Reaction torque control device and method for SBW system

Abstract

The present document relates to a device and method for controlling a reaction torque of an SBW system, which may include a yaw rate estimator for estimating a yaw rate of a vehicle, a vehicle state determinator for comparing a detection result of a yaw rate detection sensor and a yaw rate estimate which is estimated by the yaw rate estimator to determine whether the vehicle is in an under-steer or over-steer state, and a target torque compensator for compensating for a target torque by using an index which is a determination result of the vehicle state determinator and outputting a final target torque.

Claims

1. A Steer-By-Wire (SBW) system in a vehicle, the system comprising: a motor configured to steer the vehicle; and a controller configured to: determine a first yaw rate based on a vehicle speed from a vehicle speed sensor in the vehicle and a rack position from a rack position sensor in the vehicle, determine an index indicating whether the vehicle is under-steered or over-steered based on the first yaw rate and a second yaw rate from a yaw rate sensor in the vehicle, determine a plurality of first target torques based on the index and a plurality of input target torques of the motor, the first target torque including a torque obtained by compensating the input target torque using the index, determine a second target torque by adding the plurality of the first target torques, generate a final target torque signal based on the second target torque, and apply the final target torque signal to the motor.

2. The system of claim 1, wherein the controller is configured to determine the first yaw rate by using Mathematical Formula 1 below: $\begin{array}{cc}\stackrel{.}{}\left[\mathrm{deg}/s\right]=\frac{V}{L+\frac{K{V}^2}{57.3g}}\left(Gx\right)& \left[\mathrm{Mathematical}\mathrm{Formula}1\right]\end{array}$ wherein V is the vehicle speed (m/s) from the vehicle speed sensor, L is a wheel base length (m) of the vehicle, g is the gravitational acceleration, K is an under-steer gradient (deg/g), G is a converted value (deg/mm), and x is the rack position (mm) from the rack position sensor.

3. The system of claim 1, wherein the controller is further configured to: determine difference information by subtracting the first yaw rate from the second yaw rate, compare an absolute value of the difference information with a threshold, and determine whether the vehicle is in a normal state or an abnormal state based on the comparison.

4. The system of claim 3, wherein the controller is further configured to: determine the vehicle to be in the normal state in the case that the absolute value is equal or less than the threshold, or determine the vehicle to be in the abnormal state in the case that the absolute value is greater than the threshold.

5. The system of claim 4, wherein the controller is further configured to: determine whether a first sign of the difference information is the same as a second sign of the second yaw rate when the vehicle is in the abnormal state, determine that the vehicle is over-steered when the first sign is the same as the second sign, and determine the index indicating that the vehicle is over-steered.

6. The system of claim 4, wherein the controller is further configured to: determine whether a first sign of the difference information is the same as a second sign of the second yaw rate when the vehicle is in the abnormal state, determine that the vehicle is under-steered when the first sign is different from the second sign, and determine the index indicating that the vehicle is under-steered.

7. The system of claim 1, wherein the controller is configured to determine the second target torque through Mathematical Formula 2 below:
T.sub.comp=T.sub.origin{(1f)Gain+f}[Mathematical Formula 2] wherein T.sub.comp is the second target torque, T.sub.origin is the first target torque, f is the index, and Gain is any adjustable value.

8. A method for controlling a motor configured to steer a vehicle, the method comprising: determining a first yaw rate based on a vehicle speed from a vehicle speed sensor in the vehicle and a rack position from a rack position sensor in the vehicle; determining an index indicating whether the vehicle is under-steered or over-steered based on the first yaw rate and a second yaw rate from a yaw rate sensor in the vehicle; determining a plurality of first target torques based on the index and a plurality of input target torques of the motor, the first target torque including a torque obtained by compensating the input target torque using the index; determining a second target torque by adding the plurality of the first target torques; generating a final target torque signal based on the second target torque; and applying the final target torque signal to the motor.

9. The method of claim 8, wherein the first yaw rate is determined by using Mathematical Formula 1 below: $\begin{array}{cc}\stackrel{.}{}\left[\mathrm{deg}/s\right]=\frac{V}{L+\frac{K{V}^2}{57.3g}}\left(Gx\right)& \left[\mathrm{Mathematical}\mathrm{Formula}1\right]\end{array}$ wherein V is the vehicle speed (m/s) from the vehicle speed sensor, L is a wheel base length (m) of the vehicle, g is the gravitational acceleration, K is an under-steer gradient (deg/g), G is a converted value (deg/mm), and x is the rack position (mm) from the rack position sensor.

10. The method of claim 8, wherein the determining the index comprises: determining difference information by subtracting the first yaw rate from the second yaw rate, comparing an absolute value of the difference information with a threshold, and determining whether the vehicle is in a normal state or an abnormal state based on the comparison.

11. The method of claim 10, wherein the determining whether the vehicle is in the normal state or the abnormal state comprises: determining the vehicle to be in the normal state in the case that the absolute value is equal to or less than the threshold, or determining the vehicle to be in the abnormal state in the case that the absolute value is greater than the threshold.

12. The method of claim 11, wherein the determining whether the vehicle is in the normal state or the abnormal state further comprises: determining whether a first sign of the difference information is the same as a second sign of the second yaw rate when the vehicle is in the abnormal state, determining that the vehicle is over-steered when the first sign is the same as the second sign, and determining the index indicating that the vehicle is over-steered.

13. The method of claim 11, wherein the determining whether the vehicle is in the normal state or the abnormal state further comprises: determining whether a first sign of the difference information is the same as a second sign of the second yaw rate when the vehicle is in the abnormal state, determining that the vehicle is under-steered when the first sign is different from the second sign, and determining the index indicating that the vehicle is under-steered.

14. The method of claim 8, wherein the second target torque is determined through Mathematical Formula 2 below:
T.sub.comp=T.sub.origin{(1f)Gain+f}[Mathematical Formula 2] wherein T.sub.comp is the second target torque, T.sub.origin is the first target torque, f is the index, and Gain is any adjustable value.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a block diagram of the device for controlling a reaction torque of an SBW system according to a preferred exemplary embodiment of the present disclosure.

(2) FIG. 2 is an operation flowchart of a vehicle state determinator.

(3) FIG. 3 is an exemplary diagram of an over-steer case determined in the present disclosure.

(4) FIG. 4 is an exemplary diagram of an under-steer case determined in the present disclosure.

(5) FIG. 5 is a block diagram of a target torque compensator in the present disclosure.

MODES OF THE INVENTION

(6) Hereinafter, the device and method for controlling a reaction torque of an SBW system according to the present disclosure will be described in detail with reference to the accompanying drawings.

(7) Exemplary embodiments of the present disclosure are provided to describe the disclosure more fully to those of ordinary skill in the art. Exemplary embodiments described below may be modified in different forms, and the scope of the present disclosure is not limited thereto. Rather, these exemplary embodiments are provided so that the present disclosure will be thorough and complete and will fully convey the spirit of the present disclosure to those of ordinary skill in the art.

(8) Terms used herein are intended to describe particular exemplary embodiments and are not intended to limit the scope of the present disclosure. Unless the context clearly indicates otherwise, a singular form may include a plural form. As used herein, the terms comprise and/or comprising specify the presence of mentioned shapes, numbers, steps, operations, members, elements and/or groups thereof, but do not exclude the presence or addition of at least one other shape, number, step, operation, member, element and/or group thereof. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

(9) The terms first, second and the like are used to describe various members, areas and/or regions, but do not limit such members, parts, areas, layers and/or regions. These terms do not mean a certain order, top or bottom or priority and are used only to distinguish one member, area or region from another member, area or region. Therefore, a first member, area or region may indicate a second member, area or region without deviating from the spirit of the present disclosure.

(10) Hereinafter, the exemplary embodiments of the present disclosure will be described below with reference to drawings which schematically illustrate the exemplary embodiments. In the drawings, illustrated shapes may change according to, for example, manufacturing technology and/or tolerance. Accordingly, the exemplary embodiments of the present disclosure should not be construed as limited to specific shapes of areas illustrated herein and include changes in shapes that may occur during manufacturing.

(11) FIG. 1 is a block diagram of the device for controlling a reaction torque of an SBW system according to a preferred exemplary embodiment of the present disclosure.

(12) Referring to FIG. 1, the present disclosure includes a yaw rate estimator 10 for using a vehicle speed and to rack position detected by a vehicle speed sensor 11 and a rack position sensor 12, a vehicle state determinator 20 for determining the state of a vehicle by comparing a yaw rate estimate estimated by the yaw rate estimator 10 with a yaw rate detected by a yaw rate detection sensor 21, and a target torque compensator 30 for outputting a final reaction torque by using the vehicle state determined by the vehicle state determinator and the target torque.

(13) Hereinafter, the configuration and operation of the reaction torque control device of the SBW system of the present disclosure configured as described above will be described in more detail.

(14) First, the yaw rate estimator 10 estimates a yaw rate by using data measurable through a sensor and a vehicle dynamics model.

(15) To this end, the yaw rate estimator 10 detects a vehicle speed and a rack position through the vehicle speed sensor 11 and the rack position sensor 12, and estimates the yaw rate of the current vehicle by using a steady-state turning equation.

(16) The yaw rate estimator 10 uses the yaw rate gain formula of the steady-state turning equation defined by Mathematical Formula 1 below, and by reflecting the characteristics of the SBW system, the yaw rate is estimated by using the equation of Mathematical Formula 2 in which the steering angle part of the wheel is substituted by the product of the rack displacement conversion value.

(17) $\begin{array}{cc}\stackrel{.}{}\left[\mathrm{deg}/s\right]=\frac{V}{L+\frac{K{V}^2}{57.3g}}& \left[\mathrm{Mathematical}\mathrm{Formula}1\right]\end{array}$$\begin{array}{cc}\stackrel{.}{}\left[\mathrm{deg}/s\right]=\frac{V}{L+\frac{K{V}^2}{57.3g}}\left(Gx\right)& \left[\mathrm{Mathematical}\mathrm{Formula}2\right]\end{array}$

(18) In Mathematical Formulas 1 and 2 above, V is the vehicle speed (m/s), L is the wheelbase length (m) of a vehicle, g is the gravitational acceleration, K is the under-steer gradient (deg/g), is the steer angle (deg) of a vehicle wheel, G is the conversion value (deg/mm), and x is the rack position (mm).

(19) The yaw rate estimator 10 obtains a value of x from the rack position sensor 12 and a value of V from the vehicle speed sensor 11 to calculate a yaw rate estimate.

(20) The yaw rate estimate is provided to the vehicle state determinator 20.

(21) The vehicle state determinator 20 determines the current state of a vehicle by using the yaw rate estimate and the yaw rate detected by the yaw rate detection sensor 21.

(22) The vehicle state determinator 20 calculates yaw rate difference information, which is a difference between the yaw rate of the yaw rate detection sensor 21 and the yaw rate estimate, and compares the yaw rate difference information with a reference value to determine whether the vehicle is in a normal state, or an under-steer or over-steer state.

(23) To describe this in more detail, FIG. 2 is a flowchart of the calculation operation of the vehicle state determinator 20.

(24) First, as in step S21, the vehicle state determinator 20 confirms whether the absolute value of the yaw rate difference information (YawRate Diff.) is greater than a reference value (Threshold).

(25) That is, it is determined whether the absolute value of the difference between the detected yaw rate and the yaw rate estimate is greater than a preset reference value to determine whether an abnormal situation has occurred.

(26) If the absolute value of the yaw rate difference information is less than or equal to the reference value, it is determined as a normal state as in step S23, and the index is set to 1 and provided to the target torque compensator 30. The operation of the target torque compensator 30 will be described below.

(27) As a result of the determination in step S21, if the absolute value of the yaw rate difference information is greater than the reference value, it is determined that there is an abnormality as in step S22, and the type of abnormality is confirmed.

(28) In step S21, the size of the yaw rate difference information is simply checked, and in step S22, an over-steer situation or an under-steer situation is determined by using the sign value of the yaw rate difference information.

(29) More specifically, in step S22, it is confirmed whether the sign value of the yaw rate difference information and the sign of the yaw rate detected by the yaw rate detection sensor 21 are the same.

(30) The yaw rate detected by the yaw rate detection sensor 21 also indicates an under-steer or over-steer situation according to a sign.

(31) In accordance with the present disclosure, the cases for determining the over-steer state and the under-steer state of a vehicle are illustrated in FIGS. 3 and 4, respectively.

(32) Referring to FIG. 3, the over-steer state is limited to a case in which the sign of the yaw rate detected by the yaw rate detection sensor 21 is the same as the sign of the yaw rate difference information regardless of the sign of the yaw rate estimate.

(33) In addition, referring to FIG. 4, the under-steer state is limited to a case in which the sign of the yaw rate detected by the yaw rate detection sensor 21 is different from the sign of the yaw rate difference information regardless of the sign of the yaw rate estimate.

(34) Accordingly, it is possible to confirm whether the current vehicle is in an over-steer state or an under-steer state, by checking the sameness of the sign of the yaw rate detected by the yaw rate detection sensor 21 and the sign of the yaw rate difference information in step S22.

(35) In step S24, an index in the case of an over-steer situation is defined, and in step S25, an index in the case of an under-steer situation is defined.

(36) Previously, the index may be defined as 1 in a normal situation of step S23, a value of 0 or more and less than 1 may be defined in an over-steer situation, and a value of more than 1 and less than 2 may be defined in an under-steer situation.

(37) In this case, the indices in the over-steer situation and the under-steer situation are designated as a range, and the index value may be determined according to the size of the yaw rate difference information. As the absolute value of the yaw rate difference information increases, the index value may have a larger value within a corresponding range.

(38) The index value thus determined is input to the target torque compensator 30.

(39) The target torque compensator 30 receives a target torque and compensates the target torque by using the index value.

(40) The target torque is a value generated by the steering angle of the steer, and the target torque compensator 30 compensates the target torque according to the instantaneously changed steering angle by using a target torque function based on the rotation angle at that time, and the final target torque is output by adding the respective compensation results.

(41) FIG. 5 is a block diagram of the target torque compensator 30.

(42) Referring to FIG. 5, the target torque compensator 30 is configured by including a plurality of torque compensators 31 that generate compensated target torques by using target torques and an index of the vehicle state determinator 20, and a target torque output unit 32 for outputting a final target torque by adding the compensated target torques of the plurality of torque compensators 31.

(43) The target torque output unit 32 may output the target torque change factors that are not considered in the present disclosure by adding them together.

(44) The torque compensator 31 compensates the target torque through Mathematical Formula 3 below.
T.sub.comp=T.sub.origin{(1f)Gain+f}[Mathematical Formula 3]

(45) In Mathematical Formula 3, T.sub.comp is the compensated target torque, T.sub.origin is the input target torque, f is the index value, and Gain is any adjustable value.

(46) Through such processing, the present disclosure generates a reaction torque that is a steering weight of the steering wheel according to the driving situation of a vehicle such that the driver may accurately recognize the state of the vehicle and the road surface, and by inducing the driver to properly manipulate the steering wheel through the steer operation, it is possible to improve steering and secure vehicle stability.

(47) It will be apparent to those of ordinary skill in the art that the present disclosure is not limited to the above exemplary embodiments and may be variously changed and modified within the scope without departing from the technical gist of the present disclosure.