Lubrication Aspects of a Modified Hypocycloid Engine 920380
The modified hypocycloid (MH) mechanism, which uses gears to produce straight line motion, has been proposed as an alternative to the slider-crank mechanism for internal combustion (IC) engines. Advantages of the MH mechanism over the slider-crank for an IC engine include the capability of perfect balancing with any number of cylinders and the absence of piston side loads. The elimination of piston side load has the potential for lower piston friction, reduced piston slap, and less susceptibility to cylinder liner cavitation. To evaluate the concept, an experimental single cylinder four-stroke engine which utilizes the MH mechanism is currently being built at the University of Wisconsin-Madison.
The MH engine has an increased number of friction interfaces compared to a conventional slider-crank engine due to additional bearings and the gear meshes. Thus, the lubrication of these components is an important issue in total MH engine friction.
The lubrication system for the experimental engine is described. The methods and equations used for the lubrication analysis of the experimental single cylinder engine are presented. The mobility method is used for journal bearing analysis to determine the journal loci. Bearing friction, oil flow rate, and wear patterns are calculated. The crankpin bearings are found to be the most critical bearings. For gear lubrication, the equations used to predict gear tooth film thickness, oil pressure required for spray lubrication, and scoring temperature are discussed. Piston friction losses are estimated for comparison with a slider-crank engine. Some observations regarding the effects of straight line motion on piston wear are made.