GB876440A - Improvements in or relating to hydrostatic transmissions - Google Patents

Abstract

876,440. Hydraulic transmission of power. INTERNATIONAL HARVESTER CO. April 21, 1960 [April 22, 1959], No. 14012/60. Class 69 (2). [Also in Group XXXI] An automatic hydrostatic transmission for a vehicle comprises a variable-displacement fluid motor 16 having a rotary output shaft 17 and a control means 19 to vary the fluid displacement thereof, and a source 12 of fluid under pressure connected to the motor and a servo-mechanism 18 connected by lost-motion means 27 to the control means to actuate the latter for increasing fluid displacement of the motor in response to increased fluid pressure resulting from increased resistance to fluid flow whereby the torque delivered to the shaft automatically governs the speed of the shaft. The source 12 consists of a constant displacement pump driven by a motor 10 and delivers fluid from a reservoir 14 to a line 13 connected to the motor 16 which may be of the axial piston type, the displacement of which can be varied by movement of a yoke 19. A line 13a connects the line 13 to the servomotor 18 which has a piston 22 connected by the lost-motion linkage 27 to the yoke. When the vehicle is running under light load, the yoke is urged by a spring to a position corresponding to minimum displacement. On shaft 17 encountering a load, such as a hill, the pressure rises in lines 13, 13a to move the piston 22 against a spring 24. Initial movement of the piston does not affect the motor but upon increased pressure, the lost motion is taken up and the yoke is moved to increase the fluid displacement of the motor and the torque applied to the shaft 17.