Patent GB-845684-A (GB)
Title: Device for and method of changing speed in gear-boxes
Filed: 1958-05-16
Abstract: 845,684. Change-speed control. ZENS, P. M. F., and HONNORE, M. A. J. May 16, 1958 [May 21, 1957], No. 15827/58. Class 80 (2). The lubricating pump of a change-speed gear in conjunction with a pressuresensitive device controls the locking gear for the gearengaging mechanism such that gear disengagement is only permitted when the oil pressure falls below a predetermined value. A changespeed gear providing eight speeds between an input shaft 3 and an output shaft 6 comprises two countershafts 4, 5 having gears 7, 8 and 17, fixed thereon and gears 9, 10 and 13, 14, 19 free thereon respectively, engaged as necessary by dog clutches 11, 15, 22, 23. The shaft 3 is driven from an engine through a friction clutch-brake unit within a drum 2. The dog clutches, which may have bevelled engaging teeth, are shifted by rods 33 operated by fluid-pressure pistons 30, 30a and locked by detents 35 on a rod 37 acted on by a piston 38 or a spring 40. Pressure fluid, which may be compressed air, is admitted to the pistons 30, 30a from a preselector 42 having three piston valves 43 actuated by pressure from a manual disc selector valve 52. A lubricating oil pump is driven by a shaft 24 from the output shaft 6, the outlet pressure being served by a switch 26 connected to a solenoid valve 59 in the supply line 47 to the preselector 42. Movement of the selector lever 63 connects appropriate pressure and exhaust line to the preselector 52 to move the piston valves 43 to position for selecting the required ratio through pistons 30, 30a, the rods 33 of which are locked by detents 35. Actuation of an impulse release valve 74 passes pressure to a distributing valve 73 to pass pressure to the clutch-brake device, releasing the clutch and applying the brake, to stop the gear shafts, the output shaft being connected to the driven members through one-way clutches. At the same time, the line 78 to the piston 38 is exhausted and the detents 35 released, this movement of the rod 37 closes a checking valve 41 to prevent pipe 82 being re-pressurized. As the speed of the shaft 6 decreases, the oil pressure drops and causes opening of the solenoid valve 59 to pressurize pipe 47 and initiate the gear shift as preselected by pistons 43. Pressure builds up slowly through a restrictor 91 to move the valve 87 and at the same time to actuate a piston 105 opening a valve 101 and causing a bleed flow to exhaust from pipe 84 to produce partial engagement of the clutch and slight release of the brake to allow engagement of the dog teeth. On completion of the shift valve 87 closes the pipe 78 and allows locking of the rods 33. Rod 37 then opens valve 41 to reset the distributing valve 73 and pressurize piston 38. During the shift the pressure is fed to a pipe 84 to slow the engine, and on completion of the shift this pipe is exhausted and engine speed increases, the oil pressure rises and the solenoid valve 59 closes again. To facilitate shift, the clutch may have a resilient frusto-conical spring ring 108 to develop the necessary torque. A number of similar change-speed gears may be operated together under the control of a single selector 52 and a single impulse releaser 74. The selecting lever may also control the releaser valve.