Internal combustion engine igniter

Abstract

An internal combustion engine igniter of the present invention includes a current limiting circuit that limits current flowing to the IGBT by controlling a gate voltage of the IGBT in accordance with the current flowing to the IGBT, a waveform-shaping circuit that suppresses an oscillation of the current flowing to the IGBT by applying to the gate voltage of the IGBT an auxiliary voltage generated from a collector voltage of the IGBT when current is being limited by the current limiting circuit, and, in addition, a heat-generation suppressing circuit that obtains an intermediate voltage by resistively dividing the auxiliary voltage generated by the waveform-shaping circuit when current is being limited by the current limiting circuit, and that suppresses IGBT heat generation by increasing the current flowing to the IGBT in accordance with the intermediate voltage.

Claims

1. An igniter for an internal combustion engine, comprising: a power semiconductor device configured to be connected to an ignition coil of the internal combustion engine so as to control current flowing to the ignition coil in accordance with a control voltage applied to a control electrode of the power semiconductor device; a gate terminal that is configured to receive a control signal from an engine control unit, the gate terminal being connected to the control electrode of the power semiconductor device so that the control signal constitutes at least a portion of the control voltage; a current limiting circuit that limits current flowing to the power semiconductor device by controlling the control voltage applied to the control electrode of the power semiconductor device in accordance with the current flowing to the power semiconductor device; a waveform-shaping circuit that suppresses an oscillation of the current flowing to the power semiconductor device by adding to the control electrode of the power semiconductor device an auxiliary voltage generated from a voltage across main electrodes of the power semiconductor device when the current is being limited by the current limiting circuit; and a heat-generation suppressing circuit that obtains an intermediate voltage by resistively dividing the auxiliary voltage when the current is being limited by the current limiting circuit and that causes heat generation of the power semiconductor device to be suppressed in accordance with the intermediate voltage.

2. The igniter for the internal combustion engine according to claim 1, wherein the power semiconductor device is an IGBT in which the main electrodes are a collector and an emitter, and the control electrode is a gate.

3. The igniter for the internal combustion engine according to claim 1, wherein the heat-generation suppressing circuit causes a voltage threshold of the current limiting circuit to be increased in accordance with the intermediate voltage when the current is being limited by the current limiting circuit.

4. The igniter for the internal combustion engine according to claim 1, wherein the heat-generation suppressing circuit is configured so as to superimpose the intermediate voltage on the control voltage applied to the control electrode of the power semiconductor device when the current is being limited by the current limiting circuit.

5. The igniter for the internal combustion engine according to claim 1, further comprising an overheat detection circuit that detects a temperature of the power semiconductor device, the overheat detection circuit causing the control voltage applied to the power semiconductor device to be reduced so as to suppress the temperature of the power semiconductor device when the detected temperature of the power semiconductor device reaches a first overheat protection temperature threshold.

6. The igniter for the internal combustion engine according to claim 5, wherein the overheat detection circuit has a second overheat protection temperature threshold that is set lower than the first overheat protection temperature threshold, and when the detected temperature of the power semiconductor device exceeds the second overheat protection temperature threshold while the current is being limited by the current limiting circuit, the overheat detection circuit causes a threshold voltage of the current limiting circuit to be increased so as to increase the current flowing to the power semiconductor device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing the overall configuration of an igniter according to an embodiment of the present invention.

(2) FIG. 2 is a schematic diagram showing the overall configuration of an igniter according to another embodiment of the present invention.

(3) FIG. 3 is a schematic diagram showing an example of the overall configuration of a conventional igniter.

(4) FIGS. 4A and 4B are diagrams comparing the operational characteristics of an IGBT when current is being limited to the operational characteristics of the IGBT when current is not being limited.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The igniter according to the embodiments of the present invention will be explained below with reference to figures.

(6) FIG. 1 is a diagram showing the overall configuration of an igniter 10 according to an embodiment of the present invention, and the same reference characters are given to the same portions as those in the conventional igniter 1 shown in FIG. 3. Furthermore, detailed explanations of the same portions as those in the conventional igniter 1 will be omitted.

(7) In addition to the configuration of the conventional igniter 1, the igniter 10 according to this embodiment includes a heat-generation suppressing circuit 11 for coping with the occurrence of abnormalities that last for a relatively long time, such as 10 milliseconds or longer, for example. This heat-generation suppressing circuit 11 plays the role of suppressing IGBT heat generation by increasing the current flowing to an IGBT 4 in a state (during a current limiting operation) in which the current flowing to the IGBT 4 is being limited by a current limiting circuit 5.

(8) Specifically, the heat-generation suppressing circuit 11 includes resistors R2 and R3 for obtaining an intermediate voltage V2 by resistively dividing an auxiliary voltage V1, which specifically is an emitter voltage of an IGBT 9a, generated by a waveform-shaping circuit 9 in accordance with a collector voltage V.sub.ce of the IGBT 4. In addition, the heat-generation suppressing circuit 11 includes a MOSFET switch 12 that increases a voltage threshold V.sub.ref set by a constant voltage source 5a in accordance with the intermediate voltage V2 obtained via the resistors R2 and R3. This MOSFET switch 12 plays the role of raising the voltage threshold V.sub.ref provided to an operational amplifier 5b by connecting the gate and the source of the MOSFET and performing a diode operation, and by adding the intermediate voltage V2 to a constant voltage generated and outputted by the constant voltage source 5a.

(9) In this way, the heat-generation suppressing circuit 11 increases the gate voltage V.sub.ge of the IGBT 4 during a current limiting operation by raising the voltage threshold V.sub.ref of the current limiting circuit 5, thereby increasing the current I.sub.c flowing to the IGBT 4. Thus, the collector voltage V.sub.ce of the IGBT 4 is reduced in association with the increase in the current I.sub.c flowing to the IGBT 4. Incidentally, the amount of heat generated by the IGBT 4 depends more heavily on this collector voltage V.sub.ce than on the current I.sub.c flowing to the IGBT 4.

(10) Therefore, when current is being limited by the current limiting circuit 5, the collector voltage V.sub.ce of the IGBT 4 can be reduced by increasing the current I.sub.c flowing to the IGBT 4 in accordance with the collector voltage V.sub.ce of the IGBT 4. As a result of this, since the collector voltage V.sub.ce of the IGBT 4 can be kept low when an abnormal ON operation of the IGBT 4 lasts for a prolonged period of time, it becomes possible to effectively suppress the amount of heat generated by the IGBT 4.

(11) Further, the heat-generation suppressing circuit 11 only operates when the collector voltage V.sub.ce is higher than the gate voltage V.sub.ge of the IGBT 4 and the waveform-shaping circuit 9 generates an auxiliary voltage V1 as a result of this. In other words, the heat-generation suppressing circuit 11 functions effectively only when the current limiting circuit 5 is limiting the current I.sub.c flowing to the IGBT when an abnormality occurs. Therefore, the existence of the heat-generation suppressing circuit 11 does not in any way adversely affect normal operations in which the IGBT 4 is being driven to ON/OFF in accordance with control signals.

(12) Moreover, the heat-generation suppressing circuit 11 is an extremely simple configuration as described above, and by comparison to the conventional igniter 1, the configuration of the igniter 10 does not evoke pointless complexity and up sizing. What is more, the heat-generation suppressing circuit 11 can greatly relax the specifications required in the IGBT 4, including those for prolonged abnormal operations. Therefore, the present invention makes it possible to use an appropriate size IGBT 4 having breakdown characteristics capable of coping with normal operations and momentary abnormal operations. As a result of this, it becomes possible to inexpensively realize a simple-configuration igniter 10.

(13) FIG. 2 is a schematic diagram of an igniter 20 according to another embodiment of the present invention. Here, the same reference characters are given to the same portions as those in the conventional igniter 1 shown in FIG. 3 and the igniter 10 shown in FIG. 1.

(14) This igniter 20 includes a MOSFET 13 in parallel with the MOSFET switch 12 in the heat-generation suppressing circuit 11. This MOSFET 13 is turned ON by temperature information obtained from the overheat detection circuit 7, specifically, when the temperature of the IGBT 4 has reached a temperature threshold that is set lower than the temperature threshold at which the overheat detection circuit 7 turns ON the MOSFET 8.

(15) This MOSFET 13, during an ON operation thereof, plays the role of adding the intermediate voltage V2 to the constant voltage generated by the constant voltage source 5a in the current limiting circuit 5. According to the ON operation of this MOSFET 13, the intermediate voltage V2 is added to the voltage threshold V.sub.ref provided to the operational amplifier 5b, and the gate voltage V.sub.ge of the IGBT 4 is increased. As a result of this, the current I.sub.c flowing to the IGBT 4 can be increased by increasing the gate voltage V.sub.ge of the IGBT 4 in a state in which the current I.sub.c flowing to the IGBT 4 is being limited by the current limiting circuit 5. Therefore, it is possible to increase the current I.sub.c flowing to the IGBT 4 while the current I.sub.c flowing to the IGBT 4 is being limited, and it is possible to suppress abnormal heat generation in the IGBT 4 by suppressing a rise in the collector voltage V.sub.ce of the IGBT 4.

(16) Therefore, according to the igniter 20 shown in FIG. 2, it is possible to suppress abnormal heat generation in the IGBT 4 on the basis of temperature information obtained from the overheat detection circuit 7 even when an abnormal state thereof lasts for a prolonged period of time in a state in which current flowing to the IGBT 4 is being limited by the current limiting circuit 5. That is, prior to the temperature of the IGBT 4 reaching the temperature threshold of the overheat detection circuit 7 at which the IGBT 4 is forcibly turned OFF, the current I.sub.c flowing to the IGBT 4 can be limited in accordance with the temperature of the IGBT 4 obtained by the overheat detection circuit 7. As a result of this, it is possible to suppress an unintended increase in the collector voltage V.sub.ce of the IGBT 4 during a current limiting operation.

(17) Namely, the igniter 20 makes it is possible to use the heat-generation suppressing circuit 11 to suppress the current I.sub.c flowing to the IGBT 4 prior to the temperature of the IGBT 4 in a state of normal operation reaching the temperature threshold at which the overheat detection circuit 7 operates. In particular, it is possible to suppress, on the basis of the intermediate voltage V2, the current I.sub.c flowing to the IGBT 4 from the time that the temperature of the IGBT 4 in a state of normal operation reaches the second temperature threshold that is set lower than the prescribed temperature threshold. Therefore, it is possible to prevent a rise in the temperature of the IGBT 4 prior to an unintended rise in the collector voltage V.sub.ce of the IGBT 4 occurring when an overcurrent is detected. As a result of this, it becomes possible to effectively prevent a deterioration in the performance and/or the destruction of the ignition coil 3 and so forth associated with the heat generation in the IGBT 4 even when an unintended ON operation of the IGBT 4 lasts for a prolonged period of time. Therefore, similar effects to the above-described embodiment are achieved.

(18) Furthermore, the present invention is not limited to the above-mentioned embodiments. For example, when the current I.sub.c flowing to the IGBT 4 is reduced by the heat-generation suppressing circuit 11, it is also possible to add the above-mentioned intermediate voltage V2 directly to the gate voltage of the IGBT 4. Further, the overheat detection circuit 7 includes a plurality of diodes that are generally connected in series, for example, and are configured so as to output from the cathodes of these diodes (proportional) temperature information that corresponds to the temperature of the IGBT 4.

(19) Therefore, it is sufficient that the heat-generation suppressing circuit 11 be configured so as to control the operation of the MOSFET 13 using information of a plurality of temperatures obtained in the overheat detection circuit 7 as the temperature information of the IGBT 4. For example, if the overheat detection circuit 7 is set to operate when the temperature of the IGBT 4 exceeds 200 C., it is sufficient that the heat-generation suppressing circuit 11 be configured so as to operate when the temperature of the IGBT 4 exceeds 170 C. Further, the present invention is applicable even in cases where a power MOSFET, for example, is used as the power semiconductor device. In addition, various modifications can be made without departing from the spirit of the present invention.

(20) It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents. In particular, it is explicitly contemplated that any part or whole of any two or more of the embodiments and their modifications described above can be combined and regarded within the scope of the present invention.