Abstract:
A method and a device, a computer program and a computer program product for implementing a method for calibrating a fuel injector of an internal combustion engine, including the following: a) Specifying a first relationship between an injection quantity and an actuating variable of the fuel injector for implementing the injection quantity, b) Specifying a setpoint injection quantity, c) Specifying at least one setpoint value for the actuating variable of the fuel injector according to the first relationship, or implementing the setpoint injection quantity, d) Determining an indicated work resulting from the implementation of the at least one setpoint value for the actuating variable, e) Comparing a variable as a function of the determined resulting indicated work to an expected value, f) Correcting the at least one setpoint value for the actuating variable of the fuel injector as a function of the comparison result.

Description:
RELATED APPLICATION INFORMATION 
     The present application claims priority to and the benefit of German patent application no. 102008002121.0, which was filed in Germany on May 30, 2008, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention is based on a method and a control device for calibrating a fuel injector, and on a computer program and a computer program product therefor. 
     BACKGROUND INFORMATION 
     A method and a device for operating an internal combustion engine are discussed in DE 10 2005 051 701 A1, in which an overall injection is subdivided into a basic injection and at least one measured injection. The injection period of the measured injection is successively reduced and the injection period of the basic injection is increased, in such a way that an overall injection quantity determined from a characteristics curve of the valve remains unchanged. A deviation of a variable characterizing an actual mixture, provoked by the successive reduction of the injection period of the measured injection, from a variable characterizing a setpoint mixture is detected. The deviation or a characteristics curve of the fuel injector is adapted or corrected. The detection as to whether the actual fuel-air mixture is deviating from the setpoint fuel-air mixture take place with the aid of a Lambda value provided by a Lambda sensor. 
     SUMMARY OF THE INVENTION 
     In contrast, the method of the present invention, the control device of the present invention, the computer program of the present invention and the computer program product of the present invention having the features of the independent claims have the advantage that
     a) A first relationship is specified between an injection quantity and an actuating variable of the fuel injector for implementing the injection quantity;   b) A setpoint injection quantity is specified;   c) At least one setpoint value is specified for the actuating variable of the fuel injector according to the first relationship for implementing the setpoint injection quantity;   d) An indicated work resulting from the implementation of the at least one setpoint value for the actuating variable is determined;   e) A variable as a function of the determined resulting indicated work is compared to an expected value;   f) The at least one setpoint value for the actuating variable of the fuel injector is corrected as a function of the comparison result.   

     In this way a variable which is a function of the resulting indicated work is determined as feedback of the combustion independently of the fuel-air mixture. 
     Advantageous further developments and improvements of the method described in the independent claim are rendered possible by the measures delineated in the dependent claims. 
     It is especially advantageous if the at least one setpoint value for the actuating variable of the fuel injector in step c) is corrected with the aid of a first correction characteristics curve; the correction in step f) is implemented with the aid of the first correction characteristics curve; and the correction characteristics curve in step f) is corrected as a function of the correction result. This makes it possible to correct the setpoint value for the actuating variable of the fuel injector with the aid of a first correction factor averaged across several specimens of the fuel injector, which results in an improvement in the running smoothness of the internal combustion engine and a reduction in the knocking tendency of the internal combustion engine. 
     In an advantageous manner, the injection quantity is then selected as the variable as a function of the determined resulting indicated work. In combustion methods having excess air, the correction of the relationship between the injection quantity and the actuating variable of the fuel injector for implementing the injection quantity is therefore determined directly. 
     One specific embodiment, in which the injection quantity is determined as a function of the determined resulting indicated work and the engine speed, in particular with the aid of a characteristics map, is especially advantageous. This makes it possible to determine the injection quantity in an especially simple and precise manner with little effort. When using a characteristics map, additional influence variables such as the effects of the fuel type and the ambient conditions are able to be taken into account. This increases the accuracy. 
     It is especially advantageous if the setpoint injection quantity is selected as expected value since a correction factor for the relationship between the injection quantity and the actuating variable of the fuel injector for implementing the injection quantity is able to be calculated directly on the basis of the comparison of the setpoint injection quantity on the one hand and the actual injection quantity determined from, for example, the resulting indicated work and the engine speed, on the other. This allows a simple implementation of the method, which has a positive effect on the production cost. 
     One specific embodiment of the method according to the present invention, in which the resulting indicated work itself is selected as the variable as a function of the determined resulting indicated work, is especially advantageous. This avoids additional computing steps. As a result, the method is able to be implemented in a control device more easily. 
     A setpoint value for the resulting indicated work is then expediently selected as expected value since the comparison between the expected value and the determined resulting indicated work is thus able to be implemented in an uncomplicated manner in a control device. 
     Especially advantageous is a specific embodiment in which the setpoint value for the resulting indicated work is determined in the following manner: 
     The setpoint injection quantity is implemented into a single setpoint actuating variable according to the first relationship; the determined resulting indicated work that comes about is selected as setpoint value for the resulting indicated work. Thus, an expected value suitable for implementing the method according to the present invention is able to be determined with little effort for any suitable operating point of the internal combustion engine. 
     The resulting indicated work is advantageously determined as a function of the combustion chamber pressure. The use of combustion-chamber pressure sensors offers the advantage that the acquisition of the resulting indicated work takes place individually for each combustion chamber; furthermore, in combustion engines having more than one combustion chamber, a complicated und possibly error-prone conversion of the resulting indicated work, from the plurality of combustion chambers to one combustion chamber, is able to be dispensed with. This increases the precision of the correction. 
     Especially advantageous is one specific development, which is characterized by the fact that the setpoint injection quantity according to the first relationship is converted into a single setpoint actuating variable and that the correction in f) according to a first correction factor is implemented as a function of the quotient between the setpoint injection quantity on the one hand and the actual injection quantity derived from the resulting indicated work on the other hand. This makes it possible to determine the correction factor as a function of a simple division without additional complex computing steps. 
     Especially advantageous is one specific embodiment, which is characterized in that the setpoint injection quantity is subdivided into a basic injection quantity and a measured injection quantity; the basic injection quantity is implemented by a basic setpoint actuating variable as a function of the first relationship; and the measured injection quantity is implemented by a measured setpoint actuating variable as a function of the first relationship. Because of the unvarying full setpoint injection quantity, the injection quantity supplied to the combustion does not change or changes only negligibly, so that correction factors in the entire range of the injection quantities realizable by the fuel injector are able to be determined with minimal effect on the running smoothness of the internal combustion engine and while avoiding a standstill of the internal combustion engine. 
     In an advantageous manner, the basic injection quantity is implemented by the basic setpoint actuating variable according to the actuating variable of the fuel injector corrected by the first correction factor. This further increases the precision of the correction. 
     Especially advantageous is a development, which is characterized in that the measured setpoint actuating variable, assigned to the measured injection quantity via the specified first relationship, is varied as a function of the deviation between the variable as a function of the determined resulting indicated work and the expected value, in order to adjust the variable as a function of the determined resulting indicated work to the expected value; and the correction of the at least one setpoint value for the actuating variable of the fuel injector at f) is implemented as a function of a determined corrected measured actuating variable, at which the deviation between the variable as a function of the determined resulting indicated work and the expected value lies within a predefined tolerance range. By utilizing available control algorithms for the indicated work, for example, it is possible to realize an especially simple and reliable implementation of the method according to the present invention in this manner. 
     The first correction factor is advantageously determined as a function of the quotient from the measured actuating variable and the corrected measured actuating variable. This further simplifies the method according to the present invention. 
     Especially advantageous is one specific development in which the correction implemented in f) according to the first correction factor is formed as a function of the quotient between a difference from the setpoint injection quantity and the basic injection quantity on the one hand, and a difference from the actual injection quantity derived from the determined resulting indicated work and the basic injection quantity on the other hand. This makes it possible to correct the relationship between the injection quantity and an actuating variable of the fuel injector in an especially satisfactory manner since the difference between setpoint injection quantity and actual injection quantity is able to be traced back directly to the measured setpoint actuating variable. 
     In an advantageous manner, the electric control period is used as actuating variable of the fuel injector because this variable is able to be set very precisely with the aid of an electronic control device. 
     The setpoint injection quantity is advantageously selected greater than a first threshold value. In this way, the internal combustion engine is able to be operated without risking a standstill. 
     Specific embodiments of the present invention are illustrated in the drawing and explained in greater detail in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic illustration of an internal combustion engine having direct gasoline injection through a fuel injector. 
         FIG. 2  shows a first, a second, and a third relationship between an injected fuel quantity and an electric control period of the fuel injector from  FIG. 1 . 
         FIG. 3  shows a first and a second correction characteristics curve, which represents the relationship between a first and a second correction factor and the electric control period of the fuel injector from  FIG. 1 . 
         FIG. 4  shows a flow chart, which describes an exemplary sequence of the method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates the configuration of an internal combustion engine  1000 , for instance an Otto engine or a Diesel engine. This internal combustion engine  1000  has a plurality of combustion chambers  1040 , having self ignition, for implementing a homogenous combustion method; for reasons of clarity, however, only one combustion chamber is illustrated in  FIG. 1 . In addition, internal combustion engine  1000  includes an intake manifold  1050  for the supply of air, and a fuel injector  1045 , which injects fuel into combustion chamber  1040  in such a way that a homogenous air/fuel mixture comes about inside combustion chamber  1040 . This homogenous air-fuel mixture is supplied with energy by the movement of a piston  1070  by compression of the homogenous air-fuel mixture until it self-ignites inside combustion chamber  1040 . A discharge valve  1060  and an exhaust gas pipe  1065  are used to route the combustion exhaust gases to the outside. 
     The determination of the opening instants and the opening periods of intake valve  1055  and discharge valve  1060  in a working cycle is implemented with the aid of an engine control device, for example as a function of the position of piston  1070 . This piston  1070  is connected to a crankshaft  1090  via a connection rod  1095 . In the case of a four-stroke engine, the working cycle denotes the cycles of aspiration, compression, expansion and expulsion, for example. These cycles are assigned to the position of piston  1070  or a crankshaft angle detected by a crankshaft sensor  1085  in a manner known to one skilled in the art. 
     During the expansion, an energy released by the combustion of the air-fuel mixture is partially transmitted as mechanical energy to crankshaft  1090  via piston  1070  by connection rod  1095 . A resulting torque is then available at crankshaft  1090 . 
     Internal combustion engine  1000  also has an engine speed sensor  1075  for detecting the rotational speed of internal combustion engine  1000 , a sensor  1080  for detecting the combustion chamber pressure, as well as a control device  1005 . 
     Control device  1005  includes a first input unit  1010 , a second input unit  1015 , a third input unit  1020 , a determination unit  1025 , a comparison unit  1030 , a correction unit  1035 , as well as a volatile memory (not shown in  FIG. 1 ), and a non-volatile memory (not shown in  FIG. 1 ). 
     Two types of fuel injectors  1045  are typically used for the injection with the aid of fuel injector  1045 . These are solenoid valves and piezo valves. Piezo valves are characterized by high precision of the injected fuel quantity, but are currently very expensive in their production in comparison with solenoid valves. The exemplary embodiments and/or exemplary methods of the present invention is able to be used regardless of the type of fuel injector  1045  employed and is described in the following text using the example of a solenoid valve. The method of the present invention is used analogously for piezo valves. 
     In a manner known to one skilled in the art, a first relationship  204 , a first correction characteristics curve  301 , a first threshold value, a status datum, in particular a status bit SKAL, as well as a second threshold value BET are stored in the non-volatile memory of control device  1005 . 
       FIG. 2  illustrates first relationship  204  between an injection quantity Q and an actuating variable of fuel injector  1045 , especially an electric control period T i  of fuel injector  1045 , as injection behavior of a solenoid valve, for example. First relationship  204  is an unambiguous, for instance linear, relationship between injection quantity Q and electric control period T i . First relationship  204  is specified by the manufacturer of fuel injector  1045 , for example. 
     As can be gathered from  FIG. 2 , first relationship  204  is represented by a straight line, which starts on the positive axis at a point T i =T m  that differs from zero and then rises for increasing T i &#39;s. For storage, for instance in the non-volatile memory in control device  1005  of internal combustion engine  1000 , predefined values for injection quantity Q are selected from a value range. The value range encompasses all possible injection quantities Q implementable by fuel injector  1045 , such as from 0 mg to 25 mg. The predefined values for injection quantity Q and associated electric control periods T 1  are stored in a first data area in the non-volatile memory of control device  1005  in a manner known to one skilled in the art. The predefined values for injection quantity Q are represented by dots on the straight line in  FIG. 2 . 
     Solenoid valves for internal combustion engines  1000  which are used in motor vehicles exhibit a strong non-linearity with respect to the relationship of injection quantity Q and electric control period T 1 , especially for smaller injection quantities Q such as less than 7 mg. The actual injection behavior of fuel injector  1045  for a specific sample of fuel injector  1045  is shown as second relationship  201  between injection quantity Q of electric control period T i  in  FIG. 2 . It can be gathered from  FIG. 2  that second relationship  201  starts after a dead zone at a value of T i =T e1  on the positive x-axis. Injection quantity Q is equal to zero for values T i &lt;T e1 . For the values T i &gt;T e1 , second relationship  201  increases up to a maximum value. Second relationship  201  drops to a minimum value in the further course, in order to subsequently approach a linear relationship with a decreasing slope. Second relationship  201  intersects first relationship  204  before and after second relationship  201  assumes its minimum value. 
     A third relationship  205  in  FIG. 2  exemplarily represents the relationship between injection quantity Q and electric control period T i  averaged across a plurality of samples of fuel injector  1045 . To determine third relationship  205 , the injection behavior of a plurality of fuel injectors  1045  is measured on a test stand, for example, by measuring actual injection quantity Q injected by fuel injector  1045  at a specific electric control period T i , the measurement being carried out with the aid of a flow-rate meter. Afterwards, third relationship  205  is determined in the manner known to one skilled in the art by forming the average value from the injection behavior of individual fuel injectors  1045 . From  FIG. 2  it can be gathered that third relationship  205  starts after a dead zone at a value of T i =T e2  on the positive x-axis. Injection quantity Q is equal to zero for values T i &lt;T e2 . For values T i &gt;T e2 , third relationship  205  increases up to a maximum value. Third relationship  205  drops to a minimum value in the further course and then approaches a linear relationship at a decreasing slope. Third relationship  205  intersects second relationship  201  twice after third relationship  205  has exceeded its minimum value. 
     Depending on the lower running limit of the internal combustion engine, i.e., the particular injection quantity Q at which internal combustion engine  1000  will actually not come to a standstill as a function of the model type and engine speed of internal combustion engine  1000 , a first threshold value is defined, which lies between 5-8 mg per stroke or working cycle. In the case of a 4-stroke engine of a motor vehicle, for instance, a working cycle includes the cycles of aspiration, compression, working, expelling. With the aid of this first threshold value it is possible to subdivide first relationship  204  into two ranges: a first range  202  of smaller injection quantities Q, and a second range  203  of greater injection quantities Q. Smaller injection quantities Q are injection quantities Q that are smaller than injection quantity Q of the lower smooth running limit. 
     The first threshold value, for instance, is able to be determined by measuring an internal combustion engine  1000  on a test stand; a flow-rate meter measures actual injection quantity Q, which is injected during a specific electric control period T i  of fuel injector  1045 . Electric control period T i  is reduced in equidistant increments of 1 mg per stroke, starting at 10 mg, until the smooth running limit is exceeded, i.e., when internal combustion engine  1000  is coming to a standstill. Then, the first threshold value is stored, for instance in a second data area in the non-volatile memory in control device  1005 . 
       FIG. 3  shows a first correction characteristics curve  301 , which represents the correlation of electric control period T i  and first correction factors k 1   corr . Starting from a starting value that differs from zero, for example, first correction characteristics curve  301  is constant to begin with and then drops to a minimum at a steep slope. First correction characteristics curve  301  subsequently rises to a maximum, then drops at a decreasing slope and approaches the x-axis. For the storing in a non-volatile memory in control device  1005 , for instance, the same electric control periods T 1  are selected as for the storing of first relationship  204 . These electric control periods T 1  together with the associated first correction factors k 1   corr  are stored in the non-volatile memory of control device  1005  in a third data area in a manner known to one skilled in the art. The corresponding values for electric control periods T 1  and associated first correction factors k 1   corr  are represented by points on the characteristics curve. 
     For each of the first correction factors K 1   corr , the status information by which a distinction is made as to whether the particular first correction factor K 1   corr  is to be calibrated is also stored in the third data area. The status information is stored prior to the first operation of the internal combustion engine in the manner known to one skilled in the art such as with the aid of a status bit SKAL. Status bit SKAL may assume the values TRUE or FALSE, for example. TRUE means that first correction factor K 1   corr  has already been calibrated. FALSE means that first correction factor K 1   corr  was not calibrated. Status bit SKAL is set to FALSE prior to the first operation of the internal combustion engine. 
       FIG. 3  also shows a relationship between electric control period T 1  and a second correction factor k 2   corr , as a second correction characteristics curve  302 . Starting from a starting value that differs from zero, second correction characteristics curve  302  initially remains constant, for instance, and then drops sharply to a minimum. Afterwards, second correction characteristics curve  302  rises to a maximum and then drops at a decreasing slope and approaches the x-axis. First correction characteristics curve  301  intersects second correction characteristics curve  302  a first time, for instance, shortly after the maximum value of first correction characteristics curve  301 , and a second time before first correction characteristics line  301  approaches the x-axis. 
     Since first correction factors K 1   corr  are not known prior to executing the method of the exemplary embodiments and/or exemplary methods of the present invention for the first time, the corresponding second correction factor k 2   corr  from second correction characteristics curve  302  is stored for each of the first correction factors k 1   corr  in the third data area of the non=volatile memory in control device  1005 , before the internal combustion engine&#39;s first operation. 
     For this purpose, the same electric control periods T i  are selected for storage in the non-volatile memory in control device  1005  of internal combustion engine  1000  as in the storing of the first relationship  204 .  FIG. 3  shows the corresponding values for electric control periods T i  and associated second correction factors k 2   corr  as points on the characteristics curve. 
     In addition, second threshold value BET is stored in the non-volatile memory in control device  1005 . Prior to the first operation, second threshold value BET is set to equal 10 hours and stored in the non-volatile memory in control device  1005 . 
     First input unit  1010  specifies first relationship  204  to correction unit  1035 . First relationship  204  is stored in a non-volatile memory in control device  1005 , for example. 
     Second input unit  1015  specifies a setpoint injection quantity Q setpoint  to third input unit  1020  and comparison unit  1030 . Setpoint injection quantity Q setpoint  may assume random values within the specific value range. To determine setpoint injection quantity Q setpoint  an injection quantity Q driver  requested by the driver is first determined in a manner known to one skilled in the art, for instance as a function of the accelerator position if a motor vehicle is involved. From this, setpoint injection Q setpoint  is determined. In a normal operation of the internal combustion engine, injection quantity Q driver  requested by the driver is greater than the first threshold value. Setpoint injection Q setpoint  corresponds to injection quantity Q driver  requested by the driver, for instance. 
     As described in the following text, correction unit  1035  determines first correction characteristics curve  301 , status bit SKAL, second threshold value BET, and stores them in the non-volatile memory in control device  1005 , for example. 
     Third input unit  1020  determines a setpoint value for electric control period T i  of fuel injector  1045  as a function of setpoint injection quantity Q setpoint . The setpoint value for electric control period T i  of fuel injector  1045  is determined during normal operation of internal combustion engine  1000 , using first relationship  204  and first correction characteristics curve  301 . To this end, a linear electric control period T in  is determined from setpoint injection quantity Q setpoint  with the aid of the first relationship, using interpolation, for instance. Then, using first correction characteristics curve  302 , first correction factor K 1   corr  is determined from the electric control period T lin  thus determined, using interpolation, for instance. Next, electric control period T 1  is calculated by multiplying linear electric control period T lin  by first correction factor K 1   corr  associated with this linear electric control period T lin , in the following manner:
 
 T   i   =T   lin   *K 1 korr ( T   lin ).
 
     In a manner known to one skilled in the art, third input unit  1020  also determines a setpoint actuating variable for fuel injector  1045 , which corresponds to the setpoint value of electric control period T 1 , such as a current signal, and inputs it for fuel injector  1045 . 
     Determination unit  1025  continually records the engine speed of internal combustion engine  1000 , which is transmitted by engine speed sensor  1075 , the angle of crankshaft  1090 , which is recorded by crankshaft angle sensor  1085 , and the combustion chamber pressure, which is transmitted by sensor  1080 , and stores them in the volatile memory in control device  1005 , for example. Moreover, determination unit  1025  determines the resulting indicated work and an associated actual injection quantity Q actual . The resulting indicated work for a working cycle is calculated, for instance as integral of the combustion chamber pressure over the crank angle during the working cycle. Determination unit  1025  determines actual injection quantity Q actual  from the resulting indicated work and the engine speed of internal combustion engine  1000 , for example with the aid of a characteristics map that represents the relationship between resulting indicated work, the engine speed of internal combustion engine  1000 , and injection quantity Q. 
     The characteristics map for internal combustion engine  1000  is determined on a test stand during an application phase in that individual operating points having a specific engine speed of internal combustion engine  1000  and different resulting indicated works of internal combustion engine  1000  are set to stationary, and the associated injection quantity Q per working cycle is measured with the aid of a flow rate measuring device. The operating points are set at equidistant increments with respect to one another, for example. The characteristics map determined in this manner is stored in determination unit  1025 , for instance in the non-volatile memory in control device  1005 . 
     Comparison unit  1030  performs comparison operations between setpoint injection quantity Q setpoint  transmitted by second input unit  1015 , and actual injection quantity Q actual  transmitted by determination unit  1025 . 
     Because of the non-linearities in the injection behavior of an individual fuel injector  1045 , especially in first range  202 , shown in  FIG. 2  in second relationship  201  by way of example, the precision of the metering of the injected fuel that is required in order to implement the homogenous combustion method having self-ignition will not be reached if only first relationship  204  from  FIG. 2  is utilized to calculate electric control period T i  of fuel injector  1045 . To obtain the required precision in the metering of the injection quantities, the actuating variable of fuel injector  1045  is corrected with the aid of suitable first correction factors K 1   corr , and fuel injector  1045  is calibrated in this manner. 
     This calibration is described in greater detail in the following text and makes it possible, for instance, to compensate for the influences of the deviation between the actual opening period of fuel injector  1045  and electric control period T i  caused by manufacturing tolerances, installation-related tolerances, the effects of aging and/or drift on the precision of the metering of injection quantities Q injected by fuel injector  1045 . 
     A first specific embodiment will now be described on the basis of the flow chart from  FIG. 4 . 
     The program begins after the start of internal combustion engine  1000 . The method according to the present invention may be terminated at any time, for example by turning off control device  1005  of internal combustion engine  1000 . The steps towards this end are known to one skilled in the art and are not described here in greater detail. 
     Following the start of the program, an injection quantity Q driver  desired by the driver is determined in a step  400  in the manner known to one skilled in the art, such as, for example, from the accelerator position in the case of a motor vehicle. 
     The method then branches to a program point  405 . 
     In step  405  it is checked whether a suitable driving situation is at hand. If a suitable driving situation is present, then branching to step  410  takes place. If not, branching to step  407  occurs. A suitable driving situation exists, for instance, whenever internal combustion engine  1000  is operated at an approximately constant engine speed other than zero, in such a way that an approximately constant torque is available at crankshaft  1090 . 
     In step  407  it is checked, in a manner known to one skilled in the art, whether the number of operating hours is less than second threshold value BET, e.g., 10 hours. If yes, then branching to a step  445  takes place. If no, branching to a step  409  occurs. 
     In step  409 , status bit SKAL of each first correction factor k 1   corr  is set to FALSE in the third data area of the non-volatile memory in control device  1005  in a manner known to one skilled in the art. Moreover, second threshold value BET is increased by a predefined first amount, such as 10 hours, for instance. Next, branching to step  405  takes place. 
     In step  445 , setpoint injection quantity Q setpoint  is set to equal injection quantity Q driver  requested by the driver. The method then branches to a program point  447 . 
     In step  447 , first relationship  204  and first correction characteristics curve  301  are read out from the non-volatile memory in control device  1005 , for example. The method then branches to a step  450 . 
     In step  450 , linear electric control period T lin  is determined from setpoint injection quantity Q setpoint  with the aid of first relationship  204 , using interpolation, for instance. The method then branches to a step  455 . 
     In step  455 , first correction factor k 1   corr  is determined from linear electric control period T lin  with the aid of first correction characteristics curve  301 , using interpolation, for instance. The method of the present invention then continues with a step  460 . 
     In step  460 , the setpoint value for electric control period T i  is determined by multiplying linear electric control period T lin  by first correction factor k 1   corr . The method then branches to a step  465 . 
     In step  465 , fuel injector  1045  is triggered according to the setpoint value for electric control period T i . Next, branching to step  405  takes place. 
     In step  410 , setpoint injection quantity Q setpoint  is determined from injection quantity Q driver  requested by the driver. Within the specific value range of all injection quantities Q able to be realized by fuel injector  1045 , such as from 0 to 25 mg, for instance, setpoint injection quantity Q setpoint  assumes only predefined values for injection quantity Q. 
     The number of predefined values for injection quantity Q is specified by the resolution of first relationship  204 . The resolution is selected prior to the start of the method, for instance as a function of the non-volatile memory in control device  1005  available for storing first relationship  204  and first correction characteristics curve  301 . The increments between the predefined values for injection quantity Q are freely variable. Depending on the desired resolution, for example, the predefined values for injection quantity Q are subdivided in equidistant increments across the specific value range of all injection quantities able to be realized by fuel injector  1045 . At a desired resolution of 1 mg, for example, 26 interpolation points are equidistantly distributed in the specific value range of 0 mg to 25 mg, with increments of 1 mg. 
     As an alternative, it is possible to select smaller increments in order to obtain greater resolution in areas of second relationship  201  that are more heavily non-linear. Larger increments may be selected in the approximately linear areas of second relationship  201 , for example, in order to use less memory space in the non-volatile memory in control device  1005 . 
     From injection quantity Q driver  desired by the driver, setpoint injection Q setpoint  is then determined in that the particular predefined value for injection quantity Q that comes closest the injection quantity Q driver  is selected from the specific value range of all injection quantities Q able to be realized by fuel injector  1045 , for instance by commercial rounding. If, for instance, 5.5 mg is determined as injection quantity Q driver , then setpoint injection quantity Q setpoint =6 mg is specified if the next-closest predefined values for injection quantity Q are 5 mg and 6 mg. 
     Via first relationship  204 , predefined values of electric control period T i  are assigned to the predefined values for injection quantity Q. The predefined values for electric control period T i  corresponding to the predefined values for injection quantity Q form the x-interpolation points of first correction characteristics curve  301  of  FIG. 3 . 
     The method then branches to a program point  411 . 
     In step  411 , first relationship  204  is read out of the non-volatile memory in control device  1005 . The method then branches to a step  415 . 
     In step  415 , linear electric control period T lin  is determined from the predefined value for injection quantity Q with the aid of first relationship  204 . The method then branches to a step  416 . 
     In step  416 , the status of status bit SKAL for first correction factor k 1   corr  assigned to linear electric control period T lin  via first correction characteristic curve  301  is read out of the third data area of the non-volatile memory in control device  1005 . The method then branches to a step  417 . 
     In step  417  it is checked whether the status of status bit SKAL equals TRUE for first correction factor k 1   corr  assigned to the predefined value for injection quantity Q. If this is the case, branching to step  407  takes place. Otherwise, the method branches to a step  418 . 
     In step  418 , the setpoint value for electric control period T i  is determined as a function of linear electric control period T lin  and first correction factor k 1   corr , in the following manner:
 
 T   i   =T   lin   *K 1 korr ( T   lin ).
 
     The method of the present invention then continues with a step  420 . 
     In step  420 , fuel injector  1045  is triggered using a setpoint value for a current signal, for instance, which value corresponds to electric control period T i  from step  418 . The method then branches to a step  425 . 
     In step  425 , the resulting indicated work is calculated in the manner known to one skilled in the art, for instance as integral of the combustion chamber pressure over the crank angle during the working cycle in which the control in step  420  took place. To this end, the combustion chamber pressure is recorded continually and stored in the volatile memory in control device  1005  to calculate the integral, for instance in a variable. The method then branches to a step  430 . 
     In step  430 , associated actual injection quantity Q actual  is determined from the resulting indicated work and the engine speed of internal combustion engine  1000 , for example with the aid of a characteristics map that represents the relationship between resulting indicated work, the engine speed of internal combustion engine  1000 , and injection quantity Q. An average value of the rotational speed of internal combustion engine  1000  during the working cycle, for instance, is determined as rotational speed in a manner known to one skilled in the art. The method then branches to a step  435 . 
     In step  435 , first correction factor k 1   corr  is determined as a function of the comparison result of the comparison between setpoint injection quantity Q setpoint  from step  410 , and actual injection quantity Q actual  from step  430 , for instance as quotient, according to the following formula:
 
 K 1 corr   =Q   Setpoint   /Q   actual  
 
     This first correction factor K 1   corr  is stored in correction unit  1035  in the non-volatile memory in control device  1005  as part of first correction characteristics curve  301 . The status of the associated status bit is set to TRUE. The method is then continued by step  405 . 
     A second specific embodiment differs from the first specific embodiment in that, in step  410 , setpoint injection quantity Q setpoint  is subdivided into a basic injection quantity Q basic  and a measured injection quantity Q meas . 
     Measured injection quantity Q meas  is determined in such a way that it corresponds to one of the predefined values for injection quantity Q from the specific value range of all possible injection quantities Q able to be realized by fuel injector  1045 , for example from 0 mg to 25 mg. For measured injection quantity Q meas , for instance, the smallest predefined value for injection quantity Q is selected from first range  202  of smaller injection quantities, for which no first correction factor k 1   corr  has yet been determined. To this end, status bits SKAL of each first correction factor k 1   corr  are evaluated in the manner known to one skilled in the art. 
     Basic injection quantity Q basic  is determined by subtracting measured injection quantity Q meas  from setpoint injection quantity Q setpoint , for example. The method then branches to a step  411 . 
     In step  415 , in contrast to the first specific embodiment, a first basic setpoint actuating variable, in particular an electric control period T basic , for fuel injector  1045  is determined from the basic injection quantity Q basic  and as a function of the linear, electric control period T lin  and first correction factor k 1   corr , the determination being implemented in the following manner.
 
 T   basic   =T   lin ( Q   basic )* K 1 corr ( T   lin ( Q   basic )).
 
     From measured injection quantity Q meas , a measured setpoint actuating variable, in particular a second electric control period T meas , is determined as a function of first relationship  204  between injection quantity Q and electric control period T i  and as a function of linear electric control period T lin  and first correction factor k 1   corr , the determination being implemented in the following manner.
 
 T   meas   =T   lin ( Q   meas )* K 1 corr ( T   lin ( Q   meas ))
 
     Steps  416 ,  417  and  418  are omitted in the second specific embodiment. 
     In step  420 , which follows step  415 , fuel injector  1045 —in contrast to the first specific embodiment—is triggered using a first actuating variable corresponding to first electric control period T basic , and a second actuating variable corresponding to second electric control period T meas , in a manner known to one skilled in the art, in such a way that both injections do not overlap and take place in the same working cycle, e.g., during the intake stroke and/or during the compression stroke. 
     Steps  425  and  430  do not differ from the first specific embodiment. 
     In step  435 , in contrast to the first specific development, first correction factor k 1   corr  is formed as a function of the comparison result as quotient between a difference from setpoint injection quantity Q setpoint  and basic injection quantity Q basic  on the one hand, and a difference between actual injection quantity Q actual  derived from the resulting indicated work, and basic injection quantity Q basic  on the other hand. The quotient is calculated according to the following formula, for instance:
 
 K 1 corr =( Q   setpoint   −Q   basic )/( Q   actual   −Q   basic ).
 
     In this context it is assumed that basic injection quantity Q basic  has actually been injected via the electric control period T basic  specified by first relationship  204 , and that the difference from setpoint injection quantity Q setpoint  and actual injection quantity Q actual  was caused by variances of measured injection quantity Q meas  as a result of manufacturing tolerances or aging effects of fuel injector  1045 , for example. First correction factor k 1   corr  determined in this manner is once again stored in the non-volatile memory in control device  1005  as part of first correction characteristics curve  301 . The method then continues with step  405 . 
     In a third specific embodiment, in contrast to the second specific embodiment, a single setpoint value for electric control period T i  of fuel injector  1045  is determined from setpoint injection quantity Q setpoint  during the initial pass through step  410 . 
     Then, steps  420  through  430  are run though, and the resulting indicated work determined during the first pass through step  430  is stored in the volatile memory in control device  1005 , for instance as variable, for the further course of the method. 
     Step  435  is omitted in the first run-through, and the method continues with step  410 . 
     In the second pass through step  410 , setpoint injection quantity Q setpoint  is then split up, as described in the second specific embodiment, into a basic injection quantity Q basic  and a measured injection quantity Q meas . 
     In step  415 , in contrast to the second specific embodiment, a third electric control period T elin  is determined in addition, as a function of first relationship  204  between injection quantity Q and electric control period T i , in the following manner.
 
 T   elin   −T   lin ( Q   meas ).
 
     Steps  416  through  425  do not differ from the second specific development. 
     Step  430  differs from the second specific embodiment in that in this instance only the resulting indicated work is determined while the determination of actual injection quantity Q actual  is dispensed with. 
     Step  435  differs from the second specific embodiment in that the resulting indicated work previously stored in the first run-through of step  430  is forwarded to a controller as expected value. A measured actuating variable, in particular second opening duration T meas , is then corrected by the output of the controller in such a way that the resulting indicated work lies within a predefined tolerance range around the expected value for the indicated work. The tolerance range is appropriately selected for the particular type of valve on a test stand prior to implementing the method according to the present invention, or it is selected as zero. A corrected measured actuating variable obtained in this manner, in particular a corrected second electric control period T corr , is used to correct first relationship  204  from  FIG. 2 . First correction factor k 1   corr  is calculated as a function of the correction result, as quotient from the corrected second electric control period T corr , found by the control, and third electric control period T elin  associated with measured injection quantity Q meas , the calculation being implemented in the following manner:
 
 K 1 corr   =T   corr   /T   elin  
 
     This first correction factor k 1   corr  once again is stored in the non-volatile memory in control device  1005  as part of first correction characteristics curve  301 . The method then continues with step  405 . 
     In a fourth specific embodiment, if internal combustion engine  1000  includes a plurality of combustion chambers  1040 , then one of the aforementioned specific embodiments is implemented in modified form for each combustion chamber  1040  either alternatively or additionally. 
     In the case of an internal combustion engine  1000  having four combustion chambers  1040 , for instance, combustion chambers  1040  of internal combustion engine  1000  are denoted by an index i=1, 2, 3, 4. For instance, to calibrate fuel injectors  1045 , one of the aforementioned specific developments is analogously applied to each combustion chamber  1040  individually and all fuel injectors  1045  of all combustion chambers  1040  sequentially, for instance starting with combustion chamber  1040 , denoted by 1, of internal combustion machine  1000 , for example in the sequence i=1, 2, 3, 4. To this end, index i is stored in the non-volatile memory in control device  1005  as variable, for instance, and the aforementioned specific embodiment is repeated as a function of index i in the manner known to one skilled in the art until all fuel injectors  1045  of all combustion chambers have been calibrated. The exemplary embodiments and/or exemplary methods of the present invention is not restricted to the sequence 1, 2, 3, 4. The method according to the present invention is applied analogously in any other sequence or if not all combustion chambers  1040  of internal combustion engine  1000  are to be calibrated. 
     In addition, in a modification of the fourth specific embodiment, an individual setpoint injection Q ind  (i) is determined in step  410  as a function of the injection quantity Q driver  desired by the driver. For example, injection quantity Q driver  desired by the driver is first distributed to individual combustion chambers  1040  in such a way that the same individual setpoint injection Q ind  (i) is provided for each combustion chamber  1040 . For instance, the individual setpoint injections Q ind  (i) for an internal combustion engine  1000  having four combustion chambers  1040  are determined in the following manner:
 
 Q   ind (1)= Q   ind (2)= Q   ind (3)= Q   ind (4)=¼ *Q   driver .
 
     For instance, injection quantity Q driver =45.2 mg desired by the driver for combustion engine  1000  having four combustion chambers  1040  is distributed to the four combustion chambers  1040  of internal combustion engine  1000  in such a way that individual setpoint injection Q ind  (i) amounts to Q ind  (i)=11.3 mg for each combustion chamber  1040 . 
     Then, in an additional step, the particular combustion chamber  1040  in which the calibration of fuel injector  1045  is to take place is selected from among all combustion chambers  1040  disposed in internal combustion engine  1000 . For example, combustion chamber  1040  designated by index i=1 is selected first. 
     Then, setpoint injection Q setpoint  (i) is determined as a function of injection quantity Q driver  for the particular combustion chamber  1040  in which the calibration of fuel injector  1045  is carried out. The determination takes place as described in step  410  of the first specific embodiment; in this instance, however, instead of injection quantity Q driver  desired by the driver, individual setpoint injection Q ind  (i) in which the calibration of fuel injector  1045  is taking place is used for combustion chamber  1040 . For individual setpoint injection Q ind (1)=11.3 mg, for instance, setpoint injection Q setpoint (1)=11 mg is determined for combustion chamber  1040  designated by index i=1. 
     In an additional step, a difference deltaQ between individual setpoint injection Q ind  (i) and setpoint injection Q setpoint  (i) is then determined for combustion chamber  1040  in which the calibration of fuel injector  1045  is taking place. For example, difference deltaQ between setpoint injection Q setpoint  (1) and individual setpoint injection Q ind  (1) amounts to deltaQ=11.3 mg−11 mg=0.3 mg. 
     In an additional step, setpoint injection Q setpoint  (i) of combustion chambers  1045  in which no calibration of fuel injector  1045  is taking place, is then determined as a function of difference deltaQ and individual setpoint injection Q ind  (i). The difference deltaQ is added in equal parts, for instance, to individual setpoint injection Q ind  (i) of combustion chambers  1040  in which no calibration of fuel injector  1045  is taking place, in order to determine setpoint injection Q setpoint  (i) in this manner:
 
 Q   setpoint ( i )= Q   ind ( i )+delta Q /(number of combustion chambers 1040−1)
 
     For example, setpoint injections Q setpoint  (i) of combustion chambers  1040  in which no calibration of fuel injector  1045  is taking place, are determined in the following manner:
 
 Q   setpoint (2)= Q   ind (2)+delta Q/ 3=11.3 mg+0.1 mg=11.4 mg,
 
 Q   setpoint (3)= Q   ind (3)+delta Q/ 3=11.3 mg+0.1 mg=11.4 mg,
 
 Q   setpoint (4)= Q   ind (4)+delta Q/ 3=11.3 mg+0.1 mg=11.4 mg,
 
     In this way the entire injection quantity Q driver  desired by the driver is implemented as an average value across all combustion chambers  1040 , so that an abrupt change in the torque available at crankshaft  1090  is avoided. 
     The exemplary embodiments and/or exemplary methods of the present invention is explained using the example of internal combustion engine  1000  having direct gasoline injection shown in  FIG. 1 , and a combustion method having a homogenous air-fuel mixture and self-ignition. In the same way, the exemplary embodiments and/or exemplary methods of the present invention is able to be used for homogenous and stratified charge combustion methods with externally supplied ignition, such as with the aid of a spark plug. 
     In the exemplary embodiment, the determination of the actually resulting indicated work is described with the aid of the evaluation of the combustion chamber pressure. Other methods for determining the actually resulting indicated work, for instance using a torque sensor or engine speed evaluation, are possible as well. The resulting indicated work is determined from the combustion chamber pressure; the combustion chamber pressure is not measured by combustion chamber pressure sensors, but determined as a function of the torque or the acceleration of crankshaft  1090  in the manner known to one skilled in the art. In the case of the torque sensor, the combustion chamber pressure is determined as a function of the torque in the manner known to one skilled in the art. Apart from frictional losses, the torque is approximately proportional to the combustion chamber pressure. In the case of an engine speed evaluation, an acceleration of crankshaft  1090  is determined from a torque balance at crankshaft  1090  in a time window around the time of combustion in combustion chamber  1040  in which the calibration of fuel injector  1040  is taking place. The acceleration of crankshaft  1090  is proportional to the resulting indicated work in combustion chamber  1040  and is determined in a manner known to one skilled in the art. The method according to the present invention is then applied accordingly. 
     Implementing the method according to the present invention on a test stand makes it possibly to maintain a constant engine speed of internal combustion engine  1000  and a constant torque at crankshaft  1090 , so that all interpolation points of entire valve characteristics curve  201  are able to be determined successively in an uncomplicated manner. 
     For example, the method described in the exemplary embodiment is implemented in an especially simple manner as a computer program which realizes all of the steps from the flow chart illustrated in  FIG. 4 . This computer program is developed on a workstation computer outside of control device  1005 , for example, an then installed in control device  1005  with the aid of a computer program product containing the program code, for instance in the form of a machine-readable carrier such as a non-volatile memory. The computer program product is then implemented in control device  1005  by first input unit  1010 , second input unit  1015 , and third input unit  1020 , determination unit  1025 , comparison unit  1030 , and correction unit  1035 , when internal combustion engine  1000  is operated.