Exhaust Pressure Governor - Volvo D12 Service Manual

Group 25 Intake and Exhaust System

Exhaust Pressure Governor

The exhaust pressure governor(EPG) acts as an exhaust
brake when slowing the vehicle down. It also speeds en-
gine warm-up by applying a load to the engine during
idle and warm-up. Engine load is created by the (EPG)
throttling the flow of exhaust gases, causing the engine
to work against a backpressure. This increases combus-
tion temperature and shortens the warm-up period.
On engines without a pre-heater, the (EPG) is activated
before the starter motor is engaged. For engines with a
pre-heater, the (EPG) is activated after pre-heating,
start-up and post-heating have taken place.
The (EPG) is activated by a control pressure of about
200 kPa (29 psi), by a combi relay when it is used during
starting and warm-up. When used for engine braking,
the exhaust pressure governor is controlled by a single
two-position switch if the engine is equipped with an ex-
haust brake only, and by dual two-position switches if the
engine is equipped with a Volvo Engine Brake, or VEB
(both exhaust brake and compression brake).
Engines with Exhaust Brake Only
Two-position switch (ON/OFF)
With the switch in the ON position, the exhaust pressure
governor is activated by a control pressure of approx.
750 kPa (110 psi) subject to the following conditions:
•
Accelerator pedal fully up.
•
Clutch pedal fully up.
•
Engine speed above 1100 rpm.
•
Boost pressure below 52 kPa (7.5 psi).
•
When using cruise control and preselected road
speed is exceeded by 7 km/h (4 mph) (disengage-
ment at 4 km/h (3 mph) over preselected speed).
•
ABS not activated (continuous control).
Fig. 17: Exhaust pressure governor (EPG)
Fig. 18: Exhaust brake switch for WX, WG and AC
Fig. 19: Exhaust brake switch for VN/VHD
Design and Function
T2006948
W2000731
W3001324
19