eicher motors
TRANSCRIPT
IntroductionAutomotive engines are undergoing continuous meta-morphoses. The demand for higher performance and
lower fuel consumption has led to the development of
smaller, lighter engines. For these reasons, the rigid-
ity of the connecting rod has been reduced in com-
parison with increasing inertia force.
Eicher Motors Ltd., of Pithampur, India, experienced
this problem while upgrading four-cylinder engines
for improved performance and emission norms. In
trying to reduce the weight of the connecting rod, the
Engine Development Team had changed the normal
rectangular bushing of the small end bore to a trape-
zoidal shape.
During testing of their newly developed engine, the
connecting rod bushings of the smaller bore ends fre-
quently became loose.
ChallengeEicher’s Engine Design Department called VarunAgarwal, of the Structural Analysis Team, to helpdetermine the cause. With the help of Dr. A. K.
Jindal, chief of the department, he began to analyze
what an international study of similar failures sug-
gested could be “fretting phenomenon.”
Fretting is caused by a relative slip between the
inner surface of the connecting rod big bore and the
outer surface of the bushing, in circumferential and
axial directions, as the bushing inside of the con-
necting rod big bore undergoes normal cyclic load-
ing. The amount of relative slip determines the
extent of the fretting damage, which causes the
bushing to loosen.
Agarwal had to determine why the fretting occurred
in Eicher’s engine. Known causes include operating
conditions, the shapes and dimensions of the con-
necting rod and the bearings, and material and geo-
metrical imperfections.
Of these, the operating conditions are the most
unpredictable and difficult to control. Material and
geometrical imperfections are also hard to correct,
because of the many restrictions on them.
The shapes and dimensions of the connecting rod
and the bearing can easily be changed during devel-
opment.
The only way to understand the problem was to
determine the variation in the slip, so Agarwal set
out to build a finite element model (FEM) with
ANSYS in which he could change the interference
India-Based Manufacturer Eliminates Engine Fretting
E I C H E R M O T O R S L T D .
CASE STUDY
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Sliding in ( circumferential direction ) between the conrodand he bush surface, when the load is applied ( at 0.118mm initial interference )
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“ANSYS was the first FEA package in our company, and we were quicklyable to show our Product Development Group very clearly how useful it is,”says Agarwal. “On many occasions, FEA was done using ANSYS to ascer-tain the reason for field failure in test vehicles. This helped in reducing thenumber of test iterations which a new design undergoes, and resulted in sig-nificant time and cost savings.”
EXECUTIVE SUMMARY
Challenge:To solve the persistent problem of
fretting in the connecting rod bush-
ing of an engine that was being
upgraded for better performance
Solution:Use ANSYS® simulation software to
understand the cause of the fretting
Benefits: Powerful surface-to-surface
contacts
Commands that let analysts
zero in on the cause of the fretting
Key options and real constants
that help to define the conditions
values between the bushing and the connecting
rod.
One of the challenges he faced; the international
study that he had as a guide for the model was
completed more than 10 years ago. The analysts at
the time did not have the powerful contact capabil-
ities available with ANSYS. Furthermore, in most
of the documented cases, the fretting had happened
in the large bore end of the connecting rod.
Solution Using Pro/ENGINEER, the Engine DesignDepartment built a three-dimensional FEM of theconnecting rod, bushing, pin, and piston. The
model was meshed, then imported into ANSYS as
SOLID 45 elements.
Agarwal set up the ANSYS model of Eicher’s
existing small end bushing design for analysis,
using the surface-to-surface contacts in Target170
& Contact174. Contact elements were placed
between the outer surface of the bushing and the
inner surface of the small end bore, the inner sur-
face of the bushing and the outer surface of the pin,
and the outer surface of the pin and the inner sur-
face of the piston. All were given a constant coef-
ficient of friction of 0.15.
The various key options and real constants avail-
able in CONTACT174 allowed him to easily
define the initial conditions.
Putting displacement constraints on the piston’s
outer surface, using static loading only, excluding
transient effects, Agarwal conducted the run in two
load steps.
In the first, he applied an interference of 0.118 mm
between the bushing and the connecting rod, con-
trolling the value of the interference in the real
constant set.
In the second load step, he applied an external
force of 10,600 kilogram force (kgf), from the pis-
ton, onto the connecting rod. Agarwal says, “The
post-processing properties of these gap elements
are very good. To get the final results, I subtracted
the results of the first load step from those of the
second. To find the amount of slipping in circum-
ferential and axial directions, I used the direct post-
processing commands available for CONTACT174
in ANSYS/post1 GUI, and found the pressure and
slip values, as shown in the plots, that resulted
from the external loading, and not from interfer-
ence.”
The pressure distribution on the surface of the
bushing and the inner surface of the connecting rod
showed that the behavior of the model was correct.
The slip between the connecting rod and the sur-
face of the bushing under a load of 10,600 kgf was
separated into circumferential and axial compo-
nents.
Benefits“The best part of using ANSYS was its powerfulsurface-to-surface contacts,” says Agarwal. “The
commands, like Frictional Stress, in CON-
TACT174 in /post1 helped us a lot to clearly devel-
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CASE STUDY
op an understanding of the phenomenon. Also, we
were able to locate the critical zone in which the
interference between the bushing and the connect-
ing rod is of most importance. I consider all of this
to be a great capability of ANSYS.”
In additional runs, Agarwal discovered that the
slip drastically increased when the interference in
the critical zone decreased.
Based on the results of the tests, Eicher’s engi-
neers were able to fine-tune the manufacturing
process, and incorporate quality checks, to ensure
proper interference at the critical locations. The
problem of fretting was eliminated.
Since finite element analysis (FEA) is a relatively
new field in India, Eicher Motors has been using
ANSYS for only four years. In that short time,
however, it has become an invaluable tool for the
company.
“ANSYS was the first FEA package in our com-
pany, and we were quickly able to show our
Product Development Group very clearly how
useful it is,” says Agarwal. “On many occasions,
FEA was done using ANSYS to ascertain the rea-
son for field failure in test vehicles. This helped in
reducing the number of test iterations which a new
design undergoes, and resulted in significant time
and cost savings.”
As Agarwal notes, “We have also been using
ANSYS extensively throughout the development
of a new heavy commercial vehicle, to predict
failures in its various aggregates and components,
even before it was put to a field test. It has helped
us to improve the cabin, chassis, and
stubaxle/kingpin designs, as well as many other
parts of this vehicle.”
Beyond the design and testing stages, Agarwal is
looking forward to using FEA extensively in other
areas, including manufacturing, in the near future.
Surface-to-surface contact elements present betweendifferent interfaces.
“The best part of using ANSYS was its powerful surface-to-surface con-
tacts,” says Agarwal. “The commands, like Frictional Stress, in CON-
TACT174 in /post1 helped us a lot to clearly develop an understanding of
the phenomenon.”