Catalytic converter heating, function

P07.70-2016-06

Catalytic converter heating via engine control

21 Exhaust flap with vacuum unit

157 Firewall catalytic converter

159 NOX catalytic converter

B11/4 Coolant temperature sensor

B19 CAT temperature sensor

G3/1 O2 sensor downstream of catalytic converter

G3/2 O2 sensor upstream of catalytic converter

L5 Crankshaft position sensor

M16/6 Throttle valve actuator

N3/10 ME-SFI [ME] control unit

N15/3 ETC control unit
(with transmission 722)

N37/4 NOX (nitrogen oxides) control unit

N37/4b1 NOX (nitrogen oxides) sensor

R4 Spark plugs

T1/1 Cylinder 1 ignition coil

T1/2 Cylinder 2 ignition coil

T1/3 Cylinder 3 ignition coil

T1/4 Cylinder 4 ignition coil

Y32 Air pump switchover valve

CAN Databus (Controller Area Network)

The catalytic converter heating brings the catalytic convertors (firewall and NOX catalytic convertors) more rapidly to the operating temperature (300 to

450 °C) and thereby greatly reduces the exhaust emissions during a cold start and during warm-up.

The following sub-systems are involved:

 Ignition systemIn the idle speed range and in line with the coolant temperature the ignition angle is retarded for e.g. 20 seconds in order to increase the exhaust gas temperature.

 Idle speed control  Dependent on coolant temperature, the idle speed is increased to approx. 1100 to 1300 rpm for up to 20 seconds.

 Transmission shift delay (with transmission 722)  Depending on the coolant temperature, the automatic transmission is upshifted with a delay.

 Air injection  the enriched fuel-air mixture after start and in the warming-up phase contains many more uncombusted hydrocarbons in the exhaust. The injected air (afterburning) causes post-oxidation in the catalytic converters.

The ME-SFI [ME] control unit is able to detect that the operating temperature has been reached and that the catalytic converters are operating at normal efficiency from the signals supplied by the O2 and NOX sensors.

P07.70-2040-05

NOX catalytic converter heating-up/cooling off by specific exhaust gas recirculation

21 Exhaust flap with vacuum unit

157 Firewall catalytic converter

159 NOX catalytic converter

B19 CAT temperature sensor

G3/1 O2 sensor downstream of catalytic converter

G3/2 O2 sensor upstream of catalytic converter

N3/10 ME-SFI [ME] control unit

N37/4 NOX (nitrogen oxides) control unit

N37/4b1 NOX (nitrogen oxides) sensor

Y93 Exhaust flap switchover valve

a Exhaust line (for normal mode)

b Bypass line

CAN CAN data bus
(Controller Area Network)

As a result of its relatively large geographical distance to the cylinder head, the NOX catalytic converter requires an exhaust flap in order to be able to reach its operating temperature as rapidly as possible and to maintain this.

The exhaust flap also protects the NOXcatalytic converter from overheating, by opening and thus the exhaust gas flows through both exhaust pipe. This further cools the exhaust gas.

During a cold start, the exhaust flap is closed and the exhaust gas flows through the narrower and shorter bypass line. Thus the exhaust gas is not cooled to such a great degree, which beings the NOXcatalytic converter more rapidly to the operating temperature.

In normal mode the exhaust flap is opened and exhaust gas flows through both exhaust lines.

By means of this targeted exhaust guiding, the NOXcatalytic converter is always maintained within the optimal operating range.

The catalytic converter temperature sensor continuously monitors the exhaust gas temperature and the temperature of the NOXcatalytic converter at the NOX-catalytic converter input and transmits a corresponding voltage signal to the ME-SFI [ME] control unit.

The exhaust flap is actuated according to the operating status by the ME-SFI [ME] control unit via the exhaust flap switchover valve. The exhaust flap is thus closed by the vacuum unit due to the vacuum and opened by aeration.

In deenergized status (exhaust flap switchover valve) the exhaust flap is held by a spring in the open position.