Engine Brake, Function; Overview Of Components Of Valve Timing - Mercedes-Benz OM 471 Introduction Into Service Manual

Functions
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ENGINES 471.9 in MODEL 963, 964 with CODE () Engine brake, standard system
ENGINES 471.9 in MODEL 963, 964 with CODE () Engine brake, high performance system
General information
The engine brake system used is a so>called decompression brake
system.
The braking effect is generated in the process according to the
following principle:
Shortly after the beginning of the compression stroke, as the
piston moves upwards in the direction of TDC, one of the two
exhaust valves is opened for a short time on the respective
cylinder. Therefore exhaust flows out of the exhaust manifold
back into the cylinder due to the head pressure. The compression
pressure is increased as a result and the upward moving piston in
braked in its compression stroke.

Overview of components of valve timing,

shown on deactivated engine brake
1 Exhaust rocker arm
2 Exhaust rocker arm with
hydroelement
3 Brake rocker arm
4 Exhaust cams
5 Exhaust cams
Brake cam contour
6 Brake cam
17 1st peak
18 2nd peak
The brake cams (6) have two peaks with which the brake rocker arm (3) are actuated and by
which the exhaust valves (7) can be opened.
f 1st peak (17) opens the exhaust valve (7) for a short time shortly before beginning the
compression stroke.
f 2nd peak (18) opens the exhaust valve (7) for a short time shortly before ending the
compression stroke.
60

Engine brake, function

6 Brake cam
7 Outlet valve
8 Piston
9 Spring
10 Exhaust rocker shaft
– This printout will not be recorded by the update service. Status: 09 / 2011 –
The exhaust valve opens for a brief period shortly before the end
of the compression stroke. Now part of the compression pressure
is reduced. As a result the piston is less rapidly accelerated in the
direction of the BDC in its next operating cycle.
Operating conditions
The engine braking system can be activated under the following
conditions:
f Vehicle in deceleration mode, that is the driving and clutch
pedal are not actuated
f Engine speed >!1000 rpm
f Antilock brake system (ABS) not in closed>loop operation.
11 Exhaust camshaft
12 Intake rocker arm spindle
13 Intake camshaft
Y624 Engine brake solenoid valve, stage 1
Y625 Engine brake solenoid valve, stage 2
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