Abstract:
A rotary compressor, comprising: a housing ( 12 ), comprising a lubricant oil storage part for containing lubricating oil; a compression mechanism ( 20 ) disposed in the housing ( 12 ); a driving mechanism ( 30 ) driving the compression mechanism ( 20 ), the driving mechanism ( 30 ) comprising a rotation shaft ( 50 ), through-holes ( 54, 56 ) extending along the axial direction of the rotating shaft ( 50 ) are disposed inside the rotating shaft ( 50 ), and the rotation shaft ( 50 ) is in fluid connection with the lubricating oil storage part via the through-holes ( 54, 56 ); and an oil level sensor ( 120 ) in fluid connection with the through-holes ( 54, 56 ) inside the rotation shaft ( 50 ) via a pressurized collection channel ( 110 ). Also disclosed is a rotation mechanism, comprising an oil level sensor ( 120 ) in fluid connection with the through-holes ( 54, 56 ) inside the rotation shaft ( 50 ) via the pressurized collection channel ( 110 ). Accurate and reliable detection of the lubricating oil in a compressor can be done using the pressurized collection channel and the oil level sensor, thus greatly saving cost and improving compressor reliability.

Description:
[0001]    The present application claims the benefit of priorities to Chinese patent application No. 201110104725.1 titled “ROTARY COMPRESSOR AND ROTARY MACHINE”, filed with the Chinese State Intellectual Property Office on Apr. 18, 2011 and Chinese patent application No. 201120124863.1 titled “ROTARY COMPRESSOR AND ROTARY MACHINE”, filed with the Chinese State Intellectual Property Office on Apr. 18, 2011. The entire disclosures thereof are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to a rotary compressor and a rotary machine. 
       BACKGROUND OF THE INVENTION 
       [0003]    The rotary compressor generally comprises a shell, a compressing mechanism disposed in the shell, a driving mechanism for driving the compressing mechanism and so on. In order to ensure the normal operation of the compressor, there must be sufficient lubricating oil in the compressor. The lubricating oil level in the compressor should be higher than a lowest protection lubricating oil level. When the lubricating oil level in the compressor is lower than the lowest protection lubricating oil level, the compressor should be shut off. 
         [0004]    A twin compressor system or even a multiple compressor system has been used widely. In this kind of twin or multiple compressor system, one or more of the compressors may be activated selectively and the others may be shut off, therefore lubricating oil would move in these compressors which may cause lubricating oil unbalance among compressors, even results in a situation that some compressors lack of lubricating oil. 
         [0005]    In addition, lacking of lubricating oil may occur due to oil leakage in the compressor or oil leakage in the compressor system consisting of a single compressor or a plurality of compressors. 
         [0006]    Furthermore, in the large refrigeration system having long pipeline and a great number of components, the lubricating oil may be unable to circulate back to the compressor in time, which causes lubricating oil shortage in the compressor. 
         [0007]    As a result, the lubricating oil status (for example, height of lubricating oil level) in the compressor must be detected accurately to shut off the compressor timely and prevent the compressor from being damaged. 
       SUMMARY OF THE INVENTION 
     Technical Problems to be Solved 
       [0008]    However, most of the compressors have no built-in oil level sensor presently. 
         [0009]    Although there are some liquid level sensors for detecting liquid level, these liquid level sensors are only suitable for detecting the liquid level in an oil tank or in a container. These sensors includes: piezoelectric liquid level sensor, reed switches liquid level sensor, ultrasonic liquid level sensor, photoelectric liquid level sensor and so on. The above mentioned sensors generally cannot be used in a hermetic compressor, since the working environment within the hermetic compressor is rigorous. For example, the ranges of the temperature and the pressure within the compressor are wide, and the pressure and the temperature would cycle, and there may be cast impurity etc. In addition, lubricating oil foam may be formed in the compressor. Therefore, these sensors cannot detect height of lubricating oil level accurately. 
         [0010]    Accordingly, there is a need for a rotary compressor which can detect lubricating oil in the compressor more simply and reliably. 
       Technical Solutions 
       [0011]    An object of one or more embodiments of the disclosure is to provide a rotary compressor which can detect lubricating oil within the compressor simply and reliably. 
         [0012]    Another object of one or more embodiments of the disclosure is to provide a rotary machine which can detect lubricating oil within the rotary machine simply and reliably. 
         [0013]    One aspect of the description provides a rotary compressor, comprising a shell including an oil sump for receiving lubricating oil; a compressing mechanism disposed in the shell; a driving mechanism for driving the compressing mechanism, the driving mechanism includes a rotary shaft provided therein with a through hole extending in an axial direction of the rotary shaft and the rotary shaft is in fluid communication with the oil sump via the through hole; and an oil level sensor in fluid communication with the through hole in the rotary shaft through a pressure picking passage. 
         [0014]    Preferably, the rotary compressor further comprises a lower bearing housing for supporting the rotary shaft, wherein the pressure picking passage comprises a pressure picking hole extending through a side wall of the rotary shaft and in fluid communication with the through hole in the rotary shaft, a circumferential oil groove formed on the rotary shaft or the lower bearing housing and in fluid communication with the pressure picking hole, and a communicating channel extending through the lower bearing housing and in fluid communication with the circumferential oil groove and the oil level sensor. 
         [0015]    Preferably, the rotary compressor further comprises a pressure picker disposed between the rotary shaft and the oil level sensor, wherein the pressure picking passage comprises a pressure picking hole extending through a side wall of the rotary shaft and in fluid communication with the through hole in the rotary shaft, a circumferential oil groove formed on the rotary shaft or the pressure picker and in fluid communication with the pressure picking hole, and a communicating channel extending through the pressure picker and in fluid communication with the circumferential oil groove and the oil level sensor. 
         [0016]    Preferably, the pressure picking passage further comprises a pressure picking pipe disposed in the pressure picking hole and protruded toward an axis of the through hole in the rotary shaft. 
         [0017]    Preferably, a length of the pressure picking pipe is determined according to a lowest protection lubricating oil level in the oil sump. 
         [0018]    Preferably, the higher the lowest protection lubricating oil level is set, the longer the length of the pressure picking pipe is set. 
         [0019]    Preferably, the lowest protection lubricating oil level and the length of the pressure picking pipe satisfy the following equation: 
         [0000]    
       
         
           
             
               H 
               = 
               
                 h 
                 - 
                 
                   
                     
                       
                         ( 
                         
                           R 
                           - 
                           L 
                         
                         ) 
                       
                       2 
                     
                     · 
                     
                       
                         ( 
                         
                           
                             
                               n 
                               60 
                             
                             · 
                             2 
                           
                            
                           
                               
                           
                            
                           π 
                         
                         ) 
                       
                       2 
                     
                   
                   
                     2000 
                     · 
                     g 
                   
                 
               
             
             , 
           
         
       
     
         [0000]    wherein, H [mm] is a height of the lowest protection lubricating oil level from an end face of the rotary shaft; L[mm] is a length of the pressure picking pipe protruded into the rotary shaft; R [mm] is an inner radius of the rotary shaft; h [mm] is a height of a central axis of the pressure picking pipe from the end face of the rotary shaft; n [rpm] is the number of revolution of the rotary shaft; g [m/s 2 ] is the acceleration of gravity. 
         [0020]    Preferably, a height of the pressure picking hole from a certain reference surface (S) is determined according to the lowest protection lubricating oil level in the oil sump. 
         [0021]    Preferably, the higher the lowest protection lubricating oil level is set, the higher the height of the pressure picking hole is set. 
         [0022]    Preferably, the reference surface is a bottom surface of the rotary compressor or an end surface of the rotary shaft. 
         [0023]    Preferably, the rotary compressor further comprises an oil pumping mechanism which includes a plate with a hole provided at an end of the rotary shaft and an oil fork provided in the through hole of the rotary shaft. 
         [0024]    Preferably, the oil pumping mechanism includes a vane pump provided at an end of the rotary shaft. 
         [0025]    Preferably, the rotary compressor is a horizontal rotary compressor and an inner space of the rotary compressor is divided into high side acting as the oil sump and low side by a muffler plate, and the oil pumping mechanism is an oil pipe extending from the oil sump to the through hole in the rotary shaft. 
         [0026]    Preferably, the through hole comprises a concentric hole portion which is concentric with respect to the rotary shaft and an eccentric hole portion which is offset radially with respect to the concentric hole. 
         [0027]    Preferably, the oil level sensor is a pressure sensor. 
         [0028]    Preferably, the oil level sensor is a pressure switch. 
         [0029]    Preferably, the oil level sensor comprises: a fluid pressure receiving portion for receiving pressure of fluid; and a converting portion for converting the pressure of fluid into an electrical signal. 
         [0030]    Preferably, the fluid pressure receiving portion comprises a housing and a piston head which is movable axially in the housing; the converting portion comprises a terminal plug, a first contact and a second contact provided in the terminal plug, a spring for providing electrical connection between the piston head and the second contact and providing return force for the piston head, wherein the oil level sensor outputs the electric signal when the piston head contacts the first contact. 
         [0031]    Preferably, the first contact comprises a plurality of pins which are spaced with each other. 
         [0032]    Preferably, the second contact comprises an annular contact lug electrically contacted with the spring. 
         [0033]    Preferably, the rotary compressor further comprises an oil temperature sensor. 
         [0034]    Preferably, the oil temperature sensor and the oil level sensor have a common lead wire. 
         [0035]    Preferably, the oil level sensor is provided near the lower bearing housing. 
         [0036]    Preferably, the oil level sensor is directly connected with the communicating channel in the lower bearing housing or in the pressure picker. 
         [0037]    Preferably, the oil level sensor is connected with the communicating channel in the lower bearing housing or in the pressure picker through an additional pipeline. 
         [0038]    Preferably, the rotary compressor is a scroll compressor, or a screw compressor, or a rotor compressor. 
         [0039]    Preferably, the oil level sensor is disposed inside the shell or outside the shell. 
         [0040]    Preferably, when the oil level sensor is disposed outside the shell, the pressure picking passage further comprises a connecting pipe in fluid communication with the communicating channel in the lower bearing housing or in the pressure picker. 
         [0041]    Preferably, the connecting pipe is arranged horizontally or obliquely. 
         [0042]    Another aspect of the disclosure provides a rotary machine, comprising a shell including an oil sump for receiving lubricating oil; a rotary shaft disposed in the shell, wherein the rotary is provided therein with a thorough hole extending in an axial direction of the rotary shaft and the rotary shaft is in fluid communication with the oil sump via the through hole; and an oil level sensor in fluid communication with the through hole in the rotary shaft through a pressure picking passage. 
         [0043]    Preferably, the rotary machine further comprises a bearing housing for supporting the rotary shaft, wherein the pressure picking passage comprises a pressure picking hole extending through a side wall of the rotary shaft and in fluid communication with the through hole in the rotary shaft, a circumferential oil groove formed on the rotary shaft or the bearing housing and in fluid communication with the pressure picking hole, and a communication channel extending through the bearing housing and in fluid communication with the circumferential oil groove and the oil level sensor. 
         [0044]    Preferably, the rotary machine further comprises a pressure picker disposed between the rotary shaft and the oil level sensor, wherein the pressure picking passage comprises a pressure picking hole extending through a side wall of the rotary shaft and in fluid communication with the through hole in the rotary shaft, a circumferential oil groove formed on the rotary shaft or the pressure picker and in fluid communication with the pressure picking hole, and a communicating channel extending through the pressure picker and in fluid communication with the circumferential oil groove and the oil level sensor. 
       Technical Effects 
       [0045]    The advantages of the rotary compressor and the rotary machine according to one or more embodiments of the present disclosure are as follows: 
         [0046]    The compressor or the rotary machine is provide therein with an oil level detecting mechanism, therefore lubricating oil in the compressor or the rotary machine can be detected timely, accurately and reliably to prevent or reduce the damage of the compressor or the rotary machine due to insufficient lubricating oil. 
         [0047]    The oil level detecting mechanism may include an oil level sensor and a pressure picking passage in fluid communication with the through hole in the rotary shaft, and the oil level sensor may be a pressure sensor or a pressure switch. Thereby, the oil level detecting mechanism may have a relatively simple configuration and may be machined easily, which reduces the cost of the compressor or the rotary machine. 
         [0048]    In one or more embodiments of the disclosure, the lubricating oil in the compressor or the rotary machine can be detected more easily and reliably by converting the oil level detecting in the compressor or the rotary machine into hydraulic pressure detecting. And the expensive liquid level sensor can be replaced by a pressure sensor or a pressure switch having simpler configuration and lower cost. 
         [0049]    A lubricating oil level to be detected can be adjusted more easily by controlling the length of the pressure picking pipe or the height of the pressure picking hole. Therefore, it is applicable in various types or models of compressor or rotary machine more easily. 
         [0050]    The oil level sensor in one or more embodiments of the disclosure has relatively simple configuration and low cost, but has high reliability and short response time. 
         [0051]    The first contact of the oil level sensor includes a plurality of pins spaced with each other, and the ON signal may be output as long as any one of the pins contact the piston head. Therefore, the reliability of the oil level sensor is enhanced. 
         [0052]    The oil level sensor may be disposed inside or outside the shell of the compressor, and the oil level sensor may communicate directly with the pressure picking passage or communicate with the pressure picking passage through an additional pipeline, thereby greatly facilitating the arrangements of the components in the compressor. 
         [0053]    The rotary compressor in one or more embodiments of the present disclosure provides not only an oil level sensor but also an oil temperature sensor, thus can provide multi-protection for the compressor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0054]    The characteristics and advantages of one or more embodiments of the disclosure will become more apparent with reference to the description in conjunction with the accompanied drawings in which: 
           [0055]      FIG. 1  is a schematic sectional view of the rotary compressor according to an embodiment of the disclosure; 
           [0056]      FIG. 2  is an enlarged view of a lower portion of the rotary compressor shown in  FIG. 1 ; 
           [0057]      FIG. 3  is a schematic diagram of an oil level detecting mechanism according to the embodiment of the disclosure; 
           [0058]      FIG. 4  is a perspective view of a lower bearing integrated with an oil level sensor according to the embodiment of the disclosure; 
           [0059]      FIG. 5  is an oil fork provided in the rotary compressor according to the embodiment of the disclosure; 
           [0060]      FIG. 6  is a front view of an oil level sensor according to the embodiment of the disclosure; 
           [0061]      FIG. 7  is a sectional view of an oil level sensor according to the embodiment of the disclosure, showing the oil level sensor in an OFF status; 
           [0062]      FIG. 8  is a sectional view of an oil level sensor according to the embodiment of the disclosure, showing the oil level sensor in an ON status; 
           [0063]      FIG. 9  is a schematic diagram of an oil level detecting mechanism according to another embodiment of the disclosure; 
           [0064]      FIG. 10  is a schematic diagram of a variant of the oil level detecting mechanism according to another embodiment of the disclosure; 
           [0065]      FIG. 11  illustrates the relationships among a lowest protection lubricating oil level, an inner radius of the rotary shaft, height of a pressure picking pipe and length of the pressure picking pipe; 
           [0066]      FIG. 12  is a schematic diagram of an oil level detecting mechanism according to still another embodiment of the disclosure; and 
           [0067]      FIGS. 13A and 13B  are schematic sectional views of a lower portion of the rotary compressor according to a further embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0068]    The following description of the preferred embodiments is only illustrative rather than limiting the present disclosure and application or use thereof. 
         [0069]    The basic configuration of the rotary compressor according to the present disclosure will be described with reference to  FIG. 1  hereinafter.  FIG. 1  is a schematic sectional view of a rotary compressor according to an embodiment of the disclosure. The rotary compressor shown in  FIG. 1  is a scroll compressor, however, it should be appreciated by those skilled in the art that the present disclosure is not limited to the scroll compressor as shown, but may be applicable in other types of compressor with a rotary shaft, such as a screw compressor, a rotor compressor and so forth, and any types of rotary machine with a rotary shaft. In addition, the present disclosure is applicable not only in a vertical compressor with a rotary shaft oriented vertically but in a horizontal compressor with a rotary shaft oriented horizontally. 
         [0070]    The rotary compressor  10  includes a generally cylindrical shell  12 . An inlet fitting  13  for sucking gaseous refrigerant in low pressure is provided on the shell  12 . One end of the shell  12  is connected fixedly with an end cover  14 . The end cover  14  is fitted with a discharging fitting  15  for discharging compressed refrigerant. A muffler plate  16  extending transversely relative to an axial direction of the shell  12  (approximately extending in the horizontal direction in  FIG. 1 ) is provided between the shell  12  and the end cover  14 , to divide an inner space of the compressor into a high side and a low side. The space between the end cover  14  and the muffler plate  16  acts as the high side space and the space between the muffler plate  16  and the shell  12  acts as the low side space. A part of the shell  12  functions as an oil sump for receiving lubricating oil. In the example shown in  FIG. 1 , the oil sump is located at a lower portion of the shell  12 . 
         [0071]    The shell  12  has a compressing mechanism  20  and a driving mechanism  30  housed therein. In the example shown in  FIG. 1 , the compressing mechanism  20  includes a non-orbiting scroll component  22  and an orbiting scroll component  24  which are engaged with each other. The driving mechanism  30  includes a motor  40  and a rotary shaft  50 . The motor  40  includes a stator  42  and a rotor  44 . The stator  42  is connected fixedly with the shell  12 . The rotor  44  is connected fixedly with the rotary shaft  50  and rotates within the stator  42 . The first end (the upper end in  FIG. 1 ) of the rotary shaft  50  is provided with an eccentric crank pin  52  and the second end (the lower end in  FIG. 1 ) of the rotary shaft  50  may includes a concentric hole  54 . The concentric hole  54  extends to the eccentric crank pin  52  at the first end of the rotary shaft  50  via an eccentric hole  56  offset radially with respect to the concentric hole  54 . The rotary shaft  50  is in fluid communication with the oil sump through the concentric hole  54 . 
         [0072]    The first end of the rotary  50  is supported by a main bearing housing  60  and the second end thereof is supported by a lower bearing housing  70 . The main bearing housing  60  and the lower bearing housing  70  are connected fixedly to the shell  12  in proper ways. The eccentric crank pin  52  of the rotary shaft  50  is inserted into the hub  26  of the orbiting scroll component  24  via a bush  58  to rotatably drive the orbiting scroll component  24 . 
         [0073]    The second end (the lower end in  FIG. 1 ) of the rotary shaft  50  may further be provided with an oil pumping mechanism  80 . In the example shown in  FIG. 1 , the oil pumping mechanism  80  may include a plate with a hole  82  provided at the second end of the rotary shaft  50  and an oil fork  84  provided in the concentric hole  54  and rotating along with the rotary shaft  50 . The plate with a hole  82  is approximately a disc with a through hole  83  provided centrally.  FIG. 5  shows an example of the oil fork  84 . As shown in  FIG. 5 , the oil fork  84  includes an approximately rectangular base  86 , legs  87  and  88  extending in the same direction from the base  86  and branched. Planes on which the legs  87  and  88  lie are inclined with respect to a plane on which the base lies in a rotary direction A of the rotary shaft  50 , respectively. 
         [0074]    The lubricating oil in the lower portion of the shell  12  flows into the concentric hole  54  of the rotary shaft  50  through the through hole  83  of the plate with a hole  82  when the compressor operates. The lubricating oil flows radially from the center of the plate with a hole  82  to periphery of the plate with a hole  82  and an inner wall of the concentric hole  54  under the centrifugal force. Being brought by the legs  87  and  88  of the oil fork  83  rotating with the rotary shaft  50 , the lubricating oil is pumped upwardly and forms a shape which is approximately a paraboloid P in the concentric hole  54 , as shown in  FIG. 3 . And then, the lubricating oil flows into the eccentric hole  56  in fluid communication with the concentric hole  52  and arrives at an end of the eccentric crank pin  52 . After being discharged from the end of the eccentric crank pin  52 , the lubricating oil flows downwardly under the gravity and is splashed by various moving components and then lubricates and cools various moving components. 
         [0075]    In the example shown in  FIG. 1 , the oil pumping mechanism consisting of the plate with a hole  82  and the oil fork  84  is used. However, those skilled in the art should understand that, the oil pumping mechanism is not limited to what described herein and may use any mechanisms that can supply lubricating oil to the concentric hole  54  of the rotary shaft  50 . In addition, the oil pumping mechanism consisting of the plate with a hole  82  and the oil fork  84  shown in  FIG. 1  may be replaced by a vane pump. Furthermore, in a horizontal compressor, an oil pipe extending from the high side to the concentric hole of the rotary shaft at the low side may be used as the oil pumping mechanism since most of the lubricating oil is stored in the high side (in this case, the high side acts as the oil sump described above), in this circumstance, the lubricating oil may be supplied by a pressure difference between the high side and the low side. 
         [0076]    Besides, those skilled in the art should understand that, the compressing mechanism  20  and the driving mechanism  30  are not limited to the configurations shown in the figures. Instead, the compressing mechanism  20  may be a rotor compressing mechanism or a screw compressing mechanism and so forth, and the driving mechanism  30  may be a hydraulic driving mechanism, a pneumatic driving mechanism and various transmission driving mechanism provided inside the shell or outside the shell. 
         [0077]    The following documents provide the other detailed information of the rotary compressor related to the embodiments of the present disclosure: CN201206549Y, US2009/0068048A1, US2009/0068045A1, US2009/0068044A1 and US2009/0068043A1. The entire disclosures of these documents are incorporated herein by reference. 
         [0078]    There must be sufficient lubricating oil in the compressor so as to ensure the normal operation of the compressor. In other words, the compressor should be shut off when the amount of lubricating oil, for example, a height of a lubricating oil level, in the compressor is lower than a predetermined value, for example, a lowest protection lubricating oil level, to prevent the compressor from being damaged. 
         [0079]    Hereinafter, an oil level detecting mechanism will be described with reference to  FIGS. 1 to 8 .  FIG. 2  is an enlarged view of a lower portion of the rotary compressor in  FIG. 1 .  FIG. 3  is a perspective view of an oil level detecting mechanism according to the embodiment of the present disclosure.  FIG. 4  is a perspective view of a lower bearing integrated with an oil level sensor according to the embodiment of the present disclosure. 
         [0080]    As shown in  FIGS. 1 to 3 , the rotary compressor  10  according to the embodiment of the present disclosure further includes an oil level detecting mechanism  100  provided in the compressor  10 . The oil level detecting mechanism  100  according to the embodiment of the present disclosure may include an oil level sensor  120  in fluid communication with the concentric hole  54  of the rotary shaft  50  through a pressure picking passage  110 . In the example shown in  FIG. 3 , the pressure picking passage  110  may include a pressure picking hole  112  extending through a side wall of the rotary shaft  50  in an approximately radial direction, a circumferential oil groove  114  provided in the lower bearing housing  70  and in fluid communication with the pressure picking hole  112  and a communicating channel  116  provided in the lower bearing housing  70  extending through the lower bearing housing  70  in an approximately radial direction and in fluid communication with the circumferential oil groove  114  and the fluid inlet  122  of the oil level sensor  120 . The oil level sensor  120  may be provided at the lower bearing housing  70  or near the lower bearing housing  70 . During the rotation of the rotary shaft  50 , the pressure picking hole  112  on the rotary shaft  50  also be rotated. Since the circumferential oil groove  114  is provided corresponding to the rotation path of the pressure picking hole  112 , the pressure picking hole  112  can always be in fluid communication with the circumferential oil groove  114 , and in turn always be in fluid communication with the communicating channel  116 , so as to introduce the fluid stably into the oil level sensor  120  connected therewith. 
         [0081]      FIG. 6  is a front view of an oil level sensor according to the embodiment of the present disclosure, wherein the housing of the oil level sensor is not shown in the figure. 
         [0082]      FIG. 7  is a sectional view of an oil level sensor according to the embodiment of the present disclosure, showing the oil level sensor in an OFF state.  FIG. 8  is a sectional view of an oil level sensor according to the embodiment of the present disclosure, showing the oil level sensor in an ON state. 
         [0083]    As shown in  FIGS. 6 to 8 , the oil level sensor  120  may include an approximately cylindrical housing  121 , a piston cap  123  movable axially in the housing  121 , a piston head  125  moving with the piston cap  123 , a terminal plug  126  closing an end of the housing  121 , a first contact  127  and a second contact  128  provided in the terminal plug  126  and a return spring provided between the piston head  125  and the terminal plug  126 . A fluid inlet  122  is provided on a side wall of an end of the housing  121  opposing to the terminal plug  126  and a discharge outlet  124  is formed on a side wall of the shell  121 . During the axial movement of the piston head  125 , fluid between the piston head  125  and the terminal plug  126  is discharged through the discharge outlet  124  to reduce resistance to the supplied fluid. A piston rod  125   a  of the piston head  125  extends through a through hole  131  formed in the terminal plug  126  and is movable axially in the through hole  131 . The first contact  127  may include a plurality of pins  127 A and  127 B spaced with each other but connected with each other. In the example of the figures, the first contact  127  includes two pins  127 A and  127 B, however, those skilled in the art should understand that, the first contact  127  may include only one pin or more than two pins. The second contact  128  may include an annular contact lug  128 A. The annular contact lug  128 A is provided on a step of the terminal plug  126 . The return spring  129  is connected electrically with the annular contact lug  128 A of the second contact  128  and the piston head  125 . Besides, as shown in  FIG. 2 , the first contact  127  and the second contact  128  of the oil level sensor  120  lead to the outside of the compressor through an adaptor  150  provided on the shell  12 . 
         [0084]    As shown in  FIG. 7 , when there is no fluid supplied to the inlet  122  of the oil level sensor  120 , the piston head  125 , under the action of the return spring  129 , moves toward a direction opposing to the first contact  127  and the second contact  128 , so as to disconnect the first contact  127  and the second contact  128 . Meanwhile, the oil level sensor  120  outputs no signals, or outputs a signal “0”. 
         [0085]    As shown in  FIG. 8 , when fluid is supplied to the inlet  122  of the oil level sensor  120 , the piston head  125 , pushed by the fluid supplied, overcomes the force of the return spring  129  and moves towards the first contact  127  and the second contact  128 . When the piston head  125  contacts any one of the pins of the first contact  127 , the first contact  127  and the second contact  128  can be connected electrically. Then, the oil level sensor  120  outputs an ON signal, or outputs a signal “1”. 
         [0086]    A specific oil level sensor is illustrated in  FIGS. 6 to 8 . It should be appreciated by those skilled in the art that, the oil level sensor may be any kind of sensor including a fluid pressure receiving portion for receiving pressure of fluid and a converting portion for converting the pressure of fluid into an electric signal. 
         [0087]    Hereinafter, the process of detecting lubricating oil in the rotary compressor according to the embodiment of the present disclosure will be described. When there is a proper amount of lubricating oil in the shell  12  of the compressor, lubricating oil entering into the concentric hole  54  of the rotary shaft  50 , under the action of centrifugal force, forms a paraboloid P as shown in  FIG. 3 . Then, the lubricating oil flows into the fluid inlet  122  of the oil level sensor  120  through the pressure picking hole  112  on the side wall of the rotary shaft, the circumferential oil groove  114  formed in the lower bearing housing  70  and the communicating channel  116  in the lower bearing housing  70 . As described above, the piston head  125 , being pushed by the lubricating oil, moves towards the first contact  127  and the second contact  128  and connect electrically the first contact  127  and the second contact  128  finally, so as to output the signal “1” which indicates that there is a proper amount of lubricating oil in the compressor. In contrary, if there is no sufficient amount of lubricating oil in the shell  12  of the compressor, no lubricating oil arrives at the inlet  122  of the oil level sensor  120 , therefore, the oil level sensor  120  outputs the signal “0” which indicates that there is no sufficient amount of lubricating oil in the compressor. 
         [0088]    In order to detect the lubricating oil level in the compressor more accurately, a pressure picking pipe  118  protruding towards an axis of the concentric hole  54  may be disposed in the pressure picking hole  122  on a side wall of the rotary shaft. A lubricating oil level to be detected may be controlled by the length of the pressure picking pipe  118  protruding inwardly (for example, the length L shown in  FIGS. 9 and 11 ). As shown in  FIG. 3 , when a distal end  119  of the pressure picking pipe  118  is located within the oil surface denoted by the paraboloid P, lubricating oil is capable of flowing into the pressure picking pipe  118 . During the movement along the pressure picking pipe  118 , kinetic energy of the lubricating oil can be converted into the pressure, thereby a certain pressure difference is produced between the both ends of the pressure picking pipe  118 . When lubricating oil with a certain pressure flows into the oil level sensor  120 , the piston head  125  of the oil level sensor  120  is pushed thereby connecting electrically the first contact  127  and the second contact  128 , and thus the sensor outputs the signal “1”. If the distal end  119  of the pressure picking pipe  118  is located outside the oil surface donated by the paraboloid P, lubricating oil cannot flow into the oil level sensor  120  and thus the sensor outputs the signal “0”. Accordingly, when a lubricating oil level to be detected (i.e. a lowest protection lubricating oil level) is set higher, a longer pressure picking pipe  118  may be used, while when a lubricating oil level to be detected (i.e. a lowest protection lubricating oil level) is set lower, a shorter pressure picking pipe  118  may be used. Particularly, the relationship between the lowest protection lubricating oil level and a length of the pressure picking pipe  118  when the compressor is operated in a certain working state may be determined by calculation or experiment. 
         [0089]    Specifically referring to  FIG. 11 , the lower protection lubricating oil level and the length of the pressure picking pipe  118  may satisfy the following equation: 
         [0000]    
       
         
           
             
               H 
               = 
               
                 h 
                 - 
                 
                   
                     
                       
                         ( 
                         
                           R 
                           - 
                           L 
                         
                         ) 
                       
                       2 
                     
                     · 
                     
                       
                         ( 
                         
                           
                             
                               n 
                               60 
                             
                             · 
                             2 
                           
                            
                           π 
                         
                         ) 
                       
                       2 
                     
                   
                   
                     2000 
                     · 
                     g 
                   
                 
               
             
             , 
           
         
       
     
         [0090]    wherein, H [mm] is a height of the lowest protection lubricating oil level from an end face S 0  of the rotary shaft  50 ; 
         [0091]    L [mm] is a length of the pressure picking pipe  118  protruded into the rotary shaft  50 ; 
         [0092]    R [mm] is an inner radius of the rotary shaft  50 ; 
         [0093]    h [mm] is a height of a center axis of the pressure picking pipe  118  from the end face S 0  of the rotary shaft  50 ; 
         [0094]    n [rpm] is the number of revolution of the rotary shaft; and 
         [0095]    g [m/s 2 ] is the acceleration of gravity. 
         [0096]    According to the above equation, for example, if h=32 mm, L=6.9 mm, n=2000 rpm, R=9 mm, g=9.81 m/s 2 , then H≈22 mm. That is, when the number of revolution of the rotary shaft is 2000 rpm and the length of the pressure picking pipe protruded into the rotary shaft is 6.9 mm, the lowest protection lubricating oil level that can be detected by the oil level sensor is about 22 mm. That is, when the lubricating oil level in the oil sump is higher than 22 mm, the oil level sensor can output the signal “1”, indicating that the compressor can operate normally. And when the lubricating oil level in the oil sump is lower than 22 mm, the oil level sensor cannot output the signal “1” (i.e. it outputs the signal “0”), indicating that there is no sufficient lubricating oil in the compressor, then a compressor protection mechanism would shut off the compressor. 
         [0097]    Except the method of providing the pressure picking pipe mentioned above, a lubricating oil level in the compressor may be detected more accurately by adjusting the height h of the pressure picking hole  112  from a certain reference surface (for example, the reference surface S in  FIG. 9 , it may be a bottom surface of the compressor, and also may be an end surface S 0  of the rotary shaft  50 ). In particularly, when a lubricating oil level to be detected (i.e. a lowest protection oil level) is set higher, the height of the pressure picking hole  112  from a certain reference surface may be set higher, and when a lubricating oil level to be detected (i.e. a lowest protection oil level) is set lower, the height of the pressure picking hole  112  from a certain reference surface may be set lower. Specifically, the relationship between a lubricating oil level to be detected and a height of the pressure picking hole  112  from a certain reference surface when the compressor is operated in a certain working state may be determined by calculation or experiment. 
         [0098]    In the example shown in  FIG. 3 , the pressure picking passage  110  includes a pressure picking hole  112  provided on a side wall of the rotary shaft, a circumferential oil groove  114  provide in a lower bearing housing  70 , a communicating channel  116  extending through the lower bearing housing  70 , and optionally includes a pressure picking pipe  118  provided in the pressure picking hole  112 . However, the configuration of the pressure picking passage  110  is not limited to what described herein, but can have various variants. For example, the circumferential oil groove  112  may be provided on the rotary shaft  50 , rather than provided on the lower bearing housing  70 . In addition, for example, as shown in  FIGS. 9 and 10 , a pressure picker  130  may further be provide between the rotary shaft  50  and the oil level sensor  120 . In the example shown in  FIG. 9 , the pressure picker  130  is an annular element and includes a circumferential oil groove  114 A in fluid communication with the pressure picking hole  112  on the rotary shaft  50  and a communicating channel  116 A in fluid communication with the circumferential oil groove  114 A and extending through the pressure picker  130 . In the example shown in  FIG. 10 , a circumferential oil groove  114 B may be disposed on the rotary shaft  50 . The fluid inlet  122  of the oil level sensor  120  may be in fluid communication with the communicating channel  116 A of the pressure picker  130  directly or through other pipelines. The oil level sensor  120  may be arranged more flexibly by providing the pressure picker  130 , and the configuration of the lower bearing housing  70  needn&#39;t be modified. 
         [0099]    In an example of the oil level detecting mechanism according to the present disclosure shown in  FIG. 11 , an oil temperature sensor  140  may be provided further. The oil temperature sensor  140  and the oil level sensor  120  may use a common lead wire  142 . In particularly, lead wires  141  and  142  output signals of the oil level sensor  120 , and lead wires  142  and  143  output signals of the oil temperature sensor. In this embodiment, the compressor may be controlled not only based on signals of the oil level sensor  120  but also based on signals of the oil temperature sensor  140 . Thus it provides double protection for the compressor. 
         [0100]    In the embodiments shown in the figures, the oil level detecting mechanism  100  is in fluid communication with the concentric hole  54 . However, it should be understood by those skilled in the art that, the concentric hole  54  may be replaced by an eccentric hole extending axially along the rotary shaft  50 . Besides, basing on the inner design of the compressor, the oil level detecting mechanism  100  may be in fluid communication with the eccentric hole  56  of the rotary shaft  50 . Even if the holes  54  and  56  are all eccentric holes, the oil level detecting mechanism of the disclosure still can operate normally because of the centrifugal force caused by rotation of the rotary shaft. 
         [0101]    In the embodiments of the disclosure, an oil level sensor including a piston, contacts and a spring is described. Those skilled in the art should understand that, any suitable pressure sensor known in the art, specifically a pressure switch, may be used as the oil level sensor. 
         [0102]    In the embodiments mentioned above, the oil level sensor  120  is illustrated to be disposed in the shell  12  and can be in fluid communication with the communicating channel  116  in the lower bearing housing  70  or the communicating channel  116 A in the pressure picker  130  directly or by an additional pipeline. However, the present disclosure is not limited to what is described herein. As shown in  FIGS. 13A and 13B , the oil level sensor  120  may be provided outside the shell  12  and in fluid communication with the communicating channel  116  in the lower bearing housing  70  (or a communicating channel in the pressure picker) through the connecting pipe  160 . The connecting pipe  160  may be arranged horizontally (as shown in  FIG. 13A ) or be arranged obliquely (as shown in  FIG. 13B ). With this kind of configuration, the various components within the compressor can be arranged more flexibly. 
         [0103]    While various embodiments of the present disclosure have been described in detail herein, it should be understood that the present disclosure is not limited to the specific embodiments described in detail and illustrated herein, those skilled in the art can make other variants and modifications without departing from the principle and scope of the present disclosure. All these variants and modifications fall into the scope of the present disclosure. Furthermore, all the elements described herein can be replaced by the other technically equivalent elements.