Note: Descriptions are shown in the official language in which they were submitted.
1~21~4
DESCRIPTION
Method for Displayinq Load Distribution
by Monitorin~ a Work Vehicle Sus~ension
Technical Field
This invention relates generally to an apparatus
for automatically determining the distribution of payload
in a work vehicle, and more particularly, to an apparatus
for automatically determining the distribution of payload
in a work vehicle by monitoring strut pressures.
Background Art
In the field of off-highway trucks used in
mining operations, for example, it is desirable that an
accurate record be kept of the quantity of material
removed from the mining site. This information can be
used to calculate mine and truck productivity as well as
aid in forecasting profitability and work schedules.
Other systems, as disclosed in U~S. Patent
4,635,739 issued to D. Foley et al. on January 3, 1987,
have shown that strut pressure can be an accurate
indicator of payload. The apparatus disclosed therein
includes an electronic control which monitors each of the
strut pressures, compensates for various inaccuracies
introduced by load distribution and vehicle attitude, and
correlates this information into actual payload. This
payload information allows the truck to be operated
efficiently near its maximum capacity without promoting
undue vehicle wear. An overloaded vehicle hastens tire
and frame damage.
Improper payload distribution also promotes
vehicle wear. Strut, frame, and tire damage can occur
easily if the payload is distributed unevenly. The
payload monitor accurately calculates payload with an
13210~
unsymmetrical distribution, but does not fully protect the
vehicle franle and suspension from overloads. Merely
determining the actual payload to prevent overloading is
not sufficient to fully protect the vehicle, since uneven
distribution causes overloads on portions of the vehicle.
Heretofore, there have been no devices for
displaying the payload distribution of a dump truck to an
operator. Some prior art shows weight distribution on
each axle for multi-axled vehicles. However, this
information is inadequate for very large off-highway dump
trucks. Many trucks of this type use electric motors to
drive each side of an axle. If the load on one side is
much larger than the load on the opposing side, then one
electric motor works much harder than the other. The
torque output necessary to move an excessive load can
easily overdrive an electric motor. Repair and
replacement of such motors is extremely expensive.
Truck operators often park incorrectly during
loading. Level ground should be sought to prevent one
strut from receiving much more load than another. For
instance, parking with a rear tire on a small hill or
grade can cause that portion of the truck to accept as
much as 90 percent of the load, while an adjacent portion
may exhibit a negative load. The implications of such a
loading configuration are obvious. Suspension and frame
damage can easily occur during loading from an improper
loading position, due to the extreme load on the
suspension structure and the torsional forces propagating
through the frame.
The present invention is directed to overcoming
one or more of the problems as set forth above.
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Disclosure of the _nvention
An apparatus displays the distribution of a
payload on a work vehicle. The vehicle has a plurality of
hydraulic struts in supporting relation thereto. A means
senses the internal pressure of preselected struts and
delivers a plurality of first signals. Each of the first
si~nals has a value responsive to the internal pressure of
one of said respective struts. A means modifies each o~
the first signals, and delivers modified signals in
response to the modification. Each modified signal is
indicative of the payload supported by one of the
respective struts. A visual display means receives the
modified signals and displays respective visual signals in
response to the magnitude of the modified signals.
Overloading of off-highway trucks causes many
expensive failures. The frame, suspension, tires,
electric motors, and lift cylinders all wear at
accelerated rates when overloaded by an extreme payload.
The total weight of the payload should not exceed the
rated payload. However, even when this condition is met,
poor load distribution transmits irregular forces through
the suspension to the frame. Individual struts can
experience damaging forces, while others experience
negligible forces. Additionally, uneven load distribution
conveys possibly destructive torsional forces to the
vehicle's frame. Moreover, an extreme load on one corner
of the vehicle overloads the electric drive motor on the
associated wheel, due to the high output it must provide
to move the load.
A monitor capable of displaying the actual or
relative amount of payload being supported by each strut
allows the loader operator to direct subsequent loads to
the proper locations in the truck's dump body. Providing
the operator with a tool that displays the load
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characteristics facilitates even loading, which redllces
damaging forces. Merely knowing the total payload or the
axle loads is insufficient. When the load is known on
each suspension member, the operator receives more
information and a greater amount of damage may be avoided.
Brief Description of the Drawinqs
Fig. 1 illustrates a diagrammatic view of an
off-highway truck and the location of critical suspension
components;
Fig. 2 illustrates a block diagram of the
suspension monitor;
Fig. 3 illustrates a portion of one embodiment
of the functional software flowchart for the present
invention;
Fig. 4 illustrates a preferred embodiment of a
visual display of the present invention;
Fig. 5a illustrates an operating example of the
visual display;
Fig. 5b illustrates an operating example of the
visual display;
Fig. 5c illustrates an operating example of the
visual display; and
Fig. 5d illustrates an operating example of the
visual display.
Best Mode For CarrYing Out The Inven_ion
Referring now to the drawings, wherein a
preferred embodiment of the present apparatus 10 is shown,
Fig. 1 illustrates a work vehicle 12 which can be, for
example, an off-highway truck 14. The truck has at least
one front and one rear strut 16,18 disposed in supporting
relation to a load carrying portion 20 of the work vehicle
12. The preferred embodiment has two front and two rear
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struts 16L,16R,18L,18R which are the gas-over-liquid type
commonly known in the industry and not described herein.
It i5 suf.ficient in the understanding of the instant
apparatus 10 to recognize that the pressure of the fluid
is indicative of the magnitude of the load applied to the
strut 16,18, and that wide swings in the strut pressures
are normal and even expected during vehicle travel,
commonly referred to as "roading".
The load carrying portion 20 includes a
vehicular frame 22 and dump body 24. The dump body 24 is
connected to the frame 22 by pivot pin 26 and a hydraulic
cylinder 28 such that the contents of the dump body 24 can
be removed by controllably pressurizing the cylinder 28 to
effect pivotal movement of the dump body 24 about the
pivot pin 26. In the transport mode, the cylinder 28 is
not pressurized and the weight of the dump body is
transferred to the frame through the pivot pin 26 and a
support pad 30 fixed to the frame 22.
The work vehicle 12 further includes a ground
engaging portion 32 and a suspension means 34 for
supporting the load carrying portion 20 in a manner to
provide damped oscillatory motion between the ground
engaging portion 32 and the load carrying portion 20. The
suspension means 34 includes a rear axle housing 36 and an
A-frame moment arm 38. The A-frame moment arm 38 has a
first end portion 40 pivotally connected to the vehicular
frame 22 by a socket 42, and a second end portion 44
fixedly connected to the rear axle housing 36. The first
end portion 40 of the ~-frame moment arm 38 is a king bolt
arrangement, substantially spherical in shape and retained
from lateral movement by the socket 42. The rear strut 18
has a first end portion 46 pivotally connected to the
vehicular frame 22 and a second end portion 48 pivotally
~L321~2~
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connected to the second end portion 44 of the A-frame
moment arm 38.
nuring loading of the truck, as the payload
increases, the load carrying portion 20 will be displaced
in a direction toward the ground engaging portion 32. The
rear strut 18 begins to compress while the A-frame moment
arm 38 pivots about first end portion 40. A distance L2
is de~ined to be the distance between the first end
portion 40 pivot point and the second end portion 44 pivot
point of the arm 38. Therefore, it can be shown that the
rear strut pressure differential is a function of the
suspension means 34. Moreover, the rear strut pressure
differential can be related to the reaction force R
between a work surface and the ground engaging portion 32.
A force S experisnced by the rear strut 18 can be
determined by measuring the internal pressure of the strut
18, subtracting the rear strut pressure corresponding to
an unloaded truck, and multiplying the differential
pressure by the area of the strut 18. A reaction force R
is proportional to the payload of the vehicle 12 and can
be assumed to act through the center of the rear axle
housing 36 such that a summation of the moments about the
pivot point of the king bolt would derive the following
equation
teqn. 1) R = S * L2/L3
where the horizontal distance between the first end
portion 40 pivot point and the center of rear axle housing
36 is defined to be L3.
Similarly, the front strut 16 will be compressed
as the load increases; however, the front strut is
connected directly between the frame 22 and a front axle
housing 50. A more straightforward relationship exists
1321~2~
here in that a force F experienced by the front strut 16
can be determined by measuriny the internal pressure of
the strut 16, subtracting the front strut pressure
corresponding to an unloaded truck, and multiplying the
pressure by the area of the strut 16. The reaction force
F between the ground engaging portion 32 and the work
surface is substantially equivalent to the force F
experienced by the front strut 16.
The apparatus 10 is shown in Fig. 1 to
illustrate the relationship between the work vehicle 12
and the location of the apparatus 10. A more detailed
block diagram of the apparatus 10 is shown in Fig. 2 and
diagrammatically illustrates a means 52 which senses the
pressures of each of the struts 16,18 and delivers a
plurality of signals each having a value responsive to the
internal pressures of a respective strut. The means 52
includes a plurality of pressure sensors 54,56,58,60 of
the type commercially available from Dynisco as part
number PT306. The pressure sensors 54,56,58,60 are
respectively associated with the two front struts 16L,16R
and the two rear struts 18L,18R. Each of the pressure
sensors 54,56,58,60 delivers an analog signal proportional
to the magnitude of the pressure of the respective strut
16L,16R,18L,18R to respective analog to digital converters
(A/D) 62,64,66,68. The A/D's 62,64,66,68 can be of the
type commercially available from Analog Devices as part
number AD575A. Other types of A/D converters have been
contemplated by the inventor and the choice of the
particular A/D disclosed herein is simply a matter of
designer discretion. The selection of a device which
provides an analog to fre~uency output is particularly
well suited to the digital microprocessor environment
disclosed herein: however, other similar devices could be
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easily substituted without departing from the spirit of
the invention.
A peripheral interface adapter (PIA) 70 receives
the digital frequencies output by the A/D converters
62,64,66,68 and delivers these signals to a microprocessor
72 under software control. In the preferred embodiment,
the microprocessor 72 is part number 6809 provided by the
Motorola Corp. The microprocessor 72 is programmed to
have a means which modifies the front and rear strut
pressure signals by applying respective unique correction
factors thereto. These correction factors convert first
siqnals, each having a value responsive to the internal
pressure of one of said respective struts, into an
indication of force or payload on an associated strut
16,18. The modified signals are transmitted via a second
PIA 76 to a display driver 781', which is associated with
the truck. The driver 78T controls the truck's visual
display 80T in response to the modified signals. The
second PIA 76 also transmits modified signals to a
communication link 71. The communications link 71
transmits the necessary information from the
microprocessor 72 to a visual display driver 78L, which is
associated with the loader. The driver 78L controls the
loader's visual display 80L in response to the modified
signals. The communication link 71 is preferrably an
infra-red link, but any suitable type of communications
could be used without departing from the scope of the
nventlon.
Referring to Fig. 3 wherein a preferred
embodiment of a software routine is illustrated in the
form of a flowchart 100. In a block 102 the strut
pressures are monitored. Control transfers to a decision
block 104 where the software routine checks to determine
if the calibration switch 86 has been actuated. The truck
~32~o2~
operator will typically actuate the calibration switch 86
at the beyinning o~ a shift when the vehicle is known to
be empty. When the calibration switch 86 is actuated,
control transfers to a block 106, and pressure signals
corresponding to an unloaded truck are loaded into memory.
If the calibration switch 86 is not actuated, control
transfers to a decision block 108 where vehicle movement
is determined. The program monitors the strut pressures
for a predetermined period of time to determine if the
vehicle is moving. If the strut pressures are stable for
the predetermined period, then the vehicle is assumed to
be stopped. Of course, other suitable methods may be
employed. For instance, a sensor monitoring the gearbox
or transmission could transmit a signal containing the
required information. If the vehicle is stopped, control
passes to a block 110 where the strut pressure signals are
modified. Respective correction factors are applied to
each pressure signal. The correction factors modify the
pressure signals to produce signals responsive to a load
or a force on a respective strut 16,18. Next, control
passes to a block 112 where the modified signals are
transmit~ed to the visual display means 77 composed of a
display driver 78 and a visual display 80. The display
driver 7~ receives the modified signals and delivers
signals suitable to power the visual display 80 in
response to the magnitude of the modified signals.
Referring now to Fig. 4 wherein a visual display
80 of the preferred embodiment is illustrated. The visual
display 80 uses four elements 114,116,118,120. They are
usually liquid crystal displays, light emitting diode
arrays, or analog type guages. In the preferred
embodiment, the elements have a generally rectangular
configuration, however a wide variety of configurations
may be substituted without departing from the scope of the
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invention. Furthermore, the visual display elements
114,116,118,120 are arranged in a generally rectangular
configuratlon, wherein each element is representative of a
corner of the vehicle. While most of the apparatus 10
resides on the truck, the visual display means 77 is
usually located on both the truck and the loader. A
communication link 71 transmits the necessary information
from the microprocessor 72 to the loader's visual display
driver 78L. The driver 78L powers the elements
114,116,118,120 of the loader's visual display 80L, which
displays visual signals in response to the magnitude of
the respective modified signals.
The elements 114,116,118,120 are generally
divided into four sections R,Y,G,B. Each section provides
the operator with a different piece of information about
the load distribution. Typically, the visual signals
provided by the elements 114,116,118,120 vary in both
color and magnitude in response to the magnitude of the
modified signals. If analog guages are used, such as
those with d'arsenal movements, the pointer will point to
color ranges on the face of the guage. This imparts to
the operator information at a glance. This information
allows the truck operator to position the truck properly
for receiving a load, and also allows the loader operator
to load the truck properly.
Figs. 5a, 5b, 5c, and 5d illustrate a poor
loading position, a proper loading position, a poor load
distribution, and a proper load distribution,
respectively.
Referring to Fig. 5a, assume the truck is awaiting a load,
while parked on a grade. Sections 'G', 'Y', or 'R' of one
or more elements 114,116,118,120 illuminate depending on
the severity of the grade, while section 'B' of one or
more of the other elements 114,116,118,120 illuminate.
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Sections 'G', 'Y', and 'R' indicate positive loads, and
section 'B' indicates a negative load. This informs the
truck operator that even in the empty state, the truck is
poorly positioned since the load on one or more struts is
positive, while the load on others is negative. A
positive load corresponds to strut pressure increasing
pa5t a preselected point which is equated to an empty
state, and a negative load corresponds to strut pressure
decreasing below the setpoint. The larger the positive or
lo negative load, the higher the magnituds of the respective
lights. Typically, the elements act as bar graphs, so
that higher loads cause more portions of the element to
illuminate. Ideal loading conditions exist when no
portions of the elements are illuminated, or when small
portions of sections 'G' are illuminated, as is shown in
Fig. 5b.
Fig. 5c shows an example of poor load
distribution. Two elements 114,120 show very small
positive loads associated with their respective struts
16L,18R, depicted by the small portions of the sections
'G' which is illuminated. Conversely, the other elements
116,118 show extreme overloads on their respective struts
16R,18L, depicted by the sections 'G' and '~' being fully
illuminated along with a portion of the section 'R'. The
loader operator should dump the next loads in portions of
the dump body corresponding to the small loads in an
effort to evenly distribute the load. In this case, the
next loads should be placed in the front left and rear
right of the dump body 24. Fig. 5d shows an ideally
loaded truck. The display in this condition has large
portions of the section 'G' illuminated. This informs the
loader and the truck operators that the truck is evenly
loaded and near rated capacity.
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Industrial Applicabilit~
Assume that the apparatus 10 is mounted on an
off-highway truck 12. At the beginning of a shift, the
truck operator actuates the calibration switch 86 while
the truck is empty and stationary. If the strut pressures
are stabl~ for a predetermined period of time, then the
initial pressures are input to the microprocessor 72.
These pressure signals correspond to pressures of an empty
truck. Now the truck operator moves to a work site, and
lo prepares to receive a load. The visual display 80 will
display the relative loads on each strut when the truck is
stopped. The operator moves the truck until small
portions of the sections 'G' of the elements
114,116,118,120 are illuminated. This indicates that the
truck is in an ideal position to receive a load.
As the loader operator dumps portions of the
load in the dump body 24, his display 80L conveys
information about load distribution. Subsequent loads are
placed in locations having a smaller load distribution.
Of course, the truck operator may reposition the truck
during loading to improve underfoot conditons. The ideal
loaded condition exists when all of the 'G' sections of
the elements 114,116,118,120 are fully illuminated. When
portions of the 'R' sections are lit, an overload
condition exists on the associated struts. Normally,
during loading all struts show positive pressures, so the
'B' sections of the elements 114,116,118,120 are not
illuminated.
Other aspects, objects, and advantages of this
invention can be obtained from a study of the drawings,
the disclosure, and the appended claims.
