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  1. Exclusions: Pumping losses result from the flow of
  2. intake and exhaust gases. Accessories include coolant
  3. and lubricant pump, fans, and other pneumatic systems
  4. that may be powered directly by the engine. The losses
  5. in these systems depend on parameters other than
  6. the traditional concept of lubrication or a lubricant.
  7. They comprise 20%−30% of total mechanical losses
  8. for accessories for heavy-duty diesels and 30%−50%
  9. for pumping loss for gasoline engines, depending
  10. on the operating speed and load. While important,
  11. these losses are not included in the current focused
  12. discussions on mechanical or rubbing friction. With
  13. the above exclusions, the three major subsystems
  14. of the engine contributing to mechanical friction are
  15. thus: (a) piston-ring-liner system, (b) crankshaft and
  16. bearings system, and (c) valvetrain system. The exact
  17. distribution of the friction among these three groups
  18. depends on the particular engine, the component
  19. design details, and operating conditions. However,
  20. prevalent reported results show that the crankshaft
  21. system (main bearing and seals) contributes roughly
  22. 50%−100% higher friction than the valvetrain system,
  23. and the power cylinder friction approximately equals
  24. that from the valvetrain and bearing systems combined.
  25. Figure 2 shows a typical partitioning of the mechanical friction in the engine, among the three major
  26. component groups [7, 11, 13]. Friction and lubrication
  27. in these components groups will next be discussed.

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