Patent GB-836200-A (GB)
Title: Improvements in or relating to servomotor brake mechanism for vehicles
IPC: B60T13/48
Filed: 1956-08-21
Abstract: 836,200. Vacuum brakes. FEENY & JOHNSON Ltd., JOHNSON, M. E., JOHNSON, H., and CLIFTON, G. July 26, 1957 [Aug. 21, 1956], No. 25505/56. Class 103 (1). In servo - brake mechanism for coupled vehicles, comprising trailer brakes operated by a vacuum servomotor on the trailer and exhausted through a coupling pipe between the vehicles from a controlled source of vacuum on the tractor and a control valve operated mechanically and/or hydraulically, a security device on the trailer comprises a plunger attached to the coupling pipe and slidable in a casing having ports connected to the trailer servomotor, directly to the trailer's vacuum tank and to the vacuum tank via a non-return valve. Operation of the brake pedal 14 of tractor A pressurizes lines 13, 15 to move a piston 29 and plunger 28, Fig. 2, of control valve 12 against spring 30 to connect pipe 16 to the induction system of engine 10 via ports 35, 32 and pipe 11, on brake release the pipe 16 is connected to atmosphere via port 33, the pipe 16 being connected to trailer B by coupling 17 and flexible pipe 18. The security device comprising valve 23 on the trailer, consists of a plunger 36, Fig. 6, connected to pipe coupling 18 and sliding in casing 37, ports 41 and 42 in plunger 36 register in the normal position, with ports 45 and 46 in casing 37 respectively; a shoulder 38 on plunger 36 engages abutments 39, 40 in the casing 37 to limit movement of the plunger which is closed at end 43 and is provided with sealing rings 53. The valve 23 has external connections 22, 24. 25 to the vacuum servomotor 19, direct to vacuum tank 26 and to tank 26 via non-return valve 27, respectively. In brake application, control valve 12 is operated to supply vacuum to operate servomotor 19 to apply the brakes through linkage 20, 21, the plunger 36 remaining in its innermost position; if due to failing of coupling C between the vehicles the connection pipe 18 is tensioned, then plunger 36 is withdrawn to its outermost position breaking the connection between ports 41 and 45 and connecting the servomotor directly to the tank 26 via ports 45, 47 and pipe 24 to apply the brakes, the non-return valve 27 prevents air entering tank 26 via ports 41 and 46 and pipe 25 should connection pipe 18 fracture. The vacuum tank 26 is evacuated by operation of the tractor brakes and is maintained under vacuum by partial exhaustion through non-return valve 27 every time servomotor 19 is brought into operation. In an embodiment, Fig. 7 (not shown), the plunger and casing each have one set of registering ports connected to a T-piece, one arm of which, being connected to the non-return valve and the other arm to the servomotor, a second port in the casing connects the servomotor directly to the tank as before. To avoid vibration, the plunger is held in the normal position by spring-pressed balls in the casing engaging a groove in the plunger, the complete valve being mounted on the trailer tow-bar. After an emergency stop the trailer brakes are released by pushing plunger 36 to its innermost position to connect servomotor 19 to atmosphere. Specifications 662,779 and 680,738 are referred to.