3 Series E46 316Ci (N45) COUPE
In a current-free state, the fuel evaporation control valve is closed. This prevents the ingress of fuel vapour from
the activated carbon filter into the inlet pipe when the engine is switched off.
Closed-loop Lambda control system
Optimum efficiency of the catalytic converter can only be achieved if an ideal fuel/air ratio is used for combustion
(
λ
= 1). To this end, oxygen sensors are used upstream and downstream of the catalytic converter.
The oxygen sensors upstream of the catalytic converter have a steady characteristic output curve (measure
oxygen content in rich and lean ranges.)
The measurement method employed by this oxygen sensor is different to an oxygen sensor with an erratic
characteristic output curve. The oxygen sensor is therefore connected using 6 pins instead of 4.
•
Oxygen sensors upstream of catalytic converter
The oxygen sensors upstream of the catalytic converter (control sensors) are used to assess the
composition of the exhaust gas.
The control sensors are screwed into the exhaust manifold.
The oxygen sensors measure the residual oxygen content in the exhaust fumes. The voltage values
determined are relayed to the DME control unit. The DME control unit corrects the mixture composition by
adjusting the injection period.
Values which are greater or less than
λ
1 are aimed at depending on the operating condition.
•
Oxygen sensors downstream of catalytic converter
The oxygen sensors downstream of the catalytic converter (monitoring sensors) are used to monitor the
control sensors. In addition to this, the function of the catalytic converter is monitored.
In the 4-cylinder engine, the monitoring sensors have a special arrangement:
The monitoring sensor for cylinders 1 and 4 is positioned between the primary and main catalytic converter.
The monitoring sensor for cylinders 2 and 3 is positioned downstream of the main catalytic converter.
To ensure full operational reliability of the oxygen sensors upstream of the catalytic converter, a temperature of
approximately 750
°
C is required (350
°
C for oxygen sensors downstream of the catalytic converter). For this
reason, all oxygen sensors are heated.
The oxygen sensor heating is controlled by the DME control unit. When the engine is cold, the oxygen sensor
heating remains switched off, as condensation which is present would otherwise destroy a hot oxygen sensor
due to thermal strain.
This means that the lambda control becomes active shortly after the engine is started. The oxygen sensor is
initially warmed up using a reduced heating power, to avoid imposing unnecessary loads on it due to thermal
strain.
Secondary air system
(only N46 engine)
> E46 (N46B18 and N46B20)
> E83, E85 (N46B20OL)
The purpose of the secondary air system is to perform exhaust re-treatment during the engine warm-up phase.
During this process, fresh air is blown directly into the exhaust manifold thus increasing the rate at which the
catalytic converter is heated (thermal post-combustion of exhaust fumes).
The secondary air pump is activated by the DME control unit via the secondary air pump relay shortly after the
engine has started.
The switch-on period is dependent on the following marginal conditions:
•
Engine temperature
SBT Engine control for N45, N46 E46, E60, E81, E83, E85, E87, E90, E91, E92, E93
BMW AG - TIS
19.01.2013 04:18
Issue status (12/2007) Valid only until next DVD is issued
Copyright
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