Patent GB-1325221-A (GB)
Title: Anti-skid control means for liquid pressure braking systems
IPC: B60T8/50
Filed: 1971-02-23
Abstract: 1325221 Anti-skid brake systems AUTOMOTIVE PRODUCTS CO Ltd 1 Feb 1972 [23 Feb 1971] 5220/71 Heading F2F In anti-skid control means for a liquid pressure braking system of a vehicle of the kind in which liquid pressure, derived from a source at which such pressure is constantly available when the vehicle is in operation, is applied by the operation of a valve 16 under the control of the vehicle driver to motor cylinders 12, 13 acting to apply brakes to wheels 10, 11 of the vehicle, sensing means 41 responsive to conditions preliminary to skidding of the vehicle wheels being provided to control the actual pressure acting in the motor cylinders in such a way that the said actual pressure is reduced automatically when a tendency to skid is sensed and is restored automatically to a value determined by the driver-controlled valve when the tendency to skid ceases, there are provided, between the driver-controlled valve and at least some of said motor cylinders 13, a shut-off valve 23 closable to prevent flow of liquid from the source of pressure to said motor cylinders and, between said shut-off valve and the motor cylinders, a first chamber 34 in which is movable a plunger 26 operative to vary the volume of said chamber, said shut-off valve being urged towards the closed position and said plunger being urged in a direction to maximize the volume of said chamber by liquid pressure in the braking system and said shut-off valve and plunger being normally held against movement by said liquid pressure in the braking system by the opposing action of a spring 33 and of liquid pressure from the pressure source acting on a movable wall 30, the liquid pressure providing the said opposing action being produced by liquid in a second chamber 32 which is normally connected to the pressure source and is connected to a low pressure reservoir 15 by operation of the skid sensing means, there being provided, for the passage of liquid between said second chamber and said pressure source and low pressure reservoir, a flow-restricting device 36 and means such as a passage 37 and valve 38 to provide for flow of liquid in the outward direction from said second chamber, at a rate not controlled by said flow restricting device. As shown, upon actuation of the valve 16 to apply the brakes, liquid pressure is built up in the cylinders 12 and 13 to apply the front and rear brakes, the pressure in the chamber 34 corresponding to that in the cylinders 13, equal pressures are built up in the chamber 31 and the second chamber 32 which chambers are connected by the flow-restricting orifice 36 and the action of the spring 33 holds the ball valve 23 open. When a skid is sensed, the valve 35 isolates the chamber 31 from the pump 14 and connects that chamber to the reservior 15 whereby the pressure in the chamber falls and liquid passes thereinto from the chamber 32 via the orifice 36 and one way valve 38. The pressure in the chamber 32 falls and the pressure acting on the plunger 26 in the chamber 34 moves the plunger to allow the ball valve 23 to close thereby isolating the cylinders 13 from the pump 14. Continued movement of the plunger 26 after the valve 23 has closed increases the volume of the chamber 34 and so reduces the pressure acting in the cylinders 13 to allow the brakes to be released. When the tendency to skid has been removed, the sensing device 41 allows the valve 35 to return to the normal position thereof re-connecting the chamber 31 to the pump 14 the valve 38 now closing since the pressure in the chamber is greater than in the chamber 32 and liquid is passed between the chambers only by way of the orifice 36 so that pressure is built up gradually in the chamber 32 to move the piston 30 and plunger 26 to reduce the volume of the chamber 34 and eventually open the valve 23, brake applying pressure then being built up in the cylinders 13 to re-apply the brakes. The anti-skid control means may be arranged to control motor cylinders actuating all the brakes of a vehicle or any selected group of brakes, or separate anti-skid control motor cylinders operating individual or groups of brakes. In modifications, (a) the orifice 36 is replaced by an axially fixed pin (36a), Fig. 2 (not shown), passing through a hole (36b) in the piston 30 and having a longitudinally inclined flat or groove to provide a progressively variable flowrestricting passage, and/or the pin is stepped to provide an abrupt change at any chosen piston position, (b) the piston 30, to provide a more even rate of pressure release , has, apart from the restriction orifice 36, a co-axially tubular stem (42), Fig. 3, (not shown), connected at one end to the passage 37 and extending through the chamber 32 and an orifice (43) in the end wall thereof into a further chamber (44), the stem being externally tapered, (c) the valve 38 and variable flow restricting device is mounted externally of the cylinder 29, (d) the piston 30, Fig. 5, has a stem 52 slidably carrying a floating piston 53, liquid flow, when the brakes are applied and when there is a tendency for skidding, passing from the chamber 32 to the chamber 31 via orifices 59, 57 in the pistons 53, 30 and past a flutter plate 58 provided with an orifice 60, (e) the main piston 30, Fig. 6, (not shown), is cup-shaped and co-operates with a skirt (63) on a valve sleeve (62) to provide a liquid flow restriction between the chambers 31, 32, and (c) the valve 16 is connected directly to the chamber 31 through a flow restricting device and a valve is connected between that chamber and the reservoir 15.