SPOOL VALVE
TECHNICAL FIELD
[0001] The invention generally relates to a spool valve for controlling the direction of a
flow of a hydraulic fluid, and more specifically to spool for the spool valve.
BACKGROUND OF THE INVENTION
[0002] Spool valves control, i.e., switch, the direction of flow of a hydraulic fluid by
moving a spool axiatly along a longitudinal axis within a bore of a valve housing between at least a first position and a second position. Movement of the spool opens and/or closes fluid communication between various ports defined by the valve housing to direct the hydraulic fluid along at least one of a first flow path and a second flow path.
[0003] The spool includes multiple land portions that each include a diameter
substantially equal to a diameter of the bore within which the spool is disposed. The land
portions are each configured for sealing against the bore. The various land portions define
therebetween multiple fluid directing portions. The fluid directing portions are in fluid
communication with the various ports defined by the valve housing, and are sealed from each
other by the various land portions. The fluid directing portions cooperate with the bore to define
fluid chambers, through which the hydraulic fluid flows from one port to another.
[0004] In operation, the hydraulic fluid flows from the various ports into the fluid
chambers, and flows along an outer surface of the various fluid directing portions of the spool. Accordingly, the shape of the outer surface of the fluid directing portions of the spool directly affects the flow characteristics of the hydraulic fluid flowing through the fluid chambers.
SUMMARY OF THE INVENTION
[0005] In one aspect of the invention, a spool valve is disclosed. The spool valve
includes a housing, which defines a bore extending along a longitudinal axis. The housing further defines a supply port, a first load port, a second load port and at least one exhaust port. The supply port is in fluid communication with the bore and is configured for supplying a hydraulic fluid to the bore. The first load port is in fluid communication with the bore and is

configured for directing the hydraulic fluid along a first flow path. The second load port is in
fluid communication with the bore and is configured for directing the hydraulic fluid along a
second flow path. The at least one exhaust port is in fluid communication with the bore and is
configured for exhausting the hydraulic fluid from the housing. A spool is disposed within said
bore and moveable between at least a first position and a second position. The first position
opens fluid communication between the supply port and the first load port, opens fluid
communication between the second load port and the at least one exhaust port, and closes fluid
communication between the supply port and the second load port. The second position opens
fluid communication between the supply port and the second load port, opens fluid
communication between the first load port and the at least one exhaust port, and closes fluid
communication between the supply port and the first load port. The spool includes a supply
portion disposed axially along the longitudinal axis between a first land portion and a second land
portion. The supply portion defines a truncated pseudosphere configured for directing the
hydraulic fluid to the first load port when the spool is in the first position and configured for
directing the hydraulic fluid to the second load port when the spool is in the second position.
[0006] In another aspect of the invention, a spool for a spool valve is disclosed. The
spool includes a first end and a second end spaced along a longitudinal axis from the first end. A first land portion, a second land portion, a third land portion disposed between the first end and the first land portion and a fourth land portion disposed between the second land portion and the second end. Bach of the first land portion, the second land portion, the third land portion and the fourth land portion are configured for sealing against a bore of a valve housing. A supply portion is disposed axially along the longitudinal axis between the first land portion and the second land portion. A first return portion is disposed axially along the longitudinal axis between the third land portion and the first land portion. A second return portion disposed axially along the longitudinal axis between the fourth land portion and the second land portion. The supply portion defines a truncated pseudosphere configured for selectively directing a hydraulic fluid to one of a first load port and a second load port of the valve housing.
[0007] Accordingly, the shape of the spool, and more specifically the shape of the supply
portion of the spool, smoothly directs the flow of the hydraulic fluid from the supply port to one

of the first load port and the second load port, which reduces a hydraulic force generated by the hydraulic fluid that acts on the spool. Reducing the hydraulic force acting on the spool allows the spool to be moved with less effort,
[0008] The above features and advantages and other features and advantages of the
present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 is a schematic cross sectional view of a spool valve showing a first
embodiment of a spool in a first position.
[0010] Figure 2 is a schematic cross sectional view of the spool valve showing the first
embodiment of the spool in a second position.
[0011] Figure 3 is a schematic cross sectional view of an alternative embodiment of the
spool.
[0012] Figure 4 is an enlarged fragmentary schematic cross sectional view of the first
embodiment of the spool.
[0013] Figure 5 is an enlarged fragmentary schematic cross sectional view of a second
alternative embodiment of the spool.
[0014] Figure 6 is an enlarged fragmentary schematic cross sectional view of athird
alternative embodiment of the spool.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Referring to Figures 1 and 2, wherein like numerals indicate like parts throughout
the several views, a spool valve is shown generally at 20. The spool valve 20 directs a flow of a
hydraulic fluid along at least one of a first flow path, shown in Figure 1, and a second flow path,
shown in Figure 2.
[0016] The spool valve 20 is part of a hydraulic system. The hydraulic system may
include a pump (not shown) for pressurizing and circulating the hydraulic fluid, the spool valve
20 for directing the flow of the hydraulic fluid, a motor (not shown) for converting the flow of

pressurized hydraulic fluid into work, and a tank (not shown) for storing excess hydraulic fluid and circulating the hydraulic fluid back to the pump.
[0017] The spool valve 20 includes a housing 22. The housing 22 defines a bore 24,
which extends along a longitudinal axis 26. The housing 22 may be configured in any suitable
manner for the specific situation for which it is intended. Accordingly, it should be appreciated
that the housing 22 may be configured and/or shaped differently than shown. As shown, the
housing 22 further defines a supply port 28, a first load port 30, a second load port 32 and at least
one exhaust port, 34, 36. The supply port 28 is in fluid communication with the bore 24, and is
configured for supplying the hydraulic fluid to the bore 24. The first load port 30 is in fluid
communication with the bore 24, and is configured for directing the hydraulic fluid from the bore
24, along the first flow path. The second load port 32 in is fluid communication with the bore 24,
and is configured for directing the hydraulic fluid from the bore 24, along the second flow path.
The at least one exhaust port 34, 36 is in fluid communication with the bore 24, and is configured
for exhausting the hydraulic fluid from the housing 22 for return back to the tank. As shown, the
at least one exhaust port includes a first exhaust port 34 and a second exhaust port 36.
[0018] The spool valve 20 includes a spool 38, which is moveably disposed within the
bore 24. The spool 38 is moveable between at least a first position, shown in Figure 1, and a
second position, shown in Figure 2. The first position opens fluid communication between the
supply port 28 and the first load port 30, opens fluid communication between the second load
port 32 and the second exhaust port 36, and closes fluid communication between the supply port
28 and the second load port 32. The second position opens fluid communication between the
supply port 28 and the second load port 32, opens fluid communication between the first load
port 30 and the first exhaust port 34, and closes fluid communication between the supply port 28
and the first load port 30. It should be appreciated that the housing 22 and spool 38 may be
configured differently than shown, and that the first position and the second position may operate
to open and/or close fluid communication in a sequence different than shown or described herein.
[0019J The spool 38 includes a first end 40 and a second end 42. The second end 42 is
spaced along the longitudinal axis 26 from the first end 40. As shown, the spool 38 further includes a first land portion 44, a second land portion 46, a third land portion 48 and a fourth land

portion 50. The first land portion 44 and the second land portion 46 are disposed near an approximate middle of the spool 38, with the first land portion 44 disposed nearer the first end 40 than the second end 42, and the second land portion 46 disposed nearer the second end 42 than the first end 40. The third land portion 48 is disposed between the first end 40 and the first land portion 44. The fourth land portion 50 is disposed between the second land portion 46 and the second end 42.
[0020] Each of the first land portion 44, the second land portion 46, the third land portion
48 and the fourth land portion 50 include a diameter that is substantially equal to a diameter defined by the bore 24. Additionally, each of the first land portion 44, the second land portion 46, the third land portion 48 and the fourth land portion 50 are configured for sealing against the bore 24.
[0021] The spool 38 further includes a supply portion 52, a first return portion 54 and a
second return portion 56. The supply portion 52 cooperates with the bore 24 to define a supply chamber 58 therebetween, into which the hydraulic fluid is directed from the pump. The first return portion 54 cooperates with the bore 24 to define a first chamber 60. The second return portion 56 cooperates with the bore 24 to define a second chamber 62.
[0022] The supply portion 52 is disposed axially along the longitudinal axis 26 between
the first land portion 44 and the second land portion 46, and is disposed nearer an approximate midsection of the spool 38. As shown in Figure 1, the first return portion 54 is disposed to the left of the supply portion 52 between the supply portion 52 and the first end 40. More specifically, the first return portion 54 is disposed between the third land portion 48 and the first land portion 44. As shown in Figure 1, the second return portion 56 is disposed to the right of the supply portion 52 between the supply portion 52 and the second end 42. More specifically, the second return portion 56 is disposed between the second land portion 46 and the fourth land portion 50.
[0023] At least part of the supply portion 52 defines a truncated pseudosphere 64. As is
known, a pseudosphere is commonly defined as a constant negative surface generated by revolving a tractrix about its asymptote. The truncated pseudosphere 64 includes the shape of a pseudosphere with the opposing distal ends truncated. The truncated pseudosphere 64 is centered

at a midsection of the supply portion 52. The truncated pseudosphere 64 includes a first half 66 that is configured for directing the hydraulic fluid to the first load port 30 when the spool 38 is in the first position, and includes a second half 68 that is configured for directing the hydraulic fluid to the second load port 32 when the spool 38 is in the second position.
[0024] As described above, the truncated pseudosphere 64 includes an outer surface 65
having a constant negative curvature. Additionally, the first half 66 of the truncated pseudosphere 64 defines a first inverse radius (l/R) and the second half 68 of the truncated pseudosphere 64 defines a second inverse radius (l/R). The first inverse radius is equal to the second inverse radius,
[0025] The truncated pseudosphere 64 includes a ridge 70, which is disposed at the
midsection of the supply portion 52. Due to the scale of Figures 1 and 2, the ridge 70 is shown in cross section as a point, and therefore is shown defining an annular linear ring extending about a periphery of the spool 38. However, referring to Figure 4, the ridge 70 may define a flat face 71, Much extends along the longitudinal axis a pre-determined distance. Referring also to Figures 5 and 6, alternative embodiments of the ridge 70 are shown. The pre-determined distance may include any distance suitable to permit manufacture and measurement of the diameter of the ridge
0. The first half 66 and the second half 68 of the truncated pseudosphere 64 are mirror images of each other, mirrored across the ridge 70, perpendicular to the longitudinal axis 26 and are symmetrically disposed about the midsection of the supply portion 52. The ridge 70 includes a diameter that is greater than a diameter defined by any other section of the truncated pseudosphere 64. In other words, the diameter of the ridge 70 is the largest diameter defined by the truncated pseudosphere 64.
[0026] The supply portion 52 further includes a first curve portion 72 and a second curve
portion 74. The first curve portion 72 is disposed axially along the longitudinal axis 26 between the first half 66 of the truncated pseudosphere 64 and the first land portion 44. The first curve portion 72 defines a diameter that continuously decreases in size along the longitudinal axis 26, when measured in a direction moving from the first land portion 44 toward the first half 66 of the truncated pseudosphere 64. The second curve portion 74 is disposed axially along the longitudinal axis 26 between the second half 68 of the truncated pseudosphere 64 and the second
6

land portion 46. The second curve portion 74 defines a diameter that continuously decreases in
size along the longitudinal axis 26, when measured in a direction moving from the second land
portion 46 toward the second half 68 of the truncated pseudosphere 64. Accordingly, it should be
appreciated that the length of the supply portion 52 of the spool 38 along the longitudinal axis 26
includes the first curve portion 72, the truncated pseudosphere 64 and the second curve portion
74. Additionally, it should be appreciated that the diameter of the supply portion 52 when
measured in a direction moving from the first land portion 44 toward the second land portion 46
decreases in size along the first curve portion 72, increases in size along the first half 66 of the
truncated pseudosphere 64, decreases in size along the second half 68 of the truncated
pseudosphere 64 and increases in size along the second curve portion 74.
[0027] The first return portion 54 is configured for directing the hydraulic fluid from the
first load port 30 to the at least one exhaust port when the spool 38 is in the second position. More specifically, the first return portion 54 is configured for directing the hydraulic fluid from the first load port 30 to the first exhaust port 34.
(0028] The first return portion 54 includes a first outer portion 76, a first inner portion 78
and a first annular crest 80. The first annular crest 80 is disposed between the first inner portion 78 and the first outer portion 76. The first outer portion 76 includes a continuously increasing diameter along the longitudmal axis 26 when measured along the longitudinal axis 26 in a direction from the third land portion 48 toward the first annular crest 80. The first inner portion 78 includes a continuously decreasing diameter when measured along the longitudinal axis 26 in a direction from the first annular crest 80 toward the first land portion 44. Accordingly, the first inner portion 78 and the first outer portion 76 each include a rate of diametric change, i.e., a rate of change of the diameter of the first inner portion 78 and the first outer portion 76 respectively, measured along the longitudinal axis 26. The rate of diametric change of the first outer portion 76 along the longitudinal axis 26 greater than the rate of diametric change of the first inner portion 78. In other words, the diameter of the first outer portion 76 decreases in size at a faster rate than the first inner portion 78 when measured over a common distance along the longitudinal axis 26.

[0029] The first return portion 54 and the second return portion 56 are mirror images of
each other, mirrored across the midsection of the supply portion 52, i.e., the ridge 70 of the supply portion 52, transverse to the longitudinal axis 26. Accordingly, the first return portion 54 and the second return portion 56 are symmetrical relative to each other about the midsection of the supply portion 52.
[0030] The second return portion 56 is configured for directing the hydraulic fluid from
the second load port 32 to the at least one exhaust port when the spool 38 is in the first position. More specifically, the second return portion 56 is configured for directing the hydraulic fluid from the second load port 32 to the second exhaust port 36.
[0031] The second return portion 56 includes a second outer portion 82, a second inner
portion 84 and a second annular crest 86. The second annular crest 86 is disposed between the
second inner portion 84 and the second outer portion 82, The second outer portion 82 includes a
continuously increasing diameter along the longitudinal axis 26 when measured along the
longitudinal axis 26 in a direction from the fourth land portion 50 toward the second annular crest
86. The second inner portion 84 includes a continuously decreasing diameter when measured
along the longitudinal axis 26 in a direction from the second annular crest 86 toward the second
land portion 46. Accordingly, the second inner portion 84 and the second outer portion 82 each
include a rate of diametric change, i.e., a rate of change of the diameter of the second inner
portion 84 and the second outer portion 82 respectively, measured along the longitudinal axis 26.
The rate of diametric change of the second outer portion 82 along the longitudinal axis 26 is
greater than the rate of diametric change of the second inner portion 84. In other words, the
diameter of the second outer portion 82 decreases in size at a faster rate than the second inner
portion 84 when measured over a common distance along the longitudinal axis 26.
[0032] Referring to Figure 3, an alternative embodiment of the spool is shown generally
at 188. Elements of the alternative embodiment of the spool 188 that are identical to the elements of the first embodiment of the spool 38, described above, are identified by the same reference numeral increased by one hundred. For example, the first land portion, identified by the reference numeral 44 in the first embodiment of the spool 38 is identified by the reference numeral 144 in the alternative embodiment of the spool 188, the first end, identified by the

reference numeral 40 in the first embodiment of the spool 38 is identified by the reference numeral 140 in the alternative embodiment of the spool 188, the second end, identified by the reference numeral 42 in the first embodiment of the spool 38 is identified by the reference numeral 142 in the alternative embodiment of the spool 188, and the third land portion, identified by the reference numeral 48 in the first embodiment of the spool 38 is identified by the reference numeral 148 in the alternative embodiment of the spool 188.
[0033] Within the alternative embodiment of the spool 188, the first land portion 144 and
the second land portion 146 each include a frustoconical portion 190. The fiustoconical portion
190 of each of the first land portion 144 and the second land portion 146 each include a diameter
that decreases in size when measured along the longitudinal axis 126 in a direction directed
inward toward the supply portion 152. As such, the diameter of the fiustoconical portion 190 of
the first land portion 144 decreases in size when measured along the longitudinal axis 126 in a
direction from left to right on paper, i.e., from the first return portion 154 toward the supply
portion 152. Similarly, the diameter of the frustoconical portion 190 of the second land portion
146 decreases in size when measured along the longitudinal axis 126 in a direction from right to
left on paper, i.e., from the second return portion 156 toward the supply portion 152.
[0034J While the best modes for carrying out the invention have been described in detail,
those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

We claim
1. A spool valve (20) comprising:
a housing (22) defining a bore (24) extending along a longitudinal axis (26), a supply port (28) in fluid communication with said bore (24) and configured for supplying a hydraulic fluid to said bore (24), a first load port (30) in fluid communication with said bore (24) and configured for directing the hydraulic fluid along a first flow path, a second load port (32) in fluid communication with said bore (24) and configured for directing the hydraulic fluid along a second flow path, and at least one exhaust port in fluid communication with said bore (24) and configured for exhausting the hydraulic fluid from said housing (22); and
a spool (38) disposed within said bore (24) and moveable between at least a first position and a second position, wherein said first position opens fluid communication between said supply port (28) and said first load port (30), opens fluid communication between said second load port (32) and said at least one exhaust port, and closes fluid communication between said supply port (28) and said second load port (32), and wherein said second position opens fluid communication between said supply port (28) and said second load port (32), opens fluid communication between said first load port (30) and said at least one exhaust port, and closes fluid communication between said supply port (28) and said first load port (30);
said spool (38) including a supply portion (52) disposed axially along said longitudinal axis (26) between a first land portion (44) and a second land portion (46), said supply portion (52) defining a truncated pseudosphere (64) configured for directing the hydraulic fluid to said first load port (30) when said spool (38) is in said first position and directing the hydraulic fluid to said second load port (32) when said spool (38) is in said second position.
2. A spool valve (20) as set forth in claim 1 wherein said truncated
pseudosphere (64) defines a surface having a constant negative curvature.

3. A spool valve (20) as set forth in claim 2 wherein said truncated pseudosphere (64) includes a ridge (70) disposed at a midsection of said supply portion (52), wherein said ridge (70) includes a diameter greater than a diameter defined by any other section of said truncated pseudosphere (64).
4. A spool valve (20) as set forth in claim 3 wherein said truncated pseudosphere (64) includes a first half (66) and a second half (68) wherein said first half (66) and said second half (68) are mirror images of each other opposite said ridge (70).
5. A spool valve (20) as set forth in claim 4 wherein said supply portion (52) includes a first curve portion (72) disposed between said first half (66) of said truncated pseudosphere (64) and said first land portion (44), said first curve portion (72) defining a diameter continuously decreasing in size along said longitudinal axis (26) from said first land portion (44) to said first half (66) of said truncated pseudosphere (64),
6. A spool valve (20) as set forth in claim 5 wherein said supply portion (52) includes a second curve portion (74) disposed between said second half (68) of said truncated pseudosphere (64) and said second land portion (46), said second curve portion (74) defining a diameter continuously decreasing in size along said longitudinal axis (26) from said second land portion (46) to said second half (68) of said truncated pseudosphere (64).
7. A spool valve (20) as set forth in claim 4 wherein said first half (66) of said truncated pseudosphere (64) defines a first inverse radius and said second half (68) of said truncated pseudosphere (64) defines a second inverse radius with said first inverse radius equal to said second inverse radius.

8. A spool valve (20) as set forth in claim 1 wherein said spool (38) includes a first end (40), a third land portion (48) disposed between said first end (40) and said first land portion (44) and a first return portion (54) disposed between said third land portion (48) and said first land portion (44), said first return portion (54) configured for directing the hydraulic fluid from said first load port (30) to said at least one exhaust port when said spool (38) is in said second position.
9. A spool valve (20) as set forth in claim 8 wherein said spool (38) includes a second end (42), a fourth land portion (50) disposed between said second end (42) and said second land portion (46) and a second return portion (56) disposed between said fourth land portion (50) and said second land portion (46), said second return portion (56) configured for directing the hydraulic fluid from said second load port (32) to said at least one exhaust port when said spool (38) is in said first position.
10. A spool valve (20) as set forth in claim 9 wherein said first return portion (54) includes a first outer portion (76), a first inner portion (78) and a first annular crest (80) disposed between said first inner portion (78) and said first outer portion (76), wherein said first outer portion (76) includes a continuously increasing diameter along said longitudinal axis (26) from said third land portion (48) to said first annular crest (80) and said first inner portion (78) includes a continuously decreasing diameter along said longitudinal axis (26) from said first annular crest (80) to said first land portion (44).
11. A spool valve (20) as set forth in claim 9 wherein said second return portion (56) includes a second outer portion (82), a second inner portion (84) and a second annular crest (86) disposed between said second inner portion (84) and said second outer portion (82), wherein said second outer portion (82) includes a continuously increasing diameter along said longitudinal axis (26) from said fourth land portion (50) to said second annular crest (86) and said second inner portion (84) includes a continuously decreasing diameter along said longitudinal axis (26) from said second annular crest (86) to said second land portion (46).

12. A spool valve (20) as set forth in claim 9 wherein said first return portion (54) is symmetrical with said second return portion (56) about a midsection of said supply portion (52).
13. A spool valve (20) as set forth in claim 1 wherein said first land portion (44) and said second land portion (46) each include a frustoconical portion (19)0 having a diameter decreasing in size along said longitudinal axis (26) in a direction directed inward toward said supply portion (52),

ABSTRACT

A spool valve (20) includes a housing (22) defining a bore (24) that extends along a longitudinal axis (26). A spool (38) is disposed within the bore (24) and is moveable between a first position for directing a hydraulic fluid along a first flow path and a second position for directing the hydraulic fluid along a second flow path. The spool (38) includes a supply portion (52) disposed between a first land portion (44) and a second land portion (46). The supply portion (52) includes an outer surface that defines a truncated pscudosphere (64) for smoothly directing the flow of the hydraulic fluid across the surface of the spool (38).