Linear compressor drive device

Details Linear compressor drive device Linear compressor drive device

2003-04-22

2004-06-22

Mullins, Burton (Department: 2834)

Electricity: motive power systems

Linear-movement motors

C417S044110, C417S044400

Reexamination Certificate

active

06753665

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a linear compressor driving apparatus and, more particularly, to an apparatus for driving a linear compressor which generates a compressed gas in a cylinder by making a piston reciprocate with a linear motor.
BACKGROUND ART
A linear compressor utilizing a mechanical elastic member or elasticity of a gas has conventionally been known as an apparatus for generating a compressed gas.
FIG. 7
is a cross-sectional view for explaining a conventional linear compressor, and illustrates a concrete configuration of a linear compressor using a spring as an elastic member.
A linear compressor
100
has a cabinet
71
comprising a cylinder section
71
a
and a motor section
71
b
which are adjacent to each other. The cylinder section
71
a
of the cabinet
71
forms a cylindrical-shaped cylinder of the linear compressor
100
. In the cylinder section
71
a
, a piston
72
is provided slidably along a direction parallel to a center axis of the cylinder (the piston axis direction).
On the back of the piston
72
in the cabinet
71
, a piston rod
72
a
is placed in the cylinder section
71
a
and the motor section
71
b
, and an end of the piston rod
72
a
is fixed to the piston
72
. Further, a support spring (resonance spring)
81
is placed between the other end of the piston rod
72
a
and an inner wall
71
b
1
of the motor section
71
b
which is opposed to the piston rod
72
a
. The support spring
81
deforms when the piston
72
is displaced from a piston neutral position (piston reference position), and, when the support spring
81
is deformed, the support spring
81
applies a force to the piston
72
so that the piston
72
returns to the piston reference position. Further, the piston neutral position is a piston position where the support spring
81
is not deformed, and no force is applied from the support spring
81
to the piston
72
when the piston
72
is located in the piston neutral position.
Further, a magnet
73
is fixed to a portion of the piston rod
72
a
, which portion is located in the motor section
71
b
, and an electromagnet
74
comprising an outer yoke
74
a
and a stator coil
74
b
, embedded in the outer yoke
74
a
is fixed to a portion of the inner wall of the motor section
71
b
, which portion is opposed to the magnet
73
.
A linear motor
82
is constituted by the electromagnet
74
and the magnet
73
. That is, in the linear compressor
100
, the piston
72
reciprocates along its axis direction by the driving force of the linear motor
82
, i.e., the electromagnetic force generated between the electromagnet
74
and the magnet
73
, and the elasticity of the support spring
81
.
On the other hand, a compression chamber
76
, which is a closed space surrounded by a cylinder upper portion inner wall
75
, a piston compression wall
72
b
, and a cylinder peripheral wall
77
, is formed at the cylinder head side of the cabinet
71
. An end of a cooling medium inlet tube
1
a
for drawing a low-pressure cooling medium gas into the compression chamber
76
is opened at the cylinder upper portion inner wall
75
and, further, an end of a tooling medium discharge tube
1
b
for discharging a high-pressure cooling medium gas from the compression chamber
76
is opened at the cylinder upper portion inner wall
75
. An inlet valve
79
and a discharge valve
80
for preventing a back flow of the cooling medium gas are fixed to the cooling medium inlet tube la and the cooling medium discharge tube
1
b
, respectively.
In the linear compressor
100
having the above-described structure, the piston
72
reciprocates in its axis direction by an intermittent supply of a driving current from a motor driver (not shown) to the linear motor
82
, whereby drawing of the low-pressure cooling medium gas into the compression chamber
76
, compression of the cooling medium gas in the compression chamber
76
, and discharge of the compressed high-pressure cooling medium gas from the compression chamber
76
are repeatedly carried out.
By the way, in the above-mentioned linear compressor
100
, even when a current or voltage applied to the linear motor
82
is kept at a constant value, if the state of the load applied onto the linear compressor changes, the stroke of the piston
72
changes. Therefore, especially in a refrigeration compressor using the linear compressor
100
, since the thermodynamic efficiency of a refrigerating cycle is significantly improved by controlling the flow of the cooling medium according to the varying environmental temperature, a means for detecting the stroke of the piston
72
that determines the flow of cooling medium (piston stroke detection means) is needed.
Further, in the linear compressor
100
, from its structural viewpoint, there is a danger in that the front end of the piston might collide with the upper wall of the cylinder.
To be specific, the piston
72
receives not only the piston driving force of the linear motor
82
and the elasticity of the support spring
81
but also a force caused by a differential pressure between the pressure of the cooling medium gas in the compression chamber
76
and the back pressure of the piston
72
, whereby the center position of the reciprocating motion of the piston
72
(hereinafter also referred to as piston amplitude center position) is offset with respect to the piston amplitude center position when the differential pressure is zero, i.e., the piston position when the support spring is not deformed (piston neutral position). Therefore, when the internal pressure of the compression chamber
76
that acts on the piston
72
is increased/decreased due to a change of the load state, not only the stroke of the piston
72
but also the center position of the reciprocating motion of the piston
72
might change.
In order to prevent collision of the piston with the cylinder, not only the stroke detection means but also a position detection means for detecting the distance between the front end of the piston and the inner wall of the cylinder head are required. For example, in a linear compressor having no collision prevention means, the front end of the piston hits the inner wall of the cylinder head, resulting in uncomfortable noise or damage to the piston or the cylinder.
There is employed, as the above-mentioned position detection means, a sensor which can detect the degree of displacement of the piston (piston displacement) with respect to the piston reference position such as the piston neutral position, without contacting the movable members such as the piston in the linear compressor
100
. For example, a displacement meter using an eddy current system, a displacement meter using a differential transformer, and the like are employed.
However, when such sensor is used, the production cost of the linear compressor
100
is increased and, moreover, a space for mounting the sensor is needed, which leads to an increase in the size of the cabinet
71
of the linear compressor
100
. Further, since the sensor is used while being exposed to a high-temperature and high-pressure gas in the compressor
100
, there occurs a problem with then reliability of the sensor itself, in other words, a problem in that a sensor which can be reliably used under a high-temperature and high-pressure atmosphere is desired.
So, as a method for detecting the position of the piston
72
, there is proposed a method of directly measuring the linear motor driving current and voltage which are supplied to the linear compressor
100
, and deriving the position of the piston
72
on the basis of the measured values without using a position sensor placed in the linear compressor
100
(refer to Japanese Unexamined Patent Publication No. Hei. 8-508558).
Hereinafter, a description will be given of a piston position detection method used for a linear compressor, which is described in the above-mentioned literature.
FIG. 8
is a diagram illustrating an equivalent circuit of a linear motor for driving a piston of a linear compressor.
In
FIG. 8
, L indicates an equivalent inductanc

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