Patent Publication Number: US-10323654-B2

Title: Electrically driven pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to Chinese Patent Application No. 201510136356.2 titled “ELECTRICALLY DRIVEN PUMP”, filed with the Chinese State Intellectual Property Office on Mar. 26, 2015, the entire disclosure of which is incorporated herein by reference. 
     FIELD 
     This application relates to a centrifugal pump, and relates to an electrically driven pump. 
     BACKGROUND 
     In recent decades, automotive industry develops rapidly, and with the development of the automobile towards a direction of safer, more reliable, more stable, fully automatic intellectualization, environment-protecting and energy-saving, electrically driven pumps have gradually replaced conventional mechanical pumps, and have been widely used in vehicle heat dissipating circulating system. The electrically driven pumps have advantages, such as no electromagnetic interference, high efficiency, environmental protection, stepless speed regulation, and can meet the requirements of the market well. 
     The electrically driven pump has a stator assembly and a rotor assembly completely isolated by a partition, thereby avoiding an issue of liquid leakage in a conventional motor-type brushless direct-current water pump. Currently, an electronic control unit of the electrically driven pump generates heat during operation, and in a conventional design, the electronic control unit is away from a flowing working medium, thus the generated heat is hard to be carried away, which may adversely affect the performance and service life of the electrically driven pump. 
     Therefore, it is necessary to improve the conventional technology, to address the above technical issues. 
     SUMMARY 
     An object of the present application is to provide an electrically driven pump, which facilitates improving the service life of the electrically driven pump. 
     To achieve the above object, the following technical solutions are adopted in the present application. An electrically driven pump includes a first housing, a second housing, an impeller, a rear housing, a shaft, a motor assembly and an electronic control unit. The electrically driven pump includes a first receiving chamber and an impeller chamber, the impeller or at least most part of the impeller is arranged in the impeller chamber, and the impeller chamber includes a space between the first housing and the second housing; the motor assembly is arranged in the first receiving chamber, and the first receiving chamber includes a space between the second housing and the rear housing. The motor assembly includes a stator and a rotor, and the rotor is configured to drive the impeller to rotate. The electrically driven pump further includes a partition, and the partition separates the first receiving chamber into a stator chamber and a rotor chamber, the rotor chamber is arranged to be closer to a center of the electrically driven pump than the stator chamber, and the stator chamber is not in communication with the impeller chamber. The rotor chamber is in direct or indirect communication with the impeller chamber, and the stator is arranged in the stator chamber, and the rotor is arranged in the rotor chamber. The electronic control unit is configured to control an operation of the motor assembly, and the electronic control unit is electrically connected to the stator. The electrically driven pump further includes a cooling passage, and the cooling passage is in communication with the impeller chamber, the cooling passage includes a first open portion and a second open portion, and the first open portion and the second open portion are located at different positions in a radial direction of the impeller chamber, the first open portion and the second open portion are both in communication with the impeller chamber, the first open portion is arranged away from a center of the impeller chamber in the radial direction with respect to the second open portion, and at least part of a wall of the cooling passage is in direct or indirect contact with the electronic control unit. 
     Compared with the conventional technology, a cooling passage is provided in the present application, and at least part of the wall of the cooling passage is in direct or indirect contact with the electronic control unit, and the working medium in the cooling passage exchanges heat with the electronic control unit, which facilitates improving the service life of the electronic control unit, and further facilitates improving the service life of the electrically driven pump. Furthermore, the working medium in the cooling passage has a certain pressure difference, such that the working medium may flow in the cooling passage, which facilitates taking away the heat generated by the electronic control unit, to further improve the service life of the electrically driven pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing the structure of an embodiment of an electrically driven pump according to the present application; 
         FIG. 2  is a schematic sectional view of a first embodiment of the electrically driven pump in  FIG. 1  taken along line B-B; 
         FIG. 3  is a schematic perspective view showing the structure of a second housing of the electrically driven pump in  FIG. 2 ; 
         FIG. 4  is a schematic sectional view of the second housing in  FIG. 3 ; 
         FIG. 5  is a schematic perspective view showing the structure of a rear housing of the electrically driven pump in  FIG. 2 ; 
         FIG. 6  is a schematic view showing the structure of an upper surface of a first embodiment of the rear housing in  FIG. 5 ; 
         FIG. 7  is a schematic view showing the structure of a lower surface of a first embodiment of the rear housing in  FIG. 5 ; 
         FIG. 8  is a schematic view showing the structure of an upper surface of a second embodiment of the rear housing; 
         FIG. 9  is a schematic view showing the structure of a lower surface of the second embodiment of the rear housing; 
         FIG. 10  is a schematic sectional view of a second embodiment of the electrically driven pump in  FIG. 1  taken along line B-B; 
         FIG. 11  is a schematic sectional view of a third embodiment of the electrically driven pump in  FIG. 1  taken along line B-B; and 
         FIG. 12  is a schematic view showing the structure of a rear housing of the electrically driven pump in  FIGS. 10 and 11 . 
     
    
    
     DETAILED DESCRIPTION 
     The present application is further described in conjunction with drawings and embodiments. 
     Referring to  FIGS. 1 and 2 , an electrically driven pump  100  includes a first housing  1 , a second housing  2 , a rear housing  3 , an end cover  4 , an partition  5 , an impeller  6 , a stator  71 , a rotor  72 , a pump shaft  8 , and an electronic control unit  9 . The first housing  1  and the second housing  2  are fixedly connected in a detachable manner and form a relatively sealed structure by arranging a sealing ring at a portion where the first housing  1  and the second housing  2  are connected, and in this embodiment, the first housing  1  and the second housing  2  are connected by a bolt or a screw. An impeller chamber  10  includes a space defined by the first housing  1  and the second housing  2  after being fixed to each other. The impeller  6  is arranged in the impeller chamber  10 , and the impeller  6  may make centrifugal movement in the impeller chamber  10 . An inlet pipe  11  and an outlet pipe  12  are formed in the first housing  1 , the inlet pipe  11  is in communication with the impeller chamber  10 , and the outlet pipe  12  is in communication with the impeller chamber  10 . The inlet pipe  11  corresponds to a low-pressure part of the pump cavity  10 , and the outlet pipe  12  corresponds to a high-pressure part of the pump cavity  10 . In this embodiment, the inlet pipe  11  corresponds to a central portion of the impeller chamber  10 , and the outlet pipe  12  corresponds to an edge of the impeller chamber  10 . The pressure in the impeller chamber  10  is gradually increased in a radial direction from the central portion of the impeller chamber  10  to the edge of the impeller chamber  10 . In this embodiment, the outlet pipe  12  may also be arranged in the second housing  2 , and is in communication with a portion relatively outwards in the radial direction, in this way, the same effect may be achieved, and the position of the outlet pipe  12  may be chosen according to the process technique. The second housing  2  and the rear housing  3  are threadedly connected, for example, via a bolt, and form the relatively sealed structure through the sealing ring at the connecting part where the second housing  2  and the rear housing  3  are connected. A first receiving chamber  20  includes a space defined by the second housing  2  and the rear housing  3  after being fixed to each other, and the first receiving chamber  20  receives the stator  71  and the rotor  72 . The partition  5  separates the first receiving chamber  20  into a stator chamber  201  and a rotor chamber  202 , and the stator chamber  201  is not in communication with the impeller chamber  10 , and no working medium flows through the stator chamber  201 ; and the rotor chamber  202  is in direct or indirect communication with the impeller chamber  10 , and there may be working medium flowing through the rotor chamber  202 . The stator  71  is arranged in the stator chamber  201 , and the rotor  72  is arranged in the rotor chamber  202 . The shaft  8  is limited or supported by the second housing  2  and the rear housing  3 , and an end portion of the shaft  8  protruding into the inside of the impeller chamber  10  is fixed to the impeller  6 , and a portion of the shaft  8  located inside the rotor chamber  202  is fixed to the rotor  72 . The rotor  72  may rotate under the action of a magnetic excitation field generated by the stator  71  and drive the shaft  8  to rotate, and the shaft  8  drives the impeller  6  to rotate. A second receiving chamber  30  includes a space defined by the rear housing  3  and the end cover  4 , and a connecting part where the rear housing  3  and the end cover  4  are connected is provided with a sealing ring to form a relative seal, and the electronic control unit  9  is arranged in the second receiving chamber  30 . The electronic control unit  9  includes a circuit board and electronic elements on the circuit board ( 931 ), and the electronic control unit  9  is connected to an external circuit and the stator  71 . In this embodiment, the connecting part where the first housing  1  and the second housing  2  are connected is provided with the sealing ring, and the connecting part where the second housing  2  and the rear housing  3  are connected is provided with the sealing ring, a sealing ring is provided between the rear housing  3  and the end cover  4 , and a sealing ring is provided between each of two ends of the partition  5  and a respective mounting surface. The above sealing rings are configured to ensure the relative seal of the connecting parts. Of course, other sealing methods may also be adopted, for example, welding, welding may enhance the leak tightness, however, for the product of a separated-type structure, using sealing rings to realize the seal between the connecting parts may facilitate detachment and maintenance of the product. 
     A motor assembly includes the stator  71  and the rotor  72 . The stator  71  includes coils, and the rotor  72  is made of a permanent magnet material. Multiple sets of coils of the stator  71  are energized sequentially to generate a varying magnetic excitation field, and the varying magnetic excitation field and a magnetic field generated by a permanent magnet of the rotor  72  attract or repel each other, to allow the rotor  72  to rotate about the central axis of the shaft  8 . 
     The electronic control unit  9  is connected to the motor assembly, and controls the movement of the motor assembly. The electronic control unit  9  analyses and determines the position of the rotor  72  according to the currents of the coils of the stator  71  at the present instant, and sets the currents of the stator  71  at a next instant, to allow the rotor  72  to rotate at a certain speed and in a certain direction. 
     Referring to  FIGS. 2, 3 and 4 , the second housing  2  includes a top portion  21  and a side wall  22 , and an inner cavity ( 27 ) of the second housing  2  includes a space between the top portion  21  and the side wall  22 . The stator  71  and the rotor  72  are arranged in the inner cavity of the second housing  2 . An exterior of the side wall  22  is provided with a first fixing portion  23  and a second fixing portion  24 , and the first fixing portion  23  is connected to the first housing  1  via a bolt or a screw, and the second fixing portion  24  is connected to the rear housing  3  via a screw or a bolt. The top portion  21  is provided with a recessed area  211 , and the recessed area  211  is formed by being recessed from an outer surface of the top portion  21  towards the inner cavity of the second housing  2 . The recessed area  211  includes a space between a recessed bottom portion  2111  and a recessed side wall  2112 . A central portion of the recessed bottom portion  2111  is provided with a center hole  211   a , and the shaft  8  passes through the center hole  211   a  to enter into the impeller chamber  10  from the rotor chamber  202  and to be connected to the impeller  6 . 
     As shown in  FIG. 4 , an inner surface of the side wall  22  of the second housing  2  is provided with multiple position-limiting members configured to assist in limiting the position of the stator  71 . Each of the position-limiting members includes a protruding rib  25  formed by protruding from the inner surface of the side wall towards the inner cavity of the second housing  27 . The protruding ribs  25  are substantially evenly distributed on the inner side of the side wall  22  along the circumference of the side wall  22 . In this embodiment, the number of the protruding ribs  25  is three. Grooves ( 711 ) are formed in a radial outer circumferential surface of an iron core of the stator  71 , and after the stator  71  is mounted in the stator chamber  201 , the grooves and the protruding ribs  25  form a tight fit, thereby assisting in limiting the rotation of the stator  71  with respect to the second housing  2 , and limiting the position of the stator  71  with respect to the second housing  2  more reliably. In this embodiment, an inner surface of the top portion  21  of the second housing  2  is provided with a first mounting portion  26  configured to limit the position of the partition  5 , and a first bearing mounting seat  811  configured to limit the position of a first bearing  81  for supporting the shaft  8  or support the first bearing  81 . The first mounting portion  26  includes a first annular protrusion  261  and a second annular protrusion  262  arranged on the inner surface of the top portion  21 , and a first annular groove  263  formed between the first annular protrusion  261  and the second annular protrusion  262 . The first annular groove  263  includes mounting side walls and a mounting bottom wall, and the mounting side walls include an inner surface of the first annular protrusion  261  and an outer surface of the second annular protrusion  262 , and the mounting bottom wall is located between the mounting side walls. The partition  5  includes a first mounting segment  51 , and the first mounting segment  51  is inserted into the first annular groove  263 . A connecting part where the first annular groove  263  and the first mounting segment  51  are connected is provided with a sealing ring, to prevent the working medium in the rotor chamber  202  from entering into the stator chamber  201  via the connecting part between the partition  5  and the second housing  2 . The first mounting segment  51  of the partition  5  is provided with a stepped portion configured to limit the position of the sealing ring. Furthermore, a stepped portion may also be provided in the first annular groove  263  to limit the position of the sealing ring, and the object may also be realized. The first bearing mounting seat  811  includes an inner side surface of the second annular protrusion  262 , an outer surface of the first bearing  81  is configured to form a tight fit with the inner side surface of the second annular protrusion  262 , and an inner surface of the first bearing  81  is configured to be fixedly fitted with an outer surface of the shaft  8 . 
     Referring to  FIGS. 2, 5 and 8 , the rear housing  3  includes an upper surface, a lower surface and a side wall. The upper surface of the rear housing  3  is provided with a second mounting portion  36  configured to limit the position of the partition  5 , and a second bearing mounting seat  822  configured to support a second bearing  82  of the shaft  8 . The second mounting portion  36  includes a third annular protrusion  361  and a fourth annular protrusion  362  arranged on the upper surface of the rear housing  3 , and a second annular groove  363  formed between the third annular protrusion  361  and the fourth annular protrusion  362 . The second annular groove  363  includes mounting side walls and a mounting bottom wall, and the mounting side walls include an inner surface of the third annular protrusion  361  and an outer surface of the fourth annular protrusion  362 , and the mounting bottom wall is located between the mounting side walls. The partition  5  includes a second mounting segment  52 , and the second mounting segment  52  is inserted into the second annular groove  363 . The second mounting segment  52  of the partition  5  is provided with a stepped portion configured to limit the position of the sealing ring. The sealing ring is provided in the second annular groove  363  at a connecting part where the second annular groove  363  and the second mounting segment  52  are connected, to prevent the working medium in the rotor chamber  202  from entering into the stator chamber  201  via the connecting part between the partition  5  and the rear housing  3 . Furthermore, a stepped portion may also be arranged in the second annular groove  363  to limit the position of the sealing ring, and the object may also be realized. 
     Reference is made to  FIG. 6 , which is a schematic view showing the structure of a first embodiment of the upper surface of the rear housing  3 . The rear housing  3  includes a flow guiding groove  362   a . The fourth annular protrusion  362  and the flow guiding groove  362   a  are arranged at interval, and the flow guiding groove  362   a  is in communication with an area enclosed by an inner side surface of the fourth annular protrusion  362 . The fourth annular protrusion  362  further includes a stepped portion  362   b , and the height of the stepped portion  362   b  protruding from the upper surface of the rear housing  3  is lower than the height of the fourth annular protrusion  362  protruding from the upper surface of the rear housing  3 . An outer surface of the second bearing  82  is configured to form a tight fit with the inner side surface of the fourth annular protrusion  362 , an end surface of the second bearing  82  is configured to abut against an upper surface of the stepped portion  362   b , and an inner surface of the second bearing  82  is in tight fit with the outer surface of the shaft  8 . In this embodiment, in a buffer cavity  368  includes a space that is enclosed by the inner side surface of the fourth annular protrusion  362 , the rear housing  3  is provided with an auxiliary hole  365  passing through the upper surface and the lower surface of the rear housing  3 . In this embodiment, an outer periphery of the upper surface of the rear housing  3  is further provided with a peripheral protruding annulus  364 , and the peripheral protruding annulus  364  is provided corresponding to the position-limiting member of the second housing  2 . The peripheral protruding annulus  364  is provided with a communication hole  364   a  passing through the upper surface and the lower surface of the rear housing  3 . 
     As shown in  FIG. 2 , in this embodiment, the partition  5  is of a cylinder structure with two ends open, and the partition  5  includes a first mounting segment  51  and a second mounting segment  52 . A sealing ring is provided between the first mounting segment  51  and the first annular groove  263  arranged in the inner side surface of the top portion  21  of the second housing  2 , to form a relative seal structure. A sealing ring is provided between the second mounting segment  52  and the second annular groove  363  arranged in the upper surface of the rear housing  3 , to form a relative seal structure. The first mounting segment  51  of the partition  5  is inserted into the first annular groove  263  between the first annular protrusion  261  and the second annular protrusion  262  arranged on the inner side of the top portion  21  of the second housing  2 , and the second mounting segment  52  of the partition  5  is inserted into the second annular groove  363  between the third annular protrusion  361  and the fourth annular protrusion  362  arranged on the rear housing  3 . In each of the annular grooves, a sealing ring is provided between the partition  5  and the side wall of the annular groove. Of course, the partition  5  may also be a structure with one end open, in this way, the partition  5  may be integrally formed with the second housing  2  or the rear housing  3 . The partition  5  is limited in an axial direction via the bottom wall of the first annular groove  263  and the bottom wall of the second annular groove  363 . A second receiving chamber  30  is enclosed by the lower surface and the side wall of the rear housing  3  and the end cover  4 , and the electronic control unit  9  is arranged in the second receiving chamber  30 . The electronic control unit  9  is electrically connected to the stator  71 , and a front surface of the electronic control unit  9  is provided with electronic elements, and a back surface of the electronic control unit  9  is in direct contact with a baffle  50  or is in indirect contact with the baffle  50  via a thermal conductive material. The thermal conductive material includes a thermal conductive plate and a thermal conductive adhesive. The baffle  50  may be made of a metal material, to facilitate carrying away the heat generated by the electronic control unit  9 . The lower surface of the rear housing  3  is provided with three protrusions  38  and a supporting step  39 . The baffle  50  is in contact with the supporting step  39 , and the middle portion of the baffle  50  is in contact with the surfaces of the protrusions  38 , to ensure that the middle portion of the baffle  50  will not be deformed due to the gravity which may further result in the deformation of the circuit board fixed on the baffle  50 . Further, the baffle  50  and the lower surface of the rear housing  3  are relatively sealed, and a communication passage is formed between the baffle  50  and the lower surface of the rear housing  3 . In this embodiment, the scale of the thickness of the baffle  50  shown in the drawings does not necessarily indicate the real scale in a practical application, and the choosing of the thickness of the baffle  50  is related to the supporting strength of the material which is specifically used. 
     As shown in  FIG. 2 , for further dissipating the heat generated by the electronic control unit  9 , the electrically driven pump  100  is provided with a cooling passage  90  for accommodating the working medium, and the electronic control unit  9  generates heat during working and can exchange heat with the working medium in the cooling passage  90 . The cooling passage  90  includes a first passage  91 , a second passage  92 , and a third passage  93 . The first passage  91  is in communication with the impeller chamber  10 , and the communication portion where the first passage  91  is in communication with the impeller chamber  10  is away from a radial center of the impeller chamber  10 . The second passage  92  is in communication with the impeller chamber  10 , and the communication portion where the second passage  92  is in communication with the impeller chamber  10  is close to the radial center of the impeller chamber  10 . At least part of a wall of the third passage  93  is in direct or indirect contact with the electronic control unit  9 . The working medium in the third passage  93  can exchange heat directly or indirectly with the electronic control unit  9 . The first passage  91  and the second passage  92  are in communication with each other via the third passage  93 . By providing the cooling passage  90 , the electronic control unit  9  may exchange heat with the working medium in the cooling passage  90 , which facilitates reducing the temperature of the electronic control unit  9 , and further improves the service life of the electrically driven pump  100 . In this embodiment, the distance between the communication portion of the first passage  91  and the impeller chamber  10  and the radial center of the impeller chamber  10  is greater than the distance of the communication portion of the second passage  92  and the impeller chamber  10  and the radial center of the impeller chamber  10 . In this way, when the electrically driven pump  100  is working, the working pressure of the working medium gradually increases from the radial center of the impeller chamber  10  to the edge of the impeller chamber  10 , thus, a pressure difference is formed between a first open portion of the cooling passage  90 , i.e., the communication portion of the first passage  91  and the impeller chamber  10 , and a second open portion of the cooling passage  90 , i.e., the communication portion of the second passage  92  and the impeller chamber  10 , and due to the pressure difference, the working medium may flow in the cooling passage  90 . The single-headed arrows in  FIG. 2  schematically show the direction of flowing or flowing tendency of the working medium in the cooling passage  90  when the electrically driven pump  100  is working. 
     As shown in  FIGS. 2 to 4 , the first passage  91  includes a passage  251 , the passage  251  is formed by extending through an upper surface and a lower surface of the side wall of the second housing  2 . Or the passage  251  may be formed by extending through an upper surface and a lower surface of the reinforcing rib  25 . Or the passage  251  may be formed a part extending through the upper surface and the lower surface of the reinforcing rib and a part extending through the upper surface and the lower surface of the side wall of the second housing  2 . The flow path of the working medium formed by the passage  251  is substantially of a smooth straight linear shape, to reduce the flowing resistance of the working medium and facilitate the flowing of the working medium. The number of the passages  251  is at least one, and the number of the passages  251  is smaller than or equal to the number of the protruding ribs  25 . At least one of the passages  251  is arranged or partially arranged in the reinforcing rib  25  arranged relatively close to the edge of the impeller chamber  10 , in this way, this passage  251  may be in communication with the outlet of the impeller chamber  10 . Three passages  251  are provided in this embodiment and are arranged corresponding to the three reinforcing ribs  25 . Of course, the number of the reinforcing ribs  25  may be greater than the number of the passages  251 , for example, the number of the reinforcing ribs  25  may be six, and the number of the passages  251  may be three, and the number of reinforcing ribs  25  and the number of the passages  251  may be set as desired. 
     As shown in  FIG. 2 , the second passage  92  includes an axial passage  801  arranged in the shaft  8 , and the axial passage  801  is arranged along a length direction of the shaft  8  and extends through two ends of the shaft  8 . The axial passage  801  is in communication with the impeller chamber  10  at a part close to the center of the impeller chamber  10 . Specifically, the maximum radial radius of the impeller chamber  10  is R, and the part where the axial passage  801  is in communication with the impeller chamber  10  is between the center of the impeller chamber  10  and a part displaced from the center of the impeller chamber  10  by one half of the maximum radial radius R. In this embodiment, the axial passage  801  is located at the center of the impeller chamber  10 . The flow path of the working medium formed by the axial passage  801  is substantially of a smooth straight linear shape, to reduce the flowing resistance of the working medium and facilitate the flowing of the working medium. The cooling passage  90  may further include a second auxiliary passage  921 . The second auxiliary passage  921  includes a flow hole  211   c  arranged in the recessed area  211  of the second housing  2 , and the impeller chamber  10  and the rotor chamber  202  are in communication with each other via the flow hole  211   c . The flow hole  211   c  is arranged near the second passage  92 . The flow hole  211   c  is arranged in the second housing  2  between the second passage  92  and a part displaced from the center of the impeller chamber  10  by one half of the maximum radial radius R. In this way, the pressure at a part where the flow hole  211   c  is in communication with the impeller chamber  10  will be slightly greater than the pressure at a part where the second passage  92  is in communication with the impeller chamber  10 . The second auxiliary passage  921  has a rather circuitous flow path, which increases the flowing resistance of the working medium, and allows the working medium to better exchange heat with the stator  71 . The direction of the double-headed arrows in  FIG. 2  schematically shows a direction of flowing or flowing tendency of the working medium in the second auxiliary passage  921 , i.e., a direction in which the working medium flows from the third passage  93  to the impeller chamber  10  via the second auxiliary passage  921 . In the case that the cross-sectional area of the first passage  91  is large, the working medium is subjected to a small resistance when flowing through the first passage  91 , thereby allowing the pressure of the working medium entered into the third passage  93  to be greater than the pressure of the working medium at the part where the flow hole  211   c  is in communication with the impeller chamber  10 , and allowing the working medium to flow in the second auxiliary passage  921 . If the working medium is subjected to a large flowing resistance in the first passage  91 , the pressure of the working medium will drop greatly in the first passage  91 , and further the pressure of the working medium in the third passage  93  is lower than the pressure of the working medium at the part where the flow hole  211   c  is in communication with the impeller chamber  10 , thus the working medium in the second auxiliary passage  921  flows from the impeller chamber  10  to the third passage  93 , and the working medium in the third passage  93  flows into the impeller chamber  10  through the second passage  92 . 
     As shown in  FIG. 2 , a relative sealing structure is formed between the rear housing  3  and the baffle  50 , to form the third passage  93 , and the third passage  93  is in communication with the first passage  91  and the second passage  92  via respective communication structures. The wall of the third passage  93  includes the lower surface of the rear housing  3  and the upper surface of the baffle  50 . The lower surface of the rear housing  3  and the upper surface of the baffle  50  are configured to be in contact with the working medium. The lower surface of the baffle  50  is in direct contact with the electronic control unit  9  or is in indirect contact with the electronic control unit  9  via a thermal conductive material. The baffle  50  is made of a metal material. The thermal conductive material includes a thermal conductive plate and a thermal conductive adhesive, and is configured to transfer the heat generated by the electronic control unit  9  during working to the working medium in the third passage  93 , to carry away the heat by the flowing working medium. For ensuring that the third passage  93  forms a relatively sealed space, wires provided between the electronic control unit  9  and the stator  71  are arranged at the side wall of the rear housing  3  or regions other than the third passage  93 . 
     As shown in  FIGS. 2 and 6 to 8 , the first passage  91  and the third passage  93  are in communication via a first communication structure, the first communication structure includes a communication hole  364   a  arranged at an edge of the rear housing  3 . The communication hole  364   a  may be a straight passage, and may also be an inclined passage. The straight passage can be manufactured conveniently, and the inclined passage may realize a better transition between the first passage  91  and the third passage  93 . The second passage  92  and the second auxiliary passage  921  are in communication with the third passage  93  via a second communication structure. The second communication structure includes an auxiliary hole  365  arranged in the rear housing  3  and the buffer cavity  368 , and the buffer cavity  368  includes the flow guiding groove  362   a  and a recessed portion enclosed by the inner side surface of the fourth annular protrusion  362 . 
       FIGS. 8 and 9  are schematic views showing the structure of a second embodiment of the rear housing  3 . Unlike the first embodiment, in the second embodiment, the rear housing  3  is provided with an elongated hole  366  extending through an upper surface and a lower surface of the rear housing  3 , and the third passage  93  is in communication with the second auxiliary passage  921  via the elongated hole  366 . Of course, the elongated hole  366  may also have other shapes such as multiple circular holes or multiple elliptical holes, and etc. Furthermore, seen from the upper surface of the rear housing  3 , the second passage  92  and the second auxiliary passage  921  are in communication with the third passage  93  via a second communication structure. The second communication structure includes an auxiliary hole  365  arranged in the rear housing  3  and a buffer cavity  368 , and the buffer cavity  368  includes a recessed portion enclosed by the inner side surface of the fourth annular protrusion  362 . The second passage  92  and the second auxiliary passage  921  are no longer in communication with the third passage  93  via a flow guiding groove. The working medium enters into the buffer cavity  368  via the auxiliary hole  365 , and the working medium in the buffer cavity  368  enters into the second passage  92 . The third passage  93  is in communication with the second auxiliary passage  921  via the elongated hole  366  extending through the rear housing  3 . 
     As shown in  FIG. 2 , in the first embodiment, when the electrically driven pump  100  is working, since a pressure difference is formed between the first open portion and the second open portion of the cooling passage  90 , the pressure at the first open portion of the cooling passage  90  is large, thus the working medium enters into the passage  251  arranged in the second housing  2  via the first open portion of the cooling passage  90 , and enters into the third passage  93  formed by the rear housing  3  and the baffle  50  via the communication hole  364   a  arranged in the rear housing  3 . The working medium entered into the third passage  93  exchanges heat with the baffle  50  to cool the electronic control unit  9 . The working medium after exchanging heat with the baffle  50  enters into the buffer cavity  368  via the auxiliary hole  365  of the rear housing  3 , and a part of the working medium entered into the buffer cavity  368  enters into the impeller chamber  10  via the axial passage  801  of the shaft  8 , and a part of the working medium enters into the flow guiding groove  362   a , and then enters into a gap between the rotor  72  and the partition  5 , to cool the stator  71 . Or, a part of the working medium enters into the second auxiliary passage  921  via the flow hole  211   c  to cool the stator  71 , the working medium in the second auxiliary passage  921  enters into the flow guiding groove  362   a , and the working medium in the flow guiding groove  362   a  and the working medium in the third passage  93  enter into the impeller chamber  10  via the axial passage  801  of the shaft  8 . Or, a part of the working medium in the third passage  93  enters into the buffer cavity via the auxiliary hole  365  of the rear housing  3 , and then enters into the impeller chamber  10  via the axial passage  801  of the shaft  8 , and a part of the working medium in the third passage  93  enters into the second auxiliary passage  921  via the elongated hole  366  of the rear housing  3 , and then enters into a relatively medium pressure area of the impeller chamber  10  via the flow hole  211   c  arranged in the recessed area  211  of the top portion  21  of the second housing  2 . Or, a part of the working medium enters into the second auxiliary passage  921  via the flow hole  211   c  to cool the stator  71 , the working medium in the second auxiliary passage  921  enters into the buffer area, and the working medium in the buffer area enters into the third passage  93  and enters into the impeller chamber  10  via the axial passage  801  of the shaft  8 . Since the pressure at a part, corresponding to the axial passage  801  of the shaft  8 , of the impeller chamber  10  is lower than the pressure at the part where the flow hole  211   c  is in communication with the impeller chamber  10 , thus the working medium more tends to flow back to the impeller chamber  10  from the axial passage  801 . The cross-sectional area of the various passages may be matched and the flow resistance may be changed, to ensure that the working medium can flow in the second passage  92  and the second auxiliary passage  921  at the same time, for example, the cross-sectional area of the first passage  91  is greater than the cross-sectional area of the axial passage  801  of the shaft  8 , thus the flow rate of the working medium in the first passage  91  is greater than the flow rate of the working medium in the third passage  93 , to allow the working medium to enter into the second auxiliary passage  921 , i.e., to pass through the gap between the rotor  72  and the partition  5 , to better cool the stator  71  and improve the working performance of the electrically driven pump  100 . The cooling passage in this embodiment includes the second passage  92  and the second auxiliary passage  921 , and may also only include one of the second passage  92  and the second auxiliary passage  921 , and the electronic control unit  9  may be cooled as well, and the second auxiliary passage  921  is additionally provided for cooling the stator  71 . 
       FIG. 10  is a schematic sectional view of a second embodiment of the electrically driven pump  100  in  FIG. 1  taken along line B-B. The electrically driven pump  100  includes a first housing  1 , a second housing  2 , a rear housing  3 ′, an end cover  4 , a partition  5 , an impeller  6 , a stator  71 , a rotor  72 , a shaft  8 , and an electronic control unit  9 . The first housing  1  and the second housing  2  are fixedly connected in a detachable manner and form a relatively sealed structure by arranging a sealing ring at a portion where the first housing  1  and the second housing  2  are connected, and in this embodiment, the first housing  1  and the second housing  2  are connected by a bolt or a screw. An impeller chamber  10  includes a space defined by the first housing  1  and the second housing  2  after being fixed to each other. The impeller  6  is arranged in the impeller chamber  10 . The second housing  2  and the rear housing  3 ′ are threadedly connected, for example, via a bolt, and form the relatively sealed structure through the sealing ring at the connecting part where the second housing  2  and the rear housing  3 ′ are connected. A first receiving chamber  20  includes the space defined by the second housing  2  and the rear housing  3  after being fixed to each other, and the first receiving chamber  20  receives the stator  71  and the rotor  72 . The partition  5  separates the first receiving chamber  20  into a stator chamber  201 , and a rotor chamber  202  which allows the working medium to flow through. The stator  71  is arranged in the stator chamber  201 , and the rotor  72  is arranged in the rotor chamber  202 . The shaft  8  is limited or supported by the second housing  2  and the rear housing  3 ′, and an end portion of the shaft  8  protruding into the inside of the impeller chamber  10  is fixed to the impeller  6 , and a portion of the shaft  8  located inside the rotor chamber  202  is fixed to the rotor  72 . The rotor  72  may rotate under the action of an electromagnetic force of the electrically driven pump  100  and drive the shaft  8  to rotate, and the shaft  8  drives the impeller  6  to rotate. A second receiving chamber  30  is defined by the rear housing  3 ′ and the end cover  4 , and the electronic control unit  9  is arranged in the second receiving chamber  30 . The electronic control unit  9  includes a circuit board and electronic elements on the circuit board, and the electronic control unit  9  is connected to an external circuit and the stator  71 . In this embodiment, the connecting part where the first housing  1  and the second housing  2  are connected is provided with the sealing ring, and the connecting part where the second housing  2  and the rear housing  3 ′ are connected is provided with the sealing ring, a sealing ring is provided between the rear housing  3 ′ and the end cover  4 , and a sealing ring is provided between each of two ends of the partition  5  and a respective mounting surface. The above sealing rings are configured to ensure the relative seal of the connecting parts. Of course, other sealing methods may also be adopted, for example, welding, welding may enhance the leak tightness, however, for the product of a separated-type structure, using sealing rings to realize the seal between the connecting parts may facilitate detachment and maintenance of the product. 
     The main difference between this embodiment and the first embodiment of the electrically driven pump  100  shown in  FIG. 2  lies in that, the structure of the rear housing  3 ′ is different. The third passage  93  is formed in the rear housing  3 ′, and the circuit board of the electronic control unit  9  is mounted to a lower surface of the rear housing  3 ′ via a baffle  50 , the wall of the third passage  93  includes the lower surface of the rear housing  3 ′; or the circuit board of the electronic control unit  9  is mounted to the lower surface of the rear housing  3 ′ via a thermal conductive material, and the third passage  93  arranged in this way has a good leak tightness, and the sealing structure for the third passage  93  can be omitted, which reduces the production procedures and the assembling parts. In this embodiment, an inlet of the third passage  93  is arranged close to an outer edge of the rear housing  3 ′, and an outlet of the third passage  93  is arranged close to the center of the rear housing  3 ′, the direction in which the working medium flows in the third passage  93  is from the outer edge to the center of the rear housing  3 ′, and in this way, the heat of the electronic control unit  9  may be dissipated better, especially in the case that the electrically pump has only one first passage  91 , the power elements of the electronic control unit  9  are arranged close to an area near a connecting line between the inlet and the outlet of the third passage  93 . Reference may be made to  FIGS. 5 to 9  for other structures of the rear housing  3 ′. 
       FIG. 11  is a schematic sectional view of a third embodiment of the electrically driven pump  100  in  FIG. 1  taken along line B-B. Unlike the second embodiment of the electrically driven pump  100  shown in  FIG. 10 , in the third embodiment, the circuit board of the electronic control unit  9  is arranged to be in direct contact with the lower surface of the rear housing  3 ′, or is arranged to be in indirect contact with the lower surface of the rear housing  3 ′ via a thermal conductive material, in this way, the flowing working medium may flow through a third passage  93 ′ to exchange heat with the electronic control unit  9 . The wall of the third passage  93  includes the lower surface of the rear housing  3 ′. Of course, the circuit board of the electronic control unit  9  may also be designed to have a water proof structure, and a third passage  93  may be formed between the circuit board and the lower surface of the rear housing  3 ′. Thus, when the flowing working medium may flow through the third passage  93  to directly exchange heat with the electronic control unit  9 , and carry away the heat, and to further cool the electronic control unit  9 . The structures of the electrically driven pump  100  according to this embodiment other than the partition may be referred to the structure of the electrically driven pump shown in  FIG. 10 . 
       FIG. 12  is a schematic view showing the structure of the rear housing  3 ′ in  FIGS. 10 and 11 . Unlike the rear housing in  FIG. 5 , in the rear housing  3 ′ in  FIGS. 10 and 11 , the third passage  93 ′ is arranged in the rear housing  3 ′, and the third passage  93 ′ is a relatively sealed cavity, and is formed by processes such as over molding or injection molding and then assembling. The third passage  93 ′ is in communication with a buffer cavity  368  via the auxiliary hole  365  arranged in the rear housing  3 ′, and a bottom wall of the buffer cavity is a part of the upper surface of the rear housing  3 ′, and a side wall of the buffer cavity  368  is an inner surface of the fourth annular protrusion  362 . The wall of the third passage  93  includes the lower surface of the rear housing  3 ′. The third passage  93 ′ and the second auxiliary passage  912  may be in communication with the buffer cavity via the auxiliary hole  365  or an elongated hole (not shown). 
     The directions such as “upper” and “lower” in the above embodiments are only for ease of description, and the directions of “upper” and “lower” are not necessarily the directions in a state that the electronic driven pump  100  is mounted, and will not limit the direction of using the electronic driven pump. 
     It should be noted that, the above embodiments are only intended for describing the present application, and should not be interpreted as limitation to the technical solutions of the present application. Although the present application is described in detail in conjunction with the above embodiments, it should be understood by the skilled in the art that, modifications or equivalent substitutions may still be made to the present application by those skilled in the art; and any technical solutions and improvements of the present application without departing from the spirit and scope thereof also fall into the scope of the present application defined by the claims.