Hydraulic valve lift device

Claim 1

In a hydraulic valve lift device including a lifter having therein an oil pressure chamber for introduction of oil and slidably disposed in a cylindrical bore of a housing with its one end engaged by a cam on a cam shaft and a plunger slidably disposed in said lifter for opening and closing an intake or exhaust valve, of which a valve lift is made variable depending on the rotational speed of said cam due to discharge of oil from said oil pressure chamber through a throttling port, the improvement comprising a braking chamber defined by a flange portion of said plunger and said cylindrical bore, a slit adapted to communicate said braking chamber with an oil feed chamber of said plunger for flow-in of oil and to be reduced in its opening area depending upon the downward movement of said plunger, a relief valve provided in association with said braking chamber for controlling an oil pressure therein so as to cause it to be below a set value, a sensor for producing an electric signal representing a braking force generated by said braking chamber, an electromagnetic means for regulating a set working pressure of said relief valve, and a computer for energizing said electromagnetic means depending upon the output signal of said sensor to control said relief valve such that its set working pressure corresponds with a desired value, and wherein said computer comprises an amplifying circuit for amplifying the output of said sensor, an A-D converting circuit for A-D converting the output of said amplifying circuit, a ROM circuit for outputting a predetermined value depending upon the output of said A-D converting circuit and an output circuit for D-A converting and amplifying the output of said ROM circuit, said output circuit being adapted to output to said electromagnetic means.