Ignition device and method of controlling the same

Abstract

An ignition device includes a semiconductor switching element, a constant-current circuit, and a control section. The semiconductor switching element has a gate, a collector and an emitter, and is coupled with a primary winding of an ignition coil. The semiconductor switching element is configured to control a gate voltage and an electric current flowing between the collector and the emitter so as to control a coil current flowing in the primary winding, a voltage at two ends of a secondary winding, and an electric discharge at a plug coupled with the secondary winding. The constant-current circuit is coupled with the gate for supplying a constant current to the gate. The control section is configured to switch the semiconductor switching element by switching a supply or non-supply of the constant current to the gate based on an ignition signal.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-137775 filed on May 24, 2007, the contents of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ignition device for controlling an ignition with a plug and/or relates to a method of controlling the ignition device.

2. Description of the Related Art

Conventionally, an ignition device controls an electric current to be applied to a primary winding of an ignition coil for controlling an ignition of an engine by using a plug. The plug is coupled with a secondary winding of the ignition coil. When an electricity supply to the ignition coil is started, a positive voltage (i.e., an on-voltage) is generated at the plug. In this case, a spark may be generated at the plug and an early ignition may occur. Additionally, when an engine is in high compression and lean-burn, a voltage generated at the ignition coil tends to increase, and thereby the on-voltage also increases. Thus, a requirement for reducing the on-voltage further increases.

An ignition device 101 in FIG. 6 includes an insulated gate bipolar transistor (IGBT) 100, a first resistor 102 and a second resistor 103 disposed between a power source 109 and the IGBT 100, an NPN transistor 104 coupled between the first resistor 102 and the second resistor 103, and a waveform-shaping circuit 106 coupled with the NPN transistor 104 and an engine electronic control unit (engine ECU) 105. The waveform-shaping circuit 106 is disposed to shape a waveform of an ignition signal from the engine ECU 105. The NPN transistor 104 is switched in accordance with the waveform-shaped signal, thereby controlling an electric current to be supplied to a gate of the IGBT 100. In the ignition device 101, the on-voltage generated at the plug can be reduced by increasing a resistance value of the first resistor 102.

However, when the resistance value of the first resistor 102 is too high, an increasing rate of a gate voltage reduces, and a time for which the gate voltage reaches a threshold voltage becomes longer. When the gate voltage reaches the threshold voltage, a coil current starts to flow. Thus, an initial energization time from the start of the coil current flow to an ignition coil 108 becomes shorter. As a result, depending on an operating condition, for example, at a high engine rotation speed, the initial energization time may be shorter than a predetermined time and a predetermined voltage may be not generated at the ignition coil 108, and thereby a misfire may be caused. Thus, the resistance value of the first resistor 102 is selected so that the on-voltage reduces and the initial energization time is secured. Therefore, a selection of the first resistor 102 is limited.

Additionally, when electric devices mounted on a vehicle increases, an electric load to a vehicle battery increases. Thus, a battery voltage may be reduced in accordance with a running condition or an operating condition of the electric devices. For example, the battery voltage reduces easily when the vehicle starts to run. When the battery voltage reduces, the increasing rate of the gate voltage reduces and the initial energization time fluctuates. Thus, the coil current for keeping a predetermined ignition performance may not flow in the ignition coil 108. This problem may be solved by reducing the resistance value of the first resistor 102. However, if the resistance value of the first resistor 102 reduces, the on-voltage reversely increases when the battery voltage is high. As a result, considering a case where the battery voltage reduces, it is difficult to reduce the on-voltage while securing a necessary initial energization time for the ignition.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ignition device and/or a method of controlling the ignition device. Specifically, the ignition device can reduce an on-voltage while securing an initial energization time.

According to an aspect of the invention, an ignition device includes a semiconductor switching element, a constant-current circuit, and a control section. The semiconductor switching element has a metal-oxide semiconductor structure having a gate, a collector, and an emitter, and is coupled with a primary winding of an ignition coil. The semiconductor switching element is configured to control a gate voltage and an electric current flowing between the collector and the emitter so as to control a coil current flowing in the primary winding, a voltage at two ends of a secondary winding of the ignition coil, and an electric discharge at a plug coupled with the secondary winding. The constant-current circuit is coupled with the gate of the semiconductor switching element to supply a constant current to the gate, so that an electric charge is accumulated at the gate and the gate voltage increases. The control section is configured to switch the semiconductor switching element by switching a supply or non-supply of the constant current generated at the constant-current circuit to the gate of the semiconductor switching element based on an ignition signal.

According to another aspect of the invention, a method of controlling an ignition device includes: generating a constant current at a constant-current circuit; supplying the constant current to a gate of a semiconductor switching element in accordance with an ignition signal; and controlling a gate voltage of the semiconductor switching element and an electric current flowing between a collector and an emitter of the semiconductor switching element so as to control a coil current flowing in a primary winding of an ignition coil, a voltage at two ends of a secondary winding of the ignition coil, and an electric discharge at a plug coupled with the secondary winding.

In the above-described ignition device and the method of controlling the ignition device, because the electric charge is accumulated at the gate of the semiconductor switching element in accordance with the constant current generated at the constant-current circuit, an accumulating rate is maintained at a constant level, and thereby an increasing rate of the gate voltage can be reduced. Accordingly, an initial energization time can be secured, and the on-voltage of the plug can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiment when taken together with the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing an ignition system including an ignition device according to an embodiment of the invention;

FIG. 2 is a timing chart for controlling components of the ignition device according to the embodiment;

FIG. 3 is an enlarged timing chart of a gate voltage of an IGBT during a time TA shown in FIG. 2;

FIG. 4 is a timing chart for controlling components of an ignition device according to a related art;

FIGS. 5A-5C are enlarged timing charts of a gate voltage of an IGBT during a time TA shown in FIG. 4, in a case where a voltage of a power source is at a normal level, a high level, and a low level, respectively; and

FIG. 6 is a schematic diagram showing an ignition system including the ignition device according to the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An ignition device 1 according to an embodiment of the invention can be suitably used for an internal combustion engine. As shown in FIG. 1, the ignition device 1 includes a waveform-shaping circuit 2, an NPN transistor 3, a resistor 4, an insulated gate bipolar transistor (IGBT) 5, and a constant-current circuit 6. The ignition device 1 is configured to control an electricity supply from a power source 9 (e.g., battery) to a primary winding Ba of an ignition coil 8 based on an ignition signal from an engine electronic control unit (engine ECU) 7.

The waveform of ignition signal from the engine ECU 7 is shaped at the waveform-shaping circuit 2. The NPN transistor 3 is controlled by changing a gate voltage of the NPN transistor 3 based on the waveform-shaped signal. For example, the engine ECU 7 outputs an ignition signal at a low level before the ignition coil 8 is supplied with electricity, and outputs an ignition signal at a high level when the ignition coil 8 is supplied with electricity. A level of the ignition signal is reversed at the waveform-shaping circuit 2, and the NPN transistor 3 is switched by the reversed ignition signal.

A collector of the NPN transistor 3 is coupled with a gate of the IGBT 5 through the resistor 4 for protecting an input, and a gate voltage VG applied to the gate of the IGBT 5 is controlled in accordance with an on/off state of the NPN transistor 3. Specifically, when the NPN transistor 3 is on, a collector voltage of the NPN transistor 3 (i.e., the gate voltage VG of the IGBT 5) is about zero. Thus, the IGBT 5 is turned off. In contrast, when the NPN transistor 3 is off, the gate voltage VG of the IGBT 5 is high. Thus, the IGBT 5 is turned on.

When the IGBT 5 is off, the primary winding 8a of the ignition coil 8, which is coupled with the IGBT 5, is not supplied with electricity. In this case, because a potential difference is not generated between two ends of the primary winding 8a, a potential difference is not generated between two ends of a secondary winding 8b, either. In contrast, when the IGBT 5 is on, the primary winding 8a is supplied with electricity from the power source 9 (e.g., a buttery), and thereby a potential difference is provided between the two ends of the primary winding 8a. Thus, a potential difference, which is higher than the potential difference at the primary winding 8a by a ratio of the number of windings of the secondary winding 8b to the number of windings of the primary winding 8a, is generated between the two ends of the secondary winding 8b, and thereby an on-voltage is generated at an electrode of a plug 10. When the IGBT 5 is turned off after a predetermined electric current is supplied to the primary winding 8a, a collector voltage VC of the IGBT 5 increases, and the potential difference is generated at the two ends of the primary winding 8a. Thus, the potential difference, which is higher than the potential difference at the primary winding 8a by a ratio of the number of windings of the secondary winding 8b to the number of windings of the primary winding 8a, is generated between the two ends of the secondary winding 8b, and thereby the plug 10, which is coupled with the secondary winding 8b, discharges electricity. As a result, the ignition device 1 can control an ignition time of the plug 10 based on the ignition signal from the engine ECU 7.

In the ignition device 1, the constant-current circuit 6 is disposed at a channel between the power source 9 and the gate of the IGBT 5. When the transistor 3 is off, an electric charge is accumulated at the gate of the IGBT 5 in accordance with a constant-current generated at the constant-current circuit 6. Thereby, the gate voltage VG applied to the gate of the IGBT 5 increases and the IGBT 5 is turned on. For example, a current value of the constant-current circuit 6 may be about in a range from 10 μA to 200 μA.

An operation of the ignition device 1 will now be described with reference to FIGS. 2 and 3. When the ignition signal from the engine ECU 7 is at the low level, the ignition signal is reversed into the high level at the waveform-shaping circuit 2, and thereby the NPN transistor 3 is turned on. Thus, a potential difference between the collector and an emitter of the NPN transistor 3 is about zero, and the constant current generated at the constant current circuit 6 flows to the NPN transistor 3. As a result, the IGBT 5 is turned off.

When the ignition signal transitions from the low level to the high level at the time T1 shown in FIG. 2, the ignition signal is reversed into the low level at the waveform-shaping circuit 2, and thereby the NPN transistor 3 is turned off. Thus, the electric charge is accumulated at the gate of the IGBT 5 through the resistor 4 in accordance with the constant current generated at the constant-current circuit 6. Because an accumulating rate is limited by the constant current, the electric charge is accumulated at the gate of the IGBT 5 at a constant rate. The gate of the IGBT 5 has an input capacitance, and thereby an increasing rate of the gate voltage VG can be reduced until a predetermined electric charge is accumulated. Thus, when a time for accumulating the electric charge of the input capacitance of the gate of the IGBT 5 is long, the increasing rate of the gate voltage VG can be reduced. As a result, the gate voltage VG increases to a threshold voltage Vt of the IGBT 5 approximately linearly and relatively slowly by a gradient of θ1, as shown in FIG. 3.

When the predetermined electric charge is accumulated in the IGBT 5 and the gate voltage VG reaches the threshold voltage Vt at the time T2 shown in FIGS. 2 and 3, the IGBT 5 is switched from off to on. Thereby, the corrector voltage VC of the IGBT 5 reduces, a potential difference is generated between the two ends of the primary winding 8a, and the electricity is supplied to the primary winding 8a. As a result, the two ends of the secondary winding 8b have a high voltage in accordance with the ratio of the number of windings of the secondary winding 8b to the number of windings of the primary winding 8a, and thereby the on-voltage is generated by the voltage V2 at the plug 10.

When the gate voltage VG reaches the threshold voltage Vt, the coil current starts to flow. However, when the gate voltage VG is near the threshold voltage Vt, a current-carrying capacity of the IGBT 5, that is, an electric current flowing between a collector and an emitter of the IGBT 5 is limited. Thus, the corrector voltage VC of the IGBT 5 starts to reduce slowly from the voltage VB of the power source 9. When the corrector voltage VC reduces, the electric current supplied to the gate of the IGBT 5 is accumulated in accordance with a capacity between the corrector and the gate and a change in the corrector voltage VC. Thus, the gate voltage VG is maintained at the threshold voltage Vt. A maintaining time where the gate voltage VG is maintained at the threshold voltage Vt, i.e., a time between T2 and T3 shown in FIGS. 2 and 3, is determined in accordance with the constant current generated at the constant-current circuit 6. For example, when the constant current is about in the range from 10 μA to 200 μA, the maintaining time is about in a range from 5 μsec to 200 μsec.

When the corrector voltage VC reduces toward the minimum, the predetermined electric charge is accumulated at the gate of the IGBT 5. Thus, the current-carrying capacity of the IGBT 5, i.e., the electricity supply to the primary winding 8a is no longer limited, and the gate voltage VG increases approximately linearly by the gradient of θ1 again. When the predetermined electric current is supplied to the primary winding 8a, and the IGBT 5 is turned off, the corrector voltage VC of the IGBT 5 increases and the potential difference is generated between the two ends of the primary winding 8a. Thereby, the potential difference, which is higher than the potential difference at the primary winding 8a by the ratio of the number of windings of the secondary winding 8b to the number of windings of the primary winding 8a, is generated between the two ends of the secondary winding 8b. As a result, the plug 10 coupled with the secondary winding 8b discharges electricity for an ignition.

In the ignition device 1, because the electric charge is accumulated at the gate of the IGBT 5 in accordance with the constant current generated at the constant-current circuit 6, the accumulating rate is maintained at a constant level. Thus, the increasing rate of the gate voltage VG can be reduced. An initial energization time Δt0 at which the current-carrying capacity of the IGBT 5 is limited after the gate voltage VG reaches the threshold voltage Vt and the coil current starts to flow is determined based on the maintaining time where the gate voltage VG is maintained at the threshold voltage Vt. Furthermore, the maintaining time can be determined in accordance with the constant-current generated at the constant-current circuit 6. As a result, the initial energization time Δt0 can be controlled, and a decreasing rate of the corrector voltage VC also can be controlled. When the initial energization time Δt0 is long and the decreasing rate of the corrector voltage VC of the IGBT 5 is reduced, the voltage applied to the two ends of the secondary winding 8b can be reduced, and thereby the on-voltage of the voltage V2 at the plug 10 also can be reduced.

Even when the voltage VB of the power source 9 is changed to increase or decrease, the gate voltage VG changes in a manner similar to a case where the voltage VB is at a normal level, as shown by the dotted line in FIG. 3, and the initial energization time Δt0 is substantially constant regardless the voltage VB. Thus, the even when the voltage VB of the power source 9 changes, the on-voltage can be reduced.

In an ignition device 101 according a related art shown in FIG. 6, when the ignition signal transitions from the low level to the high level at the time T1 shown in FIG. 4, an electric charge is accumulated at a gate of an IGBT 100 through resistors 102 and 103. Because electricity is supplied to the gate of the IGBT 100 through the resistors 102 and 103, when a gate voltage VG increases to a threshold voltage Vt and when the gate voltage VG increases from the threshold voltage Vt, the gate voltage VG further increases along an exponential curve in accordance with a time constant of a charging circuit formed by a capacitor (i.e., a gate capacity) and the resistors 102 and 103, as shown in FIGS. 5A-5C. Additionally, a gradient θ2 of the exponential curve is larger than the gradient θ1 shown in FIGS. 2 and 3, and the maintaining time where the gate voltage VG is maintained at the threshold voltage Vt is shorter than that of the ignition device 1 according to the embodiment. Thus, an increasing rate of the gate voltage VG and a decreasing rate of a corrector voltage VC of the ignition device 101 are greater than those of the ignition device 1, as shown in FIGS. 2 and 4. As a result, a voltage V2 at two ends of a secondary winding 108b of an ignition coil 108 is higher than necessary, and thereby an on-voltage of a plug 110 increases in the ignition device 101.

Even in the ignition device 101, when a power source 109 is at the normal level (e.g., a battery voltage is about 12 V) and the maintaining time is controlled by changing a resistance value of the resistor 102 or a thickness of a gate insulating layer, a changing time of the corrector voltage VC can be controlled in a manner similar to that of the ignition device 1. Thus, a voltage at two ends of a primary winding 108a of the ignition coil 108 can be reduced, and thereby the on-voltage, which is determined in accordance with the voltage at the two ends of the secondary winding 108b, also can be reduced.

However, when the voltage of the power source 109 is higher than the normal level, the increasing rate of the gate voltage VG increases and the gradient θ2 increases, as shown in FIG. 5B. In contrast, when the voltage of the power source 109 is lower than the normal level, the increasing rate of the gate voltage VG decreases and the gradient θ2 decreases, as shown in FIG. 5C. Thus, the initial energization time Δt0 changes in accordance with the voltage of the power source 109. As a result, when the voltage of the power source 109 reduces, the ignition coil 108 may not be supplied with electricity.

In the ignition device 1 according to the embodiment of the present invention, because electric charge is accumulated at the gate of the IGBT 5 in accordance with the constant current generated at the constant-current circuit 6, the on-voltage can be reduced by a voltage Δv0 compared with the related art, and the initial energization time Δt0 can be secured, as shown in FIGS. 2 and 4. Additionally, because the constant-current circuit 6 is provided instead of a resistor having a high resistance value, a range of selection increases.

Furthermore, because the constant-current circuit 6 is used, even when the voltage VB of the power source 9 fluctuates, the initial energization time Δt0 can have a substantially constant length. Thus, even when the voltage VB of the power source 9 reduces, for example, when the battery voltage reduces, the ignition device 1 is less affected by the reduction of the battery voltage.

When a diode is disposed between the primary winding 8a and the secondary winding 8b of the ignition coil 8, a flying spark at a time where the on-voltage is generated at the plug 10 can be restricted with a high degree of certainty. However, because the on-voltage can be reduced in the ignition device 1, the ignition device 1 is not required to have the diode.

Other Embodiment

Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

In the above-described embodiment, the IGBT 5 is provided as a semiconductor switching element for a low-load driving, as an example. Alternatively, a power metal-oxide semiconductor field-effect transistor (MOSFET) may be used as the semiconductor switching element, for example.

In the above-described embodiment, the waveform-shaping circuit 2 and the NPN transistor 3 function as a control section that controls the supply of the constant current generated at the constant-current circuit 6 to the gate of the IGBT 5, as an example. Alternatively, other circuit structure may be used. For example, a metal-oxide semiconductor (MOS) transistor may be used instead of the NPN transistor 3.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.

Claims

1. An ignition device for controlling an ignition with a plug coupled with an ignition coil that includes a primary winding and a secondary winding, the ignition device comprising:

a semiconductor switching element that has a metal-oxide semiconductor structure having a gate, a collector and an emitter, and that is coupled with the primary winding, the semiconductor switching element being configured to control a gate voltage and an electric current flowing between the collector and the emitter so as to control a coil current flowing in the primary winding, a voltage at two ends of the secondary winding, and an electric discharge at the plug;

a constant-current circuit coupled with the gate of the semiconductor switching element for supplying a constant current to the gate, so that an electric charge is accumulated at the gate and the gate voltage increases; and

a control section configured to switch the semiconductor switching element by switching a supply or non-supply of the constant current generated at the constant-current circuit to the gate of the semiconductor switching element based on an ignition signal.

2. The ignition device according to claim 1, wherein:

the gate voltage of the semiconductor switching element increases approximately linearly to a threshold voltage of the semiconductor switching element by a predetermined gradient, then is maintained at the threshold voltage for a predetermined time, and further increases from the threshold voltage approximately linearly by the predetermined gradient, when the constant current is supplied to the gate.

3. The ignition device according to claim 2, wherein:

the predetermined time is about in a range from 5 μs to 200 μs.

4. The ignition device according to claim 1, wherein:

the constant current has a current value about in a range from 10 μA to 200 μA.

5. A method of controlling an ignition device that includes a semiconductor switching element and a constant-current circuit, the method comprising:

generating a constant current at the constant-current circuit;

supplying the constant current to a gate of the semiconductor switching element in accordance with an ignition signal; and

controlling a gate voltage of the semiconductor switching element and an electric current flowing between a collector and an emitter of the semiconductor switching element so as to control a coil current flowing in a primary winding of an ignition coil, a voltage at two ends of a secondary winding of the ignition coil, and an electric discharge at a plug coupled with the secondary winding.

6. The method according to claim 5, wherein:

the gate voltage of the semiconductor switching element increases approximately linearly to a threshold voltage of the semiconductor switching element by a predetermined gradient, then is maintained at the threshold voltage for a predetermined time, and further increases from the threshold voltage approximately linearly by the predetermined gradient, when the constant current is supplied to the gate.

7. The method according to claim 6, wherein:

the predetermined time is about in a range from 5 μs to 200 μs.

8. The method according to claim 5, wherein:

the constant current has a current value about in a range from 10 μA to 200 μA.