JP2527798B2 - Combustion state detection device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detection device for an internal combustion engine of an automobile or the like, and more particularly to a device for accurately detecting misfires in a plurality of cylinders with a simple configuration (Prior Art). High combustion economy and operability tend to be required, and from this viewpoint, a microcomputer or the like is applied to optimally control the combustion state. In this combustion control, it is necessary to detect the combustion state of each cylinder. As one of the methods for grasping the combustion state, there is a method for detecting the pressure of the combustion gas in the cylinder (hereinafter referred to as the cylinder pressure).
There is one described in JP-A-62-24037. In this device, an in-cylinder pressure sensor made of a piezoelectric element is fixed as a washer of an ignition plug of each cylinder, and the in-cylinder pressure sensor outputs an electric charge according to the combustion pressure in the cylinder. (Problems to be Solved by the Invention) However, in such a conventional combustion state detecting device, it is necessary to provide a sensor for each cylinder, which is costly. If it is small, it is difficult to detect a subtle cylinder pressure with high accuracy, and knocking easily occurs near the compression top dead center where the cylinder pressure is maximum, so accurate cylinder pressure and rotational fluctuation can be detected. There wasn't. Further, there is no means for eliminating the influence of the adjacent cylinders of the multi-cylinder engine, and in a multi-cylinder engine having more than four cylinders, the combustion state detection accuracy of each cylinder is affected by the influence of the combustion state of the adjacent cylinders. Further, also in the four-cylinder engine, when the engine rotation measurement timing is arbitrarily set to a value other than the predetermined crank angle, the combustion state detection accuracy is deteriorated due to the influence of the combustion state of the adjacent cylinders. (Object of the Invention) Therefore, the present invention detects a change in the rotation fluctuation measured in a predetermined crank angle section including the compression top dead center of each cylinder as a main part as corresponding to the combustion fluctuation in the previous combustion cylinder. Accordingly, it is an object of the present invention to provide a combustion state detection device for an internal combustion engine that accurately detects misfires in each cylinder and does not require complicated calculation processing. (Means for Solving the Problem) In order to achieve the above object, the combustion state detecting apparatus for an internal combustion engine according to the present invention outputs a signal for discriminating a cylinder in a combustion stroke as shown in the basic conceptual diagram of FIG. A cylinder discriminating means a, a crank angle detecting means b for outputting a signal corresponding to a predetermined unit crank angle, a counter for discriminating the cylinder discriminating compression top dead center to a predetermined crank angle after the compression top dead center, A timer that is started and stopped in synchronization with the counter counting to a predetermined crank angle, and counts the engine rotation cycle by counting from the previous predetermined crank angle to the present predetermined crank angle, It is assumed that the change of the rotation cycle for each cylinder is obtained from the output of the cycle measuring means c and the change of the rotation fluctuation measured this time corresponds to the combustion fluctuation in the previous combustion cylinder. And a combustion state detecting means d for detecting the combustion state of the cylinder. (Operation) In the present invention, the engine rotation cycle in the predetermined crank angle section after the current compression top dead center of the cylinder is measured from the predetermined crank angle after the compression top dead center of each cylinder, and the cylinder cycle is calculated from the measured value. A change in the rotation cycle is calculated, and the combustion state of the cylinder is detected as if the change in the rotation fluctuation measured this time corresponds to the combustion fluctuation in the previous combustion cylinder, so misfires in each cylinder are accurately detected. . That is, when a misfire occurs in the cylinder this time, the number of revolutions of the cylinder which becomes the next combustion stroke fluctuates significantly after the predetermined crank angle after the compression top dead center, and the influence of the misfire becomes a predetermined value after the compression top dead center. Since the number of revolutions significantly changes from the crank angle to the predetermined crank angle after the top dead center of compression, the occurrence of the misfire can be reliably detected from the change in the measurement time at that time. Therefore, by setting the measurement range of the rotation cycle in the combustion stroke of the cylinder from the predetermined crank angle after the compression top dead center to the predetermined crank angle after the current compression top dead center, the cylinder in which the misfire has occurred Can be detected with high accuracy, the detection speed can be improved, and the remaining calculation processing time can be effectively utilized for other control. In addition, by changing the crank angle at which the measurement starts from the compression top dead center as appropriate, the most accurate accuracy can be obtained according to the combustion period (explosion period) that varies depending on the conditions such as the set ignition timing, EGR rate, or engine rotation speed. In addition to being able to measure the engine rotation period in a good period, it is possible to measure the engine rotation period in an accurate period by setting the optimum measurement start period depending on the number of cylinders. Therefore, it is possible to detect misfire or the like of each cylinder only by obtaining a change in the rotation cycle in the crank angle section, and a complicated calculation process is unnecessary. (Embodiment) FIGS. 2 to 5 are views showing an embodiment of a combustion state detecting device for an internal combustion engine according to the present invention.
It is applied to a cylinder engine. First, the configuration will be described. FIG. 2 is a diagram showing the overall structure. In this figure, reference numeral 1 is a crank angle sensor, and a crank angle sensor (crank angle detecting means) 1 is provided for compressing each cylinder at each explosion interval (180 ° CA). A reference signal REF that becomes a [H] level pulse at a predetermined position before the dead center (TDC), for example, BTDC 70 °, is output, and a [H] level pulse is output for each unit angle (for example, 1 °) of the crank angle. The unit signal POS is output to the control unit 2. Further, 3 is a counter, and the counter 3 counts the unit signal POS by 360 ° / n (n: number of cylinders) from the top dead center position after the reference signal REF of the crank angle sensor 1 is input to the control unit 2. Then, the count value is output to the control unit 2. The timer A4 and the timer B5 repeatedly start and stop according to the outputs of the self-diagnosis switch 6 and the crank angle sensor 1, and output the elapsed time between them to the control unit 2. The air flow meter 7 detects the flow rate Qa of the intake air, and the water temperature sensor 8 detects the temperature Tw of the cooling water flowing through the water jacket. Further, the throttle valve opening sensor 9 detects a throttle valve opening TVO. The output from each of these sensors is input to the control unit 2.
The timer A4 has a function as a cycle measuring means, the control unit 2 has a function as a combustion state detecting means, and is composed of a CPU 10, a ROM 11 and an I / O port 13. The CPU10 fetches the external data required from the I / O port 13 according to the program written in the ROM11, and exchanges the data with the RAM12, and calculates the processing values etc. necessary for the combustion state detection. The processed data and the processed data as necessary are output to the I / O port 13. ROM11 is
A program for controlling the CPU 10 is stored, and the RAM 12 temporarily stores the data used for the calculation. I / O port 13
Each of the signals from the crank angle sensor 1, the air flow meter 7, the water temperature sensor 8 and the throttle valve opening sensor 9 and the counter 3, the timer A4, the timer B5 and the self-diagnosis switch 6 are included.
Information is input from the I / O port 13 and the injection signal Si and the ignition signal Sp are injected from the injector.
It outputs to 14a-14d and the ignition device 15. The ignition device 15 is composed of an ignition coil, an ignition plug, and the like, and generates a high voltage based on the ignition signal Sp to ignite the air-fuel mixture. Next, the operation will be described. The target value of the engine speed during idling is set in advance, and the combustion state of each cylinder is controlled so as to be within a predetermined range including this target value. That is, since the combustion state of each cylinder during idling is controlled to be substantially constant, at this time, if the elapsed time (rotation cycle) for each predetermined crank angle section closely correlating with the combustion state is measured, The combustion state of the cylinder in the combustion stroke can be detected. Therefore, in the present embodiment, attention is paid to a crank angle section (a predetermined crank angle section centered on the compression top dead center TDC of each cylinder) where the influence of misfire significantly appears, and the elapsed time (rotation cycle) in this crank angle section Is measured to improve the detection accuracy and detection speed for detecting the misfiring cylinder without performing arithmetic processing. FIG. 3 is a flowchart showing a program for detecting the combustion state, and this program is executed in synchronization with the engine rotation. The occurrence of a misfire in each cylinder by the process of the step P ₁ to P ₅ is detected, the crank angle sensor 1 shown in FIG. 4 the processing of Step P ₁ to P _5, signals outputted from the counter 3 and timer A4 This will be described with reference to the waveform and the correspondence diagram of the change in the rotation speed and the measurement time shown in FIG. In step P ₁ , a cylinder discrimination signal (Fig. 4 (a)) and a crank angle signal (Fig. 4 (b)) from the crank angle sensor 1
Based on the above, the crank angle from the top dead center of the cylinder in the combustion stroke at that time is measured, and this crank angle is 360 ° / nATD at P _2.
It is determined whether or not C (n = 4 because it is four cylinders in this embodiment). The counter 3 counts the crank angle at P _2, and the counter 3 starts counting when the cylinder discrimination signal of the crank angle sensor 1 is output, and counts up in accordance with the crank angle signal to 90 °. Stop counting when it becomes ATDC.
After the counter 3 outputs a signal corresponding to the count value to the control unit 2,

It is reset to [0] (FIG. 4 (c)). Then, at P ₃ , the previous 90
Timer A4 measures the elapsed time from ° ATDC to the current 90 ° ATDC, and outputs the timer value Ti (i: 1, 2, 3, 4) to control unit 2. Next, at P ₄ , the timer A 4 is reset in synchronization with the 90 ° ATDC of the timer A 4. The timer A4 is repeatedly started and stopped in synchronization with the 90 ° ATDC timing of the counter 3 (Fig. 4 (d)). Then
And it ends the current routine and start the timer A4 again at P _5. On the other hand, when P ₂ is not 360 ° / n ATDC, the process returns to step P ₁ . The measurement range of the elapsed time in the combustion stroke of each cylinder as described above Step P ₁ to P ₅ process since the last 90 ° ATDC of this
By setting up to 90 ° ATDC, it becomes possible to reliably detect the combustion fluctuation when a misfire occurs in a certain cylinder. Specifically, if a misfire occurs in the third cylinder, as shown in Fig. 5, the rotational speed of the fourth cylinder, which is the next combustion stroke, fluctuates greatly, and the effect of the misfire is 90 ° ATDC to the next 90 °.
° Remarkably appears in the change in the number of revolutions up to ATDC, and the occurrence of misfire can be reliably detected from the change in the measurement time at that time. Therefore, when detecting a misfire or the like of each cylinder, the rotational fluctuation of the cylinder in the next combustion stroke is larger than that of the cylinder in which the misfire has occurred due to the influence of the inertial force of the engine. By setting the measurement range of the rotation cycle from the predetermined crank angle after the previous compression top dead center to the predetermined crank angle section after the current compression top dead center,
The cylinder in which the misfire has occurred can be reliably detected only by measuring the elapsed time in the crank angle section. As a result, not only is it possible to accurately detect the misfire occurrence in each cylinder without performing complicated arithmetic processing, but it is also possible to improve the detection speed, and the extra arithmetic processing time can be used for other control. Can be effectively utilized as. Also, by appropriately changing the crank angle at which the measurement is started from the compression top dead center, the most accurate period can be obtained according to the combustion period that varies depending on the conditions such as the set ignition timing, the EGR rate, or the engine rotation speed. The engine rotation cycle can be measured, and the engine rotation cycle can be measured in an accurate period by setting the optimum measurement start period according to the number of cylinders. (Effect of the Invention) According to the present invention, the rotational fluctuation from the predetermined crank angle after the compression top dead center of each cylinder to the predetermined crank angle after the current compression top dead center of each cylinder is obtained, and the change of the rotational fluctuation this time is calculated. Since it is detected as corresponding to the combustion fluctuation in the previous combustion cylinder, the cylinder in which misfire has occurred can be detected accurately, the detection speed is improved, and the remaining calculation processing time is used for other control. It can be used effectively. In addition, by changing the crank angle at which the measurement starts from the compression top dead center as appropriate, the most accurate accuracy can be obtained according to the combustion period (explosion period) that varies depending on the conditions such as the set ignition timing, EGR rate, or engine rotation speed. In addition to being able to measure the engine rotation period in a good period, it is possible to measure the engine rotation period in an accurate period by setting the optimum measurement start period depending on the number of cylinders.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 5 are diagrams showing an embodiment of a combustion state detecting device for an internal combustion engine according to the present invention, and FIG. 2 is an overall configuration diagram thereof, and FIG. FIG. 4 is a flow chart showing a program for detecting the combustion state, FIG. 4 is a signal waveform diagram of each part thereof, and FIG. 5 is a diagram showing the relationship between the change of the engine speed and the measurement time. 1 ... Crank angle sensor (crank angle detecting means), 2 ...
... Control unit (combustion state detection means), 3 ...
Counter (cycle measuring means), 4 ... Timer A (cycle measuring means), 6 ... Self-diagnosis switch.

Claims (1)

(57) [Claims] 1. A cylinder discrimination means for outputting a signal for discriminating a cylinder in a combustion stroke, b) a crank angle detecting means for outputting a signal corresponding to a predetermined unit crank angle, and c) a compression top dead center. To a predetermined crank angle after the compression top dead center and a counter that is started / stopped in synchronization with the counting of the counter to a predetermined crank angle, from the previous predetermined crank angle to the current predetermined crank angle. A cycle measuring means including a timer for counting the rotation cycle of the engine by counting up to the angle, and d) a change in the rotation cycle for each cylinder is obtained from the output of the cycle measuring means, and the change in the rotation fluctuation measured this time is calculated. A combustion state detecting device for an internal combustion engine, comprising: a combustion state detecting means for detecting a combustion state of a previous combustion cylinder, which corresponds to a combustion fluctuation in the combustion cylinder.