Abstract:
Fluid pump ( 10 ) comprises a casing provided with a partition separating a pump chamber and a housing chamber. Impeller ( 43 ) is disposed within the pump chamber. Stator ( 33 ), semiconductor device ( 25 ), terminal ( 37 ), and sheet member ( 29   a ) are disposed within the housing chamber. Terminal ( 37 ) electrically connects the semiconductor device to the stator. Sheet member ( 29   a ) may have rubber elasticity. Preferably, the sheet member has s a first plane surface, which makes contact in a planar manner with the semiconductor device, and a second plane surface which makes contact in a planar manner with the partition of the casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2006-313363 filed on Nov. 20, 2006, the contents of which are hereby incorporated by reference into the present application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a fluid pump for circulating cooling water that can cool an engine or inverter of a motor vehicle. 
         [0004]    2. Description of the Related Art 
         [0005]    This type of fluid pump has a casing that comprises a pump chamber and a housing chamber. The pump chamber and the housing chamber are separated by a partition, such that fluid within the pump chamber does not flow into the housing chamber. An impeller is disposed within the pump chamber in a manner capable of rotation. A stator and a control device are disposed within the housing chamber. The control device has a semiconductor device and a terminal. The semiconductor device operates for converting power supplied from the exterior into power for driving the impeller. The terminal electrically connects the semiconductor device with the stator. When the driving power is supplied to the stator, the stator generates driving force for driving the rotation of the impeller. When the impeller has been driven to rotate by the stator, fluid is drawn into the pump chamber and its pressure is increased, then this pressurized fluid is discharged from the pump chamber. 
         [0006]    With this fluid pump, power supplied from the exterior is converted into power for driving a motor by the semiconductor device. The semiconductor device generates heat when power supplied from the exterior is converted into power for driving a motor, and consequently this semiconductor device must be cooled. Japanese Laid-open Patent Publication No. 2000-209810 discloses a fluid pump having a metal casing. The semiconductor device is pressed onto and maintained on a wall surface of the metal casing by means of resilient supporting members. The heat generated by the semiconductor device is radiated to the outside air via the metal housing, thus cooling the semiconductor device. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    With this type of fluid pump, the external force that the fluid applies to the impeller may vary when the amount of fluid discharged varies during operation. When the external force applied to the impeller varies, the impeller may oscillate about its rotational axis, whereby the casing vibrates. Further, in the case where the fluid pump is attached to the engine room of a motor vehicle, the vibration of the engine is transmitted, whereby the casing vibrates. In the fluid pump disclosed in Japanese Laid-open Patent Publication No. 2000-209810, the semiconductor device is pressed directly onto the metal casing. As a result, there was the problem that the vibration of the casing was also transmitted to the semiconductor device, and this caused a decrease in the durability and reliability of the semiconductor device. 
         [0008]    Accordingly, it is an object of the present teachings to provide a fluid pump capable of efficiently cooling the semiconductor device, and capable of reducing the vibration transmitted to the semiconductor device. 
         [0009]    In one aspect of the present teachings, a fluid pump may comprise a casing, an impeller, a stator, a semiconductor device, a terminal, and a sheet member. The casing may be provided with a pump chamber, a housing chamber, and a partition that separates the pump chamber and the housing chamber. The impeller may be rotatably disposed within the pump chamber. The stator may be disposed within the housing chamber. The stator generates driving force for driving the rotation of the impeller. The semiconductor device and the terminal may also be disposed within the housing chamber. The terminal electrically connects the semiconductor device to the stator. The sheet member may be disposed within the housing chamber. The first sheet member may have rubber elasticity. The sheet member may include a first plane surface, which makes contact in a planar manner with the semiconductor device, and a second plane surface which makes contact in a planar manner with the partition. 
         [0010]    In this fluid pump, the semiconductor device makes contact in a planar manner with the sheet member, and this sheet member makes contact in a planar manner with the partition. As a result, the heat of the semiconductor device is transmitted to the partition via the first sheet member, and is transmitted from the partition to the fluid in the pump chamber. The semiconductor device can thus be cooled efficiently. Further, the sheet member that has rubber elasticity is disposed between the semiconductor device and the partition. As a result, the amount of vibration transmitted from the partition to the semiconductor device is reduced by the sheet member, and the durability and reliability of the semiconductor device can consequently be increased. 
         [0011]    In another aspect of the present teachings, a fluid pump may comprise a casing, an impeller, a substrate, a stator, a semiconductor, a terminal, and a sheet member. The casing may be provided with a pump chamber, a housing chamber, and a partition separating the pump chamber and the housing chamber. The impeller may be rotatably disposed within the pump chamber. The substrate, the stator, the terminal, and the sheet member may be disposed within the housing chamber. The stator generates driving force for driving the rotation of the impeller. The semiconductor device may be mounted on an opposite surface of the substrate from the pump chamber side. A first end of the terminal may be fixed to the substrate, and a second end of the terminal may be fixed to the stator. The sheet member may have rubber elasticity. The sheet member may comprise a first plane surface, which makes contact in a planar manner with a surface at the pump chamber side of the substrate, and a second plane surface which makes contact in a planar manner with the partition of the casing. Preferably, the semiconductor device is disposed at a position corresponding to the location where the substrate is making contact with the first plane surface of the sheet member. 
         [0012]    In this fluid pump, since the semiconductor device is making thermal contact with the sheet member via the substrate, it is possible to cool the semiconductor device satisfactorily. Further, since the sheet member has rubber elasticity, it is possible to reduce the amount of vibration that is transmitted from the partition to the substrate (and to the semiconductor device). 
         [0013]    In another aspect of the present teachings, a fluid pump may comprise a casing, an impeller, a stator, a semiconductor device, and a heat insulating plate. The casing may be provided with a pump chamber, a housing chamber, and a partition separating the pump chamber and the housing chamber. The impeller may be rotatably disposed within the pump chamber. The stator, the semiconductor device, and the heat insulating plate may be disposed within the housing chamber. The stator generates driving force for driving the rotation of the impeller. The semiconductor device is electrically connected to the stator. The heat insulating plate may divide the housing chamber into a stator side and a semiconductor device side. Preferably, the stator is surrounded by the partition and the heat insulating plate. 
         [0014]    In this fluid pump, since the stator is surrounded by the partition and the heat insulating plate, heat generated by the stator is prevented from being transmitted to the semiconductor device side. It is thus possible to effectively prevent the semiconductor device from reaching a high temperature. 
         [0015]    These aspects and features may be utilized singularly or in combination in order to make an improved fluid pump. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and claims. Of course, the additional features and aspects disclosed herein may also be utilized singularly or in combination with the above-described aspect and features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a vertical sectional view of a fluid pump of a first embodiment. 
           [0017]      FIG. 2  shows a view from above of a circuit substrate of the first embodiment. 
           [0018]      FIG. 3  shows a view from below of the circuit substrate of the first embodiment. 
           [0019]      FIG. 4  shows a vertical sectional view of a fluid pump of a second embodiment. 
           [0020]      FIG. 5  shows a vertical sectional view of a fluid pump of a third embodiment. 
           [0021]      FIG. 6  shows a view from below of a circuit substrate of the third embodiment. 
           [0022]      FIG. 7  shows a view from above of the circuit substrate of the third embodiment. 
           [0023]      FIG. 8  shows a vertical sectional view of a fluid pump of a fourth embodiment. 
           [0024]      FIG. 9  shows a view from below of a circuit substrate of the fourth embodiment. 
           [0025]      FIG. 10  shows a view from above of the circuit substrate of the fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
       [0026]    A fluid pump  10  of a first embodiment of the present teachings will be described. The fluid pump  10  can be utilized to circulate cooling water for cooling an engine of a motor vehicle, and can be disposed in an engine room of the motor vehicle. As shown in  FIG. 1 , the fluid pump  10  comprises a lower body  12 , and an upper body  50  that is fixed to the lower body  12 . The lower body  12  and the upper body  50  are both molded integrally from resin material. 
         [0027]    A cylindrical convex part  15  is formed at an upper part of the lower body  12  (at the left side in  FIG. 1 ). A shaft attaching hole  16   a  is formed in a center of the convex part  15 . A lower end of a shaft  46  is fixed in the shaft attaching hole  16   a . An upper end part of the shaft  46  protrudes upward beyond an upper surface of the convex part  15 . An impeller  43  is attached in a manner allowing rotation to the upper end part of the shaft  46 . A cylinder-shaped outer wall  17  is formed at an outer circumference of the convex part  15 . The convex part  15  and the outer wall  17  are disposed concentrically. A ring-shaped concave part  20  that opens upward is formed by the convex part  15  and the outer wall  17 . A cylindrical part  45  of the impeller  43  is housed in the concave part  20 . 
         [0028]    A connector  21  is formed on the upper part of the lower body  12  (at the right side in  FIG. 1 ). Electric contact  28  is disposed in the connector  21 . A lower end of the electric contact  28  is connected with a terminal  26  of a circuit substrate  23 . An external power source (not shown) can be connected with an upper end of the connector  21 . Power from the external power source can be supplied to the circuit substrate  23  via the electric contact  28  and the terminal  26 . 
         [0029]    A lower end of the upper body  50  is fixed (by welding for example) to an upper end of the outer wall  17  of the lower body  12 . An inlet port  51  and an outlet port (not shown) are formed in the upper body  50 . An inner space formed by the lower body  12  and the upper body  50  (i.e., the inner space formed by the outer wall  17 , the convex part  15 , and the upper body  50 ) functions as a pump chamber. As a result, the upper body  50  and the lower body  12  correspond to the casing of the claims in the first embodiment. 
         [0030]    The impeller  43  is disposed within the pump chamber. The impeller  43  is molded integrally from synthetic resin. The impeller  43  may be manufactured, for example, from material including plastic that contains ferrite powder. The impeller  43  comprises the substantially cylindrically-shaped cylinder part  45 , and a blade part  44  that closes one end of the cylinder part  45 . The cylinder part  45  is magnetized (polarized) by including magnetic powder therein. A plurality of fins are provided in the blade part  44 . 
         [0031]    A shaft bearing  47  is disposed in a center of the blade part  44 . The impeller  43  and the shaft bearing  47  may be molded integrally by insert molding. The shaft bearing  47  may be formed from polyphenylene sulphide material (PPS material). The shaft  46  is inserted into the shaft bearing  47 , and the impeller  43  can rotate freely around the shaft  46 . A washer  52  is disposed between the shaft bearing  47  and the convex part  15 . A washer  48  is attached to an upper end of the shaft  46  by a screw  49 . The washer  48  prevents the impeller  43  from rising upward during rotation. When the impeller  43  is in an attached state with respect to the shaft  46 , there is a space formed between an inner surface of the impeller  43  (i.e., an inner circumference surface of the cylinder part  45  and a lower surface of the blade part  44 ) and the convex part  15  of the lower body  12 . Further, a space is also formed between an outer circumference surface of the cylinder part  45  of the impeller  43  and the outer wall  17  of the lower body  12 . Furthermore, a space is also formed between a lower surface of the cylinder part  45  of the impeller  43  and the concave part  20  of the lower body  12 . Cooling water within the pump chamber passes through these spaces and makes contact with a surface of the convex part  15  of the lower body  12 . 
         [0032]    A substrate housing part  14  is formed within the lower body  12 . A stator housing part  16  is formed within the convex part  15 . A bottom of the stator housing part  16  communicates with the substrate housing part  14 . The substrate housing part  14  is open toward the bottom. The circuit substrate  23  is inserted into the lower body  12  from the bottom of the substrate housing part  14 . When the circuit substrate  23  has been inserted into the lower body  12 , a stator  33  is housed in the stator housing part  16 , and a substrate  24  is housed in the substrate housing part  14 . 
         [0033]    In the present embodiment, a heat insulating plate  54  is disposed at the junction between the stator housing part  16  and the substrate housing part  14  (specifically, near a lower end of the stator  33 ). The stator housing part  16  and the substrate housing part  14  are compartmented by the heat insulating plate  54 . The heat insulating plate  54  may utilize, for example, a PA (polyacetal) plate. As a result of providing the heat insulating plate  54 , the stator  33  is disposed in a space surrounded by the heat insulating plate  54  and a wall surface of the convex part  15 . Potting material  41  is filled into this space (i.e. the stator housing part  16 ). The stator  33  is submerged in the potting material  41  that has been filled. As a result, heat from the stator  33  is transmitted to the wall surface of the convex part  15  via the potting material  41 . The substrate housing part  14  is not filled with potting material, and a lower end thereof is closed by a cover  56 . Closing the lower end of the substrate housing part  14  by the cover  56  prevents foreign objects, moisture, etc. from entering the substrate housing part  14 . 
         [0034]    A material with a high degree of thermal conductivity can be utilized in the potting material  41 . By utilizing material with a high degree of thermal conductivity, heat from the stator  33  can be radiated efficiently to the exterior. For example, heat radiating silicon or epoxy resin can be utilized in the potting material  41 . Alumina fibers (filler) can be mixed into these resins. The degree of thermal conductivity can be increased further by adding the alumina filler. 
         [0035]    The circuit substrate  23  is provided with the substrate  24  and the stator  33  that is fixed to the substrate  24 . The stator  33  comprises a stator core  34  and stator coils  35 . The stator core  34  is configured from layers of thin steel plate (for example, silicon steel plate) obtained by pressing. A plurality of slots are formed in the stator core  34 . A fitting hole  34   a  is formed in the center of the stator core  34 . A shaft fixing part  16   b  of the lower body  12  is fitted into the fitting hole  34   a  when the stator  33  is in a housed state in the stator housing part  16 . The position of the stator  33  is thus fixed in a predetermined position within the stator housing part  16 . When the stator  33  has been fixed in position in the stator housing part  16 , an outer circumference surface of the stator  33  faces the inner circumference surface of the cylinder part  45  of the impeller  43 . 
         [0036]    An upper end of a terminal  37  is fixed to a lower end of the stator core  34 . A lower end of the terminal  37  is soldered to a terminal land  37   a  (see  FIGS. 2 and 3 ) of the substrate  24 . That is, the stator  33  is fixed to the substrate  24  via the terminal  37  and the terminal land  37   a . An upper end part of the terminal  37  passes through the heat insulating plate  54 , a central part of the terminal  37  is bent sideways (to the left in  FIG. 1 ), and a lower part thereof is bent downward. As a result, the terminal land  37   a  is formed near a left edge of the substrate  24 . The stator coils  35  are wound around the slots of the stator core  34 . One end of the winding of the stator coils  35  is connected with the terminal  37 . 
         [0037]    As shown in  FIG. 2 , the following are mounted in addition to the stator  33  on an upper surface (i.e., the surface at the stator side) of the substrate  24 : semiconductor devices, viz. power transistors  25  and power diodes  31 , and an electronic part, viz. a choke coil  27 . The power transistors  25  are switching elements that switch the power supply to the stator coils  35 . The power diodes  31  are devices for absorbing surge voltage at the time when the power supply is switched. The choke coil  27  is a filter for removing noise generated at the time when the power supply is switched. The electronic parts  25 ,  27 , and  31  are heat generating devices that generate heat while operating. Thus, the power transistors  25  and the power diodes  31  correspond to the semiconductor device of the claims. 
         [0038]    As shown in  FIG. 3 , the following electronic parts  32  are mounted on a lower surface of the substrate  24 : chip transistors, and chip resistors. As shown clearly in  FIGS. 2 and 3 , comparatively large electronic parts are mounted on the upper surface of the substrate  24 , and comparatively small electronic parts are mounted on the lower surface of the substrate  24 . 
         [0039]    As shown in  FIG. 2 , the area surrounded by two dotted lines (i.e., the ring-shaped area surrounded by the two circular dotted lines, hereafter referred to as ring-shaped area) faces the concave part  20  of the lower body  12 . The power transistors  25  and power diodes  31  are disposed within this ring-shaped area. Further, the choke coil  27  is disposed adjacent to the ring-shaped area. As shown in  FIG. 1 , the power transistors  25  and power diodes  31  face a lower surface of the concave part  20 , and the choke coil  27  faces an outer surface of the concave part  20 . 
         [0040]    A ring-shaped sheet member  29   a  is disposed above the ring-shaped area of the substrate  24  (see  FIG. 1 ). The sheet member  29   a  is molded in a flat shape. The sheet member  29   a  has a high degree of thermal conductivity and rubber elasticity. The sheet member can be manufactured from a resilient material (e.g., silicon rubber, silicon rubber containing alumina filler, etc.). A lower surface of the sheet member  29   a  makes contact in a planar manner with a portion of upper surfaces of the power transistors  25  and with substantially the entirety of upper surfaces of the power diodes  31 . Further, as shown in  FIG. 1 , the lower surface of the sheet member  29   a  makes contact in a planar manner with the central part of the terminal  37 . An upper surface of the sheet member  29   a  makes contact in a planar manner with the lower surface of the concave part  20  of the lower body  12 . 
         [0041]    Further, as shown in  FIG. 1 , a right surface of the choke coil  27  makes contact with an inner wall surface of the lower body  12 , and a left surface of the choke coil  27  makes contact in a planar manner with a right surface of a sheet member  29   b . A left surface of the sheet member  29   b  makes contact in a planar manner with the outer surface of the concave part  20  of the lower body  12 . Like the sheet member  29   a , the sheet member  29   b  is formed in a flat shape. The sheet member  29   b  also has a high degree of thermal conductivity and rubber elasticity. The sheet member  29   b  also can be manufactured from a resilient material (i.e., silicon rubber, silicon rubber containing alumina filler, etc.). 
         [0042]    In the fluid pump  10 , power is supplied from the circuit substrate  23  to the stator coils  35  of the stator  33 . As a result, magnetic force is generated from the stator coils  35 , and this magnetic force acts on the cylindrical part  45  of the impeller  43 , causing the impeller  43  to rotate. When the impeller  43  rotates, cooling water is drawn into the pump chamber from the inlet port  51 . The rotation of the impeller  43  increases the pressure of the cooling water that has been drawn in, and this cooling water is discharged from the outlet port of the upper body  50 . At this juncture, the cooling water that has been drawn into the pump chamber also enters the concave part  20  of the lower body  12 . The cooling water that has entered the concave part  20  is agitated and frequently redistributed by the rotation of the impeller  43 . 
         [0043]    When the fluid pump  10  operates, the stator coils  35  of the stator  33  generate heat. Since the stator  33  is surrounded by the wall of the convex part  15  of the lower body  12  and the heat insulating plate  54 , the heat of the stator  33  is prevented from being transmitted toward the substrate  24 . Further, heat transmitted from the stator  33  to the terminal  37  is transmitted to the concave part  20  via the sheet member  29   a , and is radiated to the cooling water in the pump chamber by the concave part  20 . Thus, the heat of the stator  33  is prevented from being transmitted toward the substrate  24 , whereby the semiconductor devices  25 ,  31  is prevented from reaching a high temperature. Further, the potting material  41  is filled into the stator housing part  16 . As a result, the heat of the stator  33  is transmitted to the convex part  15  via the potting material  41 , and is radiated to the cooling water in the pump chamber by the convex part  15 . The heat of the stator  33  is thus radiated efficiently to the cooling water, and the stator  33  is also prevented from reaching a high temperature. 
         [0044]    When the fluid pump  10  operates, the power transistors  25 , the power diodes  31 , and the choke coil  27  mounted on the substrate  24  also generate heat. The heat of the power transistors  25  and the power diodes  31  is transmitted to the concave part  20  via the sheet member  29   a , and is radiated to the cooling water in the pump chamber by the concave part  20 . Further, the heat of the choke coil  27  is transmitted to the concave part  20  via the sheet member  29   b , and is radiated to the cooling water in the pump chamber by the concave part  20 . The electronic parts mounted on the substrate  24 , i.e. the power transistors  25 , the power diodes  31 , and the choke coil  27 , are thus prevented from reaching a high temperature. 
         [0045]    In the fluid pump  10 , the heat of the stator  33  is prevented from being transmitted toward the substrate  24 , and the heat of the power transistors  25  and the power diodes  31  and the choke coil  27  is radiated to the cooling water in the pump chamber via the sheet members  29   a ,  29   b  and the wall of the concave part  20 . The electronic parts  25 ,  27 ,  31  are thus effectively prevented from reaching a high temperature. 
         [0046]    Further, the power transistors  25 , the power diodes  31 , and the terminal  37  make contact with the concave part  20  via the sheet member  29   a  having rubber elasticity. As a result, there is a decrease in the vibration that is transmitted to the electronic parts  25 ,  31 ,  37  via the lower body  12 . The electronic parts  25 ,  31 ,  37  can consequently be maintained in a suitable manner, and electrical contact (soldered parts) between these electronic parts and the substrate  24  can consequently be maintained satisfactorily. 
         [0047]    Further, since the potting material  41  is not filled into the substrate housing part  14 , the fluid pump  10  can be made lightweight. Furthermore, since the substrate  24  is fixed to the lower body  12  via the sheet members  29   a ,  29   b  even though the substrate housing part  14  is not filled with potting material, the substrate  24  can be maintained adequately within the substrate housing part  14 . 
       Second Embodiment 
       [0048]    Next, a fluid pump  100  of a second embodiment of the present teachings will be described. The fluid pump  100  can also be utilized to circulate cooling water for cooling an engine. As shown in  FIG. 4 , the fluid pump  100  is an inner rotor fluid pump. The fluid pump  100  comprises a lower body  112 , an upper body  150  that is fixed to an upper end of the lower body  112 , and a cover  116  that is fixed to a lower end of the lower body  112 . 
         [0049]    A concave part  118  is formed in approximately the center of an upper part of the lower body  112 , and a convex part  121  is formed at an outer side of the concave part  118 . Seen from above, the convex part  121  has a ring shape surrounding the concave part  118 . The convex part  121  and the concave part  118  are disposed concentrically. A substrate housing part  114  is formed within the lower body  112 . A stator housing part  121   a  is formed within the convex part  121 . A lower end of the stator housing part  121   a  communicates with the substrate housing part  114 . 
         [0050]    A circuit substrate  123  is housed in the lower body  112 . The circuit substrate  123  comprises a substrate  124 , power transistors  125   a ,  125   b  mounted on the substrate  124 , and the stator  133  that is connected with the substrate  124  via a terminal (not shown). The power transistor  125   a  is mounted on an upper surface of the substrate  124 . The power transistor  125   b  is mounted on a lower surface of the substrate  124 . 
         [0051]    When the circuit substrate  123  is in a housed state in the lower body  112 , the stator  133  is housed in the stator housing part  121   a . Potting material  141  is filled between an upper surface of the stator  133  and an inner wall surface of the convex part  121 . Further, the power transistor  125   a  is thermally connected with a wall surface of the concave part  118  via a sheet member  129   a . As shown in  FIG. 4 , the power transistor  125   b  is disposed at a position corresponding to the location where the substrate  124  is making contact in a planar manner with a sheet member  129   b . Thus, the power transistor  125   b  is thermally connected with the wall surface of the concave part  118  via the substrate  124  and the sheet member  129   b . The sheet member  129   a ,  129   b  also have a high degree of thermal conductivity and rubber elasticity. The sheet members  129   a ,  129   b  can be configured in the same manner as the sheet members  29   a ,  29   b  of the first embodiment. 
         [0052]    A lower end of a shaft  146  is fixed at a center of the concave part  118 . An upper end of the shaft  146  is fixed to the upper body  150 . An impeller  143  is attached to the shaft  146 . The impeller  143  comprises shaft bearings  146   a ,  146   b . The impeller  143  is supported by the shaft bearings  146   a ,  146   b  such that it can rotate around the shaft  146 . A cylindrical magnet  145  is provided at the lower end of the impeller  143 . When the impeller  143  has been attached to the shaft  146 , a lower end part of the impeller  143  is housed in the concave part  118 , and the cylindrical magnet  145  faces the stator  133 . As a result, when power is supplied from the circuit substrate  123  to the stator  133 , magnetic force is generated from the stator  133 , and the impeller  143  rotates. When the impeller  143  rotates, cooling water is drawn into a pump chamber  120  (i.e., an inner space surrounded by the lower body  112  and the upper body  150 ) from an inlet port  151 . The rotation of the impeller  143  increases the pressure of the cooling water that has been drawn in, and this cooling water is discharged from an outlet port (not shown). Furthermore, the cooling water that has been drawn into the pump chamber  120  also enters the concave part  118  of the lower body  112 . The liquid that has entered the concave part  118  is agitated and frequently redistributed by the rotation of the impeller  143 . 
         [0053]    In the fluid pump  100 , as well, the heat generated by the power transistor  125   a  is efficiently transmitted to the wall surface of the concave part  118  of the lower body  112  via the sheet member  129   a , and is radiated from the wall surface of the concave part  118  to the cooling water in the pump chamber  120 . Further, the heat generated by the power transistor  125   b  is efficiently transmitted to the wall surface of the concave part  118  of the lower body  112  via the substrate  124  and the sheet member  129   b , and is radiated from the wall surface of the concave part  118  to the cooling water in the pump chamber  120 . The heat generated by the power transistors  125   a ,  125   b  is thus radiated efficiently to the cooling water in the pump chamber  120 , and the power transistors  125   a ,  125   b  are prevented from reaching a high temperature. Further, the power transistors  125   a ,  125   b  make contact with the wall surface of the lower body  112  via the sheet members  129   a ,  129   b . As a result, vibration of the lower body  112  is prevented from being transmitted to the power transistors  125   a ,  125   b.    
       Third Embodiment 
       [0054]    Next, a fluid pump  200  of a third embodiment of the present teachings will be described. The fluid pump  200  can also be utilized to circulate cooling water for cooling an engine. As shown in  FIG. 5 , the fluid pump  200  is an outer rotor fluid pump. The fluid pump  200  comprises a lower body  212 , an upper body  250  that is fixed to an upper end of the lower body  212 , and a cover  216  that is fixed to a lower end of the lower body  212 . An impeller  243  is disposed in an inner space (i.e., pump chamber)  220  surrounded by the lower body  212  and the upper body  250 . A circuit substrate  223  is housed in the lower body  212 . A ring-shaped sheet member  229  makes contact in a planar manner with an upper surface of a substrate  224  of the circuit substrate  223 . An upper surface of the sheet member  229  makes contact in a planar manner with a wall of the lower body (specifically, a wall facing a lower end surface of an impeller  243 ). The sheet member  229  also has a high degree of thermal conductivity and rubber elasticity. The sheet members  229  can be configured in the same manner as the sheet members  29   a ,  29   b  of the first embodiment. 
         [0055]    The circuit substrate  223  comprises the substrate  224  and various electronic devices mounted on the substrate  224 . As shown in  FIG. 7 , a controlling IC  240  and other electronic parts (e.g., chip transistors, chip resistors) are mounted on an upper surface of the substrate  224 . As shown in  FIG. 6 , the following electronic parts are mounted on a lower surface of the substrate  224 : a power transistor  236 , condensers  232   a ,  232   b ,  232   c ,  232   d , controlling ICs  234   a ,  234   b , and a choke coil  238 . 
         [0056]    The area surrounded by two dotted lines in  FIG. 7  is an area that makes contact in a planar manner with the sheet member  229  when the circuit substrate  223  has been housed in the lower body  212 . Further, the area surrounded by two dotted lines in  FIG. 6  shows an area corresponding to the area (i.e., the area surrounded by two dotted lines in  FIG. 7 ) that makes contact with the sheet member  229 . As is clear from  FIG. 7 , the sheet member  229  makes contact with an upper surface of the controlling IC  240 . Further, as is clear from  FIG. 6 , the power transistor  236 , the condensers  232   a ,  232   b ,  232   c ,  232   d , the controlling IC  234   b , and the choke coil  238  is thermally connected with the sheet member  229  via the substrate  224 . As a result, heat generated by these electronic parts is radiated in a suitable manner to the cooling water in the pump chamber  220  via the sheet member  229 . 
         [0057]    In the fluid pump  200 , as well, the heat generated by the power transistor  236 , the condensers  232   a ,  232   b ,  232   c ,  232   d , the controlling ICs  234   b ,  240 , and the choke coil  238  is radiated to the cooling water in the pump chamber  220  via the sheet member  229 . The heat generated by these electronic parts is thus radiated efficiently to the cooling water in the pump chamber, and these electronic parts are prevented from reaching a high temperature. Further, since these electronic parts make contact with the lower body  212  via the sheet member  229 , vibration of the lower body  212  is prevented form being transmitted to these electronic parts. 
       Fourth Embodiment 
       [0058]    Next, a fluid pump  300  of a fourth embodiment of the present teachings will be described. The fluid pump  300  can also be utilized to circulate cooling water for cooling an engine. As shown in  FIG. 8 , the fluid pump  300  is an inner rotor fluid pump. The fluid pump  300  comprises a lower body  312 , an upper body  350  that is fixed to an upper end of the lower body  312 , and a cover  316  that is fixed to a lower end of the lower body  312 . An impeller  353  is disposed in an inner space (i.e., pump chamber)  320  surrounded by the lower body  312  and the upper body  350 . A circuit substrate  323  is housed in the lower body  312 . A sheet member  329  makes contact in a planar manner with a center of an upper surface of the circuit substrate  323 . An upper surface of the sheet member  329  makes contact in a planar manner with a wall that forms the pump chamber  320 . The sheet member  329  also has a high degree of thermal conductivity and rubber elasticity. The sheet members  329  can be configured in the same manner as the sheet members  29   a ,  29   b  of the first embodiment. 
         [0059]    The circuit substrate  323  is provided with a substrate  324  and various electronic parts mounted on the substrate  324 . As shown in  FIG. 10 , comparatively small electronic parts, viz. chip transistors and chip resistors, are mounted on an upper surface of the substrate  324 . As shown in  FIG. 9 , the following electronic parts are mounted on a lower surface of the substrate  324 : a power transistor  342 , condensers  344   a ,  344   b ,  344   c ,  344   d , controlling ICs  348   a ,  348   b , and a choke coil  346 . The power transistor  342  is disposed in a center of the lower surface of the substrate  324 . Thus, the power transistor  342  is thermally connected with the sheet member  329  via the substrate  324 . 
         [0060]    In the fluid pump  300 , as well, the heat generated by the power transistor  342  is radiated to the cooling water in the pump chamber  320  via the sheet member  329 . The heat generated by the power transistor  342  is thus radiated efficiently to the cooling water in the pump chamber  320 , and the power transistor  342  is prevented from reaching a high temperature. Further, the power transistor  342  makes contact with the lower body  312  via the sheet member  329 . As a result, vibration of the lower body  312  is prevented from being transmitted to the power transistor  342 . 
         [0061]    Finally, although the preferred representative embodiments have been described in detail, the present embodiments are for illustrative purpose only and are not restrictive. It is to be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims. In addition, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above aspects and features. 
         [0062]    Furthermore, the technical elements described in this specification and the drawings demonstrate technical merit independently or in various combinations, and are not restricted to the combinations of the claims. Furthermore, the technology presented in the specifications and drawings simultaneously achieves multiple objectives but the technology has merit even if only one of the objectives is achieved.