Abstract:
A device and a method are provided for diagnosing a technical apparatus which is particularly developed as an internal combustion engine. When specified states of the technical apparatus are present, the means of diagnosis are activated, and when at least one of the specified technical states is no longer present, the means of diagnosis are deactivated. Upon the deactivation, information is stored that identifies which technical state is no longer present.

Description:
BACKGROUND INFORMATION 
     A device and a method for diagnosing an internal combustion engine are described in German Patent Application No. DE 10260721 in which, in response to specified operating states of the internal combustion engine, a diagnosis function is activated. If the conditions are not present, the system waits until they are present. 
     SUMMARY OF THE INVENTION 
     The device according to the present invention and the method according to the present invention have the advantage that, based on the stored information, one is able to determine based on which of the technical circumstances a deactivation of the means of diagnosis and the diagnosis function takes place. Thus, in the operation of the technical device, one is able to determine which of the specified states are responsible for a repeated termination of the diagnosis of the technical device, and appropriate countermeasures may be initiated in order to ensure a sufficiently frequent control. 
     It makes sense that a diagnosis can only be carried out if the specified technical conditions are present for a specified minimum time period. Using a counter, it can be checked how often the diagnosis has been successfully completed. An additional counter is able to determine how often operating states exist which, based on legal regulations, require carrying out a diagnosis of the technical device. The number of successful diagnoses can then be compared with the number of legally required diagnoses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of an internal combustion engine having an exhaust gas system and a control unit. 
         FIG. 2  shows method steps of a method for diagnosing a technical device. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , an internal combustion engine is shown schematically, having a combustion chamber  100  into which a fuel is injected by an injection  101 . Furthermore, air has been introduced into combustion chamber  100  by an air supply  102 . The fuel introduced into combustion chamber  100  by injection  101  is combusted in combustion chamber  100 , and the combustion products resulting from this are removed by an exhaust pipe  103 . A catalytic converter  104  is provided in exhaust pipe  103 , by which the exhaust gases are purified. A lambda sensor  105  is provided upstream of catalytic converter  104 , which analyzes the composition of the exhaust gas products in exhaust pipe  103 . This lambda sensor is able, in particular, to determine the residual content of oxygen in the exhaust gas, and, with respect to the air quantity, is thus able to determine whether an excess of fuel or an excess of available air was available. It is desirable, in this context, that the air/fuel ratio, with reference to the oxygen required for the combustion, is exactly  1 , since the smallest quantity possible of exhaust gases is created which, in addition is able to be purified especially well by catalytic converter  104 . Downstream from catalytic converter  104  in exhaust pipe  103 , there is situated an additional lambda sensor  106  which measures the oxygen content of the exhaust gas downstream from catalytic converter  104 . In this context, lambda probe  105  is designed in such a way that a lambda content is able to be determined very rapidly over a wide range, while probe  106  is designed in such a way that, downstream from the catalytic converter, an accurate determination in a range about a stoichiometric mixture composition (that is, lambda=1) is accurately investigated. 
     The measured values of the different sensors  105 ,  106  are reported to an engine control unit  1  via lines  107 . Based on sensor signals, engine control unit  1  calculates command signals and, for instance, also a command signal for fuel injector  101 , which is activated over appropriate lines  107 . Besides the sensors and actuators shown here, in a real engine, mounted, for example, in a motor vehicle, a multitude of sensors and actuators are provided. 
     In the exhaust system shown in  FIG. 1 , the sensors have to be checked from time to time for their operability. Various legal institutions even provide that such tests have to occur routinely, at a certain frequency, during normal driving operation. For this purpose, however, an appropriate diagnosis function can only be carried out if certain operating conditions of the internal combustion engine are implemented. If a case is involved in which the provided frequency of carrying out the diagnosis functions is not achieved, the question arises whether, perhaps, individual operating conditions, which are regarded as being required for carrying out the diagnosis, interfere with an activation of the means of diagnosis in sufficient measure. If, in this context, a correct processing of the diagnostic function is frequently caused by change in a technical state, then it may be attempted to carry out the diagnosis more frequently by changing the diagnostic function. 
     The method according to the present invention will be explained schematically, in the light of the figure, using the example of checking first lambda probe  105 , upstream of catalytic converter  104 . In a first program block  21 , general enabling requirements for a diagnosis or a diagnosis of this first lambda sensor  105  are scanned. In this context, a first initial condition is a general enabling  31 . This bit of the general enabling  31  is always set when a regular operating state of the internal combustion engine exists, that is, the internal combustion engine has been operated for a certain minimum time period and there are no general faults present in the control of the internal combustion engine, such as a faulty load sensor, or the like. As a further condition, an input bit  32  is investigated which is set only if there has already been a sufficiently long driving operation. An additional condition is that rear lambda sensor  106 , which is important for the diagnosis of front lambda sensor  105 , is operational. Therefore, as a further initial condition, functional readiness bit  33  of the rear lambda sensor is checked, which is done only if, in response to a previously executed function test of the rear lambda probe, the operability in principle of this lambda probe was determined. 
     These general initial conditions are now used in program block  21  in order to set appropriate indicator bits in a memory  23  controlled by program block  21 . The setting of the bits in memory  23  takes place only once per driving operation, in this instance, that is, for each initial operation of the internal combustion engine an appropriate bit is set once in memory  23 . Subsequently, by checking the content of memory  23 , it can then be determined whether, during the corresponding driving cycle of the internal combustion engine initial conditions  31 ,  32  and  33  were present, which means that, generally, diagnosing front lambda probe  105  was possible. If general enabling bit  31  was set at least once during the driving cycle, a corresponding bit will be set in memory location  231 . In the driving cycle, if bit  32  was determined to have been set, program block  21  sets corresponding bit  232  in memory  23 . If bit  33  was set, bit  233  is set in memory  23 . If, at any time in the operation of the internal combustion engine, both bit  31  and bit  32  were set at the same time, the bit is set in memory  234 . By scanning this bit, one can determine whether, during the running operation of the internal combustion engine, general enabling bit  31  was enabled at least for one operating state, and simultaneously a sufficiently long operation of the internal combustion engine was present. 
     If this operating state was present, and it was determined at the same time that bit  33  had been set, that is, that rear lambda probe  106  had been judged to be operational, bit  235  is set. Consequently, this bit indicates that all the initial conditions  31 - 33  were present at at least one time in the operation of the internal combustion engine. By scanning the individual bits in memory  23 , one can consequently understand very accurately whether, during the running operation of the internal combustion engine, an operating state was present at least once in which diagnosing front sensor  105  was possible. In general, the situation is that when all suppositions are present, diagnosing the sensor is attempted. 
     A further program block  22  follows program block  21 , in which additional states are investigated that are required for diagnosing lambda sensor  105 . In program step  22 , especially technical states of the internal combustion engine are investigated which are conditioned upon the operation of, or the requirements upon the internal combustion engine. For, only if certain states are present, is a meaningful diagnosis of the operability of first lambda sensor  105  possible. A first condition checked by program block  22  is the presence or the non-presence of a deceleration fuel cutoff  34 . During the deceleration fuel cutoff, in response to a running operation of the internal combustion engine, the injection of fuel is interrupted, since, for instance, a vehicle in which the engine is installed is currently in an overrun phase. Since no fuel is injected during this time, the exhaust gas also has the normal oxygen content of the air, and a corresponding signal of lambda probe  105  cannot be meaningfully checked as to whether it is functioning properly. Load dynamics  35  are checked as an additional initial condition. 
     In response to a very rapid operation of the accelerator by the driver, the charge of air in combustion chamber  100  changes very rapidly, which leads from time to time to an air quantity that is not adjusted relatively to the fuel injected by injection  101 . Therefore, in this operating state, too, it is not possible to make a meaningful diagnosis of first lambda probe  105 . As an additional condition, it is then checked whether the air flow of the air flowing into combustion chamber  101  lies within a meaningful range. A certain enrichment of the mixture is provided especially in response to a very high load, that is, a very high quantity of air flowing into combustion chamber  100 , which then also makes impossible diagnosing lambda sensor  105 . Because of the conditions scanned in program block  22 , a diagnosis that is possible in principle is obstructed. During an operating phase of the internal combustion engine, the occurrence of a deceleration fuel cutoff, load dynamics or an unsuitable rate of air flow may come about repeatedly. 
     A corresponding memory  24  is provided, in which it is recorded by program block  22  how often a diagnosis, that is possible in principle, has been obstructed or a diagnosis already begun has been terminated, based on the various initial conditions of program block  21 . For this purpose, individual bits in memory  24  are not influenced, but the storage locations of memory  24  are developed as counters. In memory location  241  a counter is stored which indicates how often a running diagnosis has been terminated based on a deceleration fuel cutoff. In memory location  242  a counter is stored which is always incremented when a running diagnosis has been terminated based on load dynamics  35 . In storage location  243  a counter is stored which is always incremented if a diagnosis has been terminated based on an air flow rate that was too low or too high, that is, initial condition  36 . Memory locations  244  and  245  may, in turn, include counters which are always incremented when combinations of initial conditions  34 ,  35  and  36  are present. 
     After an operation of the internal combustion engine it can be ascertained, by scanning the bits stored in memories  23  and  24 , or the counter readings, based on which initial assumptions, or based on the absence of which initial assumptions, a diagnosis or a diagnosis of first lambda probe  105  did not happen in the expired operating cycle of the internal combustion engine. If, in this situation, a certain assumption turns out to be that the non-occurrence of a diagnosis is especially fair as to cause, an attempt can be made to increase the frequency of carrying out the diagnosis by changing the diagnostic function. For instance, it can be provided to admit the deceleration fuel cutoff  34  only in response to a lower number of operating states, and thereby to increase the frequency of the successful run through of the diagnostic function. 
     In this context, it may naturally also make sense to investigate the presence or absence of initial assumptions  31 - 36 , over a plurality of operating cycles of the internal combustion engine. In order to do this, it is then meaningful to use the storage content of memory  23 , at the end of each operating cycle of the internal combustion engine, in order to increase counters for these bit states. The content of memory status  24  at the end of each operating cycle can simply be added to an already present counter, for these operating states. In this way, evidence can be presented as to how suitable conditions have been present, over a plurality of operating cycles of the internal combustion engine, for a diagnosis or a control function of first lambda probe  105 . 
     In addition, one more program block  25  is provided which is always called up when the diagnosis or the diagnostic function was executed successfully. In response to each successful run-through of the diagnosis or the diagnosis function, a counter  251  is incremented by program block  25 , whose count value thus states how often the diagnosis or diagnostic function was successfully completed. Moreover, one further counter  252  is provided whose count value is always incremented when further operating states of the internal combustion engine have been present. For example, the count value of counter  252  can always be incremented when an overall operating duration of the internal combustion engine of at least 600 seconds was completed, and during this time, at least one continuous idling proportion of at least 30 seconds was present, and for at least 300 seconds the motor vehicle, in which the internal combustion engine is installed, was moved at a speed of more than 40 km/h. These further operating conditions of the internal combustion engine are standard operating conditions, which were specified by a controlling authority. In relationship to the occurrence of these standardized operating conditions of the internal combustion engine, a specified number of diagnoses or diagnostic functions of the internal combustion engine have to be successfully completed. For example, it may be provided that the count value of the counter of the successful diagnoses  251  should amount to at least 10%, and in the case of more stringent requirements, even 30% of the count value of counter  252 . By comparing these two counters, it is consequently ensured that a diagnosis of the internal combustion engine is carried out sufficiently frequently so as reliably to ensure an operation of the internal combustion engine, or rather the motor vehicle, that is optimized with respect to pollutants.