GB737630A - Improvements relating to gear-change devices - Google Patents

Abstract

737,630. Friction clutches; change-speed gearing. DAIMLER-BENZ AKT.-GES. Oct. 2, 1953 [Oct. 2, 1952], No. 27086/53. Class 80 (2). Change-speed gearing, particularly for a motor vehicle, includes a hydraulically operated friction clutch for effecting a change in ratio, a part of the clutch having a steep threaded or helically toothed connection with an associated gear, which connection comprises a torque-responsive means tending to engage the clutch, e.g. when changing to a lower ratio, such engagement being prevented by a stop and being completed only when the hydraulic operating means is actuated. In one form, a multi-disc clutch 19, Fig. 2, consists of a housing 23, fast on a countershaft 12, carrying clutch plates 24 alternating with clutch plates in a disc-supporting hub 25 which has inclined teeth 26. These teeth engage inclined teeth 27 on a hub 28 integral with a gear 15 rotatable on the hub of a gear 14. The teeth 26 are shorter than the teeth 27, the threaded connection constituted by the teeth tending to screw the disc-supporting hub 25 to the left or right of Fig. 2 according to the direction of the torque transmitted between the parts 25, 28. When the disc-supporting member 25 moves to the right it moves the discs 24 &c. in the direction of clutch engagement, this movement being limited by a spring ring or stop 29 against which the teeth 26 abut, the clutch then being on the point of engaging. The engagement is completed by supplying pressure fluid to a cylinder 36 to move a piston 35 to the left of Fig. 2. The clutch is described applied to a three-speed countershaft gear, for a motor vehicle, driven through a fluid coupling 8, Fig. 1, for first and second speeds, direct drive being obtained by engaging a clutch 7. First speed is operative with a clutch 20 engaged, the disc-supporting hub 25 being screwed to the right of Fig. 2 by the residual friction in the disengaged clutch 19, which is thus ready for engagement immediately pressure fluid is admitted to the cylinder 36. In third speed (direct drive), the clutch 7 being engaged, the disc-supporting hub 25 is screwed to the left of Fig. 2 and the clutch 19 is thus held completely free. To change down from third to second speed, pressure fluid is admitted to the cylinder 36 and at the same time the clutch 7 is disengaged, thus allowing the engine speed to increase until the clutch housing 23 and countershaft 12 rotate faster than the gear 15, when the disc-supporting hub is screwed to the right. By this time, sufficient fluid has entered the cylinder 36 to move the piston 35 a short distance in the clutch-engaging direction, so that the screwing action on the hub 25 causes instantaneous clutch engagement. If the change from third to second takes place while the vehicle is overrunning the engine, the disc-supporting hub 25 remains at the left-hand end of the hub 28 and the clutch is engaged by supplying pressure to the cylinder 36; in this case clutch engagement will not take place till the piston 35 has completed its travel. In a modified form, Figs. 4, 5 (not shown), the teeth 26, 27 are omitted and the torque responsive means is constituted by helical teeth on the gear 15 and on the gear 17 which it meshes, the whole hub 28 being moved axially prior to clutch engagement by the reaction of the torque on the helical gear teeth.