Abnormality diagnosing device for internal combustion engine and abnormality diagnosing method therefor

Abstract

A temperature of a catalyst disposed in an exhaust system is raised to a target bed temperature by supplying an unburned fuel component to the catalyst. A learned value is updated based upon a catalyst bed temperature under a temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures. Whether the learned value is out of a proper range or not is determined whenever the learned value is updated. Abnormality is determined when determination that the learned value is out of the proper range is made over several successive updates of the learned value.

Description

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2006-168847 filed on Jun. 19, 2006 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an abnormality diagnosing device for an internal combustion engine and an abnormality diagnosing method therefor.

2. Description of the Related Art

Conventionally, as an exhaust gas purification system of an internal combustion engine such as, for example, a diesel engine for a vehicle, a system including a particulate matter (PM) filter and a catalytic converter disposed in an exhaust system is known. The PM filter traps PM whose major component is soot. The catalytic converter includes a storage reduction type NOx catalyst for purifying exhaust gas, i.e., nitrogen oxides (NOx). In such an exhaust gas purification system, a temperature increase control is executed to raise a temperature of the catalyst to a target bed temperature by supplying unburned fuel components to the catalyst to recover an exhaust gas purification capacity.

For example, accumulation of the particulate matter clogs the PM filter and the catalytic converter. However, the filter may be regenerated by burning (oxidizing) the particulate matter, which eliminates the clogging. The temperature increase control is executed to regenerate the filter. In the temperature increase control, the unburned fuel components are supplied to the catalyst, and components such as, for example, a hydro carbon (HC) and a carbon monoxide (CO) are oxidized in the exhaust gas or on the catalyst. The heat generated by the oxidization raises the bed temperature of the catalyst to a target bed temperature. Because the catalyst bed temperature is increased, the PM filter and the catalytic converter are placed under the high temperature circumstances. The accumulating particulate matter is thus removed. The capacity of the PM filter for the particulate matters is recovered, accordingly.

Meanwhile, occasionally, the catalyst bed temperature does not reach the target bed temperature even though the unburned fuel components are supplied to the catalyst to raise the temperature to the target bed temperature. For example, if a fuel supply system through which the unburned fuel components are supplied to the catalyst is clogged, the amount of the unburned fuel components supplied to the catalyst may be less than the amount required. The deficiency in the amount supplied causes the actual catalyst bed temperature to deviate from the target bed temperature.

In order to determine whether such abnormality occurs or not. JP-A-2003-172185 describes in paragraphs [0065] through [0068] the following abnormality diagnosis. That is, during the temperature increase control to regenerate the filter, a learned value is updated based upon the catalyst bed temperature and the target bed temperature so that the learned value corresponds to the difference between the respective temperatures. The updated learned value is reflected to the supply amount of the unburned fuel components to the catalyst. Also, presence of the abnormality is determined by determining whether the learned value is within a proper range or not. On this occasion, if the abnormality described above occurs, the learned value is outside of the proper range. The abnormality thus is determined based upon the determination that the learned value is outside of the proper range.

In the meantime, regarding the abnormality such that the catalyst bed temperature does not reach the target bed temperature even though the unburned fuel components are supplied to the exhaust system to raise the catalyst bed temperature to the target bed temperature, this abnormality does not necessarily permanently occur but can temporarily occur. The learned value that is updated to correspond to the difference between the catalyst bed temperature and the target bed temperature is out of the preset proper range as long as the abnormality continues.

As one of situations in which such a temporary abnormality occurs, a situation can be exemplified such that a supplemental fuel valve is used to supply supplemental fuel to the exhaust system for supplying the unburned fuel components to the catalyst, and, due to use of poor quality fuel, deposits adhere to the periphery of a nozzle of the supplemental fuel valve. The adhesion of the deposits to the nozzle periphery of the supplemental fuel valve decreases the amount of the unburned fuel components supplied to the catalyst. As a result, despite of the attempt to raise the catalyst bed temperature to the target bed temperature by supplying the supplemental fuel through the supplemental fuel valve, the abnormality occurs such that the catalyst bed temperature does not reach the target bed temperature. However, even though the deposits adhere to the nozzle periphery of the supplemental fuel valve due to the use of the poor quality fuel, such deposits are highly likely to depart from the nozzle periphery while the supplemental fuel being supplied. Therefore, the occurrence of the abnormality accompanying the adhesion of the deposits is temporary.

The abnormality diagnosis described in JP-A-2003-172185 may incorrectly determine that an abnormality is present. This is because the temporary abnormality affects the catalyst bed temperature, and, when the learned value that is updated to correspond to the difference between the catalyst bed temperature and the target bed temperature is outside of the preset proper range, the abnormality is immediately determined based upon the determination that the learned value is out of the proper range. That is, if the abnormality disappears after the abnormality is determined, the determination of the abnormality is incorrect.

SUMMARY OF THE INVENTION

The invention provides an abnormality diagnosing device for an internal combustion engine and an abnormality diagnosing method therefor that avoids incorrect abnormality determination when a temporary abnormality occurs.

A first aspect of this invention relates to an abnormality diagnosing device for an internal combustion engine in which a temperature increase control for increasing a temperature of a catalyst disposed in an exhaust system to a target bed temperature is executed by supplying an unburned fuel component to the catalyst, updating of a learned value is executed based upon a catalyst bed temperature under the temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures, and an abnormality is determined based upon the learned value when the learned value is updated. The abnormality diagnosing device includes learned value determining means for determining whether the learned value is outside of a proper range or not when the learned value is updated, and determines that an abnormality is present only when the learned value falls outside of the proper range over several successive updates of the learned value.

The abnormality such that the catalyst bed temperature does not reach the target bed temperature even though the unburned fuel components are supplied to the exhaust system to keep the catalyst bed temperature on the target bed temperature does not necessarily permanently occur but can temporarily occur. Even though the difference between the catalyst bed temperature and the target bed temperature is temporary, the learned value is updated to correspond to the difference, and the learned value may fall outside of the proper range. When this occurs, if the abnormality is immediately determined when the learned value falls outside of the proper range, the determination of the abnormality may be incorrect when the temporary abnormality disappears afterwards. However, according to the construction described above, even though the learned value falls outside of the proper range, the abnormality is not determined unless the learned value falls outside of the proper range over several successive updates of the learned value. Therefore, the abnormality is not incorrectly determined when the catalyst bed temperature and the target bed temperature are temporarily inconsistent with each other.

In this aspect, the internal combustion engine may have a supplemental fuel valve for supplying supplemental fuel upstream of the catalyst in the exhaust system.

According to the above construction, the supplemental fuel valve supplies supplemental fuel to supply the unburned fuel components to the catalyst disposed in the exhaust system. In this connection, if poor quality fuel is used, deposits are likely to adhere to the periphery of the nozzle of the supplemental fuel valve. The adhesion of the deposits reduces the amount of the fuel supplied through the supplemental fuel valve which causes the catalyst bed temperature to be lower than the target bed temperature. However, the deposits adhering to the nozzle periphery of the supplemental fuel valve is highly likely to come off from the nozzle periphery while the supplemental fuel being supplied. The abnormality such that the catalyst bed temperature varies from the target bed temperature thus can be temporary. Therefore, it is determined that an abnormality is not present based upon such a temporary abnormality.

In the aspect, the exhaust system of the internal combustion engine may have a filter for trapping particulate matter. The temperature increase control for increasing the temperature of the catalyst to the target bed temperature may be executed by supplying the unburned fuel component to the catalyst when to burn the particulate matter to regenerate the filter. Thus, reducing the amount of particulate matter trapped in the filter is to less than a prescribed amount.

According to the above construction, the filter regeneration is regularly made maintain the amount of particulate matter accumulating in the catalyst to less than a prescribed amount. When the temperature-increase control for the filter regeneration is executed, the abnormality may be simultaneously determined. Chances for the abnormality determination are not reduced, accordingly.

In the first aspect, the abnormality diagnosing device may have counting means for increasing a count value when the learned value determining section determines that the learned value has fallen outside of the proper range and resets the count value to an initial value, for example, “0” when the learned value determining section determines that the learned value is in the proper range. The abnormality determining means determines that an abnormality is present when the count value becomes a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, e.g., an integer such as “2”. The counting means can reset the count value to the initial value when the filter regeneration is completed.

If the abnormality that the catalyst bed temperature does not reach the target bed temperature temporarily occurs during the temperature increase control for the filter regeneration, the updated learned value fall outside of the proper range and the counting means increases the count value. If, however, the temporary abnormality does not affect the filter regeneration so much, the filter regeneration may be completed because the accumulation amount of the particulate matter on the catalyst decreases to be less than the prescribed amount before the count value exceeds the abnormality threshold value. On this occasion, if the count value is maintained above “0,” the count value reaches or exceeds the determination value soon once the learned value varies to be out of the proper range because the temporary abnormality again occurs during the subsequent temperature increase control for the filter regeneration. Consequently, the abnormality can be incorrectly determined. According to the above construction, however, the count value is reset to “0” whenever the filter regeneration is completed. The incorrect abnormality determination described above thus can be avoided.

In the first aspect, the abnormality diagnosing device can have counting means for increasing a count value when the learned value determining means determine that the learned value has fallen outside of the proper range and resets the count value to an initial value when the learned value determining means determine that the learned value is in the proper range. The learned value is updated when the catalyst bed stably maintains a catalyst bed temperature that is equal to or higher than the temperature at which the particulate matter burns. The abnormality determining means determine that an abnormality is present when the count value given by the counting means becomes a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, e.g., an integer such as “2”. The abnormality determining means may also determine that an abnormality is present, regardless of the count value, if the filter regeneration is not completed after the elapsed time from when the filter regeneration starts reaches or exceeds a permissible time period.

When the abnormality occurs such that the catalyst bed temperature does not reach the target bed temperature during the temperature increase control for the filter regeneration, the learned value is not updated unless the catalyst bed temperature stably maintains a catalyst bed temperature that is equal to or higher than the temperature at which the particulate matter accumulating in the catalyst burns even though the updated learned value may fall outside of the proper range. Under the condition, despite of occurrence of the abnormality, the filter regeneration continues with the count value remaining less than the determination value, i.e., without the abnormality being determined. The filter regeneration is highly likely to stay uncompleted under the condition because the particulate matters accumulating in the catalyst are hardly burned. According to the above construction, however, if the filter regeneration is not completed even though the time elapsing from the start moment of the filter regeneration reaches or exceeds the permissible time period, the abnormality is determined whether or not the count value is still less than the abnormality threshold value. Thus, the abnormality can be determined whenever the abnormality actually occurs.

In the aspect, the abnormality determining means can determine that an abnormality is present when the learned value determining means determine that the learned value varies to be larger than the proper range over several successive updates of the learned value.

In the aspect, the unburned fuel component can be supplied to the catalyst by an auxiliary injection made in an exhaust stroke or an expansion stroke after fuel is injected for combustion in a combustion chamber from a fuel injector.

A second aspect of this invention relates to an abnormality diagnosing method for an internal combustion engine in which a temperature increase control for increasing a temperature of a catalyst disposed in an exhaust system to a target bed temperature is executed by supplying an unburned fuel component to the catalyst, updating a learned value is executed based upon a catalyst bed temperature under the temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures, and abnormality is determined based upon the learned value when the learned value is updated. In this method, it is determined whether the learned value falls outside of a proper range every time the learned value is updated. Also, an abnormality is determined to be present when it is determined that the learned value falls outside of the proper range over several successive updates of the learned value.

In this aspect, preferably, the exhaust system of the internal combustion engine can have a filter for trapping particulate matter. The temperature increase control for increasing the temperature of the catalyst to the target bed temperature can be executed by supplying the unburned fuel component to the catalyst when a filter regeneration is made to burn the particulate matters so that an accumulation amount of the particulate matter trapped by the filter is to be less than a preset amount.

In the aspect, a count value can be increased when the learned value is determined to fall outside of the proper range. The count value is reset to an initial value when the learned value is determined to be in the proper range. An abnormality is determined to be present when the count value is greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value. The count value can be reset to the initial value when the filter regeneration is completed.

In the aspect, a count value can be increased when the learned value is determined to be outside of the proper range. The count value can be reset to an initial value when the learned value is determined to be in the proper range. The learned value can be updated when the catalyst bed temperature is stably maintained at a temperature that is equal to or above the temperature at which the particulate matter burns. The abnormality can be determined to be present when the count value is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value. The abnormality is determined to be present regardless of the count value if the filter regeneration is not completed after a time period has elapsed from a start moment of the filter regeneration reaches or exceeds a permissible time period.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic view showing an overall structure of an internal combustion engine to which an abnormality diagnosing device of this embodiment is applied.

FIGS. 2A through 2D are time charts showing a change of supply pulses for driving a supplemental fuel valve during a temperature increase control for filter regeneration, changes of a catalyst bed temperature T and a catalyst inlet port exhaust temperature Tb, transitions of integration values ΣQr, ΣQ, and a set mode of an supplement permission flag F1, respectively.

FIG. 3 is a flowchart showing control processes for fuel supplementation made by the supplemental fuel valve during the temperature increase control.

FIG. 4 is another flowchart showing successive control processes for the fuel supplementation made by the supplemental fuel valve during the temperature increase control;

FIG. 5 is a time chart showing a condition under which a stationary difference appears between the catalyst bed temperature (catalyst bed temperature average value Tave) and a target bed temperature Tt.

FIG. 6 is a time chart showing the integration values ΣQr, ΣQ in a situation that a learned value K is not reflected.

FIG. 7 is a time chart showing the integration values ΣQr, ΣQ in a situation that a learned value K is reflected.

FIG. 8A is a time chart showing transitions of the catalyst bed temperature average value Tave and the target bed temperature Tt provided when a stationary difference therebetween disappears, and FIG. 8B is a time chart showing a transition manner of the learned value K under the same condition.

FIG. 9 is a flowchart showing a learned value updating routine for storing the learned value K into a nonvolatile RAM.

FIG. 10 is a time chart showing a transition of the learned value K made each time the learned value K is updated when a temporary abnormality occurs.

FIGS. 11A and 11B are time charts showing the transition of the learned value K made each time the learned value K is updated and a transition of a count value of a counter C, respectively.

FIG. 12 is a flowchart showing abnormality diagnosing processes of this embodiment.

FIGS. 13A and 13B are time charts showing the transition of the learned value K made each time the learned value K is updated and a transition of a count value of a counter C, respectively.

FIGS. 14A through 14C are time charts showing the transition of the learned value K made each time the learned value K is updated, the transition of the count value of the counter C, and a change mode of an abnormality flag F2, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 through 14, one embodiment in which the present invention is embodied will be described below. FIG. 1 shows the structure of an internal combustion engine 10 equipped with an abnormality diagnosing device of the embodiment of the invention. The engine 10 is a diesel engine for an automobile and has a common-rail type fuel injection device.

An intake passage 12 forms part of the intake system of the engine 10. An exhaust passage 14 forms part of the exhaust system of the engine 10. The intake and exhaust passages 12 and 14 are individually connected to the combustion chambers 13 of respective cylinders of the engine 10. An airflow meter 16 and an intake throttle valve 19 are placed in the intake passage 12. A catalytic converter 25 for NOx, a PM filter 26 and a catalytic converter 27 for oxidation are placed in the exhaust passage 14 in this order from the upstream portion of the exhaust passage 14.

The catalytic converter 25 for NOx contains a storage reduction type NOx catalyst. The NOx catalyst absorbs and stores NOx in exhaust gas when the oxygen concentration of the exhaust gases is high, and discharges the NOx which has been stored when the oxygen concentration of the exhaust gas is low. Also, the NOx catalyst reduces the discharged NOx to purify the exhaust gas if sufficient unburned fuel components, which act as reducing agents, are present around the catalyst when the NOx is discharged.

The PM filter 26 is made of a porous material that traps particulate matter (PM) whose major component is soot in the exhaust gas. Similarly to the NOx catalytic converter 25, the PM filter 26 contains another storage reduction type NOx catalyst to reduce the NOx in the exhaust gases. The reaction catalyzed by the NOx catalyst burns (oxidizes) the trapped particulate matter to remove them.

The oxidation catalytic converter 27 contains an oxidation catalyst. The oxidation catalyst oxidizes hydrocarbons (HC) and carbon monoxides (CO) in the exhaust gas to purify the exhaust gas. The exhaust passage 14 has an incoming gas temperature sensor 28 positioned upstream of the PM filter 26 and an outgoing gas temperature sensor 29 positioned downstream of the PM filter 26. The incoming gas temperature sensor 28 detects the temperature of the incoming exhaust gas, which enters the PM filter 26. The outgoing gas temperature sensor 29 detects the temperature of the outgoing exhaust gas, which has passed through the PM filter 26. A differential pressure sensor 30 is arranged to the exhaust passage 14 to detect the differential pressure between a portion of the exhaust passage 14 positioned upstream of the PM filter 26 and a portion of the exhaust passage 14 positioned downstream of the PM filter 26. An air-fuel ratio sensor 31 is disposed at a portion of the exhaust passage 14 positioned upstream of the NOx catalytic converter 25 to detect an air-fuel ratio of the exhaust gases. Another air/fuel ratio sensor 32 is disposed at a portion of the exhaust passage 14 positioned between the PM filter 26 and the oxidation catalytic converter 27 to detect the air-fuel ratio of the exhaust gases.

The engine 10 has an exhaust gas recirculation (EGR) system that recirculates a portion of the exhaust gas to the intake passage 12. The EGR system includes an EGR passage 33 connecting the exhaust passage 14 and the intake passage 12 to each other. The most upstream portion of the EGR passage 33 that is upstream is connected to the exhaust passage 14. The EGR passage 33 has an EGR valve 36. The most downstream portion of the EGR passage 33 is connected to a portion of the intake passage 12 positioned downstream of the intake throttle valve 19.

On the other hand, fuel injectors 40 are arranged at the combustion chambers 13 of the respective cylinders of the engine 10 to inject fuel for combustion in the combustion chambers 13. The fuel injectors 40 of the respective cylinders are connected to a common rail 42 through high-pressure fuel delivery pipes 41. A fuel pump 43 supplies highly pressurized fuel to the common rail 42. A rail pressure sensor 44 attached to the common rail 42 detects the pressure of the highly pressurized fuel in the common rail 42. The fuel pump 43 also supplies low pressurized fuel to a supplemental fuel valve 46 through a low pressure fuel delivery pipe 45.

An electronic control unit (ECU) 50 executes various controls of the engine 10. The ECU 50 includes a CPU, ROM, RAM, input and output ports and so forth. The CPU executes various calculation processes for controlling the engine 10. The ROM stores programs and data necessary for the controls. The RAM temporarily stores the results of calculations of the CPU, or the like. The input and output ports are used for inputting and outputting signals from and to external equipment, respectively.

The input ports of the ECU 50 are connected to, in addition to the respective sensors described above, an engine speedsensor 51 that detects the engine speed, an accelerator position sensor 52 that detects the operational amount of an accelerator, a throttle valve position sensor 53 that detects the opening amount of the intake throttle valve 19, an intake temperature sensor 54 that detects the intake temperature of the engine 10, a coolant temperature sensor 55 that detects the temperature of coolant of the engine 10, and so forth. The output ports of the ECU 50 are connected to drive circuits for the intake throttle valve 19, the EGR valve 36, the fuel injectors 40, the fuel pump 43, the supplemental fuel valve 46 and so forth.

The ECU 50 outputs command signals to the drive circuits of the respective devices connected to the output ports in response to engine operational conditions grasped through detection signals input from the respective sensors. In this manner, the ECU 50 executes a control to open the intake throttle valve 19, an EGR control based upon the control of the opening of the EGR valve 36, controls of a fuel injection amount, a fuel injection time and a fuel injection pressure of each fuel injector 40, a control of the fuel supplementation through the supplemental fuel valve 46 and so forth.

In the embodiment constructed as described above, a filter regeneration is executed to prevent particulate matter from clogging the NOx catalytic converter 25 and the PM filter 26. The filter regeneration includes processes for burning the particulate matter that has accumulating in the exhaust system such as, for example, the NOx catalytic converter 25 and the PM filter 26, to regenerate them. In order to make the regenerate the filter, the NOx catalytic converter 25 and the PM filter 26 must be heated to a prescribed temperature. Thus, when the filter is regenerated, unburned fuel components are supplied to the NOx catalytic converter 25 and the NOx catalyst of the PM filter 26. Thereby, a temperature increase control is executed to raise a catalyst bed temperature to the temperature (for example, 600-700° C.) necessary for burning the particulate matter. The supplemental fuel valve 46 supplies the unburned fuel components to the catalysts in the temperature increase control.

In this connection, the temperature raising control for the filter regeneration in this embodiment starts when all of the following conditions are satisfied.

It is the time that the filter regeneration is required. The requirement of the filter regeneration at this moment is made when the accumulation amount of the particulate matters in the exhaust system estimated from the engine operational condition reaches or exceeds a permissible amount and the clogged states of the filters including the PM filter 26 are verified.

The detection value of the entering gas temperature sensor 28 (entering gas temperature thci) is equal to or higher than the lower limit temperature (for example, 150° C.) that allows the execution of the temperature raising control. Also, the catalyst bed temperature of the NOx catalyst estimated from histories of the engine operational conditions, the detection value of the entering gas temperature sensor 28 and the detection value of the outgoing gas temperature sensor 29 is equal to or higher than the lower limit temperature that allows the execution of the temperature raising control. To those lower limit temperatures, a lower limit value of the exhaust temperature and a lower limit value of the catalyst bed temperature are allotted, respectively. Both of the lower limit values of the temperatures can generate the oxidizing reaction that can raise the catalyst bed temperature.

The detection value of the entering gas temperature sensor 28 is less than the upper limit value C in a temperature range where excessive temperature raising of the catalysts by heat generation accompanying the temperature raising control can be avoided.

Similarly, the detection value of the outgoing gas temperature sensor 29 is less than the upper limit value D in a temperature range where the excessive temperature raising of the catalysts by the heat generation accompanying the temperature raising control can be avoided.

The execution of the fuel supplementation to the exhaust gases is permitted. In other words, it is under the engine operational condition that the fuel supplementation to the exhaust gases is permissible. In connection with this engine 10, the fuel supplementation to the exhaust gases is permitted under the condition that the engine is not stalling, cylinder discrimination has been finished and the output of the engine 10 is not limited.

When the accumulated amount of the particulate matter decreases to a preset amount (for example, “0” ) by the execution of the filter regeneration through the temperature increase control, it is determined that the filter regeneration process is complete. The temperature increase control for the filter regeneration thus is terminated.

Next, with reference to the time chart of FIG. 2, an outline of the temperature increase control will be described. The catalyst bed temperature T under the temperature increase control increases relative to the catalyst inlet port exhaust temperature Tb in accordance with the amount of the heat generated by the oxidizing reaction occurs when supplemental fuel is supplied through the supplemental fuel valve 46. Under the temperature increase control, the target bed temperature Tt increases incrementally, for example, 600, 630 and then 650. In order to raise the catalyst bed temperature T to the target bed temperature Tt, the supplemental fuel is supplied through the supplemental fuel valve 46 to supply the unburned fuel components. However, occasionally, if the exhaust temperature of the engine 10 is low and the exhaust gas flow amount is low, the target bed temperature Tt is temporarily lowered so that the fuel is not uselessly supplied through the supplemental fuel valve 46. This is because, in such a state, the oxidizing reaction of the unburned fuel components does not proceed and the catalyst bed temperature T cannot be raised even though the amount of fuel supplied through the supplemental fuel valve 46 increases.

The the supply of fuel through the supplemental fuel valve 46 starts when a supplement permission flag F1, shown in FIG. 2D, is set to “1” (time T1). The supplement permission flag F1 is then set to “0” after becoming “1.” When the fuel supplementation through the supplemental fuel valve 46 starts, the supplemental fuel is intermittently supplied through the supplemental fuel valve 46 in accordance with supply pulses shown in FIG. 2A. A supplemental time [a] of the fuel and a pause time [b] for the intermittent fuel supplementation are set based upon a temperature difference ΔTb between the target bed temperature Tt and the catalyst inlet port exhaust temperature Tb, and a gas-flow amount Ga of the engine 10 (corresponding to the exhaust gas flow of the engine 10) detected by the airflow meter 16. As the inlet port exhaust temperature Tb, for example, a value estimated based upon the temperatures detected by incoming exhaust gas temperature sensor 28 and the outgoing gas temperature sensor 29 are used. The intermittent fuel supplementation that has started as described above continues until the fuel supplementation is executed predetermined times. When the fuel supplementation is executed such times, the fuel supplementation is terminated (time T2).

After the start of the fuel supplementation through the supplemental fuel valve 46, a heat generating fuel amount Q is calculated every preset time. For example, a 16 ms heat generating fuel amount Q is calculated every 16 ms. The amount Q is a fuel amount that is supplied through the supplemental fuel valve 46 in the period of 16 ms. The 16 ms heat generating fuel amount Q is summed up every time when it is calculated based upon an equation “ΣQ←the last ΣQ+Q . . . (1)” to calculate the total fuel supplementation amount ΣQ supplied through the supplemental fuel valve 46 summed up from the fuel supplementation start moment (T1), i.e., a heat generating fuel amount integration value ΣQ indicative of the total fuel amount contributing to the heat generation by the oxidizing reaction. As indicated by the actual line of FIG. 2C, the heat generating fuel amount integration value ΣQ as thus calculated rapidly increases during an supply period (A) which is a time period between the start and end of the fuel supplementation. The heat generating fuel amount integration value ΣQ, however, is inhibited from increasing during a pause period of the fuel supplementation succeeding the supply period (A).

In the meantime, after the start of the fuel supplementation through the supplemental fuel valve 46, a 16 ms required fuel amount Qr is calculated every preset time (16 ms). The 16 ms required fuel amount Qr is an amount of the fuel that is required to be supplied through the supplemental fuel valve 46 in 16 ms, i.e., a supply amount of the fuel necessary for raising the catalyst bed temperature T to the target bed temperature Tt. The 16 ms required fuel amount Qr is calculated using the temperature difference ΔTb between the target bed temperature Tt and the catalyst inlet port exhaust temperature Tb, and the gas-flow amount Ga of the engine 10. The lower the catalyst inlet port exhaust temperature Tb indicated by the actual line L2 of FIG. 2B relative to the target bed temperature results in the larger the 16 ms required fuel amount Qr as thus calculated the 16 ms required fuel amount Qr is summed up every time when it is calculated based upon an equation “ΣQr←the last ΣQr+Qr . . . (2)” to calculate a required fuel amount integration value ΣQr indicative of an amount of the fuel from the fuel supplementation start moment (T1) that is necessary to designate an average amount of the catalyst bed temperature T for the target bed temperature Tt. As indicated by the dashed line of FIG. 2C, the required fuel amount integration value ΣQr as thus calculated gradually increases in comparison with the increase of the heat generating fuel amount integration value ΣQ (actual line).

When the required fuel amount integration value ΣQr reaches or exceeds the heat generating fuel amount integration value ΣQ (time T3), the supplement permission flag F1 changes to “1 (permission)” and the intermittent fuel supplementation through the supplemental fuel valve 46 starts. On this occasion, the fuel amount corresponding to the heat generating fuel amount integration value ΣQ has been supplied through the supplemental fuel valve 46 after the time T1. The heat generating fuel amount integration value ΣQ thus is subtracted from the required fuel amount integration value ΣQr. In addition, the heat generating fuel amount integration value ΣQ is cleared to be “0.” Following the start of the intermittent fuel supplementation through the supplemental fuel valve 46, the supply period (A) starts again. When this supply period (A) ends, the pause period (B) starts. Therefore, the supply period (A) and the pause period (B) alternately repeat during the temperature increase control.

Additionally, the larger the catalyst inlet port exhaust temperature Tb leaves from the target bed temperature Tt on the decrement side of this temperature Tt, the larger the calculated 16 ms required fuel amount Qr becomes and the more rapidly the required fuel amount integration value ΣQr increases. As a result, the time necessary for the required fuel amount integration value ΣQr to reach or exceed the heat generating fuel amount integration value ΣQ becomes shorter, and the pause period (B) also becomes shorter. Meanwhile, the larger the catalyst inlet port exhaust temperature Tb approaches the target bed temperature Tt, the smaller the calculated 16 ms required fuel amount Qr becomes and the more rapidly the required fuel amount integration value ΣQr increases. As a result, the time necessary for the required fuel amount integration value ΣQr to reach or exceed the heat generating fuel amount integration value ΣQ becomes longer, and the pause period (B) also becomes longer.

As thus described, the pause period (B) varies in response to the deviated condition of the catalyst inlet port exhaust temperature Tb relative to the target bed temperature Tt. Thereby, the average value of the fuel supplementation amount supplied through the supplemental fuel valve 46 per unit time varies in response to the variation of the pause period (B). The catalyst bed temperature T thus changes as, for example, indicated by the actual line L1 of FIG. 2B. A fluctuation center of the catalyst bed temperature T which increases and decreases can be controlled to be the target bed temperature Tt.

Next, with reference to flowcharts of FIGS. 3 and 4 showing a fuel supplementation control routine, control processes for the fuel supplementation through the supplemental fuel valve 46 under the temperature increase control will be described. The ECU 50 executes the fuel supplementation control routine periodically, for example, by allowing the routine to cut in for a period (16 ms in this embodiment) every preset time.

In this routine, first, at step S101 of FIG. 3, the ECU 50 determines whether the temperature increase control proceeds or not. If positively determining, the ECU 50 goes to step 102 to calculate a 16 ms required fuel amount Qr based upon a temperature difference ΔTb appearing between the target bed temperature Tt and the catalyst inlet port exhaust temperature Tb and the gas-flow amount Ga. At successive steps S103 and S104, the ECU 50 adjust the 16 ms required fuel amount Qr using a learned value K to remove the stationary difference between the catalyst bed temperature T and the target bed temperature Tt.

More specifically, at step S103, the ECU 50 reads out the learned value K stored in the nonvolatile RAM thereof. The learned value K has been calculated through another routine to be a value corresponding to the stationary difference between the catalyst bed temperature T and the target bed temperature Tt and is stored in the nonvolatile RAM. Also, at step S104, the ECU 50 sets the value obtained by multiplying the 16 ms required fuel amount Qr by the learned value K as the new 16 ms required fuel amount Qr.

The ECU 50 sums up 16 ms required fuel amount Qr calculated at steps S102 through steps S104 based upon the equation “ΣQr←the last ΣQr+Qr . . . (2)” at step S105. The required fuel amount integration value ΣQr described above is obtained through the summing up calculation. Afterwards, the ECU 50 goes to step S106.

At step S106, the ECU 50 calculates a 16 ms heat generating fuel amount Q based upon an operational condition of the supplemental fuel valve 46. Next, the ECU 50 sums up the calculated 16 ms heat generating fuel amount Q based upon the equation “ΣQ←the last ΣQ+Q . . . (1)” at step S107. The heat generating fuel amount integration value ΣQ described above is obtained through the summing up calculation.

At step S108, the ECU 50 determines whether the required fuel amount integration value ΣQr reaches or exceeds the heat generating fuel amount integration value ΣQ. If so, the ECU 50 proceeds to step S109 and sets the supplement permission flag F1 to “1 (permission).” As a result, the ECU 50 starts the intermittent fuel supplementation through the supplemental fuel valve 46. Afterwards, at step S110, the ECU 50 sets a value obtained through subtracting the heat generating fuel amount integration value ΣQ from the required fuel amount integration value ΣQr as the new required fuel amount integration value ΣQr. In addition, the ECU 50, at step S111, clears the heat generating fuel amount integration value ΣQ to be “0”.

Next, additionally referring to FIGS. 5 through 7, an outline of calculation processes for the learned value K that is used at step S103 of FIG. 3 will be described.

FIG. 5 shows a condition under which the stationary difference appears between the catalyst bed temperature T and the target bed temperature Tt during the temperature increase control and the catalyst bed temperature T (actual line) does not rise to the target bed temperature Tt (dashed line). Reasons why such a stationary difference appears are, for example, that the fuel supplementation amount varies from its proper amount due to occurrence of abnormality that the supplemental fuel valve 46 is clogged, or that the gas-flow amount Ga varies from its proper amount due to occurrence of abnormality of the airflow meter 16.

The calculated learned value K is corresponds to the difference between the catalyst bed temperature T (catalyst bed temperature average value Tave) and the target bed temperature Tt and is used to adjust the 16 ms required fuel amount Qr. When adjusting the 16 ms required fuel amount Qr using the learned value K, the increase of the required fuel amount integration value ΣQr is expedited or retarded, and the moment at which the required fuel amount integration value ΣQr reaches or exceeds the heat generating fuel amount integration value ΣQ varies. As a result, the pause periods (B) fluctuate and an average value of the fuel amount supplied through the supplemental fuel valve 46 per unit time varies. Accordingly, the learned value K is reflected in the supply of the unburned fuel components to the catalysts.

In this connection, FIGS. 6 and 7 show variations appearing between a situation in which the learned value K corresponding to the difference is reflected to the supply of the unburned fuel components to the catalysts and another situation in which the learned value K is not reflected to the supply of the unburned fuel components to the catalysts, under the condition that the stationary difference appears between the catalyst bed temperature average value Tave and the target bed temperature Tt as shown in FIG. 5.

The dashed line of FIG. 6 indicates a transition of the required fuel amount integration value ΣQr in the situation that the learned value K is not reflected. In this situation, because the 16 ms required fuel amount Qr is not multiplied by the learned value K, the 16 ms required fuel amount Qr involves the difference to the proper value, resulted from the clogging of the supplemental fuel valve 46 and the abnormality of the airflow meter 16. As a result, the required fuel amount integration value ΣQr gradually increases in corresponding to the difference to the 16 ms required fuel amount Qr. The moment at which the required fuel amount integration value ΣQr reaches or exceeds the heat generating fuel amount integration value ΣQ is likely to delay. Therefore, the pause periods (B) become longer and the average value of the fuel amount supplied through the supplemental fuel valve 46 per unit time becomes smaller. The stationary difference shown in FIG. 5 thus appears between the catalyst bed temperature average value Tave and the target bed temperature Tt.

The dashed line of FIG. 7 shows a transition of the required fuel amount integration value ΣQr in the situation that the learned value K is reflected. In this situation, because the 16 ms required fuel amount Qr is multiplied by the learned value K, the 16 ms required fuel amount Qr does not involve any difference to the proper value, resulted from the clogging of the supplemental fuel valve 46 and the abnormality of the airflow meter 16. As a result, the required fuel amount integration value ΣQr does not gradually increases but rapidly increases in corresponding to the difference to the 16 ms required fuel amount Qr. The moment at which the required fuel amount integration value ΣQr reaches or exceeds the heat generating fuel amount integration value ΣQ is likely to come earlier. Therefore, the pause periods (B) become shorter and the average value of the fuel amount supplied through the supplemental fuel valve 46 per unit time becomes larger. The stationary difference thus disappears between the catalyst bed temperature average value Tave and the target bed temperature Tt.

FIG. 8A is a time chart showing a transition manner of the learned value K when the stationary difference disappears between the catalyst bed temperature average value Tave and the target bed temperature Tt. In this regard, it is assumed that, as indicated by the dashed line and the chain line of FIG. 8, the stationary difference appears in such a manner that the catalyst bed temperature average value Tave is lower than the target bed temperature Tt.

The learned value K corresponding to such a difference is calculated using the 16 ms required fuel amount Qr (see FIG. 2C) and a 16 ms estimation heat generating fuel amount Q′.

The 16 ms estimation heat generating fuel amount Q′ is calculated every 16 ms. The 16 ms estimation heat generating fuel amount Q′ is an estimation value of the fuel amount supplied through the supplemental fuel valve 46 in 16 ms to obtain a rise amount ΔT′ of the catalyst bed temperature T that rises from the catalyst inlet opening exhaust temperature Tb. In other words, the 16 ms estimation heat generating fuel amount Q′ is an estimation value of the fuel amount that contributes to the heat generation made in 16 ms to obtain the rise amount ΔT′. The 16 ms estimation heat generating fuel amount Q′ is calculated based upon the rise amount ΔT′ that is the difference appearing between the catalyst bed temperature T and the catalyst inlet port exhaust temperature Tb and the gas-flow amount Ga. The catalyst bed temperature T can be, for example, a value estimated based upon detection amounts such as, for example, detection amounts of the entering gas temperature sensor 28 and the outgoing gas temperature sensor 29. As described above, the 16 ms required fuel amount Qr represents a fuel amount that needs to be supplied through the supplemental fuel valve 46 in 16 ms to raise the catalyst bed temperature T to the target bed temperature Tt from the catalyst inlet port exhaust temperature Tb, and the 16 ms required fuel amount Qr is calculated based upon the temperature difference ΔTb appearing between the target bed temperature Tt and the catalyst inlet port exhaust temperature Tb and the gas-flow amount Ga.

A ratio Qr/Q′ of the 16 ms required fuel amount Qr to the 16 ms assumption heat generating fuel amount Q′ both described above is a value corresponding to the difference of the catalyst bed temperature T relative to the target bed temperature which is at the calculation moment of the 16 ms required fuel amount Qr and the 16 ms assumption heat generating fuel amount Q′. Therefore, an average value of the ratio Qr/Q′ over a predetermined time period is calculated to obtain the value corresponding to the stationary difference of the catalyst bed temperature average value Tave relative to the target bed temperature Tt. The average value of the ratio Qr/Q′ over the preset time period is calculated as the learned value K. The learned value K is stored (updated) in the nonvolatile RAM when the target bed temperature Tt is stable at the value where the particulate matter is burned.

If the learned value K is updated at preset intervals, for example, at the times T4, T5, T6 in FIGS. 8A and 8B in the processes described above, the learned value K stored in the nonvolatile RAM changes as shown in FIG. 8B and the pause periods (B) under the temperature increase control are gradually shortened. As a result, the average value of the fuel amount supplied through the supplemental fuel valve 46 increases, and the catalyst bed temperature average value Tave rises to the target bed temperature Tt as shown in FIG. 8A. The stationary difference between those temperatures disappears, accordingly.

Next, with reference to the flowchart of FIG. 9 showing a learned value renewing routine, the processes for the calculation and the renewal of the learned value K will be described in greater detail. The ECU 50 executes the learned value renewing routine periodically, for example, by allowing the routine to cut in for a period (16 ms in this embodiment) every preset time.

In this routine, first, the ECU 50 determines whether the calculation of the learned value K is permitted or not (S201). The calculation of the learned value K is permitted when, for example, all of the following conditions are satisfied for a certain long period.

It is under the temperature increase control.

The state in which the gas-flow amount Ga is few does not continue for a long time such as, for example, 50 s.

It is not immediately after that the target bed temperature Tt has changed to be higher than before.

It is not immediately after the renewal of the learned value K. In other wards, it is not immediately after that the new learned value K has been reflected to the fuel supplementation.

The target bed temperature Tt does not continuously decrease: For example, the decrease of the target bed temperature Tt does not continue more than 15 s.

It is not in a prohibited period of the fuel supplementation through the supplemental fuel valve 46. The fuel supplementation is prohibited when, for example, the catalyst bed temperature T excessively rises.

The entering gas temperature sensor 28 and the outgoing gas temperature sensor 29 have no abnormality.

If negatively determining at step S201, the ECU 50 prohibits the learned value K from being calculated (S206). If positively determining, the ECU 50 calculates the ratio Qr/Q′ of the 16 ms required fuel amount Qr to the 16 ms assumption heat generating fuel amount Q′ which are calculated every 16 ms, based upon those amounts. The ECU 50 then calculates the average value of the ratio Qr/Q′ over the preset time period to set the learned value K (S202). If the calculation of the learned value K continues more than the preset time period (S203: YES) and the target bed temperature Tt is stable at a temperature (for example, 600° C.) which is equal to or larger than a temperature at which the particulate matter can be burned (S204: YES), the ECU 50 stores (renews) the calculated learned value K to the nonvolatile RAM thereof. Thus, the learned value K stored in the nonvolatile RAM is reflected to the fuel supplementation through the supplemental fuel valve 46.

In the meantime, the learned value K is the value corresponding to the difference between the catalyst bed temperature T (catalyst bed temperature average value Tave) and the target bed temperature Tt. The catalyst bed temperature T is a parameter that changes in response to the fuel supplementation through the supplemental fuel valve 46, and the target bed temperature Tt is a target value of the catalyst bed temperature T. Therefore, the lower the catalyst bed temperature average value Tave becomes than the target bed temperature Tt, the larger the learned value K leaves from the value “1.0” on the increment side of this value. Meanwhile, the higher the catalyst bed temperature average value Tave becomes than the target bed temperature Tt, the greater the learned value K deviates from the value “1.0” to be lower than this value.

On this occasion, if an abnormality occurs such that the catalyst bed temperature average value Tave cannot be adjusted to the target bed temperature during the temperature increase control, the learned value K may become excessively large or excessively small. For example, if the fuel supply system for the fuel supplementation is clogged, the supply amount of the fuel supplied through the supplemental fuel valve 46 is reduced and which causes the catalyst bed temperature average value Tave to become lower than the target bed temperature Tt. The learned value K may exceed the value “1.0.” Thus, there abnormality can be determined using the changes of the learned value K accompanying the occurrence of the abnormality described above. More specifically, the idea is to determine the abnormality based upon whether the learned value K is within a preset proper range, for example, in a range of “0.90 through 1.4” or not when the learned value K is updated.

However, the abnormality that the catalyst bed temperature Tave cannot be adjusted to the target bed temperature Tt does not necessarily permanently occur but may only be temporary.

In this connection, if deposits adhere to the periphery of a nozzle of the supplemental fuel valve 46 because of the use of poor quality fuel, the fuel amount supplied through the supplemental fuel valve 46 is less than the proper amount, and the catalyst bed temperature average value Tave is below the target bed temperature Tt. Accordingly, the abnormality may occur such that the catalyst bed temperature average value Tave cannot be adjusted to the target bed temperature Tt. In this situation, however, the deposits may occasionally depart from the nozzle periphery when the supplemental fuel is supplied through the supplemental fuel valve 46. Accordingly, even though the above abnormality occurs, it may only be temporary.

Also, in another situation such that the gas-flow amount Ga detected by the airflow meter 16 differs from an actual gas-flow amount because of adhesion of foreign substances to a detecting portion of the airflow meter 16, as a result the 16 ms required fuel amount Qr calculated based upon the gas-flow amount Ga may be larger than a proper amount. If the 16 ms required fuel amount Qr is larger than the proper amount, the pause periods B under the temperature increase control are shortened. The catalyst bed temperature average value Tave thus exceeds the target bed temperature Tt, and the abnormality occurs where the catalyst bed temperature average value Tave cannot be adjusted to the target bed temperature Tt. In this situation, however, the foreign substances adhering to the detecting portion of the airflow meter 16 may occasionally depart from the periphery of the detecting portion in the process that the air flows around the detecting portion. Accordingly, even though the above abnormality occurs, it may only be temporary.

If the abnormality is immediately determined, without considering the above situations, when the learned value K falls outside of the proper range even once when the learned value K is updated (time T7 of FIG. 10), the abnormality determination would be incorrect if the abnormality is temporary and thus disappears later and the learned value K returns to a value within the proper range when the learned value K is subsequently updated again (time T8).

In this embodiment, therefore, the ECU 50 determines whether the learned value K is out of the proper range or each time the learned value K is updated. If the learned value K falls outside of the proper range, the ECU 50 increases a count value of a counter C by “1.” If the learned value K is in the proper range, the ECU 50 resets the count value of a counter C to an initial value “0.” FIGS. 11A and 11B show the transitions of the learned value K over several updates and the transitions of the number of counts by the counter C accompanying the transitions of the learning value K, respectively. In the counter C, the initial count value is set to be “0,” and the count value increases by “1” from the initial value “0.” When the count value of the counter C exceeds a determination value, which is equal to or greater than “2” (time T10) it is determined that the learned value K has fallen outside of the proper range over several updates (three times in this embodiment) of the learned value K, the ECU 50 determines that an abnormality is present.

In this connection, when the abnormality disappears before the count value of the counter C reaches or exceeds the determination value and, as indicated by the chain double-dashed line of FIG. 11A, the learned value K returns to a value within the proper range (time 9). Accordingly, the count value is reset to the initial value “0” as indicated by the chain double-dashed line of FIG. 11B. It is determined that an abnormality is not present. That is, even though the learned value K falls outside of the proper range, it is determined that an abnormality is not present unless the learned value K continues to fall outside of the proper range over three successive updates of the learned value. Therefore, when the abnormality temporarily occurs such that the catalyst bed temperature average value Tave cannot be adjusted to the target bed temperature Tt, an incorrect determination that an abnormality is present will not be made.

Next, with reference to the flowchart of FIG. 12 showing an abnormality diagnosing routine, the processes for determining the abnormality will be described. The ECU 50 executes the abnormality diagnosing routine periodically, for example, by allowing the routine to cut in for a period (16 ms in this embodiment) at predetermined intervals.

In this routine, the ECU 50 executes processes (steps S303 through S305) for changing the count value of the counter C based upon a magnitude of the learned value K while the temperature increase control being executed (S301: YES) and the learned value K is updated at this moment (S302: YES). More specifically, first, the ECU 50 determines whether the learned value K is out of the proper range or not (S303). If the determination is positive, the ECU 50 increases the count value of the counter C by “1” (S304). If negatively determining, the ECU 50 resets the count value to the initial value “0” (S305). The ECU 50 stores the count value of the counter C into the nonvolatile RAM thereof every renewal of the learned value K. When the engine 10 starts next time, the ECU 50 sets the initial value to be the value stored in the nonvolatile RAM.

Successively, the ECU 50 determines whether the count value of the counter C reaches or exceeds the determination value (“3” in this embodiment) (S306). If positively determining, the ECU 50 determines the abnormality and stores “1 (abnormal)” as a value of an abnormality flag F2 into an allotted area of the nonvolatile RAM (S307). In addition, the ECU 50 turns a warning lamp on which is placed at a location around a driver's seat or the like of the automobile that has the engine 10 (S308) to warn the driver that an abnormality has occurred.

Meanwhile, if negatively determining, the ECU 50 further determines whether the filter regeneration has not been completed yet or not (S309). If negatively determining at step S309 (filter regeneration has been completed), the ECU 50 resets the count value of the counter C to the initial value “0” (S310). On this occasion, even though, as shown in FIG. 13A, the learned value K is out of the proper range due to the abnormality at the renewal moment, the filter regeneration can be completed before the count value of the counter C reaches the determination value (“3”), for example, when the count value reaches “2” as shown in FIG. 13B, under a condition that the abnormality does not affect the filter regeneration so much (time T11). In such a situation, the ECU 50 resets the count value of the counter C to the initial value “0.”

If the ECU 50 positively determines that the filter regeneration has not been completed yet at step S309 of FIG. 12, the ECU 50 then determines whether the time that has elapsed since the start of the filter regeneration is equal to or exceeds a permissible time period (for example, one hour) (S311). If positively determining at step S311, the ECU 50 further determines that an abnormality is present and executes steps S307, S308 in turn. On this occasion, if the learned value K, as shown in FIG. 14A, is updated to a value that falls outside of the proper range due to the abnormality, the learned value K may be again updated to a value that falls outside of the proper range later. Unless, however, the target bed temperature Tt stably maintains a catalyst bed temperature above the temperature at which the particulate matter burns, the learned value K is not actually updated to such a value falling outside of the proper range. Because the particulate matter are hardly burned in the filter regeneration under the condition, the amount of the accumulated particulate matter does not decrease to “0.” Thus, the filter regeneration thus is hardly completed. As a result, as shown in FIG. 14B, the time that has elapsed since the filter regeneration starts reaches or exceeds the permissible time period without the count value of the counter C reaching the determination value (time T12). Based upon this situation, the ECU 50 determines the abnormality and stores “1 (abnormal)” as the value of the abnormality flag F2 into the nonvolatile RAM and turns the warning lamp on.

According to the embodiment as described in detail, the following effects can be obtained.

(1) Under the temperature increase control for the filter regeneration, the abnormality can occur such that the catalyst bed temperature average value Tave cannot be adjusted to the target bed temperature Tt. However, such abnormality does not necessarily permanently occur but can temporarily occur. On this occasion, if the abnormality is immediately determined when the learned value K becomes out of the proper range even once at a renewal moment, the abnormality determination is incorrect under the condition that the abnormality is temporary and thus disappears later and the learned value K returns to a value within the proper range at a later renewal moment. In this embodiment, however, the abnormality is determined only when the determination that the learned value K at the renewal time becomes out of the proper range is made every renewal successively three times. More specifically, if the learned value K at the renewal time is out of the proper range, the count value of the counter C is increased. The count value is reset to the initial value “0” if the learned value K is in the proper range. When the count value reaches the determination value (“3” in this embodiment), the abnormality is determined. Therefore, if the abnormality temporarily occurs such that the catalyst bed temperature average value Tave cannot be adjusted to the target bed temperature Tt, the abnormality is not incorrectly determined.

(2) The learned value K necessary for determining the abnormality is updated during the temperature increase control for the filter regeneration. The filter regeneration is regularly executed every time when the accumulation amount of the particulate matter reaches or exceeds the permissible amount accompanying the operation of the engine 10. Because the learned value K is updated whenever the temperature increase control for the filter regeneration is regularly made, the abnormality can be determined together with the renewal of the learned value K. Chances for the abnormality determination can be kept sufficiently.

(3) If the abnormality temporarily occurs such that the catalyst bed temperature average value Tave does not reach the target bed temperature Tt during the temperature increase control for the filter regeneration, the updated learned value K is out of the proper range and the count value of the counter C is increased. However, if the temporary abnormality does not affect the filter regeneration, the filter regeneration can be occasionally completed because the accumulation amount of the particulate matter becomes “0” before the count value reaches or exceeds the determination value. On this occasion, if the count value is kept to be a value larger than “0” (for example, “2”), the count value early reaches or exceeds the determination value when the learned value K becomes out of the proper range because the temporary abnormality occurs again during the temperature increase control for the filter regeneration in the next time. The abnormality thus can be incorrectly determined. In this embodiment, however, the count value of the counter C is reset to the initial value “0” whenever the filter regeneration is completed. The abnormality determination described above can be avoided, accordingly.

(4) During the temperature increase control to regenerate the filter, the learned value K can be updated to a value out of the proper range when the abnormality temporarily occurs such that the catalyst bed temperature average value Tave does not reach the target bed temperature. Even though there can be such a chance of the renewal, the learned value K is not updated to be the value out of the proper range unless the target bed temperature Tt is stable at a value which is larger than the value at which the particulate matter can be burned. Under the condition, despite of the occurrence of the abnormality, the filter regeneration is continued without the count value of the counter C reaching or exceeding the determination value, i.e., without the abnormality being determined. In the filter regeneration under the condition, the accumulating particulate matter are hardly burned and the accumulation amount of the particulate matter does not decrease to “0.” The filter regeneration thus is hardly completed. In this embodiment, however, the abnormality is determined even though the count value of the counter C does not reach the determination value, if the filter regeneration is not completed although the time elapsing from the start moment of the filter regeneration reaches or exceeds the permissible time period. Therefore, the abnormality is determined whenever the abnormality actually occurs.

(5) The count value of the counter C is stored in the nonvolatile RAM of the ECU 50. The count value stored in the nonvolatile RAM is set to be the initial value when the engine 10 starts next time. Assuming that the count value of the counter C is reset to the initial value “0” every stop of the engine 10, the chances for determining the abnormality can decrease under a condition that the engine 10 frequently repeats stop and start. The abnormality thus is not able to be determined even though the abnormality actually occurs. In addition, accompanying the delay of the abnormality determination, the filter regeneration is not made properly due to the abnormality and the particulate matter can excessively accumulate. Consequently, the PM filter or relating parts can need to be exchanged. In the embodiment, however, the above problems are resolved through the treatment of the count value of the counter C provided at the start moment of the engine 10.

The embodiment described above can be modified, for example, as follows.

In the above embodiment, the abnormality is determined regardless of the count value of the counter C when the time elapsing from the start moment of the filter regeneration reaches or exceeds the permissible time period. However, this determination of the abnormality is not necessarily made.

The count value of the counter C is reset to the initial value “0” at the completion of the filter regeneration. This reset, however, is not necessarily made.

In an engine such that the temperature increase control is executed by the fuel supplementation through the supplemental fuel valve 46, the most possible causes for occurrence of the temporary abnormality is speculated to be the temporary adhesion of the deposits to the supplemental fuel valve 46. In consideration of the speculation, the count value of the counter C can be increased only when the learned value K at the renewal time becomes out of the proper range on the increment side.

In an internal combustion engine having a NOx catalyst, sulfur poisoning recovery is made to release a sulfur component occluded in the NOx catalyst. The temperature increase control is applied for the Sulfur poisoning recovery. The abnormality can be determined during the temperature increase control for the sulfur poisoning recovery.

As the determination value used for determining the abnormality, the value “2” or integers equal to or larger than “4” can replace the value “3” used in the above embodiment.

The unburned fuel components can be supplied to the exhaust system by an auxiliary injection (after-injection) made in exhaust strokes and expansion strokes after the fuel for combustion in the combustion chambers is injected through the fuel injector 40. In this connection, the supplemental fuel valve 46 can be omitted.

While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the embodiments are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the invention.

Claims

1. An abnormality diagnosing device for an internal combustion engine comprising:

a temperature increase control section for executing a temperature increase control for increasing a temperature of a catalyst disposed in an exhaust system to a target bed temperature by supplying an unburned fuel component to the catalyst;

an updating section for executing updating of a learned value based upon a catalyst bed temperature under the temperature increase control by the temperature increase control section and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures;

a learned value determining section for determining whether the learned value is outside of a proper range or not when the learned value is updated; and

an abnormality determining section for determining that an abnormality is present only when the learned value determining section determines that the learned value falls outside of the proper range over several successive updates of the learned value.

2. The abnormality diagnosing device for an internal combustion engine according to claim 1, wherein

the internal combustion engine has a supplemental fuel valve for supplying supplemental fuel upstream of the catalyst in the exhaust system.

3. The abnormality diagnosing device for an internal combustion engine according to claim 1, wherein

the exhaust system of the internal combustion engine has a filter for trapping particulate matter, the temperature increase control for increasing the temperature of the catalyst to the target bed temperature is executed by supplying the unburned fuel component to the catalyst when to burn the particulate matter to regenerate the filter so that an accumulation amount of the particulate matter trapped in the filter is to less than a prescribed amount.

4. The abnormality diagnosing device for an internal combustion engine according to claim 1, further comprising:

a counting section for increasing a count value when the learned value determining section determines that the learned value has fallen outside of the proper range and for resetting the count value to an initial value when the learned value determining section determines that the learned value is in the proper range, wherein

the abnormality determining section determines that the abnormality is present when the count value is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, and

the counting section resets the count value to the initial value when the filter regeneration is completed.

5. The abnormality diagnosing device for an internal combustion engine according to claim 1, further comprising:

a counting section for increasing a count value when the learned value determining section determines that the learned value has fallen outside of the proper range and for resetting the count value to an initial value when the learned value determining section determines that the learned value is in the proper range, wherein

the learned value is updated when the catalyst bed stably maintains a catalyst bed temperature that is equal to or higher than the temperature at which the particulate matter is capable of being burned, and

the abnormality determining section determines that the abnormality is present when the count value given by the counting section is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, and determines the abnormality regardless of the count value if the filter regeneration is not completed after the elapsed time from when the filter regeneration starts reaches or exceeds a permissible time period.

6. The abnormality diagnosing device for an internal combustion engine according to claim 4, wherein

the counting section increases “1” per once,

the initial value is “0,” and

the determination value is an integer which is equal to or greater than “2”.

7. The abnormality diagnosing device for an internal combustion engine according to claim 1, wherein

the abnormality determining section determines that the abnormality is present when the learned value determining section determines that the learned value varies to be larger than the proper range over several successive updates of the learned value.

8. The abnormality diagnosing device for an internal combustion engine according to claim 1, wherein

the unburned fuel component is supplied to the catalyst by an auxiliary injection made in an exhaust stroke or an expansion stroke after fuel injected for combustion in a combustion chamber from a fuel injector.

9. An abnormality diagnosing method for an internal combustion engine comprising:

executing a temperature increase control for increasing a temperature of a catalyst disposed in an exhaust system to a target bed temperature by supplying an unburned fuel component to the catalyst;

executing updating a learned value based upon a catalyst bed temperature under the temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures;

determining whether the learned value falls outside of a proper range or not every time the learned value is updated; and

determining abnormality when it is determined that the learned value falls outside of the proper range over several successive updates of the learned value.

10. The abnormality diagnosing method for an internal combustion engine according to claim 9, wherein

the exhaust system of the internal combustion engine has a filter for trapping particulate matter, the temperature increase control for increasing the temperature of the catalyst to the target bed temperature is executed by supplying the unburned fuel component to the catalyst when a filter regeneration is made to burn the particulate matter so that an accumulation amount of the particulate matter trapped by the filter is to be less than a preset amount.

11. The abnormality diagnosing method for an internal combustion engine according to claim 9, further comprising:

increasing a count value when the learned value is determined to fall outside of the proper range, and resetting the count value to an initial value when the learned value is determined to be in the proper range, wherein an abnormality is determined to be present when the count value is equal to or greater than a determination value which that is equal to or greater than a value that is incremented at least twice from the initial value, and

the count value is reset to the initial value when the filter regeneration is completed.

12. The abnormality diagnosing method for an internal combustion engine according to claim 9, further comprising:

increasing a count value when the learned value is determined to be outside the proper range and resetting the count value to an initial value when the learned value is determined to be in the proper range, wherein

the learned value is updated when the catalyst bed temperature is stably maintained at a temperature that is equal to or above the temperature at which the particulate matter is capable of being burned, and

the abnormality is determined to be present when the count value is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, and the abnormality is determined to be present regardless of the count value if the filter regeneration is not completed a time period has elapsed from a start moment of the filter regeneration reaches or exceeds a permissible time period.