Abstract:
The present disclosure relates to a method for controlling an application of regenerative brake torque to a plurality of wheels of at least one of a hybrid electric vehicle or an electric vehicle, to avoid brake instability. The method may involve sensing variables such as an angle of a steering wheel of the vehicle, a speed of the vehicle, a brake pedal rate as an operator engages a brake pedal, and a wheel slip of each of the front and rear wheels. A commanded lateral acceleration may be determined representing a steady state lateral acceleration that the vehicle would reach at an actual vehicle speed and with a presently sensed steering wheel angle. The application of regenerative brake torque can then be controlled based on the sensed wheel slips relative to at least one predetermined wheel slip limit. The predetermined wheel slip limit is determined based at least in part on the determined commanded lateral acceleration.

Description:
FIELD 
       [0001]    The present disclosure relates to regenerative braking systems for use with electrically powered vehicles, and more particularly to a system and method for controlling regenerative braking in a manner that controls delimiting of the regenerative braking to better maintain the vehicle stable during braking maneuvers. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    In a vehicle that is driven completely, or partly, by an electrical machine, kinetic energy can be regenerated to electrical energy and stored in a battery during braking. This is what is referred to as “regenerative braking.” Another term for this type of energy conversion is “recuperative braking.” 
         [0004]    In a hybrid electric vehicle (HEV), regenerative braking provides by far the biggest fuel savings compared to other typical HEV techniques (e.g., stopping internal combustion engine when not used/needed, engine load point shifting, etc.). In a “Battery Electric Vehicle” (BEV), regenerative braking extends the driving range of the vehicle. If the vehicle has a standard brake system (e.g., with an antilock braking system (ABS), TCS and ESP), regenerative braking will be added on top of the braking via the foundation brake system, as requested by the braking action applied by the driver, and potentially modulated by the brake controller system of the vehicle. 
         [0005]    With any HEV, an important objective is maximizing regenerative braking while still keeping the vehicle stable during braking maneuvers. Avoiding rear “over-braking”, that is excessive regenerative braking applied to the rear wheels of the vehicle, is especially important. This has been a significant challenge for various prior art systems. 
       SUMMARY 
       [0006]    In one aspect the present disclosure relates to a method for controlling an application of regenerative brake torque to a plurality of wheels of at least one of a hybrid electric vehicle or an electric vehicle, to avoid brake instability. The method may comprise sensing an angle of a steering wheel of the vehicle; sensing a speed of the vehicle; sensing a brake pedal position as an operator of the vehicle engages a brake pedal of the vehicle; sensing a wheel slip of each of a pair of front wheels of the vehicle; and sensing a wheel slip of each one of a pair of rear wheels of the vehicle. A commanded lateral acceleration may be determined representing a steady state lateral acceleration that the vehicle would reach at an actual vehicle speed and with a presently sensed steering wheel angle. The application of regenerative brake torque may then be controlled based on the sensed wheel slips relative to at least one predetermined wheel slip limit. At least one predetermined wheel slip limit is determined based at least in part on the determined commanded lateral acceleration. 
         [0007]    In another aspect the present disclosure relates to a method for controlling an application of regenerative brake torque to a plurality of wheels of at least one of a hybrid electric vehicle or an electric vehicle, to avoid brake instability. The method may comprise sensing a brake pedal position as an operator of the vehicle engages a brake pedal of the vehicle; determining a commanded lateral acceleration representing a steady state lateral acceleration that the vehicle would reach at an actual vehicle speed and with a presently sensed steering wheel angle. The method may also involve sensing a wheel slip of each one of a pair of front wheels of the vehicle and determining therefrom a minimum front wheel slip for the two front wheels. A wheel slip of each of a pair of rear wheels of the vehicle may also be sensed and used to determine a maximum rear wheel slip for the two rear wheels. The application of regenerative brake torque may be controlled such that the regenerative brake torque is not allowed to increase in response to brake pedal movement, but is instead is maintained constant in a hold condition, when either of the following conditions occurs: the maximum rear wheel slip exceeds a first predetermined limit; or the maximum rear wheel slip exceeds the front wheel minimum slip by a second predetermined limit. The first and second predetermined limits are determined based at least in part on the determined commanded lateral acceleration. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0010]      FIG. 1A  is a high level block diagram of typical major components of a hybrid electric vehicle (HEV) in which the regenerative braking system and method of the present disclosure is implemented: 
           [0011]      FIG. 1B-1C  is an activity flow diagram illustrating operation of the present system and method; 
           [0012]      FIG. 2  is a chart presenting a summary of test cases and test conditions under which specific tests were conducted using a system and method in accordance with the present disclosure; 
           [0013]      FIG. 3A  is a plot of torque and the rear wheels and the front wheels relative to time, under a straight line coasting condition without the use of the system and method of the present disclosure, and wherein the vehicle has lost its grip and begins to spin; 
           [0014]      FIG. 3B  is a plot of the slip angle of the vehicle in degrees relative to time, under the same conditions as described above for  FIG. 3A ; 
           [0015]      FIG. 3C  shows graphs of the forward velocity of the vehicle (VelocityForward) and accelerator pedal position (AccelPdPosn) relative to time, with the vehicle under the same conditions as described above for  FIG. 3A ; 
           [0016]      FIGS. 4A-4C  show plots in relation to  FIGS. 3A-3C , respectively, but with the system and method of the present disclosure being applied to control regenerative braking; 
           [0017]      FIG. 5  shows a chart of test conditions for tests conducted on a vehicle while coasting during cornering; 
           [0018]      FIGS. 6A-6C  illustrate the performance parameters described above corresponding to  FIGS. 3A-3C , respectively, but without use of the system and method of the present disclosure, and when the vehicle has lost its grip and spins while coasting during a cornering maneuver; and 
           [0019]      FIGS. 7A-7C  illustrate plots in relation to  FIGS. 6A-6C , respectively, but with the system and the method of the present invention being applied to control regenerative braking. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0021]    Referring to  FIG. 1A  a high level block diagram is shown of various components of a hybrid electric vehicle (HEV)  10  incorporating a regenerative braking system in accordance with the present disclosure. The HEV  10  in this example may include an electric motor control subsystem  12  having a torque control subsystem  14  and an inverter  16 . An output of the inverter  16  may be fed into an electric motor  18 . A speed sensor  20  may be used to monitor the speed of an output shaft  22  of the electric motor  18 . The output shaft  22  may apply an input drive signal to a rear differential  24 . The rear differential  24  has axles  26  and  28  which are used to drive the rear right wheel (RRW)  30  and rear left wheel (RLW)  32  respectively. Speed sensors  34  and  36  are used to detect the speed of each wheel  30  and  32 , respectively. 
         [0022]    The outputs of the speed sensors  34  and  36  are transmitted to a brake control subsystem  38 . The brake control subsystem  38  transmits the speed signals sensed by the sensors  34  and  36  (ω wfl , ω wfr , ω wrl , and ω wrr ), along with a brake pressure signal (PBrk) and a brake pedal position signal (aBrkPed) to a vehicle CAN (Controller Area Network) bus  40 . A high voltage (HV) battery and controller subsystem  42  and a processor based hybrid control system  44  are also in communication with the CAN bus  40 . The hybrid control system  44  may receive the following inputs: 
         [0023]    Initial Inputs for Regenerative Braking 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Brake pressure 
                 P Brk   
               
               
                   
                 Brake pedal position 
                 α BrkPed   
               
               
                   
                 Accelerator position 
                 α Sw   
               
               
                   
                 Steering wheel angle 
                 α Sw   
               
               
                   
                 Wheel angular speed FL 
                 ω wfl   
               
               
                   
                 Wheel angular speed FR 
                 ω wfr   
               
               
                   
                 Wheel angular speed RL 
                 ω wrl   
               
               
                   
                 Wheel angular speed RR 
                 ω wrr   
               
               
                   
                 Vehicle Speed 
                 v Veh   
               
               
                   
                   
               
             
          
         
       
     
         [0024]    The hybrid control system  44  uses the above-listed inputs to generate a torque request (T mreq ) signal which is input to the torque control subsystem  14 . The Tmreq signal represents an internal signal on the CAN bus  40 . T mreg  is the target for the torque control. The torque control controls the three phase AC current to achieve the target torque on the electric motor  18  axle input to the differential  24 . 
         [0025]    The CAN bus  40  also receives inputs from an inertial measurement system  46 , a steering control subsystem  48 , and an internal combustion engine (ICE) control subsystem  50 . The ICE control system  50  is operatively associated with an internal combustion engine (ICE)  52  of the HEV  10  and able to receive inputs from sensors associated with the ICE  52 , as well as to apply signals to various electronic and/or electromechanical components associated with the ICE  52 . 
         [0026]    Referring further to  FIG. 1A , the ICE  52  has an output shaft  54  which drives a front transmission/differential subsystem  56 . The transmission/differential subsystem  56  in turn applies rotational torque to each of drives axles  58  and  60  associated with the front right wheel (FRW)  62  and front left wheel (FLW)  64 . Speed sensors  66  and  68  sense the angular speeds of the FRW  62  and the FLW  64 , respectively, and send electrical signals in accordance therewith to the brake control subsystem  38 . 
         [0027]    Regenerative Braking Algorithm 
         [0028]    The present disclosure is not focused simply on defining a regenerative brake torque based on a driver request (i.e., from the accelerator and brake pedal position), but rather on more effectively limiting a request for regenerative brake torque to better avoid instability when braking the vehicle. The present disclosure is further related to how to eventually cancel regenerative braking in the event the margin for brake instability is determined to be too low. In one aspect, the regenerative braking control methodology of the present disclosure effectively makes use of the commanded lateral acceleration to help limit regenerative braking. Referring to  FIG. 1B-1C , an activity diagram  100  is shown which represents an algorithm (i.e., methodology) by which the system  10  operates. In summary, and with reference to the activity diagram  100 , the present disclosure involves monitoring and/or controlling: 
         [0029]    the Commanded Lateral Acceleration, i.e., the steady state Lateral Acceleration the vehicle would reach at the actual Vehicle Speed and Steering Wheel Angle, is monitored ( 101 ); 
         [0030]    the Max Allowed Regenerative Brake Torque ( 102 ), which is a function of Commanded Lateral Acceleration, to improve brake stability during cornering; 
         [0031]    is rate limited with individually calibrations for increasing ( 103   a ) and decreasing ( 103   b ) regenerative braking scenarios, to provide the final Max Allowed Regenerative Brake Torque ( 103   c ). This Max allowed torque is the limit when no rear rear brake instability have been detected. Typically, a fast decrease rate is allowed to avoid brake instability and a slow increase rate is used to improve drivability; 
         [0032]    Rear Brake stability is estimated by monitoring Rear Wheel Slip (max of left/right) ( 105   a ) and Front Wheel Slip (min of left/right) ( 105   b ); 
         [0033]    Driver Requested Regenerative Brake Torque ( 113 ) is not allowed to increase (e.g., as a function of brake pedal) providing a limited Driver Requested Regenerative Brake torque ( 106   a ) if rear wheel slip exceeds a limit (R_RrBrkSlipHoldLim,  106   b ) or if rear wheel max slip exceeds front wheel slip with another limit (R_RrFrtBrkSlipDiffHoldLim) ( 106   c ). Thus, either condition of rear slip exceeding R_RrBrkSlipHoldLim or rear/front difference exceeding R_RrFrtBrkSlipDiffHoldLim can lead to a “Hold condition” (i.e., when Regen brake torque isn&#39;t allowed to increase); 
         [0034]    The Hold condition( 109   a ) is latched until the driver releases the brake pedal and applies some degree of accelerator input. 
         [0035]    The potentially Limited driver request, due to Hold Condition, is then limited with final Max Allowed Regenerative Brake Torque ( 111 ). 
         [0036]    The Max Positive rate of change ( 104 ), of the limited regeneration request ( 114 ), will be a function of Brake Pedal Rate. The Rate is obtained from The Brake Pedal Position via time derivation and low pass filtering; 
         [0037]    A low Brake pedal rate=&gt;Low Regenerative Brake Torque change rate. By doing so, increased maximum allowed regenerative brake torque can be smoothly made available when the driver hold the brake pedal still. If on the other hand a change in brake pedal rate is sensed, the request will be followed with higher response, and therefore improved controllability; 
         [0038]    Regenerative braking is disabled ( 108   a ) if rear wheel slip (max of left/right) exceeds a limit (R_RrBrkSlipAlwdLim) ( 112   a ) or if rear wheel max slip exceeds front wheel slip (min of left/right) with another limit (R_RrFrtBrkSlipDiffAlwdLim) ( 112   b )=&gt;Regeneration Disable ( 108   b ); 
         [0039]    The Disable ( 109   b ) conditions is latched until the driver releases the brake pedal and applies some degree of accelerator input; 
         [0040]    The rate of disabling regenerative brake torque ( 110   b ) is a function of how serious the brake instability is. The measure for brake instability is the Slip Error ( 110   a ) (i.e., how much the rear slip or rear/front slip difference have changed after the Regen Hold Condition ( 110   a )). If Regenerative torque is not disabled a High Negative rate is allowed ( 110   c ), 
         [0041]    Allowed regenerative brake torque is reduced ( 107   a ) with the increase of foundation brake torque ( 107   b ) occurring after the hold condition ( 109   a ); 
         [0042]    The limits R_RrBrkSlipHoldLim, R_RrFrtBrkSlipDiffHoldLim, R_RrBrkSlipAlwdLim and R_RrFrtBrkSlipDiffAlwdLim are all a function of commanded lateral acceleration (not shown in  FIG. 1B-1C ) to improve brake stability during cornering. 
         [0043]    Listing of Inputs, Outputs and Internal States 
         [0044]    The following is a detailed listing of inputs, outputs, and internal states that are used by a regenerative braking algorithm (i.e., methodology) implemented by the present disclosure: 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 Transformations to Initial Inputs to Produce 
               
               
                 Inputs For FIG. 1A Activity Flow Diagram 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 M_DrvRegReq = f(α Sw , v Veh ) 
               
               
                   
                 r_RrBrkSlip = f(ω wrl,  ω wrr,  v Veh, ) 
               
               
                   
                 r_FrtBrkSlip = f(ω wfl,  ω wfr,  v Veh,  α Sw ) 
               
               
                   
                 a_LatCmd = f(v Veh , α Sw ) 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Inputs 
                   
               
               
                   
                 M_DrvRegReq 
                 Driver Requested Regen Brake Torque 
               
               
                   
                 r_RrBrkSlip 
                 Rear Brake Slip (maximum of Left and 
               
               
                   
                   
                 Right Rear Brake Slip) 
               
               
                   
                 r_FrtBrkSlip 
                 Front Brake Slip (minimum of Left and 
               
               
                   
                   
                 Right Front Brake Slip) 
               
               
                   
                 a_LatCmd 
                 Commanded Lateral Acceleration. The 
               
               
                   
                   
                 steady state Lateral acceleration the 
               
               
                   
                   
                 vehicle would reach at the actual vehicle 
               
               
                   
                   
                 speed and steering wheel angle. 
               
               
                   
                 r_BrkPed 
                 Brake pedal position 
               
               
                   
                 r_AccPed 
                 Accelerator pedal position 
               
               
                   
                 P_Brk_Press 
                 Master Cylinder Brake pressure 
               
               
                   
                 Output 
               
               
                   
                 M_ReqReq 
                 Final Regen Brake Torque request 
               
               
                   
                   
               
             
          
         
       
     
         [0045]    AAM Regen Braking Algorithm Internal States. 
         [0046]    Internal Variables 
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 r_RrBrkSlipHoldLim 
                 Hold Rear Brake Longitudinal Slip limit. 
               
               
                   
                 This is defined as a base calibration 
               
               
                   
                 multiplied by one or more factors that are 
               
               
                   
                 functions of, e.g., a_LatCmd 
               
               
                 r_RrFrtBrkSlipDiffHoldLim 
                 Hold Rear/Front Brake Slip Differential 
               
               
                   
                 limit Is defined as a base calibration 
               
               
                   
                 multiplied by one or more factors that are 
               
               
                   
                 functions of, e.g., a_LatCmd 
               
               
                 r_RrBrkSlipAlwdLim 
                 Allowed Rear Brake Longitudinal Slip. Is 
               
               
                   
                 defined as a base calibration multiplied by 
               
               
                   
                 one or more factors that are functions of, 
               
               
                   
                 e.g., a_LatCmd 
               
               
                 r_RrFrtBrkSlipDiffAlwdLim 
                 Allowed Rear/Front Slip Longitudinal 
               
               
                   
                 Differential. Is defined as a base 
               
               
                   
                 calibration multiplied by one or more 
               
               
                   
                 factors that are functions of, e.g., 
               
               
                   
                 a_LatCmd 
               
               
                 r_RrBrkSlipErr 
                 Rear Brake Slip error 
               
               
                 b_RegHold 
                 Logical state that r_RrBrkSlip or 
               
               
                   
                 r_RrBrkSlip-r_FrtBrkSlip exceeds a hold 
               
               
                   
                 level (below) 
               
               
                 b_RegDsbl 
                 Logical state that r_RrBrkSlip or 
               
               
                   
                 r_RrBrkSlip-r_FrtBrkSlip exceeds an 
               
               
                   
                 allowed level (below) 
               
               
                 M_RegMaxAlldw 
                 Max allowed Regeneative Torque. A 
               
               
                   
                 function of Commanded Lateral 
               
               
                   
                 Acceleration 
               
               
                 M_DrvRegLim 
                 Limited M_DrvRegReq due to Hold 
               
               
                   
                 condition 
               
               
                 M_RegRegLim 
                 Final Limited Regeneration Request 
               
               
                   
                 before reduction with Mechanic brake 
               
               
                   
                 increase after Hold Condition 
               
               
                 M_DrvRegReqHold 
                 M_DrvRegReq sampled and stored at 
               
               
                   
                 b_RegHold condition 
               
               
                 M_RrMechBrk 
                 Mechanical rear Brake Torque = 
               
               
                   
                 K*BrakePressure where K depends on rear 
               
               
                   
                 wheel brake cylinder diameter, rear brake 
               
               
                   
                 disc effective radius, and rear brake pad 
               
               
                   
                 friction coefficient 
               
               
                 M_RrMechBrkHold 
                 M_RrMechBrk sampled at b_RegHold 
               
               
                   
                 condition 
               
               
                 M_RrMechBrkInc 
                 Max increase of Mechanical rear Brake 
               
               
                   
                 Torque since b_RegHold condition 
               
               
                   
               
             
          
         
       
     
         [0047]    In the following description of the regenerative braking algorithm of the present disclosure, Brake Slip and Regenerative Brake Torque are positive at braking. This doesn&#39;t have to be the case in actual implementation and should not limit this application. 
         [0048]    The Max Allowed Regenerative Torque (M_RegMaxAlldw,  102 ) is set as a function of Commanded Lateral Acceleration (a_latCmd,  101 ). The rate of change is limited separately for increasing ( 103   a ) and decreasing ( 103   b ) (calibrations) providing the final M_RegMaxAlldw ( 103   c ). This Max allowed torque is the limit when no rear rear brake instability have been detected. 
         [0049]    The Brake Slip of the front and rear wheels are continuously monitored to determine the maximum (i.e., the greater one of) the left and right front brake slip (r_FrtBrkSlip,  105   a ) and the maximum of the left and right rear brake slip (r_RrBrkSlip,  105   b ). 
         [0050]    If r_RrBrkSlip is higher than r_RrBrkSlipHoldLim ( 106   b ) or r_RrBrkSlip-r_FrtBrkSlip is higher_RFrtrBrkSlipDiffHoldLim ( 106   c ) then b_RegHold will be set=true b_RegHold will be latched ( 109   a ) for the active brake cycle i.e. until the Brake pedal is released and some Accelerator is applied (removing Coast brake request). 
         [0051]    The Driver Requested Regenerative Torque ( 113 ) is not allowed to increase if b_RegHold is true providing a limited Driver Requested Regenerative Brake torque (M_Drv_RegLim,  106   a ). 
         [0052]    M_Drv_RegLim is further limited by M_RegMaxAlldw ( 111 ). 
         [0053]    If Regeneration is not disabled by b_RegDsbl ( 109   b ), described below, M_Drv_RegLim is then rate limited providing M_RegReqLim ( 114 ). 
         [0054]    The Allowed rate of change for increasing torque ( 104 ) is a function of Brake Pedal rate. A low pedal rate=&gt;Low Regenerative Brake Torque change rate. 
         [0055]    When Regeneration is not disabled the allowed decreasing torque rate is a constant High Neg Rate(calibration). 
         [0056]    The Mechanical Rear Brake Torque (M_RrMechBrk,  107   d ) torque is continuously calculated from Brake Pressure (P_Brk_Press). 
         [0057]    When the hold condition b_RegHold gets true the M_RrMechBrk is sampled in M_RrMechBrkHold ( 107   c ). 
         [0058]    If now the driver brakes harder the M_RrMechBrk will increase, after b_RegHold. The increase of mechanical brake M_RrMechBrklnc ( 107   b ) is kept track of according to: ((n) is used to indicate sample number n) M_RrMechBrklnc (n)=max(M_RrMechBrklnc (n-1), M_RrMechBrk(n) -M_RrMechBrkHold). 
         [0059]    To avoid even higher rear brake slip, the Regen Brake Torque M_ReqReqLim is then reduced with the increase in M_RrMechBrk (but is not allowed to go negative) providing the final limited Regeneration Request M_RegReq ( 115 ): 
         [0060]    M_ReqReq=max(0, M_DrvRegReqLim-M_RrMechBrklnc). 
         [0061]    Normally this will keep the Rear Brake Slip well limited, but if r_RfBrkSlip r_RrBrkSlipAlwdLim or if r_RrBrkSlip−r_FrtBrkSlip exceeds r_RFrtrBrkSlipDiffAlwd, a regeneration diable condition b_RegDsbl ( 108   a ) is set b_RegDsbl will be latched for the active brake cycle i.e. until the Brake pedal is released and some Accelerator is applied (removing Coast brake request) ( 109   b ). 
         [0062]    At b_RegDsbl the Regenerative braking is cancelled by ramping out the M_RegReqLim ( 114 ) at a rate defined by calibration and with a scaling factor that is a function of the Rear Brake Slip error (r_RrBrkSlipErr,  110   a ): 
         [0063]    r_RrBrkSlipErr=max(r_RrBrkSlip−r_RrBrkSlipHold, r_RrBrkSlip−r_FrtBrkSlip−r_RFrtrBrkSlipDiffHold). A high r_RrBrkSlipErr means that r_RrBrkSlip or r_RrBrkSlip−r_FrtBrkSlip exceeds its hold level by a significant margin. A low r_RrBrkSlipErr means M_RegReq can be ramped out slowly for better comfort. A high r_RrBrkSlipErr will call for fast ramp out in favor of brake stability. 
         [0064]      FIG. 2  shows a summary table of test results using the system and algorithm of the present disclosure for regenerative braking during a system straight line coasting condition, and where Rblim is turned off. In the following discussion the acronym “Rblim” represents the use of the algorithm (i.e., methodology) of the present disclosure for limiting brake torque  FIGS. 3A-3C  provide graphs illustrating front and rear torque ( FIG. 3A ), slip angle ( FIG. 3B ) and forward velocity relative to accelerator pedal position (AccelPdlPosn) ( FIG. 3C ) when coast braking a hybrid vehicle moving straight ahead on a low p surface, with an electric coast torque of 750 Nm, with Rblim off. The Vehicle Slip Angle indicates if the vehicle spins in this test.  FIGS. 4A-4C  illustrate graphs of the same performance parameters but with Rblim on, and a maximum body slip angle of less than 1 degree, and with the vehicle on a low μ (0, 4) surface. In this example the vehicle stays stable. Note the body slip angle is defined as the angle between the vehicle velocity vector and the vehicle body forward direction. For straight line driving, the vehicle velocity shall point in the forward direction (i.e., the slip angle is close to 0). 
         [0065]      FIG. 5  illustrates a table of test results for regenerative coast braking during cornering.  FIGS. 6A-6C  illustrate the rear torque and the front torque each plotted relative to time ( FIG. 6A ), the slip angle and StW_Angl each plotted relative to time ( FIG. 6B ), and the VelocityForward and AccelPdPosn both plotted relative to time( FIG. 6C ) with electric coast torque of 750 Nm in a corner from 40 kph with Rblim off. The Body Slip Angle indicates the vehicle spins in this test. 
         [0066]      FIGS. 7A-7C  illustrate the change in performance from the graphs of  FIGS. 6A-6C  when Rblim is turned on. The vehicle stays stable with a Body Slip Angle less than 5 degrees. 
         [0067]    While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.