VEHICLE MODELING AND ADAMS-SIMULINK CO-SIMULATION WITH INTEGRATED CONTINUOUSLY CONTROLLED ELECTRONIC SUSPENSION (CES) AND ELECTRONIC STABILITY CONTROL (ESC) MODELS A Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Graduate School of The Ohio State University By Sughosh Jagannatha Rao, B.S.M.E ******** The Ohio State University 2009 Masters Examination Committee: Approved By: Prof. Dennis A. Guenther, Advisor ____________________ Advisor Dr. Gary J. Heydinger Graduate Program in Mechanical Engineering
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
VEHICLE MODELING AND ADAMS-SIMULINK CO-SIMULATION WITH
(CES) AND ELECTRONIC STABILITY CONTROL (ESC) MODELS
A Thesis
Presented in Partial Fulfillment of the Requirements for
the Degree of Master of Science in the
Graduate School of The Ohio State University
By
Sughosh Jagannatha Rao, B.S.M.E
********
The Ohio State University
2009
Masters Examination Committee: Approved By: Prof. Dennis A. Guenther, Advisor ____________________ Advisor Dr. Gary J. Heydinger Graduate Program in Mechanical Engineering
ii
ABSTRACT
The purpose of this thesis is to evaluate the benefits of the CES suspension system
developed by Tenneco Automotive, and to evaluate the effects of the CES suspension on
the Electronic Stability Control (ESC) system using ADAMS simulation. The design of
the system and its function is explained.
The first stage of the process involved the creation of the ADAMS model of the
Ford Expedition. Next, the model was validated from the Expedition model used with the
National Advanced Driving Simulator (NADS) and experimental data collected at
Transportation Research Center (TRC). Once the vehicle model was ready, a model of
the ESC system was created using Matlab Simulink. Next, a co-simulation was set up to
integrate the ESC model with the vehicle model. The ESC equipped vehicle model was
then validated against experimental data.
The CES model supplied by Tenneco Automotive was then incorporated into the
validated model. This model was then used to evaluate the performance of the baseline
Ford Expedition and one equipped with the CES suspension system. The Sine with Dwell
maneuver was used to evaluate the ESC performance in both the cases in accordance with
the Federal Motor Vehicle Safety Standard No.126 (FMVSS No.126).
iii
DEDICATION
Dedicated to my Parents,
who are the reason I am here and
have ensured that I always had all I needed and more
To all of my family; my grandparents, uncles, aunts, cousins and friends,
for all of your love and support.
iv
ACKNOWLEGMENTS
I would like to offer thanks to a lot of people, without whom this study would not
have been possible. I would like to thank my advisors, Denny Guenther, Gary Heydinger
and Kamel Salaani for their support and constant encouragement which got me through
some really hard patches when progress was slow. More than advisors, they were like
friends, always there to answer my questions and lend a helping hand. Throughout the
project, they ensured that they did not put any unnecessary pressure. I would like to
especially thank Denny, for always keeping my interests in mind and making me feel at
home. I would also like to thank Tenneco Automotive for supporting this research with
both monetary and technical contributions, without their project, I would not be writing
this thesis.
I would also like to thank my colleagues Tejas Kinjawadekar and Neha Dixit who
kept me company and helped keep the stress low. I would also like to thank Don Butler
and Luka Wahab for their help. Thanks to my friends and roommates who have made this
journey fun and full of fond memories. Finally I would like to thank my family, without
their support and belief; this would not have been possible. Without the support of all the
people mentioned here, the completion of my Masters Degree would not have been
possible.
v
VITA
15 May 1985……………………Born – Mysore, India
June 2002……………………….Graduate, DAV Higher Sec. School
May 2006……………………….B.E.M.E. Anna University
Sept. 2006 – Aug 2007…………University Fellow, The Ohio State University
Sept. 2007 – Present……………Graduate Research Assistant, The Ohio State University
FIELDS OF STUDY
Major Field: Mechanical Engineering Vehicle Dynamics
vi
TABLE OF CONTENTS
ABSTRACT........................................................................................................................ ii
DEDICATION................................................................................................................... iii
ACKNOWLEGMENTS .................................................................................................... iv
VITA................................................................................................................................... v
TABLE OF CONTENTS................................................................................................... vi
LIST OF FIGURES ........................................................................................................... ix
LIST OF TABLES........................................................................................................... xiv
The sign of the function YR_d determines whether the vehicle is understeering or
oversteering, and depending on the magnitude of YR_d, the brake line pressure is set by
the ESC system. Figure 5.3 shows the relation between the magnitude of YR_d and the
brake cylinder pressure. These values were extracted from the experimental runs by
plotting the YR_d values and the brake pressure. (From reference [8]).
60
Brake Pressure vs Yaw Rate Difference
0
1
2
3
4
5
6
7
8
9
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Magnitude of Yaw Rate Difference YR_d (deg/s)
Bra
ke P
ressu
re (
MP
a)
Figure 5.3 ESC Brake Pressure Decision plot.
The ESC uses the sign of the lateral acceleration to determine which direction the car
is turning. When the vehicle is understeering, the ESC applies the appropriate brake on
the rear axle as the front wheel lateral forces are already saturated and when the vehicle is
oversteering, the braking is applied to the front axle (as the rear wheel lateral forces are
already saturated). For example, if the vehicle is oversteering when turning right, the
brake on the front left wheel is applied by the ESC, while on the other hand if the vehicle
is understeering while turning right, the brake on the rear right wheel is applied.
Once ESC system decides the correct brake pressure and the correct brake to be
applied, the signal is sent to the appropriate brake through a delay. The purpose of the
delay is to account for the mechanical delay in time taken for the pressure to buildup in
the brake cylinder and brake actuation on the actual vehicle. This was measured from the
experimental data to be 0.35 seconds. Thus after the delay, the appropriate brake is
applied by the ESC model.
61
5.3 Validation
Once the ESC model is created, it is integrated with the vehicle model and
simulations are run. Figure 5.4 shows the integrated Adams ESC model in Simulink. The
results are then compared to the experimental results already collected at TRC to validate
the ESC model. The Sine with Dwell maneuver is used with steering angles varying from
80 degrees to 300 degrees in steps of 20 degrees. The figures 5.5 to 5.11 show the
comparisons of the various parameters.
Figure 5.4 ESC Integrated Adams Model in Simulink
62
(a) (b)
(c) (d)
(e) (f)
Figure 5.5 Steering Profiles for Expedition with ESC for a) 80, b) 120, c) 160, d) 200, e)
240 and f) 300 degrees
63
(a) (b)
(c) (d)
(d) (e)
Figure 5.6 Lateral Acceleration Comparison for the Expedition with ESC for a) 80, b)
120, c) 160, d) 200, e) 240 and f) 300 degrees
64
(a) (b)
(c) (d)
(e) (f)
Figure 5.7 Yaw Rate Comparison for Expedition with ESC for a) 80, b) 120, c) 160, d)
200, e) 240 and f) 300 degrees.
65
(a) (b)
(c) (d)
(e) (f)
Figure 5.8 Speed Trajectory Comparisons for Expedition with ESC for a) 80, b) 120, c)
160, d) 200, e) 240 and f) 300 degrees
66
(a) (b)
(c) (d)
(e) (f)
Figure 5.9 Roll Angle Comparisons for Expedition with ESC for a) 80, b) 120, c) 160, d)
200, e) 240 and f) 300 degrees
67
(a) (b)
(c) (d)
(e) (f)
Figure 5.10 Roll Rate Comparison for Expedition with ESC for a) 80, b) 120, c) 160, d)
200, e) 240 and f) 300 degrees
68
(a) (b)
(c) (d)
(e) (f)
Figure 5.11 Pitch Rate Comparison of Expedition with ESC for a) 80, b) 120, c) 160, d)
200, e) 240 and f) 300 degrees
69
From the above graphs it is clear that the ESC model works very much like the actual
ESC for up to the 240 degree Sine with Dwell maneuver after which the results start to
deteriorate. Figure 5.6 shows lateral acceleration comparison, and there appears to be
some noise in the simulation data at around 1.5 seconds into the maneuver. This is in fact
not noise, but fluctuations caused due to rapid brake pulses that are applied at the same
time (Figure 5.12) during the simulation. Figure 5.9 shows the comparison of the roll
angles. The roll angles predicted are lower than that of the actual vehicle, which is
consistent with the previous roll angle predictions by the simulation.
To check the working of the ESC model, the brake pulses of the simulation and the
experimental runs are compared in Figures 5.12 and 5.13. These figures show the brake
pressures of the front left and front right brakes respectively. The rear brake pressures
remain zero for the experimental runs, as in this maneuver the vehicle is always
oversteering and hence the ESC activates the brakes only on the front axle. However in
the simulation the rear right wheel brake is activated for steering angles greater than 240
degrees. The brake pressure plot of the rear right wheel for the 300 degree Sine with
Dwell is shown in Figure 5.14.
70
(a) (b)
(c) (d)
(e) (f)
Figure 5.12 Left Front Brake Pressure Comparison for a) 80, b) 120, c) 160, d) 200, e)
240 and f) 300 degrees
71
(a) (b)
(c) (d)
(e) (f)
Figure 5.13 Right Front Brake Pressure Comparison for a) 80, b) 120, c) 160, d) 200, e)
240 and f) 300 degrees
72
Figure 5.14 Rear Right Brake Pressure plot for 300 deg Sine with Dwell Maneuver
From the above plots it is clear that the simulation needs much less ESC interference
than the actual vehicle to regain control. The front left brake plots indicate that the
simulation needs only one brake pulse around 1.5 seconds into the maneuver whereas the
actual vehicle has two brake pulses. A similar trend is observed for the front right brake
where the pulses in the simulation are of much less magnitude than observed on the
vehicle. Also from Figure 5.14, it is clear that the simulation vehicle starts to understeer
at around 2 seconds into the maneuver for runs with steering wheel angle greater than
240 degrees. However, the ESC model effectively brings the vehicle back to stability and
works well for most of the steering angles and can be used as a basis to quantify the
benefits of using the CES system.
73
CHAPTER 6:
CONTINUOUSLY CONTROLLED ELECTRONIC
SUSPENSION (CES) SYSTEM
6.1 Introduction
The CES system is an electronic suspension system that continuously adjusts shock-
absorber damping levels dependent on multiple driving variables, including driver inputs,
road conditions, and vehicle dynamics such as speed and cornering. The semi-active
system is able to achieve a balance between comfort and handling through the constantly
adaptive shock-absorber damping levels [9]. This system was developed by Tenneco
Automotive and the valve technology used was developed together with Öhlins Racing.
At the heart of the CES system is an electronic control unit (ECU) that processes
driver inputs and data from sensors placed at key locations on the vehicle. The sensors
include three accelerometers mounted on the vehicle body and four suspension position
sensors. The suspension position sensors give the current position of each strut on the car.
The ECU utilizes this information and sends signals that adjust independently the
damping level of each shock absorber valve in real time. Electronic dampers allow a
large range between maximum and minimum damping levels and adjust instantaneously
to ensure ride comfort and firm vehicle control [10].
74
The CES algorithm is programmed using Matlab Simulink, and a co-simulation is
setup with the ADAMS vehicle model to simulate a vehicle equipped with the CES
system.
6.2 Results
The purpose of this thesis is to evaluate the improvements, if any, in the handling of
the vehicle and performance of the ESC due to the CES system developed by Tenneco.
To investigate this, the Sine with Dwell maneuver is used as recommended by FMVSS
No.126. The following plots show the comparison between a standard Ford Expedition
equipped with ESC only and a Ford Expedition equipped with both ESC and CES doing
the Sine with Dwell maneuver for various steering angles.
75
(a) (b)
(c) (d)
(e) (f)
Figure 6.1 Steering Wheel Angle comparison for Expedition with and without CES for a)
80, b) 120, c) 160, d) 200, e) 240 and f) 300 degrees
76
(a) (b)
(c) (d)
(e) (f)
Figure 6.2 Lateral Acceleration comparison for Expedition with and without CES for a)
80, b) 120, c) 160, d) 200, e) 240 and f) 300 degrees
77
(a) (b)
(c) (d)
(e) (f)
Figure 6.3 Yaw Rate Comparison for Expedition with and without CES for a) 80, b) 120,
c) 160, d) 200, e) 240 and f) 300 degrees
78
(a) (b)
(c) (d)
(e) (f)
Figure 6.4 Speed Trajectory comparison for Expedition with and without CES for a) 80,
b) 120, c) 160, d) 200, e) 240 and f) 300 degrees
79
(a) (b)
(c) (d)
(e) (f)
Figure 6.5 Roll Angle Comparison for Expedition with and without CES for a) 80, b)
120, c) 160, d) 200, e) 240 and f) 300 degrees
80
(a) (b)
(c) (d)
(e) (f)
Figure 6.6 Roll Rate Comparison for Expediton with and without CES for a) 80, b) 120,
c) 160, d) 200, e) 240 and f) 300 degrees
81
(a) (b)
(c) (d)
(e) (f)
Figure 6.7 Pitch Rate Comparison for Expediton with and without CES for a) 80, b) 120,
c) 160, d) 200, e) 240 and f) 300 degrees
82
Figure 6.8 shows the comparison of the right front and right rear damper
characteristics between the standard vehicle and the vehicle equipped with CES. These
plots show the dynamically changing characteristics of the CES dampers. The CES
dampers are also able to offer much higher damping forces compared to the stock
dampers. Figure 6.9 shows the damper forces versus time plots for both the vehicles. The
differences in peak forces produced by the stock and CES dampers are illustrated in this
plot.
83
(a)
(b)
(c)
(Continued) Figure 6.8 Damper Characteristics Comparison Front Right and Rear Right Dampers for
Expediton with and without CES for a) 80, b) 120, c) 160, d) 200, e) 240 and f) 300
degrees
84
Figure 6.8 Continued
(d)
(e)
(f)
85
(a)
(b)
(c)
(Continued) Figure 6.9 Damper Forces Comparison for Expediton with and without CES for a) 80, b)
120, c) 160, d) 200, e) 240 and f) 300 degrees
86
Figure 6.9 Continued
(d)
(e)
(f)
87
6.3 Conclusion
From the above plots, there is no observable and consistent improvement in
performance with the vehicle equipped with CES. There is marginal decrease in peak roll
angle and roll rates with the CES equipped vehicle but the peak pitch rates observed with
the CES equipped vehicle is marginally higher. These changes are small and most likely
are not perceivable to the driver. The vehicle response is not improved, with the time
required for the vehicle to return to zero yaw rate not changing significantly either way.
Figure 6.9 shows the comparison of damper forces between the two vehicles, the
standard vehicle with ESC only and the vehicle equipped with CES and ESC. The
standard dampers in the ESC only vehicle seem to have rapid fluctuations in force
between 1.5 and 2 seconds into the maneuver, these fluctuations occur due to rapid
braking by the ESC at the corresponding times. From the damper forces plots (Figure
6.9), it is clear that the CES dampers are stiffer than the standard dampers for most of the
maneuver, offering, at some instances, twice as much damping force as the standard
dampers. Even in such cases, the difference in force between standard and CES dampers
is only about 1000 N, which is about 100 kg of force. This is negligible compared to the
forces through the springs which are in the range of 10000 N, moreover the dampers offer
only dynamic resistance and do not offer any static stiffness. Thus a momentary reduction
of about 1000 N of force from the springs does not seem to noticeably change the
handling characteristics of the vehicle.
88
CHAPTER 7:
CONCLUSIONS AND RECOMMENDATIONS
7.1 Conclusions
In an effort to evaluate the benefits of the CES system, a model of the 2003 Ford
Expedition was created in Adams View. The various parameters of the model were
validated using quasi static tests results collected by SEA, Ltd. [5] and the overall
dynamics of the model was validated using experimental maneuvers [5]. From the
simulation, the model was shown to give accurate results for the purposes of this study.
Once the model was created, the ESC model was developed in Matlab Simulink and a
co-simulation was set up to integrate the ESC model with the vehicle model. The ESC
equipped vehicle model was validated using test data, and the ESC model proved to be
accurate for Sine with Dwell maneuvers of steering wheel angles up to 240 degrees. For
higher steering wheel angles, the results are still indicative of the performance of the test
vehicle but they start to deteriorate. Overall, the ESC model effectively reduces the time
required for the vehicle model to return to zero yaw rate in the Sine with Dwell
maneuver, and the results are similar to the ESC equipped test vehicle.
Next, a co-simulation was set up to incorporate the CES model, also programmed in
Matlab Simlink, into the vehicle model. Simulations were run and results were compared
with the results from the standard ESC equipped vehicle model. From the simulations,
89
the CES equipped vehicle was shown to offer no noticeable improvement in returning the
yaw rate to zero or in significantly reducing the roll and pitch response in the Sine with
Dwell maneuver. The CES system may offer comfort and customizability to the driver,
and may even improve handling under certain circumstances, but the results of this study
show that the CES system does not improve the performance of a vehicle put through the
Sine with Dwell maneuver.
7.2 Recommendations
It would be advisable to experimentally test a CES equipped vehicle and compare the
results with the simulation. Though simulation results are preferred as an initial
indication of trends, there is no substitute for actual testing. Testing would completely
validate the advantages, if any; of the system and also help ensure that the CES model
gives damper force outputs similar to the actual physical CES system.
The current Adams model provides very accurate results for the needs of this study,
but to further increase the scope of this model, there are several improvements that need
to be made. The tire model with the current tire parameters needs to be replaced with a
better tire model that reflects the properties of the actual tires more accurately.
The compliances added to the steering system of the model were values estimated
using scientific “guess-check” techniques. Though the model is providing accurate
results, it is possible that the compliances do not reflect the real values. The model does
not contain any other suspension compliance as all other joints are modeled as ideal
joints. Omitting the compliances can also lead to erroneous results. The suspension
90
characteristics could be better modeled to reflect the suspension compliances from test
data already available.
The ESC model created for this study is a very basic one, using the very basic inputs
and a simple algorithm. There is a lot of room to improve the ESC model. The algorithm
can be improved to take in more inputs such as steering rate. Other improvements would
include implementing an ABS and a roll stability system.
Lastly, a more detailed study of the effects of damping on ESC performance needs to
be done so that the CES algorithm can be improved. To achieve this, it would be ideal to
perform a full scale vehicle test and simulation using different damper settings and
comparing the results. With these changes/additions, one would have a better model and
a better understanding of the advantages of the CES system.
91
REFERENCES
1. U.S. Department of Transportation, NHTSA, “Traffic Safety Facts 2004”, 2004, DOT HS 809919
2. U.S. Department of Transportation, NHTSA, “PROPOSED FMVSS No.126 Electronic Stability Control Systems”, August 2006
3. Dang, Jennifer N., “Preliminary Results Analyzing The Effectiveness of Electronic Stability Control (ESC) Systems” September 2004, DOT HS809790
4. Forkenbrock, Garrick J., Elsasser, Devin., O’Harra, Bryan., “NHTSA’s Light Vehicle Handling and ESC Effectiveness Research Program” 05-0221
5. Pan, W. and Papelis, Y.E., “Real-Time Dynamic Simulation Of Vehicles With Electronic Stability Control: Modeling And Validation,” Int. J. Vehicle Systems Modeling and Testing, Vol. 1, Nos. 1/2/3, 2005
6. MSC Software Corp., “Getting Started Using Adams/Controls Introducing and Starting the Tutorials”, Mechanical Dynamics Inc., 2002
7. Rajamani, Rajesh “Vehicle Dynamics and Control”, Springer 2005
8. Kinjawadekar, T., Dixit, N. Heydinger, G.J., Guenther, D.A., and Salaani, M.K., “Vehicle Dynamics Modeling and Validation the 2003 Ford Expedition with ESC using CarSim”, SAE Paper 2009-01-0452, April 2008