Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2001-04-02
2002-08-20
Doerrler, William C. (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C060S520000
Reexamination Certificate
active
06434947
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is based on Japanese Patent Application no. 2000-097757, filed on Mar. 31, 2000, which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pulse tube refrigerator.
2. Description of the Background
In recent years, various structures for a pulse tube refrigerator are proposed. One is a four valve type pulse tube refrigerator is shown in FIG.
11
. In
FIG. 11
a four valve type pulse tube refrigerator
201
includes a compressor
10
, a first high pressure on-off valve
21
and a second high pressure on-off valve
23
connected with a high pressure outlet port
10
a
of the compressor
10
, a first low pressure on-off valve
22
and a second low pressure on-off valve
24
connected with a low pressure inlet port
10
b
of the compressor
10
. A cryocooler
30
includes a regenerator
31
, a cold head
32
, a pulse tube
33
and a radiator
34
arranged in series in line. A hot end
31
b
of the regenerator
31
is connected with the first high pressure on-off valve
21
and the first low pressure on-off valve
22
. A hot end
33
b
of the pulse tube
33
is connected with the second high pressure on-off valve
23
and the second low pressure on-off valve
24
. Since the high pressure operating gas flows not only from the hot end
31
b
of the regenerator
31
but also from the hot end
33
b
of the pulse tube
33
, the displacement of the operating gas in the pulse tube
33
is restricted, and the heat invasion from the hot end
33
b
of the pulse tube
33
into the cold head
32
, which increases in accordance with the increase of the displacement of the operating gas in the pulse tube
33
, can be restricted. Accordingly, a refrigeration efficiency is improved in comparison to a orifice buffer type pulse tube refrigerator.
The above four valve type pulse tube refrigerator with a high refrigerator efficiency still has a drawback: a generation of an unnecessary fluid return (DC flow). Since the hot end
33
b
of the pulse tube
33
is connected with the second high pressure on-off valve
23
and the second low pressure on-off valve
24
, and the hot end
31
b
of the regenerator
31
is connected with the first high pressure on-off valve
21
and the first low pressure on-off valve
22
, the compressor
10
and the cryocooler
30
form a closed circuit through each on-off valve. As a consequence, the operating gas circulates in the closed circuit independently of the cooling cycle. Due to the operating gas, the heat of the relativcly high temperature portion is transmitted into the cryocooler
30
, and the refrigeration efficiency is decreased.
DC flow (Direct Current flow) is of two types, according to the direction of the flow. One of the DC flows is from the high pressure outlet port
10
a
of the compressor
10
through the first high pressure on-off valve
21
into the cryocooler
30
from the regenerator
31
side, and further from the hot end
33
b
of the pulse tube
33
through the second low pressure on-off valve
24
, and returns to the low pressure inlet port
10
b
of the compressor
10
. The other DC flows is from the high pressure outlet port
10
a
of the compressor
10
through the second high pressure on-off valve
23
into the cryocooler
30
from the pulse tube
33
side, and further from the hot end
31
b
of the regenerator
31
through the first low pressure on-off valve
22
, and returns to the low pressure inlet port
10
b
of the compressor
10
. The flow direction is determined depending on the operating condition of the pulse tube refrigerator. Both flows cause a decrease of the refrigeration efficiency due to the heat conduction by the DC flow. As a consequence, even in the four valve type pulse tube refrigerator, the improvement of the refrigeration efficiency is limited.
To solve the above explained drawbacks of the DC flow, an improved four valve type pulse tube refrigerator as shown in
FIG. 12
has been proposed. A pulse tube refrigerator
202
includes the structure of the four valve type pulse tube refrigerator
201
as shown in
FIG. 11
, and also includes a fluid shield
40
connected with the pulse tube
33
(the radiator
34
) at one end and connected with the second high pressure on-off valve
23
and the second low pressure on-off valve
24
at the other end. The fluid shield
40
is provided with a cylinder member
41
and a piston
42
slidably disposed in the cylinder member
41
. The piston
42
, and a piston ring
43
attached on the outer periphery of the piston
42
, separate the interior of the cylinder member
41
into a first space
46
connected with the inner space of the pulse tube
33
and a second space
47
connected with the second high pressure on-off valve
23
and the second low pressure on-off valve
24
. According to this structure, generation of the DC flow is interrupted by the piston
42
and the piston ring
43
. Since the heat is not conducted by the DC flow, the refrigeration efficiency can be improved.
Even the above explained improved four valve type pulse tube refrigerator has a problem relative to refrigeration efficiency: an on-off valve loss. In the pulse tube refrigerator
202
shown in
FIG. 12
, before each valve is opened, a maximum pressure difference is generated in the spaces of both sides of the on-off valves. For instance, the second high pressure on-off valve
23
is positioned between the second space
47
and the high pressure space of the high pressure outlet port
10
a
side of the compressor
10
. Immediately before the second high pressure on-off valve
23
is open, the second space
47
is under a minimum pressure condition. The second low pressure on-off valve
24
is positioned between the second space
47
and the low pressure space of the low pressure inlet port
10
b
side of the compressor
10
. Immediately before the second low pressure on-off valve is opened, the second spaces
47
is under a maximum pressure condition. If each valve opens in this condition, energy loss is generated by the momentary occurrence of a no pressure differential condition. The larger the pressure difference is, the higher the energy loss becomes. Therefore, even in the improved four valve type pulse tube refrigerator, the improvement of the refrigeration efficiency is still limited.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to overcome the above drawbacks of the conventional refrigerator.
It is another object of the present invention to improve refrigeration efficiency by decreasing an on-off valve loss in an improved four valve typed pulse tube refrigerator.
In order to achieve the above and other objects, the pulse tube refrigerator according to this invention includes a compressor, a first high pressure on-off valve and a second high pressure on-off valve connected with a high pressure outlet port of the compressor, a first low pressure on-off valve and a second low pressure on-off valve connected with the low pressure inlet port of the compressor, a cryocooler comprising a regenerator, a cold head and a pulse tube arranged in series in line and connected with the first high pressure on-off valve and the first low pressure on-off valve in the regenerator, a cylinder member connected with the pulse tube at one end, and connected with the second high pressure on-off valve and the second low pressure on-off valve at the other end, a piston slidably disposed in the cylinder member and separating the interior of the cylinder into a first space connected with the inner space of the pulse tube and a second space connected with the second high pressure on-off valve and with the second low pressure on-off valve, a buffer space connected with the second space of the cylinder member and a buffer side on-off valve provided between the buffer space and the second space.
It is a preferable feature of the invention to provide the buffer space in the pulse tube refrigerator. This buffer space is connected with the second space connec
Inoue Tatsuo
Kawano Shin
Nogawa Masahumi
Zhu Shaowei
Aisin Seiki Kabushiki Kaisha
Doerrler William C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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