Engine Brake - Volvo D12 Service Manual

Group 25 Intake and Exhaust System

Engine Brake

1 Camshaft
2 Shutter
3 Exhaust pressure governor
The Volvo Engine Brake (VEB) is a combination of two
brake systems: the exhaust brake and the compression
brake.
Exhaust brake
The exhaust pressure governor uses a shutter mounted
in the exhaust outlet from the turbocharger. This shutter,
connected to the exhaust pressure governor plunger,
can restrict the exhaust gas flow. This creates a braking
effect during the exhaust stroke when the exhaust gases
cannot evacuate freely and create an overpressure be-
tween the pistons and the shutter.
Compression brake
During the engine compression stroke and combustion
(operating) stroke, the controlled opening of the exhaust
valves creates an overpressure in the combustion cham-
ber. This, in turn, produces a braking effect on the
crankshaft.
The camshaft on an engine with a compression brake
has two extra lobes on each exhaust cam profile. The
lifting height of the extra lobes is very low when com-
pared to the normal exhaust lobes. To enable the extra
lobes to open the exhaust valves, the exhaust rocker
arms are arranged in a manner by which the valve clear-
ance can be reduced during the braking sequence.
ShimShims are available in thickness invtervals of 0.05
mm (0.0002 in). Sizes range from 2.0–2.4 mm (0.08–
0.094 in) and from 3.2–3.95 mm(0.126–0.156 in).
Thickness is stamped on the shims.
Fig. 3: D12 Engine
4
5
6
Design and Function
W2003501
Rocker arm
Control valve
Shim
11