GB576420A - A new or improved control system for motor vehicles - Google Patents

Abstract

576,420. Hydraulic transmission of power. GLENNY, A. P. Aug. 19, 1943, No. 13516. [Classes 69 (ii) and 135] [Also in Group XXXI] In a control system for a motor vehicle propelled by an internal-combustion engine through a variable speed gearing comprising a variable stroke hydraulic pump arranged to be driven by the engine and a variable stroke hydraulic motor arranged to drive the road wheels, the stroke of the motor is controlled by automatic, hydraulic, pressure-regulating mechanism adapted to regulate the working hydraulic pressure irrespective of the speed and the stroke of the pump is regulated under the control of the accelerator so that the speed ratio of the transmission is automatically adjusted to maintain a predetermined relation between engine speed and throttle opening. As shown in Fig. 1, an internal-combustion engine 1 drives the road wheels 2 through a hydraulic transmission system comprising a multi-piston pump 3 and motor 4 controlled by levers 5, 6 which vary the piston stroke from zero to a maximum, the lever 5 in one direction and the lever 6 in one or other direction for forward or reverse drive from a neutral position in which the lever is held by springs 7. The lever 6 is operated automatically by a doubleacting hydraulic motor 8 connected through a driver-controlled valve 9, which is adjustable for either forward or reverse drive, and a pressure-regulating valve 10 to a pressure conduit 11 leading from the pump 3 to the motor 4, a return conduit 12 leading back from the motor to the pump. A.spring 14 urges the valve 10 to the position shown in which it shuts off supply from the conduit 11 and opens a port 15 communicating with the valve 9 so that fluid from the motor 4 flows through the port 15 to exhaust and thence to a reservoir which maintains the pump, motor 4 and conduits 11, 12 full of liquid. The lever 5 is operated by a servomotor 20 to which pressure fluid from an engine-driven pump 19 is delivered under the control of a valve 18 operated by a speed-regulator 16 constantly driven by the engine 1, the regulator in turn being controlled by a spring 17 adjustable by the accelerator 23 which is coupled to the engine throttle 24. Hence the speed to which the regulator is set depends on the degree of throttle opening. A clearance space 25 is provided for the accelerator to ensure that when the accelerator is depressed to take up the clearance, the engine speed will be above the minimum speed for which the regulator is set. In operation, when the engine is started with the vehicle at rest, both the pump 3 and motor 4 have zero piston stroke so that the engine and road wheels are free to turn idly. To run the engine at speed without moving the vehicle, the driver opens a release valve 22 so that the servomotor 20 cannot operate and torque is not transmitted to the road wheels. To start off, the driver closes the valve 22 and moves the valve 9 to the appropriate position for forward or reverse drive. Since the engine idling speed is insufficient to operate the speed regulator 16, the pump 3 remains ineffective until the accelerator is depressed when the increased engine speed causes the regulator to move the valve 18 into a position in which pressure fluid is delivered to the servomotor 20. This causes movement of the lever 5 to increase the stroke of the pump 3 and pressure is built up in the conduit 11 and transmitted to the valve 10 and motor 4, until, when a predetermined pressure is reached, the valve 10 is moved against the spring 14 to admit fluid through the port 15 to the servomotor 8 which operates the lever 6 to cause the motor 4 to drive the road wheels. When the pressure in the conduit 11 falls below the predetermined amount, the valve 10 uncovers the port 15 so that fluid escapes to exhaust from the servomotor 8 with the result that the springs 7 move the lever 6 to decrease the stroke of the motor 4 and thus to increase the working pressure in the conduit 11. In this way, the stroke of the motor is adjusted automatically to maintain a substantially constant working pressure in the hydraulic transmission system in spite of variations in the speeds and torques of the pump 3 and motor 4. In a modification, the regulator 16, control valve 18, servomotor 20 and associated parts are omitted and the accelerator is coupled directly to the control lever 5 so that the stroke of the pump 3 is determined directly by the degree of throttle opening.