Patent GB-625416-A (GB)
Title: Improvements in and relating to variable-speed transmission mechanism
IPC: F16H61/02
Filed: 1945-10-10
Abstract: 625,416. Hydraulic power transmitters ; fluid - pressure servomotor control systems. PACKARD MOTOR CAR CO. Oct. 10, 1945, No. 26438. Convention date, Oct. 24, 1944. [Classes 69 (ii) and 135] [Also in Groups XXIV and XXVI] In a transmission mechanism for motor vehicles having both a variable-speed gear in which two fluid-actuated devices are alternatively effective to establish different speeds and a forward-neutral-reverse clutch, the clutch shift mechanism operates a valve which, when the clutch is moved to neutral position, shuts off the pressure fluid from one of the devices to render the gearing inoperative. With the clutch in forward or reverse drive position, the fluid-actuated devices are rendered alternatively effective by torque-speed responsive means operating a second valve, over-riding manual control means acting through a solenoid on a third valve being provided. As shown, the gearing comprises stepped planet gears 37 ... 39, Fig. 1, meshing respectively intermediate and low-speed driving suns 33, 34, and a driven sun 35. The suns 33, 34 are powered from the two runners 23, 22 of a fluid main clutch 13, directly and through an over-running coil clutch 32 respectively. The clutch 13 is of the kind having a continuous flow through the impeller 20 and runners 22, 23, (the runner 22 having an outer ring 24 and an inner perforated disc 25), and is so constituted that at light loads, or when starting up, the runner 22 and gear 34 take the drive whilst, when the liquid force in the clutch increases, drive will pass to the runner 23 and gear 33, the gear 34 over-running. The gearing is controlled by a reaction brake 50 and a multiplate direct-clutch 55, forming the two fluid-actuated devices referred to above. The brake 50 stations the planet carrier 40 during the above-mentioned low and intermediate speed indirect drives and the clutch 55 connects the carrier 40 and the driven shaft 16 of the gearing to lock the gearing solid for a high speed direct drive. Reversing-gearing.-The shaft 16 is connected to a load shaft 19 by a conventional forward-neutral-reverse synchromesh clutch, the movable member 95 of which is slidably splined on the planet carrier 93 of an epicyclic reversing gearing, the sun 94 and annulus 90 of which are rigid with the shafts 16, 19 respectively. The clutch member 95 can be moved from a central neutral position to engage either clutch teeth 99 on the annulus 90 to lock up the reversing gearing for a direct forward drive or fixed detent teeth 97 on the casing 10 to station the carrier 93 for reverse drive. The member 95 is manually operated from a dashboard button 106, Fig. 3, through a flexible cable 105 and yoke lever 103. Friction clutches and brakes.-The brake 50 comprises a band encircling the carrier 40, one end of the band being anchored to the casing 10 and the other being connected to the piston of a brake-operating cylinder (not shown). Both the clutch 55 and brake 50 are supplied with operating fluid such as lubricating oil from one gear pair of an engine or otherwise driven dual gear pump (not shown), the other gear pair of which supplies the fluid clutch 13. The pump feeds a conduit 72, Fig. 3, in constant communication with the brake-operating cylinder, and connected to the clutch-operating cylinder 63, Fig. 1, via a valve block 70 and conduits 69, 75, 76, 77. A cut-away valve member 73 in the block 70 is so linked to the lever 103 that fluid passes to the cylinder 63 when the clutch member 95 is in forward or reverse drive position but is cut off therefrom when the member 65 is in neutral. Below a predetermined operative pressure of the fluid, the clutch 55 is held disengaged by springs 62<SP>1</SP> and the brake 50 is held engaged by a spring in the brake-operating cylinder, whilst above this pressure the clutch engages and the brake is released. With the valve member 73 open, the fluid pressure in the whole system is maintained above the predetermined value by a spring-loaded relief valve 79 unless the conduit 76 is opened by a byepass passage 78 by the registration therewith of passage 83, Fig. 4, in a sleeve 82 turnable on the shaft 16, when the pressure falls below this value. The setting of the sleeve 82 is controlled by a torque-speed responsive device which drivingly connects the sun 35 and shaft 16 and comprises centrifugal weights 48, Fig. 4, which are pivoted on pins 49 on an extension 42 of the shaft 16 and carry turnable pins 46 slidably engaged by arms 44 on a spider 36 rigid with the sun 35. The direction of rotation is such that the transmission of torque through the weights 48 tends to collapse them against the action of centrifugal force and, through links 85 connecting the weights and sleeve 82, turn the latter from the position shown until the passages 78, 83 register. The gearing thus selects automatically between direct and indirect drive according to the conditions of speed and torque. To reduce vehicle creep through the fluid clutch 13 at idling engine speeds, spring-loaded plungers 120 act to hold the weights out against torque when the vehicle is at rest in gear with the engine running, so as to bring in the high speed ratio. The plungers 120 also act as air dashpots to damp sudden movements of the weights 48 in either direction, stems 121 being provided passing completely through the weights for this purpose. Over-riding manual control to force change-down from high speed is provided by a second relief valve 111, Fig. 3, slidable against spring action in the block 70 to open the conduit 72 to exhaust when a solenoid 113 is energized by closing a dashboard switch 116. With the valve member 73 shut and fluid cut off from the cylinder 63 so that the clutch 55 disengages, the pressure in the conduit 72 builds up sufficiently to disengage the brake 50 also, and the variablespeed gearing is rendered completely inoperative.