Effect of Crankshaft Offset on Piston Friction in a Heavy-Duty Vehicle Air Compressor: FEA of Conventional and New Mechanisms

Çetin Ö., OKUR M., Gültekin E.

International Journal of Automotive Science and Technology, cilt.10, sa.1, ss.157-168, 2026 (Scopus)

Özet

In today’s energy conversion systems, mechanical friction is one of the fundamental loss mechanisms that limit efficiency. This study examines an innovative crankshaft-connecting rod mechanism developed to reduce lateral forces generated at the piston skirt–cylinder interface in brake air compressors and compares its friction performance with that of a traditional mechanism at different crankshaft offsets. The proposed design utilizes a rigidly connected piston rod and a low-friction linear bearing system that enables linear motion. This eliminates the lateral forces on the piston caused by the angular motion of the connecting rod, ensuring that the piston moves only linearly. Since the load transfer occurs through the linear bearing, the piston skirt-cylinder contact is minimized, significantly reducing friction losses. Numerical modeling and finite element analysis conducted within the 0–12 mm crankshaft offset range evaluated the piston lateral force, moment, and friction losses depending on the crankshaft angle. The results show that a 3 mm offset in the thrust side direction is a critical comparison point and that under these conditions, the new mechanism reduces piston torque by 86% and friction losses by 84%. The linear bearing configuration has reduced friction-induced energy losses by an average of 80–85%. These findings demonstrate that crankshaft offset is an effective design parameter for increasing mechanical efficiency in auxiliary systems such as compressors and show that geometric optimization can significantly improve friction performance.