JPH09123929A - Electric power steering device - Google Patents

Abstract

(57) [PROBLEMS] To provide an electric power steering device capable of high output and excellent in reliability. SOLUTION: An inner peripheral surface of a cylindrical portion 9B is a tapered surface 35 having a large diameter on the substrate 18 side, the tapered surface 35 is divided into 12 regions at equal intervals in the circumferential direction, and one of these 12 regions is divided. The six areas in total are set as planes 36A to 36F. On each of the planes 36A to 36F, a case 21A accommodating a field effect transistor as a power element is provided with a screw 21B.
Fixed by. On the other hand, FE of the motor drive circuit
Circuits other than the T circuit are fixed on the substrate 18. That is,
Of the motor drive circuit, the FET circuit composed of the field effect transistor, which is relatively weak against heat, has a large volume and can be used as a heat sink.
Are fixed on the oblique planes 36A to 36F, and other circuits are fixed on the substrate 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for applying a steering assist torque to a steering system by utilizing a rotational force of an electric motor, and particularly, to enable high output and improve reliability. It is the one.

[0002]

2. Description of the Related Art As a conventional electric power steering apparatus, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 7-165089. That is, this conventional electric power steering device is configured to transmit the rotational force of the electric motor to the rack shaft of the rack-and-pinion steering device via a ball nut mechanism. Is coaxially arranged outside the. Further, the electric motor has a cylindrical rotor, and both ends of the rotor are rotatably supported in the housing through bearings, and the rotor is integrally provided with a ball nut mechanism. The rack shaft is slidable in the axial direction by the mechanism and a guide provided on the rear side of the pinion. With such a configuration, since the rack shaft is supported at two places, the occurrence of gouging and friction of the ball nut mechanism, the rack and pinion mechanism, etc. is reduced and the steering feeling is improved. there were.

[0003]

However, in the conventional electric power steering apparatus disclosed in the above publication, the drive circuit for driving the electric motor and the like are provided outside the motor. A harness, a connector, etc. are required to connect the exciting coil and the drive circuit, but when a current I ₁ flows through the exciting coil of the electric motor, a voltage drop I ₁ × R occurs due to the resistance R ₁ of the harness, the connector, etc. ₁ is generated, and the voltage applied to the exciting coil is reduced, and the rotation output of the electric motor is reduced accordingly. That is, in the conventional configuration in which the drive circuit is arranged outside the motor case, the harness cannot be shortened and the connector cannot be omitted, so that there is a drawback that the reduction of the rotation output cannot be easily avoided.

Further, in the above-mentioned conventional electric power steering apparatus, since an electric motor of a type having a brush for power feeding is used, abrasion of the brush becomes a problem. In order to eliminate the problem of brush wear, it is conceivable to use a brushless motor that does not have a brush for power supply in the electric power steering device.However, even in that case, the conventional brushless motor has a drive circuit for the electric motor, etc. Since it is provided outside the motor, there is a drawback that the voltage applied to the exciting coil is reduced and the rotation output of the electric motor is reduced. Moreover, in the brushless motor, since it is necessary to provide a position detection sensor including a hall element or the like inside the electric motor in order to detect the rotational position of the rotor, when the drive circuit is outside the motor, the output signal of the position detection sensor is output. It is sent to the drive circuit outside the motor, but with this, the output signal of the position detection sensor, which is usually weak power and is weak against disturbance, must be supplied to the drive circuit via a relatively long signal line. , It becomes a problem in terms of reliability.

The present invention has been made by paying attention to the unsolved problem in such a conventional electric power steering apparatus, and an electric power steering apparatus capable of high output and excellent in reliability is provided. It is intended to be provided.

[0006]

To achieve the above object, the present invention provides a torque sensor for detecting a steering torque generated in a steering system, and an electric motor capable of applying a steering assist torque to the steering system. An electric power steering apparatus comprising: a control unit that drives the electric motor according to a detection result of the torque sensor so as to reduce the steering torque. Rotatable in the circumferential direction alternately at equal intervals, a rotatable rotor, a stator having a plurality of phases of exciting coils surrounding the rotor, a position detection sensor for detecting the rotational position of the rotor, and these rotors. A motor case that houses the stator and the position detection sensor, and a motor drive circuit that supplies a current to the exciting coil according to the output of the position detection sensor. And a rotor having a hollow cylindrical shape and arranged coaxially with the advancing / retreating shaft of the steering system, the motor case also serving as a housing for the advancing / retreating shaft, and a rotating force of the rotor. Is provided with a ball nut mechanism that converts the force into a forward / backward force in the axial direction and transmits the force to the forward / backward shaft.Furthermore, a circuit other than the power element of the motor drive circuit is arranged on a substrate provided in the housing. The case containing the power element was fixed on the inner surface of the housing, which is oblique to the axial direction.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 are views showing an embodiment of the present invention, and FIG. 1 is a sectional view showing the overall configuration of an electric power steering apparatus 1 according to the present invention.
That is, in the electric power steering apparatus 1 according to the present embodiment, the rotational force of the steering wheel 2 is transmitted to the lower steering shaft 3C via the upper steering shaft 3A and the universal joint 3B. The lower end side of the steering shaft 3C is
A pinion (not shown) is formed on the lower steering shaft 3C that is inserted into the steering gear box 4 and is inserted into the steering gear box 4.

Then, the steering gear box 4 is
The rack shaft 5 extending in the vehicle width direction penetrates left and right, and the pinion of the lower steering shaft 3C and the rack of the rack shaft 5 mesh with each other. Further, tie rods 7A and 7B are connected to both ends of the rack shaft 5 extending in the left and right directions through ball joints 6A and 6B.
An outer end side (not shown) of 7B is coupled to a knuckle that rotatably supports a steered wheel (not shown) so that a steerable force can be transmitted. Both ends of the rack shaft 5 and the tie rods 7A, 7
Dust boots 5A and 5B are respectively fitted between them and B, thereby preventing dust and the like from entering the steering gear box 4 and the housing 9.

The rack shaft 5 is a cylindrical housing 9 fixed to a vehicle body (not shown) via brackets 8A and 8B.
The inside is inserted. Specifically, the housing 9 is caulked from the side closer to the steering gear box 4 to the connecting portion 9A coupled to the steering gear box 4, a relatively thick cylindrical portion 9B, and an outer peripheral surface of the cylindrical portion 9B. It is composed of a relatively thin cylindrical portion 9C that is stopped, and a preload member 9D that is screwed and fixed to the end portion of this cylindrical portion 9C, and each of the connecting portion 9A and the preload member 9D has a bracket 8A, It is fixed to the vehicle body via 8B.

Of these, a relatively thin cylindrical portion 9C
Is a large diameter portion 9a fixed to the cylindrical portion 9B and extending in the axial direction relatively long, and a small diameter portion 9b into which the preload member 9D is screwed.
And a taper portion 9 connecting the large diameter portion 9a and the small diameter portion 9b.
c. A cylindrical rotary shaft 10A is arranged inside the housing 9 so as to surround the rack shaft 5 in a non-contact manner and coaxially, and a cylindrical permanent magnet 10B is fixed to the outer peripheral surface of the rotary shaft 10A. Has been done. The permanent magnet 10B is a magnet in which S poles and N poles are alternately magnetized in the circumferential direction at equal intervals, and the rotating shaft 10
A and a permanent magnet 10B constitute a rotatable rotor 10.

At the end of the rotating shaft 10A on the preload member 9D side,
The ball nut 11 is integrally fixed in the rotational direction, and a ball screw 12 is formed on a portion of the rack shaft 5 other than the portion where the rack is formed. A plurality of balls 13 are interposed between the ball nut 11 and the ball screw 12. And
This constitutes a ball nut mechanism. The outer peripheral surface of the rotary shaft 10A on the side of the connecting portion 9A and the cylindrical portion 9
The bearing 14A is arranged between the inner peripheral surface of the B nut and the inner peripheral surface of the ball nut 11, and the bearing 14B is arranged between the inner peripheral surface of the ball nut 11 and the inner peripheral surface of the small diameter portion 9b. It is rotatably supported in the housing 9.
The rotating shaft 10A includes a bearing 14A and an inner ring bearing 14B.
A ring-shaped convex portion 10a is formed so as to abut the end surface facing the side, and the end surface facing the connecting portion 9A side of the outer ring of the bearing 14A abuts the stepped portion of the cylindrical portion 9B.
On the other hand, the ball nut 11 is formed with a step portion with which the end surface of the inner ring of the bearing 14B facing the bearing 14A side abuts,
The end surface of the preload member 9D abuts on the end surface of the outer ring of the bearing 14B facing the ball joint 6B side.
Therefore, the axial force generated by screwing the preload member 9D into the small diameter portion 9b is the bearing 14B outer ring, the bearing 14B.
B rolling element, bearing 14B inner ring, ball nut 11, rotating shaft 10A, convex portion 10a, bearing 14A inner ring, bearing 14A rolling element and bearing 14A outer ring are transmitted to the cylindrical portion 9B. Preload can be appropriately applied to 14A and 14B. In addition, in the small diameter portion 9b,
The ring-shaped fixing screw 15 is screwed onto the preload member 9D, thereby preventing the preload member 9D from loosening.

The ball nut 11 is rotatable, but the bearing 14A, which is provided by the preload member 9D,
Since it is impossible to displace in the axial direction due to the preload between 14B, the rotational force generated in the ball nut 11 is
3 and the ball screw 12, the force is converted into forward / backward force and transmitted to the rack shaft 5. On the other hand, the large diameter portion 9a
A core 16A is fixed to the inner peripheral surface of the three-phase exciting coil 1 so as to surround the permanent magnet 10B.
6B is wound, and the stator 16 is configured by the core 16A and the exciting coil 16B. Further, in a portion of the rotating shaft 10A closer to the bearing 14A than a portion to which the permanent magnet 10B is fixed, a ring in which S poles and N poles are magnetized alternately at equal intervals in the circumferential direction like the permanent magnet 10B. The permanent magnet 17 for phase detection is fixed.

Further, in the housing 9, the permanent magnet 1
7 is a circular substrate 18 close to the bearing 14A side surface of
Has been fixed. Specifically, as shown in FIG. 2, which is an enlarged view of a main part of FIG. 1, the substrate 18 is fixed to the cylindrical portion 9B by a screw 18a screwed to the cylindrical portion 9B. Actually, a plurality of screws 18a are provided in the circumferential direction, and each screw 18a is surrounded by a collar 18b,
The collar 18b is sandwiched between the substrate 18 and the cylindrical portion 9B, so that a space is formed on the bearing 18A side of the substrate 18. A detection element 19 for phase detection, which is composed of, for example, a Hall element, is fixed to the substrate 18. In addition, in reality, the detecting element 19 is the exciting coil 16
Although three pieces are provided at equal intervals in the circumferential direction corresponding to the number of phases of B, only one of them is shown since FIG. 2 is a sectional view.

FIG. 3 is a circuit diagram when the exciting coil 16B has three phases of a-phase, b-phase and c-phase. In this example, the star-connected exciting coils 16B of a-
The outer ends of the c-phases are connected to the motor drive circuit 20. Further, three detection elements 19 for phase detection as position detection sensors are provided corresponding to the number of phases of the exciting coil 16B, and the output of each detection element 19 is also supplied to the motor drive circuit 20. Has become.

The motor drive circuit 20 includes six field effect transistors T as power elements which are high power elements.
The FE has the FET circuit 21 composed of a1 to Tc2.
The T circuit 21 is connected between the power supply side and the GND side through three parallel lines, and each line has two field effect transistors (Ta1 and Ta2, Tb1 and Tb).
2, Tc1 and Tc2 are arranged in series. The exciting coil 16B is provided between the field effect transistors Ta1 and Ta2.
Of the field-effect transistor T connected to the outer end of the a phase of
Between b1 and Tb2 is connected to the outer end of the phase b of the exciting coil 16B, and between field effect transistors Tc1 and Tc2 is connected to the outer end of the c phase of the exciting coil 16B. That is,
Depending on the on / off state of each of the field effect transistors Ta1 to Tc2, a current in a predetermined direction appropriately flows in each of the a to c phases of the exciting coil 16B.

Further, the motor drive circuit 20 receives an output from the FET gate drive circuit 22 which controls the on / off state of the field effect transistors Ta1 to Tc2 by applying an appropriate voltage to the gates of the field effect transistors Ta1 to Tc2 and the output of the detection element 19. The rotational position of the rotor 10 and the detection result is detected by the FET gate drive circuit 2
2 and the rotor position detection circuit 23 for supplying to the FET circuit 2
1 and GND, and a current detection circuit 24 for detecting a current flowing through the exciting coil 16B flowing through the FET circuit 21.

Further, in addition to the motor drive circuit 20, a controller 30 for executing steering assist torque control in the electric power steering apparatus is provided, and this controller 30 has a lower steering shaft 3C as shown in FIG. A torque detection signal is supplied from the provided torque sensor 31, and the controller 30 confirms the steering torque generated in the steering system based on the torque detection signal and reduces the steering torque. A control signal is output to the FET gate drive circuit 22 of the motor drive circuit 20 so that such steering assist torque is generated in the steering system.

That is, the controller 30 outputs a control signal to the FET gate drive circuit 22 in accordance with the necessary rotation direction and magnitude of the steering assist torque. Thirty
An appropriate voltage is applied to the gates of the field effect transistors Ta1 to Tc2 of the FET circuit 21 so that the steering assist torque according to the control signal supplied from the steering system is generated in the steering system. In this case, the FET gate drive circuit 22
Is the rotor 10 based on the detection result of the rotor position detection circuit 23.
The rotational position of the FET is confirmed, and the FET is set so that the current appropriately flows in the a to c phases of the exciting coil 16B corresponding to the rotational position.
A voltage is applied to the gates of the field effect transistors Ta1 to Tc2 of the circuit 21. The controller 30 confirms the generation state of the steering assist torque based on the detection result of the current detection circuit 24.

F constituting the motor drive circuit 20
The ET circuit 21, the FET gate drive circuit 22, the rotor position detection circuit 23, and the current detection circuit 24 are arranged in the housing 9. Specifically, as shown in FIG. 4 in which FIG. 2 and the substrate 18 are omitted and FIG. 2 is viewed from the direction A, the inner peripheral surface of the cylindrical portion 9B is a tapered surface 35 having a large diameter on the substrate 18 side. The tapered surface 35 is divided into 12 regions at equal intervals in the circumferential direction, and among these 12 regions, every other 6 regions are planes 36A to 36A.
It is finished in F. That is, on the inner peripheral surface of the cylindrical portion 9,
Six flat surfaces 36A inclined with respect to the axial direction of the rack shaft 5
.About.36F are radially formed so as to surround the rack shaft 5.

On each of the planes 36A to 36F, a case 21A accommodating one of the field effect transistors Ta1 to Tc2 as a power element is fixed by a screw 21B. In this case, the axis of the screw 21B is shown in FIG.
As shown by the two-dot chain line, it passes through the central hole of the substrate 18. Further, of the six regions sandwiched by the planes 36A to 36F, the two regions at the diagonal positions are:
Shelf portions 37A and 37B forming a surface facing the substrate 18 side are formed, and screw holes 32 for fastening the screws 18a are formed in these shelf portions 37A and 37B.

On the other hand, in the motor drive circuit 20, the FET
Each of the gate drive circuit 22, the rotor position detection circuit 23, and the current detection circuit 24 is fixed on the substrate 18. That is, in the motor drive circuit 20, the FE composed of the field effect transistors Ta1 to Tc2 which are relatively weak against heat.
Since the T circuit 21 has a large volume, it is fixed on the cylindrical portion 9B having good heat dissipation that can be used as a heat sink, and the other circuits 22 to 24 are fixed on the substrate 18.

From the end face of the case 21A fixed on the planes 36A to 36F on the side close to the substrate 18, the gates, sources and drains of the field effect transistors Ta1 to Tc2 in the case 21A are connected to an external circuit. Terminals 21C for pulling out are drawn out, and each terminal 21C is connected to the substrate 1
8 to the FET gate drive circuit 22 on the substrate 18 and the exciting coil 16B.

Here, in this embodiment, the steering wheel 2, the upper steering shaft 3A, the universal joint 3B, the lower steering shaft 3C, the rack shaft 5, and the like.
The ball joints 6A and 6B, the tie rods 7A and 7B, and a knuckle (not shown) constitute a steering system. The rack shaft 5 corresponds to the advancing / retreating shaft, the controller 30 corresponds to the control means, the rotor 10, the stator 16, the detecting element 19,
The motor drive circuit 20 and the housing 9 constitute a brushless motor 1A. Therefore, in the present embodiment, the housing 9 of the rack shaft 5 also serves as the motor case of the brushless motor 1A.

With the above structure, the steering force generated by the driver steering the steering wheel 2 causes the rack shaft 5 to pass through the upper steering shaft 3A, the universal joint 3B and the lower steering shaft 3C. The tie rods 7A and 7B connected to both ends of the rack shaft 5 are moved back and forth to generate steering force on the knuckle, and the steered wheels are steered. It

When the steering wheel 2 is steered during such steering to generate a rotational force on the lower steering shaft 3C, the friction force between the steered wheels and the road surface is applied to the torsion bar 4, which constitutes the torque sensor 31, for example. Since twisting occurs due to frictional force such as gear engagement of the rack and pinion mechanism, it is detected as steering torque and supplied to the controller 30 as a torque detection signal.

Then, the controller 30 outputs a command signal to the motor drive circuit 20 so as to reduce the steering torque of the steering system in response to the supplied torque detection signal, so that the ball nut 11 of the brushless motor 1A: Rotational force is generated according to the direction and magnitude of the steering torque generated in the steering system. Further, since the rotational force generated in the ball nut 11 is converted into the advancing / retreating force of the rack shaft 5 by the ball 13 and the ball screw 12, the steering assist torque is applied to the rack shaft 5, and the steering torque is reduced. , The burden on the operator is reduced.

On the other hand, when the steering assist torque is generated, the exciting coil 16B generates heat in proportion to the current flowing through the exciting coil 16B and its resistance.
Is transmitted to the surrounding members and finally radiated from the surface of the housing 9 to the outside. In the brushless motor 1A used as the power source of the electric power steering apparatus as in the present embodiment, , Its exciting coil 1
Since a current flows through 6B only when steering assist torque is required, heat generation from the exciting coil 16B occurs sporadically, unlike a brushless motor in which a current always flows through the exciting coil. Therefore, even if the motor drive circuit 20 is provided in the housing 9, it is possible to effectively raise the temperature of the motor drive circuit 20 by merely fixing the FET circuit 21 to the large-volume cylindrical portion 9B that functions as a heat sink. This can be suppressed, and failure or the like due to the temperature rise of the motor drive circuit 20 can be prevented.

In particular, in this embodiment, the cylindrical portion 9
A flat surface 36A that is oblique to the axial direction of the rack shaft 5 on the inner surface of B
To 36F, and the case 21 in which the field effect transistors Ta1 to Tc2 are housed on the respective planes 36A to 36F.
Since A is fixed, the entire back surface of each case 21A can be covered with the cylindrical portion 9 as a heat sink without causing any serious problems.
It has an advantage that it can be brought into contact with the inner surface of B, good heat dissipation can be secured, and high reliability can be obtained.
That is, if the case 21A is to be fixed to a surface parallel to the substrate 18 such as the shelves 37A and 37B, it is necessary to insert the bearing 14A. I can't make it overhang,
A part of the back surface side of the case 21A is not in contact with the cylindrical portion 9B, and the heat dissipation is deteriorated.

The flat surfaces 36A to 36F may be parallel to the rack shaft 5 (that is, the tapered surface 35 may be a cylindrical surface parallel to the rack shaft 5), or the entire back surface of the case 21A may be brought into contact with the cylindrical portion 9. However, this causes a problem that the work of fixing the case 21A to the cylindrical portion 9 becomes troublesome. That is, as in the present embodiment, the flat surfaces 36A to 36F are arranged on the substrate 18 with respect to the rack shaft 5.
If the side faces in an oblique direction so as to spread outward, a through hole for the rack shaft 5 to pass through is formed in the central portion of the substrate 18, so that the through hole is used (that is,
A driver for fastening the screw 21 can be inserted (along the chain double-dashed line in FIG. 2), but if the flat surfaces 36A to 36F are parallel to the rack shaft 5, the screw can be fixed with a simple jig like a driver. Cannot be done. Therefore, the inclination angles of the flat surfaces 36A to 36F need to be selected within a range in which the driver can be inserted. However, in reality, the diameter of the through hole is affected in the central portion of the substrate 18, and thus the specific angle is specifically specified. Can not. However, it is considered that there is no major problem within the range of 5 to 80 °.

Furthermore, if the motor drive circuit 20 is provided in the housing 9, the harness for connecting the exciting coil 16B and the motor drive circuit 20 can be made extremely short, and no connector is required. Therefore, the voltage drop other than that of the exciting coil 16B can be slightly suppressed. Therefore, the power on the power supply side is efficiently supplied to the exciting coil 16
B can be supplied to the brushless motor 1A
The rotational output of the electric power steering apparatus 1 is improved and the high output of the electric power steering apparatus 1 is achieved.

Further, the detection element 19 and the motor drive circuit 20
Since the distance between and becomes short, it becomes possible to transmit a signal between them by only the wiring on the substrate 18, and it becomes strong against disturbance.
Moreover, the possibility of contact failure of the connector and disconnection of the signal line is extremely reduced, so the electric power steering apparatus 1
The reliability of is also improved. As described above, since heat is generated sporadically from the exciting coil 16B of the brushless motor 1A in the electric power steering device 1, the exciting coil 16B and the motor drive circuit are shielded from each other, although not particularly shown. As described above, if an iron heat shield plate having good heat conductivity is fixed in the housing 9, the exciting coil 1
Since part of the heat generated in 6B is radiated from the outer surface of the housing 9 via the heat shield plate before being transferred to the motor drive circuit side, the heat radiation effect of the cylindrical portion 9B functioning as a heat sink is combined with the FET circuit 21 and the like. The temperature rise in the motor drive circuit can be suppressed more effectively.

The rotary shaft 10 and the ball nut 11 may not be separate members, and a ball nut may be formed at the end of the rotary shaft 10, for example. Further, when there are many components of the motor drive circuit 20, the board 1
It is also possible to provide a plurality of 8 and arrange the circuit components separately on each board 18, or even if a plurality of boards 18 are provided, if each board 18 is fixed to the housing 9 in a superposed state. In particular, it does not cause deterioration of the assembling property or increase in size of the device.

In the above embodiment, the exciting coil 16B has three phases. However, the exciting coil 16B is not limited to this and may have, for example, four phases or five phases.

[0034]

As described above, according to the electric power steering apparatus of the present invention, the brushless motor is used as the electric motor and the motor drive circuit is provided in the housing for the advancing / retreating shaft which also serves as the motor case. In addition, the circuit other than the power element of the motor drive circuit is disposed on the substrate provided in the housing, and the case accommodating the power element is oblique to the axial direction on the inner surface of the housing. Since it is fixed on the surface, there is an effect that high output is possible and reliability is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an overall configuration of an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a circuit diagram of a brushless motor.

FIG. 4 is a diagram showing an arrangement relationship of cases housing field-effect transistors.

[Explanation of symbols]

1 Electric Power Steering Device 1A Brushless Motor 2 Steering Wheel 3A Upper Steering Shaft 3B Universal Joint 3C Lower Steering Shaft 5 Rack Axis (Advancing / Retracting Axis) 6A, 6B Ball Joint 7A, 7B Tie Rod 9 Housing 10 Rotor 10A Rotating Axis 10B Permanent Magnet 11 Ball nut 12 Screw shaft 13 Ball 14A, 14B Bearing 16 Stator 16A Core 16B Excitation coil 18 Substrate 19 Detection element (position detection sensor) 20 Motor drive circuit 21 FET circuit 21A Case 21B Screw 21C terminal 30 Controller (control means) 31 Torque sensor 35 Tapered surface 36A to 36F Flat surface Ta1 to Tc2 Field effect transistor (power element)

Claims (1)

[Claims] 1. A torque sensor for detecting a steering torque generated in a steering system, an electric motor capable of applying a steering assist torque to the steering system, and a detection sensor for reducing the steering torque according to a detection result of the torque sensor. And a control means for driving the electric motor by means of a control means for driving the electric motor, wherein the electric motor is rotatable such that an S pole and an N pole are alternately magnetized circumferentially at equal intervals on the outer peripheral surface. The rotor of the
A stator having a plurality of phases of exciting coils surrounding the rotor, a position detection sensor for detecting the rotational position of the rotor, a motor case accommodating the rotor, the stator and the position detection sensor, and an output of the position detection sensor. A brushless motor including a motor drive circuit that supplies a current to the exciting coil in accordance with the above is used, and the rotor has a hollow cylindrical shape and is disposed coaxially with the advancing / retreating shaft of the steering system. A ball nut mechanism is provided that doubles as a housing for the advancing / retreating shaft and converts the rotational force of the rotor into an advancing / retreating force in the axial direction and transmits the advancing / retreating shaft to the advancing / retreating shaft. Another circuit is arranged on a substrate provided in the housing, and a case accommodating the power element is provided on the inner surface of the housing. Electric power steering apparatus being characterized in that fixed on the oblique plane to the direction.