Patent GB-717868-A (GB)
Title: Improved variable-speed power transmission mechanism for motor vehicles
Inventor: HERNDON WALTER B
IPC: F16H61/02
Filed: 1952-04-07
Abstract: 717,868. Variable-speed gear. GENERAL MOTORS CORPORATION. April 7, 1952, No. 8813/52. Class 80 (2) [Also in Groups XXIX and XXXIV] On a vehicle, automatic shifts between three forward speeds under fluid servo pressure are controlled by a valve 200, Fig. 5, in a rotating block 150 and secured to a centrifugal mass 170, outward movement of which, to induce the automatic upshifts, is opposed first by springs 172 and later in two successive steps, by accelerator-pedal responsive i.e. "TV" pressure acting on pistons 215 and 214, 216. "TV" pressure is also used throughout the servo system. Shifts between second and third speeds have timed torque-overlap by a servo relay-valve 190, Fig. 5, whilst those between first and second act by overrun action in a one-way clutch 34 in first speed. A fluid-coupling 4, Fig. 1, drives in the two reduced and one reverse countershaft-geared ratios only, being by-passed by a direct-drive friction clutch 9, Fig. 1, for third speed. A steering-column mounted manual control lever 250, Fig. 7, moves in one plane between positions forward, neutral, reverse, FNR and beyond F to a towed start position TS. In the FN range the lever can be lifted to enforce a fixed second speed and depressed for fixed first. The control also includes a reverse idler disc brake, Fig. 11, which is applied automatically through a vacuum servo 62, Fig. 2, to kill idledrag of the fluid-coupling whenever the manual lever is moved from neutral towards reverse. Gear arrangement. The front end of the output shaft 50, Fig. 1, pilots in the aligned input shaft 1 and has fast on it a clutch-drum 11 which houses second- and third-speed disc clutches 8, 9 and the control valve-block 150. In first speed drive passes from the input shaft through the fluid-coupling impeller 4 and turbine 5, sleeve 6, pinion 13, countershaft wheels 24, 26, slidable wheel 47a, now meshed with 26, oneway .clutch 34 and splined inner hub 27, now mesh splines y on the shaft 50. For second speed, the automatic valve system, described below, directs oil pressure through a passage 53, to a piston 52 engaging the second speed clutch 8, whereupon drive passes, as before, through the fluid coupling and pinion 13, to the countershaft wheel 24 and thence through wheels 25, 10, sleeve 7, second-speed clutch disc 8 and drum 11 to the output shaft 50, the low-speed one-way clutch 34 then overrunning. For allmechanical direct drive the automatic valve system exhausts the second-speed clutch piston 52 and supplies pressure through a passage 54 to a piston 51 engaging the high-speed clutch 9, directly connecting the input and output shafts 1, 50 through the drum 11. The pressure-areas of the clutch-pistons 51, 52 are proportioned to their torque-demands, or the friction coefficients may be so proportioned (e.g. 0.204 for clutch 8, 0.276 for 9). The manually-shifted slidable wheel 47a has four positions; neutral as shown; an intermediate forward position meshing the countershaft wheel 26 and output-shaft splines y, as above described for low speed automatic; an extreme forward position in which teeth 30 on the inner hub of the one-way clutch 34 of the wheel 47a directly mesh teeth 31 on the gear 10 for producing a bi-directional positive second speed, still through the fluid-coupling, but independently of the friction clutches, for towed starting (shift-lever position TS); and an extreme rear position in which internal splines in the wheel 47a mesh shaft-splines, and the wheel meshes an idler 45 fast to a similar wheel 45a permanently meshing the countershaft wheel 26, for reverse. Anti-drag brake. Between the coupled reverse idlers 45, 45a are two groups of brakediscs 55, 56, Fig. 11, splined alternately to the idlers and to a stationary arm 58, Fig. 2, held against the fixed casing by a spring 63. The brake disc groups are spread apart, to brake the idlers and thus overcome idle-drag of the fluidcoupling by turning a lever 59a having cam- and-ball engagement 60 with the stationary arm 58, and operated by applying engine suction at 56 to the underside of a spring-released piston 62, Fig. 2, such application occurring automatically whenever the manual shift lever is moved to reverse from neutral, when the output shaft is stationary, as described below. Manual shift system. Turning movement of the manual shift lever. 250, Fig. 7, turns a sleeve 120 together with an inner rod 118, Fig. 3, whilst its upward and downward movement moves the rod 118 axially downwards and upwards respectively. The turning movement slides the low-reverse wheel 47a, Fig. 1a, through an arm 120d, fast on the sleeve 120, and a link 37, spring connected to an arm 36 fast on the rockshaft of a selector fork 32, Fig. 2, of the wheel 47a, which is located in operative positions by a spring-detent 32c. Fast on the inner shaft 118 but axially slidable in a slot in the outer sleeve 120 is a cam-block 120a having a cam-nose 120b which as the manual shiftlever is turned from or through neutral to position R, for reverse, depresses, through a plunger 76 and a spring 77, a valve 70, cutting off a vent 74 from and supplying engine-suction from an inlet 71 to the feed-line 66 of the vacuum piston 62, Fig. 2, which applies the idler brake 55, 56, Fig. 1a, as above described, thus preventing idledrag and facilitating rearward shift of the slidable wheel 47a into reverse. If, however, the vehicle is moving, a servo-supply pump Q, Fig. 13, driven at 50b, Fig 1a, by the output shaft 50, supplies oil pressure through a line 103, Fig. 3, to a spring-loaded piston 79, moving it rightwards to the position shown, in which it obstructs opening movement of the valve 70, so that action of the cam 120b merely compresses the spring 77 without causing suction to be supplied to the brake-piston 62, and the idle-drag brake is not called upon to brake an inertiaload beyond its capacity. The movements of the cam-block 120a are controlled by a pin 212 thereon, moving in an opening in a fixed plate 211, so patterned Fig. 4, (not shown) that axial movements of the block, with the rod 118, are permitted only between neutral and forward. Downward movement of the rod 118, caused bv raising the manual lever 250 between F. and N. positions for enforced second speed, turns a spring-loaded lever 117, about a fixed pivot 117b, which, through a link 115, Fig. 2, and rockshaft 114a, disables the automatic system decribed below, by operating a manual valve 180, Fig. 13. which selects the clutch 8, for bi-directional second speed. Downward movement of the shift lever 250 moves the valve 180. oppositely to exhaust both clutches 8, 9 thus enforcing freewheeling low, both these drives being through the fluid-coupling, and being maintained as long as the operator maintains the requisite upward or downward pressure on the lever, automatic working being restored by spring centralizing of the valve 190, as soon as he releases the lever. Fluid system. The main servo-supply line 110 is fed in common by an input-driven pump P Figs. 1 and 13, and the output driven pump Q the latter including a non-return valve 111. The supply line 110, branches to a pressure regulator 105, loaded by springs and, through a cam 175, and linkage 173, 172, Fig. 7, by the accelerator pedal 170a which latter regulates between a range of 50-130 lb/sq. in., and also feeds two ports 180, 185 of the manual valve 180. The spillport 108, of the regulator feeds the fluid coupling through a line 41 including a secondary regulator valve 221 set for 30 lb./sq. in. and inside the coupling is a relief valve 45, spilling to the clutch surfaces. In the central position of the manual shift lever 250 and between its FN range, shown, the pressure port 181 feeds a line 182 leading through a radial shaft-bore 16, Fig. 1a, and cylindrical space around an internal tube 15 to a feed-port 86 of the valve-block 150, and thence through a passage 206, Fig. 5, branching to a supply-port 204 of a centrifugal valve 200, and, through a passage 199 to a common peripheral chamber 207 where it acts radially inwards on three spring-loaded pistons 214, 215, 216 which oppose in two steps the outward movement of a radially-guided centrifugal mass 170 secured to and operating the centrifugal valve 200. Since the regulated pressure is accelerator responsive, the centrifugal valve is responsive jointly to output shaft speed and accelerator position. The centrifugal valve 200 feeds the clutches through a timing valve 190 providing torque overlap for shifts between second and third as follows. Automatic shift. Shifts between first and second require only application or release of the second speed clutch 8, which causes over-run or take up in the low-speed one-way clutch 34. Initially in low speed the centrifugal valve 200 is in its outer extreme position, outwards of that shown in Fig. 5, blanking its feed port 204, and its outer end uncovering a lateral exhaust port 220a to a port 201 leading to a port 193 of the timing valve 190, which in its initial position shown, connects port 193 to a port 194 leading radially outwards to the supply passage 53, Fig. 1 of the second speed clutch 8 which is thus exhausted. The third speed clutch supply passage 54 is connected directly to the timing valve port 192 now exhausted through port 191 and the open port 205 of the centrifugal valve. With increase in output speed the centrifugal valve 200 moves inwards opposed first by only the springs 172 and later by the central piston 215, until it pressurises the port 201, supplying the second speed clutch passage 53 through the ports 193, 194 of the timing valve, without moving the latter. The second speed clutch 8 then engages. With further increase in output speed the centrifugal valve 200 moves inwardly; now in opposition additionally to "TV" pressure on the two outer pistons 214, 216, finally pressurising the port 205 leading through the timing-valve ports 191, 192 to