JPH1144701A - Wheel speed measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a failure diagnosis by feeding a diagnostic signal to a waveform shaping circuit wave form shaping the output of a wheel speed sensor into a rectangular wave. SOLUTION: A microprocessor 15 monitors the wave form shaped output of a waveform shaping circuit 4 converting the input signal with the frequency proportional to the wheel speed into a rectangular wave, it feeds a diagnostic to the input end of the wave form shaping circuit 4 when the waveform shaped output is kept unchanged and intact, and it diagnoses the presence or absence of the failure of the waveform shaping circuit 4 based on the output response of the waveform shaping circuit 4. The microprocessor 15 feeds the diagnostic signal to the input end of the waveform shaping circuit 4 to diagnose the waveform shaping circuit 4, and it can accurately investigate on two causes including the stop of a vehicle and the failure of the waveform shaping circuit 4 imagined when the output of the waveform shaping circuit 4 is not changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wheel speed measuring device which supplies a diagnostic signal to a waveform shaping circuit for shaping the output of a wheel speed sensor into a rectangular wave so as to diagnose a failure.

[0002]

2. Description of the Related Art In an anti-lock brake control device for controlling a vehicle by suppressing wheel slip, a wheel speed sensor is usually provided for each wheel in order to monitor the behavior of four wheels. The conventional wheel speed measuring device 1 shown in FIG. 3 includes a wheel speed sensor 2 provided for each of four wheels, that is, a left front wheel and a right rear wheel.
It is connected to a wheel speed converter 5a in a microprocessor 5 via a cascade connection circuit of an interface circuit 3 and a waveform shaping circuit 4. The wheel speed sensor 2 magnetically detects the rotation of a gear coaxially fixed to the wheel, and its output is a sine wave having a frequency corresponding to the wheel speed. The output of the wheel speed sensor 2 is amplitude-limited to a signal of 0 to 5 V in the interface circuit 3, subjected to a predetermined band limiting process, and supplied to the waveform shaping circuit 4.

The waveform shaping circuit 4 compares and separates the input signal with a comparator having an offset power supply with a threshold voltage of 2.5 V, and outputs the signal to a wheel speed converter 5a in the microprocessor 5 as a wheel speed pulse composed of a rectangular wave signal. Supply. The wheel speed converter 5a has a built-in self-propelled counter that starts a clock counting operation triggered by a rising edge of a wheel speed pulse. The self-propelled counter counts between the edge trigger and the next edge trigger. The counted value is multiplied by the clock cycle to determine the cycle of the wheel speed pulse, and is converted into the number of wheel rotations per unit time.

[0004]

The above-mentioned conventional wheel speed measuring apparatus 1 is not a four-circuit independent type configuration in which the individual waveform shaping circuits 4 are individually packaged in an IC package, but is located at a diagonal position among the four wheels. The waveform shaping circuits 4 corresponding to the front and rear wheel speed sensors 2 are integrated into one package. This is based on a packaging design concept based on an empirical rule that the probability of simultaneous failure of a pair of similar packages is almost nonexistent. However, when compared to a four-package type, the circuit configuration is simplified and manufacturing is simplified. Effects such as cost reduction can be obtained. However, when a simple comparison is made with a waveform shaper in which four waveform shaping circuits 4 are housed in one package, it is also a fact that there is a problem that the manufacturing cost is high because the circuit scale is large.

On the other hand, four waveform shaping circuits 4 are connected to one IC
In the case where the integrated circuit is formed in a package, even if a signal of four channels, that is, all rotation speed pulse outputs of the four waveform shapers 4 disappear due to a failure of the IC circuit, at present, the vehicle is not operated. There is a problem that it cannot be distinguished from a situation where the output is not obtained from the wheel speed sensor 2 because the vehicle is stopped. That is, unless a proper identification method that can deal with such a problem is completed, the four waveform shaping circuits 4
However, there is a problem that it is difficult to form a four-circuit, one-package integrated circuit into one IC package. In addition, 4
If up to three of the waveform shaping circuits 4 have failed, the wheel speed pulse can be obtained as long as at least one of the circuits is operating normally, so that one normal circuit can determine the abnormality of the other circuit. . Therefore, an issue in realizing a four-circuit one-package depends on whether or not a system capable of discriminating a simultaneous failure and a stopped state of the four circuits can be constructed.

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problem. In particular, regarding a waveform shaper in which a plurality of waveform shapers are packaged in one package, it is determined whether the waveform shaper constituting the waveform shaper has completely failed. The purpose is to enable accurate diagnosis.

[0007]

In order to achieve the above object, the present invention provides a waveform shaping circuit for converting an input signal having a frequency proportional to wheel speed into a rectangular wave, and monitoring a waveform shaping output of the waveform shaping circuit. Supplying a diagnostic signal to the input terminal of the waveform shaping circuit when the waveform shaping output does not change and stops.
Diagnostic means for diagnosing the presence or absence of a failure in the waveform shaping circuit from the output response of the waveform shaping circuit.

Further, the waveform shaping circuit comprises a comparator circuit with an offset power supply, and the diagnosing means outputs a high-level diagnostic signal exceeding an output voltage of the offset power supply and an output voltage to an input terminal of the waveform shaping circuit. It is characterized by having a diagnostic signal generator for individually supplying a low-level diagnostic signal less than the low-level diagnostic signal.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of a wheel speed measuring device according to the present invention, and FIG. 2 is a flowchart for explaining a failure diagnosis operation of a waveform shaping circuit by the microprocessor shown in FIG.

The wheel speed measuring device 11 uses a waveform shaper 14 in which four waveform shaping circuits 4 are integrated into one package, and the waveform shaping circuit 4 constituting the waveform shaper 14 is completely destroyed. The diagnosis by the microprocessor 15 is made possible so that the diagnosis of whether or not it has been performed can be made accurately. Therefore, the difference in the circuit configuration from the conventional device is the existence of the waveform shaper 14 packaged in four circuits and one package, the input terminal of the specific waveform shaper 4 in the waveform shaper 14 and the output port of the microprocessor 15. However, the diagnostic operation by the microprocessor 15 according to the diagnostic software can be said to be an unprecedented great feature.

Output stage of wheel speed sensor 12 and waveform shaper 1
Interface circuit 13 interposed between input stage 4 and input stage 4
Comprises a limiter circuit 13a and a low-pass filter circuit 13b. The limiter circuit 13a connects a signal line extending from an output terminal of the wheel speed sensor 12 to a pair of clipping diodes D.
a, Db, which is connected to the power supply Vcc and the ground, and the forward voltage drop of the diodes Da, Db is Δ Δ
When Vf is set, the function of limiting the amplitude of the sinusoidal signal output from the wheel speed sensor 12 to a voltage range of 0-ΔVf to Vcc + ΔVf, that is, approximately 0-5 V here. The low-pass filtering circuit 13b is composed of a capacitor Ca and a resistor Ra connected in series to the signal line, and a capacitor Cb branched and connected to the signal line.
It works to limit the band to ２０20 kHz.

The waveform shaping circuit 4 constituting the waveform shaper 14
Here is a comparator 4a with an offset power supply,
The collector of the transistor Q, which is connected to the DC power supply Vcc by the resistor Rp, is connected to the wheel speed converter 15a in the microprocessor 15. The comparator 4a has an inverting input terminal connected to an offset power supply Ve via a resistor Rb, and has a non-inverting input terminal connected to an offset power supply Ve via a resistor Rc, and a feedback resistor Rd. 4a is connected to the output terminal. The output terminal of the comparator 4a is directly connected to the base of the transistor Q. The offset power supply Ve is for setting a threshold voltage for an input signal to be compared and separated by the comparator 4a, and here, Ve = Vcc / 2.

In the microprocessor 15, a diagnostic signal generator 15b is incorporated in addition to the four wheel speed converters 15a, and operates upon receiving a diagnostic command from a specific wheel speed converter 15a. The function of individually supplying a high-level diagnostic signal exceeding the output voltage of the offset power supply Ve and a low-level diagnostic signal less than the output voltage to the input terminal of the waveform shaping circuit 4 via the diagnostic resistor Rs. The microprocessor 15 monitors the waveform shaping output of the waveform shaping circuit 4 and issues a diagnostic command to the diagnostic signal generator 15b via the wheel speed converter 15a when the waveform shaping output does not change and stops. The operation is stipulated in the diagnostic program so that it is issued.

That is, the microprocessor 15 monitors the level change of the wheel speed pulse supplied from each waveform shaping circuit 4 to the wheel speed converter 15a, and when the wheel speed pulse shows no change, the waveform shaping circuit 4 Execute the fault diagnosis of. The output port of the diagnostic signal generator 15b is set to high impedance in the wheel speed measurement mode. However, in the diagnostic mode, a high-level diagnostic signal (5 V) exceeding the output voltage of the offset power supply Ve is output. A diagnostic signal of a low level (0 V) less than the output voltage is separately output. Here, assuming that the output voltage of the diagnostic signal generator 15b is Vs and the output voltage Vo of the comparator 4a is the applied voltage (RsVe + R) of the inverting input terminal of the comparator 4a.
bVs) / (Rs + Rb) and the applied voltage (RdVe + RcVo) / (Rd) of the non-inverting input terminal of the comparator 4a.
High / low of the output level of the comparator 4a is determined according to the magnitude relation of + Rc). Hereinafter, the diagnostic operation of the microprocessor 15 in the diagnostic mode will be described with reference to the flowchart shown in FIG.

First, in step (101) of FIG. 2, the output port of the diagnostic signal generator 15b is set to a high impedance state, and the output of the waveform shaping circuit 4, ie, the level of the wheel speed pulse, is set by the wheel speed converter 15a. Detect changes. When the waveform shaping circuit 4 is normal and the vehicle is running, 0 is output from the output terminal of the waveform shaping circuit 4.
A rectangular wave having a peak value of -5 V is output. Therefore,
In this case, since the wheel speed converter 15a detects a change in the output signal level of the waveform shaping circuit 4, the determination step (10)
In step (103) following 2), a normality determination is made.

On the other hand, in the judgment step (102),
If it is found that there is no change in the waveform shaping output of the waveform shaping circuit 4, there is a possibility that the vehicle is stopped or the waveform shaping circuit 4 is out of order.
At 04), a diagnostic signal of 0 V level is output from the diagnostic signal generator 15b. When a signal having a voltage lower than the threshold voltage is supplied in a normal state, the waveform shaping circuit 4 sets the resistances Rb, Rc, and Rc so that the output of the comparator 4a becomes high level and the collector output of the transistor Q becomes 0V.
The resistance value of Rd is set. Therefore, step (1)
If it is determined in step (105) following step 04) that the waveform shaping output is not 0 V, an abnormal determination is made immediately in step (106).

If the judgment in the judging step (105) is affirmative, in the following step (107), a diagnostic signal of 5 V is output from the diagnostic signal generator 15b. When a signal having a voltage exceeding the threshold voltage is supplied to the waveform shaping circuit 4 in a normal state, the output of the comparator 4a goes low and the collector output of the transistor Q becomes 5
The resistance values of the resistors Rb, Rc, Rd are set so as to be V. Therefore, if it is determined in step (108) following step (107) that the waveform shaping output is not 5 V, an abnormal determination is immediately made in step (109). However, if the judgment in the judgment step (108) is affirmative, a normal judgment is made in the following step (110), and further, in the final step (111), the output port of the diagnostic signal generator 15b is set to the high impedance state. Switch over and finish diagnostic work.

As described above, according to the wheel speed measuring device 11, the microprocessor 15 monitors the waveform shaping output of the waveform shaping circuit 4 for converting an input signal having a frequency proportional to the wheel speed into a rectangular wave, and performs waveform shaping. Since the diagnostic signal is supplied to the input terminal of the waveform shaping circuit 4 when the output does not change and stops, and the output response of the waveform shaping circuit 4 is used to diagnose the failure of the waveform shaping circuit 4, the waveform shaping circuit is used. Regarding the two causes of the stop of the vehicle or the failure of the waveform shaping circuit 4 assumed when the output of the waveform shaping circuit 4 does not change, a diagnostic signal is supplied to the input terminal of the waveform shaping circuit 4 to diagnose the waveform shaping circuit 4. You can find out exactly. Particularly, in a case where the waveform of the output of the wheel speed sensor 12 provided for each of the four wheels of the automobile is generated to generate a vehicle speed pulse, when the four waveform shaping circuits 4 are packaged in a single IC circuit, I
When a situation occurs in which all signals for four channels are not output due to a failure in the C circuit, it is possible to clearly identify a situation in which the vehicle is stopped and an output from the wheel speed sensor 12 cannot be obtained. Thus, the plurality of waveform shaping circuits 4 are housed in the same package to be integrated into a single IC, and the size of the circuit can be reduced by using a custom IC, and the manufacturing cost can be reduced.

The waveform shaping circuit 4 comprises a comparator circuit 4a with an offset power supply.
e, a diagnostic signal generator 15b for separately supplying a high-level diagnostic signal exceeding the output voltage and a low-level diagnostic signal less than the output voltage does not require a dedicated fault detection circuit. Is a specific waveform shaping circuit 4
, It is possible to diagnose a plurality of waveform shaping circuits 4 without complicating the circuit configuration, and it is possible to reliably detect the total anomaly of the plurality of waveform shaping circuits 4 or not. it can.

In the above embodiment, the wheel speed measuring device 11 applied to the anti-lock brake device has been described as an example. However, the wheel speed measuring device 11 may be applied to a traction control device, a four-wheel steering device, or the like. Can also.

[0021]

As described above, according to the present invention,
The diagnostic means monitors the waveform shaping output of the waveform shaping circuit that converts an input signal having a frequency proportional to the wheel speed into a rectangular wave, and outputs a diagnostic signal to the input end of the waveform shaping circuit when the waveform shaping output does not change and stops. Since the configuration is provided to diagnose the presence or absence of a failure in the waveform shaping circuit from the output response of the waveform shaping circuit, there are two types of failures, such as a vehicle stop or a failure in the waveform shaping circuit, which are assumed when the output of the waveform shaping circuit does not change. The cause can be accurately determined by diagnosing the waveform shaping circuit by supplying a diagnostic signal to the input terminal of the waveform shaping circuit, and in particular, shaping the output of the wheel speed sensors provided for each of the four wheels of the car. When four waveform shaping circuits are packaged in a single IC circuit for the purpose of generating vehicle speed pulses, all signals for four channels are not output due to failure of the IC circuit When this occurs, it is possible to clearly identify the situation where the vehicle is stopped and the output from the wheel speed sensor cannot be obtained. The use of ICs achieves excellent effects such as downsizing of the circuit scale and reduction of manufacturing cost.

Further, the waveform shaping circuit comprises a comparator circuit with an offset power supply, and the diagnostic means includes a high-level diagnostic signal exceeding the output voltage of the offset power supply and a low-level diagnostic signal lower than the output voltage at the input terminal of the waveform shaping circuit. Because it has a diagnostic signal generator that supplies diagnostic signals separately,
It is not necessary to provide a dedicated fault detection circuit, and the diagnostic system only needs to be provided for a specific waveform shaping circuit.Therefore, it is possible to diagnose a plurality of waveform shaping circuits without complicating the circuit configuration. In this case, it is possible to reliably detect whether the waveform shaping circuit is completely anomalous or not.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a wheel speed measuring device according to the present invention.

FIG. 2 is a flowchart for explaining a failure diagnosis operation of the waveform shaping circuit by the microprocessor shown in FIG. 1;

FIG. 3 is a circuit configuration diagram showing an example of a conventional wheel speed measuring device.

[Explanation of symbols]

 4 Waveform shaping circuit 4a Comparator with offset power supply 11 Wheel speed measuring device 12 Wheel speed sensor 13 Interface circuit 13a Limiter circuit 13b Low-pass filtering circuit 14 Waveform shaper 15 Microprocessor 15a Wheel speed converter 15b Diagnostic signal generator

Claims (2)

[Claims] 1. A waveform shaping circuit for converting an input signal having a frequency proportional to a wheel speed into a rectangular wave, a waveform shaping output of the waveform shaping circuit being monitored, and when the waveform shaping output stops without changing. Supply a diagnostic signal to the input end of the waveform shaping circuit,
Diagnostic means for diagnosing the presence or absence of a failure in the waveform shaping circuit from the output response of the waveform shaping circuit. 2. The waveform shaping circuit comprises a comparator circuit with an offset power supply. The diagnostic means includes a high-level diagnostic signal exceeding an output voltage of the offset power supply at an input terminal of the waveform shaping circuit and a diagnostic signal having a high level. 2. The wheel speed measuring device according to claim 1, further comprising a diagnostic signal generator for individually supplying a low-level diagnostic signal less than the low-level diagnostic signal.