Eicher Motors
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CASE STUDY
India-Based Manufacturer Eliminates Engine Fretting E I C H E R M O T O R S LT D .
EXECUTIVE SUMMARY
Challenge: To solve the persistent problem of fretting in the connecting rod bushing of an engine that was being upgraded for better performance
Introduction
Challenge
Automotive engines are undergoing continuous metamorphoses. The demand for higher performance and lower fuel consumption has led to the development of smaller, lighter engines. For these reasons, the rigidity of the connecting rod has been reduced in comparison with increasing inertia force.
Eicher’s Engine Design Department called Varun Agarwal, of the Structural Analysis Team, to help determine 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 suggested could be “fretting phenomenon.”
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 trapezoidal shape.
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 connecting rod big bore undergoes normal cyclic loading. The amount of relative slip determines the extent of the fretting damage, which causes the bushing to loosen.
During testing of their newly developed engine, the connecting rod bushings of the smaller bore ends frequently became loose.
Solution: Use ANSYS® simulation software to understand the cause of the fretting
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.
Benefits: Powerful surface-to-surface contacts
zero in on the cause of the fretting Key options and real constants that help to define the conditions
The shapes and dimensions of the connecting rod and the bearing can easily be changed during development.
Images courtesy Eicher Motors Ltd.
Commands that let analysts
Agarwal had to determine why the fretting occurred in Eicher’s engine. Known causes include operating conditions, the shapes and dimensions of the connecting rod and the bearings, and material and geometrical imperfections.
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 Sliding in ( circumferential direction ) between the conrod and he bush surface, when the load is applied ( at 0.118 mm initial interference )
www.ansys.com
“ANSYS was the first FEA package in our company, 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 reason 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.”
“The best part of using ANSYS was its powerful surface-to-surface contacts,” says Agarwal. “The commands, like Frictional Stress, in CONTACT174 in /post1 helped us a lot to clearly develop an understanding of
CASE STUDY
the phenomenon.”
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 capabilities available with ANSYS. Furthermore, in most of the documented cases, the fretting had happened in the large bore end of the connecting rod.
Solution
force of 10,600 kilogram force (kgf), from the piston, 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 circumferential and axial directions, I used the direct postprocessing 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 interference.”
Using Pro/ENGINEER, the Engine Design Department built a three-dimensional FEM of the connecting 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 surface of the bushing and the outer surface of the pin, and the outer surface of the pin and the inner surface of the piston. All were given a constant coefficient of friction of 0.15. The various key options and real constants available 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, controlling the value of the interference in the real constant set. In the second load step, he applied an external
www.ansys.com
op an understanding of the phenomenon. Also, we were able to locate the critical zone in which the interference between the bushing and the connecting 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 engineers 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.
Surface-to-surface contact elements present between different interfaces.
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.
“ANSYS was the first FEA package in our company, 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 reason 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.”
Benefits
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.”
“The best part of using ANSYS was its powerful surface-to-surface contacts,” says Agarwal. “The commands, like Frictional Stress, in CONTACT174 in /post1 helped us a lot to clearly devel-
Beyond the design and testing stages, Agarwal is looking forward to using FEA extensively in other areas, including manufacturing, in the near future.
The slip between the connecting rod and the surface of the bushing under a load of 10,600 kgf was separated into circumferential and axial components.
ANSYS Inc. Southpointe 275 Technology Drive Canonsburg, PA 15317 U.S.A. [email protected]
Toll-Free: 1.866.ANSYS.AI (1.866.267.9724) Toll-Free Mexico: 001.866.ANSYS.AI
ANSYS is registered in the U.S. Patent and Trademark Office. ©2002 SAS IP, Inc., a wholly owned subsidiary of ANSYS Inc. All Rights Reserved.
MCS0100AUG02
India-Based Manufacturer Eliminates Engine Fretting E I C H E R M O T O R S LT D .
EXECUTIVE SUMMARY
Challenge: To solve the persistent problem of fretting in the connecting rod bushing of an engine that was being upgraded for better performance
Introduction
Challenge
Automotive engines are undergoing continuous metamorphoses. The demand for higher performance and lower fuel consumption has led to the development of smaller, lighter engines. For these reasons, the rigidity of the connecting rod has been reduced in comparison with increasing inertia force.
Eicher’s Engine Design Department called Varun Agarwal, of the Structural Analysis Team, to help determine 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 suggested could be “fretting phenomenon.”
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 trapezoidal shape.
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 connecting rod big bore undergoes normal cyclic loading. The amount of relative slip determines the extent of the fretting damage, which causes the bushing to loosen.
During testing of their newly developed engine, the connecting rod bushings of the smaller bore ends frequently became loose.
Solution: Use ANSYS® simulation software to understand the cause of the fretting
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.
Benefits: Powerful surface-to-surface contacts
zero in on the cause of the fretting Key options and real constants that help to define the conditions
The shapes and dimensions of the connecting rod and the bearing can easily be changed during development.
Images courtesy Eicher Motors Ltd.
Commands that let analysts
Agarwal had to determine why the fretting occurred in Eicher’s engine. Known causes include operating conditions, the shapes and dimensions of the connecting rod and the bearings, and material and geometrical imperfections.
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 Sliding in ( circumferential direction ) between the conrod and he bush surface, when the load is applied ( at 0.118 mm initial interference )
www.ansys.com
“ANSYS was the first FEA package in our company, 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 reason 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.”
“The best part of using ANSYS was its powerful surface-to-surface contacts,” says Agarwal. “The commands, like Frictional Stress, in CONTACT174 in /post1 helped us a lot to clearly develop an understanding of
CASE STUDY
the phenomenon.”
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 capabilities available with ANSYS. Furthermore, in most of the documented cases, the fretting had happened in the large bore end of the connecting rod.
Solution
force of 10,600 kilogram force (kgf), from the piston, 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 circumferential and axial directions, I used the direct postprocessing 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 interference.”
Using Pro/ENGINEER, the Engine Design Department built a three-dimensional FEM of the connecting 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 surface of the bushing and the outer surface of the pin, and the outer surface of the pin and the inner surface of the piston. All were given a constant coefficient of friction of 0.15. The various key options and real constants available 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, controlling the value of the interference in the real constant set. In the second load step, he applied an external
www.ansys.com
op an understanding of the phenomenon. Also, we were able to locate the critical zone in which the interference between the bushing and the connecting 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 engineers 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.
Surface-to-surface contact elements present between different interfaces.
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.
“ANSYS was the first FEA package in our company, 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 reason 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.”
Benefits
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.”
“The best part of using ANSYS was its powerful surface-to-surface contacts,” says Agarwal. “The commands, like Frictional Stress, in CONTACT174 in /post1 helped us a lot to clearly devel-
Beyond the design and testing stages, Agarwal is looking forward to using FEA extensively in other areas, including manufacturing, in the near future.
The slip between the connecting rod and the surface of the bushing under a load of 10,600 kgf was separated into circumferential and axial components.
ANSYS Inc. Southpointe 275 Technology Drive Canonsburg, PA 15317 U.S.A. [email protected]
Toll-Free: 1.866.ANSYS.AI (1.866.267.9724) Toll-Free Mexico: 001.866.ANSYS.AI
ANSYS is registered in the U.S. Patent and Trademark Office. ©2002 SAS IP, Inc., a wholly owned subsidiary of ANSYS Inc. All Rights Reserved.
MCS0100AUG02
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