Abstract:
A method for adapting a measured value (MW 1 ) of an air mass sensor comprises the steps pf determining a correction value (KW) in the event of predetermined operating conditions (BB 1 ), namely depending on the measured value (MW 1 ) and a comparative value (VW) which in turn depends on at least one additional measured value (MW 2 ) of a second sensor. An adaptation value (AD 1 ) is adapted depending on the correction value (VW), on the duration (D_AD 1 ) since the last determination of the adaptation value (AD 1 ) and on the change of the adaptation value (AD 1 ) since the last adaptation of the adaptation value (AD 1 ). Subsequently measured values (MW 1 ) are corrected using the adaptation value (AD 1 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application of International Application No. PCT/EP2005/050424 filed Feb. 1, 2005, which designates the United States of America, and claims priority to German application number DE 10 2004 005 134.8 filed Feb. 2, 2004, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a method for adapting a measured value of an air mass sensor. The air mass sensor can in particular be arranged in an internal combustion engine for recording an air mass flow in cylinders of the internal combustion engine. 
       BACKGROUND 
       [0003]    These types of air mass sensor record the air mass flow which flows into a collector. The collector communicates via induction tubes with cylinders of the internal combustion engine and supplies these with fresh air. 
         [0004]    Ever more stringent legal requirements relating to pollutant emissions in motor vehicles make it necessary to set the air/fuel mixture in the individual cylinders of the internal combustion engine very precisely. This requires that the air mass drawn into the relevant cylinder is determined very precisely. The air mass sensor allows the air mass flowing into the collector to be determined very precisely. By means of corresponding physical models of the collector and the induction tubes and of the induction behavior of the cylinders of the internal combustion engine, the air mass flowing into the cylinders of the internal combustion engine can be determined very precisely. 
         [0005]    Known air mass measurers are regularly embodied in the form of a Whetstone bridge, with a high-resistance temperature-dependent resistor to compensate for the temperature of the induction air in one branch and a low-resistance temperature in the other branch of which the heat performance is characteristic for the air mass flowing past. The heating resistor is generally embodied as a so-called hot-film resistor. During the operation of the internal combustion engine particles of dirt and also oil droplets build up on the hot-film resistor. The result is that the behavior of the measuring resistor changes. 
       SUMMARY 
       [0006]    The object of the invention is to create a method for adapting a measured value of an air mass sensor that ensures precise measurement values of the air mass sensor simply and immediately over a long lifetime of the air mass sensor. 
         [0007]    The outstanding feature of the invention is a method for adapting a measured value of an air mass sensor, in which a correction value, if predefined operating conditions exist, is determined depending on the measured value and a comparison value, which is determined depending on at least one further measured value of a further sensor. An adaptation value is adapted depending on the correction value, the duration since the adaptation value was last determined and on the change of the adaptation value since the last adaptation of the adaptation value. Measured values subsequently recorded are corrected with the adaptation value. The adaptation of the adaptation value, depending on the duration since the adaptation value was last determined, can be ensured in that. Depending on the frequency of the adaptation of the adaptation value, a very precise learning of the adaptation value and thereby in the final analysis, correction of the measurement value can take place. The fact that the adaptation of the adaptation value is also dependent on the adaptation value since the last adaptation of the adaptation value additionally enables extraordinary changes of the air mass sensor to be detected and correspondingly taken into account. 
         [0008]    In an advantageous embodiment of the invention, as the duration since the last adaptation of the adaptation value increases, the adaptation value is adapted more heavily depending on the correction value. This enables account to be easily taken of the fact that, with a less frequent adaptation of the adaptation value, ageing effects of the air mass sensor are more marked and can thus be compensated for again by the heavier adaptation depending on the correction value. 
         [0009]    In a further advantageous embodiment of the invention, when the adaptation value is changed, which is characteristic of an unauthorized modification to the air mass sensor, an initialization value is assigned to the adaptation value. This type of unauthorized modification to the air mass sensor can for example be the replacement of the air mass sensor, without a control device which records and further processes the measuring signals of the air mass sensor being informed. With a motor vehicle, this can for example be a replacement of the air mass sensor outside a workshop authorized to carry out this work. 
         [0010]    An unauthorized modification can be detected especially simply by a negative change of the adaptation value occurring, the amount of which is greater than a predefined first threshold value, and a duration since the last determination of the correction being less that a predefined second threshold value The duration can in this case especially simply be a period of time, but it can also be dependent on the operating life of the air mass sensor and thus for example, for an internal combustion engine, be dependent on a specific number of driving cycles or a distance covered in the interim. 
         [0011]    It is further especially advantageous, if an extraordinary contamination of the air mass sensor is detected, and if this done when a positive change of the adaptation value, of which the amount is greater than a predefined third threshold value, and a duration since the last determination of the correction value which is less than a predefined fourth threshold value are characteristic of an extraordinary contamination of the air mass sensor. Then, if an extraordinary contamination is detected there can simply be an error reaction. 
         [0012]    Advantageously this error reaction is an indicator of an error which occurs so that a fault in a motor vehicle in which the air mass sensor can be located recognizes that an error has occurred. The error can thus be indicated visually or audibly for example. 
         [0013]    It is also advantageous for at least one first correction value and a second correction value to be determined. The first correction value is determined if predefined first operating conditions exist. The second correction value is determined, if predefined second operating conditions exist. Depending on the first correction value a first adaptation value is adapted. Depending on the second correction value a second adaptation value is adapted. Measured values of the air mass sensor recorded subsequently are corrected with an adaptation value which, depending on the current operating conditions, is interpolated between the first and the second adaptation value. This enables appropriately adapted adaptation values to be determined in a simple manner for different operating conditions and used for further correction of the measured values. If more than two correction values are determined, for corresponding predefined further operating conditions, corresponding additional adaptation values are then also adapted and the adaptation value is then also corrected by interpolation between the first, second and further adaptation values. Thus, with a growing number of adaptation values for different operating conditions, extremely precise correction of the measured value of the air mass sensor can be guaranteed over a very wide operating range of the air mass sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Exemplary embodiments of the invention are explained below with reference to schematic diagrams. The figures show: 
           [0015]      FIG. 1  an internal combustion engine with an air mass sensor, 
           [0016]      FIG. 2A ,  2 B a flowchart of a first embodiment of a program for adapting an adaptation value of an air mass sensor, 
           [0017]      FIGS. 3A and 3B  a further flowchart of a second embodiment of a program for adapting a number of adaptation values and 
           [0018]      FIG. 4  a flowchart of a program to perform the adaptation of the measured values of the air mass sensor. 
       
    
    
       [0019]    Elements for which the construction and function are the same are labeled by the same reference symbols in all figures. 
       DETAILED DESCRIPTION 
       [0020]    An internal combustion engine ( FIG. 1 ) comprises an induction tract  1 , an engine block  2 , a cylinder head  3  and an exhaust gas tract  4 . The induction tract  11  preferably comprises a throttle valve  12 , also a collector  13  and an induction tube  1 , which is routed through to the cylinder Z 1  via an inlet channel in the engine block. Furthermore an exhaust gas recirculation device  13 A can open out into the induction tract  1 , preferably in the area of the collector  12 , which routes exhaust gases from the exhaust gas tract  4  back into the induction tract  1 . The volume of the recirculated exhaust gas can be controlled using an exhaust gas recirculation valve  13 B. The engine block further comprises a crankshaft  21 , which is coupled via a connecting rod  25  to the piston  24  of the cylinder Z 1 . 
         [0021]    The cylinder head  3  comprises valve gear with an inlet valve  30 , an exhaust valve  31  and valve actuating mechanisms  32 ,  33 . The gas inlet valve  30  and the gas outlet valve  31  are driven in this case via a camshaft. The cylinder head  3  further includes an injection valve  34 . 
         [0022]    A control device  6  is also provided which can also be seen as a device for controlling the internal combustion engine and to which sensors are assigned which record different measurement variables and determine the measured value of the measurement variable in each case. The control device  6  determines setpoint values depending on at least one of the measurement variables, which are then converted into one or more control signals for controlling the actuation elements by means of the appropriate actuation drives. 
         [0023]    The sensors are a pedal position sensor  71 , which detects the position of the gas pedal  7 , an air mass measurer  14 , which detects an air mass flow upstream from the throttle valve  11 , a temperature sensor  15  which detects the induction air temperature, a pressure sensor  16 , which detects the induction tube pressure, a crankshaft angle sensor  22 , which detects a crankshaft angle to which a speed N is then assigned, a further temperature sensor  23 , which detects a coolant temperature, a camshaft angle sensor  36   a  , which detects the camshaft angle. Depending on the form of embodiment of the invention, any given subset of the said sensors or also additional sensors can be present. 
         [0024]    The actuation elements are for example the throttle valve  11 , the gas inlet and outlet valves  30 ,  31 , the injection valve  34  and the exhaust gas recirculation valve  13 B. 
         [0025]    As well as the cylinder Z 1  further cylinders Z 2 -Z 4  are also provided to which corresponding actuation elements are also assigned. 
         [0026]    A program for determining an adaptation value which is stored in the control device  6  is run during operation of the internal combustion engine. The program is started in a step S 1  ( FIG. 2A ) in which variables are initialized if necessary. The program is preferably started shortly after the beginning of the engine start sequence. 
         [0027]    In a step S 2  current operating conditions BB are determined. This is preferably done depending on the speed N, the throttle setting THR, the induction air temperature T and the exhaust gas recirculation rate EGR and where necessary also depending on further variables or also depending on just some of the specified variables. 
         [0028]    A check is made in a step S 3  as to whether the current operating conditions BB are the same as predefined first operating conditions BB 1 . The predefined first operating conditions BB 1  can for example be that the speed N has a value 1,000 RPM and the throttle setting, the temperature T and the exhaust gas recirculation rate assume predefined, where possible constant values. 
         [0029]    If the condition of step S 3  is not fulfilled, processing is continued at a step S 4  in which the program idles for a predefined waiting time T_W, before processing is continued again at step S 2 . If on the other hand the condition of step S 3  is fulfilled, a first measured value MW 1  is determined in a step S 5 . The first measured value MW 1  is preferably the measured value of the air mass sensor  14 . 
         [0030]    In a step S 6  a comparison value VW is determined, and this value depends on at least a second measured value MW 2  of a further sensor, of the induction tube sensor  16  for example. Depending on the second measured value MW 2  the comparison value is then determined, for example using a physical model, said value preferably being a comparison value of the air mass flow. 
         [0031]    In a step S 7  a first correction value KW 1  is determined depending on the first measured value MW 1  and the comparison value VW. This can for example be done by forming the difference between the comparison value VW and the first measured value MW 1 . 
         [0032]    In a step S 8  a first adaptation value AD 1  is determined. An [n] in this case refers to the value actually computed and an [n-1] means a value determined during the previous adaptation. The current first adaptation value AD 1  is then determined depending on the previous first adaptation value AD 1  and the first correction value KW 1 . This is preferably done using a first-order filter. It can however also be done using a higher-order filter or in another way with which the person skilled in the art is familiar. 
         [0033]    In a step S 10  a check is performed as to whether the first adaptation value AD 1 , which was currently determined is greater than a predefined extreme value EXTR as regards its size The extreme value is predefined so that if the extreme value is exceeded it can be assumed that exceeding the value in this way is not possible because of the properties of the air mass sensor and the signal processing and that thereby a restriction to this value must be undertaken. For example the extreme value EXTR can amount to 10 to 20% of the comparison value determined. 
         [0034]    If the condition of step S 10  is fulfilled, the in a step S 11  the first adaptation value AD 1 , depending on its leading sign, is restricted to a minimum value AD MIN or to a maximum value AD MAX. 
         [0035]    If on the other hand the condition of step S 10  is not fulfilled, then in a step S 12  ( FIG. 2B ) in check is made as to whether the change of the first adaptation value AD 1  which is determined by means of forming the difference between the current and the preceding first adaptation value AD 1 , is characteristic for an unauthorized modification of the air mass sensor. The change of the first adaptation value AD 1  is for example characteristic of an unauthorized modification UM if it has a leading sign which depends on the relevant air mass sensor and its amount exceeds and air mass sensor-dependent value and at the same time the duration since the previous adaptation is less than a predefined value. This type of unauthorized modification can arise for an air mass sensor for example when the heating resistor embodied as a hot-film resistor has been cleaned, but this information is not yet available to the control device  6 . If the condition of step S 12  is fulfilled, then in a step S 13  the first adaptation value AD 1  is given an initialization value AD 1 _INI for the first adaptation value AD 1 . This initialization value AD 1 _INI can for example amount to zero. 
         [0036]    If on the other hand the condition of step S 12  is not fulfilled, then in a step S 14  the first adaptation value AD 1  is determined once again and this time depending on the duration D_AD 1  since the last valid adaptation of the first adaptation value AD 1 , the preceding first adaptation value AD 1 , that is not the first adaptation value AD 1  determined in step S 8  during the current computation run of the program, and the correction value KW 1 . In this case account can be taken of the fact that as the duration D_AD 1  since the last valid adaptation of the first adaptation value AD 1  increases, especially if the correction value KW 1  exceeds a predefined value, the correction value KW 1  plays a greater role in the adaptation of the first adaptation value AD 1 . This allows simple account to be taken of the fact that if the operating point is rarely reached at which the predefined first operating conditions BB 1  are fulfilled, but still if the allocation of the first adaptation value AD 1  has been undertaken, a correspondingly heavy adaptation of the first adaptation value AD 1  is undertaken and thereby a reduction of a possible error in the determination of the measured value and indeed of the corrected measured value MW_KOR. 
         [0037]    After step S 14  the processing is continued at step S 2 . 
         [0038]    A second embodiment of the program for adaptation of adaptation values is described below with reference to  FIGS. 3A and 3B  and the flow diagrams shown in these figures. Only the differences from the program depicted in  FIGS. 2A and 2B  are described below. 
         [0039]    The program is started in a step S 16  in which variables are initialized where necessary. In a step S 18  the current operating conditions corresponding to step S 2  are determined. In a step S 20  a check is subsequently performed as to whether the current operating conditions BB are the same as the predefined first operating conditions BB 1 , which for example can essentially be defined by the speed and e.g. can be fulfilled in relation to the speed if this as a value of around 1,000 RPM. 
         [0040]    If the condition of step S 20  is fulfilled, then in a step S 22  the first measured value MW 1  of the air mass sensor  14  is determined. In a step S 24  the comparison value VW is subsequently determined and this is done depending on the second measured value MW 2  of at least one further sensor. This further sensor is preferably the induction tube sensor  16  and accordingly a measured value of the induction tube pressure recorded by this sensor. In addition or as an alternative it can for example also be the crankshaft angle sensor which records the speed N of the crankshaft and/or a sensor which records the throttle setting THR of the throttle flap  11 . Using a corresponding model the comparison value VW is then determined from these second measured values MW 2 . 
         [0041]    In a step S 26  the first correction value KW 1  is subsequently determined depending on the first measured value MW 1  and the comparison value. The comparison value VW is preferably considered in this case as the reference value, i.e. as the correct value. Thus in step S 26  the first correction value KW 1  is preferably determined from the difference between the comparison value VW and the first measured value MW 1 . 
         [0042]    In a step S 28  a current first adaptation value AD 1  is subsequently determined, depending on the preceding first adaptation value AD 1  and the correction value KW 1 . This is preferably done in accordance with step S 8  by means of a first order filter. It can however also be done using a higher-order filter. 
         [0043]    A check is made in a step S 30  as to whether the amount of the first adaptation value, and indeed of the current first adaptation value, is greater than the extreme value EXTR. This is done in the same way as in step S 10 . If the condition of step S 30  is fulfilled, processing is continued at a step S 32  which corresponds to the step S 11 . 
         [0044]    After step S 32  processing of the program is continued at a step S 18 . 
         [0045]    If the condition of step S 30  is not fulfilled, then in a step S 38  a value is determined which is characteristic for the unauthorized modification UM to the air mass sensor, preferably the air mass sensor  14 . This is preferably done depending on the current first adaptation value AD 1 , the preceding first adaptation value AD 1 , a first threshold value SW 1 , the duration D_AD 1  since the last valid adaptation of the first adaptation value AD 1  and a second threshold value SW 2 . In this case the unauthorized modification UM to the air mass sensor  14  has occurred if the difference between the current and the preceding first adaptation value AD 1 , i.e. its change, is greater than the predefined first threshold value SW 1  and simultaneously the duration D_AD 1  since the last valid adaptation of the first adaptation value AD 1  is less than the predefined second threshold value SW 2 . 
         [0046]    In a step S 40  a check is subsequently made as to whether an unauthorized modification UM to the air mass sensor has occurred. If its has, in the step S 42  the current first adaptation value is set equal to the initialization value AD 1 _INI of the first adaptation value AD 1  and this is done by using the initialization value AD 1 _INI of the first adaptation value AD 1 . In addition, in the step S 42 , a second adaptation value AD 2  is also initialized with an initialization value AD 2 _INI of the second adaptation value AD 2 . This then ensures that all adaptation values AD 1 , AD 2  are able to be adapted again unaffected by the preceding computation cycles AD 1 , AD 2 , and account is thus taken of the situation in which the air mass sensor was modified, e.g. replaced. 
         [0047]    In a step S 44 , if the condition of step S 40  is not fulfilled, the first adaptation value AD 1  is determined again if necessary and this is done in accordance with step S 14 . 
         [0048]    In a step S 46  a check is then made as to whether the difference between the current adaptation value AD 1  and the preceding first adaptation value AD 1  is greater than a third threshold value and simultaneously the duration D_AD 1  since the last adaptation of the first adaptation value AD 1  is less than a predefined fourth threshold value SW 4 . If the condition of step S 46  is not fulfilled, processing is continued if necessary after the predefined waiting time T_W in step S 18 . 
         [0049]    If the condition of step S 46  is fulfilled however, an error has occurred and processing is continued at a step S 48 . An error is detected if necessary only after the condition of step S 46  has been fulfilled a number of times with consecutive calculation runs and an error reaction then occurs which for example can entail the malfunction indicator lamp MIL signaling an error to the driver of a motor vehicle in which the air mass sensor is located. Subsequently processing is continued if necessary after the predefined waiting time T_W, at step S 18  again. 
         [0050]    On the other hand, if the condition of step S 20  is not fulfilled, i.e. the current operating conditions BB do not correspond to the predefined first operating conditions BB 1 , then in a step S 50  a check is made as to whether the current operating conditions BB correspond to predefined second operating conditions BB 2 . The predefined second operating conditions BB 2  very much depend for example on the speed N and are fulfilled in this regard if the speed has a value of around 3000 RPM. 
         [0051]    If the condition of step S 50  is not fulfilled, processing is continued at step S 34 . If the condition of step S 50  is fulfilled however, then in a step S 52  the first measured value MW 1  of the air mass sensor  14  is recorded. 
         [0052]    In a step S 54  the second measured value MW 2  of the further sensor, that is preferably of the induction tube pressure sensor  16 , is subsequently recorded and for example of the crankshaft angle sensor  22  and then, depending on this or these second measured value(s) MW 2 , the comparison value VW is determined. This is done in the same way as in step S 24  and step S 6 . 
         [0053]    In a step S 56  a second correction value KW 2  is subsequently determined depending on the first measured value MW 1  and the comparison value VW determined in step S 52 . This is done in the same way as in steps S 26  and S 7  by forming the difference. 
         [0054]    In a step S 58  the second adaptation value AD 2  is adapted and this is done depending on the second adaptation value AD 2  and the second correction value KW 2  adapted in a preceding adaptation. This is also done in the same way as in step S 28 . 
         [0055]    Subsequently a step S 59  is processed which corresponds to the steps S 32  to S 48  adapted for the determination of the second adaptation value AD 2 , with then, in accordance with the duration D_AD 1  since the last valid adaptation of the first adaptation value AD 1  by a duration D_AD 2 , the duration since the last valid adaptation of the second adaptation value AD 2 , of the first correction value KW 1  is replaced by the second correction value KW 2 . In addition the program can also be correspondingly tailored for adaptation of further adaptation values if third, fourth and further predefined operating conditions exist. The program depicted in  FIGS. 3A ,  3 B can however also be correspondingly tailored merely for determining the first adaptation value AD 1 . 
         [0056]      FIG. 4  shows a flowchart of a program by means of which the measured values MW 1  of the air mass sensor  14  are corrected. The program is started in a step S 60 . 
         [0057]    In a step S 62  the current operating conditions BB are determined and this is done in the same way as in step S 18 . Where necessary the current operating conditions can be determined in step S 62  that is only depending on one or more decisive measured values, thus for example merely depending on the speed N. In a step S 66  the current adaptation value AD is then determined depending on the operating conditions BB determined in the step S 62  and corresponding interpolation between the adaptation value or adaptation values AD 1 , AD 2  determined and where necessary further variables. 
         [0058]    In a step S 66  the first measured value MW 1  is then determined. In a step S 68  a corrected first measured value MW_KOR is then determined by summing the first measured value MW 1  and the current adaptation value AD. Subsequently the program idles for a predefined waiting time T_W in the step S 70  before processing is continued again at step S 62 . 
         [0059]    The adaptation value or adaptation values are basically stored and are thus available once more for each new start of the program.