EP3499011A1 - Method and control device for determining a target inlet manifold pressure of a combustion engine - Google Patents

Abstract

The present invention relates to a method for determining a target intake manifold pressure of an internal combustion engine (1) by means of an iterative method, wherein a cylinder charge (r) is determined (55) for a manifold pressure (pl1) iterated during the iterative process and the target intake manifold pressure in Dependence of the determined cylinder filling (r) is determined (57). Furthermore, the invention relates to a control device for carrying out the method according to the invention.

Description

The invention relates to a method and a control device for determining a desired intake manifold pressure of an internal combustion engine, in particular of a motor vehicle, by means of an iterative method. Furthermore, the invention relates to a method and a control device for determining a desired exhaust gas back pressure of an internal combustion engine, for example a motor vehicle, by means of a fixed point iteration.

A target intake manifold pressure, that is, a target pressure value in an intake manifold of an internal combustion engine, is usually used to determine target positions of a throttle valve and a turbocharger of the internal combustion engine in order to control the internal combustion engine taking into account the desired positions.

The DE 199 44 178 A1 discloses a method for controlling a throttle valve, wherein from a predetermined target air mass flow, a desired intake manifold pressure is determined and based on this, the throttle position is derived.

For determining the target intake manifold pressure, a charge exchange model of the internal combustion engine is typically inverted. However, such inversion of the charge cycle model may be locally inaccurate resulting in slower response and torque nonuniformity of the internal combustion engine of a vehicle and the vehicle itself.

In addition, there are also non-invertible charge exchange models. For example, due to a high dependence of the camshaft position on a cylinder air filling, millermotors require an extended charge exchange model. Such charge exchange models are not analytically invertible.

The object of the present invention is to provide a method and a control device for determining a nominal intake manifold pressure which at least partially overcome the abovementioned disadvantages.

This object is achieved by the inventive method for determining a target intake manifold pressure according to claim 1, the inventive method for determining a target exhaust back pressure according to claim 13 and the control device according to claim 15.

According to a first aspect, the present invention relates to a method for determining a desired intake manifold pressure of an internal combustion engine by means of an iterative method, wherein for an iterated during the iterative process intake manifold pressure cylinder filling is determined and the target intake manifold pressure is determined depending on the specific cylinder filling.

bestimmt wird, wobei ṁ_Abg ein Soll-Abgas-Massenstrom, A_eff eine effektive Öffnungsfläche einer Drossel, p₃ ein Soll-Abgasgegendruck, p₄ ein Solldruck nach einer Turbine, R_s die spezifische Gaskonstante des Abgases, T₃ eine Abgastemperatur vor der Turbine, c_d ein Turbinendurchflussfaktor und ψ(·) eine Durchflussfunktion ist, wobei der Soll-Abgasmassenstrom von einem vorangehend iterierten Abgasgegendruck abhängig ist.According to a second aspect, the present invention relates to a method for determining a desired exhaust gas back pressure of an internal combustion engine by means of a fixed point method, wherein an iterated exhaust back pressure from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{<figure-callout\; id="3"\; label="eff\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff\; </figure-callout>}}{p}_{}{}_3\sqrt{\frac{2}{{\mathrm{<figure-callout\; id="3"\; label="R\; s\; T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R\; </figure-callout>}}_s{T}_{}{}_3}}\psi \left(c_d,\frac{p_4}{{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3}\right)$$

is determined, where M _Abg a target exhaust gas mass flow, A _eff an effective opening area of a throttle, p _3, a desired exhaust back pressure, p _4, a target pressure by a turbine, R _{s is} the specific gas constant of the exhaust gas, T _3, an exhaust gas temperature in front of the Turbine, c _{d is} a turbine flow factor and ψ (·) is a flow function, the desired exhaust gas mass flow is dependent on a previously iterierten exhaust back pressure.

According to a third aspect, the present invention relates to a control device comprising a processor adapted to carry out a method according to the first aspect or the second aspect.

Further advantageous embodiments of the invention will become apparent from the subclaims and the following description of preferred embodiments of the present invention.

The present invention relates to a method for determining a target intake manifold pressure of an internal combustion engine by means of an iterative method. The target intake manifold pressure is usually a target pressure that should prevail in an intake manifold of an internal combustion engine configured to supply fresh air to a cylinder of the internal combustion engine.

In determining the desired intake manifold pressure, a cylinder charge is determined for an iterated intake manifold during the iterative process. The cylinder charge of an internal combustion engine is composed, for example, of different proportions of charge components within the cylinder of the internal combustion engine, such as the fresh air, the residual gas and / or the purged air. The cylinder filling can be represented by so-called swallowing curves of the internal combustion engine. The cylinder charge may be based on a non-invertible charge cycle model and determined as a function of desired camshaft positions, a current actual speed in an actual operating point of the internal combustion engine, a target exhaust backpressure for the iterated intake manifold pressure and the iterated intake manifold pressure.

Subsequently, the desired intake manifold pressure is determined depending on the specific cylinder filling. The determination of the target intake manifold pressure will be described in detail below.

The inventive method, the target intake manifold pressure can be determined for non-invertible charge exchange models without much effort. The target intake manifold pressure can be determined so very accurately, so that there is a high CO ₂ savings potential by low Zündwinkeleingriffe in a close-idle operation, a fast and harmonious torque build-up and torque reduction in dynamics and stable conditions for a leak diagnosis in a pressure line and This results in an early error detection for aggregate protection.

In some embodiments, the iterative method may be a secant method. In this case, preferably two starting points are set and between these starting points a secant is placed. Subsequently, an intersection of the secant with an x-axis, in the present case an axis, which indicates a nominal intake manifold pressure, is determined as iterated, which represents an improved starting value for a subsequent iteration. Using the secant method, iterative inversion can also be performed on swallow curves that are not differentiable.

wobei r₀ die Zylinderfüllung für den ersten Start-Saugrohrdruck und r_soll die Soll-Zylinderfüllung der Verbrennungskraftmaschine ist. Die Werte p_S2,max und p_S2,min können aus Kennfeldern ausgelesen werden. Die Kennfelder sind vorzugsweise von einer Drehzahl und der Soll-Zylinderfüllung abhängig, wobei die Kennfelder bevorzugt so bedatet sind, dass ein SuchBereich für den Soll-Saugrohrdruck möglichst klein ist, aber der gesuchte Soll-Saugrohrdruck immer innerhalb des Such-Bereichs liegt. Für den zweiten Start-Saugrohrdruck kann anschließend ebenfalls eine Zylinderfüllung bestimmt werden.In some embodiments, a cylinder charge can be determined for a first start intake manifold pressure and a second start intake manifold pressure can be determined by comparing the cylinder charge for the first start intake manifold pressure with a target cylinder charge of the internal combustion engine and the second starting intake manifold pressure as a function of Comparison result between the cylinder filling for the first start intake manifold pressure and the target cylinder filling is determined. To determine the second starting intake manifold pressure p _S2 , for example, the following may apply: $${\mathrm{<figure-callout\; id="2"\; label="p\; S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_S=\{\begin{array}{ccc}{\mathrm{<figure-callout\; id="2"\; label="p\; S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_S.& \mathit{if}& {\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="imgf0001.png"\; state="\{\{state\}\}">r</figure-callout>}}_0\le r_{\mathit{should}}\\ {\mathrm{<figure-callout\; id="2"\; label="p\; S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_S.& \mathit{if}& {\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="imgf0001.png"\; state="\{\{state\}\}">r</figure-callout>}}_0>r_{\mathit{should}}\end{array}.$$

where r _{0 is} the cylinder charge for the first start intake manifold pressure and r _{soll is} the target cylinder charge of the internal combustion engine. The values p _{S2, max} and p _{S2, min} can be read from maps. The maps are preferably dependent on a speed and the target cylinder filling, the maps are preferably bedatet so that a search range for the target intake manifold pressure is as small as possible, but the desired target intake manifold pressure is always within the search range. For the second start intake manifold pressure, a cylinder charge can then also be determined.

In some embodiments, the first starting intake manifold pressure may be an actual intake manifold pressure. The actual intake manifold pressure may be a pressure currently prevailing in the intake manifold, which pressure is preferably measured by means of a pressure sensor in the intake manifold or determined from other measured parameters.

In some embodiments, starting from the first start intake manifold pressure and the second start intake manifold pressure by means of the secant method, the iterated intake manifold pressure may be determined. For this purpose, a dependent on the intake manifold pressure size for the first start intake manifold pressure and for the second start intake manifold pressure above the intake manifold pressure can be applied and a secant by the Saugrohrdruck dependent size at the first start intake manifold pressure and the second start intake manifold pressure are set. The intersection of the secant with the x-axis (intake manifold pressure axis) can then represent the iterated intake manifold pressure (first iterated intake manifold pressure). Similarly, starting from the second start intake manifold pressure and / or the first iterated intake manifold pressure, further iterated intake manifold pressures can be determined.

In some embodiments, the iterated intake manifold pressure may be further determined depending on the cylinder charge for the first starting intake manifold pressure and the cylinder charge for the second starting intake manifold pressure. Thus, for example, the cylinder charge for the first start intake manifold pressure and the cylinder charge for the second start intake manifold pressure can be plotted above the intake manifold pressure and a secant can be applied through the cylinder charge at the first start intake manifold pressure and the cylinder charge at the second start intake manifold pressure. The intersection of the secant with the x-axis (intake manifold pressure axis) can then represent the iterated intake manifold pressure (first iterated intake manifold pressure). Below is a Cylinder filling for the first iterated intake manifold pressure are determined, these are applied to the intake manifold pressure, a secant between the cylinder filling at the second start intake manifold pressure and the cylinder filling at the first iterated intake manifold pressure are placed and read the intersection of the secant with the x-axis as a second iterated intake manifold pressure become. Analogously, starting from the cylinder filling at the first iterated intake manifold pressure and / or the cylinder charge at the second iterated intake manifold pressure, further iterated intake manifold pressures can be determined.

The iteration by means of the secant method can be terminated, for example, after two or three iteration steps. This means, for example, first two start value calculations for the current intake manifold pressure and a marginal value for the intake manifold pressure (determined via max and min maps) are determined, followed by two or three iteration steps. A maximum number of iteration steps, for example two or three iteration steps, may have been predetermined by an applicator beforehand, for example.

The cylinder charge for the iterated intake manifold pressure can be determined as a function of a desired turbocharger speed. For example, the desired turbocharger speed can be determined as a function of the intake manifold pressure underlying the iteration step. For example, the turbocharger speed for determining the cylinder charge for the first startup intake manifold pressure from the first startup intake manifold pressure, the turbocharger speed for determining the cylinder charge for the second startup intake manifold pressure from the second startup intake manifold pressure, and the turbocharger speed for determining the cylinder charge for the first iterated intake manifold pressure are determined by the first iterated intake manifold pressure. Similarly, the turbocharger speed for determining the cylinder charge for a further iterated manifold pressure may depend on the particular further iterated manifold pressure.

In some embodiments, the cylinder charge for the iterated intake manifold pressure can be determined as a function of a target exhaust backpressure, wherein the desired exhaust back pressure can be determined as a function of the intake manifold pressure underlying the iteration step. For example, the desired exhaust back pressure for determining the cylinder charge for the first start intake manifold pressure from the first start intake manifold pressure, the target exhaust back pressure for determining the cylinder charge for the second intake manifold pressure from the second start intake manifold pressure, and the target exhaust backpressure Determining the cylinder fill for the first iterated manifold pressure from the first iterated manifold pressure. Similarly, the desired exhaust back pressures for determining the cylinder charge for a depend on further iterated intake manifold pressure of the respective further iterated intake manifold pressure. Preferably, the target exhaust backpressure can continue to be determined as a function of the desired turbocharger rotational speed determined in the corresponding step.

The target exhaust gas back pressure is thus unknown and is determined during the course of the method, in particular during each calculation step or iteration step. Preferably, a desired exhaust gas back pressure is also determined for determining the cylinder charge for the first start intake manifold pressure and for the second start intake manifold pressure. In principle, therefore, the swallow curves for the target camshaft positions, the target exhaust backpressure and the current rotational speed are to be inverted in order to calculate a desired intake manifold pressure from the desired charge. The target camshaft positions are preferably known and can be determined, for example, from speed and torque-dependent maps and / or from speed and fill-dependent maps.

bestimmt werden, wobei ṁ_Abg ein Soll-Abgas-Massenstrom, A_eff eine effektive Öffnungsfläche einer Drossel, p₃ ein Soll-Abgasgegendruck, p₄ ein Solldruck nach einer Turbine, R_s die spezifische Gaskonstante des Abgases, T₃ eine Abgastemperatur vor der Turbine, c_d ein Turbinendurchflussfaktor und ψ(·) eine Durchflussfunktion ist. Die spezifische Gaskonstante des Abgases R_s kann beispielsweise als R_s =288J/kgK oder ähnlicher Wert angenommen werden. Die quadratische Approximation der Gleichung (1) aufgelöst nach dem Abgasgegendruck p₃ kann folgende Form besitzen: $$p_3=-\frac{\left(3c_d^2-2c_d{\kappa }_{\mathit{Abg}}\right)p_4}{2c_d{\kappa }_{\mathit{Abg}}-3c_d^2}\pm \sqrt{{\left(\frac{\left(3c_c^2-2c_d{\kappa }_{\mathit{Abg}}\right)p_4}{2c_d{\kappa }_{\mathit{Abg}}-3c_d^2}\right)}^2+\frac{3c_d^2{p}_4^2{A}_{\mathit{eff}}^2+{\dot{m}}_{\mathit{Abg}}^2{R}_s{T}_3{\kappa }_{\mathit{Abg}}}{A_{\mathit{eff}}^2\left(2c_d{\kappa }_{\mathit{Abg}}-3c_d^2\right)}}$$

Dabei ist κ_Abg der Isentropenexponent des Abgases. Der Isentropenexponent kann beispielsweise κ_Abg =1,37 oder einen ähnlichen Wert betragen.In some embodiments, the desired exhaust back pressure may be derived from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{<figure-callout\; id="3"\; label="eff\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff\; </figure-callout>}}{p}_{}{}_3\sqrt{\frac{2}{R_s{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_3}}\psi \left(c_d,\frac{p_4}{{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3}\right)$$

be determined, where ṁ _Abg a target exhaust gas mass flow, A _eff an effective opening area of a throttle, p ₃ a target exhaust back pressure, p ₄ a target pressure after a turbine, R _s the specific gas constant of the exhaust gas, T ₃ an exhaust gas temperature before Turbine, c _{d is} a turbine flow factor and ψ (·) is a flow function. The specific gas constant of the exhaust gas R _s can be assumed, for example, as R _s = 288J / kgK or similar value. The quadratic approximation of equation (1) resolved according to the exhaust gas back pressure p ₃ can have the following form: $${\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3=-\frac{\left(3c_d^2-2c_d{\mathrm{<figure-callout\; id="4"\; label="\kappa \; Abg\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\kappa \; </figure-callout>}}_{\mathit{Abg}}\right)p_{}{}_4}{2c_d{\kappa }_{\mathit{Abg}}-3{\mathrm{<figure-callout\; id="2"\; label="c\; d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c\; </figure-callout>}}_d^{}}\pm \sqrt{{\left(\frac{\left(3c_c^2-2c_d{\mathrm{<figure-callout\; id="4"\; label="\kappa \; Abg\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\kappa \; </figure-callout>}}_{\mathit{Abg}}\right)p_{}{}_4}{2c_d{\kappa }_{\mathit{Abg}}-3{\mathrm{<figure-callout\; id="2"\; label="c\; d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c\; </figure-callout>}}_d^{}}\right)}^2+\frac{3c_d^2{\mathrm{<figure-callout\; id="4"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_4^2{A}_{\mathit{<figure-callout\; id="2"\; label="eff"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff</figure-callout>}}^2+{\dot{m}}_{\mathit{Abg}}^2{R}_s{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_3{\kappa }_{\mathit{Abg}}}{A_{\mathit{<figure-callout\; id="2"\; label="eff"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff</figure-callout>}}^2\left(2c_d{\kappa }_{\mathit{Abg}}-3{\mathrm{<figure-callout\; id="2"\; label="c\; d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c\; </figure-callout>}}_d^{}\right)}}$$

In this case, κ _{Abg is} the isentropic exponent of the exhaust gas. The isentropic exponent may be, for example, κ _exhaust = 1.37 or a similar value.

In some embodiments, the desired exhaust back pressure may be determined by an iterative method. The iterative method for determining the desired exhaust back pressure may be a fixed point iteration. In this case, the exhaust backpressure may preferably be determined repeatedly on the basis of equation (3).

In some embodiments, a starting exhaust back pressure may be the first starting intake manifold pressure, the second starting intake manifold pressure, or the iterated intake manifold pressure. In determining the desired exhaust backpressure used to determine the cylinder charge for the first starting intake manifold pressure, the starting exhaust back pressure may be the first starting intake manifold pressure. In determining the desired exhaust backpressure used to determine the cylinder charge for the second starting intake manifold pressure, the starting exhaust back pressure may be the second starting intake manifold pressure. In determining the desired exhaust backpressure used to determine the cylinder fill for the first iterated startup intake manifold pressure, the starting exhaust backpressure may be the first iterated manifold pressure. Similarly, further iterated intake manifold pressures may be used as the starting exhaust backpressure in determining the respective desired exhaust back pressures.

In some embodiments, depending on the starting exhaust backpressure or the iterated exhaust backpressure, a reduced exhaust mass flow and VTG drive duty cycle (VTG - variable turbine geometry) of a turbocharger may be determined with VTG and, depending thereon, the subsequent iterated exhaust backpressure determined. In this case, furthermore, the VTG drive duty cycle can be determined by means of the reduced mass flow. In particular, a reduced mass flow can be determined repeatedly based on the reduced mass flow, based on the reduced mass flow, and a VTG drive duty cycle (VTG control) can be determined, and finally the iterated exhaust backpressure can be calculated. For the determination of the VTG drive duty cycle in each iteration, a stationary pre-control characteristic map can be evaluated, which is preferably dependent on the underlying exhaust backpressure and the reduced mass flow.

Alternatively or in addition to the VTG drive duty cycle, a setting of a wastegate actuator of a turbocharger with wastegate actuator can be determined and taken into account in the determination of the subsequent iterated exhaust backpressure. The procedure is preferably analogous to that in a turbocharger with VTG.

The iteration by means of the fixed point iteration can be terminated, for example, after two or three iteration steps. That is, initially, a start value calculation for the starting exhaust back pressure, for example, the current intake manifold pressure (actual intake manifold pressure) is performed and then followed by two or three iteration steps. A maximum number of iteration steps may have been previously determined, for example, by an applicator.

When a desired exhaust gas back pressure in a stationary state assumes the value of an actual exhaust backpressure, the desired exhaust gas back pressure can be superimposed stationary. The actual exhaust backpressure can then be an exhaust gas backpressure measured by means of a sensor. The stationary blending leads to an increase in accuracy.

Daraus kann das VTG-Ansteuer-Tastverhältnis und/oder die Einstellung des Stellers des Turboladers mit Wastegate bestimmt werden.Alternatively, the exhaust back pressure in each calculation step or iteration step can be calculated via the equation (3) and a reduced mass flow can be determined. For this purpose, for example, an approximation by means of the following equation: $${\dot{m}}_{\mathit{Abg}.\mathit{red}}={\dot{m}}_{\mathit{Abg}}\frac{\sqrt{T_3}}{{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3}$$

From this, the VTG drive duty cycle and / or the actuator setting of the wastegate turbocharger can be determined.

In some embodiments, alternatively, the exhaust backpressure may be determined from a desired pressure for a turbine and a power balance of the turbine and a compressor. This is a simplification compared to the evaluation of equation (3), but leads to less accurate results.

In summary, the present invention is characterized by the type of iterative calculation of the charge cycle model in combination with the inversion of the approximately linear engine slip characteristic, wherein a setpoint calculation of the exhaust gas back pressure is to be performed in a destination. In this case, no directional derivations of the charge exchange model are necessary, which are used in conventional methods.

bestimmt wird, wobei ṁ_Abg ein Soll-Abgas-Massenstrom, A_eff eine effektive Öffnungsfläche einer Drossel, p₃ ein Soll-Abgasgegendruck, p₄ ein Solldruck nach einer Turbine, R_s die spezifische Gaskonstante des Abgases, T₃ eine Abgastemperatur vor der Turbine, c_d ein Turbinendurchflussfaktor und ψ(·) eine Durchflussfunktion ist, wobei der Soll-Abgasmassenstrom von einem Start-Abgasgegendruck bzw. von einem vorangehend iterierten Abgasgegendruck abhängig ist. Die quadratische Approximation kann die Gleichung (3) oben ergeben.Furthermore, the invention relates to a method for determining a desired exhaust gas back pressure of an internal combustion engine by means of a fixed point method, wherein an iterated exhaust back pressure from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{<figure-callout\; id="3"\; label="eff\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff\; </figure-callout>}}{p}_{}{}_3\sqrt{\frac{2}{R_s{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_3}}\psi \left(c_d;\frac{p_4}{{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3}\right)$$

is determined, where M _Abg a target exhaust gas mass flow, A _eff an effective opening area of a throttle, p _3, a desired exhaust back pressure, p _4, a target pressure by a turbine, R _{s is} the specific gas constant of the exhaust gas, T _3, an exhaust gas temperature in front of the Turbine, c _{d is} a turbine flow factor and ψ (·) is a flow function, wherein the target exhaust gas mass flow is dependent on a start exhaust back pressure or on a previously iterated exhaust back pressure. The quadratic approximation can give the equation (3) above.

In some embodiments, the desired exhaust back pressure may correspond to the iterated exhaust back pressure after two or three iterations.

Further details of the method for determining a desired exhaust backpressure have been described in detail above with respect to the method of determining the desired intake manifold pressure. These features apply analogously to the method for determining a desired exhaust backpressure.

Furthermore, the invention relates to a control device for an internal combustion engine having a processor which is adapted to carry out a method for determining a target intake manifold pressure of an internal combustion engine by means of an iterative method, wherein for an iterated during the iterative process intake manifold pressure cylinder filling is determined and the target intake manifold pressure is determined as a function of the specific cylinder charge. In particular, the processor is configured to carry out the above-described method for determining a nominal intake manifold pressure.

The control device may be, for example, a motor controller. The control device may further comprise a data memory for storing maps, calculation rules, iteration instructions, specified parameters and / or the like. Furthermore, the control device can have a signal input for receiving data, for example measurement data or other data, and a signal output for outputting control signals to the internal combustion engine, in particular the controllable components of the internal combustion engine.

Furthermore, the invention relates to a control device for an internal combustion engine having a processor, which is adapted to carry out a method for determining a desired exhaust gas back pressure, as described above.

Fig. 1

schematisch eine Verbrennungskraftmaschine;

Fig. 2

schematisch eine Steuervorrichtung zum Ausführen eines Verfahrens zum Bestimmen eines Soll-Saugrohrdrucks;

Fig. 3

schematisch ein Flussdiagramm eines Ausführungsbeispiels eines Verfahrens zum Bestimmen eines Soll-Saugrohrdrucks;

Fig. 4

schematisch ein Flussdiagramm eines Verfahrens zum Bestimmen der Zylinderfüllung;

Fig. 5

schematisch das Grundprinzip eines Sekantenverfahrens; und

Fig. 6

schematisch ein Flussdiagramm eines iterativen Verfahrens zum Bestimmen eines Soll-Abgasgegendrucks.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. It shows:

Fig. 1

schematically an internal combustion engine;

Fig. 2

schematically a control device for carrying out a method for determining a target intake manifold pressure;

Fig. 3

schematically a flowchart of an embodiment of a method for determining a target intake manifold pressure;

Fig. 4

schematically a flowchart of a method for determining the cylinder filling;

Fig. 5

schematically the basic principle of a secant procedure; and

Fig. 6

schematically a flowchart of an iterative method for determining a target exhaust back pressure.

In Fig. 1 schematically an internal combustion engine is shown. A cylinder 1 has a combustion chamber 10, in which the combustion of fuel takes place, which is injected via an injection valve 11. The cylinder 1 is coupled via an inlet valve 12 to a suction pipe 13, from which fresh air enters the combustion chamber 10 through the inlet valve 12. In addition, the cylinder 1 is coupled via an exhaust valve 14 with an exhaust manifold 15, is passed through the exhaust gas or residual gas from the combustion chamber 10 in the exhaust manifold 15. Further, there is a cylinder piston 16 which is driven by a crankshaft (not shown). In the suction pipe 13 directly in front of the inlet valve 12, there is arranged a suction pipe pressure sensor 2, which is designed to detect a suction pipe pressure. In the exhaust manifold 15 directly behind the exhaust valve 14, an exhaust back pressure sensor 3 is arranged, which is adapted to detect an exhaust back pressure. In the Fig. 1 For example, the cylinder 1 is shown at a time when the intake valve 12 and the exhaust valve 14 are opened and there is a valve overlap.

Fig. 2 shows a schematic representation of a control device 4 for carrying out a method for determining a target intake manifold pressure. The control device 4 has a processor 40, which is connected to a signal input 41 for receiving data and a signal output 42 for outputting control commands to the internal combustion engine. Furthermore, the control device 4 has a data memory 43, which is provided for storing maps, calculation instructions, iteration instructions, specified parameters and the like. The processor 40 is configured to A method for determining a desired intake manifold pressure, as described below with reference to Fig. 3 to Fig. 6 is described to execute.

Fig. 3 shows a flowchart of a method 5 for determining a target intake manifold pressure.

At 50, a first start intake manifold pressure is first determined. For this purpose, an actual intake manifold pressure is measured by means of the intake manifold pressure sensor, which serves as the first start intake manifold pressure.

Subsequently, at 51, a cylinder charge is determined for the first start intake manifold pressure.

This is done, as in the diagram in Fig. 4 at 60, a desired turbocharger speed is determined depending on the first start intake manifold pressure. Depending on the first start intake manifold pressure and the specific target turbocharger rotational speed, a target exhaust backpressure is determined at 61. The calculation of the target exhaust back pressure will be described below with reference to FIG Fig. 6 described in detail. Subsequently, the cylinder filling is determined at 62 as a function of the first start intake manifold pressure and the desired exhaust backpressure.

At 52 in Fig. 3 Depending on the cylinder filling for the first start intake manifold pressure, a second start intake manifold pressure is determined. For this purpose, the cylinder charge for the first start intake manifold pressure is compared with a target cylinder charge of the internal combustion engine and depending on the comparison result according to equation (2) above from a map that defines a search range, an upper limit p _{S2, max} or a lower limit p _{S2 , min set} as the second start intake manifold pressure.

At 53, a cylinder charge for the second start intake manifold pressure is determined. The determination of the cylinder charge for the second start intake manifold pressure is analogous to determining the cylinder charge for the first start intake manifold pressure.

At 54, a first manifold pressure iterate is determined by a secant method. For this, as in Fig. 5 The cylinder _charge r _ps2 for the first start intake pipe pressure p _s1 and the cylinder _charge r _ps2 for the second start intake pipe pressure p _{s2 are} plotted against the intake pipe pressure p (x-axis) and a secant S1 is placed between the cylinder _charges r _ps1 , r _ps2 , An intersection of the secant S1 with the x-axis represents the first intake manifold pressure iterated p _l1 .

At 55, a cylinder charge is determined for the particular first intake manifold pressure iterate. The determination of the cylinder charge for the first intake manifold pressure iterated is analogous to determining the cylinder charge for the first start intake manifold pressure.

At 56, it is determined whether the iteration can be canceled or not. This can be determined as a function of a number of iterations already carried out or as a function of the cylinder charge for the first intake manifold pressure iterated. For example, the filling for the first intake pipe pressure iterate can be compared with the charge for the second starting intake manifold pressure and, depending on the comparison result, a decision can be made whether the iteration can be terminated or not.

If it is determined at 56 that the iteration may be aborted, at 57 the last determined manifold pressure iterate is output as the target manifold pressure.

If it is determined at 56 that the iteration can not be aborted, steps 54 through 56 are repeated. At 54, a second intake pipe pressure iterate is determined by, as in Fig. 5 ₂ , a secant S2 is set by the cylinder _charge r _ps2 for the second start intake manifold pressure and the cylinder _charge r _pl1 for the first intake manifold pressure _iterate , and an intersection with the x axis is set as the second intake manifold pressure _iterate p _l2 . At 55, the cylinder charge is then determined for the second intake manifold pressure iterate and at 56 it is determined whether or not the iteration can be aborted. For this purpose, the filling for the second intake manifold pressure iterated can be compared with the charge for the first intake manifold pressure iterated and it can be decided as a function of the comparison result whether the iteration can be aborted or not. If the iteration can not be aborted, steps 54 through 56 are repeated analogously for further manifold pressure iterates.

For example, the iteration is repeated a maximum of two times and then aborted. However, the maximum number of iterations can be set in advance.

In the first embodiment, the target exhaust back pressure for determining a charge to each of the intake manifold start pressures and the intake pipe pressure iterated is determined according to the target exhaust gas back pressure determining method 7.

At 70, a start exhaust backpressure is established. The starting exhaust back pressure is the intake manifold pressure which is assumed in the respective step of the method 5 for determining the target intake manifold pressure. That is, in step 51 of the method 5, the starting exhaust back pressure the first start intake manifold pressure, the second intake manifold start pressure in step 53, and the intake manifold pressure iterated in step 55 in step 55.

At 71, a reduced mass flow is determined depending on the starting exhaust backpressure.

At 72, a VTG drive duty cycle or an actuator setting of a wastegate turbocharger is then determined in response to the starting intake manifold pressure and the reduced mass flow.

At 73, an exhaust back pressure iterate is determined by the equation (3) above. Steps 71 to 73 each represent an iteration step of a fixed-point iteration.

At 74 it is checked whether the iteration can be aborted or not. This is determined depending on a number of already performed iterations. The maximum number of iterations here is 2.

If it is determined at 74 that the iteration can be aborted, at 75 the last determined exhaust backpressure iterate is output as the target exhaust back pressure.

If it is determined at 74 that the iteration can not be aborted, steps 71-74 are repeated. In each case, a reduced exhaust gas mass flow, a VTG drive duty cycle or an adjustment of an actuator of a turbocharger with wastegate and a further exhaust gas backpressure iterated are determined as a function of the exhaust back pressure iterated.

In a second embodiment, the exhaust back pressure in each calculation step 51, 53, 54 of method 5 will be calculated via equation (3) above and a reduced mass flow determined according to equation (4) above. From this, the VTG drive duty cycle or the setting of the turbocharger with wastegate is determined.

In a third exemplary embodiment, the desired exhaust backpressure in each calculation step 51, 53, 54 of the method 5 is determined from a setpoint pressure according to a turbine and a power balance of the turbine and a compressor.

LIST OF REFERENCE NUMBERS

1

Cylinder of an internal combustion engine

10

combustion chamber

11

Injector

12

intake valve

13

suction tube

14

outlet valve

15

exhaust manifold

16

cylinder piston

2

intake manifold pressure sensor

3

Exhaust back pressure sensor

4

control device

40

processor

41

signal input

42

signal output

43

data storage

5

A method of determining a desired intake manifold pressure

50

Determining a first start intake manifold pressure

51

Determining a cylinder filling for the first start intake manifold pressure

52

Determining a second start intake manifold pressure

53

Determining a cylinder filling for the second starting intake manifold pressure

54

Determining a Saugrohrdruck iterated by a secant method

55

Determining a cylinder filling for the intake manifold pressure iterated

56

Determine if the iteration can be canceled

57

Defining the last determined intake manifold pressure-Iterates as the target intake manifold pressure

60

Calculate a turbocharger speed

61

Determining a desired exhaust gas back pressure

62

Determining a cylinder filling

70

Set a start exhaust backpressure

71

Determining a reduced mass flow

72

Determining a VTG drive duty cycle

73

Determining an exhaust backpressure iterate

74

Determine if the iteration can be canceled

75

Defining the last determined exhaust back pressure iterated as the target exhaust back pressure

p _s1

first start intake manifold pressure

p _s2

second start intake manifold pressure

p _l1

first intake manifold pressure iterated

p _l2

second intake manifold pressure iterated

r _ps1

Cylinder filling for the first start intake manifold pressure

r _ps2

Cylinder filling for the second start intake manifold pressure

r _pl1

Cylinder filling for the first intake manifold pressure iterated

S1

secant

S2

secant

Claims (15)

Method for determining a desired intake manifold pressure of an internal combustion engine (1) by means of an iterative method, wherein a cylinder _charge (r _pl1 ) is determined (55) for a manifold pressure (p _l1 ) iterated during the iterative process and the target intake manifold pressure is determined as a function of the determined intake manifold pressure Cylinder _filling (r _pl1 ) is determined (57). The method of claim 1, wherein the iterative method is a secant method (54). The method of claim 2, wherein for a first starting intake manifold pressure (p _s1 ), a cylinder charge (r _ps1 ) is determined and a second starting intake manifold pressure (p _s2 ) is determined by the cylinder charge (r _ps1 ) for the first starting intake manifold pressure is compared with a target cylinder charge of the internal combustion engine (1) and the second start intake manifold pressure (p _s2 ) is determined as a function of the comparison result between the cylinder charge (r _ps1 ) for the first start intake manifold pressure (p _s1 ) and the target cylinder charge , The method of claim 3, wherein the first startup intake manifold pressure (p _s1 ) is an actual intake manifold pressure. The method of claim 3 or 4, wherein starting from the first start-Saugrohrdruck (p _s1 ) and the second start-Saugrohrdruck (p _s2 ) by means of the secant method, the iterated intake manifold pressure (p _l1 ) is determined. The method of claim 5, wherein the iterated manifold pressure (p _l1 ) is further determined in response to the cylinder charge (r _ps1 ) for the first _boost manifold pressure (p _s1 ) and the cylinder _charge (r _ps2 ) for the second _boost manifold pressure (p _s2 ) becomes. Method according to one of the preceding claims, wherein the cylinder _charge (r _pl1 ) for the iterated intake manifold pressure (p _l1 ) is determined as a function of a desired exhaust backpressure, wherein the desired exhaust back pressure is determined as a function of the iterated intake manifold pressure (p _l1 ). The method of claim 7, wherein the desired exhaust back pressure from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{eff}}{p}_3\sqrt{\frac{2}{R_s{T}_3}}\psi \left(c_d;\frac{p_4}{p_3}\right)$$

is determined, where M _Abg a target exhaust gas mass flow, A _eff an effective opening area of a throttle, p _3, a desired exhaust back pressure, p _4, a target pressure by a turbine, R _{s is} the specific gas constant of the exhaust gas, T _3, an exhaust gas temperature in front of the Turbine, c _{d is} a turbine flow factor and ψ (·) is a flow function. The method of claim 7 or 8, wherein the target exhaust back pressure is determined by an iterative method (70-75). The method of claim 9, wherein a starting exhaust back pressure is the iterated intake manifold pressure (p _l1 ). The method of claim 10, wherein a reduced exhaust gas mass flow and a VTG drive duty cycle is determined in dependence on the starting exhaust back pressure and is determined in dependence on this, the iterated exhaust back pressure. The method of claim 7, wherein the target intake manifold pressure is determined from a desired pressure according to a turbine and a power balance of the turbine and a compressor. A method for determining a desired exhaust back pressure of an internal combustion engine (1) by means of a fixed point method, wherein an iterated exhaust back pressure from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{eff}}{p}_3\sqrt{\frac{2}{R_s{T}_3}}\psi \left(c_d;\frac{p_4}{p_3}\right)$$

is determined, where M _Abg a target exhaust gas mass flow, A _eff an effective opening area of a throttle, p _3, a desired exhaust back pressure, p _4, a target pressure by a turbine, R _{s is} the specific gas constant of the exhaust gas, T _3, an exhaust gas temperature in front of the Turbine, c _{d is} a turbine flow factor and ψ (·) is a flow function, the desired exhaust gas mass flow is dependent on a previously iterierten exhaust back pressure. The method of claim 13, wherein the desired exhaust back pressure corresponds to the iterated exhaust back pressure after two iteration steps. Control device for an internal combustion engine (1) comprising a processor (40) adapted to carry out a method according to any one of the preceding claims.

Images