WO2024095355A1

WO2024095355A1 - Electric power steering device

Info

Publication number: WO2024095355A1
Application number: PCT/JP2022/040847
Authority: WO
Inventors: 裕史西村; 大輔田中
Original assignee: 三菱電機株式会社
Priority date: 2022-11-01
Filing date: 2022-11-01
Publication date: 2024-05-10

Abstract

This electric power steering device comprises: a motor driving circuit that drives a motor; a relay circuit that is capable of disconnecting electrical connection between the motor driving circuit and the motor; and a control unit that determines, by using two or more independent means, whether a regenerative current is flowing through the motor or not, and controls the relay circuit on the basis of a result of the determination.

Description

Electric power steering device

This disclosure relates to an electric power steering device.

In conventional electric power steering devices, a semiconductor relay (hereinafter referred to as the "motor relay") provided between the motor drive circuit (e.g., an H-bridge circuit) that drives the motor and the motor calculates the motor back electromotive voltage and the energy of the regenerative current based on the rotation speed of the motor, and is configured to turn off when the energy of the regenerative current is reduced to the safe operating range of the FET that constitutes the motor relay (see, for example, Patent Document 1).

Patent No. 6406406

The motor relay is provided to turn off and electrically isolate the motor drive circuit and the motor when any abnormality occurs in the electric power steering device. The motor relay is turned off when no regenerative current is flowing through the motor in order to protect the FET that constitutes the motor relay.

However, if the abnormality occurring in the electric power steering device is due to a failure in a part involved in detecting regenerative current, it may not be possible to determine that regenerative current is flowing, and the motor relay may be turned OFF while regenerative current is flowing. Alternatively, it may not be possible to determine that regenerative current is not flowing, and the motor relay may continue to be ON while no regenerative current is flowing. Thus, with conventional electric power steering devices, it may not be possible to electrically disconnect the motor drive circuit and the motor at the appropriate time.

This disclosure was made in consideration of the above circumstances, and one of its objectives is to provide an electric power steering device that electrically disconnects the motor drive circuit and the motor at the appropriate timing.

The electric power steering device according to the present disclosure includes a motor drive circuit that drives a motor, a relay circuit that can cut off the electrical connection between the motor drive circuit and the motor, and a control unit that uses two or more independent means to determine whether or not a regenerative current is flowing through the motor and controls the relay circuit based on the determination result.

The electric power steering device disclosed herein can electrically disconnect the motor drive circuit and the motor at the appropriate timing.

1 is a block diagram showing an example of the configuration of an electric power steering device according to a first embodiment; FIG. 2 is a block diagram showing an example of an H-bridge circuit and its peripheral circuits according to the first embodiment. FIG. 4 is a diagram showing an operation of the motor according to the first embodiment when it generates a regenerative current. 3 is a timing chart of the electric power steering device according to the first embodiment. 6 is a flowchart showing an example of a relay driving process according to the first embodiment. 10 is a flowchart showing an example of a relay driving process according to a second embodiment. 13 is a flowchart showing an example of a relay driving process according to the third embodiment. 10 is a timing chart of an electric power steering device according to a third embodiment. FIG. 13 is a block diagram showing a partial configuration of a vehicle equipped with an electric power steering device according to a fourth embodiment.

Hereinafter, an embodiment will be described with reference to the drawings.
First Embodiment
First, the first embodiment will be described.

FIG. 1 is a block diagram showing an example of the configuration of an electric power steering device according to the first embodiment. The electric power steering device 100 shown in FIG. 1 includes a controller 1, a torque sensor 2, a vehicle speed sensor 3, a steering angle sensor 4, and a motor 5.

The controller 1 is a control unit that controls the electric power steering device 100. The torque sensor 2 is a sensor that measures the steering force of the driver. The vehicle speed sensor 3 is a sensor that measures the traveling speed of the vehicle. The steering angle sensor 4 is a sensor that measures the steering angle of the steering wheel. The motor 5 generates power for the electric power steering device 100. For example, the controller 1 controls the output of the motor 5 based on signals input from the torque sensor 2, the vehicle speed sensor 3, and the steering angle sensor 4.

For example, the controller 1 includes a microcontroller 11 that inputs and outputs signals and performs calculations, an H-bridge circuit 12, a motor relay 13 that is provided between the H-bridge circuit 12 and the motor 5, and a current detection circuit 14 that is located on the GND side of the H-bridge circuit 12.

The H-bridge circuit 12 is an example of a motor drive circuit that drives the motor 5. The H-bridge circuit 12 drives the motor 5 by driving the built-in FETs according to the drive signals SD1 to SD4 input from the microcomputer 11.

The motor relay 13 is an example of a relay circuit provided between the H-bridge circuit 12 and the motor 5. For example, the motor relay 13 is a semiconductor relay that can cut off (disconnect) the electrical connection between the H-bridge circuit 12 and the motor 5 according to the drive signal SRY input from the microcontroller 11. When the motor relay 13 is turned ON, the H-bridge circuit 12 and the motor 5 are electrically connected, and when the motor relay 13 is turned OFF, the H-bridge circuit 12 and the motor 5 are electrically cut off.

The current detection circuit 14 detects the current flowing through the H-bridge circuit 12. For example, the current detection circuit 14 outputs a positive current value as the current detection value SCU to the microcontroller 11 when a current flows from the H-bridge circuit 12 to the GND side, and outputs a negative current value when a current flows from the GND side to the H-bridge circuit 12 side.

The microcomputer 11 includes a target current calculation processing section 11a, a drive duty calculation processing section 11b, and a relay drive processing section 11c, and is an example of a control section that controls the electric power steering device 100. The target current calculation processing section 11a calculates the target current value TCU of the motor 5 based on a signal input from the outside.

The drive duty calculation processing unit 11b compares the target current value TCU with the current detection value SCU input from the current detection circuit 14, calculates the voltage to be applied to the motor 5 based on the difference, converts it to a drive duty, and outputs it as the FET drive signals SD1 to SD4.

The relay drive processing unit 11c determines whether to turn the motor relay 13 ON (connected) or OFF (disconnected) based on the operating state SST of the electric power steering device 100, the current detection value SCU input from the current detection circuit 14, the power supply voltage SPS applied to the H-bridge circuit 12, and the terminal voltages SM1 and SM2 of the motor 5, and outputs the determination result as a relay drive signal SRY.

The operating state SST indicates a motor drive permitted state in which the motor 5 can be driven, and a motor drive stopped state in which the motor 5 cannot be driven. For example, the operating state SST is calculated inside the microcomputer 11 based on the driver's ignition key operation (not shown) or the operation of a fail-safe (not shown), etc.

FIG. 2 is a block diagram showing an example of the H-bridge circuit 12 and its peripheral circuits.
The FET drive signals SD1 and SD2 input from the microcomputer 11 are input to the

FETs

12a and 12b arranged on the upper side of the H-bridge circuit 12, respectively. The FET drive signals SD3 and SD4 input from the microcomputer 11 are input to the

FETs

12c and 12d arranged on the lower side of the H-bridge circuit 12, respectively.

When driving the motor 5, the H-bridge circuit 12 drives the upper and lower FETs arranged diagonally on the H-bridge circuit 12. For example, when driving the motor 5 by passing a current from the terminal voltage SM1 side to the terminal voltage SM2 side, the microcontroller 11 PWM drives the FET drive signals SD1 and SD4 to control

FETs

12a and 12d to be ON.

FIG. 3 is a diagram showing the operation of the block diagram shown in FIG. 2 when the motor 5 is generating a regenerative current. The FET drive signals SD1 to SD4 control the FETs 12a to 12d to be OFF. When the motor 5 is rotated by an external force, a back electromotive force proportional to the rotation speed of the motor 5 is generated between the terminal voltages SM1 and SM2, resulting in a potential difference. Which of the terminal voltages SM1 and SM2 is higher depends on the direction of rotation of the motor, but FIG. 3 shows the case where the terminal voltage SM2 is higher.

When the rotation speed of the motor 5 increases and the terminal voltage SM2 becomes sufficiently higher than the power supply voltage SPS, a regenerative current is generated through the following path: GND of the H-bridge circuit 12 → FET 12c → motor 5 → motor relay 13 → FET 12b → power supply of the H-bridge circuit 12. When a regenerative current is flowing, the current detection value SCU output by the current detection circuit 14 becomes a negative value, and the terminal voltage of the terminal voltages SM1, SM2 of the motor 5 from which current flows out of the motor 5 becomes higher than the power supply voltage SPS of the H-bridge circuit 12. The relay drive processing unit 11c can determine whether or not a regenerative current is flowing based on these states.

FIG. 4 is a timing chart of the electric power steering device according to this embodiment. In this diagram, the horizontal axis represents time, and the time axis represents the presence or absence of abnormality detection by the microcomputer 11, the operating state SST, the FET drive signals SD1 to SD4, the motor current of the motor 5 (motor current from terminal voltage SM1 to terminal voltage SM2), and the relay drive signal SRY. Here, detection of an abnormality by the microcomputer 11 refers to detection of some kind of abnormality in the electric power steering device 100, such as detection of an abnormality due to a failure of the torque sensor 2 or the current detection circuit 14.

Before the microcomputer 11 detects an abnormality, the operating state SST is the motor drive permitted state, and the FET drive signal SD1 and the FET drive signal SD4 are PWM driven to drive the motor 5 (the FET drive signal SD1 and the FET drive signal SD4 are OFF). In addition, the relay drive signal SRY is ON, and the motor relay 13 is ON.

After the microcomputer 11 detects an abnormality, the fail-safe is activated, the operating state SST becomes a motor drive stop state, and the FET drive signal SD1 and the FET drive signal SD4 turn OFF to stop the drive of the motor 5. After that, when the regenerative current stops flowing, the relay drive signal SRY turns OFF and the motor relay 13 is turned OFF.

Next, we will explain the operation of the relay drive processing in which the relay drive processing unit 11c turns off the motor relay 13 when it determines by two independent means that no regenerative current is flowing. Here, we will explain an example that uses two independent means: a means that uses the current detection value SCU output by the current detection circuit 14, and a means that uses a comparison between the power supply voltage SPS of the H-bridge circuit 12 and the terminal voltage of the motor 5.

FIG. 5 is a flowchart showing an example of a relay driving process according to the present embodiment.
In step S1, the relay drive processing unit 11c judges whether the operation state SST is a motor drive permitted state. If the relay drive processing unit 11c judges that the operation state SST is a motor drive permitted state (step S1: YES), the process proceeds to step S7 and turns on the relay drive signal SRY. On the other hand, if the relay drive processing unit 11c judges that the operation state SST is a motor drive stopped state (step S1: NO), the process proceeds to step S2.

In step S2, the relay drive processing unit 11c takes in the current detection value SCU, the power supply voltage SPS, and the terminal voltages SM1 and SM2 of the motor 5. Then, the process proceeds to step S3.

In step S3, the relay drive processing unit 11c determines whether the current detection value SCU is smaller than a predetermined value Ith (whether a large current is flowing in the negative direction). Here, the predetermined value Ith is preset as a threshold value (e.g., -2A) that can detect the flow of regenerative current. If the relay drive processing unit 11c determines that the current detection value SCU is smaller than the predetermined value Ith (a large current is flowing in the negative direction) (step S3: YES), it determines that a regenerative current is flowing and proceeds to step S7, where the relay drive signal SRY continues to be ON. On the other hand, if the relay drive processing unit 11c determines that the current detection value SCU is equal to or greater than the predetermined value Ith (step S3: NO), it proceeds to step S4.

In step S4, the relay drive processing unit 11c determines whether the terminal voltage SM1 of the motor 5 is higher than the power supply voltage SPS. If the relay drive processing unit 11c determines that the terminal voltage SM1 of the motor 5 is higher than the power supply voltage SPS (step S4: YES), it determines that a regenerative current is flowing and proceeds to step S7, where the relay drive signal SRY continues to be ON. On the other hand, if the relay drive processing unit 11c determines that the terminal voltage SM1 of the motor 5 is equal to or lower than the power supply voltage SPS (step S4: NO), it proceeds to step S5.

In step S5, the relay drive processing unit 11c determines whether the terminal voltage SM2 of the motor 5 is higher than the power supply voltage SPS. If the relay drive processing unit 11c determines that the terminal voltage SM2 of the motor 5 is higher than the power supply voltage SPS (step S5: YES), it determines that a regenerative current is flowing and proceeds to step S7, where it keeps the relay drive signal SRY ON. On the other hand, if the relay drive processing unit 11c determines that the terminal voltage SM2 of the motor 5 is equal to or lower than the power supply voltage SPS (step S5: NO), it determines that a regenerative current is not flowing and proceeds to step S6, where it turns off the relay drive signal SRY.

Here, the signals used in step S3, step S4, or step S5 are independent, so even if there is an abnormality in the signal used in step S3 and an accurate judgment cannot be made, a correct judgment can be made by step S4 or step S5.

Specifically, for example, even if an abnormality occurs in the current detection circuit 14 and the current detection value becomes higher than Ith despite the flow of regenerative current, a correct determination is made by comparing the terminal voltage SM1 of the motor 5 with the power supply voltage SPS in step S4, or by comparing the terminal voltage SM2 of the motor 5 with the power supply voltage SPS in step S5.

Similarly, even if there is an abnormality in the signal used in step S4 or step S5 and an accurate judgment cannot be made, a correct judgment will be made in step S3.

As described above, the electric power steering device 100 according to this embodiment includes an H-bridge circuit 12 (an example of a motor drive circuit) that drives the motor 5, a motor relay 13 (an example of a relay circuit) that can cut off the electrical connection between the H-bridge circuit 12 and the motor 5, and a microcomputer 11 (an example of a control unit) that uses two independent means to determine whether or not a regenerative current is flowing through the motor 5 and controls the motor relay 13 based on the determination result.

As a result, the electric power steering device 100 uses two independent means to determine whether or not a regenerative current is flowing through the motor 5, so even if one means makes an erroneous determination, the other means can make a correct determination, and the H-bridge circuit 12 and the motor 5 can be electrically disconnected at the appropriate timing. Therefore, for example, the electric power steering device 100 can prevent damage to the semiconductor elements that make up the motor relay 13.

For example, if the microcontroller 11 determines by two independent means that no regenerative current is flowing through the motor 5, it controls (turns off) the motor relay 13 to electrically disconnect the H-bridge circuit 12 from the motor 5.

As a result, the electric power steering device 100 uses two independent means to determine that no regenerative current is flowing through the motor 5. Even if one of the means erroneously determines that no regenerative current is flowing when in fact there is, the motor relay 13 will not be turned off while regenerative current is flowing. Instead, the motor relay 13 can be turned off at the appropriate timing to electrically disconnect the H-bridge circuit 12 and the motor 5.

The two independent means also include, for example, a means for determining whether or not a regenerative current is flowing through the motor 5 based on the value of the current flowing through the H-bridge circuit 12.

As a result, the electric power steering device 100 can determine whether or not a regenerative current is flowing through the motor 5 based on the value of the current flowing through the H-bridge circuit 12.

The two independent means also include, for example, a means for determining whether or not a regenerative current is flowing through the motor 5 based on a comparison between the power supply voltage (e.g., power supply voltage SPS) applied to the H-bridge circuit 12 and the terminal voltage of the motor 5 (e.g., terminal voltage SM1 or terminal voltage SM2).

As a result, the electric power steering device 100 can determine whether or not a regenerative current is flowing based on the power supply voltage of the H-bridge circuit 12 and the terminal voltage of the motor 5.

Second Embodiment
Next, a second embodiment will be described.
In the above first embodiment, a configuration was described in which the motor relay 13 is turned OFF when it is determined by two or more independent means that no regenerative current is flowing, but a configuration in which the motor relay 13 continues to be ON when it is determined by two or more independent means that a regenerative current is flowing may also be used.

FIG. 6 is a flowchart showing an example of a relay driving process according to the present embodiment.
In step S11, the relay drive processing unit 11c judges whether the operation state SST is a motor drive permitted state. If the relay drive processing unit 11c judges that the operation state SST is a motor drive permitted state (step S11: YES), the process proceeds to step S17 and turns on the relay drive signal SRY. On the other hand, if the relay drive processing unit 11c judges that the operation state SST is a motor drive stopped state (step S11: NO), the process proceeds to step S12.

In step S12, the relay drive processing unit 11c takes in the current detection value SCU, the power supply voltage SPS, the terminal voltage SM1 of the motor 5, and the terminal voltage SM2 of the motor 5. Then, the process proceeds to step S13.

In step S13, the relay drive processing unit 11c determines whether the current detection value SCU is smaller than a predetermined value Ith (whether a large current is flowing in the negative direction). Here, the predetermined value Ith is preset as a threshold value (e.g., -2A) that can detect that a regenerative current is flowing. If the relay drive processing unit 11c determines that the current detection value SCU is smaller than the predetermined value Ith (a large current is flowing in the negative direction) (step S13: YES), it determines that a regenerative current is flowing and proceeds to step S14. On the other hand, if the relay drive processing unit 11c determines that the current detection value SCU is equal to or greater than the predetermined value Ith (step S13: NO), it determines that a regenerative current is not flowing and proceeds to step S16, where it turns off the relay drive signal SRY.

In step S14, the relay drive processing unit 11c determines whether the terminal voltage SM1 of the motor 5 is higher than the power supply voltage SPS. If the relay drive processing unit 11c determines that the terminal voltage SM1 of the motor 5 is higher than the power supply voltage SPS (step S14: YES), it determines that a regenerative current is flowing and proceeds to step S17, where the relay drive signal SRY continues to be ON. On the other hand, if the relay drive processing unit 11c determines that the terminal voltage SM1 of the motor 5 is equal to or lower than the power supply voltage SPS (step S14: NO), it proceeds to step S15.

In step S15, the relay drive processing unit 11c determines whether the terminal voltage SM2 of the motor 5 is higher than the power supply voltage SPS. If the relay drive processing unit 11c determines that the terminal voltage SM2 of the motor 5 is higher than the power supply voltage SPS (step S15: YES), it determines that a regenerative current is flowing and proceeds to step S17, where it keeps the relay drive signal SRY ON. On the other hand, if the relay drive processing unit 11c determines that the terminal voltage SM2 of the motor 5 is equal to or lower than the power supply voltage SPS (step S15: NO), it determines that a regenerative current is not flowing and proceeds to step S16, where it turns off the relay drive signal SRY.

In this way, in the electric power steering device 100 according to this embodiment, when the microcomputer 11 determines that regenerative current is flowing through the motor 5 by two independent means, it keeps the H-bridge circuit 12 and the motor 5 electrically connected.

As a result, the electric power steering device 100 uses two independent means to determine that a regenerative current is flowing through the motor 5 and turns on the motor relay 13. Therefore, even if one of the means erroneously determines that a regenerative current is flowing when in fact no regenerative current is flowing, the motor relay 13 can be turned off at the appropriate timing to electrically disconnect the H-bridge circuit 12 and the motor 5.

Third Embodiment
Next, a third embodiment will be described.
In the above first and second embodiments, the motor relay 13 is kept ON as long as the judgment condition is satisfied. However, a timer process may be provided to turn the motor relay 13 OFF if the judgment condition is satisfied for a predetermined time. The relay drive process unit 11c according to this embodiment includes a timer for counting the predetermined time. Hereinafter, the count value of the timer is referred to as a timer TMR.

FIG. 7 is a flowchart showing an example of a relay driving process according to the present embodiment.
Step S21 is a processing portion in the relay drive processing according to this embodiment that does not perform the timer processing at the previous stage, and corresponds to the relay drive processing shown in FIG. 5 of the first embodiment or the relay drive processing shown in FIG. 6 of the second embodiment.

In step S22, the relay drive processing unit 11c determines whether the operating state SST is a motor drive permitted state. If the relay drive processing unit 11c determines that the operating state SST is a motor drive permitted state (step S22: YES), it ends the process. On the other hand, if the relay drive processing unit 11c determines that the operating state SST is a motor drive stopped state (step S22: NO), it proceeds to step S23, increments the timer TMR, and proceeds to step S24.

In step S24, the relay drive processing unit 11c compares the timer TMR with a predetermined value Tth and determines whether the timer TMR is smaller than the predetermined value Tth. Here, the predetermined value Tth is set in advance as a threshold value for detecting that the above-mentioned predetermined time has elapsed. If the relay drive processing unit 11c determines that the timer TMR is smaller than the predetermined value Tth (step S24: YES), it ends the processing. On the other hand, if the relay drive processing unit 11c determines that the timer TMR is equal to or greater than the predetermined value Tth (step S24: YES), it proceeds to step S25 and turns off the relay drive signal SRY.

FIG. 8 is a timing chart of the electric power steering device according to this embodiment. In this diagram, the horizontal axis represents time, and the relay drive signal SRY (before timer processing), the operating state SST, the timer TMR, and the relay drive signal SRY (after timer processing) are shown on the time axis.

The relay drive signal SRY (before timer processing) is the output of step S21 in FIG. 7, which is the previous stage of the relay drive processing, and remains ON even after the operating state SST becomes a motor drive stopped state. The timer TMR is incremented after the operating state SST becomes a motor drive stopped state. When the timer TMR becomes larger than a predetermined value Tth, the relay drive signal SRY (after timer processing) is turned OFF.

In this way, in the electric power steering device 100 according to this embodiment, even if the microcomputer 11 determines that a regenerative current is flowing through the motor 5, it controls (turns off) the motor relay 13 after a predetermined time has elapsed to electrically disconnect the H-bridge circuit 12 from the motor 5.

This allows the electric power steering device 100 to impose a time constraint on the continuation of ON of the motor relay 13 based on the determination of the regenerative current, thereby preventing the motor relay 13 from remaining ON for a period longer than necessary.

Fourth Embodiment
Next, a fourth embodiment will be described.
In the above first, second and third embodiments, the current detection value SCU, the terminal voltages SM1 and SM2 of the motor 5 and the power supply voltage SPS of the H-bridge circuit 12 are used to determine whether a regenerative current is flowing, but the rotation speed of the motor 5 may also be used. The rotation speed of the motor 5 can be obtained based on the rotation angle of the motor 5 or the steering angle obtained from the steering angle sensor 4. Here, a method of obtaining the rotation speed based on the steering angle will be described.

FIG. 9 is a block diagram showing a partial configuration of a vehicle equipped with an electric power steering device according to this embodiment. The vehicle 200 is equipped with a steering wheel 6 operated by the driver when steering, a steering shaft 7 that transmits the rotational force of the steering wheel 6, and a reduction gear 8 that connects the steering shaft 7 to the motor 5. The steering angle sensor 4 measures the rotation angle of the steering shaft 7 and outputs it to the microcomputer 11.

The rotation angle of motor 5 is the rotation angle of steering angle sensor 4 multiplied by the gear ratio of reduction gear 8, so if the change in steering angle per unit time is "dθ" and the gear ratio of reduction gear 8 is "n", the change in rotation angle of motor 5 can be calculated as "dθ x n". If the change in rotation angle of motor 5 is the motor angular velocity ω of motor 5 and the back electromotive force constant of the motor is Ke, the back electromotive force Ve generated by the motor is expressed by the following formula.

Ve = Ke × ω
(ω=dθ×n)

The microcontroller 11 calculates the counter electromotive force Ve and determines that a regenerative current is flowing if it is higher than a predetermined value (e.g., 14 V) set based on the rated voltage of the battery.

In this way, in the electric power steering device 100 according to this embodiment, the two independent means described above may include a means for determining whether or not a regenerative current is flowing through the motor 5 based on the rotation speed of the motor 5.

As a result, the electric power steering device 100 can increase the variety of combinations of means used to determine whether or not a regenerative current is flowing by using a means that uses the rotational speed of the motor 5 independent of the means that use the current detection value SCU, the terminal voltage SM1 or SM2 of the motor 5, or the power supply voltage SPS, etc., described in the first embodiment.

For example, the electric power steering device 100 may replace either of the two means, the means using the current detection value SCU and the means using a comparison between the power supply voltage SPS and the terminal voltage SM1 or terminal voltage SM2 of the motor 5, with a means using the rotation speed of the motor 5, or may add a means using the rotation speed of the motor 5 to the two means to provide three means.

In other words, in the electric power steering device 100 according to this embodiment, the microcomputer 11 may use two or more independent means to determine whether or not a regenerative current is flowing through the motor 5, and control the motor relay 13 based on the determination result.

In this way, the electric power steering device 100 detects the regenerative current using multiple independent means, and by combining and determining the results, can turn off the motor relay at the appropriate timing to electrically disconnect the H-bridge circuit 12 and the motor 5. This allows the electric power steering device 100 to prevent damage to the semiconductor elements that make up the motor relay 13, for example.

The above embodiments have been described in detail with reference to the drawings, but the specific configurations are not limited to these embodiments, and each embodiment can be modified or omitted as appropriate.

For example, in the above embodiment, an electric power steering device 100 using a brushed DC motor that is a two-phase H-bridge is described as an example, but it may also be applied to an electric power steering device that uses a brushless DC motor that is a three-phase H-bridge.

In the above embodiment, an example was described in which an H-bridge circuit 12 that controls the drive current to the motor 5 is used as the motor drive circuit that drives the motor 5. However, the H-bridge circuit 12 may be configured as a package with some or all of the components of the microcontroller 11, or a motor drive circuit other than an H-bridge may be used.

In addition, a program for implementing the functions of the microcomputer 11 (an example of a control unit) may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed to perform processing of the microcomputer 11. Note that the term "computer system" here includes hardware such as the OS and peripheral devices.

"Computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. "Computer-readable recording media" also refers to media that dynamically hold a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and media that hold a program for a certain period of time, such as volatile memory inside a computer system that serves as a server or client in such cases. The above program may be one that realizes part of the functions described above, or may be one that can realize the functions described above in combination with a program already recorded in the computer system. The above program may also be stored in a specified server, and distributed (downloaded, etc.) via a communication line in response to a request from another device.

Furthermore, some or all of the functions of the microcontroller 11 may be realized as an integrated circuit such as an LSI (Large Scale Integration). Each function may be individually processed, or some or all of the functions may be integrated into a processor. The integrated circuit method is not limited to LSI, and may be realized using a dedicated circuit or a general-purpose processor. Furthermore, if an integrated circuit technology that can replace LSI appears due to advances in semiconductor technology, an integrated circuit based on that technology may be used.

REFERENCE SIGNS LIST 1 Controller 2 Torque sensor 3 Vehicle speed sensor 4 Steering angle sensor 5 Motor 6 Steering wheel 7 Steering shaft 8 Reduction gear 11 Microcomputer 11a Target current calculation processing section 11b Drive duty calculation processing section 11c Relay drive processing section 12 H-bridge circuit 12a to 12d FET
13 Motor relay 14 Current detection circuit 100 Electric power steering device 200 Vehicle

Claims

a motor drive circuit that drives the motor;
a relay circuit capable of interrupting an electrical connection between the motor drive circuit and the motor;
a control unit that uses two or more independent means to determine whether a regenerative current is flowing through the motor and controls the relay circuit based on the determination result;
An electric power steering device comprising:
The control unit is
When it is determined by the two or more independent means that no regenerative current is flowing through the motor, the relay circuit is controlled to electrically disconnect the motor drive circuit from the motor.
2. The electric power steering device according to claim 1.
The control unit is
When it is determined by the two or more independent means that a regenerative current is flowing through the motor, the motor drive circuit and the motor are maintained in an electrically connected state.
2. The electric power steering device according to claim 1.
The control unit is
even if it is determined that a regenerative current is flowing through the motor, the relay circuit is controlled after a predetermined time has elapsed to electrically disconnect the motor drive circuit and the motor.
4. The electric power steering device according to claim 3.
The two or more independent means include a means for determining whether or not a regenerative current is flowing through the motor based on a current value flowing through the motor drive circuit.
The electric power steering device according to any one of claims 1 to 3.
The two or more independent means include a means for determining whether or not a regenerative current is flowing through the motor based on a comparison between a power supply voltage applied to the motor drive circuit and a terminal voltage of the motor.
The electric power steering device according to any one of claims 1 to 3.
The two or more independent means include a means for determining whether or not a regenerative current is flowing through the motor based on a rotation speed of the motor.
The electric power steering device according to any one of claims 1 to 3.
The motor drive circuit includes an H-bridge circuit that controls a drive current to the motor.
The electric power steering device according to any one of claims 1 to 3.