Patent Publication Number: US-2011066327-A1

Title: Power steering apparatus

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a power steering apparatus for assisting an operator in steering operation by means of a motor, which may be adapted to a power steering system of a motor vehicle. 
     Japanese Patent Application Publication No. 2007-030784 discloses a power steering apparatus for a motor vehicle, which includes a motor, an electrical control unit (ECU) for driving the motor, and a rotation sensor for measuring a rotational angle of the motor. The rotation sensor is electrically calibrated by determining and memorizing a correction value for the rotation angle of the motor, after the motor and ECU are mounted as part of the power steering apparatus to a vehicle body in a vehicle assembly factory. 
     SUMMARY OF THE INVENTION 
     For such power steering apparatuses as disclosed in Japanese Patent Application Publication No. 2007-030784, calibration of a rotation sensor in a vehicle assembly factory leads to a complicated operation in the vehicle assembly factory. 
     In view of the foregoing, it is desirable to provide a power steering apparatus for which calibration of a rotation sensor can be completed before shipment of the power steering apparatus as a module. 
     According to one aspect of the present invention, a power steering apparatus comprises: a main housing including: a motor housing section; and an electrical control unit housing section coupled to the motor housing section; a driven-device housing coupled to the motor housing section; a brushless motor including: a drive shaft housed in the motor housing section, the drive shaft including a motor-side connecting portion at an axial end portion of the drive shaft; a rotor coupled to the drive shaft; a coil disposed around the rotor, and adapted to be energized to generate a magnetic field; and a rotation sensor arranged to measure a rotation angle of the rotor; an electrical control unit housed in the electrical control unit housing section, the electrical control unit including: a memory circuit section configured to memorize a correction value for correction to a measured value of the rotation angle obtained by the rotation sensor; and a motor drive circuit section configured to drive the brushless motor on a basis of a corrected measured value of the rotation angle that is obtained by correcting the measured value with the correction value; a first electrical wiring connecting the coil and the electrical control unit to one another; a second electrical wiring connecting the rotation sensor and the electrical control unit to one another; and a driven device including: a driven shaft housed in the driven-device housing, and adapted to receive torque from the drive shaft, wherein the driven shaft includes at an axial end portion of the driven shaft a driven-side connecting portion connected to the motor-side connecting portion of the drive shaft; and an output section adapted to transmit the torque as an assist steering effort to steered wheels; wherein the correction value is set on a basis of a measured value of the rotation angle that is obtained by the rotation sensor when the rotor is rotated to a predetermined reference angular position by energization of the coil, under condition that the coil and the electrical control unit are connected to one another by the first electrical wiring, and the rotation sensor and the electrical control unit are connected to one another by the second electrical wiring. 
     According to another aspect of the present invention, a motor apparatus comprises: a main housing including: a motor housing section; and an electrical control unit housing section coupled to the motor housing section; a driven-device housing coupled to the motor housing section; a brushless motor including: a drive shaft housed in the motor housing section, the drive shaft including a motor-side connecting portion at an axial end portion of the drive shaft; a rotor coupled to the drive shaft; a coil disposed around the rotor, and adapted to be energized to generate a magnetic field; and a rotation sensor arranged to measure a rotation angle of the rotor; an electrical control unit housed in the electrical control unit housing section, the electrical control unit including: a memory circuit section configured to memorize a correction value for correction to a measured value of the rotation angle obtained by the rotation sensor; and a motor drive circuit section configured to drive the brushless motor on a basis of a corrected measured value of the rotation angle that is obtained by correcting the measured value with the correction value; a first electrical wiring connecting the coil and the electrical control unit to one another; a second electrical wiring connecting the rotation sensor and the electrical control unit to one another; and a driven device including: a driven shaft housed in the driven-device housing, and adapted to receive torque from the drive shaft, wherein the driven shaft includes at an axial end portion of the driven shaft a driven-side connecting portion connected to the motor-side connecting portion of the drive shaft; and an output section adapted to output a force based on the torque; wherein the correction value is set on a basis of a measured value of the rotation angle that is obtained by the rotation sensor when the rotor is rotated to a predetermined reference angular position by energization of the coil, under condition that the coil and the electrical control unit are connected to one another by the first electrical wiring, and the rotation sensor and the electrical control unit are connected to one another by the second electrical wiring. 
     According to a further aspect of the present invention, a calibration method for a power steering apparatus comprising: a main housing including: a motor housing section; and an electrical control unit housing section coupled to the motor housing section; a driven-device housing coupled to the motor housing section; a brushless motor including: a drive shaft housed in the motor housing section, the drive shaft including a motor-side connecting portion at an axial end portion of the drive shaft; a rotor coupled to the drive shaft; a coil disposed around the rotor, and adapted to be energized to generate a magnetic field; and a rotation sensor arranged to measure a rotation angle of the rotor; an electrical control unit housed in the electrical control unit housing section, the electrical control unit including: a memory circuit section configured to memorize a correction value for correction to a measured value of the rotation angle obtained by the rotation sensor; and a motor drive circuit section configured to drive the brushless motor; a first electrical wiring connecting the coil and the electrical control unit to one another; a second electrical wiring connecting the rotation sensor and the electrical control unit to one another; and a driven device including: a driven shaft housed in the driven-device housing, and adapted to receive torque from the drive shaft, wherein the driven shaft includes at an axial end portion of the driven shaft a driven-side connecting portion connected to the motor-side connecting portion of the drive shaft; and an output section adapted to output a force based on the torque; the calibration method comprises: a first operation of rotating the rotor to a predetermined reference angular position with respect to the coil by energization of the coil; a second operation of setting the correction value on a basis of a measured value of the rotation angle that is obtained by the rotation sensor when the rotor is rotated to the predetermined reference angular position by the first operation, for the motor drive circuit section to drive the brushless motor on a basis of a corrected measured value of the rotation angle that is obtained by correcting the measured value with the correction value; and a third operation of memorizing in the memory circuit section the correction value that is determined by the second operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a power steering apparatus according to a first embodiment of the present invention. 
         FIG. 2  is a longitudinal sectional view of a motor-and-pump unit of the power steering apparatus shown in  FIG. 1 . 
         FIG. 3  is a longitudinal sectional view of a motor unit of the motor-and-pump unit shown in  FIG. 2 . 
         FIG. 4  is a bottom view of the motor unit shown in  FIG. 3  under condition that the motor unit is uncovered. 
         FIG. 5  is a block diagram showing an electrical control unit (ECU) of the motor unit shown in  FIG. 3 . 
         FIG. 6  is a schematic diagram showing a system for calibration of a resolver of the motor unit shown in  FIG. 3 . 
         FIG. 7  is a flow chart showing a process of calibration of the resolver. 
         FIG. 8  is a flow chart showing a process performed by the ECU during the process shown in  FIG. 7 . 
         FIG. 9  is a schematic diagram showing a power steering apparatus according to a second embodiment of the present invention. 
         FIG. 10  is a longitudinal sectional view of a motor-and-gear unit of the power steering apparatus shown in  FIG. 9 . 
         FIG. 11  is a schematic diagram showing a power steering apparatus according to a modification of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following embodiments, a power steering apparatus is adapted to a power steering system of a motor vehicle. 
     In a first embodiment, a power steering apparatus  1  is a hydraulic power steering apparatus for assisting steering operation by hydraulically boosting a thrust of a rack shaft  6 . As shown in  FIG. 1 , power steering apparatus  1  includes an input shaft  2 , an output shaft  3 , a rack-and-pinion mechanism  4 , a power cylinder  5 , and a motor-and-pump unit  10 . Input shaft  2  has one axial end coupled to a steering wheel “SW” so that the input shaft  2  and steering wheel SW rotate as a solid unit. Input shaft  2  is rotated by a steering torque that is inputted from an operator to steering wheel SW. Output shaft  3  has one axial end linked to steered wheels “WR”, “WL” through the rack-and-pinion mechanism  4 , and has another axial end connected to input shaft  2  through a torsion bar not shown. Relative rotation between input shaft  2  and output shaft  3  is permitted by torsion of the torsion bar. The steering torque is transmitted from input shaft  2  to output shaft  3  through a reaction of torsion of the torsion bar, and then outputted from output shaft  3 . Power cylinder  5  is arranged between output shaft  3  and steered wheels WR, WL, and combined with rack shaft  6 . Power cylinder  5  includes first and second pressure chambers P 1 , P 2  separated from one another, and are arranged to boost a steering effort outputted from output shaft  3  by a differential pressure between first and second pressure chambers P 1 , P 2 . Motor-and-pump unit  10  selectively supplies and drains working fluid to and from first and second pressure chambers P 1 , P 2  of power cylinder  5 . 
     In rack-and-pinion mechanism  4 , a pinion gear  3   a  of output shaft  3  meshes with a rack gear  6   a  of rack shaft  6 . Output shaft  3  and rack shaft  6  cross one another at or near a right angle. Pinion gear  3   a  is formed at the periphery of an axial end portion of output shaft  3 . Rack gear  6   a  is formed at the periphery of a portion of rack to shaft  6  that expands over a predetermined distance in the axial direction. Rotation of output shaft  3  causes rack shaft  6  to travel in the axial direction of rack shaft  6 . Each longitudinal end of rack shaft  6  is connected to a tie rod  7 . Each tie rod  7  is liked to a steered wheel WR, WL through a is knuckle  8 . In this arrangement, movement of rack shaft  6  in the axial direction causes tie rods  7 ,  7  to move knuckles  8 ,  8 , and thereby turn steered wheels WR, WL. 
     Power cylinder  5  includes a cylinder tube  5   a , and a piston  5   b . Cylinder tube  5   a  is cylindrically formed. Rack shaft  6  passes through the inside of cylinder tube  5   a  in the axial direction of rack shaft  6 , and serves as a piston rod. Piston  5   b  is fitted and fixed to the periphery of rack shaft  6 . Piston  5   b  divides the internal space of cylinder tube  5   a  into first and second pressure chambers P 1 , P 2 . First pressure chamber P 1  is connected to a first fluid line  9   a  leading to a pump  11 . Second pressure chamber P 2  is connected to a second fluid line  9   b  leading to pump  11 . When supplied with hydraulic pressures from pump  11 , first and second pressure chambers P 1 , P 2  cause a thrust of rack shaft  6 , and thereby assist steering operation. 
     Motor-and-pump unit  10  includes pump  11 , a reservoir tank  12 , an electric motor  13 , and an electrical control unit (ECU)  14 , which are formed together as a unit, as shown in  FIGS. 1 and 2 . Pump  11  is a reversible type bidirectional pump for selectively supplying working fluid to first and second pressure chambers P 1 , P 2  of power cylinder  5 , and functions as a driven device of the power steering apparatus. Reservoir tank  12  stores working fluid that is circulated by pump  11 . Motor  13  is a brushless motor for driving the pump  11 . ECU  14  controls operation of motor  13 . Reservoir tank  12 , pump  11 , and motor  13  are arranged in this order from one axial end to another axial end of motor-and-pump unit  10 . ECU  14  is positioned on one side of motor  13 . Motor-and-pump unit  10  is a unit of pump  11  and a motor unit “MC” that is a unit of motor  13  and ECU  14 . 
     Pump  11  is of so-called an internal gear type, and includes a pump body  15 , a pump cover  16 , a cam ring  17 , a pumping section  18 , and a pump drive shaft  19 , as shown in  FIG. 2 . Pump body  15  is formed with a shaft insertion hole  15   a  that extends substantially through the center of pump body  15  in the z-axis direction in  FIG. 2 . Pump body  15  has a first axial end surface  15   b  that faces an outer surface  32   a  of an ECU cover  32 , and is in contact with the same. Pump cover  16  faces a second axial end surface  15   c  of pump body  15 , wherein cam ring  17  is disposed between pump body  15  and pump cover  16 . Cam ring  17  is annularly formed, and faces the second axial end surface  15   c  of pump body  15 , and is in contact with the same. Cam ring  17  is thus held and fixed between pump body  15  and pump cover  16 . Pumping section  18  is disposed radially inside the cam ring  17 , and arranged to rotate while sucking and discharging working fluid. Pump drive shaft  19  is inserted and rotatably supported in the shaft insertion hole  15   a  of pump body  15 , and connected to a motor drive shaft  23  through a shaft coupling  39  that is an Oldham&#39;s shaft coupling in this example. Pump drive shaft  19  functions as a driven shaft that is rotated by motor  13 . When rotated by motor  13 , pumping section  18  sucks working fluid from reservoir tank  12  through a suction port  16   a  of pump cover  16  that is formed to extend through pump cover  16  in the z-axis direction. The sucked working fluid is pressurized by rotation of pumping section  18 , and discharged to first and second pressure chambers P 1 , P 2  of power cylinder  5  through first and second fluid lines  9   a ,  9   b.    
     Pump body  15  is formed with a larger diameter portion  15   d  at an end portion of shaft insertion hole  15   a  closer to motor  13 . An annular seal S 4  is mounted and supported in an inside end portion of larger diameter portion  15   d . Seal S 4  serves to seal the clearance between the inside periphery of larger diameter portion  15   d  of pump body  15  and the outside periphery of a first axial end portion  19   a  of pump drive shaft  19 , and thereby prevent working fluid from leaking from the inside of pump  11  to motor  13 . The larger diameter portion  15   d  accommodates a negative z side end portion of shaft coupling  39 . At the larger diameter portion  15   d , a driven-side connecting portion  19   c  of pump drive shaft  19  at first axial end portion  19   a  which extends to the open end of larger diameter portion  15   d  is connected to shaft coupling  39 . 
     Pumping section  18  is fixed to the outside periphery of pump drive shaft  19  with a rotation stopper so that pumping section  18  cannot rotate relative to pump drive shaft  19 . Pumping section  18  includes an inner rotor  18   a  and an outer rotor  18   b . Inner rotor  18   a  has a plurality of external teeth at its outside periphery. Outer rotor  18   b  is disposed radially outside of inner rotor  18   a , and rotatably fitted to the inside periphery of cam ring  17 . Outer rotor  18   b  has a plurality of internal teeth meshing with the external teeth of inner rotor  18   a . The external teeth of inner rotor  18   a  mesh with the internal teeth of outer rotor  18   b  at a part of the circumference, defining a plurality of pump chambers therebetween which have different sizes and different shapes. 
     Pump drive shaft  19  is rotatably supported with respect to pump body  15  by first and second plane bearings PB 1 , PB 2  that are mounted in shaft insertion hole  15   a  of pump body  15 . First plane bearing PB 1  supports a central portion of pump drive shaft  19 . Second plane bearing PB 2  supports a second axial end portion  19   b  of pump drive shaft  19 . Pump drive shaft  19 , which extends close to the open end of larger diameter portion  15   d , includes at one axial end the driven-side connecting portion  19   c  that is adapted to be connected to the first axial end receiving portion  39   a  of shaft coupling  39 . The driven-side connecting portion  19   c  of pump drive shaft  19  is inserted into and coupled to first axial end receiving portion  39   a  of shaft coupling  39 . 
     Reservoir tank  12  is L-shaped as shown in  FIG. 2 . Reservoir tank  12  includes a first cylindrical portion  12   a , a second cylindrical portion  12   b , a tank cover  12   c , a cylindrical opening portion  12   d , and a cap  12   e . First cylindrical portion  12   a  is formed at one end, and has an opening directed in the positive z-axis direction. First cylindrical portion  12   a  is fixed to the periphery of the second axial end surface  15   c  of pump body  15 , entirely covering the pump cover  16  and cam ring  17 . The second cylindrical portion  12   b  of reservoir tank  12  has an opening directed in the positive x-axis direction. The opening of second cylindrical portion  12   b  is closed by tank cover  12   c  that is fixed to second cylindrical portion  12   b . The tank cover  12   c  is formed with cylindrical opening portion  12   d  at the center through which working fluid is supplied from outside. The cylindrical opening portion  12   d  projects toward outside from the flat portion of tank cover  12   c . The cylindrical opening portion  12   d  is closed by cap  12   e  that is detachable. 
     Motor  13  is a three-phase synchronous surface-mounted magnet type motor. As shown in  FIGS. 2 and 3 , motor  13  includes a motor body “MB”, and a resolver  26 . Motor body MB includes a motor drive shaft  23 , a rotor  24 , and a stator  25 . Motor drive shaft  23  has an axial end portion rotatably supported by a first ball bearing BB 1  with respect to housing  20 . First ball bearing BB 1  is retained in a cylindrical portion  28  of housing  20 . Rotor  24  is press-fitted to the outside periphery of motor drive shaft  23 , and further fixed to motor drive shaft  23  with a rotation stopper such as a key for preventing relative rotation of rotor  24 . Stator  25  is cylindrically formed, and disposed radially outside of rotor  24  with a radial clearance. Resolver  26  is disposed at the periphery of the axial end portion of motor drive shaft  23 , serving as a rotation sensor. 
     Motor  13  is controlled by ECU  14  on the basis of sensing data of a torque sensor “TS”, and data about vehicle speed. Torque sensor TS is disposed at the periphery of input shaft  2  or output shaft  3 , for sensing a steering torque inputted to input shaft  2 , as shown in  FIG. 1 . When an operator operates the steering wheel SW, the direction of rotation and output torque of motor  13  are switched according to the operation (direction, and steering torque), to drive the pump  11  so that the power cylinder  5  produces a suitable assist steering effort. 
     Housing  20  is formed integrally of a die-casting aluminum, and composed of a motor housing section  21 , and an ECU housing section  31 . Motor  13  is mounted in motor housing section  21 . ECU  14  is mounted in ECU housing section  31 . The integral formation of motor housing section  21  and ECU housing section  31  serves to simplify the structure, and eliminate the necessity of connection between motor housing section  21  and ECU housing section  31 . This enhances the efficiency of assembling operation, and thereby enhances the productivity. 
     As shown in  FIG. 3 , the motor housing section  21  of housing  20  is formed so that the diameter of motor housing section  21  contracts stepwise as followed in the negative z-axis direction. Motor housing section  21  includes a motor body accommodation portion  27 , a cylindrical portion  28 , and a stepped wall portion  29 . Motor body accommodation portion  27  is formed and located on the positive z side, having a positive z side opening, and having a larger diameter. Cylindrical portion  28  is formed and located on the negative z-axis side, having a negative z side opening, and having a smaller diameter. Cylindrical portion  28  extends through the ECU housing section  31 . Stepped wall portion  29  is formed between motor body accommodation portion  27  and cylindrical portion  28 . Cylindrical portion  28  and stepped wall portion  29  constitute a division wall “W” that serves to separate motor housing section  21  and ECU housing section  31  from one another. 
     One axial end portion (negative z side end portion in  FIG. 3 ) of motor body MB is accommodated in motor body accommodation portion  27  of motor housing section  21  of housing  20 . The other axial end portion of motor body MB projects from motor body accommodation portion  27  in the positive z-axis direction. The other axial end portion is accommodated in motor cover  22  that closes the axial end opening of motor body accommodation portion  27 . Namely, motor body MB extends both in motor housing section  21  and in motor cover  22  in the z-axis direction. 
     Motor cover  22  is formed by folding a thin plate into a hollow-cylindrical shape having a closed axial end. Motor cover  22  is formed with a flange  22   a  at the periphery of the open axial end, through which motor cover  22  is fixed to the open axial end surface of motor body accommodation portion  27  with a plurality of first mounting bolts B 1 . The closed axial end or roof  22   b  of motor cover  22  is formed with a second bearing accommodation portion  22   c  substantially at its center. Second bearing accommodation portion  22   c  accommodates and supports a second ball bearing BB 2  by which the axial end portion of motor drive shaft  23  is rotatably supported with respect to motor cover  22 . 
     Motor drive shaft  23  includes a medium diameter portion  23   a  at one axial end portion, as shown in  FIG. 3 . The medium diameter portion  23   a  is rotatably supported with respect to housing  20  by a first ball bearing BB 1 . First ball bearing BB 1  is mounted in a first bearing accommodation portion  28   a  of cylindrical portion  28  that is formed substantially at the center of the inside periphery of cylindrical portion  28  in the axial direction. Motor drive shaft  23  includes a smaller diameter portion  23   b  at the other axial end portion. The smaller diameter portion  23   b  is rotatably supported with respect to housing  20  by second ball bearing BB 2  that is mounted in motor cover  22 . The length of motor drive shaft  23  is set so that the motor drive shaft  23  extends almost over the entire length of cylindrical portion  28  in the axial direction, and reaches the neighborhood of the negative z side end of cylindrical portion  28 . Accordingly, both of motor drive shaft  23  and cylindrical portion  28  extend through the ECU housing section  31  in the axial direction. The negative z side end portion of motor drive shaft  23  is formed with a motor-side connecting portion  23   c  that is flatly formed in a plane containing the axis of motor drive shaft  23 , and adapted to be connected to the second axial end receiving portion  39   b  of shaft coupling  39 . The motor-side connecting portion  23   c  of motor drive shaft  23  is inserted into and connected to the second axial end receiving portion  39   b  of shaft coupling  39 . 
     Rotor  24  includes a rotor core  24   a , a plurality of magnets  24   b , and a magnet cover  24   c . Rotor core  24   a  is fixed to the periphery of the positive z side end portion of larger diameter portion  23   d  of motor drive shaft  23 . Magnets  24   b  are fixed to the periphery of rotor core  24   a  by bonding. Magnet cover  24   c  is disposed radially outside of the peripheries of magnets  24   b.    
     Stator  25  includes a stator core  25   a , and a stator coil  25   b  attached to stator core  25   a . Stator core  25   a  is press-fitted and fixed between motor cover  22  and the motor body accommodation portion  27  of motor housing section  21 . One end portion of stator coil  25   b  is connected to a first electric terminal T 1 , and electrically connected to a control board  30  through the first electric terminal T 1 . First electric terminal T 1  extends from stator  25  in the negative z-axis direction, and extends through a first terminal insertion hole  29   a  that is formed in the stepped wall portion  29  of motor housing section  21 , and faces and reaches the ECU housing section  31 . 
     Resolver  26  is fixed to the periphery of a negative z side end portion of larger diameter portion  23   d  of motor drive shaft  23  with a rotation stopper. Resolver  26  includes a resolver rotor  26   a , and a resolver stator  26   b . Resolver rotor  26   a  includes a plurality of rotary magnetic poles, the number of which is equal to the number of magnetic poles of rotor  24 . Resolver stator  26   b  is disposed radially outside of the resolver rotor  26   a  with a radial clearance, and press-fitted to a resolver accommodation portion  28   b  that is formed as a recess in a positive z side end portion of cylindrical portion  28 . Resolver stator  26   b  is formed with a plurality of magnetic poles, over each of which a sensor coil  26   c  is wound. One end of each sensor coil  26   c  is connected to a second electric terminal T 2 , and electrically connected to control board  30  through the second electric terminal T 2 . The rotation angle of motor drive shaft  23  is measured by sensing with resolver stator  26   b  the position of each rotary magnetic pole of resolver rotor  26   a , wherein resolver rotor  26   a  rotates in synchronization with motor drive shaft  23 . Second electric terminal T 2  extends from resolver stator  26   b  in the negative z-axis direction, and extends through a second terminal insertion hole  29   b  that is formed in the stepped wall portion  29  of motor housing section  21 , and faces and reaches the ECU housing section  31 , similar to first electric terminal T 1 . 
     ECU  14  includes control board  30 , a resolver signal sensing circuit section  33 , a calibration circuit section  34 , a memory circuit section  35 , a motor drive circuit section (PWM motor drive circuit section)  36 , and an inverter  37 , as shown in  FIG. 5 . Control board  30  is mounted in ECU housing section  31 . Resolver signal sensing circuit section  33  obtains an output signal from resolver  26 . Calibration circuit section  34  determines a correction value on the basis of the output signal from resolver signal sensing circuit section  33 , for calibration for canceling errors in the output signal from resolver  26  that is received by resolver signal sensing circuit section  33 . Memory circuit section  35  is built in calibration circuit section  34 , and configured to memorize the correction value that is determined by calibration circuit section  34 . Motor drive circuit section  36  drives motor  13  or controls operation of motor  13  according to the steering torque measured by torque sensor TS, using the correction value stored in memory circuit section  35 . Inverter  37  converts the magnetizing current supplied from motor drive circuit section  36 . 
     Control board  30  is electrically connected to stator coil  25   b  through the first electric terminal T 1  that extends through the first terminal insertion hole  29   a  into ECU housing section  31 . Control board  30  is electrically connected to sensor coil  26   c  through the second electric terminal T 2  that extends through the second terminal insertion hole  29   b  into ECU housing section  31 . Namely, motor  13  and ECU  14  are electrically connected to one another within housing  20 , constituting the motor unit MC. Accordingly, motor unit MC can be solely operated, without being connected to pump  11  and mounted to power steering apparatus  1 . Therefore, motor unit MC can be calibrated when motor unit MC is not connected to other components. 
     Control board  30  is arranged close to torque sensor TS, and directly connected to torque sensor TS through a harness. This serves to simplify the structure, and make the wiring efficient. 
     ECU housing section  31  includes a board accommodation portion  38 , and ECU cover  32 , as shown in  FIG. 3 . Board accommodation portion  38  accommodates the control board  30 , and has a wide opening through which the control board  30  can be inserted from the negative z side into the negative z side portion of housing  20 . ECU cover  32  closes the opening of board accommodation portion  38 . 
     Cylindrical portion  28  extends from a roof  38   a  of board accommodation portion  38  through the board accommodation portion  38 , and has a tip  28   c  that projects out of ECU cover  32  through a through hole  32   c  that is formed in a bottom wall portion  32   b  of ECU cover  32 . The tip  28   c  of cylindrical portion  28  is adapted to be fitted in the end portion of larger diameter portion  15   d  of shaft insertion hole  15   a  of pump body  15 . This construction makes it possible to suitably position the pump body  15  with respect to motor housing section  21  of housing  20  in the radial directions. 
     ECU cover  32  is disposed between the open end surface  38   b  of board accommodation portion  38  and the first axial end surface  15   b  of pump body  15 . ECU cover  32  is attached to the open end surface  38   b  of board accommodation portion  38  with a plurality of second mounting bolts B 2 , independently of attachment of pump body  15 . Namely, the opening of board accommodation portion  38  can be closed under condition that the pump body  15  is not attached to motor housing section  21 . 
     The open end surface  38   b  of board accommodation portion  38  includes a groove in which a seal S 1  in the form of an O-ring is fitted. Seal S 1  serves to seal the boundary between the open end surface  38   b  of board accommodation portion  38  and the contact surface  32   d  of ECU cover  32 , and thereby serves to prevent dust or the like from entering the board accommodation portion  38  from outside through the boundary between the open end surface  38   b  and contact surface  32   d . Similarly, the periphery of the tip  28   c  of cylindrical portion  28  includes a groove in which a seal S 2  in the form of an O-ring is fitted. Seal S 2  serves to seal the boundary between the inside periphery of through hole  32   c  and the periphery of the tip  28   c  of cylindrical portion  28 , and thereby serves to prevent dust or the like from entering the board accommodation portion  38  through the boundary between the through hole  32   c  and tip  28   c  from outside or prevent working fluid from entering the board accommodation portion  38  from pump  11 . The inside periphery of the tip  28   c  of cylindrical portion  28  is formed with a seal-holding portion  28   d  on the negative z side of first bearing accommodation portion  28   a . An annular seal S 3  is fitted in seal-holding portion  28   d . Seal S 3  serves to seal the boundary between the inside periphery of tip  28   c  of cylindrical portion  28  and the outside periphery of medium diameter portion  23   a  of motor drive shaft  23 , and thereby prevent working fluid from entering the resolver accommodation portion  28   b  from pump  11 . 
     In this way, seals S 1 , S 2 , S 3  serve to prevent foreign matter from entering the board accommodation portion  38  from outside, even when motor unit MC is isolated from other components, i.e. even when pump body  15  is not yet attached to housing  20 . This is advantageous, when calibration is performed for motor unit MC without pump  11 . The entrance of foreign matter is prevented, also when motor drive shaft  23  is connected to pump drive shaft  19 . Namely, the entrance of foreign matter is prevented, until the assembly of motor-and-pump unit  10  is completed after motor unit MC is assembled. 
     The following describes a method of calibration for resolver  26  according to this embodiment with reference to  FIGS. 6 to 8 . 
     The calibration of resolver  26  is so-called an electrical calibration, in which a correction value is determined based on errors in the sensing signal of resolver  26 , and then memorized in calibration circuit section  34 . The calibration makes it possible to accurately control the rotation angle of the motor  13  by supplying a magnetizing current in consideration of the correction value. 
       FIG. 6  schematically shows a system for calibration of resolver  26 . In this system, motor unit MC is connected to a dummy torque sensor “DTS” that is connected to a fail-safe valve “FV”. Dummy torque sensor DTS is further connected to a personal computer “PC” through a CAN card “CC”. Motor unit MC and dummy torque sensor DTS are connected to a battery “BT”. Dummy torque sensor DTS and fail-safe valve FV are dummies for operating the system. Specifically, dummy torque sensor DTS and fail-safe valve FV allow ECU  14  of motor unit MC to virtually recognize the connection of torque sensor TS and a fail-safe valve not shown, where the fail-safe valve is disposed in the hydraulic circuit related to pump  11 . Naturally, dummy torque sensor DTS and fail-safe valve FV may be different from actual torque sensor and fail-safe valve. Alternatively, ECU  14  may be provided with a program for simulating the connection of the torque sensor TS and the fail-safe valve, wherein the dummy torque sensor DTS and fail-safe valve FV are omitted. 
     For preparation for the calibration, motor  13  and ECU  14  are assembled to form the motor unit MC, as shown in  FIG. 3 . Specifically, motor body MB, resolver  26  and motor cover  22  are attached to motor housing section  21 , and control board  30  is mounted in ECU housing section  31 . Moreover, stator coil  25   b  and sensor coil  26   c  are electrically connected to control board  30 . Then, board accommodation portion  38  is closed with ECU cover  32 . Pump  11  is not yet attached to motor unit MC. 
       FIG. 7  shows a process of calibration of resolver  26 . The process starts at Step S 11  where personal computer PC sends a signal to ECU  14  of motor unit MC, where the signal requests selection of a resolver calibration mode. The process proceeds to Step S 12  where an ignition switch is turned on. Then, the process proceeds to Step S 13  where personal computer PC sends a signal to ECU  14 , where the signal requests execution of calibration. 
     Upon receipt of the calibration execution signal, ECU  14  performs a sub-process shown in  FIG. 8 . ECU  14  supplies a magnetizing current to rotor  24  by supplying direct current to motor terminals so that rotor  24  rotates in a clockwise direction by a predetermined angle with respect to stator coil  25   b , at steps S 101 . At step S 102 , ECU  14  measures with resolver  26  the rotation angle of rotor  24  with respect to stator coil  25   b . At Step S 103 , ECU  14  determines whether or not the measurement is normally performed. When the answer to Step S 103  is negative, then ECU  14  returns to Step S 101 , and repeats the operations of steps S 101  and S 102 . On the other hand, when the answer to Step S 103  is affirmative, then ECU  14  terminates the measurement for the clockwise movement, and proceeds to Step S 104  for similar measurement for counterclockwise movement. At Step S 104 , ECU  14  supplies a magnetizing current to rotor  24  by supplying direct current to motor terminals so that rotor  24  rotates in a counterclockwise direction by a predetermined angle with respect to stator coil  25   b . At step S 105 , ECU  14  measures with resolver  26  the rotation angle of rotor  24  with respect to stator coil  25   b . At Step S 106 , ECU  14  determines whether or not the measurement is normally performed. When the answer to Step S 106  is negative, then ECU  14  returns to Step S 104 , and repeats the operations of steps S 104  and S 105 . On the other hand, when the answer to Step S 106  is affirmative, then ECU  14  terminates the measurement for the counterclockwise movement, and proceeds to Step S 107 . At Step S 107 , calibration circuit section  34  calculates the correction value according to errors in the sensing signal of resolver  26 , based on the result of measurement of the rotation angle of rotor  24  in the clockwise direction and counterclockwise direction. Then, at Step S 108 , memory circuit section  35  memorizes the calculated correction value, and then exits from the process. 
     After the sub-process shown in  FIG. 8 , at Step S 14  in the flow chart of  FIG. 7 , personal computer PC determines whether or not the correction value determined by calibration circuit section  34  is in an allowable range, such as a range from 814 to 894 [digit]. When the answer to Step S 14  is affirmative, then the process proceeds to step S 15  where it is determined that the motor unit MC is a normal one, and the process of calibration is terminated. After this process, this motor unit MC is connected to pump  11 . On the other hand, when the answer to Step S 14  is negative, then the process proceeds to Step S 16  where it is determined that the motor unit MC is an abnormal one, and resolver  26  is replaced with another. After the replacement, the process of calibration is performed again. 
     For the normal motor unit MC for which the process of calibration is normally completed, the motor-side connecting portion  23   c  of motor drive shaft  23  is connected to the driven-side connecting portion  19   c  of pump drive shaft  19  through the shaft coupling  39  so that torque can be transmitted from motor drive shaft  23  to pump drive shaft  19 . Then, pump body  15  is fixed to housing  20 , so that the motor  13  of motor unit MC is coupled to pump  11 , thus completing the motor-and-pump unit  10 . Then, motor-and-pump unit  10  is mounted in power steering apparatus  1 , thus completing the power steering apparatus  1 . 
     The feature that the motor unit MC is composed of motor  13  and ECU  14  that are electrically connected to one another, makes it possible to complete calibration of the resolver  26  of motor unit MC so that the correction value for the signal of resolver  26  is memorized in memory circuit section  35  of ECU  14 , before motor unit MC is connected to pump  11  or mounted to power steering apparatus  1 , i.e. before shipment of motor unit MC, in contrast to conventional cases where it is necessary to perform calibration after a power steering apparatus is mounted to a vehicle in a vehicle assembly factory. This serves to reduce the work load in the vehicle assembly factory, and thereby enhance the productivity of vehicle production. 
     If the calibration is performed when motor  13  is connected to pump  11 , it may be impossible to obtain an accurate correction value, because there is a difference in friction between normal rotation and reverse rotation of pump  11 , and the difference adversely affects the calibration. According to this embodiment, the feature that calibration is performed for the motor unit MC before motor unit MC is connected to pump  11  so that motor  13  is connected to pump  11 , serves to prevent that the torque of motor  13  is canceled by friction due to operation of pump  11 . This makes it possible to obtain an accurate correction value. 
     The feature that the board accommodation portion  38  in which control board  30  is mounted is closed by ECU cover  32  even when motor unit MC is not connected to pump  11 , serves to prevent foreign matter, such as dust, from entering the board accommodation portion  38  when the calibration is performed under condition that motor unit MC is not connected to pump  11 . This eliminates troubles, such as short circuit, which may be caused by the entrance of foreign matter into board accommodation portion  38 . 
     The feature that the resolver  26  is constructed similar to motor  13 , allows that management for preventing the entrance of foreign matter such as dust and oil (referred to as contamination management) for resolver  26  may be in a lower level, similar to that for motor  13 , than that for control board  30 . Both of resolver  26  and motor  13  can be similarly dealt with, because resolver  26  is disposed in motor housing section  21  together with motor  13 , and motor housing section  21  and board accommodation portion  38  are separated from one another by division wall W. In this way, it is unnecessary to set the level of contamination management for resolver  26  high. 
     The feature that motor drive shaft  23  is positioned by fitting the tip  28   c  of cylindrical portion  28  of housing  20  to the opening end  15   e  of larger diameter portion  15   d  of shaft insertion hole  15   a  of pump body  15 , serves to accurately position the motor housing section  21  and pump body  15  with respect to one another in radial directions, and thereby accurately position the motor drive shaft  23  and pump drive shaft  19  with respect to one another, because motor drive shaft  23  is supported with respect to motor housing section  21  by first ball bearing BB 1  at the inside periphery of cylindrical portion  28 , and pump drive shaft  19  is supported with respect to pump body  15  by first and second plane bearings PB 1 , PB 2  at the inside periphery of shaft insertion hole  15   a.    
     The provision of seal S 2  at the boundary between cylindrical portion  28  and through hole  32   c , serves to lower the risk of entrance of foreign matter in board accommodation portion  38 , for the positioning structure described above. 
     The construction that board accommodation portion  38  is located at one axial end of motor body MB, cylindrical portion  28  passes through the board accommodation portion  38 , and motor drive shaft  23  passes through the board accommodation portion  38 , serves to improve the layout about electrical connection between motor body MB and control board  30 . 
       FIGS. 9 and 10  schematically show a power steering apparatus according to a second embodiment of the present invention. The power steering apparatus is adapted to an electric power steering system that is configured to assist an operator in steering operation directly based on the output torque of the motor. The basic construction, such as the construction of motor unit MC, is common between the first embodiment and second embodiment, wherein the same reference symbols are given to common components between the first embodiment and second embodiment. 
     As shown in  FIG. 9 , power steering apparatus  1  includes input shaft  2 , output shaft  3 , rack-and-pinion mechanism  4 , and a motor-and-gear unit  40 . Input shaft  2  has one axial end coupled to steering wheel SW so that the input shaft  2  and steering wheel SW rotate as a solid unit. Input shaft  2  is rotated by a steering torque that is inputted from an operator to steering wheel SW. Output shaft  3  has one axial end linked to steered wheels WR, WL through the rack-and-pinion mechanism  4 , and has another axial end connected to input shaft  2  through a torsion bar not shown. Relative rotation between input shaft  2  and output shaft  3  is permitted by torsion of the torsion bar. Torque sensor TS is disposed at the periphery of input shaft  2  or output shaft  3 , for sensing the steering torque based on the relative rotation between input shaft  2  and output shaft  3 . Motor-and-gear unit  40  includes reducer  41 , motor  13 , and ECU  14 , which are formed together as a unit, as shown in  FIGS. 9 and 10 . Namely, motor-and-gear unit  40  is a unit of reducer  41  and motor unit MC that is a unit of motor  13  and ECU  14 . Motor  13  is controlled by ECU  14  on the basis of sensing data of torque sensor TS, and data about vehicle speed, for producing an assist steering torque. Reducer  41  transmits the output torque of motor  13  to output shaft  3 , functioning as a driven device of the power steering apparatus. When an operator operates the steering wheel SW, the direction of rotation and output torque of motor  13  are switched according to the operation (direction, and steering torque), so that the reducer  41  outputs a suitable assist steering effort. 
     As shown in  FIG. 10 , reducer  41  includes a gear housing  42  and a worm gearing “WG”. Gear housing  42  serves also as a housing for output shaft  3 . Worm gearing WG is mounted in gear housing  42 , including a worm shaft  43 , and a worm wheel  44 . Worm shaft  43  has an axial end portion (positive z side end portion) screwed as a driven shaft to an axial end portion of motor drive shaft  23 , and includes a tooth portion  43   a  substantially at the center in the axial direction. Worm wheel  44  is fixed to the periphery of output shaft  3 , and includes a tooth portion  44   a  at its periphery, wherein tooth portion  44   a  meshes with tooth portion  43   a  of worm shaft  43 . 
     Worm shaft  43  is mounted in a shaft accommodation portion  45  of gear housing  42  that is formed to extend along the axis of motor drive shaft  23 . Worm wheel  44  is disposed in a wheel accommodation portion  46  of gear housing  42  that is formed to cross the shaft accommodation portion  45  and includes a portion facing the shaft accommodation portion  45 . 
     Worm shaft  43  includes an axial end portion rotatably supported by a third ball bearing BB 3  that is disposed in a larger diameter portion of shaft accommodation portion  45  at the positive z side end portion, and another axial end rotatably supported by a fourth ball bearing BB 4  that is disposed at the other axial end of shaft accommodation portion  45 . Worm shaft  43  is formed with a driven-side connecting portion  43   b  in the form of a female thread at one axial end portion of worm shaft  43 , wherein the driven-side connecting portion  43   b  engages with a driving-side connecting portion  23   e  of motor drive shaft  23  that is formed as a male thread at the periphery of the axial end portion of motor drive shaft  23 . Driven-side connecting portion  43   b  and driving-side connecting portion  23   e  are thus connected to one another. 
     The open end portion  45   b  of larger diameter portion  45   a  of shaft accommodation portion  45  is adapted to be fitted to the tip  28   c  of cylindrical portion  28  of motor housing section  21 . Motor housing section  21  and gear housing  42  are suitably positioned with respect to one another in radial directions by fitting the tip  28   c  of cylindrical portion  28  into the open end portion  45   b  of larger diameter portion  45   a  of shaft accommodation portion  45 . The gear housing  42  is fixed to the outer surface  32   a  of ECU cover  32  with a plurality of third mounting bolts B 3 . 
     As in the first embodiment, the calibration according to the second embodiment is performed when board accommodation portion  38  is dosed by ECU cover  32 , but motor unit MC is not connected to reducer  41 . This produces advantageous effects as described for the first embodiment. The effects are more significant in this embodiment, to obtain an accurate correction value for the rotation angle of motor  13 . This is because for the worm gearing WG of reducer  41 , the difference in friction between the normal direction and reverse direction is relatively large in general, but this difference does not affect the calibration and the correction value. 
       FIG. 11  shows a modification of the second embodiment in which motor-and-gear unit  40  is coupled to input shaft  2  to form a column assist type electric power steering system. This modification is advantageous similar to the second embodiment. 
     The present embodiments may be modified as follows. The shape of housing  20 , i.e. the shapes of motor housing section  21  and ECU housing section  31  may be suitably modified according to specifications of motor unit MC and specifications of the power steering system to which the power steering apparatus is adapted. Pump  11  may be of any other type reversible pump. Reducer  41  is not limited to worm gearings, but may be of any other type reducer. 
     In the present embodiments, motor housing section  21  and ECU housing section  31  of housing  20  are formed integrally with one another. However, motor housing section  21  and ECU housing section  31  may be formed separately and fixed to one another with a fixing means such as a mounting bolt, if motor housing section  21  and ECU housing section  31  are positioned with respect to one another as in the present embodiments. 
     In the first embodiment, the motor-side connecting portion  23   c  of motor drive shaft  23  and the driven-side connecting portion  19   c  of pump drive shaft  19  are coupled by shaft coupling  39 , wherein motor drive shaft  23  and pump drive shaft  19  can move with respect to one another in the axial direction. In the second embodiment, the motor-side connecting portion  23   e  of motor drive shaft  23  and the driven-side connecting portion  43   a  of worm shaft  43  are screwed to one another so that motor drive shaft  23  and worm shaft  43  are fixed to one another in the axial direction. The coupling is not so limited, if torque is suitably transmitted from motor drive shaft  23  to pump drive shaft  19  or to worm shaft  43 . 
     The position of the connection at shaft coupling  39  between motor drive shaft  23  and pump drive shaft  19  or between motor drive shaft  23  and worm shaft  43  is not limited to the boundary between housing  20  and pump body  15  or between housing  20  and gear housing  42 , but may be displaced toward motor housing section  21 , or displaced toward pump body  15  or worm shaft  43 . In such cases, construction is possible in which pump drive shaft  19  or worm shaft  43  extends through the cylindrical portion  28  in board accommodation portion  38 . 
     The following summarizes features of the embodiments, and produced advantageous effects. 
     &lt;1&gt; A power steering apparatus ( 1 ) comprises: a main housing ( 20 ) including: a motor housing section ( 21 ); and an electrical control unit housing section ( 31 ) coupled to the motor housing section ( 21 ); a driven-device housing ( 15 ) coupled to the motor housing section ( 21 ); a brushless motor ( 13 ) including: a drive shaft ( 23 ) housed in the motor housing section ( 21 ), the drive shaft ( 23 ) including a motor-side connecting portion ( 23   c ) at an axial end portion of the drive shaft ( 23 ); a rotor ( 24 ) coupled to the drive shaft ( 23 ); a coil ( 25   b ) disposed around the rotor ( 24 ), and adapted to be energized to generate a magnetic field; and a rotation sensor ( 26 ) arranged to measure a rotation angle of the rotor ( 24 ); an electrical control unit ( 14 ) housed in the electrical control unit housing section ( 31 ), the electrical control unit ( 14 ) including: a memory circuit section ( 35 ) configured to memorize a correction value for correction to a measured value of the rotation angle obtained by the rotation sensor ( 26 ); and a motor drive circuit section ( 36 ) configured to drive the brushless motor ( 13 ) on a basis of a corrected measured value of the rotation angle that is obtained by correcting the measured value with the correction value; a first electrical wiring (T 1 ) connecting the coil ( 25   b ) and the electrical control unit ( 14 ) to one another; a second electrical wiring (T 2 ) connecting the rotation sensor ( 26 ) and the electrical control unit ( 14 ) to one another; and a driven device ( 11 ,  41 ) including: a driven shaft ( 19 ) housed in the driven-device housing ( 15 ), and adapted to receive torque from the drive shaft ( 23 ), wherein the driven shaft ( 19 ) includes at an axial end portion of the driven shaft ( 19 ) a driven-side connecting portion ( 19   c ) connected to the motor-side connecting portion ( 23   c ) of the drive shaft ( 23 ); and an output section ( 11 ,  5 ;  41 ) adapted to transmit the torque as an assist steering effort to steered wheels (WR, WL); wherein the correction value is set on a basis of a measured value of the rotation angle that is obtained by the rotation sensor ( 26 ) when the rotor ( 24 ) is rotated to a predetermined reference angular position by energization of the coil ( 25   b ), under condition that the coil ( 25   b ) and the electrical control unit ( 14 ) are connected to one another by the first electrical wiring (T 1 ), and the rotation sensor ( 26 ) and the electrical control unit ( 14 ) are connected to one another by the second electrical wiring (T 2 ). This construction makes it possible to complete calibration of the rotation sensor so that the correction value is memorized in the memory circuit section of the electrical control unit, before shipment, in contrast to conventional cases where it is necessary to perform calibration in a vehicle assembly factory. This serves to reduce the work load in the vehicle assembly factory, and thereby enhance the productivity of vehicle production. 
     &lt;2&gt; In the power steering apparatus according to item &lt;1&gt;, the correction value is set under condition that the driven device ( 11 ,  41 ) is separated from the brushless motor ( 13 ), the coil ( 25   b ) and the electrical control unit ( 14 ) are connected to one another by the first electrical wiring (T 1 ), and the rotation sensor ( 26 ) and the electrical control unit ( 14 ) are connected to one another by the second electrical wiring (T 2 ). The feature that the calibration is performed before the driven device is coupled to the brushless motor, serves to obtain an accurate correction value, because the output torque of the motor generated by energization of the coil is not canceled by friction, etc. in the driven device. 
     &lt;3&gt; In the power steering apparatus according to item &lt;2&gt;: the electrical control unit housing section ( 31 ) includes: a board accommodation portion ( 38 ) housing the electrical control unit ( 14 ); and an opening ( 38   b ) through which the electrical control unit ( 14 ) is inserted into the board accommodation portion ( 38 ); and the power steering apparatus further includes a cover ( 32 ) provided separately from the driven-device housing ( 15 ), the cover ( 32 ) closing the opening ( 38   b ). The cover serves to prevent foreign matter, such as dust or oil, from entering the board accommodation portion, even when the calibration is performed under condition that the driven-device housing is not connected to the motor housing section. This eliminates troubles, such as short circuit, which may be caused by the entrance of foreign matter into the board accommodation portion. 
     &lt;4&gt; In the power steering apparatus according to item &lt;3&gt;: the electrical control unit housing section ( 31 ) is arranged between the motor housing section ( 21 ) and the driven-device housing ( 15 ); and the drive shaft ( 23 ) and the driven shaft ( 19 ) are connected to form a shaft member extending through the board accommodation portion ( 38 ). This feature serves to improve the layout about electrical connection between the brush less motor and the electrical control unit, because the board accommodation portion of the electrical control unit housing section is arranged at the axial end of the brushless motor. 
     &lt;5&gt; In the power steering apparatus according to item &lt;4&gt;: one of the motor housing section ( 21 ) and the electrical control unit housing section ( 31 ) is provided with a division wall (W) that separates the motor housing section ( 21 ) and the board accommodation portion ( 38 ) from one another; and the rotation sensor ( 26 ) is disposed in the motor housing section ( 21 ). The feature allows that management for preventing the entrance of foreign matter such as dust and oil (contamination management) for the rotation sensor may be in a lower level, similar to that for the motor, than that for the electrical control unit. Both of the rotation sensor and the motor can be similarly dealt with, because the rotation sensor is disposed in the motor housing section together with the motor, and the motor housing section and the board accommodation portion are separated from one another by the division wall. In this way, it is unnecessary to set the level of contamination management for the rotation sensor high. 
     &lt;6&gt; In the power steering apparatus according to item &lt;4&gt;: the cover ( 32 ) is formed with a through hole ( 32   c ) through which the shaft member ( 23 ,  19 ) extends; the motor housing section ( 21 ), the electrical control unit housing section ( 31 ), and the cover ( 32 ) are formed with a cylindrical portion ( 28 ) surrounding the shaft member ( 23 ,  19 ); and a seal (S 2 ) is disposed between the through hole ( 32   c ) and the cylindrical portion ( 28 ). This feature serves to prevent foreign matter, such as dust or oil, from entering the board accommodation portion, even when the calibration is performed under condition that the driven-device housing is not connected to the motor housing section. 
     &lt;7&gt; In the power steering apparatus according to item &lt;6&gt;, the motor housing section ( 21 ) and the electrical control unit housing section ( 31 ) are formed integrally with one another by molding. This makes it unnecessary to connect the motor housing section and the ECU housing section, and thereby improves the assembling operation. 
     &lt;8&gt; In the power steering apparatus according to item &lt;3&gt;: the power steering apparatus further includes a bearing (BB 2 ) disposed in the motor housing section ( 21 ), wherein the drive shaft ( 23 ) is rotatably supported by the bearing (BB 2 ); and the driven-device housing ( 15 ) is positioned with respect to the motor housing section ( 21 ) in a radial direction of the driven shaft ( 19 ). This feature serves to accurately position the drive shaft and the driven shaft with respect to one another. 
     &lt;9&gt; In the power steering apparatus according to item &lt;8&gt;, the brushless motor ( 13 ) is arranged to rotate in normal and reverse directions so as to apply assist steering effort to the steered wheels (WR, WL) in left and right steering directions. This feature serves to obtain an accurate correction value while eliminating adverse effects of friction in the driven device, even when the friction applied to the driven device is different between the normal direction and the reverse direction. 
     &lt;10&gt; In the power steering apparatus according to item &lt;9&gt;, the driven device ( 11 ,  41 ) is a worm gearing (WG). This feature serves to obtain an accurate correction value while eliminating adverse effects of friction in the driven device, even when the friction applied to the driven device is different between the normal direction and the reverse direction, although the worm gear is generally different in friction between the normal direction and the reverse direction. 
     &lt;11&gt; A motor apparatus ( 10 ,  40 ) comprises: a main housing ( 20 ) including: a motor housing section ( 21 ); and an electrical control unit housing section ( 31 ) coupled to the motor housing section ( 21 ); a driven-device housing ( 15 ) coupled to the motor housing section ( 21 ); a brushless motor ( 13 ) including: a drive shaft ( 23 ) housed in the motor housing section ( 21 ), the drive shaft ( 23 ) including a motor-side connecting portion ( 23   c ) at an axial end portion of the drive shaft ( 23 ); a rotor ( 24 ) coupled to the drive shaft ( 23 ); a coil ( 25   b ) disposed around the rotor ( 24 ), and adapted to be energized to generate a magnetic field; and a rotation sensor ( 26 ) arranged to measure a rotation angle of the rotor ( 24 ); an electrical control unit ( 14 ) housed in the electrical control unit housing section ( 31 ), the electrical control unit ( 14 ) including: a memory circuit section ( 35 ) configured to memorize a correction value for correction to a measured value of the rotation angle obtained by the rotation sensor ( 26 ); and a motor drive circuit section ( 36 ) configured to drive the brushless motor ( 13 ) on a basis of a corrected measured value of the rotation angle that is obtained by correcting the measured value with the correction value; a first electrical wiring (T 1 ) connecting the coil ( 25   b ) and the electrical control unit ( 14 ) to one another; a second electrical wiring (T 2 ) connecting the rotation sensor ( 26 ) and the electrical control unit ( 14 ) to one another; and a driven device ( 11 ,  41 ) including: a driven shaft ( 19 ) housed in the driven-device housing ( 15 ), and adapted to receive torque from the drive shaft ( 23 ), wherein the driven shaft ( 19 ) includes at an axial end portion of the driven shaft ( 19 ) a driven-side connecting portion ( 19   c ) connected to the motor-side connecting portion ( 23   c ) of the drive shaft ( 23 ); and an output section ( 11 ,  5 ;  41 ) adapted to output a force based on the torque; wherein the correction value is set on a basis of a measured value of the rotation angle that is obtained by the rotation sensor ( 26 ) when the rotor ( 24 ) is rotated to a predetermined reference angular position by energization of the coil ( 25   b ), under condition that the coil ( 25   b ) and the electrical control unit ( 14 ) are connected to one another by the first electrical wiring (T 1 ), and the rotation sensor ( 26 ) and the electrical control unit ( 14 ) are connected to one another by the second electrical wiring (T 2 ). This construction makes it possible to complete calibration of the rotation sensor so that the correction value is memorized in the memory circuit section of the electrical control unit, before shipment, in contrast to conventional cases where it is necessary to perform calibration in a process after shipment. This serves to reduce the work load in the process. 
     &lt;12&gt; In the motor apparatus according to item &lt;11&gt;, the correction value is set under condition that the driven device ( 11 ,  41 ) is separated from the brushless motor ( 13 ), the coil ( 25   b ) and the electrical control unit ( 14 ) are connected to one another by the first electrical wiring (T 1 ), and the rotation sensor ( 26 ) and the electrical control unit ( 14 ) are connected to one another by the second electrical wiring (T 2 ). The feature that the calibration is performed before the driven device is coupled to the brushless motor, serves to obtain an accurate correction value, because the output torque of the motor generated by energization of the coil is not canceled by friction, etc. in the driven device. 
     &lt;13&gt; In the motor apparatus according to item &lt;12&gt;: the electrical control unit housing section ( 31 ) includes: a board accommodation portion ( 38 ) housing the electrical control unit ( 14 ); and an opening ( 38   b ) through which the electrical control unit ( 14 ) is inserted into the board accommodation portion ( 38 ); and the motor apparatus further includes a cover ( 32 ) provided separately from the driven-device housing ( 15 ), the cover ( 32 ) closing the opening ( 38   b ). The cover serves to prevent foreign matter, such as dust or oil, from entering the board accommodation portion, even when the calibration is performed under condition that the driven-device housing is not connected to the motor housing section. This eliminates troubles, such as short circuit, which may be caused by the entrance of foreign matter into the board accommodation portion. 
     &lt;14&gt; In the motor apparatus according to item &lt;13&gt;: the electrical control unit housing section ( 31 ) is arranged between the motor housing section ( 21 ) and the driven-device housing ( 15 ); and the drive shaft ( 23 ) and the driven shaft ( 19 ) are connected to form a shaft member extending through the board accommodation portion ( 38 ). This feature serves to improve the layout about electrical connection between the brushless motor and the electrical control unit, because the board accommodation portion of the electrical control unit housing section is arranged at the axial end of the brushless motor. 
     &lt;15&gt; In the motor apparatus according to item &lt;14&gt;: the motor apparatus further includes a bearing (BB 2 ) disposed in the motor housing section ( 21 ), wherein the drive shaft ( 23 ) is rotatably supported by the bearing (BB 2 ); and the driven-device housing ( 15 ) is positioned with respect to the motor housing section ( 21 ) in a radial direction of the driven shaft ( 19 ). This feature serves to accurately position the drive shaft and the driven shaft with respect to one another. 
     &lt;16&gt; A calibration method for a power steering apparatus ( 1 ) comprising: a main housing ( 20 ) including: a motor housing section ( 21 ); and an electrical control unit housing section ( 31 ) coupled to the motor housing section ( 21 ); a driven-device housing ( 15 ) coupled to the motor housing section ( 21 ); a brushless motor ( 13 ) including: a drive shaft ( 23 ) housed in the motor housing section ( 21 ), the drive shaft ( 23 ) including a motor-side connecting portion ( 23   c ) at an axial end portion of the drive shaft ( 23 ); a rotor ( 24 ) coupled to the drive shaft ( 23 ); a coil ( 25   b ) disposed around the rotor ( 24 ), and adapted to be energized to generate a magnetic field; and a rotation sensor ( 26 ) arranged to measure a rotation angle of the rotor ( 24 ); an electrical control unit ( 14 ) housed in the electrical control unit housing section ( 31 ), the electrical control unit ( 14 ) including: a memory circuit section ( 35 ) configured to memorize a correction value for correction to a measured value of the rotation angle obtained by the rotation sensor ( 26 ); and a motor drive circuit section ( 36 ) configured to drive the brushless motor ( 13 ); a first electrical wiring (T 1 ) connecting the coil ( 25   b ) and the electrical control unit ( 14 ) to one another; a second electrical wiring (T 2 ) connecting the rotation sensor ( 26 ) and the electrical control unit ( 14 ) to one another; and a driven device ( 11 ,  41 ) including: a driven shaft ( 19 ) housed in the driven-device housing ( 15 ), and adapted to receive torque from the drive shaft ( 23 ), wherein the driven shaft ( 19 ) includes at an axial end portion of the driven shaft ( 19 ) a driven-side connecting portion ( 19   c ) connected to the motor-side connecting portion ( 23   c ) of the drive shaft ( 23 ); and an output section ( 11 ,  5 ;  41 ) adapted to output a force based on the torque; the calibration method comprising: a first operation of rotating the rotor ( 24 ) to a predetermined reference angular position with respect to the coil ( 25   b ) by energization of the coil ( 25   b ); a second operation of setting the correction value on a basis of a measured value of the rotation angle that is obtained by the rotation sensor ( 26 ) when the rotor ( 24 ) is rotated to the predetermined reference angular position by the first operation, for the motor drive circuit section ( 36 ) to drive the brushless motor ( 13 ) on a basis of a corrected measured value of the rotation angle that is obtained by correcting the measured value with the correction value; and a third operation of memorizing in the memory circuit section ( 35 ) the correction value that is determined by the second operation. This feature makes it possible to complete calibration of the rotation sensor so that the correction value is memorized in the memory circuit section of the electrical control unit, before shipment, in contrast to conventional cases where it is necessary to perform calibration in a process after shipment. This serves to reduce the work load in the process. 
     &lt;17&gt; In the calibration method according to item &lt;16&gt;, the second operation is implemented by setting the correction value under condition that the driven device ( 11 ,  41 ) is separated from the brushless motor ( 13 ), the coil ( 25   b ) and the electrical control unit ( 14 ) are connected to one another by the first electrical wiring (T 1 ), and the rotation sensor ( 26 ) and the electrical control unit ( 14 ) are connected to one another by the second electrical wiring (T 2 ). The feature that the calibration is performed before the driven device is coupled to the brushless motor, serves to obtain an accurate correction value, because the output torque of the motor generated by energization of the coil is not canceled by friction, etc. in the driven device. 
     &lt;18&gt; In the calibration method according to item &lt;17&gt;: the electrical control unit housing section ( 31 ) includes: a board accommodation portion ( 38 ) housing the electrical control unit ( 14 ); and an opening ( 38   b ) through which the electrical control unit ( 14 ) is inserted into the board accommodation portion ( 38 ); and the calibration method further includes an operation of dosing the opening ( 38   b ) with a cover ( 32 ) provided separately from the driven-device housing ( 15 ), before the first operation. The cover serves to prevent foreign matter, such as dust or oil, from entering the board accommodation portion, even when the calibration is performed under condition that the driven-device housing is not connected to the motor housing section. This eliminates troubles, such as short circuit, which may be caused by the entrance of foreign matter into the board accommodation portion. 
     &lt;19&gt; The calibration method according to item &lt;18&gt; further comprises an operation of connecting the drive shaft ( 23 ) to the driven shaft ( 19 ) after the third operation. This feature serves to obtain an accurate correction value while eliminating effects of a load of the driven device on the drive shaft. The feature further serves to enhance the efficiency of the connecting operation, because the connecting operation can be performed under condition that the motor unit is electrically separated from a system of determining and memorizing the correction value. 
     &lt;20&gt; In the calibration method according to item &lt;19&gt;: the motor apparatus further includes a bearing (BB 2 ) disposed in the motor housing section ( 21 ), wherein the drive shaft ( 23 ) is rotatably supported by the bearing (BB 2 ); and the calibration method further comprises an operation of connecting the drive shaft ( 23 ) to the driven shaft ( 19 ) after the driven-device housing ( 15 ) is positioned with respect to the motor housing section ( 21 ) in a radial direction of the driven shaft ( 19 ). This feature serves to accurately position the drive shaft and the driven shaft with respect to one another. 
     The entire contents of Japanese Patent Application 2009-215312 filed Sep. 17, 2009 are incorporated herein by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.