1. Integrated Vehicle Control SystemsIntegrated Vehicle Control Systems
Vehicle Chassis SystemsVehicle Chassis Systems
ControlControl
andand
IntegrationIntegration
September, 2002September, 2002
Dr. Mark N.W. HowellDr. Mark N.W. Howell
2. Integrated Vehicle Control System
• IntroductionIntroduction
• Systems IntegrationSystems Integration
• Subsumption ArchitectureSubsumption Architecture
• ExamplesExamples
• ConclusionsConclusions
Presentation OutlinePresentation Outline
3. Integrated Vehicle Control System
• Safety
• Predictable behaviour
• Responsive Handling
• Ride Comfort
• Maximise efficiency & performance of the vehicle
• Flexibility, modular, ‘plug and play’ architecture
IntroductionIntroduction
4. Integrated Vehicle Control System
OEMOEMRequirementsRequirements
Based on car type/OEM requirements
select required systems for interaction
Brand DNA
Product Differentiation
Performance FeelPerformance Feel
Ease of UseEase of Use
ReliabilityReliability
IntegrityIntegrity
SafetySafety
ComfortComfort
6. Integrated Vehicle Control System
• Braking Systems - ABS, TRC
• Steering - AFWS, 4WS
• Suspension - Active, Semi-active, Roll Control
• Drivetrain - Differential/ IVT/CVT
• + Cruise Control, Intelligent/Adaptive Cruise Control
• Yaw moment control, X-by-wire
• Future systems: Collision Avoidance, Parking
• Need a coherent way of integrating systems
The Need for IntegrationThe Need for Integration
7. Integrated Vehicle Control System
• Modular
• Respect IPR of suppliers
• Avoid excessive complexity
• Incorporate fault detection, diagnosis and tolerance
• Open architecture
Design RequirementsDesign Requirements
8. Integrated Vehicle Control System
Subsumption ArchitectureSubsumption Architecture
Sensors
S
T
I
M
U
L
U
S
C
O
O
R
D
I
N
A
T
I
O
N
O
Actuators
Behaviour 1
Behaviour 2
Behaviour n
A modular, behaviour based, distributed architecture
Behaviours are layers of control architectures that are event
driven
One layer can subsume control over another layer
Higher level behaviour can suppress a lower-level behaviour.
9. Integrated Vehicle Control System
• Distributed Layered Control
– Control distributed across parallel layers each with multiple modules
• Behavioural Decomposition
– different layers support different ‘task-achieving’ behaviours’
– decomposes into behavioural rather than function units
• Increasing ‘Levels of competence’
– Ascending level adds capabilities resulting in higher overall competence.
– Higher levels often operate by modulating the activities of lower levels.
• Incremental Construction
– incremental control system designing
– intermediate architecture tested and debugged before next layer added.
• Conflict resolution and communication between levels
– Higher layers subsume the roles of lower ones by suppressing their
outputs and substituting their own.
Key Aspects of SubsumptionKey Aspects of Subsumption
10. Integrated Vehicle Control System
SubsumptionSubsumption
Advantages
• Modular
• Very flexible
• Robust to system change
• Incremental control design
Disadvantages
• Complex overall system with a large number
of behaviours
• Verification difficult of overall system
behaviour
11. Integrated Vehicle Control System
Collision
Avoidance
Straight
Line
Stability
Neutral
Steer
Parking
Aid
Safety
Distance
from Obstacles
Anti -
Dive
Anti -
Squat
Yaw
Stability
Roll
Stability
Ride
Comfort
Load
Transfer
Forward
Speed
Layer 4
Behaviour
Layer 3
Behaviour
Layer 2
Behaviour
Layer 1
Behaviour
Layer 0
Hardware
ABS TCS
Side Slip
Control
Controllable
Suspension
Driver
SensorandInformationBus
Integrated Layers
Non Integrated Layers
(mostly single loop)
Lane Detection
and Tracking
Brakes Engine Transmission Suspension Steering
Subsumption SubsystemsSubsumption Subsystems
12. Integrated Vehicle Control System
Sensors
(physical)
Sensors
(Soft)
State Estimation/
Observers
Near Traffic
Condition
Driver Model
True Vehicle
Model
'Desired' Vehicle
Model
Road Condition
Estimation
Bahaviours
Lane Detection
Sensor and Information BusSensor and Information Bus
13. Integrated Vehicle Control System
Behaviour 4
Behaviour 3
Behaviour 2
Behaviour 1
ACTION
MAX (B1, B2,B3,B4)
Behaviour 4
Behaviour 3
Behaviour 2
Behaviour 1
ACTION
Respond of highest
active behaviour
Response of behaviour
with the highest
activation signal
Behaviour 4
Behaviour 3
Behaviour 2
Behaviour 1
ACTION
Voting based (Neural)
Behaviour 4
Behaviour 3
Behaviour 2
Behaviour 1
ACTION
Fuzzy Rule based
(A)
(B)
(C)
(D)
14. Integrated Vehicle Control System
Scope for Integration - ActuationScope for Integration - Actuation
• 4 Independent Brake 4
• Engine 1+(...)
• Driveline (Transmission/differential) 1,2+
• Individual Wheel Steering 4
• Active Suspension 4
Total : 15+
15. Integrated Vehicle Control System
• Stiff suspension model - nonlinear tyre model
• 7 DOF: Yaw, Sideslip, Longitudinal, Wheel spin
+ Control States
• Independent wheel braking
• Rudimentary Powertrain (torque demand)
• Active Front Wheel Steer
Simple StudySimple Study
16. Integrated Vehicle Control System
• Integrated Systems
• Non-integrated control
Driver
Throttle
Brake Input
Steer Angle
Input
Brake torque
Front Steer Angle
Throttle
Low
‘ABS’ Independent
Wheel Slip Control
Front Slip angle
control
Yaw/ Sideslip
Control
Directional
Control
HighIntermediate
Vehicle
Simple study - levels of behaviourSimple study - levels of behaviour
17. Integrated Vehicle Control System
0 2 4 6 8 10 12 14 16 18 20
-10
-5
0
5
10
15
20
25
30
time [s]
speed[m/s]
Vehicle Forward Speed
noctrl
S
sigma
S
beta10S
allS
18. Integrated Vehicle Control System
0 2 4 6 8 10 12 14 16 18 20
-200
-150
-100
-50
0
50
100
150
200
time [s]
beta[o
]
Vehicle Side Slip Angle
noctrl
S
sigma
S
beta10
S
all
S
19. Integrated Vehicle Control System
0 2 4 6 8 10 12 14 16 18 20
-4
-3
-2
-1
0
1
2
3
4
time [s]
beta[o
]
Vehicle Side Slip Angle
noctrl
S
sigma
S
beta10
S
all
S
20. Integrated Vehicle Control System
0 2 4 6 8 10 12 14 16 18 20
-60
-40
-20
0
20
40
60
time [s]
delta[o
]
Steer Angle
noctrlS
sigma
S
beta10
S
all
S
21. Integrated Vehicle Control System
0 2 4 6 8 10 12 14 16 18 20
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
time [s]
r[rad/s]
Yaw Rate
noctrl
S
sigma
S
beta10
S
all
S
22. Integrated Vehicle Control System
0 2 4 6 8 10 12 14 16 18 20
-8
-6
-4
-2
0
2
4
6
8
time [s]
a
lat
[m/s2
]
Lateral Acceleration
noctrl
S
sigma
S
beta10
S
all
S
24. Integrated Vehicle Control System
• Technical and commercial considerations restrict the
ways that integrated vehicle control systems are
implemented in practice
• Limiting total system complexity is a priority
• Layered ‘subsumption’ architectures are particularly
applicable to the control implementation, but detailed
methodologies are not yet well developed
• Issues of conflict resolution in real-time, may be solved
by extending commonly available control techniques
Main ConclusionsMain Conclusions
Different vehicle manufactures (OEMs) want different characteristics from a vehicle - the brand DNA - the system needs to be tuneable to meet the performance feel of that make of care. They also demand high levels of comfort, safety etc as well as safe, predictable responsive vehicles that have good handling and ride comfort characteristics.
To achieve these objective and maximise the efficiency and performance of the vehicle systems they need to be integrated together. It is that integration that is examined in this talk. In order to achieve the above a flexible, modular tuneable ‘plug and play’ architecture is desirable.
The need for integration becomes apparent when we look at the various different subsystems that are on the car - there are four main subsystem groups namely Braking, Suspension Steering and Powertrain/Engine each of which has had a number of different functions designed for a specific behaviour. For instance braking systems involve ABS and traction control, active suspensions and active roll control are also now available. Many other systems exist as well such as yaw moment control, x-by-wire systems as well as cruise control adaptive cruise control. Other systems such as collision avoidance and parking assist are also being developed. These systems all need to be integrated together in a coherent way
One other thing worth noting is that there are a lot more systems than actuators many of these individual systems share actuation requirements and so they a decision needs to be made by in system architecture as to which subsystem has control at any one time.
To link all these systems together and to tie up was has previously been stated we require a modular architecture so that different combinations of systems can be added together.
This architecture needs to be able to respect the IPR of the suppliers of the various systems
We also need to involve excessive complexity - it does not make sense to design a single controller for everything which will become extremely complex especially as extra code will be need to protect the system integrity. It is likely that the design of such a system would become prohibitively expensive.
We also require an open architecture approach with a standard interface design so that the subsystems can take commands in and give an indication as to the reliability of the information being supplied.
The main properties of a subsumption approach are listed here.
In order to put these ideas into context the following diagram shows the different layers of control that could be involved in an integrated chassis system design.
The lowest level controls the actual vehicle hardware - the engine, brakes, transmission suspension and steering systems.
Above this we have single behaviour systems independent controlled and mostly responsible for a single task. The ABS here for instance is independent wheel ABS and purely responsible for preventing a wheel from locking.
The driver is on this level this is only part of the drivers function and is just to show that he cannot influence the other subsystems on this level - however some can be considered to be subsuming his control.
Above this we have higher behaviours that can make use of the behaviours in the layer below them. For instance yaw stability will need to make use of and steering control that is available as well as perhaps change the brake distribution.
Cruise control can be seen as the forward speed control that would make use of the ABS and traction control and the layer above this represents adaptive cruise control where the desired behaviour is to maintain a safe distance from the car in front.
In order to put these ideas into context the following diagram shows the different layers of control that could be involved in an integrated chassis system design.
The lowest level controls the actual vehicle hardware - the engine, brakes, transmission suspension and steering systems.
Above this we have single behaviour systems independent controlled and mostly responsible for a single task. The ABS here for instance is independent wheel ABS and purely responsible for preventing a wheel from locking.
The driver is on this level this is only part of the drivers function and is just to show that he cannot influence the other subsystems on this level - however some can be considered to be subsuming his control.
Above this we have higher behaviours that can make use of the behaviours in the layer below them. For instance yaw stability will need to make use of and steering control that is available as well as perhaps change the brake distribution.
Cruise control can be seen as the forward speed control that would make use of the ABS and traction control and the layer above this represents adaptive cruise control where the desired behaviour is to maintain a safe distance from the car in front.
What scope is there to implement this integration. Well consider this example we have 4 independent brake controllers, an engine control for the traction control system but there may be others that could be added in here. Transmission control with active differentials controlling both the torque distribution left right and front rear. Individual wheel steer and active suspension also add many other potential actuators.
As a simple example of the principles discusses a 7DOF stiff suspension model with nonlinear tyre characteristics was developed. This allows for yaw, sideslip, longitudinal control and wheel spin.
The model had individual wheel braking a rudimentary torque demand for the powertrain control and active front wheel steer.
The system showing how this integration philosophy applies. At the top we have on integrated control where the driver command just feed through to the
vehicle.
In the lower diagram individual wheel ABS and front slip angle control are added. The yaw/sideslip control is a higher level that augments the ABS control decision and above that direction control can be added which override this and the drivers control decision.