Four-wheel independent steering system and its control method

Abstract

This invention discloses a four-wheel independent steering system and a method for controlling it. The four-wheel independent steering system according to an embodiment of this disclosure includes: a front / rear wheel angle ratio calculation unit configured to calculate a ratio Kss between the front wheel angle and the rear wheel angle, wherein the ratio Kss allows the vehicle slip angle to converge to "0" and allows the yaw angle and yaw rate to follow target values; and a control unit configured to perform four-wheel steering control based on the ratio Kss between the front wheel angle and the rear wheel angle. The four-wheel independent steering system and method of this invention, in the case of four-wheel independent steering control where the steering angle of the rear wheels is controlled according to the steering angle of the front wheels, allows the driver to experience dynamic steering by adjusting the turning radius in real time while following the target yaw rate.

Description

Technical Field

[0001] Exemplary embodiments of this disclosure relate to a four-wheel independent steering system and a method of controlling the same, and more specifically, to a four-wheel independent steering system and a method of controlling the same, which, in four-wheel independent steering control that controls the steering angle of the rear wheels according to the steering angle of the front wheels, allows the driver to experience dynamic steering by adjusting the turning radius in real time while following a target yaw rate. Background Technology

[0002] Recently, research has been conducted on in-wheel electric motor systems, in which electric motors are embedded in each of the four wheels of a vehicle and operate the four wheels independently.

[0003] The in-wheel electric motor system can be organically coupled to the vehicle to achieve four-wheel independent drive and four-wheel independent steering, thereby providing more flexible and diverse driving performance.

[0004] Ordinary vehicles change their direction of travel only by steering the front wheels. Therefore, the vehicle's direction of travel is not consistent with the driver's perceived direction because the front and rear wheels generate lateral forces at different times. However, this four-wheel independent steering system also applies to the rear wheels, thereby reducing the vehicle's turning radius when the driver is stationary or turning at low speeds, and improving driving stability when the driver changes direction at high speeds.

[0005] In this context, in the relevant technology, in order to determine the transmission ratio of the front and rear wheels to control the four-wheel independent steering system, the transmission ratio of the front and rear wheels is set under the assumption that the yaw rate and sideslip angle (vehicle slip angle) converge to zero.

[0006] Therefore, compared to two-wheel steering control in related technologies, four-wheel independent steering control advantageously achieves the original dynamic steering performance and reduces the turning radius. However, as mentioned above, because the yaw rate (yaw rate = vehicle speed / turning radius) converges to zero, the turning radius cannot theoretically be reduced. That is, when the yaw rate is zero, the turning radius inevitably increases, which makes it difficult to demonstrate the advantages of the original four-wheel independent steering. With the front and rear wheel transmission ratios set to a fixed target value to achieve dynamic steering performance, the performance of four-wheel independent steering control is significantly limited.

[0007] Therefore, a four-wheel independent steering control method is needed that allows the driver to experience dynamic steering by adjusting the turning radius in real time while following the target yaw rate when controlling four-wheel independent steering.

[0008] The background technology disclosed herein is disclosed in Korean Patent No. 10-2274120 (registered on July 1, 2021, entitled "Apparatus and Method for Controlling Rear Wheel Steering System"). Summary of the Invention

[0009] Various embodiments are intended to provide a four-wheel independent steering system and a method for controlling it, which, in four-wheel independent steering control that controls the steering angle of the rear wheels based on the steering angle of the front wheels, allows the driver to experience dynamic steering by adjusting the turning radius in real time while following a target yaw rate.

[0010] The technical problems to be solved by the present invention are not limited to those described above. Those skilled in the art can clearly understand other technical problems not mentioned above from the following description.

[0011] A four-wheel independent steering system according to an embodiment of the present disclosure includes: a front / rear wheel angle ratio calculation unit configured to calculate a ratio Kss between the front wheel angle and the rear wheel angle, the ratio Kss allowing the vehicle slip angle to converge to "0" and allowing the yaw angle and yaw rate to follow target values; and a control unit configured to perform four-wheel steering control based on the ratio Kss between the front wheel angle and the rear wheel angle.

[0012] In this disclosure, the front / rear wheel angle ratio calculation unit can control and change the ratio Kss between the front wheel angle and the rear wheel angle by adjusting the target understeer gradient Kus by adjusting the gain G.

[0013] In this disclosure, the front / rear wheel angle ratio calculation unit can calculate the gain G based on a lookup table (LUT), which stores the gain G corresponding to the steering angular velocity and steering angular acceleration.

[0014] In this disclosure, the front / rear wheel angle ratio calculation unit can limit the ratio Kss between the front wheel angle and the rear wheel angle by limiting the yaw rate, so that the lateral acceleration of the vehicle does not become equal to or greater than the characteristic value of the vehicle.

[0015] In this disclosure, the characteristic value of the vehicle can be based on the value of (left / right width between vehicle tires / (2 * distance from vehicle centerline to vehicle bottom)).

[0016] In this disclosure, in driver steering mode, the control unit can adjust the front wheel angle δ according to the driver's steering direction. f Multiply by the ratio Kss between the front wheel angle and the rear wheel angle to calculate the rear wheel angle δ. r And based on the front wheel angle δ f and rear wheel angle δ r Execute rear wheel steering control.

[0017] In this disclosure, in autonomous driving mode, the control unit can calculate the vehicle's rotational center degree δcg′ using the ratio Kss between the front wheel angle and the rear wheel angle, calculate the distance Rr between the rotational center and the centerline of the rear wheel using the vehicle's rotational center angle, and calculate the front wheel angle δcg′ based on the distance Rr between the rotational center and the centerline of the rear wheel. f and rear wheel angle δ r And based on the front wheel angle δ f and rear wheel angle δ r Implement four-wheel steering control.

[0018] Another embodiment of this disclosure provides a method for controlling a four-wheel independent steering system, the method comprising: calculating a ratio Kss between the front wheel angle and the rear wheel angle by a front / rear wheel angle ratio calculation unit, the ratio Kss allowing the vehicle slip angle to converge to "0" and allowing the yaw angle and yaw rate to follow target values; and performing four-wheel steering control by a control unit based on the ratio Kss between the front wheel angle and the rear wheel angle.

[0019] In this disclosure, when calculating the ratio Kss between the front wheel angle and the rear wheel angle, the front / rear wheel angle ratio calculation unit can control and change the ratio Kss between the front wheel angle and the rear wheel angle by applying a gain G to adjust the target understeer gradient Kus.

[0020] In this disclosure, when calculating the ratio Kss between the front wheel angle and the rear wheel angle, the front / rear wheel angle ratio calculation unit can calculate the gain G based on a lookup table LUT, which stores the gain G corresponding to the steering angular velocity and steering angular acceleration.

[0021] In this disclosure, when calculating the ratio Kss between the front wheel angle and the rear wheel angle, the front / rear wheel angle ratio calculation unit can limit the ratio Kss between the front wheel angle and the rear wheel angle by limiting the yaw rate, so that the lateral acceleration does not become equal to or greater than the characteristic value of the vehicle.

[0022] In this disclosure, the characteristic value of the vehicle can be based on the value of (left / right width between vehicle tires / (2 * distance from the vehicle centerline to the bottom of the vehicle)).

[0023] In this disclosure, when performing four-wheel steering control, in driver steering mode, the control unit can adjust the front wheel angle δ according to the driver's steering direction. f Multiply by the ratio Kss between the front wheel angle and the rear wheel angle to calculate the rear wheel angle δ. r And based on the front wheel angle δ f and rear wheel angle δ r Execute rear wheel steering control.

[0024] In this disclosure, when performing four-wheel steering control, in autonomous driving mode, the control unit can calculate the vehicle's rotation center angle δcg′ using the ratio Kss between the front wheel angle and the rear wheel angle, calculate the distance Rr between the rotation center and the centerline of the rear wheel using the vehicle's rotation center angle, and calculate the front wheel angle δcg′ based on the distance Rr between the rotation center and the centerline of the rear wheel. f and rear wheel angle δ r And based on the front wheel angle δ f and rear wheel angle δ r Implement four-wheel steering control.

[0025] According to the four-wheel independent steering system and method of the present disclosure, in four-wheel independent steering control that controls the steering angle of the rear wheels based on the steering angle of the front wheels, the driver can feel dynamic steering by adjusting the turning radius in real time while following the target yaw rate.

[0026] Furthermore, the effects of this disclosure are not limited to those described above, and various effects may be included within the scope that will be obvious to those skilled in the art, as described below. Attached Figure Description

[0027] Figure 1 This is an example diagram illustrating a four-wheeled model used to explain vehicle dynamics.

[0028] Figure 2 This is an example diagram illustrating a two-wheeled model used to explain vehicle dynamics.

[0029] Figure 3 This is an example diagram illustrating a single-track model used to explain vehicle dynamics.

[0030] Figure 4 This is an example diagram illustrating a schematic configuration of a four-wheel independent steering system according to an embodiment of the present disclosure.

[0031] Figure 5 This is a flowchart for explaining a method of controlling a four-wheel independent steering system according to an embodiment of the present disclosure. Detailed Implementation

[0032] As is customary in the relevant art, some exemplary embodiments may be illustrated in the accompanying drawings as functional blocks, units, and / or modules. Those skilled in the art will understand that these blocks, units, and / or modules are physically implemented by electronic (or optical) circuitry, such as logic circuits, discrete components, processors, hardwired circuits, storage elements, wiring connections, etc. When blocks, units, and / or modules are implemented by processors or similar hardware, they can be programmed and controlled using software (e.g., code) to perform the various functions discussed herein. Alternatively, each block, unit, and / or module may be implemented by dedicated hardware, or as a combination of dedicated hardware performing some functions and processors performing other functions (e.g., one or more programming processors and associated circuitry). Without departing from the scope of the inventive concept, each block, unit, and / or module of some exemplary embodiments may be physically divided into two or more interacting and discrete blocks, units, and / or modules. Furthermore, blocks, units, and / or modules 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.

[0033] In the following, a four-wheel independent steering system and its control method according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Here, for clarity and convenience, the thickness of lines, the dimensions of component elements, etc., shown in the drawings may be enlarged. Furthermore, the terminology used below is defined in consideration of its function in this disclosure and may vary based on the intent of the user or operator or common practice. Therefore, these terms should be defined based on the entire contents of this specification.

[0034] For example, the configuration described in this specification can be implemented as a method or process, an apparatus, a software program, a data stream, or a signal. Even if a single form of implementation is described (e.g., only a method is described), the described features can also be in other forms (e.g., an apparatus or a program). The apparatus can be implemented as appropriate hardware, software, firmware, etc. For example, the method can be implemented by a device such as a processor, which generally refers to a processing device including computers, microprocessors, integrated circuits, programmable logic devices, etc. Processors also include communication devices such as computers, cellular phones, portable / personal information terminals (personal digital assistants, PDAs), and other devices that facilitate information communication with end users.

[0035] Figure 1 This is an example diagram illustrating a four-wheeled model used to explain vehicle dynamics. Figure 2 This is an example diagram illustrating a two-wheeled model used to explain vehicle dynamics, and Figure 3 This is an example diagram illustrating a single-track model used to explain vehicle dynamics.

[0036] Reference Figure 1 Describe the vehicle dynamics on a four-wheel model. Typically, in autonomous driving mode, the autonomous driving module (not shown) applies the values ​​of the turning radius R, the front wheel steering angle, or the vehicle's central angle to the four-wheel independent steering system. If the autonomous driving module only applies the steering angle of the front wheels, the values ​​of the vehicle's turning radius R and the rotation center angle δcg′ need to be obtained through the use of dynamics.

[0037] First, the vehicle model analyzer (not shown) can obtain the distances Rr between the rear wheel centerline and the center of rotation by applying the turning radius R and angle δcg′ of the vehicle's center of rotation using Equation 1 below.

[0038] Equation 1

[0039] Rr=R×cosδ cg ', c=R×sinδ cg '

[0040] Then, the vehicle model analyzer can calculate the front wheel angle δ based on the vehicle parameter c and the distance Rr between the rotation center and the rear wheel centerline using the following Equation 2. f and rear wheel angle δ r .

[0041] Equation 2

[0042]

[0043] The vehicle model analyzer can then calculate each angle of the four wheels (i.e., the front and rear wheels) using Equation 3 below.

[0044] Equation 3

[0045]

[0046]

[0047] Here, δ fi This can represent the angle of the left front wheel, δ fo This can represent the angle of the right front wheel, δ ri This can represent the angle of the left rear wheel, δ ro It can represent the angle of the right rear wheel, 'a' can represent the distance between the front wheel axle and the center of gravity, 'b' can represent the distance between the rear wheel axle and the center of gravity, and 'W' can represent the distance between the left and right wheels (track width).

[0048] Furthermore, dynamics are needed to obtain the values ​​of the vehicle's turning radius R and rotation center angle δcg′. First, referencing... Figure 2 Describe a method for obtaining the turning radius R based on two wheels. Figure 2This illustrates a scenario where the autonomous driving module calculates the turning radius based on the steering angle of the front wheels and applies that turning radius to the four-wheel independent steering system.

[0049] The vehicle model analyzer can receive steering angles or vehicle angles generated by the autonomous driving system. In this case, the vehicle angle could be the front wheel angle δ. f Or the vehicle's center of gravity angle δcg. The vehicle model analyzer can obtain the turning radius R and the distance Rr between the rear wheel centerline and the center of rotation, as shown in Equation 4 below for each case. Even if four-wheel steering is actually used, the vehicle model analyzer can obtain the turning radius R and distance Rr while considering two-wheel steering.

[0050] Equation 4

[0051]

[0052] In this case, L can represent the total distance between the front and rear wheels, and b can represent the distance from the vehicle's centerline to the rear wheel.

[0053] Next, to obtain the vehicle's rotation center angle δcg′, the vehicle model analyzer can examine the ratio between the front and rear wheels determined based on the ratio Kss between the front and rear wheel angles. Then, the vehicle model analyzer can check whether the front and rear wheels are in phase or out of phase.

[0054] When the front and rear wheels are in phase, the vehicle model analyzer can calculate the front wheel angle δ using Equation 5 below. f and rear wheel angle δ r .

[0055] Equation 5

[0056]

[0057] When the front and rear wheels are out of phase, the vehicle model analyzer can calculate the front wheel angle δ using Equation 6 below. f and rear wheel angle δ r .

[0058] Equation 6

[0059]

[0060] The vehicle model analyzer can calculate the vehicle's rotation center angle δcg′ using Equation 7 below. Although Equation 7 is an in-phase expansion, out-of-phase expansion can also be calculated in a similar manner.

[0061] Equation 7

[0062]

[0063] The error is 0.05Tad(time(t)) at 30 degrees or below.

[0064] The key to this disclosure is obtaining the ratio Kss between the front wheel angle and the rear wheel angle. According to Figure 3 As shown in the dynamics, the vehicle model analyzer can define the change in the vehicle body slip angle (sideslip angle) as shown in Equation 8 below. The change in yaw rate is defined as shown in Equation 9 below.

[0065] Equation 8

[0066]

[0067] Equation 9

[0068]

[0069] Equations 10 and 11 below can be obtained by organizing equations 8 and 9.

[0070] Equation 10

[0071]

[0072] Equation 11

[0073]

[0074] Here, β represents the vehicle slip angle (sideslip angle), and wz represents the yaw angle. The meanings of these variables are defined according to vehicle dynamics.

[0075] Meanwhile, in related technologies, the ratio Kss between the front wheel angle and the rear wheel angle is the ratio of the front wheel angle to the rear wheel angle across all vehicle body slip angles β and yaw angles w. z and yaw rate This is derived from the state of convergence to "0". However, considering dynamic theories such as yaw rate (yaw rate = vehicle speed / turning radius), the vehicle will not move in the direction of travel, and the turning radius cannot be properly controlled, which leads to significant inhomogeneity for the driver or passenger and makes it difficult to smoothly follow the target turning radius.

[0076] Therefore, a technology is needed that allows the driver to experience dynamic steering in four-wheel independent steering control, which controls the steering angle of the rear wheels based on the steering angle of the front wheels, by adjusting the turning radius in real time while following the target yaw rate.

[0077] Figure 4This is an example diagram illustrating a schematic configuration of a four-wheel independent steering system according to an embodiment of the present disclosure.

[0078] refer to Figure 4 The four-wheel independent steering system 100 according to an embodiment of the present disclosure includes a front / rear wheel angle ratio calculation unit 110 and a control unit 120.

[0079] The front / rear wheel angle ratio calculation unit 110 can calculate the ratio Kss between the front wheel angle and the rear wheel angle, which allows the vehicle slip angle to converge to "0" and allows the yaw angle and yaw rate to follow the target values. In other words, the front / rear wheel angle ratio calculation unit 110 enables the four-wheel independent steering system 100 to exhibit higher vehicle control performance by maintaining the yaw angle and yaw rate at the target level or by changing the dynamics when the vehicle slip angle converges to "0".

[0080] By setting the vehicle slip angle and the change in vehicle slip angle to "0" and keeping other values ​​as in formulas 10 and 11, the front wheel angle δ is calculated using formulas 10 and 11. f It can be defined by the following formula 12.

[0081] Equation 12

[0082]

[0083] Here, kus represents the understeer gradient, L represents the total distance between the front and rear wheels, and V represents the vehicle speed. The meanings of these variables are defined according to vehicle dynamics. kus can be defined as... w f =M*g*b / L), w f =M*g*(b / L), Caf can represent turning stiffness, M can represent the weight of the vehicle, g can represent gravitational acceleration, b can represent the distance from the vehicle's centerline to the rear wheel, a can represent the distance from the vehicle's centerline to the front wheel, and L can represent the total distance between the front and rear wheels.

[0084] The performance of the four-wheel independent steering system 100 varies significantly depending on how the ratio Kss between the front and rear wheel angles is defined. The ratio Kss refers to the front wheel angle δ. f and rear wheel angle δ r The ratio between them. For example, when the ratio Kss between the front wheel angle and the rear wheel angle is 1, when the front wheel angle is 30 degrees, it indicates that the rear wheel angle is 30 degrees. Therefore, by adjusting the front wheel angle δ... f Calculate the target rear wheel angle δ by multiplying by the ratio Kss between the front wheel angle and the rear wheel angle. r (that is, δ) r=K ss *δ f ).

[0085] Therefore, Equation 13 below can be defined by expanding Equation 12 with respect to the ratio Kss between the front wheel angle and the rear wheel angle.

[0086] Equation 13

[0087]

[0088] Referring to Equation 13, the front / rear wheel angle ratio calculation unit 110 can adjust the target understeer gradient Kus by applying a gain G, thereby controlling and changing the ratio Kss between the front and rear wheel angles. In this case, the front / rear wheel angle ratio calculation unit 110 can adjust the ratio Kss between the front and rear wheel angles by applying a gain G calculated based on a lookup table (LUT), where the lookup table stores the gain G corresponding to the steering angular velocity and steering angular acceleration.

[0089] The front / rear wheel angle ratio calculation unit 110 can change the target yaw rate by applying a gain G. That is, the front / rear wheel angle ratio calculation unit 110 can output dynamic performance based on the gain G. Preferably, using the ratio Kss between the front and rear wheel angles derived from Equation 13, a stable target yaw rate can be substantially derived based on the optimized characteristics of the understeer gradient kus of a vehicle based on a two-wheel steering system. This is because drivers and passengers are generally familiar with the yaw rate behavior of typical two-wheeled vehicles. Yaw rate is a factor that can represent, to some extent, the characteristics of a vehicle based on vehicle control safety. In fact, the value of the understeer gradient kus is a characteristic value of the vehicle and usually results in understeer when designing the vehicle. In the case of oversteer, the driver or passenger can determine that vehicle control is over-exercised because the desired steering of the vehicle is performed at the turning radius level, which can lead to dangerous situations. In other words, the vehicle is controlled to a much greater extent than the driver controls the vehicle, which reduces the turning radius to an undesirable turning radius.

[0090] Therefore, by applying the gain G to adjust the target understeer gradient Kus, the ratio Kss between the front and rear wheel angles can be designed under the condition that the driver can safely control the vehicle and the occupants can obtain a comfortable ride quality to some extent.

[0091] In other words, the vehicle slip angle can converge to '0' because it is accompanied by rear-wheel control. However, the yaw rate can follow the desired target value while maintaining a steady state, and a gain G can be additionally applied to that target value. This is to perform dynamic four-wheel control that goes beyond the typical two-wheel-based target yaw rate. During four-wheel control, front-wheel and rear-wheel control are performed simultaneously. In this case, the change in yaw rate can increase instantaneously, potentially leading to a significant change in the turning radius.

[0092] The advantage of four-wheel control is that the turning radius can be instantly and significantly increased or decreased by the driver, passengers, or the autonomous driving module. Four-wheel control can provide a variety of desired turning radii in various driving environments, such as driving on a racetrack, avoiding obstacles, and operating in parking mode. The ratio Kss between the front and rear wheel angles is not obtained by simply fixing the target yaw rate, but can vary under different conditions.

[0093] In other words, the front / rear wheel angle ratio calculation unit 110 can adjust the target understeer gradient Kus by applying gain G, and in this case, the vehicle's characteristics can be instantaneously changed by using either a natural gradient or an oversteer gradient. Neither the natural gradient nor the oversteer gradient necessarily leads to instability when controlling the vehicle. The value of gain G can vary when the vehicle is drastically avoiding obstacles or needs to instantly and significantly reduce its turning radius while driving on a track, or when a comfortable ride quality is achieved by drastically reducing yaw (when reducing the turning radius is not required). That is, dynamic control is enabled.

[0094] The value of gain G can vary based on steering angular velocity or steering angular acceleration. When steering angular velocity or steering angular acceleration increases, decreasing the value of gain G allows the vehicle to momentarily exhibit natural or oversteer characteristics. When steering angular velocity or steering angular acceleration decreases, increasing the value of gain G achieves stable lateral vehicle control. Gain G can be pre-assigned in the form of a lookup table (LUT), corresponding to both steering angular velocity and steering angular acceleration. Because gain G is assigned in tabular form as described above, it is possible to find parameters that can be optimized through tuning. Since gain depends on driver habits or passenger desired ride quality, gain can be set according to the vehicle platform, allowing for individual desired values ​​to achieve dynamic performance.

[0095] As described above, the front / rear wheel angle ratio calculation unit 110 uses gain G to output more dynamic performance, thereby outputting better performance by changing the lateral vehicle control characteristics.

[0096] Furthermore, the front / rear wheel angle ratio calculation unit 110 can limit the yaw rate so that the vehicle's lateral acceleration does not become equal to or greater than the vehicle's characteristic value, thereby limiting the ratio Kss between the front and rear wheel angles. In this case, the vehicle's characteristic value can be a value based on (the left / right width between the vehicle tires / (2 * the distance from the vehicle's centerline to the bottom of the vehicle)).

[0097] In fact, when the yaw rate of a vehicle is too extreme, the lateral acceleration will also increase. Lateral acceleration α can be defined as... When the condition (a / g > T / 2H) is met, the vehicle may overturn. In this case, V can represent the vehicle's velocity, g can represent the acceleration due to gravity, T can represent the left / right width between the vehicle's tires, and H can represent the distance from the vehicle's centerline to the bottom of the vehicle.

[0098] Based on the target yaw rate, the ratio Kss between the front and rear wheel angles is set; therefore, the yaw rate can be defined as Ψ = V / R. The yaw rate is equal to the lateral acceleration... The value obtained by dividing by the value V. Therefore, when the target yaw rate is limited to a level that will not cause rollover, safety can be ensured when problems arise while controlling the vehicle. That is, the ratio Kss between the front wheel angle and the rear wheel angle meets the limits under the above conditions.

[0099] The control unit 120 can perform four-wheel steering control based on the ratio Kss between the front wheel angle and the rear wheel angle.

[0100] In driver steering mode, control unit 120 can adjust the front wheel angle δ according to the driver's steering direction. f Multiply by the ratio Kss between the front wheel angle and the rear wheel angle to calculate the rear wheel angle δ. r And based on the front wheel angle δ f and rear wheel angle δ r Execute rear wheel steering control.

[0101] When the driver controls the four-wheel independent steering system 100, the control unit 120 can apply the front wheel angle δ according to the driver's steering by applying equation 12 when the driver turns the steering wheel. f This allows for immediate setting of the rear wheel angle.

[0102] In other words, based on the driver's steering, the front wheel angle δ f It is the driver's steering angle, and the rear wheel angle δ. r It can be set based on the ratio Kss between the front wheel angle and the rear wheel angle. Since the driver has a desired vehicle orientation angle when driving, it is important to make the driver feel that the vehicle is being controlled in the direction the driver expects.

[0103] Furthermore, in autonomous driving mode, the control unit 120 can calculate the vehicle's rotation center angle δcg′ using the ratio Kss between the front wheel angle and the rear wheel angle, calculate the distance Rr between the rotation center and the centerline of the rear wheels using the vehicle's rotation center angle, and calculate the front wheel angle δcg′ based on the distance Rr between the rotation center and the centerline of the rear wheels. f and rear wheel angle δ r And based on the front wheel angle δ f and rear wheel angle δ r Implement four-wheel steering control.

[0104] In autonomous driving scenarios, the vehicle's turning radius and passenger comfort are important. Therefore, the control unit 120 can utilize the parameters expressed in Equation 7. Obtain the vehicle's rotation center angle and calculate the front wheel angle δ using Equation 5 or 6. f and rear wheel angle δ r In other words, the control unit 120 can use the vehicle's rotation center angle δ′ cg The front wheel angle δ is derived again from the expected target value of the turning radius R. f and rear wheel angle δ r .

[0105] Meanwhile, the front / rear wheel angle ratio calculation unit 110 and the control unit 120 can each be implemented by a processor mounted on a computing device that needs to execute a program. As described above, depending on their function, the front / rear wheel angle ratio calculation unit 110 and the control unit 120 can be implemented by physically independent components or as corresponding components partitioned within a single processor.

[0106] Figure 5 This is a flowchart for explaining a method of controlling a four-wheel independent steering system according to embodiments of the present disclosure.

[0107] refer to Figure 5 The front / rear wheel angle ratio calculation unit 110 calculates the ratio Kss between the front and rear wheel angles, which allows the vehicle slip angle to converge to '0' and allows the yaw angle and yaw rate to follow the target values ​​(S510). In this case, the front / rear wheel angle ratio calculation unit 110 can adjust the target understeer gradient Kus by adjusting the gain G, thereby controlling and changing the ratio Kss between the front and rear wheel angles. That is, the front / rear wheel angle ratio calculation unit 110 can change the target yaw rate by applying the gain G. In other words, the front / rear wheel angle ratio calculation unit 110 can output dynamic performance based on the gain G. In this case, the gain G can be stored in a lookup table LUT, and the gain G corresponds to the steering angular velocity and steering angular acceleration.

[0108] Furthermore, the front / rear wheel angle ratio calculation unit 110 can limit the ratio Kss between the front wheel angle and the rear wheel angle by limiting the yaw rate, so that the lateral acceleration of the vehicle does not become equal to or greater than the characteristic value of the vehicle.

[0109] When step S510 is executed, control unit 120 performs four-wheel steering control based on the ratio Kss between the front wheel angle and the rear wheel angle (S520). In this case, in driver steering mode, control unit 120 can adjust the front wheel angle δ according to the driver's steering direction. f Multiply by the ratio Kss between the front wheel angle and the rear wheel angle to calculate the rear wheel angle δ. r And based on the front wheel angle δ f and rear wheel angle δ r Execute rear wheel steering control.

[0110] Furthermore, in autonomous driving mode, the control unit 120 can calculate the vehicle's rotation center angle δcg′ using the ratio Kss between the front wheel angle and the rear wheel angle, calculate the distance Rr between the rotation center and the rear wheel centerline using the vehicle's rotation center angle, and calculate the front wheel angle δcg′ based on the distance Rr between the rotation center and the rear wheel centerline. f and rear wheel angle δ r And based on the front wheel angle δ f and rear wheel angle δ r Implement four-wheel steering control.

[0111] As described above, in the four-wheel independent steering system and method of controlling it according to the embodiments of the present disclosure, when controlling the steering angle of the rear wheels according to the steering angle of the front wheels, the driver can feel dynamic steering by adjusting the turning radius in real time while following the target yaw rate.

[0112] Although this disclosure has been described with reference to embodiments shown in the accompanying drawings, these embodiments are described merely for illustrative purposes, and those skilled in the art will understand that various modifications to these embodiments and any other equivalent embodiments are available. Therefore, the true scope of protection of this disclosure should be determined by the technical solution itself.

Claims

1. A four-wheel independent steering system, comprising: The front / rear wheel angle ratio calculation unit is configured to calculate the ratio Kss between the front wheel angle and the rear wheel angle, the ratio Kss allowing the vehicle slip angle to converge to "0" and allowing the yaw angle and yaw rate to follow the target value; as well as The control unit is configured to perform four-wheel steering control based on the ratio Kss between the front wheel angle and the rear wheel angle. In autonomous driving mode, the control unit calculates the vehicle's rotation center angle δ using the ratio Kss between the front wheel angle and the rear wheel angle. cg The distance Rr between the rotation center and the rear wheel centerline is calculated using the rotation center angle of the vehicle, and the front wheel angle is calculated based on the distance Rr between the rotation center and the rear wheel centerline. and rear wheel angle And based on the front wheel angle and the rear wheel angle Implement four-wheel steering control.

2. The four-wheel independent steering system according to claim 1, wherein, The front / rear wheel angle ratio calculation unit controls and changes the ratio Kss between the front wheel angle and the rear wheel angle by applying a gain G to adjust the target understeer gradient Kus.

3. The four-wheel independent steering system according to claim 2, wherein, The front / rear wheel angle ratio calculation unit calculates the gain G based on a lookup table (LUT), which stores the gain G corresponding to the steering angular velocity and steering angular acceleration.

4. The four-wheel independent steering system according to claim 1, wherein, The front / rear wheel angle ratio calculation unit limits the ratio Kss between the front wheel angle and the rear wheel angle by limiting the yaw rate, so that the lateral acceleration does not become equal to or greater than the characteristic value of the vehicle.

5. The four-wheel independent steering system according to claim 4, wherein, The vehicle's characteristic value is based on the following value: the left / right width between the vehicle's tires / (2 The distance from the centerline of the vehicle to the bottom of the vehicle.

6. The four-wheel independent steering system according to claim 1, wherein, In driver steering mode, the control unit will adjust the front wheel angle according to the driver's steering direction. Multiply by the ratio Kss between the front wheel angle and the rear wheel angle to calculate the rear wheel angle. And based on the front wheel angle and the rear wheel angle Execute rear wheel steering control.

7. A method for controlling a four-wheel independent steering system, the method comprising: The front / rear wheel angle ratio calculation unit calculates the ratio Kss between the front wheel angle and the rear wheel angle. This ratio Kss allows the vehicle slip angle to converge to "0" and allows the yaw angle and yaw rate to follow target values. The control unit performs four-wheel steering control based on the ratio Kss between the front wheel angle and the rear wheel angle. In the execution of four-wheel steering control, in autonomous driving mode, the control unit calculates the vehicle's rotation center angle δ using the ratio Kss between the front wheel angle and the rear wheel angle. cg The distance Rr between the rotation center and the rear wheel centerline is calculated using the rotation center angle of the vehicle, and the front wheel angle is calculated based on the distance Rr between the rotation center and the rear wheel centerline. and rear wheel angle And based on the front wheel angle and the rear wheel angle Implement four-wheel steering control.

8. The method according to claim 7, wherein, When calculating the ratio Kss between the front wheel angle and the rear wheel angle, the front / rear wheel angle ratio calculation unit controls and changes the ratio Kss between the front wheel angle and the rear wheel angle by applying a gain G to adjust the target understeer gradient Kus.

9. The method according to claim 8, wherein, When calculating the ratio Kss between the front wheel angle and the rear wheel angle, the front / rear wheel angle ratio calculation unit calculates the gain G based on a lookup table (LUT), which stores the gains G corresponding to the steering angular velocity and steering angular acceleration.

10. The method according to claim 7, wherein, When calculating the ratio Kss between the front wheel angle and the rear wheel angle, the front / rear wheel angle ratio calculation unit limits the ratio Kss between the front wheel angle and the rear wheel angle by limiting the yaw rate, so that the lateral acceleration does not become equal to or greater than the characteristic value of the vehicle.

11. The method according to claim 10, wherein, The vehicle's characteristic value is based on the following value: the left / right width between the vehicle's tires / (2 The distance from the centerline of the vehicle to the bottom of the vehicle.

12. The method according to claim 7, wherein, In the execution of four-wheel steering control, in driver steering mode, the control unit will adjust the front wheel angle according to the driver's steering direction. Multiply by the ratio Kss between the front wheel angle and the rear wheel angle to calculate the rear wheel angle. And based on the front wheel angle and the rear wheel angle Execute rear wheel steering control.

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