GB638993A - Improvements in and relating to change speed gearing for motor vehicles and other purposes - Google Patents

Abstract

638,993. Controlling change-speed gearing. WILSON, W. G. March 11, 1947, No. 6805. [Class 80 (ii)] In an epicyclic gear having a rotatable member capable of axial displacement for effecting frictional engagement of a toothed element of the gear alternatively with another toothed element thereof or with fixed reactions means to afford direct drive or a higher gear ratio respectively, helical surfaces on said axially displaceable member are engaged with helical driving surfaces for effecting said axial displacement in accordance with change in the direction of transmitted torque, and means are provided for frictionally arresting rotation of the axially displaceable member independently of torque to provide the higher gear ratio. As shown, applied to a motor vehicle overdriving auxiliary gear box, a helicallytoothed sun gear 4, Fig. 1, meshing planets 3 on a driving carrier 2 is axially movable under normal driving torque reaction to engage a clutch member 9 thereon with a driven annulus 7 for direct drive. Reverse torque, as when the output shaft drives the input shaft, moves the sun 4 in the opposite direction to engage the member 9 with a co-acting braking member 14 on the fixed gear casing and bring in the epicyclic overdrive. This overdrive may also be engaged at any time without interruption of drive by a braking member 20, co-acting with the member 9 to force it into engagement with the casing, and operated against spring pressure by the admission of pressure oil behind a piston 17. A valve 27, Fig. 4, controlling the supply of oil to the piston 17 is operatively connected through a floating lever 29 with both an engine driven speed governor 28 and the linkage between the engine throttle 23 and accelerator pedal 23a. The valve 27 is normally closed, but is opened on accelerator release or excessive engine speed. A manually-operated mechanical control for the braking member 20 may replace the above control system or a governor responsive to the output speed of the gear may be used. In Fig. 2 (not shown) straight-toothed spur gearing is used, the sun gear not being itself axially movable but having a helical spline connection with an axially movable drum provided with clutching and braking means co-acting with the annulus and casing on the side of the gearing remote from the splining so as to eliminate unbalanced axial thrusts. A separate brake member rotatable with the sun gear is engaged by a brake hydraulically or manually operated as before. According to the Provisional Specification the braking member on the casing may engage both inner conical surfaces of the member 9. The Provisional Specification also describes a gearing in which a helically-toothed sun gear and a drum helically splined on an extension of the gear have opposite axial movements under torque reaction, and are both provided with clutching and braking surfaces, the sun gear engaging the planet carrier and the drum the annulus for direct drive, and both members engaging the casing for overdrive. A separate brake member rotatable with the sun gear is engagable by a hydraulically-operated brake as above.