JP2011218878A - Electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a steering wheel 11 from being turned when a reverse input acts on a steering mechanism 10, without making a system large.SOLUTION: A reverse input detector 200 changes a reverse-input determination flag F from "0" to "1" when detecting a reverse input state where the steering wheel 11 is turned by the reverse input. A compensation-torque output controller 115 does not output a total compensation torque Tb(=Tb1+Tb2) when the reverse input state is detected (F=1), and thereby a target assist torque T* does not include the total compensation torque Tb. Accordingly, the target assist torque T* never becomes small under the effect of the total compensation torque Tb.

Description

  The present invention relates to an electric power steering device that assists a driver's steering operation by driving an electric motor.

  2. Description of the Related Art Conventionally, an electric power steering apparatus is known as an apparatus that assists a driver's steering operation by transmitting output torque of an electric motor to a steering shaft or a rack bar of a steering mechanism. When a large force is input from the tire to the steering mechanism, for example, in a case where the tire collides with a curb while the vehicle is running, the wheels are steered and a large axial force acts on the rack bar. Thus, the rack bar moves in the axial direction and the steering shaft connected to the rack bar rotates regardless of the driver's steering operation or the steering assist of the electric motor. A state in which reverse input is applied from the tire to the steering mechanism and the wheels are steered against the driver's will is referred to as a reverse input state. When the reverse input is large, the rack end member provided at the tip of the rack bar collides with a stopper portion formed on the rack housing, and an impact force acts on the steering mechanism.

  Therefore, for example, the electric power steering apparatus proposed in Patent Document 1 is configured to transmit the rotational force of the electric motor to the steering mechanism via the clutch, and the clutch is disengaged when the reverse input state is detected. Thus, the inertia torque of the electric motor is prevented from being transmitted to the steering mechanism.

JP-A-6-8839

  However, it is necessary to provide a clutch mechanism and a clutch drive circuit in the electric power steering device described above, which increases the size of the system, which is not preferable for reduction in size and weight and cost.

  An object of the present invention is to cope with the above-described problem, and is to prevent the steering wheel from being turned when a reverse input is applied to the steering mechanism without increasing the size of the system.

In order to achieve the above object, the present invention is characterized by an electric motor (20) that is provided in a steering mechanism and generates a steering assist torque, and a steering torque detection means (22) that detects a steering torque input to the steering mechanism. ), Basic assist torque calculating means (111, 211, 311) for calculating basic assist torque based on the detected steering torque, and compensation torque calculating means for calculating compensation torque for compensating the basic assist torque. (112, 113, 212, 312), target assist torque calculating means (116, 216, 316) for calculating a target assist torque obtained by adding the basic assist torque and the compensation torque, and based on the target assist torque. Motor control means (30, 120, 130, 14) for driving and controlling the electric motor. In the electric power steering apparatus equipped with a 151, 152, 153, 154) and,
A reverse input state detection means (200) for detecting a reverse input state in which the steered wheels are steered at a high speed by reverse input from a tire; and when the reverse input state is detected, the target assist torque calculating means Reverse input target assist torque changing means for changing the target assist torque calculation method using the compensation torque so that the target assist torque to be calculated is not reduced by the compensation torque or the amount of reduction is reduced. 115, 215, 312).

  In the present invention, the basic assist torque calculating means calculates the basic assist torque based on the steering torque input to the steering mechanism (for example, the steering torque input to the steering shaft), and the compensation torque calculating means calculates the basic assist torque. Compensation torque for compensation is calculated, and target assist torque calculation means calculates a target assist torque obtained by adding the basic assist torque and the compensation torque. The compensation torque is a torque added to the basic assist torque in order to improve the driver's steering feeling, and is calculated based on, for example, a steering parameter (steering angle, steering speed, steering torque differential value) and the like. The motor control means drives and controls the electric motor based on the target assist torque. Thereby, a steering assist appropriate for the steering operation of the driver can be obtained.

  When a large reverse input is applied from the tire to the steering mechanism, the wheel is steered suddenly, and accordingly, the steering wheel is turned against the driver's will. In such a situation, if a large resistance force against reverse input is generated by the electric motor, it is possible to prevent the steering handle from being turned. However, in a situation where a reverse input state occurs, the compensation torque may be set to a value that reduces the target assist torque. In such a case, the control amount (target current value) of the electric motor driven and controlled by the motor control means is reduced by the compensation torque, and the electric motor cannot generate a large resistance force against the reverse input.

  Therefore, in the present invention, the reverse input state detection means detects a reverse input state in which the steered wheels are steered at a high speed due to the reverse input from the tire. When the reverse input state is detected by the reverse input state detection means, the target assist torque changing means at the time of reverse input prevents the target assist torque calculated by the target assist torque calculation means from decreasing by the compensation torque or decreases The target assist torque calculation method using the compensation torque is changed so that the amount to be reduced is reduced. As a result, the control amount of the electric motor driven and controlled by the motor control means can be increased, and a large resistance can be generated against reverse input by flowing a large current through the electric motor.

  Therefore, according to the present invention, it is possible to satisfactorily suppress turning of the steering wheel when reverse input is applied to the steering mechanism without increasing the size of the steering system. Further, it is possible to reduce the impact and the collision sound that are generated when the rack end member collides with the stopper portion. As a result, discomfort given to the driver by reverse input can be reduced. In addition, since the existing system configuration can be used as it is without using a high-output electric motor or motor drive circuit, it is possible to meet the needs of small size, light weight and low cost.

  Another feature of the present invention is that the compensation torque computed by the compensation torque computing means includes a specific compensation torque that is set to a value that reduces the target assist torque in the reverse input state. The reverse input target assist torque changing means is configured to reduce the magnitude of the specific compensation torque to be added to the basic assist torque when the reverse input state is detected.

  In the present invention, the compensation torque calculated by the compensation torque calculation means includes the specific compensation torque set to a value that reduces the target assist torque in the situation of the reverse input state. Then, the reverse assist target assist torque changing means decreases the magnitude (absolute value) of the specific compensation torque to be added to the basic assist torque when the reverse input state is detected. Therefore, it is possible to reliably prevent the target assist torque from decreasing, or to reduce the amount by which the target assist torque decreases. Note that “decreasing the magnitude of the specific compensation torque” includes making the specific compensation torque zero.

  Another feature of the present invention is that the reverse input target assist torque changing means does not add the specific compensation torque to the basic assist torque when the reverse input state is detected.

  According to the present invention, when the reverse input state is detected, the specific compensation torque is not added to the basic assist torque. Therefore, it is possible to ensure that the target assist torque does not decrease.

  Another feature of the present invention is that the specific compensation torque has a larger positive value as the torque differential value becomes a larger positive value according to a torque differential value obtained by time differentiating the magnitude of the steering torque. The value is set such that the larger the negative value, the larger the negative value.

  In the present invention, the specific compensation torque is set according to a torque differential value obtained by time-differentiating the magnitude of the steering torque. In this case, the specific compensation torque is set so as to become a larger positive value as the torque differential value becomes a larger positive value, and to become a larger negative value as the torque differential value becomes a larger negative value. In the present specification, “size” and “large value” represent absolute values. Therefore, “a large negative value” represents a negative value and a large absolute value.

  When the specific compensation torque set in this way is added to the basic assist torque, the system can be stabilized by compensating for the delay in the generation of the assist torque when the driver operates the steering wheel. However, when a large reverse input is applied from the tire to the steering mechanism, the steering torque rapidly increases and pulsates greatly, so that the torque differential value is alternately switched between positive and negative. At this time, since the steering torque is very large, the basic assist torque reaches the upper limit value of the target assist torque. Therefore, when the torque differential value is positive, the target assist torque does not increase even if the specific compensation torque (> 0) is added. On the other hand, when the torque differential value is negative, adding the specific compensation torque (<0) greatly reduces the target assist torque. Therefore, the specific compensation torque generates a substantially negative large torque (a large torque in the opposite direction to the basic assist torque). For this reason, if the specific compensation torque is added to the basic assist torque as it is, the target assist torque is greatly reduced.

  Therefore, in the present invention, when the reverse input state is detected, the specific compensation torque is reduced or not added, so that a large current flows through the electric motor, and a large amount against the reverse input. Generate resistance. Therefore, it is possible to achieve both comfortable steering feeling (ensuring stability) and braking of the steering wheel in the reverse input state.

  Another feature of the present invention is that the specific compensation torque has a positive value as the rotational speed increases in the same direction as the steering torque according to the rotational speed of the electric motor. The larger the value in the opposite direction, the larger the negative value.

  In the present invention, the specific compensation torque is set according to the rotation speed of the electric motor. In this case, the specific compensation torque is set to be a positive value as the rotational speed increases in the same direction as the steering torque, and to a negative value as the rotational speed increases in the opposite direction to the steering torque. The

  When the specific compensation torque set in this way is added to the basic assist torque, the return performance when the driver returns the steering wheel toward the neutral position can be improved. However, when a large reverse input is applied from the tire to the steering mechanism, the electric motor is rotated, so that the direction of the steering torque and the rotation direction of the electric motor are opposite to each other. Moreover, the electric motor is rotated at a very high speed. Therefore, the specific compensation torque generates a large negative torque. For this reason, if the specific compensation torque is added to the basic assist torque as it is, the target assist torque is greatly reduced.

  Therefore, in the present invention, when the reverse input state is detected, the specific compensation torque is reduced or not added, so that a large current flows through the electric motor, and a large amount against the reverse input. Generate resistance. Therefore, it is possible to achieve both comfortable steering feeling (good return performance) and braking of the steering wheel in the reverse input state.

  Another feature of the present invention is that the motor control means includes a current limiting means (123) for limiting an upper limit value of a current flowing through the electric motor, and the current limiting means when the reverse input state is detected. A current limit canceling means (200) for canceling the current limit.

  According to the present invention, at the normal time, the upper limit value of the current flowing through the electric motor is limited by the current limiting means. For this reason, the electric current exceeding an upper limit cannot be sent through an electric motor. On the other hand, when the reverse input state is detected, the current limit release means releases the current limit by the current limit means. Therefore, in the reverse input state, a large current set based on a large target assist torque can be passed through the electric motor, and a large resistance force against the reverse input can be generated.

  Another feature of the present invention is that the motor control means includes a voltage limiting means (143) for limiting an upper limit value of a voltage applied to the electric motor, and the voltage limiting means when the reverse input state is detected. Voltage restriction canceling means (200) for canceling the voltage limit due to.

  According to the present invention, at the normal time, the upper limit value of the voltage applied to the electric motor is limited by the voltage limiting means. For this reason, a voltage exceeding the upper limit value cannot be applied to the electric motor. On the other hand, when the reverse input state is detected, the voltage limit release means releases the voltage limit by the voltage limit means. Therefore, in the reverse input state, a large current set based on a large target assist torque can be passed through the electric motor, and a large resistance force against the reverse input can be generated.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached to the configuration of the invention corresponding to the embodiments in parentheses. It is not intended to be limited to the embodiment defined by.

It is a schematic block diagram of an electric power steering device. It is a functional block diagram showing the process of the microcomputer of assist ECU. It is a graph showing a basic assist map. It is a graph showing a 1st compensation map. It is a graph showing a 2nd compensation map. It is a flowchart showing a reverse input detection routine. It is a functional block diagram of the target assist torque calculation part as a 1st modification. It is a functional block diagram of the target assist torque calculation part as a 2nd modification.

  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 the left front wheel Wfl and the right front wheel Wfr that are steering wheels by a steering operation of the steering handle 11, and an electric motor 20 that is assembled to the steering mechanism 10 and generates a steering assist torque. And a motor drive circuit 30 for driving the electric motor 20 and an electronic control device 100 for controlling the operation of the electric motor 20 as main parts. Hereinafter, the electronic control device 100 is referred to as an assist ECU 100.

  The steering mechanism 10 converts the rotation around the axis of the steering shaft 12 in conjunction with the turning operation of the steering handle 11 into the left and right stroke motion of the rack bar 14 by the rack and pinion mechanism 13. The left front wheel Wfl and the right front wheel Wfr are steered by movement. The steering shaft 12 includes a main shaft 12a connected to the upper end of the steering handle 11, a pinion shaft 12c connected to the rack and pinion mechanism 13, and a main shaft 12a and a pinion shaft 12c connected via universal joints 12d and 12e. And an intermediate shaft 12b.

  The rack bar 14 has a gear portion 14 a housed in the rack housing 15, and both left and right ends thereof are exposed from the rack housing 15 and connected to the tie rod 16. The other ends of the left and right tie rods 16 are connected to knuckles 17 provided on the left and right front wheels Wfl and Wfr. A rack end member 18 is provided at a connection portion between the rack bar 14 and the tie rod 16. On the other hand, stopper portions 15 a are formed at both ends of the rack housing 15. The rack bar 14 is mechanically limited in the range of left and right stroke movement by the contact between the rack end member 18 and the stopper portion 15a. Hereinafter, the position where the movement of the rack bar 14 is restricted by the stopper portion 15a is referred to as a stroke end. Further, the left front wheel Wfl and the right front wheel Wfr are simply referred to as the steering wheel W.

  An electric motor 20 is assembled to the steering shaft 12 (main shaft 12a) via a reduction gear 19. For example, a three-phase synchronous permanent magnet motor (brushless DC motor) is used as the electric motor 20. The electric motor 20 includes a stator fixed in a housing, forms a three-phase rotating magnetic field by flowing a three-phase current through a coil wound around the stator, and a rotor in which a permanent magnet is fixed in the three-phase rotating magnetic field. Rotates according to the three-phase current. The electric motor 20 rotationally drives the steering shaft 12 around its central axis via the reduction gear 19 by the rotation of the rotor, and applies assist torque to the turning operation of the steering handle 11.

  The electric motor 20 is provided with a rotation angle sensor 21. The rotation angle sensor 21 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, and is constituted by, for example, a resolver or a hall sensor. The rotation angle sensor 21 outputs a detection signal corresponding to the rotation angle θm of the electric motor 20 to the assist ECU 100. The assist ECU 100 calculates the electrical angle θe of the electric motor 20 from this detection signal. The electric angle θe of the electric motor 20 may be estimated based on the counter electromotive force generated by the electric motor 20 without using the rotation angle sensor 21.

  A steering torque sensor 22 is provided between the steering handle 11 and the reduction gear 19 on the steering shaft 12 (main shaft 12a). The steering torque sensor 22 detects a torsional force acting on a torsion bar (not shown) interposed in the steering shaft 12 (main shaft 12a) as a steering torque T input from the steering handle 11. For example, resolvers are provided at both ends of the torsion bar, and the steering torque T is detected based on the difference in rotational angle detected by the two resolvers.

  The steering torque T is identified not only by its magnitude but also by the sign (positive or negative) in the steering direction, which is the twisting direction of the torsion bar. In the present embodiment, the twist angle of the torsion bar is detected by a resolver, but it can also be detected by another rotational angle sensor or the like.

  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 magnitude and direction (positive / negative) of the current of two phases (for example, the U phase and the V phase) of the three phases, and outputs detection signals representing the detected currents iu and iv to the assist ECU 100. To do. Since the W-phase current iw can be calculated from the other two-phase currents (iu, iv) (iw = − (iu + iv)), only two phases are detected by the current sensor 38 in this embodiment. The three phases may be detected by the current sensor 38.

  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 assist ECU 100 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part. The assist ECU 100 connects the steering torque sensor 22, the rotation angle sensor 21, the current sensor 38, and the vehicle speed sensor 25 that detects the vehicle speed, and detects the steering torque T, the rotation angle θm, the motor currents iu and iv, and the vehicle speed Sp. Input the signal. Then, based on the input detection signal, a current command value is calculated so as to obtain an optimum steering assist torque (hereinafter simply referred to as assist torque) according to the driver's steering operation. The duty ratios of the switching elements 31 to 36 of the motor drive circuit 30 are controlled so that the electric current that flows is supplied to the electric motor 20. In driving control of the electric motor 20, vector control described in a two-phase rotating magnetic flux coordinate system (dq coordinate system) is used. The drive control of the electric motor 20 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 general in-vehicle battery 81 having a rated output voltage of 12V and an alternator 82 having a rated output voltage of 14V that is generated by the rotation of the engine. A power supply source line 83 and a ground line 84 are connected to the in-vehicle power supply device 80. The power supply source line 83 branches into a control system power line 85 and a drive system power line 86. The control system power supply line 85 functions as a power supply line for supplying power to the assist ECU 100. The drive system power supply line 86 functions as a power supply line that supplies power to both the motor drive circuit 30 and the assist ECU 100.

  An ignition switch 87 is connected to the control system power supply line 85. A main power relay 88 is connected to the drive system power line 86. The main power supply relay 88 is turned on by a control signal from the assist ECU 100 to form a power supply circuit to the electric motor 20. The control system power supply line 85 is connected to the power supply + terminal of the assist ECU 100, but is also connected to the drive system power supply line 86 on the load side of the main power supply relay 88 via the connection line 90. Further, the control system power supply line 85 is provided with a diode 89 on the load side (assist ECU 100 side) of the ignition switch 87 with the anode facing the in-vehicle power supply device 80 side. In the connection line 90, a diode 91 is provided with the anode facing the drive system power supply line 86 side. Therefore, the circuit configuration is such that power can be supplied from the drive system power supply line 86 to the control system power supply line 85 via the connection line 90, but power cannot be supplied from the control system power supply line 85 to the drive system power supply line 86. . The drive system power supply line 86 and the ground line 84 are connected to the power supply input section of the motor drive circuit 30. The ground line 84 is also connected to the ground terminal of the assist ECU 100.

  Next, control of the electric motor 20 performed by the assist ECU 100 will be described. The assist ECU 100 has a d-axis in the direction through which the magnetic field of the permanent magnet provided in the rotor of the electric motor 20 passes, and a direction orthogonal to the d-axis (a direction in which the electrical angle advances by π / 2 with respect to the d-axis). The rotation of the electric motor 20 is controlled by current vector control using the dq coordinate system in which the axes are defined. The d-axis component of the current vector is called d-axis current, and the q-axis component is called q-axis current. The q-axis current acts to generate motor torque. On the other hand, the d-axis current does not act to generate motor torque and is used for field weakening control.

  The assist ECU 100 determines the dq coordinate by detecting the electrical angle θe when performing such current vector control. The electrical angle θe is obtained from the rotation angle signal detected by the rotation angle sensor 21. The electrical angle θe is an angle formed by the axis passing through the U-phase coil and the d-axis.

  FIG. 2 is a functional block diagram illustrating an assist control process executed by program control of the microcomputer of the assist ECU 100. Each functional unit is activated by turning on the ignition switch, and repeats the process at a predetermined short calculation cycle.

  The assist ECU 100 includes a target assist torque calculation unit 110. The target assist torque calculation unit 110 includes a basic assist torque calculation unit 111, a first compensation torque calculation unit 112, a second compensation torque calculation unit 113, a compensation torque addition unit 114, a compensation torque output control unit 115, a total And an adder 116. The basic assist torque calculator 111 receives the steering torque T output from the steering torque sensor 22 and the vehicle speed Sp output from the vehicle speed sensor 25, and refers to the basic assist map Ta as shown in FIG. Is calculated. In this basic assist map, the basic assist torque Ta is set so as to increase as the steering torque T increases and decrease as the vehicle speed Sp increases. This basic assist torque Ta is set in the same direction as the direction of the steering torque T (identified by a symbol). In the present embodiment, the basic assist torque Ta is calculated using the basic assist map stored in the ROM, but the basic assist torque that changes according to the steering torque T and the vehicle speed Sp is used instead of the basic assist map. A function defining Ta may be stored, and the basic assist torque Ta may be calculated using the function. Further, the basic assist torque Ta may be set only from the steering torque T without being changed according to the vehicle speed Sp.

  The first compensation torque calculator 112 receives the steering torque T output from the steering torque sensor 22, calculates a torque differential value T ′ obtained by differentiating the steering torque T with time, and displays the first compensation map shown in FIG. The first compensation torque Tb1 is calculated by referring to it. In the first compensation map, the first compensation torque Tb1 takes a positive value when the torque differential value T ′ is positive, that is, when the magnitude of the steering torque T is increased, and the torque differential value. The size (absolute value) is set to increase as T ′ increases. On the other hand, when the torque differential value T ′ is negative, that is, when the magnitude of the steering torque T is decreased, the first compensation torque Tb1 takes a negative value and the torque differential value T ′ is negative. The larger the value (the larger the absolute value), the larger the negative value (the larger the absolute value).

  Further, the first compensation map is provided with a dead zone of the torque differential value T ′, and when the torque differential value T ′ falls within a predetermined range centered on zero (−A ≦ T ′ ≦ A), The 1 compensation torque Tb1 is set to zero. In the present embodiment, the first compensation torque Tb1 is calculated using the first compensation map stored in the ROM. However, the first compensation map is changed according to the torque differential value T ′ instead of the first compensation map. A function defining one compensation torque Tb1 may be stored, and the first compensation torque Tb1 may be calculated using the function.

  The first compensation torque Tb1 is intended to stabilize the system by compensating for the delay in the generation of assist torque when the driver operates the steering wheel.

  The first compensation torque Tb1 and the second compensation torque Tb2, which will be described later, represent a torque in the same direction as the steering torque T with a positive value and a torque in the opposite direction to the steering torque T with a negative value.

  The second compensation torque calculation unit 113 receives the rotation speed ω of the electric motor 20 calculated by the rotation speed calculation unit 155 described later, and refers to the second compensation map shown in FIG. 5 to obtain the second compensation torque Tb2. Calculate. In the second compensation map, the second compensation torque Tb2 is obtained when the rotational speed ω is positive with respect to the steering torque T, that is, when the rotation direction of the electric motor 20 is the same direction as the steering torque T. Is a positive value, and is set so that its magnitude (absolute value) increases as the rotational speed ω increases. On the other hand, when the rotational speed ω is negative with respect to the steering torque T, that is, when the rotational direction of the electric motor 20 is opposite to the direction of the steering torque T, the second compensation torque Tb2 is a negative value. And the rotation speed ω is set so as to become a negative value (absolute value is large) as the value becomes large (negative value).

  Further, the second compensation map has a dead zone of the rotational speed ω, and when the rotational speed ω falls within a predetermined range centering on zero (−B ≦ ω ≦ B), the second compensation torque Tb2 is zero. Set to In the present embodiment, the second compensation torque Tb2 is calculated using the second compensation map stored in the ROM, but the second compensation that changes according to the rotational speed ω instead of the second compensation map. A function defining the torque Tb2 may be stored, and the second compensation torque Tb2 may be calculated using the function.

  The second compensation torque Tb2 improves the return performance when the steering handle 11 is returned to the neutral position direction.

  The first compensation torque Tb1 calculated by the first compensation torque calculation unit 112 and the second compensation torque Tb2 calculated by the second compensation torque calculation unit 113 are output to the compensation torque addition unit 114. The compensation torque adding unit 114 adds the first compensation torque Tb1 and the second compensation torque Tb2, and outputs the addition result (Tb1 + Tb2) to the compensation torque output control unit 115.

  The compensation torque output control unit 115 receives a reverse input determination flag F output from a reverse input detection unit 200 (to be described later) separately from the addition result (Tb1 + Tb2) output from the compensation torque addition unit 114. When F is “0”, the addition result (Tb1 + Tb2) is output as it is as the total compensation torque Tb. On the other hand, when the reverse input determination flag F is “1”, the total compensation torque Tb is not output. Therefore, the total compensation torque Tb that is the output of the compensation torque output control unit 115 is (T1 + T2) when the reverse input determination flag F is “0”, and when the reverse input determination flag F is “1”. It becomes zero.

  The basic assist torque Ta calculated by the basic assist torque calculation unit 111 and the total compensation torque Tb output from the compensation torque output control unit 115 are input to the total addition unit 116. The total adder 116 adds the basic assist torque Ta and the total compensation torque Tb, and sets the addition result (Ta + Tb) as the final target assist torque T *. The total adding unit 116 stores a preset upper limit value of the target assist torque T *. If the calculated target assist torque T * exceeds the upper limit value, the total target assist torque T * is set to the upper limit value. Set.

The assist ECU 100 includes a biaxial current command unit 120. The 2-axis current command unit 120 includes a q-axis current calculation unit 121 that calculates a q-axis command current i _q ^* , a d-axis current calculation unit 122 that calculates a d-axis command current i _d ^* , and a q-axis command current i _q. ^The q-axis current upper limit setting unit 123 sets an upper limit value of ^* .

The q-axis current calculation unit 121 inputs the target assist torque T * calculated by the target assist torque calculation unit 110, and divides the target assist torque T * by a torque constant, whereby a q-axis command in the dq coordinate system is obtained. The current i _q ^* (q-axis target current value) is calculated. The q-axis command current i _q ^* is set to an upper limit value (maximum value) according to a command from the q-axis current upper limit setting unit 123 for overcurrent protection of the switching elements 31 to 36 of the motor drive circuit 30. . Therefore, the q-axis current calculation unit 121 determines that the q-axis command current i _q ^* calculated from the target assist torque T * exceeds the q-axis current upper limit value i _q lim commanded by the q-axis current upper limit setting unit 123. The q-axis command current i _q ^{* is set} to the q-axis current upper limit value i _q lim.

The q-axis current upper limit setting unit 123 inputs the reverse input determination flag F output from the reverse input detection unit 200. When the reverse input determination flag F is “0”, the q-axis current upper limit value i _q lim is set to q. When output to the shaft current calculation unit 121 and the reverse input determination flag F is “1”, the q-axis current upper limit value i _q lim is not output. That is, when the reverse input determination flag F is “1”, the current limitation is released to the q-axis current calculation unit 121. Therefore, the q-axis current calculation unit 121 calculates the q-axis command current i _q ^* according to the target assist torque T * without being limited in current.

The d-axis current calculation unit 122 inputs the rotation speed ω of the electric motor 20 calculated by a rotation speed calculation unit 155 described later, and a d-axis command current i _d ^* (d-axis target current value) corresponding to the rotation speed ω. Is calculated. The d-axis command current i _d ^* is set to zero (i _d ^* = 0) when the magnitude of the rotational speed ω is equal to or smaller than the set value ω1, and when the magnitude of the rotational speed ω exceeds the set value ω1. Is set so that the field weakening increases as the rotational speed ω increases. In the present embodiment, the d-axis current for field weakening control is supplied when the electric motor 20 rotates at a high speed, but the field weakening control may not be performed. In this case, the d-axis command current i _d ^* may be always set to zero (i _d ^* = 0).

The q-axis command current i _q ^* and the d-axis command current i _d ^* calculated in this way are output to the deviation calculation unit 130. The deviation calculation unit 130 includes a q-axis current deviation calculation unit 131 and a d-axis current deviation calculation unit 132. The q-axis current deviation calculation unit 131 calculates a deviation Δi _q obtained by subtracting the q-axis actual current i _q from the q-axis command current i _q ^* . d-axis current deviation calculation unit 132 calculates the d-axis command current _i ^{d *} from subtracting the d-axis actual current _{i d} deviation .DELTA.i _d.

q-axis actual current i _q and d axis actual current i _d is obtained by converting the detection values of three-phase current actually flows through the coil of the electric motor 20 iu, iv, and iw into two-phase currents of the d-q coordinate system It is. The conversion from the three-phase currents iu, iv, iw to the two-phase currents i _d , i _{q in the} dq coordinate system is performed by the three-phase / 2-phase coordinate conversion unit 153. The three-phase / two-phase coordinate conversion unit 153 receives the electrical angle θe output from the electrical angle calculation unit 154, and based on the electrical angle θe, the three-phase currents iu, iv, iw ( = − (Iu + iv)) is converted into two-phase currents i _d and i _q in the dq coordinate system.
A conversion matrix C for converting from a three-phase coordinate system to a dq coordinate system is expressed by the following equation (1).

Deviation output from the deviation calculating unit 130 Δi _q, Δi _d is outputted to the feedback control unit 140. The feedback control unit 140 includes a q-axis current feedback control unit 141 that calculates a q-axis command voltage v _q ^* , a d-axis current feedback control unit 142 that calculates a d-axis command voltage v _d ^* , and a q-axis command voltage v _q. ^The voltage upper limit setting unit 143 sets an upper limit value between ^* and the d-axis command voltage v _d ^* .

The q-axis current feedback control unit 141 causes the q-axis actual current i _q to follow the q-axis command current i _q ^* by proportional-integral control (PI control) using the deviation Δi _q , that is, the q-axis actual current i. _q is calculates the q-axis command voltage _v ^{q *} to become equal to the q-axis command current _i ^{q *.} d-axis current feedback control unit 142, a proportional integral control using a deviation .DELTA.i _d (PI control) so that the d-axis actual current _{i d} to follow the d-axis command current _i ^{d *,} that is, the d-axis actual current i _d is calculates the d-axis command voltage _v ^{d *} to become equal to the d-axis command current _i ^{d *.}

The voltage upper limit setting unit 143 sets the upper limit value of the q-axis command voltage v _q ^{* and} the upper limit value of the d-axis command voltage v _d ^* in order to limit the power consumption in the electric power steering device, and sets the set q The shaft voltage upper limit value v _q lim and the d axis voltage upper limit value v _d lim are output to the q axis current feedback control unit 141 and the d axis current feedback control unit 142, respectively. The voltage upper limit setting unit 143 sets the q-axis voltage upper limit value v _q lim that decreases as the q-axis command current i _q ^* increases, and the d-axis voltage upper limit value v _d that decreases as the d-axis command current i _d ^* increases. Set lim. Accordingly, the q-axis current feedback control unit 141 and the d-axis current feedback control unit 142 set the q-axis voltage upper limit value v _q lim and the d-axis voltage upper limit value v _d lim commanded from the voltage upper limit setting unit 143 as upper limits to q The axis command voltage v _q ^* and the d axis command voltage v _d ^* are calculated.

The voltage upper limit setting unit 143 inputs the reverse input determination flag F output from the reverse input detection unit 200, and when the reverse input determination flag F is “0”, the q-axis voltage upper limit value v set as described above. _q lim and d-axis voltage upper limit value v _d lim are output to q-axis current feedback control unit 141 and d-axis current feedback control unit 142. When reverse input determination flag F is “1”, q-axis voltage upper limit value The value v _q lim and d-axis voltage upper limit value v _d lim are not output. That is, when the reverse input determination flag F is “1”, the voltage restriction is released for the q-axis current feedback control unit 141 and the d-axis current feedback control unit 142. Therefore, q-axis current feedback control unit 141, d-axis current feedback control unit 142, without being voltage limit, the deviation .DELTA.i _q, deviation .DELTA.i q-axis command voltage corresponding to _{d v} ^q *, d-axis command voltage _{v d} ^* Is calculated.

The q-axis command voltage v _q ^* and the d-axis command voltage v _d ^* calculated by the feedback control unit 140 are output to the 2-phase / 3-phase coordinate conversion unit 151. The two-phase / three-phase coordinate conversion unit 151 converts the q-axis command voltage v _q ^* and the d-axis command voltage v _d ^* into the three-phase command voltage vu ^* , based on the electrical angle θe output from the electrical angle calculation unit 154. It converts to vv ^* , vw ^* , and outputs the converted three-phase command voltages vu ^* , vv ^* , vw ^* to the PWM signal generator 152. The PWM signal generator 152 outputs a PWM control signal 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 an assist torque that follows the target assist torque T ^* is applied to the steering mechanism 10.

  The rotation detection signal output from the rotation angle sensor 21 is output to the electrical angle calculation unit 154. The electrical angle calculation unit 154 calculates the electrical angle θe of the electric motor 20 from the rotation detection signal output from the rotation angle sensor 21, and the calculated electrical angle θe is converted into a three-phase / two-phase coordinate conversion unit 153, two-phase / 3. Output to the phase coordinate conversion unit 151 and the rotation speed calculation unit 155. The rotational speed calculator 155 calculates the rotational speed ω of the electric motor 20 by differentiating the electrical angle θe output from the electrical angle calculator 154 with respect to time. The rotational speed ω is output to the second compensation torque calculator 113, the d-axis current calculator 122, and the reverse input detector 200. The rotation speed ω is given a sign (positive or negative) corresponding to the rotation direction in order to identify the rotation direction (left and right) of the electric motor 20. The sign (positive / negative) of the rotational speed in the second compensation map described above represents the direction with respect to the steering torque T, and is different from the rotational direction here.

  In detecting the electrical angle θe, an electrical angle correction unit (not shown) that corrects the electrical angle θe to advance by an angle corresponding to the delay time by the calculation in consideration of the calculation time required for detecting the electrical angle θe. May be incorporated into the electrical angle calculation unit 154. In this case, the electrical angle correction unit may advance the electrical angle θe by an angle corresponding to a delay time proportional to the rotational speed ω of the electric motor 20. The electrical angle θe may be estimated based on the counter electromotive force generated by the electric motor 20 without using the rotation angle sensor 21.

  Next, the reverse input detection unit 200 will be described. When a large reverse input is applied from the tire to the steering mechanism 10 as in the case where the front tire collides with a road surface projection such as a curb while the vehicle is running, the steered wheels W are steered rapidly. For this reason, the rack bar 14 moves in the axial direction, and the steering handle 11 rotates at a high speed together with the steering shaft 12 connected to the rack bar 14. When the rack bar 14 reaches the stroke end, the rack end member 18 and the stopper portion 15a collide, and an impact force acts on the steering mechanism 10. The reverse input detection unit 200 is a functional unit that detects such a reverse input state before the rack bar 14 reaches the stroke end in order to weaken the impact force acting on the steering mechanism 10.

  The processing of the reverse input detection unit 200 will be described with reference to the flowchart of FIG. FIG. 6 shows a reverse input detection routine executed by the reverse input detection unit 200. The reverse input detection routine is repeatedly executed at a predetermined short cycle.

  When the reverse input detection routine starts, the reverse input detection unit 200 determines whether or not the reverse input determination flag F is set to “0” in step S201. This reverse input determination flag F is set to “1” when it is determined that it is in the reverse input state, and “0” when it is not determined that it is in the reverse input state, as will be understood from the processing described later. When the routine is started, the initial value is set to “0”. Accordingly, since the reverse input determination flag F is set to “0” here, the reverse input detection unit 200 advances the process to step S202.

  In step S <b> 202, the reverse input detection unit 200 reads the steering torque T detected by the steering torque sensor 22 and the rotation speed ω output from the rotation speed calculation unit 155. Subsequently, in step S203, it is determined whether or not the sign Sign (T) of the steering torque T is different from the sign Sign (ω) of the rotational speed ω. The steering torque T and the rotational speed ω are given signs (positive and negative) according to their directions. Therefore, in this step S203, it is determined whether or not the direction in which the steering torque T works and the rotation direction of the electric motor 20 (corresponding to the rotation direction of the steering handle 11) are different.

  When reverse input is applied to the steering mechanism 10, the direction of the steering torque T and the rotation direction of the electric motor 20 are opposite to each other. For example, when the front wheel collides with the curb and the steered wheel W turns leftward, the steering handle 11 rotates leftward via the steering mechanism 10, but due to the inertia of the steering handle 11, etc. Since the steering handle 11 side rotates with a delay compared to the wheel side, the twisting direction of the torsion bar of the steering shaft 12 is the direction when the steering handle 11 is rotated to the right. Therefore, when it is determined in step S203 that the sign Sign (T) of the steering torque T and the sign Sign (ω) of the rotational speed ω match (S203: No), it is determined that the reverse input state is not established. it can. In this case, the counter value N is cleared to zero in step S206. As can be understood from the processing described later, the counter value N represents a value obtained by counting the number of consecutive times that the reverse input determination condition is satisfied. Accordingly, when the reverse input detection condition is not satisfied, the counter value N is reset.

  If it is determined that the reverse input state is not in the reverse input state, the reverse input detection flag F (= 0) is output in step S210 after the process of step S206, and the reverse input detection routine is temporarily terminated. . The reverse input detection routine is repeated at a predetermined short cycle. If these processes are repeated and it is determined in step S203 that the sign Sign (T) of the steering torque T is different from the sign Sign (ω) of the rotational speed ω, then in step S204, It is determined whether or not the magnitude | T | of the steering torque T is larger than a predetermined determination reference torque Tref. The determination reference torque Tref is set to a large value that is not detected by a normal steering operation by the driver.

  When the reverse input acts on the steering mechanism 10, the steered wheels W are steered, and accordingly, the torsion bar of the steering shaft 12 is rapidly twisted. Since this torsional force is detected by the steering torque sensor 22 as the steering torque T, it becomes a very large value that cannot be detected by a normal steering operation. Therefore, the reverse input state can be determined by setting the determination reference torque Tref to a very large value.

  If the reverse input detection unit 200 determines that “No” in step S204, that is, the magnitude | T | of the steering torque T is not greater than the preset determination reference torque Tref, the reverse input state is not in effect. In step S206, the counter value N is cleared to zero. In step S210, the reverse input determination flag F (= 0) is output, and the reverse input detection routine is temporarily terminated.

  On the other hand, if it is determined in step S204 that “Yes”, that is, the magnitude | T | of the steering torque T is larger than the preset determination reference torque Tref, the magnitude of the rotational speed ω | It is determined whether or not ω | is larger than a preset reference speed ωref. This determination reference speed ωref is set to an appropriate value in order to prevent erroneous determination as a reverse input state when the driver performs a turning operation of the steering wheel 11.

  If the reverse input detection unit 200 determines that “No”, that is, the magnitude | ω | of the rotational speed ω is not larger than the preset determination reference speed ωref in step S205, the reverse input state is not set. In step S206, the counter value N is cleared to zero. In step S210, the reverse input determination flag F (= 0) is output, and the reverse input detection routine is temporarily terminated.

  On the other hand, if it is determined in step S205 that “Yes”, that is, the magnitude | ω | of the rotation speed ω is larger than the preset determination reference speed ωref, there is a high possibility of being in the reverse input state. That is, the direction of the steering torque T is opposite to the rotation direction of the electric motor 20 (S203: Yes), the magnitude | T | of the steering torque T is larger than the determination reference torque Tref (S04: Yes), and In the situation where the three conditions that the magnitude | ω | of the rotational speed ω is larger than the determination reference speed ωref (S205: Yes), it is considered that the reverse input state is established. Therefore, the reverse input detection unit 200 confirms whether or not the state where the three reverse input determination conditions are satisfied is continued in order to prevent instantaneous erroneous detection, and finally in the reverse input state. It is determined whether or not there is.

  When the three reverse input determination conditions are satisfied (S205: Yes), the reverse input detection unit 200 increments the counter value N by the value “1” in step S207, and in step S208, the counter value N is the reference continuous value. It is determined whether or not the number of times Nmax has been reached. The counter value N is set to “0” as an initial value when the reverse input detection routine is started. Accordingly, if “Yes” is initially determined in step S205, “No” is determined in step S208. In this case, in step S210, the reverse input determination flag F (= 0) set to “0” is output.

  If such a process is repeated and one of the three reverse input determination conditions (S203, 204, 205) is not satisfied before the counter value N reaches the reference number of consecutive times Nmax, in step S206, The counter value N is cleared to zero. On the other hand, if the counter value N reaches the reference number of consecutive times Nmax when three reverse input determination conditions are satisfied, that is, if the three reverse input determination conditions are satisfied for the set time, the reverse input is performed. In step S209, the reverse input determination flag F is set to “1”. In step S210, the reverse input determination flag F (= 1) is output.

  After the reverse input determination flag F is set to “1”, the determination in step S201 is “No”, and the process proceeds to step S211. The processes in steps S211 to S214 are processes for determining the end of the reverse input state. The reverse input detection unit 200 increments the timer value Tim by the value “1” in step S211, and determines in step S212 whether the timer value Tim has reached the reference time Tmax. This timer value Tim is set to “0” as an initial value when the reverse input detection routine is started. Therefore, the first determination in step S212 is “No”. In this case, the reverse input determination flag F (= 1) is output as it is in step S210.

  When such processing is repeated and the timer value Tim reaches the reference time Tmax (S212: Yes), the timer value Tim is cleared to zero in step S213, and the reverse input determination flag F is set to “0” in step S214. . The reverse input state is a short period from when the reverse input works until the stroke end is reached. Therefore, in steps S211 to S214, the end timing of the reverse input state is estimated by measuring the elapsed time from the time point when the reverse input state is determined. This reference time is, for example, about several tens of milliseconds. When the reverse input detection unit 200 estimates that the reverse input state has ended, it outputs a reverse input determination flag F (= 0) in step S210.

  Thus, the process returns to the initial state, and the above-described processing is repeated. Then, the reverse input determination flag F is output to the compensation torque output control unit 115, the q-axis current upper limit setting unit 123, and the voltage upper limit setting unit 143 each time.

  Next, the control mode switched according to the reverse input determination flag F will be described. When the reverse input determination flag F is “0”, that is, when the reverse input state is not detected, the compensation torque output control unit 115 adds the first compensation torque Tb1 and the second compensation torque Tb2 ( Tb1 + Tb2) is output to the total adder 116 as the total compensation torque Tb. Therefore, the final target assist torque T * is obtained by adding the total compensation torque Tb to the basic assist torque Ta, and a steering assist torque with excellent stability and steering wheel return performance can be obtained. Therefore, the steering feeling is good.

  In a situation where a large reverse input is applied to the steering mechanism 10 and the wheels W are steered, these compensation torques Tb1 and Tb2 act in a direction to reduce the target assist torque T *. When reverse input is applied to the steering mechanism 10, the torsion bar of the steering shaft 12 is rapidly twisted. At this moment, the steering torque T detected by the steering torque sensor 22 has a very large value and pulsates (increases / decreases) greatly. Due to the pulsation of the steering torque T, the differential value T ′ of the steering torque T is alternately switched between positive and negative. In the period (T ′ <0) in which the steering torque T decreases, the first compensation torque Tb1 takes a large negative value (a negative value having a large absolute value) as shown in the first compensation map of FIG. become. On the other hand, during the period in which the steering torque T increases (T ′> 0), the first compensation torque Tb1 takes a positive value, but since the steering torque T is originally large, the basic assist torque Ta is the upper limit of the target assist torque T *. The target assist torque T * cannot be increased with the first compensation torque Tb1. Therefore, in the reverse input state, the first compensation torque Tb1 is substantially a large torque in the negative direction (the direction opposite to the basic assist torque), and the first compensation torque Tb1 is changed to the basic assist torque Ta. If added, the target assist torque T * is greatly reduced.

  Further, when reverse input is applied, the direction of the steering torque T and the rotation direction of the electric motor 20 are opposite to each other. Therefore, as shown in the second compensation map of FIG. 5, the second compensation torque Tb2 is a negative torque. Moreover, when reverse input is applied, the magnitude | ω | of the rotational speed ω becomes very large, so that the absolute value of the second compensation torque Tb2 also becomes very large. For this reason, when the second compensation torque Tb2 is added to the basic assist torque Ta, the target assist torque T * is greatly reduced.

Thus, in the reverse input state, if the target assist torque T * is set by adding the compensation torques Tb1 and Tb2 to the basic assist torque Ta as they are, the target assist torque T * is reduced, and the current command value (q-axis The command current i _q ^* ) becomes small, and a large current cannot flow through the electric motor 20. When the electric motor 20 is rotated by reverse input, the kinetic energy input from the outside is converted into electric energy and recovered by the battery 81. However, if the current command value is small, a large regenerative current may flow. It is impossible to generate a large resistance against reverse input.

Therefore, in this embodiment, when the reverse input state is detected (F = 1), the compensation torque output control unit 115 does not output the total compensation torque Tb (= Tb1 + Tb2), and the total assist torque Ta is totaled. The compensation torque Tb is not added. Therefore, the target assist torque T * does not decrease due to the influence of the total compensation torque Tb. When the reverse input state is detected (F = 1), the q-axis current upper limit setting unit 123 releases the upper limit limitation of the q-axis command current i _q ^* , and the voltage upper limit setting unit 143 detects the q-axis command voltage. Releases the upper limit of v _q ^* and d-axis command voltage v _d ^* . As a result, in the reverse input state, the electric energy generated when the electric motor 20 is rotated by an external force can be regenerated to the battery 81 through the motor drive circuit 30. Therefore, a large regenerative current flows through the electric motor 20 and a large resistance force (torque in the direction opposite to the rotation direction of the electric motor 20) can be generated against reverse input.

  Thereby, according to the electric power steering apparatus of this embodiment, it can suppress that the steering handle 11 is turned rapidly by reverse input, without enlarging a steering system. Further, it is possible to reduce an impact and a collision sound generated when the rack end member 18 collides with the stopper portion 15a. As a result, discomfort given to the driver by reverse input can be reduced. In addition, since the motor control when the reverse input is activated cuts the compensation torque Tb and increases the current flowing through the electric motor 20 by that amount, there is no fear of self-steering. Further, since the motor braking force is generated by converting the kinetic energy by the reverse input into electric energy and collecting it in the battery 81, energy saving can be achieved. Further, since the existing system configuration can be used as it is without using the high-output electric motor 20 or the motor drive circuit 30, it is possible to meet the needs of small size, light weight and low cost.

  Next, an electric power steering device as a first modification will be described. This first modification is provided with a target assist torque calculation unit 210 shown in FIG. 7 in place of the target assist torque calculation unit 110 of the embodiment, and the other configurations are the same as those of the embodiment. The target assist torque calculator 210 includes a basic assist torque calculator 211 and n compensation torque calculators 212x (first compensation torque calculator 2121 to nth compensation torque calculator 212n: x = 1 to n). A compensation torque calculator 212, a gain multiplier 215 including n gain multipliers 215x (first gain multiplier 2151 to nth gain multiplier 215n: x = 1 to n), a compensation torque adder 214, A total adder 216.

  The basic assist torque calculation unit 211 has the same configuration as the basic assist torque calculation unit 111 of the embodiment. The n compensation torque calculators 212x (x = 1 to n) calculate the compensation torque Tbx (x = 1 to n) using a map or a calculation formula based on different parameters. For example, the compensation torque is calculated based on the differential value T ′ of the steering torque T and the rotational speed ω as in the embodiment. Further, for example, a compensation torque for improving the steering feeling is calculated based on the steering angle. In this case, the steering angle can be detected from the rotation angle θm of the electric motor 20.

  Each of the n gain multipliers 215x receives the compensation torque Tbx that is the calculation result of the compensation torque calculator 212x, and multiplies the compensation torque Tbx by a gain Gx (x = 1 to n). The gain multiplication unit 215x receives the reverse input determination flag F output from the reverse input detection unit 200, and sets all gains Gx to “1” when the reverse input determination flag F is “0”. Therefore, the gain multiplication unit 215x outputs the compensation torque Tbx as it is. On the other hand, when the reverse input determination flag F is “1”, the gain Gx having a preset magnitude is multiplied by the compensation torque Tbx, and the multiplication result Gx · Tbn is output. The compensation torque Tbx calculated by the compensation torque calculation unit 212x has a characteristic that takes a positive value (in the same direction as the basic assist torque) and a negative value (in the opposite direction to the basic assist torque) in a situation where reverse input works. If there is a characteristic having a positive value, the gain Gx is set to “1” for a characteristic having a positive value. On the other hand, for a characteristic having a negative value, the gain Gx is set to a value less than 1 (for example, zero). Hereinafter, in a situation where reverse input works, a compensation torque having a negative value is referred to as a specific compensation torque.

  The compensation torque adder 214 inputs and adds the calculation results (Gx · Tbx: x = 1 to n) output from the n gain multipliers 215x, and adds the results (G1 · Tb1 + G2 · Tb2 + ... + Gn · Tbn) is output to the total adder 216 as the total compensation torque Tb. The total adder 216 adds the basic assist torque Ta and the total compensation torque Tb, and sets the addition result (Ta + Tb) as the final target assist torque T *.

According to the first modification, each of the n compensation torques Tbx is multiplied by an independent gain Gx, and the specific compensation torque Tbx is detected when a reverse input is detected and during normal times. The gain Gx is switched at. For this reason, in a situation where reverse input works, the specific compensation torque Tbx acting in the direction of decreasing the target assist torque T * is set to zero or a value smaller than normal, and the current command value (q-axis command current i _q ^* ) does not decrease, or the amount of decrease can be reduced. Therefore, in addition to the effect of the above-described embodiment, even if the system configuration is provided with various compensation torques having different characteristics (different signs in the situation where reverse input is applied), the effect that it can be properly implemented. Play.

  Next, an electric power steering device will be described as a second modification. This first modification is provided with a target assist torque calculation unit 310 shown in FIG. 8 in place of the target assist torque calculation unit 110 of the embodiment, and other configurations are the same as those of the embodiment. The target assist torque calculation unit 310 includes a basic assist torque calculation unit 311 and n compensation torque calculation units 312x (first compensation torque calculation unit 3121 to nth compensation torque calculation unit 312n: x = 1 to n). A compensation torque calculation unit 312, a compensation torque addition unit 314, and a total addition unit 316 are provided.

  The basic assist torque calculator 311 has the same configuration as the basic assist torque calculator 111 of the embodiment. The n compensation torque calculators 312x (x = 1 to n) calculate the compensation torque Tbx (x = 1 to n) based on different parameters. For example, the compensation torque is calculated based on parameters such as the differential value T ′, the rotational speed ω, and the steering angle of the steering torque T. Each compensation torque calculator 312x stores a compensation map for calculating the compensation torque Tbx from the parameters.

  The compensation torque calculation unit 312x calculates a specific compensation torque having a negative value in a situation where reverse input works, and a compensation map for normal use and for reverse input is separately provided. I remember it. As the compensation map for reverse input, for example, a characteristic obtained by multiplying the characteristic of the compensation map for normal time by a gain of less than 1 as in the first modification is set.

  Among the compensation torque calculators 312x, the one that calculates the specific compensation torque is input with the reverse input determination flag F output from the reverse input detector 200, and when the reverse input determination flag F is “0”, Compensation torque is calculated using the compensation map for time, and when the reverse input determination flag F is “1”, the compensation torque is calculated using the compensation map for reverse input. On the other hand, for the compensation torque calculator 312x that does not calculate the specific compensation torque, the compensation torque is calculated using the same compensation map regardless of the reverse input determination flag F.

  The compensation torque Tbx calculated by each compensation torque calculator 312x is output to the compensation torque adder 314. The compensation torque addition unit 314 inputs and adds the compensation torque Tbx output from the compensation torque calculation unit 312x, and outputs the addition result (Tb1 + tb2 +... Tbn) to the total addition unit 316 as the total compensation torque Tb. The total adder 316 adds the basic assist torque Ta and the total compensation torque Tb, and sets the addition result (Ta + Tb) as the final target assist torque T *.

  Therefore, this second modification also has the same effect as the first modification.

  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, when three reverse input determination conditions are continuously satisfied, it is determined that the reverse input state is set (F = 1). However, the three conditions are not necessarily required and are arbitrarily set. These two may be combined, or other determination conditions may be combined. Alternatively, the determination may be made based only on the magnitude | T | of the steering torque T or the magnitude | ω | of the rotational speed ω.

  In this embodiment (FIG. 2), two types of compensation torque are set, but one type or three or more types of compensation torque may be set. The characteristics of the compensation torque can also be arbitrarily set, and a compensation torque that does not decrease the target assist torque T * in a situation where the input state is reversed may be combined. Even in this case, the configuration may be such that all the compensation torque is output to the compensation torque adding unit 114.

  Further, in the present embodiment, the upper limit limiting function for the command current and the command voltage is provided and the upper limit limiting function is canceled when a reverse input state is detected. A configuration in which a release function is not provided may be used.

  Further, a booster circuit (not shown) may be provided on the input side of the motor drive circuit 30 so that the power supply voltage is boosted by the booster circuit and the motor drive circuit 30 is supplied with power.

  The electric power steering apparatus according to the present embodiment is a column assist type in which the electric motor 20 is assembled to the steering shaft 12, but can also be applied to a rack assist type in which the electric motor 20 is assembled to the rack bar 14.

  DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 20 ... Electric motor, 21 ... Rotation angle sensor, 22 ... Steering torque sensor, 25 ... Vehicle speed sensor, 30 ... Motor drive circuit, 38 ... Current sensor, 100 ... Assist control device, 110, 210, 310 ... target assist torque calculation unit, 111, 211, 311 ... basic assist torque calculation unit, 112, 113, 212, 312 ... compensation torque calculation unit, 114, 214, 314 ... addition of compensation torque 115, compensation torque output control unit, 116, 216, 316 ... total addition unit, 120 ... bi-axis current command unit, 123 ... q-axis current upper limit setting unit, 130 ... deviation calculation unit, 140 ... feedback calculation unit, 143 ... voltage upper limit setting unit, 151 ... 2-phase / 3-phase coordinate conversion unit, 152 ... PWM signal generation unit, 15 ... 3-phase / 2-phase coordinate conversion unit, 154 ... electric angle calculation unit, 155 ... rotation speed calculation unit, 200 ... reverse input detection unit, 215 ... gain multiplication unit, Ta ... basic assist torque, Tb1, Tb2, Tb ... compensation Torque, T ... steering torque, ω ... rotational speed, Sp ... vehicle speed, W ... steering wheel, F ... reverse input determination flag.

Claims (7)

An electric motor provided in the steering mechanism for generating steering assist torque;
Steering torque detection means for detecting steering torque input to the steering mechanism;
Basic assist torque calculating means for calculating basic assist torque based on the detected steering torque;
Compensation torque calculating means for calculating a compensation torque for compensating the basic assist torque;
Target assist torque calculating means for calculating a target assist torque obtained by adding the basic assist torque and the compensation torque;
An electric power steering device comprising: motor control means for driving and controlling the electric motor based on the target assist torque;
Reverse input state detection means for detecting a reverse input state in which the steered wheels are steered at high speed by reverse input from the tire;
When the reverse input state is detected, the compensation torque is used so that the target assist torque calculated by the target assist torque calculation means is not reduced by the compensation torque or the amount of reduction is reduced. An electric power steering apparatus comprising: a reverse input target assist torque changing means for changing a target assist torque calculation method. The compensation torque computed by the compensation torque computing means includes a specific compensation torque that is set to a value that reduces the target assist torque in the reverse input state.
2. The electric motor according to claim 1, wherein the reverse input target assist torque changing means reduces the magnitude of the specific compensation torque to be added to the basic assist torque when the reverse input state is detected. Power steering device.   3. The electric power steering according to claim 2, wherein the reverse input target assist torque changing means does not add the specific compensation torque to the basic assist torque when the reverse input state is detected. apparatus.   The specific compensation torque, according to a torque differential value obtained by time differentiation of the magnitude of the steering torque, becomes a larger positive value as the torque differential value becomes a larger positive value, and as the torque differential value becomes a larger negative value. 4. The electric power steering apparatus according to claim 2, wherein the electric power steering apparatus is set to have a large negative value.   The specific compensation torque increases in accordance with the rotation speed of the electric motor as the rotation speed increases in the same direction as the steering torque, and increases as the rotation speed increases in the opposite direction to the steering torque. The electric power steering apparatus according to any one of claims 2 to 4, wherein the electric power steering apparatus is set to have a large negative value. The motor control means includes
Current limiting means for limiting an upper limit value of a current flowing through the electric motor;
6. The electric power according to claim 1, further comprising: a current limit canceling unit that cancels a current limit by the current limiting unit when the reverse input state is detected. Steering device. The motor control means includes
Voltage limiting means for limiting the upper limit value of the voltage applied to the electric motor;
The electric power according to any one of claims 1 to 6, further comprising: a voltage restriction release unit that releases a voltage restriction by the voltage restriction unit when the reverse input state is detected. Steering device.

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