| 摘要 |
784,724. Controlling change-speed gearing. HOBBS TRANSMISSION, Ltd. April 16, 1956 [June 13, 1955], No. 16943/55. Class 80 (2). In a change-speed gear where changes of ratio are made by engagement of hydraulic friction clutches or brakes and in which the pressure in the system is varied in accordance with the position of the throttle, the pressure relief valve comprises a piston urged against the pressure by three springs to give three rates of increase of pressure corresponding to different positions of the throttle control. The relief valve 17 has two diameters sliding in two bores 14, 15 of a chamber having a third bore 16, the chamber being in communication at each end 12, 13 with a channel 11 connected to an oil pump circuit. An exhaust duct 44 communicates with the chamber 14. The valve 17 seats on a ring 20 under pressure from a first spring 21 seating on a plunger 22 carried by a rod 23 actuated by an accelerator pedal 29. Under idling conditions, the valve is loaded only by the spring 21 and by differential pressure fed from the channel 11 through a shut-off valve 51 to the smaller diameter of the valve 17. A small opening of the throttle brings an abutment 38 on the rod 23 into contact with a ring 32 to compress a second spring 30 to cause an increase in the hydraulic pressure. Further movement causes spring 30 to be loaded to the initial loading of a third spring 42 between the abutment 38 and an abutment 39 on the rod 23, and the pressure is then controlled by the three springs. The spring loading is relieved from the accelerator by pressure in the chamber 13, and for at least top gear ratio the valve 51 is closed to reduce the fluid pressure in the system in the lower torque ratios. |
