Abstract:
A vehicle stability enhancement (VSE) system for a vehicle having at least one vehicle subsystem includes; at least one sensor for sensing at least one vehicle parameter, at least one vehicle control system for adjusting the at least one vehicle subsystem, at least one memory comprising at least one set of gain factors, and a controller responsive to the at least one sensor and the at least one set of gain factors for controlling the at least one vehicle control system.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to a vehicle stability enhancement (VSE) system and a method of operation thereof, and more particularly to the incorporation of VSE information into the steering system dynamics.  
         BACKGROUND  
         [0002]    Traditional vehicle chassis subsystems, such as steering, braking and suspension subsystems, are passive, meaning that their responsiveness under operating conditions is determined prior to the vehicle leaving the point of manufacture. In such traditional arrangements, the design of the particular chassis subsystem must be determined up-front and must take into consideration the purpose of the vehicle, such as, for example, whether the vehicle will be used primarily as a cruising vehicle or whether it will be used primarily as a sporty, high performance, vehicle. Steering subsystems with power steering assist may be designed with a greater degree of assistance for cruising vehicles and a lesser degree of assistance for high performance vehicles. By design, such traditional chassis subsystems cannot adapt or actively respond in real time to a change in driving conditions as commanded by the driver.  
         SUMMARY  
         [0003]    In one embodiment, a vehicle stability enhancement (VSE) system for a vehicle having at least one vehicle subsystem is provided, which comprises; at least one sensor for sensing at least one vehicle parameter, at least one vehicle control system for adjusting the at least one vehicle subsystem, at least one memory comprising at least one set of gain factors, and a controller responsive to the at least one sensor and the at least one set of gain factors for controlling the at least one vehicle control system.  
           [0004]    In another embodiment, a method for actively controlling a vehicle stability enhancement system in a vehicle having at least one vehicle subsystem is provided, which comprises; sensing at least one vehicle parameter, determining at least one control gain factor in response to the at least one vehicle parameter, determining the state of at least one control flag in response to the actuation of at least one control system, calculating at least one control command in response to the at least one control gain factor and the at least one control flag, and providing tactile actuation of the at least one vehicle subsystem in response to the at least one control command. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    Referring now to the figures, which are exemplary embodiments, and wherein like elements are numbered alike:  
         [0006]    [0006]FIG. 1 depicts a generalized schematic of a vehicle operative for implementing the present invention;  
         [0007]    [0007]FIG. 2 depicts a generalized schematic of a vehicle subsystem operative for implementing the present invention;  
         [0008]    [0008]FIG. 3 depicts a generalized flowchart for implementing the present invention;  
         [0009]    [0009]FIG. 4 depicts a block diagram of a control system for implementing the present invention;  
         [0010]    [0010]FIG. 5 depicts a block diagram of a feedback control system for implementing the present invention;  
         [0011]    [0011]FIG. 6 depicts a graphical example of the relationship between a control command and vehicle parameters in accordance with the present invention; and  
         [0012]    [0012]FIG. 7 depicts a generalized diagram of a vehicle responsive to the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0013]    A detailed description of an embodiment of the present invention is presented herein by way of exemplification and not limitation with reference to FIGS.  1 - 7 .  
         [0014]    Vehicle  
         [0015]    [0015]FIG. 1 depicts a generalized schematic of a vehicle  10  having a chassis  20 , a body  30  arranged on chassis  20 , a set of wheels (“W”)  40  rotationally coupled to chassis  20 , a steering mechanism  50  arranged for steering wheels  40 , a braking mechanism (“B”)  60  arranged for decelerating wheels  40  upon command, a suspension mechanism (“S”)  70  disposed between wheels  40  and chassis  20  for damping vibration at wheels  40 , a steering wheel  80  for transferring a driver commanded steering torque to the steering mechanism  50  and for providing the driver with tactile feedback regarding the steering mechanism  50 , and an integrated chassis control system (ICCS)  100 . Steering mechanism  50 , braking mechanism  60 , and suspension mechanism  70  are alternatively referred to as vehicle subsystems. The ICCS  100  includes: a yaw rate sensor (“Yaw”)  110  for sensing the actual vehicle yaw rate in degrees-per-second; wheel velocity sensors (“VS”)  120 ; a lateral acceleration sensor (“Lat”)  130 , such as for example an accelerometer, for sensing the absolute value of the vehicle&#39;s lateral acceleration in g-force; a longitudinal acceleration sensor  140  (“Long”) (e.g., accelerometer) for sensing the absolute value of the vehicle&#39;s longitudinal acceleration in g-force; a steering angle sensor (“SS”)  150  for sensing the angle of steer for the steering wheels; a steering torque sensor (“TS”)  152  for sensing the torque in steering mechanism  50 ; and a brake pressure sensor (“BS”)  155  for sensing the brake fluid pressure. The sensed parameters are herein referred to as vehicle parameters. The ICCS  100  also includes the following vehicle control systems: a steering mechanism control system (“WCS”)  160 , such as, for example, electronically controlled actuators, electric motors, and dampers, for adjusting the stiffness and damping characteristics of, and the degree of steering assist associated with, the steering mechanism  50 ; a braking mechanism control system (“BCS”)  170  (e.g., electronically controlled actuators, electric motors, and dampers) for adjusting the stiffiess and damping characteristics of, and the degree of pressure-apply rate associated with, the braking mechanism  60 ; and a suspension mechanism control system (“SCS”)  180  (e.g., electronically controlled actuators, electric motors, and dampers) for adjusting the stiffness and damping characteristics of the suspension mechanism  70 . The ICCS  100  further includes: a driving mode switch (“Drug Mode”)  190  for enabling a driver to selectively choose between multiple driving modes, such as, for example, “Normal” and “Sporty” modes, where the “Normal” mode may be for highway cruising and the “Sporty” mode may be for high performance handling; and a central controller  200  arranged in operable communication with sensors  110 ,  120 ,  130 ,  140 ,  150 ,  152 ,  155 , and mechanism control systems  160 ,  170 ,  180 . Control lines  162 ,  172 ,  182 , are depicted, for simplicity, as single lines, but represent both signal communication lines and operational links for communicating with and actuating the mechanism control systems  160 ,  170 ,  180 , respectively. Driving mode switch  190  may include a pushbutton type switch  192 , or any other type of switch suitable for producing a driving mode request signal, and a display  194  for providing feedback to the driver regarding the driving mode setting. BCS  170  is in operable communication with controller  200  via brake master cylinder (“Mstr Cyl”)  210 . “Mstr Cyl”  210  is also in operable communication with brake pedal (“Brk”)  220 . Braking mechanism  60  may be operated by the driver via brake pedal  220  and master cylinder  210 , or by controller  200  via the ICCS  100 , master cylinder  210 , and brake mechanism control system  170 . Brake pressure sensor  155  senses the brake fluid pressure in brake master cylinder  210 . It will be appreciated that while BCS  170  is depicted in the schematic of FIG. 1 as being located between master cylinder  210  and each braking mechanism  60 , it may also be located between controller  200  and master cylinder  210 , depending on whether individual or concurrent wheel braking is desired. Controller  200  includes a memory  230  for storing sensor information, register information and settings, discussed below, and look-up tables of gain factors, also discussed below. The vehicle electrical system  90  provides electrical power to all of the vehicle&#39;s electrically operated systems, including the controller  200  and the mechanism control systems  160 ,  170 ,  180 .  
         [0016]    It will also be appreciated that while the disclosed embodiment refers to only one steering mechanism control system  160 , the disclosed “WCS”  160  is intended to include both a steering torque assist (“STA”) arrangement, as herein disclosed, in combination with a traditional non-power steering arrangement, and a “STA” arrangement in combination with a conventional power steering arrangement. It will further be appreciated that while the disclosed embodiment refers to a vehicle, such as an automobile, having four wheels, the invention described herein is applicable to any vehicle with any number of wheels.  
         [0017]    Alternative vehicles to the disclosed embodiment may be, for example and without limitation, a three-wheel or six-wheel off-road vehicle, designed with normal, sporty, and hill climbing driving modes, and with or without power steering.  
         [0018]    Referring now to FIG. 2, a generalized schematic of steering mechanism  50  and steering mechanism control system  160  with STA actuator  240  is depicted. Steering mechanism control system  160  may also include a conventional power steering arrangement as discussed above. However, for simplicity, such an arrangement is not depicted. Electrical system  90  provides electrical power to STA actuator  240 , which may be, for example, an electric motor, and controller  200 . Steering torque sensor  152  senses the torque in steering mechanism  50 , the torque being delivered to steering mechanism  50  by an operator exerting a torque on steering wheel  80 , and sends a torque signal to controller  200 . Controller  200  calculates a control command, which will be discussed below, for STA actuator  240 , which results in actuation of STA actuator  240  and provides tactile feedback to the operator regarding the steering behavior. The torque provided by STA actuator  240  is referred to as a “steering torque assist” (“STA”) and is intended to influence the steering behavior of the operator of the vehicle.  
         [0019]    Nomenclature  
         [0020]    The nomenclature used herein for implementing the present invention includes the following variables:  
         [0021]    V x =vehicle speed (kilometers-per-hour, kph);  
         [0022]    δ=steering angle;  
         [0023]    L=vehicle wheel base;  
         [0024]    K u =understeer coefficient;  
         [0025]    fn=frequency coefficient, for example, 2 Hertz;  
         [0026]    ζ=damping coefficient, for example, 0.707;  
         [0027]    P_term=proportional term used in proportional-derivative control theory;  
         [0028]    D_term=derivative term used in proportional-derivative control theory;  
         [0029]    Kp=proportional gain factor from, for example, look-up Table 1, (Newton*meters/deg/sec);  
         [0030]    Kd=derivative gain factor from, for example, look-up Table 1, (Newton*meters/deg/sec 2 );  
         [0031]    Ycommand=yaw rate command based on driver input, (deg/sec);  
         [0032]    Yaw=vehicle actual yaw rate, (degrees-per-second, deg/sec));  
         [0033]    T=control sampling time interval, for example, 10-milliseconds (msec);  
         [0034]    k=control sampling time;  
         [0035]    Ye=vehicle yaw rate error, (deg/sec);  
         [0036]    Ye(k)=vehicle yaw rate error at time step k;  
         [0037]    Ye_est=estimated vehicle yaw rate error;  
         [0038]    Ye_est(k)=estimated vehicle yaw rate error at time step k;  
         [0039]    Ye_est(k-l)=estimated vehicle yaw rate error at prior time step (k-l);  
         [0040]    VSE_WFlag=VSE wheel flag (control flag), where VSE_WFlag is (+1) for right front and right rear wheels experiencing a braking condition under VSE system control, and (−1) for left front and left rear wheels experiencing a braking condition under VSE system control;  
         [0041]    STA_FB=steering torque assist feedback torque, (Newton*meters), (N*m);  
         [0042]    STA_FF=steering torque assist feedforward torque from, for example, FIG. 6 graph, (N*m); and  
         [0043]    STorque=steering torque from steering torque sensor, (N*m).  
         [0044]    Yaw rate command (Ycommand) may be calculated as described in commonly assigned U.S. Pat. No. 5,746,486, entitled “Brake Control System”, filed Aug. 29, 1997, which is incorporated herein by reference in its entirety, or it may be calculated according to the following equation:  
           Y command= V   x *δ/( L+K   u   *V   x   2 ).  Equa. 1.  
         [0045]    The following variables are calculated terms:  
           Ye=Y command−Yaw;   Equa. 2.  
           Ye ( k )= Y command( k )−Yaw( k );   Equa. 3.  
           g 1=2*ζ*(2*π* fn );  Equa. 4.  
           g 2=(2*π* fn ) 2 ;   Equa. 5.  
           Ye _est( k )=(1− T*g 1)* Ye _est( k− 1)+ T*g 1*Ye( k )+ T *Ye_est’( k− 1);   Equa. 6.  
           Ye _est’( k )= Ye _est’( k− 1)+ T*g 2*( Ye ( k )− Ye _est( k ));  Equa. 7.  
           P _term= Ye ( k )* Kp;   Equa. 8.  
           D _term= Ye _est’( k )* Kd;   Equa. 9.  
           STA   —   FB=VSE   —   W Flag*|( P _term+ D _term)|; and   Equa. 10.  
           T assist= STA   —   FF+STA   —   FB.    Equa. 11.  
         [0046]    Quotations (“ ”) surrounding a variable designation used herein represents a register in memory  230  containing the value of the respective variable, “| |” designates an “absolute value” operator, and a single quotation (’) following a variable designates a “derivative” operator. A variable name presented in an equation represents a valve associated with the respective variable, and a variable name presented in a process represents a command having a command signal associated with a related valve stored in a register in memory  230 .  
         [0047]    Controller  
         [0048]    Controller  200  is a microprocessor based control system adapted for actively controlling an integrated set of chassis subsytems, and more particularly, for actively providing a steering torque assist to steering mechanism  50  in accordance with control logic described herein. Controller  200  typically includes a microprocessor, ROM and RAM, and appropriate input and output circuits of a known type for receiving the various input signals and for outputting the various control commands to the various actuators and control systems. The control logic implemented by controller  200  is cycled at a control sampling rate of T, and is best seen by referring to FIGS.  3 - 6 .  
         [0049]    Referring to FIG. 3, a generalized flowchart  300  for implementing the present invention begins at start  310 , which includes an initialization procedure that resets all of the system flags, registers and timers. Control logic then enters control loop  320 , which includes the steps of; sensing  330  vehicle parameters from the various sensors discussed above (and more particularly sensing the vehicle speed, the steering angle, the yaw rate, the steering torque, and the wheel flag), determining  340  control gain factors from look-up Table 1 (discussed below), determining  345  the state of the VSE wheel flag (discussed below), calculating  350  a control command for steering mechanism control system  160 , and actuating  360  STA actuator  240  in steering mechanism control system  160  for providing tactile feedback to the operator through steering mechanism  50  and steering wheel  80  regarding the steering behavior. One pass through control loop  320  is completed for each sampling interval T. Process  300  ends  370  when controller  200  interrupts the process or electrical system  90  powers down.  
         [0050]    Step  340  involves the determination of control gain factors Kp and Kd from look-up Table 1 below, which uses vehicle speed as an input. The values provided in Table 1 are meant for exemplary purposes only, and may be changed for design reasons, such as, for example, the design of the vehicle, the intended use of the vehicle, and the desired operating characteristics of the vehicle. Vehicle speeds between or beyond those provided in Table 1 may be interpolated or extrapolated from the values provided.  
                                                                                   TABLE 1                                       Vehicle Speed (kph)                    0   50   100   150   200                            Kp   0.09   0.09   0.06   0.045   0.03           Kd   0.0036   0.0036   0.0036   0.0018   0.0018                      
 
         [0051]    Step  350  involves the calculation of a control command, hereinafter referred to as a steering torque assist (STA) command, represented by variable (Tassist), which is best seen by now referring to FIG. 4.  
         [0052]    In FIG. 4, a block diagram  400  of a control system for controlling the steering torque assist is depicted, which shows the following inputs; vehicle speed  410 , steering angle  412 , yaw rate  414 , steering torque  416 , and VSE wheel flag  418  (VSE_WFlag). The first four inputs are provided by velocity sensor  120 , steering angle sensor  150 , yaw rate sensor  110 , and steering torque sensor  152 . The last input, VSE wheel flag  418 , is provided by controller  200  in response to the vehicle  10  operating in a VSE mode.  
         [0053]    The vehicle of the present invention is considered to be operating in a VSE mode when braking mechanism control system  170  is responding to the VSE system. A brake control system similar to WCS  170  is described in commonly assigned U.S. Pat. No. 5,746,486, entitled “Brake Control System” filed Aug. 29, 1997 (the &#39;486 patent). Braking mechanism control system  170  is considered to be responding to the VSE system when it is operating in a manner similar to an active brake control system as described in the &#39;486 patent, which is herein generally described as the braking mechanism  60  responding to the controller  200 . Since controller  200  controls the action of braking mechanism  60 , controller  200  has information regarding a particular wheel  40  under a VSE system brake command. In the present invention, and as discussed above, the sign of VSE_WFlag is positive for right side wheels under a VSE brake command and negative for left side wheels under a VSE brake command, which may be determined by controller  200  and the operation of BCS  170 .  
         [0054]    Referring back to FIG. 4, block  420  responds to vehicle speed (V x ), block  410 , and steering angle (δ), block  412 , to calculate a yaw command (Ycommand) according to Equation 1 above. The output of block  420  is the yaw command (Ycommand). Block  430  responds to vehicle speed (V x ), block  410 , and steering torque (STorque), block  416 , to calculate a feed forward steering torque assist (STA_FF), block  435 , according to the graph of FIG. 6.  
         [0055]    Referring now to FIG. 6, a graph  600  of the feed forward steering torque assist (STA_FF), block  610 , as a function of the steering torque (STorque), block  620 , and vehicle velocity (V x ), block  630 , is provided. While FIG. 6 is discussed in association with the present invention, it is provided for exemplary purposes only, and it is understood that the graphical representation of output to input may be varied according to alternative design considerations. In the present invention, the sign of the feedforward steering assist (STA_FF) is positive for a right hand turn, and negative for a left hand turn, which may be sensed by steering angle sensor  150 . The control logic of controller  200  enters the graph of FIG. 6 with information relating to the steering torque, block  620 , and the vehicle velocity, block  630 , and exists the graph of FIG. 6 with information relating the the feed forward steering torque assist, block  610 . The information contained within the graph of FIG. 6 may be stored in a look-up table in memory  230 , or may be calculated from an equation. If a look-up table scheme is employed, as in the present invention, controller  200  may interpolate between or extrapolate beyond tabulated discrete data points. As can be seen from the graph of FIG. 6, the feed forward steering torque assist, block  610 , increases in magnitude as the steering torque, block  620 , increases, and decreases in magnitude as vehicle speed, block  630 , increases. Each line of the plurality of graphed lines  640 , represents a graphical relationship between steering torque, block  620 , and feed forward steering torque assist, block  610 , at a given velocity, block  630 .  
         [0056]    Referring now back to FIG. 4, the output of block  430  is the feed forward steering torque assist (STA_FF), block  435 . Block  440  responds to the yaw rate error (Ye), block  425  (which is the output (Ycommand) of block  420  minus the yaw rate (Yaw), block  414 ), the vehicle velocity (V x ), block  410 , and VSE_WFlag, block  418  (discussed above). The output of block  440  is the feedback steering torque assist (STA_FB), block  445 , which is calculated in accordance with Equation  10  above. The output (STA_FF) of block  430  is added to the output (STA_FB) of block  440 , in accordance with Equation 11 above, to provide an output (Tassist) of flowchart  400 , designated by block  450 . The steering torque assist signal (Tassist), block  450 , provides the control signal (command) to STA actuator  240  for providing tactile feedback to the operator regarding the steering behavior.  
         [0057]    [0057]FIG. 5 depicts an expanded block diagram  500  of the process represented by block  440  in block diagram  400 . Referring to FIG. 5, block  520  responds to vehicle speed (V x ), block  410 , and yaw rate error (Ye), block  512 , to calculate the proportional and derivative terms (P_term) and (D_term) in accodance with Equations 8 and 9, and Table 1, above. The absolute value of the (P_term) added to the (D_term) results in an integrated output represented by block  525 . Block  530  responds to the input VSE_WFlag, represented by block  418 . The state of VSE_WFlag is determined by controller  200  monitoring the activity of the VSE system, as discussed above in relation to the &#39;486 patent. The output of block  530  determines the direction of feedback, positive or negative, for the feedback steering torque assist (STA_FB). The output of block  530  and the integrated output represented by block  525  are then multiplied together at block  540  in accordance with Equation 10 above, resulting in feedback steering torque assist (STA_FB) represented by block  545 .  
         [0058]    It will be appreciated that the block diagrams of FIGS. 4 and 5 represent both the calculation of various control commands, as represented by the labeled blocks, and the communication of various control command signals, as represented by the connecting single lines.  
         [0059]    VSE WFlag and Vehicle Behavior Generally  
         [0060]    The positive and negative signs of VSE_WFlag and STA_FF are best understood by referring now to FIG. 7, which depicts a generalized diagram  700  of vehicle  10  responsive to understeer, block  710 , and oversteer, block  720 , conditions, with the VSE system active, block  730 , and inactive, block  740 .  
         [0061]    Regarding the understeer, block  710 , condition, and in accordance with the above discussion, the sign of STA_FF is positive (right hand turn), and the sign of VSE_WFlag is positive (right side braking wheel active). In a right hand turn understeer condition, the VSE system activates the right rear brake, block  750 , thereby setting the VSE_WFlag to (+1).  
         [0062]    Regarding the understeer, block  720 , condition, and in accordance with the above discussion, the sign of STA_FF is positive (right hand turn), and the sign of VSE_WFlag is negative (left side braking wheel active). In a right hand turn oversteer condition, the VSE system activates the left front brake, block  750 , thereby setting the VSE_WFlag to (−1).  
         [0063]    Through active intervention of the VSE system and in accordance with the invention described herein, not only will controller  200  provide braking assistance to correct the vehicle&#39;s path, but controller  200  will also provide steering assistance through tactile feedback to the driver, thereby influencing the driver to adjust the steering to correct the vehicle&#39;s path.  
         [0064]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.