Exhaust Gas Mass Flow Sensor

Kolbenschmidt Pierburg Group
Exhaust Gas Mass Flow Sensor
for Applications in Commercial
Diesel Engines –
The System for Optimizing the
Emission Characteristics

Introduction
In order to pay tribute to increasingly stringent emission standards
in the commercial vehicle sector, heavy-duty engines
have been submitted to a number of internal measures,
which in combination with suitable exhaust gas after-treatment
systems, represent the current and future state of the
art. However, the full potential of these measures, for example
cooled external exhaust gas recirculation (EGR), can only
be exploited if they are properly adjusted to all engine operating
conditions. This involves increased demands on engine
control and consequently higher standards to be met by
the sensors used in the control loop. For the future, the integration
of the second combustion partner, oxygen, promises
to release further engine control improvement potential. This
is illustrated by the findings of investigations demonstrating
that even the minutest variations in O2 concentration lead to
significant changes in the level of NOx emissions, particularly
at high EGR rates. In order to accurately adjust the O2 concentration,
it is consequently imperative to provide for exact
control of the air pathway within the engine. The definition
of the exhaust gas mass flow routed to the engine which is
necessary to this end can preferably be achieved by means
of precise and direct measurement in the exhaust gas.
The need for further, new sensor systems results from the
fact that the legislation increasingly specifies that engine
control should be OBD compatible with respect to the function
of its individual components.
NOx-Emissions
(ppm)
Smoke number
(-)
EGR rate
(%)
1000
800
600
400
200
0
6
5
4
3
2
1
0
30
25
20
15
10
5
0
Fig. 2: Simulated emissions at a sudden load variation C25 --> C100.
Control Accuracy in Stationary and Dynamic Load
Points
A comparison of control concepts based on a conventional
air mass flow sensor with those using an EGS shows the
great potential inherent in exhaust gas mass flow sensor
(EGS) technology for improving engine control. Scattered
engine raw emission levels can be significantly reduced by
using an EGS (Fig. 1).
Particulate matter (mg/kWh)
300
0.95
250
200
0.90
0.63
150
100
Concept I
AMS
50
0.6 0.7 0.8 0.9 1.0 1.1 1.2
NOx (g/kWh)
Fig. 1: Measuring-system specific spread of the emission control
quality
Besides control accuracy, the control concepts were also
analyzed in regard to their dynamic characteristics. As can
be inferred from Fig. 2, the EGS concept ensures quick control
response which leads to reduced NOx overshooting.
The response time of the exhaust gas mass flow sensor is
t 63 = 60 ms. The difference between the AMS and EGS con-
Concept IV AMS Concept V EGS Concept VI Lambda probe
-5 0 5 10
Time (s)
0.90
0.95
0.63
Concept II
EGS
0.6 0.7 0.8 0.9 1.0 1.1 1.2
NOx (g/kWh)
3

cepts in terms of dynamic behavior is negligible. In comparison,
a concept with λ-probe shows a disadvantageous
behavior with the anticipated critical NOx overshoot in the
case of a sudden load variation.
Product Benefits at a Glance
Besides high accuracy of exhaust gas flow measurement independently
of gas throughput, all requirements imposed by
engine operation are met:
4
Direct logging of the exhaust gas mass flow as control
variable
Simultaneous exhaust gas temperature measurement
Free positioning with minimum installation space
requirements allows engine-specific location
Exhaust gas temperature up to 300 °C
Accuracy of mass flow measurement +/- 2 %
Precise control of exhaust gas recirculation in all
operating ranges throughout the service life
Full OBD functionality through CAN bus
Meets all common commercial diesel requirements
Good resistance to contamination, supported by
integrated burning-off function
Flexible Application of the Exhaust Gas Mass Flow
Sensor in Engines
The exhaust gas mass flow sensor lends itself to all applications
in the on-road and off-road sector which require exhaust
gas mass flow control pursuant to demanding emission
legislation such as Euro 6 or EPA 10/13 and/or Tier 4
final.
High exhaust gas temperatures
Chemical resistance
Insensitivity to soot load
Resistance to condensate precipitation
Long service life and vibration stability
The exhaust gas mass flow sensor presented can be installed
in existing exhaust gas ducts so that only little space is required
for installing the measuring system. An uniform flow
distribution in the sensor area ensures high measuring accuracy.
An additional measuring section to be integrated into
the exhaust gas line is not necessary.
Transport and installation are facilitated by a stirrup of aerodynamic
design which prevents damage to the ceramic sensor
elements.
Design and Function
The described sensor system has the ability to determine
the exhaust gas mass flow. The exhaust gas mass flow sensor
consists of the sensor itself and an electronic evaluation
unit which are interconnected by means of a flexible, hightemperature
resistant cable. The evaluation unit is equipped
with a standard plug interface which enables the system to
be connected to the engine electronics. Through this interface,
the essential measuring variables, mass flow and temperature,
as well as all error and status messages are communicated
via CAN bus (cf. Fig. 3 “Design principle”).
The measuring principle applied is that of hot-film anemometry
which is shown schematically in Fig. 4.
51.7
80
Fig. 3: Design principle
115
Exhaust gas
mass flow m
Fig. 4: Principle of heated film exhaust gas mass flow
M8
18
69 36

Engine torque (Nm)
250
200
150
100
50
EGR mass flow – CO 2 Reference
1000 1500 2000 2500 3000 3500 4000 4500
Fig. 5: Direct EGR measurement and reference
The sensor consists of two sensor elements, one of which
measures the exhaust gas temperature ( T a ) whilst the temperature
of the other is raised ( T h ) by means of electric heating.
The gas passing the heated sensor element will cause a
heat loss Q which is a measure for the momentary exhaust
gas mass flow. In simplified terms, the following applies:
Where A stands for the flow section and c1 for a proportionality
constant.
The relative accuracy tolerance of non-calibrated sensors in
the mass flow is below 4 % already on the flow test bench in
wide ranges of the performance map. This value can be distinctly
improved further by calibration. Fig. 5 shows a direct
comparison of the measuring signal of the EGS with that resulting
from exhaust gas mass flow measurement by means
of CO2 balancing. Fig. 6 illustrates the relative accuracy tolerance
of the sensors when adding a single calibration point at
25 °C and 100 kg/h. In the application range, this tolerance
is less than 2 % at temperatures of up to 300 °C.
A further challenge for the sensor is the pulsations caused
by the load cycle effects of the engine. With the implemented
direction identification any backflows are recognized and
the gas flows exclusively in intake direction are balanced
correctly. To this end, the heating element is equipped with
two temperature sensors which are arranged in tandem in
the direction of flow. In the case of exclusive pulsation, no
temperature difference will build up between the sensors
due to the symmetric gas flow in relation to the sensor arrangement.
EGS output value kg/h
1000 1500 2000 2500 3000 3500 4000 4500
When the sensor is operated in soot-laden exhaust gas, soot
load is inevitable. As a soot deposit on the sensor elements
would significantly affect the heat transmission between sen-
sor element and exhaust gas, the measuring result would be
intolerably biased. This distortion can be avoided by regular
burning-off of the soot – a function which is already integrated
in the EGS.
Air mass test bench (kg/h)
160
140
120
100
80
60
40
1
0.64
0.55
0.17
0.66
1.5
2
0.6
0.21
0.67
0.94
1.3
Relative standard deviation (%)
0.55
0.89
0.96
0.82
0.67
0.68
1
1.1
0.82
1.1
0.73
0.71
Fig. 6: Measuring accuracy with calibration
1
1
1
1
2.4
1.9
0.5
1.5
1
Air temperature (°C)
1
1.6
1.3
1.9
2.1
2.2
1.7
2
4
6
2
3.5 4.1
4
4.7 4.3
4
3.4 3.4
2.1 2.8
2 1.7 1.4
20
0 100 200 300 400 500 600
1
2
2
2.3
5.3
3.3
4.6
5

Electrical Interface – Plug & Play
The sensor can be supplied with, optionally, 12 V and 24 V
DC under the boundary conditions of the customary standards
of industrial diesel engine applications. For communication
with the engine control unit (ECU), a CAN bus or a
PWM interface are available.
In addition to the value of the EGR mass flow, the sensor also
indicates the current EGR temperature. Via the CAN bus, the
full OBD functionality is ensured.
Validation
The sensor was validated in engine operation. To this end,
vibration and temperature cycling were tested with respect
to their impact on the sensor and the measured signals.
Moreover, the effect of aging was examined.
The sensor has been designed for operation at fluid temperatures
of up to 300 °C. As stress cracks in the ceramic
material of the sensor elements due to abrupt cooling would
only occur at substantially higher temperatures, condensate
deposits are not problematic for the sensor. An additional
tolerance increase of the sensor over its lifetime can be assumed
to be less than 2 %.
6
EU VI
EPA 10/13
Tier 4
Tier 4f
Fig. 7: Pierburg – System supplier
EGR
Mass
Sensor
Actuators
Exhaust Control
Valve
EGR
Valve
System
Development
and
Manufacturing
Intake
Throttle
Reed
Valve
EGR
Cooler
Turbo
Charger
Achieving Targets Systematically – Business Unit
„Commercial Diesel Systems“
In the ongoing endeavor to pay tribute to customer requirements,
Pierburg has pooled the relevant activities in the
“Commercial Diesel Systems” Business Unit. The comprehensive
expertise in the area of air and exhaust gas management
was combined with proven air supply products such
as intake manifolds, charge air distributors and throttles, as
well as pollutant reduction units like exhaust gas recirculation
valves, exhaust gas coolers, exhaust gas valves, exhaust
gas mass flow sensors and secondary air systems (Fig. 7).
Today, these individual elements are successfully deployed
in combustion engines as components and, by combining
several individual products, as modules. Pierburg possesses
the competence to act as your partner in engine development
in facing the challenges of present and future emission
limits (Fig. 8).
In order to be able to warrant low development costs and
high development quality, it is essential to have the right
understanding of the interaction between the individual
components and their impact on the processes taking place
inside the engine. With its fine-tuned charging system components,
Pierburg supports the engine manufacturer in this
demanding optimization process.

Pierburg is a Global Player
Long before the buzzword “globalization” became a dictum,
it was vital for the automotive and OEM supplier industries to
cross borders and establish a worldwide network of production
sites. Pierburg, too, has understood and taken this trend
into consideration early on.
Besides the German plants in Neuss, Nettetal and Berlin, the
company possesses production locations in all important
automotive markets of the world. These include production
plants and sales establishments in France, the United Kingdom,
Spain, Italy and the Czech Republic as well as North
and South America, India and China.
As an innovation and technology driving system partner of
the OEM, Pierburg is always close to its customers with its
world-wide location concept. Moreover, the plants’ specialization
and internal production network yield scale effects
and synergies, enhanced efficiency and optimized flexibility
Pierburg Exhaust Gas
Flow Sensor
Cyl. 1 to 3
Cyl. 4 to 6
Pierburg
EGR Cooler
Pierburg
Reed Valve
Fig. 8: Future engine concept (example: HDDE)
Pierburg Air Throttle
Pierburg Turbo Charger
Pierburg EGR Valve
Pierburg Bypass Valve
Further locations in low-cost regions offer customers competitive
products without trade-off in quality. For example, Pierburg
has been established in China since 2001. The plant in
Shanghai primarily caters to the Chinese market, being additionally
active as a parts supplier within the Pierburg group.
A similar strategy is pursued by Pierburg at the location Ústí
nad Labem, Czech Republic, for the European market. Pierburg
possesses a worldwide network with team spirit.
Pierburg Charge Air Cooler
(2 nd stage)
Pierburg Charge Air Cooler
(1 st stage)
PierburgTurbo Charger
Pierburg Waste Gate
Pierburg Exhaust Flap Actuator
7

Pierburg GmbH · Alfred-Pierburg-Straße 1 · 41460 Neuss · GERMANY
Tel. +49 2131 520-1 · Fax +49 2131 520-645 · www.kspg.com
Subject to alterations. Printed in Germany. A|IX|j