Note: Descriptions are shown in the official language in which they were submitted.
L INTERFACE DESIGN ~F TWO CLAMPED-TOGETHER PARTS
Backyround of the Invention
The invention concerns at least two parts that are clamped
together with at least one of the parts having a cavity
receiving a moving part and having spacers in the region of the
confronting clamping sur~aces at the interface of the two
parts.
German Patent 1,550,067 discloses one assembly of two
clamped-together parts wherein the parts are approximately
cuboid in shape and represent a valve housing and a valve
baseplate of a valve housing unit. This valve housing also has
a cover, and three screws extend through holes bored in the
cover and in the valve housing into threaded holes in the valve
baseplate. The valve housing has an axial bore that extends
1~ along the center of and parallel to the long surface of the
valve housing. The valve baseplate has various inlet and outlet
channels that carry liquid under pressure or not under pressure
to or from a device. The flow of fluid to and from inlet and
outlet channels and hence to and from the device is controlled
by means of a valve spool located in and having lands fitted to
the a~ial bore. In order to prevent the occurrence of stresses
on the valve housing ~hat might result in deformation of the
housing and binding of the valve spool when the screws are
tightened, the three screws are arranged so that they define the
points of a triangle to achieve a stress-free three-point
support. Moreover, mounted on the screws at the interface of
the valve housing and the valve baseplate are spacers in the
form of approximately 0.79 mm thick washers, which are intended
to prevent the valve housing and the valve baseplate from
touching at points outside the spacers~ since otherwise the
support would no longer be at only three points and stresses due
to irregulari~ies at the opposing points of the two parts would
occur. In addition, a gasket is located at the interface of the
valve housing and the valve baseplate to prevent loss of liquid
from the inlet and outlet channels and which is compressed by
the opposing sides of the valve housing and valve baseplate by
the screws.
Granted, a pure three-point contact in practice would be a
conceivable way of avoiding stresses in a valve housing as the
screws are tightened. In fact, however, only a theoretical
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1 approximation to the ideal three-point contact has been
achieved. In addition~ the washers can easily be displaced when
the parts are assembled and thus no longer fulfill their
function. Finally, in the case of large valve housing units,
the distances between the screws are so great that the clamping
forces between the screws no longer suffice to compress the
gasket between the valve housing and the valve baseplate
sufficiently to form a liquid-tight seal.
Summary of the Invention
ln The task on which the invention is based is then to design
at least one of the parts so that the part that contains the
movable part is not stressed when the clamping force is
applied.
This task is solved according to the invention by forming
the spacers at least in part by means of integral, deformable
knurling of the material.
In this way, the spacers can be formed by simple material
knurling and loose parts can be avoided. The position and size
of the knurling can thus be dependent on the sizes of the two
parts and need not also be determined by a specific placement of
the screws.
The deformability of the knurling in the material permits
equalization in height in the area of the contact surface and
stresses are eliminated since the prestress required for the
screws is achieved only by deformation of the knurling and not
by contact with a relatively unyielding surface. Therefore,
stresses in the part containing the moving part occurring
between the clamping surfaces need not be feared when there is a
deviation from the ideal three-point contact. Since, with the
knurling, the spacers are necessarily of the same ~aterial as
the part containing the moving part, no difficulties occur in
use as a result of using different materials.
When two or more parts are clamped together, of which one is
a valve housing with a sliding valve, then according to the
invention, the region of the valve will be kept free of stresses
by the fact that the knurling is located outside of the surface
of the valve projected onto the interface between the two
parts.
The clamping forces thus act to the side of the valve and
never on the valve bore itself. This is especially important
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1 when the valve housing containing the valve has very thin walls
in the vicinity of the bore or is made of an easily deformed
material.
The knurling in the material can be produced in a simple,
economical way that is suitable for mass production, according
to another suggestion of the invention, by forming peaks by
milling or stamping. Especially in the case of stamping, it is
possible to determine the shape and height of the knurling and
fit them to the magnitude of the clamping forces by means of the
shape of the stamp and the pressure acting on it. This results
in a particularly simple method by which stresses in the region
of the bore can be avoided.
If, according to an additional feature of the invention, the
peaks of the material undergo plastic deformation, then a
flattening of the peaks will occur only during the first
application of the clamps, and will depend on the magnitude of
the clamping forces, which may be determined using a torque
wrench, and after separating the two parts, when they are
reassembled in the same position, the freedom from stresses will
be maintained due to the preformed contact surfaces, which will
not be altered further at the same clamping force.
When the sides of the parts are suitably designed, a
sufficient freedom from stress is achieved if the knurling is
3/100 to 5/100 mm high.
The drawing represents an embodiment of the invention that
will be described in greater detail in the following.
Brief Description of the Drawings
FIG. 1 is a view of the hydraulic circuit with a valve
housing assembly.
FIG. 2 is a view of the underside of a valve housing.
FIG. 3 shows a detail section in the area of circle 3 in
FIG. 1.
FIG. 4 is a detail section in the area of circle 4 in FIG.
1.
Description of the Preferred Embodiment
A hydrualic circuit 10 shown in FIG. 1 consists of a
reservoir 12, a pump 14, a pressure relief valve 16, a valve
housing assembly 18, a device 20 and appropriate hydraulic
lines. These include a suction line 22 between the pump 14 and
the reservoir 12, a pressure line 24 between the pump 14 and the
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1 valve housing assembly 18, a first and a second device line 26
and 28 between the valve housing assembly 18 and the device 20
and a return line 30 between the valve housing assembly 18 and
the reservoir 12. In this example, the pump 14 is a variable
displacement pump and the device is a two-way hydraulic cylinder
to which hydraulic fluid can be sent by the pump 14 on either
the piston side or the rod side, as will be described below.
The valve housing assembly 18 consists essentially of a
bracket 32 and three parts, namely, a baseplate 34 and lower and
upper valve housings 36 and 38, respectively, which are
assembled in that order. The bracket 32 is U-shaped and is
arranged with a face 40 extending vertically between and joining
upper and lower horizontal legs 42 and 44 and is attached to an
unshown hydraulic unit, such as can be found on a tractor. The
lower leg 44 contains holes 46 for unshown screws, which can be
inser.ed into similarly unshown threaded holes on the tractor,
while the upper leg 42 contains threaded holes 48 into which
clamps in the form of screws 50, extending through the valve
housing assembly 18, can be screwed. To the upper leg 42 is
attached the baseplate 34. The baseplate 34 is in the form of a
cuboid having short end surfaces 56 and 58 which extend between
upper and lower planar surfaces 60 and 62. The baseplate 34
contains a pressure channel 52 having an entrance located in the
surface 56 and connected to the pressure line 24 and contains a
return channel 54 having an exit located in the surface 58 and
connected with the return line 30. The connections are made by
means of commercially available screw fittings, which are
omitted here for the sake of simplicity. Unshown holes for the
screws 50 extend through the baseplate 34 perpendicular to the
surfaces 60 and 62. The lower valve housing 36 has lower and
upper planar surfaces 64 and 66, respectively and the upper
valve housing has lower and upper planar surfaces 68 and 69,
respectively. The lower housing 36 is sandwiched between the
upper housing 38 and the baseplate 34 so that a first interface
exists at the confronting surfaces 60 and 64 and a second
interface exists at the confronting surfaces 66 and 68. The
upper and lower valve housings 38 and 36 are also cuboid in
their central portions 70 and 72 and the holes 51 for the screws
50 extend through them perpendicular to their respective upper
and lower surfaces. The holes 51 are bored at the edge of the
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1 long sides of the central portions 70 and 72, and in this
example, there are two holes on each long side. Parallel to the
upper and lower surfaces of the central portions 70 and 72 are
axial bores 74 and 76, which respectively contain valve spools
78 and 80. The bores 74 and 76 run concentric with the central
axis of the central portions 70 and 72. Attached to one end of
each central portion 70 and 72 is an end cap 82 in which is
located a restoring mechanism 84 that returns the associated
valve spool 78 or 80 to a neutral position, and at the other end
is a cap 86 that is common to the upper and lower valve housings
38 and 36. Inside the common cap 86 is an adjusting mechanism
90 that can be controlled by a lever 88 and consists of a
rotating pinion 92 located between and meshed with racks of
teeth formed on ends 94 and 96 of the valve spools 78 and 80.
The pinion 92 can be held in various positions by means of a
locking device 98. The pinion 92 operates when it i5 rotated by
means of the lever 88 to displace the valve spools 78 and 80 in
opposite directions. While the end caps 82 are attached liquid-
tight, the cap 86 is not; and sealing is achieved by seals 100
slidably receiving the valve spools 78 and 80 and located in the
housings 36 and 38 adjacent their connection to the cap 86.
Considered from left to right in FIG. 1, the valve spool 78
includes a left end 102, a first land 106, a second land 114
spaced axially from the land 106, and a shaft section 118
extending between the land 114 and the toothed end 94. The
valve spool 80 is identical to the spool 78 and includes a left
end 104, a first land 108, a second land 116 and a shaft section
120. The valve bores 74 and 76 are identical and include
respective annular pressure chambers 110 and 112, annular device
chambers 130 and 132 and annular return chambers 126 and 128,
with these sets of like chambers being connected to each other.
The supply pressure channel 52 is connected to the chamber 110
by a passage 134 that connects with a passage 138 leading to the
chamber 112. The annular device chamber 132 of the upper valve
housing 38 is connected to the first device line 26 and the
annular device chamber 130 of the lower valve housing 36 is
connected to the second device line 28. An outlet passage 136
leads from the return chamber 126 of the bore 74 to the outlet
channel 54. The passage 136 connects to an outlet passage 40
leading from the return chamber 128 of the bore 76. On the
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1 undersides of the valve housings 36 and 38 annular recesses 142
are formed at respective lower ends of each of the passages 134,
136, 138 and 140 to hold gasket eings 144 that are clamped
between the surfaces 60 and 64, and between the surfaces 66 and
68 when the valve housing assembly 18 is assembled by tightening
the screws 50 so that a liquid-tight seal is achieved.
The valve spools 78 and 80 can be jointly set to three
different settings, namely an inlet setting, a neutral setting
and an outlet setting with the spool 78 occupying its inlet
setting onl~ when the spool 80 occupies its outlet setting and
vice-versa and with the spools 78 and 80 being in their neutral
positions at the same time. In their neutral settings, as shown
in FIG. 1, the valve spools 78 and 80 are in positions in which
their lands 114 and 116 prevent the flow of liquid into or out
of the annular device chambers 130 and 132. In order to move
one of the spools 78 or 80 to its inlet setting, the particular
spool 78 or 80 is moved rightwardly by appropriate rotation of
the pinion 92 until the valve land 114 or 116 permits a
connection between the annular device chamber 130 or 132 and the
annular pressure chamber 122 or 124. At the same time, the
other of the spools 78 or %0 will have moved leftwardly to its
outlet setting wherein a connection is formed between the device
chamber 130 or 13~ and the outlet chamber 12~ or 128. These
settings are thus achieved only by sliding the spools 78 and 80
and therefore the latter must be installed in the a~ial bores 74
and 76 so that they are easy-running and liquid-tight. The
tightness of the spools 78 and 80 in the axial bores 74 and 76
is achieved by choosing their tolerance so that no undesired
flow of liquid can occur between the pressure, device and
exhaust chambers 122 to 132.
As shown in FIG 2, the undersurface 64 of the lower valve
housing 36 is machined in places, and roughened by milling or
stamping. This is also the case on the undersurface 68 of the
upper valve housing 38, although it is not visible. These
points, which will be referred to in the following as contact
surfaces 146, are located parallel to the longitudinal central
axis of the axial bore 74 and on each side of it. They are
distributed in lines more or less uniformly along the length of
the underside of the central portion 70. In this embodiment,
four contact surfaces 146 are prepared on each side of the valve
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4~ 6
1 spool on the undersurface 64 so that there is one of them on
each side of each hole 51 for the screws 50. The surface
roughness on the contact surfaces amounts to about 3/100 mm to
5/100 mm, i.e., these regions contain knurling in the material
in the form of peaks 148 (FIG. 4) of approximately this height.
The shape of the contact surfaces 146 is arbitrary; however, it
should be the same for all of them. The remaining surface area
o~ the undersurfaces 64 and 68 is either finely or coarsely
ground so that a surface roughness of less than 3/100 mm
results. Fine grinding, polishing or finishing is not
necessary. In placing the contact surfaces 146, care should be
taken that they not be located in the area o~ the projected
surface of the valve spools 78 and 80 on the undersurfaces 64
and 68.
When assembling the valve housing assembly 18, the
respective confronting surfaces of the bracket 32, the baseplate
34 and the upper and lower valve housings 36 and 38 are placed
together, during which step the sealing rings 144 are to be
placed in the recesses 142 between the baseplate 34 and the
lower valve housing and between the upper and lower valve
housings 36 and 38, as described above. Next, the screws 50 are
inserted through the holes 51 and screwed into the threaded
holes 48 until the entire valve housing assembly 18 is fixed in
place and prestressed. To achieve sufficient strength in the
valve housing assembly 18 for operation, the screws 50 are
tightened, possibly using a torque wrench so that the peaks of
material 148 on the contact surfaces 146 are pressed flat and
thus produce a sufficient tension in the screws 50 and in the
valve housing assembly 18 due to their deformation resistance
and in this way the valve housing assembly 18 is given
sufficient strength. The required screw tension is thus
achieved before the opposed sets of upper and lower surfaces 60
and 64, and 66 and 68 come into contact in the areas not
roughened. Since the material peaks 148 are higher than any
irregularities in the surfaces 60, 64, 66 and 68 and sufficient
strength has already been achieved for the valve housing
assembly 18 before these come into contact, no deformation
occurs in the valve housings 36 and 38, and particularly in the
central portions 70 and 72, which could lead to strains in the
area of the valve spools 78 and 80 and the axial bores 74 and 76
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64~
1 receiving them. This freedom from stress in the region o~ the
valve spools 78 and 80 ensures that they can slide freely in the
axial bores 74 and 76. Depending on the shape and the material
of the peaks 148, their deformation may be either elastic or
plastic.
FIGS. 3 and 4 illustrate how the joint between the upper and
lower surfaces 60 and 64 looks in the area of the sealing ring
144 and in the area of the contact surfaces 146.
Here, FIG. 3 shows that the sealing ring 144 contacts both
the lower surface 64 and also the upper surface 60, while these
are still at a slight distance apart. However, the sealing ring
144 still performs its sealing Eunction. In FIG. 4, on the
other hand, the upper surface 60 and the lower surface ~4 are in
contact at the peaks 148.
The specification of the permissible roughness of 3/100 to
5/lQ0 mm is not generally valid, but is matched to this example
since the surfaces at the interfaces of the baseplate 34 and
valve housing 36 and of the valve housings 36 and 38 must be
relatively flat in order to ensure a good fit for the cap 86 and
2~ good functioning of the adjusting device. In other
applications, the surface roughness may be greater or smaller;
however, it must always be greater than the largest irregularity
in the opposing surface.
Other applications arise whenever at least two parts must be
joined at a surface without any intermediate shim. An example
is the construction of a control plate with electric or
hydraulic control elements on a frame where no warping can be
allowed in the control plate to prevent switching errors. Such
a surface treatment would also be appropriate for highly precise
bearings, as for turbines. Another example of an application
occurs in the design of supports for ceramics, glass insulators
or shears of the same material.
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