JPH0542614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cylinder pressure detection device for detecting cylinder pressure of an internal combustion engine.

[Conventional technology]

Generally, in an internal combustion engine, due to rapid combustion due to early ignition of the unburned air-fuel mixture in the cylinder, the pressure inside the cylinder increases at multiple natural frequencies determined by the cylinder dimensions (particularly its bore diameter) and combustion temperature. (in-cylinder pressure) undergoes damped oscillation, and this damped oscillation may cause the so-called knocking phenomenon in which the internal combustion engine generates a metallic tapping sound.

Therefore, as described in, for example, JP-A-54-142425 and JP-A-56-554, knocking has been detected by detecting engine cylinder pressure, and the ignition is started according to this result. There is a control device for an internal combustion engine that avoids knocking by controlling timing.

The in-cylinder pressure detection device used in such internal combustion engine control devices uses a pressure sensor (in-cylinder pressure sensor) attached to the cylinder block of the internal combustion engine or as a washer for a spark plug, and a charge output from this in-cylinder pressure sensor. It is composed of a charge amplifier that converts a signal into a voltage signal and amplifies it.

Then, the internal combustion engine control device detects a specific frequency band (approximately 5 to 6 KHz or more) related to knocking from the detection signal output from the cylinder pressure detection device and the detection signal output from the knocking sensor.
The signal is extracted and subjected to predetermined signal processing to generate a detection signal corresponding to the combustion pressure vibration of the engine.This detection signal is compared with a predetermined reference level to determine the presence or absence of knocking, and the determination result is The ignition timing is retarded or advanced based on the

[Problem that the invention seeks to solve]

However, with such a cylinder pressure detection device, if the cylinder pressure sensor is destroyed, the wiring is broken, or the shoot or charge amplifier is damaged, the detection output may be fixed at the same state as without knocking. There is.

When such a situation occurs, the ignition timing is advanced beyond the limit, especially since modern engine controls are controlled close to the limit in order to always maximize the combustion efficiency of the engine. May lead to destruction.

Therefore, considering this point, it may be possible to limit the ignition timing advance in advance, but the knock limit may vary greatly depending on various parameters such as cooling water temperature, intake air amount, air-fuel ratio, etc. 8°), making efficient control impossible even when the cylinder pressure detection device is normal.

[Means to solve the problem]

Therefore, as shown in FIG. 1, the cylinder pressure detection device for an internal combustion engine according to the present invention includes a cylinder pressure detection means A that detects the cylinder pressure of the internal combustion engine, and a detection result of the cylinder pressure detection means A that is determined in advance. It is provided with a sample means B that samples at a plurality of crank angle positions, and an abnormality determination means C that determines whether the cylinder pressure detection means A is abnormal based on the plurality of sample values sampled by the sample means B. .

[Effect]

An abnormality in the cylinder pressure detection means is determined and output based on sample values at a plurality of crank angle positions of the detection results of the cylinder pressure, and measures for the abnormality are prompted.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is an overall schematic diagram of a control device for an internal combustion engine equipped with an in-cylinder pressure detection device embodying the present invention.

In this internal combustion engine, a mixture of air taken into an intake manifold 4 via an air cleaner 1, an air flow meter 2, and a throttle valve 3 and fuel supplied by an injector 5 is supplied to an internal combustion engine 6. The exhaust gas generated by this combustion is discharged from the exhaust pipe via the catalytic converter 8 and the muffler 9.

On the other hand, the control unit 11 which is in charge of overall control receives an intake air flow rate signal from the air flow meter 2, a throttle valve position signal from the throttle switch 12 which detects the opening degree of the throttle valve 3, and a throttle valve position signal from the crank angle sensor 13. , a neutral signal from a neutral switch 15 that detects the neutral position of the transmission 14, and a vehicle speed signal from a vehicle speed sensor 16 are input.

It also detects the fuel temperature signal from the fuel temperature sensor 17 that detects the fuel temperature and the oxygen concentration in the exhaust gas.
An oxygen concentration signal from an O ₂ sensor 18 and a water temperature signal from a water temperature sensor 19 that detects the cooling water temperature are input.

Further, a cylinder pressure signal from a cylinder pressure sensor 21 that detects combustion pressure vibrations of the engine 6 is input.

The control unit 11 drives and controls the injector 5 to control the amount of fuel supplied based on these input signals and various data stored therein, and controls the ignition to supply high voltage to the spark plug 7. Ignition is controlled by intermittent control of the primary current of the coil 22.

In addition, the AAC valve 23 is driven and controlled to control the air flow rate bypassing the throttle valve 3 to control the idle rotation speed, and the VCM valve 24 is controlled to control the EGR valve 25 to control the EGR amount. .

In addition, in this figure 2, 26 is a fuel pump, 27 is a canister, 28 is a BC valve, 2
9 is a check valve.

FIGS. 3 and 4 are a block diagram showing the configuration of the control unit 11 in the control system for this internal combustion engine, and a functional block diagram thereof.

First, the cylinder pressure sensor 21 is a piezoelectric conversion type pressure sensor, and is installed as a washer for the spark plug 7 installed in the cylinder head 6A as shown in FIG. Outputs charge signal _S1 according to internal pressure (cylinder internal pressure).

In addition, the crank angle sensor 13 detects, for example, 120 degrees of the crank angle in a 6-cylinder engine (180 degrees of the crank angle in a 4-cylinder engine) every time the engine rotates by a predetermined angle.
A reference signal S ₂ is output every time, and a position signal S ₃ is output every 1 or 2 degrees of crank angle.

In addition, the position signal _S3 is other than 0.1
The output may be output for each angle such as degrees, and the narrower the output, the better the control accuracy.

On the _other hand _{, the} charge amplifier ₃₁ of _the control unit ₁₁ , as shown in FIG. , converts the charge signal _S1 from the cylinder pressure sensor 21 into a voltage signal, and then converts this voltage signal into an operational amplifier.
It is amplified by an amplifier circuit consisting of _OP1 , resistors _R3 to _R8 , and diode _D3 , and output as a detection signal _S4 .

This charge amplifier 31 and the above-mentioned cylinder pressure sensor 21 constitute the cylinder pressure detection means A shown in FIG.

The bandpass filter 32 is the charge amplifier 3
Detection signal S from 1 to predetermined frequency from ₄ , that is, frequency band related to knocking (approximately 6 to 17 KHz)
Only the signal component of is extracted, and this extracted signal component is output as the detection signal _S5 .

The integrator 33 is timed by a set/reset signal SCR from a main control circuit 37, which will be described later, and receives a detection signal _S5 from the bandpass filter 32.
is integrated, and the integration result is output as an integral signal _S6 .

This integrator 33 passes the detection signal S ₅ from the bandpass filter 32 through an operational amplifier OP ₃ and a resistor R ₁₀ .
It is amplified by an amplifier circuit consisting of _R14 and capacitor _C2 .

Then, this amplified detection signal is transferred to an operational amplifier.
OP ₁ , resistor R ₁₅ ~ R ₁₈ , capacitor C ₃ , diode
Rectification is performed by a rectifier circuit consisting of D ₄ and D ₅ .

After that, the rectified output of this rectifier circuit and the amplified detection signal are connected to the operational amplifier _OP5 , the resistors _R19 to _R22 ,
It is synthesized and integrated by an integrating circuit consisting of a capacitor C ₄ and a Zener diode ZD, and this integrated value is used as an integrated signal.
Output as _S6 .

In this integrator 33, when the set/reset signal SSR from the main control circuit 37 is at a high level "H", the transistor _Q1 of the reset circuit consisting of the resistor _R23 and the transistor _Q1 is turned off. When the integration becomes possible and the set/reset signal SSR is “L”, the transistor
When _Q1 turns on, both ends of capacitor _C4 are shot, and the integration is stopped.

Returning to FIG. 3, the presettable counter 35
is preset to a predetermined value when the reference signal _S2 of the crank angle sensor 13 is input, counts the position signal _S3 from the crank angle sensor 13, and when the count value reaches the preset value. , outputs a first external interrupt request signal IRQ1.

Note that the external interrupt request signal IRQ1 from the presettable counter 35 is generated at a predetermined crank angle during the intake stroke of the engine (for example, it varies depending on the engine).
Select a preset value to output at 160° to 150° before TDC.

The presettable counter 36 is preset to a predetermined value when the reference signal _S2 of the crank angle sensor 13 is input, counts the position signal _S3 from the crank angle sensor 13, and calculates the count value. When the preset value is reached, a second external interrupt request signal IRQ2 is output.

Note that a preset value is selected for the external interrupt request signal IRQ2 by the presettable counter 35 so that it is output at the top dead center (TDC) of the engine.

On the other hand, the main control circuit 37 includes a CPU 38 and a ROM 3.
9. It is constituted by a microcomputer consisting of an I/O 41 having a built-in RAM 40 and an A/D converter.

This main control circuit 37 includes the crank angle sensor 13
the reference signal S ₂ and position signal S ₃ from the charge amplifier 31, the detection signal S ₄ from the charge amplifier 31, the integral signal S ₆ from the integrator 33, and the presettable counters 35, 3.
The external interrupt signals IRQ1 and IRQ2 from 6 and various detection signals as explained in FIG.

Then, a reference signal from the crank angle sensor 13
Based on _S2 and position signal _S3 , a set/reset signal SSR is output to the integrator 33 to control its integration operation.

Here, the main control circuit 37 starts the integration operation of the integrator 33 at 40 degrees before compression top dead center (BTDC40 degrees), stops the integration operation at compression top dead center (TDC), and stops the integration operation at compression top dead center (TDC). The integral operation is started again 5 degrees after the point (ATDC5°), and is stopped at ATDC45°.

The main control circuit 37 also outputs a detection signal from the charge amplifier 31 based on each input signal described above.
Sampling at a given crank angle position of S ₄ ,
Processing related to ignition timing control, such as determining abnormality of the cylinder pressure sensor 21 and charge amplifier 31, determining the level of knocking that has occurred, determining the frequency, determining the amount of modification of the ignition timing, and determining the ignition timing, is performed, and the results of this processing are Based on this, the power transistor 43 of the ignition device 42 is turned on and off to control the ignition timing.

The ignition timing control (on/off control of the power transistor 41) is performed by an advance angle value (ADV) register (not shown) provided inside the I/O 41.
Set the values (advance angle value, dwell angle) corresponding to the determined ignition timing in the dwell angle (DWELL) register, compare the values of these registers with the value of the counter that counts the position signal _S3 , When they match, the power transistor 43 is turned on or off.

The ignition device 42 has a power transistor 43 controlled on and off to cut off the primary current of the ignition coil 22 and generate a high voltage on its secondary side. The voltage is applied to the spark plug 7 to ignite a spark.

The functions related to ignition timing control of the main control circuit 37 will be explained using the functional blocks in FIG.

First, the ratio calculating section 37A calculates the
Integral signal that is the integration result between BTDC40° and TDC
The ratio (or difference) between _S6 and the integral signal _S6 , which is the result of integration between 5° and 45° ATDC, is calculated, and the calculated result is output.

The determination/correction amount determination unit 37B is the ratio calculation unit 37A.
The detected value of combustion pressure vibration from the engine is compared with a predetermined reference value to determine whether or not knocking has occurred and the type of knocking that has occurred. Based on the determination result, the amount of correction of the ignition timing is determined.

The ignition timing control unit 37C determines and determines the ignition timing determined based on the intake air amount, engine speed, etc.
The correction amount determined by the correction amount determination unit 37B is corrected, and the ignition device 42 is controlled according to the result.

The first sample section 37D (here including the presettable counter 35 in FIG. ₃ ) constitutes the sample means B in FIG. sample.

The second sampling section 37E (here including the presettable counter 36 of FIG. 3) also constitutes the sampling means B of FIG. 1, and samples the detection signal _S4 from the charge amplifier 31 at TDC.

The abnormality determining section 37F determines whether or not the cylinder pressure detection means constituted by the cylinder pressure sensor 21 and the charge amplifier 31 is abnormal based on the sample results of the first and second sample sections 37D and 37E.

Note that this main control circuit 35 also performs controls other than those related to ignition timing, but a detailed explanation thereof will be omitted.

Furthermore, in the above description, the cylinder pressure sensor 21 and charge amplifier 31 are shown for only one cylinder, but in reality, they are provided for each cylinder, and the output of each charge amplifier 31 is switched by a multiplexer and input to the bandpass filter 32. etc.

Similarly, the ignition device 42 may be provided for each cylinder, or the power transistor 43 and ignition coil 22 of the ignition device 42 may be common to each cylinder, and the high voltage generated in the ignition coil 22 may be transferred to a distributor. and distribute it to each spark plug 7.

Next, the operation of this embodiment configured as described above will be explained with reference to FIG. 8 and subsequent figures.

First, the principle of detecting knocking in this embodiment will be explained.

First, as shown in FIG. 8, for example, the power spectrum of cylinder pressure vibration is shown as a line when there is no knock, and as a line when there is a knock having a relatively large level.

Note that this is an experimental result by the present applicant when a 4-cylinder 1800 c.c. internal combustion engine was operated at full load and 4800 RPM, but it has been confirmed that it is substantially the same for other internal combustion engines.

As can be seen from FIG. 8, there is a large difference in power level in the frequency band of 6 to 17 KHz between the knocking time and the non-knocking time.

Therefore, by converting the charge signal of the cylinder pressure sensor into a voltage signal and extracting the signal component in the above frequency band from this signal, it is possible to convert the charge signal of the cylinder pressure sensor into a voltage signal and extract the signal component in the above frequency band from this signal. A signal like this (hereinafter referred to as an "extracted signal") is obtained. Note that these are waveforms of high-frequency vibrations of the cylinder pressure.

Here, the power of the signal x(t) in a specific frequency band is generally expressed as Φ=(1/2T)∫ ^T _-T X ² (t)dt... In other words, it is obtained as a time average of the square of the signal amplitude.

Therefore, considering the integral of the absolute value of the signal shown in Figure 9, 1/2T∫ ^T _-T |x(t)|dt=1/2T∫ ^T _-T √ ² (t)dt...
becomes.

Since the right-hand side of this equation indicates the RMS (root mean square) of the signal x(t), the left-hand side of this equation is a quantity that indicates the power of the signal It can be thought of as a certain amount.

Note that here, the signal x of the equation and the equation
Although it is assumed that (t) is a signal with a single frequency, it is practically acceptable even if it contains multiple frequency components.

Therefore, when the absolute value of the non-knock extraction signal shown in Figure 9A is integrated over the crank angle range from 40 degrees before top dead center (BTDC40 degrees) to top dead center (TDC), the integral signal is as shown in FIG. 10A, for example.

Similarly, when the extracted signal at the time of knock shown in Fig. 9 (b) is subjected to absolute value integration over the crank angle range from top dead center to 40 degrees after top dead center (ATDC 40 degrees), the integral signal is, for example, It becomes as shown in Figure 10B.

Each of these integral signals corresponds to the in-cylinder pressure vibration energy in the above crank angle range. In other words, the term (1/2T) is removed from the above equation.

As can be seen from FIG. 10A, when the engine is not knocking, the integral signal increases almost linearly, and a constant amplitude energy always exists regardless of the crank angle. In other words, when not knocking, the top dead center (TDC)
Assuming that T=0, the following relationship holds: ∫ ⁰ _T=-40 °x(t)dt=∫ ^T=+40 ₀ °x(t)dt...

On the other hand, as can be seen from FIG. 10B, at the time of knocking, an increase in energy due to knocking appears in the expansion stroke after TDC.

By the way, it is generally believed that the determination of knock level by human hearing is based on the relative strength difference between the sound pressure level due to constantly occurring background noise and the sound pressure level due to knocking vibration. ing.

Therefore, by directly comparing the vibration energy of the cylinder pressure during non-knocking with the vibration energy of the cylinder pressure during knocking, it is possible to detect a knocking level that closely matches the sensory evaluation.

Here, according to the above formula, it can be considered that knotting does not occur before top dead center from experience, so the integral signal before top dead center can be used to determine whether or not knocking occurs after top dead center. Regardless, it can be said that this is a predicted value of the vibration energy of the cylinder pressure during the expansion stroke after top dead center in the non-knock state.

Therefore, the (rectified) integral value of cylinder pressure vibration within a predetermined crank angle range before top dead center, and the (rectified) integral value of cylinder pressure vibration within a predetermined crank angle range after top dead center, or within a predetermined range including the range before top dead center. By comparing the (rectified) integral value of the cylinder pressure vibration, the vibration energy of the cylinder pressure during non-knocking and the vibration energy of the cylinder pressure during the combustion stroke can be directly compared, and the human sensory evaluation It is possible to detect a knocking level that is in good agreement with the

According to various experiments conducted by the present applicant, the relationship shown in FIG. 10 can be considered to hold under most operating conditions.

However, the integral interval includes spark plug vibration, suction,
It is necessary to make a selection so that the relationship of the formula does not hold true due to the influence of vibrations when the exhaust valve is seated and unseated (in this case, the
(40 degrees is selected).

Next, the control of the integration operation of the integrator 33 by the main control circuit 37 for performing such processing will be explained with reference to FIG. 11 (hereinafter referred to as "the same figure").

First, in the vicinity of a crank angle of 0 to 120 degrees, _the charge amplifier 31 outputs a detection signal _S4 as shown in FIG. A detection signal (extracted signal) _S5 as shown in D is input to the integrator 33. Note that here, this detection signal _S5 includes a knock component.

Therefore, the main control circuit 37 receives the reference signal S ₂ shown in FIG _. The internal counter is activated from , and starts counting the position signal S ₂ outputted from the crank angle sensor 13 and shown in FIG.

Then, at time _t2 when the crank angle reaches 30 degrees (BTDC40 degrees), the set/reset signal SSR is set to "H" as shown in the figure to start the integration operation of the integrator 33, and TDC is reached. At time _t3 , the set/reset signal SSR is set to "L" to stop the integration operation.

Thereafter, at time t ₄ when the crank angle reaches 75 degrees (ATDC 5 degrees), the integrator 33 starts the integration operation in the same way, and at time t ₅ when the crank angle reaches 115 degrees (ATDC 45 degrees), it stops the integration operation. .

As a result, the integral signal _S6 output from the integrator 33 becomes, for example, as shown in FIG.
The integral operation between t ₂ and _{t 3} yields an integral value that correlates to the non-knock vibration energy, and the integral operation between t ₄ and _{t 5} yields an integral value that correlates with the knock vibration energy. It will be done.

Therefore, by calculating the ratio or difference between the two and normalizing the integral value that correlates to the vibration energy when knocking based on the integral value that correlates to the vibration energy when knocking, accurate knocking detection can be performed. .

By the way, in this case, the cylinder pressure sensor 21 is destroyed;
If a wire breakage, a failure of the charge amplifier 31, etc. occur and the output of the charge amplifier 31 (detection signal S ₄ ) is fixed to the (+) side or the (-) side, the output of the bandpass filter 32 becomes approximately 0, but Since the integrator 33 detects minute electrical noise, it outputs an integral signal _S6 that is substantially the same as that in the non-knocking state. In addition, in the following, the cylinder pressure sensor 21 and the charge amplifier 31
A cylinder pressure detection device consisting of the following is called a "cylinder pressure sensor".

That is _, when the detection signal S ₄ from the charge amplifier ₃₁ during normal operation shown in FIG. Sometimes it is shown as a solid line in the figure (b), and when it is not knocked, it is shown as a broken line in the same figure.

On the other hand, when the in-cylinder pressure sensor is abnormal, the detection signal S ₅ near zero is output from the bandpass filter 32.
Integral signal _S6 from integrator 33 when integrating
The state becomes as shown in FIG. 12C, and is approximately the same as in the non-knocking state shown by the broken line in FIG. 12B.

Therefore, when knocking is determined by using the ratio or difference between the integral value of the non-knocking vibration energy detection period and the integral value of the knocking vibration energy detection period of the integrator 33 as the cylinder pressure or knocking detection output, the cylinder pressure is determined. When the internal pressure sensor is abnormal, it is determined that there is no knocking.

Therefore, in the cylinder pressure detection device (cylinder pressure sensor) of the present invention, an abnormality in the cylinder pressure sensor is determined based on the output of the charge amplifier 31.

In other words, the output of the in-cylinder pressure sensor (detection signal S ₄ ) during normal combustion is as shown in Figure 13A, for example, and after the intake valve closes, the in-cylinder pressure is compressed by the piston and gradually rises. After a slight ignition delay, the pressure reaches its maximum at about 10 degrees after TDC, drops as combustion ends, and eventually returns to approximately atmospheric pressure when the exhaust valve opens, completing one combustion cycle.

Further, the output of the cylinder pressure sensor during irregular combustion (misfire) is, for example, as shown in FIG.

As can be seen from Figure 13 A and B, in any case, the pressure at TDC is always greater than the pressure at crank angle X during the suction stroke, so by comparing the two, It is possible to determine whether the cylinder pressure sensor is normal or abnormal.

Next, the abnormality determination process for the in-cylinder pressure sensor executed by the main control circuit 37 will be described with reference to FIG. 14.

The main control circuit 37 is a presettable counter 3
External interrupt request signal IRQ1, IRQ from 5, 36
2, execution of this abnormality determination process is started.

First, in STEP1, the external interrupt request signal is
Determine whether it is IRQ1 or not.

At this time, if the external interrupt request signal is IRQ1, the A/D conversion of the detection signal _S4 from the charge amplifier 31 is started in STEP 2, the end of the A/D conversion is determined in STEP 3, and the A/D conversion is completed. When finished, save the A/D conversion results in STEP 4.
A predetermined address of RAM40 (hereinafter referred to as “address”)
INT/AD).

As a result, the output of the charge amplifier 31 (in-cylinder pressure sensor) at a predetermined crank angle position during the intake stroke is sampled and held.

On the other hand, if the external interrupt request signal is not IRQ1, that is, if it is external interrupt request signal IRQ2, A/D conversion of the detection signal _S4 from the charge amplifier 31 is started in STEP 5, and the A/D conversion of the detection signal S4 from the charge amplifier 31 is started in STEP 6. Determine the end of the conversion, and when the A/D conversion is completed, send the conversion result of the A/D conversion in STEP 7.
A predetermined address of RAM 40 (hereinafter referred to as “address”)
(referred to as "TDC・AD").

As a result, the output of the charge amplifier 31 (in-cylinder pressure sensor) at TDC is sampled and held.

After that, in STEP 8, calculate the deviation X by calculating X=TDC・AD−INT・AD, and in STEP 9, determine whether the deviation do.

At this time, if X≧10, that is, if the difference between the sample value of the detected value of the cylinder pressure at a predetermined crank angle during the suction stroke and the sample value of the detection result of the cylinder pressure at TDC is greater than or equal to the predetermined value. For example, since the in-cylinder pressure sensor is normal, the process ends immediately.

On the other hand, if X≧10, that is, the difference between the sample value of the detected value of the cylinder pressure at a predetermined crank angle during the suction stroke and the sample value of the detection result of the cylinder pressure at TDC is greater than or equal to the predetermined value. If not, it is determined that the cylinder pressure sensor is abnormal, and
Set the flag EMG/FLG (set it to “1”)
Finish the process.

In addition, abnormality judgment is basically TDC・AD＞
This can be done by distinguishing between INT and AD.

However, here, TDC・AD−INT・AD≧10
The reason why the abnormality was determined by making this determination is based on the following reasons.

So generally the pressure on the suction stroke is 300
mmHg (approximately -400mmHg) (at idle) ~780mmHg
(when fully opened), and the compression pressure at TDC is about 10 times or more than the above value because the temperature rise due to adiabatic compression is added to the mechanical compression ratio of 8 to 10.

On the other hand, the maximum combustion pressure is approximately 60 to 80 atmospheres, and if the resolution of the A/D converter is 8 bits, for example, when it is 80 atmospheres, it is expressed as FFH (hex expression).
It is common to adjust it so that it becomes (decimal 255).

Therefore, at idle with a small maximum pressure difference,
This is because the difference between the TDC/AD value and the INT/AD value is 255×(3000−300)/780×(80−1)=12.

Next, the knocking determination/correction amount determining process executed by the main control circuit 37 will be described with reference to FIG.

First, in STEP 11, it is determined whether the in-cylinder pressure sensor is normal by checking whether the flags EMG and FLG set in the abnormality determination process described above are "0".

At this time, if the flag EMG/FLG is "0", the cylinder pressure sensor is normal, so STEP12
Calculate the ratio K/B (difference K - B) between the non-knocking vibration energy correlation value B and the knocking vibration energy correlation value K, and convert the knocking vibration energy correlation value K to the non-knocking vibration energy correlation value. A K/B value calculation process is performed to normalize based on the value B.

The non-knocking vibration energy correlation value B is the A/D conversion result of the integral signal _S6 at time _t3 in FIG. 11, and the knocking vibration energy correlation value K is:
Similarly, it is an A/D conversion result of the integral signal S ₆ at time t ₅ , and these A/D conversion processes are executed in a process not shown, and the results are stored at a predetermined address in the RAM 40 .

In addition, in this K/B value calculation process, a reference value for determining knocking is determined from the K/B value corresponding to the engine speed (obtained by counting the position signal _S3 from the crank angle sensor 13 for a predetermined period of time). It also performs processing for reading from the reference value table stored in the ROM 39.

Then, in STEP 13, the presence or absence of knocking, its frequency, intensity, etc. are determined, and the amount of correction of the ignition timing is determined.
A modification amount determination process is performed to determine ADVFBK, and the process ends.

On the other hand, if the flag EMG/FLG is not "0", the in-cylinder pressure sensor is abnormal, and the amount of correction of the ignition timing cannot be determined based on its output. ADVFBK
is fixed at a predetermined amount, for example, −10°.

As a result, even if an abnormality occurs in the cylinder pressure sensor, damage to the engine can be avoided, and the vehicle can continue to run without significantly impairing drivability.

Note that an example of the correction amount determination process in STEP 13 in this notching determination/correction amount determination process is shown in the 16th
It is shown in the figure.

Before explaining this, let us first explain the first and second points in the same figure.
The reference values SL ₁ and SL ₂ will be explained below.

First, the cumulative frequency distribution of K/B values for various knocking phenomena in a six-cylinder engine is shown in FIG.

In other words, the distribution of the cumulative frequency of K/B values during non-knocking is a line, the distribution of the cumulative frequency of K/B values during trace knocking is a line, and the distribution of the cumulative frequency of K/B values during light knocking is a line. The distribution line of the cumulative frequency of K/B values at a medium knock is shown by a line, and the distribution of the cumulative frequency of K/B values at a heavy knock is shown by a line.

Therefore, basically the first reference value SL ₁ and the second
The reference value _SL2 is set to a value as shown _{in FIG} . Determine whether the knotting is small (minor) or large knotting.

However, when the engine speed is in a high rotation range, human sensory evaluation is lowered due to the influence of mechanical vibrations of the engine itself, so the tolerance zone for knocks becomes wider.

Therefore, as mentioned above, the first reference value SL ₁ and the second reference value SL ₂ are changed according to the engine speed,
This enables highly efficient operation. Note that the first reference value SL ₁ and the second reference value SL ₂ are as follows:
Of course, both or either one may be set to a fixed value.

It is also assumed that when the correction amount ADVFBK is incremented, the ignition timing is advanced, and when it is decremented, the ignition timing is retarded.

Next, to briefly explain each process in FIG. 16, in STEP 20, the K/B value calculated by the process described above is compared with the second reference value SL ₂ , and if the K/B value>SL ₂ is determined. It is determined whether or not a large knocking has occurred.

At this time, if the K/B value is not > SL ₂ , that is, if small knocking occurs or there is no knocking, the K/B value is compared with the first reference value SL ₁ in STEP 21 to determine either of the above. Then, K/B
Determine whether value > SL ₁ .

At this time, if the K/B value > SL ₁ and no knocking has occurred, step 22 will lead to step 33.
It is determined whether the flag KFLG, which is set when knocking occurs, is "0".

And if the flag KFLG is "0",
K/ from the time knotking occurs in STEP23~26
When the state of B value ≦ SL ₁ continues for 28 cycles or more, the ignition timing is advanced by 1 degree and a flag is set.
If KFLG is not "0", if the state of K/B value ≦SL ₁ continues for 28 cycles or more from the time when K/B value > SL ₁ in STEPs 27 to 31, no knock is performed.

On the other hand, when the K/B value > SL ₁ in STEP 21, that is, when a small (minor) knock occurs, in STEP 32, it is checked whether the flag KFLG is "0" and the first knock is detected. Determine whether or not it has occurred.

At this time, if the flag KFLG is "0",
Set flag KFLG in STEP33 (KFLG=1)
After that, the count value KCNT is cleared in STEP 34 and the process ends.

On the other hand, if the flag KFLG is not "0", that is, if knocking has occurred for the second time or later, in STEP 35, check whether the number of ignitions in the past is within 14 times (KCNT≦14), that is, within 14 cycles. Then, it is determined whether the K/B value > SL ₁ or not.

At this time, if KCNT≦14, the above
Execute STEP34 to end the process, and then KCNT≦
If it is 14, the correction amount ADVFBK is decremented (-1) in STEP 36 to retard the ignition timing by 1 degree, and then the above-mentioned STEP 34 is executed to end the process.

In addition, here, within 14 cycles, K/B value > SL ₁
When the knock occurs, that is, when the next knock occurs within 14 cycles after the knock occurs, the ignition timing is retarded at 7/100 in the case of a trace knock, as seen in Figure 17 mentioned above. Since the K/B value exceeds the first reference value SL ₁ at a rate of , the probability is 100/7≒14, that is, this condition (K/B value > SL ₁ ) occurs once in 14 times. It is based on what you do and what you become.

Therefore, by similarly setting this value to 100/16=6 (times) for a light knock and 100/25=(times) for a medium knock, the engine can be controlled to a desired knock level. This was confirmed through experiments conducted by the applicant.

In this way, when a small knock occurs, the frequency of occurrence of the small knock is determined, and the amount of correction of the ignition timing is determined based on the frequency determination result.

In this case, the amount of retardation of the ignition timing is set to 1.
degrees, but this can also be set to other values, such as 1/4 degrees, 1/2 degrees, etc.

Furthermore, the amount of retardation can be determined not only based on the frequency of occurrence of small knocks, but also according to the strength of small knocks, that is, the magnitude of the K/B value. Knocking can be suppressed without impairing driving performance or the like.

On the other hand, when the K/B value becomes > SL ₂ in STEP 20, that is, when a large knock occurs, the correction amount ADVFBK is decremented (-A) by a predetermined amount A in STEP 37, and the ignition timing is After retarding the angle by A degrees, STEP 34 is executed to end the process.

The predetermined amount A is a constant determined depending on the engine, operating conditions, etc., and is set to a value larger than the above-mentioned retard amount (1 degree) when a small knock occurs.

In this way, in this internal combustion engine control device, when the K/B value≦SL ₁ (no knock), the ignition timing correction amount is advanced by a predetermined angle when a predetermined condition is satisfied, and SL ₁ When ≦K/B value≦SL ₂ (small notch), the ignition timing correction amount is retarded by a predetermined angle (1 degree) when the predetermined frequency is reached, and the K/B value is
When the B value>SL ₂ (large knock), a correction amount for retarding the ignition timing by a predetermined angle (A degree) is immediately determined.

Then, the basic ignition timing determined in accordance with the intake air amount, engine speed, etc. in a process not shown is corrected by the ignition timing correction amount determined in the process described above.

In this way, the in-cylinder pressure detection device in this internal combustion engine control device also determines and outputs the abnormality of the in-cylinder pressure sensor that detects the in-cylinder pressure of the engine.

As a result, when an abnormality occurs in the cylinder pressure sensor, the ignition timing is corrected by a predetermined amount of retardation, etc., so that the engine can be driven without damaging the engine or significantly impairing drivability. It will be possible to take measures such as making it possible to continue.

In each of the above embodiments, the cylinder pressure sensor is provided on the spark plug, but a so-called vibration sensor may also be provided on the cylinder block.

Further, in the above embodiment, the detection results of the cylinder pressure sensor were sampled at a predetermined crank angle position and TDC during the intake stroke, but the crank angle positions to be sampled and the number of crank angle positions to be sampled are also limited to these. isn't it.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to detect an abnormality in the cylinder pressure detection device, so it is possible to maintain the safety of the engine even in the event of an abnormality, and to maximize combustion efficiency by eliminating restrictions in the event of an abnormality. This makes it possible to improve torque, fuel efficiency, and drivability.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram showing the configuration of the present invention, Fig. 2 is a schematic block diagram of a control device for an internal combustion engine embodying the invention, and Fig. 3 shows an example of the control unit shown in Fig. 2. 4 is a functional block diagram of the main parts of the control unit, FIG. 5 is a cross-sectional view and a plan view of an example of the cylinder pressure sensor, and FIG. 6 is an example of the charge amplifier. The circuit diagram, Figure 7, is
Similarly, a block diagram showing an example of the integrator, FIGS. 8, 9, and 10 are waveform diagrams to explain the principle of knocking detection in this embodiment, and FIG. 11 is a timing chart to explain the operation of the integrator. 12 and 13 are waveform diagrams for explaining the principle of abnormality determination in this embodiment.
FIG. 4 is a flowchart showing an example of the abnormality determination process executed by the main control circuit, FIG. 15 is a flowchart showing an example of the knocking determination/correction amount determination process executed by the main control circuit, and FIG. FIG. 15 is a flowchart showing an example of the correction amount determination process, and FIG.
K/B in each knock phenomenon for explanation of Figure 6
FIG. 3 is an explanatory diagram showing an example of cumulative frequency of occurrence of values. 11... Control unit, 13... Crank angle sensor, 21... Cylinder pressure sensor, 31...
Charge amplifier, 37...main control circuit.

Claims (1)

[Claims] 1. A cylinder pressure detection means for detecting the cylinder pressure of an internal combustion engine, a sample means for sampling the detection results of the cylinder pressure detection means at a plurality of predetermined crank angle positions, and a sample means for sampling the detection results of the cylinder pressure detection means at a plurality of predetermined crank angle positions. An in-cylinder pressure detecting device for an internal combustion engine, comprising: an abnormality determining means for determining an abnormality in the in-cylinder pressure detecting means based on a plurality of sample results. 2. The in-cylinder pressure detection device for an internal combustion engine according to claim 1, wherein the sampling means includes means for sampling the detection result of the in-cylinder pressure detection means at a predetermined crank angle position of the intake stroke of the engine. 3. The in-cylinder pressure detection device for an internal combustion engine according to claim 1 or 2, wherein the sampling means includes means for sampling the detection result of the in-cylinder pressure detection means at compression top dead center of the engine. 4. Any one of claims 1 to 3, wherein the sampling means includes means for sampling the detection result of the cylinder pressure detection means at or before the ignition timing of the engine and in the vicinity of the ignition timing. The in-cylinder pressure detection device for an internal combustion engine described in . 5. The internal combustion engine according to any one of claims 1 to 4, wherein the abnormality determining means includes means for determining an abnormality based on a determination result of a magnitude relationship of a plurality of sample results of the sample means. cylinder pressure detection device.