Abstract:
In a method for performing diagnostics on line systems, in particular crank casing venting systems of internal combustion engines, a correction value for an operating parameter of the internal combustion engine is formed in each of at least two chronologically successive determining steps. The correction values or values which are derived therefrom are used to detect a faulty state of the line system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2009 059 662.3-52, filed Dec. 19, 2009; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a method for performing diagnostics on line systems, in particular crank casing venting systems of internal combustion engines, in which method a correction value for an operating parameter of the internal combustion engine is formed in each of at least two chronologically successive determining steps. 
         [0003]    For environmental protection reasons, it is not permitted for internal combustion engines to emit blow-by gases into the open air. For this reason, crank casing venting systems have been developed which feed the blow-by gases back into the intake section of the internal combustion engine. 
         [0004]    U.S. legislation requires diagnostics to be performed on leakages in the crank casing venting system. 
         [0005]    The prior art also discloses methods for correcting an air mass flow rate measuring error during the operation of an internal combustion engine of a motor vehicle. For example, published, non-prosecuted German patent application DE 10 2005 010 785 A1 describes that correction values are determined and used in the engine control unit to carry out correction of the air mass flow rate measuring error. The correction values are formed by reconciliation of a current HFM-(hot film air mass flow rate meter) sensor air mass flow rate with an air mass flow rate which is itself calculated from a volumetric efficiency model. 
         [0006]    In order to be able to meet the abovementioned environmental protection requirements, such systems must be equipped with complex technology (additional hardware, expensive plug connections). 
       SUMMARY OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide a method for performing diagnostics on line systems of internal combustion engines which overcomes the above-mentioned disadvantages of the prior art methods of this general type, in a way which is less complex and more cost-effective compared to the prior art. 
         [0008]    With the foregoing and other objects in view there is provided, in accordance with the invention a method for performing diagnostics on a line system, including a crank casing venting system of an internal combustion engine. The method includes the steps of forming a correction value for an operating parameter of the internal combustion engine in each of at least two chronologically successive determining steps; and using the correction values or values which are derived therefrom to detect a faulty state of the line system. 
         [0009]    The method serves to perform diagnostics on line systems, in particular crank casing venting systems of internal combustion engines. In the method, a correction value for an operating parameter of the internal combustion engine is formed in each of at least two chronologically successive determining steps. The correction values or values which are derived therefrom are used to detect a faulty state of the line system. Possible correction values are, for example, correction values for correcting an air mass flow rate measuring error or correction values for a manipulated variable of an actuator (for example a throttle valve), or further correction values which are suitable for the present purpose and which are only conceivable for some other operating parameters. The term “correction value” includes according to the wording of this text both a time-discrete individual correction value and averaging over a plurality of such individual correction values. The correction values for correcting an air mass flow rate measuring error may be determined, for example, in the way described in published, non-prosecuted German patent application DE 10 2005 010 785 A1. 
         [0010]    According to one refinement of the method according to the invention, the determining steps are each carried out in an idling phase of the internal combustion engine. 
         [0011]    In one embodiment of the method according to the invention, a comparison operation is carried out which includes a comparison of the present correction value with a reference value, and a conclusion that there is an intact line system, and acceptance of the present correction value as a new reference value for a subsequent comparison operation when at least one criterion of the comparison is met. 
         [0012]    According to one embodiment variant of the method according to the invention, a first initial correction value is determined in an initial comparison operation in a first idling phase. A second initial correction value is determined in a second idling phase which follows the first idling phase. The two initial correction values are compared with one another in an initial comparison, and one of the initial correction values is accepted as the reference value depending on the result of the initial comparison. 
         [0013]    In one embodiment of the method according to the invention, when a criterion of the initial comparison is met, the method is continued in a subsequent follow-on comparison operation which follows the initial comparison operation. In this context, a further correction value is determined in the follow-on comparison operation and the further correction value is compared with the valid reference value in a follow-on comparison. It is concluded that there is a defective or intact line system depending on the result of the follow-on comparison. 
         [0014]    According to one refinement of the method according to the invention, the difference between the comparison partners which are to be respectively compared in at least one of the comparisons is formed. In addition a threshold value is predefined. The comparison criterion relates to the relative position of the difference or the absolute value of the difference from the threshold value. This makes it easily possible to test the function capability of the line system. If the difference exceeds the threshold value, an error is detected, otherwise it is concluded that there is an intact line system. 
         [0015]    For example, the formation of at least one of the correction values takes place only if predefined diagnostic conditions (for example temperature, altitude, load, length of idling etc.) which prevail at the respective time are met. 
         [0016]    In one embodiment of the method according to the invention, the respective last valid reference value of concluded diagnostics is stored in a non-volatile data memory. This makes it ultimately possible to ensure that a plurality of driving cycles can be evaluated. If a correction value is found to be “not satisfactory”, driving cycles can be compared with the original reference value in order, if appropriate, to detect a single atypical value in the measurement. 
         [0017]    The invention provides the precondition for increasing the robustness and reliability of load-detecting diagnostics even in the case of relatively high mileage/kilometrage readings. In combination with already existing diagnostics the innovative solution makes it possible to differentiate between creeping effects and spontaneous effects, which may be very useful for troubleshooting at a motor vehicle workshop. 
         [0018]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0019]    Although the invention is illustrated and described herein as embodied in a method for performing diagnostics on line systems of internal combustion engines, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0020]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0021]      FIG. 1  is a flowchart of a method according to the invention; and 
           [0022]      FIG. 2  is a diagram of two graphs represented one on top of the other, the upper graph of which shows measurement results of the method according to the invention, and the lower graph of which shows, inter alia, a time profile of the idling phases of a tested internal combustion engine. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  shows a flowchart of a method according to the invention. The method according to the invention starts in a first determining step E 1 , which is carried out in a first idling phase LP 1  (see  FIG. 2 ) of an internal combustion engine. In the first determining step E 1 , a first initial correction value K1 (see  FIG. 2 ) is formed. After the first determining step E 1  the method is continued in a second determining step E 2 , which is carried out in the second idling phase LP 2  (see  FIG. 2 ) which follows the first idling phase LP 1 . In the second determining step E 2 , which is carried out in a way analogous to the first determining step E 1 , a second initial correction value K2 (see  FIG. 2 ) is formed. 
         [0024]    The second determining step E 2  is followed by an initial comparison step VA, in which it is tested whether the difference (or the absolute value of the difference) between the first initial correction value K1 and the second initial correction value K2 is greater than or equal to a threshold value which can be applied. 
         [0025]    Given a positive test result of the initial comparison step VA (threshold value is exceeded or reached), the method according to the invention is continued in step S 2 , while in the event of a negative test result of the initial comparison step VA (threshold value is undershot) the method is continued in step S 1 . 
         [0026]    In step S 2 , it is concluded that there is a defective line system and at the same time the first initial correction value K1 is stored as a reference value in a memory. In this case, the first initial correction value K1 is required for fault recovery or for fault confirmation. The method can be ended, for example, in S 2 . 
         [0027]    In step S 1  it is concluded that there is an intact line system and at the same time the second initial correction value K2 is stored as a reference value in a memory. 
         [0028]    After the step S 1 , the method is continued in a follow-on determining step E 3  which is carried out in the third idling phase LP 3  (see  FIG. 2 ) which is the next after the second idling phase LP 2 . In the follow-on determining step E 3 , a follow-on correction value K3 is formed. The follow-on determining step E 3  is followed by a follow-on comparison step VF in which it is tested whether the difference (or the absolute value of the difference) between the follow-on correction value K3 and the currently valued reference value is greater than or equal to the threshold value T. 
         [0029]    Given a positive test result of the follow-on comparison step VF (the threshold value is exceeded or reached), the method according to the invention is continued in step F 2 , while in the event of a negative test result of follow-on comparison step VF (the threshold value is undershot) the method is continued in step F 1 . 
         [0030]    In step F 1  it is concluded that there is an intact line system. The method can be continued, for example, to step F 1  by entering a loop in step E 3 , or can also be ended, as shown in the flowchart, after step F 1 . 
         [0031]    In step F 2 , it is concluded that there is a defective line system and the method is ended, for example. 
         [0032]      FIG. 2  shows two graphs G 1 , G 2  which are illustrated one on top of the other, the upper graph G 1  of which shows measurement results of the method according to the invention. In the upper graph G 1 , the ordinate represents the diagnostic value as a percentage, and the abscissa represents the time. 
         [0033]    A lower graph G 2  shows, apart from the text and symbols which serve to explain the method sequence, a time profile of the idling phases LP 1 , LP 2 , LP 3  of the internal combustion engine which is being examined within the scope of the method according to the invention. 
         [0034]    The time axes (abscissas) of the two graphs G 1 , G 2  have simultaneous profiles, that is to say identical x values correspond in each case to identical times during the execution of the method according to the invention. 
         [0035]    The time profile of the idling phases LP 1 , LP 2 , LP 3  is illustrated in the manner of a step function in the lower graph G 2  (the ordinate is assigned the value Y=“high” when the internal combustion engine is in an idling phase LP 1 , LP 2 , LP 3  at a specific time, while y=0 means that the internal combustion engine is not in an idling phase at a specific time). 
         [0036]    In addition, the previously described correction values K1, K2, K3together with corresponding delta values are illustrated below the abscissas of the lower graph G 2 . The threshold value T has been set to 25%, as is indicated in the field FA. 
         [0037]    The first initial correction value K1 is +3%, while the second initial correction value K2 is +5%, which corresponds to a delta value of 2%. This delta value undershoots the threshold value T, that is to say the delta value is, as described under  FIG. 1 , found to be “satisfactory (O.K.)” (field FB). The first follow-on correction value K3 is 26%, which, as described under  FIG. 1 , corresponds to a delta value of 26%. This delta value exceeds the threshold value T, which means that the line system is considered to be faulty (field FA). 
         [0038]    A possible extension of the diagnostic strategy can be a comparison of the respective reference value with a plurality of successive correction values and/or the application of specific statistic functions. 
         [0039]    A possible additional condition may be, for example, that in environmental conditions which are not found to be satisfactory for an applicable number of driving cycles the system switches over to extended threshold values after a throttle valve adaptation. 
         [0040]    As a result, a basic concept of the invention can also be formulated as “relative comparison of a correction value, for example of a throttle valve correction value into two or more successive idling phases for evaluating a faulty state such as, for example, a leak in the line system”.