DE10003597A1 - Method for adjusting desired air-ratio of exhaust gas mass-flow from combustion engine, involves adjusting calculated value by altering the ignition angle of combustion engine - Google Patents

Abstract

The engine air mass flow (ml, soll) required for the desired air ratio (lambdages) is calculated and the calculated value is then adjusted by altering the ignition angle (alpha) of the combustion engine, and this avoids the method of feeding a secondary air mass flow, depending on the air ratio, into the exhaust gas.

Description

The invention relates to a method for setting a desired air ratio an exhaust gas mass flow of an internal combustion engine according to the preamble of the claim 1.

Is there a cold start in an internal combustion engine and / or is the internal combustion engine engine at idle, it is known by afterburning in the exhaust duct the internal combustion engine to the exhaust gas cleaning device arranged in the exhaust duct heat to bring it to the intended operating temperature or to a to maintain the desired temperature level. It is provided that the internal combustion engine machine is filled with a rich fuel-air mixture such that it is still unburned ter fuel gets into the exhaust duct. Through a secondary air supply in the waste gas nal then an ignitable fuel-air mixture is formed, which then ignited in the exhaust duct.

From DE 197 53 842 it is known that the secondary air flow by means of a secondary air pump into the exhaust duct. Ready to a certain mass of secondary air To be able to provide an air mass sensor and a valve is provided that the pump is subordinate. A predetermined secondary air mass flow is thus dependent The air ratio is fed into the exhaust gas. This is disadvantageous in that the through the pump and the valve, which is the secondary air delivered by the pump mass flow influenced, relatively high costs arise.

From DE 41 18 848 A1 it is known to determine the air ratio in the exhaust gas mass flow to set a rich fuel-air mixture to a fixed value, for example is at λ = 0.8. A secondary air mass flow is introduced into the exhaust duct that by post-combustion a stoichiometric equilibrium of λ = 1.0 in the exhaust gas should arise. The disadvantage of this known method is that these λ values  are only accepted. However, it has been shown that with certain motor con assume a strong dependence of the effectiveness of the afterburning on the air ratio in the exhaust gas. In this known method, it is therefore possible that the air ver Ratio in the exhaust gas can fluctuate so that the heating measures for the exhaust gas can not be achieved in all cases.

From DE 692 00 852 T2 it is also known that the seconds supplied to the exhaust gas to control the amount of digestion air.

DE 694 02 637 T2 describes a heating device for an exhaust gas purification device known, which is supplied separately fuel that is burned in the heating device. The exhaust gas from the internal combustion engine is led past this heating device in order to to heat this, causing an increase in the operating temperature of the exhaust gas supply device is to be achieved.

It is an object of the invention to provide a method for setting a desired air supply Specify ratio of an exhaust gas mass flow of an internal combustion engine, which the does not have the above-mentioned disadvantage.

This task is accomplished with a method for setting a desired air ratio nisses an exhaust gas mass flow of an internal combustion engine solved, the features of claim 1. It is envisaged that the exhaust gas mass flow through Mixing a supplied secondary air mass flow with an engine air mass flow forms, wherein the supplied secondary air mass flow is determined. For example be provided that the secondary air mass flow is measured or as a Versu Chen determined value is assumed. The method is distinguished according to the invention characterized in that the required engine air mass flow for the desired air ratio is calculated in the exhaust gas and that the calculated engine air mass flow through Verstel tion of the ignition angle of the internal combustion engine is set. That means that the Mon air mass flow is set to the value previously calculated. Thus, NEN control devices or valves and pumps for the secondary air mass flow is eliminated because the secondary air mass flow is only measured or as certain value is assumed, so that then the existence of the known Secondary air mass flow the engine air mass flow is set so that the Desired air ratio in the exhaust gas results to achieve optimal post-combustion  to be able to. In particular, it is provided that the air ratio in the exhaust gas to a ge suitable value of λ ≈ 1 is set.

In a development of the invention it is provided that, for example, the adjustment the ignition angle can only take place within a predeterminable range. Would So for example the calculated engine air mass flow an adjustment of the Zündwin kels no longer require optimal operation of the internal combustion engine can be assumed, then only the maximum possible firing angle adjustment performed.

In one embodiment, it is provided that the air ratio in the exhaust gas masses current is detected and that by means of the detection value of the air ratio a Cor correction factor is determined with which the calculated engine air mass flow through changes the ignition angle is influenced. This allows a particularly precise setting the air ratio in the exhaust gas, so that the desired air ratio still can be adjusted or regulated more precisely.

In order to determine the detection value of the air ratio in the exhaust gas mass flow, a λ probe known per se can be provided, which preferably has a broadband configuration det.

Further advantageous embodiments result from the subclaims.

The invention is based on an embodiment with reference to the drawing ago explained. The single figure shows a process sequence that is carried out by means of a flow slide is shown.

First, in a first method step 1, a secondary air _{mass flow sl is} averaged. For this purpose it can be provided that this value is read from a memory. If the secondary air mass flow changes, for example depending on the operating point of an internal combustion engine, the values for the secondary air mass flow associated with the operating points can be stored in the memory. Alternatively, in step 1 a, it is possible to measure the current secondary air mass flow. The value determined for this secondary air mass flow _sl is processed in a subsequent process step 2 .

The method for setting a desired air ratio λ _ges in the exhaust gas of the internal combustion engine is based on the relationships shown below as formulas:

In these equations, ml means the engine air mass flow, _sl the secondary air mass flow that is supplied to the exhaust gas, _f the fuel mass flow, L _st the stoichiometrically required specific air mass to achieve complete combustion of the fuel and ϕ _mot the equivalence break (enrichment factor).

The engine air mass flow required for a specific, predeterminable air ratio is given by the following equation, provided the enrichment factor ϕ _{mot is also} specified:

_l = (λ _tot ϕ _mot -1) ^-1 _sl (3)

In order to be able _to calculate the required engine air mass flow _{l, should} for heating measures of the exhaust gas purification device, a predetermined air ratio λ _tot and a predetermined enrichment factor ϕ _{mot are} assumed. Furthermore, as mentioned, the secondary air _{mass flow sl is} measured or assumed on the basis of average values or approximate values determined in tests, which can be stored in the memory.

The flowchart shown in the figure thus results in the second method step 2 , in which the required engine air mass flow I is to _be determined using equation 3 in order to be able to set the desired air ratio. In a third method step, which is shown in the flowchart as branch 3 , a decision is made as to whether a control or regulation of the air ratio λ _total should be carried out. If only one controller is provided, the next branch point 4 is passed directly to the United. Is a control of the air ratio λ _ges vorgese hen, in a step 3 a that actually present air ratio λ _measured determined in the exhaust gas mass flow. For this purpose, for example, a λ probe can be provided, which is preferably implemented in a broadband manner. In a further process step 3 b, which is arranged according to process step 3 a, the correction factor C _Corr for the engine air mass flow _{I to be set} is then _to be determined using the following equation:

At the same time in method step 3 b, the corrected engine air mass flow _{I, Korr is determined} using the following equation:

_{l, corr} = C _{l Korr, to} (6)

After method step 3 b in this branch, there is also the method step in branch 4 , in which it is determined whether the current engine air mass flow _l assigned to an operating point of the internal combustion engine is the engine air mass flow _{l determined} in method step 2 or _{is intended} in method step 3 b determined _{l, corr} corresponds. If the operating point-dependent engine air mass flow _{l is} greater than that determined in method step 2 or 3 b, the new ignition angle α is determined _anew in the next method step 5 a, the current ignition angle α _{old being} adjusted “early” by an ignition angle Da if the current one is present Engine air mass flow _{l is} greater than the calculated engine air mass flow _{l, should} , with the fact that the new ignition angle α _new ≦ is a maximum ignition angle α _max .

If it has been determined in the branch 4 that the engine air mass flow _l <as _{l, which is} assigned to the current operating point of the internal combustion engine _{, is intended} , the new ignition angle α _new is determined in the method step 5 b from the old ignition angle α _old , from which the ignition angle change Δα is subtracted becomes. It applies that the new ignition angle α _new ≧ a minimum ignition angle α _min .

The ignition angle change Δα should be selected so that the control is stable. An excessively large change in the ignition angle Δα can lead to a greatly changed pressure in the intake pipe of the internal combustion engine. This intake manifold pressure may then lead to changed fuel vapor values and thus to a dynamic enrichment with the enrichment factor ϕ _mot . Under certain circumstances, this can lead to uneven engine running.

The ignition angle change Δα can also be done indirectly via the torque of the internal combustion engine machine can be determined. With torque-controlled control or rain tion of the internal combustion engine, the ignition angle α is set so that a desired Torque is output from the internal combustion engine. To now take heating measures for Initiate the exhaust gas purification device gives the torque-controlled control way regulation a torque for the internal combustion engine, which is one such reserve torque is reduced. For example, this reserve torque is 10%. The internal combustion engine is now operated with a torque of 90%. So there is a conscious decrease in efficiency to the heating carry out measures. To adjust the reduced torque, however also the ignition angle α is adjusted so that this reduced torque sets. The principle of the ignition angle adjustment therefore also remains with torque-guided Get internal combustion engines. However, the size to be recorded for this is the reserve moment or torque. The required ignition angle adjustment Δα can therefore indirectly via a certain torque or reserve moment assigned ignition angle, that is, depending on the torque reserve torque.  

If an operating parameter of the internal combustion engine changes, the engine air mass flow _l assigned to the new operating point is then determined in a method step 6, for example from a characteristic field. In the following procedural step 1 , the secondary air mass flow _sl associated with the new operating point is again determined. This is followed by the process steps 2 to 6 just described.

The method described above is preferably used when the exhaust gas cleaning device is to be heated. This may be necessary, for example, during a cold start and / or when the internal combustion engine is idling. From the specified secondary air mass flow _sl , the required engine air mass flow _l is then determined, which is necessary to achieve a desired or necessary air ratio λ _ges in the exhaust gas mass flow of the internal combustion engine. The air ratio λ _tot = 1 is preferably set.

In the flowchart according to the figure, it is assumed that there is a choice as to whether regulation should be carried out in method step 3 or not. Of course, can in one embodiment also be provided that only one control is provided, so the method steps 3 a and 3 b not be performed. In another exemplary embodiment, it can then be provided that the control in method step 3 is always carried out.

Claims (8)

1. A method for setting a desired air ratio of an exhaust gas mass flow of an internal combustion engine, wherein the exhaust gas mass flow mixes from at least one supplied secondary air mass flow and an engine air mass flow, and wherein the supplied secondary air mass flow is determined, characterized in that the required engine air mass flow ( _{l, target} ) for the desired air ratio (λ _tot ) is calculated and that the calculated engine air mass flow ( _{l, set} ) is set by adjusting the ignition angle (α) of the internal combustion engine. 2. The method according to claim 1, characterized in that the secondary air _{mass flow} ( _sl ) is measured or determined by an approximate value. 3. The method according to any one of the preceding claims, characterized in that the calculation of the engine air mass flow ( _l ) with
_l = (λ _tot ϕ _mot -1) ^-1 _sl
takes place, where ϕ _{mot represents} the enrichment factor. 4. The method according to any one of the preceding claims, characterized in that the ignition angle adjustment (Δα) takes place within a predetermined range (α _min , α _max ). 5. The method according to any one of the preceding claims, characterized in that the air ratio (λ _ges ) is detected in the exhaust gas mass flow and that a correction factor (C _corr ) is determined by means of the detection value of the air ratio (λ _mess ) with which the calculated engine air mass flow ( _{l , should} ) be changed by changing the ignition angle (α). 6. The method according to any one of the preceding claims, characterized in that the correction factor (C _Korr ) with
and the corrected engine air mass flow ( _{l, corr} ) with
_{l, corr} = C _{Korr l should,}
is determined. 7. The method according to any one of the preceding claims, characterized in that the detection value of the air ratio (λ _mess ) is determined by means of a, preferably broad-band, λ probe. 8. The method according to any one of the preceding claims, characterized in that refer to the adjustment of the ignition angle (α) as a function of the torque approximately reserve torque of the internal combustion engine.