U.S. patent application number 10/091872 was filed with the patent office on 2003-09-11 for torque management based traction control system.
Invention is credited to Celini, Dean A., Denton, Daniel S., Potter, Kenneth J..
Application Number | 20030171869 10/091872 |
Document ID | / |
Family ID | 27765367 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030171869 |
Kind Code |
A1 |
Potter, Kenneth J. ; et
al. |
September 11, 2003 |
TORQUE MANAGEMENT BASED TRACTION CONTROL SYSTEM
Abstract
A vehicle traction control system that is based on the
management of the torque that is produced by the vehicle power
train. The actual angular acceleration of a portion of the vehicle
drive line is compared to the maximum predicted angular
acceleration of the portion of the vehicle drive line to determine
the occurrence of a wheel slipping condition. In response to the
detection of a wheel slipping condition, the amount of excess drive
torque that is being produced by the power train is quantified and
the drive torque that is produced by the power train is reduced by
an amount which corresponds to the excess. When the slipping
condition has been abated, the reduction in the magnitude of the
drive torque that is produced by the power train is reduced and
eventually eliminated.
Inventors: |
Potter, Kenneth J.; (Almont,
MI) ; Celini, Dean A.; (Highland, MI) ;
Denton, Daniel S.; (Highland, MI) |
Correspondence
Address: |
DAIMLERCHRYSLER INTELLECTUAL CAPITAL CORPORATION
CIMS 483-02-19
800 CHRYSLER DR EAST
AUBURN HILLS
MI
48326-2757
US
|
Family ID: |
27765367 |
Appl. No.: |
10/091872 |
Filed: |
March 5, 2002 |
Current U.S.
Class: |
701/84 ;
180/197 |
Current CPC
Class: |
B60T 8/175 20130101;
B60W 2710/0666 20130101; F02D 41/021 20130101; B60K 28/16 20130101;
F02D 2250/18 20130101; B60W 2510/0652 20130101 |
Class at
Publication: |
701/84 ;
180/197 |
International
Class: |
G06F 017/00 |
Claims
What is claimed is:
1. In a vehicle having a power train and a drive line, the drive
line including at least one drive wheel, a method for controlling
the power train to abate a wheel slip condition at the drive wheel,
the method including the steps of: determining an actual angular
acceleration (.alpha..sub.a) of a portion of the drive line;
determining a maximum predicted acceleration (.alpha..sub.p) of the
portion of the drive line; determining the existence of a wheel
slip condition based on .alpha..sub.a and .alpha..sub.p; if a wheel
slip condition is occurring, determining an amount of excess torque
(T.sub.x) that is being delivered to the drive line; and reducing
an amount of torque that is being delivered to the drive line by an
amount (T.sub.er) that is based on the value of T.sub.x.
2. The method of claim 1, wherein T.sub.x is calculated from the
equation T.sub.x=(.alpha..sub.a-.alpha..sub.p)(I.sub.d).
3. The method of claim 2, wherein T.sub.er is calculated from the
equation T.sub.er[(SF)(T.sub.x)]/[(GR)(STR)].
4. The method of claim 1, wherein .alpha..sub.p is calculated from
the equation .alpha..sub.p=T.sub.o.div.(I.sub.o).
5. The method of claim 1, wherein after the reducing step the
method includes the steps of: determining a new value of
.alpha..sub.a; determining a new value of .alpha..sub.p; and
modifying T.sub.er based on the new values of .alpha..sub.a and
.alpha..sub.p.
6. The method of claim 5, wherein the modifying step includes the
steps of: increasing T.sub.er if .alpha..sub.a is greater than up;
and reducing T.sub.er if .alpha..sub.a is not greater than
.alpha..sub.p.
7. The method of claim 6, wherein a fixed increment is employed to
reduce T.sub.er.
8. The method of claim 6, wherein an amount by which T.sub.er is
reduced is based on a present value of T.sub.er.
9. The method of claim 6, wherein an amount by which T.sub.er is
reduced is based on an initial value of T.sub.er.
10. The method of claim 1, wherein the step of determining
.alpha..sub.a includes the steps of: providing a speed sensor for
sensing a speed of an output member of the power train, the output
member being rotatably coupled to an input member of the drive
line; sensing the speed of the output member; and determining the
angular acceleration of the output member.
11. In a vehicle having a power train and a drive line, the drive
line including at least one drive wheel, a method for controlling
the power train to abate a wheel slip condition at the drive wheel,
the method including the steps of: determining an actual angular
acceleration (.alpha..sub.a) of a portion of the drive line;
determining a maximum predicted acceleration (.alpha..sub.p) of the
portion of the drive line, the value of .alpha..sub.p being
calculated from the equation .alpha..sub.p=T.sub.o.div.(I.sub.o);
determining the existence of a wheel slip condition based on
.alpha..sub.a and .alpha..sub.p; and if a wheel slip condition is
occurring, determining an amount of excess torque (T.sub.x) that is
being delivered to the drive line, the value of T.sub.xbeing
calculated from the equation T.sub.x=(.alpha..sub.a-.alpha..-
sub.p)(I.sub.d).
12. The method of claim 11, further comprising the step of reducing
an amount of torque that is being delivered to the drive line by an
amount (T.sub.er) that is based on the value of T.sub.x, wherein
T.sub.er is calculated from the equation
T.sub.er=[(SF)(T.sub.x)]/[(GR)(STR)].
13. The method of claim 12, wherein after the reducing step the
method includes the steps of: determining a new value of
.alpha..sub.a; determining a new value of .alpha..sub.p; increasing
T.sub.er if .alpha..sub.a is greater than .alpha..sub.p; and
reducing T.sub.er if .alpha..sub.a is not greater than
.alpha..sub.p.
14. The method of claim 13, wherein a fixed increment is employed
to reduce T.sub.er.
15. The method of claim 13, wherein an amount by which T.sub.er is
reduced is based on a present value of T.sub.er.
16. The method of claim 13, wherein an amount by which T.sub.er is
reduced is based on an initial value of T.sub.er.
17. The method of claim 11, wherein the step of determining
.alpha..sub.a includes the steps of: providing a speed sensor for
sensing a speed of an output member of the power train, the output
member being rotatably coupled to an input member of the drive
line; sensing the speed of the output member; and determining the
angular acceleration of the output member.
18. A vehicle comprising: a power train having a power source, an
output member and a power train controller, the power source
providing a source of rotary power, the output member being
operable for outputting rotary power, the power train controller
determining a magnitude of the rotary power that is produced by the
power source; a drive line having an input member and at least one
drive wheel, the input member receiving the rotary power from the
output member, the drive wheel rotating in response to receipt of
the drive torque; a plurality of sensors coupled to the power train
and the drive line, the sensors being operable for sensing a
plurality of vehicle characteristics and generating a sensor signal
in response thereto, the vehicle characteristics including a
rotational speed of a portion of the drive line; a traction control
system having a controller, the controller being coupled to the
sensors, the power train controller and at least one of the power
train and the drive line, the controller being operable for
determining if excess rotary power is being supplied by the power
train by comparing an actual angular acceleration of a portion of
the drive line to a maximum predicted angular acceleration of the
portion of the drive line, the controller being operable for
determining a reduction in the magnitude of the rotary power that
is output from the power train in response to a determination that
the power train is providing excess rotary power.
19. The vehicle of claim 18, wherein the power train includes an
engine, a torque converter and a transmission, the torque converter
being characterized by a stall torque ratio (STR), the transmission
having a plurality of gear ratios with one of the gear ratios being
an active gear ratio (GR), wherein the drive train has a moment of
inertia (I.sub.d), and wherein magnitude of the excess rotary power
(T.sub.er) is based on the relationship
[(.alpha..sub.a-.alpha..sub.p)(I.sub.d)]/[(GR)(STR)].
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to vehicle traction
control systems and more particularly to a vehicle traction control
system that controls the acceleration of any one of the vehicle,
the vehicle driveline and the vehicle power train by comparing an
actual acceleration value to a predicted maximum.
BACKGROUND OF THE INVENTION
[0002] Conventional automotive vehicles are typically equipped with
a power train for producing a source of rotary power and a
driveline for transmitting rotary power to a set of vehicle drive
wheels. While the modem power train configurations have, for the
most part, proven themselves to be satisfactory for producing
rotary power, several limitations have been noted. One such
limitation of the modern power train configurations is their
ability, on occasion, to supply too much rotary power to one or
more of the vehicle drive wheels to thereby cause wheel slip which
renders the vehicle somewhat more difficult to control.
[0003] Prior attempts to limit wheel slip typically employ a scheme
that transfers torque from one or more of the slipping wheels to
one or more of the non-slipping wheels. Although torque management
schemes such as this are known to immediately reduce the magnitude
by which the slipping wheel or wheels are slipping, the transfer of
the excess torque to a non-slipping wheel can, at times, render the
non-slipping wheels more susceptible to slip. This is particularly
true when the vehicle is being operated on a surface with a
relatively low coefficient of friction, such as on ice.
[0004] Accordingly, there is a need in the art for an improved
traction control system and method for controlling the torque that
is transmitted to the drive wheels of a vehicle.
SUMMARY OF THE INVENTION
[0005] In one preferred form, the present invention provides a
method for abating wheel slip in a vehicle having a power train and
a drive line. The method includes the steps of: determining an
actual angular acceleration (.alpha..sub.a) of a portion of the
drive line; determining a maximum predicted acceleration
(.alpha..sub.p) of the portion of the drive line; determining the
existence of a wheel slip condition based on .alpha..sub.a and
.alpha..sub.p; if a wheel slip condition is occurring, determining
an amount of excess torque (T.sub.x) that is being delivered to the
drive line; and reducing an amount of torque that is being
delivered to the drive line by an amount (T.sub.er) that is based
on the value of T.sub.x.
[0006] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0008] FIG. 1 is a perspective view of a vehicle having a traction
control system constructed in accordance with the teachings of the
present invention;
[0009] FIG. 2 is a schematic illustration of the vehicle of FIG.
1;
[0010] FIG. 3 is a schematic illustration in flow chart form of the
methodology of the present invention; and
[0011] FIGS. 4A and B are plots illustrating the effectiveness of
the traction control system and methodology of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] With reference to FIGS. 1 and 2, a vehicle 10 is illustrated
to include a traction control system 12 that is constructed in
accordance with the teachings of the present invention. The vehicle
10, which is illustrated to have a two-wheel drive configuration,
conventionally includes a body 14, a power train 18 and a drive
line 20. Those skilled in the art will understand that the
teachings of the present invention may be applied to vehicles
having other types of drive lines, including those having more than
two drive wheels. In the example provided, the power train 18 and
the drive line 20 are conventional in their construction and as
such, need not be discussed in significant detail. Briefly, the
power train 18 includes a propulsion source, such as an internal
combustion engine 22, a torque converter 24 and a transmission 26,
while the drive line 20 includes a prop shaft 28, a rear axle
assembly 30 and a pair of drive wheels 32.
[0013] The engine 22 conventionally transmits rotary power via an
output shaft (not specifically shown) into the torque converter 24,
where the rotary output of the engine 22 is multiplied in a
predetermined manner. The torque converter 24 is operable for
multiplying the magnitude of a torsional load input to the
transmission 26 via a transmission input shaft 26a. The
transmission 26 conventionally includes a plurality of gear ratios
that are selectively engagable to alter the speed ratio between the
transmission input shaft 26a and a transmission output shaft 26b.
Rotary power output from the transmission 26 is delivered to the
drive line 20 for distribution to the drive wheels 32. In this
regard, power is transmitted through the prop shaft 28 to the rear
axle assembly 30 where a differential assembly 30a distributes the
rotary power to the drive wheels 32 in a predetermined manner that
is based on the construction of the differential assembly 30a and
the methodology by which it is operated.
[0014] The traction control system 12 includes a controller 40 that
is operably coupled to a plurality of sensors 42 that are located
throughout the vehicle 10. As will be better understood from the
discussion below, the plurality of sensors 42 are operable for
generating sensor signals indicative of various vehicle
characteristics that are relevant to determine whether excess
torque is being delivered by the drive line 20, as well as the
extent to which excess torque is being supplied. Such
characteristics may include, for example, the rotational speed of a
portion of the power train 18, such as the engine crankshaft (not
specifically shown), the turbine (not specifically shown) of the
torque converter 24 or the transmission input shaft 26a, and the
rotational speed of a portion of the drive line 20, such as the
drive wheels 32 or the prop shaft 28. The sensor signals that are
generated by the plurality of sensors 42 are transmitted to the
controller 40, either directly or via a network or data bus. The
controller 40 may be integrated into an existing controller within
the vehicle 10 (e.g., engine controller, transmission controller,
body controller, anti-lock brake controller) which are commonly
integrated into modern vehicles, or may be a discrete unit.
[0015] Under normal vehicle operating conditions, the torque
transmitted through the drive line is expressed as acceleration of
the vehicle inertia or absorbed losses known as road load. Setting
the frame of reference to the transmission output shaft 54:
T.sub.o=(I.sub.o)(.alpha..sub.a)-T.sub.rl Equation 1
[0016] where T.sub.rl is the torque that is necessary to overcome
the road load; .alpha..sub.a is the angular acceleration measured
at some point in the drive line 20; and To is the magnitude of the
torque that is provided to the drive line 20, such as the torque
output from the transmission output shaft 26b.
[0017] The value T.sub.o is typically employed in the control of
the engine 22, torque converter 24 and/or transmission 26 and as
such, is typically either calculated or derived from variables that
include the rate at which the engine 22 is being fueled, the engine
speed, the operational state of the torque converter, the active
gear ratio, etc.
[0018] The value .alpha..sub.a may be calculated based on sensor
signals from sensors that sense the speed of the prop shaft 28 or
axle shafts 30b, for example. In the particular embodiment
provided, the value .alpha..sub.a is calculated from a sensor
signal produced by a speed sensor 42a that monitors the rotational
speed of the transmission output shaft 26b. While the transmission
output shaft 26b has been characterized as being part of the power
train 18, those skilled in the art will understand that as the
transmission output shaft 26b and the prop shaft 28 rotate at the
same rotational speed, a dedicated speed sensor for sensing the
speed of the prop shaft 28 is not necessary.
[0019] The value of inertia reflected at the point of measure,
I.sub.o is dependent upon the mass of the vehicle 10 and as such,
tends to be constant over relatively short periods of time. It is
presently preferred that the value I.sub.o be dynamically
calculated (e.g., each time the ignition key is turned to "start"
or each time the transmission 26 is shifted from "park" into a
forward gear ratio setting, such as "drive") so as to better
reflect the actual inertia of the vehicle 10. Commonly assigned
U.S. Pat. No. 5,738,605, entitled "Anti-hunt Strategy for an
Automatic Transmission", and U.S. Pat. No. 6,067,495, entitled
"Acceleration Based Shift Strategy for an Automatic Transmission",
which are hereby incorporated by reference as if fully set forth
herein, detail one method by which the value I.sub.o may be
calculated.
[0020] With the values T.sub.o, I.sub.o, and .alpha..sub.a being
known, the value of T.sub.rl is calculatable under a non-slip
condition. The value T.sub.rl includes friction, tire rolling
resistance, aerodynamic drag and considerations for the grade upon
which the vehicle 10 is operating and as such, the value T.sub.rl
tends to be significant, particularly when the vehicle 10 is
traveling at relatively high speeds.
[0021] For identification of slip condition, T.sub.rl can be
assumed to be equal to zero (0), permitting the calculation of the
maximum predicted acceleration of the drive line 20 from the
equation:
.alpha..sub.p=T.sub.o.div.(I.sub.o) Equation 2
[0022] where .alpha..sub.p is the maximum predicted angular
acceleration of the portion of the drive line 20 (which, in the
example provided, is the maximum predicted angular acceleration of
the prop shaft 28 and the transmission output shaft 26b).
[0023] With .alpha..sub.a and .alpha..sub.p known, a value for the
angular acceleration directly contributing to wheel slip,
.alpha..sub.s, is calculated from the equation:
.alpha..sub.s=.alpha..sub.a-.alpha..sub.p Equation 3
[0024] where .alpha..sub.s, is the angular acceleration
contributing to wheel slip. When .alpha..sub.s is negative (i.e.,
when .alpha..sub.a is less than .alpha..sub.p), there is no wheel
slip. When .alpha..sub.s is positive (i.e., when .alpha..sub.a is
greater than .alpha..sub.p), a wheel slip event is occurring, the
direct result of excess torque is being delivered to the drive line
20.
[0025] Since the angular acceleration due to wheel slip
(.alpha..sub.s) is known from Equation 3, the magnitude of the
excess torque that is delivered to the drive line 20 (e.g., the
prop shaft 28/transmission output shaft 26b) may be calculated
through the equation:
T.sub.x=(.alpha..sub.s)(I.sub.d) Equation 4
[0026] where the value I.sub.d is the reflected inertia of the
drive line components (including tires, but excluding vehicle mass)
20, which is a known constant, and the value of T.sub.x is the
excess torque delivered to the drive line 20.
[0027] With the value of T.sub.x being known from Equation 4, a
reduction in the torque output by the engine 22 can be determined
to inhibit wheel slip. The value of the torque reduction at the
engine 22 (T.sub.er) necessarily accounts for the torque
multiplication/speed reduction effects of the torque converter 24
and the transmission 26 and as such, is highly dependent upon the
configuration of the power train 18. Given that the value T.sub.x
is known, the calculation of T.sub.er is well within the
capabilities of one skilled in the art and as such, need not be
discussed in any significant detail herein.
[0028] In the particular example provided, the value of T.sub.er is
calculated through the equation:
T.sub.er=[(SF)(T.sub.x)]/[(GR)(STR)] Equation 11
[0029] The value of GR is the gear ratio of the transmission 26
(i.e., the speed ratio between the transmission input shaft 26a and
the transmission output shaft. The value of STR is the stall torque
ratio of the torque converter 24. The stall torque ratio is the
output torque of the torque converter 24 divided by the input
torque of the torque converter 24. The value of SF is a factor that
is greater than 1.0 which is employed to control the aggressiveness
with which a wheel slip condition is abated. In general, it is
desirable to aggressively abate situations where wheel slip may
occur and as such, a value of about 1.1 to about 1.25 may be
employed to initiate a reduction in torque to the drive line 20
that would bring the value of T.sub.o well below that required to
produce the predicted acceleration to thereby ensure that the wheel
slip condition was fully abated. The actual value of SF, however,
preferably also takes into account concerns for the "driveability"
of the vehicle 10 and the anticipated skill level of the driver
(which tend to drive the value of SF closer to 1.0) and for the
momentum of the engine flywheel (which tends to drive the value of
SF further from 1.0). The value of T.sub.er is delivered to the
engine controller 22a (typically via a data bus) to reduce the
amount of torque that is being produced by the engine and thereby
inhibit the wheel slip condition.
[0030] With reference to FIG. 3, the methodology of the present
invention is schematically illustrated in flowchart form. The
methodology begins at block 78 and progresses to block 80 where
inertia values I.sub.o and I.sub.d are initialized from the
appropriate source. The value of T.sub.er is set to zero at this
point to discontinue any previous torque management. The
methodology then proceeds to block 86.
[0031] In block 86, the methodology calculates values for T.sub.o,
(.alpha..sub.a, and .alpha..sub.p. The methodology then proceeds to
decision block 88.
[0032] In decision block 88 the methodology determines whether
.alpha..sub.a is greater than .alpha..sub.p. If .alpha..sub.a is
not greater than .alpha..sub.p, then slip is not detected and the
methodology proceeds to decision block 94 where it is determined if
the torque management request is still active. If .alpha..sub.a is
greater than .alpha..sub.p (indicating that wheel slip is
occurring), the methodology proceeds to block 90.
[0033] In block 90, the methodology calculates .alpha..sub.s,
T.sub.x and T.sub.er, identifying the amount of slip and necessary
reduction in engine torque. The methodology then proceeds to block
92.
[0034] In block 92, the methodology causes the engine controller
22a to implement a reduction in engine torque corresponding in
magnitude to the previously calculated T.sub.er so as to abate the
wheel slip condition. The methodology then loops back to block
86.
[0035] In decision block 94, the methodology determines if T.sub.er
is greater than zero (0). If the value of T.sub.er is not greater
than zero, no torque reduction is active, so the methodology loops
back to block 86 without requesting torque reduction. If the value
of T.sub.er is greater than zero in decision block 94, torque
management is still active and the methodology proceeds to block
98.
[0036] In block 98, the methodology reduces the value of T.sub.er
in a predetermined manner. The methodology may set T.sub.er to zero
to permit the power train 18 to provide "full" torque to the drive
line 20. It is presently preferred, however, that the methodology
gradually decrease the value of T.sub.er so as to guard against the
occurrence of a second wheel slip condition. The amount by which
T.sub.er is reduced may be, for example, a fixed, predetermined
rate, a rate that is based on the initial value of T.sub.er, or an
amount that is based on the present value of T.sub.er. The
methodology then continues to block 92 where the actual torque
reduction is implemented.
[0037] FIG. 4 is a plot that illustrating the effectiveness of the
traction control system 12 of the present invention. The plot
identified by reference numeral 200 illustrates the operation of
the vehicle 10 with the traction control system 12 in a disabled or
non-operative condition. The slip event is readily identified by
the large difference between actual 204 and predicted 206
acceleration and the resulting peak in output shaft speed 208. As
traction improves, output shaft speed decreases to match vehicle
speed.
[0038] The plot identified by reference numeral 202 illustrates the
operation of the vehicle 10 with the traction control system 12 in
an enabled or operative condition. In this example a slip event is
identified by the marked difference between actual 210 and
predicted 212 acceleration. The amount of torque reduction 212
required to abate slip is calculated and implemented. After actual
acceleration 210 is reduced to the level of predicted acceleration
212, the engine torque reduction value 214 is slowly reduced. A
second slip event 218 is clearly demonstrated in this example and
the traction control system 12 quickly responds to abate this slip.
It should be noted the output shaft speed trace 216 reveals no
peaks characteristic of a slip event.
[0039] While the invention has been described in the specification
and illustrated in the drawings with reference to a preferred
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
as defined in the claims. 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 illustrated by the drawings
and described in the specification as the best mode presently
contemplated for carrying out this invention, but that the
invention will include any embodiments falling within the foregoing
description and the appended claims.
* * * * *