Expansion valve

Abstract: The object of the present invention is to prevent a hunting phenomenon in an expansion valve in an air conditioner. The aluminum heat sensing shaft 200 of the valve driving shaft equipped in the expansion valve 10 has a hole 210 with a bottom reaching the heat sensing portion. The hole makes the heat transfer area of the heat sensing shaft small, and even when a change of heat load of the evaporator occurs, the response character of the expansion valve 10 is insensitive. Thus, unwanted hunting phenomenon in the refrigeration system is prevented.

Description: Technical Field of the Invention The present invention relates to expansion valves and, more particularly, to expansion valves used for refrigerant utilized in refrigeration cycles of air conditioner, refrigeration device and the like Background of the Invention In the prior art, these kinds of expansion valves were used in refrigeration cycles of air conditioners in automobiles and the like. FIG. 5 shows a prior art expansion valve in cross section together with an explanatory view of the refrigeration cycle. The expansion valve 10 includes a valve body 30 formed of prismatic-shaped aluminum comprising a refrigerant duct 11 of the refrigeration cycle having a first path 32 and a second path 34, the one path placed above the other with a distance inbetween. The first path 32 is for a liquid-phase refrigerant passing through a refrigerant exit of a condenser 5 through a receiver 5 to a refrigerant entrance of an evaporator 8. The second path 34 is for a gas phase refrigerant passing through the refrigerant exit of the evaporator 8 toward a refrigerant entrance of a compressor 4. An orifice 32a for the adiabatic expansion of the liquid refrigerant supplied from the refrigerant exit of the receiver 6 is formed on the first path 32. The orifice 32a is positioned on the vertical center line taken along the longitudinal axis of the valve body 30. A valve seat is formed on the entrance of the orifice 32a, and a valve means 32b supported by a valve member 32c is included thereto. The valve means 32b and the valve member 32c are welded and fixed together. The valve member 32c is fixed onto the valve means 32b and is also forced by a spring means 32d, for example, a compression coil spring. The first path 32 where the liquid refrigerant from receiver 6 is introduced is a path of the liquid refrigerant, and is equipped with an entrance port 321 and a valve room 35 connected thereto. The valve room 35 is a room with a floor portion formed on the same axis of the center line of the orifice 32a, and is sealed by a plug 39. Further, in order to supply drive force to the valve body 32b according to an exit temperature of the evaporator 8 a small hole 37 and a large hole 38 having a greater diameter than the hole 37 is formed on said center line axis perforating through the second path 34. A screw hole 361 for fixing a power element member 36 working as a heat sensor is formed on the upper end of the valve body 30. The power element member 36 is comprised of a stainless steel diaphragm 36a, an upper cover 36d and a lower cover 36h each defining an upper pressure activate chamber 36b and a lower pressure activate chamber 36c forming two sealed chambers above and under the diaphragm 36a, and a tube 36i for enclosing a predetermined refrigerant working as a diaphragm driver liquid into said upper pressure activate chamber, wherein said lower pressure activate chamber 36c is connected to said second path 34 via a pressure hole 36e formed to have the same center as the center line axis of the orifice 32a. A refrigerant vapor from the evaporator 8 is flown through the second path 34. The second path 34 is a path for gas phase refrigerant, and the pressure of said refrigerant vapor is added to said lower pressure activate chamber 36c via the pressure hole 36e. Further, inside the lower pressure activate chamber 36c is a valve member driving shaft comprising a heat sensing shaft 36f and an activating shaft 37f. The heat sensing shaft 30f made of aluminum is movably positioned through the second path 34 inside the large hole 38 and contacting the diaphragm 36a so as to transmit the refrigerant exit temperature of the evaporator 8 to the lower pressure activate chamber 36c, and to provide driving force in response to the displacement of the diaphragm 36a according to the pressure difference between the upper pressure activate chamber 36b and the lower pressure activate chamber 36c by moving inside the large hole 38. The activating shaft 37f made of stainless steel is movably positioned inside the small hole 37 and provides pressure to the valve means 32b against the spring force of the spring means 32d according to the displacement of the heat sensing shaft 36f. The heat sensing shaft 36f is equipped with a sealing member, for example an O ring 36g, so as to provide seal between the first path 32 and the second path 34. The heat sensing shaft 36f and the activating shaft 37f are contacting one another, and the activating shaft 37f is in contact with the valve member 32b. Therefore, in the pressure hole 36e, a valve member driving shaft extending from the lower surface of the diaphragm 36a to the orifice 32a of the first path 32 is positioned having the same center axis as the pressure hole. A known diaphragm driving liquid is filled inside the upper pressure activating chamber 36b placed above a pressure activate housing 36d, and the heat of the refrigerant vapor from the refrigerant exit of the evaporator 8 flowing through the second path 34 via the diaphragm 36a is transmitted to the diaphragm driving liquid. The diaphragm driving liquid inside the upper pressure activate chamber 36b adds pressure to the upper surface of the diaphragm 36a by turning into gas in correspondence to said heat transmitted thereto. The diaphragm 36a is displaced in the upper and lower direction according to the difference between the pressure of the diaphragm driving gas added to the upper surface thereto and the pressure added to the lower surface thereto. The displacement of the center portion of the diaphragm 36a to the upper and lower direction is transmitted to the valve member 32b via the valve member driving shaft and moves the valve member 32b close to or away from the valve seat of the orifice 32a. As a result. the refrigerant flow rate is controlled. That is, the gas phase refrigerant temperature of the exit side of the evaporator 8 is transmitted to the upper pressure activate chamber 36b, and according to said temperature, the pressure inside the upper pressure activate chamber 36b changes, and the exit temperature of the evaporator 8 rises. When the heat load of the evaporator rises, the pressure inside the upper pressure activate chamber 36b rises. and accordingly, the heat sensing shaft 36f or valve member driving shaft is moved to the downward direction and pushes down the valve means 32b via the activating shaft 37, resulting in a wider opening of the orifice 32a. This increases the supply rate of the refrigerant to the evaporator, and lowers the temperature of the evaporator 8. In reverse, when the exit temperature of the evaporator 8 decreases and the heat load of the evaporator decreases, the valve means 32b is driven in the opposite direction, resulting in a smaller opening of the orifice 32a. The supply rate of the refrigerant to the evaporator decreases, and the temperature of the evaporator 8 rises. In a refrigeration system using such expansion valve, a so-called hunting phenomenon wherein over supply and under supply of the refrigerant to the evaporator repeats in a short term is known. This happens when the expansion valve is influenced by the environment temperature, and. for example, the non-evaporated liquid refrigerant is adhered to the heat sensing shaft of the expansion valve. This is sensed as a temperature change, and the change of heat load of the evaporator occurs, resulting to an oversensitive valve movement. When such hunting phenomenon occurs, it not only decreases the ability of the refrigeration system as a whole, but also affects the compressor by the return of liquid to said compressor. The present applicant suggested an expansion valve shown in FIG 6 as Japanese Patent Application No H7-325357. This expansion valve 10 includes a resin 101 having low heat transfer rate being inserted to and contacting the heat sensing shaft 100 forming an aluminum valve member driving shaft. A PPS resin which will not be affected by the refrigerant and the like is used as the low heat transfer rate resin 101. Said resin 101 is not only mounted on the portion of the heat sensing shaft 100 being exposed to the second path 34 where the gas phase refrigerant passes, but also on the heat sensing portion existing inside the lower pressure activate chamber 36c. The thickness of the resin 101 can be about 1mm. Further, it should be understood that the resin 101 could only be mounted on the exposed portion of the heat sensing shaft 100 to the second path 34. By mounting such resin 101, when the non-evaporated refrigerant from the evaporator flows through the second path 34, and adheres to the heat sensing shaft of the expansion valve, the heat transfer rate of the resin 101 is low, so the change in heat load of the evaporator or increase of the heat load of the evaporator occurs, the response ability of the expansion valve 10 is low, and the hunting phenomenon of the refrigeration system is avoided. The problem of the above-explained expansion valve is that it is expensive to produce such valve because there is a need to insert the resin 101 to the aluminum heat sensing shaft 100 in the manufacturing process. A structure similar to that of Fig.5 is known from US-A-5 303 864 wherein the part of the heat sensing shaft exposed to the second path is constituted by a tube in order to reduce the hunting phenomenon. The object of the present invention is to provide a cost effective expansion valve which avoids the occurrence of hunting phenomenon in the refrigeration system with a simple change in structure. Summary of the Invention In order to solve the problem, there is provided an expansion valve according to claim 1. The expansion valve having said structure is free from said oversensitive valve open/close response even through a change in temperature often resulting in a hunting phenomenon of a refrigeration system, because the heat transfer speed of said heat sensing shaft of the valve means driving shaft is made to be slow. Brief Description of the Drawing In the drawing, FIG. 1 shows a vertical cross-sectional view of the expansion valve according to one embodiment of the present invention; FIG. 2 is a front view of the heat sensing shaft showing the main portion of one embodiment of the present invention; FIG. 3 is a vertical cross-sectional view of the heat sensing shaft showing the main portion of another embodiment which is not part of the claimed invention; FIG. 4 is a vertical cross-sectional view of the heat sensing shaft showing the main portion of yet another embodiment of the present invention; FIG. 5 is an explanatory view of the refrigeration cycle and the vertical cross-sectional view of the expansion valve of the prior art; and FIG. 6 is a vertical cross-sectional view of the expansion valve suggested by the present applicant. Detailed Description The embodiment of the present invention according to the drawings will be explained below. FIG. I shows the expansion valve 10 for controlling the refrigerant supply amount in a vertical cross-sectional view, and the same reference numbers as FIG. 5 show the same or equivalent portions. FIG. 2 is a front view of the heat sensing shaft 200 of FIG. 1. The expansion valve 10 comprises an aluminum body 30, and the aluminum body 30 is equipped with a first path 32 for liquid-phase refrigerant and a second path 34 for gas-phase refrigerant as was explained in reference with FIG. 5. A valve means 32b mounted on a valve room 35 is connected to a heat sensing shaft 200 via an activating shaft 37. The heat sensing shaft 200 is a cylindrical member made of aluminum, and comprises a receive member 202 of a diaphragm 36a, a large diameter portion 204 for being inserted moveably to a lower cover 36h of a power element portion 36, a heat sensing portion 206 being exposed inside the second path 34, and a groove 208 for supporting a seal member. As shown in detail in FIG 2, a hole 210 having a bottom is formed in the center of the heat sensing shaft 200 as a structure for making the heat transfer area small. This hole 210 is formed by a preferred method, for example, a digging process by a drill and the like. Further, in the embodiment shown in FIG 2, the hole with a bottom formed on the heat sensing shaft is formed from the portion contacting the diaphragm of the heat sensing shaft reaching the exposure portion inside the second path. However, it should be noticed that the depth of the hole with a bottom could be changed by design choice within the scope of the claims. Therefore, by the present invention, the hole 210 with a bottom is formed on the heat sensing shaft 200, so in other words, the heat sensing shaft 200 is equipped with a thin width portion, and the thickness of the thin width portion is, for example, about 1 mm. Further, in the heat sensing shaft of FIG 1 and FIG 2, the diameter of the heat sensing portion is 6.6 mm, the diameter of the hole 210 is 4.6 mm, the depth of the hole 210 is 25 mm. By the present invention, the temperature of the gas-phase refrigerant flowing through the second path 34 is transmitted to the heat sensing portion 206 of the heat sensing shaft 200, and to the gas inside the upper pressure activate chamber of the diaphragm. At this stage, when the speed of transfer of the heat from the heat sensing portion 206 to the upper pressure activate chamber 36b is too fast, it would cause unwanted hunting phenomenon. The heat sensing shaft 200 of the present invention includes a hole formed from the diaphragm receive portion reaching to the exposure portion in the second path, and having a thin wall width. By such structure, the heat sensing shaft of the present invention, even though it is made of aluminum which has a high heat-transfer character, has decreased heat transfer area, and the heat transferred to the diaphragm portion is slow. An unwanted hunting phenomenon could be prevented from occurring. Other than the above-mentioned embodiment, the heat transfer area could also be made small by forming a concave to the heat sensing shaft. FIG. 3 shows such embodiment. In the drawing, a concave 220 is formed on the heat sensing shaft 200 on the center portion of the surface of the power element portion contacting the diaphragm. By such concave, the center portion of the diaphragm will not contact the upper surface of the heat sensing shaft. The depth and the size of the concave 220 is a design choice. According to this embodiment, the temperature of the gas-phase refrigerant flowing through the second path 34 will be transmitted to the heat sensing portion 206 of the heat sensing shaft 200, and then transmitted to the gas inside the upper pressure activate chamber 356. However, the heat transfer area of the heat sensing shaft 200 is made small by a concave 220, so the transfer speed of the heat is slowed, and thus hunting phenomenon is prevented Further, FIG 4 shows another embodiment of the present invention wherein the heat sensing shaft comprises a concave portion 220 shown in FIG. 3 and a hole 210 shown in FIG 2. In this embodiment, the heat transfer area could also be made small. Further, in FIG 4, reference 220a shows the concave, and reference 210a is the hole The hole with a bottom of the heat sensing shaft in this embodiment is shown to reach the second path. However, the depth of the hole could be changed to a preferred size, and for example, the depth couid be decreased to make the heat transfer area small, and the size of the concave could also be changed to a preferred size within the scope of the claims. As could be understood from the above explanation, the expansion valve of the present invention prevents unwanted sensitive valve opening/closing response of the valve, and thus prevents a hunting phenomenon occurring in the refrigeration cycle Technical features mentioned in the claims are followed by reference sings. These reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: An expansion valve comprising: a valve body (30) having a first path (32) for a liquid-phase refrigerant to pass and a second path (34) for a gas-phase refrigerant to pass from an evaporator (8) to the compressor (4); an orifice (32a) mounted inside the first path (32); a valve means (32b) for controlling the amount of refrigerant passing the orifice (32a); a power element portion (36) formed on the valve body (30) and having a diaphragm (36a) operated by upper and lower pressure difference; and a heat sensing shaft (200) for driving the valve means (32b) contacting the diaphragm (36a) at one end and driving the valve means (32b) at the other end by a displacement of the diaphragm (36a); characterized in that the heat sensing shaft (200) includes a hole (210) with a bottom formed on the heat sensing shaft (200) from the portion contacting the diaphragm (36a), the hole (210) reaching the portion of the heat sensing shaft (200) exposed to the second path (34) such that the heat sensing shaft (200) has a decreased heat transfer area to prevent the hunting phenomenon. The expansion valve according to claim 1, characterized in that the heat sensing shaft (200) includes further a concave portion (220) formed on the surface contacting the diaphragm (36a).

Inventors: FUJIMOTO MITSUYA, WATANABE KAZUHIKO, YANO MASAMICHI, FUJIMOTO, MITSUYA, WATANABE, KAZUHIKO, YANO, MASAMICHI, Fujimoto, Mitsuya, c/o Fujikoki Corporation, Watanabe, Kazuhiko, c/o Fujikoki Corporation, Yano, Masamichi, c/o Fujikoki Corporation
Applicants: FUJIKOKI CORP, FUJIKOKI CORPORATION
Application year: 1997
Main classification: F25B41
IPC codes: F25B41