Patent GB-1061352-A (GB)
Title: Brake pressure proportioning device
IPC: B60T11/224
Filed: 1965-01-29
Abstract: 1,061,352. Hydraulic brakes. KELSEYHAYES CO. Jan. 29, 1965 [Jan. 30, 1964], No. 4111/65. Heading F2F. A brake proportioning device for a vehicle hydraulic brake system comprises a first stepped piston 301 working in a first stepped bore 225, 223 having a connection 207 to the rear brakes, and a second hollow piston, whose bore slidably receives a piston valve member 252, working in a second bore 227 having a connection 217 for the front brakes and a connection leading to the right-hand end of the stepped piston, the arrangement being such that, after initial brake application, the pressure applying movement of the first piston is opposed by fluid displaced by movement of the second piston thereby modulating the pressure delivered to the rear brakes. On initial brake application, fluid from a master cylinder enters inlet connection 203, passes through port 302, past a ball valve 319, which is spring-biased to the left by plunger 321 and held unseated by projection 327 on piston valve 252 which is itself urged into abutment with said stepped piston by a strong spring 255, through radial port 329 to the rear brake connection 207. Simultaneously, fluid is supplied from inlet 203, between the piston valve and said second piston, through port 261 to firstly the front brake connection 217 and secondly to the right-hand end of the first stepped piston, the fluid pressure being the same throughout the system at this stage. At a predetermined pressure, differential piston valve 252 moves to the left against the bias of spring 255 to seat against the second piston and simultaneously to allow valve 319 to seat. Thereafter fluid pressure is only transmitted to each respective brake set by combined movement of piston 233 and valve 252 to the left and by movement of piston 301 to the right, the former acting to amplify the front brake delivery pressure relative to the master cylinder supply pressure and the latter acting to reduce the rear brake delivery pressure relative to the master cylinder pressure. In addition the front brake delivery pressure acting on the rear of piston 301 resists movement of said piston and further modifies the rear brake delivery pressure. In the embodiment of Fig. 1 (not shown), a ball 75 rides up on inclined seat in a first stepped piston 43 at a predetermined vehicle deceleration to cut off a by-pass 65 between a fluid inlet 3 and rear brake connection 21. Thereafter, the stepped piston moves to the left and subsequently reduces the ratio of rear brake delivery pressure to master cylinder supply pressure. Port 108 communicates the rear brake pressure to chamber 33 so that as soon as ball 75 seats and the supply pressure is increased, a second stepped piston 91 moves to the left allowing ball 115 to cut-off a by-pass 103 through the piston to the front brake connection 9, delivery to the front brakes thereafter being amplified by the differential areas of piston 91. The communicating port 108 allows the delivery pressure to one set of brakes to act in opposition to modify the delivery pressure to the other set of brakes. In a final embodiment, Figs. 4-6 (not shown), the pressure proportioning device is incorporated in a tandem master-cylinder construction. In this arrangement, initial movement of directly-actuated master cylinder piston 417 supplies fluid through ports 443, 447, past piston valve 453 to rear brake connection 452 prior to sufficient compression of coupling spring 433 to move a stepped piston 427 against spring 434 to pressurize the front brakes. This arrangement is particularly suitable for a system having disc brakes on the front wheels and drum brakes on the rear. On movement of piston 427 fluid is delivered through a port 441 around an annular groove 437 in a piston 457 to the front brakes, a ball-controlled by-pass 479, 488 equalizing pressure on either side of piston 427 to ensure a 1/1 ratio of front-wheel brake delivery pressure to master cylinder pressure. Fluid is also bypassed through port 472 to the left-hand side of piston valve 447. At a predetermined pressure, ball 479 seats and the ratio of the transmitted pressure to the front brakes is increased by the differential areas and the pressures acting thereon. At a greater predetermined pressure the piston valve seats against a piston 445 to close off the rear brake connection 452 from port 443. Thereafter, the pressure transmitted to the rear brakes relative to the master cylinder pressure is reduced according to differential areas of piston 453 and the opposing front brake pressure acting on the left-hand side of piston valve 447.