JPH0270981A - Ignition timing control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve precision of trouble detecting ability by a method wherein, in an engine running region in which a noise level exceeds a knock sensor trouble threshold, inversion from a trouble decided by a trouble deciding means to a normal discriminating result is prohibited. CONSTITUTION:It is discriminated by a knock sensor trouble deciding means that through comparison of an output signal from a knock sensor with a given knock sensor trouble threshold, when a knock sensor output signal exceeds the threshold, the knock sensor is normal and reversely, when it is below the threshold, the knock sensor is in a failure in operation state. In an engine running region where the noise level of the output signal from the knock sensor exceeds knock sensor trouble decision threshold, inversion of a decision result from failure in operation decided by the knock sensor trouble deciding means to normality is prohibited by a prohibiting means. This constitution enables decision of failure in operation of the knock sensor with high precision throughout a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ignition timing control device for an internal combustion engine.

[Conventional technology]

The ignition timing of an internal combustion engine is set in such a way as to provide the best efficiency for the engine's operating conditions. In general, MB T (Minimum
um advance for Be5t Torqu
It is desirable to set the ignition timing so that it approaches e).

However, even if the ignition timing is set close to the above-mentioned MBT, or the ignition timing is set so that knocking does not occur under certain conditions, due to internal combustion engine differences, intake temperature, humidity, etc., the ignition timing may vary under different operating conditions. This may cause knocking.

Therefore, by attaching a sensor to the internal combustion engine to detect knocking, and controlling the ignition timing to retard the ignition timing when knocking occurs, and advance the ignition timing when knocking does not occur, the ignition timing is set to the closest value to the MBT. (hereinafter referred to as knock control).If the sensor that detects knocking or knocking is malfunctioning and cannot detect knocking normally, the retard control will not be performed and the reverse will be applied even though knocking has occurred. This will lead to the destruction of the internal combustion engine. Conventionally, as a countermeasure against this problem, when the knock sensor fails, knock control is prohibited and the ignition timing is set to be retarded than the MBT to prevent overadvance. but,
The knock sensor failure detection method uses a value between the minimum output value when the knock sensor is normal and the maximum output value when the knock sensor fails as the failure determination threshold. noise), etc.
In a region where the output is larger when the knock sensor is malfunctioning than when it is normal, the knock sensor is determined to be normal despite the malfunction. In addition, in Japanese Patent Publication No. 63-3557, the knock sensor signal itself becomes small at low speeds, making it difficult to determine whether it is normal or abnormal, so failure detection is prohibited below that rotation speed.
There are known devices that detect failures at higher rotation speeds.

(Problem to be solved by the invention) However, if the region where high noise occurs is above the steady-state operating speed, it is necessary to prohibit failure detection below the steady-state operating speed, including this high-noise region. Therefore, there is a problem that the knock sensor failure detection range becomes narrow and the failure detectability is poor.In addition, the area where high noise occurs is not only caused by the rotation speed, but is also related to the load on the internal combustion engine. There are cases.

The present invention is intended to solve the above problems, and aims to improve the accuracy of fault detectability.

[Means to solve the problem]

Therefore, the present invention has a knock sensor for detecting vibrations caused by knocking of an internal combustion engine, a knock detection means for detecting the presence or absence of knock based on the output from the knock sensor, and a knock detection means for detecting the presence or absence of knock by the knock detection means. ignition timing control means for controlling the ignition timing according to the detection result of the knock sensor, and comparing the output signal of the knock sensor with a predetermined knock sensor failure determination threshold; a knock sensor failure determining means for determining that the knock sensor is normal when the knock sensor is large and conversely determining that the knock sensor is malfunctioning when the knock sensor is small; The present invention provides an ignition timing control device for an internal combustion engine, which includes a prohibition means for prohibiting the reversal of the determination result from failure to normal by the failure determination means.

[Effect]

As a result, the output signal of the knock sensor is compared with a predetermined knock sensor failure judgment threshold, and if the knock sensor output signal is larger than this threshold, the knock sensor is normal, and if it is smaller than this threshold, the knock sensor is considered to be malfunctioning. Discrimination is made by a discriminating means.

Furthermore, in an engine operating region where the noise level of the output signal of the knock sensor is higher than the knock sensor failure determination threshold, the prohibition means prohibits the knock sensor failure determination means from reversing the determination result from failure to normal.

〔Example〕

The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 2 shows a block diagram of the knock control system used in the present invention. A knock sensor 1 attached to an internal combustion engine detects vibrations of the internal combustion engine as a signal. The knock detection circuit 2 is provided with a bandpass filter (B, P, F) that detects only the knocking frequency of the signal sent from the knock sensor 1, and amplifies the knocking frequency and non-amplifies frequencies other than the knocking frequency. have characteristics.

Also, by averaging the signals obtained at B, P, and F,
Create a knock detection level and compare this knock detection level with the knock sensor signals passed through B, P, and F.
Determine whether or not knocking has occurred. The engine state detection unit 3 detects the state of the internal combustion engine, such as engine speed and intake air amount. The ignition timing calculation circuit 4 advances or retards the ignition timing for knock control based on the signals obtained from the knock detection circuit 2 and the engine condition detection section 3, and is composed of a microcomputer. Reference numeral 5 denotes an igniter that performs an ignition operation in response to an ignition signal calculated by the ignition timing calculation circuit 4.

FIG. 3 shows the influence of sensor signals after B, P, and F due to noise that generates frequency noise proportional to engine speed. The solid line (E) is the minimum sensor output value when the knock sensor is normal, the broken line CF) is the maximum sensor output value when the knock sensor is malfunctioning, and the - dotted chain line (G) is (
Knock sensor failure determination threshold V located between E) and CF).

shows. In the figure, the engine speed range N8 to NIl (3
000 to 3500 rpm), for example, alternator ripple noise generates noise in the same band as the knock frequency, and the noise is amplified at B, P, and F, so in that region, CF) has a higher level value than (E). becomes. Now, the knock sensor 1 is disconnected and the engine rotation range is below Ns (for example, 3000 rpm) or Nm
(for example, 3500 rpm) or more, if the knock sensor output after B, P, and F is below (G), the knock sensor 1
is determined to be in a failure state. Thereafter, when the engine speed falls between N and N, the knock sensor output exceeds the knock sensor failure determination threshold value Vr (G) despite being in a failure state. Therefore, in this region, reversal of the result from abnormality determination to normality determination of the knock sensor 1 is prohibited, and the previously determined result (normal or abnormal) is always maintained. Thereafter, when the engine speed is N or less or N3 or more, the prohibition of reversing the result of the knock sensor 1 from abnormality determination to normality determination is canceled. In addition, even though the knock sensor 1 is normal due to some factor, the output of the knock sensor may be lower than the knock sensor failure determination threshold value vf.
If it becomes smaller, it is determined that there is a failure, and then it returns to normal, the engine speed will be N.

After confirming that the knock sensor signal has a higher output than the knock sensor failure determination threshold (2) in the range below or N or above, the failure determination is canceled.

FIG. 4 is a flowchart for carrying out the above-mentioned operation by the microcomputer constituting the ignition timing calculation circuit 4. As shown in FIG. Processing is started by an interrupt, such as a time interrupt or an angle interrupt, at the timing when knocking ends. First, in step 100, a predetermined failure determination threshold value ■ is determined according to the engine speed.

After calculating, in step 101, it is determined whether the knock determination level, which is one of the knock sensor outputs after B, P, and F, is a higher output than the failure determination threshold ■, and the result is NO. If so, the process proceeds to step 103, where it is determined that the knock sensor 1 is malfunctioning, and a malfunction flag is set. Step 1
If it is determined in step 01 that the knock determination level is higher than the failure determination threshold ■, the process proceeds to step 102;
Determine engine speed. Engine speed is N8~
If it is between N+1 (for example, 3000 to 3500 rp+a), the noise level is high and subsequent processing is not performed. If the determination in step 102 is negative, it is in a normal state, and the process proceeds to step 104 where it is determined that the knock sensor I is normal and the failure flag is reset. And when the failure flag is set,
As is well known, knock control based on the knock determination signal from the knock detection circuit 2 is prohibited, the ignition timing is set to the retarded side than the MBT, and the knock control is executed when the failure flag is reset.

As described above, by setting the region in which reversal from knock sensor failure determination to normal determination is prohibited only to the high noise generation rotation speed region, failure determination can be performed with high accuracy over a wide range, and the normal state can be returned after knock sensor failure determination. By canceling the abnormality determination, the output of the internal combustion engine can be improved.

B and P according to the engine load condition on the internal combustion engine at a predetermined rotation speed as another embodiment of the present invention.

The change in the knock sensor signal output after F is shown in FIG. 5, and will be explained using this. The solid line (H) is the minimum sensor output value when the knock sensor is normal, the broken line (1) is the maximum sensor output value when the knock sensor is malfunctioning, and the -dotted chain line (J) is the minimum value of the sensor output when the knock sensor is malfunctioning.
), the knock sensor failure determination threshold value V is located between
shows. In the figure, in the region of loads P, ~PIl, for example,
When the engine load reaches a predetermined value, noise in the same band as the knock frequency is generated due to the noise of valves that operate on and off, and this noise is amplified at B, P, and F, and in this region (1) becomes (H). be at a higher level.

Now, if the knock sensor 1 is in a disconnected state and the engine load range is below P or above 28, and the knock sensor output after B, P, and F is below (J), it is a knock sensor failure state. It is determined that Thereafter, when the engine load falls between P and -P, the knock sensor output exceeds the knock sensor failure determination threshold value vf despite being in a failure state. Therefore, in this region, the determination of whether the knock sensor 1 is normal or abnormal is not performed, the previous determination result is always maintained, and thereafter, the determination of whether the knock sensor 1 is normal or abnormal is performed again in a region where the engine load is below P3 or above P. In addition, when the knock sensor returns to normal after a knock sensor failure determination, the knock sensor output is higher than the knock sensor failure determination threshold ■ outside the high noise generation area, and then the failure determination is made. is released and determined to be normal.

Further, although not shown in the figure, further effects can be obtained by determining two-dimensional regions of engine speed and load.

〔Effect of the invention〕

As described above, in the present invention, in the engine operating range where the noise level of the knock sensor output signal is higher than the knock sensor failure determination threshold, the knock sensor failure determination means is prohibited from reversing the determination result from failure to normal. Therefore, there is an excellent effect that failure determination of the knock sensor can be performed with high precision over a wide range.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to the claims of the present invention, Fig. 2 is a block diagram showing an embodiment of the device of the present invention, Fig. 3 is a rotation speed-sensor output characteristic diagram, and Fig. 4 is a diagram showing the second embodiment of the device of the present invention. FIG. 5 is a flowchart for explaining the operation of the illustrated device, and FIG. 5 is a load-sensor output characteristic diagram. 1... Knock sensor, 2... Knock detection circuit, 3.
...Engine condition detection section, 4...Ignition timing calculation circuit.

Claims (1)

[Claims] a knock sensor that detects vibrations caused by knocking in an internal combustion engine; a knock detection means that detects the presence or absence of knock based on the output from the knock sensor; and an ignition that controls ignition timing in accordance with the detection result of the presence or absence of knock by the knock detection means. The timing control means compares the output signal of the knock sensor with a predetermined knock sensor failure determination threshold, and determines that the knock sensor is normal if the knock sensor output signal is larger than this threshold; a knock sensor failure determination means for determining that the knock sensor is malfunctioning; and a knock sensor failure determination means for determining a determination result from failure to normal by the knock sensor failure determination means in an engine operating region where the noise level of the output signal of the knock sensor is higher than the threshold value. An ignition timing control device for an internal combustion engine, comprising: prohibition means for prohibiting reversal.