Patent GB-1074968-A (GB)
Title: Improvements in vehicle power units comprising hydraulic variable-ratio transmissions
IPC: B60K17/10
Filed: 1964-08-04
Abstract: 1,074,968. Change-speed control. ROBERT BOSCH G.m-b-H. Aug. 4, 1964 [Aug. 3, 1963], No.31505/64. Heading F2D. An hydrostatic variable-ratio transmission for a motor vehicle comprises a variable-capacity and reversible swashplate pump-motor transmission 5, 6 interconnected by pipes feeding a pipe 61 through which fluid pressure is fed to a simple servo 19 energized to reduce the pump capacity, to a simple servo 62 energized to throttle-down a driving I.C. engine 1, and to a transmission ratio control valve 80 set by a hand lever 10 and an output speed actuated device 89, 94. The transmission ratio control valve 80 varies the pressure of fluid fed from the pipe 61 through a flow control valve 70 to a pipe 104, connected through a hand-actuated forward-reverse valve 109 to a pilot control servo 8 in turn controlling a follow-up servo 9, adjusting the swashplate angle and the capacity of the transmission motor 6. The follow-up servo 9 is itself energized from the transmission 5, 6 through the pipe 61. The transmission ratio control valve 80 is biased to close with increasing output speed, initially by an outputdriven pump 96 supplying fluid through a throttle 101 controlled by the hand lever 10 to a simple servo 94, and at high speeds by a centrifugal governor 89. The transmission-fed pipe 61 also supplies fluid under pressure to an hydraulic accumulator 67 and, through a valve 68, to an hydraulic servo 69 actuating an auxiliary mounted upon the vehicle. With the vehicle at rest but the engine 1 idling, and the speed control lever 10 in its neutral position, the ratio control valve 80 is open and only low pressure is fed to the pipe 104 &c. A valve 60<SP>1</SP> in the pipe circuit between the pump 5 and motor 6 is closed. The auxiliary servo 69 can thus be operated while the vehicle is at rest. Springs bias the pump 5 and motor 6 to their maximum capacity positions, as shown. To set the vehicle in motion, the valve 60<SP>1</SP> in the pumpmotor circuit is opened, e.g. by depression of the accelerator pedal or actuation of a separate lever. The pump 5 now supplies liquid to the motor 6, and the vehicle moves off slowly. By turning the lever 10 in the clockwise direction, the throttle valve 101 is moved in its closing direction. The pressure produced in the servo 94 by the output driven pump 96 is thus increased, and the servo acts to close the speed control valve 80. Pressure in the pipe 104 consequently increases, and acts in the pilot control servo 8 to move a double piston 40, 44 rightwards against the bias of a centralizing spring 54, thus sliding a valve stem 36 rightwards. The follow-up servo 9 is then energized, and tilts the swashplate of the motor 6 to a reduced capacity position, changing-up the transmission ratio. When high output speeds have been reached, the centrifugal governor 89 becomes operative further to increase the pressure in the pipe 104 &c. Ultimately, the swashplate of the pump 6 is turned until it is substantially perpendicular to the pump axis. The pump capacity is then nil, and the vehicle freewheels. If the vehicle runs downhill, the same sequence as above occurs, but increasing control pressure tilts the swashplate of the motor 6 beyond the perpendicular position, so that the motor acts as a pump, supplying the pump 5, which therefore motors and drives the engine 1. The servo 62 is energized to throttle-down the engine 1, and engine braking is obtained. As shown, the forward-reverse valve 109 is set to give forward travel of the vehicle. Hand actuation of the forward-reverse valve 109 to its other position changes the supply of fluid pressure to the pilot control servo 8 and causes its two pistons 40, 44 to slide relatively to each other, tilting the swashplate of the motor 6 in the opposite direction to that shown for reverse drive. The sequence of operations as the vehicle moves off is then as described above. As modifications, the centrifugal governor 89 may be dispensed with; the pump 96 may supply control pressure to the pipe 61, instead of the transmission pump 5; and a device for moving the valve stem 36 to its neutral position may be provided, so as to allow the vehicle to be pushed.