Patent GB-796774-A (GB)
Title: Improved variable-speed power transmission mechanism for motor vehicles
IPC: F16H61/06
Filed: 1956-03-26
Abstract: 796,774. Change-speed gear. GENERAL MOTORS CORPORATION. March 26, 1956 [April 29, 1955], No. 9317/56. Class 80 (2). A planetary change-speed gear, on a vehicle, in which ratios are selected by clutches and brakes alternatively operable by fluid pressure, has the moments of inertia of the various gear elements and masses connected thereto so arranged that on a change of ratio involving both acceleration and deceleration of gear elements, the change in angular momentum of the accelerated elements is balanced by that of the decelerated elements. A complete gear and fluid-pressure control therefor are described. Control function summary. A manual ranging valve 220 has five settings, Reverse, Neutral, Drive, Three and Two (R, N, D, 3, 2). In D setting automatic shifts between all of four forward ratios are obtained by a single automatic shift valve 310, which is moved in steps to four corresponding ratio-selecting positions by opposing fluid pressures 434, 374 responsive respectively to output speed and acceleratorpedal position. Manual valve setting 3 prevents upshift of the automatic valve 310 to fourth ratio under any conditions whilst setting 2 prevents upshift above second ratio except for a safety upshift to third on excessive engine speed. In jump-step shifts between second and fourth ratios, third is introduced temporarily to smooth the shift. Front and rear pumps 76, 142, supplying the system, are driven by gear reaction members and are individually stationary in certain ratios. Pressure augmentation is provided in reverse. Speed-responsive pressure regulation is by a single output-driven governor valve 150, acting in three stages. Gear arrangement. The gear provides two reduced ratios, direct-drive, overdrive and reverse. First and reverse only are one-way. There are two series trains B, D with a fluid coupling C therebetween, two control clutches E, F and three reaction brakes H, G, K. Torque splitting occurs in third and fourth ratios, the others being all-fluid drive. First ratio (directreduced), is by the brake G only. The front train B drives at one-to-one due to a one-way clutch 25 preventing its reaction sun 26 overrunning its planet-carrier 20 which is permanently connected to an input shaft 10 through a spring-coupling 18 and engine-plate 12. An output ring-gear 24 of the train B is fast to the impeller 28 of the fluid coupling C, the turbine 36 of which is fast on an intermediate shaft 42 which carries at its rear end an input sun 44 of the rear train D, intermeshed planets of which are carried by the final output shaft 130. The hand-brake G is applied to a drum 90 fast to a reaction sun 92 of the rear train D which thus reduces. For second ratio (overdrive-reduced), the brake G remains on, so that the rear train D is unaffected, and the clutch E is engaged to connect the rear reaction sun 92, through the drum 90 and a sleeve 66, to the front reaction sun 26 which is thus held, along with the rear sun 92 by the same brake G, and the front train B upshifts to overdrive. For third ratio (direct-direct), the clutches E and F are engaged alone and lock-up the front train B by connecting the reaction sun 26 to the output ring gear 24 through the clutch E, sleeve 66, clutch F and a sleeve 98. The output ring 24 and reaction sun 26 drive the rear reaction sun 92 mechanically through the clutches F and E respectively, whilst the ring 24 also drives the rear input sun 44 at the same speed (approximately one-to-one) through the fluid coupling C, providing split-torque direct-drive. Fourth ratio (overdrive-direct) is by engaging the brake H and clutch F, the former directly holding the front reaction sun 26 to upshift the front train B to overdrive. The overdriven ring 24 drives the rear train input sun 44 through the fluidcoupling C as before, whilst the same ring 24 mechanically drives, through the sleeve 98 and clutch F the reaction sun 92 of the rear train which thus drives at one-to-one. For reverse (direct-reverse) the double-cone brake K is applied alone to a reaction ring gear of the rear train D, the input sun 44 of which is driven through the front train B (in one-way direct drive) and fluid coupling C, as in first ratio. The rear train reverses. Clutches.-In the front clutch E, one endplate has a radial extension 62 bearing on an outer shell 46 of the clutch to serve as a retracting spring for an engaging piston 68. Momentumbalanced shifts.-In shifts between second and third ratios (and equivalent transient shift-phases referred to below), requiring shifts in both gear trains, the mass to be accelerated (considering upshift) is the front reaction sun 26, and those to be decelerated are the engine and the fluid coupling C. For momentum balance the gain and loss in momenta must be made equal, for which result the product of the moment of inertia of the reactive sun 26 and its increase in rotational speed must be equal to the sum of the products of the moments of inertia of the engine and fluid coupling and their respective reductions in speed. The Specification equates these values for shift at a particular output speed. To meet this moment of inertia requirement, the engine has no flywheel, the plate 12 being of minimum moment of inertia, whilst a flywheel ring 48 is carried by the reaction sun 26, which latter rotates in neutral to provide satisfactory engine idling. The arrangement is also such that during downshift the engine requires a minimum of energy to accelerate itself and is thus able to devote a maximum to accelerating the vehicle. This is due to the fact that on 4-3 downshift the sun gear 26 and its flywheel have to be rapidly accelerated and afford an inertia reaction for the front train. Fluid pressure supply.-Front and rear pumps 76, 142 supply a common pressure main 206 through a non-return valve 202 which closes to that pump producing the lower pressure. The front pump 76 is driven through a drum 56 by the front reaction sun 26 and is therefore stationary in second and fourth ratios. The rear pump 142 is driven by the reaction ring K of the rear train in all forward ratios and neutral, and is stationary in reverse. In some forward ratios it is driven at overspeeds. Fluid system components.-These include, in addition to the manual, automatic and governor valves 220, 310, 150, a " TV " valve 360 which provides throttle variable, (TV) pressure in a line 374 in response to loading 372 from the engine accelerator, TV pressure varying from a minimum of 22 p.s.i. with closed throttle to 75 p.s.i. with open throttle; a main pressure or regulator valve 210; accumulators 440, 450 which delay engagement, but not disengagement, of the clutch E and brake H respectively; and a timer valve 482 which, during a 4-2 downshift, delays shift in the front unit to introduce third speed for a short period during the shift. Operation. Neutral.- In N setting the manual valve 220 supplies regulated pressure 262 only to a line 270 which acts leftwards on the pressure regulator 210 in opposition to its loading spring, this line 270 remaining pressurized in all forward settings of the manual valve 220 but not in reverse setting. The regulator 210 meters pressure between an exhaust 294 and a line 274 feeding the fluid coupling C, the outlet of which, throttled at 276, feeds a lubrication line 280. If the fluid-coupling C is empty when the engine is started, it will be overdriven by reaction against the heavy sun gear assembly 26, 48, but air-drag in the fluid coupling will eventually provide reaction for drive to the sun 26 and hence the front pump 76 to provide the initial oil pressure. The manual valve 220 exhausts all other lines at 228 and the open left end of the valve. Both accumulators 440, 450 are loaded by line pressure 265 and their pistons descend in opposition to loading springs. Drive.-In D setting the manual valve 220 feeds regulated pressure 262 additionally to lines 500, 530, the former applying the bandbrake G, the latter feeding, through port 326, bore 320 and port 324 in the automatic shift valve 310, to a groove between the two left end lands of the valve 310, which groove, in the initial position shown, is blanked. With only the brake G applied the vehicle is started in first ratio when engine acceleration causes the fluid coupling C to drive. TV pressure 374 metered from line pressure 262 by accelerator loading 372 acts leftwards on the automatic shift valve 310 and rightwards at 376 on the main regulator valve 210 so that system pressure 262 is also TV responsive, i.e. increases with accelerator depression. Governor pressure 434, regulated by the output-driven governor valve 150, as described below, acts rightwards on the automatic shift valve 310 through a governor plug 350 and two concentric cylinders 340, 344, which latter carry snap rings 346, enabling the outer cylinder 340 to act rightwards on the inner 344, and the inner 344 to act similarly on the governor plug 350, the cylinders being arrested at successive steps to cancel their loading effects as detailed below. The shift-valve 310 is located in each of four stepped ratio-selecting positions by pressure-balanced spring-loaded detent balls 532, which provide additional resistance to shift movement in either direction. Upshift 1-2.-When governor pressure 434, acting on the ends of both cylinders 340, 344 and the plug 350, is able to overcome TV pressure 374 and the detent balls 532, it moves the cylinders, plug and shift-valve 310 one step to the right, the outer cylinder 340 then abutting a casing-stop 352 which cancels its rightward thrust on the inner cylinder and ensures a lower corresponding return downshift speed. Line pressure 530, 324 is now directed to a line 504 feeding the clutch E slowly through a restrictor 540, and the corresponding accumulator 440 without restriction through a parallel by-pass 552, pressure-opened ball-valve 554 and passage 558, so that clutch e