Note: Descriptions are shown in the official language in which they were submitted.
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STEERING SYSTEM FOR ARTICULATED VEHICLES
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This claims the benefit of U.S. Provisional Patent Application No.
60/407,851 filed August 30, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to articulated vehicles. In particular,
the
present invention relates to the steering systems for articulated vehicles.
BACKGROUND OF THE INVENTION
[0003] Articulated vehicles, such as wheeled feller bunchers, skidders,
forwarders, front end loaders and many other industrial vehicles, have a
chassis
consisting of two or more frames hinged together so that steering is effected
by varying
the angle of articulation between the frames.
[0004] The required articulation is accomplished using hydraulic cylinders
that are connected to the frames. The hydraulic cylinders are typically
controlled by a
directional control valve which is used to supply hydraulic fluid to the
cylinders to
change the cylinder length, thereby varying the articulation angle between the
frames.
Hydraulic fluid is only supplied to change the cylinder length. Otherwise the
cylinders
act as a solid link, and prevent the frames from articulating to some other
position. To
permit the cylinder to function as a solid link, four way, three position
control valves
having closed-center ports are used.
[0005] However, typical articulated vehicles have various inherent problems.
One problem is that they have only a single steering sensitivity level.
Because regular
directional control valves are used, hydraulic fluid is either supplied to the
hydraulic
cylinders or it is not. This only provides a single steering sensitivity for
the vehicle.
However, different steering sensitivity levels are required depending on the
operation
being performed. For example, the steering sensitivity required while
harvesting (in low
gear) are quite different from those required while traveling by road (in high
gear).
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[0006] A second problem is that typical articulated vehicles require constant
steering throughout an operation. For example, if a typical articulated
vehicle is turned to
the right, the operator must then steer the vehicle back to the left to return
to traveling in
a straight path. Typical articulated vehicles will not automatically return to
traveling in a
straight path when the steering control is operated "hands-off', unlike
typical passenger
cars that will. This makes the vehicles more difficult to control and more
fatiguing for an
operator since they must constantly be steering the vehicle.
[0007] A third problem is that typical articulated vehicles can have different
size tires installed and in some cases, when larger tires are installed, the
larger tires
interfere with steering by contacting each other at a certain amount of
articulation. To
prevent this problem, a stop must be installed to prevent articulation of the
frames to a
point where the tires will make contact. Since this stopping position
inherently involves
less than a full cylinder stroke, hydraulic cushions are not feasible. In
addition, typical
solid stops result in a violent action and a very abrupt stop.
[0008] A fourth problem is that typical articulated vehicles must have a
separate design for each steering device desired (i.e. steering wheel v.
joystick).
Currently, building one version or the other involves many parts special to
the selected
steering system. For instance, if a steering wheel is selected, then a rotary
directional
control valve (either Orbitrol or Quick steer) is connected to the steering
wheel and the
hydraulic lines used are unique to that system. Conversely., if a joystick is
selected a
special directional control valve must be installed and an entirely different
set of conduits
is required.
[0009] It would therefore be advantageous if a steering system for an
articulated vehicle could be designed that: 1 ) allowed for various steering
sensitivity
levels; 2) did not require continual steering by an operator throughout an
operation; 3)
had a more controlled and less violent st;~pping mechanism at maximum
articulation; and
4) did not require a separate design for each available steering device. In
particular, it
would be advantageous if the steering system were designed to provide
different steering
sensitivity levels depending on the gear that the vehicle is in, or depending
on operator
selection, to provide a self centering action when no steering input is
supplied, to provide
a controlled, soft stopping action when the vehicle reaches maximum
articulation, and to
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allow for a single design that would accept any desired steering device
without modifying
or redesigning other portions of the vehicle.
SUMMARY OF THE INVENTION
(0010] The present inventors have discovered a steering system for an
articulated vehicle that provides: 1) different steering sensitivity levels
based on the gear
that the vehicle is in, or based on specific operator requirements and inputs;
2) the ability
to provide an emulated caster effect to return the vehicle to travel in a
straight path when
the operator is not providing any steering input; 3) the ability to set a
maximum
articulation angle between the frames of the vehicle based on the size of the
tires installed
to avoid contact between the tires while turning; and 4) the ability to have a
single design
for the vehicle that will accept any manner of steering device desired.
[0011] In particular, the present invention relates to a steering system for
an
articulated vehicle that includes a first frame and a second frame that are
pivotally
connected by a pivot joint. Hydraulic cylinders are connected between the
first frame
and the second frame, on opposite sides of the pivot joint, for articulating
the first frame
and the second frame. Four way, three position proportional solenoids are
connected to
the hydraulic cylinders by hydraulic conduits to control the flow of hydraulic
fluid
between the hydraulic cylinders, the pressure source (e.g., a pump) and the
tank pressure.
A microprocessor is connected to and controls the operation of the
proportional solenoids
and the reversible pump. Finally, there is a means for providing electronic
steering
signals to the microprocessor. By having proportional solenoids, rather than
typical
valves which are either opened or closed, the system can better regulate the
amount and
rate of flow of the hydraulic fluid to the hydraulic cylinders, thereby giving
the system
better and smoother steering control. In addition, rather than having a
different hydraulic
design for each type of steering device available, a single articulated
vehicle design can
be used that will accept any type of steering device desired that can send
electronic
steering signals to the microprocessor.
(0012] The present invention further relates to a steering system for an
articulated vehicle that also includes a positional feedback sensor, connected
to the
microprocessor, that measures the articulation angle between the first frame
and the
second frame. The microprocessor also includes a means for returning the first
frame and
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the second frame to an aligned position, based on the articulation angle, when
no
y electronic steering signal is being received. This allows the system to
provide an
emulated caster effect wherein the articulated vehicle will return to
traveling in a straight
path in the absence of steering by an operator. This provides safer and easier
control
when traveling on roads and is less fatiguing when performing operations, such
as
harvesting.
[0013] In addition, if the steering control valve shares a source of hydraulic
pressure with other control valves, and all of the valves are controlled by
the same
processor, the processor can control the valves to give flow priority to the
steering control
valve. This eliminates the need for a separate steering pump and/or hydraulic
priority
valve.
[0014] The present invention further relates to a steering system for an
articulated vehicle that also includes an operator input device, connected to
the
microprocessor, that allows an operator to input the size of the tires
installed on the
vehicle or to otherwise change the steering sensitivity levels to his own
requirements.
The microprocessor also includes a way to determine a maximum articulation
angle
based on the size of the tires. This prevents the tires from corning into
contact with each
other during turns, no matter what size tire is installed on the articulated
vehicle, allows a
controlled stop to be set at an articulation angle ideal for thc: selected
tires, and avoids
sudden stops and violent stopping actions that typically occur with current
stopping
devices.
[0015] The present invention further relates to a steering system for an
articulated vehicle that also includes a gear selector sensor, connected to
the
microprocessor, that monitors gear information. The microprocessor also
includes a
means for controlling the displacement and/or rate of~ displacement of the
proportional
solenoids based on the gear information. This allows the system to set to
different
steering sensitivity levels according to the task being performed or according
to operator
requirements. For example, the steering sensitivity could be set to coarse
(more response
for a given operator input) while performing an operation in low gear, such as
harvesting,
or can be set to fine (less response for a given operator input) while
performing an
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operation in high gear, such as traveling on a road. This system allows the
steering
sensitivity to be varied depending on the gear or terrain variables.
BRIEF DESCRIPTION OF THE DRAVv'INGS
[0016] Fig. 1 is a partial schematic diagram of a steering system for
articulated vehicles according to the present invention; and
[0017] Fig. 2 .is a partial hydraulic schematic view of a proportional
solenoid
valve for use in the system of Fig. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
(0018] Referring to Figure 1, an articulated vehicle according to the
preferred
embodiment of the present invention has a front frame 10 and a rear frame 20,
which are
pivotally connected at pivot joint 30. A pair of hydraulic cylinders 40, 45
are connected
to the front frame 10 and the rear frame 20 and are located on opposite sides
of the pivot
joint 30 as shown. The hydraulic cylinders 40, 45 are used to steer the
articulated vehicle
by articulating the front frame 10 and the rear frame 20 around the pivot
joint 30, thereby
changing the articulation angle between the two. The front frame 10 and the
rear frame
20 are articulated around the pivot joint 30 by having one of the hydraulic
cylinders 40
extend while the other hydraulic cylinder 45 retracts.
[0019] Each of the hydraulic cylinders 40, 45 has its bore side connected to
the rod side of the other cylinder 40, 45 by a conduit 41 or 46, and the
conduits 41, 46 are
respectively connected by hydraulic conduits 130, 135 to a four way, three
position
proportional solenoid valve 52 which is controlled by proportional solenoids
50, 55.
Referring to Fig. 2, a source of hydraulic pressure, represented by pump P, is
connected
to the pressure port of the valve 52, and the reservoir tank T is connected to
the tank port
of the valve 52.
[0020] It should be noted th~it other relief or other valves could be supplied
in
the hydraulic circuit, which are not fundamental to practicing the present
invention. For
example, a pressure relief valve may be spliced into the line between the pump
P and the
valve 52 to relieve excess pressures in that line, even though the pump P
would
preferably be of the pressure compensating type. In addition, it would be
common to use
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a port relief valve in each of the lines 130, 135 to relieve excess pressures
in those lines,
such as might occur when traveling in rough terrain.
[0021] When the valve 52 is shifted in one direction, for example to the left
as
viewed in Fig. 2 by energizing one of the solenoids 50, 55 and deenergizing
the other
solenoid, line 130 is connected to pump pressure and line 135 is connected to
tank
pressure by the valve 52. This results in extension of cylinder 40 and
retraction of
cylinder 45. When the valve 52 is shifted in the opposite direction by
energizing solenoid
55 and deenergizing solenoid 50, line 130 is connected to tank pressure and
line 135 is
connected to pump pressure by the valve 52, which extends cylinder 45 and
retracts
cylinder 40. Since the solenoids 50 and 55 are proportional, the extent to
which they
provide communication between the cylinders 40, 45 and the respective pump and
tank
pressures will depend upon the signal which they are energized with, which may
be any
variable signal, such as a, variable voltage, variable current or a pulse
width modulated
signal.
[0022] The valve 52 is part of a mufti-spool control valve block 120. In
addition to the proportional 4/3 valve 52 that controls the hydraulic steering
cylinders 40,
45, the mufti-spool directional control valve block may also contain
additional valves that
can control various other hydraulic equipment on the vehicle such as hoist
cylinders, tilt
cylinders, a harvesting arm cylinder, an accumulating arm cylinder, etc., as
shown in
phantom in Fig. 1. By using a microprocessor to control all of the valves
supplied by the
hydraulic pump for the system {pump P in Fig. 2), the microprocessor can
control the
valves to give flow priority to the steering valve 52. Steering is given
priority over many,
if not all of the other functions, meaning that if a steering input signal is
received by the
processor but one or more of the other valves are using up all of the
available flow or
pressure of the system pump, the processor can close, proportionally or
totally, one or
more of the other valves to divert flow to the steering valve. The processor
can use the
output of the positional feedback sensor 70 to monitor steering response, and
when it falls
short of that expected by the processor for a given output to the steering
valve 52, the
processor can reduce the flow through one or more of the ether open valves, to
divert
flow to the steering valve. This eliminates the need for a separate steering
pump, and/or
for a hydraulic priority valve.
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[0023] As mentioned above, the proportional solenoids 50, 55 control the
s flow rate at which hydraulic fluid is transferred betwcen the hydraulic
cylinders 40, 45
and the respective pressure source and tank, thereby controlling the rate at
which the
hydraulic cylinders 40, 45 extend or retract. This is done by controlling the
size of the
orifice through which hydraulic fluid passes through the valve 52, from the
pressure
source and to the tank pressure. For example, to have the hydraulic cylinders
40, 45
expand/retract more quickly for a given steering input by the operator, and
therefore to
have the articulated vehicle react more quickly for a given steering input,
proportional
solenoids 50, 55 would be energized by a signal which is greater in magnitude
to move
the valve spool of valve 52 to a more open position i:n the desired direction,
allowing a
faster rate of flow of hydraulic fluid to and from the hydraulic cylinders 40,
45. This
would be a "coarse" setting, since for a small steering input by the operator,
a relatively
faster steering correction occurs, which would be desirable for slow speeds.
For a slower
or less sensitive motion of the hydraulic cylinders 40, 45 for a given
steering input, the
proportional solenoids 50, 55 would be energized by a signal which is lesser
in
magnitude to move the valve spool of valve 52 to a less open position in the
desired
direction, providing a slower rate of flow of hydraulic fluid to flow to and
from the
hydraulic cylinders 40, 45. This would be a "fine" setting, since a small
steering input
produces a relatively smaller steering correction, and would be more desirable
for higher
speeds of travel.
[0024] The valve 52 can also be operated to vary the magnitude of the
steering angle change for a given input. The magnitude of the steering angle
change is
proportional to the volume of hydraulic fluid pumped through the valve 52.
Once a
certain volume has been pumped through the valve 52, or the valve is open at a
certain
setting (coarse or fme) for a certain period of time, the valve can be
returned to its center
closed position (shown in Fig. 2), to cut' off the flow to and from the
steering cylinders
and hold the steering position of the front frame relative to the rear frame,
as long as the
steering input is not changed. Therefore, if a certain steering input
corresponds to a
certain open time of the valve (in one direction or the other), then the
amount of steering
angle change, also referred to as steering correction, will depend upon
whether the
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steering system is in fine or coarse mode. There will be less (and slower)
steering
y correction for a given input in the fine mode than in the coarse mode.
[0025] The proportional solenoids 50, 55 are communicatively connected to
and controlled by a microprocessor 60. In response to various signals and
commands,
which are described in more detail below, the microprocessor 60 sends signals
to the
proportional solenoids 50, 55 which control which solenoid will open or close
the valve
52, the amount that the solenoids will open or close the valve 52, the time
that they will
be open, and possibly the rate at which the solenoids will open or close the
valve.
(0026] A positional feedback sensor 70, a gear selector sensor 80, a steering
device 140, and an operator input device 110 are also communicatively
connected to the
microprocessor 60.
[0027] The positional feedback sensor 70 is connected to the front frame 10
and the rear frame 20 of the articulated vehicle and is used to measure the
articulation
angle between the front frame 10 and the rear frame 20. The output signal of
the sensor
70 is communicated to the microprocessor 60 as an input of the steering angle
of the
machine. It will be understood by those skilled in the art that the positional
feedback
sensor 70 does not have to be connected to the front frame 10 and the rear
frame 20 but
could also be connected to the pivot joint 30 to measure the angular
displacement
between the front frame l0 and rear frame 20 or could be any other means for
measuring
the angle between the front frame 10 and the rear frame 20.
[0028] The gear selector sensor 80 is connected to the transmission of the
articulated vehicle (not shown) and is used to determine the gear that the
transmission is
in. The output signal of the sensor 80 is communicated to the microprocessor
60 to
provide an input of which gear the machine is in.
[0029] The steering control device 140 is used to receive mechanical steering
inputs from the operator, to convert the mechanical steering inputs into
corresponding
electrical steering signals, and to communicate the electrical steering
signals to the
microprocessor 60. In the preferred embodiment of the invention, the steering
device 140
is an electric steering wheel 90 or an electric joystick 100. However, it will
be
understood by those skilled in the art that any type of steering device that
can accept a
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mechanical steering input from an operator and convert the mechanical steering
input into
s a corresponding electrical steering signal can be used.
[0030) The operator input device 110 is used to receive information from the
operator and to communicate this information to the microprocessor 60 as an
electrical
signal. As described in more detail below, in the preferred embodiment of the
invention
the operator input device I 10 may include a steering sensitivity selection
switch and a tire
size input device.
[0031] The steering sensitivity selection switch allows the operator to
manually select between coarse mode, fine mode, or automatic mode. As
described in
more detail below, the operator would select between coarse, fine, and
automatic modes
depending on the steering sensitivity desired.
[0032] The tire size input device allows the operator to input the size of the
tires installed on the articulated vehicle. The tire size input by the
operator is then
communicated to the microprocessor 6U and is used to determine a maximum
allowable
articulation angle between the front frame 10 and the rear frame 20, which the
microprocessor will then not exceed, based on the measured articulation angle
from the
sensor 70. The tire size may be input by any suitable method, such as direct
input, a pull
down menu or similar input interface, following which the processor 60 may
compare the
input to a look-up chart to determine the maximum allowable angle of
articulation.
[0033] Prior to operating the articulated vehicle after a tire change, the
operator would use the tire size input device of the operator input device 110
to input the
size of the tires installed on the articulated vehicle. To prevent the tires
from making
contact during a turn, the operator input device 110 would communicate the
tire size
input by the operator to the microprocessor 60, which would determine the
maximum
allowable articulation angle between the front frame 10 and the rear frame 20
to keep the
tires from contacting each other. The microprocessor 60 would then set a stop
position at
the maximum allowable articulation angle wherein the microprocessor 60 will
not allow
continued articulation of the frames beyond the stop position. Also, the
proportional
control valve 52 controlled by the microprocessor 60 permits a controlled stop
and start,
i.e., a gradual stop and start by gradually opening and closing the valve
avoiding
suddenness caused in prior designs by hitting mechanical stops or by using an
on-off
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valve, so the steering action can be smooth irrespective of the extent to
which the frames
are being articulated.
[0034] The operator would also use the steering sensitivity switch of the
operator input device 110 to select the desired steering sensitivity. This can
be done prior
to the actual operation of the vehicle or can be done at any time during the
operation of
the vehicle, although perhaps not in a certain high gear. In high gear, it may
be desirable
to make the only option fine steering sensitivity, to avoid unexpectedly
sensitive steering
response. If the operator knows that coarse steering sensitivity (more
steering response
for a given steering input, either in terms of speed or magnitude of response,
or both) will
be required, such as when the vehicle will be operated in low gear, the
operator can select
coarse mode which will remain in effect as long as it is selected (except
perhaps in high
gear as stated above). If the operator knows that fine steering sensitivity
(less steering
response - in speed, magnitude or both - for a given steering input) will be
required, such
as when traveling at higher speeds, the operator can select fine mode which
will remain
in effect for as long as it is selected. If the operator knows that there will
be a need for
changing between coarse and fine steering sensitivity depending upon the
conditions
which are input to the microprocessor, or is not sure which mode will be best
for a given
task, the operator can select automatic mode, which will then change between
coarse and
fine, depending upon the gear the vehicle is in or perhaps the speed with
which the
operator is operating the steering input device, or the range through which
the operator is
operating the input device.
[0035] If coarse mode is selected, the microprocessor 60 sends signals to the
proportional solenoids 50, 55 to fully open, or at least open more fully
and/or for longer
duration, than in the fine mode, in response to the electrical steering
signals received
from the steering device I40. This allows for faster, and for a given open
time possibly
larger, changes in the angle between the front frame 10 and the rear frame 20
in response
to any given steering input. In fine mode, the microprocessor 60 would send
signals to
the proportional solenoids 50, 55 to open a lesser amount, or to open at a
lower rate
and/or for a shorter duration, in response to the given steering input
received from the
steering device 140. This allows for more controlled changes in the angle
between the
front frame 10 and the rear frame 20 in response to the steering inputs. In
automatic
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mode, the microprocessor 60 would use the input from the gear selector sensor
80 to
determine the appropriate steering sensitivity for the particular gear. The
description of
the operation of the preferred embodiment of the invention below assumes that
the
steering sensitivity switch has been set to automatic mode.
[0036] Once the tire size has been input and the steering sensitivity, e.g.,
automatic, has been selected, the articulated vehicle is ready for operation.
In the
preferred embodiment of the invention, during operation, the positional
feedback sensor
70 is continually measuring the articulation angle between the front frame 10
and the rear
frame 20 and communicating this information to the microprocessor 60. For
example,
the articulation angle could be measured as the angle formed between the
longitudinal
axes of the front frame 10 and the rear frame 20. Therefore, when the
articulated vehicle
is traveling in a straight path, and the front frame 10 and rear frame 20 are
aligned along
their longitudinal axes, the articulation angle would be, for example,
0° or zero
articulation. Alternatively, the positional feedback sensor 70 could be set up
to
continually measure the articulation angle and only communicate with the
microprocessor 60 when there is a change (+ or -) in the articulation angle.
By knowing
the initial articulation angle between the front frame 10 and the rear frame
20, the
microprocessor 60 could then determine the articulation angle at any given
time from the
changes in articulation angle received from the positional feedback sensor 70.
[0037) Similarly, the gear selector sensor 80 continually monitors the gear
that the vehicle is in and communicates this information to the microprocessor
60.
Alternatively, the gear selector sensor 80 could be set up to continually
monitor the gear
that the transmission is in and only communicate with the microprocessor 60
when the
gear is changed. By knowing the gear that the vehicle starts in, the
microprocessor 60
could then determine the gear at any given time from the changes in gear
received from
the gear selector sensor 80. Therefore, al any given point in time, the
microprocessor 60
will have information as to the current articulation angle between the front
frame 10 and
the rear frame 20 and the gear that the vehicle is in.
[0038] To turn the articulated vehicle, the operator uses the steering device
140. For example, if the steering device 140 is a steering wheel 90, as
described above,
the operator would turn the steering wheel 90 in the direction of the desired
turn.
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Similarly, if the steering device 140 is a joystick 100, as described above,
the operator
would move the joystick 100 in the direction of the hu-n. The steering device
140 then
converts the steering input from the operator into an electrical steering
signal indicative
of the direction and magnitude of the steering input and communicates the
electrical
steering signal to the microprocessor 60.
(0039] When the microprocessor 60 receives the electrical steering signal
from the steering device 140, it compares the current articulation angle
between the front
frame 10 and the rear frame 20, received from the positional feedback sensor
70, with the
stop positions (one left and one right), which were determined based on the
tire size input
by the operator. If the auticulation angle between the front frame 10 and the
rear frame
20 is already at the stop position in the direction of the desired turn, the
microprocessor
60 will not take any action based on the electrical steering signal received.
For example,
if the stop position between the front frame 10 and the rear frame 20 is
determined to be
20° (+ or -) based on the tire size entered by the operator and the
positional feedback
sensor 70 communicates that the articulation angle between the front frame 10
and the
rear frame 20 is currently at -20° (the left stop position), if the
microprocessor 60 is
receiving an electrical steering signal to turn further to the left, the
microprocessor will
take no action in response to the electrical steering signal. If the
articulation angle
between the front frame 10 and the rear frame 20 has not yet reached the stop
position,
the microprocessor will determine the gear that the vehicle is in based on the
information
received from the gear selector sensor 80.
[0040) If the vehicle is in low gear at the time the electrical steering
signal is
received, the microprocessor 60 will send a coarse magnitude signal to the
proportional
solenoids 50, 55 to open more fully and/or for a longer duration in the
correct direction
than they would open with a fine magnitude signal for the same steering input.
This
would result in a steering response whieh was faster and/or of a greater
change in steering
angle than in the fine mode. For example, if the microprocessor 60 receives an
electrical
steering signal to turn to the left (to turn the front frame 10
counterclockwise in Fig. 1 ),
and the articulation angle between the front frame 10 and the rear frame 20
has not
reached the leftward stop position, the microprocessor 60 will send a signal
to the
proportional solenoids 50, 55 to open to a greater orifice size to result in a
higher flow
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rate for a given time, or to open for a longer period to transfer more
hydraulic fluid from
the pressure source to line 130 and more fluid from line 135 to the tank, than
in the fine
mode. Once this amount of fluid, which is directly proportional to a given
change in
articulation angle, has been reached, as long as the steering input remains
the same, the
valve 52 is returned to its closed center position so that steering changes
stop (the angle
of articulation stops changing). As mentioned above, the initial opening and
final closing
of the valve 52 are preferably done slowly, so as not to produce any hydraulic
hammer or
suddenness in response.
[0041] If the vehicle is in high gear at the time the electrical steering
signal is
received, the microprocessor 60 will send a signal to the proportional
solenoids 50, 55 to
open a predetermined portion, less than the amount they'd open in the "coarse"
setting,
and/or for a shorter duration, to transfer hydraulic fluid between the
hydraulic cylinders
40, 45 and the respective pressure source and the tank. By opening the
proportional
solenoids 50, 55 less than their full amount the transfer of hydraulic fluid
between the
hydraulic cylinders 40, 45 is slower and a smoother, more controlled turn is
achieved. 13y
opening for the same duration as in coarse mode if the flow rate is lower, or
by opening
for a shorter duration if the flow rate is the same, a smaller amount of
hydraulic fluid is
transferred to and from the steering cylinders, resulting in a smaller
displacement of
them, and a lower magnitude of change in the steering angle. Either way, the
steering
response is less, either in terms of speed of response, magnitude of response,
or both.
[0042] Upon receipt of a signal from the microprocessor 60, one or the other
of the proportional solenoids 50, 55 will be actuated according to the signal
provided to
them. Preferably, this signal starts out gradually, to gradually open the
valve 52,
develops to either the coarse or fine rate (whichever is applicable) for the
steering input,
stays open for the applicable time for the coarse or fine setting for the
steering input, and
then closes at the applicable coarse or fine rate, and in any event, complete
closing is
accomplished at a rate that eliminates suddenness. With the valve 52 in its
closed center
position, the hydraulic cylinders 40, 45 cannot move to change the
articulation angle
between the front frame 10 and the rear frame 20, so they act as a solid link
to prevent the
front frame 10 and the rear frame 20 from moving to some other position.
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CA 02440940 2003-09-12
[0043] As stated above, when the articulation angle between the front frame
and the rear frame 20 reaches the stop position, which is determined based on
the tire
size input by the operator, the microprocessor 60 sends a signal to the
proportional
solenoids 50, 55 to close the valve 52, thereby stopping the articulation of
the front frame
10 and the rear frame 20. Alternatively, as the articulation angle between the
front frame
10 and the rear frame 20 approaches the stop position, the microprocessor 60
could send
a signal to the proportional solenoids 50, 55 to start closing at a
predetermined rate so
that the proportional solenoids 50, 55 would be fully closed when the
articulation angle
reaches the stop position. This provides a smoother and more controlled stop
as the
articulation angle between the front frame 10 and rear frame 20 approaches the
stop
position.
[0044] In addition, in the preferred embodiment of the invention, the steering
system has the ability to provide an emulated caster effect wherein the
articulated vehicle
will return to traveling in a straight path when the steering device 140 is
operated "hands-
off '. For example, if an operator were to move the joystick 100 or steering
wheel 90 to
the right, the front frame 10 would rotate clockwise, through the process
described above,
thereby turning the articulated vehicle to the right. When the operator
releases the
joystick 100 or steering wheel 90, it returns to its center position and the
electrical
steering signals being sent from the joystick 100 to the microprocessor 60
would cease,
or return to the signal which is output from the device in the renter
position. In response
to that signal or lack of signal, the microprocessor 60 would check the
articulation angle
between the front frame 10 and the rear frame 20, via the information received
from the
positional feedback sensor 70, to determine if the articulation angle shows
that the
longitudinal axes of the front frame 10 and the rear frame 20 are aligned
(i.e. the
articulated vehicle is traveling in a straight path). If the longitudinal axes
of the front
frame 10 and the rear frame 20 are not aligned, the microprocessor 60 will
send signals to
the proportional solenoids 50, 55 to control the valve 52 so as to transfer
hydraulic fluid
between the hydraulic cylinders 40, 45, the pressure source P and the tank T,
to align the
longitudinal axes of the front frame 10 and the rear frame 20. This emulated
caster effect
provides safer and easier control of the articulated vehicle when traveling in
high gear (at
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CA 02440940 2003-09-12
y
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high speeds), for example when traveling on roads, and is also less fatiguing
to the
m operator when traveling in low gear (at low speeds), for example when
harvesting.
[0045] Furthermore, by using a steering device 140 that provides electrical
steering signals, rather than typical mechanical/hydraulic steering devices,
an articulated
vehicle can be manufactured with a generic interface for the steering device
140 rather
than having to manufacture different hydraulic conduits and controls,
depending on the
steering device 140 employed. This allows manufacturers to design and
manufacture a
single type of hydraulic control system interface, while still allowing
operators to choose
between different types of steering devices.
[0046] While the foregoing specification illustrates and describes the
preferred embodiments of this invention, it is to be understood that the
invention is not
limited to the precise construction or operation herein disclosed. The
invention can be
embodied in other specific forms without departing from the spirit or
essential attributes
of the invention. Accordingly, reference should be made to the following
claims, rather
than to the foregoing specification, as indicating the scope of the invention.
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