Secondary air injection
46
Exhaust system
Introduction of the smart fortwo, Model Series 451
Secondary air injection
Engine 132 is fitted with a secondary air injection
pump (electric air pump), which injects additional
fresh air in order to reduce exhaust gas emissions
after a cold start and to accelerate the warming of the
catalytic converter to its reaction temperature.
The necessary air is injected into the exhaust ports in
the cylinder head by the secondary air injection pump
via the combination valve. The secondary air injection
pump is actuated by the ME-SFI [ME] control unit via a
relay.
The secondary air injection pump switchover valve is
supplied with vacuum from the vacuum reservoir at
the intake manifold via a check valve.
When actuated, the secondary air injection pump
switchover valve releases vacuum to the combination
valve. This opens and the air injected by the
secondary air injection pump passes through to the
exhaust ports in the cylinder head.
The injected air reacts with the hot exhaust gases in
the outlet port. The carbon monoxide (CO) and hydro-
carbon (HC) are oxidized. This "afterburning"
process increases the exhaust temperature and
reduces pollutants.
The duration of secondary air injection is dependent
on the coolant temperature.
The secondary air injection pump is only actuated at a
coolant temperature of 45 °F to 97 °F (7 °C to 36 °C)
and for a maximum duration of 33 seconds.
P14.30-2183-00
Secondary air injection
1 Cylinder head
2 Combination valve
3 Air hose
4 Vacuum hose
M33 Secondary air injection pump
Y32 Secondary air injection pump switchover
valve
SN_Typ 451_us.book Seite 46 Freitag, 30. November 2007 1:56 13
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