GB1187325A - Improvements in or relating to Control Means for a Change-Speed Gear Unit - Google Patents

Abstract

1,187,325. Change-speed gear and control. LAYCOCK ENG. Ltd. 26 May, 1967 [26 May, 1966], No. 23626/66. Heading F2D. Shift establishment in a motor vehicle changespeed gear, particularly a two-speed underdrive or, as shown, overdrive unit in series with a conventional, e.g. 4-speed, change-speed gear-box is effected by, and is prevented until, pedal disengagement of a separating clutch through which the power passes in all ratios. An hydraulic cylinder 19 has its piston 18 connected to the separating clutch operating pedal (not shown) and is itself connected through a pressure line 22 to an accumulator 25, to an oil supply pump through a filter 44 and a one-way valve 24, and to a feed control valve 28. The piston 29 of the latter is (as shown), spring- urged to block flow from the pressure line 22 to a line 30, connectible through a manuallyoperated selector valve 33 to an hydraulic shift actuator 32, until the separating clutch pedal is depressed whereupon consequent rightward movement of the piston 18 rightwardly moves the accumulator piston 26 to uncover a port 27 and thereby admit line 22 pressure to act on and open the feed control valve piston 29. As shown, the piston-rod 39 of the selector valve 33 is connected to an operating member projecting through the vehicle dashboard. The shift actuator piston 38 is connected to a fork engaging a dog-sleeve 2 of a direct/overdrive unit having a casing 1 bolted to the output end of a four-speed box the input of which is driven by the vehicle engine through the separating clutch. The direct/overdrive unit described comprises stepped planets 10 mounted on an input carrier 6 and having respective steps meshing a sun 5 and an output ring 7, the sun 5 being selectively stationed or clutched to the carrier, by operation of the dog clutch sleeve 2, respectively for overdrive or direct drive. The dog clutch sleeve 2 is provided with synchronizer cones 14. To prevent engagement of overdrive in four-speed box ratios other than top, e.g. direct, the 3-4 shift rod of said fourspeed box is connected by a rod 43 to an interlock fork 42 which is arranged to co-operate with spaced abutments 41 on the selector valve piston-rod 39. In operation, starting from the position shown, with the separating clutch pedal released, and the selector valve 33 and the shift actuator 32 in direct drive conditions, depression of the separating clutch pedal and consequent rightward movement of the piston 18, accumulator piston 26 and feed control valve piston 29 results in pressurization of the line 30. When the piston-rod 39 is moved to its Overdrive position, the left- and right-hand sides of the piston 38 are respectively pressurized and vented and the shift to Overdrive ensues. Drive in Overdrive then obtains when the separating clutch is re-engaged. As the clutch pedal returns, fresh oil is drawn from the sump through the one-way valve 24, oil previously in the accumulator having been used to pressurize the actuator 32. The accompanying return movement of the accumulator piston first closes and finally opens the port 27 to exhaust, so as to allow spring return of the feed control valve 28 to trap pressure in the actuator 32. Shift to Direct drive is accomplished in a similar manner. When the interlock fork 42 is in the 3-4 selector rod neutral position (i.e. corresponding to any four-speed box ratio other than 3rd or 4th, it prevents movement of the piston-rod 39 to Overdrive, the axial lost motion between the fork 42 and the rod 39 being insufficient to allow such movement. When the fork 42 is in 3rd gear position, the rod 39 cannot be moved at all. With shift from four-speed box top gear without first disengaging Overdrive, the fork 42 moves the rod 39 into Direct drive and since such shift is accompanied by separating clutch pedal depression, the actuator 32 is actuated to shift out of Overdrive.