Abstract:
A method is described for determining an externally produced value, especially a momentum, accelerating or decelerating the vehicle, with the following steps: determination of the driving performance of the vehicle on the basis of a model, comparison of the model output values with the relative measuring values or values derived from this, and determination of the externally produced value according to the result of the comparison. The corresponding device includes a model of the driving performance of the vehicle, a comparator for model output values and measuring values or values derived from these and a device for determining the externally produced value according to the result of the comparison.

Description:
TECHNICAL FIELD 
     The present invention generally relates to vehicle stability control and more particularly relates to a method and a device for establishing a value, especially a momentum, produced externally, driving or braking a vehicle. 
     BACKGROUND OF THE INVENTION 
     The longitudinal dynamics of a vehicle—speed and acceleration—is influenced by various internal and external values, especially momentums. Within the meaning of this description, internal values/momentums are the motor torque, the brake torque or the normal resistance (which can be described internally by tables based on pragmatic values or by constants or formulas considering the motional status of the vehicle in connection with the characteristics/parameters of the vehicle). These values can be established in a relatively precise manner by various measures so that it is possible to consider their influence on the longitudinal dynamics. Additionally there are also externally produced values resulting particularly variable in addition to the normal resistance described above (which can be described internally). This includes, e.g. the slope descending force when a vehicle is driving on an inclined road. This slope descending force leads to a momentum which influences the longitudinal dynamics of the vehicle. The same applies for wind forces, extraordinary rolling resistances or similar. It is not possible (or only with difficulties) to establish these externally produced values with traditional sensors, so that usually additional sensors are required which have to be eliminated. 
     However, for some applications it is desirable to know also externally produced values driving or braking a vehicle, especially momentums. An example for such an application would be a starting aid when driving up a hill. Such starting aids shall facilitate the complicated handling of brake, parking brake, clutch and motor. At the same time it has to be assured that the vehicle never rolls back, in order do avoid e.g. collisions with vehicles being parked in downhill direction. If a vehicle shall be started driving up the hill, the rules described schematically in FIG. 4 apply in a first approximation. The weight F G  of the vehicle can be decomposed into a normal component F N  and a tangential component F T  on the wheel of a one-wheel model. Together with the wheel radius r R , F T  leads to a slope descending momentum M H  according to the formula: 
     
       
           M   H   =F   G ·sin α· r   R   
       
     
     In this case α is the angle of inclination. Without further intervention the slope descending momentum M H  would cause the vehicle to run down the hill. The brake torque M B  and the motor torque M M  introduced during the start of the vehicle, counteract against this momentum. An aid for starting up the hill can influence, e.g. the brake torque M B . But the influence has to be such to assure at all times that the inequation 
     
       
         
           M 
           H 
           &lt;M 
           B 
           +M 
           M 
         
       
     
     is complied with because only in this case the vehicle is definitely prevented from rolling back. In order to satisfy the equation mentioned above, the slope descending moment has to be known. 
     Similar considerations as above apply in dynamic situations (vehicle speed unlike zero). When driving slowly up the hill in urban traffic, the considerations mentioned above could become an important factor. Also in such cases it is desirable to know the values produced externally and driving or braking a vehicle, especially momentums, in order to influence the vehicle in an adequate manner. 
     From U.S. Pat. No. 5,455,767 a control for a vehicle drive with an automatic gear is known which determines a correction term by comparing an estimated and a measured output speed representing a basic value for the inclination angle. On the input side a motor torque and a resistance momentum of the vehicle are delivered to a time element. The difference between the estimated and the measured output speed is countercoupled to the rotation angle acceleration. 
     It is the object of the present invention to indicate a method and a device for establishing an externally produced value, especially such a momentum, which drives and brakes the vehicle. 
     The externally produced values, and in particular the momentums, are determined by an observer. The observer receives internally produced values, especially momentums, which drive or brake the vehicle, establishes, how the longitudinal dynamics of the vehicle should develop, compares this result with the measured values of the longitudinal dynamics and concludes from possible deviations that there are externally produced values, especially momentums, driving or braking a vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a block diagram of the present invention 
     FIG. 2 the observer of FIG. 1 
     FIG. 3 an exemplary model of the vehicle dynamics and 
     FIG. 4 schematically valid physical connections in an exemplary application. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically describes a first embodiment according to the present invention. The devices  10  to  12  are devices for determining internal or internally produced momentums. In particular a device  12  for determining the motor torque MMotAxis and a device  11  for determining the brake moment MBrakeAxis can be foreseen. In addition, also a device  10  for determining a normal resistance MNormalRes can be foreseen. On the other hand, the devices  10  to  12  work according to certain input values. The devices  11  and  12  can particularly be models and/or tables which model or describe the conduct of the brake and/or the motor/gear and deliver the desired output values. 
     On the basis of a model and with reference to the input values described above, the observer  13  determines the “theoretical” driving performance or the “theoretical” longitudinal dynamics, particularly the speed, of the vehicle, based on characteristic values even in this case. Characteristic values are, e.g. the tire radius or the vehicle mass. Furthermore the observer  13  receives a theoretical value from an appropriate device  14  which corresponds to the measured value. If the modeling of the longitudinal dynamics is sufficiently precise, the deviation between the theoretical and the measured value can be attributed to values, especially momentums, produced externally and not modeled, so that this external value can be concluded from this deviation. 
     FIG. 2 shows the observer  13  of FIG. 1 in a more precise representation. The observer  13  represents a model of the driving performance response the longitudinal dynamics of the vehicle, corresponding to the numerals  31  to  36 . Furthermore it shows a device for determining the external value, i.e. the numerals  21 ,  22 ,  25 . But before illustrating the function of observer  13  on the basis of FIG. 2, the model of the driving performance response the longitudinal dynamics of the vehicle is described on the basis of FIG. 3 which represents again the components  31  to  36  of FIG. 2 for illustration. 
     The model for the driving performance of the vehicle response for its longitudinal dynamics has to meet at least two conditions in order to be suitable for the present invention. 
     it must have suitable input and output values and 
     it must consider static and dynamic effects in a sufficiently precise manner. 
     The model in FIG. 3 satisfies these requirements. As input values it receives a total momentum which acts on the vehicle. This total momentum MTot corresponds to the total of all accelerating and decelerating momentums. If the total momentum MTot is zero, the vehicle will drive at a constant speed. If it is greater than zero, the vehicle will be accelerated, if it is negative, the vehicle will be decelerated. In the calibration  31  the total momentum is calibrated according to wheel radius and vehicle mass. In this case “calibration” is a proportional conversion serving e.g. for the conversion, normalization or adaptation of values. From this results a value corresponding to the acceleration. This value is integrated in integrator  32 . Thus results a value corresponding to a speed. Furthermore an assembly  33  to  36  is foreseen which imitates the dynamics. In the represented embodiment of the present invention this refers to a PT 1 -member which only gradually communicates to the output changes occurring on the input. The PT 1 -member includes a subtractor  33 , a calibration  34 , an integrator  35  and a feedback  36  introduced at the subtractor  33 . The value of the calibration  34  defines the time constant of the PT 1 -member. The PT 1 -member considers the fact that real systems react practically always with a certain delay to changes of their input values. Thus it is possible to better imitate the vehicle dynamics. The result is an output in the form of a speed VMod, which the model in FIG. 3 has determined as “theoretical” speed of the vehicle on the basis of the total momentum MTot which had been inserted. 
     The sequence of the single components can also be represented in a different way than that of FIG.  3 . However, the negative feedback  23 ,  24  of FIG. 2 should be introduced after the integrator  32 . The device  14  for determining the real vehicle speed VRefFilt can be a sensor emitting an adequate signal. A more complex device can also be foreseen, taking suitable judgement and filtering measures in order to receive signals which are possibly free from interferences. 
     The vehicle model described with reference to FIG. 3 can be considered as an example. However, also other models can be used which satisfy the requirements mentioned further above. 
     Referring again to FIG. 2, the use of the model of FIG. 3 in the observer  13  is illustrated. The “theoretical” vehicle speed VMod determined on the basis of the model is compared with the real vehicle speed VRefFilt. In particular the difference between the model speed (also called estimated vehicle speed) and the real speed (also called real vehicle speed) VRefFilt is built in the subtractor  22 . The deviation between estimated vehicle speed and real vehicle speed has to be attributed to externally produced values, and especially momentums, which are not modeled, and thus permits a conclusion to be made with regard to these external values and especially momentums. If the vehicle is running uphill, the externally produced momentum has a decelerating effect. Without considering this external momentum the estimated speed would be too high and particularly higher than the real vehicle speed. If the vehicle is running downhill, the slope descending momentum has an accelerating effect. Without considering this slope descending momentum the estimated vehicle speed VMod would thus be smaller than the real vehicle speed VRefFilt. Thus, from the deviation and in particular from the difference between the estimated and the real vehicle speed can be determined the externally produced value, in particular the externally produced momentum. In order to cause the observer  13  to work altogether in a stable manner, the external momentum already determined can be added with the right algebraic signs to the other momentums already determined (of the devices  10  to  12 ). For this reason it is introduced at the summation point  21 . The device  25  is a calibration which converts the speed difference into the relative momentum errors preferably in a proportional manner. Thus the output of the device  25 , the signal MCorrectionObs is the externally produced momentum that had originally been looked for, which can be used as output signal and can be led back into the observer at the summation point  21 , as already mentioned above. 
     From the point of view of the control technique also a feedback  23 ,  24  can be foreseen which, after the integrator, leads back a signal into the vehicle model corresponding to the difference between the estimated vehicle speed and the real vehicle speed. Thus stability and dynamic characteristics of the model are improved. The countercoupling feedback can be realized e.g. at summation point  33 . 
     The device according to the present invention can be implemented by discrete components, but also be formed by means of a suitably programmed computer which receives the relative input values, sends the desired output values and has access to the data which are also needed. The Method is executed preferably in a continuous manner or triggered periodically.