Mercedes-Benz OM 471 Introduction Into Service Manual page 66

Brake stage II
1 Exhaust rocker arm
2 Exhaust rocker arm with
hydroelement
3 Brake rocker arm
4 Exhaust cams
5 Exhaust cams
In brake stage II the brake power is provided by all cylinders.
As soon as the driver activates brake stage 2 over the engine brake
switch the engine management (MCM) control unit (A4) not only
actuates the engine brake solenoid valve, stage 1 (Y624), but also
the engine brake solenoid valve, stage 2 (Y625).
Oil is now pushed out of the engine oil circuit over the oil duct for
cylinders 1...3 (14) and oil duct for cylinders 4...6 (15) of the
exhaust rocker shaft (10) into all exhaust rocker arms with
hydrolement (2).
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.
i Introduction of engine OM 471 and exhaust aftertreatment > 09/2011 >
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 is
now opened through the downward movement of the respective
brake rocker arm (3).
If the brake stage 2 is deactivated the engine brake solenoid
valve, stage 1 (Y624) and the engine brake solenoid valve, stage 2
(Y625) are no longer actuated > the oil pressure applied in the
exhaust rocker arms with hydrolement (2) and the exhaust rocker
shaft (10) drops.
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).
Functions
W14.15>1135>79
63