Repair manual

Oil Circulation System
18
Function
This is achieved by axial displacement of the cam lobe
unit or in other words, by displacement of the oil pump
gears relative to one another. The delivery rate is highest
when both pump gears are aligned exactly opposite
each other. The greater the axial displacement of the
driven pump gear, the lower its delivery rate will be (only
oil displaced between the pump gears is conveyed).
The pump gear is displaced by the incoming filtered
oil pressure acting on the front piston face of the cam
lobe unit. A compression spring also acts upon the front
piston face of the cam lobe unit.
Filtered oil pressure is permanently applied to the rear
piston face of the cam lobe unit.
A control piston applies oil pressure through the pressure
port on the filtered oil side to the front piston face of
the cam lobe unit. The engine oil pressure that has just
been developed is used to counteract the force exerted
by the regulating spring. The application of oil pressure
is a continuous and dynamic process. The control piston
moves continuously in alternating linear directions.
Overview
Conventional Method of Control
With a conventional oil pump, the delivery rate increases
as the engine RPM increases. The oil consumers in the
engine cannot process the excess oil being delivered, so
the oil pressure increases.
Previously, pressure limiting took place inside the
pump. A mechanical valve opened for this purpose.
However, since the pump was still operating at its
maximum delivery rate, a portion of the input energy was
inefficiently converted to heat.
The concept of the new control system involves
two different pressures. The low pressure setting is
approximately 26 psi (1.8 bar). The system changes to the
high pressure setting, approximately 48 psi (3.3 bar), at
an engine speed of approximately 3500 rpm.
The pressure is regulated by controlling the delivery rate
of the pump gears. Oil delivery is controlled to produce
exactly the required filtered oil pressure downstream of
the oil cooler and oil filter.
Pumped
Oil
Pressure
Port on
Filtered
Oil Side
Oil Pressure
Regulation
Valve N428
Oil Passage
to Front
Piston Face
Driven Pump
Gear (axially
displaceable)
Compression
Spring of the
Cam Lobe Unit
Front Piston
Face of Cam
Lobe Unit
Drive Pump
Gear on
Input Shaft
Cam
Lobe
Unit
Rear Piston
Face of the Cam
Lobe Unit
Oil Passage
to Rear
Piston Face
Control
Piston
Return to Oil Pan
(pressure-less)
Oil Passage
to Front
Piston Face
Regulating
Spring
Oil Passage
to Rear
Piston Face
Switchable Pressure
Port on Filtered Oil Side
Pressure Port on
Filtered Oil Side
Low Oil Pressure
High Oil Pressure