Abstract:
A system and method for detecting a rollover of a vehicle that includes at least one wheel reaction force sensing device for transmitting wheel reaction force signals indicative of an amount of force exerted on at least one wheel of the vehicle is provided. The system includes a controller operably coupled to the at least one wheel reaction force sensing device and including at least one accelerometer sensor for transmitting acceleration signals. The controller is configured to determine a first force index in response to the wheel reaction force signals, determine a first lateral acceleration of the vehicle in response to the acceleration signals, compare the first force index to a threshold force index and the first lateral acceleration to a threshold lateral acceleration, and deploy a restraint system based on the comparison.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The embodiments of the present invention generally relate to a vehicle rollover accident detection. 
         [0003]    2. Background Art 
         [0004]    The number of fatal accidents each year in the U.S. has hovered at about 40,000 for a decade. Safety organizations, the government, and industry are working diligently to reduce that number to 30,000. Rollover based accidents account for about 30% of light-vehicle fatal accidents. A portion of vehicle rollovers may be attributed to ‘hard trips’ where a vehicle enters into a rollover state after traveling over a curb or obstacle. Other such vehicle rollovers may be attributed to ‘soft trips’ where a vehicle enters into a rollover state after traveling over sand or grass lands. 
         [0005]    In view of the number of fatalities associated with rollover accidents, original equipment manufactures (OEMs) are continuing to develop sensing algorithms to detect vehicle rollovers and implementing various advanced restraint systems to mitigate injuries of occupants from being ejected while the vehicle encounters a roll over event. 
       SUMMARY 
       [0006]    In at least one embodiment, a system for detecting a rollover of a vehicle that includes at least one wheel reaction force sensing device positioned about at least one wheel of the vehicle for transmitting wheel reaction force signals indicative of an amount of force exerted on the at least one of the wheels of the vehicle is provided. The system includes a controller operably coupled to the at least one wheel reaction force sensing device and at least one accelerometer sensor for transmitting acceleration signals indicative of vehicle body accelerations about at least one axis of the vehicle. The controller is configured to determine a first force index in response to the wheel reaction force signals, determine a first lateral acceleration of the vehicle in response to the acceleration signals, compare the first force index to a threshold force index and the first lateral acceleration to a threshold lateral acceleration, and deploy a restraint system based on a comparison of the first force index to the threshold force index and the lateral acceleration to the threshold lateral acceleration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  depicts a quarter-model vehicle suspension in a steady-state condition; 
           [0008]      FIG. 2  depicts a roll reaction on a suspended vehicle; 
           [0009]      FIG. 3  depicts wheel reaction forces in accordance to one embodiment of the present invention; 
           [0010]      FIG. 4  depicts a rollover detection system in accordance to one embodiment of the present invention; 
           [0011]      FIG. 5  depicts a first rollover detection scheme in accordance to one embodiment of the present invention; 
           [0012]      FIG. 6  depicts a force index and lateral acceleration threshold plot in accordance to one embodiment of the present invention; 
           [0013]      FIG. 7  depicts a second rollover detection scheme in accordance to one embodiment of the present invention; 
           [0014]      FIG. 8  depicts a force index and roll rate threshold plot in accordance to one embodiment of the present invention; and 
           [0015]      FIG. 9  depicts a force index and roll angle plot in accordance to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring now to  FIG. 1 , a quarter-model vehicle suspension  10  in a steady-state condition is shown. The dynamic behavior for the quarter-model vehicle suspension  10  may be obtained by applying Newton&#39;s second law for the sprung and unsprung mass as shown in  FIG. 1 . For example, the equation of motion for the unsprung mass is: 
         [0000]        M{umlaut over (Z)}   u   +C   s   Ż   u +( K   s   +K   t ) Z   u   =C   s   Ż+K   s   Z+K   s   Z   r   +F   w   (EQ. 1) 
         [0000]    where, M=mass,
       Z=sprung mass displacement,   Z u =unsprung mass displacement,   Z r =road displacement,   F w =force on the unsprung mass,   K s =suspension stiffness,   K t =wheel stiffness, and   C s =suspension damping coefficient.
 
EQ. 1 may be simplified by neglecting higher order items. In light of such, the force on the unsprung mass may be rewritten as:
       
 
         [0000]        F   w   ≈f ( Z,Z   u   ,Z   r )=( K   s   +K   t ) Z   u   −K   s   Z−K   t   Z   r +errs  (EQ. 2) 
         [0024]    In general, the loads (or force on the unsprung mass) are equivalent between left and right sides of the vehicle when the vehicle is on a horizontal surface with steady movement. However, the loads on the unsprung mass are different (e.g., between the left and right side of the vehicle) when the vehicle experiences a rollover event. In such a case, the vehicle may be unstable and lean to roll one side of the vehicle. The load on the leaned side of the vehicle may be high, while the load on the other side of the vehicle may be close to zero. 
         [0025]    Referring now to  FIG. 2 , a roll reaction on a suspended vehicle  12  is generally shown. The suspended vehicle  12  includes a body section  14  that is represented by a mass, m. A plurality of springs  16  and  18  are coupled to the body section  14 . The springs  16 ,  18  couple the body section  14  to an axle  20  having wheels  22 ,  24 . The body section  14  of the vehicle  12  includes a roll center which provides a pivot point for the body section  14  in which lateral forces are transferred from the axle  20  to the mass. By taking moments about a point where the wheel  24  contacts the ground and assuming the trailing side load of the wheel  22  (e.g., wheel off of the ground) is equal to zero provides the following: 
         [0000]    
       
         
           
             
               
                 
                   
                     ∑ 
                     
                       M 
                       o 
                     
                   
                   = 
                   
                     0 
                     = 
                     
                       
                         
                           ma 
                           y 
                         
                          
                         h 
                       
                       - 
                       
                         m 
                          
                         
                             
                         
                          
                         
                           g 
                            
                           
                             [ 
                             
                               
                                 t 
                                 2 
                               
                               - 
                               
                                 φ 
                                  
                                 
                                   ( 
                                   
                                     h 
                                     - 
                                     
                                       h 
                                       r 
                                     
                                   
                                   ) 
                                 
                               
                             
                             ] 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    From EQ. 3, the lateral acceleration (e.g., a,/g) is found to be: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       a 
                       y 
                     
                     g 
                   
                   = 
                   
                     
                       t 
                       
                         2 
                          
                         h 
                       
                     
                     - 
                     
                       φ 
                        
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               h 
                               r 
                             
                             h 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    As shown in EQ. 4, an unstable lateral acceleration generally depends on vehicle track width t, center of gravity (g), height h, the roll center h r  and roll angle φ. 
         [0026]    As exhibited above, lateral acceleration plays a role during rollover crashes. While front forces on the vehicle are discussed, rear forces on the rear of the vehicle or a combination of front and rear forces on the entire vehicle are equally contemplated. The wheel  24  at the leading side of the vehicle (e.g., the leading side of the vehicle may include one wheel at the front of the vehicle or two or more wheels at the front and rear of the vehicle) may receive an early and larger force than the wheel  22  at the trailing side of the vehicle (e.g., the trailing side of the vehicle may include one wheel at the front of the vehicle or two or more wheels at the front and rear of the vehicle) whether the vehicle is in a trip (e.g., hard or soft) rollover event. For example, a mean value of the forces acting on both sides of the front of the wheels (e.g., left and right) or to both sides of the front and rear wheels (e.g., left and right) may be measured as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     F 
                     mean 
                   
                   = 
                   
                     
                       
                         F 
                         zl 
                       
                       + 
                       
                         F 
                         zr 
                       
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     5 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where, F mean  corresponds to a mean value of force at the wheels before a rollover event is detected. F zl  may correspond to left wheel reaction forces that act on the left wheel on the front of the vehicle or to two or more left wheels on both the front and rear of the vehicle. left and right wheel reaction forces that act on the wheels on the front and the rear of the vehicle. F zr  may correspond to right wheel reaction forces that act on the right wheel on the front of the vehicle or to two or more right wheels on both the front and rear of the vehicle. In general, a wheel reaction force is the load transmitted through the wheel(s) (e.g., the tire, rim and/or suspension components due to the sprung mass). A force index may be calculated by: 
         [0000]    
       
         
           
             
               
                 
                   
                     index 
                     F 
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 F 
                                 zl 
                               
                               + 
                               
                                 F 
                                 zr 
                               
                               - 
                               
                                 2 
                                  
                                 
                                   F 
                                   mean 
                                 
                               
                             
                             
                               F 
                               mean 
                             
                           
                         
                         
                           
                             
                               where 
                                
                               
                                   
                               
                                
                               
                                 index 
                                 f 
                               
                             
                             ≥ 
                             0 
                           
                         
                       
                       
                         
                           0 
                         
                         
                           
                             
                               where 
                                
                               
                                   
                               
                                
                               
                                 index 
                                 f 
                               
                             
                             &lt; 
                             0 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where, in one example, index F  is generally a value that is larger than zero and less than two. In the event index F  is larger than 0.5, then one or both wheels on the left side may be lifted from the ground and the other such wheel(s) on the right side may be in contact with the road. Likewise, in the event index F  is larger than 0.5, then one or both wheels on the right side may be lifted from the ground and the other such wheel or wheels on the left side may be in contact with the ground. If index F  is zero, then the vehicle may be considered to be airborn. 
         [0027]      FIG. 3  illustrates wheel reaction forces for wheels at the front side of the vehicle. Values that correspond to a wheel reaction force at the leading side of the left front wheel (e.g., F zl , see EQ. 5) are generally shown at  25 . Values that correspond to a wheel reaction force at the trailing side of the left front wheel (e.g., F zr , see EQ. 5) are generally shown at  27 . Values that correspond to a pre-calculated average of a wheel reaction force (e.g., F mean , see EQ. 5) are generally shown at  29 . 
         [0028]    In general, the system and schemes as set forth herein to detect vehicle rollover events may take into account both the index F  and lateral acceleration to determine whether the vehicle is experiencing a rollover event. The index F  and lateral acceleration may provide an early detection that the vehicle is experiencing a hard or soft trip rollover event. In addition, other characteristics such as the roll rate and the roll angle may serve as an early indication to detect whether the vehicle is experiencing a vehicle rollover. 
         [0029]    Referring now to  FIG. 4 , a rollover detection system  30  in accordance to one embodiment of the present invention is shown. The system  30  includes a restraint controller  32  and a suspension controller  34 . A multiplexed communication bus  36  is operably coupled between the restraint controller  32  and the suspension controller  34  to facilitate data communication therebetween. The bus  36  may be implemented as either a high or medium speed control area network (CAN) communication data link. The bus  36  may be implemented as any such communication data link generally situated to transmit data between any two controllers in a vehicle. 
         [0030]    A plurality of wheel reaction force sensing devices  38   a - 38   n  are in electrical communication with the suspension controller  34 . Each wheel reaction force sensing device  38   a - 38   n  is generally positioned about the suspension system at each wheel/tire of the vehicle. In general, the wheel reaction force sensing devices  38   a - 38   n  are generally configured to sense the force associated with various loads applied at one or more wheels of the vehicle. The suspension controller  34  receives such information to determine the wheel reaction force (e.g., F zl  and F zr ) for each wheel. In another example, the wheel reaction force sensing devices  38   a - 38   n  may measure signals from a pressure sensor and/or acceleration sensors and transmit such data directly to the suspension controller  34  to determine the wheel reaction force for each wheel. Other such examples of wheel reaction force sensing devices  38   a - 38   n  may include a pressure sensor positioned in an active air suspension that may measure the force, a strain gauge, wheel lateral force sensors, longitudinal wheel force sensors, a vertical tire force sensor, a tire acceleration sensor, or a tire sidewall torsion sensor. 
         [0031]    As noted above in connection with  FIG. 2 , the suspension controller  34  may include F mean  (e.g., the mean value of force at the front wheels and/or the rear wheels of the vehicle before a rollover event) stored in memory therein. The suspension controller  34  may calculate the force index (e.g., see EQ. 6) for the wheels at the front and/or the rear of the vehicle in response to such information and transmit such information over the bus  36  to the restraint controller  32 . 
         [0032]    The restraint controller  32  includes a plurality of accelerometer sensors  40  positioned therein. The accelerometer sensors  40  are configured to measure car body accelerations about the x-axis (longitudinal acceleration), the y-axis (lateral acceleration), and z-axis (vertical acceleration). For illustrative purposes, a right hand coordinate system may be superimposed on the vehicle. The x-axis of the vehicle may be defined as the axis extending between the fore and aft portions of the vehicle. The positive direction of the x-axis may be the direction pointing towards the front of the vehicle. The y-axis of the vehicle may be defined as the axis extending from the passenger side of the vehicle to the driver side of the vehicle (e.g., the axis extending the width of the vehicle). The z-axis of the vehicle may be defined as the axis extending from the bottom to top of the vehicle. The positive directions of the y-axis and z-axis are considered to be pointing towards the driver side and in an upward direction, respectively. 
         [0033]    In reference to the lateral acceleration, the accelerometer sensors  40  may present hardwired data which correspond to the lateral acceleration of the vehicle body to the restraint controller  32 . The restraint controller  32  may calculate the lateral acceleration as noted in connection with EQ. 4. The restraint controller  32  may use the lateral acceleration and the force index as an indicator to determine if the vehicle is in a rollover event. The restraint controller  32  may deploy a restraint system to protect the occupants of the vehicle in response to the lateral acceleration and the force index exceeding predetermined thresholds. The restraint system may include curtain and/or side impact airbags that are utilized to protect the occupant. 
         [0034]    The restraint controller  32  further includes a roll rate sensor  42  positioned therein. The roll rate sensor  42  may measure the roll rate of the vehicle. In general, the roll rate of the vehicle is defined as the angular velocity of the vehicle as the vehicle rotates about the x-axis of the vehicle. The restraint controller  32  may calculate the roll angle φ of the vehicle (as discussed in connection with  FIG. 2 ) in response to receiving the roll rate from the roll rate sensor  42 . The restraint controller  32  may use the force index and any one or more of the lateral acceleration, the roll angle, and the roll rate of the vehicle to determine when the vehicle is in a roll over state. 
         [0035]    Referring now to  FIG. 5 , a first rollover detection scheme  50  in accordance to one embodiment of the present invention is shown. In block  52 , the restraint controller  32  receives the measured roll rate of the vehicle from the roll rate sensor  42  and filters and conditions such information to determine the roll rate. 
         [0036]    In block  54 , the restraint controller  32  determines whether the detected roll rate of the vehicle has exceeded a predetermined roll rate value. Such a value may be stored in memory of the restraint controller  32 . The predetermined roll rate value may be a calibrated value and vary based on the type of vehicle that is used. The restraint controller  32  compares the roll rate to the predetermined roll rate value. If the roll rate is not greater than the predetermined roll rate value, then the scheme  50  moves to back to block  52 . If the roll rate is greater than the predetermined roll rate value, then the scheme  50  moves to blocks  56  and  58 . 
         [0037]    In block  56 , the restraint controller  32  calculates F mean  as noted above in connection with EQ. 5. The restraint controller  32  receives F zl  and F zr  from the suspension controller  34  over the bus  36 . 
         [0038]    In block  60 , the restraint controller  32  calculates the force index as noted above in connection with EQ. 6. 
         [0039]    In block  62 , the restraint controller  32  determines the lateral acceleration. The restraint controller  32  calculates the lateral acceleration in response to information transmitted by the accelerometer sensors  40  (see EQ. 4). 
         [0040]    In block  64 , the restraint controller  32  determines whether the calculated force index and lateral acceleration exceed force index thresholds and lateral acceleration thresholds, respectively.  FIG. 6  depicts the force index thresholds and the lateral acceleration thresholds at  90 . The force index and lateral acceleration thresholds are generally calibrated values and may vary (e.g., may be different than that shown in  FIG. 6 ) depending on the type of vehicle used. The thresholds  90  for the force index and later acceleration may be achieved by the following: 
         [0000]    
       
         
           
             
               
                 
                   y 
                   = 
                   
                     
                       b 
                       ( 
                       
                         1 
                         - 
                         
                           
                             x 
                             2 
                           
                           
                             a 
                             2 
                           
                         
                       
                       ) 
                     
                     c 
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     7 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where variables a and b are derived (or obtained) in response to performing vehicle rollover tests for a particular vehicle. The variable a and b may vary based on the type of vehicle used. Variables x and y may correspond to the values of the lateral acceleration and the force index, and c is a constant that may vary based on a threshold request. 
         [0041]    Values corresponding to the calculated force index and the lateral acceleration that may be indicative of the vehicle being in a rollover state is generally shown at  92 . Values corresponding to the calculated force index and the lateral acceleration that may be indicative of the vehicle not being in a rollover state is generally shown at  64 . 
         [0042]    In reference to  FIG. 5 , while blocks  56 ,  60 ,  62 , and  64  are being executed, blocks  58  and  66  may be executed simultaneously for validation purposes to confirm that the vehicle is in a rollover state. In general, blocks  58  and  66  may be executed as a secondary measure to ensure that the vehicle is in a rollover state. 
         [0043]    In block  58 , the restraint controller  32  also performs a safing function. With such an operation, the restraint controller  32  determines the lateral acceleration and the vertical acceleration to determine whether such values are indicative of the vehicle being in a rollover state. 
         [0044]    In block  66 , the restraint controller  32  determines whether the lateral acceleration and the vertical acceleration exceed predefined safing values (e.g., predefined lateral and vertical acceleration safing values). The predefined lateral acceleration safing values are values that may or may not be different from the lateral acceleration threshold as noted in connection with block  64 . If the lateral acceleration and the vertical acceleration do not exceed the predefined safing values, then the scheme  50  moves back to block  58 . If the lateral acceleration and the vertical acceleration exceed the predefined safing values, then the scheme  50  moves to block  68 . 
         [0045]    In block  68 , the restraint controller  32  determines whether the calculated force index and the lateral acceleration exceed the force index threshold and the lateral acceleration threshold, respectively, and whether the lateral acceleration and the vertical acceleration exceed the predefined safing values. If both conditions have been met, then the scheme  50  moves to block  70 . If none or only one of the conditions of blocks  64  and  66  has been met, then the scheme  50  moves back to the start state. 
         [0046]    In block  70 , the restraint controller  32  deploys the advanced restraint system to protect the occupant(s). 
         [0047]    Referring now to  FIG. 7 , a second rollover detection scheme  100  in accordance to one embodiment of the present invention is shown. Blocks  52 ,  54 ,  56 ,  58 ,  60  and  66  are similar to the blocks  52 ,  54 ,  56 ,  58 ,  60  and  66  of  FIG. 5 . 
         [0048]    In block  102 , the restraint controller  32  obtains the roll rate of the vehicle in response to information sent by the roll rate sensor  42 . Block  102  is generally similar to the operation performed in block  52 . 
         [0049]    In block  104 , the restraint controller  32  determines whether the calculated force index and the roll rate exceed the force index threshold and the roll rate threshold, respectively.  FIG. 8  depicts the force index threshold and the roll rate threshold at  150 . The force index threshold and the roll rate threshold are generally calibrated values and may vary (e.g., may be different than those shown in  FIG. 8 ) depending on the type of vehicle used. As noted above, the thresholds  150  for the force index and roll rate may each be derived by using EQ. 7. 
         [0050]    Variables x and y as shown in accordance to EQ. 7 may correspond to the values of the roll rate and the force index. Variables a and b are derived (or obtained) in response to performing vehicle rollover tests for a particular vehicle and c is a constant that may vary based on the threshold requirement (e.g., if c is less than 1, such a condition may correspond to an upper lobe  152  as shown in  FIG. 8 , if c is larger than 1, such a condition may correspond to lower lobe  153  as shown in  FIG. 8 ). 
         [0051]    Values corresponding to the calculated force index and the roll rate that may be indicative of the vehicle being in a rollover state are generally shown at  152  in  FIG. 8 . Values corresponding to the calculated force index and the roll rate that may be indicative of the vehicle not being in a rollover state are generally shown at  154  in  FIG. 8 . 
         [0052]    In block  106 , the restraint controller  32  determines whether the calculated force index and the roll rate exceed the force index threshold and the roll rate threshold and whether the lateral acceleration and the vertical acceleration exceed predefined safing values. If both conditions have been met, then the scheme  100  moves to block  108 . If none or only one of the conditions has been met, then the scheme  100  moves back to the start state. 
         [0053]    In block  108 , the restraint controller  32  deploys the advanced restraint system to protect the occupant(s). 
         [0054]    In another embodiment, references to the roll rate as noted in connection with blocks  102 ,  104 , and  106  may be replaced with the roll angle. For example, the block  102  may calculate the roll angle of the vehicle as opposed to the roll rate of the vehicle. The roll angle is generally defined as angular rotation of the vehicle body. The roll rate is generally the angular velocity of the vehicle body. In contrast to having a roll rate threshold (see block  104 ), the roll angle threshold may be established along with the force index threshold. In such an example, the restraint controller  32  may determine whether the calculated force index and the calculated roll angle exceed the force index threshold and the roll angle threshold, respectively, as shown at  200  in  FIG. 9 .  FIG. 9  depicts the force index threshold and the roll angle threshold at  200 . The force index threshold and the roll angle threshold are generally calibrated values and may vary (e.g. may be different than that shown in  FIG. 9 ) depending on the type of vehicle used. The thresholds  200  for the force index and the roll angle may each be derived by EQ. 7 as stated above. 
         [0055]    Values corresponding to the calculated force index and the roll angle that may be indicative of the vehicle being in a rollover state is generally shown at  202 . Values corresponding to the calculated force index and the calculated roll angle that may be indicative of the vehicle not being in a rollover state is generally shown at  204 . 
         [0056]    While embodiments of the present invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.