Proceedings of the 8th Automotive Materials Conference: Ceramic Engineering and Science Proceedings, Volume 1, Issues 5/6

82 Pages·1980·5.861 MB·English

Proceedings of the
8th Automotive Materials Conference
Lawrence H. VIack
Van
Conference Director
A Collection of Papers Presented at the
8th Automotive Materials Conference
Sponsored by the
Department of Materials and
Metallurgical Engineering
University of Michigan
and
Michigan Section
The American Cemmic Society
November 29, 1979
The University of Michigan
Ann Arbor, Michigan
ISSN 0196-6219
Published by
The American Cemmic Society, Inc.
65 Ceramic Drive
Columbus, Ohio 43214
0T he American Ceramic Society, 1980
Executiue Director & Publisher Editor
Arthur L. Friedberg William J. Smothers
I Technical Director Associate Editor
Clarence E. Seeley Mary Foddai Vaughn
Director of Publications Circulation Manager
Donald C. Snyder Gay W. Panek
J
Kent Bowen; William C. Mohr; Richard M. Spriggs; Louis J. Trostel. Jr., ex
offcio;W illiam J. Srno!hers. ex oflcio; Arthur L. Friedberg, ex ofjicio.
Editorial Aduisoy Board: L. J. Trostel. Jr.. Chairman; R. L. Berger; W. G.
Coulter. R. T.D irstine; R. A. Eppler; E. J. Friebele; F. A Humrnei; W. J. Lackey;
D. McGee; G. W. Phelps; D. W. Readey; and W. R. Walle.
T.
Editorial and Subscription Offices: 65 Ceramic Drive. Columbus, Ohio,
43214. Subscription $60 a year; single copies $12 (postage outside U.S. $2
additional). Published bimonthly. Printed in the United States of America. Allow
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allowed if the subscriber fails to notify the Society of a change of address.
CESPDK Vol. 1, No. 5-6, pp. 1980
233-310,
Preface
The automotive industry has experienced several major technological advances that
have noticeably affected society a whole. The initial step was the development of
as
an internal combustion engine and its harnessing to a primitive vehicle which made
the automobile a reality. An historical change occurred with the development of the
assembly line which brought the automobile to the whole of society. The laborer
who worked in industry found that he also could utilize the products he helped
manufacture. U.S. citizens realized a significant expansion in their horizons with
the development of a nationwide thruway system. Although this technological
advance was extra-vehicular, both the automobile industry and the individual user
benefitted.
The current interaction between society and the automotive industry focuses on
the betterment of the environment, specifically of the exhalents which the au-
tomobile produces. Sophisticated technology was able to achieve a 90% reduction in
undesired emissions. However, society insists that a further 9% should also be
removed. This achievement will require a greater technological step than was
realized by any of the previous advances. Not only must also the engine operate with
the benefit of near perfect combustion design, but it must be self-correcting for
nonoptimum operating conditions and for the adversities that come with thousands
of miles of wear and tear. This demands a feedback system, which in turn requires
sensors to measure the compositions, the temperatures, and the pressures of the
engine products.
Exhaust gases are inhospitable to monitoring devices. The reactive combustion
of unburned hydrocarbons, nitrogen oxide, andor excess oxygen, all at elevated
temperatures, lead to intolerable conditions for metals and polymers. It is natural,
therefore, to look to ceramic materials. However, these sensory materials must also
serve a functional purpose in feedback circuits. While this is an unusual role for
ceramic materials, it is not an impossible one. This topic was the subject in
November, 1979, of a conference jointly sponsored by the Michigan Section of The
American Ceramic Society and the Department of Materials Engineering at The
University of Michigan,* the proceedings of which are contained in this volume.
The papers of that conference addressed the Materials Aspects of Automotive
Sensors. These included transducer applications of the following types: capacitive,
linear differential transformers, piezoresistive, potentiometric, and piezoelectric.
Also, semiconduction devices are required for oxygen potentials that involve both
ionic and electronic transport. Finally, attention was given to temperature sensitiv-
ity, both wanted and unwanted.
Lawrence H. Van Vlack
Conference Director
*The support of the following companies is gratefully acknowledged: AC Division, GMC; the
Bendix Corp.; Carborundum Co.; Engelhard Industries; Ford Motor Co.; the Garrett COT.; and
Rockwell International.
...
111
Table of Contents
.......................................
Needs for Automotive Sensors.. .233
J. G. Rivard
.....................................................
Knock Sensors.. .247
Joseph P. Dougherty
.........................................................
Transducers .248
Brenton L. Mattes
............................
Pressure Sensors: Techniques and Materials .254
Paul Votava
.....................
Materials Considerations in Wiegand-Effect Devices .266
J. David Marks
Zirconia-Oxygen Sensors: Origins of Nonideal
...........................................................
Behavior. .272
William J. Fleming
...................................
Resistive-Type Exhaust Gas Sensors .281
E. M. Logothetis
Materials Considerations the Development of
.....i.n ............................................
Automotive Sensors .302
William G. Wolber
Overview: The 8th Annual Automotive Materials
Conference .......................................................... .307
William G. Wolber
V
Ceramic Engineering and Science Proceedings
William J. Smothers
copyright@ The American Ceramic Society, 1980
Needs for Automotive Sensors
J. G. RIVARD
Electrical and Electronics Div.
Ford Motor Co., Dearborn, Mich. 48556
The present application oj sensors, and their performance, cost, and reliability are
presented. Future sensor deuelopment and the motivating jorces such as lower
sensor cost, impmued reliability. and new application requirements are outlined.
The development of low cost, reliable sensors is critical to insure the successful,
broad application of automotive electronics. This application of electronics is
stimulated in part by governmental regulations and in part by market desires for new
features and product improvements. The development of new sensors for automo-
tive requirements will be challenged by the want for laboratory precision, military
reliability, and hostile environment capabilities at consumer prices.
Ceramics is one the technologies that must be in the forefront if the technical
community is to successfully meet the challenges of the 1980’s and beyond. The
merging of ceramics and electronics has already given us thick film electronic
circuits and some sensors to meet our present needs. This development must
continue to expand to meet the automotive industry’s future needs. The progress that
has been made to date with automotive sensors and the task before the automotive
industry can best be understood by examining sensor applications and consid-
erations, sensor status today, and sensor challenges of the future.
Sensor Applications and Considerations
Currently, sensors are being utilized in the engine control, vehicle control, and
instrumentation areas. The number of sensors used on each vehicle depends on
model and options. Certain 1980 Ford vehicles are being produced with up to 12
individual sensors per vehicle. The following discussion will explain why elec-
tronics and sensors are being applied to these three automotive areas.
Engine Controls
The major impetus behind the use of sensors and electronics for engine control
has been:
0 FederaVCalifornia emissions legislation
0 Corporate Average Fuel Economy Mandate (CAFE)
0 Acceptable vehicle performance
Federal and California emission regulations, combined with the need to im-
prove fuel economy, have contributed significantly to the growth of electronic
engine control systems (Table I). In addition to the increasingly tighter standards,
there are other requirements to contend with such as the 1984 high altitude regula-
tions and tamper-proof emission control systems.
These regulations are being met through a combination of vehicle and engine
downsizing, aerodynamic and rolling resistance reductions, and engine/drivetrain
233
efficiency improvements. Electronic engine controls, including the necessary sen-
sors, play a major role in improving engine efficiency to meet these standards while
still maintaining acceptable vehicle performance. Engine control electronics offer
the opportunity for improved functional capability, improved accuracy, reduced
variability, and using closed-loop controls.
1978, Ford introduced an electronic feedback carburetor (Fig. 1) that
In
utilized one sensor, an exhaust gas oxygen sensor, and one actuator for the feedback
control of the carburetor fuel metering rods. This control is used in conjunction with
a three-way catalytic converter to achieve conversion of all major pollutants (HC,
CO, and NOx). The three-way catalyst’s effectiveness is limited to a very narrow
aidfuel ratio window (Fig. 2). Conventional carburetors are not capable of achiev-
ing this tight aidfuel ratio control because they cannot compensate for changes
in
fuel composition, component wear, and changes in the air and fuel density. The
range of aidfuel ratio variations with the conventional carburetor is four to five times
wider than required. These limitations can be overcome with the feedback car-
buretor which continuously provides the proper aidfuel ratio required for optimum
operation of the catalyst.
For 1980, Ford made available the third generation Electronic Engine Control
System with Electronic Fuel Injection (EEC IIYEFI) to meet the even more stringent
emission and fuel economy regulations while maintaining acceptable vehicle per-
formance.
The EEC IIYEFI (Fig. 3) system uses eight sensors and nine actuators along
with the electronic control module. The sensed parameters are:
0 Manifold pressure
0 Barometric pressure
0 Manifold charge temperature
0 Engine coolant temperature
0 Throttle position
0 Exhaust gas valve position
0 Crankshaft position
0 Exhaust gas oxygen
The manifold pressure and manifold charge temperature are used to calculate
the intake air manifold charge density. This, along with the engine speed provided
by the crankshaft position sensor and cylinder geometry, allows a calculation of the
air flow into the cylinders for use in controlling fuel flow rates. The crankshaft
position sensor also provides engine phase information for ignition timing. The
engine coolant temperature sensor is used to modify ignition timing, EGR flow, and
aidfuel ratio controls at low engine temperatures such as during cold start and warm
up. The throttle position sensor, by indicating driver demand, plays a role in the
transient control of ignition timing, EGR flow, and fuel flow. The exhaust gas valve
position sensor and the barometric pressure sensor are used in the control of EGR
flow. The exhaust gas oxygen sensor is a key sensor for the system. While most of
the other system sensors monitor engine input conditions, the exhaust gas sensor
monitors output conditions to provide a feedback signal to compensate for unmea-
sured variables such as fuel and air density, component tolerances, etc.
Electronic Instrumentation
The market demand for new features and product improvements, through the
cost effective replacement of mechanical systems with electronics, are major rea-
sons for developing electronic dashboard instrumentation.
234
A two sensor, Miles-to-Empty fuel indicator system was introduced by Ford in
1979 to provide drivers with an indication of distance to drive on remaining fuel. In
1980, electronic instrumentation was expanded to include the graphic diagnostic
display (Fig. 4) and the Electronic Instrument Cluster and Message Center (Fig. 5).
The Electronic Cluster and Message Center features a digital-readout elec-
tronic speedometer, a bar-graph readout electronic fuel gage, and an alpha-numeric
electronic message center display. The Electronic Message Center utilizes a speed
sensor, a level sensor, pressure switches, a temperature switch, and six other
switches and a control module to perform calendar clock functions, seven trip log
functions, and eleven warning functions.
The trip log functions which can be displayed at the driver’s request incIude:
0 Distance to empty
0 Elapsed miles (or km)
0 Elapsed time
0 Estimated arrival time
0 Distance to destination
0 Distance per gallon
0 Average speed
The system’s eleven vehicle warning functions are:
CRITICAL
0 Brake pressure
0 Alternator
0 Oil pressure
0 Engine temperature
SECONDARY
0 50 miles-to-empty
0 Trunk ajar
0 Door ajar
AUXILIARY
0 Washer fluid
0 Headlamp out
0 Taillamp out
0 Brakelamp out
When one of these warning items needs attention, a warning message will be
displayed and a tone will sound. The items are prioritized so that if there is a critical
warning, the clock or trip log information will be replaced and the warning will flash
continuously. Secondary warnings will flash for four seconds at 16 second intervals
until the condition is corrected. These warnings will not appear if critical warnings
are present. The auxiliary warnings will appear only once for four seconds when the
condition is detected. If the condition is not corrected, the warning will return the
next time the engine is started. The message center can at any time, at the command
of the driver, display in sequence, the status of all eleven items monitored by the
warning system.
Vehicle Controls
Currently, a major vehicle control system in production is speed control.
Initially, speed control was available only on vehicles with automatic transmissions.
In 1979, Ford expanded this application to manual transmission vehicles and at the
same time, increased the driver controlled functions with the addition of resume.
235
0 On/Off
0 Set
0 Accelerate
0 Coast
0 Resume
The 1980 speed control system (Fig. 6) uses a vehicle speed sensor and a
throttle position sensor. The vehicle speed sensor is the key element in the system's
major control loop while the position sensor is used in a secondw control loop to
eliminate speed regulation hunting.
Sensor Status Today
The few preceding examples of sensor applications should provide an insight
into the automotive sensor business. Sensors currently in use on Ford products can
be grouped into the following seven generic categories.
SENSORS TECHNOLOGY
0 Pressure (absolute) Capacitance
0 Exhaust gas oxygen Voltaic & resistive
0 Crankshaft position Variable reluctance
0 Temperature Resistive
0 Angular & linear Resistive
position
0 Speed Reluctance & optical
0 Liquid level Resistive
Each of these has unique performance, package, and functional requirements
but in general they have one common requirement. They must survive in a harsh
underhood environment for at least 80 467 km (or 2000 hours). This environment
+
can produce temperatures from -40" to 15OoC, vibrations up to 15g, mechanical
shock to 50g, thermal shock, immersion or contamination with brake fluid, oil,
ethylene glycol, salt spray, etc. The following discussion will identify key require-
ments and fundamental design approaches currently utilized for each of the seven
sensor areas.
Pressure Sensors
These underhood sensors are required to provide an accurate output over a
typical pressure range of 17 to 105 kPa. The most stringent requirement is Manifold
Absolute Pressure (MAP) sensing which requires a 1.5% full scale accuracy and a
response of 15 milliseconds (time constant).
Many pressure sensors use a ceramic capacitive sensing element to convert
pressure into a usable electrical output, capacitance. The capacitive signal is
processed by a thick film electronic circuit into a voltage which is sent to the
electronic control unit. This ceramic capacitive sensing element design was consid-
ered optimum for an automotive application for the following reasons.
1) It exploits the low thermal coefficient of expansion of ceramics to provide
long term stability.
2) It exploits the highly stable thermal mechanical properties to provide a
uniform response to the measured pressure.
3) The ceramic sensing element manufacturing process can use high volume
thick film circuit manufacturing equipment (such as screen printers). Ceramic
materials are typically used in the manufacture of hybrid circuits.
The ceramic sensing element consists of an alumina diaphragm and an alumina
236
substrate. A conductive electrode is screen printed on the surface of each alumina
disc. The capacitive unit and its vacuum reference are formed by bonding the
diaphragm and substrate together with a glass seal approximately 0.05 mm thick.
Exhaust Gas Sensor
The exhaust gas oxygen sensor, or EGO sensor, is another example of a high
technology sensor which takes advantage of the wide range of electrical properties
available in ceramics. Two types of EGO sensors have evolved at Ford. Each
utilizes a different electrical property to sense the same exhaust parameter-oxygen
partial pressure. The zirconium dioxide (ZrO,) EGO sensor is a galvanic cell which
generates a voltage having a logarithmic dependence on the ratio of oxygen partial
pressure inside (air reference) and outside (exhaust gas) the cell. The titanium
dioxide EGO sensor is a variable resistor. Its electrical resistance varies with the
partial pressure of oxygen raised to the llm power (where m = 4 in most cases). As
shown in Fig. 7, there is a large change in oxygen partial pressure at the stoichiomet-
ric A/F ratio. The oxygen dependent characteristic of each sensor demonstrates a
corresponding large change at the stoichiometric A/F ratio. It is this sensor charac-
teristic which is utilized to control feedback carburetor systems within the tight A/F
ratio window required for optimal three-way catalyst conversion efficiency.
The EGO sensor location within the exhaust manifold imposes severe en-
vironmental conditions not only on the functional ceramic components but on the
metal package as well. In this location the sensor sees temperature extremes ranging
from -40" to severe thermal shock, gas pressure pulses, vibration,
+lOOO"C,
chemical corrosion and mechanical abrasion conditions, in addition to the usual
underhood water and oil splash. The greatest challenge in the development of the
EGO sensor has been to build adevice with stable functional characteristics over the
operating environment extremes and 80 467 km life.
As can be seen in Fig. 8, the construction details of the 1979 production Zr02
sensor and pilot production TiOr sensor are considerably different. Both are rugged
constructions, similar in many details to automotive spark plugs. Unlike spark
plugs, which utilize the insulating properties of ceramics, the EGO sensors utilize
their active electrical properties. The designs provide a means to connect to the
active elements and appropriate packaging to maintain operation over the required
life.
Cranhbafl Position
This sensor is required to detect absolute crankshaft position with 1/4 of a
degree accuracy while being subjected to engine vibrations and temperature from
+
to 150°C. The current sensor is a variable reluctance device that consists of a
-40"
magnet and pole piece inserted in a wire wound coil. As the teeth of a crankshaft
mounted gear pass by the sensor, changes in the sensor magnetic field are produced
which in turn induce a coil current or voltage that is sensed by the control module.
Te mpemture
Engine coolant and intake manifold charge temperature sensors have 2 3%
+
accuracy requirements over -40" to 125°C ranges. The current sensor element is
an epoxy encapsulated disc thermistor which is packaged in a threaded brass bulb.
The thermistor disc is fabricated from a mixture of powdered metals and metal
oxides formulated to obtain the desired temperature coefficient (resistance vs.
temperature change).
237
Angular and Linear Position
Position sensors, as used for throttle and EGR valve sensing, are currently
required to maintain a +3% accuracy while being subjected to over 5 million dither
+
cycles at temperatures up to 150°C. The current position sensors utilize plastic
film or cermet (metal oxide slurry on a ceramic substrate) resistive elements, metal
wipers, and plastic housings to achieve a relatively cost effective design.
Speed Sensors
Currently two types of sensors are used in vehicle control applications, the
optical type speed sensor and the reluctance speed sensor. Both sensors are requked
to operate in a -40" to vehicle environment. The challenge of this device is
+85T
to provide a usable output over the entire speed range while meeting both stringent
reliability and cost objectives.
The traditional reluctance speed sensor has continued to be applied in conven-
tional speed control applications. An optical speed sensor is utilized in speed control
applications used in conjunction with electronic instrument clusters. The optical
speed sensor promises improved reliability due to its design. The optical sensor
consists of an infrared light emitting diode and an optical transistor packaged in
infrared transparent material. The optical sensor reads the pulses caused by a slotted
revolving disc which interrupts the light beam. The pulse rate is proportional to the
vehicle speed.
Fuel Level Sensor
The current customer awareness of fuel economy requires an accurate (2-3%)
level sensor which linearly indicates fuel level. This sensor must meet these
requirements for each fuel tank type with their diverse geometries and fuel tank
dynamics. A usable electrical output must also be provided for both electronic and
conventional instrument clusters.
The current design uses a wire wound potentiometer with a float operated
wiper. The windings of the fuel tank sender are tailored for each tank geometry to
provide a linear output.
The Challenge for Future Sensors
The preceding overview of automotive sensors and developments to-date has
only set the stage for the challenges of future sensor developments. The motivating
forces and direction for new sensors are:
0 Lower sensor costs
More reliable sensors
0
0 Improved sensor capabilities
New application requirements
0
Sensor Costs
One of the factors that can severely limit the use of electronics and sensors in
the future is cost. Whereas electronics has made substantial progress in improve-
ment of cost per function, sensors have not kept pace (Fig. 9). In fact, sensor costs
have remained relatively constant. This means that sensors represent a larger and
larger percentage cost of the total system. The traditional low-volume users of
sensors were able to employ $100 to $1000 sensors whereas these costs are
considered exorbitant for automotive systems containing 8 to 10 sensors. In fact,
sensor costs in the $20 to $30 range are still considered too costly. The cost goals for
238