Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Patent
1991-06-10
1993-08-17
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
188195, 188349, 188364, 303 221, 303 228, 303 975, B60T 830, B60T 1134
Patent
active
052362515
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to vehicle braking systems and in particular to vehicle braking systems in which at least one brake actuator associated with a front wheel of the vehicle and at least one brake actuator associated with a rear wheel of the vehicle are connected in a common circuit of the braking system.
Because of weight transfer from the rear wheels to the front wheels of a vehicle during braking, if the same braking effort is applied to the front and rear brakes, the rear brakes will be liable to lock, traction of the rear wheels reducing as the weight is transferred to the front wheels. One solution to this problem is to provide a proportioning valve between the brake master cylinder and rear brake actuator, which at a predetermined pressure in the brake circuit will reduce the rate at which pressure is applied to the rear brake actuator. In a further refinement, the pressure at which the proportioning valve starts to reduce pressure to the rear brake actuator may be varied by applying a load to the valve which is proportional to the travel of the rear axle, so that as weight distribution to the rear wheel decreases, the pressure in the brake circuit at which the rate at which pressure to the rear brake actuator is reduced, will also decrease.
Hitherto, axle load responsive proportioning valves of this type have been mounted on a fixed chassis member remote from the brake actuator and controlled by a lever mechanism associated with the rear axle.
The present invention provides a wheel load responsive valve means which is integral with the brake actuator.
According to one aspect of the present invention, a vehicle braking system comprises a master cylinder, a first brake associated with a front wheel of the vehicle and a second brake associated with a rear wheel of the vehicle, said brakes being connected in a common circuit to said master cylinder, characterised in that the second brake includes an actuator with integral valve means which, at a predetermined fluid pressure in the brake circuit, will vary the rate at which fluid pressure is applied to the second brake actuator, resilient loading means acting upon said valve means to set the predetermined fluid pressure at which the rate at which fluid pressure is applied to the second brake actuator is varied, means being provided to vary the load applied by said resilient loading means in proportion to the load applied to the rear wheel with which the brake actuator is associated.
The brake actuator associated with the rear wheel may have two cylinder/piston assemblies, while the valve may control the rate at which pressure is applied to both cylinders, preferably one cylinder is connected directly to the brake circuit.
According to a preferred embodiment of the present invention a vehicle braking system comprises a master cylinder, a first brake associated with a front wheel of the vehicle and a second brake associated with a rear wheel of the vehicle, said brakes being connected in a common circuit to said master cylinder, characterised in that said second brake includes an actuator with two cylinder/piston assemblies, one cylinder being connected directly to the brake circuit and the other cylinder being connected to the brake circuit via valve means which, at a predetermined fluid pressure in the brake circuit, will vary the rate at which fluid pressure is applied to said other cylinder, resilient loading means acting upon said valve means to set the predetermined fluid pressure at which the rate at which fluid pressure is applied to the second brake actuator is varied, means being provided to vary the load applied by said resilient loading means in proportion to the load applied to the rear wheel with which the brake actuator is associated.
Various embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 illustrates the wheel cylinder assembly of a rear drum brake of a braking system according to the present invention;
FIG. 2 is a sectional elevation along the l
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Haines William E.
Hales Eric C.
Harries David A.
Quinney Kenneth M.
Automotive Products plc
Butler Douglas C.
Milliken Paul E.
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