Patent GB-503276-A (GB)
Title: Power transmissions for motor vehicles and the like and controls therefor
IPC: F16H61/02
Filed: 1938-03-11
Abstract: 503,276. Fluid-pressure servomotor-control systems. GENERAL MOTORS CO. March 11, 1938, No. 7622. Convention date, March 15, 1937. [Class 135] [Also in Group XXIV] In an epicyclio gear for motor vehicles and the like wherein a clutch is engaged and a brake disengaged by fluid pressure, while the clutch is disengaged and the brake engaged by springs on release of the fluid pressure, so as to obtain solid and reduced drives respectively, the fluid pressure at which the brake is released and the clutch takes up the drive is varied according to the degree of actuation of the engine control device. On operation of a control valve 168, Fig. 9, pressure fluid can pass from a supply conduit 238 to a port 264 and to a conduit 272 leading both to a clutch cylinder 75 and to a brake cylinder 261, whereby the clutch is engaged through the agency of a piston 76 against the action of disengaging springs 89, Fig. 1, and the brake is disengaged through the agency of a piston 291, secured to a rod 290, against the action of engaging springs 97, 97a, and 97c. From the port 264, fluid has constant access to the interior of a sleeve 326 which is urged down towards the limiting position shown by a spring. A valve 320 is urged up towards the sleeve 326 by a spring, the abutment 323 of which is controlled by an arm 122 which is moved up as the accelerator pedal is depressed. With slight depression of the latter, a maximum opening exists between the members 320 and 326, and pressure fluid passes to a conduit 277 leading to a cylinder 295 to act on a second piston 294 secured to the rod 290. As the accelerator is further depressed, the opening is reduced until, at full depression, pressure fluid is prevented from passing to the conduit 277. The pressure at which the brake is disengaged and the clutch engaegd is therefore greater according to the degree of depresaion of the accelerator. The invention is applied to the rear unit M, Fig. 1, of a changespeed gear comprising two epicyclic units A and M in series, a reversing gear B being interposed between the unit A and the engine clutch shaft 5, as described in Specification 484,301. The unit A also comprises a clutch-engaging piston 72 and a brake-disengaging piston 281, pressure fluid being supplied through a conduit 278 from the conduit 238 under the control of a toggle valve 150. A branch 318 from the conduit 278 leads to the space beneath a flange 327 of the sleeve 326. Thus, when fluid is being supplied through the conduit 278, that is when the unit A is giving solid drive, the sleeve 326 is lifted to increase the opening between the latter and the valve 320, whereby the pressure at clutch engagement in the unit M is further modified. The valve 150 is operated by a rod 113 under the conjoint control of the accelerator 303 and a governor G driven from the output shaft 8 of the gear B. A rod 110, moved to the left by the governor upon increase of speed, is connected to one end of a floating lever 111, the other end of which is connected to the rod 113. A rod 361, moved to the left as the accelerator is depressed, is connected to an arm 132, another arm 131 of which has a portion constituting the arm 122 referred to above. A pin 118 on arm 131 engages with play in an aperture 127 in an arm 121 loose on the shaft 120, a spring 125 being interposed between the arm 121 and a lever 116 loose on the shaft 120. A pin 115 on the lever 116 abuts against an intermediate part of the lever 111. Thus, after a slight depression of the accelerator, during which the play of the pin 118 in the aperture 127 is taken up, depression of the accelerator tends to close valve 150, to give reduced speed in unit A, while increase of speed tends to open valve 150, to give solid drive. Below a certain speed, the governor control insists on reduced drive in unit A, and, above, another certain speed, insists on solid drive, while between these limiting speeds the governor and accelerator jointly control the drive. The valve 168 is actuated by a lever 160 having a pin 159 engaging a cam slot 155 in a plate 126 rotated by movement of a control lever 301. The latter may occupy four positions, namely: (1) position R, in which gear B is put into reverse through a lever 102, valve 168 is closed so that unit M gives reduced drive, and a hook 156 on plate 126 prevents opening of valve 150, so that gear A also gives reduced drive ; alternatively, the hook 156 may be omitted so that unit A can change automatically ; (2) position N, in which gear B is in neutral and valve 168 is open; (3) position L, in which gear B gives forward drive and valve 168 is closed, giving reduced drive in unit M; and (4 position H, in which gear B gives forward drive and valve 168 is open, giving solid drive in unit M. The lever 116 has an arm 123 coacting with the cammed periphery of plate 126 so as to limit the counterclockwise movement of lever 116, consequent on depression of the accelerator, when the lever 301 is in position L. The conduit 238, together with a conduit 220 (shown in Fig. 12) leading to lubricating passages in the gear, is supplied by a double gear pump draining oil from a sump 219 and delivering past a spring-loaded check valve 200, which latter also functions as a relief valve. The larger unit of the pump is driven from the countershaft 20 of the gear B, while the smaller unit is driven from the shaft 8, so that a supply is ensured whenever either the engine or the vehicle is in motion. The springs associated with each brake are arranged as shown so that disengagement of the brake involves a successive stressing of a 'composite spring system. In the form shown in Fig. 12, the interior of the sleeve 326 communicates directly with the conduit 238, and the supply therefrom to the conduit 277, through the variable opening between the members 320 and 326, is controlled by the valve 168, which is modified accordingly. Pressure fluid also passes through the said variable opening into a conduit 277<1> to act on a piston 285<1> secured to the operating rod 280 of the brake associated with unit A, so that the amount of depression of the accelerator also has a modifying influence on the pressure in the clutch cylinder 71 of the unit A. In this form, also, an arm 131<1>, secured to the acceleratoroperated shaft 120, coacts with a plunger 413 movable, under the action of fluid supplied through a conduit 410 branching from the line 272, in a cylinder formed in a lever 116<1> which is pivoted at 411 and which carries the pin 115 acting in the floating lever 111. Thus, when unit M is put into direct drive, plunger 413 moves out, thus increasing the influence of the accelerator on the lever 111. Further, the plate 126 is rotated by the lever 301, not positively as in Fig. 9, but through a spring 416, and an arm 420 is moved anticlockwise by the rod 110, upon the occurrence of a predetermined speed, so as to prevent clockwise movement of plate 126 and thus prevent a change of unit M from solid to reduced drive. In a modification, the sleeve 326 is omitted, the valve 320 being urged upwards by the accelerator-controlled spring and downwards by the fluid pressure supplied through conduit 318. In the modification shown in Fig. 17, the plate 126 is formed with an arm 130 co-operating with the pin 115. The lever 301 is capable of occupying a fifth position; marked 3rJ, beyond position H, and in the corresponding position of the plate 126, in which the valve 168 remains open, the arm 130 moves the pin 115 so far to the left as to maintain the unit A in reduced drive below a predetermined speed. Above this speed, the unit A goes solid. Specification 503,312, [Group XXIV], is referred to.