Abstract:
A system for braking a vehicle includes a transmission having a plurality of gear sets for establishing a plurality of forward and reverse gear ratios and an actuator for changing the gear ratios. The system also includes a plurality of sensors for detecting a plurality of vehicle operating parameters and an auxiliary brake for reducing a speed of the vehicle. A controller having a processor configured to receive a plurality of output signals from the plurality of sensors has control logic for activating one of the actuator and the auxiliary brake based on the received output signals. A method for operating the system for braking is also provided. The method includes determining road grade, determining an acceleration of the vehicle, determining an activation status of the primary brake, determining a position of the throttle, determining whether extra braking is and activating the auxiliary brake based on the extra braking determination.

Description:
FIELD 
       [0001]    The present disclosure relates to a braking system, and more particularly to a braking system and method used with an automatic transmission in a motor vehicle. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Braking a motor vehicle, whether a passenger vehicle or commercial truck, involves an operator of the vehicle manually engaging a primary brake. Engagement of the primary brake typically involves increasing the friction between the brake element and the axle of the vehicle, though other types of braking are known in the art. While this method of braking is welt known and useful for its intended purpose, relying solely on a manually operated brake while on a steep road grade can increase the wear on the brake which can reduce the useful life of the brake. For example, increased wear can lead to an increased rate of the reduction of the brake lining, increased rotor temperature, and increased brake fade. 
         [0004]    One solution to avoid excessive wear on the primary brake while on steep road grades is to apply extra braking. The extra braking can include various forms of braking, including downshifting of the transmission in the motor vehicle, activation of engine compression brakes, or activation of an exhaust brake. While useful for reducing wear on the primary brake, in the past this extra braking was manually engaged by the operator of the motor vehicle, thereby increasing the complexity of operating the vehicle. 
         [0005]    One solution to the above problem is to automatically activate downshifting, as disclosed in U.S. Pat. No. 6,212,458 B1, hereby incorporated by reference as if fully disclosed herein. While automatic downshifting is useful for its intended purpose, there is room in the art for improvement in providing additional mechanical automatic extra braking to a motor vehicle. 
       SUMMARY 
       [0006]    It is an object of the present invention to provide the art with an automatic braking system for a motor vehicle. 
         [0007]    In one aspect of the present invention, a system for braking a vehicle is provided that includes a transmission having a plurality of gear sets for establishing a plurality of forward and reverse gear ratios and an actuator for changing the gear ratios, a plurality of sensors for detecting a plurality of vehicle operating parameters, an auxiliary brake for reducing a speed of the vehicle, and a controller having a processor configured to receive a plurality of output signals from the plurality of sensors and wherein the controller has control logic for activating one of the actuator and the auxiliary brake based on the received output signals. 
         [0008]    In another aspect of the present invention, the system includes a primary brake for reducing the speed of the vehicle and the control logic includes a first control logic for determining if the primary brake is activated. 
         [0009]    In yet another aspect of the present invention, the system includes a throttle for controlling an acceleration of the vehicle the control logic includes a second control logic for determining a position of the throttle. 
         [0010]    In yet another aspect of the present invention, the control logic includes a third control logic for calculating a road grade from the input signals from the plurality of sensors. 
         [0011]    In yet another aspect of the present invention, the plurality of output signals from the plurality of sensors includes an output signal indicative of an acceleration of the vehicle and a speed of the vehicle. 
         [0012]    In yet another aspect of the present invention, the control logic includes a fourth control logic to activate one of the auxiliary brake or actuator based on the primary brake is activated, throttle activation, the road grade, the acceleration, and the speed. 
         [0013]    It is another object of the present invention to provide the art with a method for automatically providing extra braking to a motor vehicle. 
         [0014]    In one aspect of the present invention, a method for braking a vehicle having a throttle, a primary brake and an auxiliary brake is provided, the method including the steps of determining a road grade, determining an acceleration of the vehicle, determining an activation status of the primary brake, determining a position of the throttle, determining whether extra braking is desirable based on the road grade, the acceleration of the vehicle, the activation status of the primary brake, and the amount of engagement of the throttle, and activating the auxiliary brake based on the extra braking determination. 
         [0015]    In another aspect of the present invention, determining whether extra braking is desirable further comprises determining whether the road grade exceeds a road grade threshold, whether the vehicle is accelerating, whether the primary brake is activated, and the position of the throttle. 
         [0016]    In another aspect of the present invention, the method further includes determining a first amount of time the vehicle acceleration is different than a first threshold, a second amount of time the vehicle acceleration is different than a second threshold with the auxiliary brake activated, and a third amount of time the primary brake is activated. 
         [0017]    In another aspect of the present invention, determining whether extra braking is desirable includes combining the road grade, the speed of the vehicle, the amount of engagement of the throttle, the first time, the second time, and the third time into a combined factor. 
         [0018]    In another aspect of the present invention, the combined factor is compared to an auxiliary brake threshold and the auxiliary brake is activated if the combined factor is greater than the auxiliary brake threshold. 
         [0019]    In another aspect of the present invention, the vehicle includes an automatic transmission with a plurality of drive ratios, and determining whether extra braking is desirable includes comparing the combined factor to a downshift threshold and the drive ratio is changed when the combined factor is greater than the downshift threshold. 
         [0020]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0021]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0022]      FIG. 1  is a schematic diagram of a braking system in accordance with the principles of the present invention; 
           [0023]      FIG. 2  is a flow chart of a method for braking using the braking system of the present invention; and 
           [0024]      FIG. 3  is a flow chart detailing the step for determining the desire for extra braking according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0026]      FIG. 1  illustrates a braking system  10  in accordance with the principles of the present invention. The braking system  10  may be incorporated within a motor vehicle (not particularly shown). The braking system  10  includes an automatic transmission  12 . The automatic transmission  12  may be any one of a set of well known automatic transmissions known in the art and having a plurality of gear sets for establishing a plurality of forward and reverse gear ratios (not shown). 
         [0027]    The automatic transmission  12  includes a controller  14  in electronic communication with a shift actuator  16  and a gear selector  18 . The controller  14  is an electronic device having a preprogrammed digital computer or processor, control logic, memory used to store data, and at least one I/O section. The control logic includes a plurality of logic routines for monitoring, manipulating, and generating data. The shift actuator  16  is coupled to the plurality of gear sets within the automatic transmission  12  and is operable to change the gear ratio. The gear selector  18  is selectively actuated by an operator of the motor vehicle to select one of the plurality of forward or reverse gear ratios. During operation, an operator manually operates the gear selector  18  to select different gear ratios, for example, a park, reverse, neutral, or forward gear ratio. This selection is communicated to the controller  14  and the controller  14  then activates the shift actuator  16  to change the gear ratio of the automatic transmission  12 . 
         [0028]    The brake system  10  further includes a plurality of sensors  20  coupled to the motor vehicle. The sensors  20  are in electronic communication with the processor of the controller  14 . The sensors  20  collect data regarding the operating parameters of the motor vehicle and generate output signals indicative of the vehicle operating parameters. These output signals are electronically communicated to the controller  14 . The controller  14  then continuously or periodically monitors the output signals. The output signals include information regarding a speed of the vehicle and an acceleration of the vehicle. The output signals may include other kinds of data, for example, battery voltage, engine temperature, or oil pressure. 
         [0029]    The brake system  10  includes a primary brake  22  and an auxiliary brake  24 . The primary brake  22  is used to reduce the speed of the vehicle and is preferably an operator actuated friction brake, though other brakes known in the art may be used. The primary brake  22  is in electronic communication with the controller  14  such that the controller  14  receives an output signal from the primary brake  22  indicating when the primary brake is engaged. The auxiliary brake  24  is a device used to reduce the speed of the vehicle and may include an exhaust brake, an exhaust compression brake, a variable nozzle turbocharger, a variable geometry turbocharger, an input retarder, an output retarder, or an electric motor. 
         [0030]    The auxiliary brake  24  is in electronic communication with the controller  14 . When extra braking is desired, the controller  14  sends a control signal to the auxiliary brake  24  and the auxiliary brake  24  is activated or engaged. 
         [0031]    The brake system  10  includes a throttle  26  in electronic communication with the controller  14 . The throttle  26  is coupled to an engine (not shown) in the motor vehicle. The throttle  26  preferably includes a pedal (not shown) and the operator may engage the throttle  26  by depressing the pedal when the operator desires to accelerate the motor vehicle. One of the plurality of sensors  20  then sends an output signal to the controller  14  indicating a position of the throttle  26 . Alternatively, the throttle  26  sends an electronic output signal to the controller  14  indicating a position of the throttle  26 . 
         [0032]    Turning now to  FIG. 2 , a method for braking  100  employing the braking system  10  is illustrated in flowchart form. The method for braking  100  begins at step  102  where the controller  14  monitors the output signals from the plurality of sensors  20 . The output signals include data such as vehicle acceleration, the position of the throttle  26 , and vehicle speed. 
         [0033]    A road grade is then calculated at step  104  by the controller  14 . Various methods for calculating the road grade may be employed. In the present invention, the road grade is calculated as a percent grade using the following formula: 
         [0000]      % Grade=( F   TractiveEffort   −m   veh   a   veh   −F   aero   −F   RollingResistance )/( m   veh   g )   (1) 
         [0034]    wherein F TractiveEffort  is the tractive effort of the motor vehicle, m veh  is the mass of the vehicle, a veh  is the vehicle acceleration, F aero  is an aerodynamic force, and F RollingResistance  is the force of rolling resistance of the motor vehicle, and g is the constant acceleration due to gravity. F TractiveEffort  is calculated using the following formula: 
         [0000]        F   TractiveEffort =( CTR* ( M   Engine −( I   Engine *ω Engine )− M   AuxBrake )* K   TransGearRatio   *K   Tire   *K   Axle )− F   PrimaryBrake    (2) 
         [0000]    wherein CTR is the converter torque ratio, M Engine  is the engine torque, I Engine  is the engine inertia, ω Engine  is the engine acceleration, M AuxBrake  is the auxiliary braking torque, K TransGearRatio  is a pre-set automatic transmission gear ratio factor, K Tire  is a pre-set tire factor, and K Axle  is a pre-set axle factor, and F PrimaryBrake  is the force of the primary brake  22 . F PrimaryBrake  is preferably zero as the road grade is preferably calculated when the primary brake  22  is not activated. F aero  is calculated using the following formula: 
         [0000]        F   aero   =v   veh   2   *K   DrafCoeff    (3) 
         [0035]    wherein v veh  is the vehicle speed and K DragCoeff  is a pre-set drag coefficient for the motor vehicle. F RollingResistance  is calculated using the following formula: 
         [0000]        F   RollingResistance   =m   veh   *K   RollingRes    (4) 
         [0036]    wherein K RollingRes  is a pre-set rolling resistance factor for the motor vehicle. 
         [0037]    At step  106 , the controller  14  compares the road grade calculated at step  104  to a road grade threshold. The road grade threshold is a value set to indicate whether the road grade is steep. If the road grade is not steep, the method  100  proceeds back to step  102  and the controller  14  continues to monitor the output signals from the plurality of sensors  20 . If the road grade calculated at step  104  exceeds the road grade threshold, the method  100  proceeds to step  108 . 
         [0038]    At step  108 , the controller  14  determines whether the vehicle is accelerating. Acceleration of the vehicle can be determined from the output signals from the plurality of sensors  20  or alternatively by calculation using a derivative of a transmission output speed multiplied by tire and axle factors. If the vehicle is not accelerating, the method  100  proceeds back to step  102  and the controller  14  continues to monitor the output signals from the plurality of sensors  20 . If the vehicle is accelerating, the method  100  proceeds to step  110 . 
         [0039]    At step  110 , the controller  14  determines whether the primary brake  22  has been activated by the operator of the motor vehicle. If the primary brake  22  has not been activated, this indicates that the operator does not desire to slow the vehicle, and the method  100  proceeds back to step  102  where the controller  14  continues to monitor the output signals from the plurality of sensors  20 . If the primary brake  22  has been activated, this indicates that the operator is attempting to slow the vehicle, and the method  100  proceeds to step  112 . 
         [0040]    At step  112  the controller  14  determines the desire for extra braking. As will be described in further detail below, determining the desire for extra braking involves analyzing and manipulating the data from the plurality of sensors  20  to determine the type or method of extra braking desired. 
         [0041]    Once it has been determined the type or method of extra braking desired, the extra braking is activated at step  114 . The controller  14  sends a signal to activate the auxiliary brake  24 , the shift actuator  16 , or both. The controller  14  will preferably activate the auxiliary brake  24  before activating the shift actuator  16 . 
         [0042]    At step  116  the controller  14  determines whether the throttle  26  has been engaged. If the throttle  26  has not been engaged, the method  100  continues to monitor the output signals from the plurality of sensors  20 . If the throttle  26  has been engaged, this indicates that the operator no longer wishes to brake, and the extra braking is deactivated at step  118 . The method  100  then continues to monitor the output signals from the plurality of sensors  20  at step  102 . 
         [0043]    Turning now to  FIG. 3 , a flowchart illustrating a method for determining the desire for extra braking at step  112  is provided. Step  112  begins by recording a plurality of times. First, at step  120 , the controller  14  records an amount of time that the acceleration of the vehicle (a first recorded amount of time) is greater than a threshold compensated by an acceleration magnitude. The threshold is a predetermined calibrated value correlating to vehicle acceleration. Preferably, the controller  14  includes in memory a lookup table that includes the threshold values indexed by the vehicle acceleration magnitude. Accordingly, the threshold is determined by selecting the threshold from the lookup table correlating to the vehicle acceleration magnitude. At step  122  the controller  14  records a second amount of time that the acceleration of the vehicle (a second recorded amount of time) is greater than a second threshold with the auxiliary brake  24  activated, compensated by the acceleration magnitude. The second threshold is determined in a manner similar to the threshold in step  120 . At step  124  the controller  14  records a third amount of time that the acceleration of the vehicle (a third recorded amount of time) is less than a third threshold. At step  126  the controller  14  records a fourth amount of time that the acceleration of the vehicle (a fourth recorded amount of time) is less than a fourth threshold with the auxiliary brake  24  activated. The third and fourth thresholds are pre-determined to help calibrate the desire for extra braking. At step  128  the controller  14  records a fifth amount of time that the primary brake  22  has been activated. 
         [0044]    At step  130  the controller  14  combines the road grade calculated at step  104  ( FIG. 2 ), the position of the throttle  26  and vehicle speed monitored at step  102  ( FIG. 2 ), the first recorded amount of time, the second recorded amount of time, the third recorded amount of time, the fourth recorded amount of time, and the fifth time to form a combined factor. These factors may be combined in any number of ways, including weighted sums, fuzzy logic, or normalization. In the preferred embodiment, these factors are normalized by the controller  14  to a number from 0 to 1 using calibration lookup tables stored in the memory of the controller  14 . The normalized factors are then weighted and combined into the combined factor. The combined factor is determined using the following formula: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0045]    wherein K 1 , K 2 , K 3 , K 4 , K 5 , K 6 , and K 7  are weight factors, min( ) is a minimization function, “a” is the percent grade, “b” is the first time, “c” is the second time, “d” is the fifth time, “e” is the third time, “f” is the fourth time, “g” is the position of the throttle  26 , and “h” is the vehicle speed. 
         [0046]    At step  132 , the combined factor is then compared to an auxiliary brake threshold and a downshift threshold. At step  134  the controller  14  determines whether to activate the auxiliary brake  22 , whether to activate the shift actuator  16  to change the gear ratio of the automatic transmission  12  (i.e. downshift), or whether to activate both the auxiliary brake  22  and the shift actuator  16 . In the preferred embodiment, when the combined factor is greater than the auxiliary brake threshold, the controller  14  determines that it is desirable to activate the auxiliary brake  24 . If the combined factor is greater than the downshift threshold, the controller  14  determines that it is desirable to activate the shift actuator  16  to downshift the automatic transmission  12 . Alternatively, when the downshift threshold is calibrated to be greater than the auxiliary brake threshold and the combined factor is greater than the downshift threshold, the controller  14  determines that it is desirable to activate both the auxiliary brake  24  and the shift actuator  16  to downshift the automatic transmission  12 . Once the controller  14  determines the desire for extra braking at step  112 , the method  100  continues to step  114  ( FIG. 2 ) and activates the extra braking. 
         [0047]    Using the braking system  10  and braking method  100  of the present invention, extra braking can be activated automatically based on various factors and operating parameters of the vehicle. Moreover, the present invention allows various kinds and combinations of extra braking to be automatically employed to more efficiently brake the vehicle. Thus, the present braking system and method thereby allows the operator of the motor vehicle to focus on operating the vehicle rather than manually activating extra braking. 
         [0048]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.