Analysis of Failure Causes and Optimisation of Automotive Cycloidal Rotor Pumps

Cycloidal rotor pumps are widely employed in automotive and aerospace industries due to their compact structure, high volumetric efficiency, and minimal flow pulsation. With the advancement of new energy vehicles, rotor pumps are increasingly required to operate reliably under more demanding conditions, including higher rotational speeds, elevated pressures, and more severe operating environments. These requirements place greater emphasis on pump durability and structural integrity. This study investigates a fracture failure of the internal rotor observed during bench testing of a cycloidal rotor pump. Metallographic and physicochemical analyses were conducted on the failed rotor. The results indicated that the fracture was not attributable to material defects. Instead, the failure originated from improperly designed slot locations within the rotor, which created a structural weak point at the slot opening. Additionally, sharp corners introduced during machining of the slots resulted in significant stress concentrations. Subsequently, A finite element-based transient dynamic analysis of the pump was performed to simulate operational conditions. The simulation results correlated closely with experimental observations, confirming that stress concentrations occurred specifically at the roots of the rotor slots. The maximum stress reached 1135 MPa, exceeding the material's yield strength. To address these issues, a design optimization was proposed: the slot position was adjusted to avoid the critical tooth root region, and a fillet radius of 0.5 mm was introduced at the slot root to mitigate stress concentration. Simulation results demonstrated that the optimized design reduced the maximum stress in the inner rotor to 863.2 MPa—a decrease of 23.95% compared to the original design. Furthermore, fatigue life analysis performed using nCode indicated that the improved design achieves infinite fatigue life, confirming the effectiveness of the proposed modifications.