Underlying Physics of the interplay of Engine oil type, speed, normal pressure, surface characteristics and plastic material type in lowering the friction in timing chain drive systems.

Paper #:
  • 2017-01-0462

Published:
  • 2017-03-28
Abstract:
Fuel economy improvement efforts in engines have focused on reducing the parasitic losses. A significant contribution comes from the valve train chain drive system where around half of the friction is caused by the chain sliding on the plastic guide and tensioner faces. Efforts have been made to reduce this friction by optimizing the chain link profile, optimizing the geometry of the guide and tensioner rails and developments towards low friction materials in contact with the chain. In this paper we will compare different friction test methods ranging from academic level ball-on-plate geometry, through chain-on-guide bench test, to full motored and fired engine testing and demonstrate their correlation. All tests show their characteristic but varying dependency on chain speed, interface normal pressure and oil viscosity which all bear resemblance to Stribeck’s curve. We will discuss in detail how factors like oil type (viscosity and additive package), surface topology, normal pressure, temperature and polymer type take their effect on friction in the different test geometries. A notable increase in friction between fresh oil and used oil was observed well before the oil served its full extended oil exchange interval. All observations will be discussed from the perspective of tribological physics. In the light of the above, a comparison of the sliding friction of available materials for chain guide rail surfaces will be provided.
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