VARIABLE STROKE PISTON MECHANISM FOR SPARK-IGNITION ENGINES

The concept of load control in internal combustion engines by eliminat ing the inlet throttle and replacing it by controlling the piston stro ke has gained great publicity recently. Nevertheless, certain design p arameters should be considered in order to make this concept worthwhil e. In this study, an optimized mechanism for varying engine stroke has been introduced. A criterion based upon the use of complex numbers te chnique was used to analyse the mechanism kinematically and dynamicall y and the results were then verified using graphical solution. The mec hanism was found to produce up to 56% stroke variation within the cont rol actuator capabilities. The compression ratio was found unchanged ( within +/- 6%) which helps maintain steady combustion process. The ent ire mechanism is well tuned and no spark plug timing adjustment is req uired during stroke variation. The piston side thrust due to connectin g rod angularities was found to be fairly low and should not impose an y wear problems in the engine cylinder walls.