Electric power steering device

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

[Technical Field]

[0001] The present disclosure relates to an electric power steering device. [Background technology]

[0002] In conventional electric power steering devices, a semiconductor relay (hereinafter referred to as a "motor relay") provided between the motor and a motor drive circuit (e.g., an H-bridge circuit) that drives the motor calculates the motor back electromotive force and the energy of the regenerative current based on the rotational speed of the motor, and is configured to turn off when the energy of the regenerative current has decreased to the safe operating range of the FET that constitutes the motor relay (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6406406 Summary of the Invention [Problem to be solved by the invention]

[0004] The motor relay is provided to electrically disconnect the motor drive circuit and the motor by turning it off when an abnormality occurs in the electric power steering device. The motor relay is turned off when no regenerative current is flowing to the motor in order to protect the FET that constitutes the motor relay.

[0005] However, if the abnormality occurring in the electric power steering device is due to a failure in a component involved in detecting regenerative current, there is a possibility that the motor relay will be turned off while regenerative current is flowing because it cannot determine that regenerative current is flowing. Alternatively, there is a possibility that the motor relay will continue to be turned on while regenerative current is not flowing because it cannot determine that regenerative current is not flowing. As such, conventional electric power steering devices may not be able to electrically disconnect the motor drive circuit and the motor at the appropriate time.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and one of its objects is to provide an electric power steering device that electrically disconnects a motor drive circuit and a motor at an appropriate timing. [Means for solving the problem]

[0007] The electric power steering device according to the present disclosure includes a motor drive circuit that drives a motor, a relay circuit that can interrupt 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. [Effects of the Invention]

[0008] The electric power steering device according to the present disclosure can electrically disconnect the motor drive circuit and the motor at appropriate timing. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing an example of the configuration of an electric power steering device according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of an H-bridge circuit and its peripheral circuits according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the operation of the motor according to the first embodiment when it generates a regenerative current. [Figure 4]2 is a timing chart of the electric power steering device according to the first embodiment. [Figure 5] 6 is a flowchart showing an example of a relay driving process according to the first embodiment. [Figure 6] 10 is a flowchart showing an example of a relay driving process according to the second embodiment. [Figure 7] 10 is a flowchart showing an example of a relay driving process according to the third embodiment. [Figure 8] 10 is a timing chart of an electric power steering device according to a third embodiment. [Figure 9] FIG. 10 is a block diagram showing a partial configuration of a vehicle equipped with an electric power steering device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. First Embodiment First, the first embodiment will be described.

[0011] Fig. 1 is a block diagram showing an example of the configuration of an electric power steering device according to the present embodiment 1. 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.

[0012] 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.

[0013] 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 arranged on the GND side of the H-bridge circuit 12.

[0014] 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 built-in FETs in accordance with the drive signals SD1 to SD4 input from the microcomputer 11, thereby driving the motor 5.

[0015] 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 in accordance with a drive signal SRY input from the microcomputer 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.

[0016] 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 to the microcomputer 11 as a current detection value SCU when a current flows from the H-bridge circuit 12 to the GND side, and a negative current value when a current flows from the GND side to the H-bridge circuit 12 side.

[0017] The microcomputer 11 includes a target current calculation processing unit 11a, a drive duty calculation processing unit 11b, and a relay drive processing unit 11c, and is an example of a control unit that controls the electric power steering device 100. The target current calculation processing unit 11a calculates a target current value TCU of the motor 5 based on a signal input from the outside.

[0018] 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 into a drive duty, and outputs it as FET drive signals SD1 to SD4.

[0019] 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.

[0020] 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 operation of the ignition key (not shown) or the operation of a fail-safe (not shown), etc.

[0021] 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, respectively, arranged on the upper side of the H-bridge circuit 12. The FET drive signals SD3 and SD4 input from the microcomputer 11 are input to the FETs 12c and 12d, respectively, arranged on the lower side of the H-bridge circuit 12.

[0022] 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 microcomputer 11 controls the FETs 12a and 12d to be ON by PWM driving the FET drive signals SD1 and SD4.

[0023] FIG. 3 is a diagram showing the operation when motor 5 generates a regenerative current in the block diagram shown in FIG. 2. FET drive signals SD1 to SD4 control FETs 12a to 12d to be OFF. When motor 5 is rotated by an external force, a counter electromotive force proportional to the rotation speed of motor 5 is generated between terminal voltages SM1 and SM2, resulting in a potential difference. Which of terminal voltages SM1 and SM2 is higher depends on the direction of rotation of the motor, but FIG. 3 shows the case where terminal voltage SM2 is higher.

[0024] 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 along the path of the 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 and 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 a regenerative current is flowing based on these states.

[0025] 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 whether or not the microcomputer 11 has detected an abnormality, the operating state SST, the FET drive signals SD1 to SD4, the motor current of the motor 5 (the motor current from terminal voltage SM1 to terminal voltage SM2), and the relay drive signal SRY. Here, the abnormality detected by the microcomputer 11 refers to the detection of some kind of abnormality in the electric power steering device 100, such as the detection of an abnormality due to a failure of the torque sensor 2 or the current detection circuit 14.

[0026] Before the microcomputer 11 detects an abnormality, the operating state SST is the motor drive permitted state, and the FET drive signals SD1 and SD4 are PWM-driven to drive the motor 5 (the FET drive signals SD1 and SD4 are OFF). In addition, the relay drive signal SRY is ON, and the motor relay 13 is ON.

[0027] After the microcomputer 11 detects an abnormality, the fail-safe is activated, the operating state SST becomes a motor drive stop state, the FET drive signal SD1 and the FET drive signal SD4 are turned OFF, and the drive of the motor 5 is stopped. After that, when the regenerative current stops flowing, the relay drive signal SRY is turned OFF, and the motor relay 13 is turned OFF.

[0028] Next, we will explain the operation of the relay drive processing unit 11c, which 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 using two independent means: a means using the current detection value SCU output by the current detection circuit 14, and a means using a comparison between the power supply voltage SPS of the H-bridge circuit 12 and the terminal voltage of the motor 5.

[0029] FIG. 5 is a flowchart showing an example of a relay driving process according to this embodiment. In step S1, the relay drive processing unit 11c determines whether the operation state SST is a motor drive permitted state. If the relay drive processing unit 11c determines that the operation state SST is a motor drive permitted state (step S1: YES), the process proceeds to step S7, where the relay drive processing unit 11c turns on the relay drive signal SRY. On the other hand, if the relay drive processing unit 11c determines that the operation state SST is a motor drive stopped state (step S1: NO), the process proceeds to step S2.

[0030] In step S2, the relay drive processing unit 11c receives 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.

[0031] 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 set in advance as a threshold value (for example, -2 A) 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 it continues to turn on the relay drive signal SRY. 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.

[0032] 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, proceeds to step S7, and keeps the relay drive signal SRY 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.

[0033] 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, proceeds to step S7, and 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, proceeds to step S6, and turns off the relay drive signal SRY.

[0034] Here, since the signals used in step S3, step S4 or step S5 are independent, even if the signal used in step S3 has an abnormality and cannot be judged correctly, a correct judgment can be made in step S4 or step S5.

[0035] 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 judgment can be 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.

[0036] Similarly, even if an abnormality occurs in the signal used in step S4 or step S5 and the determination cannot be made correctly, the determination will be made correctly in step S3.

[0037] 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 interrupt 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.

[0038] As a result, the electric power steering device 100 determines whether or not a regenerative current is flowing through the motor 5 by two independent means, so even if one means makes an erroneous determination, the other means can make a correct determination and electrically disconnect the H-bridge circuit 12 from the motor 5 at an 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.

[0039] 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.

[0040] As a result, the electric power steering device 100 determines that no regenerative current is flowing in the motor 5 using two independent means, so 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, and the motor relay 13 can be turned off at the appropriate timing to electrically disconnect the H-bridge circuit 12 and the motor 5.

[0041] The two independent means include, for example, a means for determining whether or not a regenerative current is flowing to the motor 5 based on the value of the current flowing through the H-bridge circuit 12.

[0042] This allows the electric power steering device 100 to determine whether or not a regenerative current is flowing to the motor 5 based on the value of the current flowing through the H-bridge circuit 12.

[0043] 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).

[0044] This allows the electric power steering device 100 to determine, based on the power supply voltage of the H-bridge circuit 12 and the terminal voltage of the motor 5, whether or not a regenerative current is flowing.

[0045] <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.

[0046] FIG. 6 is a flowchart showing an example of a relay driving process according to this embodiment. In step S11, the relay drive processing unit 11c determines whether the operation state SST is a motor drive permitted state. If the relay drive processing unit 11c determines that the operation state SST is a motor drive permitted state (step S11: YES), the process proceeds to step S17, where the relay drive processing unit 11c turns on the relay drive signal SRY. On the other hand, if the relay drive processing unit 11c determines that the operation state SST is a motor drive stopped state (step S11: NO), the process proceeds to step S12.

[0047] In step S12, the relay drive processing unit 11c receives 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.

[0048] 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 set in advance as a threshold value (for example, −2 A) 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 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.

[0049] 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, proceeds to step S17, and keeps the relay drive signal SRY 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.

[0050] 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, proceeds to step S17, and 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, proceeds to step S16, and turns off the relay drive signal SRY.

[0051] In this way, in the electric power steering device 100 according to this embodiment, when the microcomputer 11 determines that a 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.

[0052] As a result, the electric power steering device 100 determines using two independent means that a regenerative current is flowing in 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 no regenerative current is actually 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.

[0053] <Third embodiment> Next, a third embodiment will be described. In the first and second embodiments, the motor relay 13 is kept ON as long as the determination condition is met. However, a timer process may be provided to turn the motor relay 13 OFF if the determination condition is met 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 will be referred to as a timer TMR.

[0054] FIG. 7 is a flowchart showing an example of a relay driving process according to this embodiment. Step S21 is a processing part in which the timer processing at the previous stage in the relay driving process according to this embodiment is not performed, and corresponds to the relay driving process shown in FIG. 5 of the first embodiment or the relay driving process shown in FIG. 6 of the second embodiment.

[0055] In step S22, the relay drive processing unit 11c determines whether the operation state SST is a motor drive permitted state. If the relay drive processing unit 11c determines that the operation state SST is a motor drive permitted state (step S22: YES), the process ends. On the other hand, if the relay drive processing unit 11c determines that the operation state SST is a motor drive stopped state (step S22: NO), the process proceeds to step S23, increments the timer TMR, and proceeds to step S24.

[0056] 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.

[0057] 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 time axis represents the relay drive signal SRY (before timer processing), the operating state SST, the timer TMR, and the relay drive signal SRY (after timer processing).

[0058] The relay drive signal SRY (before timer processing) is the output of step S21 in the first stage of the relay drive processing in Figure 7, and remains ON even after the operating state SST becomes the motor drive stopped state. The timer TMR is incremented after the operating state SST becomes the 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.

[0059] 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, thereby electrically disconnecting the H-bridge circuit 12 from the motor 5.

[0060] This allows the electric power steering device 100 to impose a time constraint on the duration of ON of the motor relay 13 based on the determination of regenerative current, thereby preventing the motor relay 13 from remaining ON for an unnecessarily long period of time.

[0061] <Fourth embodiment> Next, a fourth embodiment will be described. In the 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 rotational speed of the motor 5 may also be used. The rotational speed of the motor 5 can be obtained based on the rotational angle of the motor 5 or the steering angle obtained from the steering angle sensor 4. Here, a method of obtaining the rotational speed based on the steering angle will be described.

[0062] 9 is a block diagram showing a partial configuration of a vehicle equipped with an electric power steering device according to this embodiment. Vehicle 200 includes a steering wheel 6 operated by a 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 a motor 5. A steering angle sensor 4 measures the rotation angle of the steering shaft 7 and outputs the measured value to a microcomputer 11.

[0063] 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 amount of change in steering angle per unit time is "dθ" and the gear ratio of reduction gear 8 is "n," the amount of change in rotation angle of motor 5 can be calculated as "dθ x n." If the amount of 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.

[0064] Ve=Ke×ω (ω=dθ×n)

[0065] The microcomputer 11 calculates the counter electromotive force Ve, and if it is higher than a predetermined value (for example, 14 V) set based on the rated voltage of the battery, determines that a regenerative current is flowing.

[0066] 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 rotational speed of the motor 5.

[0067] 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 described in the first embodiment.

[0068] For example, the electric power steering device 100 may replace either of the two means, namely, 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 rotational speed of the motor 5, or may have three means by adding a means using the rotational speed of the motor 5 to the two means.

[0069] That is, 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.

[0070] In this way, the electric power steering device 100 detects the regenerative current using multiple independent means and combines and determines the detected current to turn off the motor relay at an appropriate timing, thereby electrically disconnecting the H-bridge circuit 12 and the motor 5. This allows the electric power steering device 100 to prevent, for example, damage to the semiconductor elements that make up the motor relay 13.

[0071] Although the embodiments have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and each embodiment can be modified or omitted as appropriate.

[0072] For example, in the above embodiment, the electric power steering device 100 is described as using a brushed DC motor that is a two-phase H-bridge, but the present invention may also be applied to an electric power steering device that uses a brushless DC motor that is a three-phase H-bridge.

[0073] Furthermore, in the above embodiment, an example has been described in which the 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, but the H-bridge circuit 12 may be configured as a package with some or all of the components of the microcomputer 11, or a motor drive circuit other than an H-bridge may be used.

[0074] It should be noted that a program for realizing 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 the processing of the microcomputer 11. Note that the term "computer system" here includes hardware such as an OS and peripheral devices.

[0075] Furthermore, the term "computer-readable recording medium" 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. Furthermore, the term "computer-readable recording medium" also includes devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, and devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. The program may be a program that implements part of the aforementioned functions, or may be a program that can implement the aforementioned functions in combination with a program already stored in the computer system. The program may also be stored on a designated server and distributed (e.g., downloaded) over communication lines in response to requests from other devices.

[0076] Furthermore, some or all of the functions of the microcomputer 11 may be implemented as an integrated circuit such as an LSI (Large Scale Integration). Each function may be implemented as a separate processor, or some or all of the functions may be integrated into a processor. The integrated circuit implementation method is not limited to LSI, and may be implemented using a dedicated circuit or a general-purpose processor. Furthermore, if an integrated circuit implementation technology that can replace LSI emerges due to advances in semiconductor technology, an integrated circuit based on that technology may also be used. [Explanation of symbols]

[0077] 1 Controller 2 Torque Sensor 3 Vehicle speed sensor 4 Steering angle sensor 5 motors 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~12d FET 13 Motor Relay 14 Current detection circuit 100 Electric power steering device 200 vehicles

Claims

1. 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 determines whether a regenerative current is flowing through the motor using two or more independent means and controls the relay circuit based on the determination result; An electric power steering device comprising:

2. The control unit 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.

3. The control unit 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 kept electrically connected.

2. The electric power steering device according to claim 1.

4. The control unit 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 from the motor.

4. The electric power steering device according to claim 3.

5. The two or more independent means include a means for determining whether or not a regenerative current is flowing to the motor based on a current value flowing in the motor drive circuit. The electric power steering device according to any one of claims 1 to 3.

6. 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.

7. The two or more independent means include a means for determining whether or not a regenerative current is flowing through the motor based on the rotation speed of the motor. The electric power steering device according to any one of claims 1 to 3.

8. 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.

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