Abstract:
Disclosed herein is a lane maintenance control method to control a vehicle to travel while accurately remaining in a given lane. The lane maintenance control method performs brake steering control in which, when a vehicle departs from a lane, a brake torque is applied to wheels of the vehicle close to the lane to generate an appropriate moment for lane maintenance, which allows the vehicle to finally move in an opposite direction of a direction in which the vehicle departs from the lane, resulting in accurate lane maintenance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 2010-0044717, filed on May 13, 2010 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments of the present invention relate to a lane maintenance control method to control a vehicle to travel while remaining in a given lane. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, a maximum traveling speed of a vehicle increases in proportion to enhanced engine performance. Thus, to improve vehicle traveling stability and driver convenience, various driver assistant systems have been installed in vehicles. The driver assistant systems may be basically classified into safety systems and convenience systems. 
         [0006]    First, safety systems include an Anti-lock Brake System (ABS) in which wheels are repeatedly locked and unlocked according to wheel slip during braking to achieve braking stability, a Traction Control System (TCS) to prevent slip of drive wheels during acceleration of a vehicle, an Electronic Stability Control (ESC) system as a combination of ABS and TCS to enhance vehicle stability, a Pre-Crash System (PCS) to alleviate collision shock, and the like. 
         [0007]    Convenience systems include an Adaptive Cruise Control (ACC) system as a longitudinal traveling assistant device, a Lane maintenance System (LKS) as a transversal traveling assistant device, a Lane Departure Warning (LDW) system, and the like. 
         [0008]    Of the aforementioned systems, LKS is a lane departure preventing system to assist a vehicle in remaining in a given lane by generating an appropriate moment when the vehicle departs from the lane. To this end, conventionally, steering control using Electric Power Steering (EPS) to supply assistive steering power using a motor when a driver manipulates a steering wheel has been performed. However, steering control is possible only in a vehicle provided with EPS and may confuse the driver. 
       SUMMARY 
       [0009]    Therefore, it is an aspect of the present invention to provide a lane maintenance control method to assist a vehicle in accurately remaining in a given lane by generating an appropriate moment required for lane maintenance when the vehicle departs from the lane. 
         [0010]    Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
         [0011]    In accordance with one aspect of the present invention, a lane maintenance control method includes recognizing information of a lane along which a vehicle travels, judging whether or not the vehicle departs from the lane based on the recognized lane information and transversal deviation of the vehicle, determining a look ahead distance required for lane maintenance if the vehicle departs from the lane, calculating a target moment based on the look ahead distance, and applying a brake torque to a wheel to generate the calculated target moment, thereby changing a direction of the vehicle. 
         [0012]    The application of the brake torque to the wheel may include applying a brake torque to a wheel close to the lane to generate the target moment. 
         [0013]    The application of the brake torque to the wheel may include distributing different torques to left and right wheels of the vehicle to generate the target moment. 
         [0014]    The lane maintenance control method may further include stopping brake steering control, in which the direction of the vehicle is changed as the brake torque is applied to the wheel of the vehicle, if turn signal is turned on. 
         [0015]    The lane maintenance control method may further include stopping brake steering control, in which the direction of the vehicle is changed as the brake torque is applied to the wheel of the vehicle, if driver steering input exceeds a predetermined range. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0017]      FIG. 1  is a block diagram of a lane maintenance system according to an embodiment of the present invention; 
           [0018]      FIG. 2  is a flow chart illustrating a lane maintenance control method of a vehicle according to an embodiment of the present invention; 
           [0019]      FIG. 3  is a view illustrating operation of the lane maintenance system according to the embodiment of the present invention during lane maintenance; 
           [0020]      FIG. 4  is a view illustrating the lane maintenance system according to the embodiment of the present invention when a vehicle departs from a lane; and 
           [0021]      FIG. 5  is a table illustrating yaw rate variation when the lane maintenance system according to the embodiment of the present invention distributes different brake pressures to left and right wheels of a vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0023]      FIG. 1  is a block diagram of a lane maintenance system according to the embodiment of the present invention. 
         [0024]    In  FIG. 1 , the lane maintenance system according to the embodiment of the present invention includes a sensor unit  10 , an electronic control unit  20 , a brake control unit  30 , an engine control unit  40 , a parking brake control unit  50 , and a driver interface  60 . 
         [0025]    The sensor unit  10  serves to collect various sensor information of a vehicle and includes a camera  11 , a wheel speed sensor  12 , a steering angle sensor  13 , a yaw rate sensor  14 , and an acceleration sensor  15 . 
         [0026]    The camera  11  photographs a direction in which a vehicle travels to recognize a lane and transmits the photographed signal to the electronic control unit  20 . The wheel speed sensor  12  is installed to each of wheels FL, FR, RL and RR to sense a speed of the corresponding wheel and transmits the sensed signal to the electronic control unit  20 . 
         [0027]    The steering angle sensor  13  is provided at a steering wheel column. The steering angle sensor  13  senses a steering angle and angular speed depending on manipulation of a steering wheel and transmits the sensed signal to the electronic control unit  20 . 
         [0028]    The yaw rate sensor  14  senses a yaw rate (cornering speed) of a vehicle and transmits the sensed signal to the electronic control unit  20 . 
         [0029]    The acceleration sensor  15  senses a longitudinal or transversal vehicle acceleration and transmits the sensed signal to the electronic control unit  20 . 
         [0030]    The electronic control unit  20  judges whether or not a vehicle departs from a lane upon receiving the signals transmitted from the camera  11 , the wheel speed sensor  12 , the steering angle sensor  13 , the yaw rate sensor  14  and the acceleration sensor  15 . If it is judged that the vehicle departs from the lane, the electronic control unit  20  determines a look ahead distance L required for lane maintenance and calculates a target moment M required for lane maintenance by the following Equation 1. 
         [0000]        M= 2{( F   FL   +F   RL )−( F   FR   +F   RR )}/ T   r   Equation 1
 
         [0031]    Here, “F FL ” is brake torque of a left front wheel FL, “F RL ” is a brake torque of a left rear wheel RL, “F FR ” is brake torque of a right front wheel FR, “F RR ” is brake torque of a right rear wheel RR, and “T r ” is a distance between the front wheels FL and FR or between the rear wheels RL and RR. 
         [0032]    In Equation 1, a value of the target moment M varies based on the look ahead distance L. The look ahead distance L is a forward traveling distance, required for lane maintenance, based on a vehicle speed. The look ahead distance L is a design variant of a target distance to prevent a vehicle from departing from a lane without confusing a driver. 
         [0033]    Thus, the value of the target moment M decreases if the look ahead distance L is long, and increases if the look ahead distance L is short. 
         [0034]    To this end, if it is judged that a vehicle departs from a lane, the electronic control unit  20  applies appropriate brake torque to each wheel FL, FR, RL or RR to generate the calculated target moment M. Specifically, the electronic control unit  20  generates the moment by applying brake torque to wheels close to a lane, thereby controlling the vehicle to finally move an opposite direction of a direction in which the vehicle departs the lane. 
         [0035]    During this brake steering control, the electronic control unit  20  judges whether or not turn signal is turned on or whether or not driver steering input exceeds a predetermined range. If the turn signal is turned on or the driver steering input exceeds the predetermined range, the electronic control unit  20  stops brake steering control based on driver steering intention. 
         [0036]    The brake control unit  30  controls brake pressure applied to a wheel cylinder based on a brake signal output from the electronic control unit  20 , thereby applying brake torque to the respective wheels FL, FR, RL and RR to maximize vehicle stability. 
         [0037]    The engine control unit  40  controls engine torque based on an engine control signal output from the electronic control unit  20 , thereby controlling drive force of an engine in cooperation with a Traction Control System (TCS) control block  41  to maximize vehicle stability. 
         [0038]    The parking brake control unit  50  additionally applies constant brake force to rear wheels RR and RL based on a parking brake control signal output from the electronic control unit  20 , thereby distributing brake force in cooperation with an Electronic Parking Brake (EPB) control block  51  to optimize the brake force of the vehicle. 
         [0039]    An EPB system to allow a motor to automatically operate a parking brake based on operating states of a vehicle functions to automatically operate or release the parking brake in cooperation with the electronic control unit  20 , thereby achieving braking stability in an emergency. The EPB system receives additional brake force operation information of the rear wheels RR and RL from the electronic control unit  20  via CAN communication, thereby additionally applying a constant brake force to the rear wheels RR and RL so as to optimize the brake force of the vehicle. 
         [0040]    The driver interface  60  serves as a communication interface with a driver with relation to the beginning of adaptive cruise control, adaptive cruise control modes and control states (e.g., when turn signal is turned on) and transmits an input signal preset by a driver to the electronic control unit  20 . 
         [0041]    Hereinafter, operation and effects of a lane maintenance control method using the above described lane maintenance system will be described. 
         [0042]      FIG. 2  is a flow chart illustrating the lane maintenance control method according to the embodiment of the present invention,  FIG. 3  is a view illustrating operation of the lane maintenance system according to the embodiment of the present invention during lane maintenance, and  FIG. 4  is a view illustrating the lane maintenance system according to the embodiment of the present invention when a vehicle departs from a lane. 
         [0043]    In  FIG. 2 , if a vehicle  1  begins to travel inside lanes  3  located at opposite sides of a motorway (see  FIG. 3 ), the camera  11  photographs a direction in which the vehicle  1  travels to recognize the lanes  3 , and transmits recognized information of the lanes  3  to the electronic control unit  20  ( 100 ). 
         [0044]    Thus, the electronic control unit  20  judges whether or not the vehicle  1  departs from the lane  3  as illustrated in  FIG. 4  based on information of the lanes  3  recognized by the camera  11  and transversal deviation of the vehicle  1  ( 102 ). 
         [0045]    If it is judged from the result of operation  102  that the vehicle departs from the lane  3 , the electronic control unit  20 , as illustrated in  FIG. 4 , determines a look ahead distance L required for lane maintenance ( 104 ). 
         [0046]    If the look ahead distance L required for lane maintenance is determined, the electronic control unit  20  calculates a target moment M for lane maintenance based on the look ahead distance L by the following Equation 1 ( 106 ). 
         [0000]        M= 2{( F   FL   +F   RL )−( F   FR   +F   RR )}/ T   r   Equation 1
 
         [0047]    Here, “F FL ” is brake torque of a left front wheel FL, “F RL ” is brake torque of a left rear wheel RL, “F FR ” is brake torque of a right front wheel FR, “F RR ” is brake torque of a right rear wheel RR, and “T r ” is a distance between the front wheels FL and FR or between the rear wheels RL and RR. 
         [0048]    In Equation 1, a value of the target moment M decreases if the look ahead distance L is long, and increases if the look ahead distance L is short. 
         [0049]    Thereafter, the electronic control unit  20  applies appropriate brake torque to each wheel FL, FR, RL or RR to generate the calculated target moment M. More particularly, the electronic control unit  20  applies brake torque to wheels close to the lane  3  to generate the target moment M ( 108 ). 
         [0050]    Thus, the electronic control unit  20  controls the vehicle  1  to finally move in an opposite direction of a direction in which the vehicle  1  departs from the lane  3 , thereby controlling the vehicle  1  to remain inside the lane  3  ( 110 ). 
         [0051]    A method to apply appropriate brake torque to each wheel FL, FR, RL or RR, as illustrated in  FIG. 5 , includes distributing different torques at left and right wheels of the vehicle  1  to generate the target moment M. 
         [0052]      FIG. 5  is a table illustrating yaw rate variation when the lane maintenance system according to the embodiment of the present invention distributes different brake pressures to left and right wheels of a vehicle. 
         [0053]    In  FIG. 5 , assuming that the same brake pressure of 0 bars is applied to the left wheels FL and RL and different brake pressures of 0, 20, 40, 60, 80 and 100 bars are distributed to the right wheels FR and RR, it will be appreciated that a yaw rate varies in a range of 0, 1.0, 1.2, 2.1, 2.6, 3.6. 
         [0054]    As will be appreciated from  FIG. 5 , when brakes pressure different from that applied to the right wheels FR and RR is applied to the left wheels FL and RL to generate the target moment M, brake steering control to finally change a direction of the vehicle  1  may be performed. 
         [0055]    During the above described brake steering control, if turn signal is turned on or driver steering input exceeds a predetermined range, the electronic control unit  20  stops the brake steering control based on driver steering intention. 
         [0056]    As is apparent from the above description, with a lane maintenance control method according to the embodiment of the present invention, when a vehicle departs from a lane, brake torque is applied to wheels of the vehicle close to the lane to generate an appropriate moment for lane maintenance, which allows the vehicle to finally move an opposite direction of a direction in which the vehicle departs from the lane, resulting in accurate lane maintenance. 
         [0057]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.