Patent GB-265656-A (GB)
Title: Improvements in or relating to wheel brakes for vehicles
IPC: B60T11/10
Filed: 1925-10-13
Abstract: 265,656. Pugh, J. V., and Rudge- Whitworth, Ltd. Oct. 13, 1925. Fluid-pressure; band; blocks and shoes acting on drums; force-transmitting mechanism.-In a four-wheel brake transmission system for vehicles, the pressure is transmitted to the brakes by a fluid column or columns, and means are provided whereby the apportionment of the pressure applied as between the front and rear brakes is varied as the movement of the pedal or other application member or the pressure applied thereto is increased; thus the pressure applied to the rear brakes after it has reached a predetermined value may remain constant or may decrease or may increase relatively slowly. Fig. 1 shows a system comprising a pair of pistons coupled to a pedal a and adapted to force liquid from cylinders a<3>, a<4> by pipes b, c to pairs of cylinders associated respectively with the front and rear brakes. A chamber e, Fig. 3, is disposed in the rear brake system whereby when the pressure therein reaches a predetermined value a piston e<1> in the chamber yields against a spring e<2> so that the pressure ceases to increase further or increases slowly with continued movement of the pedal while the pressure increase in the front brake system is unaffected. Instead of the chamber e, a length of rubber tube f, Fig. 5, may be interposed in the pipe system c of the rear brakes. This tube f is stretched over a perforated rigid tube f<3> or a wire coil and is protected by an outer sheath f<5>. With this device the pressure on the rear brakes may decrease beyond a certain maximum since the resistance to expansion of the tube tends to decrease. Alternatively springs may be interposed in the transmission between the fluidoperated pistons and the rear brakes. In a system in which a single pedal-operated piston transmits the pressure to both front and rear brakes, the modification or limitation of the rear braking pressure may be effected (1) by the disposition of a spring between the pistons of the rear brakes and a fixed abutment together with a spring in the transmission between the piston and the brake or (2) a stopping device may be arranged to come into action when the rear pistons have moved a predetermined amount or (3) an opposing pressure may be applied to each rear brake piston by an additional piston subject also to the fluid pressure when a predetermined pressure is reached. Fig. 9 shows one form of rear brake embodying the device referred to at (1) above. A pair of pistons l<3> in a cylinder n engage through springs l<4>, liners l connected to the ends l<1> of an external brake band. Springs l<5> are interposed between the pistons and the fixed ends of the cylinder. Disengaging springs l<7> for the band abut on a fixed part l<8>. The springs l<4>, l<5> may both be initially tensioned and the pistons may engage the springs l<5> only after a certain amount of movement. The front brakes may be similar but without the springs l<4>, l<5>. The springs l<4> may be disposed between the levers l and the ends of the band. Instead of the springs l<5>, a spring may be arranged between the pair of pistons l<3> tending to oppose their separation. A similar arrangement of pistons applied to an internal shoe brake and an arrangement in which both the cylinder and piston are movable and abut against levers such as l is shown. Fig. 13 shows an external shoe brake for front wheels comprising a pair of pistons j<2> working in fixed cylinders j<1> and engaging the ends of the shoes by struts j<4> and telescopic guides j<5>, j<6>. For the rear wheels springs are interposed between the pistons and the struts and the ends of the cylinders to act in a similar manner to the springs l<4>, l<5>, Fig. 9. Arrangements in which a single piston operates a brake through a torque shaft provided with a cam or similar device are also shown. According to the second Provisional Specification this torque shaft in the case of the front brakes may have a universal joint therein in accordance with Specification 219,419. The device referred to at (2) above may comprise a spring disposed between each rear brake piston and a fixed abutment or between a pair of pistons where such are provided so as definitely to stop the piston or pistons after a desired movement thereof. A device operating as referred to at (3) above may comprise a piston r<1>, Fig. 8, subject to the fluid-pressure acting upon the brake applying piston r<2> and opposed by an initially tensioned spring r<6>. When the fluid pressure reaches a certain value, the spring r<6> yields and the piston r<1> applies a counter-pressure to the piston r<2> through a spring r<5> so that the resultant pressure on the piston r<2> thereafter increases only slightly or decreases. According to the first Provisional Specification a separate cylinder for an opposing piston such as r<1> may be provided and the pressure fluid be committed thereto by ports controlled by either of the pistons r<1>, r<2> or by spring-loaded valves. Further it is stated in this Provisional Specification that a hydraulic system may be arranged to operate in connection with devices such as are described in Specifications 260,656, 261,498, and 262,201.