Camshaft torque

[alfons]

I need information about torque necesary to drive the camshaft, can anybody tell me where can I find this information?
And how is the influence of factors like temperature, revolutions and the valve train configuration?
I'm working on a VVT system, and need this information to find the velocity of the system to change the phase.

 

[franzh]

This is one of the most difficult areas of friction calculation in an engine. Lets explore some factors:
Camshaft material
Lifter material
Camshaft lift, and the rate of lift
Number of lifters
Valve spring pressure (multiplied by the numbers of valves)
Rocker arm ratio (multiplied pressure to the lifter)
Roller lifter vs flat surface lifter
Oil friction coefficient
RPM
Temperature (mostly related to oil viscosity degradation)
(A new factor, the degrees of overlap a camshaft exhibits may change the snap action of a camshafts rotation)

Enough? I played around with a common calculation, but haven't hit on it yet.
franzh@texas.net

 

[wayneward]

Alfons,

Try looking up elastohydrodynamic lubrication. I guess this will predict the breakdown of the oil film, and if you know enough information you could probably work out the friction while anoil film exists, and during mixed / boundary lubrication.

From this it is easy to see that the torque you are after will change with speed, and possibly decrease with speed as the angle that the cam swings through whilst maintaining a full film will be greater at higher speeds.

Good luck