JP2003137120A - Electric power steering device - Google Patents

Abstract

(57) [Summary] [Problem] To provide an assist motor 10 for generating an assist torque for assisting a steering torque by a driver, assist a steering force of a steering system, and convert a damping torque according to a steering angular velocity to the assist torque. In the electric power steering device to be applied, a damping torque according to the steering state is given so that an insufficient assist amount at the time of turning or an insufficient damping amount at the time of return occurs. SOLUTION: Based on respective outputs of a steering angular velocity estimating means 26, a steering torque calculating means 28a and a basic assist torque calculating means 28b, a steering state determining means 29 for determining a steering state such as a turning operation or a returning operation is provided. In accordance with the steering state, the damping torque calculating means 28d applies a damping torque having a magnitude of: damping torque at the return stroke> damping torque at the turning stroke> damping torque at the return stroke and in the assist dead zone. .

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 system having an assist motor for generating a steering assist force for a steering system of a vehicle.

[0002]

2. Description of the Related Art A conventional electric power steering device is
In order to assist the steering torque at the time of steering by the driver, the steering torque is detected by the torque sensor, the vehicle speed is detected by the vehicle speed sensor, and the assist motor is driven according to the detected vehicle speed and torque. The assist torque was added to the steering wheel to improve the operability of the steering wheel.

Further, in the conventional electric power steering apparatus, a damping control for giving a reaction force (damping torque) for damping the movement of the steering wheel is carried out to prevent the irregular behavior of the vehicle.

Damping control in this electric power steering apparatus is variably controlled according to the vehicle speed, as disclosed in, for example, Japanese Patent Laid-Open No. 63-291769, so that the damping torque increases as the vehicle speed increases. Was there.

[0005]

However, the electric power steering device disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-291769 has the following problems:
The damping torque was applied regardless of the steering state such as returning.

On the other hand, the self-aligning torque that produces torque in the direction of returning the tire (steering wheel) to the neutral direction acts in the steering direction when the steering wheel is returned, and in the direction opposite to the steering direction when the steering wheel is turned. The amount of generation becomes large when driving at high speed.

For this reason, if the damping torque is applied regardless of the steering state such as cutting and returning as described above, there is a problem that the assist amount is insufficient at the time of cutting and the damping amount is insufficient at the time of returning.

Further, in order to improve the steering feeling, a dead zone is provided in which the assist torque is not applied to the steering wheel. When the return control for assisting the steering wheel in the neutral direction is performed in this dead zone, this return is performed. Since control and damping control are contradictory controls, if damping torque is applied regardless of the steering state as described above, normal control may not be performed and hunting may occur.

The present invention has been made in view of the above points, and an object thereof is to provide a damping torque adapted to a steering state, and an electric power steering which does not cause a shortage of assist amount at the time of cutting or a shortage of damping amount at the time of returning. To provide a device.

[0010]

An electric power steering system according to the present invention for solving the above problems includes a motor for generating an assist torque for assisting a steering torque by a driver, and assists a steering force of a steering system. At the same time, in an electric power steering apparatus that applies a damping torque corresponding to a steering angular velocity to the assist torque, a steering state determination means for determining a steering state such as steering cut and return, and a return state determined by the steering state determination means. In this case, a damping torque applying unit that applies a larger damping torque than that in the case of the cut state is provided.

Further, the damping torque applying means is
When the steering state determination unit determines that the steering wheel is in the return state and the assist torque is in the dead zone where the steering wheel is not applied, a smaller damping torque is applied than when the steering wheel is not returned or in the dead zone. It has a feature.

Further, the steering state determination means is based on the polarity of the signal that detects the steering torque, the polarity of the signal that estimates the steering angular velocity, and the magnitude of the assist torque, and the steering torque detection signal and the steering angular velocity estimation signal. Is not the same and the magnitude of the assist torque is not zero, it is determined to be the first state, and when the polarities of the steering torque detection signal and the steering angular velocity estimation signal are the same, the second state is determined. When the steering torque detection signal and the steering angular velocity estimation signal do not match in polarity and the magnitude of the assist torque is zero, it is determined to be the third state, and the damping torque is determined. In the applying means, the magnitude of the damping torque in each of the states is such that the damping torque in the first state> the damping torque in the second state> the third
It is characterized in that a damping torque that is a damping torque in the state of is given.

[0013]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of an electric power steering device to which the present invention is applied.
In FIG. 1, the steering wheel 1 is connected to a pinion shaft 6 via an input shaft side steering shaft 2a, an output shaft side steering shaft 2b, a universal joint 3, an intermediate shaft 4 and a universal joint 5.

The lower end of the pinion shaft 6 meshes with a horizontally extending rack shaft 7, and the rack shaft 7 and the pinion shaft 6 constitute a rack and pinion mechanism. Both ends of the rack shaft 7 are connected to steering wheels (not shown) via tie rods 8a and 8b, respectively, and the rack shaft 7 is horizontally moved so that the left and right wheels are steered. .

A torque sensor 9 for detecting the steering torque of the steering wheel 1 is provided on the steering shaft 2a, and an assist motor 10 for assisting the steering force of the steering wheel 1 is connected to the steering shaft 2b via a speed reducer 11. ing.

Reference numeral 12 denotes a control unit for controlling the power steering device, which is supplied with electric power from a battery 13 via an ignition switch 14 and is based on a steering torque detected by a torque sensor 9 and a vehicle speed detected by a vehicle speed sensor 15. Then, the motor drive current (target current command value) is obtained, and the current supplied to the assist motor 10 is controlled based on the target current command value.

The control unit 12 executes a steering state discrimination function for discriminating a steering state such as steering cut and return, and a damping torque applying function for giving a damping torque according to the discriminated steering state.
For example, it has a microcomputer, and is specifically configured as shown in FIG.

In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 21 is a bridge circuit formed by bridge-connecting FETs (field effect transistors) 22a to 22d, and the assist motor 10 is connected to the bridge point. The common connection point of the FET 22a and the FET 22b is connected to the positive electrode of the battery 13 via the current detection resistor 23. The common connection point of the FET 22c and the FET 22d is grounded.

The terminal voltage of the assist motor 10 is detected by the motor terminal voltage detecting means 24, and the current flowing through the assist motor 10 is based on the current flowing through the current detecting resistor 23, for example, a motor current detecting means including an operational amplifier. Detected by 25. Reference numeral 26 is a steering angular velocity estimating means for estimating the steering angular velocity based on the output signals of the motor terminal voltage detecting means 24 and the motor current detecting means 25.

Reference numeral 27 is a vehicle speed calculating means for calculating the vehicle speed based on the output of the vehicle speed sensor 15.

Reference numeral 28a is a steering torque calculating means for calculating the steering torque based on the output of the torque sensor 9. 28
b is a vehicle speed calculation means 27 and a steering torque calculation means 28a
Is a basic assist torque calculation means for calculating the basic assist torque based on the output of 28c is vehicle speed calculation means 2
7 and a torque differential correction torque calculation means for calculating a differential correction torque based on the outputs of the steering torque calculation means 28a. 28d is a damping torque calculating means for calculating a damping torque based on the outputs of the steering angular velocity estimating means 26, the vehicle speed calculating means 27, and the steering state determining means 29. 28e is a return torque calculation means for calculating a return torque based on the outputs of the vehicle speed calculation means 27 and the steering state determination means 29.

The steering state discrimination means 29 discriminates the steering state such as cutting or returning based on the outputs of the steering angular velocity estimating means 26, the steering torque calculating means 28a and the basic assist torque calculating means 28b.

Reference numeral 30 is a basic assist torque calculating means 28.
b, torque differential correction torque calculation means 28c, damping torque calculation means 28d, and return torque calculation means 28e.
It is a command current calculation means for calculating a command current based on the total assist torque from the total assist torque. Specifically, the instruction current is calculated, for example, by multiplying the obtained total assist torque by 1 / torque constant or by referring to the total assist torque: motor current correspondence map.

Reference numeral 31 determines an on / off duty ratio for pulse width modulation (PWM) control of each FET of the bridge circuit 21 based on the outputs of the motor current detection means 25 and the instruction current calculation means 30. It is a PWM duty determining means.

Reference numeral 32 is a power element driving means for controlling the pulse width modulation (PWM) of each FET of the bridge circuit 21 based on the duty ratio determined by the PWM duty determining means 31.

The control of the bridge circuit 21 which functions as a drive circuit for the assist motor 10 is performed as follows by way of example. That is, the FET 22a or 22b is subjected to pulse width modulation control, and the FET 22c or 22d is continuously turned on.

Therefore, the current supplied from the battery 13 to the bridge circuit 21 via the current detecting resistor 23 is F
ET22a (or 22b) → assist motor 10 → FE
T22d (or 22c) → flows in the path of grounding, and the assist motor 10 rotates clockwise (or counterclockwise). As a result, the steering wheel 1 rotates in the direction in which the steering operation is performed, and assists the steering force.

The reason why the steering angular velocity estimating means 26 can estimate the steering angular velocity based on the outputs of the motor terminal voltage detecting means 24 and the motor current detecting means 25 will be described below.

The voltage equation of the motor is shown as follows.

[0030] However, V is a voltage between terminals [V], L is an inductance [H], S is d / dt, I is a current [A], R is a resistance [Ω], E is a counter electromotive voltage [V], and Ke is a reverse. Electromotive force constant [V
/ Rad / s], ω is the angular velocity [rad / s] of the motor.

Since the influence of the inductance can be ignored in the steady state, the above equation (1) is simplified and V = IR + Keω (2) From equation (2), the motor angular velocity is expressed by the following equation.

Ω = (V-IR) / Ke (3) Resistance value R [Ω], back electromotive force constant Ke [V / rad / s]
Is a constant value peculiar to the motor, the voltage V between the motor terminals is
The motor angular velocity can be obtained by measuring [V] and the motor current I [A].

The steering angular velocity [rad / s] can be obtained as 1 / reduction gear ratio of the motor angular velocity in the steady state.

However, the equation (3) and the calculation of the steering angular velocity at the final stage are a simple method in a steady state in which the transient state is ignored, the current control is feedback control by PI control, and the motor drive is Is high-speed switching of the voltage by PWM, high-frequency noise is superimposed on the measured current value and terminal voltage value. Therefore, simply applying the equation (3) estimates a practical motor angular velocity, that is, steering. It is impossible to estimate the angular velocity. Therefore, practically, at least the output of the formula (3) is subjected to LPF (low-pass filter) processing, the section average value of the current value and the terminal voltage value is used, and the moving average is performed, that is, the LPF of the input value.
It is used for processing.

The steering state determining means 29 is based on the polarity of the output signal of the steering torque calculating means 28a, the polarity of the output signal of the steering angular velocity estimating means 26 and the magnitude of the output of the basic assist torque calculating means 28b. The processing shown in FIG. 3 is executed to determine the steering state such as cutting and returning.

In FIG. 3A, first, the steering torque To is
In step S ₁ , it is determined whether or not rque is positive or 0. If it is positive or 0, it is determined in step S ₂ whether or not the steering angular velocity Strgspd is positive or 0.

Step S₂If the judgment result of is YES
If the steering torque and the steering angular velocity are both positive,
Therefore, it is judged that the steering operation is
S ₃The steering state determination value Status to "0"
Set and end processing.

When it is determined in step S ₁ that the steering torque is not positive or zero, it is determined in step S ₄ whether the steering angular velocity Strgspd is positive or zero. When the determination result in step S ₄ is NO, the steering torque and the steering angular velocity are both negative and have the same sign (same polarity), so it is determined that the steering operation is in the process of cutting, and the steering state determination value Status is determined in step S ₃ . "0"
Set to, and the process ends.

If the decision result in the step S ₂ is NO or the decision result in the step S ₄ is YES,
Steering torque and the steering angular velocity determines that being steered back for a different sign (opposite polarity), and determines whether or not the assist torque Atorque is not 0 in step S _5.

If the result of the determination in step S ₅ is YES, it is determined that assisting is being performed during return steering, and the steering state determination value St is determined in step S ₆ .
Atus is set to "1", and the process ends.

When the result of the determination in step S ₅ is NO, it is determined that the steering is in the return steering and the assist dead zone, and the steering state determination value Status is determined in step S ₇ .
Is set to "2", and the process ends.

The assist dead zone is generally set in the vicinity of the steering angle neutral in order to improve the steering feeling, but this is necessary for informing the driver that the steering wheel is neutral, and the The dead zone increases with increase.

The assist torque Atorque represents the assist torque value of the motor with respect to the steering torque Torque as shown in FIG. In FIG. 6, X ₁ is the assist dead zone when the vehicle speed is 0 [km / h], and X ₂ is the vehicle speed 10
Each of the assist dead zones at 0 [km / h] is shown.

The steering state determination value Status is, for example, the steering state on the time chart of the steering angle, steering torque, steering angular velocity, and assist torque in FIG.
It is expressed by a numerical value of 0 to 2, where Status = 0 indicates a cutting process (second state) from the steering angle midpoint, and S
status = 1 is the step of returning to the midpoint of the steering angle (first state)
And Status = 2 indicates that the process is in the returning step and is in the assist dead zone (third state).

Further, the steering state judging means 29 is shown in FIG.
The steering state may be determined by executing the processing of (b). In FIG. 3B, the steering torque Torque and the steering angular velocity S
trgspd is represented by a signed integer, and the exclusive OR of the two is taken. If the exclusive OR is negative, the two have different signs and it can be determined that the return steering is in progress. If the sum is positive, the two have the same sign, and it can be determined that the steering wheel is in the steering operation.

First, in step S ₁ , the steering torque T
The exclusive OR EXOR of orque and the steering angular velocity Strgspd is calculated.

Next, in step S ₂ , it is determined whether or not the EXOR is negative, and if the result of the determination is NO (when it is positive), it is determined that the steering operation is under cutting, and step S Steering state determination value Status in ₃
Is set to "0", and the process ends.

Further, the determination result of the step S ₂ is YES.
If (exor is negative), it is determined that the return steering is being performed, and the assist torque At is determined in step S ₄ .
It is determined whether orque is 0.

When the result of the determination in step S ₄ is NO, it is determined that assisting is being performed during return steering, and the steering state determination value St is determined in step S ₅ .
Atus is set to "1", and the process ends.

If the result of the determination in step S ₄ is YES, it is determined that the steering is in the return steering and the assist dead zone, and the steering state determination value Stat is determined in step S ₆ .
The us is set to "2", and the processing is ended.

The damping torque calculating means 28d is
Based on the outputs of the steering angular velocity estimating means 26, the vehicle speed calculating means 27, and the steering state determining means 29, the processing shown in FIG. 4 is executed to calculate the damping torque.

In FIG. 4A, it is first determined in step S ₁ whether the steering state determination value Status is 2, and if the result is NO (the determination result is 2), During the returning process and in the assist dead zone, the damping torque Damping is set to 0 in step S ₂ and the process ends.

Further, the determination result of the step S ₁ is YES.
If it is (if the determination if the result is not a 2), the steering angular velocity coefficient map D shown in FIG. 4 (b) in step S ₃
The steering angular velocity dependence coefficient DGain is calculated from the steering state determination value Status and the steering angular velocity Strgspd with reference to GMAP. At this time, DGMAP indicates the steering angular velocity Strgsp.
Reference the absolute value of d. This steering angular velocity coefficient map DGM
In the AP, data that has a larger value (DGain) when the steering state determination value Status is 1 than when it is 0 is stored as a map.

Next, at step S ₄ , the vehicle speed coefficient DVMAP shown in FIG. 4C is referred to and the vehicle speed dependence coefficient D is calculated from the steering state determination value Status and the vehicle speed VSpeed.
Calculate Vspd. In this vehicle speed coefficient map DVMAP, the vehicle speed dependent coefficient DVspd increases as the vehicle speed increases, and data in which the steering state determination value Status is 1 (DVspd) is larger than 0 is stored as a map. Has been done.

Next, at step S ₅ , the damping torque Damping is calculated by multiplying the steering angular velocity dependence coefficient DGain and the vehicle speed dependence coefficient DVspd.

Next, at step S ₆ , the steering angular velocity St
determine the direction of rgspd (determine whether it is negative),
The process ends without doing anything if it is positive, the process ends denoted by the negative sign Damping in step S ₇ if it is negative.

The return torque calculating means 28e executes the processing shown in FIG. 5 on the basis of the outputs of the vehicle speed calculating means 27 and the steering state judging means 29 to return torque RTorqu.
Calculate e.

In FIG. 5A, it is first judged whether or not the steering state judgment value Status is 2 (that is, the value in the case where the steering is in the reverse steering and the assist dead zone is present), and if the result is NO. Sets the return torque R Torque to 0 in step S ₂ and ends the process.

Further, the determination result of step S ₁ is YES.
If (Status is 2), the return torque RTorq is returned for each vehicle speed by referring to the return torque coefficient map RTMAP shown in FIG. 5B in step S ₃ .
Calculate ue. The return torque coefficient map RTMAP stores the data of the return torque R Torque corresponding to the vehicle speed as a map.

Next, in step S ₄ , the steering torque T
determine the direction of orque (determine whether it is negative),
If the result is positive, the process ends without doing anything, and if the result is negative, the return torque R Torque is given a negative sign in step S ₅ , and the process ends.

In the instruction current calculating means 30 of FIG. 2, total assist torque = basic assist torque (output of calculating means 28b) + torque differential correction torque (output of calculating means 28c) -damping torque (calculating means 2).
8d output) -return torque (output of calculation means 28e) is calculated to obtain total assist torque (motor torque), and the obtained total assist torque is multiplied by 1 / torque constant, or total assist torque: motor The instruction current is calculated by referring to the current correspondence map.

Next, the operation of the apparatus configured as described above will be described with reference to FIG. 7, which shows an example of the steering state on the time chart of the steering angle, the steering torque, the steering angular velocity, and the assist torque.

The period from the time t _n to the time t _{n + 1 in} FIG. 7 is a cutting stroke in which the steering wheel 1 in FIG. 1 is rotated to the right, and the steering torque Torque and the steering angular velocity Strgspd are both the same sign (the same sign). Because of the polarity, it is determined that the steering state determination value Status = 0 in steps S ₂ and S ₃ of FIG. 3A or 3B. Therefore, during this period, the steering angular velocity coefficient map D of FIG.
GMAP and vehicle speed coefficient map DVMAP of FIG.
Data of each Status = 0 of FIG.
Steps S _{3 to} S ₇ are executed and the damping torque Da
mping is calculated.

At this time, each of the maps DGMAP, DVM
Data Status = 0 in AP (steering speed dependency coefficient DGain, vehicle speed dependence coefficient DVspd) Since relatively small, when the cut stroke from the time t _n to the time point t _{n + 1,} the situation where the assist amount is insufficient is avoided. Since Status = 0 during this period, the return torque RTorque = as shown in steps S ₁ and S ₂ of FIG. 5A.
It becomes 0 (no return torque is applied).

As another embodiment, the damping control may be prohibited during the cutting stroke. That is, for example, the steering angular velocity coefficient map DGMAP of FIG. 4B and the vehicle velocity coefficient map DVMA of FIG.
The steering angular velocity S is set as data of each Status = 0 of P.
Data in which all values of trgspd and vehicle speed VSpeed are 0 are stored as a map.

Further, for example, the steering angular velocity coefficient map DGMAP of FIG. 4 (b) and the vehicle speed coefficient map DV of FIG. 4 (c).
Even if the data to be stored in the MAP is limited to Status = 1, and is changed so as to determine “whether or not the steering state determination value Status is 1” in step S ₁ of FIG. good.

Next, the period from time t _{n + 1} to time t _{n + 2 in} FIG. 7 is the return stroke in which the steering wheel 1 in FIG. 1 is turned back to the right, and the steering torque Torque and the steering angular velocity Strgspd are Since they have different signs (different polarities) and the assist torque is not zero (not the assist dead zone), steps S ₅ and S _{6 in} FIG.
In steps S ₄ and S ₅ of (b), the steering state determination value St
It is determined that atus = 1. Therefore, this period is
(B) Steering angular velocity coefficient map DGMAP and FIG.
Each Stat in the vehicle speed coefficient map DVMAP in (c)
Using the data of us = 1, step S of FIG.
₃ to S ₇ is executed, the damping torque Damping is calculated.

At this time, each of the maps DGMAP, DVM
Data of Status = 1 in AP (rudder angular velocity dependence
The coefficient DGain and the vehicle speed dependent coefficient DVspd) are S
If it is determined that status = 0 (in case of cutting process)
Is larger than the sum), time t _{n + 1}From time t_{n + 2}For up to
It is possible to avoid a situation where the amount of damping is insufficient during the return stroke.
It Since Status = 1 during this period, FIG.
Step S of (a)₁, S₂Return torque RT as shown in
orque = 0 (return torque is not applied).

Next, the period from time t _{n + 2} to time t _{n + 3 in} FIG. 7 is the return stroke in which the steering wheel 1 in FIG. 1 is turned back to the right and indicates the assist dead zone region. . In this state, since the assist torque is not applied, the torque that assists the steering wheel in the returning direction is only the self-aligning torque. Therefore, it is preferable to keep the damping torque to a minimum in this state.

During the period from time t _{n + 2} to time t _{n + 3} , the steering torque Torque and the steering angular velocity Strgsp
Since d has a different sign (different polarity) and the assist torque is zero (the assist dead zone), steps S ₅ and S _{7 in} FIG. 3A or steps S ₄ and S in FIG. 3B are performed. _{At 6} , it is determined that the steering state determination value Status = 2.

Therefore, during this period, the damping torque Damping = 0 (the damping torque is not applied) by executing the steps S ₁ and S ₂ of FIG. 4A, while the step S of FIG. 5A is performed. _{by 3} to S ₅ is performed, returning for each vehicle speed torque RTorque
Is calculated.

As a result, in the return stroke and in the assist dead zone, it is possible to normally assist in the return direction only by the self-aligning torque. Also,
Damping control that contradicts the return control can be suppressed and hunting can be prevented.

As another embodiment, a very small damping torque may be applied in the return stroke and in the assist dead zone. That is, for example, Stat is added to the steering angular velocity coefficient map DGMAP in FIG. 4B and the vehicle velocity coefficient map DVMAP in FIG. 4C.
Stat that is a value smaller than the value when us = 0
Data of us = 2 is stored as a map, and the map shown in FIG.
The processing of steps S ₁ and S ₂ of (a) may be deleted.

The magnitude of the damping torque in each of the steering states is as follows: Damping torque of Status = 1 (in the first state) during the return stroke> St during the cutting stroke.
damping torque of atus = 0 (in the second state)> return stroke and assist dead zone Status = 2
The damping torque is (in the third state).

The FET of the bridge circuit 21 shown in FIG.
22a to 22d are the FETs 22a or 2 as described above.
The control is not limited to PWM control of 2b and ON control of the FET 22c or 22d continuously, but may be controlled by another control method.

In FIG. 2, since the steering angular velocity estimating means 26 is constructed so as to estimate the steering angular velocity based on the output signals of the motor terminal voltage detecting means 24 and the motor current detecting means 25, the steering angle sensor and the like are specially provided. There is no need to provide it.

The vehicle speed coefficient map DVMA shown in FIG.
In P, the data in which the vehicle speed dependence coefficient DVspd increases as the vehicle speed increases is stored as a map, and the damping torque increases as the vehicle speed increases. Therefore, when the self-aligning torque is high, the vehicle speed is high. It is possible to generate a large damping torque and perform appropriate damping control.

[0078]

As described above, according to the present invention, the following excellent effects can be obtained. (1) According to the invention described in claims 1 to 3,
Since the damping torque is applied according to the returning state, there is no fear that the amount of assist at the time of cutting or the amount of damping at the time of returning will be insufficient. (2) According to the invention described in claims 2 and 3, it is possible to keep the damping torque to a minimum in the return stroke and in the assist dead zone, and the self-aligning torque alone makes the return direction normal. Can assist. Further, it is possible to suppress damping control which is contradictory to the return control and prevent hunting from occurring.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of an electric power steering device to which the present invention has been applied.

FIG. 2 is a block diagram of a main part of an embodiment of the present invention.

3A and 3B show a processing flow of a steering state determination means of the present invention, FIG. 3A is a flowchart of one embodiment, and FIG. 3B is a flowchart of another embodiment.

4A and 4B show an example of an embodiment of damping torque calculating means of the present invention, FIG. 4A is a flowchart of processing, FIG. 4B is a characteristic diagram illustrating a steering angular velocity coefficient map, and FIG. 4C is a vehicle speed coefficient map. Characteristic diagram to do.

5A and 5B show an example of an embodiment of a return torque calculation unit of the present invention, FIG. 5A is a process flowchart, and FIG. 5B is a characteristic diagram illustrating a return torque coefficient map.

FIG. 6 is a characteristic diagram of steering torque versus assist torque in the electric power steering device.

FIG. 7 is a time chart of a steering angle, a steering torque, a steering angular velocity, and an assist torque, which represents an example of a steering state in the electric power steering device.

[Explanation of symbols]

1 ... Steering wheel 9 ... Torque sensor 10 ... Assist motor 12 ... Control unit 13 ... Battery 15 ... Vehicle speed sensor 21 ... Bridge circuit 22a to 22d ... FET 23 ... Resistance for current detection 24 ... Motor terminal voltage detection means 25 ... Motor current detection means 26 ... Rudder angular velocity estimation means 27 ... Vehicle speed calculation means 28a ... Steering torque calculating means 28b ... Basic assist torque calculation means 28c ... Torque differential correction torque calculation means 28d ... Damping torque calculating means 28e ... Return torque calculation means 29 ... Steering state determination means 30 ... Instruction current calculation means 31 ... PWM duty determining means 32 ... Power element driving means

Claims (3)

[Claims] 1. An electric power steering apparatus comprising a motor for generating an assist torque for assisting a steering torque by a driver, assisting a steering force of a steering system, and imparting a damping torque according to a steering angular velocity to the assist torque. In the above, in the steering state determination means for determining the steering state such as steering cut and return, and when the steering state determination means determines the return state, a damping torque that gives a larger damping torque than in the case of the cut state is applied. An electric power steering apparatus comprising: a torque applying unit. 2. The returning state and the dead zone when the damping torque applying means is in the state where the steering state determining means determines the returning state and is in the dead zone where the assist torque is not applied to the steering wheel. The electric power steering apparatus according to claim 1, wherein a damping torque smaller than that in a non-region is applied. 3. The steering state determination means, based on the polarity of the signal that detects the steering torque, the polarity of the signal that estimates the steering angular velocity, and the magnitude of the assist torque, the steering torque detection signal and the steering angular velocity estimation signal. Is not the same and the magnitude of the assist torque is not zero, it is determined to be the first state, and when the polarities of the steering torque detection signal and the steering angular velocity estimation signal are the same, the second state is determined. It is determined that the steering torque detection signal and the steering angular velocity estimation signal do not match in polarity and the magnitude of the assist torque is zero, the third state is determined, and the damping torque is determined. The applying means is configured such that the damping torque in each of the states is such that the damping torque in the first state> the damping torque in the second state> the damping pin in the third state. The electric power steering apparatus according to claim 1 or 2, wherein a damping torque that becomes a torque is applied.