Abstract:
A method of controlling drivability of a vehicle detects an overall load acting on the vehicle. A mass of the vehicle or an estimate thereof is obtained. A controller determines whether the vehicle is negotiating a curve during a driving situation. If the vehicle is negotiating a curve during the driving situation, the controller determines whether the vehicle has a tendency to oversteer or to understeer. The load acting on the vehicle is dynamically changed or a suspension stiffness of the vehicle is dynamically adjusted to reduce the tendency of the vehicle to oversteer or to understeer.

Description:
FIELD 
       [0001]    The invention relates to passenger vehicle handling and, more particularly, to a system and method that dynamically changes the load on the vehicle or the vehicle suspension to reduce oversteer or understeer tendencies. 
       BACKGROUND 
       [0002]    Modern motor vehicles are often equipped with a vehicle dynamics control system, such as the known ESC (Electronic Stability Control) system that stabilizes the vehicle in critical driving situations. For this purpose, the braking force is usually increased in a targeted manner at individual wheels of the vehicle in order to generate a yaw moment which stabilizes the vehicle. However, the brake intervention, which is carried out particularly by the ESC system, can be sensed clearly by the driver as a vehicle deceleration, and therefore, can be unexpected and uncomfortable. The ESC system also typically reacts after the instability has occurred. 
         [0003]    Thus, there is a need to provide a system and method that dynamically changes the load on the vehicle or suspension stiffness to reduce oversteer or understeer tendencies based on vehicle load information along with other vehicle information prior to the instability. 
       SUMMARY 
       [0004]    An objective of the invention is to fulfill the need referred to above. In accordance with the principles of an embodiment, this objective is obtained by providing a method of controlling drivability of a vehicle. The method detects an overall load acting on the vehicle. A mass of the vehicle or an estimate thereof is obtained. A controller determines whether the vehicle is negotiating a curve during a driving situation. If the vehicle is negotiating a curve during the driving situation, the controller determines whether the vehicle has a tendency to oversteer or to understeer. The load acting on the vehicle is dynamically changed or a suspension stiffness of the vehicle is dynamically adjusted to reduce the tendency of the vehicle to oversteer or to understeer. 
         [0005]    In accordance with another aspect of an embodiment, a driving stability control system for a vehicle includes vehicle load sensor structure constructed and arranged to obtain an overall load acting on a vehicle. Vehicle information sensor structure is constructed and arranged to obtain vehicle information including at least yaw and steering information of the vehicle. First actuators are constructed and arranged to control aerodynamic components of the vehicle. Second actuators are constructed and arranged to control a suspension of the vehicle. A vehicle behavior controller is constructed and arranged to receive the vehicle information and the overall load acting on the vehicle and based thereon, to send a signal to the first actuators to dynamically adjust the aerodynamic components to change a load on the vehicle, or to send a signal to the second actuators to dynamically adjust the suspension of vehicle, to reduce a tendency of the vehicle to oversteer or understeer. 
         [0006]    Other objectives, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which: 
           [0008]      FIG. 1  is schematic view of a vehicle having a driving stability control system in accordance with an embodiment. 
           [0009]      FIG. 2  is a detailed schematic illustration of the driving stability control system of  FIG. 1 . 
           [0010]      FIG. 3  is a flow chart of a method of an embodiment. 
           [0011]      FIG. 4  is a schematic view of the vehicle of  FIG. 1  show with the aerodynamic downforce increased by the driving stability control system only on the front axle. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0012]    With reference to  FIG. 1 , a motor vehicle  10  includes a driving stability control system, generally indicated at  12 , in accordance with and embodiment. The vehicle  10  is preferably a two-axle, four-wheel motor vehicle having steerable wheels on at least one front axle  14  and, if appropriate, also on a rear axle  16 .  FIG. 1  shows the center of gravity CG and the forces acting on the vehicle. 
         [0013]      FIG. 2  is a detailed schematic illustration of the driving stability control system  12 . The system  12  includes a vehicle load sensor structure that can include or use the air suspension system  11  for a vehicle  10 . A conventional suspension such as an air bellows  18  is associated with a respective wheel  20 . Only one of the four wheels  20  of the vehicle  10  is shown in  FIG. 2 . An air tank and pump (not shown) of the suspension system  11  provide a source of air to the bellows  18 . A vehicle behavior controller  22 , including a processor circuit  24  and memory circuit  25 , controls a solenoid valve  42 ′ associated with the suspension system  11 . The solenoid valves are associated with the pump to control the bellows  18  and thus the suspension of the vehicle  10 . The controller  22  can be an ESC controller. 
         [0014]    The controller  22  can obtain, via signal lines  26 , real time load information on all four wheels  20 , which represents the normal force FN applied to each wheel. The total normal force FN_total or vehicle load (overall load acting on vehicle) can be calculated by summing the individual forces together. 
         [0015]    Alternatively, the vehicle load can be obtained by Continental&#39;s electronic Tire Information System (eTIS) that utilizes a sensor  28  integrated directly into the inner liner of the tire of each wheel  20 . The sensor  28  sends, via signal lines  30 , the vehicle load information at each wheel based on pressure and area to the controller  22 . 
         [0016]    With reference to  FIG. 2 , the system  12  also includes vehicle information sensor structure  32  electrically connected with the controller  22  via signal line  34 . The vehicle information sensor structure  32  preferably includes the conventional vehicle speed sensor(s), yaw rate sensor, lateral acceleration sensors and steering angle sensor, for example, as disclosed in U.S. Pat. No. 8,395,491 B2, the contents of which is hereby incorporated by reference into this specification. 
         [0017]    Returning to  FIG. 1 , if the loading of the vehicle  10  is such that the center of gravity CG shifts to the front of the vehicle, such as from the passenger and cargo loading, the result will be a vehicle that has an understeering tendency. The system  12  is configured to combine the vehicle load information (regardless of how it is obtained) with information derived from the sensor structure  32  to predict the behavior of the vehicle (oversteer and understeer tendency). This predicted behavior can then be combined with other systems such as active aerodynamics or active suspension systems to counteract the unwanted vehicle behavior. 
         [0018]    Thus, with reference to  FIG. 2 , the system  12  includes an aerodynamics controller  34  electrically coupled with the controller  22  via signal line  36 . The system  12  further includes a suspension controller  38  electrically coupled to the controller  22  via signal line  40 . Both of the aerodynamics controller  34  and the suspension controller  38  are electrically coupled to actuators  42 , the function of which will be explained below. It can be appreciated that if desired the controllers  34  and  38  can be integrated into or be part of the vehicle behavior controller  22 . 
         [0019]    With reference to  FIG. 3 , the steps or algorithm for controlling driving stability for a vehicle are shown in accordance with an embodiment. In step  44 , the vehicle load is detected by the via the suspension system or from the eTIS system as noted above, or in any other manner, and the data is stored in memory  25 . The vehicle mass is obtained in step  46 . The vehicle mass can be a constant value, a CAN message or can be estimated. Next, in step  48 , the driving situation is determined. In particular, based on information (e.g., yaw rate, steering information and speed) from the information sensor structure  32  and from the vehicle load and mass, the controller  22  determines if the vehicle is driving in a straight line in step  48 . If the vehicle is operating in a straight line driving situation, in step  50 , the controller  22  optimizes the drivability for straight line driving by dynamically controlling the aerodynamics of the vehicle  10  for acceleration, deceleration and drag/efficiency. Also, the aerodynamic force on the vehicle can be dynamically controlled during braking. With reference to  FIG. 2 , control of the aerodynamics can be performed by the controller  22  instructing the aerodynamics controller  34  to control actuators  42  to adjust the aerodynamic components  43 . 
         [0020]    If the vehicle is negotiating a curve during a driving situation, in step  52 , the processor circuit  24  determines if there is a tendency to oversteer based on the loading of the vehicle. If so, in step  54 , the controller  22  instructs the aerodynamics controller  34  to control actuators  42  to adjust the aerodynamic components  43  of the vehicle to increase the aerodynamic load on the rear of the vehicle or decrease the aerodynamic load on the front of the vehicle. Alternatively, or in conjunction with the above step to reduce oversteer, the controller  22  can instruct the suspension controller  34  to control actuators  42 ′ (e.g., the solenoids associated with the suspension system  11 ) to increase the front roll stiffness or decrease the rear roll stiffness. The controller  22  can also activate the ESC system or change the drive torque distribution to reduce the tendency to oversteer. After changing the load to reduce the oversteer tendency, the process returns to step  44  where the vehicle load is detected again for any further adjustments. 
         [0021]    While the vehicle is negotiating a curve during the driving situation and if there is no tendency to oversteer, in step  56 , the processor circuit  24  determines if there is a tendency to understeer based on the loading of the vehicle. If so, in step  56 , the controller  22  instructs the aerodynamics controller  34  to control actuators  42  to adjust the aerodynamic components  43  of the vehicle to increase the aerodynamic load on the front of the vehicle or decrease the aerodynamic load on the rear of the vehicle.  FIG. 4  shows the vehicle  10  with the increased aerodynamic downforce AF only on the front axle  14  that results in a more neutral behaving vehicle before dynamic driving is encountered. Alternatively, or in conjunction with the above step to reduce understeer, the controller  22  can instruct the suspension controller  34  to control actuators  42  (e.g., the solenoids  42 ′ associated with the suspension system  11 ) to increase the rear roll stiffness or decrease the front roll stiffness. The controller  22  can also activate the ESC system or change the drive torque distribution to reduce the tendency to understeer. After changing the load to reduce the understeer tendency, the process returns to step  44  where the vehicle load is detected again for any further adjustments. 
         [0022]    All of the adjustments to reduce the understeer or oversteer tendency happen dynamically in real time with the goal of increasing the cornering capabilities of the vehicle  10 . This could also mean increasing the aerodynamic load while cornering and decreasing it while driving straight to reduce drag. Further, the information can be used to calculate a new understeer coefficient that could be used to adjust the bike model to prevent false or sensitive activations. If desired, the severity of yaw control could be increased in critical situations as well as active roll mitigation. 
         [0023]    The operations and algorithms described herein can be implemented as executable code within the controller  22  processor circuit  24  as described, or stored on a standalone computer or machine readable non-transitory tangible storage medium that are completed based on execution of the code by a processor circuit implemented using one or more integrated circuits. Example implementations of the disclosed circuits include hardware logic that is implemented in a logic array such as a programmable logic array (PLA), a field programmable gate array (FPGA), or by mask programming of integrated circuits such as an application-specific integrated circuit (ASIC). Any of these circuits also can be implemented using a software-based executable resource that is executed by a corresponding internal processor circuit such as a microprocessor circuit (not shown) and implemented using one or more integrated circuits, where execution of executable code stored in an internal memory circuit (e.g., within the memory circuit  25 ) causes the integrated circuit(s) implementing the processor circuit  24  to store application state variables in processor memory, creating an executable application resource (e.g., an application instance) that performs the operations of the circuit as described herein. Hence, use of the term “circuit” in this specification refers to both a hardware-based circuit implemented using one or more integrated circuits and that includes logic for performing the described operations, or a software-based circuit that includes a processor circuit (implemented using one or more integrated circuits), the processor circuit including a reserved portion of processor memory for storage of application state data and application variables that are modified by execution of the executable code by a processor circuit. The memory circuit  25  can be implemented, for example, using a non-volatile memory such as a programmable read only memory (PROM) or an EPROM, and/or a volatile memory such as a DRAM, etc. 
         [0024]    The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.