Abstract:
A system and method of activating a restraint system of a vehicle is described. The method includes generating a vehicle speed signal that represents a longitudinal speed of a vehicle, generating a lateral acceleration signal that represents a lateral acceleration of the vehicle, filtering the lateral acceleration signal to generate a filtered lateral acceleration signal, comparing the filtered lateral acceleration signal to a predetermined lateral acceleration enable threshold, estimating a lateral speed of the vehicle based on the vehicle speed signal when the filtered lateral acceleration exceeds the predetermined lateral acceleration enable threshold, and activating a restraint system of the vehicle based in part on the estimated lateral velocity.

Description:
FIELD 
     The present disclosure relates to vehicle rollover detection systems, and more particularly to inferring a rollover based on vehicle speed. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Modern road vehicles may include a roll over detection system. The system detects when the vehicle is about to roll over and then activates one or more safety devices in an attempt to mitigate injury to vehicle occupants. Examples of safety devices include side air bags and curtains, seat belt pretensioners, active roll bars, and the like. 
     SUMMARY 
     A method of activating a restraint system of a vehicle is described. The method includes generating a vehicle speed signal that represents a longitudinal speed of a vehicle, generating a lateral acceleration signal that represents a lateral acceleration of the vehicle, filtering the lateral acceleration signal to generate a filtered lateral acceleration signal, comparing the filtered lateral acceleration signal to a predetermined lateral acceleration enable threshold, estimating a lateral speed of the vehicle based on the vehicle speed signal when the filtered lateral acceleration exceeds the predetermined lateral acceleration enable threshold, and activating a restraint system of the vehicle based in part on the estimated lateral velocity. 
     In other features the method includes resetting the estimated lateral speed to a predetermined value when the filtered lateral acceleration signal is less than a reset lateral acceleration threshold for a predetermined duration. The method includes monitoring a vehicle network status and employing a predetermined value for the estimated lateral speed while the vehicle network status indicates that the vehicle speed signal is in a fault condition. Activating the restraint system is further based on a roll rate sensor signal. Activating the restraint system is further based on a lateral acceleration sensor signal. Activating the restraint system is further based on a vertical acceleration sensor signal. 
     A control system for activating a restraint system of a vehicle includes a vehicle speed sensor that generates a vehicle speed signal based on longitudinal speed of a vehicle, a lateral acceleration sensor that generates a lateral acceleration signal based on lateral acceleration of the vehicle, a filter that filters the lateral acceleration signal to generate a filtered lateral acceleration signal, a comparator that compares the filtered lateral acceleration signal to a predetermined lateral acceleration enable threshold, and a processor that estimates a lateral speed of the vehicle based on the vehicle speed signal when the filtered lateral acceleration exceeds the predetermined lateral acceleration enable threshold, and a restraint system that is activated based in part on the estimated lateral velocity. 
     In other features the processor resets the estimated lateral speed to a predetermined value when the filtered lateral acceleration signal is less than a reset lateral acceleration threshold for a predetermined duration. The processor monitors a vehicle network status and employs a predetermined value for the estimated lateral speed while the vehicle network status indicates that the vehicle speed signal is in a fault condition. A roll rate sensor communicates with the processor and the restraint system is activated based on a roll rate sensor signal. A lateral acceleration sensor communicates with the processor and the restraint system is activated based on a lateral acceleration sensor signal. A vertical acceleration sensor communicates with the processor and the restraint system is activated based on a vertical acceleration sensor signal. 
     A control system for activating a restraint system of a vehicle includes vehicle speed sensing means for generating a vehicle speed signal based on longitudinal speed of a vehicle, lateral acceleration sensing means for generating a lateral acceleration signal based on lateral acceleration of the vehicle, filter means for filtering the lateral acceleration signal to generate a filtered lateral acceleration signal, comparator means for comparing the filtered lateral acceleration signal to a predetermined lateral acceleration enable threshold, processor means for estimating a lateral speed of the vehicle based on the vehicle speed signal when the filtered lateral acceleration exceeds the predetermined lateral acceleration enable threshold and for resetting the estimated lateral speed to a predetermined value when the filtered lateral acceleration signal is less than a reset lateral acceleration threshold for a predetermined duration, and restraint system means for activating a passenger restraint system based in part on the estimated lateral velocity. 
     In other features the processor monitors a vehicle network status and employs a predetermined value for the estimated lateral velocity while the vehicle network status indicates that the vehicle speed signal is in a fault condition. Roll rate sensor means communicate with the processor and the restraint system is activated based on a filtered roll rate sensor signal. Lateral acceleration sensor means communicate with the processor and the restraint system is activated based on a filtered lateral acceleration sensor signal. Vertical acceleration sensor means communicate with the processor and the restraint system is activated based on a filtered vertical acceleration sensor signal. 
     In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a computer readable medium such as but not limited to memory, non-volatile data storage and/or other suitable tangible storage mediums. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of a rollover detection system in a vehicle; 
         FIG. 2  is a logic diagram of a rollover detection method that uses estimated lateral velocity of a vehicle as an input to influence performance; 
         FIG. 3  is a logic diagram of a first embodiment of a method to estimate the lateral velocity of a vehicle; and 
         FIG. 4  is a logic diagram of a first rollover detection algorithm that employs the estimated lateral velocity. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and computer readable memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , a functional block diagram is shown of a vehicle  10 . Vehicle  10  includes a rollover detection system that employs vehicle speed along a longitudinal axis x (shown at coordinate system  24 ) to help detect a rollover. The rollover detection system includes a control module  12  that receives data from one or more sensors. Control module  12  determines whether vehicle  10  is rolling over based on the data and activates a restraints system  14  based on the determination. Restraints system  14  can include one or more of side air bags, side curtains, seat belt pretensioners, active roll bars, and the like. The sensors include a vertical acceleration sensor  16 , a lateral acceleration sensor  20 , and a roll rate sensor  22 . 
     Vertical acceleration sensor  16  generates a signal based on acceleration of vehicle  10  in the z direction as indicated by coordinate system  24 . Longitudinal acceleration sensor  18  generates a signal based on acceleration of vehicle  10  in the x direction as indicated by coordinate system  24 . Lateral acceleration sensor  20  generates a signal based on acceleration of vehicle  10  in the y direction as indicated by coordinate system  24 . Roll rate sensor  22  generates a signal based on angular rate of vehicle  10  about the longitudinal or x axis of vehicle  10 . 
     Control module  12  also receives a vehicle speed signal  26 . Vehicle speed signal  26  can be generated by a vehicle speed sensor as is known in the art and represents the speed of a wheel  28 . Control module  12  also includes a processor  30 , a timer module  32 , and memory  34 . Processor  30  executes methods that are described below. Timer module  32  implements various timers that are employed by the methods. Memory  34  stores computer instructions that implement the methods and executed by processor  30 . 
     Referring now to  FIG. 2 , a functional block diagram is shown of a method  50 . Method  50  employs the estimated lateral velocity that is determined by the vehicle speed signal  26 . The estimated lateral velocity is used to supplement data from roll rate sensor  22  and more quickly determine whether vehicle  10  is rolling over than if roll rate sensor  22  were employed alone. 
     Method  50  simultaneously evaluates the data from lateral acceleration sensor  20 , vehicle speed signal  26 , and roll rate sensor  22  to determine whether to activate restraints system  14 . The data from lateral acceleration sensor  20  is analyzed to determine whether the forward motion (x-axis) of vehicle  10  has converted to sliding motion (y-axis). To make the determination, block  54  determines whether the lateral acceleration “a” (y-axis) exceeds a predetermined lateral acceleration “a 2 ”. In some embodiments the predetermined lateral acceleration “a 2 ” is about 1.0 g. When the lateral acceleration “a” exceeds the predetermined lateral acceleration “a 2 ” then block  54  provides a logic true condition to a first input of an AND gate  60 . Otherwise block  54  communicates a logic false condition to the first input of AND gate  60 . 
     Block  56  determines whether the vehicle lateral acceleration is greater than a predetermined acceleration a 1 (v). The predetermined acceleration can be based on the vehicle speed signal  26 . If the vehicle lateral acceleration exceeds the predetermined acceleration then block  56  communicates a logic true condition to a second input of AND gate  60 . Otherwise block  56  communicates a logic false condition to the second input of AND gate  60 . 
     Block  58  evaluates the data from roll rate sensor  22  and vehicle signal  26 . Block  58  determines whether the roll rate ω exceeds a predetermined roll rate ω 1 (v). The predetermined roll rate can be based on the vehicle speed signal  26 . If the roll rate exceeds the predetermined roll rate then block  58  communicates a logic true condition to a third input of AND gate  60 . Otherwise block  58  communicates a logic false condition to the third input of AND gate  60 . When all three inputs to AND gate  60  are logic true then restraints system  14  is activated to mitigate effects of the vehicle rollover. 
     Referring now to  FIG. 3 , a logic diagram is shown of a method  100 . Method  100  estimates how much, if any, of vehicle  10  longitudinal velocity V x  has translated to a lateral velocity V y . A low pass filter  102  filters the signal from lateral acceleration sensor  20 . The filtered signal is communicated to a first input of a comparator  104  and a first input of another comparator  106 . Comparator  104  generates a logic true signal while the lateral acceleration is less than a first predetermined lateral acceleration or reset threshold. Comparator  106  generates a logic true signal while the lateral acceleration is greater than a second predetermined lateral acceleration or enable threshold. 
     A comparator  108  generates a logic true signal while the lateral velocity V y  is equal to zero. The outputs of comparators  106  and  108  are applied to an input of an AND gate  110 . An output of AND gate  110  generates a logic true while the filtered lateral acceleration from lateral acceleration sensor  20  is high and the estimated lateral velocity V y  is still zero, e.g. vehicle  10  is decelerating laterally with a level higher than most road surfaces will allow. 
     A slope limitation module  112  generates an interim value of V x  based on vehicle speed V x , which is provided by vehicle speed signal  26 . Slope limitation module  112  limits the interim value of V x  based on predetermined deceleration and acceleration thresholds. The deceleration and acceleration thresholds can be determined experimentally and in some embodiments are about 1.1 g and 1.0 g, respectively. While the output of AND gate  110  is true, an estimator module  114  latches V y  with the interim value of V x  and initializes a reset timer to a predetermined reset time. The reset timer can be implemented with timer module  32 , which is best shown in  FIG. 1 . An output of estimator module  114  communicates the estimated value of V y . 
     A process for resetting V y  will now be described. A comparator  120  generates a logic true signal while the reset timer is counting, i.e. not expired. The output of comparator  120  is communicated to an input of an AND gate  122 . A second input of AND gate  122  is communicated from the output of comparator  104 . The output of AND gate  122  therefore generates a logic true while the filtered lateral acceleration is less than the predetermined reset threshold and the reset timer is active. Block  124  decrements the reset timer so long as the output of AND gate  122  is true. 
     A comparator  126  outputs a logic true signal when the reset timer has expired, e.g. counted down to zero. When the reset timer expires a logic switch  130  resets the estimated lateral velocity V y  to zero. 
     The output of logic switch  130  communicates with an input of another logic switch  132 . Logic switch  132  provides a default value for the lateral estimated velocity in the event the vehicle speed signal  26  is lost. In the depicted embodiment vehicle speed signal  26  is communicated via a controller area network (CAN) bus as is known in the art. A CAN bus status signal  134  indicates whether the CAN bus is communicating vehicle speed signal  26  and also controls logic switch  132 . The output of logic switch  132  communicates the estimated lateral velocity to rollover sensing algorithms that are described below. 
     Referring now to  FIG. 4 , a logic diagram is shown of a first rollover detection method  200  that employs the estimated lateral velocity V y  from method  100 . When properly calibrated, method  200  activates restraints system  14  when vehicle rollover is predicted. 
     Lateral velocity V y  is communicated to respective inputs of a comparator  202  and a comparator  204 . Comparator  202  outputs logic true when the lateral velocity V y  is less than a V y  max threshold  206 , i.e. a predetermined maximum lateral velocity. Comparator  204  outputs logic true when the lateral velocity V y  is greater than a V y  min threshold  208 , i.e. a predetermined minimum lateral velocity. An AND gate  210  logically ANDs the outputs of comparators  202  and  204 . The output of AND gate  210  is logical true when the lateral velocity V y  is between the min and max thresholds  206 ,  208 , which indicates that lateral motion of vehicle  10  is plausible. A logic switch  212  communicates either a logic true or the output of AND gate  210  to an input of an AND gate  214 . Logic switch  212  is controlled by a configuration setting that indicates whether method  200  should employ the estimated lateral velocity V y  in determining a roll over condition. 
     A rollover detection module  216  communicates a signal to a second input of AND gate  214 . Rollover detection module  216  receives respective signals from one or more of vertical acceleration sensor  16 , lateral acceleration sensor  20 , and roll rate sensor  22 . Based on the signals, rollover detection module  216  employs methods known in the art to determine whether vehicle  10  is rolling over. If it is determined that vehicle  10  is rolling over then rollover detection module  216  communicates a logic true to the second input of AND gate  214 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.