Abstract:
The invention relates to a method for the cylinder-selective control of an air/fuel mixture to be burnt in a multi-cylinder internal combustion engine, in which the lambda values for different cylinders or groups of cylinders are separately sensed and controlled, and also relates to a multi-cylinder internal engine suitable for carrying out the method. In accordance with the invention, the lambda values of the individual cylinders or groups of cylinders are simultaneously controlled to different required values using an integrating I-control proportion with variable integrator slope and/or a differentiating D-control proportion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is the US National Stage of International Application No. PCT/EP2006/050741, filed Feb. 8, 2006 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2005 009 101.6 filed Feb. 28, 2005, both of the applications are incorporated by reference herein in their entirety. 
   FIELD OF THE INVENTION 
   The invention relates to a method and device for determining a corrective value used for influencing an air/fuel ratio in a respective cylinder of an internal combustion engine comprising a number of cylinders, injection valves that are assigned to the cylinders and apportion fuel, and an exhaust gas probe, which is disposed in an exhaust manifold and the test signal of which is characteristic of the air/fuel ratio in the respective cylinder. 
   BACKGROUND OF THE INVENTION 
   Ever stricter legal requirements relating to admissible pollutant emissions from motor vehicles, in which internal combustion engines are arranged, require maintaining the pollutant emissions as low as possible during operation of the internal combustion engine. This can occur on the one hand by reducing the pollutant emissions, which are produced during the combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, exhaust gas after treatment systems are used in internal combustion engines, which convert the pollutant emissions which are generated during the combustion process of the air/fuel mixture in the respective cylinders, into harmless substances. To this end, exhaust gas catalytic converters are used, which convert carbon monoxide, carbon dioxide and nitrogen oxide into harmless substances. Both the targeted influencing of the generation of pollutant emissions during the combustion as well as the conversion of the pollutant components at a high level of efficiency by means of an exhaust gas catalytic converter require a very precisely adjusted air/fuel ratio in the respective cylinder. 
   DE 199 03 721 C1 discloses a method for an internal combustion engine having a number of cylinders for the cylinder-selective control of an air/fuel mixture to be combusted, wherein the lambda values for different cylinders or cylinder groups are identified and controlled separately. To this end, a probe evaluation unit is provided, in which a time-resolved evaluation of the exhaust gas probe signal is carried out and a cylinder-selective lambda value is thus determined for each cylinder of the internal combustion engine. An individual controller is assigned to each cylinder, said controller being embodied as a PI or PID controller, the control variable of which is a cylinder-specific lambda value and the command variable of which is a cylinder-specific target value of the lambda. The actuating variable of the respective controller then influences the injection of fuel in the respectively assigned cylinder. 
   SUMMARY OF INVENTION 
   The object of the invention is to create a method and a device for determining a corrective value used for influencing an air/fuel ratio, which enable/s a precise determination of the corrective value and therefore a precise control of an internal combustion engine. 
   The object is achieved by the features of the claims. 
   The invention is characterized by a method and a corresponding device for determining a corrective value used for influencing an air/fuel ratio in a respective cylinder of an internal combustion engine comprising a number of cylinders. Injection valves which apportion fuel are assigned to the cylinders. An exhaust gas probe is disposed in an exhaust manifold. Its test signal is characteristic of the air/fuel ratio in the respective cylinder. The test signal is detected at a predetermined sampling crankshaft angle, relative to a reference position of the piston of the respective cylinder, and assigned to the respective cylinder. A control value used to influence the air/fuel ratio in the respective cylinder is determined by means of a controller in each instance as a function of the test signal detected for the respective cylinder. 
   A first adaptive value is determined as a function of the control value if predetermined first conditions are fulfilled, including a predetermined first temperature range of a temperature, which is representative of a temperature of the respective injection valve. 
   A second adaptive value is determined as a function of the control value if predetermined second conditions are fulfilled, including a predetermined second temperature range of the temperature, which is representative of the temperature of the respective injection valve. The corrective value for influencing the air/fuel ratio in the respective cylinder is determined as a function of the first and/or second adaptive value as a function of the temperature, which is representative of the temperature of the respective injection valve. The first and second temperature ranges preferably have no mutual overlapping region. The temperature can be an injection valve temperature for instance or also a coolant temperature. 
   In accordance with the invention, the corrective value which applies to the respective cylinder can be very precisely determined, which is in particular especially advantageous if injection characteristics of the different injection valves change as a function of the temperature of the respective injection valves. This is particularly relevant in conjunction with injection valves with piezo actuators. 
   According to an advantageous embodiment of the invention, an upper temperature limit value of the first temperature range is smaller than a catalytic converter start temperature value of the temperature, which is representative of the temperature of the respective injection valve, with the catalytic converter start temperature value being characteristic of a temperature-related operational readiness of the exhaust gas catalytic converter. The catalytic converter start temperature value of the temperature is representative of the temperature of the respective injection valve if the operational readiness of the exhaust gas catalytic converter is achieved. 
   This is advantageous in that a separate, first adaptive value is determined in particular during cold operation of the internal combustion engine and thus in the event that the corrective value is used to control the internal combustion engine already at a very early point in time in respect of the start of the internal combustion engine, a very precise cylinder-specific adjustment of the air/fuel ratio is possible in the respective cylinders. This can thus effect the pollutant emissions generated by the internal combustion engine during cold operation in a particularly advantageous manner and can thus contribute significantly to reducing emissions, since in the case of a still cold operation of the internal combustion engine, no or only an insignificant conversion of the pollutants can be carried out by means of the exhaust gas catalytic converter of the internal combustion engine. 
   According to a further advantageous embodiment of the invention, the corrective value is determined by a predetermined weighting of the first and second adaptive value, if the temperature, which is representative of the temperature of the respective injection value, lies between the first and second temperature ranges. In this way, when the weighting is suitably predetermined, the corrective value can also be very precisely determined between the first and second temperature range with only minimal adaptive values, such as the first and second adaptive value. 
   In a further advantageous embodiment of the invention, a third or further adaptive values are determined as a function of the control value if predetermined third or further conditions are fulfilled, which include a predetermined third or further temperature ranges of the temperature, which is representative of the temperature of the respective injection valve. The corrective value used for influencing the air/fuel ratio in the respective cylinder is then determined as a function of the third and/or further adaptive values as a function of the temperature, which is representative of the temperature of the respective injection valve. In this way, an even more precise determination of the corrective value can thus be carried out for instance. 
   In this context, it is advantageous if an upper temperature limit value of the third or further temperature ranges is smaller than the catalytic converter start temperature value of the temperature, which is representative of the temperature of the respective injection value. In this way, particularly with the use of the corrective value for controlling an internal combustion engine, the pollutant emissions are very significantly reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are described in more detail below with reference to the schematic drawings, in which; 
       FIG. 1  shows an internal combustion engine with a control device 
       FIG. 2  shows a block diagram of the control device 
       FIGS. 3 and 4  show flow diagrams of programs, which are processed in the control device, and 
       FIG. 5  shows a temperature-dependent curve of the first and second weighting values. 
   

   Elements of the same design or function are characterized across all the figures with the same reference character. 
   DETAILED DESCRIPTION OF INVENTION 
   An internal combustion engine ( FIG. 1 ) comprises an intake manifold  1 , an engine block  2 , a cylinder head  3 , and an exhaust manifold  4 . The intake manifold  1  preferably comprises a throttle valve  5 , also an accumulator  6  and an intake manifold  7 , which is guided to a cylinder Z 1  via an inlet channel into the engine block  2 . The engine block  2  also comprises a crankshaft  8 , which is coupled to the piston  11  of the cylinder Z 1  by way of a connecting rod  10 . 
   The cylinder head  3  comprises a valve mechanism having a gas inlet valve  12  and a gas outlet valve  13 . The cylinder head  3  also comprises an injection valve  18  and a spark plug  19 . Alternatively, the injection valve  18  can also be arranged in the induction manifold  7 . 
   An exhaust gas catalytic converter, which is embodied as a three-way catalytic converter  21 , is arranged in the exhaust gas manifold  4 . Furthermore, a further exhaust gas catalytic converter is also preferably arranged in the exhaust gas manifold, which is embodied as a NOx catalytic converter  23 . 
   A control device  25  is provided, to which sensors are assigned, which detect different measured variables and determine the value of the measured variables in each instance. The control device  25  determines actuating variables as a function of at least one of the measured variables, said actuating variables then being converted into one or a number of control signals for controlling the control elements by means of corresponding actuators. The control device  25  can also be referred to as a device for controlling the internal combustion engine or as a device for determining a corrective value. 
   The sensors are a pedal position sensor  26 , which detects the position of an accelerator  27 , an air mass sensor  28 , which detects an air mass flow upstream of the throttle valve  5 , a first temperature sensor  32 , which detects an intake air temperature, an induction manifold pressure sensor  34 , which detects an induction manifold pressure in the accumulator  6 , a crankshaft angle sensor  36 , which detects a crankshaft angle, to which is then assigned a rotary speed N. Furthermore, a second temperature sensor  38  is provided, which detects a coolant temperature TCO. Furthermore, a further temperature sensor is arranged in the injection valve  18 , said temperature sensor detecting the injection valve temperature. If the injection valve  18  includes a piezo actuator, this can then form the further temperature sensor. 
   Furthermore, a first exhaust gas probe  42  is provided, which is arranged upstream of the three-way catalytic converter  21  and which detects a residual oxygen content of the exhaust gas and the test signal MS 1  of which is characteristic of the air/fuel ratio in the combustion chamber of the cylinder Z 1  and upstream of the first exhaust gas probe, prior to oxidation of fuel, referred to below as the air/fuel ratio in the cylinders Z 1 -Z 4 . Furthermore, a second exhaust gas probe  43  is provided, which is arranged downstream of the three way catalytic converter  21  and which detects a residual oxygen content of the exhaust gas and the test signal of which is characteristic of the air/fuel ratio in the internal combustion chamber of the cylinder Z 1  and upstream of the second exhaust gas probe  43  prior to oxidation of the fuel, referred to below as the air/fuel ratio downstream of the exhaust gas catalytic converter. 
   The first exhaust gas probe  42  is preferably a linear lambda probe. The second exhaust gas probe  43  is a binary lambda probe. It may however also be a linear lambda probe. 
   Depending on the embodiment of the invention, any arbitrary subset if the said sensors may be available or additional sensors may also be present. 
   The control elements are the throttle valve  5  for instance, the gas inlet and gas outlet valves  12 ,  13 , the injection valve  18  or the spark plug  19 . 
   Aside from cylinder Z 1 , further cylinders Z 2  to Z 4  are still also provided, to which corresponding control elements and if necessary sensors are also assigned. 
   Blocks of the control device  25  which are relevant to the invention are shown with reference to the block diagram in  FIG. 2 . 
   A block B 1  corresponds to the internal combustion engine. The test signal MS 1  emitted by the exhaust gas probe  42  is routed to a block B 2 . In block B 2 , an assignment of the test signal MS 1  of the first exhaust gas probe  42 , which is current at this time instant, to the respective cylinder-specifically detected air/fuel ratio LAM_I [Z 1 -Z 4 ] is carried out at each determined sampling crankshaft angle CRK_SAMP relative to a reference position of the respective piston  11  of the respective cylinder Z 1 -Z 4 . The reference position of the respective piston  11  is preferably its upper dead center. 
   In a block B 3 , an average air/fuel ratio LAM_MW is determined by averaging the cylinder-specifically detected air/fuel ratio LAM_I[Z 1 -Z 4 ]. Furthermore, in block B 3 , a cylinder-specific air/fuel ratio deviation D_LAM_I[Z 1 -Z 4 ] is determined. This is then fed to block B 4 . The block B 4  comprises a controller, the output variable of which is a control value RW[Z 1 -Z 4 ] used for influencing the air/fuel ratio in the respective cylinder Z 1 -Z 4 . The controller comprises an integral component, it can however also comprise a so-called I 2 -component or proportional component. The controller of the block B 4  can also be referred to as a cylinder-specific lambda controller. 
   A block B 5  is designed to determine a first, second or further adaptive values AD 1 [Z 1 -Z 4 ], AD 2 [Z 1 -Z 4 ], ADX[Z 1 -Z 4 ] and in fact as a function of a temperature, which is representative of the temperature of the respective injection valve  18 . The injection valve temperature TE is preferably supplied to the block B 5  as a temperature which is representative of the temperature of the respective injection valve  18 . Alternatively, also to this end, the coolant temperature TCO can be fed to block B 5  for instance. The block B 5  preferably comprises a program, which is described in more detail below with reference to  FIG. 3 . 
   Block B 6  is designed to determine a corrective value LAM_FAC_I[Z 1 -Z 4 ] and in fact as a function of the first, second or further adaptive value AD 1 [Z 1 -Z 4 ], AD 2 [Z 1 -Z 4 ], ADX[Z 1 -Z 4 ], the temperature, which is representative of the temperature of the respective injection valve  18  and if necessary of the control value RW[Z 1 -Z 4 ]. The block B 6  preferably comprises a program, which is explained in more detail below with reference to  FIG. 4 . 
   A lambda controller is provided in block B 8 , the actuating variable of which is an air/fuel ratio LAM_SP which is predetermined for all cylinders Z 1 -Z 4  of the internal combustion engine and the control variable of which is the average air/fuel ratio LAM_MW. The control variable of the lambda controller is a lambda control-factor LAM_FAC_ALL. The lambda controller thus has the object of adjusting the predetermined air/fuel ratio, viewed across all cylinders of the internal combustion engine. 
   Alternatively, this can herewith also be achieved in that in block B 3 , the cylinder-specific air/fuel ratio deviation D_LAM_I is determined from the difference of the air/fuel ratio which is predetermined for all cylinders Z 1 -Z 4  of the internal combustion engine and of the cylinder-specific air/fuel ratio LAM_I[Z 1 -Z 4 ]. In this case, block B 8  can be omitted. 
   In block B 9 , a fuel quantity MFF to be apportioned is determined as a function of an air quantity MAF in the respective cylinder Z 1 -Z 4  and if necessary the speed N and the air/fuel ratio LAM_SP which is predetermined for all cylinders of the internal combustion engine. 
   At the multiplier point M 1 , a corrected fuel quantity MFF_COR to be apportioned is determined by multiplying the fuel quantity MFF to be apportioned, the lambda control factor LAM_FAC_ALL and the corrective value LAM_FA_I[Z 1 -Z 4 ]. A control signal is then generated as a function of the corrected fuel quantity MFF_COR to be apportioned, with which the respective injection valve  18  is controlled. 
   In addition to the controller structure illustrated in the block diagram in  FIG. 4 , corresponding controller structures B-Z 2  to B_Z 4  are provided for the respective further cylinders Z 2  to Z 4  for each further cylinder Z 1 -Z 4 . 
   A program for block B 5  is started in step S 1  (see  FIG. 3 ), in which variables can be initialized if necessary. 
   Step S 2  monitors whether a quasi-stationary operating status ST is present as the operating status BZ of the internal combustion engine. The quasi-stationary operating status ST can then be available for instance if the speed N is only subject to predetermined minimal fluctuations, with it being decisive in this content that respective exhaust gas packets, induced by the combustion of the air/fuel mixture in the respective cylinders Z 1 -Z 4 , can be assigned to the respective cylinder Z 1 -Z 4  with reference to the test signal MS of the first exhaust gas probe  42  with sufficient accuracy. 
   If the condition of step S 2  is not fulfilled, the processing is continued in step S 4 , in which the program is paused for a predetermined waiting time TW or is also paused for a predetermined crankshaft angle range, before the processing is continued again in step S 2 . 
   If the condition of step S 2  is contrastingly fulfilled, step S 6  monitors whether the injection valve temperature TE lies in a first temperature range TB 1 . The first temperature range TB 1  is thus predetermined such that its upper temperature limit is smaller than a catalytic converter start temperature value of the injection valve temperature. If the condition of step S 6  is fulfilled, the first adaptive value AD 1 [Z 1 -Z 4 ] is determined in step S 8  as a function of the current control value RW[Z 1 ]. This can be carried out for instance with the calculation specification specified in step S 8 , with e referring to a renewed factor, which is preferably smaller than 1. 
   If the condition of step S 6  is contrastingly not fulfilled, step S 10  monitors whether the current injection valve temperature TE lies within a second temperature range TB 2 . A lower temperature limit value of the second temperature range TB 2  is preferably predetermined such that it is larger than the catalytic converter start temperature value. The second temperature range can comprise the entire temperature range of the possible operating temperatures in a particularly simple manner, said overall temperature range being greater than the lower temperature limit value. 
   If the condition of step S 10  is fulfilled, the second adaptive value AD 2 [Z 1 ] is determined in step S 12  as a function of the current control value RW[Z 1 ]. This is carried out for instance according to the procedure of step S 8 . The processing is then continued in step S 4 . If the condition of step S 10  is not fulfilled, either the processing can be continued in step S 4  or an additional step S 14  can be provided, in which it is monitored whether the current injection valve temperature TE lies within a further temperature range. If the condition of step S 14  is then not fulfilled, the processing is continued in step S 4 . If the condition of step S 14  is then contrastingly fulfilled, the current control value RW[Z 1 ] is assigned in step S 16  to the further adaptive values ADZ[Z 1 ] according to the procedure of step S 8 . 
   A program for block B 6  is started in step S 20  ( FIG. 4 ), in which variables can be initialized if necessary. 
   Step S 22  monitors whether the current injection valve temperature TE lies in the first temperature range TB 1 . If this is the case, the first adaptive value AD[Z 1 ] is assigned to an adaptive value AD[Z 1 -Z 4 ] in step S 24 . If the condition of step S 22  is contrastingly not fulfilled, step S 26  monitors whether the injection valve temperature TE lies in the second temperature range TB 2 . If this is the case, the second adaptive value AD 2 [Z 1 ] is assigned to the adaptive value AD[Z 1 ] in step S 28 . 
   If the condition of step S 26  is contrastingly not fulfilled, the sum of a first and second term is assigned in step S 30  to the adaptive value AD[Z 1 ], with the first term being the product of a first weighting value W 1  and first adaptive value AD 1 [Z 1 ] and the second term being the product of the second weighting value W 2  and the second adaptive value AD 2 [Z 1 ]. In this case, if the condition of step S 26  is not fulfilled, the injection valve temperature TE is required to lie outside both the first and second temperature range TB 1 , TB 2 , but nevertheless between the first and second temperature ranges TB 1 , TB 2 . The first and second weighting values w 1 , w 1  are preferably predetermined as a function of the respective temperature, which is representative of the temperature of the respective injection valve, in other words the injection valve temperature TE for instance or, as is shown with reference to  FIG. 5 , the coolant temperature TCO. In this case, the injection valve temperature TE is replaced by the coolant temperature TCO in steps S 6 , S 10 , S 14 , S 22  and S 26 . 
   The correction value LAM_FAC_I[Z 1 ] is then determined in step S 32 . This is carried out as a function of the adaptive value AD[Z 1 ] and preferably also as a function of the control value RW[Z 1 ]. By way of example, the calculation can however be carried out in step S 32 , independent of the control value RW[Z 1 ], almost simultaneously with a start of the internal combustion engine, at which the exhaust gas probe  42  is not yet read for operation. By way of example, the adaptive value AD[Z 1 ] and the control value RW[Z 1 ] can be added in step S 22 . In step S 34 , the program subsequently pauses for the given waiting time T_W or the predetermined crankshaft angle. 
   Blocks B 5  and B 6  allow the strict emission limit values, particularly during cold start-up, to be guaranteed on the one hand. Furthermore, the driving behavior of the internal combustion engine during cold engine operation can however also be improved.