JP4166141B2 - Electric power steering device - Google Patents

Description

  In the present invention, when the steering wheel is further rotated at the maximum rudder angle position (hereinafter referred to as “lock-end steering”), or when the steering wheel is turned in a state where steering of the steered wheels is restricted ( The present invention relates to an electric power steering device that prevents overheating of the electric motor or loss of power consumption that occurs when the rotation of the electric motor for power assist is stopped (hereinafter referred to as “when steering restraint is maintained”).

  The conventional power steering apparatus shown in FIG. 8 has a bridge circuit 2 connected to a three-phase AC brushless electric motor 1. The bridge circuit 2 includes U-phase FETs 10 and 11, V-phase FETs 12 and 13, and W-phase FETs 14 and 15, and the FETs 10 to 15 are turned on and off to control the electric motor 1 for power assist. Is supplied with a predetermined control current.

A PWM drive circuit 3 and a power supply 4 are connected to the bridge circuit 2, and a duty ratio control means 16 is connected to the PWM drive circuit 3.
When a predetermined signal is input from the duty ratio control means 16, the PWM drive circuit 3 generates a PWM drive signal with a duty ratio corresponding to the input signal and outputs the signal to the bridge circuit 2. The bridge circuit 2 controls on / off of the FETs 10 to 15 based on the input PWM drive signal, and specifies a control current to be supplied to the electric motor 1. Based on the control current output from the bridge circuit 2, the electric motor 1 exhibits a predetermined assist force.

The duty ratio control means 16 is connected to an angle sensor 9 for detecting the rotation angle of the electric motor 1 and current sensors 7a and 7b. The rotation angle detected by the angle sensor 9 and the current value detected by the current sensors 7 a and 7 b are input to the duty ratio control means 16.
The duty ratio control means 16 is connected to the second control means 8 storing the limiter current, and the first control means 5 is connected via the second control means 8. The first control means 5 is connected to a torque sensor 6 that detects steering torque.

  The first control means 5 specifies a command current value corresponding to the value of the steering torque detected by the torque sensor 6. When the command current value is equal to or less than the limiter current stored in the second control unit 8, the specified command current value is output to the duty ratio control unit 16 as it is. On the other hand, when the specified command current value is larger than the limiter current, the command current value is limited to this limiter current and output to the duty ratio control means 16. In this way, the duty ratio control means 16 to which the command current value is input from the second control means 8 generates a PWM drive signal that realizes the command current value, and outputs the signal to the PWM drive circuit 3. .

  However, the duty ratio control means 16 is such that the control current detected by the current sensors 7a and 7b is not less than a predetermined value, and the rotational speed of the electric motor 1 obtained by calculation from the detected value of the angle sensor 9 is substantially equal. If it is determined to be 0, the PWM drive signal is controlled in a direction to reduce the control current. The reason for reducing the control current in this way will be described below.

  In the electric power steering device, the steering torque is increased because the steering of the steered wheels is restricted during the lock-end steering and the steering restraint steering, and the steering torque detected at this time is increased. If a large current is directly output to the electric motor 1 based on the above, there is a disadvantage that the electric motor 1 generates heat or a large energy loss occurs.

  Further, at the time of lock end steering or steering restraint holding, rotation of the electric motor 1 is restricted, so that a large current may be supplied to the bridge circuit 2. There is also a disadvantage that the circuit 2 generates heat and the product life of the FET is shortened. Hereinafter, the operation of the bridge circuit 2 when the rotation of the electric motor 1 is restricted will be described.

  As described above, the bridge circuit 2 is composed of the U-phase FETs 10 and 11, the V-phase FETs 12 and 13, and the W-phase FETs 14 and 15. The current value of the sine wave is output in a state where the phase is shifted by 120 ° according to the rotation angle.

  When the position where the rotation of the electric motor 1 is restricted is at the peak position of the command current of any phase, the maximum current value is continuously output in that phase. The fact that the maximum current value continues to be output in this way increases the energy consumption accordingly. Further, since the FET also generates heat when the maximum current value is output, the product life of the FET is shortened.

In particular, when the electric motor is a brushless type, a very large current is output, so that the above inconvenience becomes remarkable. That is, the brushless type electric motor supplies current only to either the high-side FET group a or the lower-side FET group b in the bridge circuit 2 when the rotation is restricted. Therefore, when the rotation of the electric motor is restricted while the current value is in a peak state, the maximum power consumption P1 is expressed by the following equation.
P1 = I ² × R = (2 ^1/2 × A) ² × R = 2A ² R (R is the resistance of the FET)
The reason why the current A is multiplied by the route 2 in the formula P1 is that the effective value is obtained.

On the other hand, when the brushless type electric motor 1 is rotating, current is alternately supplied to the high-side FET group a and the lower-side FET group b of the bridge circuit 2. Therefore, the power consumption P2 is expressed by the following equation.
P2 = I ² × R = (A / 2) ² × R = A ² R / 4 (R is the resistance of the FET)
The reason why the current A is multiplied by (1/2) in the formula P2 is that the current flows alternately to the FET group a on the high side and the FET group b on the lower side.

And when the power consumption P1 and the power consumption P2 are compared,
P2 / P1 = 2A ² R / (A ² R / 4R) = 8
Thus, the maximum power consumption P1 when the rotation of the electric motor 1 is restricted is eight times the power consumption P2 when the electric motor is rotating.
Therefore, when the electric motor 1 is a brushless type, the bridge circuit 2 and the electric motor 1 may be subjected to a very large burden at the time of lock-end steering and steered wheel restraint steering.

  Therefore, in the above-described conventional apparatus, when the current value supplied to the electric motor 1 is equal to or greater than a predetermined value and the rotation speed of the electric motor 1 is substantially 0, it is determined that the motor is overloaded, and the electric motor The supply current to 1 is reduced. By reducing the supply current in this way, it is possible to prevent the bridge circuit 2 and the electric motor 1 from being subjected to a large burden.

Japanese Patent Laid-Open No. 2001-191933

  In the above-described conventional apparatus, when the current value supplied to the electric motor 1 is equal to or greater than a predetermined value and the rotation speed of the electric motor 1 is almost zero, the overload state is determined. The load state may occur at times other than lock end steering and steering restraint holding. For example, when a heavy load is loaded and the vehicle is traveling on a curve with a substantially constant curvature (hereinafter referred to as “when driving with heavy load”), the steering torque increases as the vehicle weight increases. In addition, the current command value based on this steering torque also increases.

  However, at the time of this heavy load turning, the handle is often moved in small increments, and the electric motor 1 also rotates accordingly, so that the rotation speed does not become zero. Therefore, in the conventional apparatus, it is not possible to determine that this heavy load turning is an overload state.

That is, in the conventional apparatus, even if an overload condition occurs, it may not be determined as an overload condition. In this case, a large current is continuously supplied to the electric motor. There have been problems that the motor 1 is overheated and wastes power consumption.
An object of the present invention is to provide an electric power steering apparatus that can reliably detect an overload condition.

  According to a first aspect of the present invention, there is provided a steering condition detecting means for detecting a steering condition such as a steering torque, a rotation angle of the electric motor and a rotation speed of the electric motor, and a steering condition such as a steering torque detected by the steering condition detecting means. First control means for specifying the command current value, second control means for limiting the command current value specified by the first control means based on the limiter current, and the command current value output from the second control means A PWM drive circuit that outputs a PWM drive signal based on the above, a plurality of FETs, a bridge circuit that operates according to a PWM drive signal from the PWM drive circuit, and a control current that is output from the bridge circuit And a limiter current adjusting unit having a storage unit, a calculation unit, and a determination unit is connected to the second control unit. The calculation unit of the limiter current adjusting unit calculates a command current average value that is an average per set time of the command current value, and integrates the rotation speed of the electric motor detected or calculated by the steering condition detection unit. The determination unit determines that the command current average value is equal to or greater than the set current value stored in the storage unit, and the angle change amount is equal to or less than the set angle stored in the storage unit. In this case, the calculation unit reduces the limiter current.

  The second invention sets the lower limit value of the limiter current of the electric motor while setting the lower limit value of the electric motor to the lower limit value, and the set time calculated by the calculation unit on the premise of the first invention. When the determination unit determines that the winning steering torque change amount is equal to or larger than the set torque change amount stored in the storage unit, the calculation unit increases the limiter current.

  The third invention is characterized in that the calculation unit reduces or increases the limiter current step by step when the limiter current is decreased or increased, based on the first or second invention.

  According to the first invention, when the determination unit determines that the command current average value is equal to or greater than the set current value stored in the storage unit, and the angle change amount is equal to or less than the set angle stored in the storage unit. In addition, since the arithmetic unit is configured to reduce the limiter current, the control current can be reduced as long as the steering wheel is slightly moved as long as it is within a minute angle range. That is, according to the first aspect of the present invention, the overload state can be detected more accurately, and overheating of the electric motor and loss of power consumption can be reliably prevented.

  According to the second invention, in a state where the control current of the electric motor is decreased to the lower limit value, when the determination unit determines that the change amount of the steering torque is equal to or greater than the set torque change amount stored in the storage unit, Since the calculation unit is configured to increase the limiter current, when the steering wheel is further cut from an overload state, the assist force can be quickly increased, and insufficient assist force can be avoided.

  According to the third aspect of the present invention, when the limiter current is decreased or increased, the calculation unit decreases or increases the limiter current stepwise, so that a sudden change in assist force can be prevented. Therefore, the driver does not feel uncomfortable.

An embodiment of the present invention shown in FIGS. 1 to 7 is shown, but the same constituent elements as those in the prior art will be described with the same reference numerals.
As shown in FIG. 1, a bridge circuit 2 is connected to a three-phase AC brushless electric motor 1. The bridge circuit 2 includes U-phase FETs 10 and 11, V-phase FETs 12 and 13, and W-phase FETs 14 and 15. A control current is supplied.

A PWM drive circuit 3 and a power supply 4 are connected to the bridge circuit 2, and a duty ratio control means 16 is connected to the PWM drive circuit 3.
When a predetermined signal is input from the duty ratio control means 16, the PWM drive circuit 3 generates a PWM drive signal with a duty ratio corresponding to the input signal and outputs the signal to the bridge circuit 2. The bridge circuit 2 controls on / off of the FETs 10 to 15 based on the input PWM drive signal, and specifies a control current to be supplied to the electric motor 1. Based on the control current output from the bridge circuit 2, the electric motor 1 exhibits a predetermined assist force.

The duty ratio control means 16 is connected to an angle sensor 9 for detecting the rotation angle of the electric motor 1 and current sensors 7a and 7b. The rotation angle detected by the angle sensor 9 and the current value detected by the current sensors 7 a and 7 b are input to the duty ratio control means 16.
The duty ratio control means 16 is connected to a second control means 8 for setting a limiter current, and the first control means 5 is connected via the second control means 8. The first control means 5 is connected to a torque sensor 6 that detects steering torque.

  The first control means 5 specifies a command current value corresponding to the value of the steering torque detected by the torque sensor 6. When the command current value is equal to or less than the limiter current set in the second control unit 8, the specified command current value is output to the duty ratio control unit 16 as it is. On the other hand, when the specified command current value is larger than the limiter current, the command current value is limited to this limiter current and output to the duty ratio control means 16. In this way, the duty ratio control means 16 to which the command current value is input from the second control means 8 generates a PWM drive signal that realizes the command current value, and outputs the signal to the PWM drive circuit 3. .

A limiter current adjusting means 17 is connected to the second control means 8. The limiter current adjusting means 17 is for variably controlling the limiter current, and includes an input unit 20, a calculation unit 21, a determination unit 22, a storage unit 23, and an output unit 24.
The input unit 20 is connected to the first control means 5, the torque sensor 6, and an angle sensor 9 that detects the rotation angle of the electric motor 1.

  When the command current value specified by the first control means 5 is input via the input unit 20, the calculation unit 21 obtains an average value per set time of the command current value (hereinafter referred to as “command current average value”). "). The calculation unit 21 obtains the rotational speed of the electric motor 1 by differentiating the angle detected by the angle sensor 9 and integrates the rotational speed of the electric motor 1 with a set time, thereby obtaining the electric motor 1. The amount of change in angle is obtained.

On the other hand, the storage unit 23 stores a set current value, a set angle, a set torque change amount, a limiter current, a set value, a lower limit value, an upper limit value, and the like. These values will be described in detail later. .
The torque sensor 6 and the angle sensor 9 correspond to the steering condition detection means of the present invention.

Next, the operation of the limiter current adjusting means 17 will be described based on the flow of FIGS.
When the command current value specified by the first control unit 5 is input to the input unit 20 of the limiter current adjusting unit 17, the calculation unit 21 obtains an average value per set time of the command current value (hereinafter referred to as the command current value). "Command current average value"). And the determination part 22 determines whether this command current average value is more than the "setting current value" memorize | stored in the memory | storage part 23 (step 1).

  As shown in FIG. 6, the “set current value” refers to, for example, when the output of the current value of the U phase draws a sine wave with a peak at 90 °, with the peak at 90 ° as a boundary. This is a command value within a 45 ° range, that is, a 90 ° range from 45 ° to 135 °. In this angle range of 45 ° to 135 °, since the output current value is large, a large current is output to the electric motor 1 side. The current value at which a large current is output in this way is set as the set current value.

  In this embodiment, the set current value is set in the range of 45 ° to 135 °, but in the range of 30 ° on the left and right of the peak 90 °, that is, in the range of 60 ° to 120 °. A set current value may be set. That is, the set current value can be arbitrarily determined in relation to the output current value.

When the determination unit 22 determines in step 1 that the command current average value is equal to or greater than the set current value, the process proceeds to step 2, and in this step 2, the absolute value of the angle change amount is equal to or less than the set angle. The determination unit 22 determines whether there is any.
The “angle change amount” is a value obtained by integrating the rotation speed of the electric motor 1 within a set time. This “angle change amount” is calculated by the calculation unit 21 based on a detection signal of the angle sensor 9. I am trying to calculate. For example, when the steering wheel is moved from side to side during small turn turning, the electric motor 1 also rotates accordingly. FIG. 7 shows the state at this time. In this graph, the horizontal axis is time, the vertical axis is the rotation speed of the electric motor 1, the rotation speed in the right direction is on the plus side, and the rotation speed in the left direction is on the minus side.

  When the rotation speed of the electric motor 1 is integrated with the set time, the area shown by hatching in FIG. 7 is obtained. This area indicates how much the electric motor 1 has rotated within the set time. ing. Then, when the area in the right rotation direction is plus and the area in the left rotation direction is minus, and the both areas are summed, the total value becomes the change amount of the angle within the set time. When the amount of change in the angle thus obtained is smaller than a predetermined value, the determination unit 22 estimates that the electric motor 1 remains at a substantially constant position. This is because the case where the electric motor 1 stays at a substantially constant position is a case where the electric motor 1 is moving little by little from side to side with respect to a certain position. This is because the area on the side and the area on the minus side are substantially equal, and the amount of change, which is the sum of the area on the plus side and the area on the minus side, is also small.

  On the other hand, when the amount of change in the angle increases, it can be estimated that the electric motor 1 is also rotating significantly. This is because the case where the electric motor 1 is greatly rotated is the case where the electric motor 1 is largely rotated in either the right direction or the left direction. In such a case, the area on the plus side is This is because the area on the minus side is significantly different from the area on the minus side, and the amount of change in angle, which is the total value of the area on the plus side and the area on the minus side, also increases.

  As described above, in this embodiment, the state of the electric motor 1 is determined based on the magnitude of the angle change amount of the electric motor. In this way, even if the electric motor 1 is moving, it can be determined whether the state at that time is moving little by little from side to side with respect to a certain position. Then, when the electric motor 1 is moving little by little from side to side at a certain position, it is assumed that the electric motor 1 is stopped. By considering that the electric motor 1 is stopped, it is assumed that the electric motor 1 remains in the range of the angle of 45 ° to 135 ° shown in FIG. 6, that is, the range in which a large current is output. .

  On the other hand, when the angle change amount is large, for example, when the angle change amount is 90 degrees or more, the electric motor 1 is regarded as rotating. By assuming that the electric motor 1 is rotating, it is assumed that the electric motor 1 has moved out of the area of an angle of 45 ° to 135 ° that outputs a large current.

  In Step 2, when the determination unit 22 determines that the absolute value of the angle change amount calculated by the calculation unit 21 is smaller than the set angle, the process proceeds to Step 3 and the calculation unit 21 performs power-down processing. In the power-down process, the limiter current R is specified in step 100 as shown in FIG. This limiter current R is a value obtained by subtracting a constant decrease value G1 (for example, 5 Arms) from the limiter current at the time of entering the power-down process.

When the limiter current R is specified, the process proceeds to step 101, where the determination unit 22 determines whether the specified limiter current R is equal to or less than a set value (for example, 50 Arms).
If it is determined in step 101 that the limiter current R is larger than the set value, the process proceeds to step 4.

On the other hand, if it is determined in step 101 that the limiter current R is equal to or less than the set value, the process proceeds to step 102. In step 102, the limiter current R is maintained at 50 Arms which is the lower limit value. Then, it progresses to step 4.
The reason why the current value is maintained at the lower limit value (50 Arms) is that the output of the electric motor 1 decreases and the required assist force cannot be obtained if the current value is lowered below the lower limit value. It is for preventing.

  In step 4, the determination unit 22 determines whether or not the limiter current R after the power-down process has reached the lower limit value (50 Arms) stored in the storage unit 23. Then, when the limiter current R is not the lower limit value (50 Arms), that is, when the limiter current R has not reached the lower limit value, the process returns to step 1. If it is determined YES in step 1 and step 2 as described above, the process proceeds to step 4 where power-down processing is performed again. That is, when the current value is reduced by the power-down process, the current value is decreased by a certain decrease value G1. This is because, if the current value is rapidly decreased, the assist force based on the current value is also rapidly decreased, which makes the driver feel uncomfortable.

On the other hand, if the limiter current R has reached the lower limit value in step 4, the process proceeds to step 5.
In step 5, the calculation unit 21 obtains a steering torque change amount per set time based on the detection signal of the torque sensor 9. Then, the determination unit 22 determines whether or not the absolute value of the steering torque change amount is equal to or larger than the set torque change amount stored in the storage unit 23. If the steering torque change amount is equal to or greater than the set torque change amount, the process proceeds to step 6 where power-up processing A is performed. The power-up process A is performed because the assisting force of the electric motor 1 may be insufficient when the steering wheel is turned from the state where the current value is lowered to the lower limit value by the power-down process.

  That is, in the power-down process, the current command value is lowered to the lower limit value (50 Arms) in order to prevent a large current from being continuously output. Since the assist force is low, there is a risk that the assist force is insufficient and the driver is burdened.

Therefore, if it is determined in step 5 that the set amount of change in steering torque per time is greater than or equal to the set torque, the process proceeds to step 6 where the calculation unit 21 performs the power-up process A and the limiter current R is calculated. I try to increase it.
The power-up process A will be specifically described. As shown in FIG. 4, the limiter current R is specified at step 200. The limiter current R is a value obtained by adding a constant addition value G2 to the limiter current at the time of entering the power-up process A, that is, the limiter current R decreased in step 3 above.

  When the limiter current R is specified in this way, the process proceeds to step 201, where the determination unit 22 determines whether or not the limiter current R is greater than or equal to a set value (for example, 65 Arms). If it is determined in step 201 that the limiter current R is smaller than the set value of 65 Arms, the process proceeds to step 7.

  On the other hand, if it is determined in step 201 that the limiter current R is 65 Arms or more, the process proceeds to step 202. In step 202, the limiter current is maintained at the upper limit of 65 Arms, and the process proceeds to step 7. The reason why the limiter current R is kept at the upper limit value is that it is sufficient in the power-up process A if it is possible to produce an output sufficient to avoid an insufficient assist force when the steering wheel is turned.

In step 7, the determination unit 22 determines whether or not the limiter current R after the power-up process A is the upper limit value (65 Arms). Then, when the limiter current R has reached the upper limit value, the process returns to Step 1, but when the limiter current R has not reached the upper limit value, the process returns to Step 6. In step 6, the power-up process A is performed again, and the limiter current R is increased by the added value G2.
That is, in the power-up process A, even when the limiter current R is increased, the assist force is prevented from changing abruptly by gradually increasing the current value.

  By the way, in the said conventional apparatus, although supply current was controlled based on the rotational speed of the electric motor 1, since the electric motor 1 operate | moves based on the steering torque detected by the torque sensor 6, When the steering torque is input, that is, when the torsion bar is twisted by turning the handle, the electric motor 1 does not rotate. Therefore, in the conventional device that controls the supply current based on the rotation speed of the electric motor 1, a response delay occurs when the supply current is reduced to return to the normal state, and the steering feeling is deteriorated. There was a problem.

  On the other hand, in the above embodiment, the supply current is increased based on the steering torque. Therefore, the responsiveness is improved by the time taken until the electric motor 1 rotates, and the deterioration of the steering feeling is prevented. be able to.

On the other hand, when the determination unit 22 determines in step 1 that the absolute value of the average current command value is less than the set current command value, or in step 2, the determination unit 22 determines that the absolute value of the angle change amount is greater than the set angle. If it is determined that the value is larger, the process proceeds to step 8 where the power-up process B is performed in the calculation unit 21.
In this power-up process B, the limiter current at the time of entering this power-up process B is increased. That is, as shown in FIG. 5, in step 300, the limiter current R is specified. The limiter current R is a value obtained by adding a constant addition value G3 (for example, 6 Arms) to the limiter current immediately before entering the power-up process B.

When the limiter current R is specified, the process proceeds to step 301, where the determination unit 22 determines whether or not the limiter current R is greater than or equal to a set value (for example, 80 Arms).
If it is determined in step 301 that the limiter current R is smaller than the set value, the process proceeds to step 9.

If it is determined in step 301 that the limiter current R is greater than or equal to the set value, the process proceeds to step 302. In step 302, the limiter current R is maintained at the upper limit of 80 Arms, and the process returns to step 1.
The reason why the current value is maintained at the upper limit value (80 Arms) is that energy loss occurs when the current value is made larger than the upper limit value.

  On the other hand, if it is determined NO in step 1 or step 2, the process proceeds to step 8 where the power-up process B is performed again. That is, even when the current value is increased by the power-up process B, the current value is increased by a certain amount of addition value G3. This is because if the current value is rapidly increased, the assist force based on the current value also increases rapidly, which gives the driver a sense of incongruity.

  Although the limiter current R is controlled as described above, the limiter current R controlled in this way is sampled at a predetermined interval, and the limiter current R is output to the second control unit 8. ing. Therefore, the second control unit 8 controls the current value output to the duty ratio control means 16 based on the limiter current R at the time of sampling.

According to the above embodiment, when the command current average value is equal to or greater than the set current command value, and the angle change amount that is the integral value of the rotation speed of the electric motor is equal to or less than the set angle, the control means 5 The command value to the electric motor is reduced.
Therefore, even when the driver moves the steering wheel to the left and right during heavy load turning, if the amount of change in angle is small, it can be determined that the vehicle is overloaded. That is, according to this embodiment, the overload state can be detected more accurately. If the control current supplied to the electric motor 1 is reduced by accurately determining the overload state in this way, overheating of the electric motor 1 and waste of power consumption can be reliably prevented.

Further, since the control current supplied to the electric motor 1 is returned to the normal control state when the amount of change in angle, which is an integral value of the rotational speed of the electric motor 1, exceeds the set angle, the rotational speed is restored. Compared to the above-described conventional example that is controlled based on the above, a response delay is less likely to occur when returning from the power-down state to the normal control state. Since response delay is unlikely to occur in this way, it is possible to prevent the steering feeling from deteriorating when returning to the normal control state.
In this embodiment, the rotational speed of the electric motor 1 is obtained by differentiating the angle detected by the angle sensor 9, but the rotational speed sensor is used instead of the angle sensor 9 to rotate the electric motor 1. You may make it the structure which calculates | requires speed directly.

It is a block diagram of an embodiment. It is a flow of an embodiment. It is a control flow of a power-down process. It is a control flow of the power-up process A. It is a control flow of the power-up process B. It is a graph which shows the relationship between the electric current value of U phase, and a rotation angle. It is a graph which shows the relationship between the rotational speed of a motor, and time. It is a block diagram of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric motor 2 Bridge circuit 3 PWM drive circuit 5 1st control means 6 Torque sensor equivalent to the steering condition detection means of this invention 8 Second control means 9 Angle sensor 10-15 FET equivalent to the steering condition detection means of this invention FET
17 Limiter Current Adjusting Means 21 Calculation Unit 22 Determination Unit 23 Storage Unit

Claims (3)

  Steering condition detection means for detecting steering conditions such as steering torque, rotation angle of the electric motor, and rotation speed of the electric motor, and a command current value is specified according to the steering conditions such as steering torque detected by the steering condition detection means A first control means; a second control means for limiting the command current value specified by the first control means based on a limiter current; and a PWM drive signal based on the command current value output from the second control means. And a bridge circuit that is operated by a PWM drive signal from the PWM drive circuit, and an electric motor that is operated by a control current output from the bridge circuit. The second control means is connected to a limiter current adjusting means having a storage section, a calculation section, and a determination section. The calculation unit of the current adjusting means calculates a command current average value that is an average per set time of the command current value, and integrates the rotation speed of the electric motor detected or calculated by the steering condition detection means to change the angle. While determining the amount, when the determination unit determines that the command current average value is equal to or greater than the set current value stored in the storage unit and the angle change amount is equal to or less than the set angle stored in the storage unit. The electric power steering apparatus, wherein the calculation unit reduces the limiter current.   When the lower limit value of the limiter current of the electric motor is set and the limiter current is reduced to this lower limit value, the steering torque change amount per set time calculated by the calculation unit is the set torque change stored in the storage unit. The electric power steering apparatus according to claim 1, wherein when the determination unit determines that the amount is greater than or equal to the amount, the calculation unit increases the limiter current.   3. The power steering apparatus according to claim 1, wherein the calculation unit decreases or increases the limiter current stepwise when the limiter current is decreased or increased. 4.

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