Electric power steering device

Abstract

This electric power steering device is provided with: a motor drive circuit that drives a motor; a relay circuit capable of cutting off an electrical connection between the motor drive circuit and the motor; and a control unit that uses two or more independent units to determine whether or not the regenerative current flows through the motor, and that controls the relay circuit on the basis of the determination result.

Description

Technical Field

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

[0002] In an existing electric power steering device, a semiconductor relay (hereinafter referred to as a "motor relay") provided between a motor drive circuit (e.g., an H-bridge circuit) that drives the motor and the motor is configured to calculate the motor back electromotive force voltage and the energy of the regenerative current based on the rotational speed of the motor, and is set to be turned off when the energy of the regenerative current drops to a safe operating area of ​​the FET that constitutes the motor relay (e.g., refer to Patent Document 1). Prior art literature Patent Literature

[0003] Patent Document 1: Japanese Patent No. 6406406 Summary of the invention Technical problem to be solved by the invention

[0004] The motor relay is provided so as to be turned off when some abnormality occurs in the electric power steering device, thereby electrically disconnecting the motor drive circuit and the motor. The motor relay is turned off when the regenerative current does not flow through the motor to protect the FET constituting the motor relay.

[0005] However, when the abnormality in the electric power steering device is caused by a fault in a part related to the detection of the regenerative current, it is impossible to determine that the regenerative current is flowing, and the motor relay may be turned off while the regenerative current is flowing. Alternatively, it is impossible to determine that the regenerative current is not flowing, and the motor relay may continue to be turned on while the regenerative current is not flowing. As a result, in the existing electric power steering device, it may be impossible to electrically disconnect the motor drive circuit and the motor at an appropriate timing.

[0006] The present disclosure has been made in view of the above circumstances, and one object thereof is to provide an electric power steering device capable of electrically disconnecting a motor drive circuit and a motor at an appropriate timing. Technical means for solving technical problems

[0007] The electric power steering device involved in the present disclosure includes: a motor drive circuit, which drives the motor; a relay circuit, which can cut off the electrical connection between the motor drive circuit and the motor; and a control unit, which uses more than two independent units to determine whether a regenerative current flows through the motor or not, 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 an appropriate timing. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a block diagram showing a configuration example of the electric power steering device according to the first embodiment. Figure 2 This is a block diagram showing an example of an H-bridge circuit and its peripheral circuits according to the first embodiment. Figure 3 This is a diagram showing the operation of the motor according to the first embodiment when generating a regenerative current. Figure 4 This is a timing chart of the electric power steering device according to the first embodiment. Figure 5 This is a flowchart showing an example of the relay driving process according to the first embodiment. Figure 6 This is a flowchart showing an example of the relay driving process according to the second embodiment. Figure 7 This is a flowchart showing an example of the relay driving process according to the third embodiment. Figure 8 This is a timing chart of the electric power steering device according to the third embodiment. Fig. 9 This 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

[0010] Hereinafter, embodiments will be described with reference to the drawings. <Implementation Method 1> First, embodiment 1 will be described.

[0011] Figure 1 1 is a block diagram showing a configuration example of an electric power steering device according to the first embodiment. Figure 1 The illustrated electric power steering device 100 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 detects the running 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 the 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 microcomputer (microcontroller) 11 that performs signal input and output and calculations, an H-bridge circuit 12 , a motor relay 13 provided between the H-bridge circuit 12 and the motor 5 , and a current detection circuit 14 configured on the GND side of the H-bridge circuit 12 .

[0014] The H-bridge circuit 12 is an example of a motor driving circuit that drives the motor 5. The H-bridge circuit 12 drives the built-in FETs according to the driving signals SD1 to SD4 input from the microcomputer 11, thereby driving the motor 5. 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 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 disconnected.

[0016] The current detection circuit 14 detects the current flowing through the H-bridge circuit 12. For example, when the current flows from the H-bridge circuit 12 to the GND side, the current detection circuit 14 outputs a positive current value as the current detection value SCU to the microcomputer 11, and when the current flows from the GND side to the H-bridge circuit 12 side, the current detection circuit 14 outputs a negative current value as the current detection value SCU to the microcomputer 11.

[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 11 b compares the target current value TCU and the current detection value SCU input from the current detection circuit 14 , calculates the voltage 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 circuit 11c determines whether to turn on (connect) or turn off (disconnect) the motor relay 13 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 voltage SM1 and the terminal voltage SM2 of the motor 5, and outputs the determination result as the relay drive signal SRY. The operating state SST indicates a motor drive permission state in which the motor 5 can be driven, and a motor drive stop state in which the motor 5 cannot be driven. For example, the operating state SST is calculated inside the microcomputer 11 based on the operation of the driver's ignition key (not shown) or the operation of the failsafe function (not shown).

[0021] Figure 2 is a block diagram showing one example of the H-bridge circuit 12 and its peripheral circuits. FET drive signals SD1 and SD2 input from the microcomputer 11 are input to FETs 12a and 12b arranged on the upper side of the H-bridge circuit 12, respectively. FET drive signals SD3 and SD4 input from the microcomputer 11 are input to FETs 12c and 12d arranged on the lower side of the H-bridge circuit 12, respectively.

[0022] When driving the motor 5, the H-bridge circuit 12 drives the upper FET and the lower FET arranged diagonally on the H-bridge circuit 12. For example, when driving the motor 5 by causing a current to flow from the terminal voltage SM1 side to the terminal voltage SM2 side, the microcomputer 11 controls the FET 12a and the FET 12d to be turned on by performing PWM driving on the FET drive signal SD1 and the FET drive signal SD4.

[0023] Figure 3 It is shown in Figure 2 The block diagram shown in FIG. 1 shows the operation of the motor 5 when generating a regenerative current. The FET drive signals SD1 to SD4 control the FETs 12a to 12d to be turned 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 voltage SM1 and the terminal voltage SM2, generating a potential difference. Which of the terminal voltages SM1 and SM2 is higher depends on the direction of rotation of the motor. Figure 3 The case where the terminal voltage SM2 is high is shown in FIG.

[0024] If the rotation speed of the motor 5 increases and the terminal voltage SM2 becomes sufficiently high relative to the power supply voltage SPS, a regenerative current is generated in the path of GND of the H-bridge circuit 12→FET12c→motor 5→motor relay 13→FET12b→power supply of the H-bridge circuit 12. When the regenerative current flows, the current detection value SCU output by the current detection circuit 14 is a negative value, and the terminal voltage SM1 and SM2 of the motor 5 on the side where the current flows out of the motor 5 is higher than the power supply voltage SPS of the H-bridge circuit 12. The relay drive processing unit 11c can determine whether the regenerative current flows through these states. Figure 41 is a timing diagram of the electric power steering device involved in this embodiment. In this figure, the horizontal axis is set to time, and the time axis shows the presence or absence of abnormality detection performed by the microcomputer 11, the operating state SST, the FET drive signals SD1 to SD4, the motor current of the motor 5 (the motor current from the terminal voltage SM1 to the terminal voltage SM2), and the relay drive signal SRY. Here, the abnormality detection performed by the microcomputer 11 refers to the detection of a certain abnormality in the electric power steering device 100, for example, the detection of an abnormality caused by 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 permission state, and the FET drive signals SD1 and SD4 perform PWM drive 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 fault protection is activated, the operating state SST is changed to the 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. Thereafter, when the regenerative current does not flow, the relay drive signal SRY is turned off, and the motor relay 13 is turned off.

[0028] Next, the relay drive processing operation of the relay drive processing unit 11c for turning off the motor relay 13 when it is determined that the regenerative current is not flowing by two independent units will be described. Here, an example of two independent units, a unit using the value of the current detection value SCU output by the current detection circuit 14 and a unit using the comparison between the power supply voltage SPS of the H-bridge circuit 12 and the terminal voltage of the motor 5, will be described.

[0029] Figure 5 1 is a flowchart showing an example of the relay driving process according to the present embodiment. In step S1, the relay drive processing unit 11c determines whether the operating state SST is in the motor drive permission state. If the relay drive processing unit 11c determines that the operating state SST is in the motor drive permission state (step S1: Yes), the process proceeds to step S7, and the relay drive signal SRY is turned on. On the other hand, if the relay drive processing unit 11c determines that the operating state SST is in the motor drive stop state (step S1: No), the process proceeds to step S2.

[0030] In step S2, the relay drive processing unit 11c acquires the current detection value SCU, the power supply voltage SPS, and the terminal voltage SM1 and the terminal voltage 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 the specified value Ith (whether it flows significantly in the negative direction). Here, the specified value Ith is pre-set as a threshold value (for example, -2A) that can detect the flow of regenerative current. When the relay drive processing unit 11c determines that the current detection value SCU is smaller than the specified value Ith (flows significantly in the negative direction) (step S3: Yes), it is determined that the regenerative current is flowing, and the process proceeds to step S7 to continue the conduction of the relay drive signal SRY. On the other hand, when the relay drive processing unit 11c determines that the current detection value SCU is greater than the specified value Ith (step S3: No), the process 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. When 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 is determined that the regenerative current flows, and the process proceeds to step S7 to continue to conduct the relay drive signal SRY. On the other hand, when the relay drive processing unit 11c determines that the terminal voltage SM1 of the motor 5 is lower than the power supply voltage SPS (step S4: No), the process 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. When 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 is determined that the regenerative current is flowing, and the process proceeds to step S7 to continue the relay drive signal SRY. On the other hand, when the relay drive processing unit 11c determines that the terminal voltage SM2 of the motor 5 is lower than the power supply voltage SPS (step S5: no), it is determined that the regenerative current is not flowing, and the process proceeds to step S6 to turn off the relay drive signal SRY.

[0034] Here, the signals used in step S3, step S4 or step S5 are independent. Therefore, even if the signal used in step S3 has an abnormality and cannot be correctly determined, it can be correctly determined in step S4 or step S5.

[0035] Specifically, for example, when an abnormality occurs in the current detection circuit 14 and the current detection value is 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 and the power supply voltage SPS in step S4, or by comparing the terminal voltage SM2 of the motor 5 and the power supply voltage SPS in step S5.

[0036] Likewise, even when the signal used in step S4 or step S5 is abnormal and cannot be correctly determined, it is possible to correctly determine in step S3.

[0037] As described above, the electric power steering device 100 involved in 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), which uses two independent units to determine whether the regenerative current flows through the motor 5 or not, and controls the motor relay 13 based on the determination result.

[0038] Thus, the electric power steering device 100 can determine whether the regenerative current flows through the motor 5 or not by two independent units, so even if one unit makes an erroneous determination, the other unit can make a correct determination, and the H-bridge circuit 12 and the motor 5 can be electrically disconnected at an appropriate timing. Thus, for example, the electric power steering device 100 can prevent the semiconductor element constituting the motor relay 13 from being damaged.

[0039] For example, when the microcomputer 11 determines that the regenerative current does not flow through the motor 5 using two independent units, the microcomputer 11 controls (turns off) the motor relay 13 to electrically disconnect the H-bridge circuit 12 and the motor 5 . Thus, the electric power steering device 100 determines that the regenerative current does not flow through the motor 5 through two independent units. Therefore, even if the regenerative current flows but is mistakenly determined by one unit to be not flowing, the motor relay 13 will not be turned off when the regenerative current flows, and the motor relay 13 can be turned off at an appropriate timing to electrically disconnect the H-bridge circuit 12 and the motor 5.

[0041] The two independent units include, for example, a unit that determines whether the regenerative current flows or does not flow through the motor 5 based on the value of the current flowing through the H-bridge circuit 12 .

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

[0043] In addition, the two independent units include, for example, a unit that determines whether a regenerative current flows through the motor 5 or not based on a comparison of a power supply voltage (e.g., power supply voltage SPS) applied to the H-bridge circuit 12 and a terminal voltage (e.g., terminal voltage SM1 or terminal voltage SM2) of the motor 5.

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

[0045] <Implementation Method 2> Next, embodiment 2 will be described. The above-mentioned embodiment 1 describes the following structure: when more than two independent units determine that the regenerative current is not flowing, the motor relay 13 is turned off, but the following structure can also be adopted: when more than two independent units determine that the regenerative current is flowing, the motor relay 13 continues to be turned on.

[0046] Figure 6 1 is a flowchart showing an example of the relay driving process according to the present embodiment. In step S11, the relay drive processing unit 11c determines whether the operating state SST is in the motor drive permission state. If the relay drive processing unit 11c determines that the operating state SST is in the motor drive permission state (step S11: Yes), the process proceeds to step S17, and the relay drive signal SRY is turned on. On the other hand, if the relay drive processing unit 11c determines that the operating state SST is in the motor drive stop state (step S11: No), the process proceeds to step S12.

[0047] In step S12, the relay drive processing unit 11c acquires 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 the specified value Ith (whether it flows significantly in the negative direction). Here, the specified value Ith is pre-set as a threshold value (for example, -2A) that can detect the flow of regenerative current. When the relay drive processing unit 11c determines that the current detection value SCU is smaller than the specified value Ith (flows significantly in the negative direction) (step S13: Yes), it is determined that the regenerative current is flowing, and the process proceeds to step S14. On the other hand, when the relay drive processing unit 11c determines that the current detection value SCU is greater than the specified value Ith (step S13: No), it is determined that the regenerative current is not flowing, and the process proceeds to step S16 to turn 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. When 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 is determined that the regenerative current flows, and the process proceeds to step S17 to continue to conduct the relay drive signal SRY. On the other hand, when the relay drive processing unit 11c determines that the terminal voltage SM1 of the motor 5 is lower than the power supply voltage SPS (step S14: No), the process 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. When 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 is determined that the regenerative current is flowing, and the process proceeds to step S17 to continue the relay drive signal SRY. On the other hand, when the relay drive processing unit 11c determines that the terminal voltage SM2 of the motor 5 is lower than the power supply voltage SPS (step S15: No), it is determined that the regenerative current is not flowing, and the process proceeds to step S16 to turn off the relay drive signal SRY.

[0051] Thus, in the electric power steering device 100 according to the present embodiment, when the microcomputer 11 determines that the regenerative current flows through the electric motor 5 through the two independent units, the microcomputer 11 continues the electrical connection between the H-bridge circuit 12 and the electric motor 5 .

[0052] Thus, the electric power steering device 100 determines that the regenerative current flows through the motor 5 through two independent units and turns on the motor relay 13. Therefore, even if the regenerative current does not flow and any unit mistakenly determines that the regenerative current flows, the motor relay 13 can be turned off at an appropriate timing to electrically disconnect the H-bridge circuit 12 and the motor 5.

[0053] <Implementation Method 3> Next, implementation mode 3 will be described. In the above-mentioned embodiments 1 and 2, a structure is described in which the motor relay 13 is kept on as long as the judgment condition is satisfied, but a structure may be adopted in which a timer process is provided so that the motor relay 13 is turned off when the predetermined time continues even when the judgment condition is satisfied. The relay drive processing unit 11c involved in this embodiment is provided with a timer for counting the predetermined time. Hereinafter, the timer value of the timer is referred to as the timer TMR.

[0054] Figure 7 1 is a flowchart showing an example of the relay driving process according to the present embodiment. Step S21 is a processing portion of the relay driving process according to this embodiment in which the timer processing is not performed in the previous stage, and is equivalent to the processing of the first embodiment. Figure 5 The relay drive process or embodiment 2 shown in Figure 6 Relay drive processing.

[0055] In step S22, the relay drive processing unit 11c determines whether the operating state SST is in the motor drive permission state. If the relay drive processing unit 11c determines that the operating state SST is in the motor drive permission state (step S22: Yes), the processing ends. On the other hand, if the relay drive processing unit 11c determines that the operating state SST is in the motor drive stop 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 the specified value Tth to determine whether the timer TMR is less than the specified value Tth. Here, the specified value Tth is preset as a threshold for detecting that the above-mentioned specified time has passed. When the relay drive processing unit 11c determines that the timer TMR is less than the specified value Tth (step S24: Yes), the processing ends. On the other hand, when the relay drive processing unit 11c determines that the timer TMR is greater than the specified value Tth (step S24: Yes), the process proceeds to step S25 and the relay drive signal SRY is turned off.

[0057] Figure 8 This is a timing chart of the electric power steering device according to the present embodiment. In this figure, the horizontal axis is 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.

[0058] The relay drive signal SRY (before timer processing) is Figure 7 The output of step S21 in the front stage of the relay drive processing continues to be turned on even after the action state SST changes to the motor drive stop state. The timer TMR is incremented after the action state SST changes to the motor drive stop state. When the timer TMR is greater than the specified value Tth, the relay drive signal SRY (after the timer processing) is turned off.

[0059] Thus, in the electric power steering device 100 according to the present embodiment, even when it is determined that the regenerative current flows through the motor 5 , the microcomputer 11 controls (turns off) the motor relay 13 after a predetermined time has passed to electrically disconnect the H-bridge circuit 12 and the motor 5 .

[0060] Thus, the electric power steering device 100 can set a time limit for continuing the conduction of the motor relay 13 based on the determination of the regenerative current, and thus can prevent the motor relay 13 from continuing the conduction for an unnecessarily long period of time.

[0061] <Implementation Method 4> Next, implementation example 4 will be described. In the above-mentioned embodiments 1, 2, and 3, 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 the regenerative current flows, 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 by the steering angle sensor 4. Here, a method of obtaining based on the steering angle is described.

[0062] Fig. 9 1 is a block diagram showing a partial structure of a vehicle equipped with an electric power steering device according to the present embodiment. The vehicle 200 includes a steering wheel 6 operated by a driver when steering, a steering shaft 7 transmitting the rotational force of the steering wheel 6, and a reduction gear 8 connecting the steering shaft 7 and 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 the motor 5 is a value obtained by multiplying the rotation angle of the steering angle sensor 4 by the gear ratio of the reduction gear 8. Therefore, if the change in the steering angle per unit time is set to "dθ" and the gear ratio of the reduction gear 8 is set to "n", the change in the rotation of the motor 5 is obtained as "dθ×n". If the change in the rotation angle of the motor 5 is set to the motor angular velocity ω of the motor 5 and the back electromotive force constant of the motor is set to Ke, the back electromotive force Ve generated by the motor is as follows.

[0064] Ve=Ke×ω (ω=dθ×n)

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

[0066] Thus, in the electric power steering device 100 according to the present embodiment, the two independent units may include a unit that determines whether the regenerative current flows or does not flow through the electric motor 5 based on the rotation speed of the electric motor 5 .

[0067] Thus, the electric power steering device 100 uses a unit that uses the rotational speed of the motor 5 independently of the unit that uses the current detection value SCU, the terminal voltage SM1 or the terminal voltage SM2 of the motor 5, or the power supply voltage SPS described in Implementation 1, thereby increasing the change in the combination of units used in determining whether the regenerative current is flowing.

[0068] For example, the electric power steering device 100 can replace any one of the two units, namely, a unit using the current detection value SCU and a unit using the comparison between the power supply voltage SPS and the terminal voltage SM1 or the terminal voltage SM2 of the motor 5, with a unit using the rotational speed of the motor 5, or can add the unit using the rotational speed of the motor 5 to the two units to make a total of three units.

[0069] That is, in the electric power steering device 100 according to the present embodiment, the microcomputer 11 can determine whether the regenerative current flows or does not flow through the motor 5 using two or more independent units, and control the motor relay 13 based on the determination result.

[0070] Thus, the electric power steering device 100 detects the regenerative current by using a plurality of independent units and combines them for determination, thereby turning off the motor relay at an appropriate timing and electrically disconnecting the H-bridge circuit 12 and the motor 5. Thus, for example, the electric power steering device 100 can prevent the semiconductor element constituting the motor relay 13 from being damaged.

[0071] As mentioned above, although embodiment is described in detail with reference to drawings, the specific structure is 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 using a two-phase H-bridge, ie, a brushed DC motor is described as an example, but the present invention may also be applied to an electric power steering device using a three-phase H-bridge, ie, a brushless DC motor.

[0073] In addition, in the above-mentioned embodiment, the following example is described: as a motor driving circuit for driving the motor 5, an H-bridge circuit 12 for controlling the driving current to the motor 5 is used, but the H-bridge circuit 12 can be packaged with part or all of the parts of the microcomputer 11, and a motor driving circuit other than the H-bridge can also be used.

[0074] In addition, a program for realizing the functions of the microcomputer 11 (an example of a control unit) may be recorded in a computer-readable recording medium, and the computer system may read and execute the program recorded in the recording medium to perform processing of the microcomputer 11. In addition, the "computer system" referred to here includes hardware such as OS and peripheral devices.

[0075] In addition, "computer-readable recording medium" refers to portable media such as floppy disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into computer systems. In addition, "computer-readable recording medium" may also include media that dynamically maintain programs for a short period of time, such as communication lines when sending programs through networks such as the Internet, telephone lines, and other communication lines, and media that maintain programs for a certain period of time, such as volatile memories inside computer systems that become servers and clients in this case. In addition, the above-mentioned program can be used to implement part of the above-mentioned functions, and the above-mentioned functions can be implemented by combining with programs already recorded in the computer system. In addition, a specified server can store the above-mentioned program, and distribute (download, etc.) the program via a communication line according to requests from other devices.

[0076] In addition, part or all of the functions of the microcomputer 11 can be implemented as an integrated circuit such as LSI (Large Scale Integration). Each function can be implemented as a separate processor, or part or all of them can be integrated together as a processor. In addition, the method of integrated circuitization is not limited to LSI, and it can also be implemented by a dedicated circuit or a general-purpose processor. In addition, when a technology for integrated circuitization that replaces LSI appears due to the progress of semiconductor technology, an integrated circuit based on this technology can also be used. Description of symbols

[0077] 1 Controller 2 Torque sensor 3 Vehicle speed sensor 4 Steering angle sensor 5. Electric Motor 6 Steering wheel 7 Steering axle 8 Reduction gear 11 Microcomputer 11a Target current calculation processing unit 11b Drive duty cycle calculation processing unit 11c Relay drive processing unit 12 H-bridge circuit 12a~12d FET 13 Motor relay 14 Current detection circuit 100 Electric power steering 200 vehicles.

Claims

1. An electric power steering device, It is characterized in that include: a motor drive circuit, the motor drive circuit driving the motor; a relay circuit capable of cutting off the electrical connection between the motor drive circuit and the motor; as well as A control unit that uses two or more independent units to determine whether a regenerative current flows through the motor or not, and controls the relay circuit based on the determination result.

2. The electric power steering device according to claim 1, It is characterized in that When the two or more independent units determine that the regenerative current does not flow through the motor, the control unit controls the relay circuit to electrically disconnect the motor drive circuit from the motor.

3. The electric power steering device according to claim 1, It is characterized in that When it is determined by the two or more independent units that the regenerative current flows through the electric motor, the control unit continues the state in which the motor drive circuit and the electric motor are electrically connected.

4. The electric power steering device according to claim 3, It is characterized in that Even when it is determined that the regenerative current flows through the electric motor, the control unit controls the relay circuit after a predetermined time has elapsed to electrically disconnect the motor drive circuit from the electric motor.

5. The electric power steering device according to any one of claims 1 to 3, It is characterized in that The two or more independent units include a unit that determines whether a regenerative current flows through the motor based on a current value flowing through the motor drive circuit.

6. The electric power steering device according to any one of claims 1 to 3, It is characterized in that The two or more independent units include a unit that determines whether a regenerative current flows or does not flow 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.

7. The electric power steering device according to any one of claims 1 to 3, It is characterized in that The two or more independent units include a unit that determines whether a regenerative current flows or does not flow through the motor based on the rotation speed of the motor.

8. The electric power steering device according to any one of claims 1 to 3, It is characterized in that The motor drive circuit includes an H-bridge circuit that controls a drive current to the motor.

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