Patent GB-609130-A (GB)
Title: Change-speed mechanism for motor vehicles
Filed: 1946-03-06
Abstract: 609,130. Fluid-pressure servomotor-control systems ; centrifugally - actuated valves. GENERAL MOTORS CORPORATION. March 6, 1946, No. 6983. Convention date, March 31, 1945. [Class 135] [Also in Group XXIV] In change-speed gearing in which the speed ratios are obtained by epicyclic gearing having fluid - pressure servo - operated brakes and clutches, the fluid-pressure is proportioned to the prevailing conditions of speed and load and is selected at the time of ratio change. A driving shaft 1 carries a hollow fly-wheel 2 having an internal web 2a on each side of which are fluid-pressure operated clutches A, B, each of which comprises a hub 4, 9<1> attached to a driven shaft 7, 11 and a clutch plate 5, 8 adapted to be pressed against the faces of the web 2a by annular pistons 6, 9 respectively. Fluid for the actuation of clutch A passes from pipe 60 and passageway 60a to a speed-responsive valve 110 mounted in the fly-wheel and having three bosses a, b, c, the latter of larger crosssection, accommodated in the chambers 113, 114, 116, 115 which are open respectively to exhaust, passage 62 leading to the piston 6 and passage 60a. On rotation, a speed is reached at which the valve moves outwards to cut off the chamber 114 from exhaust, as speed increases the valve reaches a position where chambers 115, 116 are in communication which allows pressure to actuate the clutch A, the differential pressure on the bosses band c being counterbalanced by centrifugal force on the valve until a predetermined higher speed is reached. Thus, the clutch A will only engage at a predetermined engine speed and forms a starting clutch. The clutch B is similarly controlled by a valve 110<1> which is effective at higher speeds, and is cross-connected by a passage 98 which applies the pressure in passage 62 to the underside of the valve 110<1> so that when the clutch A is energized, the valve 1101 is in the open position ready to be energized with fluid-pressure from a pipe 66. A centrifugal-force and radial spring-loaded lever 80 acts between the peripheries of clutch pistons 6, 8 to neutralize the effects of centrifugal pressure in the operating fluid. The coaxial shafts 7, 11 transmit the drive to two epicyclic gear trains R, L, the two sun gears 10, 15 being rigid with the shaft 7, the planet carriers 13, 20 are connected with the shaft 11 and the output shaft 50, the annulus gears 16, 19 being connected to the planet carrier 20 and brake drum of brake 30 respectively, a brake 25 also acts on the planet carrier 13. Thus, by selective engagements of clutches A, B and the brakes of trains R, L, three forward and one reverse speeds can be obtained in the usual manner. The band of brake 25, Fig. 2, is anchored at one end by a rod fitting in a notch 25a, and is operated at the other end by a rod 26 fitting in notches 25b, 27a in the band and a lever 27 respectively, the lever 27 being operated. at its other end by a piston 28 and piston-rod 28a actuated by fluid pressure from pipe 142 acting against the return spring 31. The brake band 30 is similarly actuated by pressure from pipe 141 acting on a piston 34. Fluid pressure is generated by a pump P driven from the engine and is supplemented under conditions of overrun by pressure from a pump P<1> driven proportionally to road-speed. The main pressure in pipe 101 is fed directly through the chamber 164 of a reducing valve 160 to pipe 107 and at a reduced pressure through pipe 106. An intermediate pressure is transmitted to pipe 104 through the reducing valve 170 which is byepassed to modify this intermediate pressure according to intake manifold pressure (i.e. torque) by a valve 150 in which modified pressure on the valve 150 and manifold pressure on the lower side of the diaphragm 156 are opposed by an adjustable tension spring 155 and a similar compression spring 158a, the valve when open passing fluid through pipe 108 to the pump inlet 102. These pressures are transmitted to operate the clutches A, B and the brakes 25, 30 under the control of two valves 120, 130 which are operated from a hand lever, mounted on the steering column, which moves a forked plate connected to the two valves, definite positions of the plate being obtained for reverse, neutral, first, second and high gears by a spring detent. In operation, when the engine is started the pump P produces pressure in pipes 106, 107 and' opens the valve 170 to produce pressure in the pipe 104 which is increased as the throttle is opened, this intermediate pressure is transmitted to chambers 122, 123 and thence by the pipe 60 to the clutch A. The low pressure in the pipe 106 is transmitted to the chamber 124 and the high pressure in pipe 107 to the chamber 126 of the valve 120. With the valve 130 in the neutral position neither brake 25 nor 30 is engaged as pipes 141, 142 are not connected to fluid pressure. Movement of the valves 120, 130 to first gear position as shown in Fig. 3 connects pipe 107 to a cross-passage 133 to chamber 131 and thence to pipe 141 to apply brake 30. The position of the valve 150 is determined by manifold pressure and thus the pressure in clutch A is proportional to torque and to the position of the valve 110 which is responsive to engine speed. As the vehicle moves, pressure in pipe 101 is supplemented by the pump P<1>. Movement of the hand lever to move the valves 120, 130 into position for second speed moves valve 120 down and due to toggle action in the linkwork valve 130 ineffectively up. In this position, full pressure is transmitted from pipe 107 to cross-passage 133 to maintain the brake 30, but intermediate pressure is cut off from chamber 123 and clutch A and is applied to the chamber 121 and pipe 66 to engage clutch B through the centrifugal valve 110<1> so that the pressure applied to clutch B will be in accordance with torque and speed conditions as before. Further movement to high gear position pulls the valve 120 to its lowest position in which pressure from chamber 125 is out off from the cross-passage 133 and pushes the valve 130 to a position which opens the chambers 132, 134 to exhaust chamber 135 to release the brake 30. Simultaneously, the valve 120 admits high pressure to pipe 66 through the chamber 127 to engage the clutch B and low pressure to pipe 60 through chamber 123 to engage the clutch A to drive the two epicyclic trains solid for direct drive. For reverse, the valve 130 is moved to its lowest position in which high pressure from the crosspassage 133 is transmitted to the chamber 134 and the pipe 142 to engage the brake 25, and in which chamber 132 and pipe 141 are exhausted to release the brake 30. The valve 120 being in a position to admit intermediate pressure from the pipe 104 to the pipe 60 to engage the clutch A.