Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates in general to steering
control systems for vehicles and, in particular, to a
single lever system for controlling the operation of a
vehicle drive mechanism that is located on each side of
the vehicle. More specifically, but without
restriction to the particular use which is shown and
described, this invention relates to a single-lever
control system especially suitable for controlling the
speed and directional movement of a vehicle having two
drive or propulsion units which are mutually
exclusively connected to one fo two vehicle drive
systems on opposLte sides of the vehLcle.
In the operation of certain types of
earthmoving equipment and construction machinery such
as crawler vehicles, the vehicle steering is effected
by movement of the vehicle. By varying the rotational
speed of the crawler drive systems, located on opposite
sides of the vehicle, the directional movement of the
crawler can be changed. Such steering systems,
referred to as steering by driving, have customarily
been effected through the operation of two separate
control levers which, respectively, controlled the
speed and rotational direction of the two drive units.
Such earthmoving machines may have two separate
hydrostatic transmissions, each of which controls the
operation of one of the drive sprockets which rotate an
endless track on each side of the vehicle to support
and propel the vehicle over the ground. However,
multiple control lever systems require the highest
degree of skill from the machine operator, and a long
q~
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period of experience is necessary in order to control
machine operation. The relative position of one lever
with respect to the other, as well as the absolute
position of each lever, will effect vehicle operation.
5 The proper operation of such machines requires constant
attention and a degree of skill acquired through
extensive experience.
Therefore, to eliminate some of the problems
associated with such two-lever control systems, it is
10 desirable to control the operation of a vehicle by a
single control lever which can control both the speed
and the rotational direction of the drive units for
each side of the vehicle. Such single lever control
systems are disclosed in United States Patent Nos.
4,085,812 and RE 27,488. While the systems disclosed
in these patents utilize a single control lever to
control both the rotational speed and direction of a
pair of hydrostatic transmission units, the systems
dLsclosed herein require complicated hydraulic
circuits. Other examples are United States Patent No.
4,076,090 and German Auslegeschrift 21 33 956 which
disclose a hydraulic circuit and single control lever
which utilizes a single control lever having a pressure
ring which actuates a plunger or a valve to selectively
direct pressurized fluid to the hydrostatic
transmission. Such complex hydraulic circuitry is both
costly and in view of its complexity, susceptible to
malfunctions and a higher degree of unreliability.
To overcome such difficulties and to
eliminate the necessity of complicated structural
linkage systems such as disclosed in United States
Patent No. 4,023,636, the present invention was
developed.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention
to improve the control of vehicles which utilize two
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separate power drives to effect vehicle movement.
Another object of this invention :is to
control the operation of independent power drives to a
vehicle through a single control lever.
A further object of this invention is to
control the speed and directional movement of an
earthmoving vehicle which utilizes separate hydrostatic
transmiss:ion drives, by the operation of a single
control lever which is effective to control both the
vehicle speed and direction of movement in an efficient
and reliable manner.
These and other objects are attained in
accordance with the present invention wherein there is
provided a control lever operatively connected to a
1; multi-position controller having four valves which
control operation of a pair of distributor valves,
after one or more of the four valves has been
pre-selectively coupled :in fluid communication in a
hydraulic circuit to operate a plurality of
shuttle-valves
DESCRIPTION OF THE DRAWINGS
Further objects of this invention together
with additional features contributing thereto and the
advantages accruing therefrom will be apparent from the
following description of a preferred embodiment of the
invention which is shown in the accompanying drawings
with like reference numerals indicating corresponding
parts throughout, wherein:
; Figure 1 is a schematic diagram of a
hydraulic circuit incorporating the present invention;
Figure 2 is a perspective view of a single
control lever for selectively coupling certain elements
of the hydraulic control system into fluid
communication;
Figure 3 is a diagrammatic plan v:iew of the
positions for the single control lever to effect
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movement of the vehicle;
Figures 4 through 7 are hydraulic schematic
views of the fluid flow paths of the operating fluid
for the hydraulic circuit of Figure l under various
operating conditions; and
Figure 8 is a circular diagram of the speed
pattern of the two hydrostatic transmissions to better
illustrate the resultant output from the hydrostatic
transmissions for corresponding positions of the single
control lever.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to Figure l, there is
illustrated a pair of hydrostatic transmissions 1 and 2
of a type known to those skilled in the art. As is
known, the transmissions l and 2 are capable of
effecting clockwise and counter-clockwise movement to
the tracks of a crawler vehicle for controlling the
forward and backward motion of the vehicle and its
steering.
Pressurized hydraulic fluid is coupled to
each of the hydrostatic transmissions l and 2 through
an inlet conduit 3 and is discharged therefrom through
an outlet conduit 4 under the control of a slide valve
5 or 6, respectively. Each of the slide valves 5 and 6
is of a pilot fluid operated type wherein a movable
valve spool is used to provide a metered flow of
hydraulic fluid to the hydrostatic transmissions l and
2, respectively, in response to the position of the
inlet and discharge ports of the slide valve. Movement
of the spool or the metering element of the slide
valves S and 6 is effected by coupling pressurized
hydraulic fluid through a pilot control line to each
side of the slide valve.
As best shown in Figure l, conduits 7 and 8
control the movement of the spool or metering element
of slide valve 5, and conduits 9 and 10 control the
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movement of the corresponding element of slide valve 6.
In operation, when the hydraulic fluid creates a
pressure through conduit 7, the metering element of
slide valve 5 is positioned to cause the hydrostatic
s transmission 1 to rotate in a first direction which
propels the drive unit associated therewith in a
direction to move the vehicle forward. Coupling of
hydraulic pressure through conduit 8, will move the
metering element of the slide valve 5 in an opposite
direction to cause the hydrostatic transmission l to
rotate in an opposite direction, thereby causing the
drive unit to move in a reverse direction. Similarly,
by coupling pressure through the conduits 9 and lO,
coupled in fluid communication to the slide valve 6,
the movable element thereof will be positioned to
effect the coupling of hydraulic fluid to the
hydrostatic transmission 2 in the same manner
previously described, and as illustrated in the
hydraulic schematic.
Two pairs of selector valves, a first pair
indicated by reference numerals 15 and 16, and a second
pair identified by reference numerals 17 and 18 are
coupled into the hydraulic control circuit to control
the passage of hydraulic fluid through the pilot
pressure lines 7, 8, 9 and lO. Each of the selector
valves 15, 16, 17 and 18 include a valve body having
two inlets and an outlet. The valve body is formed
with a cavity in which a shut-off member, normally in
; the form of a ball 19, may be moved between one of two
valve inlet seats for closing one of the inlets in the
valve cavity in order to control the direction of flow
of the hydraulic fluid, or the ball l9 may be held by
the fluid pressure in a position between the two valve
inlets.
The shut-off member or ball 19 will be moved
within the valve cavity to close one of the two inlets
when the pressure of the hydraulic fluid entering from
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one of the inlets exceeds that of the fluid entering
from the other inlet. When the pressure of the fluid
entering from both inlets is the same, both Lnlets will
remain open and the shut-off member 19 held in
equilibrium under the action of the pressure exerted by
the hydraulic fluid passing into the valve body from
both of the inlets. The selector valves 15 and 16 of
the first pair have inlets 20 and 21, respectively,
coupled together by a common conduit portion 22. The
selector valves 17 and 18 of the second pair have
inlets 23 and 24, respectively, coupled together by a
common conduit portion 25. Each of the selector valves
15, 16, 17 and 18 has a discharge outlet from the
internal cavity. Selector valve 15 has a discharge
outlet 26 and selector valve 16 has a discharge outlet
27 which are connected, respectively, to the conduits 9
and 8 coupled in fluid communication with the slLde
valves 6 and 5, respectively. Selector valve 17 has a
discharge outlet 28 and selector valve 18 has a
discharge outlet 29 which are coupled in fluid
communication to the conduits 7 and 10 of the selector
valves 5 and 6, respectively. IJ1 this manner the pilot
pressure fluid can be coupled to the selector valves
15, 16, 17 and 18 through four branches of a hydraulic
circuit with each branch of the hydraulic circuit
having pressure control valve associated therewith.
A first branch of the hydraulic circuit,
indicated by reference numeral 35a, couples fluid to an
inlet port 35 of the selector valve 15 and an inlet
port 36 of the selector valve 17 under the control of a
pressure control valve indicated by reference numeral
A. A second branch of the hydraulic circuit, indicated
by reference numeral 36a, communicates hydraulic fluid
to an inlet port 37 of the selector valve 16 and an
inlet port 38 of the selector valve 18, under the
control of a pressure control valve indicated by I. A
third and fourth branch of the hydraulic circuit,
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indicated respectively by reference numerals 39 and 40,
coupled hydraulic fluid respectively to the conduit
portion 22 and the conduit portion 25. These third and
fourth branches are controlled, respectively, by a
5 pressure control valve indicated by reference numerals
D and S.
Each of the pressure control valves A, I, D
and S, is of a type comprising a movable member, the
position of which determines the pressure of the fluid
in circuit branches 35a, 36a, 39 and 40, respectively.
Fluid pressure to these pressure control valves is
coupled by means of an inlet conduit 41, and the fluid
discharged from the pressure control valves is conveyed
through a discharge conduit 42. Displacement of the
relative mobile member associated with each one of the
pressure control valves, A, I, D and S is effected by
an axially mobile pin which is biased in a return
direction by means of a return spring as best shown in
Figure 1.
The four axially mobile pins of the pressure
control valves A, I, D and S are supported by a box 44
best shown in Figure 2, and are operated by means of a
disc 45 rigidly connected with a single control lever
46 hinged to the support box 44 by means of a ball
joint 47. The position of the pins relative to the
control lever 46 is best shown with reference to
Figures 2 and 3, with each of the axes of movement of
the pins being circumferentially off-set relative to
one another about the center of the box 44, which
coincides with the center of a ball joint 47, by gO
degrees. The dimensions of the actuator disc 45 and
the position of the metering pins, which control the
fluid flow through the pressure control valves A, I, D
and S, are chosen such that when the axis of the
control lever 46 is moved substantially over a conical
surface having its vertex at the center of the ball
joint 47, the control disc 45 is able to operate one or
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two of the control pins.
Referring now to Figure 3, as shown therein,
the control pins are disposed about the box 44 such
that those pins which are movable to control the flow
of fluid through pressure control valves A and I are
movable in a plane through an X-X axis which is
parallel to a plane normal to the vehicle and extending
through the vehicle's longitudinal axis (i.e., its
normal running plane). The pin associated with
pressure control valve A is disposed in a position
corresponding to the front of the vehicle or the X-X
axis throuqh the ball joint 47, which corresponds to
actuation of the vehicle in a forward direction. The
pin associated with pressure control valve I is
disposed in an opposed position on the X-X axis
corresponding to actuation of the vehicle in a reverse
direction. The metering pins associated with each of
the pressure control valves D and S are positioned for
movement in a plane through a Y-Y axis, which is normal
to the preceeding X-X axis. In this manner, operation
of the single control lever to the right or left, as
shown with respect to Figure 3, will cause the vehicle
to turn in either of these directions in the shortest
possible turning radius in order to effect the maximum
turn.
For a better understanding of the invention,
~ the operation of the hydraulic circuit will be
; described. If the machine operator wishes to move the
vehicle in a forward direction, the control lever 46 is
moved forward so that the actuator disc 45 will actuate
the pin of pressure control valve A. Therefore, the
pressure control valve A will be opened to an extend
depending upon the amount the pin is depressed, which
corresponds to the angle through which the lever 46 is
moved. Depression of the control pin of pressure
control valve A will meter hydraulic fluid from conduit
41 through the branch 35a of the control circuit to
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cause the fluid to enter the inlets 35 and 36 of the
selector valves 15 and 17, respectively. Fluid
entering into these valves will cause each shut-off
member, ball 19, associated therewith to close the
respective inlets 20 and 23. Fluid is thereby directed
from outlets 26 and 28 through conduits 9 and 7,
respectively, to the inlet ports 11 and 14 of the slide
valves 6 and 5, respectively. Pressurization of the
slide valves 5 and 6 in this manner will cause the
metering element thereof to shift, thereby enabling the
hydrostatic transmissions 1 and 2, respectively, to
rotate at the same speed and in the same direction to
propel the vehicle in a forward direction.
If the control lever 46 is moved in an
opposite direction to contact the metering pin of
pressure control valve I, the hydraulic fluid will be
fed through pressure control valve I and the branch 36a
of the hydraulic circuit, to the inlet ports 37 and 38
of selector valves 16 and 18, respectively. The
shut-off members 19 of these valves will be moved to
close the inlets 21 and 24, respectively, enabling the
hydraulic fluid to pass through the outlet ports 27 and
29, respectively, through respective conduits 8 and 10
to the inlet ports 13 and 12 of slide valves 5 and 6.
The coupling of the slide valves 5 and 6 in fluid
communication with the hydraulic pressure in this
manner, will be effective to move the metering elements
associated therewith to cause flow of hydraulic fluid
to the hydrostratic transmissions 1 and 2. Each of the
transmissions 1 and 2 will be caused to rotate at the
same speed, but in an opposite direction to that
effected by actuation of pressure control valve A,
resulting in movement of the vehicle in a reverse
direction.
When the machine operator desires to steer
the vehicle in a maximum right or left turn, this is
accomplished by rotating the vehicle tracks -in opposite
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direction. To effect such movement, the machine
operator moves the control lever 46 into a posit;on to
actuate the metering pin assoc-iated with pressure
control valve D or S, depending upon whether a right or
S left turn, respectively, is desired. If a right turn
is desired, movement of the lever 46 to operate
pressure control valve D opens that valve the amount
determined by axial movement of the actuator pin
associated therewith. Therefore, hydraulic fluid will
be metered through the branch 39 of the hydraulic
circuit, to the conduit portion 22 for passage to the
inlet ports 20 and 21 of the selector valves 15 and 16,
respectively. Such fluid passage will be effective to
close the respective inlets 35 and 37 associated with
these valves. Fluid communication will thereby be
effected through the valves 15 and 16, and discharge
from the outlet ports 26 and 27 into pilot pressure
lines 9 and 8 which are in fluid communication with
inlet ports 11 and 13 of the slide valves 6 and 5,
respectively~ Pressurizat-ion of these inlet ports will
cause the metering elements associated with each of the
slide valves 6 and 5 to shift, causing the hydrostatic
transmission 2 to rotate in a direction to cause the
vehicle to move forward while hydrostatic transmission
1 will rotate in a direction to effect a reverse
movement of the vehicle.
When it is desired to make a maximum left
turn, the control lever 46 is moved into contact with
the metering pin of pressure control valve S. Fluid
flow is thereby established from the pressure control
valve S through the branch 40 of the hydraulic circuit
and into the conduit portion 25. By this action, the
inlet ports 36 and 38 of selector valves 17 and 18 are
closed, and the fluid is passed through conduits 7 and
10 toward the respective inlet ports 14 and 12 of the
slide valves 5 and 6, respectively. Such
pressurization of the slide valves 5 and 6 is effective
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to cause the hydrostatic transmission 1 to rotate in a
direction for forward movement of the vehicle, and the
hydrostatic transmission 2 is operated to effect a
reverse direction to the machine, thereby turning the
vehicle in a left turn in its shortest turning radius.
To effect more gradual turns of the vehicle,
the control lever 46 can be moved into a position which
is best described with reference to Figure 3. In this
drawing examplary intermediate positions between two of
the main positions already discussed (indicated by DA,
DI, SI, SA) are shown. The control disc 45 is moved to
simultaneously actuate two of the metering pins
associated with two of the four pressure control valves
A, I, D, or S. The degree of actuation of the metering
pins will determine the corresponding degree of turning
of the vehicle by metering the flow through these
pressure control valves.
For example, when the lever 46 is moved into
an intermediate position between positions A and D
Lllustrated as DA Ln Figure 3, both of the pressure
control valves A and D will be simultaneously operated.
Hydraulic fluid flow will be set up in the hydraulic
control circuit as indicated by the heavier lines and
arrowheads shown in Figure 4. Operation of pressure
control valve A couples hydraulic fluid to selector
valves 17 and 15. The hydraulic fluid entering
selector valve 17 closes the inlet port 23 so that
fluid will only flow through the outlet port 28, to
pilot pressure line 7 to the inlet port 14 of the slide
valve 5. Fluid entering the selector valve 15 is
effective to close the inlet 20 of this valve and thus
the fluid must flow solely from the outlet port 26,
through conduit 9 through the inlet port 11 of selector
valve 6. Simultaneously, actuation of pressure control
valve D will communicate fluid through the branch 39 of
the hydraulic circuit to the conduit 22 to be passed
through inlet 20 of selector valve 15, and the inlet
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port 21 of selector valve 16.
Pressure control valves A, I, D, and S are
all metering valves, and for a small opening of
pressure control valve D, as the pressure of hydraulic
fluid entering inlet port 35 of selector valve 15
exceeds the pressure of the hydraulic fluid entering
inlet port 20 of this same valve, inlet valve 20 will
be closed by movement of the valve shut-off member 19.
Fluid entering selector valve 16 is effective to close
the inlet port 37 resulting in the fluid flow passing
through outlet port 27, through conduit 8, and into
fluid communication with the inlet port 13 of slide
valve 5. Consequently, for intermediate positions of
the lever 46 between positions shown as A and DA, the
hydraulic fluid will be coupled to slide valve 5 for
effecting the fluid communication of the hydraulic
pressure to hydrostatic transmission 1 at both inlet
ports 13 and 14, but at different pressures. Since the
pressure at the inlet port 14 is greater than the
pressure at the inlet port 13, the metering element of
slide valve 5 is moved to cause the hydrostatic
transmission 1 to rotate in a forward direction, but at
a speed less than the maximum. This will be further
reduced if the control lever is moved more towards
position DA, which would correspond to a change in the
axial displacement of the metering pins of the pressure
control valves A and D. Pressurized fluid
communication with the slide valve 6, associated with
hydrostatic transmission 2, is coupled only to the
inlet port 11. Thus, the hydrostatic transmission 2 is
caused to be coupled to the hydraulic pressure lines 3
and 4 such that it is rotated in a forward direction at
the maximum speed. Under these circumstances, both of
the track units will be moved in a forward direction,
but the track unit on the left hand side moves at a
speed greater than the speed of the track unit on the
right hand side of the vehicle, and thus the machine
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will turn towards the right.
If the lever control 46 is further moved
towards the position DA, the valve D will be opened to
an increasing extent until the maximum port area is
exposed, equivalent to that of pressure control valve
A. The fluid pressure at the inlet ports 35 and 20 of
slide valve 15 thereby become equal and the shut-off
member l9 will be moved to an intermediate position
bet~een these two inlets. The hydraulic fluid reaching
inlet 13 of slide valve 5 will also have the same
pressure as that reaching the inlet 14. Slide valve 5
will therefore be moved to the neutral center position
terminating the flow of hydraulic fluid to hydrostatic
transmission l which thereby stops. The right hand
track will thereby be held at rest, and steering
towards the right will be effected by movement of the
left hand track through operation of hydrostatic
transmission 2.
When the control lever 46 is moved to other
intermediate positions between the main positions A, I,
D, S, or into intermediate positions such as DA, DI,
SA, SI, or into positions between the main positions
and the intermediate positions, various possible
movements of the machine are determined in accordance
with that previously disclosed. For example, Figures
5, 6, and 7, which are analogous to Figure 4,
illustrate diagrammatically the flow of hydraulic fluid
shown by the heavier arrowhead lines which occurs in
such intermediate positions corresponding to the
positioning of the control lever 46 at positions DI, SI
and SA. The speed and direction of rotation of the two
hydrostatic transmissions 1 and 2 are illustrated in
Figure 8 by a circular diagram which illustrates these
possibilities in accordance with the setting of the
control lever 46. In this diagrammatic illustration,
for each angular position of the control lever 46, the
speed of each drive unit 1 and 2 is represented by the
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radial segment lying between the two circular-like
figures associated with motor units 1 and 2. This
diagram is d.irectionally oriented to correspond with
the drive positions shown in Figure 3 as to forward,
reverse, left and right. This figure, when associated
with the diagram of Figures ~ through 7, illustrates
the operation of the device under all operating
conditions by showing the d:irectional movement and
relative speed of the drive units 1 and 2 relative to
each other.
While the invention has been described with
reference to a preferred embodiment, it will be
understood by those skilled in the art that various
changes may be made and equivalents may be substituted
for elements thereof without departing from the scope
of the invention. In addition any modifications may be
made to adapt a particular situation or material to the
teachings of the invention without departing from the
essential scope thereof. Therefore, it is intended
that the :invention not be l.imited to the part:icular
embodiment disclosed as the best mode contemplated for
carrying out this invention but that the invention will
include all embodiments falling within the scope of the
appended claims.
