Valve Timing Control by a Hydraulic Tappet with a Leak Hole

Abstract

For a high-speed engine, valve timing is desired to be automatically controlled by engine speed to secure a good performance over a wide range of speeds. For this purpose an attempt was made to advance valve-closing and delay valve-opening automatically according to reduction of engine speed, by means of a hydraulic tappet with a hole for leakage of oil. The valve lift was measured on a motored engine so as to examine the relation between the diameter of the leak hole and valve timing. The result shows that the leak hole on the plunger controls valve-closing time with less effect on valve-opening, while the one on the cylinder wall influences only valve-opening time. Further, the valve motion was numerically solved by an original theory, which gave a fairly good estimation of valve lift. However, at low speed operation with this tappet, valve seating velocity becomes so high that a special cam profile which has low velocity over a range of closing time is desirable.