Patent GB-662875-A (GB)
Title: Improvements relating to variable-speed power transmissions for motor vehicles
Inventor: ISSIGONIS ALEXANDER ARNOLD
IPC: F16H61/02
Filed: 1949-04-13
Abstract: 662,875. Change-speed gear. MORRIS MOTORS, Ltd. March 28, 1950 [April 13, 1949], No. 9985/49. Class 80 (ii) On a motor-vehicle, nested main friction clutches 1, 2 selecting two speed ratios, the lower including a free-wheel, are actuated through a common diaphragm 19, or individual diaphragms, Fig. 6 (not shown), by oil-pressure supplied to the diaphragm chamber 21 from a secondary chamber 33 of a control-valve unit 28, Figs. 1 and 3, this pressure being regulated by a contoured (e.g. conical) plunger 46, controlling a thin-edged, metering orifice 34, through which the secondary chamber 33 communicates with a primary chamber 32, supplied by the combined outputs of engine- and vehicledriven positive displacement pumps 23, 27, the speed-responsive pressure of which acts beneath a spring-loaded piston 36 integral and coaxial with the conical plunger 46 to govern pressure in the secondary chamber 33 in conjunction with a by-pass passage 49, controlled by a graduated valve 50 linked to the vehicle accelerator-pedal. The arrangement is such that downshift occurs at speeds considerably lower than those of upshift at the same throttle-opening. The speed-responsive pressure also provides automatic declutch at idle speeds, and the accelerator-controlled modulation causes shift-speeds both up and down to be increased with increased throttle-opening. Gear arrangement. In Fig. 1 the clutch-discs ], 2 of the cork-insert wet type, drive the front or rear axle 69 through low and high speed trains 8, 9 and 11, 12 respectively, which provide the only forward ratios; neutral and reverse being by sliding the low-speed pinion 8 to positions 8A and 8B respectively. A free-wheel is included in the lowspeed wheel 9 so that the diaphragm 19, after engaging the low-speed clutch 1, can have additional travel for engaging the high-speed clutch 2 at a higher oil-pressure without freeing the low-speed clutch 1. A small leak hole 20 permits the oil to fill the whole of the clutch casing, thus balancing centrifugal pressure on the diaphragm 19. In Fig. 6 (not shown), the shaft of the wheels 11, 12 is extended to form the two-speed countershaft of a gear having three or four additional manually selected ratios, and a clutch-pedal is provided to control a valve (Figs 7 to 9, not shown) for exhausting the clutch chamber 21 and its supplyline, to disengage both clutches 1, 2 during a shift between the manual ratios, in each of which latter two ratios are obtainable by the disc clutches 1, 2. Fluid control system. The positive displacement engine-driven pump 23, aided by the similar vehicle-driven pump 27, feeds a common inlet 31 to the control valve-unit 28, Figs. 1 and 3, through the metering orifice 34 of which the oil passes to a delivery duct 45 feeding the clutch diaphragm chamber 21 through a line 18. Speed-responsiveoil-pressure produced by the pumps acts in the primary chamber 32 below the piston 36, loaded by low- and high-rate springs 38, 39, the latter, which is adjustable, also loading a disc-valve 41, which, at idle speeds, opens to permit flow to exhaust at 44. pressure at this time being insufficient to cause clutch-engagement, although there is a slight flow to the clutch-chamber 21 escaping through the leak-hole 20. The conical plunger 46 controls the flow-area through the orifice 34 and hence clutch-delivery pressure, and at the end of the conical portion 46 is a groove 47, followed by an enlarged cylindrical portion 48. Increase in engine-speed increases pressure in the primary chamber 32, thus raising the piston 36 and increasing the spring-loading on the disc-valve 41 to cause increased delivery pressure in the secondary chamber 33, which engages the lowspeed clutch 1 and starts the vehicle. With further increase in speed, the conical portion 46 rises out of the orifice 34 and the groove 47 registers with it, causing a sudden increase in the flow passage, so as to permit further considerable rise in speed with but little movement of the piston 46. At an upper limit in speed (e.g. corresponding to 30 m.p.h. ot the vehicle in low gear) the lower cylindrical portion 48 of the piston stem occupies the orifice, resulting in a sudden increase of pressure under the piston 46, which rises rapidly to its highest position, fully compressing the loading-spring 39 of the disc-valve 41, thus increasing delivery pressure sufficiently to engage the high-speed clutch 2. With the cylindrical portion 48 occupying the orifice 34, sufficient pressure is maintained to keep the high-speed clutch engaged until engine speed has decreased to a considerably lower value (e.g. corresponding to a vehicle speed of 20 m.p.h. in high gear) than the upshift (e.g. corresponding to 30 m.p.h. in low gear), at the same throttle-opening, the downshift speed being determined by the clearance provided between the cylindrical portion 48 and orifice 34. To provide gradual shift action, the delivery line between the control valve outlet 45 and the clutch chamber 21 includes a "retarder," comprising a piston 53, Fig. 4, having an orifice 55 controlled by a convex member 56 over which the piston moves axially in either direction according to pressuredifferential in opposition to springs 54 which normally bias the piston into the minimum flow position shown. Piston movement is damped by a dashpot orifice 61, so that any sudden increase in pressure-differential only slowly increases the flowpassage, thus retarding both engagement and disengagement of the high-speed clutch 2. Alternatively an air-bottle may be included in the clutch-line, or the breathing capacity of the diaphragm chamber may be increased. Oil viscosity compensation may be provided for by a tortuous passage 62, Fig. 5, through which the pumped oil normally flows into the delivery duct 31 to the control valve 28, the inlet to this passage 62 also communicating through a passage 63 with a compensating chamber above an additional piston 65 on the lower end of the control-valve piston 36, Fig. 3. Pressure increase at the inlet to the passage 62 due to increased oil viscosity (e.g. at low temperatures), acts downwardly on the compensating piston 65, assisting the loading springs 38, 39, Fig. 3, of the control-valve piston and thus compensates for the increased upward pressure on the main piston 36 due to the same cause. A spring- loaded by-pass valve 67 relieves excess pressure in the compensating line at high speeds, and oil passing under the compensating piston exhausts at 66. Reduced reverse pressure. Sliding the low-speed pinion 8, Fig. 1, to neutral or reverse positions 8A or 8B, causes a plunger 75 to reduce the spring- loading on a ball relief valve 73, so that the available pressure in the clutch line 18 is sufficient to operate only the low-speed clutch in neutral and reverse.