Abstract:
A vehicle control method includes, among other things, recording a towing vehicle road grade for a fixed road position when a towing vehicle tows a trailered vehicle. The method further includes shifting, using a controller, the recording to provide a trailered vehicle road grade for the fixed road position based upon the towing vehicle road grade and initiating a vehicle control adjustment to control the towing vehicle based upon the trailered vehicle road grade.

Description:
BACKGROUND 
     This disclosure relates generally to estimating a road grade and, more particularly, to estimating road grade below a trailered vehicle. 
     Towing vehicles tow trailered vehicles. A truck is an example towing vehicle. A boat trailer is an example trailered vehicle. Both are example vehicles. 
     Extreme road grades may cause a trailered vehicle to exert considerable pulling force on the towing vehicle. If the towing vehicle does not account for this pulling force, the towing vehicle braking force may be insufficient. 
     The road grade beneath a vehicle can be used to determine a road gradient load torque. Measuring or estimating road grade beneath a vehicle is useful for at least this reason. 
     Although a towing vehicle and a trailered vehicle are in close proximity during towing, the road grade beneath the towing vehicle may differ considerably from the road grade beneath the trailered vehicle. Although sensors mounted to towing vehicles have been used to suitably estimate road grade beneath the towing vehicles, monitoring the road grade beneath the trailered vehicle is difficult. Towing vehicles are rarely equipped with sensors capable of monitoring road grade. 
     SUMMARY 
     A vehicle control method according to an exemplary aspect of the present disclosure includes, among other things, controlling a towing vehicle based upon a trailered vehicle road grade. 
     In another example of the foregoing method, the trailered vehicle road grade is based upon a towing vehicle road grade of the towing vehicle. 
     In another example of any of the foregoing methods, the trailered vehicle road grade at a position is based upon the towing vehicle road grade at the position. 
     In another example of any of the foregoing methods, the method includes recording the towing vehicle road grade when the towing vehicle tows the trailered vehicle forward, and shifting the recording of the towing vehicle road grade to calculate the trailered vehicle road grade, wherein the shifting comprises a spatial domain shift of the towing vehicle road grade. 
     In another example of any of the foregoing methods, the method includes initiating a vehicle control adjustment in response to the trailered vehicle road grade. 
     In another example of any of the foregoing methods, the vehicle control adjustment comprises increasing braking force applied to the towing vehicle in response to the trailered vehicle road grade. 
     In another example of any of the foregoing methods, the trailered vehicle road grade is an estimated trailered vehicle road grade. 
     A system for controlling a towing vehicle according to an exemplary aspect of the present disclosure includes, among other things, a sensor to monitor a towing vehicle road grade of the towing vehicle, and a controller configured to control the towing vehicle based upon a trailered vehicle road grade. 
     In another example of the foregoing system, the trailered vehicle road grade is based upon the towing vehicle road grade. 
     In another example of any of the foregoing systems, the towing vehicle is configured to tow the trailered vehicle. 
     In another example of any of the foregoing systems, the sensor assembly is mounted to the towing vehicle. 
     In another example of any of the foregoing systems, the controller is mounted to the towing vehicle. 
     In another example of any of the foregoing systems, the trailered vehicle road grade at a position is based upon the towing vehicle road grade at the position. 
     A system for controlling a towing vehicle according to another exemplary aspect of the present disclosure includes, among other things, a road grade assembly providing a towing vehicle road grade, and a trailered road grade based upon the towing vehicle road grade, and a controller configured to adjust operation of the towing vehicle based upon the trailered vehicle road grade. 
     In another example of the foregoing system, the controller adjusts vehicle braking based upon the trailered vehicle road grade. 
     In another example of any of the foregoing systems, the controller adjusts vehicle cruise control based upon the trailered vehicle road grade. 
     In another example of any of the foregoing systems, the controller adjusts a transmission shift schedule based upon the trailered vehicle road grade. 
     In another example of any of the foregoing systems, the trailered vehicle road grade at a position is based upon the towing vehicle road grade at the position. 
     A system for controlling a towing vehicle according to yet another exemplary aspect of the present disclosure includes, among other things, a controller configured to adjust operation of the towing vehicle based upon a trailered vehicle road grade. 
     In another example of the foregoing system, the controller adjusts vehicle braking based upon the trailered vehicle road grade. 
     In another example of any of the foregoing systems, the controller adjusts vehicle cruise control based upon the trailered vehicle road grade. 
     In another example of any of the foregoing systems, the controller adjusts a transmission shift schedule based upon the trailered vehicle road grade. 
     In another example of any of the foregoing systems, the system includes a road grade sensor assembly to sense a towing vehicle road grade, and to provide a trailered road grade. 
     In another example of any of the foregoing systems, the trailered vehicle road grade at a position is based upon the towing vehicle road grade at the position. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
         FIG. 1  illustrates an example towing vehicle towing a trailered vehicle. 
         FIG. 2  illustrates a length between the towing vehicle of  FIG. 1  and the towing vehicle and trailered vehicle of  FIG. 1 . 
         FIG. 3  illustrates a map of a towing vehicle road grade and trailered vehicle road grade verses distance traveled. 
         FIG. 4  shows a flowchart of an example method for determining the road grade of the trailered vehicle of  FIG. 1 . 
         FIG. 5  illustrates another length between the towing vehicle of  FIG. 1  and another example trailered vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the example of  FIG. 1 , a towing vehicle  10  tows a trailered vehicle  14 . The towing vehicle  10  is a truck in this example, and the trailered vehicle  14  is a trailered boat. Both are example vehicles. A mechanical arm  18  couples the towing vehicle  10  to the trailered vehicle  14 . 
     For a given vehicle towed, its associated road grade is, generally, a grade (or slope) of an area beneath the vehicle. Road grade can be expresses as a percentage of variation from a horizontal (zero) grade H g . 
     A towing vehicle road grade RG TOWING  is a grade of an area of the road beneath the towing vehicle  10 . A trailered vehicle road grade RG TRAILER  is a grade of a road beneath the trailered vehicle  14 . In this example, the trailered vehicle road grade RG TRAILER  is greater than a grade of the towing vehicle road grade RG TOWING . 
     Although described as road grade, a person having skill in this art and the benefit of this disclosure would understand that a traditional road is not required for there to be a road grade. Road grade refers generally to the area underneath a vehicle whether that area is a road or that area is an off-road. 
     The towing vehicle  10  includes a sensor assembly  20  that monitors the towing vehicle road grade RG TOWING . The assembly may include accelerometers, wheel speed sensors, etc. A person having skill in this art and the benefit of this disclosure would understand how to monitor, or estimate, the towing vehicle road grade RG TOWING  using the sensor assembly  20 . 
     The towing vehicle  10  further includes a controller assembly  30  coupled to the sensor assembly  20 . The controller assembly  30  is a specialized controller programed to estimate the trailered vehicle road grade RG TRAILER  based on the towing vehicle road grade RG TOWING . The controller assembly  30  and sensor assembly  20  together provide a trailered vehicle road grade assembly or a system for controlling the trailered vehicle  14 . 
     Notably, the example trailered vehicle  14  includes no sensor assembly or controller assembly to monitor the trailered vehicle road grade RG TRAILER . In other examples, the trailered vehicle  14  may include the sensor assembly  20 , the controller assembly  30 , or both. 
     In this example, the towing vehicle  10  has towed the trailered vehicle for a drive distance D from a start location S to the location shown in  FIG. 1 . The towing vehicle  10 , and thus the sensor assembly  20 , has passed over a position P 1 . 
     As the towing vehicle  10  has passed over the position P 1 , the towing vehicle road grade RG TOWING  at the position P 1  was previously calculated and measured. The controller assembly  30  includes a memory buffer that records or stores the measurement of the towing vehicle road grade RG TOWING . 
     After the trailered vehicle  14  is positioned over the position P 1 . The controller assembly  30  applies the stored measurement of the towing vehicle road grade RG TOWING  (when the towing vehicle  10  was at the position P 1 ) as the trailered vehicle road grade RG TRAILER . The towing vehicle  10  is thus used as a road grade sensor for the trailered vehicle  14 . 
     Referring now to  FIG. 2  with continuing reference to  FIG. 1 , the controller assembly  30  can use a length L between the sensor assembly  20  of the towing vehicle  10  and the midpoint  40  of the trailered vehicle  14  when calculating the trailered vehicle road grade RG TRAILER . In some examples, as the towing vehicle  10  tows the trailered vehicle  14  for the drive distance D, the controller assembly  30  records the towing vehicle road grade RG TOWING  for various positions along the drive distance D. Each of the position across the drive distance D has a corresponding towing vehicle road grade RG TOWING . 
     To calculate the trailered vehicle road grade RG TRAILER , the controller assembly  30  effectively shifts towing vehicle road grades RG TOWING  the length L, which corresponds to the distance between the sensor assembly  20  and the mid-point  40  of the trailered vehicle  14 . The shift is within a spatial domain having the length L. 
     The road grade for the trailered vehicle  14  is estimated based using length L from the sensor assembly  20  to the midpoint  40 . The sensor assembly  20  is at the center of gravity g of the towing vehicle  10 , and the midpoint  40  is at the center of gravity g of the trailered vehicle  14 . 
     Other areas of the towing vehicle  10 , the trailered vehicle  14 , or both could be used. Such adjustments are possible by changing the length L. 
     After calculating the trailered vehicle road grade RG TRAILER , the controller assembly  30  can provide the trailered vehicle road grade RG TRAILER  to control operations for the towing vehicle  10 . The towing vehicle  10  may make vehicle control adjustments in response to the trailered vehicle road grade RG TRAILER . In one example, the vehicle control adjustments include applying more braking force to the towing vehicle  10  to prevent the trailered vehicle  14  from destabilizing or pulling the towing vehicle  14 . In another example, the vehicle control adjustments include adjusting a cruise control setting of the towing vehicle  10 , or a transmission shift schedule of the towing vehicle  10 . The example controller assembly  30  of the system for controlling the trailered vehicle  14  thus adjusts operation of the towing vehicle based on the trailered vehicle road grade RG TRAILER . 
     For example, information about the trailer road grade RG TRAILER  can be used by a cruise controller of the towing vehicle  10  to adjust the powertrain torque delivery in a feedforward manner. Information about the trailer road grade RG TRAILER  can be used by a transmission controller of the towing vehicle  10  to adjust its gear scheduling strategy such that gear shifting will be smoother and optimized when the trailered vehicle  14  is adding additional load to the towing vehicle  10 . 
     As can be appreciated, the load on the towing vehicle  10  resulting from road grade can vary greatly when the trailered vehicle  14  is attached to, or detached from, the towing vehicle  10 . 
       FIG. 3  shows a map or visual representation of the shift between the towing vehicle road grades RG TOWING , which are represented as line  50 , and the trailered vehicle road grades RG TRAILER , which are represented as line  54 . 
     In one example method of estimating the towing vehicle road grades RG TOWING , an evaluation range is defined by l e , which is a distance parameter covering the largest allowable distance of the trailered vehicle  14  behind the towing vehicle  10 . 
     Next, in the method, an evaluation step distance l e  is defined. The evaluation step distance l e  represents the driving distance elapsed between consecutive recordings of the towing vehicle road grade RG TOWING  by the sensor assembly  20  as the towing vehicle  10  moves together with the trailered vehicle  14 . The evaluation distance l e  can be one meter, for example. In such an example, the towing vehicle road grade RG TOWING  is recorded every meter as the towing vehicle  10  moves together with the trailered vehicle  14 . 
     The method populates a vector of road gradient estimation record with the towing vehicle road grade RG TOWING  recordings. This vector is defined by V rg  and has dimensions determined by L e /l e . A buffer length V b  is provided by a rounded integer number, such as V b =round(L e /l e ). 
     The buffer provide memory for a sequence of values. The buffer length V b  is determined by the number of values needed. The more values needed, the longer buffer length V b . 
     The method saves the measurements of the towing vehicle road grade RG TOWING  as V rg  [k]. The trailered vehicle road grade RG TRAILER  are then k*l e  behind the evaluation point of the towing vehicle  10 . 
     V rg  [k] can be initialized with zeros, or with records from a previous driving cycle. After initializing V rg  [k], new towing vehicle road grades RG TRAILER  are collected, and the vector of recorded road grades V rg  [k] will shift backwards to pass a k-th record to a k+1 record position. The estimations have a length of L e  after the record of V rg  [1]. The record at k=V b  is then dropped and replaced by the record at k=V b −1. 
     The method essentially provides a signal buffer. The method may be executed on software within the controller assembly  30  of the towing vehicle  10 . 
     The proposed method is often most effective when the towing vehicle  10  is pulling or leading the trailered vehicle  14 . When reversing, there may not be a towing vehicle road grade measurement available. In that case, the records of road grade are shifted forward by removing signal recorded at k=0. Meanwhile, each buffer cell at k will be replaced by the value from its subsequent record at k+1. The record at k=V b  will then be fed by zero since no new information will be available from the trailer side. 
     Referring now to  FIG. 4 , an example of the above method is summarized in a flowchart  100 . Generally, the flowchart  100  shows that by integrating the speed signal, an algorithm knows how far the towing vehicle  10  towing the trailered vehicle  14  have moved since a previous update. Then, when a distance traveled forward by the vehicles is longer than a step distance, an update process will start if new data is available from the towing vehicle  10 . 
     More specifically, in the flowchart  100 , V spd  stands for vehicle speed, which is typically expressed in unit of meters per second. In the flowchart  100 , dt stands for control implementation cycle time, and NA represents not available, such as when an implausible value is provided. Rather than NA, the method may, in another example, use a quality factor associated with V rg  [1] to calculate whether the road information at a distance after the towing vehicle  10  can be used for control or not. Further, in  FIG. 4 , l_E is the step distance, for example, it can be 3 meters. v_b is the number of memory unit needed to save the road grade information at l_E step size up to L_E total length. 
     After V rg  is available, the trailered vehicle road grade RG TRAILER  can be evaluated. Due to variety of sizes and types of trailered vehicles  14 , the distance of the road slope evaluation point of the trailer behind the evaluation point of the truck is not fixed. In the example of  FIG. 5 , for example, a trailered vehicle  14 ′ has a single axle  60 , and the length L′ is a length from the sensor assembly  20  to the axle  60 . 
     The length L or L′ typically varies from 10 to 20 meters for commonly used utility trailers and RVs. The evaluation of the trailered vehicle road grade RG TRAILER  is done across a range rather than at a point to accommodate this variation. 
     In some examples, two distance parameters, L MIN  and L MAX  are specified for the control algorithm and 0≦L MIN ≦L MAX ≦L_E executed to calculate the trailered vehicle road grade RG TRAILER . For example, L MIN =10 meters L MAX =15 meters could be used. An evaluation vector Vect_RG TRAILER  is constructed out of V rg  by V rg  [k], L MIN ≦k*L_E≦L MAX . The final road grade under the trailer for control applications is evaluated with the vector Vect_RG TRAILER . 
     In some examples, the method may use the largest absolute value from Vect_RG TRAILER . 
     In some examples, the method can use a mean value of Vect_RG TRAILER  to provide an estimate of the average level of the road grade under the trailer. 
     In some examples, the method may use a standard deviation value of V rg . When the standard deviation is above a threshold, a maximal magnitude of is used. Otherwise, the mean value of is used for the subsequent control algorithm processing. 
     A quality of the final evaluation of the trailered vehicle road grade RG TRAILER  depends, in part, on the number of NAs in the vector V rg  [k]. A ratio between the numbers of the valid estimation to NAs can be used to indicate the quality of evaluation. 
     Methods having flows different than the method of the flowchart  100  may be utilized to calculate the trailered vehicle road grade RG TRAILER  in view of the towing vehicle road grade RG TOWING . 
     Features of the disclosed examples include a method and estimator capable of evaluating road grade under a trailered vehicle without the use of complex sensors on the trailered vehicle or an electric coupling between the trailered vehicle and the towing vehicle. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.