Dual Hydrostatic Transmission System with Power-Proportioning Control

1,177,904. Hydrostatic transmission. GENERAL SIGNAL CORP. 27 June, 1968 [15 Nov., 1967], No. 30697/68. Heading F2D. A drive from two engines 11, lid, e.g. in a dual-engine scraper, to a common load 12, includes two hydrostatic transmissions 13, 13d, each including a variable displacement pump 14, (14a), and a motor 15, (15a), in closed circuit, the pump 14 being adjusted manually, and the pump 14a being adjusted automatically by a valve 33 responsive to main line pressures in the two closed circuits to maintain these pressures in a predetermined ratio, e.g. equal, to ensure a fixed ratio between the power delivery from each motor 15, 15a. As shown, the motors share the load equally, and the pumps are reversible. On increasing the displacement of pump 14, pressure in the main line, e.g. 16, increases and acts on a valve 23 in a pressure relief circuit 22 to connect the line 16 to an hydraulic actuator 36 acting on one end of a valve 33 which, directs pressure fluid from an engine-driven make-up pump 21a to one-side or the other of a piston 29 to increase the disi. placement of pump 18a.. Subsequent increased pressure in line 16a acts on. the end of. a valve 23a in pressure relief circuit 22a and is conneeted through that valveto an hydraulic actuator 37 acting on the end of valve 33. When the pressures in lines 16, 16a are substantially equal, the valve 33 is centralized, and the pump 14a is locked in its new position. On reversing pump 14, pressure in line 17 acts on actuator 36, and on the end of a reversing valve 38 for the pump 14a. By making the effective areas of actuators 36, 37, unequal, and/or by making the motors 15, 15a of different displacements, the ratio of share loading may be of any desired value. Again, Fig. 1 (not shown), pump 14a is not reversible, and pump 14 acts alone in reverse. Lines 16, 16a are connected directly to actuators 36, 37 respectively, and the reversing valve 38 is omitted. A by-pass valve (27) is inserted between lines 16a, 17a, and is opened whenever line 17 is pressurized, i.e. whenever pump 14 is reversed.