Abstract:
A device for error monitoring in an internal combustion engine system is provided. The internal combustion engine is supplied with air at a volumetric efficiency indicating the ratio of a real volume flow of air in the internal combustion engine to an ideal, theoretically possible, volume flow of air in the internal combustion engine. The device for error monitoring is configured to determine an error in the engine system when a difference between a measured volumetric efficiency and an estimated volumetric efficiency exceeds a predetermined absolute value.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an on board diagnostic system in a vehicle having an internal combustion engine. 
         [0003]    2. Description of the Related Art 
         [0004]    On board diagnostic systems are vehicle diagnostic systems which monitor all emission-influencing systems during the operation and store possibly arising errors in a memory so that they may be queried by a specialized repair shop and, if necessary, eliminated. 
         [0005]    Most of the previously known functions in this type of on board diagnostic system measure a characteristic within the internal combustion engine at operating points, which occur rarely in most cases, and compare this characteristic to the nominal case. Alternatively, a so-called intrusive test may be carried out. This test is an intervention into the system at certain operating points to provide the conditions for the measurement. In any case, the situation in the nominal case must be saved so that the measurement may be compared to it. However, a memory is not only expensive, it also needs space which is available only to a limited extent in the engine control of a vehicle. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    According to one first aspect of the present invention, a device for error monitoring in an engine system having an internal combustion engine is provided, the engine system being designed to supply the internal combustion engine with air at a volumetric efficiency, the volumetric efficiency indicating the ratio of a real volume flow of air in the internal combustion engine to an ideal, theoretically possible, volume flow of air in the internal combustion engine, the device being designed to determine an error in the engine system based on the volumetric efficiency. 
         [0007]    The device according to the present invention has the advantage that it requires less memory space as compared to conventional devices for error monitoring in an engine system. This is achieved by selecting for the characteristic of error recognition the volumetric efficiency as a variable in the engine system, the variable being necessary, e.g., for operating the filling control, regardless of the device for error monitoring. In this way, the data do not have to be specifically determined and stored in the memory for the comparison to the nominal case. The time constant of the volumetric efficiency estimation/recognition is approximately in the range of the time constant of the filling control. In this way, the volumetric efficiency is available relatively quickly compared to previously known systems. This expands the ranges in which monitoring is possible since it is also conceivable to use the volumetric efficiency recognition during relatively short controlled operating modes. The volumetric efficiency is calculated by being compared to a variable which was previously applied for the nominal state (normal vehicle operation). It is thus not necessary to separately apply and save the situation in the nominal case. This reduces the complexity of the application and the storage space required in the control unit. 
         [0008]    In one embodiment of the present invention, the device may include the following characteristics:
       a measuring device which is suitable to measure the volumetric efficiency;   an estimation device which is suitable to estimate the volumetric efficiency; and   a checking device which is suitable to check the measured volumetric efficiency for plausibility based on the estimated volumetric efficiency.       
 
         [0012]    The estimation device may estimate the volumetric efficiency in particular based on a provided model of the internal combustion engine. 
         [0013]    In one preferred embodiment of the present invention, the device is a vehicle diagnostic system for a vehicle driven by the internal combustion engine. Vehicle diagnostic systems, such as on board diagnostic systems, are devices in a vehicle which are required by law and from which the function of the vehicle itself does not benefit at all. They are only used to comply with the regulations for environmental protection. The device according to the present invention may be used to carry out this type of vehicle diagnostic system based on the characteristics which must be calculated anyway for the vehicle to function properly, thus saving resources in the engine control unit. 
         [0014]    In another preferred embodiment of the present invention, the checking device for the plausibility check may be provided to calculate a difference between the measured volumetric efficiency and the estimated volumetric efficiency, and to output an error when the difference exceeds a predetermined absolute value. The comparison between the difference and a predetermined absolute value makes it possible to introduce tolerances into the system which allow those deviations from the nominal state to be ignored which do not result in a noteworthy malfunction of the vehicle. 
         [0015]    According to another aspect of the present invention, an engine system includes, for driving a vehicle, an internal combustion engine for receiving an intake charge of fresh air for a fuel combustion and for outputting exhaust gas after the fuel combustion, and a device according to the present invention for outputting an error when the plausibility check of the volumetric efficiency factor results in a deviation between the measured and the estimated volumetric efficiency factor. In the engine system according to the present invention, erroneous exhaust gas values may easily be recognized, without having to implement additional measuring systems in the engine system. 
         [0016]    In one refinement of the present invention, the engine system includes an intake system for taking in gas into the engine system, an exhaust gas recirculation for recirculating at least a portion of the exhaust gas into the internal combustion engine, and a mixing section for mixing the fresh air and the recirculated exhaust gas for filling. In this way, an exhaust gas recirculation is provided which makes it possible to reduce the portions of discharged harmful agents in the exhaust gas, such as nitrogen oxides. 
         [0017]    In another refinement, the device for measuring the volumetric efficiency based on the pressure, the temperature, and the rotational speed may be provided in the internal combustion engine. This makes it possible to measure the volumetric efficiency with the aid of sensors which are already present in the internal combustion engine. 
         [0018]    In an alternative or additional embodiment, the device for estimating the volumetric efficiency based on an enthalpy flow balance between the enthalpy flow of the gas taken in and the enthalpy flow of the recirculated exhaust gas may be provided. The enthalpy flow balance may be ascertained in the engine system with the aid of already present sensors so that the boundary conditions for the estimation of the volumetric efficiency are determinable without further technical changes in the engine system. 
         [0019]    In another embodiment of the present invention, the device for estimating the enthalpy flow of the recirculated exhaust gas based on a mass flow of the recirculated exhaust gas through the exhaust gas recirculation may be provided. This estimation is, for example, possible in a simple manner based on the measured variables such as the position signal/actuating signal present at the valve in the exhaust gas recirculation. 
         [0020]    In an additional embodiment of the present invention, the device for estimating the enthalpy flow of the recirculated exhaust gas based on a mass flow of the recirculated exhaust gas through the mixing section may be provided. This estimation is possible in a simple manner via an enthalpy flow balance between the enthalpy flow of the gas taken in and the enthalpy flow in the internal combustion engine. 
         [0021]    In one preferred embodiment of the present invention, the device for selecting the enthalpy flow calculated based on the actuating signal of the exhaust gas recirculation valve or the enthalpy flow modeled based on the enthalpy flow balance at the mixing location may be provided for the estimation of the volumetric efficiency. The signal quality of the volumetric efficiency with regard to the signal noise ratio is always equally good since the volumetric efficiency is calculated by using different sources of information. Here, insensitive ranges or operating modes are suppressed so that a signal of adequate quality is always available. When calculating the characteristics in previously known on board diagnostic systems, these insensitive ranges in which the signal is, for example, strongly affected by noise must be explicitly blended out with the aid of operating range restrictions. 
         [0022]    According to another aspect of the present invention, a method for error monitoring in an engine system, which fills a filling of gas into an internal combustion engine at a volumetric efficiency, the volumetric efficiency indicating the ratio of the real volume flow in the engine to the ideal (theoretically possible) volume flow in the engine, includes the following steps: measuring the volumetric efficiency, estimating the volumetric efficiency, and checking the measured volumetric efficiency for plausibility based on the estimated volumetric efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a block diagram of an engine system. 
           [0024]      FIG. 2  shows a simplified illustration of the block diagram from  FIG. 1 . 
           [0025]      FIG. 3  shows a block diagram for checking a measured volumetric efficiency based on an estimated volumetric efficiency. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Reference is made to  FIG. 1 . An engine system  2  having an internal combustion engine  4  is illustrated in  FIG. 1 . 
         [0027]    Fresh air  10  is supplied via an air supply  6  to internal combustion engine  4  initially in the flow direction identified by arrows. An air mass flow measuring device  12 , in the form of a hot film air mass flow sensor, for example, which measures fresh air mass flow  11  and outputs it to an engine control  13 , is situated in air supply  6 . Alternatively, the fresh air supply may also be modeled and the necessary sensor may be modeled at another place in the air system. 
         [0028]    Subsequently, symbol {dot over (m)} L  is assigned to fresh air mass flow  11 . 
         [0029]    Downstream from air mass flow measuring device  12  in the flow direction, one or multiple compressors  14  may be situated in air supply  6 . The compressed air is provided with reference numeral  15 . 
         [0030]    The section of air supply  6  downstream from compressor  14  in the flow direction is referred to in the following as intake manifold  16 . Exhaust gas  20  may be supplied to intake manifold  16  in a junction  17  via an exhaust gas recirculation channel  18  from an exhaust gas system  22  of engine system  2 . Engine intake air  19  resulting therefrom is supplied to internal combustion engine  4 . The flow directions of exhaust gas  20  in exhaust gas system  22  and engine intake air  19  are identified by an arrow. The recirculated exhaust gas is provided with reference numeral  21  whose flow direction is also identified by an arrow. Fuel may be injected into engine intake air  19  or into compressed air  15  as is the case in some gasoline engines, for example. Alternatively, the fuel may also be injected directly into the internal combustion engine as is customary for a diesel engine. 
         [0031]    In the flow direction downstream from junction  17  of exhaust gas recirculation channel  18  into intake manifold  16 , a pressure sensor  24  and a temperature sensor  26  are situated in intake manifold  16 . Temperature sensor  26  and pressure sensor  24  ascertain temperature  28  and pressure  30  of supplied and compressed air  15 , which, if necessary, is enriched with recirculated exhaust gas  21 , and output them to engine control  13 . The pressure and temperature information may also be modeled on the basis of other, placed sensors. 
         [0032]    An exhaust gas recirculation valve  32  is situated in exhaust gas recirculation channel  18  to control the quantity of recirculated exhaust gas  21 . As previously described, internal combustion engine  4  has on its output side exhaust gas system  22  off of which exhaust gas recirculation channel  18  branches. In the flow direction downstream from the branch-off of exhaust gas recirculation channel  18  situated in exhaust gas system  22 , one or multiple turbines  34  may be situated which drive compressor  14 , for example. Furthermore, a rotational speed sensor  36 , which ascertains rotational speed  38  of internal combustion engine  4  and outputs it to engine control  13 , is situated on internal combustion engine  4 . 
         [0033]    The mass flow of engine intake air  19 , which is referred to in the following as the filling is assigned symbol {dot over (m)} F  for subsequent calculations. The filling is yielded from the sum of intake gas mass flow  11  having symbol {dot over (m)} L , which is, for example, measured using air mass flow measuring device  12 , and the mass flow of recirculated exhaust gas  18 . In addition to the measurement by air mass flow measuring device  12  in the closed exhaust gas recirculation, filling {dot over (m)} F  may also be calculated as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       m 
                       . 
                     
                     F 
                   
                   = 
                   
                     
                       λ 
                       a 
                     
                      
                     
                       
                         
                           V 
                           H 
                         
                         · 
                         n 
                         · 
                         p 
                       
                       
                         2 
                         · 
                         R 
                         · 
                         T 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0034]    In equation (1), λ a  is volumetric efficiency  58  shown in  FIG. 3  and it indicates the ratio of the real volume flow in the engine to the ideal (theoretically possible) volume flow in the engine. V H  is the swept volume of internal combustion engine  4 . n is rotational speed  38  of internal combustion engine  4 . p is pressure  30  in intake manifold  16  measured by pressure sensor  24 . R is the general gas constant. T is temperature  28 , which is measured by temperature sensor  26  or modeled, in intake manifold  16  in the flow direction downstream from junction  17  of recirculated exhaust gas  18 . 
         [0035]    To measure volumetric efficiency  58 , exhaust gas recirculation  18  may, for example, be interrupted during a calibration measurement and the filling may be determined. The measured value for volumetric efficiency  58  is determinable by solving equation (1) according to volumetric efficiency  58 . 
         [0036]    Measured volumetric efficiency  58  is checked for plausibility according to the present invention. For this purpose, it may, for example, be estimated one more time and checked based on that. This type of estimation and check is explained based on  FIGS. 2 and 3 , as an example, where elements identical to  FIG. 1  are provided with identical reference numerals and are not described again. 
         [0037]    In  FIG. 2 , one or multiple compressor(s)  14  separate(s) the air supply in the engine into a low-pressure area and a high-pressure area. In the low-pressure area, fresh air  10  taken in is guided via a low-pressure valve  40  (not shown in  FIG. 1 ) and mixed with a portion of exhaust gas  22  downstream from turbine  34 . The quantity of exhaust gas  22  to be added in the low-pressure area is controlled via a low-pressure exhaust gas recirculation valve  42 . In the high-pressure area, the supply of compressed fresh air  15  to junction  17  is controlled via a throttle valve  48  (not shown in  FIG. 1 ). 
         [0038]      FIG. 3  shows the structure diagram of the determination of the plausibility check of measured volumetric efficiency  58  based on estimated volumetric efficiency  51 . To determine estimated volumetric efficiency  51 , the sequence shown in  FIG. 3  includes a balancing section  54  and an estimation section  56 . After the estimation, measured volumetric efficiency  58  is checked in a checking section  57  based on the estimation. 
         [0039]    In the present embodiment, the estimation of volumetric efficiency  58  is based on the mass flow of recirculated exhaust gas  21 , since this variable is redundantly determinable in most vehicles so that the value for the mass flow of recirculated exhaust gas  21 , which has the greatest information content, may always be used for the estimation. If, for example, valve  32  in exhaust gas recirculation channel  18  is closed, but one of the values for the mass flow of recirculated exhaust gas  21  is greater than zero, its information content is equal to zero, since the value is obviously incorrect. 
         [0040]    In balancing section  54 , a value  76  is determined for the mass flow of recirculated exhaust gas  21  as the estimation basis for estimation section  56 . This essentially takes place based on a balancing of the filling and fresh air mass flow  11 . For implementability reasons, not the mass flows themselves, but the enthalpy flows associated with them, are balanced, however. To carry out the calculations, pressure  30 , measured volumetric efficiency  58 , rotational speed  38 , and fresh air mass flow  11  are supplied to balancing section  56  from engine system  2 . From a temperature sensor  26  (shown in  FIG. 1 ), temperature  60  of compressed fresh air  15  prevails in balancing section  54  upstream from throttle valve  48 , which is assigned symbol T vD . Temperature  61 , which is assigned symbol T A , is detected in the same manner in exhaust gas recirculation channel  18  and made available to balancing section  54 . As an alternative to the measurement, the temperatures may also be modeled upstream from throttle valve  48  and in exhaust gas recirculation channel  18 . 
         [0041]    The determination of enthalpy flow  62  through throttle valve  48  takes place in balancing section  54  based on a first function  64  having functional derivative f 1 , which is assigned symbol {dot over (h)} L . In f 1 , fresh air mass flow  11  and temperature  60  of compressed fresh air  15  upstream from throttle valve  48  are incorporated according to the following equation: 
         [0000]        {dot over (h)}   L   =f   1 ( {dot over (m)}   L   ,T   vD )  (2)
 
         [0042]    Functional derivative f 1  of first function  64  may be derived from a thermodynamic approach to enthalpy flow determination. 
         [0043]    To determine enthalpy flow  65  through internal combustion engine  4 , volume flow  38  through internal combustion engine  4  must initially be determined, which is assigned symbol {dot over (V)} F . This takes place in a second function  66  having functional derivative f 2  based on measured volumetric efficiency  58  and rotational speed  38  according to the following equation: 
         [0000]        {dot over (v)}   F   =f   2 (λ a   ,n )  (3)
 
         [0044]    Functional derivative f 2  of second function  66  may be derived from a volume balance in the engine and may be stored in a memory of engine control  13 , for example. Enthalpy flow  65  through internal combustion engine  4 , which is assigned symbol {dot over (h)} F , is then yielded in balancing section  54  using a third function  70  having functional derivative f 3  based on previously calculated volume flow  68  and pressure  30  in internal combustion engine  4  according to the following equation: 
         [0000]        {dot over (h)}   F   =f   3 ( p,{dot over (v)}   F )  (4)
 
         [0045]    Functional derivative f 3  of third function  70  may be derived from a thermodynamic approach to enthalpy flow determination. 
         [0046]    To balance enthalpy flow  72  through valve  32  in exhaust gas recirculation channel  18  having symbol {dot over (h)} A,Balance , it is assumed in one variant that neither mass nor enthalpy may be stored in junction  17 . Balanced enthalpy flow  72  is then yielded according to the following equation: 
         [0000]        {dot over (h)}   A,Bilanz   ={dot over (h)}   L   −{dot over (h)}   F   (5)
 
       [Bilanz=Balance] 
       [0047]    This equation may be further expanded by memory effects of the mixing location as well as wall heating processes. 
         [0048]    Subsequently, balanced enthalpy flow  72  is converted using a fourth function  74  having functional derivative f 1  based on temperature  61  in exhaust gas recirculation channel  18  into first value  76  for the mass flow of recirculated exhaust gas  21 , which is assigned symbol {dot over (m)} A,Balance , according to the following equation: 
         [0000]        {dot over (h)}   A,Bilanz   =f   1 ( {dot over (m)}   A,Bilanz   ,T   A )  (6)
 
       [Bilanz=Balance] 
       [0049]    In estimation section  56 , an estimation of the actual mass flow of recirculated exhaust gas  21  is carried out based on this first value  76  for the mass flow of recirculated exhaust gas  21  and a second value  78  for mass flow {dot over (m)} A  of recirculated exhaust gas  21 , which is assigned symbol {dot over (m)} A,Valve . Second value  78  may, for example, be determined directly from a measurement of pressure ratio at exhaust gas recirculation valve  32  using a thermodynamic approach, for example, with the aid of a throttle equation. 
         [0050]    Ideally, first value  76  and second value  78  for the mass flow of recirculated exhaust gas  21  are identical. In practice, however, the two values always deviate slightly from one another. In the previously mentioned manner, that value  76 ,  78  is selected for determination of estimated volumetric efficiency  51  in estimation section  56  whose information content is greater due to certain boundary conditions. This selection takes place via an estimation function  80  in estimation section  56 , a Kalman filter, for example. 
         [0051]    From estimated mass flow  82  of recirculated exhaust gas  21 , output by estimation function  80 , an estimated enthalpy flow  86  through exhaust gas recirculation channel  18  may be calculated together with temperature  61  in exhaust gas recirculation channel  18  in a fifth function  84 , which is based on functional derivative f 1  of equation (2). By balancing this estimated enthalpy flow  86  of recirculated exhaust gas  21  and enthalpy flow  62  through throttle valve  48  output from first function  64 , an estimated enthalpy flow  88  through internal combustion engine  4  is determined in estimation section  56 , based on which estimated volumetric efficiency  51  is finally calculated via pressure  30  in a sixth function  87 , which is based on functional derivatives f 2 , f 3 . 
         [0052]    In monitoring section  57 , measured volumetric efficiency  58  is checked for plausibility by a comparison based on estimated volumetric efficiency  51 . The comparison takes place by the formation of a difference  89  which is checked for its level in a filter  90 . If measured volumetric efficiency  58  deviates too excessively from estimated volumetric efficiency  51 , an error  92  is finally output by monitoring section  57 . 
         [0053]    According to the present invention, the volumetric efficiency is used for error diagnosis in a vehicle, since it is calculated anyway within the scope of the control systems present in the vehicle, thus allowing not only for a diagnosis at smaller measurement complexity but also providing the diagnosis results on a time constant of the control which uses the volumetric efficiency.