Note: Descriptions are shown in the official language in which they were submitted.
2112018
PATENT
STEERING CONTROL VALVE WITH FLOW GAPS
WHICH CHANGE RELATIVE SIZE FOR NOISE SUPPRESSION
Backqround of the Invention
The present invention relates to a valve for
controlling flow of hydraulic fluid, and particularly
relates to a power steering control valve for controlling
the flow of hydraulic fluid from a pump to a dower steering
motor.
A known power steering control valve for controlling
flow of hydraulic fluid from a pump to a power steering
motor includes a valve sleeve having a generally
cylindrical bore and a generally cylindrical valve core
rotatably mounted in the bore in the valve sleeve. Each of
the core and sleeve has a plurality of lands and grooves
that cooperate to regulate fluid pressure within the valve
and control flow from the pump to the power steering motor.
When the valve core and valve sleeve are in a neutral
position, fluid is communicated generally equally to
opposite chambers of the power steering motor. When the
core and sleeve are relatively rotated from the neutral
position, fluid communication with the opposite chambers is
2172018
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variably restricted. Restriction of the fluid communication
causes pressurized fluid to be delivered to one of the
chambers of the power steering motor to cause motor actuation.
The restriction is provided by the lands on the core and
sleeve which define flow orifices of variable size. Relative
rotation between the core and the sleeve varies the size of
the flow orifices. Upon relative rotation from the neutral
position to a displaced position, certain pairs of lands on
the core and sleeve radially overlap to restrict the
associated flow orifice to the size of a gap between end face
surfaces of the respective pairs of lands. Due to a high
volume of hydraulic fluid flow from the pump through the flow
orifices and pressure changes, noise is generated. The noise
includes noise due to cavitation of hydraulic fluid flowing
through the flow orifices.
Summary of the Invention
According to a first broad aspect, the invention provides
a valve for controlling flow of hydraulic fluid, said valve
comprising: inlet port means for connection with a fluid
supply; return port means for connection with a fluid
reservoir; first and second device port means for connection
with first and second locations in a fluid utilization device,
respectively; first and second relatively movable valve
members, each valve member having a plurality of lands and
grooves; respective pairs of said lands having surface
segments which overlap and form flow gaps for restricting flow
of fluid between respective pairs of grooves at relative
positions of said valve members, said flow gaps including
t
p
2172018
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first and second flow gaps; and one of said first and second
flow gaps being located between a groove in direct fluid
communication with said inlet port means and a groove in
direct fluid communication with said first device port means,
the other of said first and second flow gaps being located
between a groove in direct fluid communication with said
second device port means and a groove in direct fluid
communication with said return port means, each of said flow
gaps having a minimum cross-sectional flow area defined by
said surface segments, said minimum cross-sectional flow area
of said first flow gap being larger than said minimum cross-
sectional flow area of said second flow gap at a first
relative position of said valve members and said minimum
cross-sectional flow area of said first flow gap being smaller
than said minimum cross-sectional flow area of said second
flow gap at a second relative position of said valve members.
According to a second broad aspect, the invention
provides a valve for controlling flow of hydraulic fluid, said
valve comprising: first and second relatively movable valve
members, each valve member having a plurality of lands and
grooves; respective pairs of said lands having surface
segments which overlap and form flow gaps for restricting flow
of fluid between respective pairs of grooves at relative
positions of said valve members; at least one of said flow
gaps being divergent by having a cross-sectional flow area
which increases along the direction of fluid flow therethrough
and at least one of said flow gaps being convergent by having
a cross-sectional flow area which decreases along the
': .
h y
2172018
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direction of fluid flow therethrough; and said divergent and
convergent flow gaps having minimum cross-sectional flow areas
defined by said surface segments, said minimum cross-sectional
flow area of said convergent flow gap being larger then said
minimum cross-sectional flow area of said divergent flow gap
at a first relative position of said valve members and said
minimum cross-sectional flow area of said convergent flow gap
being smaller than said minimum cross-sectional flow area of
said divergent flow gap at a second relative position of said
valve members for suppressing valve noise.
According to a third broad aspect, the invention provides
a valve for controlling flow of hydraulic fluid, said valve
comprising: first and second relatively movable valve members,
each valve member having a plurality of lands and grooves;
respective pairs of said lands having surface segments which
overlap and form flow gaps for restricting flow of fluid
between respective pairs of grooves at relative positions of
said valve members; at least one of said flow gaps being
divergent by having a cross-sectional flow area which
increases along the direction of fluid flow therethrough and
at least one of said flow gaps being convergent by having a
cross-sectional flow area which decreases along the direction
of fluid flow therethrough; and said surface segments
comprising means for enabling the fluid flow through said
convergent flow gap to be greater than the fluid flow through
said divergent flow gap at a first relative position of said
valve members and for enabling the fluid flow through said
convergent flow gap to be less than the fluid flow through
y
2172018
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said divergent flow gap at a second relative position of said
valve members to suppress valve noise.
According to a fourth broad aspect, the invention
provides a valve for controlling flow of hydraulic fluid, said
valve comprising: first and second relatively movable valve
members, each valve member having a plurality of lands and
grooves; respective pairs of said lands having surface
segments which overlap and form flow gaps, at relative
positions of said valve members away from a neutral position,
for restricting flow of fluid between respective pairs of
grooves, said flow gaps consisting of first and second flow
gaps; said surface segments comprising means for enabling a
percentage of the fluid flow flowing through said first and
second flow gaps which flows through said first flow gap at a
first relative position of said valve members to be greater
than a percentage of the fluid flow flowing through the first
and second flow gaps which flows through said first flow gap
at a second relative position of said valve members; and said
surface segments being contoured for enabling the fluid flow
through said first flow gap to be greater than the fluid flow
through said second flow gap at the first relative position of
said valve members and for enabling the fluid flow through
said first flow gap to be less than the fluid flow through
said second flow gap at the second position of said valve
members.
According to a fifth broad aspect, the invention provides
a valve for controlling flow of hydraulic fluid, said valve
comprising: first and second relatively movable valve members,
A
2172018
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each valve member having a plurality of lands and grooves;
respective pairs of said lands having surface segments which
overlap and form flow gaps, at relative positions of said
valve members away from a neutral position, for restricting
flow of fluid between respective pairs of grooves, said flow
gaps consisting of first and second flow gaps; said surface
segments comprising means for enabling a percentage of the
fluid flow flowing through said first and second flow gaps
which flows through said first flow gap at a first relative
position of said valve members to be greater than a percentage
of the fluid flow flowing through the first and second flow
gaps which flows through said first flow gap at a second
relative position of said valve members; and said first and
second flow gaps having a minimum cross-sectional flow area,
said minimum cross-sectional flow area of said first flow gap
being larger than said minimum cross-sectional flow area of
said second flow gap when said first and second valve members
are at the first relative position, said minimum cross-
sectional flow area of said first flow gap being smaller than
said minimum cross-sectional flow area of said second flow gap
when said first and second valve members are at the second
relative position.
Brief Description of the Drawings
The foregoing and other features of the present invention
will become apparent to one skilled in the art to which the
present invention relates upon consideration of the following
description of the invention with reference to the
accompanying drawings, wherein:
:~ i
2112018
- 4c -
Fig. 1 is a longitudinal cross-sectional view of a power
steering gear with a valve which embodies the present
invention;
Fi.g. 2 is a schematic view including a cross-sectional
illustration of a portion of the valve taken approximately
along line 2-2 of Fig. 1;
f
2172018
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Fig. 3 is a view generally similar to Fig. 2, showing
the valve members relatively rotated;
Fig. 4 is an enlargement of a portion of Fig. 3 with
parts in a first relative position;
Fig. 5 is an enlargement of another portion of Fig. 3
with parts in the first relative position;
Fig. 6 is a view similar to Fig. 4 with the parts in a
_., different relative position;
Fig. 7 is a view similar to Fig. 5 with the parts in
the different relative position;
Fig. 8 is a view similar to Fig. 4 with the parts in
yet another different relative position;
Fig. 9 is a view similar to Fig. 5 with the parts in
t
the other different relative position;
Fig. 10 is a view of a schematic overlay of two
geometric representations of surface profiles of the valve
of Fig. 1; and
Fig. 11 is a schematic flow diagram of the valve of
Fig. 1.
Description of Preferred Embodiment
A fluid control valve of the present invention may be
used to control fluid flow associated with mechanisms of a
variety of constructions and uses. Preferably, the control
valve 10 (Fig. 1) is utilized in a power steering gear 12
which provides power assistance for turning dirigible
wheels (not shown) of a vehicle (not shown) in opposite
directions to effect steering of the vehicle. The
2 i 7201 ~3
-6-
preferred power steering gear is a model TAS Integral Power
Steering Gear manufactured and marketed by TRW Inc.,
Commercial Steering Division of Lafayette, Indiana, and
identified as TAS40, TAS55 or TAS65. The power steering
gear 12 includes a housing 14 having an inner cylindrical
surface 16 defining a chamber 18. A piston 20 (shown
partially in section) divides the chamber 18 into opposite
chamber portions 22 and 24 located at opposite ends of the
piston 20. An 0-ring 26 carried in a groove 27 in the
piston 20 provides a fluid seal between the chamber
portions 22 and 24.
A series of rack teeth 28 are formed on the periphery
of the piston 20. The rack teeth 28 mesh with teeth 32
I
formed on a sector gear 34. The sector gear 34 is fixed on
an output shaft 38 which extends outwardly from the
steering gear 12 through an opening (not shown) in the
housing 14. The output shaft 38 is typically connected to
a pitman arm (not shown) which in turn is connected to a
mechanical steering linkage (not shown) of the vehicle.
Thus, as the piston 20 moves in the chamber 18, the sector
gear 34 and output shaft 38 are rotated to operate the
steering linkage as will be understood by those skilled in
the art.
The housing 14 includes a fluid inlet port 46 and a
fluid return port 50. The inlet port 46 and the return
port 50 are adapted to be connected in fluid communication
with hydraulic circuitry (schematically illustrated)
217201
including a power steering pump 52 which supplies
pressurized hydraulic fluid and a fluid reservoir 54. The
control valve 10 is operable to direct pressurized fluid
from the inlet port 46 to one of the chamber portions 22
and 24. Fluid from the other of the chamber portions 22
and 24 is simultaneously directed by the control valve 10
to the return port 50 which is connected with the fluid
reservoir 54.
The control valve 10 is actuated by a rotatable shaft
62. The shaft 62 is supported for rotation relative to the
housing 14 via a bearing member 66. An outer end portion
64 of the shaft 62 is splined for receiving a portion of a
shaft 68 thereon. The shaft 68 is connected with a
1
steering wheel (not shown) which is manually turned by the
operator of the vehicle to effect steering of the vehicle.
The control valve 10 includes a valve core 80 and a
hollow valve sleeve 82. The valve core 80 is located
coaxially within the valve sleeve 82 and is rotatable
relative to the valve sleeve 82 about a common axis 81
(Fig. 2). The valve sleeve 82 (Fig. 1) is supported for
rotation by bearings 83 and 84. The bearing 83 is located
between an annular projecting portion 85 of the valve
sleeve 82 and a radial wall 86 of the housing 14. Also, a
seal ring 87 is located between the outer surface of the
valve sleeve 82 and the housing 14.
The bearing 84 is a thrust bearing and is located
between a radial surface 88 of the annular projecting
2172018
_8_
portion 85 of the valve sleeve 82 and a retaining nut 89.
The nut 89 is threaded into the housing 14 and holds the
control valve 10 within'the housing 14. A seal ring 90 is
located between the nut 89 and an outer surface of the
valve sleeve 82. Another seal 91 is disposed in a groove
in the housing 14.
The valve sleeve 82 (Fig. 2) has three radially
directed passages 94 extending from its outer periphery to
its inner periphery. The passages 94 are spaced 120° apart
about the valve sleeve 82. The passages 94 communicate
with an annulus 96 (Fig. 1) in the housing 14. The annulus
96, in turn, is connected with the inlet port 46, and is
thus subjected to the fluid pressure from the pump 52.
I
The valve sleeve 82 has three axially extending
grooves 98 (Fig. 2) which are equally spaced around the
inner periphery of the valve sleeve 82. Each of the
grooves 98 communicate with a respective radially extending
passage 100. The passages 100 are spaced 120° apart about
the valve sleeve 82. The passages 100 (Fig. 1 shows only
one passage 100, in phantom) communicate with an annulus
102 in the housing 14. The annulus 102 communicates with a
housing passage 106 (shown schematically) which, in turn,
communicates with the chamber portion 24.
The valve sleeve 82 (Fig. 2) includes three axially
extending grooves 110 which are equally spaced about the
inner periphery thereof. Each of the grooves 110
communicate with a respective passage 112. The passages
211201
_g_
112 are spaced 120° apart about the valve sleeve 82. The
passages 112 (Fig. 1 shows only one passage 112, in
phantom) communicate with the chamber portion 22.
The valve core 80 has an elongated cylindrical
configuration and is integrally formed as one piece with
the shaft 62. The valve core 80 has three axially
extending grooves 116 (Fig. 2) in its outer periphery. The
grooves 116 are equally spaced 120° apart about the outer
periphery of the valve core 80 and are in direct fluid
communication with the passages 94 in the valve sleeve 82.
w The extent of the grooves 116 around the outer periphery of
the valve core 80 is such that each of the grooves 116
communicates equally with respective grooves 98 and 110
t
when the valve core 80 is in a centered or neutral position
relative to the valve sleeve 82 (as shown in Fig. 2).
Also equally spaced about the outer periphery of the
valve core 80 are axially extending grooves 122. The
extent of the grooves 122 around the outer circumference of
the valve core 80 is such that each of the grooves 122
communicates equally with respective grooves 98 and 110
when the valve core 80 is in the centered or neutral
position. Each of the grooves 122 is directly connected
with a respective passage 126 which extends from each
groove 122 into an internal passage 130 of the valve core
80. The internal passage 130 of the valve core 80 is
connected with a plurality (four) of radially extending
passages 134 (Fig. 1, only two shown) which extend through
zozon
-10-
the valve core 80. The radially extending passages 134
communicate with an annulus 136 in the housing 14. The
annulus 136, in turn, communicates with the return port 50
in the housing 14.
The valve sleeve 82 of the steering gear 10 is
integrally formed with a follow-up member 150 which has a
screw thread portion 152 formed in its outer periphery.
The valve sleeve 82 and the follow-up member 150 form an
integral one-piece unit 158. A plurality of balls 162 are
located in the screw thread portion 152. The balls 162 are
also located in an internally threaded portion 164 formed
in a bore 166 of the piston 20.
Axial movement of the piston 20 corresponds to
rotation of the follow-up member 150 and vice~versa. A
torsion spring 170 is connected between the input shaft 62
and the follow-up member 150 by pins 174 and 176,
respectively. During a power assisted steering maneuver,
the valve core 80 is rotated relative to the valve sleeve
82, away from the neutral position. Thus, when the valve
core 80 is rotated relative to the valve sleeve 82, the
piston 20 moves axially. When the steering maneuver is
terminated, the one-piece unit 158, and thus the valve
sleeve 82, will rotate relative to the valve core 80 and
return to the neutral position via the bias of the torsion
spring 170.
' " Control flow path structure of the preferred
embodiment of the valve core 80 and the valve sleeve 82 is
2172018
-11-
hereafter described. The valve sleeve 82 includes three
axially extending lands 200 (Fig. 2) located radially
opposite, in the neutral position, the grooves 116 of the
valve core 80. The lands 200 each include an axially
extending end face surface 202 which lies in an arc
extending across the respective land 200 at a radius from
the common axis 81. The lands 200 have relatively sharp
terminus edges at the ends of the end face surfaces 202
adjacent the grooves 98 and 110, which define land corners.
An associated one of the passages 94 extends through each
land 200 and through each end face surface 202 to
_,, communicate with a respective one of the grooves 116.
The valve sleeve 82 also includes three axially
i
extending lands 206 located radially opposite, in the
neutral position, the grooves 122 of the valve core 80.
The lands 206 each include an axially extending end face
surface 208 which lies in an arc extending across the
respective land 206 at a radius from the common axis 81.
The lands 206 have relatively sharp terminus edges at the
ends of the end face surfaces 208 adjacent the grooves 98
and 110, which define land corners.
The valve core 80 includes three axiallylextending
lands 212 which are located radially opposite the grooves
98 in the neutral position. Each of the lands 212 has an
axially extending end face surface 214 which lies in an arc
extending partially across the respective land 212 at a
radius from the common axis 81. Each of the lands 212
_ 2172018
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includes axially extending contoured portions 216, 217 and
218.
For each land 212,'the contoured portions 216 and 217
are adjacent to each other at one side of the land 212.
Each respective contoured portion 216 is located adjacent
to a respective one of the grooves 116, and each respective
contoured portion 217 is located between the adjacent
contoured portion 216 and the respective one of the end
face surfaces 214. Fluid flows past the three sets of
contoured portions 216 and 217 in fluid parallel relative
to each other.
Also for each land 212, the contoured portion 218 is
located on the side of the land 212 opposite to the
t
contoured portions 216 and 217. Each of the contoured
portions 218 is located between a respective one of the
grooves 122 and a respective one of the end face surfaces
214. The flows of fluid past the three contoured portions
218 are in fluid parallel with respect to each other.
In a preferred embodiment, the contoured portions 216,
217 and 218 are chamfers defined by planar surfaces. In
alternative embodiments, the contoured portions 216, 217
and 218 may include a plurality of planar surfaces and/or
one or more curved segments. Hereinafter, the contoured
portions 216 and 218 are referred to as chamfers 216, 217
and 218, respectively, with the understanding that other
contours are possible.
217201 ~
-13-
Each of the chamfers 217 tapers radially inwardly as
it~extends from~the respective end face surface 214 to the
respective chamber 216. Each of the chamfers 216 also
tapers radially inward as it extends from the respective
chamfer 217 to the groove 116. Each chamfer 216 is
inclined relative to the respective chamfer 217, and thus,
has a steeper gradient than the respective chamfer 217. A
land corner is defined at the terminus edge of each chamfer
216 at the adjacent groove 116. An intersection corner 219
is also defined where the respective chamfers 216 and 217
intersect. These intersection corners 219 may be
relatively sharp or, in the alternate embodiment, may be
rounded. Each chamfer 218 (enlarged, Fig. 4) tapers
_..
radially inwardly as it extends from the respective end
face surface 214 to the respective groove 122 and defines a
land corner at its terminus edge adjacent to the groove
122. The chamfers 218 (Fig. 2) have a steeper gradient
than the chamfers 217 and have a lesser gradient than the
chamfers 216. This is shown by the overlays of the
profiles of the chamfers 216, 217 and 218 in Fig. 10.
The valve core 80 also includes three axially
extending lands 222 which are positioned radially opposite
the grooves 110 in the neutral position. Each of the lands
222 has an axially extending end face surface 224 which
.25 lies in an arc extending partially across the respective
land 222 at a radius from the common axis 81. Each of the
2172018
-14-
lands 222 includes axially extending contoured portions
226, 227 and 228.
For each land 222,'the contoured portions 226 and 227
are adjacent to each other at one side of the land 222.
r
Each respective contoured portion 226 is located adjacent
to a respective one of the grooves 116, and each respective
contoured portion 227 is located between the adjacent
contoured portion 226 and the respective one of the end
face surfaces 224. Fluid flows past the three sets of
contoured portions 226 and 227 in fluid parallel relative
to each other.
Also for each land 222, the contoured portion 228 is
located on the side of the land 222 opposite to the
contoured portions 226 and 227. Each of the contoured
portions 228 is located between a respective one of the
grooves 122 and a respective one of the end face surfaces
224. The flows of fluid past the three contoured portions
228 are in fluid parallel relative to each other.
In the preferred embodiment, the contoured portions
226, 227 and 228 are chamfers defined by planar surfaces.
In the alternative embodiment, the contoured portions 226,
227 and 228 may include a plurality of planar~and/or one or
more curved segments. Hereinafter, the contoured portions
226, 227 and 228 are referred to as chamfers 226, 227 and
228, respectively, with the understanding that other
contours are possible.
-15- 2172018
Each of the chamfers 227 (enlarged, Fig. 5) tapers
radially inwardly as it extends from the respective end
face surface 224 to the'respective chamfer 226. Each of
the chamfers 226 also tapers radially inward as it extends
from the respective chamfer 227 to the groove 116. Each
chamfer 226 is inclined relative to the respective chamfer
227, and thus, has a steeper gradient than the respective
chamfer 227. A land corner is defined at the terminus edge
of each chamfer 226 at the adjacent groove 116. An
intersection corner 229 is also defined where the
respective chamfers 226 and 227 intersect. These
intersection corners 229 may be relatively sharp or, in the
alternative embodiment, may be rounded. Each chamfer 228
(Fig. 2) tapers radially inward as it extends~from the
respective end face surface 224 to the respective groove
122 and defines a land corner at its terminus edge adjacent
_._ to the groove 122. The chamfers 228 have a steeper
gradient than the chamfers 227 and have a lesser gradient
than the chamfers 226. The gradients of the chamfers 216
and 226 are the same, the gradients of the chamfers 217 and
227 are the same, and the gradients of the chamfers 218 and
22B are the same.
In operation, the amount of fluid flow from the
grooves 116 to either the grooves 98 or 110 is dependent
upon the proximity of the lands 212 and the lands 222 to
the lands 200, due to relative rotation between the valve
core 80 and the valve sleeve 82. The cooperation of the
2i720i8
-16-
lands 200 and the lands 212 provides a variable resistance
R1~(schematically represented in Fig. 11) to fluid flow,
and the cooperation of the lands 200 and the lands 222
provides a variable resistance R2 to fluid flow. An
increased resistance to fluid flow decreases a fluid volume
flow rate.
Further, the amount of fluid flow from either the
grooves 98 or 110 (Fig. 2) to the grooves 122 is dependent
' upon the proximity of the lands 212 and the lands 222 to
the lands 206, due to relative rotation between the valve
core 80 to the valve sleeve 82. The cooperation of the
lands 206 and the lands 222 provides a variable resistance
R3 (Fig. 11) to fluid flow and the cooperation of the lands
t
206 and the lands 212 provides a variable resistance R4 to
fluid flow. Associated with each of the resistances R1-R4
is a pressure change (drop) as the flowing fluid crosses
the area of resistance and is subjected to the resistance.
The amount of pressure drop is proportional to the amount
of resistance.
In the neutral position (Fig. 2) the lands 212 and the
lands 222 are spaced at equal distances from the lands 200.
Equal amounts of pressurized hydraulic fluid flows from the
grooves 116 into both the grooves 98 and the grooves 110.
Also, in the neutral position, the lands 212 and the lands
222 are spaced at equal distances from the lands 206.
Equal amounts of hydraulic fluid flows from the grooves 98
and 110 into the grooves 122. Thus, in the neutral
L~72018
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position, the pressures in the chamber portions 22 and 24 are
equal. Therefore, the piston 20 is not moved.
Upon rotation of the steering wheel for a power
assisted steering maneuver, the valve core 80 is rotated
relative to the valve sleeve 82, away from the neutral
position. Upon rotation of the valve core 80 in a first
direction (counterclockwise as shown in Fig. 3) relative to
the valve sleeve 82, the lands 212 are spaced a greater
distance from the lands 200 and the lands 222 are spaced a
greater distance from the lands 206 than in the neutral
position. The spacing of the lands 212 relative to the lands
200 and the spacing of the lands 222 relative to the lands 206
increases the respective areas available for fluid flow and
reduces the respective resistance R1 and R3 (Fig. 11) to
increase the flow of hydraulic fluid. Pressurized hydraulic
fluid from the pump 52 is directed into the chamber 24. Also,
hydraulic fluid from the chamber 22 is vented to the reservoir
54 to move the piston 20.
As the valve core 80 (Fig. 3) is rotated relative to
the valve sleeve 82 through a range of rotation away from the
neutral position, the lands 212 partially radially overlap the
lands 206 and the lands 222 partially radially overlap the
lands 200. The overlapping lands 222 and 200 define
restrictive flow gaps or passages 232 for hydraulic fluid
flowing from the grooves 116 to the grooves 110. The
overlapping lands 212 and 206 create restrictive flow gaps
27789-99
211218
-18-
_.. ,
or passages 234 for hydraulic fluid flowing from the
grooves 98 to the grooves 122.
Each flow gap 234 (enlarged, Fig. 4) has a cross-
sectional area defined by the end face surface 208 on a
respective one of the lands 206 and the chamfer 218 on a
respective one of the lands 212. The cross-sectional area
of each flow gap 234 for flow of hydraulic fluid from the
grooves 98 to the grooves 122 gradually increases from a
minimum cross-sectional area B immediately adjacent to the
groove 98. Thus, the flow gaps 234 are termed divergent
flow gaps. During the radial overlap, the minimum cross-
sectional area B of each flow gap 234 is defined by the
terminus edge of the end face surface 208 and the chamfered
I
portion 218.
Each flow gap 232 (enlarged, Fig. 5) has a cross-
sectional area. Depending upon the amount of radial
overlap, each respective cross-sectional area is defined
between the end face surface 202 of a respective one of the
lands 200 and the chamfer 226 on a respective one of the
lands 222 or is defined between the respective end face
surface 202 and the respective chamfers 226 and 227. The
. cross-sectional area of each flow gap 232 for~flow of
hydraulic fluid from the grooves 116 to the grooves 110
decreases to a minimum cross-sectional area A immediately
adjacent to the groove 110. Thus, the flow gaps 232 are
termed convergent flow gaps. Depending upon the amount of
the radial overlap, the minimum cross-sectional area A is
2i720i8
-19-
defined by the terminus edge of the end face surface 202
and either the chamfer 226 or the chamfer 227.
The sizes of the minimum cross-sectional areas A and
B, and thus the amount of the resistances R2 and R4, are
related to the amount of relative rotation of the valve
core 80 from the neutral position. An increase in the
amount of rotation away~from the neutral position decreases
the minimum cross-sectional areas A and B, and increases
the resistances R2 and R4.
For a first segment of relative rotation of the valve
core 80 and the valve sleeve 82 (Figs. 4 and 5), only the
chamfers 226 overlap the respective end face surfaces 202
at the flow gaps 232. The minimum cross-sect Tonal areas A
at the flow gaps 232 are defined at the respective chamfers
226 and the minimum cross-sectional areas B at the flow
gaps 234 are defined at the respective chamfer 218. The
minimum cross-sectional area A (Fig. 5) at each flow gap
232 is larger than the minimum cross-sectional area B (Fig.
4) at each flow gap 234 because the gradient of the
chamfers 226 is greater than the gradient of the chamfers
218. The resistance R2 is less than the resistance R4.
The fluid volume flow rate through the flow gap 234 is less
than the fluid volume flow rate through the flow gap 232.
However, both of the resistances R2 and R4 are not yet
very large compared to their respective valves which will
be achieved upon further rotation of the valve spool 80
relative to the valve sleeve 82. Thus, the pressure drops
_ 2172018
-20-
at the flow gaps 232 and 234 are not yet very large. Less
overall flow noise is created because the larger minimum
cross-sectional area A is at a convergent flow gap and the
smaller minimum cross-sectional area B is at a divergent
flow gap for this relatively low pressure drop situation.
As the valve core 80 is further rotated relative to
the valve sleeve 82, away from the neutral position and
past the first segment of relative rotation, both the
minimum cross-sectional flow areas A and B continue to
decrease. However, the minimum cross-sectional areas A
decrease at a faster rate than the minimum cross-sectional
areas B because of the larger gradient of the chamfers 226.
At a particular rotational position of the valve core 80
P
and the valve sleeve 82, the minimum cross-sectional areas
A and H are equal. The resistances R2 and R4 are equal,
and the fluid volume flow rates through the flow gaps 232
and 234 are equal.
The rotational position at which the minimum cross-
sectional areas A and B are equal is dependent upon the
contouring of the lands. Specifically, in the embodiment
shown in the Figures, this equal flow position is dependent
upon the size of the respective gradients of the chamfers
216, 217 and 218, and the relative lengths of the chamfers
216, 217 and 218 along their respective lands. In the
preferred embodiment, this equal flow position (Figs. 6 and
7) occurs prior to the terminus edge of each respective end
face surface 202 being radially aligned with the respective
217?_018
-21-
intersection corner 229 during the rotation of the valve
core 80 relative to the valve sleeve 82 away from the
neutral position.
This can be further understood upon consideration of
Fig. 10 in which the profiles of the chamfers 216 and 217
are overlaid on the profile of the chamfer 218. The
intersection of the profile of the chamfer 218 with the
profile of the chamfer 216 indicates a location along the
respective chamfers at which a minimum cross-sectional flow
area will be defined at the equal flow position.
Upon further continued rotation of the valve core 80
and the valve sleeve 82 away from the neutral position and
away from the equal flow position, the minimum cross-
Y
sectional areas A and B continue to decrease. However, the
minimum cross-sectional flow area A at each flow gap 232
remains smaller than the minimum cross-sectional flow areas
B at each flow gap 234. The resistance R4 is less than the
resistance R2 and the fluid volume flow rate through the
flow gap 232 is less than the fluid volume flow rate
through the flow gap 234.
Further, the flow gaps 232 and 234 are very pinched
and the resistances R2 and R4 are very large compared to
their respective values when the valve core 80 is rotated
only slightly from the neutral position relative to the
valve sleeve 82. Thus, the pressure drops at the flow gaps
232 and 234 are relatively large for these relatively
greatly rotated positions of the valve core 80 relative to
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the valve sleeve 82. Less overall noise is created because
the larger minimum cross-sectional area B is at a
convergent flow gap and'the smaller minimum cross-sectional
flow area A is at a convergent flow gap for this relatively
high pressure drop situation. Thus, the present invention
provides improved suppression of noise at both the
relatively low pressure~drop situation and the relatively
high pressure drop situation.
Upon rotation of the valve core 80 (Fig. 2) in a
second direction (clockwise, not shown) relative to the
valve sleeve 82, there is a corollary restriction of flow
of hydraulic fluid from the grooves 116 to the grooves 98
and from the grooves 110 to the grooves 122. With the
t
valve core 80 and the valve sleeve 82 relatively rotated in
such a manner, the lands 222 radially overlap the lands 206
and the lands 212 radially overlap the lands 200. Thus,
associated restrictive flow gaps are established between
the lands 222 and 206 and the lands 212 and 200.
Thus, pressurized hydraulic fluid from the pump 52
(Fig. 1) is directed into the chamber 22. Hydraulic fluid
from the chamber 24 is vented to the reservoir 54.
However, here also, the minimum cross-sectional area at the
convergent flow gaps is larger than the minimum cross-
sectional area at the divergent flow gap, during a first
segment of relative rotation of the valve core 80 away from
the neutral position. The fluid volume flow rate is larger
2112018
-23-
at the convergent flow gaps, and less overall noise is
created for this relatively low pressure drop situation.
At a segment of greater relative rotation of the valve
core 80 away from the neutral position and beyond the first
segment of relative rotation, the relative size ratios
reverse. The minimum cross-sectional area at the divergent
flow gaps is larger than the minimum cross-sectional flow
area at the convergent flow gaps. The fluid volume flow
rate is larger at the divergent flow gaps, and less noise
is created for this relatively high pressure drop
situation.
From the above description of the invention, those
skilled in the art will perceive improvements,, changes and
modifications. For example, the lands may be~contoured
such that only divergent or only convergent flow gaps are
created upon relative rotation of the valve core and the
valve sleeve. During relative rotation away from the
neutral position, the minimum cross-sectional flow area at
one or more flow gaps would be greater than the minimum
cross-sectional flow area at one or more flow gaps at a
first position or range, and would be less at a second
position or range, for noise suppression. Alternatively,
the fluid flow may be reduced by a greater amount in one or
more flow gaps than the amount of reduction in one or more
other flow gaps, thus changing the relative percentage of
the total flow which is permitted in each of the flow gaps.
Also, for example, the lands may be contoured such that the
2~ ~20~ s
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shift from a greater relative size to a lesser relative
size may be from a divergent flow gaps) to a convergent
flow gap(s). Such improvements, changes and modifications
within the skill of the art are intended to be covered by
the appended claims.
