Exclusions: Pumping losses result from the flow of

intake and exhaust gases. Accessories include coolant

and lubricant pump, fans, and other pneumatic systems

that may be powered directly by the engine. The losses

in these systems depend on parameters other than

the traditional concept of lubrication or a lubricant.

They comprise 20%−30% of total mechanical losses

for accessories for heavy-duty diesels and 30%−50%

for pumping loss for gasoline engines, depending

on the operating speed and load. While important,

these losses are not included in the current focused

discussions on mechanical or rubbing friction. With

the above exclusions, the three major subsystems

of the engine contributing to mechanical friction are

thus: (a) piston-ring-liner system, (b) crankshaft and

bearings system, and (c) valvetrain system. The exact

distribution of the friction among these three groups

depends on the particular engine, the component

design details, and operating conditions. However,

prevalent reported results show that the crankshaft

system (main bearing and seals) contributes roughly

50%−100% higher friction than the valvetrain system,

and the power cylinder friction approximately equals

that from the valvetrain and bearing systems combined.

Figure 2 shows a typical partitioning of the mechanical friction in the engine, among the three major

component groups [7, 11, 13]. Friction and lubrication

in these components groups will next be discussed.