Repair manual

Oil Circulation System
19
Engine Start-Up
The illustration below shows how the oil pump functions
when the engine is started. Engine oil passes through
the pressure port on the filtered oil side and impinges on
all surfaces of the control piston while flowing to both
sides of the cam lobe unit. Oil Pressure Regulation Valve
N428 is activated by the ECM and holds the switchable
pressure port open so that oil pressure is applied to all
surfaces of the control piston.
The cam lobe unit remains in this position. The pump
operates at maximum output until the low pressure
setting is reached (approximately 26 psi [1.8 bar]). A lower
value is also possible when the engine is idling. However,
an excessively low value would cause irreparable damage
to the engine. Therefore, the oil pressure must be
monitored, in this case by Reduced Oil Pressure Switch
F378.
Positions of the Cam Lobe Unit
Pressure Port
on Filtered
Oil Side
Oil Pressure
Regulation
Valve N428
Control Piston is
Pushed Against the
Regulating Spring
Pumped
Oil
Driven
Pump Gear
(is displaced
axially)
Compression
Spring of the
Cam Lobe Unit
Rear Piston
Face of Cam
Lobe Unit
Oil Passage
to Rear
Piston Face
Regulating
Spring
Oil Passage
to Rear
Piston Face
Oil Passage to
Front Piston
Face is Closed
Engine
Speed [rpm]
Relative Oil
Pressure [bar]
No axial displacement: maximum oil flow rate Maximum axial displacement: low oil flow rate