Patent Publication Number: US-2023159098-A1

Title: Steering System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2021-0160083, filed on Nov. 19, 2021, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle steering system and a method of controlling the same. 
     BACKGROUND 
     Recently, electric vehicles, fuel cell vehicles, and the like which are driven using an electric motor are receiving a lot of attention in terms of eco-friendliness. Such a vehicle is provided with one or two large motors. 
     On the other hand, in-wheel motors are small motors disposed on hubs of wheels, respectively, thereby enabling each of the wheels to be controlled independently. Vehicles provided with in-wheel motors have a simpler drive system compared to vehicles provided with large motors, and thus a space may be easily ensured. In addition, since wheels are controlled independently, the torque of each of the wheels can be adjusted independently, thereby improving the movement performance of the vehicle. 
     In addition, it is difficult to realize vehicle steering at a large angle of ±90° in existing axle type vehicles, and an in-wheel motor system is generally used to realize vehicle steering at a large angle of ±90°. For steering at a large angle, an actuator for steering is provided on a king pin shaft, and in order to reduce load applied to the actuator, the turning axis of the steering is set to be close to the axis of rotation of a tire. Nevertheless, large torque is necessary for the steering, and thus a large actuator is required. In this case, there are problems in that space  utilization is reduced and weight and cost are increased due to the installation of additional parts. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and accordingly it may include information that does not form the prior art that is already known to a person of ordinary skill in the art. 
     Japanese Laid-Open Patent Application No. 2016-22756, published on Feb. 8, 2016, may include information related to the subject matter of the present disclosure. 
     SUMMARY 
     The present disclosure has been made in an effort to solve the above-described problem associated with the related art, and an object of the present disclosure is to provide a steering system for independently driven wheels, wherein a steering actuator may be omitted. 
     The object of the present disclosure is not limited to the aforementioned object, and the other objects not mentioned may be clearly understood by those with ordinary skill in the art to which the present disclosure pertains (hereinafter ‘those skilled in the art’) from the following description. 
     The features of the present disclosure for achieving the object of the present disclosure, and performing the characteristic functions of the present disclosure to be described later are as follows below. 
     A steering system according to an embodiment of the present disclosure may include: an in-wheel motor disposed on a wheel of a vehicle and configured to turn the wheel; a strut arm connecting the in-wheel motor and a vehicle body; a joint clutch provided on the vehicle body and configured to engage or disengage the strut arm to allow or disallow the strut arm to pivot about the vehicle body; and a controller configured to control the in-wheel motor and the joint clutch. 
     According to the present disclosure, the steering system for independently driven wheels, wherein cost and weight may be reduced by omitting a steering actuator, and the method of controlling the same are provided. 
     The effect of the present disclosure is not limited to the aforementioned effect, and the other effects not mentioned may be clearly recognized by those skilled in the art from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present disclosure will now be described in detail with reference to certain exemplary examples thereof illustrated in the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present disclosure, and wherein: 
         FIG.  1    illustrates a vehicle including a steering system according to the present disclosure; 
         FIG.  2    is an enlarged view of one of the wheels illustrated in  FIG.  1   ; 
         FIG.  3    is a specific view of  FIG.  2   ; 
         FIG.  4    is a flowchart illustrating a control process of a steering system according to an embodiment of the present disclosure; and 
         FIGS.  5 A to  6 B  are views illustrating the principle of the steering system according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Specific structural or functional descriptions presented in exemplary embodiments of the present disclosure are only exemplified for the purpose of describing the exemplary embodiments according to the concept of the present disclosure, and the exemplary embodiments according to the concept of the present disclosure may be carried out in various forms. Further, the exemplary embodiments should not be interpreted as being limited to the exemplary embodiments described in the present specification, and should be understood as including all modifications, equivalents, and substitutes included in the spirit and scope of the present disclosure. 
     Meanwhile, in the present disclosure, terms such as first and/or second may be used to describe various components, but the components are not limited to the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, a first component may be referred to as a second component, and similarly, the second component may also be referred to as the first component, without departing from the scope according to the concept of the present disclosure. 
     When a component is referred to as being “connected” or “coupled” to another component, it should be understood that the components may be directly connected or coupled to each other, but still other component may also exist therebetween. On the other hand, when a component is referred to as being “directly connected to” or “in direct contact with” another component, it should be understood that there is no other component therebetween. Other expressions for describing the relationship between components, that is, expressions such as “between” and “directly between” or “adjacent to” and “directly adjacent to” should be also interpreted in the same manner. 
     Throughout the specification, the same reference numerals refer to the same elements. Meanwhile, the terms used in the present specification are for the purpose of describing the exemplary embodiments and are not intended to limit the present disclosure. In the present specification, the singular form also includes the plural form unless otherwise specified in the phrase. “Comprises” and/or “comprising” used in the specification specifies the presence of the mentioned component, step, operation, and/or element, and does not exclude the presence or the addition of one or more other components, steps, operations, and/or elements. 
     Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. 
     Embodiments of the present disclosure relate to a vehicle steering system and a method of controlling the same, and more particularly, to a steering system for wheels that are independently controlled and a method of controlling the same. 
     As illustrated in  FIGS.  1  and  2   , wheels  20  are coupled to corners of a vehicle body  10 , respectively. The wheels  20  include a front left wheel FL, a front right wheel FR, a rear left wheel RL, and a rear right wheel RR. 
     Each of the wheels  20  is provided with an in-wheel motor  30 . Thus, the turning of the each of the wheels  20  may be controlled independently of the other wheels by the drive of the in-wheel motor  30 . 
     According to the present disclosure, the steering of each of the wheels  20  may be controlled respectively. Each of the wheels  20  may be turned to the range of about ±90° with respect to the normal position (e.g., normal position shown in  FIG.  1   ). In this regard, a steering system according to an embodiment of the present disclosure includes a strut arm  40  and a joint clutch  50 . 
     The strut arm  40  is equipped with a suspension device (not shown), and connects each of the wheels  20  to the vehicle  10 . In an implementation, one side of the strut arm  40  is coupled to the in-wheel motor  30 , and the other side of the strut arm  40  is coupled to the joint clutch  50  by a joint  120  provided on the vehicle  10 . 
     The strut arm  40  is pivotably coupled to the joint clutch  50  by the joint  120 . The joint  120  is fixed or unfixed by the joint clutch  50 . 
     As illustrated in  FIG.  3   , the joint clutch  50  is coupled to the strut arm  40  and the joint  120 , e.g., an R-joint. The joint clutch  50  coupled to the vehicle  10 . The joint clutch  50  controls the pivoting of the joint  120 . In this regard, according to an implementation of the present disclosure, the joint clutch  50  includes a worm drive  60  and  70  and a joint motor  80 . 
     The worm drive  60  and  70  includes a worm  60  and a worm wheel  70 . The worm  60  and the worm wheel  70  are configured to control the joint  120 . Since the wheel  20  constantly applies torque to the joint clutch  50  during driving, the worm drive  60  and  70  are capable of self-locking (i.e., reverse rotation prevention). For example, the worm drive  60  and  70  can be self-locked from a predetermined lead angle. As a non-limiting example, the lead angle may be 4°. Thus, the worm drive  60  and  70  is configured to remove external force, i.e., torque input to the joint clutch  50  from the driven wheel  20 . 
     The joint motor  80  provides rotational force to the worm drive  60  and  70 . When the engaged worm drive  60  and  70  is disengaged, the joint motor  80  provides rotational force, by which the worm drive  60  and  70  is driven in the case of steering of the wheel  20 . Here, since force applied to the worm drive  60  and  70  is mainly a reverse input from the wheel  20 , it is only required for the joint motor  80  to provide a level of torque to disengage the joint clutch  50  and release the worm drive  60  and  70  in the case of steering. In addition, when the torque of the joint motor  80  is controlled, the steering angular velocity of the wheel  20  may be additionally controlled by the joint motor  80 . 
     According to an embodiment of the present disclosure, a locker  90  is further included. In an implementation, the locker  90  is a solenoid locker. The locker  90  may exclude the possibility of unlocking of the self-locking of the worm  60  due to vibrations and prevent reverse rotation. 
     In an implementation, a thrust bearing  100  is disposed to support the pivoting of the joint  120  or the strut arm  40 . 
     According to an implementation of the present disclosure, the steering system includes an angle sensor  110 . The angle sensor  110  is disposed on each of the wheels  20 , and configured to measure a turning angle of each of the wheels  20 . 
     A controller  130  drives the joint motor  80 . In an implementation, the controller  130  may adjust the torque of the joint motor  80 . In addition, the controller  130  may receive information regarding the turning angle of each of the wheels  20  from the angle sensor  110 , and may adjust the steering on the basis of the received information. In addition, the controller  130  may control the locking or unlocking of the locker  90 . 
     The controller  130  is configured to be able to control each of the in-wheel motors  30 . For example, the controller  130  may be configured to be able to communicate with the in-wheel motor  30  to control the operation of the in-wheel motor  30 . Alternatively, the controller  130  may be configured to be able to directly control the in-wheel motor  30 . In addition, the controller  130  may collect measurements of a steering angle sensor (not shown) of the steering wheel of the vehicle. In an implementation, the measurements of the steering angle sensor of the steering wheel may be angles input to a vehicle through the steering wheel by a vehicle driver. 
     According to the present disclosure, a steering actuator is omitted, and the steering is performed using force generated by a relative speed between the vehicle body and the wheel and a moment arm generated by spacing the center of turning of the wheel away from the center of a tire. 
     Referring to  FIG.  4   , a method of controlling a steering system according to some embodiments of the present disclosure is as follows. 
     First, the controller  130  receives whether or not the steering angle of the vehicle has been changed. Whether or not the steering angle of the vehicle has been changed may be determined by an input of the vehicle driver or on the basis of a steering command value of the vehicle. In the case of active steering, whether or not the steering angle of the vehicle has been changed by a steering command determined by an active steering system, i.e., a steering command of the vehicle, may be determined. 
     Specifically, the controller  130  determines whether or not a steering state is a normal state in S 10 . When the steering state is the normal state, step S 20  is performed. When the steering state is not the normal state, the steering state is determined to be a transient state in S 30 . Herein, whether the steering state is the normal state or the transient state is determined according to whether or not the steering angle has been changed. When there has been no change in the steering angle over time, i.e., the steering angle has not been changed, the steering state is determined to be the normal state. When the steering angle has been changed, the steering state is determined to be the transient state. In addition, the control of the steering system may be performed differently according to the state. 
     The controller  130  may perform a steering control in response to a specific steering request from the driver. 
     In the normal state, the controller  130  determines whether the current state is a straight driving state or a crab driving state in S 20 . When the vehicle is in the straight driving state or the crab driving state on the basis of a current steering command of the vehicle, the controller  130  sets the joint clutch  50  in an engaged position in S 40 . In addition, the controller  130  drives respective in-wheel motors  30  by setting each of the angular velocity ω R  of the right wheel  20  and the angular velocity ω L  of the left wheel  20  to be target angular velocity ω tgt  in the same manner. A target angular velocity ω tgt  refers to an angular velocity by which a target vehicle speed is to be obtained. 
     When the controller  130  determines that the current state is neither the straight driving state nor the crab driving state in the normal state, the controller  130  determines whether or not the vehicle is turning to the right in S 50 . Here, although the determination of whether or not the vehicle is turning to the right is first taken as an example, determination of whether or not the vehicle is turning to the left may precede. 
     When it is determined that turning to the right is requested on the basis of the current steering command of the vehicle in the normal state, in S 60 , the controller  130  sets the joint clutch  50  in the engaged position and only changes the angular velocities of the wheels  20  differently from the straight driving in the above step S 50 . When the steering angle has not been changed as above, the joint clutch  50  is in a constantly engaged position. In addition, the angular velocity ω R  of the right wheel  20  and the angular velocity ω L  of the left wheel  20  are set, and the respective in-wheel motors  30  are driven using the set angular velocities ω R  and ω L . That is, in the case of the right wheel  20 , a difference angular velocity cot for a wheel speed difference during turning to the right is deducted from the target angular velocity ω tgt . In contrast, in the case of the left wheel  20 , the difference angular velocity ω t  is added to the target angular velocity ω tgt . That is, in the case of the turning to the right, the right wheel is rotated at a slower speed than the left wheel. 
     A case in which the turning to the left is requested in the normal state is contrary to the turning to the right. The controller  130  sets the joint clutch  50  in the engaged position and sets the angular velocity of the right wheel  20  and the angular velocity of the left wheel  20  in S 70 . That is, in the case of the left wheel  20 , the difference angular velocity ω t  is deducted from the target angular velocity ω tgt , but, in the case of the right wheel  20 , the difference angular velocity ω t  is added to the target angular velocity ω tgt . 
     In addition, in a case in which the steering state is the transient state instead of being the normal state in S 30 , when the steering angle is changing, the controller  130  determines whether or not there is a request to turn the wheels  20  in the clockwise direction CW on the basis of the current steering command of the vehicle in S 80 . In response to the request to turn in the clockwise direction CW, the controller  130  disengages the joint clutch  50  so that the wheel  20  can turn with respect to the joint  120 . In addition, the angular velocities of the wheels  20  are set in S 90 . The respective in-wheel motors  30  are driven by setting the angular velocity ω R  of the right wheel  20  to be a value obtained by deducting a steering angular velocity cos that is an angular velocity for steering from the target angular velocity ω tgt  and the angular velocity ω L  of the left wheel  20  to be a value obtained by adding the steering angular velocity cos to the target angular velocity ω tgt . 
     Similarly, when the wheel  20  is turned in the counterclockwise direction CCW in S 100 , the controller  130  controls the joint clutch  50  to be disengaged. In addition, the controller  130  sets the angular velocity ω R  of the right wheel  20  to be a value obtained by adding the steering angular velocity cos to the target angular velocity ω tgt  and the angular velocity ω L  of the left wheel  20  to be a value obtained by deducting the steering angular velocity cos from the target angular velocity ω tgt  in S 110 . Here, similarly, although the determination of whether or not the vehicle is turning in the clockwise direction CW is first performed as an example, determination of whether or not the vehicle is turning in the counterclockwise direction CCW may precede. 
     When the wheel  20  is not turned in the clockwise direction CW or the counterclockwise direction CCW even in the transient state, i.e., even if there has been a change in the steering angle, the controller  130  determines that the state to be a state in which the wheels are controlled independently. In the case of independent controlling of the wheels, the controller  130  controls the joint clutch  50  to be disengaged, and calculates the angular velocities ω FR , ω FL , ω RR , and ω RL  of each of the wheels  20  by adding or deducting the angular velocities ω FRS , ω FLS , ω RRS , and ω RLS  for the steering of the respective wheels  20  to or from the target angular velocity ω tgt  according to the target value in S 120 . 
     Referring to  FIGS.  5 A to  6 B , some of the steering control by the steering system according to the present disclosure will be described. 
     Referring to  FIG.  5 A , in the transient state, i.e., during changing of the steering angle, when it is intended to turn the front wheels in the clockwise direction CW in order to turn right during the straight driving, the controller  130  engages the joint clutch  50 . In an implementation, the controller  130  drives the worm drive  60  and  70  by rotating the joint motor  80 . Then, the strut arm  40  is pivotable with respect to the joint  120 . In addition, the controller  130  drives the in-wheel motor  30  of the right wheel with respect to the direction of forward movement of the vehicle so that the speed of the right wheel is less than the speed of the vehicle and the in-wheel motor  30  of the left wheel  20  with respect to the direction of forward movement of the vehicle so that the speed of the left wheel is faster than the speed of the vehicle. Arrows in  FIG.  5 A  indicate different speeds. Then, as illustrated in  FIG.  5 B , due to the different relative speeds, the wheels  20  turn about the joints  120 . Here, the joint clutches  50  are disengaged only when the wheels  20  are turned, and the joint clutches  50  are engaged to prevent turning when the wheels  20  are not to be turned, such as in the case of forward movement or the like. 
     According to the present disclosure, 90° steering of the wheel  20  may be performed. In particular, 90° steering of the wheel  20  may be performed by differently setting the turning direction of the left wheels and the turning direction of the right wheels at a stopped state of the vehicle. In an implementation, as illustrated in  FIG.  6 A , the steering may be performed by rotating the left wheels forward and the right wheels backward at the stopped state. In  FIG.  6 B , a state in which the vehicle is movable parallel to the right direction of the vehicle is illustrated. In order to form this state, the controller  130  disengages the joint clutch  50  by driving the joint motor  80  during the stopped state of the vehicle so that the steering of the wheels  20  is possible. That is, the wheel  20  may be turned about the joint  120  in order to disengage the joint clutch  50 . In addition, the controller  130  drives the in-wheel motors  30  of the left wheels FL and RL so that the left wheels FL and RL rotate forward (i.e., vehicle forward movement) and the in-wheel motors  30  of the right wheels FR and RR so that the right wheels FR and RR rotate backward (i.e., vehicle backward movement). Consequently, as illustrated in  FIG.  5 B , the respective wheels  20  may be arranged to be parallel to the transverse direction of the vehicle. 
     Since the steering system according to the present disclosure is configured such that the steering motor can be omitted, weight and cost of the steering system can be reduced, and the steering system is advantageous in terms of space. 
     The aforementioned present disclosure is not limited by the aforementioned exemplary embodiments and the accompanying drawings, and it will be apparent to those skilled in the art that various substitutions, modifications, and changes may be made without departing the technical sprit of the present disclosure.