Davis, R., "The Ball Piston Engine - A New Concept in High Efficiency Power Machines," SAE Technical Paper 970066, 1997, doi:10.4271/970066.
A patented (Reference ) new power machine concept has been designed and analyzed for production, and proof of principle subscale tests have been performed, with positive results. The machine design concept is applicable as a compressor, pump, motor, or engine. Simplicity of design based on spherical ball pistons (Figures 1 and 2) enables a low moving part count, high power to weight ratio, elimination of valve train and water cooling systems, and perfect dynamic balance.The new design concept utilizes novel kinematic design to completely eliminate inertial loads that would contribute to sliding friction. Also, low leakage is maintained without piston rings by using a small clearance on the ball piston, resulting in choked flow past the ball. These features provide the potential for an engine with higher efficiency than conventional piston engines. The engine design utilizes existing recent technology to advantage, such as silicon nitride ball pistons, so a large development effort is not required.