Friction between a piston-ring assembly and a cylinder of a spark ignition engine was evaluated under the various operating conditions from the momentum-force balance relation at the piston-ring assembly. Gas pressure inside the cylinder, inertia force of the piston-ring assembly, and the force exerted by the connecting rod were measured by using a pressure transducer, an accelerometer and strain gauges respectively.
Advantages, limitations, and reliability in using this method were also discussed. Comparisons were made with the frictional force evaluated by the conventional method where the assumption of constant rotational speed of engines was adopted.
Due to the variation of rotational speed of engines, the conventional method lead to a large error in evaluation of the frictional force. At low engine speed, reasonably accurate results can also be obtained by measuring the angular acceleration of the crank shaft using a photo sensor instead of using an accelerometer; however, at high engine speed, measure-ments with an accelerometer provided more reliable results since these take account of the local vibration mode of the piston-ring assembly.