Measurement of Oil Film Thickness in the Elastohydrodymanic Contact Between a Cam and Bucket Follower in a Motored Cylinder Head Part 1: Newtonian Oils

A motored cylinder head utilising a cam and inverted bucket follower configuration has been instrumented to measure the oil film thickness in the elastohydrodynamic (EHD) contact separating cam and follower. Measurements were carried out using a capacitive divider circuit originally designed for use with deep groove ball bearings. A method is presented to convert the electrical measurements of contact capacitance into actual oil film thickness. These oil film thickness measurements are compared with a theoretical EHD analysis for this cam and follower configuration at the test temperature of 100°C.

Oil film thickness measurements are reported for seven single grade oils of viscosity range 5 to 23 mPa.s at 100°C. These oils are fully formulated with the same additive package but with base stocks varied to obtain the required viscosities. The tests were run at constant camshaft speed and temperature.

In all the tests performed on the above oils, an oil film was found to be present in the EHD contact between the cam and bucket follower. A correlation has been found between oil film thickness and oil viscosity for all the parts of the camshaft cycle investigated.