JPH1029555A - Electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the grounding of a motor terminal or failures in a motor- current detector circuit in a shorter decision period of time without providing any motor-current detector circuit for detecting failures. SOLUTION: A power steering system determines a target value of motor currents of a steering-force assist motor on the basis of the detected value of the steering torque of a steering wheel and rotates the motor so that the motor current reaches the target value to thereby assist the steering force. The power steering system comprises a steering-speed detection means S28, a steering-speed comparison means S30 for comparing the detected value by the steering-speed detection means S28 with a predetermined value, a motor- current comparison means S14 for comparing the difference between the target value and the motor current with a predetermined value, and an abnormality- occurrence detection means S32 for determining the occurrence of abnormality if the detected value is found smaller in the comparison by the steering-speed comparison means S30 as well as if the difference is found larger in the comparison by the motor-current comparison means S14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention determines a target value of a motor current of a steering force assisting motor based on a detected value of a steering torque, and drives and rotates the motor so that the motor current becomes the target value. The present invention relates to an improvement of an electric power steering device for assisting a steering force.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a main configuration of a conventional electric power steering apparatus. In this electric power steering device, a torque detected by a torque sensor 10 that detects a torque applied to a steering shaft (not shown) is:
The data is input to the CPU 12 via the interface circuit 11. The detection output of the vehicle speed sensor 13 for detecting the vehicle speed of the automobile is input to the CPU 12 via the interface circuit 14. The relay control signal output from the CPU 12 is input to the relay drive circuit 15,
Is a fail-safe relay 15a according to a relay control signal.
Is turned on or off.

[0003] In the CPU 12, a motor control signal is created in accordance with the vehicle speed and the detected torque, and the motor control signal is input to the PWM control unit 21. The PWM control unit 21
A PWM signal is created according to the motor control signal. This PWM signal switches a pair of Q1 and Q4 or a pair of Q2 and Q3 among the bridge-connected power transistors Q1, Q2, Q3, and Q4 at a required duty factor, and outputs a fail-safe relay 15a from the power supply P. Through the motor M, the motor M is rotated in a required rotation direction.

Power transistors Q1, Q2, Q3, Q
Bridge circuit consisting of 4 and fail-safe relay 15
A resistor R2 and a resistor R1 for current detection are connected between a and the bridge circuit and the ground terminal, respectively.
The voltages across the resistors R2 and R1 are input to the motor current detection circuit 20 and the motor current detection circuit 17, respectively. The detection outputs of the motor current detection circuits 20 and 17 are C
Input to PU12. The detection output of the motor current detection circuit 17 is used to control the rotation of the motor M, and the detection output of the motor current detection circuit 20 is used for failure detection.

In such an electric power steering apparatus, when the terminal of the motor M is grounded or the motor current detecting circuit 17 is out of order, the current actually flowing through the motor M is maintained when the steering wheel is maintained. Motor current detection circuit 1
The motor current value detected by 7 becomes smaller. When a ground fault occurs at the terminal of the motor M, almost no current flows through the resistor R1, and the detection value of the motor current detection circuit 17 decreases.
At this time, since the detected motor current value is smaller than the target value of the motor current, the motor drive voltage is increased (increase the duty factor of the PWM signal) so as to match the target value.

[0006] When the motor drive voltage is increased, a current larger than the target value flows to the motor, resulting in excessive assist.
The steering torque decreases. When the steering torque decreases,
The target value of the motor current decreases, the motor drive voltage decreases, and the current flowing through the motor decreases. When the current flowing through the motor decreases, the assist becomes insufficient and the steering torque increases. When the steering torque increases, the target value of the motor current increases, but the motor current value detected by the motor current detection circuit 17 is small. Therefore, the motor drive voltage is increased in order to match the target value. By repeating the above, the steering wheel vibrates.

Therefore, in this electric power steering apparatus, a motor current detection circuit 20 for detecting a failure is provided, and a difference between a detection value of the motor current detection circuit 20 and a detection value of the motor current detection circuit 17 is larger than, for example, 20A. Then, it is determined that the terminal of the motor M has been grounded or the motor current detection circuit 17 has failed, and the fail-safe relay 1
5a was turned off, and assistance to the steering wheel was stopped.

[0008]

However, the provision of a motor current detection circuit for detecting a failure has been a factor of increasing the parts cost and manufacturing cost of the electric power steering apparatus. Therefore, except for the motor current detection circuit for failure detection, if the difference between the target value and the detection value of the motor current detection circuit 17 becomes larger than, for example, 20 A,
It is conceivable to determine that a failure has occurred. However, the reason why the detection value becomes smaller than the target value is that even when the vehicle is suddenly steered, the current may be difficult to flow through the motor due to the back electromotive force of the motor. There was a problem to take.

As a technique related to such a problem, a motor drive disclosed in Japanese Patent Application Laid-Open No. 63-180567 is considered to determine an abnormality when a difference between a motor command current value and an actual current value is equal to or more than a predetermined value. Power steering control device,
There is an electric power steering apparatus described in JP-A-6-298104, which determines a ground fault on the cold side of a motor based on a motor command current value, a PWM command value, a motor terminal voltage, and a motor current value. However, the former motor-driven power steering control device does not consider the problem of the back electromotive force of the motor, and the latter electric power steering device requires a means for detecting the motor terminal voltage.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a ground fault at a motor terminal or a motor current detection circuit in a short determination time without providing a motor current detection circuit for failure detection. It is an object of the present invention to provide an inexpensive electric power steering device capable of detecting a failure of a vehicle.

[0011]

An electric power steering apparatus according to the present invention determines a target value of a motor current of a steering force assisting motor based on a detected value of a steering torque of a steering wheel. In the electric power steering apparatus that rotationally drives the motor and assists a steering force, a steering speed detecting unit that detects a steering speed,
A steering speed comparison unit that compares a detection value of the steering speed detection unit with a predetermined value, a motor current comparison unit that compares a difference between the target value and the motor current with a predetermined value, and a comparison result of the steering speed comparison unit Is characterized by comprising abnormality occurrence detection means for detecting the occurrence of an abnormality when the detected value is smaller and the comparison result of the motor current comparison means is larger than the difference.

In this electric power steering apparatus, the comparison result of the steering speed comparison means is smaller than the detection value of the steering speed detection means, and the comparison result of the motor current comparison means is smaller than the difference between the target value and the motor current. Is larger, the abnormality occurrence detecting means detects the occurrence of the abnormality.

For example, when a ground fault at the motor terminal occurs among abnormalities such as a ground fault at the motor terminal and a failure in the motor current detection circuit, the motor current flows to the ground fault side, and the detected value is deviated from the target value. Although it becomes small, this is because even at the time of sudden steering, it becomes difficult for the current to flow to the motor due to the back electromotive force of the motor,
The same thing can happen and it is indistinguishable. However, the current becomes difficult to flow to the motor due to the back electromotive force of the motor at the time of sudden steering, that is, when the rotation speed of the motor is high. Therefore, by providing a condition that the rotation speed of the motor, that is, the steering speed is smaller than a predetermined value,
It is possible to distinguish between a case where a back electromotive force of the motor due to sudden steering is generated and a case where a ground fault occurs at the motor terminal.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing a main configuration of an electric power steering apparatus according to an embodiment of the present invention. In this electric power steering apparatus, a torque detected by a torque sensor 10 for detecting a torque applied to a steering shaft (not shown) is transmitted via an interface circuit 11 to a timer C having a built-in timer TM.
It is input to the PU 12a. The CPU 12a has a built-in fail flag F for indicating a failure state when a failure of any part of the electric power steering device is detected. The output of the vehicle speed sensor 13 for detecting the vehicle speed of the automobile is transmitted to the CPU 1 via the interface circuit 14.
2a.

The relay control signal output from the CPU 12a is input to the relay drive circuit 15,
5 is a fail-safe relay 15 according to the relay control signal.
a is turned on or off. In the CPU 12a, a motor control signal is created according to the vehicle speed and the detected torque, and the motor control signal is input to the PWM control unit 21. PWM
The control unit 21 creates a PWM signal according to the motor control signal. This PWM signal is transmitted to the power transistors Q1, Q2, Q3, and Q4 of the bridge connection.
Or the pair of Q2 and Q3 is switched at a required duty factor, and the power
A current is supplied to the motor M through 5a to rotate the motor M in a required rotation direction.

The detection output of the motor rotation sensor 22 for detecting the rotation angle of the motor M is input to the CPU 12a via the interface circuit 23, and the relative steering angle of the steering wheel is calculated. A resistor R1 for detecting current is connected between a bridge circuit including the power transistors Q1, Q2, Q3, and Q4 and a ground terminal. The voltage across the resistor R1 is input to the motor current detection circuit 17, and the detection output of the motor current detection circuit 17 is input to the CPU 12a.

The operation of the electric power steering apparatus having such a configuration will be described below with reference to the flowchart of FIG. The CPU 12a includes the torque sensor 1
The motor current target value is calculated on the basis of the detected steering torque, and is read and stored in a register (S1).
0). Next, the CPU 12a sets the motor current detection circuit 17
Is read and stored in the register (S12).

Next, the CPU 12a calculates | motor current target value |-| motor current detection value | using the read and stored (S10) motor current target value and the read and stored (S12) motor current detection value. Then, it is determined whether the calculated value is larger than, for example, 20A (S14). When the calculated value is larger than 20A (S14), the counter of the timer TM is incremented by 1 as a failure timer (S1).
6). Next, immediately after the timer starts counting, when the count value of the counter is 1 (S18), the CPU
12a stores the relative steering angle (initial relative steering angle) of the steering wheel calculated from the detection output of the motor rotation sensor 22 at that time in a register (S20) and returns.

When the count value of the counter is not 1 immediately after the start of counting of the failure timer (S18)
If the count value of the counter does not correspond to 5 ms of the failure timer (S24), the process returns. When the count value of the counter corresponds to 5 ms of the failure timer (S2
4) The CPU 12a sets the motor rotation sensor 2 at that time.
The relative steering angle (current relative steering angle) of the steering wheel calculated from the detection output of No. 2 is stored in a register (S26). Next, CPU1
2a is the stored (S20) initial relative steering angle and the stored (S26) current relative steering angle, and is the steering rotation speed Δθ of the steering wheel.
= | Initial relative steering angle−current relative steering angle |
8).

Next, the CPU 12a calculates (S2
8) The steering rotational speed Δθ of the steering wheel is, for example, 0.5 ° / 5 ms.
(= 100 ° / s) (S30), and when the steering rotation speed Δθ of the steering wheel is 0.5 ° / 5 ms or less, (S3
0), assuming that an abnormality, that is, a ground fault at the motor terminal or a failure in the motor current detection circuit has occurred, set the fail flag F (S32) and return. When the fail flag F is set (S32), the CPU 12a outputs a relay control signal to the relay drive circuit 15, and
5 turns off the fail-safe relay 15a by the relay control signal.

The steering rotational speed Δθ of the steering wheel is 0.5 ° / 5 m
If it is larger than s (S30), the calculated value becomes larger than 20A due to the back electromotive force of the motor at the time of sudden steering (S1).
4), it is determined that no abnormality has occurred, the failure timer is cleared (S22), and the process returns. CPU 12
If the calculated value of | motor current target value |-| motor current detection value | is 20 A or less (S14), the failure timer is cleared (S22) and the routine returns. In the above-described embodiment, the steering speed is obtained from the detection output of the motor rotation sensor 22. Thus, the steering speed may be detected.

FIG. 4 is a block diagram showing a main configuration of the electric power steering apparatus disclosed this time. An electric power steering device that determines a target value of the motor current of the steering force assisting motor based on the detected value of the steering torque and drives the motor to rotate so that the motor current becomes the target value to assist the steering force, When returning the steering wheel (steering wheel), a steering wheel return current is passed to the steering force assist motor,
The return control of the steering wheel is performed, and the steering wheel return current is set to 0 when the steering wheel returns to near the neutral position (the steering angle midpoint) where the vehicle goes straight.

Also, even if the handle returns to the neutral position,
Since the vehicle does not stop immediately due to inertial force but stops after taking time to go to and return from the neutral position, convergence control of the handle is also performed in order to quickly converge the handle to the neutral position. For the steering wheel return control and the convergence control, the steering angle midpoint, the absolute steering angle and the steering angular velocity are used.
It is determined from the rotation angle and rotation direction of the steering force assisting motor detected by the motor rotation sensor. This electric power steering device is characterized by having a failure detection function of the motor rotation sensor.

In this electric power steering apparatus, a torque detected by a torque sensor 10 for detecting a torque applied to a steering shaft (not shown) is input to a CPU 12b containing a timer TM via an interface circuit 11. Is done. The CPU 12b has a built-in fail flag F for indicating a failure state when a failure of any part of the electric power steering device is detected. The detection output of the vehicle speed sensor 13 for detecting the speed of the vehicle is input to the CPU 12b via the interface circuit 14. The relay control signal output from the CPU 12b is input to the relay drive circuit 15, and the relay drive circuit 15 turns on or off the fail-safe relay 15a according to the relay control signal. The fail-safe relay 15a is turned off when a failure is found in any part of the electric power steering device.

In the CPU 12b, a motor control signal is created according to the vehicle speed and the detected torque, and the motor control signal is input to the PWM control unit 21. The PWM control unit 21 creates a PWM signal according to the motor control signal. This P
The WM signal is a pair of Q1 and Q4 of the power transistors Q1, Q2, Q3 and Q4 connected in a bridge or Q.
The pair of Q2 and Q3 are switched at a required duty factor, and a current is supplied from the power supply P to the motor M through the fail-safe relay 15a to drive the motor M to rotate in a required rotation direction. The detection output of the motor rotation sensor 22 for detecting the rotation angle of the motor M is output from the interface circuit 2
3, and is input to the CPU 12b to calculate the relative steering angle of the steering wheel.

Power transistors Q1, Q2, Q3, Q
A resistor R1 for current detection is connected between the bridge circuit made of 4 and the ground terminal. The voltage across the resistor R1 is input to the motor current detection circuit 17, and the detection output of the motor current detection circuit 17 is input to the CPU 12b.
The clutch control signal output from the CPU 12b is input to the clutch drive circuit 18, and the output of the clutch control signal
The electromagnetic clutch 19 for transmitting or separating the driving force to the steering mechanism is driven. The current flowing from the power source P to the fail-safe relay 15 a is also branched to the electromagnetic clutch 19 and flows through the clutch drive circuit 18.

FIG. 5 is a block diagram showing the configuration of the interface circuit 23 of the motor rotation sensor 22. The interface circuit 23 inputs the A-phase and B-phase rectangular pulse trains generated in the motor rotation sensor 22 by the rotation of the motor M to the counter 23c via the interfaces 23a and 23b, respectively. The A-phase and B-phase rectangular pulse trains are 1/4 as shown in FIGS.
The period is shifted, and the counter 23c detects the rotation direction based on which of the A-phase and the B-phase is input earlier by １ ／ cycle. For example, FIG. 6 shows that the A-phase is input first and is rotated left. The counter 23c sets the rising edge of the pulse input earlier in any of the A-phase and the B-phase to 0, and thereafter counts the rising and falling edges of both the A-phase and the B-phase to form an 8-bit parallel signal. This is given to the CPU 12b.

The count value of the counter 23c and the positive / negative of the relative steering angle corresponding thereto correspond to the left and right rotation directions of the motor M. In the CPU 12b, when the vehicle speed detected by the vehicle speed sensor 13 is equal to or higher than a predetermined value, the steering torque detected by the torque sensor 10 is equal to or lower than the predetermined value, and the steering angular speed calculated based on the output of the motor rotation sensor 22 is equal to or lower than the predetermined value,
It is determined that the vehicle is traveling straight, and the counter 2 at that time is determined.
The steering angle corresponding to the counter value of 3c is defined as a steering angle midpoint (neutral position).

The operation of the electric power steering apparatus for detecting a failure of the motor rotation sensor 22 will be described below with reference to flowcharts shown in FIGS. 1. Failure detection of motor rotation sensor at initial diagnosis. In this electric power steering apparatus, at the time of initial diagnosis performed when the vehicle starts running, the clutch 19 is turned off, the motor M is rotated by a current of 20A, and the motor M
Perform a lock check to make sure that is not locked.

In this case, when the diagnosis (failure detection) of the motor rotation sensor 22 has not been completed (S40 in FIG. 7), the CPU 12b determines the absolute value of the difference between the counter initial value of the counter 23c and the current counter value at this time. Δθ is calculated (S42). Next, when the calculated (S42) Δθ is, for example, 8 or more (S44), the CPU 12b operates the motor rotation sensor 22 normally, and the counter 23c counts the output pulses of the motor rotation sensor 22 normally. Diagnosis end flag (built-in CPU 12b)
Is set (S46), the timer TM is cleared (reset) (S47), and the routine returns. When the diagnosis end flag is set (S46), the CPU 12b ends the lock check of the motor M.

The CPU 12b calculates (S42) Δθ
Is less than 8 (S44), and the time counted by the timer TM is 1
If 00 ms has not elapsed (S48), the timer T
The counter of M is incremented (S50) and the routine returns. The CPU 12b calculates (S42) Δθ is less than 8 (S44), and the time counted by the timer TM is 100 m
If s has elapsed (S48), the fail flag F
Is set (S52). That is, the motor rotation sensor 2
By the time 100 ms elapse after the start of diagnosis 2, Δ
If θ does not exceed 8, it is determined that a failure has occurred.
The CPU 12b sets the diagnosis end flag (S4).
6) When the diagnosis of the motor rotation sensor 22 is completed (S40), the diagnosis of the motor rotation sensor 22 is not performed again.

2. Failure detection of the motor rotation sensor by monitoring the steering angle midpoint. When the steering angle midpoint is calculated and determined while the vehicle is running (S54), the CPU 12b reads the steering angle midpoint calculation value (S56 in FIG. 8). In this case, if the steering angle midpoint initial value is not stored (S58), it is read (S56).
The steering angle midpoint calculation value is stored as the steering angle midpoint initial value (S6).
6). Next, the CPU 12b calculates the absolute value Δθ of the difference between the steering angle midpoint initial value and the current steering angle midpoint calculation value (S6).
0).

The CPU 12b calculates this (S60)
When Δθ is less than 50 ° (S62), it is determined that the motor rotation sensor 22 is normal, and the timer TM is cleared (S6).
4) Return. The CPU 12b calculates (S6
0) If Δθ is equal to or greater than 50 ° (S62) and the time counted by the timer TM has not passed 100 ms (S6).
8) Then, the counter of the timer TM is incremented (S
70) Return.

The CPU 12b calculates (S60) Δθ
Is greater than or equal to 50 ° (S62), and if the time counted by the timer TM has passed 100 ms (S68), the fail flag F is set (S72). That is, Δθ is 5
If the state of 0 ° or more continues for 100 ms, it is determined that the motor rotation sensor 22 has failed. The CPU 12b
When the fail flag F is set (S72), an alarm lamp (not shown) is turned on. The CPU 12b
When the steering angle midpoint is not determined (S54), the diagnosis of the motor rotation sensor 22 is not performed.

3. Failure detection of motor rotation sensor by monitoring absolute steering angle. The CPU 12b periodically reads the absolute steering angle, which is the steering angle from the steering angle midpoint (FIG. 9, S74).
If it is less than 0 ° (S76), the motor rotation sensor 22 determines that it is normal, clears the timer TM (S78), and returns. The CPU 12b determines that the absolute value of the read absolute steering angle is equal to or greater than 700 ° (S76) (S76), and that the timer TM
If the measured time has not passed 100 ms (S8)
0), the counter of the timer TM is incremented (S
82) Return.

The CPU 12b reads (S74) if the absolute value of the absolute steering angle is equal to or more than 700 ° (S76) and the time counted by the timer TM has passed 100 ms (S74).
80), the fail flag F is set (S84). That is, the state where the absolute value of the absolute steering angle is 700 ° or more is 100
If ms continues, it is determined that the motor rotation sensor 22 has failed. When the fail flag F is set (S84), the CPU 12b turns on an alarm lamp (not shown).

4. Failure detection of motor rotation sensor by monitoring counter value. The CPU 12b periodically reads the vehicle speed of the vehicle detected by the vehicle speed sensor 13 (S86 in FIG. 10).
If it is 0 km / h or more (S88), the counter value of the counter 23c is read (S90). Next, the absolute value Δθ of the difference between the previously read counter value and the currently read counter value is calculated (S92). When the calculated (S92) Δθ is, for example, 2 or more (S94), the CPU 12b determines that the motor rotation sensor 22 is normal, and substitutes the previous value of the previously read counter with the currently read counter (S90) with the present value of the counter. Instead (S96), the timer TM is cleared (S9
8) Return.

The CPU 12b calculates (S92) Δθ
Is less than 2 (S94), and the time counted by the timer TM is 1
0s has not elapsed (S100), the timer TM
Is incremented (S102) and the routine returns. The CPU 12b sets the fail flag F (S104) when the calculated (S92) Δθ is less than 2 (S94) and the timer TM has counted 10 seconds (S100). That is, the vehicle is 10 km / h
When the output value of the motor rotation sensor 22 does not change by a predetermined value or more for 10 seconds while traveling, the motor rotation sensor 22
Judge that it is out of order.

When the fail flag F is set (S104), the CPU 12b sets an alarm lamp (not shown).
Lights up. When the vehicle speed of the vehicle detected by the vehicle speed sensor 13 is less than 10 km / h, the CPU 12b (S8)
8) The timer TM is cleared (S106) and the routine returns, and the diagnosis of the motor rotation sensor 22 is not performed.

5. Failure detection of motor rotation sensor by monitoring steering angular velocity. The CPU 12b reads the steering angle value periodically, for example, every 100 ms (S106 in FIG. 11), and calculates the absolute value Δθ of the difference between the steering angle value and the previously read steering angle value (S10).
8). When the calculated (S108) Δθ is, for example, less than 2000 ° / s (S110), the CPU 12b determines that the motor rotation sensor 22 is normal, and reads the previous value of the previously read steering angle this time (S106). The angle is replaced with the current value (S112) and the process returns.

The CPU 12b calculates (S108) Δ
If θ is equal to or greater than 2000 ° / s (S110), a fail flag F is set (S114). That is, when the steering angular velocity of the steering wheel, which is not normally considered, is calculated from the output value of the motor rotation sensor 22, it is determined that the motor rotation sensor 22 is out of order. As described above, the disclosed electric power steering device can detect the abnormality of the motor rotation sensor 22, and can prevent the vehicle from being driven in a state where the steering wheel return control and the steering wheel convergence control are not operated. .

[0042]

According to the electric power steering apparatus of the present invention, a ground fault at a motor terminal or a failure of a motor current detection circuit can be determined in a short determination time without providing a motor current detection circuit for failure detection. An inexpensive electric power steering device can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electric power steering device according to the present invention.

FIG. 2 is a flowchart showing an operation of the electric power steering device shown in FIG.

FIG. 3 is a block diagram showing a configuration of a conventional electric power steering device.

FIG. 4 is a block diagram showing a main configuration of the disclosed electric power steering device.

FIG. 5 is a block diagram showing a configuration of an interface circuit of the motor rotation sensor.

FIG. 6 is a waveform diagram showing a rectangular pulse train output by a motor rotation sensor.

7 is a flowchart showing the operation of the electric power steering device shown in FIG.

8 is a flowchart showing the operation of the electric power steering device shown in FIG.

9 is a flowchart showing the operation of the electric power steering device shown in FIG.

FIG. 10 is a flowchart showing an operation of the electric power steering device shown in FIG.

11 is a flowchart showing the operation of the electric power steering device shown in FIG.

[Explanation of symbols]

 10 Torque sensor 12a CPU 17 Motor current detection circuit 22 Motor rotation sensor M Motor P Power supply

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazuyasu Yoshida 3-5-8 Minamisenba, Chuo-ku, Osaka City, Osaka Inside Koyo Seiko Co., Ltd.

Claims (1)

[Claims] 1. A method for determining a target value of a motor current of a steering force assisting motor based on a detected value of a steering torque of a steering wheel, rotating the motor so that the motor current becomes a target value, An electric power steering apparatus that performs steering, a steering speed detecting unit that detects a steering speed, a steering speed comparing unit that compares a detection value of the steering speed detecting unit with a predetermined value, and a difference between the target value and the motor current. When the comparison result of the motor current comparison means for comparing with the predetermined value and the steering speed comparison means is smaller than the detected value, and the comparison result of the motor current comparison means is larger, the abnormality is detected. An electric power steering apparatus, comprising: an abnormality occurrence detecting means for detecting occurrence.