JPS6234575B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a skid control device that controls brake oil pressure when a wheel skid occurs during braking of a vehicle, and more particularly to a skid control device that uses a microcomputer.

In skid control, a slip rate is calculated from the calculation result of the wheel speed, and when this slip rate reaches a specified value, the brake is loosened, and then when the slip rate has recovered to the specified value, the brake is released. The system then measures the brake release time and uses the results to control the next brake release timing. Thereafter, this series of controls is repeated to maximize the coefficient of friction between the wheels and the road surface, thereby shortening the braking distance. Furthermore, it is impossible to obtain the virtual vehicle speed from only the wheel speed signal, and this control device assumes the virtual vehicle speed to be a certain constant value, for example -g, from the equation of motion between the vehicle body, wheels, and road surface. In order to correct this assumption, the timing of the second and subsequent brake release signals is changed depending on the brake release time in the previous control. That is, the slip rate required from the second time onwards is a function of the brake release time. Therefore, to determine the brake release timing and brake release time, first measure the previous brake release time, and
It is necessary to calculate a slip rate in a predetermined relationship corresponding to this time, and to control the brake release timing so as to achieve this slip rate. If a device for this control were to be implemented using a conventional discrete type circuit, it would have a very complicated configuration, so instead of finding the slip ratio, an approximate value of the slip ratio is generally calculated from the measured value of the brake release time. A method was taken. However, with this method,
Since it is not possible to perform accurate control that responds quickly to changes in driving conditions, there are drawbacks such as lack of control stability and long braking distances. A skid control device using a microcomputer is disclosed in, for example, Japanese Patent Application Laid-Open No. 1986-
It is known from Publication No. 151231.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device for quickly calculating the slip rate that determines when to release the brake.

A feature of the present invention is that slip rate calculation for skid control is performed using a microcomputer equipped with a memory into which data giving the relationship between the brake release time and the slip rate to be controlled is input. The brake release time is measured by finding the difference between the counts of the free-running counter, and based on the obtained measurement results, the slip rate to be controlled is picked up from memory.

Figure 1 shows a microcomputer (hereinafter referred to as CPU)
1 is a configuration diagram of a skid control system using a skid control system.

Power from an engine (not shown) is transmitted to a differential gear 15 via a gear box (not shown) and a propeller shaft 13 to drive rear wheels 17.

An output signal from a wheel speed sensor 19 attached to the propeller shaft 13 is input to the control device 11 via a signal line 21 . Control device 11 includes a microcomputer and input/output circuits.
Details will be described later. The actuator 23 has a solenoid 25 operated by an output signal transmitted from the control device 11 via a signal line 27. Engine manifold negative pressure is introduced into the diaphragm chamber within the actuator 23 via a pipe 29, and atmospheric pressure is introduced via an air filter 31 and a pipe 33. On the other hand, a piston rod is connected to the diaphragm in the diaphragm chamber. Further, the force generated by stepping on the brake pedal 35 is transferred to the master cylinder 37.
is converted into hydraulic pressure and sent to the hydraulic control valve 39. The hydraulic pressure output from the hydraulic control valve 39 is transmitted to the actuator 23 via a pipe 45 as a braking force for braking the front wheels 43 via a pipe 41 . The brake hydraulic pressure controlled by the piston rod within the actuator 23 is supplied via a pipe 47 as a brake force for braking the rear wheels 17. In addition, the control device 11
The negative power supply voltage of the actuator 23 and the actuator 23 are connected through a conductive wire 49, so that the potential is common. A warning lamp 51 is connected to the control device 11 to warn of an abnormality in the control operation. Further, a fuse 53 is connected to cut off the power supply to the control device 11 in order to return to the normal braking state when an abnormality occurs. When the ignition key switch 55 is turned on, power is supplied from the power supply 56 to the control device 11 via the fuse 53.

During braking, when the solenoid 25 is activated (ON), the piston rod connected to the diaphragm in the actuator 23 moves, thereby reducing the hydraulic pressure and producing the effect of loosening the brake.

A more detailed circuit diagram of the control device 11 in FIG. 1 is shown in FIG. Positive power supply terminal 1 of control device 11
11 is connected to the positive terminal of the power supply, and a voltage V _B is supplied to the control device 11 . The power supply voltage V _B is set to a constant voltage V _CC by the constant voltage circuit 113, for example, +5 (V).
is held constant. This constant voltage V _CC is
135. CPU135 is MPU115
(microprocessor), RAM117 (random access memory), ROM119 (read/read memory)
only memory) register control circuit 131,1
33, free running counter 123, 12
5, including registers 127 and 129.

Further, the constant voltage V _CC is also supplied to the input/output circuit 121 . Furthermore, MOTOROLA's model has a built-in free running counter.
MICROCOMPUTER UNIT, MC6801 is known.

The wheel speed sensor 19 detects the rotation of the rotor 136.
It is converted into an AC voltage by an electromagnetic pickup 137 and then passed through a waveform shaping circuit 139 to the input/output circuit 12.
Supply to 1. Further, the output of the input/output circuit 121 passes through amplifiers 141, 143, and 145, and is connected to a fuse 53, an alarm lamp 51, and a solenoid 25, respectively.

MPU115, RAM117, ROM1 mentioned above
19, registers 127, 129 and input/output circuit 12
1 are connected by a data bus, an address bus, and a control bus 147 (all buses are represented by 147). Furthermore, from MPU115, RAM1
17, ROM 119, free-running counters 123 and 125, and input/output circuit 121, respectively, are applied with a basic clock signal E, and data is transmitted in synchronization with this clock signal E.

Free-running counters 123 and 125 count clock signal E. When the count value overflows, an overflow signal is sent to the register control circuits 131 and 133, and the counter 12
3,125 starts counting from the beginning and repeats this. The register control circuits 131 and 133 are
It controls at what timing the free running counter value is stored in the registers 127 and 129.

Next, the operation of the skid control device of the present invention will be explained.

When a rotating body, such as a car, is moving on a plane in a constant direction at a speed of V and slips, the slip rate S is defined as follows.

S=(V-ωR)×100/V(%) ......(1) Here, R is the radius of the rotating body, ω is the angular velocity of the rotating body, and the friction coefficient μ is the friction coefficient between the wheel tire and the road surface. is expressed as a function of the slip rate S. According to experiments, the coefficient of friction μ in the traveling direction has a maximum value when the slip rate S is around 20%, and the coefficient of friction μ in the lateral direction decreases as the slip rate S increases.

Therefore, if the slip rate S is controlled to be around 20%, the coefficient of friction μ between the tire and the road surface can be maximized when skid occurs. The skid control device of the present invention controls the slip rate S to such a value when a skid occurs.

Next, FIGS. 3 and 4 are flowcharts showing the operation of the control device of the present invention. First, in step 05 of FIG. 3, the register group is initialized, and at the same time, the polarity of the trigger for storing the free running counter value in the register is also specified. In step 10, the functions of the control circuit, particularly the memory and input/output circuit, are self-checked.
A certain pattern is given from the MPU, and if a signal corresponding to that pattern is obtained, it is determined in step 15 that the check is OK. If an abnormality occurs during the self-check, the alarm lamp 15 indicates this (step 20), and at the same time, the self-check is performed a predetermined number of times in step 25. If the abnormality is not corrected even after the predetermined number of self-checks have been completed, a warning lamp will indicate this and the operation will be stopped in step 30. That is, in this case, normal braking operation is performed and skid control is not performed.

If the self-check is OK in step 15, proceed to step 35. In step 335, the free-running counter count value is stored in a register, and the wheel speed is calculated by subtracting between the registers. In step 37, it is determined whether the actuator solenoid is ON. Initially it is OFF. In step 40, it is determined from the change in wheel speed whether sudden braking has been applied. That is, if the decrease in wheel speed is equal to or greater than a predetermined value, it is determined that sudden braking is occurring.

This will be explained with reference to FIG.

Figure 5 shows vehicle speed, virtual vehicle speed, wheel speed, and increase in brake fluid pressure (ON) when sudden braking is applied and brake fluid pressure is controlled so that the coefficient of friction between the wheels and the road surface is maximized. It is a figure which showed the relationship of reduction (OFF). Assume that the car is traveling at a speed of _Vs. If sudden braking is applied in this condition,
The wheel speed decreases as in characteristic A.

Referring again to FIG. 3, if sudden braking is not applied, the process returns to step 35 and the wheel speed is calculated. During normal driving (driving without sudden braking), the closed loop of steps 35 and 40 is completed. When sudden braking is detected in step 40, control moves to step 45. Step 4
In step 5, a virtual vehicle speed is calculated from the calculated wheel speed values.

Here, the virtual vehicle speed will be explained. In the formula for calculating the slip rate S, V is defined as the absolute vehicle speed of the rotating body (this corresponds to the vehicle body speed). Therefore, the slip rate S
In order to calculate this, the vehicle speed must be detected. In the case of a car, it is impossible to directly determine the vehicle speed because it uses four-wheel braking. Therefore, it is necessary to obtain a virtual vehicle speed that corresponds to the vehicle speed and define this as one of the control elements.
Generally, a slope of -1.4 to -1.7 g is regarded as the virtual vehicle speed, and the slip rate S in equation (1) is calculated.

In FIG. 5, the broken line B indicates the virtual vehicle speed, and the vehicle decelerates at the above-mentioned slope from the deceleration starting point.
The wheel speed calculated in step 35 and step 4
From the comparison with the virtual vehicle speed calculated in step 5, it is determined in step 50 of FIG. 4 whether the specified ON slip rate, ie, the slip rate at which the actuator solenoid should be turned on, has been reached. Specified in step 50
When the ON slip rate is reached, in other words, when the point shown in FIG. 5 is reached, a brake release signal is issued in step 55. It is experimentally known that the specified ON slip rate at the point is preferably 0.5.

When the brake release signal is issued, this output is stored in the memory in step 56 and is held until the output mode of the input/output circuit section is rewritten.
After issuing the brake release signal in step 55, control returns to step 35 in FIG. At step 37, since the actuator is turned on, the process moves to step 58 of FIG. In step 58, it is determined from the comparison of the wheel speed and the virtual vehicle speed whether the slip rate has reached the slip rate at which the actuator solenoid should be turned off, that is, the specified OFF slip rate. The specified OFF slip rate is always a constant value, ie, 0.2 not only at the point in FIG. 5 but also at the point. If the predetermined OFF slip rate is not reached, for example at point 3 in FIG. 5, the process returns to step 35. When the predetermined OFF slip rate, that is, after the point in FIG. 5 is reached, the process moves to step 60.

If the actuator is not currently ON in step 60, the process returns to step 35; if it is ON, the process proceeds to step 65. In step 65, the brake release signal is canceled and in step 70, it is turned on.
Measure TIME (the time during which the brake release signal was output). In step 75, the specified ON required for the next control is determined from the ON TIME measured in step 70.
The slip rate, that is, the slip rate at the point in FIG.

The ON TIME during which the brake release signal is output changes depending on the magnitude of the friction coefficient μ.

Also, since the virtual vehicle speed is assumed to be -g,
To compensate for this, the timing of the second and subsequent brake release signals is changed depending on the ON TIME of the previous control. In other words, the slip rate required from the second time onwards is
It is a function of ON TIME.

FIG. 6 is a diagram showing the relationship between ON TIME and specified ON slip rate S. In the figure, the time during which the nth brake release signal is output is t _ON(o)
Suppose it was. The specified ON slip rate S, which determines the timing at which the n+1st brake release signal is issued, is calculated as S _o . Repeat this until the wheels stop. Since the relationship shown in FIG. 6 is difficult to express as an equation, it is made into a table at specific intervals, for example every 10 ms, and input into the memory. By doing this, t _ON
It is possible that once _(o) is measured, S _o is immediately obtained. Note that the points in FIG. 6 correspond to the points in FIG. 5, respectively.

Next, Figure 7 shows the free running counter 12.
3, 125, registers 127, 129, and register control circuits 131, 133. FIG. The basic clock signal E output from the MPU 115 is sent to the free running counter 123.
(On the other hand, it is substituted. The same applies hereafter). Regardless of the operation of the MPU, the free running counter 123 is set as shown in a and b in FIG.
The count is counted up or down in synchronization with the clock signal E from the counter value specified at initialization. A in FIG. 8 counts up from the initialized value $OO, and when the counter value reaches $FF, it becomes $OO with the next clock signal E and counts up again. At b in FIG. 8, the count is counted down from the initialized value $FF, and when the counter value reaches $OO, it becomes $FF with the next clock signal E, and the count is counted down again. Count up or count down mode can be specified depending on the control method.

In FIG. 7, the register control circuit 131 includes:
The MPU 115 issues a command to send a trigger signal to the register 127 at the rising edge of the input signal or to send the trigger signal at the falling edge of the input signal. In register 127, depending on the trigger signal,
Free running when a trigger signal occurs
The count value of counter 123 is stored. The register 127 has, for example, a 16-bit register configuration.

In this control, the virtual vehicle speed is assumed to be -g, so the slip rate S required from the second time onwards is the time during which the previous brake release signal was issued.
I mentioned earlier that it is a function of ON TIME.

FIG. 9 is a diagram showing a method for determining ON TIME. In FIG. 9, the output of the brake release signal and the output of the brake release release signal are respectively used as trigger signals, and the free running counter count values at the corresponding timings are set in the P' register 155 and the Q' register 157. Store in. After the storage is completed, subtraction is performed between both registers, the result is stored in, for example, the S' register 159, and the next timing for issuing the brake release signal is determined from that value. In Fig. 9, if the time during which the brake release signal is output is PW1, the corresponding slip rate S is 6th.
It can be determined by table search from the relationship shown in the figure, and when the slip ratio is reached, a brake release signal is issued again. If the duration is PW2, the slip rate S corresponding to that time is similarly determined by table search, and this is repeated thereafter.

In the embodiment, registers 127 and 127 are used as memories for storing free-running counter values.
Although we have shown an example using 129, it is also possible to replace both registers with latches, use the CPU's internal memory (RAM) for the counter value, and also perform subtraction between the two free running counter values between the internal memories. You can do it like this. Furthermore, the functions of the register control circuits 131 and 133 may be executed within the CPU.

According to the present invention, since the original relational expression between the slip rate and the brake release time is stored in the memory as a table, the slip rate can be determined accurately. In addition, the table can be made as fine as possible and there are no problems with circuit scale or size, which is extremely advantageous for commercialization.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a skid control device using a microcomputer according to an embodiment of the present invention, FIG. 2 is a detailed diagram of the control device portion of an embodiment of the present invention shown in FIG. 1, and FIG. , FIG. 4 is a flowchart showing the operation of the control shown in FIG. 2, and FIG. 5 shows the relationship among the vehicle speed, virtual vehicle body, wheel speed, and operation of the actuator for controlling brake oil pressure during sudden braking. FIG. 6 is a diagram showing the relationship between the brake release time and the slip rate S. Fig. 7 is an explanatory diagram of the operation between the free-running counter, register, and register control circuit; Fig. 8 is an explanatory diagram of the operation of the free-running counter; and Fig. 9 is a diagram illustrating the method for determining the ON time of the actuator. It is. 115...MPU, 117...RAM, 123...
...Free running counter, 125...Free running counter.

Claims (1)

[Claims] 1. A control circuit including a wheel speed sensor and a microcomputer, which calculates the wheel speed in response to a pulse signal from the wheel speed sensor, and outputs a brake release signal when the wheel is skidding; Accordingly, in the skid control device comprising a brake hydraulic pressure control device for controlling the hydraulic pressure of the wheel braking means, the microcomputer stores a free-running counter for counting clock pulses and a count value of the free-running counter. and a memory in which data giving the relationship between the slip rate and the brake release time are stored. During skid control, the predetermined slip rate for the timing of applying the brake is determined based on the previously controlled brake release time. A skid control device characterized in that the skid control device is configured such that data giving the relationship between the slip rate and the brake release time is calculated from a stored memory.