DE102008002039A1 - Internal combustion engine operating method for motor vehicle, involves considering changes of air mass available for ignition of fuel in final partial injection in rich operation of internal combustion engine - Google Patents

Abstract

The method involves injecting fuel in two partial injections into a combustion chamber of a cylinder (3) of an internal combustion engine (1). Actual torque delivered by the internal combustion engine is determined from operational parameters of the internal combustion engine. Moment efficiency of the respective partial injection is considered, when determining the actual torque. Changes of air mass available for ignition of the fuel in a final partial injection are considered in a rich operation of the internal combustion engine. An independent claim is also included for a computer program for a controller of an internal combustion engine, having a set of instructions to perform a method for operating the internal combustion engine.

Description

State of the art

The The present invention relates to a method for operating a Internal combustion engine and also a control device for an internal combustion engine and a computer program for a Control unit of an internal combustion engine.

Around to be able to control the performance of the internal combustion engine, is it required, the output from the engine actual torque from operating variables of the internal combustion engine, such as For example, amount of injected fuel to determine.

From the DE 10 2004 048 008 A1 a method is known for determining the actual torque as a function of the amount of fuel injected during at least two partial injections. The partial injections may consist, for example, of a main injection and a post-injection. That from the DE 10 2004 048 008 A1 known method is particularly suitable for determining the actual torque of an internal combustion engine, if several partial injections are made when the internal combustion engine is operated in lean operation (λ> 1). Under this condition, at the time of the DE 10 2004 048 008 A1 known method for each partial injection separately determines a so-called torque efficiency. The torque efficiency of the partial injections depends inter alia on the speed n and the drag torque T of the internal combustion engine.

The in the different partial injections injected amounts of fuel are weighted with the torque efficiency and in a partial torque transformed. The sum of these partial torques gives the actual torque the internal combustion engine and has a sufficiently large Accuracy on.

Around the determination and further processing of the actual torque while the system is running To simplify internal combustion engine, it is known from the prior art also known, for determining the actual torque a virtual or effective fuel quantity. This virtual or effective total fuel quantity represents that amount of fuel which, instead of the various partial injections in one single main injection into the combustion chamber of the internal combustion engine would have to be injected to the same actual torque to achieve, as if the fuel is actually in different Part injections is injected. The virtual or effective Total fuel quantity thus allows a computationally simple summary of diverse Factors that influence the actual torque of the internal combustion engine and thus efficient processing.

following becomes the virtual or effective total fuel amount as the effective amount q Eff / pole. The description of the efficiency of a post-injection by an equivalent effective amount q Eff / Pol, which under ideal Comparison conditions (excess air, optimum combustion position) is generally implemented without consideration the influence of the air mass. In the definition of the effective quantity implicit Included is the fact that changes this effective amount q Eff / Pol directly compensated by adjusting the main injection quantity become.

The effective quantity q Eff / Pol is described by an efficiency factor η _Pol (n, T). The efficiency factor η _Pol (n, T) depends only on the operating point and it is assumed that the efficiency does not depend on the post injection quantity itself: q eff pole = η pole · q pole

η_Pol:

Wirkungsgradfaktor der Energieumsetzung

q_Pol:

eingespritzte Kraftstoffmenge q

With:

η _pole :

Efficiency factor of energy conversion

q _pole :

injected fuel q

These The procedure is in conventional lean operation with lambda values greater than 1 (λ> 1) is sufficient, since in this mode enough oxygen for the combustion of the fuel in the cylinder is available, making changes the air mass has no influence on the formation of moments.

However, if a NOx storage catalyst is present in the exhaust line of the internal combustion engine, the mixture is temporarily strongly enriched to regenerate this catalyst to a reduction of in To reach the active surface of the catalyst bound nitrogen oxides. During this operating state (hereinafter rich operation) with lambda values smaller than 1 (λ <1), the combustion of the fuel is incomplete because at the end of the injection cycle, the available oxygen is largely used up.

This means that a small increase in air mass to an immediate Reaction with the excess fuel, what happens in a corresponding moment change. Accordingly, the output torque of the internal combustion engine is reduced, when the air mass is reduced.

So long the lambda value due to this quantity change of the air mass remains below 1, the moment formation of the internal combustion engine by the available oxygen and not limited by the injected fuel quantity, so that changes in the rich operation the post-injection quantity has no effect on the delivered torque to have. If the lambda value rises above 1, this results first a slight momentum increase, with growing Lambda value further strengthened.

Out For this reason, the efficiency of the post-injection quantity is in rich operation primarily also of the influencing factors air mass and Nacheinspritzmenge dependent, which in addition to the operating point dependence, in particular the speed n and the internal moment T, a four-dimensional Correspondence corresponds. There will be more dependencies of fundamental engine parameters such as combustion angle, Air mass, exhaust gas recirculation (EGR) rate, etc., indirectly via takes into account the operating point dependency.

Because of these additional dependencies on the air mass and the injection quantity of the efficiency of the post-injection quantity, provides the known from the prior art method in rich operation insufficiently accurate results.

Disclosure of the invention

Of the Invention has for its object to provide a method that in the rich operation of the internal combustion engine, the determination of the Torque contribution of a post injection in a simple way and with sufficiently high accuracy allowed.

These Object is according to the invention in a method for operating an internal combustion engine, wherein the fuel in at least two partial injections into a combustion chamber of the internal combustion engine is injected, and in which a discharged from the internal combustion engine Actual torque from operating variables of the internal combustion engine is determined, wherein in the determination of the actual torque a Torque efficiency of each partial injection considered is solved, characterized in that changes in the rich operation of the internal combustion engine the for the implementation of the fuel in the last partial injection available air mass.

By means of the method according to the invention, it is possible to map the four-dimensional dependence of the effective post-injection quantity sufficiently accurately in addition to the operating point dependency on the air mass and the post-injection quantity as a function of the injected fuel quantity q _Pol (S). In this case, the method according to the invention preferably uses an empirical functional approach.

Consequently if the method according to the invention is suitable, too in operating conditions of the internal combustion engine, in which at least the post-injection takes place in rich operation, one sufficient accurate determination of the actual torque of the internal combustion engine and on the basis of inventively determined actual moment to regulate the engine sufficiently accurately and control. The inventive method requires no additional hardware components and also the additional Computing time is relatively low, so that conventional Control devices through a software update to carry out the method according to the invention are suitable.

If, as claimed in dependent claim 6, the torque component of the post-injection is described by an effective amount q eff / pole of the post-injection, Then, the function h in the claims 2 to 5 of the Description of the effective amount and not of a torque contribution. Both representations are equivalent.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All features disclosed in the drawing, the description and the patent claims can be used individually as well as in any combination with be essential to each other invention.

It demonstrate:

1 a simplified representation of an operating according to the inventive internal combustion engine,

2 the efficiency representation of a post-injection; and

3 the air mass dependence of the post-injection effective amount.

In the 1 is an internal combustion engine 1 a motor vehicle shown in which a piston 2 in a cylinder 3 is movable back and forth. The cylinder 3 is with a combustion chamber 4 provided, inter alia, by the piston 2 , an inlet valve 5 and an exhaust valve 6 is limited. With the inlet valve 5 is an intake pipe 7 and with the exhaust valve 6 is an exhaust pipe 8th coupled.

In the area of the inlet valve 5 and the exhaust valve 6 protrudes an injection valve 9 in the combustion chamber 4 , can be injected via the fuel with one or more pilot injections, a main injection and at least in certain modes of a post-injection. In the exhaust pipe 8th is a catalyst 12 , in particular a NOx storage catalyst housed. This catalyst 12 serves the post-treatment of the resulting by the combustion of the fuel exhaust gases.

The injection valve 9 is via a pressure line with a fuel tank 13 connected. In a corresponding manner, the injection valves of the other cylinders of the internal combustion engine 1 with the fuel storage 13 connected. The fuel storage 13 is supplied via a supply line with fuel. For this purpose, a preferably mechanical fuel pump is provided which the required pressure in the fuel tank 13 builds.

Furthermore, on the fuel tank 13 a pressure sensor 14 arranged, with which the pressure in the fuel tank 13 is measurable. This pressure is the pressure with which the fuel through the injector 9 in the combustion chamber 4 the internal combustion engine is injected.

During operation of the internal combustion engine fuel is in the fuel tank 13 promoted. This fuel is delivered through the injectors 9 the single cylinder 3 in the associated combustion chambers 4 injected. By burning the in the combustion chambers 4 predominant air / fuel mixture become the pistons 2 subjected to the combustion pressure, so that the pistons 2 transmit a torque to the crankshaft, not shown, of the internal combustion engine.

A control unit 15 is of input signals 16 acted upon, the measured by means of sensors operating variables of the internal combustion engine 1 represent. For example, the controller 15 with the pressure sensor 14 , one in the intake pipe 7 arranged air mass sensor, a speed sensor and the like. Furthermore, the control unit 15 connected to an accelerator pedal sensor which generates a signal representing the torque request of the driver. The control unit 15 generates output signals 17 with which via actuators and / or actuators the behavior of the internal combustion engine 1 can be influenced. For example, the controller 15 with the injector 9 and the like, and generates the signals required to drive them.

A proven measure to fuel consumption, pollutant emissions and noise of the engine positive is to influence the amount of fuel to be injected in several partial injections, in particular one or more pilot injections, a main injection and in certain operating cases, in one or more post-injections, split. The invention Method relates in particular to the post-injection, so that in Following the presence of at least one main injection and a post-injection is assumed.

As already mentioned, the actual torque of the internal combustion engine is from the control unit 15 detected operating variables of the internal combustion engine 1 , such as the injected during the pilot injections, the main injections and the at least one post-injection amounts of fuel determined. The sum of these injected fuel quantities can be combined into a total virtual fuel quantity. The actual injected partial fuel quantities are weighted using an efficiency factor. Usually, the energy conversion or the torque takes place generation in the pilot injection and the main injection of converted amounts of fuel with the same efficiency instead. However, the post-injection takes place much later, that is, for example, about 60 ° Kurbelweilwinkel after the top dead center at which the ignition takes place, so that is to be set for this post-injection, a different efficiency than for the main injection. This top dead center is also referred to below as ignition TDC.

2 shows in the form of a flow chart, the representation of the efficiency of the post-injection.

In a first function block 21 is determined based on various input variables, the efficiency of the post-injection quantity and converted into an effective amount q eff / pole.

Input variables of the first function block 21 are the engine operating point 23 to which the static engine parameters are coupled. In another block 25 are the dynamic input variables, in particular the air mass summarized. In a block 27 is the actually injected fuel quantity q _{pole shown} as a further input variable. The input variables 23 . 25 , and 27 be in the first function block 21 processed and converted into an efficiency of the partial injections, which includes the post-injection in rich operation. Based on the injected fuel quantity q _Pol (see block 27 ) is in the first function block 21 taking into account the previously determined efficiency of the post-injection and the effective amount of the injected fuel _{pole of} q is the liquid injection-effective amount q Eff / Pol calculated. This post-injection effective quantity q Eff / Pol is in 2 with the reference number 29 Mistake.

In order not to have to depict the dependence on the factors influencing a four-dimensional characteristic, the behavior of the internal combustion engine in rich operation is described according to the invention via an empirical functional approach, in which the complexity of application parameters is reduced to a minimum. This empirical functional approach according to the invention is described below in conjunction with the 3 described.

In 3 is the observable on the engine test bench behavior of an internal combustion engine in rich operation. Plotted is the post-injection effective quantity q Eff / Pol (see also the reference numeral 29 in 2 ) as a function of the post-injection quantity q _Pol (see also the reference numeral 27 in 2 ) for different air mass deviations Δm _Air compared to a static air mass. This relationship is indicated by a second line with the reference numeral 31 represents.

The second line 31 begins at the origin of the coordinate system, wherein initially there is a nearly linear relationship between the post injection effective amount q Eff / Pol and the post injection quantity q _Pol . As the post injection quantity q _{pole increases,} the line flattens 31 from.

In the vicinity of a static post-injection quantity q (S) / pole, the post-injection effective quantity q Eff / Pol, which is proportional to the actual torque output, remains approximately constant. The static working point associated with the static post injection quantity q (S) / pole is in 3 With 33 designated.

If one now starting from the static operating point 33 the air mass drawn in by the internal combustion engine increases (Δm _Air > 0) increases the post-injection effective amount q Eff / Pol, because because of the additional air mass in rich operation, a larger part of the injected fuel can be implemented. The influence of an increased air mass on the post-injection effective quantity q Eff / Pol is in 3 by a first line with the reference numeral 35 shown.

Correspondingly, a reduction of the air mass (Δm _Air <0) causes a reduction in the post-injection effective amount q Eff / Pol. The influence of a reduced air mass on the post-injection effective quantity q Eff / Pol is in 3 by a third line with the reference numeral 37 shown.

For small post-injection quantities, the lambda value for all operating points that are relevant in practice is well above 1, so that changes in the air mass are no longer moment-effective. As a result, the lines run 31 . 35 and 37 the post-injection effective quantity q Eff / Pol in the left part of the in 3 represented values range together.

In rich operation, which in the right part of the 3 can be mapped for each air mass on the corresponding effective quantity line 35 or 37 identify a point in which the same lambda value as in the static operating point 33 is achieved when simultaneously with the change in the air mass, the main injection amount is adjusted according to the change of the effective amount.

These points are hereafter referred to as lambda points 39 be designated. The amount of lambda points 39 for different air masses can be in a so-called lambda line 41 represent.

The lambda line 41 cuts the lines 35 and 37 in the lambda points 39.1 and 39.3 , In the static operating point 33 intersect the lambda line 41 and the second line 31 , Here fall static working point 33 and lambda point 39.2 together.

The lambda point 39.1 denotes the operating point of the internal combustion engine in spite of an increased air mass, the same lambda value as in the static operating point 39.2 is present when the post-injection amount q _Pol is increased accordingly.

The lambda point 39.3 designates the operating point in which, despite a reduced air mass, the same lambda value as in the static operating point 39.2 is available. For this purpose, the post-injection quantity q _{pole must} be reduced accordingly.

As 3 it can be seen, the lines show 31 . 35 , and 37 For different air mass deviations a clear similarity, they are only along the Lambdalinie 41 postponed. This fact makes use of the method according to the invention in the following way:
First, a uniform air mass function h ₁ (Δq _Pol ) is defined for all air mass deviations. This air mass function h ₁ (Δq _Pol ) refers to the static operating point 33 : H 1 (.DELTA.Q pole ): = Δ eff pole (.DELTA.Q PoI2 ) = q eff pole (.DELTA.Q PoI2 ) - q Eff (S) pole , Δq pole = q pole - q (1)

q (S) / Pol:

Nacheinspritzmenge im statischen Arbeitspunkt 33.

q Eff(S) / Pol:

Nacheinspritzeffektivmenge im statischen Arbeitspunkt 33.

With

q (S) / pole:

Post-injection quantity in the static operating point 33 ,

q Eff (S) / Pol:

Nacheinspritzeffektivmenge in the static operating point 33 ,

For the operating point-dependent lambda value λ _BP , a lambda function h ₂ (Δm _Air ) is defined. h ₂ (Δm _Air ) describes the changes in the post-injection effective amount Δq Eff (λ) / Pol in the lambda point 39.1 or 39.3 , which is assigned to the air mass deviation Δm _Air , compared to the static operating point 33 : H 2 (Dm Air ): = q Eff (λ) pole (Dm Air ) = q Eff (λ) pole (Dm Air ) - q Eff (S) pole , Δm Air = m Air - m (S) Air (2)

m (S) / Air:

Sollluftmasse im statischen Arbeitspunkt 33.

With:

m (S) / Air:

Setpoint air mass in the static operating point 33 ,

Sizes that are based on a lambda point 39 are indicated by an upright λ.

The lambda function h ₂ (Δm _Air ) is the lambda point 39.1 respectively. 39.3 clearly defined.

In lambda point 39 the air mass change Δm _{Air is} compensated by the associated total quantity change Δq ^{(λ) of} the injected fuel quantity, so that the lambda value remains unchanged:

It follows:

gekennzeichnet.The lambda point is thus by the displacement vector

characterized.

In order to obtain for all air mass deviations a closed representation Δq Eff / Pol = h (Δq _Pol , Δm _Air ) of the effective value, in which any air mass values are taken into account, the function h ₁ (Δq _Pol ) is transformed along the displacement vector: h (.DELTA.Q pole , Δm Air ): = h 1 (.DELTA.Q pole - Δq (Λ) pole ) + Δq Eff (λ) pole (6)

It follows by inserting equations (2) and (4):

Equation (7) enables the description of the air mass dependency of the post-injection effective amount q Eff / Pol by the functional approaches h ₁ (Δq _Pol ) and h ₂ (Δm _Air ).

The approach according to the invention combines the air mass dependency Δm _Air and the quantity dependence of the post-injection quantity efficiency via the approach ( 7 ) dissolved.

This decoupling is only possible if the following assumptions are valid:
The air mass deviations are not too large, because the assumption that the effective mass flow rates for constant air mass have a uniform shape is no longer met at higher air mass deviations.

The Deviations from the linearity in the efficiency of the post-injection are due to the influence of oxygen deficiency (low lambda value) certainly.

The Combustion of the main injection is still under "lean" conditions (enough oxygen). These assumptions are among those in the practice occurring operating conditions of the internal combustion engine generally well fulfilled.

Therefore, it is possible with the method according to the invention to avoid influencing the actual torque output by the internal combustion engine due to changes in the efficiency of the post-injection. For this purpose, according to the invention, either the injected fuel quantity q _{pole is} adjusted during the post-injection in order to keep the associated effective value q Eff / Pol constant or the effective quantity change is compensated via the main injection quantity.

Of Further, a coupled quantity adjustment of main and post injection be made to additional frameworks, such as For example, the lambda value to comply. In practice, in particular the rich operation for the regeneration of the NOx storage catalyst to call. Here, main and Nacheinspritzmenge are in opposite directions adapted to the momentary influence of air mass change to compensate and at the same time to keep the lambda value constant.

The inventive method requires little additional computational effort, so it usually in the engine control unit 15 can be implemented.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 102004048008 A1 [0003, 0003, 0003]

Claims (15)

Method for operating an internal combustion engine ( 1 ), in which fuel in at least two partial injections into a combustion chamber of a cylinder ( 3 ) Is injected to the internal combustion engine and wherein a torque efficiency of the respective sub-injection is used as a basis in calculating the actual torque in which a is determined by the internal combustion engine, characterized in that (in the rich operation λ <1) of the internal combustion engine ( 1 ) Changes in the air mass (m _Air ) available for conversion of the fuel in the last partial injection are taken into account. A method according to claim 1, characterized in that a proportion h of the post-injection is represented in the total torque for different air mass deviations over a uniform functional approach depending on the associated injection quantity:

With: h (Δq _Pol = q _Pol - q (S) / Pol: deviation of the post injection quantity q _pole from the value in the static operating point q (S) / pole Δm _Air = m _Air - m (S) / Air: Deviation of the post injection quantity m _Air from the value at the static operating point m (S) / Air λ _BP : Lambda value at the static operating point A method according to claim 2, characterized in that the function h _{1 is described} according to the following approach:

With: β, x ₀ : operating-point-dependent interpolation parameters g: a fractionally rational function A method according to claim 3, characterized in that the function g is described according to the following approach:

With: α: operating point-dependent interpolation parameter. X: argument of function g Method according to one of claims 2 to 4, characterized in that a linear approach is selected for the function h ₂ : H 2 (x) = γ x With: γ: operating point dependent interpolation parameter X: argument of function h ₂ Method according to one of the preceding claims, characterized in that the torque component of the post-injection is described by an effective amount q Eff / Pol, and that the function h is used to describe the effective amount. Method according to one of the preceding claims, characterized in that between the part injections, in particular the main injection and the last post-injection, a quantity compensation is done so that the delivered moment controls and is preferably kept constant. A method according to claim 7, characterized in that the compensation takes place between the fuel quantities at the desired air mass of the operating point

A method according to claim 8, characterized in that the quantity adaptation Δq _{M1 of} the main injection and Δq _{Pol of} the post-injection are related according to the following equation: .DELTA.Q M1 = -H 1 (.DELTA.Q pole ) Method according to one of claims 7 to 9, characterized in that remaining degrees of freedom Balancing between the fuel quantities of the main injection and the post-injection can be used to combustion characteristics to influence. A method according to claim 10, characterized in that the compensation between the fuel quantities .DELTA.q _{M1 of} the main injection and .DELTA.q _{Pol of} the post-injection takes place so that the lambda value is kept constant. A method according to claim 11, characterized in that the compensation between the fuel quantities takes place according to the following equation:

Method according to one of the preceding claims, characterized in that the internal combustion engine ( 1 ) is operated in an operating mode for the regeneration of a NOx storage catalytic converter with at least one post-injection (NE), and in that the conversion of the fuel injected in the post-injection (NE) takes place under oxygen deficiency (λ <1). Computer program for a control unit ( 15 ) an internal combustion engine ( 1 ), characterized in that it performs a method according to one of the preceding claims, when it is processed. Control unit for an internal combustion engine ( 1 ), characterized in that it operates according to one of the above-claimed methods.