Patent Publication Number: US-11391154-B2

Title: Scroll expander with back pressure chamber

Description:
This application is the national phase of International Application No. PCT/CN2019/115289 titled “VORTEX EXPANDER” and filed on Nov. 4, 2019, which claims the benefit of priorities to the following two Chinese patent applications, both of which are incorporated herein by reference: Chinese Patent Application No. 201811397574.1, titled “VORTEX EXPANDER”, filed with the China National Intellectual Property Administration on Nov. 22, 2018; and Chinese Patent Application No. 201821934748.9, titled “VORTEX EXPANDER”, filed with the China National Intellectual Property Administration on Nov. 22, 2018. 
     TECHNICAL FIELD 
     The present disclosure generally relates to the field of expanders, and in particular to a scroll expander. 
     BACKGROUND 
     This section provides background information relating to the present disclosure, which may not necessarily constitute the prior art. 
     An expander is a device that uses a high-pressure fluid for expanding into a low-pressure fluid to output mechanical or electrical work. A common expander is a scroll expander. An expansion mechanism of the scroll expander includes an orbiting scroll and a fixed scroll. The orbiting scroll and the fixed scroll are engaged with each other to define a series of expansion chambers between the orbiting scroll wrap and the static scroll wrap, and the series of expansion chambers gradually increase in volume radially outward from the center of the expansion mechanism. As a result, the high-pressure fluid entering the expansion mechanism from an intake port at the center of the expansion mechanism becomes the low-pressure fluid after passing through the series of expansion chambers and is discharged out of the expansion mechanism through an exhaust port. In the process of fluid expansion, a driving torque is generated, which may for example drive the shaft to rotate to output mechanical or electrical work. 
     Regardless of whether it is a scroll expander with a floating orbiting scroll or a scroll expander with a floating fixed scroll, in a case that a back pressure chamber is usually unable to provide enough pressure to compress an orbiting scroll and a fixed scroll, it may cause the orbiting scroll and the fixed scroll to separate or an abnormal shaking of the orbiting scroll and the fixed scroll, resulting in the failure to establish a normal pressure difference in the scroll expander or wear between the orbiting scroll and the fixed scroll, thus failing to start and work normally. 
     Taking a scroll expander with a floating fixed scroll, especially a scroll expander with a floating sealing ring provided on a back side of the end plate of the fixed scroll for sealing the back pressure chamber, for example, the back pressure chamber is composed of a groove and a floating sealing ring provided on the end plate of the fixed scroll, wherein the back pressure chamber is in fluid communication with an intermediate pressure chamber defined in the expansion mechanism, which has an intermediate pressure lower than the intake pressure and higher than the exhaust pressure. By making the back pressure chamber have the same pressure as the intermediate pressure chamber, the orbiting scroll and the fixed scroll are ensured to be engaged, and this engagement is flexible, which may provide a certain flexibility in the axial direction to prevent the orbiting scroll and the fixed scroll from being severely worn under certain conditions (such as foreign particles entering into the expansion mechanism) due to rigid engagement. In addition, the floating sealing ring is pressed to be abut against a corresponding wall (especially, a top end of an upper plate of the floating sealing ring is abut against a bottom surface of a partition plate for example) through the pressure in the back pressure chamber, so that a low-pressure zone (with exhaust pressure), a high-pressure zone (with pressure of the high-pressure fluid) and the intermediate pressure zone (back pressure chamber with the intermediate pressure) in the housing of the scroll expander are isolated from each other by the floating sealing ring, so as to ensure the normal operation of the scroll expander. 
     As mentioned above, the floating sealing ring needs to rely on sufficient pressure in the intermediate pressure chamber to play a sealing role, so as to ensure a normal start and a normal operation of the scroll expander. However, in a scroll expander in the prior art, before being started, a back pressure chamber usually cannot provide enough pressure to provide enough support for a floating sealing ring. When an input of a high-pressure fluid into a high-pressure zone in the scroll expander begins, the floating sealing ring is collapsed into the back pressure chamber due to unbalanced forces (e.g., an expansion of the intermediate pressure chamber, which causes a pressure drop in the intermediate pressure chamber, and further causes that the pressure in the back pressure chamber drops to a pressure below the pressure in the low-pressure zone, resulting in unbalanced forces), so that a sealing and isolation effect cannot be performed (i.e., causing fluid to flow directly from the high-pressure zone to the low-pressure zone, which causes the expansion mechanism to be bypassed), resulting in the inability to establish a normal pressure difference in the scroll expander, thus failing to start and work normally. Therefore, an improved scroll expander is needed to overcome the above technical problems in the prior art. 
     SUMMARY 
     A general summary of the present disclosure is provided in this section, which is not the full scope of the present disclosure or a comprehensive disclosure of all features of the present disclosure. 
     The purpose of the present disclosure is to solve one or more technical problems mentioned above. 
     A scroll expander is provided according to an aspect of the present disclosure, including:
         a housing; and   an expansion mechanism provided inside the housing and configured to expand a high-pressure fluid with an intake pressure to a low-pressure fluid with an exhaust pressure, the expansion mechanism comprising a fixed scroll and an orbiting scroll and defining therein an exhaust chamber, an intake chamber and a series of closed expansion chambers, wherein a back pressure chamber is provided on the expansion mechanism, and the back pressure chamber is in fluid communication with an intermediate pressure chamber of the series of expansion chambers which has an intermediate pressure lower than the intake pressure and higher than the exhaust pressure,   wherein at least one passage in fluid communication from the back pressure chamber to a low-pressure zone with the exhaust pressure is provided, and the passage is configured such that the passage is opened when a pressure in the back pressure chamber is less than a pressure in the low-pressure zone and the passage is closed when a pressure in the back pressure chamber is greater than or equal to a pressure in the low-pressure zone.       

     By providing the passage, in a case that a pressure in the back pressure chamber is less than a pressure in the low-pressure zone, the passage can be opened to make up for the insufficient pressure in the back pressure chamber, and in a case that a pressure in the back pressure chamber is greater than or equal to a pressure in the low-pressure zone, the passage may be closed to maintain the pressure in the back pressure chamber. It can be seen that the above configuration may overcome the technical problem that the scroll expander in the prior art cannot start and work normally. 
     According to an aspect of the present disclosure, the fixed scroll is capable of floating axially relative to the orbiting scroll. 
     According to an aspect of the present disclosure, the back pressure chamber is provided at a back side of an end plate of the fixed scroll, and the back pressure chamber is sealed by a floating sealing ring. 
     According to an aspect of the present disclosure, the low-pressure zone includes a low-pressure area outside the expansion mechanism and the exhaust chamber of the expansion mechanism which is directly communicated with the low-pressure area, and the passage is provided in the end plate of the fixed scroll and is directly communicated with the low-pressure area or directly communicated with the exhaust chamber. 
     According to an aspect of the present disclosure, a check valve capable of closing and opening the passage is provided at the passage such that the passage is opened when a pressure in the back pressure chamber is less than a pressure in the low-pressure zone, and the passage is closed when a pressure in the back pressure chamber is greater than or equal to a pressure in the low-pressure zone. 
     According to an aspect of the present disclosure, the passage includes an orifice that opens into the back pressure chamber, and the check valve is provided at the orifice to close or open the orifice. 
     According to an aspect of the present disclosure, the check valve includes a valve plate and a valve stopper provided at the orifice, and the valve plate is provided as an elastically deformable valve plate fixed at one end or as an integrally movable valve plate, and the valve stopper is provided so that the valve plate is placed between the orifice and the valve stopper. 
     According to an aspect of the present disclosure, the check valve includes a cover provided at the orifice, and in a case that a pressure in the back pressure chamber is less than a pressure in the low-pressure zone, the cover causes the orifice to be opened, and in a case that a pressure in the back pressure chamber is greater than or equal to a pressure in the low-pressure zone, the cover abuts against the orifice to close it. 
     According to an aspect of the present disclosure, the cover is an elastically deformable long valve plate fixed at one end, and the check valve further includes a valve stopper. The valve stopper is configured to place the valve plate between the orifice and the valve stopper, and a side surface of the valve stopper, which faces the valve plate, is formed as an arc surface. 
     The elastically deformable long valve plate is not only simple in structure, but also has good resilience, is durable, and may accurately and timely close the orifice, and has high sensitivity. Preferably, by providing the above valve stopper, a degree of deformation of the long valve plate (a distance away from the orifice) may be effectively controlled, so as to prevent the long valve plate from being excessively deformed due to accidental large force and unable to close the orifice in time. Therefore, the sensitivity of the check valve may be further improved. 
     According to an aspect of the present disclosure, the cover is an integrally movable valve plate, and the check valve further includes a valve stopper, and the valve stopper is configured to place the cover between the orifice and the valve stopper. A predetermined space is provided between the valve stopper and the orifice, which allows the valve plate to move away from the orifice. The integrally movable valve plate has higher pressure difference sensitivity and may fully open the orifice to facilitate fluid flow. 
     According to an aspect of the present disclosure, a groove is formed, around the orifice, on a bottom wall of the back pressure chamber, and the valve stopper is fixed on an inner circumferential wall of the groove. A gap is provided between the valve stopper and the inner circumferential wall of the groove. By providing the gap between the valve stopper and the inner circumferential wall of the groove, it is convenient for fluid to enter and exit the orifice through the gap. 
     According to an aspect of the present disclosure, the cover is a circular sheet and the valve stopper has a cylindrical shape to fit the groove formed in a substantially circular shape. 
     According to an aspect of the present disclosure, the valve stopper has a central through-hole penetrating through two end surfaces, and the central through-hole is substantially perpendicular to the cover. By providing the through-hole, a fluid pressure inside the back pressure chamber may act on the valve plate more directly and evenly, which makes the valve plate difficult to move laterally or tilt, and it is convenient for the valve plate to respond more sensitively to the pressure inside the back pressure chamber, so as to move longitudinally away from or close to the orifice. 
     According to an aspect of the present disclosure, a longitudinal notch is provided on the inner circumferential wall of the groove formed in a substantially circular shape, and the longitudinal notch forms the gap. 
     According to an aspect of the present disclosure, the back pressure chamber and the intermediate pressure chamber are in fluid communication via a breathing hole, and an inner diameter of the passage is larger than an inner diameter of the breathing hole. 
     According to an aspect of the present disclosure, a spring assembly is provided in the back pressure chamber, and an upper end of the spring assembly abuts against the floating sealing ring, and a lower end of the spring assembly abuts against a bottom wall of the back pressure chamber. 
     According to an aspect of the present disclosure, the spring assembly includes at least one supporting element that abuts against the floating sealing ring and at least one elastic element that is provided below the supporting element and abuts against the bottom wall of the back pressure chamber. 
     The arrangement of the spring assembly may further provide support for the floating sealing ring. Moreover, since an elastic support is provided, the axial flexibility of the expansion mechanism is not affected. 
     According to an aspect of the present disclosure, the supporting element is a ring-shaped sheet and the elastic element is a ring-shaped element with an uneven shape in the circumferential direction. The ring-shaped element with an uneven shape in the circumferential direction may provide a better stable bearing and has certain elastic deformation ability. In addition, it only needs to occupy a small space in the longitudinal direction, which is more suitable for a narrow internal space of the back pressure chamber. 
     In general, a scroll expander according to the present disclosure brings at least the following beneficial effects: the scroll expander according to the present disclosure may effectively prevent the scroll expander in the prior art from suffering from technical problems that failing to start or work normally due to insufficient initial pressure in the back pressure chamber. Moreover, the scroll expander of the present disclosure has a simple structure, is easy to be processed and manufactured, and has a higher cost-effectiveness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings, which are merely examples and are not necessarily drawn to scale. The same reference numbers are used in the drawings to indicate the same components, and in the drawings: 
         FIG. 1  shows a longitudinal cross-sectional view of a scroll expander according to a first preferred embodiment of the present disclosure, in which a passage leading from a back pressure chamber to the outside of an expansion mechanism is shown; 
         FIG. 2  shows a schematic fluid expansion circulation system including the scroll expander shown in  FIG. 1 ; 
         FIG. 3  shows a force diagram of a floating sealing ring in an expansion mechanism of a scroll expander in the prior art when the scroll expander is started; 
         FIG. 4  shows a partial longitudinal cross-sectional view of the scroll expander in  FIG. 1 , in which a longitudinal cross-sectional view of a fixed scroll in the expansion mechanism is shown, and the passage directly leading to the outside of the expansion mechanism is shown; 
         FIG. 5 a    shows a partial longitudinal cross-sectional view of the scroll expander in  FIG. 1 , in which a cross-sectional view of a part of a fixed scroll in the expansion mechanism is shown, and a cross-sectional view of a check valve provided in the back pressure chamber is shown; 
         FIG. 5 b    shows an exploded perspective view of the check valve in  FIG. 5   a;    
         FIG. 5 c    shows an enlarged cross-sectional view of the check valve in  FIG. 5 a   , in which the check valve in a state of closing an orifice of the passage is shown; 
         FIG. 5 d    shows an enlarged cross-sectional view of the check valve in  FIG. 5 a   , in which the check valve in a state of opening an orifice of the passage is shown; 
         FIG. 6 a    shows a longitudinal cross-sectional view of a fixed scroll of the scroll expander according to a second preferred embodiment of the present disclosure, in which a cross-sectional view of a check valve provided in the back pressure chamber is shown; 
         FIG. 6 b    shows an exploded perspective view of the check valve in  FIG. 6   a;    
         FIG. 6 c    shows an enlarged cross-sectional view of the check valve in  FIG. 6 a   , in which the check valve in a state of closing an orifice of the passage is shown; 
         FIG. 6 d    shows an enlarged cross-sectional view of the check valve in  FIG. 6 a   , in which the check valve in a state of opening an orifice of the passage is shown; 
         FIG. 7  shows a longitudinal cross-sectional view of a fixed scroll of the scroll expander according to another embodiment of the present disclosure, in which the passage is shown communicating from the back pressure chamber to the exhaust chamber; 
         FIG. 8 a    shows a longitudinal cross-sectional view of an expansion mechanism of the scroll expander according to a third preferred embodiment of the present disclosure, in which a cross-section of a spring assembly provided in the back pressure chamber is shown; 
         FIG. 8 b    shows a perspective view of a supporting element in the spring assembly in  FIG. 8   a;    
         FIG. 8 c    shows a perspective view of an elastic element in the spring assembly in  FIG. 8 a   ; and 
         FIG. 8 d    shows a partial cross-sectional view of the expansion mechanism in  FIG. 8 a   , in which an enlarged cross-sectional view of the spring assembly is shown. 
     
    
    
     REFERENCE MARK LIST 
     
         
         
           
               1 : scroll expander 
               10 : housing 
               14 : top cover 
               16 : bottom cover 
               15 : partition plate 
               17 : intake pipe 
               18 : exhaust pipe 
               40 : main bearing seat 
               30 : rotating shaft 
               52 : stator 
               54 : rotor 
             EM: expansion mechanism 
               22 : fixed scroll 
               24 : orbiting scroll 
               220 : end plate of the fixed scroll 
               11 : external fluid circulation path 
               171 : high-pressure fluid pipe 
               181 : low-pressure fluid pipe 
             K 1 : high-pressure valve 
               100 : bypass pipe 
             K 2 : bypass valve 
             P 1 : first side surface of the end plate of the fixed scroll 
             I: intake port 
               26 : exhaust chamber 
             P 2 : second side surface of the end plate of the fixed scroll 
             C: back pressure chamber 
             S: floating sealing ring 
               28 : intermediate pressure chamber 
             A 1 : low-pressure area 
             A 2 : high-pressure area 
             L: passage 
             V: check valve 
             L 1 : orifice of the passage 
             V 1 : cover 
             V 10 : screw hole of the cover 
             V 2 : screw 
             O: threaded hole 
             V 3 : valve stopper 
             V 30 : screw hole of the valve stopper 
             V 31 : side surface of the valve stopper 
             L 10 : groove 
             L 102 : inner circumferential wall of the groove 
             V 32 : central through-hole of the valve stopper 
             T: spring assembly 
             T 1 : supporting element 
             T 2 : elastic element 
           
         
       
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The preferred embodiments of the present disclosure will be described in detail with reference to  FIGS. 1-8   d . The following description is merely exemplary in nature and is not intended to limit the present disclosure and the disclosure or use thereof. In each figures, corresponding elements or parts use the same reference marks. 
     In the following exemplary embodiments, the scroll expander is exemplarily shown as a vertical scroll expander with a floating fixed scroll. In some cases, the technical idea of providing a passage for fluid communication from a back pressure chamber to a low-pressure zone according to the present disclosure can also be applied to, for example, a case of a floating orbiting scroll expander in which the back pressure chamber is provided on one side of the orbiting scroll. Also, the scroll expander (hereinafter also referred to as “expander”) according to the present disclosure may also be any other suitable types of scroll expanders such as a horizontal scroll expander. 
     The basic configuration and principle of the scroll expander  1  according to the present disclosure will be described below with reference to  FIG. 1 . 
     As shown in  FIG. 1 , a scroll expander  1  includes a substantially cylindrical housing  10 , a top cover  14  provided at one end of the housing  10 , and a bottom cover  16  provided at the other end of the housing  10 . The housing  10 , the top cover  14  and the bottom cover  16  constitute a casing of the scroll expander  1  with a closed space. 
     The scroll expander  1  further includes a partition plate  15  provided between the top cover  14  and the housing  10  for separating the inner space of the expander into a high-pressure area A 2  (also referred to as high-pressure space) and a low-pressure area A 1  (also referred to as low-pressure space). A high-pressure area A 2  is defined between the partition plate  15  and the top cover  14 , and a low-pressure area A 1  is defined between the partition plate  15 , the housing  10  and the bottom cover  16 . An intake pipe  17  for introducing a high-pressure fluid (also referred to as working fluid) is provided in the high-pressure area, and an exhaust pipe  18  for discharging the expanded low-pressure fluid is provided in the low-pressure area A 1 . 
     The scroll expander  1  further includes an expansion mechanism EM composed of a fixed scroll  22  and an orbiting scroll  24 . The orbiting scroll  24  is capable of rotating in translation relative to the fixed scroll  22  (i.e., the center axis of the orbiting scroll  24  revolves around the center axis of the fixed scroll  22 , but the orbiting scroll  24  does not revolve around the central axis of the orbiting scroll  24 ). The translational rotation is achieved by, for example, an oldham coupling provided between the fixed scroll  22  and the orbiting scroll  24 . 
     The fixed scroll  22  includes an end plate  220  of the fixed scroll, a static scroll wrap extending from a first side surface P 1  of the end plate of the fixed scroll and an intake port I provided at the center of the end plate  220  of the fixed scroll for letting the high-pressure fluid enter into the expansion mechanism EM. The orbiting scroll  24  includes an end plate of the orbiting scroll and an orbiting scroll wrap extending from a side surface of the end plate of the orbiting scroll. The expansion mechanism EM defines the following various chambers: an exhaust chamber  26  in fluid communication with an exhaust port of the expansion mechanism EM (the exhaust chamber  26  is in direct fluid communication with the low-pressure area A 1 , and is collectively referred to as the low-pressure zone together with the low-pressure area A 1 ), and an intake chamber in fluid communication with the intake port I, which is formed by the engagement of the static scroll wrap and the orbiting scroll wrap, and a series of closed expansion chambers for volumetric expansion of the working fluid. Specifically, in the series of expansion chambers, the radially innermost expansion chamber is adjacent to the intake port I and has substantially the same intake pressure as the introduced high-pressure fluid, so it is referred to as high-pressure chamber, the radially outermost expansion chamber has substantially the same exhaust pressure as the low-pressure fluid that will be discharged from the expansion mechanism EM, and thus it is referred to as low-pressure chamber. The expansion chamber between the high-pressure chamber and the low-pressure chamber has an intermediate pressure lower than the intake pressure and higher than the discharge pressure, and thus is referred to as intermediate pressure chamber  28 . Wherein, a back pressure chamber C is provided on a second side surface (back side) P 2  of the end plate  220  of the fixed scroll. The back pressure chamber C is sealed by a floating sealing ring S and is in fluid communication with the intermediate pressure chamber  28  through a breathing hole (not shown in the drawings). 
     The high-pressure fluid enters the high-pressure area A 2  in the scroll expander  1  through the intake pipe  17 , and then enters the expansion mechanism EM through the intake port I. The high-pressure fluid entering the expansion mechanism EM flows through the series of expansion chambers with gradually increasing volumes to be expanded and becomes a low-pressure fluid. The low-pressure fluid is discharged to the low-pressure area A 1  outside the expansion mechanism EM, and then is discharged to the outside of the scroll expander  1  through the exhaust pipe  18  communicated with the scroll expander  1 . 
     The scroll expander  1  further includes a main bearing seat  40 . The main bearing seat  40  is fixed relative to the housing  10  by a suitable fastening method. The end plate of the orbiting scroll is supported by the main bearing seat  40 . 
     The scroll expander  1  further includes a rotating shaft (may also be referred to as an output shaft)  30 . The rotating shaft  30  is rotatably supported by a main bearing provided in the main bearing seat  40 . An end of the rotating shaft  30  is coupled to a hub of the orbiting scroll  24  to be driven to rotate. When the scroll expander  1  is running, a driving torque is generated during a fluid expansion process performed by the expansion mechanism EM, which drives the rotating shaft  30  to rotate to output mechanical or electrical work. 
     The scroll expander  1  may further include a generator composed of a stator  52  and a rotor  54 . The stator  52  is fixed to the housing  10 . The rotor  54  is provided between the stator  52  and the rotating shaft  30 . The rotor  54  is fixed to an outer circumferential surface of the rotating shaft  30  to rotate together with the rotating shaft  30  when the scroll expander  1  is operating, thereby enabling the generator to generate electricity. 
     In practical applications, a schematic fluid expansion circulation system shown in  FIG. 2  (for example, an organic Rankine cycle system using a Carnot cycle) may include: the scroll expander  1  as described above; and an external fluid circulation path  11 , wherein the external fluid circulation path  11  includes: a high-pressure fluid pipe  171  in fluid communication with an intake pipe  17  of the scroll expander  1 , and the high-pressure fluid pipe  171  is configured to supply the intake pipe  17  with high-pressure fluid from an evaporator; a low-pressure fluid pipe  181  in fluid communication with the exhaust pipe  18  of the scroll expander  1 , and the low-pressure fluid pipe  181  is configured to supply a condenser with low-pressure fluid exhausted from the scroll expander  1 ; and other pumping elements (such as a working medium pump as shown in the figure). A high-pressure valve K 1  is provided on the high-pressure fluid pipe  171 , and provided between the evaporator and the intake pipe  17 . A bypass pipe  100  branched from the high-pressure fluid pipe  171  between the high-pressure valve K 1  and the evaporator is in fluid communication with the low-pressure fluid pipe  181 , and a bypass valve K 2  is provided on the bypass pipe  100 . 
     Generally, it is necessary to preheat various elements on the external fluid circulation path  11  (especially heat exchanger such as evaporator and condenser) before supplying the high-pressure fluid into the expansion mechanism EM. First, the high-pressure valve K 1  is closed and the bypass valve K 2  is opened to establish a fluid circulation circuit composed of the high-pressure fluid pipe  171 , the bypass pipe  100 , and the low-pressure fluid pipe  181 , etc. At this time, a high-pressure side and a low-pressure side of the fluid circulation circuit are in fluid communication. Also, the low-pressure area A 1  (and the exhaust chamber  26 ) in the housing  10  of the scroll expander  1  may still be in communication with the low-pressure fluid pipe  181 , and thus a pressure in the low-pressure area A 1  (and the exhaust chamber  26 ) is basically the same as a pressure of the high-pressure fluid that is about to enter into the expansion mechanism EM. Since the low-pressure area A 1  is in fluid communication with the exhaust chamber  26  and therefore has the same fluid pressure, and hereinafter the low-pressure area A 1  is taken as an example to describe stresses of the scroll expander in the prior art during a startup process. 
     In a scroll expander in the prior art, referring to  FIG. 3 , it can be seen that when the scroll expander is started to work, a floating sealing ring is under the following forces: at first, when the high-pressure valve K 1  is opened and the bypass valve K 2  is closed, and the high-pressure fluid is started to be input into the high-pressure area A 2  in the scroll expander  1 , a high-pressure stress (or intake stress) F 1  and a low-pressure stress (or exhaust stress) F 2  in the low-pressure area A 1  (at this time, the low-pressure stress F 2  are basically the same as the high-pressure stress F 1 ) are acted on the floating sealing ring S at the same time (as shown in  FIG. 3 ) and the forces are directed at urging the floating sealing ring S to collapse into the back pressure chamber C. Also, the pressure of the fluid entering into the back pressure chamber C through the intermediate pressure chamber  28  is dropped to an intermediate pressure F 3  as the volume is expanded. It is obvious that F 3 &lt;F 1  and F 3 &lt;F 2 . Therefore, it may be clearly seen from  FIG. 3  that a resultant force F 3 +F 1  that provides support to the floating sealing ring S is less than a resultant force F 1 +F 2  that urge the floating sealing ring S to collapse into the back pressure chamber C. Therefore, since it is not capable of providing sufficient bearing force, the floating sealing ring S is unbalanced in force and therefore collapses into the back pressure chamber C and cannot play the role of sealing isolation. In particular, a top end of an upper plate of the floating sealing ring is moved away from, for example, a lower surface of the partition plate, so that the low-pressure area A 1  and the high-pressure area A 2  are directly connected, and the high-pressure fluid is then directly bypassed to the low-pressure area A 1  through the high-pressure area A 2  without entering into the expansion mechanism EM, and thus a normal pressure difference cannot be established in the scroll expander  1 , and therefore the scroll expander  1  cannot start and work normally. 
     In view of the above technical problems, the present disclosure improves the scroll expander in the prior art. In general, the present disclosure improves the back pressure chamber C to be in fluid communication with the low-pressure zone when its pressure is insufficient, and to be isolated from the low-pressure zone when its pressure reaches a certain level, which can effectively solve the above problems, and normal start-up and operation of the scroll expander are achieved. Specifically, improved scroll expanders according to several preferred embodiments of the present disclosure are described in detail below with reference to  FIGS. 4 to 8   d.    
       FIGS. 4 to 5   d  show partial views of the scroll expander in  FIG. 1  according to the first preferred embodiment of the present disclosure. Reference is made to  FIG. 4 , which shows a longitudinal sectional view of the fixed scroll  220  in the expansion mechanism EM, and shows that the passage L in the fixed scroll  220  directly extends from the back pressure chamber C to the low-pressure area A 1  outside the expansion mechanism EM (it may be seen from  FIG. 1  and  FIG. 2  that the expansion mechanism EM is in the low-pressure area A 1 ). The passage L includes an orifice L 1  that opens toward the back pressure chamber C, and a check valve V is provided near the orifice L 1  to close and open the orifice L 1 . Preferably, in the present embodiment, a groove L 10  is provided around the orifice L 1  for accommodating the check valve V in the groove L 10 , so as to better protect the check valve V from external interference. 
     Referring to  FIGS. 5 a  to 5 d   , an exemplary check valve V is shown. According to the present embodiment, the check valve V may include: a cover L 1 , wherein the cover L 1  is shown as a long valve plate with a screw hole V 10  at one end; and a screw V 2 , wherein the screw V 2  passes through the screw hole V 10  of the cover L 1  and fits to a corresponding threaded hole O to fix the cover L 1  so that the other end of the cover L 1  covers the orifice L 1 , wherein the cover L 1  is made of a material with elastic deformation property in the present embodiment, such as metal, high molecular polymers, etc., so that when a pressure in the back pressure chamber C is less than a pressure in the low-pressure area A 1  in communication with the passage L, the cover L 1  is elastically deformed and bends toward the back pressure chamber C, thereby opening the orifice L 1 . 
     According to the above configuration, in a preheating stage before starting the scroll expander  1  according to the present disclosure, a pressure in the back pressure chamber C is less than the low-pressure stress F 2  in the low-pressure area A 1  (at this time, the low-pressure stress F 2  is substantially equal to the high-pressure fluid pressure). Therefore, under the dominant action of the low-pressure stress F 2 , the cover V 1  of the check valve V elastically deforms to open the orifice L 1 , so that fluid in the low-pressure area A 1  enters into the back pressure chamber C through the passage L, until the pressure in the back pressure chamber C is approximately equal to the low-pressure stress F 2 , so that the floating sealing ring S is maintained in a force-balanced state. When the high-pressure fluid is supplied to the expansion mechanism EM (the bypass valve K 2  is closed at this time), the pressure of the high-pressure fluid is reduced after volume expansion (the high-pressure fluid reaches the back pressure chamber C through the intermediate pressure chamber  28  and then has the intermediate pressure stress F 3 , at this time F 3 &lt;F 2 , F 2 =F 1 ) and enters the back pressure chamber C so that the pressure in the back pressure chamber is less than the low-pressure stress F 2  in the low-pressure area A 1 , and thus the cover V 1  of the check valve V is elastically deformed to open the orifice L 1 . The fluid from the low-pressure area A 1  enters the back pressure chamber C to provide pressure compensation to the back pressure chamber C so as to maintain a force balance of the floating sealing ring S (referring to  FIG. 3 , it should be pointed out that there may be a certain frictional force between a sealing part of the floating sealing ring and a wall that abuts against the sealing part. Although the frictional force is not shown in  FIG. 3 , it should be understood by those skilled in the art). The floating sealing ring S keeps sealing so as to isolate the high-pressure area A 2  and the low-pressure area A 1  in the housing  10  of the scroll expander  1 . With the continuous expansion of high-pressure fluid, it becomes low-pressure fluid and is discharged into the low-pressure area A 1 , so that the low-pressure stress F 2  in the low-pressure area A 1  gradually drops to a stress equal to the exhaust pressure. Therefore, the force of the fluid in the low pressure area A 1  acting on the floating sealing ring S gradually decreases and is less than the intermediate pressure stress F 3  in the back pressure chamber C. When the intermediate pressure stress F 3  in the back pressure chamber C is sufficient to maintain a force balance of the floating sealing ring S, the check valve V in the back pressure chamber C keeps the passage L closed. At this time, a stable intermediate pressure stress F 3  is maintained in the back pressure chamber C, and a stable pressure difference is also established in the scroll expander  1  to ensure a normal operation of the scroll expander  1 . 
     In the present embodiment, preferably, the check valve V further includes a valve stopper V 3 . The valve stopper V 3  is a long sheet as shown in  FIG. 5 b   . A first end of the valve stopper V 3  has a screw hole V 30  for a screw V 2  to pass through and is fastened by the screw V 2  to abut against the cover V 1 . That is, as shown in the figure, the cover V 1  is provided between the orifice L 1  and the valve stopper V 3 , and a second end of the valve stopper V 3  is located above the orifice L 1 . In the present embodiment, a side surface V 31  of the valve stopper V 3 , facing the cover V 1 , is formed as an arc surface, and the arc surface extends away from the orifice L 1  as extending away from the first end, so that a certain gap is provided between the side surface V 31  of the valve stopper V 3  and the orifice L 1 , which allows the cover V 1  to be elastically deformed under the action of pressure of the fluid from the orifice L 1  to bend toward the back pressure chamber C, as shown in the figures, and thus the orifice L 1  is opened (referring to  FIG. 5 d   ). Since the presence of the valve stopper V 3 , a degree of elastic deformation of the cover V 1  is limited, so that the cover V 1  may quickly recover to close the orifice L 1  (referring to  FIG. 5 c   ), which makes the cover V 1  more sensitive. In practical applications, the valve stopper V 3  may have any possible shape, for example, the valve stopper V 3  itself or its side surface V 31  has a stepped shape or other shapes, as long as it may ensure that there is a certain space between the side surface V 31  of the valve stopper V 3  and the orifice L 1 . 
     In the above description, although it is shown that the cover V 1  has a flat sheet shape so that it is elastically deformed only in a case of opening the orifice L 1 , it does not exclude cases that the cover V 1  is elastically deformed only in a case of closing the orifice L 1 , and the cover V 1  is elastically deformed in both cases of closing and opening the orifice L 1 . According to actual application requirements, not only materials with suitable elastic deformation resistance may be selected, but also the shape and/or orientation of the cover V 1  may be set in advance, so that the cover V 1  may be elastically deformed only in a case of closing the orifice L 1  or in both cases of opening and closing the orifice L 1 . For example, referring to  FIG. 5 b   , the cover V 1  itself may have an arc shape, and is fixed to abut against the valve stopper V 3  under normal conditions as shown in  FIG. 5 b   . In this case, the cover V 1  opens the orifice L 1  without being elastic deformed. In a case that the cover V 1  is forced to close the orifice L 1  (as shown in  FIG. 5 c   ), the cover V 1  is elastically deformed. For another example, on this basis, the curvature of the cover V 1  is changed, so that it is in a middle position between the orifice L 1  and the valve stopper V 3  in a natural state and does not abut against either one. Obviously, the cover V 1  is elastically deformed in both cases of closing and opening the orifice L 1 . 
     In addition, in the present embodiment, the check valve V is provided at the orifice L 1  of the passage L, but in practical applications, the check valve may also be designed in the passage L or provided at the other orifice in the passage L which faces an outside opening of the expansion mechanism EM. In the case of being provided at the other orifice, only a change of position of the check valve V according to the present disclosure is involved, which is not described here. In the case of being provided in the passage L, the present embodiment may be achieved by using any suitable check valve in the prior art, for example, a flap-type valve that is elastically deformed, or an element similar to the check valve in a tire inflation hole. Even, it is also possible to consider the use of an electronic control valve, which is controlled by a controller for example to open and close according to the sensed related data or to open and close at a predetermined timing (for example, the electronic control valve is controlled to open when the expander is started and to close after a predetermined time). 
     In addition, in the present embodiment, the check valve V is shown to include a cover V 1  and a valve stopper V 3  fixed together by a screw V 2  as described above, and the cover V 1  is elastically deformed to open the orifice L 1 . However, in practical applications, the check valve V is not limited to the above structure. On the one hand, the cover V 1  and the valve stopper V 3  may be fixed in any other suitable ways, for example, snap joint, hinge joint, riveting, welding, and adhesion, etc. In addition, the cover V 1  and the valve stopper V 3  may be fixed in different ways and different positions, or only the valve stopper V 3  is fixed, and the cover V 1  is a movable element that is completely limited in position and movement range by the valve stopper V 3 . On the other hand, the cover V 1  itself may also be made of non-elastically deformable materials. For example, the cover V 1  may be in a blade form fixed by hinge joint, etc., which is pivotally openable, and the valve stopper V 3  is fixed to limit an opening size of the cover V 1  pivotally opened. Furthermore, the valve stopper V 3  may be made of a material that can be elastically deformed to a certain extent so as to restrict the opening size of the cover V 1  pivotally opened through the elastic deformation in a certain degree. 
       FIGS. 6 a  to 6 d    show the second embodiment according to the present disclosure. Referring to  FIG. 6 b   , in the present embodiment, the passage L has the same configuration as the first embodiment, and the check valve V is also provided at the orifice L 1 . The check valve V includes a cover V 1  and a valve stopper V 3 . Exemplarily, in  FIGS. 6 a  to 6 d   , the cover V 1  is shown as a circular valve plate, the valve stopper V 3  is shown as a cylindrical element, and the valve stopper V 3 , at its center, has a central through-hole V 32  that penetrates two circular end faces. Referring to  FIGS. 6 c  and 6 d   , it may be seen that the cover V 1  is placed in the groove L 10  on the outer circumference of the orifice L 1  and covers the orifice L 1 . The valve stopper V 3  is fixed at a position above the orifice L 1  in a predetermined spaced location to allow the cover V 1  reciprocate between the orifice L 1  and the valve stopper V 3 , and the central through-hole V 32  of the valve stopper V 3  is perpendicular to the cover V 1 , so that the fluid pressure in the back pressure chamber C may be uniformly applied to the cover V 1 . As mentioned above, the valve stopper V 3  in the present embodiment may also be fixed to the back pressure chamber C in various suitable ways. In the present embodiment, the valve stopper V 3  is preferably fitted in the groove L 10  by an interference snap fit. Also, as shown in the figure, there is a gap between one side of the valve stopper V 3  and an inner peripheral wall L 102  of the groove L 10 , wherein the gap may be formed by expanding a part of the groove L 10  radially outward. The gap is to facilitate fluid communication between the back pressure chamber C and an external pressure zone in a case that the orifice L 1  is opened. 
     In a case that a pressure in the back pressure chamber C is less than a pressure in the low-pressure area A 1 , the cover V 1  is pushed up to the valve stopper V 3 , the orifice L 1  is opened (referring to  FIG. 6 d   ), so that the back pressure chamber C is communicated with the low-pressure area A 1  communicated with the orifice L 1  through the gap. In a case that the pressure in the back pressure chamber C is greater than or equal to the pressure of the low-pressure area A 1 , the cover V 1  is pressed to be abut against the orifice L 1 , thereby closing the orifice L 1 . 
     Although the passage L in the above preferred embodiments is in direct communication from the back pressure chamber C to the low-pressure area A 1  outside the expansion mechanism EM, the present disclosure is not limited to this. For example, as shown in  FIG. 7 , the passage L may also be communicated from the back pressure chamber C to the exhaust chamber  26  in the expansion mechanism EM. As described above, the exhaust chamber  26  is in fluid communication with the exhaust port of the expansion mechanism EM, so as to be in fluid communication with the low-pressure area A 1 . Therefore, the passage L with this configuration may also be used to achieve the technical object of the present disclosure. 
     On the other hand, as mentioned above, the back pressure chamber C is in fluid communication with the intermediate pressure chamber  28  through the breathing hole (not shown in the drawings). Therefore, when the scroll expander is started, in a case that a pressure in the back pressure chamber C is greater than a pressure in the intermediate pressure chamber  28 , fluid in the back pressure chamber C flows into the intermediate pressure chamber  28  through the breathing hole, so that a fluid pressure in the back pressure chamber C drops to a pressure below the pressure in the low-pressure zone (the low-pressure area A 1  and the exhaust chamber  26 ). Therefore, in order to increase the pressure in the back pressure chamber C as soon as possible and better keep the pressure in the back pressure chamber C the same as the low-pressure zone, an inner diameter of the passage L may be made larger than an inner diameter of the breathing hole. In particular, the passage L may be provided so that the diameters of each cross-sections of the passage L are significantly larger than the diameter of the breathing hole, so as to ensure that the amount of fluid entering into the back pressure chamber C through the passage L is much greater than the amount of fluid flowing into the intermediate pressure chamber  28  from the back pressure chamber C through the breathing hole. 
     The above preferred embodiments are all involved with the passage L and the check valve V. However, the present disclosure may also adopt other different elements to provide support for the floating sealing ring S to ensure a normal startup and operation of the scroll expander  1 . For example,  FIGS. 8 a  to 8 d    show the third preferred embodiment according to the present disclosure. 
     According to the third preferred embodiment, on the basis of the first and second preferred embodiments, a spring assembly T is added. As shown in the figures, the spring assembly T includes a supporting element T 1  ( FIG. 8 b   ) and an elastic element T 2  ( FIG. 8 c   ), wherein the supporting element T 1  abuts against and supports the floating sealing ring S, and the elastic element T 2  is provided under the supporting element T 1  and abuts against the bottom wall of the back pressure chamber C, so as to provide elastic support for the supporting element T 1  and the floating sealing ring S. According to the present disclosure, the supporting element T 1  may be any suitable element with a stable bearing capacity, and the elastic element T 2  may be any suitable element with an elastic deformation capacity, such as a coil spring, a leaf spring, a disc spring, etc. In the present embodiment, preferably, the supporting element T 1  is shown as a ring-shaped sheet, and the elastic element T 2  is shown as a ring-shaped element having an uneven shape, preferably a wave shape, in the circumferential direction. And preferably, as shown in  FIG. 8 d   , the supporting element T 1  has a certain thickness, and the elastic element T 2  may be formed by stacking and combining multiple of the above ring-shaped elements with the irregular shape. For example, as shown in the figures, the elastic element T 2  is formed by stacking and combining two of the above ring-shaped elements with the irregular shape. 
     Those skilled in the art should understand that the spring assembly T of the above configuration is only an exemplary embodiment, and it may also be an integral part, and may have any suitable configuration. By providing such a spring assembly T, it is possible to further provide support for the floating sealing ring S to ensure the normal startup and operation of the scroll expander  1 . In addition, although the passage L, the check valve V, and the spring assembly T are all adopted in the scroll expander of the third embodiment described above, it should be understood that, in a case that the spring assembly T may provide sufficient supporting force to the floating sealing ring S, the passage L and the check valve V may not be provided at all, and only the spring assembly T is adopted. 
     Although the passage, the orifice of the passage, the check valve and its cover and valve stopper, the spring assembly and its supporting element and elastic element in the above preferred embodiment are all shown as a specific number, it should be understood that any number of the above elements may be set respectively. 
     Although the exemplary embodiments of the scroll expander according to the present disclosure are described in the above embodiments, the present disclosure is not limited thereto, but various modifications, replacements and combinations can be performed without departing from the spirit and protection scope of the present disclosure. 
     Obviously, various implementations can be further designed by combining or modifying different embodiments and each technical feature in different ways. 
     The scroll expanders according to the preferred embodiments of the present disclosure are described above in conjunction with the specific implementations. It can be understood that, the above description is merely exemplary rather than restrictive, and those skilled in the art can conceive various variations and modifications without departing from the scope of the present disclosure with reference to the above description. These variations and modifications shall still fall in the protection scope of the present disclosure.