Abstract:
A line lock braking system includes a brake module configured to selectively apply hydraulic braking pressure against first wheels and second wheels of the vehicle, and a controller in signal communication with the brake module. The controller initiates, upon receipt of a request, a vehicle line lock mode and performs line lock braking of the vehicle where the brake module is controlled to selectively apply braking pressure against the first wheels and not the second wheels such that the second wheels are free to rotate based on a throttle applied by a driver; completes the line lock mode upon release of a button being depressed to enter and maintain activation of the line lock mode such that the braking pressure against the first wheels is released; and cancels the line lock mode upon determining a number of rotations of the second wheels exceeds a predetermined number of wheel rotations.

Description:
FIELD 
       [0001]    The present application relates generally to a vehicle braking system and, more particularly, to a vehicle braking system for selectively providing a line lock condition. 
       BACKGROUND 
       [0002]    In some vehicle launch scenarios, to increase performance of the vehicle at take-off, drivers can perform a controlled spinning of the rear tires (e.g., a burnout), which warms the tires and improves grip with the road or track surface. However, in order to perform the controlled burnout, a driver is typically required to manipulate the service brake system to allow the rear wheels to spin freely while the front wheels are held stationary by the brake system. Moreover, the driver may be required to perform multiple tasks such as simultaneously interacting with the throttle, brake, and clutch, which may be difficult to safely or correctly perform. 
         [0003]    Aftermarket systems have been proposed to assist the driver with the controlled burnout. However, some such systems pose reliability issues and do not provide an automated, electrical control of the burnout. Other brake line lock systems have been developed for inclusion with the original vehicle equipment. However, such systems have drawbacks including time-based controls that prevent the controlled burnout after a certain period of time even though the driver still desires to perform the action. Accordingly, while such systems work for their intended purpose, it is desirable to provide an improved vehicle line lock braking system. 
       SUMMARY 
       [0004]    In accordance with one example aspect of the invention, a line lock braking system for a vehicle is provided. The line lock braking system includes a brake module configured to selectively apply hydraulic braking pressure against first wheels and second wheels of the vehicle, and a controller in signal communication with the brake module. The controller is configured to upon receipt of a request, initiate a vehicle line lock mode and perform a line lock braking of the vehicle where the brake module is controlled to selectively apply hydraulic braking pressure against the first wheels and not the second wheels such that the second wheels are free to rotate based on a throttle applied by a driver of the vehicle; monitor a number of wheel rotations of the second wheels while the first wheels are maintained in a substantially stationary state by the brake module; complete the vehicle line lock mode, upon release of a button being depressed to enter and maintain activation of the line lock mode, such that the braking pressure against the first wheels is released; and cancel the vehicle line lock mode upon determining the number of wheel rotations of the second wheels exceeds a predetermined number of rotations during the vehicle line lock mode. 
         [0005]    According to another example aspect of the invention, a method of performing vehicle line lock braking is provided. The method includes receiving at a controller a request for a vehicle line lock mode, initiating the vehicle line lock mode when the request is received by applying hydraulic braking pressure against first wheels and not second wheels of the vehicle such that the second wheels are free to rotate based on a throttle applied by a driver of the vehicle; and monitoring a number of wheel rotations of the second wheels while the first wheels are maintained in a substantially stationary state by a brake module. The vehicle line lock mode is completed upon release of a button being depressed to enter and maintain activation of the line lock mode, such that the braking pressure against the first wheels is released; and the vehicle line lock mode is canceled upon determining the number of wheel rotations of the second wheels exceeds a predetermined number of rotations during the vehicle line lock mode. 
         [0006]    Further areas of applicability of the teachings of the present disclosure will become apparent from the detailed description, claims and the drawings provided hereinafter, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings references therein, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the present disclosure, its application or uses. Thus, variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of an example vehicle in accordance with the principles of the present disclosure; 
           [0008]      FIG. 2  is a front view of an example driver control system in accordance with the principles of the present disclosure; 
           [0009]      FIG. 3  is a schematic view of an example vehicle control system in accordance with the principles of the present disclosure; and 
           [0010]      FIG. 4  is a flow control diagram of an example method of controlling a vehicle in accordance with the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    With initial reference to  FIG. 1 , an example vehicle is illustrated and generally identified at reference numeral  10 . The vehicle  10  includes a line locking braking system configured to selectively transition the vehicle from a normal mode to a line lock braking mode where vehicle front wheels  20  are locked and a braking pressure is selectively released on vehicle rear wheels  30 . This enables the driver to apply the throttle to rotate the rear wheels  30  and perform a controlled burnout. Additionally, the described line lock feature will deactivate when the rear wheels  30  have rotated a predetermined number of times, the driver manually aborts the feature, or the vehicle/system detects a fault or error. The vehicle then returns to the normal operating mode behavior after the line lock feature has been deactivated. 
         [0012]    With additional reference to  FIG. 2 , the vehicle  10  includes a vehicle interior  40  having a driver control system  50 , which generally comprises a steering wheel  60 , an instrument cluster  70 , and a display  80  having a user interface  90 . The driver control system  50  is in signal communication with the line locking braking system, and enables the driver to activate and deactivate the line lock braking mode. Moreover, in one exemplary implementation, the driver control system  50  assists the driver in performing the controlled burnout when the line lock braking mode is activated, for example, through a sequence of audio and/or visual cues. 
         [0013]    The steering wheel  60  may include one or more buttons  65  located thereon that may be utilized during the line lock braking mode. For example, button  65  may be required to be held down during at least a portion of a line lock braking mode sequence, as will be discussed in greater detail below. 
         [0014]    The instrument cluster  70  may include one or more displays  75  configured to provide information to the driver such as, for example, vehicle speed or engine rotational speed. The instrument cluster displays  75  may be utilized to provide information or direction to the driver during the line lock braking mode. For example, the displays  75  may provide a series of directions to the driver to enable the vehicle to perform the controlled burnout. 
         [0015]    The display  80  includes user interface  90 , which is configured to provide audio/visual information related to the line lock braking system and mode to the driver. For example, the user interface  90  may be a touch-screen configured to display one or more soft keys  95  programmed to perform a specific function when selected. In one example implementation, soft key  95  may be selected by the driver to request the line lock braking mode. Once selected, the user interface  90  can display various information related to the line lock braking mode. For example, user interface  90  may display whether one or more vehicle conditions are satisfied that will enable activation of the line lock braking mode. If the conditions are not satisfied, the user interface  90  may display information regarding the unsatisfied condition, and may subsequently deactivate the line lock braking mode or otherwise prevent initiation of the controlled burnout. 
         [0016]    Additionally, user interface  90  may provide audio communications to the driver in place of or in addition to visual displays. Moreover, the user interface  90  may also receive audio commands from the driver. However, the driver control system  50  is not limited solely to the function described herein and may be utilized in various other ways to control the line lock braking system and associated controlled burnout. 
         [0017]      FIG. 3  illustrates a vehicle control system  100  according to one exemplary implementation. The vehicle control system  100  may be in signal communication with the driver control system  50  and may be utilized as the line lock braking system for operating vehicle  10  in the line lock braking mode. As shown, the vehicle control system  100  generally includes a controller or brake module integrated control unit (ICU)  110  having a brake hydraulic control unit (HCU)  115  and a brake electronic control unit (ECU)  120 . It will be appreciated that the brake controller or module can be implemented in various other forms. As used herein, the term controller, module, or control unit refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0018]    The brake HCU  115  is coupled to a plurality of braking devices  125  each located at one of the vehicle wheels  20 ,  30 . The brake HCU  115  is configured to selectively direct hydraulic fluid to the braking devices  125  to apply hydraulic braking pressure against that wheel  20 ,  30 . As such, during the line lock braking mode, the brake HCU  115  can selectively apply hydraulic braking pressure against front wheels  20  while releasing hydraulic braking pressure against the rear wheels  30 . The braking devices  125  may be any suitable type of brake such as for example, disc brakes, drum brakes, electronic brakes, or the like. 
         [0019]    The brake ECU  120  is in signal communication with a plurality of wheel speed sensors  130  each located at one of the vehicle wheels  20 ,  30 . The brake ECU  120  is configured to receive a signal from the wheel speed sensors  130  indicating a number of rotations performed by the vehicle wheels  20 ,  30 . For example, the signal may indicate tone wheel pulses, which can be utilized to calculate the number of rotations of wheels  20 ,  30 . The number of rotations of rear wheels  30  may then be used to determine when the controlled burnout is stopped. For example, the line lock braking mode may be deactivated when the number of rotations of the rear wheels  30  exceeds a predetermined number. In one example, the predetermined number of rotations is between approximately 300 and approximately 500. in another example, the predetermined number of rotations is between 300 and 500. In yet another example, the predetermined number of rotations is approximately 400. In yet another example, the predetermined number of rotations is 400. 
         [0020]    However, it will be appreciated that the number of wheel rotations may be adjusted based on various factors such as, for example, weather conditions, ambient temperature, track surface temperature, and tire type. For example, network controller  150  may request various inputs/conditions and vary the wheel rotation threshold accordingly such as by using an algorithm for such purposes. 
         [0021]    Driver input devices  140  are in signal communication with the brake ECU  120  either directly or through a network controller  150 . The driver input devices  140  are configured to provide information and/or control the controller  150 , which controls the brake ECU  120 . For example, the driver input devices  140  can be utilized to activate the line lock braking mode and/or perform portions of the line lock braking sequence. As illustrated in the example implementation of  FIG. 2 , driver input devices  140  can include steering wheel  60 , instrument cluster  70 , user interface  90 , an accelerator pedal  155  and associated powertrain control module  160 , and a brake pedal  165 . However, the network controller  150  may be in signal communication with various other vehicle control modules and/or sensors. 
         [0022]    The network controller  150  is configured to control the distribution of hydraulic fluid between the brake HCU  115  and the individual braking devices  125  based on information received from a vehicle system or the driver (e.g., via the driver input devices  140 ). As such, the network controller  150  is configured to activate and deactivate the line lock braking mode. 
         [0023]      FIG. 4  illustrates an example method  200  of line lock braking a vehicle for a controlled burnout. The method  200  generally includes (I) receiving a request for a line lock braking mode, (II) checking initial vehicle preconditions for entering the line lock braking mode, (Ill) checking secondary vehicle conditions for entering the line lock braking mode, (IV) activating the line lock braking, and (V) deactivating the line lock braking after a predetermined condition occurs such as, for example, upon a driver releasing button  65  or when the rear wheels exceed a predetermined number of rotations during the line lock. 
         [0024]    In one exemplary implementation, at step  202 , controller  150  receives a signal indicating a driver request for the line lock braking mode. For example, the driver may initiate the request by selecting soft key  95  of the user interface  90  or by providing an audio command to the driver control system  50 . At step  204 , controller  150  directs the driver to refer to the instrument cluster  70 . For example, display  80  may provide an audio or visual indicator to the driver to refer to the instrument cluster  70 . 
         [0025]    At step  206 , controller  150  confirms one or more non-correctable or initial vehicle preconditions are satisfied. Each of the initial vehicle preconditions must be satisfied to enter the line lock mode. In one exemplary implementation, the initial vehicle preconditions include one or more of the following: (a) the internal vehicle speed is less than or equal to 10 MPH; (b) the engine RPM is greater than 500 RPM; (c) a temperature of the transmission is not over a predetermined temperature (e.g., approximately 140° C.; (d) the engine is running; (e) no current active electronic stability control (ESC) faults that inhibit line lock are present (e.g., wheel speed sensor faults, brake pressure sensor faults, internal module faults, yaw sensor faults, or any other faults that affect the integrity of the function); (f) a radiator coolant temperature is less than approximately 250° F.; (g) the odometer is greater than a predetermined number (e.g., 500 miles); (h) a valet mode is not active (e.g., where a drive mode is requested by the vehicle owner to limit the functionality of the vehicle such as reduced engine power); (i) vehicle doors are closed; (j) cruise control is not enabled or active; and (h) launch control is not active (e.g., a system that assists the driver in maintaining a set engine speed prior to launch and then manages wheel slip from launch to a predetermined speed, thereby providing a reliable and consistent acceleration profile). However, step  206  is not limited to the above described preconditions and may include additional initial vehicle preconditions. 
         [0026]    If one or more of the initial vehicle preconditions are not satisfied, at step  208 , controller  150  rejects the line lock braking mode request. At step  210  controller  150  may provide a message to the driver via driver control system  50  indicating that the line lock request has been rejected. For example, display  80  may provide a message indicating that the line lock is unavailable and the reason(s) that the line lock is unavailable (i.e., which initial preconditions were not satisfied). For example, display  80  may indicate that the vehicle speed is too high, the engine speed is too low, the coolant temperature is too high, a vehicle door is open, etc. 
         [0027]    If all of the initial vehicle preconditions are met, control proceeds to step  212  where controller  150  confirms one or more correctable or secondary vehicle preconditions are satisfied. In one exemplary implementation, the secondary vehicle preconditions include one or more of the following: (i) the vehicle speed is zero MPH; (ii) the brake pedal pressure is greater than a predetermined pressure (e.g., greater than 50 bar); (iii) in an automatic transmission, the transmission is in a forward gear (e.g., drive); (iv) in a manual transmission, the transmission is not in reverse (R); and (v) the vehicle traction control or stability setting must be “sport” or “full-off”. However, step  212  is not limited to the above described preconditions and may include additional secondary vehicle preconditions. 
         [0028]    Each of the secondary vehicle preconditions must be satisfied to enter the line lock mode. However, unlike the initial vehicle preconditions, if one or more of the secondary preconditions is not satisfied, at step  214 , the controller  150  may invite the driver to remedy the unsatisfied secondary preconditions. For example, if one of the secondary preconditions is not satisfied, controller  150  may display a tutorial on the instrument cluster  70  or display  80  that provides directions or assistance to the driver to remedy the unsatisfied condition. Moreover, controller  150  may only display one active correctable secondary precondition at a time until that secondary precondition is corrected. 
         [0029]    In one exemplary implementation, if secondary precondition (i) is not satisfied, instrument cluster  70  displays a message indicating that the vehicle speed must be zero MPH. If secondary precondition (ii) is not satisfied, instrument cluster  70  displays a message directing the driver to apply pressure to the brake pedal. If secondary precondition (iii) is not satisfied, instrument cluster  70  displays a message indicating that the vehicle must be in a forward gear. If secondary precondition (v) is not satisfied, instrument cluster  70  displays a message indicating that the stability setting must be “sport” or “full-off”. 
         [0030]    If all of the secondary vehicle preconditions are met, whether initially or through the tutorial of step  214 , control then proceeds to step  216 . However, if at step  218 , an initial precondition occurs during or immediately after tutorial steps  214 , control proceeds to step  220  where the line lock braking mode is canceled. If a secondary precondition occurs or is re-enabled at step  222 , control returns to the tutorial step  214  to attempt to remedy the precondition. 
         [0031]    At step  216 , once all of the secondary preconditions are satisfied, controller  150  directs the driver to perform an operation to activate the line lock braking. For example, controller  150  may display a message on instrument cluster  70  directing the driver to press and hold button  65  on the steering wheel  60 . If the operation is performed correctly, at step  224 , controller  150  subsequently transitions the vehicle to the line lock braking condition by releasing brake pressure from the rear wheels  30  and maintaining brake pressure at the front wheels  20 . In other words, the braking pressure is maintained or locked in the braking system lines and components associated with the front wheels  20  in an absence of use of brake pedal  165 . 
         [0032]    At step  226 , controller  150  directs the driver to release the brake pedal  165  and apply the throttle (i.e., press the accelerator pedal  155 ) while the driver continues to hold button  65 . At this point, the rear wheels  30  should begin to rotate while the front wheels  20  remain stationary, thereby performing the controlled burnout. 
         [0033]    During the controlled burnout, at step  228 , controller  150  may display a message to the driver to release or disengage the operation performed in step  216 . For example, controller  150  may display a message on instrument cluster  70  directing the driver to release the button  65  to begin forward movement of the vehicle. Moreover, the controller  150  may display the predetermined number of wheel rotations on the instrument cluster  70  and/or the user interface  90  before and/or during the controlled burnout. The controller  150  may also display the number of real-time wheel revolutions throughout the controlled burnout. When the revolutions approach the revolutions threshold, a further message may be displayed to release the button or the line lock will be canceled. At step  230 , if button  65  is released before the predetermined number of wheel rotations is exceeded, controller  150  releases the hydraulic pressure at front wheels  20  and the vehicle will drive forward if the throttle is still applied. 
         [0034]    However, prior to release of button  65 , controller  150  will cancel the line lock braking (step  232 ) if any of the following conditions occur: (1) the wheel speed sensors  130  indicate the rear wheels  30  have rotated more than the predetermined number of rotations (e.g., 400 revolutions) during the controlled burnout in the line lock braking mode; (2) an initial precondition occurs; (3) a secondary precondition occurs (except for the brake pedal pressure greater than a predetermined pressure); (4) the brake pedal  165  is pressed; (5) the accelerator  155  is released; (6) the vehicle rotates beyond a predetermined angle (e.g., the vehicle rotates or slides more than 15° from a starting position); and (7) a pressure of a rear tire  30  is less than or equal to a predetermined minimum pressure (e.g., zero PSI). However, step  232  is not limited to the above described conditions and may include additional time-independent line lock cancelling conditions. 
         [0035]    If any of the above conditions occurs, control proceeds to step  220  and the line lock braking mode is canceled. Thus, the line lock braking system described herein provides the benefit of line lock deactivation without relying on any time-based conditions. For example, the predetermined number of revolutions for the rear tires  30  is dependent on the accelerator pedal  155  position and corresponding requested engine torque. In other words, with lesser pedal depression, there will be fewer tire revolutions per minute and thus a longer burnout period as compared to greater pedal depression, which requests more torque resulting in more rear tire RPM, and thus a shorter burnout period before reaching the predetermined wheel revolutions. In this way, the rear tires are better protected from excessive wear and potential durability issues. More specifically, the revolution threshold directly correlates to wear of the tires and, in one exemplary implementation, is further tunable based on factors that relate to tire wear, such as road surface and tire type. As such, burnout potential is maximized while also accounting for durability of the rear tires  30 . 
         [0036]    Subsequently, at step  234 , controller  150  transitions the accelerator  155  to a dead pedal where accelerator pedal deflection is ignored until the accelerator pedal  155  is completely released. Subsequent pedal deflection may then be used to determine driver input. In one implementation, dead pedal only occurs when the predetermined number of wheel revolutions is exceeded. The vehicle  10  then returns to normal operating behavior once the line lock braking mode is deactivated. 
         [0037]    Described herein are system and methods for providing a controlled burnout for a vehicle. A driver control system is in communication with a network controller, which is configured to control a hydraulic brake system. Upon satisfying initial and secondary vehicle preconditions, the controller activates a line lock braking mode where brake pressure is released from the rear wheels and the brake pressure is maintained at the front wheels, thereby enabling the controlled burnout. The line lock braking mode is deactivated when the rear wheels have spun a predetermined number or times, or if the mode is aborted either manually by the driver or automatically by the vehicle/system. The vehicle then returns to normal operating behavior after the line lock braking mode is deactivated. Accordingly, there are no time-out or time based cancellation features or thresholds at any stage or state of the line lock braking feature. Instead, the described system monitors time-independent conditions and deactivates the line lock braking feature based off the number of times the vehicle&#39;s rear wheels have rotated. 
         [0038]    It should be understood that the mixing and matching of features, elements and/or functions between various examples may be expressly contemplated herein so that one skilled in the art would appreciate from the present teachings that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above.