Patent GB-1259629-A (GB)
IPC: B60T8/34
Filed: 1969-03-24
Abstract: 1,259,629. Anti-skid hydraulic control of brakes. AISIN SEIKI CO. Ltd. 24 March, 1969 [22 March, 1968; 11 Oct., 1968], No. 15411/69. Heading F2F. [Also in Division H3] A brake system for a vehicle having two or more pairs of running wheels and wherein an output signal is delivered from a skid sensor to an anti-skid means adapted for preventing skidding of a preferred wheel pair, is characterized in that the remaining wheel pair(s) is/are provided with an hydraulic pressure cut-off means between a master cylinder and the wheel brake cylinders, this cut-off means being actuated by the same output signal from the skid sensor. As shown in Fig. 1, a brake pedal 10 is connected by a pusher rod 11 to a pneumatic booster assembly 13 which operates a master cylinder 14 having two pistons and outlet conduits 16, 19 connected to front wheel cylinders 27, 28 and rear wheel cylinders 34, 35 respectively. When a skid sensor 43 (see below) associated with transmission 39 and propeller shaft 40 provides a signal, when locking of rear wheels 32, 33 is imminent or present, switch 101 is closed, in consequence of which solenoid 64 is energized. Such energization switches an air change-over valve 36 to admit atmospheric air to one side of a vacuum-suspended diaphragm in a reducing valve 20. Movement of the diaphragm first permits closure of a spring-loaded valve located between inlet 21 (from conduit 19) and outlet 29 (to conduct 30) and then effects increase in volume of the space between the valve and the conduit 30. Hence, rear wheel brake pressure is first stabilized and then reduced (in known manner) to relieve the brakes.  Closing of switch 101 also brings about energization of a relay coil 50 whose relay contacts 56, 57 are thereby closed to energize solenoid 58. Such energization permits closure of a spring-loaded cut-off valve 17 located between conduit 16 from the master cylinder and conduit 23 leading to the front wheel cylinders. Hydraulic pressure in the front wheel cylinders is thereby stabilized. Skid sensor 43 includes a conventional D.C. generator mechanically connected with the transmission 39 so that its voltage depends on the rotational speed of the rear wheels. The circuitry includes single-stage transistor amplification so that on actual or imminent wheel locking a sufficiently strong signal is provided to energize directly a relay coil which closes switch 101. A more elaborate alternative skid sensor assembly is depicted in Figs. 7 and 16 (not shown). In this case the generator is derived from a D.C. motor construction, and includes two D.C. energized diametrically-opposed poles and two similar poles, oriented 90 degrees therefrom and wound with sensing coils in series, all on the stator. The rotor is mechanically connected with the rear wheel drive. The signal arising from this generator is applied to four transistor circuits arranged in series (see Division H3) and all energized by a common constantvoltage-source circuit. The first is an amplifier circuit, while the second is a minimum-signallevel-setting circuit of Schmidt type whose function is to transmit only signals corresponding to decelerations above a predetermined value. The output from this circuit is applied to a delay circuit whose output is applied to a brake release signal circuit which operates solenoids 64 and 58 directly. Fig. 8 (not shown) is a simple modification of Fig. 1 in which the skid sensor, the air changeover valve and the hydraulic reducing valve are all associated with the front wheels, and the hydraulic cut-off valve is associated with the rear wheels. Fig. 9 is another embodiment of the invention where the reducing valve 20 is dispensed with, as such, and the air change-over valve 36 is modified and applied to the pneumatic booster assembly 13. Thus, as shown, a solenoidoperated valve 36<SP>1</SP> is connected to various parts of the booster 131 so that during a normal brake application (a) the vacuum connection from engine manifold 105<SP>1</SP> to the left hand side of the booster diaphragm is made through two adjacent openings of valve 36<SP>1</SP>; (b) a new connection through the booster casing to the right hand side of the booster diaphragm leads to one end opening of valve 36<SP>1</SP>, where it is blocked; and (c) an air inlet (not shown) to valve 36<SP>1</SP> communicates through the other end opening with the air intake pipe of booster 13<SP>1</SP>. When solenoid 64<SP>1</SP> is energized in consequence of a skid sensing signal, the following changes occur : (a) atmospheric air, instead of vacuum, is applied to the left of the booster diaphragm; (b) vacuum is now applied to the new connection on the right hand side of the diaphragm; and (c) the air supply to the air-intake pipe of booster 13<SP>1</SP> is interrupted. Consequently the diaphragm moves to the right and the hydraulic brake pressure is reduced. Simultaneously hydraulic communication between the master cylinder 14<SP>1</SP> and the front wheel cylinders 27<SP>1</SP>, 28<SP>1</SP> is cut off by solenoid-operated valve 17<SP>1</SP>, as before.  In the Fig. 1 embodiment the piston in the master cylinder controlling the rear brakes has a smaller diameter than the piston therein controlling the front brakes, ensuring greater rear brake pressure and consequently greater liability to wheel locking than for the front wheels. In the Fig. 9 embodiment, instead, a pressure control valve 185 (Fig. 11, not shown), incorporating a differential piston, may be interposed where indicated between the master cylinder outlet conduit 19<SP>1</SP> and the rear brake conduit 30<SP>1</SP>. As an alternative in Fig. 9 there may be inserted at 185 a load-sensing brake pressure control assembly, Fig. 12. This is hinged at 244 to the vehicle chassis 245 and connected at 247 by a tension spring 246 to a bolt 248 associated with the rear axle. An adjuster rod 261, to which spring 246 is attached, makes contact with a ball 261a, which in turn makes contact with a differential piston 252a, 252b, against which bears a valve member 257. Fluid communication from the master cylinder is provided by way of port 254, along passages 264, 265, 266, valve chamber 258, piston chamber 256 and port 256<SP>1</SP> to the rear wheel cylinders. When heavier pressure is applied to the brake pedal, the differential piston 252a, 252b performs rapidly-repeated reciprocating movements in a manner, described in detail in the Specification, and with frequency dependent upon the differential piston area, the load carried by the vehicle, and the degree of deceleration caused by the braking effort.