Improvement of the low-speed friction characteristics of a hydraulic piston pump by PVD-coating of TiN

Abstract

The hydraulic pump of an Electro-hydrostatic Actuator should be able to quickly feed large ume of oil into hydraulic cylinder in order to reduce the response time. On the other hand, it should be also able to precisely dispense small amount of oil through low-speed operation so t the steady state position control error of the actuator can be accurately compensated. Within the scope of axial piston type hydraulic pumps, this paper is focused on the investigation how the surface treatment of their cylinder barrel with TiN plasma coating can contribute to the reduction of the friction and wear rate of valve plate in the low-speed range with mixed rication. The results showed that the friction torque of the valve plate mated with a TiN-coated cylinder barrel could be reduced to 22% of that with an uncoated original one when load pressure was 300 bar and rotational speed 100 rpm. It means that the torque efficiency of the test p was expected to increase more than 1.3% under the same working condition. At the same time, the wear rate of the valve plate could be reduced to 40–50%.