JP2021194974A - Motor control device - Google Patents

Abstract

To provide a motor control device that can prevent a driver from feeling discomfort or anxiety when the supply of motor current to an electric motor as a source of steering auxiliary force is stopped due to the occurence of malfunction and that can stop the supply of motor current as quickly as possible.SOLUTION: A control device 7 is configured to control an electric motor 5 as a source of steering auxiliary force that assists a steering operation of a steering wheel 10 by a driver of a vehicle. The control device includes: an inverter circuit 71 including a plurality of switching elements 711 to 716; and control means 80 configured to turn on/off the plurality of switching elements 711 to 716 to supply motor current to the electric motor 5 and to control the electric motor 5. The control means 80 gradually decreases the motor current at a time ratio according to vehicle information when stopping the supply of the motor current to the electric motor 5 due to the occurence of malfunction.SELECTED DRAWING: Figure 3

Description

The present invention relates to a motor control device that controls an electric motor that is a source of steering assist force that assists a vehicle driver in steering an operation of a steering wheel.

Conventionally, some steering devices for steering the steering wheels of a vehicle are provided with a steering assist device that uses an electric motor as a drive source to generate steering assist force and assists the driver in steering the steering wheel. The steering assist device includes an electric motor, an inverter having a plurality of switching elements, and a control unit that turns the plurality of switching elements on and off to supply a motor current to the electric motor.

The motor control device described in Patent Document 1 includes a fail-safe circuit that cuts off the electric power transmitted from the battery to the inverter circuit based on a command from the MPU when an abnormality such as a failure occurs in the power steering device. .. As a result, for example, when the electric motor or the inverter is overloaded and the temperature rises, the supply of the motor current to the electric motor is cut off, and the switching element or the like is protected from thermal destruction.

Further, as described in Patent Document 2, the applicant applies to the voltage across the coil of each phase when a failure of the rotation angle sensor for detecting the rotation angle of the rotor with respect to the stator of the electric motor occurs. Based on this, the induced voltage generated in the electric motor is calculated by calculation, the estimated angular speed of the motor is obtained from the magnitude of this induced voltage, and the amount of rotation of the electric motor per calculation cycle at this estimated angular speed is calculated as the amount of change in electric angle. We are proposing an electric power steering device that calculates the rotation angle of a rotor by adding the amount of change in the electric angle to the estimated electric angle before the calculation cycle.

Re-Table 2017/006623 (see paragraph [0035]) Japanese Unexamined Patent Publication No. 2014-138530 (see paragraphs [0013], [0031], [0038])

For example, when some abnormality occurs while the driver assists the steering operation of the steering wheel with the steering assist force and the supply of the motor current to the electric motor is stopped, if the supply of the motor current is suddenly cut off, the steering is steered. The operation suddenly becomes heavy, giving the driver a sense of discomfort and anxiety. Further, if the motor current is gradually reduced when the supply of the motor current to the electric motor is stopped, it is possible to alleviate the discomfort and anxiety given to the driver, but the motor current becomes zero. It will take a long time to achieve this, and there is a risk that the switching elements and the like cannot be properly protected.

In particular, when a failure of the rotation angle sensor occurs and the electric motor is controlled based on the estimated value of the rotation angle, it is necessary to increase the motor current so that the actual rotation position of the rotor does not deviate from the electric angle. Therefore, when the switching element tends to be overheated, for example, when the temperature of the switching element exceeds the rated temperature, it is necessary to stop the supply of the motor current as soon as possible.

The present invention has been made in view of such circumstances, and an object thereof is great for the driver when the supply of the motor current to the electric motor which is the source of the steering assist force is stopped due to the occurrence of an abnormality. It is an object of the present invention to provide a motor control device capable of stopping the supply of a motor current as soon as possible while suppressing the feeling of discomfort and anxiety.

The present invention is a motor control device that controls an electric motor that is a source of steering assist force that assists a vehicle driver in steering an steering wheel in order to achieve the above object, and comprises a plurality of switching elements. It is provided with an inverter circuit having an inverter circuit and a control means for controlling the electric motor by turning on and off the plurality of switching elements to supply a motor current to the electric motor, and the control means transfers the motor to the electric motor due to the occurrence of an abnormality. Provided is a motor control device that gradually reduces the motor current at a time rate according to vehicle information when the supply of the motor current is stopped.

According to the motor control device according to the present invention, when the supply of the motor current to the electric motor, which is the source of the steering assist force, is stopped due to the occurrence of an abnormality, the driver may feel a great sense of discomfort or anxiety. It is possible to stop the supply of the motor current as soon as possible while suppressing it.

It is a schematic diagram which shows the structural example of the steering apparatus which has the control apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the structural example of a control device and an electric motor. It is a block diagram which shows the control composition example of a control part. It is a table which shows the relationship between the running mode of a vehicle, the steering mode of a steering wheel, and the corresponding tapering time. It is a graph which shows an example of the temporal change of the tapering gain for tapering a motor current.

[Embodiment]
Embodiments of the present invention will be described with reference to FIGS. 1 to 5. It should be noted that the embodiments described below are shown as suitable specific examples for carrying out the present invention, and there are some parts that specifically exemplify various technically preferable technical matters. , The technical scope of the present invention is not limited to this specific aspect.

(Construction of steering device)
FIG. 1 is a schematic diagram showing a configuration example of a steering device having a control device according to an embodiment of the present invention. FIG. 1 shows a state in which the steering device is viewed from the front of the vehicle, and the left side of FIG. 1 corresponds to the right side of the vehicle and the right side of FIG. 1 corresponds to the left side of the vehicle.

The steering device 1 includes a steering shaft 2 including a torsion bar 20 twisted by a steering torque applied to the steering wheel 10, and a front wheel 11 which is a steering wheel of a vehicle due to axial movement accompanying rotation of the steering shaft 2. A rack shaft 3 that steers the steering wheel, a torque sensor 41 that detects the amount of twist of the torsion bar 20, a steering speed sensor 42 that detects the steering speed, and a source of steering assist force that assists the steering operation of the steering wheel 10. It includes a certain electric motor 5, a deceleration mechanism 6 that decelerates the rotation of the electric motor 5 and transmits it to the steering shaft 2, and a control device 7 that controls the electric motor 5. The electric motor 5, the deceleration mechanism 6, and the control device 7 constitute the steering assist device 100.

The steering shaft 2 is formed between a column shaft 21 having a steering wheel 10 fixed to one end thereof, a pinion shaft 23 having pinion teeth 231 meshing with the rack teeth 31 of the rack shaft 3, and the column shaft 21 and the pinion shaft 23. It has an intervening intermediate shaft 22. The column shaft 21 and the intermediate shaft 22 and the intermediate shaft 22 and the pinion shaft 23 are connected by universal joints 24 and 25, respectively.

The column shaft 21 has a first shaft member 211 and a second shaft member 212, and the first shaft member 211 and the second shaft member 212 are connected by a torsion bar 20. The first shaft member 211 rotates integrally with the steering wheel 10, and the steering torque applied to the steering wheel 10 is transmitted to the second shaft member 212 via the torsion bar 20. The torque sensor 41 detects the steering torque applied to the steering wheel 10 by the driver by the amount of twist of the torsion bar 20.

The speed reduction mechanism 6 is composed of a worm gear mechanism including a worm 61 that is rotationally driven by an electric motor 5 and a worm wheel 62 that rotates integrally with the second shaft member 212. The output torque of the electric motor 5 is amplified by the deceleration mechanism 6 and transmitted to the second shaft member 212 to serve as a steering assist force.

The rack shaft 3 is housed in a cylindrical housing 30 and is axially movable along the vehicle width direction. Ball joint sockets 12 are fixed to both ends of the rack shaft 3, and tie rods 13 connected to the rack shaft 3 by these ball joint sockets steer the left and right front wheels 11 via knuckle arms (not shown). Let me. The ball joint socket 12 accommodates a spherical connecting portion 131 provided at one end of the tie rod 13. A bellows 14 made of bellows-shaped rubber or resin is arranged on the outer peripheral side of the ball joint socket 12.

When the steering wheel 10 is steered by the driver of the vehicle, the pinion shaft 23 connected to the steering wheel 10 via the column shaft 21 and the intermediate shaft 22 rotates, and the pinion teeth 231 and the rack teeth 31 mesh with each other. The rack shaft 3 moves in the axial direction. Then, the left and right front wheels 11 are steered via the tie rod 13 by the axial movement of the rack shaft 3. The control device 7 controls the electric motor 5 based on the steering torque, the steering speed, the vehicle speed, and the like, and generates a steering assist force.

FIG. 2 is a schematic diagram showing a configuration example of the control device 7 and the electric motor 5. The electric motor 5 is a three-phase brushless motor, and has a rotor 51 having a plurality of magnetic poles, a stator 52 arranged on the outer periphery of the rotor 51, and a rotation angle (motor rotation angle) of the rotor 51 with respect to the stator 52. ) Is included in the rotation angle sensor 53. The rotor 51 has an N pole 511 and an S pole 512, and the stator 52 has a U-phase coil 521, a V-phase coil 522, and a W-phase coil 523. The rotor 51 has a plurality of pairs of N poles 511 and S poles 512, and the stator 52 has a plurality of sets of U-phase coils 521, V-phase coils 522, and W-phase coils 523. , FIG. 2 shows only a pair of N-poles 511 and S-poles 512 and a corresponding set of U-phase coils 521, V-phase coils 522, and W-phase coils 523 for ease of explanation. ..

The control device 7 includes an inverter circuit 71 having first to sixth switching elements 711 to 716 connected by a three-phase bridge, a temperature sensor 72 for detecting the temperature of the inverter circuit 71, and first to sixth switching elements. It has a control unit 73 for turning 711 to 716 on and off. The first to sixth switching elements 711 to 716 are mounted on a metal substrate 710 having excellent thermal conductivity. The first and second switching elements 711 and 712, the third and fourth switching elements 713 and 714, and the fifth and sixth switching elements 715 and 716 are placed between the upper bus 717 and the lower bus 718. , Each connected in series. A DC voltage of, for example, 12 V is supplied to the upper bus 717 from a DC power source 15 such as a battery, and the lower bus 718 is electrically grounded.

Between the first switching element 711 and the second switching element 712, between the third switching element 713 and the fourth switching element 714, and between the fifth switching element 715 and the sixth switching element 716. U-phase bus bar 741 and V-phase that supply motor currents (U-phase current, V-phase current, and W-phase current) to the U-phase coil 521, V-phase coil 522, and W-phase coil 523 of the electric motor 5, respectively. The bus bar 742 and the W-phase bus bar 743 are connected. The bus bars 741,742,743 of each of these phases have first to third voltage detection units 751, 752, 753 for detecting the U-phase voltage value Vu, the V-phase current value Vv, and the W-phase voltage value Vw, respectively. It is connected. The detection signals of the first to third voltage detection units 751, 752, 753 are output to the control unit 73.

In the present embodiment, the first to sixth switching elements are N-channel MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) with freewheeling diodes. The switching element constituting the inverter circuit 71 is not limited to the FET, and a power transistor such as an IGBT (Insulated Gate Bipolar Transistor) may be used.

The U phase is between the second switching element 712 and the lower bus 718, between the fourth switching element 714 and the lower bus 718, and between the sixth switching element 716 and the lower bus 718. First to third current detection units 76, 77, 78 for detecting the current value Iu, the V phase current value Iv, and the W phase current value Iw, respectively, are provided. The first to third current detection units 76, 77, 78 include a shunt resistor 761, 771, 781 and a voltage sensor 762,772,782, and the detection signal of the voltage sensor 762,772,782 is a U-phase current value Iu. , V-phase current value Iv, and W-phase current value Iw are output to the control unit 73.

Switching elements 711 to 716 of the first to sixth is OFF by the PWM signal _a 1 ~a ₆ output from the control unit 73. The PWM signal _a 1 ~a _6, is input to the gates of the switching elements 711 to 716 of the first to sixth, when the switching element 711 to 716 of the first to sixth are turned on, the drain - between source Becomes a conductive state.

The temperature sensor 72 is attached to a metal substrate 710 on which the first to sixth switching elements 711 to 716 are mounted, and when the first to sixth switching elements 711 to 716 generate heat due to the drain current, the heat is generated. It conducts heat to the metal substrate 710 and is detected by the temperature sensor 72. The temperature sensor 72 is not limited to one, and a plurality of temperature sensors 72 may be attached to the metal substrate 710. Further, one or a plurality of temperature sensors 72 may be attached to any or all of the first to sixth switching elements 711 to 716.

Further, the control unit 73 can acquire information on the vehicle speed, the yaw rate and the front-rear acceleration generated when the vehicle is running, and the wheel speeds of the four wheels (front-rear left-right wheels) by communication by, for example, CAN (Controller Area Network). Information on vehicle speed, yaw rate, front-rear acceleration, four-wheel wheel speed, steering torque, and steering speed is an example of vehicle information indicating the state of the vehicle. The control unit 73 turns on and off the first to sixth switching elements 711 to 716 based on the vehicle information, and supplies the motor current to the electric motor 5 to control the electric motor 5.

In the present embodiment, the control unit 73 has a rotation angle sensor backup function capable of continuing control of the electric motor 5 even when a failure occurs in the rotation angle sensor 53. Further, the control unit 73 protects the first to sixth switching elements 711 to 716 when the temperature detected by the temperature sensor 72 becomes higher than a predetermined value, so that the control unit 73 motors at a time ratio according to the vehicle information. Decrease the current. The temperature sensor 72 corresponds to the temperature detection means of the present invention.

FIG. 3 is a block diagram showing a control configuration example of the control unit 73. The control unit 73 outputs current command value calculation units 801, first subtraction units 802, and second as control means 80 for outputting _{PWM signals a 1 to} a _{6 to turn on / off the first to sixth switching elements 711 to 716.} Subtraction unit 803, first feedback control unit 804, second feedback control unit 805, two-phase / three-phase conversion unit 806, duty instruction value calculation unit 807, PWM signal generation unit 808, and three-phase / two-phase conversion unit 809. Prepare.

^{The current command value calculation unit 801 uses the d-axis current command value Id *,} which is the current command value on the d-axis in the d / q coordinate system, and the q-axis, which is the current command value on the q-axis, based on the vehicle speed and steering torque. Calculate the current command value Iq ^{*. Specifically, the d-axis current command value Id *} and the q-axis current command value Iq ^* are set so that the electric motor 5 generates a larger torque as the steering torque becomes larger and the vehicle speed becomes slower.

The three-phase / two-phase conversion unit 809 maps each phase current value Iu, Iv, Iw on the d / q coordinate based on the motor rotation angle θ, so that the d-axis current value Id and the d-axis current value Id in the d / q coordinate system Calculate the q-axis current value Iq. The first subtraction unit 802 obtains the deviation ΔId between the d-axis current command value Id ^* and the d-axis current value Id. Further, the second subtraction unit 803 ^{obtains the deviation ΔIq between the q-axis current command value Iq *} and the q-axis current value Iq.

The first feedback control unit 804 calculates the ^{d-axis voltage command value Vd *} by performing current feedback control based on the d-axis current deviation ΔId in order to make the d-axis current value Id follow the d-axis current command value Id ^*. do. Further, the second feedback control unit 805 performs current feedback control based on the q-axis current deviation ΔIq in order to make the ^{q-axis current value Iq follow the q-axis current command value Iq * , thereby performing the q-axis voltage command value Vq *.} Is calculated. The d-axis voltage command value Vd ^* calculated by the first feedback control unit 804 and the q-axis voltage command value Vq ^* calculated by the second feedback control unit 805 are input to the two-phase / three-phase conversion unit 806. ..

The two-phase / three-phase conversion unit 806 ^{maps the d-axis voltage command value Vd *} and the q-axis voltage command value Vq ^* onto the three-phase AC coordinate system based on the motor rotation angle θ, thereby causing the three-phase. Calculate each phase voltage command value Vu ^* , Vv ^* , Vw ^{* in the AC coordinate system. Each phase voltage command value Vu *} , Vv ^* , Vw ^* calculated by the two-phase / three-phase conversion unit 806 is input to the duty instruction value calculation unit 807.

The duty instruction value calculation unit 807 calculates the target duty ratios Du, Dv, Dw for PWM control of the first to sixth switching elements 711 to 716. The target duty ratios Du, Dv, and Dw are duty ratios that are the ratio of the time during which the first switching element 711, the third switching element 713, and the fifth switching element 715, which correspond to the upper arm of the inverter circuit 71, are turned on. Represents each.

PWM signal generating unit 808, based on a comparison of the target duty ratio Du, Dv, Dw and PWM control carrier wave (carrier), generates a PWM signal _a 1 ~a _6, and outputs to the inverter circuit 71. As a result, the motor current corresponding to the target duty ratios Du, Dv, and Dw is supplied to the electric motor 5, and steering assist force is generated.

_{Further, the control unit 73 estimates the motor rotation angle estimated value θ 2} , which is an estimated value of the rotation angle of the rotor 51, based on each phase current value Iu, Iv, Iw and each phase voltage value Vu, Vv, Vw. Motor rotation angle calculation unit 81, rotation angle sensor abnormality determination unit 82 for determining whether or not an abnormality has occurred in the rotation angle sensor 53, two-phase / three-phase conversion unit 806, and three-phase / two-phase conversion unit. As the motor rotation angle θ used in the 809, the _{switching unit 83 for switching whether the detection value θ 1} of the rotation angle sensor 53 or the motor rotation angle estimated value θ ₂ is used, and the detection temperature T of the temperature sensor 72 are predetermined values. It has a temperature abnormality determination unit 84 for determining whether or not it is higher than the above.

The motor rotation angle calculation unit 81 is generated in the U-phase coil 521, the V-phase coil 522, and the W-phase coil 523 based on, for example, each phase current value Iu, Iv, Iw and each phase voltage value Vu, Vv, Vw. _{The motor rotation angle estimated value θ 2} is calculated by calculating the induced voltage and integrating the estimated angular velocity obtained from the calculated magnitude of the induced voltage. The rotation angle sensor abnormality determination unit 82 causes an abnormality in the rotation angle sensor 53, for example, when a signal from the rotation angle sensor 53 is not sent or when the signal from the rotation angle sensor 53 is unstable. It is determined that it is.

A predetermined value as a determination standard of the temperature abnormality determination unit 84 is, for example, the rated temperature of the first to sixth switching elements 711 to 716. When the rotation angle sensor abnormality determination unit 82 determines that an abnormality has occurred in the rotation angle sensor 53, the switching unit 83 _{outputs the motor rotation angle estimated value θ 2} as the motor rotation angle θ, and in other cases. (In the normal state), the detection value θ ₁ of the rotation angle sensor 53 is output as the motor rotation angle θ.

The determination result of the rotation angle sensor abnormality determination unit 82 and the determination result of the temperature abnormality determination unit 83 are sent to the current command value calculation unit 801. When the current command value calculation unit 801 determines that an abnormality has occurred in the rotation angle sensor 53, the current command value (d-axis current) is higher than when it is determined that no abnormality has occurred in the rotation angle sensor 53. Increase the command value Id ^* and the q-axis current command value Iq ^* ). As a result, a large motor current is supplied to the stator 52, and the rotation position of the rotor 51 is prevented from deviating from the electric angle.

As described above, the control of the electric motor 5 based on the _{estimated motor rotation angle θ 2} when the rotation angle sensor 53 fails is an example of the degenerate control. Here, the degenerate control means that even if a part of the function for controlling the electric motor 5 with high accuracy and high efficiency is lost, the lost function is replaced by other means, and the performance is higher than the original performance. It means to continue the control of the electric motor 5 although it is limited or inefficient. The control unit 73 performs degeneracy control not only when the rotation angle sensor 53 fails, but also when, for example, the torque sensor 41 fails.

Further, the current command value calculation unit 801 supplies a large motor current to the stator 52 when it is determined that an abnormality has occurred in the rotation angle sensor 53, for example, so that the first to sixth switching elements 711 When ~ 716 generates heat and the detection temperature T of the temperature sensor 72 is determined to be higher than a predetermined value, the motor current is gradually reduced at a time ratio according to the vehicle information, and the supply of the motor current is stopped. That is, when the degeneration control cannot be continued during the degeneration control due to the occurrence of an abnormality, the control means 80 gradually reduces the motor current at a time ratio according to the vehicle information.

Here, the vehicle information is some detection value of the running state or the steering state of the vehicle detected by an external sensor of the control device 7, and in the present embodiment, the vehicle speed, yaw rate, front-rear acceleration, and four-wheel wheels. Information on speed, steering torque, steering speed, and motor rotation angle corresponds to this. The detection values of the first to third current detection units 76, 77, 78, the first to third voltage detection units 751, 752, 753, and the temperature sensor 72 of the control device 7 itself are included in the vehicle information. However, for example, in the case of shrinkage control when an abnormality occurs in the rotation angle sensor 53, the motor rotation angle information estimated and calculated by the motor rotation angle calculation unit 81 is included in the vehicle information.

The control unit 73 includes a steering mode determination unit (steering mode estimation means) 85, a travel mode determination unit (travel mode determination means) 86, and as components for gradually reducing the motor current at a time ratio according to vehicle information. It is provided with a gradual decrease time setting unit (gradual decrease time setting means) 87. The steering mode determination unit 85 estimates the steering mode of the steering wheel 10 based on vehicle information related to the steering state, more specifically, steering torque and steering speed information. The traveling mode determination unit 86 estimates the traveling mode of the vehicle based on the vehicle information related to the traveling state of the vehicle, more specifically, the yaw rate, the front-rear acceleration, and the information of the four-wheel wheel speed.

The gradual reduction time setting unit 87 sets the gradual reduction time when the motor current is gradually reduced based on the estimated steering mode and traveling mode. When the supply of the motor current to the electric motor 5 is stopped, the current command value calculation unit 801 gradually reduces the motor current so that the motor current becomes zero in the tapering time set by the tapering time setting unit 87. Next, an example of processing of the steering mode determination unit 85, the traveling mode determination unit 86, and the tapering time setting unit 87 will be described in more detail with reference to FIGS. 4 and 5.

FIG. 4 is a table showing the relationship between the traveling mode and the steering mode and the tapering time corresponding to the traveling mode and the steering mode. FIG. 5 is a graph showing an example of a temporal change in the gradual decrease gain for gradual reduction of the motor current in the current command value calculation unit 801.

Based on the information of yaw rate, forward / backward acceleration, and four-wheel wheel speed, the traveling mode determination unit 86 determines whether the traveling mode of the vehicle is an emergency avoidance mode, a circular turning mode, a slalom traveling mode, a straight traveling mode, or a stop. Judge whether it is inside. The emergency avoidance mode is a mode for avoiding another vehicle, a pedestrian, or the like that has jumped out in front of the vehicle in the traveling direction, for example. The circular turning mode is a mode for traveling on a curve having a large turning radius at a substantially constant speed, for example. The slalom driving mode is a mode when a relatively large right curve and a left curve are continuous. Further, the straight running mode is a mode in which the steering angle is substantially zero and the vehicle goes straight.

In the traveling mode determination unit 86, for example, whether or not the yaw rate and the front-rear acceleration are values within the range set corresponding to each mode, and the mutual relationship between the wheel speeds of the left and right front and rear wheels are predetermined conditions. It is determined which mode the traveling mode corresponds to depending on whether or not the condition is satisfied.

The steering mode determination unit 85 determines whether the steering mode is a steep steering mode, a steering holding mode, a slow steering mode, or a non-steering mode based on the information of the steering torque and the steering speed. This mode determination is performed, for example, by whether or not the steering torque and the steering speed are values within the range set according to each mode.

The gradual decrease time setting unit 87 prohibits gradual decrease of the motor current in the case of the emergency avoidance mode and the sudden steering mode, and in the case of the circular turning mode and the steering holding mode. That is, even if the detected temperature T of the temperature sensor 72 is higher than the predetermined value, the motor current is not gradually reduced. Further, the tapering time setting unit 87 sets the tapering time to Ta in the slalom running mode and the slow steering mode. Further, the gradual decrease time setting unit 87 sets the gradual decrease time to Tb in the case of straight running mode and non-steering, and sets the gradual decrease time to Tc in the case of stopping and non-steering. Tb is longer than Tc and Ta is even longer than Tb. Ta is, for example, 2 seconds or more and less than 3 seconds, and Tb is, for example, 1 second or more and less than 2 seconds. Tc is, for example, less than 1 second. In addition, Tc may be set to zero.

The current command value calculation unit 801 corrects and outputs the ^{q-axis current command value Iq *} that contributes to the output torque of the electric motor 5 when the motor current is gradually reduced due to the occurrence of an abnormality. As shown in FIG. 5, this correction is performed by multiplying the gradually decreasing gain having a different time change rate (time ratio) according to the gradually decreasing time by the q-axis current command value Iq ^{* before the correction.} The gradual decrease gain is a value of 1 or less, and is corrected so that the ^{q-axis current command value Iq * becomes smaller by multiplying the gradual decrease gain.} The gradual decrease gain is 1 at the start of gradual decrease of the motor current, and becomes monotonously small so that the motor current becomes zero in the gradual decrease time (Ta, Tb, Tc) set by the gradual decrease time setting unit 87.

In this way, the tapering time setting unit 87 sets the tapering time shorter when the steering wheel 10 is not steered (in the case of non-steering) as compared with the case where the steering wheel 10 is steered. Further, when the traveling mode estimation unit 86 estimates that the traveling mode is the emergency avoidance mode, the circular turning mode, or the slalom traveling mode, the gradual decrease time setting unit 87 estimates that the traveling mode is the straight traveling mode. Set the tapering time longer than in the case of.

According to the present embodiment described above, when the supply of the motor current to the electric motor 5 is stopped due to the occurrence of an abnormality, the gradual decrease time is set long in a situation where the driver tends to feel uncomfortable or anxious. It is possible to stop the supply of the motor current as soon as possible while suppressing the driver from feeling a great deal of discomfort or anxiety.

(Additional note)
Although the present invention has been described above based on the embodiments, the embodiments do not limit the invention according to the claims. It should also be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

Further, the present invention can be appropriately modified and implemented by omitting a part of the configuration or adding or replacing the configuration within a range not deviating from the gist thereof.

10 ... Steering wheel 5 ... Electric motor 7 ... Control device (motor control device)
71 ... Inverter circuit 711-716 ... 6th switching element 72 ... Temperature sensor (temperature detection means)
80 ... Control means 85 ... Steering mode determination unit (steering mode estimation means)
86 ... Driving mode determination unit (driving mode determination means)
87 ... Gradual decrease time setting unit (gradual decrease time setting means)

Claims (6)

It is a motor control device that controls an electric motor that is a source of steering assist force that assists the steering operation of the steering wheel by the driver of the vehicle.
Inverter circuits with multiple switching elements and
A control means for turning the plurality of switching elements on and off to supply a motor current to the electric motor and controlling the electric motor is provided.
The control means gradually reduces the motor current at a time ratio according to vehicle information when the supply of the motor current to the electric motor is stopped due to the occurrence of an abnormality.
Motor control device. The control means gradually reduces the motor current at a time rate according to the vehicle information when the degeneration control cannot be continued during the degeneration control due to the occurrence of an abnormality.
The motor control device according to claim 1. A temperature detecting means for detecting the temperature of the inverter circuit is provided.
The control means gradually reduces the motor current at a time rate according to the vehicle information when the temperature detected by the temperature detecting means becomes higher than a predetermined value.
The motor control device according to claim 1 or 2. A steering mode estimation means that estimates the steering mode of the steering wheel based on the vehicle information including the steering speed and the steering torque of the steering wheel.
A driving mode estimation means that estimates the driving mode of the vehicle based on the vehicle information including information on the vehicle speed and yaw rate.
It is provided with a gradual decrease time setting means for setting a gradual decrease time when the motor current is gradually decreased based on the estimated steering mode and the traveling mode.
When the supply of the motor current to the electric motor is stopped, the control means gradually reduces the motor current so that the motor current becomes zero in the tapering time set by the tapering time setting means.
The motor control device according to any one of claims 1 to 3. The tapering time setting means sets the tapering time shorter when the steering wheel is not steered as compared with the case where the steering wheel is steered.
The motor control device according to claim 4. When the traveling mode estimating means estimates that the traveling mode is an emergency avoidance mode, a circular turning mode, or a slalom traveling mode, the traveling mode is estimated to be a straight traveling mode. The tapering time is set longer than in the case.
The motor control device according to claim 4 or 5.

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