Abstract:
In a thermostatic expansion valve having a refrigerant passage ( 11 ) for guiding a refrigerant in a predetermined direction, a seat member ( 209 ) is placed in the refrigerant passage to divide the refrigerant passage into a high-pressure chamber ( 10 ) and a low-pressure chamber ( 14 ). The seat member is movable in the predetermined direction and provided with a valve seat ( 200   a ). An urging arrangement ( 210 ) urges the seat member towards the high-pressure chamber. In the high-pressure chamber, a valve body ( 201 ) is movable for adjusting a flow of the refrigerant in cooperation with the valve seat. A control arrangement ( 205, 206, 207, 208 ) controls movement of the valve body in response to temperature of the refrigerant.

Description:
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 ΔT. 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 outdoor temperature region while a temperature-pressure characteristics are maintained. 
     Other objects of the present invention will become clear as the description proceeds. 
     According to the present invention, there is provided a thermostatic expansion valve included in a refrigeration cycle for expansion of a refrigerant which is contained in the refrigeration cycle. The thermostatic expansion valve 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 control means for controlling movement of the valve body in response to temperature of the refrigerant. The thermostatic expansion valve further comprises a seat member placed between the high-pressure and the low-pressure chambers to be movable in the predetermined direction. The seat member is provided with the valve seat. The thermostatic expansion valve further comprises urging means connected to the seat member for urging the seat member towards the high-pressure chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a sectional elevation of a thermostatic expansion valve according to an embodiment of the present invention, showing a basic structure thereof; 
     FIG. 2 is an enlarged sectional view of a part of a principal portion of the thermostatic expansion valve shown in FIG. 1; 
     FIG. 3 is an enlarged sectional view of a part of a thermostatic expansion valve according to another embodiment of the invention; 
     FIG. 4 is a sectional elevation of an example of the conventional thermostatic expansion valve in an earlier technology, showing a basic structure; and 
     FIG. 5 is a graph showing temperature-pressure characteristics under a predetermined inlet pressure condition of the thermostatic expansion valve shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, the description will be made as regards a thermostatic expansion valve according to an embodiment of the present invention. Similar parts are designated by like reference numerals. 
     The thermostatic expansion valve is included in a refrigeration cycle  5  and is for expansion of a refrigerant which is contained in the refrigeration cycle  5 . The thermostatic expansion valve is suitable for air conditioning system in automobiles. 
     In the expansion valve unit  2 , a low-pressure chamber  14  is separately confined from the high-pressure chamber  10 . The low-pressure and the high-pressure chambers  14  and  10  are communicated with the high-pressure passage  11 . A combination of the low-pressure and the high-pressure chambers  14  and  10  is referred to as a refrigerant passage which is for guiding the refrigerant in a predetermined direction. 
     The valve casing  200  is disposed at a central portion of the casing  1  and is for closing or cutting off a passage between the high-pressure passage  11  and the valve unit insertion portion  13 . The valve body  201  is disposed in the high-pressure chamber  10  and is for opening/closing the high-pressure passage directing to the evaporator  4 . The spring  203  is for urging the valve body  201  in a valve-closing direction through the guide  202 . The adjustment screw  204  is for adjusting spring force of the spring  203 . 
     The temperature sensing portion  205  is disposed in the low-pressure passage  12  directing from the outlet of the evaporator  4  to the compressor suction chamber. An upper end of the temperature sensing portion  205  is mounted to the closure member  3  in the valve unit insertion portion  13 . The diaphragm  206  is displaceable in accordance with difference between the pressure in the temperature sensing portion  205  and the pressure of the outlet of the evaporator  4 . The transmission rod  207  is movably supported by the valve casing  200  and is for opening and closing the valve body  201  in accordance with the displacement of the diaphragm  206 . The transmission rod  207  is contacted at its end to the diaphragm  206  and fixed at its other end to the valve body  201 . The spring  208  is for urging the transmission rod  207  against the diaphragm  206 . 
     The expansion valve unit  2  of the thermostatic expansion valve further comprises a seat member  209  placed between the high-pressure and the low-pressure chambers  10  and  14  and a compression spring  210  interposed between the valve casing  200  and the seat member  209 . The seat member  209  is movable in the predetermined direction and is provided with the valve seat  200   a  facing the valve body  201  and surrounding the port  200   b . Here, the seat member  209  is in contact with the valve member  201  when the pressure difference between the high-pressure chamber  10  and the low-pressure chamber  14  is below a predetermined value which is determined in relation to spring force of the compression spring  210 . So that, the seat member  209  serves to prevent the high pressure refrigerant from flowing into the evaporator  4 . 
     The compression spring  210  is disposed in the low-pressure chamber  14  and is for urging the seat member towards the high-pressure chamber  10  or the valve body  201 . The compression spring  210  is referred to as an urging arrangement. 
     With reference to FIG. 2, the description will be proceeded. The expansion valve unit  2  of the thermostatic expansion valve further comprises a stopper  200   e  for preventing the seat member  209  from movement thereof towards the low-pressure chamber  14  in the predetermined direction. Therefore, the seat member  209  is kept in contact with the stopper  200   e  when the pressure difference between the high-pressure chamber  10  and the low-pressure chamber  14  is above the predetermined value. 
     Incidentally, a gap between the seat member  209  and the valve casing  200  is formed minimum to prevent any leakage of the refrigerant. A relationship among a pressing force (f 1 ) of the spring  203 , a pressing force (f 2 ) of the spring  210 , and a pressing force (f 3 ) of the spring  208  is determined as f 1 &gt;f 2 &gt;f 3 . 
     In the structure described above, a refrigerant (R134a) and an adsorbent are sealed in the temperature sensing portion  205  which is exposed to the refrigerant discharged from the outlet of the evaporator  4 , and a pressure in the temperature sensing portion  205  varies in accordance with the temperature of the refrigerant discharged from the outlet of the evaporator  4 . In this case, the seat member  209  is displaced in the up-down direction on the sheet-surface of FIG. 1 of the drawing by a magnitude of the pressure difference (Δp) between the high-pressure chamber  10  and the low-pressure chamber  14  and a spring force of the spring  210 . 
     In other words, if a force by the pressure difference (Δp) is larger than the spring force of the spring force  210 , the seat member  209  is moved upward on the sheet-surface of FIG.  1  and then contacted with the stopper  200   e  of the valve casing  200 . In this state, the seat member  209  is integral with the valve casing  200  and, therefore, the same functions (a characteristic of superheat degree) as in the conventional expansion valve can be obtained. Accordingly, in the state described above, a characteristic of superheat degree is determined primarily by a force of the pressure difference relative to the both surfaces of the diaphragm  206  (that is, a difference between a force urging the diaphragm  206  against the valve body  201  and a force affecting in the valve-closing direction of the valve body  201 ), and a spring force of the spring  203 . 
     If, on the other hand, the pressure difference (Δp) is smaller than the spring force of the spring  210 , the seat member  209  is displaced downward on the sheet-surface of FIG. 1 while the valve body  201  is opened, and then contacted with the valve body  201  as shown in FIG.  2 . Thus, the high-pressure passage  11  directing to the evaporator  4  is closed. 
     The pressure difference (Δp) becomes smaller as the outdoor temperature becomes lower and, therefore, if the seat member  209  is set to operate by a very small difference of pressure, the both high pressure side and the low pressure side are cut off when the outdoor temperature is low. A displacement of the refrigerant from the high-pressure side to the low pressure side in the range of low outdoor temperature while a temperature-pressure characteristic is maintained. 
     With reference to FIG. 3, the description will be made as regards a thermostatic expansion valve according to another embodiment of the present invention. Similar parts are designated by like reference numerals. 
     In the thermostatic expansion valve, the seat member  209  has at least one orifice  200   f  which extends in the predetermined direction to communicate the high-pressure chamber  10  with the low-pressure chamber  14  at an outside of the valve seat  200   a . The orifice  200   f  is referred to as a passage. The seat member  209  is in contact with the valve body  201  when the pressure difference between the high-pressure chamber and the low-pressure chamber is below the predetermined value. Even in this condition, a very small amount of the high pressure refrigerant is flown from the high-pressure chamber  10  to the low-pressure chamber  14  through the orifice  200   f  to limit the flow the high pressure refrigerant into the evaporator  4 . 
     In other words, though the high-pressure passage  11  directing to the evaporator  4  is not completely cut off due to the existence of the orifice  200   f  while the seat member  209  is in contact with the valve body  201 . However, an opening area of the orifice  200   f  is satisfactorily small enough relative to the opening area of the port  200   b  and, therefore, a flow of the refrigerant from the high pressure side to the low pressure side is much more restricted than that of the structure shown in FIG.  4 . 
     While the present invention has thus far been described in connection with a few embodiments thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners. For example, a groove may be made instead of the orifice on the seat member to communicate the high-pressure chamber  10  with the low-pressure chamber  14  at the outside of the valve seat.