DAF CF65 Series Service Manual page 307

4
XE ENGINE INLET/EXHAUST SYSTEM
CF65/75/85 series General
2.2 SYSTEM DESCRIPTION, TURBOCHARGER
Wastegate
To make the engine more responsive at lower
engine speeds, a turbocharger is used that
produces a better charge ratio at these speeds.
Without provision having been made for this, the
boost pressure yielded by this turbocharger
would be too high at maximum engine speeds.
Use of a wastegate prevents this.
The turbocharger's compressor housing has an
air coupling connected to a diaphragm. The boost
pressure yielded by the turbocharger operates
the diaphragm and the control rod connected to it.
The control rod operates a valve in the turbine
housing.
The valve in the turbine housing is opened when
the maximum pre-set pressure has been
reached.
When the valve is opened, some of the exhaust
gases will be discharged directly to the exhaust
pipe rather than being used to propel the
turbocharger's turbine wheel.
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Compression housing by-pass
At higher boost pressures, the turbocharger
compressor tends to allow this pressure to return
to the intake underpressure area. To prevent this,
the turbocharger's compression housing has
been adapted.
This adaptation consists of bypass ducts and a
stop plate.
9
Boost pressure attempting to return to the intake
area will do so at the outer circumference of the
compression housing.
The compression housing has been fitted with an
air slot to force this pressure to flow back through
special air ducts on the outside until it is arrested
by the stop plate.
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