Patent Publication Number: US-11040738-B2

Title: Electric drive device and electric power steering device

Description:
TECHNICAL FIELD 
     The present invention relates to an electric drive device and an electric power steering device, and more particularly to an electric drive device and an electric power steering device in which an electronic control unit is mounted. 
     BACKGROUND ART 
     In a field of general industrial equipment, a mechanical control element is driven by an electric motor. In recent years, so-called electrically mechanically integrated electric drive device, which is configured such that an electronic control unit formed from a semiconductor element etc. controlling a rotation speed and/or a rotation torque of the electric motor is integrally mounted in the electric motor, has been used. 
     As an example of the electrically mechanically integrated electric drive device, for instance, an electric power steering device is configured such that a turning direction and a turning torque of a steering shaft that turns by driver&#39;s operation of a steering wheel are detected, and on the basis of these detection values, the electric motor is driven so as to rotate in the same direction as the turning direction of the steering shaft, then a steering assist torque is generated. To control this electric motor, the power steering device is provided with an electronic control unit (ECU: Electronic Control Unit). 
     As a related art electric power steering device, for instance, an electric power steering device disclosed in Japanese Unexamined Patent Application Publication No. 2013-060119 (Patent Document 1) is known. Patent Document 1 discloses the electric power steering device configured by an electric motor unit and an electronic control unit. An electric motor of the electric motor unit is housed in a motor housing having a cylindrical portion that is made of aluminum alloy etc. Boards (substrates) on which electronic elements or components of the electronic control unit are mounted are housed in an ECU housing that is located on an opposite side to an output shaft of the motor housing in an axial direction of the motor housing. The boards housed in the ECU housing are provided with a power supply circuit unit, a power conversion circuit unit having a power switching element such as a MOSFET and an IGBT that drive and control the electric motor, and a control circuit unit that controls the power switching element. Output terminals of the power switching element and input terminals of the electric motor are electrically connected through a bus bar. 
     Power is supplied to the electronic control unit housed in the ECU housing from a power supply through a connector terminal assembly made of synthetic resin. Further, detection signals concerning an operating state etc. are sent to the electronic control unit from detection sensors. The connector terminal assembly functions as a lid member or a cover member, and is connected to the electronic control unit so as to cover an opening formed at the ECU housing. The connector terminal assembly is fixed to an outer surface of the ECU housing with fixing bolts. 
     As another electric drive device configured such that the electronic control unit and the electric motor unit are integrated, electric brake and an electric hydraulic pressure controller for a various kinds of hydraulic pressure control are known. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-060119 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     Since the electric power steering device disclosed in Patent Document 1 is placed in an engine room of the vehicle, size reduction in configuration of the electric power steering device is required. In particular, there has been a tendency in recent years for various auxiliary devices such as an exhaust gas control device and a safety precaution device to be disposed in the engine room of the vehicle. It is therefore required for the auxiliary devices including the electric power steering device to be as small as possible. Further, reduction in component count of the auxiliary devices including the electric power steering device is required. 
     In the electric power steering device having a configuration disclosed in Patent Document 1, the power supply circuit unit, the power conversion circuit unit and the control circuit unit are mounted on two boards that are arranged in a radial direction. For this reason, since component count of electrical component required to control the electric motor is roughly determined, when these electrical components are mounted on the two boards, size of the ECU housing accommodating therein the electronic control unit necessarily increases in the radial direction. 
     Further, safety is particularly required of the electric power steering device to steer the vehicle, and an electronic control unit having a redundant system such as a dual-redundancy system is required. Therefore, two systems of the electronic control unit, which are the same as each other, are necessary as a configuration of the redundant system. Also from this point of view, there is a tendency for the size of the ECU housing to further increase. 
     Here, from a structural viewpoint, limit of an axial length of the electric power steering device in a longitudinal direction is not strict, but there is a tendency to limit increase in size of the electric power steering device in the radial direction. Hence, under present circumstances, size reduction of the electric drive device in the radial direction is required. In addition to this, the electrical component forming the power supply circuit unit and the power conversion circuit unit has a large heat value. Therefore, when reducing the size of the electric drive device, it is required for this heat to efficiently radiate to the outside. 
     Further, the board of the electronic control unit is fixed to a heat radiation base body. As this kind of fixing manner, there is known a fixing manner in which a fixing flange is formed at an outer periphery of the heat radiation base body, and this fixing flange is fixed to an outer periphery of the motor housing with fixing bolts. However, when the heat radiation base body and the motor housing are fixed at their outer peripheral sides, the size tends to increase more in the radial direction by an amount of the fixing of the outer peripheral sides. 
     An object of the present invention is therefore to provide a new electric drive device and a new electric power steering device which are capable of suppressing the increase in size in the radial direction of the electric drive device formed by the electric motor unit in which the electronic control unit having the redundant system is integrated, and which have a simple heat radiation structure configured by as small the component count as possible. 
     Solution to Problem 
     An electric drive device of the present invention comprises: a motor housing accommodating therein an electric motor that drives a mechanical control element; a pair of supporting stems arranged so as to face to each other on an end surface, which is an opposite side to an output shaft portion of a rotation shaft of the electric motor, of the motor housing and extending in a direction of the rotation shaft which is an opposite direction to the output shaft portion; a heat radiation base body arranged between the pair of supporting stems and extending in the same direction as those of the supporting stems; fixing bolts screwed into the heat radiation base body from a radially outer side to a radially inner side through the supporting stems and connecting the supporting stems and the heat radiation base body; one electronic control unit of a redundant system, the one electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed; and the other electronic control unit of the redundant system, the other electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed. 
     Effects of Invention 
     According to the present invention, by fixing the board of the electronic control unit extending along the axial direction of the electric motor to the heat radiation base body extending along the axial direction of the electric motor with thermal conduction between the board and the heat radiation base body allowed, size reduction of the electric drive device in the radial direction can be achieved. Further, since the heat from each board radiates to the housing of the electric motor unit through the heat radiation base body, even though the size reduction is made, it is possible to efficiently radiate the heat from the board to the outside. Moreover, since the fixing bolts are screwed into the heat radiation base body from the radially outer side to the radially inner side through the supporting stems, the heat radiation base body and the motor housing are not fixed at their outer peripheral sides. With this, size reduction of the of the control unit EC can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general perspective view of a steering device as an example to which the present invention is applied. 
         FIG. 2  is a general perspective view of a related art electric power steering device. 
         FIG. 3  is a perspective exploded view of an electric power steering device according to an embodiment of the present invention. 
         FIG. 4  is a perspective view showing a state in which a rotation position detection circuit board is mounted in an electric motor unit. 
         FIG. 5  is a perspective view of a heat radiation base body secured to the electric motor unit. 
         FIG. 6  is a perspective view showing a state in which the heat radiation base body is mounted on the electric motor unit. 
         FIG. 7  is a cross section for explaining a fixing way of the electric motor unit and the heat radiation base body. 
         FIG. 8  is a perspective view showing a state in which an electronic control means (an electronic control unit) having a redundant system is fixed to the heat radiation base body. 
         FIG. 9  is a longitudinal cross section of an A-A line of  FIG. 8 , and explains a modified example. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention will be explained in detail below with reference to the drawings. The present invention is not limited to the following embodiment, and includes all design modifications and equivalents belonging to the technical scope of the present invention. 
     Before explaining the embodiment of the present invention, a configuration of a steering device as an example to which the present invention is applied will be briefly explained using  FIG. 1 . Further, to facilitate the understanding of the present invention, a configuration of a related art electric power steering device will also be briefly explained using  FIG. 2 . 
     First, a steering device to steer front wheels of a vehicle will be explained. A steering device  1  is configured as shown in  FIG. 1 . A pinion (not shown) is provided at a lower end of a steering shaft  2  connecting to a steering wheel (not shown). This pinion is engaged with a rack (not shown) that extends in right and left directions of a vehicle body. A tie rod  3  to steer the front wheels in the right and left directions is each connected to both ends of the rack. The rack is accommodated in a rack housing  4 . Between the rack housing  4  and each tie rod  3 , a rubber boot  5  is provided. 
     The steering device  1  is provided with an electric power steering device  6  to assist torque when performing a turning operation of the steering wheel. That is, a torque sensor  7  that detects a turning direction and a turning torque of the steering shaft  2  is provided. And, an electric motor unit  8  that provides a steering assistive force to the rack via a gear  10  on the basis of a detection value of the torque sensor  7  is provided. Further, an electronic control unit (ECU)  9  that controls an electric motor disposed in the electric motor unit  8  is provided. The electric motor unit  8  of the electric power steering device  6  is connected to the gear  10  at three portions of an outer periphery at an output shaft side of the electric motor unit  8  with bolts (not shown). The electronic control unit  9  is disposed on an opposite side to the output shaft side of the electric motor unit  8 . 
     As shown in  FIG. 2 , the electric motor unit  8  of the related art electric power steering device is formed from a motor housing  11 A having a cylindrical portion made of aluminum alloy etc. and the electric motor (not shown) disposed in the electric motor unit  8 . The electronic control unit  9  is formed from an ECU housing  11 B located on an opposite side to an output shaft of the motor housing  11 A in an axial direction of the motor housing  11 A and made of aluminum alloy etc. and an electronic control assembly (not shown) housed in the ECU housing  11 B. 
     The motor housing  11 A and the ECU housing  11 B are fixedly connected to each other on their opposing end surfaces with fixing bolts. The electronic control assembly housed in the ECU housing  11 B is configured by a power supply circuit unit that generates a required power, a power conversion circuit unit having a power switching element formed from a MOSFET or an IGBT that drives and controls the electric motor of the electric motor unit  8 , and a control circuit unit that controls the power switching element. Output terminals of the power switching element and input terminals of the electric motor are electrically connected through a bus bar. 
     A synthetic-resin-made lid member (or cover member)  12 , which is also used as a connector terminal assembly, is fixed to an end surface of the ECU housing  11 B with fixing bolts. The lid member  12  is provided with a connector terminal forming portion  12 A for power supply, a connector terminal forming portion  12 B for detection sensors, and a connector terminal forming portion  12 C for control state output by which a control state is outputted to an external device. The electronic control assembly housed in the ECU housing  11 B is supplied with power from a power supply through the connector terminal forming portion  12 A for power supply of the synthetic-resin-made lid member  12 . Further, the electronic control assembly is provided with detection signals of an operating condition etc. from the detection sensors through the connector terminal forming portion  12 B for detection sensors. A current control state signal of the electric power steering device is outputted from the electronic control assembly through the connector terminal forming portion  12 C for control state output. 
     Here, the lid member  12  is shaped so as to cover an entire opening of the ECU housing  11 B. However, size of each of the connector terminals could be reduced, then each connector terminal could be connected to the electronic control assembly through insertion holes formed at the ECU housing  11 B. 
     In the electric power steering device  6 , when the steering shaft  2  is turned in any turning direction by the steering wheel operation, the torque sensor  7  detects the turning direction and the turning torque of the steering shaft  2 . The control circuit unit calculates a drive operation amount of the electric motor on the basis of these detection values. The electric motor is then driven by the power switching element of the power conversion circuit unit on the basis of the calculated drive operation amount. And, an output shaft of the electric motor rotates so as to drive and rotate the steering shaft  2  in the same direction as a direction of the steering wheel operation. This rotation of the output shaft of the electric motor is transmitted to the rack (not shown) through the pinion (not shown) and the gear  10 , and the vehicle is steered. Since such configuration and workings are well known, a further explanation will be omitted here. 
     In such electric power steering device, as mentioned above, there has been a tendency in recent years for various auxiliary devices such as the exhaust gas control device and the safety precaution device to be disposed in the engine room of the vehicle. It is therefore required for the auxiliary devices including the electric power steering device to be as small as possible. 
     In the electric power steering device having such configuration, the power supply circuit unit, the power conversion circuit unit and the control circuit unit are mounted on the two boards, and are arranged in the radial direction so as to be orthogonal to an axis of the ECU housing. For this reason, since component count of the electrical component required to control the electric motor is roughly determined, when these electrical components are mounted on the two boards, size of the ECU housing accommodating therein the electronic control unit necessarily increases in the radial direction. 
     Further, safety is particularly required of the electric power steering device to steer the vehicle, and an electronic control unit having a redundant system such as a dual-redundancy system is required. Therefore, two systems of the electronic control unit, which are the same as each other, are necessary as a configuration to improve the redundant system, and the number of electronic elements or components is the double. Also from this point of view, the size of the ECU housing further increases. 
     Here, from a structural viewpoint, limit of the axial length of the electric power steering device in the longitudinal direction is not strict, but there is a tendency to limit increase in size of the electric power steering device in the radial direction. Hence, under present circumstances, size reduction of the electric drive device in the radial direction is required. In addition to this, the electrical component forming the power supply circuit unit and the power conversion circuit unit has a large heat value. Therefore, when reducing the size of the electric drive device, it is required for this heat to efficiently radiate to the outside. 
     Further, the board of the electronic control unit is fixed to a heat radiation base body. As this kind of fixing manner, there is known a fixing manner in which a fixing flange is formed at an outer periphery of the heat radiation base body, and this fixing flange is fixed to an outer periphery of the motor housing with fixing bolts. However, when the heat radiation base body and the motor housing are fixed at their outer peripheral sides, the size tends to increase more in the radial direction by an amount of the fixing of the outer peripheral sides. 
     From such background, the present embodiment proposes the electric power steering device having the following configuration. 
     That is, in the present embodiment, an electric drive device comprises: a motor housing accommodating therein an electric motor; a pair of supporting stems arranged so as to face to each other on an end surface, which is an opposite side to an output shaft portion of a rotation shaft of the electric motor, of the motor housing and extending in a direction of the rotation shaft which is an opposite direction to the output shaft portion; a heat radiation base body arranged between the pair of supporting stems and extending in the same direction as those of the supporting stems; fixing bolts screwed into the heat radiation base body from a radially outer side to a radially inner side through the supporting stems and connecting the supporting stems and the heat radiation base body; one electronic control unit of a redundant system, the one electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed; and the other electronic control unit of the redundant system, the other electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed. 
     In the following description, a configuration of the electric power steering device according to the embodiment of the present invention will be explained in detail with reference to  FIGS. 3 to 9 .  FIG. 3  is a drawing, viewed from an oblique direction, with components of the electric power steering device of the embodiment dismantled.  FIGS. 4 to 9  are drawings showing each assembly state of the components of the electric power steering device when assembled in assembly order. The explanation will be made with reference to each drawing as necessary. 
       FIG. 3  is a perspective exploded view of the electric power steering device  6 . An iron-made annular side yoke (not shown) is fitted to an inside of a motor housing  20 . The electric motor is accommodated inside this side yoke. An output shaft portion  21  of the electric motor provides the steering assistive force to the rack via the gear. Since a specific structure of the electric motor is well known, its explanation will be omitted here. 
     The motor housing  20  is made of aluminum alloy, and acts as a heat sink that radiates heat generated at the electric motor and heat generated in electronic elements or components mounted on after-mentioned electronic control boards to the outside atmosphere. The electric motor and the motor housing  20  form an electric motor unit EM. 
     An electronic control unit EC is connected to an end surface of the motor housing  20  which is opposite side of the output shaft portion  21  of the electric motor unit EM. The electronic control unit EC is formed from a rotation position detection circuit board  22 , a heat radiation base body  23 , a first power conversion circuit board  24 , a first control circuit board  25 , a second power conversion circuit board  26 , a second control circuit board  27 , and a power supply connector  28 . 
     Here, the first power conversion circuit board  24 , the first control circuit board  25 , the second power conversion circuit board  26  and the second control circuit board  27  form a redundant system. A main electronic control means (a main electronic control unit) is formed by the first power conversion circuit board  24  and the first control circuit board  25 . A sub-electronic control means (a sub-electronic control unit) is formed by the second power conversion circuit board  26  and the second control circuit board  27 . 
     In a normal condition, the electric motor is driven and controlled by the main electronic control unit. However, if an abnormal condition or a failure occurs to the first power conversion circuit board  24  or the first control circuit board  25  of the main electronic control unit, the control is switched to the sub-electronic control unit, and the electric motor is driven and controlled by the second power conversion circuit board  26  and the second control circuit board  27  of the sub-electronic control unit. 
     Therefore, normally, heat from the main electronic control unit is transmitted to the heat radiation base body  23 . If the abnormal condition or the failure occurs to the main electronic control unit, the main electronic control unit stops and the sub-electronic control unit operates, then heat from the sub-electronic control unit is transmitted to the heat radiation base body  23 . These will be described later. 
     However, both of the main electronic control unit and the sub-electronic control unit could operate as a regular electronic control unit, although the present invention does not apply this configuration. And, if the abnormal condition or the failure occurs to one of the electronic control units, the other electronic control unit drives and controls the electric motor by half ability. In this case, although capability of the electric motor is half, so-called limp-home function is secured. Therefore, in the normal condition, heat from the main electronic control unit and the sub-electronic control unit is transmitted to the heat radiation base body  23 . 
     The electronic control unit EC is not housed in the ECU housing of the related art as shown in  FIG. 2 . Therefore, heat of the electronic control unit EC does not radiate from the ECU housing. In the present embodiment, the electronic control unit EC is configured to be secured to and supported by the motor housing  20 . And, heat of the electronic control unit EC radiates mainly from the motor housing  20 . When completing assembling the electronic control unit EC and the electric motor unit EM, the electronic control unit EC is covered by a cover  29 . The cover  29  and the motor housing  20  are connected to each other with the cover  29  facing to the end surface of the motor housing  20 . 
     The cover  29  could be made of synthetic resin or metal. The cover  29  is fixedly connected to the motor housing  20  by fixing way or fixing means such as adhesion (adhesive), welding and bolt. In this manner, in the present embodiment, in the electric power steering device, a sealing part is only a connecting portion between the motor housing  20  and the cover  29 . Therefore, an additional structure of the sealing part and a sealing component required for the seal can be reduced. 
     Further, since it is not necessary for the cover  29  to support the electronic control unit EC, a thickness of the cover  29  can be thin, which contributes to size reduction of the control unit EC in the radial direction and weight reduction of the control unit EC. If the cover  29  is made of metal (e.g. aluminum alloy or iron), the cover  29  has a heat radiation function. Therefore, heat from the motor housing  20  is transmitted to the cover  29 , then a heat radiation effect is further improved. 
     As described above, in the present embodiment, the rotation position detection circuit board  22  is fixed to the end surface of the motor housing  20 . The first power conversion circuit board  24 , the first control circuit board  25 , the second power conversion circuit board  26  and the second control circuit board  27  are fixed to the heat radiation base body  23  with these boards facing to each other. Further, the heat radiation base body  23  is fixed to the end surface of the motor housing  20  so as to cover the rotation position detection circuit board  22 . Furthermore, the cover  29  and the motor housing  20  are configured such that the cover  29  is liquid-tightly connected to the end surface of the motor housing  20 . This configuration is one of outstanding features of the present embodiment. 
     That is, the present embodiment does not require the ECU housing like the electric power steering device of the related art as shown in  FIG. 2 , which is located on the opposite side to the output shaft of the motor housing in the axial direction of the motor housing and is made of aluminum alloy etc. 
     Consequently, the ECU housing like the related art, a seal to secure liquid tightness of the ECU housing and a bolt to fix the motor housing and the ECU housing are not necessary in the present embodiment. It is therefore possible to reduce a whole body size of the electric power steering device. Further, component count can be reduced, thereby reducing man-hour of assembly or assembly processes. With this, a final product piece rate (or a final product unit price) can be suppressed, and this gives rise to improvement in product-competitiveness. 
     Returning to  FIG. 3 , a rotor portion (not shown) of the electric motor is disposed in a middle portion of the motor housing  20 . A stator winding is wound around this rotor portion. The stator winding is connected by star connection. An input terminal  30  of the winding of each phase and a neutral terminal  31  of each phase, for one of the redundant system, protrude from an opening  32  that is formed at the motor housing  20 . In the present embodiment, since the redundant system is configured, for the other of the redundant system, other input terminal  30  of the winding of each phase and other neutral terminal  31  of each phase protrude from an opening  32  formed at the motor housing  20 . These input terminals  30  and neutral terminals  31  protrude from the openings  32  with the terminals  30  and  31  for one of the redundant system and the terminals  30  and  31  for the other of the redundant system arranged at 180° angular space. 
     The input terminal  30  of the winding is connected to an output terminal of the first power conversion circuit board  24  forming the main electronic control unit for each phase. The neutral terminal  31  for each phase is connected to the rotation position detection circuit board  22  through a wiring pattern on the wiring board  22 , and forms a neutral point. Likewise, for the other of the redundant system, the input terminal  30  of the winding is connected to an output terminal of the second power conversion circuit board  26  forming the sub-electronic control unit for each phase. Also, for the other of the redundant system, the neutral terminal  31  for each phase is connected to the rotation position detection circuit board  22  through the wiring pattern on the wiring board  22 , and forms the neutral point. These configurations are basically almost the same because of the redundant system. 
     These configurations are also one of the outstanding features of the present embodiment. Since the neutral terminals  31  of the main electronic control unit and the sub-electronic control unit for each phase are connected to the rotation position detection circuit board  22  through the wiring pattern on the wiring board  22  in this manner, no complicated wiring route of the neutral terminals  31  is required, then a wiring structure is extremely simple. In addition, since complicated wiring route of the input terminals  30  to the respective power conversion circuit boards  24  and  26  is not required, a space for this complicated wiring route is also not required. Size reduction of the electronic control unit EC can therefore be achieved. This will be explained using  FIG. 8 . 
     Here, a bearing that supports a rotation shaft forming the rotor portion is provided between the two openings  32  of the motor housing  20 , although this is not illustrated in the drawing. A sealing plate  33  is provided at the end surface side of the motor housing  20  so as to cover this bearing portion from the outer side. The sealing plate  33  is a plate that shields the rotor portion from the outside, and is provided so that after the cover  29  is fixed, a filler that fills an inside of the cover  29  does not enter the rotor portion. Here, although the filler flows to the winding side through the opening  32 , since the windings do not rotate, this produces no ill effect. 
     As shown in  FIGS. 3 and 4 , the rotation position detection circuit board  22  is fixed to the end surface of the motor housing  20  with bolts  34 . The neutral terminal  31  for each phase is connected to this rotation position detection circuit board  22  through the wiring pattern on the wiring board  22 , and then forms the neutral point. Further, the input terminal  30  of the winding for each phase extends along an axial direction from a gap between the opening  32  and the rotation position detection circuit board  22 . As described later, the input terminals  30  are connected to the output terminals of the respective power conversion circuit boards  24  and  26  for each phase. 
     A GMR (Giant Magneto Resistance effect) element (not shown) is provided on a surface, at the sealing plate  33  side, of the rotation position detection circuit board  22 . The GMR element is configured to obtain magnetic pole position information of the rotor portion in cooperation with a position detection permanent magnet that is fixed to a rotation shaft located at an opposite side to the output shaft portion  21 . Further, a magnetic shield plate  35  is provided on a surface opposite to the surface on which the GMR element of the rotation position detection circuit board  22  is provided. 
     This magnetic shield plate  35  has the function of suppressing an influence of magnetism on the GMR element, which is caused by operation of the electronic elements or components mounted on the first power conversion circuit board  24 , the first control circuit board  25 , the second power conversion circuit board  26  and the second control circuit board  27 . 
     Supporting stems  36  that stand on the end surface of the motor housing  20  toward an opposite side to the output shaft portion  21  in the axial direction are formed integrally with the motor housing  20 . Therefore, the supporting stem  36  is made of aluminum alloy, and its thermal conductivity is high. The supporting stems  36  are arranged at 180° angular space on opposite sides of the rotation position detection circuit board  22 . As described later, the supporting stems  36  have the function of not only fixing and supporting the heat radiation base body  23  but also transmitting heat from the heat radiation base body  23  to the motor housing  20 . 
     The supporting stems  36  are formed into a shape that thermally touches or contacts the heat radiation base body  23  at three surfaces of the supporting stem  36  which are a front surface and side surfaces formed at both sides of the front surface of the supporting stem  36 . Then, in order to increase a thermal conductive area of the supporting stem  36 , the side surfaces of the supporting stem  36  are shaped into an oblique surface that obliquely extends toward an axial direction tip end. With this shape, a length of the side surface of the supporting stem  36  is longer, and a large thermal conductive area can be secured. On the front surface and a back surface of the supporting stem  36 , insertion holes into which fixing bolt is inserted are formed. 
     In  FIGS. 3, 5 and 6 , the heat radiation base body  23  is made of aluminum alloy having a good thermal conductivity, and is formed into a substantially rectangular parallelepiped. Basically, the heat radiation base body  23  is placed in a substantially middle on the end surface of the motor housing  20 . In other words, the heat radiation base body  23  is disposed on the motor housing  20  so as to pass through an area on an extension line of the rotation shaft of the rotor portion and so as to extend toward an opposite side to the output shaft portion  21  in the axial direction. The after-mentioned electronic control boards of the redundant system are arranged in the axial direction with this heat radiation base body  23  being a center or a middle. This configuration is also one of the outstanding features of the present embodiment. 
     At a lower side of each of both side surfaces  23 S of the heat radiation base body  23 , a supporting stem fixing portion  38  to which the supporting stem  36  is fixed is formed. At an upper side of each of the both side surfaces  23 S, a connector fixing portion  39  is formed. The supporting stem fixing portion  38  is formed into a recessed shape having a surface that faces to the front surface of the supporting stem  36  and surfaces that face to the respective side surfaces of the supporting stem  36 . The supporting stem  36  is accommodated and fitted in this recessed-shaped portion. On the surface of the supporting stem fixing portion  38  which faces to the front surface of the supporting stem  36 , bolt insertion holes  40  into which the fixing bolt is screwed are formed. 
     The surfaces of the supporting stem fixing portion  38  which face to the respective side surfaces of the supporting stem  36  are formed into oblique surfaces so as to narrow toward an upper side in line with the oblique supporting stem  36 . With this shape, a large thermal conductive area of heat transmitted from the heat radiation base body  23  toward the supporting stem  36  can be secured. In addition, this shape can act as a guide when inserting or fitting the heat radiation base body  23  (the supporting stem fixing portions  38 ) onto or to the supporting stem  36 . 
     Further, since the side surfaces of the supporting stem  36  and the surfaces of the supporting stem fixing portion  38  which face to these side surfaces of the supporting stem  36  are the oblique surfaces, the respective opposing surfaces are closely fitted, then play or vibration between the supporting stem  36  and the heat radiation base body  23  can be suppressed. It is therefore possible to suppress unnecessary vibration of the heat radiation base body  23 . 
     The connector fixing portion  39  provided at the upper side of the heat radiation base body  23  is formed into a shape to which the power supply connector  28  is fitted. This will be explained using  FIG. 8 . 
       FIG. 6  shows an assembly state of the heat radiation base body  23 , viewed from an opposite side to the side surface  23 S of the heat radiation base body  23  shown in  FIG. 5 . 
     As shown in  FIG. 6 , the supporting stem fixing portions  38  of the heat radiation base body  23  is moved downward along the supporting stem  36  formed at the motor housing  20 . Then, when the supporting stem fixing portions  38  reaches a predetermined position, the supporting stem  36  and the heat radiation base body  23  are firmly fixed with the fixing bolts  41 . In this state, the heat radiation base body  23  is secured on the end surface of the motor housing  20  at the substantially middle position on the end surface of the motor housing  20 . Here, in the present embodiment, since a length of a fixing surface of the heat radiation base body  23  fixed to the end surface of the motor housing  20  is made substantially identical to sizes of the after-mentioned control circuit boards  25  and  27 , the heat radiation base body  23  is fixed so as to cross the middle of the end surface of the motor housing  20 . 
     Then, with this structure, it is possible to transmit heat from the after-mentioned electronic control boards to the heat radiation base body  23  and further transmit heat of the heat radiation base body  23  to the supporting stem  36 . Hence, since heat from the electronic control boards can radiate from the motor housing  20  without using the conventional ECU housing of the related art, it is possible to reduce the whole body size of the electric power steering device. Further, component count can be reduced, thereby reducing man-hour of assembly or assembly processes. Here, regarding a contact portion between the supporting stem  36  and the heat radiation base body  23 , in order to increase thermal contact (in order to decrease an interfacial thermal resistance), a heat radiation function member such as an adhesive having good thermal conductivity, a heat radiation sheet and a heat radiation grease could be interposed between the supporting stem  36  and the heat radiation base body  23 . 
     Returning to  FIG. 5 , on a board fixing surface  23 F corresponding to a front surface side of the heat radiation base body  23 , a fixing surface where the first power conversion circuit board  24  and the first control circuit board  25  are fixed is formed. As shown in  FIGS. 3 and 8 , the first power conversion circuit board  24  is fixed on the front surface side of the heat radiation base body  23 , and the first control circuit board  25  is fixed from an outer side of the first power conversion circuit board  24 . 
     Likewise, on a board fixing surface  23 F corresponding to a back surface side of the heat radiation base body  23 , a fixing surface where the second power conversion circuit board  26  and the second control circuit board  27  are fixed is formed. As shown in  FIG. 3 , the second power conversion circuit board  26  is fixed on the back surface side of the heat radiation base body  23 , and the second control circuit board  27  is fixed from an outer side of the second power conversion circuit board  26 . 
     The first power conversion circuit board  24  and the second power conversion circuit board  26  are each provided, on metal substrates thereof made of metal such as aluminium having a good thermal conductivity, with a power switching element configured from a plurality of MOSFETs which forms a power conversion circuit and an output connector for output of this power switching element. Further, the first power conversion circuit board  24  and the second power conversion circuit board  26  are each provided with coils forming a power supply circuit, switching elements configured from MOSFETs, and various connector terminals. Since a large number of switching elements, each of which carries out the switching of a large current, are mounted on these first power conversion circuit board  24  and second power conversion circuit board  26 , a heat value of each of the first power conversion circuit board  24  and the second power conversion circuit board  26  is high. The first power conversion circuit board  24  and the second power conversion circuit board  26  are therefore main heat generation sources. Although heat is generated also from the first control circuit board  25  and the second control circuit board  27 , this heat is transmitted to the heat radiation base body  23 , and radiates from the heat radiation base body  23 . This will be described later. 
     The metal substrates of these first power conversion circuit board  24  and second power conversion circuit board  26  are fixed to accommodation recessed portions  42  formed on the front and back surfaces of the heat radiation base body  23 , as shown in  FIGS. 5 and 6 , with fixing bolts. The power switching element is positioned between the metal substrate and the accommodation recessed portion  42 . In order to improve thermal conductive performance, a heat radiation function member such as an adhesive having good thermal conductivity, a heat radiation sheet and a heat radiation grease is interposed between the power switching element and the accommodation recessed portion  42 . 
     Here, needless to say, it is possible to employ a configuration in which the metal substrate contacts the accommodation recessed portion  42  with the power switching element positioned at an opposite side to the accommodation recessed portion  42 . However, in the present embodiment, in order to efficiently transmit heat of the power switching element to the heat radiation base body  23 , the configuration in which the power switching element contacts the accommodation recessed portion  42  is employed. 
     In this manner, by employing the configuration in which the first power conversion circuit board  24  and the second power conversion circuit board  26  are accommodated in the respective accommodation recessed portions  42  formed at the heat radiation base body  23 , in the present embodiment, the first power conversion circuit board  24  and the second power conversion circuit board  26  are accommodated in the heat radiation base body  23 , thereby suppressing the increase in size in the radial direction of the electronic control unit EC. 
     Further, as shown in  FIG. 3 , the first control circuit board  25  and the second control circuit board  27  are fixed to the respective board fixing surfaces  23 F of the heat radiation base body  23  so as to cover the first power conversion circuit board  24  and the second power conversion circuit board  26  with fixing bolts  47 . That is, each of the first control circuit board  25  and the second control circuit board  27  is fixed to a fixing flat surface portion  44  that encloses the accommodation recessed portion  42  formed on the board fixing surface  23 F of the heat radiation base body  23  with the fixing bolts  47 . 
     A microcomputer  48  that controls the switching elements of the power conversion circuit and its peripheral device  49  are mounted on a resin board, made of synthetic resin etc., of each of the first control circuit board  25  and the second control circuit board  27 . In the present embodiment, an electrolytic capacitor  43  that forms the power supply circuit is mounted on each of the first control circuit board  25  and the second control circuit board  27 . 
     Since a body size of the electrolytic capacitor  43  is large, it is difficult for the electrolytic capacitor  43  to be accommodated in the accommodation recessed portion  42 . Therefore, the electrolytic capacitor  43  is mounted on each of the first control circuit board  25  and the second control circuit board  27 . Since a space from the cover  29  sufficiently exists as shown in  FIG. 3 , even though the electrolytic capacitors  43  are arranged, this produces no ill effect. 
     Here, between the accommodation recessed portion  42  and the fixing flat surface portion  44 , a passage space  45  that becomes a passage when the first control circuit board  25  and the second control circuit board  27  are fixed to the heat radiation base body  23  is formed. This passage space  45  is formed to cool the accommodation recessed portion  42  by the air. Therefore, heat from the first control circuit board  25  and the second control circuit board  27  flows or is transmitted to the air in the passage space  45 , and also transmitted to the heat radiation base body  23  through the fixing flat surface portion  44 . 
     As shown in  FIG. 5 , a connector accommodation recessed portion  46  is formed on an upper end surface of the heat radiation base body  23  at an opposite side to a fixing side of the heat radiation base body  23 . This connector accommodation recessed portion  46  accommodates therein an inner side end of the power supply connector  28 , and has the function of making positioning of the power supply connector  28 . 
       FIG. 7  is a cross section for explaining a fixing state of the supporting stem  36  and the heat radiation base body  23 . An end portion of a rotation shaft  50 , which is an opposite side to the output shaft portion  21 , is positioned on the end surface of the motor housing  20 . A magnet retaining member  51  is fixed to this end portion of the rotation shaft  50 . The magnet retaining member  51  accommodates therein the position detection permanent magnet  52  that forms a position detection sensor. This position detection permanent magnet  52  is polarized so that a plurality of unit magnets are arranged annularly. 
     The sealing plate  33  is disposed between the position detection permanent magnet  52  and the rotation position detection circuit board  22 . This sealing plate  33  is secured to the end surface of the motor housing  20 , and shields a space in which the rotation shaft  50  is disposed from a space located at the rotation position detection circuit board  22  side. With this, the space in which the rotation shaft  50  is disposed can be shielded liquid-tightly or hermetically from the rotation position detection circuit board  22  side space. 
     Therefore, water or moisture coming through the rotation shaft  50  is blocked from moving to or entering a space in which the electronic control boards are arranged, thereby suppressing ill effect on the electronic elements or components mounted on the electronic control boards due to the water or moisture. As a matter of course, dust or particles generated by rotation of the electric motor can be blocked from entering. This gives rise to an effect of preventing failure of the electronic elements or components. 
     Here, a sensor that senses the water or moisture could be provided on the rotation position detection circuit board  22 , then senses the entering of the water or moisture. In the present embodiment, since the connecting portion is formed only at a facing surface between the motor housing  20  and the cover  29 , it is conceivable that the water or moisture will enter inside from this connecting portion. Since the rotation position detection circuit board  22  is fixed close to the end surface of the motor housing  20 , if the sensor sensing the water or moisture is disposed on the rotation position detection circuit board  22 , it is possible to sense the water or moisture earliest. 
     The GMR element  53  is mounted on the surface, at the position detection permanent magnet  52  side, of the rotation position detection circuit board  22 , and arranged at a position facing to the position detection permanent magnet  52 . Therefore, the GMR element  53  is fixedly connected to the motor housing  20 . That is, the rotation shaft  50  to which the position detection permanent magnet  52  is fixed is supported by the end surface of the motor housing  20 , and the rotation position detection circuit board  22  on which the GMR element  53  is mounted is also fixed to the end surface of the motor housing  20 . Because of this, since positions of the position detection permanent magnet  52  and the rotation position detection circuit board  22  are determined on the end surface of the motor housing  20 , accuracy of assembly of the GMR element  53  can be improved, and a precise detection signal can be obtained. 
     In  FIG. 7 , in a state in which the supporting stem fixing portions  38  of the heat radiation base body  23  are moved to and fitted onto the respective supporting stems  36 , the fixing bolts  41  are screwed into the heat radiation base body  23  from a radially outer side to a radially inner side through the supporting stems  36 , and the supporting stems  36  and the heat radiation base body  23  are firmly fixed with the fixing bolts  41 . 
     This fixing direction of the fixing bolt  41  is also one of the outstanding features of the present embodiment. In the present embodiment, the fixing bolts  41  are screwed into the heat radiation base body  23  from the radially outer side to the radially inner side through the supporting stems  36 . With this, size reduction of the of the control unit EC can be realized. As this kind of fixing manner, there is known a fixing manner in which a fixing flange is formed at an outer periphery of the heat radiation base body  23 , and this fixing flange is fixed to an outer periphery of the motor housing  20  with fixing bolts. However, when the heat radiation base body  23  and the motor housing  20  are fixed at their outer peripheral sides, the size tends to increase more in the radial direction by an amount of the fixing of the outer peripheral sides. 
     In contrast to this, the present embodiment utilizes the space formed by the heat radiation base body  23  and the cover  29 , and the fixing bolts  41  are positioned in this space. Therefore, since the fixing bolts  41  are screwed into the heat radiation base body  23  from the radially outer side to the radially inner side through the supporting stems  36 , the heat radiation base body  23  and the motor housing  20  are not fixed at their outer peripheral sides. With this, size reduction of the of the control unit EC can be realized. 
     Further, the two supporting stems  36  at the motor housing  20  are cantilevers. Therefore, when fixing the heat radiation base body  23  and the supporting stem  36  with the fixing bolt  41 , the supporting stem  36  is fixed with a slight flexure given to the supporting stem  36 . Since a load in an axial direction always acts on a screw thread of the fixing bolt  41  by this slight flexure, the fixing bolt  41  can be prevented from loosening. 
     After the heat radiation base body  23  is fixed to the motor housing  20 , subsequently, the electronic control boards of the redundant system are fixed. 
     In  FIG. 8 , the metal substrates of the first power conversion circuit board  24  and the second power conversion circuit board  26  are fixed to the accommodation recessed portions  42  formed on the front and back surfaces of the heat radiation base body  23  with fixing bolts. In this  FIG. 8 , since the first control circuit board  25  and the second control circuit board  27  are assembled, the first power conversion circuit board  24  and the second power conversion circuit board  26  are not illustrated. By employing the configuration in which the first power conversion circuit board  24  and the second power conversion circuit board  26  are accommodated in the respective accommodation recessed portions  42  formed at the heat radiation base body  23 , in the present embodiment, the first power conversion circuit board  24  and the second power conversion circuit board  26  are accommodated in the heat radiation base body  23 , thereby suppressing the increase in size in the radial direction of the electronic control unit EC. 
     Further, the first control circuit board  25  and the second control circuit board  27  are fixed to the respective board fixing surfaces  23 F of the heat radiation base body  23  so as to cover the first power conversion circuit board  24  and the second power conversion circuit board  26  with the fixing bolts  47 . The electrolytic capacitor  43  used for the power supply circuit, the microcomputer  48  controlling the switching elements of the power conversion circuit and its peripheral device  49  are mounted on each of the first control circuit board  25  and the second control circuit board  27 . 
     The power supply connector  28  is connected to the upper end surface of the heat radiation base body  23 , and fixed at the connector fixing portions  39  shown in  FIG. 5  with fixing bolts  56 . The power supply connector  28  is connected to a vehicle-mounted battery (not shown) through a cable (not shown). Therefore, power supplied from the power supply connector  28  is supplied to the first power conversion circuit board  24 , the first control circuit board  25 , the second power conversion circuit board  26  and the second control circuit board  27 , and further supplied to the electric motor, then the electric motor is driven. Subsequently, the cover  29  is fixed to the end surface of the motor housing  20  so as to seal the electronic control unit EC. 
     As explained above, the first power conversion circuit board  24  and the first control circuit board  25  are provided on the front surface of the heat radiation base body  23 , and the second power conversion circuit board  26  and the second control circuit board  27  are provided on the back surface of the heat radiation base body  23 . Therefore, in the normal condition, a part of the heat generated in an operating condition of the first power conversion circuit board  24  and the first control circuit board  25  is stored (or accumulated) in the second power conversion circuit board  26  and the second control circuit board  27  through the heat radiation base body  23 . It is thus possible to remove the heat of the first power conversion circuit board  24  and the first control circuit board  25  rapidly and efficiently. As a matter of course, needless to say, most of the heat, except this heat, radiates from the motor housing  20  through the heat radiation base body  23 . 
     Further, an output terminal  54  for each phase of each of the first power conversion circuit board  24  and the second power conversion circuit board  26  protrudes from an upper surface of the rotation position detection circuit board  22  to the radially outer side. The output terminals  54  are connected to the input terminals  30  of the winding for the respective phases. Since the input terminals  30  of the winding, protruding from the openings  32 , are directly connected to the output terminals  54  for the respective phases around the openings  32  without requiring complicated wiring route in this manner, an unnecessary space for this complicated wiring route is not required. Size reduction of the electronic control unit EC can therefore be achieved. 
     Further, the neutral terminal  31  for each phase is connected to the rotation position detection circuit board  22  through the wiring pattern on the wiring board  22 , and forms the neutral point. Likewise, for the other of the redundant system, the neutral terminal  31  for each phase is connected to the rotation position detection circuit board  22  through the wiring pattern on the wiring board  22 , and forms the neutral point. Since the neutral terminals  31  of the main electronic control unit and the sub-electronic control unit for each phase are connected to the rotation position detection circuit board  22  through the wiring pattern  55  on the wiring board  22  in this manner, no complicated wiring route of the neutral terminals  31  is required, then the wiring structure is extremely simple. In addition, since complicated wiring route of the input terminals  30  to the respective power conversion circuit boards  24  and  26  is not required, a space for this complicated wiring route is also not required. Size reduction of the electronic control unit EC can therefore be achieved. 
     Furthermore, in the electronic control unit EC assembled as described above, in particular, a part of the heat generated in the first power conversion circuit board  24  (or the second power conversion circuit board  26 ) is stored (or accumulated) in the second power conversion circuit board  26  (or the first power conversion circuit board  24 ) through the heat radiation base body  23 , and most of the heat transmitted to the heat radiation base body  23  is transmitted to the motor housing  20  through the supporting stems  36  and radiates from the motor housing  20 . 
     In the configuration explained above, the fixing surface where the first power conversion circuit board  24  and the first control circuit board  25  are fixed is formed on the board fixing surface  23 F corresponding to the front surface side of the heat radiation base body  23 . The fixing surface where the second power conversion circuit board  26  and the second control circuit board  27  are fixed is formed on the board fixing surface  23 F corresponding to the back surface side of the heat radiation base body  23 . Then, the board fixing surface  23 F corresponding to the front surface side of the heat radiation base body  23  and the board fixing surface  23 F corresponding to the back surface side of the heat radiation base body  23  are formed so as to be substantially parallel to each other. Therefore, the first power conversion circuit board  24 , the first control circuit board  25 , the second power conversion circuit board  26  and the second control circuit board  27  are also arranged to be substantially parallel to each other. 
     However, it is advantageous for a heat capacity of the board that rapidly stores (or accumulates) the heat generated in the electronic elements or components to be large in efficiently removing the heat generated in the electronic elements or components of the electronic control unit. Further, it is advantageous for a heat capacity of the other electronic control unit (e.g. the sub-electronic control unit) to be large in efficiently removing the heat generated in one electronic control unit (e.g. the main electronic control unit). For the same reason, it is advantageous for a contacting area that contacts the heat radiation base body  23  to be large in efficiently removing the heat generated in the electronic control unit. From such reasons, the present embodiment employs the following configuration. This configuration is also one of the outstanding features of the present embodiment. 
     In the present embodiment, first, the first control circuit board  25  and the second control circuit board  27  are fixed to the heat radiation base body  23  with these boards  25  and  27  slanting or leaning, and a board area of each of the first control circuit board  25  and the second control circuit board  27  is set to be large, then a large heat capacity to store (or accumulate) the heat is secured. Further, the first power conversion circuit board  24  and the second power conversion circuit board  26  are fixed to the heat radiation base body  23  with these boards  24  and  26  slanting or leaning, and a contact area of each of the first power conversion circuit board  24  and the second power conversion circuit board  26  to the heat radiation base body  23  is set to be large, then rapid removal of the heat from the first power conversion circuit board  24  and the second power conversion circuit board  26  to the heat radiation base body  23  is secured. 
     In  FIG. 9 , the first control circuit board  25  and the second control circuit board  27  are fixed to the heat radiation base body  23  with these boards  25  and  27  slanting or leaning so as to expand or broaden toward a lower side with respect to the heat radiation base body  23 . When the first control circuit board  25  and the second control circuit board  27  slant or lean in this manner, as compared with a case where, as shown in  FIG. 3 , the first control circuit board  25  and the second control circuit board  27  are arranged to be substantially parallel to each other, the board area is increased. Therefore, since additional heat storing or accumulation by this increased board area can be made, it is possible to rapidly remove the heat generated in the electronic elements or components mounted on the boards to the boards. Heat resistance of the electronic elements or components can therefore be improved. 
     Further, the first power conversion circuit board  24  and the first control circuit board  25  are provided on the front surface of the heat radiation base body  23 , and the second power conversion circuit board  26  and the second control circuit board  27  are provided on the back surface of the heat radiation base body  23 . Therefore, in the normal condition, a part of the heat generated in an operating condition of the first power conversion circuit board  24  and the first control circuit board  25  is stored (or accumulated) in the second power conversion circuit board  26  and the second control circuit board  27  through the heat radiation base body  23 . It is thus possible to remove the heat of the first power conversion circuit board  24  and the first control circuit board  25  rapidly and efficiently. 
     Moreover, by leaning the first control circuit board  25  and the second control circuit board  27 , a distance between an inner surface of the cover  29  and each of the first control circuit board  25  and the second control circuit board  27  is shortened, and the heat from the first control circuit board  25  and the second control circuit board  27  is easily transmitted to the cover  29 , thereby increasing a heat radiation amount from the cover  29 . 
     Next, although the following configuration is not illustrated in  FIG. 9 , the heat radiation base body  23  could be formed into a shape that slants or leans so as to expand or broaden toward a lower side in line with the leaning shapes of the first control circuit board  25  and the second control circuit board  27 , and the first power conversion circuit board  24  and the second power conversion circuit board  26  could be fixed to leaning surfaces of the heat radiation base body  23  with these boards  24  and  26  leaning. When the first power conversion circuit board  24  and the second power conversion circuit board  26  slant or lean in this manner, as compared with a case where, as shown in  FIG. 3 , the first power conversion circuit board  24  and the second power conversion circuit board  26  are arranged to be substantially parallel to each other, a contact area of each of the first power conversion circuit board  24  and the second power conversion circuit board  26  to the heat radiation base body  23  can be increased. Therefore, since additional rapid heat removal from the first power conversion circuit board  24  and the second power conversion circuit board  26  to the heat radiation base body  23  by this increased contact area can be made, heat resistance of the electronic elements or components can be improved. 
     As described above, in the present embodiment, by fixing the board of the electronic control means (the electronic control unit) extending along the axial direction of the electric motor to the heat radiation base body extending along the axial direction of the electric motor with thermal conduction between the board and the heat radiation base body allowed or secured, size reduction of the electric drive device in the radial direction can be achieved. Further, since the heat from each board radiates to the housing of the electric motor unit through the heat radiation base body, even though the size reduction is made, it is possible to efficiently radiate the heat from the board to the outside. 
     Further, the present embodiment utilizes the space formed by the heat radiation base body and the cover, and the fixing bolts are positioned in this space. Therefore, since the fixing bolts are screwed into the heat radiation base body from the radially outer side to the radially inner side through the supporting stems, the heat radiation base body and the motor housing are not fixed at their outer peripheral sides. With this, size reduction of the of the control unit EC can be realized. 
     As explained above, the present invention has the following configuration. An electric drive device comprises: a motor housing accommodating therein an electric motor; a pair of supporting stems arranged so as to face to each other on an end surface, which is an opposite side to an output shaft portion of a rotation shaft of the electric motor, of the motor housing and extending in a direction of the rotation shaft which is an opposite direction to the output shaft portion; a heat radiation base body arranged between the pair of supporting stems and extending in the same direction as those of the supporting stems; fixing bolts screwed into the heat radiation base body from a radially outer side to a radially inner side through the supporting stems and connecting the supporting stems and the heat radiation base body; one electronic control unit of a redundant system, the one electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed; and the other electronic control unit of the redundant system, the other electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed. 
     According to the configuration of the present invention, by fixing the board of the electronic control means (the electronic control unit) extending along the axial direction of the electric motor to the heat radiation base body extending along the axial direction of the electric motor with thermal conduction between the board and the heat radiation base body allowed or secured, size reduction of the electric drive device in the radial direction can be achieved. Further, since the heat from each board radiates to the housing of the electric motor unit through the heat radiation base body, even though the size reduction is made, it is possible to efficiently radiate the heat from the board to the outside. Moreover, since the fixing bolts are screwed into the heat radiation base body from the radially outer side to the radially inner side through the supporting stems, the heat radiation base body and the motor housing are not fixed at their outer peripheral sides. With this, size reduction of the of the control unit EC can be realized. 
     The present invention is not limited to the above embodiment, and includes all design modifications. The above embodiment is an embodiment that is explained in detail to easily understand the present invention, and the present invention is not necessarily limited to the embodiment having all elements or components described above. Further, a part of the configuration of the embodiment can be replaced with a configuration of other embodiments. Also, the configuration of other embodiments could be added to the configuration of the embodiment. Moreover, regarding a part of the configuration of the embodiment, the configuration of other embodiments could be added, removed and replaced. 
     As the electric drive device and the electric power steering device based on the above embodiment, for instance, the followings are raised. 
     That is, as one aspect of the present invention, An electric drive device comprises: a motor housing accommodating therein an electric motor that drives a mechanical control element; a pair of supporting stems arranged so as to face to each other on an end surface, which is an opposite side to an output shaft portion of a rotation shaft of the electric motor, of the motor housing and extending in a direction of the rotation shaft which is an opposite direction to the output shaft portion; a heat radiation base body arranged between the pair of supporting stems and extending in the same direction as those of the supporting stems; fixing bolts screwed into the heat radiation base body from a radially outer side to a radially inner side through the supporting stems and connecting the supporting stems and the heat radiation base body; one electronic control unit of a redundant system, the one electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed; and the other electronic control unit of the redundant system, the other electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed. 
     As a preferable aspect of the electric drive device, the supporting stem is formed integrally with the end surface of the motor housing, and the motor housing and the heat radiation base body are made of the same metal. 
     As another preferable aspect of the electric drive device, in any of the above electric drive devices, the heat radiation base body is fixed to the end surface of the motor housing at a position close to an area where the rotation shaft is disposed, and the one electronic control unit and the other electronic control unit are arranged at opposite sides of the heat radiation base body. 
     As another preferable aspect of the electric drive device, in any of the above electric drive devices, the heat radiation base body has fixing surfaces of the boards of the one electronic control unit and the other electronic control unit, accommodation recessed portions formed on the respective fixing surfaces, and fixing flat surface portions enclosing the respective accommodation recessed portions, power conversion circuit boards that form the one and the other electronic control units are fixed to the accommodation recessed portions, and control circuit boards that form the one and the other electronic control units are fixed to the fixing flat surface portions so as to cover the respective power conversion circuit boards. 
     As another preferable aspect of the electric drive device, in any of the above electric drive devices, a power conversion circuit and a power supply circuit except an electrolytic capacitor are mounted on the power conversion circuit boards forming the one and the other electronic control units, and a microcomputer that controls the power conversion circuit, a peripheral device and the electrolytic capacitor of the power supply circuit are mounted on the control circuit boards forming the one and the other electronic control units. 
     From the other view point, an electric power steering device comprises: an electric motor providing a steering assistive force to a steering shaft on the basis of an output from a torque sensor that detects a turning direction and a turning torque of the steering shaft; a motor housing accommodating therein an electric motor that drives a mechanical control element; a pair of supporting stems arranged so as to face to each other on an end surface, which is an opposite side to an output shaft portion of a rotation shaft of the electric motor, of the motor housing and extending in a direction of the rotation shaft which is an opposite direction to the output shaft portion; a heat radiation base body arranged between the pair of supporting stems and extending in the same direction as those of the supporting stems; fixing bolts screwed into the heat radiation base body from a radially outer side to a radially inner side through the supporting stems and connecting the supporting stems and the heat radiation base body; one electronic control unit of a redundant system, the one electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed; and the other electronic control unit of the redundant system, the other electronic control unit arranged along a direction in which the heat radiation base body extends and having a board that is fixed to the heat radiation base body with thermal conduction to the heat radiation base body allowed. 
     As a preferable aspect of the electric power steering device, the supporting stem is formed integrally with the end surface of the motor housing, and the motor housing and the heat radiation base body are made of the same metal. 
     As another preferable aspect of the electric power steering device, in any of the above electric power steering devices, the heat radiation base body is fixed to the end surface of the motor housing at a position close to an area where the rotation shaft is disposed, and the one electronic control unit and the other electronic control unit are arranged at opposite sides of the heat radiation base body. 
     As another preferable aspect of the electric power steering device, in any of the above electric power steering devices, the heat radiation base body has fixing surfaces of the boards of the one electronic control unit and the other electronic control unit, accommodation recessed portions formed on the respective fixing surfaces, and fixing flat surface portions enclosing the respective accommodation recessed portions, power conversion circuit boards that form the one and the other electronic control units are fixed to the accommodation recessed portions, and control circuit boards that form the one and the other electronic control units are fixed to the fixing flat surface portions so as to cover the respective power conversion circuit boards. 
     As another preferable aspect of the electric power steering device, in any of the above electric power steering devices, a power conversion circuit and a power supply circuit except an electrolytic capacitor are mounted on the power conversion circuit boards forming the one and the other electronic control units, and a microcomputer that controls the power conversion circuit, a peripheral device and the electrolytic capacitor of the power supply circuit are mounted on the control circuit boards forming the one and the other electronic control units.