Abstract:
A device to monitor sensors in a motor vehicle, with the sensors generating signals, each representing different physical is provided. The device includes first arrangement with which identically defined comparison variables for the sensors are determined for at least two sensors on the basis of at least the signals generated by them. Furthermore, the device includes a second arrangement with which a reference variable is determined on the basis of at least two of the identically defined comparison variables and is taken into account in monitoring performed in a third arrangement for at least one sensor. To form the reference variable, a variable describing the difference between the identically defined comparison variable and the other identically defined comparison variables of the minimum of two identically defined comparison variables is determined for each of the minimum of two identically defined comparison variables. The identically defined comparison variable is evaluated using this variable.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device and a method for monitoring sensors used in a motor vehicle. In particular, the device and the method are intended for monitoring sensors used in a system for regulating the driving dynamics of a motor vehicle. 
     BACKGROUND INFORMATION 
     Devices and methods for monitoring sensors used in a vehicle are known from the related art in a variety of versions. 
     The patent application filed with the German Patent Office German Patent Application No. 196 36 443 describes a method and a device for monitoring sensors used in a vehicle. With this method and device, sensors each representing different physical parameters are monitored. The device contains means with which identically defined comparison variables are determined for at least two sensors, starting from at least the signals generated by them. The device also contains other means with which one reference variable is determined as a function of at least the determined comparison variables. A sensor reference variable is determined for each of the individual sensors on the basis of this reference variable. Taking into account the sensor reference variables, monitoring and/or correction is performed for each sensor. The above-mentioned patent application describes the following procedure for determining the reference variable. 
     On the basis of the identically defined comparison variables, a reference variable is determined by comparison of these comparison variables. To determine the reference variable, first the comparison variable having the greatest difference from the reference variable determined last is determined. Since this comparison variable has the greatest difference from the reference variable determined last, it can be concluded that under some circumstances the respective sensor might be defective. Consequently, this comparison variable is not taken into account in determining the instantaneous reference variable. The new reference variable is determined by forming a weighted average. First, the remaining comparison variables and second, the differences between the remaining comparison variables enter into the formation of the weighted average. 
     Systems for regulating the driving dynamics of a vehicle are described, for example, in the article “FDR—die Fahrdynamik-Regulung von Bosch (Regulating Drive Mechanics—the Bosch Method) published in the automotive engineering journal  Automobiltechnische Zeitschrift  (ATZ), volume 16, number 11 (1994) pages 674-689. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to improve upon the monitoring by sensors used in a vehicle. 
     This object is achieved by the features of claim  1  and by those of claim  7 . 
     SUMMARY OF THE INVENTION 
     The present invention permits monitoring of sensors that generate signals, each representing a different physical variable. For at least two sensors, identically defined comparison variables are advantageously determined for the sensors on the basis of at least the signals they generate. A reference variable is advantageously determined on the basis of at least two of the identically defined comparison variables and is taken into account in monitoring at least one sensor. 
     To form the reference variable, a variable describing the difference between the identically defined comparison variable and the other identically defined comparison variables of the at least two identically defined comparison variables is advantageously determined for each of the at least two identically defined comparison variables. The identically defined comparison variable is evaluated using this variable. 
     It is of particular interest when the identically defined comparison variables determined represent a physical variable, preferably corresponding to a variable detected with one of the sensors installed in the vehicle, in particular a yaw rate. 
     A variable representing the vehicle speed is advantageously determined on the basis of some of the signals generated with the help of the sensors, each representing different physical variables. On the basis of the reference variable and this variable representing the vehicle speed, a sensor reference variable is determined for at least one sensor and is taken into account in monitoring the at least one sensor. 
     It is especially advantageous if the signal generated by at least one sensor is corrected for that sensor at least on the basis of its sensor reference variable and the signal generated by it. 
     For a vehicle having wheel rpm sensors, a rotational rate sensor or a yaw rate sensor, a transverse acceleration sensor and a steering angle sensor, the reference variable is advantageously determined as follows: 
     for the wheel rpm sensors, an identically defined comparison variable omeganij is determined at least on the basis of the variable representing the vehicle speed and the signals generated by it; 
     for the rotational rate sensor or yaw rate sensor, an identically defined comparison variable omegakorr is determined at least on the basis of the signal generated by it and its sensor reference variable; 
     for the transverse acceleration sensor, an identically defined comparison variable omegaay is determined at least on the basis of the signal generated by it, the variable representing the vehicle speed and its sensor reference variable; 
     for the steering angle sensor, an identically defined comparison variable omegadelta is determined at least on the basis of the signal generated by it, the variable representing the vehicle speed and its sensor reference variable, and the reference variable is determined according to the equation:             omegaref   =               omegakorr     D12   ·   D13   ·   D14       +     omegadelta     D12   ·   D23   ·   D24       +                 omeganij     D13   ·   D23   ·   D34       +     omegaay     D14   ·   D24   ·   D34                         1     D12   ·   D13   ·   D14       +     1     D12   ·   D23   ·   D24       +                 1     D13   ·   D23   ·   D34       +     1     D14   ·   D24   ·   D34                                          
     where the terms: 
     D12=|omegakorr−omegadelta|, D13=|omegakoor=omeganij|, D14=|omegakoor−omegaay|, D23=|omegadelta−omeganij|, D24=|omegadelta−omegaay| and D34=|omeganij−omegaay| 
     describe the differences between two identically defined comparison variables. 
     Another advantage of the method invention and the device according to the present is the sturdiness of the reference variable. Furthermore, the sensor reference variable does not exhibit any sudden changes. 
     Other advantageous embodiments of the present invention can be derived from the subclaims and the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a device for implementing a method according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described with reference to FIG.  1 . 
     The specific form of the embodiment selected—use of the device and the method according to the present invention in a system for regulating the driving dynamics of a vehicle—is not intended to represent a restriction of the present invention in any way. 
     In FIG. 1, block  101  shows a control unit which is used in the device according to the present invention to carry out the method according to the present invention. 
     A steering angle sensor  102  can detect a quantity deltamess that describes the steering angle set on the vehicle. Signal deltamess generated with the help of steering angle sensor  102  is sent to a block  106  as well as blocks  112  and/or  113 . With the help of a rotational rate sensor or yaw rate sensor  103 , a variable describing the yawing motion of the vehicle about its vertical axis is detected. Signal omegamess detected with the help of rotational rate sensor or yaw rate sensor  103  is sent to a block  107  as well as to blocks  112  and  114 . With a transverse acceleration sensor  104 , a variable describing the transverse acceleration acting on the vehicle is detected. Signal aymess generated with the help of transverse acceleration sensor  104  is sent to blocks  108 ,  112  and  114 . Blocks  105   vr,    105   vl,    105   hr  and  105   hl  represent wheel rpm sensors assigned to the wheels of the vehicle. Simplified notation  105   ij  is introduced below for the wheel rpm sensors. Index i indicates whether the wheel is on the rear axle (h) or on the front axle (v). Index j shows the assignment to the right (r) or left (l) side of the vehicle. This notation using two indices i and j is the same for all variables and components used here. Signals nijmess generated with the help of wheel rpm sensors  105   ij  are sent to blocks  109 ,  110 ,  112  and  113 . 
     On the basis of signals nijmess generated with wheel rpm sensors  105   ij,  a variable vf describing the vehicle speed is generated in a block  109 . This variable vf describing the vehicle speed is sent from block  109  to blocks  106 ,  108 ,  110  and blocks  111  and  112 . Optionally variable vf may also be sent to block  107 . 
     Identically defined comparison variables are determined for sensors  102 ,  103 ,  104  and  105   ij  in blocks  106 ,  107 ,  108  and  110 . In the present embodiment, it is assumed that the comparison variables for the sensors represent a yaw rate as a physical variable. 
     In a block  106 , an identically defined comparison variable omegadelta is determined on the basis of signal deltamess supplied to it as well as variable vf describing the vehicle speed and variable deltaref supplied to block  106 . Identically defined comparison variable omegadelta is sent from block  106  to blocks  111  and  112 . Identically defined comparison variable omegadelta is determined as follows, for example, in block  106 : 
     First, an offset value for signal deltamess is determined on the basis of signal deltamess, variable vf describing the vehicle speed and a signal deltaref, which describes a reference value, known as the sensor reference variable, for the steering angle detected with the help of steering angle sensor  102 . Signal deltaref is corrected on the basis of the offset value thus determined. Using the corrected signal, identically defined comparison variable omegadelta is determined with the help of a mathematical model, taking into account variable vf describing the vehicle speed. 
     Determination of identically defined comparison variable omegaay takes place in block  108  on the basis of signals aymess, vf and ayref supplied to it in accordance with the determination of identically defined comparison variable omegadelta in block  106 . Identically defined comparison variable omegaay is sent to a block  111  as well as a block  112 . 
     As described above, the identically defined comparison variables for the sensors represent a yaw rate as a physical variable, thus identically defined comparison variable omegakorr determined in block  107  corresponds to the offset-corrected signal omegamess, because in this case it is not necessary to convert the offset-corrected sensor signal to a yaw rate with the help of a mathematical model. As described above in conjunction with blocks  106  and  108 , an offset value for signal omegamess is determined in block  107  on the basis of signal omegamess as well as variable omegaref. Identically defined comparison variable omegakorr is calculated from signal omegamess with the help of this offset value. Variable omegakorr is sent to a block  111  and a block  112 . 
     For the case when the identically defined comparison variables for the sensors represent a variable other than the yaw rate as a physical variable, a conversion of the offset-corrected signal with the help of a mathematical model must also be performed in block  107 . For this reason, variable vf describing the vehicle speed is shown as being supplied to block  107 . 
     In a block  110 , an identically defined comparison variable omeganij is determined for wheel rpm sensors  105   ij  on the basis of signals nijmess generated with the help of wheel rpm sensors  105   ij  as well as variable vf representing the vehicle speed. Identically defined comparison variable omeganij is sent from block  110  to blocks  111  and  112 . 
     Two processes take place in block  111 . First, a reference variable omegaref is determined in block  111  on the basis of identically defined comparison variables omegadelta, omegakorr, omegaay and omeganij supplied to the block. 
     A proposed method of determining the reference variable is by forming the following weighted mean:             omegaref   =               omegakorr     D12   ·   D13   ·   D14       +     omegadelta     D12   ·   D23   ·   D24       +                 omeganij     D13   ·   D23   ·   D34       +     omegaay     D14   ·   D24   ·   D34                         1     D12   ·   D13   ·   D14       +     1     D12   ·   D23   ·   D24       +                 1     D13   ·   D23   ·   D34       +     1     D14   ·   D24   ·   D34                                          
     where 
     
       
           D 12=|omegakorr−omegadelta|  (2),  
       
     
     
       
           D 13=|omegakorr−omeganij|  (3),  
       
     
     
       
           D 14=|omegakorr−omegaay|  (4),  
       
     
     
       
           D 23=|omegadelta−omeganij|  (5),  
       
     
     
       
           D 24=|omegadelta−omegaay|  (6),  
       
     
     
       
           D 34=|omeganij−omegaay|  (7).  
       
     
     As shown by equation (1) above, a variable describing the difference between this identically defined comparison variable and the other identically defined comparison variables is determined for each identically defined comparison variable. 
     The differences between variable omegakorr and variables omegadelta, omeganij and omegaay enter into the first term of the numerator formed with identically defined comparison variable omegakorr. The differences between variable omegadelta and variables omegakorr, omeganij and omegaay enter into the second term of the numerator formed with identically defined comparison variable omegadelta. The differences between variable omeganij and variables omegakorr, omegadelta and omegaay enter into the third term of the numerator formed with identically defined comparison variable omeganij. The differences between variable omegaay and variables omegakorr, omegadelta and omegnij enter into the fourth term of the numerator formed with identically defined comparison variable omegaay. 
     The weighting method according to the above formulation is selected so that when the identically defined comparison variables are equidistant in pairs, it yields exactly the arithmetic mean of these identically defined comparison variables. Furthermore, this ensures that when two of the four identically defined comparison variables coincide in the present embodiment, for example, reference variable omegaref will also assume this value. 
     Second, sensor reference variables for sensors  102 ,  103  and  104  are determined in block  111 . These sensor reference variables are determined on the basis of reference variable omegaref and taking into account variable vf describing the vehicle speed with the help of various mathematical models. For sensor  102 , the steering angle sensor, sensor reference variable deltaref is determined and sent from block  111  to block  106  and block  112 . For sensor  103 , the rotational rate sensor or yaw rate sensor, sensor reference variable omegaref is used and is sent from block  111  to block  107  and block  112 . For sensor  104 , the transverse acceleration sensor, sensor reference variable ayref is determined and is also sent from block  111  to block  108  and block  112 . Determination of ayref takes place like the determination of deltaref. 
     Sensors  102 ,  103  and  104  are monitored in block  112  on the basis of sensor reference variables deltaref and ayref supplied to it, reference variable omegaref, identically defined comparison variables omegadelta, omegakorr, omegaay and omeganij and variable vf representing the vehicle speed. The result of this monitoring is output with the help of variable Fi and sent to block  113 . Variable Fi contains information on whether the sensor is defective for each of the above-mentioned sensors. Monitoring for the individual sensors is performed on the basis of plausibility queries. 
     Block  113  is the regulator of control unit  101 . Measurement signals deltamess, omegamess, aymess and nijmess are sent to block  113 . Furthermore, block  113  receives from engine  115  a signal mot 2  describing the engine rpm, for example. Furthermore, block  113  receives signals ST 2  sent from a block  114 , which is the control logic for actuators  116   ij  and the engine. These signals may be, for example, control times Aij of actuators  116   ij,  which are designed as brakes in particular. On the basis of the measurement signals and signals ST 2  and taking into account variable Fi, regulator  113  determines, in accordance with the control it implements, signals ST 1  which are sent to control logic  114 . Formation of signals ST 1  can be modified if regulator  113  is notified by signal Fi that one of sensors  102 ,  103  or  104  is defective. 
     In block  114 , a control signal mot 1  for engine  115  and control signals Aij for actuators  116   ij  are determined on the basis of signals ST 1  supplied to that block. Regulation of a motion variable representing the motion of the vehicle is implemented through the corresponding control of engine  115  and actuators  116   ij,  which are designed as brakes in particular. With signals ST 2  generated in block  114 , the status of actuators  116   ij,  for example, is relayed to regulator  113 .