Optical Ways to Improve the Tribology of Valve Guides

Abstract

The function of the system valve stem - valve guide is dependent on the material combination and the available amount of oil. The wear on both components must be low at high running times to ensure a save function and keep the emission of the engine low. The knowledge about the friction- and wear mechanism is not obviously caused by missing information about the real amount of oil in the guide and over the oil transportation. This paper describes, in which way it is possible to visualize the valve behavior in a valve guide. Two test rigs with valve guides made out of glass are built up to investigate the behavior of the valve under running conditions. This research work realized for the first time, taking photographs of the oil distribution in a original scaled valve guide under running conditions. The following could be visualized: • The oil film and the oil pressure distribution between valve stem and valve guide with different clearances had been investigated. A closed hydrodynamic oil film only can built up in a capillary gap. • At a great valve clearance no sufficient oil film pressure could build up. Increasing the oil content does not solve this problem. By missing oil film pressure wear is visible immediately. • The amount of oil transported towards the valve head - represents a part of the oil consumption in a real engine with a negative influence for the emissions- increased excessively with the valve stem clearance. • The influence of worn out valve stem sealing is more severe, the greater the valve clearance is. • The very complex secondary movement of the valve in the guide is strongly dependent on the amount of oil. In this paper fundamental knowledge for understanding the system valve stem - valve guide are described.