Automatic temperature and humidity regulation – Thermostatic – With pressure control
Reexamination Certificate
1999-07-08
2001-04-03
Tapolcai, William E. (Department: 3744)
Automatic temperature and humidity regulation
Thermostatic
With pressure control
C062S225000
Reexamination Certificate
active
06209793
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thermostatic expansion valve which is extensively but primarily used for a refrigeration cycle system such as automotive air conditioning apparatus.
Such a thermostatic expansion valve is included in a refrigeration cycle and is for expansion of a refrigerant which is contained in the refrigeration cycle. The thermostatic expansion valve in an earlier technology comprises a refrigerant passage for guiding the refrigerant in a predetermined direction, a valve seat dividing the refrigerant passage into a high-pressure chamber and a low-pressure chamber, a valve body movable in the high-pressure chamber for adjusting a flow of the refrigerant in cooperation with the valve seat, and a control arrangement for controlling movement of the valve body in response to temperature of the refrigerant.
With reference to
FIG. 4
, description will be made as a thermostatic expansion valve of the type described above. The thermostatic expansion valve is generally used for automotive or car air conditioning system employing a volume valuable compressor of a piston stroke controlling type such as a swash plate type compressor.
The thermostatic expansion valve has a casing
1
, an expansion valve unit
2
and a closure member
3
in the casing
1
. In a casing
1
, there are provided a high-pressure passage
11
which serves as the refrigerant passage directing to an evaporator
4
for a high pressure refrigerant which is discharged from a compressor discharging chamber, low-pressure passages
12
,
12
which serve as a passage directing to a compressor suction chamber for a low pressure refrigerant which is discharged from the evaporator
4
, and a valve unit insertion portion
13
which is disposed between the low-pressure passages
12
. The closure member
3
is located at an upper portion of the valve unit insertion portion
13
such that an end of the expansion valve
2
is adaptable by the use of engagement member.
The expansion valve unit
2
has a valve seat
200
a
which is located to form a high-pressure chamber
200
a
and a port
200
b
in the high-pressure passage
11
of the casing
1
, a valve casing
200
disposed at a center of the casing
1
to close a passage between the high-pressure passage
11
and the valve unit insertion portion
13
, a valve body
201
which is disposed in the high-pressure chamber
10
and contacted with, and spaced from, the valve seat
200
a
to open/close a passage directing to the evaporator
4
through the high-pressure passage
11
, the valve seat
200
a
, and the port
200
b
, a spring
203
for biasing the valve body
201
toward a valve-closing direction (an upward direction in the illustration of
FIG. 4
) through a guide member
202
, and an adjustment screw
204
for adjusting a pressing force of the spring
203
. Further, there is disposed a temperature sensing portion
205
which is disposed in the valve unit insertion portion
13
of the casing
1
such that an end portion of the temperature sensing portion
205
is mounted to the closure member
3
and which is disposed in the midst of the low-pressure passage
12
directing from the outlet portion of the evaporator
4
to the suction (or inlet) chamber of the compressor and, in addition, a diaphragm
206
which is displaced in accordance with pressure difference between the inner pressure of the temperature sensing portion
205
and the pressure of the outlet of the evaporator
4
, a transmission rod
207
which is displaceably supported to the valve casing
200
such that one end thereof is contacted with the diaphragm
206
and the other end is provided with the valve body
201
so that the valve body
201
is opened/closed in accordance with the displacement of the diaphragm
206
, and a spring
208
for urging the transmission rod
207
toward the diaphragm
206
. A combination of the temperature sensing portion
205
, the diaphragm
206
, the transmission rod
207
, and the spring
208
is referred to as the control arrangement.
The expansion valve unit
2
has a passage
200
c
at the valve casing
200
so that the diaphragm
206
receives, or effected by, the pressure from the evaporator
4
by the passage
200
c.
Within the temperature sensing portion
205
which is exposed to the refrigerant from the outlet of the evaporator
4
, a refrigerant (R134a) and an adsorbent (oil) is sealed therein, and the pressure in the temperature sensing portion
205
is set to be varied in accordance with the temperature of the refrigerant from the outlet of the evaporator
4
.
By the structure described above, a superheat degree characteristic is determined by a force due to a difference of the pressure added to both surfaces of the diaphragm
206
(that is, difference between a force for pressing the diaphragm
206
toward the valve body
201
and a force acting in the valve opening/closing direction of the valve body
201
), and a spring force of the spring
203
.
FIG. 5
shows a characteristic of temperature (° C.)-pressure (kg/cm
2
G) under a predetermined pressure condition of the inlet of the thermostatic expansion valve described above. In
FIG. 5
, the characteristic C
1
with respect to the expansion valve represents a linear line which shows that a pressure proportionally increases as the elevation of the temperature, whereas the characteristic C
2
with respect to the refrigerant (R134a) represents a curve which shows that a pressure gradually varies and increases as the elevation of the temperature. As seen from
FIG. 5
, it is prescribed that the characteristic C
1
extends across the characteristic C
2
.
Namely, in comparison between characteristic C
1
and characteristic C
2
, if temperatures are compared with reference to pressure elevation up to 2.0 kg/cm
2
G, the temperature of characteristic C
1
represents ° C. whereas the temperature of characteristic C
2
represents a temperature value slightly higher than ° C. However, if temperatures are then compared with reference to pressure elevation up to 2.7 kg/cm
2
G, the temperature of characteristic C
1
represents 10° C. whereas the temperature of characteristic C
2
represents a temperature value lower than 10° C. by &Dgr;T. Thus, a relationship of the temperatures relative to the pressure is reversed at a temperature above ° C. and around 1.2° C. to form a break-even or cross-over point. This is aimed to obtain restriction of hunting of an expansion valve especially at a low and middle temperature range and returning of the refrigerant (including an oil) to the compressor, because the compressor is in a continuous operation to a low outdoor temperature range and a circulation amount of the refrigerant is extremely reduced in this region.
In case of the thermostatic expansion valve described above, the characteristic C
1
of the expansion valve is located at a higher position than the characteristic C
2
of the refrigerant in the region of lower temperature than the cross-point. In this state, the expansion valve is always opened, and the high pressure side and the low pressure side are not closed or cut off even in the suspended state of the compressor and, accordingly, the refrigerant which has been trapped at the high pressure side due to the change of the temperature in and out of the vehicle is moved to the low pressure side through the expansion valve so that it is likely that a great amount of the refrigerant is stored in the interior of the compressor itself and in its suction passage. If, in this state, the compressor is driven, liquid compression is generated to cause serious problems such as damage and breakage in the compressor. Accordingly, it is necessary that the cases that the liquid refrigerant is delivered from the thermostatic expansion valve side to the compressor itself and/or its suction passage must be avoided.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a thermostatic expansion valve which can prevent any movement of the refrigerant from the high pressure side to the low pressure side in the low o
Baker & Botts L.L.P.
Sanden Corporation
Tapolcai William E.
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