JPH1183883A - Wheel speed computation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the computation accuracy of wheel speed by nullifying an edge generating subsequently when edges of same kind generate for a specified time in rising and falling edges. SOLUTION: When a sine-wave shaped wheel speed signal is output from a wheel speed sensor according to the rotation of a wheel, a rectangular wave is formed out of the sine wave from the sensor. Then, when pulse measurement processing means detects a rising or falling edge of the rectangular wave, measurement of pulse number is carried out, and furthermore wheel speed estimation means computes the wheel speed on the basis of the number of pulses measured in a specified cycle. In performing such the computation of wheel speed, compensation processing part determines the subsequent edge to be noise and nullifies it when edges of same kind generate in the rectangular wave formed by the rectangular forming means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for calculating a wheel speed from a wheel speed signal from a wheel speed sensor, which is used in an anti-lock brake (hereinafter, referred to as ABS) system or the like.

[0002]

2. Description of the Related Art As a wheel speed calculating device, a device configured to remove a noise component of a wheel speed sensor signal by a low-pass filter of an electronic circuit, or a digital filter configured by software to remove a noise component. Such a device is common.

[0003]

However, in such a conventional wheel speed calculating device, even if the low-pass filter of the electronic circuit can remove the noise component of the wheel speed sensor signal, the output of the low-pass filter circuit can be reduced. If noise is superimposed due to external factors between the stage and the input port of the microcomputer (hereinafter referred to as CPU), C
It is conceivable that the PU performs a calculation using the noise component as a wheel speed sensor signal and calculates a wheel speed far from the actual wheel speed. In this case, there is a possibility that a malfunction occurs in the ABS control. Also, if a digital filter is configured by software, phase delay will occur and real-time control will not be possible, or effective filtering will not be possible due to saving of sampling time, and controllability may deteriorate. Can be SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In a wheel speed calculation device, a value close to an actual wheel speed can be calculated even when noise is superimposed due to an external factor. Along with
It is an object of the present invention to improve the calculation accuracy of the wheel speed without causing a phase delay.

[0004]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 comprises a rectangular wave shaping means for inputting a sine wave wheel speed signal from a wheel speed sensor and shaping it into a square wave. A pulse measurement processing unit that detects a rising edge or a falling edge of the rectangular wave formed by the rectangular wave shaping unit and starts a pulse measurement process;
Wheel speed estimating means for estimating the wheel speed based on the number of pulses measured within a predetermined period, wherein the same type of edge among the rising edge and the falling edge is When a plurality of occurrences occur, a correction processing unit for invalidating an edge that occurs later is provided. According to a second aspect of the present invention, in the wheel speed computing device according to the first aspect, the predetermined time serving as an invalid determination criterion of the correction processing unit is a predetermined time when a wheel speed is set based on vehicle performance or a control target. When it was the maximum value, it was set as the period of the rectangular wave formed by the rectangular wave shaping means.

[0005]

When a sine-wave-shaped wheel speed signal is output from the wheel speed sensor with the rotation of the wheel, the wheel speed calculating device forms a rectangular wave from the sine wave from the wheel speed sensor by the rectangular wave forming means. Then, when the pulse measurement processing means detects a rising edge or a falling edge edge of the rectangular wave, it starts counting the number of pulses,
Further, the wheel speed estimating means calculates the wheel speed based on the number of pulses measured within a predetermined cycle. In performing such a calculation of the wheel speed, when a plurality of edges of the same type occur in the rectangular wave formed by the rectangular wave shaping unit, the correction processing unit determines that the later generated edge is noise or the like. And invalidate. Therefore, the pulse measurement processing means does not start measuring the number of pulses based on the edge generated thereafter, that is, does not calculate the wheel speed based on the edge generated thereafter. In addition, as described above, the predetermined time serving as a reference when the correction processing unit determines that an edge is invalid is a short time in which a plurality of edges cannot occur originally. When the wheel speed is a predetermined maximum value set on the basis of the vehicle performance or the control target as in the invention of the third aspect, the period of the rectangular wave formed by the rectangular wave forming means is set. Therefore, when the same type of edge is output within a time when the same type of edge cannot be output, it can be determined that the edge is abnormal and processed as invalid.

[0006]

Embodiments of the present invention will be described below. A description will be given of an example in which the present invention is applied to an ABS control device. Figure 1 shows the vehicle ABS
It is a block diagram which shows an apparatus, In the figure, 6a, 6
b and 6c are wheel speed sensors, 7 is a brake switch, and these are connected to the input interface 3 of the control unit 1. The wheel side sensor 6a
6c are provided at a total of three places: the left and right front wheels and the midway of driving force transmission to the rear wheels.

Reference numeral 9 denotes an ignition switch. When the ignition switch 9 is closed, a battery power supply 8 is connected to the control unit 1, and the signals of the wheel speed sensors 6a to 6c and the signal of the brake switch 7 are input to the input interface. The data can be input to the microcomputer 2 via the face 3. The battery power supply 8 is connected to the power supply regulator 5, and the power supply
Generates a voltage for operating the control unit 1, for example, 5V.

[0008] The microcomputer 2 executes arithmetic processing by a program stored in the ROM 12 based on the input signal of the input interface 3, and outputs an ABS hydraulic unit (hereinafter referred to as H / H) through the output interface 4.
The drive signal is output to a warning lamp 18 when a system abnormality is detected. Furthermore, the microcomputer 2
Is connected to a watchdog circuit 17. The watchdog circuit 17 monitors the program run signal from the microcomputer 2 and outputs a reset signal from the watchdog circuit 17 to the microcomputer 2 when the program run signal stops.

FIGS. 2 to 4 show the flow charts of the wheel speed pulse number measurement processing based on the inputs from the respective wheel speed sensors 6a to 6c. This process is a process of generating an interrupt process at the rising edge or the falling edge of the wheel speed pulse and measuring the number of pulses. FIG.
FIG. 3 shows a processing flow for measuring the wheel speed pulse edge on the front right (FR-RH).
FIG. 4 of LH) shows the measurement processing flow of each wheel speed pulse edge of the rear (RR). However, since each flow is almost the same, only the flow of FIG. 2 will be described, and the description of FIGS. Is omitted.

First, at step 19, the stack of the register is saved, and at step 20, the interrupt flag of this interrupt factor is cleared. Next, in step 21, it is determined whether or not the overflow flag (OVF) is set (1 or not). If it is set, the overflow flag OVF is cleared in step 22 and the overflow counter (OVF_CNT) is incremented in step 23.

The processing in steps 22 and 23 is essentially performed in the overflow interrupt processing (FIG. 5). However, if the pulse measurement interrupt processing of any of the three channels occurs prior to the overflow interrupt processing due to the priority of the interrupt and the state of interrupt enable / disable, the overflow occurs despite the overflow. There is a possibility that it is determined that the pulse has not been detected, resulting in erroneous pulse measurement. Therefore, the overflow counter (OVF_CNT) is generated by the earliest interrupt processing of the four interrupt factors of the pulse measurement interrupt processing and the overflow interrupt processing of the three channels.
S2 that can recognize the presence or absence of an overflow also in the pulse measurement interrupt processing so that
2, S23 was added. This eliminates erroneous determination of pulse measurement due to missing the overflow determination.

Next, at step 24, 1 is stored in the register A.
The free running timer value (T3FR) at the time of occurrence of the rising edge, which is 0 msec before, is read, and it is determined in step 25 whether or not the current interrupt is due to the fall. If it is due to the falling edge, the value of the free running timer (T1FR) at the time of occurrence of the falling edge, which is 10 msec before, is stored in the register A in step 26.
Read.

Next, at step 27, a comparison is made between the free running timer value (ICRA) at the time of occurrence of the current edge and the value of the register A. If the value of the register A is larger, the program proceeds to step 28. , This time (ICRA)
And the judgment value (P_CAN #) is compared with the absolute value of the difference between the free lining timer value and the judgment value (P_CAN #) at 10 msec before being read into the register A. It moves to step 33. On the other hand, if the absolute value of the difference (ICRA-A) is less than the threshold value, “2” is set in the register B, and the routine proceeds to step 32.

If the value of the register A is equal to or smaller than the free running timer value at the time of occurrence of the current edge, at step 30, the absolute value of the difference between the current value and the free running timer value of 10 msec before and the judgment threshold value ( P_CAN #)
If the value is equal to or larger than the threshold value, the process proceeds to step 33. If the value is smaller than the threshold value, "1" is set in the register B.

Next, at step 32, the overflow counter (OVF_CNT) and the value of F at 10 msec before are set.
The difference between the overflow counter (OVF_CNT_FR) at the time of calculation of R-RH (wheel speed of the right front wheel) is compared with the register B, and if the register B is smaller, it is determined that the input pulse is abnormal. The pulse number counting and time setting processing of steps 34 to 36 are cancelled, and the routine goes to step 37.

This means the following. 10mse
c is the difference between the free running timers and the judgment threshold (P_C
AN #) indicates that a pulse is input at a cycle shorter than the set time. At this time, (OVF) is determined by the presence or absence of overflow for 10 msec or the number of times.
_CNT-OVF_CNT_FR) to determine whether a pulse is input in a really short cycle. That is, if the number of overflows is equal to or less than the judgment threshold value (P_CAN #) under a predetermined number of overflows, the data size of the free running timer
* Since there is a time between the previous pulse input and the current pulse input for (the clock cycle inside the microcomputer), even if it is less than the determination threshold (P_CAN #), it cannot be said that a pulse is abnormal. Also, in this embodiment, two types of overflow count judgment (the register B) are set.
This is because the overflow state differs depending on the type of edge generation of the current and previous pulses.

If it is determined in step 32 that the value is equal to or greater than the determination threshold value, the overflow count at the time of the current pulse measurement is stored in step 33, and then in step 3
In the case of the rising edge input this time in step 4, step 3
At 5, the free running timer value for the operation after 10 msec is set (T3FR = ICRA) and the number of rising edges is counted (N3FR = N3FR + 1).
Move to step 37. In the case of the falling edge input this time, the free running timer value for the operation after 10 msec is set (T1FR
= ICRA) and rising edge count (N1FR)
= N1FR + 1), and the routine goes to Step 37. Finally, in step 37, the stack is returned to the original register, and the interrupt processing is terminated.

FIG. 5 shows a processing flow when the free running timer in the CPU 10 overflows.
This process is an interrupt process that is performed each time the free running timer in the microcomputer overflows.

First, at step 76, registers are stacked, and at step 77, the overflow flag (OVF) is cleared for the next overflow interrupt. Next, at step 78, the overflow timer (OVF_CNT) is incremented, and at step 79, the stacked registers are returned to the original state, and this interrupt processing ends.

FIGS. 6 to 8 show examples of operation patterns according to the present embodiment. To explain the symbols in the figure, FRC is a free-running timer inside the microcomputer, OVF_CNT is an overflow timer, and OVF_CNT_FR (FL, RR)
Is the overflow timer (OVF_CN) used in the previous calculation.
T), OVF is an overflow flag, T3FR (F
L, RR) are free running timer (FRC) values when a rising edge occurs, and T1FR (FL, RR) are free running timers (FR) when a falling edge occurs.
C) Value, N3FR (FL, RR) is a rising edge counter, and N1FR (FL, RR) is a falling edge counter.

First, referring to the pattern of FIG. 6, when the rising pulse a is generated, the free running timer value (FRC1) at that time is set to T3FR (FL, FL).
RR) and the rising edge counter (N3F
R (FL, RR)), and increments the current value n + 1 of the overflow timer (OVF_CNT) by the overflow timer (OVF_CNT_FR) at the time of the self-calculation.
(FL, RR)).

Thereafter, when the rising edge b occurs, the free running timer value (FRC2) at the time when the rising edge b occurs and the FRC value (FRC1) at the time when the previous rising edge a occurred are compared according to the above-described flow. And the difference (t1) is determined by the determination threshold (P_CAN).
If it is larger than #), it is determined that the current edge b is valid, and T3FR (FL, RR) and N3FR (F
L, RR) and OVF_CNT_FR (FL, RR).

The pattern shown in FIG. 7 is similar to the pattern shown in FIG.
The difference (t1) between the free running value and the edge b is a pattern equal to or larger than the determination threshold value (P_CAN #). In this example, an overflow occurs between the edge a and the edge b, and the free running occurs. The magnitude relation of the values is opposite to the pattern of FIG. However, since the difference (t1) is equal to or greater than the determination threshold value (P_CAN #), T3FR (FL, RR), N3FR
(FL, RR), OVF_CNT_FR (FL, RR)
Perform data capture of

Next, the pattern of FIG. 8 shows a case where the difference (t1) between the free running values between the edge a and the edge b is equal to or smaller than the judgment threshold value (P_CAN #). this is,
A pulse is input at a cycle equal to or shorter than a predetermined value, and it is determined that a pulse is abnormal, so that a free running value when an edge b occurs is not taken in (it remains FRC1 when an edge a occurs), and a rising edge counter (N3FR) (FL, R
R)) is not updated (n + 1), and the overflow counter (OVF_CNT_FR) at the time of its own calculation is used.
The value of (FL, RR) is not updated (n + 1). That is, despite the occurrence of the edge, the data related to the pulse measurement is not updated, and a state as if the edge did not occur is realized.

To explain a specific example, if the operation cycle of the control system operated by the CPU 10 is 10 (msec), A
Vmax is the maximum value of wheel speed used for BS control calculation.
(Km / h), the number (X) of wheel speed pulses generated in 10 (msec) is as follows. X = (Vmax / 3.6 × N) / 2πr where N is the number of teeth of the sensor rotor, and r is the tire radius (m). In this case, in the ABS control, when X or more sensor pulses are input, such pulse input can be regarded as unnecessary input as long as the maximum value of the wheel speed is set to V (km / h).

Then, the pulse period (T) at the wheel speed Vmax (km / h) is T (sec) = (0.01 × 2πr) / (Vmax /
3.6 × N). After inputting the reference wheel speed pulse, T
The wheel speed pulse generated until (sec) is not used for wheel speed calculation (not counted as a pulse)
Accordingly, even when a high-frequency signal is superimposed on the wheel speed input port of the CPU 10 due to noise or the like, the wheel speed is not excessively calculated, and the stable ABS is prevented without increasing the braking distance. Control can be realized.

Although the preferred embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this preferred embodiment, and a design change or the like may be made without departing from the gist of the present invention. Even if present, it is included in the present invention.

[0028]

As described above, according to the present invention, when a plurality of edges of the same type among the rising edge and the falling edge occur within a predetermined time, the correction that invalidates the later edge is made invalid. Since the processing unit is provided, even if noise is superimposed due to an external factor, the noise can be invalidated and processed to calculate a value close to the actual wheel speed. Therefore, the effect that the calculation accuracy of the wheel speed can be improved can be obtained, and in the control such as the ABS control performed based on the wheel speed calculated by the wheel speed calculation device, the calculation including the noise is performed. An effect is obtained in that defective control is not performed by the wheel speed.
According to the second aspect of the present invention, when the wheel speed is a predetermined maximum value set based on the vehicle performance or the control target,
Since the configuration is a period of the rectangular wave formed by the rectangular wave shaping means, the calculated wheel speed does not become higher than a predetermined maximum wheel speed due to noise or the like. It is possible to keep the error within a predetermined error range, and it is possible to prevent the malfunctioning control from being performed based on the calculated wheel speed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ABS device.

FIG. 2 is a flowchart of a wheel speed pulse measurement process for a right front wheel.

FIG. 3 is a flowchart of a wheel speed pulse measurement process for a front left wheel.

FIG. 4 is a flowchart of a rear wheel wheel speed pulse measurement process.

FIG. 5 is an interrupt processing flow when a free-running timer in a CPU overflows.

FIG. 6 is a time chart showing an operation waveform for each pattern according to the embodiment.

FIG. 7 is a time chart showing an operation waveform for each pattern according to the embodiment;

FIG. 8 is a time chart showing an operation waveform for each pattern according to the embodiment.

[Explanation of symbols]

 Reference Signs List 1 control unit 2 microcomputer 3 input interface 4 output interface 5 power supply regulator 6a wheel speed sensor 6b wheel speed sensor 6c wheel speed sensor 7 brake switch 8 battery power supply 9 ignition switch 10 CPU 11 RAM 12 ROM 13 input / output unit 14 timer 15 A / D converter 16 ABS hydraulic unit 17 Watch dock circuit 18 Warning lamp

Claims (2)

[Claims] 1. A rectangular wave shaping means for inputting a sine-wave-shaped wheel speed signal from a wheel speed sensor and shaping it into a rectangular wave, and a rising edge or a falling edge of a rectangular wave formed by the rectangular wave shaping means. The wheel speed calculation device comprising: a pulse measurement processing unit that detects and starts a pulse measurement process; and a wheel speed estimation unit that estimates a wheel speed based on the number of pulses measured within a predetermined period. A wheel speed calculation device, comprising: a correction processing unit that invalidates a later generated edge when a plurality of edges of the same type out of an edge and a falling edge occur within a predetermined time. 2. The rectangular wave shaping means is provided when the wheel speed is a predetermined maximum value set based on vehicle performance or a control object, and the predetermined time serving as an invalid judgment reference of the correction processing unit is formed. The wheel speed calculation device according to claim 1, wherein the period is a period of a rectangular wave.