Application area

Shafts

Triboconditioning of crankshafts improves lubricant film strength and system resilience to crankshaft misalignment and oil contamination. The camshaft plays a vital role in internal combustion engine. Synchronized with the crank shaft, it sets the valve timing for optimal engine performance.
crankshaft

Crankshafts

Modern highly loaded engines, particularly long life diesel engines, require main and connecting-rod bearings that combine fatigue and wear resistance with ability to combat dirt and slight misalignment. With the extended oil drain intervals, corrosion resistance is also ever important.

When the tribology of connecting rod bearing and cranckshaft main bearing systems in an internal combustion engine is concerned, it should be remembered that the said systems are supposed to operate in the full film lubrication regime over their lifetime. In this regime, friction modifiers have no effect on the system tribology. Moreover, deployment of certain friction modifiers, such as molybdenum phosphothioates or thiocarbamates, in engine oils has been indicated as a potential cause of copper/lead/tin bearing corrosion in diesel engines.

If the engine bearings or crankshaft journals become worn, oil pressure will drop and the engine may start to burn oil. Under normal conditions, bearing wear occurs immediately after a cold start, before the normal oil pressure builds up. The main journals and the connecting rod journals of crankshafts are hardened so that excessive wear of the shaft itself is rather uncommon.

Triboconditioning of crankshafts (main journals and the connecting rod journals) improves lubricant film strength and system resilience to crankshaft misalignment and oil contamination.

Due to incompatibility of WS2 with copper-containing alloys used in engine bearings, triboconditioning of crankshafts requires use of sulfur-free process fluids, resulting in a different tribofilm chemistry.

 


Camshafts

The camshaft plays a vital role in internal combustion engine. Synchronized with the crank shaft, it sets the valve timing for optimal engine performance.

With the continuing trend toward increasing fuel injection pressures, Hertzian stresses on the valvetrain has grown to the point that cam lobe contact fatigue has become a critical issue for engine durability, especially for fleets with frequent engine starts and shutdowns. Contact fatigue affects both the injector lobes and the exhaust and inlet lobes. A high pressure contact situation also contributes to valvetrain friction, another important issue impairing fuel economy.

Triboconditioning is a potent tool for enhancing the tribological properties of camshafts, especially well suit for mechanical bucket tappet valve trains. Depending on engine design, Triboconditioning can be performed in two different area of the camshaft: on the bearing surfaces and on the cams.

ANS triboconditioned camshafts much better endure high load situations, when the cam pushes a valve with a force of nearly 20 kN, resulting in Hertzian contact pressure in the range of 3.5 – 4.0 GPa, and allow one to reduce valvetrain friction by upto 30%, thus improving fuel economy. The greatest friction-reducing effect is observed at low engine speeds (heavily charged engines), high oil temperatures, and in combination with thinner engine oils of SAE 20 and SAE 30 viscosity grades.

A list of key metrics:

  • Enduring high-pressure contact situations
  • Treatment of non-rotationally symmetrical geometry
  • Compatible with super-finishing equipment

camshaft_braking_torque_tribocondition

Effect of ANS triboconditioning on valvetrain friction measured using a motored cylinder head friction rig (after B. Zhmud et al., Application of mechanochemical surface finishing for improving the tribological properties of valve train components, VDI Conference “Ventiltrieb und Zylinderkopf 2012”, November 27-28, 2012, Würzburg, Germany).

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