Patent GB-524517-A (GB)
Title: Improvements in or relating to change-speed power transmissions for motor vehicles
IPC: F16H61/02
Filed: 1939-01-31
Abstract: 524,517. Change-speed gearing ; positive clutches; yielding couplings; fluid-pressure servomotor-control systems. CHRYSLER CORPORATION. Jan. 31, 1939, No. 3285. Convention date, May 13, 1938. [Class 80 (ii)] [Also in Group XXIX] Two-speed auxiliary planetary gearing C, Figs. 1 and 9, on a motor-vehicle is controlled in part by the engine accelerator-pedal 248, depression of which beyond the full-open position releases the higher speed (direct-drive) and allows a previously-overrunning lower speed (geared underdrive) to become. effective. Engagement of the higher-speed is automatic in response to vehicle-speed unless prevented by either the accelerator-pedal or a manual overriding control described below. The underdrive gear is used to produce an effect similar to existing auxiliary two-speed overdrive gears, this effect being obtained by the use of a higher axle-ratio (3.5) than that (4.3) customarily used, whereby direct-drive in the underdrive gear provides a ratio equivalent to existing overdrive ratios, whilst underdrive therein is the equivalent of existing direct-drives. The provision of the "step-down" accelerator pedal control places at the disposal of the driver an easy and natural means of changing down for acceleration purposes and advantage is taken of this control to allow the higher ratio (quasi-overdrive) to be introduced automatically at a considerably lower speed (20 m.p.h.) than that (40 m.p.h.) at which existing overdrive gears customarily become effective, whereby the higher-ratio is used to a much greater extent than existing overdrives and is available even in city traffic. The two-speed underdrive gear is arranged in front of, i.e., on the unmultiplied torque side of the main change-speed gear D which is of the countershaft type providing two synchromeshed speeds and reverse, this arrangement providing four forward speeds and two reverse speeds. The engine may be connected to the underdrive gearing through a hydraulic clutch B, Fig. 9, a simple disc clutch, a spring coupling or directly. In the last two cases the clutch of the transmission is provided by friction drive disconnecting means in the underdrive ratio. The underdrive gear comprises a driving annulus 72, Fig. 9, integral with the driven shaft 64 of the hydraulic main clutch B, a planetcarrier 77 fast on the driven shaft 70 and a loose sun-wheel 80, the backward reaction of which in geared drive is taken to the casing through a one-way device F and a controllable friction disc-brake G. A multi-disc friction clutch J connects the loose sun-wheel 80 directly to the driven shaft 70 for solid drive. Engagement of the direct-drive clutch J, with consequent overrun in the one-way detent F, is effected by oilpressure acting on an annular piston K and supplied by a gear-pump L on the driven shaft 70, the pressure being responsive to the speed of that shaft in such a manner that the direct-drive clutch J is automatically engaged at a predetermined vehicle speed of 20 m.p.h. with the following countershaft gear D in direct-drive. The delivery port 168, Fig. 19, of the pump L, which is described below, communicates with the direct-drive clutch-motor K through a pistonvalve 181 and passages 171, 172, 176, Fig. 9, the piston-valve being controlled by the "step-down" accelerator and other controls as follows. Depression of a manual dash-board push-button 198, Fig. 1, acts through a Bowden cable 197 and a three-armed lever 190, Fig. 19, to close the valve 181 against a spring 185, thereby locking out the high-ratio direct-drive under all conditions. The valve 181 is similarly and independently closed by energization of a solenoid O, which takes place whenever the acceleratorpedal 248 is depressed beyond the wide-open throttle position so that a projection 267 on a lever 265 rocked by the accelerator-pedal closes a switch 269, completing a circuit to earth 242 from a battery 231, through an ammeter 233 and the solenoid O. The yielding of a spring 264 in the throttle-rod 256 causes the operator to feel an additional resistance during this overtravel of the accelerator pedal for shifting down to underdrive. The planetary unit C is maintained in underdrive until the accelerator pedal is fully released, whereupon a spaced projection 266 on the lever 265 opens the switch 269, de-energizing the downshift solenoid O. The spring 185, Fig. 19, thereupon returns the valve 181 to the upward open position shown, return movement being retarded by an air dashpot N so that reengagement of the direct-drive clutch J is cushioned. The servo-oil pump L, Fig. 9, is of known type comprising an inner driving tooth wheel 152, keyed to the driven shaft 70 and meshing with a surrounding loose eccentric internally toothed wheel 156 having one tooth more than the inner wheel. The pump L also lubricates the planetary gear by supplying pressure oil to an axial boring 169, Figs. 9 and 19, extending the full length of the driven shaft 70 and feeding the gears and clutches through the various radial borings shown. The oil-supply also extends rearwardly to the countershaft unit D. Pressure-oil always reaches the internal boring 169 through a crescent-shaped space 276, Fig. 19, a bleed opening 287 in an excess pressure relief-valve 284 and a radial boring 292 in the shaft 70. At a predetermined pressure, the valve 284 opens and supplies the excess to the lubrication system. In order to provide a means for declutching the planetary unit C entirely, the underdrive reaction brake G can be released by pressing down a pedal 129, Fig. 1, which is used like a clutch-pedal, and creates oil-pressure in a master cylinder 125 communicating with a group of interconnected brake-releasing pistons H, Fig. 18. At the same time the pedal 129 mechanically or hydraulically closes a switch 225 which independently energizes the valveoperating solenoid O whereby the direct-drive clutch J is also disengaged. When the hydraulic clutch B is provided, the pedal 129 is used only to remove the drag of the hydraulic clutch to allow a gear to be engaged in the countershaft unit D when starting the vehicle from rest. When no main-clutch is provided, the pedal 129 is used as an ordinary clutch-pedal. The two shifter-rods 367, 369, Fig. 15, of the associated countershaft gearing are remotely controlled by a manual lever 311, Figs. 2 and 3, mounted on the steering column 301, the lever having the usual H-movement with the exception that the one leg of the H in alignment with the reverse leg is omitted since the lever controls only two speeds and reverse. The inner end of the shifter-lever 311 is forked and pivoted to an internal tube 303, which turns with the lever 311 for establishing the gears through links 342, 347, Fig. 1, and a lever 348 on a rockshaft 349, Figs. 1, 14, 15. In the normal position shown, this movement of the shifter-lever 211 between the positions 311<1>, 311<11>, Fig. 2, establishes low-speed and direct-drive respectively, an arm 360, Fig. 15, on the rockshaft 349 being in engagement with the shifter-rod 367 controlling these speeds. Upward movement of the shifter-lever 311 causes it to rock on a fulcrum 308, Fig. 3, impart an axial downward movement to tube 303, which is transmitted through a Bowden cable 339 to effect a cross-shift of the rockshaft 349, disengaging it from the low- and high-speed selector-rod 367 and engaging it with that 369 for reverse which is engaged when the shifter-lever is swung forwardly towards the position 311'. The Bowden cable 339 terminates in plungers 319, Fig. 1, and 358, Fig. 14, which always bear respectively on segments 318, 357 turning with the connected members 303, 349 so that the cable is always effective. A spring 370, Fig. 14, biasses the cross-shift mechanism and shifter-lever 311 into the plane for selecting low and high forward speeds, and a spring detent 317. Fig. 3, locates the shifter-lever in its operated positions. In order to eliminate the necessity for actuating the clutch-like pedal 129 for making changes in the countershaft unit D whilst the vehicle is in motion, the movement of the lower end of the shifter-tube 303 is arranged to close a switch 334, Fig. 1, energizing the solenoid O thereby releasing the direct-drive clutch J in the planetary unit C. Release of the brake G therein is unnecessary since reaction is taken thereto through the one-way detent F. The switch 334 is actuated by a spring-pressed plunger 326, Fig. 7, which, in gear and neutral positions, lies in one of three axial grooves 322 in a segment 321- carried by the'shifter-tube 303, and is cammed upwardly to close the switch 334 whenever the shifter tube is turned out of such positions, whereby the direct-drive clutch J is released during the shift and re-engaged after it. The countershaft unit D comprises a driving shaft 70, Fig. 11, which is the driven shaft of the preceding planetary unit C, and an aligned driven shaft 391. Reverse is by sliding a normally stationary idler into mesh with wheels 413, 414 respectively on the countershaft and driven shaft, whilst the two forward speeds are controlled by a double synchromesh clutch of the blocker type. This clutch comprises a dogclutch barrel 384, splined to a member 403 fast on the driven shaft 391 and carrying synchronizing cones 399 and 407 for frictional engagement with the wheels 396 or 408 to be clutched. The positive clutch-barrel 384 is frictionally connected with the synchronizing cones by an expansible friction ring 406 which, on the first axial movement of the positive barrel 384, produces frictional engagement of the respective cone, thus turning the latter relative to the positive barrel so that blocker teeth 400 on the synchronizing cone obstruct further axial movement of the positive barrel until synchronization is effected, whereupon the barrel slips over the ring 406 and engages clutch teeth 397 or 409 on the respective wheels. In modifications,