U.S. patent number RE34,746 [Application Number 07/822,245] was granted by the patent office on 1994-10-04 for open-center steering control unit with flow amplification.
This patent grant is currently assigned to Eaton Corporation. Invention is credited to Donald M. Haarstad, Herman P. Schutten, Dwight B. Stephenson.
United States Patent |
RE34,746 |
Schutten , et al. |
October 4, 1994 |
Open-center steering control unit with flow amplification
Abstract
An open-center fluid controller (15) is disclosed for
controlling the flow of fluid to a steering cylinder (25). The
controller includes a fluid meter (29) and valving arrangement
(27), including a valve spool (43) and a sleeve (45), which define
a main fluid path. The main path includes a fixed flow control
orifice (86), a variable flow control orifice (87), the fluid meter
(29), and a variable flow control orifice (89). In accordance with
the invention, the spool and sleeve define an amplification fluid
path (101), including a variable amplification orifice (99), in
parallel with the main fluid path, and disposed to amplify the flow
of fluid through the meter (29). In order to facilitate manual
steering, the amplification orifice (99) reaches its maximum flow
area when the spool and sleeve are in a normal operating position
(FIG. 6). The amplification orifice then decreases and closes as
the displacement between the spool and sleeve reach a maximum
displacement (FIG. 7). As a result, the amplification fluid path
(101) is closed at maximum valve displacement, thus making it
possible to manually steer the vehicle.
Inventors: |
Schutten; Herman P. (Bayside,
WI), Stephenson; Dwight B. (Savage, MN), Haarstad; Donald
M. (Chaska, MN) |
Assignee: |
Eaton Corporation (Cleveland,
OH)
|
Family
ID: |
26943803 |
Appl.
No.: |
07/822,245 |
Filed: |
January 17, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
254067 |
Oct 6, 1988 |
4862690 |
|
|
Reissue of: |
325721 |
Mar 20, 1989 |
04958493 |
Sep 25, 1990 |
|
|
Current U.S.
Class: |
60/384;
137/596.13; 137/625.24; 91/375R |
Current CPC
Class: |
B62D
5/097 (20130101); B62D 5/32 (20130101); Y10T
137/86662 (20150401); Y10T 137/87185 (20150401) |
Current International
Class: |
B62D
5/06 (20060101); B62D 5/09 (20060101); B62D
5/097 (20060101); B62D 5/32 (20060101); F16D
031/02 () |
Field of
Search: |
;60/384 ;91/370,375R,467
;137/596.13,625.21,625.24 ;180/132 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Look; Edward K.
Assistant Examiner: Ryznic; John
Attorney, Agent or Firm: Kasper; L. J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. Ser. No.
254,067, filed Oct. 6, 1988, now U.S. Pat. No. 4,862,690 in the
name of Donald M. Haarstad for a "STEERING CONTROL UNIT WITH BOTH
FLOW AMPLIFICATION AND MANUAL STEERING CAPABILITY".
Claims
We claim:
1. An open-center controller operable to control the flow of fluid
from a source of fluid to a fluid pressure operated device; said
controller being of the type including housing means defining a
fluid inlet port for connection to the source of fluid, a returna
port for connection to a reservoir, and first and second control
fluid ports for connection to the fluid pressure operated device;
valve means disposed in said housing means and defining a neutral
position and a first operating position; said housing means and
said valve means cooperating to define a neutral fluid path
communicating between said inlet port and said return port, and
including a variable neutral orifice having its maximum flow area
when said valve means is in said neutral position, and a decreasing
flow area as said valve means is displaced from said neutral
position toward said first operating position; said housing means
and said valve means cooperating to define a main fluid path
communicating between said inlet port and said first control fluid
port, and between said second control fluid port and said return
port when said valve means is in said first operating position;
fluid actuated means for imparting follow-up movement to said valve
means proportional to the volume of fluid flow through said fluid
actuated means, said fluid actuated means being disposed in series
flow relationship in said main fluid path between said inlet port
and said first control fluid port; said main fluid path including a
first, .[.fixed.]. flow control orifice disposed between said inlet
port and said fluid actuated means, a second, variable flow control
orifice disposed between said first flow control orifice and said
fluid actuated means, and a third, variable flow control orifice
disposed between said fluid actuated means and said first control
fluid port, said second and third flow control orifices having
minimum flow areas when said valve means is in said neutral
position, and increasing flow areas as said valve means is
displaced from said neutral position toward said first operating
position; characterized by:
(a) said housing means and said valve means cooperating to define
an amplification fluid path in parallel with said main fluid path,
said amplification fluid path being in fluid communication with
said main fluid path at a first location disposed between said
fluid inlet port and said first.[., fixed.]. flow control orifice,
and at a second location disposed between said third, variable flow
control orifice and said first control fluid port;
(b) said amplification fluid path including a variable
amplification orifice having its minimum flow area when said valve
means is in said neutral position, and an increasing flow area as
said valve means is displaced from said neutral position toward
said first operating position; and
(c) said variable amplification orifice begins to open at
substantially the same time as said second and third, variable flow
control orifices begin to open.
2. An open-center controller as claimed in claim 1 characterized by
said valve means comprising a primary, rotatable valve member and a
cooperating, relatively rotatable, follow-up valve member, said
primary and follow-up valve members defining said neutral position
relative to each other.
3. An open-center controller as claimed in claim 2 characterized by
said primary and follow-up valve members cooperating to define said
first, second, and third flow control orifices, the flow areas of
said second and third flow control orifices varying in response to
relative rotation of said primary and follow-up valve members.
4. An open-center controller as claimed in claim 2 characterized by
said amplification fluid path and said variable amplification
orifice being wholly defined by said primary and follow-up valve
members.
5. An open-center controller as claimed in claim 1 characterized by
said main fluid path including a fourth, variable flow control
orifice disposed between said third, variable flow control orifice
and said first control fluid port.
6. An open-center controller as claimed in claim 5 characterized by
said amplification fluid path being in fluid communication with
said main fluid path at a second location disposed between said
third and fourth variable flow control orifices.
7. An open-center controller as claimed in claim 2 characterized by
said fluid actuated means comprises a fluid meter including a
metering member movable to measure the volume of fluid flowing
through said main fluid path, said controller further comprising
means coupling said metering member to said follow-up member.
8. An open-center controller as claimed in claim 1 characterized by
said controller having a generally constant amplification ratio as
said valve means is displaced from said neutral position to said
first operating position, and a decreasing amplification ratio as
said valve means moves from said first operating position toward a
maximum displacement.
9. An open-center controller as claimed in claim 1 characterized by
said variable amplification orifice having its maximum flow area
when said valve means is in said first operating position, and a
decreasing flow area as said valve means is displaced from said
first operating position toward a maximum displacement
position.
10. An open-center controller as claimed in claim 1 characterized
by said housing means and said valve means cooperating to define a
second main fluid path communicating between said inlet port and
said second control fluid port, and between said first control
fluid port and said return port when said valve means is in a
second operating position.
11. An open-center controller as claimed in claim 10 characterized
by said housing means and said valve means cooperating to define a
second amplification fluid path in parallel with said second main
fluid path, said amplification fluid path being in fluid
communication with said second main fluid path at a first location
disposed between said fluid inlet port and said first, .[.fixed.].
flow control orifice, and at a second location disposed between a
third, variable flow control orifice and said second control fluid
port.
12. An open-center controller as claimed in claim 11 characterized
by said second amplification fluid path including a second variable
amplification orifice having its minimum flow area when said valve
means is in said neutral position, and an increasing flow area as
said valve means is displaced from said neutral position toward
said second operating position, said second variable amplification
orifice begins to open at substantially the same time as said
third, variable flow control orifice begins to open.
13. An open-center controller operable to control the flow of fluid
from a source of fluid to a fluid pressure operated device; said
controller being of the type including housing means defining a
fluid inlet port for connection to the source of fluid, a return
port for connection to a reservoir, and first and second control
fluid ports for connection to the fluid pressure operated device;
valve means disposed in said housing means and defining a neutral
position and a first operating position; said housing means and
said valve means cooperating to define a neutral fluid path
communicating between said inlet port and said return port, and
including a variable neutral orifice having its maximum flow area
when said valve means is in said neutral position, and a decreasing
flow area as said valve means is displaced from said neutral
position toward said first operating position; said housing means
and said valve means cooperating to define a main fluid path
communicating between said inlet port and said first control fluid
port, and between said second control fluid port and said retuen
port when said valve means is in said first operating position;
fluid actuated means for imparting follow-up movement to said valve
means proportional to the volume of fluid flow through said fluid
actuated means, said fluid actuated means being disposed in series
flow relationship in said main fluid path between said inlet port
and said first control fluid port; said main fluid path including a
first, .[.fixed.]. flow control orifice disposed between said inlet
port and said fluid actuated means, and a variable flow control
orifice disposed between said fluid actuated means and said first
control flow port, said variable flow control orifice having its
minimum flow area when said valve means is in said neutral
position, .[.at.]. .Iadd.and .Iaddend.an increasing flow area as
said valve means is displaced from said neutral position toward
said first operating position; characterized by:
(a) said housing means and said valve means cooperating to define
an amplification fluid path in parallel with said main fluid path,
said amplification fluid path being in fluid communication with
said main fluid path at a first location disposed between said
fluid inlet port and said first.[., fixed.]. flow control orifice,
and at a second location disposed upstream of said variable flow
control orifice;
(b) said amplification fluid path including a variable
amplification orifice having its minimum flow area when said valve
means is in said neutral position and an increasing flow area as
said valve means is displaced from said neutral position toward
said first operating position; and
(c) said variable amplification orifice begins to open before said
variable flow control orifice begins to open, said variable
amplification orifice having its maximum flow area when said valve
means is in said first operating position, and a decreasing flow
area as said valve means is displaced from said first operating
position toward a maximum displacement position, said variable
amplification orifice being closed before said valve means reaches
said maximum displacement position.
14. An open-center controller as claimed in claim 13 characterized
by said valve means comprising a primary, rotatable valve member
and a cooperating, relatively rotatable, follow-up valve member,
said primary and follow-up valve members defining said neutral
position relative to each other.
15. An open-center controller as claimed in claim 14 characterized
by said primary and follow-up valve members cooperating to define
said variable, neutral orifice, said first.[., fixed.]. flow
control orifice, and said variable flow control orifice, the flow
areas of said variable orifices varying in response to relative
rotation of said primary and follow-up valve members.
16. An open-center controller as claimed in claim 14 characterized
by said amplification fluid path and said variable amplification
orifice being wholly defined by said primary and follow-up valve
members. .Iadd.17. An open-center controller as claimed in claim 1,
characterized by said first flow control orifice comprising a fixed
flow control orifice..Iaddend. .Iadd.18. An open-center controller
as claimed in claim 13, characterized by said first flow control
orifice comprising a fixed flow control orifice..Iaddend.
Description
BACKGROUND OF THE DISCLOSURE
The present invention relates to open-center fluid controllers of
the type used to control the flow of fluid from a source of fluid
to a fluid pressure operated device, such as a steering
cylinder.
A typical fluid controller of the type to which the present
invention relates includes a housing which defines various fluid
ports, and further includes a fluid meter and valving, and an
arrangement for imparting follow-up movement to the valving in
response to flow through the fluid meter. In an open-center
controller, the flow through the controller is not directly
proportional to a main variable flow control orifice, and to the
deflection (displacement) of the valving. Instead, the deflection
of the valving in an open-center controller depends upon the load,
as represented by the pressure drop across the controller.
It has long been an object of those skilled in the art to provide a
steering system, including a fluid controller, in which the total
flow through the steering system is substantially greater than the
flow through the controller, but with the overall system flow being
related to the flow through the controller, in a known manner. See,
for example, U.S. Pat. No. 4,052,929 in which the controller
receives fluid from one pump then generates a pilot signal to
control a pilot operated valve which receives fluid from a second
pump. The total steering flow comprises the flow through the pilot
operated valve, plus the flow from the controller. Such a system is
theoretically satisfactory, but the cost of such a system becomes
nearly prohibitive because of the addition of the pilot operated
valve and the second pump.
U.S. Pat. No. 4,759,182, assigned to the assignee of the present
invention, and incorporated herein by reference, discloses a
load-sensing (closed-center) fluid controller in which the valving
defines an amplification fluid path, including a variable
amplification orifice in parallel with the main fluid path. In the
preferred embodiment of the device of the above-incorporated
patent, the amplification fluid path is in fluid communication with
the main fluid path at a first location disposed between the fluid
inlet port and a first variable flow control orifice, typically
referred to as the main variable flow control orifice, or simply
the A1 orifice. As is well known to those skilled in the art, in
load-sensing controllers, the pressure drop across the A1 orifice
is maintained substantially constant, and therefore, the flow
through the A1 orifice, and the controller, is directly
proportional to the size of the A1 orifice.
In open-center controllers of the type to which the present
invention relates, however, there is no main variable flow control
orifice. Instead, in an open-center controller, there is a constant
flow of fluid through the controller valving to the reservoir when
the controller is in neutral, and the pressure of this fluid flow
is inherently just slightly above the pressure in the reservoir. As
the valving is displaced from neutral, the neutral flow control
orifice to the reservoir begins to close and build pressure, and
the operator continues to displace the steering wheel and the
valving until the fluid pressure builds to a level sufficient to
overcome the load on the steering cylinder.
On many of the vehicles which utilize open-center controllers, it
is also desirable for the controller to provide a manual steering
capability, i.e., the ability to generate pressurized fluid by
rotation of the steering wheel, valving, and fluid meter when the
pump is inoperative, or for some other reason is unable to generate
fluid pressure. It has been discovered that when the amplification
fluid path of U.S. Pat. No. 4,759,182 is applied to fluid
controllers, any attempts to manually steer the vehicle tend to be
unsuccessful.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
improved steering system and open-center controller, wherein the
controller has the capability of providing a steering flow which is
substantially larger than the flow through the fluid meter of the
controller, without the need for additional valves or other
components.
It is another object of the present invention to provide an
improved open-center controller which accomplishes the
above-identified object, without inhibiting the capability of the
controller to operate in a manual steering mode.
The above and other objects of the present invention are
accomplished by the provision of an improved open-center controller
operable to control the flow of fluid from a source of fluid to a
fluid pressure operated device. The controller is of the type
including housing means defining a fluid inlet port for connection
to the source of fluid, a return port for connection to a
reservoir, and first and second control fluid ports for connection
to the fluid pressure operated device. Valve means is disposed in
the housing means and defines a neutral position and a first
operating position, the housing means and valve means cooperating
to define a neutral fluid path communicating between the inlet port
and the return port, including a variable neutral orifice having
its maximum flow area when the valve means is in the neutral
position and a decreasing flow area as the valve means is displaced
from the neutral position toward the first operating position. The
housing means and the valve means cooperate to define a main fluid
path communicating between the inlet port and the first control
fluid port, and between the second control fluid port and the
return port when the valve means is in the first operating
position. Fluid actuated means is included for imparting follow-up
movement to the valve means proportional to the volume of fluid
flow through the fluid actuated means, the fluid actuated means
being disposed in series flow relationship in the main fluid path
between the inlet port and the first control fluid port. The main
fluid path includes a first, fixed flow control orifice disposed
between the inlet port and the fluid actuated means; a second,
variable flow control orifice disposed between the first flow
control orifice and the fluid actuated means; and a third, variable
flow control orifice disposed between the fluid actuated means and
the first control fluid port. The second and third flow control
orifices have minimum flow areas when the valve means is in the
neutral position, and increasing flow areas as the valve means is
displaced from the neutral position toward the first operating
position. The improved open-center controller is characterized by
the housing means and the valve means cooperating to define an
amplification fluid path in parallel with the main fluid path, the
amplification fluid path being in fluid communication with the main
fluid path at a first location disposed between the fluid inlet
port and the first, fixed flow control orifice, and at a second
location disposed between the third, variable flow control orifice
and the first control fluid port. The amplification fluid path
includes a variable amplification orifice having its minimum flow
area when the valve means is in the neutral position, and an
increasing flow area as the valve means is displaced from the
neutral position toward the first operating position. The variable
amplification orifice begins to open at substantially the same time
as the second and third variable flow control orifices begin to
open.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a hydraulic schematic of an open-center, hydrostatic
power steering system of the type with which the present invention
may be utilized.
FIG. 2 is an axial cross-section of a fluid controller of the type
to which the present invention relates.
FIG. 3 is a unidirectional flow diagram illustrating the fluid
controller shown schematically in FIG. 1, as well as the various
orifices shown in FIG. 1, and including the teachings of the
present invention.
FIG. 4 is an overlay view of the valving used in the fluid
controller shown in FIG. 2, but on a larger scale than in FIG. 2,
and with the valving shown in the neutral position.
FIGS. 5-7 are enlarged, fragmentary overlay views, similar to FIG.
4, but with the valving displaced from the neutral position.
FIG. 8 is a graph of flow versus valve displacement, showing the
main fluid path and the amplification fluid path of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, which are not intended to limit the
invention, FIG. 1 is a hydraulic schematic of a vehicle hydrostatic
steering system including a fluid controller made in accordance
with the teachings of the present invention. The system includes a
fluid pump 11, shown herein as a fixed displacement pump, having
its inlet connected to a system reservoir 13. The output of the
pump 11 is directed to the hydrostatic steering system, and more
specifically, to a fluid controller 15.
Referring still to FIG. 1, the fluid controller 15 includes an
inlet port 17, a return port 19, and a pair of control (cylinder)
fluid ports 21 and 23, which are connected to the opposite ends of
a steering cylinder 25.
The fluid controller 15, which will be described in greater detail
in conjunction with FIG. 2, may be of the general type illustrated
and described in U.S. Pat. No. Re. 25,126, assigned to the assignee
of the present invention and incorporated herein by reference. More
specifically, the controller 15 is of the open-center type.
Disposed within the controller 15 is a valving arrangement,
generally designated 27, which is movable from its neutral position
shown in FIG. 1 to either a right turn position R or a left turn
position L. When the valving arrangement 27 is in either of the
turn positions, the pressurized fluid flowing through the valving
27 also flows through a fluid meter 29, one function of which is to
measure (meter) the proper amount of fluid to be communicated to
the appropriate control port 21 or 23. As is well known to those
skilled in the art, the other function of the fluid meter 29 is to
provide follow-up movement to the valving 27, such that the valving
27 is returned to its neutral position after the desired amount of
fluid has been communicated to the steering cylinder 25. In FIG. 1,
this follow-up movement is achieved by means of a mechanical
follow-up connection, indicated schematically at 31.
As is shown schematically in FIG. 1, the valving 27 defines a
plurality of variable orifices whenever the valving is moved from
its neutral position to one of its operating positions, either a
right turn position R or a left turn position L. These variable
orifices will be described in greater detail subsequently in
conjunction with the detailed description of FIGS. 3 and 4.
Fluid Controller 15
Referring now to FIG. 2, the construction of the fluid controller
will be described in some detail. The controller 15 comprise
several sections, including a housing section 33, a port plate 35,
a section comprising the fluid meter 29, and an end plate 37. These
sections are held together in tight, sealing engagement by means of
a plurality of bolts 39, which are in threaded engagement with the
housing section 33. The housing section 33 defines the inlet port
17, the return port 19, and the control ports 21 and 23.
Rotatably disposed within a valve bore 41 defined by the housing
section 33 is the valving arrangement 27, shown schematically in
FIG. 1. The valving 27 comprises a primary, rotatable valve member
43 (hereinafter referred to as the "spool"), and a cooperating,
relatively rotatable follow-up valve member 45 (hereinafter
referred to as the "sleeve"). At the forward end of the spool 43 is
a portion having a reduced diameter and defining a set of internal
splines 47 which provide for a direct mechanical connection between
the spool 43 and a steering wheel (not shown). The spool 43 and
sleeve 45 will be described in greater detail subsequently.
The fluid meter 29 may be of the type well known in the art, and
includes an internally-toothed ring 49, and an externally-toothed
star 51. The star 51 defines a set of internal splines 53, and in
splined engagement therewith is a set of external splines 55,
formed at the rearward end of a drive shaft 57. The drive shaft 57
has a bifurcated forward end permitting driving connection between
the shaft 57 and the sleeve 45, by means of a pin 59 passing
through a pair of pin openings 61 in the spool 43. Thus,
pressurized fluid flowing through the valving 27, in response to
rotation of the spool 43, flows through the fluid meter 29, causing
orbital and rotational movement of the star 51 within the ring 49.
Such movement of the star 51 causes follow-up movement of the
sleeve 45, by means of the drive shaft 57 and pin 59 (which
comprise the follow-up connection 31 of FIG. 1), to maintain a
particular relative displacement between the spool 43 and sleeve
45. As is well known to those skilled in the art, in an open-center
controller, the relative displacement between the spool 43 and
sleeve 45 is dependent upon the steering load, i.e., the hydraulic
pressure being communicated to the steering cylinder 25. A
plurality of leaf springs 63 extend through an opening in the spool
45, biasing the sleeve 45 toward the neutral position, relative to
the spool 43.
It may be seen in FIG. 2 that the housing section 33 defines four
annular chambers surrounding the spool 45, to provide fluid
communication between the outer surface of the spool 45 and the
various ports 17, 19, 21 and 23, the annular chambers being
designated by the reference numeral of the respective port,
accompanied by the letter "c".
The toothed interaction of the star 51, orbiting and rotating
within the ring 49, defines a plurality of expanding and
contracting fluid volume chambers, and adjacent each chambers, the
port plate 35 defines a fluid port (not shown in FIG. 2). As is
well known to those skilled in the art, the housing section 33
provides a plurality of axial bores (not shown in FIG. 2), each of
which is in open communication at one end with one of the fluid
ports and one of the volume chambers and, at its other end, with
the valve bore 41.
Valuing Arrangement 27
Referring now primarily to FIG. 4, the spool 43 and sleeve 45 will
be described in greater detail. It should be noted that in FIG. 4,
the spool 43 and sleeve 45 are shown in their proper relative
rotational position to define therebetween the neutral condition
illustrated schematically in FIG. 1. The sleeve 45 defines a
plurality of pressure ports 65, in communication with the annular
chamber 17c. To the left of the ports 65 is a plurality of meter
ports 67, which communicate between the valving arrangement 27 and
the expanding and contracting volume chambers of the fluid meter
29. Disposed to the left of the meter ports 67 is a plurality of
cylinder ports 69, in communication with the annular chamber 23c,
and further to the left, a plurality of cylinder ports 71, in
communication with the annular chamber 21c.
The spool 43 defines an annular groove 73, and in communication
therewith, a plurality of axial slots 75. Circumferentially,
displaced from each of the axial slots 75 is a longer axial slot
77, and circumferentially aligned with each of the axial slots 75
is an even longer axial slot 79, the function of which will be
described subsequently. To the right of the annular groove 73, the
spool 43 defines a plurality of axial, open-center slots 81, each
of which is in open communication, toward its right end, with the
interior of the spool 43. To the right of the pressure ports 65,
the sleeve 45 defines a plurality of pairs of open-center holes
83.
Operation of Valving
It is believed that the basic operation of the controller 15 and
the valving 27 described thus far should be readily apparent in
view of the teachings of the above-incorporated patent. However,
the operation of the controller and valving will be described
briefly, partly to relate the structure illustrated in FIGS. 2 and
4 to the schematics of FIGS. 1 and 3.
Referring still primarily to FIG. 4, when the valving is in the
neutral position (no rotation of the steering wheel), inlet fluid
is communicated from the inlet port 17 into the annular chamber
17c. Both the pressure ports 65 and the pairs of open-center holes
83 are in open communication with the annular chamber 17c, but flow
through the pressure ports 65 and into the annular groove 73 does
not occur, because the axial slots 75 are blocked from
communication with the meter ports 67, in the neutral position
shown in FIG. 4. Instead, inlet fluid flows from the annular
chamber 17c through the open-center holes 83 and into the
respective open-center slot 81. Each of the slots 81 is in open
communication with the interior of the spool, as mentioned
previously, and the interior of the spool is in open, relatively
unrestricted fluid communication with the system reservoir 13 by
means of the annular chamber 19c and return port 19. Therefore, in
an open-center controller, with the valving in the neutral position
shown in FIG. 4, the inlet fluid is not pressurized, i.e., the
pressure of the inlet fluid is only slightly greater than the
pressure in the system reservoir 13.
The communication between each pair of open-center holes 83, and
the respective open-center slot 81 defines a variable orifice,
having its maximum flow area when the valving is in neutral, the
composite of these individual orifices comprising a variable
neutral flow control orifice 85 (see FIGS. 1 and 3).
Referring now to FIG. 4, in conjunction with FIG. 5, when the spool
43 is displaced from the neutral position, relative to the sleeve
45, every other meter port 67 begins to communicate with the
adjacent axial slot 75, such that inlet fluid now begins to flow
through the pressure ports 65 into the annular groove 73; then
through the axial slots 75 and into these meter ports 67. Each
pressure port 65 defines a fixed orifice, the composite of these
individual orifices comprising a fixed flow control orifice 86 (see
FIGS. 1 and 2). The inlet fluid flows from these meter ports 67 to
the expanding volume chambers of the meter 29. At the same time,
fluid flows from the contracting volume chambers of the meter 29
back to the remaining, alternate meter ports 67, which are just
beginning to communicate with the axial slots 77.
The communication between each of the axial slots 75 and every
other meter port 67 define a variable orifice, the composite of
these individual variable orifices comprising a variable flow
control orifice 87 (see FIG. 3). At the same time, the
communication between the alternate meter ports 67 and the axial
slots 77 defines a variable orifice, the composite of these
individual variable orifices comprising a variable flow control
orifice 89. The variable orifice 87 is also frequently referred to
as the A2 orifice, while the variable orifice 89 is frequently
referred to as the A3 orifice.
As may be seen in FIG. 5 (wherein the spool has been rotated about
two degrees relative to the sleeve), as the variable orifices 87
and 89 are beginning to open, the flow area of the neutral flow
control orifice 85 is beginning to decrease, such that the pressure
of the inlet fluid begins to increase.
After slightly more relative rotation between the spool 43 and
sleeve 45, each axial slot 77 begins to communicate with its
respective cylinder port 69, the communication therebetween
defining a variable orifice. The composite of these individual
variable orifices comprises a variable flow control orifice 91 (see
FIGS. 1 and 3). The flow control orifice 91 is also frequently
referred to as the A4 orifice. At the same time, each of the axial
slots 79 begins to communicate with its respective cylinder port
71, the communication therebetween defining a variable orifice. The
composite of these individual variable orifices comprises a
variable flow control orifice 93 (see FIGS. 1 and 3). The flow
control orifice 93 is also frequently referred to as the A5
orifice. Except as noted specifically hereinafter, the exact "phase
relationship" among the various flow control orifices 87, 89, 91
and 93 is not an essential feature of the present invention, and
will not be described in further detail. It is also not an
essential feature of the present invention that the controller 15
have the particular arrangement of flow control orifices described
hereinabove. For example, it is known in one controller produced
commercially by the assignee of the present invention to have
valving which does not require either an A2 orifice or an A3
orifice but does require a variable A1 orifice.
It should be noted that all of the structure and function described
up to this point is generally well known in connection with
open-center controllers of the type sold commercially by the
assignee of the present invention. The additional structure
provided by the present invention will now be described.
Amplification Fluid Path
Referring still primarily to FIGS. 4 and 5, the sleeve 45 defines a
plurality of pairs of amplification bores 95. With the valving in
the neutral position shown in FIG. 4, the bores 95 in each pair are
centered with respect to an extension 97, which is in communication
with the right end of the axial slot 77 in FIG. 4. As the spool 43
is displaced relative to the sleeve 45, one of each of the pairs of
amplification bores 95 begins to communicate with the extension 97,
and therefore, with the axial slot 77. The communication between
each amplification bore 95, and its respective extension 97 defines
a variable orifice, the composite of these individual orifices
comprising a variable amplification orifice 99 (see FIG. 3). In the
subject embodiment, the variable amplification orifice 99 begins to
open at substantially the same time as the variable flow control
orifices 87 and 89, for reasons which will be apparent to those
skilled in the art.
As the spool 43 is displaced, relative to the sleeve 45, to the
position shown in FIG. 5, and then beyond, inlet fluid flows from
the annular chamber 17c through one of each pair of amplification
bores 95, then through the extension 97 and into the axial slot 77.
The fluid path just described will be referred to hereinafter as an
amplification fluid path 101 (see FIG. 3), which includes the
variable amplification orifice 99. As may best be seen in FIG. 3,
the amplification fluid path 101 is in communication with the main
fluid path at a location upstream of the fixed orifice 86. The
fluid flowing through the amplification fluid path 101 then
recombines with the main fluid path at a location downstream of the
variable flow control orifice 89, but upstream of the variable flow
control orifice 91. It will be understood by those skilled in the
art that, when utilizing the present invention, it is necessary to
increase the flow capacity of variable flow control orifices 91 and
93 to accommodate the total flow through both the main fluid path
and the amplification fluid path.
Referring now primarily to FIG. 6, the spool 43 has been displaced,
relative to the sleeve 45, by about 7 degrees which, in the subject
embodiment, would constitute a normal "operating position". At the
displacement shown in FIG. 6, one of each pair of the amplification
bores 95 is in complete communication with the extension 97, such
that the variable amplification orifice 99 has now reached its
maximum flow area. At the same time, the communication between the
open-center holes 83 and the open-center slots 81 is greatly
reduced, such that the neutral flow control orifice 85 is
approaching its minimum flow area, which typically would be a zero
flow, or closed position. Referring now to the graph of FIG. 8, it
may be seen that the flow through the amplification fluid path 101
has reached its peak at the position shown in FIG. 6, although the
flow through the amplification path 101 increases at a decreasing
rate as the displacement approaches 7 degrees, whereas the flow
through the main fluid path, designated "87", continues to increase
almost linearly. It should be understood that the flow curve
labeled "87" represents the rate of flow through the series
combination of the flow control orifice 87, the fluid meter 29, and
the flow control orifice 89.
Referring now to FIG. 7, as the displacement of the spool 43,
relative to the sleeve 45 increases from the 7 degrees shown in
FIG. 6 to the 11 degrees shown in FIG. 7, the communication between
each amplification bore 95 and the extension 97 actually decreases,
such that the variable amplification orifice 99 begins to decrease,
as does the flow through the amplification fluid path 101, as may
be seen in FIG. 8. It should also be noted that the neutral flow
control orifice 85, which was still open at the 7-degree
displacement shown in FIG. 6, has already closed (at about 8
degrees displacement), so that the leak path to the reservoir
represented by the neutral flow control orifice 85 is completely
closed before the variable amplification orifice 99 closes
completely. In the subject embodiment, with the amplification
orifice 99 closing at approximately 11 degrees, as shown in FIG. 7,
the maximum displacement possible between the spool 43 and sleeve
45 is approximately 12 degrees.
The reason for closing the variable amplification orifice 99 before
the spool and sleeve reach maximum displacement is to permit
operation of the controller 15 in the manual steering mode. As is
well known to those skilled in the art, when the controller is
operating in the manual steering mode, manual rotation of the
steering wheel rotates the star 51 of the fluid meter 29, causing
the meter to function as a hand pump, and generate pressurized
fluid to actuate the steering cylinder. By closing the variable
amplification orifice 99 prior to maximum displacement of the spool
and sleeve, the amplification fluid path is not able to serve as a
"shortcircuit", which would make it practically impossible to
generate sufficient pressure to steer the vehicle. See co-pending
application U.S. Ser. No. 254,067, filed Oct, 6, 1988, in the name
of Donald M. Haarstad, for a "STEERING CONTROL UNIT WITH BOTH FLOW
AMPLIFICATION AND MANUAL STEERING CAPABILITY"
Referring again to the graph of FIG. 8, in the subject embodiment,
the flow through the main flow path, designated "87" is nearly the
same as the flow through the amplification fluid path 101, until
approximately 5 or 6 degrees of displacement between the spool 43
and sleeve 45. The above is true only if the flow restriction
through the amplification fluid path 101 is substantially identical
to the flow restriction through the series combination of the
variable orifice 87, the fluid meter 29, and the variable orifice
89. If those two flow restrictions are equal, the result is an
amplification ratio of 2:1, i.e., the total flow out of the control
fluid port (21 or 23) is twice the flow through the nu& fluid
path. It is also possible, and would be within the ability of those
skilled in the art, to vary the relationship between the flow
restrictions of the amplification fluid path and main fluid path to
provide an amplification ratio other than 2:1.
The foregoing specification has described the operation of the
present invention as the controller valving is displaced from
neutral to a first operating position (right turn in FIG. 1). It
should be apparent to those skilled in the art that the foregoing
description is equally applicable with regard to operation of the
controller valving from the neutral position to a second operating
position (left turn in FIG. 1), in which case the spool 43 is
displaced in the opposite direction relative to the sleeve 45
("upward" in FIGS. 5, 6 and 7). In that case, amplification flow
would be through the other of each pair of amplification bores 95.
In addition, communication of amplification flow and of metered
fluid through the axial slots 77 would flow to the cylinder port 71
(rather than the cylinder port 69), thus flowing eventually to the,
control fluid port 21.
The invention has been described in great detail in-the foregoing
specification, sufficient to enable one skilled in the art to
practice the same, and it is believed that various alterations and
modifications of the invention will become apparent to those
skilled in the art from a reading and understanding of the
specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come
within the scope of the appended claims.
* * * * *