1995-02-01

Hydrodynamic Mobility Analysis of the Vane Lift Mechanism for the Rand Cam™ Engine 950450

In this paper, a new method for the hydro-dynamic analysis of a sliding cylinder in a fully lubricated parallel track is presented. The method is an extension of Booker's “Mobility Method” (developed for cylindrical journal bearings) to the case of sliding cylinders, in which the clearance between the track and the cylinder, the viscosity of the lubricant, the radius and length of the pin, the sliding velocity and the applied transverse load determine the hydrodynamic behavior of the cylinder.In the Rand Cam™ Engine [1]*, the axicycloidal motion of vanes is driven by a rotor and a cylindrical cam, and one of the alternative designs to provide this function is based on a cylindrical pin sliding within a track which follows the profile of the motion of the main cams of the engine. This function is very important for the engine, since it separates the load bearing function from the sealing function left to the apex-like seals.Results are presented for the particular case of an engine running at constant speed, in which the inertia forces, friction forces and thermodynamic cycle pressures are taken into account to determine the loads on the pins of the vanes. Results show departures from the purely cycloidal lift-dwell-return motion of the vanes due to the hydrodynamic performance of the pins.For the case selected here, the following results are produced: pin eccentricity paths, minimum lubricant film thickness history, peak film pressure history and pressure distributions on the pin at any point of the motion.

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