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

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

1 INTRODUCTION ...................................................................................................... 1

1.1 Motivation........................................................................................................... 1

1.2 Modeling/Simulation .......................................................................................... 3

1.3 Thesis Outline ..................................................................................................... 3

1.3.1 First Objective – Create Vehicle Model in Adams View ........................... 3

1.3.2 Second Objective – Create ESC model using Simulink ............................. 4

1.3.3 Third Objective – Setup Adams and Simulink Co-Simulation................... 4

1.3.4 Fourth Objective – Simulate Maneuvers on the Model .............................. 4

1.3.5 Fifth Objective – Obtain and Analyze Simulation Data ............................. 5

2 MODELING ............................................................................................................... 6

2.1 Overview............................................................................................................. 6

2.2 Hard Point Locations .......................................................................................... 6

vii

2.3 Multibody Model and Inertia Properties........................................................... 10

2.4 Springs and Shock Absorbers ........................................................................... 14

2.5 Tires and Road .................................................................................................. 14

2.6 Drive Train........................................................................................................ 15

2.7 Modeling Measures........................................................................................... 15

2.7.1 Wheel Camber Angle................................................................................ 15

2.7.2 Front Wheel Steer Angle .......................................................................... 16

2.7.3 Roll Angle................................................................................................. 16

2.7.4 Accelerometer Readings ........................................................................... 17

3 VALIDATION.......................................................................................................... 18

3.1 Introduction....................................................................................................... 18

3.2 Quasi-Static Tests ............................................................................................. 18

3.2.1 Bounce Tests............................................................................................. 18

3.2.2 Roll Test.................................................................................................... 23

3.2.3 Steering Ratio Test.................................................................................... 27

3.3 Dynamic Maneuvers ......................................................................................... 28

3.3.1 Slowly Increasing Steer Maneuver ........................................................... 28

3.3.2 Sine with Dwell Maneuver ....................................................................... 33

4 CO-SIMULATION................................................................................................... 43

4.1 Overview........................................................................................................... 43

4.2 Input and Output Variables............................................................................... 44

4.3 Setting up the Co-simulation ............................................................................ 46

4.3.1 Loading Adams/Controls .......................................................................... 46

viii

4.3.2 Defining Input and Output Variables........................................................ 47

4.3.3 Referencing Input Variables ..................................................................... 49

4.3.4 Exporting Adams block ............................................................................ 50

4.3.5 Connecting the Adams Block and the CES Block in Simulink. ............... 51

4.3.6 Running the Co-simulation ....................................................................... 55

4.3.7 Things to Remember................................................................................. 56

5 ELECTRONIC STABILITY CONTROL ................................................................ 57

5.1 Overview........................................................................................................... 57

5.2 ESC Model........................................................................................................ 58

5.3 Validation.......................................................................................................... 61

6 CONTINUOUSLY CONTROLLED ELECTRONIC SUSPENSION (CES)

SYSTEM........................................................................................................................... 73

6.1 Introduction....................................................................................................... 73

6.2 Results............................................................................................................... 74

6.3 Conclusion ........................................................................................................ 87

7 CONCLUSIONS AND RECOMMENDATIONS ................................................... 88

7.1 Conclusions....................................................................................................... 88

7.2 Recommendations............................................................................................. 89

REFERENCES ................................................................................................................. 91

ix

LIST OF FIGURES

Figure 2.1 Rear suspension roll stability bar ...................................................................... 8

Figure 2.2 Front Roll stability bar....................................................................................... 9

Figure 2.3 Adams Model of the Ford Expedition............................................................. 11

Figure 2.4 Topology map of Ford Expedition model. ...................................................... 12

Figure 2.5 Vertical Acceleration Measure of Accelerometer ........................................... 17

Figure 3.1 Front Suspension Spring Rate plot .................................................................. 19

Figure 3.2 Front Suspension Bounce Steer plot................................................................ 20

Figure 3.3 Front Suspension Bounce Camber plot ........................................................... 20

Figure 3.4 Rear Suspension Spring Rate plot ................................................................... 21

Figure 3.5 Rear Suspension Bounce Steer plot................................................................. 22

Figure 3.6 Rear Suspension Bounce Camber plot ............................................................ 22

Figure 3.7 Front Overall Roll Stiffness plot ..................................................................... 24

Figure 3.8 Front Roll Steer plot ........................................................................................ 24

Figure 3.9 Front Roll Camber Angle plot ......................................................................... 25

Figure 3.10 Rear Overall Roll Stiffness plot .................................................................... 26

Figure 3.11Rear Roll Steer plot ........................................................................................ 26

Figure 3.12 Rear Roll Camber plot................................................................................... 27

Figure 3.13 Steering Ratio Test plot of the model............................................................ 28

x

Figure 3.14 Steering Profile of Slowly Increasing Steer Maneuver ................................. 29

Figure 3.15 Speed Profile comaprison.............................................................................. 30

Figure 3.16 Yaw Rate comparison.................................................................................... 30

Figure 3.17 Lateral Acceleration comparison................................................................... 31

Figure 3.18 Roll Angle Comparison................................................................................. 31

Figure 3.19 Roll Rate comparison .................................................................................... 32

Figure 3.20 Pitch Rate comparison................................................................................... 32

Figure 3.21 Steering profiles for a) 80, b) 100, c) 120, d) 140 and e) 160 deg. ............... 34

Figure 3.22 Lateral Acceleration comparisons for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees .............................................................................................................................. 35

Figure 3.23 Yaw Rate Comparison for a) 80, b) 100, c) 120, d) 140 and e) 160 degrees.36

Figure 3.24 Speed Trajectory comparison plots for a) 80, b) 100, c) 120, d) 140 and e)

160 degrees. ...................................................................................................................... 37

Figure 3.25 Roll Angle comparison plots for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees. ............................................................................................................................. 39

Figure 3.26 Roll Rate comparison plots for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees. ............................................................................................................................. 40

Figure 3.27 Pitch Rate Comparison Plots for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees. ............................................................................................................................. 41

Figure 4.1 Schematic of Co-simulation ............................................................................ 43

Figure 4.2 Plugin Manager to load Adams/Controls ........................................................ 47

Figure 4.3 Create State Variable dialogue box for output variable .................................. 48

Figure 4.4 Create State Variable dialogue box for input variable .................................... 48

xi

Figure 4.5 Modify Force dialogue box ............................................................................. 49

Figure 4.6 Adams Controls Plant Export dialogue box. ................................................... 50

Figure 4.7 Adams Block Diagram in Simulink ................................................................ 52

Figure 4.8 Adams model subsystem ................................................................................. 53

Figure 4.9 Function Block Parameters dialogue box........................................................ 54

Figure 4.10 Expedition with CES control diagram in Simulink....................................... 55

Figure 5.1 Functioning of Yaw Stability Control System from reference [6]. ................. 57

Figure 5.2 Schematic of the ESC System ......................................................................... 59

Figure 5.3 ESC Brake Pressure Decision plot. ................................................................. 60

Figure 5.4 ESC Integrated Adams Model in Simulink ..................................................... 61

Figure 5.5 Steering Profiles for Expedition with ESC for a) 80, b) 120, c) 160, d) 200, e)

240 and f) 300 degrees...................................................................................................... 62

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 ................................................................. 63

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.......................................................................................... 64

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 ............................................................................. 65

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.......................................................................................... 66

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.......................................................................................... 67

xii

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.......................................................................................... 68

Figure 5.12 Left Front Brake Pressure Comparison for a) 80, b) 120, c) 160, d) 200, e)

240 and f) 300 degrees...................................................................................................... 70

Figure 5.13 Right Front Brake Pressure Comparison for a) 80, b) 120, c) 160, d) 200, e)

240 and f) 300 degrees...................................................................................................... 71

Figure 5.14 Rear Right Brake Pressure plot for 300 deg Sine with Dwell Maneuver...... 72

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 ....................................................... 75

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 ....................................................... 76

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 ......................................................................... 77

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 ............................................................. 78

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 ................................................................. 79

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 ......................................................................... 80

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 ......................................................................... 81

xiii

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 .............................................................................................................................. 83

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 ................................................................. 85

xiv

LIST OF TABLES

Table 2.1 Front left suspension hard points. ....................................................................... 7

Table 2.2 Rear left suspension hard points ......................................................................... 7

Table 2.3 Front and Rear Roll Stability Bar Hard Point coordinates ............................... 10

Table 2.4 Body Mass and Inertia data. ............................................................................. 13

Table 4.1 Adams Input Variables ..................................................................................... 44

Table 4.2 Adams Output variables.................................................................................... 45

1

CHAPTER 1:

INTRODUCTION

1.1 Motivation

Based on the 2004 Fatality Analysis Reporting Systems (FARS) and 2000-2004

National Automotive Sampling System (NASS) Crashworthiness Data System (CDS),

The National Highway Traffic Safety Administration (NHTSA) estimates that there were

34,314 police-reported passenger vehicle fatal crashes and over 2.5 million serious non-

fatal crashes (defined as at least one involved passenger vehicle was towed away). About

33,907 passenger vehicle occupant fatalities and 2,182,460 non-fatal injuries were

associated with these crashes. Single-vehicle crashes, which frequently include roadway

departure, accounted for about 53 percent (18,321 fatal crashes) of the fatal crashes and

33 percent (820,218 crashes) of the tow away crashes. A total of 15,611 occupant

fatalities and 516,500 non-fatal injuries were associated with these single-vehicle crashes.

Rollovers comprised a large share of these single-vehicle crashes and were responsible

for a disproportionate number of fatalities. Rollovers accounted for 42 percent (or 7,734

crashes) of the single-vehicle fatal crashes and 56 percent (8,487 fatalities) of the

occupant fatalities.

Single vehicle loss of control may occur when the driver attempts a sudden maneuver

(for example, to avoid an object or because one misjudged the severity of a curve), and

2

the vehicle responds differently than it does in ordinary driving as it nears the limits of

road traction.

Loss of control can result in either the rear of the vehicle “spinning out” or the front

of the vehicle “plowing out”. As long as there is sufficient road traction, a professional

race driver could maintain control in many spinout or plow out conditions by using

counter steering and other techniques. However, in a panic situation when the vehicle

begins to spin out, average drivers would be unlikely to counter steer like a race driver

and regain control. Under these circumstances, the ESC system is very effective. ESC

would potentially prevent many loss-of-control accidents from occurring and thus would

reduce associated fatalities and injuries. Based on NHTSA’s ESC effectiveness study [3]

& [4], which found that ESC is highly effective against rollovers, a large portion of these

benefits would be from rollover prevention.

Primarily, the ESC system uses automatic braking of individual wheels to adjust the

vehicle’s heading if it departs from the intended direction the driver is steering. Thus, it

prevents the heading from changing too quickly (spinning out) or not quickly enough

(plowing out) and maintains the vehicle in the direction of the heading. Although it

cannot increase the available traction, ESC controls the heading and provides sufficient

response to steering so that the driver has the maximum possibility of keeping the vehicle

on the road and avoiding obstacles in an emergency maneuver.

Over the last decade, ESC technology has advanced from just an electronic braking

control device to include other components of the vehicle like throttle control, engine

torque control and computer controlled shock absorbers to maintain stability and improve

responsiveness of the vehicle during extreme maneuvers. In their quest to constantly

3

improve the ESC performance, Tenneco Automotive has designed one such computer

controlled damper system called the Continuously Controlled Electronic Suspension

(CES) system.

The research outlined in this thesis is focused on evaluating the performance of the

CES system using simulation on a model created in Adams. The improvements in the

ESC performance due to the CES system are evaluated using the Sine with Dwell

maneuver.

1.2 Modeling/Simulation

Industries these days rely heavily on computer simulation to study the general trends

before investing heavily on actual experimental testing. Testing typically requires

multiple vehicles, numerous sets of tires and expensive instrumentation to obtain

indicative data on all the relevant parameters, and after all this there is still a possibility

that the results show that the desired results cannot be obtained thus making the whole

experiment a waste of resources. To alleviate the expenses associated, a model is first

created and simulations are run on it, to make sure that the trend shows improvement and

that one may indeed go ahead and invest in the experimentation.

1.3 Thesis Outline

1.3.1 First Objective – Create Vehicle Model in Adams View

The first portion of this thesis work involved creating a model of the Ford Expedition

in Adams View (using modeling data available from [5]). Once the model was created it

was validated using the experimental data already collected by NHTSA’s Vehicle

4

Research and Test Center (VRTC) of the basic vehicle. The Slowly Increasing Steer and

the Sine with Dwell maneuvers were used to validate the model. By varying the vehicle

compliance and tire parameters, the vehicle model was modified to provide results

consistent with real world values.

1.3.2 Second Objective – Create ESC model using Simulink

The second portion of this thesis work involved creating a black box ESC model to be

used in conjunction with the Adams vehicle model. Experimental data was used to create

look-up tables of brake pressure versus the difference in actual to desired yaw rate. This

look up table was used to create the ESC model in Simulink.

1.3.3 Third Objective – Setup Adams and Simulink Co-Simulation

The third portion of this thesis work involved setting-up the communication between

Adams and Simulink so that the ESC and CES models, both of which are modeled in

Simulink, can be incorporated into the vehicle model.

1.3.4 Fourth Objective – Simulate Maneuvers on the Model

The fourth portion of this thesis work involved simulating the Sine with Dwell

maneuver on the basic Ford Expedition with ESC and the Ford Expedition equipped with

both CES and ESC systems. The test was run for various steering wheel angles and initial

speeds of the vehicle.

5

1.3.5 Fifth Objective – Obtain and Analyze Simulation Data

The fifth part of this thesis work involved the collection and consolidation of data

from the simulations. The data was compared to determine the improvements in the

vehicle yaw response and ESC performance in the CES equipped Expedition in the

NHTSA Sine with Dwell maneuver.

6

CHAPTER 2:

MODELING

2.1 Overview

The vehicle model is created in Adams, using the graphical user interface of Adams

View. The modeling process is structured to facilitate ease of modification later in the

design, starting with creating hard points denoting the various key locations of the

suspension system. This is followed by creating links using those hard points, and finally

adding joints and constraints between the links to complete the geometry. The mass and

inertia properties are then added to the components of the suspension system.

2.2 Hard Point Locations

The SAE coordinate system was used while modeling the vehicle, with x forward, y

to the right, and z downward. The origin is located directly below the front axle and at the

middle of the track. SI units are used, i.e. meters for length, newtons for force, kilogram

for mass and seconds for time.

The data for the hard point locations were measured by SEA, Ltd. and they measured

the vehicle mass and inertia properties using their Vehicle Inertia Measurement Facility

[5]. Table 2.1 lists the hard point coordinates of the left front side suspensions hard

points. The right side hard points are coded as mirror images of left points about the x-z

7

plane. Hard-coding the right side as a mirror image of the left makes it simpler to make

changes in the suspension geometry, as changing the coordinates of a point on the left

side automatically maintains the symmetry of the right side. Table 2.2 lists the hard point

coordinates for the rear left suspension. Here again the right side is hard coded as the

mirror image of the left.

Table 2.1 Front left suspension hard points.

Table 2.2 Rear left suspension hard points

The hard point coordinates for the front and rear roll stability bars were measured

directly from the vehicle with the help of Mr. Masahiro Chuma at SEA, Ltd. Figures 2.1

8

and 2.2 show some pictures taken while the measurements were being made. The key

parts of the roll stability bar have been marked in the figures.

Figure 2.1 Rear suspension roll stability bar

a – Rear roll stability bar

b – Roll bar support, connecting the chassis to the roll bar

c – link (small rod) connecting roll bar to lower control arm

9

Figure 2.2 Front Roll stability bar

1 – Front Roll stability bar

2 – Link (small rod) connecting Roll bar to Lower control arm

3 – Support connecting roll bar to the chassis

The hard point coordinates for the front and rear anti roll bars are listed in Table 2.3.

The left side hard points are coded to be the mirror images of the right hard points about

the x-z plane.

10

Table 2.3 Front and Rear Roll Stability Bar Hard Point coordinates

2.3 Multibody Model and Inertia Properties

The suspension parts are created using the cylinder member in the Adams View tool

box. The hard points already created mark the end points of each of the suspension links,

these points are used to create the suspension geometry. Each suspension element is

modeled as a separate part, connected to other parts through joints. Figure 2.3 shows the

Ford Expedition model in Adams View. For clarity, the graphics of the Expedition body

are not modeled; however, the mass and inertia properties of the body are incorporated in

the model.

The Expedition employs a Double A-arm suspension on all four wheels. For each

wheel a lower control arm, upper control arm and knuckle are modeled as parts. The

upper and lower control arms are connected to the chassis with bushings and to the

knuckles with spherical joints. The bushings are used to introduce some steering

compliance and they are modeled to be extremely stiff in the vertical and longitudinal

11

directions compared to the lateral direction. The Expedition uses a rack and pinion

steering system. The rack is connected to the chassis with a translational joint. The tie

rods are connected to the rack with universal joints and to the knuckle with spherical

joints. Figure 2.4 is a topology map showing the various parts and how they are

constrained to each other through joints.

Figure 2.3 Adams Model of the Ford Expedition

12

Figure 2.4 Topology map of Ford Expedition model.

S – Spherical Joint R – Revolute Joint

U – Universal Joint T – Translational Joint

B – Bushing

Once the parts are created, their mass and inertia properties are defined. The data for

the mass, inertia and joint locations were also measured by SEA, Ltd. [5]. The mass and

13

inertia properties of all the parts are shown in the Table 2.4. It should be noted that the

knuckle properties include the wheel, tire and rotor. These values were split accordingly

between the knuckle and the wheel in the model.

Number Name Mass (kg)

Ixx/Ixy (kg m2)

Iyy/Ixz (kg m2)

Izz/Iyz (kg m2)

963.40 4719.8 4956.0 1 Chassis 2419.4

0.15047 202.55 2.2664 0.00100 0.01383 0.01383

2 Rack 1.760 0.00000 0.00000 0.00000 0.09030 0.06888 0.04230

3 FR_uca 3.357 0.00000 0.00000 0.00000 0.31631 0.20812 0.15104

4 FR_lca 8.845 0.00000 0.00000 0.00000 1.86040 0.39191 1.89370

5 FR_knuckle 63.321 0.00000 0.00000 0.00000 0.09030 0.06888 0.04230

6 FL_uca 3.357 0.00000 0.00000 0.00000 0.31631 0.20812 0.15104

7 FL_lca 8.845 0.00000 0.00000 0.00000 1.86040 0.39191 1.89370

8 FL_knuckle 63.321 0.00000 0.00000 0.00000 0.10548 0.06252 0.04664

9 RR_uca 3.266 0.00000 0.00000 0.00000 0.41095 0.28797 0.15619

10 RR_lca 10.297 0.00000 0.00000 0.00000 1.41640 0.26311 1.59400

11 RR_knuckle 57.470 0.00000 0.00000 0.00000 0.10548 0.06252 0.04664

12 RL_uca 3.266 0.00000 0.00000 0.00000 0.41095 0.28797 0.15619

13 RL_lca 10.297 0.00000 0.00000 0.00000 1.41640 0.26311 1.59400

14 RL_knuckle 57.470 0.00000 0.00000 0.00000

Table 2.4 Body Mass and Inertia data.

The x axis of the upper and lower control arms is the line of the pivot of the revolute

joint connecting the control arms to the chassis. The y axis is normal to the line of pivot

through the point of the spherical joint connecting the control arm to the knuckle. The z

14

axis is then normal to each of these axes. The y axis of the knuckles is the rotation axis of

the wheel pointing to the right of the vehicle. The x axis is in the forward direction and

the z axis is downward. The x axis for the rack is along its direction of motion. The y and

z axes are arbitrarily chosen as normal to the x axis.

2.4 Springs and Shock Absorbers

The springs are modeled as nonlinear single component forces (S force in Adams)

acting between two points which are the mounting points of the strut. The force is defined

by a 2D curve with spring deflection on the x axis and force on the y axis. The spring

stiffness curves were calculated from the results of bounce tests performed by SEA, Ltd.

[5].

The shock absorbers are modeled as nonlinear single component forces acting

between the same points as the strut. The force is defined by a 2D curve with deformation

velocity along the x axis and force on the y axis. The front and rear shocks were tested at

Detroit Testing Laboratory, Inc. on a shock dynamometer. A curve fit was done on all the

data points for the various frequencies. This curve is used as the damping curve in the

model and the frequency dependence of the shock absorber is not modeled.

2.5 Tires and Road

The tires and road are modeled using the Adams Tire module available in Adams

View. One of the default flat road profiles available in the Adams database is used for the

road. The tire property file suitable for P264/70R17 113S tires was used.

15

2.6 Drive Train

The vehicle model is run only in coast mode for testing the ESC and CES systems,

and for this reason a drive train is not incorporated in the model. Instead, forced motions

are applied at the wheels to control the speed. The motions are then switched off using

scripted controls to let the vehicle coast while the maneuver is performed. Since the

scripted controls cannot be used during co-simulation with Matlab, torques are used

instead of the forced motions to control the vehicle speed when co-simulating with

Matlab.

2.7 Modeling Measures

Since Adams View is a general purpose multibody dynamics simulation software, it

does not have any specialized tools to measure the various vehicle parameters that need

to be monitored and recorded to compare the performance of the vehicle. Hence the

different tools to measure and monitor various parameters like steering angle, camber

angle, roll angle etc are created. Listed below are a few examples of these tools.

2.7.1 Wheel Camber Angle

The wheel camber angle is measured using two markers that are positioned on the

knuckle of the wheel. The first marker (steerangle_ref2) is situated at the wheel center on

the knuckle, and the second marker (steerangle_ref) is positioned on the axis of rotation

of the wheel but slightly inboard. The measure is defined in Adams as the equation:

)_refsteerangle_ref2,steerangle(

angle_ref)steer e_ref2,(steerangl

DY

DZATANSteerangle = (2.1)

16

DZ gives the z displacement and DY gives the y displacement between the two

markers specified with respect to the global origin. ATAN is the command for the inverse

tangent.

2.7.2 Front Wheel Steer Angle

The road wheel steer angle is calculated using the same markers used to measure the

camber angle. The steer angle measure is defined by the equation:

body.cm) _ref,steerangle gle_ref2,DY(steeran

body.cm) _ref,steerangle gle_ref2,DX(steeranATANSteer = (2.2)

The command DX is followed by the names of three markers, which returns the x

displacement between the first two markers with respect to the coordinate system of the

third marker (body.cm) which is the center of gravity of the chassis. This is done so that

the readings are consistent when the vehicle is moving.

2.7.3 Roll Angle

The chassis roll angle is calculated in a similar fashion to the camber angle and steer

angle using two markers. The two markers are fixed to the chassis of the vehicle, the first

marker (body.cm) is at the center of gravity of the body while the second marker

(roll_measure) is on the same horizontal plane but slightly to one side of the first marker.

The measure is defined by the equation:

).,.,_(

).,_(

cmbodycmbodymeasurerollDY

cmbodymeasurerollDZASINRollAngle = (2.3)

The ASIN command returns the inverse sine of the value supplied.

17

2.7.4 Accelerometer Readings

The CES system requires the vertical accelerations from three accelerometers that are

placed in specific points on a horizontal plane. The CES system uses these readings to

compute the roll angle, roll rate, pitch angle and pitch rate of the vehicle. These

accelerations are measured by placing three markers at the specified locations and then

measuring their z component of their acceleration. Figure 2.5 shows the measure dialogue

box.

Figure 2.5 Vertical Acceleration Measure of Accelerometer

18

CHAPTER 3:

VALIDATION

3.1 Introduction

In any computer model, the accuracy of the simulation relies on the accuracy of the

model and the vehicle parameters used to build the model. Hence the mode is checked

against experimental data to ensure that the data matches to confirm the accuracy of the

model. Different quasi-static tests and dynamic maneuvers are used to validate the model.

The experimental laboratory suspension characteristic data was collected by SEA, Ltd.

using their in-house Suspension Parameter Measurement Device (SPMD), reference

[5].The experimental field data was collected by NHTSA’s VRTC at the Transportation

Research Center (TRC), reference [5].

3.2 Quasi-Static Tests

Five different quasi-static tests are used to validate the model, namely: Front Bounce

Test, Rear Bounce Test, Front Roll Test, Rear Roll Test and Steering Ratio Test. These

tests validate the suspension parameters and the suspension kinematics of the vehicle.

3.2.1 Bounce Tests

In the bounce tests, a static load is applied to the chassis of the vehicle through a bar

attached to the frame. For several loads the steer angle and camber angle are measured

19

against the suspension deflection for both the front and rear axle. During the test, the

steering wheel is locked and the tires are positioned on free floating wheel-pad units so

that no lateral or longitudinal forces, or aligning moments would exist at the tires. This is

simulated in the model by setting the road friction to zero.

3.2.1.1 Front Bounce Test

Figures 3.1, 3.2 and 3.3 show the comparison between the experimental and

simulation data for the front bounce test.

Front Suspension Rate

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

-0.10 -0.05 0.00 0.05 0.10 0.15

Suspension Deflection (m)

Ve

rtic

al F

orc

e (

N)

Simulation Experimental

Figure 3.1 Front Suspension Spring Rate plot

20

Front Suspension Bounce Steer

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

-0.10 -0.05 0.00 0.05 0.10 0.15

Front Suspension Deflection (m)

Ste

er

An

gle

(d

eg

)

Simulation Experimental

Figure 3.2 Front Suspension Bounce Steer plot

Front Suspension Bounce Camber

-4.0

-3.0

-2.0

-1.0

0.0

1.0

-0.10 -0.05 0.00 0.05 0.10 0.15

Suspension Deflection (m)

Ca

mb

er

An

gle

(d

eg

)

Simulation Experimental

Figure 3.3 Front Suspension Bounce Camber plot

Reviewing the plots, it is clear that the model is very close to the experimental data

and confirms the accuracy of the front suspension parameters.

21

3.2.1.2 Rear Bounce Test

Figures 3.4, 3.5 and 3.6 show the plots comparing the experimental and simulation

data for the rear bounce test.

Rear Suspension Rate

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

-0.10 -0.05 0.00 0.05 0.10

Suspension Deflection (m)

Ve

rtic

al

Fo

rce

(N

)

Simulation Experimental

Figure 3.4 Rear Suspension Spring Rate plot

22

Rear Suspension Bounce Steer

-1.60

-1.20

-0.80

-0.40

0.00

0.40

-0.10 -0.05 0.00 0.05 0.10

Suspension Deflection (m)

Ste

er

An

gle

(d

eg

)

Simulation Experimental

Figure 3.5 Rear Suspension Bounce Steer plot

Rear Suspension Bounce Camber

-6.00

-4.00

-2.00

0.00

2.00

4.00

6.00

-0.10 -0.05 0.00 0.05 0.10

Suspension Deflection (m)

Ca

mb

er

An

gle

(d

eg

)

Simulation Experimental

Figure 3.6 Rear Suspension Bounce Camber plot

The simulation and experimental data match well for the rear spring rate plot while

some deviation is observed in the Rear Bounce Steer and Bounce Camber plots. Since the

magnitudes of the angles in question are very small, these deviations have only a

23

secondary effect on full vehicle response. These tests validate the rear suspension

parameters.

3.2.2 Roll Test

The roll test is performed by rolling the chassis of the vehicle with respect to the

wheels. The roll moment, camber angle and steer angles are measured against the roll

angle for both the front and rear axles. Similar to the bounce test, the wheels are placed

on free moving pads and the steering wheel is locked. This test serves to check the

accuracy of the roll stiffness bar and suspension kinematics.

3.2.2.1 Front Roll Test

Figures 3.7, 3.8 and 3.9 show the comparison of experimental and simulation data for

the front roll test. Reviewing the plots, it is clear that the model very closely follows the

experimental results. A minor deviation is observed in the Roll Steer plot, but since it is

only to the order of a fraction of a degree, it can be neglected. This test confirms the

accuracy of the kinematics as well as the roll stiffness parameters of the front suspension.

24

Front Overall Roll Stiffness

-10000

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

-5 -4 -3 -2 -1 0 1 2 3 4 5

Roll Angle (deg)

Ro

ll M

om

en

t (N

-m)

Simulation Experimental

Figure 3.7 Front Overall Roll Stiffness plot

Front Roll Steer

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0

Roll Angle (deg)

Ste

er

An

gle

(d

eg

)

Simulation Experimental

Figure 3.8 Front Roll Steer plot

25

Front Roll Camber

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

-5.00 -4.00 -3.00 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00

Roll Angle (deg)

Cam

ber

An

gle

(d

eg

)

Simulation Experimental

Figure 3.9 Front Roll Camber Angle plot

3.2.2.2 Rear Roll Test

Figures 3.10, 3.11 and 3.12 show the corresponding plots for the rear roll test. The

plots show that the model replicates the experimental data very closely. The deviations

observed in the Roll Steer and Roll Camber plots are negligible considering the small

magnitudes of the angles and their effects on the overall behavior of the vehicle. This test

confirms the accuracy of the kinematics and the roll stiffness parameters of the rear

suspension.

26

Rear Overall Roll Stiffness

-6000

-4000

-2000

0

2000

4000

6000

-5 -4 -3 -2 -1 0 1 2 3 4 5

Roll Angle (deg)

Ro

ll M

om

en

t (N

-m)

Simulation Experimental

Figure 3.10 Rear Overall Roll Stiffness plot

Rear Roll Steer

-0.50

-0.30

-0.10

0.10

0.30

0.50

-5 -4 -3 -2 -1 0 1 2 3 4 5

Roll Angle (deg)

Ste

er

An

gle

(d

eg

)

Simulation Experimental

Figure 3.11Rear Roll Steer plot

27

Rear Roll Camber

-4

-3

-2

-1

0

1

2

3

4

-5 -4 -3 -2 -1 0 1 2 3 4 5

Roll Angle (deg)

Cam

ber

An

gle

(d

eg

)

Simulation Experimental

Figure 3.12 Rear Roll Camber plot

3.2.3 Steering Ratio Test

The steering ratio test is performed by rotating the hand steering wheel and measuring

the steer angle of the road wheel. This test is used to measure the ratio of hand wheel

angle to road wheel angle. Figure 3.13 shows the plot of hand wheel angle versus the

road wheel angle of the model. The steering wheel ratio from the plot 20.11 given by the

slope of the plot compares will with the experimental value of 19.71 from reference

[5].This test validates the steering system kinematics of the model.

28

Steering Ratio Testy = 20.111x + 0.6187

-50

0

50

100

150

200

250

300

-2 0 2 4 6 8 10 12 14 16

Road Wheel Steer Angle (deg)

Han

d W

heel

Ste

er

An

gle

(d

eg

)

Figure 3.13 Steering Ratio Test plot of the model.

3.3 Dynamic Maneuvers

Dynamic field test maneuvers are used to validate the vehicle model as a whole

including the tire and road parameters and the vehicle handling. The Slowly Increasing

Steer maneuver and the Sine with Dwell maneuver are used for this purpose.

3.3.1 Slowly Increasing Steer Maneuver

Slowly Increasing Steer maneuver is a pseudo quasi-static maneuver where the

steering wheel is rotated at a constant rate up to a preset angle, held there for a short

period and then returned to zero degrees very quickly while the vehicle is held at constant

speed. The Slowly Increasing Steer maneuver used in this case drove the actual vehicle

and the model to their limits. In the experimental run, the vehicle was held at 50 mph (80

kph) while the steering angle was changed from 0 to 270 degrees in 20 seconds followed

29

by a dwell of 2 seconds and then brought back to 0 degrees in 4 seconds. The same

steering profile is used for the simulation runs to compare the plots. Figures 3.14 – 3.20

show the plots comparing the simulation and experimental results.

Figure 3.14 Steering Profile of Slowly Increasing Steer Maneuver

30

Figure 3.15 Speed Profile comaprison

Figure 3.16 Yaw Rate comparison

31

Figure 3.17 Lateral Acceleration comparison

Figure 3.18 Roll Angle Comparison

32

Figure 3.19 Roll Rate comparison

Figure 3.20 Pitch Rate comparison

33

Reviewing the plots, we can see that the Adams model replicates the experimental

data well. The maximum yaw rate and lateral accelerations match well, but the test

vehicle did not maintain full test speed beyond about 17 seconds. This reduction in test

speed resulted in reduced yaw rate and lateral acceleration responses between 17 and 22

seconds. The roll angle magnitudes are consistently lower than the experimental values,

but closely follow the same trends as do the other plots.

3.3.2 Sine with Dwell Maneuver

According to the Federal Motor Vehicle Safety Standards 126 (FMVSS 126) set by

the National Highway Transportation Safety Association (NHTSA), the Sine with Dwell

maneuver is the preferred maneuver to quantify the ESC effectiveness. Since the purpose

of this thesis is to study the effect of the CES shock absorber system on the performance

of the ESC, it is critical that the model gives accurate results for this maneuver.

In this maneuver, the vehicle is accelerated up to 50 mph (80 kph) and the throttle is

cut off to let it coast. As soon as the vehicle starts to coast down from the preset speed the

steering input is started. The steering input is in the form of a 0.7 Hz sinusoidal wave

with a 500 ms pause after the third quarter-cycle. The maneuver used in the experimental

runs is replicated in the model for various peak steering angles ranging from 80 degrees

to a maximum of 160 degrees and the results are compared in the Figures 3.21 to 3.26.

34

(a) (b)

(c) (d)

(e)

Figure 3.21 Steering profiles for a) 80, b) 100, c) 120, d) 140 and e) 160 deg.

35

(a) (b)

(c) (d)

(e)

Figure 3.22 Lateral Acceleration comparisons for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees

36

(a) (b)

(c) (d)

(e)

Figure 3.23 Yaw Rate Comparison for a) 80, b) 100, c) 120, d) 140 and e) 160 degrees.

37

(a) (b)

(c) (d)

(e)

Figure 3.24 Speed Trajectory comparison plots for a) 80, b) 100, c) 120, d) 140 and e)

160 degrees.

38

From the figures plotted above, it is clear that the model generates very good

predictions for lateral acceleration and yaw rate for the Sine with Dwell maneuver. Figure

3.24 compares the speed trajectory between the simulation and the experimental data.

There seems to be large deviation in these graphs. This is in fact misleading as in the first

four cases, the test maneuver ends before 3.5 seconds when the yaw rate drops to zero.

Thus the experimental speed data after about 3.5 seconds is when the driver has taken

control of the vehicle and braked. This causes the speed difference to look large at the

end of 5 seconds, whereas in reality this data is not relevant for the test. Taking this into

consideration, it is clear that the model predicts the vehicle behavior very accurately.

Studying case (e) with 160 degrees steering, it is clear that both the experimental run

and the simulation yaw rates do not return to zero. This case is the “loss of control” run

for both simulation and experiment. This reiterates that the model is very well tuned to

correlate with experimental data.

Figures 3.25 below shows the roll angle plots for the five cases. Though the

simulation predicts the trends very well, the roll angle magnitudes are consistently lower

than the experimental values. This trend is consistent with that observed with the Slowly

Increasing Steer maneuver (Figure 3.18). Though the roll inertias have been modeled as

measured for the actual vehicle, this may be due to the fact that the actual vehicle has

more dynamic roll compliances, due to bushings etc., than measured on the SPMD and

that the real vehicle is not a perfect rigid body as it is in the model.

39

(a) (b)

(c) (d)

(e)

Figure 3.25 Roll Angle comparison plots for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees.

40

(a) (b)

(c) (d)

(e)

Figure 3.26 Roll Rate comparison plots for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees.

41

(a) (b)

(c) (d)

(e)

Figure 3.27 Pitch Rate Comparison Plots for a) 80, b) 100, c) 120, d) 140 and e) 160

degrees.

42

Figure 3.27 shows the Pitch Rate comparison plots, and there appears to be quiet a lot

of deviation here. Just as in the speed plots, it should be noted that the maneuver ends at

3.5 seconds in the first 4 cases and the data plotted after that is not relevant. The results

are good for the first couple of seconds. After the initial few oscillation peaks, the model

does not seem to capture all the oscillations observed in the real vehicle. The model

seems to predict a lower pitch frequency than that observed in the experimental data

especially as the maneuver progresses. This is probably because the model has limited

number of degrees of freedom, whereas the actual vehicle is more complex tending to

excite higher frequencies.

It is clear from the above plots that the model generates accurate predictions and can

be used to make further predictions about the behavior of the vehicle. Thus the model has

been validated for both static and dynamic tests and the model is ready for use.

43

CHAPTER 4:

CO-SIMULATION

4.1 Overview

Co-simulation is the process of simulating a system where two or more separate

simulation programs are simultaneously used to model various aspects of the system and

these simulation programs communicate during run-time, to simulate the whole system,

thus affecting each other’s output. In this case the vehicle is modeled in Adams-View

whereas the CES damper system is modeled in Simulink and a co-simulation is setup to

run the vehicle model in Adams using the damper model in Simulink.

Figure 4.1 Schematic of Co-simulation

Figure 4.1 is a simple schematic that shows how co-simulation is effected. The output

variables from the Adams vehicle model are exported to the damper model in Simulink.

The damper forces are calculated according to these vehicle parameters and are fed back

into Adams.

44

4.2 Input and Output Variables

The various input and output variables from Adams required by the CES are listed

below in Table 4.1 and 4.2.

Variable Name Description

Fr_damper_force Front right damper force

Fl_damper_force Front left damper force

Rl_damper_force Rear left damper force

Rr_damper_force Rear right damper force

steeringangle Peak angle value for Sine with Dwell maneuver

Table 4.1 Adams Input Variables

45

Variable Name Description

Az_S1 Vertical Accleration of sensor 1

Az_S2 Vertical Accleration of sensor 2

Az_S3 Vertical Accleration of sensor 3

Fl_damper_displacement Front left damper displacement

fr_damper_displacement Front right damper displacement

Rl_damper_displacement Rear left damper displacement

rr_damper_displacement Rear right damper displacement

Speed Vehicle speed

steeringangle Steering wheel angular displacement

steering_rate Steering wheel velocity

Brake_pressure Master cylinder pressure

Throttle Throttle position

Engine_torque Torque output at engine crank shaft

Engine_angular_speed Engine angular speed

Engine_angular_acc Engine angular acceleration

lateralaccleration Lateral Acceleration

Fl_damper_velocity Front left damper velocity

fr_damper_velocity Front right damper velocity

Rl_damper_velocity Rear left damper velocity

rr_damper_velocity Rear right damper velocity

Vz Vertical velocity of vehicle

Pitchrate Pitch Rate

Rollrate Roll Rate

Vertical_acc Vertical acceleration of chassis

Pitch_acc Pitch Acceleration

Roll_acc Roll Acceleration

Yawrate Yaw Rate

Rollangle Roll Angle

Table 4.2 Adams Output variables

46

4.3 Setting up the Co-simulation

The various steps involved in setting up a co-simulation between Adams and

Simulink are:

1. Loading Adams/Controls

2. Defining Input and Output Variables

3. Referencing Input Variables in the Adams Model

4. Exporting the Adams Block

5. Connecting the Adams Block and the CES Block in Simulink

6. Running the Co-simulation

7. Things to Remember

4.3.1 Loading Adams/Controls

Adams/Controls is a plug-in that is available in Adams/View that acts as an interface

between Adams and controls simulation packages such as Easy 5 and Simulink. The

vehicle model is opened in Adams-View and Tools ���� Plugin Manager is selected to

open the Plugin Manager dialogue box. As shown in Figure 4.2, the Load and the Load

at Startup check boxes next to Adams/Controls are selected. OK is selected to close the

dialogue box and save the settings. This adds the Controls menu onto the main menu bar

of Adams-View.

47

Figure 4.2 Plugin Manager to load Adams/Controls

4.3.2 Defining Input and Output Variables

Adams/Controls and controls applications such as Simulink communicate using what

are called as state variables. All input and output variables have to be defined as Adams

state variables. To create a new state variable, from the Build menu, System Element �

State Variable � New, is selected.

48

Figure 4.3 Create State Variable dialogue box for output variable

Figure 4.3 shows how output variables are defined, the name of the state variable is

entered in the Name box, and Run-Time Expression is selected in for the Definition box.

The expression to calculate the output variable is entered in the F(time,…) box.

As shown in Figure 4.4, input variables are also defined as state variables following

the same steps as for the output variables, except that the F(time,…) box is left with the

default value of zero. All the input and output variables, listed in Table 4.1 and 4.2, are

similarly defined.

Figure 4.4 Create State Variable dialogue box for input variable

49

4.3.3 Referencing Input Variables

Once the input and output variables have been defined, the input variable values that

are obtained from Simulink have to be applied/referenced at the proper location in the

Adams model. In this case, the value of the damper forces obtained from Simulink have

to be referenced at the respective damper s-forces. To reference the input variable,

Edit����Modify is selected. This opens the database navigator from which fr_damping is

double clicked. This opens the Modify Force dialogue box as shown in Figure 4.5.

Figure 4.5 Modify Force dialogue box

The Function box is filled in as VARVAL(fr_damper_force), where the command

VARVAL is used to reference the value of the input variable fr_damper_force as the

value to be used for the s-force fr_damping. The other input variables are also similarly

referenced at the corresponding s-forces and motions.

50

4.3.4 Exporting Adams block

Once the Input variables are referenced properly in Adams, the Adams model is ready

to be exported to Simulink as a control system block. To export the model,

Controls����Plant Export in selected which opens the Adams/Controls Plant Export

dialogue box, shown in Figure 4.6.

Figure 4.6 Adams Controls Plant Export dialogue box.

The input variables and output variables are listed in the order in which the respective

pins in the control block are to appear. It is important that the correct input and output

51

pins are connected to the correct control system elements for the proper functioning of

the system. For this reason the output variables are listed in the same order that the CES

controller reads them. Once the dialogue box is completed, OK is selected. This exports

three files with the file name specified in the File Prefix field of the dialogue box

followed by the extensions .adm, .cmd and .m. In this case the file name is specified as

Expedition_CES and thus the three files are Expedition_CES.adm, Expedition_CES.cmd

and Expedition_CES.m. These are saved in the working directory of Adams.

4.3.5 Connecting the Adams Block and the CES Block in Simulink.

To setup the control system with the Adams model, the Adams block diagram is first

opened in Matlab. To do this, Matlab is started and the working directory of Matlab is

changed to the working directory used in Adams (i.e. the same directory that has the files

Expedition_CES.adm, .cmd and .m). At the Matlab prompt, Expedition_CES is typed.

This initializes the input and output variables of the Adams model as variables in Matlab.

Next the command Adams_sys is typed at the prompt, which opens a new window with

the Adams block diagram as shown in Figure 4.7.

52

Figure 4.7 Adams Block Diagram in Simulink

Double clicking on the Adams_sub block opens the Adams subsystem in a new

window showing the components as shown in Figure 4.8.

53

Figure 4.8 Adams model subsystem

Double clicking on the Adams Plant box opens the Function Block Parameters

dialogue box for the Adams Plant. This dialogue box shown in Figure 4.9 can be used to

set various simulation parameters for the simulation. The Communication interval field

specifies how often Adams communicates with Simulink and the Number of

Communications per Output step field specifies the number of communications between

Adams and Simulink for which one output step is written. The Animation mode field is

set to interactive so that the simulation is shown graphically as it is being computed,

alternatively it can be set to batch.

54

Figure 4.9 Function Block Parameters dialogue box.

55

The Adams_sub block is then copied and pasted onto a new model window along

with the CES control system. The outputs from the Adams_sub block are then connected

to the inputs of the CES system and the outputs from the CES are fed back into the

Adams_sub block. Figure 4.10 shows the whole system.

Figure 4.10 Expedition with CES control diagram in Simulink.

4.3.6 Running the Co-simulation

Once the system is setup, the simulation time is entered in the box on top of the

screen and the play button is clicked to run the simulation. Simulink invokes Adams and

runs the model in Adams/View while the damper forces are calculated in Simulink and

fed into Adams while the simulation is running. Thus co-simulation is achieved.

56

4.3.7 Things to Remember

The variable ADAMS_cwd in the matlab file stands for Adams current working

directory, and stores the path of the current working directory that was in use when the

file was exported. This path has to match with the directory in which the Adams files are

when they are run. Thus if the files are moved, or the directory name changed, the

ADAMS_cwd variable has to be accordingly updated.

Adams Host name: The Adams Host Name field in the Adams Controls Plant Export

dialogue box (Figure 4.6) specifies the name of the computer along with the network

path. This information is stored in the variable ADAMS_host in the matlab file. This

information changes from computer to computer and from network to network. Thus this

file can only be run from the computer it was first exported from while it is connected to

the same network as it was when it was exported. To run from another system, all the

files have to be copied to the new system and the value of the ADAMS_host variable has

to be changed to match that of the new system, also the ADAMS_cwd variable has to be

updated to match the path in the new system.

57

CHAPTER 5:

ELECTRONIC STABILITY CONTROL

5.1 Overview

Electronic stability control (ESC) systems are active control systems that act to

prevent the vehicle from spinning and drifting out. Figure 5.1 shows a schematic of the

functioning of a yaw stability system.

Figure 5.1 Functioning of Yaw Stability Control System from reference [7].

58

In the figure, the lower curve shows the trajectory the vehicle should follow in

response to a steering input from the driver if the road were dry and had a high tire road

friction coefficient. In this case, the high friction is able to provide sufficient lateral

forces to the car to negotiate the curved road. If the coefficient of friction of the road was

low or if the vehicle was traveling too fast, the vehicle would be unable to follow the

same curvature, but instead follow a wider curve like the one depicted by the upper curve

of Figure 5.1. The function of the ESC is to restore the yaw velocity of the vehicle as

much as possible to the nominal motion expected by the driver. If the friction is too low,

the ESC may not be able to entirely achieve the nominal yaw rate that is expected on a

high friction surface. In this case the ESC would partially succeed by making the yaw

rate as close to the nominal rate as possible as shown by the middle curve in Figure 5.1.

(From reference [7])

The active control can be effected in different ways, either by active torque

distribution, where the power delivered to each wheel is controlled to achieve the yaw

rate or by steer-by-wire where steering corrections are given by the computer to

compensate for the yaw rate. The Expedition uses a differential braking ESC system,

where the brakes on each wheel are individually applied to correct the yaw rate and

heading of the vehicle.

5.2 ESC Model

The ESC system used with the Adams model is modeled in Matlab Simulink. It is a

modified version of the ESC system used with the CarSim Expedition model developed

59

by Kinjawadekar et al (reference [8]). Figure 5.2 shows a schematic of how the ESC

system works.

Figure 5.2 Schematic of the ESC System

The ESC system takes three inputs; the vehicle yaw rate, the forward vehicle speed

and the vehicle lateral acceleration. The ESC calculates the desired yaw rate by dividing

the lateral acceleration by the speed. The yaw rate is then compared with the desired yaw

using a function YR_d which is equal to the difference between the actual yaw rate and

the ideal yaw rate.

YR_d = Yaw Rate – Lateral Acceleration/Speed (5.1)

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

9. http://www.trucktrend.com/features/news/2008/163_news080811_tenneco_will_p

rovide_ces_shock_absorbers_for_2009_volvo_xc60/index.html

10. http://www.tenneco.com/news/press/archive/press_2007/05082007.html