Patent GB-1338571-A (GB)
Title: Dual braking systems
IPC: B60T13/26
Filed: 1971-07-29
Abstract: 1338571 Dual braking systems; anti-skid systems; actuators; valves DUNLOP HOLDINGS Ltd 29 July 1971 [6 Aug 1970] 37909/70 Heading F2F A dual braking system for a vehicle, more particularly for the tractor of a [tractor-trailer combination, comprises aservice braking function brake applying line 17 and a secondary braking function brake applying line 28 for emergency or parking brake applications which lines 17, 28 control the operation of brake actuators 1, 21 (2, 22) respectively, which actuators may be separate units or may be contained in a common housing; the system also incorporates an antiskid line 18 with a skid control valve 13 which is operable by a skid-detecting device to release the operative brake actuator when a tendency of a wheel to lock under braking is detected and to re-apply the previously operative brake actuator when the tendency for the wheel to lock has been overcome. Fig. 1 shows a pneumatic system wherein the service line 17 includes a driver's valve 11, a sensitivity control valve 9 and a combined balanced exhaust and non-return valve 8; the anti-skid line 18 has a solenoid operated control valve 16 and includes a restrictor 19; the secondary line 28 incorporates a differential protection valve 29, an inverter valve 30 and a hand control valve 31 and also a quick exhaust valve 35 and a shut-off valve 36. The valve 9 is connected to the anti-skid line 18 via a line 20 and the valve 36 is connected to the anti-skid line 18 via a line 39; the lines 18 and 28 are further connected by a non-return valve 34. The line 17 is connected to a first working chamber 4 of the service actuator 1 and the line 18 is connected to a second working chamber 5 thereof. The line 28 is connected to a chamber 27 of the secondary actuator 21, and the pressure in chamber 27 acts on a piston (or diaphragm) 27 is opposition to a brake-applying spring 26. During a service brake application the valve 11 is operated to connect a reservoir 12 with the chamber 4 whereby a diaphragm 6 is moved to actuate a brake operating rod 7. Upon a skid being sensed valve 13 connects a reservoir 15 with the chamber 5 whereby the diaphragm 6 and the rod 7 are moved in a brake releasing direction. The pressure in line 18 during an anti-skid operation acts on the valve 9 to prevent any excessive rise in pressure in the line 17, and the valve 8 acts to vent excess pressure. During a secondary brake application the valve 31 is operated to release pressure in the chamber 27 via the intermediary of the inverter valve 30 and the quick exhaust valve 35. Upon a skid being sensed, chamber 5 is pressurized and shut-off valve 36 is operated to stop further pressure fall in chamber 27. Subsequently if the skid is not corrected air can flow through the non-return valve 34 to pressurize chamber 27. In the embodiment of Fig. 5 the service and secondary actuators 82 (83) are combined in a single housing, and both the first working chamber 44 and the secondary brake applying chamber 55 act to give brake application by increase in pneumatic pressure therein. The system incorporates sensitivity control valves 86, 95 and exhaust and non-return valves 88, 97. Figs. 2, 3, 4 illustrate actuators suitable for use with the Fig. 5 embodiment. In Fig. 2 (not shown) two diaphragms (46, 52) form three chambers (44,45,55): diaphragm (52) is provided with a block (53) and a seal (57) co-operable with a port (56) connected to the secondary line. In Fig. 3 a piston 60 and a diaphragm 61 act to define chambers 62, 63, 64; rod 76 may be operated manually. Fig. 4, which is generally similar to Fig. 2, incorporates a third diaphragm 102 to define an additional chamber 105 to thereby retain the secondary braking function should the diaphram 52a fail. The invention is said to be applicable to other fluid pressure or vacuum operated systems such as hydraulic and combined hydraulic/pneumatic braking systems.