Oljefilmens tjocklek mellan kolvring och cylinderlopp

Sammanfattning: Hägglunds Drives in Mellansel, Sweden, manufacture radial piston hydraulic motors foremost within applications in the industry. These motors have several sliding contacts, one of these, is the contact between piston ring and cylinder bore. The radial piston hydraulic motors advantage is to produce high torque in very low rotation velocity, this result in that the maximum sliding velocity between piston ring and cylinder bore, during the whole stroke, is very low. The consequence of this low sliding velocity is that the contact between piston ring and cylinder bore, during the whole stroke, is bound to the boundary lubrication regime. This result in, that the 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 the piston ring and cylinder bore. When the build up of oil film thickness is evaluated, more could be understood 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 thickness between piston ring and cylinder bore, in a test rig, simulating the radial piston hydraulic motor from Hägglundes Drives. The method investigated is based on the use of capacitive transducers that are placed in the cylinder bore and measure the distance from the placement of transducer to the piston ring. The transducer is placed with an offset from the cylinder bore whereas the oil film thickness is based on the distance between transducer and piston ring minus the distance from transducer to cylinder bore. Change in the oil film thickness as a function of piston speed has been observed, though within the area of standard deviation for the tests, despite this, there is a clear trend towards an increase of oil film thickness for the working pressure of 30 MPa.