Modifications of a Quad 4 Engine to Permit Late Intake Valve Closure 921663
Previous studies have shown Late Intake Valve Closure (LIVC) through Variable Valve Timing (VVT) to offer reduced fuel consumption through reduced pumping work. Load modulation through the controlled phasing of one of two intake valves/cylinder is one means of accomplishing the LIVC strategy on a multi-valve engine. Experimental studies of LIVC show that cycle-to-cycle variations and reduced flame velocity in single or synchronized multiple intake valve engines are associated with performance which, though superior to throttled engine performance, falls short of its promised fuel economy. To examine if the higher mixture velocity promised by valve phasing relative to single or synchronized LIVC mitigates cycle-to-cycle variations and flame velocity defects, a modification of the Quad 4 engine has been designed and built and is, at the present writing, being tested.
The design employs a third camshaft placed above the original intake valve camshaft. The original intake camshaft has been modified to permit four yoked pushrods to drive the phased set of intake valves from the camshaft above. Phase shift between intake valves is accomplished by driving the third camshaft from the power steering takeoff through a phase shift linkage. This paper describes the design, gives the stress/mass considerations governing the yoke design, the machining of the original castings required and the experimental results acquired thus far.
Measurements thus far show a 6.3% reduction in the Brake Specific Fuel Consumption (BSFC) at 1500 RPM and 36% power, a decrease in the exhaust noise level, slight changes in emissions and a significant decrease in the tendency to knock. In addition, this study has found that the phased intake closure has enhanced the combustion quality at some operating conditions, increasing the heat release rate during the first 50% of the mass fraction burned.
To our knowledge, this modification of a production engine to permit experiments in LIVC represents the simplest, least expensive alternative presently available and may be of interest to those for whom a low engine profile is not essential.