GB861687A - Hydraulic shifting device of clutch-operated change-speed and reversing transmissions more particularly for tractors - Google Patents

Abstract

861,687. Change-speed and reverse control; gearing for stopping and starting machinery. KLANE, H. July 21, 1959, No. 25025/59. Class 80 (2). In a caterpillar tractor, a change-speed gear comprising ratio establishing clutches 22 ... 25 in series with a reverse gear consisting of forward and reverse clutches 37, 36 has engagement of one or other of the ratio establishing clutches 22 ... 25 effected by movement of a handoperated control-lever 7 along the central slot 8<SP>1</SP> of a multi-slot gate to act through a lever 18 conditioning a valve 13 1 which admits the full pressure of an oil pump 31 thereto, cushioned engagement of either the forward or the reverse drive clutch 37, 36 then being obtained by movement of the lever 7 up or down into the adjacent slot 8 of the gate to act through a lever 18<SP>1</SP> and open one or other of two valves 13 2 , 133 to supply oil under pressure through pipes 45, the valves 13 2 , 13 3 being so constructed that the rate of engagement of the forward or reverse clutch is proportional to the speed with which the control lever 7 is pushed into the gate slot. The two valves 13 2 , 13 3 are similar, each comprising an inlet port 49 to which oil is supplied from the pump 31 through a pipe 12 2 , a valve piston 42 floating under the opposed biases of a spring 41 to one side and a spring 44 plus the pressure of the oil in the associated forward-reverse clutch 37, 36 on the other side. When, e.g., the control-valve 13 2 is moved to the ratio established position, the associated spring 41 is compressed and forces the floating valve piston 42 leftwards of Fig. 2 so that a port 47 therein comes adjacent to the inlet port 49. Oil under pressure is admitted therethrough to a central bore 48 in the valve piston whence it passes to the space containing the spring 44 and, through the pipe 45, to the reverse clutch 36. As pressure in the servo device engaging the clutch 36 increases, the pressure in the space containing the spring 44 correspondingly increases, so that the floating valve piston 42 is biased rightwards against the compressed spring 41. Accordingly the port 47 is moved relatively to the inlet port 49 to tend to prevent the ingress of oil, and a cushioned engagement is effected, the floating valve piston 42 reciprocating about a mean position. On movement of the hand lever 7 into the central slot 8<SP>1</SP> of the gate, the force of the spring 41 is reduced, so that the spring 44, together with the pressure of the oil, is able to move the valve piston 42 rightwards, and position an exhaust port 46 in the valve piston adjacent the end of a pipe 50 leading back to a sump 30, so that the pressure engaging the clutch 36 is relieved. The forward drive clutch 37 is similarly controlled by the valve 13 3 , The valve 13 1 , controlling the ratio-establishing clutches 22 ... 25, is fed with oil from the pump 31 through a pipe 12 1 , and comprises a piston 17 having an inlet duct 19 connected through a bore 20 with a control orifice 21, which, on actuation of the lever 18, is positioned adjacent ports leading through pipes 32 ... 35 to the ratio-establishing clutches. In a preferred construction, the lever 18 has a segment-shaped end, Fig. 4 (not shown), engaging with the end of the valve piston 17, which is retained in a desired position by a spring-biased ball detent, Fig. 3 (also not shown), and the lever has ball-and-socket mounting in its supporting casing so that it may be turned to operate through two levers upon the valves 13 2 , 13 3 , which are mounted upon the control lever casing.