A valve system for use in internal combustion engines includes a means for controllably varying the preload force imposed on a valve spring in correlation with engine speed. At low engine speeds the preload force is maintained at a minimal level whereby the normal load at the cam/follower interface is maintained at a minimal value. At higher engine speeds, the preload force on the valve spring is selectively increased to assure positive closure of the valve head. The increased preload forces are imposed by extending a hydraulically actuated, moveable spring seating surface whereby the installed length of the spring is shortened. The hydraulic actuating fluid is continuously circulated through inlet and outlet ports, communicating with an expandable chamber associated with the moveable seating surface, during low engine speed operation to abate the problem of temperature rise in static fluid systems.
Jongmin Lee;Susumu Ariga