A valve assembly for operating and providing variable timing of a gas exchange valve for an I.C. engine

摘要

A device to activate a gas exchange valve of an I.C. engine comprises an upper camshaft 2 having a cam 4, a lower camshaft 3 having a cam 5, the cam 4 of the upper camshaft 2 and the cam 5 of the lower camshaft 3 operating a single valve 1 where the cam 4 of the upper camshaft 2 acts on a first rocker arm 6 mounted on a first fixed shaft 7, and a second rocker arm 9 is mounted on a second mobile shaft 8 located on the first rocker arm 6 at an end distanced from the first shaft 7 and which provides greatest rocker movement, the second rocker arm 9 comprising a first and second portions 9a, 9b extending on each side of the mobile shaft 8, and the cam 5 of the second camshaft 3 acting on the first portion 9a of the second rocker arm 9 to open the single valve 1. Closure of the valve 1 is provided by the upper camshaft 1 so that variation in the point of commencement of opening may be completely disassociated from the point of closing. A second aspect to the invention is provided by a mechanism installed between a camshaft driving gear 13 and the camshaft 2, 3 of the engine comprising a sliding bushing 14 having an inside and outside set of helical teeth 15, 16. The teeth cooperate with helical teeth 18 on the camshaft 2, 3 to provide relative rotation between the camshafts and a crankshaft of the engine in order to provide variable valve timing at different engine speeds and conditions.