Sensitivity study and optimization of magic formula tire parameters for vehicle handling and steering targets
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Examensarbete för masterexamen
Modellbyggare
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Vehicle handling and steering is one of the most important attribute which defines
the overall performance and driving dynamics for a car. The factors which primarily
define the handling and steering performance are its chassis, suspension and tire
characteristics. There are multiple Multi Body Dynamics (MBD) tools currently
used in order to better understand and develop the chassis and suspension performance
of a car respectively. But the tire development is currently dependent on
physical prototyping and testing. This makes the whole process of understanding
the tire attributes and its impact on the dynamics of the car difficult and expensive.
This calls for further development of tire models and tire simulation tools
to aid virtual development of tires. This thesis mainly focuses on developing a tool
which optimizes Magic Formula tire parameters to meet the desired vehicle dynamic
targets using Magic formula tire 5.2 (PAC2002) which is an empirical tool which
defines the forces and moments developed by a tire under the influence of load and
slip accurately.Thereby aiding the development and understanding of impact of tire
parameters on vehicle handling and steering targets.
This thesis looks into the Magic Formula Tire model 5.2, which is widely used to
study vehicle dynamic handling and steering attributes of a car. It is an empirical
formula which efficiently captures the physical dynamics of a tire and its impact
on a car. This study looks at Magic Formula pure lateral force parameters and
their influence on lateral force characteristics of a tire under various load and slip
conditions. Simulation software VI-CarRealTime was used in this study in order to
integrate Magic Formula tire properties to a vehicle model and to analyse the effect of
Magic Formula tire parameters on handling and steering performance of a car. The
first part of the study includes the parameter analysis and identification of the most
influential Magic Formula tire parameters. Then the study includes identification of
suitable maneuvers and vehicle dynamic performance metrics in order to study the
influence of Magic Formula tire parameters on handling and steering targets. Once
the vehicle dynamic metrics and most influential Magic Formula Tire parameters
are identified, a sensitivity study is carried out with Magic Formula Tire parameters
varied in equal steps over a fixed range. During the sensitivity run, respective
vehicle dynamic metrics and the influence of Magic Formula Tire parameters on
these vehicle dynamic metrics are recorded in the form of a objective sensitivity
matrix for a reference vehicle used for this study. The objective sensitivity matrix
was also developed based on the sensitivity of Magic Formula tire parameters on
the axles of a car. Using the objective sensitivity matrix and the weights assigned to the vehicle dynamic metrics by the attribute leaders, an objective function was
set up. The minimum value of this objective function will then provide a reference
vehicle equipped with the optimized set of tires which will satisfy as many handling
and steering targets as possible, including the possibility to optimize a set of tires
for individual axles.
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Ämne/nyckelord
Magic Formula Tire 5.2 (PAC 2002), Handling and steering targets, optimization, Passenger cars, co-simulation, Matlab API, Parameter and sensitivity study