APPARATUS FOR FOUR-WHEEL INDEPENDENT STEERING AND METHOD OF CONTROLLING SAME

Abstract

An apparatus for four-wheel independent steering. The apparatus may include: a rear wheel angle computation unit configured to compute a rear wheel angle (δ.sub.r) resulting by multiplying a front wheel angle (δ.sub.f) by a predetermined front/rear wheel angle ratio (Kss) corresponding to a vehicle speed (V); a gain computation unit configured to compute a gain (A) corresponding to a steering angle acceleration and the vehicle speed and then to output a final rear wheel angle (δ.sub.r) resulting by multiplying the rear wheel angle (δ.sub.r) computed by the rear wheel angle computation unit by the computed gain (A); and a control unit configured to perform rear wheel steering control based on the front wheel angle (δ.sub.f) and the final rear wheel angle (δ.sub.r).

Claims

1. An apparatus for four-wheel independent steering, comprising: a rear wheel angle computation unit configured to compute a rear wheel angle by multiplying a front wheel angle by a predetermined front/rear wheel angle ratio corresponding to a vehicle speed; a gain computation unit configured to compute a gain corresponding to a steering angle acceleration and the vehicle speed and to output a final rear wheel angle by multiplying the rear wheel angle computed by the rear wheel angle computation unit by the computed gain; and a control unit configured to perform rear wheel steering control based on the front wheel angle and the final rear wheel angle.

2. The apparatus of claim 1, wherein the gain computation unit computes the gain based on a look-up table in which the gain corresponding to the steering angle acceleration and the vehicle speed is stored.

3. The apparatus of claim 1, wherein, as the steering angle acceleration increases, the gain increases, and the gain computation unit increases and outputs the final rear wheel angle.

4. A method of controlling an apparatus for four-wheel independent steering, the method comprising: computing, by a control unit, a rear wheel angle by multiplying a front wheel angle by a predetermined front/rear wheel angle ratio corresponding to a vehicle speed using a rear wheel angle computation unit; computing, by the control unit, a gain corresponding to a steering angle acceleration and the vehicle speed using a gain computation unit, and outputting a final rear wheel angle computed by multiplying the rear wheel angle computed by the rear wheel angle computation unit by the computed gain; and performing, by the control unit, rear wheel steering control based on the front wheel angle and the final rear wheel angle.

5. The method of claim 4, wherein, in the computing of the gain, the gain computation unit computes the gain based on a look-up table in which the gain corresponding to the steering angle acceleration and the vehicle speed is stored.

6. The method of claim 4, wherein, in the computing of the gain, as the steering angle acceleration increases, the gain increases, and thus the gain computation unit increases and outputs the final rear wheel angle.

7. An apparatus for four-wheel independent steering, comprising: a rear wheel angle computation unit configured to compute an error amount of a yaw rate by comparing an actual yaw rate feedback with a predetermined target yaw rate and then compute a corrected rear wheel angle by multiplying a predetermined front/rear wheel angle ratio by a gain being used to correct the error amount; and a control unit configured to perform rear wheel steering control based on the front wheel angle and the corrected rear wheel angle.

8. The apparatus of claim 7, wherein the error amount is a difference value between the actual yaw rate and the target yaw rate.

9. The apparatus of claim 7, wherein the gain used to correct the error amount is provided in a look-up table.

10. A method of controlling an apparatus for four-wheel independent steering, the method comprising: computing, by a control unit, an error amount of a yaw rate by comparing an actual yaw rate feedback with a predetermined target yaw rate using a rear wheel angle computation unit; computing, by the control unit, a corrected rear wheel angle by multiplying a predetermined front/rear wheel angle ratio by a gain being used to correct the error amount; and performing, by the control unit, rear wheel steering control based on the front wheel angle and the corrected rear wheel angle.

11. The method of claim 10, wherein, in the computing of the error amount of the yaw rate, the error amount is a difference value between the actual yaw rate and the target yaw rate.

12. The method of claim 10, wherein the gain used to correct the error amount is provided in a look-up table.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is an exemplary diagram illustrating a schematic configuration of an apparatus for four-wheel independent steering according to a first embodiment of the present disclosure.

[0025] FIG. 2 is a flowchart for describing a method of controlling the apparatus for four-wheel independent steering in FIG. 1.

[0026] FIG. 3 is an exemplary diagram illustrating a schematic configuration of an apparatus for four-wheel independent steering according to a second embodiment of the present disclosure.

[0027] FIG. 4 is a flowchart for describing a method of controlling the apparatus for four-wheel independent steering in FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0028] As is traditional in the corresponding field, some exemplary embodiments may be illustrated in the drawings in terms of functional blocks, units, and/or modules. Those of ordinary skill in the art will appreciate that these block, units, and/or modules are physically implemented by electronic (or optical) circuits such as logic circuits, discrete components, processors, hard-wired circuits, memory elements, wiring connections, and the like. When the blocks, units, and/or modules are implemented by processors or similar hardware, they may be programmed and controlled using software (e.g., code) to perform various functions discussed herein. Alternatively, each block, unit, and/or module may be implemented by dedicated hardware or as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed processors and associated circuitry) to perform other functions. Each block, unit, and/or module of some exemplary embodiments may be physically separated into two or more interacting and discrete blocks, units, and/or modules without departing from the scope of the inventive concept. Further, blocks, units, and/or module of some exemplary embodiments may be physically combined into more complex blocks, units, and/or modules without departing from the scope of the inventive concept.

[0029] Hereafter, an apparatus for four-wheel independent steering and a method of controlling the same will be described below with reference to the accompanying drawings through various exemplary embodiments.

[0030] In such a process, the thicknesses of lines or the sizes of components illustrated in the drawings may be exaggerated for the clarity and convenience in description. Further, terms to be described hereinafter have been defined in consideration of functions in the disclosure, and may differ depending on a user or an operator's intention, or practice. Accordingly, each term should be defined based on the contents over the entire specification.

[0031] FIG. 1 is an exemplary diagram illustrating a schematic configuration of an apparatus for four-wheel independent steering according to a first embodiment of the present disclosure.

[0032] As illustrated in FIG. 1, the apparatus for four-wheel independent steering according to the first embodiment of the present disclosure includes a rear wheel angle computation unit 110, a gain computation unit 120, and a control unit 130.

[0033] The control unit 130 receives information on a front wheel angle (δ.sub.f).

[0034] Here, the control unit 130 may receive the information on the front wheel angle (δ.sub.f) detected by an electronic control unit (ECU) (not illustrated).

[0035] The rear wheel angle computation unit 110 receives the information on the front wheel angle (δ.sub.f) and information on a vehicle speed (V), and computes a rear wheel angle (by multiplying the front wheel angle (δ.sub.f) by a front/rear wheel angle ratio (Kss). The front/rear wheel angle ratio (Kss) is predetermined to correspond to the vehicle speed (V).

[0036] Here, the information on the vehicle speed (V) may be input by being detected by the ECU (not illustrated).

[0037] For reference, the front/rear wheel angle ratio (Kss) is a ratio between the front wheel angle (δ.sub.f) and the rear wheel angle (δ.sub.r). For example, when the front/rear wheel angle ratio (Kss) is 1, it means that the rear wheel angle is 30 degrees when the front wheel angle is 30 degrees. Accordingly, a target rear wheel angle is computed by multiplying the front wheel angle (by the front/rear wheel angle ratio (Kss) (i.e., δ.sub.r=K.sub.ss*δ.sub.f).

[0038] For reference, the front/rear wheel angle ratio (Kss) is calculated by Equation 1 below.

[00001]$\begin{array}{cc}{K}_{\mathrm{ss}}=\left(\left(\left(1-\left(\frac{b}{\mathrm{bg}-\mathrm{fc}}\right)*\left(\frac{V}{L+\left(\mathrm{kus}*V^2\right)}\right)\right)*\frac{\mathrm{bg}-\mathrm{fc}}{\mathrm{fd}-\mathrm{bh}}\right)\right)& \left[\mathrm{Equation}1\right]\end{array}$

[0039] Here, kus denotes an understeer gradient, L denotes an overall distance between a front wheel and a rear wheel. V denotes a vehicle speed.

[00002]$a=-\left(\frac{C_f+C_r}{mV}\right),b=\left(\frac{C_r{l}_r-C_f{l}_f}{{\mathrm{mV}}^2}-1\right),c=\frac{C_f}{mV},d=\frac{C_r}{mV},$$e=\frac{C_r{l}_r-C_f{l}_f}{\mathrm{IV}},f=-\left(\frac{C_f{l}_f^2+C_r{l}_r^2}{\mathrm{IV}}\right),ℊ=\frac{C_f{l}_f}{I},\mathrm{and}h=-\frac{C_r{l}_r}{I},$

wherein the meaning of these variables is defined according to vehicle dynamics.

[0040] The gain computation unit 120 computes a gain (A) that is predetermined to correspond to a steering angle acceleration and the vehicle speed (V).

[0041] For example, the gain (A) may be predetermined in the form of a look-up table (LUT) corresponding to the steering angle acceleration and the vehicle speed (V), and the corresponding gain (A) increases as the steering angle acceleration increases, for instance.

[0042] Accordingly, the gain computation unit 120 outputs a final rear wheel angle (δ.sub.r) computed by multiplying the rear wheel angle (δ.sub.r) by the gain (A). The rear wheel angle (δ.sub.r) is computed by the rear wheel angle computation unit 110, and the gain (A) is computed to correspond to the steering angle acceleration and the vehicle speed (V).

[0043] The control unit 130 outputs a lateral acceleration (α.sub.L) a body slip angle (β), a yaw rate ({dot over (ω)}.sup.2), the vehicle speed (V), and the like to a rear wheel steering actuator (not illustrated) based on the front wheel angle (δ.sub.f) and the final rear wheel angle (δ.sub.r) to perform rear wheel steering control.

[0044] For example, assuming that the vehicle speed (V) is constant, as the steering angle acceleration increases, the corresponding gain (A) increases and, consequently, the final rear wheel angle (δ.sub.r) increases as well. That is, as the steering angle acceleration increases, the final rear wheel angle (δ.sub.r) increases, and the control unit 130 controls a rear wheel based on the increased final rear wheel angle (δ.sub.r), resulting in a decrease in turning radius momentarily, and thus a user can get a dynamic steering feel.

[0045] FIG. 2 is a flowchart for describing a method of controlling the apparatus for four-wheel independent steering in FIG. 1.

[0046] Referring to FIG. 2, the control unit 130 receives the information on a front wheel angle (δ.sub.f), vehicle speed (V), and steering angle acceleration (S101).

[0047] In addition, the control unit 130 computes a rear wheel angle (δ.sub.r) through the rear wheel angle computation unit 110 by multiplying the front wheel angle (δ.sub.f) by a front/rear wheel angle ratio (Kss) that is predetermined to correspond to the vehicle speed (V) (S102). Through the gain computation unit 120, the control unit 130 computes a gain (A) that is predetermined to correspond to the steering angle acceleration and the vehicle speed (V) (S103).

[0048] In addition, the control unit 130 controls the rear wheel steering with the final rear wheel angle (δ.sub.r) that results from multiplying the rear wheel angle (δ.sub.r) by the gain (A), wherein the rear wheel angle (δ.sub.r) is computed by the rear wheel angle computation unit 110, and the gain (A) is computed to correspond to the steering angle acceleration and the vehicle speed (V) (S104).

[0049] As described above, according to the present embodiment, since the rear wheel steering is controlled after the final rear wheel angle (δ.sub.r) is computed using the gain (A) corresponding to the steering angle acceleration, the turning radius can decrease momentarily according to the steering angle acceleration when the steering angle acceleration increases, thereby providing the advantageous effect of giving a dynamic steering feel to a user.

[0050] Hereinafter, a method of performing four-wheel steering control (i.e., rear wheel steering control) according to another embodiment of the present disclosure will be described. According to the method, the four-wheel steering control follows a target yaw rate under any circumstances, wherein an actual yaw rate may follow the target yaw rate in such a manner that an error amount (i.e., a difference between the actual yaw rate and the target yaw rate) of the actual yaw rate and the target yaw rate are obtained from feedback of the actual yaw rate, and then the Kss gain is multiplied by a Kp gain (i.e., P gain in PID control) which is used to correct the error amount (i.e., the difference between the actual yaw rate and the target yaw rate).

[0051] FIG. 3 is an exemplary diagram illustrating a schematic configuration of an apparatus for four-wheel independent steering according to the second embodiment of the present disclosure.

[0052] As illustrated in FIG. 3, the apparatus for four-wheel independent steering according to the second embodiment of the present disclosure includes a rear wheel angle computation unit 210 and a control unit 220.

[0053] The control unit 220 receives information on a front wheel angle (δ.sub.f).

[0054] Here, the control unit 220 may receive the information on the front wheel angle (δ.sub.f) detected by an ECU (not illustrated).

[0055] The rear wheel angle computation unit 210 receives a steering angle acceleration, a vehicle speed (V), and an actual yaw rate ({dot over (ω)}.sup.2).

[0056] The rear wheel angle computation unit 210 computes an error amount of the yaw rate (i.e., the difference value between the actual yaw rate and the target yaw rate) by comparing the actual yaw rate ({dot over (ω)}.sup.2) feedback with the predetermined target yaw rate and computes a corrected rear wheel angle (δ.sub.r) by multiplying a predetermined front/rear wheel angle ratio (Kss) by a gain (Kp gain, i.e., P gain in PID control). The Kp gain is used to correct the error amount (i.e., the difference value between the actual yaw rate and the target yaw rate).

[0057] For reference, the front/rear wheel angle ratio () to compute the corrected rear wheel angle (δ.sub.r) is calculated by Equation 2 below. The corrected rear wheel angle (δ.sub.r) is used for the actual yaw rate to follow the target yaw rate.

[00003]$\begin{array}{cc}\stackrel{\_}{K_{\mathrm{ss}}}=\left(1-\left(\frac{b}{\mathrm{bg}-\mathrm{fc}}\right)*K_p*\left(\left(\frac{V}{L+\left(\mathrm{kus}*G*V^2\right)}\right)-\stackrel{.}{w}z\right)*\frac{\mathrm{bg}-\mathrm{fc}}{\mathrm{fd}-\mathrm{bh}}\right)& \left[\mathrm{Equation}2\right]\end{array}$

[0058] Here, kus denotes an understeer gradient, L denotes an overall distance between a front wheel and a rear wheel, V denotes a vehicle speed,

[00004]$a=-\left(\frac{C_f+C_r}{mV}\right),b=\left(\frac{C_r{l}_r-C_f{l}_f}{{\mathrm{mV}}^2}-1\right),c=\frac{C_f}{mV},d=\frac{C_r}{mV},$$e=\frac{C_r{l}_r-C_f{l}_f}{\mathrm{IV}},f=-\left(\frac{C_f{l}_f^2+C_r{l}_r^2}{\mathrm{IV}}\right),ℊ=\frac{C_f{l}_f}{I},\mathrm{and}h=-\frac{C_r{l}_r}{I},$

wherein the meaning of these variables is defined according to vehicle dynamics.

[0059] When compared to Equation 1, an additional G gain (variable according to the vehicle speed and the steering angle acceleration) is applied to Equation 2 to have advantages of the four-wheel control because the gain (Kp gain) and the target yaw rate are set to maintain a normal understeer gradient of an existing two-front-wheel drive vehicle. The Kp gain is used to correct the error amount (i.e., the difference value between the actual yaw rate and the target yaw rate).

[0060] In this case, Equations 1 and 2 are described to show that the embodiments of the present disclosure can be implemented and are not intended to limit the embodiments.

[0061] The control unit 220 outputs a lateral acceleration (α.sub.L) a body slip angle (β), a yaw rate ({dot over (ω)}.sup.2), the vehicle speed (V), and the like to a rear wheel steering actuator (not illustrated) based on the front wheel angle (δ.sub.f) and the corrected rear wheel angle (δ.sub.r) and performs rear wheel steering control. Thus, the control unit 220 may allow the actual yaw rate ({dot over (ω)}.sup.2) to follow the target yaw rate desired by a user.

[0062] For example, when the four-wheel independent steering control is performed, the control unit 220 may allow the actual yaw rate to follow the target yaw rate under any circumstances by performing the rear wheel steering control with the corrected rear wheel angle (δ.sub.r) that is computed by comparing actual yaw rate feedback with the target yaw rate desired by the user and then multiplying the front/rear wheel angle ratio (Kss) by the Kp gain. The Kp gain may be used to correct a difference between the actual yaw rate and the target yaw rate.

[0063] FIG. 4 is a flowchart for describing a method of controlling the apparatus for four-wheel independent steering in FIG. 3.

[0064] Referring to FIG. 4, the control unit 220 receives information on a front wheel angle (δ.sub.f) vehicle speed (V), and steering angle acceleration (S201).

[0065] The control unit 220 computes an error amount of the yaw rate (i.e., a difference value between the actual yaw rate and the target yaw rate) through the rear wheel angle computation unit 210 by comparing the actual yaw rate ({dot over (ω)}.sup.2) feedback with the predetermined target yaw rate (S202).

[0066] In addition, the control unit 220 computes the corrected rear wheel angle (δ.sub.r) by multiplying a predetermined front/rear wheel angle ratio (Kss) by the gain (Kp gain, i.e., P gain in PID control), wherein the Kp gain is used to correct the error amount (i.e., the difference value between the actual yaw rate and the target yaw rate) (S203).

[0067] In this case, the gain (Kp gain) used to correct the error amount may be provided in the form of a look-up table in advance.

[0068] In addition, the control unit 220 may perform the rear wheel steering control based on the front wheel angle and the corrected rear wheel angle and thus allow the actual yaw rate ({dot over (ω)}.sup.2) to follow the target yaw rate desired by the user (S204).

[0069] Meanwhile, for the convenience in description, the present embodiments are classified into the first embodiment and the second embodiment. However, depending on mode setting, option setting, or driving conditions (ambient conditions), the first embodiment and second embodiment may be combined or selectable, which makes it possible to allow the turning radius to be adjusted momentarily according to the conditions while following the target yaw rate and thus to allow a user to feel the steering stability and the dynamic steering feel selectively.

[0070] As described above, in a case where the four-wheel independent steering control is performed, the present embodiments provide the advantageous effect that the actual yaw rate can follow the target yaw rate under any circumstances by performing the rear wheel steering control with the corrected rear wheel angle (δ.sub.r) that is computed by comparing the actual yaw rate feedback with the target yaw rate desired by the user and then multiplying the front/rear wheel angle ratio (Kss) by the Kp gain. The Kp gain can be used correct the difference between the actual yaw rate and the target yaw rate.

[0071] Hereinabove, the present disclosure has been described with reference to exemplary embodiments illustrated in the accompanying drawings, but this is only for exemplary purposes, and those skilled in the art will appreciate that various modifications and other equivalent exemplary embodiments are possible therefrom. Thus, the true technical scope of the disclosure should be defined by the following claims. The implementations described in the present specification may be performed by, for example, a method or a process, an apparatus, a software program, a data stream, or a signal. Although discussed only in the context of single-form implementation (e.g., discussed only as a method), the discussed features may also be implemented as another form (e.g., apparatus or program). The apparatus may be implemented using proper hardware, software, and firmware. The method may be implemented as, for example, an apparatus, such as a processor generally referring to a processing device including a computer, a microprocessor, an integrated circuit, or a programmable logic device. The processor also includes a communication device such as a computer, a cellular phone, a personal digital assistant (PDA), or another device that facilitates the communication of information between end users.