Method Development to Virtually Validate Farm Tractor Skid for Front End Loader Application

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2019-26-0080 Published 19 Jan 2019
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Method Development to Virtually Validate Farm
Tractor Skid for Front End Loader Application
Prasanna Balaji Subbaiyan, Abhay Kumar, Jaju Mayur, Balaramakrishna Nizampatnam,
and S.A Bhanuprakash Mahindra Research Valley
Dave Schneider KMW Ltd
Citation: Subbaiyan, P.B., Kumar, A., Mayur, J., Nizampatnam, B. et al., “Method Development to Virtually Validate Farm Tractor
Skid for Front End Loader Application,” SAE Technical Paper 2019-26-0080, 2019, doi:10.4271/2019-26-0080.
Abstract
In farm tractors, front end loaders are becoming popular
attachments for primarily material handling such as
loading, moving and unloading of woodchips, sand,
gravels etc. It is also used for some severe load application
such as tree uprooting and ripping operation which requires
validation of loader frame and tractor as well. To validate
the design, a standard pull-push test is carried out on
tractor with loader in a laboratory. In this test front loader
bucket is pushed against a rigidly clamped fixture with full
engine throttle and maximum hydraulic cylinder pressure
of loader. To avoid surprise failures during the test, a virtual
simulation method needs to bedeveloped and validated.
In this paper, a method has been proposed by authors for
the above objective. A multi-body dynamics model of tractor
with loader is created in MSC ADAMS and actual event is
simulated using test loads & boundary conditions. Forces and
moments are extracted on all tractor skid attachments points
from MBD model. Aerwards, an inertia relief durability
analysis is done in MSC Nastran using the extracted loads.
Strain gauges are pasted on tractor front axle support, clutch
housing and data acquisition activity is carried to extract
strain level during test operation. e durability results are
correlated with measured strain data and achieved more than
80% correlation.
Introduction
The basic application of farm tractor is to provide high
tractive force on the wheels at low speed to carryout
farming operation such as plowing, rotavation,
puddling etc. [1]. Tractor usage can be extended by adding
additional attachments like front end loader, trailer, backhoe
etc. for other farming tasks at low cost. Wheel loaders are
specically designed machines widely used in construction
application for scooping gravels and other materials. In
farming, front end loaders are popular accessories used for
loading and unloading bales of hay, seeds, manure gathering
and ground leveling. It consists of loader arm, bucket, loader
mount, parallel links and pressure cylinders [2].
Tractor chassis usually called as Skid or Base which binds
together many components. It consists of front axle support,
engine housing, clutch housing, transmission housing,
hydraulic housing, rear axle carrier etc. Tractor skid are to
bedesigned to bear various shock loads during an operation.
Loader mount is usually bolted on to tractor skid at front axle
support, clutch housing and rear axle carrier locations.
Schematic diagram of the loader with tractor skid is shown
in Figure 1.
Reliability and reduction of time to market like automo-
tive trend seen in tractor manufacturers lately [3]. In tractor
development process, it is mandatory to validate the tractor
skid for loader applications by carrying out accelerated
durability testing to nd out potential failure modes in short
time. ese t ypes of tests are usually carried out in eld condi-
tions to replicate the real-world usage pattern and sometimes
it is simulated in laboratories with help of test rigs [4]. Testing
conditions can bereplicated consistently in labs and thereby
achieving standard process.
Some of the lab testing carried out to validate durability
of front end loader are center pull test, center push test, corner
pull test, corner push test and drop & catch test.
In addition to conventional physical testing, in todays’
world computer simulation using nite element analysis are
used extensively in design process. The emergence of
FIGURE 1 Tractor skid with front end loader attachment
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METHOD DEVELOPMENT TO VIRTUALLY VALIDATE FARM TRACTOR SKID FOR FRONT END LOADER APPLICATION 2
simulation driven product development helps to reduce time
and cost to great extent. For the same, virtual validation
process need to beestablished by comparing its performance
with physical test. Using virtual validation helps to validate
design during design phase itself, thereby avoiding surprise
failures during testing.
Before developing a virtual simulation method in-house
for validating tractor skid for front end loader application,
literatures survey was carried out. Some researchers have
studied the failure modes of front end loader for conventional
test methods such as drop & catch test, corner pull test and
corner push test [5]. But virtual validation of tractor skid for
loader applications were not found.
In this work, method is developed to validate tractor skid
for combined center pull and push test load condition only.
Center pull test is done by placing the loader bucket below the
rigidly clamped xture called dead-man and then it is tried
to li using loader pressure cylinders. Similarly, in center push
test loader bucket is pushed forward inside dead-man.
e main challenge is to simulate the actual lab testing in
virtual and get right load values to correlate with the test. In
this paper, weare proposing a virtual validation method to
simulate above explained pull-push test. First step is to v irtually
simulate the pull-push event in multibody dynamics; then
extract the loads at loader- skid attachment and axle locations;
and nally do the durability a nalysis. Outputs is correlated w ith
measured test d ata and na l process is established. Met hodology
owchart for the work is shows in Figure 2.
VirtualSimulation
Multi-Body Dynamics
Modeling and Simulation
To simulate loader pul l-push test multi-body dy namics (MBD)
model is built in ADAMS/View simulation environment.
CAD models of various subsystem of tractor were used to
dene parts with mass and inertia properties. Appropriate
joints and ex connections such as revolute joint, spherical
joint, bushing etc. are modeled to dene the motion of parts.
Full tractor MBD model consist of following subsystems:
Front end loader attachment, Hydraulic three-point linkage
assembly, Front axle & steering assembly, skid, front and rear
wheel assembly. Structural exibility included on following
parts loader arm, mount and front axle support considered
by incorporating nite element model (Model neutral le)
using Craig-Bampton reduction.
More attention is given to the modeling of tractor skid
which consist of various components rigidly connected to
each other by bolt connections. To model this connection,
exible connector Beams are used. A beam creates a linear
translational and rotational force between two marker loca-
tions. Beam forces and moments are calculated based on the
translational and the rotational deections of the I marker
with respect to the J marker is shown in below Figure 3. e
inputs for the beam connection are applied based on the bolt
material and cross section.
e Constitutive Equations for Beams used in ADAMS
is shown in Figure 4.
Default msc_truck_pac2002.tir model from shared library
used by updating the tractor tire data such as dimension and
stiness. Figures 5, 6, 7 and 8 shows the ADAMS model of
full tractor, front end loader, three-point linkage and skid.
To predict accurate durability loads on the tractor compo-
nents, it is important to understand loads acting on the tractor
during combined center pull-push test. Pressure cylinders
generate vertical pull force on the bucket tip based on cylinder
area and system pressure. is force can also bereferred as
Breakout force [7]. Another force that acts on the bucket tip is
FIGURE 2 Method flowchart
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FIGURE 3 Beam Forces [6]
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FIGURE 4 Beam equations [6]
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METHOD DEVELOPMENT TO VIRTUALLY VALIDATE FARM TRACTOR SKID FOR FRONT END LOADER APPLICATION 3
tractor Drawbar pull. e drawbar pull or traction ability of
tractor depends on tractor mass, contact area between tire &
surface and soil strength [8]. is is calculated based on gross
vehicle weight and coecient of traction. Below Figure 9
shows forces direction generated by pressure cylinders, tires
and reaction forces on the bucket due to dead-man.
To model this testing condition a three-component Vforce
is created between bucket and the ground part. Here,
dead-man is considered as ground part. The maximum
breakout force and drive force is applied on the bucket as a
function of time. To achieve equilibrium condition in simula-
tion, degrees of freedom on pressure cylinders and wheels is
locked by creating a motion constrain.
Durability loads are extracted on all loader - skid and
axle- skid attachment locations. ese loads are used for the
nite element analysis.
FEA Analysis
FE model is built in Hypermesh w ith tractor skid components
is shown in Figure 10. Tractor skid model consisting of front
axle support, engine assembly, clutch housing assembly, speed
housing assembly, rear housing assembly, rear axle carrier
assembly, hydraulic system, etc. are modeled for inertia relief
analysis. Tractor other component masses like cabin, fender
assembly, front hood assembly, radiator and cooling assembly,
seat assembly, battery mounting assembly etc. are modeled as
virtual masses.
Extracted loads from MBD simulation for push and pull
condition of tractor is applied at front end loader mounting
and axle locations as shown in Figure 11 and then analysis
is done.
Result and Discussion
Output plot of MBD simulation Figure 12 shows that the front
tire reaction increases and rear tire reaction decreases to zero.
is behavior is expected and conrmed with the physical
test. At time 0.68 sec in Figure 12, rear tire starts liing and
load is transferred to front axle. As the test vehicle is four
FIGURE 5 MSC ADAMS/View full tractor
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FIGURE 6 Front end loader assembly
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FIGURE 7 Hydraulic three-point linkage assembly
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FIGURE 8 Tractor Skid
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FIGURE 9 Loads acting on the tractor during test
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FIGURE 10 FE Model of tractor loader
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METHOD DEVELOPMENT TO VIRTUALLY VALIDATE FARM TRACTOR SKID FOR FRONT END LOADER APPLICATION 4
wheel driven, the power availability on front wheels provide
sufficient traction to the vehicle even after rear tire
lied condition.
Displacement plot Figure 13 shows maximum defor-
mation is occurring in front axle support. From stress plot
Figure 14, front axle support and clutch housing are critical
parts on the tractor skid prone to fail during the test. e
advantage of virtual simulation is that the critical locations
are identied much in advance and suitable design improve-
ment can bedone for the same.
FEA- Test Correlation
Any virtual simulation must becorrelated with actual test
to evaluate correctness of the method. In this case, from FE
analysis, strain gauge locations and direction are identied
based on maximum principal strain direction. At identied
locations, either uni-axial strain gauge or rosettes are pasted
along the principal direction and strain levels are measured.
e test and FE strain values are then correlated. Fig ure 15
shows the strain contour & gauge location on the front axle
support; whereas Fig u re 16 shows for the clutch housing.
Based on the high strain location and their principle
direction from initial FEA analysis, three locations are
suggested on front axle support Fig ure 17 and two locations
on clutch housing Figu re 18.
Figure 19 shows the measured strain reading of all strain
gauge pasted on the tractor skid. Channel 02 is strain reading
of location-1 center gauge, Channel 04 is of location-2 and
channel 10 is of location-3 center gauge on FAS. ese values
have been compared with t he strain limit for fatigue. Any thing
lying above low cycle fatigue limit is very critical for the
design. Strain below high cycle fatigue means there is scope
for optimization. And the strain lying in between is safe. As
this test cycles are limited to few cycles, the strain level closer
to low cycle fatigue limit is considered optimum.
Using above proposed methodology, average 92% strain
correlation is achieved for front axle support and 80% for
clutch housing as shown in Ta ble 1. Here only the peak values
FIGURE 11 Load application at loader mount location
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FIGURE 12 Front and Rear Tire Reaction during simulation
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FIGURE 13 Displacement plot for pull-push test
loader simulation
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FIGURE 14 Strain plot for tractor skid
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FIGURE 15 FE strain level on front axle support
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FIGURE 16 FE strain level on clutch housing
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METHOD DEVELOPMENT TO VIRTUALLY VALIDATE FARM TRACTOR SKID FOR FRONT END LOADER APPLICATION 5
are compared for correlation. With this high level of correla-
tion, the correctness of FE analysis is established and this
method can becondently used for tractor skid validation in
front end loader test.
SummaryConclusions
A tractor level simulation methodology is developed to validate
the tractor skid for pull-push test before doing any physical test.
e process showed easy to use approach on how to map physical
test to virtual test. e MBD and FE analysis methodology is
successfu lly established. A un ique exible connector usi ng beam
element are used in MBD simulation to accurately predict the
forces on the loader-skid attachment locations. Aer that inertia
relief FE analysis is done to identify the critical components in
the design. Based on the critical identied locations, a reliable
design can bemade by improving the design of critical compo-
nents. e proposed method is successfully correlated with the
test by 90% to 94% on front ax le support and 80% on clutch housing.
Major Benets arr ived at from the developed methodology is:
•It is validated with actual test data.
•Avoiding surprising failure in test.
•Design cycle for skid is reduced.
•Skid design can beoptimized for mass & cost reduction.
•Component level analysis can beperformed quickly.
•is methodology can behorizontally deployed for
similar tests like dozer, backhoe, etc.
References
1. Vinod, V., Saravanan, V., Dinesh, R., Arun, M. et al.,
“Agricultural Tractor Hydraulic Li Arm Assembly Design for
Durability and Correlation with Physical Test,” SAE Technical
Paper 2016-28-0237, 2016, doi:10.4271/2016-28-0237.
2. Latorre-Biel, J.I., Arana, I., Ballesteros, T., Pintor, J.M. et al.,
“Front End Loader with Automatic Levelling for Farm
Tractors ,” Biosystem Engineering I48:III-I26, 2016.
3. Mattetti, M., G. Molari, A., and Vertua, A.G., “Tractor
Accelerated Test on Test Rig,” Journal of Agricultural
Engineering X LIV(s2):e76, 2013.
4. Mattetti, M., Molari, G., and Sedoni, E., “Methodology for
the Realisation of Accelerated Structural Tests on Tractors,”
Biosystems Engineering 113(3):26 6 -271, Nov. 2012 .
5. Lim, G. and Lee, B., “Study on the Impact Analysis of Front
Loader for Tractor,” Journal of the Korea Academia-
Industrial Cooperation, Society 16(8):5051-5059, 2015.
6. MSC Soware Corp., “Adams User Manual (2017 Release).”
7. ISO 14397-2:2007, Earth-Moving Machinery- Loaders and
Backhoe Loaders- Part 2: Test Method for Measuring
Breakout Forces and Li Capacity to Maximum Li Height,
Second Edition.
8. Damanauskas, V. and Janulevicius, A., “Dierences in
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FIGURE 17 Strain gauged location on FAS
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FIGURE 18 Strain gauged location on Clutch housing
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TABLE 1 FEA- Test strain correlation
Loadcases Location
Correlation % for
Front Axle Support
Correlation % for
Clutch Housing
Center
pull-push
Location -1 91.4 79.5
Location -2 90.8 80
Location -3 94.0 -
Average 92.0 80
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FIGURE 19 Measured strain data
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METHOD DEVELOPMENT TO VIRTUALLY VALIDATE FARM TRACTOR SKID FOR FRONT END LOADER APPLICATION 6
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ISSN 0148-7191
Contact Information
Prasanna Balaji S
Mahindra & Mahindra ltd
Mahindra Research valley
Chennai (T.N) 603004, India
s.prasanna@mahindra.com
Acknowledgments
We would like to thank Mr Abhijit Londhe, Sr Principal
Engineer, M&M, Mr Dinesh Redkar, Principal Engineer,
M&M, for their invaluable guida nce and time. Also, wewould
like to thank Mahindra USA technical team for performing
test and data measurement.
Definitions/Abbreviations
MBD - Multi-Body Dynamics
FEA - Finite element analysis
FAS - Front axle support
DVP - Design verication plan
FAW - Front axle reaction
R AW - Rear axle reaction
A DAMS - Automatic Dynamics A nalysis of Mechanical Systems
CAD - Computer Aided Design
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