Note: Descriptions are shown in the official language in which they were submitted.
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TRAILER BACKING UP DEVICE AND TABLE BASED METHOD
FIELD OF THE INVENTION
The present invention relates to trailer systems, and more particularly to
trailer systems
comprising means to direct the vehicle in which way to steer so as to
precisely back and
control the direction of a trailer while pushing that trailer.
SUMMARY OF THE INVENTION
Trailers have been around for many years, yet every summer and winter one can
observe
the owners of boats and snowmobiles, respectively, backing up those devices on
trailers
with great difficulty. The problem arises from the fact that a trailer being
backed-up is an
inherently unstable system. A trailer being pushed wants to turn around and be
pulled
(i.e., to jackknife) instead. To compensate for this instability, the driver
must skillfully
alternate the direction of his steerin& so as to cause the trailer to want to
turn around and
be pulled from opposite sides thereby repeatedly crossing the centerline of
the pushing
vehicle. The moment when the trailer crosses this centerline is the moment
when the
system goes unstable and yet is the position in which the driver would most
desire to
have the trailer travel.
Prior art reveals several attempts to address the problems associated with
backing a
trailer. The simplest solutions address parts of the problem ranging from ways
of sensing
the angle of the hitch
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(see: Kollitz, U.S. Pat. No. 4,122,390), to sensing and displaying the angle
of the hitch (see: Gavit,
U.S. Pat. No. 3,833,928), to sounding an alarm when a jackknife condition
exists or is imminent
(see: Kimmel, U.S. Pat. No. 4,040,006). While these solutions are helpful,
they only each address a
part of the backing problem.
To be most beneficial, the solution must address the whole problem.
Furthermore, a solution must
be economical, be simple in operation, and be adaptable to most two-vehicle
configurations
(wherein one vehicle is powered and controls the backing and the other is the
trailer). Solutions
such as Kendall proposed in his U.S. Pat. No. 5,247,442 is a complete solution
but fails some of
these tests. The Kendall solution utilizes a wound up string that is pulled
out towards the desired
direction of travel of the trailer, making it complex to use and potentially
requiring multiple
operators for safe operation. A superior solution, as will be shown herein, is
to solve the basic
mathematical relationships rather than comparing the differences between the
angle of an unfurled
string and the trailer's bumper as an approximation of the steering error for
which the system must
correct. Furthermore, a proper mathematical solution will naturally
incorporate into a single
solution the proper handling of left and right turns, rather than requiring
separate machine states.
A preferred approach to implement the Kendall solution, as shown herein, would
be to enable the
driver of the tractor (the control vehicle) to operate a pointer such that
that driver would either
maintain the direction of the pointer in the desired direction and then be
shown where to turn the
steering or, perhaps even better, to maintain the direction of the pointer in
the desired direction and
then have the steering follow automatically.
Kimbrough et al. in their U.S. Pat. No. 5,579,228 teach a complete solution
and one should
applaud their rigorous approach to the mathematics. But, the Kimbrough
solution requires that the
wheels of the trailer be steerable by electromechanical servos controlled by
the central processing
unit and therefore fails the test of adaptability as most trailers have wheels
that are not steerable.
The Kimbrough solution also fails the economical test as a steerable trailer
as suggested would be
costly and the extensive mathematical solutions could potentially require a
more costly central
processing unit to run the calculations in real time. The many parameters (and
their sensors) to the
mathematical calculations will likely increase complexity and cost.
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Deng et al. in their U.S. Pat. No. 6,292,094 likewise teach a complete
solution. But again fail the
economical and adaptability tests with a control vehicle having both front and
rear wheel steering.
Many other attempts at solving this problem fail to provide an acceptable
solution along the lines
of the present invention.
Offerle at al. in their U.S. Patent 7,950,751 as well as their U.S. Patent
Application (publication
number 20050206225) also fail the economical and adaptability tests with a
trailer in which
breaking control to the wheels on the trailer is used to effect the steering
of that trailer.
Shepard in his U.S. Patent No. 7,715,953 (the '953 patent) teaches a complete
working system that
solves all of the above problems. However, in that teaching, some new problems
arise that are
addressed by the teaching of the present invention. In particular, the
mathematically intense
solution of the '953 patent requires the use of a sufficiently fast
microprocessor to perform the
iterative calculations thereby consuming the entire capability of an
inexpensive microprocessor. In
practice, as such a device is incorporated into other driving control systems,
this could require a
dual processor solution (whereby the second processor would be dedicated to
the backing
algorithm), unnecessarily driving up the cost of any implementation of the
invention. The '953
patent taught a variation that would compute the targeted directions of a
plurality of measures of
the turning radius and hitch angle in advance and stored this data in a table
in the device's memory
to provide a solution whereby a low cost microprocessor could be utilized and
the direction of the
pointer could be looked up from the values of the steering and hitch angle.
But, this could result in
a long start-up sequence that would unnecessarily extend the start-up time.
Alternatively, the table
could be preloaded for a given trailer of known length.
Finally, while the '953 patent teaches a solution to project the path of the
trailer for a given pair of
inputs (i.e., a turning radius and a hitch angle), it does not also project
the range of all possible
paths for a given hitch angle. In operation, this projection of a range of
possible paths is useful
when steering the trailer with a turning radius that will result in a
jackknife condition (or
otherwise) for those situations where the driver desires to put the trailer
onto a path that is not
reachable given the current hitch angle such as may be the case when one
desires to reverse the
sign of the hitch angle (i.e., have the trailer turn to the side opposite to
that to which it is presently
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turning). Having an indication of this range of paths can obviate the need to
reverse direction (i.e.,
to drive forward in order that the towing vehicle and the trailer will be
better aligned). Such limits
can be displayed by a meter having multiple needles, by an LCD display
indicating multiple
pointer directions, overlay lines on a video display, and the like. In some
situations, these
projected limit paths may not be displayed, but rather may be internally
computed such that they
may be used for projecting more complex paths.
The present invention solves the shortcomings of the '953 patent by
incorporating a pre-
computed a table for a typical trailer. The present invention finds a solution
for a standard
configuration of a vehicle backing with a trailer (either by table lookup or
by optimized
calculation) and then proportionally converts that solution into the actual
current situation path
solution with a simple ratiometric calculation that requires no iterations.
When used in
conjunction with a trailer to be backed-up, the present invention will still,
like the '953 patent,
indicate to the driver which direction to steer his vehicle as well as when
and how much to steer
and this is still accomplished with an inexpensive mechanism that can be
adapted to any
combination of vehicle and trailer. However, the mathematical solution to
project the angle at
which the vehicle and trailer become in-line is now computed in advance, in
whole or in part, for
any combination of vehicle and trailer and stored in the unit thereby further
reducing the cost and
any start-up time. Furthermore, for any given hitch angle, the upper and lower
limits to where the
projected paths can go are both projected by scanning the line in the lookup
table for the current
hitch angle and locating and displaying the projected paths for the most and
least extreme
projected paths. These two projected limits will correspond to the projected
path of least trailer
rotation while backing (i.e., the tightest turning radius that the pushing
vehicle can perform) and
most (infinite) trailer rotation while backing (i.e., the largest turning
radius possible without
jackknifing which will also be approximately the turning radius for which the
trailer turns on an
identical radius to the tow vehicle). These two extremes of possible steering
are desirable for
those situations whereby the desired direction lies outside of the range
delineated by these two
limits and where realignment of the tow vehicle and trailer (such as by
driving forward) is
undesirable. Knowing these two limits is desirable when the operator's desired
direction for
which the trailer is to travel is indicated by the operator and the steering
of the tow vehicle is
automated by servo control.
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The present invention can be installed in any vehicle equipped for pushing a
trailer. In operation in
a typical vehicle, a pointer would indicate, for the current position of the
vehicle's steering wheel,
the direction the trailer is projected to follow; to back-up the trailer, the
driver would turn the
vehicle's wheel such that the pointer is kept pointing in the direction of the
intended trailer
destination. With minimal modification to the towing vehicle, one would still
have the option,
though at a greater expense, of incorporating servomechanisms which would
cause the towing
vehicle to steer itself while the driver would simply indicate the direction
desired for the trailer to
travel (along with controlling the acceleration and breaking). Throughout this
description, the
terms "trailer" or (because the trailer is pushed ahead of the tow vehicle
while reversing) "first
vehicle" are synonymous and used interchangeably; the terms "tow vehicle" or
"tractor" or
(because the trailer is pushed ahead of the tow vehicle while reversing)
"second vehicle" or,
simply, "vehicle" are synonymous and used interchangeably; the term "projected
path" or
"projection of the path" refers to a path that is projected to be the path
followed by the trailer and
tow vehicle based on the amount of steering and the hitch angle [as opposed to
what is sometimes
termed a projection in the field of optics or photography whereby an image is
cast by a projector].
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a trailer being backed up an incremental straight distance
when the trailer and
backing force are in-line.
FIG. 2A-B illustrates the change in the hitch angle between a trailer and a
vehicle pushing the
trailer an incremental straight distance for two initial angular orientations
of the trailer and vehicle.
FIG. 3 illustrates the vector forces on the trailer at the hitch relating to
rotating the trailer and to
backing-up the trailer.
FIG. 4 illustrates the rotation resulting from the rotational component of the
backing force when
backing up and the associated geometries for such calculations.
FIG. 5 illustrates the change in the hitch angle between a trailer and a
vehicle as that vehicle moves
an incremental distance in an arc.
FIG. 6 illustrates the geometries associated with calculating the turning
radius of a vehicle from
the angular position of the turned front tire.
FIG. 7 illustrates a schematic for a remote angular position sensor.
FIG. 8 illustrates a remote angular position sensor with attachment mechanism.
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FIG. 9 illustrates possible positions for the sensors and the metering
indicator for directing an
operator while backing up a trailer.
FIG. 10 lists a table.of resulting directions (in degrees) for a given initial
hitch angle and steering
angle for a single set of parameters, according to the prior art.
FIG. 11 is a partial source code listing showing an iterative implementation
of the backing equation.
FIG. 12 is a partial source code listing showing an approximation of a turning
radius calculation.
FIG. 13 is a flow chart for collecting the hitch and steering angle and
displaying the projected path.
FIG. 14A-D is a range of depictions showing the relationship of the projected
path limits.
FIG. 15A-E is a range of depictions showing how the projected path would be to
parallel park a
tow vehicle with an attached trailer according to the present invention.
FIG. 16 lists a table of resulting directions (in degrees) for a given initial
hitch angle and turning
radius for a single set of parameters, according to the present invention.
In the figures, certain numerical indicators refer to items in the figures as
follows. In Figure 5,501
is the towing vehicle, 502 is the trailer represented by the trailer's
centerline, 503 is the front
wheels of the towing vehicle, and 504 is the path of the towing vehicle along
the circular arc of the
vehicle's turning radius. In Figure 6,601 is the front wheel of the towing
vehicles, 602 is the rear
wheel of the towing vehicle, 603 is the point of intersection of a line that
is perpendicular to the
direction of the front wheel with line that is perpendicular to the direction
of the rear wheel (drawn
from the center of each wheel), and 604 is the hitch-ball. In Figure 7,701 is
a serial signal input
(RxD), 702 is a signal buffer/receiver, 703 is a Reset-Set (R-S) flip-flop,
704 is a serial output
analog-to-digital converter, 705 is a crystal oscillator, 706 is an output
line driver, 707 is a serial
signal output (TxD), 708 is a potentiometer, 709 is a magnetic rotary encoder
(such as the Austria
Microsystems AG part AS5040), 710 is a resistor and 711 is a capacitor that
together form a low
pass filter, 712 is a resistor and 713 is a capacitor that together form a low
pass filter, 714 is an
output voltage representing the rotational position of a magnet proximate to
the magnetic rotary
encoder, and 715 is an output voltage representing the rotational position of
potentiometer (708).
In Figure 8,801 is the shaft of potentiometer (802), 802 is the body of a
potentiometer, 803 is the
center-line of the shaft (801) of potentiometer (802), 804 is an attachment
arm on shaft (801) of
potentiometer (802), and 805 is attaching an spring to attachment arm (804).
In Figure 9,901 it the
hitch angle sensor, 902 is the hitch, 903 is the trailer, 904 is the tow
vehicle, 905 is the
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microcomputer with display, 906 is the steering angle sensor, and 907 is an
optional
steering actuator servomotor. In Figure 13,300 through 316 are various
software
functions in a flow chart.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is a means to accurately back up one vehicle while
controlling the
backing of a trailer while keeping that trailer precisely aimed at and guided
towards a
targeted destination. The present invention can be applied anywhere one
vehicle must
control another vehicle by pushing through a single point of contact and
includes car and
trailer, tractor and wheeled container, or tow truck and broken-down car, to
name a few.
The connection between the two vehicles is accomplished with a pivotable
connection or
a ball-joint (called a hitch). When the two vehicles are in a straight line,
the angle of the
hitch, known as the hitch angle (also known as the articulation angle or the
hinge), is zero
degrees. This in-line position can be achieved by driving the vehicle forward
far enough
to cause the trailer to be pulled directly behind the vehicle.
Refer now to the figures, which show a preferred embodiment of the invention.
FIG. 1
shows the ideal behavior of a trailer being pushed by a vehicle. As the
vehicle backs up
some distance, Ax, the trailer moves an equal distance in the same direction.
FIG. 2
shows a more typical behavior of a trailer being pushed by a vehicle.
In FIG. 2A, the centerline of the trailer and the Ax direction are
perpendicular. In this
case, all of the incremental motion, Ax, results in rotation of the trailer as
the hitching
point of the trailer is moved along the circumference (where L is the distance
from the
axel of the trailer to the hitching point of the trailer and where Ax/27EL is
the percentage
of the total circumference corresponding to
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incremental motion, Ax, and where the amount of rotation, in degrees, is
therefore equal to 360Ax/
21i). This is why the shorter the trailer, the greater the rotational
component for an increment of
motion, and the more unstable and difficult that trailer is to back up.
In FIG. 2B, as is most often the case in normal operation, a portion of the
force in the Ax direction
is translated into backing up the trailer while a portion is translated into
rotating the trailer.
Typically, most of the incremental motion in the Ax direction is translated
into backing up the
trailer because the centerline of the trailer and the Ax direction (along the
center line of the vehicle)
are usually kept close to parallel. However, following this backing up of the
distance Ax, the
centerline of the trailer and the Ax direction will be less parallel due to
the rotation that occurred.
As a result, if the vehicle were to back up an additional distance of Ax, an
even greater portion of
the incremental motion would be translated into rotating the trailer. Each
successive distance Ax
backed up (when backing up in a straight line) will translate into a growing
portion to be applied to
rotating the trailer until, and as is shown in FIG. 2A, the center line of the
trailer and the Ax
direction are perpendicular. If the vehicle backs up even further, the part of
that force that is in the
direction of backing up the trailer becomes negative which is to say that the
trailer begins to be
pulled and will move towards the center line of the vehicle until the trailer
is ultimately towed
directly behind the vehicle--the most stable position of the vehicle and
trailer in motion. Of course,
in real life, if this backing were continued, the trailer would keep turning
until it collides with the
side of the vehicle. This action of a trailer turning around to follow the
point that is pushing it is
called jackknifing.
Refer now to FIG. 3 for an explanation of this pair of vector forces on the
trailer when a vehicle is
backing up in a straight line a distance of Ax. FIG. 3 shows that the force,
f, at the hitch point of
the trailer, T, is the sum of two vectors, b and r, that meet each other at a
right angle. When a force,
f, is applied to the hitch point of a trailer by a backing vehicle, part of
that force, b, is parallel to
(i.e., in-line with) the centerline of the trailer and is, therefore, in the
direction of backing up the
trailer. However, the other part of the force, r, is perpendicular to the
centerline of the trailer and is
in the direction of rotating the trailer about a point midway between its two
wheels (i.e., on the
centerline of the trailer). The angle between the direction of the applied
force and the direction of
the centerline of the trailer is called the hitch angle and, for this
discussion, shall be called Theta
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(8). If we assume that the force, f, applied is proportional to the distance
backed up, Ax, we can
calculate the magnitudes of b and r as being AxCos(0) and AxSin(9),
respectively. In practice, the
hitch angle is a ball joint that enables some motion in the vertical
direction, but this aspect of
motion is ignored in the present invention as this motion does not
significantly change the resulting
operation of a system equipped with the present invention and to do otherwise
would only cause an
implementation of the solution to be more costly without adequate benefit to
justify that cost.
For the purpose of this explanation, we will speak in terms of discreet steps
of distance, Ax, instead
of in terms of calculus and integrals because the solution discussed herein is
performed with an
approximation technique. To re-obtain an in-line position of vehicle and
trailer, the vehicle must
turn while backing. As a result, a series of Ax distances backed up will
actually fall along an arc,
not a straight line. The radius of that arc and the total distance backed (sum
of Ax's or, more
precisely, the integral) determine how quickly the vehicle and trailer will
return to an in-line
position.
When the operator of a vehicle attempts to back up a trailer, he wants to keep
the trailer following
a path that runs directly at the target--the intended line of travel. While
backing up, the trailer will
turn away from the intended line of travel due to the jackknifing effect. A
highly skilled operator
will turn the vehicle toward the side to which the trailer is jackknifing and
will gradually reduce
the arc of his turn as the trailer approaches the intended line of travel such
that the vehicle will be
moving in a straight line (the radius of the arc approaches infinity) just as
the trailer once again
parallel's the intended line of travel. As soon as this alignment of intended
line of travel, trailer
direction and vehicle direction are reached, the system becomes unstable
wherein the trailer will
begin to jackknife. To gain control, the operator must again turn the vehicle
toward the side to
which the trailer is jackknifing.
What often happens with the less skillful operator is that at the moment when
the trailer is returned
to the intended line of travel, the vehicle is not also in-line with the
trailer. In this case, with only
the trailer on the intended line of travel, the operator must now turn the
vehicle back to also be in-
line with the intended line of travel. But this additional backing to get the
vehicle on the intended
line of travel will cause the trailer to continue to turn beyond the intended
line of travel. By the
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time the vehicle and trailer are once again in-line, the trailer is no longer
heading in the intended
line of travel. Often, the amount by which the trailer is off the intended
line of travel to this second
side is greater than the amount by which it had been off on the first side.
When this occurs, the
operator finds himself in a growing oscillation wherein the trailer keeps
backing generally toward
the intended target but with less and less control. Frequently, this
oscillation can only be halted by
driving the vehicle forward, directly away from the target which returns the
vehicle and trailer to
an in-line position that is pointed at the target, but a portion of the
distance that had been covered
while backing up will have been lost to the driving forward needed to rescue
the operation.
The present invention provides an indication of the direction in which the
trailer and vehicle will
be headed when both trailer and vehicle are in-line. This indication is
computed from constant
information such as the length of the trailer from the axel to the hitch and
variable information
such as the current radius of the arc of the vehicle and the angle of the
centerline of the trailer and
the vehicle at the hitch (the hitch angle). There are many ways to process the
necessary
information.
To compute the change in the hitch angle resulting from an incremental
displacement, Ax, of the
hitch, two components must be considered: the increase associated with the
rotation of the trailer
and the decrease associated with the turning of the vehicle. The sum of these
two components must
be decreasing when compared over two successive increments of motion (Ax) in
order to obtain
convergence on a solution. When this does not occur, the vehicle operator must
be alerted to
change his steering or to drive forward (directly away from the target) to get
the vehicle, trailer and
target all in-line before continuing.
Referring to FIG. 4, to calculate the angular contribution from the rotation
of the trailer, a, to the
change in hitch angle resulting from an incremental displacement, Ax, one must
recognize the
geometry of that rotation. The length of the trailer, L, forms two of the
sides of a triangle formed
when the trailer rotates about point p, where the third side is the rotation
contribution component,
r, as discussed above and shown in FIG. 3. From that discussion, r has the
magnitude Ax Sin(0).
The angle of rotation, a, is bisected in the formation of two similar right
triangles each having L
for their hypotenuse and y for half of bisected angle a. Simple geometry
dictates the relationship
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Sin y=1/2r/L which can be restated as y=Sin-1(1/2r/L). The angular
contribution from the
rotation of the trailer, a, is therefore equal to 2 Sin-f(r/2L). Substituting
in for r yields:
a=2 Sin -'(Ax Sin(0)/2L).
Referring to FIG. 5, a vehicle, 501, pushes a trailer, 502, as it backs up in
an arc. To calculate
the contribution from the turning of the vehicle, to the change in hitch angle
resulting from
an incremental backing displacement, Ax, one must recognize the geometry of
the curved path
of the vehicle as well. Even if the vehicle and the trailer are momentarily in-
line resulting in no
angular change in the direction of the trailer, the vehicle is assumed to be
following a circular
path and the angular change in the direction of the vehicle will effect the
angle between the
vehicle and the trailer. The radius of this circle, R, is the turning radius
and is a function of the
steering angle of the front wheels, 503. The circumference of the circular
path, 504, on which
the vehicle travels equals 2aR and corresponds to 3600. The angular
contribution of the vehicle
by following this curved path is determined by taking the same percentage out
of 3600 that the
incremental distance traveled by the vehicle takes out of the entire
circumference of the circle
on which this curved path exists. In other words, Ax/27tR=13/360 or
13=1804x/7a.
Computation of the turning radius of a vehicle can be simplified and is shown
geometrically in
FIG. 6. Front wheel, 601, of the vehicle steers by turning about a point of
rotation at or near its
center that is approximately in line with rear wheel, 602, and their centers
are separated by a
distance called the wheel base, w. When steering occurs, front wheel, 601,
rotates some amount
shown as angle ci). The center point, 603, of the circle of turning is found
at the point of
intersection of two lines, one each drawn through the center of and
perpendicular to the path of
travel of each wheel; this dictates that these two lines will meet at an angle
equal to the steering
angle, ill). Rear wheel turning radius, R, is computed with simple geometry
as: R=co/Tan(4)).
This approximation will be good enough in many cases. But, it can be made more
precise
without much effort by incorporating the added distance, (d, from the center
of rear wheel, 602,
to the hitch-ball, 604, that is at the point of the hitch rotation (assuming
the hitch ball is in-line
with the two wheels). This is computed using the Pythagorean theorem resulting
in the equation
for the turning radius, R', of the hitch-ball, 604, at the point of the hitch
rotation:
R=SQRT(((n/Tan()) 2+w'2)
It should be noted that this is an approximation and, as will be addressed
below regarding
CA 02783664 2014-02-18
precision, does not have to be perfect (further accuracy would require that
the second front and
rear wheels be included in the calculation as well as the positioning of the
hitch-ball half way
between the left and right rear wheels rather than assuming it is in-line with
the front and rear
wheel). It should also be noted that with front and rear wheel steering, this
formula would be
modified.
Since the steering wheel is coupled to the wheel steering mechanism, it would
be possible to put
a sensor on the steering wheel or its shaft and detect the angular position of
that steering wheel or
shaft and translate that angular position into the angular position of the
front wheels.
Furthermore, a sensor relating to the steering of the vehicle could include
sufficient
computational capability (even if only in the form of a lookup table to
convert from one measure
to another) to sense either the steering wheel or shaft's angular position or
the wheel's angular
position and return the turning radius thereby saving the main processor the
computation time of
performing that translation. These variations will be clear to those skilled
in the art.
Now, by combining the increase associated with the rotation of the trailer and
the decrease
associated with the turning of the vehicle into a single equation, the change
in hitch angle, AO,
resulting from an incremental distance, Ax, traveled by the vehicle can be
expressed as:
A0=2 Sin '(Ax Sin(0)/2L)-180Ax/aR
The new hitch angle, 0', resulting from an incremental distance, Ax, traveled
by the vehicle is
expressed as:
01=0+2 Sin '(Ax Sin(0)/2L)-180Ax/Ta.
This shall be called the backing equation.
The angle of the front wheels in steering (i.e., the angle that the wheels are
turned relative to their
position when the vehicle is driving in a straight line) and the angle of the
hitch (i.e., the angle
formed by the intersection of the centerline of the tow vehicle and the
centerline of the trailer,
where the vertex of said angle is located at the hitch, a pivotable point of
connection between the
tow vehicle and the trailer, and where a measure of zero degrees occurs when
the centerline of the
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tow vehicle and the centerline of the trailer are collinear) can be measured
with simple remote
angle sensors. FIG. 7 shows a schematic diagram of an example implementation
of such a sensor
(in practice, for a heavily used device, which would include most trailers
being towed over long
distances, the angle sensors should be a magnetic rotation sensor for which
there is no wear as
opposed to a potentiometer which would experience significant friction while
towing and would
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have an excessively short lifetime; the sensor depicted in Figure 7 shows both
input types and is
for illustrative purposes). With this circuit, a data byte is sent into the
sensor unit via a serial
interface at input RxD, 701, to request a sample of the current angular
position be taken and
returned. This signal is buffered by line interface receiver, 702, for the
voltage levels of the serial
link (e.g., an RS-232 receiver) and the start bit of that data byte sets an R-
S Flip-Flop, 703, formed
by two NAND gates such that a serial Analog-to-Digital Converter, 704, such as
the ADC0831 is
enabled to run a sample conversion. A crystal oscillator, 705, such as the
CD4060 is also enabled
and drives the circuit until Analog-to-Digital (A-to-D) Converter, 704, has
transmitted its entire
sample byte, including start and stop bits, at which point the R-S Flip-Flop,
703, is reset and the
process halts until restarted by another incoming data byte. The sample byte
transmitted is buffered
through line driver, 706, and output from the sensor unit at TxD, 707. The
value sampled is the
voltage on the input, 716, of the A-to-D, 704. The angle sensing can come from
a potentiometer,
708, whereby the output, 715, from the potentiometer, 708, is a voltage
proportional to the
rotational position of the potentiometer shaft. Alternatively, the angle
sensing can come from a
magnetic rotary encoder such as the AS5040 from Austria Microsystems AG or an
equivalent part.
A variety of angular position sensors are commercially available, including
magnetic rotational
sensors (such as several commercially available devices from Austria
Microsystems AG) that will
not wear out as quickly as the resistive surfaces within a potentiometer
would. The AS5040
magnetic rotary encoder, 709, has a pulse-width modulation output which can be
passed through a
simple two stage low-pass filter (such as 710 and 711 followed by 712 and 713)
as is shown in that
company's application notes (other connections to the AS5040 not shown). The
output from these
two low-pass filters, 714, is a voltage representative of the rotational
position of a magnet
positioned proximate to the AS5040. Output, 714, would be connected to the
input 716 of the
A-to-D, 704, instead of the potentiometer, 708. With either the potentiometer
implementation or
the magnetic rotary encoder implementation, either the shaft of the
potentiometer or a shaft to
which a magnetic is mounted for operation with a magnetic rotary encoder is
provided, and the
output is a function of the mechanical linkages between the sensor unit and
the two sides of the
angle being measured.
The sensor can be packaged in many ways, with one possible configuration shown
in FIG. 8.1n
this example, the shaft (of either the potentiometer or of the magnet for
operation with a magnetic
12
CA 02783664 2012-07-18
rotary encoder), 801, extends out of a box, 802, housing the electronics. This
box, 802, is mounted
above the angle to be measured such that the centerline, 803, of the
potentiometer, 801, is
generally in line with the axis of rotation of the angle to be measured. The
box is mounted in a
fixed position on one side of the angle to be measured (e.g., to the hitch arm
when measuring the
hitch angle or to the frame of the vehicle when measuring the steering angle).
An attachment is
made to the shaft of the potentiometer, 801, with an attachment arm, 804, by
means of a spring,
805, or other device to a point on the other side of the angle to be measured
(e.g., to the trailer near
the hitch when measuring the hitch angle or to a point on the support of the
front wheel that moves
with that wheel when that wheel is turned when measuring the steering angle).
With the above equations and an understanding of the angle sensors, one can
understand an
embodiment of the invention as shown in FIG. 9. The hitch angle is measured by
way of a
sensor,901, in close proximity to the hitch, 902, pivotably connecting the
trailer, 903, to the
vehicle, 904. This sensor measures absolute angular position whereby a
measurement of zero
degrees is calibrated for when the trailer and vehicle are in-line. This angle
data is digitized and
fed into the microcomputer, 905. The vehicle's turning radius can be
determined by measuring
the steering angle with an angular position sensor, 906, on the front wheel
assembly of the
vehicle. The calculations require that certain measurements of the vehicle-
trailer system are
known and/or have been input into the system including the wheel base, co, the
hitch length, co'
and the trailer length, L. (An optional servo control 907 to actuate the
steering can be included.)
Calibration of the angle sensors includes determining the limits of travel and
the center point of
travel. Calibration values could be stored in non-volatile memory in the
microcomputer. It has
been noted that the angular sensors could perform a translation from the
measured angle into other
forms. The hitch angle could translate a reading from degrees into radians.
The turning radius
could be determined by measuring the steering angle or the steering wheel
angle and translating
into the turning radius (this would require that the steering angle sensing
module would have, at
least, the wheel base of the vehicle and, preferably, the wheel base and the
hitch length).
Furthermore, the angle sensing module could be preprogrammed with other data;
for example, the
hitch angle sensor module could be sold as a matched unit with a trailer in
which case the hitch
angle module could come preprogrammed with the length of that trailer and
enable the central
13
CA 02783664 2015-06-09
microcomputer to query that module for this additional data value rather than
require the operator
to have to enter the data during a configuration process or when a different
trailer is being backed
up.
Assuming that the turning radius of the vehicle does not change, the original
value sensed for the
turning radius is kept constant and, using this newly projected value for the
hitch angle, the
backing equation is recomputed. This continues in an iterative fashion, using
the backing equation
with the original turning radius and each newly projected value for the hitch
angle, until the
projected hitch angle reaches 0 . With each iteration, a variable is
incremented to keep track of the
number of iterations that have occurred. The iterations stop when the
projected hitch angle reaches
or crosses zero.
Just as a single increment of distance, Ax, can be used to determine the
angular change in the
vehicle's direction with the equation from above,13=180Ax/nR, the total
angular change in the
vehicle's direction can be determined from the number of iterations, k, by
multiplying by k in that
same equation, or Zi3=k180Ax/- nR. Since the terminal hitch angle of 0
implies that the trailer and
vehicle are in-line, the terminal direction of the vehicle indicates the
direction of both the vehicle
and the trailer when they are in-line. In other words, El3 is the angular
change in direction the
vehicle will undergo to come in-line with the trailer, given the initial hitch
angle and the current
turning radius of the vehicle. The above approach can be used to build a table
of angular change
entries for a range of hitch angles and steering angles for a trailer of known
length.
FIG. 10 lists a prior art table of example data for a set of initial hitch
angles (across the top of the
table) and steering angles (along the left side of the table) for a single set
of parameters comprising
the wheel base of the vehicle, the trailer length, a standard hitch length,
and a backing increment
(Ax). The data points in the table correspond to the change in direction of
the vehicle, in degrees,
between the current position and point at which the vehicle and trailer become
in-line with each
other. An entry of "J" indicates a jackknife condition. As an example, if the
hitch angle is 5 to the
right and the steering angle is 10 the vehicle and trailer will become in-
line at the point where the
vehicle will have changed its direction by 7 from its starting direction.
This table would be unique
for a given set of parameters. It will be noticed that the upper
14
CA 02783664 2015-06-09
left quadrant of the table is nearly identical (except for the sign) to the
lower right quadrant (and all
values in the other two quadrants represent a jackknife condition) and as a
result, only one
quadrant (e.g., the lower right quadrant) of this table is needed to be able
to store enough of the
table to represent the table in its entirety.
In FIG. 16, for an optimized device according to the present invention,
angular changes in
direction of the tow vehicle (measured relative to an initial position of the
tow vehicle)
corresponding to a range of turning radii and hitch angles would be pre-
computed and stored in
such a one quadrant table. This table of data would be pre-computed for a
standard sized trailer. In
one sense, this is possible because the units of measure (e.g., inches verses
centimeters verses feet,
for example) are not necessarily defined. As such, the table could be
constructed for, say, a trailer
having a length of 304.8 inches (25.4 feet) and the system can then be
considered to be in inches.
But, if a different trailer is used (say, a 10 foot trailer or an equivalent
120 inches or an equivalent
304.8 centimeters), since the units of measure are not defined, the system can
now be considered to
be in centimeters and the same table will apply. It should be obvious that
this system can be used
for any arbitrary unit of measure (including a newly invented unit of measure,
such as units of
"trailer length") as long as the length of the trailer, when measured in this
unit of measure, is 304.8
units long. This means the same table can be used for trailers of any length
as long as the units of
measure are transformed such that, in this example, the trailer is always
304.8 of these units in
length. Of course, the turning radius of the vehicle towing the trailer must
be transformed as well
to the same units of measure, but the calculation to do the transformation is
a very straight forward
ratiometric scaling of the units of measure used to construct the table
compared to the units of
measure that yields the proper length trailer and this calculation is quite
manageable for even a low
powered microprocessor (i.e., multiplication by a ratiometric scaling factor).
The "Trailer Length
Conversion Factor" (TLCF) will be the scaling factor that, when multiplied by
a value measured in
the same units of measure from which the TLCF was created will give a new
value in the
appropriate "Trailer Length" Unit of Measure (TLUM).
In this way, a low cost microprocessor (one that might not be powerful enough
to perform the
iterative calculations in real time or that might not even be able to
efficiently build the table during
an initialization sequence) could be utilized and the projected direction
could be looked up from
CA 02783664 2012-07-18
the transformed value of the turning radius and the value of the hitch angle.
This approach requires
a large enough capacity storage device to hold the table and this will add to
the cost of the system.
Additionally, only certain representative or key points from the table need be
calculated and the
values in between could be interpolated (thereby reducing the capacity of the
storage device in or
with the microcomputer and the associated additional cost). Furthermore, these
data points could
be determined empirically by measuring the hitch and steering angle and the
resulting in-line
trailer direction for a given vehicle and trailer configuration (a rather
laborious approach that
would work best if a common configuration of vehicle and trailer was
anticipated and the
calculated approach was, as a result of processor limitations or other
reasons, impractical or
unavailable). The table could be constructed for combinations of hitch angle
and turning radius in
which case the vehicle based sensor would have to provide turning radius
instead of steering angle
(thereby incorporating the wheel base and hitch length) and the table could
then be
preprogrammed for the specific trailer to be used therewith (this table might
be stored in the hitch
angle sensor unit). The number of hitch angle entries (e.g., columns) and
steering angle or turning
radius entries (i.e., the number of data points within the table) is
proportional to the accuracy
obtainable and, for economic reasons, would be matched to the application (for
example, when a
human operator is integral to the system feedback loop by guiding/steering the
tow vehicle lower
accuracy may be possible because of the ability of the operator to correct the
path being followed
whereas if the steering is being controlled by a servo operated towing vehicle
higher accuracy may
be desired). This variation might be appealing to trailer manufacturers who
might desire to build a
trailer with the present invention included without regard to the vehicle with
which it may be used.
In the event that an in-line position between the tow vehicle and trailer
cannot be reached given the
initial hitch angle and the current turning radius of the vehicle, an alarm
could be signaled (e.g.,
visually) to notify the operator that the trailer has or is on track to
jackknife to one side or the
other. This visual notification should indicate to which side the trailer has
begun to jackknife
because it might not be immediately apparent when the vehicle and trailer are
nearly in-line.
To run the iterative calculation, a computer reads the current hitch angle and
the vehicle's steering
angle and each time the set of readings is made, the computer runs a set of
calculations. The
16
CA 02783664 2012-07-18
calculations are run iteratively for a given pair of readings (see FIG. II for
an example of code to
iteratively compute the projected in-line direction of the vehicle and trailer
from these two
readings, relative to the vehicle's starting position--note that in this C
source code, the backing
equation is calculated entirely in radians to eliminate the need to convert
from degrees to radians
and back again on every iteration of the calculation). A constant incremental
value for Ax is used;
the smaller the value of Ax the more accurate the result, but the longer the
iterative computation
will take to complete. A tradeoff between accuracy and processing time (which
is also a function of
the processing speed of the computer) may have to be made. In running the
solution, the program
iteratively computes the backing equation for the set of readings to project
what the new hitch
angle will be following each additional increment of travel, Ax. This
iterative calculation continues
until the new hitch angle reached or crosses through zero which corresponds to
the vehicle and
trailer being in-line (when the angle equals zero). The number of iterations
that are required until
the new hitch angle crosses through zero is the number of increments of Ax
that the vehicle will
have to back up, given the initial values of the hitch angle and steering
angle, in order for the
trailer and vehicle to become lined up. The steering angle is presumed to not
change during the
calculation and so too the turning radius is presumed not to change. As a
result, since the number
of increments has been calculated as a part of the iterative solution, the
distance traveled along the
arc of the turning radius can be computed and so too the change in angular
direction of the vehicle.
(The distance to be backed up could, optionally with additional display
electronics, be displayed to
the operator.) If the vehicle were to travel this distance (if it were to
actually back up the distance
computed in the iterative calculation while keeping the steering angle, and
therefore the turning
radius, constant), the vehicle and the trailer would be in-line with each
other. As a result, by
displaying the projected change in angular direction on a meter such that the
number of degrees of
change in angular direction calculated is the number of degrees of deflection
shown on the needle
of the meter, that meter can be positioned flat on the shoulder of the
driver's seat such that the
needle will point in that direction of the path behind the vehicle where the
vehicle and trailer will
be headed when the vehicle and trailer are in-line. Note that the meter would
be positioned and
calibrated such that a value of zero, that is to say that the calculation
indicates that no change in
direction will result in the vehicle and trailer being lined up (i.e., the
trailer and vehicle were
already lined up at the start of the calculation when the hitch angle and the
vehicle's steering angle
were sampled), would have the needle of the meter pointing directly back
behind the vehicle. The
17
CA 02783664 2014-02-18
iterative backing calculation requires that some constant values will also
have to be stored in the
computer; these include, in addition to the hitch angle and the turning
radius, the number of
degrees that the meter can display or that can be displayed by a one-half
scale deflection of the
meter and the trailer length. In order to compute the turning radius (see FIG.
12 for an example of
code to compute an estimate of the turning radius having sufficient accuracy
to implement the
prototype), in addition to having a value for the steering angle (measured in
degrees or radians),
some constant values will also have to be stored in the computer; these
include the wheel base and
the hitch length (the square of the hitch length can be precomputed to save
processing time). In
operation, when the hitch angle is large and the steering angle is small, many
more iterations are
required to converge on a solution. As a result, performance can be sluggish
under this condition
and backing speed should be slowed to be most accurate. With the present
invention, the iterative
solution is replaced by a ratiometric conversion of the inputs along with a
more efficient algorithm.
Note that the precision of the operator guided system need only be as accurate
as the operator can
perceive given the resolution of the user interface. If a mechanical metering
output device is
utilized, one's eye might not be able to distinguish the difference between
one projected direction
and another projected direction if those two directions only differ by a few
degrees or a fraction of
a degree. As such, the accuracy of the calculations need not be more precise
than the operator
could perceive on that output device such that bringing the vehicle and
trailer in-line need only be
generally in-line enough to guide the operator. This ability to limit the
precision should help to
keep the cost of the system down as the calculations can be simplified,
iterated to a lesser degree of
precision, or otherwise approximated. This also applies to the precision used
for the sensing of the
angular inputs and their translation into other forms, as would be the case
when sensing the
steering angle and translating that steering angle into the turning radius or
in deciding whether or
not to include the hitch length. However, when the steering of the tow vehicle
is servo controlled,
greater precision may be desirable.
Variations on the computation may involve calculating the various order
derivatives of the hitch
angle. For example, knowing the hitch angle and backing up some distance Ax
and then rereading
18a
CA 02783664 2014-02-18
the hitch angle will yield the first derivative (change in hitch angle per
change in position, Ax);
backing up an additional distance Ax will not only yield a second measure of
the first derivative
18b
CA 02783664 2012-07-18
but will also yield a measure of the second derivative. With these various
order derivatives one
could employ a Taylor Series expansion-like approach. One could also use Runge-
Kutta, Adams-
Moulton or other forms of Numerical Calculus or Dynamic Simulation or the
like. An analog
circuit could be constructed using such analog circuits as op-amps,
integrators, adders, and the
like.
The angular change in direction, Ep, is shown graphically to the operator. As
stated above, one
way this can be done is by converting EI3 to an analog voltage; this voltage
is displayed on a
traditional analog needle meter. The zero point would be set to the center of
the meter's deflection
range. The meter would be positioned in the vehicle in view of the operator
when he is turned to
look out the back of the vehicle (just as he would be looking when backing up
with a trailer
without the present invention) such that the needle would point straight out
the back of the vehicle
when Ei3 reads zero. For the particular meter used, the angles of the needle
should be measured on
the face of the meter for its maximum and minimum deflections from this center
position. These
angles will correspond to the largest angle to the left and right that can be
displayed. Scaling the
output voltage for Ef3 to fit the meter's scale should be clear to those
versed in the art. When the
needle is deflected to either its maximum or minimum position, the operator
must assume that a
potential jackknife condition may exist. Many types of display mechanisms
could be used instead
of the meter -- LCD displays or other electronic graphical displays showing a
pointer or otherwise
indicating a direction, LED's along the top edge of the rear window, projected
beams of light from
a laser diode movably mounted, and a wind-vane like pointer movably mounted on
top of a rod
extending up from the top of the hitch are a few alternate display
possibilities.
But, a preferred solution is to replace the meter type pointing device with a
video system or use the
video in addition to a pointing device. Such a solution comprises a video
camera or image sensor
on the back of the vehicle (such as when a boat trailer is empty) or on the
back of the trailer (such
as when the trailer is carrying a boat) along with a video monitor visible to
the operator. This might
be especially useful for tall trailers that may block the view from the
vehicle. The camera could be
movably mounted such that the left to right direction of the camera is motor
controlled (i.e.,
motorized panning) instead of or in addition to the pointer. In this way, the
image on a monitor
screen in the vehicle would show where the trailer is going to go by turning
the camera such that
19
CA 02783664 2012-07-18
the target is kept in the center of the screen. The angle would be adjusted
because if the camera is
on the trailer and the trailer is already turned by the angle of the hitch,
one would not want to
incorporate the hitch angle component of the projected direction twice (the
projected angle reflects
the amount of turning of the vehicle to come in-line with the trailer, but the
trailer is already partly
turned in the direction of that projected direction). In addition, an on
screen indicator could notify
the driver when a jackknife condition is reached or imminent and to which side
(instead of having
the camera swing off to that side). Alternatively, the camera could remain
fixed while an on screen
indicator (e.g., a superimposed line, arrow, icon, or other graphic) would
identify the target
direction of the trailer on the video monitor. This solution has the added
benefit of a safety camera
monitoring system for safer backing. Some drivers may prefer a left-to-right
mirror imaging of the
camera image to facilitate more comfortable steering.
When the video system variation is used in conjunction with a towing vehicle
having servo
controlled steering, the operator would turn a knob which would cause the
video camera to pan in
proportion to the knob turning; this would enable the operator to turn the
knob until the desired
destination for the trailer is visible in the center of the video screen. The
angle of panning of the
camera would then also be the angle of the projected direction (being careful
to distinguish the
difference between the vehicle mounted camera and the trailer mounted camera
which is adjusted
to not double-count the hitch angle). Without a video system, a pointer
mounted on a knob could
be used to thereby enable the operator to turn the knob until the pointer is
pointing in the desired
direction, and this angle of the pointer would be the angle of the projected
direction. With either
operator input mechanism (or any other), the system would then perform a
reverse lookup from the
table (i.e., to search the line in the table corresponding to the current
hitch angle in order to find the
angle of the projected direction or the two adjacent angles of the projected
direction to facilitate an
interpolated solution) in order to identify the turning radius from the table
(or interpolated
therefrom). This turning radius (with any adjustment for its being in Trailer
Units) is transfered to
the servo steering control to cause the towing vehicle to adjust its steering
angle (i.e., to turn the
steering wheel).
The knob in both the video system variation and in the simple knob mounted
pointer variation
could be thought of as a miniature steering wheel. The operator would
continuously maintain the
CA 02783664 2012-07-18
indication of the direction as the vehicle and trailer are moving. In other
words, as the vehicle
backs up and the trailer and/or vehicle turns, the knob will have to be turned
in the opposite
direction (to offset such turning of the trailer and/or vehicle) such that the
direction of the intended
path is kept the same.
A second design utilizing a low cost microcomputer chip uses the single
precomputed table
approach with unit of measure transformation. This design incorporates display
means to indicate
the range of projected directions for the vehicle to become in-line with the
trailer. This display
means can comprise either a meter pointing device, an LCD display panel,
and/or a rearview video
screen with superimposed curves indicating the limits to the range of
projected directions with
either the current projected direction centered on the screen or indicated
with an additional
superimposed curve.
A flow chart for this prototype is shown in Fig. 13. In this flow chart, the
process operates as an
interrupt routine where interrupts are triggered by reception of the input
angle values and the
resulting projected to become in-line value is determined and output on the
display device. The
software routine is entered when a value is received from the steering sensor
301 or from the hitch
angle sensor 306. This routine entry could be caused by an interrupt on a
serial port. When an
interrupt occurs for the steering sensor serial port 301, the steering sensor
value is read in from the
steering serial port 302 and converted into the corresponding value for a
turning radius 303. This
conversion is accomplished by looking up the turning radius in a list that
provides a turning radius
value for a given steering sensor value. This conversion will also apply the
scaling factor, TLCF, to
the turning radius value to convert from the units of measure of the turning
radius list into the units
of measure for the projected direction look-up table (wherein the units of
measure in the table are
=
in the "trailer length" unit of measure -- TLUM). This may optionally include
interpolating for the
final turning radius value from the two closest (one higher and one lower)
list entries for steering.
This final TLUM turning radius value is stored in a variable and a steering
value flag is set to
indicate that the turning radius value is ready. A check is made to see if
both the turning radius
value and the hitch angle value are available 310 and, if both are not
available, the process returns
to waiting mode 300. When an interrupt occurs for the hitch angle sensor
serial port 306, the hitch
angle sensor value is read in from the hitch angle serial port 307 and this
value is stored in a
21
CA 02783664 2012-07-18
variable and a hitch angle flag is set to indicate that the hitch angle value
is ready. A check is made
to see if both the turning radius value and the hitch angle value are
available 310 and, if both are
not available, the process returns to waiting mode 300. This waiting mode 300
would be a main
loop wherein other functions would be monitored and performed (such as display
refreshing and
processing events from a user interface). Alternatively, the serial ports for
steering and for the hitch
could be monitored in a main loop (along with other functions) and this
routine could be entered
by branching from that main loop when data is received in either serial port;
in this case, the steps
to be performed when a steering value is received 301-305 and the steps to be
performed when a
hitch angle value is received 306-309 (along with the conditional test to
branch 310) could be
incorporated in that main loop. Note that the angle sensors can be made free-
running in which case
no step to initiate a new sample 305 & 309 would be required; if not free-
running, the angle
sensors would have to be started up in an initialization routine.
Once both the turning radius value (TRV) and the hitch angle value (HAV) are
ready, the projected
direction when both the vehicle and trailer are in-line is looked-up.
Interpolating a value not
specifically included in the table is performed by first looking-up the
closest values on one axis of
the table for the hitch angle, i.e., the closest value below (HAVL) and above
(HAVH) the hitch
angle value (HAV) and for the final turning radius, i.e., the closest value
below (TRVL) and above
(TRVH) the final turning radius value (TRV) in 311. This will enable the look-
up of four Table
Entries for hitch angle low & turning radius low (TELL), hitch angle low &
turning radius high
(TELH), hitch angle high & turning radius low (TEHL), and hitch angle high &
turning radius high
(TEHH) in 312. Next, in 313, a final value is determined by first
interpolating two values -- one
value,TEL is interpolated from the two looked-up values corresponding to hitch
angle low &.
turning radius low (TELL) and hitch angle low & turning radius high (TELH) and
the other value
TEH is interpolated from the two looked-up values corresponding to hitch angle
high & turning
radius low (TEHL) and hitch angle high & turning radius high (TEHH) by finding
the value
proportionally between them. These are calculated from the proportional
distance between the two
turning radius values and this proportionality factor is TRV = (TRV-
TRVL)/(TRVH-TRVL) such
that TEL = (TRV *1(TELL)-(TELH)I + TELL) and TEL = (TRV *I(TEHL)-(TEHH)1+
TEHL). The
final interpolated value is calculated from the proportional distance between
the two hitch angles
and this proportionality factor is HAVA (HAV-HAVL)/(HAVH-HAVL) such that TE =
(HAVA*
22
CA 02783664 2012-07-18
(TEL)-(TEH)I + TEL). This angle, TE, is then displayed on the display device,
such as a meter
pointing device, as outlined above. Any other display updates would be
performed in 315,
including the display of the upper and lower limits to where the projected
paths can go for the
hitch angle HAV. Interpolation for these upper and lower limits is optional in
that, given HAV, the
greater low value and the lesser high value will generally suffice. These can
be found by locating
the line in the table corresponding to HAVL and scanning down that table line
for the first and last
values (where one value will be the extreme corresponding to the tightest
turning radius available
and the other will be the extreme corresponding to the point just before
jackknifing). For example,
looking at table in Fig, 10, if the hitch angle value, HAV, is 13 degrees and
the tightest turning
radius for the vehicle corresponds to the steering angle of "50" then the
lower limit can be
estimated to be 18 (i.e, the greater of 11 and 18) and the upper limit can be
estimated to be 30 (i.e,
the lesser of 30 and 42). Finally, in 316, the steering value flag and hitch
angle value flag are
cleared and program control returns to the wait routine 300 (this includes any
interrupt service
routine return functions if interrupt driven control is utilized). To prevent
against a lost data byte
due to a communications glitch, a watch-dog timer routine can be utilized to
clear the serial ports
and data values and to reinitiate sampling requests to both sensors.
The path of the trailer can be overlaid on the video screen. The tow vehicle's
path for each of these
projected paths is easily projected based on the vehicle's turning radius
alone and could be used as
a good approximation of the path from the starting position to the final
position (at which point the
tow vehicle and trailer will be approximately in-line). The two extreme paths
(i.e., the ISL and the
TTL) can likewise be displayed.
While the table described above is said to be in units of trailer length, such
a unit is arbitrary and is
used as a possible unit out of many. The units could have just as easily been
1/10 of a trailer, two
feet, or whatever. The essence of the present invention is that a table can be
used for rapid lookup
of answers with interpolation being used for values not in the table and
ratiometric scaling used for
trailers having a length measured in units that are different from the units
used to build the table. It
is contemplated by the present invention that other approaches to obtaining
the projected direction
can be utilized; for example, a calculated solution could be implemented
whereby this calculation
is optimized for a tow vehicle and trailer of a known length (in Trailer
Units) in order to make the
23
CA 02783664 2014-02-18
calculation most efficient in software while incorporating ratiometric scaling
for trailers having a
length measured in units that are different from the units used to process the
calculation.
Figure 14A-D depicts four scenarios of tow vehicle steering with the hitch
angle to the left. Left-
right mirror images apply for hitch angles to the right. A hitch angle to the
left is arbitrarily defined
as a positive valued hitch angle whereas a hitch angle to the right is a
negative value. A steering
angle to the left is defined as a positive valued steering angle whereas a
steering angle to the right
is a negative value. Because of this mirror symmetry, the sign of the hitch
angle can be ignored for
the purpose of determining the projected angular change in direction of the
tow vehicle to where
the tow vehicle and the trailer become generally in-line and then the sign
restored before using that
projected result. (This is consistent with only storing a single quadrant from
the table as described
above for Figure 10.)
Figure 14A shows the tow vehicle steered to drive straight backwards (note the
position of the
front wheels of the tow vehicle). In this scenario with the hitch angle to the
left, as the tow vehicle
reverses the trailer will jackknife to the left. Figure 14B depicts the first
limit condition, that of
infinite turning. In this scenario, a backing increment will be translated
into motion by the trailer
whereby a portion of that backing increment will go into backing the trailer
and a portion into
rotating the trailer, as described above. When the incremental amount of
trailer rotation matches
the amount of tow vehicle turning as a function of the steering angle, the
hitch angle will be
unchanged after completing the backing increment from what it was before the
backing increment.
As a result, the next backing increment (assuming no change to the steering
angle) will result in
the same hitch angle again and, in theory (because in real life, imperfections
in the apparatus,
driving surface, and the like will prevent the perfect outcome) the tow
vehicle and trailer could
drive indefinitely along the arc of a circle defined by this steering angle
(and matched by this hitch
angle). This steering angle (or, of course, it's corresponding turning radius)
defines the first limit
condition and this is a function of the trailer length. Any steering angle
that moves away from this
infinite turning steering angle towards the straight line steering condition
(or beyond) will result in
jackknifing to the left where the farther from the infinite turning angle the
more rapidly jackknifing
will occur. Any steering angle that moves away from this infinite turning
steering angle in the
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CA 02783664 2014-02-18
opposite direction (i.e., away from the straight line steering condition) will
result in a controlled
steering of the trailer and this is depicted in Figure 14C. However, as
depicted in Figure 14D, there
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CA 02783664 2014-02-18
is a second limit which is a function of the vehicle and is obtained when the
steering angle reaches
the greatest or sharpest angle (i.e., tightest turning radius) that the tow
vehicle can turn. One most
commonly thinks of controlled backing with a trailer as occurring between the
Infinite Steering
Limit (ISL) and the Tightest Turning Limit (TTL). There is an ISL and a TTL to
both the left side
and the right side of the vehicle center line. However, it is the steering
outside of these limits that
requires special understanding if maneuvers such as Parallel Parking with a
trailer and Reversing
Directions with a trailer are to be affected. Therefore, to increase the hitch
angle, the tow vehicle
must temporarily steer in the range where jackknifing would occur and to
decrease the hitch angle,
the tow vehicle must steer in the range between the ISL and the TTL,
inclusively. To reverse the
hitch angle, the tow vehicle must steer in the range between the ISL and the
TTL, and continue
backing beyond the point where the tow vehicle and the trailer become
generally in-line. One or
more of these limit lines can be displayed by superimposing an arc
corresponding to these turning
angles, as is known in the prior art.
As an example of operation when parallel parking with a trailer into a parking
space (with the curb
on the right), the vehicle and trailer initially pull forward of the space (at
which point they are in-
line). The vehicle is first steered to the left (see Figure 15A) by an amount
that will not cause the
front right corner of the vehicle to strike a parked car while backing up.
This first steering is
estimated by the operator if the present invention is being used as a
direction indicator, or if servo
controlled steering is being used with automated back-up control (as is known
in the art), this first
steering can be determined based on the right side collision sensors. As is
now shown in Figure
15B, this will cause the trailer to turn to the right, directing its back end
into the space. Backing
continues until the back of the space falls between the left side ISL and TTL.
The vehicle is now
secondly steered to the right with an amount of steering close to the TTL, and
as shown in Figure
15C, this will cause the trailer to move only a little bit farther into the
space (to allow room for the
straightening step) and to cause the vehicle to start to become in-line with
the trailer. The vehicle
continues to back up to the point where the vehicle and trailer become in-
line. Then, as shown in
Figure 15D, the vehicle continues to back up beyond that the point where the
vehicle and trailer
became in-line, causing the trailer to cross the center line of the vehicle.
At this point, the trailer
will be generally in the space and the vehicle is thirdly steered to the left
with the aid of the present
invention by an indicated amount that will direct the trailer to the back of
the space. With this third
CA 02783664 2012-07-18
steering, as shown in Figure 15E, the vehicle continues to back up until the
trailer and vehicle
become generally in-line within the parking space. In the prior art, Fischer
et al. in their U.S.
Patent 7,089,101 (at column 9 line 43 through column 10 line 39), while no
method for
determining the path of a tow vehicle backing with a trailer is disclosed, a
method is disclosed to
retard the speed of the tow vehicle if the actual path deviates from a
projected path (however it is
determined), and this method could be utilized along with the present
invention. However, the
present invention is likewise envisioned to be utilized in situations where
the steering is controlled
by servos but the accelerator and break are controlled conventionally by the
operator.
Obstacle sensors are recommended for partially automatic guided (and required
for fully automatic
guided) trailer backing systems. However, such sensors will need to be trailer
mounted as vehicle
mounted sensors could be blocked by the trailer and sensor selection will be
limited to those
sensors that will not be affected by being submerged along with a boat
trailer, often into water
containing dirt or plant or other debris that could obscure or otherwise
diminish or defeat the
sensors' operation. An operator guided system, even if the steering is servo
controlled, would have
minimal risk of the operator erroneously relying on sensors that are not
obscured.
The foregoing description of an example of the preferred embodiment of the
invention and the
variations thereon have been presented for the purposes of illustration and
description. It is not
intended to be exhaustive or to limit the invention to the precise forms
disclosed. Many
modifications and variations are possible in light of the above teaching. It
is intended that the scope
of the invention be limited not by this detailed description, but rather by
any claims appended
hereto.
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