Expansion device

0001The invention relates to an expansion device according to the preamble of claims 1 and 32.

0002A refrigeration cycle known from JP-A-H11-257802 uses an accumulator on an outlet side of an evaporator, and an expansion device of a supercooling degree control type that comprises an orifice (restriction flow passage) controlling the flow rate in response to changes in the supercooling degree and dryness of high-pressure refrigerant flowing out from a condenser, and a differential pressure valve that provides control such that a predetermined degree of supercooling is obtained.

0003The expansion device comprises a cylinder fixed within piping of the refrigeration cycle, and a valve element within the cylinder. The valve element slides within the cylinder and is supported by a spring. Refrigerant passages, including a predetermined orifice, are formed at a boundary between the inside of the valve element and the cylinder such that movement of the valve element within the cylinder in response to a change in the differential pressure across the expansion device causes a change of the dimension of the flow passage. When the differential pressure across the expansion device is small, the size of the flow passage corresponds to the size of the predetermined orifice. When the differential pressure has become equal to or higher than a predetermined value, an additional flow passage is opened to prevent an abnormal pressure rise. Further, to prevent an abnormal pressure rise and to protect the expansion device, a this safety rupture plate is provided in the cylinder in advance. The rupture of the plate relieves too high pressure.

0004To assure that the valve element normally operates under high-pressure conditions, it is necessary to secure the elastic force of the spring, and hence a large-sized compression spring is needed which increases the size of the expansion device, resulting in increased manufacturing costs and mounting space.

0005It is an object of the invention to provide a compact expansion device capable of effectively preventing an abnormal internal pressure rise caused by the differential pressure across the expansion device.

0006That object is achieved by the features of claims 1 and 32.

0007The term "elastic member" means any of various elastic members, such as springs and bimetals. "The predetermined value" depends on the elastic force of the elastic member, the degree of cancellation of the refrigerant pressure by the pressure-cancelling structure, etc. The characteristics of the elastic member and the pressure-cancelling structure can be properly selected by a person who designs the expansion device according to the specifications of the expansion device and the like.

0008As at least a part of the refrigerant pressure is cancelled in the expansion device by the pressure-cancelling structure, it is possible to use a small-sized elastic member and to design the expansion device with compact size.

0009A more concrete embodiment is contained in claim 2.

0010The "stepped portion of the cylinder" may be integrally formed with the cylinder or may be formed by a hollow cylindrical member fixed to the cylinder.

0011In this embodiment part of the refrigerant pressure is cancelled by the pressure-cancelling structure. That is, in addition to the valve-opening pressure-receiving surface for receiving the refrigerant pressure applied in a downstream direction, the valve element is formed with the valve-closing pressure-receiving surface for receiving the pressure in an opposite or upstream direction, whereby the resultant of the pressure received at the valve-closing pressure-receiving surface and the elastic force of the elastic member acts against the refrigerant pressure received at the valve-opening pressure-receiving surface. Therefore, the elastic force required of the elastic member can be reduced by the amount of pressure received at the valve-closing pressure-receiving surface. As a result, it is possible to employ a small-sized elastic member as the elastic member.

0012Further, when the differential pressure across the expansion device has become equal to or higher than the predetermined value, the relief mechanism is capable of allowing at least part of the refrigerant flowing in from the upstream side to escape into the flow passage other than the refrigerant passage within the valve element. This makes it possible to prevent an abnormal rise in the refrigerant pressure inside the expansion device, to thereby prevent breakage of the internal components.

0013A further preferred embodiment is contained in claim 20.

0014In this embodiment the "first predetermined value" depends on the elastic force of the first elastic member, the degree of cancellation of the refrigerant pressure by the pressure-cancelling structure. The "second predetermined value" depends on the elastic force of the second elastic member, etc. The characteristics of the first elastic member, the pressure-cancelling structure, and the second elastic member can be properly selected by a person who designs the expansion device according to the specifications.

0015In this embodiment the pressure-cancelling structure allows to realize a compact configuration of the entire expansion device. The relief mechanism has two stages, i.e. the first relief mechanism and the second relief mechanism. By shifting the timing of relief of the pressure, the pressure reduction inside the expansion device can be carried out in two stages. Differentiating the amounts of relief between the two mechanisms allows to perform the pressure reduction control in various manners, i.e. to attain a delicate pressure reduction control such that the operation of the internal components of the expansion device is not adversely affected. This prevents breakage damage of internal components.

0016As a part of the refrigerant pressure is cancelled by the pressure-cancelling structure, the elastic force of the elastic member that supports the valve element acting against the refrigerant pressure may be relatively small and the elastic member may be small. The configuration of the expansion device is compact in size. The relief mechanism prevents an abnormal inside pressure rise in the expansion device and prevents damage of internal components.

0017Embodiments of the invention are described with reference to the drawings. <dl id="dl0001"><dt>Fig.1</dt><dd>is an explanatory view of an expansion device (first embodiment) disposed in a piping of a refrigeration cycle.</dd><dt>Figs 2A and 2B</dt><dd>are cross-sectional views of the expansion device of Fig. 1.</dd><dt>Fig. 3A</dt><dd>is a cross-section on line A-A of Fig. 2A.</dd><dt>Fig. 3B</dt><dd>is a cross-section on line B-B of Fig. 2A.</dd><dt>Fig. 4</dt><dd>is a diagram of the relation between the differential pressure across the expansion device and the opening area of the refrigerant passage.</dd><dt>Figs 5A, 5B,</dt><dd>are cross-sections of an expansion device (second</dd><dt>5C</dt><dd>embodiment).</dd><dt>Figs 6A, 6B, 6C</dt><dd>are cross-sections of an expansion device (third embodiment).</dd><dt>Figs 7A, 7B, 7C</dt><dd>are longitudinal cross-sections of an expansion device (fourth embodiment).</dd><dt>Fig. 8</dt><dd>is a cross-section on line E-E of Fig. 7A.</dd><dt>Fig. 9</dt><dd>is a diagram of the relation between the differential pressure across the expansion device and the opening area of the refrigerant passage.</dd><dt>Figs 10A, 10B, 10C</dt><dd>are longitudinal cross-sections of an expansion device (fifth embodiment).</dd><dt>Figs 11A, 11B, 11C</dt><dd>are longitudinal cross-sections of an expansion device (sixth embodiment).</dd><dt>Figs 12A, 12B 12C, 12D, 12E</dt><dd>are cross-sections of an inner cylinder of an expansion device.</dd><dt>Figs 13A, 13B, 13C</dt><dd>are longitudinal cross-sections of an expansion device (seventh embodiment).</dd><dt>Fig. 14</dt><dd>is a cross-section on line G-G of Fig. 13A.</dd><dt>Figs 15A, 15B, 15C</dt><dd>are longitudinal cross-sections of an expansion device (eight embodiment).</dd><dt>Fig. 16</dt><dd>is a diagram of the relation between the differential pressure and the opening area.</dd><dt>Figs 17A, 17B, 17C</dt><dd>are longitudinal cross-sections of an expansion device (ninth embodiment).</dd><dt>Fig. 18</dt><dd>is a cross-section on line H-H of Fig. 17A.</dd><dt>Fig. 19</dt><dd>is diagram of the relation between the differential pressure and the opening area.</dd><dt>Figs 20A, 20B, 20C</dt><dd>are longitudinal cross-section of an expansion device (tenth embodiment).</dd><dt>Fig. 21</dt><dd>is a cross-section on line I-I of Fig. 20A.</dd><dt>Figs 22A, 22B, 22C</dt><dd>are longitudinal cross-sections of an expansion device (eleventh embodiment).</dd><dt>Fig. 23</dt><dd>is a cross-section on line J-J of Fig. 22a.</dd><dt>Fig. 24</dt><dd>is a diagram of the relation between the differential pressure and the opening area.</dd><dt>Figs 25A, 25B</dt><dd>are longitudinal cross-sections of an expansion device (twelfth embodiment).</dd><dt>Fig. 26</dt><dd>are transverse sections of Figs 25A, 25B.</dd><dt>Figs 27A, 27B, 27C</dt><dd>are cross-sections of an expansion device (thirteenth embodiment)</dd><dt>Figs 28A, 28B, 28C</dt><dd>are cross-sections of an expansion device (fourteenth embodiment).</dd><dt>Fig. 29</dt><dd>is a cross-section on Line N-N of Fig. 28A.</dd><dt>Figs 30A, 30B, 30C</dt><dd>are longitudinal cross-sections of an expansion device (fifteenth embodiment).</dd><dt>Figs 31A, 31B</dt><dd>are longitudinal cross-sections of an expansion device (sixteenth embodiment).</dd><dt>Figs 32A, 32B</dt><dd>are longitudinal cross-sections of an expansion device (seventeenth embodiment).</dd><dt>Figs 33A, 33B</dt><dd>are transverse sections in Figs 32A, 32B.</dd><dt>Figs 34A, 34B, 34C</dt><dd>are different configurations of a restriction mechanism.</dd><dt>Fig. 35</dt><dd>is a diagram of the relation between the differential pressure and the opening area.</dd><dt>Figs 36A, 36B</dt><dd>are longitudinal cross-sections of an expansion device (eighteenth embodiment).</dd><dt>Figs 37A, 37B</dt><dd>are transverse sections in Figs 36A, 36B.</dd><dt>Figs 38A,</dt><dd>are longitudinal cross-sections of an expansion device</dd><dt>38B</dt><dd>(nineteenth embodiment).</dd><dt>Figs 39A, 39B</dt><dd>are transverse sections in Figs 38A, 38B.</dd><dt>Fig. 40</dt><dd>is a diagram of the relation between the differential pressure and the opening area.</dd></dl>

0018An expansion device 1 in Fig. 1 is disposed in a refrigerant piping 50 of a refrigeration cycle of an automotive air conditioner. The expansion device 1 is a differential pressure valve controlling a differential pressure such that a predetermined supercooling degree is obtained. The right and the left sides, in Fig. 1 are sometimes referred to as "upstream and downstream sides" with reference to the flow direction indicated by arrows.

0019In Fig. 2A, the expansion device 1 comprises a hollow cylinder 10 and a hollow cylindrical valve element 20 inserted in the cylinder 10.

0020The cylinder 10 has a body 11 and a valve seat 12 formed by a stepped portion at an upstream location inside the body 11. The refrigerant passage through the cylinder 10 consists of a small pipe portion 13 toward the upstream end, and a large pipe portion 14 on the downstream side of the small pipe portion 13. The large pipe portion 14 has a larger passage cross-section than the small pipe portion 13.

0021At an upstream end of the cylinder 10, a strainer 15 is provided, and a radial flange 16 is formed for securing the expansion device 1 to the piping 50. A fitting groove 10a for an O-ring extends circumferentially in the periphery of the small pipe portion 13. A stopper 17 formed like a bottomed hollow cylinder is fixed in the cylinder 10 in the vicinity of the downstream end of the large pipe portion 14. A spring 18 is interposed between the stopper 17 and the valve element 20.

0022The valve element 20 has a stepped hollow cylindrical body 21 and a valve portion 22 at an upstream end. The valve portion 22 cooperates with the valve seat 12. A guided portion 23 is formed downstream of the valve portion 22and is guided along the inner surface of the cylinder 10. A refrigerant passage 24 extends axially through the body 21.

0023The valve portion 22 is tapered such that the outer diameter progressively decreases toward the upstream end of the body 21. When the valve portion 22 seats on the valve seat 12, the foremost end of the valve portion 22 dives into the small pipe portion 13 by a predetermined amount.

0024The guided portion 23 is formed by three regularly distributed (120°) protrusions 23a extending from the body 21 toward the inner surface of the cylinder 10. Other separate refrigerant passages than the refrigerant passage 24 are defined between the protrusions 23a. The foremost ends of the protrusions 23a contact the inner surface of the cylinder 10.

0025The refrigerant passage 24 has a stepped portion 25 from the upstream side toward the downstream side. From the wider side of the stepped portion 25, an inner hollow cylindrical shaft member 30 is inserted functioning as a restriction mechanism. That is, the flow passage through the inner shaft member 30 forms a restriction that has a cross-section smaller than the cross-section of the refrigerant passage 24, and decompresses refrigerant flowing through the refrigerant passage 24. The inner shaft member 30 is only movably supported by the valve element 20 but is not fixed to any part. A part of the inner shaft member 30 protrudes downward from the valve element 20. The downstream end face is in abutment with the bottom of the stopper 17 such that the downstream movement of the inner shaft member 30 is limited.

0026Where the stopper 17 contacts the inner shaft member 30, there is formed a through hole 17a having a larger cross-section than the restriction through the inner shaft member 30. The hole 17a prevents that the flow is blocked even when the inner shaft member 30 is slightly radially displaced. As shown in Fig. 3B, around the through hole 17a, there are provided four slots 17b (second through holes) that are connected to the separate refrigerant passages. The sum of the areas of these four slots 17b is sufficiently larger than the flow passage area of a gap formed between the valve portion 22 and the valve seat 12 when the valve element 20 is opened in order to suppress a pressure loss in the slots 17b.

0027The spring 18 is a compression coil spring having a predetermined elastic coefficient. An upstream portion of the spring 18 is inserted around the body 21 of the valve element 20. One spring end abuts on the bottom of the stopper 17. The other spring end abuts at a downstream end face of the guided portion 23, to urge the valve element 20 toward the valve seat 12 (in the valve-closing direction) with a predetermined elastic force.

0028The stopper 17 has an outer external thread. A downstream end of the cylinder 10 has an internal thread mating with the external thread. By adjusting the screwing depth of the stopper 17 in the cylinder 10, the position of the stopper 17 and the elastic force or preload of the spring 18 can be adjusted.

0029The piping 50 in Fig. 1 has a joint structure between a downstream-side pipe 51 and an upstream-side pipe 52, at the location of the expansion device. The downstream-side pipe 51 has a stepped portion 53. The downstream end of the upstream-side pipe 52 is inserted into the expanded portion of the downstream-side pipe 51. The junction is sealed by an O-ring 54 received in a groove in the downstream end of the upstream-side pipe 52.

0030The flange 16 is sandwiched between the stepped portion 53 of the downstream-side pipe 51 and the downstream end face of the upstream-side pipe 52. A sealing O-ring 10b is provided within a fitting groove 10a in the cylinder 10

0031In Fig. 2A the valve portion 22 has a valve-opening pressure-receiving surface 26 facing upstream. The refrigerant pressure acts on the valve element in valve-opening direction. The stepped portion 25 of the valve element 20 has a valve-closing pressure-receiving surface 27 receiving refrigerant pressure on the valve element 20 in valve-closing direction. Pressure in the inner space between the stepped portion 25 and the inner shaft member 30 applies pressure to the valve element 20 in valve-closing direction (rightward as viewed in FIG. 2A) , to cancel part of the refrigerant pressure on the valve element 20 in valve-opening direction. The passage cross-section of the small pipe portion 13 is larger than the cross-section of the expanded pipe side of the stepped portion 25. When the valve element 20 seats on the valve seat 12, the valve-closing pressure-receiving surface 27 is smaller than the valve-opening pressure-receiving surface 26. The resultant of pressure at the valve-closing pressure-receiving surface 27 and of the elastic spring force acts against the pressure at the valve-opening pressure-receiving surface 26.

0032In Figs 2A and 2B, when the differential pressure across the expansion device 1 has become equal to or higher than a predetermined value (the valve portion 22 moved away from the valve seat 12) most of refrigerant from the upstream side escapes through the gap between the valve portion 22 and the valve seat 12, and flows downstream through the separate refrigerant passages between the valve element 20 and the cylinder 10 and through the slots 17b.

0033In Fig. 4, as long as the valve element 20 seats on the valve seat 12 (Fig. 2A), even if the differential pressure rises, the opening area corresponds to the cross-sectional area of the refrigerant passage 24. When the differential pressure is higher than the predetermined value, the valve element 20 leaves the valve seat 12. The refrigerant escapes through the other refrigerant passages outside the valve element 20 to relieve the pressure. Thus, the opening area is instantly increased (Fig. 2B).

0034As described above, the pressure-cancelling structure cancels part of the refrigerant pressure. For that reason the elastic spring force can be reduced by the force amount resulting from the pressure on the valve-closing pressure-receiving surface 27. The spring 18 can be small-sized such that the expansion device 1 is compact in size.

0035In Fig. 5A, the expansion device 201 comprises the hollow cylinder 210 and the hollow cylindrical valve element 220 inserted into the cylinder 210.

0036The cylinder 210 contains a valve seat portion 213 as a separate hollow cylindrical member fixed to the inside of the cylinder 210. A large pipe portion 214 having a larger passage cross-section than the valve seat portion 213 communicates with the downstream side of the valve seat portion 213. A guide pipe portion 215 having a smaller passage cross-section than the large pipe portion 214 communicates with the downstream side of the large pipe portion 214.

0037One end of the valve seat portion 213 opens in upstream direction, and is formed with a valve seat 212 at the other end, for the valve element 220.

0038When the expansion device 201 is disposed within the piping 50, the large pipe portion 214 and the guide pipe portion 215 define a refrigerant passage.

0039In Fig. 5C, in the large pipe portion 214 a valve portion 222 of the valve element 220 is inserted. A pair of lateral communication holes 214a extend through the wall of the portion 214 for communicating the inside with the above-mentioned refrigerant passage. The portion 214 has a space portion 241 communicating with the communication holes 214a.

0040The guide pipe portion 215 slidably receives a guided portion 223 of the valve element 220. An orifice hole 215a (restriction mechanism) is formed in a central portion of the downstream end of the portion 215c.

0041The valve element 220 has a hollow cylindrical body 221 inserted in the cylinder 201. The valve portion 222 formed at an upstream end of the body 221, for being removably seated on the valve seat 212, and the guided portion 223 formed on the downstream side of the valve portion 222. A refrigerant passage 224 axially extends through the body 221.

0042The valve portion 222 is tapered such that the outer diameter progressively decreases toward the upstream end of the body 221. When the valve portion 222 is seated on the valve seat 212, the foremost end of the valve portion 222 dives into the small pipe portion 213 by a predetermined amount.

0043A spring 218 is interposed between the downstream end face of the guided portion 223 and the downstream end face of the guide pipe portion 215, for urging the valve element 220 toward the valve seat 212 (in valve-closing direction).

0044The refrigerant passage 224 extends with the same cross-section from the upstream side to the downstream side. Refrigerant having passed through passage 224 is decompressed when passing through the orifice hole 215a.

0045The valve seat portion 213 has an external thread. An upstream end of the cylinder 210 has an internal thread mating with the external thread, adjusting the elastic spring force via the valve element 220.

0046In Fig. 5A, the valve portion 222 has a valve-opening pressure-receiving surface 226 facing upstream for receiving pressure acting on the valve element 220 in valve-opening direction. A downstream end face of the guided portion 223 has a valve-closing pressure-receiving surface 227 for pressure acting on the valve element 20 in valve-closing direction. Refrigerant introduced into the guide pipe portion 215 via the guided portion 223 of the valve element 220 applies pressure to the valve element 220 in valve-closing direction (rightward in Fig. 5A) , to cancel a part of the pressure acting on the valve element 220 in valve-opening direction. The passage cross-section of the valve seat portion 213 is larger than of the guide pipe portion 215. When the valve element 220 is seated on the valve seat 212, the valve-closing pressure-receiving area of the surface 227 is smaller than the area of the valve-opening pressure-receiving surface 226. The resultant of the pressure force at the valve-closing pressure-receiving surface 227 and of the elastic sponge force acts against the pressure at the valve-opening pressure-receiving surface 226.

0047In Figs 5A and 5B when the differential pressure across the expansion device 201 is equal or higher than a predetermined value, the valve portion 222 moves away from the valve seat 212. Most of the refrigerant from the upstream side escapes through a gap between the valve portion 222 and the valve seat 212, between the piping 50 and the cylinder 210 via the space portion 241 and the communication holes 214a.

0048Since the pressure-cancelling structure cancels part of the refrigerant pressure, a small-sized spring 218 can be employed.

0049In Figs 6A, to 6C the expansion device 301 comprises the hollow cylinder 310, and the valve element 320 with the body 321 inserted in the cylinder 310. A small pipe portion 313 slidably supports a guided portion of the valve element 320. The large pipe portion 314 has a larger passage cross-section than the small pipe portion 313, and contains a valve portion 323 of the valve element 320. The valve seat 312 is formed by a stepped portion.

0050The small pipe portion 313 (Fig. 6C) has a pair of introducing holes 313a in the side wall. An upstream end of the small pipe portion 313 is closed. A downstream end communicates with the large pipe portion 314. The small pipe portion 313 is expanded by a predetermined amount toward the large pipe portion 314 to form an expanded pipe portion 313b in the vicinity of the valve seat 312. A strainer 315 is fitted on the small pipe portion 313. A hollow cylindrical stopper 317 is fixed to the large pipe portion 314 in the vicinity of the downstream end. The spring 318 is inserted between the stopper 317 and the valve element 320. The body 321 has the guided portion 322 sliding along the inner surface of the small pipe portion 313, and the valve portion 323 for connection with valve seat 312. An axial a refrigerant passage 324 extends through the body 321. A space portion 341 communicating with the introducing holes 313a is defined between the valve element 320 and the small pipe portion 313, at the location of a pipe portion 325.

0051The pipe portion 325 has an orifice hole 331 in the side wall connecting the space portion 341 and the refrigerant passage 324, and functioning as a restriction mechanism. When the valve element 320 is seated, the refrigerant from the piping 50 is introduced via the introducing holes 313a and the orifice hole 331 into the refrigerant passage 324. At the downstream end of the refrigerant passage 324 an expanded pipe portion 332 is expanded by a predetermined amount for suppressing a flow pressure loss.

0052The stopper 317 has an external thread, and the downstream end of the cylinder 310 has an internal thread mating with the external thread, for adjusting the elastic force of the spring 318.

0053In Fig. 6A the valve portion 323 is formed with a valve-opening pressure-receiving surface 326 facing upstream for receiving pressure acting in valve-opening direction. The downstream end has a valve-closing pressure-receiving surface 327 for pressure acting on the valve element 320 in valve-closing direction. Refrigerant introduced into the space portion 341 through the introducing hole 313a applies pressure to the valve-opening pressure-receiving surface 327 in valve-closing direction (rightward in Fig. 6A), and also to the valve-opening pressure-receiving surface 326 in valve-opening direction (leftward in Fig. 6A) to cancel part of the pressure acting in valve-opening direction. Due to the expanded pipe portion 313b, when the valve element 320 seats on the valve seat 312, the valve-closing pressure-receiving surface area is smaller than the valve-opening pressure-receiving surface area. The resultant of the pressure force on the surface 327 and the elastic spring force acts against the pressure force received at the surface 326.

0054In Figs 6A and 6B, when the differential pressure across the expansion device 301 is equal or higher than a predetermined value, the valve portion 323 moves away from the valve seat 312. Most of the refrigerant from the upstream side escapes through a refrigerant passage separate from the passage 324 formed by a gap between the valve portion 323 and the valve seat 312, to downstream through the large pipe portion 314. Hence, the spring 318 can be small-sized.

0055In Figs 7A-7C, Fig 8, the expansion device 401 comprises a hollow cylinder 10 and the valve element 420 having a body 421 in the form of a stepped hollow cylinder. The valve portion 422 is formed at a body upstream end for co-action with the valve seat 12. The refrigerant passage 424 axially extends through the body 421.

0056The valve portion 422 has a tapered end the outer diameter of which decreases toward the upstream end of the body 421, and has an extended portion on the tapered end for being fitted into the small pipe portion 13 by a predetermined axial amount when the valve element 420 is seated. In Fig.. 8, a slit 431 is formed in a side wall of an upstream end of the valve portion 422, which opens toward the small pipe portion 13.

0057The pressure-cancelling structure of the expansion device 401 has an upstream facing valve-opening pressure-receiving surface 426 on the valve portion 422 for receiving pressure acting on the valve element 420 in valve-opening direction. The surface 420 has a shape slightly different from the surface 26 of the first embodiment. The function, however, is the same.

0058In Figs 7A to 7C, when the differential pressure is equal to or higher than a predetermined value, the valve portion 422 starts to move away from the valve seat 12. Part of refrigerant from the upstream side flows downstream through a refrigerant passage separate from passage 424 and formed between the valve element 420 and the cylinder 10 by the slit 431.

0059When the differential pressure further rises, the opening connecting the small pipe portion 13 and the large pipe portion 14 is progressively increased due to the function of the slit 431. When the upstream end of the valve portion 420 is removed from the small pipe portion 13, the opening will be sharply increased, such that most of the refrigerant escapes downstream into a flow passage separated from the refrigerant passage 424.

0060In Fig. 9, so long as the valve element 420 is seated on the valve seat 12 (state in Fig. 7A), even if the differential pressure rises, the opening area corresponds to the cross-section area of the restriction of the inner shaft member 30. When the differential pressure is higher than a predetermined value, the refrigerant escapes through the slit 431. The opening area is gently increased in response to changes in the differential pressure across the expansion device 401 (state in Fig. 7B). When the differential pressure further rises, the upstream end of the valve element 420 is removed from the small pipe portion 13 to instantly increase the opening area (state in Fig. 7C).

0061In the expansion device 401 the refrigerant from the upstream side escapes in a stepwise manner, to prevent an abnormal inside pressure rise in the refrigerant pressure inside the expansion device 401, to thereby prevent breakage or the like of the internal components. Further, by the stepwise relief of the refrigerant pressure, the flow characteristics representative of the relationship between the differential pressure across the expansion device 401 and the opening area of the refrigerant passage thereof can be set differently from those of the first embodiment.

0062In Figs 10A-10C, the expansion device 501 has the hollow cylinder 210, and the valve element 520 inserted into the cylinder 210. The valve portion 522 of the valve element 520 has a tapered end extended upstream by a predetermined amount such that the outer diameter decreases toward the upstream end of a body 521, and is configured fit into the valve seat portion 213 by the predetermined amount when the valve element 520 is seated. A slit 531 in the side wall of an upstream end of the valve portion 522 opens toward the valve seat portion 213. The slit 531 shown in FIGS. 10A to 10C operates similarly to the slit 431 of the fourth embodiment.

0063The refrigerant from upstream escapes in a stepwise manner. This allows to set the flow characteristics differently from the characteristics of the first embodiment.

0064In Figs 11A, 12A-12E, the expansion device 601 has the hollow cylinder 602 which is axially longer than the cylinder 10 of the first embodiment. A first relief mechanism 610 is inserted into an upstream part of the cylinder 602. A second relief mechanism 620 inserted into a downstream part.

0065The first relief mechanism 610 comprises a first valve element 20 co-acting with a first valve seat 12 formed by a stepped portion in the cylinder 602 (similar to the relief mechanism of the first embodiment). The first valve element 20 also has the pressure-cancelling structure of the first embodiment.

0066The second relief mechanism 620 comprises an inner cylinder 640 downstream of the first relief mechanism 610 in a manner continuous therewith, and a second valve element 650.

0067The inner cylinder 640 has a hollow circular body (Figs 12A to 12E) and a stepped portion 641 with a reduced inner diameter formed at an upstream end. The upstream body end holds the downstream end of the inner shaft member 30. A communication hole 644 is formed through the stepped portion 641 and is connected to the restriction of the inner shaft member 30.

0068The upstream end side wall of the inner cylinder 640 has a pair of slits 642 which open to the upstream direction. The downstream end has a slightly-increased outer diameter and an adjusting portion 643. The slits 642 connect a refrigerant passage between the inner cylinder 640 and the cylinder 602 and the inside of the inner cylinder 640, to allow the refrigerant to flow downstream of the second valve element 650.

0069In Figs 11A to 11C, the upstream end face of the inner cylinder 640 is loaded by a spring 18 abutting at the first valve element 20. The adjusting portion 643 has an external thread. A downstream end of the cylinder 602 has an internal thread mating with the external thread, to adjust the elastic force of the spring 18. Further, the downstream end of the inner cylinder 640 has a fixed hollow cylindrical stopper 617. A spring 618 (second elastic member) having a smaller elastic or spring constant than the spring 18 is interposed between the stopper 617 and the second valve element 20.

0070The second valve element 650 has a hollow cylindrical body inserted into the inner cylinder 640, and a valve portion 651 and a guided portion 653. A second refrigerant passage 654 having a smaller cross-section than the cross-section of the restriction of the inner shaft member 30 extends trough the inside of the body.

0071The guided portion 653 outer diameter is substantially equal to the inner diameter of the communication hole 644. An upstream end of the guided portion 653 forms the valve portion 651. Downstream of the guided portion 653, a radial flange 652 supports one end of the spring 618. A portion of the second valve element 650 downstream of the flange 652 is tapered with the outer diameter decreasing downstream. The second valve element 650 relative to the stepped portion 641 while being guided along the communication hole 644. The valve portion 651 seats on a downstream end valve seat face of the inner shaft member 30 (second valve seat).

0072The stopper 617 has an external thread. A downstream end of the inner cylinder 640 has an internal thread mating with the external thread, to adjust the elastic spring force.

0073In Figs 11A to 11C, when the differential pressure is equal to or higher than a first predetermined value, the first relief mechanism 610 operates. When the differential pressure is equal to or higher than a second predetermined value, the second relief valve 620 will operate. The first predetermined value is set larger than the second. The amount of refrigerant allowed to escape by the first relief mechanism 610 is set larger than the amount of refrigerant allowed to escape by the second relief mechanism 620. The second relief mechanism 620 is first operated to allow refrigerant to escape at a small flow rate, and thereafter, the first relief mechanism 610 is operated to allow the refrigerant to escape at a larger flow rate.

0074When the differential pressure is equal to or higher than the second predetermined value (Figs 11A and 11B), the upstream end face of the second valve element 650 of the second relief mechanism 620 moves away from the downstream end face of the inner shaft member 30, whereby part of refrigerant flowing through the restriction of the inner shaft member 30 into the communication hole 644 escapes through a gap between the downstream end face of the inner shaft member 30 and the upstream end face of the second valve element 650. The refrigerant flows via the slit 642 and the refrigerant passage between the inner cylinder 640 and the cylinder 602 to downstream of the second valve element 650.

0075When the differential pressure is equal to or higher than the first predetermined value the valve portion 22 moves away from the valve seat 12. Most of the refrigerant from the downstream side escapes via the gap between the valve portion 22 and the valve seat 12 further downstream via the refrigerant passage between the first valve element 20 and the cylinder 602, the refrigerant passage between the inner cylinder 640 and the cylinder 602, and through the slit 642.

0076The relief mechanisms 610, 620 define two stages. By shifting the timing of the relief of the pressure, the pressure in the expansion device 601 is reduced in two stages. By differentiating the amounts of relief between the two mechanisms, it is possible to carry out reduction control of the pressure in various manners. It is possible to realize a delicate pressure reduction control such that the operations of the internal components of the expansion device 601 are not adversely affected, to effectively prevent breakages of internal components.

0077In Figs 13A-13C, the expansion device 701 comprises the hollow cylinder 702 formed axially longer than the cylinder 10 of the first embodiment, a first relief mechanism 710 inserted into an upstream part, and a second relief mechanism 720 inserted into a downstream part of the cylinder 702.

0078The first relief mechanism 710 is formed by the first valve element 20 and the first valve seat 12 formed by a stepped portion inside the cylinder 702. The second relief mechanism 720 has the second valve element 20 and a second valve seat 752 formed by a downstream end of a stopper 750 disposed within the cylinder 702. Both mechanisms are similar to the relief mechanism of the first embodiment. However, the passage cross-section of the inner shaft member 730 of the second relief mechanism 720 is smaller than that of the inner shaft member 30 of the first relief mechanism 710 by a predetermined amount.

0079In Figs 13A to 13C, the valve-opening and valve-closing pressure-receiving surfaces of the first valve element 20 on the upstream side form a first valve-opening pressure-receiving surface area and a first valve-closing pressure-receiving surface area, and the valve-opening and valve-closing pressure-receiving surfaces of the second valve element 20 on the downstream side form a second valve-opening pressure-receiving surface area and a second valve-closing pressure-receiving surface area.

0080The first and second valve elements 20 each have the pressure-cancelling structure described in the first embodiment.

0081The stopper 750 is a bottomed hollow cylinder. At a location where the stopper 750 contacts the inner shaft member 30, there is formed a through hole 751 having a larger passage cross-section than that of the inner shaft member 30, prevent that the flow can be blocked even when the inner shaft member 30 is slightly radially displaced. In Fig. 14, a part of the outer periphery of the stopper 750 has as a cut-out portion 753 parallel to the axis, for forming a refrigerant passage between the cut-out 753 and the cylinder 702 communicating the upstream and the downstream sides of the stopper 750.

0082The stopper 750 has an external thread. An inner wall of the cylinder 702 has an internal thread mating with the external thread, to adjust the elastic force of the spring 18.

0083In Figs 13A to 13C, the spring constants of the springs 18, 718 of the first and the second relief mechanism 718, 720 are different from each other, such that when the differential pressure across the expansion device 701 is equal to or higher than a first predetermined value, the first relief mechanism 710 will operate, and when the differential pressure is equal to or higher than a second predetermined value, the second relief valve 720 will operate. The first predetermined value is set larger than the second. The second relief mechanism 720 is operated first to allow refrigerant to escape at a small flow rate, and thereafter, the first relief mechanism 710 is operated to allow refrigerant to escape at a large flow rate.

0084When the differential pressure is equal to or higher than the second predetermined value (Figs 13A and 13B), the valve portion 22 moves away from the second valve seat 752. Part of the refrigerant from upstream via the inner shaft member 30 and the stopper 750 escapes through a gap between the valve portion 22 and the valve seat 752, and flows downstream via the refrigerant passage formed between the second valve element 20 and the cylinder 702.

0085When the differential pressure is equal to or higher than the first predetermined value the other valve portion 22 is moved away from the valve seat 12. Most of the refrigerant from upstream escapes via the gap between the valve portion 22 and the valve seat 12, and flows downstream via the refrigerant passage formed between the first valve element 20 and the cylinder 702, the refrigerant passage between the cut-out portion 753 and cylinder 702, and the refrigerant passage between the second valve element 20 and the cylinder 702.

0086In Figs 15A-15C, the expansion device 801 comprises a the hollow cylinder 10, and a hollow cylindrical valve element 820.

0087The valve element 820 has a stepped hollow cylinder body 821 inserted in the cylinder 10: A valve portion 822 is formed at an upstream end of the body 821, for co-action with the valve seat 12. A refrigerant passage 824 axially extends through the body 821.

0088The valve element 822 tapered such that the outer diameter decreases toward the upstream end of the body 821. When the valve element 820 is seated, the upstream end thereof is inserted into the small pipe portion 13 such that a predetermined gap is formed between the upstream end and the inner wall of the small pipe portion 13.

0089The pressure-cancelling structure of the expansion device 801 differs from that of the first embodiment in that an upstream facing valve-opening pressure-receiving surface 826 on the valve portion 822 has a shape slightly different from the receiving surface 26 of the first embodiment, but the function is the same.

0090In Figs 15A and 15C, when the differential pressure is equal to or higher than a predetermined value the valve portion 822 starts to move away from the valve seat 12. A part of refrigerant from upstream leaks through the gap between the valve element 820 and the small pipe portion 13. When the upstream end of the valve element 820 is moved away from the small pipe portion 13, the refrigerant escapes at a larger flow rate. The refrigerant escapes downstream into another flow passage than the refrigerant passage 824 of the valve element 820 in a stepwise increasing manner.

0091In Fig. 16, when the valve element 820 seats on the valve seat 12 (state in Fig. 15A), even if the differential pressure rises, the opening area corresponds to the cross-sectional area of the refrigerant passage 824. When the differential pressure is higher than a predetermined value, the aforementioned gap provides an opening, which once increases the opening area (state in Fig. 15B). As the gap continues to provide a fixed opening area, the differential pressure across the expansion device 801 further rises. The upstream end of the valve element 820 moves away from the small pipe portion 13 and instantly increases the opening area in response to a change in the differential pressure (state in Fig. 15C). The refrigerant from upstream escapes in a stepwise manner.

0092Thereby, special flow characteristics can be realized, which also is true for the sixth and seventh embodiments.

0093In Figs 17A-17C, Fig. 18, the expansion device 901 comprises the hollow cylinder 10, and a hollow cylinder valve element 920. The valve element 920 includes a stepped hollow cylinder body 921 inserted in the cylinder 10. A valve portion 922 is formed at an upstream end of the body 921, for co-action with the valve seat 12. A refrigerant passage 924 axially extends through the body 921.

0094The refrigerant passage 924 has a stepped portion 925 which is expanded from the upstream to the downstream side. Into the expanded side of the stepped portion 925 there is inserted an inner shaft member 930 which functions as a restriction mechanism. The stepped portion 925 is disposed at a location downstream of the guided portion 23. The inner shaft member 930 is axially shorter than the inner shaft member 30 of the first embodiment.

0095In Fig. 18, a portion of a side wall slightly downstream of the stepped portion 925 contains a communication hole 941 for communication between the inside and outside of the restriction passage 924.

0096The pressure-cancelling structure of the expansion device 901 is the same as that of the first embodiment.

0097In Figs 17A and 17C, when the valve element 920 is seated, the communication hole 941 is opened. Part of the refrigerant flowing through the refrigerant passage 924 escapes into another flow passage. When the differential pressure is equal to or higher than a predetermined value the valve portion 922 starts to move away from the valve seat 12. The upstream end of the inner shaft member 930 closes the communication hole 941. As soon as the upstream end of the valve element 920 is removed from the small pipe portion 13, most of the refrigerant from upstream escapes through a gap between the valve portion 922 and the valve seat 12, and flows downstream via the refrigerant passage formed between the valve element 920 and the cylinder 10 and the plurality of slots 17b of the stopper 17.

0098In Figs. 18, 19, when the valve element 920 seats on the valve seat 12 (state in Fig. 17A), even if the differential pressure rises, the opening area corresponds to the sum of the cross-sectional areas of the refrigerant passage 924 and of the communication hole 942. When the differential pressure is higher than a predetermined value, the communication hole 941 starts to be closed. The cross-sectional area is once decreased (state in Fig. 17B). When the differential pressure further rises, the upstream end of the valve element 920 is removed from the small pipe portion 13 to instantly increase the opening area in response to a change in the differential pressure (state shown in Fig. 17C). By once stopping the escape of refrigerant and once decreasing the opening area, the flow characteristics (Fig. 19) represented by the relation between the differential pressure and the opening area of the refrigerant passage(s) can be set differently from those of the first embodiment.

0099The cooling performance of the expansion device 901 is enhanced e.g. by increasing the degree of supercooling (subcooling) by once decreasing the opening area to thereby temporarily decrease the flow rate of the refrigerant.

0100In Figs 20A-20C, Fig. 21, the expansion device 1001 comprises the hollow cylinder 210, and a hollow cylindrical valve element 1020.

0101In Fig. 21 as well, a portion of the side wall of the valve element 1020 at a location opposed to the space portion 241 on the downstream side of the valve portion 222 contains a communication hole 1041 between the inside and the outside of the refrigerant passage 224.

0102In Figs 20A to 20C, when the valve element 1020 is seated, the communication hole 1041 is opened. A part of the refrigerant flowing through the refrigerant passage 224 to be introduced into the refrigerant passage formed between the piping 50 and the cylinder 210 via the space portion 241 and the communication holes 214a, flows downstream. When the differential pressure is equal to or higher than a predetermined value the valve portion 222 starts to move away the valve seat 212. The valve element 1020 is moved downstream, whereby the communication hole 1041 is closed by the guided pipe portion 215. When the upstream end of the valve element 1020 is removed from the valve seat portion 213, most of the refrigerant from upstream escapes via a gap created between the valve portion 222 and the valve seat 212.

0103By the provision of the communication hole 1041, the refrigerant from upstream escapes in a stepwise manner. The flow characteristics representing the relation between the differential pressure across the opening area of the refrigerant passage(s) can be set differently from those of the second embodiment.

0104The cooling performance is enhanced e.g. by increasing the degree of supercooling (subcooling) by once decreasing the opening area to thereby temporarily decrease the flow rate of the refrigerant.

0105In Figs 22A-22C, Fig. 23, the expansion device 1101 comprises a first relief mechanism 710 inserted in a upstream part and a second relief mechanism 1220 inserted in a downstream part the cylinder 702.

0106The second relief mechanism 1220 comprises a second valve element 1120, and a stopper 750. The second valve element 1120 has a stepped hollow cylinder body. An upstream end of the body is reduced in a tapered manner. From the forward end of the reduced portion a guided portion 1122 extends axially. A downstream end has a radial flange 1123. The guided portion 1122 is slidably inserted in the hollow cylinder stopper 750. A stepped portion 1125 is formed inside the tapered portion. The cross-section of the downstream side of the stepped portion 1125 is larger than the passage cross-section of the stopper 750. The outer surface of the tapered portion forms a valve portion 1121 for the valve seat 752 on the downstream end of the stopper 750.

0107In Fig. 23, a portion of the side wall of the guided portion 1122 in the vicinity of the tapered portion contains a communication hole 1141 between the inside and the outside of the refrigerant passage 1124. The downstream end of the valve element 1120 has a tapered shape the outer diameter of which decreases downstream, and is in abutment with the end face of the stopper 17. The refrigerant passage formed between the valve element 1120 and the cylinder 702 communicates with the slots 17b. A spring 1118 is interposed between the flange 1123 and the downstream end face of the stopper 750, for urging the second valve element 1120 in the downstream direction.

0108In Figs 22A to 22C, when the differential pressure is lower than the second predetermined value, the valve element 1120 is not seated. The communication hole 1141 is open. A part of the refrigerant flowing through the refrigerant passage 1124 is introduced via the communication hole 1141 into the refrigerant passage formed between the valve element 1120 and the cylinder 702 and flows downstream via the outside of the flange 1123 and the slots 17b. When the differential pressure is equal to or higher than the second predetermined value the valve element 1121 starts to move toward the valve seat 752. The second valve element 1120 is moved upstream, so that the stopper 750 starts to close the communication hole 1141. When the valve element 1121 is seated on the valve seat 752, the communication hole 1141 is completely closed.

0109When the differential pressure is equal to or higher than the first predetermined value (which is higher than the second predetermined value) the first relief mechanism 710 operates as described. More specifically, the valve portion 22 of the valve element 20 is moved away from the valve seat 12, to allow most of refrigerant from upstream to escape through a gap between the valve portion 22 and the valve seat 12, to flow downstream through a refrigerant passage formed between the first valve element 20 and the cylinder 702, and refrigerant passages formed between the cut-out portion 753 and the cylinder 702 and between the valve element 1120 of the second relief mechanism 1220 and the cylinder 702.

0110In Fig. 24, before the second valve element 1120 seats on the valve seat 752, even if the differential pressure rises, the opening area corresponds to the sum of the cross-sectional areas of the refrigerant passage 1124 and of the communication hole 1141 (state in Fig. 22A). When the differential pressure is higher than a second predetermined value, the communication hole 1141 starts to be closed to once decrease the area of the opening. When the communication hole 1141 is completely closed, the opening area is held constant again (state in Fig. 22B). When the differential pressure further rises, the valve portion 22 of the first relief mechanism 710 is removed from the valve seat 12, to instantly increase the opening area in response to a change in the differential pressure (state in Fig. 22C).

0111Due to the provision of the communication hole 1141, the refrigerant from upstream escapes in a stepwise manner. The flow characteristics represented by the relation between the differential pressure and the opening area of the refrigerant passage(s) can be set differently from those of the seventh embodiment.

0112The cooling performance of the expansion device 1101 is enhanced by once decreasing the opening area to temporarily decrease the flow rate of refrigerant, to enhance the supercooling degree.

0113In Figs 25A, 25B, 26A, 26B in the expansion device 1201, an inner shaft member 1230 is a solid cylindrical member, fixed at a downstream end to a stopper 1217. In Fig. 26A as well, the outer diameter of the inner shaft member 1230 is smaller than the inner diameter of a stepped portion 25 of the valve element 20 by a predetermined amount, whereby a gap 1225 is formed between the inner shaft member 1230 and the inner wall of the valve element 20. This gap 1225 communicates with the refrigerant passage 24 and functions as the restriction mechanism.

0114The stopper 1217 is similar to the stopper 17 of the first embodiment, but has a pair of slots 1217a in upper and lower halves of the bottom (Fig. 26B). A circular fixing portion 1217b is formed between the slots 1217a, for fixing one end of the inner shaft member 1230 the stopper 1217.

0115In Figs 25A and 25B the valve element 20 is seated on the valve seat 12 when the differential pressure is lower than a predetermined value. The refrigerant from upstream is introduced into the refrigerant passage 24 and is decompressed as it passes through the gap 1225 to flow downstream via the slots 1217a.

0116When the differential pressure is equal to or larger than the predetermined value the valve portion 22 moves away from the valve seat 12. Most of the refrigerant from upstream escapes through the refrigerant passage between the valve element 20 and the cylinder 10 and flows downstream.

0117The inner shaft member 1230 is fixed to the stopper 1217. The gap 1225 thus substantially remains constant, thereby securing the repeatability of the refrigerant flow.

0118If the repeatability of the refrigerant flow does not matter, the inner shaft member 1230 needs not to be fixed to the stopper 1217.

0119In Figs 27A-27C in the expansion device 1301, the valve element 1320 corresponds to the second valve element 1120 of the eleventh embodiment, but the communication hole 1141 is missing, and the guided portion 1122 is slidably inserted into the small pipe portion 13. The downstream end of the valve element 1320 forms a valve portion 1321 which can be seated on the upstream end face (valve seat) of the stopper 17 disposed on the downstream side. A spring 1118 interposed between a flange 1123 of the valve element 1320 and a stepped portion of the cylinder 1310 urges the valve element 1320 in the downstream direction.

0120In Fig. 27C, on the downstream side of the valve element 1320, a cylindrical inner shaft member 1330 is inserted which has a cut-out portion 1330a formed by cutting off a side portion along the axis thereof while leaving a downstream end cut-out form a refrigerant passage 1331 between the cut-out portion 1330a and the inner surface of the valve element 1320.

0121In Figs 27A and 27B the valve element 1320 is seated on the upstream end face of the stopper 17 when the differential pressure is lower than a predetermined value. The refrigerant from upstream into the refrigerant passage 1124 is decompressed by passing through the restriction extending through the inner shaft member 1330 to downstream via the through hole 17a.

0122When the differential pressure is equal to or larger than the predetermined value the valve portion 1321 moves away from the stopper 17. The refrigerant passage 1331 opens to the cylinder 1310. Most of the refrigerant from upstream escapes downstream through the refrigerant passage 1331, between the inner shaft member 1330 and the cylinder 1310, and the slots 17b.

0123In Figs 28A-28C and 29, the expansion device 1401 includes an inner shaft member 1430 which is a modification of the inner shaft member 1330 of the thirteenth embodiment, such that a groove 1430a of a predetermined width is formed in the inner shaft member 1330 at a location circumferentially shifted from the cut-out portion 1330a, in side view. The groove 1430a extends further downstream by a predetermined amount with respect to the cut-out portion 1330a to form a refrigerant passage 1432 having a smaller passage cross-section than the refrigerant passage 1331, between the groove 1430a and the inner surface of the valve element 1320.

0124In Figs 28A to 28C, when the differential pressure is equal to or higher than a predetermined value the valve portion 1321 starts to move away from the stopper 17. First, the refrigerant passage 1432 is made open to the cylinder 1310 to allow part of refrigerant from upstream to escape downstream through the refrigerant passage 1432, a flow passage formed between the inner shaft member 1430 and the cylinder 1310, and the slots 17b. When the differential pressure rises further, the valve element 1320 is moved further upstream to open the refrigerant passage 1331, to thereby allow most of the refrigerant from upstream to escape downstream via the refrigerant passage 1331, the flow passage between the inner shaft 1430 and the cylinder 1310, and the slots 17b_o

0125In Figs 30A-30C, the valve element 1520 of the expansion device 1501 has a guided portion 1442 as a modification of the side wall of the guided portion 1122. A communication hole 1521 communicates the inside and the outside of the refrigerant passage 1124, at a location in the vicinity of the tapered portion on the upstream side of the valve element 1320 in the thirteenth embodiment.

0126In Figs 30A and 30C when the differential pressure is lower than the second predetermined value, the communication hole 1521 is open. Part of the refrigerant flowing through the refrigerant passage 1124 is introduced via the communication hole 1521 into the refrigerant passage formed between the valve element 1520 and the cylinder 1310, and flows downstream via the outside of the flange 1123 and the slots 17b. When the differential pressure is equal to or higher than the second predetermined value, the valve element 1520 moves upstream, and the small pipe portion 13 closes the communication hole 1521.

0127When the differential pressure is equal to or higher than the first predetermined value (larger than the second predetermined value), the valve element 1520 is moved further upstream. The refrigerant passage 1331 is open. Most of refrigerant from upstream escapes through the refrigerant passage 1331, a flow passage between the inner shaft member 1330 and the cylinder 1310, and the slots 17b.

0128In Figs 31A, 31B in the expansion device 1601, the inner shaft member 1630 is a solid cylindrical member fixed to a stopper 1217. The diameter of the inner shaft member 1630 is smaller than the inner diameter of the stepped portion 1125 of the valve element 1320 by a predetermined amount, whereby a gap 1625 is formed between the inner shaft member 1630 and the inner wall of the valve element 1320. This gap 1625 communicates with the refrigerant passage 1124 and functions as the restriction mechanism. The inner shaft member 1630 has a cut-out portion 1630a formed by cutting off a portion along the axis, while leaving a downstream end thereof uncut, whereby a flow passage 1631 is formed between the cut-out portion 1630a and the inner surface of the valve element 1320.

0129In Figs 31A and 31B when the differential pressure is lower than a predetermined value, the refrigerant flowing from upstream is decompressed by passing through the gap 1625, and flows downstream via the slots 1217a.

0130When the differential pressure is equal to or larger than the predetermined value the valve portion 1321 is moved away from the stopper 1217. Most of the refrigerant from upstream escapes downstream through the refrigerant passage 1631, a flow passage between the inner shaft member 1630 and the cylinder 1310, and the slots 17b.

0131The embodiment in Figs 32A, 32B, 33A, 33B has a configuration that enhances the accuracy of the pressure cancellation. More specifically, similarly to the first embodiment in Fig. 2, with the tapered pressure-receiving surface of the valve portion 22, the effective pressure-receiving area of the valve element 20 tends to become smaller as the valve element 20 is moved away from the valve seat 12. As a result, as designated by a dotted line in FIG. 35, with a rise in the differential pressure, the rate of the increase of the opening area is lowered to cause the balance of the pressure cancellation to be lost, or degrade the relieving operation. The expansion device 1701 according to the present embodiment solves the problem.

0132In Fig. 32A, the expansion device 1701 comprises the hollow cylinder 10, and a hollow cylinder valve element 1270. The large pipe portion 14 of the cylinder 10 has a stopper 1717 in the form of a fixed disk at a location in the vicinity of the downstream end. The spring 18 is interposed between the stopper 1717 and the valve element 1720, and urges the valve element 1720 toward the valve seat 12 (in valve-closing direction).

0133The valve element 1720 comprises a stepped hollow cylinder body inserted in the cylinder 10, a hollow cylinder valve portion 1721 co-acting with the valve seat 12, and a stepped hollow cylinder guided portion 1722 on the downstream side of the valve portion 1721.

0134The upstream end of the valve portion 1721 is provided with a tapered portion the outer diameter of which decreases upstream. When the valve portion 1721 is seated, the foremost end of the tapered portion 1721 is inserted into the small pipe portion 13 by a predetermined amount.

0135In Fig. 33A, the guided portion 1722 comprises a generally hexagonal cross-section body 1723, and a reduced hollow cylinder pipe portion 1724 formed continuous with the downstream side of the body 1723. Each vertex portion of the body 1723 has an arcuate shape extending along the inner peripheral surface of the large pipe portion 14. Refrigerant passages are formed between the vertex portions. The valve element 1720 is stably moved forward and backward within the cylinder 10, with the vertex portions sliding along the inner surface of the large pipe portion 14. The reduced pipe portion 1724 contains one end of the spring 18.

0136The upstream end of the body 1723 is slightly expanded. The downstream end of the valve portion 1721 is press-fitted to the body 1723. In a space portion S1 between the valve portion 1721 and the reduced pipe 1724 of the guided portion 1722 a stepped cylinder shaft member 1730 is partially inserted.

0137The stopper 1717 (Fig. 33B) has a central screw hole 1717. Around the screw hole 1717a, there are three elongated holes 1717b at equal intervals (of 120 degrees) defining a sufficiently larger flow passage area than the area of a gap between the valve portion 1721 and the valve seat 12. This prevents a pressure loss in the holes 1717b. The stopper 1717 has an external thread. A downstream end of the cylinder 10 has an internal thread mating with the external thread, to adjust the elastic spring force. The screw hole 1717a contains a set screw 1740 (slotted head or a hexagon socket) (engaging member) holding the downstream end face of the shaft member 1730. The position of the set screw 1740 adjusts the axial position of the shaft member 1730 within the cylinder 10.

0138In Figs 34A-34C, the shaft member 1730 upstream end has a tapered portion 1731 the cross-section of which increases upstream. A restriction passage is formed by a gap between the tapered portion 1731 and an inner peripheral edge 1724a of the reduced pipe portion 1724. In Fig. 34B, so long as the valve element 1720 seats on the valve seat 12, the restriction passage by the gap holds a predetermined value c1 (the passage cross-section of the normal restriction mechanism). The pressure is high on the upstream side and low on the downstream side of the gap. However, in Fig. 34C, when the valve element 1720 has left the valve seat 12, the gap has a value c2 larger than c1. The flow rate will be larger but the function of the restriction mechanism is worse. The size of the restriction passage (in the closed state of the valve) can be set by adjusting the position of the shaft member 1730 using the adjusting mechanism.

0139The upstream end face of the shaft member 1730 has a diametrical groove 1732 (Fig. 33A),. The remaining portion of the end face holds the valve portion 1721, and the valve element 1720 from the downstream side. The groove 1732 communicates with the refrigerant passage through the valve portion 1721, even when the valve portion 1721 engages at the shaft member 1730. Refrigerant can flow through the communication passage formed by the groove 1732, the space portion S1, and the reduced pipe portion 1724.

0140In the expansion device 1701 in Fig. 34B, to receive high-pressure refrigerant from upstream in the refrigerant passage in the small pipe portion 13, a valve-opening pressure-receiving surface is formed by a portion 1751 of the upstream end face of the valve portion 1721 and an upstream end face 1752 of the reduced pipe portion 1724 of the guided portion 1722. A valve-closing pressure-receiving surface is formed by the downstream end face 1753 of the valve portion 1721. The inner diameter of the reduced pipe portion 1724 is smaller than that of the small pipe portion 13 (dotted lines in Fig. 34B) such that the pressure-receiving area of the entire valve-opening pressure-receiving surface becomes larger than the pressure-receiving area of the entire valve-closing pressure-receiving surface. Refrigerant in the space S1 within the valve element 1720 urges the valve element 1720 in the valve-closing direction (rightward in Fig. 34A) to cancel part of the pressure acting on the valve element 1720 in valve-opening direction. The resultant of the pressure at the valve-closing pressure-receiving surface and the force of the spring 18 acts against the pressure received at the valve-opening pressure-receiving surface.

0141In Figs 32A and 32Bwhen the differential pressure is equal to or higher than a predetermined value the valve portion 1721 moves away from the valve seat 12. Most refrigerant flowing from upstream escapes through a gap between the valve portion 1721 and the valve seat 12, to downstream through a refrigerant passage formed between the valve element 1720 and the cylinder 10 and the elongated holes 1717b of the stopper 1717.

0142In Fig. 35, when the valve element 1720 seats on the valve seat 12 (Fig. 32A), even if the differential pressure rises, the opening area is held constant by the restriction passage. When the differential pressure becomes higher than a predetermined value, the valve element 1720 moves away from the valve seat 12. The refrigerant escapes into the outside refrigerant passage to relieve the pressure. The opening area is instantly increased (Fig. 32B). So it is possible to prevent or suppress a lowering in the rate of increase of the opening area which might occur as the differential pressure rises (dotted line in Fig. 35), whereby it is possible to prevent a change of the characteristics of the expansion device 1701 due to lowering in the received pressure (solid line Fig. 35), thereby enabling the refrigerant to escape such that the refrigerant pressure is sufficiently relieved.

0143It is presumed that this is because a change (decrease) of the effective pressure-receiving area of the valve element 1720 and a change (increase) of the effective pressure-receiving area of the reduced pipe portion 1724 cancel each other. This cancels a variation of the received pressure caused by the lift of the valve element 1720.

0144When the differential pressure is equal to or higher than the predetermined value, refrigerant from upstream escapes into the other flow passage (not into the normal refrigerant passage) extending by way of the restriction passage. This prevents an abnormal inside pressure rise and damage of internal components.

0145The passage cross-section of the restriction passage on the downstream side is increased according to the valve opening condition of the valve element 1720.

0146This prevents variation in the characteristics caused by the decrease in the received pressure, maintains the balance of the pressure cancellation, and improves the relieving operation.

0147The inner diameters of the reduced pipe portion 1724 and of the small pipe portion 13 may be equal. Even with this configuration, due to the configuration in which the passage cross-section of the restriction passage on the downstream side is increased, it is possible to expect the effects of maintaining the balance of the pressure cancellation and the like.

0148There may be provided a guide means for stably holding the shaft member 1730 within the cylinder 10. For example, the shaft member 1730 comprise several guide portions extending radially outward from the periphery of the upstream end for being guided by the inner peripheral surface of the guided portion 1722.

0149In Figs 36A, 36B, 37A, 37B, the expansion device 1801 comprises the hollow cylinder 10, a hollow cylinder valve element 1820 in the cylinder 10, and a ball valve seat 1830 supported within the cylinder 10. In the vicinity of the downstream end of the large pipe portion 14 of the cylinder 10, a bottomed hollow cylinder stopper 1817 is secured. The ball valve seat 1830 is interposed between the stopper 1817 and the valve element 1820. A spring 18 between the downstream end face of the small pipe portion 13 and the valve element 1820 urges the valve element 1820 toward the ball valve seat 1830 (in valve-closing direction).

0150The valve element 1820 has a stepped hollow cylinder body which is expanded downstream in two stages. A hollow cylindrical portion as a central part of the body forms a body portion 1821, with a reduced pipe portion 1822 formed on the upstream side of the body portion 1821 by reducing the diameter of a corresponding portion of the body, and a guide portion 1823 formed on the downstream side of the body portion 1821 by increasing the diameter of a corresponding portion of the body. A hollow cylinder valve portion 1824 is formed by the downstream end of the body portion 1821.

0151The reduced pipe portion 1822 has an outer diameter slightly smaller than that of the small pipe portion 13, and is movably inserted into the small pipe portion 13. The gap between the reduced pipe portion 1822 and the small pipe portion 13 forms a restriction passage (restriction mechanism). The junction of the reduced pipe portion 1822 and the body portion 1821 is tapered with the outer diameter decreasing toward the upstream body end.

0152In Fig. 37A, the guide portion 1823 has an approximately hexagonal cross-section, and vertex portions each of an arcuate shape extending along the inner peripheral surface of the large pipe portion 14, defining refrigerant passages therebetween. The vertex portions of the guide portion 1823 slide along the inner surface of the large pipe portion 14, whereby the valve portion 1820 can be stably moved forward and backward within the cylinder. The inside of the guide portion 1823 is tapered such that the cross-section increases downstream. A downstream end face of the tapered portion facing downstream can receive the ball valve seat 1830 such that an upstream portion of the ball valve seat 1830 is covered. In Fig. 36A, when the valve portion 1824 of the valve element 1820 is seated on the ball valve seat 1830, a predetermined gap is formed between the tapered portion and the ball valve seat 1830. At this time, the ball valve seat 1830 is supported by the upstream end face of the stopper 1817 and the valve portion 1824 in a manner sandwiched therebetween. The spring 18 is fitted on the body portion 1821, and interposed between an upstream end face of the guide portion 1823 and a downstream end face of the small pipe portion 13.

0153In Fig. 37B the stopper 1817 has three slots 1817a at equal intervals (of 120 degrees), which form refrigerant passages. The cross-sectional area of the three slots 1817a is sufficiently larger than a flow passage area formed by a gap between the valve portion 1824 and the ball valve seat 1830. This prevents a pressure loss in the slots 1817a. The stopper 1817 has an external thread. A downstream end of the cylinder 10 has an internal thread mating with the external thread, to adjust the position of the ball valve seat 1830.

0154In the expansion device 1801, an upstream end face of the reduced pipe portion 1822 forms a valve-closing pressure-receiving surface, and a downstream facing surface of the tapered portion at the boundary of the reduced pipe portion 1822 and the body portion 1821 within the valve element 1820 forms a valve-opening pressure-receiving surface which has a larger pressure-receiving area than the valve-closing pressure-receiving surface. Refrigerant introduced from upstream acts on the valve element 1820 in valve-closing direction (leftward in Fig. 36B) to cancel a part of the pressure acting on the valve element 1820 in valve-opening direction. The resultant of the pressure received at the valve-closing pressure-receiving surface and the spring force acts against the refrigerant pressure received at the valve-opening pressure-receiving surface.

0155In Figs 36A and 36B, when the differential pressure is equal to or higher than a predetermined value the valve portion 1824 moves away from the ball valve seat 1830. Most refrigerant from upstream escapes through a gap between the valve portion 1824 and the ball valve seat 1830, and flows downstream through the slots 1817a of the stopper 1817. This prevents an abnormal inside pressure rise.

0156In the expansion device 1801 the relation between the differential pressure and the opening area is approximately the same as in Fig. 35.

0157When the valve element 1820 is seated on the ball valve seat 1830 (state in Fig. 36A), even if the differential pressure rises, the opening area is held constant by being limited by the restriction passage formed by the gap between the reduced pipe portion 1822 and the small pipe portion 13. When the differential pressure becomes higher than a predetermined value, the valve element 1820 moves away from the ball valve seat 1830. Refrigerant escapes into an inner refrigerant passage to relieve the pressure. The opening area is instantly increased (state in Fig. 36B). The pressure-cancelling structure cancels part of the pressure.

0158When the differential pressure is equal to or higher than a predetermined value, the relief mechanism prevents an abnormal rise of the differential pressure.

0159Since the decrease in the effective pressure-receiving area is small when the valve element 1820 is opened, but on the contrary, the surface thereof urged in the valve-opening direction is increased. This increases the accuracy of the pressure cancellation, and initiates the relieving function more rapidly. The differential pressure across the expansion device can be small before the required maximum valve lift is reached, so that the pressure load can be reduced to protect the same.

0160In Figs 38A, 38B, 39A, 39B, the expansion device 1901 comprises the hollow cylinder 10 and a hollow cylinder valve element 1920. In the vicinity of the downstream end of the large pipe portion 14 a hollow cylinder stopper 1917 is secured. A spring 18 between the stopper 1917 and the valve element 1920, urges the valve element 1920 toward the small pipe portion 13 (in valve-closing direction).

0161The downstream end of the small pipe portion 13 has a bottomed hollow cylinder guide pipe 1930 extending downstream from the downstream-side opening of the small pipe portion 13. The guide pipe 1930 (Fig. 39A), has communication holes 1931 in a side wall between the inside and the outside. The valve element 1920 is slidable one the guide pipe 1930. The downstream end of the guide pipe 1930 has with a tapered portion 1932 forming a valve seat the cross-section of which decreases downstream.

0162The valve element 1920 comprises a valve portion 1921 having a stepped hollow cylinder body inserted in the cylinder 10, and a guided portion 1922 guided by the guide pipe 1930, and can be held by the downstream facing surface of a stepped portion at a boundary between the small and large pipe portions 13, 14, i.e. by a downstream end face 1912 of the small pipe portion 13.

0163The guided portion 1922 has an upstream portion which has an inner diameter approximately equal to the outer diameter of the guide pipe 1930 and is slidable thereon, whereby the valve element 1920 can be stably moved forward and backward within the cylinder 10. A downstream portion of the guide pipe 1922 is slightly increased in inner diameter to thereby form a space portion S2. Further, as shown in FIG. 39B, a portion of the upstream end of the guided portion 1922 is formed with a slit 1922a communicating between the inside and outside of the guided portion 1922, whereby the high-pressure refrigerant leaked through a gap between the guided portion 1922 and the guide pipe 1930 can be allowed to flow downstream.

0164The valve portion 1921 has a reduced pipe portion 1924 extending downstream with a reduced size. One end of the spring 18 is fitted on the reduced pipe portion 1924. An upstream end of the valve portion 1921 has a slightly increased inner diameter, and the downstream end of the guided portion 1922 is press-fitted in the upstream end of the valve portion 1921. Within the valve element 1920 a space portion S2 is defined by the valve portion 1921, the guided portion 1922, and the guide pipe 1930. The space portion S2 communicates with the upstream side via the communication holes 1931.

0165The tapered surface of the tapered portion 1932 and an inner peripheral edge 1924a of the reduced pipe portion 1924 form a restriction passage. When the valve element 1920 is held on the downstream end face 1912 of the small pipe portion 13, the restriction passage holds the gap at a preset value realizing the passage cross-section of the normal restriction mechanism. However, when the valve element 1920 is fully moved away from the downstream end face 1912, the function of the restriction mechanism is actually terminated, but a new refrigerant passage having an increased flow passage area is formed. That is, the other refrigerant passage than the refrigerant passage that is open in the closed state of the valve is opened in an integrating manner.

0166An adjusting mechanism may be provided between the valve portion 1921 and the guided portion 1922 to set the size of the restriction passage as desired.

0167The stopper 1917 has an external thread. A downstream end of the cylinder 10 has an internal thread mating with the external thread to adjust the spring force.

0168In the expansion device 1901, within the space portion S2, the downstream facing surface of the guided portion 1922 forms a valve-closing pressure-receiving surface. The upstream end of the reduced pipe portion 1924 forms a valve-opening pressure-receiving surface area larger than the valve-closing pressure receiving surface area. The inner diameter of the reduced pipe portion 1924 is smaller than that of the guided portion 1922 such that the pressure-receiving area of the valve-opening pressure-receiving surface becomes larger than that of the valve-closing pressure-receiving surface. Refrigerant introduced into the space S2 acts on the valve element 1920 in valve-closing direction (rightward in Fig. 38A) to cancel part of the pressure acting on the valve element 1920 in valve-opening direction. The resultant of the pressure at the valve-closing pressure-receiving surface and of the spring force acts against the pressure at the valve-opening pressure-receiving surface.

0169In Figs 38A and 38B, when the differential pressure is equal to or higher than a predetermined value the guided portion 1922 moves away from the downstream end face 1912. The opening area of the gap between the reduced pipe portion 1924 and the guide pipe 1930 is increased against the urging force of the spring 19. Refrigerant from upstream escapes at an increased flow rate.

0170In Fig. 40, so long as the valve element 1920 is held on the downstream end face 1912 of the small pipe portion 13 (state in Fig. 38A), even if the differential pressure rises, the opening area is held constant by being limited by the restriction passage. When the differential pressure becomes higher than a predetermined value, the valve element 1920 moves away from the downstream end face 1912. Refrigerant flows downstream at increased flow rate. Thus, the opening area is instantly increased (state in Fig. 38B). In this case the rate of increase in the opening area is larger than in FIG. 35.

0171In the expansion device 1901 when the valve element 1920 opens, there occurs no decrease of the effective pressure-receiving area, which enables the balance of the pressure cancellation to be maintained, and improves the relieving operation. Further, in relieving the refrigerant pressure, the refrigerant passage can be expanded instantly, which decreases the differential pressure across the expansion device required for setting the maximum valve lift. Therefore, the pressure load on the expansion device can be reduced.

0172In the above-described embodiments, the cylinder of each expansion device is directly fixed to the piping 50. As an alternative, the expansion device may be provided with a casing or the like which accommodates the cylinder, and then the casing or the like may be fixed to the piping. Further at least one of the outer peripheral surface of the inner shaft member and the inner peripheral surface of the valve element may be formed with at least one labyrinth groove. It should be noted that internal components used for constructing the expansion device may e.g. consist of synthetic resin.