Patent GB-505880-A (GB)
Title: Change-speed gearing for motor vehicles and the like
IPC: F16H61/02
Filed: 1938-08-19
Abstract: 505,880. Fluid-pressure servomotorcontrol systems. GENERAL MOTORS CORPORATION. Aug. 19, 1938, No. 24446. Convention date, Aug. 21, 1937. Addition to 503,276. [Class 135] [Also in Group XXIV] The rate of application of a fluid-servo actuated brake 30 and clutch 45, alternatively operable to produce respectively a geared under- or over-drive and a direct-drive in a two-speed epicyclic gear on a motor vehicle, is controlled by the position of the engine accelerator-pedal in such a manner that, during changes, the brake and clutch are engaged more slowly when the accelerator-pedal is released than when it is fully depressed, whereby the brake and clutch are prepared in advance for whatever torque is needed at.the time of the change, .and shocks in the transmission are avoided. The direct-drive plate-clutch 45 connects a driven (or driving) planet-carrier 14 and a driving (or driven) annulus 11, whilst the. brake 30 acts on a reaction sun-wheel 20. Directdrive is produced by opening a common valve 90, Fig. 3, which supplies pressure-liquid from a gear-pump 80, driven at 131, Fig. 1, simultaneously to cylinders 35 having pistons 36 for engaging the direct-drive clutch 45 against springs 47, and to a cylinder 60 having a piston 58 for disengaging the band-brake 30, against its engaging springs 61. The accelerator-pedal control of the rate of clutch and brake engagement is effected by means of a modifying cylinder 67, having a piston 70, Fig. 2, formed on the piston-rod 57 on which the main piston 58 has limited sliding movement. The sequence for engagement of direct drive after opening the control-valve 90 (position shown) is as follows. Pressure-liquid from the pipe 38 acts on the brake-position 58 forcing it downwards against the springs 61, the consequent large increase in volume resulting in a gentle increase of pressure on the direct-drive clutch-pistons 35 until an abutment 59 on the brake pistonrod contracts a slidable collar 66, whereafter an.additional spring 63 opposes the brakepiston 58, and rise of pressure on the clutchpistons'35 is more rapid. A graduated increase of clutch-engaging pressure is thus provided. If the change to direct-drive is taking place with the accelerator-pedal released, an arm 10, connected to the pedal, allows a valve 100 to fall to the position shown, in which full linepressure has access through a compensating- line 75, spring-loaded check-valve 105, differential valve 115, port 118, passage 118 and pipe 68 to the modifying cylinder 67. This modifying pressure acting on the piston 70 helps the main piston 58 to compress the brake-springs 61, 63, so that a lesser initial pressure will be effective in the line 38 and so on the clutchpistons 36 at the point of brake-disengagement. The initial clutch-engaging pressure and therefore the rate of clutch-engagement will thus be less than if the accelerator-pedal has been fully depressed, in which case the valve 100 would be raised, venting the compensating line 75 to a small or zero pressure. In all cases the final clutch-engaging pressure after the change is always the same, viz.: line-pressure 38. The following sequence takes place after closing the valve 90 to change from direct to geared drive. The clutch and brake line 38 vents at a predetermined rate through a blade-spring valve 97, and the subsequent upward engaging movement of the brake-piston 58 under the influence of the springs 61, 63 acts through a spring 71 on the auxiliary piston 70. The liquid thereby compressed above the piston 70 acts through the pipe 68 and passage 119 on the left face of the differential piston 115, forcing it to the right and opening the pipe 68 through a vent 120 to a passage 114. If the shift to geared drive is being made with the accelerator-pedal released, the compensating- line 75 is under pressure, and the rate of brake engagement will be slow, being determined by the rate at which the auxiliary piston 70 can vent the modifying cylinder 67 and the line 68 through a fixed bleed opening 124 in the passage 114. If the shift is being made with the accelerator-pedal fully depressed, the valve 100 will be closed in its upper position, venting the compensating-line 75 to a low or zero pressure, so that, in addition to the bleed opening 124, the auxiliary piston 70 can vent the line 68 through a check-valve 110, the compensating line 75 and the vent 69 of the acceleratorcontrolled valve 100. Brake engagement will therefore be rapid. A spring-pressed accumulator-piston 111, with relief port 122, limit and maintain the modifying pressure above the auxiliary piston 70. The pump 80 has a pressure-regulating valve 83, which also supplies a lubrication-main 135 feeding the bearings and gears through a chamber 134, Fig. 1. The speed-changing valve 90 may be operated by hand or foot, or by governor mechanism responsive to speed and /or torque, by acceleration- and deceleration-responsive controls or by combinations or any of these with operatorcontrolled means such as the engine-throttle. The Specification as open to inspection under Sect. 91 states also that the change-speed gear may be of the fixed countershaft type, the brake being replaced by another clutch. The clutching devices may be liquid or electrical. This subject-matter does not appear in the Specification as accepted.