GB619234A - Improvements in or relating to variable-ratio power transmission apparatus - Google Patents

Abstract

619,234. Change-speed control. HOBBS TRANSMISSION, Ltd., and HOBBS, H. F. July 3, 1946, No. 19924. [Class 80 (ii)] A change-speed gear of the kind (e.g. as in Specifications 602,319, 602,323 and 619,226), having one or more hydraulically-actuated friction-clutches and/or brakes, and gearing having one or more toothed elements slidable into and out of mesh with other toothed elements, is controlled by a piston and cylinder 2, 1, which are relatively rotatable to control ports, e.g. 26, supplying pressure-oil from inlets 20, 21 to and from the ends 41, 42 of the piston so as to cause the cylinder and piston to have relative axial movement for operating the toothed elements through axially - movable striker-rods 5, 6, and also for controlling further ports, e.g. 28, supplying the respective friction-clutches through ducts 24, 25. As shown, the control is for a gear providing three reduced speeds, direct-, over-drive and reverse, and includes accelerator kickdown shift from any one ratio to the next. Balk-means or synchromesh is provided for the meshing toothed elements. The cylinder 1 is fixed and the piston 2 is turned to ratio-selecting positions by a steering-column-mounted shift-lever (not shown), acting through an arm 12, and Bowden cable 11 on an axially-fixed arm 10, which latter is splined on an inner selector-shaft 3, which is splined at 46 inside the piston 2 and carries at its other end an arm 9 operatively engaging forked parts on the striker-rods 5, 6. The striker-rod 6 has two operative and a central neutral positions, whilst that, 5, has a neutral and one operative positions, the latter giving reverse. The selector-rod 3, in addition to being splined in the piston 2, is connected to it for axial movement through compression-springs 47, 48, so that, when the piston 2 moves axially to move the selector-rod 3 axially into a selected operative position, the selector-rod 3 may remain behind if detained by torque-loading on the toothed elements or the balk-means, causing compression of the appropriate spring 47 or 48, which subsequently meshes the toothed elements with a snap-action when they are freed for movement. The ports in the piston 2 are selectively arranged peripheral grooves 26 and axial drillings 28, controlling the supply of pressure-oil from the inlets 20, 21 to the piston-faces 41, 42 and, through the ducts 24, 25 to the friction clutches, exhaust being through ducts 22, 23. In operation, movement of the shift-lever into a position to introduce a desired speed, turns the piston 2 to. the appropriate position for selecting either striker-rod 5 or 6, and for supplying pressure to the appropriate face or faces of the piston 2, which then moves axially to introduce the desired toothed combination and also to direct fluid to the desired friction-clutch combination. The porting may be such that during certain upshifts, e.g. that from first to second speeds, involving changes in the meshing toothed elements, tooth unloading and synchronising may be effected by temporarily engaging a friction-clutch, combination producing a higher ratio than that finally required, and such ratio may be additional to those provided for use as normal drive-ratios in the transmission. Thus, in changing up from first to second gear, the porting is such that in its initial movement from extreme right to extreme left the piston supplies fluid to a friction-clutch, e.g. through port 24, producing in the unchanged toothed-combination, a third (normally inactive) gear slightly higher than second, which rapidly reduces the speed of the driving gear parts producing an " over-synchronized " condition for the ratio finally required. During subsequent movement of the piston this clutch is first cut out and the finally-required frictionclutch is momentarily engaged and disengaged to reduce the speed of the gear parts to unload the meshing toothed members and permit them to move to the balked position for the finallyrequired ratio. The piston then completes its travel, compressing the spring 48 and re-engaging the finally-required friction-clutch through the port 25, so that, when the enginespeed has increased sufficiently to unbalk and synchronize the toothed elements, these are snapped into engagement by the spring 48, and the new ratio is effective. Thus, although the shift is an upward one, the temporary " over-synchronization " results in the final synchronization being effected by increase in engine-speed as for a normal downshift, which is a simpler operation. With this arrangement, the balk-device may act in the upshift direction only, whereby second and third speeds can be selected with the vehicle stationary. Where known types of synchromesh are used the area of the oil-ways may be proportioned to produce a delay for synchronizing. As shown, the selector-arm 9 remains in engagement with the reverse-striker 6 for the first two angular positions of the control-lever, changes to the three-position striker 5 at its third (neutral) angular position, and remains in engagement therewith during the remaining five forwardspeed angular positions. For the kick-down shift from any ratio, overtravel of the accelerator-pedal 17 acts against a spring 15 on the abutment at one end of the Bowden casing 50, thus producing the same effect as moving the control-lever to the next angular position for downshift, a return upshift to the leverselected position being effected by release of the accelerator-pedal. The Provisional Specification states also that the accelerator-pedal may have a ratchet connection to the piston to give upshift on full release and downshift on full depression of the pedal.