Abstract:
A method for determining the temperature or the ohmic resistance of an electrical component, especially of a coil of a magnetic valve. The component temperature is estimated with the aid of a temperature model, which is able to determine the curve of the component temperature even during a control of the valve. The temperature model is corrected regularly based on the measured value, in this context.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for determining the temperature or the resistance of an electrical component, as well as a control unit having a temperature model. 
     BACKGROUND INFORMATION 
     Magnetic valves, as used, for example, in the brake circuit of motor vehicles, include a coil for generating a magnetic field by which an armature is actuated. The magnitude of the current flow determines the strength of the magnetic field, in this instance, and with that the setting of the valve (open, closed or intermediate setting). The current flow through the coil is usually set by a valve output stage which includes essentially an output stage switch (MOSFET), which is controlled by drive electronics. The control of the output stage switch takes place mostly by a PWM signal (PWM: pulse width modulation). 
     During the control of a magnetic valve, for instance, within the scope of an ESP regulation, a heat loss is generated which leads to the heating of the magnetic valve. This raises the ohmic resistance of the valve. Conversely, the magnetic valve cools off when at rest, whereby the resistance goes down as well. Consequently, in a vehicle regulation the problem arises that one and the same PWM signal leads to different valve conditions at various valve temperatures. This impairs the accuracy of the control interventions. 
     In order to eliminate this problem, it is known, for example, from German Patent No. DE 10 2006 041 193 that one may determine the resistance of a magnetic coil directly via a voltage measurement and readjust the control signal (PWM) of the magnetic valve correspondingly. 
     However, a resistance measurement is possible only at those times at which the corresponding valve is not being controlled. By contrast, during the control of the valve, the valve temperature and its resistance are not able to be determined. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method and a device by the use of which the ohmic resistance of the electrical component is able to be determined even during a control phase of the valve. 
     One important aspect of the present invention is to estimate the temperature development of the electrical component with the aid of a model which reflects the thermophysical processes in the electrical component. To improve the accuracy of the temperature model, it is provided that one measure the temperature of the electrical component (or of a system included in the component) at certain times directly or indirectly, and to correct the temperature model, based on the measured value(s). This correction preferably also takes into account at least one parameter (KC, KH), which is a function of a temperature deviation (swing), namely the difference between a model-based estimated component temperature and the environmental temperature. This has the substantial advantage that the temperature or the resistance of the magnetic coil is able to be determined accurately even during the control of the valve. 
     The component temperature is preferably determined indirectly via the resistance of the component, that is, the resistance value is simply recalculated to give the temperature. The resistance, in turn, is determined from a voltage drop at the component or rather, at a device including the component (also indirectly). Because of the unique relationships between the variables named, they may simply be recalculated into another one. The terms “temperature”, “resistance” and “voltage” should therefore be understood to be synonymous. For the sake of simplicity, only the term temperature is used in the following. 
     The parameter (KC, KH) is preferably read off from a characteristics curve as a function of the temperature deviation. The characteristics curve may be generated, for example, in an offline simulation, with the aid of a Kalman filter. The characteristics curve simulates the essential properties of a genuine Kalman filter, and particularly has the advantage that the reading out of a parameter requires substantially less calculating power than a genuine Kalman filter. Parameters KC, KH are filter parameters of the Kalman filter, in this case. 
     According to the present invention, the component temperature is measured at certain times, for instance, every 20 s (preferably indirectly via a resistance measurement). Between these points in time, the component temperature is preferably estimated with the aid of a temperature model. 
     According to one preferred specific embodiment of the present invention, if a measured value of the component temperature is present, the temperature model is corrected as follows:
 
 T   mod   :=T   mod−1   +KC ·( T   mess   −T   mod )
 
where T mess  is the measured component temperature and KC is a parameter read out from the characteristics curve. To the left of the equals sign, the new value T mod  is given, and to the right the old value T mod−1  is given. The characteristics curve is preferably a function of the temperature deviation, that is, the difference between the model-based component temperature T mod  and an environmental temperature T U .
 
     The environmental temperature T u  is preferably also estimated with the aid of the temperature model, but could also be measured. In the first case, a temperature model is provided for the environmental temperature. This model is preferably also corrected based on the measured value(s). In this context, a further parameter (KH) is taken into account which is read out from a characteristics curve that is a function of the temperature deviation. 
     According to one preferred specific embodiment of the present invention, the environmental temperature is corrected as follows:
 
 T   U:   =T   U−1   +KH ·Sum( T   mess   −T   mod ).
 
     In this context, T mess  is the (directly or indirectly) measured component temperature and KH is a parameter. To the left of the equals sign, the new value T U  is given, and to the right the old value T U−1  is given. 
     The algorithms described above are preferably filed in a control unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a circuit for determining the ohmic resistance of a coil of a magnetic valve. 
         FIG. 2  shows the important method steps of a method for determining the resistance of a magnetic coil with the aid of a temperature model. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic circuit diagram of a valve output stage  1  for two current-controlled valves  9   a ,  9   b , such as ones installed in known passenger car braking systems, for example. Of the valves  9   a ,  9   b , only the appertaining coils  2   a  and  2   b  are shown here. The two coils  2   a ,  2   b , connected in parallel are connected to a supply voltage U 1  via a common main switch  3 . Switch  3  is durably closed in normal operation, and may be opened in case of a fault at one of valves  2   a ,  2   b , or in case of a resistance measurement of the valve resistances. In the first case, switch  3  is used essentially as a safety switch. 
     Each one of valves  9   a ,  9   b  includes an associated output stage switch  5   a ,  5   b , which is controlled by a drive electronics (control unit  7 ). In normal operation, output stage switches  5   a ,  5   b  are controlled using a PWM signal PWM 1 , PWM 2 , whose pulse duty factor determines the current flow through coils  2   a ,  2   b , and thus determines the setting of the associated valve. 
     Since the ohmic resistance of coils  2   a ,  2   b  is temperature-dependent, one and the same PWM signal leads to different valve states in the case of different valve temperatures. With the aid of a temperature determination of valves  9   a ,  9   b  it is possible to readjust PWM signals PWM 1 , PWM 2 . 
     The valve temperature is measured indirectly via a resistance measurement, in this instance. For this purpose, the voltage dropping off to ground is measured at a supply side node D 2  of coils  2   a ,  2   b  and from this the coil resistance is calculated, knowing the current that is flowing through coils  2   a ,  2   b . The coil resistance, in turn, is able to be recalculated to a temperature, in a simple manner. 
     The resistance measuring device includes a current source  6 .and a reference resistor  4 , which is connected in series to coils  2   a ,  2   b . The resistance measurement may be carried out only outside of control of output stage switches  5   a ,  5   b , for otherwise it would interfere with the operation of valves  9   a ,  9   b . During measurement operation, main switch  3  is opened, so that coils  2   a ,  2   b  are then supplied exclusively by current source  6 . As desired, by the appropriate control of output stage switches  5   a ,  5   b , voltage U mess  may now be measured via coils  2   a  and output stage switch  5   a , via coils  2   b  and output stage switches  5   b , or the voltage drop may be measured via the entire parallel device  2   a ,  2   b ,  5   a ,  5   b . Measured voltage U mess  is a measure for the resistance of the respective measuring path, in this instance. 
     In order to check first valve  9   a , for instance, the associated first output stage switch  5 a is closed (and the other output stage switch  5   b  is opened). Current I injected by D.C. source  6  flows, in this instance, via reference resistor  4 , measuring node D 2  through coils  2   a  and output stage switch  5   a  to ground. In this context, the voltage dropping off at node D 2  is measured. In order to check second valve  9   b , associated output stage switch  5   b  is closed (and switch  5   a  is opened). Current I injected by direct current source  6  in this case flows via reference resistor  4  through second coil  2   b  and output stage switch  5   b  towards ground. In this context, in turn, voltage U mess  dropping off at node D 2  is measured. Optionally, both output stage switches  5   a ,  5   b  could also be closed, in order to check both valves  9   a ,  9   b  in parallel at the same time. During this measuring phase, switch  3  remains open. 
     In order to determine the coil resistance of coils  2   a ,  2   b , the steps shown in  FIG. 2 , blocks  10  to  12  are carried out. According to block  10 , first of all, the voltage dropping off over one of coils  2   a ,  2   b  and also over reference resistor  4  is measured. If the reference resistor is a resistor having very low tolerances, current I supplied by current source  6  is able to be determined very accurately with the aid of the voltage measurement. This calculation of current I takes place in block  11 ,  FIG. 2 . From the voltage dropping off at node  2  and current value I determined before, the resistance of coils  2   a  or  2   b  may now be very accurately determined in step  12 . Control signal PWM and PWM 2  of output stage switches  5   a ,  5   b  may consequently be readjusted appropriately. 
     The temperature measurement or the resistance measurement of coils  2   a ,  2   b  is able to be determined only outside the control phases, as was mentioned above. In order also to be able to ascertain the coil resistance during the control phases, a mathematical temperature model  8  is provided in this instance, that is integrated into control unit  7 . Temperature model  8  reflects the thermophysical properties of coils  2   a ,  2   b  and includes appropriate mathematical algorithms. In order to improve the accuracy of temperature model  8 , it is regularly corrected based on temperature measured values. This correction of temperature model  8  will be explained below, in light of blocks  13  to  18 . 
     In step  13 , if there is a new resistance measured value, this resistance measured value is recalculated to a corresponding coil temperature T mess . For the corrected temperature T mod , the following applies, for example:
 
 T   mod   :=T   mod−1   +KC ·( T   mess   −T   mod ).
 
     In this equation, KC is a value read out from the characteristics curve that is a function of its temperature deviation. The temperature deviation is the difference obtained from a model-based calculated coil temperature and a model-based calculated environmental temperature. The characteristics curve mentioned may be generated, for example, in an offline simulation, with the aid of a Kalman filter. Thus, it simulates the properties of a genuine Kalman filter. 
     In order to determine the new, updated coil temperature T mod , in step  14  the temperature deviation is first determined, and in step  15 , parameter KC is read out from the characteristics curve. Finally, in step  17 , updated temperature value T mod  is calculated according to the above equation, where T mod−1  is the current coil temperature. Temperature model  8  may now be adjusted to the new value T mod . 
     Temperature model  8  preferably also includes a model which models the environmental temperature of valves  9   a ,  9   b , and in particular calculates the temperature of a heat sink into which the valves are press-fit. This second temperature model, too, is preferably calibrated from time to time to a reference value. The reference value is preferably also calculated based on measured component temperature T mess  (step  18 ). For example, the following correction may be carried out:
 
 T   U   :=T   U−1   +KH· Sum( T   mess   −T   mod ).
 
     In step  15 , parameter KH is read out from a characteristics curve that is a function of the temperature deviation. The KH characteristics curve is preferably also obtained from a simulation having a genuine Kalman filter. Temperature model  8  may now be adjusted to the new value T U . 
     Steps  15 ,  17  and  16 ,  18  may optionally also be carried out sequentially.