JPH07259633A - Combustion state detecting device of internal combustion engine - Google Patents

Abstract

PURPOSE:To enable the combustion state to be detected at high precision regardless of the driving state of an internal combustion engine. CONSTITUTION:An ignition voltage sensor 10 for detecting ignition voltage of an ignition plug 5 is provided, and a comparison level VCOMP set according to peak voltage of the ignition voltage is compared with the ignition voltage, thereby the combustion state is judged. When the internal combustion engine is in the driving range less than the specific rotational speed and less than the specific load, the combustion state is judged by the specific timing after recharging voltage is applied in recharging, and the state including irregular combustion is accurately detected. While, when the engine is in the driving range more than the specific rotational speed and more than the specific load, recharging is prohibited, so as to restrain generation of early stage brake-down phenomenon. The combustion state is judged by the specific timing earlier than that in recharging, thereby the state including misfire (F1 misfire) caused by a fuel system can be accurately detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detecting device for an internal combustion engine, and more particularly to a combustion state detecting device for an internal combustion engine which detects a misfire related to a cause of a fuel system.

[0002]

2. Description of the Related Art Conventionally, the applicant of the present invention has proposed various misfire detecting devices for detecting misfire of an internal combustion engine as this kind of combustion state detecting device. For example, JP-A-5-65868
The misfire detection device described in Japanese Patent Application No. 3-326509 includes a voltage sensor for detecting the ignition voltage of a spark plug, and a period in which an ignition voltage value after a spark discharge exceeds a predetermined comparison value is a reference value. If it exceeds, it is determined that a misfire has occurred. FIG. 13 is a waveform diagram showing the voltage of the spark plug in this conventional misfire detection device. 13A shows the waveform of the ignition voltage (solid line a) during normal combustion, which is normal combustion, and FIG. 13C shows the waveform of the ignition voltage during misfire. In these figures, the misfire determination signal (solid line c) obtained by comparing the ignition voltage (solid line a) with the comparison level (broken line b) becomes a signal with a relatively short pulse width during normal combustion (A), At misfire, the signal has a relatively long pulse width. Therefore, misfire can be determined by comparing the pulse width of this misfire determination signal with a reference value.

Another misfire detecting device (Japanese Patent Application No. 4-89).
No. 401), in order to accurately distinguish between the normal combustion state and the misfire state of the internal combustion engine, an ignition voltage is generated by a normal voltage application to the ignition plug of the internal combustion engine for ignition of the air-fuel mixture, and spark discharge is generated. After that, the spark plug is energized again (hereinafter referred to as "recharge"), and the floating capacitance in the vicinity of the spark plug is charged. The electric charge stored in the floating capacitance near the spark plug is immediately discharged by the ions existing between the spark plugs when the combustion is normally performed by the spark discharge, but when the combustion does not occur and the misfire occurs, it is ignited. Since there are no ions between the plugs, it is hard to be discharged. Therefore, it is possible to determine that a misfire has occurred when the period during which the voltage of the spark plug exceeds the predetermined voltage value exceeds the reference value.

[0004]

However, in the former misfire detection device, normal combustion is achieved under an unstable operating condition where the combustion condition of the internal combustion engine is below a predetermined rotation speed or below a predetermined load. In some cases, so-called irregular combustion ((B) in FIG. 13) that continues until the combustion is late is generated. When such irregular combustion occurs, the pulse width of the misfire determination signal (solid line c) becomes long enough to exceed the reference value as in the case of misfire ((C) in the figure), despite normal combustion. Will end up.

As a result, there is a problem that irregular combustion is erroneously detected as misfire.

On the other hand, the latter misfire detection device has a problem that the misfire state cannot be accurately detected when the internal combustion engine is in an operating state at a predetermined rotation speed or higher or a predetermined load or higher. That is, at the time of misfire, the charge stored in the stray capacitance near the spark plug is blocked by the diode and held at a high level and gradually attenuated, but the combustion cycle becomes shorter when the rotational speed is equal to or higher than a predetermined speed or a predetermined load or higher. Due to the early drop of the cylinder pressure due to the lowering of the piston and the above-mentioned recharge, the voltage across the spark plug immediately after the recharge breaks down relatively earlier than the original breakdown timing that occurs at the time of misfire. Also, the phenomenon of dielectric breakdown called so-called early breakdown easily occurs.

FIG. 14 is a waveform diagram showing the voltage of the spark plug which is in a misfire state when the number of revolutions is equal to or higher than a predetermined value. Same figure (A)
Shows the case where the early breakdown occurred before the recharge, and FIG. 7B shows the case where the early breakdown occurred after the recharge. Since the early breakdown is likely to occur early due to the additional energy given when the spark plug is recharged, the frequency of the early breakdown occurring before the recharge as shown in FIG. As shown in FIG. 7B, the frequency of early breakdown after recharging tends to increase. Further, in the case of FIG. 9A, misfire determination by recharging is possible.

When a breakdown occurs after recharging as shown in FIG. 14 (B), despite a misfire, a predetermined timing t3 (the misfire determination signal is high during normal combustion and Hi is high).
The misfire determination signal at the time (at which the level should reach the level) becomes the Hi level, that is, at the early time as in the case of normal combustion, the misfire cannot be detected.

Therefore, the present invention has been made to solve the above problems, and provides a combustion state detecting device for an internal combustion engine which can detect the combustion state with high accuracy regardless of the operating state of the internal combustion engine. With the goal.

[0010]

In order to achieve the above object, a combustion state detecting device for an internal combustion engine according to claim 1 of the present invention detects a voltage generated in a spark plug by spark discharge, and the detected voltage is detected. In a combustion state detection device for an internal combustion engine that detects the combustion state of the internal combustion engine based on the voltage, engine operating state detection means that detects the operating state of the engine, and based on the detected operating state of the engine, And a voltage applying means for applying a voltage to the spark plug after the spark discharge.

In the combustion state detecting apparatus for an internal combustion engine according to a second aspect of the invention, the voltage applying means applies a voltage when the operating state of the engine is below a predetermined rotation speed or below a predetermined load.

In the combustion state detecting device for an internal combustion engine according to a third aspect of the present invention, the voltage applying means causes the ignition at a predetermined time when the cylinder pressure of the engine reaches a peak after a voltage is generated in the spark plug by the spark discharge. Apply voltage to the plug.

In the combustion state detecting device for an internal combustion engine according to a fourth aspect of the present invention, when the operating state of the engine is at a predetermined rotation speed or higher or a predetermined load or higher, voltage application is prohibited by the voltage applying means. Means are provided.

A combustion state detecting apparatus for an internal combustion engine according to a fifth aspect of the present invention compares the voltage generated at the spark plug at a predetermined time after the voltage is applied to the spark plug by the voltage applying means with the predetermined voltage to compare the engine with the predetermined voltage. The combustion state determination means for determining the combustion state is provided, and when the voltage application is prohibited by the voltage application means, the predetermined timing for performing the comparison is set earlier than when the voltage application is performed.

[0015]

In the combustion state detecting device for an internal combustion engine according to claim 1 of the present invention, the voltage generated in the spark plug due to spark discharge is detected, and the combustion state of the internal combustion engine is detected based on the detected voltage. Further, the engine operating state detecting means detects the operating state of the internal combustion engine, and the voltage applying means applies a voltage to the spark plug after the spark discharge based on the detected operating state.

In the combustion state detecting apparatus for an internal combustion engine according to a second aspect of the present invention, the voltage application to the spark plug by the voltage applying means is performed when the operating state of the internal combustion engine is below a predetermined rotation speed or below a predetermined load. Be seen.

According to a third aspect of the present invention, there is provided a combustion state detecting device for an internal combustion engine, wherein the voltage applying means causes the ignition at a predetermined time when a pressure in the cylinder of the engine reaches a peak after a voltage is generated in the spark plug by the spark discharge. Apply voltage to the plug.

In the combustion state detecting device for an internal combustion engine according to a fourth aspect, when the operating state of the engine is at a predetermined speed or more or a predetermined load or more by the voltage application prohibiting means, the voltage applying means applies the voltage. Ban.

According to a fifth aspect of the present invention, there is provided a combustion state detecting device for an internal combustion engine, wherein the voltage generated by the spark plug is compared with a predetermined voltage at a predetermined time after the voltage is applied to the spark plug by the voltage applying means. The combustion state is determined by the combustion state determination means, and when the voltage application is prohibited by the voltage application means, the predetermined time for performing the comparison is set earlier than when the voltage application is performed.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A combustion state detecting device for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a combustion state detecting device for an internal combustion engine according to a first embodiment of the present invention.

In the figure, the power supply voltage (battery voltage)
A power supply terminal T1 to which VB is supplied is connected to an ignition coil 1 including a primary side coil 2 and a secondary side coil 3, and the primary side coil 2 and the secondary side coil 3 are connected to each other at one end thereof. The other end of 2 is connected to the collector of the transistor 4, and the base of the transistor 4 has an ignition command signal A
Is connected to an input terminal T2 for inputting, and its emitter is grounded. The other end of the secondary coil 3 is connected to the anode of the diode 7, the cathode of the diode 7 is connected to the center electrode 5a of the spark plug 5 via the distributor 6, and the ground electrode 5b of the spark plug 5 is grounded. ing.

An ignition voltage sensor 10 which is electrostatically coupled to the connecting line 15 (which forms a capacitor of several PF) with the connecting line 15 in the middle of the connecting line 15 connecting the distributor 6 and the center electrode 5a. Is provided, and the output of the ignition voltage sensor 10 is an electronic control unit (hereinafter referred to as E
It is connected to the misfire determination circuit 12 (referred to as CU) 8.
The misfire determination circuit 12 is connected to a CPU (central processing unit) 11, and its output is input to the CPU 11. CP
U11 performs timing control related to the determination of the combustion state,
This is performed according to a combustion state determination routine described later.

The CPU 11 has an operating parameter sensor (engine operating state detecting means) for detecting the values of various engine operating parameters such as the engine speed Ne and the intake pipe absolute pressure PBA as an engine load parameter via the input circuit 13. 9
Is connected, and the detected value of the engine operation parameter that is the output is input. Further, the CPU 11 is the drive circuit 1
Connected to the base of transistor 4 via 4,
The energization control signal A is supplied to the transistor 4.

FIG. 2 is a block diagram showing a specific configuration of the misfire determination circuit 12. The input terminal T3 is connected to the inverting input of the comparator 25 via the input circuit 21. The output of the peak hold circuit 22 is connected to the non-inverting input of the comparator 25 via the comparison level setting circuit 24. Further, the peak hold circuit 22 receives a reset signal R1 for resetting the peak hold value at an appropriate timing.
Supplied from PU11.

FIG. 3 is a circuit diagram showing a specific configuration of the input circuit 21, the peak hold circuit 22 and the comparison level setting circuit 24 shown in FIG. In the figure, the input terminal T3 is
It is connected to a non-inverting input of an operational amplifier (hereinafter referred to as “op amp”) 216 via a resistor 215. The input terminal T1 is connected to ground via a circuit in which a capacitor 211, a resistor 212, and a diode 214 are connected in parallel, and is connected to a power supply line VBS via a diode 213. The capacitor 211 uses, for example, a capacitor of about 104 pF, and has a function of dividing the voltage detected by the voltage sensor 13 into several thousandths.

As the resistor 212, for example, a resistor of about 500 KΩ is used. The diodes 213 and 214 are provided so that the input voltage of the operational amplifier 216 falls within the range of approximately 0 to VBS. Operational amplifier 21
The inverting input of 6 is connected to its output, and the operational amplifier 216 operates as a buffer amplifier (impedance conversion circuit). The output of the operational amplifier 216 is the comparator 25.
Of the operational amplifier 221 and the non-inverting input of the operational amplifier 221.

The output of the operational amplifier 221 is the diode 22.
Connected to the non-inverting input of operational amplifier 227 via 2,
The inverting inputs of the operational amplifiers 221 and 227 are both connected to the output of the operational amplifier 227. Therefore, these operational amplifiers also operate as buffer amplifiers.

The non-inverting input of the operational amplifier 227 is a resistor 22.
3 and the capacitor 226 to be grounded, and the resistor 223
The connection point between the capacitor 226 and the capacitor 226 is connected to the collector of the transistor 225 via the resistor 224. The emitter of the transistor 225 is grounded, and the reset signal R1 that is at a high level at the time of reset is input to the base from the CPU 11.

The output of the operational amplifier 227 is grounded through the resistors 241 and 242 which form the comparison level setting circuit 24, and the connection point of the resistors 241 and 242 is connected to the non-inverting input of the comparator 25.

According to the circuit shown in FIG. 3, the peak value of the detected ignition voltage V (the output of the operational amplifier 216) is held by the peak hold circuit 22, and the peak hold value is changed from the value 1 by the comparison level setting circuit 24. It is multiplied by a small predetermined number and supplied to the comparator 25 as the comparison level VCOMP. Therefore, a low level signal is output to the terminal T4 when V> VCOMP. The CPU 11 determines the combustion state based on the output signal from the terminal T4, that is, the misfire determination signal.

The operation of the combustion state detecting device having the above-mentioned structure will be described. FIG. 4 is a flowchart showing a combustion state detection routine executed by the CPU 11 at every predetermined timing (for example, every predetermined crank angle). The CPU 11 stores in advance, as a map, an operating state region in which recharging is performed according to the operating state of the engine. FIG. 5 is an explanatory diagram showing a map of a region in which recharging is performed according to the engine speed Ne and the intake pipe absolute pressure PBA as an engine load parameter.

In FIG. 4, the CPU 11 first reads the values of the engine speed Ne and the absolute pressure PBA in the intake pipe from the operation parameter sensor 9 (step S1), and the read engine speed Ne is a predetermined speed Ne1 (for example, 1500 rpm). It is then determined whether or not the intake pipe absolute pressure PBA is equal to or lower than a predetermined value PBA1 (for example, 560 mmHg) (steps S2 and S3). Recharging is performed when the engine speed Ne is less than or equal to the predetermined speed Ne1 and the intake pipe absolute pressure PBA is less than or equal to the predetermined value PBA1, that is, when the internal combustion engine is in the operating region of the predetermined speed or less and the predetermined load or less. Yes (step S4).
On the other hand, recharging is prohibited when the internal combustion engine is not in the operating range below the predetermined rotation speed and below the predetermined load, that is, in the operating range above the predetermined rotation speed or above the predetermined load (step S5). Subsequently, the CPU 11 determines the combustion state based on the misfire determination signal from the terminal T4 of the comparator 25 (step S6) and ends this routine.

By the way, the timing of recharging voltage application during recharging is set to a predetermined timing at which the cylinder pressure reaches a peak in the compression stroke of the engine. Also,
The timing t3 for determining the misfire determination signal is at a predetermined time after the recharge voltage is applied when the recharge is executed (see FIG. 6), and at a time earlier than the predetermined time when the recharge is executed when the recharge is prohibited. It is set (see FIG. 7). The CPU 11 determines the combustion state based on the misfire determination signal read at the timing t3.

Next, a method of determining the combustion state when recharging is performed and when recharging is prohibited will be described. FIG. 6 is a timing chart for explaining the misfire detection operation at the time of recharging. The figure (A) shows the characteristics at the time of normal combustion with fast combustion, the figure (B) shows the characteristics at the time of irregular combustion with slow combustion, and the figure (C) shows the misfire related to the cause of the fuel system (hereinafter referred to as " It is called "FI misfire").

Further, A indicates an energization control signal, and B and B1
And B2 are the detected ignition voltage (input circuit 21
Output voltage) V, C, C1 and C2 indicate comparison levels VCOMP, and D, D1 and D2 indicate misfire determination signals of the comparator 25, respectively.

In the operating state in which recharging is executed, that is, when the engine speed is below a predetermined number of revolutions and below a predetermined load, an ignition command signal is generated at time t0 (the primary coil 2 is energized for a period required for ignition). , After the current is cut off at time t0) and after the period T1 has elapsed, recharge (a period from time t1 to t2) is performed. At the time of recharging at time t2, a voltage is applied between the electrodes of the spark plug 5 to such an extent that no discharge is generated, and this voltage causes electric charges to be stored in the stray capacitance of the spark plug 5 and its peripheral circuits. This voltage is called the recharge voltage.

In FIG. 5A, immediately after time t0 when the ignition command signal is generated, the ignition voltage V rises to a value that destroys the insulation of the fuel mixture (between the discharge gaps of the spark plugs), and after the breakdown. Is the capacity discharge state before dielectric breakdown (discharge state for a very short time by current of several hundred amperes)
To an inductive discharge state in which the discharge voltage is substantially constant (a discharge period of about several milliseconds due to a current of about tens of milliamperes). The induced discharge voltage rises as the pressure in the cylinder increases with the compression stroke after time t0. This is because the higher the pressure, the higher the voltage required for induction discharge. At the final stage of the induction discharge, the voltage between the spark plug electrodes becomes lower than the voltage for maintaining the induction discharge due to the reduction of the induction energy of the ignition coil, the induction discharge disappears and the capacity discharge state (the latter capacity discharge Status)
Move to. In the capacity discharge state, the voltage between the spark plug electrodes rises because the insulation of the fuel mixture is destroyed again, but the energy remaining in the ignition coil 1 is small and the voltage rise is slight. This is because when the combustion occurs, the electric resistance between the plug gaps is low, and is due to the fact that the fuel mixture at the time of combustion is ionized.

The charge stored in the stray capacitance between the diode 7 and the spark plug 5 (the charge remaining without being discharged between the electrodes) is not discharged to the ignition coil 1 side because of the diode 7. However, since it is neutralized by the ions existing in the vicinity of the electrode of the spark plug 5, the ignition voltage V at the end of the capacitive discharge is rapidly reduced.

After that, the time t at which the cylinder pressure reaches its peak.
2. When the recharge voltage is applied at 2, the ignition voltage V
Is again increased, but the charge charged at this time is neutralized by the ions existing in the vicinity of the electrode of the ignition plug 5 as in the case immediately after the end of the latter-stage capacity discharge described above, and thus is rapidly reduced.

On the other hand, the comparison level VCOMP has a value corresponding to the peak value of the ignition voltage V after the previous reset until the time t5.
A predetermined low level (> 0) fixed state is set from time t5 to t2, and the state is released at time t2. Therefore, after the time t2, the value becomes a value corresponding to the ignition voltage V that has become the peak value due to the recharge voltage (in this embodiment, the value is about 2/3 of the peak value). As a result, the output D of the comparator 25 that compares the ignition voltage V with the comparison level VCOMP becomes a low level near time t0, times t6 to t7, and times t2 to t8. The output D of the comparator 25 detected at a predetermined timing t3 after the recharge command signal becomes a Hi level signal, indicating that the combustion has been normally performed.

In the case of the irregular combustion with slow combustion shown in FIG. 7B, the latter capacity discharge state is gradually performed and the output D1 of the comparator 25 is low level for a relatively long period from time t6 to time t7. However, before re-energization, combustion ends normally and ions are generated near the electrodes of the spark plug 5. Therefore, the charge accumulated in the spark plug 5 after the recharge voltage is applied is neutralized by the ions existing in the vicinity of the electrodes, so that the ignition voltage V at the end of the capacitive discharge after the recharge voltage is applied is rapidly reduced. Therefore, the predetermined timing t
The output D1 detected at 3 becomes a Hi level signal, indicating that the combustion is normally performed as in the normal combustion.

On the other hand, in FIG. 6C, the fuel mixture is in a lean state or a cut state due to an abnormality in the fuel supply system or the like, and FI misfire occurs (when combustion does not occur). At this time, immediately after the generation time t0 of the ignition command signal, the ignition voltage V (B2) rises to a value that destroys the insulation of the fuel mixture between the spark plug electrodes, but the value of the breakdown voltage at this time is The air mixture occupies a larger proportion of air than in the normal state, the dielectric strength of the fuel mixture increases, and since no combustion occurs, the fuel mixture is not ionized and the plug Since the electric resistance between the gaps tends to increase, it becomes higher than the voltage value during normal combustion. After this, the state of induction discharge shifts to the same state as in normal combustion, but since the discharge resistance is also higher than in normal combustion, it tends to shift to the capacity discharge state earlier than in normal combustion. The value of the capacity discharge (the latter capacity discharge) that occurs at the final stage of the induction discharge is much larger than that during normal combustion because the dielectric breakdown voltage of the fuel mixture is larger than that during normal combustion.

At this time, since almost no ions exist near the electrode of the ignition plug 5, the charges accumulated between the diode 7 and the ignition plug 5 are not neutralized by the ions, and the diode 7 prevents the ignition coil 1 from being charged. Since it cannot flow back to, it is retained as it is. Therefore, when the pressure in the cylinder decreases and the discharge required voltage becomes equal to the voltage applied by this charge, the spark plug 5
It will gradually decrease until the above-mentioned breakdown phenomenon, in which the electrode is discharged, occurs. When the ignition voltage V is high, it is discharged relatively early, but in FIG. 6C, the breakdown phenomenon does not occur until the recharge voltage is applied, and the ignition voltage V gradually decreases until the recharge voltage is applied. Has been shown.

After that, when the recharge voltage is applied at the time t2, the ignition voltage V rises again, there is no neutralization by ions between the plug electrodes as described above, and the high voltage state is generated by the action of the diode 7. continue. When the pressure in the cylinder drops and the required discharge voltage becomes equal to the ignition voltage V, a breakdown phenomenon occurs and the plug electrodes are discharged (time t11).

The comparison level VCOMP (C2) is at time t.
The value up to 9 is a value corresponding to the peak value of the ignition voltage V after the previous reset, and after time t9, the value increases as the ignition voltage V increases, and the level corresponding to the peak value is held until time t5. A predetermined low level is fixed at times t5 to t2, and after time t2, a value corresponding to the ignition voltage V that has reached a peak value due to the recharge voltage is held.

As a result, the output D2 of the comparator 25 becomes the time t.
It becomes low level near 0, slightly before time t9, at times t9 to t10 and times t5 to t11. After that, the output D2 of the comparator 25 detected at a predetermined timing t3 is L
It becomes a signal of o level and indicates that FI misfire has occurred.

In this embodiment, at the time t2, the recharge voltage having a value that does not cause the discharge between the plug electrodes is applied, so that the FI misfire is caused even when the ignition voltage V becomes a high voltage. It can be reliably detected. Also, in the case of irregular combustion with slow combustion, since the ions are present in the vicinity of the electrodes of the spark plug 5, the voltage after applying the recharge voltage is rapidly reduced, and normal combustion can be reliably detected.

Next, the determination of the combustion state when recharging is prohibited will be described. FIG. 7 is a waveform diagram showing the characteristics of the fuel mixture when prohibiting recharging. The same figure (A) shows the characteristics at the time of normal combustion with fast combustion,
FIG. 6B shows the characteristics when the FI is misfiring. Further, as in the above, A indicates an energization control signal (ignition command signal), B and B2 indicate detected ignition voltages (output voltage of the input circuit 21) V, and C and C2 indicate comparison levels VCOMP. , D and D2 are comparators 25, respectively.
The misfire determination signal of is shown.

In the operating region where the recharging is prohibited above a predetermined rotation speed or above a predetermined load, unlike the operation region below a predetermined load and below a predetermined rotation speed, slow combustion irregular combustion does not occur, but instead as described above. When the recharge is performed, the early breakdown phenomenon is likely to occur after the recharge voltage is applied. Therefore, the timing t3 for prohibiting the recharge and determining the combustion state is set earlier than when the recharge is performed as described above. It is set.

In the detection of the combustion state in which recharging is prohibited, if the ignition command signal is generated at time t0, the subsequent recharging is not performed. Therefore, in the case of the normal combustion of FIG.
Since it is neutralized by the ions existing near the electrode of
The ignition voltage V at the end of the capacity discharge rapidly decreases and falls below the comparison level VCOMP, and the misfire determination signal D of the comparator 25 detected at a predetermined timing t3 becomes a Hi level signal, indicating that the combustion is normal. .

On the other hand, when the FI misfire occurs, as shown in FIG. 6B, the ignition voltage V (B2) is the fuel between the spark plug electrodes immediately after the ignition command signal generation time t0 as described above. It rises to a value that destroys the insulation of the air-fuel mixture, then the fuel mixture is not combusted and is not ionized, so the electrical resistance between the plug gaps is high and the spark plug voltage is the voltage value during combustion. Will be higher than. After this, the state shifts to the induction discharge state as in the normal combustion, but since the discharge resistance is also larger than that in the normal combustion, it tends to shift to the capacity discharge state earlier than in the normal combustion, but the capacity discharge gradually. To be done. Therefore, the misfire determination signal of the comparator 25 detected at the predetermined timing t3 becomes a Lo level signal, indicating that misfire has occurred.

As described above, according to the combustion state detecting device of the present embodiment, recharging is performed in the operating region where the engine speed is equal to or lower than the predetermined speed and the load is equal to or lower than the predetermined load, and the irregular combustion is surely detected as the normal combustion. You can In addition, by prohibiting recharging in an operating range of a predetermined rotation speed or higher or a predetermined load or higher, the occurrence of an early breakdown phenomenon can be suppressed, and the combustion state of the internal combustion engine can be accurately detected.

Next, a combustion state detecting device for an internal combustion engine according to a second embodiment of the present invention will be described.

In the first embodiment, the combustion state is determined from the level of the misfire determination signal at the predetermined timing t3 after the recharge voltage is applied, but in the present embodiment, the misfire determination signal is used instead of the level of the misfire determination signal. The determination method is characterized by whether or not the period in which the signal is at the predetermined level exceeds the predetermined period, that is, the period in which the ignition voltage value exceeds the predetermined comparison voltage value. The present embodiment is the same as the first embodiment except for the configuration of the misfire determination circuit 12 of FIG. 1, and the other configurations are the same.

FIG. 8 is a block diagram showing a specific configuration of the misfire determination circuit 12A of the second embodiment. In the figure,
The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

First comparator 25A of misfire determination circuit 12A
Unlike the first embodiment, the non-inverting input of the input terminal T
3 are connected via the input circuit 21. Also, the first
The peak hold circuit 22 is connected to the inverting input of the comparator 25A.
The output side of is connected via the comparison level setting circuit 24.

The output of the first comparator 25A is input to the pulse generation period measuring circuit 27 via the terminal 4 and the gate circuit 26, and the measuring circuit 27 indicates that the gate circuit 26 is outputting the input signal as it is. The period during which the output of the first comparator 25A is high level is measured, and the voltage VT corresponding to the length of the measured period is measured by the second comparator 2.
9 non-inverting inputs. The reference value setting circuit 28 is connected to the inverting input of the second comparator 29, and the reference voltage VTREF for misfire determination is supplied. VT> VTRE
When F is satisfied, the output of the second comparator 29 becomes high level, and it is determined that a misfire such as FI misfire has occurred. The reference voltage VTREF is set according to the engine operating state. Further, the gate signal G that determines the gate period of the gate circuit 26 and the reset signal R2 that determines the reset timing of the period measuring circuit 27 are supplied from the CPU 11 (FIG. 1).

FIG. 9 is a circuit diagram showing a specific configuration of the gate circuit 26 and the pulse measurement period measurement circuit 27. The gate circuit 26 includes transistors 41 to 43 and resistors 44 to.
51 forms a three-stage inverting circuit. A transistor 61 is interposed between the collector of the transistor 42 and ground, and the gate signal G is supplied from the CPU 11 to the base of the transistor 61. Therefore, during the gate period when the gate signal G is low level, the collector of the transistor 43 becomes low level / high level corresponding to the high / low voltage of the terminal T4, and when the gate signal G is high level, the transistor 43 The collector of 43 is at a high level regardless of the voltage of the terminal T4. The collector of the transistor 43 is connected to the base of the transistor 54 via the resistor 52 of the pulse measuring period measuring circuit 27, and the base of the transistor 54 is connected to the power supply line VBS via the resistor 53. Transistor 54
The emitter is connected to the power supply line VBS, and the collector is connected to the ground via the resistor 55 and the capacitor 57. The connection point between the resistor 55 and the capacitor 57 is connected to the terminal T5 via the operational amplifier 59 and the resistor 60. The operational amplifier 59 is a buffer amplifier. Resistance 5
The connection point between the capacitor 5 and the capacitor 57 is connected to the collector of the transistor 58 via the resistor 56.
The eight emitters are grounded. The reset signal R2 is input from the CPU 11 to the base of the transistor 58.

According to the circuit of FIG. 9, when the gate signal G is at the low level and the terminal T4 is at the high level, the transistor 4 is
The collector of 3 becomes low level, the transistor 54 is turned on, the capacitor 57 is charged, and the gate signal G
Is high level or the terminal T4 is low level, the transistor 54 is turned off and the charging of the capacitor 57 is stopped.
Therefore, at the terminal T5, the voltage VT proportional to the period in which the pulse signal input to the terminal T4 is at the high level in the gate period is obtained.

A method of determining the combustion state in the combustion state detecting apparatus of the second embodiment having the above construction will be described.

10 and 11 are time charts for explaining the operation of the misfire determination circuit 12A during recharging. In the figure, (A), (B), and (C) are respectively the same as in the first embodiment, during normal combustion, during irregular combustion,
The case of a misfire is shown.

During normal combustion (A), the charge accumulated in the floating capacitance between the diode 7 and the spark plug 5 after combustion occurs is neutralized by the ions existing in the vicinity of the electrode of the spark plug 5. The ignition voltage V at the end of the capacity discharge rapidly decreases. After that, when the recharge voltage is applied at the time t2, the ignition voltage V rises, but the electric charge charged at this time is also neutralized by the ions existing in the vicinity of the electrodes of the spark plug 5, so that it rapidly decreases. .

On the other hand, the comparison level VCOMP is the first level.
Similar to the embodiment, until time t5, the value corresponds to the peak value of the ignition voltage V after the previous reset,
After the time t2, which is the reset timing, the value becomes a value corresponding to the ignition voltage V that is the peak value due to the recharge voltage. As a result, the output of the first comparator 25A that compares the ignition voltage V with the comparison level VCOMP is near time t0, at times t6 to t7, and at time t2, as shown in FIG.
The output of the gate circuit 26 becomes a high level at the times t3 to t7 and the times t2 to t8 within the gate period TG in which the gate signal G is at a low level. Therefore, the pulse generation period measuring circuit 27
Output VT changes as shown in FIG. 7E, does not exceed the reference voltage VTREF, and is determined to be normal combustion.

Further, in the case of the same figure (B) at the time of irregular combustion, the output of the first comparator 25A for comparing the ignition voltage V with the comparison level VCOMP is near time t0 and time t6.
~ High level at t7 and time t2 to t8,
The output of the gate circuit 26 is the time t3 within the gate period TG.
High level only at ~ t7 and t2 ~ t8. Therefore, the output VT of the pulse generation period measuring circuit 27 becomes a voltage higher than that in the normal combustion of FIG. 9A, but it does not exceed the reference voltage VTREF as shown in FIG. It

Further, in the case of the same figure (C) when the FI misfire occurs, the output of the first comparator 25A is the same figure (j).
As shown in FIG. 5, the output of the gate circuit 26 is at a high level near time t0, slightly before time t9, and at times t9 to t10 and times t5 to t11. It goes high only at t11. Therefore, the output VT of the pulse generation period measuring circuit 27 changes as shown in FIG.
2 exceeds the reference voltage VTREF and the second comparator 2
The output of 9 is time t12 to t4, as shown in FIG.
, And a FI misfire is detected.

FIG. 12 is a time chart for explaining the operation of the misfire determination circuit when prohibiting recharge. In the figure, (A) and (B) show the cases of normal combustion and misfire, respectively. During normal combustion (A), the output VT of the pulse generation period measurement circuit 27 is the same as during recharge.
Is judged to be normal combustion without exceeding the reference voltage VTREF.
At the time of misfire (B), the output V of the pulse generation period measuring circuit 27
T exceeds the reference voltage VTREF and is determined to be FI misfire.

In this way, the ignition voltage V is compared with the comparison level VC.
The combustion state can also be reliably detected by determining whether the period exceeding OMP exceeds a predetermined reference period.

By comparing the integrated value of the portion where the ignition voltage V exceeds the comparison level VCOMP with a predetermined value,
Further, it goes without saying that the combustion state may be determined by comparing the number of clock pulses (comparison determination pulses) measured during the period when the ignition voltage V exceeds the comparison level VCOMP with a predetermined value.

[0069]

According to the combustion state detecting device for an internal combustion engine according to claim 1 of the present invention, the voltage generated in the spark plug due to the spark discharge is detected, and the combustion state of the internal combustion engine is detected based on the detected voltage. In a combustion state detection device for an internal combustion engine for detecting, an engine operating state detecting means for detecting an operating state of the engine, and based on the detected operating state of the engine,
Since it is provided with a voltage applying means for applying a voltage to the spark plug after the spark discharge, by applying the voltage after the spark discharge only in the optimum operating state, it is possible to reliably and highly accurately regardless of the operating state. The combustion state can be detected.

According to the combustion state detecting device of the internal combustion engine of the second and fourth aspects, the voltage applying means applies the voltage when the operating state of the engine is below a predetermined rotation speed or below a predetermined load. Therefore, so-called irregular combustion, which is slow in combustion, can be detected as normal combustion, and the occurrence of an early breakdown phenomenon can be suppressed by prohibiting the voltage application when the engine is operating at a predetermined speed or higher or a predetermined load or higher. Can be detected.

According to the combustion state detecting apparatus for the internal combustion engine of the third aspect, the voltage applying means is arranged such that the pressure in the cylinder of the engine reaches a peak after a voltage is generated in the spark plug due to the spark discharge, Since a voltage is applied to the spark plug, the electric charge stored in the floating capacitance of the spark plug and its peripheral components is neutralized by the ion by re-energization performed when ions are present near the electrode of the spark plug during normal combustion. Therefore, the combustion state can be accurately detected.

According to the combustion state detecting device for the internal combustion period of the fourth aspect of the invention, when the operating state of the engine is at a predetermined rotational speed or higher or a predetermined load or higher, a voltage for prohibiting voltage application by the voltage applying means is applied. Since the application prohibition means is provided, it is possible to reliably distinguish between irregular combustion and misfire.

According to the combustion state detecting apparatus for the internal combustion engine of the fifth aspect, by comparing the voltage generated in the spark plug at a predetermined time after the voltage is applied to the spark plug by the voltage applying means with the predetermined voltage. A combustion state determination unit that determines the combustion state of the engine is provided, and when the voltage application is prohibited by the voltage application unit, the predetermined time for performing the comparison is set earlier than when the voltage application is performed. In addition to suppressing the occurrence of the early breakdown phenomenon, the occurrence of misfire can be detected more reliably.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing a combustion state detection device for an internal combustion engine of the present embodiment.

FIG. 2 is a block diagram showing a specific configuration of a misfire determination circuit 12.

FIG. 3 is a circuit diagram showing a specific configuration of an input circuit 21, a peak hold circuit 22, and a comparison level setting circuit 24.

FIG. 4 is a flowchart showing a combustion state detection routine executed by the CPU 11.

FIG. 5: Engine speed Ne and absolute pressure PB in intake pipe
FIG. 6 is an explanatory diagram showing a map of a region in which recharging is performed according to A.

FIG. 6 is a timing chart explaining a misfire detection operation at the time of recharging.

FIG. 7 is a timing chart illustrating a misfire detection operation when prohibiting recharge.

FIG. 8 is a block diagram showing a specific configuration of a misfire determination circuit 72 according to a second embodiment.

FIG. 9 is a gate circuit 26 and a pulse measurement period measurement circuit 2
7 is a circuit diagram showing a specific configuration of No. 7.

FIG. 10 is a diagram showing a time chart for explaining the operation of the misfire determination circuit.

FIG. 11 is a diagram showing a time chart for explaining the operation of the misfire determination circuit.

FIG. 12 is a diagram showing a time chart for explaining the operation of the misfire determination circuit when prohibiting recharge.

FIG. 13 is a waveform diagram showing a voltage of a spark plug in a conventional misfire detection device.

FIG. 14 is a waveform diagram showing the voltage of the spark plug at the time of misfiring when the rotation speed is equal to or higher than a predetermined value.

[Explanation of symbols]

 1 ... Ignition coil 5 ... Spark plug 8 ... ECU 9 ... Operating parameter sensor 10 ... Ignition voltage sensor 11 ... CPU 12 ... Misfire determination circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jiro Takagi 1-4-1 Chuo, Wako-shi, Saitama Inside the Honda R & D Co., Ltd. (72) Inventor Koichi Osaki 1-4-1 Chuo, Wako-shi, Saitama Stock Company Honda Technical Research Institute

Claims (5)

[Claims] 1. A combustion state detection device for an internal combustion engine, which detects a voltage generated in a spark plug by spark discharge, and detects a combustion state of the internal combustion engine based on the detected voltage. And a voltage applying means for applying a voltage to the spark plug after the spark discharge based on the detected operating status of the engine. apparatus. 2. The combustion state of an internal combustion engine according to claim 1, wherein the voltage applying means applies a voltage when the operating state of the engine is below a predetermined rotation speed or below a predetermined load. Detection device. 3. The voltage applying means applies the voltage to the spark plug at a predetermined time when the pressure in the cylinder of the engine reaches a peak after the voltage is generated in the spark plug by the spark discharge. Item 3. A combustion state detection device for an internal combustion engine according to item 1 or 2. 4. A voltage application prohibiting means for prohibiting voltage application by the voltage applying means when the operating condition of the engine is equal to or higher than a predetermined rotation speed or a predetermined load or higher, is provided. 4. A combustion state detecting device for an internal combustion engine according to any one of 3 to 3. 5. A combustion state determination means for determining the combustion state of the engine by comparing the voltage generated in the spark plug at a predetermined time after the voltage is applied to the spark plug by the voltage application means with a predetermined voltage. 5. The combustion state detection of an internal combustion engine according to claim 4, wherein when the voltage application is prohibited by the voltage application means, a predetermined time for performing the comparison is set earlier than when the voltage application is performed. apparatus.