Abstract:
A rotating electric machine system includes: a rotating electric machine including a stator and a rotor arranged with a gap to the stator; a casing configured to hold the stator; an electric power conversion apparatus held by the casing, and configured to drive the rotating electric machine; and a first cooling flow path arranged in a portion of the casing between the stator and the electric power conversion apparatus, via which cooling medium is caused to flow so as to cool the stator and the electric power conversion apparatus. And; the electric power conversion apparatus comprises a power module configured to include a power semiconductor element therein; the power module comprises a heat radiation fin; and the heat radiation fin is arranged to protrude toward a cooling medium side via an opening formed between the power module and the first cooling flow path.

Description:
TECHNICAL FIELD 
     The present invention relates to a rotating electric machine (rotating electric machine system) having a structure monolithically integrated with an electric power conversion apparatus. 
     BACKGROUND ART 
     With conventional techniques, electric vehicles and hybrid vehicles have a typical configuration in which a rotating electric machine and an electric power conversion apparatus are mounted on the vehicle as separate respective components. From the perspective of the mounting space for mounting such components in the vehicle, and from the perspective of the optimum cooling method for cooling such components, in many cases, such components are preferably mounted as separate respective components. However, from the perspective of the demand to reduce the number of components, and from the perspective of a requirement to prevent surge from occurring between the rotating electric machine and the electric power conversion apparatus, such components are preferably configured as a single unit. 
     CITATION LIST 
     Patent Literature 
     
         
         PATENT DOCUMENT 1: Japanese Laid Open Patent Publication No. 2005-224008 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Patent document 1 discloses an inverter-integrated rotating electric machine. Such an inverter-integrated rotating electric machine employs a configuration including a cooling tank or the like, leading to a problem in that such an apparatus is required to have a large overall size. 
     The present invention provides a technique for allowing a rotating electric machine (rotating electric machine system) monolithically integrated with an electric power conversion apparatus to have a reduced size without a worsening of its performance. 
     Solution to Problem 
     According to the 1st aspect of the present invention, a rotating electric machine system comprises: a rotating electric machine including a stator and a rotor arranged with a gap to the stator; a casing configured to hold the stator; an electric power conversion apparatus held by the casing, and configured to drive the rotating electric machine; and a first cooling flow path arranged in a portion of the casing between the stator and the electric power conversion apparatus, via which cooling medium is caused to flow so as to cool the stator and the electric power conversion apparatus, wherein: the electric power conversion apparatus comprises a power module configured to include a power semiconductor element therein; the power module comprises a heat radiation fin; and the heat radiation fin is arranged to protrude toward a cooling medium side via an opening formed between the power module and the first cooling flow path. 
     According to the 2nd aspect of the present invention, in the rotating electric machine system according to the 1st aspect, it is preferred that the rotating electric machine system further comprises a second cooling flow path arranged in a portion of the casing outside of the stator to extend along a direction of rotation of the rotating electric machine, via which the cooling medium flows; and the second cooling flow path communicates with the first cooling flow path such that the cooling medium cools the stator after cooling the electric power conversion apparatus. 
     According to the 3rd aspect of the present invention, in the rotating electric machine system according to the 2nd aspect, it is preferred that: the first cooling flow path has a structure configured to change a direction in which the cooling medium flows; and the second cooling flow path communicates with the first cooling flow path such that the cooling medium cools the stator after cooling the electric power conversion apparatus and the second cooling flow path has a greater cross-sectional area than a cross-sectional area of the first cooling flow path at a communicating portion. 
     According to the 4th aspect of the present invention, in the rotating electric machine system according to the 1st aspect, it is preferred that: the power module is configured to include power semiconductor elements in two rows; and the first cooling flow path is configured such that the cooling medium cools the power semiconductor elements arranged in a first row, following which a direction in which the cooling medium flows is changed, and the cooling medium cools the other power semiconductor elements arranged in a second row. 
     According to the 5th aspect of the present invention, in the rotating electric machine system according to the 1st aspect, it is preferred that: the rotating electric machine system further comprises a temperature sensor arranged in a vicinity of the heat radiation fin; and cooling is controlled based upon temperature data acquired by the temperature sensor. 
     According to the 6th aspect of the present invention, a rotating electric machine system comprises: a rotating electric machine including a stator and a rotor configured to rotate with a gap to the stator; an electric power conversion apparatus held by a casing configured to hold the stator, and configured to drive the rotating electric machine; a first cooling flow path arranged at a portion of the casing between the stator and the electric power conversion apparatus, via which cooling medium is caused to flow so as to cool the electric power conversion apparatus; and a second cooling flow path arranged in a portion of the casing outside of the stator, and configured such that the stator is cooled by the cooling medium that flows via the second cooling flow path along a direction of rotation of the rotating electric machine, wherein: the first cooling flow path has a structure configured to change a direction in which the cooling medium flows; and the second cooling flow path communicates with the first cooling flow path such that the cooling medium cools the stator after cooling the electric power conversion apparatus, and the second cooling flow path has a greater cross-sectional area than a cross-sectional area of the first cooling flow path at a communicating portion. 
     According to the 7th aspect of the present invention, in the rotating electric machine system according to the 6th aspect, it is preferred that the electric power conversion apparatus comprises a power module configured to include power semiconductor elements in two rows; and the first cooling flow path is configured such that the cooling medium cools the power semiconductor elements arranged in a first row, following which a direction in which the cooling medium flows is changed, and the cooling medium cools the other power semiconductor elements arranged in a second row. 
     According to the 8th aspect of the present invention, in the rotating electric machine system according to the 7th aspect, it is preferred that: a heatsink plate of the power module includes a heat radiation fin; and the heat radiation fin is configured to protrude toward a cooling medium side via an opening formed between the power module and the first cooling path. 
     According to the 9th aspect of the present invention, in the rotating electric machine system according to the 8th aspect, it is preferred that: the rotating electric machine system further comprises a temperature sensor in a vicinity of the heat radiation fin; and cooling is controlled based upon temperature data acquired by the temperature sensor. 
     Advantageous Effect of the Invention 
     An electric power conversion apparatus employing a direct water cooling method provides low thermal resistance as compared with an electric power conversion apparatus employing a typical indirect water cooling method. Thus, such an arrangement requires only a small area to cool power semiconductor elements. That is to say, a water flow path is shared by the rotating electric machine and the electric power conversion apparatus, which are integrally configured as a single unit. Furthermore, the electric power conversion apparatus is cooled by means of a direct cooling method. Thus, such an arrangement provides a rotating electric machine system including a small-size electric power conversion apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external view ( 1 ) of a rotating machine system. 
         FIG. 2  is an external view ( 2 ) of the rotating machine system. 
         FIG. 3  is an external view ( 3 ) of the rotating machine system. 
         FIG. 4  is an external view ( 4 ) of the rotating machine system. 
         FIG. 5  is a main circuit diagram. 
         FIG. 6  is a diagram for describing a comparison between a direct water cooling method and an indirect water cooling method. 
         FIG. 7  is a diagram ( 1 ) for describing a flow path structure (U-turn structure). 
         FIG. 8  is a diagram ( 2 ) for describing the flow path structure (relation  1  between the inlet and the outlet for cooling water). 
         FIG. 9  is a diagram ( 3 ) for describing the flow path structure (relation  2  between the inlet and the outlet for cooling water). 
         FIG. 10  is an external view ( 1 ) of a power module (internal layout). 
         FIG. 11  is an external view ( 2 ) of the power module (relation between fins and water flow). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIGS. 1 through 4  show an embodiment of the present invention.  FIG. 5  shows a main circuit according to the present embodiment, and shows a configuration of how each principal component is electrically connected. For convenience, the electric power conversion apparatus will be referred to as the “inverter” and the rotating electric machine will be referred to as the “motor” hereafter. It should be noted that such a rotating electric machine functions not only as a motor but also functions as a generator. The motor includes a stator, and a rotor (not shown) arranged so as to rotate with a gap between it and the stator. Furthermore, the inverter is held by a housing configured to hold the stator, and is configured to drive the motor. 
     First, description will be made regarding an electrical function of the present embodiment. The portion surrounded by a broken line corresponds to an inverter-integrated motor  1  which will be described in the present embodiment. The inverter-integrated motor  1  can be roughly classified into two units, i.e., an inverter unit  2  and a motor unit  3 . The inverter unit  2  is configured to perform switching of a power semiconductor element  5  in a regular manner so as to convert input (DC) electric power into AC electric power, and to transmit the AC electric power thus converted to the motor unit  3 . Here, the motor is represented by the motor impedance  7  of the motor coil in the electric circuit diagram shown in  FIG. 5 . The AC electric power converted by the inverter passes through the motor impedance  7 . Description will be made in the present embodiment assuming that the power semiconductor element  5  is configured as an IGBT (Insulated Gate Bipolar Transistor). Also, other kinds of power semiconductor elements (e.g., MOS-FET etc.) may be employed depending on the required frequency and voltage. Description will be made below regarding an arrangement including three IGBTs  5   a  and three flywheel (freewheel) diodes  6   a  on the positive electrode side (upper arm side) and the same number of IGBTs  5   b  and flywheel diodes  6   b  on the negative electrode side (lower arm side). With such an arrangement, each upper arm and lower arm pair corresponds to a single corresponding phase. 
     The pulsation (ripple) that occurs in the switching operation is smoothed by a smoothing capacitor  21  arranged between the battery  4  and a set of the power semiconductor elements  5 . 
     Next, description will be made with reference to  FIG. 1 . The rectangular parallelepiped portion arranged in the upper portion in  FIG. 1  corresponds to the inverter unit  2 , and the cylindrical portion in the lower portion corresponds to the motor unit  3 . Description will be made in the present embodiment regarding an arrangement in which a single metal housing (outer housing  10 ) is shared by the inverter unit  2  and the motor unit  3 , thereby forming a monolithically integrated unit. That is to say, the upper section of the outer housing  10  corresponds to the inverter unit  2 . 
     The interior space of the inverter unit  2  corresponds to an inverter chamber  13  mounting components configured to provide a function as an inverter. In practical use, a cover, which is not shown in the drawing in order to show the interior, is arranged at the top portion of the inverter unit in order to prevent foreign matter or fluid from contaminating the interior of the inverter chamber  13 . 
     As can be clearly understood with reference to  FIGS. 1 and 2 , an inner housing  11  configured as a separate unit is arranged on the inner side of the outer housing  10  of the motor unit  3 . Furthermore, a coil  14  of the motor is arranged on the inner side of the inner housing  11 . The outer housing  10  includes a flange  12  which allows the inverter-integrated motor  1  to be mounted on an engine, transmission, gearbox, or the like, of a vehicle. Bolt holes are formed in the flange  12  in a desired manner, which are not shown in the drawing. 
     As shown in  FIGS. 1 and 3 , the inverter chamber  13  includes a motor control board  20  configured to control the motor, a smoothing capacitor  21  configured to smooth voltage ripples, a gate driving board  22  configured to control the on/off operation of the switching element according to an instruction received from the motor control board, and a power module  23  mounting the power semiconductor elements  5 , with these components arranged such that they are stacked in this order, beginning from the top, and with the power module  23  as the bottom portion of the inverter unit. The inverter according to the present embodiment includes a discharging resistor  25 . When the inverter is turned off, the charge stored in the smoothing capacitor  21  is discharged via the discharging resistor  25 . A signal connector  26  is arranged on the external wall of the inverter chamber  13 , which allows signals to be transmitted/received between the inverter and the vehicle side. The signal connector  26  is connected to one terminal of a flat cable  27  on the inner side of the wall of the inverter chamber  13 . The other terminal of the flat cable  27  is connected to the motor control board  20 . 
     The DC electric power received from an external battery  4  is input via a high-electric-power connector  28  arranged at one terminal of the inverter unit  2 . The DC electric power is transmitted to a DC terminal  55  of the power module  23 , and is converted by the power module  23  into AC electric power. The AC electric power thus converted is transmitted to the coil  14  via a lead wire  17  from an AC terminal  56  of the power module  23 . In this state, the AC current is transmitted to the coil  14  via a current sensor  24 . The AC current that passes through this path is detected by the current sensor  24 . The current value of the AC current thus detected is transmitted to the motor control board  20 , and is used to control the motor. The connection line that connects the lead wire  17  and the power module  23  is designed to be as short as possible in order to suppress the effects of surge and noise. 
       FIG. 6  is a schematic diagram showing a longitudinal configuration of the power module  23 .  FIGS. 10 and 11  are detailed external diagrams showing the power module  23 . The power module  23  includes, in its lower portion, a heatsink plate  42  configured to release heat generated in the switching operation of the power semiconductor elements  5  arranged as internal components thereof. Fins  43  configured to radiate or release heat are arranged on the bottom face of the heatsink plate  42 . Description is being made in the present embodiment regarding an arrangement in which the fins  43  are arranged as multiple cylindrical pin-shaped fins. However, the fins  43  may be formed in other shapes. The power module  23  is fixed by engaging each bolt  57  with a corresponding bolt hole  36  such that the power module  23  functions as a cover for an opening  35  formed in the bottom face of the inverter chamber  13 . In this state, the fins  43  are arranged such that they protrude downward via the opening  35 . 
       FIG. 7  shows only the inner housing  11 . A cooling flow path  37  having a long recessed belt-like structure is formed along the circumference of the outer face of the inner housing  11 . The cooling flow path  37  is arranged around the surface of the inner housing in an approximately belt-like structure. By mounting the inner housing  11  within the outer housing  10 , the outer housing  10  functions as a cover for the cooling flow path  37 . In this state, a flow path inlet  39  is arranged downstream of an inlet pipe  15 . Furthermore, O-rings or otherwise liquid sealing members are arranged on both sides of the cooling flow path  37  such that they extend in parallel with each other around the inner housing, which are not shown in the drawing, thereby providing a measure for preventing water leakage. 
     The fins  43  of the power module  23  are arranged such that they protrude via the opening  35  toward the flat face  38  of the cooling flow path  37 . That is to say, the present embodiment employs a direct water cooling method in which heat generated by the power semiconductor elements  5  reaches the fins  43  monolithically integrated with the heatsink plate  42  via the heatsink plate  42 , and the power semiconductor elements  5  are cooled by directly cooling the fins  43 . It should be noted that description is being made assuming that water cooling using cooling water is employed. However, the cooling medium is not restricted to water. 
       FIG. 6  is a schematic diagram showing a longitudinal internal structure of the power module  23  in order to make a comparison between a direct water cooling method and an indirect water cooling method.  FIG. 6( a )  shows an arrangement employing a direct water cooling method, and  FIG. 6( b )  shows an arrangement employing an indirect water cooling method. Typically, the power module  23  has a longitudinal internal structure including the power semiconductor elements  5 , an insulating substrate  45 , and the heatsink plate  42  arranged in this order, beginning from the top. 
     With such an indirect water cooling arrangement, the fins  43  are arranged on the water flow path side of the casing inner wall  47  of the inverter casing  46 . The power module  23  is arranged on the opposite face of the casing inner wall  47  with respect to the fins  43 . At this stage, typically, thermal grease  48  is applied between the heatsink plate  42  of the power module and the inner wall  47  of the inverter casing, thereby contributing to improving the thermal conductivity of the interface at which a metal member is in contact with another metal member. That is to say, heat generated by the power semiconductor elements  5  is radiated or released to cooling water  44  from the heatsink plate  42  via the thermal grease  48  and the inverter casing inner wall  47 . 
     With such a direct water cooling arrangement, the power module  23  is fixed at the inverter casing  46  in the same way as the aforementioned indirect water cooling arrangement. The point of difference between these arrangements is that, with such a direct water cooling arrangement, an opening is formed in the face on which the power module  23  is to be mounted, and the power module  23  is mounted so as to cover the opening. That is to say, with such an arrangement in which the fins  43  are arranged on the heatsink plate  42 , the fins  43  are arranged such that they protrude on the cooling water side. Thus, the cooling water  44  is directly in contact with the heatsink plate  42  and the fins  43 , thereby releasing heat generated by the power semiconductor elements  5 . 
     With such an arrangement employing an indirect water cooling method, the thermal resistance through the path from the power semiconductor elements (IGBTs)  5  to the cooling water  44  is on the order of 0.15° C./W. With such an arrangement employing a direct water cooling method, the thermal resistance is on the order of 0.09° C./W. That is to say, an arrangement employing an indirect water cooling method provides a thermal resistance 1.5 times higher than with a direct water cooling method. In other words, from the perspective of the required heatsink area, such an arrangement employing a direct water cooling method requires the power module  23  to have only a small bottom area, which is 1/1.5 smaller than that in a case in which an indirect water cooling method is employed. 
     For such an inverter-integrated motor having a configuration in which an inverter is mounted on a housing of the motor, it is important to allow the inverter to have a small bottom area, as compared with an arrangement in which an inverter and a motor are mounted as separate respective units. Thus, such a direct water cooling method can be effectively applied to the present embodiment. At the same time, such an arrangement provides increased torque per volume as compared with an arrangement employing an indirect water cooling method. 
     Furthermore, as shown in  FIG. 10 , the power module  23  employed in the present embodiment has a layout in which six power semiconductor elements  5  are arranged such that three of the power semiconductor elements  5  respectively face the other three power semiconductor elements  5  (i.e., the power semiconductor elements  5  are arranged in two rows in parallel), thereby allowing the water flow path to have a reduced length in the longitudinal direction. That is to say, such an arrangement provides a power module structure suitable for mounting an a cylindrical motor housing. 
     Furthermore, the present invention has the following function for cooling the power module  23 . Typically, the cooling flow path  37  shown in  FIG. 7  is designed assuming that fluid flows in one direction from the inlet to the outlet. However, with the present embodiment as shown in  FIG. 7 , the cooling how path  37  is formed such that fluid makes a U-turn at a flat portion  38  that corresponds to the lower portion of the power module. In this region, the water flow path has a narrow width. Thus, such an arrangement provides an increased flow rate (or flow velocity) at the lower portion of the power module, thereby effectively cooling the six power semiconductor elements  5  arranged as internal components while requiring only a small cooling space. 
     With the present embodiment, the cooling flow path  37  is formed of two cooling flow paths (i.e., a first cooling flow path and a second cooling flow path). The first cooling flow path is provided to the casing portion between the stator and the electric power conversion apparatus, thereby cooling the electric power conversion apparatus by means of a cooling medium that flows through the flow path. In this stage, the flow direction of the cooling medium changes after it has cooled the power semiconductor elements arranged in the first row, following which it cools the other power semiconductor elements arranged in the second row. Meanwhile, the second cooling flow path is provided to the casing portion outside of the stator. By means of the cooling medium flowing via the flow path around the rotating electric machine along the motor rotation direction, such an arrangement is capable of cooling the stator. 
     As described above, in  FIG. 7 , the first cooling flow path has a structure configured such that the cooling medium makes a U-turn at the flat portion  38 .  FIG. 7  shows such a cooling flow path structure configured such that the cooling medium makes a U-turn for exemplary purposes only. Also, the first cooling flow path may be configured in other structures as long as the flow direction of the cooling medium changes at the flat portion  38  so as to raise the flow rate (or flow velocity) of the cooling medium. 
     The second cooling flow path is formed such that it communicates with the first cooling flow path such that the cooling medium cools the stator after it has cooled the inverter. Furthermore, the second cooling flow path employs a structure configured such that, at the communicating portion, the second cooling flow path has a greater cross-sectional area than that of the first cooling flow path. 
     With the present embodiment, the cooling water has a function as motor cooling water for cooling the motor stator core and the coil  14 , in addition to a function for cooling the inverter unit  2 . 
     The important point to be noted here is the difference between the allowable temperature of the coil  14  of the motor and the operating temperature of the power module  23 . Typically, the coil  14  of the motor is likely to have a high temperature. Accordingly, the temperature of the cooling water rises when it flows around the outer housing  10  and the inner housing  11 . In ordinary cases, the maximum temperature of the coil  14  is estimated to reach up to a temperature in the vicinity of 180° C. However, the upper limit of the operating temperature of the power module  23  is on the order of 125° C. to 150° C., which includes an increase in the temperature due to the heat generated by the power module  23  itself. That is to say, such an inverter-integrated motor requires a design for suppressing to a minimum the effects of the temperature of the coil  14  on the power module  23 . 
       FIG. 8  is a simplified cross-sectional diagram showing the present embodiment. The arrow indicates the cooling water flow. In the drawing, the cooling water input via the inlet pipe  15  makes a U-turn after it passes below the heatsink plate  42  of the power module  23  and through between the fins  43 , as shown in  FIG. 7 . Thus, at this position (right side of the flat face  38  of the flow path) in  FIG. 8 , the cooling water flows toward the back of the drawing. Subsequently, the cooling water flows around the circumference of the motor coil counterclockwise in the figure, and flows toward the output pipe  16 . As described above, the present embodiment is designed such that the distance between the inlet pipe  15  for the cooling water and the power module  23  is reduced as much as possible, thereby cooling the power module  23  in the first stage using the cooling water at its lowest temperature. By employing such a design, such an arrangement is capable of suppressing to a minimum the thermal effects of the high temperature of the coil  14  on the power module  23 . 
     Also,  FIG. 9  shows a modification obtained by modifying the structure of the inlet pipe  15  shown in  FIG. 8 . Such a modification has a structure in which the inlet pipe  15  is arranged in parallel with the flat portion  38 . Thus, such a modification provides increased momentum in the flow of the cooling water input via the inlet pipe  15 , thereby providing an increased flow rate as compared with an arrangement shown in  FIG. 8 . As a result, such a modification provides a structure with improved effectiveness of cooling the power semiconductor elements  5  without involving a large cooling space. 
     It should be noted that description has been made with reference to an example in which the inverter unit  2  and the motor unit  3  are completely monolithically integrated as a single unit. Also, such an inverter unit  2  and a motor unit  3  may be formed as separate respective units, and these separate units may be monolithically integrated in a subsequent stage, thereby providing an inverter-integrated motor. Examples of the advantages of such an arrangement include an advantage in that, in a case in which either one of the inverter unit  2  or the motor unit  3  is damaged, such an arrangement requires that only the damaged unit be repaired, and so forth. However, it should be noted that such an arrangement requires as sealing member such as an O-ring or the like to be applied to the interface between the two units. 
     The temperature of the cooling water  44  corresponds to the temperature of the motor cooling water, and at the same time corresponds to the temperature of the inverter cooling water. That is to say, a temperature sensor may be arranged in the vicinity of the fins  43  immersed in the cooling water  44 , which is not shown in the drawing showing the present embodiment, and the information obtained by the temperature sensor may be supplied to the motor control board  20 , thereby allowing the water temperature for cooling the motor and the water temperature for cooling the inverter to be controlled at the same time. Such an arrangement can be effectively applied to an arrangement in which each component is required to be maintained in its own temperature range, or an arrangement in which cooling should be controlled for each component. For example, such an arrangement enables a control operation in which the current is controlled (i.e., a limit is placed on the torque) according to the water temperature in a case in which there is a high probability of increased water temperature having adverse effects on the power module or otherwise on the stator side of the motor. 
     Description has been made above regarding various kinds of embodiments and modifications. However, the present invention is not restricted to the contents of such embodiments and modifications. Also various other kinds of embodiments may be made without departing from the technical scope of the present invention, which are also encompassed in the present invention. 
     The entire contents disclosed in Japanese Patent Application No. 2010-041233 (filed on Feb. 26, 2010) are incorporated herein by reference.