Advanced Control System of Variable Compression Ratio (VCR) Engine with Dual Piston Mechanism

A dual piston Variable Compression Ratio (VCR) engine has been newly developed. This compact VCR system uses the inertia force and hydraulic pressure accompanying the reciprocating motion of the piston to raise and lower the outer piston and switches the compression ratio in two stages. For the torque characteristic enhancement and the knocking prevention when the compression ratio is being switched, it is necessary to carry out engine controls based on accurate compression ratio judgment. In order to accurately judge compression ratio switching timing, a control system employing the Hidden Markov Model (HMM) was used to analyze vibration generated during the compression ratio switching. Also, in order to realize smooth torque characteristics, an ignition timing control system that separately controls each cylinder and simultaneously performs knocking control was constructed. As a result, highly reliable compression ratio judgment and accurate ignition timing control were achieved to switch the compression ratio without torque steps. In addition, the fuel economy was improved to 7.4% by combining the Atkinson cycle with high compression ratio operation in Japanese 10-15 mode.