Dynamic analysis has shown that for a V-6 engine with a DOHC valvetrain layout, a Cam Torque Actuated phaser can be actuated rapidly enough to have the net effect of retarding the valve opening and advancing the valve closing within one valve event, hence; reducing the event duration. Reducing the cam duration from the fixed cam-lobe duration can have benefits at Cold-Start, Cold-Idle, Hot Engine Idle, and low-speed Part-Throttle operation.
The approach taken for this investigation was to model the duration-reduction system at engine cranking speeds with GT-Power. Engine simulation showed that we can achieve sonic velocity at the valve seat at engine cranking speeds, and concurrently maximize the effective compression ratio. Based on these promising results, a prototype system was built and tested. A dyno-based test was devised to simulate repeated cold-start first-firing cycles to examine the effect of the system on lean ignition limit and cumulative HC during a cold-start.
The dyno-tests on a port-injected SI engine demonstrated a greater than 30% reduction Fuel/air lean-limit for first firing cycle, and cold-start HC emissions, compared to the baseline on 2 different combustion chamber arrangements.
This report covers the simulation and testing of a prototype device at engine cranking speed. A future report will discuss the design and testing of a practical version of a cam phaser that can change between the normal mode of operation and the event duration reduction mode, and that has acceptable NVH. Future reports will also cover performance of this type of device at higher engine speeds.