GB1153317A - Improvements in or relating to Track-Laying Vehicles - Google Patents

Abstract

1,153,317. Vehicle controls; steering endlesstrack vehicles. BOFORS A.B. 6 Dec., 1966 [17 Dec., 1965], No. 54593/66. Heading B7H. [Also in Division F2] In an endless track vehicle which is steered by simultaneous operation of a de-clutching servo 13 or 14 and a brake servo 15 or 16 associated with a drum 11 or 12 on the appropriate side of the vehicle, under control of a steering valve 10 having manually-operated levers 45, 46 which operate separate valve elements to control hydraulic pressure in conduits 28, 29 leading to the respective servos on opposite sides of the vehicle, a valve assembly 17 is provided which, in response to hydraulic pressure in a pilot conduit 24 occurring when a gear is selected in a non - synchromesh hydraulically controlled gear-box through which the vehicle is driven, connects the conduits 28, 29 with corresponding conduits 26, 27 leading from the steering valve, but which during a change of gear or when the gear-box is in neutral cuts off these connections and simultaneously connects both conduits 28, 29 to pump 21 via an adjustable pressure reducer 19 so as to provide automatic braking of the vehicle to a selected degree in these circumstances. For this purpose, the assembly 17 comprises a spool valve 18 which is biased to the automatic braking position shown by a spring 23 and is movable to the steering position by pressure in the pilot conduit 24. In the latter position grooves 22A, 22B and 22C respectively connect pump 21 to the steering valve inlet conduit 25, conduit 26 to conduit 28, and conduit 27 to conduit 29, whereas in the former position shown conduits 25-27 are isolated and groove 22D connects pump 21 to the inlet side of a pressure reducing valve consisting of a piston 31 having a by-pass passage 37 closable upon movement of the piston away from an abutment 39 against which a pin 40 normally rests, the outlet 50 from the reducing valve being connected simultaneously by grooves 22C and 22E to both conduits 28, 29, so that both brakes are applied. The degree of braking is adjustable by a control knob 36 connected to a lever 34 having a cam portion acting on the cap 33 of a spring 32 biasing the piston 31 to the left. In order that the braking may be variable between zero and maximum and be co-ordinated with the operation of the clutch servos, the brake servos are double-acting, their pistons 43, 44 providing annular chambers of different effective area on opposite sides, the chambers 41, 42 of smaller area being constantly supplied with fluid at maximum pressure direct from the pump, while the opposing chambers are fed with the pressure controlled by either the steering valve 10 or the pressure reducer 19, the clutches controlled by the servos 13, 14 being arranged to be disengaged just before the brakes are applied.