GB2092249A

GB2092249A - Vehicle Skid Control Arrangements

Info

Publication number: GB2092249A
Application number: GB8103391A
Authority: GB
Original assignee: Nabco Ltd
Current assignee: Nabco Ltd
Priority date: 1981-02-04
Filing date: 1981-02-04
Publication date: 1982-08-11
Also published as: DE3103967C2; GB2092249B; DE3103967A1

Abstract

A vehicle skid control arrangement includes a wheel speed detector 2, a differentiator 5, a deceleration signal generator 6, generating a deceleration signal when the output signal of the differentiator 5 exceeds a predetermined threshold deceleration, and an acceleration signal generator 7 generating an acceleration signal when the output signal of the differentiator 5 exceeds a predetermined threshold acceleration. The arrangement controls a valve solenoid 28 for decreasing the brake pressure when the deceleration signal is present, and a valve solenoid 25 for holding the brake pressure constant or allowing it to increase slowly when the acceleration signal is present. In addition the valves allow a rapid increase in pressure for a predetermined time while the acceleration signal is present. This arrangement compensates for the error in acceleration and deceleration detection due to the flexibility of the structure on which the fixed part of the wheel speed sensor is mounted. <IMAGE>

Description

SPECIFICATION Vehicle Skid Control Arrangements This invention relates to vehicle skid control arrangements.

Vehicle skid control arrangements are used to avoid wheel locking and to obtain good braking performance on any road. In a conventional skid control arrangement, rotational conditions of a wheel, such as deceleration, slip and acceleration are measured to skid-control the wheel. When the deceleration or slip of the wheel exceeds a predetermined threshold deceleration or a predetermined threshold slip, the brake pressure to the brake is decreased, and when the acceleration of the wheel exceeds a predetermined threshold acceleration, the brake pressure to the wheel is maintained constant, namely at the decreased brake pressure, or gradually increased.

A wheel speed sensor is associated with the wheel for detecting the rotational speed of the wheel. The acceleration, deceleration and slip of the wheel are measured on the basis of the output of the wheel speed sensor. A part of the wheel speed sensor is mounted to be rotated with the wheel, and a stationary part of the wheel speed sensor is mounted on the chassis or body of the vehicle. When the vehicle is decelerated or accelerated, an inertial force is applied to the body or chassis of the vehicle. Accordingly, the body or chassis of the vehicle moves relative to the wheel, so that the stationary part of the wheel speed sensor rotates relative to the rotary part of the wheel speed sensor.The rotational direction of the stationary part relative to the rotary part is in a direction decreasingly to detect the actual rotational speed of the wheel, when the brake pressure to the wheel is increased to reduce the rotational speed of the wheel. And it is in the opposite direction, increasingly to detect the actual rotational speed of the wheel, when the brake pressure to the wheel is decreased, to raise the rotational speed of the wheel. The actual rotational speed of the wheel responds to the change of the brake pressure almost without delay. However, the rotation of the stationary part relative to the part in the wheel speed sensor responds to the change of the brake pressure with some lag.

Accordingly, the magnitude of the change of the wheel speed detected by the wheel speed sensor is larger than that of the actual change of the wheel speed and the wheel speed detected by the wheel speed sensor lags in phase behind the actual wheel speed. When the acceleration or deceleration of the wheel changes slowly, the amplification of the change of the wheel speed and the phase lag of the wheel speed are small.

When the acceleration or deceleration of the wheel changes rapidly, the amplification of the wheel speed and the phase lag of the wheel speed are large.

Particularly in a two-wheeled vehicle such as a motor cycle, the above rotation of the stationary part relative to the rotary part is large. The wheel speed sensor is associated with the front wheel, which is rotatably supported by two front forks having relatively low rigidity. The stationary part of the wheel speed sensor is mounted on the front forks. When the brake pressure to the brake is changed, the front forks move substantially relative to the front wheel on which the rotary part of the wheel speed sensor is mounted. The change of the wheel speed detected by the wheel speed sensor, when the deceleration or acceleration of the wheel changes rapidly, is much amplified in comparison with the actual change of the wheel speed, and the detected wheel speed lags substantially in phase behind the actual wheel speed.The control of the brake pressure is disturbed by this amplification and phase lag. Particularly when the decrease of the brake pressure is stopped with a predetermined level of the acceleration or deceleration of the wheel, the brake pressure is lowered excessively, that is reduced more than required. Accordingly, the braking distance of the vehicle is increased.

According to the present invention there is provided a vehicle skid control arrangement comprising: wheel speed detecting means for providing an output signal representative of the speed of a wheel of a vehicle; differentiating means for differentiating said output signal of the wheel speed detecting means and providing an output signal representative of acceleration or deceleration of said wheel; a deceleration signal generator connected to said differentiating means, said deceleration signal generator generating a deceleration signal when the output signal of said differentiating means exceeds a predetermined threshold deceleration; an acceleration signal generator connected to said differentiating means, said acceleration signal generator generating an acceleration signal when the output signal of said differentiating means exceeds a predetermined threshold acceleration;; brake relieving means for decreasing the brake pressure to the brake for said wheel in response to the deceleration signal of said deceleration signal generator; first brake control means for maintaining the brake pressure to the brake for said wheel constant, or gradually increasing the brake pressure to the brake for said wheel, in response to the acceleration signal of said acceleration signal generator; and second brake control means for rapidly increasing the brake pressure to the brake for said wheel for a predetermined time within the time when said acceleration signal generates the acceleration signal.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an embodiment of vehicle skid control arrangement according to the invention; Figure 2 is a schematic view of a brake apparatus in the arrangement of Figure 1; and Figure 3 are time charts for explaining the operation of the arrangement of Figure 1.

Referring to Figure 1, a vehicle skid control arrangement comprises a wheel speed sensor 1 associated with one wheel of the vehicle to generate a pulse signal having a frequency proportional to the rotational speed of the wheel.

The pulse signal of the wheel speed sensor 1 is supplied to a wheel speed generating circuit wheel speed detector 2 to be converted to a wheel speed signal V having an analog or digital value proportional to the rotational speed of the wheel.

The wheel speed signal V from the wheel speed detector 2 is supplied to an approximate body (vehicle) speed generator 3, a slip signal generator 4 and a differentiator 5. Since the actual speed of the vehicle cannot be conveniently measured directly, the vehicle speed is simulated by the approximate vehicle speed generator 3. The simulated (approximate) vehicle speed signal E (shown in Fig. 3A) from the approximate vehicle speed generator 3 is supplied to the slip signal generator 4 to determine the sip of the wheel. In the slip signal generator 4, the simulated vehicle speed signal E is compared with the wheel speed signal V.Generally, a slip S is given by the following formula: wheel speed S=1- vehicle speed When (I--V/E) is larger than a predetermined threshold slip (for example 0.20), the slip signal generator 4 generates a slip signal S, namely the output of the slip signal generator 4 becomes of higher level "1". And when (1--V/E) is smaller than the predetermined threshold slip, the output of the slip signal generator 4 becomes of lower level "0".

The wheel speed signal V of the wheel speed signal detector 2 is differentiated with respect to time in the differentiator 5. A signal 9 proportional to the acceleration or deceleration of the wheel is generated in the differentiator 5, and it is supplied to a deceleration signal generator 6 and an acceleration signal generator 7. In the deceleration signal generator 6, the output signal V of the differentiator 5 is compared with a predetermined threshold deceleration which is, for example, equal !o -1.5 9. When the absolute value of the signal V is larger than that of the predetermined threshold deceleration, the deceleration signal generator 6 generates a deceleration signal -h, namely the output of the deceleration signal generator 6 becomes "1".And when the absolute value of the signal V is smaller than that of the predetermined threshold deceleration, the output of the deceleration signal generator 6 becomes "0".

In the acceleration signal generator 7, the output signal 2 of the differentiator 5 is compared with a predetermined threshold acceleration which is, for example, equal to 0.5 g. When the signal V is larger than the predetermined threshold acceleration, the acceleration signal generator 7 generates an acceleration signal +b, namely the output of the acceleration signal generator 7 becomes "1". And when the signal V is smaller than the predetermined threshold acceleration, the output of the acceleration signal generator 7 becomes "0".

An output terminal of the deceleration signal generator 6 is connected to a set terminal S of a flip-flop 8, an input terminal of an OR gate 9, and OFF-delay timer 21, and an input terminal of another OR gate 26. Another input terminal of the OR gate 26 is connected to an output terminal of the slip signal generator 4.

The output of the OFF-delay timer 21 becomes "1" at the same time as the deceleration signal -b is generated from the deceleration signal generator 6. It is maintained at "1" for a predetermined time, for example, 0.1 second, after the deceleration signal -h disappears namely the output of the deceleration signal generator 6 becomes "0" and then it also becomes "0".

An inversion output terminal Q of the flip-flop 8 is connected to another input terminal of the OR gate 9. A reset terminal R of the flip-flop 8 is connected to an output terminal of the acceleration signal generator 7. An output terminal of the OR gate 9 is connected to a reset terminal R of a first UP-counter 10. A clock terminal C of the counter 10 is connected to an output terminal of an AND gate 11. An input terminal of the AND gate 12 is connected to a pulse generator 12 which generates clock pulses fo having a predetermined frequency. Output terminals 0 of the counter 10 are connected to input terminals 12 of a comparator 13. A predetermined digital value N is set at other input terminals 1, of the comparator 13.An output terminal 0 of the comparator 13 is connected to a negation input terminal of the AND gate 11.

The output terminals 0 of the counter 10 are further connected to input terminals D of a latch circuit 14. A latch terminal L of the latch circuit 1 4 is connected to the output terminal of the acceleration signal generator 7. The latch circuit 14 memorizes a counted value of the counter 10 at the moment that the output of the acceleration signal generator 7 becomes "1". An inversion output Q having a complementary value to the counted value of the counter 10 is obtained from output terminals Q of the latch circuit 14, and it is supplied to input terminals Ii of a second comparator 1 5. Other input terminals 12 of the comparator 1 5 are connected to output terminals O of a second UP-counter 16.

A clock terminal C of the counter 16 is connected to an output terminal of an AND gate 1 7. An input terminal of the AND gate 17 is connected to the pulse generator 12. A reset terminal R of the counter 16 is connected to an output terminal of an invenor 29. An input terminal of the invertor 29 is connected to the output terminal of the acceleration signal generator 7. An output terminal 0 of the comparator 1 5 is connected to a set terminal S of a flip-flop 18, and negation input terminal of the AND gate 1 7.

When the output of the latch circuit 14 becomes equal to a counted value of the counter 16, the output of the comparator 15 becomes "1" to set the flip-flop 18 and to close the AND gate 1 7.

An output terminal of the OR gate 26 is connected through an AND gate 20 to a reset terminal R of the flip-flop 1 8. A negation input terminal of the AND gate 20 is connected to the output terminal of the acceleration signal generator 7. An output terminal Q of the flip-flop 18 is connected to one input terminal of and AND gate 1 9. Another input terminal of the AND gate 1 9 is connected to the output terminal of the acceleration signal generator 7 which is further connected to a negation input terminal of an AND gate 22. Another input terminal of the AND gate 22 is connected to the output terminal of the OFF-delay timer 21.

An output terminal of the AND gate 1 9 is connected to a first input terminal of an OR gate 23. An output terminal of the AND gate 22 is connected to a second input terminal of the OR gate 23. The output terminal of the AND gate 20 is connected to a third input terminal of the OR gate 23. An output terminal of the OR gate 23 is connected through an amplifier 24 to a solenoid 25 of an inlet valve 32 which is shown in Figure 2. The output terminal of the AND gate 20 is further connected through an amplifier 27 to a solenoid 28 of an outlet valve 33 which is shown in Figure 2. When the output of the OR gate 23 or the output of the AND gate 20 becomes "1", a current Is is supplied from the amplifier 24 to the solenoid 25 of the inlet valve 32 to energize it.

When the output of the AND gate 20 becomes "1", a current le is supplied from the amplifier 27 to the solenoid 28 of the outlet valve 33 to energize it and further the current 1, is supplied from the amplifier 24 into the solenoid 25 of the inlet valve 32 to energize it.

The flip-flop 8, the OR gate 9, the counter 10 and the latch circuit 14 form a circuit to measure a decrease inclination of the wheel deceleration or an increase inclination of the wheel acceleration. The flip-flop 8 is set with the the time when the deceleration of the wheel has reached the predetermined threshold deceleration after exceeding the maximum deceleration, to the time when the acceleration of the wheel has reached the predetermined threshold acceleration. the flip-flop 8 is set with the deceleration signal -b, of the deceleration signal generator 6. The Q output of the flip-flop 8 becomes "0". Then, when the deceleration signal -b disappears the output of the OR gate 9 becomes "0", to release the reset of the counter 10. The counter 10 starts to count the clock pulses fo from the pulse generator 12.The counted value of the counter 10 is transmitted to the latch circuit 14. At the moment that the acceleration signal +b is generated from the acceleration signal generator 7, the counted value of the counter 10 is memorized by the latch circuit 14. The memorized counted value is proportional to the time interval extending from the time when the deceleration of the wheel has reached the predetermined threshold deceleration after exceeding the maximum deceleration, to the time when the acceleration of the wheel has reached the predetermined threshold acceleration. Accordingly, the fact that the memorized counted value is small, means that the decrease inclination of the wheel deceleration or the increase inclination of the wheel acceleration is large.And the fact that the memorized counted value is large, means that the decrease inclination of the wheel deceleration or the increase inclination of the wheel acceleration is small.

In the comparator 13, the counted value of the counter 10 is compared with the predetermined value N. When the counted value of the counter 10 reaches the predetermined value N, the output of the comparator 13 becomes "1" to close the AND gate 11. The clock pulses fo from the pulse generator 1 2 no longer reach the counter 10.

Accordingly, the latter is prevented from counting more than the predetermined value N.

The counter 16, the second comparator 15, the flip-flop 18 and the AND gate 1 9 form a circuit to set a predetermined time rapidly to raise the brake pressure to the wheel immediately after the acceleration of the wheel reaches the predetermined threshold acceleration. At the moment that the acceleration signal +b is generated from the acceleration signal generator 7, or the output of the invertor 29 ioecomes "O, the counter 1 6 starts to count the clock pulses fo from the pulse generator 12. The counted value of the counter 16 is transmitted to the comparator 15. The output Q of the latch circuit 14, which is complementary to the memorized digital value, is compared with the counted value of the counter 1 6.When the counted value of the counter 16 becomes equal to the output Q of the latch circuit 14, the output of the comparator 16 becomes "1" to set the flip-flop 1 8. The output of the flip-flop 1 8 becomes "1". Since the acceleration signal +b is still applied to the other input terminal of the AND gate 19, the output of the AND gate 19 becomes "1", when the flip-flop 1 8 is set. At the same time, the AND gate 1 7 is closed with the output of the comparator 1 6 to intercept the clock pulses fo from the pulse generator 12. The counter 1 6 is prevented from counting more.

Thus, the predetermined time rapidly to raise the brake pressure to the wheel is equal to the time interval extending from the time when the counter 1 6 starts to count the clock pulses fo from the pulse generator 12 with the occurence of the acceleration signal +b, to the time when the counted value of the counter 1 6 reaches the inversion of complement output 0 of the latch circuit 1 4. Accordingly, when the counted value of the counter 10 memorized by the latch circuit 14 is large, the predetermined time rapidly to raise the brake pressure to the wheel is short. And when the counted value of the counter 10 memorized by the latch circuit 14 is small, the predetermined time rapidly to raise the brake pressure to the wheel is long.

Next, there will be described with reference to Figure 2 a vehicle braking system with the skid control arrangement of Figure 1.

Referring to Figure 2, a master cylinder 30 is connected through a conduit 31, the inlet valve 32, the outlet valve 33, and a conduit 34 to a brake cylinder 36 of a disc brake 35 which is mounted on the wheel.

Although schematically shown in Figure 2, the inlet valve 32 and the outlet valve 33 have wellknown constructions, and they are called also "cut-off valve" and "discharge valve", respectively. A discharge opening of the outlet valve 33 is connected through a conduit 39 to a reservoir 37 which is connected through a conduit 40 to an inlet of a pump 38. An outlet of the pump 38 is connected through a conduit 41 to the conduit 31.

When the solenoids 25 and 28 of the inlet and outlet valves 32 and 33 are not energized, the master cylinder 30 communicates with the brake cylinder 36 of the disc brake 35 so that the brake pressure to the wheel is increased. When both the solenoids 25 and 28 are energized, the communication between the master cylinder 30 and the brake cylinder 36 is cut off, and a discharge opening of the outlet valve 33 is connected to the brake cylinder 36 to discharge brake fluid into the reservoir 37, so that the brake pressure to the wheel is lowered. The brake fluid is returned through the conduits 40 and 41 to the conduit 31 by the pump 38.And when only the solenoid 25 of the inlet valve 32 is energized, the communication between the master cylinder 30 and the brake cylinder 36 is cut off, and however, a supply opening of the outlet valve 33 remains connected with the brake cylinder 36, so that the brake pressure to the wheel is maintained constant.

Next, there will be described the operation of the above-described system with reference to Figures 1 to 3.

The driver of the vehicle operates the master cylinder 30 at time to. Since both of the solenoids 25 and 28 of the inlet and outlet valves 32 and 33 are not still energized, the master cylinder 30 communicates through the inlet and outlet valves 32 and 33 with the brake cylinder 36.

Accordingly, the brake pressure P to the wheel increases, as shown in Figure 3H, with the operation of the master cylinder 30 to lower the wheel speed. The wheel speed signal V from the wheel speed signal detector 2 and the output V representing acceleration of deceleration from the differentiator 5 decreased with the rise of the brake pressure P, as shown in Figures 3A and 3B.

ON the other hand, the simulated vehicle speed signal E from the approximate vehicle speed signal generator 3 slowly falls with time, as shown in Figure 3A.

At time t1, the deceleration of the wheel reaches the predetermined threshold deceleration, or the output V of the differentiator 5 reaches the threshold -go as shown in Figure 38. The deceleration signal -b is generated from the deceleration signal generator 6 as shown in Figure 3C, and it is supplied through the OFFdelay timer 21 to the AND gate 22. The acceleration signal generator 7 connected to the negation input terminal of the AND gate 22 still does not generate the acceleration signal +b.

Accordingly the output of the AND gate 22, and therefore the output of the OR gate 23 become "1 ". The current 1, is supplied from the amplifier 24 to the solenoid 25 of the inlet valve 32 to energize it. At the same time, the deceleration signal -b is supplied to the OR gate 26. The output of the OR gate 26, and therefore the output of the AND gate 20 become "1".

Accordingly, the current 1" is supplied from the amplifier 27 to the solenoid 28 of the outlet valve 33 to energize it. Thus the inlet valve 32 and the outlet valve 33 are concurrently actuated to cut off the communication between the master cylinder 30 and the brake cylinder 36. The brake fluid is discharged from the brake cylinder 36 into the reservoir 37. Thus, the brake pressure P of the brake cylinder 36 decreases with time, as shown in Figure 3H.

On the other hand, the deceleration signal -b is supplied to the set terminal S of the flip-flop 8 to set it. The output 0 of the flip-flop becomes "0".

The deceleration of the wheel starts to reduce with the decrease of the brake pressure P. At time t2, it becomes smaller than the threshold -go after exceeding the maximum. The deceleration signal -b disappears. Accordingly, the output of the OR gate 26, and therefore the output of the AND gate 20 becomes "0", and the solenoid 28 of the outlet valve 33 is de-energized. The outlet valve 33 assumes the inoperative position.

However, since the output of the OFF-delay timer 21 is maintained at "1" due to the OFF-delay function, the inlet valve 32 remains energized.

Accordingly, the brake pressure P is maintained constant, as shown in Figure 3H.

At the same time when the deceleration signal -b disappears, the output of the OR gate 9 becomes "0" to release the reset of the counter 10, which starts to count the clock pulses fo from the pulse generator 12.

Meanwhile, acceleration occurs in the wheel.

At time ta, the acceleration of the wheel becomes higher than the predetermined acceleration threshold, or the output V of the differentiator 5 becomes higher than the threshold +go as shown in Figure 38. The acceleration signal +b is generated from the acceleration signal generator 7, and it is supplied to the negation input terminal of the AND gate 22. The output of the AND gate 22 becomes "0". Since the flip-flop 1 8 is not still set, and the deceleration signal -b has already disappeared, the signals to the first and third input terminals of the OR gate 23 are at "0".

Accordingly, the output signal of the OR gate 23 becomes "0" with the output "0" of the AND gate 22. The current Is stops flowing to the solenoid 25 of the inlet valve 32, as shown in Figure 3F. Thus the solenoid 25 is de-energized. The inlet valve 32 assumes the inoperative position. Now, since both of the inlet and outlet valves 32 and 33 assume the inoperative positions as shown in Figure 2, the master cylinder 30 communicates with the brake cylinder 36 to transmit the brake pressure of the master cylinder 30 to the brake cylinder 36. The brake pressure P of the brake cylinder 36 rapidly rises as shown in Figure 3H.

On the other hand, the acceleration signal +b is supplied to the latch terminal L of the latch circuit 14, and the input terminal of the invertor 29 whose output terminal is connected to the reset terminal R of the counter 1 6. The counted value of the counter 10 at the moment that the acceleration signal +b is supplied to the latch terminal L of the latch circuit 14, is memorized by the latch circuit 14. Concurrently, the counter 16 starts to count the clock pulses fo from the pulse generator 12.

At the time t4 when the counted value of the counter 1 6 reaches the complementary output Q to the memorized counted value of the latch circuit 14, the output signal of the comparator 1 5 becomes "1" to set the fiip-flop 18. The output signal Q of the flip-flop 18 becomes "1", and it is supplied to the one input terminal of the AND gate 1 9. Since the acceleration signal +b is still supplied to the other input terminal of the AND gate 19, the output signal of the AND gate 19 becomes "1" with the set of the flip-flop 18.

Accordingly, the current is starts to flow into the solenoid 25 of the inlet valve 32 to energize it.

Thus, the brake pressure P to the wheel is maintained constant.

In this embodiment, as above described, the brake pressure P to the wheel is maintained constant from the time t4 when the flip-flop 18 is set with the output signal of the comparator 1 5.

However, the brake pressure P may be gradually increased from the time t4. In that case, a pulse generator from which rectangular pulses having a predetermined frequency are generated, is arranged between the output terminal Q of the flip-flop 1 8 and the one input terminal of the AND gate 1 9. The pulse generator is driven with the output of the flip-flop 1 8. The solenoid 25 of the inlet valve 32 is discontinuously energized with the output pulses of the pulse generator so that the brake pressure P is stepwisely increased with time, or, in other words, it is gradually increased.

The wheel speed signal V approaches the simulated vehicle speed signal E. At time t5, the acceleration b of the wheel becomes smaller than the threshold go. The acceleration signal +b disappears as shown in Figure 3D. The output signal of the AND gate 19, and therefore the output signal of the OR gate 23 becomes "0" with the disappearance of the acceleration signal +b. The delay time of the OFF-delay timer 21 for which the output thereof is at "1" lapses before the acceleration signal +b disappears.

Accordingly, the solenoid 25 of the inlet valve 32 is de-energized with the disappearance of the acceleration signal +b at the time t5. The brake pressure P increases with time, as shown in Figure 3H.

The deceleration of the wheel increases with the brake pressure P. At time t6, it reaches the threshold -go. The deceleration signal -b is generated from the deceleration signal generator 6. The output of the AND gate 20, and therefore the output of the OR gate 23 become "1". The currents ls and 1e are supplied to the solenoids 25 and 28 of the inlet and outlet valves 32 and 33, respectively, as shown in Figures 3F and 3G. The brake pressure P of the brake cylinder 36 again decreases with time, from the time toe as shown in Figure 3H.

The deceleration of the wheel decreases with the lowering of the brake pressure P after exceeding the maximum, as shown in Figure 3B.

At time t7, it becomes smaller than the threshold -go. The deceleration signal -b disappears. The counter 10, as above described, starts to count the clock pulses fo from the pulse generator 12.

However, in this case, the ratio of the wheel speed signal V to the simulated vehicle speed signal E becomes smaller than the predetermined ratio T, before the deceleration signal -b disappears. The predetermined ratio T is equal to (1 - the predetermined threshold slip), which is, for example, 0.80. Thus the slip of the wheel becomes larger than the predetermined threshold slip before the time t7. The slip signal S is generated from the slip signal generator 4 as shown in Figure 3E, and it is supplied through the OR gate 26 to the AND gate 20. Accordingly, the output of the AND gate 20, and therefore the output of the OR gate 23 remain "1", although the deceleration signal -b diappears at the time t,.The brake pressure P continues to decrease after the time t7, as shown in Figure 3H.

The deceleration of the wheel decreases with 'the lowering of the brake pressure P, after exceeding the maximum. At time t8, the acceleration \ > of the wheel reaches the threshold +go. The acceleration signal +b is generated from the acceleration signal generator 7. The output of the AND gate 20, that of the AND gate 22 and that of the OR gate 23 become "0". The solenoids 25 and 28 of the inlet and outlet valves 32 and 33 are de-energized rapidly to raise the brake pressure P of the brake cylinder 36. Concurrently, the counted value of the counter 10 at that moment is memorized by the latch circuit 14, and the counter 1 6 starts to count the clock pulses fo from the pulse generator 12.

The output signal of the comparator 1 5 becomes "1" at the time t9 when the counted value of the counter 1 6 reaches the inversion output Q of tbe latch circuit 14. The flip-flop 1 8 is set. The output of the flip-flop 1 8 is supplied through the AND gate 19 to the OR gate 23. The solenoid 25 of the inlet valve 32 is energized with the output signal of the OR gate 23. The solenoid 28 of the outlet valve 33 was de-energized at the time t8 when the acceleration signal +b was generated from the acceleration signal generator 7. Accordingly, the brake pressure P is maintained constant from the time t9.

The second decreasing speed of the deceleration of the wheel, or the interval extending from the time t7 when the deceleration V of the wheel again reaches the threshold deceleration -go after exceeding the maximum, to the time 4 when the acceleration t of the wheel again reaches the threshold acceleration +go, is higher or shorter than the first decreasing speed of the deceleration of the wheel, or the interval extending from the time t2 when the deceleration 2 of the wheel first reaches the threshold decelerationgo after exceeding the maximum, to the time 4 when the acceleration V of the wheel first reaches the threshold acceleration +go.Accordingly, the second time for rapidly increasing the brake pressure, or the interval extending from the time 4 when the counter 1 6 starts to count the clock pulses fo, to the time 4 when the counted value of the counter 16 again reaches the complementary output of the latch circuit 14, is longer than the first time for rapidly increasing the brake pressure, or the interval extending from the time 4 when the counter 1 6 starts to count the clock pulses fo, to the time t4 when the counted value of the counter 16 first reaches the complementary output of the latch circuit 14.

The wheel speed signal V approaches the simulated vehicle speed signal E with the maintainance of the brake pressure P. At time t1O, the acceleration signal +b ends, namely becomes "0". The solenoid 25 of the inlet valve 32 is deenergized to raise the brake pressure P.

Hereafter, the above-described operations are repeated to control the brake pressure P to the wheel in the optimum way.

In the above embodiment, the time interval extending from the time when the deceleration of the wheel reaches the threshold decelerationgo after exceeding the maximum, to the time when the acceleration of the wheel reaches the threshold acceleration +go, is measured to set the time for rapidly increasing the brake pressure P. However, the time interval extending from the time when the output 9 of the differentiator 5 becomes a minimum or reaches a level other than the threshold deceleration -go, to the time when the output 9 of the differentiator 5 reaches the threshold acceleration +go, may be measured to set the time for rapidly increasing the brake pressure P. Or the output of the differentiator 5 may be differentiated during the time when the deceleration of the wheel decreases, to set the time for rapidly increasing the brake pressure P.

As above described, the excessive lowering of the brake pressure due to the amplification and time lag of the wheel speed which are caused by the rotation of the stationary part of the wheel speed sensor 1 relative to the rotating part thereof on braking the vehicle, is compensated by the rapid increase of the brake pressure during the time when the acceleration signal +b is generated. Thus, the skid control operation is optimized.

Moreover, the excessive lowering of the brake pressure due to hysteresis phenomena of the brake cylinder which is caused by friction between the cylinder and the piston, is compensated by the above-described rapid increase of the brake pressure.

Claims

1. A vehicle skid control arrangement comprising: wheel speed detecting means for providing an output signal representative of the speed of a wheel of a vehicle; differentiating means for differentiating said output signal of the wheel speed detecting means and providing an output signal representative of acceleration or deceleration of said wheel; a deceleration signal generator connected to said differentiating means, said deceleration signal generator generating a deceleration signal when the output signal of said differentiating means exceeds a predetermined threshold deceleration; an acceleration signal generator connected to said differentiating means, said acceleration signal generator generating an acceleration signal when the output signal of said differentiating means exceeds a predetermined threshold acceleration;; brake relieving means for decreasing the brake pressure to the brake for said wheel in response to the deceleration signal of said deceleration signal generator; first brake control means for maintaining the brake pressure to the brake for said wheel constant, or gradually increasing the brake pressure to the brake for said wheel, in response to the acceleration signal of said acceleration signal generator; and second brake control means for rapidly increasing the brake pressure to the brake for said wheel for a predetermined time within the time when said acceleration signal generator generates the acceleration signal.

2. An arrangement according to claim 1 wherein said second brake control means includes time set means for setting said predetermined time.

3. An arrangement according to claim 2 wherein said time set means is controlled in accordance with the inclination of the output signal of said differentiating means.

4. An arrangement according to claim 2 wherein said time set means is controlled on the basis of the deceleration and acceleration signals of said deceleration and acceleration signal generators.

5. An arrangement according to claim 4 wherein said time set means includes a clock pulse generator, and a first counter for counting clock pulses from said clock pulse generator.

6. An arrangement according to claim 5 wherein said first counter starts to count the clock pulses from said clock pulse generator at the end of said deceleration signal and ends counting of the clock pulses from said clock pulses generator at the beginning of said acceleration signal, and said predetermined time isdetermined by the counted value of said first counter.

7. An arrangement according to claim 6 wherein said time set means includes a flip-flop, and the end of said deceleration signal and the beginning of said acceleration signal are detected by said flip-flop.

8. An arrangement according to claim 7 wherein the beginning of said predetermined time corresponds to the beginning of said acceleration signal.

9. An arrangement according to claim 8 wherein said time set means includes a second counter for counting the clock pulses from said clock pulses generator, and a comparator, said second counter starts to count the clock pulses from said pulse generator at the beginning of said acceleration signal and ends counting of the clock pulses from said pulse generator at the time when said comparator detects that the counted value of said second counted has reached the complement to the counted value of said first counter.

10. An arrangement according to claim 9 wherein said predetermined time corresponds to the counted value of said second counter at the time when said comparator detects that the counted value of said second counter has reached the complement to the counted value of said first counter.

11. An arrangement according to claim 10 wherein said time set means includes a second flip flop, and the detecting output of said comparator is supplied to a set terminal of said second flipflop to determine the end of said predetermined time.

12. An arrangement according to claim 6 wherein said first brake control means includes a rectangular pulse generator gradually to increase the brake pressure to the brake for said wheel.

1 3. A vehicle skid control arrangement substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

14. A vehicle skid control arrangement substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.