Patent GB-955604-A (GB)
Title: Improvements in and relating to hydraulic drives for vehicles
IPC: B60K6/12
Filed: 1960-09-21
Abstract: 955,604. Hydraulic transmissions. R. C. PEARSON. Aug. 21, 1961 [Sept. 21, 1960; Oct. 24, 1960], Nos. 23503/60 and 36422/60. Heading F2C. A vehicle transmission system in which an internal combustion engine drives an hydraulic pump which drives an hydraulic motor for driving the vehicle wheels is provided with an hydraulic accumulator from which the hydraulic motor is supplied when its demands exceed the pump output and to which fluid is supplied by the motor when acting as a pump, e.g. during vehicle retardation, and means whereby an abundance of energy in the accumulator automatically reduces the pump output. As shown in the drawing accompanying Provisional Specification 32503/60, the internal combustion engine 1 of the vehicle drives an adjustable fixed displacement swash plate pump 2 and a booster pump 11 connected by lines 4 and 12 respectively to the reservoir 3 in which the hydraulic fluid is stored under pressure admitted through a charging point 42. The output from pump 2 is directed through line 5 to a valve 6 and from thence to either the hydraulic accumulator 8 through a check valve 7 or to the reservoir 3. The vehicle wheels 41 are driven by a variable displacement swash plate motor 38 through a propeller shaft 39 and differential 40, the motor being supplied with fluid from the accumulator 8 through a line 31 and discharging to the reservoir 3 through a line 55, the angularity of the swash plate being controlled through a follow up servomechanism by a single hand lever or a pair of pedals 35 and 36 centred by springs 37 and so connected that one pedal controls the motor for forward movement and the other for reverse movement. For braking in the one direction, the pedal movement in the opposite direction is applied, and in the period during which the torque exerted by the wheels exceeds the output torque of the motor, the motor acts as a pump supplying liquid from the reservoir to the accumulator. The output from the booster pump 11 is taken through a line 13 to a direction control valve 23 and thence to line 132 or 44 leading to opposite sides of a piston 25 in valve 6. The hydraulic accumulator 8 is maintained under pressure by a piston 14 subjected to the pressure of air from a charging valve 17 and bottle 16. As the piston 14 rises or falls due to the level of liquid in the accumulator, it will move a control switch 21 in one direction or the other whereby the direction of the electric current in a circuit containing a solenoid 22 is determined, the solenoid governing the position of the valve 23 and so the direction of the output of pump 11 to either of lines 132 or 44, the other being connected to the reservoir 3. The line 132 is connected by a line 133 provided with a flow restrictor 29, in series with a non-return valve allowing unrestricted fluid return, to one side of a piston 27 connected to the engine speed governor 28. A line 44<SP>1</SP> connects the other side of the piston 27 with line 44 which is connected to the valve 6 through a flow restrictor 50 in parallel with a non-return valve 51 allowing free flow of return fluid, the arrangement being such that when the piston 14 is raised, the piston 27 is depressed whereby the engine power is reduced, the flow restrictors preventing engine stalling and ensuring that the engine revolutions are sufficiently raised before the pump 2 is working. Adjustable stops 53 and 54 are provided to limit the engine range and an over-riding switch may be actuated by the piston 14 in its limit position whereby the engine is operated at maximum power. Pressure relief valves 9, 10 and 24 are provided. In the modification illustrated with reference to the drawing accompanying Provisional Specification 36422/ 60, the engine 1 drives pumps 4 and 11, the output of pump 4 being in parallel with the hydraulic driving motor 8 and the hydraulic accumulator 9. The pump 11 supplies the controlling servomotors, one servomotor 40 controlled by pedals 41 and 42 being provided to determine the output and direction of motor 8. A piston 19 subjected to the output pressure of pump 4 and the pressure of a spring 20 is connected to a cam 24 which operates, through a follower 25 and link 27, a servomotor 28 controlling the output of the pump 4. The piston 19 is also connected to a cam 30 which controls a servomotor 32 operating the speed control 33 of the engine, and which may be stepped so as to give three engine speeds. A check valve 46 is provided to reduce drag losses at idling speeds.