Identification of tyre lateral force characteristic - Ukintpress ...

Identification of tyre lateral force characteristic from handling
data and functional suspension model
Marco Pesce, Isabella Camuffo
Centro Ricerche Fiat
Vehicle Dynamics & Fuel Economy
Christian Girardin
Fiat Group Automobiles
E&D – Chassis & Vehicle Dynamics
Stuttgart, June 22, 2010

About CRF
Centro Ricerche Fiat S.C.p.A. (C.R.F.) since 1976 is the reference centre for
the activities of innovation and research of Fiat Group.
Date of establishment:1976
Employees: ~800
Average age: 39
Headquarters: Orbassano
Branches: Trento,
Valenzano (BA)
Foggia
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 2
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Contents
Background
The role of synthesis models in the product development cycle
Goal and constraints
Evolution of synthesis model for vehicle dynamics analysis
Linear single track model
Non linear single track model
From axle identification to tyre identification
Results / Applications
Conclusions and Next steps
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 3
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Background
Vehicle Dynamics & Fuel Economy Department is involved in the
development of innovative methods / tools for Objective Evaluation and
Virtual Analysis regarding:
Handling/Steering
Braking
Ride Comfort
Driveability
Fuel Consumption
All methods cover the target setting and deployment phases in order to
define and achieve customer oriented product targets.
Purchase Criteria
& Perceived Quality
Perceived Quality
Measurements (Q.I.)
Deplyoyment procedure
& simulation tools
Voice Voice
of of
Customer
Vehicle Vehicle
Target Target
Setting Setting
Sub-systems Sub-systems
Target Target
Deployment Deployment
Components
Target Target
Achieving Achieving
Design Design
Specifications
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 4
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Background
The role of synthesis models in the product development cycle
Purchase Criteria
& Perceived Quality
Perceived Quality
Measurements (Q.I.)
Deplyoyment procedure
& simulation tools
Voice Voice
of of
Customer
Vehicle Vehicle
Target Target
Setting Setting
Sub-systems Sub-systems
Target Target
Deployment Deployment
Components
Target Target
Achieving Achieving
Design Design
Specifications
Simplified models
Check of consistency of VTS (Vehicle Technical Specifications)
Definition of macro target for vehicle subsystems, e.g.:
Front & Rear cornering stiffness
Roll stiffness and damping
Capability evaluation of active systems
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 5
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Goal and constraints
GOAL
CONSTRAINTS
Identification of simple vehicle models that can be used to support target
setting
No additional time and costs with respect to the standard test protocol used for
handling objective evaluation:
Target consistency check (which means realistic target)
first level target deployment
evaluation of the potential impact of active systems
Development of automated tools that support the vehicle dynamics engineer:
identification of simple vehicle models
simulation of handling tests for sensitivity analysis of VTS to variation of the main
design parameters
No increase of complexity of the standard sensor setup used for vehicle dynamics
objective evaluation
No increase of number of tests
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 6
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Goal and constraints
Basic sensor setup required for simple models identification
Transducer
Measured variables
Vehicle speed
Optical sensor
Side slip angle
Steering wheel angle
Measurements steering wheel
(Steering wheel torque)
Lateral acceleration
Longitudinal acceleration
Inertial Measurement Unit
Yaw rate
Roll rate
Pitch Rate
Objective tests
Driving condition
Linear transient behaviour
Steady state cornering
Objective test
Frequency sweep sine
Constant radius cornering / Slow ramp
steer input / track laps
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 7
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
Road map of implementation in custom software for vehicle dynamics objective
evaluation and linked tools: W-HandsPlus©CRF
Detail (model complexity)
Single track linear model
Input
• Front & Rear Mass
• Wheelbase
• Steering ratio
Output
• F & R Cornering stiffness
• Relaxation lengths
• Yaw inertia (if unknown)
Single track non linear model
Input
• Front & Rear Mass
• Wheelbase
• Steering ratio
• Yaw inertia
Output
• F & R force characteristics
(MF)
Input
Tyre “reduced” model
• Front & Rear Mass
• Wheelbase
• Steering ratio
• Basic suspension params
Output
• “Reduced” set of MF
coefficients: shape,
stiffness(Fz), peak(Fz)
Late ’90s
Beg. 2000
nowadays
Time
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 8
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
The linear single track model
Basic theory
Based on the linear
single track model
Input
• Front & Rear Mass
• Wheelbase
• Steering ratio
Output
• F & R Cornering stiffness
• Relaxation lengths
• Yaw inertia (if unknown)
Reference tests for parameters identification
Frequency sweep sine at constant speed
Identification approach
Minimum error between measured and calculated motion
variables (yaw rate, lateral acceleration)
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 9
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
The linear single track model
Example of results: automatic identification of linear single track model
integrated in W-HandsPlus
Identified parameters for single track linear model
Experimental Frequency Response function and
identified linear model superposition
Lat. Acc / SWA
Yaw Rate / SWA
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 10
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
The non linear single track model
Basic theory
The motion equations provide estimation of the lateral
force and slip angle of the front and rear axle, based
on inertial vehicle data and measured motion
variables.
The axles’ force vs. slip angle characteristics are fitted
by the Magic Formula, identifying coefficients “B y
”,
“C y
”, “D y
”, “E y
”
Input
• Front & Rear Mass
• Wheelbase
• Steering ratio
• Yaw inertia
Output
• F & R force characteristics
(MF)
Reference tests for parameters identification
Steady state or near-steady state test: constant radius
cornering, slow ramp steer input (spiral), track laps
Identification approach
Minimum error between experimental and calculated
force vs. slip angle characteristics
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 11
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
The non linear single track model
Example of results: automatic identification of non linear single track model
integrated in W-HandsPlus
Fitting of front and rear
force characteristics
Equivalent front and rear
axles’ cornering stiffness
MF coefficients of
front and rear axles
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 12
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
The non linear single track model
Example of results
Same car in a baseline configuration, equipped with different tyre and with a
different suspension setup.
Proven correlation between the driver’s subjective perception of the vehicle and
the different cornering force characteristics.
Front axle
Rear axle
9000
6000
8000
7000
5000
6000
4000
Fy [N]
5000
4000
Fy [N]
3000
3000
Base
2000
Base
2000
1000
Tyre
Susp
1000
Tyre
Susp
0
0 2 4 6 8 10 12 14
Slip angle [deg]
0
0 1 2 3 4 5 6
Slip angle [deg]
The method is effective in order to evaluate changes related to tyre or suspension…
…but does not allow to split the contribution of tyre and suspension
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 13
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
From axle properties to tyre properties identification
Basic theory
Based on a synthesis four corner model
Main assumptions
Fixed front and rear roll center
Linear toe K&C
Linear camber K&C
Tyre model
“Reduced” MF for identification. Camber effect not
included yet at current stage
“Full” MF possible for simulation
Reference tests for parameters identification
Steady state or near-steady state test: constant radius
cornering, slow ramp steer (spiral), handling track laps
Identification approach in two steps
First step based on the non linear single track model
Second step based on additional suspension data that
must be known a priori or measured by other tests
Input
• Front & Rear Mass
• Wheelbase
• Steering ratio
• Basic suspension params
Output
• “Reduced” set of MF
coefficients: shape,
stiffness(Fz), peak(Fz)
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 14
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
From axle properties to tyre properties identification
Identification flow chart
Fy vs. slip characteristic (MF)
Steady state Fy
vs. slip angle data
Fitting
8000
7000
6000
Non linear axle characteristics
Evaluation of suspension effects
Lateral load transfer
Linear toe variation
Fy [N]
5000
Fy Front
4000
Fy Rear
Fit Front
3000
Fit Rear
2000
1000
0
0 2 4 6 8 10 12 14 16 18
Slip angle [deg]
Approx. Fy carpet with Fz effect
8000
Carpet Fy
Intermediate Fy
vs. slip angle data
Fitting
“Reduced” Magic Formula
Fy [N]
7000
6000
5000
4000
3000
2000
2000
3000
4000
5000
6000
7000
8000
1000
0
0 2 4 6 8 10 12 14 16 18
Slip angle [deg]
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 15
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Evolution of synthesis model for vehicle dynamics analysis
From axle properties to tyre properties identification
Advantages
This approach allows a first level split of tyre and suspension effect on the overall
cornering properties of a vehicle
The “reduced” tyre model, identified on a known vehicle, can be used to have a quick
prediction of the effect of the main vehicle parameters, e.g.
Effect of vehicle mass and mass repartition front / rear
Effect of roll stiffness balance front / rear
Effect of toe variation under lateral load or suspension travel
8000
Carpet Fy
3000
Cornering stiffness
7000
2500
Fy [N]
6000
5000
4000
3000
2000
1000
2000
3000
4000
5000
6000
7000
8000
dFy/dAlfa [N/deg]
2000
1500
1000
500
2000
3000
4000
5000
6000
7000
8000
0
0 2 4 6 8 10 12 14 16 18
Slip angle [deg]
0
0 2 4 6 8
Slip angle [deg]
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 16
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Results and applications
Use of the identified tyre data in a simplified four corner vehicle model
Simulation tool integrated in W-HandsPlus©CRF
Basic vehicle design
parameters
“Reduced” set of Fy parameters
(identified or known a priori)
Carpet Fy
8000
7000
Extended set of Fy
parameters (if available)
Fy [N]
6000
2000
5000
3000
4000
4000
5000
3000
6000
7000
2000
8000
1000
0
0 2 4 6 8 10 12 14 16 18
Slip angle [deg]
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 17
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Results and applications
Use of the identified tyre data in a simplified four corner vehicle model
Steady state:
cornering and roll
Frequency response:
cornering
Frequency response:
roll
Given a reference tyre identified on a known
reference vehicle, a sensitivity analysis can be
performed quickly about the main vehicle
design parameters and tyre parameters.
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 18
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Conclusions and next steps
Achievements
Procedures for identification of simplified handling models based on
standard handling experimental setup and objective evaluation tests
as limited as possible set of vehicle and suspension data
Easy to use automated tools for simple model identification and simulation
integrated in a custom software already used for handling data analysis and
objective evaluation
Related topics
Cross-link between testing domain and virtual analysis domain
Tuning/Identification of tyre parameters using functional and Multi Body models
Diagnostic/Reverse engineering
Next steps
Development of procedures for identification of more parameters, e.g.
Steering system and self aligning moment
Camber sensitivity
Longitudinal force vs. slip
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 19
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF

Thank you
Questions?
June 22, 2010
Vehicle Dynamics Expo – Open Technology Forum This document contains information which are proprietary of CRF. Neither this document 20
nor the information contained herein shall be used, duplicated nor communicated by any
means to any third party, in whole or in part, except with the prior written consent of CRF