GB876140A - Improvements in or relating to hydrostatic transmission systems - Google Patents

Abstract

876,140. Hydraulic transmission of power. INTERNATIONAL HARVESTER CO. April 21, 1960 [April 22, 1959], No. 14013/60. Class 69 (2). [Also in Group XXXI] In an hydrostatic transmission system comprising two fluid motors operated from a common pressure fluid source an automatic means is provided for controlling the relative speeds of the motors comprising a flow divider having a pressure fluid inlet, two ports communicating with the respective motors and a valve member movable against resilient means in response to a pressure differential between the two ports whereby the relative flow distribution is altered to maintain the fluid motors with a selected speed ratio by increasing the flow to the higher pressure port and vice versa. In the construction shown an engine 10 drives a pump 12 supplying fluid to motors 31, 31<SP>1</SP> through a flow divider 16. Servomotors 34, 341 responsive to the motor supply pressures operate to increase the output torque of the motors when the pressure rises by pivoting the motors 31, 31<SP>1</SP> within the casings 25, 25<SP>1</SP> to increase the motor piston displacements. Normally the valve member 58 (Figs. 1 and 5) is held in a central position in the flow divider 16 by a pair of springs 55, 57 in chambers 63, 64 which communicate through ports 61, 62 and pipes 24a, 24a<SP>1</SP> with the pipes 24, 241 from the flow divider outlets 17, 18 to the motors. Should wheel 30 skid or slip the pressure will drop in the motor 31, pipe 24 and chamber 61, allowing the valve member 58 to rise, Fig. 1, decreasing the area of port 17 and increasing the area of port 18 and thus decreasing the relative flow to wheel 30. Meanwhile the reduced pressure on the servomotor 34 causes it to reduce the piston displacement of the motor and hence its. torque output. Simultaneously the pressure rises in line 24<SP>1</SP> as the load on the motor 31<SP>1</SP> increases operating servomotor 34<SP>1</SP> to increase the piston displacement and torque output of the motor 31<SP>1</SP>. The valve member and servomotors are so chosen that as the displacement and fluid flow of the motors alters the speeds remain sensibly equal. Fig. 2 shows an alternative form of valve member 44 movable in response to pressure differential between its end faces. There is provided a connection with the steering means 19, 20, 20a whereby the outer wheel on a curve will travel faster than the inner wheel comprising a threaded bracket 22 and frame 23 which move the spring seatings longitudinally to displace the valve member from its central position. The flow divider may also be applied to vehicles with constant displacement motors.