JP5831392B2 - Ignition device - Google Patents

Description

  The present invention relates to an ignition device for an internal combustion engine, and more particularly to an ignition device that suppresses the occurrence of pre-ignition.

  As an ignition device for an internal combustion engine, an electronically controlled ignition device such as an igniter is used. The ignition device controls the value of the current flowing through the primary coil by an insulated gate bipolar transistor (IGBT) or the like so that a predetermined voltage is generated in the secondary coil. Usually, the primary coil is connected to the collector electrode of the IGBT, and the emitter electrode is grounded. Further, a comparator for controlling on / off of the IGBT is connected to the gate electrode. The comparator is connected to a non-inverting input terminal and an inverting input terminal, respectively, with a drive signal and a reference potential serving as a reference for operation. When the potential at the non-inverting input terminal exceeds the potential at the inverting input terminal, a predetermined voltage is applied to the gate electrode, the IGBT is turned on, and a current flows through the primary coil. The current flowing through the primary coil is controlled by controlling on / off of the IGBT. And ignition is performed based on the electric potential which arises in a secondary coil by electromagnetic induction.

  When an abnormal current flows through an electronic circuit, the ignition device may generate preignition that ignites earlier than desired timing. Patent Document 1 describes an ignition device provided with a thermal shut-off circuit for preventing abnormal operation due to heat generation during energization of a primary coil. In such a configuration, energization of the IGBT is stopped when the temperature detected by the temperature detection circuit exceeds the allowable temperature while the primary coil is energized. And when the temperature of the element which comprises an ignition device falls with the stop of IGBT, it will supply with electricity to IGBT again. For this reason, the IGBT is normally turned on at all times and the primary coil must be energized, but the IGBT is turned on and off, and unexpected ignition may occur. In order to solve the above problem, Patent Document 1 proposes an ignition device that suppresses an unexpected signal change by attaching a latch circuit to a thermal shut-off circuit and suppresses the occurrence of pre-ignition.

Japanese Patent Laid-Open No. 9-42129

  The invention described in Patent Document 1 suppresses an abnormal current caused by the temperature of an element constituting an electronic circuit. For this reason, preignition due to an abnormal current caused by disconnection of the wiring constituting the electronic circuit cannot be suppressed.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress pre-ignition caused by disconnection of wiring, particularly disconnection of wiring that grounds a primary coil.

In order to achieve the above object, the present invention provides:
A primary coil (11) and switching elements (13, 19) disposed between the main power source (15) and the ground (16) and connected in series;
A control circuit (20) for controlling on / off of the switching element,
The control circuit
A power terminal (20a) and a ground terminal (20b);
A non-inverting input terminal (20d) and an inverting input terminal (20c) as input terminals;
An output terminal (20e) for outputting an output signal having two polarities of High bias or Low bias based on a potential difference between the non-inverting input terminal and the inverting input terminal;
The inverting input terminal is connected to the first power supply (17) which is lower than the main power supply and has a potential not to turn on the switching element
The non-inverting input terminal is connected to a second power source (18) that defines the polarity of the output signal,
The ground terminal is connected to the ground,
A first element (21, 25) and a second element (22, 26) connected in series between the first power source and the ground and having a predetermined resistance value,
The first power supply and the output terminal of the control circuit are connected via a protection switch (24),
The protection switch is turned on / off according to a midpoint potential between the first element and the second element.

  By adopting the present invention, when the wiring that electrically connects the primary coil and the control circuit to the ground (hereinafter referred to as PGND) is disconnected, the operation of the control circuit becomes unstable and control is performed. It is possible to prevent the output signal of the circuit from changing at an unexpected timing.

  In the PGND, the primary coil and the control circuit are grounded in common. When PGND is disconnected for some reason, the primary coil and the control circuit are electrically floating. In such a state, a current flows from the main power source toward the first power source having a lower potential than the main power source. In addition, since the ground terminal of the control circuit is connected to the main power supply without going through PGND, the operation becomes unstable. For this reason, it becomes impossible to control the output of the control circuit, that is, the timing of outputting the high bias or the low bias, and the switching element is turned on or off at an unexpected timing. Thereby, the generation timing of the voltage generated in the secondary coil also becomes irregular. For this reason, pre-ignition occurs.

  In the configuration described above, the first element and the second element are arranged between the first power supply and PGND. In the present invention, a protection switch that is turned on / off according to the midpoint potential between the first element and the second element is disposed. The midpoint potential is defined by the potentials of the main power source and the first power source and the resistance values of the first element and the second element. The protection switch is interposed between the first power supply and the output terminal of the control circuit. When the protection switch is turned on, the potential of the output terminal is forcibly set to the same value as that of the first power supply. By setting the resistance values of the first element and the second element so as to be turned on when the PGND is disconnected, it is possible to prevent the switching element from being turned off at an unexpected timing. Therefore, it is possible to prevent the generation timing of the voltage generated in the secondary coil from becoming irregular.

  The first element and the second element are preferably diodes (21, 22) connected in series so that the first power supply side becomes a cathode.

  According to this, it is possible to protect the circuit against a surge such as electrostatic discharge (ESD) in which a large current flows from the first power source toward PGND. In addition to the protection of the circuit, the above-described effects can be achieved. That is, it is possible to prevent the generation timing of the voltage generated in the secondary coil from becoming irregular while ensuring ESD resistance.

  In addition, when the part connected to PGND is electrically floating and the polarity of the output signal turns on the switching element, the threshold voltage of the protection switch is protected before the polarity of the output signal changes. It is preferable that the switch is set to be turned on.

  According to this, the protection switch is turned on and the switching element is turned off before the switching element is turned off due to the unstable operation of the control circuit. For this reason, a switching element can be turned off in the state where the electric current which flows through a primary coil is lower. Therefore, the induced voltage of the secondary coil generated by electromagnetic induction can be made smaller than when the switching element is turned off due to instability of the control circuit. In other words, by setting the threshold voltage of the protection switch so that the protection switch is turned on in a state where the current flowing from the main power source to the first power source is smaller, the induced voltage generated in the secondary coil is changed to the voltage leading to ignition. Can be made smaller. Therefore, the occurrence of pre-ignition can be suppressed.

It is a circuit diagram of the ignition device concerning a 1st embodiment. It is a figure which shows the time change of the voltage and electric current value in one ignition cycle in the structure which does not have a protection switch. It is a figure which shows the time change of the voltage and electric current value in one ignition cycle in the structure which has a protection switch. It is a circuit diagram of the ignition device which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same reference numerals are given to the same or equivalent parts.

(First embodiment)
Initially, with reference to FIG. 1, schematic structure of the ignition device which concerns on this embodiment is demonstrated.

  The ignition device 10 according to the present embodiment is a circuit constituting an igniter used for an internal combustion engine of an automobile. The ignition device 10 includes a primary coil 11 and a secondary coil 12, an insulated gate bipolar transistor (hereinafter referred to as IGBT) 13 as a switching element, and a microwave integrated circuit (hereinafter referred to as MIC) 14. .

  The primary coil 11 and the IGBT 13 are connected in series between the main power supply 15 (shown as Vbat in FIG. 1) and the PGND 16 as the ground. For example, the voltage of the main power supply 15 in this embodiment can be set to Vbat = 20V.

  One end of the primary coil 11 is connected to the main power supply 15, and the other end is connected to the PGND 16 via the IGBT 13. In the state where the IGBT 13 is on, a current flows from the main power source 15 toward the PGND 16. When the IGBT 13 is turned off, the current is interrupted and the amount of current changes. A secondary coil 12 is disposed in the vicinity of the primary coil 11, and a voltage (shown as VOUT in FIG. 1) corresponding to a change in the current flowing through the primary coil 11 due to electromagnetic induction is generated in the secondary coil 12. Ignition is performed by this VOUT.

  The IGBT 13 has a collector connected to the primary coil 11 and an emitter connected to the PGND 16. The gate is connected to one terminal of the MIC 14. The IGBT 13 is turned on or off when an output signal output from the MIC 14 is applied to the gate. For example, in the present embodiment, when a voltage higher than a threshold voltage (high bias described later) is applied to the gate, the gate is turned on.

  The MIC 14 in this embodiment is an integrated circuit having four terminals and has terminals A, B, C, and D. A terminal A is an output terminal and is connected to the gate of the IGBT 13. The terminal B is a grounding terminal and is connected to the PGND 16. Terminals C and D are input terminals to which, for example, an engine control unit (ECU) for igniter control (not shown) is connected. Specifically, the terminal C is connected to a first power supply 17 (indicated as V1 in FIG. 1) that supplies a voltage to an inverting input terminal 20c of a comparator 20 (described later) that is built in the ECU and constitutes the MIC 14. ing. The terminal D is connected to a second power supply 18 (indicated as V2 in FIG. 1) that supplies an input signal to the non-inverting input terminal 20d of the comparator 20 that is built in the EUC. This input signal defines the polarity of the output signal output to the output terminal.

  The MIC 14 includes a comparator 20 as a control circuit, a first diode 21 as a first element, a second diode 22 as a second element, and a voltage adjustment circuit 23, and an NPN bipolar as a protection switch. A transistor 24 (hereinafter referred to as an NPN transistor 24) is included.

  The comparator 20 is an element that compares two input signals and switches the polarity of the output signal depending on whether or not a predetermined condition is met. The comparator 20 includes a power supply terminal 20a, a ground terminal 20b, an inverting input terminal 20c and a non-inverting input terminal 20d as input terminals, and an output terminal 20e.

  A power supply (indicated as VCC in FIG. 1) for operating the comparator 20 is connected to the power supply terminal 20a. For example, in this embodiment, VCC = 5V can be set. In the present embodiment, a configuration in which VCC is a power source different from the main power source 15 is shown, but these may be common.

  The PGND 16 is connected to the ground terminal 20 b via the terminal B of the MIC 14.

  A first power supply 17 is connected to the inverting input terminal 20c via a terminal C of the MIC 14, and a voltage adjustment circuit 23 for adjusting a voltage to be input to the inverting input terminal 20c to a constant voltage is connected. The voltage input to the inverting input terminal 20 c is constant and becomes a reference voltage among the two voltages compared to the comparator 20. For example, in the present embodiment, the voltage applied to the inverting input terminal 20c can be adjusted to approximately 2.5V. At this time, the voltage of the first power supply 17 defined by the ECU can also be set to 0 V (ground potential), for example. However, the voltage V1 of the first power supply 17 is not limited to the ground potential, and can be changed according to product specifications. In the present embodiment, there is a relationship of V1 <Vbat.

  A second power supply 18 is connected to the non-inverting input terminal 20d through a terminal D of the MIC 14. The second power supply 18 outputs a clock bias generated by the ECU. For example, in this embodiment, a binary output of V2 = 0V or V2 = 5V can be obtained. This clock bias V2 is an input signal input to the non-inverting input terminal 20d.

  The output terminal 20 e is connected to the gate of the IGBT 13 via the terminal A of the MIC 14. The voltage output from the output terminal 20e depends on the voltage input to the inverting input terminal 20c and the non-inverting input terminal 20d. For example, in the present embodiment, when the voltage input to the non-inverting input terminal 20d exceeds the inverting input terminal 20c, a high bias is output from the output terminal 20e. Conversely, when the voltage difference falls below the threshold, a low bias is output. The High bias in this embodiment is the same as VCC and is 5V. The low bias is the same as PGND16 and is 0V. Then, the high bias is output from the output terminal 20e, whereby the IGBT 13 is turned on.

  As shown in FIG. 1, the first diode 21 and the second diode 22 are connected in series between the first power supply 17 and the PGND 16. The two diodes 21 and 22 are arranged such that the cathode is on the first power supply 17 side. These diodes 21 and 22 suppress an unexpected current flow from the first power supply 17 to the PGND 16, and are elements contributing to an improvement in ESD resistance, as will be described later.

  The base of the NPN transistor 24 is connected between the first diode 21 and the second diode 22. The emitter is connected to the terminal C so as to have the same potential as the first power supply 17. The collector is connected to the terminal A so as to have the same potential as the output terminal 20 e of the comparator 20. The NPN transistor 24 is turned on when a current flows from the main power supply 15 toward the first power supply 17 and a predetermined voltage is applied to the base. Then, the first power supply 17 and the output terminal 20e of the comparator 20 are electrically connected. The threshold voltage at which the NPN transistor 24 in the present embodiment is turned on can be set to 0.5 V, for example. This threshold voltage is set so that the NPN transistor 24 is turned on before the voltage applied to the ground terminal 20b of the comparator 20 reaches a voltage (for example, 3 V) at which the operation of the comparator 20 becomes unstable. Yes.

  Next, with reference to FIG. 2 and FIG. 3, the effect of the ignition device 10 which concerns on this embodiment is demonstrated. 2 and 3 are diagrams showing voltage and current values in one ignition cycle with the horizontal axis as time. 2 and 3, V2 is the voltage of the second power supply 18, Sig is the output signal of the comparator 20, I is the current flowing through the primary coil 11, and VOUT is the induced voltage generated in the secondary coil 12.

  The first feature of the ignition device according to the present embodiment is that an NPN transistor 24 is provided as a protection switch. The second feature is that the first element and the second element are diodes 21 and 22. The third feature is that the comparator 20, the first diode 21, the second diode 22, and the voltage adjustment circuit 23 are packaged by the same MIC 14.

  First, the protection switch as the first feature will be described.

  First, with respect to FIG. 1, it is assumed that the PGND 16 is opened in a configuration having no protection switch. That is, it is assumed that the wiring that electrically connects the primary coil 11 and the comparator 20 and the PGND 16 is disconnected. In this case, the portion connected to PGND 16 becomes electrically floating. As shown in FIG. 2, the voltage V2 of the second power supply 18 is a clock bias. The operation of the ignition device 10 in this case will be described step by step.

  In this embodiment, V2 transitions from 0V to 5V at time t1. Thereby, the output signal Sig output to the output terminal 20e of the comparator 20 becomes a High bias. Along with this, the IGBT 13 is turned on, and a current starts to flow through the primary coil 11. By assumption, PGND 16 is open. Further, there is a relationship of V1 <Vbat. Therefore, a current flows from the main power supply 15 toward the first power supply 17 via the first diode 21 and the second diode 22. Then, due to the voltage drop of the first diode 21 and the second diode 22, a potential higher than 0V (for example, about 3V) is applied to the ground terminal 20b of the comparator 20. For this reason, the comparator 20 stops operation without obtaining a potential difference required for operation between the power supply terminal 20a and the ground terminal 20b. At time t2, the output signal Sig transitions from a high bias to a low bias. As a result, the IGBT 13 is turned off, and the current flowing through the primary coil 11 is interrupted. Due to this sudden change in current, an induced voltage is generated in the secondary coil 12. Thus, pre-ignition occurs due to an unexpected induced voltage before the voltage V2 of the second power supply transitions from 5V to 0V. When the potential of the ground terminal 20b of the comparator 20 returns from approximately 3V to 0V, the output signal Sig becomes High bias again, and the IGBT 13 is also turned on. Then, current begins to flow through the primary coil 11. Thereafter, the operation between time t1 and time t2 is repeated. In this embodiment, the process is repeated until time t5. That is, as shown in FIG. 2, preignition occurs four times before regular ignition (time t6). At time t6, the voltage V2 of the second power supply 18 transitions from 5V to 0V, and the output signal Sig of the comparator 20 also transitions from High bias to Low bias. For this reason, IGBT13 is turned off and the electric current which was flowing into the primary coil 11 is interrupted | blocked. Due to this change in current, normal ignition is performed by the induced voltage generated in the secondary coil 12. As described above, pre-ignition occurs before regular ignition in a configuration without a protection switch.

  On the other hand, in the configuration having the NPN transistor 24 as a protection switch (FIG. 1), it is assumed that the PGND 16 is open. In the present embodiment, the threshold voltage of the NPN transistor 24 is set so that the NPN transistor 24 is turned on before the comparator 20 stops operating due to the potential rise of the ground terminal 20b. The operation of the ignition device 10 in this case will be described with reference to FIG.

  At time t1, V2 changes from 0V to 5V. Thereby, the output signal Sig output to the output terminal 20e of the comparator 20 becomes a High bias. Along with this, the IGBT 13 is turned on, and a current starts to flow through the primary coil 11. Assuming that PGND 16 is open, a potential higher than 0 V is applied to the ground terminal 20 b of the comparator 20. However, before the operation of the comparator 20 stops, the NPN transistor 24 is turned on, and the output signal Sig becomes the same as the potential V1 of the first power supply 17 (0 V in this embodiment). That is, the output signal Sig transitions from the high bias to the low bias. The NPN transistor 24 is turned on earlier than the operation of the comparator 20 is stopped. For this reason, the period of transition between the high bias and the low bias in the output signal Sig is shorter than that in the configuration without the protection switch. Therefore, the change in the amount of current flowing through the primary coil 11 is also reduced, and the induced voltage generated in the secondary coil 12 is also reduced. As described above, with the configuration having the protection switch, the induced voltage generated in the secondary coil 12 before the normal ignition can be reduced as compared with the configuration without the protection switch. Unexpected ignition can be suppressed. Further, in such a configuration, the induced voltage generated in the secondary coil 12 is reduced even during normal ignition (time t6). For this reason, it is possible to prevent the engine from being ignited in an abnormal state (a state in which PGND 16 is open).

  Next, the second feature, that the first element and the second element are diodes 21 and 22, will be described.

  According to this, the circuit can be protected by arranging the diode in the reverse direction against a surge such as ESD in which a large current flows from the first power supply 17 toward the PGND 16. That is, ESD tolerance can be ensured.

  Next, the third feature, that is, the comparator 20, the first diode 21, the second diode 22, and the voltage adjustment circuit 23 are packaged by the same MIC 14 will be described.

  In conventional ignition devices, a protection circuit against ESD is often provided separately from the comparator 20. For this reason, there existed a problem that the physique of an ignition device will become large. On the other hand, in the present embodiment, the ESD protection circuit and the circuit that invalidates the malfunction of the comparator 20 are packaged in the same MIC 14, so that these are used as separate chips. The physique of the ignition device 10 can be reduced. The ignition device 10 according to the present embodiment is suitable for an automobile ignition device that has been increasingly integrated in recent years.

(Second Embodiment)
In the present embodiment, the following points are different from the first embodiment. As a switching element, a power MOS transistor 19 is used instead of the IGBT 13. Further, a MOS transistor 27 is used in place of the NPN transistor 24 as a protection switch. Furthermore, as the first element and the second element, a first resistor 25 and a second resistor 26 are used in place of the first diode 21 and the second diode 22, respectively.

  About the part except an above-described element, since it is the same as that of 1st Embodiment, the description is abbreviate | omitted.

  Also in this embodiment, the ignition device 10 has a protection switch (power MOS transistor 19). Therefore, also in this embodiment, the same effect as that of the protective switch described in the first embodiment can be obtained.

  Further, the first element (first resistor 25) and the second element (second resistor 26) are packaged in the same MIC 14 together with the comparator 20 and the voltage adjustment circuit 23. Therefore, also in this embodiment, it can suppress that the physique of the ignition device 10 becomes large similarly to 1st Embodiment.

  However, when the first element and the second element are replaced with the resistors 25 and 26 from the diodes 21 and 22, the ESD resistance between the first power supply 17 and the PGND 16 cannot be ensured. For this reason, the first element and the second element are preferably diodes 21 and 22 as in the first embodiment.

(Other embodiments)
The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In each of the above-described embodiments, an example in which the comparator 20 is used as the control circuit has been described. However, it is not limited to the above example. Regardless of whether the control circuit is an analog circuit or a digital circuit, the control circuit includes a power supply terminal 20a, a ground terminal 20b, an inverting input terminal 20c and a non-inverting input terminal 20d as input terminals, and an output terminal 20e. Just do it. The ground terminal 20b may be an element that outputs an output signal for turning on / off the switching element to the output terminal 20e based on the voltage applied to the input terminals 20c and 20d while being connected to the PGND16.

  Further, in each of the above-described embodiments, an example in which the IGBT 13 or the power MOS transistor 19 is used as the switching element has been described. However, the present invention is not limited to the above example, and any three-terminal switching element that turns on and off according to the output signal of the control circuit (comparator 20) can be employed.

  Further, in each of the above-described embodiments, an example in which the NPN transistor 24 or the MOS transistor 27 is used as the protection switch has been described. However, the present invention is not limited to the above example, and any three-terminal switching element that turns on and off according to the midpoint potential between the first element and the second element can be employed.

  In each of the above-described embodiments, the comparator 20, the first element (the first diode 21 or the first resistor 25), the second element (the second diode 22 or the second resistor 26), and the voltage adjustment are included in the same MIC 14. The example in which the circuit 23 and the protection switch (NPN transistor 24 or MOS transistor 27) are all arranged is shown. However, each element may be arranged as a separate chip.

  In each of the above-described embodiments, the example in which the voltage V1 of the first power supply 17 is set to the ground potential (0 V) has been described. However, V1 is not limited to the ground potential, and may be changed according to product specifications. Is possible. However, since the switching element needs to be turned off when the protection switch is on, V1 must be set smaller than the threshold voltage of the switching element.

  In each of the embodiments described above, the voltage Vbat of the main power supply 15, the voltage V2 of the second power supply 18, and the voltage VCC of the power supply for operating the comparator 20 are examples, and are limited to the above examples. It is not something.

  FIG. 1 shows a state in which the first diode 21 and the second diode 22 are arranged one by one. FIG. 4 also shows a state in which the first resistor 25 and the second resistor 26 are arranged one by one. However, each of the first element and the second element may have a plurality of diodes or resistors. For example, the first element may be composed of two diodes connected in series, and the second element may be composed of one diode.

DESCRIPTION OF SYMBOLS 10 ... Ignition device 11 ... Primary coil 13 ... Insulated gate bipolar transistor (IGBT)
15 ... Main power supply 16 ... Power ground (PGND)
17 ... 1st power supply, 18 ... 2nd power supply 20 ... Comparator 21 ... 1st diode, 22 ... 2nd diode 24 ... NPN transistor

Claims (7)

A primary coil (11) and switching elements (13, 19) disposed between the main power source (15) and the ground (16) and connected in series;
A control circuit (20) for controlling on / off of the switching element,
The control circuit
A power terminal (20a) and a ground terminal (20b);
A non-inverting input terminal (20d) and an inverting input terminal (20c) as input terminals;
An output terminal (20e) for outputting an output signal having two polarities of High bias or Low bias based on a potential difference between the non-inverting input terminal and the inverting input terminal;
The inverting input terminal is connected to a first power supply (17) that is lower than a main power supply and has a potential not to turn on the switching element,
The non-inverting input terminal is connected to a second power source (18) that defines the polarity of the output signal;
The ground terminal is connected to the ground;
A first element (21, 25) and a second element (22, 26) connected in series between the first power source and the ground and having a predetermined resistance value,
The first power supply and the output terminal of the control circuit are connected via a protection switch (24, 27),
The ignition device according to claim 1, wherein the protection switch is turned on / off according to a midpoint potential between the first element and the second element.   The ignition device according to claim 1, wherein the first element and the second element are diodes (21, 22) connected in series so that the first power supply side becomes a cathode. In a state where the portion connected to the ground is electrically floating, and the polarity of the output signal turns on the switching element,
3. The ignition device according to claim 1, wherein the threshold voltage of the protection switch is set such that the protection switch is turned on before the polarity of the output signal is changed.   Ignition according to any one of the preceding claims, characterized in that the control circuit, the first element, the second element and the protection switch are arranged in a common chip (14). apparatus.   The ignition device according to any one of claims 1 to 4, wherein the control circuit is a comparator (20).   The ignition device according to any one of claims 1 to 5, wherein the protection switch is a bipolar transistor (24) or a MOS transistor (27).   The ignition device according to any one of claims 1 to 6, wherein the switching element is an insulated gate bipolar transistor (13) or a power MOS transistor (19).

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