DE102005062681B4 - Method for determining an upper limit of the pressure of a gas upstream of a flow element, and a computer program and a control device - Google Patents

Abstract

Method for determining an upper limit value (p) of a pressure (p) of a gas upstream of a flow element (7, 8, 10, 11, 12, 13), characterized in that the limit value of the pressure upstream of the flow element (p) from state variables of the Gas (p, T) downstream of the flow element (7, 8, 10, 11, 12, 13) and a change in state (Δp, ΔT) of the gas caused by the flow element (7, 8, 10, 11, 12, 13) becomes.

Description

State of the art

The present invention relates to a method for determining an upper limit value of a pressure of a gas upstream of a flow element, and to a computer program and a control device for carrying out the method.

In the prior art, internal combustion engines with a two-stage supercharging are known, two compressors being connected in series in the intake tract of an internal combustion engine. If turbochargers are involved, two turbines are connected in series in the exhaust system. These work through the available enthalpy gradient one after the other. The two turbine stages are differentiated into high-pressure and low-pressure turbines; the high-pressure turbine is arranged in the flow direction of the exhaust gas upstream of the low-pressure turbine, and is therefore arranged directly at the engine outlet of the internal combustion engine. In principle, instead of two turbines, more than two turbines can be used. In general, controllable exhaust gas turbines are used, for example, from a parallel connection of an uncontrolled exhaust gas turbine with a controllable bypass valve or a turbine with an adjustable turbine geometry, for. B. with adjustable baffles, or a combination of both. In this way, the enthalpy of the exhaust gas converted into mechanical energy by each turbine can be controlled, ie it can be controlled how much work or power the turbine takes from the exhaust gas. Since the ambient pressure at the outlet of the exhaust system corresponds to the atmospheric ambient pressure, a change in the power consumption by the exhaust gas turbines results in a change in the exhaust gas pressure and the exhaust gas temperature at the inlet of the high-pressure turbine. This exhaust gas pressure corresponds to the exhaust gas pressure at the engine outlet, that is to say the pressure present immediately on or after the exhaust valves in the exhaust system, usually an exhaust manifold that brings together the exhaust gases of several cylinders. A change in the power consumption of the turbines, in particular the high-pressure turbine, from the exhaust gas thus results in a change in temperature and pressure at the engine outlet. The pressure at the engine outlet is first of all determined by the opening times of the gas exchange valves, i.e. the intake and exhaust valves, and the pressure conditions before, during and after combustion in the internal combustion engine and thus, for. B. controlled by ignition timing, injection quantity, injection process and injection timing. A maximum exhaust gas pressure at the engine outlet can be specified for an operating point of the internal combustion engine, at which a gas exchange rate desired or necessary for the operating point is achieved. The permissible exhaust gas pressure at the engine outlet depends, among other things, on whether a complete gas change in the cylinder is to be achieved or whether, for example, an internal exhaust gas recirculation is to be effected by not allowing complete gas exchange in the exhaust phase of the internal combustion engine. The permissible exhaust gas pressure at the engine outlet is thus predetermined by the internal combustion engine itself for any operating point. The workable enthalpy gradient and thus the power consumption of the exhaust gas turbines, in particular the high-pressure turbine, must therefore be selected so that the maximum exhaust gas pressure at the engine outlet is not exceeded. Furthermore, the power consumption must be set so that a maximum turbine output is not dynamically exceeded in order to limit the mechanical load (e.g. due to overspeed) of the turbocharger with regard to durability.

The DE 697 12 056 T2 discloses a control system for a variable geometry turbocharger which has a turbine driven by exhaust gas discharged from an engine exhaust manifold after an exhaust gas inlet of the turbocharger and which has a turbine driven compressor to draw air through an air outlet of the turbocharger after an engine intake manifold, comprising means for monitoring a parameter that is a function of the pressure within the engine exhaust manifold and closed loop control means for controlling the displacement of a variable geometry upstream turbine mechanism to the monitored parameter within predetermined limits to keep, characterized in that the monitored parameter is a function of the difference between the pressures within the engine exhaust manifold and the engine intake manifold.

Prior Art Problems

No method and no device is known in the prior art which provide a limitation of the exhaust gas pressure at the engine outlet for a multi-stage exhaust gas turbine. This applies in particular to dynamic operating states such as transient processes, i.e. load changes, operating point changes, operating range changes, etc., in which the states of the turbochargers can differ greatly from stationary operating states.

It is therefore an object of the present invention to provide a method and a device which enable an upper limit value of the exhaust gas pressure of an internal combustion engine to be determined upstream of a controllable exhaust gas turbine.

Advantages of the invention

This problem is solved by a method for determining an upper limit value of a pressure of a gas upstream of a flow element, the limit value of the pressure upstream of the flow element being determined from state variables of the gas downstream of the flow element and a change in state of the gas caused by the flow element. The change in state brought about by the flow element is in particular the thermodynamic change in state that can be observed between immediately upstream of the flow element and immediately downstream of the flow element. Upstream denotes the direction opposite to the flow direction of the gas, downstream denotes the direction in the flow direction of the gas.

It is preferably provided that the state variables of the exhaust gas downstream of the flow element are the pressure and the temperature of the gas; accordingly, the change in state is the change in pressure and temperature of the gas brought about by the flow element. These are preferably not measured, but from a state model of the flow element, in an exhaust system of an internal combustion engine, for example, the state model can also determine the entire exhaust system from the engine outlet to the outlet of the exhaust gases into the environment. The state model is a model as a controlled system, in which input variables such as, in particular, the pressure and temperature of the gas are linked to output variables, which in turn are, in particular, the temperature and pressure of the gas, with the state change that is carried out in between.

It is preferably provided that the pressure and the temperature of the gas downstream of the flow element are determined iteratively based on the dynamic changes in state. A loop is thus run through, in which, starting from an arbitrarily selected initial value for pressure and temperature, new values for pressure and temperature are repeatedly determined in a loop. The loop is preferably run through at predetermined time intervals, for example 20 milliseconds, so that a new limit value of the pressure of the gas upstream of the flow element is available with each loop run. Iteration here is not to be understood as a computing method in which a loop pass is terminated after an abort criterion has been reached, but rather a computing method that is carried out continuously without an abort criterion.

• -Bestimmen eines Startwertes für den Druck und eines Startwertes für die Temperatur des Gases stromab des Strömungselementes;
• -Ermitteln der Dichten des Gases stromauf und stromab des Strömungselementes aus dem Wert für Druck den und dem Wert für die Temperatur des Gases stromab des Strömungselementes;
• -Ermitteln des effektiven Strömungsquerschnittes des Strömungselementes aus dem Wert für Druck den und dem Wert für die Temperatur des Gases stromab des Strömungselementes;
• -Ermitteln eines neuen Wertes für den Druck stromab des Strömungselementes aus den Dichten des Gases stromauf und stromab des Strömungselementes sowie des effektiven Strömungsquerschnittes des Strömungselementes;
• -Ermitteln eines neuen Wertes für die Temperatur stromab des Strömungselementes aus dem Druck stromab sowie stromauf des Strömungselementes.

The iteration preferably comprises the steps

• Determining a starting value for the pressure and a starting value for the temperature of the gas downstream of the flow element;
• Determining the densities of the gas upstream and downstream of the flow element from the value for the pressure and the value for the temperature of the gas downstream of the flow element;
• Determining the effective flow cross section of the flow element from the value for the pressure and the value for the temperature of the gas downstream of the flow element;
• Determining a new value for the pressure downstream of the flow element from the densities of the gas upstream and downstream of the flow element and the effective flow cross section of the flow element;
• -Determining a new value for the temperature downstream of the flow element from the pressure downstream and upstream of the flow element.

It is preferably provided that the flow element comprises a controllable exhaust gas turbine. It is further preferably provided that the flow element comprises a controllable high-pressure turbine in an exhaust system of an internal combustion engine. It can further advantageously be provided that the flow element comprises a low-pressure turbine in an exhaust system of an internal combustion engine. It is preferably provided that the temperature of the gas upstream of the flow element is determined using a model of the internal combustion engine. In a preferred embodiment it is provided that the flow element is a controllable high-pressure turbine, in particular high-pressure turbine with high-pressure turbine bypass valve, which is arranged downstream of a controllable low-pressure turbine, in particular low-pressure turbine with a low-pressure turbine bypass valve, the limit value of the pressure upstream of the flow element being the limit value of the Pressure upstream of the controllable high-pressure turbine and the pressure downstream of the flow element is the pressure downstream of the controllable high-pressure turbine and the temperature downstream of the flow element is the temperature downstream of the controllable high-pressure turbine.

In this case, the gas is, in particular, an exhaust gas from the internal combustion engine. State changes are caused in particular by the controllable exhaust gas turbine (or by several controllable exhaust gas turbines in a multi-stage process). The change in state of the exhaust gas by the controllable exhaust gas turbine can be determined from the current turbine output, for example from the mechanical power output, such as, for. B. the shaft power of the turbine is determined. In the The state model of the exhaust system includes in particular an exhaust gas pressure at the engine outlet and / or an exhaust gas temperature at the engine outlet and / or an opening cross section of a bypass valve. The temperature of the exhaust gas at the engine outlet of the internal combustion engine is preferably determined from a model of the internal combustion engine. This model is known in the prior art and is preferably implemented in a control unit for the internal combustion engine. The engine outlet is understood to mean the exhaust system immediately after the exhaust valves of a four-stroke internal combustion engine or the exhaust port from the cylinder of a two-stroke internal combustion engine. The controllable exhaust gas turbine can be, for example, an exhaust gas turbine with a bypass valve connected in parallel, or an exhaust gas turbine with an adjustable turbine geometry, such as an adjustable guide vane, or a combination of both. The exhaust gas turbine can be a single turbine stage in the exhaust system of an internal combustion engine, but is preferably a high-pressure turbine of a two-stage exhaust-gas turbine system, to which a controllable high-pressure turbine bypass valve is connected in parallel. In this case, the high-pressure stage is followed by a low-pressure stage, which can likewise comprise a controllable exhaust gas turbine as a low-pressure exhaust gas turbine with a parallel low-pressure turbine bypass valve. The method according to the invention can then also be used in the low pressure stage. With the method according to the invention, it is possible to provide an upper limit value of the exhaust gas pressure at the engine outlet of the internal combustion engine for further use in a control circuit for controlling the controllable exhaust gas turbine.

The problem mentioned at the outset is also solved by a computer program for determining an upper limit of the pressure of a gas upstream of a flow element, the limit value of the pressure upstream of the flow element being determined from state variables of the gas downstream of the flow element and a change in the state of the gas caused by the flow element, in particular by means of a computer program for carrying out a method for determining an upper limit value of the exhaust gas pressure at the engine outlet of an internal combustion engine with a controllable exhaust gas turbine, the exhaust gas pressure at the engine outlet being determined from state variables of the exhaust gas behind the exhaust gas turbine and the change in state of the exhaust gas by the controllable exhaust gas turbine.

The problem mentioned at the outset is also solved by a control device for determining an upper limit value of the pressure of a gas upstream of a flow element, the limit value of the pressure upstream of the flow element being determined from state variables of the gas downstream of the flow element and a change in state of the gas caused by the flow element, in particular by a control unit for an internal combustion engine with a controllable exhaust gas turbine, in particular an exhaust gas turbine with a controllable bypass valve, the control unit comprising means for determining an upper limit value of the exhaust gas pressure at the engine outlet, the exhaust gas pressure at the engine outlet from state variables of the exhaust gas behind the exhaust gas turbine and the change in state of the engine Exhaust gas is determined by the controllable exhaust gas turbine.

Figure list

• 1 eine Skizze einer Brennkraftmaschine mit zweistufiger Aufladung;
• 2 eine Skizze der Hochdruckturbinenstufe in 1;
• 3 ein Ablaufdiagramm des Verfahrens;
• 4 eine Skizze eines Ausführungsbeispiels eines Regelkreises.

An exemplary embodiment of the present invention is explained in more detail below with reference to the accompanying drawing. Show:

• 1 a sketch of an internal combustion engine with two-stage supercharging;
• 2nd a sketch of the high pressure turbine stage in 1 ;
• 3rd a flow chart of the method;
• 4th a sketch of an embodiment of a control loop.

1 shows a sketch of an internal combustion engine with two-stage supercharging, the two-stage supercharging comprising two turbochargers. Upstream denotes the direction opposite to the direction of flow of the gas, downstream indicates the direction in the direction of flow of the gas. The multi-cylinder internal combustion engine 5 is at the engine outlet, that is at cylinder outlets, thus downstream, for example from exhaust valves of a four-stroke internal combustion engine, with an exhaust system 6 connected which is an exhaust gas turbine 7 and a controllable high-pressure turbine bypass valve connected in parallel 8th in the form of a controllable exhaust flap. The entrances to both are via an exhaust manifold 9 with the engine outlet of the internal combustion engine 5 connected. The high pressure turbine 7 and the high-pressure turbine bypass valve 8th form a high pressure stage 10th to which a low pressure stage 11 connects, which in turn is a parallel connection of a low pressure turbine 12th and a low pressure turbine bypass valve 13 includes. At the output of the low pressure stage 11 closes an exhaust system, not shown 14 which, for example, can also include a soot filter or the like. The area between the outlet of the high pressure turbine stage 10th and the entrance of the low pressure turbine stage 11 is used here as an intermediate stage 21 designated. The high pressure turbine 7 is used to drive a high pressure compressor 15 with a controllable or automatic high pressure compressor bypass valve 16 can be bridged. The low-pressure turbine serves accordingly 12th the Drive a low pressure compressor 17th . Between low pressure compressors 17th and high pressure compressors 15 is a first intercooler 18th arranged between the high pressure compressor 15 and the inlet into the cylinders 19th is a second intercooler 20 arranged. The upstream of the low pressure compressor 17th arranged elements, such as an air filter, an air mass meter and the like, are not shown here. The thermodynamic states of the gas, this is the intake air or the exhaust gas, are in 1 with the numbers shown in a circle 1 to 4th designated. Reference numerals 1 denotes the thermodynamic state of the intake air before it enters the low pressure compressor 17th . Reference numerals 2nd denotes the thermodynamic state of the intake air after exiting the second charge air cooler 20 and before entering the internal combustion engine 5 . Reference numerals 3rd denotes the thermodynamic state of the from the internal combustion engine 5 ejected gas (hereinafter also referred to as exhaust gas for easier distinction) before entering the high-pressure turbine stage 10th . It is assumed as an approximation that the state of the internal combustion engine 5 exhaust gas immediately downstream of the exhaust valves and the condition of the exhaust gas immediately upstream of the high pressure turbine stage 10th is about the same. This is permissible if the change in state between them is negligible, the heat transfer to the exhaust manifold 9 and the pressure drop in the exhaust manifold 9 are negligible. If this is not negligible, the change in state from downstream of the exhaust valves to upstream of the high-pressure turbine stage must be taken into account, for example, by modeling the transmission path or, for example, by constant values for pressure and temperature difference between these points. The reference number 3 ' denotes the thermodynamic state of the exhaust gas in the intermediate stage 21 after leaving the high pressure turbine stage 10th or before entering the low-pressure turbine stage 11 . Reference numerals 4th denotes the thermodynamic state of the exhaust gas after leaving the low-pressure stage 11 . Thus p _{3 is} the pressure and T _{3 is} the temperature of the exhaust gas at the engine outlet or upstream of the high-pressure turbine stage 10th , p ₃ 'the pressure and T ₃ ' the temperature of the exhaust gas in the intermediate stage 21 or downstream of the high pressure turbine stage 10th . The high pressure turbine stage 10th and the low pressure turbine stage 11 as flow elements each cause a thermodynamic change in state of the gas (exhaust gas) when it flows from upstream of the respective flow elements through it to downstream of the flow element.

The two turbochargers, comprising the high pressure turbine 7 and the high pressure compressor 15 or the low pressure turbine 12th and the low pressure compressor 17th , are connected in series in order to obtain a two-stage expansion via the two turbines and a two-stage compression via the two compressors. The disadvantages of unregulated two-stage turbocharging processes are the high-pressure turbine bypass valve 8th and high pressure compressor bypass valve 16 avoided as regulators for bypassing the high pressure turbine and the high pressure compressor.

schreiben: $$\mathrm{\Delta }p={\xi }_k\frac{\rho }{2}{v}^2$$

To obtain a simplified representation of the exhaust gas pressure, only the exhaust system is considered. For a state model as a flow element, the assumption is made that the turbines and the bypass valves behave like throttling points, with the turbines receiving constant pressure loss coefficients and the bypass valves having a variable pressure loss coefficient (manipulated variable). The pressure loss across such a throttling point can be calculated using the coefficient

write: $$\mathrm{\Delta }p={\xi }_k\frac{\rho }{\mathrm{2nd}}{v}^{\mathrm{2nd}}$$

For a given cross section (area A), the mass flow follows: $$\dot{m}=A\sqrt{\frac{\mathrm{2nd}\rho \mathrm{\Delta }p}{{\xi }_k}}$$

The effective flow cross section is defined as follows $$A_{eff}=\frac{A}{\sqrt{\xi }}$$

bestimmt. Demnach sind Massenstrom, Eintrittstemperatur und Druckverhältnis die entscheidenden Größen, um die Turbinenleistung zu beeinflussen. Da das Hochdruckturbinen-Bypassventil 8 unmittelbar auf den Abgasdruck p₃ wirkt, wird die Gleichung für die Turbinenleistung umgestellt: $$p_3=p_{3\text{'}}{\left[1-\frac{P_{T,HD}}{{\eta }_{is}{\dot{m}}_{HD}{c}_p{T}_3}\right]}^{\frac{\kappa }{1-\kappa }}$$

This means that the corresponding constant effective flow cross-sections are determined for all components with fixed values (turbines) and the associated characteristic curves for all components with variable values. These are determined by measurements. With known turbine maps, a determination without measurement is possible. The turbine performance of the high pressure turbine 7 becomes from the equation $$P_{T,HD}={\eta }_{is}{\dot{m}}_{HD}{c}_p{T}_{\mathrm{3rd}}\left[1-{\left(\frac{p_{\mathrm{3rd}\text{'}}}{p_{\mathrm{3rd}}}\right)}^{\frac{\kappa -1}{\kappa }}\right]$$

certainly. Accordingly, mass flow, inlet temperature and pressure ratio are the decisive factors in influencing the turbine performance. Because the high pressure turbine bypass valve 8th directly affects the exhaust gas pressure p ₃ , the equation for the turbine power is changed: $$p_{\mathrm{3rd}}=p_{\mathrm{3rd}\text{'}}{\left[1-\frac{P_{T,HD}}{{\eta }_{is}{\dot{m}}_{HD}{c}_p{T}_{\mathrm{3rd}}}\right]}^{\frac{\kappa }{1-\kappa }}$$

An upper limit value of the exhaust gas pressure ep _{3, max} , which depends on the maximum permissible turbine output, can thus be established for both regulation and control of the pressure p ₃ . The maximum permissible turbine power P _{HD, max} (the index HD stands for the high-pressure turbine, max for the maximum power) can be specified, for example, in a map depending on the engine operating point (given, for example, by injection quantity and engine speed) or by any function. The turbine produces a change in the enthalpy of the exhaust gas and causes a change in the state of the exhaust gas, in particular the pressure of the exhaust gas via the exhaust gas turbine changing by a value Δp and the temperature of the exhaust gas changing by a value ΔT. This change in state of the exhaust gas is essentially converted into mechanical work of the exhaust gas turbine. The change in state of pressure and temperature Δp, ΔT of the exhaust gas is thus directly linked to the turbine output. This enables maximum use of the dynamic potential in transient processes. The maximum pressure at the inlet of the turbine depends on the pressure at its outlet and the maximum power of the turbine. For the high pressure turbine 7 applies $${\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="DE102005062681B4\_0044.png,DE102005062681B4\_0045.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{3,}max}=p_{\mathrm{3rd}\text{'}}{\left[1-\frac{P_{T,HD,max}}{{\eta }_{is}{\dot{m}}_{HD}{c}_p{T}_{\mathrm{3rd}}}\right]}^{\frac{\kappa }{1-\kappa }}$$

The maximum power P _{T, HD, max of} the high-pressure turbine depends on the temperature of the exhaust gas and is stored, for example, in a map. The temperature T ₃ at the engine outlet can be determined using a model of the internal combustion engine known in the prior art. The mass flow ṁ _HD through the high pressure turbine and the condition 3 ' in the intermediate stage are modeled as previously described.

2nd shows a sketch of the high pressure stage 10th . The exhaust gas has the state at its entrance 3rd , the state at the exit 3 ' . The state of the exhaust gas at the outlet of the high pressure turbine 7 is marked here with 3 "(two lines). The mixed state 3 ' is determined by pressure and temperature. About the high pressure turbine 7 polytropic expansion takes place on the high-pressure turbine bypass valve 8th an isenthalpic throttle point is assumed. This follows for the high pressure turbine 7 alone a relaxation on the state 3 " : $$\frac{T_{\mathrm{3rd}}}{T_{\mathrm{3rd}\text{'}\text{'}}}={\left(\frac{p_{\mathrm{3rd}}}{p_{\mathrm{3rd}\text{'}}}\right)}^{\frac{n_{HD-1}}{n_{HD}}}$$

The polytropic exponent n _HD must be known for the respective work area. A sufficient approximation for the entire operating range of the turbine can be assumed to be constant and is determined in an experiment or from the turbine map. The temperature of an ideal gas does not change via the isenthalpic restriction. Through the parallel connection of the high pressure turbine 7 with the high pressure turbine bypass valve 8th there is a mixed temperature for the condition 3 ' : $$T_{\mathrm{3rd}\text{'}}=T_{\mathrm{3rd}}\frac{{\dot{m}}_{HD}{\left(\frac{p_{\mathrm{3rd}\text{'}}}{p_{\mathrm{3rd}}}\right)}^{\frac{n-1}{n}}+{\dot{m}}_{ARK}}{{\dot{m}}_{HD}+{\dot{m}}_{ARK}}$$

$$T_{3\text{'}}=T_3\frac{A_{eff,HD}{\left(\frac{p_{3\text{'}}}{p_3}\right)}^{\frac{n-1}{n}}+A_{eff,ARK}}{A_{eff,HD}+A_{eff,ARK}}$$

The ratio of the mass flows follows from the effective flow cross-sections: $$\frac{{\dot{m}}_{HD}}{{\dot{m}}_{HD}+{\dot{m}}_{ARK}}=\frac{A_{eff,HD}}{A_{eff,HD}+A_{eff,ARK}}$$

$$T_{\mathrm{3rd}\text{'}}=T_{\mathrm{3rd}}\frac{A_{eff,HD}{\left(\frac{p_{\mathrm{3rd}\text{'}}}{p_{\mathrm{3rd}}}\right)}^{\frac{n-1}{n}}+A_{eff,ARK}}{A_{eff,HD}+A_{eff,ARK}}$$

bestimmt, dies ist vorzugsweise für $p_{3\text{'}}^0=p_4$

und für $T_{3\text{'}}^0=T_3.$

p₃, p₄ und T₃ liegen entweder als gemessene oder als modellierte Werte der Motorsteuerung vor.A denotes the cross-sectional area of the passage openings, the index ARK refers to the cross-sectional area of the opening of the high-pressure turbine bypass valve 8th (also referred to as an exhaust gas control valve), the index WG refers to the cross-sectional area of the opening of the low-pressure turbine bypass valve 13 (also known as a waste gate). The relationships shown above can be evaluated iteratively. The associated procedure is in 3rd shown. A _{eff, HD,} A _{eff, ND} , A _{eff, ARK} , A _{eff, WG} , P ₄ , T ₃ , n _{HD are known;} determine p _3max . This will be done in a first step 101 the starting values for $p_{\mathrm{3rd}\text{'}}^0,T_{\mathrm{3rd}\text{'}}^0$

determined, this is preferably for $p_{\mathrm{3rd}\text{'}}^0=p_{\mathrm{4th}}$

and for $T_{\mathrm{3rd}\text{'}}^0=T_{\mathrm{3rd}}.$

p ₃ , p ₄ and T ₃ are available either as measured or as modeled values of the engine control.

sowie die Dichte des Abgases am Motoraustritt ${\rho }_3^v$

ermittelt $${\rho }_{3\text{'}}^v=\frac{p_{3\text{'}}^v}{R{T}_{3\text{'}}^v}$$

$${\rho }_3^v=\frac{p_3}{R{T}_3}$$

In step 102 becomes the density of the exhaust gas in the intermediate stage 21 ${\rho }_{\mathrm{3rd}\text{'}}^v$

and the density of the exhaust gas at the engine outlet ${\rho }_{\mathrm{3rd}}^v$

determined $${\rho }_{\mathrm{3rd}\text{'}}^v=\frac{p_{\mathrm{3rd}\text{'}}^v}{R{T}_{\mathrm{3rd}\text{'}}^v}$$

$${\rho }_{\mathrm{3rd}}^v=\frac{p_{\mathrm{3rd}}}{R{T}_{\mathrm{3rd}}}$$

$$A_{eff,ND+WG}=A_{eff,ND}+A_{eff,WG}$$

Thereupon step 103 the effective flow cross-sections of high-pressure turbines 7 and high pressure turbine bypass valve 8th and low pressure turbine 12th and low pressure turbine bypass valve 13 determined $$A_{eff,HD+ARK}=A_{eff,HD}+A_{eff,ARK}$$

$$A_{eff,ND+WG}=A_{eff,ND}+A_{eff,WG}$$

bestimmt und in Schritt 105 die Temperatur in der Zwischenstufe $$T_{3\text{'}}^{v+1}=T_3\frac{A_{eff,HD}{\left(\frac{p_{3\text{'}}^{v+1}}{p_3}\right)}^{\frac{n-1}{n}}+A_{eff,ARK}}{A_{eff,HD}+A_{eff,ARK}}$$

bestimmt. Aus diesen Werten wird in Schritt 106 der obere Grenzwert des Abgasdruckes stromauf der Hochdruckstufe 10 p_3,max mit $p_{\mathrm{3,}max}=p_{3\text{'}}{\left[1-\frac{P_{T,HD,max}}{{\eta }_{is}{\dot{m}}_{HD}{c}_p{T}_3}\right]}^{\frac{\kappa }{1-\kappa }}$

ermittelt. Dieser Wert soll einen stationär ermittelten Maximalwert, der beispielsweise in einem Kennfeld in Abhängigkeit des Betriebspunktes abgelegt ist, nicht unterschreiten.This becomes step 104 the pressure in the intermediate stage $$p_{\mathrm{3rd}\text{'}}^{v+1}=p_{\mathrm{3rd}}\frac{{\rho }_{\mathrm{3rd}}{A}_{eff,HD+ARK}^{\mathrm{2nd}}+{\rho }_{\mathrm{3rd}\text{'}}^v\frac{p_{\mathrm{4th}}}{p_{\mathrm{3rd}}}{A}_{eff,ND+WG}^{\mathrm{2nd}}}{{\rho }_{\mathrm{3rd}}{A}_{eff,HD+ARK}^{\mathrm{2nd}}+{\rho }_{\mathrm{3rd}\text{'}}^v{A}_{eff,ND+WG}^{\mathrm{2nd}}}$$

determined and in step 105 the temperature in the intermediate stage $$T_{\mathrm{3rd}\text{'}}^{v+1}=T_{\mathrm{3rd}}\frac{A_{eff,HD}{\left(\frac{p_{\mathrm{3rd}\text{'}}^{v+1}}{p_{\mathrm{3rd}}}\right)}^{\frac{n-1}{n}}+A_{eff,ARK}}{A_{eff,HD}+A_{eff,ARK}}$$

certainly. These values are used in step 106 the upper limit of the exhaust gas pressure upstream of the high pressure stage 10th p _{3, max} with ${\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="DE102005062681B4\_0044.png,DE102005062681B4\_0045.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{3,}max}=p_{\mathrm{3rd}\text{'}}{\left[1-\frac{P_{T,HD,max}}{{\eta }_{is}{\dot{m}}_{HD}{c}_p{T}_{\mathrm{3rd}}}\right]}^{\frac{\kappa }{1-\kappa }}$

determined. This value should not fall below a stationary maximum value that is stored, for example, in a map as a function of the operating point.

und der in Schritt 105 ermittelten Temperatur $T_{3\text{'}}^{v+1}=T_3$

wird das Verfahren als Iteration ab Schritt 102 wiederholt indem die Werte mit Index v + 1 in Schritt 105 als neue Ausgangswerte der Iteration mit Index v in Schritt 102 verwendet werden. Die Iteration ist eine Endlosschleife ohne Abbruchkriterium, wird also erst z.B. mit Motorstillstand beendet. Die Iteration wird also nicht punktuell z.B. für einen bestimmten Zeitpunkt bis zur Konvergenz auf einen Wert durchlaufen, sondern läuft ständig in Echtzeit ab, wobei jeder ermittelte Wert für p_3,max einem oder mehreren Reglern zur Verfügung gestellt wird. Auf diese Weise können zu jedem Zeitpunkt der Druck p₃ und die Temperatur T₃ in der Zwischenstufe 21 sowie der daraus folgende Druck p₃ am Motoraustritt bestimmt werden. Gleichzeitig folgt mit dem Massenstrom über die Hochdruckturbine 7 $${\dot{m}}_{HD}={\dot{m}}_{Abgass}\frac{A_{eff,HD}}{A_{eff,HD}+A_{eff,ARK}}$$

die aktuelle Leistung, die der Hochdruckturbine 7 angeboten wird.The index v designates the respective run of the iteration, the index v + 1 corresponds to the following run. With that in step 104 determined pressure $p_{\mathrm{3rd}\text{'}}^{v+1}=p_{\mathrm{3rd}}$

and the step 105 determined temperature $T_{\mathrm{3rd}\text{'}}^{v+1}=T_{\mathrm{3rd}}$

the process is iterated from step 102 repeated by the values with index v + 1 in step 105 as new starting values of the iteration with index v in step 102 be used. The iteration is an endless loop without termination criteria, so it is only ended, for example, when the engine is stopped. The iteration is therefore not carried out selectively, for example for a specific point in time until convergence to a value, but runs continuously in real time, with each determined value for p _{3, max being} made available to one or more controllers. In this way, the pressure p ₃ and the temperature T ₃ in the intermediate stage can at any time 21 as well as the resulting pressure p ₃ at the engine outlet. At the same time follows with the mass flow via the high pressure turbine 7 $${\dot{m}}_{HD}={\dot{m}}_{AbGass}\frac{A_{eff,HD}}{A_{eff,HD}+A_{eff,ARK}}$$

the current output of the high pressure turbine 7 is offered.

The limitation of the maximum permissible exhaust gas pressure p _3max can, for example, in the case of a _lower-level control circuit for boost pressure control, as in 4th shown, used. All process steps that were carried out for the high pressure stage can also be carried out for the low pressure stage and any further stage. In the case of two-stage supercharging, this means that the performance of the low-pressure turbine can also be limited and thus a maximum permissible pressure in the intermediate stage 3 ' is set. This enables targeted control of the low-pressure compressor bypass valve 14 in order to avoid overloading the low pressure stage and to use the full dynamic potential here as well. The method can also be used for a one-stage system, the iteration steps no longer being necessary for this.

In 4th An embodiment of a controller is shown. The example shows a classic control circuit with a regulator R for the pressure p ₃ at the engine outlet. The controller R supplies manipulated variables for one or more actuators, in the present case a manipulated variable H for the high-pressure turbine bypass valve 8th and a manipulated variable N of the low-pressure turbine bypass valve 13 . With these manipulated variables, the controlled system RS, which includes the high pressure stage 10th and the low pressure stage 11 , controlled. The controlled variable is the pressure p ₃ at the engine _outlet , which is returned to the controller R subtracted from a limited _target variable p _3set-m . The setpoint p _3soll-m is formed by a limiter max, to which a setpoint p _3soll for the exhaust gas pressure p ₃ and as a limitation of the maximum permissible exhaust gas pressure p _3max are applied. The setpoint p _3soll for the exhaust gas pressure p ₃ is limited by the limiter max to the maximum permissible exhaust gas pressure p _3max , even if the setpoint p _3soll for the exhaust gas pressure p _{3 is} greater than p _3max , this is only due to the limited setpoint p _3soll-m the maximum permissible exhaust gas pressure p _3max .

Claims (13)

Method for determining an upper limit value (p _3max ) of a pressure (p ₃ ) of a gas upstream of a flow _element (7, 8, 10, 11, 12, 13), characterized in that the limit value of the pressure upstream of the flow element (p _{3, max} ) from state variables of the gas (p, T) downstream of the flow element (7, 8, 10, 11, 12, 13) and a change in state caused by the flow element (7, 8, 10, 11, 12, 13) (Δp, ΔT) of the gas is determined. Procedure according to Claim 1 , characterized in that the state variables of the gas downstream of the flow element (7, 8, 10, 11, 12, 13) are the pressure (p ₃ ') and the temperature (T ₃ ') of the gas. Procedure according to Claim 2 , characterized in that the pressure (p ₃ ') and the temperature (T ₃ ') downstream of the flow element (7, 8, 10, 11, 12, 13) from a state model of the flow element (7, 8, 10, 11, 12, 13) can be determined. Procedure according to Claim 3 , characterized in that in the state model a pressure (p ₃ ) upstream of the flow element (7, 8, 10, 11, 12, 13) and / or a temperature (T ₃ ) upstream of the flow element (7, 8, 10, 11 , 12, 13) and / or an opening cross-section (A) assigned to the flow element (7, 8, 10, 11, 12, 13) and / or a gas cross-section assigned to the flow element (7, 10, 11, 12) Power (P _{T, max} ). Procedure according to Claim 4 , characterized in that the pressure (p ₃ ') and the temperature (T ₃ ') of the gas downstream of the flow element (7, 8, 10, 11, 12, 13) are determined iteratively. Procedure according to Claim 5 , characterized in that the iteration steps 6.0 determining a starting value $\left(p_{\mathrm{3rd}\text{'}}^0\right)$

for printing $\left(p_{\mathrm{3rd}\text{'}}^v\right)$

and a starting value $\left(T_{\mathrm{3rd}\text{'}}^0\right)$

for the temperature $\left(T_{\mathrm{3rd}\text{'}}^v\right)$

of the gas downstream of the flow element (7, 8, 10, 11, 12, 13) 6.1 Determining the densities ${\rho }_{\mathrm{3rd}\text{'}}^v$

of the gas upstream $\left({\rho }_{\mathrm{3rd}}^v\right)$

and downstream $\left({\rho }_{\mathrm{3rd}\text{'}}^v\right)$

of the flow element (7, 8, 10, 11, 12, 13) from the value for the pressure $\left(p_{\mathrm{3rd}\text{'}}^v\right)$

and the value for the temperature $\left(T_{\mathrm{3rd}\text{'}}^v\right)$

of the gas downstream of the flow element (7, 8, 10, 11, 12, 13) 6.2 Determine the effective flow cross-section (A _{eff, HD + ARK} , A _{eff, ND + WG} ) of the flow element (7, 8, 10, 11, 12 , 13) from the value for pressure $\left(p_{\mathrm{3rd}\text{'}}^v\right)$

and the value for the temperature $\left(T_{\mathrm{3rd}\text{'}}^v\right)$

of the gas downstream of the flow element (7, 8, 10, 11, 12, 13) 6.3 Determining a new value for the pressure $\left(p_{\mathrm{3rd}\text{'}}^{v+1}\right)$

downstream of the flow element (7, 8, 10, 11, 12, 13) from the densities ${\rho }_{\mathrm{3rd}\text{'}}^v$

of the gas upstream $\left({\rho }_{\mathrm{3rd}}^v\right)$

and downstream $\left({\rho }_{\mathrm{3rd}\text{'}}^v\right)$

the flow element (7, 8, 10, 11, 12, 13) and the effective flow cross-section (A _eff , _{HD + ARK} , A _{eff, ND + WG} ) of the flow element (7, 8, 10, 11, 12, 13) 6.4 Determine a new value for the temperature $\left(T_{\mathrm{3rd}\text{'}}^{v+1}\right)$

downstream of the flow element (7, 8, 10, 11, 12, 13) from the pressure downstream $\left(p_{\mathrm{3rd}\text{'}}^{v+1}\right)$

and upstream (p ₃ ) of the flow element (7, 8, 10, 11, 12, 13). Method according to one of the preceding claims, characterized in that the flow element comprises a controllable exhaust gas turbine (7, 8, 10, 11, 12, 13). Procedure according to Claim 7 , characterized in that the flow element comprises a controllable high-pressure turbine (7, 8, 10, 11, 12, 13) in an exhaust system (6) of an internal combustion engine. Procedure according to Claim 7 or 8th , characterized in that the flow element comprises a low-pressure turbine (12) in an exhaust system (6) of an internal combustion engine. Procedure according to one of the Claims 7 to 9 , characterized in that the temperature of the gas upstream of the flow element (T ₃ ) is determined using a model of the internal combustion engine. Method according to one of the preceding claims, characterized in that the flow element is a controllable high-pressure turbine (7), in particular high-pressure turbine (7) with high-pressure turbine bypass valve (8), which is a controllable low-pressure turbine (12), in particular low-pressure turbine (12) with a downstream Low-pressure turbine bypass valve (13), is arranged downstream, the limit value of the pressure (p _{3, max} ) upstream of the flow element, the limit value of the pressure upstream of the controllable high-pressure turbine (7) and the pressure downstream of the flow element (p ₃ ,) the pressure downstream of the controllable high pressure turbine (7) and the temperature downstream of the flow element (T _{3 '} ) is the temperature downstream of the controllable high-pressure turbine (7). Computer program for determining an upper limit value (p _3max ) of the pressure (p ₃ ) of a gas upstream of a flow _element (7, 8, 10, 11, 12, 13), characterized in that the limit value of the pressure upstream of the flow element (p _{3, max} ) from the state variables of the gas (p, T) downstream of the flow element (7, 8, 10, 11, 12, 13) and a change in state (Δp, ΔT) of the gas caused by the flow element. Control _device for determining an upper limit value (p _3max ) of the pressure (p ₃ ) of a gas upstream of a flow _element (7, 8, 10, 11, 12, 13), characterized in that the limit value of the pressure upstream of the flow element (p _{3, max} ) from the state variables of the gas (p, T) downstream of the flow element (7, 8, 10, 11, 12, 13) and a change in state (Δp, ΔT) of the gas caused by the flow element.

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