Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
1999-07-07
2001-11-06
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S201000
Reexamination Certificate
active
06311506
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a control unit for a refrigerating machine and, more particularly, to a control unit capable of securing refrigerating capability more than required.
DESCRIPTION OF THE PRIOR ART
FIG. 8
shows the whole construction of a temperature control system that acts as a refrigerating machine and incorporates a chiller
10
. This temperature control system chiefly consists of the chiller
10
, a controlled object
1
whose temperature is to be controlled, and a circulatory fluid line
3
between the chiller
10
and the controlled object
1
. For example, the controlled object
1
is a vacuum chamber that surface-processes or otherwise processes semiconductor wafers under a desired temperature.
In the chiller
10
described above, a compressor
12
, a condenser
13
, an expansion valve
14
, and an evaporator
11
are connected in series via a conduit
15
. A refrigerant
16
is passed through this conduit
15
to carry out refrigeration cycles. A brine (anti-freezing fluid)
17
circulating through the circulatory fluid line
3
exchanges heat with the refrigerant
16
, thus cooling the brine
17
. Thus, it is maintained at a preset temperature. As a result, the controlled object
1
is controlled to a target temperature.
FIG. 11
particularly shows the line arrangement in the chiller
10
.
This chiller
10
has a hot gas bypass line
18
that provides a bypass line for gas delivered from the compressor
12
and sends it to the evaporator
11
.
A pressure regulating valve
19
is mounted in the hot gas bypass line
18
to open this line
18
when the vapor pressure of the refrigerant
16
in the evaporator
11
becomes equal to or less than a given pressure, thus permitting passage of the hot gas. When the vapor pressure of the refrigerant
16
in the evaporator
11
becomes higher than the given pressure, the regulating valve
19
closes the hot gas bypass line
18
, thus cutting off the hot gas.
The pressure regulating valve
19
is installed to maintain the vapor pressure higher than the preset pressure, for the following reason. If the vapor pressure becomes equal to or lower than the preset pressure (atmospheric pressure), the refrigerant
16
does not sufficiently vaporize within the evaporator
11
and returns to the compressor
12
while maintained in a liquid state. This is so-called the phenomenon of the fluid back and may damage the compressor
12
.
The pressure regulating valve
19
operates according to the difference between the vapor pressure of the entering refrigerant
16
and the force of a spring.
Because of the mechanical structure of the prior art pressure regulating valve
19
, the valve operates according to the difference between the vapor pressure of the entering refrigerant
16
and a spring force, even if the vapor pressure becomes higher than the given pressure, the valve
19
is slightly open, and the hot gas is bypassed to the evaporator
11
via the hot gas bypass line
18
.
If the hot gas is unnecessarily bypassed to the evaporator
11
, the refrigerating capability becomes deteriorated. As the preset temperature of the brine
17
(i.e., the target temperature of the controlled object
1
) becomes lower, the refrigerating capability becomes lower. Therefore, if the hot gas is undesirably bypassed where the preset temperature of the brine
17
is low, the refrigerating capability drops conspicuously.
The chiller
10
according to the present invention is required to exhibit a refrigerating power of more than 1 kW when the temperature of the brine
17
is −20° C., and to exhibit a refrigerating power of 2 kW or more where the temperature of the brine
17
is 0° C.
FIG. 10
shows the relation between the brine temperature and the cooling power where the hot gas is not bypassed (indicated by the broken line) and bypassed (indicated by the solid line). As can be seen from the graph of
FIG. 10
, where the brine
17
has a high temperature of 0° C., a refrigerating power of 2 kW or more is secured, whether the hot gas is bypassed or not. Thus, the required performance is satisfied.
However, as the temperature of the brine
17
becomes lower, the refrigerating power drops conspicuously where the hot gas is bypassed. Where the temperature of the brine
17
is −20° C., the power is much lower than the required power of 1 kW. Consequently, it is impossible to meet the required performance.
If the compressor
10
is replaced by one having a sufficiently large capacity, the refrigerating performance may be enhanced, and the required refrigerating power may be secured even if the hot gas is bypassed.
However, increasing the capacity of the compressor
10
to a sufficiently large value will incur an increase in cost. Furthermore, the equipment will become bulky, which in turn will occupy more space. Moreover, the electric power consumption will increase. Accordingly, increasing the capacity of the compressor
10
is not acceptable.
SUMMARY OF THE INVENTION
In view of the foregoing circumstances, the present invention has been made. It is a first object of the present invention to provide a control unit capable of imparting required refrigerating capability to a refrigerating machine without incurring an increase in cost, size, or electric power consumption.
The prior art pressure regulating valve
19
has intrinsic problems. That is, if the vapor pressure is higher than a given pressure, the valve
19
is slightly open, because the valve mechanically operates in response to the vapor pressure as mentioned above. If the hot gas is undesirably bypassed by the opening of the valve
19
, the refrigerating capability will be deteriorated. Especially, if the vapor pressure is low, the amount of refrigerant circulated becomes small and so the refrigerating power decreases conspicuously.
It is a second object of the invention to provide a control unit that causes pressure regulating valve
19
of a refrigerating machine to operate more precisely in response to vapor pressure than that of the prior art, thus preventing the refrigerating capability from deteriorating.
A first embodiment of the present invention achieves the first object described above and provides a control unit for use with a refrigerating machine in which a compressor, a condenser, and an evaporator are connected in series via a conduit. The refrigerating machine further includes a hot gas bypass line for bypassing hot gas discharged from the compressor. A pressure regulating valve is installed in the hot gas bypass line to open the hot gas bypass line, if the vapor pressure of a refrigerant inside the evaporator becomes equal to or lower than a given pressure, thus passing the hot gas. If the vapor pressure of the refrigerant in the evaporator becomes higher than the given pressure, the pressure regulating valve closes the hot gas bypass line to cut off the hot gas. The refrigerant exchanges heat with a brine passing through the evaporator to maintain the brine at a preset temperature.
A temperature-responsive valve is mounted in the hot gas bypass line. If the temperature of the brine is equal to or higher than the given temperature, the temperature-responsive valve opens the hot gas bypass line. If the temperature of the brine is lower than the given temperature, the temperature-responsive valve closes the hot gas bypass line.
In the first embodiment of the invention described above, as shown in
FIG. 1
, a temperature-responsive valve
20
is mounted in a hot gas bypass line
18
. If the preset temperature Tr of the brine
17
rises equal to or higher than a given temperature (0° C.), the valve
20
opens the hot gas bypass line
18
. If the preset temperature Tr of the brine
17
is lower than the given temperature (0° C.), the valve
20
closes the hot gas bypass line
18
.
Therefore, when the preset temperature of the brine is equal to or higher than the given temperature of 0° C., the hot gas bypass line
18
is opened. The pressure regulating valve
19
operates and bypasses the hot gas. At this time the temperature of the brine a
Hatanaka Tsutomu
Kamei Toshiyuki
Takahashi Norio
Komatsu Ltd.
Tanner Harry B.
Vardnell & Vardnell, PLLC
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