EP3499011B1 - Method and control device for determining a target inlet manifold pressure of a combustion engine - Google Patents

Description

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

A target intake manifold pressure, i.e. 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 the target positions into account.

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

To determine the target intake manifold pressure, a gas exchange model of the internal combustion engine is typically inverted. However, such an inversion of the gas exchange model can be inaccurate in places, which leads to a slower response and torque irregularity of the internal combustion engine of a vehicle and the vehicle itself.

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

The US6,968,824 B1 describes a method for determining a target boost pressure using an iterative method. A delivery level is determined on the basis of a measured boost pressure and an iterated boost pressure is determined on the basis of the delivery level, which is then evaluated. Depending on the evaluation result, a decision is made as to whether a further iteration step is carried out or whether the iterated boost pressure is selected as the target boost pressure.

The object of the present invention is to provide a method and a control device for determining a target intake manifold pressure, which at least partially overcome the above-mentioned disadvantages.

This object is achieved by the inventive method for determining a target intake manifold pressure according to claim 1 and the control device according to claim 7.

According to a first aspect, 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, wherein a cylinder charge is determined for an intake manifold pressure iterated during the iterative method and the target intake manifold pressure is determined as a function of the determined cylinder charge.

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

Further advantageous embodiments of the invention emerge 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 using 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 that is designed to supply fresh air to a cylinder of the internal combustion engine.

When determining the target intake manifold pressure, a cylinder charge is determined for an intake manifold pressure iterated during the iterative process. The cylinder charge of an internal combustion engine is composed, for example, of various proportions of charge components within the cylinder of the internal combustion engine, such as fresh air, residual gas and/or flushed air. The cylinder charge can represented by so-called intake curves of the internal combustion engine. The cylinder filling can be based on a non-invertible gas exchange model and determined depending on target camshaft positions, a current actual speed at a current operating point of the internal combustion engine, a target exhaust back pressure for the iterated intake manifold pressure and the iterated intake manifold pressure.

The target intake manifold pressure is then determined depending on the specific cylinder charge. The determination of the target intake manifold pressure is described in detail below.

The method according to the invention allows the target intake manifold pressure to be determined without great effort even for non-invertible gas exchange models. The target intake manifold pressure can thus be determined very precisely, resulting in a high CO ₂ saving potential through low ignition angle interventions in near-idling operation, a fast and harmonious torque build-up and torque reduction in the dynamics and stable conditions for leak diagnosis in a pressure section and thus early error detection for unit protection.

The iterative method is a secant method. Two starting points are defined and a secant is placed between these starting points. Then an intersection point of the secant with an x-axis, in this case an axis that indicates a target intake manifold pressure, is defined as an iterate, which represents an improved starting value for a subsequent iteration. Using the secant method, an iterative inversion of absorption curves that are not differentiable can also be carried out.

wobei ro 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.A cylinder charge is determined for a first starting intake manifold pressure and a second starting intake manifold pressure is determined by comparing the cylinder charge for the first starting intake manifold pressure with a target cylinder charge of the internal combustion engine and determining the second starting intake manifold pressure depending on the comparison result between the cylinder charge for the first starting intake manifold pressure and the target cylinder charge. For example, the following can apply to determine the second starting intake manifold pressure p _S2 : $${\mathrm{<figure-callout\; id="2"\; label="p\; S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_S=\{\begin{array}{ccc}{\mathrm{<figure-callout\; id="2"\; label="p\; S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_S,& \mathit{if}& r_0\le r_{\mathit{should}}\\ {\mathrm{<figure-callout\; id="2"\; label="p\; S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_S,& \mathit{if}& r_0>r_{\mathit{should}}\end{array},$$

where ro is the cylinder charge for the first starting 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 characteristic maps. The characteristic maps are preferably dependent on a speed and the target cylinder charge, whereby the characteristic maps are preferably data-rich in such a way that a search area for the target intake manifold pressure is as small as possible, but the target intake manifold pressure sought is always within the search range. A cylinder charge can then also be determined for the second starting intake manifold pressure.

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

In some embodiments, the iterated intake manifold pressure can be determined using the secant method based on the first starting intake manifold pressure and the second starting intake manifold pressure. To do this, a variable that is dependent on the intake manifold pressure can be plotted against the intake manifold pressure for the first starting intake manifold pressure and for the second starting intake manifold pressure, and a secant can be placed through the variable that is dependent on the intake manifold pressure at the first starting intake manifold pressure and at the second starting intake manifold pressure. The intersection point 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, further iterated intake manifold pressures can be determined based on the second starting intake manifold pressure and/or the first iterated intake manifold pressure.

In some embodiments, the iterated intake manifold pressure can also be determined as a function of the cylinder charge for the first starting intake manifold pressure and the cylinder charge for the second starting intake manifold pressure. For example, the cylinder charge for the first starting intake manifold pressure and the cylinder charge for the second starting intake manifold pressure can be plotted against the intake manifold pressure and a secant can be drawn through the cylinder charge at the first starting intake manifold pressure and the cylinder charge at the second starting intake manifold pressure. The intersection point of the secant with the x-axis (intake manifold pressure axis) can then represent the iterated intake manifold pressure (first iterated intake manifold pressure). Subsequently, a cylinder charge for the first iterated intake manifold pressure can be determined, this can be plotted against the intake manifold pressure, a secant can be drawn between the cylinder charge at the second starting intake manifold pressure and the cylinder charge at the first iterated intake manifold pressure, and the intersection point of the secant with the x-axis can be read off as the second iterated intake manifold pressure. Analogously, further iterated intake manifold pressures can be determined based on the cylinder filling at the first iterated intake manifold pressure and/or the cylinder filling at the second iterated intake manifold pressure.

The iteration using the secant method can be terminated after two or three iteration steps, for example. This means, for example, that two starting value calculations for the current intake manifold pressure and a boundary value for the intake manifold pressure (determined via max and min maps) are first determined, followed by two or three iteration steps. A maximum number of iteration steps, for example two or three iteration steps, can have been specified in advance, for example by an application engineer.

The cylinder charge for the iterated intake manifold pressure can be determined depending on a target turbocharger speed. For example, the target turbocharger speed can be determined depending on the intake manifold pressure underlying the iteration step. For example, the turbocharger speed for determining the cylinder charge for the first starting intake manifold pressure can be determined from the first starting intake manifold pressure, the turbocharger speed for determining the cylinder charge for the second starting intake manifold pressure can be determined from the second starting intake manifold pressure, and the turbocharger speed for determining the cylinder charge for the first iterated intake manifold pressure can be determined from the first iterated intake manifold pressure. Similarly, the turbocharger speed for determining the cylinder charge for a further iterated intake manifold pressure can depend on the respective further iterated intake manifold pressure.

The cylinder charge for the iterated intake manifold pressure is determined depending on a target exhaust back pressure, wherein the target exhaust back pressure can be determined depending on the intake manifold pressure underlying the iteration step. For example, the target exhaust back pressure for determining the cylinder charge for the first starting intake manifold pressure can be determined from the first starting intake manifold pressure, the target exhaust back pressure for determining the cylinder charge for the second starting intake manifold pressure can be determined from the second starting intake manifold pressure, and the target exhaust back pressure for determining the cylinder charge for the first iterated intake manifold pressure can be determined from the first iterated intake manifold pressure. Similarly, the target exhaust back pressures for determining the cylinder charge for a further iterated intake manifold pressure can depend on the respective further iterated intake manifold pressure. Preferably, the target exhaust back pressure can also be determined depending on the target turbocharger speed determined in the corresponding step.

The target exhaust back pressure is therefore unknown and is determined during the process, in particular during each calculation step or iteration step. Preferably, a target exhaust back pressure is also determined to determine the cylinder charge for the first starting intake manifold pressure and for the second starting intake manifold pressure. In principle, the Absorbtion curves for the target camshaft positions, the target exhaust back pressure and the current speed are inverted in order to calculate a target intake manifold pressure from the target charge. The target camshaft positions are preferably known and can be determined, for example, from speed and torque-dependent characteristic maps and/or from speed and charge-dependent characteristic 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: $$p_3=-\frac{\left(3c_d^2-2c_d{\kappa }_{\mathit{Abg}}\right)p_4}{2c_d{\kappa }_{\mathit{Abg}}-3c_d^2}\pm \sqrt{{\left(\frac{\left(3c_c^2-2c_d{\kappa }_{\mathit{Abg}}\right)p_4}{2c_d{\kappa }_{\mathit{Abg}}-3c_d^2}\right)}^2+\frac{3c_d^2{p}_4^2{A}_{\mathit{eff}}^2+{\dot{m}}_{\mathit{Abg}}^2{R}_s{T}_3{\kappa }_{\mathit{Abg}}}{A_{\mathit{eff}}^2\left(2c_d{\kappa }_{\mathit{Abg}}-3c_d^2\right)}}$$

In some embodiments, the target exhaust back pressure may be determined from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{<figure-callout\; id="3"\; label="eff\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff</figure-callout>}}{p}_{}{}_3\sqrt{\frac{2}{{\mathrm{<figure-callout\; id="3"\; label="R\; s\; T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_s{T}_{}{}_3}}\psi \left(c_d,\frac{p_4}{{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3}\right)$$

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

Here, K _Abg is the isentropic exponent of the exhaust gas. The isentropic exponent can be, for example, K _Abg =1.37 or a similar value.

In some embodiments, the target exhaust back pressure can be determined using an iterative method. The iterative method for determining the target exhaust back pressure can be a fixed point iteration. The exhaust back pressure can 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. When determining the target exhaust back pressure 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. When determining the target exhaust back pressure 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. When determining the target exhaust back pressure, which is used to determine the cylinder charge for the first iterated starting intake manifold pressure, the starting exhaust back pressure can be the first iterated intake manifold pressure. Similarly, further iterated intake manifold pressures can be used as starting exhaust back pressure when determining the respective target exhaust back pressures.

In some embodiments, a reduced exhaust gas mass flow and a VTG control duty cycle (VTG - variable turbine geometry) of a turbocharger with VTG can be determined depending on the starting exhaust gas back pressure or the iterated exhaust gas back pressure, and the subsequent iterated exhaust gas back pressure can be determined depending on this. The VTG control duty cycle can also be determined using the reduced mass flow. In particular, a reduced mass flow can be determined repeatedly starting from a starting exhaust gas back pressure, a VTG control duty cycle (VTG control) can be determined on the basis of the reduced mass flow, and finally the iterated exhaust gas back pressure can be calculated. To determine the VTG control duty cycle in each iteration, a stationary pilot control map can be evaluated, which is preferably dependent on the underlying exhaust gas back pressure and the reduced mass flow.

Alternatively or in addition to the VTG control duty cycle, a setting of a wastegate actuator of a turbocharger with wastegate actuator can be determined and taken into account when determining the subsequent iterated exhaust back pressure. The procedure is preferably analogous to that for a turbocharger with VTG.

The iteration using the fixed point iteration can be terminated after two or three iteration steps, for example. This means that first a starting value calculation is carried out for the starting exhaust back pressure, for example the current intake manifold pressure (actual intake manifold pressure), and then two or three iteration steps follow. A maximum number of iteration steps can be set in advance, for example by an application engineer.

If a target exhaust back pressure assumes the value of an actual exhaust back pressure in a stationary state, the target exhaust back pressure can be blended in a stationary manner. The actual exhaust back pressure can then be an exhaust back pressure measured by a sensor. The stationary blending leads to an increase in accuracy.

Alternatively, the exhaust back pressure can be calculated in each calculation step or iteration step using equation (3) and a reduced mass flow can be determined. For example, an approximation can be made using 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 control duty cycle and/or the setting of the actuator of the turbocharger with wastegate can be determined.

In some embodiments, the exhaust back pressure can alternatively be determined from a target pressure after a turbine and a power balance of the turbine and a compressor. This represents 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 gas exchange model in combination with the inversion of the approximately linear engine consumption characteristic curve, whereby a setpoint calculation of the exhaust gas back pressure is to be carried out at a target point. No directional derivatives of the gas 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.In the following, a method for determining a target exhaust back pressure of an internal combustion engine using a fixed point method is described, which, however, is not in accordance with the invention, wherein an iterated exhaust back pressure is derived from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{<figure-callout\; id="3"\; label="eff\; p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">eff</figure-callout>}}{p}_{}{}_3\sqrt{\frac{2}{R_s{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_3}}\psi \left(c_d,\frac{p_4}{{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="imgf0001.png"\; state="\{\{state\}\}">p</figure-callout>}}_3}\right)$$

is determined, where ṁ _Abg is a target exhaust gas mass flow, A _eff is an effective opening area of a throttle, p ₃ is a target exhaust gas back pressure, p ₄ is a target pressure after a turbine, R _{s is} the specific gas constant of the exhaust gas, T ₃ is an exhaust gas temperature before the turbine, c _d is a turbine flow factor and Ψ (·) is a flow function, where the target exhaust gas mass flow depends on a starting exhaust gas back pressure or on a previously iterated exhaust gas back pressure. The quadratic approximation can yield equation (3) above.

The target exhaust back pressure can correspond to the iterated exhaust back pressure after two or three iteration steps.

Further details of the method for determining a target exhaust back pressure were described in detail above with regard to the method for determining the target intake manifold pressure. These features apply analogously to the method for determining a target exhaust back pressure.

The invention further relates to a control device for an internal combustion engine, which has a processor that is designed to carry out a method for determining a target intake manifold pressure of an internal combustion engine by means of an iterative method, wherein a cylinder charge is determined for an intake manifold pressure iterated during the iterative method and the target intake manifold pressure is determined as a function of the determined cylinder charge. In particular, the processor is designed to carry out the method described above for determining a target intake manifold pressure.

The control device can be, for example, an engine controller. The control device can also have a data memory for storing characteristic maps, calculation rules, iteration rules, defined 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, which has a processor which is designed to carry out a method for determining a desired exhaust 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, in which:

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 shows a flow chart of an embodiment of a method for determining a target intake manifold pressure;

Fig.4

schematically shows a flow chart of a method for determining the cylinder filling;

Fig.5

schematically the basic principle of a secant method; and

Fig.6

schematically shows a flow chart of an iterative method for determining a target exhaust back pressure.

In Fig.1 an internal combustion engine is shown schematically. 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 an intake manifold 13, from which fresh air enters the combustion chamber 10 through the inlet valve 12. In addition, the cylinder 1 is coupled via an outlet valve 14 to an exhaust manifold 15, through which exhaust gas or residual gas from the combustion chamber 10 is guided into the exhaust manifold 15. Furthermore, there is a cylinder piston 16 which is driven by a crankshaft (not shown). In the intake manifold 13 directly in front of the inlet valve 12, an intake manifold pressure sensor 2 is arranged, which is designed to detect an intake manifold pressure. In the exhaust manifold 15 directly behind the outlet valve 14, an exhaust back pressure sensor 3 is arranged, which is designed to detect an exhaust back pressure. In the Fig.1 Cylinder 1 is shown at a time when the intake valve 12 and the exhaust valve 14 are open and valve overlap occurs.

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 characteristic maps, calculation rules, iteration rules, fixed parameters and the like. The processor 40 is designed to carry out a method for determining a target intake manifold pressure, as described below with reference to Fig. 3 to Fig. 6 described.

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

At 50, a first starting intake manifold pressure is determined. To do this, the intake manifold pressure sensor is used to measure an actual intake manifold pressure, which serves as the first starting intake manifold pressure.

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

For this purpose, as shown in the diagram in Fig.4 shown, a target turbocharger speed is determined at 60 depending on the first starting intake manifold pressure. Depending on the first starting intake manifold pressure and the determined target turbocharger speed, a target exhaust back pressure is determined at 61. The calculation of the target exhaust back pressure is described below with reference to Fig.6 described in detail. The cylinder charge is then determined at 62 depending on the first starting intake manifold pressure and the target exhaust back pressure.

At 52 in Fig.3 a second starting intake manifold pressure is determined depending on the cylinder charge for the first starting intake manifold pressure. To do this, the cylinder charge for the first starting 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, an upper limit p _S2,max or a lower limit p _S2,min is determined as the second starting intake manifold pressure from a map that defines a search range.

At 53, a cylinder charge for the second starting intake manifold pressure is determined. The cylinder charge for the second starting intake manifold pressure is determined in a similar way to the cylinder charge for the first starting intake manifold pressure.

At 54, a first intake manifold pressure iteration is determined using a secant method. For this purpose, as in Fig.5 shown, the cylinder charge r _ps1 for the first starting intake manifold pressure p _s1 and the cylinder charge r _ps2 for the second starting intake manifold pressure p _s2 are plotted against the intake manifold pressure p (x-axis) and a secant S1 is placed between the cylinder charges r _ps1 , r _ps2 . An intersection point of the secant S1 with the x-axis represents the first intake manifold pressure iterated p _I1 .

At 55, a cylinder charge is determined for the determined first intake manifold pressure iterate. The cylinder charge for the first intake manifold pressure iterate is determined analogously to the cylinder charge for the first starting intake manifold pressure.

At 56 it is determined whether the iteration can be aborted or not. This can be determined depending on the number of iterations already carried out or depending on the cylinder filling for the first intake manifold pressure iteration. For example, the filling for the first intake manifold pressure iteration can be compared with the filling for the second starting intake manifold pressure and depending on the comparison result it can be decided whether the iteration can be aborted or not.

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

If it is determined at 56 that the iteration cannot be aborted, steps 54 to 56 are repeated. In doing so, a second intake manifold pressure iteration is determined at 54 by, as in Fig.5 shown, a secant S2 is placed through the cylinder charge r _ps2 for the second starting intake manifold pressure and the cylinder charge r _pI1 for the first intake manifold pressure iterate and an intersection point with the x-axis is defined as the second intake manifold pressure iterate p _I2 . At 55 the cylinder charge for the second intake manifold pressure iterate is then determined and at 56 it is determined whether the iteration can be aborted or not. To do this, the charge for the second intake manifold pressure iterate can be compared with the charge for the first intake manifold pressure iterate and depending on the comparison result it can be decided whether the iteration can be aborted or not. If the iteration cannot be aborted, steps 54 to 56 are repeated analogously for further intake 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 is determined at each of the starting intake manifold pressures and the intake manifold pressure iterated according to the method 7 for determining a target exhaust back pressure.

At 70, a starting exhaust back pressure is determined. The starting exhaust back pressure is the intake manifold pressure that is used as a basis in the respective step of method 5 for determining the target intake manifold pressure. This means that in step 51 of method 5, the starting exhaust back pressure is the first starting intake manifold pressure, in step 53 the second starting intake manifold pressure and in step 55 the intake manifold pressure iterated in step 54.

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

At 72, a VTG control duty cycle or a setting of an actuator of a turbocharger with wastegate is then determined depending on the starting intake manifold pressure and the reduced mass flow.

At 73, an exhaust back pressure iteration is determined using 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 the number of iterations already performed. The maximum number of iterations here is 2.

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

If it is determined at 74 that the iteration cannot be aborted, steps 71 to 74 are repeated. In each case, a reduced exhaust gas mass flow, a VTG control duty cycle or a setting of an actuator of a turbocharger with wastegate and a further exhaust gas back pressure iterate are determined depending on the exhaust gas back pressure iterate.

In a second embodiment, the exhaust back pressure is calculated in each calculation step 51, 53, 54 of method 5 using equation (3) above and a reduced mass flow is determined using equation (4) above. The VTG control duty cycle or the setting of the actuator of the turbocharger with wastegate is then determined from this.

In a third embodiment, the target exhaust back pressure is determined in each calculation step 51, 53, 54 of the method 5 from a target pressure after a turbine and a power balance of the turbine and a compressor.

List of reference symbols

1

Cylinder of an internal combustion engine

10

Combustion chamber

11

Injector

12

Inlet valve

13

Intake manifold

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

Method for determining a target intake manifold pressure

50

Determining a first starting intake manifold pressure

51

Determining a cylinder charge for the first starting intake manifold pressure

52

Determining a second starting intake manifold pressure

53

Determining a cylinder charge for the second starting intake manifold pressure

54

Determining an intake manifold pressure iterate using a secant method

55

Determining a cylinder charge for the intake manifold pressure iterated

56

Determine whether the iteration can be aborted

57

Setting the last determined intake manifold pressure iterate as target intake manifold pressure

60

Calculating a turbocharger speed

61

Determining a target exhaust back pressure

62

Determining a cylinder filling

70

Setting a starting exhaust back pressure

71

Determining a reduced mass flow

72

Determining a VTG drive duty cycle

73

Determining an exhaust back pressure iterate

74

Determine whether the iteration can be aborted

75

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

ps1

first start intake manifold pressure

ps2

second starting intake manifold pressure

pI1

first intake manifold pressure iteration

pI2

second intake manifold pressure iterate

rps1

Cylinder filling for the first start-up intake manifold pressure

rps2

Cylinder filling for the second starting intake manifold pressure

rpI1

Cylinder filling for the first intake manifold pressure iteration

S1

secant

S2

secant

Claims (7)

1. Method for determining a desired intake manifold pressure of an internal combustion engine (1) by means of an iterative method, wherein the method is carried out by means of a control device for an internal combustion engine (1), which control device has a processor (40), wherein a cylinder filling (r_pI1) is determined (55) for an intake manifold pressure (p_I1) iterated during the iterative method, and the desired intake manifold pressure is determined (57) depending on the determined cylinder filling (r_pI1),

   characterized in that the iterative method is a secant method (54), wherein two starting points are defined and a secant is placed between these starting points, wherein an intersection of the secant having an axis which indicates a desired intake manifold pressure is defined as an iteration which represents an improved starting value for the subsequent iteration,

   wherein a cylinder filling (r_ps1) is determined for a first start intake manifold pressure (p_s1) and a second start intake manifold pressure (p_s2) is determined by comparing the cylinder filling (r_ps1) for the first start intake manifold pressure with a desired cylinder filling of the internal combustion engine (1), and the second start intake manifold pressure (p_s2) is determined depending on the comparison result between the cylinder filling (r_ps1) for the first start intake manifold pressure (p_s1) and the desired cylinder filling,

   wherein the cylinder filling (r_pI1) for the iterated intake manifold pressure (p_I1) is determined depending on a desired exhaust gas back pressure, wherein the desired exhaust gas back pressure is determined depending on the iterated intake manifold pressure (p_I1),

   wherein the last determined intake manifold pressure iteration is defined as desired intake manifold pressure.
2. Method according to claim 1, wherein the first start intake manifold pressure (p_s1) is an actual intake manifold pressure.
3. Method according to either of the preceding claims, wherein the desired exhaust gas back pressure is determined from a quadratic approximation of the equation $${\dot{m}}_{\mathit{Abg}}=A_{\mathit{eff}}{p}_3\sqrt{\frac{2}{R_s{T}_3}}\psi \left(c_d,\frac{p_4}{p_3}\right)$$

   

   wherein ṁ_Abg is a desired exhaust gas mass flow, A_eff is an effective opening area of a throttle, p₃ is a desired exhaust gas back pressure, p₄ is a desired pressure after a turbine, R_s is the specific gas constant of the exhaust gas, T₃ is an exhaust gas temperature before the turbine, c_d is a turbine flow factor and Ψ(·) is a flow function.
4. Method according to any of the preceding claims, wherein the desired exhaust back gas pressure is determined by means of an iterative method (70-75), and wherein a starting exhaust gas back pressure is the iterated intake manifold pressure (p_I1).
5. Method according to claim 4, wherein a reduced exhaust gas mass flow and a VTG drive duty cycle are determined depending on the start exhaust gas back pressure and the iterated exhaust gas back pressure is determined depending thereon.
6. Method according to claim 1, wherein the desired intake manifold pressure is determined from a desired pressure after a turbine and from a power balance of the turbine and a compressor.
7. Control device for an internal combustion engine (1), which control device has a processor (40) that is designed to carry out a method according to any of the preceding claims.

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