Control mechanism for hydrostatic transmission

Abstract

An HST control mechanism includes a rotary member, a servo unit, a telescopic member, and a biasing device. The rotary member for controlling a displacement of a hydrostatic transmission (HST) is pivoted outside of a casing incorporating the HST. The servo unit includes a telescopically movable actuator and a valve controlling the telescopic movement of the actuator. The actuator is interlockingly connected to the rotary member. The servo unit is pivotally supported on the casing via a first pivot. The servo unit rotates centered on the first pivot as the rotary member rotates according to the telescopic movement of the actuator hydraulically controlled by the valve. The telescopic member is pivotally supported on the casing via a second pivot. The telescopic member is provided with the biasing device that biases the telescopic member and the rotary member toward a position corresponding to a neutral state of the HST.

What is claimed is: 
     
         1 . A control mechanism for controlling a displacement of a hydrostatic transmission, comprising:
 a rotary member for controlling the displacement of the hydrostatic transmission, the rotary member being pivoted outside of a casing incorporating the hydrostatic transmission;   a servo unit including a telescopically movable actuator and a valve controlling the telescopic movement of the actuator, the actuator being interlockingly connected to the rotary member; and   a first pivot via which the servo unit is pivotally supported on the casing,   wherein the servo unit rotates centered on the first pivot as the rotary member rotates according to the telescopic movement of the actuator hydraulically controlled by the valve.   
     
     
         2 . The control mechanism according to  claim 1 , wherein the first pivot is located in the telescopic movement direction of the actuator so as to coincide to a position corresponding to a neutral state of the hydrostatic transmission. 
     
     
         3 . The control mechanism according to  claim 1 , further comprising:
 a telescopic member interlockingly connected to the rotary member; and   a second pivot via which the telescopic member is pivotally supported on the casing,   wherein the telescopic member is provided with a biasing device biasing the telescopic member and the rotary member toward a position corresponding to a neutral state of the hydrostatic transmission,   wherein the telescopic member moves telescopically and rotates centered on the second pivot as the rotary member rotates according to the telescopic movement of the actuator hydraulically controlled by the valve, and   wherein, when the hydrostatic transmission returns to the neutral state, due to the biasing force of the biasing device, the telescopic member moves telescopically and rotates centered on the second pivot so as to rotate the rotary member, whereby the servo unit rotates centered on the first pivot and the actuator returns to the position corresponding to the neutral state of the hydrostatic transmission.   
     
     
         4 . The control mechanism according to  claim 3 , wherein the rotary member further comprises:
 a first arm;   a second arm; and   a link connecting the first arm to the second arm,   wherein the first arm is pivoted on the casing via a trunnion shaft of a movable swash plate of the hydrostatic transmission,   wherein the second arm is pivoted on the casing via a pivotal shaft other than the trunnion shaft,   wherein the telescopic member is pivotally connected to the first arm, and   wherein the actuator is pivotally connected to the second arm.