T 3tT 477-

Crank Angle (rad )

2.0 Litre L-4 Engine, 800RPM Motoring, 368 mm Hg MAP SAE 30 Oil, 93°C Oil-Water Temp.

Figure 4. Typical cylinder pressure, covnecting rod, and inertia forces.

It is difficult to determine the factors that contribute to the shape of the friction force curve. This is because that curve reflects the skirt, the three piston rings, and the piston pin friction. Each component is operating in a somewhat different lubrication regime. Near the dead centers the piston rings dominate the friction results. There, the rings operate in the mixed or boundary lubrication regime. In midstrokes, probably all components are operating in the hydrodynamic regime.

The frictional work associated with these forces results from the product of friction force times piston velocity. The velocity is shown in the center portion of the figure. That product is the instantaneous friction power dissipated, and is shown in the lower portion of the figure. The area under the curve of power versus crankangle is the total energy loss due to friction. That frictional work divided by the displacement of the cylinder is termed the friction mean effective pressure (fmep) of the piston ring assembly.

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