Abstract:
The invention relates to a method and device for controlling an internal combustion engine comprising an inlet pipe leading to a cylinder input where a gas input valve is placed. Said engine also comprises a drive for the gas input valve which makes it possible to adjust a gas input valve lift for at least two values. The engine also comprises an injection valve for metering fuel and a spark plug which controls the crankshaft angle of air-fuel mixture ignition. Said internal combustion engine is controlled in a following manner: a fuel is metered at least once during the intake stroke of a cylinder when the valve lift (VL) passes from one value to the other and at least one final injection is carried out in a dosing manner only when the valve lift (VL) is really carried out.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is the US National Stage of International Application No. PCT/EP2004/052906, filed Nov. 10, 2004 and claims the benefit thereof. The International Application claims the benefits of German Patent applications No. 10356257.5 DE filed Dec. 2, 2003, all of the applications are incorporated by reference herein in their entirety. 
   FIELD OF THE INVENTION 
   The invention relates to a method and device for controlling an internal combustion engine 
   BACKGROUND OF THE INVENTION 
   Increasingly high demands are made on internal combustion engines with regard to their performance and efficiency. At the same time, because of stringent legal regulations, the emissions must also be low. Such requirements can be met properly if the internal combustion engine is equipped with gas-changing valves and corresponding drives for this internal combustion engine in which the valve lift curve differs depending on the operating point of the internal combustion engine. Because of this, throttle losses in the case of air intake can be reduced and, if required, higher exhaust gas recirculation rates can quickly be set. 
   Adjusting the valve lift of a gas intake valve of the internal combustion engine between a lower and a higher valve lift is known. The Porsche 911 Turbo for example is thus equipped with a device for adjusting the valve lift of the gas intake valve and the gas outlet valve. In addition, the internal combustion engine of this vehicle is provided with a camshaft on which for each gas intake valve, one cam with a lower lift and two additional cams with a higher lift are embodied. The cam lift is transferred by means of a transfer unit to the gas intake valve. The transfer unit is embodied as a cup-shaped tappet comprising a cylinder element and a ring cylinder element arranged concentrically to this cylinder element. The cam with a lower lift acts on the cylinder element while the cams with the higher lift act on the ring cylinder element. Depending on a switch position of the cup-shaped tappet, either the lower or the higher lift is transferred to the gas intake valve. While the internal combustion engine is idling, the lower cam lift is transferred to the gas intake valve. This results in lower frictional losses based on the small diameter of the cam and the cylinder element used in this mode of operation and the lower valve lift. 
   In addition, a higher loading movement is achieved. This enables the emissions of the internal combustion engine to be decreased and at the same time, the fuel consumption to be kept low. The lower valve lift is maintained in the case of a lower and average load. Throttle losses can also be reduced by a corresponding phase adjustment between the gas intake valve and the gas outlet valve and a resulting internal exhaust gas recirculation rate. In the case of higher load requirements made on the internal combustion engine, the valve lift passes to the higher value. For a high driving comfort of a vehicle in which such an internal combustion engine is arranged and for low emissions of noxious substances, it is important that the passage from the lower valve lift to the higher valve lift takes place without misfiring. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to create a method and a device for controlling an internal combustion engine which ensures that low emissions of noxious substances are generated. 
   The object of the invention is solved by the features of the independent patent claims. Advantageous embodiments of the invention are characterized in the subclaims. 
   The invention is characterized by a method and a corresponding device for controlling an internal combustion engine comprising an intake pipe leading to a cylinder intake where a gas intake valve is placed. Said engine also comprises a drive for the gas-changing valve, which makes it possible to set a gas intake valve lift for at least two values. The engine also comprises an injection valve for metering the fuel and a spark plug which controls the crankshaft angle of the air/fuel mixture ignition. Said internal combustion engine is controlled in the following manner: fuel is metered at least once during the intake stroke of a cylinder, when the valve lift passes from one value to the other and at least one final injection is carried out in a dosing manner only when the valve lift has actually been carried out. Therefore, it can easily be ensured in this manner that no misfiring or combustion with very high fuel excess takes place, therefore, a considerably larger amount of fuel than the stoichiometric air/fuel ratio occurs even if it is very difficult to predict when an actual valve lift will pass from one value to the other value. 
   In an advantageous embodiment of the method for controlling the internal combustion engine, fuel is metered at least once during the intake stroke of a cylinder and the amount of fuel is determined depending on whether or not the passage of the valve lift from one value to the other value has actually been carried out. This has the advantage that it is very easy to implement. 
   In an additional advantageous embodiment of the method for controlling an internal combustion engine, fuel is metered at least once during the intake stroke of a cylinder without taking into consideration whether or not the passage of the valve lift from one value to the other value has actually been carried out. Because of this a proper preparation of the air/fuel mixture can be guaranteed, the requirement being a proper combustion process and accordingly low emissions of noxious substances of the internal combustion engine. 
   In an additional advantageous embodiment of the method, at least one final injection is carried out in a dosing manner only when the valve lift passage from one value to the other value has actually been carried out. Because of this, a very advantageous mixture preparation can simply be guaranteed, on the one hand, if the value with a lower valve lift was actually set and, therefore, low emissions of noxious substances were ensured. On the other hand, a desired air/fuel ratio can also be set if the value with a higher valve lift has actually been set. 
   In an additional advantageous embodiment of the method, the amount of fuel which is metered without taking into consideration whether or not the passage of the valve lift from one value to the other value has actually been carried out, is determined in such a way that there is a desired air/fuel ratio when the valve lift has actually been carried out with the value with a lower valve lift. Because of this, the mixture can simply be prepared very thoroughly and an air/fuel ratio can be set exactly if the value has actually been set with a lower lift. 
   In an additional advantageous embodiment of the method, the amount of fuel which is metered without taking into consideration whether or not the passage of the valve lift from one value to the other value has actually been carried out, is determined in such a way that the amount of fuel is higher than the desired air/fuel ratio if the valve lift has actually been carried out with the value with a lower valve lift. This has the advantage of an improved mixture preparation if the value with a higher valve lift has actually been set. 
   In an additional advantageous embodiment of the method, fuel is metered at least once during the intake stroke of a cylinder, when the valve lift passes from one value to the other and at least one final injection is carried out in a dosing manner only when the valve lift has actually been carried out if the rotational speed is greater than a predetermined threshold value which preferably is approximately 2000 revolutions per minute. This has the advantage that, on the one hand, the cost of determining the amount of fuel to be metered is reduced to below this threshold value and, on the other hand, surprisingly enough, the probability that the valve lift will not pass to another value is considerably higher for rotational speeds exceeding the predetermined threshold value than for rotational speeds below the predetermined threshold value and therefore the risk of misfiring is small. 
   In an additional advantageous embodiment of the method, the ignition angle is adapted depending on a variable which characterizes the metering of fuel and which depends on whether or not the valve lift passage from one value to the other value has actually been carried out. This has the advantage that a possibly poorer mixture preparation can be taken into consideration when setting the ignition angle and indeed in such a way that lower emissions of noxious substances are guaranteed. 
   An additional advantageous embodiment of the method is the variable of the amount of fuel and/or the crankshaft angle of metering the fuel, which depends on whether or not the valve lift passage from one value to the other value has actually been carried out. This has the advantage that these variables are characteristic of the mixture preparation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in detail below as an embodiment on the basis of the accompanying drawings. They are as follows: 
       FIG. 1  an internal combustion engine with a control unit, 
       FIG. 2  an additional view of parts of the internal combustion engine in accordance with  FIG. 1 , 
       FIG. 3  a flowchart of a first embodiment of a program for controlling an internal combustion engine for a desired passage of the valve lift from a lower valve lift to a higher valve lift, 
       FIG. 4  a flowchart of the program in accordance with  FIG. 3  for controlling an internal combustion engine for a desired passage of the valve lift from a higher valve lift to a lower valve lift and 
       FIGS. 5 and 6  an additional embodiment of a program for controlling an internal combustion engine. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Elements with the same design and function are characterized in all the figures with the same reference symbols. 
   An internal combustion engine ( FIG. 1 ) includes an intake tract  1 , an engine block  2 , a cylinder head  3  and an exhaust gas tract  4 . The intake tract preferably includes a throttle valve  11 , a manifold  12  and an intake pipe  13 , which is guided to a cylinder Z 1  via an intake port in the engine block. The engine block also includes a crankshaft  21 , which is connected to the piston  24  of a cylinder Z 1  by means of a connecting rod  25 . 
   The cylinder head includes a drive with an intake valve  30 , an exhaust valve  31  and valve gears  32 ,  33 . The gas intake valve  30  and the gas exhaust valve  31  are driven by means of a camshaft  36  (see  FIG. 2 ) on which cams  39 ,  39   a  and  39   b  are embodied for driving the gas intake valve  30 . In addition, cams which are not shown are provided on an additional camshaft which drive the gas intake valve  31 . 
   A total of three cams  39 ,  39   a,    39   b  ( FIG. 2 ) are allocated to the gas intake valve  30 . The cams  39 ,  39   a,    39   b  drive the gas-changing valve  30  via a transfer unit  38 . The transfer unit  38  is embodied as a cup-shaped tappet. It includes a cylinder element  38   a  and a ring cylinder element  38   b  arranged concentrically to the cylinder element. A cam  39  drives the cylinder element  38   a.  The cams  39   a,    39   b  drive the ring cylinder element  38   b.  In a switching position of the cup-shaped tappet, only the lift of the cam  39 , which is lower than the cam  39   a  and  b,  is transferred to the gas intake valve  30 . In an additional switching position of the cup-shaped tappet, the lifts of the cams  39   a  and  b  are transferred to the gas intake valve  30 . The switching position of the cup-shaped tappet can be achieved by a corresponding activation of an actuator provided in the cup-shaped tappet and preferably takes place hydraulically. 
   However, the drive  31 ,  32  can also be embodied in an alternative way. The camshaft can for example be embodied in such a way and engage with an actuator so that, depending on the desired valve lift, different cams drive the gas changing-valve. 
   The cylinder head  3  ( FIG. 1 ) also includes both an injection valve  34  and a spark plug  35 . Alternatively, the injection valve can also be arranged in the intake pipe  13 . 
   The exhaust gas tract  4  includes a catalytic converter  40 . From the exhaust gas tract  4 , an exhaust recirculation line can be guided to the intake tract  1 , particularly to the manifold  12 . 
   In addition, a control unit  6  is provided to which sensors have been allocated, said sensors detecting the different measured quantities and in each case determining the measured value of the measured quantity. The control unit  6  determines, in accordance with at least one of the measured quantities, the controlling variables which are then converted into one or several adjusting signals for controlling the final control elements by means of corresponding actuators. 
   The sensors are a pedal position indicator  71  which detects the position of an acceleration pedal  7 , an air mass flow meter  14  which detects an air mass flow upstream of the throttle valve  11 , a temperature sensor  15  which detects the intake air temperature, a pressure sensor  16  which detects the intake pipe pressure, a crankshaft angle sensor  22  which detects a crankshaft angle to which a rotational speed N is allocated, a further temperature sensor  23  which detects a coolant temperature, a camshaft angle sensor  36  which detects the camshaft angle, a further temperature sensor which detects an oil temperature and an oxygen sensor  41  which detects a residual oxygen content of the exhaust gas and, if required, a sensor which detects whether or not the gas intake valve  30  is operated with a lower or a higher valve lift. Depending on the embodiment of the invention, there can be any subset of the mentioned sensors or even additional sensors. 
   The final control elements are, for example, the throttle valve  11 , the gas intake and the gas exhaust valves  30 ,  31 , the injection valve  34 , the spark plug  35 , the setting mechanism  37  or the transfer unit  38 . 
   In addition to the cylinder Z 1 , the internal combustion engine can also have other cylinders, namely the cylinders Z 2 , Z 3 , Z 4  to which corresponding sensors and final control elements are allocated and controlled accordingly. The control unit  6  conforms to a device for controlling the internal combustion engine. 
   A program for controlling the internal combustion engine is preferably started when the internal combustion engine is started. The start takes place in a first step S 1  ( FIG. 3 ), in which variables are initialized, if required. 
   In a step S 2 , a test is performed to determine whether or not the current rotational speed N is greater than a predetermined threshold value N_THR of the rotational speed, which preferably is approximately 2000 revolutions per minute. If the condition of step S 2  has not been met, a third amount of fuel MFF 3  is determined in a step S 6  with due consideration of the air mass in the cylinder to be expected for this operating cycle, in which case for this purpose the desired step of the valve lift VL is used as a basis and with due consideration of the air/fuel ratio to be set. In addition, the metering of the third amount of fuel MFF 3  is then controlled in a step S 6 . 
   On the other hand, if the condition of a step S 2  has been met, a test is then performed in a step S 4  to determine whether or not since the last operating cycle of the cylinder Z 1 , a passage of the valve lift VL from a lower valve lift LO to a higher valve lift HI was requested. 
   If this is not the case, processing will continue in a step S 6 . Subsequently to a step S 6 , the processing will be continued in a step S 8  in which an ignition angle IGN is then determined depending on the rotational speed N, a desired torque TQ_REQ and, if required, additional variables. In this way, for example, instead of the desired torque TQ_REQ, another variable representing the load of the internal combustion engine can also be used. In addition, the ignition angle IGN can also be determined depending on additional variables with regard to the desired minimizing of emissions of noxious substances such as NOX emissions. 
   The program then remains in a step S 10  for a predetermined waiting period T_W or also for a predetermined crankshaft angle before processing is continued anew in a step S 2 . 
   On the other hand, if the condition of a step S 4  is met, a first amount of fuel MFF 1  is determined in a step S 12  and the first amount of fuel MFF 1  is for example determined in such a way that a desired air/fuel ratio has been set in the cylinder Z 1 , on the condition that the valve lift VL of the gas intake valve  30  is lower than in the current intake stroke of the lower valve lift LO. In addition, the actual metering of the first amount of fuel MFF 1  is then controlled in a step S 12 . Alternatively, in a step S 12 , the first amount of fuel MFF 1  can then also be selected in such a way that there is a higher amount of fuel in the cylinder Z 1  than the desired air/fuel ratio, on the condition that the valve lift VL of the gas intake valve  30  is the lower valve lift LO. 
   The program then remains in a step S 14  for a predetermined waiting period T_W, which can differ from that of step S 10 . The waiting period T_W in a step S 14  preferably has to be metered in such a way that in the case of a subsequent processing of a step S 16  it is possible to determine whether or not the valve lift VL in the current intake lift is actually the lower valve lift LO or actually the higher valve lift HI. However, it is metered so low that a step S 16  can possibly be finished early. 
   The actual valve lift VL is preferably either determined by means of the suitable sensor or in a simple embodiment the passage from a lower valve lift LO to a higher valve lift HI can take place on the basis of the curve of the intake pipe pressure or also on the basis of the curve of a hydraulic pressure, in the case in which the passage takes place hydraulically or is also detected on the basis of electrical signals if the passage takes place electrically. In this way, it is for example possible to determine on the basis of the actual curve of the intake pipe pressure, while the gas intake valve  30  is in its open position, by comparing with corresponding values for the lower valve lift LO and/or the higher valve lift HI, whether or not the actual lower valve lift LO or the higher valve lift HI has been set. 
   If it is detected in a step S 16  that the actual valve lift VL is the lower valve lift LO, processing will be continued in a step S 8 . 
   On the other hand, if it is detected in a step S 16  that the actual valve lift VL is the higher valve lift HI, a second amount of fuel MFF 2  is then determined in a step S 18 . The second amount of fuel MFF 2  is then determined in such a way that the sum of the first and the second amount of fuel MFF 1 , MFF 2  corresponds with the desired air/fuel ratio in the cylinder Z 1  in the case of the higher valve lift HI. In addition, the metering of the second amount of fuel MFF 2  is controlled in a step S 18 . 
   A correction value IGN_COR is then determined in a step S 20  for the ignition angle IGN and indeed depending on the second amount of fuel and/or the crankshaft angle CRK_MFF 2  of the metering of the second amount of fuel MFF 2 . Because of this correction value, the quality of the mixture preparation, which has possibly decreased because of the metering of the second amount of fuel MFF 2  occurring only at a later stage, can be determined and in this way by influencing the ignition angle IGN the minimizing of emissions of noxious substances can be ensured. 
   The ignition angle IGN is then determined in a step S 22  depending on the correction value IGN_COR, the rotational speed, the desired torque TQ_REQ and, if required, additional or alternative variables, which the specialist then uses for this purpose. In addition, in a step S 22 , the ignition of the air/fuel mixture in the cylinder Z 1  is controlled. The processing is then continued in a step S 10 . The waiting period T_W in a step S 10  should preferably be metered in such a way that subsequent to a step  50 , the processing is then continued in a step S 2  if a new operating cycle of the cylinder Z 1  has started. 
   If in a step S 12 , the first amount of fuel MFF 1  is determined in such a way that the desired air/fuel ratio has been set for the lower valve lift, it is ensured that the emissions of noxious substances in the case of an actual non-executed passage of the valve lift from the lower valve lift LO to the higher valve lift HI is minimized. On the other hand, if in the case of a step S 12 , a first amount of fuel MFF 1  increased for this purpose has been determined, this indeed still causes increased emissions of noxious substances in the case where a passage from the lower valve lift LO to the higher valve lift HI did not actually take place. This has the advantage that in the case of a possibly more probable actual passage from a lower valve lift LO to a higher valve lift HI, an improved mixture preparation based on the earlier metering of a higher first amount of fuel MFF 1  is guaranteed. 
   Tests have shown that the reason for a deviation between the desired and the actually set valve lift VL, for example, in the case of a hydraulic system can be a foaming-up of the hydraulic fluid while operating the internal combustion engine. Gas bubbles in this foamed-up fluid lead to a changed compressibility of the fluid which, on the other hand, can lead to the fact that a desired passage did not place in good time. Surprisingly, however, this foaming-up occurred strongly, in particular, above the threshold value N_THR. 
   The embodiment of the program for controlling an internal combustion engine in accordance with  FIG. 4  differs from that in accordance with  FIG. 3  in that in a step S 4 ′ a test is performed to determine whether or not a passage of the valve lift VL from the higher valve lift HI to the lower valve lift LO was requested. In addition, a test is carried out in a step S 16 ′ to determine whether or not the actual valve lift VL passed from a higher valve lift HI to a lower valve lift LO. The programs in accordance with the  FIGS. 3 and 4  are preferably finished parallel to each other. 
     FIGS. 5 and 6  show an alternative embodiment of the program in accordance with  FIG. 3 , in which case likewise only the steps which differ from those in accordance with  FIG. 3  are described. A step S 4  is followed by a step S 26  in which the program for the waiting period T_W remains when change of the valve lift VL from the lower valve lift LO to the higher valve HI is requested. The waiting period T_W is selected in a step S 26  in such a way that a subsequent step S 28  is finished if it can be determined whether or not the valve lift VL actually passed from the lower valve lift LO to the higher valve lift. On the other hand, the waiting period T_W of step S 26  is selected in such a way that a step S 28  is finished as early as possible. 
   In a step S 28  a test is then performed to determine whether or not the actual valve lift VL has changed from the lower valve lift LO up to the higher valve lift HI. 
   If this is the case, then in a step S 30  the sum of the first and second amount of fuel MFF 1 , MFF 2  is determined and a metering of the sum of the first and second amount of fuel MFF 1 , MFF 2  is controlled. In this way, the metering of both the first and the second amount of fuel MFF 1 , MFF 2 , in this case, only takes place in a period of time, in which it already has been specified whether or not the actual valve lift VL has changed from the lower valve lift LO to the higher valve lift HI. In this case, the amount of fuel required for the desired air/fuel ratio can always be metered reliably in this manner. 
   The correction value IGN_COR is then determined in a step S 32  depending on the sum of the first and the second amount of fuel MFF 1 , MFF 2  and/or the crankshaft angle CRK_MFF 12  of the metering of the amount of fuel in the cylinder Z 1 . The ignition angle IGN is then determined in a step S 34  depending on the correction value IGN_COR, the rotational speed N, the desired torque TQ_REQ and, if required, additional variables or alternatively from other variables. 
   On the other hand, if the condition of a step S 28  has not been met, i.e. the actual valve lift VL from the lower valve lift LO to the higher valve lift HI has not changed, the first amount of fuel MFF 1  is determined in a step S 38 . 
   The correction value IGN_COR of the ignition angle IGN is then determined in a step S 40  depending on the first amount of fuel MFF 1  and/or the crankshaft angle CRK_MFF 1  of the metering of the first amount of fuel MFF 1  in the cylinder Z 1 . 
   The ignition angle IGN is then determined in a step S 42  depending on the correction value IGN_COR, the rotational speed N, the desired torque TQ_REQ and additional variables or alternative variables and the ignition is then controlled in the case of the predetermined ignition angle IGN. 
   On the other hand, in all the embodiments the metering of the first, the second and the third amount of fuel MFF 1 , MFF 2 , MFF 3  can again be divided into more than one actual injection. Corresponding programs are also finished for the additional cylinders Z 2 -Z 4 .