JPH0727773A - Detecting apparatus for fault of wheel velocity sensor - Google Patents

Abstract

PURPOSE:To judge the fault of a wheel velocity sensor with good accuracy. CONSTITUTION:The wheel velocity sensor 1 is connected to a voltage source 3 via a resistor 2. Two connection points alpha, beta, are constituted in an electricity- feeding route between the resistor 2 and the wheel velocity sensor 1, and a voltage signal (sine waves) from the wheel velocity sensor 1 corresponding to a wheel velocity appears at the connection points alpha, beta. The time or the number of times at which a voltage value at the connection point alpha becomes continuously a prescribed threshold value or higher is counted. When a counted value becomes a prescribed value or higher, it is judged that the wheel velocity sensor 1 is faulty. When a pulse signal corresponding to the voltage signal at the connection point beta, exists, the counted value is reset to 0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wheel speed sensor failure detection device.

[0002]

2. Description of the Related Art In automobiles, it is often required to detect wheel speeds, and particularly when anti-lock brake control or traction control is performed, a wheel speed sensor is provided for each wheel. A pickup type sensor is usually used as such a wheel speed sensor. That is, a sine wave having a frequency corresponding to the rotation speed is output from the wheel speed sensor, and the wheel speed is calculated by counting the frequency of this sine wave as the number of pulses.

Detecting a failure of the wheel speed sensor is important for satisfactorily performing various controls based on the wheel speed. For this reason, the wheel speed sensor disclosed in Japanese Unexamined Patent Publication No. 4-366766 has a problem. A failure monitoring method is disclosed. This is achieved by connecting the wheel speed sensor to a voltage source via a resistor and comparing the voltage value, that is, the partial pressure value, between the wheel speed sensor and the resistor with a predetermined threshold value. It is designed to detect whether the wheel speed sensor is broken or shorted. Then, in the one described in this publication, the partial pressure value is once filtered to be smoothed.

[0004]

However, in the one described in the above publication, since the failure is detected only by the magnitude of the voltage value, it is erroneously determined to be a failure although it is not a failure due to the influence of noise. There is a strong risk of doing so.

Therefore, an object of the present invention is to provide a wheel speed sensor failure detection device capable of more accurately detecting a wheel speed sensor failure.

[0006]

In order to achieve the above object, the present invention has the following configuration. That is, in a wheel speed sensor failure detection device that detects a failure of a wheel speed sensor connected to a voltage source through a resistor, the voltage value between the wheel speed sensor and the resistor has a predetermined threshold value. Counting means for counting the time or the number of times that the value has been continuously exceeded, judging means for judging that the wheel speed sensor has a failure when the count value of the counting means exceeds a predetermined value, and the wheel When a pulse signal based on the output of the speed sensor is received, resetting means for resetting the count value of the counting means is provided.

In a preferred aspect of the present invention, the voltage value may be input to the counting means without passing through a smoothing filter.

[0008]

According to the present invention, a failure is basically determined by whether or not the voltage value exceeds a predetermined threshold value for a predetermined time or a predetermined number of times. Even if the threshold value is temporarily exceeded, there is no risk of erroneous failure determination. Further, when there is a pulse signal from the wheel speed sensor, that is, when the wheel speed sensor is operating normally, the counting means is reset, so that the voltage value input to the counting means is greatly smoothed. It becomes less necessary or unnecessary, and is preferable in order to enhance the response of failure determination as much as possible and to make the filter more inexpensive when using the filter.

By adopting the structure as described in claim 2, it is preferable in that the filter is eliminated, the response of failure determination is sufficiently enhanced, and the cost is reduced.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, reference numeral 1 denotes a wheel speed sensor of a pickup type. This wheel speed sensor 1 has one terminal connected to a constant voltage source 3 (5 V in the embodiment) via a resistor 2 and the other side. The terminal is grounded. The wheel speed sensor 1 has an internal resistance of 1 KΩ, and the resistance value of the resistor 2 is also 1 KΩ.

A first connection point α and a second connection point β are formed in the power feeding path between the wheel speed sensor 1 and the resistor 2. The first connection point α is connected to the first input terminal 11 of the control unit U via the first path 4. The second connection point β is connected to the second input terminal 12 of the control unit U via the second path 6 to which the waveform shaping circuit 5 is connected.

When the wheel speed sensor 1 is normal, a sine wave is output from the wheel speed sensor 1 according to the rotation of the wheel,
The frequency of the sine wave is increased as the rotational speed of the wheel is increased, and its amplitude is increased as the frequency is increased as shown in FIG. The sine wave is used for failure determination as described later, after passing through the A / D converter 13 connected to the first input terminal 11 from the first connection point α. Further, the sine wave is input to the second input terminal 12 from the second connection point or β as the number of pulse signals according to the frequency by the waveform shaping circuit 5, and in addition to the wheel speed calculation by the control unit U, It is used as a signal for failure determination described later.

At the connection point α or β, the sine wave from the wheel speed sensor 1 swings with reference to 2.5 V as shown in FIG. 4, and when it reaches 5 V, the wheel speed sensor 1 may be disconnected. When there is a moment, when the voltage reaches 0V
It is when there is a possibility.

Next, the point of failure judgment by the control unit U will be described with reference to the flow chart shown in FIG. In the following description, Q indicates a step. First,
At Q1, by checking the state of the input signal to the second input terminal 12, it is determined whether or not a pulse signal is generated. When the determination in Q1 is NO, it is determined in Q2 whether the input voltage to the first input terminal 11 is 5 V or higher as the upper limit threshold. If NO in this Q2 determination, in Q3, the first input terminal 11
It is determined whether or not the input voltage of is less than or equal to 0V as the lower limit threshold. When the determination in Q3 is NO, the wheel speed sensor 1 is normal, and in this case, the wheel speed sensor 1 is returned to Q1.

If YES in the determination in Q3, the timer is counted up in Q4, and then it is determined in Q5 whether or not the count of the timer is equal to or more than a predetermined value. If NO in this Q5 determination, the process returns to Q1.
If YES in the determination in Q5, it is determined in Q6 that the wheel speed sensor 1 is in a short state, and the control is terminated (in this case, an alarm lamp indicating a failure, an alarm device such as a buzzer, etc.). And the wheel speed obtained based on the signal from the wheel speed sensor 1 is not used for other control.

When the determination in Q2 is YES, after the timer is counted up in Q7, it is determined in Q8 whether or not the count value of the timer is equal to or more than a predetermined value. When the determination in Q8 is NO, the process returns to Q1. However, when the determination in Q8 is YES, it is determined in Q9 that the wheel speed sensor 1 is broken, and the control ends.

When the determination in Q1 is YES, Q10
In Q4 or Q7, the count value of the timer is reset to zero, and then the process returns to Q1. After this Q10, the determination in Q5 or Q8 does not become YES, and the wheel speed sensor 1 is normal. It is said that Of course, Q5,
The predetermined value in Q8 is a value sufficiently larger than this pulse interval in consideration of the pulse interval to be input to the second input terminal 12.

The meaning of the control contents by the above-mentioned control unit U will be further supplementarily described with reference to FIG. First, at t1 in FIG. 4, the input voltage to the first input terminal 11 is 5 V or more. At time t2 when the time period of 5 V or more continues for a predetermined time or more (time point when the determination in Q8 is YES), it is determined that the wheel speed sensor 1 is broken and a failure determination is performed in Q9. Above t1
When the pulse signal is input to the second input terminal 12 within the time period of up to t2, the predetermined time period shown in FIG. 4 is reset to zero. As long as the wheel speed sensor 1 is normal, t
The pulse signal is not always input within a predetermined time corresponding to 1 to t2, and it is not determined that the wheel speed sensor 1 is out of order.

The processing of Q3 to Q6 is t1 in FIG.
It is when the input voltage to the first input terminal 11 becomes 0 V or less from the time point and this time continues until the time point t2. The predetermined values (predetermined time) of Q5 and Q8 can be set as different values.

Here, since the first path 4 is not provided with a filter for smoothing, a voltage signal having a considerably large amplitude may be input to the first input terminal 11. Therefore, depending on the setting of the threshold value for failure determination, the input voltage to the first input terminal 11 may exceed the threshold value even though the wheel speed sensor 1 is normal. However, in this case, as long as the wheel speed sensor 1 is normal, since the pulse signal is input to the second input terminal 12 and the reset process is performed in Q10, it is not possible to erroneously make a failure determination.

It should be noted that it is conceivable to determine the failure of the wheel speed sensor 1 only by the presence or absence of the pulse signal to the second input terminal 12. However, in this case, when the wheels are locked, as seen in, for example, anti-lock brake control, a pulse signal is input to the second input terminal 12 even if the wheel speed sensor 1 is normal. As a result, it is difficult to accurately determine the failure.

Although the embodiment has been described above, the present invention is not limited to this, and a predetermined number of times may be used instead of the predetermined time in Q5 and Q8 (equal to or higher than the upper threshold or lower than or equal to the lower threshold). Count of times). Also, the first route 4
Further, a filter for smoothing may be connected, but this filter can be an inexpensive one with a small degree of smoothing. Further, a separate resistor may be connected between the connection point β (α) and the wheel speed sensor 1, or a separate resistor may be connected between the wheel speed sensor 1 and the ground terminal. .

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a failure determination circuit according to the present invention.

FIG. 2 is a diagram showing output characteristics of a wheel speed sensor.

FIG. 3 is a flow chart showing a control example of the present invention.

FIG. 4 is a diagram schematically showing the control content of the present invention.

[Explanation of symbols]

 1: Wheel speed sensor 2: Resistor 3: Constant voltage source 4: First path 5: Waveform shaping circuit 6: Second path 11: First input terminal 12: Second input terminal U: Control unit α: First connection Point β: Second connection point

Claims (2)

[Claims] 1. A wheel speed sensor failure detection device for detecting a failure of a wheel speed sensor connected to a voltage source via a resistor, wherein a voltage value between the wheel speed sensor and the resistor is predetermined. Means for counting the time or the number of times that the threshold value is continuously exceeded, and a judging means for judging that the wheel speed sensor has a failure when the count value of the counting means exceeds a predetermined value. And a reset unit that resets the count value of the counting unit when receiving a pulse signal based on the output of the wheel speed sensor. 2. The device according to claim 1, wherein the voltage value is input to the counting means without passing through a smoothing filter.