KR102200093B1 - 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 provides a control method of an electric steering system that improves the steering feel and steering stability of a steering wheel by varying a torque for assisting a driver's steering force according to a road surface gradient of a driving road. It has its main purpose. In order to achieve the above object, calculating a steering assist torque for assisting a driver's steering according to a driver's steering wheel operation; Calculating a front tire radius change amount and a rear tire radius change amount of the vehicle based on the tire condition information acquired through the tire pressure monitoring system; Determining whether the driving road is a slope based on the calculated front tire radius change amount and the rear tire radius change amount; Determining a compensation torque corresponding to a difference between a front and rear tire radius variation, which is a difference between a front tire radius variation and a rear tire radius variation; And controlling the driving of a steering motor to output the compensated torque by compensating the steering auxiliary torque by the compensation torque when it is determined that the driving road is a slope. The control method of an electric steering system comprising:

Description

Control method of electric steering system {CONTROL METHOD OF MOTOR DRIVEN POWER STEERING SYSTEM}

The present invention relates to a control method of an electric steering system, and more particularly, by varying the torque for assisting the driver's steering force according to the road surface gradient of the driving road It relates to the control method.

In general, as a power assist steering system to reduce the driver's steering force when steering a vehicle, a hydraulic power steering system (HPS: Hydraulic Power Steering) that assists the driver's steering force by using hydraulic pressure formed by a hydraulic pump. System) and an electric steering system (MDPS: Motor Driven Power Steering System, hereinafter referred to as'MDPS') that assists the driver's steering force by using the driving torque of an electric motor is known.

Among them, MDPS provides improved steering performance and steering feel compared to a hydraulic steering system because the power of the electric motor is automatically controlled according to the driving conditions of the vehicle and performs the steering force assist function according to the driver's steering wheel operation.

Accordingly, MDPS, which can change and control a steering assist force generated by motor output according to driving conditions, has been widely applied in recently released vehicles.

MDPS is a steering angle sensor that detects the steering angle (column input angle) according to steering wheel operation, a torque sensor that detects steering torque (steering wheel torque, column torque) input through the steering wheel, a vehicle speed sensor that detects vehicle speed, and wheel speed. It may be configured to include sensors, such as a sensor, an engine speed sensor, and a yaw rate sensor, a controller (MDPS ECU), and a steering motor (hereinafter referred to as'MDPS motor').

In this configuration, in order to control the driving and output of the MDPS motor, the controller provides steering input information such as steering angle, steering angular velocity (angular velocity value taken from the differential signal of the steering angle signal), steering torque, etc. and vehicle state information (vehicle speed, Wheel speed, engine speed, yaw rate, etc.) are received.

At this time, the controller controls the driving force (motor output) of the MDPS motor according to the vehicle speed to generate an adjusted auxiliary torque to assist the steering force.At low speeds, the motor output is increased so that the driver can lightly operate the steering wheel to assist. And, at high speed, the motor output is reduced so that the steering wheel can be heavily manipulated, so that the driving stability of the vehicle can be secured.

If the steering wheel is too light during high-speed driving of the vehicle, a dangerous situation may occur even with a slight steering wheel operation, so driving stability is lost. Therefore, the steering assist characteristics are changed according to the vehicle speed, so that the steering wheel is operated more heavily when traveling straight at high speed. By assisting you to do it, you can operate the steering wheel with a sense of stability.

Usually, the output of the MDPS that assists the driver's steering force, that is, the output of the MDPS motor is achieved by the controller controlling the motor current applied to the MDPS motor.

At this time, the controller basically calculates a current value corresponding to the determined output value (steering system output torque, that is, MDPS motor output torque) based on the steering input information and the vehicle status information as tuned and applies it to the MDPS motor. It generates a force to assist the driver's steering force through the motor drive.

Meanwhile, in the conventional electric steering system, in controlling the motor torque for assisting the driver's steering force, proper torque compensation according to the road surface gradient of the driving road is not performed.

Therefore, as shown in FIG. 1, when the driving road is on an uphill road, the weight of the vehicle is shifted to the rear. Therefore, the steering wheel's operating force and steering feel compared to when driving on a flat land due to the movement of the load to the rear wheels and the reduction of the external force to the front tires. It becomes lighter.

On the other hand, in the case of a downhill road, since the weight of the vehicle is shifted forward, the steering wheel's maneuverability and steering feel are heavier than when driving on a flat ground due to the movement of the load to the front wheels and the increase of the external force to the front tires.

As a result, since proper motor torque control according to the slope condition of the driving road is not performed, optimal steering assistance cannot be achieved, and since the driver does not feel the same steering feeling as when driving on flat land, there is a problem of generating a sense of heterogeneity and deteriorating steering stability.

Accordingly, the present invention has been created to solve the above problems, and the electric steering system that improves the steering feel and steering stability of the steering wheel by varying the torque for assisting the driver's steering force according to the road surface gradient of the driving road. Its purpose is to provide a control method.

In order to achieve the above object, according to the present invention, there is provided a method comprising: calculating a steering assist torque for assisting a driver's steering according to a driver's steering wheel operation; Calculating a front tire radius change amount and a rear tire radius change amount of the vehicle based on the tire condition information acquired through the tire pressure monitoring system; Determining whether the driving road is a slope based on the calculated front tire radius change amount and the rear tire radius change amount; Determining a compensation torque corresponding to a difference between a front and rear tire radius variation, which is a difference between a front tire radius variation and a rear tire radius variation; And controlling the driving of the steering motor to output the compensated torque by compensating the steering auxiliary torque by the compensation torque when it is determined that the driving road is a slope. It provides a control method of an electric steering system comprising a.

Accordingly, in the control method of the electric steering system according to the present invention, the compensation torque corresponding to the road surface gradient is calculated, and the steering assistance torque calculated according to the existing MDPS logic is compensated using the calculated compensation torque. It is possible to assist the steering force according to the gradient, and it is possible to improve the operation feeling and steering stability of the steering wheel.

1 is a view for explaining the movement of a load when driving a vehicle uphill and when driving downhill.
2 is a block diagram showing the configuration of an electric steering system to which the control process of the present invention is applied.
3 is a flow chart showing the control process of the present invention.
4 is a reference diagram showing tire information.
5 is a flow chart showing a process of calculating a tire radius change amount in the present invention.
6 is a diagram showing an example of a compensation torque setting in the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention.

The present invention relates to a method of controlling an electric steering system (MDPS), and more particularly, to a method of controlling a torque output of an MDPS motor for assisting steering force.

The present invention is characterized in that the MDPS motor torque is varied according to the road surface gradient of the driving road, and more specifically, the compensation torque corresponding to the road surface gradient is calculated according to the compensation logic, and the steering auxiliary torque calculated according to the MDPS logic. It is characterized in that it compensates by using the calculated compensation torque.

Consequently, by controlling the driving of the MDPS motor to output the torque compensated by the compensation torque, the steering force assistance according to the road surface gradient of the driving road can be provided, and the steering feel and steering stability of the steering wheel can be improved.

In addition, in the present invention, based on the tire condition information of each wheel acquired through a tire pressure monitoring system (TPMS) mounted on the vehicle, it is determined whether the vehicle is driving on a slope, and when it is determined that the vehicle is driving on a slope, the tire After calculating the tire radius change amount of the front and rear wheels from the state information, the compensation torque is calculated from the calculated tire radius change amount of the front and rear wheels.

Here, as is well known, the tire pressure monitoring system is one of a kind of safety and convenience device that detects the air pressure of the tire and warns the driver through a cluster when it falls below the prescribed air pressure.

This tire pressure monitoring system (hereinafter referred to as'TPMS') includes a TPMS sensor mounted on the tires of each wheel to measure the tire pressure, and in the control process of the present invention, the controller is acquired through the TPMS sensor of each tire. The tire pressure (tire air pressure) information is received and used to determine the slope and calculate the compensation torque.

2 is a block diagram showing the configuration of an electric steering system to which the control process of the present invention is applied, and FIG. 3 is a flow chart showing the control process of the present invention.

As shown, the electric steering system includes a steering angle sensor 11 that detects a steering angle (column input angle) according to steering wheel operation, and a torque that detects steering torque (steering wheel torque, column torque) input through the steering wheel. A sensor 12, sensors such as a vehicle speed sensor 13 for detecting vehicle speed, a controller (MDPS ECU) 20, and a motor unit 30 including an MDPS motor and an inverter.

In addition, as other sensors, it may further include a wheel speed sensor 14, an engine speed sensor 15, a yaw rate sensor 16, etc., and the controller 20 controls the driving and output of the MDPS motor. It receives steering input information such as steering angle, steering angular velocity (angular velocity value taken from the differential signal of the steering angle signal), steering torque acquired through the sensors, and vehicle status information such as vehicle speed, wheel speed, engine speed, and yaw rate.

At this time, the MDPS logic unit 21 of the controller 20 calculates the motor torque for assisting the driver's steering force, that is, the steering assist torque based on the steering input information according to the driver's steering wheel manipulation and the vehicle state information such as vehicle speed. do.

In addition, in a normal case, when the steering auxiliary torque is calculated by the MDPS logic unit 21, the controller 20 outputs a control signal for controlling the driving of the MDPS motor so that the calculated steering auxiliary torque is output. The drive of the MDPS motor is controlled by controlling the motor current applied to the MDPS motor through the inverter according to the control signal.

Meanwhile, in the present invention, a TPMS 17 that acquires tire state information of each wheel through a TPMS sensor is additionally used, and the tire state information acquired from the TPMS 17 is input to the controller 20.

Here, the tire condition information may be the tire pressure of each wheel, and when the TPMS sensor detects the tire pressure and outputs a signal, the tire pressure information of each wheel detected by the TPMS sensor is input to the controller 20. do.

In a typical passenger car, TPMS sensors are installed on each tire of the left and right wheels of the front wheel, and the left and right wheels of the rear wheel, and the pressure detection signal of the TPMS sensor is transmitted wirelessly to the TPMS controller (TPMS ECU). .

Therefore, in the present invention, when the TPMS controller receives and receives the pressure detection signal output from the TPMS sensor through the wireless receiver, the tire pressure information of each wheel obtained through the TPMS sensor is transmitted to the TPMS controller through CAN communication. It may be configured to transmit to the controller (MDPS ECU) 20 of the.

Accordingly, the controller 20 of the electric steering system performing the control process of the present invention receives tire pressure information of each wheel, determines a slope from the tire pressure information, and calculates a compensation torque.

Of course, the controller 20 of the electric steering system may be configured to wirelessly receive a pressure detection signal directly from the TPMS sensor through a wireless receiver.

In FIG. 2, the compensation logic unit 22 in the controller 20 calculates the compensation torque from the tire pressure information, and the motor control logic unit 23 outputs the torque compensated by the compensation torque. Outputs a control signal for controlling driving.

In addition, the motor unit 30 controls the motor current applied to the MDPS motor by driving the inverter according to the control signal output from the motor control logic unit 23 of the controller 20, and outputs the compensated torque. The motor is driven to generate a steering assist force reflecting the road surface gradient.

Hereinafter, the control process of the present invention will be described in detail with reference to FIGS. 3 to 6.

First, when there is a driver steering input (driver steering wheel manipulation) while driving the vehicle, the controller 20 provides driver steering input information (steering angle, steering torque, steering angular speed, etc.) and vehicle status information (vehicle speed, wheel speed, etc.) according to the MDPS logic. Based on the engine speed, yaw rate, etc.), the steering assist torque for assisting the driver's steering force is calculated, and the process of calculating the steering assist torque of this MDPS logic is not different from that of a conventional electric steering system, so a detailed description is omitted. To

In addition, the controller 20 calculates the amount of change in the tire radius of each wheel by using the tire state information, that is, tire pressure information received from the TPMS 17 (S11).

4 is a reference diagram showing tire information, where P is a tire pressure, R _t is a normal tire intrinsic radius in a state in which no deformation is applied, and R _w is a wheel radius.

In addition, θ represents the deformation angle of the tire, and δ represents the amount of change in the tire radius.

In the present invention, the controller 20 receives the tire pressure of each wheel transmitted from the TPMS 17 (S21), and tire pressure using the tire and wheel specific information set and input for each wheel and the received tire pressure information The current tire volume is calculated from the relationship between the change and the volume change (S22).

Equation 1 below is an equation showing the relationship between the pressure change and the volume change of the tire.

[Equation 1]

ΔP =-βΔV

Here, β represents the rate of change in the volume of air.

In Equation 1, when the current tire pressure received from the TPMS 17 is known when the reference pressure and the tire volume at the reference pressure, that is, the reference volume is known, the current tire volume V _t can be calculated.

Here, the reference pressure may be a normal tire pressure on a flat ground, and the reference volume may be a tire volume when the tire pressure is the reference pressure.

The values of the reference pressure, the reference volume, and the volume change rate (β) of air are preset and input to the controller 20.

Accordingly, when the controller 20 receives and knows the current tire pressure from the TPMS 17, it is possible to know the current tire volume V _t .

In Equation 1, ΔP represents the difference between the reference pressure and the current tire pressure, and ΔV represents the difference between the reference volume and the current tire volume.

As described above, the controller 20 calculates the tire volume (V _t ) using Equation 1 from the tire pressure received from the TPMS 17, and then calculates the tire deformation angle (θ) from the tire volume (V _t ). Calculate (S23).

The tire radius change amount (δ) and the tire area (A) in contact with the ground are as shown in Equations 2 and 3 below, and Equation 4 is the tire deformation angle, which is real-time information and unique information about the tire and wheel of each wheel. This is an equation for obtaining the tire volume (V _t ) from θ).

[Equation 2]

[Equation 3]

In Equation 3, t represents the tire thickness.

In the end, when the tire volume (V _t ) is calculated using Equation 1, the tire volume (V _t ) and the tire and wheel-specific information (t, R _t , R _w ) of the corresponding wheel using Equation 3 From the tire deformation angle θ can be calculated.

In addition, when the tire deformation angle θ of each wheel is calculated by the above method, the tire radius change amount (δ) is calculated from the tire deformation angle θ and the tire intrinsic radius R _t using Equation 2. Can be (S24).

The tire radius change amount (δ) as described above is obtained for the tires of the front and rear wheels. Since the front and rear wheels have left and right wheels, respectively, in the present invention, the tire radius change amount (δ) of the front and rear wheels is left Any one of the wheel and right wheel tire radius variation may be selectively used.

Alternatively, if the tire radius change amount is calculated for all four wheels, the average value of the tire radius change amount of the left wheel and the tire radius change amount of the right wheel for the front and rear wheels is calculated and used as the tire radius change amount of the front wheel and the tire radius change amount of the rear wheel. Can be set to

As described above, when the tire radius change amount of the front wheel and the tire radius change amount of the rear wheel are obtained in real time, the controller 20 is the difference between the tire radius change amount of the front wheel and the tire radius change amount of the rear wheel (hereinafter referred to as'the difference between the tire radius change amount of the front and rear wheels' ) Is obtained, and it is determined whether the current driving road is a slope from the difference in the amount of change in the radius of the front and rear tires (S12).

When the vehicle is running uphill, the weight of the vehicle is shifted to the rear, so the load of the vehicle moves to the rear wheels, and the tire radius change (δ) is larger in the rear wheels than in the front wheels.

On the other hand, when the vehicle is driving downhill, the weight of the vehicle is shifted to the front, so the load of the vehicle moves to the front wheels, and the tire radius change (δ) is larger than that of the front wheels.

Therefore, when the difference in the amount of change in the front and rear tire radius is defined as'the amount of change in the tire radius of the front wheel-the amount of change in the tire radius of the rear wheel', if the difference in the amount of change in the front and rear tire radius is positive, the vehicle is driving downhill. It is driving uphill.

When the difference in the amount of change in the radius of the front and rear tires is obtained as described above, it is possible to determine whether the vehicle is traveling uphill or downhill.

In addition, in the present invention, only when the absolute value of the difference in the radius change amount of the front and rear tires is greater than or equal to the reference value, it is determined that the driving situation is on the slope, and the motor driving control is performed to reflect the compensation torque.

That is, torque compensation control according to the road surface gradient is performed only when the driving road has a large road surface gradient (road slope) above a certain level, otherwise, torque compensation control according to the road surface gradient is not performed (compensation torque '0 As in the past, the driving of the MDPS motor is controlled to output the steering assist torque calculated by the MDPS logic unit 21 (S16).

In addition, in a preferred embodiment, in the case of a driving situation on a slope, it is further determined whether the vehicle is rapidly accelerating or decelerating (S13), and the motor driving control that reflects the compensation torque is performed only when the vehicle behavior is not the sudden acceleration or deceleration. do.

This is to ignore the difference in the amount of change in the radius of the front and rear tires caused by the movement of the load due to the sudden acceleration and deceleration of the vehicle.In the case of rapid acceleration and deceleration, torque compensation control according to the road surface gradient is not performed (compensation torque ' 0') As in the past, the driving of the MDPS motor is controlled so that the output can be made with the steering auxiliary torque calculated by the MDPS logic unit 21 (S16).

The sudden acceleration and deceleration of the vehicle as described above can be determined using the differential signal of the vehicle speed signal, and if the acceleration and deceleration of the vehicle obtained from the differential of the vehicle speed signal are higher than the set value, the rapid acceleration (positive acceleration is set. Value) or rapid deceleration (when the absolute value of deceleration, which is a negative value, is greater than or equal to the set value).

In the present invention, processes such as calculation of the amount of change in tire radius, calculation of difference in the amount of change in radius of front and rear tires, determination of the slope, and determination of rapid acceleration and deceleration of the vehicle may be set to be performed by the compensation logic unit 22 in the controller 20. have.

Next, the compensation logic unit 22 of the controller 20 calculates a compensation torque corresponding to the road surface gradient when the driving road is a slope and the vehicle behavior is not rapid acceleration or rapid deceleration (S14), the compensation torque is It is determined by the difference in the radius change of the rear tire.

The difference in the amount of change in the radius of front and rear tires is a value that varies depending on the road surface gradient.The larger the road surface gradient of the driving road is, the greater the absolute value of the difference in the amount of change in the radius of the front and rear tires increases. It becomes a road with a large gradient.

To this end, the controller 20 is preset with a compensation torque corresponding to the difference in the amount of change in the front and rear tire radius, and FIG. 6 shows an example in which the compensation torque is set for the difference in the amount of change in the radius of the front and rear tires (absolute value).

Referring to the diagram of FIG. 6, the compensation torque is set to increase as the difference (absolute value) of the front and rear tire radius changes increases.

However, when the difference (absolute value) of the front and rear tire radius change amount exceeds a predetermined value, a limit value of the compensation torque is preset so that the compensation torque can be obtained as a constant value.

That is, even if the difference (absolute value) of the front and rear tire radius changes increases beyond the predetermined value, the compensation torque is set so that it does not increase beyond the threshold value. Accordingly, in the condition above the predetermined value, the compensation torque is obtained as the threshold value. Has been.

After the compensation torque is obtained as described above, torque compensation is performed by reducing the steering assist force by an amount corresponding to the compensation torque in case of an uphill road (that is, torque compensation is achieved by subtracting the compensation torque from the steering assist torque), and steering in case of a downhill road Torque compensation is achieved by increasing the auxiliary force by an amount corresponding to the compensation torque (ie, torque compensation by adding the compensation torque from the steering auxiliary torque).

At this time, the compensation torque calculated by the compensation logic unit 22 is added to or subtracted from the steering auxiliary torque calculated by the MDPS logic unit 21 so that torque compensation equal to the compensation torque is performed (S15), and the motor control logic unit 23 A control signal for controlling the driving of the MDPS motor is output so that the torque compensated for) is output.

Accordingly, the driving of the MDPS motor is controlled according to the control signal, and as a result, torque steering force assistance can be performed according to the road surface gradient.

As the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by the person skilled in the art using the basic concept of the present invention defined in the following claims The form is also included in the scope of the present invention.

11: steering angle sensor 12: torque sensor
13: vehicle speed sensor 14: wheel speed sensor
15: engine speed sensor 16: yaw rate sensor
17: TPMS 20: controller
21: MDPS logic unit 22: Compensation logic unit
23: motor control logic unit 30: motor unit

Claims (9)

Calculating a steering assist torque for assisting a driver's steering according to a driver's steering wheel operation;
Calculating a front tire radius change amount and a rear tire radius change amount of the vehicle based on the tire condition information acquired through the tire pressure monitoring system;
Determining whether the driving road is a slope based on the calculated front tire radius change amount and the rear tire radius change amount;
Determining a compensation torque corresponding to a difference between a front and rear tire radius variation, which is a difference between a front tire radius variation and a rear tire radius variation; And
When it is determined that the driving road is a slope, controlling the driving of the steering motor to output the compensated torque by compensating the steering auxiliary torque by the compensation torque;
Control method of an electric steering system comprising a.
The method according to claim 1,
The step of calculating the tire radius change amount,
Calculating a current tire volume (V _t ) from the relationship between the tire pressure change (ΔP) and the volume change (ΔP) using the tire pressure (P) information of the corresponding wheel acquired by the tire pressure monitoring system;
Calculating a tire deformation angle (θ) using the calculated tire volume (V _t ) and unique information about the set tire and wheel; And
Calculating a tire radius change amount (δ) using the calculated tire deformation angle (θ) and tire intrinsic radius information (R _t ) in a state in which no deformation is applied;
Control method of an electric steering system comprising a.
The method according to claim 2,
The tire deformation angle θ is
Characterized in that it is calculated by the following equation using the tire volume (V _t ), tire thickness (t), tire intrinsic radius (R _t ), and wheel radius (R _w ), which are specific information on the tire and wheel How to control the electric steering system.
[Equation]

The method according to claim 2,
The tire radius change amount (δ) is a control method of an electric steering system, characterized in that calculated by the following equation.
[Equation]

The method according to claim 1,
The control method of an electric steering system, wherein the compensation torque is set to a larger value as the difference (absolute value) of the front and rear tire radius change amount increases.
The method of claim 5,
The control method of an electric steering system, characterized in that, when the difference (absolute value) of the front and rear tire radius change amount exceeds a predetermined value or more, a limit value of the compensation torque is set so that the compensation torque can be obtained as a constant value.
The method of claim 5,
The difference in the amount of change in the front and rear tire radius is defined as'the amount of change in the tire radius of the front wheel-the amount of change in the tire radius of the rear wheel',
If the difference in the radius change amount of the front and rear tires is a positive value, torque compensation is performed by subtracting the compensation torque from the steering assist torque,
If the difference in the radius change amount of the front and rear tires is a negative value, torque compensation is performed by adding a compensation torque from a steering assist torque.
The method according to claim 1,
A control method of an electric steering system, comprising performing torque compensation for compensating the steering assist torque by the compensation torque by determining that the driving condition is on a slope only when the absolute value of the difference in the amount of change in the radius of the front and rear tires is greater than the reference value. .
The method according to claim 1,
In the case of a sudden acceleration in which the acceleration of the vehicle is greater than or equal to a set value or a rapid deceleration in which the deceleration (absolute value) of the vehicle is greater than or equal to the set value, torque compensation for compensating the steering assist torque by the compensation torque is not performed. Control method.

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