JP4895905B2 - Combustion detection device for internal combustion engine - Google Patents

Description

  The present invention relates to a combustion detection device for an internal combustion engine that always operates properly regardless of whether or not it is in a standard combustion state.

  Recently, Homogeneous Charge Compression Ignition Combustion has attracted attention as a combustion method that can achieve better fuel efficiency and exhaust performance than conventional engines. According to this HCCI combustion system, it is expected that high efficiency comparable to a diesel engine can be achieved without exhausting nitrogen oxides (NOx) and soot.

However, even when the HCCI combustion method is adopted, there is a timing at which the engine enters the SI combustion state. Therefore, when a conventionally known ion detection circuit (for example, Patent Document 1) is used, during SI (standard ignition) combustion, A malfunction occurs in any operating state during HCCI combustion.
JP 2006-283568 A

  For example, when the ion detection circuit described in Patent Document 1 is used, an ion current can be appropriately detected during SI combustion, while in HCCI combustion, the detection level may be too low to detect self-ignition timing. Therefore, in order to increase the detection level, the bias voltage of the ion detection circuit can only be increased. However, this causes a problem that the spark plug is discharged at an unintended timing at the time of SI combustion.

  The present invention has been made paying attention to the above problems, and provides a combustion detection device for an internal combustion engine that always operates properly regardless of whether or not it is in a standard combustion state. Objective.

In order to achieve the above object, a combustion detection apparatus for an internal combustion engine according to the present invention corresponds to a variable power supply unit capable of linearly changing an output voltage based on a control signal, and an output voltage of the variable power supply unit. A voltage generation circuit for generating a bias voltage for current detection that changes linearly, and by increasing the output voltage as necessary, the combustion is performed regardless of whether it is in a standard combustion state or not. The present invention is characterized in that a weak current flowing through an internal combustion engine during or after combustion can be detected.

  In the present invention, the output voltage of the variable power supply unit can change linearly based on the control signal. Therefore, the bias voltage for current detection can be changed linearly instead of stepwise. The standard combustion state means, for example, the SI combustion state, and the non-standard combustion state means, for example, the HCCI combustion state, but is not limited to this.

  The voltage generation circuit is preferably configured to include a capacitor charged by the variable voltage received from a variable power supply unit, and a switching element connected in parallel to the capacitor, and the capacitor on the ignition transformer secondary side. It is preferable that the switching element is controlled to be turned on at a timing when a high voltage in the same direction as the charging voltage is generated.

  Preferably, the voltage generation circuit is connected between the capacitor charged by the variable voltage received from the variable power supply unit and the low voltage side of the ignition transformer secondary side and the ground in a direction to prevent the discharge of the capacitor. A directional current element; a positive side terminal of the capacitor in a charged state; and a current limiting member connected between the ignition transformer secondary side low voltage side.

  The variable power supply unit typically includes a booster circuit that generates a voltage higher than the battery voltage by performing a switching operation in response to the battery voltage. The variable power supply unit preferably outputs a variable voltage having a level corresponding to the voltage level of the control signal. In the standard combustion state, it is effective that the variable power supply unit starts a boost operation corresponding to the timing at which the spark plug is discharged. In this case, in the step-up operation, it is more effective to generate the maximum voltage at the start of the operation for discharging the spark plug and then suppress the generated voltage.

  Preferably, for the operating time of the variable power supply unit other than the standard combustion state and the voltage value to be output during the operating time, a combination of each optimum value corresponds to the operating state of the internal combustion engine at that time in advance. It has been decided. In this case, during the operation time, it is effective to control the voltage value so as to increase gradually with time.

  According to the present invention described above, it operates properly in any case depending on whether it is a standard combustion state, typically, whether it is SI combustion or HCCI combustion. A combustion detection device for an internal combustion engine can be realized.

  Hereinafter, the present invention will be described in more detail based on examples. FIG. 1 illustrates an ion current detection circuit ION that can appropriately change the operation content depending on whether SI combustion or HCCI combustion.

  As shown in the figure, the ion current detection circuit ION is configured to be connected in series to the ignition plug PG and the secondary coil L2, and together with the ignition plug PG and the secondary coil L2, configures a secondary circuit of the ignition transformer T. Yes. The primary side of the ignition transformer T includes a primary coil L1, a switching transistor Q1 (IGBT: Insulated Gate Bipolar Transistor), bias resistors R1 and R2 of the transistor Q1, a current limiting resistor R3, and a Zener diode for protecting the transistor. It is composed of ZD1.

  During SI combustion, an ignition pulse VS from an ECU (Engine Control Unit) is supplied to the base terminal of the transistor Q1, and the transistor Q1 performs an ON / OFF operation according to the level of the ignition pulse VS. As a result, a secondary voltage Vpg is generated in the secondary coil L2 of the ignition transformer T when the transistor Q1 is turned ON / OFF (see FIG. 4). In this embodiment, the secondary voltage Lpg is reduced when the ignition pulse VS falls. The secondary coil L2 is configured to generate a secondary voltage Vpg that is high in the positive direction. At the time of SI combustion, the ignition plug PG is ignited and discharged by a positive high voltage at the falling timing of the ignition pulse VS (plus discharge).

  On the other hand, during HCCI combustion, the ignition pulse VS is not supplied to the transistor Q1, and a high voltage is not generated in the secondary coil L2 of the ignition transformer T. Therefore, the internal combustion engine burns by the self-ignition operation of the spark plug PG. In this embodiment, the ignition timing is reliably detected by the ion current detection circuit ION that operates optimally according to the operation state of the internal combustion engine. Is done.

  The ion current detection circuit ION includes a booster circuit 1 that boosts the battery voltage BATT according to the voltage level of the analog control signal Vcnt supplied from the ECU, and a bias voltage generation circuit 2 that detects the ion current I. , And the voltage conversion circuit 3 of the ionic current I.

  The booster circuit 1 includes a Zener diode ZD2, a choke coil L3, a switching transistor (IGBT) Q2, a PWM wave generation circuit 4, a rectifier diode D4, and a smoothing capacitor C2, and constitutes a chopper circuit as a whole. is doing. Zener diode ZD2 is connected between battery voltage BATT and ground GND to absorb battery voltage fluctuations.

  The PWM wave generation circuit 4 is a circuit that generates a PWM wave having a duty ratio corresponding to the voltage level of the analog control signal Vcnt. Then, the PWM set to an appropriate duty ratio is supplied to the base terminal of the transistor Q2, so that the transistor Q2 performs a switching operation for an arbitrary ON time. Note that the battery voltage BATT is supplied to the collector terminal of the transistor Q2 via the choke coil L3, and the emitter terminal is supplied to the ground GND.

  A rectifier diode D4 and a smoothing capacitor C2 are connected in series between the collector terminal and the emitter terminal of the transistor Q2, and the boosted voltage V1 that is the voltage across the smoothing capacitor C2 is supplied to the diode D3 of the bias circuit 2. .

  Since the booster circuit 1 of this embodiment is configured as described above, the voltage V1 across the smoothing capacitor C2 is proportional to the duty ratio (= Ton / T) of the PWM wave supplied to the base terminal of the transistor Q2. Will do. When a high bias voltage V1 is required as in the case where the internal combustion engine is in HCCI combustion, the on-time Ton is lengthened to increase the duty ratio. The control signal Vcnt is an analog control signal, and the PWM wave generation circuit 4 outputs a PWM wave having an on time Ton proportional to the analog level of the control signal Vcnt. When the control signal Vcnt = 0, no PWM wave is output from the PWM wave generation circuit 4, and the output voltage to the base terminal of the transistor Q2 is maintained at the L level, so that the transistor Q2 is steadily turned off. It becomes.

  The bias voltage generation circuit 2 includes a diode D1, a series circuit of a resistor R4, a capacitor C1, and a diode D2, and a diode D3 that receives the boosted voltage V1 from the booster circuit 1. The diode D1 has a cathode terminal connected to the low voltage side of the secondary coil L2, and an anode terminal connected to the ground GND. The series circuit of the resistor R4, the capacitor C1, and the diode D2 is connected in parallel to the diode D1, and the cathode terminal of the diode D3 is connected to the connection point between the resistor R4 and the capacitor C1. The anode terminal of the diode D2, which is a connection point with the capacitor C1, is connected to the voltage conversion circuit 3.

  The voltage conversion circuit 3 includes an OP amplifier AP and a feedback resistor Rd connected between the inverting input terminal and the output terminal of the OP amplifier. Accordingly, all of the input current I indicated by the arrow flows through the feedback resistor Rd, and the output voltage VO is VO = Rd × I in proportion to the input current I.

Next, the operation content of the ion current detection circuit ION of FIG. 1 will be described with reference to FIGS. FIG. 2 is an operation explanatory diagram during SI combustion, FIG. 3 is an operation explanatory diagram during HCCI combustion, and FIG. 4 is a time chart during each combustion.
<Operation during SI combustion>
First, based on FIG.2 and FIG.4 (a), the operation | movement at the time of SI combustion is demonstrated. As described above, the operation of the booster circuit 1 is controlled by the voltage level of the control signal Vcnt. When Vcnt = 0, the transistor Q2 is OFF and the booster circuit 1 does not function as a chopper circuit. . On the other hand, when Vcnt> 0, the transistor Q2 is turned on by a PWM wave having a pulse width corresponding to the voltage level of the control signal Vcnt, and the booster circuit 1 functions as a chopper circuit.

  As shown in FIG. 4A, the ignition pulse VS rises at the timing T0. In this state, the control signal Vcnt is 0 level, and the booster circuit 1 is not functioning. Further, at this timing T0, a negative secondary voltage Vpg opposite to the charging voltage of the capacitor C1 is induced in the secondary coil L2 of the ignition transformer T. Therefore, there is no possibility that the ignition plug PG will inadvertently cause an ignition discharge. .

  Thereafter, when the ignition pulse VS falls at timing T1, a secondary voltage Vpg that is high in the positive direction is induced in the secondary coil L2 of the ignition transformer T, and the ignition plug PG is ignited and discharged by the high voltage Vpg. The discharge current flows through a path of diode D1 → secondary coil L2 → ignition plug PG. The ignition discharge starts combustion of the internal combustion engine.

  Before or after this ignition discharge, the ECU raises the control signal Vcnt to an appropriate level (timing T2). This voltage level is experimentally determined in advance in accordance with the operating state of the internal combustion engine at that time, and the voltage level is selected.

  Since the control signal Vcnt> 0, the PWM wave generation circuit 4 outputs a PWM wave having a duty ratio corresponding to the voltage level of the control signal Vcnt to the transistor Q2. Therefore, the booster circuit 1 boosts and outputs the battery voltage BATT corresponding to the voltage level of the control signal Vcnt. The output boosted voltage V1 is an appropriate value determined within a voltage range of about 70 to 300V, for example.

  When the booster circuit 1 starts operation, the capacitor C1 is charged to the level of the boosted voltage V1 (see FIG. 2A). At this time, since the internal combustion engine is combusting, the discharge from the capacitor C1 can be considered. However, since the resistor R4 is connected to the low voltage side of the capacitor C1 and the secondary coil L2, the capacitor C1 The discharge operation is appropriately suppressed.

  Thereafter, at timing T3 at which the combustion of the internal combustion engine ends, the control signal Vcnt = 0 and the boosting operation of the booster circuit 1 is stopped. Note that the timing T3 at which the boosting operation should be stopped is determined experimentally in advance corresponding to the operating state of the internal combustion engine, or is determined based on the current of the secondary circuit of the ignition transformer T or the like.

The operation after the boosting operation of the booster circuit 1 is prohibited is as shown in FIG. 2 (b). The feedback resistor Rd → capacitor C1 → resistor R4 → secondary coil L2 → ignition plug PG of the voltage conversion circuit 3 An ion current I flows through the path. The voltage conversion circuit 3 outputs an I × Rd ion detection voltage VO proportional to the ion current.
<Operation during HCCI combustion>
Subsequently, the operation during HCCI combustion will be described based on FIGS. 3 and 4B. During HCCI combustion, the ECU does not output the ignition pulse VS. Then, the chopper operation of the booster circuit 1 is started at an optimum ON timing T4 determined experimentally in advance corresponding to the operation state of the internal combustion engine at that time. Specifically, an appropriate level of control voltage Vcnt is supplied to the PWM generation circuit 4.

  The voltage level value of the control voltage Vcnt is uniquely determined in advance according to the operating state of the internal combustion engine together with the ON timing T4 and its pulse width WD, and the parameter values (Vcnt, T2, WD) are selected. Is done. Specifically, the control voltage level Vcnt is selected so that the boosted voltage V1 as high as possible can be obtained under the condition that the spark plug PG does not self-ignite even if supplied at the timing (T2). The boosted voltage V1 varies depending on the operating state of the internal combustion engine. In any case, the boosted voltage V1 is higher than the boosted voltage V1 during SI combustion. For example, a voltage of about 800 V or more is selected. 3A illustrates a state in which the capacitor C1 is charged by the boosted voltage V1 output from the booster circuit 1. FIG.

  Thereafter, when the internal combustion engine self-ignites, the cylinder internal pressure rapidly increases and a detection current shown in FIG. 3B flows. The flow path of the detection current I is the same as that during SI combustion, and flows in the path of the feedback resistance Rd → capacitor C1 → resistance R4 → secondary coil L2 → ignition plug PG of the voltage conversion circuit 3. Since the voltage conversion circuit 3 outputs the detection voltage VO of I × Rd, the ECU can reliably grasp the timing of self-ignition by this detection voltage.

  As described above, in the present embodiment, since the bias voltage V1 of the ion current detection circuit ION can be significantly changed between the SI combustion and the HCCI combustion, the HCCI combustion can be performed by significantly increasing the bias voltage during the HCCI combustion. The weak ion current at the time can be reliably detected. In addition, during SI combustion, the bias voltage V1 can be greatly reduced compared to that during HCCI combustion. Therefore, during SI combustion, the spark plug PG is connected at a timing when the cylinder internal pressure is lower than the originally scheduled timing. There is no discharge.

  The embodiment of FIG. 1 has been described above, but the specific circuit configuration does not particularly limit the present invention and can be changed as appropriate. For example, FIG. 5 shows a modification of the booster circuit. The booster circuit 1A includes a Zener diode ZD2, a choke coil L3, a switching transistor (IGBT) Q2, a drive control circuit 5, a rectifier diode D4, and a smoothing circuit. The capacitor C2 and the linear operation circuit 6 are included to constitute a chopper circuit as a whole.

  The drive control circuit 5 is provided in place of the PWM wave generation circuit 4 of FIG. 1, and outputs a drive pulse with a fixed duty ratio. That is, when the voltage level of the control signal Vcnt is 0 (Vcnt = 0), the drive control circuit 5 outputs an L level voltage, but when the control signal Vcnt is a positive level (Vcnt> 0). Outputs a control pulse having a constant pulse width regardless of the voltage level.

  On the other hand, the linear operation circuit 6 provided on the output side of the smoothing capacitor C2 includes a transistor Q3 that performs a linear amplification operation, voltage dividing resistors R7 and R8 that generate a base voltage of the transistor Q3, an emitter terminal of the transistor Q3, and a ground An emitter resistor R6 connected between the GND and a collector resistor R5 for supplying the boosted voltage V1 of the capacitor C2 to the collector terminal of the transistor Q3. The control signal Vcnt is supplied to the base terminal of the transistor Q3 through the resistor R7.

  The linear operation circuit 6 functions as an active load for the chopper circuit including the choke coil L3, the switching transistor Q2, the rectifier diode D4, and the smoothing capacitor C2. That is, when the control signal Vcnt is low, the equivalent resistance of the linear operation circuit 6 is high. However, as the control signal Vcnt increases, the equivalent resistance of the linear operation circuit 6 decreases. Therefore, the boosted voltage of the booster circuit 1 decreases as the voltage level of the control signal Vcnt increases, and the boosted voltage of the booster circuit 1 increases as the voltage level of the control signal Vcnt decreases.

  Therefore, in this embodiment, the voltage output V1 of the booster circuit 1 is set to an appropriate value by linearly changing the equivalent resistance of the linear operation circuit 6 according to the control signal Vcnt. However, the circuit configurations of the voltage generation circuit 2 and the voltage conversion circuit 3 for the bias voltage are the same as those in FIG. 1, and the operation as the ion current detection circuit ION is also the same as the circuit in FIG.

  By the way, as explained first, in the circuits of FIGS. 1 and 5, at the time of SI combustion, the ignition plug PG is ignited by positive high voltage at the fall timing of the ignition pulse VS (plus discharge). However, the present invention suitably functions also when the spark plug PG is ignited and discharged by a negative high voltage (minus discharge).

  6 and 7 are circuit diagrams illustrating an ion current detection circuit ION in which the spark plug is negatively discharged during SI combustion. 6 and 7 have the same circuit configuration except that the booster circuits 1 and 1A are different.

  As shown in the figure, in this ion current detection circuit, a thyristor Q4 is provided in parallel with a capacitor C3 that holds a bias voltage for ion current detection. A capacitor C4 is connected between the gate terminal of the thyristor Q4 and the ground GND.

  The output voltage of the differentiation circuit 7 is supplied to the gate terminal of the thyristor Q4. The differentiation circuit 7 is connected between the OP amplifier AP2, a series circuit of an input resistor R10 and a differentiation capacitor C5 connected to the inverting input terminal of the OP amplifier AP2, and between the inverting input terminal of the OP amplifier AP2 and the ground GND. The resistor R12 includes a feedback resistor R11 connected between the output terminal and the inverting input terminal of the OP amplifier AP2.

  A logically inverted ignition pulse VS bar is supplied to the series circuit of the input resistor R10 and the differential capacitor C5. That is, the input voltage to the differentiation circuit 7 falls at the timing T0 when the ignition pulse VS rises and the switching transistor Q1 is turned on. Therefore, the output of the differentiating circuit 7 rises at the timing T0, and the thyristor Q4 is turned on only at that moment.

  6 and 7 in which the spark plug PG performs a negative discharge operation, since a positive voltage is induced on the secondary side of the ignition transformer T at the timing T0, the positive voltage and the charging voltage of the capacitor C3 are added. Therefore, there is a possibility that the spark plug PG may be accidentally discharged at the timing T0.

  However, at timing T0, the thyristor Q4 is turned on, so that the voltage applied to the spark plug PG drops, so that the above-described erroneous discharge is reliably prevented. Since the output of the differentiation circuit 7 quickly falls to the steady level after the timing T0, the thyristor also quickly returns to the OFF state, and as a result, the capacitor C3 is recharged to a predetermined value based on the output of the booster circuit. Is done.

  In the ion current detection circuit ION shown in FIGS. 6 and 7 as well, the appropriate boosted voltage V1 is supplied to the voltage generation circuit 2 of the bias voltage depending on whether the combustion is in SI combustion or HCCI combustion. The combustion timing can be reliably detected during HCCI combustion.

  In any of the above embodiments, the output voltage V1 of the booster circuits 1 and 1A is changed to a binary target value. However, the duty ratio of the PWM wave and the level of the control signal Vcnt are appropriately changed. Thus, the output voltage V1 can be changed more precisely according to the purpose.

  For example, as shown in FIG. 8, it is preferable to change the boosted voltage V1 in a stepwise manner by changing the level of the control signal Vcnt in a stepwise manner during SI combustion. If the operation mode as shown in FIG. 8 is adopted, it is possible to reliably suppress the voltage drop across the capacitor C1 when the spark plug is discharged (see FIG. 2A).

  In addition, as shown in FIG. 9, it is preferable that the boosted voltage V1 is gradually increased similarly by gradually increasing the level of the control signal Vcnt during HCCI combustion. In this case, since the high boosted voltage V1 is not applied to the secondary side of the ignition transformer T at a timing when the cylinder internal pressure is low, the internal combustion engine can be self-ignited at an optimal timing.

It is a circuit diagram of an ion current detection circuit according to the first embodiment. It is drawing explaining the operation | movement content at the time of SI combustion of the ion current detection circuit of FIG. It is drawing explaining the operation | movement content at the time of HCCI combustion of the ion current detection circuit of FIG. It is a time chart explaining the operation | movement content of the ion current detection circuit of FIG. It is a circuit diagram which shows the modification of the ion current detection circuit of 1st Example. It is a circuit diagram of the ion current detection circuit which concerns on 2nd Example. It is a circuit diagram which shows the modification of the ion current detection circuit which concerns on 2nd Example. It is a time chart explaining another control method at the time of SI combustion. It is a time chart explaining another control method at the time of HCCI combustion.

Explanation of symbols

Vcnt control signal V1 output voltage 1 variable power supply unit 2 voltage generation circuit ION combustion detection device

Claims (9)

A variable power supply unit capable of linearly changing an output voltage based on a control signal, and a voltage generation circuit for generating a bias voltage for current detection that linearly changes in response to the output voltage of the variable power supply unit. Prepared,
The present invention is characterized in that a weak current flowing through an internal combustion engine during or after combustion can be detected by increasing the output voltage as necessary, regardless of whether or not the engine is in a standard combustion state. A combustion detection device for an internal combustion engine. The voltage generation circuit includes a capacitor charged by the output voltage received from a variable power supply unit, and a switch element connected in parallel to the capacitor,
The combustion detection device according to claim 1, wherein the switch element is controlled to be turned on at a timing at which a high voltage in the same direction as the charging voltage of the capacitor is generated on the secondary side of the ignition transformer. The voltage generation circuit includes:
A capacitor charged by the output voltage received from the variable power supply unit;
A unidirectional current element connected in a direction to prevent discharge of the capacitor between the low voltage side of the secondary side of the ignition transformer and the ground;
A current limiting member connected between the positive terminal of the capacitor in a charged state and the low voltage side of the ignition transformer secondary side;
The combustion detection device according to claim 1 or 2, comprising the above.   The combustion detection device according to claim 1, wherein the variable power supply unit includes a booster circuit that generates a voltage higher than the battery voltage by performing a switching operation in response to the battery voltage.   The combustion detection device according to claim 1, wherein the variable power supply unit outputs a voltage having a level corresponding to a voltage level of the control signal.   The combustion detection device according to any one of claims 1 to 5, wherein the variable power supply unit starts a boosting operation corresponding to a timing at which the spark plug is discharged in a standard combustion state.   The combustion detection device according to claim 6, wherein in the boosting operation, a maximum voltage is generated at the start of an operation of discharging the spark plug, and thereafter, the generated voltage is suppressed.   The combination of the optimum values for the operation time of the variable power supply unit in a state other than the standard combustion state and the voltage value to be output during the operation time is determined in advance corresponding to the operation state of the internal combustion engine. Item 8. The combustion detection device according to any one of Items 1 to 7.   The combustion detection device according to claim 8, wherein the voltage value is controlled to increase gradually with time during the operation time.

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