JP5554370B2 - Electric power steering device - Google Patents

Description

  The present invention relates to a failure detection of a switching element for driving a motor in an electric power steering apparatus.

  The electric power steering device reduces the steering force by using the driving force of the motor as an auxiliary force. Therefore, if an abnormal assisting force is generated due to a failure of the device, steering may become impossible, which is not preferable for safety. In order to solve such a problem, an invention has been made to ensure safety even if a monitoring unit is provided and the apparatus breaks down. In particular, since the switching element that controls the current supplied to the motor performs on / off control of a large current, the failure detection of this switching element is important.

JP 2001-57012 A

  In the device of Patent Document 1, in order to detect a failure of an FET that is a switching element that controls a motor current, only one FET is turned on and the others are turned off, and the motor terminal voltage is monitored to detect the presence or absence of the failure. Is. In order to detect the ON failure and OFF failure of multiple FETs, it is possible to check whether the FETs are turned on one by one or whether they are actually turned on, or whether they are actually turned off by the motor terminal voltage value. is there.

However, in reality, it may be difficult to detect by the conventional method. For example, when the motor current is controlled, the conventional one-by-one inspection can be performed only at an ultra-high speed that does not affect the motor current control. Further, in a normal FET, stray capacitances (C1 and C2 in FIG. 1) exist between the drain / gate and the gate / source. Further, in many cases, duty control that is quickly turned on and off is performed when the motor current is supplied. In the drive mode in which the upper FET of one arm is duty controlled and the lower FET is turned off, if the stray capacitance (capacitor C1 in FIG. 1) is large and the duty control cycle is early, the gate of the lower FET is open failure In this case, a phenomenon occurs in which the gate voltage of the lower FET gradually increases due to the duty driving of the upper FET, and the lower FET is turned on halfway. If the upper and lower FETs are simultaneously turned on by one arm, a failure occurs in which a large current flows. When such a failure occurs at the start of motor control, it cannot be detected, and the element and circuit may be destroyed.
Therefore, the present invention is capable of detecting a failure of the switching element in advance and starting the check time for whether or not it is the shortest before starting the steady control of the switching element with a simple configuration and method. The main object is to provide a possible electric power steering device.

In addition, there are actually models that have more than four switching elements. Therefore, the conventional apparatus requires a large number of monitoring circuits and CPU input ports, which is disadvantageous in terms of cost and circuit scale.
Accordingly, a secondary object of the present invention is to enable failure detection with a single input port of a CPU for a plurality of switching elements, and to reduce the circuit scale and cost.

An electric power steering apparatus according to the present invention includes a motor that assists the steering force of a steering wheel, and a control unit that controls the current of the motor and drives the motor, and supplies a target motor current to the control unit. In an electric power steering apparatus having a CPU that outputs a control signal and a plurality of switching elements that directly control the motor current in accordance with the control signal,
The control unit includes a monitoring circuit that is provided between each terminal of the motor and the CPU and inputs a voltage obtained by synthesizing the voltage of each terminal of the motor to the CPU.
The CPU drives each of the switching elements at least when the CPU is activated, and checks whether the voltage detected by the monitoring circuit is a predetermined value, thereby checking each switching element of the plurality of switching elements. a that electric power steering apparatus having a initial check function for detecting a failure,
Fail detection of each of the plurality of switching elements is performed before the motor current is steadily controlled according to the control signal,
The monitoring circuit includes a voltage dividing circuit using resistors, and resistors for connecting a voltage dividing point of the voltage dividing circuit and terminals of each phase of the motor, and the CPU has a predetermined voltage at the voltage dividing point. Determining whether each of the plurality of switching elements fails by checking whether or not it is a value based on the voltage at the voltage dividing point;
Each of the switching elements is sequentially driven every predetermined time .

According to the electric power steering apparatus of the present invention, the motor includes a motor that assists the steering force of the steering wheel, and a control unit that controls the current of the motor and drives the motor, and supplies the target motor current to the control unit. In an electric power steering apparatus having a CPU that outputs a control signal so as to perform, and a plurality of switching elements that directly control the motor current according to the control signal,
The control unit includes a monitoring circuit that is provided between each terminal of the motor and the CPU and inputs a voltage obtained by synthesizing the voltage of each terminal of the motor to the CPU.
The CPU drives each of the switching elements at least when the CPU is activated, and checks whether the voltage detected by the monitoring circuit is a predetermined value, thereby checking each switching element of the plurality of switching elements. a that electric power steering apparatus having a initial check function for detecting a failure,
Fail detection of each of the plurality of switching elements is performed before the motor current is steadily controlled according to the control signal,
The monitoring circuit includes a voltage dividing circuit using resistors, and resistors for connecting a voltage dividing point of the voltage dividing circuit and terminals of each phase of the motor, and the CPU has a predetermined voltage at the voltage dividing point. Determining whether each of the plurality of switching elements fails by checking whether or not it is a value based on the voltage at the voltage dividing point;
Since each of the switching elements is sequentially driven every predetermined time, a failure of the switching element can be detected with a simple configuration / method.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows Embodiment 1 of this invention, and is a figure which shows an example of the whole circuit of an electric power steering apparatus. FIG. 2 is a diagram illustrating the first embodiment of the present invention, and is a diagram illustrating an example of an overall schematic function / operation of a CPU in FIG. It is a figure which shows Embodiment 1 of this invention, and is a figure which shows an example of the function and operation | movement of an initial check with a flowchart. It is a figure which shows Embodiment 1 of this invention, and is a figure which illustrates on / off of a switching element with a timing chart. FIG. 5 is a diagram illustrating the first embodiment of the present invention, and is a diagram illustrating a relationship between on / off of a switching element and an ADM capture voltage in a timing chart. It is a figure which shows Embodiment 2 of this invention, and is a figure which shows an example of the function and operation | movement of a 2nd initial check with a flowchart. It is a figure which shows Embodiment 3 of this invention, and is a figure which shows the other example of the whole circuit of an electric power steering apparatus.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to FIGS.
FIG. 1 is an electric circuit diagram of the entire electric power steering apparatus.
In FIG. 1, a control unit (hereinafter referred to as ECU) 1, a power source 2, a vehicle speed sensor 3, a torque sensor 4 for steering a steering wheel, a battery 5, and a motor 6 are mainly configured. In addition, the ECU 1 is an interface (I / F) 12, 13, 3 phase for inputting the outputs of the CPU 10, which is responsible for control and fail-safe, the 5 V power source 11 that generates a 5 V constant voltage from the power source 2, the vehicle speed sensor 3, and the torque sensor 4. A drive unit 14 for driving switching elements (hereinafter referred to as FETs) T1 to T6 constituting an inverter of the bridge, a relay 15 for supplying power for the motor, and a current flowing through the resistors R1 to R3, the motor It is mainly composed of a current detection unit that detects current. The drive unit 14 includes not only the FET drive but also a detected motor current conversion unit and a relay 15 drive unit. In FIG. 1, ◯ indicates a 5V power supply, and □ indicates a 12V power supply.

In the apparatus configured as described above, a duty signal for driving each FET is output to the drive unit 14 so that a target motor current corresponding to the torque and vehicle speed detected by the CPU 10 from time to time is supplied to the drive unit 14, and the actual motor current is resisted. The signals are detected by R1 to resistor R3 and transmitted to A / D ports AD1 to AD3 (hereinafter simply referred to as AD1 to AD3) which are current signal input terminals of the CPU to perform feedback control. Further, when the intended motor current is not flowing, it has a fail-safe function such as interrupting the control of each FET or turning off the relay to cut off the power supply itself according to the failure mode. These are the same as those of the conventional apparatus.

  In the first embodiment, the monitoring circuit 16 detects the respective voltages of three terminals of the motor 6 (each phase terminal of the armature coil is illustrated in the present embodiment) Mu, Mv, and Mw. Has been added. In this monitoring circuit 16, resistors R4, R5, and R6 are connected from the motor terminals Mu, Mv, and Mw, respectively, and these resistors R4 to R6 are connected to the motor terminals Mu, Mv, and Mw opposite to each other. The A / D port (hereinafter simply referred to as a voltage signal input terminal of the voltage dividing point VDP of the CPU 10) is connected to the voltage dividing point VDP obtained by dividing 5V by the resistors R7 and R8. The voltage signal of the voltage dividing point VDP is inputted to (abbreviated as ADM). A diode D16 and a capacitor C16 provided in parallel with the resistor R4 and the resistor R5 are provided in the vicinity of the CPU 10 for smoothing a voltage (voltage at the voltage dividing point VDP) taken into the ADM.

Here, R4 = R5 = R6 = 30 KΩ, R7 = 33 KΩ, and R8 = 20 KΩ. The resistance value of the motor itself is very small compared to the resistance values of the monitoring circuit 16 and can be ignored. However, the inductance component is related to responsiveness and cannot be ignored. First, when all the FETs T1 to T6 are off, the ADM capture voltage is approximately 1.89 V due to the divided voltage of the resistors R7 and R8.
When at least one of the lower arm FETT2, FETT4, and FETT6 is on, the ADM capture voltage is approximately 0.84V.
Further, when the relay 15 is on and at least one of the upper arm FETT1, FETT3, and FETT5 is on, the ADM capture voltage is approximately 5V.
These three kinds of voltages can be considered statically. Further, the voltage does not change instantaneously due to the inductance of the motor, the delay of each element, etc., and it is necessary to consider the delay of a predetermined time in consideration of the variation of each part, the temperature change, etc. Since this delay can be obtained by experiment or calculation, a predetermined time delay can be grasped in advance.

  A failure detection method using the monitoring circuit 16 will be described with reference to FIGS. Both figures are flowcharts showing the software of the CPU 10. FIG. 2 shows the entire software. In FIG. 2, when the power supply 5V is supplied to the CPU 10, the software is started in accordance with the clock of the CPU 10. First, in step S1, each RAM, port, etc. are initialized. Thereafter, in step S2, it is checked whether or not to perform the failure detection of the present invention. This initial check is performed when the CPU is activated. If the initial check is not completed in step S2 (N), an initial check routine is executed in step S3. Details of steps S2 and S3 will be described later with reference to FIG.

  When the initial check is completed (Y), if there is no failure due to the initial check in step S10 (Y), a normal fail check is performed in step S4. If there is a failure due to the initial check in step S10 (N), processing corresponding to the failure is performed in step S8. For example, not only the check of FETT1 to FETT6 but also the failure detection according to the operation mode at that time including the abnormality of the torque sensor 4 and the abnormality of the motor current is performed. When a failure is detected, a flag corresponding to the failure is set. Next, in step S5, it is determined whether or not there are all failures including the initial check failure. If no failure is detected (Y), the motor current is controlled in step S6. Although this process constitutes power steering control, the description is omitted because it is the same as the conventional apparatus. Next, in step S7, since no abnormality has occurred, the fail lamp is turned off.

  On the other hand, if there is a failure (N in step S5), processing corresponding to the failure is performed in step S8. In the case of the severest failure, all FETs are turned off, and the relay 15 is also opened to interrupt the power steering function. Further, depending on the content of the failure, the motor current may be limited or reduced. In order to notify the driver, the fail lamp is turned on in step S9. Each process from step S4 to step S9 is repeated.

Next, the FET defect detection function / operation by the initial check will be described with reference to FIG.
In FIG. 3, the voltage value of ADM is read in step S20.
Next, the FET drive mode is selected using a counter. If the count value of the counter is CT, if CT = 0 (Y), it is checked in step S22 whether the ADM capture voltage value is about 1.89V. When CT = 0, all FETs are off, so if the device is normal, the voltage taken in by the ADM is a divided value by each resistance value.
If the ADM capture voltage value is not 1.89 V (N), it is checked in step S23 if the ADM capture voltage value is 5.0 V. If the ADM capture voltage value is 5V (Y), 5V is detected even though the power is not supplied, so it is stored in step S24 as a motor power failure (upper FET on-fail). .
On the other hand, if the ADM capture voltage value is not 5V (N), it is stored as a motor ground fault (lower FET on-fail) in step S25.

If the ADM capture voltage value is about 1.89 V in step S22 (Y), only the FET T2 is turned on in step S26.
In step S27, 1 is added to the counter value.
Step S28 is a process for waiting for a predetermined time, and not only the processes shown in FIG. 3 are performed for a predetermined time, but also the delay of the detection value due to the FET drive, for example, 10 msec is adjusted in this standby.

If CT is not 0 in step S21 (N), it is checked in step S29 whether CT = 1. If CT = 1 (Y), it is checked in step S30 whether the ADM capture voltage value is about 0.84V. In this routine, only FETT2 should be on, so it is normal that the partial pressure value is low. If the ADM capture voltage value is not 0.84 V (N), it is stored in step S31 as FET T2 being open-failed. On the other hand, if it is normal, the failure is not stored.
Next, in step S32, the control is changed so that only the FET T4 is turned on.

  If CT = 1 is not 1 in step S29 (N), it is checked in step S33 whether CT = 2. As a result of this check, if CT = 2 (Y), it is checked in step S34 whether the ADM capture voltage value is approximately 0.84 V. If the ADM capture voltage value is not 0.84 V (N), step S34 is performed. In S35, FETT4 stores an open failure. In step S36, only FETT6 is turned on.

Similarly, the open failure of the FET T6 is checked in steps S37 to S39.
In step S40, only FETT1 is turned on. Note that the relay (15) in FIG. 1 is closed. Thereafter, in step S41, it is checked whether CT = 4. If CT = 4 (Y), it is checked in step S42 whether the ADM capture voltage value is about 5.0V. If it is normal, only the FET T1 is turned on, so that the divided voltage value of the dividing point VDP should be 5V. If the ADM capture voltage value is not 5V (N), the open failure of the FET T1 is stored in step S42.
In step S43, only FETT3 is changed to ON.

Similarly, in step S44 to step S46, the open failure of the FET T3 is checked, and only the FET T5 is turned on in step S47. Thereafter, an open check of the FET T5 is similarly performed in steps S48 and S49.
Finally, in step S50, all FETs are turned off.

  Here, the counter CT changes from 0 to 6. It is possible to check whether or not the initial check has been completed using this counter. The initial check is in progress until CT = 0 to 5, and the initial check is completed when CT = 6. Therefore, in the initialization of step S1 in FIG. 2, the counter CT is also reset (0), and it can be checked whether the initial check of step S2 has been completed based on the value of the counter CT.

In FIG. 2, an initial check is performed each time the CPU is started. This is an initial check when the ignition switch is turned on when viewed from the vehicle.
Furthermore, even when the engine is operating, an initial check may be performed when it is certain that the vehicle is stopped. For example, the initial check may be performed under the condition that both the vehicle speed sensor 3 and the torque sensor 4 are 0 and the parking brake is applied.

Although the power supply relay 15 has not been described, when the upper FETT1, FETT3, and FETT5 are turned on, not only the relay is turned on, but also the relay is turned on and off when checking when all FETs are turned off. You may check the relay.
As described above, each switching element is driven by a single monitor (ADM) at an initial check every predetermined time, so that a failure (fail) of each FET is detected with a simple additional circuit and a simple processing routine. Is possible.

Here, the point that the check (normal / abnormal determination) of FETT2, FETT4, and FETT6 can be performed in the shortest time will be described. FIG. 4 shows the time of checking FETT2, FETT4, and FETT6. When normal, it is determined at the shortest 10 msec, and when abnormal, it is determined at the maximum 40 msec. As shown in FIG. 5A, in the normal state, for example, when only FETT2 is turned on, it waits for 10 msec, and if the ADM capture voltage value has decreased to 0.84 V at that time, it is determined that the normal state is reached. Move on to the check of FETT4. This 10 msec differs depending on the circuit and can be obtained by experiment or calculation, so that a predetermined time delay can be grasped in advance and the shortest time can be set.
As shown in FIG. 5B, in the event of an abnormality, for example, when the FET T6 is open, the ADM capture voltage value increases to 5 V, and the abnormality determination is confirmed after waiting for a maximum of 40 msec so as not to make an erroneous determination.

Embodiment 2. FIG.
Next, in the second embodiment, a second initial check will be described with reference to FIG. The function of this second initial check is to check while supplying current to the motor. First, before explaining the method, assuming that the maximum current of the motor is 40A, for example, if a large current is supplied, there is a possibility that the handle rotates. Therefore, a current that does not rotate the motor, for example, about 10% of the maximum current is passed. I will check. Assuming that a current of about 4 A is supplied, the rise state is examined in advance by the influence of the inductance included in the motor. That is, the rate of increase of the current value with respect to the current supply time is examined, and for example, in 10 msec, it is grasped that it reaches about 3.5 A in the normal state. Further, considering the temperature change, the variation of the motor coil, and the like, when β1A to β2A are reached after 10 msec, it is regarded as normal. The current values of β1 and β2 are converted into the intake values α1 and α2 of the A / D ports AD1 to AD3.

Based on the above assumption, the second initial check can be inserted after step S27 in FIG. 3 of the first embodiment.
In step S50 of FIG. 3, all the FETs are not turned off, and output is performed so that FETT5 and FETT2 are turned on. In step S28, the process waits for a predetermined time, and in FIG. 4, values AD1 to AD3 are input in step S60. In step S61, it is checked whether or not the counter CT = 7. If it is 7 or more, it can be considered that the second initial check is being performed. When CT = 7 (Y), it is checked whether or not the input value of the input AD1 is between α1 and α2. Since it is after a predetermined time (for example, 10 msec), if it is a normal device, the converted motor current values are α1 to α2. If AD1 is not in the meantime (N), a U-phase failure is stored in step S63. In step S64, FETT1 and FETT4 are turned on.

  If CT = 7 is not satisfied in step S61 (N), it is checked in step S65 whether CT = 8. If CT = 8 (Y), it is checked in step S66 whether the AD2 capture value falls between α1 and α2. If the AD2 fetch value is not between α1 and α2 (N), the failure of the V-phase system is stored in step S67 and the check process is forcibly terminated. In the case of (Y), the pair of FETT3 and FETT6 is turned on in step S68.

  Similarly, in step S69, the AD3 capture value is checked. If AD3 is not between α1 and α2 (N), a failure of W-phase failure is stored in step S70. With this series of processing, current is passed through the all-phase windings and the FETs, so that all the FETs are turned off as the check processing is completed in step S71.

  The second initial check is completed by the processing as described above. As a result, each element and motor is checked by flowing a current larger than that of the first embodiment, so that even in another mode, such as a failure mode, can be detected in advance. Also, the initial check in step S2 of FIG. 2 ends with CT = 10 because the second initial check is inserted. The initial check and the second initial check in the first embodiment can perform the same time management and equivalent step management, and also have the effect of suppressing software waste. Note that the motor current detection circuits and AD1 to AD3 are not circuits added for the second initial check, but are circuits that have been conventionally used for power steering control.

  Although the FET is continuously turned on for a predetermined time when the current is supplied, it can be replaced with the same duty control as that used in normal power steering control. In addition, the current supply is performed by selecting two phases from the three-phase winding, but the present invention is not limited to two phases, and a method of sequentially controlling all three phases may be used. Further, although one of the CPU input terminals AD1 to AD3 is selected, this is not limited to one, and an improved method such as checking a detected value in which no current is flowing may be used.

  Furthermore, fail detection can be performed by monitoring the ADM in the first embodiment by using the FET drive mode in the second embodiment. In this case, the ADM can be monitored and checked at a time earlier than the time delay until the predetermined current flows.

Embodiment 3 FIG.
Next, Embodiment 3 will be described with reference to FIG. The difference from FIG. 1 is that motor relays RY1 to RY3 are inserted between the FETs T1 to FET6 and the motor 6. The motor relays RY1 to RY3 are controlled by signals from the CPU 10, respectively. Although illustrated as an electronic relay using FETs in FIG. 7, it may be a mechanical relay having a contact like the relay 15. Moreover, although the motor relay was inserted in all the motor terminals, it is not necessary to insert it in all.

  In FIG. 7, the motor terminals are at positions of Mu, Mv, and Mw, and the voltage at each motor terminal is detected by the monitoring circuit 16. The checking method in the CPU 10 is almost the same as that shown in FIGS. 3 and 6, but it is possible to add a function of checking the open / closed states of the motor relays RY1 to RY3 together when checking the FETs. Specifically, when the upper stage FETT1, FETT3, and FETT5 are driven, each motor relay is opened and further closed to check the motor terminal voltage, thereby using the same processing routine as in the first embodiment. Can be implemented.

  As described above, even in a system in which a motor relay is provided, the motor relay can be checked by the same circuit and the same time management as the FET failure check.

As described above, the first to third embodiments have the following technical features.
A motor for assisting the steering force of the steering wheel, and a control unit for controlling the current of the motor to drive the motor, and a CPU for outputting a control signal to supply a target motor current to the control unit; In the electric power steering apparatus having a plurality of switching elements that directly control the motor current according to the control signal, the control unit is provided with a monitoring circuit between each terminal of the motor and the CPU. The monitoring circuit is connected to each terminal of the motor, detects the motor terminal voltage, and then is synthesized into a single signal and input to the CPU. The CPU at least activates the switching element when the CPU is activated. By driving each, the voltage detected by the monitoring circuit after a predetermined time becomes a predetermined value Has an initial check function to check whether or not going on.
There are two or more motor terminals, each connected with a resistor, and the other end of these resistors is connected to one place and connected to an intermediate point divided between the power source and the ground with a predetermined resistance value. Input to the A / D port of the CPU.
The initial check of the CPU has means for driving each switching element in turn at predetermined time intervals and determining whether or not the switching element is faulty from the detected voltage.
The control unit has a current detection circuit for detecting the motor current, drives each switching element so as to supply a current that does not rotate the motor at the initial check of the CPU, and the motor current detected after a predetermined time is predetermined. It has a second initial check function for checking whether or not it is within the range.
The CPU checks the presence / absence of a failure collectively from the failure detected during the initial check and the failure detected during power steering control, and takes measures when a failure is detected.
A motor relay is arranged between the plurality of switching elements and the motor terminal, and the CPU outputs a signal for controlling the opening and closing of the motor relay, and when driving each switching element in turn in the initial check, The motor terminal voltage is checked according to the control signal.

The first to third embodiments also have the following technical features from a different point of view.
A motor for assisting the steering force of the steering wheel, and a control unit for controlling the current of the motor to drive the motor, and a CPU for outputting a control signal to supply a target motor current to the control unit; In the electric power steering apparatus having a plurality of switching elements that directly control the motor current according to the control signal, the control unit is provided between each terminal of the motor and the CPU. Whether the voltage detected by the monitoring circuit is a predetermined value by driving each of the switching elements at least when the CPU is started up. By checking whether or not each of the plurality of switching elements is An initial check function for detecting a failure of the switching element.
The fail detection of each of the plurality of switching elements is performed before the motor current is constantly controlled according to the control signal.
The monitoring circuit includes a voltage dividing circuit using resistors, and resistors that connect the voltage dividing points of the voltage dividing circuit and the terminals of the motor, respectively, and the CPU is configured such that the voltage at the voltage dividing point is a predetermined value. The failure of each of the plurality of switching elements is detected by checking whether or not it is.
Each of the switching elements is sequentially driven every predetermined time.
The control unit includes a current detection circuit that detects a motor current, drives each switching element so as to supply a current that does not rotate the motor during the initial check of the CPU, and the motor current detected after a predetermined time is A second initial check function is provided for checking whether or not it is within a predetermined range.
The current detection circuit has a plurality of current detection resistors connected between each terminal of the motor and ground, and the control unit has a data current flowing through the current detection resistor within a predetermined range. Check if it is in.
The control unit includes a motor relay connected between the plurality of switching elements and each terminal of the motor, and the CPU outputs a signal for controlling opening and closing of the motor relay, and in the initial check When the switching elements are sequentially driven, the terminal voltage of the motor is checked in accordance with a control signal of the motor relay.

In the present invention, each embodiment can be appropriately modified or omitted within the scope of the invention.
Moreover, in each figure of FIGS. 1-7, the same code | symbol shows the same or an equivalent part.

1 control unit (ECU), 2 power supply,
3 Vehicle speed sensor, 4 Torque sensor,
5 battery, 6 motor,
10 CPU, 11 5V power supply,
12, 13 interface (I / F),
14 drive unit, 15 relay,
16 Monitoring circuit,
AD1, AD2, AD3 Current signal input terminal (CPU A / D port),
ADM voltage signal input terminal (CPU A / D port),
C1, C2 Gate-source stray capacitance,
C16 smoothing capacitor, D16 smoothing diode,
Mu, Mv, Mw Motor 6 terminals,
R1, R2, R3 current detection resistors,
R4, R5, R6 Voltage detection resistors,
R7, R8 resistors for voltage division,
RY1, RY2, RY3 motor relay,
T1, T2, T3, T4, T5, T6 switching element (FET),
VDP partial pressure point.

Claims (5)

A motor for assisting the steering force of the steering wheel, and a control unit for controlling the current of the motor to drive the motor, and a CPU for outputting a control signal to supply a target motor current to the control unit; In an electric power steering apparatus having a plurality of switching elements that directly control the motor current according to the control signal,
The control unit includes a monitoring circuit that is provided between each terminal of the motor and the CPU and inputs a voltage obtained by synthesizing the voltage of each terminal of the motor to the CPU.
The CPU drives each of the switching elements at least when the CPU is activated, and checks whether the voltage detected by the monitoring circuit is a predetermined value, thereby checking each switching element of the plurality of switching elements. a that electric power steering apparatus having a initial check function for detecting a failure,
Fail detection of each of the plurality of switching elements is performed before the motor current is steadily controlled according to the control signal,
The monitoring circuit includes a voltage dividing circuit using resistors, and resistors for connecting a voltage dividing point of the voltage dividing circuit and terminals of each phase of the motor, and the CPU has a predetermined voltage at the voltage dividing point. Determining whether each of the plurality of switching elements fails by checking whether or not it is a value based on the voltage at the voltage dividing point;
The electric power steering apparatus , wherein each of the switching elements is sequentially driven every predetermined time . 2. The electric power steering apparatus according to claim 1, wherein the control unit includes a current detection circuit that detects a motor current of each phase, and supplies a current that does not rotate the motor during the initial check of the CPU. The electric power steering apparatus further comprises a second initial check function for driving each switching element and checking whether or not the motor current of each phase detected after a predetermined time is within a predetermined range . 3. The electric power steering apparatus according to claim 2, wherein the current detection circuit includes a plurality of current detection resistors connected between a terminal of each phase of the motor and a ground, and the control unit includes the control unit An electric power steering apparatus characterized by checking whether or not the motor current of each phase flowing through a current detection resistor is within a predetermined range . 4. The electric power steering apparatus according to claim 1, wherein the CPU collectively determines whether or not a failure has occurred in the failure detected during the initial check and the failure detected during the power steering control. An electric power steering apparatus characterized by performing a check and taking a countermeasure when a failure is detected . 5. The electric power steering apparatus according to claim 1, wherein the control unit includes a motor relay connected between the plurality of switching elements and each terminal of the motor, The CPU outputs a signal for controlling the opening and closing of the motor relay, and checks the terminal voltage of the motor according to the control signal of the motor relay when sequentially driving the switching elements in the initial check. An electric power steering device.

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