Experimental Research on Friction Characteristics of DLC Coated Cylinder Block/Valve Plate Interface in Aerospace Integrated Motor Pumps

Integrated motor-pump has been adopted to aerospace electrohydrostatic actuators due to its high efficiency and dynamic response. To meet the challenges brought by the complicated working conditions in aerospace applications to the cylinder block/valve plate interface of integrated motor-pump, strengthening the surface of the friction pair has been a key issue. Previous studies on surface coatings have shown that the hard-on-soft matching materials perform relatively better friction characteristics while the hard-on-hard ones have better wear performance. In this study, the friction characteristics of a novel DLC coated cylinder block/valve plate interface is studied. An optimized specific friction simulation test apparatus is adopted, which could accurately obtain the friction performance of the cylinder block/valve plate interface under wide range of rotational speed and pressure. Specially, a simulated piston structure design is adopted in the apparatus to make it able to simulate the churning behavior. Friction performance of the interface is characterized by friction coefficients which are evaluated from the obtained friction torque. The effect of rotational speed and pressure on friction performance of the interface is analyzed, and the friction characteristics of DLC coating is compared with other pairing materials under the same working conditions. Results show that compared with nitrided valve plate, DLC coating can significantly reduce the friction loss of the cylinder block/valve plate interface under a wide range of rotational speed.