JP2003019971A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a steering auxiliary characteristic adapted to a load state to steering, and to realize a superior steering feeling by compensating for a lateral difference in steering effort. SOLUTION: The steering direction is detected (S11, and S12), and load state adapting processing is respectively executed on right directional steering and left directional steering (S15, and S13). Thus, a right directional steering time correction factor k- right and a left directional steering time correction factor k- left are determined so as to be respectively adapted to a right directional steering time load state and a right directional steering time load state, and these correction factors are substituted in a correction factor k to thus compensate the lateral difference in the steering effort used by a change with the lapse of time of a system and an individual difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for assisting steering by transmitting a steering assist force generated by an electric motor to a steering mechanism of a vehicle.

[0002]

2. Description of the Related Art An electric power steering device is a device for assisting steering by mechanically transmitting a driving force generated by an electric motor to a steering mechanism of a vehicle by a gear mechanism or the like. In order to obtain a good steering feel, the target current value of the electric motor is set based on the output of the torque sensor that detects the steering torque applied to the steering wheel and the output of the vehicle speed sensor that detects the speed of the vehicle. It has become.

The relationship between the steering torque and the target current value (assist characteristic) is created in advance as an assist table. This assist table is set so that a good steering feeling can be obtained on a dry asphalt road surface which is a standard road surface. An electronic control unit (ECU) for an electric power steering apparatus includes a microcomputer, which includes a memory that stores an assist table and determines a target current value based on the assist table.

[0004]

However, since the assist table is prepared on the assumption of a dry asphalt road surface, when the friction coefficient of the road surface is low (on snow, wet road surface, etc.), the assist becomes excessive, On the contrary, when the friction coefficient of the road surface is high (dry concrete road surface, etc.), the assist is insufficient. In addition, the amount of tire air pressure may cause an excess or deficiency of assist.

Therefore, for example, when steering is performed, a load state that varies depending on the road surface friction coefficient, the tire state, etc. is determined based on the integrated value of the steering angular velocity and the integrated value of the steering torque, and this load state is determined. It has been proposed by the applicant of the present application to obtain a correction coefficient that conforms to the above and multiply the target current value of the assist table by the correction coefficient. Thereby, the assist control adapted to the change of the load state is achieved. However, in the method proposed above, the common correction coefficient is applied regardless of whether the steering is to the right or to the left. Therefore, when there is a difference between the load during rightward steering and the load during leftward steering due to changes over time or individual differences in the system, the required steering force differs between rightward and leftward. As a result, there is a problem that the steering feeling is deteriorated.

Therefore, an object of the present invention is to solve the above-mentioned technical problems, to realize a steering assist characteristic suited to a load state for steering, and also to compensate for a left-right difference of a steering force to obtain a good steering feel. An object is to provide an electric power steering device that can realize a ring.

[0007]

In order to achieve the above object, the invention according to claim 1 transmits the steering assist force generated by the electric motor (M) to the steering mechanism (3). An electric power steering device for assisting steering, comprising a torque sensor (10) for detecting a steering torque applied to an operating member (1), and a steering direction detecting means (2) for detecting a steering direction by operating the operating member.
2, S11, S12), initial steering assist characteristic setting means (18a) for setting an initial steering assist characteristic which is a standard characteristic of a target current value of the electric motor with respect to a steering torque detected by the torque sensor, and When the operating member is steered in either direction, load state detection means (12,
S35) and rightward steering coefficient detecting means for computing a rightward steering correction coefficient in accordance with the load state detected by the load state detecting means when rightward steering is detected by the steering direction detecting means. (12, S15, S38
~ S49) and a leftward correction coefficient calculation for calculating a leftward steering correction coefficient in accordance with the load state detected by the load state detection means when leftward steering is detected by the steering direction detection means. Means (12, S13, S3
8 to S49) and the rightward steering correction coefficient calculated by the rightward correction coefficient calculating means and the leftward steering correction coefficient calculated by the leftward correction coefficient calculating means, the initial steering assist characteristic is calculated. Target current value setting means (12, S7) for setting a target current value of the electric motor based on the steering torque detected by the torque sensor according to the corrected steering assist characteristic, and the target current value setting means. Motor drive means (12, 12) for driving the electric motor based on the target current value set by
S9, S10) are included in the electric power steering device. The alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies in this section below.

According to this structure, the correction coefficient for rightward steering and the correction coefficient for leftward steering are individually obtained based on the load state detected during steering. Therefore, when steering to the right, steering assistance is performed in accordance with the steering assist characteristic in which the initial steering assist characteristic is corrected by the correction coefficient for right steering, and in steering to the left, steering assistance in which the initial steering assist characteristic is corrected by the correction coefficient for left steering. Steering assistance is provided according to the assistance characteristics. As a result, it is possible to reduce or eliminate the left-right difference in the steering force due to the time-dependent change of the system, individual difference, and the like, so that the steering feeling can be improved.

The electric power steering apparatus may further include a steering angular velocity detecting means (S2) for detecting a steering angular velocity which is an operating speed of the operating member. In this case, the load state detection means integrates the steering angular speed integration means (S35) for integrating the steering angular speed detected by the steering angular speed detection means for a predetermined time, and the steering torque for integrating the steering torque detected by the torque sensor for the predetermined time. Accumulating means (S35)
And a storage means (18c) for storing a standard relationship between the integrated value of the steering angular velocity and the integrated value of the steering torque at the predetermined time.
And the load state is determined by collating the steering angular velocity integrated value integrated by the steering angular velocity integrating means and the steering torque integrated value integrated by the steering torque integrating means with the standard relationship stored in the storage means. It is preferable that the load status determining means (S38 to S50) is included (claim 2).

In this case, the load state judging means reads out from the storage means a standard steering torque integrated value corresponding to the steering angular speed integrated value integrated by the steering angular speed integrating means, and the read standard value. Comparing means (S38 to S4) for comparing the actual steering torque integrated value with the steering torque integrated value integrated by the steering torque integrating means.
2, S45 to S47), and the rightward correction coefficient calculation means and the leftward correction coefficient calculation means respectively generate a rightward steering correction coefficient and a leftward steering correction coefficient based on the comparison result by the comparison means. It is preferable to define it (Claim 3).

More specifically, the rightward correction coefficient calculating means and the leftward correction coefficient calculating means are, for example, a predetermined number of times when the integrated steering torque integrated value is larger than the standard steering torque integrated value. For a predetermined number of control cycles), or when the accumulated steering torque integrated value is smaller than the standard steering torque integrated value for a predetermined number of consecutive times, the correction coefficient for the right steering and the steering for the left direction Means for changing the correction coefficient (S40 and S41)
YES, S45 and S46 YES, S43, S4
9) may be included. With this configuration, it is possible to prevent the correction coefficient from varying due to a local change in the road surface, and thus it is possible to prevent a feeling of strangeness in steering.

Further, the rightward correction coefficient calculating means and the leftward correction coefficient calculating means are, for example, the first steering torque integrated value which is a predetermined first steering torque integrated value more than the standard steering torque integrated value.
When the state of being larger than the threshold value is continued for a predetermined number of times (for a plurality of predetermined control cycles), or the integrated steering torque integrated value is smaller than the standard steering torque integrated value by a predetermined second threshold value or more for a predetermined number of times continuously. Sometimes, means for changing the correction coefficient for right steering and the correction coefficient for left steering (YES in S40 and S41, S45 and S4, respectively).
6 YES, S43, S49) may be included. With this configuration, it is possible to more reliably prevent fluctuations in the correction coefficient due to local changes in the road surface.

The load state detecting means may be shared during rightward steering and leftward steering, and means for individually detecting the load state during rightward steering and leftward steering is provided. It may be provided.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering device according to an embodiment of the present invention. This electric power steering device includes a steering wheel 1
The steering torque applied to the steering shaft 2 is detected, and the electric motor M is drive-controlled based on the steering torque. The steering shaft 2 is mechanically coupled to a steering mechanism 3 of the vehicle.
Further, the driving force of the electric motor M is mechanically transmitted as a steering assist force via a gear mechanism or the like.

A torque sensor 10 is provided to detect the steering torque applied to the steering shaft 2. The steering shaft 2 is an input shaft 2 coupled to the steering wheel 1 side.
A and an output shaft 2B connected to the steering mechanism 3 are connected via a torsion bar 4. By detecting the twist amount and the twist direction of the torsion bar 4, the direction and the magnitude of the steering torque can be detected. A signal indicating the steering torque detected by the torque sensor 10 is supplied to the microcomputer 12 via an interface circuit (I / F) 11.

The microcomputer 12 further includes
An output signal of a vehicle speed sensor 20 that detects the speed of the vehicle is input through an interface circuit 21, and a steering angle sensor 22 that detects the steering angle of the steering wheel 1.
The steering angle signal of is input through the interface circuit 23. The microcomputer 12 controls the steering torque,
Based on the vehicle speed, the steering angle, and the motor current flowing through the electric motor M, the assist table storage unit 18 in the memory 18
The motor control signal is created by referring to the correction coefficient storage unit 18b that stores the correction coefficient for correcting the assist table and the vehicle characteristic table storage unit 18c. This motor control signal is given to the motor drive circuit 13. The motor drive circuit 13 supplies electric power from the vehicle-mounted battery 15 to the electric motor M such as a brushless motor based on the supplied motor control signal, and drives the electric motor M to rotate.

When the electric motor M rotates, a rotor position detector 14 such as a resolver or a rotary encoder detects the rotor position. The detected rotor position is given to the motor drive circuit 13. The motor drive circuit 13 is
P based on the detected rotor position signal
Drive control is performed by WM (Pulse Width Modulation) control. The motor current of the electric motor M flowing through the motor drive circuit 13 is detected by the motor current detection circuit 17, and the detection signal is given to the microcomputer 12.

FIG. 2 is a flow chart for explaining the processing that the microcomputer 12 repeatedly executes for each control cycle. The microcomputer 12 reads the steering angle signal detected by the steering angle sensor 22 (step S
1) The read steering angle signal is differentiated to calculate the steering angular velocity N (step S2). Further, the microcomputer 12 reads the torque detection signal detected by the torque sensor 10 as steering torque Th (step S3), and reads the vehicle speed V (vehicle speed signal) detected by the vehicle speed sensor 20 (step S4).

Next, the microcomputer 12 selects one assist table in the assist table storage section 18a based on the vehicle speed V, and sets the target current value Ti associated with the steering torque Th in this assist table. Read out (step S5). Further, the microcomputer 12 performs an assist correction process for obtaining a correction coefficient k for correcting the assist table according to the load condition (road condition and / or tire air pressure condition, etc.) (step S6). The obtained correction coefficient is stored in the correction coefficient storage unit 18b.

Then, the microcomputer 12 reads the correction coefficient k stored in the correction coefficient storage section 18b, and multiplies the target current value Ti read in step S5 by the read correction coefficient k to obtain the target current. The value k · Ti is calculated (step S7). The assist table stored in the assist table storage unit 18a is
Initial assist characteristics (initial steering characteristics) that are specified to provide good steering assistance on dry asphalt road surfaces
Is represented. Since the correction coefficient k is determined according to the load state, it can be said that the target current value k · Ti is a value determined according to the assist characteristic (steering assist characteristic) changed according to the load state.

Next, the microcomputer 12 reads the motor current signal detected by the motor current detection circuit 17 (step S8) and compares the read motor current with the calculated target current value. Based on the comparison result, the microcomputer 12 determines the output level and the rotation direction so that the target current flows through the electric motor M (step S9), and sends the instruction signal of the output level and the rotation direction to the motor drive circuit 13. Give (step S10) and return.

As a result, the motor drive circuit 13 rotationally drives the electric motor M based on the target current value k · Ti obtained by correcting the target current value Ti with the correction coefficient k. FIG. 3 is a flowchart for explaining the assist correction process for determining the assist correction coefficient k. The microcomputer 12 refers to the output of the steering angle sensor 22 to determine whether leftward steering, rightward steering, or substantial steering is not performed. (Steps S11, 12).

When the leftward steering is being performed (YES in step S11), the leftward steering correction coefficient target value k
Load state adaptation processing for determining _left is executed (step S13), and the leftward steering correction coefficient target value k_left determined thereby is substituted for the correction coefficient k (step S14). When the rightward steering is being performed (YES in step S12), the rightward correction coefficient target value k
A load state adaptation process for determining _right is executed (step S15), and the rightward steering correction coefficient target value k_right determined thereby is substituted for the correction coefficient k (step S16).

Therefore, the correction coefficient k is set independently for the rightward steering and the leftward steering, thereby reducing the difference between the left and right steering forces caused by the aging of the system and individual differences. Or it is being resolved. When no substantial steering is detected (steps S11, S12
No), the processing of steps S13 to S16 is omitted, and the correction coefficient k is held at the previous value. 4 and 5 show
It is a flow chart for explaining details of load state adaptation processing (Steps S13 and S15). The microcomputer 12 first determines whether or not the vehicle is traveling by determining whether or not the vehicle speed V read in step S4 of FIG. 2 is higher than a predetermined value Va (step S31). If the vehicle is traveling (YES in step S31), the microcomputer 12 determines whether or not the steering currently being performed is steering from the neutral position of the steering angle at which the vehicle should go straight (step S31). S32).

If the current steering is steering from the neutral position of the steering angle at which the vehicle should go straight (YES in step S32), the microcomputer 12 determines that the steering is the time of sampling in the previous control cycle. It is determined whether or not the directions are the same (step S33). If the steering direction is the same as the direction of the previous sampling (YES in step S33), the microcomputer 12 determines whether a waiting time (for example, 0.1 seconds) has elapsed since the steering was started. (Step S34).

If the waiting time has elapsed (YES in step S34), the microcomputer 12 integrates the read steering torque T (step S3 in FIG. 2) and further calculates the calculated steering speed (step S2 in FIG. 2). ) Is integrated to calculate a steering torque integrated value ΣT and a steering angular velocity integrated value ΣN (step S35). Further, the microcomputer 12 waits for the waiting time to elapse (step S3
4) It is determined whether or not a predetermined integration time for integrating the steering torque T and the steering angular velocity N has elapsed (step S36). If this integrated time has elapsed (YES in step S36), it is determined whether the integrated steering angular velocity integrated value ΣN is within the applicable range (b <ΣN <c: b, c is a positive constant). Yes (step S37). This is stored in the vehicle characteristic table as shown in FIG. 7 (stored in the vehicle characteristic table storage section 18c. See FIG. 1), and the steering angular velocity integrated value ΣN out of the applicable range (abnormal steering such as sudden steering is detected. This is because, if performed, for example) is not adopted for assist correction.

The vehicle characteristic table storage section 18c stores a vehicle characteristic table representing vehicle characteristics that differ depending on the weight of the vehicle, tires, and the like. That is, the relationship between the steering angular velocity integrated value ΣN and the steering torque integrated value ΣT (reference steering torque integrated value ΣT ^* ) is stored in advance as a reference (for each vehicle speed) on a dry asphalt road surface. . The microcomputer 12
If the integrated steering angle speed value ΣN is within the applicable range, the reference steering torque integrated value ΣT ^* corresponding to the integrated steering angle speed value ΣN and the vehicle speed V is read from the vehicle characteristic table storage unit 18c (step S38). Microcomputer 12
Using the read reference steering torque integrated value ΣT ^* and the calculated steering torque integrated value ΣT, ΣT ^* −Σ
T = D0 is calculated (step S39).

Next, the microcomputer 12 determines whether or not the calculated difference D0 is larger than the positive predetermined number a (step S40 in FIG. 5), and the calculated difference D0 is larger than the positive predetermined number a. If it is larger, the previous accumulated time (step S3
It is determined whether or not the similar difference D1 in the cycle of 6) is larger than the positive predetermined number a (step S41). When the difference D1 is larger than the positive predetermined number a (YES in step S41), the microcomputer 12 compares the current correction coefficient target value k_obj with the minimum value kmin of the correction coefficient k (k_obj>
kmin + d, d: positive constant) is performed (step S4)
2). However, the correction coefficient target value k_obj corresponds to the left-hand steering correction coefficient target value k_left in the load state adaptation processing executed when the leftward steering is detected (step S11 of FIG. 3), and the rightward steering In the load state adaptation processing executed when is detected (step S12 in FIG. 3), it is assumed that the correction coefficient target value k_right for rightward steering is equivalent.

If the microcomputer 12 has a margin to decrease the assist coefficient target value k by the constant d as a result of the comparison (YES in step S42), k_obj-d is updated as a new correction coefficient target value k_obj (step S42). S4
3) If there is no margin to decrease the correction coefficient target value k_obj by the constant d (NO in step S42), the minimum value kmin of the correction coefficient k is updated as a new correction coefficient target value k_obj (step S44).

Next, the microcomputer 12 substitutes the difference D0 calculated in the cycle of the present integration time into D1 (step S50), and integrates the steering angular velocity integration value ΣN, the steering torque integration value ΣT and the reference steering torque integration value ΣT. ^* (Parameter for load state adaptation processing) is reset (step S52), and the process returns. In this case, for example, the situation corresponds to the situation in FIG. 7 and indicates that the assist is excessive. Therefore, the correction coefficient target value k_obj is decreased, and as shown in the corrected assist table of FIG. Decrease the target current value).

The microcomputer 12 determines whether the calculated difference D0 is larger than a predetermined positive number a, and when the difference D0 is equal to or smaller than the predetermined positive number a (N in step S40).
O), it is determined whether the difference D0 is smaller than the predetermined number −a (step S45). When the difference D0 is smaller than the predetermined number-a (YES in step S45), it is determined whether or not the similar difference D1 in the cycle of the previous integration time is smaller than the predetermined number-a (step S46). When the difference D1 is smaller than the predetermined number -a (YES in step S46), the microcomputer 12 compares the current correction coefficient target value k_obj with the maximum value kmax of the correction coefficient k (k_obj> kmax-d,
d: positive constant) is performed (step S47).

As a result of this comparison, if there is a margin to increase the correction coefficient target value k_obj by the constant d (NO in step S47), the correction coefficient target value k_obj is updated to k_obj + d (step S49), and the correction coefficient target value k_obj. If there is no margin to increase the value by a constant d (YE in step S47)
S), the maximum value kmax of the correction coefficient k is updated as a new correction coefficient target value k_obj (step S48). Next, the microcomputer 12 substitutes the difference D0 calculated in this cycle of the integration time into D1 (step S5).
0), the steering angular velocity integrated value ΣN, the steering torque integrated value ΣT, and the reference steering torque integrated value ΣT ^* are reset (step S52) and the process returns.

This situation corresponds to, for example, the case in FIG. 7, and since the assist is insufficient, the assist torque (target current value) is increased by increasing the correction coefficient target value k_obj as shown in FIG. Will be increased. When the difference D1 is a positive predetermined number a or less (NO in step S41), the difference D0 is a predetermined number −a or more (NO in step S45), or the difference D1 is a predetermined number −a or more. Time (NO in step S46)
Substitutes the difference D0 calculated at the beginning of the current integration time into the difference D1 without updating the correction coefficient target value k_obj (step S50), and also calculates the steering angular velocity integration value ΣN, the steering torque integration value ΣT, and the reference steering. The integrated torque value ΣT ^* is reset (step S52) and the process returns.

This situation corresponds to, for example, the case shown in FIG. 7 and to the case where the vehicle is in a proper assist state or the road surface state locally changes. In this case, the correction coefficient target value k_obj is deferred, and steering assist is performed according to the conventional assist characteristic, as shown in FIG. The microcomputer 12 executes step S
When it is determined in 31 that the vehicle is not traveling (NO in step S31), the steering angular velocity integrated value ΣN and the steering torque integrated value ΣT are reset (step S51), the load state adaptation process is interrupted, and the process returns.

If it is determined in step S32 that the steering currently being performed is not steering from the neutral position of the steering angle at which the vehicle should go straight, the process is returned without any processing. Further, in step S33, if the steering direction is not the same direction as the previous sampling, it means that the steering direction has changed before the waiting time and the integration time elapse, as shown in FIG. The integrated value ΣN and the steering torque integrated value ΣT are reset (step S51), the load condition adaptation process being executed is interrupted, and the process returns.

Before the waiting time elapses (step S34
NO in step S36 or before the cumulative time has elapsed (N in step S36)
In step O), the processing returns to the above without performing the subsequent processing in order to continue the load state adaptation processing. Further, when the microcomputer 12 determines in step S37 that the steering angular velocity integrated value ΣN is out of the applicable range (step S37).
No of 37), the steering angular velocity integrated value ΣN and the steering torque integrated value ΣT are reset (step S51), and the load state adaptation processing is interrupted.

This corresponds to the situation shown in FIG. 7 and is a case where the steering angular velocity integrated value ΣN is out of the conforming range. In this case, as shown in FIG. 8, steering assist is performed with the assist characteristic according to the previous correction coefficient target value k_obj. In the above example, the range of the width 2a is provided centering on the reference steering torque integrated value ΣT ^* , and the magnitude of this range and the steering torque integrated value ΣT detected in actual traveling is determined. The reference steering torque integrated value ΣT ^* and the steering torque integrated value Σ detected in actual driving without setting the range of
The size of T may be determined.

As described above, according to this embodiment, the correction coefficient target value k_obj (k_left or k_right) is calculated based on the tendency of the steering angular velocity integrated value ΣN and the steering torque T.
Is changed from time to time, it becomes possible to assist the steering in accordance with the load condition such as the road surface friction coefficient while the vehicle is traveling.
Moreover, the load state adaptation processing (S15, S13) is independently performed during rightward steering and leftward steering, and the correction coefficient target value k that is suitable for both rightward steering and leftward steering.
Since _right and k_left are determined, it is possible to reduce or eliminate the difference between the left and right steering forces due to the time-dependent change of the system and individual differences. Thereby, an excellent steering feeling can be realized.

Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms.
For example, in the above-described embodiment, the load state is detected based on the steering angular velocity integrated value ΣN and the steering torque integrated value ΣT, but either the steering torque integrated value or the steering angular velocity integrated value is used to detect the load state. Only one may be used, and the detection of the load state may be performed based on other parameters. In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining a process repeatedly executed by a microcomputer of the electric power steering device in each control cycle.

FIG. 3 is a flowchart illustrating an assist correction process for determining an assist correction coefficient.

FIG. 4 is a flowchart for explaining details of load state adaptation processing.

FIG. 5 is a flowchart for explaining details of load state adaptation processing.

FIG. 6 is a diagram for explaining determination of suitability of determination of a load state.

FIG. 7 is a diagram showing an example of a vehicle characteristic table.

FIG. 8 is a diagram for explaining correction of an assist table.

[Explanation of symbols]

1 steering wheel 2 steering axis 3 Steering mechanism 10 Torque sensor 12 Microcomputer 13 Motor drive circuit 14 Rotor position detector 15 In-vehicle battery 17 Motor current detection circuit 18 memory 18a Assist table storage unit 18b Correction coefficient storage unit 18c Vehicle characteristic table storage unit 20 vehicle speed sensor 22 Rudder angle sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62D 137: 00 B62D 137: 00 F term (reference) 3D032 CC08 DA03 DA15 DA19 DA63 DA64 DC03 DC08 DC09 DC10 DC33 DC34 DD01 DD10 EB11 EC23 GG01 3D033 CA13 CA16 CA17 CA20 CA21

Claims (3)

[Claims] 1. An electric power steering device for assisting steering by transmitting a steering assist force generated by an electric motor to a steering mechanism, comprising: a torque sensor for detecting a steering torque applied to an operating member; and an operation of the operating member. Steering direction detecting means for detecting a steering direction by the steering wheel, and initial steering assisting characteristic setting means for setting an initial steering assisting characteristic which is a standard characteristic of the target current value of the electric motor with respect to the steering torque detected by the torque sensor. When the operating member is steered in either direction, load state detection means for detecting a load state related to steering during the steering, and rightward steering detected by the steering direction detection means, A rightward correction coefficient calculation for calculating a rightward steering correction coefficient in accordance with the load state detected by the load state detecting means. And a leftward correction coefficient calculating means for calculating a leftward steering correction coefficient in accordance with the load state detected by the load state detecting means when leftward steering is detected by the steering direction detecting means. Obtained by correcting the initial steering assist characteristic using the rightward steering correction coefficient calculated by the rightward correction coefficient calculation means and the leftward steering correction coefficient calculated by the leftward correction coefficient calculation means. A target current value setting unit that determines a target current value of the electric motor based on the steering torque detected by the torque sensor in accordance with the steering assist characteristic, and the target current value set by the target current value setting unit. An electric power steering apparatus comprising: a motor driving unit that drives an electric motor. 2. A steering angular velocity detecting means for detecting a steering angular velocity which is an operating speed of an operating member, wherein the load state detecting means integrates the steering angular velocity detected by the steering angular velocity detecting means for a predetermined time. Means and
Steering torque integration means for integrating the steering torque detected by the torque sensor for the predetermined time, storage means for storing a standard relationship between the steering angular speed integrated value and the steering torque integrated value at the predetermined time, and the steering angular speed integration Load state determining means for determining a load state by collating the steering angular velocity integrated value integrated by the means and the steering torque integrated value integrated by the steering torque integrating means with the standard relationship stored in the storage means. The electric power steering apparatus according to claim 1, comprising: 3. The load state determination means reads out from the storage means a standard steering torque integrated value corresponding to the integrated steering angular speed integrated by the integrated steering angular speed integrated means,
The right-direction correction coefficient calculation means and the left-direction correction coefficient calculation include the comparison means for comparing the read standard steering torque integrated value with the steering torque integrated value integrated by the steering torque integrating means. 3. The electric power steering apparatus according to claim 2, wherein the means determines the correction coefficient for rightward steering and the correction coefficient for leftward steering, respectively, based on the comparison result by the comparison means.