EP1409865B1 - Method for compensating injection quantity in each individual cylinder in internal combustion engines - Google Patents

Description

State of the art

The invention relates to a method for operating a Internal combustion engine, in particular of a motor vehicle, in which Fuel injected into the cylinders of the internal combustion engine in which the injected into the individual cylinders Amount of fuel is adjusted, and at which a lambda value In the exhaust pipe of the internal combustion engine is determined. Further relates to the invention a for carrying out this method suitable control device for an internal combustion engine.

Such a method and such a control device are known from DE 199 03 721 C1.

Furthermore, it is known that to minimize pollutants in the catalytic aftertreatment of exhaust gases with the help of a Regulated three-way catalyst the air-fuel mixture must have a certain mass ratio. This Ratio is indicated by the so-called air ratio lambda and can by a lambda probe located in the exhaust pipe be determined.

Known methods introduce the measured values of the lambda probe Closed loop to, during operation of the internal combustion engine the injection quantities of the individual cylinders in dependence of lambda value controls.

For a single lambda probe located in the exhaust pipe However, this regulation is only about the individual Cylinder averaged lambda value.

Mixture differences in the individual cylinders, which despite same injection quantity or the same default values of a Injection quantity control unit due to Component tolerances and aging effects can not and with regard to the design of the cylinder-specific injection quantity also not be taken into account.

Improved procedures see a temporal assignment of the Exhaust pipe flowing through exhaust gases and their lambda values the individual cylinders. In principle, this is one Individual cylinder control of the injection quantity with a single Lambda sensor possible, however, the measurement accuracy by mixing effects and turbulences directly in time successive exhaust gas quantities of different cylinders in the Exhaust pipe affected.

Solutions where each cylinder is assigned a lambda probe is, are technically very complicated.

Purpose and advantages of the invention

It is therefore an object of the present invention, a method to the cylinder individual adjustment of the injection quantity Internal combustion engine with a arranged in the exhaust pipe Lambda probe provide.

This object is achieved by a method according to claim 1 and solved by a control device according to claim 11.

The method according to claim 1 uses a method from the statistical experimental design to the influence of Injected quantities attributed to the individual cylinders the measured in the exhaust pipe, averaged over all cylinders Air ratio to determine.

In this case, the predetermined by a control unit Injection quantities following an orthogonal design Gradually cylinder-individually changed. After every Step of the experimental plan is the lambda value in Exhaust pipe, resulting in the change of the Injection amount results, detected, and detected with these Values will be available at the end of each experiment Cylinder a correction value for the injection quantity determined individually.

These correction values are for subsequent Injections to adjust the injection quantities cylinder used individually, so that in each Cylinder always the optimal air-fuel mixture established.

The essential advantage of the method according to the invention is that using a single Lambda probe the optimal injection quantity for each cylinder the internal combustion engine can be determined.

This is done by a mathematical modeling of the lambda value reached. This is done by means of a polynomial sentence for the dependent variable lambda is the influence of several independent variables determined on the value of lambda.

The independent variables correspond to each cylinder individually metered injection quantities, so that the mathematical model lambda as a function of Injection quantities of the individual cylinder supplies, where Coefficients of the polynomial a weighting of influence reflect the injection quantities of the cylinders.

These coefficients may e.g. from the under the orthogonal experimental design become. It is also possible to estimate coefficients or determined by plausibility considerations.

Depending on the degree of polynomial chosen for the approach also interactions between injection quantities of several Cylinders are determined.

A mathematical model obtained in this way for lambda allows using a setpoint default for lambda, e.g. lambda = 1, and solution of the resulting Equation the calculation of the injection quantities for each Cylinders where the specified setpoint is set.

The injection quantities calculated with the model differ i.a. from the injection quantities given by the control unit from. This difference is essentially based on different combustion conditions and tolerances in the valve control or in the valves of the single cylinder and forms the correction value for Adjustment of injection quantity.

Another significant advantage is the ability to Injectors with much larger tolerances too use.

In conventional injection systems are the requirements to the flow tolerance of injectors very high, what about corresponding rejects in their production leads.

The balancing method according to the invention also allows for strongly different flow characteristics different injection valves a corresponding Adjustment of the injection quantities of the individual cylinders, whereby the optimum lambda value for an exhaust gas aftertreatment can be adjusted.

Thus, the proposed method is also suitable, the Cost of manufacturing corresponding injection systems at simultaneous improvement of emission behavior too reduce by using cheaper injectors with used larger tolerances and the influences of this Tolerances on the lambda value by the inventive Procedures are eliminated.

Moreover, the invention has Matching method the advantage, not throughout the whole Operating time of the internal combustion engine or the regulating them To run control unit. This results Savings in the cycle time of the processor means of the Controller that can be used elsewhere.

An advantageous development of the invention The method consists in the determined correction values in Control unit to save and this at the next Call vehicle start. This makes it possible to work in regular intervals such as e.g. in the maintenance of the Vehicle, make a new adjustment, and the new determined correction values for further vehicle operation to provide.

The periodic determination of the correction values in Driving is also possible, which makes the system too on short-term changes in the properties of the Injectors, such as e.g. Contamination of a nozzle react and the injection quantities cylinder individually new situation.

Particularly useful is already a manufacturer immediately after the production of the motor vehicle performed comparison.

A further embodiment of the method according to the invention is characterized in that a broadband lambda probe is used, which allows the lambda value in one Interval of 0.7 <lambda <4 continuous to value to capture.

Another, particularly advantageous embodiment of inventive method provides the use of a so-called. Jump probe, a lambda probe with characteristic jump before. When using this inexpensive probe type must a change in the lambda value as a result of a Change in the injection amount indirectly, e.g. from the Control deviation of a lambda controller can be determined because the jump probe only a characteristic jump at lambda = 1 has, i. unlike the broadband lambda probe none continuous value detection of lambda allows.

Another variant of the method according to the invention sees before that the order of an orthogonal design underlying regression polynomial depending on lambda is selected. If after a calibration process with a regression polynomial of lesser order the desired one Value of lambda can not be regulated with sufficient accuracy can, it is possible in this embodiment, a Regression polynomial of higher order to choose the Accuracy of the matching process to improve.

Of particular importance is the realization of the inventive method in the form of a Computer program for a control unit Internal combustion engine, in particular of a motor vehicle, is provided. In this case, the computer program is particular executable on a microprocessor and to execute the inventive method suitable. In this case will So the invention realized by the computer program, so this computer program in the same way the Invention represents as the method to its execution the computer program is suitable. The computer program can be stored on an electrical storage medium be, for example on a flash memory or a Read-only memory.

Other features, uses and benefits of Invention will become apparent from the following description of embodiments of the invention shown in FIGS the drawing are shown. All form described or illustrated features alone or in any combination the subject of the invention, regardless of their summary in the Claims or their dependency as well as independently from their formulation or presentation in the description or in the drawing.

Embodiments of the invention

Fig. 1

shows a schematic block diagram of a Embodiment of an inventive Internal combustion engine,

Fig. 2

shows a flowchart of a preferred Embodiment of the method according to the invention, and

Fig. 3

shows part of an orthogonal design with four influencing factors.

In Fig. 1, an internal combustion engine 1 is a Motor vehicle shown, in which a piston 2 in a Cylinder 3 is reciprocable. The cylinder 3 is with a combustion chamber 4 provided, inter alia, by the Piston 2, an intake valve 5 and an exhaust valve. 6 is limited. With the inlet valve 5 is an intake pipe. 7 and an exhaust pipe 8 is coupled to the exhaust valve 6.

In the area of the intake valve 5 and the exhaust valve 6 protrude an injection valve 9 and a spark plug 10 in the Combustion chamber 4. It is also possible, the injection valve 9 in To arrange intake pipe 7.

Fuel can flow into the combustion chamber via the injection valve 9 4 are injected. With the spark plug 10, the Fuel in the combustion chamber 4 are ignited.

In the intake pipe 7 is a rotatable throttle valve 11th accommodated, via the intake pipe 7 air supplied is. The amount of air supplied depends on the Angular position of the throttle valve 11. The exhaust ports of the individual cylinder 3 run together in front of the catalyst 12 and form the exhaust pipe 8, in which a lambda probe 13th is appropriate. The catalyst 12 is used to clean the by the combustion of the fuel resulting exhaust gases and the lambda probe 13 detects the air-fuel ratio in the exhaust pipe 8.

During operation of the internal combustion engine 1 fuel over the injectors 9 of the individual cylinder 3 in the associated combustion chambers 4 injected. With the help of Spark plugs 10 become burns in the combustion chambers 3 generated by the piston 2 in a back and forth Be moved. These movements are on transmit a non-illustrated crankshaft and practice on this one torque out.

A controller 15 is of input signals 16 applied, measured by sensors operating variables represent the internal combustion engine 1. For example, that is Control unit 15 with an air mass sensor, a Speed sensor and the lambda probe 13 connected. Of Further, the control unit 15 with an accelerator pedal sensor connected, which generates a signal indicating the position of a operated by a driver accelerator pedal and thus the indicates requested torque. The control unit 15 generates Output signals 17, with which via actuators or actuators the behavior of the internal combustion engine 1 can be influenced can. For example, the control unit 15 with the Injector 9, the spark plug 10 and the throttle valve 11 and the like connected to and generates the Activation required signals.

Among other things, the controller 15 is provided to the Control operating variables of the internal combustion engine 1 and / or to regulate. For example, that of the injection valve 9 in the combustion chamber 4 injected fuel mass of the Control unit 15, in particular with regard to a small Fuel consumption and / or a low Controlled pollutant development and / or regulated. To For this purpose, the control unit 15 with a Microprocessor in a storage medium, especially in a flash memory a computer program stored, which is suitable to the said To perform control and / or regulation.

In Fig. 2 is a flow chart of a preferred Embodiment of the method according to the invention for Individual adjustment of the injection quantity with cylinder an internal combustion engine, the three Method steps a), b), c) contains.

The method step a) of FIG. 2 comprises the Processing of an orthogonal design, of which the first four steps a1 to a4 by way of example in the table of Fig. 3 are shown.

The entire design plan shows N steps (not shown) on and includes according to the number of cylinders one exemplarily selected four-cylinder internal combustion engine. 1 four influencing variables Z1 to Z4, each on a associated output L_ai (i = 1, .., N) act.

The influencing variable Zk (k = 1, .., 4) denotes the Injection amount of the cylinder k, i. the amount of fuel attributed to the cylinder k as part of the design plan becomes.

The output quantity L_ai corresponds to that over a sufficient one long averaged, from a lambda probe 13 in the Exhaust pipe 8 measured 1 ambda value of step i (i = 1, .., N) of the orthogonal experimental design.

The purpose of the orthogonal design is to be as possible a few steps an analytical relationship between the Lambda value in the exhaust pipe 8 and the injection quantities of to determine individual cylinder 3.

This is done by a quadratic regression function Using a Polynomansatzes formed, the lambda as To model the function of injection quantities.

A part of a quadratic regression polynomial for the lambda value in the exhaust pipe 8 as a function of the injection quantities of the four cylinders 3 is listed below, with only the ones containing the factor Z1 being shown for the sake of clarity of the terms of higher order. lambda (Z1, Z2, Z3, Z4) = b0 + b1 * Z1 + b2 * Z2 + b3 * Z3 + b4 * Z4 + b11 * Z1 * Z1 + b12 * Z1 * Z2 + b13 * Z1 * Z3 + b14 * Z1 * Z4 + ....

To find the unknown coefficients bi (i = 0, .., N), bij (i, j = 1, .., N, i <j) and bii (i = 1, .., N), N + 1 steps of the experiment plan must be carried out.

A step ai is to set the injection quantities for the four cylinders 3 to the scheme shown in Fig. 3 Z1, Z2, Z3, Change Z4 following. After that it will be in succession this change adjusting lambda value L_ai detected.

The change in injection quantity is indicated by '+' or '-' symbolizes, where '+' an increase in the injection quantity of the corresponding cylinder 3 by e.g. 4% and '-' one Reduction by the same value describes. As initial value for this change in the injection quantity is the respective for the normal operation of the internal combustion engine 1 of the Control unit 15 to use predetermined value.

For example, in step a1 of FIG. 3, the first three cylinders are charged with an injection quantity of only 96%, while the fourth cylinder receives 104%. The associated lambda value L_a1 is determined to be 1.03, for example. This leads to the following equation: L_a1 = 103% = b0 + b1 * 96% + b2 * 96% + b3 * 96% + b4 * 104% + O (Z * Z)

For clarity, the terms of order Z * Z are to Summands O (Z * Z) are summarized.

With a sufficiently large number N + 1 at test steps, the N + 1 equations of the above mentioned Can deliver the kind Coefficients bi, bij, bii of the regression polynomial be determined.

Usually even several coefficients, in particular coefficients of the terms of higher order, neglected, thereby reducing the computational burden is, i. that not all N trial steps to Determination of the coefficients must be carried out.

Under knowledge of the coefficients of the regression polynomial lambda (Z1, Z2, Z3, Z4) can be used in process step b) of Fig. 2 of the balancing method according to the invention Correction values for the injection quantity of each cylinder 3 be determined. These correction values correspond to Difference from the solution of the equation lambda (Z1, Z2, Z3, Z4) = 1 determined injection quantities and that of the Control unit 15 predetermined injection quantities.

Process step c) of FIG. 2 provides for each cylinder 3 an adjustment of the predetermined by the control unit 15 Injection quantity using the correction values.

Through this comparison, it is possible, more cost-effective Injectors with much larger tolerances too use, as well as extreme deviations of the properties an injection valve on the correction of the respective Injection quantity can be compensated.

The accuracy of the adjustment can be increased even more, by choosing a higher-order regression polynomial. In addition, the selection of the order of the Regression polynomial depending on the control behavior of the lambda controller.

The lambda value is measured using a broadband lambda probe 13, which is a continuous value acquisition of lambda in an interval between lambda = 0.7 and lambda = 4 allowed.

The measurement of the lambda value can also be done with a Jump probe whose characteristic curve jumps at lambda = 1. It does not allow continuous value Detection of lambda, but only the detection of the Transition from lambda <= 0 to lambda> 0 and vice versa.

In order to determine lambda with such a jump probe, must for example, from a first lambda value in the so-called Lean operation (lambda> 1) based on the injection quantity be increased until the next lambda jump occurs, i. until the change from lambda> 1 to lambda < 1 takes place.

The necessary increase in the injection quantity is a measure for the first lambda value.

The in process step b) of Fig. 2 of the Inventive adjustment method Correction values are stored in the control unit 15 and can be retrieved at the start of the vehicle and to Correction of injection quantities can be used.

The correction values may be e.g. in an EEPROM memory which are often used to store Operating variables used in control units.

An initial implementation of the matching procedure can be direct done after the production of the motor vehicle; It is also possible, the adjustment process periodically while driving or perform maintenance at short notice Consider changes in the injection system during adjustment to be able to.

Claims (11)

1. Method for operating an internal combustion engine

   (1) in particular of a motor vehicle, in which fuel is injected into the cylinders (3) of the internal combustion engine (1), in which the fuel quantity to be injected into the individual cylinders (3) is balanced, and in which a lambda value is determined in the exhaust pipe (8) of the internal combustion engine,

   characterized in that

   a) injection quantities predetermined by a control unit (15) are altered, following an orthogonal test plan, for the individual cylinders (3) over a plurality of steps, and the lambda value for each step of the test plan, taken as a mean value over a sufficiently long period of time and a plurality of injections, is determined after the respective step,

   b) after the test plan has ended, correction values for the injection quantities of each cylinder (3) are determined from the lambda values determined, and in that

   c) the correction values are used to balance the injection quantities predetermined by the control unit (15).
2. Method according to Claim 1, characterized in that the correction values are stored in the control unit (15), called up each time the motor vehicle is started and used for operation of the internal combustion engine (1).
3. Method according to one of the preceding claims, characterized in that the correction values are determined immediately after production of the motor vehicle.
4. Method according to one of the preceding claims, characterized in that the correction values are determined periodically while the vehicle is driving.
5. Method according to one of Claims 1 to 4,
   characterized in that a wide-band lambda sensor (13) is used.
6. Method according to one of Claims 1 to 4,
   characterized in that a step-change sensor (13) is used.
7. Method according to one of the preceding claims, characterized in that the order of a regression polynomial forming the basis of the orthogonal test plan is selected as a function of the lambda value.
8. Computer program for a control unit (15) of an internal combustion engine (1) in particular of a motor vehicle, programmed for applying the method according to one of Claims 1 to 7.
9. Computer program according to Claim 8,
   characterized by its storage on a memory element, in particular a flash memory.
10. Control unit (15) for an internal combustion engine (1) in particular of a motor vehicle, designed to apply the method according to one of Claims 1 to 7.
11. Control unit (15) according to Claim 10,
    characterized by its use in an internal combustion engine (1) in particular for a motor vehicle.

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