Design of Movable Casing for Friction Reduction of External Gear Pump for Hydraulic Actuators

In a hydraulic system that uses an external gear pump, the clearance between the gear teeth and the casing varies due to changes in differential pressure. The challenge is that increasing the clearance to avoid friction leads to increased internal leakage. To address this issue, a movable casing is proposed as a mechanism with low friction and small clearance between the gear teeth and the casing. The proposed movable casing pump has a two-layered casing, with the inner casing moving freely according to the eccentricity of the gear teeth, without resistance. Therefore, even with a small clearance between the gear teeth and the casing, significant friction can be avoided. This paper proposes the design concept of a movable casing and verifies friction using a prototype.