ROAD-SPEED RELATED SHIFT-LOCK FOR GEAR-TRAINS

摘要

The invention is concerned with a road-speed related shift-lock for gear-trains, for preventing engagement of a reverse gear in a motor-vehicle gearbox when the vehicle is moving at a speed higher than a predetermined speed and in the forward direction, the reverse-gear comprising a coupling element which is secured against rotation relative thereto and has external teeth adapted to engage internal teeth of a sliding sleeve upon the engagement of the reversegear. The shift-lock according to the invention is characterized in that a locking ring is arranged between the reverse-gear and the coupling element, the locking ring comprising two half-shells held together by a spring substantially encompassing the half-shells. Each halfshell comprises on a side facing the coupling element a locking lug provided with an annular surface and a chamfer which define a step. The coupling element has in its periphery axial recesses adapted to receive the respective locking lugs of the half shells and the sliding sleeve has an internal bore and a chamfer extending parallel to the chamfer of the locking lug. When the vehicle moves at a speed higher than the predetermined speed, centrifugal forces cause the half-shells to move radially outwardly against the retaining force exerted by the spring such that the internal bore of the sleeve slides over the annular surface of the locking lug until the chamfer of the sleeve abuts against the chamfer of the locking lug, thereby preventing further movement of the sleeve and thus engagement of the internal teeth of the sleeve with the external teeth of the coupling element.