JPH04311649A - Misfire detecting method for internal combustion engine - Google Patents

Abstract

PURPOSE:To detect the continuous misfire of a multiple cylinder engine simply and positively. CONSTITUTION:Whether a cylinder is in the misfire state is discriminated on the basis of output rotating speed change in a speed detecting period from the compression top dead center of the concerned cylinder to that of a following cylinder. In the case of judging the misfire state of the concerned cylinder, the output rotating speed change, in each speed detecting period, of each cylinder following the concerned cylinder is detected in succession so as to specify the speed detecting period indicating the specified increase tendency of the output rotating speed for the first time after the above-mentioned misfire judgment. All the cylinders to the concerned cylinder from the cylinder right in front of the normally ignited cylinder corresponding to the specific speed detecting period are then judged to be in the misfire state.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misfire detection method for an internal combustion engine, which is mainly applied to multi-cylinder engines for automobiles.

0002

2. Description of the Related Art In order to prevent deterioration of emissions and drivability, it is desired to appropriately detect misfires caused by abnormalities in spark plugs, improper adjustment of air-fuel ratio, etc., and to take immediate action.

[0003] As a method of detecting a misfire, for example, as shown in previously filed Japanese Patent Application No. 2-249825, the output rotation speed near the compression top dead center of each cylinder is sequentially detected. Some devices detect whether a misfire has occurred by calculating the difference between the detected output rotation speed and the previously detected output rotation speed, and comparing the difference with a predetermined comparison judgment value. As a specific method according to this, the period from the compression top dead center of each cylinder to the compression top dead center of the next cylinder is set as a speed detection period, and the amount of change in the output rotational speed within that speed detection period is detected. Some misfire detection parameters are used as misfire detection parameters, and by comparing the misfire determination parameters with a predetermined comparative determination value, it is determined whether or not each cylinder has misfired.

0004

However, with this method, there is a problem in that when a plurality of cylinders misfire in succession, it is difficult to appropriately detect the misfire status of each cylinder. For example, in a 4-cylinder 4-cycle engine in which each cylinder is fired in the order of first, third, fourth, and second,
The case where each cylinder misfires consecutively will be explained with reference to FIG. 4. The amount of change in the output rotational speed during the speed detection period of the first cylinder that misfired first shows a relatively large value. However, the amount of change in the output rotational speed (corresponding to B-A) in the next third cylinder speed detection period decreases in value. Since these first and third cylinders misfire, the amount of change in output rotational speed (corresponding to D-C) during the subsequent speed detection period of the fourth cylinder, and the amount of change in the output rotation speed during the speed detection period of the second cylinder The amount of change in output rotational speed (corresponding to FE) will show a very small value. Therefore,
It becomes impossible to detect misfire conditions in these fourth and second cylinders. In other words, if the comparison judgment value is set to a value small enough that even such a small change in output rotational speed can be judged as a misfire, a misfire may be incorrectly judged even when normal combustion continues. There is a high possibility that you will end up doing this.

[0005] The present invention aims to eliminate such inconveniences.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention takes the following measures. That is, the misfire detection method for an internal combustion engine according to the present invention detects whether a cylinder has misfired based on a change in the output rotational speed during the speed detection period from compression top dead center of a cylinder to compression top dead center of the next cylinder. If it is determined that the misfire has occurred in the relevant cylinder, the change in the output rotational speed of each cylinder following the relevant cylinder during each speed detection period is sequentially detected, and the misfire is detected. After the determination, the speed detection period in which the output rotational speed first showed a predetermined upward trend is identified, and all cylinders from the cylinder immediately before the normally ignited cylinder corresponding to that speed detection period to the relevant cylinder are misfired. The feature is that the judgment is made.

[0007]

[Effect] When multiple cylinders misfire in succession, as mentioned above, the output rotational speed decreases significantly at first, but
The degree of decrease gradually becomes smaller. As long as the misfire continues, the output rotational speed will not rise above a certain value. If normal ignition occurs in this state, the output rotational speed will increase significantly. Therefore, based on the change in output rotation speed caused by the first misfire, which is easy to detect, and the change in output rotation speed caused by normal ignition immediately after the misfire, which is also easy to detect, By identifying the cylinders that have returned to normal ignition and estimating the cylinders between them to be misfired, it becomes possible to accurately determine continuous misfires that match the current situation.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

An internal combustion engine 1 schematically shown in FIG.
Every 80°CA (crank angle), 1st cylinder → 3rd cylinder
It is set so that ignition is performed in the order of cylinders → fourth cylinder → second cylinder, and includes an electronic control device 2.

The electronic control unit 2 includes a central processing unit 3,
It is mainly composed of a microcomputer unit comprising a memory 4, an input interface 5, and an output interface 6, and has a function of detecting misfire. As shown in FIG. 3, the input interface 5 receives the compression top dead center (compression TD
An N signal indicating C) is inputted every 180° CA, and a P signal for knowing the output rotational speed is inputted from the electromagnetic pickup 8, for example, every 18° CA. The electromagnetic pickup 8 is a conventional one in which a coil (not shown) is wound around the outer periphery of a magnetic iron core 8a, and the iron core 8a is arranged close to the outer periphery of a signal plate 9. The signal plate 9 has 20 teeth 9a protruding from its outer periphery at equal intervals, and is fixed to the end of the crankshaft 10. When the sensing gear 9 rotates, the magnetic field generated in the iron core 8a is interrupted and an alternating current voltage is generated in the coil.The alternating voltage is shaped by a waveform shaping circuit (not shown) and sent to the input interface 5. It is designed to be input as a signal.

The electronic control unit 2 has a built-in program as schematically shown in FIG. 2 in order to carry out the misfire detection method of the present invention. This program is 180°C
Interrupt processing is performed every time A, that is, every time an N signal is input. First, in step 51, it is determined whether or not the determination start flag Q is set to 0. If it is determined that the determination start flag Q is set to 0 and continuous misfire determination has not been started, the process proceeds to step 52;
Based on the calculation result in the latest cylinder speed detection period for which the calculation regarding the output rotational speed has been completed, it is determined whether or not the cylinder is misfiring. Specifically, an interrupt calculation routine (not shown) is executed every unit crank angle (18° CA), that is, every time the P signal is input, and the unit crank angle passing time T is sequentially calculated and stored. In step 52, the difference (Te-Ts) between the unit crank angle passing time Ts at the initial stage and the unit crank angle passing time Te at the final stage in the speed detection period of the cylinder is calculated,
It is determined whether the difference (Te-Ts) exceeds a predetermined comparison determination value. If the difference (Te-Ts) exceeds a predetermined comparison judgment value and it is determined that the output rotational speed has decreased by a certain level or more, the process proceeds to step 53, where it is determined that the cylinder in question has misfired. is stored as the cylinder that first misfired. After that, step 5
At step 4, the process to indicate that the continuous misfire determination has started, that is, the determination start flag Q is set to 1, and the interrupt routine ends.

In step 51, the judgment start flag Q is set to 1.
is set, step 55
Proceed to. In step 55, the initial stage unit crank angle passing time T in the latest speed detection period for which calculation has been completed.
The difference between s and the final stage unit crank angle passing time Te (
Te-Ts), it is determined whether the output rotational speed has shown a predetermined upward trend. Specifically, the difference (Te
-Ts) is smaller than a preset negative comparison determination value. However, in this step 55,
It is determined whether or not the cylinder corresponding to the speed detection period has been ignited normally. If it is determined that the output rotational speed has increased and ignition has occurred normally, the process proceeds to step 56; otherwise, the process proceeds to subroutine 58. In step 56, the normally ignited cylinder is identified, and all the cylinders from the cylinder immediately before that cylinder to the cylinder at the beginning of the misfire stored in step 53 are determined to have misfired, and the cylinder has continuously misfired. The number of cylinders, etc. are stored in the memory as misfire data, and the process proceeds to step 57. In step 57, processing is performed to indicate that the continuous misfires have been interrupted, that is, the determination start flag is set to 0, and the process proceeds to subroutine 58. In the subroutine 58, it is determined whether or not the misfire rate is abnormal based on the misfire data, and if it is determined that it is abnormal, a warning is issued. As a warning method, a diagnostic lamp may be turned on to notify that an abnormality has occurred, or a diagnostic output terminal may be provided on the electronic control unit 2.
It should be possible to detect abnormalities using a tester or the like connected to the terminal. The criteria for determining whether to issue a warning and the warning method may be determined as appropriate.

Next, the operation of this embodiment will be explained by taking as an example the case where the first, third, fourth, and second cylinders misfire successively as shown in FIG. In this example, it is assumed that the first cylinder first misfires after being normally ignited. First, when the N signal is output at the time point W1 when the third cylinder should be ignited and the interrupt routine shown in FIG. Once the determination is made, steps 53 and 5
Proceed to step 4. Next, when the crankshaft rotates by 180° CA and the interrupt routine shown in FIG. 2 is executed again at time point W2, the control starts from step 51 because the determination start flag is set to 1. Proceed to step 55. In this example, since the next third cylinder has also misfired, control jumps to step 58 and ends the interrupt processing. Similarly, the 4th cylinder and 2nd cylinder also misfired, so at time W3,
Even when the interrupt routine shown in FIG. 2 is executed at W4, the control proceeds in the order of steps 51→55→return. Note that since the next first cylinder is ignited normally, when the interrupt routine shown in FIG. 2 is executed at time W5, the control proceeds from step 51 to step 55, where the output rotational speed increases. It is determined that the change has occurred, and the process proceeds to step 56. Then, in step 56, it is determined that misfires occur continuously from the first cylinder that misfired to the immediately preceding second cylinder, and in step 57, a state is set in which continuous misfire determination can be started again. Ru. As the above operations are repeated, the number of misfires counted increases depending on the misfire situation. When the misfire rate exceeds a certain level, a warning to the effect that there is an abnormality will be issued when subroutine 58 is executed.

Note that the method for determining that a misfire has occurred from a normal ignition state is not limited to that of the embodiment described above; Various modifications can be made without departing from the spirit of the present invention, such as using the difference between the output rotation speed and the output rotation speed as the misfire determination parameter.

[0015]

Effects of the Invention As described in detail above, the present invention improves the change in output rotational speed caused by the first misfire, which is easy to detect, and the change in output rotational speed caused by normal ignition after successive misfires, which is also easy to detect. Based on this, the first cylinder that caused continuous misfires and the cylinder that subsequently returned to normal ignition are identified, and all cylinders in between are presumed to have misfired, making it possible to accurately determine continuous misfires that match the current situation. becomes possible. Therefore,
Appropriate misfire information can be obtained without using complicated and large-capacity arithmetic processing means.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart diagram schematically showing the control procedure of the embodiment.

[Fig. 3] Timing chart diagram showing the control mode of the same embodiment.

[Figure 4] Timing chart diagram for explaining conventional problems

[Explanation of symbols]

1...Internal combustion engine 2...Electronic control device 7...Crank angle reference position sensor 8...Electromagnetic pickup 9...Signal plate 10...Crankshaft

Claims (1)

[Claims] Claims: 1. Based on a change in output rotational speed during a speed detection period from compression top dead center of a cylinder to compression top dead center of the next cylinder, it is determined whether or not the cylinder is misfiring; If it is determined that a cylinder has misfired,
Changes in the output rotational speed of each cylinder following the cylinder concerned are sequentially detected during each speed detection period, and after the misfire determination, the speed detection period in which the output rotational speed first shows a predetermined increasing trend is determined, and the speed detection period is determined. 1. A misfire detection method for an internal combustion engine, characterized in that all cylinders from the cylinder immediately before a normally ignited cylinder corresponding to the cylinder to that cylinder are determined to be misfiring.