Analysis on the Mixed Friction between the Guide made of Cast Iron and the Valve Stem made of Ti6Al4V with and without Protective Layer
Maciej Kuchar 1  
,  
 
 
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Lodz University of Technology
Publish date: 2014-08-25
 
The Archives of Automotive Engineering – Archiwum Motoryzacji 2014;64(2):37–47
ABSTRACT
Lightweight valves are commonly used in modern combustion engines with cam and camless valve train. They can be made of TiAl alloys and in particular the inlet valves can be made of Ti6Al4V. The stems of such valves can be coated by protective layer obtained by nitridation, chroming or the other one. The stems can mate with guides made of cast iron, of phosphor bronze or berylium bronze. Mating can take place in conditions of mixed friction with different share of lubricated friction. The researches have been provided in the tribotester. The analyzed valve has been driven electromagnetically, for the different valve strokes and frequencies. The mating takes place in the condition of oil absence. The valve has been loaded by additional mass to induce the normal force between valve stem and its guide. It has been measured the acceleration and the displacement of the valve, the impact force of the valve into its seat insert, friction force between valve stem and its guide and the sound level. The aim of the researches is to obtain and compare values and courses of friction coefficient between the guide made of cast iron and valve stem made of Ti6Al4V for certain number of the valve strokes and frequencies. The researched stem could be uncoated or coated by Cr layer or by nitridation. The analytical model has been elaborated to calculate the contact pressure and the friction force between valve stem and its guide for the conditions of mixed friction occurring for the selected engine oil and the valve motion relative to its guide as obtained from the tribotester. The obtained dry friction coefficient values have been used in the model.  Results of researches have been presented in the article.
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