Device and method for controlling a rear wheel steering system

Abstract

Device (10) for controlling a rear wheel steering, comprising: a turning state estimator (12) configured to obtain steering angle information from a steering angle sensor and to estimate a turning state by calculating a steering angular velocity from the steering angle information; a normal-state lateral acceleration predictor (13) configured, when the current state is a transient state, to predict a normal-state lateral acceleration by taking into account the steering angle and the wheel speed information in response to determining that the steering angular speed is equal to or greater than a speed threshold; and a rear wheel steering angle calculating means (14) configured to calculate a rear wheel steering angle based on the steering angle and the normal state lateral acceleration; and a controller configured to control a rear wheel actuator based on the rear wheel steering angle and the normal state lateral acceleration.

Description

BACKGROUNDFIELD OF DISCLOSUREThe present disclosure relates to an apparatus and a method for controlling steering of a vehicle capable of performing rear wheel driving.DESCRIPTION OF THE RELATED ARTA four-wheel drive vehicle can transmit power simultaneously to four wheels and thus exhibits better performance in terms of stability and drive balance compared to a two-wheel drive vehicle. The four-wheel drive controls or adjusts steering of the rear wheels based on a steering angle and a steering angular velocity during steering by the driver. As shown in FIG. 1 according to the related art, at low speed, a turning radius of the vehicle is decreased by performing rear wheel steering (e.g., phase-shifted control) in a direction opposite to the steering direction of the driver, and at high speed, rear wheel steering (e.g., in-phase control) is performed in a direction equal to the steering direction of the driver, to improve stability during high-speed turning.However, according to the four-wheel drive system in the related art described above, the rear-wheel steering occurs continuously during the steering by the driver, and this may cause the occurrence of heterogeneity of the steering as compared with the two-wheel drive. During steering by the driver, the vehicle moves in the order of the steering angle event, yaw rate event, and roll angle event. In particular, as a delay between the steering angle and the yaw rate or between the yaw rate and the roll angle increases, the driver feels that the handling response of the vehicle becomes slower. During in-phase control at high speed, a low yaw rate occurs, and thus it is difficult for the driver to experience a quick steering feel.From KR 10 2019 0 831 A, a device or a method for controlling a rear wheel steering depending on a determined driving state of the vehicle is known, wherein the rear wheel steering angle is set depending on a difference between the current yaw rate and a normal state yaw rate.DE 10 2011 122 535 B4 teaches controlling a rear axle steering system so that a transverse jerk is significantly reduced when steering into a curve, i.e. the transverse acceleration does not exceed a normal state transverse acceleration even when steering into a curve.The foregoing description of background technology is intended merely to aid in understanding the background of the present disclosure and does not mean that the present disclosure is within the scope of the related art that is already known to those of ordinary skill in the art.OVERVIEWIt is an object of the present disclosure to provide an apparatus and a method for controlling a rear wheel steering that provides a driver with a sense of unity during turning by decreasing the yaw rate roll delay time by a control or setting of the rear wheel steering during steering by the driver.The object is achieved by a device for controlling a rear wheel steering system having the features of claim 1 and a method having the features of claim 4.Other objects and advantages of the present disclosure may be understood from the following description and become apparent with reference to the exemplary embodiments of the present disclosure. In addition, it will be apparent to one skilled in the art to which the present disclosure pertains that the objects and advantages of the present disclosure can be realized by the means claimed and combinations thereof.In an aspect of the present disclosure, a device for controlling a rear wheel steering may include: a turning state estimating device configured to obtain steering angle information from a steering angle sensor and estimate a turning state by calculating a steering angle speed from the steering angle information; a normal state lateral acceleration predicting device configured to predict a normal state lateral acceleration by considering the steering angle and the wheel speed information in response to determining that the required steering angle speed is equal to or greater than a speed threshold; a rear wheel steering angle calculating device configured to calculate a rear wheel steering angle according to the steering angle and the lateral acceleration; and a controller configured to control a rear wheel actuator based on the rear wheel steering angle and the normal state lateral acceleration.Further, the apparatus may further include a steering intention determining means configured to obtain steering torque information from a steering torque sensor and determine a driver's turn intention by the steering torque information. The means for estimating a turn state may be configured to estimate the turn state in response to determining that the steering torque is equal to or greater than a torque threshold.In another aspect of the present disclosure, a method for controlling a rear wheel steering may include: calculating a steering angular velocity; comparing the steering angular velocity with a velocity threshold; calculating a normal state lateral acceleration by considering steering angle information detected by a steering angle sensor and wheel velocity information detected by a wheel velocity sensor in response to determining that the steering angular velocity is equal to or greater than the velocity threshold; calculating a rear wheel steering angle based on the normal state lateral acceleration; and controlling a rear wheel steering actuator based on the rear wheel steering angle and the normal state lateral acceleration by the controller.The method may further include decreasing a rear wheel steering angle control amount in response to determining that the steering angle speed is less than the speed threshold. Further, the calculating of the normal state lateral acceleration may include calculating the normal state lateral acceleration by considering the steering angle information obtained from a steering angle sensor and wheel speed information obtained from a wheel speed sensor. The method may also include comparing a steering torque to a torque threshold prior to calculating the steering angle speed. In response to determining that the steering torque is equal to or greater than the torque threshold, the steering angle speed may be calculated, whereas in response to determining that the steering torque is less than the torque threshold, control may end.According to the apparatus and method for controlling the rear wheel steering according to the present disclosure, since the lateral force is rapidly generated at the rear wheel at the initial stage of steering, the delay time of the event of the yaw rate and the roll angle can be reduced, and thus the feeling of unity can be provided to the driver during turning. Further, the magnitude of the lateral slip and the variation width of the front and rear wheels at the initial stage of steering can be reduced, and thus stable turning becomes possible to improve the vehicle stability. In addition, it may be possible to minimize the heterogeneity due to the rear wheel steering felt by the driver by reducing the rear wheel steering control amount in the normal state of turning.It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed.BRIEF DESCRIPTION OF THE DRAWINGSThe above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a diagram showing a general rear wheel steering system according to the related art; FIG. 2 is a block diagram illustrating the configuration of a device for controlling a rear wheel steering according to an exemplary embodiment of the present disclosure; FIG. 3 is a diagram illustrating a rear wheel steering control state according to time according to an exemplary embodiment of the present disclosure; FIG. 4 is a diagram illustrating a method of controlling a rear wheel steering according to an exemplary embodiment of the present disclosure in sequence; FIG. 5 is a diagram illustrating an example of a rear wheel steering system according to an exemplary embodiment of the present disclosure; FIG. 6 is a diagram illustrating a change in a roll angle according to an exemplary embodiment of the present disclosure; and FIG. 7 is a diagram illustrating a change in lateral slip of a tire according to an exemplary embodiment of the present disclosure.DETAILED DESCRIPTIONIt will be understood that the term "vehicle" or "vehicular" or other similar term as used herein includes motor vehicles in general such as passenger automobiles including off-road vehicles (SUV), buses, trucks, various commercial vehicles, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle having two or more sources of power, such as both gasoline-powered and electric-powered vehicles.Although an example embodiment is described as using a plurality of units to perform the example process, it is understood that the example processes may also be performed by one module or a plurality of modules. In addition, it is understood that the term controller / controller refers to a hardware device including a memory and a processor. The memory is configured to store the modules, and the processor is specifically configured to execute the modules to perform one or more processes described further below.Furthermore, the control logic of the present disclosure may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller / controller, or the like. Examples of the computer readable media include read only memories (ROMs. Read Only Memory), Random Access Memory (RAM). Random Access Memory), Compact Disc Read Only Memories (CD-ROMs), magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices, but are not limited thereto. The computer readable storage medium may also be distributed in network coupled computer systems such that the computer readable medium is stored and executed in a distributed manner, e.g., by a telematics server or a controller area network (CAN).The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a / an" and "the / s" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one / more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.Unless specifically stated or evident from context, the term "about" as used herein is to be understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. "About" may be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% or 0.01% of said value. Unless otherwise clear from context, all numerical values provided herein are modified by the term "about.".The above-described objects, features, and advantages of the present disclosure will be described in detail with reference to the accompanying drawings, and thus, those skilled in the art to which the present disclosure pertains will fully understand and easily embody the technical concept of the present disclosure.In describing the exemplary embodiments of the present disclosure, a detailed description of well-known technologies related to the present disclosure will be reduced or omitted in the case of determining that it obscures the subject matter of the present disclosure in unnecessary detail.FIG. 2 is a block diagram illustrating the configuration of a device for controlling a rear wheel steering according to the present disclosure, and FIG. 3 is a diagram illustrating a rear wheel steering control state according to time according to the present disclosure. Hereinafter, with reference to FIGS. 2 and 3, a device for controlling a rear wheel steering according to an exemplary embodiment of the present disclosure will be described.A rear wheel steering control apparatus according to the present disclosure minimizes a yaw rate roll delay time during turning of a vehicle by steering by the driver to provide a feeling of the unit to the driver during turning. Further, in order to rapidly generate rolling, a lateral force of a rear wheel tire should be rapidly generated. To this end, according to the present disclosure, the rear wheel steering may be set to predict a lateral acceleration desired by a driver in advance in an initial state (transitional state) of the steering by the driver, and the lateral acceleration in the transitional state may be rapidly generated.Thereafter, when the vehicle enters a normal state, a control amount may be decreased to minimize heterogeneity of the rear wheel steering control. The rear wheel steering control apparatus 10 according to the present disclosure may include a steering intention determination apparatus 11, a turning state estimation apparatus 12, a normal state lateral acceleration prediction apparatus 13, and a rear wheel steering angle calculation apparatus 14. Each component may be actuated by a controller. The rear wheel steering control device 10 may be implemented as a partial configuration and function of an electronic control unit (ECU) or may be configured separately.The rear wheel steering control device 10 may be configured to control or adjust a rear wheel steering actuator by successively calculating a lateral acceleration and a rear wheel steering angle using sensor measurement values of a steering torque sensor, a steering angle sensor, and a wheel speed sensor. First, the steering intention determining means 11 may be configured to determine a driver's turn intention based on steering torque information obtained from the steering torque sensor. Consequently, the steering intention determining means 11 prevents intervention in rear wheel steering control when steering occurs due to a disturbance such as a ground wave or a keyhole without a turning intention.The turning state estimating device 12 may be configured to calculate the steering angle speed intended by a driver by differentiating steering angle information obtained from the steering angle sensor to determine whether the current state is a transition state of turning or a normal state of turning during steering by the driver. Further, the normal state lateral acceleration prediction means 13 may be configured to predict a normal state lateral acceleration based on the steering angle and wheel speed information obtained from the steering angle sensor and the wheel speed sensor.The rear wheel steering angle calculator 14 may then be configured to calculate the rear wheel steering angle for rapidly generating a lateral force of the rear wheel tire based on the steering angle of the driver in a transition state of turning and the lateral acceleration information. Thereafter, when the vehicle enters the normal state of turning, the rear wheel steering control amount may be decreased to reduce heterogeneity caused by the rear wheel steering control.Prediction of the magnitude of the lateral acceleration and determination of the magnitude of the rear wheel steering angle, on the other hand, will be described in more detail by distinguishing the state of transition of turning and the state of normal turning from each other with reference to FIG. 3. First, the steering intention determining means 11 in the turning transition state may be configured to detect the change in the driver's steering torque and operate the rear wheel steering control means.The means 12 for estimating a turning state may be further configured to detect by the steering angle differentiation that the steering angle speed is fast and determine the transition to the transition state of the turning. Then, the normal state lateral acceleration prediction means 13 may be configured to predict the magnitude of the lateral acceleration, and the magnitude of the lateral acceleration may be predicted by the following expression. A y predicted lateral acceleration v x vehicle speed (wheel speed) L wheel base κ vehicle characteristic coefficient δ sw steering angle λ steering gear ratioAs described above, the lateral acceleration may be predicted, and finally, the rear wheel steering angle calculator 14 may be configured to calculate the rear wheel steering angle for generating a lateral force of a rear wheel tire to rapidly generate the lateral acceleration. Further, in the normal state of turning, the steering intention determining means 11 may be configured to detect the steering angle of the driver and the remaining steering torque, and continuously operate the rear wheel steering control means to cope with the additional steering by the driver.The means 12 for estimating a turn state may be configured to detect that the steering angular velocity is very low (e.g. less than a predetermined threshold) and determine the transition to the normal state of the turn. Consequently, the normal state lateral acceleration prediction means 13 predicts no magnitude of the lateral acceleration. Further, the rear wheel steering angle calculator 14 may be configured to decrease the rear wheel steering control amount remaining to decrease the heterogeneity of the driver caused by the rear wheel steering control in the normal state of turning.Meanwhile, the calculation of the rear wheel steering angle in the turning transition state and in the turning normal state may be performed as follows. First, the rear wheel steering angle calculator 14 in the turning transition state may be configured to set the rear wheel steering angle in the same direction as the driver's steering angle so that the lateral force to be generated in the turning normal state is increased in advance at an initial stage of the steering, and the magnitude of the rear wheel steering angle may be determined by the following expression.Further, when the rear wheel control amount remains in the normal state of turning, steering heterogenity can be provided to the driver, and thus the remaining rear wheel steering control amount can be gradually decreased. Specifically, the magnitude of the rear wheel steering angle may be determined by the following expression.In mathematical expressions 2 and 3, coefficients are defined as follows. C rws Rear wheel steering gain τ Rear wheel steering time coefficient κ Control amount reduction coefficientAs described above, the rear wheel steering control apparatus according to the present disclosure performs the control operation by the above-described configuration. Based on this, a method of controlling a rear wheel steering according to the present disclosure will be described below with reference to FIG. 4. The method described below may be performed by a controller.The rear wheel steering control device 10 may be configured to receive information from sensors such as a steering torque sensor, a steering angle sensor, and a wheel speed sensor (S 11), and the steering intention determination device 11 may be configured to compare the steering torque with a torque threshold Tq_Thd (S 12). In response to determining that the steering torque is equal to or greater than the torque threshold value as a result of the comparison, a turn intention of the driver may be detected and the rear wheel steering control may be started. However, in response to determining that the steering torque is less than the torque threshold, the rear wheel steering control may end.By the start of the rear wheel steering control, the turning state estimating device 12 may be configured to calculate the steering angular velocity (S 13). The turning state estimating device 12 may be further configured to compare the steering angular velocity with a velocity threshold Spd_Thd (S 14). In response to determining that the steering angle speed is equal to or greater than the speed threshold as a result of comparing the steering angle speed with the speed threshold, the turning state estimating device 12 may be configured to determine that the current state is the transition state of the turning. In response to determining that the steering angle speed is less than the speed threshold, the turning state estimator 12 may be configured to determine that the current state is the normal state of the turning.When the transition state of the turning is determined as a result, the normal state lateral acceleration prediction means 13 may be configured to calculate the lateral acceleration using the steering angle and the wheel speed (S 15). Based on the lateral acceleration calculated at S 15, the rear wheel steering angle calculator 14 may be further configured to calculate (S 16) the rear wheel steering angle and operate the rear wheel actuator according to the calculated value.On the other hand, when the normal state of turning is determined as a result of the determination at S 14, the rear wheel steering angle calculator 14 may be configured to calculate the corresponding rear wheel steering angle and decrease the remaining rear wheel steering control amount (S 17). Further, it may be possible to combine the above-described control method according to the present disclosure with the existing control method. In other words, referring to FIG. 5, by combining the low-speed out-of-phase control with the high-speed in-phase control as described above with reference to the drawings, the in-phase control after the rapid control can be performed in the transition state of turning based on the steering angle of the driver.As described above, according to the apparatus and method for controlling the rear wheel steering according to the present disclosure, since the lateral force is rapidly generated at the rear wheel at an initial stage of steering, the delay time of the event of the yaw rate and the roll can be reduced as shown in FIG. 6, and thus a feeling of the unit can be provided to the driver during the turn. Further, as shown in FIG. 7, in an initial stage of steering, the magnitude of the lateral slip and the variation width of the front and rear wheels can be reduced, and thus more stable turning becomes possible to improve the vehicle stability. In addition, by reducing the rear wheel steering control amount in the normal state of turning, heterogeneity that the driver feels due to the rear wheel steering can be minimized.

Claims

An apparatus (10) for controlling a rear wheel steering, comprising: a turning state estimating apparatus (12) configured to obtain steering angle information from a steering angle sensor and estimate a turning state by calculating a steering angle speed from the steering angle information; a normal state lateral acceleration predicting apparatus (13) configured, when the current state is a transition state, to predict a normal state lateral acceleration by considering the steering angle and the wheel speed information in response to determining that the steering angle speed is equal to or greater than a speed threshold; and a rear wheel steering angle calculating apparatus (14) configured to calculate a rear wheel steering angle based on the steering angle and the normal state lateral acceleration; and a controller configured to control a rear wheel actuator based on the rear wheel steering angle and the normal state lateral acceleration.The apparatus according to claim 1, further comprising: a steering intention determining means (11) configured to obtain steering torque information from a steering torque sensor and determine a driver's turn intention using the steering torque information.The apparatus of claim 2, wherein the means (12) for estimating a turn condition is configured to estimate the turn condition in response to determining that the steering torque is equal to or greater than a torque threshold.A method for controlling a rear wheel steering, comprising: calculating, by a controller, a steering angle speed; comparing, by the controller, the steering angle speed with a speed threshold; calculating, by the controller, a normal state lateral acceleration by considering steering angle information detected by a steering angle sensor and wheel speed information detected by a wheel speed sensor in response to determining that the steering angle speed is equal to or greater than the speed threshold; calculating, by the controller, a rear wheel steering angle based on the lateral acceleration; and controlling, by the controller, a rear wheel steering actuator based on the rear wheel steering angle and the normal state lateral acceleration.The method of claim 4, further comprising: decreasing, by the controller, a rear wheel steering angle control amount in response to determining that the steering angle speed is less than the speed threshold.The method according to claim 4, wherein the calculating the normal state lateral acceleration includes: calculating the normal state lateral acceleration by reflecting, by the controller, steering angle information obtained from a steering angle sensor and wheel speed information obtained from a wheel speed sensor.The method of claim 4, further comprising: comparing, by the controller, a steering torque to a torque threshold prior to calculating the steering angle velocity.The method of claim 7, further comprising: calculating, by the controller, the steering angle speed in response to determining that the steering torque is equal to or greater than the torque threshold; and terminating, by the controller, the method in response to determining that the steering torque is less than the torque threshold.

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