GB640228A - Improvements in or relating to change-speed gears for motor vehicles - Google Patents

Abstract

640,228. Change-speed control. ROLLS-ROYCE, Ltd. Aug. 19, 1946, No. 24681. [Class 80(ii)] In countershaft changespeed gearing having at least three forward countershaft speeds, a one-way clutch, coaxial with the output shaft and having its driven member clutchable thereto and its driving member meshed with a gear driven by the input shaft to provide one gear ratio, is overrun, to provide a higher gear ratio, by coupling its driven member, at will and irrespective of the output shaft speed or torque, directly or indirectly with the input shaft. As shown, the output shaft 20, Fig. 1, carries a normal first speed, neutral and reverse sliding wheel 19 and a synchromesh double clutch member 23 alternatively clutchable to the second speed gear 18 and to a hollow shaft 25 rotatable on the output shaft and forming the driven member of a one-way roller clutch 28 whose driving member is the third speed gear 17. A dog clutch member 29 slidably splined on the shaft 25 co-acts, for a fourth speed direct drive, with clutch teeth formed on the input gear 11, which powers the gears 17-19 through a layshaft 13. The clutch member 23 and sliding, wheel 19 are controlled mechanically by alternative-member shift mechanism from a hand lever 33, Fig. 3, on the vehicle steering column. Vertical pivotal movement of the lever 33 slides a rod 37 to select one or other of linkages 39, 42 controlling the actuating levers 40, 43 of the wheel 19 and clutch member 23 respectively, and sideways pivotal movement of the lever 33 operates the selected linkage. The lever 33 can thus execute changes between reverse, neutral, first and second gear; and can also engage the clutch member 23 with shaft 25, when third speed or direct drive will be operative according to the position of the clutch member 29 which is independently controlled by means associated with the accelerator pedal 50. A solenoid 46 is in circuit with a switch 49 which is controlled by the pedal 50 so that the solenoid is energized only when the pedal is fully depressed. The switch 49 may also be actuated by a dashpot device as described in Specification 640,230 to cause energization of the solenoid above a predetermined rate of downward movement of the pedal 50 within its normal range of travel. The solenoid, when energized, acts through a bell-crank on the member 29 to bias it towards disengagement, a spring acting to reverse the bias when the solenoid is deenergized. Actual engagement and disengagement of the member 29 only takes place upon torque lowering or reversal, which to change up, is effected by partial or complete release of the pedal 50, and, to change down, is produced by momentary interruption of the engine ignition through means controlled by the solenoidal energization. Balking means, which may be of the kind described in Specification 640,227, may also be provided to allow engagement only upon torque reversal. With both clutch members 23, 29 engaged, the direct drive and third speed will automatically become operative simultaneously to act as a sprag if the road wheels tend to drive the engine reversely. This may be prevented by providing, means, such as those described in Specification 640,233 and 640,240, which hold the free-wheel coupling 28 in its free position on reverse rotation. The solenoidal control of the member 29 may že replaced by hydraulic, pneumatic or mechanical control by a lever independent of the lever 33. In Fig. 5. (not shown), the free-wheel coupling is duplicated to give a fifth forward speed, a second hollow shaft analogous to the shaft 25 and carrying a countershaft driven gear giving a lower ratio than the gear 17 being interposed between the shaft 25 and the clutch member 23, and positive clutching means analogous to the clutch 29, 11 and operated by a further solenoid being provided between the two hollow shafts. The two solenoids may be controlled by pedal-actuated switches of the kind described in Specification 640,229. Such duplicated couplings may also be used in gearings having only four forward speeds.