JP2010137627A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the faulty determination of a reverse assist abnormality in two-phase drive due to an energization failure in one phase of a three-phase motor. <P>SOLUTION: When the energization failure to an electric motor 20 occurs only in one phase, a command current for two-phase energization is calculated based on a current calculating expression for the two-phase energization for generating a torque not changed relative to a change in the electrical angle of the motor 20, the maximum current regulating the upper limit current of the motor 20, and an advance angle amount advancing the phase of the command current, and then, the motor 20 is controlled by the two-phase energization by this command current. On this occasion, the reverse assist abnormality is determined by a code mismatch between the command current and an actual current, however, in a region in the vicinity of the electrical angle having the code of the command current inverted, the determination of the reverse assist abnormality is not performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering device that generates a steering assist torque by drivingly controlling a three-phase motor based on a driver's steering operation.

  2. Description of the Related Art Conventionally, an electric power steering apparatus calculates a target assist torque of an electric motor based on a steering operation performed by a driver, and controls an energization amount of the electric motor so as to obtain this target assist torque. An electric power steering apparatus using a three-phase motor as an electric motor has also been generalized. When a three-phase motor is used, current feedback control using a dq coordinate system is generally performed. For example, a target assist torque is calculated based on the steering torque or vehicle speed input to the steering wheel by the driver, and a q-axis command current for generating the target assist torque and a d-axis command current (in a direction in which no torque is generated) ( For example, zero) is calculated. On the other hand, a three-phase motor current is detected by a current sensor, and this actual current is converted into an actual q-axis current and an actual d-axis current in the dq coordinate system. Then, current feedback control is performed so that the actual q-axis current is equal to the q-axis command current and the actual d-axis current is equal to the d-axis command current. An electric power steering apparatus that controls a motor using such a dq coordinate system is proposed in Patent Document 1.

  In addition, the electric power steering apparatus proposed in Patent Document 1 compares the q-axis command current and the actual q-axis current to monitor the abnormality of the control system, and compares the q-axis command current and the actual q-axis current. When the deviation exceeds the threshold, it is determined that an abnormality of the motor control system has occurred. Furthermore, this electric power steering device uses two normal phases when a power failure occurs in one of the three phases due to disconnection of the power supply system, failure of the switching element of the motor drive circuit, or the like. The motor is driven by flowing a sine wave current in two phases. Even when the two-phase energization drive is performed, the motor control system is monitored for abnormalities. In this case, the threshold for determining the deviation between the q-axis command current and the actual q-axis current is changed so as to correspond to the fluctuation of the actual q-axis current to prevent erroneous determination.

JP 2008-211191 A

この例は、Ｗ相が通電不良となったときのＶ相の電流演算式であり、Ｔは目標モータトルク、ｅ₀はトルク定数、θｅはモータ電気角を表す。また、Ｕ相は、Ｖ相を反転したもの（Ｉu＝−Ｉv）となる。 However, in the electric power steering device proposed in Patent Document 1, since the sine wave current flows in the two phases where no conduction failure occurs during the two-phase energization drive, the torque increases with the change in the motor electrical angle. It will fluctuate. On the other hand, if energization is controlled using a two-phase energization current calculation formula for generating a constant torque with respect to a change in motor electrical angle, the torque becomes theoretically constant. This two-phase energization current calculation formula can be expressed, for example, as follows.

This example is a V-phase current calculation formula when the W-phase becomes a current-carrying failure, where T represents a target motor torque, e ₀ represents a torque constant, and θe represents a motor electrical angle. In addition, the U phase is obtained by inverting the V phase (Iu = −Iv).

  In this case, since the current value on the arithmetic expression becomes infinite at a specific electrical angle, the current of each phase is limited to a predetermined maximum current value or less. Therefore, the current waveform is as shown in FIG.

  When a current having such a waveform flows in two normal phases, the current value changes suddenly from positive to negative or from negative to positive before and after a specific electrical angle (90 deg and 270 deg in this example). . For this reason, when determining abnormality of a control system based on this electric current, there exists a possibility of misjudging.

  An object of the present invention is to cope with the above-described problem, and suppresses erroneous determination of an abnormality in a motor control system even when one phase of a three-phase motor is poorly energized and driven by two-phase energization. There is.

  In order to achieve the above object, the present invention is characterized by a three-phase motor that is provided in a steering mechanism and generates steering assist torque, and motor control means for controlling energization of the motor based on a steering operation of a driver. The motor control means includes: current detection means for detecting current flowing in each phase of the motor; electrical angle detection means for detecting an electrical angle of the motor; and each of the motors An electrical angle of the motor is detected by using an energization failure detecting means for detecting the occurrence of an energization failure in the phase and two phases in which no energization failure occurs when only one phase of the energization failure occurs in the motor. A command current for two-phase energization is calculated on the basis of a two-phase energization current calculation formula for generating torque that does not fluctuate with respect to changes in the motor and a maximum current that defines the upper limit current of the motor. Two-phase energization control means for driving and controlling the motor by energizing the two phases in which energization failure has not occurred with the calculated two-phase energization command current, the two-phase energization command current, and the current detection An abnormality determining means for determining an abnormality of the motor control system based on a comparison with the current detected by the means, and the abnormality in the vicinity of the motor electrical angle where the energization direction of the command current for the two-phase energization is reversed. An abnormality determination limiting unit that prohibits the abnormality determination by the determination unit or invalidates the abnormality determination determined by the abnormality determination unit.

  In the present invention, the steering assist torque is generated in the steering mechanism by controlling the energization of the three-phase motor by the motor control means. A three-phase brushless motor is suitable as the three-phase motor. The motor control means is able to drive the motor using the normal two-phase even if a power failure to the three-phase motor occurs, and properly correct the motor control system abnormality even when driving the motor using the two-phase. Current detection means, electrical angle detection means, conduction failure detection means, two-phase conduction control means, abnormality determination means, and abnormality determination restriction means.

  When it is detected by the energization failure detecting means that only one phase of energization to the motor has occurred, the two-phase energization control means drives and controls the motor using two normal phases. In this case, the two-phase energization control means includes a two-phase energization current calculation formula for generating torque that does not fluctuate with respect to a change in the electrical angle of the motor, and a maximum current (maximum current value) that defines the upper limit current of the motor. Based on the above, a command current (command current value) for two-phase energization is calculated, and the motor is driven and controlled by energizing the two phases in which no conduction failure has occurred with the calculated two-phase energization command current .

  The current calculation formula for two-phase energization sets the current for two-phase energization corresponding to the electrical angle of the motor detected by the electrical angle detection means, but the magnitude of the current (absolute value when approaching a specific electrical angle) ) Increases rapidly and passes through the specific electrical angle, the sign (current direction) is reversed and the current magnitude (absolute value) decreases. The maximum current is set to protect the motor and motor drive circuit. Therefore, the magnitude (absolute value) of the command current for two-phase energization is limited to the maximum current in the region near the specific electrical angle. Note that the current calculation formula for two-phase energization is set at a phase corresponding to the phase of the energization failure, and therefore the specific electrical angle varies accordingly.

  The abnormality determination means determines whether the motor control system is abnormal based on a comparison between the command current for two-phase energization and the current detected by the current detection means when the motor is driven and controlled by the two-phase energization control means. To do. When a motor is driven based on a command current for two-phase energization, the sign (direction of current) of the command current is suddenly reversed at a specific electrical angle, so the command current and the actual current are in the vicinity of the specific electrical angle. When compared with (the current detected by the current detection means), there is a possibility that the abnormality determination is made even if the motor control system is normal.

  Therefore, in the present invention, abnormality determination limiting means is provided. The abnormality determination limiting unit prohibits abnormality determination by the abnormality determination unit in a region near the motor electrical angle where the energization direction of the command current for two-phase energization is reversed when the motor is driven and controlled by the two-phase energization control unit. Alternatively, the abnormality determination determined by the abnormality determination means is invalidated. Thereby, erroneous determination of abnormality in the motor control system can be suppressed.

  Note that the motor control means may control the energization of the motor using, for example, a command current in the dq coordinate system, when there is no failure in energizing the three phases. In this case, the motor control means sets the target assist torque based on the steering torque and the vehicle speed input to the steering handle, the q-axis command current corresponding to the target assist torque, and the d-axis command that does not generate the assist torque. Calculate the current. Further, the current flowing in the three phases detected by the current detecting means is converted into an actual q-axis current and an actual d-axis current in the dq coordinate system. Then, the actual q-axis current and the actual d-axis current are fed back to the q-axis command current and the d-axis command current, the deviation between the q-axis command current and the actual q-axis current, and the d-axis command current and the actual d-axis current. The three-phase energization amount (voltage or current) corresponding to the deviation is calculated, and the motor is driven with this energization amount. In this case, the two-phase energization control means may set a two-phase energization current calculation formula based on the target assist torque or the q-axis command current.

  In addition, a feature of the present invention is that the abnormality determination unit is configured such that when the direction of the command current for the two-phase energization does not match the direction of the current detected by the current detection unit, the motor It is determined that it is a reverse assist abnormality that generates a steering torque in a direction opposite to the steering direction.

  In the present invention, the abnormality determination unit determines whether or not the direction of the command current for two-phase energization matches the direction of the current detected by the current detection unit. If the directions (signs) of the currents do not match, the motor is generating the steering torque in the opposite direction to the driver's steering direction (the direction in which the target assist torque is generated). Therefore, the abnormality determination means determines the reverse assist abnormality by detecting such a mismatch in the current direction. In this case, the abnormality determination is restricted by the abnormality determination limiting means in the vicinity of the motor electrical angle where the direction of energization of the command current for two-phase energization is reversed, or the abnormality determination is invalidated. An erroneous determination of abnormality can be suppressed.

  Another feature of the present invention is that the two-phase energization control means advances the electric angle of the motor in the current calculation formula for two-phase energization by a predetermined advance amount, and the command current for the two-phase energization Is to calculate.

  When the motor is driven and controlled by the two-phase energization control means, the maximum current limit acts in the vicinity of the electrical angle where the energization direction is reversed, and the torque that can be generated by the motor is reduced. In addition, a reaction force is generated in the steering mechanism, which is a force in the opposite direction to return the tire with respect to the steering direction. Therefore, the motor torque is insufficient in the region near the electrical angle where the energization direction is reversed, and the motor may not be able to rotate from that position. For this reason, a large steering force of the driver is required. Therefore, in the present invention, the command current is calculated by advancing the electrical angle of the motor in the two-phase energization current calculation formula by a preset advance amount. In other words, the current calculation formula for two-phase energization is an arithmetic expression for obtaining the current flowing to the motor from the electric angle of the motor, but the two-phase energization control means sets the actual electric angle detected by the electric angle detection means in the motor rotation direction. The current for the electrical angle advanced by the advance amount is calculated from the current calculation formula for two-phase energization, and the command current is calculated by adding the maximum current limit.

  In this case, when the motor torque characteristic with respect to the electrical angle increases when the torque increases at a position of an electrical angle smaller than a specific electrical angle (advancing by the advance amount) at which the direction of energization of the command current is reversed, and exceeds the specific electrical angle As a result, the torque suddenly decreases and torque in the reverse direction is generated. As the electrical angle increases, the torque in the reverse direction becomes weaker and gradually increases as it turns to the torque in the forward direction. Accordingly, an over-assist region where a steering assist torque larger than the reaction force can be generated and a reverse assist region where torque is generated in the opposite direction to the steering direction is formed across the specific electrical angle. In addition, in the region where the electrical angle is larger than the reverse assist region, a short assist region is formed in which the torque is increased in the steering direction as the electrical angle increases to reach the over assist region.

  In such motor characteristics, when the motor stops in the shortage assist region, the motor rotates in the reverse direction due to a reaction force for returning the tire with respect to the steering direction. Then, when the electrical angle is returned to the rotational position that becomes the reverse assist region, the rotational position is further reversely rotated to the over assist region by the reverse torque generated by the motor itself. When the motor is returned to the over assist area, the motor generates a large torque in the steering direction that overcomes the reaction force, rotates in the steering direction, and passes through the reverse assist area and the insufficient assist area by the kinetic energy stored in the over assist area. can do. Thereby, a motor can be rotated favorably using two phases.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an electric power steering apparatus for a vehicle according to the embodiment.

  The electric power steering apparatus includes a steering mechanism 10 that steers steered wheels by a steering operation of a steering handle 11, an electric motor 20 that is assembled to the steering mechanism 10 and generates a steering assist torque, and an electric motor 20 for driving the electric power steering apparatus. The motor drive circuit 30 and the electronic control device 100 that controls the operation of the electric motor 20 are provided as main parts. Hereinafter, the electronic control device 100 is referred to as an assist ECU 100.

  The steering mechanism 10 is a mechanism for turning the left and right front wheels FWL and FWR by a rotation operation of the steering handle 11, and includes a steering shaft 12 connected to the steering handle 11 so as to rotate integrally with the upper end. A pinion gear 13 is connected to the lower end of the steering shaft 12 so as to rotate integrally. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 and constitutes a rack and pinion mechanism together with the rack bar 14. Knuckles (not shown) of the left and right front wheels FWL and FWR are steerably connected to both ends of the rack bar 14 via tie rods 15L and 15R. The left and right front wheels FWL and FWR are steered left and right according to the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis.

  An electric motor 20 is assembled to the rack bar 14. The electric motor 20 is a three-phase brushless motor. The rotating shaft of the electric motor 20 is connected to the rack bar 14 via the ball screw mechanism 16 so as to be able to transmit power, and the rotation gives the steering force to the left and right front wheels FWL and FWR to assist the steering operation. The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter, and decelerates the rotation of the electric motor 20 and converts it into a linear motion and transmits it to the rack bar 14.

  A steering torque sensor 21 is provided on the steering shaft 12. The steering torque sensor 21 includes, for example, resolvers (not shown) assembled to upper and lower ends of a torsion bar (not shown) interposed in an intermediate portion of the steering shaft 12, and detection angles of upper and lower resolvers. A detection signal representing the torsion angle of the torsion bar is output using the difference. Thus, the steering torque acting on the steering shaft 12 by the turning operation of the steering handle 11 is detected. Hereinafter, the value of the steering torque detected by the signal output from the steering torque sensor 21 is referred to as steering torque Tr. As for the steering torque Tr, the operation direction of the steering wheel 11 is identified by positive and negative values. In the present embodiment, the steering torque Tr when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Tr when the steering handle 11 is steered in the left direction is indicated by a negative value. Therefore, the magnitude of the steering torque Tr is the absolute value thereof.

  The steering shaft 12 is provided with a steering angle sensor 23 that detects the rotation angle of the steering handle 11. Hereinafter, the steering angle value detected by the signal output from the steering angle sensor 23 is referred to as a steering angle θh. As for the steering angle θh, the operation direction of the steering wheel 11 is identified by a positive or negative value. In the present embodiment, the steering angle θh in the right direction from the neutral position of the steering handle 11 is indicated by a positive value, and the steering angle θh in the left direction is indicated by a negative value. Therefore, the magnitude of the steering angle θh is the magnitude of its absolute value. A value obtained by differentiating the steering angle θh with respect to time is used as the steering speed ω of the steering handle 11.

  The electric motor 20 is provided with a rotation angle sensor 22. The rotation angle sensor 22 is incorporated in the electric motor 20 and outputs a detection signal corresponding to the rotation angle position of the rotor of the electric motor 20. Hereinafter, the rotation angle value detected by the rotation angle sensor 22 is referred to as a motor rotation angle θm. The motor rotation angle θm is used for calculating the electrical angle θe of the electric motor 20.

  The motor drive circuit 30 comprises a three-phase inverter circuit composed of six switching elements 31 to 36 made of MOS-FET (Metal Oxide Semiconductor Field Effect Transistor). Specifically, a circuit in which a first switching element 31 and a second switching element 32 are connected in series, a circuit in which a third switching element 33 and a fourth switching element 34 are connected in series, a fifth switching element 35 and a first switching element A circuit in which 6 switching elements 36 are connected in series is connected in parallel, and a power supply line 37 to the electric motor 20 is drawn from between two switching elements (31-32, 33-34, 35-36) in each series circuit. Adopted.

  The motor drive circuit 30 is provided with a current sensor 38 that detects a current flowing through the electric motor 20. The current sensor 38 detects the current flowing in each phase (U phase, V phase, W phase) and outputs a detection signal corresponding to the detected current value to the assist ECU 100. Hereinafter, the measured current values of the three phases are collectively referred to as motor current Iuvw, and the respective phase current values are represented by Iu, Iv, and Iw.

  As for each switching element 31-36 of the motor drive circuit 30, a gate is connected to assist ECU100, respectively, and a duty ratio is controlled by the PWM control signal output from assist ECU100. Thereby, the drive voltage of the electric motor 20 is adjusted to the target voltage. Incidentally, as indicated by circuit symbols in the figure, the MOSFETs constituting the switching elements 31 to 36 are parasitically structured with diodes.

  The power supply line 37 from the motor drive circuit 30 to the electric motor 20 is provided with a shut-off circuit 39 having a switch that can be opened and closed independently for each phase. The shut-off circuit 39 is controlled to be opened and closed independently for each phase by a signal from the assist ECU 100.

  The assist ECU 100 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part. The assist ECU 100 is connected to a steering torque sensor 21, a steering angle sensor 23, a rotation angle sensor 22, a current sensor 38, and a vehicle speed sensor 25 that detects a vehicle speed, and a steering torque Tr, a steering angle θh, a motor rotation angle θm, a motor A detection signal indicating the current Iuvw and the vehicle speed v is input. Then, based on the input detection signal, a command current (target current) to be passed through the electric motor 20 is calculated so as to obtain an optimum steering assist torque according to the driver's steering operation so that the command current flows. The duty ratio of each switching element 31 to 36 of the motor drive circuit 30 is controlled.

  The assist ECU 100 also detects a failure (energization failure) in the energization path for supplying electric power to the electric motor 20 for each phase, and when detecting an energization failure of only one phase, the assist ECU 100 is electrically operated using two normal phases. A function of performing two-phase energization control for driving the motor 20 is provided. In addition, it also has a function of detecting reverse assist abnormality in which energization is performed in which the direction of the steering torque generated by the electric motor 20 is opposite to the steering operation direction of the driver. The function of the assist ECU 100 will be described later.

  Next, a power supply system of the electric power steering apparatus will be described. The electric power steering device is supplied with power from an in-vehicle power supply device 80. The in-vehicle power supply device 80 is configured by connecting in parallel a main battery 81 that is a general in-vehicle battery having a rated output voltage of 12V and an alternator 82 having a rated output voltage of 14V that is generated by the rotation of the engine. A power supply source line 83 and a ground line 84 are connected to the in-vehicle power supply device 80. The power supply source line 83 branches into a control system power line 85 and a drive system power line 86. The control system power supply line 85 functions as a power supply line for supplying power to the assist ECU 100. The drive system power supply line 86 functions as a power supply line that supplies power to both the motor drive circuit 30 and the assist ECU 100.

  An ignition switch 87 is connected to the control system power supply line 85. A main power relay 88 is connected to the drive system power line 86. The main power supply relay 88 is turned on by a control signal from the assist ECU 100 to form a power supply circuit to the electric motor 20. The control system power supply line 85 is connected to the power supply + terminal of the assist ECU 100, and includes a diode 89 on the load side (assist ECU 100 side) from the ignition switch 87 in the middle. The diode 89 is a backflow prevention element that is provided with the cathode facing the assist ECU 100 and the anode facing the in-vehicle power supply device 80, and allows energization only in the power supply direction.

  The drive system power line 86 is provided with a connecting line 90 branched from the main power relay 88 and connected to the control system power line 85 on the load side. This connection line 90 is connected to the assist ECU 100 side from the connection position of the diode 89 in the control system power supply line 85. A diode 91 is connected to the connecting line 90. The diode 91 is provided with the cathode facing the control system power line 85 side and the anode facing the drive system power line 86 side. Therefore, the circuit configuration is such that power can be supplied from the drive system power supply line 86 to the control system power supply line 85 via the connection line 91, but power cannot be supplied from the control system power supply line 85 to the drive system power supply line 86. . The drive system power supply line 86 and the ground line 84 are connected to the power supply input section of the motor drive circuit 30. The ground line 84 is also connected to the ground terminal of the assist ECU 100.

  Next, functions of the assist ECU 100 will be described with reference to FIG. FIG. 2 is a functional block diagram showing functions processed by program control of the microcomputer of the assist ECU 100. The assist ECU 100 switches the motor control mode depending on whether or not an energization failure to each phase of the electric motor 20 is detected. If all three phases are normally energized to the electric motor 20, motor control using three phases (hereinafter referred to as three-phase energization control) is performed, and an energization failure is detected when a one-phase energization failure is detected. The control is switched to perform motor control using two phases that are not performed (hereinafter referred to as two-phase energization control). In addition, when energization failure of two or more phases is detected, the motor control is stopped because the motor cannot be driven. In addition, when the three-phase energization control and the two-phase energization control are being performed, a reverse assist abnormality determination is performed in parallel therewith. First, the three-phase energization control that is normal will be described.

  As shown in FIG. 2, the assist ECU 100 includes an assist current command unit 101. As shown in FIG. 14, the assist current command unit 101 stores a basic assist map for setting the basic assist torque Tas according to the steering torque Tr and the vehicle speed v. The assist current command unit 101 inputs the steering torque Tr output from the steering torque sensor 21 and the vehicle speed v output from the vehicle speed sensor 25, and calculates the basic assist torque Tas by referring to this basic assist map. In this case, the basic assist torque Tas increases as the steering torque Tr increases and decreases as the vehicle speed v increases. The assist current command unit 101 receives the steering angle θh detected by the steering angle sensor 23 and calculates a compensation value Trt for the basic assist torque Tas. The compensation value Trt is, for example, for the return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θh and the rotation of the steering shaft 12 that increases in proportion to the steering speed ω obtained by time-differentiating the steering angle θh. Calculated as the sum of the return torque corresponding to the resistance force. The assist current command unit 101 sets the sum of the calculated basic assist torque Tas and the compensation value Trt as the target assist torque T *, and divides the target assist torque T * by the torque constant, thereby obtaining the dq coordinate system. A q-axis command current Iq * is calculated.

  When performing three-phase energization control, the assist ECU 100 is electrically controlled by vector control described in a dq coordinate system in which the rotation direction of the electric motor 20 is the q axis and the direction orthogonal to the rotation direction is the d axis. The rotation of the motor 20 is controlled. The d-axis current does not act to generate the torque of the electric motor 20 and is used for field weakening control. In the present embodiment, the assist current command unit 101 sets the d-axis command current Id * to zero (Id * = 0).

  The q-axis command current Iq * and the d-axis command current Id * calculated in this way are output to the feedback control unit 102. The feedback control unit 102 calculates a deviation ΔIq obtained by subtracting the q-axis actual current Iq from the q-axis command current Iq *, and the q-axis actual current Iq is changed to the q-axis command current Iq * by proportional-integral control using the deviation ΔIq. The q-axis command voltage Vq * is calculated so as to follow. Similarly, a deviation ΔId obtained by subtracting the d-axis actual current Id from the d-axis command current Id * is calculated, and the d-axis actual current Id follows the d-axis command current Id * by proportional-integral control using the deviation ΔId. D-axis command voltage Vd * is calculated.

  The q-axis actual current Iq and the d-axis actual current Id are obtained by converting the detected values Iu, Iv, and Iw of the three-phase current actually flowing in the coil of the electric motor 20 into the two-phase current in the dq coordinate system. . Conversion from the three-phase currents Iu, Iv, and Iw to the two-phase currents Id and Iq in the dq coordinate system is performed by the three-phase / two-phase conversion unit 103. The three-phase / two-phase conversion unit 103 inputs the motor electrical angle θe output from the rotation angle conversion unit 104, and based on the motor electrical angle θe, the three-phase currents Iu, Iv, Iw is converted into two-phase currents Id and Iq in the dq coordinate system. The rotation angle conversion unit 104 is an electrical angle detection unit that calculates the motor electrical angle θe based on the rotation angle θm output from the rotation angle sensor 22. Hereinafter, the motor electrical angle θe is simply referred to as an electrical angle θe.

  The q-axis command voltage Vq * and the d-axis command voltage Vd * calculated by the feedback control unit 102 are output to the 2-phase / 3-phase coordinate conversion unit 105. The two-phase / three-phase coordinate conversion unit 105 converts the q-axis command voltage Vq * and the d-axis command voltage Vd * into the three-phase command voltages Vu * and Vv * based on the electrical angle θe output from the rotation angle conversion unit 104. , Vw *, and the converted three-phase command voltages Vu *, Vv *, Vw * are output to the PWM signal generator 106. The PWM signal generator 106 outputs PWM control signals corresponding to the three-phase command voltages Vu *, Vv *, Vw * to the switching elements 31 to 36 of the motor drive circuit 30. As a result, the electric motor 20 is driven, and a steering assist torque that follows the target assist torque T * is applied to the steering mechanism 10.

  Next, two-phase energization control will be described. First, the command current for two-phase energization will be described. As shown in FIG. 3A, the electric motor 20 normally applies a sinusoidal current having a phase difference of 120 degrees in electrical angle to the three phases. In this case, a constant motor torque is obtained with respect to the electrical angle. However, if one of the three phases is defective in energization due to disconnection or the like, the motor torque varies greatly depending on the electrical angle, as shown in FIG. For this reason, the steering operation is caught.

この例は、Ｗ相が通電不良となったときのＶ相の電流演算式であり、ｅ₀はトルク定数を表す。また、Ｕ相は、Ｖ相を反転したもの（Ｉu＝−Ｉv）となる。 Therefore, at the time of two-phase energization, if the command current is calculated using the two-phase energization current calculation formula in which the motor torque is constant with respect to the change in the motor electrical angle, Theoretically, a constant motor torque can be obtained. This current calculation formula for two-phase energization can be expressed as follows.

This example is a V-phase current calculation formula when the W-phase is in poor conduction, and e ₀ represents a torque constant. In addition, the U phase is obtained by inverting the V phase (Iu = −Iv).

  According to the current calculation formula for two-phase energization, the current for two-phase energization is infinite at the rotational position where the electrical angle θe is 90 deg or 270 deg, but the electric motor 20 and the motor drive circuit 30 are protected from overcurrent. In order to do this, the assist ECU 100 is preset with a maximum current that can flow to the electric motor 20. Accordingly, the current waveform of the command current during two-phase energization is as shown in FIG. In the figure, the area surrounded by the broken line is the area where the current limit is applied. FIG. 4A shows the current waveform of one phase, and the current waveform of the other phase is obtained by inverting the sign of this waveform.

  When such an electric current is supplied to the electric motor 20, the torque generated by the electric motor 20 decreases in a region where the current limit is applied as shown in FIG. Therefore, the motor torque is insufficient in the vicinity of the electrical angle, and the electric motor 20 may not be able to rotate from that position. For this reason, the steering operation is caught.

  Therefore, in the present embodiment, the command current is calculated by advancing the electrical angle θe in the motor rotation direction by a preset advance amount θa. That is, the electric angle θe of the two-phase energization current calculation formula is corrected and calculated so that the current for two-phase energization is advanced by the advance amount θa with respect to the electric angle θe, and obtained by this calculation. The command current is calculated by adding a maximum current limit to the current. The command current with the advanced electrical angle has a waveform as shown by a solid line in FIG. In this example, the advance amount θa is set to about 20 deg.

  When the command angle is set by advancing the electrical angle in this way, the motor torque has characteristics as shown in FIG. In the figure, T0 represents a reaction force for returning the tire in the direction opposite to the steering direction under preset traveling conditions. Therefore, if the motor torque exceeds the reaction force T0, the vehicle can be steered without the driver's steering force. If the motor torque does not reach the reaction force T0, the driver's steering force is required by the shortage. As can be seen from this figure, there are an electrical angle region where the motor torque exceeds the reaction force T0 and an electrical angle region where the motor torque is less than the reaction force T0. Hereinafter, an electrical angle region where the motor torque exceeds the reaction force T0 is referred to as an over assist region A, and an electrical angle region where the motor torque is less than the reaction force T0 is referred to as an insufficient assist region B.

  Further, in the shortage assist region B, there is also an electrical angle region where the motor torque works in the direction opposite to the steering direction. In the following, when the shortage assist region B is described separately as an electric angle region where the motor torque works in the same direction as the steering direction and an electric angle region where the motor torque works in the opposite direction, the former electric angle region is referred to as the short assist normal region. The latter electrical angle region is called a reverse assist region B2. The point at which the over assist area A is switched to the reverse assist area B2 is a rotational position (electrical angle) at which the sign of the phase current of the electric motor 20 is reversed. In this example, the over assist area A is switched to the reverse assist area B2 at electrical angles of (90 deg−θa) and (270 deg−θa).

  In the present embodiment, an over assist area A and a reverse assist area B2 are provided in the motor torque characteristics, so that the electric motor 20 can be rotated without being caught using these areas A and B2. The reason will be described below.

  When the electric motor 20 rotates in the rotation direction shown in FIG. 7, the electric motor 20 accelerates in the over assist region A and stores kinetic energy. Then, when entering the shortage assist region B, this time it is decelerated by the reaction force. That is, the over assist area A is an acceleration section, and the insufficient assist area B is a deceleration section. In this case, if the kinetic energy stored in the over assist area A is greater than the kinetic energy lost in the short assist area B, the electric motor 20 can rotate without being caught.

  However, when torque feedback responds, for example, when the steering speed (rotational speed of the motor) is low, the motor torque decreases as shown in FIG. For this reason, the over assist area A decreases, and the over assist area A cannot be sufficiently accelerated. If sufficient acceleration cannot be obtained, if the sum of the motor torque and the steering force (the steering force applied by the driver to the steering wheel) in the shortage assist region B is smaller than the reaction force T0, the shortage assist region B is passed. The electric motor 20 rotates in the reverse direction due to the reaction force. For example, it stops at the electrical angle θs of the short assist normal region B1 shown in FIG. 9, and returns from the position in the direction of the arrow.

  In this case, the electric motor 20 always returns to the reverse assist region B2, and generates torque that is in the opposite direction to the steering direction, and the combined force of the torque and the reaction force makes it into the over assist region A as it is. Return. As a result, the electric motor 20 generates torque in the forward rotation direction in the over assist region A and starts acceleration. That is, the rotational position (electrical angle θe) of the electric motor 20 is returned to the over assist area A using the reverse assist area B2, and is accelerated again in the over assist area A. And it passes through the shortage assist area | region B using the kinetic energy stored while passing the overassist area | region A. FIG. Thereby, the electric motor 20 can be rotated without generating a catch. In addition, when it cannot pass through the short assist area B even if it returns to the over assist area A and re-accelerates, it returns to the over assist area A via the reverse assist area B2 again, so that it is insufficient by repeating the above-described operation. The assist area B can be passed. Even if the electric motor 20 repeats forward and reverse rotations, the electric motor 20 and the steering mechanism 10 are connected by the ball screw mechanism 16, and the angle at which the steering shaft 12 rotates with respect to the rotation angle of the electric motor 20. Since the rotation is very small and the slight rotation is absorbed by the torsion bar provided on the steering shaft 12, there is almost no influence on the steering operation.

  The function of the assist ECU 100 that performs such two-phase energization control will be described with reference to FIG. The assist ECU 100 includes a two-phase energization command unit 107. The two-phase energization command unit 107 starts operation when a one-phase energization failure detection signal is input from the energization failure detection unit 108.

  The conduction failure detection unit 108 receives the PWM control signal output from the PWM signal generation unit 106, the steering angle θh output from the steering angle sensor 23, and the three-phase currents Iu, Iv, Iw output from the current sensor 38. Thus, a failure in energization of the electric motor 20 is detected separately for each phase. The failure of energization to the electric motor 20 means a failure in which electric power cannot be supplied satisfactorily to the electric motor 20. For example, a failure in the motor drive circuit 30 (particularly, a contact failure of the switching elements 31 to 36), the motor drive circuit 30. To the electric motor 20 due to disconnection of the power supply line 37 or the like.

  For example, when the phase current detected by the current sensor 38 is smaller than a preset reference current, the conduction failure detection unit 108 determines the magnitude (absolute value) of the steering speed ω obtained by time differentiation of the steering angle θh. It is determined whether the duty ratio is smaller than the reference speed and the duty ratio (on duty ratio) specified by the PWM control signal is larger than the reference duty ratio. When the steering speed | ω | is smaller than the reference speed and the duty ratio is larger than the reference duty ratio, it is determined that an energization failure has occurred in that phase. That is, in the state where the steering speed | ω | is small and the generation of the counter electromotive force is small, it is determined that the energization is defective when the phase current that should originally flow does not flow according to the PWM control signal output to the motor drive circuit 30.

  The energization failure detection unit 108 periodically performs such energization failure determination for each phase, and outputs an energization normal signal while no energization failure is detected. Then, when an energization failure is detected, an energization failure detection signal for specifying an energization failure phase is output instead of the normal normal signal. In addition, when the energization failure detection unit 108 detects an energization failure, the energization failure detection unit 108 outputs an OFF signal to a switch corresponding to the energization failure phase of the cutoff circuit 39 provided in the power supply line 37 of the electric motor 20, and Turn off the power. Hereinafter, the signals output from the energization failure detection unit 108 (energization normality signal and energization failure detection signal for specifying the energization failure phase) are referred to as energization determination signals.

この例は、Ｗ相が通電不良となったときのＶ相の２相通電用電流演算式である。Ｕ相は、Ｖ相を反転したもの（Ｉu＝−Ｉv）となる。また、２相通電用電流演算式は、通電不良相に応じて位相が１２０degずれたものとなる。 When the two-phase energization command unit 107 receives a one-phase energization detection signal from the energization failure detection unit 108, the two-phase energization command unit 107 is used for two-phase energization based on the current calculation formula for two-phase energization, the maximum current, and the advance angle θa. The command currents Iu *, Iv *, Iw * are calculated. In this case, the command current for the poorly energized phase is not calculated. The current calculation formula for two-phase energization is expressed as follows using the q-axis command current q * output from the assist current command unit 101 and the electrical angle θe output from the rotation angle conversion unit 104.

This example is a V-phase two-phase energization current calculation formula when the W-phase has an energization failure. The U phase is an inverted version of the V phase (Iu = -Iv). In addition, the current calculation formula for two-phase energization is a phase that is shifted by 120 degrees depending on the energization failure phase.

  In the present embodiment, as described above, in order to rotate the electric motor 20 without being caught, the current for two-phase energization with respect to the electrical angle advanced by the advance angle θa in the motor rotation direction from the actual electrical angle θe is obtained. Calculate. That is, the calculation is performed by replacing θe in the current calculation formula for two-phase energization with (θe + θa). Therefore, the command current for two-phase energization has a waveform shown by a solid line in FIG. The advance amount θa may be a constant value, but in the present embodiment, as shown in FIG. 10, it is set to a value corresponding to the steering torque Tr. In this example, the magnitude of the advance angle | θa | increases as the steering torque Tr increases in the vicinity where the steering torque Tr becomes zero, and is a constant value of 20 degrees except in the vicinity where the steering torque Tr becomes zero. Set to Therefore, the two-phase energization command unit 107 reads the steering torque Tr output from the steering torque sensor 21 when calculating the command current. When the steering torque Tr works in a negative direction (left direction), the advance amount θa also takes a negative value. That is, when the electric motor 20 is rotated to the side where the electrical angle increases, the positive advance amount θa is set, and when the electric motor 20 is rotated to the side where the electrical angle decreases, the negative advance amount θa is set. To do. Thereby, the electrical angle can be advanced in the direction in which the electric motor 20 is rotated.

  The command currents Iu *, Iv *, and Iw * for two-phase energization calculated in this way (command currents that flow through the two phases that are normal among the three phases) are output to the feedback controller 109 for two-phase energization. The The two-phase energization feedback control unit 109 starts operation when a one-phase energization failure detection signal is input from the energization failure detection unit 108. At this time, the energization failure detection signal is also output to the feedback control unit 102. The feedback control unit 102 stops its operation when an energization failure detection signal is input. Therefore, when a one-phase energization failure is detected, current feedback control for two-phase energization is started instead of current feedback control using the dq coordinate system.

  The two-phase energization feedback control unit 109 inputs the three-phase currents Iu, Iv, and Iw (actual currents flowing in the two phases that are normal among the three phases) output from the current sensor 38, and for two-phase energization. Deviations ΔIu, ΔIv, ΔIw from command currents Iu *, Iv *, Iw * (command currents for two phases that are normal phases among the three phases) are calculated, and proportional integration using these deviations ΔIu, ΔIv, ΔIw By controlling, the three-phase currents Iu, Iv, Iw follow the command currents Iu *, Iv *, Iw * for two-phase energization, so that the command voltages Vu *, Vv *, Vw * for three-phase energization (three-phase Of these, the command voltage for the two phases that are normal phases) is calculated.

  The two-phase energization feedback control unit 109 outputs the calculated command voltages Vu *, Vv *, and Vw * for two-phase energization to the PWM signal generation unit 106. The PWM signal generator 106 outputs PWM control signals corresponding to the command voltages Vu *, Vv *, Vw * for two-phase energization to the switching elements 31 to 36 of the motor drive circuit 30. As a result, the electric motor 20 is driven, and a steering assist torque that follows the target assist torque T * is applied to the steering mechanism 10. In this case, since the electrical angle θe of the current calculation formula for two-phase energization is advanced by the advance amount θa, the rotation of the electric motor 20 is not caught and good steering assist can be performed.

  The assist ECU 100 of the present embodiment further has a function of monitoring a reverse assist abnormality that is an abnormality of the motor control system and performing an abnormality process (stopping the steering assist control) when the reverse assist abnormality is detected. The reverse assist abnormality is an abnormality in which the electric motor 20 is energized so that a motor torque in the reverse direction is generated with respect to the motor rotation direction (driver steering direction) commanded by the assist ECU 100. This is different from driving the electric motor 20 by actively using the reverse assist region during the above-described two-phase energization control.

  In order to monitor this reverse assist abnormality, the assist ECU 100 includes a reverse assist detection unit 110. Since the reverse assist detection unit 110 detects an abnormality in the steering assist control system, the reverse assist detection unit 110 is preferably configured using a microcomputer different from the microcomputer that controls the steering assist control described above. The reverse assist detection unit 110 includes an energization determination signal output from the energization failure detection unit 108 and two-phase energization command currents Iu *, Iv *, Iw * output from the 2-phase energization command unit 107 (normal among the three phases). Command current flowing in two phases), three-phase currents Iu, Iv, Iw output from the current sensor 38, q-axis command current Iq * output from the assist current command unit 101, and three-phase / two-phase conversion The q-axis actual current Iq output from the unit 103 and the electrical angle θe output from the rotation angle conversion unit 104 are input.

  The reverse assist detection unit 110 executes a reverse assist abnormality detection routine as shown in FIG. This reverse assist abnormality detection routine is stored as a control program in the ROM of the assist ECU 100, and is started after the ignition switch 87 is turned on and the initial diagnosis is completed.

  In step S10, the reverse assist detection unit 110 reads the energization determination signal output from the energization failure detection unit 108, and in subsequent step S11, determines whether the two-phase energization control is performed based on the energization determination signal. . If the energization determination signal is a normal energization signal, three-phase energization control is performed, and if it is a one-phase energization failure signal, two-phase energization control is performed. If the three-phase energization control is being performed (S11: No), in step S12, the q-axis command current Iq * output from the assist current command unit 101 and the q-axis actual current Iq output from the three-phase / 2-phase conversion unit 103. And read. In step S13, the signs of the q-axis command current Iq * and the q-axis actual current Iq (the direction of the q-axis current and the direction in which the torque is generated) are compared, and if the signs match ( S13: No), it is determined that no reverse assist abnormality has occurred, and the process returns to step S10.

  On the other hand, if it is determined in step S11 that the two-phase energization control is being performed, the electrical angle θe output from the rotation angle conversion unit 104 is read in step S14. Subsequently, in step S15, it is determined whether or not the read electrical angle θe is in a determination prohibited area corresponding to the current-carrying failure phase. If the electrical angle θe is in the determination prohibited area (S15: Yes), the process returns to step S10. If the electrical angle θe is not within the determination prohibited area (S15: No), in step S16, the two-phase energization command currents Iu *, Iv *, Iw * (3 Command current to flow into two phases which are normal phases) and three-phase currents Iu, Iv and Iw output from the current sensor 38 are read. Then, the sign (current direction) of the corresponding normal phase command current and the actual current is compared, and if the signs match (S17: No), it is determined that no reverse assist abnormality has occurred, and the process is performed. Return to step S10.

  During the two-phase energization control, a determination prohibition area for prohibiting the determination of reverse assist abnormality is set, and the reverse assist abnormality determination is not performed when the electrical angle θe is in the determination prohibition area. Yes. Here, the reason why the determination prohibited area is provided will be described.

  The command current for two-phase energization is calculated from the current calculation formula for two-phase energization, the maximum current, and the advance amount θa, and thus has a current waveform as shown in FIG. This current waveform is a U-phase command current waveform at the time of W-phase energization failure. A solid line waveform indicates a case where the advance amount θa is maximum (for example, 20 deg), and a broken line waveform indicates a case where the advance angle amount θa is 0 deg. . As can be seen from this current waveform, the sign (current flow direction) of the command current for two-phase energization suddenly reverses before and after the specific electrical angle. In this example, the specific electrical angle is (90−θa) deg or (270−θa) deg.

  Therefore, the specific electrical angle at which the sign is inverted also changes depending on the setting of the advance amount θa. Further, the specific electrical angle also changes depending on the detection variation error of the rotation angle of the rotation angle sensor 22. For this reason, if the sign of the command current and the actual current is compared when the electrical angle θe is in the vicinity of the specific electrical angle, there is a risk of erroneous determination of reverse assist abnormality. Therefore, in the reverse assist abnormality detection routine of the present embodiment, the region near the specific electrical angle is set as the determination prohibited area, and the reverse assist abnormality is not determined when the electrical angle θe is in the determination prohibited area. I have to.

  Therefore, the determination prohibition area is set based on the maximum value θamax (20 deg in this example) of the advance amount θa and the error consideration αdeg. For example, in the case of a W phase energization failure, as shown in FIG. 12, between (90−θamax−α) deg and (90 + α) deg and between (270−θamax−α) deg and (270 + α) deg. Is set as a prohibited area. An electrical angle area other than the determination prohibited area is a determination permission area. Moreover, since the specific electrical angle differs depending on the phase in which the energization failure has occurred, if the energization failure of the other phase, the determination prohibited area may be set to be advanced or delayed by 120 degrees. If the advance amount θa is not set (θa = 0), a determination prohibited area may be set between (specific electrical angle−α) deg and (specific electrical angle + α) deg.

  Returning to the description of the reverse assist abnormality detection routine (FIG. 11). In step S13 or step S17, the reverse assist detection unit 110 determines that a reverse assist abnormality has occurred in step S18 and outputs a steering assist stop command in step S18. In response to the steering assist stop command, the assist ECU 100 stops the steering assist control. In step S13 or step S17, the determination result “Yes” is output when the code mismatch continues for a predetermined time, and “No” is determined for the instantaneous mismatch and noise or the like. It is good to prevent the influence by. Subsequently, the reverse assist detection unit 110 outputs an off signal to the main power supply relay 88 to open the main power supply relay 88 in step S19. Thereby, the power supply to the motor drive circuit 30 is interrupted.

  The reverse assist abnormality detection routine ends after performing the process of step S19. Therefore, the steering assist control is continued while the reverse assist abnormality is not detected, and the steering assist control is stopped instantaneously after the reverse assist abnormality is detected. Thereby, the abnormal operation of the electric motor 20 can be prevented. In the present embodiment, the reverse assist abnormality determination during the three-phase energization control is performed by sign comparison between the q-axis command current Iq * and the q-axis actual current Iq. A deviation ΔIq (| Iq * −Iq |) between * and the q-axis actual current Iq may be calculated, and when the deviation ΔIq is larger than the determination reference value, it may be determined that the reverse assist abnormality has occurred. .

  According to the electric power steering apparatus of the present embodiment described above, even when a one-phase energization failure of the three-phase electric motor 20 occurs, by performing two-phase energization control with an advance amount provided. The electric motor 20 can be rotated without being caught. Thereby, the fall of the steering operation feeling at the time of two-phase electricity supply control can be suppressed. Further, the reverse assist abnormality can be detected even during the two-phase energization control. In addition, when determining the reverse assist abnormality, since the abnormality determination is prohibited in the electrical angle vicinity region where the sign of the command current for two-phase energization is reversed, erroneous determination can be suppressed. As a result, the reliability of the steering assist control system is improved.

  The electric power steering apparatus according to the present embodiment has been described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in this embodiment, in the reverse assist abnormality detection routine, abnormality determination in the determination prohibited area is not performed, but the procedure may be changed as shown in FIG. That is, during the two-phase energization control, after determining the reverse assist abnormality in steps S16 and S17, it is determined in steps S14 and S15 whether or not the electrical angle θe is in the determination prohibited area, and the electrical angle θe. May be returned to step S10 and the determination result may be invalidated.

  In the present embodiment, the command current is calculated by giving the advance amount θa to the two-phase energization current calculation formula, but it is not always necessary to give the advance amount. In the present embodiment, the rack assist type electric power steering device that applies the torque generated by the electric motor 20 to the rack bar 14 has been described. However, the column assist that applies the torque generated by the electric motor to the steering shaft 12 has been described. It may be an electric power steering device of the type.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a functional block diagram showing the process of the microcomputer of assist ECU. It is a graph showing the motor torque characteristic at the time of a three-phase current waveform and a one-phase disconnection. It is a graph showing a current waveform using a current calculation formula for two-phase energization and motor torque characteristics. It is a graph which compares the current waveform using the current calculation formula for two-phase energization between the case where an advance angle is given and the case where no advance angle is given. It is a graph showing the motor torque characteristic at the time of giving an advance angle to the current calculation formula for two-phase energization. It is a graph for demonstrating an acceleration area and a deceleration area. It is a graph showing the change of the motor torque characteristic which decreases by torque feedback. It is a graph explaining the operation | movement which reversely rotates to an over assist area | region using a reverse assist area | region. It is a graph showing the setting map of advance amount. It is a flowchart showing a reverse assist abnormality detection routine. It is a graph explaining a determination prohibition area. It is a flowchart showing the reverse assist abnormality detection routine as a modification. It is a graph showing a basic assist map.

  DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 20 ... Electric motor, 21 ... Steering torque sensor, 22 ... Rotation angle sensor, 23 ... Steering angle sensor, 25 ... Vehicle speed sensor, 30 ... Motor drive circuit, 37 DESCRIPTION OF SYMBOLS ... Power supply line, 38 ... Current sensor, 39 ... Shut-off circuit, 83 ... Power supply source line, 86 ... Drive system power supply line, 88 ... Main power relay, 100 ... Electronic control unit (assist ECU), 101 ... Assist current command , 102 ... Feedback control unit, 103 ... 3-phase / 2-phase conversion unit, 104 ... Rotation angle conversion unit, 105 ... 3-phase / 2-phase coordinate conversion unit, 106 ... PWM control signal generation unit, 107 ... 2-phase energization command , 108... Energization failure detection unit, 109... Two-phase energization feedback control unit, 110.

Claims (3)

A three-phase motor that is provided in the steering mechanism and generates steering assist torque;
An electric power steering apparatus comprising: motor control means for controlling energization of the motor based on a steering operation of a driver;
The motor control means includes
Current detection means for detecting current flowing in each phase of the motor;
An electrical angle detection means for detecting an electrical angle of the motor;
An energization failure detection means for detecting the occurrence of energization failure to each phase of the motor;
Two-phase energization for generating torque that does not fluctuate with respect to changes in the electrical angle of the motor, using two phases in which the energization failure does not occur when only one phase of the energization failure occurs in the motor Based on the current calculation formula and the maximum current that defines the upper limit current of the motor, a command current for two-phase energization is calculated, and no conduction failure occurs with the calculated two-phase energization command current Two-phase energization control means for energizing two phases to drive and control the motor;
An abnormality determination means for determining an abnormality of the motor control system based on a comparison between the command current for the two-phase energization and the current detected by the current detection means;
In the vicinity of the motor electrical angle where the energization direction of the command current for the two-phase energization is reversed, an abnormality that prohibits the abnormality determination by the abnormality determination means or invalidates the abnormality determination determined by the abnormality determination means An electric power steering apparatus comprising: a determination limiting unit.   When the direction of the command current for the two-phase energization and the direction of the current detected by the current detection unit do not coincide with each other, the abnormality determination unit is configured so that the motor is in a direction opposite to the steering direction of the driver. 2. The electric power steering apparatus according to claim 1, wherein it is determined that the reverse assist abnormality that generates the steering torque is detected.   The two-phase energization control means calculates the command current for the two-phase energization by advancing a motor electrical angle in the two-phase energization current calculation formula by a predetermined advance amount. 3. The electric power steering apparatus according to 1 or 2.

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