GB854219A - Improvements in or relating to hydraulic power transmission systems with a variable displacement pump and motor - Google Patents

Abstract

854,219. Fluid-pressure servomotor-control systems ; hydraulic control systems. GESELLSCHAFT DER L. VON ROLL'SCHEN EISENWERKE A.G. Nov. 19, 1956 [Nov. 19, 1955], No. 35374/56. Classes 69 (2) and 135. A diesel engine 1, Fig. 5, drives the axle 9 of a vehicle via reduction gearing 7, 8 and an hydraulic transmission comprising a variable displacement vane, radial or rotary-cylinder pump and motor 4 and 5, respectively ; the fuel supplied to the engine is controlled by a regulator 73. The engine may consist of any type of thermal engine or an electric motor. Forward control.-Forward movement of the vehicle is obtained by axially pulling a control wheel 41 in the forward direction, the wheel having been previously set in the B position, so that a sleeve 43 engages a wheel 45 ; the control wheel 41 is then rotated clockwise to a position +#B, thereby turning a cam plate 35 until it covers another identical cam plate 34 so freeing a crank-pin 25 for movement in the arcuate slots in the cam plates. The position of crankpin 25 is determined by a power governor 10 comprising a piston 17 connected to the pressure line 20 of the hydraulic transmission via a line 18 and a rotary valve 19 ; the rod 22 of piston 17 extends through a spring housing 23 and is pivotally connected to a rod 24 supporting the crank-pin 25. The housing 23 contains a spring 26 having a hyperbolic compression characteristic which at one end bears on a disc attached to the rod 22 and at the other end abuts a piston 28 slidable in the housing 23, the underside of the piston 28 being open to line 18 through a restriction 31. The crank-pin 25 is connected by a cable 16 to a pilot valve 13 having a moving seat follow-up with a piston 14, also supplied with fluid from line 18, that controls the displacement of the pump 4 in the range +#1. A wheel 52 is turned concomitantly with control wheel 41 in the direction of the arrow V so setting the valve 19 to connect lines 18, 56 to the line 20, the line 56 leading to a pressure regulator 11 comprising a cylinder 57, the piston 58 in which sets the displacement of the motor 5 ; the opposite end of the cylinder 57 is also connected to line 56 via a restriction 60. When the control wheel 41 reaches position - #B it is pushed axially into the central position so disengaging the sleeve 43. Reverse control.-The control wheel 41 is pushed axially from the central position to engage sleeve 43 with a wheel 44, the wheel 41 then being turned anticlockwise to the position - #B in order to obtain reverse movement of the vehicle, the sequence of events being as described above but in the opposite direction with cam 34 moving over cam 35 and lines 18 and 56 being connected by valve 19 with a line 55 which now carries pressure fluid between the pump 4 and motor 5. Constant torque control.-Rotation of the control wheel 41 beyond either position + or - #B towards # max. regulates the engine speed and the speed at which the transmission functions through a shaft 64 driven from the wheel 41 on which shaft are cams 65a, 65b, 66 and 67 ; cams 65a, 65b control brake valves 69, 70 in lines 20, 55 respectively, cam 66 is connected to a bridge valve 71 between lines 20, 55 and cam 67 controls the fuel regulator 73. When the control wheel 41 is in the position -j- or - #B the valves 69, 70 are closed, the valve 71 is open and the regulator 73 is set for engine idling, hence the motor 5 is at a standstill. With the control wheel 41 in either position + or - #0, the valves 69, 70, 71 are open, the engine continues to idle and the motor remains stationary. With the wheel 41 in either position + or - #1 the valve 71 closes so that the motor 5 begins to operate and the engine speeds up. As the wheel 41 reaches the # max. position the engine 1 and hence pump 4 attains normal speed. The output speed of the transmission is controlled for primary regulation by adjusting the pump displacement from zero to a maximum whilst the motor 5 is in the position of maximum displacement; secondary regulation is effected when the pump is at maximum displacement and the motor displacement is reduced. During engine run-up the transmission hydraulic pressure is first held constant by the governor 10 and in a higher speed range by the regulator 11. The governor 10 provides a constant output torque. Variable torque operation.-The governor 10a, Fig. 8, is provided with a spring 76 the bias of which is varied by rotating and axially displaaing a conical member 77 ; rotation is effected by link 79 and axial displacement is effected by a further cam on the shaft 64, Fig. 5. The spring 76 acts upon a valve 75 which determines whether one side of a piston F1 is open to pressure or exhaust, the other side of the piston being permanently open to pressure ; the piston varies the displacement of the pump 4 and operates the link 79. The member 97 (not shown) and link 79 may be dispensed with.