Patent GB-570589-A (GB)
Title: Improvements in or relating to hydro-mechanical power transmission drives
IPC: F16H47/04
Filed: 1943-06-19
Abstract: 570,589. Variable-speed gearing. VINTER, R. A., and CULL, W. June 19, 1943, No. 9896. [Class 80 . (ii)] [Also in Group XXIX] A hydromechanical variable-speed transmission comprises a hydraulic unit, of variable capacity and capable of acting as a pump or motor, in driving connection with the input gear of an epicyclic train and in hydraulic connection with a second hydraulic unit connected to the reaction gear of the epicyclic train, the parts being arranged to operate so that the torque at the input gear of the train is the algebraic sum of the engine torque and the hydraulic torque furnished by the reaction between the two hydraulic units. As shown, an input shaft 2 is fixed to the toothed annulus 3, the driven shaft 6 to the planet cage 5 and a hollow shaft 8 has a sun gear 7 fixed thereto. Cylinder blocks 47, 43, of hydraulic units 11, 9, are fixed to the shafts 2, 8, respectively, the pistons 13 of unit 11 co-operating with an adjustable non-rotatable swash-plate 12, and the pistons 42 of unit 9 co-operating with a fixed swash-plate 41. The units 9, 11, are connected by piping 10a, 10b, including valves 15, 17. Free flow between the pipes 10a, 10b, through valve 15 is prevented upon-actuation of a lever 16, whereas if the pressure in one of the pipes exceeds a predetermined amount the valve 17 opens to permit flow to the other pipe. An engine driven oil pump 32 supplies oil to the pipes 10a, 10b, to make up losses, and supplies oil through a valve 30 and pipes 30a to a valve and servomotor unit C which controls the angular position of the swash plate 12. The valve 30 is controlled by a governor driven by the output shaft 6 so that the pressure in the pipes 30a is proportional to the speed of the shaft 6. The unit C includes a differential piston comprising a fixed piston 51 telescoping a movable piston 52 and being subjected to the pressure in the piping 30a and to the pressure in the pipe 10a via a pipe 18. The piston 52 is connected to an arm 55 on a valveplug 56, Fig. 4, mounted in one of the gudgeons of the swash-plate 12. Springs 66, 67 urge the arm to a central position. Radial ducts in the valve plug 56 co-operate with ports 59, 60 in the gudgeon, which ports 59, 60 are connected by ducts 68, 69 to opposite sides of a servomotor piston 71 connected by an arm 73 to the other gudgeon of the swash-plate. Springs 74 tend to centralise the piston 71 so that when the apparatus is inactive the capacity of the hydraulic unit 11 is zero. In operation,'when the driven vehicle is at rest and the engine is idling, the sun gear 7 and shaft 8 are driven backwardly to cause the hydraulic unit 9 to circulate oil idly through the pipes 10a, 10b, the valve 15 being open. Upon closure of the valve 15 by the lever 16 and speeding up of the engine, pressure is generated in the pipe 10a so that the reaction torque of the sun gear 7 is increased and the shaft 6 is driven forwardly. The apparatus is then controlled automatically by change in the angle of the swash-plate 12 through the control unit C. For a reverse drive any ordinary reverse gear, such as shown at 76, 78, may be used. Alternatively, the action of the hydraulic units 9, 11 may be reversed by use of a cross-flow valve across the pipes 10a, 10b so that the sun gear is driven at a high speed in its idling direction to cause the planet carrier to rotate in the opposite direction to the driving shaft 2. In a modification, the movement of the swash-plate 12 is also controlled by an engine-driven governor.