U.S. patent application number 14/563086 was filed with the patent office on 2016-04-14 for trailer sensor module and associated method of wireless trailer identification and motion estimation.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Christos Kyrtsos, Erick Michael Lavoie, Thomas Edward Pilutti.
Application Number | 20160101811 14/563086 |
Document ID | / |
Family ID | 55654916 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160101811 |
Kind Code |
A1 |
Kyrtsos; Christos ; et
al. |
April 14, 2016 |
TRAILER SENSOR MODULE AND ASSOCIATED METHOD OF WIRELESS TRAILER
IDENTIFICATION AND MOTION ESTIMATION
Abstract
A method of identifying a trailer with a vehicle includes a step
of transmitting a unique identifier with a wireless transmitter
attached to the trailer. The wireless transmitter may be housed as
part of a sensor module with a sensor that senses a parameter of
the trailer for operating a trailer backup assist system. The
housing of the sensor module may be adapted to be removably
attached to the trailer. The unique identifier emitted by the
wireless transmitter is received with a wireless receiver on the
vehicle. After the unique identifier is recognized by a controller
on the vehicle, a parameter of the trailer may be accessed for
autonomously guiding the trailer along a desired backing path.
Inventors: |
Kyrtsos; Christos; (Beverly
Hills, MI) ; Pilutti; Thomas Edward; (Ann Arbor,
MI) ; Lavoie; Erick Michael; (Dearborn, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
55654916 |
Appl. No.: |
14/563086 |
Filed: |
December 8, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14512859 |
Oct 13, 2014 |
|
|
|
14563086 |
|
|
|
|
Current U.S.
Class: |
701/25 |
Current CPC
Class: |
B62D 15/0285 20130101;
B62D 13/06 20130101; G05D 1/0088 20130101 |
International
Class: |
B62D 13/06 20060101
B62D013/06; G05D 1/00 20060101 G05D001/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. A method of identifying a trailer with a vehicle, comprising:
transmitting a unique identifier with a wireless transmitter
attached to the trailer; receiving the unique identifier with a
wireless receiver on the vehicle; determining that the trailer
associated with the unique identifier is coupled with a hitch of
the vehicle based on the wireless receiver consistently receiving
signals from the wireless transmitter; and accessing a parameter of
the trailer based on the received unique identifier for
autonomously guiding the trailer along a desired backing path.
22. The method of claim 21, wherein the parameter is a dimension of
the trailer saved in a memory unit accessible by a controller, and
wherein the controller recognizes the unique identifier from a
database before accessing the parameter of the trailer.
23. The method of claim 21, wherein the parameter is a variable of
a kinematic relationship used to generate steering commands for the
vehicle to guide the trailer along the desired backing path.
24. The method of claim 21, wherein the parameter is a sensed yaw
rate of the trailer generated by a yaw rate sensor attached to the
trailer.
25. The method of claim 21, wherein the unique identifier includes
a radio frequency with a coded signal configured for a controller
to decode and associate with the trailer.
26. The method of claim 21, wherein the wireless receiver is
configured to receive the unique identifier within a proximity
distance from a rear portion of the vehicle.
27. A trailer sensor module for communicating with a vehicle,
comprising: a yaw rate sensor sensing a yaw rate of a trailer; and
a wireless transmitter emitting a unique identifier configured to
be recognized by the vehicle and, upon recognition, transmitting
the yaw rate of the trailer to the vehicle.
28. The trailer sensor module of claim 27, wherein the yaw rate is
used by the vehicle to determine a hitch angle between the trailer
and the vehicle for autonomously guiding the trailer with the
vehicle along a desired backing path.
29. The trailer sensor module of claim 27, further comprising a
housing enclosing the wireless transmitter and the yaw rate sensor
and adapted to be removably attached to the trailer.
30. The trailer sensor module of claim 29, wherein the housing
includes a fluid seal to prevent the wireless transmitter and the
yaw rate sensor from being exposed to liquid.
31. The trailer sensor module of claim 29, further comprising: a
solar element coupled with the housing for providing electricity to
the yaw rate sensor and the wireless transmitter.
32. The trailer sensor module of claim 27, wherein the unique
identifier includes a radio frequency with a coded signal emitted
to be received by the vehicle within a proximity distance from a
rear portion of the vehicle.
33. The trailer sensor module of claim 27, wherein the wireless
transmitter consistently emits a radio frequency transmission, and
wherein the vehicle determines that the trailer associated with the
unique identifier is detached from a hitch of the vehicle when the
vehicle fails to receive the radio frequency transmission for a
threshold period of time.
34. A trailer backup assist system for a vehicle reversing a
trailer, comprising: a wireless transmitter coupled with the
trailer and emitting a unique identifier; a wireless receiver
coupled with the vehicle for receiving the unique identifier; and a
controller on the vehicle identifying the trailer based on the
unique identifier and accessing a parameter of the identified
trailer for autonomously guiding the trailer with the vehicle along
a desired backing path, wherein the parameter includes a yaw rate
of the trailer generated by a yaw rate sensor attached to the
trailer, and wherein upon identification of the trailer, the
wireless transmitter emits the yaw rate of the trailer for
determining a hitch angle between the vehicle and the trailer.
35. The trailer backup assist system of claim 34, wherein the
wireless transmitter is removably coupled with the trailer.
36. The trailer backup assist system of claim 34, further
comprising: a protective housing enclosing the wireless transmitter
and adapted to be removably attached to the trailer.
37. The trailer backup assist system of claim 36, wherein the
protective housing includes a fluid seal to prevent the wireless
transmitter from being exposed to liquid and a solar element for
providing electricity to the wireless transmitter.
38. The trailer backup assist system of claim 34, wherein the
parameter includes a dimension of the trailer saved in a memory
unit of the controller.
39. The trailer backup assist system of claim 34, wherein the
wireless transmitter consistently emits a radio frequency
transmission, and wherein the controller determines that the
trailer associated with the unique identifier is detached from a
hitch of the vehicle when the wireless receiver fails to receive
the radio frequency transmission for a threshold period of time.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application is a continuation-in-part of
co-pending U.S. patent application Ser. No. 14/512,859, which was
filed on Oct. 13, 2014, entitled "TRAILER MOTION AND PARAMETER
ESTIMATION SYSTEM," which has a common Applicant herewith and the
entire contents of which is hereby incorporated by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The disclosure made herein relates generally to trailer
identification and motion estimation, and more particularly to a
trailer sensor module in communication with a towing vehicle for
wireless trailer identification and hitch angle estimation to
assist with autonomous vehicle guidance of the trailer, such as a
trailer backup assist system.
BACKGROUND OF THE INVENTION
[0003] Reversing a vehicle while towing a trailer can be
challenging for many drivers, particularly for drivers that drive
with a trailer on an infrequent basis or with various types of
trailers. Systems used to assist a driver with backing a trailer
frequently estimate the position of the trailer relative to the
vehicle with a sensor that determines a hitch angle. The accuracy
and reliability of this hitch angle estimation can be critical to
the operation of the backup assist system. It is also understood
that reliable hitch angle estimation can be useful for additional
vehicle features, such as monitoring for trailer sway.
SUMMARY OF THE INVENTION
[0004] According to one aspect of the present invention, a method
of identifying a trailer with a vehicle includes transmitting a
unique identifier with a wireless transmitter attached to the
trailer. The method also includes receiving the unique identifier
with a wireless receiver on the vehicle. Further, the method
includes accessing a parameter of the trailer based on the received
unique identifier for autonomously guiding the trailer along a
desired backing path.
[0005] According to another aspect of the present invention, a
trailer sensor module for communicating with a vehicle includes a
sensor that senses a parameter of the trailer for operating a
trailer backup assist system. The trailer sensor module also
includes a wireless transmitter that emits a unique identifier
configured to be recognized by the vehicle and, upon recognition,
transmits the parameter to the vehicle. A housing encloses the
wireless transmitter and the sensor, whereby the housing is adapted
to be removably attached to the trailer.
[0006] According to yet another aspect of the present invention, a
trailer backup assist system for a vehicle reversing a trailer
includes a wireless transmitter removably coupled with the trailer.
The wireless transmitter emits a unique identifier. A wireless
receiver is coupled with the vehicle for receiving the unique
identifier. Also, a controller on the vehicle identifies the
trailer based on the unique identifier and accesses a parameter of
the identified trailer for autonomously guiding the trailer with
the vehicle along a desired backing path.
[0007] These and other aspects, objects, and features of the
present invention will be understood and appreciated by those
skilled in the art upon studying the following specification,
claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] In the drawings:
[0009] FIG. 1 is a top perspective view of a vehicle attached to a
trailer with one embodiment of a sensor module for operating a
trailer backup assist system;
[0010] FIG. 2 is a block diagram illustrating one embodiment of the
trailer backup assist system having a steering input device, a
curvature controller, and a trailer braking system;
[0011] FIG. 3 is a schematic diagram that illustrates the geometry
of a vehicle and a trailer overlaid with a two-dimensional x-y
coordinate system, identifying variables used to determine a
kinematic relationship of the vehicle and the trailer for the
trailer backup assist system, according to one embodiment;
[0012] FIG. 4 is a schematic block diagram illustrating portions of
a curvature controller, according to an additional embodiment, and
other components of the trailer backup assist system, according to
such an embodiment;
[0013] FIG. 5 is schematic block diagram of the curvature
controller of FIG. 4, showing the feedback architecture and signal
flow of the curvature controller, according to such an
embodiment;
[0014] FIG. 6 is a schematic diagram showing a relationship between
a hitch angle and a steering angle of the vehicle as it relates to
curvature of the trailer and a jackknife angle;
[0015] FIG. 7 is a plan view of a steering input device having a
rotatable knob for operating the trailer backup assist system,
according to one embodiment;
[0016] FIG. 8 is a plan view of another embodiment of a rotatable
knob for selecting a desired curvature of a trailer and a
corresponding schematic diagram illustrating a vehicle and a
trailer with various trailer curvature paths correlating with
desired curvatures that may be selected;
[0017] FIG. 9 is a schematic diagram showing a backup sequence of a
vehicle and a trailer implementing various curvature selections
with the trailer backup assist system, according to one
embodiment;
[0018] FIG. 10 is a flow diagram illustrating a method of operating
a trailer backup assist system using an operating routine for
steering a vehicle reversing a trailer with normalized control of
the desired curvature, according to one embodiment;
[0019] FIG. 11 is a top perspective view of a trailer sensor module
attached to a trailer for communicating with a vehicle, according
to one embodiment;
[0020] FIG. 12 is a side elevational view of the trailer sensor
module shown in FIG. 11;
[0021] FIG. 13 is a block diagram illustrating one embodiment of
the trailer sensor module communicating with one embodiment of the
trailer backup assist system;
[0022] FIG. 14 is a flow diagram illustrating a method of
identifying a trailer and accessing a parameter of the trailer
based on a unique identifier, according to one embodiment; and
[0023] FIG. 15 is a flow diagram illustrating a method of
estimating a hitch angle using a hitch angle estimation routine,
according to one embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] For purposes of description herein, it is to be understood
that the disclosed trailer backup assist system and the related
methods may assume various alternative embodiments and
orientations, except where expressly specified to the contrary. It
is also to be understood that the specific devices and processes
illustrated in the attached drawings, and described in the
following specification are simply exemplary embodiments of the
inventive concepts defined in the appended claims. While various
aspects of the trailer backup assist system and the related methods
are described with reference to a particular illustrative
embodiment, the disclosed invention is not limited to such
embodiments, and additional modifications, applications, and
embodiments may be implemented without departing from the disclosed
invention. Hence, specific dimensions and other physical
characteristics relating to the embodiments disclosed herein are
not to be considered as limiting, unless the claims expressly state
otherwise.
[0025] Referring to FIGS. 1-15, reference numeral 10 generally
designates a trailer backup assist system for controlling a backing
path of a trailer 12 attached to a vehicle 14 by allowing a driver
of the vehicle 14 to specify a desired curvature 26 of the backing
path of the trailer 12. In one embodiment, the trailer backup
assist system 10 automatically steers the vehicle 14 to guide the
trailer 12 on the desired curvature or backing path 26 as a driver
uses the accelerator and brake pedals to control the reversing
speed of the vehicle 14. The trailer backup assist system 10 may
more precisely guide the trailer 12 on the desired curvature or
backing path 26 with an accurate understanding of the parameters of
the trailer 12, which may include the trailer dynamic variables,
such as yaw rate and/or acceleration, and trailer dimensions, such
as trailer length. In one embodiment, a trailer sensor module 20
may be attached to the trailer 12 and provided with a wireless
transmitter 29 for transmitting a unique identifier associated with
the trailer 12. Accordingly, in such an embodiment, the vehicle 14
may include a wireless receiver 31 that receives the unique
identifier and a corresponding controller that accesses a parameter
of the trailer 12 based on recognition of the received unique
identifier. It is contemplated that the trailer sensor module 20
may be used in association with additional or alternative vehicle
features for the trailer backup assist system 10, such as a trailer
sway avoidance system.
[0026] To monitor the position of the trailer 12 relative to the
vehicle 14, the trailer backup assist system 10 may include a
sensor system 16 that senses or otherwise determines a hitch angle
.gamma. between the trailer 12 and the vehicle 14. In one
embodiment, the sensor system 16 may include the sensor module 20
attached to the trailer 12 that monitors the dynamics of the
trailer 12, such as yaw rate, and communicates with a controller 28
of the trailer backup assist system 10 to determine the
instantaneous hitch angle .gamma.. Accordingly, one embodiment of a
sensor module 20 is adapted to attach to the trailer 12 and
generate a trailer yaw rate .omega..sub.2. Upon recognition of the
attached trailer 12, the wireless transmitter 29 may then transmit
the trailer yaw rate .omega..sub.2 to the vehicle 14. The trailer
backup assist system 10 according to such an embodiment may also
include a vehicle sensor system 17 that generates a vehicle yaw
rate .omega..sub.1 and a vehicle speed v.sub.1. The controller 28
of the trailer backup assist system 10 may thereby estimate a hitch
angle .gamma. based on the trailer yaw rate .omega..sub.2, the
vehicle yaw rate .omega..sub.1, and the vehicle speed v.sub.1 in
view of a kinematic relationship between the trailer 12 and the
vehicle 14. In another embodiment, the sensor system 16 may,
separate from the sensor module 20, include a hitch angle sensor
44, such as a vision-based system that employs a camera 46 on the
vehicle 14 to monitor a target 52 on the trailer 12 to determine
the hitch angle .gamma. and thereby increase accuracy and
reliability of the estimated hitch angle .gamma..
[0027] With respect to the general operation of the trailer backup
assist system 10, a steering input device 18 may be provided, such
as a rotatable knob 30, for a driver to provide the desired
curvature 26 of the trailer 12. As such, the steering input device
18 may be operable between a plurality of selections, such as
successive rotated positions of a knob 30, that each provide an
incremental change to the desired curvature 26 of the trailer 12.
Upon inputting the desired curvature 26, the controller may
generate a steering command for the vehicle 14 to guide the trailer
12 on the desired curvature 26 based on the estimated hitch angle
.gamma. and a kinematic relationship between the trailer 12 and the
vehicle 14. Therefore, the accuracy of the hitch angle estimation
is critical to operating the trailer backup assist system 10.
However, it is appreciated that such a system for instantaneously
estimating hitch angle may be used in association with additional
or alternative vehicle features, such as trailer sway
monitoring.
[0028] With reference to the embodiment shown in FIG. 1, the
vehicle 14 is a pickup truck embodiment that is equipped with one
embodiment of the trailer backup assist system 10 for controlling
the backing path of the trailer 12 that is attached to the vehicle
14. Specifically, the vehicle 14 is pivotally attached to one
embodiment of the trailer 12 that has a box frame 32 with an
enclosed cargo area 34, a single axle having a right wheel assembly
and a left wheel assembly, and a tongue 36 longitudinally extending
forward from the enclosed cargo area 34. The illustrated trailer 12
also has a trailer hitch connector in the form of a coupler
assembly 38 that is connected to a vehicle hitch connector in the
form of a hitch ball 40. The coupler assembly 38 latches onto the
hitch ball 40 to provide a pivoting ball joint connection 42 that
allows for articulation of the hitch angle .gamma.. It should be
appreciated that additional embodiments of the trailer 12 may
alternatively couple with the vehicle 14 to provide a pivoting
connection, such as by connecting with a fifth wheel connector. It
is also contemplated that additional embodiments of the trailer may
include more than one axle and may have various shapes and sizes
configured for different loads and items, such as a boat trailer or
a flatbed trailer.
[0029] Still referring to FIG. 1, the sensor system 16 in the
illustrated embodiment includes both a sensor module 20 and a
vision-based hitch angle sensor 44 for estimating the hitch angle
.gamma. between the vehicle 14 and the trailer 12. The illustrated
hitch angle sensor 44 employs a camera 46 (e.g. video imaging
camera) that may be located proximate an upper region of the
vehicle tailgate 48 at the rear of the vehicle 14, as shown, such
that the camera 46 may be elevated relative to the tongue 36 of the
trailer 12. The illustrated camera 46 has an imaging field of view
50 located and oriented to capture one or more images of the
trailer 12, including a region containing one or more desired
target placement zones for at least one target 52 to be secured.
Although it is contemplated that the camera 46 may capture images
of the trailer 12 without a target 52 to determine the hitch angle
.gamma., in the illustrated embodiment, the trailer backup assist
system 10 includes a target 52 placed on the trailer 12 to allow
the trailer backup assist system 10 to utilize information acquired
via image acquisition and processing of the target 52. For
instance, the illustrated camera 46 may include a video imaging
camera that repeatedly captures successive images of the trailer 12
that may be processed to identify the target 52 and its location on
the trailer 12 for determining movement of the target 52 and the
trailer 12 relative to the vehicle 14 and the corresponding hitch
angle .gamma.. It should also be appreciated that the camera 46 may
include one or more video imaging cameras and may be located at
other locations on the vehicle 14 to acquire images of the trailer
12 and the desired target placement zone, such as on a passenger
cab 54 of the vehicle 14 to capture images of a gooseneck trailer.
Furthermore, it is contemplated that additional embodiments of the
hitch angle sensor 44 and the sensor system 16 for providing the
hitch angle .gamma. may include one or a combination of a
potentiometer, a magnetic-based sensor, an optical sensor, a
proximity sensor, an ultrasonic sensor, a rotational sensor, a
capacitive sensor, an inductive sensor, or a mechanical based
sensor, such as a mechanical sensor assembly mounted to the
pivoting ball joint connection 42, energy transducers of a reverse
aid system, a blind spot system, and/or a cross traffic alert
system, and other conceivable sensors or indicators of the hitch
angle .gamma. to supplement or be used in place of the vision-based
hitch angle sensor 44.
[0030] The embodiment of the sensor module 20 illustrated in FIG. 1
includes a housing 21 mounted on the tongue 36 of the trailer 12
proximate the enclosed cargo area 34 and includes left and right
wheel speed sensors 23 on laterally opposing wheels of the trailer
12. The sensor module 20 may generate a plurality of signals
indicative of various dynamics of the trailer 12. The signals may
include a yaw rate signal, a lateral acceleration signal, and wheel
speed signals generated respectively by a yaw rate sensor 25, an
accelerometer 27, and the wheel speed sensors 23. Accordingly, in
the illustrated embodiment, the yaw rate sensor 25 and the
accelerometer 27 are contained within the housing 21, although
other configurations are conceivable as described in greater detail
herein. It is contemplated that these sensor signals could be
compensated and filtered to remove offsets or drifts, and smooth
out noise. Further, the controller 28 may utilize processed signals
received outside of the sensor system 16, including standard
signals from the brake control system 72 and the power assist
steering system 62, such as vehicle yaw rate .omega..sub.1, vehicle
speed v.sub.1, and steering angle .delta., to estimate the trailer
hitch angle .gamma., trailer speed and related trailer parameters.
As described in more detail below, the controller 28 may estimates
the hitch angle .gamma. based on the trailer yaw rate
.omega..sub.2, the vehicle yaw rate .omega..sub.1, and the vehicle
speed v.sub.1 in view of a kinematic relationship between the
trailer 12 and the vehicle 14. The controller 28 of the trailer
backup assist system 10 may utilize the estimated trailer variables
and trailer parameters to control the steering system 62, brake
control system 72, and the powertrain control system 74 to assist
backing up the vehicle-trailer combination.
[0031] With reference to the embodiment of the trailer backup
assist system 10 shown in FIG. 2, the hitch angle sensor 44 is
provided in dashed lines to illustrate that in some embodiments it
may be omitted, such as when the trailer sensor module 20 is
provided with a means to estimate the hitch angle .gamma.. The
illustrated embodiment of the trailer backup assist system 10
receives vehicle and trailer status-related information from
additional sensors and devices. This information includes
positioning information from a positioning device 56, which may
include a global positioning system (GPS) on the vehicle 14 or a
handled device, to determine a coordinate location of the vehicle
14 and the trailer 12 based on the location of the positioning
device 56 with respect to the trailer 12 and/or the vehicle 14 and
based on the estimated hitch angle .gamma.. The positioning device
56 may additionally or alternatively include a dead reckoning
system for determining the coordinate location of the vehicle 14
and the trailer 12 within a localized coordinate system based at
least on vehicle speed, steering angle, and hitch angle .gamma..
Other vehicle information received by the trailer backup assist
system 10 may include a speed of the vehicle 14 from a speed sensor
58 and a yaw rate of the vehicle 14 from a yaw rate sensor 60. It
is contemplated that in additional embodiments, the hitch angle
sensor 44 and other vehicle sensors and devices may provide sensor
signals or other information, such as proximity sensor signals or
successive images of the trailer 12, that the controller of the
trailer backup assist system 10 may process with various routines
to determine an indicator of the hitch angle .gamma., such as a
range of hitch angles.
[0032] As further shown in FIG. 2, one embodiment of the trailer
backup assist system 10 is in communication with a power assist
steering system 62 of the vehicle 14 to operate the steered wheels
64 (FIG. 1) of the vehicle 14 for moving the vehicle 14 in such a
manner that the trailer 12 reacts in accordance with the desired
curvature 26 of the trailer 12. In the illustrated embodiment, the
power assist steering system 62 is an electric power-assisted
steering (EPAS) system that includes an electric steering motor 66
for turning the steered wheels 64 to a steering angle based on a
steering command, whereby the steering angle may be sensed by a
steering angle sensor 67 of the power assist steering system 62.
The steering command may be provided by the trailer backup assist
system 10 for autonomously steering during a backup maneuver and
may alternatively be provided manually via a rotational position
(e.g., steering wheel angle) of a steering wheel 68 (FIG. 1).
However, in the illustrated embodiment, the steering wheel 68 of
the vehicle 14 is mechanically coupled with the steered wheels 64
of the vehicle 14, such that the steering wheel 68 moves in concert
with steered wheels 64, preventing manual intervention with the
steering wheel 68 during autonomous steering. More specifically, a
torque sensor 70 is provided on the power assist steering system 62
that senses torque on the steering wheel 68 that is not expected
from autonomous control of the steering wheel 68 and therefore
indicative of manual intervention, whereby the trailer backup
assist system 10 may alert the driver to discontinue manual
intervention with the steering wheel 68 and/or discontinue
autonomous steering.
[0033] In alternative embodiments, some vehicles have a power
assist steering system 62 that allows a steering wheel 68 to be
partially decoupled from movement of the steered wheels 64 of such
a vehicle. Accordingly, the steering wheel 68 can be rotated
independent of the manner in which the power assist steering system
62 of the vehicle controls the steered wheels 64 (e.g., autonomous
steering as commanded by the trailer backup assist system 10). As
such, in these types of vehicles where the steering wheel 68 can be
selectively decoupled from the steered wheels 64 to allow
independent operation thereof, the steering wheel 68 may be used as
a steering input device 18 for the trailer backup assist system 10,
as disclosed in greater detail herein.
[0034] Referring again to the embodiment illustrated in FIG. 2, the
power assist steering system 62 provides the controller 28 of the
trailer backup assist system 10 with information relating to a
rotational position of steered wheels 64 of the vehicle 14,
including a steering angle. The controller 28 in the illustrated
embodiment processes the current steering angle, in addition to
other vehicle 14 and trailer 12 conditions to guide the trailer 12
along the desired curvature 26. It is conceivable that the trailer
backup assist system 10, in additional embodiments, may be an
integrated component of the power assist steering system 62. For
example, the power assist steering system 62 may include a trailer
backup assist algorithm for generating vehicle steering information
and commands as a function of all or a portion of information
received from the steering input device 18, the hitch angle sensor
44, the power assist steering system 62, a vehicle brake control
system 72, a powertrain control system 74, and other vehicle
sensors and devices.
[0035] As also illustrated in FIG. 2, the vehicle brake control
system 72 may also communicate with the controller 28 to provide
the trailer backup assist system 10 with braking information, such
as vehicle wheel speed, and to receive braking commands from the
controller 28. For instance, vehicle speed information can be
determined from individual wheel speeds as monitored by the brake
control system 72. Vehicle speed may also be determined from the
powertrain control system 74, the speed sensor 58, and the
positioning device 56, among other conceivable means. In some
embodiments, individual wheel speeds can also be used to determine
a vehicle yaw rate, which can be provided to the trailer backup
assist system 10 in the alternative or in addition to the vehicle
yaw rate sensor 60. In certain embodiments, the trailer backup
assist system 10 can provide vehicle braking information to the
brake control system 72 for allowing the trailer backup assist
system 10 to control braking of the vehicle 14 during backing of
the trailer 12. For example, the trailer backup assist system 10 in
some embodiments may regulate speed of the vehicle 14 during
backing of the trailer 12, which can reduce the potential for
unacceptable trailer backup conditions. Examples of unacceptable
trailer backup conditions include, but are not limited to, a
vehicle 14 over speed condition, a high hitch angle rate, trailer
angle dynamic instability, a calculated theoretical trailer
jackknife condition (defined by a maximum vehicle steering angle,
drawbar length, tow vehicle wheelbase, and an effective trailer
length), or physical contact jackknife limitation (defined by an
angular displacement limit relative to the vehicle 14 and the
trailer 12), and the like. It is disclosed herein that the trailer
backup assist system 10 can issue an alert signal corresponding to
a notification of an actual, impending, and/or anticipated
unacceptable trailer backup condition.
[0036] The powertrain control system 74, as shown in the embodiment
illustrated in FIG. 2, may also interact with the trailer backup
assist system 10 for regulating speed and acceleration of the
vehicle 14 during backing of the trailer 12. As mentioned above,
regulation of the speed of the vehicle 14 may be necessary to limit
the potential for unacceptable trailer backup conditions such as,
for example, jackknifing and trailer angle dynamic instability.
Similar to high-speed considerations as they relate to unacceptable
trailer backup conditions, high acceleration and high dynamic
driver curvature requests can also lead to such unacceptable
trailer backup conditions.
[0037] With continued reference to FIG. 2, the trailer backup
assist system 10 in the illustrated embodiment may communicate with
one or more devices, including a vehicle alert system 76, which may
prompt visual, auditory, and tactile warnings. For instance,
vehicle brake lights 78 and vehicle emergency flashers may provide
a visual alert and a vehicle horn 79 and/or speaker 81 may provide
an audible alert. Additionally, the trailer backup assist system 10
and/or vehicle alert system 76 may communicate with a human machine
interface (HMI) 80 for the vehicle 14. The HMI 80 may include a
vehicle display 82, such as a center-stack mounted navigation or
entertainment display (FIG. 1). Further, the trailer backup assist
system 10 may communicate via wireless communication with another
embodiment of the HMI 80, such as with one or more handheld or
portable devices, including one or more smartphones. The portable
device may also include the display 82 for displaying one or more
images and other information to a user. For instance, the portable
device may display one or more images of the trailer 12 and an
indication of the estimated hitch angle on the display 82. In
addition, the portable device may provide feedback information,
such as visual, audible, and tactile alerts.
[0038] As further illustrated in FIG. 2, the trailer backup assist
system 10 includes a steering input device 18 that is connected to
the controller 28 for allowing communication of information
therebetween. It is disclosed herein that the steering input device
18 can be coupled to the controller 28 in a wired or wireless
manner. The steering input device 18 provides the trailer backup
assist system 10 with information defining the desired backing path
of travel of the trailer 12 for the controller 28 to process and
generate steering commands. More specifically, the steering input
device 18 may provide a selection or positional information that
correlates with a desired curvature 26 of the desired backing path
of travel of the trailer 12. Also, the trailer steering commands
provided by the steering input device 18 can include information
relating to a commanded change in the path of travel, such as an
incremental change in the desired curvature 26, and information
relating to an indication that the trailer 12 is to travel along a
path defined by a longitudinal centerline axis of the trailer 12,
such as a desired curvature value of zero that defines a
substantially straight path of travel for the trailer. As will be
discussed below in more detail, the steering input device 18
according to one embodiment may include a movable control input
device for allowing a driver of the vehicle 14 to command desired
trailer steering actions or otherwise select and alter a desired
curvature. For instance, the moveable control input device may be a
rotatable knob 30, which can be rotatable about a rotational axis
extending through a top surface or face of the knob 30. In other
embodiments, the rotatable knob 30 may be rotatable about a
rotational axis extending substantially parallel to a top surface
or face of the rotatable knob 30. Furthermore, the steering input
device 18, according to additional embodiments, may include
alternative devices for providing a desired curvature 26 or other
information defining a desired backing path, such as a joystick, a
keypad, a series of depressible buttons or switches, a sliding
input device, various user interfaces on a touch-screen display, a
vision based system for receiving gestures, a control interface on
a portable device, and other conceivable input devices as generally
understood by one having ordinary skill in the art. It is
contemplated that the steering input device 18 may also function as
an input device for other features, such as providing inputs for
other vehicle features or systems.
[0039] Still referring to the embodiment shown in FIG. 2, the
controller 28 is configured with a microprocessor 84 to process
logic and routines stored in memory 86 that receive information
from the sensor system 16, including the trailer sensor module 20,
the hitch angle sensor 44, the steering input device 18, the power
assist steering system 62, the vehicle brake control system 72, the
trailer braking system, the powertrain control system 74, and other
vehicle sensors and devices. The controller 28 may generate vehicle
steering information and commands as a function of all or a portion
of the information received. Thereafter, the vehicle steering
information and commands may be provided to the power assist
steering system 62 for affecting steering of the vehicle 14 to
achieve a commanded path of travel for the trailer 12. The
controller 28 may include the microprocessor 84 and/or other analog
and/or digital circuitry for processing one or more routines. Also,
the controller 28 may include the memory 86 for storing one or more
routines, including a hitch angle estimation routine 130, an
operating routine 132, and a curvature routine 98. It should be
appreciated that the controller 28 may be a stand-alone dedicated
controller or may be a shared controller integrated with other
control functions, such as integrated with the sensor system 16,
the power assist steering system 62, and other conceivable onboard
or off-board vehicle control systems.
[0040] With reference to FIG. 3, we now turn to a discussion of
vehicle and trailer information and parameters used to calculate a
kinematic relationship between a curvature of a path of travel of
the trailer 12 and the steering angle of the vehicle 14 towing the
trailer 12, which can be desirable for a trailer backup assist
system 10 configured in accordance with some embodiments, including
for use by a curvature routine 98 of the controller 28 in one
embodiment. To achieve such a kinematic relationship, certain
assumptions may be made with regard to parameters associated with
the vehicle/trailer system. Examples of such assumptions include,
but are not limited to, the trailer 12 being backed by the vehicle
14 at a relatively low speed, wheels of the vehicle 14 and the
trailer 12 having negligible (e.g., no) slip, tires of the vehicle
14 having negligible (e.g., no) lateral compliance, tires of the
vehicle 14 and the trailer 12 having negligible (e.g., no)
deformation, actuator dynamics of the vehicle 14 being negligible,
and the vehicle 14 and the trailer 12 exhibiting negligible (e.g.,
no) roll or pitch motions, among other conceivable factors with the
potential to have an effect on controlling the trailer 12 with the
vehicle 14.
[0041] As shown in FIG. 3, for a system defined by a vehicle 14 and
a trailer 12, the kinematic relationship is based on various
parameters associated with the vehicle 14 and the trailer 12. These
parameters include:
[0042] .delta.: steering angle at steered front wheels of the
vehicle;
[0043] .alpha.: yaw angle of the vehicle;
[0044] .beta.: yaw angle of the trailer;
[0045] .gamma.: hitch angle (.gamma.=.beta.-.alpha.);
[0046] W: wheel base of the vehicle;
[0047] L: length between hitch point and rear axle of the
vehicle;
[0048] D: distance between hitch point and axle of the trailer or
effective axle for a multiple axle trailer (axle length may be an
equivalent); and
[0049] r.sub.2: curvature radius for the trailer.
[0050] One embodiment of a kinematic relationship between trailer
path radius of curvature r.sub.2 at the midpoint of an axle of the
trailer 12, steering angle .delta. of the steered wheels 64 of the
vehicle 14, and the hitch angle .gamma. can be expressed in the
equation provided below. As such, if the hitch angle .gamma. is
provided, the trailer path curvature .kappa..sub.2 can be
controlled based on regulating the steering angle .delta. (where
{dot over (.beta.)} is trailer yaw rate and {dot over (.eta.)} is
trailer velocity).
.kappa. 2 = 1 r 2 = .beta. . .eta. . = ( W + KV 2 g ) sin .gamma. +
L cos .gamma. tan .delta. D ( ( W + KV 2 g ) cos .gamma. - L sin
.gamma. tan .delta. ) ##EQU00001##
[0051] This relationship can be expressed to provide the steering
angle .delta. as a function of trailer path curvature .kappa..sub.2
and hitch angle .gamma..
.delta. = tan - 1 ( ( W + KV 2 g ) [ .kappa. 2 D cos .gamma. - sin
.gamma. ] DL .kappa. 2 sin .gamma. + L cos .gamma. ) = F ( .gamma.
, .kappa. 2 , K ) ##EQU00002##
[0052] Accordingly, for a particular vehicle and trailer
combination, certain parameters (e.g., D, W and L) of the kinematic
relationship are constant and assumed known. V is the vehicle
longitudinal speed and g is the acceleration due to gravity. K is a
speed dependent parameter which when set to zero makes the
calculation of steering angle independent of vehicle speed. For
example, vehicle-specific parameters of the kinematic relationship
can be predefined in an electronic control system of the vehicle 14
and trailer-specific parameters of the kinematic relationship can
be inputted by a driver of the vehicle 14, determined from sensed
trailer behavior in response to vehicle steering commands, or
otherwise determined from signals provided by the trailer 12.
Trailer path curvature .kappa..sub.2 can be determined from the
driver input via the steering input device 18. Through the use of
the equation for providing steering angle, a corresponding steering
command can be generated by the curvature routine 98 for
controlling the power assist steering system 62 of the vehicle
14.
[0053] In an additional embodiment, an assumption may be made by
the curvature routine 98 that a longitudinal distance L between the
pivoting connection and the rear axle of the vehicle 14 is equal to
zero for purposes of operating the trailer backup assist system 10
when a gooseneck trailer or other similar trailer is connected with
the a hitch ball or a fifth wheel connector located over a rear
axle of the vehicle 14. The assumption essentially assumes that the
pivoting connection with the trailer 12 is substantially vertically
aligned with the rear axle of the vehicle 14. When such an
assumption is made, the controller 28 may generate the steering
angle command for the vehicle 14 as a function independent of the
longitudinal distance L between the pivoting connection and the
rear axle of the vehicle 14. It is appreciated that the gooseneck
trailer mentioned generally refers to the tongue configuration
being elevated to attach with the vehicle 14 at an elevated
location over the rear axle, such as within a bed of a truck,
whereby embodiments of the gooseneck trailer may include flatbed
cargo areas, enclosed cargo areas, campers, cattle trailers, horse
trailers, lowboy trailers, and other conceivable trailers with such
a tongue configuration.
[0054] Yet another embodiment of the curvature routine 98 of the
trailer backup assist system 10 is illustrated in FIG. 4, showing
the general architectural layout whereby a measurement module 88, a
hitch angle regulator 90, and a curvature regulator 92 are routines
that may be stored in the memory 86 of the controller 28. In the
illustrated layout, the steering input device 18 provides a desired
curvature .kappa..sub.2 value to the curvature regulator 92 of the
controller 28, which may be determined from the desired backing
path 26 that is input with the steering input device 18. The
curvature regulator 92 computes a desired hitch angle .gamma.(d)
based on the current desired curvature .kappa..sub.2 along with the
steering angle .delta. provided by a measurement module 88 in this
embodiment of the controller 28. The measurement module 88 may be a
memory device separate from or integrated with the controller 28
that stores data from sensors of the trailer backup assist system
10, such as the hitch angle sensor 44, the vehicle speed sensor 58,
the steering angle sensor, or alternatively the measurement module
88 may otherwise directly transmit data from the sensors without
functioning as a memory device. Once the desired hitch angle
.gamma.(d) is computed by the curvature regulator 92 the hitch
angle regulator 90 generates a steering angle command based on the
computed desired hitch angle .gamma.(d) as well as a measured or
otherwise estimated hitch angle .gamma.(m) and a current velocity
of the vehicle 14. The steering angle command is supplied to the
power assist steering system 62 of the vehicle 14, which is then
fed back to the measurement module 88 to reassess the impacts of
other vehicle characteristics impacted from the implementation of
the steering angle command or other changes to the system.
Accordingly, the curvature regulator 92 and the hitch angle
regulator 90 continually process information from the measurement
module 88 to provide accurate steering angle commands that place
the trailer 12 on the desired curvature .kappa..sub.2 and the
desired backing path 26, without substantial overshoot or
continuous oscillation of the path of travel about the desired
curvature .kappa..sub.2.
[0055] As also shown in FIG. 5, the embodiment of the curvature
routine 98 shown in FIG. 4 is illustrated in a control system block
diagram. Specifically, entering the control system is an input,
K.sub.2, which represents the desired curvature 26 of the trailer
12 that is provided to the curvature regulator 92. The curvature
regulator 92 can be expressed as a static map, p(K.sub.2, (5),
which in one embodiment is the following equation:
p ( .kappa. 2 , .delta. ) = tan - 1 ( .kappa. 2 DW + L tan (
.delta. ) .kappa. 2 DL tan ( .delta. ) - W ) ##EQU00003##
[0056] Where,
[0057] .kappa..sub.2 represents the desired curvature of the
trailer 12 or 1/r.sub.2 as shown in FIG. 3;
[0058] .delta. represents the steering angle;
[0059] L represents the distance from the rear axle of the vehicle
14 to the hitch pivot point;
[0060] D represents the distance from the hitch pivot point to the
axle of the trailer 12; and
[0061] W represents the distance from the rear axle to the front
axle of the vehicle 14.
[0062] With further reference to FIG. 5, the output hitch angle of
p(.kappa..sub.2, .delta.) is provided as the reference signal,
.gamma..sub.ref, for the remainder of the control system, although
the steering angle .delta. value used by the curvature regulator 92
is feedback from the non-linear function of the hitch angle
regulator 90. It is shown that the hitch angle regulator 90 uses
feedback linearization for defining a feedback control law, as
follows:
g ( u , .gamma. , v ) = .delta. = tan - 1 ( W v ( 1 + L D cos (
.gamma. ) ) ( v D sin ( .gamma. ) - u ) ) ##EQU00004##
[0063] As also shown in FIG. 5, the feedback control law, g(u,
.gamma., v), is implemented with a proportional integral (PI)
controller, whereby the integral portion substantially eliminates
steady-state tracking error. More specifically, the control system
illustrated in FIG. 58 may be expressed as the following
differential-algebraic equations:
.gamma. . ( t ) = v ( t ) D sin ( .gamma. ( t ) ) + ( 1 + L D cos (
.gamma. ( t ) ) ) v ( t ) W .delta. _ ##EQU00005## tan ( .delta. )
= .delta. _ = W v ( t ) ( 1 + L D cos ( .gamma. ( t ) ) ) ( K P ( p
( .kappa. 2 , .delta. ) - .gamma. ( t ) ) - v ( t ) D sin ( .gamma.
( t ) ) ) ##EQU00005.2##
[0064] It is contemplated that the PI controller may have gain
terms based on trailer length D since shorter trailers will
generally have faster dynamics. In addition, the hitch angle
regulator 90 may be configured to prevent the desired hitch angle
.gamma.(d) to reach or exceed a jackknife angle .gamma.(j), as
computed by the controller or otherwise determined by the trailer
backup assist system 10, as disclosed in greater detail herein.
[0065] Referring now to FIG. 6, in the illustrated embodiments of
the disclosed subject matter, it is desirable to limit the
potential for the vehicle 14 and the trailer 12 to attain a
jackknife angle (i.e., the vehicle/trailer system achieving a
jackknife condition). A jackknife angle .gamma.(j) refers to a
hitch angle .gamma. that while backing cannot be overcome by the
maximum steering input for a vehicle such as, for example, the
steered front wheels of the vehicle 14 being moved to a maximum
steered angle .delta. at a maximum rate of steering angle change.
The jackknife angle .gamma.(j) is a function of a maximum wheel
angle for the steered wheels of the vehicle 14, the wheel base W of
the vehicle 14, the distance L between hitch point and the rear
axle of the vehicle 14, and the length D between the hitch point
and the axle of the trailer 12 or the effective axle when the
trailer 12 has multiple axles. When the hitch angle .gamma. for the
vehicle 14 and the trailer 12 achieves or exceeds the jackknife
angle .gamma.(j), the vehicle 14 may be pulled forward to reduce
the hitch angle .gamma..
[0066] A kinematic model representation of the vehicle 14 and the
trailer 12 can also be used to determine a jackknife angle for the
vehicle-trailer combination. Accordingly, with reference to FIGS. 3
and 6, a steering angle limit for the steered front wheels requires
that the hitch angle .gamma. cannot exceed the jackknife angle
.gamma.(j), which is also referred to as a critical hitch angle
.gamma.. Thus, under the limitation that the hitch angle .gamma.
cannot exceed the jackknife angle .gamma.(j), the jackknife angle
.gamma.(j) is the hitch angle .gamma. that maintains a circular
motion for the vehicle/trailer system when the steered wheels 64
are at a maximum steering angle .delta.(max). The steering angle
for circular motion with hitch angle .gamma. is defined by the
following equation.
tan .delta. max = w sin .gamma. max D + L cos .gamma. max
##EQU00006##
[0067] Solving the above equation for hitch angle .gamma. allows
jackknife angle .gamma.(j) to be determined. This solution, which
is shown in the following equation, can be used in implementing
trailer backup assist functionality in accordance with the
disclosed subject matter for monitoring hitch angle .gamma. in
relation to jackknife angle.
cos .gamma. _ = - b .+-. b 2 - 4 ac 2 a ##EQU00007##
[0068] where,
[0069] a=L.sup.2 tan.sup.2.delta.(max)+W.sup.2;
[0070] b=2 LD tan.sup.2.delta.(max); and
[0071] c=D.sup.2 tan.sup.2.delta.(max)-W.sup.2.
[0072] In certain instances of backing the trailer 12, a jackknife
enabling condition can arise based on current operating parameters
of the vehicle 14 in combination with a corresponding hitch angle
.gamma.. This condition can be indicated when one or more specified
vehicle operating thresholds are met while a particular hitch angle
.gamma. is present. For example, although the particular hitch
angle .gamma. is not currently at the jackknife angle for the
vehicle 14 and attached trailer 12, certain vehicle operating
parameters can lead to a rapid (e.g., uncontrolled) transition of
the hitch angle .gamma. to the jackknife angle for a current
commanded trailer curvature and/or can reduce an ability to steer
the trailer 12 away from the jackknife angle. One reason for a
jackknife enabling condition is that trailer curvature control
mechanisms (e.g., those in accordance with the disclosed subject
matter) generally calculate steering commands at an instantaneous
point in time during backing of a trailer 12. However, these
calculations will typically not account for lag in the steering
control system of the vehicle 14 (e.g., lag in a steering EPAS
controller). Another reason for the jackknife enabling condition is
that trailer curvature control mechanisms generally exhibit reduced
steering sensitivity and/or effectiveness when the vehicle 14 is at
relatively high speeds and/or when undergoing relatively high
acceleration.
[0073] Jackknife determining information may be received by the
controller 28, according to one embodiment, to process and
characterize a jackknife enabling condition of the vehicle-trailer
combination at a particular point in time (e.g., at the point in
time when the jackknife determining information was sampled).
Examples of the jackknife determining information include, but are
not limited to, information characterizing an estimated hitch angle
.gamma., information characterizing a vehicle accelerator pedal
transient state, information characterizing a speed of the vehicle
14, information characterizing longitudinal acceleration of the
vehicle 14, information characterizing a brake torque being applied
by a brake system of the vehicle 14, information characterizing a
powertrain torque being applied to driven wheels of the vehicle 14,
and information characterizing the magnitude and rate of driver
requested trailer curvature. In this regard, jackknife determining
information would be continually monitored, such as by an
electronic control unit (ECU) that carries out trailer backup
assist (TBA) functionality. After receiving the jackknife
determining information, a routine may process the jackknife
determining information for determining if the vehicle-trailer
combination attained the jackknife enabling condition at the
particular point in time. The objective of the operation for
assessing the jackknife determining information is determining if a
jackknife enabling condition has been attained at the point in time
defined by the jackknife determining information. If it is
determined that a jackknife enabling condition is present at the
particular point in time, a routine may also determine an
applicable countermeasure or countermeasures to implement.
Accordingly, in some embodiments, an applicable countermeasure will
be selected dependent upon a parameter identified as being a key
influencer of the jackknife enabling condition. However, in other
embodiments, an applicable countermeasure will be selected as being
most able to readily alleviate the jackknife enabling condition. In
still another embodiment, a predefined countermeasure or predefined
set of countermeasures may be the applicable countermeasure(s).
[0074] As previously disclosed with reference to the illustrated
embodiments, during operation of the trailer backup assist system
10, a driver of the vehicle 14 may be limited in the manner in
which steering inputs may be made with the steering wheel 68 of the
vehicle 14 due to the power assist steering system 62 being
directly coupled to the steering wheel 68. Accordingly, the
steering input device 18 of the trailer backup assist system 10 may
be used for inputting a desired curvature 26 of the trailer 12,
thereby decoupling such commands from being made at the steering
wheel 68 of the vehicle 14. However, additional embodiments of the
trailer backup assist system 10 may have the capability to
selectively decouple the steering wheel 68 from movement of
steerable wheels of the vehicle 14, thereby allowing the steering
wheel 68 to be used for commanding changes in the desired curvature
26 of a trailer 12 or otherwise selecting a desired backing path
during such trailer backup assist.
[0075] Referring now to FIG. 7, one embodiment of the steering
input device 18 is illustrated disposed on a center console 108 of
the vehicle 14 proximate a shifter 110. In this embodiment, the
steering input device 18 includes a rotatable knob 30 for providing
the controller 28 with the desired backing path of the trailer 12.
More specifically, the angular position of the rotatable knob 30
may correlate with a desired curvature, such that rotation of the
knob to a different angular position provides a different desired
curvature with an incremental change based on the amount of
rotation and, in some embodiments, a normalized rate, as described
in greater detail herein.
[0076] The rotatable knob 30, as illustrated in FIGS. 7-8, may be
biased (e.g., by a spring return) to a center or at-rest position
P(AR) between opposing rotational ranges of motion R(R), R(L). In
the illustrated embodiment, a first one of the opposing rotational
ranges of motion R(R) is substantially equal to a second one of the
opposing rotational ranges of motion R(L), R(R). To provide a
tactile indication of an amount of rotation of the rotatable knob
30, a force that biases the knob toward the at-rest position P(AR)
can increase (e.g., non-linearly) as a function of the amount of
rotation of the rotatable knob 30 with respect to the at-rest
position P(AR). Additionally, the rotatable knob 30 can be
configured with position indicating detents such that the driver
can positively feel the at-rest position P(AR) and feel the ends of
the opposing rotational ranges of motion R(L), R(R) approaching
(e.g., soft end stops). The rotatable knob 30 may generate a
desired curvature value as function of an amount of rotation of the
rotatable knob 30 with respect to the at-rest position P(AR) and a
direction of movement of the rotatable knob 30 with respect to the
at-rest position P(AR). It is also contemplated that the rate of
rotation of the rotatable knob 30 may also be used to determine the
desired curvature output to the controller 28. The at-rest position
P(AR) of the knob corresponds to a signal indicating that the
vehicle 14 should be steered such that the trailer 12 is backed
along a substantially straight backing path (zero trailer curvature
request from the driver), as defined by the longitudinal direction
22 of the trailer 12 when the knob was returned to the at-rest
position P(AR). A maximum clockwise and anti-clockwise position of
the knob (i.e., limits of the opposing rotational ranges of motion
R(R), R(L)) may each correspond to a respective signal indicating a
tightest radius of curvature (i.e., most acute trajectory or
smallest radius of curvature) of a path of travel of the trailer 12
that is possible without the corresponding vehicle steering
information causing a jackknife condition.
[0077] As shown in FIG. 8, a driver can turn the rotatable knob 30
to provide a desired curvature 26 while the driver of the vehicle
14 backs the trailer 12. In the illustrated embodiment, the
rotatable knob 30 rotates about a central axis between a center or
middle position 114 corresponding to a substantially straight
backing path 26 of travel, as defined by the longitudinal direction
22 of the trailer 12, and various rotated positions 116, 118, 120,
122 on opposing sides of the middle position 114, commanding a
desired curvature 26 corresponding to a radius of the desired
backing path of travel for the trailer 12 at the commanded rotated
position. It is contemplated that the rotatable knob 30 may be
configured in accordance with embodiments of the disclosed subject
matter and omit a means for being biased to an at-rest position
P(AR) between opposing rotational ranges of motion. Lack of such
biasing may allow a current rotational position of the rotatable
knob 30 to be maintained until the rotational control input device
is manually moved to a different position. It is also conceivable
that the steering input device 18 may include a non-rotational
control device that may be configured to selectively provide a
desired curvature 26 and to override or supplement an existing
curvature value. Examples of such a non-rotational control input
device include, but are not limited to, a plurality of depressible
buttons (e.g., curve left, curve right, and travel straight), a
touch screen on which a driver traces or otherwise inputs a
curvature for path of travel commands, a button that is
translatable along an axis for allowing a driver to input backing
path commands, or a joystick type input and the like.
[0078] Referring to FIG. 9, an example of using the steering input
device 18 for dictating a curvature of a desired backing path of
travel (POT) of the trailer 12 while backing up the trailer 12 with
the vehicle 14 is shown. In preparation of backing the trailer 12,
the driver of the vehicle 14 may drive the vehicle 14 forward along
a pull-thru path (PTP) to position the vehicle 14 and trailer 12 at
a first backup position Bl. In the first backup position Bl, the
vehicle 14 and trailer 12 are longitudinally aligned with each
other such that a longitudinal centerline axis L1 of the vehicle 14
is aligned with (e.g., parallel with or coincidental with) a
longitudinal centerline axis L2 of the trailer 12. It is disclosed
herein that such alignment of the longitudinal axis L1, L2 at the
onset of an instance of trailer backup functionality is not a
requirement for operability of a trailer backup assist system 10,
but may be done for calibration.
[0079] After activating the trailer backup assist system 10 (e.g.,
before, after, or during the pull-thru sequence), the driver begins
to back the trailer 12 by reversing the vehicle 14 from the first
backup position B1. So long as the rotatable knob 30 of the trailer
backup steering input device 18 remains in the at-rest position
P(AR) and no other steering input devices 18 are activated, the
trailer backup assist system 10 will steer the vehicle 14 as
necessary for causing the trailer 12 to be backed along a
substantially straight path of travel, as defined by the
longitudinal direction 22 of the trailer 12, specifically the
centerline axis L2 of the trailer 12, at the time when backing of
the trailer 12 began. When the trailer 12 reaches the second backup
position B2, the driver rotates the rotatable knob 30 to command
the trailer 12 to be steered to the right (i.e., a knob position
R(R) clockwise rotation). Accordingly, the trailer backup assist
system 10 will steer the vehicle 14 for causing the trailer 12 to
be steered to the right as a function of an amount of rotation of
the rotatable knob 30 with respect to the at-rest position P(AR), a
rate movement of the knob, and/or a direction of movement of the
knob with respect to the at-rest position P(AR). Similarly, the
trailer 12 can be commanded to steer to the left by rotating the
rotatable knob 30 to the left. When the trailer 12 reaches backup
position B3, the driver allows the rotatable knob 30 to return to
the at-rest position P(AR) thereby causing the trailer backup
assist system 10 to steer the vehicle 14 as necessary for causing
the trailer 12 to be backed along a substantially straight path of
travel as defined by the longitudinal centerline axis L2 of the
trailer 12 at the time when the rotatable knob 30 was returned to
the at-rest position P(AR). Thereafter, the trailer backup assist
system 10 steers the vehicle 14 as necessary for causing the
trailer 12 to be backed along this substantially straight path to
the fourth backup position B4. In this regard, arcuate portions of
a path of travel POT of the trailer 12 are dictated by rotation of
the rotatable knob 30 and straight portions of the path of travel
POT are dictated by an orientation of the centerline longitudinal
axis L2 of the trailer 12 when the knob is in/returned to the
at-rest position P(AR).
[0080] In the embodiment illustrated in FIG. 9, in order to
activate the trailer backup assist system 10, the driver interacts
with the trailer backup assist system 10 and the automatically
steers as the driver reverses the vehicle 14. As discussed above,
the driver may command the trailer backing path by using a steering
input device 18 and the controller 28 may determine the vehicle
steering angle to achieve the desired curvature 26, whereby the
driver controls the throttle and brake while the trailer backup
assist system 10 controls the steering.
[0081] With reference to FIG. 10, a method of operating one
embodiment of the trailer backup assist system 10 is illustrated,
shown as one embodiment of the operating routine 132 (FIG. 2). At
step 134, the method is initiated by the trailer backup assist
system 10 being activated. It is contemplated that this may be done
in a variety of ways, such a making a selection on the display 82
of the vehicle HMI 80. The next step 136, then determines the
kinematic relationship between the attached trailer 12 and the
vehicle 14. To determine the kinematic relationship, various
parameters of the vehicle 14 and the trailer 12 must be sensed,
input by the driver, or otherwise determined for the trailer backup
assist system 10 to generate steering commands to the power assist
steering system 62 in accordance with the desired curvature or
backing path 26 of the trailer 12. As disclosed with reference to
FIGS. 3-6, the kinematic parameters to define the kinematic
relationship include a length of the trailer 12, a wheel base of
the vehicle 14, a distance from a hitch connection to a rear axle
of the vehicle 14, and a hitch angle .gamma. between the vehicle 14
and the trailer 12, among other variables and parameters as
previously described. Accordingly, after the kinematic relationship
is determined, the trailer backup assist system 10 may proceed at
step 160 to determine the current hitch angle by processing the
hitch angle estimation routine 130.
[0082] As shown in FIG. 11, one embodiment of the trailer sensor
module 20 is illustrated having a housing 21 removably attached to
the trailer 12, although the housing may be welded or otherwise
permanently fixed to the trailer 12 in additional embodiments of
the sensor module 20. The housing 21 of the illustrated embodiment
is shaped as a rectangular prism with a bottom surface 19 in
abutting contact with an upper surface 35 of the tongue 36 of the
trailer 12. Various shapes and designs of the housing 21 are
contemplated for additional embodiments to account for differently
packaged components, specific weather or environmental conditions,
and aesthetic purposes, among other considerations. To prevent the
housing 21 from moving relative to the tongue 36, a surface feature
may be provided integrally or separately on at least one of the
bottom surface 19 of the housing 21 and the upper surface 35 of the
tongue 36, such as an elastomeric pad, an adhesive, or an etching
for increasing friction therebetween. Also to provide secure
attachment, the illustrated embodiment includes a strap 33 that
connects between opposing lateral sides of the housing 21 and
surrounds the tongue 36. The strap 33 may be made from any
conventional material, such as nylon, leather, or rubber, and is
configured to be tightened to secure against at least a lower
surface 37 of the tongue 36. Various means of tightening the strap
33 may be implemented, as generally understood in the art.
[0083] As also depicted in the embodiment illustrated in FIGS.
11-12, a top surface 15 of the housing 21 is defined by an exposure
surface of a solar element 39 coupled with the housing 21 for
providing electricity to the sensor module 20. The illustrated
sensor module 20 also includes a battery 41 electrically connected
to the solar element 39 for storing electricity generated by the
solar element 39 and supplying electricity to the components of the
sensor module 20. The solar element 39 may be a panel or any other
form or configuration of photovoltaic cells or portions thereof
having material for converting solar energy to electricity. In
additional embodiments of the sensor module 20, the solar element
39 may be omitted or otherwise configured, which may allow the top
surface 15 of the housing 21, in some embodiments, to include the
target 52 (FIG. 1) for the vision-based hitch angle sensor 44.
[0084] With further reference to FIG. 12, the illustrated housing
21 is shown enclosing the wireless transmitter 29, the yaw rate
sensor 25, and the accelerometer 27. It is contemplated that the
housing 21 may enclose all or a portion of the components of the
sensor module 20. The housing 21 may also be hermetically sealed or
otherwise sealed with a fluid seal to prevent the enclosed
components from being exposed to liquid, dust, or other debris that
may damage or cause the sensor module 20 to malfunction. In one
embodiment, the fluid seal may include a gasket secured along a
seam of the housing to provide the protective fluid sealing.
[0085] The sensor module shown in FIG. 12 is shown with the
wireless transmitter 29 in communicable range from the wireless
receiver 31 of the vehicle 14, depicted attached to the tongue 36
of the trailer 12 at in an acceptable distance 170, less than a
proximity distance 172. The wireless receiver 31 is configured to
communicate with and receive signals within the proximity distance
172, defined as a distance from a rear portion 174 of the vehicle
14, beyond which communication with the wireless receiver 31 is not
likely to be associated with a trailer attached to the vehicle 14.
The controller 28 may estimate the distance at which the wireless
transmitter 29 is located away from the receiver 31 based on the
strength of the transmitted signals from the wireless transmitter
29. Accordingly, the illustrated wireless transmitter 29 is
attached to the trailer 12 within the proximity distance 172 to be
in communicable range with the wireless receiver 31. It is
contemplated that the wireless receiver 31 may also be used for
receiving signals emitted from a key fob, such as door lock and
unlock commands, hatch open commands, vehicle ignition start
commands, and other conceivable commands.
[0086] In one embodiment, the wireless transmitter 29 may
consistently emit a radio frequency transmission, such that the
vehicle 14 determines that the trailer 12 associated with the radio
frequency transmission has been detached from the hitch ball 40 or
hitch of the vehicle 14 when the wireless receiver 31 of the
vehicle 14 fails to receive the radio frequency transmission for a
threshold period of time, such as 3 seconds or another conceivable
time period during which the radio frequency transmission was
expected to be received. Also, the vehicle 14 may determine that
the trailer 12 associated with the radio frequency transmission has
been detached from the hitch ball 40 or hitch of the vehicle 14
when signal strength of the transmissions from the wireless
transmitter 29 are indicative of the wireless transmitter moving
rearward a distance beyond the length of the trailer or otherwise
outside of the proximity distance 172. In an instance when the
controller 28 of the vehicle 14 determines that the trailer 12 may
be detached, a warning may be generated to the driver via the
vehicle HMI 80 and/or the vehicle alert system 76.
[0087] Referring now to FIG. 13, an embodiment of the sensor module
20 is schematically illustrated to show a sensor module controller
43 that may be used to control the transmission of radio signals
and the operation of the sensors of the sensor module 20. The
sensors illustrated include a yaw rate sensor 25 that generates a
yaw rate of the trailer 12 for use in determining the hitch angle
.gamma.. The sensors of the illustrated embodiment of the sensor
module 20 also include an accelerometer 27 for sensing the lateral
acceleration of the trailer 12 for use in determining the trailer
position and movement. It is contemplated that the sensor module 20
may include additional or alternative sensors from those
illustrated for determining a dynamic parameter of the trailer 12
or a constant parameter of the trailer 12. For instance, in one
embodiment the sensor module 20 may include a positional sensor
that determines the location of the target 52 on the trailer tongue
36 for the vision-based hitch angle sensor 44. Another conceivable
sensor of the sensor module 20 for determining a constant parameter
of the trailer 12 includes a height sensor to determine the
distance of the tongue 36 away from the ground surface, which may
be used to assist with the vision-based hitch angle sensor 44 or
take into consideration the pitch of the trailer 12 in operating
the trailer backup assist system 10.
[0088] As also shown in FIG. 13, the sensor module controller 43
includes a microprocessor 45 to process logic and routines stored
in a corresponding memory unit 47 of the sensor module controller
43. As such, the memory unit 47 may store a unique identifier for
the wireless transmitter 29 to emit, such as a radio frequency with
a coded signal configured for the controller 28 on the vehicle to
decode and associate with the sensor module 20 and any
corresponding trailer. In the illustrated embodiment, the sensor
module controller 43 may communicate with the wireless receiver 31
of the trailer backup assist system 10 via the wireless transmitter
29 to determine when the unique identifier has been received and
decoded, so it may proceed to transmit a parameter of the trailer
12, as described in more detail below. The sensor module controller
43, in additional embodiments, may be a stand-alone dedicated
controller or may be a shared controller integrated with other
control functions, such as integrated with the controller 28 of the
trailer backup assist system 10, the power assist steering system
62, and other conceivable onboard or off-board vehicle control
systems. Accordingly, it is contemplated that in one embodiment,
the sensor module 20 may transmit both the unique identifier and
the parameter simultaneously without a sensor module controller 43,
such that the controller 28 on the vehicle 14 may accesses the
parameter after the unique identifier is recognized to be from a
sensor module 20 on a trailer 12 attached to the vehicle.
[0089] One embodiment of a method of identifying a trailer 12
having a sensor module 20 is shown in FIG. 14, where at step 176
the unique identifier is transmitted with the wireless transmitter
29 of the sensor module 20. At step 178, the wireless receiver 31
on the vehicle 14 receives the unique identifier and performs an
operation to determine if the unique identifier is associated with
a known trailer or a trailer otherwise determined to be compatible
with the vehicle 14. This operation may include decoding a coded
signal of the unique identifier to determine if the unique
identifier is recognizable or otherwise contained within a database
of the memory 86 before accessing the parameter of the trailer 12.
At step 180, the vehicle 14 may access a parameter of the trailer
12 based on the recognized unique identifier. In one embodiment,
the parameter is a dimension of the trailer 12 saved in the memory
unit 47 of the sensor module controller 43 or the controller 28 of
the trailer backup assist system 10, such as a length of the
trailer 12 or other necessary variable of the kinematic
relationship used to generate steering commands for the vehicle 14
to guide the trailer along the desired backing path 26. In another
embodiment, the parameter may be a dynamic variable of the trailer
12, such as a yaw rate .omega..sub.2 of the trailer 12 sensed by
the yaw rate sensor 25 of the sensor module 20. It is also
contemplated that the parameter may include multiple variables,
both dynamic and static variable that provide the trailer backup
assist system 10 with more accurate steering commands to guide the
trailer 12 along the desired backing path 26. Further, at step 182,
it is contemplated that in one embodiment, the controller 28 may
monitor the wireless transmissions to determine that the trailer
associated with unique identifier is coupled with the vehicle based
on, at step 184 determining that the wireless receiver 31
consistently receives the continuous or otherwise intermittent
signals from the wireless transmitter 29. At step 186, it is
conceivable that it may be determined that the trailer 12
associated with unique identifier is no longer attached to the
vehicle 14 due to a failure to receive the radio frequency
transmission from the transmitter 29 for a threshold period of
time.
[0090] Referring again to FIG. 3, one embodiment of a kinematic
relationship between the trailer 12 and the vehicle 14 is developed
with the illustrated schematic diagram that shows the geometry of a
vehicle and a trailer overlaid with a two-dimensional x-y
coordinate system, identifying variables, such as the trailer yaw
rate .omega..sub.2 and the vehicle yaw rate .omega..sub.1, which
are used to determine the corresponding hitch angle .gamma.. As
such, hitch angle estimation may be determined using trailer yaw
rate signal .omega..sub.2, vehicle speed signal v.sub.1 and vehicle
yaw rate signal .omega..sub.1. More specifically, the yaw rate of
the trailer may be given by the following kinematic equation, which
can also be rearranged to estimate trailer hitch angle .gamma.:
.omega. 2 = v 1 D sin .gamma. - L D cos .gamma..omega. 1
##EQU00008##
[0091] Referring now to FIG. 15, one embodiment of the hitch angle
estimation routine 130 is illustrated, whereby the above-noted
kinematic relationship is utilized to instantaneously estimate the
hitch angle .gamma.. This routine may be used in conjunction with
operation of the trailer sensor module to provide the
instantaneously estimate the hitch angle .gamma.. At step 138, the
sensor signals are received for executing the steps to determine
the hitch angle .gamma.. The sensor signals may include the trailer
yaw rate signal .omega..sub.2, the vehicle speed signal v.sub.1,
and the vehicle yaw rate signal .omega..sub.1, along with other
sensor signals that may be used in some embodiments, such as the
steering angle .delta. signal, trailer lateral acceleration
a.sub.y2, the measure hitch angle from the hitch angle sensor 44
among other potential sensor signals. At step 140, these signals
may be filtered and any potential offsets may be compensated before
proceeding to further process the sensor signals.
[0092] Still referring to FIG. 15, in one embodiment, the vehicle
speed v.sub.1 may be received from the speed sensor 58 on the
vehicle 14 and not require any further processing or derivation to
proceed with calculating the instantaneous hitch angle .gamma..
However, at step 142, in some embodiments, the vehicle speed
v.sub.1 may be derived from wheel speed sensors on the vehicle 14,
the positioning device 56, or other conceivable means to determine
the vehicle speed v.sub.1. Also, according to one embodiment, the
vehicle yaw rate .omega..sub.1 may be received directly from the
yaw rate sensor 60 on the vehicle 14 and not necessitate any
further derivation. However, it is also contemplated that at step
142, the vehicle yaw rate .omega..sub.1 may additionally or
alternatively be derived from left and right wheel speed sensors on
the vehicle14. Further, according to an additional embodiment, the
vehicle yaw rate .omega..sub.1 may be derived from the steering
angle .delta. of the vehicle 14 and the vehicle speed v.sub.1,
along with the vehicle wheelbase W, which is known or otherwise
stored in the memory 86 of the controller 28. In one embodiment,
the vehicle yaw rate .omega..sub.1 may be determined based on the
steering angle .delta., the vehicle wheelbase W, and the vehicle
speed v.sub.1.
[0093] As shown in FIG. 15, the trailer yaw rate .omega..sub.2 may
also be provided directly by the sensor system 16 at step 138 or
determined from processing the sensor signals at step 142. For
instance, the trailer yaw rate .omega..sub.2 may be received
directly from the yaw rate sensor 25 of the sensor module 20
mounted on the trailer 12. Additionally or alternatively, the
trailer yaw rate .omega..sub.2 may be derived from the left and
right wheel speed sensors 23 on the trailer 12. Also, in addition
or in the alternative, the trailer yaw rate .omega..sub.2 may be
calculated using the trailer speed v.sub.2 and the lateral
acceleration a.sub.y2 of the trailer, as sensed by the
accelerometer 27 of the trailer sensor module 20, in one
embodiment. One embodiment to determine the trailer yaw rate
.omega..sub.2 is lateral acceleration a.sub.y2 of the trailer
divided by the trailer speed v.sub.2, where lateral acceleration
a.sub.y2 of the trailer may be derived from the accelerometer 27
and trailer speed v.sub.2 may be derived from the wheel speed
sensor.
[0094] When wheel speed sensors 23 are not available or otherwise
included on the trailer sensor module 20 or the sensor system 16,
the above-referenced kinematic equation may then be reordered to
solve for the trailer speed v.sub.2. As such, the accuracy of the
trailer speed v.sub.2 and the resultant calculated hitch angle
.gamma. will rely more heavily on the accuracy of the other sensors
utilized to determine the vehicle speed v.sub.1, vehicle yaw rate
.omega..sub.1, and the trailer yaw rate .omega..sub.2, as
previously mentioned, along with the accuracy of the vehicle and
trailer dimensions L and D.
[0095] As illustrated in FIG. 15, when the sensor signals have been
received and the necessary parameters received or otherwise
determined, at step 144, the controller 28 processes the following
equation, based on the kinematic relationship of the trailer 12 and
the vehicle 14, to solve for the instantaneous hitch angle
.gamma..
.gamma. = sin - 1 ( v 1 .omega. 2 D + .omega. 1 L v 1 2 + .omega. 1
2 L 2 - .omega. 2 2 D 2 v 1 2 + .omega. 1 2 L 2 ) ##EQU00009##
[0096] Further, should the sensor system 16 be unequipped to
provide the controller 28 with the trailer yaw rate .omega..sub.2,
in another embodiment, at step 144, the instantaneous hitch angle
.gamma. may still be determined, as follows:
.gamma. = sin - 1 v 2 .omega. 1 L .+-. v 1 v 1 2 + .omega. 1 2 L 2
- v 2 2 v 1 2 + .omega. 1 2 L 2 or ##EQU00010## .gamma. = sin - 1 v
2 v 1 2 + .omega. 1 2 L 2 - tan - 1 v 1 .omega. 1 L .
##EQU00010.2##
[0097] In this equation, the hitch angle .gamma. is determined
based on the vehicle speed v.sub.1, trailer speed v.sub.2, and
vehicle yaw rate .omega..sub.1, whereby such parameters are relied
upon more heavily for accuracy. The above equation solving for the
hitch angle .gamma. is based on a kinematic relationship for the
trailer speed v.sub.2, which does not incorporate the trailer yaw
rate .omega..sub.2. With this identified relationship, it is
conceivable that if the hitch angle is known by another means, such
the hitch angle sensor 44, and the trailer speed v.sub.2 may
therefore be solved for with the above equation. Also, trailer
speed v.sub.2 may be determined based on the trailer yaw rate
.omega..sub.2 and the lateral acceleration a.sub.y2 of the trailer,
such as from the trailer yaw rate sensor 25 and the accelerometer
27, respectively. Accordingly, when the trailer speed v.sub.2 is
sensed or otherwise determined from other variables, such as the
trailer yaw rate .omega..sub.2 and the lateral acceleration
a.sub.y2 of the trailer, then the hitch angle .gamma. calculation
may incorporate this parameter to provide a more accurate
value.
[0098] Referring again to FIG. 15, at step 146 the presently
estimated hitch angle .gamma. may be filtered to provide a more
accurate estimate. More specifically, the hitch angle .gamma.
estimated with the hitch angle estimation routine 130 may be less
accurate at low vehicle speed v.sub.1 when the denominator of the
above-noted equations approaches zero. In one embodiment, the hitch
angle .gamma. may be filtered by using the trailer yaw rate
.omega..sub.2 and the vehicle yaw rate .omega..sub.1. For instance,
the estimated hitch angle .gamma. could be filtered with a
discrete-time Kalman filter, whereby the filtered estimate is
obtained from the following equation:
{circumflex over (.gamma.)}.sub.k-1={circumflex over
(.gamma.)}.sub.k+(.omega..sub.2,k-.omega..sub.1,k0T.sub.s+K.sub.k(.gamma.-
.sub.k-{circumflex over (.gamma.)}.sub.k).
[0099] In this embodiment, T.sub.s is the sampling time, k is an
integer representing the k.sup.th sampling instance, K.sub.k is the
Kalman gain, and .gamma..sub.k is the calculated hitch angle from
the above-noted equations. However, when the vehicle 14 is stopped,
the filtered estimate is "frozen" at the previously known good
value (e.g. {circumflex over (.gamma.)}.sub.k+1={circumflex over
(.gamma.)}.sub.k). This is the filter to determine when the vehicle
14 is stopped or traveling at low speeds, as provided at step 148,
which precedes step 144. If the vehicle 14 is not determined to be
stopped or traveling slow at step 148, the hitch angle .gamma. is
estimated and filtered at steps 144 and 146, as described above.
When the result of an accurate hitch angle .gamma. from the
above-noted kinematic equations is temporarily not available or
inaccurate (e.g., at low speed), the filtered estimate is obtained
from the following equation:
{circumflex over (.gamma.)}.sub.k-1={circumflex over
(.gamma.)}.sub.k+(.omega..sub.2,k-.omega..sub.1,k)T.sub.s.
[0100] In an additional or alternative embodiment, the hitch angle
.gamma. may be filtered by using the vehicle yaw rate .omega..sub.1
and vehicle speed v.sub.1. For instance, this may be desired if the
trailer yaw rate .omega..sub.2 is noisy, whereby the filtering
described above and shown in FIG. 15 may not generate desired
results. In this case, a nonlinear extension of the Kalman filter
may be applied, which is often referred to as an extended Kalman
filter by those skilled in the art. To do so, when the results are
generally available and accurate for the hitch angle .gamma.
determined at step 144, such as when the vehicle 14 is moving a
sufficient speed, the filter may be estimated from the following
equation:
.gamma. ^ k + 1 = .gamma. ^ k + ( v 1 , k D sin .gamma. ^ k -
.omega. 1 , k L D cos .gamma. ^ k - .omega. 1 , k ) T s + K k (
.gamma. k - .gamma. ^ k ) ##EQU00011##
Accordingly, when the results are temporarily not available or
inaccurate for the hitch angle .gamma. determined at step 144, such
as at low speeds, the filtered estimate may is obtained from the
following equation:
.gamma. ^ k + 1 = .gamma. ^ k + ( v 1 , k D sin .gamma. ^ k -
.omega. 1 , k L D cos .gamma. ^ k - .omega. 1 , k ) T s
##EQU00012##
[0101] There are many alternative ways to express the Kalman gain,
and one of the formulations is given as follows:
A k = ( v 1 , k D cos .gamma. ^ k + .omega. 1 , k L D sin .gamma. ^
k ) T s + 1 , K k = P k ( P k + R ) - 1 , P k + 1 = A k ( 1 - K k )
P k A k T + Q , ##EQU00013##
[0102] where A.sub.k is the derivative matrix, Q is the process
noise covariance, R is the measurement noise covariance, and
P.sub.k is the estimation error covariance.
[0103] As shown in FIG. 15, upon estimating and filtering the hitch
angle .gamma., at step 152 the trailer length D and vehicle
wheelbase W can be estimated or refined to improve the accuracy of
later calculations. As such, trailer length D may be estimated
based on the trailer speed v.sub.2, the vehicle speed v.sub.1, the
vehicle yaw rate .omega..sub.1, and the trailer yaw rate
.omega..sub.2, as determined from the previous steps of the hitch
angle estimation routine 130. For instance, if the length L between
hitch point and rear axle of the vehicle 14 is measured or
otherwise known, the trailer length D can be calculated as
follows:
D = v 1 2 + .omega. 1 2 L 2 - v 2 2 .omega. 2 2 . ##EQU00014##
[0104] Similarly, if the trailer length D is measured or otherwise
known, the length L between hitch point and rear axle of the
vehicle 14 may be estimated based on the trailer speed v.sub.2, the
vehicle speed v.sub.1, the vehicle yaw rate .omega..sub.1, and the
trailer yaw rate .omega..sub.2, as determined from the previous
steps of the hitch angle estimation routine 130. As such, the
length L can be calculated as follows:
L = v 2 2 + .omega. 2 2 D 2 - v 1 2 .omega. 1 2 . ##EQU00015##
[0105] As also shown in FIG. 15, at step 154 the hitch angle
estimation routine 130 may proceed to estimate or refine the
trailer turning radius r.sub.2 and the curvature .kappa..sub.2 of
the trailer trajectory for improving the accuracy of later
calculations. This may be done using the following equations:
r 2 = v 2 .omega. 2 , and ##EQU00016## .kappa. 2 = .omega. 2 v 2 .
##EQU00016.2##
[0106] Referring again to FIG. 10, at step 160 the hitch angle
.gamma. is determined between the vehicle 14 and the trailer 12,
although this may be done continuously during operation of the
trailer backup assist system 10. It is contemplated that in
additional embodiments of the trailer backup assist system 10 that
the steps of determining the kinematic relationship and sensing the
hitch angle .gamma. may occur before the trailer backup assist
system 10 is activated or at any other time before steering
commands are generated. Accordingly, at step 162, the position and
rate of changes is received from the steering input device 18, such
as the angular position and rate of rotation of the rotatable knob
30, for determining the desired curvature 26. At step 164, steering
commands may be generated based on the desired curvature,
correlating with the position and rate of change of the steering
input device 18. The steering commands and actuation commands
generated may be generated in conjunction with processing of the
curvature routine 98, as previous discussed. At step 166, the
steering commands and actuation commands have been executed to
guide the trailer 12 on the desired curvature provided by the
steering input device 18.
[0107] In parallel with performing the operations for receiving the
trailer backup assist requests, determining the desired curvature
26 of the trailer 12, and generating the vehicle steering commands,
the trailer backup assist system 10 may perform an operation for
monitoring if an unacceptable trailer backup condition exists.
Examples of such monitoring include, but are not limited to
assessing a hitch angle .gamma. to determine if a hitch angle
.gamma. threshold is exceeded, assessing a backup speed to
determine if a backup speed threshold is exceeded, assessing
vehicle steering angle to determine if a vehicle steering angle
threshold is exceeded, assessing other operating parameters (e.g.,
vehicle longitudinal acceleration, throttle pedal demand rate and
hitch angle rate) for determining if a respective threshold value
is exceeded, and the like. Backup speed can be determined from the
wheel speed information obtained from one or more wheel speed
sensors 58 of the vehicle 14. If it is determined that an
unacceptable trailer backup condition exists, an operation may be
performed for causing the current path of travel of the trailer 12
to be inhibited (e.g., stopping motion of the vehicle 14), followed
by the operation being performed for ending the current trailer
backup assist instance. It is disclosed herein that prior to and/or
in conjunction with causing the current trailer path to be
inhibited, one or more actions (e.g., operations) can be
implemented for providing the driver with feedback (e.g., a
warning) that such an unacceptable hitch angle condition is
impending or approaching. In one example, if such feedback results
in the unacceptable hitch angle condition being remedied prior to
achieving a critical condition, the method can continue with
providing trailer backup assist functionality in accordance with
operations. Otherwise, the method can proceed to operation for
ending the current trailer backup assist instance. In conjunction
with performing the operation for ending the current trailer backup
assist instance, an operation can be performed for controlling
movement of the vehicle 14 to correct or limit a jackknife
condition (e.g., steering the vehicle 14, decelerating the vehicle
14, limiting magnitude and/or rate of driver requested trailer
curvature input, limiting magnitude and/or rate of the steering
command, and/or the like to preclude the hitch angle from being
exceeded).
[0108] With the sensor system 16 and/or controller 28 providing the
trailer yaw rate .omega..sub.2, this parameter may additionally or
alternatively be utilized to improve the electronic stability
control provided with the power assist steering system 62 when the
vehicle 14 is towing a trailer. Some electronic stability control
systems use a so called bicycle model (without trailer) to obtain a
reference vehicle yaw rate commanded by the driver. However, when
the vehicle is towing a trailer, the towing vehicle may exhibit
more oversteer or more understeer tendencies during a turn,
compared to the same vehicle without a trailer attached. Thus the
electronic stability control performance may degrade, and/or
unintended activations may occur, when the vehicle is towing a
trailer.
[0109] By using the sensed or otherwise determined trailer yaw rate
signal .omega..sub.2, together with other electronic stability
control signals, the additional oversteer or understeer tendencies
of the vehicle (compared to when not towing a trailer) can be
identified. Accordingly, the existing electronic stability control
system can be sensitized or desensitized (e.g., by modifying the
control thresholds for the brake and engine controllers). The brake
and engine control actions can also be increased or reduced by
changing the controller gains. Therefore, an additional controller
which uses trailer yaw rate signal .omega..sub.2 (or the difference
between trailer and vehicle yaw /rate, i.e.,
.omega..sub.2-.omega..sub.1) and its derivative may be integrated
with the existing electronic stability control system. Such a
controller is beneficial for improving the overall vehicle-trailer
combination stability
[0110] In addition, it is contemplated that using the trailer yaw
rate signal .omega..sub.2 and trailer lateral acceleration signal
a.sub.y2, together with other standard electronic stability control
signals, may further identify additional oversteer or understeer
tendencies of the vehicle. It is also conceivable that a controller
that uses the trailer hitch angle .gamma. as a feedback signal may
be integrated with the existing electronic stability control system
for improving the overall vehicle-trailer combination
stability.
[0111] As previously mentioned, the hitch angle .gamma. determined
by the hitch angle estimation routine 130 may also be used to
identify and stabilize a swaying trailer. More specifically, the
vehicle-trailer combination becomes less damped when its speed is
increased. With any driver inputs or external disturbances, the
trailer may start to oscillate and the oscillation may sustain for
a long time. If the speed is above certain "critical speed", the
system may become unstable, causing the oscillation amplitude to
grow larger and eventually cause vehicle instability and/or a
jackknife condition. A controller which uses trailer yaw rate
signal .omega..sub.2 (or the difference between trailer and vehicle
yaw rate, i.e., .omega..sub.2-.omega..sub.1) and its derivative can
be designed to actively control the vehicle/trailer to damping out
the oscillation. In addition, the trailer yaw rate .omega..sub.2
and the trailer lateral acceleration a.sub.y2, together with other
standard electronic stability control signals, may be used to
stabilize a swaying trailer. Since both trailer yaw rate signal
.omega..sub.2 and trailer lateral acceleration signal a.sub.y2
directly provide information about the trailer motion, they can be
used to quickly identify whether the trailer is swaying.
[0112] It will be understood by one having ordinary skill in the
art that construction of the described invention and other
components is not limited to any specific material. Other exemplary
embodiments of the invention disclosed herein may be formed from a
wide variety of materials, unless described otherwise herein.
[0113] For purposes of this disclosure, the term "coupled" (in all
of its forms, couple, coupling, coupled, etc.) generally means the
joining of two components (electrical or mechanical) directly or
indirectly to one another. Such joining may be stationary in nature
or movable in nature. Such joining may be achieved with the two
components (electrical or mechanical) and any additional
intermediate members being integrally formed as a single unitary
body with one another or with the two components. Such joining may
be permanent in nature or may be removable or releasable in nature
unless otherwise stated.
[0114] It is also important to note that the construction and
arrangement of the elements of the invention as shown in the
exemplary embodiments is illustrative only. Although only a few
embodiments of the present innovations have been described in
detail in this disclosure, those skilled in the art who review this
disclosure will readily appreciate that many modifications are
possible (e.g., variations in sizes, dimensions, structures, shapes
and proportions of the various elements, values of parameters,
mounting arrangements, use of materials, colors, orientations,
etc.) without materially departing from the novel teachings and
advantages of the subject matter recited. For example, elements
shown as integrally formed may be constructed of multiple parts or
elements shown as multiple parts may be integrally formed, the
operation of the interfaces may be reversed or otherwise varied,
the length or width of the structures and/or members or connector
or other elements of the system may be varied, the nature or number
of adjustment positions provided between the elements may be
varied. It should be noted that the elements and/or assemblies of
the system may be constructed from any of a wide variety of
materials that provide sufficient strength or durability, in any of
a wide variety of colors, textures, and combinations. Accordingly,
all such modifications are intended to be included within the scope
of the present innovations. Other substitutions, modifications,
changes, and omissions may be made in the design, operating
conditions, and arrangement of the desired and other exemplary
embodiments without departing from the spirit of the present
innovations.
[0115] It will be understood that any described processes or steps
within described processes may be combined with other disclosed
processes or steps to form structures within the scope of the
present invention. The exemplary structures and processes disclosed
herein are for illustrative purposes and are not to be construed as
limiting.
[0116] It is also to be understood that variations and
modifications can be made on the aforementioned structures and
methods without departing from the concepts of the present
invention, and further it is to be understood that such concepts
are intended to be covered by the following claims unless these
claims by their language expressly state otherwise.
* * * * *