Patent Publication Number: US-2020300241-A1

Title: Electric oil pump

Description:
The present application claims the priority to Chinese Patent Application No. 201710769833.8, titled “ELECTRIC OIL PUMP”, filed with the National Intellectual Property Administration on Aug. 31, 2017, which is incorporated herein by reference in its entirety. 
     FIELD 
     The present application relates to the field of vehicles, and in particular to components of a vehicle lubrication system and/or a vehicle cooling system. 
     BACKGROUND 
     The automobile industry is developing rapidly. With the automobile performance developing toward safer, more reliable, more stable, fully automated, intelligent and environment-friendly and energy saving, electric oil pumps are widely used in vehicle thermal management systems, and can well meet the market requirements. 
     The electric oil pump mainly provides power for the vehicle lubrication system and/or the vehicle cooling system. How to design the structure of the electric oil pump to improve the structure and the performance of the electric oil pump is an urgent technical problem to be solved. 
     SUMMARY 
     An object of the present application is to provide an electric oil pump. 
     In order to achieve the above object, the following technical solution is provided according to the present application. 
     The electric oil pump includes a pump housing, a first rotor assembly, a pump shaft, a second rotor assembly, a stator assembly and a circuit board assembly. The pump housing at least includes a first housing, a second housing and a third housing. The electric oil pump has a pump inner chamber, the pump inner chamber includes a first inner chamber and a second inner chamber, a sidewall forming the first inner chamber includes part of the first housing and part of the second housing, and a sidewall forming the second inner chamber includes part of the second housing and part of the third housing. The first rotor assembly is accommodated in the first inner chamber. The second rotor assembly, the stator assembly and the circuit board assembly are accommodated in the second inner chamber. The electric oil pump includes a partition portion, the partition portion is located between the first housing and the third housing, and the first inner chamber and the second inner chamber are located on two sides of the partition portion. The first inner chamber and the second inner chamber are separated by the partition portion; or the electric oil pump further includes a sealing portion, and the first inner chamber and the second inner chamber are separated by the partition portion and the sealing portion. Since a working medium in the first inner chamber of the electric oil pump is not in communication with a working medium in the second inner chamber, the working medium in the first inner chamber cannot enter the second inner chamber. Thus, the second inner chamber does not need to be additionally provided with other structures to prevent the components in the second inner chamber from corrosion, and the electric oil pump has better sealing performance and a simpler structure, which helps to reduce costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a first embodiment of an electric oil pump according to the present application; 
         FIG. 2 a    is a schematic sectional view of the electric oil pump shown in  FIG. 1  taken along one direction; 
         FIG. 2 b    is a schematic sectional view of a second embodiment of the electric oil pump according to the present application; 
         FIG. 2 c    is a schematic sectional view of a third embodiment of the electric oil pump according to the present application; 
         FIG. 2 d    is a schematic sectional view of a fourth embodiment of the electric oil pump according to the present application; 
         FIG. 3  is a schematic sectional view of the electric oil pump shown in  FIG. 1  taken along another direction; 
         FIG. 4  is a schematic front view of the electric oil pump shown in  FIG. 1 ; 
         FIG. 5  is a schematic front view of the electric oil pump that is not assembled with the first housing shown in  FIG. 1 ; 
         FIG. 6  is a schematic perspective view of a first embodiment of the first housing shown in  FIG. 1  viewed from one direction; 
         FIG. 7  is a schematic perspective view of the first embodiment of the first housing shown in  FIG. 1  viewed from another direction; 
         FIG. 8  is a schematic front view of the first housing shown in  FIG. 6  viewed from one direction; 
         FIG. 9  is a schematic front view of the first housing shown in  FIG. 6  viewed from another direction; 
         FIG. 10  is a schematic sectional view of the first housing shown in  FIG. 6  taken along one direction; 
         FIG. 11  is a schematic sectional view of the first housing shown in  FIG. 6  taken along another direction; 
         FIG. 12  is a schematic sectional view of another embodiment of the first housing shown in  FIG. 1 ; 
         FIG. 13  is a schematic perspective view of a first embodiment of the second housing shown in  FIG. 1  or  FIG. 2 a    viewed from one direction; 
         FIG. 14  is a schematic perspective view of the first embodiment of the second housing shown in  FIG. 1  or  FIG. 2 a    viewed from another direction; 
         FIG. 15  is a schematic sectional view of the second housing shown in  FIG. 13 ; 
         FIG. 16  is a partially enlarged schematic view of portion B of the second housing shown in  FIG. 15 ; 
         FIG. 17  is a schematic sectional view of a fifth embodiment of the electric oil pump according to the present application; 
         FIG. 18  is a schematic sectional view of the second housing shown in  FIG. 17 ; 
         FIG. 19  is a schematic sectional view of a sixth embodiment of the electric oil pump according to the present application; 
         FIG. 20  is a schematic perspective view of the third housing shown in  FIG. 1  viewed from one direction; 
         FIG. 21  is a schematic front view of the third housing shown in  FIG. 19 ; 
         FIG. 22  is a schematic perspective view of the third housing shown in  FIG. 1  viewed from another direction; 
         FIG. 23  is another schematic front view of the third housing shown in  FIG. 19 ; 
         FIG. 24  is a schematic sectional view of the third housing shown in  FIG. 19 ; 
         FIG. 25  is a schematic perspective view of the partition plate shown in  FIG. 2 a    to  FIG. 3  viewed from one direction; 
         FIG. 26  is a schematic perspective view of the partition plate shown in  FIG. 2 a    to  FIG. 3  viewed from another direction; 
         FIG. 27  is a schematic front view of the partition plate shown in  FIG. 25  or  FIG. 26 ; 
         FIG. 28  is a schematic sectional view of the partition plate shown in  FIG. 25  or  FIG. 26 ; 
         FIG. 29  is a schematic perspective view of a combination of a mounting bracket and a capacitor shown in  FIG. 2 a    to  FIG. 3 ; 
         FIG. 30  is a schematic front view of the combination of the mounting bracket and the capacitor shown in  FIG. 29 ; 
         FIG. 31  is a schematic perspective view of the mounting bracket shown in  FIG. 2 a    to  FIG. 3 ; 
         FIG. 32  is a schematic front view of the mounting bracket shown in  FIG. 31 ; and 
         FIG. 33  is a partially enlarged schematic view of portion C of the mounting bracket shown in  FIG. 31 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present application is further illustrated hereinafter in conjunction with drawings and specific embodiments. 
     An electric oil pump can be applied in a vehicle lubrication system and/or a vehicle cooling system to provide circulating power for the working medium in the vehicle lubrication system and/or the vehicle cooling system, and the vehicle lubrication system and/or the vehicle cooling system can provide lubricating oil and/or cooling oil for a transmission system. 
     Referring to  FIG. 1 ,  FIG. 2 a    and  FIG. 3 , an electric oil pump  100  includes a pump housing, a second rotor assembly  3 , a stator assembly  4 , a pump shaft  5 , a first rotor assembly  8  and a circuit board assembly  6 . The first rotor assembly  8 , the second rotor assembly  3  and the circuit board assembly  6  are arranged along an axial direction of the electric oil pump  100 , so that the axial arrangement of the electric oil pump  100  can be more compact. Specifically, the second rotor assembly  3  is arranged between the first rotor assembly  8  and the circuit board assembly  6 . The electric oil pump has a pump inner chamber. The second rotor assembly  3 , the stator assembly  4 , the pump shaft  5 , the first rotor assembly  8  and the circuit board assembly  6  are accommodated in the pump inner chamber. When the electric oil pump  100  is in operation, the circuit board assembly  6  controls the stator assembly  4  to generate a varying excitation magnetic field by controlling a current passing through the stator assembly  4  to change according to a certain rule, the second rotor assembly  3  rotates under the action of the excitation magnetic field, and the second rotor assembly  3  drives the first rotor assembly  8  to rotate by the pump shaft  5 . When the first rotor assembly  8  rotates, the working medium is extruded out of a second flow port, thereby generating the power for flowing. 
     The pump housing at least includes a first housing, a second housing and a third housing. Specifically, referring to  FIG. 2 a   , in the present embodiment, the pump housing includes a first housing  1 , a second housing  2  and a third housing  7 . The electric oil pump can form a pump inner chamber, and in the present embodiment, the pump inner chamber includes a first inner chamber  80  and a second inner chamber  90 . The working medium can flow through the first inner chamber  80 , and the first rotor assembly  8  is arranged in the first inner chamber  80 . No working medium flows through the second inner chamber  90 . The stator assembly  4 , the second rotor assembly  3  and the circuit board assembly  6  are arranged in the second inner chamber  90 . A sidewall forming the first inner chamber  80  includes part of the first housing  1  and part of the second housing  20 , and a sidewall forming the second inner chamber  90  includes part of the second housing  20  and part of the third housing  7 . Referring to  FIG. 2 a   , the electric oil pump  100  includes a partition portion  22 . The first inner chamber  80  and the second inner chamber  90  are located on two sides of the partition portion  22 , respectively. The electric oil pump  100  further includes a sealing portion  50 . The first inner chamber  80  is separated from the second inner chamber  90  by the partition portion  22  and the sealing portion  50 , so that the working medium in the first inner chamber  80  is not in communication with the working medium in the second inner chamber  90  through the separation by the partition portion  22  and the sealing portion  50 . Such an arrangement completely separates the stator assembly  4  and the circuit board assembly  6  from the working medium, thereby ensuring that the performance of the stator assembly and the circuit board assembly is not affected by the working medium. Structures of the sealing portion  50  and the partition portion  22  are described in detail hereinafter. 
     Referring to  FIG. 1 ,  FIG. 2 a    and  FIG. 3 , the first rotor assembly  8  is close to one end of the pump shaft  5 , the first rotor assembly  8  is connected with part of the pump shaft  5 , the second rotor assembly  3  is close to the other end of the pump shaft  5 , and the second rotor assembly  3  is connected with part of the pump shaft  5 , so that the second rotor assembly  3  can drive the first rotor assembly  8  to rotate by the pump shaft  5 . The circuit board assembly  6  is close to one end of the pump shaft  5  mounted with the second rotor assembly  3 . One end of the pump shaft  5  extends into the first inner chamber  80 , and the other end of the pump shaft  5  extends into the second inner chamber  90 . Specifically, one end of the pump shaft  5  close to the first rotor assembly  8  extends into the first inner chamber  80 , and the other end of the pump shaft  5  close to the second rotor assembly  3  extends into the second inner chamber  90 . 
     The electric oil pump includes the partition portion. The first inner chamber and the second inner chamber are located on two sides of the partition portion, respectively. The partition portion is located between the first housing and the second housing. The first rotor assembly and the second rotor assembly are arranged on two sides of the partition portion, and the first inner chamber is separated from the second inner chamber through the partition portion. Four embodiments about the arrangement of the partition portion are described below. 
     Referring to  FIG. 1  and  FIG. 2 a   ,  FIG. 1  and  FIG. 2 a    are schematic structural views of a first embodiment of the electric oil pump. The structure of the first embodiment of the electric oil pump is described below. 
     Referring to  FIG. 1  and  FIG. 2 a   , in the present embodiment, the pump housing includes the first housing  1 , the second housing  2  and the third housing  7 . The second housing  2  is closer to the second rotor assembly  3  than the first housing  1 , the first housing  1  is detachably connected with the second housing  2 , and the second housing  2  is detachably connected with the third housing  7 , which facilitates the inspection and maintenance for the components arranged in the chamber compared with non-detachable housing connection. For example, if the connection between the first housing  1  and the second housing  2  is opened, an operation status of the first rotor assembly  8  can be inspected, and the first rotor assembly  8  can be replaced as needed; and if the connection between the second housing  2  and the third housing  7  is opened, an operation status of the circuit board assembly  6  can be inspected, and the circuit board assembly can be maintained and replaced as needed, without destroying other components of the electric oil pump, which helps to reduce costs and improve the maintenance efficiency. Specifically, in the present embodiment, the first housing  1  is detachably connected with the second housing  2  through a first connection portion, and the second housing  2  is detachably connected with the third housing  7  through a second connection portion. The first connection portion and the second connection portion are not arranged in the first inner chamber  80  or the second inner chamber  90 . The first connection portion and the second connection portion are described in detail below. 
     Referring to  FIG. 2 a    and  FIG. 15 , the second housing  2  includes the partition portion  22 . The partition portion  22  can support the first rotor assembly  8 . The second housing  2  further includes a main body portion  21 , the main body portion  21  extends along an axial direction of the second housing  2 , the main body portion  21  is cylindrical, and an inner wall of the main body portion  21  can form at least part of the sidewall of the second inner chamber  90  shown in  FIG. 2 a   . The first housing  1  is detachably connected with the main body portion  21 , and the main body portion  21  is detachably connected with the third housing  7  as well. In the present embodiment, the sidewall forming the first inner chamber  80  in  FIG. 2 a    includes part of the first housing  1  and part of the second housing  2 , and the sidewall forming the second inner chamber  90  in  FIG. 2 a    includes part of the second housing  2  and part of the third housing  7 . In the present embodiment, the partition portion  22  is circumferentially arranged along the inner wall of the main body portion  21 , that is, the partition portion  22  is fixed to the main body portion  21 . In the present embodiment, the partition portion  22  is integrally formed with the main body portion  21 , and the partition portion  22  is arranged substantially perpendicular to the main body portion  21 , where the “substantially” refers to that the perpendicularity is within a range of 1 mm. In the present embodiment, the partition portion  22  is arranged at a middle-upper portion of the second housing  2 , the second inner chamber  90  is formed between the partition portion  22  and the third housing  7 , and the first inner chamber  80  is formed between the first housing  1  and the partition portion  22 . Such a structure can ensure the sealing of the connection between the partition portion  22  and the main body portion  21 , and can prevent the working medium in the first inner chamber  80  in  FIG. 2 a    from leaking through the connection between the main body portion  21  and the partition portion  22 , and the structure is simple. 
     Referring to  FIG. 2 b   ,  FIG. 2 b    is schematic structural view of a second embodiment of the electric oil pump. The structure of the second embodiment of the electric oil pump is described below. 
     In the second embodiment of the electric oil pump, the electric oil pump further includes a fourth housing, and the second housing includes the partition portion. Specifically, referring to  FIG. 2 b   , an electric oil pump  100   a  includes a first housing  1   a , a second housing  2   a , a third housing  7   a  and a fourth housing  40   a . The first housing  1   a  is detachably connected with the second housing  2   a  and the fourth housing  40   a . The third housing  7   a  is detachably connected with the fourth housing  40   a . Specifically, the second housing  20   a  includes a main body portion  21   a , the first housing  1   a  is connected with the main body portion  21   a  of the second housing  2   a  through screws or bolts, and the main body portion  21   a  of the second housing  2   a  is connected with the fourth housing  40   a  through screws or bolts. An electric oil pump  100   b  includes a partition portion  22   a , and the partition portion  22   a  is integrally formed with the second housing  2   a . Specifically, the partition portion  22   a  is integrally formed with the main body portion of the second housing  20   a . Compared with the first embodiment of the electric oil pump, in the present embodiment, the electric oil pump further includes the fourth housing  40   a , and the structure of the second housing  20   a  in the present embodiment is different from the structure of the second housing in the first embodiment of the electric oil pump. The structure of the second housing in the present embodiment is equivalent to dividing the second housing in the first embodiment of the electric oil pump into two components, which is relatively advantageous for saving raw materials during component processing and is further advantageous for reducing material costs during processing. 
     Referring to  FIG. 2 c   ,  FIG. 2 c    is schematic structural view of a third embodiment of the electric oil pump. The structure of the third embodiment of the electric oil pump is described below. 
     In the third embodiment of the electric oil pump, the partition portion is an individual component. Specifically, referring to  FIG. 2 c   , the electric oil pump  100   b  includes a first housing  1   b , a second housing  2   b , a third housing  7   b  and a fourth housing  40   b , the first housing  1   b  is detachably connected with the second housing  2   b , and the third housing  7   b  is detachably connected with the fourth housing  40   b . In the present embodiment, the electric oil pump  100   b  further includes a partition portion  22   b , and the partition portion  22   b  is arranged between the second housing  2   b  and the fourth housing  40   b . In the present embodiment, the partition portion  22   b  is detachably connected with the first housing  1   b  and the second housing  2   b . The first housing  1   b , the second housing  2   b , the partition portion  22   b  and the fourth housing  40   b  are detachably connected with each other through screws and bolts. Apparently, in order to ensure the sealing of the connections of the components, sealing rings can be provided at the connections. Compared with the first embodiment of the electric oil pump, in the present embodiment, the partition portion is an individual component, which is advantageous for relatively reducing the processing difficulty of the second housing and saving raw materials during the component processing, and is further advantageous for reducing the material costs during processing. 
     Referring to  FIG. 2 d   ,  FIG. 2 d    is schematic structural view of a fourth embodiment of the electric oil pump. The structure of the fourth embodiment of the electric oil pump is described below. 
     In the fourth embodiment of the electric oil pump, the electric oil pump further includes a fourth housing, and the fourth housing includes a partition portion. Specifically, referring to  FIG. 2 d   , an electric oil pump  100   c  includes a first housing  1   c , a second housing  20   c , a third housing  7   c  and a fourth housing  40   c . The first housing  1   c  is detachably connected with the second housing  2   c  and the fourth housing  40   c , and the third housing  7   c  is detachably connected with the fourth housing  40   c . Specifically, the first housing  1   c  is connected with the second housing  2   c  and the fourth housing  40   c  through screws or bolts, and the fourth housing  40   c  is connected with the third housing  7   c  through screws or bolts. The fourth housing  40   c  includes a partition portion  22   c , and the partition portion  22   c  can support the first rotor assembly. Compared with the first embodiment of the electric oil pump, the structure of the second housing in the present embodiment is equivalent to dividing the second housing in the first embodiment of the electric oil pump into two components, which is advantageous for saving raw materials during the component processing, and is further advantageous for reducing the material costs during processing. 
     Referring to  FIG. 2 a    to  FIG. 5 , in the present embodiment, the electric oil pump  100  includes the first rotor assembly  8 . The first rotor assembly  8  includes a first rotor  81  and a second rotor  82 , the first rotor  81  includes multiple external teeth, and the second rotor  82  includes multiple internal teeth. Referring to  FIG. 5 , a hydraulic chamber  801  is formed between the internal teeth of the second rotor  82  and the external teeth of the first rotor  81 . In the present embodiment, the second rotor  82  is sleeved on the circumference of the first rotor  81 , and part of the internal teeth of the second rotor  82  engage with part of the external teeth of the first rotor  81 . Referring to  FIG. 1  to  FIG. 5 , the electric oil pump  100  includes a first flow port  11  and a second flow port  12 , the first flow port  11  is used for the inflow of the working medium, and the second flow port  12  is used for the outflow of the working medium. Specifically, the working medium can enter the hydraulic chamber  801  through the first flow port  11 , and can leave the hydraulic chamber  801  through the second flow port  12 . Since there is a certain eccentric distance between the first rotor  81  and the second  82 , when the first rotor  81  rotates, part of the external teeth of the first rotor  81  engage with part of the internal teeth of the second rotor  82 , thereby driving the second rotor  82  to rotate. Volume of the hydraulic chamber  801  changes during one cycle of the rotation of the first rotor assembly  8 . Specifically, when the first rotor assembly  8  is rotated by a certain angle from a starting point, the volume of the hydraulic chamber  801  is gradually increased to form partial vacuum, and the working medium is sucked from the first flow port  11  into the hydraulic chamber  801 . When the first rotor assembly  8  continues rotating, the volume of the hydraulic chamber  801  filled with the working medium is gradually decreased, and the working medium is squeezed, so that the working medium entering the hydraulic chamber  801  is extruded out to the second flow port  12 , thereby generating the power for flowing. In the present embodiment, the first inner chamber  80  is in communication with the first flow port  11  and the second flow port  12 , and the first inner chamber  80  is not in communication with the second inner chamber  90 . Since the first inner chamber of the electric oil pump is not in communication with the second inner chamber, the working medium cannot enter the second inner chamber. Thus, the second inner chamber does not need to be additionally provided with other structures to prevent the components in the second inner chamber from corrosion, and the electric oil pump has better sealing performance and a simpler structure, which helps to reduce costs. In the present embodiment, a first communication cavity is provided between the first flow port  11  and the hydraulic chamber  801 , and a second communication cavity is arranged between the second flow port  12  and the hydraulic chamber  801 . Such a structure buffers the working medium through the first communication cavity and the second communication cavity, which is advantageous for damping vibration and noise. The specific structure is described below. 
     Referring to  FIG. 1  to  FIG. 8 , the first housing  1  is detachably connected with the second housing  2  through a first connection portion  123 , and the second housing  2  is detachably connected with the third housing  7  through a second connection portion  232 . The first connection portion  124  and the second connection portion  234  are not arranged in the first inner chamber  80  or the second inner chamber  90 . Specifically, in the present embodiment, the first connection  124  includes first screws  1231  (as shown in  FIG. 2 a   ). Referring to  FIG. 6 , in order to improve the reliability of the connection, the first housing  1  includes a first flange portion  15 . The first flange portion  15  extends along a radial direction of the electric oil pump, the first flange portion  15  is formed with first communication holes  13 , and the first communication holes  13  are close to an edge of the first flange portion  15 . The second housing  2  is formed with first threaded holes  231 , and the first threaded holes  231  are formed along the main body portion  21  of the second housing  2 . The first screws  1231  pass through the first communication holes  13  and are mounted from a side close to the first housing  1 , and are screwed to the second housing  2 . Such an arrangement allows at least part of the first screws  1231  to be disassembled outside the housing, and makes the disassembly of the electric oil pump more convenient, thereby facilitating the maintenance of the first rotor assembly of the electric oil pump. Apparently, the first housing  1  may be connected with the second housing  2  in other ways, for example, some detachable connection ways such as insertion and latching. Referring to  FIG. 11 , in order to prevent the electric oil pump from interfering with other components when the electric oil pump is mounted on the transmission system, the first communication hole  13  includes a first counterbore  131  and a first through hole  132 . A diameter of the first counterbore  131  is greater than a diameter of the first through hole  132 , and a depth of the first counterbore  131  is slightly greater than a height of a nut of the first screw  1231 , such that a top surface of the first screw  1231  is lower than an upper surface of the first flange portion  15  after the first screw  1231  is mounted, thereby preventing the first screw  1231  from interfering with other components. Apparently, in a case that a first screw avoidance portion is provide in a portion of the transmission system corresponding to the electric oil pump, it is not necessary to provide the first counterbore  131  for the first communication hole  13 , and only the first through hole  132  is needed, such that the first communication hole  13  can be allowed to be closer to the radial edge of the first flange portion  15  or a distance between the first communication hole  13  and the edge of the first flange portion  15  can be larger, which facilitates the layout of the first communication hole. 
     Referring to  FIG. 2 a   , the second housing  2   a  is detachably connected with the third housing  7  through the second connection portion  232 . Specifically, in the present embodiment, the second connection portion  232  includes second screws  2321 . Referring to  FIG. 14  and  FIG. 19 , the third housing  7  is formed with second communication holes  73 , the second housing  2  is formed with second threaded holes  241 , the second threaded holes  241  are formed along the main body portion  21  of the second housing  2 , and the second screws  2321  are mounted from a side close to the third housing  7  and is screwed to the second housing  2 . Apparently, the third housing  7  may be formed with the second threaded hole, the second housing  2  may be formed with the second communication hole, and the second screws  2321  may be mounted from a side close to the second housing  2  and may be screwed to the third housing  7 . The specific structure can be designed according to requirements of the electric oil pump. Such an arrangement makes the disassembly of the electric oil pump more convenient, thereby facilitating the inspection and maintenance of the components in the electric oil pump such as the circuit board assembly. Apparently, the second housing  2  may be connected with the third housing  7  in other detachable connection ways such as insertion and latching. In order to improve the reliability of the connection between the second housing  2  and the third housing  7  and to simplify the structure, a wall thickness of the third housing  7  at the second communication holes  73  is greater than a wall thickness of the third housing  7  at other portions. Referring to  FIG. 13  and  FIG. 14 , the main body portion  21  of the second housing  2  includes a cylindrical portion  201  and a second flange portion  24 . The cylindrical portion  201  forms at least part of the second inner chamber. The second flange portion  24  is formed by the cylindrical portion  201  protruding toward the circumference of the cylindrical portion  201 . The second flange portion  24  is formed with the second threaded holes  241 , and the wall thickness of the second flange portion  24  at the second threaded holes  241  is greater than the wall thickness of the second flange portion  24  at other portions. Apparently, in order to simplify the structure and reduce the profile dimensions of the electric oil pump, the second housing  2  may not include the second flange portion, and the cylindrical portion  201  may be formed with the second threaded holes  241 . To ensure the connection strength, the wall thickness of the cylindrical portion  201  at the second threaded holes is greater than or equal to the wall thickness of the cylindrical portion at other portions. 
     Referring to  FIG. 6  to  FIG. 11 ,  FIG. 6  to  FIG. 11  are schematic structural views of a first embodiment of the first housing shown in  FIG. 2 a   . In the present embodiment, the first housing  1  includes a first main body portion  14  and the first flange portion  15 , and a diameter of the first main body portion  14  is smaller than a diameter of the first flange portion  15 . The first housing  1  at least includes two first communication holes  13 , and the first communication holes  13  are distributed in an array along a circumference of the first housing  1 . In the present embodiment, the first communication holes  13  are formed on the first flange portion  15 , and the first communication hole  13  is a counterbore. Specifically, the first communication hole  13  is a cylindrical counterbore. The first communication hole  13  includes the first counterbore  131  and the first through hole  132 , where the diameter of the first counterbore  131  is greater than the diameter of the first through hole  132 , and the depth of the first counterbore  131  is slightly greater than the height of a nut of the first screw  1231 , such that the top surface of the first screw  1231  is lower than the upper surface of the first flange portion  15  after the first screw  1231  is mounted, thereby preventing the first screw  1231  from interfering with other components. Apparently, the first communication hole  13  may be a tapered counterbore or an end face counterbore. Such an arrangement can, on the one hand, ensure that the electric oil pump does not interfere with a mounting portion of a gearbox after the first screw  1231  is mounted, and on the other hand, makes the overall structure of the electric oil pump elegant. A minimum distance between the edge of the first communication hole  13  and an outer circumferential surface of the first flange portion  15  of the first housing  1  is greater than or equal to 1 mm, such that it can be ensured that no gap is formed at the edge while processing the first communication hole  13  and no damage is done to the outer circumferential surface of the first flange portion  15  of the first housing  1 . A minimum distance between the edge of the first communication hole  13  and an outer circumferential surface of the first main body portion  14  is greater than or equal to 1 mm, such that no damage is done to the outer circumferential surface of the first main body portion  14  of the first housing  1  while processing the first communication hole  13 . 
     Referring to  FIG. 6  to  FIG. 11 , the first housing  1  is further formed with the first flow port  11 , the second flow port  12 , the first communication cavity  112  and the second communication cavity  121 . Referring to  FIG. 2 a    and  FIG. 5 , the first communication cavity  112  is arranged between the first flow port  11  and the hydraulic chamber  801 , the first communication cavity  112  is in communication with the first flow port  11 , the second communication cavity  121  is arranged between the second flow port  12  and the hydraulic chamber  801 , and the second communication cavity  121  is in communication with the second flow port  12 . The first communication cavity  112  and the second communication cavity  121  are configured to buffer the working medium, which is advantageous for damping vibration and noise. In the present embodiment, the first flow port  11  is formed at the first main body portion  14  of the first housing  1 , the first communication cavity  112  is arranged at the first flange portion  15  of the first housing  1 , and the first flow port  11  is substantially circular. The “substantially circular” refers to that the roundness is within a range of 1 mm. Apparently, the first flow port  11  may also in other shapes such as an ellipse. Referring to  FIG. 9 , the first communication cavity  112  is substantially arc-shaped, the first communication cavity  112  includes a head portion  1121  and a tail portion  1122 , and a flow sectional area of the first communication cavity  112  gradually increases from the head portion  1121  to the tail portion  1122 . In the present embodiment, an inner circumferential surface of the first communication cavity  112  is arc-shaped, and other features such as recess portions or protruding portions may be provided on the inner circumferential surface of the first communication cavity. The first flow port  11  is arranged corresponding to the tail portion  1122 , which cooperates with the hydraulic chamber  801  in  FIG. 5  to form a certain degree of vacuum at the tail portion  1122 , and is advantageous for the suction of the working medium. 
     The second communication cavity  121  and the first communication cavity  112  are substantially circumferentially distributed in the first housing  1 , and a line connecting a center of the first flow port  11  and a center of the second flow port  12  substantially passes through a center of the first housing  1 , which is advantageous for taking advantage of the entire circumference of the entire electric oil pump and improving the working pressure of the working medium passing through the electric oil pump. 
     A flow sectional area at the connection between the second flow port  12  and the second communication cavity  121  is greater than the flow sectional area at other portions of the second communication cavity  121 , which allows the working medium entering the second communication cavity  112  from the hydraulic chamber  801  in  FIG. 5  to be discharged as soon as possible. 
     In the present embodiment, a fluid flow direction at the second flow port  12  and a fluid flow direction at the first flow port  11  are both arranged along the axial direction of the electric oil pump, that is, the fluid flow direction at the second flow port  12  and the fluid flow direction at the first flow port  11  are arranged in a same direction of the electric oil pump, and an inflow direction of the working medium is substantially parallel to an outflow direction thereof, such that only one sealing portion is required to be arranged between the electric oil pump and the transmission system and the structure is simple. Apparently, the fluid flow direction at the first flow port may be arranged perpendicular to the fluid flow direction at the second flow port, the second flow port may not be arranged in the first housing  1 , but be arranged in the second housing  2 , for example, such that the inflow direction of the working medium is arranged perpendicular to or at an angle to the outflow direction thereof, to facilitate the assembly of the electric oil pump and the transmission system or to hang the electric oil pump outside the transmission system. 
     Referring to  FIG. 12 ,  FIG. 12  is a schematic structural view of a second embodiment of the first housing shown in  FIG. 2 a   . Compared with the first embodiment of the first housing, in the present embodiment, a connection hole  13 ′ of a first housing  1 ′ is a through hole, which is advantageous for improving the connection strength between the first housing and the second housing. 
     Referring to  FIG. 2 a   , the electric oil pump  100  includes an outer sealing portion, the outer sealing portion includes a first sealing ring  30  and a second sealing ring  32  sleeved on the outer circumferential surface of the second housing  2 , the first sealing ring  30  is close to the first housing  1 , and the second sealing ring  32  is close to the third housing  7 . Referring to  FIG. 15 , the first sealing ring  30  is sleeved on a second groove  271  of the second housing  2 , and the second sealing ring  32  is sleeved on a third groove  281  of the second housing  2 . Referring to  FIG. 2 , such an arrangement can separate the working medium at the inlet and outlet from a space between the first sealing ring  30  and the second sealing ring  32 , such that the two do not affect with each other. Referring to  FIG. 2 a   , in the present embodiment, the electric oil pump further includes a third sealing ring  31 . Referring to  FIG. 10 , the first main body portion  14  is provided with a first groove  141 , the third sealing ring  31  is arranged in the first groove  141  of the first housing  1 . In a case that the electric oil pump  100  is mounted in a gearbox of a vehicle or in an electric drive unit of a vehicle, such an arrangement is advantageous for isolating the low-pressure working medium on the inlet side from the high-pressure working medium on the outlet side. 
     Referring to  FIG. 13  and  FIG. 14 , the main body portion  21  includes the cylindrical portion  201  and the second flange portion  24 , the cylindrical portion  201  includes a first end portion  23  and a second end portion  27 , the second flange portion  24  is integrally formed with the second end portion  27 , and the first end portion  23  is arranged away from the second flange portion  24 . Specifically, in the present embodiment, the first end portion  23  is formed with the first threaded holes  231 , the first threaded holes  231  are distributed in a circumferential array or uniformly distributed, the first communication holes  13  of the first housing  1  are arranged corresponding to the first threaded holes  231  of the second housing  2 , and the first housing  1  is connected with the second housing  2  through the first connection portion  123 . The second flange portion  24  is formed with the second threaded holes  241 , and the second threaded holes  241  are arranged corresponding to the second communication holes  73  of the third housing  7 . Referring to  FIG. 2 a   , the second housing  2  is connected with the third housing  7  through the second connection portion  232 , wherein the first threaded holes  231  and the second threaded holes  241  are both blind holes. Specifically, the first housing  1  is connected with the second housing  2  through the first screws  1231 , the second housing  2  is connected with the third housing  7  through the second screws  2321 . In the present embodiment, the second flange portion  24  further includes a first protrusion  242 , and the second threaded holes  241  are formed on the first protrusion  242 . A thickness of the second flange portion  24  at the first protrusion  242  is greater than the thickness of the second flange portion  24  at other portions, which is advantageous for improving the connection strength without increasing the overall thickness and weight of the second housing  2 , and is beneficial to reduce costs. Apparently, in a case that the thickness of the second flange portion  24  of the second housing  2  is thick enough, the second flange portion  24  may not be provided with the first protrusion  242 , where the “thick enough” refers to that the thickness of the second flange portion is greater than or equal to 3 mm. 
     Referring to  FIG. 2 a    and  FIG. 15 , the partition portion  22  further includes a first support portion  29  and a main body portion  221  of the partition portion, the main body portion  221  of the partition portion can support the first rotor assembly  8 , and the first support portion  29  protrudes from the main body portion  221  of the partition portion toward the second inner chamber  90 . The first support portion  29  can directly or indirectly support the pump shaft  5 . Referring to  FIG. 2 b    to  FIG. 2 d   , according to the arrangement of the partition portion, the first support portion  29  changes correspondingly with the position of the partition portion  22 , which will not be further described herein. 
     Referring to  FIG. 15 , the second housing  2  is formed with an upper chamber  291  and a lower chamber  292 , the upper chamber  291  is separated from the lower chamber  292  through the partition portion  22 , and the partition portion  22  is integrally formed with the first support portion  29 . 
       FIG. 15  is a first embodiment of the second housing shown in  FIG. 2 a   . Referring to  FIG. 2 , the electric oil pump  100  includes a first bearing  60 , the pump shaft  5  is supported on the first support portion  29  by the first bearing  60 , an inner circumferential surface of the first bearing  60  is in contact with an outer circumferential surface of the pump shaft  5 , and an outer circumferential surface of the first bearing  60  is in contact with an inner circumferential surface of the first support portion  29 . Specifically, referring to  FIG. 15 , the first support portion  29  includes a first accommodating portion  290 , the first accommodating portion  290  is formed with at least part of a first accommodating cavity, and at least part of an inner circumferential surface of the first accommodating portion  290  surrounds the first accommodating cavity. Referring to  FIG. 2 a    or  FIG. 3 , the pump shaft  5  passes through the first accommodating cavity, and at least part of the outer circumferential surface of the pump shaft  5  is in a clearance fit with the inner circumferential surface of the first accommodating portion  290 ; or the first bearing  60  is provided in the first accommodating cavity, referring to  FIG. 2 a    or  FIG. 3 , the pump shaft  5  passes through the first bearing  60 , and the outer circumferential surface of the first bearing  60  is in an interference fit with the inner circumferential surface of the first accommodating portion  290 . Specifically, in the present embodiment, the electric oil pump is provided with the first bearing  60 , the first bearing  60  is arranged in the first accommodating cavity, and the pump shaft  5  passes through the first bearing  60 , such that the first support portion  29  indirectly supports the pump shaft through the first bearing  60 . 
     Referring to  FIG. 17 ,  FIG. 17  is a schematic structural view of a fifth embodiment of the electric oil pump.  FIG. 18  is the second embodiment of the second housing shown in  FIG. 17 . Referring to  FIG. 17  and  FIG. 18 , in the present embodiment, the pump shaft  5  is directly supported on a first support portion  29 ′. Specifically, the first support portion  29 ′ includes a first accommodating portion  290 ′, and the first accommodating portion  290 ′ can form at least part of the first accommodating cavity. In the present embodiment, the first accommodating cavity is in communication with part of the first inner chamber  80 , the pump shaft  5  passes through the first accommodating cavity, and at least part of the outer circumferential surface of the pump shaft  5  is in a clearance fit with the inner circumferential surface of the first accommodating portion  290 ′. The inner circumferential surface of the first support portion  29 ′ is provided with a lubrication groove  298 , which is helpful to lubricate the pump shaft and thereby facilitates the rotation of the pump shaft. Compared with the first embodiment of the electric oil pump, in the present embodiment, the first support portion  29  can directly support the pump shaft by the tolerance fit between the first accommodating portion  290 ′ and the pump shaft  5  without additionally providing the first bearing, thereby making the structure of the electric oil pump more compact. 
     Referring to  FIG. 15 , the partition portion  22  is provided with a communication hole  2933 , and the communication hole  2933  communicates the upper chamber  291  with the lower chamber  292 . Referring to  FIG. 2 a   , the pump shaft  5  extends into the upper chamber  291  through the communication hole  2933 . 
     The first inner chamber  80  is isolated from the second inner chamber  90 . There are two embodiments about the isolation arrangement herein. In the first embodiment, referring to  FIG. 2 a   , the electric oil pump  100  includes the sealing portion, at least part of the sealing portion is supported by the first support portion  29 , the working medium in the first inner chamber  80  is not in communication with the working medium in the second inner chamber  90  due to the sealing portion  50  and the partition portion  22 . Specifically, referring to  FIG. 15 , the first support portion  29  includes a second accommodating portion  296 , the second accommodating portion  296  is formed with at least part of a second accommodating cavity, and at least part of the inner circumferential surface of the second accommodating portion  296  surrounds the second accommodating cavity. Referring to  FIG. 2 a   , the sealing portion  50  includes an oil seal, and the oil seal is provided in the second accommodating cavity. The pump shaft  5  shown in  FIG. 2  passes through the oil seal, and the inner circumferential surface of the oil seal is in contact with at least part of the outer circumferential surface of the pump shaft  5 . The outer circumferential surface of the oil seal  50  is sealingly fitted to the inner circumferential surface of the second accommodating portion  296 , which can prevent the working medium in the first inner chamber from flowing into the second inner chamber and can thereby avoid damage to the circuit board assembly in the second inner chamber. 
     In the second embodiment, referring to  FIG. 19 ,  FIG. 19  is a schematic structural view of a sixth embodiment of the electric oil pump. Referring to  FIG. 15 , the pump shaft  5  passes through the second accommodating portion  296  in  FIG. 15 . A clearance is formed between the inner circumferential surface of the second accommodating portion  296  and at least part of the outer circumferential surface of the pump shaft  5 , and the clearance is small enough that the working medium in the first inner chamber  80  cannot flow through. The clearance can prevent the working medium in the first inner chamber  80  in  FIG. 2  from entering the second inner chamber  90  in  FIG. 2 a    through the clearance. The specific size of the clearance is determined by parameters such as the roughness of the outer circumferential surface of the pump shaft  5 , the roughness of the inner circumferential surface of the second accommodating portion and the viscosity of the oil. In the second embodiment, the working medium in the first inner chamber is not in communication with the working medium in the second inner chamber by the arrangement of the clearance. 
     Referring to  FIG. 2 a   , the electric oil pump  100  further includes a second support portion  91 . The pump shaft  5  can be directly or indirectly supported on the second support portion  91 . The first support portion  29  and the second support portion  91  are coaxially arranged, which is advantageous for improving the stability of supporting the pump shaft  5 . 
     Referring to  FIG. 2 a   , the electric oil pump  100  further includes a partition plate  9 . The partition plate  9  is arranged in the second inner chamber  90 , the second support portion  91  is integrally formed with the partition plate  9 , and the second support portion  91  is arranged protruding from the partition plate  9  toward the second inner chamber  90 . The structure of the second support portion  91  is described in detail below. 
     The second support portion  91  can directly or indirectly provide support for the pump shaft  5 . Referring to  FIG. 25  to  FIG. 28 , the partition plate  9  includes a third accommodating portion  911 , the third accommodating portion  911  is formed with at least part of a third accommodating cavity, and at least part of an inner circumferential surface of the third accommodating portion  911  surrounds the third accommodating cavity. There are two embodiments. In the first embodiment, referring to  FIG. 2 a   , the electric oil pump includes a second bearing  70 , the second bearing  70  is provided in the third accommodating cavity, and the pump shaft  5  in  FIG. 2 a    passes through the second bearing  70 . Specifically, the inner circumferential surface of the second bearing  70  is in contact with at least part of the outer circumferential surface of the pump shaft  5 , and an outer circumferential surface of the second bearing  70  is in an interference fit with the inner circumferential surface of the third accommodating portion  911 , such that the first support portion  29  indirectly provides support for the pump shaft through the second bearing  70 . In the second embodiment, the pump shaft  5  in  FIG. 2 a    passes through the third accommodating cavity, and at least part of the outer circumferential surface of the pump shaft  5  in  FIG. 2 a    is in a clearance fit with the inner circumferential surface of the third accommodating portion  911 , such that the second support portion  91  can directly provide support for the pump shaft by the tolerance fit between the third accommodating portion  911  and the pump shaft  5  in  FIG. 2 a    without additionally providing the second bearing, thereby making the structure of the electric oil pump more compact. Referring to  FIG. 2 a   , the first bearing  60  and the second bearing  70  can be rolling bearings or sliding bearings. For medium and low speeds, the electric oil pump with the sliding bearing can meet the requirements of wear and rotation accuracy while reducing the cost. For high-speed electronic oil pumps, wear, rotation accuracy and bearing capacity are key factors in bearing selection. In such cases, rolling bearings will be preferred. 
     Referring to  FIG. 25  to  FIG. 28 , the partition plate  9  includes the second support portion  91 , a first bottom portion  92 , a first annular protrusion  94  and reinforcing ribs  93 . The reinforcing ribs  93  are distributed in the circumferential array or uniformly distributed. Specifically, the reinforcing ribs  93  connect the second support portion  91  with the first bottom portion  92 . Such an arrangement can ensure the mechanical strength of the second support portion  91 , such that the second support portion  91  is less likely to be deformed. In the present embodiment, the reinforcing rib  91  has a substantially triangular shape. Apparently, the reinforcing rib may also have other shapes such as rectangular or trapezoidal. Compared with the second support portion  91 , the first annular protrusion  94  is arranged closer to the outer edge of the partition plate  9 . A diameter of an outer wall of the first annular protrusion  94  is greater than that of the second support portion  91 . Referring to  FIG. 2 a    or  FIG. 3 , in the present embodiment, the partition plate  9  is fixedly connected with the second housing  2 . Specifically, referring to  FIG. 33  and  FIG. 15 , the first annular protrusion  94  is in an interference fit with the inner circumferential surface of the cylindrical portion of the second housing  2 . Apparently, the partition plate  9  may be connected with the second housing  2  by screws or bolts or by riveting. An outer circumferential surface of the first bottom portion  92  of the partition plate  9  is in an interference fit with the second housing  2 . Referring to  FIG. 26  to  FIG. 28 , the partition plate  9  further includes at least two third annular protrusions  95 , and the third annular protrusions  95  axially extend in a direction away from the second support portion  91 . Specifically, in the present embodiment, the partition plate  9  includes three third annular protrusions  95 , and the third annular protrusions  95  are substantially distributed in the circumferential array or uniformly distributed. A threaded hole  951  is arranged at a center of each third annular protrusion  95 , which facilitates the fixation and installation of the subsequent components such as a mounting bracket  10  in  FIG. 2   a.    
     Referring to  FIG. 15  and  FIG. 16 , the second housing  2  further includes a first stepped portion  294 . The first stepped portion  294  includes a first position-limiting surface  2941  and a second position-limiting surface  2942 . The first stepped portion  294  is arranged in the lower chamber  292  of the second housing  2 , and the first stepped portion  294  can serve as a position-limit for the stator assembly  4  in  FIG. 2 a    in the axial direction of the electric oil pump. Referring to  FIG. 15  and  FIG. 16 , the second housing  2  further includes a second stepped portion  295 . The second stepped portion  295  includes a third position-limiting surface  2951  and a fourth position-limiting surface  2952 , and the second stepped portion  295  is closer to the second flange portion  24  of the second housing  2  than the first stepped portion  294 . The stator assembly  4  in  FIG. 2 a    is in an interference fit with the second housing  2 . Specifically, an outer wall of the stator assembly  4  is in an interference fit with at least part of the second position-limiting surface  2942  of the first stepped portion  294  of the second housing  2 . The first position-limiting surface  2941  of the first stepped portion  294  abuts against the stator assembly  4 , thereby realizing the position-limiting of the stator assembly  4  in  FIG. 1  by the first stepped portion  294  in the axial direction of the electric oil pump and facilitating the position-limiting of the stator assembly. 
     Referring to  FIG. 20  to  FIG. 24 , the third housing  7  includes a main body  71  and a connection portion  72 . Taking the main body  71  as a reference surface, the connection portion  72  is located below the main body  71 . The third housing  7  is formed with the second communication holes  73 , the second communication holes  73  are arranged corresponding to the second threaded holes  241  of the second housing  2  in  FIG. 14 . In the present embodiment, the second housing  2  is connected with the third housing  7  through the second screws  2321  in  FIG. 2 a   . Apparently, the two may also be connected with each other by other connection ways such as insertion, latching or welding. Referring to  FIG. 24 , the connection portion  72  includes a position-limiting portion  76 , and a height H 2  of the position-limiting portion  76  is substantially equal to a height H 1  of a position-limiting portion  243  of the second housing  2  in  FIG. 15  where the “substantially equal” refers to that an absolute value of the height difference is within 0.3 mm. Such an arrangement can ensure that contact faces of the third housing  7  and the second housing  2  are as close as possible, and the third housing  7  does not incline during the assembly process, thereby avoiding affecting the insertion between the socket and the connector. The third housing  7  is further formed with mounting holes  77 , and the mounting holes  77  are configured to connect with the gearbox or the drive unit. Two mounting holes  77  are provided in the present embodiment. 
     Referring to  FIG. 20  to  FIG. 24 , the third housing  7  is further formed with protruding ribs  74 , the protruding ribs  74  are integrally formed with the third housing  7 , and the protruding ribs  74  protrude toward a direction away from the second housing  2 . In the present embodiment, the protruding ribs  74  are arranged on the third housing  7  as much as possible to increase a heat dissipation area, which facilitates the heat dissipation of the circuit board. In the present embodiment, the shape of a transverse section of the protruding rib  74  is rectangular. Apparently, the transverse section may also be in other shapes such as trapezoid, triangle, and arc-shaped. 
     Referring to  FIG. 2 a    and  FIG. 29  to  FIG. 33 , the circuit board assembly  6  includes a circuit board  61 , electronic components and the mounting bracket  10 . The mounting bracket  10  is arranged between the circuit board  61  and the partition plate  9 . The mounting bracket  10  is fixedly connected with the partition plate  9 . Specifically, the mounting bracket  10  is connected with the partition plate  9  by screws and bolts. Apparently, the mounting bracket  10  may also be connected with the partition plate  9  by other connection ways such as riveting. The mounting bracket  10  is electrically connected with the circuit board  61 , and the mounting bracket  10  can support large-volume electronic components. Referring to  FIG. 29  to  FIG. 33 , the mounting bracket  10  includes an accommodating portion  102 . The accommodating portion  102  is integrally formed with the mounting bracket  10  by injection molding. The accommodating portion  102  includes a bottom supporting portion  1021  and a side portion  1022 , the bottom supporting portion  1021  and the side portion  1022  form the accommodating cavity. In the present embodiment, the accommodating cavity is provided with a large-volume electronic component, and the large-volume electronic component is a capacitor  101 . In the present embodiment, the bottom supporting portion  1021  is substantially arc-shaped, the bottom supporting portion  1021  is in contact with part of an outer circumferential surface of the capacitor  101 , and the bottom supporting portion  1021  and the side portion  1022  are provided to facilitate circumferential positioning of the capacitor  101 , thereby ensuring that the capacitor  101  do not move circumferentially. The mounting bracket  10  further includes as least two latching portions  103 . In the present embodiment, the mounting bracket includes two latching portions  103 , and the two latching portions  103  are arranged two sides of the capacitor  101 . The latching portion  103  includes a first surface  1031 . During the process of mounting the capacitor  101  into the accommodating portion  102 , the capacitor  101  come into contact with the first surface  1031  of the latching portion  103  first, and at this time, the first inclined surface  1031  is tangent to the outer circumferential surface of the capacitor  101 . When the capacitor  101  is further mounted into the accommodating portion  102 , there will be a component force acting on the first surface  1031 , so that the latching portion  103  is opened outward. When the part of the outer circumferential surface of the capacitor  101  is in contact with the bottom supporting portion  1021 , no acting force is generated between the part of the outer circumferential surface of the capacitor  101  and the first surface of the latching portion  103 , and at this time, the latching portion  103  which was originally in the open state is restored to its initial position. On the one hand, such an arrangement can ensure that the large capacitor does not move in a vertical direction, and on the other hand, it will make the disassembly and assembly of the large capacitor simpler, thereby improving the disassembly and assembly efficiency of the large capacitor. The mounting bracket  10  further includes at least two through holes  104 , and the through holes  104  are substantially distributed in the circumferential array or uniformly distributed. In the present embodiment, the number of the through holes  104  is substantially equal to the number of the threaded holes  951  of the third annular protrusions  95  of the partition plate  9 . Specifically, the mounting bracket  10  includes three through holes  104 , and the number of the through holes  104  is equal to the number of the threaded holes  951  of the third annular protrusions  95  of the partition plate  9 . 
     It should be understood that the above embodiments are only intended to illustrate the present application and not to limit the technical solutions described in the present application. Although the present specification has been described in detail with reference to the embodiments described above, it should be understood by those skilled in the art that, various modifications and equivalents can be made to the technical solutions of the present application without departing from the spirit and scope of the present application, all of which should be contained within the scope of the claims of the present application.