U.S. patent application number 11/660732 was filed with the patent office on 2008-09-04 for linear compressor.
This patent application is currently assigned to LG Electronics, Inc.. Invention is credited to Man-Seok Cho, Bong-Jun Choi, Chang-Yong Jang, Young-Hoan Jeon, Hyun Kim, Shin-Hyun Park, Chul-Gi Roh, Jong-Min Shin.
Application Number | 20080213108 11/660732 |
Document ID | / |
Family ID | 36000240 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080213108 |
Kind Code |
A1 |
Choi; Bong-Jun ; et
al. |
September 4, 2008 |
Linear Compressor
Abstract
The present invention discloses a linear compressor in which a
piston is driven by a linear motor and linearly reciprocated inside
a cylinder to suck, compress and discharge refrigerants. The linear
compressor synchronizes an operation frequency of the linear motor
with a natural frequency of the piston, considering that an elastic
force of a mechanical spring and a gas spring which elastically
support the piston in the motion direction is varied by load. Even
if the load is varied, the linear motor is operated in the
resonance state, to maximize efficiency. The linear compressor
varies a stroke of the piston according to the load, thereby
actively handling and rapidly overcoming the load and reducing
power consumption.
Inventors: |
Choi; Bong-Jun;
(Kyungsangnam-Do, KR) ; Jang; Chang-Yong;
(Gwangju, KR) ; Cho; Man-Seok; (Kyungsangnam-Do,
KR) ; Park; Shin-Hyun; (Busan, KR) ; Kim;
Hyun; (Kyungsangnam-Do, KR) ; Shin; Jong-Min;
(Busan, KR) ; Jeon; Young-Hoan; (Kyungsangnam-Do,
KR) ; Roh; Chul-Gi; (Kyungsangnam-Do, KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
LG Electronics, Inc.
Seoul
KR
|
Family ID: |
36000240 |
Appl. No.: |
11/660732 |
Filed: |
August 30, 2004 |
PCT Filed: |
August 30, 2004 |
PCT NO: |
PCT/KR2004/002177 |
371 Date: |
October 22, 2007 |
Current U.S.
Class: |
417/417 |
Current CPC
Class: |
F04B 35/045 20130101;
F04B 2201/0806 20130101; F04B 2207/045 20130101 |
Class at
Publication: |
417/417 |
International
Class: |
F04B 35/04 20060101
F04B035/04; F04B 17/03 20060101 F04B017/03 |
Claims
1. A linear compressor, comprising: a fixed member having a
compression space inside; a movable member linearly reciprocated in
the fixed member in the axial direction, for sucking refrigerants
into the compression space and compressing the refrigerants; one or
more springs installed to elastically support the movable member in
the motion direction of the movable member, spring constants of
which being varied by load; and a linear motor installed to be
connected to the movable member, for linearly reciprocating the
movable member in the axial direction, and synchronizing its
operation frequency with a natural frequency of the movable member
dependent upon the spring constants.
2. The linear compressor of claim 1, wherein the spring constants
of the springs are varied in proportion to the load, and the
operation frequency of the linear motor is varied in proportion to
the load.
3. The linear compressor of claim 2, which is installed in a
refrigeration/air conditioning cycle, wherein the load is
calculated in proportion to a difference between a pressure of
condensing refrigerants (condensing pressure) and a pressure of
evaporating refrigerants (evaporating pressure) in the
refrigeration/air conditioning cycle.
4. The linear compressor of claim 3, wherein the load is
additionally calculated in proportion to a pressure that is an
average of the condensing pressure and the evaporating pressure
(average pressure).
5. The linear compressor of any one of claims 1 to 3, wherein the
springs comprise: a mechanical spring being installed to support
the movable member at both sides of the motion direction of the
movable member, and having a constant mechanical spring constant;
and a gas spring having a gas spring constant varied by the load of
the refrigerants sucked into the compression space.
6. The linear compressor of claim 5, wherein the mechanical spring
and the gas spring are formed so that the ratio of the mechanical
spring constant to the total spring constant obtained by adding up
the mechanical spring constant and the gas spring constant can be
below 90%.
7. The linear compressor of claim 5, wherein the mechanical spring
constant and the gas spring constant of the mechanical spring and
the gas spring are determined so that the natural frequency of the
movable member can be set in a low frequency area between 30 and 55
Hz.
8. The linear compressor of claim 5, wherein the linear motor
varies a stroke that is a linear reciprocation distance of the
movable member by the load.
9. The linear compressor of claim 8, wherein the linear motor
linearly reciprocates the movable member to reach a top dead center
even if the stroke of the movable member is varied.
10. The linear compressor of claim 9, wherein an initial position
of the movable member is closer to the top dead center according to
decrease of the mechanical spring constant.
11. A linear compressor, comprising: a fixed member having a
compression space inside; a movable member linearly reciprocated in
the fixed member in the axial direction, for compressing
refrigerants sucked into the compression space; a mechanical spring
being installed to elastically support the movable member at both
sides of the motion direction of the movable member, and having a
constant mechanical spring constant; a gas spring having a gas
spring constant varied by load of the refrigerants sucked into the
compression space; and a linear motor installed to be connected to
the movable member, for linearly reciprocating the movable member
in the axial direction, wherein the mechanical spring constant and
the gas spring constant of the mechanical spring and the gas spring
are set so that a stroke that is a linear reciprocation distance of
the movable member can be varied by the load.
12. The linear compressor of claim 11, which is installed in a
refrigeration/air conditioning cycle, wherein the load is
calculated in proportion to a difference between a pressure of
condensing refrigerants (condensing pressure) and a pressure of
evaporating refrigerants (evaporating pressure) in the
refrigeration/air conditioning cycle.
13. The linear compressor of claim 12, wherein the load is
additionally calculated in proportion to a pressure that is an
average of the condensing pressure and the evaporating pressure
(average pressure).
14. The linear compressor of claim 11, wherein the mechanical
spring constant and the gas spring constant of the mechanical
spring and the gas spring are set so that the movable member can be
linearly reciprocated to reach a top dead center even if the stroke
of the movable member is varied.
15. The linear compressor of claim 14, wherein an initial position
of the movable member is closer to the top dead center according to
decrease of the mechanical spring constant.
Description
TECHNICAL FIELD
[0001] The present invention relates to a linear compressor which
can actively handle load and efficiently perform an operation, by
synchronizing an operation frequency with a natural frequency of a
movable member varied by the load.
BACKGROUND ART
[0002] In general, a compressor that is a mechanical apparatus for
increasing a pressure, by receiving power from a power unit system
such as an electric motor or turbine and compressing air,
refrigerants or other various operation gases has been widely used
for home appliances such as a refrigerator and an air conditioner
or in the whole industrial fields.
[0003] The compressors are roughly divided into a reciprocating
compressor having a compression space through which operation gases
are sucked or discharged between a piston and a cylinder, so that
the piston can be linearly reciprocated inside the cylinder to
compress refrigerants, a rotary compressor having a compression
space through which operation gases are sucked or discharged
between an eccentrically-rotated roller and a cylinder, so that the
roller can be eccentrically rotated on the inner walls of the
cylinder to compress refrigerants, and a scroll compressor having a
compression space through which operation gases are sucked or
discharged between an orbiting scroll and a fixed scroll, so that
the orbiting scroll can be rotated with the fixed scroll to
compress refrigerants.
[0004] Recently, among the reciprocating compressors, a linear
compressor has been mass-produced because it has high compression
efficiency and simple structure by removing mechanical loss by
motion conversion by directly connecting a piston to a driving
motor performing linear reciprocation.
[0005] Generally, the linear compressor which sucks, compresses and
discharges refrigerants by using a linear driving force of the
motor includes a compression unit consisting of a cylinder and a
piston for compressing refrigerant gases, and a driving unit
consisting of a linear motor for supplying a driving force to the
compression unit.
[0006] In detail, in the linear compressor, the cylinder is fixedly
installed in a closed vessel, and the piston is installed in the
cylinder to perform linear reciprocation. When the piston is
linearly reciprocated inside the cylinder, refrigerants are sucked
into a compression space in the cylinder, compressed and
discharged. A suction valve assembly and a discharge valve assembly
are installed in the compression space, for controlling suction and
discharge of the refrigerants according to the inside pressure of
the compression space.
[0007] In addition, the linear motor for generating a linear motion
force to the piston is installed to be connected to the piston. An
inner stator and an outer stator formed by stacking a plurality of
laminations at the periphery of the cylinder in the circumferential
direction are installed on the linear motor with a predetermined
gap. A coil is coiled inside the inner stator or the outer stator,
and a permanent magnet is installed at the gap between the inner
stator and the outer stator to be connected to the piston.
[0008] Here, the permanent magnet is installed to be movable in the
motion direction of the piston, and linearly reciprocated in the
motion direction of the piston by an electromagnetic force
generated when a current flows through the coil. Normally, the
linear motor is operated at a constant operation frequency f.sub.c,
and the piston is linearly reciprocated by a predetermined stroke
S.
[0009] On the other hand, various springs are installed to
elastically support the piston in the motion direction even though
the piston is linearly reciprocated by the linear motor. In detail,
a coil spring which is a kind of mechanical spring is installed to
be elastically supported by the closed vessel and the cylinder in
the motion direction of the piston. Also, the refrigerants sucked
into the compression space serve as a gas spring.
[0010] The coil spring has a constant mechanical spring constant
K.sub.m, and the gas spring has a gas spring constant K.sub.g
varied by load. A natural frequency f.sub.n of the piston (or
linear compressor) is calculated in consideration of the mechanical
spring constant K.sub.m and the gas spring constant K.sub.g.
[0011] The thusly-calculated natural frequency f.sub.n of the
piston determines the operation frequency f.sub.c of the linear
motor. The linear motor improves efficiency by equalizing its
operation frequency f.sub.c to the natural frequency f.sub.n of the
piston, namely, operating in the resonance state.
[0012] Accordingly, in the linear compressor, when a current is
applied to the linear motor, the current flows through the coil to
generate an electromagnetic force by interactions with the outer
stator and the inner stator, and the permanent magnet and the
piston connected to the permanent magnet are linearly reciprocated
by the electromagnetic force.
[0013] Here, the linear motor is operated at the constant operation
frequency f.sub.c. The operation frequency f.sub.c of the linear
motor is equalized to the natural frequency f.sub.n of the piston,
so that the linear motor can be operated in the resonance state to
maximize efficiency.
[0014] As described above, when the piston is linearly reciprocated
inside the cylinder, the inside pressure of the compression space
is changed. The refrigerants are sucked into the compression space,
compressed and discharged according to changes of the inside
pressure of the compression space.
[0015] The linear compressor is formed to be operated at the
operation frequency f.sub.c identical to the natural frequency
f.sub.n of the piston calculated by the mechanical spring constant
K.sub.m of the coil spring and the gas spring constant K.sub.g of
the gas spring under the load considered in the linear motor at the
time of design. Therefore, the linear motor is operated in the
resonance state merely under the load considered on design, to
improve efficiency.
[0016] However, since the actual load of the linear compressor is
varied, the gas spring constant K.sub.g of the gas spring and the
natural frequency f.sub.n of the piston calculated by the gas
spring constant K.sub.g are changed.
[0017] In detail, as illustrated in FIG. 1A, the operation
frequency f.sub.c of the linear motor is determined to be identical
to the natural frequency f.sub.n of the piston in a middle load
area at the time of design. Even if the load is varied, the linear
motor is operated at the constant operation frequency f.sub.c. But,
as the load increases, the natural frequency f.sub.n of the piston
increases.
f n = 1 2 .pi. K m + K g M Formula 1 ##EQU00001##
[0018] Here, f.sub.n represents the natural frequency of the
piston, K.sub.m and K.sub.g represent the mechanical spring
constant and the gas spring constant, respectively, and M
represents a mass of the piston.
[0019] Generally, since the gas spring constant K.sub.g has a small
ratio in the total spring constant K.sub.t, the gas spring constant
K.sub.g is ignored or set to be a constant value. The mass M of the
piston and the mechanical spring constant K.sub.m are also set to
be constant values. Therefore, the natural frequency f.sub.n of the
piston is calculated as a constant value by the above Formula
1.
[0020] However, the more the actual load increases, the more the
pressure and temperature of the refrigerants in the restricted
space increase. Accordingly, an elastic force of the gas spring
itself increases, to increase the gas spring constant K.sub.g.
Also, the natural frequency f.sub.n of the piston calculated in
proportion to the gas spring constant K.sub.g increases.
[0021] Referring to FIGS. 1A and 1B, the operation frequency
f.sub.c of the linear motor and the natural frequency f.sub.n of
the piston are identical in the middle load area, so that the
piston can be operated to reach a top dead center (TDC), thereby
stably performing compression. In addition, the linear motor is
operated in the resonance state, to maximize efficiency of the
linear compressor.
[0022] However, the natural frequency f.sub.n of the piston gets
smaller than the operation frequency f.sub.c of the linear motor in
a low load area, and thus the piston is transferred over the TDC,
to apply an excessive compression force. Moreover, the piston and
the cylinder are abraded by friction. Since the linear motor is not
operated in the resonance state, efficiency of the linear
compressor is reduced.
[0023] In addition, the natural frequency f.sub.n of the piston
becomes larger than the operation frequency f.sub.c of the linear
motor in a high load area, and thus the piston does not reach the
TDC, to reduce the compression force. The linear motor is not
operated in the resonance state, thereby decreasing efficiency of
the linear compressor.
[0024] As a result, in the conventional linear compressor, when the
load is varied, the natural frequency f.sub.n of the piston is
varied, but the operation frequency f.sub.c of the linear motor is
constant. Therefore, the linear motor is not operated in the
resonance state, which results in low efficiency. Furthermore, the
linear compressor cannot actively handle and rapidly overcome the
load.
[0025] On the other hand, in order to actively handle and rapidly
overcome the load, the conventional linear compressor varies the
operation frequency f.sub.c of the linear motor by controlling an
input current in proportion to the load. Especially, the linear
compressor controls the operation frequency f.sub.c of the linear
motor to be more lowered in the low load area. Thus, compression is
not performed in the resonance state, which seriously reduces
efficiency of the linear compressor. Nevertheless, because
efficiency of the whole refrigeration cycle increases, the whole
efficiency is not much changed.
[0026] In order to perform compression in the resonance state even
in the low load area, the conventional linear compressor is
intended to be operated in the low frequency area so that the
operation frequency f.sub.c of the linear motor can be equalized to
the natural frequency f.sub.n of the piston. However, in the linear
compressor having the large mechanical spring constant K.sub.m, it
is difficult to control the operation frequency f.sub.c of the
linear motor to the low frequency by adjusting the input current.
Furthermore, the linear compressor cannot efficiently vary the
compression capacity.
DISCLOSURE OF THE INVENTION
[0027] The present invention is achieved to solve the above
problems. An object of the present invention is to provide a linear
compressor which can be operated in the resonance state regardless
of variations of load, by synchronizing an operation frequency of a
linear motor with a natural frequency of a piston, even if the
natural frequency of the piston is varied by the load.
[0028] Another object of the present invention is to provide a
linear compressor which can efficiently vary a compression
capacity, by enabling a linear motor to simultaneously or
individually vary an operation frequency by load and control a
stroke of a piston.
[0029] In order to achieve the above-described objects of the
invention, there is provided a linear compressor, including: a
fixed member having a compression space inside; a movable member
linearly reciprocated in the fixed member in the axial direction,
for sucking refrigerants into the compression space and compressing
the refrigerants; one or more springs installed to elastically
support the movable member in the motion direction of the movable
member, spring constants of which being varied by load; and a
linear motor installed to be connected to the movable member, for
linearly reciprocating the movable member in the axial direction,
and synchronizing its operation frequency with a natural frequency
of the movable member.
[0030] Preferably, the spring constants of the springs are varied
in proportion to the load, and the operation frequency of the
linear motor is varied in proportion to the load.
[0031] Preferably, the linear compressor is installed in a
refrigeration/air conditioning cycle, and the load is calculated in
proportion to a difference between a pressure of condensing
refrigerants (condensing pressure) and a pressure of evaporating
refrigerants (evaporating pressure) in the refrigeration/air
conditioning cycle. More preferably, the load is additionally
calculated in proportion to a pressure that is an average of the
condensing pressure and the evaporating pressure (average
pressure).
[0032] Preferably, the springs include a mechanical spring being
installed to support the movable member at both sides of the motion
direction of the movable member, and having a constant mechanical
spring constant, and a gas spring having a gas spring constant
varied by the load of the refrigerants sucked into the compression
space.
[0033] Preferably, the mechanical spring and the gas spring are
formed so that the ratio of the mechanical spring constant to the
total spring constant obtained by adding up the mechanical spring
constant and the gas spring constant can be below 90%, and the
mechanical spring constant and the gas spring constant are
determined so that the natural frequency of the movable member can
be set in a low frequency area between 30 and 55 Hz.
[0034] Preferably, the mechanical spring constant and the gas
spring constant of the mechanical spring and the gas spring are set
so that a stroke that is a linear reciprocation distance of the
movable member can be varied by the load. More preferably, the
mechanical spring constant and the gas spring constant of the
mechanical spring and the gas spring are set so that the movable
member can be linearly reciprocated to reach a top dead center even
if the stroke of the movable member is varied.
[0035] Preferably, an initial position of the movable member is
closer to the top dead center according to decrease of the
mechanical spring constant, so that the movable member can be
stably elastically supported by the mechanical spring and the gas
spring.
[0036] According to another aspect of the present invention, a
linear compressor includes: a fixed member having a compression
space inside; a movable member linearly reciprocated in the fixed
member in the axial direction, for compressing refrigerants sucked
into the compression space; a mechanical spring being installed to
elastically support the movable member at both sides of the motion
direction of the movable member, and having a constant mechanical
spring constant; a gas spring having a gas spring constant varied
by load of the refrigerants sucked into the compression space; and
a linear motor installed to be connected to the movable member, for
linearly reciprocating the movable member in the axial direction,
wherein the mechanical spring constant and the gas spring constant
of the mechanical spring and the gas spring are set so that a
stroke that is a linear reciprocation distance of the movable
member can be varied by the load.
[0037] Preferably, the linear compressor is installed in a
refrigeration/air conditioning cycle, and the load is calculated in
proportion to a difference between a pressure of condensing
refrigerants (condensing pressure) and a pressure of evaporating
refrigerants (evaporating pressure) in the refrigeration/air
conditioning cycle. More preferably, the load is additionally
calculated in proportion to a pressure that is an average of the
condensing pressure and the evaporating pressure (average
pressure).
[0038] Preferably, the mechanical spring constant and the gas
spring constant of the mechanical spring and the gas spring are set
so that the movable member can be linearly reciprocated to reach a
top dead center even if the stroke of the movable member is
varied.
[0039] Preferably, an initial position of the movable member is
closer to the top dead center according to decrease of the
mechanical spring constant, so that the movable member can be
stably elastically supported by the mechanical spring and the gas
spring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The present invention will become better understood with
reference to the accompanying drawings which are given only by way
of illustration and thus are not limitative of the present
invention, wherein:
[0041] FIG. 1A is a graph showing a stroke by load in a
conventional linear compressor;
[0042] FIG. 1B is a graph showing efficiency by the load in the
conventional linear compressor;
[0043] FIG. 2 is a cross-sectional view illustrating a linear
compressor in accordance with the present invention;
[0044] FIG. 3A is a graph showing a stroke by load in the linear
compressor in accordance with the present invention;
[0045] FIG. 3B is a graph showing efficiency by the load in the
linear compressor in accordance with the present invention;
[0046] FIG. 4 is a graph showing changes of a gas spring constant
by the load in the linear compressor in accordance with the present
invention;
[0047] FIG. 5 is a graph showing changes of the gas spring constant
by variations of an ambient temperature, a mass of a piston, a
mechanical spring constant and a natural frequency in the linear
compressor in accordance with the present invention;
[0048] FIG. 6 is a structure view illustrating the stroke by the
load in part of the linear compressor in accordance with the
present invention; and
[0049] FIGS. 7A to 7C are side-sectional views illustrating an
operation state of the linear compressor in accordance with the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0050] A linear compressor in accordance with preferred embodiments
of the present invention will now be described in detail with
reference to the accompanying drawings.
[0051] As shown in FIG. 2, in the linear compressor, an inlet tube
2a and an outlet tube 2b through which refrigerants are sucked and
discharged are installed at one side of a closed vessel 2, a
cylinder 4 is fixedly installed inside the closed vessel 2, a
piston 6 is installed inside the cylinder 4 to be linearly
reciprocated to compress the refrigerants sucked into a compression
space P in the cylinder 4, and various springs are installed to be
elastically supported in the motion direction of the piston 6.
Here, the piston 6 is connected to a linear motor 10 for generating
a linear reciprocation driving force. As depicted in FIGS. 3A and
3B, even if a natural frequency f.sub.n of the piston 6 is varied
by load, the linear motor 10 controls its operation frequency
f.sub.c to be synchronized with the natural frequency f.sub.n of
the piston 6, so that the resonance operation can be performed in
the whole load areas to improve compression efficiency.
[0052] In addition, a suction valve 22 is installed at one end of
the piston 6 contacting the compression space P, and a discharge
valve assembly 24 is installed at one end of the cylinder 4
contacting the compression space P. The suction valve 22 and the
discharge valve assembly 24 are automatically controlled to be
opened or closed according to the inside pressure of the
compression space P, respectively.
[0053] The top and bottom shells of the closed vessel 2 are coupled
to hermetically seal the closed vessel 2. The inlet tube 2a through
which the refrigerants are sucked and the outlet tube 2b through
which the refrigerants are discharged are installed at one side of
the closed vessel 2. The piston 6 is installed inside the cylinder
4 to be elastically supported in the motion direction to perform
the linear reciprocation. The linear motor 10 is connected to a
frame 18 outside the cylinder 4. The cylinder 4, the piston 6 and
the linear motor 10 compose an assembly. The assembly is installed
on the inside bottom surface of the closed vessel 2 to be
elastically supported by a support spring 29.
[0054] The inside bottom surface of the closed vessel 2 contains
oil, an oil supply device 30 for pumping the oil is installed at
the lower end of the assembly, and an oil supply tube 18a for
supplying the oil between the piston 6 and the cylinder 4 is formed
inside the frame 18 at the lower side of the assembly. Accordingly,
the oil supply device 30 is operated by vibrations generated by the
linear reciprocation of the piston 6, for pumping the oil, and the
oil is supplied to the gap between the piston 6 and the cylinder 4
along the oil supply tube 18a, for cooling and lubrication.
[0055] The cylinder 4 is formed in a hollow shape so that the
piston 6 can perform the linear reciprocation, and has the
compression space P at its one side. Preferably, the cylinder 4 is
installed on the same straight line with the inlet tube 2a in a
state where one end of the cylinder 4 is adjacent to the inside
portion of the inlet tube 2a.
[0056] The piston 6 is installed inside one end of the cylinder 4
adjacent to the inlet tube 2a to perform linear reciprocation, and
the discharge valve assembly 24 is installed at one end of the
cylinder 4 in the opposite direction to the inlet tube 2a.
[0057] Here, the discharge valve assembly 24 includes a discharge
cover 24a for forming a predetermined discharge space at one end of
the cylinder 4, a discharge valve 24b for opening or closing one
end of the cylinder 4 near the compression space P, and a valve
spring 24c which is a kind of coil spring for applying an elastic
force between the discharge cover 24a and the discharge valve 24b
in the axial is direction. An O-ring R is inserted onto the inside
circumferential surface of one end of the cylinder 4, so that the
discharge valve 24a can be closely adhered to one end of the
cylinder 4.
[0058] An indented loop pipe 28 is installed between one side of
the discharge cover 24a and the outlet tube 2b, for guiding the
compressed refrigerants to be externally discharged, and preventing
vibrations generated by interactions of the cylinder 4, the piston
6 and the linear motor 10 from being applied to the whole closed
vessel 2.
[0059] Therefore, when the piston 6 is linearly reciprocated inside
the cylinder 4, if the pressure of the compression space P is over
a predetermined discharge pressure, the valve spring 24c is
compressed to open the discharge valve 24b, and the refrigerants
are discharged from the compression space P, and then externally
discharged along the loop pipe 28 and the outlet tube 2b.
[0060] A refrigerant passage 6a through which the refrigerants
supplied from the inlet tube 2a flows is formed at the center of
the piston 6. The linear motor 10 is directly connected to one end
of the piston 6 adjacent to the inlet tube 2a by a connection
member 17, and the suction valve 22 is installed at one end of the
piston 6 in the opposite direction to the inlet tube 2a. The piston
6 is elastically supported in the motion direction by various
springs.
[0061] The suction valve 22 is formed in a thin plate shape. The
center of the suction valve 22 is partially cut to open or close
the refrigerant passage 6a of the piston 6, and one side of the
suction valve 22 is fixed to one end of the piston 6a by
screws.
[0062] Accordingly, when the piston 6 is linearly reciprocated
inside the cylinder 4, if the pressure of the compression space P
is below a predetermined suction pressure lower than the discharge
pressure, the suction valve 22 is opened so that the refrigerants
can be sucked into the compression space P, and if the pressure of
the compression space P is over the predetermined suction pressure,
the refrigerants of the compression space P are compressed in the
close state of the suction valve 22.
[0063] Especially, the piston 6 is installed to be elastically
supported in the motion direction. In detail, a piston flange 6b
protruded in the radial direction from one end of the piston 6
adjacent to the inlet tube 2a is elastically supported in the
motion direction of the piston 6 by mechanical springs 8a and 8b
such as coil springs. The refrigerants included in the compression
space P in the opposite direction to the inlet tube 2a are operated
as gas spring due to an elastic force, thereby elastically
supporting the piston 6.
[0064] Here, the mechanical springs 8a and 8b have constant
mechanical spring constants K.sub.m regardless of the load, and are
preferably installed side by side with a support frame 26 fixed to
the linear motor 10 and the cylinder 4 in the axial direction from
the piston flange 6b. Also, preferably, the mechanical spring 8a
supported by the support frame 26 and the mechanical spring 8a
installed on the cylinder 4 have the same mechanical spring
constant K.sub.m.
[0065] However, the gas spring has a gas spring constant K.sub.g
varied by the load. When an ambient temperature rises, the pressure
of the refrigerants increases, and thus the elastic force of the
gases in the compression space P increases. As a result, the more
the load increases, the higher the gas spring constant K.sub.g of
the gas spring is.
[0066] While the mechanical spring constant K.sub.m is constant,
the gas spring constant K.sub.g is varied by the load. Therefore,
the total spring constant is also varied by the load, and the
natural frequency f.sub.n of the piston 6 is varied by the gas
spring constant K.sub.g in the above Formula 1.
[0067] Even if the load is varied, the mechanical spring constant
K.sub.m and the mass M of the piston 6 are constant, but the gas
spring constant K.sub.g is varied. Thus, the natural frequency
f.sub.n of the piston 6 is remarkably influenced by the gas spring
constant K.sub.g varied by the load. In the case that the algorithm
of varying the natural frequency f.sub.n of the piston 6 by the
load is obtained and the operation frequency f.sub.c of the linear
motor 10 is synchronized with the natural frequency f.sub.n of the
piston 6, efficiency of the linear compressor can be improved and
the load can be rapidly overcome.
[0068] The load can be measured in various ways. Since the linear
compressor is installed in a refrigeration/air conditioning cycle
for compressing, condensing, expanding and evaporating
refrigerants, the load can be defined as a difference between a
condensing pressure which is a pressure of condensing refrigerants
and an evaporating pressure which is a pressure of evaporating
refrigerants. In order to improve accuracy, the load is determined
in consideration of an average pressure of the condensing pressure
and the evaporating pressure.
[0069] That is, the load is calculated in proportion to the
difference between the condensing pressure and the evaporating
pressure and the average pressure. The more the load increases, the
higher the gas spring constant K.sub.g is. For example, if the
difference between the condensing pressure and the evaporating
pressure increases, the load increases. Even though the difference
between the condensing pressure and the evaporating pressure is not
changed, if the average pressure increases, the load increases. The
gas spring constant K.sub.g increases according to the load.
[0070] As illustrated in FIG. 4, a condensing temperature
proportional to the condensing pressure and an evaporating
temperature proportional to the evaporating pressure are measured,
and the load is calculated in proportion to a difference between
the condensing temperature and the evaporating temperature and an
average temperature.
[0071] In detail, the mechanical spring constant K.sub.m and the
gas spring constant K.sub.g can be determined by various
experiments. Referring to FIG. 5, when the mechanical spring
constant K.sub.m decreases, the ratio of the gas spring constant
K.sub.g to the total spring constant K.sub.T obtained by adding up
the mechanical spring constant K.sub.m and the gas spring constant
K.sub.g increases. In addition, the higher the ambient temperature
is, namely, the more the load increases, the higher the ratio of
the gas spring constant K.sub.g to the total spring constant
K.sub.T is. When the ratio of the gas spring constant K.sub.g to
the total spring constant K.sub.T increases, the natural frequency
f.sub.n is remarkably changed.
[0072] Preferably, the ratio of the gas spring constant K.sub.g to
the total spring constant K.sub.T is set below 90%.
[0073] For example, when the ratio of the gas spring constant
K.sub.g to the total spring constant K.sub.T exceeds 10% by setting
the mechanical spring constant K.sub.m below 35.5 kN/m, the natural
frequency f.sub.n is remarkably varied due to changes of the
ambient temperature. Therefore, the operation frequency f.sub.c of
the linear motor 10 is easily controlled, so that the linear motor
10 can be operated in the resonance state. Moreover, the load is
rapidly overcome, to reduce power consumption.
[0074] However, when the ratio of the gas spring constant K.sub.g
to the total spring constant K.sub.T becomes lower than 10% by
setting the mechanical spring constant K.sub.m over 35.5 kN/m, the
natural frequency f.sub.n is rarely varied by changes of the
ambient temperature. Accordingly, the operation frequency f.sub.c
of the linear motor 10 is not easily controlled, so that the linear
motor 10 cannot be operated in the resonance state.
[0075] As described above, when the ratio of the gas spring
constant K.sub.g to the total spring constant K.sub.T is high, the
natural frequency f.sub.n of the piston 6 is remarkably varied by
changes of the load, and the operation frequency f.sub.c of the
linear motor 10 is easily synchronized with the natural frequency
f.sub.n of the piston 6. Thus, the linear motor 10 is operated in
the resonance state, thereby maximizing efficiency. Furthermore,
even if the operation frequency f.sub.c of the linear motor 10 is
operated in the low frequency area, the load can be rapidly
overcome by high efficiency, which results in low power
consumption.
[0076] Accordingly, the natural frequency f.sub.n of the piston 6
is determined at the time of design by the mechanical spring
constant K.sub.m, the gas spring constant K.sub.g and the mass M of
the piston 6. If the natural frequency f.sub.n of the piston 6 is
set in the low frequency area ranging from 30 to 55 Hz, which is
lower than the general natural frequency f.sub.n of the piston 6,
the linear compressor can be efficiently operated, rapidly
overcoming the load.
[0077] Especially, when the linear compressor is designed, the
mechanical spring constant K.sub.m is set relatively small, and the
ratio of the gas spring constant K.sub.g to the total spring
constant K.sub.T is set high. As a result, the operation frequency
f.sub.c of the linear motor 10 is equalized to the natural
frequency f.sub.n of the piston 6 even in the low load, so that the
linear motor 10 can be operated in the resonance state to improve
efficiency of the linear compressor. Since the linear motor 10 is
operated in the low frequency area, efficiency of the whole
refrigeration cycle can be improved.
[0078] The linear motor 10 includes an inner stator 12 formed by
stacking a plurality of laminations 12a in the circumferential
direction, and fixedly installed outside the cylinder 4 by the
frame 18, an outer stator 14 formed by stacking a plurality of
laminations 14b at the periphery of a coil wound body 14a in the
circumferential direction, and installed outside the cylinder 4 by
the frame 18 with a predetermined gap from the inner stator 12, and
a permanent magnet 16 positioned at the gap between the inner
stator 12 and the outer stator 14, and connected to the piston 6 by
the connection member 17. Here, the coil wound body 14a can be
fixedly installed outside the inner stator 12.
[0079] In the linear motor 10, when a current is applied to the
coil wound body 14a to generate an electromagnetic force, the
permanent magnet 16 is linearly reciprocated by interactions
between the electromagnetic force and the permanent magnet 16, and
the piston 6 connected to the permanent magnet 16 is linearly
reciprocated inside the cylinder 4.
[0080] When the current is applied, the linear motor 10 can vary
the compression capacity by changing the operation frequency
f.sub.c. In addition, as shown in FIG. 6, the linear motor 10 can
vary the compression capacity by changing a stroke S which is a
linear reciprocation distance of the piston 6 into first and second
strokes S1 and S2 according to the load, by adjusting the
externally-inputted current.
[0081] While linearly reciprocated inside the cylinder 4, the
piston 6 forms the compression space P. Preferably, even though the
stroke S of the piston 6 is varied, the piston 6 is linearly
reciprocated to a point in which the piston 6 is completely
compressed in the cylinder 4 not to form the compression space P,
namely, a top dead center (TDC), to prevent compression efficiency
from being reduced by the short stroke S.
[0082] Here, the linear motor 10 can increase both the operation
frequency f.sub.c and the stroke S of the piston 6 or only the
stroke S of the piston 6 according to increase of the load.
[0083] However, when the load increases in the linear compressor,
the gas spring constant K.sub.g increases to increase the elastic
force of the gas spring, and thus the stroke S of the piston 6 is
more reduced than when the load is small. Therefore, the operation
of the linear motor 10 must be controlled in consideration of the
mechanical spring constant K.sub.m and the gas spring constant
K.sub.g reflecting this fact.
[0084] At an initial stage, the piston 6 is installed to be
separated from the TDC at a predetermined interval. When the linear
compressor is designed to increase the ratio of the gas spring
constant K.sub.g to the total spring constant K.sub.T by decreasing
the mechanical spring constant K.sub.m, the initial position of the
piston 6 is set to be closer to the TDC according to decrease of
the mechanical spring constant K.sub.m, so that the piston 6 can
completely reach the TDC.
[0085] The operation of the linear compressor in accordance with
the present invention will now be explained.
[0086] First, when the current is applied to the coil wound body
14a, the permanent magnet 16 is linearly reciprocated by
interactions between the electromagnetic force generated at the
periphery of the coil wound body 14a and the permanent magnet 16,
and the piston 6 connected to the permanent magnet 16 by the
connection member 17 is linearly reciprocated inside the cylinder
4. As the piston 6 is linearly reciprocated inside the cylinder 4,
the compression space P in the cylinder 4 is changed, and the
refrigerants are sucked into the compression space P, compressed
and discharged.
[0087] In detail, when the piston 6 is transferred in the direction
of expanding the compression space P inside the cylinder 4, as
illustrated in FIG. 7A, the inside pressure of the compression
space P is reduced lower than a predetermined suction pressure, to
open the suction valve 22. The refrigerants sucked through the
inlet tube 2a are sucked into the compression space P via the
refrigerant passage 6a of the piston 6.
[0088] Thereafter, when the piston 6 is transferred in the
direction of compressing the compression space P inside the
cylinder 4, as shown in FIG. 7B, the inside pressure of the
compression space P increases in the close state of the suction
valve 22 and the discharge valve 24b, and thus the refrigerants are
compressed into high temperature high pressure gas
refrigerants.
[0089] In the case that the piston 6 is transferred in the
direction of compressing the compression space P inside the
cylinder 4 to reach the TDC, as depicted in FIG. 7C, the inside
pressure of the compression space P is higher than a predetermined
discharge pressure. Accordingly, the valve spring 24c is compressed
to open the discharge valve 24b, and the refrigerants compressed in
the compression space P are externally discharged through the loop
pipe 28 and the outlet tube 2b via the discharge space.
[0090] The linear compressor compresses the refrigerants by
repeating the above procedure. The linear compressor performs the
operation in the resonance state to improve efficiency, by
synchronizing the operation frequency f.sub.c of the linear motor
10 with the natural frequency f.sub.n of the piston 6 calculated in
consideration of the gas spring constant K.sub.g varied by the
load. In addition, the linear compressor varies the compression
capacity by controlling the stroke S of the piston 6 by adjusting
the current supplied to the linear motor 10 according to increase
of the load, thereby rapidly handling the load and remarkably
reducing power consumption.
[0091] As discussed earlier, when the mechanical spring constant is
set lower than the general mechanical spring constant, the gas
spring has greater influences than the general gas spring. In
accordance with the present invention, as the influences of the gas
spring increase, when the load increases, the natural frequency of
the piston automatically increases.
[0092] The natural frequency of the piston is remarkably varied by
the load, and the operation frequency of the linear motor is easily
synchronized with the natural frequency of the piston. As a result,
the linear motor is operated in the resonance state to maximize
efficiency and rapidly overcome the load. Furthermore, the
operation in the low frequency area reduces power consumption.
[0093] In addition, the stroke of the piston is controlled by
adjusting the external current applied to the linear motor, thereby
actively handling and rapidly overcoming the load and reducing
power consumption.
[0094] The linear compressor in which the moving magnet type linear
motor is operated and the piston connected to the linear motor is
linearly reciprocated inside the cylinder to suck, compress and
discharge the refrigerants has been explained in detail on the
basis of the preferred embodiments and accompanying drawings.
However, although the preferred embodiments of the present
invention have been described, it is understood that the present
invention should not be limited to these preferred embodiments but
various changes and modifications can be made by one skilled in the
art within the spirit and scope of the present invention as
hereinafter claimed.
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