JPH04134165A - Knock detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To remove a magnetic noise period due to ignition from a knock detection period without fail as well as to prevent any wrong detection of engine knocking by installing a reset signal control part which determines the release timing of a reset signal for an interface circuit on the basis of a specified crank angle and ignition timing. CONSTITUTION:An interface circuit 20 inserted into an interval between a knock sensor 1 and an analog-to-digital converter 3 is composed of a peak hold circuit 26 by way of example. A reset signal R' to this peak hold circuit 26 is generated out of an engine control unit 40 in synchronization with rotation of an internal combustion engine, and it is formed from a pulse, rising up at a reference position to each cylinder and being released, namely, falling down at another reference position. Accordingly, the engine control unit 40 is provided with at least a reset signal control part 46 which outputs a crank angle signal Q conformed to a turning position of each cylinder and an ignition signal F. In brief, this reset signal control part 46 makes the reset signal R' rise up and resets the peak hold circuit 26 at a reference position when a vibration level Vp at the reference position of a crank angle is made into sampling.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for detecting knock in an internal combustion engine such as an automobile gasoline engine, and particularly relates to a knock detection device for an internal combustion engine that improves the reliability of knock detection. It is something.

[Prior Art] Generally, an internal combustion engine such as an automobile gasoline engine is driven by a plurality of cylinders, and it is necessary to combust the air-fuel mixture compressed in each cylinder at an optimal ignition position. For this reason, a microcomputer (E
CU) to optimally control the ignition timing by the igniter and the order of fuel injection by the injector for each cylinder.

However, if the ignition position is controlled too far to the advanced side, vibrations called knocking will occur due to abnormal combustion, and there is a risk of damaging the cylinder. (For example, it is necessary to control the ignition position to the retarded side).

FIG. 4 is a block diagram showing a conventional knock detection device for an internal combustion engine.

In the figure, (1) is a knock sensor attached to one or each of the cylinders for driving the internal combustion engine, and is composed of a piezoelectric element for vibration detection.

(2) is a knock detection circuit that receives the output signal A of the knock sensor (1), and includes a filter (21) that passes a frequency specific to knocking (for example, 7 kHz), and a knock detection circuit that converts the output signal of the filter (21) into a predetermined range. A gate (22) that periodically passes through the gate (22), a BGL generator (23) that generates a background level BGL based on a signal obtained by averaging the output signal A' of the gate (22), and a gate (22).
a comparator (24) that compares the output signal ^' of 2) with a background level BGL and turns on the output signal when the output signal ^' exceeds the background level BGL;
An integrator (25) that integrates the output signal of the comparator (24) is provided. (3) is an AD converter that converts the output signal of the integrator (25) into a digital signal (2).

(4) retards the ignition position of each cylinder based on the output signal ■ of the AD converter (3), and controls the gate (22).
A microcomputer (hereinafter, E
CU), and the output signal V of the AD converter (3),
The engine includes a retard reflection processing unit (45) that generates a retard control angle θ1 for retarding the cylinder ignition position based on the ignition position of the cylinder.

Next, the operation of the conventional knock detection device for an internal combustion engine shown in FIG. 4 will be described with reference to the waveform diagram in FIG. 5.

Normally, each cylinder is ignited on the advance side from a position (B5°) about 5° before TDC (Top Dead Center - 0°), and the explosion of the mixture occurs at a crank angle of about 10” to 60° past TDC. Since this occurs near the angular position (A10° to A60°), knocking due to abnormal combustion also occurs at this explosion timing.

Therefore, when cylinder vibration noise (especially knock) occurs, the output signal A of the knock sensor (1) has a periodic and large-amplitude waveform as shown in FIG.

E CU (4) outputs a mask signal M that is inverted every predetermined period to the gate (22) so that the knock detection circuit (2) can efficiently receive the output signal A.

For example, this mask signal M is set to rise at about B75° and fall at about B5° for the cylinder to be detected, and has a level r) (gauge when J) (2
2) is prohibited. Also, a reset signal R is output to the integrator (25) at predetermined intervals.
The output timing coincides with the rise of the mask signal M.

The filter (21) in the knock detection circuit (2) passes the frequency component at the time of knock occurrence, and the gate (22) passes the output signal A only during the period when the mask signal M is at rl, . The BGL generator (23) is connected to the gate (22)
The background included in the output signal A' is determined based on the output signal A', and a background level BGL is generated as a reference for knock detection.

The comparator (24) determines that the output signal A' is at the knock occurrence level when it exceeds the background level BGL, and sets the output signal to the rH level. Integrator (
25) integrates the output signal of the comparator (24) every time it is reset by the reset signal R, and the AD converter (3) converts the output signal of the integrator (25) into digital integral values V, l. Convert and input to ECU'(4>).

E CU (4) takes in the AD-converted integral value VR for each cylinder ignition, generates a retard control angle θ8 based on this, and retards the ignition position in a direction that suppresses knocking. At this time, the retard reflection processing unit (45) cumulatively adds the current retard amount Δθ to the previous retard control angle θS to generate the current retard control angle θ8. Therefore, the current retard control angle θ4 is expressed as θ,=θS+Δθ, . . .■. Also, in formula (2), the current retard amount Δθ8 is expressed as ΔθR=VRXL where L: reflection rate.

By the way, as mentioned above, the ignition timing of each cylinder of the internal combustion engine is normally advanced from the crank angle B5', but when the engine speed is low, it is controlled to be retarded from B56. Sometimes. If the ignition timing is controlled to be retarded than B5°, the ignition timing will be included in the knock detection period from crank angle B5° to the next B75°, and electromagnetic noise due to discharge between the spark plug electrodes will be output. It is superimposed on signals A and 8'. Therefore, knocking is erroneously detected even though no knocking has occurred, resulting in unnecessary retarding control and reducing the efficiency of the internal combustion engine.

[Problems to be Solved by the Invention] As described above, the conventional knock detection device for an internal combustion engine sets the knock detection period based only on a predetermined crank angle, so the ignition timing is controlled to the retarded side. In some cases, there was a problem in that knocking was erroneously detected due to the superposition of electromagnetic noise.

This invention was made to solve the above-mentioned problems, and provides a highly reliable knock detection device for internal combustion engines that does not falsely detect knock even when the ignition timing is controlled to the retarded side. The purpose is to obtain.

[Means for Solving the Problems] A knock detection device for an internal combustion engine according to the present invention is provided with a reset signal control section that determines the fall of a reset signal for an interface circuit based on a predetermined crank angle and ignition timing. be.

[Operation] In this invention, if the ignition has been completed at a predetermined crank angle, the reset signal is lowered at the predetermined crank angle, and if the ignition has not been completed, the reset signal is output a predetermined time after the actual end of the ignition. stand down. This reliably removes the electromagnetic noise period due to ignition from the knock detection period (sampling period).

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram showing one embodiment of the present invention.
), (3) and (45) are the same as described above.

(20) is an interface circuit inserted between the knock sensor (1) and the AD converter (3), and is composed of, for example, a peak hold circuit (26).

The reset signal R' for the peak hold circuit (26) is generated from the ECU (40) in synchronization with the rotation of the internal combustion engine, and for example, as shown in FIG. ) and falls at another reference position (B5°). Therefore, the peak hold circuit (26) generates a peak level at the reference position B75° of each cylinder, and transmits this peak level to the vibration level Vp through the AD converter as the vibration level Vp.
).

The E CU (40) averages the vibration level Vp obtained for each cylinder ignition to obtain a first background level (
First filter (41) that generates BGLI (first average value)
and a second filter (42) that averages the first average value BGLI every predetermined period to generate a second background level (second average value) BCl2, and a second average value BGL2.
A calculation unit (43) that generates a threshold for knock discrimination based on the vibration level ■2 is the threshold V? ) A comparison unit (44) that outputs a knock discrimination signal Vk when the knock discrimination signal Vk is exceeded, and a retard reflection process that generates a retard control angle θ8 for retarding the ignition position of the cylinder based on the knock discrimination signal Vk. (45), and a reset signal control section (46) that outputs a reset signal R' in response to a crank angle signal Q and an ignition signal F corresponding to the rotational position of each cylinder.

Incidentally, the crank angle signal Q input to the reset signal control section (46) is obtained from a known crank angle sensor provided on the crankshaft or camshaft. Also, the ignition signal F is an ECtJ that cuts off the coil current flowing through the ignition coil.
(40) from the ignition control section (not shown).

Next, the operation of the knock detection device for an internal combustion engine according to the present invention shown in FIG. 1 will be described with reference to the waveform diagram in FIG. 2.

First, the knock sensor (1) detects the vibration of the cylinder for driving the internal combustion engine, as described above, and generates an output signal A for detecting a knock state. Further, the ECU (40>) converts the peak level of the output signal A of the knock sensor (1) into AD and captures it every time a cylinder is ignited.

That is, the peak hold circuit (26) is connected to the knock sensor (
The peak level of the output signal A of 1) is held, and this peak level is converted into a digital vibration level Vp by the AD converter (3) and then input to the ECU (40).

When the vibration level Vp at the crank angle reference position 1i B 75° is sampled, the reset signal control section (46) in the E CU (40) raises the reset signal R' as shown in Fig. 2. , the peak hold circuit (26) is reset at the reference position B75° (actually slightly after B75°).

The peak hold circuit 1 (26) continues to be reset while the reset signal R' is on, and starts operating from the falling edge of the reset signal R' (for example, at B5°). Therefore, the E CU (40) repeats the above B75° interrupt processing routine every time the vibration level Vp at the reference position 75° is obtained.

As shown in Fig. 2, the vibration level Vp obtained for each cylinder at each reference position B of 75° is determined by the output signal A of the knock sensor (1).
varies from sampling cycle to sampling cycle.

At this time, since the output signal A is reset on the advance side of the predetermined crank angle B5°, cylinder valve noise and electromagnetic noise during normal ignition are not superimposed.

Furthermore, although fluctuations in the output signal A include knocks and noises other than knocks, considering changes in the vibration level Vp over time, etc., in order to reliably detect knocks, it is necessary to follow the vibration level Vp to some extent. We need to find the background level. However, when the vibration level Vp suddenly increases and the background level follows the vibration level Vp, the threshold (2) and distortion rapidly increase and knock detection cannot be performed accurately.

Therefore, the first filter (41) in E CU (40)
averages the vibration level Vp based on a predetermined constant N1, and BGL1=BGLI low(N+-1>/N, +Vρ/N(
However, B is the L1 army, and the first average value BGL1 is generated from the previous average value). This first average value B
Ll is shifted to a value that reflects the current vibration level Vp with respect to the first average value BGLI up to the previous time, and is rewritten each time.However, if a knock is determined, the vibration at that time In order to reduce the reflection rate of the level Vp with respect to the first average value BGLI, the value of N is changed to a large value.

Further, in the second filter (42), timer interrupt processing is performed every predetermined period, and further averaging processing is performed on the first average value B obtained by the first filter (41) and Ll. Then, the second average value BGL2 is calculated as BGL2=BCl2
House (Nz-1>/N2+BGL1/N 2 However, BCl
2": Previous second average value N2: Obtained from the averaging processing constant. This second average value BGL2 is the current first average value BGLI with respect to the second average value BGL2K up to the previous time.
is shifted to the value that reflects it, and is rewritten each time. Through this averaging process, the second average value BGL2 becomes a stable value that does not significantly contribute to fluctuations in the vibration level Vp. Note that each constant N1 and N2 can be set arbitrarily.

Next, in the B75°75° processing routine, the calculation section (4
3) amplifies L2 to the second average value B and offsets V
ov is added to finally determine the threshold V? used to determine knocking. o, V Tl1=: K −BGL2+ Vo=However, K
: Determined from the amplification coefficient. At this time, since L2 has been sufficiently smoothed to the second average value B, the threshold V? M has a highly reliable value with fluctuations suppressed from cycle to cycle.

Next, in order to compare the vibration level Vp and the threshold level VB, the comparison unit (44) serving as a knock detection means calculates the difference Vk between the two from Vk=Vp-Vya, and determines whether the difference Vk is positive or not. do. Then, when the vibration level Vp exceeds the threshold value ■T, I, that is, when Vk>O, this is outputted as a knock discrimination signal Vk indicating the occurrence of knocking.

When the knock discrimination signal Vk is obtained, the delay angle reflection processing unit (
45) is the retardation amount Δθ8 necessary for knock suppression, Δθ*
=(Vk/VtM)XL' However, L': Calculated from the reflection rate. At this time, the retard amount Δθ is determined based on the ratio between the knock discrimination signal Vk and the threshold level V T N.
8 is calculated, an appropriate retard amount Δθ8 can always be obtained even if the vibration level Vp itself changes over time.

Further, based on the retard amount Δθ8, the retard angle reflection processing unit (45) calculates the retard angle control angle θ8 for retarding the ignition position in the knock suppression direction using the above-mentioned formula 0 as θ8=θ88+Δ
θR However, θ-: Determined from the previous retard control angle.

In this way, the ignition position of the cylinder to be controlled is corrected to the retarded side by the retard control angle θ8, so knocking no longer occurs.

On the other hand, if the comparator (44) determines that Vk<O, the knock discrimination signal Vk is not output, so the retard amount Δθ8 becomes 0, and the retard control angle θ8 remains at the previous value.

Next, the fall control operation of the reset signal R' by the reset signal control section (46) will be explained with reference to the flowchart shown in FIG.

First, based on the crank angle signal Q and the ignition signal F, it is determined whether ignition has ended at a predetermined crank angle B5 (step Sl).

If the ignition ends on the advance side of B5°, then B5
If the ignition signal F is retarded than B5° and ignition has not been completed, the reset signal R' is lowered at
00 microseconds), the reset signal R' is lowered (step S3).

In this way, when the ignition timing is controlled to be retarded than the predetermined crank angle B5°, by canceling the reset signal R' after a predetermined time τ after confirmation of completion of ignition,
Superimposition of electromagnetic noise at ignition timing can be prevented.

That is, as shown by the dashed line in FIG. 2, the vibration level Vp during the retard control of the ignition signal F rises after the generation of the electromagnetic noise A ends. Therefore, erroneous knock detection can be prevented, and knock detection can be performed with high reliability and accuracy.

In the above embodiment, the fall of the reset signal R' is delayed by a predetermined time τ in the reset signal control section (46), but the delay is made by hardware on the input side of the peak hold circuit (26). You can.

Further, although the interface circuit (20) for generating the vibration level Vp is configured by the peak hold circuit (26), the same effect can be achieved even if it is configured by an integrator.

Further, although the comparator (44) outputs the difference Vk between the vibration level Vp and the threshold VTH as a knock discrimination signal, the vibration level Vp is not equal to the threshold Vy.
When M is exceeded, the comparison section (44) simply detects rH.

A level output signal may be generated.

Furthermore, it goes without saying that the predetermined time τ is not limited to 100 μsec, but can be set to any time as needed.Furthermore, although the case where the ignition timing is retarded is shown, other control parameters may be set to the knock suppression side. It is also possible to perform delay angle control.

[Effects of the Invention] As described above, according to the present invention, a reset signal control unit is provided which determines the fall of a reset signal to the interface circuit based on a predetermined crank angle and ignition timing, and normally the reset signal is output at a predetermined crank angle. The electromagnetic noise period caused by ignition is reliably removed from the knock detection period by lowering the reset signal after a predetermined time after ignition ends if ignition has not finished at a predetermined crank angle. This has the effect of providing a highly reliable knock detection device for an internal combustion engine that does not erroneously detect knock even when controlled to the retarded side.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a knock detection device for an internal combustion engine according to the present invention, FIG. 2 is a waveform diagram showing the operation of the device shown in FIG. 1, and FIG. 3 is an embodiment of the invention. FIG. 4 is a block diagram showing a conventional knock detection device for an internal combustion engine, and FIG. 5 is a waveform diagram showing the operation of the conventional device shown in FIG. 1) Knock sensor (20) Interface circuit (43) Calculation section <44) Comparison section (46) Reset signal control section A Knock sensor output signal Vp...Vibration level V 7M...Threshold Vk...Knock discrimination signal F...Ignition signal Q.
...Crank angle signal R'...Reset signal τ...
・Predetermined time Note that in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] A knock sensor that detects vibrations of an internal combustion engine, an interface circuit that generates a vibration level based on an output signal of the knock sensor, and a calculation means that generates a threshold for knock discrimination based on the vibration level. and a comparison means for outputting a knock determination signal when the vibration level exceeds the threshold, the knock detection device for an internal combustion engine comprising: a comparison means for outputting a knock determination signal when the vibration level exceeds the threshold; A reset signal control unit is provided to determine a fall of the reset signal, and if ignition has ended at the predetermined crank angle, the reset signal is reduced at the predetermined crank angle, and ignition is stopped at the predetermined crank angle. A knock detection device for an internal combustion engine, characterized in that, if the ignition has not ended, the reset signal falls after a predetermined period of time after the end of ignition.