Abstract:
In a method for controlling the composition of a combustible air-fuel mixture present in a combustion chamber of a spark-ignited internal combustion engine having external mixture formation, at least two fluids containing air are generated, of which at least one is an air-fuel mixture; the fluids are supplied to the combustion chamber, wherein the quantity proportions of the fluids are controlled such that their total composition corresponds to the predetermined composition.

Description:
CROSS REFERENCE 
     This application is the U.S. national stage filing of International Application No. PCT/EP2005/004424 filed Apr. 25, 2005, which claims priority to German patent application no. 10 2005 014 789.5 filed Mar. 31, 2005. 
     TECHNICAL FIELD 
     The invention concerns a method for controlling the composition of the combustible air-fuel mixture present in a combustion chamber of a spark-ignited internal combustion engine having external mixture formation. The invention further concerns a device for performing such a method. 
     BACKGROUND ART 
     The composition of the combustible air-fuel mixture in the combustion chamber is of decisive importance for fuel consumption as well as for the pollutant content of the exhaust gas. Precise controlling of the mixture formation is very important, especially for internal combustion engines tuned for lean operation. The following fuel metering methods are known and usable for internal combustion engines having external mixture formation: 
     The fuel metering can take place in a cylinder-selective manner by feeding the fuel into individual intake pipes leading to the individual cylinders by means of fuel injection values disposed close to the intake valves. These fuel injection valves usually function such that they can be switched between two positions—valve “fully open” and valve “fully closed”—and the injected fuel quantity is changed exclusively by manipulating the time duration of the opening as well as, if desired, by manipulating the phase position of this opening relative to the phase position of the opening of the intrinsic intake valve. As a result, it can rapidly respond to varying quantity demands, i.e. the system operates highly dynamically. Due to the fact that the mixture mass flowing into the cylinder proceeds as a function in accordance with the piston movement, which piston movement is predetermined by the crankshaft design, the fuel mass flow remains constant at a constant load, but a relatively inhomogeneous mixture composition results inside the combustion chamber. At the lean operating limit, this leads in particular to large standard deviations in the cylinder mean effective pressure and to high NOx-emissions. 
     In the other fuel metering methods, the fuel metering takes place remotely in a manner centrally for all cylinders and relatively far from the intrinsic intake valves. Consequently, a buffer volume exists between the fuel metering location and the intake valves, whereby a good homogeneity of the inflowing air-fuel mixture is in fact achieved, but wherein the dynamic capability is restricted due to the long way between the fuel metering location and the intake valves, i.e. the composition of the inflowing air-fuel mixture can be adapted to the varying demands only with a certain lag. 
     SUMMARY OF THE INVENTION 
     The object underlying the invention is to provide a possibility, with which the composition of the combustible air-fuel mixture present in the combustion chamber of a spark-ignited internal combustion engine having external mixture formation can be adapted to varying demands as precisely and/or as quickly as possible. 
     In one aspect of the present teachings, a method is disclosed for controlling the composition of the combustible air-fuel mixture present in a combustion chamber of a spark-ignited internal combustion engine having external mixture formation, such that the mixture has a predetermined composition. In this method, at least two fluids containing air are generated, of which at least one is an air-fuel mixture and the fluids are supplied to the combustion chamber. The quantity proportions of the fluids are controlled such that their total composition corresponds to the predetermined composition. 
     Preferably, the quantity control of the fluids supplied to the combustion chamber first takes place either shortly before their entrance into the combustion chamber or upon their entrance into the combustion chamber. In addition or in the alternative, one fluid is preferably a rich air-fuel mixture and the other fluid is preferably a lean air-fuel mixture, wherein the rich air-fuel mixture has a higher fuel content than the mixture having the predetermined composition and the lean air-fuel mixture has a lower fuel content than the mixture having the predetermined composition. 
     In another aspect of the present teachings, an apparatus is disclosed for controlling the composition of a combustible air-fuel mixture present in a combustion chamber of a spark-ignited internal combustion engine having external mixture formation, so that the mixture has a predetermined composition. The apparatus preferably comprises a first mixture generating device for generating a rich mixture and a second mixture generating device for generating a lean mixture. Preferably, both mixtures are generated by adding fuel to fresh air, which is supplied to the combustion engine, the rich mixture having a higher fuel proportion than the mixture having the predetermined composition and the lean mixture having a lower fuel proportion than the mixture having the predetermined composition. A first device is provided for supplying the rich mixture to a first intake leading into a combustion chamber of the internal combustion engine and a second device is provided for supplying the lean mixture to a second intake leading into a combustion chamber of the internal combustion engine. A first valve device operates in the first intake and controls the quantity of the rich mixture supplied to the combustion chamber. A second valve device operates in the second intake and controls the quantity of the lean mixture supplied to the combustion chamber. A control device is provided for controlling the valve devices such that the sum of the quantities of the rich mixture and the lean mixture flowing into the combustion chamber results in a mixture having the predetermined composition. 
     The invention is particularly suited for supercharged gas engines, i.e. for engines, to which a compressed fresh air charge and/or a compressed mixture of fresh air and fuel is supplied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in an exemplary manner and in further detail in the following with the assistance of schematic drawings. 
       In the Figures: 
         FIG. 1  shows a principle view of an inventive, multi-cylinder, reciprocating-piston internal combustion engine and 
         FIG. 2  shows a principle sectional view of a control valve employable in the internal combustion engine according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to  FIG. 1 , the exemplary-illustrated, reciprocating-piston internal combustion engine includes six cylinders  4  arranged in a row, each of which has two intake valves  27  and  39 , which are commonly operated by camshafts (not shown), and a not-illustrated exhaust valve. 
     Exhaust gas conduits of the three cylinders  4  on the left side according to  FIG. 1  lead to an exhaust gas turbine  6  of a first exhaust gas turbocharger  8 . Exhaust gas conduits of the three cylinders  4  on the right side according to  FIG. 1  lead to an exhaust gas turbine  10  of a second exhaust gas turbocharger  12 . 
     A first conduit  16  leads from an air filter  14  through a first fuel metering device  18  into a supercharger turbine  20  of the exhaust gas turbocharger  8 . The output of the supercharger turbine  20  leads into a first manifold  22 , from which individual intake pipes  24  lead through respective control valves  26  to an inlet into the respective cylinder; an intake valve  27 , normally formed as a plate valve and/or as a charge change valve, operates in the cylinder in a known manner. 
     Another conduit  28  leads from the air filter  14  through a fuel metering device  30  to the supercharger turbine  32  of the exhaust turbocharger  12 . The output of the supercharger turbine  32  is connected with another manifold  34 , from which individual intake pipes  36  lead through respective control valves  38  to the respective other intake of a respective cylinder  4 , in which the other intake valve  39  operates. 
     A fuel metering valve  40 ,  42 , respectively, is disposed in each of the fuel metering devices  18  and  30 ; fuel is supplied to the fresh air, which is flowing through the fuel metering device, by means of the valve  40 ,  42 , respectively, in an amount that depends upon the air flow rate, such that a predetermined air-fuel ratio is present downstream of the respective fuel metering device  18 ,  30 , respectively. Such fuel metering devices are generally known and thus will not be explained herein. The air flow rate (quantity flow rate) is measured and the respective fuel metering valve  40 ,  42  is controlled such that a corresponding fuel quantity is metered dependent upon the predetermined air flow rate and a to-be-maintained mass ratio between the air and fuel. Together with the conduit  16 ,  28 , respectively, each of the fuel metering devices  18  and  30  thus forms a mixture forming device for generating a mixture that is supplied to the respective supercharging turbine  20 ,  32  and then to the respective manifold  22 ,  34 . By disposing the respective fuel metering device upstream of the supercharging turbine, an excellent homogenization of the mixture takes place in the supercharging turbine, wherein it is additionally advantageous for the homogenization to smooth the flow, which is pulsating in the series of opening intake valves downstream of the respective supercharging turbine, upstream of the supercharging turbine. 
     The controlling and/or regulation of the air-fuel ratio of the mixture flowing into the cylinder  4  takes place by adding varying amounts of fuel to the fresh air flowing through the two fuel metering devices  18  and  30 , so that, for example, a rich mixture is present in manifold  22  and a lean mixture is present in manifold  34 . For example, the rich mixture has an air-to-fuel ratio of 0.9 relative to the stoichiometric ratio and the lean air-fuel mixture has a ratio of 1.1 relative to the stoichiometric ratio. The rich mixture composition is advantageously at least as rich as the richest mixture necessary for driving. The lean air-fuel ratio is advantageously at least as lean as the leanest mixture necessary for operation. 
     The adjustment of the air-fuel ratio inside of the cylinder takes place by means of control valves  26  and  38 , which are disposed directed in front of the respective intake valves  27 ,  39  and which determine the quantity ratio and preferably also the quantity of the air-fuel mixture flowing into the cylinder during one intake stroke. If the same quantities flow in, the air-fuel ratio in the cylinder is 1 in the described example. If only rich mixture flows in, it is 0.9; if only lean mixture flows in, it is 1.1. 
     An electronic control device  44  serves to control the fuel metering valves  40  and  42  as well as the control valves  26  and  28 ; the electronic control device  44  comprises a microprocessor having program-memory and data-memory in a known manner. Inputs  46  of the electronic control device are connected with sensors that supply signals relevant for the quantity and the composition of the air-fuel mixture to be fed into the cylinders. Output signals are generated at the outputs  48  from these signals for actuating the fuel metering valves  40  and  42  and the control valves  26  and  38 , wherein the control valves  26  and  38  are actuated in a cylinder-selective manner. 
     The actuation of the fuel metering valves  40  and  42  as well as the control valves  26  and  38  takes place in a controlled manner or in a regulated manner with use of feedback by supplying the signals from the exhaust gas sensors  48  and  50 , which determine, e.g., the oxygen content in the exhaust gas, to the inputs  46  of the control device  44 . 
     In the illustrated example, the conventional intake valves, which directly abut on the combustion chamber, can be actuated in a purely mechanical manner by the crankshaft via a camshaft as well as, if desired, a phase controller, so that the opening time and stroke range of the intake valves does not change in dependence on the load, but rather, if desired, are only shifted in the phase relative to the crankshaft. 
     The control valve  26  and  38  are advantageously constructed such that their opening time points and closing time points, as well as if desired their opening stroke range, can be freely controlled.  FIG. 2  shows a section through an exemplary control valve  26 ,  38 , respectively. 
     The individual cylinder intake pipe  24 ,  36 , respectively, leading to the cylinder includes a dividing wall  70 , which is meander-shaped in the longitudinal cross-section through the intake pipe; four valve openings  72  are formed in the dividing wall  70  transverse to the axial direction of the intake pipe in the illustrated example. A valve member denoted as a whole with  74  extends transversely through the intake pipe and through the valve openings; the valve member  74  includes a shaft  76  and disks  78  surrounding the shaft  76  and rigidly attached thereto. The arrangement is such that, in the opened position of the valve, which open position is illustrated in  FIG. 2 , the uppermost and third-from-the-uppermost disks  78  are located downstream of the associated valve openings  72  with reference to the intake flow through the intake pipe; the two other disks  78  are located upstream of the associated valve openings  72 . The diameter of the disks  78  corresponds approximately to the diameter of the valve openings  72 , so that the valve is closed when the shaft  76  together with the disks  78  according to  FIG. 2  have moved so far upwards that the disks  78  are located inside the openings  72 . The disks  78  are advantageously formed in an aerodynamic manner. 
     The shaft  76  includes a cylindrical extension  80  outside of the intake pipe for actuation of the control valve; a coil  82  is accommodated in the extension  80  and is encircled by an electromagnet  84  that is accommodated in a housing  86  attached to the intake pipe. 
     The shaft  76  is longitudinally displaceably guided in the intake pipe within bushings  88 . The cylindrical extension  80  is designed such that the stroke movement of the shaft  76  and/or the valve member  74  is limited on the one side by its abutment on the outer side of the intake pipe and on the other side by its abutment on an extension of the housing  86  protruding into it. 
     A spring  90  urges the valve member  74  into its opened position. 
     The function of the described control valve is as follows: 
     The coil  82  is connected to the control device  44 . The valve is normally opened due to the force of the spring  90 . By applying current to the coil  82 , the valve member according to  FIG. 2  will be moved upwardly into a position, in which the disks  78  are located inside of the valve openings  72  and close these openings  72 . As is apparent, in the closed position of the valve, when for example a positive pressure prevails on the left side of the valve, this positive pressure acts on the uppermost and the third-from-the-uppermost disks such that the valve member is pressed downwardly, whereas the positive pressure acts on the lowermost and the third-from-the-lowermost disk such that the valve member is pressed upwardly, so that the valve member as a whole is not influenced by forces independent of the pressure difference. 
     An advantage that is achieved with the depicted valve is that it is movable in an extraordinarily rapid manner from the closing position into the opening position and vice versa, so that a precise control of the timings is possible with the lowest possible current wastage. 
     In the preferred, illustrated embodiment, the shaft  76  acts together with a position path sensor  91 , which supplies information concerning the exact instantaneous position of the shaft  76  and thus of the disks  76 . The control device  44  regulates the current through the coil  82  such that the actual position of the valve body  76 ,  78  at each time point corresponds to the target position, which is programmed and predetermined by the control device. As a result, not only the opening time point and the closing time point of the control valve can be freely controlled, but also its stroke range. 
     When the mixture quantities flowing into the cylinder are exclusively controlled by the stroke of the control valves  26  and  38  and their opening time point and closing time point are the same, a very homogenous composition of the mixture especially results in the combustion chamber. When the flow volumes are influenced by the engine valve timings of the control valves, more intense stratified charging effects can also be achieved by letting the lean mixture flow in temporarily before the rich mixture. 
     The described control valves are known from European Patent No. 1 236 875 B1. They can not only be utilized for controlling the quantity and thereby also the composition of the mixture in the combustion chamber, but also for a further reduction of the charge changing loses in the partial load range by using the partial load resonance charging described in this publication. 
     The invention can be modified in various ways. 
     For example, the turbochargers are not necessary and the invention can also be employed in naturally-aspirated engines. For turbo-engines, both turbochargers can be powered by one common exhaust gas turbine, through which the entire exhaust gas of the internal combustion engine flows. Further, externally-powered superchargers can also be utilized. 
     The control valves  26  and  38  are not necessarily required. The controlling of the quantity and of the composition of the mixture flowing into the cylinders can also be controlled by an appropriate design of the intake valves  27 ,  39 , which directly abut on the combustion chamber. Further, it is possible to replace the control valves with throttle valves contained in the individual cylinder intake pipes and to open these throttle valves in an appropriate manner. Also, the individual throttle valves are not necessarily required. They can be each replaced with a throttle valve in the conduits  16  and  28 . 
     The control valves can have a different construction than depicted; for example, they can be formed as rotating disk valve, whose opening cross-section can be changed by means of a stepping motor with respect to opening-beginning and closing-beginning as well as with respect to opening cross-section. 
     The mixture composition in the manifold  22  and in the manifold  34  can be changed during operation. For example, the lean mixture can be set to infinitely lean (no fuel metering). It is thereby possible, during suitably set engine valve timings of the control valves during the first phase of the intake, during which the intake valves overlap, to connect the cylinder combustion chamber exclusively with the individual cylinder intake pipe that is supplying pure air and then subsequently to direct the mixture into the cylinder through the other intake pipe. As a result, an overflow of mixture and/or fuel into the exhaust tract can be prevented during the valve overlapping phase of the main valves. 
     In summary, the invention offers multiple possibilities for improving the operational performance with regard to torque development and power development, operational efficiency and exhaust gas quality. The invention is particularly suitable for usage in gas motors, into which combustible gas is fed via fuel metering valves  40  and  42 . 
     Reference Number List 
       4  Cylinder 
       6  Exhaust gas turbine 
       8  Exhaust gas turbocharger 
       10  Exhaust gas turbine 
       12  Exhaust gas turbocharger 
       14  Air filter 
       16  Conduit 
       18  Fuel metering device 
       20  Supercharging turbine 
       22  Manifold 
       24  Individual cylinder intake pipe 
       26  Control valve 
       27  Intake valve 
       28  Conduit 
       30  Fuel metering device 
       32  Supercharging turbine 
       34  Manifold 
       36  Individual cylinder intake pipe 
       38  Control valve 
       39  Intake valve 
       40  Fuel metering valve 
       42  Fuel metering valve 
       42  Electronic control device 
       46  Inputs 
       48  Outputs 
       70  Dividing wall 
       72  Valve opening 
       74  Valve member 
       76  Shaft 
       78  Disk 
       80  Extension 
       82  Coil 
       84  Electromagnet 
       86  Housing 
       88  Bushing 
       90  Spring 
       91  Position path sensor