Development of a test methodology for detailed friction analysis in the piston ring and cylinder liner tribosystem at constant high relative speeds

Friction and wear are critical factors in the performance and longevity of mechanical systems and have a significant impact on their efficiency, operating costs and overall life. Among the many components of an engine, the tribological contact between the piston ring and cylinder liner is particularly important. Especially with the current trend to use low viscosity oils to minimise friction, which can lead to increased wear. Friction and wear in these systems are influenced by various parameters such as load, temperature and relative speed, making it difficult to predict their behaviour without testing. In engines, the piston ring and cylinder liner are exposed to harsh environmental conditions not only at low speeds near the top dead centre, where most research is focused, but also at higher speeds during mid-stroke, which is less studied. This Master's thesis focuses on developing a test methodology to accurately measure friction at these higher relative speeds. To achieve this, the linear motion of the piston ring is converted into a rotational motion. The piston ring is rotated so that its axis of rotation is perpendicular to the axis of rotation of the cylinder liner. If a small section of the piston ring is used, it will now run around the inner circumference of the cylinder liner when moved. Inside the test cell, the cylinder liner remains stationary while three piston ring specimens are driven by an electric motor. The system is heated to operating temperature and the piston ring samples are accelerated to simulate the relative motion within an engine. The piston ring specimens are pressed against the cylinder liner under controlled conditions while the friction is continuously measured with a load cell. The test methodology and the quality of the friction measurement have been evaluated and improved over a total of 27 tests. Extensive testing has led to continuous improvements resulting in a more robust test methodology and consistent test conditions. The developed test methodology emphasises high precision of friction measurement, repeatability of tests and sensitivity to changes in temperature and lubrication. These characteristics enable the test methodology to simulate and measure friction under different operating conditions.