WO2013056944A1

WO2013056944A1 - Method for controlling an internal combustion engine

Info

Publication number: WO2013056944A1
Application number: PCT/EP2012/068844
Authority: WO
Inventors: Wolfgang Tiebel; Andreas Rupp
Original assignee: Robert Bosch Gmbh
Priority date: 2011-10-17
Filing date: 2012-09-25
Publication date: 2013-04-25
Also published as: KR101886906B1; CN103874840B; DE102011084635A1; CN103874840A; KR20140075738A

Abstract

The invention relates to a method for operating an internal combustion engine comprising at least two cylinders in at least two modes of operation, all cylinders being fired in a first mode of operation and only some cylinders being fired in a second mode of operation. In said method, an actual cumulative lambda value of the internal combustion engine is adjusted to a desired cumulative lambda value using a lambda controller by adjusting the amount of fuel and/or air delivered to the fired cylinders. When switching from the first mode of operation to the second one, a pilot control value is fed to the lambda controller, said pilot control value compensating for a change in the actual cumulative lambda value that occurs if the mode of operation is switched without feeding a pilot control value.

Description

Description title

Method for controlling a combustion engine

The present invention relates to a method for operating an internal combustion engine and a computing unit for its implementation.

State of the art

The air / fuel ratio is adjusted in gasoline engines for the so-called homogeneous operation by a lambda control such that the average value of the lambda values of all cylinders λ = 1, 0. As a result, a low-emission operation is possible with conventional three-way catalysts, which are known to have their greatest effectiveness in stoichiometric combustion

Due to die tolerances and cylinder-specific air / filling differences, e.g. due to system tolerances, the lambda values in the individual cylinders of an internal combustion engine may deviate from each other despite identical control. The lambda value, which is also referred to below as the lambda sum actual value and measured in the exhaust gas, which is composed of the contributions of the respective individual cylinders, can therefore assume the desired value 1, 0, even though the actual lambda individual values fluctuate around this mean value.

For example, the cylinder Cyl. 1 to Cyl. 4 of a four-cylinder engine with lambda _{individual actual values} λ _Ζν ι _. 1 = 1, 1, λ _Ζν ι _. 2 = 0.9, λ _Ζν ι _. 3 = 1, 2 and

Azyi. 4 = 0.8 a lambda sum actual value λ _Ζν ι. ^■ ... A ⁼ 1, 0. A corresponding deviation of individual cylinders from the mean value (that is, with respect to the individual cylinders, a trimming) is referred to in the context of this application as Zylinderunausge- equivalent. A cylinder imbalance has a number of disadvantages. The trimming of the cylinder-specific lambda value initially leads directly to an increase in fuel consumption. If the trim exceeds a certain threshold, the emissions may also deteriorate. In addition, the so-called strandedness of the exhaust gas, ie the formation of flow filaments in the exhaust gas mass flow, eg due to different cylinder charges, also plays a role. It is desirable and in part demanded by the legislator to be able to recognize such exhaust gas deteriorations and / or to be able to regulate them by suitable control strategies.

Different methods for detecting or compensating for a cylinder imbalance in homogeneous operation are known from the prior art.

On the one hand, the signal of the lambda probe can be analyzed, whereby this signal is broken down into individual, cylinder-related values and evaluated. This is described, for example, in WO 96/35048 A1. The utility of this method, however, is highly dependent on the geometry of the exhaust line and places high demands on the engine and exhaust system design, which often can not be met.

On the other hand, speed-based methods provide for the detection of engine mass errors in lean operation (λ> 1). In this case, all cylinders are simultaneously transferred to the lean operation and evaluated a cylinder-specific feature for rough running. In contrast to the homogeneous operation, the engine torque is linearly correlated with the injection quantity in lean operation. In order to ensure an exhaust-neutral operation and to obtain a sum lambda of λ = 1.0, a late, inoperative post-injection is discontinued. The method is therefore not suitable for intake manifold engines. Corresponding methods and further aspects of this are, for example, in

DE 195 27 218 A1, DE 43 19 677 A1, DE 10 2004 010 412 A1, DE 197 33 958 A1, EP 0 929 794 B1 and DE 10 2006 026 390 A1 discloses and explains. All of these methods require a so-called full engine operation in which all cylinders are fired. However, modern engine concepts envisage switching off individual cylinders completely in order to save fuel in the low part-load range, so that combustion no longer takes place in them. Such operation is also referred to as half or partial engine operation.

Therefore, an optimal lambda setting in half or partial engine operation is desirable. Disclosure of the invention

Against this background, the present invention proposes a method for operating an internal combustion engine and a computing unit for carrying it out with the features of the independent patent claims. Advantageous embodiments are the subject of the respective subclaims and the following description.

The measures proposed according to the invention are used in the context of a method for operating an internal combustion engine having at least two cylinders, which is operated in at least two operating modes. In a first

Operating mode while all the cylinders of the internal combustion engine are fired to generate a corresponding engine torque, ie in the usual engine operation, e.g. a four-stroke operation, with an air / fuel mixture applied and actively ignited or subjected to auto-ignition. In at least one further operating mode, only a part of the cylinders, possibly also only a single cylinder, is fired.

In all modes, a lambda sum actual value of the internal combustion engine by means of a lambda controller by an adjustment of the respective fueled cylinders (total) supplied fuel and / or air quantity to one

Lambda sum setpoint set. This is called global lambda control and is well known in the art. As already partially explained above, the lambda actual value indicates the stoichiometric ratios prevailing in the internal combustion engine. By increasing the respective guided fuel quantity with respect to the present air, a corresponding fuel / air mixture "enriched", the lambda value thus shifted to values <1, and vice versa by reducing the amount of fuel to run a fuel / air mixture "emaciated", the lambda value accordingly in one Range> 1 to be moved.

If a partial engine operation, that is to say a further operating mode in which only a part of the cylinders is fired, is to be realized, then, when switching from the first to the second operating mode, the omission of individual cylinders may result in a change in the lambda total actual value. Namely, as previously explained, each actual lambda value need not necessarily correspond to the lambda sum actual value, e.g. if Zumesstoleranzen and / or cylinder individual air / Füllungsunterschiede exist. The lambda individual actual values can therefore deviate from the lambda sum actual value which they form in their entirety. If no additional measures are taken, a mixture that is too lean or too rich, ie an excessively high or too low sum lambda actual value, can therefore be present immediately after switching over. Such a lambda error degrades the emission behavior of the internal combustion engine and must be corrected.

According to the invention, therefore, when switching from the first operating mode (full engine operation) to another operating mode (the partial engine operation), the lambda controller (or its controller output) is supplied with a precontrol value, which counteracts a displacement of the lambda total actual value, and this preferably as far as possible compensated. Thus, if the lambda total actual value is increased by switching off part of the cylinders, a lambda controller (or its controller output) can be supplied with a precontrol value which correspondingly increases the fuel quantity supplied to the engine (and / or reduces the air quantity), so that the desired lambda sum setpoint (of, for example, 1) results again. Conversely, if switching from the first operating mode to the other operating mode would result in a reduction in the lambda value, the lambda controller (or its controller output) can be supplied with a precontrol value which reduces the fuel quantity (and / or increases the amount of air). , The present invention therefore effects an advantageous pilot control of a global lambda control with which a shift in the lambda sum actual value can be counteracted. A suitable precontrol value can be determined, for example, by observing a change in the lambda controller output when switching over. The change is stored as a suitable precontrol value.

A particular advantage of the measures according to the invention can be seen in the fact that the controlled variable (that is to say the lambda total actual value) remains virtually unchanged by the said additional intervention at the output of the lambda controller. A lambda correction is unfavorable during operation because the manipulated variables of the lambda controller are frequently monitored by motor vehicle systems and can lead to unfavorable adaptation values to error entries (in this case false-positive) in error generators.

In a particularly preferred embodiment, a cylinder-specific lambda control is provided in addition to the global lambda control. In the case of the cylinder-specific lambda control, a correction factor for correcting the fuel and / or air quantity supplied to the respective cylinder is determined for each fired cylinder in order to obtain a lambda individual actual value of the respective cylinder to a desired individual lambda nominal value, usually substantially λ = 1 to adjust. In this embodiment, the invention can develop particular advantages. In fact, in the case of certain cylinder-specific lambda readings, the correction factors are determined in such a way that they average

100% result (so that the resulting correction of the overall system by the cylinder-specific adaptation values is lambda-neutral, there is currently no shift of the lambda sum actual value desired). Therefore, it will usually happen that, when switching over, the correction factors of the remaining cylinders do not yield 100% and are tracked accordingly.

However, this tracking changes the lambda sum actual value and causes an intervention of the lambda controller, which should be avoided. The cylinder-specific lambda control is advantageously carried out when the lambda sum actual value is set by the lambda controller of the internal combustion engine to the lambda sum desired value and the cylinders are each supplied with identical nominal fuel quantities. In this context, the cylinder-specific deviations can best be determined. The fuel oil does not necessarily have to correspond to the supplied fuel actual amounts, for example when deviations in the injection behavior of the injection valves are present, nozzle needles are occupied or the like. A setpoint actual value discrepancy can be a source of cylinder-specific lambda deviations, but does not have to be the only source. In the first

Mode, i. when all the cylinders are fired, the fuel quantity supplied to each fired cylinder is adjusted on the basis of the respectively determined parameter by means of one of the (global) lambda control superimposed adaptation value (local, ie cylinder-individual lambda control) such that each individual lambda actual value at least largely corresponds to the lambda sum actual value equivalent. If, as explained above, an individual cylinder has a lambda value of> 1, the corresponding fuel quantity is correspondingly increased by the adaptation value (and / or the amount of air is reduced). Conversely, the fuel quantity is reduced (and / or the amount of air increased) when the cylinder-specific lambda value is <1. In other words, there is a cylinder-specific adaptation of the lambda individual actual values to the lambda total actual value.

The required correction, i. Corresponding pilot control values for the lambda governor which are used during the changeover can be determined, for example, by the internal combustion engine being transferred from the first operating mode to the other (eg within the framework of a test operating mode) and a shift of the lambda total actual value caused thereby , The specific shift of the lambda sum actual value can later be taken over directly into a corresponding feedforward control in the context of a control operation.

It may also be advantageous to determine the precontrol value in that an expected shift of the lambda sum actual value is based on the Correction factors (adaptation values) of each fired cylinder is determined. For this purpose, for example, a characteristic curve can be used in which corresponding deviations of the sum adaptation values are converted into lambda correction values. Alternatively or additionally, a correction from a reaction or manipulated variable change of the lambda controller after (initially uncorrected) switching to the partial or half engine operation can be determined.

An arithmetic unit according to the invention, e.g. a control unit of a motor vehicle or of an internal combustion engine is, in particular programmatically, configured to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings FIG. 1 shows an internal combustion engine in which aspects of the invention can be implemented, in plan view.

FIG. 2 shows an internal combustion engine in which aspects according to the invention can be realized, in side view.

Figure 3 shows a method in which aspects of the invention can be realized, in a schematic representation. Embodiment (s) of the invention

1 shows a detail of a motor vehicle having an internal combustion engine 10 with fuel system 20, air supply system 30 and exhaust system 40 and a computing unit 50 as a control device for the control schematically shown in plan view. The internal combustion engine 10 is preferably designed as a gasoline engine with direct fuel injection. The internal combustion engine 10 includes in the illustrated embodiment, four cylinders 1 1, 12, 13, 14, but it is also possible any other number of cylinders. Fuel is provided by the fuel system 20 and injected via respective injectors 21 into the cylinders 11, 12, 13, 14, respectively.

The cylinders 1 1, 12, 13, 14, air is supplied via the air supply system 30, wherein for each of the cylinders 1 1, 12, 13, 14, an inlet valve 31 is provided. Combustion exhaust gas is discharged via exhaust valves 41 from the cylinders 1 1, 12, 13, 14 and discharged via the exhaust system 40. In the exhaust system 40, a catalyst 42 is provided, which converts, inter alia, carbon monoxide and nitrogen oxides and is advantageously designed as a three-way catalyst.

The control unit 50 is in operative connection with actuators of the internal combustion engine 10, the fuel system 20, the air supply system 30 and / or the exhaust system 40 in order to actuate them in a suitable manner. In detail, the control unit 50 controls, for example, the injection valves 21, the intake valves 31, the exhaust valves 41 and other actuators. In particular, the control unit 50 is designed to provide a defined quantity of fuel by means of the injection valves 21. give. The control unit 50 may have a lambda controller 52 formed as part of the controller 50. The control unit 50 is program-technically designed to carry out a method according to the invention.

Furthermore, suitable sensors, such as in particular a lambda probe 51, which is arranged in the exhaust system 40 upstream of the catalytic converter 42, as well as not shown temperature and / or pressure sensors are provided to detect corresponding engine conditions, so that the operation of

Bennkraftmaschine 10 can be realized in response to these by means of the control unit 50. The lambda probe 51 is arranged to detect an oxygen content in the exhaust system 40 and communicates this or a corresponding value derived therefrom e.g. to the lambda controller 52 implemented in the control unit 50.

The control unit 50 controls the internal combustion engine by means of control commands O or by transmitting corresponding parameters in order to provide a drive torque. For this purpose, the control unit 50 inputs I, for example, include external requirements, such as a driver's desired torque, an accelerator pedal position and the like, with which a drive torque request can be specified externally. Furthermore, the control unit 50 receives from the sensors mentioned corresponding information about engine conditions as inputs I, for example, a speed, pressures and temperatures in the air supply system 20 and / or in the exhaust system 40th

In full engine operation, all the cylinders 1 1, 12, 13, 14 of the internal combustion engine 10 are active and are e.g. according to a well-known and not explained in detail here four-stroke operation in a predetermined order fired.

Depending on the desired operating state, for example, the specification of a driver's desired torque or an operating state of the internal combustion engine 10, such as an idling operation, the controller 50 may decide that the drive torque of only one or only part of the cylinder 1 1, 12, 13, 14th should be provided. In this case, at least one of the cylinders 1 1, 12, 13, 14 is switched off and the entire drive torque only one fired cylinder 1 1, 12, 13, 14 or a corresponding set of fired cylinders 1 1, 12, 13, 14 are provided. A corresponding partial shutdown is referred to as partial engine operation. If half of the cylinders 11, 12, 13, 14 are switched off, this is called a half-moon operation. Semi-motor operation represents the standard of partial engine operation since it is the least stressful to the mechanics of internal combustion engine 10. It can also be provided to switch from one set of cylinders 1 1, 12, 13, 14 to another set of cylinders 1 1, 12, 13, 14, so that in a first mode, for example, the cylinders 1 1 and 13 and in a second mode, the cylinders 12 and 14 are fired.

Figure 2 shows an alternative view of the detail of Figure 1 in side view, wherein the Figure 1 corresponding elements for clarity are not explained again. The illustration of a number of components, in particular of the fuel system 20, the air supply system 30 and the exhaust system 40 was dispensed with.

In the cylinders 1 1, 12, 13, 14 each piston 1 1 ', 12', 13 ', 14' are arranged. On the piston 1 1 ', 12', 13 ', 14' when firing the corresponding cylinder 1 1, 12, 13, 14 acting gas forces are on this associated piston rods 1 1 ", 12", 13 ", 14" on a Crankshaft 15 transmitted. In a cylinder imbalance explained previously, e.g. at different fuel quantities, the gas forces acting on the pistons 1 1 ', 12', 13 ', 14' and thus also the uniformity of the rotational movement of the crankshaft 15 vary. A corresponding nonuniformity is referred to as uneven running.

With the crankshaft 15, a donor wheel 16 is rotatably coupled to determine the rough running. The rotational movement of the encoder wheel 16 forms e.g. in a signal 53 'of a rotation angle sensor 53 from. The control unit 50 or a correspondingly provided evaluation module 54 evaluates the signal 53 'and determines therefrom cylinder-individual values.

The encoder wheel 16, which can be seen in a side view in FIG. 2, has markings 16 'distributed over its circumference. In these markings 16 'can they are, for example, ferromagnetic projections whose flanks generate steep edges in the signal 53 'when they pass by an inductive sensor used as a rotational speed sensor 53. The encoder wheel 16 may be divided into segments. Each segment may have a predetermined number of markings 16 '. By counting the signal edges, the controller 50 respectively determines the beginning and end of a corresponding segment and determines segment times in which the segments pass the speed sensor 53.

In FIG. 3, a method according to a particularly preferred embodiment of the invention is shown schematically and designated 100 as a whole.

In a first method step 1, an internal combustion engine, such as, for example, the internal combustion engine 10 of FIGS. 1 and 2, runs in a full-engine mode. A lambda controller continuously sets a lambda sum actual value of the internal combustion engine 10 to a lambda sum desired value, for example the

Value 1, 0 to achieve a homogeneous operation, a. By a suitable method, for example by means of a non-running process, cylinder-specific lambda deviations are determined and in each case compensated by adaptation values superposed according to the lambda control, i. Also, individual lambda values of the individual cylinders are regulated to an individual lambda nominal value, for example the value 1, 0.

In a second method step 2, a corresponding drive signal 50 'is obtained from a control device, for example the control device 50 of FIGS. 1 and 2, requesting a partial or half-motor operation. If a corresponding signal 50 'is obtained, the lambda controller 52 is activated with a pilot control signal 52', which counteracts an intervention of the lambda controller 52. For this purpose, in particular the output signal of the lambda controller, in particular multiplicatively, is subjected to a precontrol value. The precontrol value can, as explained above, be stored in a corresponding control device. It can be determined, for example, by detecting and storing the response of the lambda controller after a first switchover. For later switching operations, the stored result is then used as pre-control value switched to the lambda output, so that the lambda controller itself no longer needs to respond.

In a third method step 3, the internal combustion engine runs in half-engine operation, wherein the corresponding pilot control for the lambda control 52 is active and this keeps a sum lambda at the desired desired value. The process may be carried out cyclically and, as illustrated by the dashed arrow 110, return to step 1, i. the internal combustion engine 10 can be converted again into a full engine operation.

For example, in a four-cylinder engine in full engine operation for the individual cylinders ZyM to Zyl_4, the following injection amounts (EM) could result at a target injection amount of 100%: EM_Zyl_1 = 100%, EM_Zyl_2 = 100%, EM_Zyl_3 = 100%, EM_Zyl_4 = 140%.

The lambda individual actual values behave in sufficient proportion indirectly proportional to the injection quantity,

λ_ΖγΙ_1 = 1, _Zyl_2 = 1, _Zyl_3 = 1, λ_Zyl_4 «0.71,

resulting in a lambda sum actual value of about 0.93.

The global lambda control could reduce the injection quantity across all cylinders to:

EM_Zyl_1 «93%, EM_Zyl_2« 93%, EM_Zyl_3 «93%, EM_Zyl_4 = 130% to achieve a lambda sum actual value of 1.

The lambda individual actual values in sufficient accuracy are now approximately: λ_ΖγΙ_1 ^« 1, 08, λ_Zyl_2 ^« 1, 08, λ_Zyl_3 ^« 1, 08, λ_Zyl_4 ^« 0.77.

The cylinder-specific lambda control could determine the following correction factors (FAK) with mean value = 1:

FAK_Zyl_1 «1, 08, FAK_Zyl_2« 1, 08, FAK_Zyl_3 «1, 08, FAK_Zyl_4« 0.77. This would result in full engine operation:

EM_Zyl_1 = 100%, EM_Zyl_2 = 100%, EM_Zyl_3 = 100%, EM_Zyl_4 = 100%. A shutdown, for example, the cylinders 3 and 4 would lead to a change in the correction factors to obtain the mean = 1:

FAK_Zyl_1 = 1, FAK_Zyl_2 = 1

and accordingly to global emaciation:

EM_Zyl_1 «93%, EM_Zyl_2« 93%.

Here the lambda controller would start and enrich the mixture, in the present example by a factor of 1. 08. This should be avoided for the reasons already explained above. Moreover, this enrichment would have at a later

Downshift to full engine operation are corrected again. Both interventions of the lambda controller are actually unnecessary.

In the implementation of the invention, a pilot control within the global lambda control is now carried out parallel to the switchover to the half-engine operation. As a result of this intervention, the reduction due to the adjustment of the correction factors is compensated by a simultaneous enrichment by the pilot-controlled lambda controller (in the above example the global lambda output would be precontrolled by a factor of 1, 08). The pilot control of the lambda controller can, for. B. be determined by previous application. In this case, as explained, a corresponding correction of the lambda controller is stored for each rich or lean shift that can occur when switching to half-engine operation by the adaptation values. Alternatively, it is also conceivable to measure the lambda change after switching to the half-engine mode and to permanently adapt the resulting correction of the lambda controller for a pilot control.

A particular advantage of the proposed method is that possibly existing "defective vision" (systematic errors) of the lambda probe in half-engine operation are taken into account in the precontrol. As a result, after an adaptation during the first changeover to a partial engine operation, a corresponding value is learned, so that no further reaction of the lambda controller is necessary in future switchovers.

Claims

claims

1 . Method for operating an internal combustion engine (10) having at least two cylinders (1 1 - 14) in at least two operating modes, wherein in a first operating mode all cylinders (1 1 - 14) and in a second operating mode only a part of the cylinders (1 1 - 14) 14) are fired, wherein a lambda sum actual value of the internal combustion engine (10) by means of a lambda controller (52) by adjusting the fired cylinders (1 1 - 14) supplied fuel and / or air amount is set to a desired lambda sum setpoint,

wherein when switching from the first to the second mode of operation, the lambda controller (52) is acted upon by a precontrol value which counteracts a shift of the lambda sum actual value taking place without being acted upon by the switching.

2. The method of claim 1, wherein in the at least two operating modes for each cylinder (1 1 - 14) an individual correction factor for correcting the respective cylinder (1 1 - 14) supplied fuel and / or air quantity is determined by a lambda -Initial value of the respective cylinder (1 1 - 14) to set a desired lambda single setpoint.

3. The method of claim 2, wherein the lambda individual actual values are set to the same lambda single setpoint.

4. The method of claim 2 or 3, wherein the pilot value is determined by the fact that an expected shift of the lambda sum actual value based on a change in the correction factors of the fired in the second mode cylinder (1 1 - 14) is determined when switching.

5. The method of claim 1, wherein the precontrol value is determined by the fact that the internal combustion engine is switched over from the first operating mode to the second, and a shift of the lambda total actual value caused thereby is determined.

6. The method (100) according to any one of the preceding claims, wherein the internal combustion engine (10) is operated depending on the load in the first mode or in the second mode.

7. The method according to claim 6, wherein the second operating mode comprises a half-engine operation in which exactly half of the cylinders of the internal combustion engine are not fired.

8. arithmetic unit (50) which is adapted to perform a method according to any one of the preceding claims.