JP2010167881A - Steering device of vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excellently rotate an electric motor when performing two-phase current-carrying drive when one phase of the electric motor causes a current-carrying failure. <P>SOLUTION: A two-phase current-carrying command part 117 arithmetically operates a command electric current for two-phase current-carrying based on a theoretical two-phase current-carrying current operation expression for generating steering assist torque which is not varied with respect to a change in an electrical angle θe by using two phases of not causing the current-carrying failure when the current-carrying failure to the electric motor 31 is caused only in one phase, a maximum electric current for regulating the upper limit current of the electric motor 31 and an ignition timing advance angle for advancing the electrical angle θe in the two-phase current-carrying current operation expression. A steering angle ratio change command part 120 outputs a steering angle ratio change command to a steering angle ration variable device when existing in an electrical angle position in which the rotation of the electric motor 31 is difficult to be started. Thus, the electrical angle of the electric motor 31 is changed to become rotatable. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle steering device including an electric power steering device and a steering angle ratio variable device.

  Conventionally, an electric power steering device that drives and controls an electric motor to apply steering assist torque to a steering mechanism, and a steering angle ratio that varies a steering angle ratio that is a ratio of a steering angle of a steered wheel to a steering angle of a steering wheel A steering apparatus including a variable device is known. Such a steering apparatus is proposed in Patent Document 1, for example. The steering angle ratio variable device is provided between an input steering shaft having a steering handle fixed to the upper end and an output steering shaft having a pinion gear meshing with a rack bar fixed to the lower end, and an output steering shaft with respect to the rotation angle of the input steering shaft. The rotation angle can be continuously changed.

  The electric power steering apparatus includes an electric motor for outputting a steering assist torque in a steering column or a rack bar, sets a target assist torque based on the steering torque input to the steering handle, and the set target assist torque is As a result, the energization amount of the electric motor is controlled. An electric power steering apparatus using a three-phase motor as an electric motor has also been generalized. When using a three-phase motor, use a normal two phase even if 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, etc. The motor can be driven. Such a two-phase energization driving technique for a three-phase motor has been proposed in Patent Document 2, for example.

JP 2006-21562 A 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は目標アシストトルク、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 2, a sinusoidal current is passed through the two phases in which the energization failure has not occurred during the two-phase energization drive, so that the torque increases as the motor electrical angle changes. It will fluctuate. On the other hand, torque fluctuation does not theoretically occur if energization control is performed using a two-phase energization current calculation formula for generating a constant torque with respect to a change in motor electrical angle. 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 is poorly energized, where T is the target assist torque, e ₀ is the torque constant, and θe is the motor electrical angle. In addition, the U phase is obtained by inverting the V phase (Iu = −Iv).

  According to this two-phase energization current calculation formula, since the current value becomes infinite at a specific electrical angle, it is necessary to limit the current of each phase to a predetermined maximum current value or less. Therefore, the current waveform is as shown in FIG. When the maximum current is limited in this way, motor torque shortage occurs in a specific electrical angle region as shown in FIG. 4B. As a result, the motor cannot be rotated well.

  An object of the present invention is to solve the above-described problem, and even when one phase of a three-phase motor of an electric power steering apparatus is poorly energized and is driven by two-phase energization, the motor is rotated satisfactorily. There is.

In order to achieve the above object, the present invention is characterized by an electric power steering device that drives and controls a three-phase motor to apply a steering assist torque to a steering mechanism, and a steering angle of a steering wheel with respect to a steering angle of a steering wheel In a steering apparatus for a vehicle provided with a steering angle ratio variable device that varies a steering angle ratio that is a ratio of
The electric power steering device includes: an electrical angle detection unit that detects an electrical angle of the motor; a conduction failure detection unit that detects occurrence of a conduction failure to each phase of the motor; and a conduction failure to the motor in one phase. The theoretical current calculation formula for two-phase energization for outputting a steering assist torque that does not fluctuate with respect to a change in the electric angle of the motor using two phases in which no energization failure has occurred And calculating a command current for two-phase energization based on the maximum current that defines the upper limit current of the motor and the advance amount of the electric angle of the motor in the two-phase energization current calculation formula The two-phase energization control means for energizing the two-phase energization with the two-phase energization command current to control the drive of the motor by energizing the two phases where no energization failure has occurred, and the motor is driven and controlled by the two-phase energization control means. When Steering torque input to the rudder shaft is detected, and the motor is driven and controlled by steering torque determination means for determining whether or not the steering torque is equal to or greater than a predetermined determination reference steering torque, and the two-phase energization control means. The rotational speed of the motor or the steering shaft is detected, rotational speed determination means for determining whether the rotational speed is less than a preset reference speed, and the steering torque by the steering torque determination means Is determined to be greater than or equal to the determination reference steering torque, and the rotation speed determination means determines that the rotation speed is less than the determination reference speed, the steering angle ratio with respect to the steering angle ratio variable device Steering angle ratio change command means for outputting the change command.

  The steering device of the present invention includes an electric power steering device and a steering angle ratio variable device. The electric power steering device applies steering assist torque to the steering mechanism by controlling energization of the three-phase motor. For example, the target assist torque is set based on the steering torque input to the steering wheel, and the driver's steering operation is assisted by controlling the energization amount of the motor so as to obtain the target assist torque. A three-phase brushless motor is suitable as the three-phase motor. The electric power steering device has an electrical angle detection means, a conduction failure detection means, a two-phase conduction control means, a steering torque so that even when a conduction failure to a three-phase motor occurs, the motor can be driven using normal two phases. Judgment means, rotational speed judgment means, and steering angle ratio change command means are provided.

  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 theoretical two-phase energization current calculation formula for outputting a steering assist torque that does not fluctuate with respect to a change in the electrical angle of the motor, and a maximum current that defines the upper limit current of the motor. Based on the (maximum current value) and the advance amount by which the electrical angle of the motor is advanced in the current calculation formula for two-phase energization, a command current (command current value) for two-phase energization is calculated, and the calculated two-phase energization The motor is driven and controlled by energizing the two phases with no energization failure with the 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 current for two-phase energization is limited to the maximum current in the region near the specific electrical angle. This current limitation reduces the torque that can be generated by the motor. 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 current calculation formula for two-phase energization. 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.

  Considering the case of driving the motor in the direction in which the electrical angle increases when the electrical angle in the two-phase energization current calculation formula is advanced, the motor torque characteristic with respect to the electrical angle is a specific electrical angle at which the energization direction of the command current is reversed. The torque increases at a position of a smaller electrical angle (which is advanced by the advance amount), and when it exceeds a specific electrical angle, the torque decreases rapidly and a 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. 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.

  As described above, during the two-phase energization driving, the motor can be rotated even if there is an electrical angle region where the motor torque is insufficient by providing the over assist region and the reverse assist region. Due to the relationship with the reaction force, there may be a case where a short assist region occurs between the over assist region and the reverse assist region (the reverse assist region on the rotation direction side of the over assist region). In such a case, when starting motor rotation from a short assist region between the over assist region and the reverse assist region, or when the motor tries to pass this short assist region by extremely low speed steering, The torque generated by itself cannot overcome the reaction force and rotate to the reverse assist region. Moreover, even if it is rotated in the reverse rotation direction by the reaction force, it cannot return to the over assist region. For this reason, a large steering force is temporarily required for the driver, which gives a sense of incongruity.

  Therefore, in the present invention, the steering torque determining means determines whether or not the steering torque input to the steering shaft is greater than or equal to a predetermined determination reference steering torque, and the rotational speed determining means is the rotational speed of the motor or the steering shaft. Is less than a preset reference speed. When the steering torque determination means determines that the steering torque is greater than or equal to the determination reference steering torque, and the rotation speed determination means determines that the rotation speed of the motor or the steering shaft is less than the determination reference speed, the motor is over-assisted. It can be determined that the rotation starts from the insufficient assist area between the area and the reverse assist area. At this time, the steering angle ratio change command means outputs a steering angle ratio change command to the steering angle ratio variable device. The rudder angle ratio changing device varies the rudder angle ratio, which is the ratio of the steered wheel turning angle to the steering angle of the steering wheel. For example, a target rudder angle ratio setting unit that sets a target rudder angle ratio according to the vehicle speed, an electric actuator that changes the rudder angle ratio, and a rudder that drives and controls the electric actuator so that the rudder angle ratio becomes the target rudder angle ratio. Angle ratio control means. Therefore, the steering angle ratio changing device steers the steered wheels when the steering angle ratio change command is input from the steering angle ratio change command means. Along with this, the rotational position of the motor of the electric power steering apparatus changes. Therefore, the electric angle of the motor exits from the insufficient assist region between the over assist region and the reverse assist region.

  As a result, according to the present invention, even when one phase of the three-phase motor of the electric power steering apparatus is poorly energized and driven in two-phase energization, the motor can be rotated well, and at the time of extremely low speed steering. It is possible to prevent the driver from feeling uncomfortable.

1 is a schematic configuration diagram of a vehicle steering apparatus according to an embodiment of the present invention. It is a functional block diagram showing the process of the microcomputer part of steering 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 graph for demonstrating the necessity of a trigger torque. It is a flowchart showing a rotation assist control routine. It is a flowchart showing a steering angle ratio change routine. It is a graph showing a vehicle speed-coefficient map.

  A vehicle steering apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a vehicle steering apparatus according to the embodiment.

  A vehicle steering apparatus includes a steering handle 11 that is turned by a driver and fixed to a steering shaft 12. The steering shaft 12 includes a steering shaft 12a (hereinafter referred to as an input steering shaft 12a) for fixing the steering handle 11 to the upper end, and a steering shaft 12b (hereinafter referred to as an output steering shaft 12b) for fixing the pinion gear 13 to the lower end. The upper and lower parts are divided into two. The pinion gear 13 meshes with the rack teeth of the rack bar 14. The rack bar 14 extends in the left-right direction (vehicle width direction), and both ends of the rack bar 14 are connected to the knuckle of the left and right front wheels 15a, 15b as steering wheels via a tie rod (not shown). Accordingly, the rotation of the steering handle 11 is transmitted to the rack bar 14 via the steering shaft 12 and the pinion gear 13, and the rack bar 14 is displaced in the axial direction to steer the left and right front wheels 15a and 15b. Such a steering shaft 12, pinion gear 13, rack bar 14 and the like constitute a steering mechanism.

  A steering angle ratio, which is a ratio of the steering angles of the front wheels (steering wheels) 15a and 15b to the steering angle of the steering handle 11, is set between the input steering shaft 12a and the output steering shaft 12b of the steering shaft 12 divided in two. A steering angle ratio variable mechanism 20 to be changed is interposed. The steering angle ratio variable mechanism 20 includes a cylindrical casing 21 connected so as to rotate integrally with a lower end portion of the input steering shaft 12a. An electric motor 22 is fixed in the casing 21. An output shaft 22a of the electric motor 22 is rotatably supported by the casing 21, and is connected to the output steering shaft 12b so as to be integrally rotatable at the lower end. The electric motor 22 has a built-in speed reduction mechanism, and the rotation of the electric motor 22 is decelerated and output to the output shaft 22a.

  The electric motor 22 is provided with a relative angle sensor 43. The relative angle sensor 43 is assembled to the output shaft 22a of the electric motor 22 and outputs a detection signal corresponding to the rotation angle of the output steering shaft 12b with respect to the casing 21. The value of the rotation angle detected by the relative angle sensor 43 is hereinafter referred to as a relative angle Δθv. Therefore, the rotation angle of the output steering shaft 12b is the sum of the steering angle θh and the relative angle Δθv.

  The rack bar 14 is provided with a power assist mechanism 30 that outputs a steering assist torque to assist the driver in turning the steering handle. The power assist mechanism 30 includes an electric motor 31 and a ball screw mechanism 32. The rotation of the electric motor 31 is converted into an axial movement of the rack bar 14 by the ball screw mechanism 32 and transmitted to the rack bar 14, and a steering force is applied to the left and right front wheels 15a and 15b to allow the driver to perform a steering operation. Assist.

  As the electric motor 31, a three-phase brushless motor is used. The electric motor 31 is provided with a rotation angle sensor 40 necessary for rotation control. The rotation angle sensor 40 is incorporated in the electric motor 31 and outputs a detection signal corresponding to the rotation angle position of the rotor of the electric motor 31. Hereinafter, the value of the rotation angle detected by the rotation angle sensor 40 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 31.

  A steering angle sensor 41 and a steering torque sensor 42 are assembled in the steering mechanism. The steering angle sensor 41 is assembled to the input steering shaft 12a, and outputs a detection signal corresponding to the rotation angle from the neutral position of the steering handle 11, that is, the steering angle. The value of the rotation angle detected by the steering angle sensor 41 is hereinafter referred to as a steering angle θh. The steering torque sensor 42 is assembled to the output steering shaft 12b, and outputs a detection signal representing torque acting on the output steering shaft 12b, that is, steering torque accompanying steering of the left and right front wheels 15a and 15b. The steering torque value detected by the steering torque sensor 42 is referred to as steering torque Tr. Note that the steering angle θh, the steering torque Tr, and the relative angle Δθv represent a right angle and torque by a positive value, and a left angle and torque by a negative value.

  The electric motor 22 of the steering angle ratio variable mechanism 20 is driven and controlled by a steering angle ratio electronic control unit 50 (hereinafter referred to as a steering angle ratio ECU 50). The steering angle ratio ECU 50 includes a microcomputer unit 60 including a microcomputer including a CPU, a ROM, a RAM, and the like as main parts, and a motor drive circuit 70. The microcomputer unit 60 connects a steering angle sensor 41, a relative angle sensor 43, and a vehicle speed sensor 44 for detecting a vehicle speed via an input interface (not shown), and outputs a signal representing the steering angle θh, a signal representing the relative angle Δθv, and the vehicle speed v. Input a signal to represent. The motor drive circuit 70 is an H-bridge circuit or an inverter circuit, and the duty ratio of the internal switching element is controlled by the PWM control signal output from the microcomputer unit 60, so that the energization amount and the rotation direction of the electric motor 22 are controlled. Adjust.

  The steering angle ratio variable device 80 includes the steering angle ratio variable mechanism 20, the steering angle ratio ECU 50, and the above-described sensors (the steering angle sensor 41, the relative angle sensor 43, and the vehicle speed sensor 44). The steering angle ratio adjusted by the steering angle ratio variable device 80 means the ratio (β / α) of the turning angle β of the front wheels 15a, 15b to the rotation angle α of the input steering shaft 12a. The larger the wheel, the larger the front wheel can be steered with fewer steering operations, and the smaller the steering angle ratio, the larger the steering operation required to steer the front wheels. Since the turning angle δ of the front wheels 15a and 15b is uniquely determined from the rotation angle θout of the output steering shaft 12b, the ratio of the rotation angle θout of the output steering shaft 12b to the rotation angle (steering angle θh) of the input steering shaft 12a ( The steering angle ratio can be controlled by controlling [theta] out / [theta] h). Further, the rotation angle θout of the output steering shaft 12b is equal to the sum of the steering angle θh and the relative angle Δθv. Therefore, the steering angle ratio can be controlled to the target value by the rotation angle control of the electric motor 22 by the steering angle ratio ECU 50.

The microcomputer unit 60 calculates the target relative angle Δθv * by executing the calculation of the following equation using the input steering angle θh and the vehicle speed v. In addition, the coefficient K1 in the following formula is a predetermined constant. The coefficient Kv is referred to a vehicle speed-coefficient map (see FIG. 14) provided in the ROM of the microcomputer unit 60, so that the coefficient Kv increases from a predetermined value larger than “1.0” to “1.0” as the vehicle speed v increases. The value is gradually decreased.
Δθv * = K1 ・ (Kv−1) ・ θh

  The microcomputer unit 60 calculates a deviation (Δθv * −Δθv) between the calculated target relative angle Δθv * and the actual relative angle Δθv input from the relative angle sensor 43, and feedback according to the deviation (Δθv * −Δθv). A control signal (PWM control signal) is output to the motor drive circuit 70. The motor drive circuit 70 adjusts the duty ratio of the internal switching element by the PWM control signal output from the microcomputer unit 60 and drives the electric motor 22 to rotate the steering shaft 12b to the target relative angle Δθv *.

  In this state, if the steering angle (that is, the rotation angle from the reference rotation position of the steering shaft 12a) is θh, the rotation angle of the steering shaft 12b is θh + Δθv *, and the left and right front wheels 15a, 15b have this rotation angle θh + Δθv *. It is steered by a proportional turning angle. Accordingly, the lower the vehicle speed v, the larger the left and right front wheels 15a and 15b are steered with respect to the rotation of the steering handle 11. That is, the steering angle ratio increases as the vehicle speed v decreases, and the vehicle turning performance becomes better. Further, the running stability of the vehicle during high speed running is improved.

  The electric motor 31 (three-phase brushless motor) of the power assist mechanism 30 is driven and controlled by a steering assist electronic control unit 100 (hereinafter referred to as a steering assist ECU 100). The steering assist ECU 100 includes a microcomputer unit 110 having a microcomputer including a CPU, a ROM, a RAM, and the like as main parts, and a motor drive circuit 130 including a three-phase inverter circuit. The motor drive circuit 130 detects a current flowing in each phase (U phase, V phase, W phase) of the electric motor 31 and outputs a detection signal corresponding to the detected current value to the microcomputer unit 110. A sensor 131 is provided. 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.

  The microcomputer unit 110 connects the steering angle sensor 41, the steering torque sensor 42, the rotation angle sensor 40, the current sensor 131, and the vehicle speed sensor 44 via an input interface (not shown), and represents a signal representing the steering angle θh and the steering torque Tr. A signal, a signal representing the motor rotation angle θm, a signal representing the motor current Iuvw, and a signal representing the vehicle speed v are input. Then, based on the input detection signal, a command current (target current) to be passed through the electric motor 31 is calculated so that an optimum steering assist torque corresponding to the driver's steering operation can be obtained, so that the command current flows. A PWM control signal is output to the motor drive circuit 130. The motor drive circuit 130 adjusts the energization amount and the rotation direction of the electric motor 31 by controlling the duty ratio of each switching element constituting the three-phase inverter circuit by this PWM control signal.

  In addition, the microcomputer unit 110 detects a failure (energization failure) in the energization path for supplying power to the electric motor 31 for each phase, and when only one phase energization failure is detected, the normal two phases are used. A function of performing two-phase energization control for driving the electric motor 31 is provided.

  The electric power steering apparatus 200 includes the power assist mechanism 30, the steering assist ECU 100, and the above-described sensors (the steering angle sensor 41, the steering torque sensor 42, the rotation angle sensor 40, the current sensor 131, and the vehicle speed sensor 44). Further, the microcomputer unit 110 of the electric power steering apparatus 200 is communicably connected to the microcomputer unit 60 of the steering angle ratio variable device 80, and can exchange control commands with each other.

  Next, functions of the microcomputer unit 110 in the electric power steering apparatus 200 will be described with reference to FIG. FIG. 2 is a functional block diagram showing functions processed by program control of the microcomputer unit 110. The microcomputer unit 110 switches the motor control mode in accordance with whether or not an energization failure to each phase of the electric motor 31 is detected. If all three phases are normally energized to the electric motor 31, motor control using three phases (hereinafter referred to as three-phase energization control) is performed, and when one-phase energization failure is detected, the energization failure is detected. The control is switched to perform motor control using two phases (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.

  As shown in FIG. 2, the microcomputer unit 110 includes an assist current command unit 111. The assist current command unit 111 receives the steering torque Tr output from the steering torque sensor 42 and the vehicle speed v output from the vehicle speed sensor 44, and calculates the basic assist torque Tas by referring to the basic assist map. The basic assist map is set and stored with a basic assist torque Tas that increases as the steering torque Tr increases and decreases as the vehicle speed v increases. The assist current command unit 111 receives the steering angle θh detected by the steering angle sensor 41 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 ωh 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 111 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 microcomputer unit 110 performs vector control described in a dq coordinate system in which the rotation direction of the electric motor 31 is the q axis and the direction orthogonal to the rotation direction is the d axis. The rotation of the electric motor 31 is controlled. The d-axis current does not work to generate torque of the electric motor 31 and is used for field weakening control. In the present embodiment, the assist current command unit 111 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 112. The feedback control unit 112 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 converted into 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 31 into the two-phase current in the dq coordinate system. . Conversion from the three-phase currents Iu, Iv, Iw to the two-phase currents Id, Iq in the dq coordinate system is performed by the three-phase / 2-phase coordinate conversion unit 113. The three-phase / two-phase coordinate conversion unit 113 receives the motor electrical angle θe output from the rotation angle conversion unit 114, and the three-phase currents Iu and Iv output from the current sensor 131 based on the motor electrical angle θe. , Iw are converted into two-phase currents Id, Iq in the dq coordinate system. The rotation angle conversion unit 114 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 40. 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 112 are output to the 2-phase / 3-phase coordinate conversion unit 115. The two-phase / three-phase coordinate conversion unit 115 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 114. , Vw *, and the converted three-phase command voltages Vu *, Vv *, Vw * are output to the PWM signal generator 116. The PWM signal generator 116 outputs a PWM control signal corresponding to the three-phase command voltages Vu *, Vv *, Vw * to each switching element of the motor drive circuit 130. As a result, the electric motor 31 is driven, and a steering assist torque that follows the target assist torque T * is applied to the steering mechanism.

  Next, two-phase energization control will be described. As shown in FIG. 3A, the electric motor 31 normally supplies a sine wave current having a phase difference of 120 deg in electrical angle in three phases. In this case, a constant motor torque can be obtained with respect to changes in 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 31 and the motor drive circuit 130 are protected from overcurrent. In order to do this, a maximum current that can be passed through the electric motor 31 is preset in the microcomputer unit 110. 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 applied to the electric motor 31, the torque generated by the electric motor 31 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 31 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 31 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, the over assist region A and the reverse assist region B2 are provided in the motor torque characteristics, so that the electric motor 31 can be rotated without being caught using these regions A and B2. The reason will be described below.

  When the electric motor 31 rotates in the rotation direction shown in FIG. 7, the electric motor 31 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 31 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 31 reversely rotates in the middle 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 31 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 31 starts to accelerate by generating torque in the forward rotation direction in the over assist region A. That is, the rotational position (electrical angle θe) of the electric motor 31 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 31 can be rotated in the steering direction 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.

  The function of the microcomputer unit 110 that performs such two-phase energization control will be described with reference to FIG. The microcomputer unit 110 includes a two-phase energization command unit 117 and an energization failure detection unit 118. The two-phase energization command unit 117 starts operating when a one-phase energization failure detection signal is input from the energization failure detection unit 118.

  The conduction failure detection unit 118 receives the PWM control signal output from the PWM signal generation unit 116, the steering angle θh output from the steering angle sensor 41, and the three-phase currents Iu, Iv, Iw output from the current sensor 131. Thus, a failure in energization of the electric motor 31 is detected separately for each phase. The failure in energization of the electric motor 31 means a failure in which electric power cannot be supplied satisfactorily. For example, a failure in the motor drive circuit 130 (particularly, a contact failure of the switching element), the motor drive circuit 130 to the electric motor. This is a failure caused by disconnection of the power supply line to 31.

  For example, when the phase current detected by the current sensor 131 is smaller than a preset reference current, the conduction failure detection unit 118 determines the magnitude (absolute value) of the steering speed ωh 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 130.

  The energization failure detection unit 118 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 118 detects the energization failure, the energization failure is output to the switch corresponding to the energization failure phase of the cutoff circuit (not shown) provided in the power supply line of the electric motor 31, Shut off the energization of the phase. Hereinafter, signals output from the energization failure detection unit 118 (energization normality signal and energization failure detection signal 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 117 receives a one-phase energization detection signal from the energization failure detection unit 118, the two-phase energization command unit 117 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 111 and the electrical angle θe output from the rotation angle conversion unit 114.

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.

  Due to this arithmetic expression and the limitation on the maximum current, 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 117 reads the steering torque Tr output from the steering torque sensor 42 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 31 is rotated to the side where the electrical angle increases, the positive advance amount θa is set, and when the electric motor 31 is rotated to the side where the electrical angle decreases, the negative advance amount θa is set. To do. Thereby, an electrical angle can be advanced in the direction in which the electric motor 31 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 control unit 119 for two-phase energization. The The two-phase energization feedback control unit 119 starts operation when a one-phase energization failure detection signal is input from the energization failure detection unit 118. At this time, the energization failure detection signal is also output to the feedback control unit 112. The feedback control unit 112 stops its operation when receiving the energization failure detection signal. 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 119 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 131 and are used 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 119 outputs the calculated two-phase energization command voltages Vu *, Vv *, and Vw * to the PWM signal generation unit 116. The PWM signal generator 116 outputs a PWM control signal corresponding to the command voltages Vu *, Vv *, Vw * for two-phase energization to the motor drive circuit 130. As a result, the electric motor 31 is driven, and a steering assist torque that follows the target assist torque T * is applied to the steering mechanism. In this case, since the electric angle θe of the two-phase energization current calculation formula is advanced by the advance amount θa, the rotation of the electric motor 31 is not caught and good steering assist can be performed.

  By the way, when the electric motor 31 is energized in two phases, the electric motor 31 can be rotated favorably by providing the over assist area A and the reverse assist area B2 by advancing the electrical angle as described above. As shown in FIG. 11, due to the relationship between the motor torque characteristic and the reaction force, the insufficient assist region C is between the over assist region A and the reverse assist region B2 (the reverse assist region B2 on the rotational direction side of the over assist region A). There are cases that occur. And when starting motor rotation from the short assist region C between this over assist region A and the reverse assist region B2, or when the electric motor 31 reaches this short assist region C by extremely low speed steering, The electric motor 31 cannot overcome the reaction force with the torque generated by itself and cannot rotate to the reverse assist region B2, and can return to the over assist region A even if it is rotated in the reverse rotation direction due to the reaction force. Can not. Therefore, for example, in order to rotate the electric motor 31 from the electrical angle θ1 in FIG. 11, a trigger torque Ttr for advancing to the reverse assist region is required, and accordingly, the driver has a large steering force temporarily. Necessary and uncomfortable.

  Therefore, in this embodiment, in order to prevent a sense of incongruity when such a situation occurs, the microcomputer unit 110 includes a steering angle ratio change command unit 120. The steering angle ratio change command unit 120 receives the energization determination signal output from the energization failure detection unit 118, the steering torque Tr output from the steering torque sensor 42, and the electrical angle θe output from the rotation angle conversion unit 114. When the energization determination signal becomes an energization failure detection signal, the operation is started.

  The function of the steering angle ratio change command unit 120 will be described with reference to the flowchart shown in FIG. This flowchart represents a rotation assist control routine executed by the steering angle ratio change command unit 120, and is stored as a control program in the ROM of the microcomputer unit 110, while a power failure detection signal is input as a power supply determination signal. It is repeatedly executed in a short cycle.

  When the rotation assist control routine is started, the steering angle ratio change command unit 120 reads the electrical angle θe detected by the rotation angle conversion unit 114 in step S11, and in step S12, determines the magnitude of the change in the electrical angle θe. The electric angular velocity | ωe | represented is calculated. The electrical angular velocity | ωe | can be obtained by time differentiation of the electrical angle θe. This electrical angular velocity | ωe | represents the rotational speed of the electric motor 31.

  Subsequently, the steering angle ratio change command unit 120 determines whether or not the detected electrical angular speed | ωe | is smaller than the determination reference speed ωe0 in step S13. The determination reference speed ωe0 is a threshold value for determining an extremely low speed steering operation (including a case where the steering handle 11 is not rotating), and thus is set to a very small value.

  If the rudder angle ratio change command unit 120 determines in step S13 that the extremely low speed steering operation is not being performed, in step S14, the rudder angle ratio change flag F determines whether or not the rudder angle ratio change flag F is set to “1”. . The steering angle ratio change flag F is set to “1” when a steering angle ratio change command to be described later is output, and is set to “0” when the rotation assist control routine is started. . Therefore, here, since F = 0, it is determined as “No”, and the rotation assist control routine is temporarily ended. The rotation assist control routine is repeated at a predetermined short cycle. Therefore, the processes of steps S11, S12, S13, and S14 are repeated.

  When it is determined in step S13 that the steering operation is extremely low, the steering angle ratio change command unit 120 reads the steering torque Tr detected by the steering torque sensor 42 in step S15, and in the subsequent step S16, It is determined whether or not the steering torque Tr is greater than or equal to the determination reference steering torque Tr0. For example, when the motor rotation is started from the electrical angle θ1 shown in FIG. 11 or when the short assist region C is entered by the extremely low speed steering operation, the motor torque shortage occurs and the steering torque Tr increases. In this case, the determination in step S16 is “Yes”, and the steering angle ratio change command unit 120 outputs a steering angle ratio change command to the microcomputer unit 60 of the steering angle ratio variable device 80 in step S17. The vibration stop control routine is temporarily terminated. This steering angle ratio change command is issued by setting the steering angle ratio change flag F to “1”.

  The microcomputer unit 60 of the steering angle ratio variable device 80 controls the drive of the electric motor 22 so that the target relative angle Δθv * set according to the vehicle speed v is obtained as described above. When a steering angle ratio change command (F = 1) is input from the 110 steering angle ratio change command unit 120, the target relative angle Δθv * is changed. FIG. 13 shows a steering angle ratio change routine executed by the microcomputer unit 60 of the steering angle ratio variable device 80. The steering angle ratio changing routine is repeated at a predetermined short cycle. In step S21, the microcomputer unit 60 reads the steering angle ratio change flag F output from the microcomputer unit 110 (steering angle ratio change command unit 120) of the electric power steering apparatus 200, and the steering angle ratio change flag F is “1”. It is determined whether or not. If the steering angle ratio change flag F is “0”, the steering angle ratio change routine is finished as it is.

  On the other hand, if the steering angle ratio change flag F is “1”, in step S22, an angle obtained by adding a preset rotation assist angle θva to the target relative angle Δθv * is set as a new target relative angle Δθv *. . Therefore, when the steering angle ratio change flag F is switched from “0” to “1”, the electric motor 22 rotates by the rotation assist angle θva. This rotation assist angle θva is set to a minute angle that allows the electric angle of the electric motor 31 of the electric power steering apparatus 200 to move to the reverse assist region B2. Accordingly, when the electric motor 22 of the steering angle ratio variable device 80 rotates by the rotation assist angle θva, the rotor of the electric motor 31 is rotated via the steering mechanism. Thereby, as shown in FIG. 11, the electric motor 31 proceeds from the insufficient assist region C to the reverse assist region B <b> 2. Accordingly, torque that is opposite to the steering direction is generated in the reverse assist region B2, and the torque and reaction force are combined to return to the over assist region A all at once. Then, in the over assist area A, torque is generated in the forward rotation direction to start acceleration, and the kinetic energy stored therein passes through the insufficient assist area C, the reverse assist area B2, and the insufficient assist area B1. Thereby, the electric motor 31 can be rotated in the steering direction without generating a catch. The rotation assist angle θva may be set to an angle that allows the electric angle of the electric motor 31 to advance to the adjacent reverse assist region B2 or an angle that advances the steering angle in the steering direction.

  Returning to the description of the rotation assist control routine of FIG. The rotation assist control routine is repeatedly executed even after the steering angle ratio change flag F is switched to “1”. When the steering angle ratio change flag F is switched to “1”, since the electric motor 31 of the electric power steering device 200 is rotated by the operation of the steering angle ratio variable device 80, the electrical angular velocity | ωe | increases. It becomes larger than the judgment reference speed ωe0. Therefore, the steering angle ratio change command unit 120 determines “No” in step S13, and determines whether the steering angle ratio change flag F is “1” in subsequent step S14. In this case, since the steering angle ratio change flag F is set to “1”, next, in step S18, the steering angle ratio change flag F is set in a state where the electrical angular speed | ωe | is larger than the determination reference speed ωe0. It is determined whether the time “1” has reached a predetermined time set in advance. While the predetermined time has not been reached, the rotation assist control routine is directly exited. When the electrical angular speed | ωe | is larger than the determination reference speed ωe0 and the time when the steering angle ratio change flag F is “1” reaches a predetermined time, the steering angle ratio change command unit 120 performs step S19. , The steering angle ratio return command is output to the microcomputer unit 60 of the steering angle ratio variable device 80, and the rotation assist control routine is temporarily ended. This steering angle ratio return command is issued by resetting the steering angle ratio change flag F to “0”.

  When the steering angle ratio change flag F is reset to “0”, the microcomputer unit 60 of the steering angle ratio variable device 80 determines “No” in step S21 in the steering angle ratio change routine, and the target relative angle Δθv * is determined. The addition correction of the rotation assist angle θva is not performed. Therefore, the target relative angle Δθv * is returned to the original target relative angle Δθv *. For this reason, the electric motor 22 rotates in the reverse direction by the rotation assist angle θva. In this case, the electric motor 31 of the electric power steering apparatus 200 is also rotated accordingly. However, since the electric motor 31 has already been rotated to some extent by the time lapse process in step S18, the electric motor 31 has the same electric power. There is no return to the angular position. Further, the rotation of the electric motor 22 does not give the driver any uncomfortable feeling because the rotation assist angle θva is a minute angle.

  According to the vehicle steering apparatus of the present embodiment described above, the two-phase energization control that gives the advance amount θa even when the one-phase energization failure of the electric motor 31 in the electric power steering apparatus 200 occurs. By performing the above, the electric motor 31 can be rotated satisfactorily. Thereby, the fall of the steering operation feeling at the time of two-phase electricity supply control can be suppressed. Further, when the electric motor 31 starts to rotate from the position of the insufficient assist region C between the over assist region A and the reverse assist region B2, a steering angle ratio change command is output to the steering angle ratio variable device 80 to be electrically operated. Since the electrical angle of the motor 31 is shifted, the electric motor 31 can be smoothly rotated. Therefore, it is possible to prevent the driver from feeling uncomfortable.

  As mentioned above, although the vehicle steering device of this embodiment was demonstrated, this invention is not limited to the said embodiment, A various change is possible unless it deviates from the objective of this invention.

  For example, in the present embodiment, the rotational speed of the electric motor 31 is detected by the electrical angular speed ωe, but the steering speed ωh may be detected instead of the electrical angular speed ωe. In this case, instead of the determination reference speed ωe0 in step S13, a determination reference speed ωh0 for determining an extremely low speed steering operation may be used.

  In this embodiment, the rack assist type electric power steering device that applies the torque generated by the electric motor 31 to the rack bar 14 is provided, but the column that applies the torque generated by the electric motor to the steering shaft 12 is provided. An assist type electric power steering apparatus may be provided.

  DESCRIPTION OF SYMBOLS 11 ... Steering handle, 12 ... Steering shaft, 20 ... Steering angle ratio variable mechanism, 22 ... Electric motor, 30 ... Power assist mechanism, 31 ... Electric motor, 40 ... Rotation angle sensor, 41 ... Steering angle sensor, 42 ... Steering torque Sensor: 43 ... Relative angle sensor, 44 ... Vehicle speed sensor, 50 ... Steering angle ratio ECU, 60 ... Microcomputer unit, 100 ... Steering assist ECU, 110 ... Microcomputer unit, 111 ... Assist current command unit, 112 ... Feedback control unit, 113 ... 3 phase / 2 phase coordinate conversion unit, 114 ... rotation angle conversion unit, 115 ... 2 phase / 3 phase coordinate conversion unit, 116 ... PWM control signal generation unit, 117 ... 2 phase energization command unit, 118 ... energization failure detection unit DESCRIPTION OF SYMBOLS 119 ... Feedback control part for 2 phase electricity supply, 120 ... Steering angle ratio change command part, 130 ... Motor drive circuit, 131 ... Current sensor.

Claims (1)

An electric power steering device that drives and controls a three-phase motor to apply a steering assist torque to the steering mechanism;
In a vehicle steering apparatus comprising: a steering angle ratio variable device that varies a steering angle ratio that is a ratio of a steering angle of a steered wheel to a steering angle of a steering wheel.
The electric power steering device is
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;
Theory for outputting a steering assist torque that does not fluctuate with respect to changes in the electrical angle of the motor, using two phases in which no current failure has occurred, when there is only one phase of current failure in the motor. Two-phase energization based on the above two-phase energization current calculation formula, the maximum current that defines the upper limit current of the motor, and the advance amount of the electric angle of the motor in the two-phase energization current calculation formula 2-phase energization control means for energizing the motor to drive the motor by energizing the 2-phase in which energization failure does not occur with the calculated 2-phase energization command current;
When the motor is driven and controlled by the two-phase energization control means, the steering torque input to the steering shaft is detected, and the steering for determining whether or not the steering torque is greater than or equal to a preset reference steering torque. Torque determination means;
When the motor is driven and controlled by the two-phase energization control means, the rotational speed of the motor or the steering shaft is detected to determine whether the rotational speed is less than a preset reference speed. A determination means;
When the steering torque determining means determines that the steering torque is greater than or equal to the determination reference steering torque, and the rotation speed determination means determines that the rotation speed is less than the determination reference speed, the steering angle A steering apparatus for a vehicle, comprising: a steering angle ratio change command means for outputting a steering angle ratio change command to the variable ratio device.

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