Electronic Continuous Variable Valve Timing for Small SI Engine 2008-01-1778
An electronic variable valve timing system for a spark ignition engine was designed and built in order to investigate the performance of ideal valve actuation timing and facilitate further research. The solenoid actuated EVVT system was installed on a single cylinder 80 ccm, 1.7 kW Briggs & Stratton SI engine. The system is controlled by a PIC micro-controller unit, which in turn controls a 120V solenoid driver circuit to power the solenoids.
The continuous variable valve timing adjustment enables ideal combustion conditions during all speed ranges and loads. This leads to cleaner, more efficient and more powerful combustion once the control algorithm is mapped for all conditions. Furthermore, it makes controlled auto ignition achievable using negative valve overlap, which is a promising emission-reducing combustion mode.
A DC dynamometer engine test bed was used to compare the performance of normal SI operation and improved operation using the EVVT system with regular 95-octane petrol. Rotational sensors and a PIC control unit, on which valve opening and closing can be altered, control the valve operation.
The obtained results demonstrate improved efficiency with the application of the EVVT system when electrical energy is neglected and valve timing remains unchanged. During testing, the solenoids used as valve actuators proved to be suitable for this application due to their high precision timing capabilities when operated by a digital control unit. However, they require a lot of power to open and close and have limited minimum holding times, which implies the use of more efficient devices for further implementation.