Experimental Wear Testing Of The Piston In An Offset Crank-Slider Hydraulic Pump

Abstract

Hydraulic piston pumps and motors are frequently utilized in low-speed-high-torque(LSHT) applications. In such piston-cylinder geometries, side load is a prevalent issue that leads to friction and wear. It’s crucial to ensure adequate lubrication at the pistoncylinder interface to minimize wear and friction while enhancing efficiency. This thesis aims to shed light on the effects of side load and the resultant wear in an offset slider crank mechanism, which simulates the Variable Displacement Linkage Pump/Motor. In this research, multiple pistons were tested at distinct cylinder pressures (10.4 MPa, 17.2 MPa, 21 MPa) and shaft speeds (15 rpm, 25 rpm, 45 rpm) within a custom offset slider crank pump. Wear data was gathered via two methodologies: a custom-designed profilometer wear measurement rig and a precision balance. The specially constructed profilometer rig enabled capturing surface roughness data. The analysis showed that wear increases with increasing pressure and decreasing speed. The research included an analysis of wear after 1000 and 10000 cycles, uncovering an initial ”break-in” period during the initial 1000 cycles. Upon extending the testing to 10000 cycles, there was a noticeable decrease in wear over this extended cycle range. To put the results in perspective two case studies are presented that state the importance of speed in pistoncylinder interface in hydraulic applications from the accelerated test performed in this test. The study provides guidance on Archard’s wear coefficient as a function of side load and velocity enabling pump design for specific operating conditions.