JP2830305B2 - Device for detecting combustion state of internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a combustion state detecting device for an internal combustion engine.

In order to grasp the combustion state such as misfire of <Prior Art> engine, there is a method of detecting the in-cylinder pressure (combustion chamber pressure), the maximum cylinder pressure and the indicated mean effective pressure P _i (hereinafter in the specific operating state , and so as to determine the actual combustion state by obtaining the abbreviated as P _i). As a conventional example of such a combustion state detecting device,
There are the following (see “Internal Combustion Engine”, Vol. 1, page 19, published by Sankaido Co., Ltd. in September 1962).

That is, the cylinder pressure as detected period of two rotation per each cylinder (720 ° crank angle in the 4-cycle engine), and calculates the P _i by the detected cylinder pressure by the cylinder pressure sensor.

<Problems to be Solved by the Invention> By the way, most of the on-vehicle engines are usually multi-cylinder engines having four or more cylinders, and when the above-mentioned conventional example is applied to these multi-cylinder engines, there are the following problems.

That is, if the in-cylinder pressure is detected for each cylinder for two rotations and _Pi is calculated for each cylinder, the detected in-cylinder pressure can be A / D even if a microcomputer is used.
There is a disadvantage that a CPU for calculating the A / D converter fast as is required in addition P _i to be converted is also costly requires a high speed ones.

Also, in order to solve the above problem, Japanese Patent Application Laid-Open No. 61-2655
There is one shown in Japanese Patent Publication No. 48. As this is the pseudo P _i basically in the predetermined crank angle range (e.g., 180 °) in the cylinder detected by the pressure P and the small cylinder volume variation ΔV of each crank angle is calculated by the following equation I have to.

Further, in JP-A-62-238433, the cylinder pressure is a predetermined value or more sections, which determine a pseudo P _i is disclosed by the arithmetic expression.

Further, in JP-A-62-238434, in-cylinder pressure from the ignition timing is a predetermined value or more sections, which determine a pseudo P _i is disclosed by the arithmetic expression.

However, with these, the pseudo _Pi is calculated in a predetermined crank angle range. Therefore, when the combustion state deteriorates and the combustion period becomes longer as indicated by the chain line in FIG. 22, the pseudo _Pi is calculated. correlation between P _i at _i and 720 ° period 23
As shown in the figure, there is a problem that the accuracy of the detection of the combustion state is deteriorated and the control accuracy of the ignition timing, the air-fuel ratio, the exhaust gas recirculation amount and the like is deteriorated.

Further, Japanese Patent Application Laid-Open No. 62-203036 discloses that the actual in-cylinder pressure is detected near the compression top dead center, and the operating state (intake air flow rate, throttle valve opening, engine rotation speed, etc.) in other sections. discloses that map searching cylinder pressure from calculates the P _i in these cylinder 720 ° period by pressure in accordance with the.

However, since the fluctuation always combustion state, it is intended to find the in-cylinder pressure from a preset map data, to predict the actual in-cylinder pressure is difficult, the detection accuracy of the detection accuracy i.e. the combustion state of the P _i There is a problem that it gets worse.

The present invention has been made in view of such circumstances,
An object of the present invention is to provide a combustion state detection device for an internal combustion engine that can improve the detection accuracy of a combustion state.

<Means for Solving the Problems> For this reason, as shown in FIG. 1, the present invention provides an in-cylinder pressure detecting means A for detecting an in-cylinder pressure in an engine combustion chamber, and a crank for detecting a crank angle of the engine. Angle detecting means B; and sampling means C for sampling the in-cylinder pressure detection signal during a sampling period in a predetermined crank angle range.
A combustion chamber volume setting means D for setting a combustion chamber volume for each crank angle; and a cylinder pressure detection signal of at least two points among the sampled cylinder pressure detection signals and a combustion chamber volume at that time. A bias amount setting means E for setting a bias amount of the in-cylinder pressure detection signal with respect to the true in-cylinder pressure; and correcting the sampled in-cylinder pressure detection signal based on the set bias amount to adjust the in-cylinder pressure. In-cylinder pressure correction means F to be obtained, and in-cylinder pressure prediction means G for predicting in-cylinder pressure based on the combustion chamber volume and the corrected in-cylinder pressure during the non-sampling period during the non-sampling period.
Effective pressure calculating means H for calculating the indicated mean effective pressure based on the corrected in-cylinder pressure and the predicted in-cylinder pressure.
And, was prepared.

<Operation> As described above, in the predetermined sampling period, the sampled in-cylinder pressure signal is corrected by the bias amount to obtain the in-cylinder pressure, and in the non-sampling period, the corrected in-cylinder pressure and combustion chamber volume are obtained. From this, the in-cylinder pressure is predicted. Then, the indicated average effective pressure is determined from the corrected in-cylinder pressure and the predicted in-cylinder pressure.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 2, in-cylinder pressure sensors 1 to 6 as in-cylinder pressure detecting means for detecting the in-cylinder pressure of the engine combustion chamber are provided for each cylinder (six cylinders in this embodiment). 6 converts the in-cylinder pressure into a charge signal by a piezoelectric element and outputs the charge signal to charge amplifiers 7 to 12. The charge amplifiers 7 to 12 convert the charge signals into voltage signals and output them to the multiplexer 13.

The multiplexer 13 outputs detection signals of the in-cylinder pressure sensors 1 to 6 of the cylinder selected based on a switching signal described later via the low-pass filter 14 to the I / O interface 16 of the control device 15.
Output to The low-pass filter 14 removes a high-frequency component that is unnecessary for detecting in-cylinder pressure such as knocking vibration and ignition noise and causes erroneous detection, and passes only a low-frequency component equal to or lower than a predetermined frequency.

The control device 15 includes a CPU 17, a ROM 18, a RAM 19, an A / D converter 20.
The CPU 17 reads the required external data from the I / O interface 16 according to the program written in the RCM 18, and exchanges data with the RAM 19 while performing the combustion state. The processing value required for calculating the parameters related to the calculation is processed, and the processed data is output to the I / O interface 16 as necessary. I / O
The interface 16 receives signals from the low-pass filter 14, a crank angle sensor 21 as a crank angle detecting means, and an air flow meter 22, and outputs a switching signal from the I / O interface 16 to the multiplexer 13 in accordance with a command from the CPU 17. Is done.

The A / D converter 20 A / D converts an external signal input to the I / O interface 16 according to a command from the CPU 17. The ROM 18 stores programs in the CPU 17 and the RAM 19
Stores data used for calculation and the like in the form of a map or the like.

The crank angle sensor 21 outputs a reference signal at a predetermined crank angle position before a compression top dead center of each cylinder at every predetermined crank angle (a crank angle of 120 ° in a six-cylinder engine), and outputs a unit crank angle (for example, 1) Output a unit signal every time. Therefore, the engine speed can be detected from the input cycle or the count number of the reference signal. Further, the air flow meter 22 outputs a signal corresponding to the intake air flow rate.

Here, the CPU 17 constitutes sampling means, combustion chamber volume setting means, bias amount setting means, in-cylinder pressure correcting means, in-cylinder pressure predicting means, and effective pressure calculating means.

Next, the operation will be described with reference to the flowcharts of FIGS.

First, the sampling routine for in-cylinder pressure data is described in the third section.
This will be described with reference to the flowchart in FIG. This routine is executed at a predetermined crank angle position determined by the reference signal and the unit signal (this embodiment will be described at 60 ° before the compression top dead center).

At S1, the in-cylinder pressure detected by the in-cylinder pressure sensors 1 to 6 is A / D-converted by an A / D converter 20 at a predetermined crank angle (in this embodiment, the crank angle is described as 4 °). Read.

In S2, the read in-cylinder pressure is associated with the cylinder number i and the sampling order (corresponding to the crank angle) j.
PE _ij is stored in the RAM 19. Here, the reading order j based on the detected values is 30 to 60.

In S3, A / D conversion end timing (60% after compression top dead center)
゜) is determined, and if YES, the process proceeds to S4, and if NO, the process returns to S1.

 In S4, a calculation flag = 1 described later is set.

In S5, it is determined whether or not it is the next A / D conversion timing, and YES
If the answer is NO, the process proceeds to S6, and if the answer is NO, the process returns to S5.

In S6, 1 is added to the cylinder number i and incremented.

In S7, it is determined whether or not the cylinder number i has reached 6, and YE
If S, proceed to S8, and if NO, terminate the routine.

In S8, the cylinder number i is set to zero, and the routine ends.

In this way, from 60 ゜ before compression top dead center to after compression top dead center
In-cylinder pressure PE _ij is detected for each cylinder during a crank angle period of 120 ° up to 60 °.

Next, the calculation routine will be described with reference to the flowchart of FIG.

In S11, it is determined whether or not the operation flag is 1 and YES
If NO, proceed to S12, and if NO, end the routine.

In S12, the polytrope coefficient PN in the compression process is searched from the map. This polytropic coefficient PN is generally set to about 1.3.

In S13, the bias amount X is calculated according to the flowchart of FIG. 5 described later.

In S14, the in-cylinder pressure PE _ij is corrected by the bias amount X in accordance with the flowchart of FIG. 6 described later, and the corrected in-cylinder pressure P _ij is stored in the RAM 19 (j = 30 to 60).

In S15, the in-cylinder pressure P is set when j is in the range of 0 to 29 (the crank angle is 0 ° to 116 ° based on the start of the compression stroke).
_ij is predicted by calculating according to the flowchart of FIG. 7 described later.

In S16, the polytropic coefficient PNE in the expansion stroke is
The calculation is performed according to the flowchart of FIG.

At S17, when j is in the range of 61 to 90 (the crank angle is 244 ° to 360 ° in the same manner as described above), the in-cylinder pressure P _{ij is changed} to a ninth to be described later.
According to the flowchart in the figure, the prediction is performed by calculation.

In S18, P _i ⁺ is calculated by calculating according to the flowchart of FIG. 10 described later.

In S19, after setting the operation flag to zero, the routine ends.

Next, a calculation routine of the bias amount X will be described with reference to the flowchart of FIG.

In S21, the value before ignition timing (which can be assumed to be adiabatic change)
The in-cylinder pressures PE _ix and PE _iy of the same cylinder detected at the two crank angle positions x and y are read from the RAM 19.

In S22, the combustion chamber volumes VX and VY at the timings x and y (crank angles) are searched from a map.

In S23, a coefficient A is calculated from the combustion chamber volumes VX and VY and the polytropic coefficient PN by the following equation.

A = (VX / VY) In the ^PN S24, the bias amount X is calculated by the following equation.

X = ( _PEix × A- _PEiy ) / (1-A) By the way, the detected in-cylinder pressure based on the output values of the in-cylinder pressure sensors 1 to 6 and the true in-cylinder pressure of the combustion chamber are shown in FIG. As shown, an error is likely to occur. In particular, in the case of an in-cylinder pressure sensor attached to the washer of the ignition plug, the output value tends to fluctuate due to a change in ambient temperature or the like. Therefore, a coefficient A corresponding to a true in-cylinder pressure change at the time of adiabatic change is calculated from the combustion chamber volumes VX, VY and the polytrope coefficient PN at two crank angle positions, and this coefficient A and the in-cylinder pressure sensors 1 to 6 are calculated. The bias amount X (see FIG. 15) is calculated from the in-cylinder pressure detected by the above-described method, and the true in-cylinder pressure can be detected from the output values of the in-cylinder pressure sensors 1 to 6. Here, the bias amount X changes every cycle depending on the start, warm-up, load, and the like, and therefore the bias amount X is always calculated.

The reason why the bias amount X is obtained by the above equation is as follows.

If the true in-cylinder pressure at crank angles x, y is _Pix , _Piy ,
In the compression stroke, the following relationship is established. VX and VY are combustion chamber volumes at crank angles x and y, and PN is a polytropic coefficient.

P _ix × VX ^PN = P _iy × VY ^PN (1) Therefore, P _iy / P _ix = (VX / VY) ^PN (2)

Here, the coefficient A in S23 is as follows: A = (VX / VY) ^PN (3)

On the other hand, if the detected in-cylinder pressure at the crank angle x, y is PE _ix , PE _iy, and the bias amount at this time is constant, and this is X, then PE _ix + X = P _ix (4) PE _iy Since there is a relationship of + X = P _iy (5), from the equation (1), (PE _ix + X) × VX ^PN = (PE _iy + X) × VY ^PN (6), and (3) , (6), (PE _ix + X) × A = (PE _iy + X) (7)

From Expression (7), X is calculated as follows: X = ( _PEix × A- _PEiy ) / (1-A) (8)

Therefore, in S24, the bias amount X
, And the detected in-cylinder pressure (PE _ix , PE _iy ) is corrected in S33 described later, so that the true in-cylinder pressure P _ix , P _iy is obtained.

As described above, the bias amount X is supported by the mathematical formula.

When using the combustion chamber volume at two preset crank angles, the routine shown in the flowchart of FIG. 11 may be used instead of the routine shown in the flowchart of FIG.

That is, in S25, the coefficient A is searched from the map, and in S26, the bias amount X is calculated by the above equation.

Next, a routine for correcting the in-cylinder pressure will be described with reference to the flowchart of FIG.

 In S31, the initial value of j is set to 30.

In S32, it is determined whether or not j is less than 61.
Proceeding to S33, if NO, end the routine.

In S33, the corrected in-cylinder pressure P _ij is calculated by adding the bias amount X to the detected in-cylinder pressure PE _ij , and this in-cylinder pressure P _ij is stored in the RAM 19.

 In S34, j is incremented by 1, and the process returns to S32.

In this way, the in-cylinder pressure P _ij becomes j = 30 to j = 60.
Are sequentially corrected.

Next, a routine for predicting the in-cylinder pressure in the compression stroke will be described with reference to the flowchart of FIG.

 In S41, the initial value of j is set to 30.

In S42, it is determined whether or not j has become zero. If YES, the routine ends, and if NO, the process proceeds to S43.

At S43, the combustion chamber volumes V _j , V
_j-1 is searched from a map stored corresponding to a preset crank angle.

In S44, the combustion chamber volumes V _j , V _j-1 and the polytropic coefficient
From PN, a coefficient C is calculated by the following equation.

In C = (V _j / V _j-1 ) ^PN S45, the in-cylinder pressure P _ij corrected when j = 30
Alternatively, from the in-cylinder pressure P _ij and the coefficient C predicted previously,
The in-cylinder pressure _{Pi (j-1)} at a crank angle position smaller by a predetermined crank angle position is predicted by calculating using the following equation.

In P _{i (j−1)} = P _ij × C S46, j is decremented by 1 and the process returns to S42.

In this way, the in-cylinder pressure _{Pi (j-1)} is increased from j = 30 to 0.
And stores it in the RAM 19.

Incidentally, instead of the routine shown in the flowchart of FIG. 7, as shown in the flowchart of FIG. 12, a coefficient C preset for j, that is, corresponding to the crank angle is searched from the map in S47. Is also good.

Next, the calculation routine of the polytropic coefficient PNE in the expansion stroke will be described with reference to the flowchart of FIG.

In S51, the combustion chamber volume V at 60 ° after the compression top dead center (the crank angle is 240 ° at the start of the compression stroke).
₆₀ and the combustion chamber volume V ₉₀ at the expansion bottom dead center (360 ° crank angle) retrieves from the map based on the crank angle.

In S52, based on the searched combustion chamber volumes V ₆₀ and V ₉₀ ,
The coefficient D is calculated by the following equation.

D = log (V ₉₀ / V ₆₀ ) At S53, a coefficient E is calculated by the following equation from the detected in-cylinder pressure _Pi 60 at 60 ° after the compression top dead center and the constant in-cylinder pressure P _FIX .

E = log (P _i60 / P _FIX ) Here, the in-cylinder pressure at the 360 ° crank angle position was set to a constant P _FIX because the exhaust valve was open at this position, regardless of the operating state. This is because no problem occurs assuming that the in-cylinder pressure is constant.

In S54, a polytrope coefficient PNE (= E / D) is calculated.

As shown in the flowchart of FIG. 13, the coefficient D may be searched from the map in S55, and the coefficient E may be searched from the map set according to _Pi60 in S56.

Next, a routine for predicting the in-cylinder pressure in the expansion stroke will be described with reference to the flowchart of FIG.

 In S61, the initial value of j is set to 60.

In S62, it is determined whether j is less than 90, and if YES,
Proceeding to S63, if NO, end the routine.

In S63, the combustion chamber volumes V _j , V
Search for _{j + 1} from the map.

In S64, the combustion chamber volumes V _j and V _{j + 1} and the polytropic coefficient PNE
Then, the coefficient F is calculated by the following equation.

F = (V _j / V _{j + 1} ) In ^PNE S65, the cylinder pressure P _ij corrected when j = 60
Alternatively, the in-cylinder pressure P _{i (j + 1)} at a crank angle position larger by a predetermined crank angle is calculated by the following equation from the previously predicted in-cylinder pressure P _ij and the coefficient F.

In the case of P _{i (j + 1)} = P _ij × F S66, j is incremented by 1 and the process returns to S62.

In this way, the cylinder pressure P _{i (j + 1)} is increased from j = 60 to 90
And stores it in the RAM 19.

Incidentally, as shown in the flowchart of FIG. 14, the coefficient F may be retrieved from the map in S67 to predict the in-cylinder pressure P _ij .

It will be described with reference to the flowchart in FIG. 10 the routine for calculating P _i.

In S71, the initial value of the total work k is set to zero, and in S72
Then, the initial value of j is set to zero.

In S73, it is determined whether or not j is less than 91.
Proceed to S74 and if NO, proceed to S79.

In S74, the sampling period of the in-cylinder pressure (4 in this example)
The combustion chamber volume change amount ΔV _j in ゜) is retrieved from the map in correspondence with the j.

In S75, the corrected or predicted in-cylinder pressure P _ij is read from the RAM 19.

In S76, a partial work l is obtained by multiplying the retrieved combustion chamber volume ΔV _j by the read in-cylinder pressure P _ij .

In S77, a new total work k is obtained by adding the calculated partial work 1 to the total work k set in the previous routine.

In S78, j is incremented by 1, and the process returns to S73. In this way, the total work k in the crank angle range from j = 0 to j = 90, that is, 0 to 360 ° (compression stroke and expansion stroke) in crank angle is calculated.

In S79, the P _i ⁺ i predicted by calculating the following equation for each cylinder on the basis of the total work load k of the crank angle range.

P _i ⁺ i = k / V _s V _s is the total combustion chamber volume at the crank angle of 0 to 360 °.

As described above, the in-cylinder pressure from the in-cylinder pressure sensors 1 to 6 is read in a crank angle range (120 to 240 degrees) centered on the compression top dead center, and the crank angle is determined based on the in-cylinder pressure. the cylinder pressure at 120 DEG before and after the range to each prediction. Thus to calculate the P _i ⁺ i on the basis of these in-cylinder pressure, the following advantages.

That is, since the detection values of the in-cylinder pressure sensors 1 to 6 of a predetermined cylinder are read in a range of 120 ° around the compression top dead center, each cylinder (6 Cylinder pressure) can be detected with good timing. Here, in this embodiment, the sampling period is set to 120 ° for a six-cylinder engine, but the sampling period can be represented by 720 ° / the number of cylinders.

Further, since the in-cylinder pressure detected by the in-cylinder pressure sensors 1 to 6 is corrected by the bias amount, the true in-cylinder pressure of the combustion chamber can be detected with high accuracy, and the detection accuracy of P _i ⁺ i can be improved. As shown in FIG. 17, it can be greatly improved. Further, based on the corrected in-cylinder pressure and the predicted in-cylinder pressure, P _i ⁺ i in the 360 ° crank angle range, which is the compression stroke and the expansion stroke, is calculated, so that the combustion state deteriorates. Even if the combustion period is prolonged (see the chain line in FIG. 22), P _i
⁺ i can be detected with high accuracy. Meanwhile, total P _i of one cycle, as shown in FIG. 16, the suction and P _i ⁺ i in the compression stroke and the expansion stroke stroke and P in the exhaust stroke _i ^- i and it is obtained by adding, P _i ^- i is the operating condition, which is determined by the engine characteristics and the like, the combustion state for which corresponds to the P _i ⁺ i, is obtained as is obtained in this embodiment the P _i ⁺ i.

Next, an embodiment in which the present apparatus is applied to misfire determination is shown in FIGS.
This will be described with reference to FIG. Note that the configuration is the same as in FIG. 2, and a description thereof will be omitted.

 FIG. 18 shows a first embodiment of the misfire determination.

That is, in S81, P _i ⁺ i calculated in S79 is read.

In S82, P _i ⁺ i which is read is determined whether less than a predetermined value, when the NO proceeds to S82 when YES, the process proceeds to S84.

In S83, the fact that a misfire has occurred is stored in the RAM 19 as the misfire flag = 1.

In S84, the misfire flag = 0 indicating that no misfire occurred
Is stored in the RAM 19.

In this way, misfire determination is made for each cylinder. In this way, when the misfire determination, it is possible to predict correspond to the actual P _i the P _i ⁺ i as described above with high precision, thereby improving the misfire determination accuracy greatly.

Next, a second embodiment of the misfire determination will be described with reference to the flowchart of FIG.

 In S91, the detected engine speed is read.

In S92, the basic injection amount corresponding to the engine load T _P (= KQ / N;
K is a constant, Q is the intake air flow rate, and N is the engine speed.

In S93, P _i ⁺ i calculated in S79 is read.

In S94, the average learning number C is retrieved from the map according to the detected engine speed, basic injection amount _TP, and cylinder number. The average number of learning C, for each cylinder, and is stored in the RAM19 in correspondence with the engine rotational speed and the basic injection quantity T _P.

In S95, it searches the map according to the P _i ⁺ i mean AVEP _i ⁺ engine speed and the basic injection quantity T _P and the cylinder number. AV
EP _i ⁺ is stored in the RAM19 to correspond to the engine rotational speed and the basic injection quantity T _P for each cylinder.

In S96, it is determined whether or not the searched average learning number C is less than a predetermined value. If YES, the process proceeds to S97, and if NO, the process proceeds to S9.
Go to 9.

In S97, M is calculated by multiplying the average number of learning times C searched in S94 by the searched AVEP _i ⁺ in S95.

In S98, AVEP _i ⁺ is calculated by the following simple average formula based on P _i ⁺ i read in S93, the M, and the average number of times of learning C.

AVEP _i ⁺ = (M + P _i ⁺ i) / (C + 1) On the other hand, in S99, AVEP _i ⁺ is calculated by the following weighted average formula.

AVEP _i ⁺ = AVEP _i ⁺ + (P _i ⁺ i−AVEP _i ⁺ ) / Y Y is a predetermined value exceeding 1.

In S100, the AVEP _i ⁺ computed at S98 or S99 in correspondence to the engine rotational speed and the basic injection quantity T _P and the cylinder number is stored in the map.

In S101, the average learning number C is incremented by one and stored in the map.

In S102, the AVEP _i ⁺ calculated in S98 or S99 and S9
Calculate the ratio q (= P _i ⁺ i / AVEP _i ⁺ ) to P _i ⁺ i read in 3.

In S103, it is determined whether or not the calculated ratio q is equal to or less than a predetermined value (for example, zero). When YES, the process proceeds to S104, and when NO, the process proceeds to S105.

In S104, the occurrence of misfire is stored in the RAM 19 as the misfire flag = 1.

In S105, the misfire flag = 0 indicating that no misfire occurred.
Is stored in the RAM 19.

 In this way, misfire determination is made for each cylinder.

Next, a third embodiment of the misfire determination will be described with reference to the flowchart of FIG. Note that, in the following embodiments,
Elements that are the same as the steps in FIG. 19 are given the same step numbers as in FIG. 19, and description thereof is omitted.

That is, in S110, the AVEP _i ⁺ searched in S95
And the ratio γ (= P _i ⁺ i / AVEP _i ⁺ ) between P _i ⁺ i read at S93.

In S111, the calculated γ it is determined whether more than a predetermined value, the S96 when namely P _i ⁺ i when YES is NO the process proceeds to S102 without passing through the S96~S101 when small relative AVEP _i ⁺ move on.

In this manner, when the operation state (the combustion state is poor) where P _i ⁺ i is small continues, AVEP _i ⁺ is not updated, so that the misfire determination accuracy can be improved.

Next, a fourth embodiment of the misfire determination will be described with reference to the flowchart of FIG.

In S121, searches the map based AVEP _i ⁺ maximum MAXP _i of on the engine rotational speed and the basic injection quantity T _P. MAXP
_i is to correspond to the engine rotational speed and the basic injection quantity T _P, is set to all the cylinders the same map.

In S122, it is determined whether or not the AVEP _i ⁺ calculated in S98 or S99 or S99 exceeds the retrieved MAXP _i . If YES, the process proceeds to S123, and if NO, the process proceeds to S124.

In S123, the calculated AVEP _i ⁺ is stored in the map of the RAM 19 as MAXP _i .

In S124, the AVEP _i ⁺ calculated in S98 or S99 and S9
Based on P _i ⁺ i and MAXP _i read in 3, the ratio S is calculated by the following equation.

In ^{_{S = MAXP i × P i +}} i / AVEP i + S125, when the calculated ratio S is determined whether a predetermined value or less, the NO in S104 it is determined that a misfire has occurred when the YES S105 Proceed to.

In this manner, the same MAXP _i is set for all cylinders, and the ratio S is calculated for each cylinder by using this MAXP _i . Therefore, the output values of the in-cylinder pressure sensors 1 to 6 vary for each cylinder. Also, misfire determination can be performed with high accuracy in each cylinder.

<Effects of the Invention> As described above, the present invention predicts in-cylinder pressure in another crank angle range based on in-cylinder pressure detected in a predetermined crank angle range, and based on these in-cylinder pressures. since so as to calculate the P _i Te, can detect P _i with high accuracy, it has to detect the combustion state such as misfire with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to the claims of the present invention, FIG. 2 is a block diagram showing one embodiment of the present invention, FIGS. 3 to 14 are flowcharts of the same, and FIGS. FIG. 18 is a flowchart for explaining a first embodiment in which the apparatus of the present invention is applied to misfire determination, FIG. 19 is a flowchart of a second embodiment in which the apparatus of the present invention is applied to misfire determination, and FIG. 20 is a misfire determination. FIG. 21 is a flowchart of the third embodiment applied to misfire determination, and FIG. 21 is a flowchart of the fourth embodiment applied to misfire determination.
FIG. 23 is a view for explaining a conventional disadvantage. 1-6: In-cylinder pressure sensor, 15: Control device, 17: CP
U, 19 …… RAM, 21 …… Crank angle sensor

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Claims (1)

(57) [Claims] 1. An in-cylinder pressure detecting means for detecting an in-cylinder pressure of an engine combustion chamber, a crank angle detecting means for detecting a crank angle of an engine, and the in-cylinder pressure detection signal during a sampling period within a predetermined crank angle range. Sampling means for sampling; combustion chamber volume setting means for setting a combustion chamber volume for each crank angle; at least two in-cylinder pressure detection signals of the sampled in-cylinder pressure detection signals; and a combustion chamber volume at that time A bias amount setting means for setting a bias amount of the in-cylinder pressure detection signal with respect to a true in-cylinder pressure based on the in-cylinder pressure detection signal, and correcting the sampled in-cylinder pressure detection signal based on the set bias amount. In-cylinder pressure correction means for obtaining pressure, and in the non-sampling period, the combustion chamber volume in the non-sampling period and the corrected Based on the corrected in-cylinder pressure and the predicted in-cylinder pressure based on the corrected in-cylinder pressure and the predicted in-cylinder pressure. A combustion state detection device for an internal combustion engine, comprising: