Patent Publication Number: US-2012041667-A1

Title: Device and method for operating an internal combustion engine, computer program, computer program product

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to selective control of injection valves of an internal combustion engine. 
     2. Description of Related Art 
     From published German patent application document DE 40 09 305, an electronic ignition control device is known in which ignition coils are used to produce ignition sparks at spark plugs in combustion chambers of an internal combustion engine. 
     From published German patent application document DE 39 02 254, a method is known for assigning ignition signals to a reference cylinder in which different signal levels of the main and supporting sparks, or the time shift between the beginning of the main and supporting sparks, are used for the assignment. For this purpose, frequency dividers are used that supply a signal via which the occurrence of the high-voltage pulses is inferred. 
     In other internal combustion engines having double-spark ignition systems, the recognition of the active cylinder takes place using a phase sensor that measures the position of the camshaft. 
     In low-cost internal combustion engines, double-spark ignition systems are often used, and the phase sensor is omitted in order to further reduce production costs. In such engines, the recognition of the active cylinder should take place as far as possible without the use of additional components such as the phase sensor or the frequency divider, in order to avoid additional production costs for these components. 
     BRIEF SUMMARY OF THE INVENTION 
     In comparison to the above, the device, the method, and the computer program product according to the present invention have the advantage that a first injection valve is used to inject fuel for combustion in a first combustion chamber and a second injection valve is used to inject fuel for combustion in a second combustion chamber,
         the internal combustion engine being operated in a first operating mode in which fuel is injected using the first and second injection valve,   a first operating characteristic of the internal combustion engine being determined during operation of the internal combustion engine in the first operating mode,   the internal combustion engine being operated in a second operating mode in which the injection of fuel by the first injection valve is suppressed,   a second operating characteristic of the internal combustion engine being determined during operation of the internal combustion engine in the second operating mode,   the first operating characteristic being compared to the second operating characteristic,   as a function of the result of the comparison, the internal combustion engine being operated in the second operating mode or in a third operating mode in which the injection of the fuel by the second injection valve is suppressed.       

     In an internal combustion engine having two cylinders situated in the same crankshaft plane, in this way in an internal combustion engine that in particular has double-spark ignition the cylinder in which a misfire has occurred is easily deactivated. Production costs are saved due to the omission of the additional components such as phase sensors or frequency dividers. If the phase sensor is provided for other reasons, the method according to the present invention can be used to operate the internal combustion engine even if the phase sensor is defective. 
     It is particularly advantageous if a changeover takes place from the first operating mode to the second operating mode as soon as, in the first operating mode, a plurality of misfires, in which the combustion of the fuel does not take place in the first and/or second combustion chamber, are recognized. Driver comfort is increased if the recognition is not activated until a misfire has actually been recognized in one of the two cylinders of the internal combustion engine. 
     It is particularly advantageous if the first and second operating characteristic is a signal that enables inference of the combustion or non-combustion of fuel in the combustion chambers. In this way, misfires can be recognized, and subsequently the combustion can be suppressed in the cylinder or cylinders in which the combustion did not take place or was incomplete. 
     It is particularly advantageous if the first and/or the second operating characteristic characterize a running smoothness of the internal combustion engine, a pressure in the combustion chamber, a vibration in a sealing gap between the cylinder head and the cylinder block, and/or an ion stream of an exhaust gas that results during combustion. The determination of the running smoothness by an increment sensor on a crankshaft of the internal combustion engine enables particularly simple determination of misfires using sensors already present in the internal combustion engine. If other sensors are already installed in the internal combustion engine, such as a combustion chamber pressure sensor, a knock sensor, or an ion stream sensor, the misfires are also determined particularly reliably by evaluating the signals thereof. 
     It is particularly advantageous if a first piston that limits the first combustion chamber and a second piston that limits the second combustion chamber are situated in the same plane of a crankshaft of the internal combustion engine. 
     This situation ensures robust operation of the internal combustion engine with double-spark ignition, even without a phase sensor or in case of failure of the phase sensor. 
     It is particularly advantageous if a first spark plug situated at the first combustion chamber and a second spark plug situated at the second combustion chamber are simultaneously ignited. The double-spark ignition is thus realized at particularly low cost for example by an individual ignition coil that simultaneously controls both spark plugs. 
     It is particularly advantageous if the first operating characteristic is determined while the first piston essentially outputs a torque contribution to the crankshaft, and the second operating characteristic is determined while the second piston essentially outputs a torque contribution to the crankshaft, or the first operating characteristic is determined while the second piston essentially outputs a torque contribution to the crankshaft and the second operating characteristic is determined while the first piston essentially outputs a torque contribution to the crankshaft. 
     In an internal combustion engine having camshaft drive and double-spark ignition, the cams of the camshaft are set in such a way that the second cylinder is in the intake stroke when the first cylinder is in the power stroke. In one working cycle of a four-stroke internal combustion engine, the crankshaft runs through an angular range of 0 to 720°. 
     In the process, both the first and the second cylinder each run through one power stroke and one intake stroke. However, due to the absence of the phase sensor, it is not possible to carry out a clear assignment of the strokes to particular crankshaft angles. For example, at a crankshaft angle of 0° the first cylinder may be either in the power stroke or in the intake stroke. Through the coding of a pole wheel provided for the determination of the segment times in an increment sensor, said wheel having for example 60-2 teeth, the position of the crankshaft is unambiguously assigned either to the power stroke or to the intake stroke. 
     If, for example, the crankshaft position of 0° is assigned to the position of the crankshaft in which 72° has already been moved through since recognition of the gap in the pole wheel, and if the first piston and the second piston are each at top dead center when this is the case, then the beginning of the power stroke or of the intake stroke is unambiguously assigned to crankshaft position 0° or 360°. 
     At these crankshaft angles, the first piston and the second piston are at top dead center. Here the length of the strokes is 180° of crankshaft angle. In order to determine the running smoothness of the internal combustion engine, the crankshaft angular range should be observed in which one of the two cylinders outputs a torque contribution to the crankshaft. 
     Thus, if the first time duration is determined in a crankshaft angular range of 0° to 180°, and the second time duration is determined in a crankshaft angular range from 360° to 540°, then the segment times for the two power strokes of the first and of the second cylinder are determined. 
     What is decisive for the running smoothness is the segment region in which a torque contribution is outputted to the crankshaft by the first cylinder or by the second cylinder. Thus, the segment region that is to be observed, and thus the first time duration and the second time duration, are not necessarily identical with the crankshaft angle of 0° to 180°, or 360° to 540°. Therefore, it is provided that the segments that are to be observed for the determination of the first and the second time duration are aligned with the beginning and ending of the power stroke of one of the cylinders. However, the observed angular segments can also be selected so as to differ from the beginning and ending of the power stroke, in the region in which the torque contribution of the first or of the second cylinder to the crankshaft is outputted. 
     It is particularly advantageous if the comparison takes place as a function of a difference or a ratio between the magnitude of the first operating characteristic and the magnitude of the second operating characteristic. In this way, the comparison is carried out particularly simply. 
     It is particularly advantageous if longer-term mean values, in particular averaged over more than three values, are used for the comparison. Through the use of the filter, the comparison is carried out particularly robustly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows an internal combustion engine. 
         FIG. 2  shows a flow diagram of an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an externally ignited internal combustion engine, for example a four-stroke spark-ignition engine having for example four cylinders and a double-spark ignition system, designated with reference character  100 . For the sake of clarity, only two of the cylinders are shown in  FIG. 1 . The method and the device according to the present invention are not limited to spark-ignition engines having four cylinders. The invention applies analogously to internal combustion engines having two or more cylinders. 
     Internal combustion engine  100  has for example four cylinders, of which  FIG. 1  shows a first cylinder  103  and a second cylinder  113 . First cylinder  103  encloses, with first piston  102 , a first combustion chamber  101 . First piston  102  is connected to a crankshaft  120  via a first connecting rod  121 . 
     Second cylinder  113  encloses, with second piston  112 , a second combustion chamber  111 . Second piston  112  is connected to crankshaft  120  via a second connecting rod  122 . 
     First connecting rod  121  and second connecting rod  122  are situated in the same plane as crankshaft  120 . This means that first connecting rod  121  and second connecting rod  122  are fastened to crankshaft  120  in such a way that first piston  102  and second piston  112  are simultaneously raised or lowered when crankshaft  120  rotates. Due to this synchronous movement of first piston  102  and second piston  112 , the two pistons simultaneously reach top dead center and bottom dead center. 
     In first cylinder  103  there are situated a first intake valve  104  and a first exhaust valve  105 . In second cylinder  113  there are situated a second intake valve  114  and a second exhaust valve  115 . The intake and exhaust valves are connected to crankshaft  120  for example via a camshaft that is not shown in  FIG. 1 . In a known manner, the intake and exhaust valves are opened or closed by the camshaft synchronously with the movement of the pistons of internal combustion engine  100 . 
     During a working cycle of first cylinder  103  and second cylinder  113 , crankshaft  120  goes through two rotations, corresponding to a crankshaft angular range of 0° to 720°. The working cycle of first cylinder  103  is here made up of a first intake stroke, a first compression stroke, a first power stroke, and a first exhaust stroke. The working cycle of second cylinder  113  is made up of a second intake stroke, a second compression stroke, a second power stroke, and a second exhaust stroke. Here the valve controlling via the camshaft is constructed or set in such a way that second cylinder  113  is always in the intake stroke when first cylinder  103  is in the power stroke. 
     The injection of fuel by a first injection valve  141  into a first intake pipe  143  creates a first fuel-air mixture that moves into first combustion chamber  101  through intake valve  104  during the first intake stroke. This first fuel-air mixture is compressed in combustion chamber  101  in the first compression stroke, and is ignited by a first spark plug  154 , for example shortly before first piston  102  reaches top dead center. 
     Thermal energy that results from the combustion of the first fuel-air mixture in the first power stroke is at least partly converted into mechanical energy by first piston  102 , and is transmitted to crankshaft  120  by first connecting rod  121 . 
     A first exhaust gas resulting from the combustion of the first fuel-air mixture is expelled through first exhaust valve  105  into a first exhaust pipe  106 , in the first exhaust stroke. 
     The injection of fuel by a second injection valve  142  into a second intake pipe  144  creates a second fuel-air mixture that moves into second combustion chamber  111  through second intake valve  114  in the second intake stroke. This second fuel-air mixture is compressed in combustion chamber  111  in the second compression stroke, and is ignited by a second spark plug  155 , for example shortly before second piston  112  reaches top dead center. 
     Thermal energy that results from the combustion of the second fuel-air mixture in the second power stroke is at least partly converted into mechanical energy by second piston  112 , and is transmitted to crankshaft  120  by second connecting rod  122 . 
     In the subsequent, second exhaust stroke, a second exhaust gas resulting from the combustion of the second fuel-air mixture is expelled through second exhaust valve  115  into a second exhaust pipe  116 . 
     Alternatively to a camshaft controlling, the controlling of the intake and exhaust valves can also take place using a variable valve drive. The method according to the present invention is then applied in an analogous manner. 
     The injection of the fuel by the injection valves can, in addition or alternatively, also take place directly into the combustion chambers of the cylinders. The method according to the present invention is then applied in an analogous manner. 
     As fuel, for example gasoline may be used. The method according to the present invention is applied in an analogous manner if, instead of gasoline, for example compressed natural gas or some other fuel is used. 
     The ignition of the first fuel-air mixture and of the second fuel-air mixture takes place for example using a double-spark ignition system. A double-spark ignition system is made up for example of first spark plug  154  and second spark plug  155 , which are connected to a common ignition coil. The ignition coils are for example made up of a primary coil  150  and a secondary coil  151  that are magnetically coupled. In addition, the ignition coil includes for example a first switch  152 , for example a transistor. Primary coil  150  is connected at the input side to battery voltage Ubat, and is connected at the output side to switch  152 . The switch is connected at the input side to primary coil  150  and is connected at the output side to ground. 
     An electrode of first spark plug  154  and an electrode of second spark plug  155  are also connected to ground. The second electrode of first spark plug  154  is connected to the first input of secondary coil  151 . The second electrode of second spark plug  155  is connected to the second input of secondary coil  151 . 
     If no ignition is to take place, switch  152  is closed, so that a current flows through coil  150 . At the time of ignition, switch  152  is opened and the flow of current through primary coil  150  is interrupted. Through this change of the flow of current, via secondary coil  151  an ignition voltage is induced that simultaneously causes a spark formation in first spark plug  154  and in second spark plug  155 . 
     If uncombusted first fuel-air mixture is present in compressed form in first combustion chamber  101 , the ignition spark in first spark plug  154  causes the ignition of the first fuel-air mixture. Otherwise, first cylinder  103  is in the exhaust stroke, and the ignition spark in spark plug  154  has no effect with respect to an ignition. The same holds correspondingly for second cylinder  113 . 
     The time of ignition is determined for example by a control device  160  situated in internal combustion engine  100 . 
     Alternatively, the time of ignition can also be produced by a signal of a Hall sensor situated on crankshaft  120 . Typically, the ignition time is selected such that the ignition takes place shortly before first piston  102  or second piston  112  reaches top dead center. 
     Control device  160  includes a first prespecification device  161 , a second prespecification device  162 , a third prespecification device  163 , an acquisition device  164 , and a calculating device  165 . 
     Acquisition device  164  acquires the signal of an increment sensor  170  that transmits signals to acquisition device  164  using a pole wheel situated on crankshaft  120 . For example, a pole wheel having 60-2 teeth is used in which the gap corresponding to two missing teeth is situated on crankshaft  120  in such a way that the gap is recognized by increment sensor  170  precisely at the point at which 72° of crankshaft angle still have to be moved through before first piston  102  and second piston  112  are at top dead center. 
     From the falling edges of the signal sent by increment sensor  170 , acquisition device  164  determines crankshaft angle KW, for example in a known manner. For example, crankshaft angle KW is determined in the range 0° to 720° for two rotations of crankshaft  120 . For example, the crankshaft angle of 0° is recognized precisely when 720° of crankshaft angle have been moved through, after the tooth gap of pole wheel  171  was recognized for the first time by increment sensor  170  when internal combustion engine  100  was started. Moreover, acquisition device  164  determines a first operating characteristic L 1  and a second operating characteristic L 2 . For this purpose, acquisition device  164  acquires a first segment time ts k  for the crankshaft angular range from 0° to 180°, and acquires a second segment time tsk+1 for the crankshaft angular range from 360° to 540°. 
     First operating characteristic L 1  and second operating characteristic L 2  are then for example determined as a function of first segment time ts k  and of second segment time ts k+1 , and the number z of cylinders of internal combustion engine  100  is determined for example according to the following equation: 
     
       
         
           
             
               L 
                
               
                   
               
                
               1 
             
             , 
             
               
                 L 
                  
                 
                     
                 
                  
                 2 
               
               = 
               
                 
                   
                     ts 
                     
                       k 
                       + 
                       1 
                     
                   
                   - 
                   
                     ts 
                     k 
                   
                 
                 
                   
                     
                       ( 
                       
                         z 
                         / 
                         2 
                       
                       ) 
                     
                     2 
                   
                   * 
                   
                     
                       ( 
                       
                         
                           
                             ts 
                             k 
                           
                           + 
                           1 
                           + 
                           
                             ts 
                             k 
                           
                         
                         2 
                       
                       ) 
                     
                     3 
                   
                 
               
             
           
         
       
     
     First operating characteristic L 1  and second operating characteristic L 2  characterize a smooth running operation of the internal combustion engine. Alternatively or in addition, instead of the signal of increment sensor  170 , a pressure in the combustion chamber, a vibration in an air gap between the cylinder head and the cylinder block, and/or an ion stream of an exhaust gas that arises during combustion may be used to determine first operating characteristic L 1  and second operating characteristic L 2 . 
     Acquisition device  164  transmits first operating characteristic L 1  and second operating characteristic L 2  to calculating unit  165 . 
     Calculating unit  165  compares first operating characteristic L 1  to second operating characteristic L 2 , for example as a function of the difference between the magnitude of first operating characteristic L 1  and the magnitude of second operating characteristic L 2 . Alternatively, a filter, for example a lowpass filter, is used that forms longer-term mean values, in particular averaged over more than three values. These mean values are used for the comparison. For example, a starting value of the filter is selected as a function of first operating characteristic L 1 , and an input value of the filter is selected as a function of second operating characteristic L 2 . The comparison is then carried out as a function of the change in the output of the filter. 
     For example, for the comparison it is checked whether the difference between the magnitude of first operating characteristic L 1  and the magnitude of second operating characteristic L 2  is smaller than a first threshold value S 1 . Alternatively, it is checked whether the change in an output signal of the filter is smaller than a second threshold value S 2 . 
     If the difference between the magnitude of first operating characteristic L 1  and the magnitude of second operating characteristic L 2  is greater than or equal to first threshold value S 1 , a misfire is recognized in one of the cylinders of internal combustion engine  100 . The same holds for the case in which the change in the output signal of the filter is greater than or equal to second threshold value S 2 . 
     Due to the symmetry of the piston movements of first piston  102  and second piston  112 , from the signal of increment sensor  170  it is not possible to distinguish which of the two cylinders is currently in the power stroke. Therefore, it also cannot be distinguished in which of the cylinders the recognized misfire has taken place. Through the additional installation of a phase sensor for acquiring the camshaft rotational angle, it is possible to determine the position of the camshaft, and thus also the cylinder index of the cylinder currently in the power stroke. In the case in which the signal of the phase sensor is interfered with, or a phase sensor is not installed for reasons of cost, this measured information is not available. Therefore, according to the present invention, calculating device  165  changes over from a first operating mode, in which injection takes place using first injection valve  141  and second injection valve  142 , to a second operating mode as soon as the misfire has been recognized. 
     In the second operating mode, the injection using first injection valve  141  is suppressed. For this purpose, calculating unit  165  determines a first quantity Z 1   AUS  and a second quantity Z 2   AUS . First quantity Z 1   AUS  is set to the value 0 if the injection is to take place using first injection valve  141 . First quantity Z 1   AUS  is set to the value 1 if the injection using first injection valve  141  is to be suppressed. Second quantity Z 2   AUS  is set to the value 0 if the injection is to take place using second injection valve  142 . Second quantity Z 2   AUS  is set to the value 1 if the injection using second injection valve  142  is to be suppressed. In the second operating mode, therefore, first quantity Z 1   AUS  is set to the value 1 and second quantity Z 2   AUS  is set to the value 0. 
     In a third operating mode, first quantity Z 1   AUS  is set to the value 0 and second quantity Z 2   AUS  is set to the value 1. In this way, in the third operating mode internal combustion engine  100  is operated in such a way that the injection by second injection valve  142  is suppressed. The use of the third operating mode is further described below. 
     First quantity Z 1  is communicated by calculating device  165  to first prespecification device  161  and to acquisition device  164 . Second quantity Z 2  is communicated by calculating device  165  to second prespecification device  162 . 
     First prespecification device  161  also receives crankshaft angle KW from acquisition device  164 . The first prespecification device determines a control signal for first injection valve  141  as a function of crankshaft angle KW and first quantity Z 1 . In a known manner, injection valve  141  is for example opened by a current signal as a function of crankshaft angle KW, for example when the crankshaft angle is 0°. If first quantity Z 1  has the value 1, the controlling of first injection valve  141  is suppressed. 
     Second prespecification device  162  also reads crankshaft angle KW from acquisition device  164 . The determination of the control signal for second injection valve  142  takes place in second prespecification device  162  in a manner analogous to the determination of the control signal for first injection valve  141 . For example, in a known manner second injection valve  142  is opened whenever the crankshaft angle is 0°. If second quantity Z 2  has the value 1, the controlling of second injection valve  142  is suppressed. 
     Through the injection at a crankshaft angle 0°, in both intake pipes there arises a fuel-air mixture that moves into the combustion chamber of the respective cylinder as soon as the respective intake valve is opened. This system ensures that the fuel-air mixture is ready to be provided for each cylinder when the respective intake valve is opened. The injection can also take place at a crankshaft angle differing from 0°. 
     The changeover of the operating modes and the determination of first operating characteristic L 1  and of second operating characteristic L 2  take place for example according to the flow diagram of an exemplary embodiment shown in  FIG. 2 . 
     The method according to the present invention is for example started whenever a combustion misfire has been recognized. The recognition of the misfire can take place for example using the described comparison of first operating characteristic L 1  with second operating characteristic L 2 , or, alternatively, using a misfire recognition device that, in modern internal combustion engines, monitors in a known manner whether a misfire has occurred. Subsequently, the method is continued in a step  200 . 
     In step  200 , first quantity Z 1  and second quantity Z 2  are initialized with the value 0. Subsequently, a step  201  is executed. 
     In step  201 , first segment time ts k  for crankshaft angular range 0° to 180° is determined. As a function of the time at which first piston  102  or second piston  112  outputs its torque contribution to crankshaft  120 , it can be provided that first segment time ts k  is determined for a different crankshaft range, which for example coincides precisely with the crankshaft angular range in which the torque contribution takes place. A step  202  is subsequently executed. 
     In step  202 , second segment time ts k+1  is determined in the crankshaft angular range from 360° to 540°. Alternatively, the second segment time ts k+1  is determined in the crankshaft angular range in which the torque contribution to crankshaft  120  actually takes place. A step  203  is subsequently executed. 
     In step  203 , a first auxiliary quantity luts is determined as a function of first segment time ts k , second segment time ts k+1 , and the number z of cylinders of the internal combustion engine, for example using the following equation: 
     
       
         
           
             luts 
             = 
             
               
                 
                   ts 
                   
                     k 
                     + 
                     1 
                   
                 
                 - 
                 
                   ts 
                   k 
                 
               
               
                 
                   
                     ( 
                     
                       z 
                       / 
                       2 
                     
                     ) 
                   
                   2 
                 
                 * 
                 
                   
                     ( 
                     
                       
                         
                           ts 
                           k 
                         
                         + 
                         1 
                         + 
                         
                           ts 
                           k 
                         
                       
                       2 
                     
                     ) 
                   
                   3 
                 
               
             
           
         
       
     
     Subsequently, a step  204  is executed. 
     In step  204 , it is checked whether first quantity Z 1  has the value 0. If first quantity Z 1  has the value 0, a step  205  is executed; otherwise, a step  207  is executed. 
     In step  205 , first quantity Z 1  is set to the value 1, and the injection using first cylinder  103  is thereby suppressed. A step  206  is subsequently executed. 
     In step  206 , first operating characteristic L 1  is set to the value of first auxiliary quantity luts. Step  201  is subsequently executed. 
     In step  207 , second operating characteristic L 2  is set to the value of first auxiliary quantity luts. A step  208  is subsequently executed. 
     In step  208 , first operating characteristic L 1  is compared to second operating characteristic L 2 . For example, for this purpose it is checked whether the difference in magnitude between first operating characteristic L 1  and second operating characteristic L 2  is smaller than a first threshold value S 1 . If this is the case, the method according to the present invention terminates; otherwise, a step  209  is executed. 
     In step  209 , first quantity Z 1  is set to the value 0 and second quantity Z 2  is set to the value 1. This causes internal combustion engine  100  to change over to the third operating mode, in which the injection using second injection valve  142  is suppressed. The method according to the present invention subsequently terminates. 
     The described method ensures that precisely that cylinder is shut off in which the misfire has taken place. This makes it possible to create the assignment in the absence of a phase sensor or in the presence of a defective phase sensor.