15-06-2012, 12:07 PM
Combined active steering and traction for mechatronic bogie
vehicles with independently rotating wheels
[attachment=24535]
Abstract
The benefits of substituting the conventional solid wheelset by independently rotating wheels (IRW) in actively steered trailed railway
vehicles have already been presented in many works. If a traction system is included in this kind of vehicle it will interact strongly with the
active steering system.
Introduction
The ability of railway vehicles to follow the track path is
based on the properties of the solid wheelset. The conic
shape of the wheels makes their rolling radius dependent on
the lateral position with respect to the track. As the two
wheels are constrained to have the same rotating speed, the
yaw movement of the wheelsets is coupled to their lateral
displacements, thus generating a self-centering mechanism.
Unfortunately, this movement is not stable.
Strategies for active steering of trailed railway
vehicles
Even though the objective of this paper is not to study the
active steering system itself, it is necessary to introduce the
basic strategies that will be used in the rest of the work.
From the broad range of strategies presented in the literature
for the active steering of railway vehicles, only two will be
used here, one for vehicles with solid wheelsets and the other
for vehicles with independently rotating wheels. Though, it
is likely that the concepts of traction/steering combination
are extensible to most of the strategies presented in other
works.
Strategies for combined active steering and traction
The strategies presented up to now have been formulated
and verified for the case that the mechanical relationship
between the behaviour of the two wheels is completely
defined by the wheelset configuration (i.e. solid or IRW).
When the separated traction is provided to the wheels it is
necessary to define the mechanical relationship between
the traction torques transmitted to the two wheels of a
wheelset so that the active steering strategy formulated is
still valid, or even improved by the action of the motors. Two
different concepts are presented, one to be used with solid
wheelset steering strategies and the other for IRW steering
strategies.
Control of traction motors
Modern electrical railway traction systems are very
complex. Asynchronous induction motors are often used to
replace dc traction motors for a number of practical reasons,
but they are much more difficult to control and significantly
more complex to model mathematically. However, advances
in high power switching devices as well as motor control
methods (such as PWM and vector control techniques) have
enabled an induction motor to behave very similarly to a
separately excited dc motor in the range of frequencies of
interest for this application (below 15 Hz).
Conclusions
This paper shows that the active steering of IRWvehicles
with distributed traction is possible with an appropriate
design of the controls of the traction motors and the active
steering actuators. The approach followed consists of
reproducing the features of either a solid wheelset or an
IRW wheelset through the control of the amount of
differential traction supplied to the wheels, so that almost
any of the active steering strategies for solid wheelsets or
IRWexisting in the literature can be applied. It has been seen
that an appropriate control of the traction motors preserves
or improves the curving performance of the actively steered
vehicle.
vehicles with independently rotating wheels
[attachment=24535]
Abstract
The benefits of substituting the conventional solid wheelset by independently rotating wheels (IRW) in actively steered trailed railway
vehicles have already been presented in many works. If a traction system is included in this kind of vehicle it will interact strongly with the
active steering system.
Introduction
The ability of railway vehicles to follow the track path is
based on the properties of the solid wheelset. The conic
shape of the wheels makes their rolling radius dependent on
the lateral position with respect to the track. As the two
wheels are constrained to have the same rotating speed, the
yaw movement of the wheelsets is coupled to their lateral
displacements, thus generating a self-centering mechanism.
Unfortunately, this movement is not stable.
Strategies for active steering of trailed railway
vehicles
Even though the objective of this paper is not to study the
active steering system itself, it is necessary to introduce the
basic strategies that will be used in the rest of the work.
From the broad range of strategies presented in the literature
for the active steering of railway vehicles, only two will be
used here, one for vehicles with solid wheelsets and the other
for vehicles with independently rotating wheels. Though, it
is likely that the concepts of traction/steering combination
are extensible to most of the strategies presented in other
works.
Strategies for combined active steering and traction
The strategies presented up to now have been formulated
and verified for the case that the mechanical relationship
between the behaviour of the two wheels is completely
defined by the wheelset configuration (i.e. solid or IRW).
When the separated traction is provided to the wheels it is
necessary to define the mechanical relationship between
the traction torques transmitted to the two wheels of a
wheelset so that the active steering strategy formulated is
still valid, or even improved by the action of the motors. Two
different concepts are presented, one to be used with solid
wheelset steering strategies and the other for IRW steering
strategies.
Control of traction motors
Modern electrical railway traction systems are very
complex. Asynchronous induction motors are often used to
replace dc traction motors for a number of practical reasons,
but they are much more difficult to control and significantly
more complex to model mathematically. However, advances
in high power switching devices as well as motor control
methods (such as PWM and vector control techniques) have
enabled an induction motor to behave very similarly to a
separately excited dc motor in the range of frequencies of
interest for this application (below 15 Hz).
Conclusions
This paper shows that the active steering of IRWvehicles
with distributed traction is possible with an appropriate
design of the controls of the traction motors and the active
steering actuators. The approach followed consists of
reproducing the features of either a solid wheelset or an
IRW wheelset through the control of the amount of
differential traction supplied to the wheels, so that almost
any of the active steering strategies for solid wheelsets or
IRWexisting in the literature can be applied. It has been seen
that an appropriate control of the traction motors preserves
or improves the curving performance of the actively steered
vehicle.