Mercedes-Benz OM 471 Introduction Into Service Manual page 65

Functions
Brake stage I
1 Exhaust rocker arm
2 Exhaust rocker arm with
hydroelement
3 Brake rocker arm
4 Exhaust cams
5 Exhaust cams
In brake stage I the brake power is achieved by cylinders 1...3.
The engine management (MCM) control unit (A4) actuates the
engine brake solenoid valve, stage 1 (Y624) just as soon as the
driver activates brake stage 1 over the engine brake switch.
Oil is now pushed out of the engine oil circuit over the oil duct for
cylinders 1...3 (14) of the exhaust rocker shaft (10) into the exhaust
rocker arm with hydrolement (2) of cylinders 1...3.
In the exhaust rocker arms with hydroelement (2), oil first flows
through the check valve (16) in flow direction and thus the space
under the piston (8) is filled. If there is no gap anymore between
the piston (8) and brake rocker arm (3) then the check valve (16) is
closed by the now accumulating back pressure.
62
6 Brake cam
7 Outlet valve
8 Piston
9 Spring
14 Cylinder 1...3 oil duct
– This printout will not be recorded by the update service. Status: 09 / 2011 –
15 Cylinder 4...6 oil duct
16 Check valve
Y624 Engine brake solenoid valve, stage 1
Y625 Engine brake solenoid valve, stage 2
In this way a frictional connection is made between the brake
rocker arm (3) and the piston (8). The respective exhaust valve (7)
is now opened through the downward movement of the
respective brake rocker arm (3).
If brake stage I is deactivated, the solenoid valve, stage 1 (Y624) is
no longer actuated > the applied oil pressure in the exhaust rocker
arms with hydrolement (2) and the exhaust rocker shaft (10)
reduce.
The pistons (8) are pushed back to the downstop by spring force.
The missing frictional connection between the brake rocker arm
(3) and the exhaust rocker arm with hydroelement (2) means that
the downward movement of the brake rocker arm (3) is no longer
transferred to the exhaust valve (7).
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