U.S. patent application number 10/622334 was filed with the patent office on 2005-08-11 for high pressure two-stage reciprocating positive displacement compressor unit.
Invention is credited to Lucchi, Fabio.
Application Number | 20050175469 10/622334 |
Document ID | / |
Family ID | 34814942 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050175469 |
Kind Code |
A1 |
Lucchi, Fabio |
August 11, 2005 |
High pressure two-stage reciprocating positive displacement
compressor unit
Abstract
A reciprocating positive displacement compressor unit comprises
a central body, a motor having a shaft which rotates about an axis
of rotation, two cylinders, two pistons, each of which moves with
alternating motion in a respective cylinder to compress the air
contained in it, a first, axial fan for generating an air flow for
cooling the compressor unit and a second, radial fan for
circulating air inside the central body, the first, axial and
second, radial fans both being driven by the shaft.
Inventors: |
Lucchi, Fabio; (Sasso
Marconi (Bologna), IT) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Family ID: |
34814942 |
Appl. No.: |
10/622334 |
Filed: |
July 18, 2003 |
Current U.S.
Class: |
417/234 |
Current CPC
Class: |
F04B 25/005 20130101;
F04B 39/066 20130101 |
Class at
Publication: |
417/234 |
International
Class: |
F04B 053/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2003 |
IT |
BO2003A000097 |
Claims
What is claimed is:
1. A two-stage reciprocating positive displacement compressor unit
for compressing air to pressures between approximately 23 and
approximately 30 bar comprising a central body, a motor for driving
the compressor unit, connected to the central body and having a
shaft rotating about an axis of rotation, two cylinders connected
to the central body and having respective axes, two pistons, each
inside one of the two cylinders and moving with alternate motion in
the cylinder, for compressing the air, driven by the rotary shaft,
cooling means comprising at least one first rotary ventilation part
driven by the rotary shaft, for generating a cooling air flow,
wherein the cylinders are opposite one another, the shaft axis of
rotation and the axes of the cylinders substantially lie in the
same plane.
2. The compressor unit according to claim 1, wherein the cooling
means comprise a conveyor element for conveying onto the opposite
cylinders the air flow generated by the first rotary ventilation
part.
3. The compressor unit according to claim 2, wherein the conveyor
element is shaped in such a way that it conveys the air flow onto
the motor at a tangent.
4. The compressor unit according to claim 1, wherein the cooling
means comprise a second rotary ventilation part driven by the
rotary shaft, the second rotary ventilation part being located
inside the central body.
5. The compressor unit according to claim 4, wherein the central
body has at least one opening for air exchange with the outside,
the opening being located close to the second rotary ventilation
part.
6. The compressor unit according to claim 4, wherein the first and
second rotary ventilation parts are respectively connected to the
rotary shaft at its opposite ends, on opposite sides of the
motor.
7. The compressor unit according to claim 1, wherein the cooling
means comprise an intermediate cooling part for cooling the
compressed air as it passes from the first to the second cylinder,
the intermediate cooling part comprising at least one tubular pipe
for the passage of the air, extending in a curved trajectory.
8. The compressor unit according to claim 7, wherein for at least
one section of the curved trajectory the tubular pipe comprises two
tubular portions through which the compressed air passes in
parallel.
9. The compressor unit according to claim 8, wherein the two
tubular portions of the pipe are substantially positioned alongside
one another.
10. The compressor unit according to claim 7, wherein the conveyor
element is shaped in such a way that it conveys the cooling air
flow onto the intermediate cooling part.
11. The compressor unit according to claim 1, comprising guide
shoes keyed to the pistons and inserted between the pistons and the
cylinders, the shoes being made of a material with low friction
coefficient.
12. The compressor unit according to claim 11, wherein the guide
shoes are made of polytetrafluoroethylene.
13. The compressor unit according to claim 1, wherein the first
rotary part comprises an axial fan with an external ring connecting
the individual blades, the external ring constituting a flywheel
mass for the rotary shaft.
14. The compressor unit according to claim 1, in which the
cylinders respectively form a first and a second air compression
stage, wherein the ratio between the cylinder capacities of the
first and the second stage is between 5.37 and 5.40.
15. A portable air compressor, comprising a compressor unit
according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a reciprocating positive
displacement air compressor unit.
[0002] In particular, the present invention relates to a high
pressure compressor unit which can be used to supply air to
pneumatic tools.
[0003] Pneumatic tools are used in a lot of technical work due to
their practicality and strength. For example, such work may include
the application of rivets to sheets metal, nails in wood,
tightening and unscrewing the screws which secure the wheels on
motor vehicles.
[0004] Above all in the professional field, increasing levels of
performance are required of such types of tools.
[0005] Obviously, improved performance normally corresponds to an
increase in the overall dimensions of the tools and the compressor
units which power them.
[0006] In recent years, to avoid such an unwanted increase in tool
dimensions, the direct consequence of which is a loss of tool
practicality, the production of high pressure compressors began.
The forces required to perform the above-mentioned work being the
same, these compressors, developing air pressure values close to 30
bar, allow a considerable reduction in the dimensions and weight of
the tools which until now were normally used with air operating
pressures varying between 10 and 15 bar.
[0007] The use of high pressure compressed air, a term which in the
present text refers to the above-mentioned pressure values close to
30 bar, has brought a series of important problems both to the use
and construction of the compressor units.
[0008] In particular, the high pressure compressors currently made
have many disadvantages, most of which are linked to the difficulty
of achieving efficient cooling of the various parts of the
compressor. Reaching high air pressures for lengthy periods such as
those normally required during professional use of the compressor
results in considerable heating of the compressor components and of
the air itself, with an evident reduction in the device's overall
performance.
[0009] Another disadvantage of the known high pressure compressors
is their complexity and the dimensions and weight of their
mechanical components. Such complexity means that production costs
are high, constituting another disadvantage of known
compressors.
SUMMARY OF THE INVENTION
[0010] The aim of the present invention is to overcome the
above-mentioned disadvantages by providing a high pressure
compressor unit with efficient cooling, which is functional, simple
to produce and practical to use.
[0011] The technical features of the present invention, in
accordance with the above-mentioned aims, are clearly indicated in
the claims herein, in particular claim 1 and, preferably, by any of
the claims which are directly or indirectly dependent on claim
1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Moreover, the advantages of the invention are more clearly
indicated in the detailed description which follows, with reference
to the accompanying drawings which illustrate a preferred
non-restricting embodiment of it and in which:
[0013] FIG. 1 is a perspective top view with some parts cut away
for the sake of clarity, of a preferred embodiment of the
compressor unit made according to the present invention;
[0014] FIG. 2 is a schematic plan view with some parts in
cross-section, of the compressor unit illustrated in FIG. 1;
[0015] FIG. 3 is a schematic side elevation of a portable
compressor fitted with a compressor unit illustrated in the
previous figures;
[0016] FIG. 4 is a schematic front view of the compressor unit
illustrated in FIG. 1;
[0017] FIG. 5 is a schematic perspective top view, of a detail of
the compressor unit made according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] As illustrated in FIGS. 1 and 2, the numeral 1 denotes a
positive displacement compressor unit for compressing air at high
pressure, designed for integration, for example, in a portable
compressor of the type illustrated in FIG. 3 and labeled 2.
[0019] The compressor unit 1 is of the two-stage reciprocating
type.
[0020] In this text the term high pressure refers to air pressures
between approximately 23 and approximately 30 bar, that it to say,
pressures significantly higher than those normally supplied by most
compressors available on the market.
[0021] As illustrated in FIGS. 1 and 2, the compressor unit 1
comprises a central body 3 which has a substantially cylindrical
shape, from the sides of which there extend a first and a second
cylinder, labeled 4 and 5 respectively.
[0022] The central body 3 is connected, at its first end 3a to an
electric motor 6 which has a shaft 7 rotating about an axis of
rotation A. The shaft 7 is supported by two bearings of the known
type and, therefore, not described in further detail.
[0023] A circular removable lid 8 is fixed to the second end 3b of
the central body 3, opposite the first end 3a.
[0024] The first and second cylinders 4, 5 are opposite one another
and have respective axes B and C which are parallel with one
another.
[0025] The axes B, C of the cylinders 4, 5 and the axis of rotation
A of the shaft 7 substantially lie in the same plane, labeled P in
FIG. 4.
[0026] The first cylinder 4, which is larger than the second
cylinder 5 and has a bigger cylinder capacity, provides a first
stage of air compression for the unit 1. The second cylinder 5
provides a second stage of air compression.
[0027] Inside each cylinder 4, 5 there are, respectively, a first
and a second piston 9 and 10 which slide along the axes B, C.
[0028] The rotary shaft 7 is connected to the first and the second
pistons 9, 10 by a first and a second connecting rod, respectively
11 and 12.
[0029] At a respective small end, 11a, 12a, each connecting rod 11,
12, is rotatably connected to the respective piston 9, 10 by a pin
13. Around each piston 9, 10, in suitable hollows made in its
cylindrical side surface, two shoes 14 are keyed, which guide the
alternate motion of the piston 9, 10 in the cylinder 4, 5.
Therefore, the guide shoes 14 are inserted between the piston 9, 10
and the relative cylinder 4, 5.
[0030] The shoes 14 are advantageously made of
polytetrafluoroethylene, a material with a low friction
coefficient.
[0031] As illustrated in FIG. 2, on each of the pistons 9, 10,
close to the crown, there is at least one compression ring 15, of
the known type and therefore, not described in further detail.
[0032] At a first end 7a connected to the central body 3, the shaft
7 has a counterweight 16 to balance the rotation.
[0033] As illustrated in FIG. 2, at the first end 7a, two
cylindrical elements 17, 18 are attached to the shaft 7, the
elements mounted off-center on the shaft 7 so that, when roller
bearings 19 of the known type are inserted between them, they form
cranks for the connecting rods 11 and 12.
[0034] The cylindrical elements 17, 18 are positioned and attached
to one another and on the rotary shaft 7 by two pegs 20 and more
fastening parts of the known type and not illustrated.
[0035] At a second end 7b of the shaft 7 longitudinally opposite
the first end 7a and outside the motor 6, a first, axial fan 21 is
fitted on the shaft 7, this fan forming a first rotary ventilation
part 22 for the unit 1.
[0036] The first, axial fan 21 has a plurality of blades, of the
known type and not illustrated, and an external ring 23 which
connects the individual blades, the ring 23 constituting a flywheel
mass for the rotary shaft 7 to which the fan 21 is connected.
[0037] A second, radial fan 24 which forms a second rotary
ventilation part 25 for the unit 1 is attached on the cylindrical
element 17 relative to the first connecting rod 11 and not adjacent
to the rotary shaft 7, the fan being attached coaxially to the
shaft 7.
[0038] As illustrated in FIG. 1, on a cylindrical side surface 26
of the central body 3, at the second, radial fan 24, there is a
plurality of openings 27 for the exchange of air with the
outside.
[0039] In particular with reference to FIGS. 1 and 2, the
compressor unit 1 comprises a conveyor 28 of a flow 29 of cooling
air generated by the first, axial fan 21 which forms the first
rotary ventilation part 22.
[0040] The conveyor 28 comprises a laminar structure, extends
longitudinally along the axis A and has a first air inlet hole 30
and a second outlet hole 31. The first hole 30, is close to the
first, axial fan 21 and the second outlet hole 31 gives onto the
cylinders 4, 5.
[0041] As it extends, the conveyor 28 surrounds the electric motor
6 and the latter is struck at a tangent by the cooling air flow 29
conveyed by the conveyor 28.
[0042] As illustrated in FIGS. 1 and 4, the conveyor 28 has a
substantially octagonal cross-section close to the first, axial fan
21 and, along its longitudinal length, from its two opposite side
faces there extend side portions 32, 33, each designed to direct
the cooling air flow 29 onto a cylinder 4, 5.
[0043] The conveyor 28 is rigidly attached to the motor 6 and to
the central body 3 by a plurality of fastening elements 34, of
which one is illustrated in FIG. 1.
[0044] As illustrated in FIG. 5, the compressor unit 1 comprises an
intermediate cooling part 35 for cooling the compressed air exiting
the first cylinder 4, before it enters the second cylinder 5 which
forms the second stage.
[0045] The intermediate cooling part 35 comprises a tubular 36 pipe
for the passage of the compressed air. The pipe extends along a
curved trajectory T and close to the central body 3 and the
electric motor 6, outside them.
[0046] For a stretch of the curved trajectory T, the tubular pipe
36 comprises two tubular portions 37, 38 through which the
compressed air exiting the first cylinder 4 runs in parallel.
[0047] The two tubular portions 37, 38 into which the pipe 36 is
divided advantageously allow an increase in the heat exchange
surface area of the pipe 36, improving the cooling of the
compressed air.
[0048] The intermediate cooling part 35 is at least partially
inserted between the motor 6 and the conveyor 28.
[0049] The first and second ventilation parts 22, 25, the conveyor
28 and the intermediate cooling part 35 together form cooling means
39 for the compressor unit 1.
[0050] In practice, during a normal compressor 2 operating cycle,
for example, to supply compressed air to one or more pneumatic
tools which are not illustrated, the compressor unit 1 compresses
the air in its cylinders 4, 5, driven by the electric motor 6.
[0051] By means of its rotary shaft 7, the electric motor 6 not
only drives the alternate motion of the pistons 9, 10, but at the
same time drives the rotation of the first rotary ventilation part
22 and the second rotary ventilation part 25.
[0052] The first rotary part 22, consisting of the first, axial fan
21, generates the above-mentioned cooling air flow 29, the flow 29
being channeled into the conveyor 28, and heading towards the
central body 3 of the unit 1. On this path, the air flow 29 strikes
the electric motor 6 at a tangent, carrying heat away from it.
Moreover, since the electric motor 6 has radial fins, the heat
exchange between the motor 6 and the outside is further increased
by the speed at which the air flow 29 travels thanks to the first,
axial fan 21.
[0053] The cooling air flow 29 is also directed, by each of the
side portions 32, 33, onto a respective cylinder 4, 5.
[0054] As described above with reference to the motor 6, the air
flow 29 strikes each of the two cylinders 4, 5 carrying heat away
from them.
[0055] The cylinders 4, 5 also have cooling fins, of the known
type, designed to increase the surface area for heat exchange with
the outside and, therefore, the extent and efficiency of the heat
exchange.
[0056] Advantageously, the cylinders 4, 5, being opposite one
another, allow optimization of the cooling action exerted on them
by the air flow 29, achieving improved ventilation.
[0057] Moreover, the cooling air flow 29 strikes the intermediate
cooling part 35, located and extending close to the electric motor
6, inserted between the latter and the air flow 29 conveyor 28.
[0058] The air flow 29, striking the tubular pipe 36 of the
intermediate cooling part 35, carries heat away from it and cools
the partially compressed air exiting the first cylinder 4 before it
enters the second cylinder 5 where the second stage of compression
takes place.
[0059] This intermediate cooling of the compressed air optimizes
the compression cycle and its efficiency is increased by the
presence of the two tubular portions 37, 38 into which the pipe 36
is divided, the portions 37, 38 advantageously increasing the pipe
36 heat exchange surface area.
[0060] The second rotary ventilation part 25, consisting of the
second, radial fan 24, circulates air in the central body 3, with
relative exchange with the outside through the openings 27 made in
the cylindrical side surface 26 of the central body 3.
[0061] Advantageously, to optimize compression unit 1 compression,
it has been proved that the optimum ratio between the respective
cylinder capacities of the first cylinder 4 and the second cylinder
5, that is to say, the cylinder capacity ratio between the first
and the second stage, is between 5.37 and 5.40.
[0062] The present invention is suitable for evident industrial
applications, it can also be subject to modifications and
variations without thereby departing from the scope of the
inventive concept. Moreover, all the details of the invention may
be substituted by technically equivalent elements.
* * * * *