Abstract:
A vehicle stability control system operates by detecting a wheel speed potentially indicative of the presence of a mini-spare wheel at a wheel location of a vehicle with a wheel speed sensor and determines that a mini-spare tire is present responsive to the wheel speed remaining within a predefined band for predefined time. A threshold value that triggers action by a vehicle stability control system is adjusted to provide the mini-spare wheel with a value different than a wheel speed threshold value indicative of wheel slipping for a standard wheel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/041,817 filed Aug. 26, 2014. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to an automotive vehicle traction control system and electronic stability control systems. Such systems utilize information relating to vehicle conditions to maintain stability and wheel traction. Such systems may actuate a brake system or modify engine operation to maintain desired vehicle stability. The information provided to the vehicle comes from various sources and the system relies on the accuracy of information provided. 
         [0003]    Vehicles often include a mini-spare tire instead of a full size (spare) tire. The use of the mini-spare is desirable as it saves both cost and weight. However, the different size of the mini-spare changes how a vehicle operates and thereby can diminish the accuracy of information relied on by traction control and stability control systems. 
       SUMMARY 
       [0004]    In one disclosed embodiment, a method of operating a vehicle control system includes the steps of detecting a wheel speed potentially indicative of the presence of a mini-spare wheel at a wheel location of a vehicle with a wheel speed sensor. The method further includes determining that a mini-spare tire is present responsive to the wheel speed remaining within a predefined band for predefined time. A threshold value that triggers action by a vehicle stability control system is temporarily adjusted to compensate for the increased speed of the mini-spare wheel until wheel speed values for that wheel can be compensated for such that the threshold value may be returned to the original threshold value indicative of wheel slipping for a standard wheel. 
         [0005]    In another disclosed embodiment, a traction control system includes a controller configured to receive signals for detecting a wheel speed indicative of the presence of a mini-spare wheel and increasing a threshold value that triggers an intervention response to wheel slipping. The controller is configured to determine that a mini-spare wheel is present responsive to the wheel speed remaining within a predefined band for predefined time, and to generate an output for adjusting the threshold value for the wheel determined to include the mini-spare. 
         [0006]    These and other features of the disclosed examples can be understood from the following description and the accompanying drawings, which can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic view of an exemplary vehicle including Electronic Stability Control and a Traction Control System with a mini-spare wheel installed. 
           [0008]      FIG. 2  is a schematic view of a signal utilized for determining the presence of a mini-spare wheel. 
           [0009]      FIG. 3  is a schematic representation of a threshold value adjusted for a mini-spare wheel. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIG. 1 , a vehicle  10  is shown schematically and includes a Traction Control System (TCS)  12  and an Electronic Stability Control system (ESC)  14 . The TCS  12  and ESC  14  receive information regarding vehicle operation and use that information to initiate actions to provide desired vehicle operation. In this example, the TCS  12  and ESC  14  are part of a vehicle controller  15  configured to receive signals and generate commands for controlling vehicle systems such as brakes  16 . The controller  15  can be part of a vehicle controller, or part of sub system that operates in concert with the vehicle controller. 
         [0011]    In one disclosed embodiment, the TCS  12  utilizes wheel speed sensors  22  to detect slipping of one of the vehicle wheels. Wheel slip is indicated when one of the wheels is rotating faster than the other wheels, or faster than expected for vehicle operation. The TCS  12  and ESC  14  may then initiate actuation of a brake  16  at the slipping wheel to slow that wheel and regain traction. 
         [0012]    In response to a flat tire experienced on the roadway, a temporary spare tire is typically installed in place of the standard vehicle tire. In many instances, the spare is a mini-spare  18 , meaning that the diameter and width is much smaller than the standard tire  20  (normally 5%˜20% smaller than the standard tire). The smaller diameter of the mini-spare  18  results in that tire rotating at an increased wheel speed compared to the standard tire  20  at a common vehicle speed. The increased wheel speed of the mini-spare  18  may be improperly identified by the TCS  12  and ESC  14  as wheel slipping. Accordingly, the TCS  12  and ESC  14  may intervene by actuating the brake  16  for that wheel until the system recognizes or learns that a mini-spare  18  has been installed. Once the existence of the mini-spare  18  is established, compensation is made for the increased wheel speed such that the system may return to normal threshold values. The system compensates for the increased wheel speeds and the threshold value can therefore be returned to the original threshold value. 
         [0013]    The lag in time that is required for the vehicle controller  15  to recognize the presence of a mini-spare  18  can be undesirably long and result in undesired intervention of the TCS  12  to slow the vehicle. During the recognition process, the mini-spare wheel  18  introduces artificial wheel slips due to the increased wheel speeds, and may cause intervention by the TCS  12  as a brake actuation and/or engine torque reduction. Undesired intervention may lead to very poor vehicle acceleration, especially for vehicles with a very small mini-spare. 
         [0014]    The example method and system supplements the current system and enables faster recognition of the mini-spare  18  without undesired intervention by the TCS  12  or the ESC  14 . Once the presence of a mini-spare  18  is recognized, the TCS  12  and ESC  14  thresholds are temporarily adjusted to compensate for the increased wheel speeds to reduce and prevent false TCS intervention caused by false wheel slip indications. Once the existence of the wheel speeds is recognized, a compensation value is applied to wheel velocity readings from that wheel. The threshold value may then be returned to the original threshold value. 
         [0015]    Referring to  FIG. 2 , a graph  24  relates time  26  to wheel velocity  28 . A band  30  is illustrated that represents the dynamics of the wheel velocity recognized as mini-spare wheel speed to remove disturbance influence from wheel speeds, i.e., avoid false detection of mini-spare caused by a split surface or speed bump. The band  30  represents the range of wheel velocities that is recognized as a min-spare. As is shown, the band  30  is narrow to prevent incorrect categorization of slipping of a normal wheel as a mini-spare. However, the band  30  also requires more time to confirm the presence of a mini-spare. 
         [0016]    Line  32  represents wheel velocity for a normal tire over the same time as that of the mini-spare represented by line  34 . A period of time is required to confirm that the faster wheel speeds are due to the installation of the mini-spare  18 . The disclosed wheel velocities represented by the line  34  and the line  32  are determined utilizing a corrected wheel velocity. The corrected wheel velocity refers to a speed of the wheels based on a speed of the vehicle determined at a center of the vehicle  25  (Shown schematically in  FIG. 1 ). Velocity at the center of the vehicle  25  is utilized to eliminate differences between wheels and to generate a quicker indication of differences in wheel velocities that are indicative of the presence of a mini-spare. The corrected wheel velocity also eliminates the influence of wheel velocity difference for the curve inside and outside wheels when the vehicle is driving on a curve. 
         [0017]    Accordingly, if the vehicle is driving stable (even on a curve), all four wheel velocities should have very close values. In order to identify a mini-spare within band  30 , the learning process is very robust, but slow. Accordingly, sometimes a vehicle might have already slowed down due to intervention by the TCS  12  and/or ESC  14  caused by false wheel slip from mini-spare wheel during this learning process. In order to avoid false TCS and/or ESC  14  intervention during this learning process, a second band  36  is provided for quicker mini-spare identification. If one wheel velocity is quicker than the others and the difference between them is within a mini-spare range of wheel velocities indicated by the second band  36 , the TCS  12  and ESC  14  will switch to the new monitoring of the mini-spare. If the wheel velocity is within the band  36  for a predefined time, for example, one second, then a temporary threshold for the mini-spare is recognized. In one disclosed example, the range is nominally 5˜20% of the sensed wheel velocity. In another example, the band  36  maybe from 8˜10% greater than the normal wheel velocity. It should be understood that the range of wheel velocity is dependent on the size of the min-spare and that other ranges are within the contemplation of this disclosure depending on the size of the mini-spare compared to the normal wheel. Therefore, if the actual measured wheel velocity for the mini-spare  18  as is indicated by line  34  falls within the range of the band  30 , the controller  15  will recognize the presence of the mini-spare  18 . 
         [0018]    The broader range  36  is utilized to provide a temporary detection and recognition of the mini-spare  18 . If the wheel velocity  34  of the mini-spare falls within the second larger band  36 , the system temporarily recognizes the presence of a mini-spare  18 . The temporary recognition provides additional time for recognition without interference from the TCS  12  and the ESC  14 . In response to the recognition of the presence of the mini-spared  18 , the dynamics for the TCS  12  and ESC  14  are altered for the mini-spare  18 . 
         [0019]    If after a defined monitoring time, the dynamics of the difference is within a defined window during the whole period, a possible mini-spare wheel can be identified. If the dynamics of the difference is outside the defined window or the difference falls below a nominal mini-spare range by a defined amount, the learning functions are reset. 
         [0020]    Referring to  FIG. 3 , an initial threshold value  40  is illustrated that indicates when the TCS  12  and ESC  14  would take corrective action. Wheel speed velocities that exceed the initial threshold  40  would indicate wheel slipping in standard and normal sized wheels for the vehicle. However, because wheel speed velocity of the mini-spare  18  indicated by line  42  exceeds the initial threshold value  40 , the disclosed method and system adjusts the threshold  40  to a new adjusted threshold value as is indicated at  38 . The threshold value  38  is therefore adjusted to a value that is indicative of wheel slip for the mini-spare  18 . In addition, the speed may be adjusted for the axle including the mini-spare  18  wheel. 
         [0021]    The increase in the threshold  38  value avoids intervention by the TCS  12  and or ECS  14  so that the vehicle can achieve desired acceleration and performance. Once the standard mini-spare learning process is finished, wheel speeds will be compensated with the mini-spare difference reflected. The compensations made upon recognition of the mini-spare wheel  18  results in a wheel velocity signal that is reduced and within limits similar to those for a normal wheel. In the illustrated example, the wheel velocity of the mini-spare  18  is compensated for as shown by portion  44 . The line portion  44  is reduced and within the threshold limits provided by the original threshold value indicated at  40 . The threshold value  40  is therefore returned and operates to detect wheel velocities within the original limitations. 
         [0022]    The disclosed process of recognizing and adapting to the presence of a standard mini-spare is operable during operation of the vehicle at higher speeds. In one disclosed embodiment the method and process is configured to provide the desired threshold modification at speeds in excess of 50 mph (80 kph). The disclosed system uses corrected wheel velocities to enable learning even when vehicle starts on a curve such as for example a high way entrance ramp. 
         [0023]    The disclosed method and system may be implemented as part of software programmed to operate the controller  15  configured to receive signals and generate comments to actuate various vehicle systems. The controller  15  may be configured to perform the method steps of detecting differences in vehicle wheel speed, determining that wheel speed exists and evaluating whether a mini-spare is present. The controller  15  may also be configured to adjust threshold values based on the initial indication and determination that the mini-spare  18  is installed on the vehicle. 
         [0024]    The disclosed system and method enables quicker reaction and learning by the ESC system so that unnecessary TCS intervention can be avoided and desirable vehicle acceleration can be achieved once the mini-spare is installed. It is within the contemplation of this disclosure to apply the temporary threshold increases for use with other vehicle systems that may utilize wheel velocities. Moreover, the method and system of this disclosure could be part of other software utilized in other vehicle systems that receive information indicative of wheel speed. 
         [0025]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.