U.S. patent application number 10/469422 was filed with the patent office on 2004-04-08 for screw vacuum pump comprising additional flow bodies.
Invention is credited to Dreifert, Thomas, Giebmanns, Wolfgang.
Application Number | 20040067149 10/469422 |
Document ID | / |
Family ID | 7676962 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040067149 |
Kind Code |
A1 |
Giebmanns, Wolfgang ; et
al. |
April 8, 2004 |
Screw vacuum pump comprising additional flow bodies
Abstract
The invention relates to a screw vacuum pump comprising two
rotors (4, 5) which respectively have a hub (6, 7) and a thread (8,
9), additionally comprising a housing (2) wherein the rotors whose
threads engage with each other are accommodated in such a way that
they form, together with the housing, inlet cross sections (15, 16)
on the inlet side thereof and form outlet cross sections (29) on
the pressure side thereof causing gas to be conveyed from the inlet
side to the pressure side during rotation of the rotors (4, 5).
According to the invention, in order to improve inflow and outflow
conditions, the rotors (4, 5) are provided on the inlet side with
flow bodies (21, 22; 26, 27, 28; 36, 37) which are arranged
upstream from the inlet cross sections (15, 16) in such a way that
the inflow conditions of the gas to be transported to the inlet
cross sections (15, 16) are improved.
Inventors: |
Giebmanns, Wolfgang;
(Erftstadt, DE) ; Dreifert, Thomas; (Kerpen,
DE) |
Correspondence
Address: |
Fay Sharpe Fagan
Minnich & McKee
Seventh Floor
1100 Superior A venue
Cleveland
OH
44114-2579
US
|
Family ID: |
7676962 |
Appl. No.: |
10/469422 |
Filed: |
August 27, 2003 |
PCT Filed: |
January 9, 2002 |
PCT NO: |
PCT/EP02/00122 |
Current U.S.
Class: |
418/151 |
Current CPC
Class: |
F04C 18/084 20130101;
F04C 29/0021 20130101; F04C 29/122 20130101; F04C 18/16
20130101 |
Class at
Publication: |
418/151 |
International
Class: |
F01C 001/16 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2001 |
DE |
101 11 525.3 |
Claims
1. Screw vacuum pump comprising two rotors (4, 5) which
respectively have a hub (6, 7) and a thread (8, 9), additionally
comprising a housing (2) wherein the rotors whose threads engage
with each other are accommodated in such a way that they form,
together with the housing, inlet cross sections (15, 16) on the
inlet side thereof and form outlet cross sections (29) on the
pressure side thereof causing gas to be conveyed from the inlet
side to the pressure side during rotation of the rotors (4, 5),
wherein the rotors (4, 5) are provided on the inlet side with flow
bodies (21, 22; 26, 27, 28; 36, 37) which are arranged upstream
from the inlet cross sections (15, 16) in such a manner that the
conditions for the inflow of the gases to be conveyed to the inlet
cross sections (15, 16) are improved.
2. Pump according to claim 1, wherein in the instance of
multi-thread screws, at least one thread ridge is equipped with a
flow body.
3. Pump according to claim 1, wherein the flow body extends in the
instance of a single thread screw over 90.degree. to
180.degree..
4. Pump according to one of the claims 1, 2 or 3, wherein the flow
body (21, 22) substantially is an extension of the ridge (8, 9)
with reduced ridge width.
5. Pump according to one of the claims 1 to 4, wherein there is
located in the area of the respective inlet cross-sections at least
one further flow body independent of thread ridge (8, 9), said flow
body having the shape of the blade.
6. Pump according to claim 5, wherein the blades are curved such
that they extend on the pressure side approximately in the
direction of the thread ridges (8, 9) and are designed to be
steeper on the intake side.
7. Pump according to one of the above claims, wherein in the area
running behind the face side of the thread ridge (8, 9) there is
present a recess (23, 24).
8. Pump according to one of the above claims, wherein the rotor
outlet is equipped with corresponding flow bodies.
9. Pump according to one of the above claims, wherein the flow
body/bodies (21, 22; 26, 27, 28; 31, 32, 33; 34, 35; 36, 37) and
the corresponding hub section (6, 7) are fitted by way of a
separate component to the face side respectively the rear side of
the rotor (4, 5).
10. Pump according to one of the above claims, wherein the flow
bodies with respect to their design, arrangement and/or mass are so
designed that they substantially remove the imbalance of the
related rotor (4, 5)
11. Screw vacuum pump comprising two rotors (4, 5) which
respectively have a hub (6, 7) and a thread (8, 9), additionally
comprising a housing (2) wherein the rotors whose threads engage
with each other are accommodated in such a way that they form,
together with the housing, inlet cross sections (15, 16) on the
inlet side thereof and form outlet cross sections (29) on the
pressure side thereof causing gas to be conveyed from the inlet
side to the pressure side during rotation of the rotors (4, 5),
wherein the rotors (4, 5) are provided on the pressure side and/or
inlet side with balancing weights (21, 22; 26, 27, 28; 31, 32, 33;
34, 35; 36, 37) which are designed in such a manner that they
improve the conditions for the inflow (respectively outflow) of the
gases to be conveyed.
12. Pump according to claim 11 wherein the balancing weights
exhibit the shape of flow bodies in accordance with one of the
claims 1 to 10.
Description
[0001] The present invention relates to a screw vacuum pump having
the characteristics of patent claim 1. A pump of this kind is known
from the international patent application WO/00/12900.
[0002] In the instance of a screw pump, threads engaging into each
other establish sealed off volumes, which during the synchronised
rotation of the rotors are conveyed from the inlet to the outlet.
Inlet and outlet are commonly so designed that the thread ridges of
the rotors--generally single threads--commence, respectively
terminate, in a plane perpendicular to the rotor axes. The
effective inlet cross-section (respectively outlet cross-section)
of the active pumping elements for this reason corresponds in each
instance to the total of the surfaces which form the respective hub
of the rotors, the housing, respectively--depending on the position
of the rotor--the adjacent rotor, as well as the limits at the side
of respective the thread's ridge. In single threads, the inlet
cross-section extends in each instance over 180.degree..
[0003] Drawing FIGS. 1 and 2 depict a rotor inlet according to the
state-of-the-art in which the rotors are equipped with single
threads. In the drawing FIGS. 1 and 2, the only partially depicted
screw vacuum pump is designated as 1, its housing as 2, its inlet
as 3, the rotors as 4 and 5, the rotor hubs as 6 respectively 7,
their thread ridges as 8 respectively 9, and the rotor axes as 10
respectively 11. In drawing FIG. 2, a developed view of the rotor 5
is depicted.
[0004] The two thread ridges 8, 9 commence in a plane extending
perpendicularly with respect to the rotor axes 10, 11, said plane
being designated as 14 in both drawing figures. Thus there results
for each rotor an inlet cross-section 15 respectively 16, being
created by the involved components, which extends--in the instance
of single thread ridges 8, 9--over 180.degree..
[0005] It is the task of the present invention to improve the
conditions for the inflow and also the outflow in the instance of a
screw vacuum pump.
[0006] This task is solved through the present invention by the
characterising features of the patent claims.
[0007] Through the present invention an "inlet booster" is
implemented. The arrangement of flow bodies upstream of the inlet
cross-sections has the effect of improving the filling degree of
the volumes conveyed by the rotors from the inlet to the outlet, so
that a pump designed in accordance with the present invention will
have improved pumping properties, in particular an improved pumping
capacity. Also in the area of the rotor outlets likewise designed
flow bodies assigned to the outlet cross-sections can improve the
conditions of the outflow, such that the flow losses in the exhaust
system can be reduced. Aerodynamically, flow bodies arranged on the
delivery side are capable of reducing the flow velocities and the
residual swirl, and also the static pressure may be increased
additionally through a widening cross-section, so that in the
downstream exhaust system lower flow losses occur due to deflection
and friction. Since in the exhaust area the back pressure is in any
case continuously at 1 bar, the aerodynamic improvements may here
be also effective across the entire operating range of the screw
pump. Due to the aforementioned benefits, there finally also exists
the possibility of employing shorter rotors.
[0008] The present invention may be implemented independently of
the geometrical arrangement of the screw (single-thread or
multi-thread screws, constant or variable pitch, variable pitch
with areas of constant pitch, cylindrical, stepped or cone-shaped
rotors, single or double flow rotors, cantilevered rotors or rotors
with double sided bearings).
[0009] An advantageous further developed embodiment of the present
invention is such, that the thread ridge of the adjacent rotor in
each instance (second rotor) is equipped in the area which
interacts with the flow body or flow bodies of the first rotor,
with a recess.
[0010] Thus closing of the inlet cross-section of the first rotor
is delayed while simultaneously reliably filling the increased
inlet volume due to the recess. In this manner a pre-compression is
effected which improves efficiency of the pump and reduces its
power requirements.sup.2). 2) Translator's note: The German text
states "Leitungsbedarf" whereas "LeistungsbedarF" is more
appropriate. Thus the latter has been assumed for the
translation.
[0011] A further advantage of the present invention is such, that
the flow bodies may simultaneously be employed as masses for
balancing. Imbalances of the rotors which are unavoidable owing to
the design of the end areas of the threads, can be completely or at
least to a substantial extent removed through the flow bodies. Even
in the instance of the rotors being manufactured by casting, only
fine balancing will be required. With regard to rotor dynamics,
flow bodies on the outlet side offer the possibility of reducing
the initial imbalance.sup.3) of a screw rotor additionally in a
second plane by calculative/design means and to utilise these then
also as the second compensation plane during fine balancing, such
that the inner moments in the entire rotor may be minimised.
Translator's note: The German text states "U-runwucht" whereas
"U-runwucht" is more appropriate. Thus the latter has been assumed
for the translation.
[0012] The outlet contours may also be applied to all screw
geometries. Through the reduced cross-sectional areas in the thread
of the screw, only a small wall thickness remains in the instance
of threads in which the ridge width reduces at the pressure side of
the rotor, whereby said small wall thickness does not leave much
room for designing blade contours. Of course almost any outlet
contour may be added through an additional part, but post-forming
an additional thread by metal cutting, being viable in the instance
of a vacuum screw with variable pitch owing to the large pitch on
the inlet side, may be employed on the outlet side only in rare
cases. It might be conceivable, after providing corresponding slots
along the diameter of the hub, to produce through well controlled
bending of the remaining thin walled contour, the shape of the
blade, which by means of a solid material joint (through welding,
soldering or gluing) would then again have to be affixed to the
hub. It is more advantageous to manufacture this geometry directly
during the manufacture of the thread, so as to obtain a
cost-effective and operationally reliable contour which, in
addition, may be optimally adapted to rotor dynamic
requirements.
[0013] The integral manufacture of screw geometry and inlet and
outlet contours through metal cutting operations offers a further
benefit. Through facing, perpendicularly with respect to the rotor
axis, there result in the instance of a conventional screw rotor
sharp inlet and outlet edges at both ends, which frequently need to
be cut back in order to prevent the remaining thin materials from
being deformed or breaking off. In contrast to this in the instance
of integrally manufactured contours, a steady transition may be
attained, which simultaneously improves stiffening of the edges at
the ends.
[0014] Further advantages and details of the present invention
shall be explained with reference to the examples of embodiments
depicted in drawing FIGS. 3 to 8.
[0015] Depicted are in
[0016] drawing FIGS. 3, 4 and 8, solutions with one flow body in
each instance,
[0017] drawing FIGS. 5, 6 and 7, solutions with several flow bodies
in each instance.
[0018] In the example of an embodiment in accordance with drawing
FIGS. 3 and 4 (drawing FIG. 4 again depicts a developed view of the
rotor 5) the rotor hubs 6, 7 have been extended beyond the plane 14
of the inlet cross-sections 15, 16 by an amount equivalent to the
width of one or two thread ridges. Said rotor hubs serve the
purpose of supporting one each flow body 21, 22 each located above
the inlet cross-sections 15 respectively 16, also limiting the pump
chamber on the side of the hub. This is approximately an extension
of the thread ridges 8, 9 with reduced ridge width (approximately
1/3). In the instance--as depicted--of single threads, each flow
body extends over just under less than half the rotor circumference
and subsequently there is just over half the rotor circumference
available to the open partial area. Turned by 180.degree. with
respect to each other, each of the flow bodies engages in each
instance in a non-contact manner into the corresponding gap of the
adjacent rotor. The slope of the in each instance forerunning edges
of the flow bodies 21, 22 increases slightly in the direction of
the intake side. The area of the ends is rounded off. The gases
flowing into the still open volume which is to be conveyed, are
indicated in drawing FIG. 4 by arrows.
[0019] The areas of the face sides of the thread ridges 8, 9
running behind the flow body 21, 22, are equipped with the recesses
23 (rotor 4, not visible), 24. They delay sealing off of the pumped
volumes and will ensure simultaneously that these are completely
filled.
[0020] The flow body 21 respectively 22 in each instance, may be
manufactured with its hub section as a separate part, and may be
retrofitted to the cut off face surface of the screw. However,
especially advantageous is an integral manufacture in which the hub
section and the flow body are formed by milling, for example, and
specifically from the remaining material which has been left over
(depicted by dashed lines in drawing FIG. 4) in the production of
the screw profile (by milling, spinning, rolling, turning
etc.).
[0021] Drawing FIG. 5a depicts an embodiment corresponding to that
of drawing FIG. 4 with the difference, that the width and pitch of
the ridge 9 decrease in the direction of the pressure side. In an
embodiment of this kind, the pressure side may be designed in
accordance with drawing FIG. 5b. The hub 7 extends beyond the
outlet cross section 29 by about four times the width of the thread
ridge on the pressure side and supports a blade-like extension 25
of the thread 9. This extends with strongly increasing slope and
ridge width in the direction of the pressure side over
approximately 140.degree..
[0022] Drawing FIG. 6a depicts by way of a developed view, the
rotor inlet of a further example of an embodiment for the rotor 5.
The not depicted rotor 4 is designed accordingly. Ahead of the
inlet cross section 16 there are located independent flow bodies
26, 27, 28 being independent of the thread ridge 9. These are
supported at the hub 7 and exhibit approximately the shape of rotor
blades, their slope increases in the direction of the intake side,
specifically commencing approximately with the slope of thread
ridge 9.
[0023] The drawing FIGS. 6b and 6c depict two embodiments for the
rotor outlet, depending on whether the thread 9 has a constant
pitch and ridge width or a decreasing pitch and ridge width. On the
pressure side, the hub 7 is in each instance extended beyond the
outlet cross-section 29 and carries the blades 31, 32, 33
respectively 34, 35. Said blades are independent of thread 9 and
have a slope which increases in the direction of the pressure side.
In the embodiment in accordance with drawing FIG. 6b, the blades
are designed to be approximately mirror symmetrical with respect to
the blades 26, 27, 28. In the embodiment in accordance with drawing
FIG. 6c, the ridge width of the blades 34, 35 increases in the
direction of the pressure side. In these embodiments, the blades on
the inlet side and the outlet side with their hub sections consist
expediently of separately manufactured rings, which after having
been fitted to the face side, are components of the rotors 4, 5.
This solution allows to adapt the conditions for the inflowing
flow--and under certain conditions--also the conditions for the
outgoing flow in a simple manner, by exchanging the blade rings in
accordance with customers requirements.
[0024] The flow bodies 25 (drawing FIG. 5b) and 34 (drawing FIG.
6c) on the pressure side have a relatively large volume. Thus in
the outlet area of the pump a sufficient mass is available for
balancing the rotors.
[0025] In the embodiment in accordance with drawing FIG. 7a, two
flow bodies 36, 37 are provided. Flow body 36 is--substantially
like in the embodiment in accordance with drawing FIGS. 3, 4--an
extension of the thread ridge 8 but reduced in width (here
approximately 1/5). The base of the blade shaped flow body 37 is
located approximately at the centre of the inlet cross section 16.
In an embodiment with a thread 9 of constant ridge width and pitch,
the rotor outlet may be designed correspondingly (approximately a
mirror image).
[0026] Drawing FIG. 7b depicts the rotor outlet in an embodiment
with a thread 9, the pitch and ridge width of which decreases in
the direction of the pressure side. In the area of the extension of
the hub 7 beyond the outlet cross section 29, the pitch of the
thread increases strongly whereby the ridge width is further
reduced in the direction of the pressure side.
[0027] Finally, drawing FIG. 8 depicts by way of a perspective view
an embodiment which substantially corresponds to the embodiment in
accordance with drawing FIGS. 3, 4. The difference is, that the
hubs 6, 7 only extended in the area of the flow bodies 21, 22. They
extend in each instance only up to the inside edges of the
respective flow bodies 21, 22.
[0028] It is expedient to design the flow bodies such that, be it
with respect to their design, arrangement and/or mass, they
simultaneously remove the imbalance of the screw rotors 4, 5.
Beneficially, especially at the location where the arrangement of
aerodynamically effective flow bodies is expedient, it is required
also to add balancing masses. Great initial imbalances are thus
avoided, involved balancing processes can be dispensed with. For
this reason, the flow bodies may also be considered as balancing
weights, being so designed that they improve the conditions for the
inflow (respectively outflow) of the gases to be pumped, i.e. that
they have the shape of flow bodies.
* * * * *