U.S. patent application number 10/491770 was filed with the patent office on 2005-03-10 for oscillating-piston drive for a vacuum pump and an operating method for said drive.
Invention is credited to Bahnen, Rudolf, Hodapp, Josef.
Application Number | 20050053490 10/491770 |
Document ID | / |
Family ID | 7701745 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050053490 |
Kind Code |
A1 |
Bahnen, Rudolf ; et
al. |
March 10, 2005 |
Oscillating-piston drive for a vacuum pump and an operating method
for said drive
Abstract
An oscillating-piston drive for a vacuum pump (1) with a piston
(2), which presents has two piston sections (3,4) and an
intermediate zone provided with a drive magnet (11). Cylinder
sections (8, 9) slidingly receive the piston sections (3, 4). An
annular recess (12) is defined between the cylinder sections (8, 9)
at a central yoke (19). The recess provides space for movement of
the drive magnet (11). An electromagnetic drive which surrounds the
piston (2) includes yoke components (17, 18, 19) and coils (15, 16)
situated to the sides of said central yoke. Negative influences on
the delivery rate of the pump are reduced by a can (34) which
delimits the recess (12) peripherally or by controlling the current
supply to the coils, such that only one coil conducts current at a
time.
Inventors: |
Bahnen, Rudolf; (Roetgen,
DE) ; Hodapp, Josef; (Koln, DE) |
Correspondence
Address: |
Fay Sharpe Fagan
Minnich & McKee
Seventh Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Family ID: |
7701745 |
Appl. No.: |
10/491770 |
Filed: |
April 2, 2004 |
PCT Filed: |
September 28, 2002 |
PCT NO: |
PCT/EP02/10921 |
Current U.S.
Class: |
417/418 |
Current CPC
Class: |
F04B 2201/0201 20130101;
F04B 35/045 20130101; F04B 2203/0401 20130101 |
Class at
Publication: |
417/418 |
International
Class: |
F04B 017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2001 |
DE |
101 49 506.4 |
Claims
1. An oscillating piston drive for a vacuum pump comprising: a
piston having two piston sections and a central zone; a drive
magnet mounted in the central zone; cylinder sections in which the
piston sections are slidably received; an annular recess located
between the cylinder sections at the level of a central yoke said
recess receiving and forming space for movement for the drive
magnet; an electromagnetic drive with yoke components encompassing
the piston with coils located to the side of the central yoke; and
a can peripherally delimiting the recess.
2. The drive according to claim 1, wherein the can is constructed
of a material with good sliding properties.
3. The drive according to claim 1, wherein the can is constructed
of a ferromagnetic material.
4. The drive according to claim 3, further including: stator
permanent magnets which delimit the recess in an axial direction
and outside the central yoke zone, the can (34) extending into the
area of the stator permanent magnets.
5. The drive according to claim 4, wherein the stator permanent
magnets (13, 14) are magnetized such that they exert a repelling
force on the drive magnet.
6. The drive according to claim 3, wherein the wall thickness of
the can at least outside the central yoke zone is so selected, that
the drive magnet magnetizes the respective can section to the
saturation point when said magnet is located in the zones outside
the central yoke.
7. The drive according to claim 6, wherein the can has in the zone
of the central yoke a greater wall thickness.
8. The drive according to claim 1, wherein the drive magnet is a
rare earth magnet.
9. An operating method for an oscillating piston drive with the
characteristics of claim 1, wherein current flow through the coils
is controlled such that current passes through only one coil at a
time.
10. An operating method for an oscillating piston drive for a
vacuum pump including a piston with two piston sections and a
central zone equipped with a drive magnet, cylinder sections
associated to the piston sections, an annular recess defined
between the cylinder sections adjacent the central yoke, said
recess forming space for movement for the drive magnet, and an
electromagnetic drive with yoke components encompassing the piston
with coils located to the side of the central yoke, the method
comprising: supplying an alternating current to the coils with only
one current polarity being supplied to each of the coils.
11. The operating method according to claim 10, wherein the current
flows through the coils such that they alternately exert repelling
forces on the drive magnet.
12. The operating method according to claim 10 further including:
adjusting amplitudes of the current flows to each of the coils with
a thyristor regulator.
13. The operating method according to claim 12, further including:
adjusting current amplitude to the coils by means of a phase angle
regulator.
14. The operating method according to claim 13, wherein an input
signal for the phase angle regulator is one of: defined at a fixed
value for a given pump application, dependent on the mains voltage,
defined by a sensor for detecting a position of the piston, or
defined by a sensor for observing valve movement.
15. The operating method according to claim 13, wherein the current
amplitude is adjusted with thyristor regulators.
16. The oscillating piston drive according to claim 1, further
including: thyristor regulators for controlling current flow to the
coils.
17. The oscillating piston drive according to claim 1, further
including: a means for supplying an alternating current to the
coils with only one current polarity being supplied to each of the
coils.
18. The oscillating piston drive according to claim 17, wherein the
means for supplying alternating current to the coil includes: a
phase angle regulator and a means for supplying an input signal to
the phase angle regulator which input signal is one of: a fixed
value for a given pump application, dependent on a voltage of
supply means, defined by a sensor for detecting a position of the
piston, or defined by a sensor for observing valve movement.
Description
[0001] The invention relates to an oscillating-piston drive for a
vacuum pump with a piston, which presents two piston sections and
an intermediate zone provided with a drive magnet, cylinder
sections associated to said piston sections, an annular recess
arranged between the cylinder sections at a central yoke, said
recess forming the space for movement of said drive magnet and an
electromagnetic drive surrounding the piston, which comprises yoke
components and coils situated to the sides of said central yoke.
Moreover, the present invention relates to an operating method for
the drive.
[0002] Generally it is the aim of the here affected developers and
designers to improve the delivery rate or effect (pumping capacity,
compression) of a vacuum pump while simultaneously maintaining or
even reducing, if possible, the construction volume and/or
preferably even reducing energy consumption. This aim is equivalent
in that in the course of the further development, respectively
design of a pump of the affected type, measures which become
necessary must not be associated with impairments affecting the
delivery rate.
[0003] It is the task of the present invention to propose an
oscillating piston drive for a vacuum pump in which delivery rate
impairments are reduced.
[0004] This task is solved through the present invention through
the characterising features of the patent claims.
[0005] An oscillating piston drive of the aforementioned kind is
known from WO 00/63 556, drawing FIG. 8. It exhibits a number of
components (coils, pole components, cylinders etc.), adjacent with
respect to the space for movement of the drive magnet and which
have an influence on the delivery rate. There exists the risk that
the space for movement be linked by means of slots between the
components or current feedthroughs to the outer surroundings.
Through such slots, air enters into the space for movement and
increases the low pressure forming during operation of the pump
within the space for movement. Measures for sealing these slots
(for example, adhesive or sealant layers) may impair the efficiency
of the electromagnetic drive, since these will increase the
distance between the individual components.
[0006] By means of a first solution for the posed task, it is
proposed that a can delimits peripherally the outer recess. A pipe
section peripherally delimiting the space for movement of the drive
magnet reduces the number of slots opening out into the space for
movement so that the risk of unwanted pressure increases in this
volume is substantially removed. The wall thickness of the pipe may
be very small, below 1 mm, for example, so that impairments in the
efficiency of the electromagnetic drive are negligible.
[0007] Expedient materials for the can are those which offer good
sliding properties, like plastic, aluminium, stainless steel.sup.1)
or alike (not--or only weakly ferromagnetic).sup.2). .sup.1)
Translator's note: The German text states "Edelstahlt" here whereas
"Edelstahl" would be appropriate. Therefore the latter has been
assumed for the translation. .sup.2) Translator's note: In the
German text the right bracket is missing. It has been added to the
translation.
[0008] Alternatively the can may consist of a more strongly
ferromagnetic material, and its wall thickness selected at least in
the area of the sections outside the central yoke such that the
drive magnet magnetises the respective section to the saturation
point when it is located in the zones outside of the central yoke.
This embodiment of the can has the effect that it at least partly
becomes part of the drive. The in each instance saturated section
is practically no longer existent for the magnetic field of the
related coil. This has an effect equivalent to an enlargement of
the air gap for this coil and results in a reduction in the
inductance of specifically this coil. The current in a coil is
built up when the drive magnet is located in the area of this coil,
i.e. the corresponding can section is saturated. Lower inductance
means faster current build-up at a given voltage. With the magnetic
field of this current, now the drive magnet of this coil is
repelled towards the axially opposing coil. The saturation effect
of the drive magnet on the can disappears. But since the current
now has the required level, the increase in inductance is not
disturbing.
[0009] This operating principle requires that the magnetic field of
the drive magnet be stronger compared to that of the coil. If this
were not the case, then the field of the coil would practically
"overwrite" the field of the drive magnet in the can (the
directions of the fields oppose each other) thereby cancelling the
saturation immediately. In the instance of this drive, the
necessary forces may, however, only be implemented by sufficiently
strong rare earth magnets, for example. In the instance of these
magnets this requirement is always fulfilled.
[0010] From the above descriptions it is apparent that it is
expedient to control the current through the coils such that a
current is allowed to flow only through one coil at a time. In this
manner it is achieved that the current in one coil is built up
precisely when the drive magnet is located in the area of this
coil.
[0011] Controlling the drive by means of semiconductor switches
allows the avoidance of further losses. To explain this
improvement, the existence of a linear drive in accordance with
drawing FIG. 8 of WO 00/63 556 is again assumed. In the instance of
this linear drive, the magnetic field of one of the two coils will
only generate a force on the piston provided the corresponding
piston section is located in the area of the respective coil. The
other--current carrying--coil is ineffective during this time. When
commonly letting a current flow through both coils simultaneously
thus higher losses in the coils are created as would be necessary
for producing the forces. Moreover, letting a current flow
simultaneously through both coils implies that the drive
electronics must be capable of switching on and off both polarities
of the current. This not only increases the power loss but also the
complexity for the drive electronics.
[0012] In a second solution for the task of the present invention
it is proposed that only one current polarity be assigned to each
of the coils, i.e. the positive current polarity is assigned to one
coil and the negative current polarity to the other. For example,
the two polarities of the 50 Hertz mains AC can be "distributed" to
both coils.
[0013] This may be implemented with a simple thyristor regulator.
The current amplitude of each half-wave may be adjusted by means of
a simple, cost-effective phase angle regulator, as is known from
electric drilling machines, for example.
[0014] The input signal for the phase angle regulator may for
example be
[0015] defined at a fixed value for a pump application (pressure,
mains voltage, number of stages)
[0016] made to depend on the mains voltage,
[0017] defined by a sensor for detecting the position of the piston
or
[0018] defined by a sensor for observing the valve movement.
[0019] The frequency of the piston's stoke will in all cases result
from the frequency of the supplied alternating current.
[0020] The advantages of these measures are on the one hand that
losses in the coils are reduced, since the current is allowed to
flow only through one coil at a time. Also the implementation of
the control electronics is more simple, since it is no longer
required for the currents to flow simultaneously through both
coils.
[0021] Further advantages and details of the present invention
shall be explained with reference to the examples of embodiments
depicted in the drawing FIGS. 1 to 3.
[0022] Depicted is in
[0023] drawing FIG. 1, a sectional view through a piston vacuum
pump equipped with a drive in accordance with the present
invention,
[0024] drawing FIG. 2, a partial sectional view at the level of the
can and
[0025] drawing FIG. 3, a schematic representation of a pump in
accordance with the present invention with means for supplying the
drive coils with current.
[0026] The drawing figures each depict a piston vacuum pump 1 with
a piston 2. This exhibits piston sections 3 and 4, to the
unoccupied face sides of which each a cylindrical pump chamber 5,
respectively 6 is assigned. The piston 2 and the pump chambers 5, 6
are located in a housing 7 with cylinder sections 8, 9 for the
piston sections 3, 4. The materials for the sliding cylinder
surfaces and the corresponding piston surfaces are selected in a
basically known manner such that the pump may be operated dry, i.e.
without lubricant.
[0027] A linear drive is assigned to the piston 2. Said linear
drive comprises on the side of the piston a permanent magnet ring
11, encompassing the piston 2 at its central zone. The permanent
magnet ring 11 moves in the annular volume (recess 12) encompassing
the piston 2. On the stator side, further permanent magnet rings
13, 14 are assigned to the permanent magnet 12 on the side of the
piston, said further permanent rings axially delimiting the annular
recess 12. At the level of these permanent magnetic rings, also
cylinder sections 8, 9 terminate.
[0028] Moreover, the coils 15 and 16 are components of the linear
drive on the stator side. These are partly encompassed by yoke
components 17, 18 and jointly with these yoke components said coils
encompass the cylinder sections 8, respectively 9. Located between
the coils 15, 16 and the yoke components 17, 18 is an annular
center yoke 19, the inner surfaces of which face the annular
chamber 12. Currents are made to flow through coils 15, 16 such
that the magnetic field produced by the coils and guided by the
yoke components 17 to 19 interact with the magnetic fields of the
permanent magnet rings 11, 13 and 14 in the desired manner. The
piston 2 shall oscillate about its centre position such that during
this movement the face sides of the piston may fulfil their pumping
function.
[0029] For the purpose of fulfilling the desired pumping effect,
the compression chambers 5, 6 are each equipped with an inlet valve
and an outlet valve (only depicted in drawing FIG. 1). To each of
the inlet valves there is associated an inlet aperture 21,
respectively 22 which is each located between an outer inlet
chamber 23, respectively 24 and the corresponding pump chamber 5,
respectively 6. The inlet apertures 21, 22 are designed by way of
slot-like radially extending openings in the respective cylinder
wall 8, respectively 9. The piston sections 3 and 4 release the
respective inlet aperture when assuming one of their two dead
centres (each in the retracted position in the cylinder section).
The outlet valves 26, 27 are located at the respective face sides.
There closure components 28, 29 separate the respective compression
chamber 5, respectively 6 from an outlet chamber 31, 32 so long
until they are opened by the respective piston section 3,
respectively 4--at high pressure differences also by the generated
pressure. The closure components 28, 29 are designed by way of
flexible discs extending over the entire cross-section of the
cylinder sections 3, 4, said disks being centrally affixed at the
housing 7 and which are peripherally actuated by the produced
pressure or the face sides of the piston 2. To this end, the piston
face sides have been designed to have a concave contour. The face
sides of the components forming the cylinder sections 8, 9 have the
function of the valve seats.
[0030] In all, two compression stages are present. They may be
operated in series or in parallel. Details on this are not
presented.
[0031] In all drawing figures the can is designated as 34. It
encompasses the annular chamber, respectively the recess 12, and
extends into the area of the stator permanent magnet rings 13,
14.
[0032] Drawing FIG. 2 depicts that the can 34 exhibits two lateral
sections 35, 36 of relatively small wall thickness and a centre
section with a greater wall thickness. The wall thickness of the
lateral sections 35, 36 is below 1 mm, preferably 0.7 mm. At these
wall thicknesses, the desired saturation through the drive magnet
11 occurs, provided the drive magnet is located in the vicinity of
the sections 35, 36. The greater wall thickness in the centre zone
is only required when the can needs to offer a sufficient degree of
mechanical strength.
[0033] Drawing FIG. 3 depicts the vacuum pump 1 with its linear
drive only in a highly schematic manner. Additionally depicted is
an embodiment for the power supply in accordance with the present
invention for the coils 15, 16. Through the connection 41 an
alternating current, preferably the mains current at 50 Hz is
supplied to two thyristor regulators 42, 43, of which each is
connected to one coil 15, respectively 16. Regulator 42 allows the
passage only of the positive half-wave, regulator 43 allows the
passage of only the negative half-wave of the alternating current.
Passing of currents through the coils is thus no longer effected
simultaneously but alternatingly at only one of the two current
polarities. The current/time diagrams 44, 45, 46 presented in each
instance the area of the current feed and between the regulators
42, 43 and the coils 15, 16, render apparent the power supply in
accordance with the present invention.
[0034] Expediently the coils 15, 16 are switched on in the
respective supply circuit in such a manner that they effect
repelling forces on the drive magnet 11. Thus the piston will
oscillate about its central position at the frequency of the
supplied alternating current.
[0035] The permanent magnets 13, 14 are expediently magnetised such
that they will effect on the drive magnet a repelling action. This
solution offers the advantage that mechanical springs which move
the piston back to its central position can be omitted.
* * * * *