# Patent

## Title
Trailer backup aid speed limiting via braking

## Abstract

A trailer backup assist system for a vehicle reversing a trailer is provided herein. The system includes a brake system and a steering system of the vehicle. A controller is configured to output a brake torque request to the brake system and a steering command to the steering system, wherein the brake torque request and the steering command are each based at least in part on a trailer mass.

## Background
CROSS-REFERENCE TO THE RELATED APPLICATION
This application is a continuation-in-part of U.S. patent application Ser. No. 14/682,204, filed Apr. 9, 2015, and entitled “TRAILER BACKUP AID SPEED LIMITING VIA BRAKING,” now U.S. Pat. No. 9,744,972, the entire disclosure of which is hereby incorporated herein by reference.


FIELD OF THE INVENTION
The present invention generally relates to systems for controlling vehicle parameters during vehicle guidance of a trailer, such as in a trailer backup assist system. In particular, various systems are disclosed for controlling the speed or a vehicle during use of a trailer backup assist system.
BACKGROUND OF THE INVENTION
Reversing a vehicle while towing a trailer can be challenging for many drivers, particularly for drivers that drive with a trailer on an infrequent basis or with various types of trailers. Systems used to assist a driver with backing a trailer can control various vehicle systems to attempt to keep the speed of the vehicle below a limit where such systems become unreliable, particularly at preventing the trailer from converging toward a jackknife angle or the like. Further advances in such systems may be desired.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a trailer backup assist system for a vehicle reversing a trailer is provided. The system includes a brake system and a throttle sensor module outputting a throttle application signal. A controller outputs a brake torque request to the brake system based at least in part on a trailer mass and the throttle application signal.
According to another aspect of the present invention, a trailer backup assist system for a vehicle reversing a trailer is provided. The system includes a brake system and a steering system of the vehicle. A controller is configured to output a brake torque request to the brake system and a steering command to the steering system, wherein the brake torque request and the steering command are each based at least in part on a trailer mass.
According to another aspect of the present invention, a method of reversing a trailer towed by a vehicle is provided. The method includes the steps of determining a trailer mass, outputting a brake torque request to a brake system of the vehicle, and outputting a steering command to a steering system of the vehicle if it's determined that the trailer is being reversed along a straight path. The brake torque request and the steering command are each based at least in part on the trailer mass.
These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a schematic depiction of an example vehicle and trailer;
FIG. 2 is a schematic depiction of the vehicle and the trailer of FIG. 1 after reversing;
FIG. 3 is a schematic block diagram of a portion of a system for assisting the vehicle in reversing the trailer and including functionality for limiting the speed of the vehicle;
FIG. 4 is a flowchart showing a method for limiting the speed of the vehicle, including by determining a road grade beneath the trailer of FIGS. 1 and 2;
FIG. 5 is a schematic block diagram of a portion of an alternative system for assisting the vehicle in reversing the trailer and including functionality for limiting the speed of the vehicle;
FIG. 6 is a flowchart showing an alternative method for limiting the speed of the vehicle, including by dynamically adjusting a target speed of the system.
FIG. 7 is a schematic block diagram of a system for limiting the speed of a vehicle reversing a trailer based on a trailer mass, according to one embodiment;
FIG. 8 is a schematic block diagram of an alternative embodiment of the system shown in FIG. 7;
FIG. 9 is a schematic block diagram of a trailer backup assist system according to one embodiment; and
FIG. 10 is a flowchart showing a method of reversing a trailer towed by a vehicle according to one embodiment.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in FIG. 1. However, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.
Referring to FIGS. 1-3, reference numeral 10 generally designates a vehicle that includes a system 12 for assisting vehicle 10 in backing up a trailer 14 coupled therewith. System 12 includes a brake system 16 (FIG. 3) and a throttle sensor 22 (FIG. 3) that outputs a signal 24 relating to an amount of throttle being applied. System 12 further includes a controller 30 that estimates a road grade RGt beneath the trailer 14 and outputs a brake torque request 34 to the brake system 16 based on the estimated road grade RGt and the throttle application signal 24.
Referring to FIG. 1, vehicle 10 is shown in an example scenario towing trailer 14. An arm 18 of trailer 14 extends toward and couples trailer 14 with vehicle 10 via a hitch (not shown) on the rear of vehicle 10. In this example, the vehicle 10 is reversing to move the trailer 14 from the position of FIG. 1 to the position of FIG. 2. In the example of FIGS. 1 and 2, the vehicle 10 is a truck and the trailer 14 is a boat trailer and the reversing of vehicle 10 may be so as to move trailer 14 into in a body of water at a boat lift, for example. The reversing may be carried out using system 12, which is generally configured to assist a driver of vehicle 10 in various ways in reversing vehicle 10 and trailer 14. In one example, such a trailer backup assist system 12 can includes both actions carried out by the driver of vehicle 10 as well as by system 12. In particular, the driver may initiate system 12 after driving vehicle 10 along a path to a desired location at which the reversing is to begin and placing vehicle 10 in reverse. Once system 12 is activated, the driver may, for example, select a desired vehicle curvature using an input device (such as a dedicated knob or, in some examples, the steering wheel (not shown) of vehicle 10), while simultaneously controlling the longitudinal motion (i.e., speed) of vehicle 10 using the throttle and brakes. In general, system 12 executes an operating routine to determine if the desired curvature can be safely executed, which may mean that the desired curvature will maintain the hitch angle (i.e., an angle defined between the vehicle 10 and the trailer 14 along a lateral plane at the point of coupling therebetween) below a “jackknife angle.” In general, a jackknife angle is described as an angle at which a maximum steering input in either direction will fail to decrease the hitch angle. System 12 causes vehicle 10 to steer automatically, such as by control of an electronic power assisted steering (“EPAS”) system, to implement either the desired curvature or a modified curvature determined to be appropriate for preventing a jackknife condition, which may be determined by controller 30.
As mentioned, while system 12 is causing vehicle 10 to automatically steer to maintain an appropriate curvature, the driver may maintain the general responsibility for controlling the longitudinal motion of vehicle 10 using the throttle and brakes. Initially, such control should cause vehicle 10 to begin rearward motion. As vehicle 10 accelerates, it may be generally the responsibility of the driver to maintain sufficient vehicle speed until a desired position is reached based on the curvature along which system 12 steers vehicle 10. Upon vehicle 10 reaching the desired location, the driver may slow vehicle 10 by reducing throttle position and applying brake torque before placing vehicle 10 in park and deactivating system 12, at which point system 12 relinquishes control of the steering system.
The speed at which vehicle 10 travels while system 12 steers, however, can affect the ability of system 12 to avoid a jackknife condition or other adverse conditions. In particular, at higher vehicle speeds, the dynamics of the yaw rate of trailer 14 with respect to that of vehicle 10 and, accordingly, the hitch angle may occur at a rate that is too fast for system 12 to react to avoid a hitch angle increase to or beyond a jackknife angle, as explained above. Accordingly, it may be desirable for system 12 to be able to determine if the speed of vehicle 10 is at or is approaching a threshold at which system 12 may be unable to reliably control the hitch angle and to act to slow vehicle 10, if necessary. Further, it is noted that an EPAS system may only function to control the steering of vehicle 10 while vehicle 10 is traveling below a cutoff speed. Conversely, it may also be useful for system 12 to allow the driver to utilize as much of the speed band as possible for purposes of flexibility and sense of control.
Accordingly, systems such as system 12 can include the ability within controller 30 to limit the speed of vehicle 10 by automatically applying the brakes, via an input to the vehicle brake system 16. A controller 30 can be configured for speed limiting by the incorporation of a proportional-integral-derivative (“PID”) controller 42 to monitor the difference between the vehicle speed and the target speed (such difference being designated a speed error) to request a brake torque request that will be sent to the brake system 16. This brake system 16 in turn applies the brakes appropriately, which alters the vehicle speed and the speed error 40. For the purposes of speed limiting within a system such as system 12, the desired response is a system that quickly limits the vehicle speed to the target speed with very little overshoot. It is noted that minimizing overshoot overall, as opposed to simply reducing overshoot quickly is desired, as the vehicle speed is desirably maintained below the EPAS cutoff speed, for example, at all times, but flexibility through increased speed availability may also be desired. Accordingly, system 12 is configured to adjust to the outside disturbances of road grade and throttle apply input, which may be the most likely disturbances to significantly affect system 12 and the overall speed of vehicle 10.
It is for this reason that system 12 uses feed forward tables based on a road grade estimate 32 and the amount of throttle applied (“throttle apply”) to increase the robustness of the speed limiting controller for use in system 12, as shown in FIG. 3. In particular, system 12 is configured such that controller 30 receives a vehicle speed input 28 from speed detector 26, which is compared with a vehicle target speed 38, which may be stored in memory 36, to arrive at a speed error signal 40, which is input into PID controller 42 to arrive at an initial brake torque request signal 43. Simultaneously, system 12 can, using sensor assembly 20 (and possibly various other inputs, as described further below) estimate the road grade RGt below trailer 14 to determine if additional brake torque is desirable. In general, such additional torque can be added to the initial brake torque demand signal 43 to compensate for an additional load on vehicle 10 by trailer 14 being on an increased road grade (i.e. an additional disturbance). An additional torque demand can be correlated with variation in road grade RGt in feed forward tables stored in memory within controller 30 and can vary with trailer 14 weight, brake system 16 parameters, desired response characteristics of system 12 and the like.
Still further, controller 30 can receive a throttle apply input 24 from throttle sensor 22 and can determine a desired additional brake torque demand corresponding to an amount of disturbance (if any) affecting system 12 due to an increased throttle application by the driver. An additional brake torque demand can be correlated with variation in throttle in another feed forward table stored in memory 36 within controller 30 and can vary with engine characteristics, engine control settings, desired response characteristics of system 12, and the like. The feed forward gain added to the initial brake torque demand 43 can result in a modified brake torque request 34 that can be output from controller 30 to brake system 16 to slow vehicle 10 appropriately.
Referring to FIG. 4, a method 50 for controlling the speed of vehicle 10 using the system 12, is described, along with example steps by which controller 30 can estimate the road grade RGt beneath trailer 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 expressed as a percentage of variation from a horizontal (zero) grade Hg. A road grade RGv beneath vehicle 10 vehicle is a grade of an area of the road beneath vehicle 10. A trailer road grade RGt is a grade of a road beneath the trailer 14. In the example of FIGS. 1 and 2, the trailer road grade RGt and the vehicle road grade RGv are the same in FIG. 1 and different in FIG. 2. In FIG. 2, the trailer road grade RGt is greater than the vehicle road grade RGv.
As discussed above, vehicle 10 includes a sensor assembly 20 that monitors the vehicle road grade RGv. The assembly may include accelerometers, wheel speed sensors, and the like, that may monitor the vehicle road grade RGv according to known methods. The vehicle 10 further includes controller 30 coupled to the sensor assembly 20. The controller 30 is a specialized controller and includes programming to estimate the trailer road grade RGt based, in part, on the vehicle road grade RGv. The controller 30 and sensor assembly 20 together provide a trailer road grade assembly or system 12 for controlling the trailer 14. Although described as road grade, it is to be understood that a traditional road is not required for there to be a road grade. Road grade refers generally to the area underneath a vehicle 10 whether that area is a road or that area is an off-road.
With continuing reference to FIG. 4, an example trailer road grade estimating and speed control method 50 includes the step 52 of estimating a first total mass of vehicle 10 and trailer 14. The step 52, thus, establishes a reference total mass. Notably, road grade RGt beneath the trailer 14 is one of the variables used to estimate the total mass. In this example, changes in the total mass are attributed to changes in the road grade RGt beneath the trailer 14 relative to the road grade RGv beneath vehicle 10. Subsequently, at a step 54, the method 50 estimates a second total mass of vehicle 10 and trailer 14. The step 54 occurs after movement in a reverse direction of the trailer 14 such as from a first position (e.g. as shown in FIG. 1) to a second, different position (e.g. as shown in FIG. 2). At a step 56, the method 50 calculates whether the first total mass is different than the second total mass. If not, the method 50 returns to the step 54 and estimates another second total mass after more movement of the trailer 14.
If the second total mass is different than the first total mass, the method 50 moves to step 58. At step 58 the difference between the first total mass and the second total mass are used to calculate the road grade beneath the trailer 14. The method 50 may then correlate the road grade RGt beneath trailer 14 with an additional brake torque demand in step 60 before feeding such additional brake torque demand to an initial brake torque demand 43 from PID controller 42 in step 62, which may be effective to adjust the response of system 12 to an overspeed condition, such as by automatically applying additional braking force that that which would otherwise be demanded by controller 30. As discussed above, the method 50 can also feed forward values based on torque apply to a brake torque demand from PID controller 42 to further adjust the final brake torque demanded by controller 30.
In a more specific example of the method 50, the step 52 includes estimating the total mass of the vehicle 10 and the trailer 14 using the equation:




  
    
      M
      c
    
    =
    
      
        
          T
          pt
        
        -
        
          T
          brk
        
      
      
        
          R
          w
        
        ⁢
        
          a
          x
          s
        
      
    
  
  ,




    
    
        where:
        Mc represents the total unit mass of the vehicle 10 added to the total mass of the trailer 14;
        Rw represents the wheel radius;
        axs represents an acceleration output from an accelerometer;
        Tpt represents a torque output from a powertrain of the vehicle 10; and
        Tbrk represents a braking force output from a frictional brake of the vehicle 10, the trailer 14, or both.
    
    


The above equation may be utilized to calculate total mass when, for example, the vehicle 10 and trailer 14 are moving forward. If the vehicle 10 and the trailer 14 stray from forward movements and, for example, begin to reverse, the example method 50 uses an alternative formula to instantaneously estimate mass the of the vehicle 10 and the trailer 14. The equation below shows an example formula that demonstrates relationships between variables when the vehicle 10 and the trailer 14 are reversing:




  
    
      
        M
        ⋓
      
      c
    
    =
    
      
        
          M
          c
        
        +
        
          
            m
            tlr
          
          ⁢
          g
          ⁢
          
            
              (
              
                
                  sin
                  ⁢
                  
                    
                  
                  ⁢
                  
                    α
                    
                      r
                      ⁢
                      
                        
                      
                      ⁢
                      2
                    
                  
                
                -
                
                  sin
                  ⁢
                  
                    
                  
                  ⁢
                  
                    α
                    
                      r
                      ⁢
                      
                        
                      
                      ⁢
                      1
                    
                  
                
              
              )
            
            
              a
              x
              s
            
          
        
      
      =
      
        
          
            T
            pt
          
          -
          
            T
            brk
          
        
        
          
            R
            w
          
          ⁢
          
            a
            x
            s
          
        
      
    
  
  ,




    
    
        where:
        {hacek over (M)}c is the instantaneously estimated mass for the vehicle 10 plus the trailer 14;
        mtlr is a mass of the trailer 14;
        αr1 is a road grade under the vehicle 10;
        g represents the gravity of earth; and
        αr2 is the road grade under the trailer 14.
    
    


Changes in the instantaneously estimated mass {hacek over (M)}c as the vehicle 10 and the trailer 14 reverse are used to determine the grade αr2 under the trailer 14. To derive the grade αr2 under the trailer 14, the changes in the instantaneously estimated mass {hacek over (M)}c are determined using the equation:

RGload+=mtlrg(sin αr2−sin αr1)=({hacek over (M)}c−Mc)axs,

    
    
        where RGload+ represents changes in load due to changes in road grade beneath the vehicle 10 relative to the trailer 14.

The estimated road grade αr2 beneath the trailer 14, is then determined using the equation:

    
    






  
    
      α
      
        r
        ⁢
        
          
        
        ⁢
        2
      
    
    =
    
      
    
    ⁢
    
      arcsin
      ⁡
      
        [
        
          
            
              
                (
                
                  
                    
                      M
                      ⋓
                    
                    c
                  
                  -
                  
                    M
                    c
                  
                
                )
              
              ⁢
              
                a
                x
                s
              
            
            
              
                (
                
                  
                    M
                    c
                  
                  -
                  
                    m
                    trk
                    *
                  
                
                )
              
              ⁢
              g
            
          
          +
          
            sin
            ⁢
            
              
            
            ⁢
            
              α
              
                r
                ⁢
                
                  
                
                ⁢
                1
              
            
          
        
        ]
      
    
  
  ,




    
    
        where m*trk is an estimated mass of the vehicle 10.

The mass of the vehicle 10 may be determined by weighing the vehicle 10 or through some other technique, for example. A first technique uses a constant value of the truck curb weight as m*trk. Such a nominal value may be evaluated during or after assembling the vehicle 10 at a factory and may be based on the standard truck loading condition. In such an example, m*trk would remain constant. In a second example technique, m*trk may be an estimated mass based on the vehicle 10 mass for a specific trip. This is useful when, for example, the vehicle 10 is periodically heavily loaded with cargo. This second technique may provide a better estimate than the constant of the first technique. The mass of the vehicle 10 for the second example technique may be obtained using many different methods. An example is to estimate mass of the vehicle 10 using active suspension sensor. Deflection of the active suspension sensor at a steady state tells the load variation on truck unit. The estimated truck unit mass m*trk in such an example will be the truck curb weight plus the indicated load weight from the suspension deflection.

    
    


In some examples, the estimated road grade can be used to calculate a total road grade torque exerted on the vehicle 10. This total road grade torque, represented as τrgl, can be calculated using the equation:

τrgl=(Mc−m*trk)g sin αr2+m*trkg sin αr1.

The total road grade torque can, as described above, be used as a feedforward to derive a compensating torque to control the backup speed of the trailer 14 during an automatic backup procedure. As also mentioned previously, additional feedforward compensating torque for backup speed control can also be provided by the torque apply signal 24.

With respect to FIG. 5, another embodiment of a system 112 including a controller 130 for assisting in maintaining the speed of vehicle 10 below at maximum level when reversing a trailer 14, including under various forms of automated assistance from system 112, is described. In particular, controller 130 operates using a PID controller 142 in a manner similar to that described above with respect to FIG. 3, where PID controller 142 provides a brake torque request 134 to brake system 116 to attempt to slow vehicle 10 to reduce an error signal 140 between a detected speed 128 and a target speed 150. However, controller 130 can employ a dynamic adjustment of the vehicle speed error to adjust the controller for steady state error or variation in overshoot. Such a controller 130 can be used in a vehicle 10 that is not configured for providing an estimate for the road grade below trailer 14 or can be incorporated into the above described system 12 to provide for robust overshoot control in a condition where a road grade estimate is not available (such as when the associated system has not yet accumulated enough data to implement the above equations or the like).
System 112, in particular, dynamically adjusts the target vehicle speed to force the controller to come back to the desired steady state speed based on the effect the adjustment on the target speed has on the speed error 140. In particular controller 130 includes the ability, illustrated in module 144 to receive as input the vehicle speed 128 from speed detector 126, which can be compared against a predetermined condition in the form of an initial (non-adjusted) target speed plus a predetermined maximum allowable error (which may be referred to as a “threshold speed”). Module 144 can then determine if the vehicle speed plus the maximum error is less than the non-adjusted target speed plus the maximum error. If such a condition is present, module 144 can maintain a “NoAdj” mode, in which the non-adjusted target speed is output from memory 136 for use in the error calculation for output of the error 140 to PID controller 142. If module 144 determines that the current speed 128 plus the maximum error is greater than the target speed plus the maximum error, an adjusted (lowered) target speed can be substituted for the predetermined target speed in determining the error 140 provided to PID controller 142. A dynamically lowered error 140 increases the brake torque request 134 output by controller 142, which forces system 112 to lower the speed of vehicle 10 faster than it would using the non-adjusted target speed.
FIG. 6 illustrates a method 166 by which system 112 can operate to attempt to regulate the speed of vehicle 10 during an assisted backup operation. In particular, once initiated in step 168, system 112 operates with controller 130 utilizing the actual, non-adjusted target speed to send to PID controller 142 (step 170 ). If, however, in step 172 module 144 determines that the detected speed 128 of vehicle 10 is greater than the target speed plus the maximum error, module 144 can cause controller 130 to transition to a “timer” state. As the maximum error may be the maximum amount of error that is desired for the steady state behavior of the controller, the timer state is used as a timeout period to ensure that the overshoot of the controller does not affect the steady state behavior by lowering the target speed in response to controllable overshoot. Accordingly the delay in step 174 may correlate with the response time of PID controller 142 or other, related parameters of system 112. If the detected speed 128 is brought back down such that the speed 128 plus the maximum error is lower than the non-adjusted target speed plus the maximum error before the delay in step 174 is over, then the system transitions back to the “NoAdj” state (step 170).
If the speed 128 is still such that speed 128 plus the maximum error is greater than the non-adjusted target speed plus the maximum error after the delay 174 is over, then the system 112 in step 176 transitions to an “Adjustment” state. In such a state, the target speed 150 that is fed into the PID controller 142 is substituted with a downward adjusted target speed 148 to pull the steady state speed back towards the actual target speed. If after another delay period (step 180) the speed is still high (as determined in step 182), the adjusted target speed 148 will be adjusted downward again (step 178). This will continue until the speed 128 is within the determined range, as determined in step 182.
If the speed 128 drops such that the speed plus the maximum error is below the non-adjusted target speed plus the maximum, such as when the driver is applying the brakes to slow down or the trailer 14 is no longer on a higher road grade area than vehicle 10, the system 112 transitions into a “slowrise” state 184. This state is designed to slowly raise the adjusted target speed 148 back up to the non-adjusted target speed at a controlled rate. The slow raising of the adjusted target speed 148 can help prevent undesirable behavior in the controller 130. Finally, once the adjusted target speed 148 reaches the non-adjusted target speed again, the system 112 reenters the “NoAdj” state (step 170) until system 112 is deactivated.
Referring to FIG. 7, another embodiment of a system 212 for limiting the speed of a vehicle 10 based on a mass of trailer 14 is described. The system 212 includes controller 230, which receives a vehicle speed input 228 from speed detector 226. Vehicle speed input 228 is compared with a vehicle target speed 238 stored in memory 236 to arrive at a speed signal error 240. Speed signal error 240 is inputted into PID controller 242 to ultimately arrive at brake torque request 234, which is outputted from controller 230 to brake system 216 to slow vehicle 10 appropriately. In the illustrated embodiment, PID controller 242 may be modified directly based on the mass of trailer 14. According to one embodiment, PID controller 242 is tuned for different trailer masses and the gains of PID controller 242 are determined using lookup tables, which may be stored to a memory (e.g., 236) of controller 230.
Alternatively, with reference to FIG. 8, controller 230 may be configured as a feed forward controller where PID controller 242 outputs an initial brake torque request signal 243 that is added to a feed forward trailer mass gain 250 that may be supplied from trailer mass estimation module 252 and helps compensate for variations in trailer mass. The PID controller 242 may be nominally tuned and the value of the feed forward trailer mass gain 250 will depend on the mass of trailer 14. While not shown in FIG. 7 or 8, it should be appreciated that brake torque request 234 may include contributions from a road grade estimate, a throttle apply input, and/or other considerations described previously herein.
Referring to FIG. 9, controller 230 is shown in one embodiment of a system 312 for assisting a vehicle 320 backing a trailer 325, also referred to herein as a trailer backup assist system. Controller 230 may be configured similarly to that shown in either FIG. 7 or 8 and includes a memory 332 having instructions 334 stored thereon. The instructions 334 may be tangibly embodied as non-transitory computer readable medium and are executable by a processor 336. The instructions are configured to cause the processor 336 to carry out operations for generating a steering command 338 for a steering system 340 of the vehicle 320, which may include an electric power assisted steering (EPAS) system. Additionally, the instructions 334 are configured to cause the processor 336 to carry out operations for generating a brake torque request 234 to a brake system 216 of the vehicle, as described previously herein.
The steering command 338 may be generated in part based on a hitch angle and a kinematic relationship determined between the vehicle 320 and the trailer 325. In turn, a power-steering system controls steered wheels of the vehicle 320 based on the steering command 338. The steering of the vehicle 320 may be performed autonomously by the system 312 or manually via an input device such as a rotatable knob or steering wheel of the vehicle 320. Additional information regarding trailer backup assist systems and the generation of a steering command is found in U.S. Patent Publication No. 2014/0379219 to Rhode et al., entitled “TRAILER BACKUP ASSIST CURVATURE CONTROL,” filed Sep. 10, 2014, the entire disclosure of which is incorporated herein by reference.
According to one embodiment, the steering command 338 and the brake torque request 234 are each generated, at least in part, as a function of a mass of the trailer 325. This may be achieved by modifying the gains of the controller 230 to compensate for variation in the mass of the trailer 325. Compensating for variation in trailer mass is particularly advantageous because trailers of different masses will behave differently while being reversed. For example, if backed along a curved trajectory, a lighter trailer will generally turn more quickly than a heavier trailer. Thus, if trailer mass is not compensated for, a driver along with other vehicle occupants will encounter inconsistent experiences when reversing trailers of different masses. To provide a more consistent experience, the gains of controller 230 may be increased or decreased based on how heavy or light the trailer 325. In one embodiment, the controller 230 may be tuned for a particular trailer mass and the gains of the controller 230 may be increased if the trailer 325 is heavier or decreased if the trailer 325 is lighter. In so doing, the driver and any other vehicle occupants are provided a more consistent experience whenever the vehicle 320 reverses a trailer 325, regardless of what the trailer mass is. As described herein, the gains of the controller 230 may be determined using lookup tables.
In operation, the mass of the trailer 325 may be determined in a variety of manners. According to one embodiment, a sensor system 345 operatively coupled to the trailer 325 determines the mass of the trailer 325 and sends the corresponding trailer mass information 350 to the controller 230. Additionally or alternatively, the mass of the trailer 325 may be determined by first weighing the trailer 325 (e.g., via a weigh scale) and then using a user-input device 352 to send the corresponding trailer mass information 354 to the controller 230. The trailer mass information 354 may be supplied to the controller 230 using a user-input device 352 located within the vehicle 320 such as a touchscreen display of a center console. It is also contemplated that the mass of the trailer 325 may also be supplied to the controller 230 using a portable electronic device configured to wirelessly communicate with the controller 230. Such electronic devices may include smartphones, tablets, and the like. Additionally or alternatively still, the mass of the trailer 325 may be determined based on trailer dynamics while the vehicle 320 and trailer 325 are in motion, as described in U.S. Pat. No. 8,793,035 to Yu et al., entitled “DYNAMIC ROAD GRADIENT ESTIMATION,” filed Jan. 7, 2013 the entire disclosure of which is incorporated herein by reference.
Referring to FIG. 10, a method 400 for assisting a vehicle 320 in reversing a trailer 325 is described with continued reference to the system 312 disclosed in FIG. 9. The method 400 may be embodied as instructions 334 stored in memory 332 and executable by processor 336 of controller 230. In describing the method 400, it is assumed that the vehicle 320 and trailer 325 are about to engage in a reversing maneuver. For example, the method 400 may be initiated at step 410 when a driver of the vehicle 320 shifts into reverse or otherwise communicates his or her intent to perform a reversing of the trailer 325. At step 420, the mass of the trailer 325 is determined. As described herein, there are several ways in which the trailer mass can be computed such as, but not limited to, using sensor system 345, weighing the trailer mass and inputting the trailer mass to the system 312 via user-input device 352, or via calculations related trailer dynamics while the trailer 325 is in motion. Next, at step 430, the controller 230 checks whether a straight backup maneuver is being performed, that is, whether the trailer 325 is being reversed in a substantially straight line. If so, the controller 230 generates a brake torque request as a function of the trailer mass at step 440. As described herein, the brake torque request is sent to the brake system 216 to control the speed in which the vehicle 320 and the trailer 325 are being reversed. The brake torque request may additionally or alternatively be a function of other considerations described herein such as, but not limited to, a road grade estimate and/or a throttle application signal. If it is determined at step 430 that a straight backup maneuver is not being performed, the controller 230 generates a brake torque request along with a steering command, each being a function of trailer mass, as illustrated in steps 450 and 460, respectively. As described herein, the steering command is sent to the steering system 340 to control steered wheels of the vehicle 320 while the trailer 325 is being reversed. As further described herein, the steering command may also be a function of a hitch angle and a kinematic relationship determined between the vehicle 320 and the trailer 325. It should be appreciated that the controller 230 may modify the brake torque request and the steering command (when applicable) as needed so long as the trailer 325 is being reversed. Once the vehicle 320 and the trailer 325 are parked (e.g., the driver places the vehicle 320 in park), trailer backup assist functionality may come to an end at step 470.
Accordingly, trailer backup assist system has been described herein that is configured to generate a brake torque request for limiting the speed of a vehicle and a steering command for controlling a steering system responsible for automatically steering the vehicle while the vehicle reverses the trailer. The brake torque request and the steering command may each be based at least in part on a mass of the trailer. In this manner, a more consistent driving experience is achieved by virtue of the trailer backup assist system being able to compensating for trailer mass during a backing maneuver.
It will be understood by one having ordinary skill in the art that construction of the described invention and other components is not limited to any specific material. Other exemplary embodiments of the invention disclosed herein may be formed from a wide variety of materials, unless described otherwise herein.
For purposes of this disclosure, the term “coupled” (in all of its forms, couple, coupling, coupled, etc.) generally means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components (electrical or mechanical) and any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature or may be removable or releasable in nature unless otherwise stated.
It is also important to note that the construction and arrangement of the elements of the invention as shown in the exemplary embodiments is illustrative only. Although only a few embodiments of the present innovations have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present innovations. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present innovations.
It will be understood that any described processes or steps within described processes may be combined with other disclosed processes or steps to form structures within the scope of the present invention. The exemplary structures and processes disclosed herein are for illustrative purposes and are not to be construed as limiting.
It is also to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.

## Claims

1. A trailer backup assist system for a vehicle reversing a trailer, comprising:
a brake system; and
a controller configured to:
generate a speed signal error by comparing a stored vehicle target speed with a vehicle speed input received from a speed detector;
generate a brake torque request based on the speed signal error and a trailer mass; and
output the brake torque request to the brake system;
wherein the controller is further configured to calculate an estimated road grade of a surface on which the trailer is positioned;
wherein the estimated road grade is determined by estimating a first total mass of the vehicle and trailer and comparing the first total mass to a second total mass of the vehicle and trailer that is estimated after movement of the trailer in a reverse direction from a first position to a second position;
wherein the estimated road grade is based on the difference between the first and second total mass; and
wherein the brake torque request is further based on the estimated road grade and a throttle application signal from a throttle sensor.

2. The trailer backup assist system of claim 1, wherein the trailer mass is obtained via user input.

3. The trailer backup assist system of claim 1, wherein the trailer mass is obtained via sensors disposed on the trailer.

4. The trailer backup assist system of claim 1, wherein the trailer mass is estimated based on trailer dynamics while the trailer is in motion.

5. The trailer backup assist system of claim 1, wherein the controller comprises a proportional-integral-derivative controller configured to receive the speed signal error and generate the brake torque request, and wherein the proportional-integral-derivative controller is tuned for different trailer masses and the gains of the proportional-integral-derivative controller are determined using lookup tables.

6. The trailer backup assist system of claim 1, wherein the controller is further configured to output a steering command to a steering system of the vehicle, wherein the steering command is based at least in part on the trailer mass.

7. A trailer backup assist system for a vehicle reversing a trailer, comprising:
a brake system of the vehicle; and
a controller configured to:
generate a speed signal error from a stored vehicle target speed and a vehicle speed input received from a speed detector;
generate an initial brake torque request signal from the speed signal error;
generate a brake torque request from the initial brake torque request signal and a feed forward gain that is based on trailer mass and supplied from a trailer mass estimation module; and
output the brake torque request to the brake system;
wherein the controller is further configured to calculate an estimated road grade of a surface on which the trailer is positioned;
wherein the estimated road grade is determined by estimating a first total mass of the vehicle and trailer and comparing the first total mass to a second total mass of the vehicle and trailer that is estimated after movement of the trailer in a reverse direction from a first position to a second position;
wherein the estimated road grade is based on the difference between the first and second total mass; and
wherein the brake torque request is further based on the estimated road grade and a throttle application signal from a throttle sensor.

8. The trailer backup assist system of claim 7, wherein the trailer mass is obtained via at least one of user input and sensors disposed on the trailer.

9. The trailer backup assist system of claim 7, wherein the trailer mass is estimated based on trailer dynamics while the trailer is in motion.

10. A method of controlling the speed of a vehicle towing a trailer, comprising the steps of:
receiving a vehicle speed input from a speed detector;
generating a speed signal error from a stored vehicle target speed and the vehicle speed input;
generating an initial brake torque request signal from the speed signal error;
generating a brake torque request from the initial brake torque request signal, a feed forward gain that is based on trailer mass and supplied from a trailer mass estimation module, an estimated road grade of a surface on which the trailer is positioned, and a throttle application signal from a throttle sensor; and
outputting the brake torque request to a brake system of the vehicle;
wherein the estimated road grade is determined by estimating a first total mass of the vehicle and trailer and comparing the first total mass to a second total mass of the vehicle and trailer that is estimated after movement of the trailer in a reverse direction from a first position to a second position; and
wherein the estimated road grade is based on the difference between the first and second total mass.

11. The method of claim 10, wherein the trailer mass is obtained via at least one of user input and sensors disposed on the trailer.

12. The method of claim 10, wherein the trailer mass is estimated based on trailer dynamics while the trailer is in motion.

13. The method of claim 10, wherein the initial brake torque request signal is generated by a proportional-integral-derivative controller using the speed signal error as input.

14. The method of claim 10, further comprising the step of outputting a steering command to a steering system of the vehicle, wherein the steering command is based on the trailer mass, a hitch angle, and a kinematic relationship between the vehicle and the trailer.