U.S. patent application number 11/813602 was filed with the patent office on 2008-06-12 for driving rod for the piston of a reciprocating compressor.
This patent application is currently assigned to WHIRLPOOL S.A.. Invention is credited to Egidio Berwanger, Alberto Bruno Feldmann, Dietmar Erich Bernhard Lilie, Rinaldo Puff.
Application Number | 20080134833 11/813602 |
Document ID | / |
Family ID | 36777584 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080134833 |
Kind Code |
A1 |
Lilie; Dietmar Erich Bernhard ;
et al. |
June 12, 2008 |
Driving Rod For The Piston Of A Reciprocating Compressor
Abstract
A driving rod for the piston of a reciprocating compressor of
the type that comprises: a cylinder block defining a compression
chamber; a piston reciprocating within the compression chamber; a
driving means to apply reciprocating forces to the piston; and a
driving rod disposed between the piston and the driving means and
comprising a number, greater than 1, of rods disposed side by side
along the axis of the driving rod and each presenting a
cross-section that is dimensioned and configured to impart to the
driving rod, jointly with the other rods, a required axial rigidity
and a flexibility, in at least one direction transversal to the
axis of the driving rod, sufficient to absorb, at least
substantially, the forces exerted on the piston by the driving rod
and by the driving means.
Inventors: |
Lilie; Dietmar Erich Bernhard;
(Joinville, BR) ; Berwanger; Egidio;
(Joinville-SC, BR) ; Puff; Rinaldo; (Joinville-SC,
BR) ; Feldmann; Alberto Bruno; (Joinville-SC,
BR) |
Correspondence
Address: |
DARBY & DARBY P.C.
P.O. BOX 770, Church Street Station
New York
NY
10008-0770
US
|
Assignee: |
WHIRLPOOL S.A.
Sao Paulo - SP
BR
|
Family ID: |
36777584 |
Appl. No.: |
11/813602 |
Filed: |
February 1, 2006 |
PCT Filed: |
February 1, 2006 |
PCT NO: |
PCT/BR06/00011 |
371 Date: |
July 27, 2007 |
Current U.S.
Class: |
74/581 |
Current CPC
Class: |
F04B 35/045 20130101;
Y10T 74/2144 20150115; F04B 39/0022 20130101 |
Class at
Publication: |
74/581 |
International
Class: |
F04B 53/14 20060101
F04B053/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2005 |
BR |
PI0500338-5 |
Claims
1. A driving rod for the piston of a reciprocating compressor of
the type that comprises: a cylinder block defining, therewithin, a
compression chamber; a piston axially reciprocating within the
compression chamber according to the axis of the latter; a driving
means mounted in the cylinder block to apply reciprocating forces
to the piston; and a driving rod coupled to the piston and to the
driving means, wherein the driving rod comprises a bundle of "n"
rods disposed side by side along the axis of the driving rod, each
rod presenting a cross-section that is dimensioned and configured
to impart to the driving rod, jointly with the other rods an axial
rigidity sufficient to transmit the reciprocating forces to be
applied to the piston, as well as a flexibility, in at least one
direction transversal to the axis of the driving rod, which is
sufficient to absorb, at least substantially, the forces exerted on
the piston, in said transversal direction, by the driving rod and
by the driving means in the region of the compression chamber.
2. The driving rod as set forth in clam 1, wherein each one of the
rods present a cross-section area corresponding to 1/n the
cross-section area needed to impart to the driving rod the
sufficient axial rigidity, the cross-section of the rods being
dimensioned and configured so that the sum of the moments of
inertia of the rods, in said transversal direction is a fraction of
the moment of inertia, in said transversal direction, of a
single-piece rod having a cross-section area corresponding to the
sum of the cross-section areas of the rod.
3. The driving rod as set forth in claim 2, wherein the sum of the
moments of inertia of the rods corresponds to a fraction "n" of the
moment of inertia of a single-piece driving rod with a
cross-section area corresponding to the sum of the cross-section
areas of the rods.
4. The driving rod as set forth in claim 2, wherein the sum of the
moments of inertia of the rods corresponds to a fraction "n2" of
the moment of inertia of a single-piece driving rod with a
cross-section area corresponding to the sum of the cross-section
areas of rods.
5. The driving rod as set forth in claim 2, wherein the rods are
symmetrically disposed around the displacement axis of the piston
and laterally seated to each other.
6. The driving rod as set forth in claim 5, wherein the rods are
rectilinear and parallel to each other.
7. The driving rod as set forth in claim 5, wherein the rods are
disposed in a helical arrangement.
8. The driving rod as set forth in claim 5, wherein the rods
present a circular cross-section with equal flexibility in any
transversal direction.
9. The driving rod as set forth in claim 5, wherein the rods are
rectilinear, parallel and laterally seated to each other, each rod
having a rectangular cross-section with a dimension corresponding
to a dimension (L) of the rectangular cross-section of a
single-piece driving rod, and with the other dimension (h)
corresponding to the fraction "n" of the other dimension (H) of the
cross-section of said single-piece driving rod, the cross-section
of the latter corresponding to the sum of the cross-section areas
of the "n" rods of the driving rod with multiple rods.
10. The driving rod as set forth in claim 2, wherein the rods are
jointly and medianly surrounded by at least one sleeve occupying
part of the longitudinal extension of the driving rod.
11. The driving, rod as set forth in claim 10, wherein the sleeve
is defined by an elastic ring pressing the rods against each
other.
12. The driving rod as set forth in claim 10, wherein the sleeve is
defined by a helical spring tightly mounted around the rods of the
driving rod.
13. The driving rod as set forth in claim 10, wherein the sleeve is
defined by a tube extension mounted with a small clearance around
the rods of the driving rod.
14. The driving rod as set forth in claim 2, wherein the rods
present opposite ends defining the ends of the driving rod, said
rods having each of the opposite ends jointly affixed to a terminal
block.
15. The driving rod as set forth in claim 14, wherein each terminal
block comprises a tubular body incorporating an enlarged end head
turned to the rods and presenting, internally, a housing axially
defined through the enlarged end head and through at least part of
the extension of the tubular body.
16. The driving rod as set forth in claim 15, wherein the tubular
body is externally threaded, the enlarged end header being in the
form of a hexagonal nut.
17. The driving rod as set forth in claim 14, wherein the opposite
ends of the rods are laterally curved, defining an anchorage
deformation, each terminal block being rolled over one of the
opposite ends of the rods.
18. The driving rod as set forth in claim 17, in wherein each
terminal block comprises an elongated body incorporating an
enlarged end head turned to the rods.
19. The driving rod as set forth in claim 18, wherein the elongated
body is externally threaded, the enlarged end head being in the
form of a hexagonal nut.
20. The driving rod as set forth in claim 14, wherein the terminal
blocks are each formed by a pair of plates to be affixed to each
other, sandwiching a respective end of the rods.
21. The driving rod as set forth in claim 14, wherein the terminal
blocks are defined by eyes of a driving rod in the form of a
connecting rod of a reciprocating compressor.
Description
FIELD OF THE INVENTION
[0001] The present invention refers to a driving rod to be applied
to a reciprocating compressor with an electric motor of the rotary
or linear type, said driving rod being constructed to operatively
couple a driving means to a piston to be reciprocated in the
interior of a compression chamber of the compressor, according to
the axis of said chamber.
PRIOR ART
[0002] The reciprocating compressors that are driven by a rotary or
linear electric motor generally comprise a cylinder block defining,
internally, a compression chamber inside which axially reciprocates
a piston coupled to a driving means mounted to the cylinder block
and operatively associated with the electric motor of the
compressor.
[0003] The piston is coupled to the driving means so as to allow
forces to be transferred therebetween and to make the piston move
inside the compression chamber according to an axial direction
coinciding with the axis of said compression chamber in order to
minimize the transversal reaction forces of the cylinder block
against the piston inside the compression chamber. As known, the
transversal reaction forces of the cylinder block against the
piston can provoke excessive friction between the piston and the
cylinder block, leading to an increase of energy consumption,
consequently reducing the efficiency of the compressor, and to an
accelerated wear of the components submitted to high friction
levels, reducing the useful life of the compressor.
[0004] A known reciprocating compressor with a linear electric
motor, as illustrated in FIG. 1 of the appended drawings, comprises
a cylinder block 10 defining, internally, a compression chamber 11
presenting an axis 12 and with a piston 20 axially reciprocating
therewithin. The compression chamber 11 has an end that is
generally closed by a valve plate 13 and by a cylinder head 14, the
valve plate 13 being provided with a suction valve 13a and a
discharge valve 13b of adequate construction to control the
admission and discharge of gas in relation to the compression
chamber 11 upon the movement of the piston 20.
[0005] In the known construction illustrated in FIG. 1, the piston
20 is operatively coupled to a driving means DM, which in the case
of a compressor with a linear electric motor, comprises an actuator
30 in the form of a tubular structure, concentric and external to
the compression chamber 11 and carrying a magnetic element 31 to be
operatively impelled, with the actuator 30, upon the energization
of a linear electric motor 40 mounted to the cylinder block 10
around the compression chamber 11. In this example, the driving
means further comprises a set of springs 60 mounted between the
cylinder block 10 and the piston 20.
[0006] To the piston 20 is directly or indirectly coupled an end of
a driving rod 50 whose opposite end is coupled to the springs 60,
helical springs for example, which are mounted in such a way as to
exert opposite axial forces on the piston 20 upon its axial
reciprocating movement in the interior of the compression chamber
11 provoked by the driving means DM comprising the actuator 30 and
the springs 60. The piston 20, the actuator 30 and the springs 60
form the resonant assembly of the compressor with a linear
motor.
[0007] These compressors are designed and constructed so that the
axis of the axial reciprocating movement of the piston 20 coincides
with the axes of both the piston 20 and the compression chamber 11,
aiming at minimizing or even suppressing the transversal reaction
forces between the piston 20 and the cylinder block 10. However, in
use, said axes can become misaligned and thus undesirable
transversal reaction forces may occur between the piston 20 and the
cylinder block 10 by reason of some constructive characteristics
inherent to the compressors, such as the geometrical errors in the
construction of the helical springs and the transversal rigidity
thereof when they are axially and elastically deformed.
[0008] Besides the aspects above, one should consider the fact that
misalignments commonly occur in the construction and assembly of
mechanical components, as perfection is not usually reached in
terms of dimensions and forms of the different components of a
mechanical device.
[0009] In the construction illustrated in FIG. 1, the driving rod
50 has the form of a generally tubular and transversally rigid
axial rod, whereby the piston-actuator assembly behaves as a single
body onto which are applied magnetic axial forces of the linear
motor 40 which do not produce, over the piston 20, transversal
components capable of causing excessive friction between said
piston 20 and the cylinder block 10.
[0010] However, the springs 60 exert over the piston-actuator
assembly, not only the axial forces resulting from the compression
thereof during the movement of the piston 20, but also transversal
forces whose intensity varies as a function of the errors of
construction and assembly of the springs 60. Such undesirable
transversal forces, produced by the operational deformation of the
springs, tend to misalign the piston 20 in relation to the axis of
the compression chamber 11, giving rise to transversal reaction
forces of the cylinder block 10, as well as a consequent higher
friction between the latter and the piston 20 axially reciprocating
within the compression chamber 11.
[0011] U.S. Pat. No. 5,525,845, from Sumpower Inc., describes a
constructive solution for the problem cited above, according to
which the driving rod, which can be mounted in different manners
between the piston and the driving means, is constructed so as to
present a required axial rigidity and also a transversal
flexibility sufficient to prevent all the transversal forces acting
on the piston, including the force exerted by the driving rod
itself, from surpassing the centralizing transversal forces applied
to the piston by a pneumatic bearing provided between the latter
and the cylinder block.
[0012] This prior solution uses a single-piece driving rod
dimensioned to present the necessary axial rigidity and a
transversal flexibility in a degree compatible with the
centralizing transversal forces produced on the piston by the
pneumatic bearing. Said prior art solution do not permit an
adequate flexibility in the dimensioning of the driving rod in
relation to compressors in which the axial force to be transmitted
or supported by the driving rod requires a cross-section area for
the latter which hinders, in the length available for the
single-piece driving rod, the latter from presenting the desired
transversal flexibility. The use of multiple rods is suggested
(FIG. 8) only in a spaced-apart relationship, each rod being
dimensioned to present the desired characteristics of axial
rigidity and transversal flexibility. This is a complex
construction, requiring the provision of the pneumatic bearing to
maintain the piston adequately centralized in the compression
chamber.
[0013] It should be further noted that the provision of multiple
rods disposed spaced apart and symmetrical in relation to the axis
of the compression chamber, as suggested in FIG. 8 of U.S. Pat. No.
5,525,845, does not eliminate completely the deficiencies already
discussed in relation to the single-piece driving rod. The proposed
prior arrangement provides a plurality of rods spaced from each
other, connecting the set of flat springs of a linear motor
compressor with the structure that supports the cylinder block.
These multiple rods can be dimensioned to provide, jointly, the
necessary rigidity and the desired degree of flexibility in the
transversal direction. However, due to the fact of being spaced
apart, said prior art multiple rods do not absorb transversal
forces produced by angular misalignments of the axis of the driving
means in relation to the axis of the compression chamber. Such
misalignments are not absorbed by the spaced-apart rods, since the
latter would have to be axially deformed, partially by expansion
and partially by construction. On the other hand, the required
axial rigidity of the rods prevents them from being dimensioned to
bend, reducing their length upon the occurrence of said angular
misalignments.
[0014] As illustrated in FIG. 2 of the appended drawings, the
reciprocating compressors with a connecting rod-crankshaft
mechanism driven by a rotary motor also present problems related to
geometrical and assembly errors. Such compressors also comprise a
cylinder block 10 defining, internally, a compression chamber 11
with a reciprocating piston 20 axially moving therewithin. The
compression chamber 11 presents an axis 12 and an end closed by a
valve plate 33 provided with a suction valve 13a and a discharge
valve 13b, and a cylinder head 14.
[0015] In the compressor of the type illustrated in FIG. 2, the
piston 20 is driven by a driving means DM, in the form of a
crankshaft 35, rotatively supported in the cylinder block and
mounted to a rotary motor (not illustrated), the crankshaft having
an end receiving the larger eye of a driving rod 50 in the form of
a connecting rod, whose smaller eye is rotatively supported on the
known diametrical articulating pin 21 inside the piston 20.
[0016] In the reciprocating compressors with a connecting
rod-crankshaft mechanism, geometrical and assembly errors, as
exaggeratedly illustrated in FIG. 2, can lead to the transmission
of reaction forces FR transversal to the axis 12 of the compression
chamber 11, a situation in which the piston 20 tends to work
misaligned with said axis 12. These reaction forces FR, acting
mainly in the direction of the articulating pin 21 of the piston
20, tend to produce undesirable levels of friction between the
piston 20 and the cylinder block 10, increasing the consumption of
energy in the operation of the compressor as well as the wear of
the mutually frictional parts, reducing the reliability and the
useful life of the machine.
[0017] Also in this type of compressor, the solution taught by the
prior art is to dimension the driving rod 50 with a cross-section
which, in the length defined in the compressor project, leads to
the necessary axial rigidity of the driving rod, so that the latter
can withstand the transmission of forces between the driving means
DM (crankshaft) and the piston 20, but which however gives to the
driving rod 50, in the form of a connecting rod, a flexibility in a
transversal direction which minimizes the transmission of moment to
the piston 20.
[0018] While being of low cost and easy to execute, said
construction, as already mentioned in relation to the driving rod
of the linear motor compressors, makes the dimensioning of the
cross-section a problematic task due to the length limitations of
the driving rod and to the degree of transversal flexibility
required to reduce the transmission of moments to the piston 20 to
desirable levels.
SUMMARY OF THE INVENTION
[0019] Due to the dimensioning limitations of the cross-section of
the driving rods of the reciprocating compressors with a linear or
rotary motor, it is the object of the present invention to provide
a driving rod presenting a construction that allows obtaining a
flexibility, in at least one transversal direction, as well as an
axial rigidity which can comply with the requirements of the
compressor project regardless of the length defined for the driving
rod.
[0020] The driving rod proposed by the present invention offers a
simple solution that is easy to implement in the construction of
reciprocating compressors, particularly those of the hermetic type
used is refrigeration systems of household electric appliances in
which the piston is designed to be axially displaced in a
reciprocating movement inside a compression chamber, without being
submitted to transversal reaction forces of the cylinder block
caused by the acceptable geometrical or assembly errors of the
component parts involved, but which are sufficiently relevant to
cause friction that abbreviates the useful life of the
compressor.
[0021] In order to attain the object cited above, the present
driving rod comprises a bundle of "n" rods arranged side by side
along the axis of the driving rod, each rod presenting a
cross-section that is dimensioned and configured to impart to the
driving rod, jointly with the other rods, an axial rigidity
sufficient to transmit the reciprocating forces between the driving
means and the piston, and a flexibility, in at least one
transversal direction to the axis of the driving rod, sufficient to
absorb, at least substantially, the forces applied to the piston,
in said transversal direction, by both the driving rod and the
driving means in the region of the compression chamber.
[0022] According to the solution proposed by the invention, the
number and the cross-section of the rods that form the driving rod
can be defined to impart to the latter optimized axial rigidity and
transversal flexibility so that the reciprocating movement of the
piston inside the compression chamber of the cylinder block occurs
with little or no friction that abbreviates the useful life of the
compressor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be described below, with reference being
made to the appended drawing, given by way of example of ways of
carrying out the invention and in which:
[0024] FIG. 1 is a schematic and simplified longitudinal sectional
view of the cylinder block and the resonant assembly of a
reciprocating compressor driven by a linear motor and in which the
driving rod is constructed according to the prior art;
[0025] FIG. 2 is a schematic and simplified longitudinal sectional
view of the cylinder block of a reciprocating compressor driven by
a rotary motor, by a crankshaft and by a driving rod in the form of
a connecting rod constructed according to the prior art, with the
piston being exaggeratedly misaligned in the interior of the
compression chamber;
[0026] FIG. 3 is a schematic and simplified longitudinal sectional
view of the cylinder block and the resonant assembly of a
reciprocating compressor driven by a linear motor and presenting a
driving rod constructed according to the present invention;
[0027] FIG. 4 is a perspective view of driving rod formed by a
plurality of parallel rectilinear rods, with a circular
cross-section and laterally seated to each other;
[0028] FIG. 5 is a similar view to that of FIG. 4, but illustrating
the rods disposed in a helical arrangement;
[0029] FIG. 6 is a rather schematic perspective view of a median
portion of a driving rod formed by a plurality of rods surrounded
by a sleeve in the form of an elastic ring;
[0030] FIG. 7 is a perspective view of the driving rod illustrated
in FIG. 4, with the rods being surrounded by a sleeve in the form
of a helical spring;
[0031] FIG. 8 is a view similar to that of FIG. 7, but with the
sleeve defined by a tube extension mounted around the rods of the
driving rod;
[0032] FIG. 9 is a perspective view of a driving rod with the
opposite end of its rods being jointly affixed to respective
terminal blocks;
[0033] FIG. 10 is a longitudinal sectional view of a terminal block
inside which are mounted the respective ends of the rods of a
partially illustrated driving rod;
[0034] FIG. 11 is an exploded perspective view of a driving rod
formed by multiple rods, with two end terminal blocks;
[0035] FIG. 12 is a longitudinal sectional view of the terminal
block illustrated in FIG. 11 and inside which are secured the
respective ends of the rods of the partially illustrated driving
rod;
[0036] FIG. 13 is a perspective exploded view of a terminal block
and the respective end of a driving rod formed by multiple
rods;
[0037] FIG. 14 is a perspective view of a driving rod formed by a
plurality of rods with a rectangular cross-section, with opposite
ends being affixed to eyes to be respectively mounted to a piston
and to a crankshaft of the compressor; and
[0038] FIG. 15 is a cross-sectional view of the driving rod
illustrated in the previous figure.
DETAILED DESCRIPTION OF THE INVENTION
[0039] As already mentioned, the construction of the driving rod of
the present invention is designed to be applied to reciprocating
compressors driven by a linear motor or by a rotary motor.
[0040] FIG. 3 illustrates, basically, the same elements that
constitute a reciprocating compressor with a linear motor,
contained in FIG. 1 and identified by the same reference numbers,
constructive differences existing only in relation to the
construction and assembly of the driving rod 50.
[0041] According to FIG. 3, the driving means DM is defined by an
actuator 30 and by a pair of springs 60, the actuator 30 comprising
a basic structure 30a, transversal to the axis 12 of the
compression chamber 11 and incorporating an internal tubular
projection 30b, rigidly secured to the piston 20, and an external
tubular projection 30c that carries the magnetic element 31, the
driving rod 50 being constructed so as to have an end secured to
the piston 20 and an opposite end secured to a support 70 to which
are mounted the adjacent ends of two springs 60, which in the
illustrated construction have a helical form concentric to the axis
12 of the compression chamber 11, the opposite ends of the two
springs 60 being mounted to the cylinder block 10, so that the
springs 60 can exert, over the support 70, opposite axial forces to
be transmitted to the piston 20 by the driving rod 50 disposed
according the axis 12 of the compression chamber 11.
[0042] The support 70 can be constructed in different manners, but
bearing in mind the necessity of its axial reciprocating movement,
in conjunction with the piston 20 and with the adjacent ends of the
springs 60, being effected with no interference of the driving
means 30. In the illustrated exemplary construction, the support 70
comprises a pair of shoes 71 disposed in planes that are parallel
to each other, orthogonal to the axis 12 of the compression chamber
11 and located on opposite sides of the basic structure 30a of the
actuator 30, said shoes 71 being axially interconnected by spacers
72 disposed through respective windows 33 provided in the basic
structure 30a of the actuator 30.
[0043] The exemplary construction illustrated in FIG. 3 makes the
transversal forces produced by the springs 60, when the latter are
elastically and axially deformed, to have the tendency to be
transferred to the piston 20 through the driving rod 50.
[0044] According to the invention, in order to absorb the expected
transversal forces produced by the springs 60, the driving rod 50
comprises a bundle "n" of rods 51 disposed side by side along the
displacement axis of the piston 20, each rod 51 presenting a
cross-section that is dimensioned and configured to impart to the
driving rod 50, jointly with the other rods 51, an axial rigidity
that is sufficient to transmit the axial forces to be applied to
the piston 20 by the springs 60 upon movement of the actuator 30,
as well as a flexibility, in at least one direction transversal to
the axis of the driving rod 50, which is sufficient to absorb, at
least substantially, the forces exerted over the piston 20, in said
transversal direction, by the driving rod 50 and by the driving
means DM in the region of the compression chamber 11. The
construction of the driving rod 50 in the form of a bundle of rods
51 in an adequate material, usually steel, allows each rod 51 to be
dimensioned with a cross-section area that corresponds to 1/n of a
cross-section area necessary to give to the driving rod 50, in the
length determined in project, an axial rigidity sufficient to
withstand the required transmission of axial forces between the
piston 20 and the driving means DM, which in the construction
illustrated in FIGS. 3-13, comprises the actuator 30 and the
springs 60.
[0045] Besides the characteristics above, the cross-section of the
rods 51 should be dimensioned and configured so that the sum of the
moments of inertia of the rods 51, in the determined transversal
direction, is an integer fraction of the moment of inertia, of said
transversal direction, of a single piece driving rod having a
cross-section area corresponding to the sum of the cross-section
areas of the rods 51.
[0046] In the constructions illustrated in FIGS. 4-13, in which the
rods 51 present the same circular cross-section, the transversal
flexibility of the driving rod 50 is equally achieved in any
direction transversal to the axis of said driving rod 50.
[0047] In the case of rods 51 with the same circular cross-section,
the sum of the moments of inertia of the rods 51, in the axial
direction, corresponds to a fraction "n" of the moment of inertia,
in the same axial direction, of a single-piece driving rod 50 with
its cross-section area corresponding to the sum of the
cross-section areas of the "n" rods 51, as explained below,
considering: [0048] A1 as being the circular cross-section area of
a single-piece driving rod; [0049] A2 as being the circular
cross-section area of each of the rods 51 of a driving rod formed
by a bundle of "n" rods 51; [0050] K1 e K2 as being the transversal
rigidity of the single-piece driving rod and of each rod 51,
respectively; [0051] K2 res. as being the resultant transversal
rigidity of the bundle "n" of rods 51; [0052] R1 e R2 as being the
radiuses of the single-piece driving rod and of the driving rod
defined by multiple rods 51, respectively; and [0053] I as being
the moment of inertia of each rod 51 in the transversal direction.
[0054] Thus:
[0054] A 2 = A 1 n .pi. R 2 2 = .pi. R 1 2 n R 2 = R 1 2 n ou R 2 =
R 1 n ##EQU00001##
[0055] Rigidity (K) proportional to the moment of inertia
( I ) = .pi. R 4 4 = .pi. D 4 64 ##EQU00002## K 1 proportional R 1
4 ##EQU00002.2## K 2 proportional R 2 4 = ( R 1 n ) 4 for a rod
##EQU00002.3## K 2 res . = n K 2 ##EQU00002.4## K 2 res . = n R 1 4
n 2 = R 1 4 n ##EQU00002.5##
Resulting
[0056] Thus, the transversal rigidity (K2 res.) of the bundle of
"n" rods 51 of circular section will correspond only to a fraction
"n" of the transversal rigidity (K1) of a single-piece driving rod,
with a cross-section area (A1) of the "n" rods 51 that form the
bundle that defines the driving rod.
[0057] As illustrated in FIGS. 4, 5, 7, 8, 11 and 13, the rods 51
are symmetrically disposed around the axis of the driving rod 50
and being usually rectilinear and parallel to each other. In the
construction illustrated in FIG. 5, the rods 51 are provided in a
helical arrangement, symmetrically disposed in relation to said
axis and around the length of the driving rod 50.
[0058] In case the project of the driving rods 50 leads to a larger
number "n" of thinner rods 51, i.e., with a reduced cross-section,
one or more rods 51 of the bundle of rods submitted to axial forces
may be deformed, provoking collapse of the driving rod. In these
cases, the rods 51 of the bundle can be jointly and medianly
surrounded by one or more sleeves 80, occupying part of the
longitudinal extension of the driving rod 50. In FIG. 6, the sleeve
80 takes the form of an elastic ring 81, in a metallic of
elastomeric material and dimensioned to press the rods
K 2 res . K 1 = R 1 4 n R 1 4 = 1 n ##EQU00003## K 2 res . = K 1 n
##EQU00003.2##
51, one against the others. In FIG. 7, the sleeve 80 is defined by
a helical spring 82, metallic or elastomeric and which is tightly
mounted around the bundle of rods 51 of the driving rod 50. In FIG.
8, the sleeve is defined by a tube extension 83, also made of any
adequate material to impart to the driving rod 50 a certain
transversal flexibility and which is mounted, with a small
clearance, around the bundle of rods 51.
[0059] As illustrated in FIGS. 9-14, the rods 51 present opposite
ends which define the ends of the driving rod 50 and which are
jointly secured in respective terminal blocks 90 which may present
different constructions in different metallic or non-metallic
materials;
[0060] In the case of the driving rods 50 applied to the
compressors driven by linear motors, the terminal blocks 90 are
configured to define the mounting means of the driving rod 50 in
the piston 20 and in the support 70 of the springs 60.
[0061] In the embodiment illustrated in FIGS. 9 and 10, each
terminal block 90 comprises a tubular body 91 that is usually
externally threaded and incorporates an enlarged end head 91a,
preferably in the form of a hexagonal end nut turned to the rods 51
and presenting, internally, a housing 91b axially defined through
the enlarged end head 91a and through at least part of the length
of the tubular body 91. This constructive arrangement, also
illustrated in FIG. 3, allows the terminal blocks 90 to have the
tubular body 91 thereof threaded in a corresponding threaded
orifice 23, 73 provided in the piston 20 and in the support 70,
respectively (FIG. 3). In the constructive arrangement illustrated
in FIG. 10, the ends of the bundle of rods 51 are preferably
tightly fitted and affixed by processes such as interference,
welding, gluing, mechanical riveting or any other adequate process
in the interior of the housing 91b of the respective tubular body
91.
[0062] In the embodiment of FIGS. 11 and 12, the terminal blocks 90
comprise an elongated body 92 externally threaded and incorporating
an enlarged end head 92a. However, in this construction, the ends
52 of the rods 51 are laterally curved, so that the terminal blocks
90 can be molded or injected in aluminum, plastic or any other
adequate material, directly on said ends 52, guaranteeing the
necessary mechanical anchorage between the driving rod 50 and the
terminal blocks 90. In the embodiment illustrated in FIG. 13, each
terminal block is formed by a pair of plates 93 to be secured to
each other, sandwiching a respective end of the rods 51. One or
both the plates 93 are internally provided with a recess 93a
configured to receive and fit a respective cross-section portion of
an extension of the adjacent end of the bundle of rods 51, said
extension being laterally curved or bent to facilitate locking the
end of the driving rod 50 in each terminal block 90.
[0063] The plates 93 of each pair are preferably provided with
orifices 93b for the passage of tightening screws (not
illustrated).
[0064] As already mentioned above and illustrated in FIGS. 14 and
15, the driving rod 50 can be designed in the form of a connecting
rod to operate in a reciprocating compressor of the type in which
the piston 20 is driven by a driving means DM in the form of a
crankshaft 35 (see FIG. 2). In this type of construction, the
terminal blocks 90 of the driving rod 50 are defined by eyes 94 to
be respectively rotatively supported around the articulating pin 21
of both the piston 20 and the crankshaft 35.
[0065] In the assemblies in which the actuator 30 is defined by a
crankshaft 35, the driving rod 50 comprises a number "n" of
rectilinear parallel rods 51 which are laterally seated in relation
to each other, each rod 51 having a rectangular cross-section with
a dimension L corresponding to a dimension "L" of the rectangular
cross-section of a single-piece driving rod and with the other
dimension "h" corresponding to the fraction "n" of the other
dimension "H" of the cross-section of said single-piece driving
rod. Thus, the same rectangular cross-section area of each rod 51
corresponds to the fraction "n" of the cross-section area of said
single-piece driving rod. The same ratio is applied to the relation
between the moment of inertia, in the axial direction of each rod
51 and the moment of inertia in the axial direction of the
single-piece driving rod. The sum of the cross-section areas of the
rods 51 corresponds to the cross-section area of said reference
single-piece driving rod. Thus, the driving rod 50 with "n" rods 51
has an axial rigidity equivalent to that obtained with the driving
rod formed by only one rod having a cross-section area
corresponding to the sum of the cross-section areas of the "n" rods
51 of the driving rod 50 with multiple rods.
[0066] In the construction of FIGS. 14 and 15, in which the rods 51
have a rectangular section, the moment of inertia of each rod 51 in
the transversal direction, parallel to the larger dimension "L",
corresponds to the moment of inertia, in the same direction, of a
single-piece driving rod with the same cross-section dimension "L".
It should be noted that the driving rod 50 is mounted so that said
transversal direction is orthogonal to the axis of the articulating
pin 21 of the piston 20. The articulation of the driving rod 50 to
the piston 20 allows the latter to stay in a coaxially aligned
position in the compression chamber 11, independently of the
relative angular positioning of the driving rod 50.
[0067] However, in the direction of the other dimension "h" of the
rectangular cross-section of the rods 51, which direction is
parallel and coplanar to the axis of the articulating pin 21 of the
piston 20, the sum of the moments of inertia of the rods 51 in said
other direction, orthogonal to the anterior direction, corresponds
to a fraction "n2" of the moment of inertia, in the same
transversal direction, of a single-piece driving rod, with the
corresponding cross-section dimension "L", in the same direction,
being equal to the sum of the dimensions "h" of the rods 51 in the
same direction, as exposed below, and further considering: [0068]
A1 as being the rectangular cross-section area of a single-piece
driving rod; [0069] A2 as being the rectangular cross-section area
of each one of the rods 51 of a driving rod formed by a bundle of
"n" rods 51; [0070] K1 e K2 as being the transversal rigidity of
the single-piece driving rod and of each rod 51 of the driving rod
with "n" rods 51, respectively; [0071] K2res. as being the
resultant rigidity of the bundle of "n" rods 51, in said
transversal direction; and [0072] I1 e I2 as being the moments of
inertia of the single-piece driving rod and of each rod 51, in said
transversal direction, respectively.
[0073] Thus:
A 2 = A 1 n = L H n e h = H n ##EQU00004##
[0074] Considering that the single-piece driving rod and the rods
51 of the driving rod 50 with multiple rods present the same
dimension "L" for the larger side of the rectangular
cross-section.
Rigidity ( K ) proportional I = L h 3 12 ##EQU00005## I 1 = L H 3
12 e I 2 = L h 3 12 = L 12 H 3 n 3 ##EQU00005.2## K 2 res . = n K 2
proportional n I 2 = n L 12 H 3 n 3 ##EQU00005.3## resulting
##EQU00005.4## K 2 res . K 1 = L 12 H 3 n 2 L 12 H 3 = 1 n 2
##EQU00005.5## K 2 res = K 1 n 2 ##EQU00005.6##
[0075] Thus, the transversal rigidity (K2res.) of the bundle of "n"
rods 51 with a rectangular section will correspond only to a
fraction "n2" of the transversal rigidity (K1) of a single-piece
driving rod presenting a cross-section area (A1) corresponding to
the sum of the cross-section areas (A2) of the "n" rods 51 that
form the bundle that defines the driving rod 50 of the invention,
as well as a cross-section dimension "H", in said direction,
corresponding to the sum of the corresponding cross-section
dimensions (h) of the rods 51 that form the driving rod 50.
[0076] It should be understood that the bundle of rods 51 of the
driving rod 50 illustrated in FIGS. 14 and 15 could be surrounded
by at least one sleeve 80 constructed according to any one of the
forms described in relation to FIGS. 6, 7 and 8.
* * * * *