Tài Liệu Hệ Thống Xử Lý Khí Thải Selective Catalytic Reduction SCR Động Cơ Diesel Audi

Basic design overall systemMultiple temperature sensors are integrated in the exhaust system upstream and downstream of the turbocharger together with the oxidising catalytic converter,

Service Training

Second generation Audi clean diesel

Self Study Programme 622

For internal use only

Reducing the nitrous oxide content (NOx) in exhaust emissions is a

global challenge facing automobile manufacturers, who are

required to meet the new statutory limits set by the Euro 6

stand-ard and equivalent international regulations on exhaust emission

limits

A modern "Selective Catalytic Reduction" (SCR) emission control

system utilises the chemical synthesis product of urea (AdBlue®)

to reduce NOx emissions

In SCR systems, AdBlue® reacts with the NOx emissions to produce

water vapour and nitrogen NOx is short for nitrous oxide gases;

they occur during the combustion process in diesel engines and are

reduced by means of SCR technology ''

AdBlue® is manufactured by a solution of a chemical called urea (also called carbamide) in water Urea is a synthetic product which usually is made from natural gas and used in fertilizers, plastics and cosmetics AdBlue® is not made from recycled agricultural products For exhaust gas aftertreatment in the AdBlue® SCR system, the exhaust system requires additional components such

as the heated catalyst1), the water-cooled metering valve, the diesel particulate filter with integrated DeNOx catalytic converter and the ammonia blocking catalytic converter

AdBlue® is a registered trademark of Verband der trie (VDA)

Automobilindus-The SCR system - the key to achieving the tougher EU 6-1 (W), BIN 5, Tier 2 and LEV III emission standards

Learning objectives of this self study programme:

This Self Study Programme describes the design and function of an

exhaust gas aftertreatment system adapted for the use of AdBlue®

reducing agent Once you have completed this Self Study

Pro-gramme you will be able to answer the following questions:

1) Installed in a limited number of models only.

• What is the function of the heated catalyst?

• Which new sensors are integrated in the reduction system?

• Why does the exhaust gas temperature have to be relatively high?

• What is the function of the ammonia blocking catalytic verter?

con-622_023

Reference

The Self Study Programme teaches a basic knowledge of the design and functions of new models, new

auto-motive components or new technologies

It is not a Repair Manual! Figures are given for explanatory purposes only and refer to the data valid at the

time of preparation of the SSP This content is not updated.

For further information on maintenance and repair work, always refer to the current technical literature

Introduction

Emission standard 4Audi models based on the Modular Longitudinal Matrix (MLB) with SCR system 5

Exhaust gas aftertreatment by an SCR system

Basic design (overall system) 6

Exhaust systems

Introduction _ 81.6l / 2.0l TDI engine (EA288) 83.0l V6 TDI engine _124.2l V8 TDI engine _16

Fuel and reducing agent tank

Reducing agent tank _18Audi Q7 18Audi A6 ’11 and Audi A7 Sportback 20Audi A4 ’14 _22Audi A8 ’10 and Audi A8 ’14 24Swirlpot in active tank _27

Sensors and actuators

System overview (shown using the 3.0l V6 TDI engine as an example) 28Reducing agent pump V437 30Reducing agent tank sender G684 (level sender) _31Particulate sensor G784 with control unit _32Reducing agent injector N474 (metering valve) 32

Display strategy

Overview 35Messages relating to reducing agent fill level 36Fault warnings 37

Emission standard

Emission limits from the emission standards

The emission standard for motor vehicles limits sets out limits for

carbon monoxide (CO), nitrous oxide (NOx), hydrocarbons (HC) and

particulate matter (PM) and subdivides vehicles thus into emission

classes Specific key numbers are assigned and used, for instance,

to calculate road tax and to classify vehicles for low emission

zones Emission limits vary according to engine type (petrol or

diesel engine) and vehicle type

LEV Low Emission Vehicle

ULEV Ultra Low Emission Vehicle

SULEV Super Ultra Low Emission Vehicle

BIN 5 Emission standard for California and other US states

The term "BIN" stems from the word "bag"; this is because the exhaust gases are collected in bags during emission tests and analysed There are 10 categories ranging from BIN 10 (highest emissions) to BIN 1 (lowest emisisons)

Particulate matter (PM)

Hydrocarbons (HC) and nitrous oxides (NO x )

Carbon monoxide (CO)

They are subject to ongoing tightening within the European region The values are measured in type tests within the driving cycle, and the vehicle manufacturer has to guarantee the compliance with these limits for a specified period of time and mileage This is achieved by in-service monitoring and by carrying out recalls in case of systematic faults Some vehicles are subject to limits on evaporative fuel emissions and mandatory On-Board Diagnostics (OBD)

Abbreviations

Nitrous oxides (NO x ) Nitrous oxides (NO x )

Introduction

Phase-in dates of EU emission standards for diesel engines

2.0l R4 TDI 3.0l V6 TDI

3.0l V6 MPI 3.0l V6 MPI

4.2l V8 TDI

3.0l V6 MPI4.2l V8 TDI

Audi models based on the Modular Longitudinal Matrix (MLB) with SCR system

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Reference

For information on the design and function of the SCR system in the Audi A3 saloon (USA), refer to Self Study Programme

625 "Audi A3 saloon"

Basic design (overall system)

Multiple temperature sensors are integrated in the exhaust system upstream and downstream of the turbocharger together with the oxidising catalytic converter, the diesel particulate filter, the oxygen sensor and the NOx sender The exhaust aftertreatment process is monitored with the aid of the various sensors

The exhaust gas aftertreatment system comprises the reducing

agent tank system together with the water-cooled reducing agent

injector, a close-coupled heated catalyst1), an SCR-coated diesel

particulate filter and an ammonia blocking catalytic converter

located upstream of the main silencers

Components

Ammonia blocking catalytic converter

NOx sender 2 with control unit G687

Catalyst heater control unit 1 1)

Oxygen sensor

G39

Oxidising catalytic converter

with catalyst heater 1)

SCR-coated diesel particulate filter

1) Installed in a limited number of models only.

Exhaust gas aftertreatment by an SCR system

Task of the SCR system

In the first stage, emissions and fuel consumption are reduced by

minimising friction; in the second stage, emissions are minimised

by the exhaust gas aftertreatment system

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To achieve the EU 6 emission limits, new components, sensors and actuators are used to minimise nitrous oxide emissions in addition

to the familiar AdBlue® reducing agent

Reducing agent metering system control unit J880

Swirlpot with reducing agent pump

V437

Reducing agent active tank

Reducing agent transfer pump V436

Reducing agent passive tank

Reducing agent filler neck

Heater metering line

con-Exhaust gas treatment module, see

"Exhaust gas treatment module with

The design and function of engines from the Modular Diesel System (EA288) are explained in Self Study Programme 608

"Audi 1.6l / 2.0l 4-cylinder TDI engines"

Engine modifications

To meet the EU 6 requirements, the existing 2.0l and 1.6l TDI

engines have been upgraded to include the following components:

• Variable valve timing

• High pressure exhaust recirculation

• Cylinder pressure control system

• 2000 bar injection system

Exhaust gas temperature sender 4 (downstream of diesel particulate filter) G648

To meet the requisite emission standards, modern exhaust

systems are no longer configured simply as silenced exhaust

systems, but as exhaust gas treatment and monitoring systems

They comprise:

• Oxidising catalytic converter with/without catalyst heater1)

• SCR-coated diesel particulate filter

• Ammonia blocking catalytic converter

The complex open and closed-loop control functions have been

integrated into the engine control unit

The exhaust systems has the following sensors:

• Oxygen sensors

• NOx sensors

• Differential pressure sensors

In addition, there are several temperature sensors which monitor the temperature levels in the exhaust system

1) Installed in a limited number of models only.

Exhaust systems

Exhaust gas treatment module

To achieve the EU 6 emission limits, an NOx aftertreatment system

will be integrated into the close-coupled exhaust gas treatment

module from the EU 5 engine together with the oxidising catalytic

converter and the coated particulate filter

Achieving the EU 6 emission limits requires the use of a Selective

Catalytic Reduction (SCR) system

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Versions

Depending on model version, a distinction will be made in future between two EU 6 variants of the close-coupled exhaust gas treatment module:

• System with NOx accumulator catalyst (NSK) for smaller and lighter vehicles based on the Modular Transverse Matrix (MQB)

• System with Selective Catalytic Reduction (SCR) for vehicles based on the Modular Longitudinal Matrix (MLB) with a larger flywheel mass (EU 6 heavy duty)

Exhaust gas treatment module Turbocharger

Exhaust gas recirculation servomotor 2

V339

Overview

EGR valve

EGR cooler

The substrate of the close-coupled exhaust gas treatment module

is made of metal, enabling the module to reach its operating

termperature more quickly This metal body is coated with a

substrate of metal oxides, e.g aluminium oxide, with additional

layers of platinum and palladium These precious metals act as

catalysts for hydrocarbons and carbon monoxide

Integrating the SCR coating into the particulate filter using copper

zeolite enables the system to be positioned close to the engine

After cold-starting the engine, the operating temperature of the

SCR catalyst is reached more quickly and maintained for longer

during low-load vehicle operation

Additional engine modifications are required for heating the catalytic converter The reducing agent injector N474 is integrated directly downstream of the oxidising catalytic converterand above the transition funnel, with the result that the entire volume in the funnel is available for carburetion

Since air cooling is no longer sufficient due to the high thermal load, the reducing agent injector has a coolant jacket which, in addition to the valve, protects the electrical connection against overheating

The reducing agent injector is integrated in the low-temperature circuit of the engine cooling system, see page 34

Reducing agent injector

N474 (water cooled)

Oxidising catalytic converter

Exhaust gas treatment module with SCR system

Exhaust gas temperature sender 3 G495

Exhaust gas temperature sender 2 G448

NO x sender G295

Oxygen sensor G39

Exhaust gas temperature sender 1 G235

Differential pressure sender

Ammonia blocking catalytic converter

An ammonia blocking catalytic converter with a combined SCR and

oxidising catalyst coating is located downstream of the SCR-coated

diesel particulate filter and performs two tasks:

Its first task is to oxidise the carbon monoxide (CO) produced

during soot regeneration to carbon dioxide (CO2) through reaction

with the precious metal-containing coating

The task of the control unit is to generate a slight backpressure

downstream of the diesel particulate filter by means of a

motor-ised exhaust gas flap

This produces an excess pressure of approx. 30 – 40 mbar

down-stream of the particulate filter relative to the exhaust pressure

downstream of the exhaust flap This excess pressure results in a

positive flow gradient (purging rate) in the EGR cooler and in the

downstream EGR valve The flow of recirculated exhaust gas is

controlled (mapped) by the EGR valve This backpressure is

meas-ured by exhaust gas pressure sensor 1 G450

Exhaust valve control unit J883

The 73° operating range of the exhaust flap is defined by:

• the exhaust pressure downstream of the exhaust flap

• the nominal exhaust pressure upstream of the exhaust flap

• the mass flow through the exhaust flap

In the event of failure of exhaust gas recirculation servomotor 2 V339, the exhaust valve control unit J883 takes on the task of controlling the exhaust gas recirculation rate

Its second task is to ensure that no NH3 leaves the exhaust system During this process, NH3 is oxidised to N2 and H2O

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Design and sensors

Ammonia blocking catalytic converter

Exhaust flap control unit J883

Exhaust pipe from exhaust gas treatment module

3.0l V6 TDI engine

What state-of-the-art diesel and direct injection petrol engines

have in common are ever-decreasing exhaust gas temperatures

Automatic start-stop systems, regular intermittent operation of

compact internal combustion engines, or the more effective

conversion of combustion energy to mechanical drive power often

result in temperatures below the light-off temperature of the

Exhaust gas temperature sender 2

(upstream of oxidising catalytic

Z119

SCR-coated diesel particulate filter, see

"Oxidising catalytic converter and diesel particulate filter" on page 14

1) Installed in a limited number of models only.

Ammonia blocking catalytic converter, see

"Ammonia blocking catalytic converter"

on page 15

Sensors and connections on the diesel particulate filter

Exhaust gas temperature sender 2 G448 and exhaust gas

tem-perature sender 3 G495 are used, respectively, upstream and

downstream of the oxidising catalytic converter in order to

monitor the operating temperature of the oxidising catalytic

converter The values measured by both exhaust gas

tempera-ture sensors are also important variables for the

regen-eration of the diesel particulate filter To determine the

load on the particulate sensor, the exhaust pressure is

measured upstream and downstream of the particulate

filter and not against atmospheric pressure

Exhaust gas temperature sender 4 G648 monitors the

regeneration temperature

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Connection for exhaust gas temperature sender 3 (downstream of oxidising cata- lytic converter) G495

Connection for differential pressure sensor downstream of diesel particulate filter

Oxygen sensor G39

Exhaust gas temperature sender 2 (upstream of oxidising catalytic converter) G448

Connection for differential pressure sensor upstream of diesel particulate filter

NOx sender 2 G687

Oxidising catalytic converter and diesel particulate filter

In some models, an electric heating plate1) has been integrated

into the oxidising catalytic converter to enable the oxidation

catalyst reach its light-off temperature more quickly The heated

catalyst1) consists of a thin sheet of wound metal substrate, which

is installed upstream of the catalytic converter and energised as

required

The exhaust gases are additionally heated with 500 watts of power

at cold start, after which the heating plate1) is energised at low engine load (partial load) in order to maintain the temperature of the catalytic converter

Overview

Oxidising catalytic converter

Exhaust pipe to ammonia blocking catalytic converter

Connection for differential pressure sensor upstream of diesel particulate filter

Exhaust gas temperature sender 2

(upstream of oxidising catalytic

converter) G448

Heating plate 1)

1) Installed in a limited number of models only.

Ammonia blocking catalytic converter

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An ammonia blocking catalytic converter is used in place of the

previous DeNOx catalytic converter Now, an ammonia blocking

catalytic converter with a combined SCR and oxidation catalyst

coating is installed downstream of the SCR-coated diesel

particu-late filter and performs the following two tasks:

First, to oxidise the carbon monoxide (CO) produced during soot

regeneration to carbon dioxide (CO2) through reaction with the

precious metal-containing coating

The second task of the ammonia blocking catalytic converter is to ensure that no NH3 leaves the exhaust system During this process,

NH3 is oxidised to N2 and H2O

Ammonia blocking cat

Design and sensors

NOx sender 2 G687

4.2l V8 TDI engine

In the large-displacement 4.2l V8 TDI engine, an oxidising catalytic

converter with a 500 watts heating plate is fitted in each exhaust

pipe This means that an oxygen sensor and an exhaust gas

tem-perature sensor are installed upstream and downstream,

respec-tively, of the oxidising catalytic converter

Both exhaust pipes subsequently merge into one

To ensure the even distribution of reducing agent via a mixer, the air-cooled metering valve is installed in the most favourable position The exhaust system then splits again in order to accom-modate the two SCR-coated diesel particulate filters Two exhaust gas temperature sensors located at the outlet of the diesel particu-late filter monitor the regeneration temperature

The metering valve is an air-cooled solenoid valve, and its task is to

provide a continuous supply of reducing agent to the SCR-coated

diesel particulate filter The reducing agent injector is activated by

the engine control unit in a pulse-width-modulated (PWM)

fashion An even distribution of ammonia in the SCR-coated diesel

particulate filter is the key to a high degree of implementation

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Mixer Reducing agent injector

Exhaust gas temperature sender 2 for bank 2 G449

Connection of catalytic converter heater 1 Z119

Oxygen sensor G39

NOx sender G295

Catalytic converter heater 2

Z120

Oxygen sensor 2 G108

Heated catalyst 2

Flexible pipe

Exhaust gas temperature sender 3 for cylinder bank 1 G496

Flexible pipe Heated catalyst

Reducing agent injector N474 (metering valve) and mixer

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Exhaust gas temperature sender 4 for bank 1 G651

SCR-coated diesel particulate filter

Exhaust gas temperature sender 4 for bank 2 G649

NOx sender 2 G687

Rear section of exhaust system

In the further course of the exhaust system, both pipes merge into

a connecting pipe The combined exhaust gas streams then flow into the two main silencers

The NOx sender 2 G687 is mounted on the connecting pipe housing

This sensor monitors the carbon monoxide (CO) produced during the regeneration cycle and the small quantities of ammonia arising from the high temperature gradients during regeneration of the diesel particulate filter Both values influence the quantity of reducing agent injected

The active heating plate provides a significant reduction in sions both during the start phase and at low engine load The heating plate has a power output of 500 watts and is located directly upstream of the main catalytic converter In SCR systems, the heated catalyst is able to optimally evaporate the injected reducing agent and thereby increases the efficiency of the SCR catalytic converter

emis-These heated metal catalytic converter not only increase the operating temperature by up to 100 °C, but also allow NOx conver-sion to begin much earlier by injecting the reducing agent onto the heated diesel particulate filter

To keep the catalytic converter warm for as long as possible, the heating plate and the catalytic converter are encased in an insulat-ing layer and a second stainless steel housing

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Connecting pipe

Catalytic converter heater Z119 and Z120

Connection of catalytic converter heater 1 Z119

Oxygen sensor G39

Exhaust gas perature sender 3 for cylinder bank 1 G496

tem-Exhaust gas temperature sender 2 G448

Oxidising catalytic converter Heating plate

Reducing agent tank

An active fuel tank and, depending on model, an auxiliary passive

fuel tank serving as a reducing agent reservoir are used in addition

to the conventional diesel fuel tank

The pressure relief valve has also been deleted with the integration

of the service vent into the diaphragm filler cap Both tanks, if available, are connected to the filler neck by ventilation lines

Audi Q7

Two reducing agent reservoirs, an active tank and a passive tank,

have been added to the conventional diesel fuel tank

The capacity of the diesel fuel tank has been kept at 100 litres by

making optimal use of available underbody design space

The reducing agent storage capacity of approximately 23 litres is distributed to the reducing agent active tank directly below the filler neck (7.5 litres) and the underbody reducing agent passive tank (15.5 litres) The diesel fuel tank is filled, as is customary, via the tank filler neck Both filler necks can be accessed via the tank flap

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Overview

Reducing agent

filler neck

Reducing agent active tank (7.5 litres)

Reducing agent pump V437

Reducing agent passive tank

Reducing agent active tank

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The reducing agent pump V437, the overflow connection for filling

the reducing agent passive tank, the connection for filling the

reducing agent passive tank, and the heated supply and return

lines are mounted on the reducing agent active tank

The reducing agent passive tank serves as additional storage

capacity, is not heated and does not have any built-in sensors The

reducing agent transfer pump V436 which circulates the reducing

agent is mounted on it The pump is configured as a diaphragm

piston pump and activated by the engine control unit by means of

analogue signals

The transfer pump V436 is activated by the engine control unit

J623 and pumps the reducing agent from the reducing agent

passive tank into the reducing agent active tank The reducing

agent transfer pump V436 is activated whenever the reducing

agent tank sender G684 in the reducing agent active tank detects a

low fill level, and provided that the vehicle is travelling faster than

10 kph

The fuel tank sender may not be at its max level for short times

due to sloshing movement of the reducing agent on winding roads

The engine control unit J623 recognises this condition and likewise

activates the reducing agent transfer pump

The reducing agent active tank is heated and has built-in sensors When the active tank is filled, the reducing agent flows into the reducing agent passive tank under gravity after the preset level in the reducing agent active tank is reached

View from below

Reducing agent passive tank

Return line Supply line

Overflow fitting Swirl pot

Connection to reducing agent injector N474

Overflow

Connection to passive tank

Reducing agent pump V437

Reducing agent transfer pump V436

Audi A6 ’11 and Audi A7 Sportback

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A 17-litre reducing agent tank is used on the underbody in addition

to the fuel tank, which holds approx 73 litres

This reducing agent tank is configured as the active tank

It is filled from the exterior via a filling line located adjacent to the filler neck and is identified by a black filler cap It is made from high-grade plastic and adapted to the underbody contours by blow moulding

Diesel / reducing agent filler neck

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