A variable displacement engine with independently controllable stroke length and compression ratio

Document Type

Conference Proceeding

Publication Date



Department of Mechanical Engineering-Engineering Mechanics


A variable displacement engine with the capability to vary stroke length and compression ratio independent of one another has been designed, prototyped, and successfully operated. Reasons for investigation of such an engine are the potential for improvement in fuel economy and/or performance. Literature has shown that engines with variable compression ratio can significantly decrease specific fuel consumption. Engines with variability in stroke length can maintain peak efficiency running conditions by adjusting power output through displacement change verses through the efficiency detriment of throttling. The project began with the synthesis of a planar 2-dimensional rigid body mechanism. Various synthesis techniques were employed and design took place with a collection of computer software. MATLAB code performed much of the synthesis, kinematic, and dynamic analysis. Adams aided in mechanism analysis and design, and Unigraphics NX for much of the individual component modeling through Motion and Finite Element Analysis. An engine was provided by the Kohler Company for prototyping. Major modifications took place to the base, 20 HP, V-twin engine. The engine block was cut in two, the lower half relocated with respect to the top half, block material removed, oil passages and valve gearing re-connected, and ignition timing readjusted to allow implementation of the newly designed variable displacement mechanism. The engine started on the first attempt; a finished engine is available for study of the variety of effects that the new mechanism creates.

Publisher's Statement

Copyright © 2006 SAE International. Publisher’s version of record: https://doi.org/10.4271/2006-01-0741

Publication Title

SAE Technical Papers