Device and method for controlling a vehicle steering system using lateral acceleration

Abstract

Device for controlling the vehicle steering, the device comprising: a reference lateral acceleration extractor configured to extract a reference lateral acceleration based on a vehicle speed and steering angle; a condition determiner for a damping application that is configured to determine whether a damping application condition is satisfied based on the reference lateral acceleration and the actual lateral acceleration; and a damping current controller configured to control a damping current applied to an EPS motor when it is determined that the damping application condition is met.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present disclosure relates to a device and a method for controlling a vehicle steering system. 2. Description of the state of the art

[0002] For a vehicle's yaw stability, a modern EPS (Expanded Power Steering) receives steering angle information from an angle sensor and applies damping control according to the magnitude and speed of the steering angle. "Damping control" means controlling the current applied to the EPS motor to exert a force that turns the steering wheel (handle) in the opposite direction to its current rotation. Damping control is necessary to improve the vehicle's yaw stability.

[0003] However, conventional damping control, known for example from US 2016 / 0096545A1, is not only applied to the case where the steering wheel is turned back, i.e., the steering angle is returned to the center (0°), but also to the case where the steering wheel is turned, i.e., where the absolute value of the steering angle increases, and thus some drivers feel damping or friction.

[0004] If the damping current in the damping control is minimized to solve the problem that occurs when the steering wheel is released after turning while the vehicle is moving at high speed, i.e., when a driver is not holding the steering wheel, an oversteering problem may occur due to an excessively high self-aligning torque.

[0005] DE 10 2015 219 443 A1 describes a system for controlling a vehicle steering system with electric motor assistance, wherein the assistance depends on the coefficient of friction between the road surface and the wheels of the vehicle.

[0006] DE 10 2006 019 732 B4 discloses a system for controlling a vehicle steering system with electric motor assistance, whereby the driver receives a warning of approaching the vehicle's dynamic limits.

[0007] DE 42 39 831 A1 discloses a system for controlling a vehicle steering system with electric motor assistance, wherein the driver receives a reaction torque from the steering wheel when the vehicle drives on a smooth road surface and therefore the manual steering input torque becomes small. BRIEF SUMMARY OF THE INVENTION

[0008] Accordingly, to solve the problems, a reference lateral acceleration can be derived according to a vehicle speed and a steering angle, and the damping current applied to an EPS motor can be controlled on the basis of the reference lateral acceleration and the actual lateral acceleration in the present disclosure.

[0009] The problem is solved by a device having the features of claim 1 and by a method having the features of claim 9. Advantageous embodiments are set forth in the dependent claims. According to the present disclosure, it is possible to minimize oversteer and improve the yaw stability of the vehicle by applying a minimal damping current when the vehicle's steering wheel is turned normally and immediately applying a large amount of damping current when the vehicle's steering wheel is turned rapidly back. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above-mentioned and other aspects, features and advantages of the present disclosure will become apparent from the following detailed description in conjunction with the accompanying drawings, in which: Fig. Figure 1 illustrates the configuration of a device for controlling the vehicle steering according to one embodiment; Fig. Figure 2 illustrates the reference lateral acceleration based on a steering angle according to one embodiment; Fig. Figure 3 illustrates the actual lateral acceleration based on the steering angle when a steering wheel is turned and then turned back while the steering wheel is held according to one embodiment; Fig. Figure 4 illustrates the actual lateral acceleration based on the steering angle when the steering wheel is turned and then turned back while the steering wheel is released according to one embodiment; Fig. Figure 5 illustrates a region in which the damping current is applied when the steering wheel is turned and then turned back while the steering wheel is released according to one embodiment; Fig. Figure 6 is a flowchart illustrating a method for controlling the vehicle steering according to one embodiment; and Fig. Figure 7 is a flowchart illustrating a process for controlling the damping current applied to the EPS motor by the vehicle steering control device according to one embodiment. DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES

[0011] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. In the following description, identical components are designated by the same reference numerals, even though they are shown in different drawings. Furthermore, a detailed description of the known functions and configurations contained herein is omitted in the following description of the present disclosure if it is determined that such a description might obscure the subject matter of the present disclosure.

[0012] Furthermore, terms such as first, second, A, B, (a), (b), or the like may be used herein to describe components of the present disclosure. These terms serve only to distinguish one structural element from other structural elements, and a property, order, sequence, and the like of a corresponding structural element are not limited by the term. It should be noted that if the patent specification describes one component as being "connected," "coupled," or "joined" to another component, a third component may be "connected," "coupled," or "joined" between the first and second components, even though the first component may be directly connected, coupled, or joined to the second component.

[0013] The lateral acceleration of a vehicle is an acceleration applied in the side direction of the vehicle. When a driver turns the steering wheel left or right, the vehicle rotates and thus experiences centrifugal force, and the driver feels lateral acceleration. Lateral acceleration exhibits different characteristics when applied in a right-hand and a left-hand direction. Therefore, absolute values ​​of lateral acceleration should be used for comparing its magnitude.

[0014] The present disclosure is described in detail below with reference to the drawings.

[0015] Fig. Figure 1 illustrates the configuration of a device for controlling the vehicle steering according to one embodiment.

[0016] With reference to Fig. 1 A device 100 for controlling the vehicle steering may include a reference lateral acceleration setting unit 110, a condition determining unit for the damping application 120 and a damping current control 130.

[0017] The reference lateral acceleration adjustment unit 110 can extract the reference lateral acceleration based on a vehicle speed and a steering angle. The reference lateral acceleration adjustment unit 110 can acquire the value of the current steering angle from a steering angle sensor 10 installed in the vehicle and the value of the current vehicle speed from a vehicle speed sensor 20.

[0018] At this point, the reference lateral acceleration is a measurement of the lateral acceleration that serves as a reference to determine how much damping current is applied to an EPS motor 40. The reference lateral acceleration can be determined based on the current vehicle speed and steering angle, or influenced by other factors.

[0019] For example, the 110 reference lateral acceleration setting unit can determine the reference lateral acceleration proportional to the square of the vehicle speed and the size of the steering angle. The vehicle's lateral acceleration is proportional to the square of the vehicle speed and inversely proportional to the radius of rotation, since lateral acceleration is essentially a value generated by dividing the centrifugal force by the mass. As the vehicle's steering angle increases, its turning circle becomes smaller, thus increasing its lateral acceleration. Accordingly, the reference lateral acceleration can be determined to be proportional to the square of the vehicle speed and the size of the steering angle.

[0020] In another example, the reference lateral acceleration setting unit 110 can determine that the reference lateral acceleration is proportional to a result value generated by replacing the vehicle speed with a lateral acceleration gain function, and proportional to the magnitude of the steering angle. The vehicle's lateral acceleration can be influenced not only by the vehicle speed and steering angle, but also by other factors. Accordingly, to accurately set the reference lateral acceleration, lateral acceleration data as a function of vehicle speed and steering angle can be measured and recorded in advance, and the lateral acceleration gain function can be specified based on the recorded data.

[0021] At this point, the lateral acceleration gain function is a function that derives the change in actual lateral acceleration as a function of vehicle speed. The lateral acceleration gain function can take the form of a table containing a vehicle speed-lateral acceleration pair and a predefined equation, and can be updated based on experimental values.

[0022] The damping application condition determiner unit 120 can determine whether a damping application condition is met, based on the reference lateral acceleration extracted by the reference lateral acceleration setting unit 110 and the actual lateral acceleration. The damping application condition determiner unit 120 can acquire a value of the actual lateral acceleration from the lateral acceleration sensor 30 installed in the vehicle. The damping application condition determiner unit 120 can detect whether the steering wheel is being turned or turned back by analyzing the change in the actual lateral acceleration and the difference between the actual lateral acceleration and the reference lateral acceleration, and can detect whether the driver is holding the steering wheel or has released it. The damping application condition determiner unit 120 can identify the damping application condition, i.e.,Based on steering wheel status information and steering angle, determine whether the damping current should be applied to the EPS motor. The following illustrates this. Fig. 2, Fig. 3, Fig. 4 to Fig. 5 the damping application condition in detail.

[0023] When the damping application condition determiner 120 determines that the damping application condition is met, the damping current controller 130 can control the damping current applied to the EPS motor. At this point, the damping current generates a torque, causing the steering wheel to move closer to the center, i.e., a position with a steering angle of 0 degrees. Accordingly, the damping current controller 130 is required when the steering wheel is turned back after a higher angular velocity to reduce the steering wheel's angular velocity by applying a higher damping current as it approaches the center. Therefore, the damping current controller 130 can control the application of the damping current proportional to the difference between an absolute value of the actual lateral acceleration and an absolute value of the reference lateral acceleration.

[0024] To vary the damping current magnitude depending on vehicle speed, steering torque, and steering angle, the Damping Current Controller 130 can also apply weighted values ​​based on these factors and control the application of the damping current. This ensures the damping current is optimally suited to the vehicle's condition at the EPS motor, further improving the vehicle's yaw stability. The weighted values ​​can be determined based on actual test data.

[0025] For example, the damping current controller 130 can be used to apply the damping current proportionally to the vehicle speed. If the driver suddenly releases the steering wheel and thus quickly returns it to the center position, the steering angle also changes rapidly. If the change in the steering angle becomes larger at high vehicle speeds, the vehicle's movement increases rapidly, and its stability can be reduced. Accordingly, at high vehicle speeds, it is necessary to prevent a rapid change in steering angle when returning the steering wheel by increasing the applied damping current proportionally to the vehicle speed.

[0026] In another example, the damping current controller 130 can control the application of the damping current inversely proportional to the magnitude of the steering torque. An increase in steering torque can occur when the driver wants to change the vehicle's steering input accordingly. If the damping current interrupts the steering input change, the timing of the intended steering change is delayed, and a greater torque must be applied to execute the intended steering change. Therefore, as the magnitude of the steering torque increases, the applied damping current must be reduced inversely proportional to the steering torque.

[0027] Fig. Figure 2 illustrates the reference lateral acceleration based on the steering angle according to one embodiment.

[0028] With reference to Fig. 2. If an x-axis is the steering angle and a y-axis is the lateral acceleration, a diagram of the reference lateral acceleration corresponding to the steering angle (hereafter defined as (+) in right-hand drive and (-) in left-hand drive) has the form of a straight line divided by the dashed line in Fig. 2 is marked. This is because the reference lateral acceleration is proportional to the size of the steering angle. The slope of the line can be determined by other factors, including the vehicle speed, and can be proportional to the result value obtained by substituting the square of the vehicle speed or the vehicle speed for the given lateral acceleration gain function, as described above.

[0029] Fig. Figure 3 illustrates the actual lateral acceleration based on the steering angle when the steering wheel is turned and then turned back while the steering wheel is held according to one embodiment.

[0030] With reference to Fig. 3. A change in the actual lateral acceleration according to the steering angle exhibits the shape of an oval in the upper right part or in the lower left part of Fig. 3. The graph shows the change in lateral acceleration when the driver turns the steering wheel and then turns it back while holding the wheel. The oval in the upper right corresponds to a graph showing the change in lateral acceleration when turning the steering wheel back to the right, and the oval in the lower left corresponds to a graph showing the change in lateral acceleration when turning the steering wheel back to the left.

[0031] It is known that the absolute value of the difference between the reference lateral acceleration and the actual lateral acceleration is equal to or less than a certain threshold, based on a comparison of the difference between the actual lateral acceleration and the reference lateral acceleration. That is, the change in lateral acceleration occurs within a dead zone, i.e., a region in which the absolute value of the difference between lateral acceleration and reference lateral acceleration is less than the respective threshold in the graph. Fig. 3. Because the driver holds the steering wheel firmly and exerts a reaction force on the steering wheel to prevent a rapid change in the steering angle when turning the steering wheel back.

[0032] Fig. Figure 4 illustrates the actual lateral acceleration based on the steering angle when the steering wheel is turned and then turned back while the steering wheel is released according to one embodiment.

[0033] With reference to Fig. 4. The steering angle increases when the steering wheel is turned to the right (①), and the lateral acceleration also increases as the vehicle turns in accordance with the steering input. The steering angle then decreases and returns to 0 degrees when the steering wheel is turned back (②).

[0034] At this point, releasing the steering wheel means the driver is no longer applying force to prevent a rapid change in the steering angle, and thus the steering angle decreases rapidly. However, since the vehicle's rotation is achieved by changing the steering angle, the magnitude of the actual lateral acceleration for the current steering angle becomes greater than the magnitude of the reference lateral acceleration for that same steering angle. As the steering wheel absorbs a force that sets the steering angle to 0 degrees, the steering angle further passes through 0 degrees and absorbs the force again in the opposite direction, thus entering a state where the steering angle is 0 degrees.

[0035] Even when the steering wheel is turned to the left (③) and then back (④), the same phenomenon can occur as when the steering wheel is turned to the right (①) and then back (②), with the only difference being that the direction is reversed.

[0036] Fig. Figure 5 illustrates a region in which the damping current is applied when the steering wheel is turned and then turned back while the steering wheel is released according to one embodiment.

[0037] With reference to Fig. 5. The damping current is applied for a force to turn the steering wheel in a direction opposite to the direction in which the steering wheel is turned back, in order to increase the vehicle's yaw stability. Therefore, if the damping current is also applied when the steering wheel is turned, the driver may feel damping or friction. Consequently, it is possible that the damping current will not be applied when the steering wheel is turned, i.e., when the absolute value of the steering angle increases.

[0038] The driver continues to hold the steering wheel while it is turned back, as in Fig. Figure 3 illustrates the area where the absolute value of the difference between the actual lateral acceleration and the reference lateral acceleration is less than a certain threshold, i.e., in the dead zone. In this case, it is determined that the steering wheel is controlled by the user's intention, and therefore the damping current is not applied.

[0039] Furthermore, the damping current is applied for a force to turn the steering wheel in a direction opposite to the direction in which the steering wheel is turned back. Accordingly, applying the damping current after the steering wheel angle has reached a predetermined threshold angle (e.g., 0 degrees at center), while the steering wheel is being turned back, will tend to increase the steering wheel angle in the opposite direction to the direction in which it is turned back. Therefore, the damping current should only be applied before the steering wheel angle reaches the predetermined threshold angle, and from that point on, the damping current should no longer be applied.

[0040] This means that if the steering wheel is turned back in the state in which it is released, the damping current can only be applied before the steering wheel reaches the set threshold angle. Accordingly, black areas on the diagram represent regions where the damping current must be applied.

[0041] Accordingly, the damping application condition 120 of the device 100 for controlling the vehicle steering can determine that the damping application condition is met before the steering angle reaches the predetermined threshold angle, if it is determined that the steering wheel is turned back in the state in which it is released. When the damping application condition is met, the damping current control 130 can perform a control operation to apply the damping current proportional to the difference between the absolute value of the actual lateral acceleration and the absolute value of the reference lateral acceleration, as described above.

[0042] Fig. Figure 6 is a flowchart illustrating a method for controlling the vehicle steering according to one embodiment.

[0043] The following describes the method performed by device 100 for controlling the vehicle steering, which refers to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5 is described by way of example.

[0044] With reference to Fig. 6. The method for controlling the vehicle steering can include a reference lateral acceleration extraction step for extracting the reference lateral acceleration based on a vehicle speed and a steering angle in S610. As described above, the reference lateral acceleration extractor 110 of the vehicle steering device 100 can adjust the reference lateral acceleration to be proportional to the square of the vehicle speed and the magnitude of the steering angle. Furthermore, the vehicle steering device 100 can adjust the reference lateral acceleration to be proportional to a result value generated by replacing the vehicle speed with a predetermined lateral acceleration gain function and the magnitude of the steering angle.

[0045] Furthermore, the method for controlling the vehicle steering can include a step to determine the damping application condition in order to determine whether a damping application condition is satisfied based on the reference lateral acceleration and the actual lateral acceleration in S620. As described above, the damping application condition determiner 120 of the device 100 for controlling the vehicle steering can determine that the damping application condition is satisfied before the magnitude of the steering angle reaches a predetermined threshold angle. At that point, when an absolute value of the actual lateral acceleration is greater than an absolute value of the reference lateral acceleration by a predetermined threshold or more, the damping application condition determiner 120 can determine that the steering wheel is released.

[0046] If it is determined that the damping application condition is met, the method for controlling the vehicle steering may include a damping current control step for controlling the damping current applied to an EPS motor in S630. If it is determined that the damping application condition is met, the damping current control 130 of the device 100 for controlling the vehicle steering may control the damping current applied to the EPS motor 40.

[0047] As described above, the damping current can be proportional to the difference between the absolute value of the actual lateral acceleration and the absolute value of the reference lateral acceleration, and can be determined using weighted values ​​depending on vehicle speed, steering torque, and steering angle. For example, the damping current can be proportional to the vehicle speed. In another example, the damping current can be inversely proportional to the magnitude of the steering torque.

[0048] Fig. Figure 7 is a flowchart illustrating a process for controlling the damping current applied to the EPS motor by the vehicle steering control device according to one embodiment.

[0049] The following describes the process carried out by device 100 for controlling the vehicle steering, which, with reference to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5 is described by way of example.

[0050] With reference to Fig. 7. The device 100 can extract a reference lateral acceleration for controlling the vehicle steering based on the steering angle measured by the steering angle sensor 10 and the vehicle speed measured by the vehicle speed sensor 20 in S710. At this point, the extracted reference lateral acceleration can be proportional to the square of the vehicle speed and the magnitude of the steering angle, and also proportional to the result obtained by replacing the vehicle speed with a predetermined lateral acceleration gain function and the magnitude of the steering angle, as described above. Fig. 1 described, is generated.

[0051] The device 100 for controlling the vehicle steering can determine whether the damping application condition is met based on the reference lateral acceleration extracted in S710 and the actual lateral acceleration measured by the lateral acceleration sensor 30.

[0052] First, the damping control condition 120 of the device 100 for controlling the vehicle steering determines whether the steering wheel is turned back to position S720. As described above, if the damping control is applied when turning the steering wheel, the driver can feel damping and friction. If the steering wheel is not turned back to position S720-N, the damping current is not applied to the EPS motor 40.

[0053] If it is determined that the steering wheel is turned back in S720-Y, the condition determiner for the damping application 120 of the device 100 for controlling the vehicle steering determines whether the steering wheel is released in S730. Whether the steering wheel is released can then be determined whether the absolute value of the actual lateral acceleration is greater than the absolute value of the reference lateral acceleration by the specified threshold or more. If the steering wheel is not released in S730-N, the damping current is not applied to the EPS motor 40.

[0054] When it is determined that the steering wheel is released in S730-Y, the condition determiner for the damping application 120 of the device 100 for controlling the vehicle steering determines whether the steering angle reaches a predetermined threshold angle in S740. This is intended to prevent the steering angle of the steering wheel from increasing in a direction opposite to the direction in which the steering wheel is turned back, as described in relation to Fig. 5 described. When the steering angle reaches the specified threshold angle in S740-Y, the damping current is not applied to the EPS motor 40.

[0055] Before the steering angle reaches the specified threshold angle in S740-N, the damping current control 130 of the device 100 for controlling the vehicle steering can control the damping current applied to the EPS motor 40 proportionally to the difference between the absolute value of the actual lateral acceleration and the absolute value of the reference lateral acceleration in S750.

[0056] Although it has been described above that all components of an embodiment of the present disclosure are coupled as a single unit or coupled as a single unit for operation, the present disclosure is not necessarily limited to such an embodiment. That is to say, at least two elements of all structural elements can be selectively joined and function without deviating from the scope of the present disclosure.

[0057] Although the embodiments of the present disclosure have been described for illustrative purposes, those skilled in the art will understand that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the disclosure. Therefore, the embodiments of the present disclosure should not be considered limiting, but rather illustrating the technical idea of ​​the present disclosure, and the scope of the technical idea of ​​the present disclosure is not limited by the embodiments. The scope of the present disclosure is to be interpreted on the basis of the related claims such that all technical ideas included in the claims to an equivalent scope belong to the present disclosure.

Claims

[1] Device for controlling the vehicle steering, the device comprising: a reference lateral acceleration extractor configured to extract a reference lateral acceleration based on a vehicle speed and steering angle; a condition determiner for a damping application that is configured to determine whether a damping application condition is satisfied based on the reference lateral acceleration and the actual lateral acceleration; and a damping current controller configured to control a damping current applied to an EPS motor when it is determined that the damping application condition is met. [2] Device according to claim 1, characterized by that the reference lateral acceleration is proportional to the square of the vehicle speed and a magnitude of the steering angle. [3] Device according to claim 1, characterized by, that the reference lateral acceleration is proportional to a result value generated by replacing the vehicle speed with a predetermined lateral acceleration gain function, and is proportional to a magnitude of the steering angle. [4] Device according to claim 1, characterized by , that if it is determined that the steering wheel is turned back in a state in which the steering wheel is released, the damping application condition determiner determines that a damping application condition is satisfied before a quantity of the steering angle reaches a predetermined threshold angle. [5] Device according to claim 4, characterized by , that if an absolute value of the actual lateral acceleration is greater than an absolute value of the reference lateral acceleration by a predetermined threshold speed or more, the condition determiner for the damping application determines that the steering wheel is released. [6] Device according to claim 1, characterized by , that the damping current is proportional to the difference between the absolute value of the actual lateral acceleration and the absolute value of the reference lateral acceleration. [7] Device according to claim 1, characterized by that the damping current is proportional to the vehicle speed. [8] Device according to claim 1, characterized by , that the damping current is inversely proportional to the magnitude of a steering torque. [9] Method for controlling a vehicle steering system, comprising the method: a step towards extracting a reference lateral acceleration to extract the reference lateral acceleration based on a vehicle speed and a steering angle; a step to determine a damping application condition, to determine whether a damping application condition is satisfied based on the reference lateral acceleration and the actual lateral acceleration; and a step to control the damping current to control the damping current applied to an EPS motor when it is determined that the damping application condition is met. [10] Method according to claim 9, characterized by that the reference lateral acceleration is proportional to the square of the vehicle speed and a magnitude of the steering angle. [11] Method according to claim 9, characterized by , that the reference lateral acceleration is proportional to a result value generated by replacing the vehicle speed with a predetermined lateral acceleration gain function, and is proportional to a magnitude of the steering angle. [12] Method according to claim 9, characterized by, that the step to determine the damping application condition includes that, when it is determined, the steering wheel is turned back to a state in which the steering wheel is released, determining that a damping application condition is satisfied before a quantity of the steering angle reaches a preset threshold angle. [13] Method according to claim 12, characterized by , that the step to determine the damping application condition includes determining that the steering wheel will be released when an absolute value of the actual lateral acceleration is greater than an absolute value of the reference lateral acceleration with a preset threshold speed or more. [14] Method according to claim 9, characterized by , that the damping current is proportional to the difference between an absolute value of the actual lateral acceleration and an absolute value of the reference lateral acceleration.

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