KR20170069717A - Control method of motor driven power steering system - Google Patents

Abstract

The present invention relates to a control method of an electric steering system, and more particularly, to an electric steering control system which suppresses changes and differences in steering feeling that may occur due to wear and durability degradation of components in an electric steering system, The main purpose is to provide a method. In order to achieve the above-described object, a torque compensation amount is determined by comparing the change rate average data (learning, accumulating and averaging) of the steering torque (or the rack thrust value) with respect to the steering angle to a reference value to determine a torque compensation amount, A control apparatus and control method of an electric steering system capable of effectively suppressing a change in steering feeling that may occur due to component wear and deterioration by applying a learning control method for compensating an input torque and maintaining an initial steering feeling is disclosed do.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a control method of an electric steering system,

The present invention relates to a control method for an electric steering system, and more particularly, to a control method for an electric steering system, in which an electric steering system can suppress a change or a difference in steering feeling that may occur due to durability such as wear or deterioration of components, The present invention relates to a control method of an electric steering system.

Generally, as a power assisted steering system for reducing the steering force of a driver in the steering of a vehicle, there is a hydraulic steering system (HPS) that assists the driver's steering force by using the hydraulic pressure formed by the hydraulic pump (MDPS), which assists the driving force of a driver by using the driving torque of an electric motor, is known as a power steering system.

Among them, the MDPS provides the steering performance and steering feeling as compared with the hydraulic steering system because the output of the electric motor for the steering assist can be controlled according to the driving condition of the vehicle in performing the steering assist function according to the driver's steering wheel operation. do.

Recently, the MDPS which can change and control the steering assist force generated by the motor output according to the driving condition is widely applied to the recently released vehicle.

The MDPS includes a steering angle sensor for detecting a steering angle (column input angle) according to steering wheel operation, a torque sensor for detecting a steering torque (steering wheel torque, column torque) inputted through the steering wheel, a vehicle speed sensor for detecting a vehicle speed, (MDPS ECU), a steering motor (MDPS motor), sensors such as a sensor, an engine speed sensor, a yaw rate sensor, and the like.

In this configuration, the controller is configured to receive information about the steering such as steering angle, steering angle velocity (angular velocity value taken from the differential signal of the steering angle signal), steering input information such as steering torque, Vehicle state information (vehicle speed, wheel speed, engine speed, yaw rate, etc.).

At this time, the controller controls the driving force (motor output) of the steering motor according to the vehicle speed to generate the adjusted auxiliary torque for the steering assist. At the low speed, the motor output is increased to assist the driver to lightly operate the steering wheel , The motor output can be made small so that the steering wheel can be operated heavily at high speed so that the stability of the vehicle can be secured.

If the steering wheel is too light when the vehicle is running at a high speed, it may cause a dangerous situation even if a slight steering wheel operation is performed. Therefore, the stability of the driving operation is lost. Therefore, the steering assist characteristic is changed according to the vehicle speed, So that a stable steering wheel operation can be performed.

The output of the steering motor, which normally assists the steering assist force, is controlled by controlling the motor current (assist control current amount control) applied to the steering motor by the controller.

At this time, the controller basically calculates the amount of current corresponding to the output value (steering system output torque, i.e., the steering motor output torque) determined based on the steering input information and the vehicle state information as tuned and applies it to the steering motor, And generates a force to assist the driver's assist force through the motor drive.

As components for transmitting the steering assist force generated in accordance with the driver assist force and steering force applied through the steering wheel in the steering system described above, there are a steering column installed at a lower portion of the steering wheel, a rotational force transmitted from the steering column A gear box for converting the direction of the tire into a straight-ahead force, and a universal joint for transmitting the rotational force transmitted to the steering column to the gear box.

The gear box includes a rack bar having a pinion gear and a pinion gear meshed with the pinion gear to receive rotational force from the universal joint. When the pinion gear rotates, the rack bar moves linearly to the left and right .

At this time, the force acting by the rectilinear movement of the rack bar is transmitted to the tire through the tie rod and the ball joint, thereby changing the direction of the tire.

As described above, when the motor is driven to output a torque for steering assist, the motor output is transmitted to the rack through the reduction gear, and then the rectilinear force of the rack, that is, the rack force is transmitted to the tire, do.

FIG. 1 is a flow chart showing a conventional MDPS control process. Basically, the controller collects information about steering during running of the vehicle, that is, driver's steering input information and vehicle state information input from the sensors (S1) (Assist control current amount) for steering assist based on the collected information (S2, S3), and then controls the motor current applied to the motor by using the calculated motor current amount as the target value, And generates a motor torque (S5, S6).

In addition, in order to protect the steering motor, when the malfunction of the driver, that is, the full steering which makes the steering wheel full-turn from left to right in the stopped state is repeated a plurality of times, The overload protection logic is performed (S2, S4, S7) and then the overload protection logic is released when normal running starts.

On the other hand, as the use period of the components of the electric power steering system increases, wear or deterioration of the components may occur, which may cause an output change of the electric power steering system.

If there is a change in the output of the electric power steering system, there is a problem that the steering feeling experienced by the driver is different from that of the conventional steering system. Therefore, an output compensation scheme for the wear and deterioration of the components is required.

FIG. 2 is a view for explaining a problem of the prior art, showing durability test data of a rack and pinion gear, in which the steering wheel is rotated in the left / right full turn This is the data recording the degree of friction of the rack-and-pinion gear relative to the amount of load of the dura- tion test steering number, which is the number of times of steering wheel left / right ful- tain steering for repeated durability test.

As shown in FIG. 2, it can be seen that the degree of friction of the rack-and-pinion gears is decreased due to the occurrence of wear as the cumulative amount of the durability test steering number increases.

Such wear and tear of rack-and-pinion gears may cause wear and tear on parts such as steering motors, bushings, tie rods and ball joints of yokes, yokes, gear mating parts of steering motors, steering columns, etc., The output of the steering system can be changed even under the same conditions due to the reduction of friction between parts and the like, which causes the driver to feel a sense of steering.

FIGS. 3 and 4 are diagrams for explaining the problems of the prior art. FIG. 3 is a graph showing the steering angle and the steering torque at a specific vehicle speed condition, in which (a) (B) is a hysteresis curve showing the steering torque changed when the driving of the electric power steering system is performed for a predetermined period of time and the durability deteriorates.

As shown in FIG. 3, the frictional degree of the vehicle traveling for a long period of time can be reduced to a maximum of 65%. When the degree of friction is reduced due to wear or deterioration, And feel a loose steering feeling (the steering becomes smaller in the port).

In some cases, as shown in FIG. 4, the steering effort (steering assist force) is significantly reduced in the on-center, which is the neutral position of the steering wheel, and the steering wheel clearance near the on- It becomes quite a lot.

Therefore, even if wear or deterioration of the parts occurs, a control logic is required to feel the initial steering feeling before the occurrence of the parts.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an electric steering system capable of suppressing a change or difference in steering feeling that may occur due to durability, And to provide a control method of an electric-powered steering system.

According to an aspect of the present invention, there is provided a method of controlling a steering system, the method comprising: determining whether a state of friction reduction of a steering system due to an endurance progression from driver's steering input information collected by a sensor; Determining a torque compensation amount based on the steering angle detected by the steering angle sensor, the steering torque detected by the torque sensor, and the vehicle speed detected by the vehicle speed sensor when it is determined that the vehicle is in the friction reduction state; Calculating the steering torque detection value as a driver input torque value by compensating the detected steering torque detection value according to the determined torque compensation amount; Calculating a motor control value for steering assist from driver's steering input information including the steering angle detection value and the driver input torque value and vehicle state information including the vehicle speed detection value; And controlling the driving of the steering motor in accordance with the calculated motor control value.

Here, the step of determining whether or not the friction reduction state is determined may include a condition that the steering angle detection value detected by the steering angle sensor fluctuates within a left and right set angle range including an on-center angle, a condition that the steering torque detection value detected by the torque sensor is And when the condition that the steering angle speed is equal to or higher than the set value is satisfied, it is determined that the friction reduction state is caused by the endurance progression.

Further, when the steering angle detected value detected by the steering angle sensor is within the left set angle range based on the on-center angle, or when the biased steering input within the right set angle range is detected for more than the set time, .

The steering torque detected by the torque sensor is compared with a steering torque reference value corresponding to the current vehicle speed and steering angle detected by the vehicle speed sensor and the steering angle sensor, and a torque compensation amount corresponding to the difference is determined. do.

Thus, according to the control method of the electric power steering system according to the present invention, it is possible to recognize the occurrence of friction reduction from the steering wheel operating state of the driver and to perform the friction compensation control in the friction reduction occurrence state, It is possible to suppress the change or difference in the sense of steering which may appear due to the progress and to maintain the initial steering feeling.

1 is a flowchart showing a control process of an electric steering system according to the prior art.
2 is a graph showing that the degree of friction of rack-and-pinion gears is reduced due to wear in an electric steering system.
3 and 4 are hysteresis curves showing the steered torque as the durability progresses in the electric steering system.
5 is a flowchart illustrating a control process of an electric power steering system according to an embodiment of the present invention.
FIG. 6 is a flowchart illustrating an endurance diagnosis process and a friction compensation control process in the control process of the electric-powered steering system according to the embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

 An object of the present invention is to provide a control system and a control method of an electric power steering system capable of suppressing a change in steering feeling that may occur due to durability such as wear and deterioration of parts in an electric steering system and maintaining an initial steering feeling.

5 is a flowchart illustrating a control process of an electric power steering system according to an embodiment of the present invention.

First, the controller receives information about the steering during running of the vehicle, that is, the driver's steering input information and the vehicle state information detected by the in-vehicle sensors in real time and collects it (S11).

Here, the sensors include a steering angle sensor for detecting a steering angle (column input angle) in accordance with steering wheel operation, a torque sensor for detecting a steering torque (driver input torque, steering wheel torque, column torque) inputted through the steering wheel, A vehicle speed sensor, a wheel speed sensor, an engine speed sensor, a yaw rate sensor, and the like.

With these sensors, the controller can obtain driver's steering input information such as a steering angle, a steering angle velocity (an angular velocity value taken from a differential signal of a steering angle signal), a steering torque, and vehicle state information such as a vehicle speed, a wheel speed, Can be collected.

Then, it is determined whether the degree of friction of the steering system is reduced due to the durability of the parts constituting the steering system, such as wear or deterioration. To this end, a predetermined durability diagnosis process is performed (S12).

When it is determined that the degree of friction of the steering system is reduced due to the wear or deterioration of the parts during the durability diagnosis process, that is, the durability of the vehicle, the motor torque control is performed accordingly.

We will discuss this in more detail later.

If the degree of friction of the steering system is not reduced, it is determined whether the vehicle is in the full steering state of the stopped state (S13). If the state of the steering system is not the full steering state, The motor drive and control for the motor is performed.

That is, a motor current amount (assist control current amount) for steering assist is calculated based on the information collected from the MDPS basic logic (S14), and the motor current applied to the motor is controlled using the calculated motor current amount as a target value And generates a motor torque (steering assist torque) for steering assist (S16, S17).

For example, when the vehicle speed, which is a detection value of the vehicle speed sensor, is a stopping vehicle representing a stopping state of the vehicle, and the steering angle, which is the detection value of the steering angle sensor, It can be determined that the vehicle is in the fully-steered state of the stopped state when it is judged that the wheel is in the left-right full turn operation state.

At this time, if the left and right full-turn operation of the steering wheel is repeated a predetermined number of times, it can be determined that the vehicle is in a full-steering state in a stopped state requiring an overload prevention.

If it is determined in step S13 that the vehicle is in the fully-steered state in the stopped state, the assist amount of the steering motor, that is, the steering assist torque by the motor is reduced to the set level through the motor current control, The overload prevention logic is executed (S15, S18), and then the overload prevention logic is released when the normal running starts.

Meanwhile, FIG. 6 is a flow chart showing the durability diagnosis process and the friction compensation control process, and the durability diagnosis and the torque compensation control process performed after step S11 will be described with reference to FIG.

In the durability diagnosis and torque compensation control process, motor torque (steering assist torque) compensation is performed to determine whether the friction system of the steering system is reduced in accordance with the duration of the running from the driver's steering input information and to compensate for the friction reduction phenomenon in the friction reduction state .

When the vehicle is operated for a long period of time, the friction between the parts of the steering system is reduced. In such a vehicle, the steering wheel clearance near the on center is increased, the steering wheel is lightly operated, It becomes uneasy.

In order to compensate for this, in the present invention, occurrence of the friction reduction is recognized from the steering wheel operating state of the driver, and torque compensation is performed in the case of the friction reduction occurrence state.

If the degree of friction of the steering system is decreased due to the durability, the driver frequently operates the left and right steering wheel near the on-center. Likewise, when the degree of friction of the steering system changes, the vehicle tilts to the left or right Therefore, the driver constantly operates the steering wheel biased to one side based on the on center.

More specifically, if the clearance of the steering wheel is considerably increased near the center due to the reduction in friction between the parts, the driver feels an anomaly, and he or she can see the angle near the center, for example, within a range of -2 degrees Speed steering operation can be performed.

Such steering operation of the driver can be detected through the steering angle signal of the steering angle sensor and the torque signal of the torque sensor. If the controller determines that the steering angle detection value detected by the steering angle sensor is continuous , And when the condition that the steering torque detection value (driver input torque) detected by the torque sensor is within the set torque value is satisfied, it can be determined that it is the friction reduction state due to the endurance running.

In addition, a condition that the steering angle speed is equal to or greater than the set value may be further included, and if the steering input is within the set angle range and below the set torque value and the steering angle speed is higher than the set value, (S12-1).

As described above, the signal indicating the fast left and right steering input near the on-center is an input signal that does not occur in the normal steering system. When the steering input is detected, it is determined that the vehicle is in the friction reduction state.

In addition, if the friction between the parts continuously causes the vehicle to move to the left or right of the vehicle finely, the driver continuously operates the steering wheel biased toward one side (for example, for a few seconds) .

Therefore, when the deviation of the steering input from the steering angle signal is within the left set angle range or the right set angle range is detected for more than the set time, it can be determined to be the friction reduced state (S12-2) .

When it is determined that the controller is in the friction reduction state due to the running progression from the driver's steering input information as described above, in steps S12-3 and S12-4, the controller, based on the vehicle speed and the steering angle detected by the sensor, And calculates the torque compensation amount for compensation.

At this time, the steering torque is compared with the steering torque reference value corresponding to the current vehicle speed and the steering angle to calculate the difference value, and the torque corresponding to the calculated difference value The compensation amount is calculated.

The steering torque reference value is a value that is set in advance in the controller and determined according to the current vehicle speed and steering angle. The steering torque reference value is determined based on the initial value of the system when the electric steering system is mounted on the vehicle for the first time, Is an initial value of the system in a state in which no friction reduction due to the vehicle speed is generated. It may be an initial value data which is set to a value according to the vehicle speed and the steering angle, and is stored in the controller.

The initial value data for the steering torque can be acquired and stored at the initial driving of the system after the vehicle is mounted, or may be input to and stored in the controller after being obtained from the vehicle speed and the steering angle through the preceding research and testing.

When the torque compensation amount is determined as described above, the steering torque value detected by the torque sensor (driver input torque value) is compensated using the determined torque compensation amount, and the compensated steering torque value is set as the driver input torque for steering assistance So that the driving of the steering motor is controlled.

That is, for the motor torque compensation, the compensated steering torque value is used as driver steering input information for controlling the driving of the steering motor, and the controller uses the driver steering input information including the compensated steering torque value The motor current amount (assist control current amount) is calculated as in the conventional method, and the motor torque output for controlling the steering is controlled by controlling the motor current applied to the motor in accordance with the calculated motor current amount.

As a result, it is possible to improve deterioration of the steering feel due to the running of the steering system through the friction compensation control as described above, and to maintain the initial steering feeling even when the steering system is used for a long period of time.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments. Forms are also included within the scope of the present invention.

Claims (4)

Determining from the driver's steering input information collected by the sensor whether the state of friction of the steering system is reduced due to endurance progression;
Determining a torque compensation amount based on the steering angle detected by the steering angle sensor, the steering torque detected by the torque sensor, and the vehicle speed detected by the vehicle speed sensor when it is determined that the vehicle is in the friction reduction state;
Calculating the steering torque detection value as a driver input torque value by compensating the detected steering torque detection value according to the determined torque compensation amount;
Calculating a motor control value for steering assist from driver's steering input information including the steering angle detection value and the driver input torque value and vehicle state information including the vehicle speed detection value; And
And controlling the driving of the steering motor in accordance with the calculated motor control value.
The method according to claim 1,
Wherein the step of determining whether the friction-
A condition that the steering angle detection value detected by the steering angle sensor fluctuates within a left and right set angle range including an on center angle, a condition that the detected steering torque detection value detected by the torque sensor is within a set torque value, Or more is satisfied, it is determined that the friction reduction state is caused by the endurance progression.
The method according to claim 1,
When it is detected that the steering angle detected value detected by the steering angle sensor is within the left set angle range or within the right set angle range based on the on center angle for more than the set time, Control method of electric steering system.
The method according to claim 1,
The steering torque detected by the torque sensor is compared with a steering torque reference value corresponding to the current vehicle speed and steering angle detected by the vehicle speed sensor and the steering angle sensor, and the torque compensation amount corresponding to the difference is determined. A method of controlling a steering system.

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