Engine Brake*/Constantly-Open; Throttle Valves - Mercedes-Benz OM 904 LA Operating Instructions Manual

Before commissioning
General information

Engine brake*/constantly-open

throttle valves*

To increase the braking power, the engine
2
can be equipped with an exhaust brake
valve on the exhaust gas turbocharger in
conjunction with constantly-open throttle
valves on the cylinders.
Whereas exhaust gas backpressure, acting
through the exhaust brake valves, can be
used to increase the braking power, the
constantly-open throttle valves cause a
reduction of compression in the power
stroke (3rd stroke), leaving compression
(2nd stroke) practically unaffected.
The constantly-open throttle valves are
valves in the cylinder head. When open,
they connect the combustion chamber to
the exhaust duct, which generates the re-
quired decompression in the power stroke.
24
Constantly-open throttle valves on the
4-cylinder engine
When the engine brake is engaged, the
constantly-open throttle valves are opened
pneumatically on the 4-cylinder engine and
hydraulically on the 6-cylinder engine. At
the same time, the exhaust brake valve on
the exhaust gas turbocharger is closed.
i
Hydraulic constantly-open throttle
valves
The constantly-open throttle valves are
not actuated in the lower engine speed
range between 900 and 1,300 rpm or if
the engine oil temperature is less than
40 °C.
Observe these restrictions during oper-
ation.