Note: Descriptions are shown in the official language in which they were submitted.
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"Reciprocating compressor for a cooling device"
*****
FIELD OF THE INVENTION
The present invention relates to a reciprocating compressor for a cooling
device.
KNOWN PREVIOUS ART
In particular, the present reciprocating compressor is used in those cooling
devices
comprising a closed circuit in which a determined flow rate of coolant
circulates and
that is provided with a main branch and at least one economizer and/or
secondary
branch. In such branches of the closed circuit two defined fractions of the
overall
flow rate of the coolant circulate, then exiting from the compressor. Such an
economizer, or secondary, branch is fluidically connected to a section of the
closed
circuit comprised between the condenser and the expansion valve, on the one
hand,
and to the cylinder of the reciprocating compressor for the re-injection, into
the
compressor itself, of the fraction of flow rate crossing the secondary branch,
on the
other hand. Still in a known way, along such a closed circuit a condenser, an
expansion valve, an evaporator and the reciprocating compressor itself are
fluidically
connected one to the other. Yet still in a known way, the fraction of coolant
circulating in the economizer, or secondary, branch, that can comprise an
additional
expansion valve and an heat exchanger or an additional evaporator, has a
pressure
value intermediate between the highest and the lowest of the circuit of the
cooling
device, i.e. between the pressure of the fluid to the condenser and that one
to the
evaporator being along the main branch.
In general, in compressors usually adopted in refrigeration devices, the exact
point of
the compressor in which the aforementioned fraction of flow rate coming from
the
secondary economizer branch is entered, can always be determined. For example,
in
a screw compressor, in which as it is known the pressure increases along the
compressor axis according to a known law, the exact point of injection of the
fraction
of flow rate coming from the secondary economizer branch can always be
located.
The same applies also for other types of compressors such as, for example,
screw or
scroll compressors, although the operating principle as well as the pressure
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distribution inside the compression chamber are different with respect to that
one of
the screw compressors, however also in the scroll compressor it can always be
known how great is the pressure in any point of the compression chamber.
In case of use of reciprocating compressors, i.e. provided with cylinder and
piston
reciprocatingly moving inside the cylinder, the pressure instead varies with
time and
is anytime substantially the same in the whole cylinder for every position of
the
piston during its inlet and compression stroke.
However, in order to allow using economizer, or secondary, branches in cooling
devices employing a reciprocating compressor, in document US2014/0170003 in
the
name of Emerson Climate Technologies Inc. the use of cylinders is described
that,
beside comprising a conventional suction duct located on the header, are also
provided with a side inlet port with circular section for the entrance of such
a fraction
of flow rate coming from the afore mentioned economizer branch at a defined
intermediate pressure. At the inlet port being in the compressor cylinder a
valve is
located whose opening and closing is synchronized with the compressor drive
shaft
through a complicated mechanism consisting of at least one cam and at least
one
respective follower. This allows the aforementioned fraction of flow rate of
coolant
coming from the secondary economizer branch to be entered only shortly before
a
pressure slightly smaller than the pressure of the afore mentioned fraction of
secondary flow rate is reached in the piston.
In order to avoid using complex synchronization systems, as those described in
US2014/0170003, other solutions have been studied. In particular, in document
WO-
A1-2007064321 in the name of Carrier Corporation, it is taught how to
implement on
the compressor cylinder an inlet port with circular section that is exposed by
the
piston in its inlet stroke and remains covered, still by the piston, during
the
compression stroke of the latter. Unfortunately, with respect to reciprocating
compressors having the same displacement, but free from side port, a
remarkable
reduction of the possible compressor work is obtained, since a part of the
piston
stroke is used to allow the inflow fraction of the flow rate of coolant coming
from the
economizer, or secondary, branch. In particular, in cases where such a
fraction of
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flow rate is considerable, up to 50% of the overall flow rate value, the use
of
compressors having the same displacement as those employed in cooling devices
free
of economizer, or secondary, branch, becomes highly difficult. In fact, in
such cases,
the inlet port for the flow rate of coolant has remarkable dimensions along
the axis of
the cylinder with the result that a compressor having a displacement greater
than
those normally used, and thus with an increase of overall costs, has to be
employed.
Therefore, object of the present invention is to realize a reciprocating
compressor
that can be used in cooling devices provided with at least one economizer, or
secondary, branch, but that - the performance being the same - has a
displacement
lower than the displacement at present employed in such cooling devices.
Further object of the invention is to realize a reciprocating compressor that,
in
addition to achieving the afore mentioned object, is highly simple to
implement, even
starting from know compressors free of side port.
SUMMARY OF THE INVENTION
These and other objects are achieved by the reciprocating compressor for
cooling
device provided with a closed circuit having a main branch, in which a first
flow rate
of circulating coolant enters in said compressor, and at least one first
economizer
branch, or secondary branch, in which a second flow rate of coolant circulates
under
a pressure different from the pressure of said first flow rate of coolant,
said
compressor being provided with at least one cylinder and at least one piston
reciprocatingly moving in said at least one cylinder, between a top dead
centre and a
bottom dead centre, and comprising at least one suction duct for the entrance
of said
first flow rate of coolant, and at least one port obtained in the wall of said
cylinder
for the entrance of said second flow rate of coolant, in such a way that said
piston
exposes at least in part said at least one first inlet port, at least during
its inlet stroke,
and covers said at least one port at least during its compression stroke,
characterized
in that said at least one first inlet port has a slit shape with the main
dimension
substantially transverse to the axis of said cylinder.
In practice, the presence of a first inlet port having the shape of a slit,
with the main
dimension, the length one, substantially transverse to the axis of the
cylinder, allows
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a remarkable amount of flow rate of coolant coming from an economizer, or
secondary, branch to enter the cylinder, without this concretely affecting the
dimensions of the displacement of the compressor itself. In fact, the slit
dimensions
are highly limited along the axial direction of the cylinder, thus in height,
whereas
they are remarkably larger transversely to the cylinder axis, thus in length.
As
mentioned, this allows a remarkable flow rate of coolant to flow in the
cylinder in the
same very short time equal to the piston stroke during the opening and
subsequent
closing of the side port.
It has to be observed that the term slit has to be intended as any notch, of
any shape,
made in the cylinder wall and having a dominant dimension (also named as main
dimension) with respect the other. In particular, in the present instance, the
main or
dominant or more relevant dimension is that one lying on a plane transverse to
the
axis of the compressor cylinder, thus not the slit dimension parallel to the
axis of the
compressor cylinder and defined as slit height.
According to the herein described embodiment, said at least one first port is
arranged
next to the bottom dead centre of said at least one piston and, preferably,
said at least
one first port has a lower side substantially flush with the bottom dead
centre of said
piston. Such a solution allows avoiding an excessive loss of compressor
displacement and compression work, simultaneously, in its inlet and
compression
stroke at the side port.
According to the invention, said at least one closed circuit of said cooling
device
further comprises at least an additional economizer branch, or secondary
branch, in
which an addition flow rate of said coolant is circulating, said compressor
further
comprising at least one second port obtained in the wall of said cylinder for
the
entrance of said additional flow rate of said coolant in said at least one
compressor,
wherein said at least one second port has a slit shape with the main dimension
substantially transverse to the axis of said cylinder and is arranged at a
distance from
said bottom dead centre greater than the distance at which said at least one
first port
is positioned, so that said piston exposes said at least one second inlet port
at least
during its inlet stroke, and covers said at least one port at least during its
compression
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stroke. Such a configuration is particularly suited in case the additional
flow rate s
coming from an additional economizer, or secondary, branch has a pressure
lower
than the pressure of said second flow rate coming from the economizer, or
secondary, branch, and entering the cylinder of the compressor through said at
least
one first port.
According to the embodiment herein described, said at least one first port and
said at
least one second port, both having a slit shape, are substantially or mainly
rectangular-shaped, i.e. the slit surface, that one facing the inner face of
the
compressor cylinder, has substantially the shape of a rectangle lying on the
inner
cylindrical surface of the compressor cylinder. Such a substantially
rectangular
shape, where the top or bottom side has dimensions greatly larger than those
of the
two height sides, i.e. along the axial direction of the compressor cylinder,
could also
have sides blent one to another, i.e. without sharp edges, falling however in
the
definition of surface having substantially a shape of rectangle lying on the
inner
surface of the cylinder.
Furthermore, the ratio between height and length dimensions, i.e. along the
main
direction, of said at least one first port and/or said at least one second
port is smaller
than 0.5, preferably 0.2. In fact, the Applicant tested that such dimensional
values are
those that allow obtaining the best performances. It has to be noted that the
slit length
has to be calculated along the arc of a circle of the cylinder along which the
same slit
extends, on a plane transverse to the cylinder axis and passing in the middle
of the
slit height.
In addition, the lower side of said at least one second port is flush with the
upper side
of said at least one first port.
According to a further embodiment, said at least one first inlet port and/or
said at
least one second inlet port comprises/comprise at least one functionally-
combined
non-return valve. Such non-return valves allow preventing the coolant entered
the
compressor through the first and the second port from being biased towards
them in
the opposite way, during the rising step of the piston, i.e. the coolant
compression
step.
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More specifically, such at least one non-return valve is of deformable reed
type and
is housed in the wall of said at least one cylinder. This makes the compressor
even
more compact, however avoiding the presence of complicated elements employed
for
synchronizing the opening or closing of the side ports.
BRIEF DESCRIPTION OF THE DRAWINGS
For illustration purposes only, and without limitation, several particular
embodiments
of the present invention will be now described referring to the accompanying
figures,
wherein:
figure 1 is a schematic view of a cooling device provided with a reciprocating
compressor according to the invention;
figure 2 is a P-h diagram of the refrigeration cycle relating to the
refrigeration device
of figure 1;
figures 3a-3d are schematic and sectional longitudinal views of the inside of
the
compressor cylinder during the inlet and compression steps;
figures 4a and 4b are respectively two longitudinal and transverse sectional
views of
the cylinder of the reciprocating compressor according to the invention, with
particular reference to the first and the second port obtained in the wall of
the
compressor cylinder;
figure 5 is a schematic view of another cooling device provided with a
reciprocating
compressor according to the invention;
figure 6 is a P-h diagram of the refrigeration cycle relating to the
refrigeration device
of figure 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
INVENTION
Referring particularly to such figures, with numeral 100 is denoted the
reciprocating
compressor according to the invention.
In figure 1 the scheme of a cooling device 200 provided with a reciprocating
compressor 100 according to the invention provided with a cylinder 110 and a
piston
111 reciprocatingly moving in the cylinder 110, between a top dead centre S
(see
figure 3d) and a bottom dead centre I (see figure 3c), is shown. In
particular, the
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refrigeration device 200 comprises a closed circuit C in which a certain flow
rate of
coolant is circulating. Such a closed circuit C comprises, in its turn, a main
branch
M, in which a first flow rate X of coolant is circulating and enters the
compressor
100 through a suction duct 109, a first secondary branch E and a second
secondary
branch E'. In such a first secondary branch E a second flow rate X1 of coolant
circulates, whereas in the additional secondary branch E' an additional flow
rate X2
of coolant circulates. The sum of the flow rates circulating in the main
branch M and
in the two secondary branches E and E' is the flow rate circulating in the
closed
circuit C and exiting from the reciprocating compressor 100.
According to the scheme of figure 1, the cooling device 200 further comprises
a
condenser 101, a first expansion valve 102 and a first evaporator 103. Both
the first
expansion valve 102 and the first evaporator 103 are located along the main
branch
M of the closed circuit C so that the flow rate X circulating in the same,
which is
given by the difference between the overall flow rate circulating in the
closed circuit
C and the flow rates X1 and X2 circulating in the two secondary branches E and
E',
directly enters the reciprocating compressor 100 through the suction duct 109
(see
figure 3a) being in the reciprocating compressor 100, above the cylinder 110.
The two secondary branches E and E' each comprise a second expansion valve
130,
130' and a respective second evaporator 140 and 140'; in practice, in each
secondary
branch E, E', all the values of the circulating flow rate and the pressure and
temperature will be different. In this type of configuration, in practice, the
cooling
device 200 is able to cool three different chambers connected to the
respective
evaporators 103, 140 and 140'. In particular, the second flow rate X1 and the
additional flow rate X2 respectively circulating along the secondary branch E
and the
additional secondary branch E' are at different temperatures and pressures. In
particular, the pressure of the flow rate X1 circulating along the secondary
branch E
is intermediate between the pressure of the fluid at the condenser 101 and the
pressure at the first evaporator 103, whereas the pressure of the additional
flow rate
X2 of coolant circulating in the additional secondary branch E' has an
intermediate
value between the value of the fluid of the first flow rate X and that of the
fluid of the
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second flow rate Xl.
Note that in figure 1 the thermodynamic states of the coolant circulating in
the closed
circuit C of the refrigeration device 200 are denoted in brackets, with
numbers from
1 to 8. Then in figure 2 the thermodynamic cycle made by the coolant in the
device
200 is shown, with the information of the thermodynamic condition of the fluid
in
the corresponding points of the closed circuit C. The references 9 and 10
shown in
the graph of figure 2 correspond to the thermodynamic state of the coolant in
the
compressor 100 in the inlet step (figure 3b and 3c) at the opening of the
second port
112 and the first port 107 that are on the wall 110a of the cylinder 110 of
the
reciprocating compressor 100, as it will be described later.
In figure 5, an additional cooling device 200' comprising a reciprocating
compressor
100 similar to that one of the embodiment shown in figure 1 is shown.
The cooling device 200' comprises a closed circuit C comprising a main branch
M
along which a first flow rate X of the coolant is circulating at a defined
pressure, a
condenser 101, an evaporator 103, and a first expansion valve 102 arranged
between
the condenser 101 and the evaporator 103. Such a closed circuit C also
comprises a
first economizer branch E along which a second flow rate X1 of the coolant
circulates. Such a first economizer branch E is fluidically connected to the
compressor 100 and to a section 106 of the closed circuit C comprised between
the
condenser 101 and the expansion valve 102.
In the herein described embodiment, the closed circuit C further comprises an
additional economizer branch E' for an additional flow rate X2 of the coolant.
Still according to the herein described embodiment, the economizer branch E
and the
additional secondary economizer branch E' comprise a second expansion valve
150,
150' and at least one heat exchanger 160, 160' with the section 106 of the
closed
circuit C comprised between the condenser 101 and the expansion valve 102.
According to the herein described embodiment, such a second flow rate X1 has
an
inlet pressure P8 in the cylinder 110 of the compressor 100 intermediate
between the
pressure at the condenser P2 and the inlet pressure in the cylinder 110, i.e.
the
pressure P1 of the flow rate X of fluid entering the cylinder 110 of the
compressor
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from the suction duct 109, during the inlet step of the compressor 100.
Note that in figure 5 the thermodynamic states of the coolant circulating in
the closed
circuit C of the refrigeration device 200' are denoted in brackets, with
numbers from
1 to 10. Then, in figure 6 the thermodynamic cycle made by the coolant in the
closed
circuit C is shown, with the information of the respective thermodynamic
condition
of the coolant. The references 11 and 12 shown in the graph of figure 6
correspond to
the thermodynamic states of the coolant in the compressor 100 in the inlet
step
(figures 3b and 3c) at the opening of the second port 112 and the first port
107 that
are on the wall 110a of the cylinder 110 of the reciprocating compressor 100,
as it
will be described later.
According to the invention, in both the cooling devices 200 and 200' the
reciprocating compressor 100 comprises a first side port 107 obtained on the
wall
110a of the cylinder 110 for the entrance of the aforementioned second flow
rate X1
of coolant.
The compressor 100 further comprises a second inlet port 112 for the entrance
of
such an additional flow rate X2 of coolant. More specifically, the second
inlet port
112 is arranged at a distance D from the bottom dead centre I of the piston
111
greater than the distance d at which the first port 107 is located. Such a
distance is
assessed with respect to two planes P and P1 transverse to the axis A of the
cylinder
110 and passing in the middle of the height H of the port 107, 112.
According to the herein disclosed embodiment, the first inlet port 107 for the
second
flow rate X1 of coolant, that in the present instance is R404a, is a slit and
is arranged
at the bottom dead centre I of the piston 111, so that the piston exposes the
first inlet
port 107 during its inlet stroke and covers such a first inlet port 107 during
its
compression stroke. In addition, the second inlet port 112 for the entrance of
such an
additional flow rate X2 of coolant arranged, as mentioned afore, at a distance
D from
the bottom dead centre I of the piston 111 greater than the distance d at
which the
first port 107 is located, is also a slit. Also the second slit 112 is
arranged on the wall
110a of the cylinder so that the piston exposes the second inlet port 112,
during its
inlet stroke, and before exposing the first inlet port 107, and covers it
during its
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compression stroke, after covering the first port 107.
In particular, both the first inlet port 107 and the second inlet port 112
comprise a slit
whose main dimension L is substantially transverse to the axis A of the
cylinder 110.
In particular, the slit has a substantially rectangular-shaped surface, lying
on the
inner surface 110c of the cylinder 110, thus along an arc of a circle of the
cylinder
110. More specifically, for example such a surface is obtained through a
cutting by
milling machine of the wall 110a of the cylinder 110, obtained with the
rotation axis
of the milling machine parallel to the axis A of the cylinder 110 and forward
direction of the milling machine orthogonal to the axis of the cylinder 110.
Therefore
the so obtained surface is substantially rectangular-shaped, despite the
rectangle sides
are not reciprocally connected by sharp edge, but are blent one to the other.
Preferably, the ratio between the H height dimension and L length dimension
(also
main dimension), the latter being measured along the arc of a circle traveled
by the
slit along the inner surface of the cylinder 110c (see in particular the
dotted line
shown in figure 4b), is 0.2. In particular, the length L has to be measured on
a plane
P. or P 1 , transverse to the axis of the cylinder A and passing in the middle
of the
height H of the respective slit.
Note that, anyway, any slit having a dimensional ratio of height H to length L
smaller
than 0.5 still falls within the protection scope of the present invention. In
addition it
has to be noted that the slit, i.e. the surface extending on the inner face
110c of the
cylinder 110, has lower and upper sides blent to the respective connecting
sides,
since it follows the shape of the wall 110a of the cylinder 110 itself.
In particular, as visible in figures 3a to 3d, the first port 107 has a lower
side 107a
substantially flush with the bottom dead centre I of the piston 111. More
particularly,
the lower side 112a of the second port 112 is flush with the upper side 107b
of the
first port 107.
According to the embodiment shown in the figures 3a to 3d, only the second
inlet
port 112 comprises a functionally-combined non-return valve 180; whereas, in
the
embodiment shown in figures 4a and 4b, both the first inlet port 107 and the
second
inlet port 112 comprise a functionally-combined non-return valve 180 of
deformable
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reed type.
Such a non-return valve 180 is, in practice, dimensioned so as to deform only
after a
defined pressure is exceeded. In addition, such a non-return valve 180 is
housed in
the wall 110a of the cylinder 110 of the compressor 101 and, when in a not
deformed
condition, is in abutment against a pair of projections 190 and 191 contacting
the
outer surface 110b of the cylinder 110.
It has to be mentioned that, although a compressor 100 provided with a first
port 107
and a second port 112 and, thus, a cooling device 200 or 200' provided with a
secondary, or economizer, branch E and an additional secondary, or economizer,
branch E' has been described heretofore, however a solution in which the
compressor
100 is provided with at least one first port 107, but free of said at least
one second
port 112, and thus a cooling device 200 or 200' provided with the only
economizer,
or secondary branch E, still falls within the protection scope of the present
invention.
In this case the first flow rate, that entering the compressor 100 through the
suction
duct 109, is given by the difference between the overall flow rate circulating
in the
closed circuit C and the only second flow rate X 1 .
The operation of the reciprocating compressor 100 being in the two
refrigeration
devices 200, 200' respectively described in figure 1 and 5, is explained in
figures 3a
to 3d. In practice, during the inlet step of the compressor, i.e. when the
piston 111 of
the compressor 101 slides downwards from the top dead centre S to the bottom
dead
centre I, the suction valve 113 of the compressor 100 is open to accommodate
the
flow rate of fluid X coming from the main circuit M, through suction duct 109
(see
figure 3a). Subsequently, the piston 111 exposes the second port 112 from
which an
additional flow rate X2 of coolant coming from the additional secondary
economizer
branch E' comes; due to the pressure increase, the suction valve 109 closes.
The
pressure of such an additional flow rate X2 of coolant is higher than the
pressure
being in the cylinder 110, thus resulting in a pressure increase inside the
cylinder 110
(thermodynamic state 9 or 11, depending on the cooling device 200 or 200'). Of
course during such a step the non-return valve 180 remains open (see figure
3b).
Then, the piston exposes the first port 107 thus allowing the second flow rate
X1 of
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coolant coming from the secondary economizer branch E accessing the cylinder
110.
Of course, the pressure of the second flow rate X1 of coolant coming from such
an
economizer, or secondary, branch E is higher than the pressure of the
additional flow
rate X2 of coolant and the suction pressure. Anyway, since the mixing there is
an
increase of the pressure in the cylinder 110 of the compressor 100
(thermodynamic
state 10 or 12, depending on the cooling device 200 or 200'), before the
latter starts
its compression stroke. Subsequently, the piston 111 rises again and
compresses the
fluid in the cylinder 110, until reaching the top dead centre S. When the
pressure in
the cylinder exceeds the condensation pressure, the opening of the exhaust
valve 114
occurs. It has to be noted that during the rising of the piston 111, the non-
return valve
180 placed in the part 110a of the cylinder 110 remains closed as the pressure
in the
cylinder 110 exceeds the pressure of the additional flow rate X2 coming from
the
additional, or secondary, economizer branch E'.
Lastly, note that the implementation of the first port 107 and/or the second
port 112
preferably occurs through a simple milling operation, or similar technological
operation, of the cylinder 110 along a plane transverse to the axis A of the
cylinder
110 itself. This allows the cylinders of existing reciprocating compressors,
that are
free of through side port, being converted by means of a simple milling
operation of
the cylinder 110. In this way, such cylinders are made adapted to operate in
cooling
devices having at least one secondary, or economizer, branch without the need
of
subjecting the cylinder to complex interventions, from a technical point of
view, or
economically unattractive.
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