Abstract:
A method of regulating an internal combustion engine, in particular involving a lean-burn mode of operation, for achieving predeterminable nitrogen oxide emission values from the internal combustion engine, wherein the λ-value of a fuel-air mixture to be burnt in the internal combustion engine or an equivalent engine parameter in a defined relationship with said λ-value is regulated in dependence on the amount of fuel supplied per unit of time or in dependence on the fuel energy supplied per unit of time (Q zu ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to Austrian Application No. A 185/2004, filed Feb. 9, 2004, the contents of which are incorporated by reference in their entirety. 
   The present invention concerns a method of regulating an internal combustion engine, in particular with a lean-burn mode of operation, to achieve predeterminable nitrogen oxide emission values for the internal combustion engine, and a corresponding regulating apparatus and internal combustion engine. 
   It is already known from EP 0 259 382 B1 for an internal combustion engine for driving an electrical generator to be operated with constant nitrogen oxide emission values, by regulating the mixture pressure upstream of the inlet valves of the cylinders in dependence on the electrical power delivered by the generator. In that situation the reference value in respect of the mixture pressure upstream of the inlet valves is taken from a family of curves which shows the dependency of the mixture pressure on the delivered electrical power, at constant emission values. Then, the measured actual value of the pressure upstream of the inlet valves is regulated to its reference value determined by way of the family of curves, by way of adjustment of the fuel-air ratio in a gas mixer. The curve used for that purpose is produced by measuring at least two operating points involving identical NO x  emission values. By means of that previously known method, it is possible for an internal combustion engine to very accurately maintain the desired emission values in a wide power range. The system known from the stated European patent enjoys the advantage that it involves practically no wear and ageing of sensitive sensors. 
   European patent application EP 1 225 330 A2 sets forth a further improved system of the general kind set forth, in which the regulating layout known from EP 0 259 382 B1 has been further supplemented by ignition timing adjustment in order to provide a regulating reserve margin for rapid reaction to changes in load, in any operating condition. In addition that regulating system serves to always operate the internal combustion engine at optimum efficiency. 
   A disadvantage of those known regulating systems is that a signal which is characteristic of the power delivered by the internal combustion engine must always be available. The electrical power delivered can be used for that purpose, in the case of internal combustion engines which drive a generator for producing electrical current. However, for other engines, for example for driving pumps, a corresponding power signal is generally not available and therefore would have to be measured as an additional operation by means of expensive additional sensors in order to use the above-indicated regulating layouts. 
   SUMMARY 
   Therefore the object of the present invention is to provide a regulating method of the general kind set forth, in which it is possible to forego a measured power signal. 
   In accordance with the invention that is achieved in that the λ-value of a fuel-air mixture to be burnt in the internal combustion engine or an equivalent engine parameter in a defined relationship with said λ-value is regulated in dependence on the amount of fuel supplied per unit of time or in dependence on the fuel energy supplied per unit of time. 
   In accordance with the invention therefore it is provided that, instead of the power delivered by the internal combustion engine, the amount of fuel supplied per unit of time or the fuel energy supplied per unit of time is to be used as the base parameter for regulation. In that respect, the λ-value or an equivalent engine parameter related thereto is regulated. As is generally known the λ-value describes the air ratio in combustion processes, wherein λ=1 corresponds to a stoichiometric combustion. The equivalent engine parameter used can be for example the pressure upstream of the inlet valves of the internal combustion engine or the calorific value of the fuel-air mixture to be burnt or however also a nitrogen oxide emission value from the exhaust gases. The amount of fuel supplied per unit of time is desirably determined by means of a through-flow measurement procedure. If regulation is based on the fuel energy supplied per unit of time, the through-flow measurement procedure is executed in combination with a calorific value measurement procedure in respect of the fuel. Multiplication of the two measurement values gives the fuel energy supplied per unit of time. 
   Besides the stated method the invention also concerns a regulating apparatus for carrying out the method and an internal combustion engine including such a regulating apparatus. 

   
     Further details and features of the present invention are apparent from the specific description hereinafter. In the drawing: 
       FIG. 1  is a diagrammatically illustrated family of curves for use in the method according to the invention, 
       FIG. 2  is a diagrammatic view of a first embodiment of a regulating method according to the invention, and 
       FIG. 3  is a second embodiment according to the invention which additionally also includes ignition timing adjustment. 
   

   DETAILED DESCRIPTION 
     FIG. 1  diagrammatically shows the dependency of the λ-reference value on the fuel energy supplied per unit of time, as indicated at Q zu . All those operating points of the internal combustion engine, which each involve a given nitrogen oxide emission value, lie on the curve  10  shown as a solid line. The curve or the family of curves is produced by calibration measurement procedures, for example when the internal combustion engine is set in operation. That is effected by a procedure whereby a λ-reference value is so set at an operating point  9  at a given Q zu -value, thus giving the desired nitrogen oxide emission value from the internal combustion engine. In order to produce a curve  10 , suitably setting another value in respect of the fuel energy supplied per unit of time then provides at least one second operating point  9 , in which case in turn the λ-reference value is determined for example by adjustment of the fuel-air ratio at which the desired nitrogen oxide emission value is attained. The two operating points  9  which are determined in that way afford in a first approximation a linear curve  10 ′ (shown in broken line). When more than two operating points  9  are measured with the above-indicated operating procedure, at a constant nitrogen oxide emission value, a curved curve, like the curve  10 , can also be afforded therefrom. 
   In the case of internal combustion engines in which certain operating parameters such as for example the temperature t 2 ′ of the fuel-air mixture or the ignition point indicated at ZZP or the quality of the fuel supplied can change greatly, it may also be appropriate to also take account of the influence of those parameters. That then generally affords a family of curves.  FIG. 1  shows by way of example in broken lines various curves  10 ″ which are produced with suitable measurement of operating points  9 ″ at respectively constant nitrogen oxide emission values and respectively different temperature values t 2 ′. When a plurality of influencing parameters are taken into consideration, that then overall affords a multi-dimensional family of curves. Alternatively, based on a single curve  10 , it is however also possible to take account of corresponding correction values for the temperature of the fuel-air mixture t 2 ′ or the ignition point (at ZZP) or further influencing parameters. In order to keep the expenditure involved when measuring the family of curves using the above-depicted mode of operation within limits, it is also possible to apply estimates if the influence of a given parameter is known. 
   Even if  FIG. 1  only shows one family of curves for the dependency between the reference value of λ and the supplied fuel energy (indicated at Q zu ), similar curves or families of curves are nonetheless afforded in respect of the dependencies of the specified equivalent engine parameters (pressure upstream of the inlet valves, calorific value of the fuel-air mixture or nitrogen oxide emission value) on the supplied amount of fuel per unit of time or the supplied fuel energy per unit of time. 
     FIG. 2  shows a first regulating method according to the invention for an internal combustion engine. It firstly has, as is known per se, a power regulator in which a PID regulator  1  adjusts a power setting member  2  (for example a throttle butterfly valve or a by-pass blow-off valve of the internal combustion engine to be regulated), in such a fashion that the power P produced by the engine  5  corresponds to the desired power reference value indicated at P soll . Now, in accordance with the invention, there is provided a regulating section for the engine  5 , in which the dependency, established in the family of curves  6 , of the λ-value or an equivalent engine parameter on the amount of fuel supplied per unit of time or the fuel energy supplied per unit of time (indicated at Q zu ) is used to achieve constant nitrogen oxide emission values (NO x ). That regulating line is firstly described with reference to an example based on the dependency of the λ-value on the fuel energy supplied per unit of time (Q zu ). 
   In operation of the internal combustion engine the through-flow amount and the calorific value of the fuel are measured by means of a through-flow measuring device and a calorific value probe in the fuel feed line of the internal combustion engine. Multiplication of those two values gives the fuel energy supplied per unit of time Q zu  (in J/s). Then, by reference to that Q zu  value, the corresponding λ-reference value is determined in the family of curves  6  described with reference to  FIG. 1 . In that respect, as required, it is possible to take account of the temperature t 2 ′ of the fuel-air mixture and/or the ignition point ZZP and/or the calorific value of the fuel H UB  and/or the stoichiometric minimum air requirement L min . The reference value determined in that way in respect of the λ-value is compared in the comparator  11  to an actual value in respect of λ, which is measured by means of the λ-probe  4  in the exhaust tract. Adaptation of the actual value to the reference value is effected by means of a PID regulator  1  which actuates a device  3  for adjusting the fuel-air mixture. 
   The regulating system described with reference to  FIG. 2  on the basis of the parameters Q zu  and the λ-value also operates in a similar manner for the equivalent engine parameters which have already been mentioned (as an equivalent substitute for the λ-value) and the amount of fuel supplied per unit of time (as an equivalent substitute for Q zu ) For that purpose it is only necessary to use a respectively appropriate family of curves  6  and a corresponding measuring probe. If the calorific value of the fuel-air mixture is selected as the equivalent engine parameter, then a preferably online-measuring calorific value probe  4 ′ (shown in broken line as an alternative) is to be arranged in order to determine the actual value of the fuel-air mixture in the fuel-air mixture feed conduit  12 . If the pressure upstream of the inlet valves is selected as the equivalent engine parameter, a corresponding pressure measuring device is thus to be adopted. That is also desirably arranged in the fuel-air mixture feed conduit  12 . As an alternative thereto however, if the regulating system is to be based on the nitrogen oxide emission value from the internal combustion engine, it is also possible to use a device  8  at the exhaust gas side, for measuring the nitrogen oxide emission values. That variant is shown in broken line in  FIG. 2 . The operation of determining the parameters t 2 ′, ZZP, H UB  and/or L min  which are optionally to be taken into consideration in the family of curves is effected in accordance with the state of the art, a suitable temperature probe for measuring t 2 ′ desirably also being arranged in the fuel-air mixture feed conduit  12 . Replacement of the parameter Q zu  by the amount of fuel supplied per unit of time, which is only determined by means of a through-flow measurement procedure (unit m 3 /s; possibly converted to normal conditions) is generally recommended only if the fuel is of uniform quality. The quality of the fuel can be characterised for example by a calorific value measurement operation conducted on the fuel. 
   The first regulating system according to the invention, as shown in  FIG. 2 , is also supplemented by a regulating section for ignition timing adjustment in  FIG. 3 . That regulating section can ensure that there is always a regulating reserve margin available for rapid reaction to changes in load at the internal combustion engine  5 . For that purpose, a signal U which is characteristic in respect of the regulating reserve margin of the power setting member  2  is taken off between the power setting member  2  and the associated PID regulator  1 . Upon comparison at the point  13 , a check is made to ascertain whether the regulating reserve margin is greater than a predetermined minimum U min . If that is not the case, adjustment of the ignition point is effected within predetermined limits ZZP min  and ZZP max  by means of the ignition timing control device  14 . In addition that arrangement may also include a knock regulator  7  which, by limiting the range of adjustment, prevents the engine  5  from suffering from knock by virtue of displacement of the ignition point. The regulating section additionally shown in  FIG. 3  both ensures the desired regulating reserve margin and also always achieves optimum efficiency for the internal combustion engine. In addition adaptation to the ambient conditions (for example pressure and temperature) is also possible by adjustment of the ignition point. Ignition point adjustment itself corresponds to the operating procedure disclosed in European patent application EP 1 225 330 A2 so that attention is directed thereto. 
   The method according to the invention is favorable in particular for the operation of spark-ignition and/or mixture-charged, preferably stationary, Otto-cycle engines which are preferably operated with a combustible gas, for example methane, as the fuel.