Patent GB-616533-A (GB)
Title: Improvements in or relating to gear shifting mechanism
IPC: F16H61/02
Filed: 1945-07-19
Abstract: 616,533. Variable-speed gearing; screw-andnut gearing. STEVENS, A. H. (Eaton Manufacturing Co.). July 19, 1945, No. 18513. [A Specification was laid open to inspection under Sect. 91 of the Acts, Dec. 13, 1945.] [Classes 80 (ii) and 80 (iii)] A shiftable sleeve 70 carrying a sun gear 72 of an epicyclic two-speed gear combined in the driving axle of a vehicle with the differential gear is adapted to be pre-loaded by a selective operation on the part of the driver and then operated to effect the speed change by a release of the driving torque such as by the driver lifting his foot from the accelerator pedal. As shown in Fig. 2, the ring gear 56 of the axle gear has an annulus 66 secured thereto which drives the planet cage 34 of the normal differential unit, which carries the planet pinions 46 of the epicyclic gear, either at a reduced speed by holding the sun gear 72 or directly by locking the epicyclic train. In the position shown, the sun gear is held by teeth 74 engaging teeth 76 on the fixed housing 20. On movement of the sleeve 70 to the right by an actuating lever 80, the teeth 74, 76 disengage and the sun gear 72 engages with teeth 42 on the cage 34 to lock the epicyclic train. The actuation of lever 80 is effected by means of a selecting switch 196, Fig. 1, on the conventional gear lever 190, a reversible electric motor 150 and a spring unit 100. The switch 196 controls the operation of the motor 150 which drives through a screw-and-nut mechanism 160, 164, Figs. 5 and 7, an arm 132 of a pre-loading member 112 of the spring unit 100. This member 112 is pivoted on a. shaft 108 and has an axial projection 136 adapted to engage either end 142 or 144 of a helical spring 140, the other end of which engages with a similar axial projection 134 of a driven member 110 of the spring unit. The member 110 has a ball- and-slot connection 118, 120 with one end of lever 80, the other end of which actuates sleeve 70. The arrangement is such that the axial projection 136 on member 112, which is at a smaller radius than the projection 134 on member 110, moves in either direction to load the spring 140 which thus acts on member 110, the motor being switched off automatically after the desired movement of the arm 132 by operation of a spring contact 186 by the arm. Movement of member 110 and hence the sleeve 70 to effect a speed change is prevented whilst torque is being transmitted by the friction between the gear teeth of the epicyclic train, but as soon as this torque is relieved the spring 140 moves member 110 to actuate lever 80 and sleeve 70. The screw-and-nut mechanism 160, 164, Fig. 7, comprises a helical groove 167 on the screw 160, a series of annular grooves 168 in the nut 164 and a single interengaging ball 169 in each of the grooves 168 held in position by a cage 170. Rotation of the screw 160 rolls the balls around it at a slower speed and moves the nut axially at approximately half the pitch movement of screw 160. At each end of its travel the nut is arrested by the end balls coming up against stops 171 in the thread groove 167 of the screw 160, the balls then sliding round in the annular grooves 168 in the nut. This allows the motor to continue running under its inertia without damage to the mechanism and without the provision of a brake. A spring clip 173 carried by the nut 164 engages a hexagonal head 172 on the motor shaft at the ends of its travel to hold the nut resiliently in its end positions. The control switch 196 is preferably in circuit with an ignition switch 204 and a switch contact 230 operated by the member 110 of the spring unit 100 is adapted to operate a change speed device 210 for the normal speedometer drive.