The 4-stroke SI engine offers better performance if its valve events can be varied depending on the operating conditions. Some engines in production are therefore incorporated with variable valve timing (VVT) mechanisms. All of such mechanisms available today however are for two-mode change-over between low-and high-speed operations.
To achieve even better output and fuel economy, a new multi-mode VVT mechanism has been developed, featured by a unique hydraulic device for three-mode change-over as follows:
Deactivate both intake and exhaust valves Select low-speed cam with moderate lifts and short durations Select high-speed cam with high lifts and long durations
Deactivate both intake and exhaust valves
Select low-speed cam with moderate lifts and short durations
Select high-speed cam with high lifts and long durations
This mechanism enables shutting off unnecessary cylinders during low-speed cruise, or select optimum valve events during WOT acceleration over the entire engine speed range. The engine with this VVT demonstrates a fuel economy improvement up 16% during the Japanese test driving cycle and a power increase by 20% from its predecessor.