Advanced Design of Variable Compression Ratio Engine with Dual Piston Mechanism

A Dual Piston Variable Compression Ratio (VCR) engine has been newly developed. In order to ensure the strength of the Dual Piston, the design guidelines were established. There are two advantages of this design. One is the compactness and the compatibility with a mass production engine block. Another is less power consumption required during compression ratio switching. However, the durability is a challenge for this design because of the impact load during the switching driven by the inertial force of a reciprocating piston. In order to achieve a durable configuration, it was necessary to consider the dynamics of the stress after impact, from analysis of the impacting process during the switching. The analysis of stress and deformation mode was improved in accuracy by using Computer Aided Engineering (CAE) in the designing process. In addition, the results of stress measurements of the piston in firing engine operation were fed back for further enhancements, and the design guidelines against switching load were established. To verify the durability of the VCR engine manufactured according to these guidelines, the durability tests were performed with continuous switching at 1 Hz. As a result, the test proved the switching durability of over 1×10⁶ cycles at 2500 rpm.