Patent Publication Number: US-8116949-B2

Title: Method and device for determining an initial float angle for skid detection in rollover sensing

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and a device for determining an initial float angle for skid detection in rollover sensing. 
     BACKGROUND INFORMATION 
     German Patent Application Nos. DE 100 19 416 A1, DE 100 19 417 A1, and DE 100 19 418 A1 describe general concepts for rollover sensing using methods and devices based on the analysis of a yaw rate sensor and two acceleration sensors which are integrated in the central airbag control unit. The yaw rate sensor ascertains, by the gyroscopic principle, the rotation rate about the longitudinal axis of the vehicle; in addition, the acceleration sensors measure the acceleration of the vehicle in the direction of the transverse and vertical axes of the vehicle. The yaw rate is analyzed in the main algorithm. Using the measured values of the acceleration sensors, the type of rollover may be recognized, and these values are also used for plausibility checking. If the yaw rate algorithm detects a rollover, safety measures are activated only if they are enabled by the plausibility check at the same time. 
     A timely deployment decision in the event of a rollover at a high lateral acceleration by taking into account a float angle and a transverse velocity of the vehicle, as well as a vehicle tipping motion, is described in German Patent Application No. DE 101 49 112 A1. 
     However, the float angle and therefrom the lateral velocity as needed for rollover detection are not determinable by conventional methods such as used in vehicle dynamics control, for example, in an angle range greater than 20°. These methods, such as those using a model from tire characteristics and lateral force, for example, are suitable only for angle ranges of less than 10°. The reason for the small validity range is that vehicle dynamics control may no longer be successfully performed at larger float angles. 
     German Patent Application No. DE 102 39 406 A1 describes a device for determining float angles greater than 20° and the lateral velocity for rollover detection. This device divides the vehicle&#39;s state into chronologically consecutive phases and determines the float angle and the vehicle&#39;s transverse velocity from the vehicle dynamics data differently in the individual phases. The disadvantage here is that the initial float angle for “setting up” the algorithm is a constant parameter, which is a function of the application and of the vehicle. 
     SUMMARY 
     A method and device according to an example embodiment of the present invention for determining an initial float angle for skid detection in rollover sensing may make it possible to continuously estimate the initial float angle. This may have the advantage over the related art that even in the case of larger float angles a correct “setup” of the algorithm is ensured, from which then a correct lateral velocity results. 
     In accordance with the present invention, a continuous initial float angle estimate, which, in the case of a break-away of the vehicle, is used as the initial angle of the algorithm. The ascertained initial angle may assume magnitudes from ±0 to a parametrizable value on the order of 40°. 
     Critical driving maneuvers occur in practice, which may result in a slow increase in the float angle, especially in the case of low friction coefficients, i.e., on ice or a wet road surface. If the vehicle dynamics control system, such as ESP, for example, is unable to provide active support, the likelihood of a potential rollover in which the vehicle lands laterally on the hard shoulder increases. Up to a certain point in time, the signals which are barely relevant for the vehicle dynamics analysis algorithm (FDA or VDA) in the case of a slow drift may occur. This means that the quantities used for determining the lateral velocity, such as yaw rate, longitudinal and lateral accelerations and longitudinal velocity, are such that they do not result in the algorithm being activated via the set threshold values. However, if the thresholds are further lowered, this results in misuse situations which may manifest in undesirable effects. One advantage of the present invention may be that the initial float angle is continuously estimated in the background and, if the critical thresholds are exceeded, an initial float angle adapted to the particular situation is made available to the vehicle dynamics algorithm. 
     This provides an additional advantage that the sturdiness of the algorithm is not impaired, while the lateral velocity is better estimated. The difference or phase shift that occurs between actual and estimated float angle may thus be minimized, and the determination of the lateral velocity may be exactly reproduced when the critical velocity is attained. Improved resolution performance may thus be achieved, because the point in time at which the vehicle may or may not roll over in the case of a soil trip event may be determined more accurately. The reliability of other applications that use the lateral velocity as an input quantity is thus also increased. 
     In one embodiment, a method is provided for determining an initial float angle for skid detection in rollover sensing of a rollover of a vehicle having at least one sensor system for vehicle-dynamic signals and a control unit for activating a restraining device. The example method divides the driving state of the vehicle into chronologically consecutive state phases, and includes the following method steps carried out continuously in the first state phase:
     (S1) calculating a change in the float angle from the vehicle-dynamic signals;   (S2) comparing the calculated change in the float angle with a predefinable threshold value; and   (S3) determining the initial float angle on the basis of the calculated change in the float angle as a function of the threshold value for a first range of small changes in the float angle or for a second range of larger values of changes in the float angle.   

     It may be advantageous if method step (S3) has the following substeps:
     (S3.1) resetting or inputting the output values of the vehicle-dynamic signals using a reset logic;   (S3.2) determining the initial float angle by integrating the calculated change in the float angle using an integration constant in the first range; or   (S3.3) determining the initial float angle by integrating the calculated change in the float angle without an integration constant in the second range;   (S3.4) outputting the initial float angle thus determined for the second state phase at a breakaway point in time; or   (S3.5) returning to the method step if the comparison with the predefinable threshold value again results in the first range.   

     The integration constant is parametrizable and has values &lt;1. Advantageously, in this way the float angle does not result in distortions due to the continuous integration and the related problem of long-time drift. 
     The first range of small changes in the float angle ({dot over (β)}) is advantageously formed for 0°&lt;|β|&lt;4°, and the second range of larger changes in the float angle ({dot over (β)}) for Y°&lt;|β|&lt;X°, parameters Y and X being predefinable or parametrizable. In this case, straight-line travel may be advantageously distinguished from dynamic cornering, a breakaway being more likely in the case of cornering. 
     In one embodiment, a device is provided for determining an initial float angle for skid detection in rollover sensing of a rollover of a vehicle having at least one sensor system for vehicle-dynamic signals and a control unit for activating a restraining device, which divides the driving state of the vehicle into chronologically consecutive state phases. The device has a computing unit for continuous computing of the initial float angle. 
     In a particularly preferred embodiment, the computing unit has an initial float angle determination unit having:
         a first logic block for determining a change in the float angle from the vehicle-dynamic signals;   a second logic block for determining a change in the float angle from the vehicle-dynamic signals;   a comparison block for comparing the change in the float angle from the second logic block and for outputting a comparison signal;   a third logic block for selecting a subphase unit on the basis of the comparison signal from the comparison block;   an integration block for integrating the change in the float angle delivered by the first logic block;   a reset logic for resetting or ascertaining the output values of the vehicle-dynamic signals;   a first subphase unit for calculating the initial float angle, having a first formula using the output values of the reset logic and of the integration block;   an output block for outputting the calculated initial float angle to a downstream second state phase; and having   a memory device for storing predefinable data values.       

     It may be advantageous if the computing unit is designed as a component of the software of the control unit, so that no additional space is needed for the device according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is explained below in detail with reference to the exemplary embodiment depicted in the figures. 
         FIG. 1  shows a graphic representation of an estimated float angle curve compared with a reference float angle according to the related art. 
         FIG. 2  shows a state diagram of a vehicle dynamics algorithm. 
         FIG. 3  shows a state diagram of a vehicle dynamics algorithm in an embodiment according to the present invention. 
         FIG. 4  shows a block diagram of a specific embodiment of an initial float angle determination unit according to the present invention. 
         FIG. 5  shows a graphic representation of a float angle curve estimated continuously, compared with a reference float angle according to a specific embodiment of the present invention. 
         FIG. 6  shows a schematic block diagram of an example device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Passive safety in the event of vehicle rollover is very important, since a large proportion of fatal single-vehicle accidents are caused by rollover. Vehicle rollover currently represents approximately 20 percent of all accidents. 
     Against this background, there are concepts for rollover sensing which are capable of recognizing a vehicle rollover, for example, at an early point in time. This ensures that safety devices such as seatbelt tensioners, head airbags, and rollover bars are deployed in a timely manner and a risk of injury is reduced. Previous rollover detection systems consider the rolling motion and the accelerations in the x, y, and z directions of the vehicle. Reliable detection of a vehicle rollover is possible on this basis. However, it is possible to make a reliable decision only at a later point in time of the rollover, which is typically at a roll angle of 20° to 40°. In certain rollover cases, this is, however, too late, for example, in the event of so-called soil trips, in which the vehicle gets onto the hard shoulder and may skid due to the different characteristics of road and hard shoulder. 
     Such a decision made too late may not sufficiently protect the occupants, since they have already experienced a sideways displacement due to a high lateral acceleration, which limits the usefulness of window airbags, for example. 
     In order to be able to make this late decision earlier, a float angle of the vehicle is also taken into account in a rollover detection as in the related art described above.  FIG. 1  shows the initial situation in which the present invention is deployed; it shows a graphic representation of an estimated float angle curve  5  compared with a reference float angle  3 . 
     The variation of actual float angle β in the event of a skid is plotted against time t as a reference float angle  3 . Curve  5  represents a second float angle, estimated by the algorithm. The vehicle is in an initial driving state in which reference float angle  3  is first small, however later increases due to a driving state that is becoming critical, until the vehicle enters a skid at a breakaway point in time t x . At this point in time, the starting value of second estimated float angle  5  is 2° in this example. This starting value is obtained from a constant as explained with respect to the related art. The float angle is now further calculated in the algorithm from this starting value as a function of vehicle dynamic values. It is clearly apparent that this calculated value follows the variation of actual float angle  3 ; however, there is a difference of approximately 11°, which is also referred to as a phase shift. 
     This second estimated float angle  5  is now used for calculating a lateral velocity v y  using the following equation:
 
 v   y   =v   x *tan(β)  (1)
 
where v x  is the vehicle velocity and β is estimated float angle  5 . Therefore, with float angle β, which is 11° less than the actual float angle, an excessively low lateral velocity is also obtained, which may result in excessively late deployment of restraining means.
 
     The present invention makes it possible to calculate the starting value of the float angle continuously, so that it is as close as possible to the actual float angle at breakaway point in time t x , making it possible for the algorithm to perform a further correct calculation. 
     One possible implementation is described in an exemplary specific embodiment below. For this purpose,  FIG. 2  shows a state diagram of a vehicle dynamics algorithm having four state phases  10 ,  11 ,  12 , and  13 , through which a vehicle goes consecutively in the event of a skidding sequence. The solid arrows here indicate transitions between the state phases; the dashed arrows indicate the transmission of values between the state phases. 
     The arrangement of the vehicle dynamics algorithm at that time is characterized by detection of longitudinal velocity v x , yaw rate ω z  (i.e., the rate of rotation about the vertical axis of the vehicle), lateral acceleration a y , and optionally the wheel speeds, longitudinal acceleration a x , and an estimate of float angle β (which, however, is only valid for small float angles). 
     First state phase  10  characterizes the stable driving state of the vehicle. At the moment of a breakaway, the starting value of the float angle is transmitted to second state phase  11  as initial float angle β init , which characterizes the breakaway state of the vehicle. In this case float angle β 1  is calculated based on initial float angle β init  and transmitted to third state phase  12 , which characterizes the skid state of the vehicle, when a skid is detected. Subsequently v x  and β 2  are further calculated for transmission to a third state phase  13 . If it is recognized, during state phases  11 ,  12 , and  13 , that a stable state has been assumed again, the algorithm returns to the particular previous state phase. 
     Initial float angle β init  is calculated in first state phase  10 , which is illustrated in  FIG. 3 . State phase  10  is shown enlarged with an initial float angle determination unit  14 , which has a first subphase unit  15  and a second subphase unit  16 . The improved initial float angle estimate runs in the background in first state phase  10 . The initial float angle ascertained in second subphase unit  16  is then transmitted to second state phase  11  as initial float angle β init  when a vehicle breakaway is detected. 
     In state phase  10  the vehicle is in normal operation, i.e., in a stable driving state. Cornering operations at a small float angle β are also included in this case. If this state is present, float angle β and lateral velocity v y  are irrelevant for rollover detection, since they are too small to initiate a rollover motion. Estimated lateral velocity v y  is then zero, which is visible to other algorithms. In this first state phase  10 , both subphase units  15  and  16  may be implemented. For this purpose, a distinction is made between the following cases: 
     For first subphase unit  15 : 0°&lt;|β|&lt;Y° 
     First subphase unit  15  is relevant for “normal” driving, in which small float angles β on the order of magnitude of Y≈4° occur. Estimated initial float angle β init  is calculated from:
 
β init =Const·β 0   +∫{dot over (β)}dt   (2)
 
     Integration constant Const is parametrizable and has values &lt;1, so that the float angle does not result in distortions due to the continuous integration of a change in float angle {dot over (β)} and the related problem of long-time drift. In this case, β 0  is an application-dependent and vehicle-dependent value for the initial float angle β. A change in float angle {dot over (β)} then results from the quantities of longitudinal and transverse accelerations a x , a y , yaw rate ω z , and vehicle velocity v x , which is set to be equal to the longitudinal velocity, which are delivered by the sensor system located in the vehicle. The change in float angle {dot over (β)} is calculated as follows: 
     
       
         
           
             
               
                 
                   
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     For second subphase unit  16 : 4°&lt;|β|&lt;X° 
     where Y and X are parametrizable. 
     If larger float angle changes occur, such as in the event of highly dynamic driving onto or off the superhighway, a threshold value is then queried via the simple relationship 
                     β   .     ≈       ω   z     -         a   y       v   x       ⁢           ⁢   for   ⁢           ⁢   small   ⁢           ⁢   β               (   4   )               
so that a change from first subphase unit  15  to second subphase unit  16  takes place. Initial float angle β init  is then calculated in second subphase unit  16  from:
 
β init =β 0   +∫{dot over (β)}dt   (5)
 
     The change in float angle {dot over (β)} used here is calculated using equation (3). 
     This results overall in the specific embodiment according to the present invention, shown in  FIG. 4  as an example, of an initial float angle determination unit  14  in the form of a block diagram for determining initial float angle β init . 
     The vehicle dynamic quantities a x , a y , v x , ω z  are delivered from a vehicle dynamics system present in the vehicle or from corresponding sensors and used by a first and a second logic block  17 ,  18  according to equation (3) for determining the change in float angle {dot over (β)}. At the same time, these and the change in float angle {dot over (β)} are supplied to a reset logic  20  as input quantities; the reset logic also receives information about a steering angle LW and an initial float angle β provided by the driving dynamics system. 
     A comparison block  22  compares the change in float angle {dot over (β)}, with a predefinable threshold value and supplies the result to a third logic block  19 , which then decides which subphase unit  15 ,  16  will be used for determining initial float angle β init . This is the above-described differentiation between cases. 
     An integration block  21  first performs the integration of float angle change {dot over (β)} for formulas (2) and (5) and supplies it, according to the differentiation between cases, to third logic block  19  of first or second subphase unit  15 ,  16 . 
     First subphase unit  15  determines initial float angle β init  according to equation (2) and second subphase unit  16  according to equation (5). 
     Initial float angle β init  thus calculated is supplied to an output block and is available there to the next state phase for relaying. 
     Reset logic  20  ascertains initial values and boundary conditions for the calculations in subphase units  15  and  16 . 
     It also performs a reset to initial values if stability is detected. 
     A memory device  23  is used for storing the predefinable threshold value and further application-dependent and vehicle-dependent values. 
       FIG. 5  finally shows the effect of the use of the method according to the present invention for determining initial float angle β init . The dashed curve marked  4  represents first estimated initial float angle β init , which is transmitted to the algorithm for second state phase  11  at breakaway point in time t x . It is apparent that the determination according to the present invention of initial float angle β init  follows the average curve of the reference float angle as actual float angle; at breakaway point in time t x  there is little or no difference with respect to the actual float angle, and the curve of second estimated float angle  5  calculated by the algorithm in the subsequent state phases follows the curve of the actual float angle with a very small difference. 
     The reliability of the rollover algorithm is thus considerably increased in that the estimate of the lateral velocity is improved. 
       FIG. 6  shows a schematic block diagram of a device  1  according to the present invention in a vehicle  2 . A sensor system  8 ,  8 ′,  8 ″ is connected to a system control unit  7 , which is a vehicle dynamics controller, for example. Reference numerals  8 ′ and  8 ″ refer, for example, to lateral acceleration sensors and wheel speed sensors. The signal values sampled by sensor system  8 ,  8 ′,  8 ″ are related to a computing unit  9  in control unit  6 . Sensor system  8 ,  8 ′,  8 ″ may also be totally or partially connected to computing unit  9 . Computing unit  9  determines initial float angle β init . 
     The present invention is not limited to the above-described exemplary embodiments, but may be modified in many ways. 
     The reliability of other applications which use the lateral velocity as input quantity may also be increased. These include, for example, the activation or improved deployment performance in the event of side crash deployment. 
     Computing unit  9  may be designed as software, i.e., a component or a subprogram of the software of control unit  6 . 
     It is also possible that computing unit  9  is a separate unit or a component of system control unit  7 .