Abstract:
A rotating electric machine for vehicles is capable of improving a cooling performance of switching elements forming an inverter module, and small-sizing the entire rotating electric machine. The rotating electric machine includes: a stator; a rotor, a cooling fan; a front bracket and a rear bracket; and a cover; and in which a pair of switching elements are disposed axially adjacent to each other between the rear bracket and the cover; a ventilation hole for sucking outside air is formed in a radially outer circumferential portion of the cover; and by rotation of the cooling fan, the outside air flows radially from the ventilation hole with respect to the switching elements and goes through a suction port and is discharged through a discharge port.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a rotating electric machine on which a power element unit making an inverter control is mounted and, more particularly, to a power inverter type an electric rotating machine for vehicles used in, e.g., motor generators, and power steering motors.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, a power element unit for making an inverter control of a rotating electric machine, for example, as disclosed in the Japanese Patent Publication (unexamined) No. 274992/2004 (pages 17 to 19, FIGS. 1 to 5), is provided with an inverter module that is formed of a plurality of switching elements (power elements such as power transistors, MOSFET, or IGBT) and diodes connected in parallel to each of the switching elements.  
         [0005]     In the inverter module, letting the switching element and diode forming an upper arm and the switching element and diode forming a lower arm that are connected in series one set, these three sets are connected in parallel.  
         [0006]     An armature winding is in Y-connection. Ends of each phase of the Y-connection are electrically connected to an intermediate point between the switching elements of the upper arm and the switching elements of the lower arm that are connected in series forming one set via an AC wiring corresponding to each of the phases.  
         [0007]     Furthermore, as to terminals of a battery, a positive electrode terminal is electrically connected to the positive electrode side of the inverter module, and a negative electrode terminal is electrically connected to the negative electrode side of the inverter module, respectively via a DC wiring.  
         [0008]     In the inverter module, the switching operation of each of the switching elements is controlled by commands from a control circuit. Further, the control circuit controls a field current control circuit to adjust a field current to carry through the field winding of the rotor.  
         [0009]     Since a large power loss occurs at the time of switching and conduction of the switching elements in the inverter module in driving the mentioned conventional rotating electric machine, it is a particularly important problem to be solved that each of the switching elements forming an inverter module is cooled.  
         [0010]     For example, in the cooling system disclosed in the Japanese Patent Publication (unexamined) No. 274992/2004, a power element unit containing an inverter module is located in a circumferential direction on a heat sink at one end in an axial direction of the rotating electric machine, a cooling air is made to flow in flow paths of cooling fins one after another along the cooling fins provided with the flow paths in the radial direction, thereby cooling the heat sinks.  
         [0011]     Since the power element unit containing an inverter module according to the mentioned prior art is located in the circumferential direction on the heat sink at one end in the axial direction of the rotating electric machine, a cooling air is made to flow in flow paths of cooling fins one after another along the cooling fins provided with the flow paths in the radial direction, thereby cooling the heat sinks, a problem exists in that a cooling air having been warmed flows into the next cooling fin, eventually resulting in lower cooling performance.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention has been made to solve the problems as mentioned above, and has an object of providing an rotating electric machine for vehicles capable of improving a cooling performance of switching elements forming an inverter module, and making the entire rotating electric machine small-sized.  
         [0013]     An rotating electric machine for vehicles according to the invention comprises a stator provided with an armature winding, a rotor including a rotary shaft and which is located inside the stator, a cooling fan located at the rotor, a housing that supports and fixes the stator, as well as supports the rotary shaft in a rotatable manner, and a cover that is located outside of one wall surface of the housing in an axial direction of the rotary shaft so as to cover the one wall surface, and that forms a space with the one wall surface of the housing. In this rotating electric machine, switching elements of an upper arm and a lower arm that are connected in series forming an inverter circuit to be connected to the armature winding are disposed adjacent to each other in the axial direction of the rotary shaft. A ventilation hole for sucking an outside air is formed in a radially outer circumferential portion of the cover. A suction port through which an air in the space is sucked into the housing is formed in the one wall of the housing. A discharge port through which the air in the housing is discharged is formed in the radially outer circumferential portion of the mentioned housing. And when the cooling fan is brought in rotation, the outside air flows in through the ventilation hole from the radially outer circumferential portion to the radially inner circumferential portion with respect to the switching elements of the upper arm and the lower arm, goes through the suction port, and then is discharged from the discharge port.  
         [0014]     In the rotating electric machine of above construction according to the invention, it is possible to improve a cooling performance of switching elements, as well as to make the entire rotating electric machine for vehicles small-sized.  
         [0015]     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a cross sectional view showing a first preferred embodiment of an rotating electric machine for vehicles according to the present invention;  
         [0017]      FIG. 2  is a side view taken along the axial direction of a power element unit of  FIG. 1 ;  
         [0018]      FIG. 3  is a circuit diagram for explaining operation of the rotating electric machine provided with the power element unit; and  
         [0019]      FIG. 4  is a cross sectional view showing a second embodiment of the rotating electric machine for vehicles according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Several preferred embodiments of a rotating electric machine for vehicles according to the present invention are hereinafter described referring to the drawings.  
       Embodiment 1  
       [0021]      FIG. 1  is a cross sectional view showing a first embodiment of a rotating electric machine for vehicles according to the invention, and  FIG. 2  is a side view of a power element unit of  FIG. 1  taken along the axial direction. This rotating electric machine for vehicles is an electric rotating machine in which the power element unit is mounted as an integral part, or in the vicinity thereof.  
         [0022]     As shown in  FIG. 1 , the rotating electric machine  1  is provided with a housing formed of a front bracket  10  and a rear bracket  11 , a stator  16  including an armature winding  16   a , and a rotor  15  including a shaft (rotary shaft)  13  and a field winding  14 . In this rotating electric machine  1 , the stator  16  is supported in and fixed to the housing, and the rotor  15  is located inside the stator  16  so that the field winding  14  thereof is opposite to the armature winding  16   a ; as well as the shaft  13  of the rotor  15  is supported by supporting bearings  12  that is located at the housing, and the rotor  15  can rotate coaxially with the stator  16 . To both of the axial end faces of the rotor  15 , cooling fans  17  are fixed.  
         [0023]     A pulley  18  is fixed to the end portion on the front side of the shaft  13  (on the outside of the front bracket  10 ). A brush holder  19  is attached to the rear bracket  11  on the rear side of the shaft  13  (on the outside of the rear bracket  11 ); a pair of slip rings  21  is mounted onto the rear side of the shaft  13 ; and a pair of brushes  20  to slide in contact with the slip rings  21  is located in the brush holder  19 . Further, a rotational position detection sensor (e.g., resolver)  22  is provided at the rear side end of the shaft  13 . The pulley  18  is connected to a rotary shaft of an engine via a belt, not shown, and the rotation of the engine is transmitted to the pulley  18 . The brush holder  19 , the brushes  20  and the slip rings  21  form a power supply mechanism for supplying a DC power to the field winding  14 .  
         [0024]     A cover  30  that cover the power supply mechanism such as brush holder  19  is provided on the further rear side of the rear bracket  11 . A power element unit  4  is located at a space between the rear bracket  11  and the cover  30 . A control circuit board  44   a  on which a control circuit  44  is mounted is located on the axially outer wall surface of the cover  30 , and this control circuit board  44   a  is covered with a plate  32 .  
         [0025]     The power element unit  4  includes a pair of an inside heat sink  50  and an outside heat sink  51  in opposition forming a predetermined gap in the axial direction. The inside heat sink  50  and the outside heat sink  51  are fixed to the rear bracket  11  with a support bar  6  shown in  FIG. 2 . As shown in  FIGS. 1 and 2 , plural sets of switching elements  41   a  and  41   b  of the upper arm and the lower arm are arrayed in a circumferential direction on the opposed inner wall surfaces in the axial direction of the inside and outside heat sinks  50  and  51 . The inside and outside heat sinks  50  and  51  are provided with cooling fins  50   a  and  51   a  including flow paths in the radial direction on the axially opposed outer wall surfaces. As a result of providing the inside heat sink  50  and the outside heat sink  51 , a larger cooling effect is achieved.  
         [0026]     It is preferable that the cooling fins  50   a  and  51   a  are located all over the faces of the inside and outside heat sinks  50  and  51 , or located at regular intervals in the circumferential direction.  
         [0027]     The switching elements  41   a  and  41   b  are joined to the inside and outside heat sinks  50  and  51  by soldering respectively.  
         [0028]     Ventilation holes  31   a  and  31   b  adjacent to each other and opposed to the outer peripheral surface of each of the cooling fins  50   a  and  51   a  are provided in the circumferential wall of the cover  30 . The ventilation holes  31   a  and  31   b  are preferably open so as to be opposite to the switching elements  41   a  and  41   b.    
         [0029]     By the rotation of the cooling fans  17 , as shown with arrows F, there is formed an air course of a fresh outside air that goes in from the ventilation holes  31   a  and  31   b  and through each of the cooling fins  50   a  and  51   a , and is sucked from a suction port  11   a  of the rear bracket  11  and goes out from a discharge port  11   b . Thus, the inside and outside heat sinks  50  and  51  are cooled with the outside cooling air all the times. Preferably, the suction port  11   a  of the rear bracket  11  is formed at portions in the vicinity of the inner circumferential ends of the cooling fins  50   a  and  51   a  in view of enhancement in cooling effect.  
         [0030]     As mentioned above, the inside and outside heat sinks  50  and  51  are cooled by the fresh outside cooling air at all times, so that a cooling performance of cooling the switching elements  41   a  and  41   b  can be improved. Furthermore, the space between the rear bracket  11  and the cover  30  is utilized, so that the entire rotating electric machine can be small-sized.  
         [0031]     As shown in  FIG. 2 , a power element unit  4  is formed of three-phases, U, V, W of sections (U-phase section, V-phase section, and W-phase section) of the switching elements  41   a  of the upper-side arm in which phase four switching elements  41   a  are connected in parallel on the wall surface of the inside heat sink  50 , and three phases, U, V, W of sections (U-phase section, V-phase section, and W-phase section) of the switching elements  41   b  of the lower-side arm in which phase four switching elements  41   b  are connected in parallel on the wall surface of the outside heat sink  51 . The switching element  41   a  and  41   b  may be discrete type, TPM type, or bare-chip type.  
         [0032]     In this manner, by connecting plural numbers of switching elements  41   a  and  41   b  in parallel respectively, the amount of current to carry through each of the switching elements  41   a  and  41   b  can be made smaller. Consequently, it is possible to employ inexpensive switching elements  41   a  and  41   b  of a small current-carrying capacity, and thus to reduce costs.  
         [0033]      FIG. 3  is a circuit diagram for explaining operation of a rotating electric machine provided with a power element unit.  
         [0034]     As shown in  FIG. 3 , a rotating electric machine section  1   a  is provided with an armature winding  16   a  wound around a stator, and a field winding  14  wound around a rotor. The armature winding  16   a  is constructed of three phases (U-phase, V-phase, W-phase) of coils in Y-connection (star-connection). The power element unit  4  is provided with an inverter module  40  that is formed of a plurality of switching elements (power transistor, MOSFET, IGBT or the like)  41   a  and  41   b , and diodes  42  connected in parallel to each of the switching elements  41   a  and  41   b , and a capacitor  43  that is connected in parallel to the inverter module  40 . In the inverter module  40 , the switching element  41   a  and diode  42  forming an upper arm  46  and the switching element  41   b  and diode  42  forming a lower arm  47  that are connected in series constitutes one set, and these three sets are connected in parallel.  
         [0035]     Ends of each phase of the Y-connection in the armature winding  16   a  are electrically connected to intermediate points between the switching elements  41   a  of the upper arm  46  and the switching elements  41   b  of the lower arm  47  in corresponding sets via an AC wiring  9 . Furthermore, a positive electrode terminal and a negative electrode terminal of a battery  5  are electrically connected to the positive electrode side and the negative electrode side of the inverter module  40  via a DC wiring  8  respectively.  
         [0036]     The switching operation of each of the switching element  41   a  and  41   b  in the inverter module  40  is controlled by commands from a control circuit  44 . Further, the control circuit  44  controls a field current control circuit  45  to adjust a field current carrying through the field winding  14  of the rotor.  
         [0037]     With reference to the circuit diagram shown in  FIG. 3 , when the engine is started, a DC power is supplied to the power element unit  4  via the DC wiring  8  from the battery  5 , the control circuit  44  makes ON/OFF control of each of the switching elements  41   a  and  41   b  of the inverter module  40 , and the DC power is converted to a three-phase AC power. A three-phase AC power having been converted is supplied to the armature winding  16   a  of the rotating electric machine section  1   a  via the AC wiring  9 , a rotating magnetic field is given around the field winding  14  of the rotor to which a field current is supplied from the battery  5  by means of the field current control circuit  45 , the rotor is driven to rotate, and then the engine is started via a pulley attached to the shaft of the rotor, a belt, a crank pulley, and a clutch (ON).  
         [0038]     When the engine is started, a rotational power of the engine is transmitted to a rotor via the crank pulley, the belt, and the pulley attached to the shaft of the rotor of the rotating electric machine section  1   a , the rotor is driven to rotate resulting in induction of a three-phase AC voltage at the armature winding  16   a , the control circuit  44  makes ON/OFF control of each of the switching elements  41   a  and  41   b , the three-phase AC voltage having been induced at the armature winding  16   a  is converted to a DC power, and the battery  5  comes to be charged.  
       Embodiment 2  
       [0039]      FIG. 4  is a cross sectional view showing a second embodiment of the rotating electric machine for vehicles according to the invention, and the same reference numerals indicates the same or like parts as those in  FIG. 1 .  
         [0040]     With reference to  FIG. 4 , the construction of each part is substantially the same as in the above-mentioned first embodiment. There are differences from the first embodiment in the aspects that there is provided a ventilation hole  31   c  at the outer circumferential portion of the cover  30 , and that there is provided a guide  60  with which a protrusion  60   a  having a triangular cross section is integrally formed so as to connect the outer peripheral edges of the inside and outside heat sinks  50  and  51 .  
         [0041]     According to this second embodiment, when the cooling fans  17  are brought in rotation, as indicated by the arrows F, an air course is formed such that a fresh outside air is sucked in from the ventilation hole  31   c ; the outside air having been sucked is distributed into two directions with the guide  60  on which the protrusion  60   a  is formed; and the outside air having been distributed goes through each of the cooling fins  50   a  and  51   a , is sucked from a suction port  11   a  of the rear bracket  11 , and goes out from the discharge port  11   b.    
         [0042]     As mentioned above, the inside and outside heat sinks  50  and  51  are cooled by a fresh outside cooling air at all times, so that a cooling performance of cooling the switching elements  41   a  and  41   b  can be improved. Further, the space formed between the rear bracket  11  and the cover  30  is utilized, so that the entire rotating electric machine can be small-sized. Furthermore, the rotating electric machine according to this second embodiment has a structure of distributing an outside air having been sucked by means of the guide  60 , so that one ventilation hole  31   c  is sufficient, and it is possible to make the structure simple.  
         [0043]     In addition, according to the above-mentioned first and second embodiments, although an example, in which the switching elements  41   a  and  41   b  are located at the heat sinks  50  and  51  respectively, is described, it is preferable that one of the switching elements  41   a  and  41   b  is mounted onto a heat sink, and the other switching elements are mounted on, for example, the surface of a mere resin plate. Furthermore, it is preferable that both of the heat sinks are eliminated, and that, for example, the switching elements  41   a  and  41   b  are mounted on a pair of resin plate surfaces respectively.  
         [0044]     In addition, although a rotating electric machine for vehicles, in which the field winding  14  of the rotor  15  and the brush holder  19  are located, is described, the above-mentioned embodiments according to the invention can be applied to any other rotating electric machine for vehicles in which a magnetic pole of a rotor is formed of a permanent magnet, and there are not the field winding  14  and the brush holder  19 .  
         [0045]     The rotating electric machine for vehicles according to the invention can be effectively utilized as a rotating electric machine to be mounted on, e.g., automobiles.  
         [0046]     While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.