JPH10132835A - Wheel speed detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evade malfunction of an ABS(antilock brake system) due to erroneous detection of wheel speed, by a method wherein a plurality of capacitors of a filter circuit are connected in parallel so that an incorrect pulse is not generated when any capacitor is in the state of half contact. SOLUTION: A wheel speed input circuit is provided with a low pass filter circuit FL, a bypass filter circuit FH, and a comparator circuit G. The low pass filter circuit FL is constituted of a resistor R1 and a capacitor C1 wherein a plurality of capacitors C11, C12, ...C1n are connected in parallel. The number of capacitors in the low pass filter circuit FL is so set that a specified hysteresis voltage width ΔV is not exceeded when any capacitor becomes imperfect and noise is generated in a wheel speed detecting signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wheel speed detection circuit, for example, a wheel speed detection circuit which generates a pulse signal from a detection signal of a wheel speed sensor and outputs the pulse signal to a control circuit of an anti-lock brake system of an automobile. .

[0002]

2. Description of the Related Art Conventionally, for example, a wheel speed detection circuit used for controlling an anti-lock brake system (ABS) of an automobile receives a detection signal of a wheel speed sensor and removes high frequency or low frequency noise from the detection signal. The filter circuit includes one resistor and one capacitor.

[0003]

However, in the above-described conventional filter circuit, a half-contact state (e.g., contact or non-contact between the capacitor electrode and the mounting land due to vibration or temperature change) due to breakage or poor contact of the capacitor. In the case where contact is repeated), an incorrect pulse signal is generated from the wheel speed detection signal, and as a result, an erroneous detection that the wheel speed has increased may cause a malfunction of the ABS. There is.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to connect a plurality of capacitors of a filter circuit in parallel so that even if one of the capacitors is in a semi-contact state, an unauthorized connection is made. It is an object of the present invention to provide a wheel speed detection circuit that does not generate a pulse signal and can avoid malfunction of the ABS based on erroneous detection of wheel speed.

[0005]

SUMMARY OF THE INVENTION To solve the above problems,
In order to achieve the object, a wheel speed detection circuit according to the present invention has the following configuration. That is, a detection signal of the wheel speed sensor is input, and a filter means for removing noise in a predetermined frequency region by a capacitor from the detection signal, and a predetermined hysteresis width, and a pulse signal from the detection signal is set in accordance with the hysteresis width. , And a plurality of capacitors of the filter means are connected in parallel.

Preferably, the filter means includes:
High frequency filter means for removing high frequency noise from the detection signal and low frequency filter means for removing low frequency noise are provided.

Preferably, a plurality of capacitors of the high frequency filter means are connected in parallel.

Preferably, a plurality of capacitors of the low-frequency filter means are connected in parallel.

[0009] Preferably, a plurality of capacitors of the high frequency filter means and a plurality of capacitors of the low frequency filter means are connected in parallel.

[0010] Preferably, the pulse signal generated by the comparing means is output to a control means of an anti-lock brake system in an automobile.

Preferably, the number of capacitors of the filter means is set to a number such that the noise level of the detection signal does not exceed a predetermined hysteresis width even when one of the capacitors is defective.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment according to the present invention, a wheel speed detecting circuit provided in an ABS control unit of an automobile will be described in detail with reference to the accompanying drawings. [Overall System] FIG. 1 is a control block diagram of an automobile ABS control system according to an embodiment of the present invention.

As shown in FIG. 1, an ABS control unit 30 includes a front right (FR) wheel speed sensor 9 for a right front wheel and a front left (FL) wheel FL (front) for a vehicle.
Left) wheel speed sensor 10, right rear wheel RR (rear right) wheel speed sensor 11, left rear wheel RL (rear left)
A detection signal is input from the wheel speed sensor 12. Each of the wheel speed sensors 9 to 12 is connected to the FR wheel speed input circuit 5, the FL wheel speed input circuit 6, the RR wheel speed input circuit 7, and the RL wheel speed input circuit 8, and has a sine wave as an electromagnetic pickup type sine wave generator. Outputs a wave signal. Each wheel speed input circuit 5-8
Is connected to an ABS controller 1 including a CPU, a ROM, a RAM, etc., converts a sine wave signal input from each of the wheel speed sensors 9 to 12 into a digital signal, and outputs the digital signal as a wheel speed detection pulse.

The ABS controller 1 receives an on / off signal of an ignition switch 13 via a power supply circuit 3 and an on / off operation signal of a brake switch 14 via an input circuit 4. . AB
The S controller 1 detects the locked / unlocked state of each wheel by estimating and calculating the vehicle speed and the deceleration based on the wheel speed detection pulses output from each of the wheel speed input circuits 5 to 8, and the locked state is determined. When detected, an ABS control signal is output to the output circuit 2.

The output circuit 2 includes an FR solenoid 1 for controlling the brake oil pressure of each wheel based on the ABS control signal.
5. The FL solenoid 16, the RR solenoid 17, and the RL solenoid 18 are energized to drive a valve for controlling the ABS line pressure. The output circuit 2 is connected to a fail-safe relay circuit 20 driven by a linear solenoid. The output circuit 2 is connected to the battery power source B when the solenoid is energized, and is grounded when the solenoid is not energized. Also,
The output circuit 2 is connected to a pump motor relay circuit 21 driven by a linear solenoid. The pump motor relay circuit 21 is turned on when the solenoid is energized, and drives a pump motor 22 that controls a brake oil pressure by a battery power source B. The fail-safe relay circuit 20 controls the brake hydraulic pressure of each wheel when an abnormality occurs in the ABS.
It is provided to stop the brake control by the R solenoid 15, the FL solenoid 16, the RR solenoid 17, and the RL solenoid 18. The output circuit 2 turns on the warning lamp 19 when any abnormality occurs in the ABS.

[Wheel Speed Input Circuit] Next, a detailed configuration of the wheel speed input circuit shown in FIG. 1 illustrating the features of the present invention will be described.

FIG. 2 is a detailed block diagram of the wheel speed input circuit shown in FIG. FIG. 3 is a waveform diagram of a sine wave signal output from the wheel speed sensor to the wheel speed input circuit. FIG. 4 is a waveform diagram illustrating functional features of the wheel speed input circuit shown in FIG.

As shown in FIG. 2, the wheel speed input circuit includes a low-pass filter circuit FL for removing high-frequency noise, a high-pass filter circuit FH for removing low-frequency noise, and a comparator circuit G. Low-pass filter circuit FL
Is composed of a resistor R1 and a capacitor C1 in which a plurality of capacitors C11, C12,... C1n are connected in parallel. The high-pass filter circuit FH includes a resistor R2 and one capacitor C
Consists of two. The comparator G is a positive feedback circuit in which the power supply voltage Vd is applied and the output voltage VO is fed back to the + input, and the + input voltage VN is determined by the reference voltage VREF applied to the + input and the resistors R3 to R6. The hysteresis circuit is set to a predetermined hysteresis voltage width ΔV. The output signal VO of the comparator G is output to the ABS controller 1.

Wheel speed sensors 9 to 12 provided for each wheel
Outputs the sine wave signal VS shown in FIG. 3 to the wheel speed input circuit as a wheel speed detection signal, and the sine wave signal VS is filtered by a low-pass filter FL and a high-pass filter FH to remove high-frequency and low-frequency noise. As shown in the figure, the signal is inputted as the negative input signal VI of the comparator G. -Input signal V
I is the hysteresis voltage width ΔV of the comparator G (the difference between the HIGH level reference voltage VIH and the LOW level reference voltage VIL: Δ
(V = VIH-VIL), and is converted to a digital signal and output to the ABS controller as a wheel speed detection pulse.

[Functional Features of Wheel Speed Input Circuit]
The functional features of the wheel speed input circuit shown in FIG. 1 will be described.

In normal ABS control, the vehicle speed is calculated from the wheel speed, and the brake oil pressure is released in accordance with the difference between the vehicle speed and the wheel speed, thereby preventing the wheels from being locked.

Referring to FIG. 4, first, a conventional filter circuit composed of one resistor and one capacitor will be examined.
Since the noise C ′ generated when the ND-side electrode or the signal-side electrode is intermittent (in a state where open and short-circuits are repeated) exceeds the hysteresis voltage width ΔV, the wheel speed detection pulse VO is incorrect as shown by the pulse signal D. A pulse signal is generated, the wheel speed detection pulse for calculating the estimated vehicle speed is incorrectly increased, and the vehicle speed is increased in the calculation. Then, since the other wheel speeds are normal, the difference between the vehicle speed and the wheel speed becomes relatively large, and the ABS may operate to release the brake hydraulic pressure.

On the other hand, in the present embodiment, a plurality of capacitors C11, C12,... C1n are connected in parallel to the low-pass filter FL and, as shown in FIG. ... Any one of C1n (for example, the capacitor C11) is damaged or contact failure occurs, and the GND side electrode (point A shown in FIG. 2) or the signal side electrode (point B shown in FIG. 2) When intermittent (in a state where open and short are repeated), the negative input signal V
The number of capacitors is determined so that the noise C generated in I does not exceed the hysteresis width. Thus, even if any one of the capacitors is in the intermittent state, an incorrect pulse signal is not generated, and the malfunction of the ABS based on the erroneous detection of the wheel speed can be avoided.

[First Modification] Next, a first modification will be described.

FIG. 5 shows a first example of the wheel speed input circuit shown in FIG.
It is a detailed block diagram based on the modification of.

As shown in FIG. 5, in the first modification, the low-pass filter circuit FL of the wheel speed input circuit shown in FIG. 1 comprises a resistor R1 and one capacitor C1, and the high-pass filter circuit FH comprises a resistor R2. And a plurality of capacitors C21, C22,
.., C2n are composed of capacitors C2 connected in parallel. Other configurations are the same as those in FIG.

In this first modification, even if any one of the capacitors C21, C22,... C2n of the high-pass filter FH is damaged or a contact failure occurs, an incorrect pulse signal is not generated, and The malfunction of the ABS based on the false speed detection can be avoided.

[Second Modification] Next, a second modification will be described.

FIG. 6 shows a second example of the wheel speed input circuit shown in FIG.
It is a detailed block diagram based on the modification of.

As shown in FIG. 6, in the second modification, the low-pass filter circuit FL of the wheel speed input circuit shown in FIG. 1 has a resistor R1 and a plurality of capacitors C11, C12,... C1n connected in parallel. The high-pass filter circuit FH includes a resistor R2 and a plurality of capacitors C21, C22,.
2n is composed of a capacitor C2 connected in parallel. Other configurations are the same as those in FIG.

In the second modification, the capacitor C1 of the low-pass filter FL and the capacitor C1 of the high-pass filter FH
Regarding C2, even if one of the capacitors C1 and C2 is damaged or a contact failure occurs, an incorrect pulse signal is not generated, and the malfunction of the ABS based on the erroneous detection of the wheel speed can be avoided.

It should be noted that the present invention can be applied to modifications or changes of the above embodiment without departing from the spirit thereof.

[0033]

As described above, according to the present invention, a detection signal of a wheel speed sensor is input, and a plurality of capacitors of filter means for removing frequency noise from the detection signal by a capacitor are connected in parallel. Therefore, even if a plurality of capacitors of the filter circuit are connected in parallel, even if one of the capacitors is in a semi-contact state, an incorrect pulse signal is not generated and malfunction of the ABS based on erroneous detection of the wheel speed is avoided. it can.

[0034]

[Brief description of the drawings]

FIG. 1 is a control block diagram of an automobile ABS control system according to an embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of a wheel speed input circuit shown in FIG.

FIG. 3 is a waveform diagram of a sine wave signal output from a wheel speed sensor to a wheel speed input circuit.

FIG. 4 is a waveform diagram illustrating functional features of the wheel speed input circuit shown in FIG. 1;

FIG. 5 is a detailed configuration diagram based on a first modification of the wheel speed input circuit shown in FIG. 1;

FIG. 6 is a detailed configuration diagram based on a second modification of the wheel speed input circuit shown in FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ABS controller 2 output circuit 3 power supply circuit 4 input circuit 5 FR wheel speed input circuit 6 FL wheel speed input circuit 7 RR wheel speed input circuit 8 RL wheel speed input circuit 9 FR wheel speed sensor DESCRIPTION OF SYMBOLS 10 ... FL wheel speed sensor 11 ... RR wheel speed sensor 12 ... RL wheel speed sensor 13 ... Ignition switch 14 ... Brake switch 19 ... Warning lamp 20 ... Fail safe relay circuit 21 ... Motor relay circuit 22 ... Pump motor B ... Battery FL ... Low pass filter FH: High pass filter G: Comparator (hysteresis circuit)

Claims (7)

[Claims] 1. A filter means for receiving a detection signal of a wheel speed sensor and removing noise in a predetermined frequency region from the detection signal by a capacitor, and a predetermined hysteresis width, wherein the detection signal is set in accordance with the hysteresis width. And a comparison means for generating a pulse signal from the filter means, wherein a plurality of capacitors of the filter means are connected in parallel. 2. The high frequency filter means for removing high frequency noise from the detection signal,
2. The wheel speed detection circuit according to claim 1, further comprising a low frequency filter for removing noise in a low frequency region. 3. The wheel speed detection circuit according to claim 2, wherein a plurality of capacitors of said high frequency filter means are connected in parallel. 4. The wheel speed detection circuit according to claim 2, wherein a plurality of capacitors of said low frequency filter means are connected in parallel. 5. The wheel speed detection circuit according to claim 2, wherein a plurality of capacitors of said high frequency filter means and a plurality of capacitors of said low frequency filter means are connected in parallel. 6. The wheel speed detecting circuit according to claim 1, wherein the pulse signal generated by said comparing means is output to a control means of an anti-lock brake system in a vehicle. 7. The number of capacitors of the filter means is:
The wheel speed detection circuit according to claim 1, wherein even if one of the capacitors is defective, the noise level of the detection signal is set to a number that does not exceed a predetermined hysteresis width.