Abstract:
An electric water pump apparatus may include a body having a stator chamber and a rotor chamber therein, a stator having a hollow cylindrical shape and being disposed in the stator chamber and generating a magnetic field, wherein the stator fluidly insulates the stator chamber and the rotor chamber, a rotor disposed in the rotor chamber and enclosed by the stator, wherein the rotor is rotated by the magnetic field, and a pump cover connected to the body and forming a volute chamber therein, wherein the volute chamber and the rotor chamber are fluidly-communicated through a connecting hole formed to the body and a coolant is supplied to the rotor chamber through the connection hole, wherein the stator includes a stator groove formed in an inner circumference therein and the stator groove is fluid-connected to the rotor chamber and the volute chamber through the connection hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Korean Patent Application No. 10-2009-0112236 filed on Nov. 19, 2009, the entire contents of which is incorporated herein for all purposes by this reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electric water pump. More particularly, the present invention relates to an electric water pump having improved performance and durability. 
         [0004]    2. Description of Related Art 
         [0005]    Generally, a water pump circulates coolant to an engine and a heater in order to cool the engine and heat a cabin. The coolant flowing out from the water pump circulates through and exchanges heat with the engine, the heater, or the radiator, and flows back in the water pump. Such a water pump is largely divided into a mechanical water pump and an electric water pump. 
         [0006]    The mechanical water pump is connected to a pulley fixed to a crankshaft of the engine and is driven according to rotation of the crankshaft (i.e., rotation of the engine). Therefore, the coolant amount flowing out from the mechanical water pump is determined according to rotation speed of the engine. However, the coolant amount required in the heater and the radiator is a specific value regardless of the rotation speed of the engine. Therefore, the heater and the radiator do not operate normally in a region where the engine speed is slow, and in order to operate the heater and the radiator normally, the engine speed must be increased. However, if the engine speed is increased, fuel consumption of a vehicle also increases. 
         [0007]    On the contrary, the electric water pump is driven by a motor controlled by a control apparatus. Therefore, the electric water pump can determines the coolant amount regardless of the rotation speed of the engine. Since components used in the electric water pump, however, are electrically operated, it is important for electrically operated components to have sufficient waterproof performance. If the components have sufficient waterproof performance, performance and durability of the electric water pump may also improve. 
         [0008]    Currently, the number of vehicles having an electric water pump is tending to increase. Accordingly, various technologies for improving performance and durability of the electric water pump are being developed. 
         [0009]    The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    Various aspects of the present invention are directed to provide an electric water pump having advantages of improved performance and durability and to provide an electric water pump which minimizes magnetic flux leakage of a permanent magnet by optimizing a shape of a rotor core. 
         [0011]    In an aspect of the present invention, the electric water pump apparatus may include a body having a hollow cylindrical shape and including a stator chamber and a rotor chamber therein, a stator having a hollow cylindrical shape and being disposed in the stator chamber and generating a magnetic field according to a control signal, wherein the stator fluidly insulates the stator chamber and the rotor chamber, a rotor disposed in the rotor chamber and enclosed by the stator, wherein the rotor is rotated by the magnetic field generated at the stator, and a pump cover connected to the body and forming a volute chamber therein, wherein the volute chamber and the rotor chamber are fluidly-communicated through a connecting hole formed to the body and a coolant having flowed into the volute chamber is supplied to the rotor chamber through the connection hole, wherein the stator includes a stator groove formed in an inner circumference therein and the stator groove is fluid-connected to the rotor chamber and the volute chamber through the connection hole. 
         [0012]    The rotor core having a hollow cylindrical shape may include a coupling groove formed along an inner circumference in a length direction therein and the rotor core is splined to the shaft through the coupling groove. 
         [0013]    The stator may include a stator core having a hollow cylindrical shape to receive the rotor therein and provided with the stator groove at an inner circumference thereof along a length direction, and a stator case mounted at both distal ends of the stator core, wherein the stator case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction. 
         [0014]    The stator case may be provided with a fixing groove and a driver providing the control signal is slidably and detachably coupled thereto. 
         [0015]    The rotor may include a rotor core having a hollow cylindrical shape to receive a shaft therein, and provided with a plurality of recesses formed by a plurality of guiding protrusions formed at an exterior circumference thereof along a length direction, a plurality of permanent magnets respectively mounted in the plurality of recesses of the rotor core, a rotor cover mounted at both distal ends of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other, and a rotor case enclosing an exterior circumference of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnet each other in a state that the rotor core and the plurality of permanent magnets are mounted at the rotor cover, wherein the rotor case may be made of a bulk mold compound including a potassium family that has a low coefficient of contraction. 
         [0016]    The plurality of permanent magnets may be mounted in such a manner that N pole and S pole are alternatively disposed. 
         [0017]    The rotor cover may be provided with a plurality of balance holes and rotational balance of the rotor may be kept by changing positions of the balance holes. 
         [0018]    In addition, the stator case may be provided with a plurality of balance holes and rotational balance of the stator may be kept by changing positions of the balance holes. 
         [0019]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a perspective view of an exemplary electric water pump according to the present invention. 
           [0021]      FIG. 2  is a cross-sectional view taken along the line A-A in  FIG. 1 . 
           [0022]      FIG. 3  is a perspective view showing a stator of an exemplary electric water pump according to the present invention. 
           [0023]      FIG. 4  is a perspective view of a rotor cover used in an exemplary electric water pump according to the present invention. 
           [0024]      FIG. 5  is a perspective view showing a shape of a rotor core used in an exemplary electric water pump according to the present invention. 
           [0025]      FIG. 6  is a schematic diagram showing processes for mounting rotor covers to both ends of a rotor core and a permanent magnet in an exemplary electric water pump according to the present invention. 
           [0026]      FIG. 7  is a schematic diagram showing processes for manufacturing a rotor used in an exemplary electric water pump according to the present invention. 
       
    
    
       [0027]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0028]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0030]    An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
         [0031]      FIG. 1  is a perspective view of an electric water pump according to an exemplary embodiment of the present invention, and  FIG. 2  is a cross-sectional view taken along the line A-A in  FIG. 1 . 
         [0032]    As shown in  FIG. 1  and  FIG. 2 , an electric water pump  1  according to an exemplary embodiment of the present invention includes a pump cover  10 , a body  30 , a driver case  50 , and a driver cover  70 . The body  30  is engaged to a rear end of the pump cover  10  so as to form a volute chamber  16 , the driver case  50  is engaged to a rear end of the body  30  so as to form a rotor chamber  38  and a stator chamber  42 , and the driver cover  70  is engaged to a rear end of the driver case  50  so as to form a driver chamber  64 . 
         [0033]    In addition, an impeller  22  is mounted in the volute chamber  16 , a rotor  200  (referring to  FIG. 7 ) fixed to a shaft  82  is mounted in the rotor chamber  38 , a stator  101  is mounted in the stator chamber  42 , and a driver  80  is mounted in the driver chamber  64 . The shaft  82  has a central axis x, and the rotor  200  as well as the shaft  82  rotate about the central axis x. The stator  101  is disposed coaxially with the central axis x of the shaft  82 . 
         [0034]    The pump cover  10  is provided with an inlet  12  at a front end portion thereof and an outlet  14  at a side portion thereof. Therefore, the coolant flows in the electric water pump  1  through the inlet  12 , and the pressurized coolant in the electric water pump  1  flows out through the outlet  14 . A slanted surface  18  is formed at a rear end portion of the inlet  12  of the pump cover  10 , and a rear end portion  20  of the pump cover  10  is extended rearward from the slanted surface  18 . The rear end portion  20  of the pump cover  10  is engaged to a cover mounting portion  44  of the body  30  by fixing means such as a bolt B. The slanted surface  18  is slanted with reference to the central axis x of the shaft  82 , and an intersecting point P of lines extended from the slanted surface  18  is located on the central axis x of the shaft  82 . 
         [0035]    The volute chamber  16  for pressurizing the coolant is formed in the pump cover  10 , and the impeller  22  for pressurizing and discharging the coolant through the outlet  14  is mounted in the volute chamber  16 . The impeller  22  is fixed to a front end portion of the shaft  82  and rotates together with the shaft  82 . For this purpose, a bolt hole  29  is formed at a middle portion of the impeller  22  and a thread is formed at an interior circumference of the bolt hole  29 . Therefore, an impeller bolt  28  inserted in the bolt hole  29  is threaded to the front end portion of the shaft  82  such that the impeller  22  is fixed to the shaft  82 . A washer w may be interposed between the impeller  22  and the impeller bolt  28 . 
         [0036]    The impeller  22  is provided with a confronting surface  26  corresponding to the slanted surface  18  at the front end portion thereof. Therefore, an intersecting point of lines extended from the confronting surface  26  is also positioned on the central axis x of the shaft  82 . The coolant having flowed into the water pump  1  may be smoothly guided and performance of the water pump  1  may be improved as a consequence of disposing centers of the impeller  22  and the rotor  200  that are rotating elements of the water pump  1  and a center of the stator  101  that is a fixed element of the water pump  1  on the central axis x. 
         [0037]    In addition, the impeller  22  is divided into a plurality of regions by a plurality of blades  24 . The coolant having flowed into the plurality of regions is pressurized by rotation of the impeller  22 . 
         [0038]    The body  30  has a hollow cylindrical shape that is opened rearward, and is engaged to the rear end of the pump cover  10 . The body  30  includes a front surface  32  forming the volute chamber  16  with the pump cover  10 , the stator chamber  42  that is formed at an exterior circumferential portion of the body  30  and in which the stator  101  is mounted, and the rotor chamber  38  that is formed at an interior circumferential portion of the stator chamber  42  and in which the rotor  200  is mounted. 
         [0039]    The front surface  32  of the body  30  is provided with the cover mounting portion  44 , a first stator mounting surface  40 , a first bearing mounting surface  48 , and a penetration hole  34  formed sequentially from an exterior circumference to a center thereof. 
         [0040]    The cover mounting portion  44  is engaged to the rear end portion  20  of the pump cover  10 . Sealing means such as an O-ring O may be interposed between the cover mounting portion  44  and the rear end portion  20  in order to prevent leakage of the coolant from the volute chamber  16 . 
         [0041]    The first stator mounting surface  40  is protruded rearward from the front surface  32 , and defines a boundary between the stator chamber  42  and the rotor chamber  38 . In a state that the sealing means such as an O-ring O is mounted at the first stator mounting surface  40 , the front end of the stator  101  is mounted at the first stator mounting surface  40 . 
         [0042]    The first bearing mounting surface  48  is protruded rearward from the front surface  32 . A first bearing  94  is interposed between the first bearing mounting surface  48  and the front end portion of the shaft  82  in order to make the shaft  82  smoothly rotate and to prevent the shaft  82  from being inclined. 
         [0043]    The penetration hole  34  is formed at a middle portion of the front surface  32  such that the front end portion of the shaft  82  is protruded to the volute chamber  16  through the penetration hole  34 . The impeller  22  is fixed to the shaft  82  in the volute chamber  16 . It is exemplarily described in this specification that the impeller  22  is fixed to the shaft  82  by the impeller bolt  28 . However, the impeller  22  may be press-fitted to an exterior circumference of the shaft  82 . 
         [0044]    Meanwhile, a connecting hole  36  is formed at the front surface  32  between the first stator mounting surface  40  and the first bearing mounting surface  48 . Therefore, the rotor chamber  38  is fluidly connected to the volute chamber  16 . Heat generated at the shaft  82 , the rotor  200 , and the stator  101  by operation of the water pump  1  is cooled by the coolant flowing in and out through the connecting hole  36 . Therefore, durability of the water pump  1  may improve. In addition, floating materials in the coolant are prevented from being accumulated in the rotor chamber  38 . 
         [0045]    The rotor chamber  38  is formed at a middle portion in the body  30 . The shaft  82  and the rotor  200  are mounted in the rotor chamber  38 . 
         [0046]    A stepped portion  83 , the diameter of which is larger than that of the other part, is formed at a middle portion of the shaft  82 . According to an exemplary embodiment of the present invention, a hollow shaft  82  may be used. A spline portion (not shown) may be formed at an exterior circumference of the stepped portion  83  along the central axis x. 
         [0047]    The rotor  200  is fixed on the stepped portion  83  of the shaft  82 , and is formed in an unsymmetrical shape. Thrust is exerted on the shaft  82  toward the front surface  32  by the unsymmetrical shape of the rotor  200  and a pressure difference between the volute chamber  16  and the rotor chamber  38 . The thrust generated at the shaft  82  pushes the shaft  82  toward the front surface  32 . Thereby, the stepped portion  83  of the shaft  82  may be interfere and collide with the first bearing  94  and the first bearing  94  may be damaged, accordingly. In order to prevent interference and collision of the stepped portion  83  of the shaft  82  and the first bearing  94 , a cup  100  is mounted between the stepped portion  83  of the shaft  82  and the first bearing  94 . Such a cup  100  is made of an elastic rubber material, and relieves the thrust of the shaft  82  exerted to the first bearing  94 . 
         [0048]    Meanwhile, in a case that the cup  100  directly contacts the first bearing  94 , the thrust of the shaft  82  exerted to the first bearing  94  can be relieved. However, rotation friction may be generated between the first bearing  94  and the cup  100  of a rubber material, and thereby performance of the water pump  1  may be deteriorated. Therefore, a thrust ring  98  is mounted between the cup  100  and the first bearing  94  in order to reduce the rotation friction between the first bearing  94  and the cup  100 . That is, the cup  100  reduces the thrust of the shaft  82  and the thrust ring  98  reduces the rotation friction of the shaft  82 . It is exemplarily described in this specification that a groove is formed at an exterior circumference of the cup  100  and the thrust ring  98  is mounted in the groove. However, a method for installing the thrust ring  98  to the cup  100  is not limited to the exemplary embodiment of the present invention. For example, a groove may be formed at a middle portion of the cup  100  and the thrust ring  98  may be mounted in this groove. Further, it is to be understood that any thrust ring  98  interposed between the cup  100  and the first bearing  94  may be included in the spirit of the present invention. 
         [0049]    The rotor  200  includes a rotor core  86 , a permanent magnet  88 , a rotor cover  84 , and a rotor case  90 . 
         [0050]    As shown in  FIG. 2  and  FIG. 5 , the rotor core  86  has a hollow cylindrical shape and is fixed to the stepped portion  83  of the shaft  82  by press-fitting or welding, or is splined to the stepped portion  83  of the shaft  82 . It is exemplarily described in this specification that the rotor core  86  is splined to the stepped portion  83  of the shaft  82 . For this purpose, a coupling groove  204  is formed at an interior circumference of the rotor core  86  along the central axis x and is splined to the stepped portion  83 . 
         [0051]    A plurality of guiding protrusions  202  is formed at the exterior circumference of the rotor core  86  along the central axis x, and a plurality of recesses  203  is formed between the guiding protrusions  202  along the central axis x. In addition, the permanent magnets  88  are insertedly mounted in each recess  203 . Therefore, the plurality of guiding protrusions  202  prevents the permanent magnet  88  from rotating. In addition, the plurality of guiding protrusions  202  does not cover both ends of the permanent magnet  88  so as to limit axial movement of the permanent magnet  88 . If the guiding protrusion  202  covers both ends of the permanent magnet  88 , magnetic flux generated by the permanent magnet  88  may leak. Such a leakage of the magnetic flux causes that the more and the larger permanent magnet  88  should be used. Therefore, size of the water pump  1  may increase. According to an exemplary embodiment of the present invention, the guiding protrusion  202 , however, does not cover both ends of the permanent magnet  88 , and thus leakage of the magnetic flux may be reduced. Therefore, sufficient capacity of the water pump  1  may be achieved without increasing the size of the water pump  1 . 
         [0052]    The permanent magnet  88  is mounted in the recess  203  formed at the exterior circumference of the rotor core  86 . The permanent magnet  88  includes N pole and S pole and is mounted in such a manner that the N pole and the S pole are alternately disposed. 
         [0053]    As shown in  FIG. 2  and  FIG. 4 , a pair of rotor covers  84  is mounted at both ends of the rotor core  86  and the permanent magnet  88 . A permanent magnet guider  201  is formed at an interior circumference of the rotor cover  84  such that movement of the permanent magnet  88  mounted at the rotor core  86  along the central axis x is restricted. Therefore, the rotor cover  84  primarily fixes the rotor core  86  and the permanent magnet  88 , and is made of copper or stainless steel that has high specific gravity. In addition, the rotor cover  84 , as shown in  FIG. 7 , is formed of a plurality of balance holes  205 . If the rotor  200  is manufactured, it is checked whether the rotor  200  is rotationally balanced. If the rotor  200  is not rotationally balanced, noise or vibration may occur when the water pump  1  operates. Thereby, performance of the water pump  1  may be deteriorated. Therefore, positions of the balance holes  205  are changed such that the rotor  200  is rotationally balanced. 
         [0054]    In a state in which the rotor core  86  and the permanent magnet  88  are mounted to the rotor cover  84 , the rotor case  90  wraps exterior circumferences of the rotor core  86  and the permanent magnet  88  so as to secondarily fix them. The rotor case  90  is made of a bulk mold compound (BMC) including a potassium family that has a low coefficient of contraction. A method for manufacturing the rotor case  90  will be briefly described. 
         [0055]    The rotor core  86  and the permanent magnet  88  are mounted to the rotor cover  84 , and the rotor cover  84  to which the rotor core  86  and the permanent magnet  88  are mounted is inserted in a mold (not shown). After that, the bulk mold compound including the potassium family is melted and high temperature (e.g., 150° C.) and high pressure BMC is flowed into the mold. Then, the BMC is cooled in the mold. As described above, if the rotor case  90  is made of BMC having the low coefficient of contraction, the rotor case  90  can be precisely manufactured. In general, the coefficient of contraction of a resin is 4/1000-5/1000, but the coefficient of contraction of the BMC is about 5/10,000. If the rotor case  90  is manufactured by flowing the high temperature resin into the mold, the rotor case  90  is contracted and does not have a target shape. Therefore, if the rotor case  90  is manufactured by the BMC including the potassium family that has the low coefficient of contraction, contraction of the rotor case  90  by cooling may be reduced and the rotor case  90  may be precisely manufactured. In addition, since BMC including the potassium family has good heat-radiating performance, the rotor can be cooled independently. Therefore, the water pump  1  may be prevented from being heat damaged. 
         [0056]    In addition, according to a conventional method for manufacturing the rotor, the permanent magnet is fixed to the exterior circumference of the rotor core with glue. However, as the rotor rotates, high temperature and high pressure are generated near the rotor. Thereby, the glue may be melted or the permanent magnet may be disengaged from the rotor core. The permanent magnet  88  mounted to the rotor core  86 , on the contrary, is fixed primarily by the rotor cover  84  and secondarily by the rotor case  90  according to an exemplary embodiment of the present invention. Thus, the permanent magnet  88  may not be disengaged from the rotor core  86 . 
         [0057]    The stator chamber  42  is formed in the body  30  at a radially outer portion of the rotor chamber  38 . The stator  101  is mounted in the stator chamber  42 . 
         [0058]    The stator  101  is fixed to the body  30  directly or indirectly, and includes a stator core  102 , an insulator  104 , a coil  108 , and a stator case  109 . 
         [0059]    The stator core  102  is formed by stacking a plurality of pieces made of a magnetic material. That is, the plurality of thin pieces is stacked up such that the stator core  102  has a target thickness. 
         [0060]    The insulator  104  connects the pieces making up the stator core  102  to each other, and is formed by molding a resin. That is, the stator core  102  formed by stacking the plurality of pieces is inserted in a mold (not shown), and then molten resin is injected into the mold. Thereby, the stator core  102  at which the insulator  104  is mounted is manufactured. At this time, coil mounting recesses  106  are formed at front and rear end portions of the stator core  102  and the insulator  104 . 
         [0061]    The coil  108  is coiled at an exterior circumference of the stator core  102  so as to form a magnetic path. 
         [0062]    The stator case  109  wraps and seals the stator core  102 , the insulator  104 , and the coil  108 . The stator case  109 , the same as the rotor case  90 , is manufactured by insert molding the BMC including the potassium family. 
         [0063]    In addition, when the stator case  109  is insert molded, a Hall sensor  112  and a Hall sensor board  110  may also be insert molded. That is, the stator  101 , the Hall sensor  112 , and the Hall sensor board  110  may be integrally manufactured as one component. 
         [0064]    The Hall sensor  112  detects the position of the rotor  200 . A mark (not shown) for representing the position thereof is formed at the rotor  200 , and the Hall sensor  112  detects the mark in order to detect the position of the rotor  200 . 
         [0065]    The Hall sensor board  110  controls a control signal delivered to the stator  101  according to the position of the rotor  200  detected by the Hall sensor. That is, the Hall sensor board  110  makes a strong magnetic field be generated at one part of the stator  101  and a weak magnetic field be generated at the other part of the stator  101  according to the position of the rotor  200 . Thereby, initial mobility of the water pump  1  may be improved. 
         [0066]    A case mounting portion  46  is formed at an exterior surface of the rear end of the body  30 . 
         [0067]    The driver case  50  is engaged to the rear end of the body  30 , and is formed of a case surface  52  at a front end portion thereof. The rotor chamber  38  and the stator chamber  42  are formed in the body  30  by engaging the driver case  50  to the rear end portion of the body  30 . A body mounting portion  60  is formed at an external circumference of the front end portion of the driver case  50  and is engaged to the case mounting portion  46  by fixing means such as a bolt B. 
         [0068]    The case surface  52  is provided with an insert portion  54 , a second stator mounting surface  56 , and a second bearing mounting surface  58  formed sequentially from an exterior circumference to a center thereof. 
         [0069]    The insert portion  54  is formed at an external circumferential portion of the case surface  52  and is protruded forward. The insert portion  54  is inserted in and closely contacted to the rear end portion of the body  30 . Sealing means such as an O-ring O is interposed between the insert portion  54  and the rear end portion of the body  30  so as to close and seal the stator chamber  42 . 
         [0070]    The second stator mounting surface  56  is protruded forward from the case surface  52  so as to define the boundary between the stator chamber  42  and the rotor chamber  38 . The rear end of the stator  101  is mounted at the second stator mounting surface  56  with a sealing means such as an O-ring O being interposed. The stator chamber  42  is not fluidly connected to the rotor chamber  38  by the O-ring O interposed between the first stator mounting surface  40  and the front end of the stator  101  and the O-ring O interposed between the second stator mounting surface  56  and the rear end of the stator  101 . Therefore, the coolant having flowed in the rotor chamber  38  does not flow to the stator chamber  42 . 
         [0071]    The second bearing mounting surface  58  is protruded forwardly from the case surface  52 . A second bearing  96  is interposed between the second bearing mounting surface  58  and the rear end portion of the shaft  82  so as to make the shaft  82  smoothly rotate and to prevent the shaft  82  from being inclined. 
         [0072]    The rear end of the driver case  50  is open. The driver chamber  64  is formed between the driver case  50  and the driver cover  70  by engaging the driver cover  70  of a disk shape to the rear end of the driver  50  by fixing means such as a bolt B. For this purpose, a protruding portion  72  is protruded forward from an exterior circumference of the driver cover  70 , and this protruding portion  72  is inserted in and closely contacted to an exterior circumference  62  of the rear end of the driver case  50 . Sealing means such as an O-ring O is interposed between the protruding portion  72  and the exterior circumference  62  so as to prevent foreign substances such as dust from entering the driver chamber  64 . 
         [0073]    The driver  80  controlling operation of the water pump  1  is mounted in the driver chamber  64 . The driver  80  includes microprocessors and a printed circuit board (PCB). The driver  80  is electrically connected to a controller (not shown) disposed at an exterior of the electric water pump  1  through a connector  74  and receives a control signal of the controller. In addition, the driver  80  is electrically connected to the Hall sensor board  110  so as to transmit the control signal received from the controller to the Hall sensor board  110 . 
         [0074]    Meanwhile, the driver chamber  64  is isolated from the rotor chamber  38  by the case surface  52 . Therefore, the coolant in the rotor chamber  38  does not flow into the driver chamber  64 . 
         [0075]    Hereinafter, the stator  101  of the electric water pump  1  according to an exemplary embodiment of the present invention will be described in further detail with reference to  FIG. 3 . 
         [0076]      FIG. 3  is a perspective view showing a stator of an electric water pump according to an exemplary embodiment of the present invention. 
         [0077]    As shown in  FIG. 3 , a plurality of fixing grooves  105  are formed at the external circumference of the rear end of the stator case  109 . The insert portion  54  is inserted in the fixing groove  105  so as to limit rotational and axial movements of the stator  101  according to the rotation of the rotor  200 . Such a fixing groove  105  can be formed together with the stator case  109  when the stator case  109  is insert molded, and an additional process or an additional device is not required for forming the fixing groove  105 . Therefore, processes for manufacturing the stator  101  do not increase. In addition, since the stator  101  is fixed to the body  30  neither with glue nor by press-fitting, the stator  101  can be easily disassembled from the body  30 . Therefore, if the stator  101  is out of order, the stator  101  can be easily replaced. 
         [0078]    In addition, as shown in  FIG. 2 , the interior circumference of the stator case  109  forms a part of the rotor chamber  38 . As described above, the coolant flows into the rotor chamber  38  and moves in the rotor chamber  38  by rotation of the shaft  82  and the rotor  200 . Since a stator groove  122  is formed at the interior circumference of the stator case  109  along the length direction thereof, the coolant in the rotor chamber  38  flows along the stator groove  122  and removes floating materials attached to the interior circumference of the stator case  109 . The shape of the stator groove  122  can be easily determined by a person of ordinary skill in the art considering the flow of the coolant in the rotor chamber  38 . 
         [0079]    Further, in order to reduce vibration and noise according to the rotation of the rotor  200  and to reduce vibration generated when a vehicle drives, a plurality of damping holes  120  are formed at the stator case  109 . Vibration and noise according to the rotation of the rotor  200  and vibration generated when the vehicle drives are absorbed by movement of gas in the stator chamber  42  through the damping hole  120 . The position and shape of the damping hole  120  can be easily determined by a person of ordinary skill in the art according to vibration frequency and pressure frequency of the stator  101 . In addition, a frothing resin or sound absorbing material may be filled in the damping hole  120  so as to further reduce vibration and noise. 
         [0080]    Meanwhile, the stator groove  122  and the damping hole  120  may be formed at the rotor  200 . That is, grooves (not shown) may be formed at the exterior circumference of the rotor case  90  such that the coolant in the rotor chamber  38  flows along the grooves and removes the floating materials attached to the exterior circumference of the rotor case  90 . In addition, vibration and noise according to the rotation of the rotor ( 84 ,  86 ,  88 , and  90 ) and vibration when the vehicle drives may be absorbed by forming holes (not shown) at the rotor case  90 . 
         [0081]      FIG. 7  is a schematic diagram showing processes for manufacturing a rotor used in an electric water pump according to an exemplary embodiment of the present invention. 
         [0082]    If the rotor core  86  provided with the plurality of recesses  203  at the exterior circumference thereof is provided as shown in  FIG. 7A , the permanent magnets  88  are inserted in each recess  203  as shown in  FIG. 7B . At this time, the permanent magnets  88  are mounted in such the manner that the N pole and the S pole are alternately disposed. 
         [0083]    After that, the rotor covers  84  are mounted at both ends of the rotor core  86  and the permanent magnet  88  as shown in  FIG. 7C . Thereby, the permanent magnets  88  are primarily fixed to the rotor core  86 . 
         [0084]    After that, the rotor case  90  is molded to the exterior circumference of the rotor core  86  and the permanent magnet  88  as shown in  FIG. 7D . 
         [0085]    When the rotor  200  is manufactured as described above, it is checked whether the rotor  200  is rotationally balanced. If the rotor  200  is not rotationally balanced, the positions of the balance holes  205  are determined in order to keep the rotational balance of the rotor  200 . Then, the balance holes  205  are formed at the rotor cover  84 . 
         [0086]    Since a stator and a rotor that are electrically operated are wrapped by a resin case having waterproof performance according to an exemplary embodiment of the present invention, performance and durability of an electric water pump may improve. 
         [0087]    In addition, since a Hall sensor and a Hall sensor board are mounted in the stator and a control signal is changed according to an initial position of the rotor, initial mobility of the electric water pump may improve. 
         [0088]    Further, the shape of the rotor core may be optimized so as to minimize leakage of magnetic flux of the permanent magnet. Therefore, sufficient capacity of the water pump may be achieved without increasing the size of the water pump. 
         [0089]    For convenience in explanation and accurate definition in the appended claims, the terms “interior”, “exterior”, “inner”, and “outer” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0090]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.