Abstract:
A rollover warning and detection method for a transport vehicle is adaptively adjustable to take into account the CG height of the vehicle. Measures of the vehicle speed, lateral acceleration and yaw rate are sampled during normal driving conditions and used to estimate the CG height of the vehicle. The centrifugal acceleration acting on the vehicle is calculated as the product of vehicle speed and yaw rate, and the CG height is estimated based on the relationship between the calculated centrifugal acceleration and the measured lateral acceleration. The estimated CG height of the vehicle is used to adjust various calibrated rollover detection thresholds so that algorithm outputs such as rollover warnings automatically take into consideration vehicle loading effects.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to vehicle rollover sensing, and more particularly to a rollover early warning and detection method for transport vehicles such as heavy duty trucks.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various rollover warning and detection systems have been developed for the heavy duty truck market. These systems can warn the driver when the risk of rollover is considered to be high and/or intervene (by braking, for example) to reduce the likelihood of rollover. The measurable vehicle parameters relevant to rollover include the steering wheel angle and the vehicle&#39;s roll angle, lateral acceleration, yaw rate and speed. In the U.S. Pat. No. 6,542,792 to Schubert et al., for example, an impending rollover is detected by comparing the roll rate vs. roll angle operating point of the vehicle to a calibrated threshold. However, the rollover susceptibility of a transport vehicle varies dramatically with the placement, distribution and weight of its cargo load because these factors alter the vehicle&#39;s center-of-gravity (CG). For example, a semi trailer with a full load of cotton candy will have a lower weight but a higher CG than a flatbed trailer loaded with a single slab of pig iron. Accordingly, what is needed is a rollover warning and detection method for a transport vehicle that adapts to different load conditions.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention provides an improved transport vehicle rollover warning and detection method that is adaptively adjustable to take into account the CG height of the vehicle. Measures of the vehicle speed, lateral acceleration and yaw or steering rate are sampled during normal driving conditions and used to estimate the CG height of the vehicle. The centrifugal acceleration acting on the vehicle is calculated as the product of vehicle speed and yaw or steering rate, and the CG height is estimated based on the relationship between the calculated centrifugal acceleration and the measured lateral acceleration. The estimated CG height of the vehicle is used to adjust various calibrated rollover detection thresholds so that algorithm outputs such as rollover warnings automatically take into consideration vehicle loading effects. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1A  is a diagram of a heavy duty truck equipped with various sensors and a microprocessor-based controller for carrying out the method of the present invention;  
         [0005]      FIG. 1B  is an isometric representation of the heavy duty truck of  FIG. 1A ;  
         [0006]      FIG. 2  is a block diagram depicting a rollover warning method carried out with the sensors and controller of  FIG. 1A  according to this invention;  
         [0007]      FIG. 3  is a diagram describing a portion of the block diagram of  FIG. 2  pertaining to rollover detection threshold adjustment;  
         [0008]      FIG. 4  is a block diagram detailing of portion of the block diagram of  FIG. 2  pertaining to CG height estimation; and  
         [0009]      FIG. 5  depicts a set of baseline traces describing centrifugal acceleration vs. lateral acceleration for the truck of  FIGS. 1A-1B  for CG heights H 1 , H 2 , H 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]     Referring to  FIGS. 1A-1B , the reference numeral  10  generally designates a semi tractor-trailer including a tractor  12  and a trailer  14  connected to the tractor  12  by a conventional fifth-wheel coupling (not shown). Of course, the invention also applies to other types of transport vehicles such as straight trucks, box trucks, vans, etc., and even to aerospace vehicles, for example. In general, transport vehicles such as the truck  10  are subject to wide variation in loading. The weight and distribution of the cargo load both influence the CG height of the truck, and therefore, its rollover propensity. Lateral and longitudinal variations in the CG can also influence the vehicle&#39;s rollover propensity, but the primary variation of interest is the CG height. The CG of the trailer  14  is identified in  FIG. 1B , and its height above the road surface is given by the letter H. The lateral acceleration Ay experienced by the trailer  14  acts through the CG, creating a moment or torque that produces tilt or roll of the truck  10 . This torque is directly proportional to the CG height, and the CG also shifts laterally once the trailer  14  starts to tilt, further increasing the likelihood of rollover. Other factors represented in  FIG. 1B  that influence rollover include the vehicle speed V and its yaw rate Ψ. In the case of truck  10 , the lateral acceleration Ay applies primarily to the trailer  14 , while the speed V and yaw rate Ψ apply primarily to the tractor  12 . In other vehicle configurations where no trailer is involved, these distinctions do not apply.  
         [0011]     Referring to  FIG. 1A , the rollover warning and detection method of this invention is implemented with a low-g lateral acceleration sensor  18 , a vehicle speed sensor  20 , a yaw rate sensor  22 , a microprocessor-based controller  24  and a rollover warning device  26 . The lateral acceleration sensor  18  is situated on the longitudinal axis  16   a  of the trailer  14 , on a surface such as the loading bed. The yaw rate sensor  22  measures yaw rate about a vertical axis, and is situated on the longitudinal axis  16   b  of the tractor  12 . The speed sensor  20  may be a wheel or shaft speed sensor as is well known in the art. The controller  24  samples and processes the signals produced by the sensors  18 ,  20  and  22 , and activates the warning device  26  via line  28  in the event of an impending rollover event. The warning produced by device  26  may be audible or visual, and in a preferred implementation, additionally includes a wireless transmission to notify a home office or authorities that a rollover or near-rollover has occurred. Interventional controls such as braking, steering or engine controls may also be included.  
         [0012]     The block diagram of  FIG. 2  describes the functionality of the controller  24  of  FIG. 1A . The vehicle speed and yaw rate inputs V and Ψ are filtered by the low-pass filter blocks  32  and  34 , and applied to block  36  which calculates a corresponding centrifugal acceleration CA according to the product (V*Ψ). Alternatively, the yaw rate input may be replaced with a steering rate input, such as a time-derivative of steering wheel angle. The lateral acceleration input Ay is similarly filtered by the low-pass filter block  38 , and the filtered lateral acceleration is applied to the CG Height Estimator block  40  along with the calculated centrifugal acceleration CA. The operation of CG Height Estimator block  40  is described below in reference to  FIGS. 4-5 , and it is sufficient at this point to note that the block  40  outputs two parameters: a CG height estimate H on line  40   a , and an estimation confidence metric CM on line  40   b.    
         [0013]     The embodiment of  FIG. 2  includes a first rollover detection block  42  for detecting impending rollover due to tight turns and a second rollover detection block  44  for detecting impending rollover due to a ditch drift condition where the truck  10  drifts off a roadway toward a ditch or embankment. Of course, different or additional rollover detection blocks could be included if desired. In general, the detection blocks  42  and  44  each involve comparing a measured, calculated or estimated parameter to a calibrated threshold that represents a predetermined likelihood or risk of rollover. In the case of tight-turn rollover detection (block  42 ), the calculated centrifugal acceleration CA is compared to a calibrated threshold. In the case of ditch drift rollover detection (block  44 ), an estimate of the trailer roll angle or tilt is compared to a calibrated threshold. In the illustrated embodiment, the block  46  estimates the trailer roll angle as a function of the difference (CA−Ay). The computed centrifugal acceleration CA is the lateral acceleration the trailer  14  should experience in the absence of tilting, whereas the lateral acceleration Ay measured by sensor  18  is augmented by gravitational acceleration when the trailer  14  is experiencing tilt or roll. The block  48  combines the outputs of rollover detection blocks  42  and  44 , and determines if rollover warning device  26  should be activated, and at what level. As indicated above, the possible levels of rollover warning could include audible warnings, visual warnings, or even a wireless transmission to notify a home office or authorities that a rollover or near-rollover has occurred.  
         [0014]     The method of the present invention utilizes the outputs of block  40  to adaptively adjust the rollover detection logic for variations in the CG height of truck  10 . In the illustrated embodiment, this is achieved by blocks  50  and  52 , which adjust the calibrated thresholds used by the rollover detection blocks  42  and  44 , respectively. An alternate but equivalent approach would be to similarly adjust the vehicle parameter input—that is, the calculated centrifugal acceleration CA in the case of rollover detection block  42 , and the trailer roll angle estimate in the case of rollover detection block  44 .  
         [0015]     The diagram of  FIG. 3  describes a technique for carrying out the functionality of threshold adjustment blocks  50  and  52  using a look-up table. The rollover detection blocks  42  and  44  include calibrated default thresholds as mentioned above, and the blocks  50  and  52  develop adjustments for the respective default thresholds based on the CG height and confidence outputs H, CM of block  40 .  FIG. 3  depicts a look-up table in which H and CM are the independent variables and the threshold adjustment is the dependent variable. The zero values in the table indicate no threshold adjustment, and occur when the CG height H is approximately equal to a predetermined or typical height and/or the confidence metric CM is low. The positive values in the table increase the default threshold to reduce the likelihood of rollover detection, and occur with lower than usual CG height H. The negative values in the table decrease the default threshold to increase the likelihood of rollover detection, and occur with higher than usual CG height H. In cases where the CG height H is outside the usual or typical range, the magnitude of the adjustment increases with increasing values of the confidence metric CM. Of course, the values shown in the table are for illustration only, and it will be recognized that the mathematical calculations could be used instead of a look-up table.  
         [0016]     As indicated above, CG height H is estimated according to this invention based on the calculated centrifugal acceleration CA and the measured lateral acceleration Ay. These parameters are related to the CG height because the centrifugal acceleration CA acts through the CG to produce tilting of the trailer  14 , and the tilting causes Ay to become larger than CA. However, since direct calculation of CG height is not feasible due to variability in vehicle operation, road condition and other factors, the block  40  estimates the CG height H by collecting CA vs. Ay data and comparing the collected data with previously established baseline data. As illustrated in  FIG. 5 , the baseline data can take the form of a family of CA vs. Ay curves for various payloads having increasing values H 1 , H 2 , H 3  of CG height. A linear or non-linear regression function is applied to the baseline data to produce the curves, and the curves are stored in the memory of controller  24 , represented in  FIG. 4  by the block  60 . In subsequent vehicle operation, block  40  periodically collects CA vs. Ay data and determines CG height H by comparing the collected data to the stored family of baseline curves. Referring to  FIG. 4 , the block  62  samples the measured lateral acceleration Ay for different values of centrifugal acceleration CA representing driving conditions under various speed and turning conditions of the truck  10 . The data can be represented as a scatter-plot, and when a representative amount of data has been collected, the block  64  applies a least-squares regression fit to the scatter-plot to produce a curve (linear or non-linear) that is comparable with the stored family of baseline curves. The block  64  determines the shape of the curve, and produces a measure of how well the data conforms to the curve using a R-squared, variance or standard deviation calculation, for example. This “goodness-of-fit” measure is referred to herein as the confidence metric CM, which is used in the threshold adjustment of blocks  50  and  52  as described above. In general, the confidence metric CM will have a relatively high value if the sampled CA vs. Ay data conforms well to the curve and a relatively low value if the sampled data conforms poorly to the curve. The block  66  compares the CA vs. Ay curve produced by block  64  to the family of baseline curves stored at block  60 , and determines a corresponding CG height H by interpolation.  
         [0017]     In summary, the present invention provides a rollover warning and detection method for a transport vehicle that automatically adapts to changing load conditions that influence the CG height of the vehicle. While the invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the system can be configured for direct entry of the CG height if known, data obtained from a global positioning satellite (GPS) system could be used to determine vehicle parameters such as speed, heading and roadway curvature, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.