DAF 95XF. Manual - part 424

4

XE ENGINE INLET/EXHAUST SYSTEM

General

95

XF series

2-2

8

11

10

9

6

7

i 400394

6.

Glow filaments

7.

Electro-pneumatic boost pressure valve

8.

Inlet manifold

9.

Pressure-reducing valve

10. Supply line
11.

Engine brake valve

6

©

 0008

4

95

XF series

General

XE ENGINE INLET/EXHAUST SYSTEM

2-3

2.2

DESCRIPTION OF TURBOCHARGER SYSTEM WITH WASTEGATE

Wastegate
To make the engine more responsive at lower
engine speeds, a turbocharger is used that
produces a better fill ratio at such speeds.
If no special provisions were made, the boost
pressure yielded by such a turbocharger would
be too high at maximum engine speeds. This is
prevented by using a wastegate.
The boost pressure is measured by a sensor on
the inlet manifold.
The boost pressure control valve (1), which -
depending on the boost pressure measured - is
activated by the electronic unit, operates the
diaphragm of the wastegate (2) and the control
rod connected to it, using air pressure. The air
supply available via a pressure reducing
valve (3) is used for activating the air pressure
valve. The control rod operates a valve in the
turbine housing.
The valve in the turbine housing is opened when
the maximum allowable pressure has been
reached. When the valve is opened, some of the
exhaust gases will be discharged to the exhaust
pipe rather than being used to propel the
turbocharger’s turbine wheel.

Compression housing by-pass
At higher boost pressures, the compressor of
the turbocharger tends to allow this pressure to
return to the inlet underpressure area. To
prevent this, the compression housing of the
turbocharger has been adapted.
This adaptation consists of bypass ducts and a
stop plate.
Boost pressure attempting to return to the inlet
area, will do so at the outer circumference of the
compression housing.
Providing the compression housing with an air
slot forces this pressure to flow through special
air ducts on the outside until it is arrested by the
stop plate.

i400387

2

1

3

6

©

 0008

4

XE ENGINE INLET/EXHAUST SYSTEM

General

95

XF series

2-4

Electro-pneumatic boost pressure valve
There are three connection points at the upper
side of the electro-pneumatic boost pressure
valve (1).
Point A (coding “ATM”) is connected to the air
supply via a pressure reducing valve.
For the pressure at connection point A, see the
main group “Technical data”.
Point B (coding “OUT”) is connected to the
wastegate of the turbocharger.
Point C (coding “VAC”) is the air-bleed
connection.
The electrical connection point (2) for activation
of the magnetic valve is located at the bottom of
the electro-pneumatic boost pressure valve (1).
This magnetic valve is activated proportionally,
using a duty cycle.

Situation wastegate not activated
If the maximum boost pressure calculated by the
electronic unit has not yet been reached, the
electronic unit activates the magnetic valve (3)
with a high duty cycle-value (current value).
This high duty cycle-value creates a powerful
magnetic field.
The supply pressure at connection point A is
also exerted under the diaphragm surface.
A pressure of approx. 0.8 bar under the
diaphragm surface suffices to move the
magnetic valve (3) upwards against the force of
the magnetic field.

This forces valve (4) downwards, as a result of
which the bleeding facility C is closed and there
will be an interconnection between points A
and B.
The pressure at the upper side of the magnetic
valve (3) will now move the magnetic valve
downwards again, which creates a state of
balance.
So, in this situation, the supply pressure at the
wastegate connection (point B) will always be
approximately 0.8 bar lower than the reservoir
pressure at connection point A, as a result of
which the wastegate will not be activated.

4

3

A

B

C

B

C

A

3

4

E500607

C

B

A

2

1

VAC
OUT

ATM

6

©

 0008

4

95

XF series

General

XE ENGINE INLET/EXHAUST SYSTEM

2-5

Situation wastegate activated
This is the situation in which the maximum boost
pressure calculated by the electronic unit is
achieved.
The electronic unit will now activate the
magnetic valve (3) with a lower duty cycle-value
(current value).
The supply pressure prevailing under the
diaphragm surface can now move the magnetic
valve (3) upwards against the force of the
magnetic field.
This forces valve (4) downwards, as a result of
which the bleeding facility C is closed and there
will be an interconnection between points A
and B.
The rise in pressure at connection point B will
now cause the wastegate to be activated.

Once the boost pressure calculated has been
reached. the duty cycle-value will again
increase. This will again intensify the magnetic
field.
The magnetic valve (3) will now again move
downwards under the influence of the magnetic
field strength and the pressure on the upper side
of the magnetic valve.
The interconnection between A and B is closed
and bleed facility C opened.
The pressure at connection point B will now
drop, until a state of balance is again achieved.
This allows accurate adjustment of the desired
boost pressure.

Note:
If the electronic unit is unable to activate the
electro-pneumatic boost pressure valve (for
instance, due to an open circuit), the supply
pressure from the pressure-reducing valve,
which prevails under the diaphragm surface, will
move the magnetic valve (3) upwards.
This creates a connection between the air
supply at connection point A and the wastegate
at connection point B.
The wastegate is now activated (opened), as a
result of which the maximum boost pressure will
not be reached.

4

3

A

B

C

B

C

A

3

4

E500607

C

B

A

2

1

VAC
OUT

ATM

6

©

 0008