Abstract: A reservoir assembly for a vehicle hydraulic braking system includes two chambers (2, 3) for the storage of hydraulic fluid. The reservoir assembly is provided with a structure for increasing the effective volume of one of the chambers (2), for example a bellows (12) or a bucket (30), and which may be operable in conjunction with the fitting of a filler cap (17) to seal a filler opening (5) for that chamber. This enables a volume of fluid to be accommodated in a chamber of increased volume, thereby substantially eliminating the possibility of volume in excess of a given volume from overflowing from the chamber (2, 3). When the reservoir assembly is installed in a vehicle braking system of a brake-by-wire electro-hydraulic type (EMB) having a first power circuit (51), and a second back-up hydrostatic circuit (60), the one chamber (2) supplies fluid to the hydrostatic circuit, and the other chamber (3) supplies fluid to the power circuit.

Abstract: An hydraulic braking system of the brake-by-wire type has an hydraulic pressure source comprising an hydraulic accumulator adapted to be charged by a pump. An accumulator isolating valve is so positioned and biased to correspond to the direction of flow from the accumulator to a solenoid-operated proportional valve. The valve is biased into a closed position in opposition to the flow from the pump to the accumulator.

Abstract: In a braking system in which brake application is controlled electronically by the use of electrically controlled actuators (5, 6), a pedal-operated hydrostatic master cylinder (31) is connected to a brake (12) through at least one of the actuators (5). A first normally open valve (7) is provided so that upon failure of the electronic means (15a, 15b, 60), the value opens to permit hydrostatic pressure to apply both the front wheel brakes (1, 2) by putting them in fluidic communication. A second normally-open isolator valve (44) can be provided which is closed during normal brake operation to prevent hydrostatic pressure from being utilised to apply the brake, the valve opening automatically upon failure of the electronic means (15a, 15b, 60).

Abstract: In a hydraulic braking system, during normal service braking, the output from a master cylinder (3) is disabled and a brake (12) is applied from a high pressure hydraulic source (24) under the control of electric control means (30) including a solenoid operated actuator (6) responsive to electrical signals from a transducer (2) associated with the pedal (1), and upon failure of the electrical control means a direct flow path is defined between the master cylinder (3) and the brake (12) and through which the brake can be applied from the master cylinder by movement of the pedal in the "push through" mode.

Abstract: An hydraulic braking system is disclosed which comprises a fluid source and brake actuators, wherein a first master control valve is provided to supply substantially equal pressures to all brake actuators and additional control valves are provided to regulate pressures applied to respective ones of said brake actuators. The first control valve and the additional control valves are provided in series between the fluid source and the brake actuators so that operation of the master control valve allows equal hydraulic pressures to be applied to each actuator while the additional control valves allow individual brake regulation and in an emergency operation of the master control valve allows for automatic operation of all the actuators.

Abstract: A brake booster having a fluid actuated piston in the form of a diaphragm (5) to which the supply of fluid is controlled by a valve mechanism (8A, 14A, 17), actuated by a driver-operated force input member (16) which acts via a reaction element (19) on an output member (10) providing power assisted input to a master cylinder. The booster includes a force transmission assembly (14,8) providing surfaces through which force is transmitted between the input and output members (16,10). A spring (24) is arranged to yield under a predetermined force to permit relative movement between parts (14) and (8) such as to change the ratio of the operative surface areas and thereby increase the boost ratio.

Abstract: A solenoid-operated flow control valve is disclosed which comprises a housing having a bore, a solenoid coil, an armature, an inlet and an outlet, a permanent communication between an inlet and an outlet comprising a first and a second flow path connected in parallel between the inlet and the outlet, the first flow path being closable and the second flow path providing permanent communication between the outlet, an exhaust, a seating and a valve assembly including a hollow valve body working in the bore, the armature being responsive to the coil to open the exhaust to determine a pressure differential across the valve body, the pressure differential in turn causing the valve body to move in the bore so as to co-operate with the seating, whereby the valve body provides selective communication between the inlet, outlet and exhaust, and whereby upon deenergisation of the coil the flow control valve controls the rate of reapplication of pressure to the outlet.

Abstract: The present specification discloses a servo unit for use in a vehicle braking system, the servo unit comprising a housing within which a flexible diaphragm separates a vacuum pressure chamber from an atmospheric pressure chamber. An actuator rod assembly extends through the housing and includes a valve assembly having a valve control piston which has a laterally extending key, the key being engageable with a fixed stop in the housing to limit the movement of the valve control piston and cause a balance in the valve assembly between the vacuum and atmospheric pressure. A solenoid valve is also provided, the solenoid valve being controllable to either connect a flexible passage member extending around the actuator rod assembly across the vacuum pressure chamber between the housing and the diaphragm in the region of the valve assembly, to the vacuum pressure chamber, or to connect both the flexible passage member and a bypass leading from the solenoid valve to the atmospheric pressure chamber, to the atmosphere.

Abstract: A pneumatically operated servo booster has a housing divided by a diaphragm assembly into front and rear chambers respectively. A hub movable with the partition carries a vacuum valve seat and a plunger slidable within the hub carries an atmospheric valve seat, the seats co-operating with a spring-urged poppet valve to control fluid flow to the chamber. A stack of Belleville washers normally transmits input force from an input rod, the washers yielding at a predetermined input force to allow a cup member to engage an abutment carried by the hub, causing the hub to move relative to the valve member and temporarily open the valve seat to cause a reduction in boost compensating for the excess input force.

Abstract: In a rotary flywheel skid sensing device for a vehicle hydraulic braking system a flywheel assembly is driven from a braked wheel, and has a flywheel member, a reaction member and a ball and ramp mechanism co-operating with the two members and operative, on relative angular movement of the members when the deceleration of the braked wheel exceeds a predetermined value, to cause relative axial movement of the members to actuate means for modulating the brake pressure. The flywheel assembly is driven by and located on a collar driven by the wheel, with the ball and ramp mechanism located in complementary conical surfaces on the flywheel and reaction members. The reaction member is supported on the collar to locate the assembly rotationally and axially, and drive is transmitted from the collar to the assembly through a clutch provided by a direct engagement between the collar and the reaction member.

Abstract: In an anti-skid modulator assembly a flywheel mechanism operates a dump valve through a lever which is adapted to pivot about a fulcrum at an intermediate point in its length. The dump valve comprises a spring normally urging a valve member into engagement with a seating. The valve member has a head at its outer end with which the lever co-operates to open the dump valve. Normally when the dump valve is closed, the lever is in engagement with the fulcrum and is spaced from the head by a degree of lost-motion.

Abstract: In an anti-skid hydraulic braking system of the pump/re-apply type fluid is dumping from a working chamber into an auxiliary reservoir between a springloaded piston and the dump valve in response to a skid signal. When the dump valve closes the pump first withdraws fluid from the auxiliary reservoir in an unrestricted manner to re-apply the brake in a first stage up to a knee point at which a valve defined by the engagement of a head on the piston with a seating isolates the pump directly from the auxiliary reservoir. Thereafter the pump draws fluid from a main reservoir but at a reduced rate through a restricted orifice in the piston.

Abstract: An anti-skid hydraulic braking system incorporates a modulator assembly for modulating the supply of fluid from a master cylinder to a brake in accordance with skid signals. The modulator assembly comprises a de-boost piston located in a bore in a housing, an expander chamber connected to the brake, a first valve between the master cylinder and the chamber, and a second valve for controlling the application of the de-boost piston of a fluid sustained-support force. The modulator assembly incorporates a safety piston which prevents the first valve from closing unless a device, suitably an hydraulic accumulator or pump, and which provides the fluid sustained-support force, is operative.

Abstract: The concern is with reducing the deceleration rate of an over-running flywheel following actuation of an associated camming means, by reducing the torque of an axially biassed clutch, to provide a more reliable wheel speed analogue. In one construction the clutch may consist of two clutch discs engaging with the thrust member of a camming means. The clutch torque is reduced following expansion of the camming means by reducing the frictional engagement force between one disc and the thrust member, this being effected by a change in the mechanical advantage of a lever acting on the flywheel as the lever accommodates expansion of the camming means. In another construction the fluid pressure force on a clutch biassing piston is varied to vary the clutch torque, and in yet other arrangements, a magnetic clutch biassing force is varied.

Abstract: An hydraulic brake actuator comprises opposed pistons which work in bore portions in a housing and fluid pressure in a pressure chamber urges the pistons in opposite directions to separate adjacent ends of a pair of brake shoes. A pressure proportioning valve controls communication between pressure spaces constituted by the pressure chamber. The valve is normally open to equalize the pressure in the pressure spaces but closes at a predetermined pressure so that any further increase in pressure is operative in only one pressure space, the pressure in which space acting to keep the valve closed. In use in a brake of the one-leading one-trailing shoe-drum type the increased pressure acts on the piston which applies the trailing shoe to the drum, in order to equalize the torque.

Abstract: Valve assemblies for single and dual circuit braking systems are described. An assembly for a single circuit (FIG. 1) has a primary piston provided with a normally open valve seat engageable by a deceleration sensing ball housed in the primary piston. An annular secondary piston is slidably mounted on the larger diameter end of the primary piston. Primary piston has an area (A.sub.2) exposed to outlet pressure in a chamber and a smaller area (A.sub.1) exposed to inlet pressure in a housing bore portion, and is capable of rearward movement against biassing of a spring. Rearward movement of secondary piston is restricted firstly by a flange on the primary piston and secondly by a step on the housing.

Abstract: An hydraulic anti-skid system incorporates a pump having a piston assembly. The piston assembly comprises a pump plunger which is reciprocable in a bore of a drive mechanism, a signal piston coupled to the pump plunger, and a spring for urging the pump plunger out of engagement with the drive mechanism. The signal piston has a first area which is exposed to the pressure from a master cylinder or the brake when the brake is applied to urge the signal piston in a direction such that the pump plunger can engage with the drive mechanism. A dump valve is provided for controlling fluid in a stop chamber to which the piston assembly is exposed at least after the brake has been applied.

Abstract: The disclosure concerns an anti-skid brake control system of the kind which senses the presence of skid conditions at a hydraulically braked wheel and then automatically relieves the brake pressure at that wheel by expanding the volume of a chamber connected to the wheel brake. In the system disclosed, a regulator is connected in a high pressure fluid supply line so as to control the rate at which the volume of the chamber is reduced on cessation of the skid conditions, thereby controlling the rate at which the brakes are re-applied. In the particular embodiment described, the regulator comprises a cup-shaped piston reciprocable within a cylinder bore. A first restriction of predetermined size is defined by the end wall of the piston and a second restriction of variable size is formed between a number of radial ports in the bore wall and an annular recess in the outside of the piston, this recess being permanently connected to the inner space of the piston.

Abstract: In a fluid-pressure operated anti-skid braking system operation of a brake applying relay valve is controlled by application pressure in an application chamber. A memory chamber is connected to the application chamber through a one-way valve and a restrictor permits pressure in the memory chamber to decay into the application chamber when the pressure in the application chamber reduces at a skid point. Application pressure is supplied to the application chamber through a normally open latch valve. Re-application of the brakes following a skid is controlled by closure of the latch valve which permits only a restricted flow of application pressure into the application chamber. This is sufficient to re-apply the brakes rapidly in a first stage until the pressure in the application chamber becomes equal to that of the decayed pressure in the memory chamber.

Abstract: In a pressure modulator for an anti-skid braking system a spring acts through a modulator piston to bias a piston assembly into a position in which an inlet for connection to a pressure source is connected to an outlet for connection to a wheel brake. Normally the spring force is augmented by pressure supplied to the modulator piston through an anti-skid mechanism which cuts off the pressure supply if deceleration of a wheel exceeds a predetermined value, whereby the piston assembly moves into a position in which the outlet is cut-off from the inlet.