Patent Publication Number: US-9840278-B2

Title: Illuminated vehicle control management pushbutton knob

Description:
FIELD OF THE INVENTION 
     The disclosures made herein relate generally to steering assist technologies in vehicles and, more particularly, to trailer backup assist system having a rotatable driver interface for controlling trailer path. 
     BACKGROUND OF THE INVENTION 
     It is well known that backing up a vehicle with a trailer attached is a difficult task for many drivers. This is particularly true for drivers that are untrained at backing with trailers such as, for example, those that drive with an attached trailer on an infrequent basis (e.g., have rented a trailer, use a personal trailer on an infrequent basis, etc). One reason for such difficulty is that backing a vehicle with an attached trailer requires counter-steering that is opposite to normal steering when backing the vehicle without a trailer attached and/or requires braking to stabilize the vehicle-trailer combination before a jack-knife condition occurs. Another such reason for such difficulty is that small errors in steering while backing a vehicle with an attached trailer are amplified thereby causing the trailer to depart from a desired path. 
     To assist the driver in steering a vehicle with trailer attached, a trailer backup assist system needs to know the driver&#39;s intention. One common assumption with known trailer backup assist systems is that a driver of a vehicle with an attached trailer wants to back up straight and the system either implicitly or explicitly assumes a zero curvature path for the vehicle-trailer combination. Unfortunately, most of real-world use cases of backing a trailer involve a curved path and, thus, assuming a path of zero curvature would significantly limit usefulness of the system. Some known systems assume that a path is known from a map or path planner, which can result in such systems having a fairly complex human machine interface (HMI) and vehicle/trailer position determination. 
     Therefore, an approach for backing a trailer that provides a simple human machine interface and that overcomes other shortcomings of known trailer backup assist systems would be advantageous, desirable and useful. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a control system for a vehicle includes a steering system, an input including a rotatable rotary element, and a controller. The controller receives a trailer backup assist mode initiation command from the input and activates a trailer backup mode including outputting a vehicle steering command based on a first instantaneous position of the rotary element to the steering system. The controller further receives a terrain management mode initiation command from the input and activating a terrain management mode. 
     According to another aspect of the present invention, a vehicle includes a steering system, an input including a rotatable element, and a controller. The controller receives a first mode selection from the input corresponding to a trailer backup assist mode initiation command and executes a trailer backup assist mode including interpreting a first instantaneous position of the rotary element as a trailer control commanding position and outputting a vehicle steering command based thereon to the steering system. 
     According to another aspect of the present invention, a method for controlling a vehicle includes receiving a first mode selection and, when the first mode selection corresponds to a trailer backup assist mode, determining a first instantaneous position of a rotary element within the vehicle, interpreting the first instantaneous position as a trailer control position, and outputting a corresponding steering command to a steering system. When the first mode selection corresponds to an additional vehicle control mode, the method further includes requesting selection of a first mode parameter. 
     These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a top perspective view of a vehicle attached to a trailer with one embodiment of a hitch angle sensor for operating a trailer backup assist system; 
         FIG. 2  is a block diagram illustrating one embodiment of the trailer backup assist system having a steering input device, a curvature controller, and a trailer braking system; 
         FIG. 3  is a schematic diagram that illustrates the geometry of a vehicle and a trailer overlaid with a two-dimensional x-y coordinate system, identifying variables used to determine a kinematic relationship of the vehicle and the trailer for the trailer backup assist system, according to one embodiment; 
         FIG. 4  is a schematic block diagram illustrating portions of a curvature controller, according to an additional embodiment, and other components of the trailer backup assist system, according to such an embodiment; 
         FIG. 5  is a plan view of a steering input device having a rotatable knob for operating the trailer backup assist system, according to one embodiment; 
         FIG. 6  is a plan view of another embodiment of a rotatable knob for selecting a desired curvature of a trailer and a corresponding schematic diagram illustrating a vehicle and a trailer with various trailer curvature paths correlating with desired curvatures that may be selected; 
         FIG. 7  is a schematic diagram showing a backup sequence of a vehicle and a trailer implementing various curvature selections with the trailer backup assist system, according to one embodiment; 
         FIG. 8  is a perspective view of a variation of the rotatable knob for the trailer backup steering input apparatus of  FIG. 5 ; 
         FIG. 9  is a top plan view of the rotatable knob of  FIG. 8 ; 
         FIG. 10  is a side view of the rotatable knob of  FIG. 8 ; 
         FIG. 11  is a schematic diagram showing a backup sequence of a vehicle and a trailer implementing various curvature selections with the trailer backup assist system; 
         FIG. 12  is a top plan view of the rotatable knob of  FIG. 9  shown during implementation of the various curvature selections; 
         FIG. 13  shows a display screen presenting various menu items for selection using the rotatable knob of  FIG. 8 ; 
         FIG. 14  is a perspective view of a further variation of a rotatable knob for the trailer backup steering input apparatus of  FIG. 5 ; 
         FIG. 15  shows a display screen presenting various menu items for selection using the rotatable knob of  FIG. 14 ; 
         FIG. 16  is a schematic diagram showing the vehicle implementing various parking actions using a park assist system; 
         FIG. 17  is a perspective view of a further variation of a rotatable knob for the trailer backup steering input apparatus of  FIG. 5 ; 
         FIG. 18  is a side elevation view of the rotatable knob of  FIG. 17  in a position during use thereof to select a vehicle control mode; and 
         FIG. 19  is a flow diagram illustrating a method of estimating a hitch angle using a hitch angle estimation routine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” “interior,” “exterior,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawing, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. Additionally, unless otherwise specified, it is to be understood that discussion of a particular feature of component extending in or along a given direction or the like does not mean that the feature or component follows a straight line or axis in such a direction or that it only extends in such direction or on such a plane without other directional components or deviations, unless otherwise specified. 
     Referring to  FIGS. 1-15 , reference numeral  10  generally designates a trailer backup assist system for controlling a backing path of a trailer  12  attached to a vehicle  14  by allowing a driver of the vehicle  14  to specify a desired curvature  26  of the backing path of the trailer  12 . In one embodiment, the trailer backup assist system  10  is implemented by a control system of vehicle  14  that includes an interface  212 , (as shown in  FIG. 8 ) including a rotatable rotary element  232  and a controller (such as controller  28  in  FIG. 2 ). The controller executes a trailer backup assist mode including interpreting a first instantaneous position of the rotary element  232  as a trailer control commanding position and generating a vehicle steering command based thereon. The controller also executes a parking assist mode including implementing a parking assist action corresponding to a second instantaneous position of the rotary element  232 . 
     With respect to the general operation of the trailer backup assist system  10 , a steering input device  18  may be provided, such as a rotatable knob  30 , for a driver to provide the desired curvature  26  of the trailer  12 . As such, the steering input device  18  may be operable between a plurality of selections, such as successive rotated positions of a knob  30 , that each provide an incremental change to the desired curvature  26  of the trailer  12 . Upon inputting the desired curvature  26 , the controller may generate a steering command for the vehicle  14  to guide the trailer  12  on the desired curvature  26  based on the estimated hitch angle γ and a kinematic relationship between the trailer  12  and the vehicle  14 . Therefore, the accuracy of the hitch angle estimation is critical to operating the trailer backup assist system  10 . However, it is appreciated that such a system for instantaneously estimating hitch angle may be used in association with additional or alternative vehicle features, such as trailer sway monitoring. 
     With reference to the embodiment shown in  FIG. 1 , the vehicle  14  is a pickup truck embodiment that is equipped with one embodiment of the trailer backup assist system  10  for controlling the backing path of the trailer  12  that is attached to the vehicle  14 . Specifically, the vehicle  14  is pivotally attached to one embodiment of the trailer  12  that has a box frame  32  with an enclosed cargo area  34 , a single axle having a right wheel assembly and a left wheel assembly, and a tongue  36  longitudinally extending forward from the enclosed cargo area  34 . The illustrated trailer  12  also has a trailer hitch connector in the form of a coupler assembly  38  that is connected to a vehicle hitch connector in the form of a hitch ball  40 . The coupler assembly  38  latches onto the hitch ball  40  to provide a pivoting ball joint connection  42  that allows for articulation of the hitch angle γ. It should be appreciated that additional embodiments of the trailer  12  may alternatively couple with the vehicle  14  to provide a pivoting connection, such as by connecting with a fifth wheel connector. It is also contemplated that additional embodiments of the trailer may include more than one axle and may have various shapes and sizes configured for different loads and items, such as a boat trailer or a flatbed trailer. 
     Still referring to  FIG. 1 , the sensor system  16  in the illustrated embodiment includes both a sensor module  20  and a vision-based hitch angle sensor  44  for estimating the hitch angle γ between the vehicle  14  and the trailer  12 . The illustrated hitch angle sensor  44  employs a camera  46  (e.g. video imaging camera) that may be located proximate an upper region of the vehicle tailgate  48  at the rear of the vehicle  14 , as shown, such that the camera  46  may be elevated relative to the tongue  36  of the trailer  12 . The illustrated camera  46  has an imaging field of view  50  located and oriented to capture one or more images of the trailer  12 , including a region containing one or more desired target placement zones for at least one target  52  to be secured. Although it is contemplated that the camera  46  may capture images of the trailer  12  without a target  52  to determine the hitch angle γ, in the illustrated embodiment, the trailer backup assist system  10  includes a target  52  placed on the trailer  12  to allow the trailer backup assist system  10  to utilize information acquired via image acquisition and processing of the target  52 . For instance, the illustrated camera  46  may include a video imaging camera that repeatedly captures successive images of the trailer  12  that may be processed to identify the target  52  and its location on the trailer  12  for determining movement of the target  52  and the trailer  12  relative to the vehicle  14  and the corresponding hitch angle γ. It should also be appreciated that the camera  46  may include one or more video imaging cameras and may be located at other locations on the vehicle  14  to acquire images of the trailer  12  and the desired target placement zone, such as on a passenger cab  54  of the vehicle  14  to capture images of a gooseneck trailer. Furthermore, it is contemplated that additional embodiments of the hitch angle sensor  44  and the sensor system  16  for providing the hitch angle γ may include one or a combination of a potentiometer, a magnetic-based sensor, an optical sensor, a proximity sensor, a rotational sensor, a capacitive sensor, an inductive sensor, or a mechanical based sensor, such as a mechanical sensor assembly mounted to the pivoting ball joint connection  42 , energy transducers of a reverse aid system, a blind spot system, and/or a cross traffic alert system, and other conceivable sensors or indicators of the hitch angle γ to supplement or be used in place of the vision-based hitch angle sensor  44 . 
     The embodiment of the sensor module  20  illustrated in  FIG. 1  includes a housed sensor cluster  21  mounted on the tongue  36  of the trailer  12  proximate the enclosed cargo area  34  and includes left and right wheel speed sensors  23  on laterally opposing wheels of the trailer  12 . It is conceivable that the wheel speed sensors  23  may be bi-directional wheel speed sensors for monitoring both forward and reverse speeds. Also, it is contemplated that the sensor cluster  21  in additional embodiments may be mounted on alternative portions of the trailer  12 . 
     The sensor module  20  generates a plurality of signals indicative of various dynamics of the trailer  12 . The signals may include a yaw rate signal, a lateral acceleration signal, and wheel speed signals generated respectively by a yaw rate sensor  25 , an accelerometer  27 , and the wheel speed sensors  23 . Accordingly, in the illustrated embodiment, the yaw rate sensor  25  and the accelerometer  27  are contained within the housed sensor cluster  21 , although other configurations are conceivable. It is conceivable that the accelerometer  27 , in some embodiments, may be two or more separate sensors and may be arranged at an offset angle, such as two sensors arranged at plus and minus forty-five degrees from the longitudinal direction of the trailer or arranged parallel with the longitudinal and lateral directions of the trailer, to generate a more robust acceleration signal. It is also contemplated that these sensor signals could be compensated and filtered to remove offsets or drifts, and smooth out noise. Further, the controller  28  may utilizes processed signals received outside of the sensor system  16 , including standard signals from the brake control system  72  and the power assist steering system  62 , such as vehicle yaw rate ω 1 , vehicle speed ν 1 , and steering angle δ, to estimate the trailer hitch angle γ, trailer speed, and related trailer parameters. As described in more detail below, the controller  28  may estimate the hitch angle γ based on the trailer yaw rate ω 2 , the vehicle yaw rate ω 1 , and the vehicle speed ν 1  in view of a kinematic relationship between the trailer  12  and the vehicle  14 . The controller  28  of the trailer backup assist system  10  may also utilize the estimated trailer variables and trailer parameters to control the steering system  62 , brake control system  72 , and the powertrain control system  74 , such as to assist backing the vehicle-trailer combination or to mitigate a trailer sway condition. 
     With reference to the embodiment of the trailer backup assist system  10  shown in  FIG. 2 , the hitch angle sensor  44  is provided in dashed lines to illustrate that in some embodiments it may be omitted when the trailer sensor module  20  is provided. The illustrated embodiment of the trailer backup assist system  10  receives vehicle and trailer status-related information from additional sensors and devices. This information includes positioning information from a positioning device  56 , which may include a global positioning system (GPS) on the vehicle  14  or a handheld device, to determine a coordinate location of the vehicle  14  and the trailer  12  based on the location of the positioning device  56  with respect to the trailer  12  and/or the vehicle  14  and based on the estimated hitch angle γ. The positioning device  56  may additionally or alternatively include a dead reckoning system for determining the coordinate location of the vehicle  14  and the trailer  12  within a localized coordinate system based at least on vehicle speed, steering angle, and hitch angle γ. Other vehicle information received by the trailer backup assist system  10  may include a speed of the vehicle  14  from a speed sensor  58  and a yaw rate of the vehicle  14  from a yaw rate sensor  60 . It is contemplated that in additional embodiments, the hitch angle sensor  44  and other vehicle sensors and devices may provide sensor signals or other information, such as proximity sensor signals or successive images of the trailer  12 , that the controller of the trailer backup assist system  10  may process with various routines to determine an indicator of the hitch angle γ, such as a range of hitch angles. 
     As further shown in  FIG. 2 , one embodiment of the trailer backup assist system  10  is in communication with a power assist steering system  62  of the vehicle  14  to operate the steered wheels  64  ( FIG. 1 ) of the vehicle  14  for moving the vehicle  14  in such a manner that the trailer  12  reacts in accordance with the desired curvature  26  of the trailer  12 . In the illustrated embodiment, the power assist steering system  62  is an electric power-assisted steering (EPAS) system that includes an electric steering motor  66  for turning the steered wheels  64  to a steering angle based on a steering command, whereby the steering angle may be sensed by a steering angle sensor  67  of the power assist steering system  62 . The steering command may be provided by the trailer backup assist system  10  for autonomously steering during a backup maneuver and may alternatively be provided manually via a rotational position (e.g., steering wheel angle) of a steering wheel  68  ( FIG. 1 ). However, in the illustrated embodiment, the steering wheel  68  of the vehicle  14  is mechanically coupled with the steered wheels  64  of the vehicle  14 , such that the steering wheel  68  moves in concert with steered wheels  64 , preventing manual intervention with the steering wheel  68  during autonomous steering. More specifically, a torque sensor  70  is provided on the power assist steering system  62  that senses torque on the steering wheel  68  that is not expected from autonomous control of the steering wheel  68  and therefore indicative of manual intervention, whereby the trailer backup assist system  10  may alert the driver to discontinue manual intervention with the steering wheel  68  and/or discontinue autonomous steering. 
     In alternative embodiments, some vehicles have a power assist steering system  62  that allows a steering wheel  68  to be partially decoupled from movement of the steered wheels  64  of such a vehicle. Accordingly, the steering wheel  68  can be rotated independent of the manner in which the power assist steering system  62  of the vehicle controls the steered wheels  64  (e.g., autonomous steering as commanded by the trailer backup assist system  10 ). As such, in these types of vehicles where the steering wheel  68  can be selectively decoupled from the steered wheels  64  to allow independent operation thereof, the steering wheel  68  may be used as a steering input device  18  for the trailer backup assist system  10 , as disclosed in greater detail herein. 
     Referring again to the embodiment illustrated in  FIG. 2 , the power assist steering system  62  provides the controller  28  of the trailer backup assist system  10  with information relating to a rotational position of steered wheels  64  of the vehicle  14 , including a steering angle. The controller  28  in the illustrated embodiment processes the current steering angle, in addition to other vehicle  14  and trailer  12  conditions to guide the trailer  12  along the desired curvature  26 . It is conceivable that the trailer backup assist system  10 , in additional embodiments, may be an integrated component of the power assist steering system  62 . For example, the power assist steering system  62  may include a trailer backup assist algorithm for generating vehicle steering information and commands as a function of all or a portion of information received from the steering input device  18 , the hitch angle sensor  44 , the power assist steering system  62 , a vehicle brake control system  72 , a powertrain control system  74 , and other vehicle sensors and devices. 
     As also illustrated in  FIG. 2 , the vehicle brake control system  72  may also communicate with the controller  28  to provide the trailer backup assist system  10  with braking information, such as vehicle wheel speed, and to receive braking commands from the controller  28 . For instance, vehicle speed information can be determined from individual wheel speeds as monitored by the brake control system  72 . Vehicle speed may also be determined from the powertrain control system  74 , the speed sensor  58 , and the positioning device  56 , among other conceivable means. In some embodiments, individual wheel speeds can also be used to determine a vehicle yaw rate, which can be provided to the trailer backup assist system  10  in the alternative or in addition to the vehicle yaw rate sensor  60 . In certain embodiments, the trailer backup assist system  10  can provide vehicle braking information to the brake control system  72  for allowing the trailer backup assist system  10  to control braking of the vehicle  14  during backing of the trailer  12 . For example, the trailer backup assist system  10  in some embodiments may regulate speed of the vehicle  14  during backing of the trailer  12 , which can reduce the potential for unacceptable trailer backup conditions. Examples of unacceptable trailer backup conditions include, but are not limited to, a vehicle  14  over speed condition, a high hitch angle rate, trailer angle dynamic instability, a calculated theoretical trailer jackknife condition (defined by a maximum vehicle steering angle, drawbar length, tow vehicle wheelbase, and an effective trailer length), or physical contact jackknife limitation (defined by an angular displacement limit relative to the vehicle  14  and the trailer  12 ), and the like. It is disclosed herein that the trailer backup assist system  10  can issue an alert signal corresponding to a notification of an actual, impending, and/or anticipated unacceptable trailer backup condition. 
     The powertrain control system  74 , as shown in the embodiment illustrated in  FIG. 2 , may also interact with the trailer backup assist system  10  for regulating speed and acceleration of the vehicle  14  during backing of the trailer  12 . As mentioned above, regulation of the speed of the vehicle  14  may be necessary to limit the potential for unacceptable trailer backup conditions such as, for example, jackknifing and trailer angle dynamic instability. Similar to high-speed considerations as they relate to unacceptable trailer backup conditions, high acceleration and high dynamic driver curvature requests can also lead to such unacceptable trailer backup conditions. 
     With continued reference to  FIG. 2 , the trailer backup assist system  10  in the illustrated embodiment may communicate with one or more devices, including a vehicle alert system  76 , which may prompt visual, auditory, and tactile warnings. For instance, vehicle brake lights  78  and vehicle emergency flashers may provide a visual alert and a vehicle horn  79  and/or speaker  81  may provide an audible alert. Additionally, the trailer backup assist system  10  and/or vehicle alert system  76  may communicate with a human machine interface (HMI)  80  for the vehicle  14 . The HMI  80  may include a vehicle display  82 , such as a center-stack mounted navigation or entertainment display ( FIG. 1 ). Further, the trailer backup assist system  10  may communicate via wireless communication with another embodiment of the HMI  80 , such as with one or more handheld or portable devices, including one or more smartphones. The portable device may also include the display  82  for displaying one or more images and other information to a user. For instance, the portable device may display one or more images of the trailer  12  and an indication of the estimated hitch angle on the display  82 . In addition, the portable device may provide feedback information, such as visual, audible, and tactile alerts. 
     As further illustrated in  FIG. 2 , the trailer backup assist system  10  includes a steering input device  18  that is connected to the controller  28  for allowing communication of information therebetween. It is disclosed herein that the steering input device  18  can be coupled to the controller  28  in a wired or wireless manner. The steering input device  18  provides the trailer backup assist system  10  with information defining the desired backing path of travel of the trailer  12  for the controller  28  to process and generate steering commands. More specifically, the steering input device  18  may provide a selection or positional information that correlates with a desired curvature  26  of the desired backing path of travel of the trailer  12 . Also, the trailer steering commands provided by the steering input device  18  can include information relating to a commanded change in the path of travel, such as an incremental change in the desired curvature  26 , and information relating to an indication that the trailer  12  is to travel along a path defined by a longitudinal centerline axis of the trailer  12 , such as a desired curvature value of zero that defines a substantially straight path of travel for the trailer. As will be discussed below in more detail, the steering input device  18  according to one embodiment may include a movable control input device for allowing a driver of the vehicle  14  to command desired trailer steering actions or otherwise select and alter a desired curvature. For instance, the moveable control input device may be a rotatable knob  30 , which can be rotatable about a rotational axis extending through a top surface or face of the knob  30 . In other embodiments, the rotatable knob  30  may be rotatable about a rotational axis extending substantially parallel to a top surface or face of the rotatable knob  30 . Furthermore, the steering input device  18 , according to additional embodiments, may include alternative devices for providing a desired curvature  26  or other information defining a desired backing path, such as a joystick, a keypad, a series of depressible buttons or switches, a sliding input device, various user interfaces on a touch-screen display, a vision based system for receiving gestures, a control interface on a portable device, and other conceivable input devices as generally understood by one having ordinary skill in the art. It is contemplated that the steering input device  18  may also function as an input device for other features, such as providing inputs for other vehicle features or systems. 
     Still referring to the embodiment shown in  FIG. 2 , the controller  28  is configured with a microprocessor  84  to process logic and routines stored in memory  86  that receive information from the sensor system  16 , including the trailer sensor module  20 , the hitch angle sensor  44 , the steering input device  18 , the power assist steering system  62 , the vehicle brake control system  72 , the trailer braking system, the powertrain control system  74 , and other vehicle sensors and devices. The controller  28  may generate vehicle steering information and commands as a function of all or a portion of the information received. Thereafter, the vehicle steering information and commands may be provided to the power assist steering system  62  for affecting steering of the vehicle  14  to achieve a commanded path of travel for the trailer  12 . The controller  28  may include the microprocessor  84  and/or other analog and/or digital circuitry for processing one or more routines. Also, the controller  28  may include the memory  86  for storing one or more routines, including a hitch angle estimation routine  130 , an operating routine  132 , and a curvature routine  98 . It should be appreciated that the controller  28  may be a stand-alone dedicated controller or may be a shared controller integrated with other control functions, such as integrated with the sensor system  16 , the power assist steering system  62 , and other conceivable onboard or off-board vehicle control systems. 
     With reference to  FIG. 3 , we now turn to a discussion of vehicle and trailer information and parameters used to calculate a kinematic relationship between a curvature of a path of travel of the trailer  12  and the steering angle of the vehicle  14  towing the trailer  12 , which can be desirable for a trailer backup assist system  10  configured in accordance with some embodiments, including for use by a curvature routine  98  of the controller  28  in one embodiment. To achieve such a kinematic relationship, certain assumptions may be made with regard to parameters associated with the vehicle/trailer system. Examples of such assumptions include, but are not limited to, the trailer  12  being backed by the vehicle  14  at a relatively low speed, wheels of the vehicle  14  and the trailer  12  having negligible (e.g., no) slip, tires of the vehicle  14  having negligible (e.g., no) lateral compliance, tires of the vehicle  14  and the trailer  12  having negligible (e.g., no) deformation, actuator dynamics of the vehicle  14  being negligible, and the vehicle  14  and the trailer  12  exhibiting negligible (e.g., no) roll or pitch motions, among other conceivable factors with the potential to have an effect on controlling the trailer  12  with the vehicle  14 . 
     As shown in  FIG. 3 , for a system defined by a vehicle  14  and a trailer  12 , the kinematic relationship is based on various parameters associated with the vehicle  14  and the trailer  12 . These parameters include: 
     δ: steering angle at steered front wheels of the vehicle; 
     α: yaw angle of the vehicle; 
     β: yaw angle of the trailer; 
     γ: hitch angle (γ=β−α); 
     W: wheel base of the vehicle; 
     L: drawbar length between hitch point and rear axle of the vehicle; 
     D: distance (trailer length) between hitch point and axle of the trailer or effective axle for a multiple axle trailer; and 
     r 2 : curvature radius for the trailer. 
     One embodiment of a kinematic relationship between trailer path radius of curvature r 2  at the midpoint of an axle of the trailer  12 , steering angle δ of the steered wheels  64  of the vehicle  14 , and the hitch angle γ can be expressed in the equation provided below. As such, if the hitch angle γ is provided, the trailer path curvature κ 2  can be controlled based on regulating the steering angle δ (where {dot over (β)} is trailer yaw rate and {dot over (η)} is trailer velocity). 
     
       
         
           
             
               κ 
               2 
             
             = 
             
               
                 1 
                 
                   r 
                   2 
                 
               
               = 
               
                 
                   
                     β 
                     . 
                   
                   
                     η 
                     . 
                   
                 
                 = 
                 
                   
                     
                       
                         ( 
                         
                           W 
                           + 
                           
                             
                               KV 
                               2 
                             
                             g 
                           
                         
                         ) 
                       
                       ⁢ 
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       γ 
                     
                     + 
                     
                       L 
                       ⁢ 
                       
                           
                       
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                       ⁢ 
                       
                           
                       
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                     D 
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                       ( 
                       
                         
                           
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                           ⁢ 
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                           ⁢ 
                           
                               
                           
                           ⁢ 
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                           ⁢ 
                           γtan 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           δ 
                         
                       
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     This relationship can be expressed to provide the steering angle δ as a function of trailer path curvature κ 2  and hitch angle γ. 
     
       
         
           
             δ 
             = 
             
               
                 
                   tan 
                   
                     - 
                     1 
                   
                 
                 ( 
                 
                   
                     
                       ( 
                       
                         W 
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                             KV 
                             2 
                           
                           g 
                         
                       
                       ) 
                     
                     ⁡ 
                     
                       [ 
                       
                         
                           
                             κ 
                             2 
                           
                           ⁢ 
                           D 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           cos 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           γ 
                         
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                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           γ 
                         
                       
                       ] 
                     
                   
                   
                     
                       DL 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         κ 
                         2 
                       
                       ⁢ 
                       sin 
                       ⁢ 
                       
                           
                       
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                       ⁢ 
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                       ⁢ 
                       
                           
                       
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               = 
               
                 F 
                 ⁡ 
                 
                   ( 
                   
                     γ 
                     , 
                     
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                       2 
                     
                     , 
                     K 
                   
                   ) 
                 
               
             
           
         
       
     
     Accordingly, for a particular vehicle and trailer combination, certain parameters (e.g., D, W and L) of the kinematic relationship are constant and assumed known. V is the vehicle longitudinal speed and g is the acceleration due to gravity. K is a speed dependent parameter which when set to zero makes the calculation of steering angle independent of vehicle speed. For example, vehicle-specific parameters of the kinematic relationship can be predefined in an electronic control system of the vehicle  14  and trailer-specific parameters of the kinematic relationship can be inputted by a driver of the vehicle  14 , determined from sensed trailer behavior in response to vehicle steering commands, or otherwise determined from signals provided by the trailer  12 . Trailer path curvature κ 2  can be determined from the driver input via the steering input device  18 . Through the use of the equation for providing steering angle, a corresponding steering command can be generated by the curvature routine  98  for controlling the power assist steering system  62  of the vehicle  14 . 
     In an additional embodiment, an assumption may be made by the curvature routine  98  that a longitudinal distance L between the pivoting connection and the rear axle of the vehicle  14  is equal to zero for purposes of operating the trailer backup assist system  10  when a gooseneck trailer or other similar trailer is connected with the a hitch ball or a fifth wheel connector located over a rear axle of the vehicle  14 . The assumption essentially assumes that the pivoting connection with the trailer  12  is substantially vertically aligned with the rear axle of the vehicle  14 . When such an assumption is made, the controller  28  may generate the steering angle command for the vehicle  14  as a function independent of the longitudinal distance L between the pivoting connection and the rear axle of the vehicle  14 . It is appreciated that the gooseneck trailer mentioned generally refers to the tongue configuration being elevated to attach with the vehicle  14  at an elevated location over the rear axle, such as within a bed of a truck, whereby embodiments of the gooseneck trailer may include flatbed cargo areas, enclosed cargo areas, campers, cattle trailers, horse trailers, lowboy trailers, and other conceivable trailers with such a tongue configuration. 
     Yet another embodiment of the curvature routine  98  of the trailer backup assist system  10  is illustrated in  FIG. 4 , showing the general architectural layout whereby a measurement module  88 , a hitch angle regulator  90 , and a curvature regulator  92  are routines that may be stored in the memory  86  of the controller  28 . In the illustrated layout, the steering input device  18  provides a desired curvature κ 2  value to the curvature regulator  92  of the controller  28 , which may be determined from the desired backing path  26  that is input with the steering input device  18 . The curvature regulator  92  computes a desired hitch angle γ(d) based on the current desired curvature κ 2  along with the steering angle δ provided by a measurement module  88  in this embodiment of the controller  28 . The measurement module  88  may be a memory device separate from or integrated with the controller  28  that stores data from sensors of the trailer backup assist system  10 , such as the hitch angle sensor  44 , the vehicle speed sensor  58 , the steering angle sensor, or alternatively the measurement module  88  may otherwise directly transmit data from the sensors without functioning as a memory device. Once the desired hitch angle γ(d) is computed by the curvature regulator  92  the hitch angle regulator  90  generates a steering angle command based on the computed desired hitch angle γ(d) as well as a measured or otherwise estimated hitch angle γ(m) and a current velocity of the vehicle  14 . The steering angle command is supplied to the power assist steering system  62  of the vehicle  14 , which is then fed back to the measurement module  88  to reassess the impacts of other vehicle characteristics impacted from the implementation of the steering angle command or other changes to the system. Accordingly, the curvature regulator  92  and the hitch angle regulator  90  continually process information from the measurement module  88  to provide accurate steering angle commands that place the trailer  12  on the desired curvature κ 2  and the desired backing path  26 , without substantial overshoot or continuous oscillation of the path of travel about the desired curvature κ 2 . 
     Specifically, entering the control system is an input, κ 2 , which represents the desired curvature  26  of the trailer  12  that is provided to the curvature regulator  92 . The curvature regulator  92  can be expressed as a static map, p(κ 2 , δ), which in one embodiment is the following equation: 
     
       
         
           
             
               p 
               ⁡ 
               
                 ( 
                 
                   
                     κ 
                     2 
                   
                   , 
                   δ 
                 
                 ) 
               
             
             = 
             
               
                 tan 
                 
                   - 
                   1 
                 
               
               ⁡ 
               
                 ( 
                 
                   
                     
                       
                         κ 
                         2 
                       
                       ⁢ 
                       D 
                     
                     + 
                     
                       L 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         tan 
                         ⁡ 
                         
                           ( 
                           δ 
                           ) 
                         
                       
                     
                   
                   
                     
                       
                         κ 
                         2 
                       
                       ⁢ 
                       DL 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         tan 
                         ⁡ 
                         
                           ( 
                           δ 
                           ) 
                         
                       
                     
                     - 
                     W 
                   
                 
                 ) 
               
             
           
         
       
     
     Where, 
     κ 2  represents the desired curvature of the trailer  12  or I/r 2  as shown in  FIG. 3 ; 
     δ represents the steering angle; 
     L represents the distance from the rear axle of the vehicle  14  to the hitch pivot point; 
     D represents the distance from the hitch pivot point to the axle of the trailer  12 ; and 
     W represents the distance from the rear axle to the front axle of the vehicle  14 . 
     The output hitch angle of p(κ 2 , δ) is provided as the reference signal, γ ref , for the remainder of the control system, although the steering angle δ value used by the curvature regulator  92  is feedback from the non-linear function of the hitch angle regulator  90 . It is shown that the hitch angle regulator  90  uses feedback linearization for defining a feedback control law, as follows: 
     
       
         
           
             
               g 
               ⁡ 
               
                 ( 
                 
                   u 
                   , 
                   γ 
                   , 
                   v 
                 
                 ) 
               
             
             = 
             
               δ 
               = 
               
                 
                   tan 
                   
                     - 
                     1 
                   
                 
                 ( 
                 
                   
                     W 
                     
                       v 
                       ⁡ 
                       
                         ( 
                         
                           1 
                           + 
                           
                             
                               L 
                               D 
                             
                             ⁢ 
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 γ 
                                 ) 
                               
                             
                           
                         
                         ) 
                       
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       u 
                       - 
                       
                         
                           v 
                           D 
                         
                         ⁢ 
                         
                           sin 
                           ⁡ 
                           
                             ( 
                             γ 
                             ) 
                           
                         
                       
                     
                     ) 
                   
                 
                 ) 
               
             
           
         
       
     
     The feedback control law, g(u, γ, ν), is implemented with a proportional integral (PI) controller, whereby the integral portion substantially eliminates steady-state tracking error. More specifically, the control system illustrated in  FIG. 5  may be expressed as the following differential-algebraic equations: 
     
       
         
           
             
               
                 γ 
                 . 
               
               ⁡ 
               
                 ( 
                 t 
                 ) 
               
             
             = 
             
               
                 
                   
                     v 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   D 
                 
                 ⁢ 
                 
                   sin 
                   ⁡ 
                   
                     ( 
                     
                       γ 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     ) 
                   
                 
               
               + 
               
                 
                   ( 
                   
                     1 
                     + 
                     
                       
                         L 
                         D 
                       
                       ⁢ 
                       
                         cos 
                         ⁡ 
                         
                           ( 
                           
                             γ 
                             ⁡ 
                             
                               ( 
                               t 
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                   ) 
                 
                 ⁢ 
                 
                   
                     v 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   W 
                 
                 ⁢ 
                 
                   δ 
                   _ 
                 
               
             
           
         
       
       
         
           
             
               tan 
               ⁡ 
               
                 ( 
                 δ 
                 ) 
               
             
             = 
             
               
                 δ 
                 _ 
               
               = 
               
                 
                   W 
                   
                     
                       v 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             L 
                             D 
                           
                           ⁢ 
                           
                             cos 
                             ⁡ 
                             
                               ( 
                               
                                 γ 
                                 ⁡ 
                                 
                                   ( 
                                   t 
                                   ) 
                                 
                               
                               ) 
                             
                           
                         
                       
                       ) 
                     
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     
                       
                         K 
                         P 
                       
                       ⁡ 
                       
                         ( 
                         
                           
                             p 
                             ⁡ 
                             
                               ( 
                               
                                 
                                   κ 
                                   2 
                                 
                                 , 
                                 δ 
                               
                               ) 
                             
                           
                           - 
                           
                             γ 
                             ⁡ 
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         ) 
                       
                     
                     - 
                     
                       
                         
                           v 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                         D 
                       
                       ⁢ 
                       
                         sin 
                         ⁡ 
                         
                           ( 
                           
                             γ 
                             ⁡ 
                             
                               ( 
                               t 
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     It is contemplated that the PI controller may have gain terms based on trailer length D since shorter trailers will generally have faster dynamics. In addition, the hitch angle regulator  90  may be configured to prevent the desired hitch angle γ(d) to reach or exceed a jackknife angle γ(j), as computed by the controller or otherwise determined by the trailer backup assist system  10 , as disclosed in greater detail herein. 
     Referring now to  FIG. 5 , one embodiment of the steering input device  18  is illustrated disposed on a center console  108  of the vehicle  14  proximate a shifter  110 . In this embodiment, the steering input device  18  includes a rotatable knob  30  for providing the controller  28  with the desired backing path of the trailer  12 . More specifically, the angular position of the rotatable knob  30  may correlate with a desired curvature, such that rotation of the knob to a different angular position provides a different desired curvature with an incremental change based on the amount of rotation and, in some embodiments, a normalized rate, as described in greater detail herein. 
     The rotatable knob  30 , as illustrated in  FIG. 6 , may be biased (e.g., by a spring return) to a center, or at-rest position P(AR) between opposing rotational ranges of motion R(R), R(L). In the illustrated embodiment, a first one of the opposing rotational ranges of motion R(R) is substantially equal to a second one of the opposing rotational ranges of motion R(L), R(R). To provide a tactile indication of an amount of rotation of the rotatable knob  30 , a torque that biases the knob toward the at-rest position P(AR) can increase (e.g., non-linearly) as a function of the amount of rotation of the rotatable knob  30  with respect to the at-rest position P(AR). Additionally, the rotatable knob  30  can be configured with position indicating detents such that the driver can positively feel the at-rest position P(AR) and feel the ends of the opposing rotational ranges of motion R(L), R(R) approaching (e.g., soft end stops). The rotatable knob  30  may generate a desired curvature value as function of an amount of rotation of the rotatable knob  30  with respect to the at-rest position P(AR) and a direction of movement of the rotatable knob  30  with respect to the at-rest position P(AR), which itself may correspond to a zero-curvature command  26 . It is also contemplated that the rate of rotation of the rotatable knob  30  may also be used to determine the desired curvature  26  output to the controller  28 . The at-rest position P(AR) of the knob corresponds to a signal indicating that the vehicle  14  should be steered such that the trailer  12  is backed along a substantially straight backing path  214  ( FIG. 6 ) zero trailer curvature request from the driver), as defined by the longitudinal direction  22  of the trailer  12  when the knob was returned to the at-rest position P(AR). A maximum clockwise and anti-clockwise position of the knob (i.e., limits of the opposing rotational ranges of motion R(R), R(L)) may each correspond to a respective signal indicating a tightest radius of curvature (i.e., most acute trajectory or smallest radius of curvature) of a path of travel of the trailer  12  that is possible without the corresponding vehicle steering information causing a jackknife condition. 
     As shown in  FIG. 6 , a driver can turn the rotatable knob  30  to provide a desired curvature  26  while the driver of the vehicle  14  backs the trailer  12 . In the illustrated embodiment, the rotatable knob  30  rotates about a central axis between a center or middle position  114  corresponding to a substantially straight backing path  26  of travel, as defined by the longitudinal direction  22  of the trailer  12 , and various rotated positions  116 ,  118 ,  120 ,  122  on opposing sides of the middle position  114 , commanding a desired curvature  26  corresponding to a radius of the desired backing path of travel for the trailer  12  at the commanded rotated position. It is contemplated that the rotatable knob  30  may be configured in accordance with embodiments of the disclosed subject matter and omit a means for being biased to an at-rest position P(AR) between opposing rotational ranges of motion. Lack of such biasing may allow a current rotational position of the rotatable knob  30  to be maintained until the rotational control input device is manually moved to a different position. 
     Referring to  FIG. 7 , an example of using the steering input device  18  for dictating a curvature of a desired backing path of travel (POT) of the trailer  12  while backing up the trailer  12  with the vehicle  14  is shown. In preparation of backing the trailer  12 , the driver of the vehicle  14  may drive the vehicle  14  forward along a pull-thru path (PTP) to position the vehicle  14  and trailer  12  at a first backup position B 1 . In the first backup position B 1 , the vehicle  14  and trailer  12  are longitudinally aligned with each other such that a longitudinal centerline axis L 1  of the vehicle  14  is aligned with (e.g., parallel with or coincidental with) a longitudinal centerline axis L 2  of the trailer  12 . It is disclosed herein that such alignment of the longitudinal axis L 1 , L 2  at the onset of an instance of trailer backup functionality is not a requirement for operability of a trailer backup assist system  10 , but may be done for calibration. 
     After activating the trailer backup assist system  10  (e.g., before, after, or during the pull-thru sequence), the driver begins to back the trailer  12  by reversing the vehicle  14  from the first backup position B 1 . So long as the rotatable knob  30  of the trailer backup steering input device  18  remains in the at-rest position P(AR) and no other steering input devices  18  are activated, the trailer backup assist system  10  will steer the vehicle  14  as necessary for causing the trailer  12  to be backed along a substantially straight path of travel, as defined by the longitudinal direction  22  of the trailer  12 , specifically the centerline axis L 2  of the trailer  12 , at the time when backing of the trailer  12  began. When the trailer  12  reaches the second backup position B 2 , the driver rotates the rotatable knob  30  to command the trailer  12  to be steered to the right (i.e., a knob position R(R) clockwise rotation). Accordingly, the trailer backup assist system  10  will steer the vehicle  14  for causing the trailer  12  to be steered to the right as a function of an amount of rotation of the rotatable knob  30  with respect to the at-rest position P(AR), a rate movement of the knob, and/or a direction of movement of the knob with respect to the at-rest position P(AR). Similarly, the trailer  12  can be commanded to steer to the left by rotating the rotatable knob  30  to the left. When the trailer  12  reaches backup position B 3 , the driver allows the rotatable knob  30  to return to the at-rest position P(AR) thereby causing the trailer backup assist system  10  to steer the vehicle  14  as necessary for causing the trailer  12  to be backed along a substantially straight path of travel as defined by the longitudinal centerline axis L 2  of the trailer  12  at the time when the rotatable knob  30  was returned to the at-rest position P(AR). Thereafter, the trailer backup assist system  10  steers the vehicle  14  as necessary for causing the trailer  12  to be backed along this substantially straight path to the fourth backup position B 4 . In this regard, arcuate portions of a path of travel POT of the trailer  12  are dictated by rotation of the rotatable knob  30  and straight portions of the path of travel POT are dictated by an orientation of the centerline longitudinal axis L 2  of the trailer  12  when the knob  230  is in/returned to the at-rest position P(AR). 
     In the embodiment illustrated in  FIG. 7 , in order to activate the trailer backup assist system  10 , the driver interacts with the trailer backup assist system  10  and the automatically steers as the driver reverses the vehicle  14 . As discussed above, the driver may command the trailer backing path by using a steering input device  18  and the controller  28  may determine the vehicle steering angle to achieve the desired curvature  26 , whereby the driver controls the throttle and brake while the trailer backup assist system  10  controls the steering. 
     Turning now to  FIGS. 8-10 , a further embodiment of a control knob  230  is illustrated and can be used to control vehicle  14  in reversing a trailer  12  based on a trailer control command, such as along a curvature path  26  by adjusting the desired trailer control command according to a particular, selectable command position. In an embodiment, the trailer control command may be a particular curvature path  26  according to the manner discussed above with respect to  FIGS. 5-7 . In particular, knob  230  can be used to adjust curvature path  26  by turning a control element  232  thereof, against a biasing torque, away from the at rest position P(AR) within either the left range of motion R(L) or a right range of motion R(R) extending away therefrom. Such a knob  230  can also be used in this manner to adjust a controlled hitch angle γ of trailer  12  relative to vehicle  14  using the same type of center-biased movement in connection with a backup assist system that is angle-based, rather than curvature based. 
     As illustrated and described herein, knob  230  can comprise a multi-function interface for control of vehicle  14  in reversing trailer  12  using controller  28  in implementing curvature routine  98 , as well as in activating curvature routine  98  and, further, controlling and operating additional systems of vehicle  14 . Knob  230  includes a body  234 , mounted on a portion  236  of console  108  or another portion of the associated instrument panel or other interior structure of vehicle  14  with such structure extending outwardly from knob  230 . An annular control element  232  is mounted on body  234  in such a manner as to be rotatable thereabout, including within the indicated left range of motion R(L) and right range of motion R(R). In an embodiment, control element  232  can be spring-biased toward the at-rest position P(AR) such that control element  232  is rotated away from the at rest position P(AR) under increasing torque back toward the at-rest position P(AR) and returns thereto when no external force (such as from a user) acts thereon. In another embodiment, control element  232  can mechanically decouple from the associated spring-biasing element (which can include a spring or the like) either upon manipulation of knob  230  or automatically by controller  28 , as described in co-pending, commonly-assigned U.S. patent application Ser. No. 14/813,642, the entire disclosure of which is incorporated by reference herein. A button  242  is also mounted with body  234  and is positioned inside control element  232 . Button  242  may be depressable to transmit a signal to controller  28 , which in one example, may give button  242  the general functionality of an “enter” or “ok” key useable to begin certain functionality (including implementation of curvature routine  98 ) or to act as a selection or confirmation button in relation to a selectable item in a navigable menu, as described further below. Button  242  may include a status indicator  250  thereon that can present information to a user, including information regarding, for example, the action that may be implemented by depressing button  242  or the vehicle system being controlled or manipulated by control element  232 , as described further below. Such a status indicator  250  may include a display screen embedded within button  242  or a plurality of illuminable icons. In another embodiment the surface of the body  234  or button  242  (whichever portion of knob  230  is exposed within the inner profile of control element  232 ) may include or be defined by a display element (e.g. a thin-film transistor (“TFT”) display or the like) in which the icons can be graphical elements displayed thereon. 
     In yet another embodiment, control element  232  can be coupled with body  234  by an internal electromechanical element that can be controlled to optionally implement a simulated biasing action for control element  232  with respect to body  234  and, thusly, causing the movement of control element  232  to be restricted to within the above described, spring-biased movement type  238 . As discussed herein, an electromechanical element can be any device or element that uses an electrical current to achieve a mechanical or physical action. In an example, electromechanical element may include a motor, alone or in combination with other mechanical elements, such as various linkages, springs, gears, and the like, which may be arranged to replicate the effects of various other physical coupling between control element  232  and body  234 . Such an arrangement of a knob  230  including an electromechanical element is described further in co-pending, commonly-assigned U.S. patent application Ser. No. 14/878,227, the entire disclosure of which is incorporated by reference herein. 
     With further reference to  FIGS. 11-13 , control of vehicle  14  in reversing trailer  12  using knob  230  is described. In one example scenario, the curvature routine  98  may be activated by depressing button  242 , which may be done to confirm the selection of a “Trailer Backup Assist” (or “TBA”) mode (item  284   a ) on a navigable menu  286 , as depicted in  FIG. 13 . The menu  286  may be navigated by scrolling or moving through the various menu items  284   a ,  284   b , and  284   c  included in an first, initial menu level  286   a  using control element  232 , which may be rotated to change the designation (indicated, for example, by highlighting or being displayed in a different color or tone) of a particular one of the menu items  284   a ,  284   b , and  284   c  as a selectable menu item. In one embodiment, where control element  232  is coupled with body  234  in fixed, spring-biased manner, keeping the control element  232  in the at-rest position P(AR) may lead to selection of menu item  284   b , or the central of a three item display, such selection being changeable to item  284   a  by rotation of control element  232  in the left range of motion R(L) by a predetermined distance (e.g. 20°). Similarly, menu item  284   c  may be selected by rotation of control element  232  in the right range of motion R(R) by the predetermined distance. In the present example, once the desired menu item  284   a  is highlighted, button  242  may be depressed, an “OK” message being displayed on indicator  250  to signal that button  242  is designated with “enter” functionality and/or that curvature routing  98  may be activated. In either of the above-described embodiments, wherein control element  232  can be changed between different movement types, including free rotation and spring-biased rotation away from an at rest position P(AR) (either by an electromechanical element or otherwise), when control element  232  is being used for selection of a menu item  284   a ,  284   b , or  284   c , for example, knob  230  can be configured to allow free rotation of control element  232  and may switch (such as by input from controller  28  to the spring-biased movement type upon activation of curvature routine  98 . 
     Once curvature routine  98  is activated, indicator  250  may change to display an icon or text according to an indication mode informing a user that the trailer backup assist mode has been entered, as depicted in  FIG. 12 . In such operation, control element  232  may be rotated away from the at rest position P(AR), such as within the left range of motion R(L) or the right range of motion R(R) to adjust the curvature command  26  away from center knob position  214  into an instantaneous one of the indicated rotated directional positions  216 ,  218 ,  220 , and  222 , which include various directional positions opposed about the at rest position P(AR). As shown in  FIG. 8 , the positions of control element  232  correspond to various adjusted curvature paths shown in  FIG. 11 . In this manner, and as further discussed above with reference to  FIG. 6 , controller  28  may accordingly control the steering of vehicle  14  to maintain trailer  12  along the desired path that corresponds to a particular instantaneous trailer control commanding position of control element  232 , as interpreted by controller  28  based on the particular position of control element  232 . In the example described above, in which an electromechanical element is included incorporated within knob  230  in an operable relationship with control element  232 , the electromechanical element can be used to control the movement types of control element  232  with respect to body  234 . In this manner, respective end points of rotation in the left range R(L) and the right range R(R) may be implemented and adjusted in real-time by electromechanical element to correspond to the calculated maximum curvature that can be commanded to keep hitch angle γ beneath the critical hitch angle γ c , as calculated according to the procedure discussed above. 
     As discussed above, the use of a knob with a rotatable control element, such as knob  230  with control element  232  operably disposed thereon, can be used to control other systems or operational modes of vehicle  14 . As shown in  FIG. 13 , knob  230  can be used to implement various additional vehicle  14  functions by selecting corresponding menu items  284   b  and  284   c  presented on display  282 . In the example shown in  FIG. 13 , such menu items  284   b  and  284   c  can respectively correspond to hill descent control (“HDC”) functionality and terrain management system (“TMS”) functionality and can be activated by an appropriate initiation command using knob  230 . In general, HDC may provide smooth and controlled hill descent by vehicle  14  in rough terrain without the driver needing to touch the brake pedal. When enabled, such as by navigation to menu item  284   b , which can correspond with an input position of control element  232  when, for example, in a free rotation movement mode or type among a plurality of menu command positions, and confirmation by depressing button  242 , vehicle  14  will descend using the ABS brake system  72  to control the speed of each wheel individually, as needed to maintain vehicle  14  below a desired speed (which in an embodiment may also be selected or altered using knob  230 ). Similarly, HDC can alter engine, transmission, and brake use or performance to provide specific vehicle control or movement dynamics tuned to different terrains on which vehicle  14  may be drive, including, for example, sand, gravel, mud, snow, normal road surfaces and the like. As further shown in  FIG. 13 , when selecting TMS mode, for example, a sub menu  288  may be presented including various additional menu items  284   d ,  284   e , and  284   f , corresponding to additional sub-functions of the selected functionality, which in the illustrated example relate to terrain options within the TMS. Such menu items  284   d ,  284   e , and  284   f  may be navigated to and selected in a manner similar to menu items  284   a ,  284   b , and  284   c , within the first level menu  286 . Further, display  282  may present direction indicators  292   a  and  292   b  to inform a user as to the direction in which control element  232  can be rotated to change the selected menu item  284   a ,  284   b , or  284   c . As described in previously-incorporated U.S. patent application Ser. No. 14/825,434, knob  230  may also be used in one or more of the various movement types described above to navigate within additional menus within display  282  (which may be related to system  10 , as well as additional vehicle systems and operation, such as climate-control, multimedia, etc.), as well as among menu items displayed thereon in certain instances and to input or confirm various information presented on display  282 . 
     As shown in  FIG. 14 , another embodiment of knob  330  can include a plurality of mode selection buttons  340   a ,  340   b ,  340   c , and  340   d  that can respectively correspond to the trailer backup assist (“TBA”) functionality (implemented using curvature routine  98 ), TMS, HDC, and active park assist (“APA”) functionality, as discussed further in co-pending, commonly-assigned, U.S. patent application Ser. No. 14/859,551, the entire disclosure of which is incorporated by reference herein. Buttons  340   a ,  340   b ,  340   c , and  340   d  may be disposed on an upper face  390  of body  334  and may encircle or otherwise surround confirmation button  342 . A user may interact with such a knob  330  by direct selection of a system to be implemented or controlled by depressing the corresponding one of buttons  340   a ,  340   b ,  340   c , and  340   d . As discussed above, upon a selection of TBA functionality, the user may control the desired curvature path  26  of the vehicle  14  and trailer  12  combination by rotation of control element  332 , which as discussed above, may be spring-biased toward an at-rest position corresponding to a zero curvature command. TMS and HDC functionality may also be controlled in a similar manner to that which is discussed above with respect to knob  330 , including the use of control element  332  to navigate among menu items displayed in a sub-menu  388  on display  382 , as also described further below, and confirmation of a selection using button  342 . 
     APA may be implemented by a parking assist system that is also included within vehicle  14  and can make use of various sensors of vehicle  14 , including those included in sensor system  16 , to control the power assist steering system  62  (and, optionally, powertrain control system  74  and brake control system  72 ) to provide autonomous, semi-autonomous, or assisted parking functionality in at least one of various parking modes. It is noted that the parking assist mode, including the various sub-modes or schemes described below, for example, differs from the trailer backup assist mode in that it implements steering commands based on a path determined for entry to or exit from a parking space, rather than a curvature path or desired hitch angle. The parking assist mode may be configured to only operate when no trailer  12  is coupled with vehicle  14  and may further operate in both reversing and forward driving. In general, the parking assist functionality can be included within a single vehicle controller  28  that also implements the above-described curvature routine  98  for trailer backup assist functionality. Accordingly, in such an example, the parking assist “system” can overlap with the trailer backup assist system  10  and can be represented by additional programming or modules associated with controller  28 . In such an example, knob  330 , as well as buttons  340   a ,  340   b ,  340   c , and  340   d  can be electrically coupled directly with controller  28  for selection or initiation of the various modes associated with knob  330  and use of knob  330  for control or entering of other inputs in such modes. 
     As illustrated in  FIGS. 14-16 , the park-assist system can be capable of providing parallel-parking assistance. With reference to  FIG. 16 , a user can, upon positioning vehicle  14  in an appropriate location with respect to a parallel parking space  370 , can depress button  340   d  to send a park assist initiation signal to the appropriate controller. Upon receiving such a signal, the controller can present a sub-menu  388 , as shown in  FIG. 15 , with various parking options, including parallel park  384   a , perpendicular park  384   b , and park out assist  384   c . The user can then select the desired mode, e.g. parallel park  384  using control element  332  and button  340  in a similar manner to that which is discussed above with respect to  FIG. 13 . When implementing the parallel park assist mode, controller  28  can await a selection of a side of vehicle  14  on which the parallel parking space  370  is located. An indication that such a selection is needed can be presented to user via display  382 , for example. The selection of the appropriate vehicle  14  side (the driver side in the example depicted in  FIG. 16 ) can be made by user by rotating control element  332  in the appropriate direction through a predetermined angle (e.g. about 10° or more), at which point the selection can be confirmed by indication on HMI  80 , an audible indication, or by illumination of one of arrows  354   a ,  354   b  on the corresponding side of knob  330 . In another example, the user can move a cursor (or appropriately-sized visual indicator) superimposed on an image of the surroundings of vehicle  14 , which can be obtained, for example, by camera  46  and presented display  382 . Such a cursor or other indicator can be moved laterally in a manner that corresponds with the rotation/instantaneous position of control element  332 . Selection can be confirmed by depressing button  340 , for example. 
     After the appropriate side or position selection is made, the controller can implement the desired or available parallel parking assist mode. In one example, such a mode can be a semi-autonomous parallel parking mode, wherein the user retains control of the speed of vehicle by the throttle and brake (in a manner similar to the above-described trailer backup assist mode) with the vehicle  14  indicating the distance to adjacent vehicles using proximity alerting by audible signals or by visual indication on display  382 , which can also be used to provide instructions (“reverse,” “pull forward,” etc.) to the driver of vehicle  14 . Simultaneously, the park-assist system can control EPAS  62  such that vehicle  14  follows a parallel park-in path  372 . In another mode, the parallel park assist system can implement a fully-autonomous parallel parking mode in which vehicle  14  can both control EPAS  62  as well as brake system  72  and powertrain control system  74  to control the speed of vehicle  14  while controlling EPAS  62  such that vehicle  14  follows the parallel park-in path  272 . Other modes of parallel park assist are possible and can be implemented using knob  330  in a similar manner. Further, knob  230  can also be used to implement a similar parking assist mode by addition of a corresponding menu item to menu  286 , as presented on display  282  ( FIG. 13 ). 
     As shown in  FIGS. 17 and 18 , in another embodiment, a knob  430  can be tilted away from a central position ( FIG. 17 ) to make selections, including the above described selections of the trailer backup assist mode, parking assist mode, HDC, and TMS. Such tilting may be in a plurality of constrained tilt directions  440   a ,  440   b ,  440   c , and  440   d , to selection positions respectively corresponding to the above-described trailer backup assist mode, park assist mode, HDC and TMS. In one example, knob  430  can be mounted to console  108  by a mounting structure including an extension element  434  that coupled within console  108  at an interface therebetween that can include electronic circuitry, such as in the form of internal contact elements. The electronic circuitry is configured to transmit a signal to the appropriate controller, such as controller  28 , for example, upon tilting of knob  430  in one of the above-mentioned tilt directions  440   a ,  440   b ,  440   c , and  440   d . In one example, the tilting movement of knob  430  can be spring biased toward the center (i.e. un-tilted) position and the tilting movement thereof can be constrained to within the described directions  440   a ,  440   b ,  440   c , and  440   d . In various aspects, the tilting of knob  430  can be used for additional menu navigation and/or selection. Selections of various parameters, sub-functions, or the like may be made using control element  432  to navigate among menu items in a manner similar to that which is described above with respect to  FIGS. 13 and 15 . Similarly, control of the curvature path  26  in connection with curvature routine  98 , as implemented during TBA functionality, can be carried out using control element  432  in a manner similar to that which is discussed above with respect to  FIGS. 11 and 12 . 
     With reference to  FIG. 19 , a method of operating one embodiment of the trailer backup assist system  10  is illustrated, shown as one embodiment of the operating routine  132  ( FIG. 2 ). At step  134 , the method is initiated by the trailer backup assist system  10  being activated, such as by a user depressing button  242  of a knob  230  ( FIG. 9 ). It is further contemplated that system  10  may be activated in a variety of other ways, such a making navigating through a menu sequence on display  82  of the vehicle HMI  80  and confirming an initiation of the routine  132  using knob  30  or  230 , as discussed above. The next step  136 , then determines the kinematic relationship between the attached trailer  12  and the vehicle  14 . To determine the kinematic relationship, various parameters of the vehicle  14  and the trailer  12  must be sensed, input by the driver, or otherwise determined for the trailer backup assist system  10  to generate steering commands to the power assist steering system  62  in accordance with the desired curvature or backing path  26  of the trailer  12 . As disclosed with reference to  FIGS. 3-6 , the kinematic parameters to define the kinematic relationship include a length of the trailer  12 , a wheel base of the vehicle  14 , a distance from a hitch connection to a rear axle of the vehicle  14 , and a hitch angle γ between the vehicle  14  and the trailer  12 , among other variables and parameters as previously described. Accordingly, after the kinematic relationship is determined, the trailer backup assist system  10  may proceed at step  160  to determine the current hitch angle by processing the hitch angle estimation routine  130 . 
     It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise. 
     For purposes of this disclosure, the term “coupled” (in all of its forms, couple, coupling, coupled, etc.) generally means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components (electrical or mechanical) and any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature or may be removable or releasable in nature unless otherwise stated. 
     It is also important to note that the construction and arrangement of the elements of the invention as shown in the exemplary embodiments is illustrative only. Although only a few embodiments of the present innovations have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present innovations. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present innovations. 
     It will be understood that any described processes or steps within described processes may be combined with other disclosed processes or steps to form structures within the scope of the present invention. The exemplary structures and processes disclosed herein are for illustrative purposes and are not to be construed as limiting.