KR20180007061A - Motor driven power steering system control method - Google Patents

Abstract

A method for controlling an electric steering system is disclosed. The method for controlling an electric steering system according to the present invention includes: determining a neutral running state of a vehicle by a controller; detecting a skewed amount of a steering angle in the neutral running state by the controller; calculating a deflection compensation value of a rack bar corresponding to the skewed amount of the steering angle, by the controller; and controlling, by the controller, output torque by applying the deflection compensation value of the rack bar to the position of the rack bar.

Description

TECHNICAL FIELD [0001] The present invention relates to a control method for an electric power steering apparatus,

More particularly, the present invention relates to a control method of an electric steering apparatus, and more particularly, to a control method of an electric steering apparatus in real time based on a steered steering angle or a motor angle at the time of neutral running of the vehicle when the wheel alignment is broken after the end learning is completed in the rack and stop logic of the electric- The present invention relates to a control method for an electric steering apparatus that corrects a deviation of a wheel alignment to improve end steering noises and a sense of heterogeneity and maintains a steering end feeling.

2. Description of the Related Art Generally, a power assist steering apparatus for reducing a driver's steering force at the time of steering (or steering) a vehicle includes a hydraulic power steering system ), And an electric motor-driven steering system that assists the steering force by using the driving torque of the electric motor.

Such an electric steering apparatus employs a rack and stop (Rack EndStop) or SoftEndLock logic which reduces the amount of impact generated when the driver steers the vehicle.

In such a rack and stop (soft and lock) logic, steering is performed at one end (that is, the left end or the right end) of the steering angle (or the steering angle) and then the end of the running direction Steering noise and shock and heterogeneity due to the tire's elastic characteristics (ie, the inertia characteristic that is already twisted to the end and then tilted back to the end when the tail end is steered after the reverse steering) In order to solve the problem, the steering noise and the feeling of heterogeneity are improved by limiting the output according to the rack position and the speed at the end steering after each learning at the end.

However, when the wheel alignment of the vehicle is wrong, the position for reducing the output by the amount of the wrong end is not optimized, thereby generating steering noise and a sense of heterogeneity.

In other words, when the wheel alignment of the vehicle is turned to the right, if the driver steers to the left side, the end is hit before reaching the end control position set as the end, so that the rack and stop logic does not operate, If the right side steering is performed, the output is restricted too soon before the vehicle reaches the end, so that there is a problem that the steering angle is further changed when the vehicle is driven after the unevenness and the end steering.

BACKGROUND ART [0002] The background art of the present invention is disclosed in Korean Patent Registration No. 10-0247334 (Registered Electric Power Steering Device, Dec. 10, 1999).

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a steering angle control apparatus and a steering angle control method, So as to correct the deviation of the wheel alignment in real time, thereby improving end steering noises and heterogeneity, and maintaining the end steering feeling.

According to an aspect of the present invention, there is provided a control method of an electric power steering apparatus including: a controller determining a neutral traveling state of a vehicle; The controller detecting a misfit amount of the steering angle in the neutral running state; Calculating a deflection compensation value of the rack bar corresponding to the defective amount of the steering angle; And controlling the output torque by reflecting the compensation value of the rack bar to the rack bar position by the controller.

In the present invention, the step of determining the neutral running state may include: determining whether the vehicle is traveling from the vehicle speed sensor; Determining whether the yaw rate is within a left or right yaw rate when the vehicle is traveling; And a step of the controller determining whether the column torque value is equal to or lower than a set torque.

In the present invention, the step of judging the yaw rate value and the column torque value by the controller is characterized by judging that the value is inputted over the set time.

In the present invention, the step of controlling the output torque includes the steps of: determining that the controller is in the end holding state; Turning the damping boost gain application mode on or off according to a determination result of the end holding travel; Multiplying a value output by the controller according to on or off of the damping boost gain applying mode by a value output from the damping output value detecting unit and outputting as a damping correction value; And controlling the output torque of the motor in the rack and stop control section by reflecting the damping correction value.

In the present invention, the end holding traveling is a traveling operation in which the driver performs a full turn operation of the steering wheel in either one direction.

In the present invention, the controller is characterized in that the end holding travel is determined based on at least one or more pieces of information of a rack bar that is learned and output from a learning unit that learns a vehicle speed, a rack bar position, and a maximum position of the rack bar.

In the present invention, when driving after the end holding steering, the controller turns on the damping boost gain application mode and then outputs the damping boost gain value calculated in consideration of at least one of the steering angle, the initial position of the rack bar, .

In the present invention, when the end holding steering run is not performed, the controller turns off the damping boost gain application mode and then outputs '1' as the damping boost gain value, thereby practically not using the damping boost gain value .

The step of controlling the output torque in the present invention includes the steps of: the controller determining the friction state of the road surface; If the road surface is in the high friction mode, the controller turns off the output restriction; Applying the existing output limit value outputted by the controller according to the preset rack-and-stop function when the road surface is in the friction mode according to the judgment; And controlling the output torque of the motor in the rack and stop control section, when the road surface is in the low friction mode according to the determination.

In the present invention, the controller is configured such that the rack-and-wait function is applied and output according to a conventional method in the rack-bar position, the rack-bar speed, the rack-bar position learned and output from the learning unit that learns the maximum position of the rack- And the output control value, based on at least one of the output control value and the output control value.

In the present invention, the controller learns the position of the end rack bar through the learning unit, and then, based on the threshold value (threshold value) according to the rack speed and the rack thrust at the point (a) Mode is judged, and the high, medium and low friction modes according to the rack thrust are further re-determined at the point (b) (end angle -γ), and the points (a) and (b) The friction mode of the road surface is finally determined according to whether the condition and the slope pattern are satisfied.

In the present invention, the step of turning off the output limitation is a step of turning off the controller so as not to apply the current or raising the limit value since the road surface is already in a state of being sufficiently restricted by high friction.

In the present invention, the step of applying the additional output limit value is a step of applying less current to the controller than when the controller is in the middle friction state because the friction of the road surface is less than the middle friction.

A method of controlling an electric power steering apparatus according to an aspect of the present invention is a method of controlling an electric power steering apparatus in real time based on a steered steering angle or a motor angle during a neutral running of the vehicle when the wheel alignment is broken after the end learning is completed in the rack and sled logic of the electric- It is possible to improve the end steering noise and the heterogeneity and to maintain the end steering feeling by correcting the deviation.

FIG. 1 is a diagram illustrating a schematic configuration of a control apparatus for an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG.
FIG. 2 is a graph showing the friction mode determined at the tip angle in FIG.
3 is a flowchart illustrating a method of controlling an electric steering apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method of controlling an electric steering apparatus according to the present invention will be described with reference to the accompanying drawings. In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention or custom of the user, the operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

FIG. 1 is a diagram illustrating a schematic configuration of a control apparatus for an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG.

1, the control apparatus for an electric steering system according to the present embodiment includes a steering angle sensor 10, a vehicle speed sensor 20, a torque sensor 30, a controller 40, a motor 50, And a rate sensor 70.

In the present embodiment, the motor-driven steering device may employ a Motor Driven Power Steering System (MDPS) that assists the steering force by using the motor 50. In the present embodiment, the MDPS includes a column drive system (C-MDPS) in which a motor 50 is coupled to a steering shaft (not shown), a pinion drive system in which a motor 50 is coupled to a pinion gear P-MDPS), and a rack driving system (R-MDPS) in which the motor 50 is coupled to a rack gear (not shown). For reference, in this embodiment, the rack driving system (R-MDPS) will be described as an example.

Generally, the rack driving method is a method of realizing the axial movement of a rack bar (not shown) in response to the driving torque by the motor 50, by changing the rotational force of the motor 50 to the axial linear movement force of the rack bar A belt, a pulley and a ball nut, a bearing, and a ball screw type rack bar are used for this purpose. That is, the ball nut is rotatably supported by the bearing in the reducer, and the driving pulley is fixed to the driving shaft of the motor 50 so that the driven pulley transmits rotational force to the ball nut coupled to the rack bar A belt is connected between the drive pulley on the motor 50 side and the driven pulley on the ball nut side to transmit the rotational force of the motor 50 to the rack bar through the pulley and the belt. At this time, the rotational force of the motor 50 is converted into a power by the straight line of the rack bar by the ball screw structure of the ball nut and the rack bar.

The torque sensor 30 detects the steering torque of a steering wheel (not shown) and inputs it to the controller 40.

The steering angle sensor 10 detects the steering angle of the steering wheel and inputs it to the controller 40.

The vehicle speed sensor 20 senses the vehicle speed of the vehicle and inputs it to the controller 40. [

The yaw rate sensor 70 senses the tilted state of the vehicle and inputs the yaw rate value to the controller 40.

The controller 40 detects the steering angle based on the steering torque, the steering angle, the vehicle speed, the steering angle, and the yaw rate value input from the torque sensor 30 and the steering angle sensor 10, the vehicle speed sensor 20 and the yaw rate sensor 70, The output control value is detected according to the output control value output logic of the motor driven power steering system using the rack movement speed detected through the steering angle speed or the motor rotation speed, And controls the output torque of the motor 50 based on the detected rack and stop control period after setting the rack and stop control period based on the current position of the rack bar that compensates the detected rack and stop control period.

The controller 40 includes an output control value detector 45, a learning unit 41, an initial output limit value detector 42, a damping output value detector 43, a final output limit value detector 44, an output torque controller 46, A damping boost gain output unit 62, a damping correction value output unit 63, a road surface friction determination unit 64, a skid detection unit 71, and a skew compensation unit 72 .

Generally, when the driver operates the steering wheel in a full turn, the rack and stop function reduces the output torque of the motor 50 to limit the current applied to the motor 50, Minimizes impact between IBJ sockets (housings). The rack and stop control section for this purpose is a position range of the rack bar just before the collision between the stopper of the rack bar and the IBJ socket (housing) of the gear box as described above.

Accordingly, when the rack bar enters the rack and stop control section, the controller 40 limits the output torque of the motor 50 to minimize the impact due to the collision between the stopper of the rack bar and the IBJ socket of the gear box, Thereby preventing mechanical damage to the components.

The rack and stop control section is set based on the maximum position of the rack bar.

For example, when the maximum position of the rack bar is set to '-77 to +77' in the left and right directions, the rack and stop control section is set to '-77 to -70' and '+70 to +77' Lt; / RTI > In this case, when the present position of the rack bar reaches '-77 to -70' or '+70 to +77', the controller 40 limits the output torque to be outputted to the motor 50 so that the stopper of the rack bar and the gear box Minimizes impact between IBJ sockets (housings).

Meanwhile, the rack and stop control section is set based on the maximum position of the rack bar as described above. The maximum position of the rack bar is different from the target value due to hardware differences such as the length of the gear box rack bar, Lt; / RTI >

The controller 40 newly detects the maximum position of the rack bar based on the current position of the rack bar when the driver makes a full turn of the steering wheel, learns the rack and stop control section based on the detected maximum position, And controls the output torque of the motor 50 on the basis of the newly learned rack and stop control section.

To this end, the learning unit 41 detects the current position of the rack bar, compares the current position of the rack bar with the maximum position of the predetermined rack bar, and updates the maximum position of the rack bar according to the comparison result.

Here, the maximum position of the rack bar may be the initial value set at the time of manufacture as described above, but may also include the maximum position of the rack bar previously detected in the driver's steering process.

On the other hand, the learning unit 41 updates the maximum position of the rack bar to the current position of the rack bar when the current position of the rack bar exceeds the maximum position of the rack bar as a result of comparing the current position of the rack bar and the maximum position of the predetermined rack bar.

In this case, the learning unit 41 uses the updated maximum position of the rack bar to set the rack and stop control zone, and shifts the rack and stop control zone by the difference between the current position of the rack bar and the maximum position of the rack bar. In this case, the learning unit 41 moves the entry position and the end position of the rack and stop control section by the difference value, respectively.

The learning section 41 steers the steering wheel in the leftward direction or the rightward direction so that the current position of the rack bar is shifted to the maximum position of the rack bar And the rack and stop control section is set independently for each of the left steering direction and the right side steering direction each time the steering angle is exceeded.

The initial output limit value detector 42 detects the current position of the rack bar and the moving speed of the rack bar as described above, and detects the initial output limit value using the current position and the moving speed of the rack bar. In addition, the initial output limit value detector 42 compensates the initial output limit value after detecting a predetermined vehicle speed gain corresponding to the vehicle speed. Here, the initial output limit value is composed of a two-dimensional look-up table according to the current position and the moving speed of the rack bar.

The damping output value detector 43 detects the damping output value using at least one of the steering speed, the rotation speed of the motor 50, and the moving speed of the rack bar. In this case, the damping output value is pre-set for either the above-mentioned steering speed, the rotational speed of the motor 50, or the moving speed of the rack bar. Here, the damping output value is used to detect the final output limit value by correcting the initial output limit value.

The final output limit value detector 44 receives the initial output limit value and the damping output value from the initial output limit value detector 42 and the damping output value detector 43 and detects the final output limit value using the initial output limit value and the damping output value .

In this case, the final output limit value detector 44 subtracts the damping output value from the initial output limit value and detects the final output limit value. In this case, if the damping output value is relatively larger than the initial output limit value, the final output limit value may become (-) value.

In this case, when the final output limit value is (+), the output of the electric power steering apparatus is limited. When the final output limit value is (-), an output opposite to the output direction of the electric steering apparatus can be generated.

The output control value detection unit 45 detects the output control value based on the steering angle detected by the steering torque, the steering angle, the vehicle speed, and the steering angle inputted from the torque sensor 30, the steering angle sensor 10 and the vehicle speed sensor 20, And the output control value is detected according to the output control value output logic of the steering apparatus.

Here, the output control value detector 45 detects the output control value according to the output control value output logic of the existing electric steering system, and detects the output control value applied with the rack and stop function according to the conventional method. At this time, the output control value output logic of the electric steering system is generally employed in the motor control of the electric steering system, and a detailed description thereof will be omitted here.

The output torque control unit 46 receives the final output limit value and the output control value from the final output limit value detection unit 44 and the output control value detection unit 45, compares the final output limit value and the output control value, And controls the motor 50 based on any one of the final output limit value and the output control value.

That is, the output torque control unit 46 compares the final output limit value with the output control value. The output torque control unit 46 controls the output torque of the motor 50 according to a relatively small value of the final output limit value and the output control value, If the limit value is smaller than the output control value, the output torque of the motor 50 is controlled according to the final output limit value.

Here, limiting the output torque of the motor 50 through the final output limit value or the like can be replaced by limiting the output current of the motor 50. [

Instead of the position of the rack bar, the steering angle detected by the steering angle sensor 10 or the detected steering angle through the motor rotational angle may be employed, and instead of the moving speed of the rack bar, through the steering angle speed or the motor rotational speed obtained through the steering angle The acquired steering angle velocity can be employed.

As described above, the controller of the electric power steering apparatus according to the present embodiment changes the rack and stop control period based on the end position of the rack bar, detects the output limit value of the electric steering apparatus based on the changed rack and stop control period, It improves the performance difference by mass production scattering.

Further, the control apparatus of the electric steering system according to the present embodiment reduces the amount of impact generated when the steering angle is steered, thereby mitigating the impact caused by the collision between the stopper of the rack bar and the IBJ socket (housing) of the gear box, Prevent mechanical damage of parts.

The end holding running determination unit 61 determines whether the driver manipulates the steering wheel in a full turn.

The end holding running determination unit 61 determines whether the driver manipulates the steering wheel based on at least one of the vehicle speed, the rack bar position, and the rack bar position that is learned and output from the learning unit 41 .

The damping boost gain output unit 62 turns on the damping boost gain applying mode at the time of driving after the full-wheel steering according to the determination result of the end holding driving determination unit 61. When the damping boost gain applying mode is turned ON, the damping boost gain output section 62 outputs the damping boost gain value calculated in consideration of the vehicle speed.

On the other hand, when the full-wheel-steer-traveling is not performed, the damping boost gain output unit 62 turns off the damping boost gain application mode. When the damping boost gain application mode is turned off, the damping boost gain output unit 62 outputs '1' as the damping boost gain value.

The damping correction value output unit 63 multiplies the value output from the damping output value detector 43 by the value output from the damping boost gain output unit 62 and outputs the calculated damping correction value.

When the value output from the damping boost gain output unit 62 is '1', the damping correction value output unit 63 outputs the value output from the damping output value detection unit 43 directly to the final output limit value detection unit 44 , And when the value output from the damping boost gain output unit 62 is not '1', the final output limit value detecting unit 44 multiplies the value by the value output from the damping boost gain output unit 62, .

Therefore, when the driver drives the steering wheel after performing a full turn operation, the final output limit value detector 44 can further reduce the existing output limit Max value according to the application of the damping boost gain.

For example, assuming that the road is formed in the form of an S-shape, such as a road formed on a mountainous slope, the driver may turn the steering wheel in one direction and then rotate the steering wheel in a direction Steering noise, shock and a sense of heterogeneity are additionally generated according to the elastic characteristics of the steering wheel (i.e., the characteristic of returning to a twisted state). However, in this embodiment, damping boost gain values are applied to the damping The correction value is outputted to the final output limit value detector 44 so that the existing output limit Max value can be further reduced, thereby reducing the steering noise, the shock and the heterogeneity.

The road surface friction determination unit 64 determines the friction state of the road surface.

That is, the road surface friction judging unit 64 judges whether or not the rack position (i.e., the rack position), the rack bar speed (i.e., rack speed), the rack bar position learned by the learning unit 41, Based on information of at least one of the output control values to which the rack and stop function is applied and outputted according to the conventional method.

For example, after learning the end rack position (rack bar position) through the learning unit 41, the road surface friction determination unit 64 determines the rack speed and the rack speed at a point (end angle?) (I.e., And the high, medium, and low friction modes are determined according to the threshold value according to the rack thrust. Further, the high, medium and low friction modes are determined according to the rack thrust according to the rack thrust at the point (end angle-γ) The low and low friction modes are re-determined (see the graph of FIG. 2).

FIG. 2 is a graph showing the friction mode determined at the tip angle in FIG.

In the graph of Fig. 2, the x-axis represents the position of the rack bar and the y-axis represents the current value.

Referring to FIG. 2, the road surface friction determination unit 64 applies a second additional determination criterion at the end point when changing the road surface load after mode switching at a point (edge angle-beta).

Accordingly, in the case of fine steering at the end of a normal road surface, only a small torque is required, and therefore, there is a problem in that it can be misjudged when discriminating high and low friction road surfaces. Therefore, ) Judging from the first-order point in the steering condition (eg, specific speed, specific steering angle) and maintaining the rising pattern of the torque up to the second point, it is judged as high and low friction road surface.

Actually, the torque increases as the steering is steered to the end during normal steering. The amount of current is measured under the condition that the pattern is below a certain level or above, and the two points (i.e., the first point and the second point) If the set current condition is satisfied (for example, the tilt increasing condition as shown in FIG. 2 is satisfied) and the pattern is satisfied, it is determined that the friction road is a corresponding friction road (for example, high friction road surface, heavy friction road surface, low friction road surface).

The road surface friction determination unit 64 determines whether or not the output limit is OFF in the high friction mode (i.e., the current is not applied because the limit is already sufficiently limited due to the high friction) (Ie, less current is applied than in the case of heavy friction due to low friction).

Accordingly, in the normal environment, the driver can reduce the noise generated by the steering at the end of the steering wheel through the motor control, and when the driver holds the end of the vehicle at the predetermined end position according to the vehicle speed and the end learning, By further increasing the elasticity in consideration of the elasticity, noise and heterogeneity can be improved.

Further, by determining the abnormal road surface (i.e., low and high friction road surface) and varying the output limit value accordingly, the driver can maintain the optimized steering feeling under any condition.

Then, the misalignment detecting unit 71 detects the misalignment of the wheel alignment of the vehicle.

That is, the deviation detector 71 receives the vehicle speed, the yaw rate value, the steering angle and the column torque from the vehicle speed sensor 20, the yaw rate sensor 70, the steering angle sensor 10 and the torque sensor 30, And detects a deviation.

The skid detection unit 71 determines the running state of the vehicle through the vehicle speed and determines whether the vehicle meets the neutral running condition based on the yaw rate value when the vehicle is running. That is, it is determined whether or not the yaw rate value is inputted within the set yaw rate for the set time or longer. Here, when the vehicle is in the neutral running state, the yaw rate value of the vehicle is maintained in the straight running state within the left and right set yaw rate without turning to the right or left.

Further, the deviation detector 71 determines whether or not the column torque value according to the vehicle speed is equal to or lower than the set torque for a predetermined period of time. Here, the set torque can be set differently according to the vehicle speed and the self-alignment characteristic.

In this way, when the vehicle is in the neutral running state, the skid detection unit 71 can determine that the wheel alignment is turned to the left or right when the steering angle or the motor angle is received and is larger than a general offset or a hysteresis error.

Therefore, the deviation detection unit 71 detects the steering angle or the amount of misalignment of the motor angle when the wheel alignment is distorted in the neutral running state of the vehicle.

The skew compensation unit 72 calculates the skew compensation value of the rack bar corresponding to the skewed amount of the steering angle detected by the skew detection unit 71 and outputs the skew compensation value to the initial output limit value detection unit 42 and the road surface friction determination unit 64, And compensates the left and right ends of the rack bar position learned in the step 41.

The deflection compensating unit 72 converts the steering angle detected by the deflection detecting unit 71 or the amount of the motor angle into a wrong length of the rack bar in consideration of mechanical characteristics.

For example, when the steering angle is 20 deg from the neutral driving state and 20/360 * C-Factor (60 mm / rev) is applied to the electric steering system of the R-MDPS, The bar can be converted to a wrong one. Therefore, 3.33mm offset amount is offset to the left and right ends of the learned rack bar.

That is, when the left and right ends of the learned rack bar are offset from the left -77 mm / right 77 mm, the offset can be corrected to 73.67 mm left / right and 80.33 mm right.

In this way, it is possible to correct the deviation of the wheel alignment in real time based on the steering angle or the motor angle that is changed during the neutral traveling of the vehicle, thereby improving the end steering noise and the sense of heterogeneity and maintaining the end steering feeling.

3 is a flowchart illustrating a method of controlling an electric steering apparatus according to an embodiment of the present invention.

As shown in FIG. 3, the control method of the electric power steering apparatus according to an embodiment of the present invention first determines whether the controller 40 is in the neutral traveling state of the vehicle.

That is, the controller 40 receives the vehicle speed from the vehicle speed sensor 20 and determines whether the vehicle is running (S10).

If the vehicle is running in step S10, the controller 40 receives the yaw rate from the yaw rate sensor 70 and determines whether the yaw rate is less than the set yaw rate (step S20).

Further, the controller 40 receives the column torque value from the torque sensor 30 and determines whether it is less than the set torque (S30).

Here, the set torque can be set differently according to the vehicle speed and the self-alignment characteristic.

In step S20, the controller 40 determines whether or not the yaw rate is greater than the set time to determine the neutral running state of the vehicle when the yaw rate is less than the left and right set yaw rates and the column torque value is less than the set torque in step S30. It is determined whether a torque value is input (S40).

However, if the yaw rate value exceeds the left and right set yaw rate at step S20 and the column torque value exceeds the preset torque at step S30, the controller 40 returns to step S10 to determine whether the vehicle is running Thereby determining the neutral running state of the vehicle.

In step S40, the controller 40 also returns to step S10 to determine whether or not the yaw rate and the column torque are continuously input even when the yaw rate and the column torque are not inputted to the left and right set yaw rate and the set torque beyond the set time.

If the vehicle is in the neutral traveling state, the controller 40 receives the steering angle from the steering angle sensor 10 and detects the amount of steering angle deviation (S50).

Here, the controller 40 receives the steering angle, determines that the wheel alignment has been changed to the left or right when it is larger than the general offset or the hysteresis error, and detects a wrong amount of the steering angle

In step S50, the controller 40 calculates the deflection compensation value of the rack bar corresponding to the defective amount of the steering angle (S60).

That is, the controller 40 converts the detected amount of the detected steering angle into a wrong length of the rack bar in consideration of mechanical characteristics.

For example, when the steering angle is 20 deg from the neutral driving state and 20/360 * C-Factor (60 mm / rev) is applied to the electric steering system of the R-MDPS, The bar can be converted to a wrong one.

Thereafter, the controller 40 compensates the deflection compensation value of the rack bar calculated in step S60 by reflecting the left and right ends of the rack bar position learned in the learning unit 41 (S70).

For example, offset compensation is performed to the left and right ends of the learned rack bar, where the calculated compensation value of the rack bar is 3.33 mm.

That is, when the left and right ends of the learned rack bar are offset from the left -77 mm / right 77 mm, the offset can be corrected to 73.67 mm left / right and 80.33 mm right.

After correcting the learned left and right positions of the rack bar in step S70, the controller 40 is inputted to the initial output limit value detector 42 and the road surface friction determiner 64 to perform the output torque control (S80) .

Thus, by correcting the deviation of the wheel alignment in real time based on the steered steering angle or the motor angle during the neutral driving of the vehicle, the output torque can be controlled to improve the end steering noise and the heterogeneity and maintain the steering feeling at the end when performing the rack and stop function .

As described above, according to the control method of the electric power steering system according to the embodiment of the present invention, when the wheel alignment is broken after the end learning is completed in the rack and sled logic of the electric steering system, It is possible to correct the deviation of the wheel alignment in real time to improve the end steering noise and the sense of heterogeneity and to maintain the end steering feeling.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. I will understand.

Accordingly, the true scope of the present invention should be determined by the following claims.

10: steering angle sensor 20: vehicle speed sensor
30: torque sensor 40: controller
41: learning section 42: initial output limit value detecting section
43: damping output value detecting section 44: final output limit value detecting section
45: output control value detecting section 46: output torque control section
50: motor 61: end holding driving judging unit
62: Damping boost gain output section 63: Damping correction value output section
64: road friction judging unit 70: yaw rate sensor
71: Distortion detection unit 72: Distortion compensation unit

Claims (13)

Determining a neutral running state of the vehicle by the controller;
The controller detecting a misfit amount of the steering angle in the neutral running state;
The controller calculating a deflection compensation value of the rack bar corresponding to the defective amount of the steering angle; And
And controlling the output torque by reflecting the compensation value of the rack bar to the rack bar position by the controller.
2. The method of claim 1, wherein the determining of the neutral running condition comprises:
Determining whether the vehicle is traveling from the vehicle speed sensor;
Determining whether the yaw rate is within a left or right yaw rate when the vehicle is traveling; And
And the controller determines whether the column torque value is equal to or lower than a set torque.
3. The method according to claim 2, wherein the step of the controller determining the yaw rate value and the column torque value is determined to be a value input over a set time.
2. The method of claim 1, wherein controlling the output torque comprises:
Determining that the controller is in the end holding driving state;
Turning the damping boost gain application mode on or off according to a determination result of the end holding travel;
Multiplying the value output from the damping output value detecting unit by a value output according to on or off of the damping boost gain applying mode and outputting the result as a damping correction value; And
And controlling the output torque of the motor in the rack and stop control section based on the damping correction value.
5. The method according to claim 4,
Wherein the driver is a traveling operation in which the steering wheel is operated in a full turn operation in any one direction.
5. The apparatus of claim 4,
Wherein the end holding travel is determined on the basis of at least one or more information of a rack bar that is learned and output from a learning unit that learns a vehicle speed, a rack bar position, and a maximum position of the rack bar.
5. The apparatus of claim 4,
Wherein the damping boost gain calculating means outputs the damping boost gain value calculated in consideration of at least one of the steering angle, the initial position of the rack bar, and the steering speed, when the vehicle runs after the end holding steering, / RTI >
5. The apparatus of claim 4,
When the end holding steering operation is not performed, the damping boost gain application mode is turned off, and then '1' is outputted as the damping boost gain value to substantially do not use the damping boost gain value Way.
2. The method of claim 1, wherein controlling the output torque comprises:
Determining the friction state of the road surface by the controller;
Turning off the output limit when the road surface is in the high friction mode according to the determination;
Applying the existing output limit value output by the controller according to the preset rack-and-stop function when the road surface is in the abrasion mode according to the determination; And
And controlling the output torque of the motor in a rack and stop control period by applying the additional output limit value when the road surface is in a low friction mode according to the determination.
10. The apparatus of claim 9,
At least one or more pieces of information among the rack bar position, the rack bar speed, the rack bar position learned and learned by the learning unit learning the maximum position of the rack bar, and the output control value to which the rack- Wherein the friction of the road surface on which the vehicle is currently traveling is detected based on the detected friction coefficient.
10. The apparatus of claim 9,
After learning the position of the end rack bar through the learning department,
The high, medium, and low friction modes are determined according to the threshold value according to the rack speed and the rack thrust at the ⓐ (end angle-β) point. High, medium, and low friction modes,
Wherein the final determination of the friction mode of the road surface is made according to whether the two points (a) and (b) satisfy the preset current condition and the tilt pattern according to the high, medium, and low friction modes.
10. The method of claim 9, wherein turning off the output limit comprises:
Wherein the controller is turned off or the limit value is raised so that the controller does not apply the current because the road surface has already been sufficiently restricted by high friction.
10. The method of claim 9, wherein applying the additional output limit comprises:
Wherein the controller is configured to apply less current than when the controller is in the middle of friction because the friction of the road surface is less than that of the middle friction.

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