JP2010167880A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily rotate a motor while suppressing energy loss and torque fluctuation when one phase of a three-phase motor is energized and two-phase energization driving is performed.
SOLUTION: A two-phase energization command unit 107 responds to a change in an electrical angle θe by using two phases with no energization failure when only one phase of energization failure to the electric motor 20 occurs. A theoretical two-phase current calculation formula for generating a steering assist torque that does not fluctuate, a maximum current that defines the upper limit current of the electric motor 20, and an advance angle that advances the electrical angle θe in the two-phase current calculation formula Based on the quantity θa, a command current for two-phase energization is calculated. The advance amount setting unit 110 sets the advance amount θa according to the kinetic energy of the electric motor 20 at a position immediately before the direction of energization of the command current is reversed.
[Selection] Figure 2

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.

  Conventionally, the electric power steering apparatus assists the driver to reduce the steering operation force by controlling the energization of the electric motor based on the steering operation performed by the driver. 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. For example, Patent Document 1 proposes a two-phase energization drive technique for an electric motor in an electric power steering apparatus.

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 cope with the above problem, and is to rotate a motor satisfactorily even when one phase of a three-phase motor is poorly energized and driven by two-phase energization.

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 that controls energization of the motor based on a steering operation of a driver. In the electric power steering device with
The motor control means includes an electrical angle detection means for detecting an electrical angle of the motor, an energization failure detection means for detecting the occurrence of an energization failure to each phase of the motor, and an energization failure to the motor of only one phase. A theoretical two-phase energization current calculation formula for generating a steering assist torque that does not fluctuate with respect to a change in the electrical angle of the motor, using two phases that do not cause energization failure when they occur; The command current for two-phase energization is calculated 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 Two-phase energization control means for energizing two motors that are not energized with a command current for two-phase energization to control the drive of the motor, and the electric angle of the electric motor is determined by the two-phase energization control means Communication of the calculated command current Motor position detecting means for detecting that the electric angle is just before the direction is reversed, and the electric angle of the electric motor becomes the electric angle just before the direction of applying the command current is reversed by the motor position detecting means. An energy calculating means for calculating the kinetic energy of the electric motor at the time of detection, and when the magnitude of the kinetic energy calculated by the energy calculating means is larger than a reference value, if less than the reference value Compared to the above, there is provided an advance amount setting means for setting the advance amount to be smaller.

  In the present invention, the steering assist torque corresponding to the steering operation is generated 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 includes an electrical angle detection means, a conduction failure detection means, a two-phase conduction control means, and a motor so that the motor can be driven satisfactorily using normal two phases even when a conduction failure to the three-phase motor occurs. Position detection means, energy calculation means, and advance amount setting 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 generating 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.

  Thus, during the two-phase energization drive, 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. However, energy loss and torque fluctuation due to the reverse assist region occur. Therefore, it is desirable not to provide the reverse assist area more than necessary.

  When the electrical angle of the motor is advanced, the reverse assist region is where the specified current angle in which the direction of energization of the command current is reversed. Therefore, if the amount of advance in the region near the specific electrical angle is reduced, the reverse assist region is reduced. (Including erasure). However, when the reverse assist area becomes small, the motor may not be able to rotate smoothly.

  Therefore, in the present invention, the kinetic energy of the motor is calculated at a position immediately before the electrical angle of the motor enters the reverse assist region, and the reverse assist region is adjusted based on the magnitude of this kinetic energy. The position where the electrical angle of the motor is just before entering the reverse assist region is captured by the motor position detection means that is the electrical angle immediately before the direction of energization of the command current calculated by the two-phase energization control means is reversed. Detected. And an energy calculation means calculates the kinetic energy of the motor in this rotation position. The kinetic energy can be calculated, for example, as a value proportional to the square of the rotational angular velocity by detecting the rotational angular velocity of the electric motor.

  When the kinetic energy is large, the motor can be rotated with the kinetic energy, so there is no need for a reverse assist region. Conversely, when the kinetic energy is small, the reverse assist is required to rotate the motor. An area is required. Accordingly, the advance amount setting means sets the advance amount to be smaller when the calculated magnitude of the kinetic energy is larger than the reference value, compared to the case where it is less than the reference value. Thereby, when the magnitude | size of kinetic energy is larger than a reference value, a reverse assist area | region becomes narrow compared with the case where it is less than a reference value, and while being able to reduce an energy loss, a torque fluctuation can be suppressed.

  As a result, according to the present invention, even when one phase of the three-phase motor is energized and the two-phase energization driving is performed, the motor can be rotated satisfactorily while reducing energy loss and torque fluctuation.

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 a basic advance amount setting map. It is a flowchart showing an advance amount setting routine.

  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. 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 and the drive system power supply line 86 are connected by a connection line 90, but power is supplied from the drive system power supply line 86 to the control system power supply line 85 via the connection line 91 by diodes 89 and 91. However, the circuit configuration is such that 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.

  As shown in FIG. 2, the assist ECU 100 includes an assist current command unit 101. 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 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 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. . The conversion from the three-phase currents Iu, Iv, Iw to the two-phase currents Id, Iq in the dq coordinate system is performed by a three-phase / 2-phase coordinate conversion unit. The three-phase / two-phase coordinate conversion unit 103 receives the motor electrical angle θe output from the rotation angle conversion unit 104, and the three-phase currents Iu and Iv output from the current sensor 38 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 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. 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 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 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 electric current θe is advanced in the motor rotation direction by the advance amount θa set by the advance amount setting unit 110 described later, and the command current is calculated. 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 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. 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.

  By the way, during the two-phase energization of the electric motor 20, the electric motor 20 can be rotated by providing the over assist region A and the reverse assist region B2 by advancing the electrical angle as described above. The presence of B2 causes energy loss and torque fluctuation. Therefore, in the present embodiment, an advance amount setting unit 110 that variably sets the advance amount θa so as to obtain an appropriate reverse assist region B2 according to the rotation state of the electric motor 20 is provided.

  The advance amount setting unit 110 stores a basic advance amount setting map as shown in FIG. The basic advance amount setting map sets a basic advance amount θa1 corresponding to the steering torque Tr. In the vicinity where the steering torque Tr becomes zero, the basic advance amount θa1 increases as the steering torque Tr increases. And the basic advance angle θa1 is set to a constant value (20 deg in this example) except in the vicinity where the steering torque Tr becomes zero. 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.

  Next, processing performed by the advance amount setting unit 110 will be described. FIG. 11 is a flowchart showing an advance amount setting routine performed by the advance amount setting unit 110. The advance amount setting unit 110 starts an advance amount setting routine when an energization failure signal is input from an energization failure detection unit 108 described later.

  When the advance amount setting routine is started, the advance amount setting unit 110 reads the electrical angle θe output from the rotation angle conversion unit 104 in step S11. Subsequently, it is determined whether or not the electrical angle θe is a position immediately before entering the reverse assist region B2, that is, an electrical angle immediately before a position where the energization direction of the electric motor 20 is reversed. For example, in the example of FIGS. 5 and 6, the position where the energization direction of the electric motor 20 is reversed is (90 deg−θa) or (270 deg−θa). Accordingly, a motor rotation position that is an electrical angle that is a predetermined minute angle from the reverse position with respect to the rotation direction is set as a detection target position. Hereinafter, this detection target position is referred to as an energy determination position. When the advance amount setting routine is activated, the advance amount θa is set to the basic advance amount θa1.

If the electrical angle θe of the electric motor 20 is not at the energy determination position (S11: No), the advance amount setting unit 110 temporarily ends the advance amount setting routine. Therefore, the advance amount θa is maintained at the basic advance amount θa1. The advance amount setting routine is repeated at a predetermined short cycle. Therefore, while the electric angle θe of the electric motor 20 is not at the energy determination position, the above-described processing (S11, S12) is repeated. When it is determined in step S12 that the rotational position of the electric motor 20 is the energy determination position, the kinetic energy E of the electric motor 20 is calculated by the following equation in step S13.
E = (1/2) × Mi × ωm ²
Here, Mi represents the moment of inertia of the electric motor 20, and ωm represents the rotational angular velocity of the motor. The rotational angular velocity ωm is calculated by a change (time differentiation) of the electrical angle θe.

  Subsequently, in step S14, the advance amount setting unit 110 determines whether or not the kinetic energy E is larger than a preset determination reference value E0. When the kinetic energy E is larger than the determination reference value E0, the advance amount θa is set to the reduced advance amount θa2. This reduced advance amount θ2 is set smaller than the basic advance amount θ1. For example, the reduction advance amount θ2 is set to a value obtained by multiplying the basic advance amount θ1 by a reduction coefficient K (an integer smaller than 1). Therefore, the reverse assist area is narrowed.

  That is, when the kinetic energy E possessed by the electric motor 20 immediately before entering the reverse assist region B2 is larger than the determination reference value E0, the tire is returned even if the reverse assist region is decreased (including those that are eliminated). Therefore, it is determined that the electric motor 20 can be rotated by overcoming the reaction force, and the advance angle amount θa is set small to narrow the reverse assist region.

  The advance amount setting routine ends once the advance amount θa is set. Then, the set advance amount θa is maintained until the rotational position of the electric motor 20 becomes the energy determination position again. When the rotational position of the electric motor 20 becomes the energy determination position again (S12: Yes), in step S13, the kinetic energy E at that time is calculated (S13), and the kinetic energy E and the determination reference value E0 are compared. (S14). If the kinetic energy E exceeds the determination reference value E0, the advance amount θa is maintained as it is as the reduced advance amount θ2.

  On the other hand, if the kinetic energy E has decreased to the determination reference value E0 or less, the advance amount θa is changed to the basic advance amount θ1 in step S16. In other words, the kinetic energy E possessed by the electric motor 20 may be defeated by the reaction force trying to return the tire, and the electric motor 20 may stop, so it is determined that it is necessary to secure a predetermined reverse assist region. Thus, the advance amount θa is returned to the basic advance amount θ1. Therefore, the electric motor 20 can rotate satisfactorily.

  Next, the function of the assist ECU 100 that performs the two-phase energization control will be described with reference to FIG. The assist ECU 100 includes a two-phase energization command unit 107 and an energization failure detection unit 108. 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 failure detection signal from the energization failure detection unit 108, the two-phase energization current calculation formula, the preset maximum current, and the advance amount setting unit 110 are set. The command currents Iu *, Iv *, Iw * for two-phase energization are calculated based on the advance amount θa. 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.

  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.

  According to the electric power steering device of the present embodiment described above, the two-phase energization control that gives the advance amount θa is performed even when the one-phase energization failure of the three-phase electric motor 20 occurs. Thus, the electric motor 20 can be rotated favorably. Thereby, the fall of the steering operation feeling at the time of two-phase electricity supply control can be suppressed. Further, when the kinetic energy E possessed by the electric motor 20 immediately before entering the reverse assist region B2 is larger than the determination reference value E0, in order to set the advance amount θa to the reduced advance amount θ2, it is reversed more than necessary. The assist region is not formed, energy loss due to the reverse assist region can be reduced, and torque fluctuation of the electric motor 20 can also be suppressed.

  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 the present embodiment, the determination reference value E0 for kinetic energy is a constant value, but the kinetic energy required for the electric motor 20 to rotate by two-phase energization drive also changes depending on various vehicle conditions. The reference value E0 may be variable. For example, a reference value setting unit that sets the determination reference value E0 as the vehicle speed decreases may be provided.

  In the present embodiment, the advance amount θa is switched between two types, but it may be changed in a plurality of steps or continuously. For example, an advance amount setting means for setting the advance amount θa to be smaller as the kinetic energy E is larger can be provided.

  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.

  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 ... Cutoff circuit, 100 ... Electronic control unit (assist ECU), 101 ... Assist current command part, 102 ... Feedback control part, 103 ... Three-phase / two-phase coordinate conversion part, 104 DESCRIPTION OF SYMBOLS Rotation angle conversion part 105 ... 2-phase / 3-phase coordinate conversion part 106 ... PWM control signal generation part 107 ... 2-phase energization command part 108 ... Energization failure detection part 109 ... 2-phase energization feedback control part, 110. Advance angle amount setting unit.

Claims (1)

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
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 generating a steering assist torque that does not fluctuate with respect to a change in the electrical angle of the motor, using two phases in which there is no failure in energization when there is only one phase in energization of 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;
Motor position detecting means for detecting that the electrical angle of the electric motor is the electrical angle immediately before the direction of energization of the command current calculated by the two-phase energization control means is reversed;
Energy calculating means for calculating the kinetic energy of the electric motor at the time when the motor position detecting means detects that the electric angle of the electric motor has become an electric angle immediately before the direction of energization of the command current is reversed; ,
When the magnitude of the kinetic energy calculated by the energy calculating means is larger than a reference value, an advance amount setting means for setting the advance amount to be smaller than that when it is less than the reference value. An electric power steering device.

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