DE102019202404A1 - Method for controlling the coasting behavior of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for controlling the coasting behavior of an internal combustion engine in the exhaust pipe of which a three-way catalytic converter is arranged. The length of a run-down of the internal combustion engine is predicted and the run-down behavior is then controlled so that an oxygen loading (B) of the three-way catalytic converter at the end of the run-down is in the range of 40% to 60% of the oxygen storage capacity of the three-way catalytic converter.

Description

The present invention relates to a method for controlling the coasting behavior of an internal combustion engine. The present invention also relates to a computer program that executes each step of the method, as well as a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

The storage capacity of oxygen in a three-way catalytic converter in the exhaust system of an internal combustion engine has a considerable influence on the conversion behavior of the catalytic converter. The temperature-dependent ability of oxygen storage is indicated by the value OSC (Oxygen Storage Capacity). With an oxygen load of significantly more than 50% of the OSC, there is a risk of nitrogen oxide breakthroughs. Unwanted short-term deviations in the mixture control in the direction of excess oxygen in the exhaust gas, in connection with an excessively high oxygen loading of the catalytic converter, can lead to such a high oxygen supply that the oxidation of incompletely burned components such as hydrocarbons or carbon monoxide can largely take place without a simultaneous reduction of nitrogen oxides.

With an oxygen loading of significantly less than 50% of the OSC, there is a risk of hydrocarbon breakthroughs and carbon monoxide breakthroughs. Undesired short-term deviations in the mixture control in the direction of a lack of oxygen are more difficult to compensate for when the catalytic converter has a low oxygen load. Although nitrogen oxides are reduced, the oxygen load in the catalytic converter is also used up. Ultimately, however, the oxygen supply drops so far that the unburned components can no longer be oxidized.

Disclosure of the invention

The method is used to control the coasting behavior of an internal combustion engine in whose exhaust system a three-way catalytic converter is arranged. It can be used both when the internal combustion engine is switched off and in a fuel cut-off phase. A length of a run-down of the internal combustion engine is predicted. The leakage behavior is then controlled so that the oxygen loading of the three-way catalytic converter at the end of the run-out is in a predeterminable range, preferably in the range from 40% to 60% of the oxygen storage capacity of the three-way catalytic converter. In order to ensure an optimal conversion of exhaust gas pollutants even with significant deviations from λ = 1, an oxygen load in this area should be aimed for in order to reduce these dangers. This prevents the subsequent start of the internal combustion engine from causing significantly worsened emissions downstream of the catalytic converter due to an excessively high or low oxygen loading of the catalytic converter in conjunction with a too lean or too rich mixture stoichiometry.

In the fired operation of the internal combustion engine, the instantaneous oxygen loading of the catalytic converter can be modeled from the measured values of lambda sensors upstream and downstream of the catalytic converter and is therefore sufficiently known.

In the fired operation of the internal combustion engine, the most optimal setting of the oxygen loading in the catalytic converter is possible by controlling or regulating the λ value. This is possible in overrun phases or while the engine is coasting by controlling / regulating the intake manifold pressure. The intake manifold pressure and the number of unfired work cycles determine the fresh air that is fed into or through the catalytic converter. In general, this means that a high intake manifold pressure causes a high air throughput in the catalytic converter and the oxygen reservoir is filled. A low intake manifold pressure means a low to backward air flow in the catalytic converter, which means that the oxygen load remains unchanged. Many work cycles lead to a large air throughput, a few work cycles to a smaller air throughput. The change in oxygen loading is therefore proportional to the product of the intake manifold pressure and the number of work cycles in the outlet.

If the oxygen loading is below the range at the beginning of the outlet, the intake manifold pressure of the internal combustion engine in the outlet is preferably reduced in order to increase the oxygen loading. Due to the length of the outlet known from the prediction, the intake manifold pressure can be selected as small as necessary. In this way, the comfort of a motor vehicle driven by the internal combustion engine is not impaired or is impaired only to a minor extent.

If the oxygen loading is above the range at the start of the run-out, preferably torque-neutral burns, i.e. burns with a late ignition angle, with a λ value of less than 1 and / or fuel injections without ignitions in the internal combustion engine are discontinued in order to increase the oxygen charge in a targeted manner reduce. Because the number of work cycles still to be performed is known from the prediction, it can be ensured that the unburned hydrocarbons of the Fuel injections can still reach the catalytic converter at operating temperature. There they are oxidized to water and carbon dioxide, thereby reducing the oxygen load.

The prediction takes place in particular in that the speed when the internal combustion engine is running is determined on the basis of the difference between square values of the internal combustion engine speeds occurring when the internal combustion engine is running down. The difference between these square values is a reliable measure of the energy dissipation in the run-out phase.

The resulting when the engine is running down speeds z. B. at empirically specifiable crankshaft positions, z. B. at 1440, ..., 720, 540, 360 and 180 ° CA before a certain ZOT, can be predicted on the basis of a typical, predetermined and predeterminable stopping behavior. A typical stopping behavior can consist in regulating the intake manifold pressure of the internal combustion engine concerned to 650 mbar, with an inlet valve located on a combustion chamber of the internal combustion engine closing at 120 ° CA before TDC and an outlet valve located on the combustion chamber afterwards at 148 ° CA ZOT is controlled to open.

The prediction procedure is based in particular on the technical effect that the energy dissipation of the kinetic energy when the internal combustion engine is running down is essentially constant. Since both the moment of inertia of the internal combustion engine is constant and the drag torque of the internal combustion engine usually does not change during the run-down, the above-mentioned difference in the speed squares represents a reliable measure of the energy dissipation in the run-out phase ) or the ignition interval from a top dead center (ZOT) or a multiple thereof constant.

The method can provide for the prediction to be based on an evaluation angle that is as free of angular errors as possible. This can be achieved in that only those between matching teeth of a crankshaft encoder wheel are used as angle values.

In particular, the prediction can be performed very early, i.e. e.g. a few thousand degrees of crankshaft angle before the internal combustion engine actually comes to a standstill.

The prediction also enables speed-influencing or speed-shaping interventions to be carried out early in the run-out. Such interventions can be carried out on various system components that influence the stopping behavior of the internal combustion engine, e.g. B. a throttle valve, a high pressure pump, a power generator or even an electric engine can be realized. This can be used in particular to specify a number of work cycles still to be performed by the internal combustion engine in the run-out.

For this purpose, in particular at the run-out by means of a change in a control variable of the internal combustion engine carried out before the start of the run-out, B. changes the efficiency of the combustion, influences the speed of the internal combustion engine or the crankshaft, in particular in order to shape the speed curve over time to achieve a certain stopping behavior.

For known curves of the temporal coasting behavior, on the basis of a desired speed that is present shortly before the end of the coasting down, in particular on the basis of a desired speed of the last exceeded ZOT at an empirically predeterminable or defined operating point of the internal combustion engine, e.g. At 175 rpm, a higher or earlier target speed can be calculated backwards, which automatically leads to the desired speed before the end of the run-down due to the above-mentioned reduction in kinetic energy.

For this purpose, it is preferred that the change in the control variable of the internal combustion engine brings about a named change in the efficiency of the combustion before the internal combustion engine starts to run down and that a last fuel metering, e.g. B. a last injection, and / or a change in the combustion engine operating variables relevant to the combustion based on the last fuel metering, e.g. B. a throttle valve angle or a variable valve adjustment takes place.

Furthermore, it can be provided that the control variable of the internal combustion engine is changed by changing the metered fuel quantity and / or by changing the ignition angle.

The computer program is set up to carry out each step of the method, in particular when it runs on the computing device or an electronic control device. It enables the implementation of different embodiments of the method on an electronic control device without having to make structural changes to it. For this purpose it is stored on the machine-readable storage medium.

By uploading the computer program to a conventional electronic control device, this will, if necessary, block the regeneration of the exhaust gas particle sensor based on the method.

Figure list

• 1 zeigt schematische eine Brennkraftmaschine, deren Auslauf mittels Verfahren gemäß Ausführungsbeispiel der Erfindung gesteuert werden kann.
• 2 zeigt typische Drehzahlverläufe der Brennkraftmaschine, in Abhängigkeit von Werten eines Kurbelwellenwinkels in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens.
• 3 zeigt ein Ablaufdiagramm eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

• 1 shows a schematic of an internal combustion engine, the run-down of which can be controlled by means of a method according to an exemplary embodiment of the invention.
• 2 shows typical speed curves of the internal combustion engine as a function of values of a crankshaft angle in an exemplary embodiment of the method according to the invention.
• 3 shows a flow chart of an embodiment of the method according to the invention.

Embodiments of the invention

1 shows schematically the structure of an internal combustion engine 10 , in which the method according to the invention can be applied. This internal combustion engine 10 has a combustion chamber 20th , its volume by a piston 21st is limited by a connecting rod 22nd with a crankshaft 30th is coupled, and upon rotation of the crankshaft 30th performs an up and down movement in a characteristic way. An electronic control unit 40 controls one in a suction tube 50 arranged throttle valve 51 , an injector 52 , a spark plug 23 and the up and down movement of an intake valve 24 that has a first cam 61 with a camshaft 60 and / or the up and down movement of an exhaust valve 25th that has a second cam 62 to the camshaft 60 is coupled.

The crankshaft 30th is via a mechanical coupling 31 with an electric machine 32 connected. The electric machine 32 is in the present case a conventional starter and the mechanical coupling 31 includes a ring gear and a pinion with which the starter is engaged. A crankshaft angle sensor 33 is provided to the angular position of the crankshaft 30th to capture and send them to the control unit 40 to submit.

Air gets through the suction pipe 50 sucked in and through an exhaust pipe 70 pushed out. In the exhaust pipe 70 is a three-way catalyst 71 arranged. Upstream of the three-way catalyst 71 is a first lambda probe 72 located and downstream of the three-way catalyst 71 is a second lambda probe 73 arranged. In the fired operation of the internal combustion engine 10 becomes the oxygen loading of the three-way catalyst 71 from measured values of the two lambda probes 72 , 73 modeled.

Before switching off the internal combustion engine 10 a length of their run-out is predicted. For this purpose, it is assumed that the aforementioned energy reduction of the kinetic energy in the run-down of the internal combustion engine 10 is essentially constant. Since the moment of inertia of the internal combustion engine 10 is constant and the drag torque of the internal combustion engine 10 usually does not change or changes only very slightly during the run-down, represents the difference between the speed squares of the internal combustion engine 10 represents a reliable measure for the energy reduction in the run-out. This energy reduction measure is constant in particular for the various crankshaft angles (° CA) or the ignition interval from a top dead center (ZOT) or a multiple thereof.

One embodiment of the method according to the invention provides that the predictive calculation of the speed is based on an evaluation angle that is as free of angular errors as possible. This is achieved in that only those between matching teeth of a crankshaft encoder wheel are used as angle values, for example a ZOT tooth 17th to an identical ZOT tooth 17th .

In the exemplary embodiment, the respective predicted speed values are updated every 180 ° CA, ie the so-called update angle δ is 180 ° CA here. The speed is calculated at the respective upper ignition dead center (ZOT) of the crankshaft 30th .

At the end of the internal combustion engine 10 the energy reduction ΔE is proportional to the drag torque MS of the internal combustion engine 10 and the mass moment of inertia θ of the masses of the internal combustion engine involved in the run-down 10 . For the so-called run-out coefficient MS / Φ in the unit [Nm / kg · m ² ], formula 1 then applies: $$\text{MS}/\mathrm{\theta }=\mathrm{\pi }/10\cdot \mathrm{<figure-callout\; id="2"\; label="\Delta \; n"\; filenames="DE102019202404A1\_0009.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{\text{n}}^{}{}^2/\Delta \mathrm{\varphi }\text{ZA}$$

MS denotes the drag torque in the unit [Nm], ΔϕZA the ignition interval in the unit [° KW], which for a four-cylinder internal combustion engine is, for example, the already mentioned 180 ° KW, and n is the engine speed 10 in the unit [rpm].

In a four-cylinder internal combustion engine 10 is available when predicting the speed n basically two possibilities, namely the prediction of the speed n when the internal combustion engine is running down 10 at the (subsequent) time when 180 ° CA is present (case 1 ) F1 or at the time of the existence of 720 ° CA (case 2 ) F2, as in 2 to see where, depending on the crankshaft angle KW in the unit [°], the corresponding angle dependency of two ZOT teeth Z, namely tooth 17th and tooth 47 , is shown, as well as the respective affected cylinder Cyl 0, 1, 2, and 3.

The corresponding prediction angle is referred to below as β and corresponds to the case mentioned 1 the ignition interval itself or in the case 2 the ignition interval between one and the same cylinder, ie in the case of a four-cylinder internal combustion engine 10 applies 4 180 ° CA = 720 ° CA.

To in the case 1 , ie to be able to predict the speed at 180 ° CA, information from the previous angle range of 540 ° CA is required. This angle range is referred to below as the result angle γ and is calculated according to formula 2 using the speed formation angle α: $$\mathrm{\gamma }=\mathrm{\alpha }+\mathrm{\beta \; =}360°\text{KW}+180°\text{KW}=540°\text{KW}$$

To in the case 2 , ie to be able to predict the speed at 720 ° CA, information from the previous angular range of 1080 ° CA is required. This angle range, in turn called the result angle γ, is calculated according to formula 3: $$\mathrm{\gamma }=\mathrm{\alpha }+\mathrm{\beta \; =}360°\text{KW}+720°\text{KW}=1080°\text{KW}$$

It should be noted that the prediction by means of the prediction angle β = 720 ° CA is to be preferred if the information required for this from the past, i.e. are present at a result angle of γ = 1080 ° CA in the unfired stop of the internal combustion engine, since then any cylinder-specific differences in the drag torque that are present cannot be reflected in the prediction result. On the other hand, using the prediction angle β = 180 ° CA is to be preferred if only little information from the past, i.e. at a result angle of β = 540 ° CA, are present in the unfired stop of the internal combustion engine.

As in 3 is shown starts 80 the procedure when the internal combustion engine 10 should be switched off. A prediction now takes place first 90 the length of the spout. This is in the case 1 initially for the current operating state of the internal combustion engine 10 in ZOT _i the predicted speed n _{i of} the internal combustion engine described 10 calculated on the basis of the last angular error-free speed formation angle α = 360 ° KW 91 and cached 92 . For a previous ITDC _i-1 , for the prediction angle β = 180 ° CA, the specified speed n _{i-1 has} already been calculated 93 and also cached 94 and is now read out 95 . A calculation is carried out on the basis of the two speed values n _i and n _i-1 96 of the constant energy reduction dimension DNQ _{180 ° CA} since the last operating condition at β = 180 ° CA, i.e. the difference between the speed squares according to formula 4: $${\text{<figure-callout id="180" label="DNQ" filenames="DE102019202404A1\_0009.png" state="{{state}}">DNQ</figure-callout>}}_{180°\text{KW}}=\mathrm{<figure-callout\; id="2"\; label="\Delta \; n"\; filenames="DE102019202404A1\_0009.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{\text{n}}^{}{}^2{}_{180°\text{KW}}={\text{n}}^2{}_{\text{i}-1}-{\text{n}}^2{}_{\text{i}}$$

This results in the result angle γ = 540 ° CA, which corresponds to a previous angle on which the prediction result is based. Based on the thus calculated energy reduction measure the speed square n ² _{i + 1} for the next (different) ZOT _{i + 1} predicted 97, ie β = 180 ° CA in accordance with n ² _{i + 1} = n ² _i - DNQ _{180 ° kw .} By pulling the square root, the predicted speed n _{i + 1} for the next (different) ZOTi + 1 is calculated 98 . Furthermore, in the calculation 98 According to formula 5, further predicted speeds ni + _j (with j = 2, 3, 4, ...) in the future are calculated for further ZOTs in a corresponding manner until the resulting speeds n _{i + j} can no longer be achieved Have values less than zero: $$n_{i+j}=\sqrt{n_i^2-j\cdot \mathrm{<figure-callout\; id="180"\; label="D.\; N\; Q"\; filenames="DE102019202404A1\_0009.png"\; state="\{\{state\}\}">D.\; </figure-callout>}N{Q}_{}{}_{180°K\mathrm{W.}}}$$

This is now used to determine 99 at what time the expiry will end.

In the case 2 will be in crotch 95 those for a previous matching ITDC _i-4 , ie for the prediction angle β = 720 ° CA on the basis of the last angular error-free speed formation angle α = 360 ° CA in step 93 calculated and also cached 94 predicted speed n _i-4 read out. On the basis of the two speed values n _i and n _i-4 , step 96 again the constant energy reduction dimension DNQ _{720 ° CA of} the last prediction angle β = 720 ° CA is calculated, ie the difference between the speed squares according to formula 6: $${\text{<figure-callout id="720" label="DNQ" filenames="DE102019202404A1\_0009.png" state="{{state}}">DNQ</figure-callout>}}_{720°\text{KW}}=\Delta {\text{n}}_{2720°\text{KW}}={\text{n}}^2{}_{\text{i}-\mathrm{4th}}-{\text{n}}^2{}_{\text{i}}$$

It follows in the case 2 as the result angle γ = 1080 ° CA, which in turn corresponds to a previous angle on which the prediction result is based. Based on the thus calculated energy reduction measure the speed square n ² _{+ i 4 i} for the next same or matching ZOT _{+ 4} predicated 96 , ie for β = 720 ° CA according to n ² _{i + 4} = n ² _i - DNQ _{720 ° CA.} By pulling the square root, the predicted speed n _{i + 4} for the next identical ITDC _{i + 4 is} calculated 98 . Furthermore, in the calculation 98 According to formula 7, further predicted speeds n _{i + j} (with j = 8, 12, 16, ...) in the future are calculated for further ZOTs in a corresponding manner until the resulting speeds n _{i + j are} not have more achievable values less than zero: $$n_{i+j}=\sqrt{n_i^2-\frac{j}{\mathrm{4th}}\cdot \mathrm{<figure-callout\; id="720"\; label="D.\; N\; Q"\; filenames="DE102019202404A1\_0009.png"\; state="\{\{state\}\}">D.\; </figure-callout>}N{Q}_{}{}_{720°K\mathrm{W.}}}$$

Here, too, is now being determined 99 at what time the expiry will end.

From the last measured values of the lambda sensors 71 , 72 is now the oxygen loading B of the three-way catalyst 71 determined at the beginning of the run-out. An examination is then carried out 82 whether this is below, in or above a range of 40% to 60% of the oxygen storage capacity of the three-way catalyst 71 lies. If it is lower, there is pressure in the intake manifold 50 depending on the determined length of the run-out is reduced so that the oxygen loading B again reaches a value within the range during the run-out 82 . If it is in the range, there is no intervention 83 . If the oxygen loading B is above the range, then, depending on the determined length of the outlet, there are torque-neutral combustions with a lambda value of less than 1 and / or fuel injections without ignitions in the internal combustion engine 10 so that the oxygen loading B reaches a value within the range again during the run-out 85 .

In a further exemplary embodiment of the method, it is provided that the number of work cycles still to be performed by the internal combustion engine 10 is specified in the outlet in order to achieve the optimum outlet length for setting the oxygen loading B. For this purpose, the speed n in the run-down is determined by a change in the metered fuel quantity carried out before the start of the run-down of the internal combustion engine and / or by a change in the ignition angle of the internal combustion engine 10 changed so that on the basis of a predetermined, temporal stopping behavior of the speed n and on the basis of a desired speed existing before the end of the stop at a predefinable operating point of the internal combustion engine 10 a respective higher or earlier target speed can be calculated backwards, which leads to the desired speed before the end of the run-down. The speed curve of the internal combustion engine becomes 10 Formed in the outlet by the change in the combustion efficiency. For this purpose, the change in the efficiency of the combustion before the engine starts to run down 10 causes. There is a last fuel metering and / or a change in operating parameters of the internal combustion engine that are relevant for the combustion based on the last fuel metering 10 .

Claims (15)

Method for controlling the stopping behavior of an internal combustion engine (10) in the exhaust pipe (70) of which a three-way catalytic converter (71) is arranged, characterized in that a length of a stopping of the internal combustion engine (10) is predicted (90) and the stopping behavior is then predicted is controlled so that an oxygen loading (B) of the three-way catalytic converter (71) at the end of the outlet is in a predeterminable range of the oxygen storage capacity of the three-way catalytic converter (71). Procedure according to Claim 1 , characterized in that a pressure in an intake manifold pressure (50) of the internal combustion engine (10) is lowered in the outlet when the oxygen charge (B) is below the range (83) at the beginning of the outlet. Procedure according to Claim 1 or 2 , characterized in that torque-neutral burns with a lambda value of less than 1 and / or fuel injections without ignitions in the internal combustion engine (10) are discontinued in the run-out if the oxygen charge (B) is above the range (85) at the start of the run-out. . Method according to one of the Claims 1 to 3 , characterized in that the prediction (90) takes place in that the speed when the internal combustion engine is running is determined on the basis of the difference between square values of the internal combustion engine speeds occurring when the internal combustion engine is running down. Procedure according to Claim 4 , characterized in that the difference between the square values is used as a measure for the energy dissipation of the internal combustion engine (10) in the run-down. Procedure according to Claim 4 or 5 , characterized in that when the internal combustion engine (10) is running down, the resulting rotational speeds at prescribable positions of its crankshaft (30) before a prescribable top dead center with ignition of the crankshaft (30) are determined on the basis of a prescribable coasting behavior. Method according to one of the Claims 4 to 6th , characterized in that the predictive determination of the speed is based on an evaluation angle for which only angle values between matching teeth of a sensor wheel of the crankshaft (30) are used. Method according to one of the Claims 1 to 7th , characterized in that a number of work cycles still to be performed by the internal combustion engine (10) is specified in the run-out. Procedure according to Claim 8 , characterized in that the presetting takes place in that a speed of the internal combustion engine (10) in the run-down is changed by a change in a control variable of the internal combustion engine (10) carried out before the start of the run-down of the internal combustion engine (10) so that on the basis of a predetermined, Temporal run-down behavior of the speed and on the basis of a desired speed at a predeterminable operating point of the internal combustion engine (10) before the end of the run-down a higher or earlier target speed can be calculated backwards, which leads to the desired speed before the end of the run-down. Procedure according to Claim 9 , characterized in that the speed curve of the internal combustion engine (10) is shaped in the run-out by a change in the efficiency during combustion. Procedure according to Claim 10 , characterized in that the change in the control variable of the internal combustion engine (10) causes a change in the efficiency of the combustion before the engine (10) starts to run down and that a last fuel metering and / or a change in for the combustion due to the last fuel metering relevant operating variables of the internal combustion engine (10) takes place. Method according to one of the Claims 9 to 11 , characterized in that the control variable of the internal combustion engine (10) is changed by changing a metered amount of fuel and / or by changing an ignition angle. Computer program which is set up, each step of a method according to one of the Claims 1 to 12 perform. Machine-readable data carrier on which a computer program according to Claim 13 is stored. Electronic control device (40), which is set up, the coasting behavior of an internal combustion engine (10) by means of a method according to one of the Claims 1 to 12 to control.

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