GB1142531A - Improvements in or relating to motor vehicles, particularly tractors - Google Patents

Abstract

1,142,531. Change-speed control. BOFORS A.B. 7 April, 1966 [26 April, 1965], No. 15800/66. Heading F2D. A hydromechanical change-speed system for a crawler tractor transmission comprises a rotary-sliding manual control member 23, 25, the rotary movement of which operates, through bevel gearing 26, 27, a rotary ratio selector valve 29 and the sliding movement establishes the drive through the main clutch 46. Mechanical transmission.-The arrangement shown comprises a disc clutch 46 with locking brake 50 arranged between the engine and a six-speed gear train 47. The latter comprises forward and reverse control clutches 62 operated by a double-acting hydraulic piston actuator 57, and ratio clutches 73, 81, 113 operated by actuators 71, 78, 107 respectively. Hydraulic control system.-Pressure liquid is supplied by an engine-driven pump 11 connected by lines 12, 13 to the main control valve 14, the latter comprising drive clutch and ratio clutch control valves 31, 32 connected to the shaft 25 of the gear change member. Valve 31 consists of opposed spring-loaded members 37, 38 controlling the pressure supply to the drive clutch line 45, while valve 32 controls supply lines 56, 119 to the forward and reverse actuator 57 and a line 65 connected to the rotary selector valve 29, Fig. 5 (not shown). The latter communicates with the ratio actuators 71, 78, 107 by lines 69, 117, 77, 112, 115. Valve 14 also includes a spring-loaded pressure regulating valve 16 and blocking valves 75, 85 which normally prevent release of a ball detent 88 limiting axial movement of valve 31. In addition valve 32 is acted upon by a retarding dashpot latch 94 to delay the initial movement of the valve and commencement of gear shift. Operation.-In neutral the clutch 46 is non- pressurized and held locked by brake 50, while valves 31, 32 are engaged by detent 88 and retarding latch 94. To engage gear, control member 23 is first rotated to the desired setting so that valve 29 makes communication with the required ratio actuator 71, 78 or 107, and is then moved axially in the forward or reverse direction to the limited extent allowed by detent 88. Liquid from the valve pressure chamber 33 then passes via valve 37 or 38 to line 45 and main clutch 46 which is permitted to slip due to release of brake 50. At the same time pressure in lines 56, 119 conditions the forward and reverse actuator 57, and in line 65 causes engagement of the appropriate ratio clutch. Pressure build-up then operates valves 75, 85 to release detent 88 so that valve 31 may be moved to the fully open position and thus allow maximum pressure to be supplied to clutch 46 to establish the drive. Member 23 may be moved to a setting in which the rotary valve 29 is connected to exhaust and the blocking valves 75, 78 are by-passed to allow full control pressure to be applied to the main clutch 46.