Abstract:
The present invention provides an electric power steering apparatus, in which reduction and thickness thereof can be achieved, radiation performance thereof can concurrently be ensured, and manufacturing and running costs thereof can also be reduced, even when the apparatus includes a structure having a motor and a motor control device integrated therewith. The apparatus includes a motor which assists in steering operations, a motor control device which controls the motor, and a housing which accommodates the motor and the motor control device. The housing includes a motor accommodation portion which accommodates the motor, and a control device accommodation portion which accommodates the motor control device. The motor control device includes a drive unit which drives the motor, and a control unit which controls the motor. The drive unit is disposed in a position in the control device accommodation portion, the position being in proximity to the motor accommodation portion.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electric power steering apparatus for a vehicle and, more particularly, relates to an electric power steering apparatus in which reliability thereof is improved by enhancing the heat radiation performance of a motor control device which controls a motor and size reduction thereof is achieved.  
         [0003]     2. Description of the Related Art  
         [0004]     Generally, an electric power steering apparatus mounted on a vehicle is designed so that, when a driver performs a steering operation, a torque sensor detects a steering torque produced on a steering shaft, and a motor control device controls a motor based on the detected torque value in order to assist in the steering.  
         [0005]     Recently, such an electric power steering apparatus has been widely used, being mounted on compact cars and midsize cars in addition to light cars. Mainly, the motor and the motor control device are individually mounted on separated positions away from each other outside and inside a vehicle compartment, respectively. Thus, a long wiring harness is used to provide electric connection between the motor and the motor control device. The adoption of the long wiring harness causes various problems such as power loss due to wiring resistance, noise emission by the apparatus while the motor is being driven, and increases in the number of components.  
         [0006]     As an example of an electric power steering apparatus in view of the above problems, there has been proposed an electric power steering apparatus including a motor accommodated in a housing, and a control circuit unit accommodated in a casing, in which the housing is disposed adjacently to the casing, and in which the motor is connected by a bus bar to the control circuit unit, whereby the motor and the control circuit unit are made into an integral structure (see JP Patent Publication (Kokai) No. 2003-204654 A).  
         [0007]     Also proposed is, in addition to the above example, an electric power steering apparatus including a control device accommodated in the space defined by a housing and a cover of the housing, and an electric motor which is controlled by the control device, in which motor terminals each projecting from an opening of the cover for the control device is electrically connected within the electric motor (see JP Patent Publication (Kokai) No. 2003-267233 A).  
       SUMMARY OF THE INVENTION  
       [0008]     Incidentally, the proportion of accommodation space (e.g. car interior space) to vehicle size has recently tended to increase in order to seek comfort. It is therefore essential that a small-sized electric power steering apparatus be mounted by taking mounting space into account.  
         [0009]     However, the electric power steering apparatus such as the above includes a structure having the motor and the motor control device integrated therewith, which causes an increase in the height of the apparatus in a direction perpendicular to a rotating shaft of the motor. Accordingly, sufficient space for the apparatus has to be secured in order to mount the apparatus on an automobile.  
         [0010]     There is also a demand that the electric power steering apparatus be adapted to a large type of vehicle in the future. This demand tends to cause a further increase in a generating torque required of the motor, and hence a further increase in the amount of heat generated by a switching element and a large-sized passive component (controlunit) such as a capacitor or a coil while the motor is being driven.  
         [0011]     To take countermeasures against the generated heat, the electric power steering apparatus as previously mentioned is provided with a heat radiation fin, which is disposed in the housing in the vicinity of a motor drive circuit board in order to radiate the heat generated by the switching element while the motor is being driven. However, the heat radiation fin leads to a further increase in the outer dimensions of the electric power steering apparatus.  
         [0012]     The present invention has been made in view of the foregoing problems. It is an object of the invention to provide an electric power steering apparatus, in which reduction in size and thickness thereof can be achieved, heat radiation performance thereof can concurrently be ensured, and manufacturing and running costs thereof can also be reduced, even when the apparatus includes a structure having a motor and a motor control device integrated therewith.  
         [0013]     In order to achieve the above object, provided is an electric power steering apparatus according to the present invention including a motor which assists in steering, a motor control device which controls the motor, and a housing which accommodates the motor and the motor control device. The housing includes a motor accommodation portion which accommodates the motor, and a control device accommodation portion which accommodates the motor control device. The motor control device includes a drive unit which drives the motor, and a control unit which controls the motor. The drive unit is disposed in a position in the control device accommodation portion, the position being located in proximity to the motor accommodation portion.  
         [0014]     In the case of the electric power steering apparatus of the present invention, the motor and the motor control device are accommodated in a single housing to thereby form an integral structure. This structure reduces a distance between the motor and the motor control device, thus enabling suppression of power loss, heat generation due to the resistance of wiring which provides connection therebetween, and also improving productivity. Additionally, the drive unit is disposed in proximity to the motor accommodation portion in the housing. With this disposition, heat generated by a switching element and the like which constitutes the drive unit, in particular, can be conducted to the motor along the shortest path, so that high heat radiation performance can be ensured even without the use of a heat radiation fin. In the manner as described above, it is possible to achieve reduction in cost and size of the apparatus.  
         [0015]     In the case of the electric power steering apparatus of the present invention, the control unit is disposed in a position in the control device accommodation portion formed in a projecting portion of the housing, the position being away from the motor accommodation portion.  
         [0016]     In the case of the electric power steering apparatus of the present invention, the motor control unit, including a power relay, a motor relay, a coil or a capacitor, which drives and controls motor drive, is disposed away from the drive unit in one direction. This disposition makes it possible to disperse heat generated by the drive unit and the control unit, thus preventing local high temperature. Moreover, this disposition makes it possible to radiate the heat generated by the control unit to the outside of the apparatus, thus achieving efficient heat radiation. Furthermore, the control unit is disposed in the accommodation portion in the projecting portion of the housing as mentioned above. This disposition reduces the thickness of the overall motor control device in the direction of the height thereof (that is, the thickness of the device in a direction perpendicular to a rotating shaft of the motor), thus making it possible to achieve reduction in size and thickness of the apparatus.  
         [0017]     The electric power steering apparatus of the present invention is characterized in that the housing is made of a metallic material having high heat conductance. In the case of the electric power steering apparatus of the present invention, it is possible to radiate the heat generated by the switching element for driving the motor and by the heat-generating component such as the capacitor or the coil, regardless of a use environment inside a vehicle compartment or an engine room. This makes it possible to improve the heat radiation performance of the apparatus.  
         [0018]     The electric power steering apparatus of the present invention is characterized in that the metallic material having high heat conductance is an aluminum alloying material. In the case of the electric power steering apparatus of the present invention, the aluminum alloying material is used for the metallic housing of the motor control device, thereby enhancing the heat radiation performance of the apparatus and achieving weight reduction of the apparatus.  
         [0019]     The electric power steering apparatus of the present invention is characterized in that the drive unit is in surface contact with the control device accommodation portion with high-heat-conductance grease interposed in between. In the case of the electric power steering apparatus of the present invention, the drive unit is in surface contact with the control device accommodation portion with the high-heat-conductance grease interposed in between, thereby further facilitating the conduction of heat to the motor, thus making it possible to further enhance the heat radiation performance.  
         [0020]     In the case of the electric power steering apparatus of the present invention, the motor control device includes a bus bar wiring board which supplies a drive current to the motor, the motor includes motor drive power terminals each projecting in a direction perpendicular to a rotating shaft of the motor, and the motor drive power terminals are connected to the bus bar wiring board.  
         [0021]     In the case of the electric power steering apparatus of the present invention, the motor drive power terminals project toward the inside of the motor control device in the direction perpendicular to the rotating shaft of the motor, and are electrically connected to the bus bar wiring board within the motor control device. Accordingly, a wiring harness for external connection is not needed, wiring resistance is reduced, and thus heat generation is reduced, and noise emissions also reduced. Moreover, the number of components can also be reduced, thereby achieving low cost of the apparatus.  
         [0022]     The electric power steering apparatus of the present invention is characterized in that the housing includes a cover which covers an opening of the control device accommodation portion, and the motor drive power terminals, control unit terminals, and drive unit current terminals are welded to the bus bar wiring board from the side of the cover.  
         [0023]     In the case of the electric power steering apparatus of the present invention, the motor drive power terminals, the control unit terminals, and the drive unit current terminals are welded to the bus bar wiring board from the side of the cover of the motor control device. This enables the welding of the terminals at once after the completion of assembly of the apparatus, thus enabling an improvement in working efficiency and hence an improvement in productivity.  
         [0024]     The electric power steering apparatus of the present invention is characterized in that the drive unit has a stacked structure including a current circuit wiring portion having the switching element mounted thereon, an insulating layer made of an electrical insulating material, and a metal plate in surface contact with the control device accommodation portion. In the case of the electric power steering apparatus of the present invention, this stacked structure makes it possible to ensure electrical insulation between the current circuit wiring portion and the metal plate, thereby the metal plate can efficiently diffuse the heat generated by the switching element.  
         [0025]     The electric power steering apparatus of the present invention is characterized in that the metal plate is made of a copper alloying material. In the case of the electric power steering apparatus of the present invention, the copper alloying material having high heat conductance is used for the metal plate, so that heat generated by the switching element can be efficiently diffused to the metal plate made of the copper alloy having high heat conductance.  
         [0026]     The electric power steering apparatus of the present invention is characterized in that the switching element is a bare chip. In the case of the electric powersteering apparatus of the present invention, the bare chip is used as the switching element, thereby making it possible to reduce a mounting area and hence the size of the drive unit.  
         [0027]     The electric power steering apparatus of the present invention is characterized in that the switching element is soldered to the current circuit wiring portion of the drive unit. In the case of the electric power steering apparatus of the present invention, this connection makes it possible to efficiently diffuse the heat produced by the switching element.  
         [0028]     The electric power steering apparatus of the present invention is characterized in that a top surface of the switching element is soldered to the current circuit wiring portion of the drive unit by means of a strip-shaped conductive bridge. In the case of the electric power steering apparatus of the present invention, the electrical connection by means of the strip-shaped conductive bridge for makes it possible to omit a conventional bonding process, specifically wire bonding using a plurality of aluminum wires, thus enabling productivity improvements. Moreover, the cross-sectional area for a current to pass through the strip-shaped bridge is large, so that the resistance is low and heat generation is suppressed.  
         [0029]     The electric power steering apparatus of the present invention is characterized in that the strip-shaped conductive bridge is made of a copper alloying material. In the case of the electric power steering apparatus of the present invention, the copper alloying material is used for the strip-shaped conductive bridge, thereby making it possible to improve the radiation of the heat generated by the switching element. Moreover, since the copper alloying material has high electrical conductivity, it is possible to reduce wiring resistance.  
         [0030]     The electric power steering apparatus of the present invention is characterized in that the drive unit inside the housing is sealed with a hardening resin from the upside of the current circuit wiring portion. In the case of the electric power steering apparatus of the present invention, the use of the hardening resin makes it possible to fix the components mounted on the current circuit wiring portion, thus preventing damage to soldered connections, and thus improving the reliability of electrical connection.  
         [0031]     In the case of the electric power steering apparatus of the present invention, it is possible to ensure the heat radiation performance of the apparatus main body, and to concurrently achieving reduction in size and thickness of the apparatus. Moreover, the structure with high efficiency of assembly operation makes it possible to reduce the cost of manufacturing the apparatus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]      Fig. 1  is a general perspective view of an electric power steering apparatus in the case of the present embodiment.  
         [0033]      FIG. 2  is an exploded perspective view of the electric power steering apparatus shown in  FIG. 1 .  
         [0034]      FIG. 3  is a sectional view taken along the line A-A of  FIG. 1 .  
         [0035]      FIG. 4  is a sectional view taken along the line B-B of  FIG. 3 .  
         [0036]      FIG. 5  is an enlarged view of a principal part of the section of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     The description will be given below with reference to the drawings with regard to one embodiment of an electric power steering apparatus of the present invention.  
         [0038]     FIGS.  1  to  5  show a preferred structure of the electric power steering apparatus for an automobile in the case of the present embodiment.  FIG. 1  is a general perspective view of the electric power steering apparatus  1  in the case of the present embodiment.  FIG. 2  is an exploded perspective view of the electric power steering apparatus  1  shown in  FIG. 1 .  FIG. 3  is a sectional view taken along the line A-A of  FIG. 1 .  FIG. 4  is a sectional view taken along the line B-B of  FIG. 3 .  FIG. 5  is an enlarged view of a principal part of the section of  FIG. 3 .  
         [0039]     As shown in FIGS.  1  to  5 , the electric power steering apparatus  1  of the present invention for the automobile is provided mainly with a motor  10  which acts to assist in steering operations, a motor control device  20  which controls the motor  10 , a housing  30  which accommodates the motor  10  and the motor control device  20 , and a cover  38  which closes an opening  34  of the housing  30 . The motor  10  has a main body  14  shaped like a cylinder, a motor shaft ( a rotating shaft)  11  projecting from the main body  14 , and a backup flange  15  fixed to the main body  14  in the circumference of the motor shaft  11 .  
         [0040]     The housing  30  has a motor accommodation portion  31  whose side is opened to accommodate the motor  10 , and a control device accommodation portion  32  whose top is opened to accommodate the motor control device  20  which controls and drives the motor  10 . The motor accommodation portion  31  and the control device accommodation portion  32  are integrally formed. The motor accommodation portion  31  has inner space  31   a  shaped like a cylinder, which is formed to extend from the side opening in the direction of the rotating shaft (i.e. the x axis of FIG.  1 ). It is possible to accommodate the motor  10  in the housing  30  by inserting the motor main body  14  through the opening into the inner space  31   a.  The opening of the motor accommodation portion  31  is configured to be closed with the backup flange  15  after the accommodation of the motor  10 .  
         [0041]     On the other hand, the control device accommodation portion  32  is a casing which is shaped like a rectangle section, whose plane shape extends in the direction of the rotating shaft (i.e. the x axis) and in the direction of the y axis perpendicular to the rotating shaft. The width of the control device accommodation portion  32  in the direction of the x axis is approximately equal to the width of the motor accommodation portion  31  (in the direction of the x axis). The width of the control device accommodation portion  32  in the direction of the y axis is greater than the width of the motor accommodation portion  31  (in the direction of the y axis) so as to form the housing  30  having a projecting portion  30   a.  A bottom  33  of the control device accommodation portion  32  has a stepped bottom surface having bottoms at different depths in the direction of the z axis. A shallow-depth bottom  35  is formed in series with a great-depth bottom portion  36  with a slope  37  in between. The shallow-depth bottom portion  35  of the control device accommodation portion  32  is adjacent to the motor accommodation portion  31  in a vertical direction (in the direction of the z axis) with the shallow-depth bottom portion  35  (a partition wall) interposed in between. The great-depth bottom portion  36  of the control device accommodation portion  32  constitutes a port of the portion projecting in the direction of the y axis (that is, the projecting portion  30   a ).  
         [0042]     As mentioned above, the motor  10  and the motor control device  20  can be made into an integral structure. This structure makes it possible to reduce the length of wiring which connects the motor  10  and the motor control device  20 , thus enabling suppression of power loss due to resistance, heat generation and the like, and also enabling productivity improvements.  
         [0043]     Moreover, in the housing  30 , the shallow-depth bottom portion  35  of the control device accommodation portion  32  is vertically laid on and adjacently (or in proximity) to the motor accommodation portion  31 , and the great-depth bottom portion  36  which is one end of the control device accommodation portion  32  extends out (i.e. projects) horizontally. This configuration enables a side-by-side disposition of a drive unit  40  (to be described later) to the shallow-depth bottom portion  35 , and a side-by-side disposition of a control unit  28  (to be described later) to the great-depth bottom portion  36  located away from the motor accommodation portion  31 . This arrangement makes it possible to reduce the vertical height of the electric power steering apparatus as a whole.  
         [0044]     Moreover, the motor  10  is a three-phase brushless motor. The motor shaft  11  which constitutes a rotor of the motor  10  is provided with a rotational position sensor  13  which detects the rotation angle of the motor shaft  11 . A detection signal from the rotational position sensor  13  is electrically connected through a signal connector  61  to the motor control device  20  (to be described later). In addition a motor coil  13  which constitutes a stator of the motor  10  is provided with motor drive power terminals  51  which provide electric connection to the motor control device  20 . The motor drive power terminals  51  project toward the motor control device  20  in the direction perpendicular (or vertical) to the motor shaft  11 , and are electrically connected to a bus bar wiring board  26  (to be described later).  
         [0045]     The motor control device  20  is disposed in the control device accommodation portion  32  of the housing  30 , in parallel with the motor shaft  11  of the motor  10  (around the rotating shaft) . The motor control device  20  includes a resin circuit board  25  having a microcomputer mounted thereon for controlling a drive output of the motor  10 , the bus bar wiring board  26  which is a path for supplying a large drive current to the motor  10 , the drive unit  40  having a motor drive switching element  41  mounted thereon, and a passive component (control unit)  28  (to be described later). The resin circuit board  25 , the bus bar wiring board  26  and the drive unit  40  are disposed in the control device accommodation portion  32  of the housing  30 , in sequence from the opening  34  of the control device accommodation portion  32  toward the bottom  33  thereof.  
         [0046]     Incidentally, the motor control device  20  is provided on its side with a battery power connector  62  which provides connection to a vehicle battery, and the signal connector  61  which receives communications signals for vehicle control and detection signals from the rotational position sensor  13  of the motor shaft  11 .  
         [0047]     In addition, the drive unit  40  is disposed in proximity to the motor accommodation portion  31  in the control device accommodation portion  32 . The drive unit  40  has a three-layer structure having a current circuit wiring portion  44 , an insulating layer  43  made of an electrical insulating material, and a metal plate  42  made of a copper alloying material, which are stacked in sequence. On the current circuit wiring portion  44 , mounted are the switching element  41 , a shunt resistor which detects a current while themotor is being driven by the switching element  41 , and a temperature sensor which detects the temperature of the drive unit. The metal plate  42  of the drive unit  40  is disposed on the shallow-depth bottom portion  35  in the control device accommodation portion  32 . With this disposition of the drive unit  40 , heat generatedby the switching element  41  while the motor is being driven can be conducted from the drive unit  40  to the motor  10 . In the drive unit  40 , the metal plate  42  of the drive unit  40  and the shallow-depth bottom portion  35  are in surface contact with each other with high-heat-conductance grease interposed in between. The metal plate  42  is fixed to the shallow-depth bottom portion  35  with screws or the like. This configuration makes it possible to further improve the conduction of the heat to the motor  10 .  
         [0048]     Moreover, it is preferable that a wiring portion of the current circuit wiring portion  44  is made of a copper alloying material and that the insulating layer  43  is made of a silicon nitride material, an aluminum nitride material, or an epoxy resin material with high heat conductance. It is preferable that a tough pitch copper material or an oxygen-free copper material with higher heat conductance and lower thermal expansion than other metallic materials, for example, is used for the metal plate  42 . In addition to these materials, an aluminum alloy with higher heat conductance and lower specific gravity than other metallic materials, or a copper-molybdenum alloy, a copper-tungsten alloy or aluminum-silicon-carbide whose characteristic is an extremely low coefficient of thermal expansion may also be used for the metal plate  42 .  
         [0049]     On the other hand, the large-sized passive component (control unit)  28  for controlling the motor  10  is configured of a power relay, a motor relay, a coil, and a capacitor and so on. As shown in  FIG. 3 , the passive component  28  is disposed in a position in the control device accommodation portion  32  formed in the projecting portion  30   a  of the housing  30 , the position being away from the motor accommodation portion  31 . The passive component  28  is disposed away from the drive unit  40  in one direction, as mentioned above. Accordingly, local heat generation is prevented, and concurrently the heat generated by the passive component  28  is radiated to the outside of the apparatus (i.e. radiated into the atmosphere). Moreover, the drive unit  40  and the passive component  28  are disposed in parallel with the bottom  33  of the housing  30 . This disposition makes it possible to reduce the thickness of the electric power steering apparatus  1  in the direction of the height thereof (that is, the height of the control device accommodation portion  32 ), thus achieving reduction in size and thickness of the apparatus.  
         [0050]     Moreover, the drive unit  40  includes drive unit signal terminals  52  with a cross section shaped like “L” provided on one end of the current circuit wiring portion  44 , and drive unit current terminals  53  with a cross section shaped like “L” provided on the other end of the current circuit wiring portion  44 . Connections  52   a  and  53   a  of the terminals  52  and  53  are disposed so as to project perpendicularly to the board surfaces of the bus bar wiring board  26  and the resin circuit board  25  which are disposed above the current circuit wiring portion  44 . The connections  52   a  of the drive unit signal terminals  52  are soldered to the resin circuit board  25 , and the connections  53   a  of the drive unit current terminals  53  are welded to the bus bar wiring board  26 . The provision of the connections  52   a  and  53   a  of the terminals  52  and  53  perpendicular to the board surfaces of the bus bar wiring board  26  and the resin circuit board  25 , as mentioned above, enables terminal connection from one direction, thus improving the workability of terminal connection.  
         [0051]     Moreover, the switching element  41  mounted on the drive unit  40  is a bare chip, which is soldered to the current circuit wiring portion  44 . This chip configuration enables reducing a mounting area and hence the size of the drive unit  40 .  
         [0052]     In addition, an electrode pad on a top surface of the switching element  41  is soldered to the current circuit wiring portion  44  by means of a strip-shaped conductive bridge (so-called a lead frame)  46 . The strip-shaped conductive bridge  46  is made of a copper alloying material. Preferably, a tough pitch copper material or an oxygen-free copper material having high heat conductance and low thermal expansion, for example, is used as the copper alloying material. In addition to these materials, however, a copper-molybdenum alloy material or a copper-tungsten alloy material whose characteristic is an extremely low coefficient of thermal expansion as compared to other metallic materials may be used as the copper alloying material.  
         [0053]     Moreover, the drive unit  40  disposed on the shallow-depth bottom portion  35  of the control device accommodation portion  32  is sealed with a thermal hardening resin  49  from the upside of the current circuit wiring portion  44 . This results in fixing the components mounted on the current circuit wiring portion  44 , thus preventing damage to the soldered connections, and thus improving the reliability of electric connection.  
         [0054]     The bus bar wiring board  26  is formed by pressing a thick copper plate, which is used as a raw material, to form a current wiring portion (not illustrated) and a signal wiring portion (not illustrated), and then by performing insert molding to the resultant wiring portions with a thermal hardening resin. As previously mentioned, the bus bar wiring board  26  is disposed by being interposed in between the resin circuit board  25  and the drive unit  40 .  
         [0055]     Moreover, the current wiring portion of the bus bar wiring board  26  is welded to the motor drive power terminals  51 , the drive unit current terminals  53 , and passive component terminals (control unit terminals)  54  (to be described later) from the side of the housing cover  38  of the housing  30 . Specifically, the signal wiring portion of the bus bar wiring board  26  is welded to the passive component  28  (to be described later) with the passive component terminals  54  interposed in between in order to transmit control signals from the passive component  28  to the resin circuit board  25 , and the signal wiring portion is also soldered to the resin circuit board  25 . Incidentally, all the terminals extending from each of the components and boards toward the bus bar wiring board  26  are bent toward the housing cover  38  perpendicularly to the board surface of the bus bar wiring board  26 . This terminal structure achieves Simplification of the manufacturing process and hence an improvement in the productivity of the apparatus.  
         [0056]     Moreover, as mentioned above, the resin circuit board  25  is disposed parallel to the bus bar wiring board  26  and toward the housing cover  38 , and the resin circuit board  25  is electrically connected through a screwed signal connector  61  to the outside. Moreover, the resin circuit board  25  is electrically connected to a shunt resistor of the drive unit  40 , and is provided with a microcomputer (not illustrated) which detects a current while the motor  10  is being driven and which controls an output of the motor  10  depending on a steering torque produced on a steering shaft.  
         [0057]     Incidentally, it is preferable that the housing  30  which accommodates the motor  10  and the motor control device  20  is made of a metallic material having higher heat conductance than other metallic materials. More preferably, the housing  30  is made of an aluminum alloying material, such as cast aluminum produced by aluminum die casting, in terms of improvements in mass production, weight reduction and heat radiation performance. Alternatively, cutting may be performed to form the housing  30 . A metallic material such as an aluminum alloy material formed by pressing is used for the housing cover  38  in terms of improvements in mass production and heat radiation performance. In addition to this, the housing cover  38 , however, may be made of a heat resistance synthetic resin, specifically a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin or a PBT (polybutylene terephthalate) resin, since these resins are lightweight and excellent in heat resistance.  
         [0058]     The electric power steering apparatus configured as mentioned above functions as follows. When a driver performs steering, the switching element  41  mounted on the drive unit  40  of the motor control device  20  is energized, so that the drive unit  40  generates heat. Then, the heat generated by the drive unit  40  is conducted from the drive unit  40  through the metal plate  42  to the motor  10  along the shortest path. Accordingly, the radiation of the heat from the motor control device  20  can be accelerated.  
         [0059]     Moreover, in order to control an output of the motor  10 , the passive component  28  is also energized and generates heat. The passive component  28  is disposed away from the drive unit  40 , and concurrently, the passive component  28  is disposed in the projecting portion  30   a  of the housing  30  (i.e. in a position in the control device accommodation portion  32 , the position being away from the motor accommodation portion  31 ). This disposition prevents local high temperature and also facilitates the radiation of the heat generated by the passive component  28  from the apparatus to the outside.  
         [0060]     Although the detailed description has been given above with regard to one embodiment of the electric power steering apparatus according to the present invention, it is to be understood that the invention is not limited to the above embodiment and that various design changes may be made in the invention without departing from the spirit and scope of the invention as defined in the appended claims.  
         [0061]     In the embodiment of the present invention, the control device accommodation portion is configured to have the shallow-depth bottom portion and the great-depth bottom portion. However, the control device accommodation portion may have a flat bottom portion. In other words, the control device accommodation portion may have any configuration, provided that the motor accommodation portion is in proximity to the drive unit of the motor control device. In addition, the motor accommodation portion is not limited to having the inner space shaped like a cylinder but may have inner space shaped like a rectangular parallelepiped. The inner space is not particularly limited in its shape, provided that the inner space can accommodate the motor.  
         [0062]     As an example, the passive component of the motor control device is disposed away from the drive unit in one direction. However, the passive components may be dispersedly disposed, provided that the passive component can be disposed away from the drive unit.  
         [0063]     Incidentally, in the embodiment of the present invention, the drive unit within the housing is sealed with a hardening resin from the side of the current circuit wiring portion. However, a thermal hardening resin may be used as the hardening resin, provided that the resin can fix the components mounted on the current circuit wiring portion. The type of resin is not particularly limited.