Exhaust System - Service Techniques BMW M3 E90

Scheme 11

Introduction

The EURO 4 exhaust emission regulations are stipulated for homologation of new vehicle models in Europe from 1 January 2005 (homologation = registration of a series-production vehicle model in the international approval list). The EURO 4 exhaust emission regulations are stipulated for all new vehicle registrations from 1 January 2006. The EURO 4 exhaust emission regulations constitute a further reduction in the pollutant limits for exhaust gases.

For the M57TU, the E60/E61 is fitted with a diesel particulate filter for the first time. The diesel particulate filter removes the soot particulates from the exhaust with a high filter efficiency (> 95 %). The nitrogen oxide emissions are not affected by the diesel particulate filter. The nitrogen oxide emissions are reduced by internal modifications to the engine.

The new diesel particulate filter developed by BMW does not constitute and disadvantages for the customer in terms of

1. extent of maintenance work
2. fuel consumption
3. engine performance
4. noise levels

The diesel particulate filter is currently designed for a service life of 200, 000 kilometers (monitored by Condition Based Service). The use of an additive for regeneration of the diesel particulate filter is not necessary (additive reduces ignition temperature of the soot).

Brief description of components

For compliance with the EURO 4 exhaust emission regulations, the M47TU/M57TU have the following new or modified components

1. Oxygen sensor For compliance with the exhaust emission limits, an oxygen sensor is necessary. The oxygen sensor is required for the adaptation of the mean injection quantity. The oxygen sensor measures the fuel-air ratio. In case of deviations, the DDE adjusts the exhaust gas recirculation rate to the new fuel-to-air ratio.
2. Injectors The injector characteristic map for injection quantity has been adapted. Design changes have given the injectors a continuous characteristic curve. This means that changes in the injection time have a direct effect on changes in injection quantity.
3. Charge-air pressure actuator (electrical actuator drive on turbocharger) The exhaust-gas turbocharger has a variable turbine geometry (VNT = "variable nozzle turbine"). To ensure compliance with the EURO 4 exhaust emission regulations, an electrical charge-air pressure actuator now adjusts the variable turbine geometry (on previous versions, an electropneumatic pressure converter adjusted the variable turbine geometry). Because of the increased adjustment speed and by acting on changes more quickly, a more precise boost pressure control is achieved.
4. Cylinder head and pistons The swirl port and tangential port of the cylinder head have been geometrically redesigned. The piston crown bowl has been modified for improved mixture formation. This has also resulted in a change to the shape of the coolant port in the piston.
5. Exhaust gas recirculation cooler The exhaust recirculation cooler is now longer. Consequently, the exhaust recirculation cooler has a greater cooling capacity. The new exhaust gas recirculation cooler enables the exhaust-gas temperature to be reduced by approx. 100 C (in EURO 4 driving cycle).
6. Diesel particulate filter (M57TU in E60/E61 only) The diesel particulate filter has a catalytic coating and absorbs the soot particulates in the exhaust. The stored soot particulates are continuously burned off at exhaust temperatures above approx. 350 °C. The stored soot particulates are cyclically burned off at exhaust temperatures above approx. 600 °C. With the use of the diesel particulate filter, the Digital Diesel Electronics (DDE) require the following additional components: Throttle valve A throttle valve restricts the intake air flow under certain operating conditions. In combination with 1 or 2 post-injection phases, this brings about an increase in the exhaust temperature (regeneration of diesel particulate filter). Exhaust backpressure sensor upstream of diesel particulate filter, exhaust temperature sensor upstream of catalytic converter and exhaust temperature upstream of diesel particulate filter The exhaust backpressure sensor is used to calculate the charge level of the diesel particulate filter when the vehicle is being driven. If the diesel particulate filter has stored too large a quantity of soot particulates, generation is initiated. As another variable, the exhaust temperature upstream of the diesel particulate filter is measured. Measurement of the exhaust backpressure by the exhaust backpressure sensor is insufficient on its own (dependence on load). From the two signals, the DDE calculates the precise charge level of the diesel particulate filter. The exhaust temperature sensor upstream of the catalytic converter monitors the exhaust temperature upstream of the oxidation catalytic converter. The diesel particulate filter cannot be regenerated until the exhaust reaches a temperature of approx. 350 °C.
7. Gas-tight swirl flaps The M57TU has completely gas-tight swirl flaps (electrically operated on E46, otherwise vacuum-operated). This means that there is no leakage past the swirl flaps at lower engine loads, thereby increasing the degree of swirl. In addition, a wide range of intermediate swirl-flap settings can be achieved by electrical operation of the flaps.

System functions

Despite the component tolerances and lifetime-effects on components (e.g. wear), the following points must be noted: The exhaust emission limits must be achieved with a sufficiently large safety margin. Major fluctuations relevant to emissions are principally expected for the following components

1. Injectors
2. Mass air flow sensor
3. Rail pressure sensor

Compensation must be made for the tolerances of the components and the influences on components over the running time. The following system functions are provided for the DDE (digital diesel electronics) for compensation

1. Injection quantity compensation
2. Zero-quantity adaptation
3. Mean quantity adaptation
4. Regeneration of diesel particulate filter (M57TU in E60/E61 only)

Injection quantity compensation

Injection quantity compensation is the definition of correction values for the pre-injection and main injection of an injector. Injection quantity compensation is carried out at the end of the production process.

Tolerances during production of the injectors mean that the actual quantity of fuel injected will differ slightly from the quantity of fuel calculated. After production, this difference is determined for each injector at various operating points by conducting measurements.

From these measurements, an adjustment value (code) is generated for each injector.

The structure of the alphanumerical code depends on the emissions standard of the engine.

1. EURO 3 exhaust emission regulations: six-digit (e.g. 78SNGT)
2. EURO 4 exhaust emission regulations: seven-digit (e.g. 88S66NB)

During vehicle assembly, the adjustment value of each injector is stored in the DDE control unit after the DDE control unit has been installed. The adjustment values are assigned to the individual cylinders according to the installation of the injectors. With these adjustment values, the DDE control module makes slight corrections to the calculated injection quantities and thus reduces the deviation specific to the injection quantity for each cylinder.

If injectors are renewed or exchanged, care must be taken to ensure that the alphanumerical code printed on each injector is assigned to the correct cylinder in the DDE control unit.

The BMW diagnosis system has the service function "Injection quantity compensation". With this service function, the code for each cylinder can be changed and stored on the DDE control unit.

For cylinders that do not need a new adjustment value, the previous adjustment values remain unchanged in the DDE control unit. Injection quantity compensation must also be performed if the DDE control unit is replaced and communication was no longer possible with the old control unit.

The codes for the injectors installed must be read off and stored in the DDE control unit.

Zero-quantity adaptation

Zero-quantity adaptation is the adaptation process that guarantees that a defined pre-injection is available for each injector after the running-in phase (approx. 1500 km).

For the engine to comply with the EURO 4 exhaust emission regulations, the pre-injection quantity, which is very small, must be precisely metered.

Because of the deviation in the injection quantity over the running time, the zero-quantity adaptation is performed continuously by the DDE control module.

For each cylinder, a small quantity of fuel is injected in overrun mode. This quantity is continuously adjusted until the DDE recognizes the required torque. The irregular rotation of the crankshaft is used to calculate the torque. The irregular rotation is recorded by the crankshaft sensor.

The DDE can thus recognize the activation duration from which the respective cylinder starts to work. During zero quantity adaptation, the amount of fuel injected is used by the DDE as a correction value for the pre-injection characteristic map.

Zero-quantity adaptation takes place alternately from one cylinder to the next during each overrun phase

1. Engine speed: 1500 to 2500 RPM (engine at operating temperature)

Zero-quantity adaptation has no effect on fuel consumption, as only a very small amount of fuel (approx. 1 mm 3 ) is injected into each cylinder.

Mean quantity adaptation

Mean quantity adaptation is the adaptation process in which the fuel-to-air ratio is corrected (partial-load range). This correction is performed by adjusting the air mass using the exhaust gas recirculation valve.

While the injection quantity compensation and zero-quantity compensation do not require additional components, an oxygen sensor is required for mean quantity adaptation. The oxygen sensor is a broadband oxygen sensor with continuous characteristic curve.

Mean quantity adaptation is not a "quick" adjustment, but rather an intelligent learning process.

A lambda error is "learnt" in a characteristic map and is permanently stored in the DDE control unit (EEPROM).

The characteristic map must be reset (deleted) in the EEPROM if any of the following components is replaced

1. Mass air flow sensor
2. Injectors
3. Rail pressure sensor

For resetting the data map, the BMW diagnosis system has the service function "Mean quantity adaptation".

Regeneration of diesel particulate filter (only on M57TU in E60/E61)

The level of charge of the diesel particulate filter is calculated by the DDE using the operating statuses of the engine.

The diesel particulate filter can be regenerated continuously or cyclically.

1. Continuous regeneration: In operating ranges in which the exhaust temperature is higher than the ignition temperature of the soot (> 350°C), the soot particulates are immediately converted. This involves the slow oxidation of the soot particulates to carbon monoxide (CO) and carbon dioxide (CO 2 ). The nitrogen dioxide present in the exhaust (NO 2 ) acts as the oxidizing agent. The nitrogen dioxide is formed from nitrogen monoxide (NO) in the oxidation catalytic converter. If the exhaust temperature is insufficient for this process, the soot particulates are initially collected and stored in the diesel particulate filter and then burned off the next time the exhaust temperature is increased.
2. Cyclic regeneration: If the driving pattern does not permit continuous regeneration of the diesel particulate filter (e.g. long periods of low engine load in urban traffic conditions with low exhaust temperatures), selective regeneration is initiated. This process is controlled by the signals from the exhaust backpressure sensor and the two exhaust temperature sensors. Like continuous regeneration, cyclic regeneration takes place without any noticeable effects on vehicle behavior. Dependent on the engine load, the regeneration is performed by selective restriction of the intake air flow in combination with 1 or 2 post-injection phases. This increases the exhaust temperature to approx. 600 °C. The remaining oxygen (O 2 ) enables combustion of the soot. The length of the regeneration cycle for the diesel particulate filter may be several minutes. The intervals between regeneration cycles depend on the conditions under which the vehicle has been operated over the last 500 kilometers. At high exhaust temperatures, continuous burn-off of soot particulates means that less soot is stored. In addition, the diesel particulate filter is regenerated every 700 to 2, 500 kilometers (depending on driving pattern). If the exhaust backpressure sensor or one of the exhaust temperature sensors fails, the diesel particulate filter is regenerated every 500 kilometers.