JP2000008940A - Fail detection device for knock sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a fail for a knock sensor accurately in an entire rotation area. SOLUTION: A high frequency voltage is impressed to a knock sensor output consisting of a piezoelectric element through a condensor 34 or the reactance circuit of a coil and also the knock sensor output voltage is detected and if it is not at 30% to 70% of the high frequency voltage, it is judged to be failure such as disconnection, damage to the piezoelectric element and grounding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a failure detection device for a knock sensor.

[0002]

2. Description of the Related Art An internal combustion engine is generally provided with a knock sensor composed of a piezoelectric element, and outputs a signal in accordance with the vibration of the internal combustion engine. This output is compared with a knock determination level generated from background noise, and it is detected whether or not knock (abnormal combustion) has occurred in the engine combustion chamber according to the comparison result.

As a fail detection device for such a knock sensor, a technique described in Japanese Patent Application Laid-Open No. 56-83568 is known. In this prior art, the output of a vibration sensor (knock sensor) for detecting vibration of the engine is peak-held, and when the held value is not within a predetermined range, it is detected as a knock sensor failure.

[0004]

However, when the engine speed is low, the vibration is small. Therefore, the detection method of the prior art is not always satisfactory in the accuracy in the low rotation range.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned inconvenience and to provide a knock sensor fail detecting device capable of accurately detecting a knock sensor fail over the entire rotation range of the engine. .

[0006]

According to a first aspect of the present invention, there is provided a knock detection device for a knock sensor which comprises a piezoelectric element and outputs a signal corresponding to vibration of an internal combustion engine. A high-frequency oscillation circuit that applies a high-frequency voltage to the knock sensor output via a reactance circuit, an output voltage detection circuit that detects the output voltage of the knock sensor, and compares the detected output voltage of the knock sensor with the high-frequency voltage. And a failure detecting means for detecting a failure of the knock sensor based on the comparison result.

As a result, the failure of the knock sensor can be accurately detected throughout the entire rotation range of the engine.

According to a second aspect of the present invention, the high-frequency voltage has a frequency higher than a knock frequency. Thus, in addition to the above-described operation and effect, the failure of the knock sensor can be detected without affecting the knock detection.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram generally showing a failure detecting device for a knock sensor according to the present invention.

In FIG. 1, a knock sensor 10 made of a piezoelectric element such as a ceramic, which is disposed on a cylinder head (not shown) of an internal combustion engine (not shown, hereinafter referred to as "engine"), responds to vibration of the engine. Output a signal.

The output of the knock sensor 10 is sent to a buffer (amplifier, Amp) 14 of an electronic control unit (hereinafter referred to as "ECU") 12. The buffer 14 outputs a sensor output of about 5 V as shown by a solid line in FIG. Amplify so that the inversion is repeated around.

The output of the buffer 14 is input to a band-pass filter (BPF) 16,
Is a predetermined frequency (knock frequency. For example, 5 kHz
pass only from z to 15 kHz).

The output of the band-pass filter 16 is
2 and the output of the comparator 22 is input to the microcomputer 24. The microcomputer 24
Input circuit 24a, CPU 24b, storage means (memory) 2
4c and an output circuit 24d.

The comparator 22 compares the reference value supplied from the CPU 24b via the D / A conversion circuit 26 with the sensor output supplied through the band pass filter 16, and sends the comparison result to the microcomputer 24. .

That is, as shown in FIG. 3, the CPU 24b
A value (noise level) near the peak value of the sensor output (shown as VNOISE in the figure) indicating the background value of the engine vibration in a crank angle range (noise gate) not in a combustion state is detected and amplified (GAMP times). , And a knock determination level, which is supplied to the comparator 22 through the D / A conversion circuit 26.

The comparator 22 outputs a pulse every time the sensor output exceeds the knock determination level. The pulse output is input to the microcomputer 24, and the CPU 24b
When a pulse is output in a crank angle range (knock gate) in which the engine is in a combustion state, it is determined that knock has occurred, and the ignition timing is retarded by a predetermined amount.

Next, the failure detection of the knock sensor will be described.

Since knock sensor 10 is arranged on the cylinder head (not shown) of the engine and ECU 12 is arranged near the dashboard (not shown) of the driver's seat, knock sensor 10 and ECU 12 have a signal line. Although the connection is made at 30, the knock detection described above becomes impossible if a knock sensor failure occurs such that the signal line is disconnected or the sensor piezoelectric element element is damaged.

Therefore, the fail detection device for a knock sensor according to the present invention includes a high-frequency oscillation circuit 32 and a capacitor (reactance circuit, more specifically, a capacitive reactance circuit) 34, and a knock at the connection point 36 via the capacitor 34. A high-frequency voltage is applied to the sensor output.

As a result, as shown by a broken line in FIG. 3, a harmonic is superimposed on the knock sensor output. The voltage at the connection point 36 is detected via a voltage detection circuit 38, and the detected value is sent to the microcomputer 24.

Here, the high-frequency voltage output from the high-frequency oscillation circuit 32 has a frequency higher than the knock frequency described above,
For example, it is set to 100 kHz. In other words, the configuration is such that the frequency of the voltage output by the high-frequency oscillation circuit 32 is in the cut-off frequency band of the band-pass filter 16 described above.

Further, the output voltage of the high-frequency oscillation circuit 32 is set to a value of about 1 V to 5 V. By setting the output frequency and voltage of the high-frequency oscillation circuit to the above ranges,
The influence on knock detection can be avoided and the circuit configuration can be simplified.

The piezoelectric element constituting the knock sensor 10 is as follows.
Since it has the same electrical properties as a capacitor,
If the capacitance component of the capacitor 34 is C1 and the capacitance component of the knock sensor 10 is C2, the high-frequency circuit of FIG. 1 can be rewritten as shown in FIG.

In FIG. 4, if the high-frequency oscillation circuit voltage is Vs and the output voltage of knock sensor 10 is V2, the value can be obtained as follows.

V2 = Vs · [(1 / 2πfC2) /
{(1 / 2πfC2) + (1 / 2πfC1)}]
[V]

Here, C1 = C2, that is, the capacitor 3
4 is set equal to the knock sensor capacitance component, V
The value of 2 can be determined as follows. V2 = Vs × (１ ／) [V]

In the above description, if the signal line 30 is broken or the knock sensor piezoelectric element component is damaged, the value of V2 is as follows. V2 = Vs [V] When the signal line 30 is short-circuited (ground fault), the following occurs. V2 = 0 [V]

Therefore, in the circuit of FIG. 1, the CPU 24b of the microcomputer 24 detects the voltage at the connection point 36, that is, V2, through the voltage detection circuit 38, and a predetermined range (for example, 30% to 70%) with respect to Vs. , It is possible to determine whether or not knock sensor 10 has failed (disconnection, breakage, ground fault) as described below.

V2 is between 30% and 70% of Vs. . . Knock sensor normal V2 is not 30% to 70% of Vs. . . Knock sensor failure

As described earlier, the knock sensor output decreases when the engine speed is low. However, in this embodiment, the knock sensor output is determined from the ratio of the sensor output to the high-frequency circuit voltage. The failure of the knock sensor 10 can be accurately detected throughout the entire rotation range without being affected by the rotation speed.

FIG. 5 is a circuit diagram similar to FIG. 1 showing a knock sensor fail detecting device according to a second embodiment of the present invention.

As shown, in the second embodiment, a coil (reactance circuit, more specifically, an inductive reactance circuit) 40 and a resistor r are used in place of the capacitor.
And an RL circuit composed of a coil L
A high-frequency voltage is applied to the knock sensor output via the resistor r. FIG. 6 shows an equivalent circuit thereof.

FIG. 6 shows that the output voltage V of knock sensor 10
2 can be obtained as follows.

V2 = Vs · [(1 / 2πfC2) /
{(1 / j2πfC2) + j2πfL + r}] [V]

Here, if 1 / (2πfC2) is set to be 2πfL, that is, if a resonance state is established,
The value of V2 can be determined as follows. V2 = Vs / (2πfC2 · r) [V]

In the above, if the value of r is appropriately set so that V2 is larger than Vs at normal time, for example, about twice, the signal line 30 is disconnected or the knock sensor piezoelectric element is disconnected. If the element components are damaged,
The value of V2 becomes V2 = Vs [V], and when the signal line 30 is short-circuited (ground fault), V2 becomes 0 [V].

Accordingly, the CPU 24b can determine whether or not the knock sensor 10 has failed (disconnection, breakage, ground fault) as described below.

V2 is higher than Vs. . . Knock sensor normal V2 is below Vs. . . . Knock sensor failure

The fact that the failure detection is not affected by the engine speed is the same in the second embodiment. Therefore, the failure of the knock sensor 10 can be accurately detected over the entire rotation range. .

In this embodiment, as described above, in the fail detecting device of the knock sensor 10 which is composed of a piezoelectric element and outputs a signal corresponding to the vibration of the internal combustion engine, a reactance circuit (capacitive reactance circuit (capacitive reactance circuit) A high-frequency oscillation circuit 32 for applying a high-frequency voltage Vs via an inductive reactance circuit (coil) 40), an output voltage detection circuit (voltage detection circuit 38) for detecting an output voltage of the knock sensor, and the detection The output voltage V2 of the knock sensor is converted to the high-frequency voltage V
s and a failure detecting means (CPU 24b of the microcomputer 24) for detecting a failure of the knock sensor based on the comparison result.

Further, the high-frequency voltage is configured to have a frequency (for example, 100 kHz) higher than a knock frequency (for example, 5 kHz to 15 kHz).

In the above description, it is desirable to set the frequency of the high-frequency oscillation circuit to the cut-off frequency of the band-pass filter 16 so as not to affect knock detection. However, if necessary, the cut-off frequency may be set to the pass frequency of the band-pass filter. good.

In the above description, a known capacitance detecting circuit may be provided in place of the voltage detecting circuit, the capacitance of the knock sensor may be detected, and when the value deviates from a normal value, a failure may be determined.

[0045]

According to the present invention, the failure of the knock sensor can be accurately detected throughout the entire rotation range of the engine.

According to the second aspect of the invention, in addition to the above-described functions and effects, the failure of the knock sensor can be detected without affecting the knock detection.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an overall failure detection device for a knock sensor according to the present invention.

FIG. 2 is a waveform diagram showing an output of a knock sensor in the device of FIG.

FIG. 3 is a time chart showing a knock detection operation of the apparatus of FIG. 1;

FIG. 4 is an equivalent circuit diagram of a high-frequency component of the device in FIG. 1;

FIG. 5 is a circuit diagram similar to FIG. 1, according to a second embodiment of the present invention.

6 is an equivalent circuit diagram of a high-frequency component of the device in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Knock sensor 12 ECU (Electronic control unit) 14 Buffer (amplifier; operating voltage applying means) 16 Band pass filter (BPF) 22 Comparator 24 Microcomputer 24b CPU 26 D / A conversion circuit 30 Signal line 32 High frequency oscillation circuit 34 Capacitor (Capacitive reactance circuit) 38 Voltage detection circuit (output voltage detection circuit) 40 Coil (inductive reactance circuit)

Claims (2)

[Claims] 1. A fail detecting device for a knock sensor, comprising a piezoelectric element and outputting a signal corresponding to vibration of an internal combustion engine, comprising: a. A high-frequency oscillation circuit for applying a high-frequency voltage to the knock sensor output via a reactance circuit, b. An output voltage detection circuit for detecting an output voltage of the knock sensor; and c. A fail detecting means for comparing the detected output voltage of the knock sensor with the high-frequency voltage and detecting a failure of the knock sensor based on a comparison result. 2. The fail detecting device for a knock sensor according to claim 1, wherein the high-frequency voltage has a frequency higher than a knock frequency.