JP5154372B2 - Ion current detector - Google Patents

Description

  The present invention relates to an ion current detection device capable of detecting an ion current generated by combustion of an internal combustion engine at a quick timing.

  In an internal combustion engine such as an automobile engine, energy is generated by burning an air-fuel mixture introduced into a combustion chamber by ignition discharge of a spark plug. In such an internal combustion engine, molecules in the combustion chamber are ionized during combustion, so that an ionic current can be acquired by applying a high voltage to the spark plug at an appropriate timing.

The presence or absence of knocking can be determined based on whether or not a knock signal is superimposed on the acquired ion current. The frequency of the knock signal varies depending on the structure of the internal combustion engine, but is about 5 kHz to 10 kHz, for example. As an ionic current detection device, for example, a circuit configuration described in Patent Document 1 is known.
JP 2006-077763 A

  FIG. 5 illustrates a circuit configuration of Patent Document 1. In this ion current detection device, when the switching element Q is turned off, a high voltage in the direction illustrated is generated in the secondary coil L2 of the ignition coil. Thus, the spark plug PG is discharged. Further, at the time of this OFF transition, the discharge current of the spark plug PG flows through the path of the secondary coil L2 → zener diode ZD11 and capacitor C11 → diode D22, and the capacitor C11 is charged. Then, after the discharge current has converged, the ion current i flows in the direction of the broken line using the voltage across the capacitor C11 as the bias power supply, and the detection signal Rf * i corresponding to the ion current i is output from the OP amplifier 30.

  However, in the circuit configuration of Patent Document 1, since the ionic current flows through the secondary coil L2, the impedance with respect to the frequency of the knock signal increases, and it is difficult to detect a minute level knock signal. There is. Further, in this circuit configuration, the spark plug PG is a negative discharge that discharges from the ground, and there is a problem that a positive discharge that discharges toward the ground cannot be realized.

Therefore, as a circuit that does not include the secondary coil L2 in the ion current path and enables positive discharge, for example, the circuit configuration of Patent Document 2 is known.
JP 2002-180949 A

  FIG. 6 illustrates the circuit configuration of Patent Document 2, and when the switching element Q is turned OFF, the ignition plug PG is discharged by generating a high voltage in the direction illustrated in the secondary coil L2 of the ignition coil. doing. At the time of this OFF transition, the capacitor C11 is charged through the path of the primary coil L1, the resistor R11, the Zener diode ZD11, and the capacitor C11 → the diode D22. Then, when the voltage across the spark plug PG drops thereafter, the ion current i flows in the direction of the broken line using the voltage across the capacitor C11 as a bias power supply, and the detection signal Rf * i is output from the OP amplifier 30. .

  In the circuit configuration of FIG. 6, a diode D20 for preventing discharge at the ON time is usually arranged so that the spark plug PG is not discharged at the ON transition time of the switching element Q. In addition, an IGBT (Insulated Gate Bipolar Transistor) is preferably used as the switching element Q, and for example, a Zener diode ZD is often connected in parallel to the IGBT.

  Therefore, in the circuit configuration of FIG. 6, the maximum charging voltage of the capacitor C11 depends on the breakdown voltage characteristics of the Zener diode ZD. For example, the charging voltage of the capacitor C11 is increased to 200V or more, for example, about 800V. Then, a special insulation design and energy resistant design corresponding to this are required, and there is a problem that the ignition circuit cannot be reduced in size and weight.

  Further, in the circuit configuration of FIG. 6, the reverse current blocking diode D21 and the ON-state discharge preventing diode D20 are indispensable, so that the discharge path of the charge charge of the secondary side stray capacitance such as the spark plug PG is high. There is also a problem that the detection start timing of the ion current is delayed by that amount.

  Here, even if the detection start timing of the ionic current is advanced, the value of increasing the detection start timing is halved if other adverse effects occur.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an ion current detection circuit capable of starting detection of ion current at a quick timing without causing any harmful effects.

  In order to solve the above-described problem, an ion current detection device according to the present invention includes an ignition coil in which a primary coil and a secondary coil are electromagnetically coupled, a switching element that controls ON / OFF of the current of the primary coil, A spark plug that discharges toward ground based on a high voltage induced in the secondary coil when the switching element is turned off; a first capacitor C1; and a first Zener diode ZD1, and when the spark plug is discharged, A bias circuit that charges the first capacitor C1 in accordance with the breakdown voltage of the first Zener diode ZD1 based on the high voltage; and a current detection circuit that detects a discharge current of the first capacitor C1. A series circuit of an auxiliary capacitor C2 and an auxiliary diode D4 is connected in parallel to both ends of the first capacitor C1. And, during discharge of the spark plug, the with the auxiliary capacitor C2 is charged, the first capacitor C1, and characterized by being configured to be charged via the auxiliary diode.

  In the present invention, since the first Zener diode ZD1 and the first capacitor C1 can be separated from the switching element in a DC manner, the charging voltage of the capacitor can be set to an optimum level without considering the breakdown voltage of the switching element.

  In the present invention, names such as a Zener diode, a capacitor, and a diode are used as a general term for electronic elements that exhibit equivalent functions, and do not mean specific electronic elements that are actually distributed. Therefore, the cathode terminal generally means a current outflow terminal, and the anode terminal generally only means a current inflow terminal.

  In the present invention, the first capacitor and the auxiliary capacitor are charged to substantially the same level in the same direction at the same timing, and the first capacitor is charged via the auxiliary diode. Even if a voltage in the discharge direction is applied, the charge of the first capacitor is not discharged, and no adverse effect occurs at the time of ON transition.

  Here, if the capacitance of the auxiliary capacitor is much smaller than that of the first capacitor, the adverse effect on the primary coil due to the discharge current from the auxiliary capacitor is greatly reduced. Preferably, the capacitance of the auxiliary capacitor C2 should be 1/1000 or less that of the first capacitor C1. However, the capacitance of the auxiliary capacitor C2 should be set equal to or slightly larger than the stray capacitance of the spark plug.

  Further, a first diode D1 is disposed between the high voltage side terminal when the first capacitor C1 is charged and the high voltage side terminal when the spark plug is discharged, so that the potential of the high voltage side terminal of the spark plug drops. Then, it is preferable that the first diode D1 is turned on, and the discharge current of the first capacitor C1 flows through the first capacitor C1, the first diode D1, and the spark plug. is there.

  In addition, it is preferable that a second Zener diode ZD2 is disposed between the secondary coil and the first Zener diode ZD1 in the direction opposite to the first Zener diode. By adopting such a configuration, the impedance of the path for discharging the charging charge of the spark plug is reduced. Here, the first and second Zener diodes are preferably set to have substantially the same breakdown voltage.

  The first Zener diode ZD1 and the first capacitor C1 are preferably connected with a second diode D2 and a third diode D3, respectively, for blocking current in the direction opposite to that during discharge of the spark plug. In particular, the third diode is optimally disposed between the capacitor and ground.

  According to the above-described ion current detection device of the present invention, detection of an ion current can be started at a quick timing without causing any harmful effects.

  Hereinafter, an embodiment of the present invention will be described based on an ion current detection device according to an example. FIG. 1 is a circuit diagram of an ion current detection device according to an embodiment.

  As shown in the figure, this ion current detection device includes an ignition coil 1 in which a primary coil L1 and a secondary coil L2 are electromagnetically coupled, a switching element 2 that controls ON / OFF of a current in the primary coil L1, capacitors C1, C2, and A bias circuit 3 centered on the Zener diodes ZD1 and ZD2, a spark plug PG connected in series to the bias circuit 3 and the secondary coil L2, and a current detection circuit 4 using an OP amplifier AMP are mainly configured.

  Specifically, the switching element 2 is configured by an IGBT (Insulated Gate Bipolar Transistor). An ignition pulse SG is supplied to the gate terminal G of the IGBT, the collector terminal C is connected to the primary coil L1, and the emitter terminal E is connected to the ground. The cathode terminal C and anode terminal A of the Zener diode ZD are connected to the collector terminal C and emitter terminal E of the IGBT.

  The primary coil L1 and the secondary coil L2 constituting the ignition coil 1 are wound in the secondary coil L2 when the coil winding is wound in the opposite phase and the switching element 2 is turned OFF to interrupt the current of the primary coil L1. The high voltage in the direction shown in the drawing is generated.

  The bias circuit 3 includes a Zener diode ZD2 connected to the low-voltage side terminal of the secondary coil L2, a series circuit of the Zener diode ZD1 and the diode D2 connected to the Zener diode ZD2, and a capacitor C2 connected in parallel to the series circuit. And a series circuit of the diode D3, a series circuit of the diode D4 and the capacitor C1 connected in parallel to the capacitor C2, and a diode connected between the connection point of the capacitor C1 and the diode D3 and the high voltage side terminal of the spark plug PG. D1.

  One of the parallel connection circuits including the Zener diode ZD1, the diode D2, the capacitors C2 and C1, and the diodes D3 and D4 is connected to the anode terminal of the Zener diode ZD2, and the other is connected to the ground.

  As illustrated, the cathode terminal of the diode D4 is connected to the capacitor C2, and the anode terminal is connected to the capacitor C1. Therefore, when an upward current flows from the ground, not only the charging path of the capacitor C1 → the diode D4 but also the charging path of the capacitor C2 functions in parallel. On the other hand, when a current flows in the opposite direction, only the discharge path of the capacitor C2 functions.

  In this parallel connection circuit, the capacitor C1 is a charge capacitor charged with a bias voltage for detecting the ionic current, and has a capacitance of, for example, about 0.01 to 0.044 μF. On the other hand, the capacitor C2 is an auxiliary capacitor that forms a discharge path through which excessive transient current does not flow when the switching element 2 is turned on, and has a capacitance that is equal to or slightly larger than the stray capacitance Cc of the spark plug PG. have.

  The stray capacitance Cc of the spark plug PG is, for example, about 20 pF, and in this case, the capacitance of the auxiliary capacitor C2 is about 20-50 pF. In any case, the electrostatic capacities of the charge capacitor C1 and the auxiliary capacitor C2 are C2 << C1, and 1000 * C2 <C1.

  The Zener diode ZD2 has a cathode terminal connected to the secondary coil L2 so that the spark plug PG is not discharged when the switching element 2 is turned on. However, in this embodiment, not a normal diode but a Zener diode ZD2 is used. Therefore, when a voltage higher than its own breakdown voltage is applied to both ends of the Zener diode ZD2, a reverse current flows from the cathode terminal to the anode terminal.

  The anode terminal of the Zener diode ZD1 is connected to the anode terminal of the Zener diode ZD2. On the other hand, the cathode terminal of the Zener diode ZD1 is connected to the cathode terminal of the diode D2. Therefore, in the series circuit of the Zener diode ZD1 and the diode D2, an upward current flows in the figure when the Zener diode ZD1 breaks down, but a downward current in the figure is blocked by the diode D2.

  By the way, in this circuit configuration, since the Zener diode ZD1 and the switching element 2 are in a DC separated state, the breakdown voltage of the Zener diode ZD1 has no particular upper limit, and an appropriate high breakdown voltage can be selected. it can. Preferably, a Zener diode having a breakdown voltage of 200 V or higher should be used. In this embodiment, a Zener diode ZD1 having a breakdown voltage of about 300 V is used as an example. The Zener diode ZD1 and the Zener diode ZD2 preferably have substantially the same breakdown voltage. In the present embodiment, the breakdown voltage of the Zener diode ZD2 is about 300V.

  The diode D3 has a cathode terminal connected to the capacitors C1 and C2, and an anode terminal connected to the ground. The cathode terminal of the diode D3 is also connected to the anode terminal of the diode D1. Therefore, when the diode D1 is in the OFF state, the capacitor C1 can be charged by the upward charging current in the drawing along the path of the diode D3 → the capacitor C1 → the diode D4. On the other hand, when the diode D1 is turned on, the charge of the capacitor C1 can be discharged through a path from the capacitor C1 to the diode D1.

  The current detection circuit 4 includes an OP amplifier AMP, an input resistor R1, a detection resistor R2, and a capacitor C2. The OP amplifier AMP operates with a single power supply Vcc, and a non-inverting input terminal is connected to the ground. Then, the ion current detection signal Vout is output from the output terminal of the OP amplifier AMP.

  The input resistor R1 is connected between the capacitor C1 and the inverting input terminal of the OP amplifier AMP. The input resistor R1 has a resistance value of, for example, about 100 KΩ, and limits the current value flowing through the path of the detection resistor R2 → the input resistor R1 to an appropriate level.

  The detection resistor R2 and the capacitor C2 are connected in parallel to each other, and this parallel circuit is connected between the inverting input terminal and the output terminal of the OP amplifier AMP. For this reason, the OP amplifier AMP functions as an integrating circuit as a whole to enhance noise resistance.

  2 to 4 are diagrams for explaining the operation content of the ion current detection device according to the embodiment. The time chart of FIG. 4 schematically shows from the timing T1 at which the spark plug PG starts spark discharge to the timing T3 at which detection of ion current is started after the spark discharge end timing T2. The potential Vp on the high voltage terminal side of the secondary coil L2 is nothing but the potential of the spark plug PG. Therefore, FIG. 4 shows the potential Vp of the spark plug PG and the detection signal Vout of the OP amplifier AMP, but the detection signal Vout up to the timing T3 is not shown.

<Timing T1-Timing T2>
First, the timing after the timing T1 at which the ignition pulse SG falls and the switching element 2 makes an OFF transition will be described with reference to FIG. 2 (a) and FIG.

  When the switching element 2 makes an OFF transition, a high voltage in the direction shown in FIG. 2A is generated in the secondary coil L2, and the discharge current i1 flows through the path of the bias circuit 3 → secondary coil L2 → ignition plug PG. . As a result, the capacitor C1 and the capacitor C2 are rapidly charged in the direction shown in the drawing to, for example, 300 V in accordance with the breakdown voltage of the Zener diode ZD1. At this time, if the induced voltage of the secondary coil L2 is, for example, about 1100V, the potential Vp of the spark plug PG in the discharge operation state is about 800V.

  On the other hand, the potential Vc at the connection point between the diode D3 and the diode D1 is about 1 V corresponding to the forward voltage of the diode D3 at this timing. Therefore, the diode D1 is in the OFF state, and the charge of the capacitor C1 is not discharged via the diode D1. At this timing, since the current i2 also flows through the path from the resistor R2 to the resistor R1, the detection signal Vout becomes a positive saturation voltage.

<Timing T2 to Timing T3>
Thereafter, the spark discharge ends at timing T2, and the potential Vp of the spark plug PG starts to drop. FIG. 2B and FIG. 4B illustrate this state, and a solid line indicates a state in which the electric charge of the spark plug PG is quickly discharged via the secondary coil L2 and the Zener diode ZD2. Show.

  In FIG. 4B, the operation when the diode D ′ is arranged in place of the Zener diode ZD2 is indicated by a broken line. The diode D ′ also functions effectively in the sense of preventing the discharge at the time of ON, but the diode D ′ limits the discharge path of the charge of the spark plug PG, so that the potential Vp of the spark plug PG drops. The speed becomes slow as shown by the broken line in FIG.

  On the other hand, in this embodiment, the Zener diode ZD2 is arranged in the discharge path of the charge of the spark plug PG, and the breakdown voltage thereof is approximately the same as the breakdown voltage of the Zener diode ZD1 (here, about 300V). ) Is set. Therefore, the breakdown Zener diode ZD2 and the stray capacitance and leakage resistance of the bias circuit 3 function effectively as a discharge path, and the potential Vp of the spark plug PG quickly drops. Since the equivalent capacity Cc of the spark plug PG is, for example, a small capacity of about 20 pF, it has been experimentally confirmed that the discharge path functions effectively.

<Timing T3>
Thereafter, at timing T3, when the potential Vp of the spark plug PG drops to about the positive potential Vc of the capacitor C1, the diode D1 is turned on, and the ionic current i shown in FIG. Note that the potential Vp of the spark plug PG at the timing T3 is about 300 V corresponding to the breakdown voltage Vz of the Zener diode ZD1.

  After the diode D1 is turned on, the voltage across the capacitor C1 is used as a bias voltage, and the ion current i flows through the path of the detection resistor R2, the input resistor R1, the capacitor C1, the diode D1, and the spark plug PG, and the detection signal Vout = i * R2 is output from the OP amplifier AMP. At this time, a current also flows in the path of diode D4 → capacitor C2 → diode D1.

  In this embodiment, since the breakdown voltage Vz of the Zener diode ZD1 can be set appropriately high, the elapsed time until the potential Vp of the spark plug PG reaches the potential Vc on the positive side of the capacitor C1 is short. Ion current detection can begin.

  4A and 4B show a case where a diode D ′ is used instead of the Zener diode ZD2, and the breakdown voltage Vz of the Zener diode ZD1 is set to 300 V, for example, and 200 V, for example. This case is indicated by a broken line. In any case, since the diode D ′ is used to prevent the discharge at the ON time, the rate of decrease in the potential Vp of the spark plug PG is slower than when the zener diode ZD2 is used as in this embodiment (see FIG. 4 (b) (see broken line).

  Specifically, when the breakdown voltage Vz of the Zener diode ZD1 is set low using the diode D ′, the ion current cannot be detected unless it is after the timing T3 ″ as shown in the figure. On the other hand, according to the configuration of the present embodiment, there is an advantage that the ion current can be detected early by the time difference τ2 between T3 and T3 ″.

  Further, when the diode D ′ is used, even if the breakdown voltage is set to a high value (for example, 300 V), the rate of decrease in the potential Vp of the spark plug PG is slow. Cannot be detected. Therefore, according to the configuration of the present embodiment, there is an advantage that the ion current can be detected early by the time difference τ1 between T3 and T3 'by using the zener diode ZD2 for preventing discharge at ON.

<At ON transition of switching element>
Subsequently, the operation when the switching element 2 makes an ON transition corresponding to the rising of the ignition pulse SG will be described with reference to FIGS. 3B and 3C.

  When the switching element 2 makes an ON transition, the illustrated induced voltage is generated in the primary coil L1, and a reverse induced voltage is generated in the secondary coil L2. As shown in the figure, the induced voltage of the secondary coil L2 is generated in the same direction as the charging voltage of the capacitor C1, so if the auxiliary diode D4 and the auxiliary capacitor C2 are not present, the short-circuit path shown in FIG. Will work.

  Therefore, in the circuit configuration shown in FIG. 3C, an excessive short-circuit current ic flows through the secondary coil L2 until the charge of the capacitor C1 is discharged and the Zener diode ZD2 returns from the breakdown state. Then, in response to the short-circuit current ic of the secondary coil L2, an excessive current corresponding to the turn ratio of the ignition coil 1 flows also in the primary coil L1, so that a large stress is applied to the switching element 2.

  However, in this embodiment, since the auxiliary diode D4 and the auxiliary capacitor C2 are provided, even when a short-circuit current flows when the switching element 2 is turned on, it converges in an extremely short time. There is no adverse effect. Therefore, according to the present embodiment, the detection timing of the ionic current can be effectively advanced without causing a trouble when the switching element 2 is turned on.

  As mentioned above, although the structure and effect of the Example of this invention were demonstrated in detail, the concrete description content does not specifically limit this invention.

It is a circuit diagram which shows the ion current detection apparatus which concerns on an Example. It is a circuit diagram explaining the operation | movement content of the ion current detection apparatus of FIG. It is a circuit diagram explaining the operation | movement content of the ion current detection apparatus of FIG. It is a time chart explaining the operation | movement content of the ion current detection apparatus of FIG. It is a circuit diagram explaining a prior art. It is a circuit diagram explaining another prior art.

Explanation of symbols

L1 Primary coil L2 Secondary coil 1 Ignition coil 2 Switching element 3 Bias circuit 4 Current detection circuit PG Spark plug C1 First capacitor ZD1 First Zener diode C2 Auxiliary capacitor D4 Auxiliary diode

Claims (6)

Based on an ignition coil in which a primary coil and a secondary coil are electromagnetically coupled, a switching element that controls ON / OFF of the current of the primary coil, and a high voltage induced in the secondary coil when the switching element is turned off And a first capacitor C1 and a first Zener diode ZD1, which correspond to the breakdown voltage of the first Zener diode ZD1 based on the high voltage when discharging the spark plug. A bias circuit for charging the first capacitor C1 and a current detection circuit for detecting a discharge current of the first capacitor C1,
A series circuit of an auxiliary capacitor C2 and an auxiliary diode D4 is connected in parallel to both ends of the first capacitor C1,
An ionic current detection circuit configured to charge the auxiliary capacitor C2 and to charge the first capacitor C1 via the auxiliary diode when the spark plug is discharged.   When the first diode D1 is disposed between the high-voltage side terminal during charging of the first capacitor C1 and the high-voltage side terminal during discharge of the spark plug, and the potential of the high-voltage side terminal of the spark plug drops, 2. The configuration according to claim 1, wherein the first diode D <b> 1 is turned on so that a discharge current of the first capacitor C <b> 1 flows through the first capacitor C <b> 1, the first diode D <b> 1, and the spark plug. Ion current detector. The ion current detection device according to claim 1 or 2 , wherein a second Zener diode ZD2 is disposed between the secondary coil and the first Zener diode ZD1 in a direction opposite to the first Zener diode. 4. The ion current detection device according to claim 3 , wherein the first and second Zener diodes are set to have substantially the same breakdown voltage. The second diode D2 and the third diode D3 are connected to the first Zener diode ZD1 and the first capacitor C1, respectively. The second diode D2 and the third diode D3 block current in the direction opposite to the direction when the spark plug is discharged. 4. The ion current detection device according to any one of 4 above.   The ion current detection device according to claim 3, wherein the third diode is disposed between the capacitor and the ground.

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