U.S. patent application number 11/936860 was filed with the patent office on 2008-09-25 for vehicle maneuvering aids.
Invention is credited to Andrew Stephen Bell Crawford, Jeremy John Greenwood, Stephen Nicholls.
Application Number | 20080231701 11/936860 |
Document ID | / |
Family ID | 38008758 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080231701 |
Kind Code |
A1 |
Greenwood; Jeremy John ; et
al. |
September 25, 2008 |
VEHICLE MANEUVERING AIDS
Abstract
A vehicle 1 towing a trailer 4 is fitted with three video
cameras 5, 6, 7 fitted to the rear of the vehicle and on each door
mirror. A view from any camera can be presented to the driver on a
display 11. A predicted trailer path, calculated in a computing
unit 10, is also presented to the driver on the display 11 as guide
lines overlaid on the camera view. The computing unit 10 is also
configured to calculate a hitch angle by tracking the position of a
trailer-mounted marker in the camera view.
Inventors: |
Greenwood; Jeremy John;
(Sutton Coldfield, GB) ; Nicholls; Stephen; (Long
Hanborough, GB) ; Crawford; Andrew Stephen Bell;
(Warwick, GB) |
Correspondence
Address: |
FORD GLOBAL TECHNOLOGIES, LLC
FAIRLANE PLAZA SOUTH, SUITE 800, 330 TOWN CENTER DRIVE
DEARBORN
MI
48126
US
|
Family ID: |
38008758 |
Appl. No.: |
11/936860 |
Filed: |
November 8, 2007 |
Current U.S.
Class: |
348/148 ;
348/E7.085 |
Current CPC
Class: |
G06T 7/20 20130101; B60R
2300/50 20130101; B62D 13/06 20130101; B62D 15/021 20130101; B60R
1/003 20130101; G08G 1/168 20130101; G06K 9/00791 20130101; B60R
2300/108 20130101; B60R 2300/301 20130101; H04N 5/2253 20130101;
G08G 1/167 20130101; B60R 2300/8086 20130101; B60R 1/00 20130101;
B60R 2300/305 20130101; B60W 50/14 20130101; G08G 1/16 20130101;
G01B 11/272 20130101; G08G 1/166 20130101; B62D 15/024 20130101;
H04N 7/183 20130101; B60R 2300/101 20130101; B60R 2300/802
20130101; G06T 7/0008 20130101; B60R 2300/806 20130101; B60R
2300/8093 20130101; B60W 2050/143 20130101 |
Class at
Publication: |
348/148 ;
348/E07.085 |
International
Class: |
H04N 7/18 20060101
H04N007/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2007 |
GB |
0705336.6 |
Claims
1. An apparatus displaying the predicted path of a trailer attached
to a vehicle, comprising: at least one rearward-looking video
camera having an output; a steering angle sensor outputting the
steering angle of the vehicle; a computing unit receiving the video
camera output and steering angle and computing a predicted trailer
path; and a display displaying the video camera output and the
predicted trailer path.
2. The apparatus of claim 1, wherein the predicted trailer has
wheels and the predicted trailer path is represented as overlay
tracks beginning at the trailer wheels.
3. The apparatus of claim 2, wherein the predicted trailer path is
shown while traveling in a forwards direction.
4. The apparatus of claim 1, wherein the computing unit derives a
hitch angle .theta..sub.t from the camera output and uses the hitch
angle .theta..sub.t to determine the predicted trailer path.
5. The apparatus of claim 1, wherein said at least one
rearward-looking video camera comprises a camera mounted on each
vehicle side mirror.
6. The apparatus of claim 1, wherein the trailer has a geometry and
further comprising a store receiving the trailer geometry.
7. The apparatus of claim 6, further comprising the computing unit
learning the trailer geometry from observing a maneuver and storing
the learned geometry in the store.
8. An apparatus displaying the predicted path of a trailer having
trailer wheels attached to a vehicle, comprising: at least one
rearward-looking video camera mounted on each vehicle side mirror
having an output; a steering angle sensor outputting the steering
angle of the vehicle; a computing unit receiving the video camera
output and steering angle and derives a hitch angle .theta..sub.t
from the camera output and uses the hitch angle .theta..sub.t to
determine the predicted trailer path; and a display displaying the
video camera output and the predicted trailer path is represented
as overlay tracks beginning at the trailer wheels.
9. An apparatus tracking objects close to the path of a vehicle,
comprising: at least one vehicle-mounted video camera with pan
capability, the camera having an output; a vehicle-mounted
proximity sensor sensing the location of the object; a steering
angle sensor outputting the steering angle of the vehicle; a speed
sensor outputting the speed of the vehicle; a computing unit
receiving the speed and steering angle and calculating a relative
position of the object and panning the camera to follow the object;
and a display displaying the video camera output.
10. The apparatus of claim 9, wherein the camera further comprises
zoom capability and the computing unit zooms the camera when
following the object.
11. An apparatus informing a vehicle when a trailer is hitched to
the vehicle, comprising a rearward-looking camera having an output;
and an image processor receiving the output and comparing the
output with parameters stored in a store to determine the presence
of the trailer.
12. The apparatus of claim 11, further comprising comparing the
output with the stored parameters to determine the type of
trailer.
13. The apparatus of claim 12, further comprising using the trailer
type in a vehicle control system.
14. The apparatus of claim 13, wherein the vehicle control system
is a stability control system and the type of trailer is trailer
weight.
15. The apparatus of claim 12, wherein the trailer type is
confirmed by monitoring the dynamic behavior of the vehicle and
trailer.
16. An apparatus for assisting in hitching a trailer having a tow
hitch to a vehicle, comprising: at least one vehicle-mounted video
camera having an output; an image processor receiving the camera
output and identifying the tow hitch and displaying the output as
an image; a display displaying the image, the image processor
zooming the image to display a close-up of the tow hitch and
adjusting the image zoom as the vehicle moves relative to the
trailer to maintain the tow hitch in the image.
17. The apparatus of claim 16, further comprising a steering angle
sensor outputting the steering angle of the vehicle; a computing
unit receiving the video camera output and steering angle and
computing a projected vehicle trajectory; and displaying the
projected vehicle trajectory overlaid as a guide line on the zoomed
image.
18. The apparatus of claim 17, wherein the vehicle has a tow ball
not visible to the camera and further comprising displaying a
virtual location of the tow ball on the display.
19. A method of predicting the path of a trailer attached to a
vehicle comprising the steps of: obtaining a view from a first
rearward-looking, vehicle-mounted video camera on a screen visible
to the driver; determining the predicted path of the trailer;
displaying the predicted trailer path as an overlaid track on the
rearward-looking view.
20. The method of claim 19, further comprising the step of
determining a hitch length, H, between an axle of the trailer and a
point of attachment of the trailer to the vehicle and using H to
calculate the predicted trailer path.
21. The method of claim 19, further comprising the step of
determining a hitch angle, .theta..sub.t, between the vehicle and
trailer and using .theta..sub.t to calculate the predicted trailer
path.
22. The method of claim 19, further comprising the step of
calculating a turning radius R where R=H/.theta..sub.t, where the
trailer is predicted to follow the circumference of a circle of
radius R and using R to calculate the predicted trailer path.
23. The method of claim 19, further comprising the steps of:
determining a hitch length, H, between an axle of the trailer and a
point of attachment of the trailer to the vehicle; determining a
hitch angle, .theta..sub.t, between the vehicle and trailer;
calculating a turning radius R where R=H/.theta..sub.t, where the
trailer is predicted to follow the circumference of a circle of
radius R; and using H, .theta..sub.t, and R to calculate the
predicted trailer path.
24. The method of claim 21, wherein the hitch length H is
determined by driving the vehicle-trailer combination in a circular
path, while measuring a vehicle steering angle .theta..sub.s,
calculating the radius R of the circular path from .theta..sub.s
and knowledge of the dimensions of the vehicle, measuring a hitch
angle .theta..sub.t and calculating a hitch length H from the
relationship H=R.theta..sub.t.
25. The method of claim 19, further comprising the steps of:
obtaining a view from a second rearward-looking, vehicle-mounted
video camera, determining which of the first and second camera
views shows the trailer; and displaying the determined view on the
screen.
26. The method of claim 21, wherein the hitch angle .theta..sub.t
is determined by the steps of: tracking a marker associated with
the trailer across a field of view of the rearward-looking video
camera; and converting a lateral displacement of the marker in the
field of view to an angular displacement.
27. A method of predicting the path of a trailer attached to a
vehicle comprising the steps of: measuring the vehicle steering
angle; obtaining first and second views from at least two
rearward-looking, vehicle-mounted video cameras; determining a
trailer view from the first and second camera views; displaying the
trailer view on a screen visible to the driver; determining a hitch
angle, .theta..sub.t, between the vehicle and trailer and using the
trailer view; calculating a predicted path of the trailer from the
hitch angle and steering angle; and displaying the predicted
trailer path as an overlaid track on the trailer view.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] None
BACKGROUND OF THE INVENTION
[0002] This invention relates to maneuvering aids for vehicles and
particularly for vehicles which are towing a trailer, such as a
caravan.
[0003] It is known to equip vehicles with external video cameras
for displaying to the driver an image of the surroundings in order
to provide assistance with parking and reversing maneuvers. A track
for a given steering angle can be superimposed on the displayed
image including systems that display the view from a
rearward-looking video camera onto a touch screen which is used to
input a desired destination, such as a parking bay. Steering cues
are also displayed on the screen for assisting the driver in the
maneuvering operation.
BRIEF DESCRIPTION OF THE INVENTION
[0004] A first feature provides a method for determining hitch
angle in a vertical or horizontal plane between a vehicle and a
trailer attached to the vehicle by means of a tow hitch. The method
includes the steps of tracking a marker associated with the trailer
across a field of view of a rearward-looking video camera and
converting a lateral displacement of the marker in the field of
view to an angular displacement.
[0005] A second feature provides a means for predicting a path of a
trailer and displaying the predicted path to the driver of a
vehicle to which the trailer is attached. The path being displayed
as an overlay on a view from a vehicle-mounted video camera. One
method of predicting the trailer path includes the steps of
determining a hitch angle, .theta..sub.t, between the vehicle and
trailer, determining a hitch length, H, between an axle of the
trailer and a point of attachment of the trailer to the vehicle,
calculating a turning radius R where R=H/.theta..sub.t, where the
trailer is predicted to follow the circumference of a circle of
radius R. A view from a video camera mounted on the rear of the
vehicle or on a door mirror is utilized.
[0006] A third feature tracks obstacles close to the path of a
vehicle using multiple vehicle-mounted video cameras with pan and
zoom capability. One method of tracking these obstacles includes
the steps of detecting the proximity of an obstacle using a
vehicle-mounted proximity sensor, panning a vehicle-mounted video
camera towards the location of the obstacle, and displaying a video
camera view of the obstacle to a driver of the vehicle. A fourth
feature reliably informs the vehicle and driver when a trailer is
hitched to the vehicle. This is so that systems concerned with
dynamic stability control or active suspension, e.g. can be set to
the correct operating conditions. Systems that only monitor the
trailer's electrical connection cannot distinguish between a
trailer and light bars. A rearward-looking camera may be used to
detect the presence of a trailer. One method of detecting the
trailer includes the steps of comparing an image from a
rearward-looking, vehicle mounted video camera with stored data
representing a trailer. A fifth feature provides a method for
assisting in hitching a trailer to a vehicle. One method of
assisting includes the steps of displaying a view from a
rearward-looking, vehicle-mounted video camera on a screen visible
to the driver, identifying a tow hitch in the displayed view,
zooming the camera view to display a close-up of the vehicle's tow
ball and the trailer's tow hitch and adjusting the camera's zoom
facility as the vehicle and trailer move relative to one another to
maintain a displayed view of the tow ball and hitch.
[0007] A sixth feature includes using one or more vehicle-mounted
cameras configured to detect strobed light, such as that emitted by
emergency vehicles. A warning message can then be generated for
display to the driver of the vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic view of a trailer and vehicle, the
latter incorporating apparatus for effecting methods of assisting
maneuvers of the trailer-vehicle combination, and
[0009] FIGS. 2 and 3 are plan views of the vehicle-trailer
combination of FIG. 1 showing certain geometrical parameters of the
combination.
DETAILED DESCRIPTION OF THE INVENTION
[0010] In FIG. 1 a vehicle 1 is provided with a tow ball 2 to which
the hitch 3 of a trailer 4 is attached.
[0011] The vehicle 1 is fitted with three video cameras. A first
video camera 5 is mounted on the rear of the vehicle 1 and looks
rearwards towards the trailer 4. This rearward-looking camera has a
zoom facility. Two door mirror mounted video cameras 6, 7 are also
provided. These door mirror mounted cameras 6, 7 may be panned so
that they look forwards, rearwards and to a side of the vehicle 1.
All three cameras 5, 6, 7 are controlled by a camera controller 8
and the outputs from each camera are fed to an image processor
9.
[0012] Outputs of the image processor 9 are fed to a computing unit
10 and display screen 11 and the camera controller 8. The computing
unit 10 generates signals for controlling the camera controller 8
and display screen 11 which is visible to the driver of the vehicle
1. The computing unit 10 receives signals from a speed sensor 12, a
steering angle sensor 13 and a vehicle and trailer parameter store
14. A mode selector switch 15 has an output which is connected to
the image processor 9.
[0013] Ultrasonic parking distance sensors 16-23 are provided on
the front and the rear of the vehicle. Their outputs are connected
to the camera controller 8. Four sensors are fitted at each end of
the vehicle in order to give good coverage and resolution.
[0014] Operation of a first embodiment, comprising a method of
measuring the hitch angle (in a horizontal plane between the
vehicle 1 and the trailer 4) will now be described with reference
to FIGS. 1 and 2. The method utilizes a tracking marker such as a
mark or sticker attached to the trailer or a vertical edge of the
trailer which is visible to the rearward-looking video camera 5.
The image processor 9 locates this marker within the camera's field
of view and feeds this information to the computing unit 10 which
calculates the hitch angle.
[0015] In a first example, a high visibility marker 24 is placed on
the centre-line of the trailer 4 (see FIG. 2). From knowledge of
the trailer and vehicle geometric parameters e.g. tow hitch length
(held in the store 14) and the position of the marker within the
camera's 5 field of view, the computing unit 10 can calculate the
hitch angle .theta..sub.t. Placement of the marker on the trailer's
centre-line may not always be possible or convenient. So in a
second example, a marker 25 is placed offset from the centre-line
by an offset angle .theta..sub.o. Then, the hitch
angle=.theta..sub.c-.theta..sub.o where .theta..sub.c is the target
angle which is calculated in the computing unit 10.
[0016] The offset angle .theta..sub.o is derived by the computing
unit 10, in a learning phase, by noting the value of .theta..sub.c
when the vehicle is traveling in a straight line, i.e. when the
steering angle sensor 13 outputs a value of zero for steering angle
.theta..sub.s. So, when this condition is fulfilled,
.theta..sub.o=.theta..sub.c, so the offset angle is now known.
[0017] Extending the principle of the above second example, the
image processor 9 can pick out its own marker on the trailer 4.
This could be a caravan window or an edge of the trailer, for
example. The feature selected can be highlighted on the display
screen 11 so that the driver can confirm that it is actually
rigidly connected to the trailer. The computing unit 10 is then
adapted to compare the movement of this target with steering
movements and check for any anomalies.
[0018] As a refinement to the hitch angle calculation, some
averaging of the measurements is carried out, particularly in the
learning phase. This helps to cancel out the errors due to flexing
of the trailer structure.
[0019] The learning phase can be eliminated on trailer re-use. The
computing unit 10 can store the learned geometry of the trailer so
that it can be recalled. Alternatively, the learning phase can be
run continually as a check on the stored values with updating as
required. This continual check is useful in any case as a
compensation for drift due to other variables.
[0020] By comparing the measured hitch angle .theta..sub.t with a
reference value held in the store 14 for a given trailer length,
the computing unit 10 can detect the onset of jack-knifing while
reversing. When this occurs, the computing unit 10 generates a
warning signal to the driver. This warning can be audible or a
visual signal on the display screen 11.
[0021] In addition to measuring hitch angle, the invention provides
a method for measuring the pitch angle (i.e. in a vertical plane),
between the vehicle 1 and trailer 4. Pitch angle is usually zero or
close to zero but can deviate from zero when traveling on uneven
ground or reversing down a slipway, for example. The same
principles apply, with the image processor 9 selecting a mark or
horizontal edge of the trailer. By comparing the pitch angle
determined by the computing unit 10 with a reference value, the
unit 10 can detect imminent grounding of the hitch 3 and signal a
warning to the driver.
[0022] A second embodiment of the invention provides a method of
predicting a trailer reversing path and displaying it to the driver
by means of an overlay on the display.
[0023] Say, for example, the driver needs to reverse the vehicle
and trailer combination into a parking bay.
[0024] Knowing the hitch angle .theta..sub.t, (either from the
method of the first embodiment described above or from some other
method or sensor output), and the hitch length H (the distance
between the trailer's axle and tow hitch, see FIG. 3) the computing
unit 10 computes a trailer path.
[0025] The path of the trailer 4 can be described by a turning
radius R. In practice R and .theta..sub.t vary during the maneuver
but for small steering angle movements can be assumed to be
constant. With reference to FIG. 3, it can be seen that the hitch
angle .theta..sub.t, hitch length H and turning radius R are
associated approximately by equation:
.alpha.+.beta.+.delta.=.pi.
[0026] Substituting .beta.=.pi./2 and
.alpha.=.pi./2-.theta..sub.t
[0027] gives .theta..sub.t=.delta.
[0028] tan .delta.=H/R=.delta.=.theta..sub.t for small
.theta..sub.t
So R=H/.theta..sub.t (.theta..sub.t in radians) Equation (1)
[0029] The hitch length H may be manually entered into the store 14
for the particular trailer 4 or it may be calculated in the
computing unit 10 while the driver performs the following
maneuver.
[0030] The vehicle-trailer combination is driven in a circular path
and R is derived from the steering angle, .theta..sub.s, and the
dimensions of the vehicle. The value of .theta..sub.t is derived
from the camera 5 view. These values are then inserted into
equation (1) to give a value for H.
[0031] In an alternative learning process for hitch length, H,
while the vehicle-trailer combination is being driven, the value of
.theta..sub.t calculated from equation (1) using a calculated value
for R (from steering angle and vehicle dimensions) and an estimate
for H is compared with the measured value of .theta..sub.t. The
value of H is varied in subsequent calculations until the best
match is achieved with the measured value for .theta..sub.t. This
value of H is then stored.
[0032] The path of the reversing trailer 4 computed by the
computing unit 10 is displayed on the display screen 11 as an
overlay on top of the view from one of the cameras 5, 6, 7. The
path is computed by building up incremental changes as a function
of .theta..sub.t and R. The projected path is continuously updated
as the steering angle .theta..sub.s and consequently the hitch
angle .theta..sub.t vary.
[0033] The path can be overlaid on the rear camera's view, but will
only be useful to the driver if the rear corners of the trailer are
also displayed, e.g. for a low trailer. For a large trailer, e.g. a
caravan, this is not so useful. In this latter case, the projected
path is overlaid on to a view from one of the door mirror mounted
cameras 6, 7, specifically, the camera which can see the trailer 4
at that particular moment in the maneuver. A correction has to be
applied, however, if the trailer path is calculated with respect to
the rear camera view.
[0034] Any misalignment in either camera will introduce errors in
the information presented to the driver. This is remedied by
electronically adjusting the view from the camera by aligning the
image (or at least, the pixel data) with known hard points on the
vehicle. For example, the mirror camera is looking rearwards but is
misaligned laterally. The image processor 9 re-aligns the image to
correct the alignment. Taken to the extreme, this will allow the
arrangement to be used with the mirror folded in.
[0035] This embodiment can be extended to show the path of the
trailer wheels while traveling in a forwards direction so that
"kerbing" of the inside trailer wheels can be avoided on sharp
bends. Conveniently, the trailer's path can be overlaid on the view
from a forward-looking, door mirror mounted camera.
[0036] The learning process can be eliminated on trailer re-use.
The store 14 can store the learned geometry of the trailer so that
it can be recalled. Reversing assistance is then available straight
away. The learning process is then run continually as a check on
the stored values with updating as required. This continual check
is useful in any case as a compensation for drift due to other
variables.
[0037] The overlay tracks showing the projected path of the trailer
can, conveniently have their starting point at the trailer's
wheels. If the pitch angle of the tow hitch changes markedly then
the guide lines comprising the overlay can appear to be in mid air
rather than on the ground. If the pitch angle is known, then the
computing unit 10 can effect a correction to the guide lines.
[0038] Operation of a third embodiment of the invention, which
facilitates the tracking of obstacles, will now be described.
[0039] In this example, the door mirror mounted cameras 6, 7 are
triggered by one or more of the parking distance sensors 16-19 when
the vehicle comes within close range of an object. On the display
screen 11, the driver will be presented with a view of the obstacle
and a part of the exterior of the vehicle closest to it.
[0040] In an off-road or other tight maneuvering situation, the
driver may want to continue to observe the object while driving
past it. For example, while driving past a boulder, the driver will
want to ensure that the boulder is not contacted by the side of the
vehicle.
[0041] Clearly it is possible for the driver to manually control
the camera to adjust its aim while driving past the object.
However, this requires intervention by the driver and may distract
him/her from other driving tasks.
[0042] This embodiment makes use of the ability of the cameras 6, 7
to pan and zoom electronically.
[0043] By virtue of the parking distance sensors 16-23 the location
of an object relative to the vehicle 1 is known. This information
is fed to the camera controller 7 so that the most appropriately
located camera can be panned and zoomed in towards the position of
the detected obstacle.
[0044] As a further refinement, the computing unit 10 is also
provided with the location of the object relative to the vehicle
along with steering angle (from the sensor 13) and speed (from the
speed sensor 12).
[0045] As the vehicle moves onwards, the relative position of the
object can be calculated from the wheel speeds combined with the
steering angle or from individual wheel speeds. Hence an
approximate real time location can be calculated and the camera
panned to follow the object without driver intervention, with the
computing unit 10 providing a control signal for the camera
controller 7.
[0046] There may be instances where the ground is slippery causing
individual wheels to slip or the vehicle to slide. In such cases,
speed measurements and/or steering measurements will be in error.
To overcome this problem, the image processor 9 is adapted to
analyze the image and match the object in the field of view between
consecutive frames. This will allow ground velocity errors to be
detected and corrected. For example, if the vehicle is sliding
sideways towards the object, the camera can be made to pan towards
the vehicle.
[0047] As a further enhancement to this second embodiment, the same
recognition algorithm is employed in the image processor to enable
the cameras 6, 7 to follow a moving object, following initial
detection by the parking distance sensors 16-23.
[0048] For example, a child or animal which has been detected is
shown as an image on the display screen 11 by the relevant camera.
The image processor 9 then tracks the child's (or animal's)
position through consecutive frames and the camera controller 7
adjusts pan and zoom controls to keep the moving object in the
field of view.
[0049] The video cameras 6, 7, 8 may have an enhanced infra-red
capability so that they are particularly sensitive in locating hot
objects such as people and animals. Such "hot-spots" can be
identified by the image processor 9 and highlighted on the display
screen 11.
[0050] In an alternative arrangement, the zooming and panning
operations are performed by the computing unit 10 instead of by the
cameras 6, 7.
[0051] Operation of a fourth embodiment, which enables detection of
a trailer, will now be described.
[0052] The rearward facing camera 5 detects the presence of the
trailer 4 and sends its image to the computing unit 10 via the
image processor 9. By comparing the received image with parameters
stored in the store 14, the computing unit can determine the type
of trailer, e.g. caravan, low loader etc. The size and shape of the
trailer can thus give an indication of its weight and aerodynamic
drag. This information can be used by vehicle systems such as
stability control systems.
[0053] Once the vehicle-trailer combination is on the move, the
trailer type can further be confirmed by monitoring the dynamic
behavior of the combination using on-board sensors (not shown).
[0054] Operation of a fifth embodiment will now be described. This
embodiment provides a means for assisting in attaching the trailer
4 to the vehicle 1.
[0055] Using the camera system shown, it is possible to simplify
the trailer hitching process in that both the trailer and the tow
hitch can be seen in a camera image by the driver. This allows
hitching of a trailer without the need for external guidance.
[0056] However, the image must necessarily be wide to allow the
trailer to be approached but then the image of the tow ball and
hitch are small and difficult to resolve. Also, the driver's
judgment is still required to steer the vehicle appropriately based
on the image.
[0057] This embodiment provides a solution to both these problems.
The rear camera image is processed in the image processor 9.
[0058] Firstly, the driver selects a "hitch mode" using the mode
selector switch 15. In response, the image processor 9 selects the
rear camera view to display on the screen 11 and searches for an
object with the triangular shape and size characteristics of a
typical A-frame tow hitch. When detected, the image is zoomed in to
contain the vehicle tow ball 2 and the tow hitch 3. This can be
done electronically by the computing unit 10 or by activating a
zoom facility on the camera 5 via the camera controller 7.
[0059] There may be an optional "confirm" function for the driver
to confirm that the identified object is the trailer or to adjust
the location for unusually shaped hitches. As the vehicle
approaches (or moves away from) the trailer, the zoom setting is
adjusted to maintain the view of both the hitch and tow ball.
Consequently, when the tow ball 2 is close to the hitch 3, the
driver will be given the optimum view to allow accurate
alignment.
[0060] In an alternative mode of operation, the image processor 9
is continuously monitoring the rear camera's output and the driver
does not need to use the mode selector switch. On detection of the
hitch 3, the image processor 9 presents the rear camera view to the
display 11.
[0061] Optionally, and as an additional safety feature, if the
parking distance sensors 16-23 detect an object in the path of the
vehicle and close enough to risk a collision but outside the zoomed
image, the image is zoomed out to show the object.
[0062] In a further mode of operation of this fourth embodiment,
the computing unit 10 generates an overlay image on the display
screen 11 which is the projected trajectory of the tow ball 2. This
is calculated from the vehicle's steering angle (provided by the
steering angle sensor 13) and from vehicle geometry parameters held
in the store 14. (This projected trajectory can assist in initially
finding the hitch by panning the camera to look along the
trajectory).
[0063] The trajectory is overlaid as a guide line on the zoomed
image. In this way, the driver can adjust the steering angle to
cause the trajectory and hitch to coincide. Reversing the vehicle
will then place the hitch over the tow ball.
[0064] In some vehicles, it may not be possible to locate a camera
on the body of the vehicle such that it has the view of the tow
ball. For example, the tow ball may be obscured by the bumper. In
this case, a "virtual tow ball" is applied to the image, i.e. a dot
vertically above the actual location of the tow ball, to allow
alignment and ranging of the hitching operation. The exact
placement of the dot can be determined with reference to other
fixed points in the image, e.g. the periphery of the vehicle as
well as a predetermined absolute position. This allows for
tolerance in the installation of the camera.
[0065] As the computing unit 10 knows the location of the tow ball
2 and the hitch 3 and also knows the current steering angle, it is
possible to display to the driver instructions to steer left or
right to optimize the alignment.
[0066] This could be integrated with other vehicle control
mechanisms (not shown) such that the guidance information is
applied automatically via the power steering system to steer the
vehicle to align the tow hitch. The brake and throttle could be
controlled automatically as well.
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