Patent GB-639578-A (GB)
Title: Improvements in or relating to a drive for transmitting motion from an engine to a shaft, such as that of an automotive vehicle
IPC: F16H47/02
Filed: 1947-07-16
Abstract: 639,578. Hydraulic transmission of power; fluid-pressure control-systems. OIL GEAR CO. July 16, 1947, No. 18958. Convention date, Nov. 18, 1940. [Classes 69 (ii) and 135] [Also, in Groups XXIV, XXVI and XXVIII] In a drive for transmitting motion from an engine, not shown, to a shaft 2, including a mechanical transmission, such as a clutch 3, and shafts 51, 52 and 53, having one part connected to the shaft 2, a hydraulic transmission including a pump 4 driven by the engine and a motor 5 energized by the pump for driving the shaft 2, means, such as piston motor 31 and valve 42, for varying the displacement of the motor 5 between a predetermined minimum and a predetermined maximum in accordance with the torque on the motor 5, means, for example a piston motor 138 and a solenoid-actuated valve 140, for adjusting the mechanical transmission to connect or disconnect the two parts thereof and thereby render the mechanical transmission effective or ineffective to drive shaft 2, and other means, such as torque coupling 50 and switch 64 independent of the displacement varying means for rendering the hydraulic transmission effective or ineffective to drive shaft 2, there are provided means, such as switch 65 for effecting substantially simultaneous operation of the adjusting means 138 and 140 and the other means 50 and 64 to thereby render one transmission effective and the other transmission ineffective to drive shaft 2. Torque coupling.-The engine-driven shaft 1 is connected to shaft 51 through the torque coupling 50 which provides firstly a solid drive and then a spring drive as a predetermined value of torque is exceeded. Operation of switches 64 and 65 is provided for as the spring drive becomes effective. Control of motor displacement; fluid-pressure control-systems.-The displacement of the motor 5 is varied by the motor 31 supplied with liquid through check valves from either pump conduits 11a, or 12, depending upon the direction of discharge of the pump 4, under the control of valve 42. The piston-rod of motor 31 is also arranged to operate a switch 159. In order that the clutch 3 may be engaged without shock the displacement of pump 4 is adapted to be adjusted by means of a control mechanism so that the speed of the motor 5 is related to that of the pump in order to synchronize shafts 52 and 53. The clutch 3 is operated through a lever by the piston motor 138 which is supplied with liquid from a gear pump 76 under the control of the solenoid valve 140. The control mechanism includes a pilot valve 67, which directs the liquid flow to and from a cylinder 28, a differential unit 68 (see Group XXVI) which has a shaft 99 driven from a friction-disc transmission 69 at a speed in proportion to that of the pump 4 and a casing driven at a speed proportional to the speed of the motor 5 so that a shaft 101 rotates when the speed of the motor 4 and pump 5 depart from a preset ratio. The two end ports of the pilot valve 67 are connected to the control cylinder 28 whilst the centre port is supplied with liquid under constant pressure from the gear pump 76 through a throttle valve 79. The pilot-valve member 73 has its stem connected to one end of a floating lever 81 which is connected intermediate its ends by a link 82 and a crank 83 to the shaft 101 of the differential unit 68, whilst the other end of the lever 81 is connected to a follow-up nechanism which is operated to close the pilot valve 67 when the adjustment of the displacement of the pump 4 has corrected the departure from the preset speed ratio of motor 5 and pump 4. The control cylinder 28 adjusts the displacement and direction of discharge of the pump 4 by means of its piston 27 operating a rack and cam mechanism (see Group XXVIII). The friction disc transmission for the differential unit 68 comprises a driven disc 102 fixed upon the shaft 99, a driving disc 103 fixed upon a shaft 104 driven from the shaft 52 at a speed proportional thereto and a transfer disc 106 for transmitting motion from discs 103 to 102. The transfer disc 106, which will not drive the disc 102 when it engages the centre of disc 103, is capable of limited sliding-motion between the discs 102, 103. Operation (hydraulic drive).-When the vehicle engine is started the pump 4 and gear pump 76, which latter may supercharge the pump 4, are driven, and draw liquid from a reservoir 77. The pump 4 will discharge through a byepass valve 6 and pump 76 will maintain a constant pressure in a conduit 78, the surplus liquid from the latter being discharged through a relief valve 80. The first part of the movement of a lever 119, which is depressed to cause forward movement of the vehicle, rocks a cam lever 112 through a small angle as well as moving a fuelcontrol rod 123 a short distance to increase the fuel to the engine. Movement of cam lever 112 moves the transfer disc 106 a short distance below the centre of the disc 103 and closes a switch 115 to position the byepass valve 6 so that the pump 4 supplies the motor 5. Since shafts 52 and disc 103 are rotating and propeller shaft 2 is stationary the downward movement of the transfer disc 106 will cause rotation of disc 102 and therefore rotation of shaft 101 which in turn will actuate pilot valve 67 and piston 27 to condition the transmission pump 4 to discharge into conduit 11a and thereby cause the motor 5 to rotate shaft 2. If the torque is insufficient to start the vehicle when the displacement of the motor 5 is a minimum, the pressure of pump 4 rises and piston motor 31 brings about an increase in the motor displacement, the surplus liquid being exhausted through a high-pressure relief valve 44. The rate of vehicle acceleration is now determined by the throttle valve 79 which limits the rate at which the displacement is increased by controlling the flow of liquid to the cylinder 28. As the torque required to enable the spring drive of the torque coupling to become effective is less than the torque the motor 5 is able to exert when its displacement is a minimum, the switch 64 is closed before this increase in displacement takes place. At this time the circuit over the switch 64 is broken by another switch 132, operable by cam-rod 112, so that the increase in displacement continues until the piston motor 31 opens the switch 159 and prevents engagement of the clutch 3 until the motor displacement is again reduced to a minimum. Operation (mechanical drive).-Continuous movement of the lever 119 increases the amount of fuel delivered to the engine and moves the transfer disc 106 to the limit of its downward movement and permits the lever 119 to further increase the supply of engine-fuel. The cam rod 112 now closes switch 132. As the vehicle moves the drop in liquid pressure permits the piston motor 31 to reduce the motor displacement and so increase the speed of the propeller shaft 2. When the displacement of motor 5 is a minimum, switch 159 is closed to actuate the solenoid valve 140 and hence the piston motor 138, so engaging the clutch 3 and opening a switch 149 to operate the byepass valve 6, whereupon the vehicle is driven solely through the mechanical transmission and its speed is controlled entirely by the lever 119 varying the fuel to the engine. Operation (reintroduction of hydraulic drive).- If nearly maximum torque is required, the spring of the torque coupling yields further and causes operation of the switch 65 to energize the solenoid byepass valve 6 and the vehicle is then driven through the hydraulic transmission. At the same time the solenoid valve 140 is de-energized so that the piston motor 138 is connected to the reservoir 77 and the clutch 3 is disengaged. To reverse the vehicle a lever 120 is depressed to bring about a similar chain of events to those described above. In a modification, the differential unit is dispensed with and an over-running clutch is provided in the shaft between the main pump and the clutch since the pump and motor shafts may now have a different speed at the instant when the mechanical transmission is made effective. The transmission pump is of the unidirectional variable-displacement type and a hand-operated valve enables the motor to be reversed. The gear pump is provided with a solenoid-operated byepass-valve and the displacement of the main pump is effected by means of a rod and spring connection. The vehicle can only be operated in reverse through the hydraulic transmission.