GB2193275A

GB2193275A - Anti skid control

Info

Publication number: GB2193275A
Application number: GB08618695A
Authority: GB
Inventors: Tetsuro Arikawa
Original assignee: Nippon ABS Ltd
Current assignee: Nippon ABS Ltd
Priority date: 1986-07-31
Filing date: 1986-07-31
Publication date: 1988-02-03
Anticipated expiration: 2006-07-31
Also published as: GB2193275B; DE3625906A1; GB8618695D0

Abstract

Front wheel cylinders 7a, 7b, and rear wheel cylinders 11a, 11b, are provided in an X-system; a first valve device 4a for controlling pressure at the wheel cylinder 7a is arranged between a first pressure chamber of a tandem master cylinder 1 wheel cylinder 7a; a second valve device 4b for controlling the pressure at the wheel cylinder 7b is arranged between a second chamber of the master cylinder 1 and the wheel cylinder 7b; a control unit 31 supplied with signals from wheel speed sensors 28a, 28b, 29a, 29b generates signals for controlling the valve devices 4a, 4b; and a valve apparatus 8 (see Fig. 4 for details) has pressures from cylinders 7a, 7b applied thereto at input ports 9,18 respectively normally communicated with output ports 10,14 to rear wheel cylinders 12b, 12a: the control unit 31 (see Figs. 3,5,6,7) logically combines judge signals derived in judge circuits 35a, 35b in logic circuits 36a, 36b and a detailed description of operations on these signals and their interaction with the valve devices is given. The unit 31 further generates a drive signal Q for a motor 22 driving a pump 20. <IMAGE>

Description

SPECIFICATION Anti-skid control apparatus for a vehicle braking system This invention relates to an anti-skid control apparatus for a vehicle braking system which can prevent the locking of the vehicle wheels.

An anti-skid control apparatus for a vehicle braking system is known that includes a fluid pressure control valve device arranged between a master cylinder and a wheel cylinder of a brake for the wheel, said fluid pressure control valve device receiving control signals of a control unit measuring the skid condition of the wheel to control the brake fluid pressure to said wheel cylinder; a hydraulic reservoir which, when the brake fluid pressure to said wheel cylinder is decreased with control of said fluid pressure control valve device, reserves the brake fluid discharge through said fluid pressure control valve device from said wheel cylinder; a pressure fluid supply conduit connecting said master cylinder with said fluid pressure control valve device; and a fluid pump for returning the brake fluid from said hydraulic reservoir into said pressure fluid supply conduit.

When the fluid pressure control valve device is provided for each of four wheels, and the fluid pressure of them are independently controlled, there is no problem on control operation. Or when the fluid pressure control valve device is provided for each of front wheels, and for both of rear wheels in common, there is no problem on control operation. In the latter case, the one common fluid pressure control valve device is controlled on the basis of the lower one of the speeds of the rear wheels.

However, in the above cases, three or four fluid pressure control valve devices are used.

Accordingly, the whole anti-skid control apparatus is large-sized, and very heavy. Since the fluid pressure control valve device is expensive, it requires high cost.

For example, it is considered that the brake fluid pressures of the front wheels are controlled by the two fluid pressure control valve devices respectively in the diagonal or X-type conduit system, and the brake fluid pressures of the rear wheels are controlled in common with the front wheels. However, when the vehicle runs on the road, the right and left sides of which are considerably different in frictional coefficient from each other, there is the fear that the one rear wheel being diagonal to the one front wheel on the higher frictional coefficient side is locked. In that case, the steering of the vehicle becomes unstable, and that is very dangerous.

Futher, is it considered that proportioning valves are provided for the rear wheels, respectively. However, the brake fluid pressures of the rear wheels increases in proportion to the input fluid pressures to the proportioning valves. The fear of locking cannot be avoided.

Accordingly, in order to provide an anti-skid control apparatus for a vehicle braking system which can be small-sized and light, and can avoid the fear of locking of rear wheels, this applicant previously proposed an anti-skid control apparatus for a vehicle braking system which includes; a fluid pressure control valve device arranged between a master cylinder and a wheel cylinder of a brake for the wheel, said fluid pressure control valve device receiving control signals of a control unit measuring the skid condition of the wheel to control the brake fluid pressure to said wheel cylinder; a hydraulic reservoir which, when the brake fluid pressure to said wheel cylinder is decreased with control of said fluid pressure control valve device, reserves the brake fluid discharged through said fluid pressure control valve device from said wheel cylinder; a pressure fluid supply conduit connecting said master cylinder with said fluid pressure control valve device; and a fluid pump for returning the brake fluid from hydraulic reservoir into said pressure fluid supply conduit; said fluid pressure control valve device being provided for a pair of front wheels, respectively, a valve apparatus receiving fluid pressures of wheel cylinders of said front wheels being arranged between said pair of front wheels and a pair of rear wheels, and when any one of said fluid pressure control valve devices starts to control, at least the fluid pressure of the one of said rear wheels, being at the same side as the one of said front wheels, the fluid pressure of the wheel cylinder of which is lower, is controlled in accordance with the lower one of the fluid pressures of the wheel cylinders of said front wheels by said valve apparatus.

In the above-described anti-skid control apparatus, the control signals of the control unit are formed by judging the skid conductions of the respective front wheels. On the assumption that the front and rear wheels are provided with the tyres of the same kind, the braking forces are so distributed to the wheels that the front wheels tend sooner to lock than the rear wheels, when the vehicle is rapidly braked on the road which js uniform in frictional coefficient.

However, when the above assumption is not fulfilled, for example, when only the front wheels are provided with spike tyres or chains for running on a snow or ice road, and the rear wheels are provided with the normal tyres, the rear wheels tend sooner to lock than the front wheels. In the above anti-skid control apparatus, the brake fluid pressure is not controlled with the locking of the rear wheel. When the brake fluid pressure of the front wheel is controlled over the limit locking pressure of the rear wheel, the locking of the rear wheel is not released, and so the steering stability cannot be maintained.

Even in the case that the front and wheels are provided with the tyres of the same kind, the rear wheel may tend sooner to lock than the front wheel, when the frictional coefficient of the brake lining becomes excessively low due to thermal fade phenomemon in a front wheel brake apparatus and the limit lock pressure of the front wheel becomes excessively high, and particularly when the vehicle is rapidly braked on a high u road. When a proportioning valve is used, the fluid pressure of the rear wheel is lower than that of the front -wheel. However, it increases in proportion to the fluid pressure of the front wheel, and reaches the limit lock pressure. The above described problem occurs.

Fig. 1 of the accompanying drawings shows the above described problem. Fig. 1 shows the changes of the wheel speeds during the time when the vehicle is braked. Fig. 1B shows the control signals of the control unit.

And Fig. 1C shows the changes of the brake fluid pressures of the wheels.

When the front and rear wheels are provided with the tyres of the same kind, and they run on the road being uniform in frictional coefficient, the brake fluid pressures P and P' of the front and rear wheels change with time, as shown- by the solid lines in Fig. 1C, when the brake pedal is trodden at time tO. The control unit generates a brake maintaining instuction at time ti. The fluid pressure control valve device is constituted by an inlet valve and an outlet valve. The control signals consist of signals EV and AV for the inlet and outlet valves respectively.

Although AV is still "0", EV becomes "1" at time tl. Thus, the brake fluid pressure P of the front wheel is maintained at constant. The control unit generates a brake relieving instruction at time t2. Thus; EV is still "1", and AV becomes "1" from '40". As shown in Fig.

1C, the brake fluid pressure P of the front wheel decreases as shown in Fig. 1C. AV becomes "0" at time t3, while EV is still "1". Thus, the brake fluid pressure is maintained at constant.

EV becomes "0" at time t4. The brake fluid pressure rises again. EV brakes again "1' at time t5. The brake fluid pressure is maintained at constant. Hereafter, the brake pressure P step-wisely increases as above described. AV becomes "1" at time t5, while EV is "1".

Accordingly the brake fluid pressure P decreases.

In the above-described manner, the brake fluid pressure P of the front wheel changes with time. The brake fluid pressure P' of therear wheel is reduced by the proportioning valve, and changes with time in accordance with the brake pressure P of the front wheel.

The proportioning valve causes the hysteresys phenomenon by which the brake fluid pressure P' of the rear wheel changes a little later than that P of the front wheel. However, such a time lag is neglected in Fig. 1C.

Generally, a larger amount of brake fluid is required for an constant increase of brake fluid pressure in the lower pressure range under the influence of rigidity of the wheel cylinder in the rear wheel brake apparatus. Accordingly, the change range of the brake fluid pressure P' of the rear wheel is less than that of the front wheel, as shown in Fig. 1C.

The wheel speeds V, V' of the front and rear wheels change with time, as shown by the solid lines in Fig. 1 A, in accordance with the above described changes of the brake fluid pressures. The preferable anti-skid control is effected. The wheel speeds are decreased without locking of the wheels.

However, when only the front wheels are provided with chains, or when the thermal fade phenomenon occcurs in the front brake apparatus, the limit lock pressure of the front wheel is increased. At such a case, the brake fluid pressure P of the front wheel change with time, as shown by dash-lines in Fig. 1A.

It changes above the level of the brake fluid pressure shown by the solid line. On the other hand, the brake fluid pressure P' of the rear wheel changes beyond the rear limit lock pressure R, as shown by the dash line. Hereafter, even when the brake fluid pressure P of the front wheel is decreased, the rear wheel cannot be relieved from locking, partly for the reason why the range of the change of the brake fluid pressure P' is less. The front wheel is prevented from locking, as shown by the dash line in Fig. 1 A. However, the rear wheel is locked. The anti-skid control is not preferably effected. The steering stability is lost. That is very dangerous.

According to the present invention there is provided an anti-skid control apparatus for a vehicle braking system including: (A) a pair of front wheels, and a pair of rear wheels in which wheel cylinders are diagonally connected by conduits; (B) a first fluid pressure control valve device for controlling the brake fluid pressure of the wheel cylinder of one of said front wheels, arranged between a first fluid pressure generating chamber of a tandem master cylinder and said wheel cylinder of the one front wheel; (C) a second fluid pressure control valve device for controlling the brake fluid pressure of the wheel cylinder of another of said front wheels, arranged between a second fluid pressure generating chamber of said tandem master cylinder and said wheel cylinder of the other front wheel; (D) a control unit for measuring or judging the skid conditions of said front and rear wheels and for generating instructions for controlling said first and second fluid pressure control valve devices; and (E) a valve apparatus for generating a fluid pressure in accordance with the lower one of the brake fluid pressures of said front wheels controlled with said first afld second fluid pressure control valves devices, being arranged between said wheel cylinders of the front wheels and those of the rear wheels; the improvements in which said control unit combines logically the measuring or judging result of the skid conduction of the one front wheel with that of the one rear wheel being at the same road side as said one front wheel for generating the instruction for controlling said first fluid pressure control valve device, and combines logically the measuring or judging result of the skid condition of the other front wheel with that of the other rear wheel being at the same road side as said other front wheel for generating the instruction for controlling said second fluid pressure control valve device.

The foregoing and other objects, features, and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 shows graphs for explaining operations of a prior art anti-skid control apparatus; Figure 2 is a schematic view of a anti-skid control apparatus according to an embodiment of this invention; Figure 3 is a block diagram of a control unit in Fig. 2; Figure 4 is an enlarged cross-sectional view of a valve apparatus in Fig. 2; Figure 5 is a circuit diagram of a first judge circuit in Fig. 3; Figure 6 is a circuit diagram of a first logic circuit in Fig. 3; Figure 7 is a circuit diagram of a motor drive circuit in Fig. 3; and Figure 8 and Figure 9 are graphs for explain ing operations of the embodiment of this invention.

In Fig. 2, a brake pedal 2 is connected to a tandem master cylinder 1. One fluid pressure chamber of the tandem master cylinder 1 is connected to a wheel cylinder 7a of a right front wheel 6a through a conduit 3, an electro-magnetic two position valve device 4a and a conduit 5. The conduit 5 is further con nected to a first input port 9 of a valve appa ratus 8 to be hereinafter described in detail.

The first input port 9 normally communicates with a first output port 10 in the valve appa ratus 8. The first output port 10 is connected to a wheel cylinder 1 2a of a left rear wheel 1 1b through a conduit 13 and a proportioning valve 23b.

Another fluid pressure chamber of the tan dem master cylinder 1 is connected to a wheel cylinder 7b of a left front wheel 6b through a conduit 16, an electro-magnetic two position valve device 4b and a conduit 17.

The conduit 17 is further connected to a second input port 18 of the valve apparatus 8.

The second input port 18 normally communicates with a second output port 14 in the valve apparatus 8. The second output port 14 is connected to a wheel cylinder 12a of a right rear wheel 11 a through a conduit 25 and a portional valve 32a.

The two position valve devices 4a and 4b consist of inlet and outlet valves 32a, 34a and 33b, 34b, respectively. Discharge openings of the outlet valves 34a and 34b are connected through conduits 60a and 60b to hydraulic reservoirs 25a and 25b, respectively.

The hydraulic reservoirs 25a and 25b include pistons 27a and 27b slidably fitted to a casing and relatively weak springs 26a and 26b.

Reserving chambers of the reservoirs 25a and 25b are connected to suction openings of a fluid pressure pump 20.

Although the fluid pressure pump 20 is schematically shown, it consists of a pair of casings 21, pistons slidably fitted to the casings 21, an electro-motor 22 reciprocating the pistons, and check valves 23a, 23b, 24a, 24b. Supply openings of the fluid pressure pump 20, or the sides of the check valves 23a, 23b are connected to the conduits 3 and 16.

Wheel speed sensors 28a, 28b, 29a and 29b are associated with the wheels 6a, 6b, 11 a and 1 1 b respectively, and they generate pulse signals having frequencies proportional to the rotational speeds of the wheels 6a, 6b, 11 a and 11 b. The pulse signals of the wheel speed sensors are supplied to a control unit 31.

As shown in Fig. 3 the control unit 31 consists of first and second judge circuits 35a and 35b, first and second logic circuits 36a and 36b and a motor drive circuit 37. The circuits 35a, 35b, 36a and 36b will be hereinafter described in de detail. Output terminals of the wheel speed sensors 28a and 29b are connected to input terminals a 1 and a2 of the first judge circuit 35a, while output terminals of the wheel speed sensors 28b and 29a are connected to input terminals al' and a2' In other words, the first judge circuit 35a receives the wheel speed signals of the right front wheel 6a and left rear wheel 11 b, judges them and supplys the judge results to the first or second logic circuit 36a and 36b.As will be hereinafter described the judge results are logically combined with each other in the logic circuits 36a and 36b, and control signals EV and AV are generated at output terminal cl and c2 of the control unit 31. The second judge circuit 35b receives the wheel speed signals of the left front wheel 6b and right rear wheel 11 a, judges them and supplys the judge results to the first or second logic cir cuit 36a and 36b. As will be hereinafter de scribed, the judge results are logically combined with each other in the logic circuits 36a and 36, and control signals EV' and AV' are generated at output terminal C'1 and C'2 of the control unit 31. The control signal EV, AV, EV' and AV' are supplied to solenoid portions Sa, Sa', Sb and Sb' of the valves 33a, 34a, 33b and 34b, respectively. Dash lines represent electric lead wires.

Although schematically shown, the electromagnetic valves 33a, 34a and 34b have wellknown constructions. When the control signals AV, EV and AV', EV' are "0", the valves take first positions A and C for increasing the brake pressure to the brake for the wheel, respectively. In the first positions A and C, the master cylinder side and the wheel cylinder side are made to communicate with each other. When the control signals AV, EV AV', EV' and "1", the valves take second positions B and D for decreasing the brake pressure to the brake, respectively. In the second positions B and D, the communication between the master cylinder side and the wheel cylinder side is interrupted, while the communication between the wheel cylinder side and the reservoir side is made.The brake fluid is discharged through the conduit 60a and 60b into the reservoir 25a and 25b from the wheel cylinders 7a, 7b and -12a and 12b.

When the control signals AV, AV and EV, EV' are "0" and "1", respectively, the valves 33a and 33b take the second positions B, and the values 34a and 34b take the first positions C.

Thus, the brake pressure to the brake are maintained at constant.

The control unit 31 further generates a drive signal Q for the motor 22, and it is kept during the skid control operation.

Next, the details of the valve apparatus 8, to which the brake fluid pressures are applied from the wheel cylinders 7a and 7b of the front wheels 6a and 6b, will be described which reference to Fig. 4.

A stepped through hole 61a is axially formed in a casing 61 for the valve apparatus 8. A cover member 62 provided with a seal ring 65 is screwed to a right opening portion of the casing 61. Another cover member 66 provided with a seal ring 67 is screwed to a left opening portion of the casing 61. The above described first and second input ports 9 and 18 are formed in the cover members 62 and 66, respectively.

A piston 38 provided with seal rings 39 and 40 is slidably fitted to a central portion of the stepped hole 61a. Rod portion 41a and 41b of the piston 38 normally contact with valve balls 47a and 47b across output chambers 50a and 50b, respectively. The valve balls 47a and 47b are positioned in input chambers 49a and 49b, and are urged towards valves seats 46a and 46b by springs 48a and 48b. The one valve seat 46b is formed in the inner wall of the casing 61. The other valve seat 46a is formed in a valve forming member 45 which is pressedly fitted to a cylindrical member 44. The above output chamber 50a is inside of the cylindrical member 44, and it communicates throgh holes 44a made in the circumferential wall portion, with the first output port 10. The other output chamber 50b communicates directly with the second output port 14.

Spring receiving rings 42a and 42b are slidably fitted to the rod portions 41a and 41b of the piston 38 for receiving springs 43a and 43. They are urged towards the center by the springs 43a and 43b. Normally, flange portions of the spring receiving rings 42a and 42b contact with stepped portions 58a and 58b of the casing 61. There are little gaps between the spring receiving rings 42a, 42b and a main portion 59 of the piston 38. Thus, the neutral position of the piston 38 is determined in the stepped hole 61a.

A switch 52 provided with a seal ring 53 is tightly fitted into a hole made in the central wall of the casing 61. An actuator of the switch 52 is engaged with a groove 51 made in the circumference of the piston 38, in the neutral position. An electric wire 54 from the switch 52 is connected through a contact 55 of a contact type relay, and a warning lamp 56 to a positive terminal of a battery 57. The warning lamp 56 is energized, when the contact 55 remains closed and the switch 55 is operated. The contact 55 of the contact type relay normally closes, and when the antiskid apparatus of Fig. 2 operates in order, it is opened. For example, when the fluid pressure pump 20 operates, it is opened.

In the shown neutral position of the piston 38, the valve balls 47a and 47b are separated from the valve seats 46 and 46b by the rod portions 41a and 41b. The input chambers 49a and 49b are made to communicate with the output chambers 50a and 50b.

In Fig. 2, check valves 19a and 19b are connected in parallel with the electromagnetic valves 4a and 4b. They permit brake fluid to flow only in the direction from the wheel cylinder side towards the master cylinder side.

Both sides of the valves 4a and 4b communicate with each other through throttling holes in the A- and C- positions. Accordingly, pressurized fluid is rapidly returned through the check valves 19a and 19b to the master cylinder 1 from the wheel cylinders 7a, 7b, 12a and 12b, when the brake is released.

The first and second judge circuits 35a and 35b have the same circuit constructions. Accordingly, only the first judge circuit 35a will be described in detail with reference to Fig. 5.

The first and second judge circuits 35a and 35b consist of front wheel judge parts 35a1, 35b1 and rear wheel judge parts 35a2, 35b2, respectively. The signals from the wheel speed sensors 28a and 29b are supplied to wheel speed signal generators 72a and 72b.

Digital or analogue outputs proportional to the wheel speeds are obtained from the wheel speed signal generators 72a and 72b, and they are supplied to approximate vehicle or body speed sinal generators 76a and 76b, slip signal generators 77a and 77b and differenciators 73a and 73b.

The approximate vehicle speed signal generators 76a and 76b receive the outputs of the speed signal generator 72a and 72b. The outputs of the approximate vehicle speed signal generators 76a and 76b are equal to the outputs of the wheel speed signal generators 72a and 72b, until the deceleration of the wheel reach a predetermined value. After it becomes higher than the predetermined value, the outputs of the approximate vehicle speed signal generators 76a and 76b decrease at a predetermined gradient with time. The initial outputs are equal to the outputs at the time when the deceleration of the wheel has reached the predetermined value. The outputs of the approximate vehicle speed signal generators 76a and 76b are supplied to a selecting circuit 71.The higher of the outputs of the approximate vehicle speed generators 76a and 76b is selected by the selecting circuit 71, and it is supplied to the slip signal generators 77a and 77b to be compared with the outputs of the wheel speed signal generators 72a and 72b.

A predetermined reference ratio or amount is set in the respective slip signal generators 77a and 77b. The reference ratio or amount is for example, 0.15 (15%).

Generally, a slip ratio S of the wheel is given by the following formula: wheel speed (V, V') S=1- vehicle speed (E) V, V' When (1 - ) is larger than the E reference ratio, a slip signal S is generated from the slip signal generator 77a or 77b, namely the output of the slip signal generator 77a, or 77b becomes a higher leyel "1" of the two levels "1"and"0".

The differentiators 73a and 73b receive the outputs of the wheels speed signal generators 72a and 72b, and differentiate them with respect to time. The outputs of the differentiators 73a and 73b are supplied to deceleration signal generators 75a and 75b. A predetermined threshold deceleration (for example, 1.5g) is set in the deceleration signal generators 75a and 75b, and it is compared with the outputs of the differentiators 73a and 73b. A predetermined threshold acceleration (for example, 0.5g) is set in the acceleration signal generators 74a and 74b, and it is compared with the outputs of the differentiators 73a and 73b.When the deceleration of the wheel becomes larger than the predetermined threshold deceleration (-1.59), a deceleration signal -b is generated from the deceleration signal generator 75a or 75b. When the acceleration of the wheel becomes larger than the predetermined threshold acceleration (0.59), an acceleration signal +b is generated from the acceleration signal generator 74a, or 74b.

Output terminals of the acceleration signal generators 74a and 74b are connected to negation input terminals (indicated by circle 0) of AND gates 92a, 92b, negation input terminals of AND gates 90a, 90b, OFF delay timers 88a, 88b and first input terminals of OR gates 94a, 94b. Output terminals of the OFF delay timers 88a, 88b are connected to input terminals of the AND gates 90a, 90b. Output terminals of the AND gates 90a, 90b are connected to input terminals of pulse generators 78a, 78b and input terminals of AND gates 93a, 93b. Output terminals of the pulse generators 78a, 78b are connected to negation input terminals of the AND gates 93a, 93b.

Stepwise brake-increasing signal generators 81a, 81b are constituted by the acceleration signal generators 74a, 74b, the OFF-delay timers 88a, 88b, the pulse generator 7a, 78b, the OR gates 94a, 94b, and the AND gates 90a, 90b, 93a, 93b, and they generate pulse signals to slowly increase the brake pressure for delay time of the OFF delay timers 88a, 88b. Output terminals of the AND gates 93a, 93b are connected to second input terminals of the OR gates 94a, 94b.

Output terminals of the deceleration signal generators 7a, 75b are connected to third input terminals of the OR gates 94a, 94b and to input terminals of the approximate vehicle speed signal generators 77a, 76b. Output terminals of the slip signal generators 77a, 77b are connected to other input terminals the AND gates 92a, 92b. Output terminals of the AND gates 92a, 92b are connected to fourth input terminals of the OR gates 94a, 94b.

Signals EV1, EV2 and AV1, AV2 at output terminals of the OR gates 94a, 94b and AND gates 92a, 92b are supplied to the following stage, or the first or second logic circuit 36a or 36b.

The output terminals of the AND gates 92a, 92b are further connected to OFF delay trimmers 95a, 95b. Signals AV1Z and AV2Z at the output terminals of the OFF-delay timers 95a, 95b are supplied to the motor drive circuit 37. The delay time is so sufficiently long to maintain the output of the OFF-delay timers 95a, 95b at the higher "1" of the two levels "1" and "0" during the anti-skid control operation, after the outputs of the AND gates 92a, 92b become the lower levei "0" of the two levels "1" and "O".

Signals EV1', EV2', AV1', AV2' corresponding to the above signals EV1, EV2 AV1, AV2, respectively, are similarly formed in the sec ond judge circuit 35b.

The first and second logic circuits 37a and 36b have the same circuit construction. Accordingly only the first logic circuit 37a will be described with reference to Fig. 6.

The first logic circuit 36a receives the output signals EV1, AV1, AV1Z of the first judge circuit 35a and the output signals EV2', AV2' of the second judge circuit 35b. The output signal EV1 is supplied to a first input terminal of an OR gate 100. The output signal AV1 is supplied to one input terminal of another OR gate 103. The output signal EV2' is supplied to another input terminal of an AND gate 101.

The output signal AV1Z is supplied through a NOT gate 102 to another input terminal of the AND gate 101. The output signal AV2' is supplied to one input terminal of another AND gate 104 and further it is supplied through an ON-delay timer 105 and a NOT gate 106 to another input terminal of the AND gate 104.

Output terminals of the OR gates 100 and 103 are connected through amplifiers 107 and 108-to the solenoid portions Sa and Sa' of the inlet and outlet valves 33a and 34a, shown in Fig. 2. The amplified control signals EV, AV of the amplifiers 107 and 108 are supplied to the solenoid portions Sa, Sa' of the inlet and outlet valves 33a and 34a. The signal Av2' represents that the slip of the right rear wheel 11 a becomes higher than the predetermined slip value. The brake fluid pressure of the right front wheel 7a is decreased with the signal Av2'. When the signal AV2' continues too long, it is limited to a predetermined time for preventing excessive decrease of the brake of the right front wheel 7a. The predetermined time is set as a delay time in the ON- delay timer 105.

Fig. 7 shows the motor drive circuit 37 which consists of an OR gate 109 and an amplifier 110. The output signals AV1Z and AV2Z of the first judge circuit 35a are supplied to first and second input terminals of the OR gate 109. The signals AV1Z and AV2Z are formed by the skid conditions of the right front wheel 7a and left rear wheel 1 1b, in the first judge circuit 35b. Similarly signals AV1Z' and AV2Z' are formed by the skid conditions of the left front wheel 6b and right rear wheel 11 a. They are supplied to fourth and third input terminals of the OR gate 109. The second and forth input terminals of the OR gate 109 are connected to the first and second logic circuits 36a an 36.In the one logic circuit 36a, as shown in Fig. 6, the second input terminal is connected through the NOT gate 102 to the AND gate 101. An output of the OR gate 109 is amplified by the amplifier 110.

The output signal 0 of the amplifier 110 is supplied to the motor 22 shown in Fig. 2.

Signals EV', AV' corresponding tithe signals EV, AV are similarly formed by the second logic circuit 36b. They are supplied to the solenoid portions Sb, Sb' of the inlet and outlet valves 33b, 34b.

Next, there will be described operations of the above described anti-skid apparatus.

It is now assumed that the wheels 7a, 7b, 1 1a and 1 1b are provided with the tyres of the same kind and run on the road which is uniform in frictional coefficient.

The vehicle driver treads the brake peal 2.

At the beginning of the braking, the control signals EV, AV, EV', AV' are "0" from the control unit 31. Accordingly, the valves 33a, 33b and 34a, 34b are in the A-position and the C-position. Pressurized fluid is supplied from the master cylinder 1 to the wheel cylinders 7a and 7b of the front wheels 7a and 7b through the conduits 3, 17, the valves 33a, 33b, 34a, 34b and the conduits 5, 17. Further it is supplied to the wheel cylinders 12a, and 12b of the rear wheels 1 1a and 1 1b through the first and second input ports 9, 18, the input chambers 49a, 49b, the output chambers 50a, 50b, the first and second output ports 10, 14 in the valve apparatus 8, and the conduits 13 and 15.Thus, the wheels 7a, 7b, 1 1a and 19b are braked. The proportioning valves 32a and 32b effect the wellknown operations. When the input pressure is lower than a predetermined value, it is, as it is, transmitted to the output side without reduction. When the input pressure is higher than the predetermined value, it is reduced nearly at a constant rate, and transmitted to the output side.

When the deceleration of the wheels 6a, 7b, 11 a and 11 b becomes higher than the predetermined deceleration with the increase of the brake fluid pressure, the deceleration signal -b is generated from the deceleration signal generators 75a, 75b in the judge circuits 35a, 35b. For facilitating the understanding, it is assumed that the decelerations or slips of the wheels 7a, 7b, 1 1a, 1 1b reach the predetermined deceleration or slip at the same time.

The signals EV1, EV2, EV1', EV2' become "1" with the deceleration signal -b. The output signals EV, EV' of the logic circuits 37a, 36b becomes "1" with the signals EV1, EV2, EV1', EV2'. The solenoid portions Sa and Sb are energized. The valves 33a and 33b take the second position B. The conduits 3, 16 are interrupted for the conduits 5, 17. Further, the conduits 5, 17 are interrupted from the conduits 60a, 60b. Thus the brake fluid pressures of the wheel cylinders 7a, 7b, 12a, and 12b are maintained at constant.

When the decleration of the wheels becomes lower than the predetermined deceleration, the deceleration signal -b disappears from the deceleration signal generators 75a, 75b, and the valves 33a, 33b are again changed into the position A. Thus, the brake fluid pressure again increases. When the slip of the wheels reaches the predetermined slip, the slip signal S is generated from the slip signal generators 77a, 77b. The acceleration signal generators 74a, 74b do not yet generate the acceleration signal tb. Accordingly, the output AV1, AV2, Av1', AV2' of the AND gates 92a, 92b becomes "1". The outputs AV, AV', EV, EV' of the logic circuits 37a, 37b become "1". The valves 33a, 33b and 34a, 34b are changed over into the positions B and D. The conduits 3 and 16 are interrupted from the conduits 5 and 17, respectively.However, the conduits 5 and 17 are made to communicate with the conduits 60a and 60b. The pressurized fluid is discharged from the wheel cylinders 7a an 7b of the front wheels 6a and 6b into the hydraulic reservoirs 25a and 25b through the conduits 5, 17, 60a and 60b. The pressurized fluid from the wheel cylinders 12a and 12b of the rear wheels 1 la and 1 1b is discharged through the conduits 15, 13 the ouput ports 14, 10, the output chambers 50a, 50b, the input chambers 49a, 49b, the input ports 18, 9 in the valve apparatus 8, and the conduits 17, 5, 60a and 60b, into the hydraulic reservoirs 25a and 25. Thus the brakes of the wheels 6a, 6b, 1 lea and 11 are relieved.

The fluid pressure pump 20 starts to drive with the signals AV, AV2, AV1', AV2'. The brake fluid is sucked from the reservoirs 25a and 25b and supplied towards the conduits 3 and 16, nearly at the same rate by the fluid pressure pump 20. Accordingly, the fliud pressures at both sides of the piston 38 are decreased nearly at the same rate. The piston 38 remains stopped at the neutral position, and the valve balls 47a and 47b remain separated from the valve seats 476a and 46b.

When the wheel speeds become higher, and the accelerations of the wheels reach the predetermined acceleration, the accelerator signal +b is generated from the acceleration signal generators 74a, 74b. Thus, the outputs EV1, EV2, EV1', EV2' of the judge circuits 35a, 35b become "1". The outputs EV, EV' of the logic circuits 37a, 37b become "1". Accordingly, the breake fluid pressure of the wheels is maintained at constant.

The pulse generators 78a, 78b start to drive with disappearance of the acceleration signal +b. The outputs EV1,EV2,EV1',EV2' change as "O", "1", "0", " 1 ", . . . for the delay time of he OFF-delay timers 88a, 88b.

Accordingly, the outputs EV, EV' of the logic circuits 37a, 36b change similarly. The brake pressures of the wheel stepwiseíy rise up.

Hereafter, the above-described operations are repeated. When the running speed of the vehicle reaches the desired speed, or when the vehicle stops, the brake pedal 2 is released from treading. The brake fluid is returned from the wheel cylinders 7a, 7b, 12a, 1 2b to the master cylinder 1 through the conduits, the valve apparatus 8, the valves 4a, 4b, the check values 1 9a and 19b.

In the above description, the control signals EV1, EV2, EV1', EV2' or AV1, AV2, AV1', AV2' become "0" or "1" at the same time.

However, when the frictional coefficients of the road are considerably different at the right and left sides, the control signals do not become "O" or "1" at the same time. For example, when the frictional coefficient of the right side of the road is relatively small, the control signal EV, EV2' or AV1, AV2' first becomes "1". Next, such a case will be described.

For simplifying the description, it is assumed that the deceleration signals -b or slip signals of the right wheels 7a, 1 1a are generated at the same time. In other words, the outputs EV1, EV2' or AV1, AV2' of the judge circuits 35a, 35b become "0" or "1" at the same time. The output EV or AV of the first logic circuit 37a becomes "0" or "1" with the output EV1 or AV2. The brake fluid pressure of the right front wheel 6a is maintained at constant or decreased by functions of the valves 33a, 34a. The left wheels 7b an 1 1b on the higher frictional road side (high ,u side) do not yet tend to lock. Accordingly, the outputs EV', AV' are "0". The valves 33a, 34b are not energized. The brake fluid pressure of the front wheel 6b continues to rise.

In the valve apparatus 8 shown in Fig. 4, the fluid pressure is decreased in the input and output chambers 49a and 50a at the right side of the piston 38. On the other hand, the brake fluid continues to be supplied to the wheel cylinders 7b and 1 2a from the master cylinder 1. Accordingly, the rightward pushing force to the piston 38 becomes larger. The piston 38 is moved rightwards. Thus, the left valve ball 47b comes to seat the valve 46b by spring action of the spring 48b. On the other hand, the right valve ball 47a is further separated from the valve seat 46a by the rod portion 41a. The right input chamber 49a remains communicating with the right output chamber 50a, while the left input chamber 49b is interrupted from the left output chamber 50b.Thus, the fluid supply to the wheel cylinder 12a of the one rear wheel 1 lea is interrupted from the master cylinder 1.

When the piston 38 is further moved rightwards with the decrease of the fluid pressure of the right input and output chambers 49a and 50a, the volume of the left output chamber 50b interrupted from the left input chamber 49ab is increased. In other words, the fluid pressure of the wheel cylinder 1 2a of the rear wheel 1 1a is lowered since the wheel cylinder 1 2a communicates with the left output chamber 50b through the output port 14 and the conduit 15.

When the control signals EV, AV become again "0" to increase the fluid pressure of the input and output chambers 49a and 50a, the piston 38 is moved leftwards to decrease the volume of the left output chamber 50b, while the left valve ball 47b seats the valve seat 46b. Thus, the brake fluid pressure of the wheel cylinder 12a of the rear wheel 1 1a is again increased. The above-described operation means that the brake fluid pressure of the wheel cylinder 1 2a of the rear wheel 11 a at the same side as the front wheel 7a is controlled in accordance with the brake fluid pressure of the wheel cylinders 7a of the front wheel 7a. Thus, the rear wheel 11 a running on the lower frictional coefficient side of the road is prevented from locking, similarly to the front wheel 67a at the same side.If the brake fluid pressure of the wheel cylinder 12a of the rear wheel 11 a is controlled in common with the brake fluid pressure of the wheel cylinder 7b of the front wheel 6b running on the higher frictional coefficient side, the rear wheel 1 1a would be locked.

There have been above described the case that all of the wheels are provided with the tyres of the same kind. Next, there will be described the case that only the front wheels 7a, 7b are provided with spike tyres or chains. It is assumed that the vehicle runs on the split road, the frictional coefficients of which are considerably different at the right and left sides, and further it is assumed that the right front and rear wheels 6a, 11 a run on the low-,u side and the left front and rear wheels 6b, 11 b run on the high- side.

When the brake pedal 2 is rapidly trodden, the brake fluid pressure P of the front wheel 6a increases as shown in Fig. 8B. The output EV1 of the first judge circuit 35a becomes "1" at time t 1. Accordingly, the output EV of the first logic circuit 36a becomes "1" at time t1 as shown in Fig. 8C. Thus, the brake fluid pressure P is maintained at constant.

The output AV1 of the first judge circuit 35a becomes "1" at time t2. Accordingly the output AV of the first logic circuit 36a becomes "1" as shown in Fig. 8C. Thus, the brake fluid pressure P is decreased as shown in Fig. 8B. Although the output AV1 disappears at time t3, the output EV1 is still "1".

Accordingly, the output EV is "1", and the brake fluid pressure P is maintained at constant.

The output AV2' becomes "1" at time t4.

Thus, the slip of the right rear wheel 1 lea reaches the predetermined value. As clear from the circuit of Fig. 5, when the output AV2' is "1", the output EV2' is "1". However, after the output AV1Z of the front wheel is generated, the output of the AND gate 101 becomes "0". On the other hand, the output of the AND gate 104 receiving the output AV2' of the rear wheel is supplied to the OR gate 100. Accordingly, although the output EV, becomes "0", the output EV remains "1". Thus, the brake fluid pressure P is decreased at time t4 as shown in Fig. 8B.

The output AV2' disappears at time t5.

However, the output EV1 of the front wheel becomes again "1" before time t5. However, the brake fluid pressure P is maintained at constant. The duration of the output AV is equal to that of the output AV2'. Or it is within the limit time determined by the ONdelay timer 105.

Hereinafter, the output REV 1 becomes periodically "0", "1", "0" . . . . . Accordingly, the brake fluid pressure P stepwisely rises as shown in Fig. 8B. The output AV1, and therefore the output AV become again "1" at time t6. The output EV is "1", while the output AV is "1". The brake fluid pressure P is decreased for the duration of the output AV.

As the result, the brake fluid pressure P of the front wheel 6a changes as shown in Fig.

8B. The wheel speed V of the front wheel 6a changes as shown in Fig. 8A. On the other hand, the brake fluid pressure P' of the rear wheel 11 a changes by function of the valve apparatus 8, as shown in Fig. 8B, and the wheel speed V' of the rear wheel changes as shown in Fig. 8A. All of the wheels are prevented from locking. The left wheels 6b and 11 b are controlled in the similar manner.

When the skid conditions of only the front wheels 7a, 6b are judged as in the prior art, in which the approximate vehicle speed is formed from all of the wheels, and when the fluid pressure control valve devices 4a, 4a are controlled with the thus obtained judge results, the brake fluid pressures P, P' of the front and rear wheels would change as shown by the dash-lines in Fig. 8B. The front wheel is so skid-controlled as to be prevented from locking. However, the rear wheel is locked.

Since the limit lock pressure of the front wheel is very high, the brake fluid pressure of the rear wheel would become higher than the limit lock pressure R. Although the brake fluid pressure of the rear wheel changes with the control of the brake fluid pressure of the front wheel, as shown by the dqsh-lines in Fig. 8B, the change range of the fluid pressure of the rear wheel is little, and the brake fluid pressure of the rear wheel remains higher than the limit lock pressure R. As shown by the dashlines in Fig. 8A, the wheel speed of the front wheel is decreased under the skid control operation. However, the wheel speed of the rear wheel would rapidly become zero, or be locked.

Next, there will be described the case that the front wheels are provided with spike tyres or chains, and that the vehicle runs on the road which is uniform in frictional coefficient.

For simplifying the description, it is assumed that both of the rear wheels reach the skid condition at the same time. The deceleration signal is generated from the deceleration signal generators 75b (hereinafter designated only with respect to the one conduit system) for the rear wheels 1 la, 1 1b. In Fig. 5, the outputs EV2, EV2' of the Or gates 94b become "1". On the other hand, the slip signal is not yet generated from the slip signal gen erators 77a for the front wheels 6a, 7b, and so the outputs AV1, AV', of the AND gates 92 a are "0". Accordingly, the outputs AV1Z and AV1Z' are "0".

Referring to Fig. 6, the outputs of the AND gates 101, and therefore, the outputs EV and EV' of the logic circuits 36a and 36b become "1" at time t1 as shown in Fig. 9C. Accordingly, the brake fluid pressure P and P' of the front wheels 6a, 6b and rear wheels 1 1a, 1 1b are maintained at constant.

The slip signal S is generated from the slip signal generators 77b at time t2. Or the slip of the rear wheels 11 a, 11 b becomes larger than the predetermined slip. The outputs AV2, AV2' of the AND gates 92b become "1".

Thus, the outputs AV, AV' of the logic circuits 36a, 37b become "1" at time t2, as shown in Fig. 9C. The brake fluid pressure P of the front wheels 6a, 6b decreases with time, as shown in Fig. 9B. Accordingly, the brake fluid pressure P' of the rear wheels 11 a, 11b decreases.

The outputs EV2, EV2' disappear at time t3.

However the output of the OR gate 100 remains "1", and therefore the outputs EV, EV' of the logic circuits 36a, 36b remain "1".

Accordingly, the brake fluid pressures P and P' of the front and rear wheels continue to decrease as shown in Fig. 9B.

The acceleration signal +b is generated from the acceíeration signal generators 74b.

Even when the slip signal S is still generated from the slip signal generators 77b, the outputs AV2, AV2' of the AND gates 92b become "0". However, the accelerator signal +b is supplied to the fourth input terminals of the OR gates 94b. Accordingly, the outputs EV2, EV2' or he OR gates 94b remain "1".

The outputs AV1Z and AV1Z' are still "0".

The outputs AV and AV' of the logic circuits 36a and 36b become "0". However, the outputs EV and EV' remain "1", as shown in Fig.

9C. Accordingly, the brake fluid pressures P and P' of the front and rear wheels are maintained at constant.

The acceleration signal +b disappears at time t5. The pulse generator 81b start to operate. The outputs EV2, EV2', and therefore EV, EV change periodically as "O", "1", "0", ''1", ... Accordingly, the brake fluid pres- sures P and P' stepwisely increase, as shown in Fig. 9B.

As above described, as soon as the rear wheels 1 lea, 1 1b tend to lock, the brake fluid pressure P' is maintained at constant or decreased. Accordingly, although the brake fluid pressure P' may temporarily become higher than the limit lock pressure R, it can be ra pidly lowered under the limit lock pressure R.

The rear wheels are prevented from locking.

The front wheels 6a, 6b are controlled with the skid condition of the rear wheels 11 a, 11 b, before they tend to lock. Accordingly, the front wheels do not lock.

When both of the rear wheels do not reach the skid condition at the same time, the one front wheel is controlled with the skid condition of the one rear wheel at the same side.

The other rear wheel is controlled in accordance with the fluid pressure of the one front wheel through the valve apparatus 8.

Next, there will be described the case that one of the conduit systems fails.

For example, when brake fluid leaks from the one conduit system including the conduit 3, the fluid presssures of the wheel cylinders 7a and 1 2b do not increase by treading the brake pedal 12. On the other hand, the fluid pressure of the other conduit system including the conduit 16 increases by treading the brake pedal 2. Accordingly, the piston 38 is moved rightwards in the valve apparatus 8. Since the anti-skid control is not effected, the contact 55 remains closed. The switch 52 is actuated with the movement of the piston 38. Electric current flows through the warning lamp 56 from the battery 57. The warning lamp 56 lights. Thus, the vehicle driver knows that the anti-skid apparatus fails.When the anti-skid apparatus does not fail, the contact 55 is opened with the beginning of the anti-skid control operation (for example, the beginning of the drive of the fluid pressure pump 20).

Accordingly, the warning lamp 57 does not light with the movement of the piston 38.

The further effects or advantages of the above described embodiment are as follows: Even when some circuits such as wheel speed signal generators 28b, 29a for the one conduit system are out of order, the front and rear wheels 7a, 6b, 1 lea, 1 1b can be nearly adequately skid-controlled.

The brake fluid pressure of the rear wheels 11 a, 11 b are controlled in accordance with the lower of the brake fluid pressures of the front wheels 6a, 6b through the valve apparatus 8. Accordingly, both of the rear wheels 11 a, 11 b are prevented from locking even on the split road. If both of them are locked, the steering ability would be lost. Also when the one of the fluid pressure control valves 4a and 4b is out of order, both of the rear wheels are prevented from locking.

As shown in Fig. 5, the approximate vehicle speed signals E are formed from the respective wheel speeds, and the higher of the two approximate vehicle signals from the front and rear wheels of each conduit system is selected for calculating the slips of the respective wheels. The higher is nearer to the true vehicle speed, and the slips from the higher approximate vehicle speed are nearer to the true slip.

In a general vehicle, one of the front and rear axles is a drive axis. The drive wheel is later in response to the brake torque under the influence of engine torque. When the higher of the wheel speeds of the drive and non-drive wheels is selected, the change of the approximate vehicle speed is nearer to that of the true vehicle speed.

When the vehicle is rapidly braked, cornering on the high-,u-road, the load changes to the wheels occur due to the centrifugal force acting latelally on the vehicle and to the braking force in the moving direction of the vehicle. The loads to the wheels are reduced in the order of the outer front wheel with respect to the cornering ~ the inner front wheel with respect to the cornering + the outer rear wheel with respect to the cornering the iner rear wheel with respect to the cornering. The larger the load is, the harder to lock the wheel is. When the rotational data of the two wheels diagonally combined with each other in the conduit system are combined and the higher wheel speed is selected, the approximate vehicle speed signal represents the nearer to the true vehicle speed.Accordingly, the slips of the wheels can be more accurately calculated.

While the preferred embodiment has been described, variations thereto will occur to those skilled in the art within the scope of the present inventive concepts which are delineated by he following claims.

For example, the judge circuit is not limited to that of Fig. 5, but a well-known judge circuit may be applied to this invention.

In the above embodiment, when the durations of the outputs AV2, AV2' are too long, they are limited to the predetermined time by the ON-delay timer 105. However, the outputs AV2, AV2' may be directly supplied to the OR gates 100 and 103 without limitation of time.

Further, in the above embodiment, the fluid pressure control valves 4a and 4b consist of inlet and outlet valves 33a, 34a, and 33b, 34b, respectively. However, they may consists of a single three-posjtion valves, respectively.

Further, in the above embodiment, the higher of the two approximate vehicle speed signals is selected for calculating the slip. Insteads, the higher of the two wheel speed signals may be selected for forming the approximate vehicle speed signal.

Further, the approximate vehicle speed may be formed from all of the wheel speed signals.

Further in the above embodiment, the proportioning valves 32a and 32b are arranged between the valve apparatus 8 and the wheel cylinders 1 2a and 12b. However, they may be omitted.

Claims

1. In an anti-skid control apparatus for a vehicle braking system including: (A) a pair of front wheels, and a pair of rear wheels in which wheel cylinders are diagonally connected by conduits; (B) a first fluid pressure control valve device for controlling the brake fluid pressure of the wheel cylinder of one of said front wheels, arranged between a first fluid pressure generating chamber of a tandem master cylinder and said wheel cylinder of the one front wheel; (C) a second fluid pressure control valve device for controlling the brake fluid pressure of the wheel cylinder of another of said front wheels, arranged between a second fluid pressure generating chamber of said tandem master cylinder and said wheel cylinder of the other front wheel;; (D) a control unit for measuring or judging the skid conditions of said front and rear wheels and for generating instructions for controlling said first and second fluid pressure control valve devices; and (E) a valve apparatus for generating a fluid pressure in accordance with the lower one of the brake fluid pressures of said said front wheels controlled with said first and second fluid pressure control valve devices, being arranged between said wheel cylinders of the front wheels and those of the rear wheels; the improvements in which said control unit combines logically the measuring or judging result of the skid condition of the one front wheel with that of the one rear wheel being at the same road side as said one front wheel for generating the instruction for controlling said first fluid pressure control valve device, and combines logically the measuring or judging result of the skid condition of the other front wheel with that of the other rear wheel being a the same road side as said other front wheel for generating the instruction for controlling said second fluid pressure control valve device.

2. An anti-skid control apparatus according to claim 1, in which said measuring or judging results of the skid conditions of said front and rear wheels include control signals for relieving the brake of said front or rear wheel, and for maintaining the brake of said front or rear wheel at constant, and when said control signal is obtained from said front or rear wheel on the same road side, said corresponding fluid pressure control valve device is controlled for relieving the brake or maintaining the brake at constant.

3. An anti-skid control apparatus according to claim 2, in which the duration of the control signal for relieving the brake is limitted to a predetermined time.

4. An anti-skid control apparatus according to claim 1, in which a slip signal is formed in said control unit, and the larger of approximate vehicle speed signals formed from wheel speeds of said front and rear wheels connected diagonally to each other in the conduit system is selected for forming said slip signal.

5. An anti-skid control apparatus according to claim 1, in which said valve apparatus comprises a casing, a piston slidably fitted to said casing, input and output chambers formed at both sides of said piston, input ports commu nicating with said input chambers, respectively, output ports communicating with said output chambers, respectively, and valve members arranged between said input and output chambers, and operated by said piston, wherein one of said input ports is connected to the wheel cylinder of the right front wheel, one of said output ports which communicates with the one of said output chambers being at the same side as the input chamber communicating said one of the input ports, is connected to the wheel cylinder of the left rear wheel, the other of said input ports is connected to the wheel cylinder of left front wheel, the other of said output ports which communicates with the other of said output chambers being at the same side as the input chamber communicating said other of the input ports, is connected to the wheel cylinder of the right rear wheel.

6. An anti-skid control apparatus according to claim 5, in which a fail detecting switch is erigaged with said piston.

7. An anti-skid control apparatus for a vehicle braking system, substantially as hereinbefore described with reference to and as illustrated in Figs. 2 to 9 of the accompanying drawings.