Variable Stroke Crank Shaft for an Internal Combustion Engine

Abstract

Our planet is continuously being depleted of its natural resources leading to a need to conserve energy and the environment. One of the major energy consumers is the conventional internal combustion engine. Many attempts have been made to make these conventional internal combustion engines more efficient focussing mostly on the combustion side of the engine. The focus of this study is on the modification of the reciprocating and rotating components of the sub-assembly of a conventional internal combustion engine. An in-depth review was carried out on the fundamentals of spark ignition internal combustion engines and savings on fuel consumptions. A prototype single piston internal combustion engine was developed that can adjust its stroke length. Lengthening or shortening the stroke and simultaneously extending or retracting the connecting rod’s travel distance, allows the internal combustion engine to function very efficiently consequently reducing the free space between the piston and cylinder head at TDC position. This allows the internal combustion engine to alter its power capability on demand whilst maintaining relatively high compression efficiency. The method of altering the stroke length is achieved by manipulating gears situated internally and externally of the engine sub-assembly. The control of these eccentric gears lowers or lifts the crankshaft in a radial motion. The eccentrics also control the automatic extension or retraction of the connecting rod’s travel distance. The externally concentric gears control the mechanism that allows the internal combustion engine to change its capacity easily as adapted for automation. This study does not extend into the automation issues of the external mechanism. The prototype engine that was built could not endure vigorous testing and it failed after running for a short while. The primary focus had been on the kinematics of the engine mechanism – and to show whether the idea was feasible. The engine passed the kinematics test but failed possibly due to dynamic loads. Investigating this requires measuring instantaneous temperatures from which peak pressures can be deduced. This was not done because it was outside the scope of the project.