U.S. patent application number 10/807752 was filed with the patent office on 2004-09-30 for vehicle speed dependent compensator for electric steering systems.
Invention is credited to Katch, Gregory, Kleinau, Julie, Pattok, Kathryn, Wittig, William.
Application Number | 20040189228 10/807752 |
Document ID | / |
Family ID | 32994985 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040189228 |
Kind Code |
A1 |
Katch, Gregory ; et
al. |
September 30, 2004 |
Vehicle speed dependent compensator for electric steering
systems
Abstract
An electric power steering control system comprising: an
electric motor disposed in a vehicle to apply torque to a steerable
wheel; a torque sensor disposed in the vehicle for detecting a
steering wheel torque and generating a torque signal indicative
thereof; a vehicle speed sensor, the vehicle speed sensor
generating a vehicle speed signal; a controller coupled to the
torque sensor, the vehicle speed sensor and the electric motor. The
controller generates a scheduled compensated torque command to the
electric motor. The scheduled compensated torque command is based
on at least one of: a torque command signal responsive to the
torque signal; a compensated torque command signal; and a blend of
the torque command signal and the compensated torque command
signal. At least one of the torque command signal, the compensated
torque command signal and the blend is based the vehicle speed
signal.
Inventors: |
Katch, Gregory; (Linden,
MI) ; Wittig, William; (Saginaw, MI) ; Pattok,
Kathryn; (Frankenmuth, MI) ; Kleinau, Julie;
(Bay City, MI) |
Correspondence
Address: |
Keith J. Murphy
CANTOR COLBURN LLP
55 Griffin Road South
Bloomfield
CT
06002
US
|
Family ID: |
32994985 |
Appl. No.: |
10/807752 |
Filed: |
March 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60458701 |
Mar 28, 2003 |
|
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Current U.S.
Class: |
318/432 |
Current CPC
Class: |
B62D 5/0463
20130101 |
Class at
Publication: |
318/432 |
International
Class: |
H02P 007/00 |
Claims
What is claimed is:
1. An electric power steering system comprising: an electric motor
disposed in a vehicle to apply torque to a steerable wheel; a
vehicle speed sensor, said vehicle speed sensor generating a
vehicle speed signal; a controller coupled to said vehicle speed
sensor and said electric motor; wherein said controller generates a
scheduled compensated torque command to said electric motor, said
scheduled compensated torque command based on at least one of a
torque command signal, a compensated torque command signal, and a
blend of said torque command signal and said compensated torque
command signal, wherein at least one of said torque command signal,
said compensated torque command signal and said blend is based on
said vehicle speed signal.
2. The system of claim 1 wherein said scheduled compensated torque
command is based on a blend scheduling signal.
3. The system of claim 1 wherein said blend scheduling signal is
based on a look-up table responsive to said vehicle speed
signal.
4. The system of claim 1 wherein said torque command signal is
based on a torque signal and is indicative of a desired assist
torque for said steering system.
5. The system of claim 1 wherein said compensated torque command
signal is based on applying a compensator to said torque command
signal.
6. The system of claim 5 wherein said compensator is responsive to
a blend scheduling signal, wherein coefficients of said compensator
are based on said blend scheduling signal.
7. The system of claim 5 wherein said compensator comprises a
filter configured to modify spectral content of said compensated
torque command signal.
8. The system of claim 7 wherein said compensator comprises at
least one of: at least one pole, at least one pole and at least one
zero, and a schedulable gain.
9. The system of claim 7 wherein said compensator comprises a
frequency based notch filter configured to maintain stability of a
torque control of said electric power steering system.
10. The system of claim 1 wherein said blend comprises a
combination of said torque command signal and said compensated
torque command signal, said combination responsive to a blend
scheduling signal.
11. The system of claim 1 wherein said blend comprises a selectable
threshold for scheduling a combination of said torque command
signal and said compensated torque command signal.
12. The system of claim 1 wherein said scheduled compensated torque
command is configured to facilitate characterization of at least
one of: system stability, torque disturbance rejection; and input
impedance.
13. The system of claim 1 wherein said scheduled compensated torque
command is configured to characterize on-center feel of said torque
control of said electric power steering system.
14. A method of controlling an electric power steering system, the
method comprising: receiving a torque command signal; receiving a
vehicle speed signal responsive to a speed of a vehicle; and
generating a scheduled compensated torque command, said scheduled
compensated torque command based on at least one of said torque
command signal, a compensated torque command signal, and a blend of
said torque command signal and said compensated torque command
signal, wherein at least one of said torque command signal, said
compensated torque command signal and said blend is based on said
vehicle speed signal.
15. The method of claim 14 wherein said scheduled compensated
torque command is based on a blend scheduling signal.
16. The method of claim 14 wherein said blend scheduling signal is
based on a look-up table responsive to said vehicle speed
signal.
17. The method of claim 14 wherein said torque command signal is a
based on said torque signal and is indicative of a desired assist
torque for said steering system.
18. The method of claim 14 wherein said compensated torque command
signal is based on applying a compensator to said torque command
signal.
19. The method of claim 18 wherein said compensator is responsive
to a blend scheduling signal, wherein coefficients of said
compensator are based on said blend scheduling signal.
20. The method of claim 18 wherein said compensator comprises a
filter configured to modify spectral content of said compensated
torque command signal.
21. The method of claim 20 wherein said filter comprises at least
one of: at least one pole, at least one pole and at least one zero,
and a schedulable gain.
22. The method of claim 20 wherein said compensator comprises a
frequency based notch filter configured to maintain stability of a
torque control of said electric power steering system.
23. The method of claim 14 wherein said blend comprises a
selectable threshold for scheduling a combination of said torque
command signal and said compensated torque command signal.
24. The method of claim 14 wherein said blend comprises a
combination of said torque command signal and said compensated
torque command signal, said combination responsive to a blend
scheduling signal.
25. The method of claim 14 wherein said scheduled compensated
torque command is configured to facilitate characterization of at
least one of: system stability, torque disturbance rejection; and
input impedance.
26. The method of claim 14 wherein said scheduled compensated
torque command is configured to characterize on-center feel of said
torque control of said electric power steering system.
27. A storage medium encoded with a machine-readable computer
program code; said code including instructions for causing a
computer to implement a method for controlling an electric power
steering system, the method comprising: receiving a torque command
signal; receiving a vehicle speed signal responsive to a speed of a
vehicle; and generating a scheduled compensated torque command,
said scheduled compensated torque command based on at least one of
said torque command signal, a compensated torque command signal,
and a blend of said torque command signal and said compensated
torque command signal, wherein at least one of said torque command
signal, said compensated torque command signal and said blend is
based on said vehicle speed signal.
28. A computer data signal comprising: said computer data signal
comprising code configured to cause a processor to implement a
method for controlling an electric power steering system, the
method comprising: receiving a torque command signal; receiving a
vehicle speed signal responsive to a speed of a vehicle; and
generating a scheduled compensated torque command, said scheduled
compensated torque command based on at least one of said torque
command signal, a compensated torque command signal, and a blend of
said torque command signal and said compensated torque command
signal, wherein at least one of said torque command signal, said
compensated torque command signal and said blend is based on said
vehicle speed signal.
29. An electric power steering control system comprising: a means
for detecting a vehicle speed and generating a speed signal
indicative thereof; a means for receiving said torque command
signal; a means for receiving said vehicle speed signal; a means
for generating a scheduled compensated torque command, said
scheduled compensated torque command based on at least one of said
torque command signal, a compensated torque command signal, and a
blend of said torque command signal and said compensated torque
command signal, wherein at least one of said torque command signal,
said compensated torque command signal and said blend is based on
said vehicle speed signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
application No. 60/458,701 filed Mar. 28, 2003 the contents of
which are incorporated by reference herein in their entirety.
BACKGROUND
[0002] Existing compensation structures for Electric Power Steering
(EPS) systems often use torque loop compensation for an electric
motor control system. In such existing EPS systems, a torque
compensator, commonly a notch filter, is employed in the torque
path to provide phase lead to ensure that the system remains
stable. However, application of a torque compensator may make the
EPS system sensitive to disturbances that include frequency content
near the notch frequency. The compensator may also cause the
on-cener feel (torque gradient) to feel less precise.
[0003] While well suited for its intended purposes, the torque
compensator may not provide desired characteristics under all
operating conditions. For example, such a system may not provide
desired characteristics under all vehicle speed conditions. With
the aforementioned considerations, it may be difficult to apply
torque compensation in some vehicles and tune the control system to
achieve acceptable performance. Therefore, what is needed is a
method for modifying the compensation utilized as a function of
vehicle operating parameters.
SUMMARY
[0004] Disclosed herein, in an exemplary embodiment, is an electric
power steering control system comprising: an electric motor
disposed in a vehicle to apply torque to a steerable wheel; a
vehicle speed sensor, the vehicle speed sensor generating a vehicle
speed signal; a controller coupled to the vehicle speed sensor and
the electric motor. The controller generates a scheduled
compensated torque command to the electric motor. The scheduled
compensated torque command is based on at least one of: a torque
command signal; a compensated torque command signal; and a blend of
the torque command signal and the compensated torque command
signal. At least one of the torque command signal, the compensated
torque command signal and the blend is based on the vehicle speed
signal.
[0005] Also disclosed herein, in another exemplary embodiment, is a
method of controlling an electric power steering system, the method
comprising: receiving a torque command signal; receiving a vehicle
speed signal responsive to a speed of a vehicle; and generating a
scheduled compensated torque command. The scheduled compensated
torque command is based on at least one of: the torque command
signal, a compensated torque command signal, and a blend of the
torque command signal and the compensated torque command signal. At
least one of the torque command signal, the compensated torque
command signal and the blend is based on the vehicle speed
signal.
[0006] Further disclosed herein, in yet another exemplary
embodiment, is a electric power steering control system comprising:
a means for applying torque to a steerable wheel; a means for
detecting a vehicle speed and generating a speed signal indicative
thereof; a means for receiving the vehicle speed signal; and a
means for generating a scheduled compensated torque command. The
scheduled compensated torque command is based on at least one of: a
torque command signal; a compensated torque command signal; and a
blend of the torque command signal and the compensated torque
command signal. At least one of the torque command signal, the
compensated torque command signal and the blend is based on the
vehicle speed signal.
[0007] Also disclosed herein is a storage medium encoded with a
machine-readable computer program code for controlling an electric
power steering system, the storage medium including instructions
for causing controller to implement the disclosed method.
[0008] Further disclosed is a computer data signal embodied in a
carrier wave for controlling an electric power steering system, the
data signal comprising code configured to cause a controller to
implement the disclosed method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will now be described, by way of an
example, with references to the accompanying drawings, wherein like
elements are numbered alike in the several figures in which:
[0010] FIG. 1 depicts a vehicle control system for electronic
steering;
[0011] FIG. 2 depicts a partial simplified block diagram of a
torque control architecture in accordance with an exemplary
embodiment; and
[0012] FIG. 3 depicts a flowchart of an illustrative methodology in
accordance with an exemplary embodiment.
DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT
[0013] Electric power systems often employ a torque compensator,
commonly a notch filter, in the torque path to provide phase lead
to ensure that the system remains stable. It should be appreciated
that deeper notch filters (e.g., those exhibiting more gain
reduction at the notch frequency) while providing necessary
stability often degrade the disturbance rejection properties of the
system at the notch frequency. Further, it should be recognized
that a closed loop system cannot reject disturbances where the gain
is very low, as it is at the notch center frequency. Additionally,
notch filters may also affect the closed loop response of the
system (e.g., input impedance) if their gain and phase
characteristics intrude on the frequency range of operator inputs.
The ill effects of the low frequency sensitivity are transmitted to
and felt by the driver in the form of disturbances caused by
friction in mechanical parts. It should also be evident therefore,
that a compensator with a given frequency characteristics cannot
always address disturbance rejection considerations while
maintaining control system stability.
[0014] An exemplary embodiment of the invention, by way of
illustration, is described herein and may be applied to a torque
control system for an electric motor in a vehicle steering system.
While a preferred embodiment is shown and described, it will be
appreciated by those skilled in the art that the invention is not
limited to the embodiment described herein, but also to any control
system employing an electric machine with torque compensation.
[0015] Referring to FIG. 1, reference numeral 40 generally
designates a motor vehicle electric power steering system suitable
for implementation of the disclosed embodiments. The steering
mechanism 36 is a rack-and-pinion type system and includes a
toothed rack (not shown) within housing 50 and a pinion gear (also
not shown) located under gear housing 52. As the steering wheel 26
is turned, the upper steering shaft 29 turns and the lower steering
shaft 51, connected to the upper steering shaft 29 through
universal joint 34, turns the pinion gear. Rotation of the pinion
gear moves the rack, which moves tie rods 38 (only one shown) in
turn moving the steering knuckles 39 (only one shown), which turn a
steerable wheel(s) 44 (only one shown).
[0016] Electric power steering assist is provided through the
control apparatus generally designated by reference numeral 24 and
includes the controller 16 and the electric motor 46. The
controller 16 is powered by the vehicle power supply 10 through
line 12. The controller 16 receives a vehicle speed signal 14
representative of the vehicle speed. Steering pinion gear angle is
measured through position sensor 32, which may be an optical
encoding type sensor, variable resistance type sensor, or any other
suitable type of position sensor, and supplies to the controller 16
a position signal 20. Motor velocity may be measured with a
tachometer and transmitted to controller 16 as a motor velocity
signal 21. Alternatively, motor velocity may be derived from motor
position as the time rate of change of position. It will be
appreciated that there are numerous well-known methodologies for
performing the function of a derivative.
[0017] As the steering wheel 26 is turned, torque sensor 28 senses
the torque applied to the steering wheel 26 by the vehicle
operator. The torque sensor 28 may include a torsion bar (not
shown) and a variable resistive-type sensor (also not shown), which
outputs a variable torque signal 18 to controller 16 in relation to
the amount of twist on the torsion bar. Although this is the
preferable torque sensor, any other suitable torque-sensing device
used with known signal processing techniques will suffice.
[0018] In response to the various inputs, the controller 16 sends a
command 22 to the electric motor 46, which supplies torque assist
to the steering system through worm 47 and worm gear 48, providing
torque assist to the vehicle steering.
[0019] In order to perform the prescribed functions and desired
processing, as well as the computations therefore (e.g., the
execution of motor control algorithm(s), the control processes
prescribed herein, and the like), controller 16 may include, but
not be limited to, a processor(s), computer(s), memory, storage,
register(s), timing, interrupt(s), communication interfaces, and
input/output signal interfaces, as well as combinations comprising
at least one of the foregoing. For example, controller 16 may
include input signal filtering to enable accurate sampling and
conversion or acquisitions of such signals from communications
interfaces. Additional features of controller 16 and certain
processes therein are thoroughly discussed at a later point
herein.
[0020] FIG. 2 depicts a partial simplified block diagram of a
torque control architecture as may be implemented in controller 16
for controlling the motor 46 including the blending processes 100
of an exemplary embodiment. In an exemplary embodiment the torque
command of control system 24 is modified by a blending function
120. In other words, the the compensator 110 of existing
configurations is replaced by a compensator 110a and blending
function 120 of an exemplary embodiment. In an exemplary embodiment
the blending function 120 provides as an output, denoted herein as
scheduled compensated torque command 122, a blend of the
compensated torque command 112, and the torque command 114.
[0021] The blending function 120 is responsive to a vehicle speed
based blend scheduling 132 also denoted Blend_PT in the figure. In
an implementation of an exemplary embodiment the speed based blend
scheduling 132 is based on blend look-up table 130 responsive to
the vehicle speed 14. In an exemplary embodiment the speed based
blend scheduling 132 is configured as a two state multiplier with a
range of zero percent to 100 percent. Namely, if the vehicle speed
14 is less than or equal to a first selected threshold, then the
speed based blend scheduling 132 is set to 100 percent. For vehicle
speeds 14 greater than or equal to a second selected threshold,
then the speed based blend scheduling 132 is set to 0 percent.
Finally, for vehicle speeds 14 greater than the first selected
threshold and less than the second selected threshold, then the
speed based blend scheduling 132 smoothly transitions from 100
percent to 0 percent. It will be appreciated that while in an
exemplary embodiment a look-up table is disclosed, any form of
scheduling for the vehicle speed 14 is possible. It will also be
appreciated that the form of transitioning from one value to
another for the speed based blend scheduling 132 may include, but
not be limited to, switched, nonlinear, a linear ramp, polynomial
and the like, as well as combinations thereof.
[0022] Continuing now with FIG. 2 and moving to the compensator
blend function 120, in an exemplary embodiment, the output of the
blending function is as follows:
Scheduled_Comp_Tq.sub.--CMD=(COMP_OUT*BLEND_PT)
+(Torque.sub.--CMD)*(100%-- BLEND_PT))
[0023] In one implementation of an exemplary embodiment a simple
blending is employed. It will be appreciated that the speed based
blend scheduling 132 or in this instance the Blend Point (BLEND_PT)
could also be a function of one or more threshold conditions. For
example, a selected compensation or blend of compensations for
vehicle speeds 14 below a first selected threshold, a second
compensation or second blend of compensations for speeds greater
than or equal to the first selected threshold and yet less than or
equal to a second selected threshold, and finally, yet another
compensation or blend of compensations for vehicle speeds 14 above
the second selected threshold.
[0024] Similarly, in yet another alternative embodiment, additional
thresholds are employed with multiple blends of compensations being
employed for a variety of ranges of vehicle speed. Moreover, it
will be appreciated that the blending function may very well be a
function of yet another variable. In an exemplary embodiment, the
torque compensation at compensator 110a is blended as a function of
vehicle speed 14, however, it will be appreciated that other
parameters may readily be employed to modify or schedule the
blending disclosed herein. Additionally, while multiple blends may
utilized, likewise, multiple compensators 110a may be employed. For
example, one or more compensators with the outputs therefrom being
blended to formulate the final torque command.
[0025] Moreover, in yet another exemplary embodiment, it will be
appreciated that a simple switching function may also be employed
to facilitate the blend function. It should readily be appreciated
that variations of the blending function with respect to a
particular implementation may readily be employed without deviating
from the scope and breadth of the claims.
[0026] Finally, in yet another alternative embodiment, the
compensator 110a may readily be integrated with the blend function
120 and the coefficents of the filter(s) of the compensator 110a
may directly be scheduled based on the speed based blend scheduling
132 or in this instance the Blend Point (BLEND_PT) and thereby,
vehicle speed 14. The compensator 110a may include a scaling and/or
one or more frequency based filter(s) configured to manipulate the
spectral characteristics of the torque command 114. Manipulation of
the coefficients of the compensator 110a facilitates closed loop
torque control to ensure stability and characterization of steering
system response. Moreover, one skilled in the art will appreciate
that in any instance of blending or manipulating of the filter
characteristics for compensator 110a considerations of filter
characteristics, dynamics and overall system (control loop)
characteristics should be addressed to ensure acceptable
performance over the desired operating range.
[0027] Additionally, while a look-up table and filter are disclosed
for generation of speed based blend scheduling 132 and compensation
respectively, it will be appreciated that other configurations are
possible. For example, the blend look-up table 130, could be
configured as gains, scaling, multipliers, schedulers, and the
like, which may be configured to be dynamic and may also be the
function of other parameters. Similarly, other filters and filter
orders and topologies are possible for the compensator 110a.
Moreover, it may be desirable to employ varied filter topologies
based upon different conditions, system dynamic conditions and
considerations, sensor characteristics, implementation constraints,
and the like, as well as combinations of the foregoing. For example
it may be desireable to employ a higher order filter to ensure that
a wide variety of dynamic conditions may be addressed or to address
implementation constraints such as commonality of filter topologies
or to enable varied filter types in a single topology.
[0028] Turning now to FIG. 3, an illustrative flowchart of an
exemplary methodology 200 is depicted. At process block 210, a
torque command signal is received. The torque command signal may be
indicative of the desired assist torque in the steering system 40.
At process block 220, a vehicle speed signal is received. The
vehicle speed is indicative the speed of the vehicle. At process
block 230, a blended torque is fomulated with one or more
compensated torque command signals e.g., 112 and the torque command
signal e.g. 114, and finally at block 240 the scheduled compensated
torque command 122 to the motor 46 is generated. As stated earlier,
the scheduled compensated torque command 122 is based on at least
one of the torque command signal, a compensated torque command
signal, and a blend of the torque command signal and the
compensated torque signal. Continuing with FIG. 3, at process block
250 the optional process of a modified compensator 110a with
schedulable coefficients is depicted. The resultant of the modified
compensator 110a with scheduling is utilized to generate the
scheduled compensated torque command 122 to the motor 46.
[0029] It is important to note that all the examples provided
herein relate to a vehicle having steerable wheels. However, it
should be understood that the embodiments disclosed herein may
readily be extended to a vehicle with any number of wheels to be
steered. Moreover, it will be appreciated that the use of first and
second or other similar nomenclature for denoting similar items is
not intended to specify or imply any particular order unless
otherwise stated.
[0030] The disclosed method may be embodied in the form of
computer-implemented processes and apparatuses for practicing those
processes. The method can also be embodied in the form of computer
program code containing instructions embodied in tangible media,
such as floppy diskettes, CD-ROMs, hard drives, or any other
computer-readable storage medium 13, wherein, when the computer
program code is loaded into and executed by a computer, e.g.
controller 16, the computer becomes an apparatus capable of
executing the method. The present method can also be embodied in
the form of computer program code, for example, whether stored in a
storage medium 13, loaded into and/or executed by a computer, or as
data signal 15 transmitted whether a modulated carrier wave or not,
over some transmission medium, such as over electrical wiring or
cabling, through fiber optics, or via electromagnetic radiation,
wherein, when the computer program code is loaded into and executed
by a computer, the computer becomes an apparatus capable of
executing the method. When implemented on a general-purpose
microprocessor, the computer program code segments configure the
microprocessor to create specific logic circuits.
[0031] While the invention has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *