Hydraulic valve actuation systems and methods to provide variable lift for
one or more engine air valves by way of a variable position hard stop.
Various embodiments are disclosed, including embodiments controlling lift
by providing a choice of two different fixed stops, three different fixed
stops, stops continuously variable throughout a range of lifts, and a
fixed stop and stops continuously variable throughout a range of lifts.
The valves controlled by a variable position hard stop may be a single
engine intake or exhaust valve, or multiple valves of any number, and of
either intake or exhaust valves or both, or of one intake or one exhaust
valve for one or more cylinders in engines having more than one intake or
exhaust valve per cylinder. Dashpot deceleration of engine valve velocity
on opening to the hard stop and on engine valve closure is disclosed, as
are other aspects and embodiments of the invention.