Oljefilmens tjocklek mellan kolvring och cylinderlopp
Hägglunds Drives in Mellansel, Sweden, manufacture radial piston hydraulic motors foremostwithin applications in the industry. These motors have several sliding contacts, one of these, isthe contact between piston ring and cylinder bore. The radial piston hydraulic motors advantageis to produce high torque in very low rotation velocity, this result in that the maximum slidingvelocity between piston ring and cylinder bore, during the whole stroke, is very low. Theconsequence of this low sliding velocity is that the contact between piston ring and cylinderbore, during the whole stroke, is bound to the boundary lubrication regime. This result in, thatthe piston ring is exposed to wear, thus affect the service life of the complete hydraulic motor.To minimize wear of piston ring, it is essential to determine the oil film thickness between thepiston ring and cylinder bore. When the build up of oil film thickness is evaluated, more could beunderstood about different surfaces ability to build up oil film thickness in low sliding velocities.The purpose of this master thesis, is to evaluate a method for measuring oil film thicknessbetween piston ring and cylinder bore, in a test rig, simulating the radial piston hydraulic motorfrom Hägglundes Drives. The method investigated is based on the use of capacitive transducersthat are placed in the cylinder bore and measure the distance from the placement of transducer tothe piston ring. The transducer is placed with an offset from the cylinder bore whereas the oilfilm thickness is based on the distance between transducer and piston ring minus the distancefrom transducer to cylinder bore.Change in the oil film thickness as a function of piston speed has been observed, though withinthe area of standard deviation for the tests, despite this, there is a clear trend towards an increaseof oil film thickness for the working pressure of 30 MPa.