GB891042A - Hydraulic controls for change speed gears - Google Patents

Abstract

891,042. Change-speed control. CATERPILLAR TRACTOR CO. July 17, 1959 [March 18, 1959], No. 24592/59. Class 80 (2). [Also in Group XXXIV] In a vehicle transmission having speed ratio trains and forward and reverse trains selectable by hydraulically applied brakes, a selector valve 18 controls the supply of fluid from an enginedriven pump 14 to brake cylinders 1, 2, 3 for first, second and third gears, and a valve 20 controls the supply to brake cylinders F, R for forward and reverse, and the arrangement is such that the forward and reverse brakes can only be applied after the application of one of the gear ratio brakes. A valve 28 controls the rate at which the pressure rises in a selected brake cylinder. The transmission, which is described in Specification 891,041, is of the planetary type and a main clutch is dispensed with. Valves 18, 20 are manually operated and, as shown are in their neutral positions. The pump supplies liquid through a line 30, the pressure in which is determined by the valve 28 which is loaded by a spring 44 compressed by a piston 43 subject to pressure derived from the line 30 through a restricted orifice 32 and passages 38 in a valve 26, and through a restricted orifice 41 in a floating check valve spool 39. Valve 18 is moved successively to the right to open the speed ratio brakes to pressure, and a valve 22 is interconnected with the valve 18 and prevents flow of liquid from a line 33 to the valve 20 when the valve 18 is in its neutral position; and thus the forward and reverse brakes can only be applied after the selection of a gear ratio brake. If valves 18, 20 are actuated simultaneously the restricted orifice 32 maintains a pressure differential sufficient to ensure that the gear ratio brake is applied first. The rate of application of the brakes is controlled, since when valve 18 is operated to open a brake line to the line 30 the pressure in line 30 drops while the brake line is being filled and the valves 28, 26 move to the left. Piston 43 is moved to the right by the spring 44 and the expelled liquid moves the check valve 39 to the left, uncovering an exhaust line 40 to give rapid exhaust. When the brake line is filled valve 28 is opened by liquid entering a cavity in its spool through orifices 34, and the loading on the valve is gradually increased to increase the pressure in the brake cylinders, by pressure liquid admitted to the piston 43 through the restrictions 38, 41.