A four-stroke cycle reciprocating internal combustion engine includes a piston
mounted for reciprocal movement within a power cylinder and primary and secondary
intake valves. The primary valve has a fixed event, in terms of both duration and
lift, and the secondary valve has variable duration and lift. Although the timing
of the primary and secondary valve events may be retarded from a standard timing
value, both valves close at the same time regardless of the presence of timing
retard. The dual event strategy, combined with camshaft timing retard for part
load conditions, produces excellent charge motion by staggering the respective
lifted flow areas of the primary and secondary valve events and by delaying the
secondary valve opening.
