DE10256906B4 - Method for controlling an air / fuel mixture in an internal combustion engine - Google Patents

Abstract

A method for controlling an air / fuel mixture in an internal combustion engine (1), wherein an injected fuel mass is corrected for an adaptation of an air / fuel mixture ratio that in a multiple injection of fuel with multiple injections for a combustion process in a cylinder ( 5) of the internal combustion engine (1) the correction of the injected fuel mass is performed for each of these injection events, characterized in that the adaptation of the correction value for the fuel mass at an operating point of the internal combustion engine (1) is carried out at substantially constant speed and air supply

Description

State of the art

The invention is based on a method for controlling an air / fuel mixture in an internal combustion engine according to the preamble of the main claim.

From the DE 199 45 618 A1 For example, a method of controlling a fuel injection system is known. The activation duration of an electrically actuated valve determines the quantity of fuel to be injected. In certain operating states, the minimum actuation duration is determined at which fuel is being injected. Starting from a starting value, the activation duration is increased or decreased. The drive duration at which a change of a signal occurs is used as the minimum drive duration.

Furthermore, from the DE 199 31 823 A1 A method for controlling an internal combustion engine is known. The fuel injection is divided into at least a first and a second partial injection. A correction value for one of the partial injections is determined. Based on this correction value, the correction value for the other partial injection is determined by weighting.

rlp

die erwartete relative Luftfüllung,

fr

der Regelfaktor der Lambda-Regelung,

fra

ein multiplikativer Korrekturwert für die Kraftstoffmasse,

rka

ein additiver Korrekturwert für die Kraftstoffmasse und

lamsbg

ein Sollwert für das von der Lambda-Regelung einzustellende Luft-/Kraftstoff-Gemisch-Verhältnis λ sind.

In today's internal combustion engines or engines with electronically controlled injection of fuel is ensured by the so-called lambda control and a mixture adaptation that the air / fuel mixture ratio λ is correctly precontrolled. The injected relative fuel mass rk is corrected as follows: rk = rlp + rka / lamsbg · fr fra (1) in which

rlp

the expected relative air charge,

Fri.

the control factor of the lambda control,

fra

a multiplicative correction value for the fuel mass,

rka

an additive correction value for the fuel mass and

lamsbg

are a setpoint for the adjusted by the lambda control air / fuel mixture ratio λ.

Thus, according to equation (1), it is assumed that the total error of the air / fuel mixture ratio results from the fuel path, that is, due to the injected relative fuel mass rk. Therefore, according to equation (1), only the relative fuel mass rk is corrected to obtain the target value lamsbg for the air-fuel mixture ratio λ. Although this gives the desired air / fuel ratio, but not necessarily correct values for the relative fuel mass rk and the relative air charge rl.

In the correction of the relative fuel mass rk according to equation (1), only a single fuel injection per combustion process is considered. For multiple injections per combustion process, the correction of the relative fuel mass rk according to equation (1) no longer gives a correct result.

Advantages of the invention

The inventive method for controlling an air / fuel mixture in an internal combustion engine with the features of the main claim has the advantage that in a multiple injection of fuel with multiple injection events for a combustion process in a cylinder of the internal combustion engine, the correction of the injected fuel mass for each of these Injection operations is performed. In this way, even with multiple injections per combustion process, a correct pilot control of the relative fuel mass rk for setting the desired setpoint value lamsbg for the air / fuel mixture ratio λ is obtained. It is particularly advantageous if the adaptation of the correction value for the fuel mass is performed at an operating point of the internal combustion engine with a substantially constant speed and air supply. In this way, a reliable elimination of the error of the relative fuel mass rk is ensured, so that a remaining deviation of the air / fuel mixture ratio from the predetermined target value lamsbg can be unambiguously identified as an error of the relative air mass rl.

The measures listed in the dependent claims advantageous refinements and improvements of the main claim method are possible.

It is particularly advantageous that a correction value for the fuel mass is adapted in such a way that an approximately equal control factor for the setting of a given air / fuel mixture results for combustion processes with a different number of injection events. In this way, an error of the relative fuel mass rk from a fault of the relative air charge rl in deviations of the actual air / fuel ratio can be separated from the predetermined setpoint lamsbg and thereby both the fuel path, so the relative fuel mass rk, and the Air path, so the relative air filling rl correct for example by adaptation. Thus, both the relative fuel mass rk, and the relative air charge rl can be adjusted substantially correctly. This is advantageous in the case of the relative fuel mass rk, because in this way fuel is not consumed unnecessarily. Since the relative air charge rl is used as the input variable of a multiplicity of characteristic curves of the engine control, greater accuracy also has an advantageous effect here.

Furthermore, it is particularly advantageous if the correction value for the fuel mass is adapted until a change in the control factor for combustion processes with a different number of injection events remains below a predetermined threshold. In this way, an iterative adaptation method is realized, which can be used with very little effort to eliminate the error of the relative fuel mass rk.

It is furthermore advantageous if an idling operating state of the internal combustion engine is selected as the operating point and an additive correction value is selected as a correction value for the fuel mass. The idling operation state has the advantage that it can be maintained particularly easily constant with regard to rotational speed and air supply, wherein the use of an additive correction value in the idling operating state is particularly effective.

A further advantage results when an operating state of the internal combustion engine at high load is selected as the operating point and a multiplicative correction value is selected as a correction value for the fuel mass. At high load, a multiplicative correction value has a stronger effect and is therefore particularly suitable for correcting the relative fuel mass rk.

It is particularly advantageous if the deviation of the control factor remaining after completion of the adaptation of the fuel mass correction value from a desired value or the remaining deviation of the actual air / fuel mixture ratio from the predetermined desired value lamsbg by adapting a correction value for the supplied air mass is compensated. In this way, the desired according to the predetermined target value lamsbg desired air / fuel mixture ratio can be correctly pre-tax without a mistake of the relative fuel mass rk and a error of the relative air mass rl must be taken into account.

drawing

An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description.

Show it

1 a block diagram of an internal combustion engine and

2 a flowchart for explaining the method according to the invention.

Description of the embodiment

In 1 features 1 an internal combustion engine comprising an internal combustion engine. The internal combustion engine can be designed as a gasoline engine or as a diesel engine. In the following, it is assumed by way of example that the internal combustion engine is designed as a gasoline engine. In this case, the internal combustion engine includes 1 at least one cylinder 5 with a piston 40 and a combustion chamber 35 , The combustion chamber 35 is about an air supply 10 , which is also referred to below as the suction tube, fresh air can be supplied. The supplied air mass is thereby by the position of a throttle 15 in the intake manifold 10 controlled. Further, the combustion chamber 35 to the intake manifold 10 I'm over an inlet valve 25 accessible or lockable. In the intake manifold 10 is according to 1 furthermore an injection valve 20 arranged over the fuel in the intake manifold 10 is injected to form an air / fuel mixture with the supplied air through the open inlet valve 25 in the combustion chamber 35 can get. There, the air / fuel mixture with the help of a spark plug 30 ignited and initiated a combustion of the air / fuel mixture, which the piston 40 drives. The burned exhaust gas may be via an exhaust valve 45 in an exhaust tract 50 the internal combustion engine 1 escape. In the exhaust tract 50 is an oxygen sensor 55 arranged, which is also referred to as lambda probe and the air / fuel mixture ratio in the exhaust system 50 determined. In the 1 arrangement described thus represents an internal combustion engine with intake manifold injection. Alternatively, the fuel also directly into the combustion chamber 35 be injected. For the inventive method, it is irrelevant whether the fuel, as in 1 shown in the intake manifold 10 or directly into the combustion chamber 35 is injected. By referring to the throttle 15 supplied air mass to the maximum volume of the combustion chamber 35 as well as standard conditions, such as a given temperature and a given air pressure, we obtain the so-called relative air mass rl. According to obtained by reference via the injection valve 20 injected fuel mass to the maximum volume of the combustion chamber 35 and the described standard conditions the so-called relative fuel mass rk. Furthermore, the internal combustion engine comprises 1 also a control unit 60 , which is also referred to as engine control. The engine control 60 controls the opening angle of the throttle 15 as well as the injection time and injection duration of the injector 20 , In this way, the motor control 60 set the relative air mass rl and the relative fuel mass rk. The inlet valve 25 and the exhaust valve 45 can open and close the combustion chamber 35 to the intake manifold 10 or to the exhaust tract 50 also from the engine control 60 be controlled. This is called fully variable valve timing. Alternatively, intake valve 25 and exhaust valve 45 opened and closed by camshafts, one from the piston 40 driven crankshaft are driven. The method according to the invention can be used for both types of activation of the intake valve 25 and the exhaust valve 45 realize, both types are known in the art and therefore for the sake of clarity in 1 not shown. The engine control 60 also controls the spark plug in a manner known to those skilled in the art 30 for clarity, this control also in 1 not shown. In this way, the engine control 60 set the ignition timing. For detecting the engine speed of the internal combustion engine 1 can be a speed sensor 65 be provided, which measures the revolutions of the crankshaft and the engine control 60 transfers.

Also from the lambda sensor 55 measured air / fuel mixture ratio is the engine control 60 supplied for evaluation.

For different operating modes of the internal combustion engine 1 can in the engine control 60 different setpoints lamsbg be given for the air / fuel mixture ratio. Thus, for example, for a so-called homogeneous operation of the internal combustion engine 1 the setpoint lamsbg = 1 and for a so-called lean operation of the internal combustion engine 1 For example, the setpoint lamsbg may be equal to 2. Thus, in homogeneous operation, the relative air mass rl should correspond to the relative fuel mass rk, whereas in the lean operation described by way of example the relative air mass rl should be twice as large as the relative fuel mass rk. As a rule, there is a combustion process in which the combustion chamber 35 combusted air / fuel mixture, a single injection of fuel for a certain injection duration based, regardless of whether the injection in the intake manifold 10 or directly into the combustion chamber 35 of the cylinder 5 takes place, provided that in the case of the intake manifold injection ensures that the injected fuel through the inlet valve 25 essentially completely in the combustion chamber 35 has arrived. For this case, one thus obtains a fuel injection per combustion process. In this case, the injected relative fuel mass rk is corrected according to equation (1) in order to realize the described pilot control of the air / fuel mixture ratio. The correction of the relative fuel mass rk to be injected is necessary above all because the injection valve 20 clogged with time and therefore decreases the injected relative fuel quantity rk with time at the same injection duration. This coking of the injection valve can be calculated via the additive correction value rka for the fuel mass and the multiplicative correction value fra for the fuel mass 20 be taken into account in the pilot control of the air / fuel mixture. The corrected in this way relative fuel mass rk can then from the engine control 60 be realized by a prolonged injection duration. In this way, by the coking of the injection valve 20 Conditional errors of the relative fuel mass rk be compensated. The coking of the injection valve 20 Here is just one example of a cause of a faulty relative fuel mass rk, which can be compensated by the correction values rka and fra. In addition, the correction values rka and fra for the fuel mass more generally allow the correction of an erroneous relative mass of fuel rk according to equation (1) due to an erroneous behavior of the injector 20 ,

In this case, the predicted relative air charge rlp, which is determined from one or more previous combustion processes, is used for the correction of the relative fuel mass rk according to equation (1). In the simplest case, simply the in the previous combustion process, for example by means of an in 1 Air mass meter, not shown, for example, measured a hot-film air mass meter and to the maximum volume of the combustion chamber 35 as well as the described standard conditions related relative air mass used. Alternatively, the mean value of the relative air mass determined in the case of several previous burns can also be used as the predicted relative air mass rlp. The setpoint lmsbg for the air / fuel ratio is the value in the combustion chamber 35 for this ratio is to be achieved and therefore can from the lambda control in the engine control 60 not directly with the Lambda sensor 55 be compared determined actual air / fuel mixture ratio, but only after a known to the expert conversion. The motor control determines the control factor fr 60 the relative fuel mass rk according to equation (1) such that at the lambda probe 55 measured air / fuel mixture ratio the setpoint lamsbg taking into account the described conversion from the combustion chamber 35 to the exhaust tract 50 is tracked. The correction values rk and fra correct as described the behavior of the injection valve 20 ,

For example, for preheating one of the lambda probe 55 in the exhaust tract 50 subsequent and in 1 Not shown catalyst may be advantageous during a Combustion process in the combustion chamber 35 At least one more time, preferably towards the end of the combustion, to inject fuel. By the equation (1), however, only the first injection during a combustion process is considered for the correction of the relative fuel mass rk, but not one or more further injection events during the same combustion process. In such multiple injections, therefore, the relative fuel mass rk is not sufficiently corrected using equation (1). According to the invention, therefore, in an operating mode of the internal combustion engine with multiple injection per combustion process, the additive correction value rka for the fuel mass is calculated for each injection process of a combustion process, so that: rk (xE) = (rlp + x · rka) / lamsbg · fr · fra (2)

Here, x is the number of injections per combustion process and rk (xE) is thus the corrected or pre-controlled relative fuel mass for x injection events E per combustion process.

Thus, for a pilot control or an adaptation of an air / fuel mixture ratio in the combustion chamber 35 For example, an injected fuel mass in a multiple injection of multi-injection fuel for a single combustion operation performs the correction of injected fuel mass for each of these injection events, this being illustrated in this embodiment by relative mass of fuel. Thus, even in the case of multiple injections per combustion operation, the relative fuel mass rk is correctly corrected.

Based on the correction of the relative fuel mass rk according to equation (2), it is now provided according to a development of the method according to the invention to perform a comparison of the control factors fr, resulting for combustion processes with a different number of injection events. In this case, the relative fuel mass is adapted in such a way by correction that for these combustion processes with a different number of injection processes, an approximately equal control factor fr for setting the predetermined according to the desired value lamsbg air / fuel mixture ratio in the combustion chamber 35 results. The correction takes place with the aid of the additive correction value rka and / or with the aid of the multiplicative correction value fra for the fuel mass. Via the additive correction value rka and / or the multiplicative correction value fra, only the error of the relative fuel mass rk is corrected. If the additive correction value rka and / or the multiplicative correction value fra have settled, then the control factor fr is at the selected steady-state operating point of the internal combustion engine 1 for the combustion processes with the different number of injections approximately the same. The error of the relative fuel mass rk is then compensated. The control factor fr then possibly contains only one error of the relative air charge rl. By means of the described correction of the relative fuel mass rk with the aid of combustion processes with a different number of injection processes, errors of the relative fuel mass rk and errors of the relative air mass rl can thus be separated and thus compensated without errors.

In the following, the method according to the invention will be described by way of example with reference to the flowchart 2 described. It is exemplified as a stationary operating point of the internal combustion engine 1 an idling operating state and selected as correction value for the fuel mass, the additive correction value rka, which acts considerably stronger in idle mode, as the multiplicative correction value fra. The method according to the invention for correcting the error of the relative fuel mass rk can be carried out, for example, in homogeneous operation for an air / fuel mixture ratio λ = 1. However, the chosen value for λ is not significant for the implementation of the method and may also be greater or less than 1, for example, a lean mode with λ = 2 can be selected for carrying out the method. Furthermore, the method according to the invention is described by way of example and without restriction of generality in the case where the fuel mass additive correction value rka is adapted alternately for combustion processes with exactly one injection and with exactly two injections. By the choice of the stationary operating point, in this example, the idle operating state of the internal combustion engine 1 ensures that for the adaptation of the additive correction value rka the engine speed and the air supply or the relative air mass rl remains substantially constant. This is the precondition for the fact that, after the correction of the relative fuel mass rk, the control factor fr can essentially comprise only one error of the relative air mass rl, which can thus be corrected separately adaptively.

After the start of the program initiates the engine control 60 at a program point 100 an operation of the internal combustion engine 1 with combustion processes in the combustion chamber 35 , each characterized by a single injection of fuel. In order to correct the relative fuel mass rk, both equation (1) and equation (2) can be used, wherein x = 1 is set in equation (2) and in both equations the multiplicative correction value fra remains set to a constant value , for example, to 1. The additive correction value rka can first be set to 0. The resulting values for the control factor fr for tracking the of the lambda probe 55 measured air / fuel mixture ratio to the setpoint lamsbg taking into account the transition between the combustion chamber 35 and exhaust tract 50 be from the engine control 60 averaged and the average formed as the first mean value frm1 in the engine control 60 stored. Subsequently, becomes a program point 105 branched.

At program point 105 turns off the engine control 60 in a double injection operation in which every combustion process in the combustion chamber 35 includes exactly two injections. For the double injection operation, equation (2) must now be used to correct the relative fuel mass rk and x = 2 set. The engine control also determines in double injection operation 60 an average value for the resulting control factors fr, which is referred to as second mean value frm2. It is at program point 105 from the engine control 60 the additive correction value rka is adapted until the second mean value frm2 corresponds to the stored first average value frm1. Subsequently, becomes a program point 110 branched.

At program point 110 turns off the engine control 60 back into operation with just one injection of fuel per combustion cycle. This forms the engine control 60 now a new first median frm1n for the control factors, which can be found in the under program point 110 investigated combustion processes. For the additive correction value rka, the under program point 105 used adapted value. The engine control 60 then compares the new first mean value frm1n with the previous first mean value frm1. Subsequently, becomes a program point 115 branched.

At program point 115 checks the engine control 60 whether the difference between the new first mean value frm1n and the previous first mean value frm1 is smaller than a predetermined threshold in absolute value. If this is the case, then becomes a program point 120 otherwise it becomes a program point 135 branched. At program point 135 saves the engine control 60 the new first mean value frm1n as the previous first mean value frm1 and then branches again to the program point 105 to iteratively continue the described method.

At program point 120 Thus, it is the case that the difference between the new first mean value frm1n and the previous first mean value frm1 falls below the predetermined threshold. The predetermined threshold is chosen so low in an advantageous manner that to program point 120 is only branched when the first mean value frm1 for the control factor does not change significantly. With branching to the program point 120 Thus, the error of the relative fuel mass rk is substantially compensated. The engine control 60 now determines the deviation of the first mean value frm1 from a desired value, which results in error-free calculated relative fuel mass rk and error-free calculated relative air mass rl and is usually about 1. This deviation then results only from an error of the supplied relative air charge rl, since the relative fuel mass rk has already been completely corrected. Subsequently, becomes a program point 125 branched.

At program point 125 checks the engine control 60 whether the described deviation between the first mean value frm1 for the control factor and the value desired for the control factor exceeds in magnitude a second predetermined threshold. If this is the case, then becomes a program point 130 otherwise the program is exited. The second predetermined threshold is also chosen as low as possible, so that the program is only left when the first mean value frm1 corresponds approximately to the desired value for the control factor and thus the error of the relative air mass rl is substantially compensated.

At program point 130 however, the relative air mass rl from the engine control 60 corrected by appropriate adaptation, for example, using a Saugrohrdrucksensor characteristic, a measurement signal of an air mass measuring device or the like to adapt the first mean value frm1 for the control factor to the desired value for the control factor and thus compensate for the error of the relative air mass rl possible. Subsequently, becomes the program point 125 branches back. The adaptation of the relative air mass rl can take place both during operation with combustion processes that include only one injection process, as well as in operation with combustion processes that include exactly two injection events. This is because the first mean of frm1 branches to program point 120 and thus for the adaptation of the relative air mass rl no longer deviates significantly from the second mean value of frm2 for the control factor.

By the described method, therefore, the relative fuel mass rk and the relative air mass rl can be adapted separately and thus adjusted substantially error-free.

After the adaptive correction value rka has been adapted in the manner described, one can also adapt the multiplicative correction value fra at higher loads. Again, a stationary operating point must be set for such a higher load, where the engine speed and air supply are constant. They will be higher than in idle mode. The adaptation of the multiplicative correction value fra can also according to the flowchart described after 2 will be realized.

In practice, the adaptation of the multiplicative correction value fra at higher loads is more difficult to implement than the adaptation of the additive correction value rka in the idle operating state, since at higher loads setting a constant operating point is more difficult. Since the error of the relative air mass rl is usually lower at higher loads than in the idle operating state, an adaptation of the multiplicative correction value fra may possibly also be dispensed with, so that in this case only the error of the relative fuel mass rk would be corrected for higher loads and this correction also takes into account the error of the relative air mass rl.

For the adaptation of the relative fuel mass rk according to the described method, it is not assumed that in the case of combustion processes with multiple injection, each injection process is characterized by the same injected fuel mass.

However, it should be prevented that the injection time of an injection event is too close to the minimum injection time.

According to the invention, therefore, the air / fuel mixture ratio can be controlled by determining the relative fuel mass rk according to equation (1) in the case of single injection per combustion process and according to equation (2) in the case of multiple injection per combustion process, wherein errors of the relative fuel mass rk and the relative air mass rl can be adaptively corrected separately. In this way, the air / fuel mixture ratio in the combustion chamber can be 35 adaptive essentially correct in advance.

Claims (7)

Method for controlling an air / fuel mixture in an internal combustion engine ( 1 ), wherein an injected fuel mass is corrected for an adaptation of an air / fuel mixture ratio, that in a multiple injection of fuel with multiple injection events for a combustion process in a cylinder ( 5 ) of the internal combustion engine ( 1 ) the correction of the injected fuel mass is carried out for each of these injection events, characterized in that the adaptation of the correction value for the fuel mass in an operating point of the internal combustion engine ( 1 ) is performed at a substantially constant speed and air supply A method according to claim 1, characterized in that a correction value for the fuel mass is adapted such that results for combustion processes with different number of injection events, an approximately equal control factor for the setting of a given air / fuel mixture. A method according to claim 2, characterized in that the correction value for the fuel mass is adapted until a change in the control factor for combustion processes with a different number of injection events remains below a predetermined threshold. Method according to Claim 1, characterized in that an idling operating state of the internal combustion engine ( 1 ) and an additive correction value is selected as a correction value for the fuel mass. Method according to Claim 1, characterized in that an operating state of the internal combustion engine ( 1 ) is selected at high load and as a correction value for the fuel mass, a multiplicative correction value. Method according to one of claims 2 to 5, characterized in that the correction value for the fuel mass is alternately adapted for combustion processes with an injection and with two injections. Method according to one of claims 2 to 6, characterized in that after completion of the adaptation of the correction value for the fuel mass remaining deviation of the control factor is compensated by a desired value by adapting a correction value for the supplied air mass.

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