Abstract:
Methods and apparatus are provided for integrating a torque vectoring differential (TVD) and a stability control system in a motor vehicle. The integrated system is utilized for more efficiently correcting understeer and/or oversteer slides in a motor vehicle. In correcting these slides, the integrated system utilizes the TVD to rotate two wheels on opposite sides of the motor vehicle at different rates to create a yaw moment at the vehicle&#39;s center of gravity until the TVD reaches a saturation point and the understeer or oversteer slide is not corrected. Once the saturation point is reached without correcting the understeer or oversteer slide, the stability control system is employed to selectively apply one or more of the vehicle&#39;s brakes in a further effort to correct the understeer or oversteer slide.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to motor vehicles, and more particularly relates to integrating a torque vectoring differential and an electronic stability control system in a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Systems and methods for aiding a driver to regain control of a motor vehicle when it becomes unstable has been a focus of research for some time. The most common types of unstable conditions are generally referred to as “understeer” or “oversteer” slides. An understeer slide is the situation where the front end of the vehicle moves toward the outside of a turn instead of following the curvature of the turn. An oversteer slide is the situation where the rear of the motor vehicle moves toward the outside of the turn (i.e., fish-tailing). 
     One system known to correct or minimize an understeer or oversteer slide is a torque vectoring differential (TVD). Typically, a TVD is an electronically-controlled differential that can create an understeering or oversteering moment about the center of gravity of a motor vehicle independent of the speeds of the wheels. In other words, a TVD is able to distribute engine power to a wheel regardless of whether that particular wheel is rotating at a faster or slower rate than the other wheel sharing the differential. In this manner, a TVD is different from a Limited Slip Differential (LSD), which generates understeer or oversteer moments as a function of distributing the wheel speed from the faster rotating wheel to the slower rotating wheel across the differential. Accordingly, a TVD utilizes the concepts of understeer and oversteer gradients to affect the dynamics of the vehicle. Thus, the ability of a TVD to create an understeering or oversteering moment about the center of gravity of the vehicle independent of the speeds of the wheels, up to a fixed limit of wheel speed difference (i.e., a saturation point), greatly increases the range of authority that a TVD has on vehicle dynamics, as compared with an LSD. 
     A TVD typically includes one or more sensors in communication with one or more controllers (e.g., microcontrollers). The sensors are located at a variety of places on the vehicle and continually monitor the vehicle for any signs of instability. Once instability is detected, the sensors notify the controller(s), and once notified, the controller(s) provide differing amounts of power to the wheels such that the wheels are able to rotate at different rates. By rotating the wheels at different rates, a TVD is able to correct or minimize the effects of an understeer or oversteer situation by creating an understeer or oversteer moment at the center of gravity. 
     Another system to help the driver regain control of the vehicle when the vehicle begins to experience instability is a stability control system (SCS). Typically, an SCS include one or more controllers (e.g., microcontrollers) coupled to one or more sensors located at various places on the vehicle that are able to detect understeer and oversteer slides. Once an understeer and oversteer slide is detected, the sensors notify the controller(s), which “automatically” applies braking to one or more wheels to thereby stabilize the vehicle. In other words, an SCS is designed to deliver transparent intervention the moment a situation becomes unstable by applying the brakes at one or more selected wheels depending on whether the unstable condition is a left-turn or right-turn understeer slide, or a left-turn or right-turn oversteer slide. 
     An SCS is more effective for correcting or minimizing an understeer or oversteer slide than a TVD; however, because an SCS utilizes the vehicle&#39;s brakes to correct or minimize an understeer/oversteer slide, a significant amount of the vehicle&#39;s energy is converted into mechanical “heat” (i.e., kinetic energy is lost). By contrast, although utilizing a TVD to correct or minimize the effects of an understeer/oversteer slide is less effective than an SCS, a TVD is more efficient from an energy loss point of view. Moreover, although a TVD is not as effective as an SCS, a TVD is sufficient to correct or minimize the effects of most understeer and oversteer slides. Accordingly, it is desirable to provide a system and method for integrating a TVD with an SCS to provide a more efficient system of regaining control of a vehicle experiencing an unstable condition. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY OF THE INVENTION 
     An integrated system is provided for more efficiently correcting unstable conditions (e.g., understeer slides and oversteer slides) in a motor vehicle. The integrated system, in one embodiment, includes a first system (e.g., a TVD) coupled to a first wheel having a first brake and a second wheel having a second brake, wherein the first system is configured to rotate the first wheel and the second wheel at different rates to correct or minimize the effects of the unstable condition. Furthermore, the integrated system includes a second system (e.g., an SCS) coupled to a third brake associated with a third wheel and coupled to a fourth brake associated with a fourth wheel, the second system being configured to selectively apply at least one of the first brake and the second brake to correct or minimize the effects of the unstable condition. Moreover, the integrated system includes a controller coupled to the first system and the second system, and at least one sensor coupled to the controller, wherein the sensor is configured to detect the unstable condition and notify the controller of the unstable condition, and the controller is configured to instruct the first system to rotate the first wheel and the second wheel at different rates and/or the second system to selectively apply at least one of the first brake and the second brake in response to the notification. 
     A method is provided for more efficiently correcting unstable conditions in a motor vehicle. The method, in one embodiment, comprises detecting one of a right-turn oversteer, a left-turn oversteer, a right-turn understeer, and a left-turn understeer. Once detected, the method includes utilizing a first system (e.g., a TVD) to correct the right-turn oversteer, the left-turn oversteer, the right-turn understeer, or the left-turn understeer until the first system reaches a saturation point. When the saturation point is reached, the method utilizes a second system (e.g., an SCS) to correct the right-turn oversteer, the left-turn oversteer, the right-turn understeer, or the left-turn understeer, whatever the case may be. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a diagram illustrating one embodiment of a motor vehicle including a system comprising an integrated torque vectoring differential and stability control system; 
         FIG. 2  is a diagram illustrating one example of the system in  FIG. 1  operating to correct or minimize an understeer slide; 
         FIG. 3  is a diagram illustrating another example of the system in  FIG. 1  operating to correct or minimize an oversteer slide; and 
         FIG. 4  is a flow diagram of a method of controlling a motor vehicle slide utilizing the integrated system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
       FIG. 1  is a diagram illustrating a bottom view of a motor vehicle  100  including one embodiment of a system  105  to correct oversteer and understeer slides. As illustrated, motor vehicle  100  includes four wheels (e.g., wheel  102 , wheel  104 , wheel  106 , and wheel  108 ), wherein there are two “front” wheels (e.g., wheels  102  and  104 ) separated by a distance defining a track width L (i.e., wheelbase width), two “rear” wheels (e.g., wheels  106  and  108 ), two “driver-side” wheels (e.g., wheels  104  and  108 ), and two “passenger-side” wheels (e.g., wheels  102  and  106 ) for a left-sided driver (the opposite is true for a right-sided driver). Furthermore, each of wheels  102 ,  104 ,  106 , and  108  includes at least one brake (e.g., brake  112 , brake  114 , brake  116 , and brake  118 ) associated with it such that, when applied, brakes  112 ,  114 ,  116 , and  118  are able to slow down and/or stop the rotational speed of wheels  102 ,  104 ,  106 , and  108 , respectively. 
     In accordance with one embodiment, system  105  includes a plurality of sensors  107  to detect understeer and oversteer slides, a torque vectoring differential (TVD)  120  to create a yaw moment about the center of gravity  101 , a TVD controller  123  coupled to TVD  120 , a stability control system (SCS)  130 , and an electronic braking control module (eBCM)  140  coupled to TVD  120  and SCS  130 , wherein each of these components is in communication with one another via a bus  109  (e.g., a large area network (LAN) bus). TVD  120 , in one embodiment, includes an axle  125  comprising a portion  125   a  and a portion  125   b . Portions  125   a  and  125   b , in one embodiment, are not constrained together; thus, portions  125   a  and  125   b  are capable of being separately driven by the engine (not shown) of motor vehicle  100 , which enables wheels  106  and  108  to rotate at different rates. For example, portion  125   a  is able to be driven at a faster rate than portion  125   b , which allows wheel  106  to rotate at a faster rate than wheel  108 . Similarly, portion  125   b  is able to be driven at a faster rate than portion  125   a , which allows wheel  108  to rotate at a faster rate than wheel  106 . 
     As discussed above, TVD  120  is configured to rotate wheels  106  and  108  at speeds independent of one another. In other words, TVD  120  is capable of transferring wheel speed “to” wheel  106  “from” wheel  108  (via portions  125   a  and  125   b ) regardless of whether wheel  106  is rotating faster or slower than wheel  108 . Likewise, TVD  120  is capable of transferring wheel speed to wheel  108  from wheel  106  (via portions  125   a  and  125   b ) regardless of whether wheel  108  is rotating faster or slower than wheel  106 . 
     As illustrated in  FIG. 1 , TVD  120  is coupled to TVD controller  123 . Moreover, TVD controller  123  is coupled to sensors  107  and configured to receive notification from sensors  107  that motor vehicle  100  is experiencing an unstable condition. In accordance with one embodiment, TVD controller  123  is a controller (i.e., a microcontroller) configured to receive and/or store a desired yaw rate and a measured yaw rate for motor vehicle  100 . In another embodiment, TVD controller  123  is configured to receive and/or store a yaw rate error and a desired yaw acceleration rate (i.e., yaw rate commands) for motor vehicle  100 . Moreover, TVD controller  123  is configured to output to TVD  120  a representation of a delta torque value based on the desired yaw rate and the measured yaw rate, or the yaw rate error and the desired yaw acceleration rate, wherein the delta torque value is a representation of the difference in torque between wheel  106  (i.e., right-rear (RR) wheel torque  116 ′) and wheel  108  (i.e., left-rear (LR) wheel torque  118 ′) or (RR wheel torque  116 ′−LR wheel torque  118 ′). 
     In operation, TVD  120  generates a yaw moment based on the delta torque value received from TVD controller  123  and various other known characteristics of motor vehicle  100 . In one embodiment, the yaw moment generated by TVD  120  can be expressed by the following equation:
 
Yaw Moment=(RR wheel torque  116 ′−LR Wheel Torque  118 ′)·( L /(2(Tire Radius))),
 
where L and the tire radius of motor vehicle  100  are the known characteristics.
 
     Moreover, TVD controller  123  is configured to monitor the speeds of wheels  106  and  108  to determine if TVD  120  has reached a saturation point, and upon reaching the saturation point, notifying eBCM  140  that TVD  120  has reached such saturation point. In one embodiment, the saturation point is the point at which TVD  120  can no longer create a difference in torque between wheels  106  and  108 . In other words, the point at which TVD  120  can no longer affect the speeds at which wheels  106  and  108  rotate. In another embodiment, the saturation point is a temperature below which TVD  120  is unable to generate enough power to affect the speeds at which wheels  106  and  108  rotate. In yet another embodiment, the saturation point is a voltage below which TVD  120  is unable to generate enough power to affect the speeds at which wheels  106  and  108  rotate. 
     In addition, system  105  includes SCS  130 , which includes one or more stability control (SC) controllers  135  (e.g., microcontrollers), coupled to TVD  120  and to each of brakes  112 ,  114 ,  116 , and  118  via bus  109 . SC controller  135  is configured to selectively apply one or more of brakes  112 ,  114 ,  116 , and  118  as needed to correct or minimize understeer or oversteer slide, depending upon whether motor vehicle  100  is experiencing a left-turn understeer, a right-turn understeer, a left-turn oversteer, or a right-turn oversteer. Notably, SCS  130  generally includes an anti-lock brake system (ABS), a traction control system, an electronic brake differential, and an engine drag control to selectively apply one or more of brakes  112 ,  114 ,  116 , and  118 , as is known in the art, although these are not illustrated in  FIG. 1 . 
     In accordance with one embodiment, system  105  includes eBCM  140  in communication with TVD  120  and SCS  130  via bus  109 . eBCM  140 , in one embodiment, is a module configured to supervise TVD  120  and integrate TVD  120  with SCS  130  (and the ABS). In addition, eBCM  140  is configured to receive the yaw moment data generated by TVD  120  and a notice from TVD  120  that TVD  120  is operating at a saturation point. Furthermore, eBCM  140  is configured to instruct SCS  130  to begin operating (i.e., begin selectively applying one or more of brakes  112 ,  114 ,  116 , and  118 , as needed) and/or instruct TVD  120  to cease operating. 
     In accordance with one embodiment, eBCM  140  is configured to instruct TVD  120  to cease operating prior to instructing SCS  130  to commence operating. In another embodiment, SCS  130  is only active on the front wheels and brakes (i.e., wheel  102  and brake  112 , and wheel  104  and brake  114 ) such that eBCM  140  instructs SCS  130  to begin applying brake  112  or brake  114  (depending upon which is needed) in addition to TVD  120  rotating wheels  106  and  108  at different speeds. 
       FIG. 2  is a diagram illustrating one example of the operation of system  105  when motor vehicle  100  is experiencing a left-turn understeer slide. As illustrated, motor vehicle  100  should be turning along curve  200 ; however, the actual path  103  of motor vehicle  100  “over-shoots” curve  200 . In this situation, sensor(s)  107  detects the understeer slide and notifies eBCM  140  and/or TVD controller  123  of the left-turn understeer slide. Upon receiving the notification from sensor  107  and/or eBCM  140 , TVD  120  begins rotating wheel  106  at a faster rate than wheel  108  to create a yaw moment  170  about center of gravity  101 . This is created by RR wheel torque  116 ′ being greater than LR wheel torque  118 ′, and shown by RR wheel torque  116 ′ being annotated with more arrows than LR wheel torque  118 ′. 
     If, however, the saturation point of TVD  120  is reached and motor vehicle  100  is not sufficiently corrected, TVD  120  notifies eBCM  140  that TVD  120  is operating at saturation. At this point, eBCM  140  instructs SCS  130  to begin selective braking. Since this is a left-turn understeer slide, SCS  130  will begin applying brake  118  (as needed) to wheel  108 . 
     In one embodiment, prior to instructing SCS  130  to begin selective braking, eBCM  140  will instruct TVD  120  to cease rotating wheels  106  and  108  at different rates since it is desirable that TVD  120  and SCS  130  not be functioning on the same wheel at the same time. Notably, the opposite of the description with reference to  FIG. 2  occurs when motor vehicle  100  is experiencing a right-turn understeer slide (i.e., wheel  108  rotates faster prior to saturation, and brake  116  is applied after saturation). 
       FIG. 3  is a diagram illustrating one example of the operation of system  105  when motor vehicle  100  is experiencing a left-turn oversteer slide. As illustrated, motor vehicle  100  should be turning along curve  300 ; however, the actual path  103  of motor vehicle  100  “under-shoots” curve  300 . In this situation, sensor(s)  107  detects the oversteer slide and notifies eBCM  140  and/or TVD controller  123  of the left-turn oversteer slide. Upon receiving the notification, TVD  120  begins rotating wheel  108  at a faster rate than wheel  106  to create a yaw moment  175  about center of gravity  101 . This is created by LR wheel torque  118 ′ being greater than RR wheel torque  116 ′, and shown by LR wheel torque  118 ′ being annotated with more arrows than RR wheel torque  116 ′. 
     If, however, the saturation point of TVD  120  is reached and motor vehicle  100  is not sufficiently corrected, TVD  120  notifies eBCM  140  that TVD  120  is operating at saturation. At this point, eBCM  140  instructs SCS  130  to begin selective braking. Since this is a left-turn oversteer slide, SCS  130  will begin applying brake  112  (as needed) to wheel  102 . In one embodiment, eBCM  140  may instruct TVD  120  to cease rotating wheels  106  and  108  at different rates prior to instructing SCS  130  to begin selective braking. In other embodiment, TVD  120  and SCS  130  may operate at substantially the same time to correct or minimize the left-turn oversteer slide. In other words, TVD is rotating wheel  108  at a faster rate than wheel  106  and SCS  130  is applying brake  112 , as needed. Notably, the opposite of the description with reference to  FIG. 3  occurs when motor vehicle  100  is experiencing a right-turn oversteer slide (i.e., TVD  120  rotates wheel  106  faster than wheel  108 , and/or brake  114  is applied to wheel  104 ). 
       FIG. 4  is a flow diagram illustrating a representation of one embodiment of a method  400  of correcting a motor vehicle slide (e.g., oversteer slides and an understeer slides). Method  400 , in one embodiment, includes detecting a right-turn oversteer slide, a left-turn oversteer slide, a right-turn understeer slide, or a left-turn understeer slide (step  410 ). 
     Once a slide is detected, method  400  includes utilizing a first system (e.g., TVD  120 ) to correct the detected right-turn oversteer slide, the left-turn oversteer slide, the right-turn understeer slide, or the left-turn understeer slide (step  420 ). In accordance with one embodiment, step  420  includes rotating a rear, passenger-side wheel at a higher rate than a rear, driver-side wheel to correct the left-turn understeer (step  422 ), rotating the rear, driver-side wheel at a higher rate than the rear, passenger-side wheel to correct the right-turn understeer (step  424 ), rotating the rear, driver-side wheel at a higher rate than the rear, passenger-side wheel to correct the left-turn oversteer (step  426 ), and rotating the rear, passenger-side wheel at a higher rate than the rear, driver-side wheel to correct the right-turn oversteer (step  428 ). 
     In accordance with one embodiment, method  400  includes utilizing the first system until the first system reaches a saturation point (step  430 ). Once the saturation point is reached, method  400  includes utilizing a second system (e.g., SCS  130 ) to correct the right-turn oversteer slide, the left-turn oversteer slide, the right-turn understeer slide, or the left-turn understeer slide (step  440 ). Step  440 , in one embodiment, includes applying a front, passenger-side brake to correct the left-turn oversteer (step  442 ) and applying a front, driver-side brake to correct the right-turn oversteer (step  444 ). Moreover, step  440  includes applying a rear, driver-side brake to correct the left-turn understeer (step  446 ) and applying a rear, passenger-side brake to correct the right-turn understeer (step  448 ). 
     Method  400 , in another embodiment, includes ceasing to utilize the first system prior to utilizing the second system when the saturation point is reached (step  450 ). In another embodiment, step  450  includes ceasing to utilize the first system when the first system can no longer rotate the rear, passenger-side wheel and the rear, driver-side wheel at different rates (step  455 ). 
     Notably, method  400  has been described with reference to a motor vehicle having a left-sided driver. However, one skilled in the art is capable of applying method  400  to a motor vehicle having a right-sided driver since the reference points (i.e., the driver-side and passenger-side) are opposite for a right-sided driver than the embodiment described with reference to  FIG. 4 . 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.