GB1205950A - Hydrostatic transmission dual pressure charge-servo system - Google Patents

Abstract

1,205,950. Hydrostatic transmissions. INTERNATIONAL HARVESTER CO. 10 Oct., 1967, No. 46168/67. Headings F2C and F2D. In a hydrostatic transmission having a variable displacement swash-plate pump connected in closed circuit with a variable displacement swash-plate motor, and hydraulic servomechanisms selectively controlling the pump and motor swash-plate inclinations, an engine driven auxiliary pump 14 having low and high pressure outlets 15, 20 respectively supplies make-up fluid to the power circuit from the outlet 15 at a pressure limited by a relief valve 17 and fluid to the servo-mechanisms from the outlet 20 at a higher pressure limited by a relief valve 22. Make up fluid from the outlet 15 reaches pump and motor kidney-shaped ports 49, 49a, 50, 50a (Fig. 2) via lines 18, 44, 44a and check valves 45, 45a. Cross-connected relief valves 47, 47a relieve overload pressures in the power circuit. Heated fluid from the low pressure side of the power circuit passes via a line 51 or 51a and a spring-centred shuttle valve 52, lines 32, 33, and a relief valve 34 to a cooler 36 and thence via a by-pass control valve 38 and a line 41 to lubrication sprays 42 for the pump and motor or to a relief valve 43 discharging to a sump 10. The three position by-pass valve 38 (Fig. 5, not shown) has a combined valve sleeve and piston (77) moved against a spring (78) by pressure in a by-pass line 37. At low inlet pressures, the by-pass line is closed and all the flow from relief valve 34 passes to the cooler. At a higher pressure, the cooler by-pass line 37 is also opened to the line 41. At a still higher pressure, by-pass line 37 and the cooler outlet are both connected to line 41 and to a drain line 40. The relief valve 22 discharges to a lubricant spray 28 for the pump and motor and to the sump (Fig. 1) or to the low pressure line 16 (Fig. 3, not shown). The servo-fluid supply from outlet 20 passes to the hollow anchor pin 57 of the servo-mechanisms, and enters cylinders 61, 61a through orifices 60b, 60c. Cam-controlled outlets 62, 62a from the cylinders regulate the discharge therefrom and hence the setting of the piston-cylinder combinations to control the pump and motor swash-plate settings.