JPH0476821B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an anti-skid control method for a vehicle having three or more wheels.

Prior Art As a four-wheel anti-skid control device, a vehicle speed sensor is installed in the transmission that transmits power to the driving wheels, and in the left and right driven wheels, which are wheels other than the driving wheels. Detecting the wheel speed, estimating the vehicle speed of the vehicle from the maximum wheel speed among the detected wheel speeds, determining a reference wheel speed from this estimated vehicle speed,
Compare this reference wheel speed with each wheel speed, and set the slip rate of each wheel to the optimum slip rate.
A system has been proposed that controls a brake device provided on each wheel. The reference wheel speed is usually found by subtracting the reference speed difference from the estimated vehicle speed, and the reference speed difference is sometimes taken as a constant value, but it is better to set it as a value proportional to the estimated vehicle speed to reduce the slip rate. This is desirable in order to maintain the correct value accurately.

However, since this anti-skid control device uses the maximum wheel speed of each wheel speed as a factor in creating the estimated vehicle speed, for example, if a sudden accelerator operation is performed just before the start of braking, causing an acceleration slip. In this case, the wheel speed of the driving wheel, which is rotating at a higher speed than the driven wheel due to slippage, is selected as the maximum wheel speed, and the estimated vehicle speed becomes a value larger than the actual vehicle speed. To make a concrete comparison, for example, if a vehicle starts off on a road with a relatively small coefficient of friction with its drive wheels slipping, and then immediately brakes suddenly, the drive wheels will slip as shown in Figure 1. The wheel speed Xw ₁ becomes a value larger than the wheel speed Vw ₂ of the driven wheel, which approximates the actual vehicle speed, and the estimated vehicle speed Vsb′ obtained from the maximum wheel speed becomes a large value.
Therefore, the reference vehicle speed Vs' is set based on the estimated vehicle speed, for example, the reference wheel speed Vs' is set to a value smaller than the estimated vehicle speed Vsb' by ΔV, and serves as the criterion for loosening the brakes. At the time Ts when braking is started by operation, the value becomes larger than the wheel speed Vw ₂ of the driven wheel, and the hydraulic pressure supplied to the brake device installed on the driven wheel is controlled to be lowered, which tends to lead to a decrease in braking force. Become.

Therefore, the vehicle speed is estimated based on the maximum wheel speed of the driven wheels instead of the driving wheels, a reference wheel speed is set from this estimated vehicle speed, and the braking force of each wheel is calculated based on this reference wheel speed. It is also possible to make adjustments. However, with this method, during normal braking, the reference wheel speed decreases faster at the beginning of braking than the drive wheel speed, so the braking force of the drive wheels loosens and braking is delayed, making it more likely to lock up. There are cases.

Purpose of the Invention Therefore, the purpose of the present invention is to estimate the estimated vehicle speed for determining the reference wheel speed based on the maximum wheel speed at all times, and to estimate it based on the intermediate wheel speed during acceleration slip. In particular, the purpose is to prevent the braking force from becoming too loose during braking immediately after an acceleration slip and to prevent skids from occurring during normal braking.

Structure of the Invention In order to achieve this object, the present invention calculates a maximum wheel speed and an intermediate wheel speed, which are the maximum and intermediate magnitudes, from the wheel speeds of three or more wheels, and calculates the intermediate wheel speed and the maximum wheel speed. If the difference is smaller than the set value, the reference speed difference is subtracted from the maximum wheel speed to obtain the reference wheel speed, and if the difference is greater than the set value, the reference speed difference is subtracted from the intermediate wheel speed. is characterized in that the reference wheel speed is determined by the reference wheel speed.

Effects of the Invention According to the present invention, the reference wheel speed is always determined from the maximum wheel speed, and when the speed difference between the maximum wheel speed and the intermediate wheel speed exceeds a set value,
The estimated vehicle speed for determining the reference wheel speed when determining an acceleration slip is switched from the maximum wheel speed to an intermediate wheel speed, so that skids do not occur during normal braking, and the braking force can be relaxed during braking immediately after an acceleration slip. You can prevent overdoing.

Therefore, regardless of changes in vehicle running conditions, the vehicle speed can be estimated to be close to the actual speed, and the braking force of each wheel can be adjusted so that the slip rate of each wheel becomes the optimum slip rate. I can do it.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a system diagram showing the overall configuration of one embodiment.
6, and the wheel speeds of the right rear wheel 18 and the left rear wheel 20, which are the driving wheels, are detected by the driving wheels 1
8, 20, and each wheel 10, 14, 18, 20 has a hydraulic brake device 26, 28, 3, respectively.
0 and 32 are arranged, and these hydraulic brake devices 2
6, 28, 30, and 32, the hydraulic pressure generated by the hydraulic cylinder 36 or the hydraulic pump 38,
It is configured to be supplied via each actuator 48, 50, 52, respectively. The hydraulic cylinder 36 generates brake hydraulic pressure when the driver depresses the brake pedal 34, and the hydraulic pump 38 generates hydraulic pressure according to engine rotation, and is also used as, for example, a power steering pump. be.

The actuator 48 is connected to the hydraulic brake device 26 of the right front wheel 10 by a hydraulic line 40,
Further, the actuator 50 is connected to the hydraulic brake device 28 of the left front wheel 14 through the hydraulic line 42, and further, the actuator 52 and the hydraulic line 44
Hydraulic brake device 3 of drive wheels 18, 20 by
0,32. These actuators 48, 50, 52 are operated by each hydraulic brake device 26, 28, 30,
The computer 46 adjusts the oil pressure supplied to each wheel speed sensor 12, 1.
A control command is issued in accordance with the deviation state between each wheel speed detected by the wheel speeds 6 and 24 and the reference wheel speed determined from the wheel speeds.

Each actuator 48, 50, 52 has a third
As shown in the figure, there is a regulator section 53 that adjusts the hydraulic pressure of the hydraulic pump 38 to a predetermined pressure, a control valve section 54 that includes an increase/decrease direction control solenoid for switching the increase/decrease direction of the brake hydraulic pressure, and a control valve section 54 that controls the increase/decrease gradient of the brake hydraulic pressure between high and low levels. A brake oil pressure adjustment section 56 including an increase/decrease gradient control solenoid for switching between stages is provided. The increase/decrease direction control solenoid of the control valve section 54, for example, causes the oil pressure to decrease in the direction of decrease when energized, and the increase/decrease gradient control solenoid of the brake oil pressure adjustment section 56, for example, makes the increase/decrease gradient of the oil pressure steep when energized. It's like that.

The computer 46 in the embodiment is a general-purpose microcomputer, and as is well known, the computer 46 is a general-purpose microcomputer.
The CPU performs arithmetic operations according to programs stored in the ROM. Of this program, the reference wheel speed calculation routine is a feature of the present invention, and this routine will be explained according to the flowchart of FIG. 4.

First, wheel speeds VwFR, VwFL, and VwR of the right wheel 10, left wheel 14, and rear wheels 18, 20 are calculated according to the outputs of the respective wheel speed sensors 12, 16, and 24. Next, these wheel speeds VwFR,
The maximum wheel speed Vwmax is calculated from VwFL and VwR using the following formula.

Vwmax = MAX (VwFR, VwFL, VwR) Additionally, the minimum speed Vwmin is calculated using the following formula.

Vwmin=MIN (VwFR, VwFL, VwR) Next, the minimum value is determined from the remaining wheel speeds excluding the minimum speed Vwmin using the following formula, and is set as the intermediate wheel speed Vwmed.

Vwend = MIN (other wheel speeds excluding Vwmin) Additionally, maximum wheel speed Vwmax and intermediate wheel speed
The difference ΔVw in Vwmed is calculated by the following equation.

ΔVw=Vwmax−Vwmed Here, the time during which the speed difference ΔVw exceeds the upper threshold value ΔVw ₀ is defined as T, and when T exceeds the set time To, the selected wheel speed Vwx is given by the following equation.

Vwx=Vwmed Furthermore, when the difference ΔVw falls below the lower threshold value _ΔVw1 before the above is established or after the above is established, the selected wheel speed Vwx is given by the following equation.

Vwx=Vwmax Selected wheel speed Vwx obtained in this way
A first reference wheel speed Vsan, which is a temporary reference wheel speed, is calculated using the following equation using the reference speed difference ΔV and the reference speed difference ΔV.

Vsan=Vwx−ΔV Here, ΔV is calculated by the following formula using the fixed speed Vo and the speed coefficient Kv.

ΔV=Vo+Kv・Vwx As is clear from the above explanation, the selected wheel speed
Vwx is used as the estimated vehicle speed,
Normally, the maximum wheel speed Vwmax is used as the estimated vehicle speed, and if the difference ΔVw between the maximum wheel speed Vwmax and the intermediate wheel speed Vwmed exceeds the upper threshold ΔVw ₀ , the intermediate wheel speed Vwmed is used as the estimated vehicle speed. It is.

However, in this embodiment, the selected wheel speed
What is obtained from Vwx is the primary reference wheel speed Vsan, which is the reference wheel speed for the time being.
This is not always used as the reference wheel speed. If the deceleration of the primary standard wheel speed Vsan becomes an impossible deceleration of the vehicle body, the speed calculated based on the primary standard wheel speed Vsan is used as the standard wheel speed. Sometimes it is done.

That is, the final reference wheel speed Vsn is determined by the following equation.

Vsn=MAX (Vsan, Vsbn) However, Vsbn in the above equation is the reference wheel speed Δt time after the previous time, which is obtained from the following equation using the previous reference wheel speed Vsn-1 and the reference deceleration αo. This can be called fixed deceleration speed.

Vsbn=Vsn−1−αo・Δt This deceleration fixed speed Vsbn is determined by changing the current wheel speed from the previous wheel speed Vsn−1 based on the idea that the actual vehicle deceleration cannot be larger than the reference deceleration αo. This is an estimate of the reference wheel speed Vsn, and is a reference wheel speed candidate that is opposed to the first reference wheel speed Vsan. While the deceleration of the primary standard wheel speed Vsan is smaller than the standard deceleration, the primary standard wheel speed Vsan is finally determined as the standard wheel speed, and the deceleration of the primary standard wheel speed Vsan is the standard deceleration. If it becomes larger, the other reference wheel speed candidate, deceleration fixed speed Vsbn, is finally determined as the reference wheel speed.

As mentioned above, the standard wheel speed Vsn, intermediate wheel speed Vwmed, obtained from the maximum wheel speed Vwmax
From the reference wheel speed Vsn obtained from the reference wheel speed Vsn obtained from the reference wheel speed Vsn obtained by fixing the deceleration,
When each of the above-mentioned conditions is met, one reference wheel speed Vsn is selected and used, so that the reference wheel speed Vsn is as shown in FIG. 5 when braking is started during an acceleration slip. It will be switched as shown.

The brake oil pressure of each wheel is controlled according to the deviation state between the reference wheel speed Vsn obtained in this way and the wheel speeds VwFR, VwFL, and VwR of each wheel. Specifically, as shown in the flowchart of FIG. 6, first, the reference wheel speed Vsn and the wheel speed Vwn of each wheel are compared, and the wheel speed Vwn of the corresponding wheel is smaller than the reference wheel speed Vsn. In this case, the increase/decrease direction control solenoid of the corresponding actuator is turned on, and the hydraulic pressure to the corresponding brake device is relaxed. On the other hand, when the wheel speed Vwn is higher than the reference wheel speed Vsn, the increase/decrease direction control solenoid is turned off and the hydraulic pressure to the brake device is increased. In addition, the current wheel speed
By dividing the difference between Vwn and the previous wheel speed Vwn-1 by the sampling time Δt, the wheel acceleration (negative deceleration) V〓wn of each wheel is determined by the following equation.

V〓wn=(Vwn−Vwn−1)/Δt Next, the on/off state of the increase/decrease direction control solenoid is checked, and if the increase/decrease direction control solenoid is turned on, the wheel acceleration V〓wn increases. Wheel acceleration compared with threshold GTH1
If V〓wn is less than the upper threshold GTH1,
The increase/decrease gradient control solenoid is turned on to increase the gradient of the brake oil pressure and quickly lower the brake oil pressure. On the other hand, when the wheel acceleration V〓wn exceeds the previous threshold value GTH1, the increase/decrease gradient control solenoid is turned off and the brake oil pressure is gradually lowered. In addition, when the increase/decrease direction control solenoid is off, the wheel acceleration V〓wn is compared with the lower threshold GTH2, and if the wheel acceleration V〓wn exceeds the lower threshold GTH2, the increase/decrease The gradient control solenoid is turned on and the brake oil pressure is quickly increased. On the other hand, if the wheel acceleration V〓wn is less than the lower threshold GTH2, the gradient control solenoid is turned off and the control oil pressure is gradually increased. It will be done.

Each wheel speed VwFR, VwFL in this example,
FIG. 7 shows the relationship between VwR and the wheel acceleration V wFR of the right front wheel 10, the operating states of the increase/decrease direction control solenoid and increase/decrease gradient control solenoid of the actuator 48 of the right front wheel 10, and the brake oil pressure of the output of the actuator 48. . As is clear from the figure, no acceleration slip occurs before braking, and the reference wheel speed Vsn is the wheel speed
The value is lower by the reference speed difference ΔV from Vwmax, which is the value obtained by tracing the maximum wheel speeds of VwFR, VwFL, and VwR. Furthermore, if the deceleration of Vwmax is greater than or equal to the reference deceleration αo, the deceleration is set to the reference deceleration. The speed is fixed at speed αo, and when a speed lower than Vwmax by the standard speed difference ΔV becomes greater than the speed decelerated at standard deceleration αo, the latter speed is again set as the standard wheel speed Vsn. .

The reference wheel speed Vsn calculated in this way and the wheel speed of the corresponding wheel, for example, the right front wheel 10, VwFR
The magnitude relationship between the wheel speed VwFR and the reference wheel speed Vsn is compared, and at times t ₁ , t ₇ , and t ₁₂ when the wheel speed VwFR becomes smaller than the reference wheel speed Vsn, the increase/decrease direction control solenoid is turned on and the brake oil pressure is decreased. Furthermore, when this brake oil pressure is in the decreasing direction, the wheel acceleration V〓wFR is
At times _t3 and _t8 when the upper threshold value GTH1 is exceeded, the increase/decrease gradient control solenoid is turned off, and the decrease gradient of the brake oil pressure is made gentler. On the other hand, the time when wheel speed VwFR exceeds reference wheel speed Vsn
At _t4 and _t10 , the increase/decrease direction control solenoid is turned off, and the brake oil pressure is increased. Furthermore, when the increase/decrease direction control solenoid is turned off, at times _t5 and _t11 when the wheel acceleration V〓wFR becomes less than the lower threshold GTH2, the increase/decrease gradient control solenoid is turned off, The gradient of increase in brake oil pressure is assumed to be gradual.

Although specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and includes various embodiments within the scope of the claims. For example, the reference wheel speed may be determined by detecting the speeds of all wheels using separate wheel speed sensors.

[Brief explanation of drawings]

Fig. 1 is a time chart showing the reference wheel speed calculated by a conventional anti-skid control device, Fig. 2 is a system diagram showing the overall configuration of an embodiment of the present invention, and Fig. 3 is an embodiment of the present invention. FIG. 4 is a block diagram showing the main part configuration of the actuator in the example. FIG. 4 is a flowchart showing the control flow of the computer for determining the reference wheel speed in the example. FIG. 5 shows changes in the reference wheel speed. FIG. 6 is a flowchart showing a control flow for operating an actuator by a computer in one embodiment, and FIG. 7 is a time chart showing an example of operation waveforms of each part in one embodiment. 10... Right front wheel, 12, 16, 24... Wheel speed sensor, 14... Left front wheel, 18, 20... Rear wheel, 22... Transmission, 26, 28,
30, 32... Hydraulic brake device, 34... Brake pedal, 36... Hydraulic cylinder, 38... Hydraulic pump, 40, 42, 44... Hydraulic pipe line, 46
... Computer, 48, 50, 52 ... Actuator, 53 ... Requilator section, 54 ... Control valve section, 56 ... Brake oil pressure adjustment section, VwFR
...Wheel speed of the right front wheel, VwFL...Wheel speed of the left front wheel, VwR...Wheel speed of the rear wheel, Vwmax...
Maximum wheel speed, Vwmed……Intermediate wheel speed, Vsan
...Primary reference wheel speed, Vsbn...Deceleration fixed speed, Vsn...Reference wheel speed, Vsn-1...Previous reference wheel speed, Vo...Fixed speed, Kv...Speed coefficient.

Claims (1)

[Claims] 1. The speed of each wheel of a vehicle having three or more wheels is detected, a reference wheel speed is determined from the wheel speeds, and the speed is added to each wheel so that each wheel speed matches the reference wheel speed. An anti-skid control method for adjusting the braking force of the three or more wheels, wherein a maximum wheel speed and an intermediate wheel speed, which are the maximum and intermediate magnitudes, are determined from the wheel speeds of the three or more wheels, and the intermediate wheel speed and the maximum wheel speed are determined. If the difference is smaller than the set value, subtract the reference speed difference from the maximum wheel speed to obtain the reference wheel speed, and if the difference is greater than the set value, subtract the reference speed difference from the intermediate wheel speed. An anti-skid control method characterized in that the speed is set as a reference speed.