Abstract:
A method and a device for adjusting the braking effect and/or driving effect at the wheels of a motor vehicle. For this purpose, a tire tolerance adjustment has at least two different operating modes. It is determined whether a mounted spare wheel or temporary spare wheel is present. One of the operating modes is selected as a function of the determined existence of a spare wheel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and a device for adjusting the braking and/or driving effect at the wheels of a motor vehicle. 
     BACKGROUND INFORMATION 
     A plurality of systems for anti-lock braking control, for traction control, and/or for vehicle stability in motor vehicles are known from the related art. These systems generally start from at least the wheel rotational speeds or the wheel speeds of the vehicle wheels. However, before the wheel speeds are used for regulation, they are generally corrected by a so-called tire tolerance adjustment. Such a regulating system for a motor vehicle is described in German Published Patent Application No. 42 30 295, for example, in which errors in the wheel speeds created by tolerances between the tires are equalized. Such tolerances are due to different wheel diameters, for example. For example, a low-pass filtering in conjunction with a tire tolerance adjustment is described in German Published Patent Application No. 42 30 295. 
     Furthermore, a slip regulation system is known, for example, from European Published Patent Application No. 0 510 466, where the wheel rotational speeds are used for slip formation. To equalize the tire tolerances, the wheel speeds are corrected. When determining the appropriate correction factors, possibly existing cornering of the vehicle must be taken into consideration. 
     The variations for adjusting tire tolerances known from the related art generally require relatively long time intervals. If the braking regulation and/or driving regulation is acted upon shortly after the vehicle is started, a slow tire tolerance adjustment can potentially result in unfavorable conditions. 
     If there is tire damage on a motor vehicle, often only a temporary spare wheel or spare wheel is provided. In contrast to standard wheels, this temporary spare wheel or spare wheel has a significantly smaller diameter which is to be taken into consideration by a tire tolerance adjustment. A detection of such temporary spare wheels or spare wheels is known from European Published Patent Application No. 0 449 845, for example. 
     SUMMARY OF THE INVENTION 
     As mentioned, the present invention relates to a method and a device for adjusting the braking effect and/or driving effect at the wheels of a motor vehicle. Assigned to the wheels are sensors that emit speed signals representing the rotary motions of the wheels. These speed signals are corrected via a correction, i.e., the tire tolerance adjustment. The braking and/or driving effect is/are adjusted at least as a function of corrected sensor speed signals. 
     According to the present invention, the correction, i.e., the tire tolerance adjustment, has at least two different modes of operation. Furthermore, it is determined whether a mounted spare wheel or temporary spare wheel having a smaller diameter than the remaining wheels is present. One of the operating modes is then selected in accordance with the present invention, as a function of the determined existence of a spare wheel. 
     According to the present invention, a selection module is connected in series with and upstream from the actual tire tolerance adjustment, the selection module selecting a specific operating mode in response to a temporary spare wheel being present. This certain operating mode of the tire tolerance adjustment advantageously enables a particularly quick tire tolerance adjustment. The actual, slow tire tolerance adjustment, which is, however, generally more precise, follows the first, quick tire tolerance adjustment. As a result of this adjustment algorithm, the rotational speed of a temporary spare wheel or spare wheel is very quickly adjusted to the other wheel speeds. As a result of the present invention, the temporary spare wheel adjustment is carried out in such a manner that the complete functionality of an anti-lock control system, traction control system, and/or vehicle stability system or of an electronic braking force distribution system is already present when braking for the first time. Thus, no additional measures are necessary. 
     In an advantageous embodiment of the present invention, it is provided that the correction, i.e., the tire tolerance adjustment, is carried out more quickly in a first operating mode having a smaller filtering time constant than in a second operating mode having a larger filtering time constant. 
     A further embodiment of the present invention start from the assumption that the standard, slow tire tolerance adjustment is carried out as a function of the output torque of the vehicle engine. This can be inferred, for example, from the document German Published Patent Application No. 42 30 295 mentioned at the outset. Thus, for the standard, i.e., slow, tire tolerance adjustment, a certain condition is given for the engine torque in order for the tire tolerance adjustment to be carried out. For example, the drive torque or the drag torque acting on the wheels is sufficiently low. However, this condition slows the tire tolerance adjustment in cases in which the engine torque does not satisfy this condition. According to this embodiment of the present invention, it is provided that the correction is carried out in a first, quick operation mode of the tire tolerance adjustment, independently of the engine torque. 
     It is further known to attach the tire tolerance adjustment to the condition that no cornering exists. In an additional embodiment of the present invention, it is provided that it be determined whether the vehicle is traveling on a curve. According to this embodiment, the tire tolerance adjustment is performed in the first, quick operating mode, independently of determined cornering. 
     In a further embodiment of the present invention, it is provided that, in the first, quick operating mode, the tire tolerance adjustment is performed at lower forward speeds of the vehicle than in a second, slower operating mode. 
     However, the determination of whether there is a mounted temporary spare wheel or spare wheel is advantageously only begun when a predefinable speed threshold value for the vehicle&#39;s forward speed is exceeded. 
     In a further advantageous embodiment of the present invention, it is provided that the determination of whether there is a mounted temporary spare wheel or spare wheel occurs in such a manner that 
     the wheel having the highest rotational speed is determined from the speed signals; 
     a check is performed to determine whether the rotational speed of the wheel having the highest rotational speed deviates in a predefinable manner from the rotational speed having the speed of at least one other wheel, in particular of the wheel mounted on the same vehicle axle; 
     it is determined from the differences of the rotational speeds of the wheels on the axle on which the wheel having the highest rotational speed is not mounted whether cornering exists; and 
     the wheel having the highest rotational speed is determined as the temporary spare wheel or spare wheel provided that the rotational speed of this wheel deviates in a predefinable manner and especially for a predefinable period of time from the rotational speed of at least one other wheel, and there is no cornering. 
     In a further embodiment of the present invention, it is provided that the mode selected when a temporary spare wheel or spare wheel is present is terminated as a function of the result of a comparison of the corrected output signal of the temporary spare wheel or the spare wheel to an output signal of at least one sensor at another wheel. This is because the quick and tolerant tire tolerance adjustment is only intended to enable a first, quick adaptation of the temporary spare wheel to the reference wheel. The standard tire tolerance adjustment including its release conditions is to subsequently apply again. The quick and tolerant tire tolerance adjustment is, therefore, ended when the rotational speed of the temporary spare wheel or spare wheel deviates less than 1.5%, for example, from the other wheel rotational speeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an overview of a block diagram of the present invention. 
     FIG. 2 shows the basic sequence of the adjustment of the braking effect and/or driving effect at the wheels. 
     FIG. 3 shows the detailed sequence of a specific embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are described below in light of the exemplary embodiments. 
     FIG. 1 shows a schematic view of a vehicle having vehicle wheels  101   ij.  In the following, the index i designates the association of the corresponding quantity with the rear (i=h) or the front (i=v) vehicle axle. The index j indicates the association of the corresponding quantity with the right (j=r) or the left (j=l) side of the vehicle. Speed sensors  105   ij  and wheel brake units  106   ij  are mounted on vehicle wheels  101   ij.  Wheel speed sensors  105   ij  send their output signals Nij to control unit  104 . In control unit  104 , drive signals Bij for wheel brake units  106   ij  are formed at least as a function of wheel speed values Nij. This occurs in a generally known manner, for example, by forming slip values for individual vehicle wheels  101   ij  from wheel speeds Nij, the braking effect and/or the driving effect at the individual vehicle wheels being subsequently adjusted via signals Bij and/or A in such a manner that a specific brake slip or drive slip is not exceeded. 
     In addition, the vehicle&#39;s drive train is sketched in FIG.  1 . In this context, reference numeral  103  designates the vehicle engine whose output power or output torque or output rotational speed can be controlled or regulated via control unit  104 , using drive signal A. The output torque of engine  103 , which, in engine management, generally exists as torque signal Mmot, is directed to control unit  104 . 
     Vehicle engine  103  is connected to transmission  105  via clutch  108 . Transmission  105  is then connected via differential  102  to the drive gears on the back axle. The output rotational speed of the transmission is determined via speed sensor  107 . Corrected by the transmission ratio of differential  102  and/or by the wheel diameter at the driving wheels, the output rotational speed of the transmission is a measure of forward speed V of the vehicle. 
     The adjustment of the braking and/or driving effect at vehicle wheels  101   ij  via control unit  104  is shown schematically in FIG.  2 . After initial step  201 , wheel speed signals Nij and additional signals are detected in following step  202 . In step  203 , the drive signals for wheel brakes  106   ij  (drive signal Bij) and drive signal A for vehicle engine  103  are formed at least as a function of detected wheel speed signals Nij. This is indicated in step  203  by functional dependence F and G. After final step  204 , the sequence shown in FIG. 2 is restarted. The formation of drive signals Bij and A is described frequently in the related art and will not be explained in greater detail here. 
     FIG. 3 shows a detailed sequence of an exemplary embodiment according to the present invention. 
     After start step  301 , counter value T is first set to zero in step  302 . In step  303 , wheel speeds Nij or the vehicle&#39;s forward speed is/are determined. 
     In query  304 , forward speed V of the vehicle is compared to a threshold value SWI. If forward speed V of the vehicle does not exceed threshold value SWI, the following conditions for quick tire tolerance adjustment  309  are not checked. In this case, standard tire tolerance adjustment  310  including its special acceptance conditions (e.g. conditions for the engine torque, cornering, etc.) is carried out. 
     However, if forward speed V of the vehicle does exceed threshold value SW 1 , the vehicle is traveling at a sufficiently high vehicle speed, whereupon the fastest rotating wheel is determined in step  305 . This wheel exhibits non-corrected wheel speed Nfast. Furthermore, non-corrected wheel speed Nref of the other wheel of the same axle (reference wheel) is loaded into a temporary register for further processing. 
     In addition, a tolerance band Tb is formed in step  305 . Predefinable threshold values SWu and SWo are provided for this purpose. Using wheel speed Nref of the reference wheel, tolerance band Tb is calculated in correspondence with the possibly mounted temporary spare wheels. For this purpose, a lower value SWu as well as an upper value SWo are added to wheel speed Nref of the reference wheel. In this manner, one obtains tolerance band Tb: 
     
       
           Tb=[ ( Nref+SWu ); ( Nref+SWo )] 
       
     
     Step  306  determines whether speed Nfast of the fastest wheel is within tolerance band Tb. If this is not the case, the fastest wheel is obviously not a temporary spare tire or spare tire. Standard tire tolerance adjustment  310  is then performed. 
     However, if step  306  determines that rotational speed Nfast is within the tolerance band, this wheel is a temporary spare wheel or a spare wheel. Subsequent step  307  then determines whether the vehicle is cornering at the moment. Cornering is checked for in light of the following condition. 
     The difference in the wheel speeds of the axle on which the supposed temporary spare wheel (fastest wheel) is not located is to be less than or equal to a certain threshold value. If this is the case, it can be assumed that the vehicle is traveling on a curve having a larger radius of curve or is traveling straight. In this case, step  308  is the next step. However, if the vehicle is traveling on a curve having a small radius of curve, standard tire tolerance adjustment  310  including its special acceptance conditions is performed. If it is determined, for example, that the temporary spare wheel (fastest wheel) is located on the front axle, the amount of the rotational speed difference ΔN=|(Nhr−Nhl)|of the back wheels is compared to a relatively small threshold value SW 3 , which can, for example, be selected as a function of the vehicle&#39;s forward speed, in order to detect curves. If rotational speed difference ΔN is less than threshold value SW 3 , there is essentially no cornering. If rotational speed difference ΔN exceeds threshold value SW 3 , there is cornering. 
     To detect curves in step  307 , a steering angle signal, a transverse acceleration signal, and/or a yaw angle signal can be used, provided that the appropriate sensors are present in or on the vehicle. 
     Query  308  determines whether counter value T exceeds a corresponding, predefinable threshold value SW 2 . If this is not the case, the counter value is increased by one counter value in step  311 , and the already described sequence is restarted with step  303 . 
     However, if step  308  determines that the counter value exceeds threshold value SW 2 , the conditions for quick tire tolerance adjustment  309  have been present for a sufficient length of time. In this case, quick tire tolerance adjustment  309  is performed. 
     The quick and tolerant tire tolerance adjustment  309  is only intended to enable a first, quick adaptation of the temporary spare wheel to the reference wheel. The standard tire tolerance adjustment including its release conditions is to subsequently apply again. This is achieved in that wheel speed Nfast of the temporary spare wheel is corrected to form corrected wheel speed Nfast,kor in step  313 . In subsequent step  314 , corrected value Nfast,kor is compared to rotational speed Nref of the reference wheel. As long as corrected value Nfast,kor is greater than reference rotational speed Nref, quick tire tolerance adjustment  309  is maintained. However, as soon as corrected value Nfast,kor exceeds rotational speed Nref of the reference rotational speed, the quick tire tolerance adjustment is terminated in final step  312 . In step  314 , the difference (Nfast,kor−Nref) can also be compared to a threshold value that is 1.5% of Nref, for example. 
     After the correction is terminated in operating mode RTA quick , this operating mode RTA quick  is blocked for at least a period of time. In particular, it can be provided that the blocking is maintained at least until the vehicle is started again. In this manner, a further, possibly incorrect, quick adjustment during the remaining drive is prevented. However, the blocking of this operating mode RTA quick  can be canceled or not induced when the existence of cornering is detected during operating mode RTA quick . In this case, mode RTA quick  continues to be allowed. 
     According to the present invention, a software module detects the typical speed difference of a temporary spare wheel or spare wheel with respect to other wheel rotational speeds. Certain conditions are then checked in accordance with the present invention: 
     The vehicle is traveling at a significantly high speed (query  303 ). 
     No additional wheel satisfies the temporary spare wheel or spare wheel condition. 
     A time criterion is satisfied (query  308 ). 
     If these conditions are satisfied, the subsequent tire tolerance adjustment module is modified, so that it is enabled as being tolerant and is quickly carried out until the temporary spare wheel is adjusted to a certain percentage. This occurs such that 
     the tire tolerance adjustment is begun upon initiating travel; 
     the tire tolerance adjustment is carried out independently of the engine torque; 
     the tire tolerance adjustment is carried out more quickly (smaller filtering time constant); and 
     the tire tolerance adjustment is carried out in a curve-tolerant manner, i.e., independently of whether cornering exists. 
     The quick and tolerant, tire tolerance adjustment is terminated when the rotational speed of the temporary spare wheel or spare wheel deviates less than 1.5%, for example, from the other wheel rotational speeds. By way of exception, the quick tire tolerance adjustment is repeated after cornering when this quick tire tolerance adjustment was performed before or during cornering. 
     As a result of the present invention, the temporary spare wheel adjustment is carried out in such a manner that the complete functionality of an anti-lock control system or of an electronic braking force distribution system is already present when braking for the first time. Thus, no additional measures are necessary. 
     In a further embodiment of the present invention, it is provided that a status signal is generated when a mounted temporary spare wheel or spare wheel is present. The functioning of other vehicle systems, such as systems for anti-lock brake control, for traction control, and/or for vehicle stability are modified as a function of this status signal. 
     In this context, it is particularly provided that the status signal is supplied via a data line, in particular via a bus system (CAN bus, Controller Area Network), to other vehicle systems for controlling and/or regulating vehicle functions. Thus, for example, provision can be made for the vehicle&#39;s forward speed to be limited when a temporary spare wheel or a spare wheel is detected. 
     Furthermore, the status signal can be used for triggering a display that can be observed by the driver. In the event that a temporary spare wheel or a spare wheel is present, this is displayed to the driver. As a result, the driver is continually reminded that a temporary spare wheel or a spare wheel is mounted. 
     Furthermore, a monitoring element can be provided via which slip values of the wheels are measured and evaluated in such a manner that, given the existence of slip values of a certain, preselectable magnitude, predefinable measures are introduced. For example, in the case of such sustained slip monitoring, it can be provided that braking and/or driving systems are switched off when sufficiently high slip values have been present for a sufficient period of time. If the monitoring element evaluates the uncorrected wheel rotational speeds, the monitoring element is deactivated when a temporary spare wheel or a spare wheel is detected.