Brake-by-Steer Concept
Steer-by-wire application with
independently actuated wheels
used for stopping a vehicle
9-4-2015
Master Thesis Presentation
Department of Precision and Microsystems Engineering
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
Bas Jansen
25-03-2010
1
Content
1. Introduction
-
SKF
-
Drive-by-wire
-
Brake-by-steer concept
2. Modeling the Brake-by-Steer system
9-4-2015
-
Tire model
-
Vehicle model
-
Brake-by-steer cases
3. Implementation on a Go-Kart
-
Go-kart introduction
-
Design Implementations
4. Test Results
-
Braking performance
-
Lateral behavior
5. Conclusion & Recommendations
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
2
1.
Introduction
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
3
Introduction
SKF - Svenska Kullagerfabriken AB
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
4
Introduction
SKF - Svenska Kullagerfabriken AB
9-4-2015
SKF European Research Centre
Nieuwegein
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
5
Introduction
What is Steer-by-Wire
Steering wheel
Steering shaft
Conventional steering system
Rack & Pinion
Steer-by-wire with independently
9-4-2015
actuated
wheels
Data transport
Steering Controller
Sensor &
actuator
Sensor &
actuator
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
6
Introduction
What is Brake-by-Wire
Electro mechanical
braking actuators
Data transport
Replace hydraulic brake system
with an individually electrically
Braking controller
actuated brake system
Brake pedal
& sensor
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
7
Introduction
Why By-Wire
Modular design provides design freedom,
reduces weight and requires less space
Personalized and adaptive driving
9-4-2015
experience by varying control settings
Increased safety potential in combination
with intelligent vehicle safety systems
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
8
Introduction
Safety challenge for By-Wire
Primary systems with
redundant back-up systems
Increase safety level:
• Implemented redundant components
• Assign secondary function to initial
9-4-2015
primary function of a sub system
• Steer by uneven distributed brake force
• Brake-by-steer concept
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
9
Introduction
Brake-by-Steer concept
Position the front wheels such that
they generate a braking force
Research Question:
Is it possible to stop a vehicle with the
brake-by-steer concept and how does this
influence the steering controllability?
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
10
2.
Modeling the Brake-by-Steer system
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
11
Brake-by-Steer Modeling
Model construction
Ftire
Model build-up:
• Tire model
• Vehicle (kart) model
• Brake-by-Steer cases
9-4-2015
Vtire
Vvehicle
m, I
Length
Width
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
12
Brake-by-Steer Modeling
Tire modeling
x, u
Tire behavior:
• No resistance force in longitudinal direction (x)
• Resistance force in lateral direction (y)
V

Slip angle:
The angle between tire’s direction of travel (V) and
9-4-2015
the direction towards which it is pointing (x)
tan    
Delft
University of
Technology
Challenge the future
v
u
y, v
x, y  Tire coordinates
u , v  Tire velocities
V  Tire velocity vector
  Slip angle
Brake-by-Steer Concept
13
Brake-by-Steer Modeling
Tire modeling
x, u
V
Lateral tire force (N)

Lateral Tire Force
1
0.8
0.6
Flateral tire
y, v
0.4
9-4-2015
0.2
0
C
0
5
10

15
Slip
angle
Slip angle (deg)
20
C  , for    saturate
 Fsaturate , for    saturate

FLat  

Flat  d sin c tan 1 b  
Delft
University of
Technology
Challenge the future

25
30
x, y  Tire coordinates
u , v  Tire velocities
V  Tire velocity vector
  Slip angle
FLat  Lateral tire force
Brake-by-Steer Concept
14
Brake-by-Steer Modeling
Vehicle Model
Vehicle equations of motion


x, u
V
u
V
m, I
X 9-4-2015
y, v
v
Flateral tire
Y
FX  Flateral tire cos   
FY  Flateral tire sin   
X

FX
m
F
v  ur  Y
m
M Z
r
I
u  vr 
Y
Tricycle model
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
15
Brake-by-Steer Modeling
Steady state straight line driving brake force
Symmetric
Toe-in
9-4-2015
Toe-out
Asymmetric
Toe-out
Steering angle Right
Toe-out
Brake force [N]
Brake-by-Steer cases
Toe-in
Toe-in
Steering angle Left
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
16
Brake-by-Steer Modeling
Effect of longitudinal vehicle force for vehicle heading
Toe-in steer to the right
Ftire
FX left

Toe-out steer to the right
FX left
FX right

FX right
Ftire
9-4-2015
t
M vehicle  t   FX right  FX left 
Steering to the right results in
vehicle moment to the left
Delft
University of
Technology
Challenge the future
Ftire
t
M vehicle  t   FX right  FX left 
Steering to the right results in
vehicle moment to the right
Brake-by-Steer Concept
17
Brake-by-Steer Modeling
Effect of lateral vehicle force for vehicle heading
Toe-in steer to the right
Ftire
FY left

Toe-out steer to the right
FY right
FX left

FX right
Ftire
9-4-2015
Ftire
FY  FY left  FY right
Steering to the right results in
lateral vehicle force to the left
Delft
University of
Technology
Challenge the future
FY  FY right  FY left
Steering to the right results in
lateral vehicle force to the left
Brake-by-Steer Concept
18
Brake-by-Steer Modeling
Theoretical Results – Lateral Behavior
Steering angle Right
Summation Lateral Vehicle Force [N]
Toe-out
9-4-2015
Symmetric toe equilibrium
Asymmetric toe equilibrium
There is no asymmetric
toe-out equilibrium line
Toe-in
Steering angle Left
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
19
3.
Implementation on a Go-Kart
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
20
Implementation on a Go-Kart
Go-Kart Introduction
Caster angle
Kingpin inclination
Remove
mechanical linkage
9-4-2015
Caster angle
Kart specific features:
• No individual wheel suspension
• Flexible tube frame acts as suspension
• Fixed rear axle
• Caster angle and kingpin inclination
Rotational path
Left tire side view
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
21
Implementation on a Go-Kart
Electromechanical Modifications
Steering Wheel
Toe handle
• Absolute magnetic encoder measures
steering angle
• DC
motor provides force feedback sense
9-4-2015
• Toe levers measure toe angle setpoints
Steering wheel actuator
Steering wheel angle sensor
Steering shaft
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
22
Implementation on a Go-Kart
Electromechanical Modifications
Wheels
Extension brackets
• DC motor positions the wheels
• Encoder used as control position signal
• Absolute angle sensor used homing during initialization
Encoders
Motor + gear
9-4-2015
Stub axle
Delft
University of
Technology
Challenge the future
Absolute angle sensor
Brake-by-Steer Concept
23
Implementation on a Go-Kart
Control algorithm
Toe mode selection
+/-

C
Controller

9-4-2015
Force
K
Force feedback to
steering wheel
Delft
University of
Technology
Challenge the future
Motor currents
Feedback position control
for wheel positions
Brake-by-Steer Concept
24
Implementation on a Go-Kart
Control algorithm
Vkart
0

Toe mode selection
K

+/Mimic steering torque with speed
9-4-2015
dependent return to center torque

C
Controller

Feedback position control
for wheel positions
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
25
Implementation on a Go-Kart
Implemented design
Steering wheel actuation
Electronics
Velocity sensor
9-4-2015
Batteries
Left wheel actuation
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
26
4.
Test Cases and Results
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
27
Test cases & Results
Test cases
• Braking performance of the brake-by-steer concept
• Lateral vehicle behavior during brake-by-steer maneuver
9-4-2015
Test track at SKF ERC Nieuwegein
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
28
10
Velocity
Test cases & Results
(m/s)
Acceleration (m/s 2)
Brake Force (kN)
8
6
Results – Braking Performance
(Various)
4
2
0
-2
-4
-6
0
Toe in
Toe out
One wheel
Theoreticle data
-0.2
Brake force (kN)
-0.4
0
1
2
3
4
Time (sec)
5
Theoretical maximum:
-0.6
1.5 kN
9-4-2015
-0.8
-1
-1.2
-1.4
Fbrake  Ftire saturate 
-1.6
0
20
40
Delft
University of
Technology
Challenge the future
60
80
100
120
Effective toe angle (deg)
140
160
6
180

i left ,right
Brake-by-Steer Concept
sin  i
29
7
Slip angles
Test cases & Results
40
Results – Lateral behavior
30
20
10
Calculated driven path for symmetric toe-in (30º)
with steering offset of 2, 4, 6, 8 degrees to the right
0
-10
-0.06
-20
-30
-0.04
0
0.5
1
1.5
2
2.5
3
3.5
Path for L: 38 (rad), R: -22 (deg),
Velocities
-0.02
Velocity: 5 [m/s], C1: 850, C2: 1200
9-4-2015
0
5
Y [m]
u (m/s)
v (m/s)
r (deg/s)
0.02
various
0
0.04
0.06
-5
0
1
2
3
4
5
6
7
8
9
X [m]
-10
Delft
University of
Technology
Challenge the future
0
0.5
1
1.5
2
Time (sec)
Brake-by-Steer Concept
2.5
3
30
3.5
Test cases & Results
Right
Left
Rear
80
Results – Lateral behavior
60
Slip angle (deg)
Calculated driven path for symmetric toe-out (60º)
with steering offset of 2, 4, 6, 8 degrees to the right
Slip angles
100
40
20
0
-20
-0.25
-40
-60
-0.2
0
0.2
0.4
0.6
0.8
1
Time (sec)
Path for L: -52 (rad), R: 68 (deg),
1.2
1.4
Velocities
Velocity: 5 [m/s], C1: 850, C2: 1200
6
-0.15
Y [m]
9-4-2015
u (m/s)
v (m/s)
r (deg/s)
4
2
-0.1
0
various
-2
-0.05
-4
-6
0
-8
0
0.5
1
1.5
X [m]
2
2.5
3
-10
-12
-14
Delft
University of
Technology
Challenge the future
0
0.2
0.4
0.6
0.8
Time (sec)
Brake-by-Steer Concept
1
1.2
31
1.4
5.
Conclusions & Recommendations
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
32
Conclusions & Recommendations
Conclusions Brake-by-Steer Concept
Brake-by-steer concept can back-up failing brakes with a
reduced braking performance (~50%).
Lateral behavior changes drastically and ranges of inverted
steering occur. These make the vehicle uncontrollable for the
driver.
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
33
Brake-by-Steer Modeling
Conclusions Toe-modes
Theory and practice differ on effectiveness of toe modes due to
due to caster angle and kingpin inclination induced roll motion.
The kart tire that is turned out the most gains vertical axle load and
dictates the lateral behavior of the vehicle.
9-4-2015
Toe-in
Symmetric
Asymmetric
Good braking capability
Not effective braking
Good steering capability
Good steering capability
(although inverted)
Toe-out
Good braking capability
Not effective braking
Good steering capability
Impossible to drive straight
(although partly inverted)
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
34
Conclusions & Recommendations
Recommendations Brake-by-Steer Concept
Before the brake-by-steer concept can be applied in cars, the
relation between steering angle and vehicle heading must be
restored. Calculate how to position the wheels to generate a
brake force and follow expected steering input according toe
strategy.
Steering angle
Brake9-4-2015
pedal
Controller
Velocity
Lateral accelerations
...
Wheel
actuators
To create this model the presented conceptual model needs to
be extended and validated on a car in stead of a go-kart
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
35
Thank you for your attention
9-4-2015
Questions?
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
36
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
37
9-4-2015
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
38
Implementation on a Go-Kart
Steering system design requirements
Angle sensor
Strain gages
Performance requirements:
• Wheel steering rate typical 80 º/s
• Steering frequency typical 1 Hz (amp =
~10 deg)
• Steering torque at wheels
• Nominal 8 Nm
• Peak 50 Nm
9-4-2015
Measured braking performance
• Braking Force 1,2 kN
Velocity sensor
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
39
Brake-by-Steer Modeling
Brake-by-Steer cases – Vehicle controllability
Flateral vehicle  Flateral tire  cos  
force (N) Force [N]
Vehicle
LateralLateral
1000
9-4-2015
800
A0
600
A1
400
200
0
-200
-400
B0
-600
B1
-800
-1000
-80
-60
-40
-20
0
20
Slip angle (deg)
40
60
80
Slip angle 
Inverted steering occurs at symmetric
toe mode for  > 
saturate
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
40
BACKUP
Siemens VDO eCorner
9-4-2015
The hub motor (2) is located inside the wheel rim (1).
The electronic wedge brake (3) uses pads driven by
electric motors.
An active suspension (4) and electronic steering (5)
replace conventional hydraulic systems.
Delft
University of
Technology
Challenge the future
Brake-by-Steer Concept
41
BACKUP
Ftire
Ftire

Ftire
9-4-2015

FX vehicle left
FX vehicle right
Ftire
Delft
University of
Technology
Challenge the future
FX vehicle left
Brake-by-Steer Concept
FX vehicle right
42