JPH07198733A - Wheel speed sensor monitoring device - Google Patents

Abstract

(57) [Abstract] [Purpose] Provided is a wheel speed sensor monitoring device capable of detecting that a normal output is not produced when the detection characteristic is changed due to adhesion of iron powder to the sensor and the output is reduced. To do. [Configuration] A lower limit value in which a frequency and a voltage to be output are preset for a wheel speed sensor (1A to 1C) that generates a frequency by rotating wheels (1A to 1C) and outputs a voltage corresponding to the frequency. And a means (3) for checking the output voltage when the output frequency becomes the lower limit value as a result of the comparison, and for judging that the output is not normal when the output voltage is lower than the lower limit value. And.

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 monitoring device, and more particularly to a wheel speed sensor monitoring device, which is used to provide information relating to a wheel rotation speed to a control unit or the like of an antilock brake device provided in an automobile. And a monitoring device for a wheel speed sensor.

[0002]

2. Description of the Related Art An anti-lock brake device (hereinafter referred to as AB
(S) is provided in order to prevent the vehicle from easily skidding or spinning when the braking force becomes too large due to a sudden braking operation and making it difficult to control. Control methods have been used. In addition to a normal brake device, such an ABS includes a wheel speed sensor and a control unit (hereinafter referred to as ECU) that calculates acceleration and the like based on electric signals from the wheel speed sensors and outputs a control signal.
An actuator for appropriately controlling the brake fluid pressure of each wheel by a control signal from the CU.

Further, as the wheel speed sensor, a kind of pulse generator type which is generally a combination of a tooth type roller and an electromagnetic pickup has been used. In such a wheel speed sensor, when magnetic foreign matter such as iron powder adheres to the head portion of the electromagnetic pickup, the output characteristics change and the detection function deteriorates. Therefore, a method for preventing this is disclosed in, for example, Japanese Patent Application No. 58-50688.

[0004]

By the way, the ABS EC
In U, in the wheel speed sensor, the change in magnetic flux generated between the tooth profile of the tooth profile roller and the head of the pickup is captured as a frequency (Hz), and the vehicle speed corresponding to the frequency is represented by the curve C _P in FIG. As shown in the voltage V _PP (V)
Is entered as. However, when the sensitivity decreases due to the adhesion of iron powder or the like to the head, the characteristics of the frequency f and the voltage V _PP change as shown by the curve C _E. In addition,
Possible because operation of the vehicle speed in response to input signals from the wheel speed sensors in ECU is the the T _C or more regions in FIG. 3, therefore, the output from the wheel speed sensors in the region equal to or less than the above-mentioned regions T _C There is a fear that it cannot be detected accurately.

An object of the present invention is to prevent erroneous control by detecting that normal output is not performed when the detection characteristics change due to the adhesion of iron powder to the head and the output drops. To provide a monitoring device of a wheel speed sensor for doing so.

[0006]

In order to achieve such an object, the present invention is to generate a frequency by the rotation of wheels,
For a wheel speed sensor capable of detecting the wheel speed by the output of the voltage corresponding to the frequency, monitoring means for comparing the output of the frequency and voltage with respective preset lower limit values, and the result of the comparison by the monitoring means , When the frequency of the output reaches the lower limit value, examine the corresponding voltage output,
Means for determining that the voltage output is not normal when the voltage output is lower than the lower limit value.

[0007]

According to the present invention, as a result of comparison by the monitoring means,
When the output frequency reaches the lower limit value of the output frequency, the output voltage is checked, and if the output voltage is lower than the lower limit value of the output voltage, the judging means judges that the output from the sensor is not normal. In a device such as ABS, which is controlled based on the voltage output from the sensor, it is possible to prevent the malfunction due to the misjudgment from occurring.

[0008]

Embodiments of the present invention will be described in detail and specifically below with reference to the drawings.

FIG. 1 schematically shows the construction of an ABS control circuit in which the wheel speed sensor of the present invention is incorporated. In this example, 1A to 1C are, for example, the right front wheel 2A, the left front wheel 2B and This is a wheel speed sensor of an electromagnetic pickup system incorporated in each of the rear wheels 2C. The wheels 2A to
2C has a wheel cylinder (not shown),
The hydraulic pressure sent to the wheel cylinders is reduced and increased by the actuator 4 controlled via the control unit 3 so as to prevent the occurrence of lock. Reference numeral 5 is a CPU which is a central processing unit of the control unit 3, and 6 is a judgment circuit as a monitoring device according to the present invention, which is based on the output voltages and frequencies from the wheel speed sensors 1A to 1C. Whether or not the 1C is in the normal detection state is determined as described later, and the CPU 5 is caused to take appropriate action. Reference numeral 7 is a master cylinder that generates a brake hydraulic pressure via a pedal 8.

The output voltage V _PP is input to the determination circuit 6 via the control circuit 5 or directly from the wheel speed sensors 1A to 1C together with the frequency f corresponding to the wheel speed. Further, the decision circuit 6 constantly monitors the input frequency, and the input frequency is lowered and the limit frequency f _L set in advance to prevent erroneous detection (in the case of this example, as shown in FIG. 3). 50 Hz), the control circuit 5 is made to check whether or not the wheel speed sensors 1A and 1B are in a normal detection state according to a routine to be described later.

FIG. 2 shows the procedure. First, in step S1, the frequency f input from each of the wheel speed sensors 1A to 1C is set to a limit frequency f to prevent erroneous detection.
Whether or not it becomes _L is determined, and if the determination is affirmative, the process proceeds to step S2, and the output voltage V _PP at the time of this detection is checked. If the output voltage V _PP is lower than the limit voltage A _L in step S2, iron powder or the like adheres to the head of the wheel speed sensor in step S3, and it is assumed that the normal rotation speed is not detected in step S4. Then, the wheels 2A to 2C are braked in the normal brake mode without depending on the antilock brake control.

In step S2, the output voltage V
_{When PP} is higher than the limit voltage A _L , the process proceeds to step S5, the speed of the wheel is calculated based on the input frequency f, and based on the calculated wheel speed, the antilock brake is performed according to the routine as before. The actuator 4 is controlled so that the control is performed.

With the above control, in FIG. 3, the outputs from the wheel speed sensors 1A to 1C become normal in the range where the frequency f is 0 to 50 Hz and the output voltage V _PP is limited to the range of 0 to 0.3 V. By disabling the anti-lock brake control without recognizing it, it is possible to prevent unnecessary troubles from occurring.

In the above description, the control when the output from the wheel speed sensor is not normal is described. By the way, the ABS control in the normal normal operating condition will be described with reference to FIGS. 4 and 5. deep.

The control unit 3 shown in FIG. 1 controls the braking pressure at the time of braking by the ABS, but when the wheel speed Vw is decelerated as shown in FIG. 4A, it is shown in FIG. The control is performed by the procedure.
That is, in step S11, the wheel speed Vw of the right front wheel 2A.
FR, the wheel speed VwFL of the left front wheel 2B and the wheel speed VwR of the rear wheel 2C are calculated based on the output voltage and frequency from the respective speed sensors 1A, 1B and 1C,

[0016]

[Outer 1]

Is calculated. FIG. 4B shows

[0018]

[Outside 2]

Next, in step S13, the pseudo vehicle speed Vi shown in FIG. 4A is calculated, and in step S14, the pressure reduction threshold value λ ₁ is calculated.

As the pseudo vehicle speed Vi here, the vehicle speed ViF having a larger value among the vehicle speeds of the front left and right wheels is compared with the vehicle speed VwR of the rear wheels, and the larger value is taken. As shown in step S14, the decompression threshold value λ ₁ is

[0021]

[Number 1] is calculated by _{λ 1 = Vi × K-X} ... (1) Equation (1).

In the equation (1), for example, K is 0.
When set to 95, X is 8 depending on whether the road surface friction coefficient μ is high or low.
Is set to ~ 4.

Then, in step S15, the wheel speed Vw is
The above threshold value λ for each of the wheels 2A to 2C ₁ Compared to the wheels
The speed Vw is the threshold λ₁ Branch to step S18 in the following cases
And here,

[0024]

[Outside 3]

It is determined whether or not it is low. If the determination is affirmative, the wheel speed Vw is less than or equal to the pressure reduction threshold, and

[0026]

[Outside 4]

In step S20, the pressure is reduced as shown in (C) of FIG. If the determination is negative in step S18,

[0028]

[Outside 5]

Assuming that the wheels tend to be released from the lock state, the routine proceeds to step S19, where the brake pressure is maintained in that state as shown in (C) of FIG.

If the determination in step S15 is negative, the process proceeds to step S16

[0031]

[Outside 6]

Whether it is low or not is judged. If the result is negative, that is, the upper limit value B is exceeded, step S1 is performed.
9, the brake pressure is maintained as it is, as shown in (C) of FIG. 4 because it tends to return to the pseudo vehicle speed Vi. Furthermore, if the determination in step S16 is affirmative, it is assumed that the wheel speed has returned to the pseudo speed,
The pressure is increased as shown in (C) of FIG.

[0033]

As described above, according to the present invention, the frequency is generated by the rotation of the wheel, and the wheel speed sensor capable of detecting the wheel speed by the output of the voltage corresponding to the frequency is used. Monitoring means for comparing the output of the frequency and the voltage with respective preset lower limit values, and when the frequency of the output reaches the lower limit value as a result of the comparison by the monitoring means, the voltage of the output is checked and the output Since the output voltage from the wheel speed sensor is reduced due to the adhesion of iron powder to the head, etc., the output voltage from the wheel speed sensor is reduced to a normal wheel speed because the output is not normal when the voltage is lower than the lower limit value. Even if it does not correspond, the ABS control based on the incorrect wheel speed is prevented.

The application of the present invention is not limited to the ABS control, but can be widely applied to an apparatus which is controlled based on an output signal from a wheel speed sensor by an electromagnetic pickup type head.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an ABS control circuit to which the present invention is applied.

FIG. 2 is a flowchart showing a procedure of monitoring operation of a wheel speed sensor according to the present invention.

FIG. 3 is a characteristic curve diagram showing the relationship between the frequency and the output voltage of the wheel speed sensor according to the present invention.

FIG. 4 is a curve diagram showing the relationship between ABS wheel speed, acceleration, and brake pressure control.

FIG. 5 is a flowchart showing a procedure of an ABS control operation.

[Explanation of symbols]

1A, 1B, 1C wheel speed sensors 2A, 2B, 2C wheel 3 control unit 5 control circuit (CPU) 6 judging circuit C _P, C _E Frequency - Output voltage characteristic curve f _L limit frequency A _L limit voltage

Claims (1)

[Claims] 1. A wheel speed sensor capable of generating a frequency by rotation of a wheel and detecting a wheel speed by outputting a voltage corresponding to the frequency, and a lower limit value for which each of the frequency and voltage outputs is preset. When the frequency of the output reaches the lower limit value as a result of the comparison by the monitoring unit, the corresponding voltage output is checked, and when the voltage output is lower than the lower limit value, the voltage output is A monitoring device for a wheel speed sensor, comprising: means for determining that the wheel speed sensor is not normal.