U.S. patent application number 11/795093 was filed with the patent office on 2008-05-22 for axially driven piston-cylinder unit.
This patent application is currently assigned to BSH Bosch und Siemens Hausgerate GmbH. Invention is credited to Michael Muth, Georg Slotta.
Application Number | 20080118375 11/795093 |
Document ID | / |
Family ID | 35999600 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080118375 |
Kind Code |
A1 |
Muth; Michael ; et
al. |
May 22, 2008 |
Axially Driven Piston-Cylinder Unit
Abstract
An axially driven piston-cylinder unit comprising a cylinder, a
piston that can be moved back and forth in the axial direction of
the cylinder, between first and second piston positions, and a
drive element that can be moved back and forth in the axial
direction of the cylinder and is mechanically connected to the
piston by means of a piston rod. The piston rod is connected to the
piston or the drive element against the pretension of an elastic
device, in such a way that it can be moved axially in relation to
the piston or the drive element, such that when the piston head
comes into contact with the front wall of the cylinder borehole, on
the side of the cylinder head, the other movement of the drive
element is performed against the force of the elastic device, thus
braking the drive element.
Inventors: |
Muth; Michael; (Munchen,
DE) ; Slotta; Georg; (Neufahrn, DE) |
Correspondence
Address: |
BSH HOME APPLIANCES CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
100 BOSCH BOULEVARD
NEW BERN
NC
28562
US
|
Assignee: |
BSH Bosch und Siemens Hausgerate
GmbH
Munich
DE
|
Family ID: |
35999600 |
Appl. No.: |
11/795093 |
Filed: |
January 11, 2006 |
PCT Filed: |
January 11, 2006 |
PCT NO: |
PCT/EP06/00191 |
371 Date: |
July 10, 2007 |
Current U.S.
Class: |
417/363 ;
92/63 |
Current CPC
Class: |
F04B 39/0022 20130101;
F04B 35/04 20130101; F04B 35/045 20130101; F04B 39/0005 20130101;
F02G 1/0435 20130101 |
Class at
Publication: |
417/363 ;
92/63 |
International
Class: |
F04B 35/00 20060101
F04B035/00; F01B 7/00 20060101 F01B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2005 |
DE |
10 2005 001 470.4 |
Claims
1-7. (canceled)
8. An axially driven piston-cylinder unit comprising: a cylinder
having a cylinder bore with a top end face wall; a piston having a
piston head and being movable back and forth along an axial
direction of the cylinder between a first piston position, in which
a cylinder chamber enclosed between the piston and the cylinder is
largest, and a second piston position, in which the cylinder
chamber is smallest; a drive element being movable back and forth
along the axial direction of the cylinder; and a piston rod
mechanically coupling the drive element and the piston and
including a first end coupled to the piston and a second end
coupled to the drive element; and an elastic device coupling the
piston rod to at least one of the piston and the drive element with
the piston rod being movable axially relative to at least one of
the piston and the drive element respectively against a
pretensioning force of the elastic device such that, when the
piston moves into the second piston position at the top end face
wall, the piston head lands on the top end face wall of the
cylinder bore, then the further movement of the drive element is
made against the force of the elastic device, and thus the drive
element is braked.
9. The axially driven piston-cylinder unit as claimed in claim 8,
further comprising: an opening provided in the piston head and the
first end of the piston rod extending through the opening; the
piston rod being movable in relation to the piston in the axial
direction of the piston; the elastic device coupling the piston rod
and the piston; and the elastic device pretensioning the piston rod
from the piston towards the drive device, the piston rod including
a piston end-stop restricting the piston rod from coming out of the
opening.
10. The axially driven piston-cylinder unit as claimed in claim 9,
wherein the piston rod has a sealed passage into the piston opening
and a seal surrounding the piston rod.
11. The axially driven piston-cylinder unit as claimed in claim 9,
wherein the elastic device includes an annular spring disk.
12. The axially driven piston-cylinder unit as claimed in claim 8,
further comprising: an opening provided in the drive element and
the second end of the piston rod extends through the opening; the
piston rod being movable in relation to the drive element in the
axial direction of the drive element; the drive elastic device
coupling the piston rod and the drive element; and the drive
elastic device pretensioning the piston rod from the drive element
towards the piston, the piston rod including a drive end-stop
restricing the piston rod from coming out of the drive opening.
13. The axially driven piston-cylinder unit as claimed in claim 12,
wherein the elastic device includes a spring.
14. The axially driven piston-cylinder unit as claimed in claim 8,
wherein the piston is subject to the back and forth drive from a
movable drive element of a linear drive.
15. A compressor for producing a pressurized fluid comprising: at
least one axially driven piston-cylinder unit comprising: a
cylinder having a cylinder bore with a top end face wall; a piston
having a piston head and movable back and forth along an axial
direction of the cylinder between a first piston position, in which
a cylinder chamber enclosed between the piston and the cylinder is
largest, and a second piston position, in which the cylinder
chamber is smallest; a drive element being movable back and forth
along the axial direction of the cylinder; and a piston rod
mechanically coupling the drive element and the piston and
including a first end coupled to the piston and a second end
coupled to the drive element; and an elastic device coupling the
piston rod to at least one of the piston and the drive element with
the piston rod being movable axially relative to at least one of
the piston and the drive element respectively against a
pretensioning force of the elastic device such that, when the
piston moves into the second piston position at the top end face
wall, the piston head lands on the top end face wall of the
cylinder bore, then the further movement of the drive element is
made against the force of the elastic device, and thus the drive
element is braked.
16. The compressor as claimed in claim 15, further comprising: an
opening provided in the piston head and the first end of the piston
rod extending through the opening; the piston rod being movable in
relation to the piston in the axial direction of the piston; the
elastic device coupling the piston rod and the piston; and the
elastic device pretensioning the piston rod from the piston towards
the drive device, the piston rod including a piston end-stop
restricting the piston rod from coming out of the opening.
17. The compressor as claimed in claim 16, wherein the piston rod
has a sealed passage into the piston opening and a seal surrounding
the piston rod.
18. The compressor as claimed in claim 16, wherein the elastic
device includes an annular spring disk.
19. The compressor as claimed in claim 15, further comprising: an
opening provided in the drive element and the second end of the
piston rod extends through the opening; the piston rod being
movable in relation to the drive element in the axial direction of
the drive element; the drive elastic device coupling the piston rod
and the drive element; and the drive elastic device pretensioning
the piston rod from the drive element towards the piston, the
piston rod including a drive end-stop restricing the piston rod
from coming out of the drive opening.
20. The compressor as claimed in claim 19, wherein the elastic
device includes a spring.
21. The compressor as claimed in claim 15, wherein the piston is
subject to the back and forth drive from a movable drive element of
a linear drive.
Description
[0001] The invention relates to an axially-driven piston-cylinder
unit.
[0002] A piston-cylinder unit is known, for example, from U.S. Pat.
No. 5,525,845. In that, the piston rod is rigidly joined, both to
the axially-movable drive element of the linear drive and also to
the piston. During operation of the piston, which is driven by the
linear motor, a state can arise in which the axial oscillation of
the unit comprising the movable drive element, piston rod and
piston, experiences an increase in the amplitude of the
oscillations, so that the piston head of the piston can strike
against the top of the cylinder bore. This can result in damage to
the piston head or the top end face wall of the cylinder bore.
[0003] The object of the present invention is to design a generic
axially-driven piston-cylinder unit in such a way that the danger
of damage to the piston or the cylinder is reduced.
[0004] This object is achieved by the features specified in the
claims.
[0005] In normal operation of the piston-cylinder unit, the piston
rod is exactly located, both on the piston and on the drive
element, and no relative movement occurs between the drive element,
piston rod and piston. Only in the case of an overload, when the
force applied by the drive element exceeds the pretensioning force
of the elastic device does a relative movement occur between the
drive element and the piston rod or between the piston rod and the
piston.
[0006] By the decoupling of the mass of the drive element from the
piston, by means of the elastic device, the drive element is braked
by the elastic device if the piston lands on the top end face wall
of the cylinder bore during a movement of the piston into the
compression position. By this means, only the mass of the piston,
possibly including the mass of the piston rod but not including the
mass of the drive element, will strike the top end face wall of the
cylinder bore. The shock pulse which arises from this is
significantly less, compared to a rigid unit comprising the piston,
piston rod and drive element, so that the danger of damage to the
piston head or the top end face wall of the cylinder bore, is also
greatly reduced.
[0007] In an advantageous embodiment, the piston head is provided
with an opening through which the first end of the piston rod is
passed, such that the piston rod can move relative to the piston in
the axial direction of the piston, where the elastic device is
provided between the piston rod and the piston and whereby the
elastic device pretensions the piston rod from the piston towards
the driver device, where the piston rod is provided with an
end-stop which prevents the piston rod from coming out of the
opening. With this form of embodiment, the mass striking against
the top end face wall is yet further reduced, because the mass of
the piston rod is also decoupled from the piston.
[0008] It is particularly advantageous here if the passage of the
piston rod through the opening is sealed, for which purpose a seal
which encircles the piston rod is preferably provided. With this
form of embodiment, the compression efficiency is improved, because
the medium which is compressed by the piston cannot leak through
the annular gap around the piston rod.
[0009] Another advantageous form of embodiment is distinguished by
the fact that the drive element is provided with an opening through
which the second end of the piston rod is passed, that the piston
rod can move relative to the drive element, in the axial direction
of the drive element, that the elastic device is provided between
the piston rod and the drive element and that the elastic device
pre-tensions the piston rod from the drive element towards the
piston, where the piston rod is provided with an end-stop which
prevents the piston rod from coming out of the opening. With this
variant, the decoupling is effected by means of the elastic device
on the drive element side, so that a fixed joint can be provided
between the piston and the piston rod and it is not necessary to
provide an expensive seal on an opening in the piston head.
[0010] Preferably, the elastic device will have a spring or will be
made of a spring. Particularly preferred here is the provision of a
disk-spring arrangement or a spiral spring under compression or
tension.
[0011] A realization of the present invention is especially
effective in the case of a linear drive, for example a linear
motor, where the piston is subject to the back and forward drive of
a movable drive element of the linear drive.
[0012] A preferred application of the axially driven
piston-cylinder unit in accordance with the invention is its use in
a compressor for producing a pressurized fluid.
[0013] The invention is explained in more detail below using an
example, with reference to the drawing. In this
[0014] FIG. 1 shows a first form of embodiment of the invention
with a decoupling mechanism in the region of the piston, and
[0015] FIG. 2 shows an enlarged diagram of the passage of the
piston rod through the piston head, in the form of embodiment shown
in FIG. 1.
[0016] FIG. 1 shows a longitudinal section through a
piston-cylinder unit 1 with a cylinder 2 and a piston 3. The
cylinder 2 has a cylinder bore 10, in which the piston 3 is
accommodated so that it is freely guided and can move back and
forth along the direction of the longitudinal axis X of the
cylinder bore 10. The piston 3 has a gas bearing in the cylinder 2.
The top end face wall 12 of the cylinder bore 10, formed in a
cylinder head 23, the internal circumferential wall 14 of the
cylinder bore 10 and the piston head 16 delimit the cylinder
chamber 18.
[0017] An inlet manifold 22 with a valve 20, which is shown
schematically, opens out into the top end face wall 12 of the
cylinder bore 10. Also provided in the top end face wall 12 is an
exhaust manifold 24, which has a corresponding valve 26; this
exhaust manifold also opens out into the cylinder bore 10.
[0018] When the piston 3 makes a movement to the left in FIG. 1,
fluid is drawn into the cylinder space 18 through the inlet
manifold 22 and the inlet valve 20, and when the piston 3 makes a
movement to the right this fluid is expelled in a compressed state
through the exhaust valve 26 and the exhaust manifold 24. The
piston-cylinder unit 1 shown is part of a piston-drive machine in
which the expelled fluid is in gaseous form, such as is the case
for a compressor, for example. However, the invention can in
principle also be used with other piston-drive machines, such as
for example pumps.
[0019] The piston 3 is driven by a drive element 50, of a linear
drive 5 shown only schematically in the figure, which can execute
oscillatory longitudinal movements back and forth along an axis Y.
The movable drive element 50 is joined mechanically to the piston 3
by a piston rod 4. The piston rod 4 is inelastic in the axial
direction, and is thus capable of transmitting axial forces from
the drive element 50 to the piston 3.
[0020] The piston rod 4 is rigidly joined to the drive element 50.
The piston rod 4 is guided in the piston 3 so as to be movable in
the direction of the longitudinal axis X of the cylinder 2, or of
the longitudinal axis X' of the piston 3, which is coaxial with the
former. For this purpose, the piston rod 4 has a bearing in an
annular radial support 31 in the inside of the piston 3, where
there is a fixed joint between the piston 3 and the radially
outermost perimeter of the radial support 31, which has a central
opening through which the piston rod 4 is guided so that it is
movable.
[0021] A central through-hole 16' is provided in the piston head
16, (FIG. 2), through which the first end 4' of the piston rod 4,
at the piston end, is passed in such a way that it can move
axially. The face of the first end 4' of the piston rod 4, at the
piston end, is provided with a mushroom-shaped head 41, the domed
surface of which faces towards the cylinder head 23. On the side
which faces backwards towards the piston head 16, the
mushroom-shaped head 41 forms an annular landing area 41', the
outer diameter of which is greater than the diameter of the opening
16' in the piston head 16 so that the piston rod 4 is secured
against slipping out, towards the left in the figures.
[0022] The first end 4' of the piston rod 4, at the piston end, has
a reduced diameter compared with the rest of the piston rod 4.
Around this diameter can be arranged a seal 43 which seals the
first end section 4' of the piston rod 4, at the piston end,
against the inner circumference 16' of the piston head 16.
[0023] In the inside of the piston 3, in the region of the radial
position support 31, an elastic device 6 is provided in the form of
a domed annular disk-spring 44 with its outer perimeter fixed to
the piston 3 and having a central hole through which the piston rod
4 is passed, where the inner circumference of the annular
disk-spring 44 is fixed to the piston rod 4. In FIG. 1, the dome of
the disk-spring 44 is convex towards the left, that is towards the
drive element 50, so that the disk-spring 44 applies a pretension
to the piston rod 4, towards the left in FIG. 1, as a result of
which the annular surface 41' of the mushroom-shaped head 41 on the
first end 4' of the piston rod 4, at the piston end, is brought
into contact with the piston head 16 under the tension from the
spring 44.
[0024] If the piston 3 is moved to the right in the figure, that is
into the compression position in which the enclosed cylinder
chamber 18 is minimal, then the piston head 16 moves to land on the
top end face wall 12 of the cylinder head 23. Due to the mass
inertia of the movable drive element 50 and piston rod 4, the drive
element 50 and piston rod 4 continue their movement towards the
right, against the force of the disk-spring 44, and are braked by
the spring force of the disk-spring 44. When this happens, the
mushroom-shaped head 41 on the end 4' of the piston rod 4, at the
piston end, lifts off from the piston head 16 and moves into a
recess 25 which is formed in the cylinder head 23 in the region
where the exhaust manifold 24 opens out into the cylinder chamber
18. In this way, the impact when the piston head 16 meets the top
end face wall 12 is limited to the mass of the piston 3, while the
masses of the drive element 50 and the piston rod 4 are braked by
the spring 44, at a point in time after the piston head 16 hits the
top end face wall 12.
[0025] Alternatively, the piston rod 4 can also have a fixed joint
to the piston 3, with an axially movable bearing for the piston rod
4 being provided in the drive element 50, and the elastic element
formed by the spring 44 being provided between the piston rod 4 and
the drive element 50.
[0026] The invention is not restricted to the above exemplary
embodiment, which is only for the purpose of explaining in general
the core idea of the invention. Rather the device in accordance
with the invention can, within the scope of the protection, assume
other forms of embodiment than that described above. In this case
the device can, in particular, have characteristics which represent
a combination of the relevant individual characteristics of the
claims.
[0027] The sole purpose of reference marks in the claims, in the
description and in the drawings is to aid understanding of the
invention, and they should not restrict the scope of the
protection.
* * * * *