Method of and device for determination of characteristic values of an internal combustion engine

In a method of and device for providing data of a model for determination of characteristic variables for controlling an internal combustion engine, in particular an internal combustion engine with direct injection or suction pipe injection, for each predetermined operation point of the internal combustion engine at least one local model in particular of low order is provided with data.

BACKGROUND OF THE INVENTION
 The present invention relates to a method of and a device for data
 determination of a model for determination of characteristic variables of
 an internal combustion engine, in particular an internal combustion engine
 with direct injection or suction pipe injection.
 The non published patent application DE 197 45 682 discloses a method of
 and a device for determination of characteristic variables, which are a
 part of a model for controlling a drive unit, and depending on the type of
 the drive unit, can be different. There first, by automatic processing of
 a predetermined measuring program, measuring data are determined for at
 least one operational variable of the drive unit for different operation
 points of the drive unit. Then, in a second step the characteristic
 variables are measured by optimization of the deviation, and the
 operational variable is determined on the basis of the calculated value of
 the characteristic variables.
 SUMMARY OF THE INVENTION
 Accordingly, it is an object of present invention to provide a method of
 the above mentioned general type which is improved in that, with lowest
 possible measuring expenses, a model of an internal combustion engine can
 be exactly provided with data, for obtaining optimal characteristic
 variables for controlling an internal combustion engine.
 In keeping with these objects and with others which will become apparent
 hereinafter, one feature of present invention resides, briefly stated, in
 a method of data determination of a model for determination of
 characteristic variables for controlling an internal combustion engine in
 which for each predetermined operation point of the internal combustion
 engine, at least one local model, in particular of low order, is provided
 with data.
 An especially great advantage of the present invention is that the data
 determination of a local model of an internal combustion engine is
 possible with a minimum expense for the measurements. This stands in
 contrast to the expensive screen measurement.
 The data determination of a model means in this connection that the model
 coefficients or model parameters are determined so that the deviation
 between the real internal combustion engine and the model of the internal
 combustion engine is minimal. A local model means that the model is
 provided with data only for a predetermined operation point of the
 internal combustion engine and only for this predetermined operation point
 of the internal combustion it is valid.
 For example, for data determination of a model of an internal combustion
 engine by means of a screening process, when only one operational variable
 and three actuation variable of the internal combustion engine are
 considered and when the actuation variable are varied only in three steps,
 3.sup.3 =27 measurements are needed. With a local model of second order,
 to the contrary, only 10 measurements are needed in order to completely
 determine or provide the model with data.
 With increased number of actuation variable and operational variables, the
 advantage of a local modeling is more pronounced. When for example five
 actuation variable and one operational variable of the internal combustion
 engine are considered in a model and when the five actuation variable for
 providing data of the model are changed in five steps, then 5.sup.5 =3125
 measurements must be performed. In contrast, for example with a local
 model of second order with alternating action of a first order, only 26
 measurements are needed to provide data or to determine the model. In
 order to prevent a model error or to compensate the measuring error
 better, in practice more than 26 measurements are performed.
 A further advantage of the present invention is that with the use of local
 models of low order, a simple and clear mathematical model of the internal
 combustion engine is provided.
 The novel features which are considered as characteristic for the present
 invention are set forth in particular in the appended claims. The
 invention itself, however, both as to its construction and its method of
 operation, together with additional objects and advantages thereof, will
 be best understood from the following description of specific embodiments
 when read in connection with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS
 The present invention is illustrated for example as an internal combustion
 engine with direct injection. However, the invention can be used for
 controlling any electromechanical system, in particular a motor vehicle,
 which is provided with a control device.
 As shown in FIG. 1, in an internal combustion engine with direct injection
 10 fresh air is supplied by means of a suction pipe 19 through an inlet
 valve 20 to a combustion chamber 21. The quantity of the fresh air supply
 into the combustion chamber 21 can be controlled by a throttle flap 22. An
 air quantity measuring device 23 determines the fresh air flowing into the
 internal combustion engine.
 An injection valve 24 and a spark plug 45 are arranged in a cylinder head
 25. A high pressure pump 26 supplies the fuel at a working pressure and
 injects it through a fuel supply conduit 27 and an injection valve 24 into
 the combustion chamber 21.
 The injected fuel is ignited by means of the spark plug 45. A piston 44 is
 driven by expansion of the ignited fuel. Furthermore, the combustion
 chamber 21 has an outlet valve 28 for ejection of exhaust gas produced
 during combustion.
 A lambda probe 29 is arranged in an exhaust gas pipe 30. By means of the
 lambda probe 29, in the exhaust gas pipe 30 the oxygen fraction in exhaust
 gas can be measured. Thereby the air-fuel ratio in the mixture can be
 determined. A catalyst 46 is further arranged in the exhaust gas pipe 30.
 The catalyst 46 operates for converting damaging exhaust gas components
 such as CO HC and NO into CO.sub.2, H.sub.2 O and N.sub.2.
 An AGR conduit 31 connects the exhaust pipe 30 with the suction pipe 19.
 Thereby, due to the higher pressure in the exhaust pipe 30 exhaust gasses
 are supplied from the exhaust pipe 30 into the suction pipe 19. By means
 of the AGR valve 32, the exhaust gas stream in the AGR conduit 31 can be
 controlled.
 A tank ventilating conduit 34 leads from a fuel tank or and activated
 carbon container 33 to the suction pipe 19. Thereby additional oxygen can
 be supplied into the suction pipe 19 and therefore into the combustion
 chamber 21. The fuel flow in the tank ventilation conduit 34 can be
 controlled by a tank ventilation valve 35.
 The control of the total internal combustion engine 10 is performed by a
 control device 11. Furthermore, the control device 11 can control a
 transmission 16, a brake system 17 and any further electromechanical
 systems 18. Various sensors and actuators are controlled by the control
 device 11 through signal and control conductors 36.
 The internal combustion engine 10 can operate in different operation modes,
 which substantially differ by the injection time, the ignition time and
 the cylinder filling. The control device 11 can convert the internal
 combustion engine 10 from one operational mode to another. The important
 operational mode of the internal combustion engine are the homogenous
 operation "hom" and the shift operation "sch".
 In the homogenous operation "hom", the fuel is injected by the injection
 valve 24 into the combustion chamber 21 during a suction phase which is
 caused by the piston movement. Simultaneously air is aspirated via the
 throttle flap 22. The aspirated air whirls the fuel, which thereby is
 distributed in the combustion chamber approximately uniformly or
 homogeneously. The fuel-air mixture is subsequently compressed, for
 igniting by a spark plug 45. The ignited fuel-air mixture extends and
 drives the piston 44. The produced torque depends in the homogenous
 operation substantially on the position of the throttle flap 22 and
 therefore is substantially proportional to the fresh gas filling in the
 cylinders. In order to obtain a high torque and a low pollutant generation
 during the combustion, the air-fuel mixture is adjusted as close as
 possible to lambda=1 or lambda &lt;1. The homogenous operation is set in
 full load operation of the internal combustion engine.
 In the shift operation "sch" the throttle flap 22 is widely opened, and
 thereby the internal combustion engine operates approximately unthrottled.
 The fuel is injected during the compression phase so that at the time of
 ignition an ignitable air-fuel cloud is located in the immediate
 surrounding area of the spark plug. Then the air-fuel cloud is ignited by
 the spark plug 45, and the piston 44 is driven by the following expansion
 of the ignited air-fuel cloud. The thusly produced torque depends in the
 shift operation substantially on the injected fuel mass rk. The shift
 operation is set in a partial load region of the internal combustion
 engine.
 In order to obtain an optimal torque and a low pollutant generation during
 combustion, in the shift operation several actuation variable more than in
 homogenous operation must be considered. In the homogenous operation as a
 rule only the ignition angle zw and the standardized air-fuel ratio lambda
 are considered as dominant actuation variables. In contrast, in the shift
 operation as a rule the ignition angle zv, the standardized air-fuel ratio
 lambda, the angle of the injection start wesb, the ratio of suction pipe
 pressure to environment pressure ps/pu, the exhaust gas return rate agr,
 the fuel pressure prail, the position of the charge movement flap lb and
 the valve overlapping vvc are considered as dominant actuation variables.
 With the selection of the dominant operational variables of the internal
 combustion engine with direct injection, the relationships are similar. In
 homogenous operation as a rule only the specific fuel consumption be, the
 knocking kl and the exhaust gas temperature tab are considered as
 operational variables. In the shift region as a rule after seven
 operational variables are considered. They include the specific fuel
 consumption be, the knocking kl, the exhaust gas temperature tab, the
 running unquietness LU, the hydrocarbon emission EHC, the nitrogen
 emission ENO.sub.S, the soot fraction in exhaust gas SZB and the average
 combustion pressure pmi.
 Due to the plurality of dominant acting and operational variables,
 approximately by the factor 10.sup.3 more measurements in the shift
 operation than in the homogenous operation of the internal combustion
 engine are needed, for providing data for a model of the shift operation
 by means of the screen process.
 FIG. 2a schematically shows an internal combustion engine with a direct
 injection, wherein in particular variables which are relevant for the
 shift operation are illustrated. In a block 201, the variables are shown
 which characterize an operation point of the internal combustion 10 in a
 shift operation.
 Operation point variables:
 nmot: Rotary speed
 rk: Relative fuel mass
 In a block 202 the actuation variables of the internal combustion engine in
 shift operation are shown.
 Actuation variables:
 zw: Ignition angle
 wesb: Angle of injection start
 ps/pu: Ratio of suction pipe pressure to surrounding pressure
 agr: Exhaust gas return rate
 prail: Fuel pressure
 lb: Position of the charge movement flap
 vvs: Valve overlapping.
 lambda Standardized air-fuel ratio.
 In block 203 schematically the internal combustion engine is illustrated.
 In block 204 the operational variables of the internal combustion engine
 is visible region are shown.
 Operational variables:
 be: Fuel consumption, which in fifth operation is proportional to output
 moment Md.
 EHC: Hydrocarbon emission.
 ENO.sub.X Nitrogen emission.
 SZB: Soot fraction in exhaust gas (soot number).
 pmi: Average combustion pressure.
 LU: Running unquiteness.
 tab: Exhaust gas temperature.
 In block 205 edge conditions are illustrated, which are required for
 providing data of the model. For example, they are a stationary operation
 of the internal combustion engine, a shift operation as an adjusted
 operational mode, and an evaluation of the raw exhaust gas emission.
 An example for a model setup is illustrated in FIG. 2a. With it the
 relationship between the operational variables of the internal combustion
 engine and the actuation variable in a shift operation can be determined.
 This model is assembled for each operation point of the internal
 combustion engine for the shift operation. An operation point in the shift
 operation is formed from a rotary speed not and a relative fuel mass rk,
 wherein the fuel mass is proportional to the output moment.
 The values which are representative of the operation point of the internal
 combustion engine are substantially dependent on the adjusted operational
 mode. For example, in the homogenous operation an operation point is
 formed of a rotary speed nmot and the cylinder filling rl, wherein here
 the cylinder filling is substantially proportional to the output moment.
 For providing data of this model, or in other words for determination of
 the relationship between the actuation variables and the operational
 variables, the coefficients a.sub.xx b.sub.xx and c.sub.xx of the
 corresponding terms must be determined.
 The first equation determines the relationship between the fuel consumption
 be and the actuation variable of the internal combustion engine dar,
 wherein for the sake of the space, not all terms are determined. The
 second equation determines the relationship between the hydrocarbon
 emission EHC and the actuation variables of the internal combustion engine
 dar. The third equation determines the relationship between the nitrogen
 emission ENO.sub.X and the actuation variables of the internal combustion
 engine. Further equations of the model are not illustrated for the space
 reasons.
 The selected model setup is here shown only exemplary and can be expanded
 to any number of operating variables and actuating variables. FIG. 3 shows
 a flow chart of the individual steps of the inventive method. After a
 start of the method, first in step 310 operating points of the internal
 combustion engine are determined, for which individually a local model
 must be provided with data. In the shift operation this operation points
 are formed by the rotary speed nmot and the injected fuel mass rk. The
 operation points are determined within the maximum permissible rotary
 speed and the maximum possible injecting fuel mass for the shift operation
 of the internal combustion engine.
 In step 320 a region of the change of the actuating variables is
 determined, in which a permissible operation of the internal combustion
 engine in the shift operation is guaranteed. For this purpose for example
 two actuating variables of the internal combustion engine are varied,
 while the other actuating variables are maintained constant.
 Simultaneously the running unquiteness LU and/or the average combustion
 pressure PMI are measured. By evaluation of these measured variables, for
 example by comparison with a threshold value the permissible change region
 of the actuating variable can be determined.
 In step 330 the order of the local model for describing the shift operation
 of the internal combustion engine is selected. The order of the model can
 be predetermined or can be arbitrarily selectable. Measurements have shown
 that a model of second order with alternating actions of first order
 sufficiently accurately describe the shift operation of an internal
 combustion engine with direct inject, and maintain the measuring expenses
 for providing data of the model in justifiable limits.
 In step 340 the optimal measuring points are determined, which are required
 for providing data of the model and completely determine this model. The
 number of the measurements is determined in dependence on the model order,
 on permissible region of the changes of the actuating variables of the
 internal combustion engine, and on the desired model accuracy. For example
 for this purpose a method for research planning, for example "Design of
 Experiments" (DOE) can be used.
 In a step 350 automatically each predetermined operation point of the
 internal combustion engine is set, and measurements required for providing
 data of the local model are performed.
 In a step 360, the model of the shaft operation of the internal combustion
 engine for each operating point is optimized. For this purpose the
 coefficients of the set local model for each operation point are changed
 so that the distance between the operating variables calculated by the
 model and the operating variables determined by the measurement is
 minimal. For example as a measure for the distance, an average square
 distance or an amount of an average distance are selected.
 In step 370, the optimal characteristic variables for an operation of the
 internal combustion engine are determined. In step 380 the determined
 optimal characteristic variables are stored in the control device.
 For the sake of completeness it should be mentioned that both with the
 predetermined actuating variables and also the operating variables,
 depending on model, motor, vehicle, etc., not all of them must be used.
 It will be understood that each of the elements described above, or two or
 more together, may also find a useful application in other types of
 methods and constructions differing from the types described above.
 While the invention has been illustrated and described as embodied in
 method of and device for determination of characteristic values of an
 internal combustion engine, it is not intended to be limited to the
 details shown, since various modifications and structural changes may be
 made without departing in any way from the spirit of the present
 invention.
 Without further analysis, the foregoing will so fully reveal the gist of
 the present invention that others can, by applying current knowledge,
 readily adapt it for various applications without omitting features that,
 from the standpoint of prior art, fairly constitute essential
 characteristics of the generic or specific aspects of this invention.