JP2003231476A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device providing smooth steering feeling by preventing output fluctuation of a brushless motor and fluctuation of steering assist force. <P>SOLUTION: The power steering device is provided with a steering torque detecting means for detecting steering wheel steering torque, a motor providing assist torque to a steering system, a motor rotational angle detecting means for detecting a rotational angle of the motor, a motor current detecting means for detecting current carried to the motor, and a motor control means for carrying out PWM drive control of the motor on the basis of at least signals outputted from the steering torque detecting means, the motor rotational angle detecting means and the motor, current detecting means. The motor is the brushless motor 101, the motor rotational angle detecting means includes a resolver 102, and either one of a PWM driving frequency controlling drive of the brushless motor 102 or an exciting frequency of the resolver is an integral multiple of the other. <P>COPYRIGHT: (C)2003,JPO

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, and more particularly, to an electric power steering apparatus for a vehicle steering apparatus, in which power of a motor is applied to a steering system to reduce a burden of a steering force on a driver. It is a thing.

[0002]

2. Description of the Related Art In an electric power steering system, a motor control unit drives and controls a motor based on signals output from a steering torque detection unit for detecting a steering torque of a steering wheel, a vehicle speed detection unit for detecting a vehicle speed, and the like. Is being reduced. An electric power steering device using a brushless motor for the motor is known.

An electric power steering system using a brushless motor does not cause a drop or fluctuation in the motor output due to a voltage drop between the brush and the commutator, so that a stable steering assist force can be obtained. Further, since the moment of inertia of the motor is smaller than that of the motor with a brush, a good steering feeling can be obtained when traveling straight at high speed or when switching the steering wheel.

However, when a brushless motor is used as the motor, it is necessary to control the energization amount of the motor current according to the rotation angle of the motor instead of the brush and the commutator, so that the rotation angle of the motor is detected. A motor rotation angle detector and a motor current detector are provided, and the brushless motor is PWM-controlled based on the output signals of the motor rotation angle detector and the motor current detector.

FIG. 5 is a block diagram showing a motor controller for controlling the rotation of the brushless motor. A resolver 102 for detecting the rotation angle of the brushless motor 101 is attached to the brushless motor 101.

The motor control unit 100 for controlling the rotation angle of the brushless motor 101 includes a phase correction unit 103, an inertia correction unit 104 and a damper correction unit 105.

The phase correction unit 103 includes a steering torque detection unit 1
The steering torque signal T from 06 is phase-corrected based on the vehicle speed signal v from the vehicle speed detection unit 107, and the corrected steering torque signal T ′ is output to the target current setting unit 108. The inertia correction unit 104 includes a steering torque signal T from the steering torque detection unit 106 and a vehicle speed signal v from the vehicle speed detection unit 107.
And a signal corresponding to the rotational angular velocity ω
An inertia correction signal d for performing inertia correction from a signal corresponding to the angular acceleration obtained by differentiating with
i is generated and the inertia correction signal di is output to the addition operator 109. The damper correction unit 105 is a damper correction signal dd for performing damper correction from the steering torque signal T from the steering torque detection unit 106, the vehicle speed signal v from the vehicle speed detection unit 107, and a signal corresponding to the rotational angular velocity ω.
Is generated and the damper correction signal dd is subtracted from the subtraction operator 11
Output to 0.

The target current setting unit 108 determines the two-phase target current Id based on the corrected steering torque signal T'and the vehicle speed signal v.
1, Iq1 is calculated and output. Target currents Id1 and Iq1
Correspond to the d-axis in the same direction as the permanent magnet and the q-axis orthogonal thereto in the rotating coordinate system synchronized with the rotating magnetic flux generated by the permanent magnet on the rotor of the brushless motor 101. Id1 and Iq1 are referred to as "d-axis target current" and "q-axis target current", respectively.

The inertia correction signal di is added to the target currents Id1 and Iq1 in the addition calculation unit 109,
Target currents Id2 and Iq2 after inertia correction are output. The inertia corrected target currents Id2 and Iq2 are subtracted by the damper correction signal dd in the subtraction calculation unit 110, and the damper corrected target currents Id3 and Iq3 are output. The damper corrected target currents Id3 and Iq3 are referred to as "d-axis final target current Id ^* " and "q-axis final target current Iq ^* ", respectively.

Final target currents I on the d-axis and the q-axis
d ^* and Iq ^* are the d-axis and q
The deviation D is obtained by subtracting the d-axis and q-axis detected currents Id and Iq from the final target currents Id ^* and Iq ^* of the axes, respectively.
Id and DIq are calculated and output to the PI setting unit 112.

The PI setting unit 112 executes the calculation using the deviations DId and DIq to detect the detected current I of the d-axis and the q-axis.
The d-axis and q-axis target voltages Vd and Vq are calculated so that d and Iq follow the d-axis and q-axis final target currents, respectively. The d-axis and q-axis target voltages Vd and Vq are corrected to the d-axis and q-axis corrected target voltages Vd ′ and Vq ′ by the decoupling control unit 113 and the calculation unit 114, and dq.
It is output to the -3 phase conversion means 115.

In the above description, in FIG. 5, for convenience of illustration, a pair of addition calculation unit 109, subtraction calculation unit 110, and deviation calculation unit 1 are provided.
11, the PI setting unit 112 and the calculation unit 114 are shown, but in practice, the set of these circuit elements has two target currents Id.
It is provided individually for each of 1 and Id2.

The decoupling control unit 113 decouples the d-axis and q-axis target voltages Vd and Vq based on the d-axis and q-axis detection currents Id and Iq and the rotor rotational angular velocity ω. Calculate the control correction value.

The calculation unit 114 subtracts the decoupling control correction values from the d-axis and q-axis target voltages Vd, Vq, respectively, to obtain the d-axis and q-axis corrected target voltages Vd ',
Vq ′ is calculated and output to the dq-3 phase conversion means 115.

The dq-3 phase conversion means 115 converts the d-axis and q-axis corrected target voltages Vd 'and Vq' into the three-phase target voltage Vu.
^* , Vv ^* , Vw ^* are converted into three-phase target voltages Vu ^* , Vv
Outputs ^* and Vw ^* to the motor drive unit 116.

The motor drive unit 116 includes a PWM voltage generator and an inverter circuit. The motor driving unit 116 uses a PWM voltage generating unit (not shown) in the motor driving unit 116 to generate a PW corresponding to the three-phase target voltages Vu ^* , Vv ^* , Vw ^*.
The M control voltage signals UU, VU, WU are generated and output to an inverter circuit (not shown) in the motor drive unit 116.
The inverter circuit includes PWM control voltage signals UU, VU, W
Three-phase AC drive currents Iu, Iv, and Iw corresponding to U are generated, and these are supplied to the brushless motor 101 via the three-phase drive current paths 117, respectively. The three-phase AC drive currents Iu, Iv, and Iw are respectively applied to the brushless motor P
It is a sine wave current for WM driving.

Motor current detectors 118 and 119 are provided on two of the three-phase drive current paths 117, and the motor current detectors 118 and 119 are connected to the brushless motor 101.
Of the three-phase drive currents Iu, Iv, and Iw supplied thereto, the two drive currents Iu and Iw are detected and output to the three-phase to dq converter 120. The three-phase to dq converter 120 also calculates the remaining drive current Iv based on the detected drive currents Iu and Iw. The 3-phase-dq conversion unit 120 converts these 3-phase detection drive currents Iu, Iv, Iw into 2-phase d-axis and q-axis detection currents Id, Iq.

The signal from the resolver 102 is continuously supplied to the RD (resolver digital) converter 121. The RD conversion unit 121 calculates the angle (rotation angle) θ of the rotor of the brushless motor 101 with respect to the stator, and converts the signal corresponding to the calculated angle θ to the dq-3 phase conversion unit 115 and the 3-phase-dq conversion. It is supplied to the part 120. Also,
The RD conversion unit 121 calculates the rotational angular velocity ω of the rotor of the brushless motor 101 with respect to the stator, and outputs a signal corresponding to the calculated rotational angular velocity ω to the damper correction unit 1.
05, the differential processing unit 121d, and the decoupling control unit 113. The resolver 102 and the RD converter 121 form a motor rotation angle detector 102A.

As shown in FIG. 6, the motor control unit 100 having the above structure is housed in an electronic circuit unit except for various sensors and inverter circuits, and is composed of a microcomputer 122. Then, each unit in the electronic circuit unit is adapted to realize each function by program processing.

In FIG. 6, the interface circuit 12
Reference numeral 3 denotes an A / D converter for converting an analog signal of the steering torque signal T obtained by the steering torque detection unit 106, the vehicle speed signal v from the vehicle speed detection unit 107, and the engine rotation signal r from the engine rotation detection unit 124 into a digital signal. And converts the input analog signals into digital signals and inputs them to the microcomputer 122.

The interface circuit 125 has a drive current I detected by the motor current detectors 118 and 119.
u and Iw are converted into digital signals and input to the microcomputer 122. The interface circuit 126 is
The exciting current from the RD converter 127 is applied to the resolver 102.
The output signal from the resolver 102 is sent to the RD converter 127. As will be described later, the RD converter 127 outputs an angle signal from the output signal from the resolver 102 and sends it to the microcomputer 122. The motor drive unit 116 includes a predrive circuit 128 and an inverter circuit including six power FETs.

A crystal oscillator 129 and capacitors 130 and 131 are externally connected to the microcomputer 122. In the microcomputer 122, the oscillation frequency of the crystal oscillator 129 is divided to drive the brushless motor 101. The frequency of the PWM signal (PWM frequency) f _PWM is generated.

The RD converter 127 includes a crystal oscillator 1
32 and capacitors 133 and 134 are connected, and R
In the D converter 127, the oscillation frequency of the crystal oscillator 132 is divided, and the frequency (excitation frequency) f _RES of the excitation signal of the VR resolver 102 is generated.

[0024]

In order to obtain an electric power steering apparatus having a smooth steering feeling, a smooth brushless motor output is required. Therefore, as described above, based on the output signals of the motor rotation detection unit and the motor current detection unit, the motor control unit vector-controls the brushless motor, and the sinusoidal current is supplied as the motor current, so that the torque fluctuation is small. It is possible to obtain the output.

The sine-wave current is supplied to the brushless motor through a motor drive section (inverter) composed of switching elements such as FETs and peripheral circuits. Such a switching element is driven at a frequency f _PWM outside the audible range,
1 to power.

Further, since the absolute angle of rotation of the brushless motor is required for vector control, a motor rotation angle (others, angular velocity, angular acceleration) detector such as a resolver is used. The resolver detects a rotation angle by detecting a gap change in the rotor core.

FIG. 7 is a schematic diagram showing the principle of the resolver. In the vicinity of the rotor R, there is a coil A as a coil on the excitation side, and on the opposite side thereof are coils B and C as two coils on the output side forming a right angle with each other. Since the magnetic field generated by the current flowing through the coil A passes through the inside of the coils B and C and the current changes with time, induced electromotive force is generated in the coils B and C according to Faraday's law.

That is, one phase is applied to the terminals R1 and R2 on the excitation side.
As excitation, the angular frequency ω in equation (1) _EThe voltage of
It

[0029]

[Equation 1]

As a result, when the rotor R is at the angle θ, the voltage represented by the equation (2) is output to the terminals S1 and S3 of the coil B, and the voltage (3) is output to the terminals S2 and S4 of the coil C. The voltage represented by the equation is output.

[0031]

[Equation 2]

[0032]

[Equation 3]

FIG. 8 shows R in the RD converter 127.
The principle of D conversion is shown. The output voltage E _S1-S3 input to the RD converter 127 is calculated by the operation unit 135 as the product of the sine sin φ of the angle φ of the internal ROM. In addition, the output voltage E _S2-S4 and the internal ROM
Calculate the product of the angle φ of c and the cosine cos φ. Calculation unit 13
The difference D1 represented by the equation (4) is obtained from 7.

[0034]

[Equation 4]

This difference D1 is transformed into the following equation (5).

[0036]

[Equation 5]

The signal of this difference D1 is synchronously detected with the excitation input voltage in the synchronous detection section 138. Thereby,
The signal D2 represented by the equation (6) is output.

[0038]

[Equation 6]

The VCO section 139 and the counter 140 increase / decrease the value of φ for the signal D2 so that the signal D2 is always zero, and output the angle θ.

In this way, one phase is excited by the sine wave represented by the equation (1), and the two phases (sine wave, cosine wave) modulated into the sine wave and the cosine wave represented by the equations (2) and (3) Wave) output.
Then, an angle output is obtained by performing the RD conversion on the two-phase output. Here, the excitation drive frequency f
_RES is approximately 10 kHz.

[0041] At this time, if you've switching noise ride by PWM driving the resolver output, the frequency f1 = f _PWM -f _RES difference PWM frequency f _PWM and the exciting frequency f _RES to the output of the RD converter 127, or respectively F2 = nxf _PWM- m
xf _RES (n = 1, 2, ..., M = 1, 2, ...) Output fluctuation occurs, and as a result, output of brushless motor also f1 (Hz) or f2 (Hz) output fluctuation. . In the conventional motor control means shown in FIG. 6, even if the PWM frequency f _PWM and the excitation frequency f _RES are set to the same frequency, this output fluctuation occurs for the following reason.

In FIG. 6, the frequency f _PWM of the PWM signal
Is a crystal oscillator 129 in the microcomputer 122.
The oscillation frequency of is divided and generated. Further, the frequency f _{RES of the} excitation voltage is generated by dividing the oscillation frequency of the crystal oscillator 132 in the RD converter 127. As described above, since the PWM frequency f _PWM and the excitation frequency f _RES are respectively generated from two different crystal oscillation circuits, the load due to the variations of the crystal oscillator and the variations of the capacitors 130, 131, 133, 134, etc. Even if the crystal oscillation has a stable frequency, there is a difference in the frequencies of the signals generated from the two different crystal oscillation circuits. Therefore, the PWM frequency f
It was difficult to make the _PWM and the excitation frequency f _RES exactly the same. From the above, there is a problem that the output of the RD converter 127 fluctuates, and as a result, the steering assist force also fluctuates, resulting in vibration of the steering wheel and impairing the steering feeling.

In order to solve the above problems, an object of the present invention is to use a brushless motor that is free from feeling deterioration due to brush wear and rotor inertia moment, and there is no output variation of the brushless motor and variation of steering assist force. It is an object of the present invention to provide an electric power steering device that has a smooth steering feeling without any noise.

[0044]

In order to achieve the above object, the electric power steering apparatus according to the present invention is constructed as follows.

A first electric power steering apparatus (corresponding to claim 1) is a steering torque detecting means for detecting a steering torque of a steering wheel, a motor for giving an auxiliary torque to a steering system, and a motor for detecting a rotation angle of the motor. The rotation angle detection means, the motor current detection means for detecting the motor current supplied to the motor, and the PWM drive control of the motor based on the signals output from at least the steering torque detection means, the motor rotation angle detection means, and the motor current detection means. An electric power steering apparatus including a motor control means, wherein the motor is a brushless motor, and the motor rotation angle detection means includes a resolver, and a PWM drive frequency for driving and controlling the brushless motor and an excitation frequency of the resolver. Characterized by making one of them an integer multiple of the other That.

According to the first electric power steering device
For example, the PWM drive frequency that drives and controls the brushless motor
f_PWMAnd the excitation frequency f of the resolver_RESOne of
Is an integral multiple of the other, so f1 = f_PWM-F_RESOr
f2 = nxf_PWM-Mxf_RES(N = 1, 2, ..., M =
1, 2, ...) is 0 Hz or f1 or f2 is f
_RESThe output from the RD converter is stable.
Output fluctuation of the brushless motor
And the steering assist force does not fluctuate.
Therefore, a smooth steering feeling can be obtained.

The second electric power steering apparatus (corresponding to claim 2) is preferably a PW in the above construction.
By performing M drive and resolver excitation with a signal generated and output from the same oscillator, one of the PWM drive frequency for drive control of the brushless motor and the resolver excitation frequency is made an integral multiple of the other. Characterized.

According to the second electric power steering device, the PWM drive frequency f _{PWM for} controlling the drive of the brushless motor and the exciting frequency f _{RES of the} resolver are generated by the output of the same oscillator, and f _PWM and f _RES are _combined . Since one of them is an integral multiple of the other, f1 = f _PWM −f _RES or f2
= Nxf _PWM- mxf _RES (n = 1, 2, ..., M = 1,
2, ...) is certainly 0 Hz or f1 or f2 is f
_Since it becomes an integral multiple of _RES and the output of the RD converter does not fluctuate, the output of the brushless motor does not fluctuate, the steering assist force does not fluctuate, and a smooth steering feeling can be obtained. it can.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention, showing a left end portion and a right end portion in cross section. This drawing shows that the rack shaft 11 of the electric power steering device 10 is accommodated in a housing 12 extending in the vehicle width direction (left and right direction in the drawing) slidably in the axial direction. Reference numeral 13 is a gear box, 14 is a steering torque detector, 15 is a motor controller, and 16 is a brushless motor which is a motor. The rack shaft 11 is a shaft in which ball joints 17 are threadedly connected to both ends in the longitudinal direction protruding from the housing 12, and left and right tie rods 18 are connected to these ball joints 17. The housing 12 is provided with brackets 19 for attaching to a vehicle body (not shown), and stoppers 20 attached to both ends in the longitudinal direction. Further, 80 is an ignition switch, 81 is a battery,
82 is ACG.

When the rack shaft 11 slides to the right by a predetermined amount, the contact end surface (rack end) 21 of the left ball joint 17 contacts the stopper 20. When the rack shaft 11 slides to the left by a predetermined amount, the right ball joint 1
The abutting end surface (rack end) 21 of 7 contacts the stopper 20. By limiting the movement amount of the rack shaft 11 in this manner, the maximum steering angle of the left and right steered wheels (not shown) can be limited. That is, when the rack shaft 11 moves to the end of movement, the steering angles of the left and right steered wheels become maximum.
In the figure, 22 is a dust seal boot.

FIG. 2 is a sectional view taken along line 4-4 of FIG. 1 and shows a vertical sectional structure of the electric power steering apparatus 10. The electric power steering apparatus 10 has an input shaft 23, a rack and pinion mechanism 24, a steering torque sensor 25, a torque limiter, and a gear type speed reduction mechanism 26 housed in a housing 12, and an upper opening of the housing 12 is covered with a lid 27. Is. The steering torque sensor 25 is attached to the housing 12 or the lid 27.

The housing 12 is set in a vertical position by rotatably supporting the lower end portion and the longitudinal center portion of the input shaft 23 via two upper and lower bearings 28 and 29, and a rack guide 30. Equipped with. Reference numeral 31 is a lid mounting bolt, and 32 is a retaining ring.

The pinion 33 and the rack 34 are characterized by being plastically worked products such as cast products (including rolled products). Specifically, the input shaft 23 is a pinion shaft having a pinion 33 integrally formed in the lower portion, a screw portion 35 formed in the lower end portion, and an upper end portion protruding outward from the lid 27. The rack 34 is formed integrally with the rack shaft 11. By screwing the nut 36 into the screw portion 35, the movement of the input shaft 23 in the longitudinal direction (axial direction) can be restricted. 37 is a cap nut, 38 is an oil seal, and 39 is a spacer.

The rack guide 30 is composed of a guide portion 40 that contacts the rack shaft 11 from the side opposite to the rack 34, and an adjusting bolt 42 that pushes the guide portion 40 via a compression spring (adjusting spring) 41. According to such a rack guide 30, the adjusting bolt 42 screwed into the housing 12 pushes the guide portion 40 with an appropriate pressing force via the compression spring 41, so that the guide portion 40 applies a preload to the rack 34. Then, the rack 34 can be pressed against the pinion 33. 43 is a pad member for sliding the back surface of the rack shaft 11, 4
4 is a lock nut.

FIG. 3 is a sectional view taken along line 5-5 of FIG. 2, showing the relationship between the input shaft 23, the electric motor 16, the torque limiter 45, and the gear type speed reducing mechanism 26. The electric motor 16 has an output shaft 46.
Is horizontally mounted on the housing 12, and the output shaft 46 is extended in the housing 12.

The gear type speed reduction mechanism 26 is a torque transmission means for transmitting the auxiliary torque generated by the electric motor 16 to the input shaft 23, and is composed of a worm gear mechanism having a combined structure of a drive gear and a driven gear. Specifically, the gear type speed reduction mechanism 26 is coupled to the output shaft 46 of the electric motor 16 via the torque limiter 45, a worm 48 formed on the transmission shaft 47, and meshes with the worm 48 and is coupled to the input shaft 23. And a worm wheel 49.
The auxiliary torque of the electric motor 16 can be transmitted to the rack and pinion mechanism via the input shaft 23.

The transmission shaft 47 is arranged concentrically with the output shaft 46 and is rotatably supported by the housing 12 via two bearings 50 and 51. The housing 12 is such that a first bearing 50 located near the output shaft 46 is attached so as to be immovable in the axial direction, and a second bearing 51 located far from the output shaft 46 is fitted so as to be movable in the axial direction. Further, the end surface of the outer ring of the second bearing 51 is pushed toward the output shaft 46 side by the adjusting bolt 53 via the leaf spring 52. By applying a preload to the first and second bearings 50 and 51 by the pressing force of the adjusting bolt 53 and the thin plate-shaped leaf spring 52, the transmission shaft 47 is adjusted so that there is no play in the axial direction, that is, You can remove the backlash. Moreover, the worm 48
The axial displacement of the worm 48 can be adjusted so that the engagement between the worm 48 and the worm wheel 49 can be adjusted appropriately so that there is no backlash while maintaining friction. Further, due to the elasticity of the leaf spring 52, thermal expansion of the transmission shaft 47 in the axial direction can be absorbed. 54 is a lock nut, and 55 is a retaining ring.

2 and 3, the input shaft 23 of the gear box 13 is rotatably supported by bearings 28 and 29, and is rotatably connected via a handle, a universal joint, a column shaft and the like (not shown). Input shaft 2 from the handle
The rotation of No. 3 is converted into an axial displacement of the rack shaft 11 via the pinion gear 24 and the rack gear 34, and the axial displacement causes the front wheel (not shown) to swing via the tie rods 18 to steer the vehicle.

A worm wheel 49 is fixed above the pinion gear 24 of the input shaft 23. The worm wheel 49 is meshed with a worm gear 48 which is rotatably supported by bearings 50 and 51 as shown in FIG.

A serration 56 is provided on the inner circumference of the input shaft 23, and the serration 56 is provided on the serration 56.
Serration 57 provided on the outer peripheral surface of the output shaft 46 of No. 6
, The output of the brushless motor 16 becomes the clutch 58.
Is transmitted to the worm gear via.

The motor control unit 15 described above basically
This is the same as that described in FIGS. 5 and 6, and as shown in FIG. 4, a one-chip microcomputer and peripheral circuits, a predrive circuit, an FET bridge, a current sensor, a relay, and an RD.
It is composed of a converter and the like. In FIG. 4, the same elements as those described in the conventional motor control unit are designated by the same reference numerals. It is housed in an electronic circuit unit except for various sensors and an inverter circuit, and is configured by a microcomputer 122. Then, each unit in the electronic circuit unit is adapted to realize each function by program processing. Further, conventionally, two crystal oscillators, a crystal oscillator 129 connected to the microcomputer 122 and a crystal oscillator 132 connected to the RD converter 127, have been used in the motor control unit, but in the present embodiment, 1 crystal oscillator is used. One crystal oscillator is connected to both the microcomputer 122 and the RD converter 127.

In FIG. 4, the interface circuit 12
Reference numeral 3 denotes an A / D converter for converting an analog signal of the steering torque signal T obtained by the steering torque detection unit 106, the vehicle speed signal v from the vehicle speed detection unit 107, and the engine rotation signal r from the engine rotation detection unit 124 into a digital signal. And converts the input analog signals into digital signals and inputs them to the microcomputer 122.

The interface circuit 125 has an exciting current I detected by the motor current detectors 118 and 119.
u and Iw are converted into digital signals and input to the microcomputer 122. The interface circuit 126 is
The exciting current from the RD converter 127 is applied to the resolver 102.
The output signal from the resolver 102 is sent to the RD converter 127. As will be described later, the RD converter 127 outputs an angle signal from the output signal from the resolver 102 and sends it to the microcomputer 122. The motor drive unit 116 includes a predrive circuit 128 and an inverter circuit including six power FETs.

A crystal oscillator 70 and capacitors 71 and 72 are externally connected to the microcomputer 122. In the microcomputer 122, the crystal oscillator 7 is connected.
The oscillation frequency of 0 is divided, and the frequency of the PWM signal for driving the brushless motor 101 (PWM frequency) f
_PWM is generated.

Crystal oscillator 70 and capacitors 71 and 72
Is also connected to the RD converter 127 in parallel with the microcomputer 122. In the RD converter 127, the oscillation frequency of the crystal oscillator 70 is divided, and the frequency (excitation frequency) f _RES of the excitation signal of the VR resolver 102 is generated.

Next, the operation of this embodiment will be described.
The steering torque of the steering wheel is detected by the steering torque detection unit 106, and the steering torque signal output from the steering torque detection unit 106 is output to the motor control unit 1. In the motor control unit 1, the motor energization target currents (d-axis and q-axis final target currents Id ^* , Iq ^* ) are calculated based on the steering torque signal output from the steering torque detection unit 106, the vehicle speed, and the like.

Motor energization target current and motor current detector 1
18, 119 generate motor currents (driving currents Iu, I
w) and PWM for driving the brushless motor 101 based on the motor rotation angle signal generated by the motor rotation angle detection unit
The duty ratio is calculated, and a sine wave current (driving current Iu, driving current Iu, to the winding of the brushless motor 101 via the pre-drive circuit 128 and the FET bridge in the motor driving unit 116.
Iv, Iw) is energized to perform vector control. The motor rotation angle detectors 118 and 119 are provided for the VR resolver 102 and R, respectively.
It is composed of a D converter 127 and its peripheral circuits.

PWM for driving the brushless motor 101
The frequency is out of the audible range, and is generated by dividing the oscillation frequency of the crystal oscillator 70 connected to the microcomputer 122 in the microcomputer 122.
The crystal oscillator 70 is used in the microcomputer 12
The VR resolver 102 is also connected to the RD converter 127, which is an element of the motor rotation angle detection unit, in parallel with the VR resolver 102.
The excitation frequency is generated by dividing the oscillation frequency of the crystal oscillator 70 in the RD converter 127.

Here, the PWM frequency f _PWM is 20 kHz,
The resolver excitation frequency f _RES is 10 kHz, but since these frequencies are generated from the same crystal oscillation circuit, the PWM frequency f _PWM is exactly an integral multiple of the excitation frequency f _RES . Therefore, the difference frequency f1 = f _PWM
-F _RES is exactly 10 Hz, which matches the excitation frequency f _RES . In addition, the frequency difference f2 = nx
f _PWM −mxf _RES (n = 1,2, ..., m = 1,2 ,.
・) Is equal to 0 Hz or the excitation frequency f _RES or becomes an integral multiple. Therefore, the output sin (θ) after the synchronous detection in the synchronous detection unit 138 at the time of the RD conversion shown in FIG.
-Φ) does not fluctuate, and the difference frequency f1 or f2 does not fluctuate in the output from the RD converter. As a result, the output fluctuation of the brushless motor does not occur. Therefore, it is possible to obtain the electric power steering apparatus having a smooth steering feeling in which the steering assist force does not change at low frequencies.

In the present embodiment, one crystal oscillator is connected in parallel to the microcomputer and the RD converter and the clock frequency is made common so that the PWM frequency becomes an integral multiple of the resolver excitation frequency. However, the crystal oscillator is connected to the microcomputer and the clock frequency signal is output from the microcomputer.
The PWM frequency may be set to an integral multiple of the resolver excitation frequency by sending it to the D converter. Conversely, the crystal oscillator is connected to the RD converter and the clock frequency signal is supplied to the RD converter.
The PWM frequency may be an integral multiple of the resolver excitation frequency by sending it from the converter to the microcomputer.

[0072]

As is apparent from the above description, the present invention has the following effects.

Since either one of the PWM drive frequency f _{PWM for} controlling the drive of the brushless motor and the excitation frequency f _RES of the resolver is set to an integral multiple of the other, f1 = f _PWM -f
_RES or f2 = nxf _PWM- mxf _RES becomes 0 Hz or becomes the excitation frequency f _RES or becomes an integral multiple, the output of the brushless motor does not fluctuate, the steering assist force does not fluctuate, and a smooth steering feel is obtained. You can get the ring.

The PWM drive frequency f _{PWM for} controlling the drive of the brushless motor and the excitation frequency f _{RES of the} resolver are generated by the output of the same oscillator, and either one of the PWM drive frequency f _PWM and the excitation frequency f _RES of the resolver is generated. Since it is an integral multiple of the other, f1 or f2 surely becomes 0 Hz or the excitation frequency f _RES or becomes an integral multiple, and the output fluctuation of the brushless motor does not occur and the steering assist force also does not fluctuate. It is possible to obtain a smooth steering feeling.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an electric power steering device according to the present invention.

FIG. 2 is a sectional view taken along line 4-4 of FIG.

3 is a sectional view taken along line 5-5 of FIG.

FIG. 4 is a circuit diagram showing electric motor control means of the electric power steering apparatus according to the present invention.

FIG. 5 is a block diagram showing a motor control means of a conventional electric power steering device.

FIG. 6 is a circuit diagram showing an electric motor control means of a conventional electric power steering device.

FIG. 7 is a schematic diagram showing the principle of a resolver.

FIG. 8 is a diagram showing the principle of RD conversion in the RD converter.

[Explanation of symbols]

10 Electric power steering system 13 gearbox 14 Steering torque detector 15 Motor control unit 16 brushless motor 70 Crystal oscillator 71 Capacitor 72 Capacitor 102 resolver 122 Microcomputer 123 Interface circuit 124 Interface circuit 125 interface circuit 126 RD converter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuo Shimizu             1-4-1 Chuo Stock Market, Wako City, Saitama Prefecture             Inside Honda Research Laboratory (72) Inventor Takashi Kuribayashi             1-4-1 Chuo Stock Market, Wako City, Saitama Prefecture             Inside Honda Research Laboratory F-term (reference) 3D033 CA03 CA13 CA16 CA19 CA20                       CA21                 5H560 AA10 BB04 BB07 BB12 DA10                       DB20 DC12 DC20 EB01 EC01                       EC10 GG04 SS02 TT15 TT20                       UA05 XA02 XA12 XA13

Claims (2)

[Claims] 1. A steering torque detecting means for detecting a steering torque of a steering wheel, a motor for applying an auxiliary torque to a steering system, a motor rotation angle detecting means for detecting a rotation angle of the motor, and a motor energized by the motor. An electric motor equipped with a motor current detecting means for detecting a current and at least a motor controlling means for performing PWM drive control of the motor based on signals output from the steering torque detecting means, the motor rotation angle detecting means and the motor current detecting means. In the power steering device, the motor is a brushless motor, and the motor rotation angle detection means includes a resolver, and one of the PWM drive frequency for controlling the drive of the brushless motor and the excitation frequency of the resolver. Electric power characterized by making one of them an integral multiple of the other Steering system. 2. The P that drives and controls the brushless motor by performing the PWM drive and the resolver excitation with a signal generated and output from the same oscillator.
2. The electric power steering apparatus according to claim 1, wherein one of the WM drive frequency and the excitation frequency of the resolver is set to an integral multiple of the other.