Abstract:
The invention relates to a monitoring method for a control device system with several electronic control devices for driving an internal combustion engine in a motor vehicle, whereby operating variables of the individual control devices are compared with each other, in order to detect a malfunction of the control devices. It is proposed that the control devices are monitored across-the-system, by comparing the operating variables of different control devices of the control device system with one other.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefits of German application No. 10 2006 057 743.4 filed Dec. 7, 2006, and is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The invention relates to a monitoring method for a control device system with several electrical control devices for driving an internal combustion engine in a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Modern internal combustion engines of motor vehicles are controlled by an electronic motor controller (ECU: Electronic Control Unit), which contains an increasingly complex functional software. In the operation of the internal combustion engine, the functional software of the electronic control unit is normally monitored according to a 3-level concept. In this concept, errors in the execution of monitoring-relevant scopes of the functional software are detected in a so-called “level 1”, whereby calculated torques are monitored. This is done by simulating the torques in the so-called “level 2” and comparing them with each other. 
     In addition, internal combustion engines are known that are controlled not by a single electronic control device but by several electronic control devices, whereby the individual control devices, for example in a twelve-cylinder engine with two cylinder banks, is responsible for one of the two cylinder banks in each instance. In the case of such a control device system with several electronic control devices the functional monitoring of the individual control devices is customarily carried out separately for the individual control devices, which is, however, relatively complex. 
     SUMMARY OF INVENTION 
     The object of the invention is thus to suitably improve the afore-described known method for monitoring a control device system having several electronic control devices for driving an internal combustion engine in a motor vehicle. 
     This object is achieved in accordance with the invention by a monitoring method as claimed in the claims. 
     The invention includes the general technical teaching which involves not monitoring the individual control devices of a control device system separately and independently of each other, but instead monitoring the control devices on an across-the-system basis, by comparing the operating variables of different control devices of the control device system with one other, whereby a malfunction in the control device system can be detected with minimal effort. 
     The operating variables of the individual control devices that are compared with each other during the monitoring method according to the invention, are preferably torque values of the internal combustion engine, wherein, for example, a nominal torque of the internal combustion engine is compared with the actual torque of the internal combustion engine, as is also the case with the conventional monitoring method mentioned in the introduction. Therefore the functional software in the individual control devices is preferably checked by comparing the simulated torques, i.e. of nominal torque and actual torque. An error is detected when the deviation of the simulated actual torques deviates to an unacceptable extent from the simulated nominal torque and error responses are initiated. 
     In a preferred exemplary embodiment of the invention, nominal torques of the internal combustion engine and actual torques of the internal combustion engine are determined for the individual control devices in each instance. 
     The maximum deviation between the nominal torques determined on the one hand and the actual torques determined is then determined. To this end, the maximum value of the individual actual torques and the minimum value of the individual nominal torques is preferably determined first. Subsequently a comparison is made between the maximum value of the actual torque and the minimum value of the nominal torques, in order to detect a malfunction in the control device system. By way of example, an error signal can then be generated, if the deviation between the maximum value of the individual actual torque on the one hand, and the minimum value of the individual nominal torque on the other hand, exceeds a preset limit value. 
     The comparison between the maximum value and the minimum value is preferably made not only in one single control device, but in several control devices, so as to create a redundancy in the comparison. In order to maximize the redundancy, the comparison between the maximum value and the minimum value can even be undertaken in each of the control devices. 
     In a possible exemplary embodiment of the invention the actual torques in the individual control devices are calculated in each instance from at least one base factor of the respective control device, whereby, for example, the respective air-mass flow, the ignition angle, the injection timing, the injection period and/or a load signal can be taken into consideration. Further possible base factors for determining the actual torques are the inlet manifold pressure, the injection pressure and/or the air ratio, which can be measured for example using a conventional lambda probe. Hereby, every change in the functional software and in the hardware, as well as in the system configuration, which could influence the calculation of the torques or the base factors thereof, are allowed for when ensuring the functional reliability of the base factors and calculating the simulated torques. 
     The monitoring of control devices having identical functional software in a control device system advantageously allows the monitoring of the functional software to be simplified considerably. 
     In the preferred exemplary embodiments of the invention, the internal combustion engine has several cylinder banks, with the individual control devices being responsible in each instance for one of the cylinder banks. The invention nevertheless also allows the responsibility of the individual control devices to be allocated differently. For example, the individual control devices can be responsible for driving different units of the internal combustion engine. 
     In addition the invention also comprises a computer program product, which executes the monitoring method as claimed in one of the preceding claims, when it is loaded into a program memory of one of the control devices and runs on the control device. 
     Finally the invention also comprises a control device with a program memory, into which a computer program is loaded, which program executes the monitoring method according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantageous developments of the invention are identified in the subclaims or are explained below in greater detail together with the description of the preferred exemplary embodiments of the invention using the figures, in which; 
         FIG. 1  shows a simplified block diagram of a control device system according to the invention with two control devices for controlling two cylinder banks of an internal combustion engine, 
         FIG. 2  shows a block diagram representation of the mode of operation of the monitoring method in the control device system according to  FIG. 1 , 
         FIG. 3  shows a modification of the block diagram in  FIG. 2 , 
         FIG. 4  shows the monitoring method according to the invention in the form of a flow chart, and 
         FIG. 5  shows a further exemplary embodiment of a control device system according to the invention with three control devices. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The block diagram in  FIG. 1  shows, in a very simplified form, a control device system  1  for controlling an internal combustion engine  2  in a motor vehicle. 
     In this exemplary embodiment, the internal combustion engine  2  is a 12-cylinder spark ignition engine with 2 cylinder banks  3 ,  4 , wherein a control device  5  or  6  (ECU: Electronic Control Unit) is allocated in each instance to the two cylinder banks  3 ,  4  in the control device system  1 . 
     The control device system  1  herewith allows across-the-system monitoring of the functional software of the two control devices  5 ,  6 , as is described below using the block diagram according to  FIG. 2 . 
     Thus the software in the two control devices  5 ,  6  has a computing module  7 , which on the input side records simulated nominal values M NOMINAL,1 , M NOMINAL,2  for the torque of the internal combustion engine  2 , whereby the nominal value M NOMINAL,1  is simulated by the control device  5 , while the nominal value M SOLL,2  is simulated by the other control device  6 . The computing module  7  then calculates a minimum value M NOMINAL,MIN  of the nominal values that may have been simulated from these nominal values recorded on the input side and forwards the minimum value M NOMINAL,MIN  to a comparator module  8 . 
     In addition, the software of the two control devices  5 ,  6  has an additional computing module  9 , which on the input side records actual values M ACTUAL,1 , M ACTUAL,2  of the torque of the internal combustion engine  2 , whereby the actual value M ACTUAL,1  is simulated by the control device  5 , while the other actual value M ACTUAL,2  is simulated by the other control device  6 . The computing module  9  calculates a maximum value M ACTUAL,MAX  of the actual values recorded on the input side from these actual values M ACTUAL,1 , M ACTUAL,2  recorded on the input side and sends this maximum value M ACTUAL,MAX  to the comparator module  8 . 
     The comparator module then determines the deviation between the minimum value M NOMINAL,MIN  and the maximum value M ACTUAL,MAX  and generates an error signal if a preset maximum deviation is exceeded, said error signal indicating a malfunction in the control device system  1 . 
       FIG. 3  shows a modification of the block diagram according to  FIG. 2 , wherein the modification largely matches the above exemplary embodiment according to  FIG. 2 , so that reference is made to the above description in order to avoid repetitions, whereby for corresponding details the same reference characters are used in the following. 
     A special feature of this exemplary embodiment is that the maximum value M ACTUAL,MAX  of the torque is calculated by a computing module  10  from a maximum value Q LM,MAX  of two air-mass flows Q LM,1 , Q LM,2 , wherein a further computing module  11  determines the maximum value Q LM,MAX . 
     In the following, the operational sequence of the monitoring method according to the invention is described using the flow chart according to  FIG. 4 . 
     In a first step S 1 , a nominal torque M NOMINAL,1  is first determined in the control device (“ECU 1 ”). 
     In a second step S 2 , the nominal torque M NOMINAL,2  is then determined in the other control device  6  (“ECU 2 ”). 
     From these two nominal torques M NOMINAL,1 , M NOMINAL,2  the maximum value M NOMINAL,MAX  is then determined in a further step S 3 . 
     Subsequently, in step S 4  the actual torque M ACTUAL,1  is determined by the control device  5  (“ECU 1 ”). 
     In step S 5  the actual torque M ACTUAL,2  is determined by the other control device  6  (“ECU 2 ”). 
     Then from the two actual torques M ACTUAL,1 , M ACTUAL,2  the minimum value M ACTUAL,MIN  is determined in step S 6 . 
     In a further step S 7  a comparison is made between the minimum value M ACTUAL,MIN  and maximum value M NOMINAL,MAX  in the control device  5  (“ECU 1 ”). 
     If the deviation between these values exceeds a preset limit value, then in step S 8  the sequence jumps to a further step S 11 , in which an error signal is generated, which indicates a malfunction of the control device system. 
     If, on the other hand, the comparison in the control device  5  (“ECU 1 ”) does not show any error, then a further comparison is subsequently made in step S 9 , but this time in the other control device  6  (“ECU 2 ”). The repetition of the comparison in the other control device  6  advantageously offers a redundancy. 
     If this second comparison indicates that a limit value has been exceeded, then in step S 10  the sequence moves to step S 11 , in which the error signal is generated. Otherwise the monitoring method with steps S 1  to S 11  is continuously repeated during the operation of the internal combustion engine. 
     Finally,  FIG. 5  shows a further exemplary embodiment of a control device system  1 , wherein this exemplary embodiment largely matches the exemplary embodiment according to  FIG. 1 , so that reference is made to the afore-mentioned description in order to avoid repetitions. 
     A special feature of the control device system  1  consists in this exemplary embodiment in that in addition to the two control devices  5 ,  6  for the two cylinder banks  2 ,  3 , a third control device  12  (TCU: Transmission Control Unit) forms part of the control device system  1 , wherein the control device  12  controls an automatic transmission  13 . 
     The three control devices  5 ,  6  and  12  of the control device system  1  exchange actual torques M ACTUAL  and nominal torques M NOMINAL  between each other, wherein the monitoring method according to the invention compares these torque values with each other. If one of the control devices  5 ,  6 ,  12  provides deviating torque values, while the two other control devices provide matching torques, it can be assumed that the control device in question is defective. In comparison with the exemplary embodiment according to  FIG. 1 , the additional control device  12  thus makes it possible not only to determine whether one of the control devices  5 ,  6 ,  12  is defective, but also allows the defective control devices to be identified.