Tribology in Automotive Industry

33
Paper Il(iii)
Tribological design -The automotive industry
P. A. Willermet
Rapid and continuing change within the automotive industry demands continual improvement in the
quality, performance and reliability of vehicles. At the same time, competitive forces demand
shorter product cycle times and new organizational approaches to the design process. The
introduction of new technology and increased reliance on suppliers demand better methods of
evaluating designs and materials. All of these factors lead to increased opportunities for the
introduction of improved tribological design methods as well as the introduction of improved designs
and materials.
1 INTRODUCTION
The automotive industry is in a period of rapid
change. This change is driven by pressures from
several sources: increased international
competition, higher customer expectations, and
social pressures in the form of regulations
relating to emissions, fuel economy and safety.
Automotive technology has advanced
significantly in the last few years in response
to these needs. These advances include items
such as electronic engine controls and catalytic
converters which are not tribological in nature,
but which may impact tribological components.
Other advances include the implementation of
design changes which directly involve tribology
(see appendix).
The challenge faced by automotive
manufacturers, however, is not simply one of
achieving a certain level of technical
sophistication. The challenge is also to
develop better ways to implement continual
product improvement within the constraints
unique to the industry.
This paper will focus on current
applications of tribological principles to
automotive design, and on ways technology
transfer might be improved. Because
manufacturers have different approaches and
organizational structures, and because much of
the technology is proprietary in nature, the
discussion will necessarily be somewhat general.
However, it is to be hoped that the presentation
will be of use to those attempting to facilitate
the translation of research results to a
practical end use.
2 APPLICATION OF TRIBOLOGY TO DESIGN
2.1 m e desien - D rocesg
The general characteristics of a new model and
its placement in the product cycle are almost
always defined by a management consensus
process. This process must take into account
many non technical factors, including marketing,
financial considerations and the technological
vision the corporation aims to imprint on the
future product.
Advanced engineering teams propose and
evaluate design alternatives. Many factors will
enter into the choices made, many of them not
immediately obvious. For example, space
limitations may exclude certain powertrain
options, especially for low drag coefficient
front wheel drive vehicles.
In the past, such forward looking teams
have tended to carry out the task with only
minimum input from outside sources. This
approach has been found to lead to
inefficiencies in implementing and producing the
final design as well as to design shortcomings
which are difficult to correct after the fact.
The current trend is to bring other
organizations into the design process early on.
These organizations may include manufacturing,
component suppliers, tooling suppliers for
manufacturing, and design support groups. In
the case of joint ventures, which are becoming
increasingly common, even other automotive
manufacturers may be included. Ultimately,
needs for quality, manufacturing efficiency, and
shorter product cycles lead to the adoption of
simultaneous engineering, in which product and
manufacturing engineering decisions proceed in
parallel.
In the final design stage, the selected
design is finalized, refined and released for
manufacturing. This may be the responsibility
of forward model teams, which retain
responsibility for monitoring the vehicle in
production. These teams do detailed
development, calibration for performance and
emission objectives and durability testing.
2.2 The role of triboloizy
At this point one may ask: “Who does the
tribology?” . Tribology was not explicitly
mentioned at any point. Tribology is an organic
part of the process, and tribology specialists
are brought into the design process as described
below.
CornDonen t SUDDl iers; Many parts which are
subject to friction and wear may be designed and
furnished by component suppliers (Table 1).
Accordingly, design responsibility may be rather
diffuse. When a supplier assumes responsibility
34
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table 1. Partial list of powertrain parts
having tribological significance which are often
obtained from suppliers
Engines
Camshaft
Tappets
Valves
Crankshaft
Rods
Pis tons
Rings
Seals
Pumps
Bearings
Engine Oil
- - - - - - - - - - - -
Transmissions Axles
Clutch Plates CV Joints
Transmission Bearings
f h i d Seals
Bearings Gear Oil
. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ - - - - - - - - - - - - - - - - -
Seals
Brakes Tires
Friction Tires
materials
Seals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
for the design of a part, the automotive
manufacturer relies on his knowledge. It is not
always easy to know how sophisticated various
suppliers are because of a wish to protect
proprietary technology on the part of the
supplier and lack of a perceived need to know on
the part of the automotive manufacturer.
Obviously, there will be wide variations. For
example, some suppliers have established
reputations for depth of understanding in
tribology which rests on a substantial body of
publications in the open literature. Clearly,
visible competence in this area makes a supplier
more attractive to the vehicle producer. Other
suppliers may not have established reputations
in this manner, but the fact that the components
supplied function with low failure rates
suggests at least some empirical knowledge.
Unless the automobile manufacturer has retained
expertise in design of the particular component
and applies it to evaluate designs and supplier
capabilities, it will be difficult to know
whether the part functions as well as it could.
This will continue to be an issue, as
competitive pressures lead to greater reliance
on supplier research and expertise.
Desien ennineers; Few engineers have extensive
prior training in tribology. Generally
speaking, knowledge is obtained from design
practice documents, from colleagues, from
vendors and from experience. Forward thinking
organizations actively encourage continued
education through participation in seminars and
courses. In such organizations, design
engineers are usually competent practical
tribologists in their areas of responsibility.
However, the move to ever higher standards of
reliability and durability will demand more
sophisticated approaches than are commonplace
today. In addition, design engineers will need
to take the lead in evaluating suppliers for
competence in design of tribological components.
Desien analvsts: Mathematical analysis of
tribological interactions is critical for highly
stressed contacts such as cam/tappet contacts,
journal bearings and gearing. Design analysis
computer programs fill these needs and are
progressively becoming more powerful and
flexible. These will be discussed more fully
below.
Triboloev mecialists; These are understood to
include metallurgists, lubrication specials and
the like as well as tribologists per se. These
resources are typically employed during a
specific design exercise if and when a need is
perceived by design engineers. If no problems
are encountered, these resources often are not
employed. If the link between design engineer
and specialist is too weak, design issues which
would benefit from deeper understanding may be
dealt with by an extrapolation of existing
methods. The tribology specialist should
accordingly make sure that lines of
communication with his design colleagues remain
open.
Lubricant sumliers; The role of the lubricants
supplier is somewhat special, particularly in
the case of engine oils. Gear oils, which are
rarely replaced, are specified by manufacturers.
Automatic transmission performance is critically
dependent on the frictional behavior of the
fluid/friction material couple. 'Accordingly,
the properties of these fluids are also
specified and controlled by manufacturers.
Engine oils are periodically replaced by the
vehicle owner. They usually are described
generically for better customer identification,
especially in North America. Suppliers and
manufacturerd work together to define test
methods and sometimes also specifications
covering viscosity and performance properties
such as antiwear protection, oxidation
resistance, bearing corrosion, etc. Because of
the quasi-generic nature of automotive
lubricants, properties are usually taken as
typical for the current generation of fluids
during the design process. When possible,
unique fluids are avoided because of service
availability concerns.
2.3 The design process - summary
Competitive pressures are leading to shorter
product cycles, simultaneous engineering
practices, and to greater demands for product
quality, performance and economy. At the same
time, improved productivity on the part of
design groups will be required.
The automotive industry relies heavily on
the design capabilities of suppliers, and this
reliance is growing. Accordingly, ensuring that
the supplier community is using the latest
design methods and technology should have a high
priority .
Knowledge of applied tribology is
widespread among design engineers, although few
have much formal academic training in the
subject. Even s o, the drive for continual
improvement in the product as well as the
importance of critically assessing supplier
designs show the need for increased
sophistication.
Shortening of the product cycle and
implementation of simultaneous engineering make
it essential that tribological concepts be
applied to the design process at the very
beginning.
. Improving the sophistication and
capabilities of design tools
. Introducing new tools and methods
. Helping design engineers to upgrade skills
. Evaluating and improving supplier
This can be done by:
35
capab i 1 it ie s
Improving links between specialists and
design engineers
.
The tribology community can participate by:
Working with automotive manufacturers and
suppliers to develop new and upgraded
design tools.
Organizing courses and seminars aimed at
design engineers.
consultants, suppliers and in-house experts
as well as by universities and professional
societies.
Communicating research results and
tribology concepts in forms accessible to
the general engineering community'.
2.4 Triboloeical design methods and design
This can be done by
issues
Design tools, generally in the form of computer
programs or reference handbooks, are the best
means of formalizing the incorporation of
tribology concepts and methods into the design
process. Considerable advances can be made by
application of information already available to
the tribology community. Some open issues,
however, will require new information for
satigfactory resolution.
Desien euide; Design guides describe and set
limits on parameters such as physical dimen-
sions, materials, stress levels and the like,
which are to be used in designing a component.
These are intended to be a compilation of the
state of the design art as practiced by the
manufacturer. Although such documents are not
primarily,-tribological design tools, practices
specified therein impact the tribological
behavior of the final product. A design guide
is, of course, updated periodically and will
grow in sophistication as better information
becomes available to design engineers. Efforts
to encourage the development of expertise
through education in its many forms should
assist the transfer of new technology into
design guides.
Enginehowertrain simulation Drovrams; These
allow evaluation of design alternatives early in
the design process with a minimum of experimen-
tal input. Friction and durability are less
important in these global models than combustion
efficiency, emissions and power output, but they
do play a role. For programs of this sort,
reasonable approximations of friction losses or
stress levels are more appropriate than precise
calculations requiring detailed input.
Accordingly, well documented scaling algorithms
could be of practical value in this application.
Bearine desien D rovrams;
programs calculate the film thickness and
temperature rise in dynamically loaded
crankshaft journal bearings. This is no small
task, since loads and film thicknesses change
continually in complex ways (1, 2 ) . These
programs are used to optimize a number of design
variables, including bearing dimensions. This
is particularly important for transversely
Bearing analysis
mounted front wheel drive configurations, which
can place severe restrictions on the overall
crankshaft length.
important in assessing the impact of reduced
engine oil viscosity as part of the North
American move toward 5W30 oils. While these
programs are very useful, additional work needs
to be done to establish quantitative correlation
with operating engines. This will be
increasingly important as higher loads drive
bearing operating conditions further into the
mixed lubrication regime, and as higher maximum
engine speeds put greater thermal stress on
lubricants. Other challenges are to incorporate
and verify methods of dealing with non-ideal
conditions, such as misalignment ( 3 ) .
They have also been
Viscometrics: Improved bearing design programs,
lubricant viscometrics and bearing properties
are linked issues which are of importance to
both automotive manufacturers and suppliers.
Lubricant suppliers are particularly interested
because engine oil specifications will
ultimately reflect the critical parameters
determining bearing performance. Improved
understanding of the relationships between the
performance of multigrade engine oils and
viscosity as measured at high temperature and
high shear rate (HTHS viscosity) ( 4 ) has led to
HTHS limits for factory fill oils, and may lead
to a redefinition of API viscosity. However,
open issues still remain. Is HTHS viscosity an
adequate lubricant parameter for defining film
thickness, or will further development of
viscometric methods be needed ( 5 ) ? Since EHD
film thickness and traction calculations require
parame ter s such as pressure-viscosity
coefficient and glass transition
pressure/temperature, should oil specifications
ultimately include similar parameters? The
answers are not obvious to this researcher.
Bearing performance is ultimately a
function of oil additive composition, bearing
materials and surface finish as well as design
and viscometrics. Accordingly, it is necessary
to not only determine relationships between film
thickness and oil viscosity, but also between
film thickness, oil and bearing composition, and
bearing performance. This is a difficult
experimental task being pursued by manufacturers
and lubricant suppliers (1, 2, 6, 7).
Low friction oils; Oils formulated to give
lower friction losses have resulted in some
improvement in fuel economy (see appendix).
There is reason to believe, however, that
further improvements in fuel economy may be
achievable through improvements in friction
reducing additive technology (8). Further
improvements in friction reducing oil technology
would not only result in improved fuel economy,
but would also affect the economics controlling
the selection of design options. For example,
if the friction losses in sliding cam/tappet
contacts were reduced by 50% by low friction
oils, then the costbenefit ratio for roller cam
followers would increase by a factor of 2.
Accordingly, it is important to know what is the
ultimate level of friction reduction attainable
with practical oil formulations so that the
industry can work toward implementation of
improved technology.
I. Examples would include Society of Automotive
Engineers technical papers and "Lubrication
Engineering", published by STLE.
36
Surface uroperties: Although considerable
progress has been made in surface measurement
techniques, experience has shown that the
description of engineering surfaces embodied in
specifications is often inadequate.
For example, a finishing method may be given,
together with a surface roughness value. If the
surface is inadequately specified, the finishing
method might go out of control without the
knowledge of the operator, resulting in
inexplicable field problems. Difficulties have
been encountered in the industry when
implementing new finishing methods because
surfaces which appear the same have performed
very differently. Potential problems include
noisy cams and failed bearings. Because
surfaces need to be statistically controlled in
production, an ideal result would entail
characterization methods sufficiently
straightforward to allow use in factories on a
routine basis. Failing that, more complex
methods could be useful in problem solving or
quality control.
Valve gear desien uroerams; A considerable
effort has been devoted to developing
computational methods for the design and
analysis of valve trains (9). These have
resulted in proprietary computer programs which
are used on a routine basis for analyzing the
kinematics, stresses and thermal behavior of
cam/tappet contacts. Programs are used on a
more limited basis for analyzing more
complicated issues related to valve train
dynamics. Stress levels and flash temperatures
are used as criteria to define design limits,
for example, to exclude excessively aggressive
cam profiles. These criteria can also be used
to select materials appropriate for the demands
placed on them by a particular design approach.
The utility of such programs could be further
enhanced by the application of EHD and mixed
lubrication theory to allow estimations of oil
film thickness and friction losses to be made as
well (10, 11).
Improved computer methods are being
developed, spurred by developments in computer
technology and by increasingly user friendly
software. Since this work does not appear to
directly impact material specifications, it is
less visible than the efforts referred to above,
and is generally proprietary. Finite element
analysis and CAD/CAM methods are being applied,
as are approaches obtained from studies of
elastohydrodynamic lubrication.
Valve eear desipn oDtions; Valve train friction
is a significant fraction of total engine
friction. In the United States, government
mandated Corporate Average Fuel Economy (CAFE)
objectives make low friction design options like
roller cam followers attractive in many designs
despite their higher cost. The move to 4-valve
engines, however, doubles the cost of this
particular approach. Accordingly, minimizing
sliding cam/tappet friction by attention to
design details deserves careful attention.
Piston rinP/cvlinder bore models: Some
manufacturers have in-house models aimed at
calculating ringbore friction and wear (12,
13). These do not appear to be widely used as
design tools by the automotive industry, because
pistons and rings are generally designed by
outside suppliers, who provide needed
engineering data to engine designers. Models
focussed on evaluating design variables such as
side loading, bore distortion and scaling
effects, rather than the details of the
ringbore interface, could see wider use.
Other desien models; Computer methods are
widely used to assist in many design problems.
Examples include finite element analysis methods
applied to cylinder block distortion and
connecting rod stresses. Although these and
other issues are not tribological in nature,
they may influence tribological behavior. For
example, if cylinder bores distort on engine
assembly or during operation at temperature,
then ring tension must be high to achieve
effective sealing. Maintaining round cylinder
bores allows the designer to minimize ring
tension and thus reduce piston/cylinder bore
friction. Similarly, reduced reciprocating mass
leads to reduced loads, greater oil film
thickness and lower friction in rings and
bearings.
Material/surface treatment selection Droerams;
Data bases, especially in combination with
improved data retrieval methods, may greatly
enhance the ability of design engineers and
tribologists to choose better materials and
surface treatments. Such programs are not in
widespread use at the moment, but current
developments suggest that they may be developing
rapidly into valuable tools. Some programs are
being developed on a proprietary basis, but
others, in various stages of development, have
been presented in the open literature (14, 15).
It seems probable that specialized data bases
will see widespread use well before a general
tribology data base is far enough advanced to be
applied to automotive issues.
For the longer term, the idea of a general
tribology data base has considerable appeal,
even though the task of constructing such a
system appears formidable. An effort sponsored
by agencies of the United States government is
underway, with input from technical and
industrial committees (16). At this point, only
preliminary work to define program structure has
been completed (17), but even this much progress
holds out the hope that the vast body of
tribological data may eventually be made
generally accessible.
2 . 5 Desien methods and desien issues - summarv;
A substantial 'body of tribological information,
much of it formalized by inclusion in computer
programs, is now being applied in the design
process. More information must be made
available to design engineers to improve design
quality, This information must be in readily
accessible and easily usable form to ensure its
use and to shorten design time. Improved
methods for characterizing materials are also
needed. These must be sufficiently
straightforward to be carried out at a well
equipped industrial laboratory and should not
require expert interpretation. Additional
information in certain areas would also be
clearly useful. Some suggestions are as
follows :
Well documented engine friction scaling
algorithms could be incorporated in engine
simulation programs.
37
. Bearing design programs needs validation
for high transient load conditions which
may push bearings into the mixed
lubrication regime.
Programs need verified means of dealing
with non-ideal conditions such as
misalignment. Friction calculation
algorithms for mixed lubrication would also
be useful.
. What information is required to adequately
characterize a lubricant in terms of its
tribological behavior? What are the
necessary parameters and how should they be
measured?
not only viscometrics (perhaps including
viscoelastic effects), but also a general
method for characterizing friction
modifiers.
A complete answer would include
What is the lowest "boundary" friction
coefficient attainable with the ultimate
friction modified oil?
that goal be approached with a practical
engine oil?
What set of measurements will adequately
characterize a tribological surface? This
issue impacts how materials, coatings and
surface treatments are selected, specified
and controlled in production.
How closely can
. Valve train analysis programs could benefit
from the incorporation of friction and
perhaps durability calculations based on
EHD theory and lubricant chemical effects.
Alternate valve train design approaches
need to be explored to reduce friction
losses in a cost effective manner.
.
. Piston ring/cylinder bore models focussed
on assessing the effects of design
variables and dimensional effects could be
of value.
. How can we best optimize material
combinations, select materials or coatings
for an application and screen new
materials? Efforts to introduce new
materials or to use old materials in new
applications are often wasted because
information available to experts is not
readily available to designers.
2.6 Technoloev transfer
New desims and materials: In order to be
easily accepted into a vehicle program, a new
technology must be low risk and cost effective.
If the material or device is to be supplied by a
vendor, production capacity must be available,
Little time can be devoted to development once a
vehicle program begins, and competitive
pressures are reducing the available time even
more.
A high degree of confidence in the new
technology is required because of economic,
marketing and safety considerations. This is
more true of the automotive industry than it is
of many others, and can induce a certain degree
of conservatism.
Accordingly, development and introduction
of new technology can be a lengthy process.
This can be done by working directly with a
vehicle manufacturer. However, suppliers are
often in a better position to perform
development work in their area of
specialization. As supplier companies come to
work more and more closely with their automotive
customer, they become more and more able to
initiate development work earlier in the product
cycle to anticipate needs.
Automotive companies can promote the
introduction of new technology by improving
technology management practices. That is,
identifying areas of new technology which are
promising and adopting management structures and
methods which facilitate technology development.
Originators of new technology should recognize
that multiple input points exist, and that these
may be either at the automotive manufacturer or
at a supplier. A long term commitment and
perhaps a substantial investment in testing and
development may be required.
Design methods: New design methods can
potentially be adopted as they become available,
regardless of the timing of the product cycle.
The initial input point may be to any of several
areas in the organization: design analysis
groups, advanced or forward engineering groups,
or research and development groups. The new
method does not necessarily need to be a
completely finished product to be useful, as
long as it expands the ability of the customer
to design better products or to design more
efficiently. Possibilities exist for
cooperative development over extended and
imperfectly defined time periods.
Effective internal development and transfer
of technology requires good communication
channels and a cooperative attitude on the
working level as well as good technology
management practices on the management level.
These are sometimes problem areas in large
organizations. Much has been written on the
subject, and each organization must find its own
ways to improve communication and cooperation.
These factors are important not only for the
transfer of technology developed in-house, but
also for the transfer of technology developed
outside from the point of input to the point of
application.
Design Engineers need to remain current
through participation in professional societies
and through the stimulation afforded by
cooperative research.
industry must
communicate with the automotive customer at some
input point. While publication in scientific
journals is an excellent way to reach
researchers, design engineers are often reached
more directly by industry publications (eg., the
Society of Automotive Engineers).
Those outside the automotive
3 CONCLUSIONS
Significant changes are taking place in the
automotive industry and in automotive
technology. These changes are driven by intense
competition and the resultant need to provide a
high quality, economical product in a timely
manner. Both the design of tribological
components and the design process itself have
been affected.
The automotive industry relies heavily on
the design capabilities of suppliers and this
reliance is growing. Accordingly, ensuring that
the supplier community is using the latest
design methods and technology should have a high
priority.
Increasing competition, the need for
continual improvement in product quality and
performance as well as the need to critically
assess supplier designs show the need for
increased knowledge of tribology. Knowledge can
be increased by participation in courses and
seminars obtainable at universities, through
consultants, by use of in-house expertise and
through supplier presentations.
Tribological design tools include design
guides and computer programs aimed principally
at calculating parameters affecting bearing and
valve train performance.
upgraded and validated on a continuing basis.
Data bases for the selection of tribological
materials are being developed. Opportunities
exist for the tribology community to participate
in these developments by introducing established
methods and information into design practice and
by generating new information in critical areas.
New technology can often be best
implemented during the design stage. In order
to be easily accepted, the new technology should
be low risk, cost effective and available.
Accordingly, development work must be close to
completion before implementation. Originators
of new technology should recognize the existence
of multiple input points and should be prepared
to make a long term commitment to development of
the technology, in cooperation with an
automotive company or supplier.
design methods may
be less constrained in terms of timing and
completeness of product development. Long term
development of new or upgraded methods in
cooperation with industry may be easier to
implement than introduction of new technology.
Cooperation in research work is one way for
universities to develop contacts in the
industry.
These are being
The introduction of new
REFERENCES
SPIKES, R. H., and ROBINSON, S. M. 'Engine
Bearing Design up-to-Date', paper C1/82,
from 'Tribology, Key to the Efficient
Engine', I. Mech. E. Conference
Publications 1982-1, Mechanical Engineering
Publications Ltd., London (1982).
GOODWIN, G. and HOLMES, R. 'On Bearing
Deformation and Temperature Distribution in
Dynamically Loaded Journal Bearings', paper
C2/82, ibid.
REASON, B. R., and SIEW, A. H., 'A
Numerical Solution for the Design and
Performance Evaluation of Journal Bearings
with Misalignment', paper C9/82 from
'Tribology, Key to the Efficient Engine',
I. Mech. E. Conference Publications 1982-1,
Mechanical Engineering Publications Ltd.,
London (1982).
American Society for Testing Materials Test
Methods D4683 and D4741, Coordinating
European Council (CEC) Test Method L-36,
Institute of Petroleum (IP) Standard IP-
370.
HUTTON, J. F., JACKSON, K. P. and
WILLIAMSON, B. P. 'Effects of Lubricant
Rheology of the Performance of Journal
Bearings', ASLE Trans., 2, 1 (1986) 52-
60.
BATES, T. W., WILLIAMSON, B. SPEAROT, J. A.
and MURPHY, C. K. 'A Correlation Between
Oil Rheology and Oil Film Thickness in
Engine Journal Bearings', SAE Int. Cong.
and Exposition, Detroit, MI, USA, February
24-28 (1986), paper 860376.
SCHILOWITZ, A. M. and WATERS, J. L. 'Oil
Film Thickness in a Bearing of a Fired
Engine - Part IV: Measurements in a Vehicle
on the Road', SAE Int. Fuels and Lubricants
Meeting, Philadelphia, PA, USA, October 6-9
(1986), paper 861561.
WILLERMET, P. A., PIEPRZAK, J. M. and
DAILEY, D. P., 'Friction Reduction in Valve
Trains: the Influence of Friction Reducing
Oil Additives', to be submitted to SAE.
FAN Y. CHEN, 'Mechanisms and Design of Cam
Mechanisms', 1982 (Pergamon Press, Inc.,
New York).
(10) STARON, J. T. and WILLERMET, P. A. 'An
Analysis of Valve Train Friction in Terms
of Lubrication Principles', SAE
International Congress and Exposition,
Detroit, MI, USA, February 28-March 4
(1983), paper 830165.
(11) DOWSON, D., TAYLOR, C. M., and ZHU, G.
'Mixed Lubrication of a Cam and Flat Faced
Follower', paper XX(i), from 'Fluid Film
Lubrication - Osborne Reynolds Centenary',
D. Dowson, C. M. Taylor, M. Godet and D.
Berthe, eds., Elsevier Science Publishers
BV., Amsterdam (1987).
(12) PARKER, D. A. and ADAMS, D. R., 'Friction
Losses in the Reciprocating Internal
Combustion Engine', paper C5/82, from
'Tribology, Key to the Efficient Engine',
I. Mech. E. Conference Publications 1982-
1, Mechanical Engineering Publications
Ltd., London (1982).
(13) TING, L. L., 'Lubricated Piston Rings and
Cylinder Bore Wear', from 'Wear Control
Handbook', M. B. Peterson and W. 0. Winer,
eds., The American Society of Mechanical
Engineers, New York, pg 609-666, (1980).
(14) SYAN, C. S . , MATTHEWS, A. and SWIFT, K. G.
'Knowledge Based Expert Systems in Surface
Coating and Treatment Selection for Wear
Reduction', Surface and Coatings Tech., 33
(15) SWINDELLS, N. and SWINDELLS, R. J. 'System
for Engineering Materials Selection', Met.
Mater. (Inst. Met.) 1, 5, (1985) 301-304.
(16) ANON 'A Computerized Tribology Information
System', Lubrication Eng., 1987, 42, 4 ,
228,
(17) TALLIAN, T. E. 'Tribological Design
Decisions Using Computerized Databases',
ASME Trans., Journal of Tribology, 1987
(1987) 105-115.
- 109, 381-387.
APPENDIX
A1 RECENT/CURRENT TECHNOLOGY IMPLEMENTATION
Some of the more significant recent applications
of tribological principles to automotive design
are given below. These show the results of some
of the driving forces for change in the industry
- the customer driven needs for performance,
economy and durability. Also, they illustrate
the extent to which the implementation of new
technology can depend on cooperation among
automotive manufacturers and suppliers.
39
Roller followers. Roller followers have been
widely implemented in North America as a means
of reducing valve train friction.
of rollers has required changes in camshaft
metallurgy because of the need for improved
fatigue resistance. Where fatigue failure has
been eliminated by the proper choice of
materials, long term durability has been
enhanced. Since both roller followers and
fatigue resistant camshafts are more expensive,
their use entails significant cost penalties;
these are considered worthwhile in view of the
improved fuel economy obtainable through reduced
friction. If use of roller followers became
general, this might eventually lead to reduced
antiwear protection requirements for engine
oils, resulting in less use of antiwear
additives such as zinc dithiophosphates.
Low friction rinP Packs. Low friction rings
have been introduced in a number of vehicles.
This has been accomplished largely by attention
to maintaining bore roundness, thus allowing use
of lower tension rings.
5W30 eneine oils. SAE 5W30 engine oils have
become an ever larger factor world wide. The
reduction in viscosity grade not only improves
cold start, but results in lower viscous
friction losses for most vehicles.
Introduction
ImDroved friction reducine oils. Since engine
oils are replaced periodically by the customer,
who may obtain them from any of a large number
of vendors, it was necessary to define
categories of energy conserving oils in order to
assure availability of these oils to the general
public. This has been accomplished through the
cooperative work of the automotive, oil and
additive industries in SAE and ASTM. The
American Petroleum Institute (API) defines an
energy conserving oil as one providing a fuel
economy improvement of 1.6% over a reference oil
and energy conserving I1 oil as one providing a
2.7% improvement. Both viscometric properties
and additive chemistry are important in
formulating energy conserving oils.
Concinuouslv variable transmissions. Contin-
uously variable transmissions, long proposed as
a means of improving efficiency and performance,
are now beginning to enter production in Europe.
Current models are based on the Van Doorne metal
belt drive, although other types are still under
consideration. Friction and wear as well as
manufacturing issues have been obstacles to
overcome in introducing this technology. In
addition to metallurgical, design and
manufacturing parameters, transmission fluid
composition can also affect the performance of
the belt/cone contact by influencing friction
and durability.
Lock-up toraue converters. Lock-up torque
converters have been introduced in a number of
automatic transmissions to minimize viscous
losses. These designs, together with the desire
to maximize fluid life and to achieve the
smoothest possible shifts, have led to changes
in the composition and performance of automatic
transmission fluids. A smooth engagement
together with a firm lock-up requires control of
the friction versus sliding speed curve. To
avoid shudder, the static to dynamic friction
ratio should be less than 1. If the ratio is
too low, however, slipping can occur. Actual
fluid requirements depend on design philosophy.
If the weight and size penalties are considered
to be acceptable, a lower friction coefficient
can be accommodated by increasing the friction
material area.
ImDroved transmission fluids. Ford has recently
introduced a new class of automatic transmission
fluids. General Motors is expected to in the
near future. The Ford fluid is characterized by
closely controlled frictional behavior during
clutch engagements and by improved stability
over time. The General Motors fluid is expected
to emphasize smooth shifts by producing an
appropriate friction versus sliding speed curve.
These demands have required significant changes
in transmission fluid additive packages.