35
5V Turbo
G39
G62
V101
N122
J299
J220
The vacuum box for the charge pressure con-
trol valve is controlled in the cold start phase
by the electro-pneumatic secondary air con-
trol valve N112 while the secondary air system
is in operation.
The control pressure acts on the turbocharger
waste gate, and the exhaust gas flow is routed
past the turbine wheel up to the upper load
range.
The hot exhaust gases help the secondary air
system to quickly heat the catalytic converter
up to operating temperature during the cold
start phase.
To improve the exhaust gas composition,
these constituents must be reduced.
The secondary air system is responsible for
this task.
The system injects air upstream of the outlet
valves during this phase, thus enriching the
exhaust gases with oxygen. This causes post-
combustion of the uncombusted hydrocar-
bons contained in the exhaust gases.
The catalytic converter reaches operating tem-
perature more quickly due to the heat released
during postcombustion.
Secondary air system
SSP207/21
Vacuum box for charge
pressure control valve
energised
de-energised
Combi-valve
In the cold start phase, the exhaust
gases contain a high proportion of
uncombusted hydrocarbons.
