E3 is supplied to the electrically heated catalyst 4 until the amount of electric energy Q becomes larger than the required amount of electric energy Q1. By setting the first electric power E3 at this time to a relatively large electric power, a larger amount of heat can be quickly supplied to the electrically heated catalyst 4. For that reason, the mean temperature of the electrically heated catalyst 4 can be caused to rise in a quicker manner. Moreover, when the amount of electric energy Q becomes larger than the required amount of electric energy Q1, heat is moved from the high temperature locations to the low temperature locations by stopping the supply of electric power, so that the temperature difference inside the electrically heated catalyst 4 can be made to diminish before the starting of the internal combustion engine 1. With this, it is possible to activate a wider range of the catalyst 4B, so that the purification rate of the exhaust gas in the electrically heated catalyst 4 can be enhanced.

Third Embodiment

In the temperature rise control according to the first embodiment, the electric power is always supplied in the second period of time. In addition, in the temperature rise control according to the second embodiment, the electric power is always not supplied in the second period of time. On the other hand, in temperature rise control according to this third embodiment, in a second period of time after a first period of time for supplying a first electric power E4 expires, a period of time in which the electric power to be supplied is set to 0, and a period of time in which the electric power to be supplied is set to a second electric power E5 smaller than the first electric power E4, are provided in this order. The other components and so on in this third embodiment are the same as those in the first embodiment, so the explanation thereof is omitted.

FIG. 17 is a time chart showing the changes over time of electric energy supplied to the electrically heated catalyst 4, a stop counter, an engine state, and electric power supplied to the electrically heated catalyst 4 in the temperature rise control according to this third embodiment of the present disclosure. In FIG. 17, the stop counter indicates an elapsed period of time from a point in time T2A at which the amount of electric energy Q reaches the switch amount of electric energy Q2. T1 is a start point in time of the first period of time; and T2A is an end point in time of the first period of time and a start point in time of the second period of time. T3 is an end point in time of the second period of time and a point in time of starting of the internal combustion engine 1. In FIG. 17, the supply of electric power is stopped at the end point in time T2A of the first period of time, and the stop counter begins to increase. Then, at a point in time T2B at which the stop counter reaches a stop threshold value, the supply of the second electric power E5 is started. The stop threshold value is set to such a value as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of enlargement of the temperature difference inside the electrically heated catalyst 4 compatible with each other.

Here, in the first period of time, the temperature of locations where the electric resistance is small goes up quickly, by supplying the first electric power E4. As a result, at the end point in time T2A of the first period of time, the temperature difference inside the electrically heated catalyst 4 has become large. Then, by stopping the supply of electric power in a first or former half of the second period of time (i.e., setting the electric power to 0), the mean temperature of the electrically heated catalyst 4 does not rise, but heat is transmitted from the high temperature locations of the electrically heated catalyst 4 to the low temperature locations, so the temperature difference inside the electrically heated catalyst 4 diminishes. For this reason, the temperature can be decreased in the high temperature locations.

Moreover, by supplying the second electric power E5 in the second or latter half of the second period of time, the temperature rise in the locations where electric resistance is small becomes slower than at the time of supplying the first electric power E4. Further, when the second electric power E5 is supplied, too, heat is transmitted from the high temperature locations to the low temperature locations, so it is possible to suppress the temperature difference inside the electrically heated catalyst 4 from being enlarged. In this manner, it is possible to diminish the temperature difference inside the electrically heated catalyst 4 at the end point in time of the second period of time. Then, at the end point in time T3 of the second period of time, the amount of electric energy Q has reached the required amount of electric energy Q1, so the mean temperature of the electrically heated catalyst 4 has reached the activation temperature. In addition, the enlargement of the temperature difference inside the electrically heated catalyst 4 has been suppressed, so that the activation temperature has been reached in a wider range of the inside of the electrically heated catalyst 4. Accordingly, at the end point in time T3 of the second period of time, the exhaust gas purifying ability of the electrically heated catalyst 4 has become a high state, so the internal combustion engine 1 can be started.

FIG. 18 is a time chart showing the change over time of the temperature of each portion of the electrically heated catalyst 4 in the case where the electric power to be supplied until it reaches the required amount of electric energy has been initially set constant at 4 kW, then set to 0 kW, and thereafter further set constant at 2 kW. The required amount of electric energy in FIG. 18 is 120 kJ. In FIG. 18, TA indicates a point in time at which the amount of electric energy reaches the required amount of electric energy. FIG. 18 can be said to be a view in the case of carrying out the temperature rise control according to this third embodiment. Here, note that, as shown by an alternate long and short dash line and an alternate long and two short dashes line, the location of the lowest temperature inside the electrically heated catalyst 4 is changed in the middle of these lines. In FIG. 18, a period of time in which the electric power of 4 kW is supplied corresponds to the first period of time, and a period of time from the termination of the supply of electric power of 4 kW until the termination of the supply of electric power of 2 kW corresponds to the second period of time. It can be seen that in a period of time in which the electric power is not supplied from the start point in time of the second period of time, the temperature difference in the electrically heated catalyst 4 diminishes. Further, it can be seen that in a subsequent period of time in which the electric power of 2 kW is supplied, too, the temperature difference is suppressed from enlarging.

Here, FIG. 19 is a view showing the temperature distribution of the electrically heated catalyst 4 in the case where the electric power is initially set constant at 4 kW and supplied for 20 seconds, and then is not supplied for 10 seconds, and thereafter is further set to 2 kW and supplied for another 20 seconds. The required amount of electric energy in FIG. 19 is 120 kJ. FIG. 19 can be said to be a view in the case of carrying out the temperature rise control according to this third embodiment. Thus, the temperature distribution shown in FIG. 19 is wider in the intervals of the isotherm lines and smaller in the temperature difference than the temperature distribution shown in FIG. 10 which is the case where there is not provided a period of time in which the supply of electric power is stopped at the start time of the second period of time.

FIG. 20 is a view similar to FIG. 9 and FIG. 11, showing the temperature distribution related to FIG. 19, In the electric power in FIG. 20, “4-0(10)-2” indicates a case where the electric power is initially set constant at 4 kW and supplied for 20 seconds, and then is not supplied for 10 seconds, and thereafter is further set to 2 kW and supplied for another 20 seconds (i.e., in the case of supply of the electric power related to FIG. 19). Also, “4-0(5)-2” indicates a case where the electric power is initially set constant at 4 kW and supplied for 20 seconds, and then is not supplied for 5 seconds, and thereafter is further set to 2 kW and supplied for another 20 seconds. As shown in FIG. 20, the difference in temperature between a location of the highest temperature and a location of the lowest temperature becomes smaller, as the period of time in which the electric power is not supplied from the start point in time of the second period of time becomes longer.

Here, note that the first electric power E4 and the second electric power E5 according to this third embodiment do not necessarily need to be the same as the first electric power E1 and the second electric power E2, respectively, according to the first embodiment. The first electric power E1 and the second electric power E5 have been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of overheating of the electrically heated catalyst 4 compatible with each other. Also, the second electric power E5, the second period of time and the stop threshold value have been obtained in advance by experiments, simulations or the like, in such a manner as to achieve the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of enlargement of the temperature difference inside the electrically heated catalyst 4.

FIG. 21 is a flow chart showing a flow or routine for the temperature rise control according to this third embodiment. The routine in this flow chart is carried out by means of the ECU 10 at each predetermined time interval. For those steps in which the same processings as in the flow chart shown in FIG. 12 or FIG. 16 are carried out, the same reference numerals and characters are attached and the explanation thereof is omitted. The routine in the flow chart shown in FIG. 13 has been carried out in advance before the flow chart shown in FIG. 21 is carried out. Here, note that the routine in the flow chart shown in FIG. 21 is carried out only for a period of time until the internal combustion engine 1 is started for the first time after an ignition switch (IG-SW) has been turned on.

In the flow chart shown in FIG. 21, in cases where an affirmative determination is made in step S104, the routine goes to step S301. In step S301, the electric power to be supplied to the electrically heated catalyst 4 is set to the first electric power E4.

On the other hand, in the flow chart shown in FIG. 21, in cases where a negative determination is made in step S104, the routine goes to step S302. In step S302, it is determined whether the stop counter exceeds the stop threshold value. The stop counter indicates the elapsed period of time from the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2, as explained in FIG. 17. In step S302, it is determined whether it is time to start the supply of the second electric power E5. In cases where an affirmative determination is made in step S302, the routine goes to step S305, but on the other hand, in cases where a negative determination is made, the routine goes to step S303.

In step S303, the electric power to be supplied to the electrically heated catalyst 4 is set to 0. Then, in step S304, the stop counter is counted up. Also, in step S305, the electric power to be supplied to the electrically heated catalyst 4 is set to the second electric power E5.

In addition, in the flow chart shown in FIG. 21, various parameters are reset in step S306. The parameters to be reset in step S306 are, for example, the amount of electric energy Q and the stop counter. That is, the amount of electric energy Q and the stop counter are reset to 0.

Here, note that in this third embodiment, a period of time from a start point in time of electrical energization until the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 corresponds to the first period of time in the present disclosure, and a period of time from the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 until the point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 corresponds to the second period of time in the present disclosure. Also, a period of time from the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 until the point in time at which the stop counter reaches the stop threshold value corresponds to a stop period of time before supply of the second electric power in the present disclosure, and a period of time from the point in time at which the stop counter reaches the stop threshold value until the point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 corresponds to a second electric power supply period of time in the present disclosure. In addition, in this third embodiment, the processing in which the ECU 10 sets the electric power to be supplied to the first electric power in the first period of time corresponds to the first processing in the present disclosure, and the processing in which the ECU 10 successively sets the electric power to be supplied to zero and the second electric power E5 in the second period of time corresponds to the second processing in the present disclosure.

As described above, in this third embodiment, by setting the electric power to the relatively large first electric power E4 until the amount of electric energy Q reaches the switch amount of electric energy Q2, a larger amount of heat can be supplied to the electrically heated catalyst 4, so that the mean temperature of the electrically heated catalyst 4 can be caused to rise more quickly. Moreover, when the amount of electric energy Q reaches the switch amount of electric energy Q2, heat can be moved from the high temperature locations to the low temperature locations by once stopping the supply of electric power, so that the temperature difference inside the electrically heated catalyst 4 can be made to diminish. Thereafter, by setting the electric power to the relatively small second electric power E5, overheating in the high temperature locations can be suppressed, and at the same time, an enlargement of the temperature difference inside the electrically heated catalyst 4 can be suppressed due to transfer of heat from the high temperature locations to the low temperature locations. With this, it is possible to activate a wider range of the catalyst 4B, so that the purification rate of the exhaust gas in the electrically heated catalyst 4 can be enhanced.

Fourth Embodiment

In temperature rise control according to this fourth embodiment, in a second period of time after a first period of time for supplying a first electric power E6 expires, a period of time in which the electric power to be supplied is set to 0, a period of time in which the electric power to be supplied is set to a second electric power E7 smaller than the first electric power E6, and a period of time in which the electric power to be supplied is set to 0, are provided in this order. The other components and so on in this fourth embodiment are the same as those in the first embodiment, so the explanation thereof is omitted.

FIG. 22 is a time chart showing the changes over time of electric energy supplied to an electrically heated catalyst 4, a stop counter, a completion counter, an engine state, and electric power supplied to the electrically heated catalyst 4 in the temperature rise control according to this fourth embodiment of the present disclosure. In FIG. 22, T1 is a start point in time of the first period of time; and T2A is an end point in time of the first period of time and a start point in time of the second period of time. T2B is a start point in time of the supply of the second electric power, and T2C is an end point in time of the supply of the second electric power. T3 is an end point in time of the second period of time, and a point in time of starting of the internal combustion engine 1. The electric power is not supplied to the electrically heated catalyst 4 in a period of time from the end point in time T2A of the first period of time until the start point in time T2B of the supply of the second electric power, and in a period of time from the end point in time T2C of the supply of the second electric power until the point in time T3 of starting of the internal combustion engine 1.

Here, in the first period of time, by supplying the first electric power E6, the temperature of locations where the electric resistance is small goes up quickly, so that a temperature difference occurs inside the electrically heated catalyst. Thereafter, by once stopping the supply of the electric power at the start time of the second period of time, the mean temperature of the electrically heated catalyst 4 does not rise, but heat is transmitted from the high temperature locations of the electrically heated catalyst 4 to the low temperature locations thereof, so the temperature difference inside the electrically heated catalyst 4 diminishes. For this reason, the temperature can be lowered in the high temperature locations. After that, by supplying the second electric power E7, the temperature rise in the locations where electric resistance is small becomes slower than at the time of supplying the first electric power E6. Further, in the period of time in which the second electric power E7 is supplied, too, heat is transmitted from the high temperature locations to the low temperature locations, so it is possible to suppress the temperature difference inside the electrically heated catalyst 4 from being enlarged. Then, by further providing a period of time in which the supply of electric power is stopped before starting the internal combustion engine 1, the mean temperature of the electrically heated catalyst 4 does not rise, but heat is transmitted from the high temperature locations of the electrically heated catalyst 4 to the low temperature locations thereof, so the temperature difference inside the electrically heated catalyst 4 further diminishes.

As explained in FIG. 18, in a period of time from the start point of the second period of time until the start point of the supply of the second electric power E7, in which the electric power is not supplied, the temperature difference inside the electrically heated catalyst 4 diminishes. In addition, it can be seen that in the period of time in which the second electric power E7 is supplied, too, an enlargement of the temperature difference is suppressed. Moreover, it can also be seen that the temperature difference diminishes after the end point in time of the supply of the second electric power indicated at TA in FIG. 18, too.

Here, note that the first electric power E6, the second electric power E7, the first period of time, the second period of time, and a period of time in the second period of time in which the electric power is not supplied, according to this fourth embodiment do not necessarily need to be the same as in the above-mentioned embodiments. Also, note that the first electric power E6 and the first period of time according to this fourth embodiment have been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of overheating of the electrically heated catalyst 4 compatible with each other. In addition, the second electric power E7, the second period of time, and the period of time in the second period of time in which the electric power is not supplied, according to this fourth embodiment have been obtained in advance by experiments, simulations or the like, in such a manner as to make the shortening of the period of time required for the temperature rise of the electrically heated catalyst 4 and the suppression of enlargement of the temperature difference inside the electrically heated catalyst 4 compatible with each other.

FIG. 23 is a flow chart showing a flow or routine for the temperature rise control according to this fourth embodiment. The routine in this flow chart is carried out by means of the ECU 10 at each predetermined time interval. For those steps in which the same processings as in the flow chart shown in FIG. 12, FIG. 16 or FIG. 21 are carried out, the same reference numerals and characters are attached and the explanation thereof is omitted. The routine in the flow chart shown in FIG. 13 has been carried out in advance before the flow chart shown in FIG. 23 is carried out. Here, note that the routine in the flow chart shown in FIG. 23 is carried out only for a period of time until the internal combustion engine 1 is started for the first time after an ignition switch (IG-SW) has been turned on.

In the flow chart shown in FIG. 23, in cases where an affirmative determination is made in step S104, the routine goes to step S401. In step S401, the electric power to be supplied to the electrically heated catalyst 4 is set to the first electric power E6.

On the other hand, in the flow chart shown in FIG. 23, in cases where a negative determination is made in step S104, the routine goes to step S402. In step S402, it is determined whether the stop counter exceeds a stop threshold value. The stop counter indicates an elapsed period of time from a point in time at which the amount of electric energy Q reaches a switch amount of electric energy Q2. A stop threshold value does not necessarily need to be the same as the stop threshold value according to the third embodiment, and has been obtained in advance by experiments, simulations, or the like. In cases where an affirmative determination is made in step S402, the routine goes to step S403, but on the other hand, in cases where a negative determination is made, the routine goes to step S303. In step S403, the electric power to be supplied to the electrically heated catalyst 4 is set to the second electric power E7.

In step S404, it is determined whether the completion counter exceeds a starting threshold value. The starting threshold value is set based on a period of time until the temperature difference in the electrically heated catalyst 4 diminishes into an allowable temperature difference range. The starting threshold value according to this fourth embodiment does not necessarily need to be the same as the starting threshold value according to the second embodiment, and has been obtained in advance by experiments, simulations, or the like. In cases where an affirmative determination is made in step S404, the routine goes to step S109, whereas in cases where a negative determination is made, the routine goes to step S108.

In addition, in the flow chart shown in FIG. 23, various parameters are reset in step S405. The parameters to be reset in step S405 are, for example, the amount of electric energy Q, the completion counter and the stop counter. That is, the amount of electric energy Q, the completion counter and the stop counter are reset to 0.

Here, note that in this fourth embodiment, a period of time from a start point in time of electrical energization until the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 corresponds to the first period of time in the present disclosure, and a period of time from the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 until a point in time at which the completion counter reaches the starting threshold value corresponds to the second period of time in the present disclosure. Also, a period of time from the point in time at which the amount of electric energy Q reaches the switch amount of electric energy Q2 until a point in time at which the stop counter reaches the stop threshold value corresponds to the stop period of time before supply of the second electric power in the present disclosure, and a period of time from the point in time at which the stop counter reaches the stop threshold value until a point in time at which the amount of electric energy Q reaches a required amount of electric energy Q1 corresponds to the second electric power supply period of time in the present disclosure. In addition, a period of time from the point in time at which the amount of electric energy Q reaches the required amount of electric energy Q1 until the point in time at which the completion counter reaches the starting threshold value corresponds to a stop period of time after supply of the second electric power in the present disclosure. Moreover, in this fourth embodiment, the processing in which the ECU 10 sets the electric power to be supplied to the first electric power in the first period of time corresponds to the first processing in the present disclosure, and the processing in which the ECU 10 successively sets the electric power to be supplied to zero, the second electric power E7 and zero in the second period of time corresponds to the second processing in the present disclosure.

As described above, in this fourth embodiment, by setting the electric power to the relatively large first electric power E6 until the amount of electric energy Q reaches the switch amount of electric energy Q2, a larger amount of heat can be supplied to the electrically heated catalyst 4 in a quick manner, so that the mean temperature of the electrically heated catalyst 4 can be caused to rise more quickly. Moreover, when the amount of electric energy Q reaches the switch amount of electric energy Q2, heat can be moved from the high temperature locations to the low temperature locations by once stopping the supply of electric power, so that the temperature difference inside the electrically heated catalyst 4 can be made to diminish. Thereafter, by setting the electric power to the relatively small second electric power E7, overheating in the high temperature locations can be suppressed, and at the same time, an enlargement of the temperature difference inside the electrically heated catalyst 4 can be suppressed due to transfer of heat from the high temperature locations to the low temperature locations. Further, by providing the period of time in which the supply of electric power is stopped during a period of time until the internal combustion engine 1 is started after the supply of the second electric power E7 is completed, heat is moved or transferred from the high temperature locations to low temperature locations, so that the temperature difference inside the electrically heated catalyst 4 can be further diminished. Accordingly, the temperature difference inside the electrically heated catalyst 4 can be made smaller. With this, it is possible to activate a wider range of the catalyst 4B, so that the purification rate of the exhaust gas in the electrically heated catalyst 4 can be enhanced.

Claims

1. An exhaust gas purification apparatus for an internal combustion engine comprising:

an electrically heated catalyst that includes a heat generation element arranged in an exhaust passage of the internal combustion engine for generating heat by receiving supply of electric power, and a catalyst supported by said heat generation element;

a power supply that supplies electric power to said heat generation element; and

a controller configured to adjust the electric power to be supplied to said heat generation element from said power supply;

wherein in a first period of time and a second period of time in which said internal combustion engine is stopped and which are before starting said internal combustion engine, said second period of time being after said first period of time, said controller is configured to supply electric power such that a total amount of electric energy to be supplied to said heat generation element from said power supply becomes a required amount of electric energy; and

said controller is further configured to carry out first processing, in which the electric power to be supplied to said heat generation element from said power supply is set to a first electric power in said first period of time such that a temperature inside said heat generation element falls within an allowable temperature range, and second processing, in which at least one of setting the electric power to be supplied to said heat generation element from said power supply to a second electric power smaller than said first electric power, and/or setting the electric power to be supplied to said heat generation element from said power supply to zero, is performed in said second period of time such that a difference in temperature inside said heat generation element falls within an allowable temperature difference range.

2. The exhaust gas purification apparatus for an internal combustion engine as set forth in claim 1, wherein

said controller is configured to set the electric power to be supplied to said heat generation element from said power supply to 0 in a stop period of time before supply of the second electric power, which is included in said second period of time, and also set the electric power to be supplied to said heat generation element from said power supply to said second electric power in a second electric power supply period of time, which is included in said second period of time and which is after said stop period of time before supply of the second electric power.

3. The exhaust gas purification apparatus for an internal combustion engine as set forth in claim 1, wherein

said controller is configured to set the electric power to be supplied to said heat generation element from said power supply to said second electric power in a second electric power supply period of time which is included in said second period of time, and also set the electric power to be supplied to said heat generation element from said power supply to 0 in a stop period of time after the second electric power supply period of time, which is included in said second period of time and which is after said second electric power supply period of time.

4. The exhaust gas purification apparatus for an internal combustion engine as set forth in claim 1, wherein

said controller is configured to set said first electric power, said first period of time, said second electric power and said second period of time in such a manner that the amount of electric energy at an end point in time of said second period of time becomes the required amount of electric energy, and start said internal combustion engine at a point in time at which said second period of time expires.