Abstract:
A system and method for preventing hunting of a thermal expansion valve used to control the flow of refrigerant supplied to an evaporator in a refrigeration cycle. A refrigeration apparatus is provided with a compressor, a condenser, a receiver, an expansion valve, and an evaporator connected in this order, spherically activated carbon made of phenol having pore sizes fit for molecular sizes of a working fluid is prepared; and the spherically activated carbon is provided into the expansion valve; whereby hunting, or the repeated opening and closing of the expansion valve, is prevented.

Description:
This is a continuation of application Ser. No. 09/619,476 filed Jul. 19, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a thermal expansion valve used for controlling the flow of the refrigerant and for reducing the pressure of the refrigerant being supplied to the evaporator in a refrigeration cycle. 
     DESCRIPTION OF THE RELATED ART 
     A conventionally-used thermal expansion valve is formed as shown in FIGS. 4 and 5. 
     In FIG. 4, a prismatic-shaped valve body  510  comprises a first refrigerant passage  514  to which an orifice  516  is formed, and a second refrigerant passage  519 , which are formed independently from each other. One end of the first refrigerant passage  514  is communicated to the entrance of an evaporator  515 , and the exit of the evaporator  515  is communicated through the second refrigerant passage  519 , a compressor  511 , a condenser  512 , and a receiver  513  to the other end of the first refrigerant passage  514 . A valve chamber  524  communicated to the first refrigerant passage  514  is equipped with a bias means  517 , which in the drawing is a bias spring for biasing a spherical valve member  518 . The valve member  518  is driven to contact to or separate from an orifice  516 . The valve chamber  524  is sealed by a plug  525 , and the valve member  518  is biased through a support unit  526 . A power element  520  with a diaphragm  522  is fixed to the valve body  510  in a position adjacent to the second refrigerant passage  519 . An upper chamber  520   a  formed to the power element  520  and defined by a diaphragm  522  is air-tightly sealed, and within the upper chamber is sealed a temperature-responsive working fluid. 
     A short pipe  521  extending from the upper chamber  520   a  of the power element  520  is used for the deaeration of the upper chamber  520   a  and the filling of the temperature-responsive working fluid into the chamber  520   a,  before the end portion of the pipe is sealed. The extending end of a valve drive member  523  working as a temperature sensing/transmitting member which starts at the valve member  518  and penetrates through the second refrigerant passage  519  within the valve body  510  is contacted to the diaphragm  522  inside a lower chamber  520   b  of the power element  520 . The valve drive member  523  is formed of a material having a large heat capacity, and it transmits the temperature of the refrigerant vapor flowing from the exit of the evaporator  515  through the second refrigerant passage  519 , to the temperature-responsive working fluid sealed inside the upper chamber  520   a  of the power element  520 , which generates a working gas having a pressure corresponding to the temperature being transmitted thereto. The lower chamber  520   b  is communicated through the gap around the valve drive member  523  to the second refrigerant passage  519  within the valve body  510 . 
     Accordingly, the diaphragm  522  of the power element  520  adjusts the valve opening of the valve member  518  against the orifice  516  (in other words, the quantity of flow of the liquid-phase refrigerant entering the evaporator) through the valve drive member  523  under the influence of the bias force provided by the bias means  517  of the valve member  518 , according to the difference in pressure of the working gas of the temperature-responsive working fluid inside the upper chamber  520   a  of the diaphragm and the pressure of the refrigerant vapor at the exit of the evaporator  515  within the lower chamber  520   b.    
     According to the thermal expansion valve of the prior art, a problem such as a hunting phenomenon was likely to occur, in which the valve member repeats an opening/closing movement. 
     In a prior art example aimed at preventing such hunting from occurring, an adsorbent such as an activated carbon is sealed inside a hollow valve driving member. 
     FIG. 5 is a vertical cross-sectional view showing the prior art thermal expansion valve in which an activated carbon is sealed therein. The basic composition of the valve shown in FIG. 5 is substantially the same as that shown in FIG. 4, except for the structure of a diaphragm and a valve drive member acting as a temperature sensing/pressure transmitting member. In FIG. 5, the thermal expansion valve includes a prismatic-shaped valve body  50 , and the valve body  50  comprises a port  52  through which a liquid-phase refrigerant flowing from a condenser  512  via a receiver tank  513  is introduced to a first passage  62 , a port  58  for sending out the refrigerant from the first passage  62  to an evaporator  515 , an entrance port  60  of a second passage  63  through which a gas-phase refrigerant returning from the evaporator travels, and an exit port  64  for sending out the refrigerant towards a compressor  511 . 
     The port  52  through which the liquid-phase refrigerant travels is communicated to a valve chamber  54  placed above a central axis of the valve body  50 , and the valve chamber  54  is sealed by a nut plug  130 . The valve chamber  54  is communicated through an orifice  78  to a port  58  for sending out the refrigerant to the evaporator  515 . A spherical valve member  120  is placed at the end of a narrow shaft  114  which penetrates the orifice  78 . The valve member  120  is supported by a supporting member  122 , and the supporting member  122  biases the valve member  120  towards the orifice  78  by a bias spring  124 . By moving the valve member  120  and varying the gap formed between the valve and the orifice  78 , the passage area of the refrigerant may be adjusted. The liquid-phase refrigerant expands while travelling through the orifice  78 , and flows through the first passage  62  and exits from the port  58  to be sent out to the evaporator. The gas-phase refrigerant returning from the evaporator is introduced from the port  60 , travels through the second passage  63  and exits from the port  64  to be sent out to the compressor. 
     The valve body  50  further includes a first hole  70  formed from the upper end of the body along the axis, and a power element  80  is fixed by a screw and the like to the first hole. The power element  80  comprises a housing  81  and  91  which constitute a temperature sensing unit, and a diaphragm  82  being sandwiched between and welded to the housing  81  and  91 . Further, an upper end of a temperature sensing/pressure transmitting member  100  acting as a valve drive member is fixed, together with a diaphragm support member  82 ′, to the round hole formed to the center of the diaphragm  82  by welding the whole circumferential area thereof. The diaphragm support member  82 ′ is supported by the housing  81 . 
     The housing  81 ,  91  is separated by the diaphragm  82 , thereby defining an upper chamber  83  and a lower chamber  85 . A temperature-responsive working fluid is filled inside the upper chamber  83  and a hollow portion  84 . After filling the working fluid, the upper chamber is sealed by a short pipe  21 . Further, a plug body welded onto the housing  91  may be utilized instead of the short pipe  21 . 
     The temperature sensing/pressure transmitting member  100  is formed of a hollow pipe-like member exposed to the second passage  63 , and to the interior of which is stored an activated carbon  40 . The peak portion of the temperature sensing/pressure transmitting member  100  is communicated to the upper chamber  83 , and a pressure space  83   a  is defined by the upper chamber  83  and the hollow portion  84  of the temperature sensing/pressure transmitting member  100 . The pipe-like temperature sensing/pressure transmitting member  100  penetrates through a second hole  72  formed on the axis line of the valve body  50 , and is inserted to a third hole  74 . A gap exists between the second hole  72  and the temperature sensing/pressure transmitting member  100 , through which the refrigerant inside the passage  63  is introduced to the lower chamber  85  of the diaphragm. 
     The temperature sensing/pressure transmitting member  100  is inserted slidably to the third hole  74 , and the end portion of the member  100  is connected to one end of a shaft  114 . The shaft  114  is inserted slidably to a fourth hole  76  formed to the valve body  50 , and the end portion of the shaft  114  is connected to a valve member  120 . 
     According to the structure, an activated carbon is utilized, so that the time needed to achieve the temperature-pressure equilibrium between the activated carbon and the temperature-responsive working fluid contributes to stabilize the control characteristics of the refrigeration cycle. 
     SUMMARY OF THE INVENTION 
     However, the activated carbon used as the adsorbent in the prior art expansion valves were crushed carbon mainly consisting of palm or coal. The pore sizes of such activated carbon for adsorbing the working fluid are not fixed, so the adsorption quantity differs according to each carbon used. As a result, the temperature-pressure characteristics of each thermal expansion valve may be varied depending on the activated carbon used, which leads to low reliability of the valve. 
     Therefore, the present invention aims at providing a thermal expansion valve having a constant temperature-pressure characteristics, and which is capable of delaying its response property so as to stabilize the control of the valve. Actually, the present invention aims at providing a thermal expansion valve capable of being stably controlled, by simply changing the adsorbent to be mounted inside the thermal expansion valve, without changing the design of the conventional valve. 
     In order to achieve the above-mentioned objects, the thermal expansion valve according to the present invention includes a temperature sensing member and a working fluid sealed inside said temperature sensing member, the pressure of said working fluid varying according to temperature, wherein an adsorbent having pore sizes fit for the molecular sizes of said working fluid is placed inside said temperature sensing member. 
     Moreover, the present invention relates to a thermal expansion valve including a refrigerant passage formed to the interior of said thermal expansion valve which extends from an evaporator to a compressor constituting a refrigerant cycle, and a temperature sensing/pressure transmitting member formed within said passage having a temperature sensing function and comprising a hollow portion formed therein, said thermal expansion valve controlling the opening of a valve according to the temperature of a refrigerant detected by said temperature sensing/pressure transmitting member, wherein a working fluid which varies its pressure according to said temperature is sealed inside said hollow portion, and an adsorbent having pore sizes fit for the molecular sizes of said working fluid is placed inside said hollow portion. 
     Moreover, the thermal expansion valve of the present invention includes a temperature sensing pipe for sensing the temperature of a refrigerant at the exit of an evaporator constituting a refrigeration cycle, said thermal expansion valve controlling the opening of a valve according to said refrigerant temperature sensed by said temperature sensing pipe, wherein a working fluid which varies its pressure according to said temperature is sealed inside said temperature sensing pipe, and an adsorbent having a pore size fit for the molecular size of said working fluid is placed inside said hollow portion. 
     Further, the thermal expansion valve of the present invention includes a refrigerant passage formed to the interior of said thermal expansion valve which extends from an evaporator to a compressor, and a temperature sensing/pressure transmitting member formed within said passage having a temperature sensing function and comprising a hollow portion formed therein, wherein the end of said hollow portion of the temperature sensing/pressure transmitting member is fixed to the center opening of a diaphragm constituting a power element for driving said member, an upper pressure chamber formed by said diaphragm to the interior of said power element and said hollow portion being connected to form a sealed space to which a working fluid is sealed, and wherein an adsorbent having pore sizes fit for the molecular sizes of said working fluid is placed inside said hollow portion. 
     Even further, the thermal expansion valve of the present invention comprises a power element having a diaphragm being displaced according to the change in the pressure transmitted from a heat sensing pipe to which is sealed a working fluid which converts temperature into pressure, and a working shaft contacting said diaphragm at one end and displacing a valve member at the other end, wherein an adsorbent having pore sizes fit for the molecular sizes of said working fluid is placed inside said temperature sensing pipe. 
     According to the actual embodiment of the thermal expansion valve of the present invention, the adsorbent placed inside the valve is an activated carbon made of phenol. 
     Moreover, according to another preferred embodiment of the thermal expansion valve of the present invention, the adsorbent is an activated carbon having a pore size distribution with a pore radius peak in the range of 1.7 to 5.0 times the molecular size of said working fluid. 
     The thermal expansion valve being formed as above includes an adsorbent placed inside the temperature sensing member having pore sizes accommodated to the molecular sizes of the working fluid, which is advantageous in that the adsorption quantity of the activated carbon is constant, and the control of the valve may be stabilized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical cross-sectional view showing one embodiment of the thermal expansion valve according to the present invention; 
     FIG. 2 is a chart showing the characteristics of an activated carbon used in the thermal expansion valve of FIG. 1; 
     FIG. 3 is a vertical cross-sectional view showing another embodiment of the thermal expansion valve according to the present invention; 
     FIG. 4 is a vertical cross-sectional view showing the thermal expansion valve of the prior art; and 
     FIG. 5 is a vertical cross-sectional view showing another thermal expansion valve of the prior art. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     One preferred embodiment of the thermal expansion valve according to the present invention will now be explained with reference to the drawings. 
     FIG. 1 is a vertical cross-sectional view showing one embodiment of the thermal expansion valve according to the invention. The thermal expansion valve of the present embodiment differs from the prior art valve shown in FIG. 4 only in the point that the adsorbent placed inside a hollow portion of a hollow valve driving member in the present embodiment differs from that of the prior art. Other structures and members of the present valve are the same as those of the prior art, so the common members are provided with the same reference numbers, and their detailed explanations are omitted. 
     In FIG. 1, reference number  40 ′ shows an adsorbent placed inside a hollow pipe-like member constituting a temperature sensing/pressure transmitting member  100  acting as a valve drive member. According to the present embodiment, the adsorbent  40 ′ is a spherical activated carbon made of phenol. In this embodiment, KURARAY COAL (manufactured by Kuraray Chemical Co., Ltd.) is used. The characteristic curve showing the pore radius sizes (Å) and the pore volume (ml/g) of the spherical activated carbon made of phenol is shown by the continuous line of FIG.  2 . In the characteristic curve, grade 10, grade 15, grade 20 and grade 25 correspond to activated carbons made of phenol (KURARAY COAL) having minimum pore radiuses of 9 Å, 12 Å, 16 Å and 20 Å, respectively, each has a sharp downward peak at the minimum pore radius as shown in FIG.  2 . In each of the pore radius groups, the pore volume is regular. In other words, the pore volume is roughly fixed without individual differences between each activated carbon, and therefore, the adsorption quantity of the carbon is also fixed. In contrast, according to an activated carbon made of palm, the pore volumes are not fixed, and therefore, the adsorption quantity is also inconstant. 
     According to the present embodiment, an activated carbon comprising many pores having sizes corresponding to the molecular sizes of a working fluid is used to adsorb the fluid. According to the embodiment, the adsorption quantity of the carbon is fixed, which leads to stabilized control performance. The activated carbon used in the embodiment comprises pore radiuses which are 1.7-5.0 times the sizes of the molecular of the working fluid, and forms a pore size distribution with a sharp peak as shown in FIG.  2 . Accordingly, by using the activated carbon of the present embodiment, a constant adsorption may be performed without any noticeable difference of performance between individual carbons, which leads to realizing a stable valve control. According to one example, a stable control is realized by utilizing a spherical activated carbon made of phenol and classified as group  15 , that is, with a pore radius of 12 Å, to adsorb a refrigerant R23 which is trifluoromethane (CHF 3 ) acting as the working fluid and having molecular sizes of 4.1-5.0 Å. 
     The present invention may not only be applied to the thermal expansion valve shown in FIG. 1, but may also be applied to other conventional thermal expansion valves, for example, in which a working fluid sealed inside a temperature sensing pipe varies its pressure according to the temperature. FIG. 3 is a vertical cross-sectional view showing an embodiment of the present invention being applied to such thermal expansion valve. The valve of FIG. 3 comprises a valve unit  300  for decompressing a high-pressure liquid refrigerant, and a power element  320  for controlling the valve opening of the valve unit  300 . 
     The power element  320  includes a diaphragm  126  sandwiched by and welded to the outer peripheral rim of an upper lid  322  and a lower support  124 . The upper lid  322  and the diaphragm  126  constitute a first pressure chamber on the upper portion of the diaphragm. The first pressure chamber is communicated via a conduit  150  to the inside of a temperature sensing pipe  152  acting as a temperature sensor. The temperature sensing pipe  152  is mounted to an exit portion of an evaporator, and senses the temperature of the refrigerant close to the exit of the evaporator. The sensed temperature is converted to a pressure P 1 , which is applied to the first pressure chamber of the power element. When increased, the pressure P 1  presses the diaphragm  126  downwards, and provides force in the direction opening the valve  106 . 
     On the other hand, a refrigerant pressure P 2  at the exit of the evaporator is directly conducted from a pipe mounting portion  162  through a conduit  160  to a second pressure chamber formed to the lower portion of the diaphragm  126 . The pressure P 2  is applied to the second pressure chamber  140  formed to the lower portion of the diaphragm  126 , and provides force in the direction closing the valve  106  together with the spring force of a bias spring  104 . In other words, when the degree of superheat (the difference between the refrigerant temperature at the exit of the evaporator and the evaporation temperature: which may be taken out as force by P1-P2) is large, the valve is opened wider, and when the degree of superheat is small, the opening of the valve is narrowed. As explained, the amount of refrigerant flowing into the evaporator is controlled. 
     A valve unit  300  includes a valve body  102  comprising a high-pressure refrigerant entrance  107 , a low-pressure refrigerant exit  109 , and a pressure equalizing hole  103  for connecting a pressure equalizing conduit  132 . A stopper member (displacement limiting member)  130  for limiting the displacement of the diaphragm  126  to the lower direction, a working shaft  110  for transmitting the displacement of the diaphragm  126  to the lower direction, restricting members  116  and  118  mounted to the working shaft  110  so as to provide a certain restriction to the movement of the shaft, a valve member  106  (shown as a ball valve in the drawing) positioned so as to contact to or separate from a valve seat, a bias spring  104  and an adjuster  108  for adjusting the biasing force of the spring  104  are assembled to the valve body  102 . 
     According to the thermal expansion valve formed as above, an adsorbent  40 ″ is placed inside the temperature sensing pipe  152 . The adsorbent  40 ′, is a spherical activated carbon made of phenol, which is similar to the activated carbon  40 ′ used in the expansion valve of FIG. 1, and which has pore radiuses that are 1.7-5.0 times the molecular sizes of the temperature-responsive working fluid, forming a pore radius distribution with a sharp peak. 
     By placing the activated carbon  40 ″ inside the temperature sensing pipe  152 , the valve may be controlled stably, with a constant temperature-pressure characteristics. 
     As explained, the thermal expansion valve according to the present invention utilizes an activated carbon having pores with sizes corresponding to the molecular sizes of the temperature-responsive working fluid as the adsorbent, such activated carbon advantageously having very little individual differences. Since the adsorption quantity of such adsorbent is fixed, a thermal expansion valve having a high reliability with a stable control performance may be provided. 
     Moreover, since there is no major change in design from the conventional thermal expansion valve, the present thermal expansion valve may be manufactured at a relatively low cost. 
     The contents of Japanese patent application No. 11-204979 filed Jul. 19, 1999 is incorporated herein by reference in its entirety.