Patent GB-1338971-A (GB)
Title: Hydraulic braking system
IPC: F16D65/28
Filed: 1972-01-03
Abstract: 1338971 Dual-circuit hydraulic disc brakes; alternative spring actuation BENDIX CORP 3 Jan 1972 [20 Jan 1971] 155/72 Headings F2F and F2E An hydraulic braking system comprising one or more brakes including a service actuator in a first hydraulic circuit and including a spring actuator with brake-applying resilient means and pressure-responsive releasing means, has operator-operated means including an hydraulic motor connected to a master cylinder, the hydraulic motor having a pressure chamber connectible to a fluid pressure source and being connected through a second hydraulic circuit to the above-mentioned pressure-responsive releasing means, the first and second hydraulic circuits being separate. As shown in Fig. 1, a pump 18, operative when the vehicles' engine is running, pumps automatic-transmission fluid through conduit 25 and via brake booster 10 and conduit 27 to steering gear 26, the return conduit having T-connections 24 and 70. Booster 10 has a piston 14 and a spool valve 16 (see below) both operated by a pedal 22, piston 14 serving to operate a master cylinder 28 which pressurizes two brake-fluid circuits 30, 32. Circuit 30 applies front brakes 35, while circuit 32 communicates with inlet port 100, Fig. 2, to provide, via piston 98, service application of rear wheel disc brakes 82 to 86. The rear wheel disc brakes may also be applied by Belleville spring washers 104, Fig. 2, acting via piston 102, extensible member 106, and piston 98. The spring washers may be counteracted by fluid pressure applied at port 110 to chamber 108 by intensifier 40, Fig. 1, along conduit 74, the intensifier being pressurized in turn from booster pressurechamber 12 via non-return valve 68. Intensifier apply pressure may be relieved via manuallyoperated valve 72 and conduit 70 to the lowpressure side of pump 18. In the position of Fig. 1 the vehicle is assumed to be parked with the spring actuator 102, 104, Fig. 2, operative. In operation, to move the vehicle from rest, the operator starts the engine, whereupon pump 18 begins to operate. He then closes valve 72 and depresses brake pedal 22. This moves piston 14, which causes a service application of all the brakes and also moves spool valve 16, which thereupon diverts some of the fluid from the output side of pump 18 into pressurechamber 12 of booster 10, whence it flows to pressure-chamber 56 of intensifier 10 to tend to release the brakes via chamber 58, conduit 74 and inlet 110. When the operator releases pedal 22, service application of the brakes ceases, but because of non-return valve 68, chamber 56 is still pressurized, so spring-actuation of the rear brakes is counteracted. The vehicle may now be driven away, and the service-brake circuits used normally by the brake pedal. For parking-brake application when the vehicle has come to rest, (pump 18 having stopped, spool valve 16 being in the Fig. 1 position and pressure chamber 12 being unpressurized), the operator merely opens valve 72, whereupon chamber 56 is de-pressurized, piston 50, 52, 54 is urged leftwards by spring 62, chamber 108 is consequently depressurized, Fig. 2, and the rear brakes are spring-applied. The Fig. 1 position is thus regained. Whenever chamber 58 is de-pressurized a pressure-resposive switch 76 actuates a warning light 78 to remind the operator that the brakes are spring- applied. If the engine cannot be started and in consequence the spring application cannot be counteracted in the manner described above, a crank 64, Fig. 1, may be rotated, to move piston 50, 52, 54, against spring 62 and thereby pressurize chamber 58 to release the brake. Extensible member 106 lengthens as friction elements 84, 86, wear to limit retraction of piston 98 to a constant distance.