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451_072
Oil pump
The chain-driven oil pump is a gear pump configured as a fixed
displacement pump. It integrates the cold start valve and the
control piston.
Function of the pressure regulation system
A bypass branches off from the main oilway and back into the oil
pump (see Fig. 451_032), where prevailing oil pressure acts on the
spring-loaded control piston. If the pressure acting on the face of
the piston exceeds the force produced by the control spring, the
control piston will be pushed back, thereby opening a port in the
pump.
Pump gearControl piston
Driven pump gearPump cover Pump housing Drive gear
Cold start valveIntake from the oil pan
Flow-off to intake side
Control piston is displaced
Oil pressure
Control piston
Bypass
Full delivery
Control spring
The control piston opens at pressures of up to 3.7 (+0.7) bar.
The cold start valve opens at pressures of up to 13 bar.
The surplus oil is thus recirculated to the intake side of the pump
until the oil pressure is just below 3.7 bar, when the force of the
control spring pushes the control piston back and re-closes the
bypass. In this way, a constant oil pressure of 3.7 (+0.7) is main-
tained across the entire engine speed engine (except at idle and at
low rpm).
Delivery with flow-off
Reference
A self-regulating oil pump will be adopted from calendar week 36/2010. The design and function of a self-regulating oil
pump of this type are described in Self-Study Programme 436 " Modifications to the chain-driven 4-cylinder TFSI engine".
451_079
