JPH03246374A - Misfire detecting device of internal combustion engine - Google Patents

Abstract

PURPOSE:To decide a misfire highly accurately by correcting a cylinder inner pressure detecting signal with a bias amount to find a cylinder inner pressure, and at the same time, deciding whether there is the misfire or not from the peak position of the cylinder inner pressure, the cylinder inner pressure, and the estimated motoring pressure in a noncombustion condition. CONSTITUTION:In a sampling period in the scope of a specific crank angle, the cylinder inner pressure detecting signal of a cylinder inner pressure detecting means A is sampled (by a sampling means C), and at the same time the combustion chamber volume of each crank angle is set by a setting means D. And depending on the combustion chamber volume and the cylinder inner pressure detecting signal, a bias amount of the cylinder inner pressure detecting signal is set (by a setting means E), and depending on the bias amount, the cylinder inner pressure detecting signal is corrected by a correcting means F to find the cylinder inner pressure. And depending on the cylinder inner pressure after the correction, the peak position of the cylinder inner pressure is decided by a deciding means G, and the same time, depending on the cylinder inner pressure after the correction and the combustion chamber volume, the motoring pressure in a noncombustion condition is estimated by an estimate means H, and depending on the motoring pressure and the peak position, a misfire is decided by a deciding means I.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a misfire detection device for an internal combustion engine.

<Prior Art> As a conventional example of a misfire detection device for an internal combustion engine, there is the following (see Japanese Patent Laid-Open No. 63-63933).

That is, the peak position of the cylinder pressure is determined from the cylinder pressure detected by the cylinder pressure sensor. Then, the in-cylinder pressure at the peak position is the basic injection amount (equivalent to engine load).
A misfire is determined by comparing the value divided by the set value with the set value.

<Problem to be Solved by the Invention> However, in such a conventional misfire detection device, if there is variation in the sensitivity of the in-cylinder pressure sensor for each cylinder, the set value for determining a misfire must be set differently for each cylinder. There is a problem in that it is complicated to configure the settings. Furthermore, depending on the set value, there is a possibility that a misfire misjudgment may occur.

Further, Japanese Patent Application Laid-Open No. 62-35075 discloses a system in which a misfire is determined when the cylinder pressure detected during a predetermined sampling period is less than or equal to a set value. However, in this method, the set value is searched from a map assigned to the engine load, so there are problems similar to those of the conventional example.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a misfire detection device that can detect the presence or absence of a misfire with high precision even in a multi-cylinder internal combustion engine.

<ll! Means for Solving Problem a> For this reason, the present invention, as shown in FIG. means B, sampling means C for sampling the in-cylinder pressure detection signal in a sampling period of a predetermined crank angle range, combustion chamber volume setting means for setting a combustion chamber volume for each crank angle, and bias amount setting means E for setting a bias amount of the cylinder pressure detection signal based on the combustion chamber volume and the sampled cylinder pressure detection signal; an in-cylinder pressure correction means F that corrects the detection signal to obtain the in-cylinder pressure; a peak position determination means G that determines the peak position of the in-cylinder pressure based on the corrected in-cylinder pressure or the sampled in-cylinder pressure; a motoring pressure prediction means H that predicts the motoring pressure in the non-combustion state based on the corrected in-cylinder pressure and the combustion chamber volume; and the determined peak position, the corrected in-cylinder pressure, and the motoring pressure. Misfire determination means for determining misfire based on ■
I tried to prepare for this.

<Operation> In this way, the cylinder pressure detection signal of the cylinder pressure detection means is corrected by the bias amount, and the cylinder pressure is determined.
The peak position of the cylinder pressure is determined, and the motoring pressure at the time of no combustion is predicted using the corrected cylinder pressure and combustion chamber volume. Then, the presence or absence of a misfire is determined from the peak position, in-cylinder pressure, and motoring pressure.

<Example> An example of the present invention will be described below based on FIGS. 2 to 14.

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

The multiplexer 13 outputs detection signals from the in-cylinder pressure sensors 1 to 6 of the selected cylinder based on a switching signal, which will be described later, to the I10 interface 16 of the control device F15 via the low-pass filter 14. The low-pass filter 14 is
This removes high-frequency components such as knocking vibrations and ignition noise that are unnecessary for detecting cylinder pressure and can cause false detection, and allows only low-frequency components below a predetermined frequency to pass through.

The control device 15 includes a CPU 17. ROM18. RAM
19. An A/D converter 20 is provided, and a CPU 17
is executed according to the program written in ROM1B.
10 reads necessary external data from the interface 16, and while exchanging data with the RAM 19, calculates the processing values necessary for calculating parameters related to the combustion state, and as necessary. The processed data is output to the I10 interface 16. The I10 interface 16 includes the low pass filter 14. Crank angle sensor 21 as crank angle detection means. As the signal from the air flow meter 22 is input, I1
A switching signal is output from the 0 interface 16 to the multiplexer 13 in accordance with a command from the CPU 17.

The A/D converter 20 operates according to instructions from the CPU 17.
10 The external signal input to the interface 16 is
D-convert. Further, the ROM 1B stores programs for the CPU 17, and the RAM 19 stores data used for calculations etc. 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 compression top dead center of each cylinder at every predetermined crank angle (120 degrees in crank angle for a 6-cylinder engine), and also outputs a reference signal at a predetermined crank angle position before compression top dead center of each cylinder. A unit signal is output every 1°). Therefore, the engine rotational speed can be detected based on the input cycle of the reference signal and the number of counts. Also,
Air flow meter 22 outputs a signal corresponding to the intake air flow rate.

Here, the CPU 17 constitutes a sampling means, a combustion chamber volume setting means, a bias amount setting means, an in-cylinder pressure correction means, a motoring pressure prediction means, a peak position determination means, and a misfire determination means.

Next, the operation will be explained according to the flowcharts shown in FIGS. 3 to 1θ.

First, the sampling routine for in-cylinder pressure data will be explained according to the flowchart of FIG. This routine is executed at a predetermined crank angle position (in this embodiment, 44 degrees before compression top dead center) determined by the reference signal and unit signal.

In Sl, the cylinder pressure detected by the cylinder pressure sensors 1 to 6 is set at a predetermined crank angle (in this example, the crank angle is 4).
The data is A/D converted and read by the A/D converter 20 (described in Section 3).

In S2, the read cylinder pressure PE,j is stored in the RAM 19 in association with the cylinder number i and the sampling order (corresponding to the crank angle) j.

Here, the reading order j based on the detected values is 34 to 64.

In S3, A/D conversion end timing (7 after compression top dead center)
6°), and if YES, proceed to S4, and if NO, return to S1.

In S4, a calculation flag, which will be described later, is set to 1.

In S5, it is determined whether it is the next A/D conversion timing,
When the answer is YES, the process advances to S6, and when the answer is No, the process returns to S5.

In S6, the cylinder number i is incremented by 1.

In S7, it is determined whether the cylinder number i has become 6, and Y
When the answer is ES, the process advances to S8, and when the answer is No, the routine is ended.

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

In this way, the cylinder pressure P during a crank angle period of 120 degrees from 44 degrees before compression top dead center to 76 degrees after compression top dead center
E1i is detected for each cylinder.

Next, the calculation routine will be explained according to the flowchart shown in FIG.

In Sll, it is determined whether the calculation flag is 1 or not, and Y
When the answer is ES, the process advances to S12, and when the answer is NO, the routine is ended.

At 312, the polytropic coefficient PN in the compression stroke 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, which will be described later.

In S14, k is initialized to 34.

In S15, the ignition timing ADV in the sampled engine cycle is read.

In S16, the read ignition timing ADV (BTDC)
Based on this, a sampling number f ((180-ADV)/4) corresponding to the crank angle of the ignition timing is calculated.

In S17, it is determined whether the k is less than 64, and YES.
If so, the process advances to 818, and if NO, the process advances to S22.

31B, the detected cylinder pressure PEi is expressed as the sixth
The corrected cylinder pressures P and j are corrected using the bias amount X according to the flowchart shown in the figure, and the corrected cylinder pressures P and j are stored in the RAM 19 (j=34 to 64).

In S19, the motoring pressure P M OT = t is predicted according to the flowchart of FIG. 7, which will be described later.

In S20, the peak position θPMAX of the in-cylinder pressure is determined according to the flowchart of FIG. 8, which will be described later.

In step 321, k is incremented by 1 and the process returns to S17.

When k exceeds 64 in this manner, a misfire determination is made in S22 according to the flowchart of FIG. 9, which will be described later.

In step 323, the calculation flag is set to zero, and then the routine is ended.

Next, the calculation routine for the bias amount X will be explained according to the flowchart shown in FIG.

In S31, 2 before the ignition timing (which can be assumed to be an adiabatic change)
The in-cylinder pressure PEi, , PE, , of the same cylinder searched at the crank angle 11ffix, y is stored in RAM1.
Read from 9.

In S32, the timing of the X and y (crank angle)
The combustion chamber volumes vx and vy at are searched from the map.

In S33, a coefficient A is calculated from the searched combustion chamber welds VX, VY and the polytropic coefficient PN using the following equation.

A=(VX/VY)’N At 534, the bias amount X is calculated using the following equation.

X= (PE=,XA-PEtX)/(I A
) By the way, as shown in FIG. 11, errors tend to occur between the cylinder pressure detected by the output values of the cylinder pressure sensors 1 to 6 and the true cylinder pressure of the combustion chamber. In particular, in the case of an in-cylinder pressure sensor attached to a washer of a spark plug, the output value tends to fluctuate due to changes in ambient temperature, etc. Therefore, from the combustion chamber volumes VX and VY at two crank angle positions and the polytropic coefficient PN, a coefficient A corresponding to the true in-cylinder pressure change during an adiabatic change is calculated, and this coefficient A and the in-cylinder pressure sensor 1
By calculating the bias amount X (see FIG. 11) from the cylinder pressure detected by cylinder pressure sensors 1 to 6, the true cylinder pressure can be detected from the output values of cylinder pressure sensors 1 to 6. Here, since the bias amount X changes every cycle due to startup, warm-up, load, etc., the bias amount X is always calculated.

Note that when using the combustion chamber volumes at two preset crank angles, the routine shown in the flowchart of FIG. 10 may be used instead of the routine shown in the flowchart of FIG. 5.

That is, in S35, coefficient A is searched from the map, and 33
In step 6, the bias amount X is calculated using the old method.

Next, the cylinder pressure correction routine will be explained according to the flowchart of FIG. 6. In S41, the cylinder pressure PE,
Calculate the corrected cylinder pressure Pij by adding the bias amount X to
Stored on AM19.

In this way, when j is from 34 to 64, the cylinder pressure Pi
Calculate j.

Next, the motoring pressure prediction routine will be explained according to the flowchart of FIG.

In 351, it is determined whether or not k is less than or equal to l calculated in 516. If YES, the process proceeds to 352, and if No, the process proceeds to S53.

In S52, the corrected cylinder pressure Pij is stored in the RAM 19 as a motoring pressure PMOT.

This is because before the ignition timing, the in-cylinder pressure Pij and the motoring pressure PMOT, . . . substantially match as shown in FIG. 13.

On the other hand, when k>2, k-1 is set to m in S53, and the process proceeds to S54.

In S54, the combustion chamber volume V at the sampling time (crank angle) corresponding to m and k.

■Search for 6 from the map.

In S55, a coefficient n is calculated by the following equation based on the combustion chamber volumes v, , L and the polytropic coefficient PN.

n = (V ea/V k) In PNS56, k
Motoring pressure PMO at the sampling period corresponding to
Tik is calculated using the following equation.

PMOT=to=PMOTi, eXn POMT+ is the motoring pressure when the sampling time is one (4') earlier than PMOTik,
The initial value is the corrected cylinder pressure P1.

In this way, the motoring pressure PMOT is calculated until k is 64 (76° after compression top dead center).

Since this can be regarded as an adiabatic change in the unburned state, the motoring pressure PMOT,j
can be calculated.

Note that the coefficient n for the value of k is stored in the map,
The coefficient n may be searched from a map.

Next, the peak position determination routine will be explained according to the flowchart of FIG.

In 361, it is determined whether k=34 (initial value), and YE
If S, proceed to 362; if NO, proceed to 363.

In S62, MAX is initialized to a predetermined value A (approximately 0) and set to 3.
Proceed to step 63.

In S63, the pressure difference O between the corrected cylinder pressure Pik and motoring pressure PMOT is calculated (see FIG. 14).

In 364, it is determined whether the MAX set in 362 is less than or equal to 0 pressure difference, and if YES, the process advances to S65 and No.
If so, the process advances to S67.

In S65, the pressure difference 0 calculated in S63 is set as MAX.

In S66, the sampling number k (corresponding to the crank angle) at this time is set as the peak position θPMAX of the in-cylinder pressure.

In S67, it is determined whether k has reached 64 (sampling end time), and if YES, the process advances to 368 and NO.
When , the routine ends.

In step 368, it is determined whether MAX is less than a predetermined value B (substantially zero), and if YES, the process advances to S69, and if NO, the routine is ended.

In S69, the peak position θPMAX is set to 45 (corresponding to compression top dead center), and the routine is ended.

Next, the misfire determination routine will be explained according to the flowchart of FIG.

In S71, it is determined whether the peak position θPMAX is 45 or not. If YES, it is determined that the peak position is at the compression top dead center and the process proceeds to 373; if NO, the process proceeds to S75.

372, the cylinder pressure P at the peak position θPMAX
, □ and motoring pressure PMOT, , , ratio q
(= pr-asx/P MOT i@ax) is calculated.

In S73, it is determined whether the calculated ratio q is less than or equal to a predetermined value C(~l). If YES, the process proceeds to S74; if NO, the process proceeds to S75.

In S74, the misfire flag is set to 1 and stored in the RAM 19 to indicate that a misfire has occurred.

In S75, the misfire flag = 0 indicates that no misfire has occurred.
It is stored in the RAM 19 as .

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

As explained above, 120
After correcting the in-cylinder pressure detected by the in-cylinder pressure sensors 1 to 6 in the crank angle range of ° by the bias amount, and determining the motoring pressure and peak position when no combustion occurs in the crank angle range, Since a misfire is determined based on the internal pressure, motoring pressure, and peak position, the motoring pressure and cylinder pressure corresponding to the misfire are compared, so misfire can be determined with high accuracy. I can do it. In addition, since the in-cylinder pressure detected by the in-cylinder pressure sensors 1 to 6 is corrected by the bias amount, even if there are variations in the sensitivity of the in-cylinder pressure sensors 1 to 6 of each cylinder, the true in-cylinder pressure of each cylinder Pressure can be detected with high precision, and misfires can therefore be determined with high precision.

<Effects of the Invention> As explained above, the present invention corrects the detected value of the in-cylinder pressure detection means by the bias amount, determines the peak position of the in-cylinder pressure and the motoring pressure, and uses those values to detect misfire. Since the determination is made, the presence or absence of a misfire in each cylinder can be detected with high accuracy even if the sensitivity of the cylinder pressure detection means is different.

[Brief explanation of drawings]

Fig. 1 is a diagram corresponding to the claims of the present invention, Fig. 2 is a configuration diagram showing an embodiment of the present invention, Figs. 3 to 10 are flowcharts of the same, and Figs. It is a figure for explaining. 1 to 6...Cylinder pressure sensor -5...Control device
17...CPU 19...RAM 21.
・・Crank angle sensor

Claims (1)

[Claims] In-cylinder pressure detection means for detecting in-cylinder pressure in the engine combustion chamber;
a crank angle detection means for detecting a crank angle of the engine; a sampling means for sampling the in-cylinder pressure detection signal during a sampling period of a predetermined crank angle range; and a combustion chamber volume setting means for setting a combustion chamber volume for each crank angle. , a bias amount setting means for setting a bias amount of the in-cylinder pressure detection signal based on the combustion chamber volume in a set sampling period and the sampled in-cylinder pressure detection signal, and based on the set bias amount, an in-cylinder pressure correction means for correcting the sampled in-cylinder pressure detection signal to obtain the in-cylinder pressure; and a peak position for determining the peak position of the in-cylinder pressure based on the corrected in-cylinder pressure or the sampled in-cylinder pressure. determining means; motoring pressure prediction means for predicting motoring when no combustion occurs based on the corrected in-cylinder pressure and the combustion chamber volume; and the determined peak position, the corrected in-cylinder pressure and motoring. 1. A misfire detection device for an internal combustion engine, comprising: misfire determination means for determining misfire based on pressure.