Patent Publication Number: US-7711464-B2

Title: Steering system with lane keeping integration

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of patent application Ser. No. 10/865,208 filed Jun. 10, 2004. 
    
    
     BACKGROUND 
     The present disclosure relates generally to vehicle steering control systems and, more particularly, to an electric power steering system having a lane keeping function integrated therewith. 
     A number of vehicle systems have been devised to assist the vehicle in maintaining a central position within a driving lane. Generally, a “lane keeping” system will include a device such as a video camera that gathers information on the current position of the vehicle, along with sensors for detecting certain dynamic state variables of the vehicle. Changes in the curvature of the road path is treated as unknown disturbances. Through the use of information on the deviation of the vehicle from the center of the driving lane, as well as the dynamic state variables of the vehicle, an appropriate feedback indication is provided to the driver. 
     For example, the feedback indication could be in the form of an audio signal, a visual signal, and/or a haptic signal to the driver. Such a signal would alert the driver that a corrective action may be required if the driver&#39;s intent is not to deviate from the center of the driving lane. In addition to driver feedback, the lane keeping system may also be integrated within the steering system of the vehicle to provide a corrective input thereto when a path deviation is detected. However, it may not always be desirable for the lane keeping function to assume total control over the steering but rather to assist the driver in maintaining control of the vehicle&#39;s path in accordance with the driver&#39;s intent. 
     Conventional lane keeping systems usually employ a camera system and control system integrated with a steering system to provide a lane keeping assist torque. In addition, such systems may employ various means to evaluate the driver&#39;s intent to ascertain whether a torque input in intentional or just a deviation of the vehicle from a desired path. However, such systems are very complex, involving multiple sensor systems and utilize multiple control loops to maintain a lane keeping function. Accordingly, an assistive lane keeping system is desired that provides operator cues to assist an driver with lane keeping, yet may be configured for autonomous operation that is less complex than existing systems. 
     BRIEF SUMMARY OF THE INVENTION 
     The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a system for steering a vehicle comprising: an actuator disposed in a vehicle to apply torque to a steerable wheel; a driver input device disposed in the vehicle receptive to driver commands for directing the vehicle; and a first sensor disposed in the vehicle for determining an intent of a driver and generating a first signal indicative thereof. The system also includes: a lane keeping system for detecting a location of the vehicle relative to a lane marker and generating a lane position signal indicative thereof and transmitting at least one of a lane position signal and a lane position deviation; a controller in operable communication with the actuator, the driver input device, the first sensor, and the lane keeping system. The controller provides a command to the actuator responsive to the intent of the driver, the lane position, and a desired lane position. The controller executes a lane keeping algorithm consisting of a single control loop based on at least one of the lane position and the lane position deviation. 
     Also disclosed herein in another exemplary embodiment, is a method for steering a vehicle with an electric power steering system, the method comprising: determining an intent of a driver of the vehicle; ascertaining a location of the vehicle relative to a lane marker and generating a lane position signal indicative thereof and transmitting at least one of a lane position signal and a lane position deviation; applying a lane keeping algorithm comprising a single control loop based on at least one of the lane position and the lane position deviation; and generating a command to an actuator disposed in the vehicle to apply torque to a steerable wheel, the command responsive to the intent of the driver, a desired lane position, and the at least one of the lane position and the lane position deviation. 
     In another exemplary embodiment disclosed herein is a system for steering a vehicle with an electric power steering system comprising: a means for determining an intent of a driver of the vehicle; a means for ascertaining a location of the vehicle relative to a lane marker and generating a lane position signal indicative thereof and transmitting at least one of a lane position signal and a lane position deviation to a controller; a means for applying a lane keeping algorithm comprising a single control loop based on at least one of said lane position and said lane position deviation; and a means for generating a command to an actuator disposed in the vehicle to apply torque to a steerable wheel, the command responsive to the intent of the driver, a desired lane position, and the at least one of the lane position and the lane position deviation. 
     Further, disclosed herein in another exemplary embodiment is a storage medium encoded with a machine readable computer program code, the code including instructions for causing a computer to implement the abovementioned method for steering a vehicle with an electric power steering system. 
     Also disclosed herein in yet another exemplary embodiment is computer data signal, the computer data signal comprising code configured to cause a processor to implement the abovementioned method for steering a vehicle with an electric power steering system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures: 
         FIG. 1  is a diagram depicting a vehicle in a lane with lane markers; 
         FIG. 2  is a simplified block diagram of a lane keeping system in accordance with an exemplary embodiment; 
         FIG. 3  is a diagram of a steering system in accordance with an exemplary embodiment; 
         FIG. 4  is a simplified block diagram of an exemplary methodology for lane keeping in accordance with an exemplary embodiment; 
         FIG. 5  is a diagram depicting a vehicle in a lane with lane markers; 
         FIGS. 6 and 7  are block diagrams depicting other exemplary embodiments of a lane keeping system. 
         FIGS. 8   a  and  8   b  are block diagrams depicting an alternate exemplary embodiment of a lane keeping system; and 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein is a lane keeping system integrated with an electric steering system. Existing systems commonly employ multiple control loops to maintain stability. Primarily they include lane position, lane curvature and heading angle control loops. Multiple control loops are often necessitated by low bandwidth of sensors and/or camera system. The lane keeping system of an exemplary embodiment employs a single control loop with lead-lag compensation to provide stable operation with reduced latency with a low bandwidth sensor system and camera. Advantageously, the lane keeping system of an exemplary embodiment operates with a single (only one) lane keeping control loop in a stable configuration reducing complexity, integration effort, and cost relative to existing systems. 
     The present invention may be utilized in various types of vehicles employing electronic steering or steer by wire systems or with the addition of a electric motor on an hydraulic steering system. A preferred embodiment of the invention, by way of illustration is described herein as it may be applied to an automobile employing an electric power steering system. While a preferred embodiment is shown and described by illustration and reference to an automobile steering system, it will be appreciated by those skilled in the art that the invention is not limited to the automobiles alone by may be applied to all vehicles employing electronic steering systems, steer by wire systems, or even hydraulically controlled steering systems where a lane keeping command may be integrated with existing steering commands. 
     Referring now to  FIG. 1 , there is depicted a vehicle  1  in a lane with various lane markers  2  to the left, right, (there is no lane center marker, it is calculated). The lane keeping system provides two modes of operation, a helper or assist mode, and an autonomous mode. In helper mode the operator is hands on, and the system provides audio warning(s) and/or tactic feedback warnings (for example, to simulate the noise/feel of a rumble strip) on the side of the vehicle that indicates the vehicle is approaching a lane marker. The warnings and cues may be overridden by activation of a turn signal indicating operator intent to change lanes. For example, in the helper (assist) mode, because application of torque nudges can cause the vehicle  1  to dart back and forth between lane markers  2  if the driver were not controlling the steering wheel, it desirable to determine if the drivers is, in fact holding the wheel. If so, then a torque nudge may be applied. As disclosed at a later point herein, a pressure/force sensor may be employed to determine if the driver is controlling the steering wheel. 
     In Autonomous mode the system is enabled after the operator has maintained the vehicle  1  within a tolerance band from the lane center for a selected period. The lane keeping system warns the operator of an impending engagement of the autonomous mode with a chime, and then engages. The autonomous mode maintains the vehicle  1  in the lane and requires no operator input to control the vehicle  1 . In an exemplary embodiment, the lane keeping system employs a left marker as the primary marker but can readily transition to the right marker or a center marker if the left marker cannot be identified. For example, in the autonomous mode, the torque sensor is used for determining driver intent. In this mode, the driver may want to make a correction and/or over ride the lane keeping system  100 . So, when the driver inputs a torque greater than about, for example, 0.25 Nm, the lane keeping system  100  transitions to the helper (assist) mode. When the driver has completed his correction the lane keeping system  100  transitions back to autonomous mode when the driver is within 0.5 meters of the lane center, for a duration of 5 seconds, when both of these conditions have been met the lane keeping system transitions back to the autonomous mode. 
     Continuing with  FIG. 1 , the lane keeping system can be configured to operate with either a keep out functionality, or a constant correction from center (with a dead band) functionality. With the keep out functionality, the lane keeping system responds only when the vehicle  1  is within some predefined distance from a boundary line. When the vehicle  1  approaches a boundary line, the system activates a visual warning lamp, audible warnings, and provides a torque nudge to the operator via the steering wheel in the direction away from the lane boundary line. Similarly, with the correction from center functionality, when the vehicle  1  deviates from the center of the lane by a selected offset, the lane keeping system provides a visual warning and torque nudge. 
     In an exemplary embodiment, the lane keeping system is enabled for a selected speed range of the vehicle  1 . The system may be configured to operate only over a small range of total system authority and rates. In an exemplary embodiment, the lane keeping system  100  utilizes ten percent of total system control authority. It will be appreciated that other configurations are conceivable. 
     Referring also to  FIG. 2 , there is shown a simplified block diagram of a lane keeping system  100  in accordance with an exemplary embodiment. A lane departure warning system  110  including a lane tracking system  112  is integrated with an electric steering system  40 . The lane tracking system  112  may include but not be limited to, a camera system for detection of lane markers/markings and computing a lane position signal  114 . The lane keeping system  100  is also optionally integrated with auxiliary sensors such as a global positioning system (GPS with map navigation system)  120  and dynamic sensors  130  such as, but not limited to a yaw rate sensor. The lane keeping system  100  is also integrated with various controls  140  and enunciators  150  to provide indications and feedback to the operator. 
     The integration of GPS may be employed for route planning and navigation. Furthermore, GPS may be employed to inform the lane keeping system  100  when the vehicle  1  is approaching a defined point in the roadway, such as, an exit, but not limited thereto. Under such conditions, the lane keeping system  100  can identify the type of lane marker  2 , e.g., dashed or solid. If, for example, the right line is solid, it may be inferred that the vehicle  1  is in the right most lane. The lane keeping system  100  would switch to the left line if the route planning indicates that the intention is to continue along the present course. This switch will ensure that the lane keeping system  100  does not direct the vehicle  1  down the exit. It; on the other hand, it is intended to take the exit, the lane keeping system  100  would be in the right lane (if it is an right exit) and track the right most lane marker  2 , to direct the vehicle  1  on to the exit. 
     In an exemplary embodiment, the lane keeping system also includes a driver attention monitoring device  170 . The driver attention monitoring device  170  facilitates the lane keeping system  100  taking action when the operator&#39;s attention is not focused on the roadway. The driver attention monitoring device  170  informs the lane keeping system  100  that the driver is at some level of drowsiness/inattentiveness. The driver attention monitoring device  170  includes, but is not limited to a camera system with infrared flood (or equivalent apparatus) to monitor the status of the operator, in particular, an operator&#39;s eyes. In one exemplary embodiment the driver attention monitoring device  170  monitors the operator&#39;s eye(s) to ascertain a percentage eye closure. The lane keeping system  100  may then employ such a determination by to take action and provide warnings to the operator. For example, the driver attention monitoring device  170  may be employed as an indicator when the driver has taken their eyes off the roadway for a duration exceeding a selected time. 
     When the driver attention monitoring device  170  ascertains that a driver is inattentive, the lane keeping system  100  responds with torque nudges, if the driver&#39;s hands are on the steering wheel  26  (helper (Assist) mode). In addition, audible (raising and lowering of the radio may be part of this feature) and visual warnings may be activated along with steering wheel buzz (as described herein). If the driver does not take control of the vehicle  1  or the driver attention monitoring device  170  does not indicate that the driver is awake, the lane keeping system may enter autonomous mode. The system may communicate to other systems in the vehicle  1  that the driver is not responding. The lane keeping system  100  may be integrated with other systems such as speed control and steering to slow the vehicle  1 , or pull off to the side of the road and stop. Moreover in vehicles  1  equipped with OnStar® type capability, the OnStar® system may be activated. Advantageously, such systems may be highly beneficial for cases of medical emergencies and the like. 
     Referring to  FIG. 3 , reference numeral  40  generally designates a motor vehicle electric power steering system suitable for implementation of the disclosed embodiments. Examples of other steering systems that may be suitable for implementation of the disclosed embodiments may be found in commonly assigned: U.S. Pat. No. 6,122,579 to Collier-Hallman et al.; U.S. Pat. No. 5,704,446 to Chandy et al.; U.S. Pat. No. 5,719,766 to Bolourchi et al.; U.S. Pat. No. 5,668,722 to Kaufmann et al.; U.S. patent application Ser. No. 10/165,037 to Patankar; U.S. Pat. No. 6,363,305 to Kaufmann et al.; and U.S. Pat. No. 6,370,460 to Kaufmann et al. the disclosures of which are incorporated by reference herein in their entirety. 
     Returning with  FIG. 3 , the steering mechanism  36  is a rack-and-pinion type system and includes a toothed rack (not shown) within housing  50  and a pinion gear (also not shown) located under gear housing  52 . As the operator input, hereinafter denoted as a steering wheel  26  (e.g. a hand wheel and the like) is turned, the upper steering shaft  29  turns and the lower steering shaft  51 , connected to the upper steering shaft  29  through universal joint  34 , turns the pinion gear. Rotation of the pinion gear moves the rack, which moves tie rods  38  (only one shown) in turn moving the steering knuckles  39  (only one shown), which turn a steerable wheel(s)  44  (only one shown). 
     Electric power steering assist is provided through the control apparatus generally designated by reference numeral  24  and includes the controller  16  and an electric machine  46  in this instance a brushless DC motor hereinafter denoted motor  46 . The controller  16  is powered by the vehicle power supply  10  through line  12 . The controller  16  receives a vehicle speed signal  14  representative of the vehicle velocity. Steering angle is measured through position sensor  32 , which may be an optical encoding type sensor, variable resistance type sensor, or any other suitable type of position sensor, and supplies to the controller  16  a position signal  20 . Motor velocity may be measured with a tachometer and transmitted to controller  16  as a motor velocity signal  21 . A motor velocity denoted ω m  may be measured, calculated or a combination thereof. For example, the motor velocity ω m  may be calculated as the change of the motor position θ as measured by a position sensor  32  over a prescribed time interval. For example, motor speed ω m  may be determined as the derivative of the motor position θ from the equation ω m =Δθ/Δt where Δt is the sampling time and Δθ is the change in position during the sampling interval. Alternatively, motor velocity may be derived from motor position as the time rate of change of position. It will be appreciated that there are numerous well-known methodologies for performing the function of a derivative. 
     As the steering wheel  26  is turned, torque sensor  28  senses the torque applied to the steering wheel  26  by the vehicle operator. The torque sensor  28  may include a torsion bar (not shown) and a variable resistive-type sensor (also not shown), which outputs a variable torque signal  18  to controller  16  in relation to the amount of twist on the torsion bar. Although this is the preferable torque sensor, any other suitable torque-sensing device used with known signal processing techniques will suffice. In response to the various inputs, the controller sends a command  22  to the electric motor  46 , which supplies torque assist to the steering system through worm  47  and worm gear  48 , providing torque assist to the vehicle steering. 
     It should be noted that although the disclosed embodiments are described by way of reference to motor control for electric steering applications, it will be appreciated that such references are illustrative only and the disclosed embodiments may be applied to any motor control application employing a motor, e.g., steering, valve control, and the like. Moreover, the references and descriptions herein may apply to many forms of parameter sensors, including, but not limited to torque, position, speed and the like. It should also be noted that reference herein to electric machines including, but not limited to, motors, or more specifically switched reluctance motors, hereafter, for brevity and simplicity, reference will be made to motors only without limitation. 
     In the control system  24  as depicted, the controller  16  utilizes the torque, position, and speed, and like, to compute a command(s) to deliver the required output power. Controller  16  is disposed in communication with the various systems and sensors of the motor control system. Controller  16  receives signals from each of the system sensors, quantifies the received information, and provides an output command signal(s) in response thereto, in this instance, for example, to the motor  46 . Controller  16  is configured to develop the necessary voltage(s) out of inverter (not shown), which may optionally be incorporated with controller  16  and will be referred to herein as controller  16 , such that, when applied to the motor  46 , the desired torque or position is generated. Because these voltages are related to the position and speed of the motor  46  and the desired torque, the position and/or speed of the rotor and the torque applied by an operator are determined. A position encoder is connected to the steering shaft  51  to detect the angular position θ. The encoder may sense the rotary position based on optical detection, magnetic field variations, or other methodologies. Typical position sensors include potentiometers, resolvers, synchros, encoders, and the like, as well as combinations comprising at least one of the forgoing. The position encoder outputs a position signal  20  indicating the angular position of the steering shaft  51  and thereby, that of the motor  46 . 
     Desired torque may be determined by one or more torque sensors  28  transmitting torque signals  18  indicative of an applied torque. An exemplary embodiment includes such a torque sensor  28  and the torque signal(s)  18  therefrom, as may be responsive to a compliant torsion bar, T-bar, spring, or similar apparatus (not shown) configured to provide a response indicative of the torque applied. In addition, steering wheel pressure may be determined by one or more force/pressure sensors  30  at the steering wheel  26 . The force/pressure sensors  30  generate force/pressure signals  31  indicative of an applied pressure to steering wheel  26 , which are transmitted to the controller  16 . 
     Optionally, a temperature sensor(s)  23  located at the electric machine  46 . Preferably, the temperature sensor  23  is configured to directly measure the temperature of the sensing portion of the motor  46 . The temperature sensor  23  transmits a temperature signal  25  to the controller  16  to facilitate the processing prescribed herein and compensation. Typical temperature sensors include thermocouples, thermistors, thermostats, and the like, as well as combinations comprising at least one of the foregoing sensors, which when appropriately placed provide a calibratable signal proportional to the particular temperature. 
     The position signal  20 , velocity signal  21 , and a torque signal(s)  18  among others, are applied to the controller  16 . The controller  16  processes all input signals to generate values corresponding to each of the signals resulting in a rotor position value, a motor speed value, and a torque value being available for the processing in the algorithms as prescribed herein. Measurement signals, such as the abovementioned are also commonly linearized, compensated, and filtered as desired or necessary to enhance the characteristics or eliminate undesirable characteristics of the acquired signal. For example, the signals may be linearized to improve processing speed, or to address a large dynamic range of the signal. In addition, frequency or time based compensation and filtering may be employed to eliminate noise or avoid undesirable spectral characteristics. 
     In order to perform the prescribed functions and desired processing, as well as the computations therefore (e.g., the lane keeping and steering functions, control algorithm(s), and the like), controller  16  may include, but not be limited to, a processor(s), computer(s), DSP(s), memory, storage, register(s), timing, interrupt(s), communication interface(s), and input/output signal interfaces, and the like, as well as combinations comprising at least one of the foregoing. For example, controller  16  may include input signal processing and filtering to enable accurate sampling and conversion or acquisitions of such signals from communications interfaces. Additional features of controller  16  and certain processes therein are thoroughly discussed at a later point herein. 
     As exemplified herein and disclosed above one such process may be a lane-keeping algorithm. Controller  16  receives various input signals including, but not limited to, those identified above, to facilitate such processing and may provide one or more output signals in response. Also received by the controller  16  are a variety of implementation specific parameters, signals and values for initialization and characterization of the prescribed processes and to identify various states of the processes herein. 
     Controller  16  may also be interfaced with a communications bus  160  to facilitate communications in the vehicle  1 . In an exemplary embodiment a serial communications bus, denoted CAN is employed. The CAN enables communications with the lane departure warning system  110  and an optional GPS and map navigation system  120 . It will be appreciate that the communications bus  160  may be employed for communication with various sensors, systems, actuators and the like. For example, in an exemplary embodiment, the communications bus provides communications between the lane tracking system lane departure warning system  110  and steering system  40 . More particularly, the communications bus  160  is employed to transmit lane position to the steering system  40  and transmit various vehicle parameters to the lane departure warning system  110 . The GPS may use NEMA-0183 RS-232 bus utilized in Marine Systems or similar equivalent communications interfaces. 
     Turning now to the lane departure warning system  110  and more particularly the lane keeping system  112 , in an exemplary embodiment the lane keeping system  112  employs an optical sensor  114  and image processing system  116  that detects and tracks lane markings  2 . When an unplanned or uninitiated lane departure is detected, a warning signal is generated. The warning signal indicates on which side of the vehicle  1 /lane the departure is occurring. In addition, the lane keeping system  112  transmits data regarding the position of the vehicle  1  in the lane and an estimate of road curvature. In an exemplary embodiment, the AutoVue™ system form Iteris™ Inc. is configured for application as the lane keeping system  112 , however other systems with similar capabilities are feasible. The lane keeping system employs a ruggedized, embedded image capture and analysis computer. An imaging sensor creates a two dimensional digitized image of the area ahead of the vehicle  1 . The computer provides algorithms for analysis of the captured image information to ascertain desired information including, but not limited to lane position, deviation from desired lane position, and roadway curvature. 
     In an exemplary embodiment, the lane keeping system  112  includes an interface to the communications bus  160  for interfacing with the vehicle  1  and more particularly the steering system  40 . The frame rate, response time, and data rate of the lane keeping system  112  and communications bus  160  is configured to ensure a latency of less than about 44 milliseconds for communication of information to the steering system  40 . 
     Turning now to  FIG. 4  a simplified block diagram of an illustrative system and methodology for lane keeping in accordance with an exemplary embodiment is depicted. Similar configurations are employed for applying torque commands to the steering system responsive to the Lane keeping system  100 . In the helper or assist mode, audible warning(s), visual enunciations (e.g., telltale on the instrument panel) and/or tactile feedback warnings are generated (for example, to simulate the noise/feel of a rumble strip) or torque disturbances (nudges) or torque resistance on the side of the vehicle  1  that indicates the vehicle  1  is approaching a lane marker. Tactile feedback may be achieved with a separate oscillatory actuator, for example, a motor with and eccentric weight applied to the steering wheel of the vehicle  1  or via existing steering actuators. The warnings and cues may be overridden by activation of a turn signal indicating operator intent to change lanes. In the autonomous mode, the lane keeping system  100  warns the operator with an audible warning of an impending engagement of the autonomous mode, and then engages, providing steering corrections to maintain the vehicle  1  on the marked roadway. Similarly, the lane keeping system  100  may be employed to provide feedback to the operator in instances when a lane change is intended but the operator has not indicated the intention by employing a turn signal. In an exemplary embodiment, the lane keeping system employs a left marker  2  as the primary lane marker  2  but can readily transition to the right lane marker  2  if the left lane marker  2  cannot be identified. Such transitions would be automated and essentially transparent to the operator. In an exemplary embodiment, the lane keeping system may also maintain an estimate of the lane width. Lane width is calculated when both left and right lane markers  2  are present. When one of the lane markers  2  cannot be found, the lane width is maintained and not recalculated until both markers  2  are present once again. 
     Transitions between the helper mode and autonomous mode may be operator selected or automated based on determinations of driver intent. For example, engagement of a turn signal is employed as an indication of driver intent to turn or change lanes. In addition, in an exemplary embodiment transitions application of a torque to the steering wheel  26  for a selected duration is utilized as an indication of driver intent to make a driver input e.g., turn or change lanes. Under such conditions, the lane keeping system  100  automatically transitions from the autonomous mode to the helper mode. Conversely, in one embodiment, when in the helper mode, maintaining the vehicle  1  within a selected position tolerance in the lane for a selected duration enable transitioning to the autonomous mode. 
     Similarly, under selected conditions, steering wheel force/pressure is employed as an indicator that the operator intends to be making steering corrections, and therefore is employed for selected mode transitions. In exemplary embodiment transitions the presence of steering wheel force/pressure for a selected duration is utilized as an indication of driver intent to make a driver input e.g., turn or change lanes. Likewise, in another exemplary embodiment, under selected conditions, steering wheel rate or torque rates may be employed as an indicator that the operator intends to be making steering corrections, and therefore is employed for selected mode transitions. Under such conditions, the lane keeping system  100  automatically transitions from the autonomous mode to the helper mode. It will be appreciated that determination of driver intent is a note necessarily deterministic and that turn signals, torque applied to the steering wheel, and steering wheel force/pressure are only indicators of driver intent. Therefore, each of the various sensors alone or in combination may be employed to ascertain driver intent with varying degrees of accuracy. 
     Returning to  FIG. 4 , a steering torque control algorithm  200  is depicted with the addition of a lane-keeping algorithm  300 . In an exemplary embodiment, controller  16  of the steering system  40  executes the algorithms of the lane keeping functions as well as the algorithms for the steering functions. The lane tracking system  112  tracks lane markers  2  generally on the roadway to ascertain a lane position. The lane tracking system  112  transmits various signals to the lane keeping algorithm  300 , including, but not limited to a signal indicative of lane position  118  and a status and/or validity of the data  119 . The lane-keeping algorithm  300  receives lane position signal  118 , vehicle status signals, an enable signal as well as vehicle parameters such as, but not limited to, vehicle speed, torque and optionally yaw rate. The lane-keeping algorithm  300  formulates a lane keeping command  320  that is combined with the vehicle steering system motor torque command  220  of the steering control algorithm  200  to formulate a composite steering torque command  222  that is ultimately directed to the steering motor  46 . 
     Turning now to  FIG. 5  as well, in an exemplary embodiment, to maintain stability of the lane-keeping system  100 , and more specifically the lane keeping algorithm  300  employs only a single control loop based on lane position e.g.,  118  and/or lane position deviation as an input to a steering torque control algorithm  200 . Conversely, existing systems generally utilize multiple control loops to ensure stability. Advantageously, a single control loop is simpler to implement and often more readily tuned and optimized to achieve desired performance of the lane keeping system  100 . 
     As stated above, the lane keeping algorithm  300  receives a signal indicative of a position  118  for comparison with a reference  302  e.g., lane center, and the like, to ascertain a lane deviation  304 . Alternatively, the lane keeping system  112  could compute a lane deviation  304  from a selected reference and transmit the deviation to the lane keeping algorithm  300 . While it is described herein that the lane keeping algorithm  300  performs a computation to ascertain a lane position deviation  304 , it will be appreciated that there are numerous means of implementation for ascertaining the deviation of the vehicle  1  from a selected reference lane position  302 , all of which should be considered within the scope of the claims. Continuing with the lane keeping algorithm  300  the lane position deviation is applied to a selected loop gain  306  to ultimately formulate a lane keeping command  320  for the steering algorithm  200 . 
     It will be appreciated that to maintain stability of the lane-keeping system  100 , the lane keeping control algorithm  300  may include a compensator  308  to address the bandwidth and/or dynamic characteristics of various system elements. For example, based on the update rates and latency of the lane departure warning system  100  e.g. cameras  114  and associated processing  116 , additional compensation may be required. In an exemplary embodiment a lead-lag type compensator  308  is coupled in the lane keeping motor torque control loop to provide sufficient phase lead to maintain stability. Furthermore, in an exemplary embodiment, the compensator  308  is configured to provide stability of the lane keeping system  100  at sufficient gains to achieve an overall lane keeping loop bandwidth greater than about 3 Hz, preferably greater than about 5 Hz. Once again, while a particular implementation is described as an exemplary embodiment, it will be appreciated that other configurations may be possible and within the scope of the claims. 
     It will be appreciated that the lane keeping control algorithm  300  and/or steering torque control algorithm  200  may optionally include one or more limiters  310  to address clamping the magnitude of the contribution to the composite steering torque command  222  from the lane keeping command  320 . For example in an exemplary embodiment a limiter  310  constrains the maximum contribution to no more than 5 Newton-meters (Nm) of bias torque to the steering algorithm  100  to limit lane keeping inputs to the steering system  40 . 
     It will be appreciated that while the disclosed embodiments refer to a configuration utilizing gain e.g.  306  or scaling in implementation, various alternatives will be apparent. It is well known that such gain as depicted may be implemented employing numerous variations, configurations, and topologies for flexibility. For example, the processes described above could employ in addition to or in lieu of scaling gains, look-up tables, direct algorithms, parameter scheduling or various other methodologies, which may facilitate execution of the desired functions, and the like, as well as combinations including at least one of the foregoing. 
     In a similar manner, it will be appreciated that the compensator  308  may be implemented employing a variety of methods including but not limited to passive, active, discrete, digital, and the like, as well as combinations including at least one of the foregoing. More over the compensator  308  as disclosed are illustrative of an exemplary embodiment and is not limiting as to the scope of what may be employed. It should also be noted, that in an exemplary embodiment compensator  308  could also take the form of simple scaling, scheduling look-up tables and the like as desired to tailor the content or spectral content of the position signals employed as compensation. Such configuration would depend on the constraints of a particular control system and the level of compensation required to maintain stability and/or achieve the desired control loop response characteristics. 
     Turning now to the particulars of selecting the proper transfer function for the compensator  308 . In an exemplary embodiment, the compensator  308  is depicted with a first-order lead-lag exhibiting a substantially constant gain at frequencies above a cutoff. An advantageous feature of the exemplary embodiment disclosed herein is that it provides opportunity to tune the performance of the lane keeping control algorithm  300  independent of the steering algorithm  200  and ultimately the steering system  40  to satisfy a variety of desired characteristics. Furthermore, it will be appreciated that the compensator  308  is configured as illustrated based on the dynamic characteristics of the components e.g., lane departure warning system  110  for a given implementation. Utilization of higher bandwidth components e.g., lane keeping system  100 , processing, actuators  46  and the like as well as combinations including any of the foregoing, may readily yield simplification or elimination of compensation elements yet still permit maintaining stability of the lane keeping system  100 . It is also noteworthy to appreciate that increasing the bandwidth of the steering algorithms  200 , lane keeping system  100  and/or lane keeping algorithm  300 , or overall steering system  40  may also improve the total dynamic characteristics of the of the lane keeping system  100 . As a result, a compensation means such as compensator  308  may be designed so that increases the bandwidth of the steering algorithms  200 , lane keeping algorithms  300 , and/or the entire steering system  40  also changes the dynamic characteristics of the lane keeping system  100 . Once again, bandwidth increases in one part of the system may provide for improved performance and/or relaxed requirements for other portions of the system. 
       FIG. 5  illustrates an example of a vehicle operating on a roadway. A vehicle  501  has a vehicle center  503  and a vehicle width  515 . The roadway includes a left marker  505  and a right marker  507 . A distance from the vehicle center  503  to the left marker  505  is  509  and a distance from the vehicle center  503  to the right marker  507  is  511 . Keep out zones  513  are illustrated on the right and left of the vehicle  501 . 
     As the vehicle  501  moves along the roadway, the roadway narrows. Because the roadway narrows, the keep out zones  513  narrow.  FIGS. 6 ,  7 ,  8   a , and  8   b  illustrate a block diagram of an exemplary method of operation of the lane tracking system  112  (of  FIG. 1 ). 
     Referring to  FIG. 6 , a keep out distance that defines the keep out zones  513  is defined by receiving a lane width value  602  and a vehicle speed value  604 . The lane width value  602  and the vehicle speed value  604  are used in a function  601  that defines the keep out distance  606 . In some embodiments, the function  601  may be used to create a keep out distance table that is used to determine the keep out distance thereby decreasing processing time. By using the function of the lane width value  602  and the vehicle speed value  604 , the keep out distance  606  may be adjusted when the lane width changes and when the vehicle speed changes. 
       FIG. 7  illustrates an alternate method for determining the keep out distance. The lane width value  602  and the vehicle speed value  604  are used in a function to define a keep out percentage in block  701 . In some embodiments, the function  701  may be used to create a keep out percentage table that is used to determine the keep out percentage thereby decreasing processing time. The lane width value  602  and the keep out percentage are multiplied to result in the keep out distance  606 . 
       FIG. 8   a  further illustrates a method for lane keeping. A vehicle width is received in block  601  and divided by 2 to result in a one-half vehicle width value. The vehicle center to the left marker distance  509  is received at block  808 , and the keep out distance  606  is received at block  606 . The vehicle center to the left marker distance  509 , the one-half vehicle width value, and the keep out distance  606  are added to result in a left value received in a u 1  input of block  603 . Block  603  also receives a signal at a u 2  input that indicates whether the left lane marker  505  is available. For example, if the camera system  114  that detects the left lane marker  505  has a clear picture of the left lane marker  505 , the signal will be 1, whereas if the camera does not detect the left lane marker  505 , the signal will be 0. In the block  603 . logic is used to determine if u 1 &gt;0 and if u 2 =1. If the conditions are met,  603  outputs a 1 value. If u 2 =0, or any other else condition exists, block  603  outputs a 0 value. The outputs merge in block  619  and are operative to enable a left warning in block  816  if the output from the block  619  is 1. 
     The vehicle center to the right marker distance  511  is received at block  812 . The keep out distance  606  and the one-half vehicle width value are subtracted from the vehicle center to the right marker distance  511  resulting in a right value that is received by block  605  in a u 1  input. A u 2  input to block  605  indicates whether the right lane marker  505  is detected. In the block  605 , logic is used to determine if u 1 &lt;0 and if u 2 =1. If the conditions are met,  605  outputs a 1 value. If u 2 =0, or any other else condition exists, block  605  outputs a 0 value. The outputs merge in block  621  and are operative to enable a right warning in block  818  if the output from the block  621  is 1. 
     Referring to  FIG. 8   b , the enable left warning in block  816  is received in a block  623  at a u 1  input and the enable right warning in block  818  is received in the block  623  at a u 2  input. In the block  623 , logic is used to determine whether the u 1  input value or the u 2  input value are 1. If the u 1  input value is 1, the left value is input as “B” in a block  625 . Elseif the u 2  input is 1, the right value is input as “A” in a block  627 . All other inputs are else and output as a 0 value in a block  629 . The outputs from the blocks  625 ,  627 , and  629  are merged to result in a torque warning signal  820 . 
     The torque warning signal  820  may be processed with a gain value to send a signal to a motor that is operative to impart a torque disturbances (nudges) or torque resistance on the side of the vehicle  501  that indicates the vehicle  501  is approaching a lane marker. 
     The enable left warning  8  and the enable right warning  9  may be used to actuate audible warning(s), visual enunciations (e.g., telltale on the instrument panel) and/or tactile feedback warnings are generated (for example, to simulate the noise/feel of a rumble strip). 
     It should also be noted that the figures may depict additional elements, connections, interconnections and the like as may be employed for implementation of a selected control configuration. For example, transport delays may be employed to ensure that date time coherency is addressed. Likewise, scaling may be employed to address unit conversions and the like, and limiters may be employed to clamp selected signals. 
     As will be appreciated, the disclosed invention can be embodied in the form of computer or controller implemented processes and apparatuses for practicing those processes. The present invention can also be embodied in the form of computer program code containing instructions embodied in tangible media  13 , such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer or controller, the computer becomes an apparatus for practicing the invention. The present invention may also be embodied in the form of computer program code or signal  15 , for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. 
     It will be appreciated that the use of first and second or other similar nomenclature for denoting similar items is not intended to specify or imply any particular order unless otherwise stated. 
     While the invention has been described with reference to a preferred embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.