JP2007325495A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering system which gives smooth feeling of steering, and which does not have output fluctuations of a brushless motor or the fluctuations of steering auxiliary force. <P>SOLUTION: The motor power steering system is provided with a steering torque detection means, a motor for imparting auxiliary torque to the steering system, a motor rotating angle detection means for detecting the rotational angle of the motor, a motor current detection means for detecting motor current, and a motor control means 15 for PWM for drive-controlling the motor, based on signals output from the steering torque detection means, the motor rotational angle detection means, and the motor current detection means. The motor is a brushless motor 101, and the motor rotational angle detection means is constituted to include a resolver 102. PWM driving and resolver magnetization are operated by a signal generated and outputted from the same oscillator, so that either a PWM drive frequency for drive-controlling the brushless motor 101 or the magnetizing frequency of the resolver is set to an integral multiple of the other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus, and more particularly, to an electric power steering apparatus that reduces the burden on a driver's steering force by applying motor power to a steering system in an automobile steering apparatus.

  The electric power steering device performs driving control of the motor by the motor control unit to reduce the steering force based on signals output from the steering torque detection unit that detects the steering torque and the vehicle speed detection unit that detects the vehicle speed. Yes. An electric power steering apparatus using a brushless motor as the motor is known.

  Since the electric power steering apparatus using the brushless motor does not have a decrease or fluctuation in the motor output due to a voltage drop between the brush and the commutator, a stable steering assist force can be obtained. Further, since the moment of inertia of the motor is smaller than that of a motor with a brush, a good steering feeling can be obtained when the vehicle goes straight at a high speed or when the steering wheel is switched.

  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. An angle detection unit and a motor current detection unit are provided, and PWM drive control of the brushless motor is performed based on output signals of the motor rotation angle detection unit and the motor current detection unit.

  FIG. 5 is a block diagram showing a motor control unit 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.

  A 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 corrects the phase of the steering torque signal T from the steering torque detection unit 106 based on the vehicle speed signal v from the vehicle speed detection unit 107, and outputs the corrected steering torque signal T ′ to the target current setting unit 108. To do. The inertia correction unit 104 is an angle obtained by differentiating 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 by the differentiation processing unit 121d. An inertia correction signal di for correcting the inertia is generated from the signal corresponding to the acceleration, and the inertia correction signal di is output to the addition operator 109. The damper correction unit 105 generates a damper correction signal dd for correcting the damper 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, The damper correction signal dd is output to the subtraction operator 110.

  The target current setting unit 108 calculates and outputs the two-phase target currents Id1 and Iq1 based on the corrected steering torque signal T ′ and the vehicle speed signal v. The 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 created by the permanent magnet on the rotor of the brushless motor 101, respectively. These target currents Id1 and Iq1 are referred to as “d-axis target current” and “q-axis target current”, respectively.

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

The final target current their d-axis and q-axis Id ^*, Iq ^* in the deviation calculation unit 111, the final target current of the d-axis and q-axis Id ^*, the detected current Id of the d-axis and q-axis from the Iq ^*, and Iq Deviations DId and DIq are calculated by subtraction, respectively, and output to PI setting section 112.

  The PI setting unit 112 executes the calculation using the deviations DId and DIq so that the d-axis and q-axis target currents Id and Iq follow the final target currents of the d-axis and q-axis. The voltages Vd and Vq are calculated 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 non-interacting control unit 113 and the calculation unit 114, and dq-3 phase conversion means 115. Is output.

  In FIG. 5, for convenience of illustration, FIG. 5 shows one set of addition calculation unit 109, subtraction calculation unit 110, deviation calculation unit 111, PI setting unit 112, and calculation unit 114. Are individually provided for each of the two target currents Id1, Id2.

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

  The calculation unit 114 calculates the d-axis and q-axis correction target voltages Vd ′ and Vq ′ by subtracting the non-interacting control correction values from the d-axis and q-axis target voltages Vd and Vq, respectively. Output to the three-phase conversion means 115.

The dq-3 phase conversion unit 115 converts the d-axis and q-axis correction target voltages Vd ′ and Vq ′ into the three-phase target voltages Vu ^* , Vv ^* and Vw ^*, and converts the three-phase target voltages Vu ^* and Vv ^*. , Vw ^* is output to the motor drive unit 116.

Motor drive unit 116 includes a PWM voltage generation unit and an inverter circuit. The motor drive unit 116 generates PWM control voltage signals UU, VU, WU corresponding to the three-phase target voltages Vu ^* , Vv ^* , Vw ^* by a PWM voltage generation unit (not shown) in the motor drive unit 116 to drive the motor. The data is output to an inverter circuit (not shown) in the unit 116. The inverter circuit generates three-phase AC drive currents Iu, Iv, and Iw corresponding to the PWM control voltage signals UU, VU, and WU, and supplies these to the brushless motor 101 via the three-phase drive current path 117, respectively. . Three-phase AC drive currents Iu, Iv, and Iw are sinusoidal currents for PWM driving the brushless motor.

  Motor current detectors 118 and 119 are provided in two of the three-phase drive current paths 117, and each of the motor current detectors 118 and 119 is provided with a three-phase drive current Iu, Two drive currents Iu and Iw of Iv and Iw are detected and output to the three-phase-dq converter 120. In the three-phase-dq converter 120, the remaining drive current Iv is also calculated based on the detected drive currents Iu and Iw. The three-phase-dq converter 120 converts these three-phase detection drive currents Iu, Iv, Iw into two-phase d-axis and q-axis detection currents Id, Iq.

  A signal from the resolver 102 is continuously supplied to an RD (resolver digital) converter 121. The RD conversion unit 121 calculates an angle (rotation angle) θ of the rotor of the brushless motor 101 with respect to the stator, and outputs a signal corresponding to the calculated angle θ to the dq-3 phase conversion unit 115 and the 3-phase-dq conversion. To the unit 120. Further, 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 decouples the signal corresponding to the calculated rotational angular velocity ω from the damper correction unit 105 and the differential processing unit 121d. This is supplied to the control unit 113. The resolver 102 and the RD conversion unit 121 form a motor rotation angle detection unit 102A.

  As shown in FIG. 6, the motor control unit 100 configured as described above is housed in an electronic circuit unit except for various sensors and an inverter circuit, and is configured by a microcomputer 122. And each part in an electronic circuit unit implement | achieves each function by program processing.

  In FIG. 6, the interface circuit 123 converts 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 analog signal of the engine rotation signal r from the engine rotation detection unit 124 into digital signals. An A / D converter for conversion is provided, and those input analog signals are converted into digital signals and input to the microcomputer 122.

  The interface circuit 125 converts the drive currents Iu and Iw detected by the motor current detection units 118 and 119 into digital signals and inputs the digital signals to the microcomputer 122. The interface circuit 126 sends the excitation current from the RD converter 127 to the resolver 102 and sends the output signal from the resolver 102 to the RD converter 127. The RD converter 127 outputs an angle signal from the output signal from the resolver 102 and sends it to the microcomputer 122 as described later. The motor driving unit 116 includes a pre-drive 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, and PWM for driving the brushless motor 101. The frequency of the signal (PWM frequency) f _PWM is generated.

A crystal oscillator 132 and capacitors 133 and 134 are connected to the RD converter 127. In the RD converter 127, the oscillation frequency of the crystal oscillator 132 is divided, and the frequency (excitation frequency) of the excitation signal of the VR resolver 102. f _RES is generated.

  In order to obtain an electric power steering apparatus having a smooth steering feeling, a smooth output of a brushless motor is required. For this reason, as described above, based on the output signals of the motor rotation detection unit and the motor current detection unit, the motor control unit performs vector control of the brushless motor and energizes the sine wave current as the motor current so that the torque fluctuation is small. It is conceivable to obtain an output.

The brushless motor is energized with a sine wave current through a motor drive unit (inverter) constituted by a switching element such as an FET and a peripheral circuit. Such a switching element is driven at a frequency f _PWM outside the audible range and supplies power to the brushless motor 101.

  Furthermore, since the absolute rotation angle of the brushless motor is required for vector control, a motor rotation angle (others, angular velocity, angular acceleration) detection unit such as a resolver is used. The resolver detects the rotation angle by detecting the gap change of 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 an exciting coil, and coils B and C are two output coils that are perpendicular to each other on the opposite side. Since the magnetic field due to the current flowing through the coil A passes through the coils B and C and the current changes with time, induced electromotive forces are generated in the coils B and C according to Faraday's law.

That is, the voltage of the angular frequency ω _{E in} the equation (1) is applied to the excitation side terminals R1 and R2 as one-phase excitation.

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

FIG. 8 shows the principle of RD conversion in the RD converter 127. The output voltage E _S1-S3 input in the RD converter 127 is calculated by the arithmetic unit 135 with the product of the internal ROM angle φ and the sine sin φ. Further, the calculation unit 136 calculates the product of the output voltage E _S2 -S4 and the cosine cos φ of the angle φ of the internal ROM. The calculation unit 137 obtains the difference D1 expressed by the equation (4).

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

  The signal of the difference D1 is synchronously detected by the synchronous detection unit 138 with the excitation input voltage. As a result, the signal D2 expressed by the equation (6) is output.

  The signal D2 is increased or decreased by the VCO unit 139 and the counter 140 so that the signal D2 is always zero, and the angle θ is output.

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

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 each higher order, F2 = nxf _PWM− mxf _RES (n = 1, 2,..., M = 1, 2,...), And as a result f1 (Hz ) Or f2 (Hz) output fluctuation occurs. In the conventional motor control means shown in FIG. 6, this output fluctuation occurs for the following reason even if the PWM frequency f _PWM and the excitation frequency f _RES are set to the same frequency.

In FIG. 6, the frequency f _PWM of the PWM signal is generated by dividing the oscillation frequency of the crystal oscillator 129 in the microcomputer 122. The excitation voltage frequency f _RES is generated by dividing the oscillation frequency of the crystal oscillator 132 in the RD converter 127. As described above, the PWM frequency f _PWM and the excitation frequency f _RES are generated from two different crystal oscillation circuits, respectively. Therefore, the load depends on the variation of the crystal oscillator and the variations of the capacitors 130 and 131 and the capacitors 133 and 134. The capacitance varies, and even if the crystal oscillation is stable in frequency, a difference occurs in the frequency of signals generated from two different crystal oscillation circuits. Therefore, it is difficult to make the PWM frequency f _PWM and the excitation frequency f _RES exactly the same. From the above, the output of the RD converter 127 varies, and as a result, the steering assist force also varies. This causes a problem that the steering feel is disturbed and the steering feeling is hindered.

  The object of the present invention is to solve the above problems, in the case of using a brushless motor that does not have a feeling of deterioration due to brush wear or rotor inertia moment, there is no fluctuation in output of the brushless motor, and there is no fluctuation in steering assist force. It is an object of the present invention to provide an electric power steering device that has a smooth steering feeling.

  The electric power steering apparatus according to the present invention is configured as follows to achieve the above object.

A first electric power steering apparatus (corresponding to claim 1) includes a steering torque detecting means for detecting a steering torque, a motor for applying an auxiliary torque to a steering system, and a motor rotation angle detection for detecting a rotation angle of the motor. Motor current detecting means for detecting motor current supplied to the motor, and motor control means for PWM driving control of the motor based on signals output from at least steering torque detecting means, motor rotation angle detecting means, and motor current detecting means The motor is a brushless motor, and the motor rotation angle detection means includes a resolver, and a signal generated and output from the same oscillator for PWM drive and resolver excitation. PWM drive frequency that controls the drive of a brushless motor by And one of the excitation frequencies of the resolver is made an integral multiple of the other.

According to the above electric power steering apparatus, since the other integral multiple of either one of the excitation frequency f _RES of the PWM driving frequency f _PWM and the resolver for driving and controlling the brushless motor, f1 = f _PWM -f _RES or f2 = nxf _PWM− mxf _RES (n = 1, 2,..., m = 1, 2,...) is 0 Hz or f1 or f2 is an integral multiple of f _RES , and output fluctuation from the RD conversion unit is eliminated. Therefore, the output fluctuation of the brushless motor does not occur, the steering assist force does not vary, and a smooth steering feeling can be obtained.

In addition , 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 one of f _PWM and f _RES 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 surely 0 Hz or f1 or f2 is an integral multiple of f _RES , Since fluctuations in the output from the RD converter are eliminated, fluctuations in the output of the brushless motor do not occur, fluctuations in the steering assist force do not occur, and a smooth steering feeling can be obtained.

As is apparent from the above description, the present invention has the following effects.
PWM drive frequency f for driving and controlling the brushless motor _PWM And resolver excitation frequency f _RES Since one of them is an integral multiple of the other, f1 = f _PWM -F _RES Or f2 = nxf _PWM -Mxf _RES Is 0 Hz or excitation frequency f _RES Or an integral multiple of the output of the brushless motor, the fluctuation of the output of the brushless motor is not generated, the fluctuation of the steering assist force is not generated, and a smooth steering feeling can be obtained.
PWM drive frequency f for driving and controlling the brushless motor _PWM And resolver excitation frequency f _RES Is generated by the output of the same oscillator, and the PWM drive frequency f _PWM And resolver excitation frequency f _RES Since one of them is an integral multiple of the other, f1 or f2 is reliably 0 Hz or the excitation frequency f _RES Or an integer multiple, the brushless motor output does not fluctuate, the steering assist force does not fluctuate, and a smooth steering feeling can be obtained.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention, and shows a left end portion and a right end portion in cross section. This figure shows that the rack shaft 11 of the electric power steering apparatus 10 is accommodated in a housing 12 extending in the vehicle width direction (left-right direction in the figure) so as to be slidable in the axial direction. The component 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 screwed to both ends in the longitudinal direction protruding from the housing 12 and left and right tie rods 18 are connected to the ball joints 17. The housing 12 is provided with brackets 19 for attachment 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, and 82 is an 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 hits the stopper 20. When the rack shaft 11 slides to the left by a predetermined amount, the contact end surface (rack end) 21 of the right ball joint 17 comes into contact with the stopper 20. By restricting the amount of movement of the rack shaft 11 in this way, the maximum steering angle of left and right steering wheels (not shown) can be limited. That is, when the rack shaft 11 moves to the end of movement, the steering angle of the left and right steering wheels is maximized. In the figure, 22 is a dust seal boot.

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

  The housing 12 is set in a vertical orientation 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 includes a rack guide 30. Reference numeral 31 denotes a lid mounting bolt, and 32 denotes a retaining ring.

  The pinion 33 and the rack 34 are plastic processed products such as cast products (including rolled products). Specifically, the input shaft 23 is a pinion shaft in which a pinion 33 is integrally formed at a lower portion, a screw portion 35 is further formed at a lower end portion, and an upper end portion is projected outward from the lid 27. The rack 34 is formed integrally with the rack shaft 11. By screwing the nut 36 into the screw part 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 includes a guide portion 40 that contacts the rack shaft 11 from the opposite side of the rack 34, and an adjustment bolt 42 that pushes the guide portion 40 via a compression spring (adjustment spring) 41. According to such a rack guide 30, a preload is applied to the rack 34 by the guide portion 40 by pressing the guide portion 40 with an appropriate pressing force via the compression spring 41 with the adjusting bolt 42 screwed into the housing 12. Thus, the rack 34 can be pressed against the pinion 33. 43 is a contact member for sliding the back surface of the rack shaft 11, and 44 is a lock nut.

  3 is a cross-sectional view taken along line 5-5 of FIG. 2, and shows a relationship among the input shaft 23, the electric motor 16, the torque limiter 45, and the gear type reduction mechanism 26. The electric motor 16 is attached to the housing 12 with the output shaft 46 facing sideways, and the output shaft 46 extends into the housing 12.

  The gear 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 includes a worm gear mechanism that is a combined structure of a drive gear and a driven gear. Specifically, the gear type reduction mechanism 26 is coupled to the output shaft 46 of the electric motor 16 via a torque limiter 45, a worm 48 formed on the transmission shaft 47, meshed with the worm 48 and coupled to the input shaft 23. 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 a shaft that 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 configured such that a first bearing 50 located near the output shaft 46 is attached so as not to move 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 face of the outer ring of the second bearing 51 is pushed toward the output shaft 46 by the adjusting bolt 53 via the leaf spring 52. The preload is applied to the first and second bearings 50 and 51 by the pressing force of the adjusting bolt 53 and the thin disc-shaped leaf spring 52, thereby adjusting the transmission shaft 47 so that there is no play in the axial direction. The backlash can be removed. In addition, the axial displacement of the worm 48 can be adjusted so that the meshing between the worm 48 and the worm wheel 49 can be adjusted so that there is no backlash while maintaining proper friction. Further, due to the elasticity of the leaf spring 52, the thermal expansion or the like of the transmission shaft 47 in the axial direction can be absorbed. Reference numeral 54 denotes a lock nut, and 55 denotes 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, etc. (not shown). The rotation of the input shaft 23 from the steering wheel is converted into the axial displacement of the rack shaft 11 through the pinion gear 24 and the rack gear 34, and the front wheel (not shown) is swung through the tie rod 18 by this axial displacement to steer the vehicle. I do.

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

  A serration 56 is provided on the inner periphery of the input shaft 23, and a serration 57 provided on the outer peripheral surface of the output shaft 46 of the brushless motor 16 is engaged with the serration 56, and the output of the brushless motor 16 is transmitted through the clutch 58 to the worm gear. Is transmitted to.

  The motor control unit 15 described above is basically the same as that described with reference to FIGS. 5 and 6. As shown in FIG. 4, a one-chip microcomputer and peripheral circuits, a pre-drive circuit, an FET bridge, a current sensor, It consists of a relay, RD converter, etc. In FIG. 4, the same reference numerals are given to the same elements as those described in the conventional motor control unit. Except for various sensors and inverter circuits, they are housed in an electronic circuit unit, and are constituted by a microcomputer 122. And each part in an electronic circuit unit implement | achieves each function by program processing. Conventionally, in the motor control unit, two crystal oscillators of the crystal oscillator 129 connected to the microcomputer 122 and the crystal oscillator 132 connected to the RD converter 127 are used. Two crystal oscillators are connected to both the microcomputer 122 and the RD converter 127.

  In FIG. 4, the interface circuit 123 converts 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 analog signal of the engine rotation signal r from the engine rotation detection unit 124 into digital signals. An A / D converter for conversion is provided, and those input analog signals are converted into digital signals and input to the microcomputer 122.

  The interface circuit 125 converts the excitation currents Iu and Iw detected by the motor current detection units 118 and 119 into digital signals and inputs them to the microcomputer 122. The interface circuit 126 sends the excitation current from the RD converter 127 to the resolver 102 and sends the output signal from the resolver 102 to the RD converter 127. The RD converter 127 outputs an angle signal from the output signal from the resolver 102 and sends it to the microcomputer 122 as described later. The motor driving unit 116 includes a pre-drive 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 oscillation frequency of the crystal oscillator 70 is divided, and PWM for driving the brushless motor 101. The frequency of the signal (PWM frequency) f _PWM is generated.

The crystal oscillator 70 and the capacitors 71 and 72 are 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 detection unit 106 detects the steering torque of the steering wheel, 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, motor energization target currents (d-axis and q-axis final target currents Id ^* and Iq ^* ) are calculated based on the steering torque signal output from the steering torque detection unit 106, the vehicle speed, and the like.

  The PWM duty ratio for driving the brushless motor 101 is calculated based on the motor energization target current, the motor current (drive currents Iu, Iw) generated by the motor current detection units 118 and 119, and the motor rotation angle signal generated by the motor rotation angle detection unit. Then, a sinusoidal current (drive currents Iu, Iv, Iw) is supplied to the windings of the brushless motor 101 via the pre-drive circuit 128 in the motor drive unit 116 and the FET bridge to perform vector control. The motor rotation angle detection units 118 and 119 are configured by the VR resolver 102, the RD converter 127, and its peripheral circuits.

  The PWM frequency for driving the brushless motor 101 is a frequency outside 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 also connected in parallel with the microcomputer 122 to an RD converter 127 that is an element of the motor rotation angle detection unit. The excitation frequency of the VR resolver 102 is equal to the oscillation frequency of the crystal oscillator 70 RD. The frequency is generated by dividing in the converter 127.

Here, the PWM frequency f _PWM is 20 kHz and the resolver excitation frequency f _RES is 10 kHz. Since these frequencies are generated from the same crystal oscillation circuit, the PWM frequency f _PWM is accurately an integer of the excitation frequency f _RES . It has doubled. Therefore, the frequency f1 = f _PWM -f _RES differences are exactly 10Hz becomes consistent with the excitation frequency f _RES. Moreover, the frequency f2 = nxf _PWM− mxf _RES (n = 1, 2,..., M = 1, 2,...), Which is the difference between the higher-order frequencies, coincides with 0 Hz or the excitation frequency f _RES or becomes an integral multiple. Therefore, no fluctuation occurs in the output sin (θ−φ) after the synchronous detection in the synchronous detection unit 138 at the time of the RD conversion shown in FIG. 8, and the fluctuation of the difference frequency f1 or f2 appears in the output by the RD converter. Absent. As a result, the output fluctuation of the brushless motor does not occur. Therefore, it is possible to obtain an electric power steering apparatus having a smooth steering feeling in which the steering assist force is not accompanied by a low frequency fluctuation.

  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 is an integer multiple of the resolver excitation frequency. By connecting the crystal oscillator to the microcomputer and sending the clock frequency signal from the microcomputer to the RD converter, the PWM frequency may be made an integer multiple of the resolver excitation frequency. Conversely, the crystal oscillator is connected to the RD converter, The PWM frequency may be set to an integral multiple of the resolver excitation frequency by sending a clock frequency signal from the RD converter to the microcomputer.

INDUSTRIAL APPLICABILITY The present invention is used as a device that does not cause a change in steering assist force in an electric power steering device that assists the steering force of a steering system in a passenger car or the like.

1 is an overall configuration diagram of an electric power steering apparatus according to the present invention. FIG. 4 is a sectional view taken along line 4-4 of FIG. FIG. 5 is a sectional view taken along line 5-5 of FIG. It is a circuit diagram which shows the electric motor control means of the electric power steering apparatus which concerns on this invention. It is a block block diagram which shows the electric motor control means of the conventional electric power steering apparatus. It is a circuit diagram which shows the electric motor control means of the conventional electric power steering apparatus. It is a schematic diagram which shows the principle of a resolver. It is a figure which shows the principle of RD conversion in an RD converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 13 Gear box 14 Steering torque detection part 15 Motor control part 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

Claims (1)

Steering torque detection means for detecting steering torque, a motor for applying auxiliary torque to the steering system, motor rotation angle detection means for detecting the rotation angle of the motor, and a motor for detecting motor current supplied to the motor An electric power steering apparatus comprising: current detection means; and motor control means for performing PWM drive control of the motor based on signals output from at least the steering torque detection means, the motor rotation angle detection means, and the motor current detection means. And
The motor is a brushless motor, and the motor rotation angle detection means includes a resolver,
By performing the PWM drive and the resolver excitation with a signal generated and output from the same oscillator, either the PWM drive frequency for driving the brushless motor or the excitation frequency of the resolver is set to the other integer. Electric power steering device characterized by doubling.

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