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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority to Japanese Patent Applications No. 2014-161495, filed on Aug. 7, 2014, and No. 2014-162729, filed on Aug. 8, 2014.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a control mechanism for controlling the output rotary speed and direction of a hydrostatic transmission (hereinafter, “HST”). Especially, the control mechanism is a servomechanism including a servo unit that combines a telescopic (linearly movable) actuator and a valve.[0004]2. Related Art[0005]As disclosed by JP 2002-250437 A (hereinafter, “D1”), JP H06-100278 B (hereinafter, “D2”), and JP 2013-096449 A (hereinafter, “D3”), an HST used as a transmission for a tractor is usually disposed in a casing that also serves as a vehicle body frame (chassis) of the tractor. Also, as disclosed by D1, D2 and D3, it is well-known that a piston in a hydraulic cylinder serves as the actuator for controlli...

AI Technical Summary

Benefits of technology

The invention provides a simple configuration for accurately and stably interlocking connection between a telescopic movement of an actuator and a rotational movement of a trunnion shaft of a movable swash plate of an HST control mechanism, even if the servo unit is separated from the HST. Minimization of the servo unit and facilitation of attachment and detachment of the servo unit are also included in the object of the invention. The rotation of the servo unit ensures that the telescopic linear movement of the actuator is converted to rotational movement without twisting stress. The weight balance of the servo unit is improved, reducing the rotation required, and there is no need for a biasing device, which improves minimization and reduces costs. The existing telescopic member for rotating the trunnion shaft can be used, with only an additional first arm. The invention provides a simplified solution for interlocking the HST control mechanism.

Problems solved by technology

However, in the case of D1, the part of the vehicle pivotally supporting the cylinder bottom is weighed on or loaded eccentrically because it cantilevers the cylinder, so that it is liable to a twisting stress due to the rotation of the cylinder.

As a result, the cost of the configuration of D2 becomes great.

However, the actuator needs a biasing means that biases the actuator to a position corresponding to a neutral position of the movable swash plate, i.e., a neutral position of the HST.

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