Hydraulic valve lifter mechanism for internal combustion engine

Claim 1

In a valve train for an internal combustion engine, having a lobed cam mounted on a camshaft and a push rod linked with a valve to be intermittently opened according to the rotation of the cam, a hydraulic valve lifter mechanism comprising: a hollow cylindrical body which has an open end and a closed end and is slidably received in a bore formed through an engine block such that said closed ends keeps sliding contact with said cam; a piston connected to said push rod and slidably received in an end portion of said bore; a plunger which is slidably received in said bore and in an end portion thereof slidably intrudes into said cylindrical body so as to define a first oil pressure chamber in a closed end portion of said body and a second oil pressure chamber in said bore between said plunger and said piston; means for applying an oil pressure which is variable depending on the operating condition of the engine to said first oil pressure chamber; and an oil-reversing chamber formed in said engine block so as to communicate with said second oil pressure chamber through a hole which is open to said second oil pressure chamber while said oil pressure is relatively low so that said plunger is relatively distant from said piston but is closed by said plunger while said oil pressure is relatively high so that said plunger is moved relative to said body towards said piston, whereby the amount of lift of said valve depends on said oil pressure applied to said first oil pressure chamber and, in a medium range of said oil pressure, the amount of the valve lift varies depending on a resistance offered by said hole in a partly closed state to the outflow of oil from said second oil pressure chamber into said oil-reserving chamber while said body and said plunger are moved towards said piston by the rotating cam.