Patent GB-696411-A (GB)
Title: Improvements in or relating to variable speed power transmission
IPC: F16H61/02
Filed: 1948-02-05
Abstract: 696,411. Change-speed gear. CHRYSLER CORPORATION. Feb. 5, 1948 [Oct. 9, 1940], No. 3396/48. Class 80 (ii). On a motor-vehicle a direct-reduced speed countershaft unit A, Fig. 1, drives, through an intermediate shaft 20 a direct-overdrive planet unit B, Fig. 3, the latter upshifting automatically above a predetermined vehicle speed, the former, A, also upshifting on accelerator-release above a predetermined speed of the intermediate shaft, both controls being such that, by use of the accelerator, the operator can at will cause or permit shifts in either unit whilst the other unit is set for operation in either of its ratios, thus providing for alternative shift sequences as desired. Accelerator kickdown shift is provided for the planetary unit B, and a fluid-coupling and main-clutch are also employed. Countershaft unit.-This unit, A, is conditioned for semi-automatic operation, as above, by shifting a toothed clutch-sleeve 25, splined on a hub 40 fast on the output shaft 20, from the neutral position shown, into a forward position in which it makes balked synchronised engagement with the driven member 19 of the centrifugal positive clutch C, thus connecting the latter to the driven shaft 20, and at the same time engages additional clutch-teeth 44 with teeth 45 on the outer driven member 46 of a oneway roller-clutch D driven by the freely mounted reduced-speed wheel 32. This provides for an initial reduced free-wheeling drive from the input shaft 13 through the wheel-pairs 15, 16; 35, 32, roller-clutch D, clutch-sleeve 25 and hubmember 40. The centrifugal positive clutch is of the Keller type in which adjustably spring- loaded pawls 62, Figs. 1 and 4, radially guided in a driving member 18, are biased centrifugally outwards at a predetermined speed, but are unable to enter into clutching engagement in slots 63 in the surrounding driven shell 19 until the driver 18 is retarded to synchronism by eccelerator-releaso. The pawls 62 then complete their outward movement introducing direct-drive, with overrun in the reduced-drive roller-clutch D. The clutch-sleeve 25 can be moved rearwardly for balked-synchronised direct clutching to the reduced speed wheel 32, providing an enforced bi-directional reduced speed under all conditions. A manually - controlled sliding splined wheel 52 is meshed with an idler 53 for reverse, and, if desired, with an additional countershaft-wheel for an emergency low speed; Fig. 2 (not shown). Planet unit.-The planetary overdrive unit B, Fig. 3, comprises a driving planet-carrier 85 fast on the input shaft 20, which is the output shaft of the preceding countershaft unit A, a driven ring-gear 90 fast to the final output shaft 76, and a freely-mounted reaction sun 93, splined on the hub of which is a clutch sleeve 98, having external clutch-teeth, which, in the direct-drive position shown, engage teeth 100 on the planetcarrier to lock the train solid. Fast to the direct-drive clutch sleeve 98 is a brake disc 103, which, when fluid-pressure is applied to a group of pistons 114, is moved axially to the left, to withdraw the clutch-sleeve 98 out of engagement and to become clamped between friction facings on the casing and on a presser-plate 104 splined in the casing, thus holding the sun 93 for overdrive. The direct-drive clutch-teeth 100 are of the bevel-faced (Maybach) type to engage only when synchronised, engagement being effected by springs 101, 109 when fluid pressure is released from the brake 103. To provide immediate drive take-up if the clutch-teeth do not engage, a forward driving one-way roller clutch E is arranged directly between the driving and driven shafts. Fluid control.-The fluid control of the planetunit overdrive brake 103 is as described in U.S.A. Specification 2,238,746, and comprises an output-shaft-driven gear-type oil pump J, the delivery pressure of which, below a predetermined vehicle speed, drops below a critical value thus allowing the overdrive brake 103 to disengage and the planet unit B to downshift to direct. A similar automatic upshift action above the critical pressure speed is also produced (unless prevented as described below), this speedresponse being obtained under all conditions. The pump-delivery is subject to a two-stage relief-valve, Fig. 12 (not shown), having two sequentially arranged relief-ports, the first of which delays build-up to a pressure sufficient to engage the overdrive brake below a predetermined vehicle speed, whilst the second relieves excess pressure during normal operation. In addition there is a valve K, Figs. 8-14 (not shown), arranged in the brake-line and opened by overtravel accelerator-kickdown and by an independent driver-control on the instrument-panel, for exhausting the overdrive brake 103 for downshift to direct in the planet unit at any time. The accelerator kickdown control is such that, after kickdown opening, the valve K is not restored to the closed (brake-effective) position until the accelerator is fully released. Ratio shift sequence. -In accelerating the vehicle from rest, the normal shift sequence (which may however be reversed) is that, starting with the countershaft unit A in low and the ,planet unit B in direct (i.e. overall low-direct), at the critical speed of the pump J, the planet unit upshifts first and entirely automatically, the countershaft unit remaining in low to give overall low-overdrive, which is a first intermediate ratio. Above a predetermined higher vehicle-speed, release of the accelerator upshifts the countershaft unit giving overall direet-overdrive or top speed. In this condition,accelerator-kickdown, operation of the independent control, or reduction of vehicle-speed below the critical pump speed, exhausts the overdrive brake, downshifting the planet unit and giving overall direct-direct which is a second intermediate ratio midway between the first intermediate (low-overdrive) and top (direct-overdrive). The above sequence can be varied by the operator as follows. If, during acceleration from rest, the operator keeps the accelerator fully depressed to the kickdown position the overdrive brake 103 is maintained exhausted so that the shift from low-direct to low-overdrive does not occur, but when the higher vehicle speed for operating the countershaft-gear clutch C is passed, the accelerator can be released sufficiently to allow engagement of the clutch C without closing the overdrive exhaust-valve K, so that the countershaft unit upshifts to direct whilst the planet unit remains in direct, giving overall direct-direct, i.e. the second intermediate speed instead of the normal first intermediate above described. Subsequent full release of the accelerator closes the overdrive exhaust valve K, upshifting the planet unit and giving overall direct-overdrive, top, as before. . Thus by appropriate use of the accelerator, shifts in either unit may be obtained whilst the other unit is set in either of its ratios. Specifications 696,442, 696,443 and 696,444 also are referred to.