GB829034A - Gear change preventing mechanism - Google Patents

Abstract

829,034. Change-speed control. ELECTROHYDRAULICS Ltd. Feb. 21, 1958 [March 1, 1957], No. 6971/57. Class 80 (2). A selector rod 2 is slidden left or right from the neutral position shown to establish the ratio in a change-speed gear driven through a hydrodynamic torque converter, establishment of the ratio not selected then being prevented so long as an engine-driven pump (not shown) is driven at a relatively high speed and supplies fluid under pressure through a port 6 to act on a piston 8 against the bias of a spring 14, the pressure of the fluid sliding the piston within its bore so that a locking plunger 11 is projected into the space between a collar 3 on the selector rod and two collars on either side thereof, axial movement of the selector rod thereby being limited. The gearing may be a forward and reverse hydraulically-controlled planetary gear in a fork-lift truck, the engine of which drives the pump supplying the fluid under pressure. The piston 8 has a port 9 in its crown through which the oil flows freely to a venting passage 7 whence it returns to the pressure-fluid circuit and the pump. The spring 14 engages a threaded plug 13 screwed in-and-out of its bore to adjust the compression of the spring to a value such that, with the engine idling, the piston 8 is held in the left-hand position shown, so that the plunger 11 moves to the position shown and the selector rod 2 can then be slidden from one ratio position to the other. The collar 3 on the selector rod 2 is of such axial thickness that, with the plunger 11 projecting into the bore containing the selector rod, an established ratio can be disengaged by movement of the selector rod but further movement of the selector rod to establish the other ratio is prohibited.