JP2001021574A - Wheel speed detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wheel speed detecting device capable of precisely monitoring wheel speed information. SOLUTION: The wheel speed detecting device outputs wheel speed information (first wheel speed) based on information on the angular frequency of an AC signal outputted from a wheel speed sensor 10. The AC signal is converted into a square wave signal and the wheel speed information is monitored based on the period (second wheel speed) of the square wave signal. Since square waves have high noise resistance, precise monitoring of wheel speed information can be effected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wheel speed detecting device.

[0002]

2. Description of the Related Art A conventional wheel speed detecting device is disclosed in Japanese Patent Laid-Open No. 7-12 / 1995.
No. 8352. This device calculates two pieces of wheel speed information using filters having different pass bands, and selects one of the pieces of wheel speed information as necessary. In order to detect a wheel speed abnormality, it is considered that mutual monitoring should be performed based on each other's wheel speed information.

[0003]

However, in the above-described conventional wheel speed detecting device, both wheel speed information are liable to change with respect to noise, and more reliable monitoring of the wheel speed information is expected. An object of the present invention is to provide a wheel speed detecting device capable of monitoring accurate wheel speed information.

[0004]

In order to solve the above-mentioned problems, a wheel speed detecting device according to the present invention provides a wheel speed which outputs wheel speed information in accordance with angular frequency information of an AC signal output from a wheel speed sensor. In the detection device, the AC signal is converted into a square wave signal, and the wheel speed information is monitored based on the square wave signal.

When the vehicle travels on a rough road or the like, the output of the sensor itself has a noise component due to the impact from the road surface, and when there is a noise electromagnetic wave outside or inside the vehicle, the sensor outputs a noise. A noise component is superimposed on the signal transmission path. The angular frequency of the AC signal output from the wheel speed sensor changes due to such noise, but the cycle of the signal converted to a square wave signal is substantially proportional to the wheel speed, which is accurate especially at low speed. Although not limited, it is highly resistant to noise. Therefore, if the wheel speed information is monitored based on the square wave signal, accurate monitoring of the wheel speed information can be performed.

It is preferable that a lower limit threshold value that changes in accordance with the cycle of the square wave signal is set, and that when the wheel speed information falls below the lower limit threshold value, it is determined that the wheel speed information is abnormal.

In the above case, it is preferable to set an upper limit threshold value that changes according to the cycle of the square wave signal, and to determine that the wheel speed information is abnormal when the wheel speed information exceeds the upper limit threshold value. .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a wheel speed detecting device according to an embodiment will be described. The same reference numerals are used for the same elements or elements having the same functions, and overlapping descriptions are omitted.

FIG. 1 is a schematic configuration diagram of a vehicle equipped with a wheel speed detecting device according to an embodiment.

This vehicle has four wheels (front wheels W _FL , W _FR , rear wheels W _RL , W W) provided rotatably with respect to a vehicle body BDY.
_RR ). Wheel speed sensors 10, 10x, 10y, and 10W correspond to the wheels W _FL , W _FR , W _RL , and W _RR , respectively.
z are provided, and the output is proportional to the left and right wheel speeds. Here, the wheel speed sensors 10, 10x,
10y and 10z detect the rotation speed of the wheel electrically / magnetically or optically and output a pulse corresponding to the rotation speed. The number of pulses per unit time is proportional to the rotation speed, that is, the repetition angular frequency of the output AC pulse signal is proportional to the rotation speed of the wheel. In this example, the wheel speed sensor is a power generation type wheel speed sensor (magnetic pickup sensor: MPU) using a permanent magnet and a detection coil.

Outputs from the sensors 10, 10x, 10y, and 10z are input to an ECU (Electronic Control Unit) 100 disposed inside the vehicle, and the ECU 100 calculates the wheel speed of each wheel based on the input information. Then, the vehicle speed calculated from the calculated wheel speeds is displayed on a display device, and, if necessary, a driving means (for example, a brake, a suspension, etc.) for controlling the vehicle body behavior based on the wheel speeds is controlled. I do. For example, the ECU 100 controls the lock timing of the wheels W _FL , W _FR , W _RL , and W _{RR in} an ABS (anti-lock brake system) based on the wheel speeds,
Execute C (traction control).

The method for calculating the wheel speed is as follows.
Since the same applies to signals from 0, 10x, 10y, and 10z, a configuration for obtaining wheel speeds (wheel speed information) from output signals of the sensors 10 on behalf of four sensors will be described for simplicity in this example. .

An AC signal output from the wheel speed sensor 10 is input to a processor 24 via an A / D converter 12. That is, the A / D converter 12 samples the AC signal from the wheel speed sensor 10 at a predetermined sampling timing, converts it into a digital signal, and supplies it to the processor 24.

The processor 24 processes digital signals using a program stored in the ROM 16, detects and outputs wheel speed information. The processor 24 and the ROM
16. The RAM 18 can be constituted by a microcomputer. Here, the sensor will be described briefly.

FIG. 2 is an explanatory diagram showing the relationship between the sensor R and the rotor R provided coaxially with the wheel _WFL .
A tooth surface is formed around the rotor R, and the shortest distance between the rotor R and the sensor 10 fluctuates in a pulsed manner according to the rotation. The sensor 10 outputs a signal Vw according to the distance change. By extracting the angular frequency ω from the AC signal Vw and dividing the angular frequency ω by the number N of teeth of the rotor, the rotational speed of the wheel is calculated.

FIG. 3 is a block diagram showing the internal configuration of the processor 24. The angular frequency ω of the AC signal input from the wheel speed sensor 10 via the A / D converter 12
Although the signal Vw including the information is in a digital state,
Vw = f (ω) cos (ωt + θ).

This angular frequency ω is proportional to the rotation speed of the wheel,
If the angular frequency ω is high, the wheel speed is high, and if the angular frequency ω is low, the wheel speed is low. The function f (ω) is the amplitude of the output signal of the wheel speed sensor 10 and depends on the angular frequency ω (wheel speed). Here, θ indicates the phase. Note that a semiconductor sensor using the Hall effect can be used as the wheel speed sensor 10 instead of the MPU. In this case, f (ω) can be considered as a constant independent of ω.

The processor 24 includes an adaptive filter 24x for removing unnecessary angular frequency components from the AC signal Vw according to the angular frequency, and an AC signal Vw from which unnecessary angular frequency components have been removed.
An angular frequency extractor 24y that extracts an angular frequency ω from the motor and a divider 24z that divides the extracted ω by the number of teeth of the rotor R to calculate a wheel speed (rotational speed ω / N) (A). Have. The angular frequency ω extracted by the angular frequency extractor 24y is fed back to the adaptive filter 24x. Adaptive filter 24x functions as a band pass filter for removing frequencies other than the frequency components of the center frequency omega ₀ near the angular frequency omega that is input.

Here, the sine wave signal Vw is output from the processor 2
4 is input to the square wave converter 24a. The square wave converter 24a is composed of a circuit such as a comparator, and outputs a square wave having the same repetition frequency as the fundamental frequency of the input sine wave. The period of this square wave is proportional to the wheel speed. The rotation speed (cycle) calculation unit 24b calculates a wheel speed (rotation speed) (referred to as B) in proportion to the cycle of the square wave signal.

The wheel speeds calculated by the two routes are both input to the determination unit 24c. The wheel speed (A) directly obtained from the sine wave signal has high accuracy even at low speed, but the wheel speed (B) calculated based on the square wave signal has low accuracy. However, since the square wave signal has high noise resistance, the signal (B) has higher reliability.

The determination unit 24c sets a lower threshold Th _L that varies according to the length of the period of the square wave signal (alpha B), the signal is a wheel speed information (A) is below the lower threshold value Th _L In this case, it is determined that the wheel speed information is abnormal. The determining unit 24c determines the length of the period of the square wave signal (信号 B).
Set the upper limit threshold Th _U which varies depending on the wheel speed information when the signal is a wheel speed information (A) exceeds the upper limit threshold Th _U may be determined to be abnormal. More specifically, assuming that B−α = Th _L and B + α = Th _U (α is a constant), if the condition: B−α <A <B + α is satisfied, the wheel speed information A is normal; Determines that the wheel speed information A is abnormal.

The gate circuit 24d opens and closes according to the determination result of the determination section 24c. If the abnormality is determined, the output of the wheel speed (A) is prohibited.
Is output. Note that the output prohibition of the wheel speed (A) may be a reset of the wheel speed calculation.

The processor 24 can be constituted by a so-called DSP (digital signal processor) or HIC (hybrid integrated circuit), or
(Central processing unit) or a combination of any two of them. The function of each component may be shared by any of the DSP, HIC, and CPU, and may be configured by an analog circuit if the functions are the same.

Note that the wheel speed can be detected without the application filter 24x. Here, the angular frequency extraction unit 2
4y will be described.

FIG. 4 is a block diagram of the angular frequency extracting unit 24y. The angular frequency extraction unit 24y includes an arithmetic unit 14A that performs an operation for removing the phase component θ of the AC signal Vw from the AC signal Vw, and a converter 30 that extracts the angular frequency information ω based on the operation value. I have.

In this example, the output of the arithmetic unit 14A is ω ² · f ²
(Ω), and the converter 30 calculates the previously measured ω ² · f
A map storing the relationship between ² (ω) and ω is provided, and ω corresponding to ω ² · f ² (ω) input from the arithmetic unit 14A is provided.
Is output.

Input AC signal Vw = f (ω) · cos (ω
Although various configurations of the arithmetic unit 14A for outputting the output signal ω ² · f ² (ω) in response to (t + θ) are conceivable, a preferred configuration is shown in FIG. That is, the arithmetic unit 14A includes a differentiator 14a, multipliers 14b and 14d, an integrator 14c, a subtractor 14e, and differentiators 14x, 14y, and 14z.

More specifically, the arithmetic unit 14A receives the input signal V
It has a differentiator 14y for differentiating w (cos wave) with time, and a multiplier 14b for squaring the differential value of the differentiator 14y. Thereby, the square function (= Vb) of the sine wave is output from the multiplier 14b.

The arithmetic unit 14A includes an integrator 14c for sequentially integrating and differentiating the input signal Vw with time and a differentiator 1
4z, which is used as signal transmission means. Here, since the signal transmission means functions as a signal transmission path that does not perform signal processing as a result, the integrator 14c and the differentiator 14z can be omitted. In other words, the output value of the signal transmission means is It suffices if the result is integrated and differentiated.

Further, the computing unit 14A multiplies the differentiator groups 14a and 14x for differentiating the input signal Vw one more time than the number of times of differentiation by the differentiator 14y, and multiplies the output values of the signal transmitting means and the second differentiating means. Vessel 14d. As a result, the square function of the cos wave (= V
d) is output.

The subtractor 14e adds the square functions Vb and Vd of the sine wave and the cosine wave by inverting one of the signs, and adds
Only the amplitude component is output. That is, in the case of the present example, the sign of the square of the sine wave and the sign of the square of the cosine wave are opposite, so that the square of the sine wave and the square of the cosine wave are input to the subtractor 14e as an adding means. , And the two codes are made to coincide with each other and added.

With this configuration, the amplitude component in the input signal is extracted, and the output from the subtractor 14e is ω ² · f ² (ω). In other words, the subtractor 14e
The output values of the first and second multipliers 14b and 14d are added so that an amplitude component can be extracted.

When the phase θ component can be ignored, the differentiators 14x, 14y and 14z may be removed from each path. In this case, the apparatus assumes that the AC signal Vw from the sensor 10 is a sine wave function having no phase shift, and branches the signal into three to form first, second, and third AC signals. Differentiating one AC signal and squaring it, integrating the second AC signal,
The frequency information in the input signal is extracted by differentiating the third AC signal, adding a value obtained by multiplying the integral value and the differential value, and the square value. The angular frequency extracting unit 24y can be variously modified.

FIG. 5 is a block diagram showing the internal configuration of the processor 24 when the wheel speed sensor 10 is a semiconductor sensor. The processor 24 includes a differentiator 31 at a stage preceding the arithmetic unit 14A, and the output of the arithmetic unit 14A is ω ^4.
f ² (ω). In this case, if reference to FIG. 4, in terms of unit 30 has a map storing a previously measured ω ⁴ · f ² (ω) and the relationship of omega, ⁴ · omega input from the arithmetic unit 14A It is assumed that ω corresponding to f ² (ω) is obtained and output.

In the above description, the output ω ^{2 of the} arithmetic unit 14A
· Corresponding ω based on f ² (ω) or ω ⁴ · f ² (ω)
Is read from the map, but the lookup table method is used.
The angular frequency information ω as the wheel speed information may be extracted by deleting the function f (ω) using 4B.

FIG. 6 is a block diagram showing the internal configuration of the angular frequency extracting unit 24y in such a case. in this case,
Input signal Vw is branched into two in the circuit, One of the branched signals is input to the arithmetic unit 14A sequentially through a differentiator group _{24 a1, 24 a2 ··· 24 an} , the other signal differentiator is input to the arithmetic unit 14B sequentially through a group _{24 b1, 24 b2 ··· 24 bn} , 24 bn + 1. In other words, the input signal Vw =
f (ω) · cos (ωt + θ) is time-differentiated n times while passing through one path and n + 1 times while passing through the other path.

By one differentiation, the cos function or si
The angular frequency ω in a trigonometric function such as an n function is included in the amplitude component. In other words, the order of the angular frequency ω increases in proportion to the number of times of differentiation. That is,
The order obtained by differentiating Vw n times and that obtained by n + 1 times differ from each other, and the function values represented by ω and f (ω) with the phase component removed from the arithmetic units 14A and 14B. Is output.

Since the order of f (ω) of these function values is the same and the order of ω is different, it is necessary to input these to the divider 24c to eliminate f (ω). Thus, a function of only the power of the wheel speed information (angular frequency) ω can be obtained. When the divider 24c outputs the k-th power of ω, the k-th root calculator 24d arranged on the subsequent stage side
Calculates the k-th root of this. Therefore, ω is output as a result from the angular frequency extraction unit 24y.

Note that f (ω) often differs from vehicle to vehicle due to sensor assembly errors and the like.
Since c eliminates the function f (ω), there is an advantage that such an effect can be suppressed.

As described above, the wheel speed detection device outputs wheel speed information (A: first wheel speed) in accordance with angular frequency information of an AC signal output from a wheel speed sensor. In the device, the AC signal is converted into a square wave signal, and the wheel speed information is monitored based on the cycle (∝B: second wheel speed) of the square wave signal. It can be carried out.

[0041]

As described above, according to the wheel speed detecting device of the present invention, accurate monitoring of wheel speed information can be performed by monitoring wheel speed information based on a square wave signal. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a vehicle equipped with a wheel speed detection device according to an embodiment.

FIG. 2 is an explanatory diagram showing a relationship between a rotor R provided coaxially with a wheel W _FL and a sensor 10;

FIG. 3 is a block diagram showing an internal configuration of a processor 24.

FIG. 4 is a block diagram showing an internal configuration of an angular frequency extraction unit 24y.

FIG. 5 is a block diagram showing an internal configuration of an angular frequency extraction unit 24y according to another embodiment.

FIG. 6 is a block diagram showing an internal configuration of an angular frequency extraction unit 24y according to still another embodiment.

[Explanation of symbols]

10 Wheel speed sensor, 24 Processor, 24y Angular frequency extraction means.

Claims (3)

[Claims] 1. A wheel speed detecting device for outputting wheel speed information in accordance with angular frequency information of an AC signal output from a wheel speed sensor, wherein the AC signal is converted into a square wave signal, and based on the square wave signal. A wheel speed detecting device for monitoring the wheel speed information. 2. The method according to claim 1, wherein a lower limit threshold value that changes in accordance with a cycle of the square wave signal is set, and the wheel speed information is determined to be abnormal when the wheel speed information falls below the lower limit threshold value. The wheel speed detection device according to claim 1. 3. The method according to claim 1, wherein an upper limit threshold value that changes in accordance with a cycle of the square wave signal is set, and when the wheel speed information exceeds the upper limit threshold value, the wheel speed information is determined to be abnormal. The wheel speed detecting device according to claim 1 or 2, wherein: