DE102023000107A1 - Method for calculating the efficiency of an internal combustion engine, in particular a motor vehicle - Google Patents

Abstract

The invention relates to a method for calculating the delivery rate (10) of an internal combustion engine designed as a reciprocating piston engine, in which a base delivery rate (16) is calculated as a function of at least one map value stored in a map for a reference state. At least one pressure correction value is determined as a function of a deviation of an actual pressure ratio from a reference pressure ratio assigned to the reference state. At least one dynamic correction value is determined as a function of a deviation of at least one actual wall heat flow from a stationary wall heat flow assigned to a steady state. The degree of delivery (10) is calculated as a function of the basic degree of delivery (16), the pressure correction value and the dynamic correction value.

Description

The invention relates to a method for calculating the volumetric efficiency, i.e. the ratio of the mass actually contained in the cylinder after completion of the gas exchange to the theoretically maximum possible mass of an internal combustion engine, in particular a motor vehicle.

The DE 10 2015 207 252 A1 a method for the model-based optimization of a technical device can be seen as known. In the method, at least one first parameter relating to the technical device to be optimized is recorded, with the parameter characterizing a physical quantity.

The object of the present invention is to provide a method by means of which the efficiency of an internal combustion engine designed as a reciprocating piston engine can be calculated in a particularly advantageous manner.

This object is achieved by a method having the features of patent claim 1. Advantageous configurations with expedient developments of the invention are specified in the remaining claims.

The invention relates to a method for calculating the efficiency of an internal combustion engine designed as a reciprocating piston engine and also referred to as an internal combustion engine or internal combustion engine, in particular a motor vehicle. For example, the method is carried out using an electronic computing device, in particular the motor vehicle. It is also conceivable for the method to be carried out during fired or unfired operation of the internal combustion engine and/or for the delivery rate to be calculated in real time during ongoing vehicle operation in the production control unit. In the method, a base delivery level is calculated as a function of at least one map value that is stored in a map for a reference state. For example, the map is stored in a particular electrical or electronic memory device such as a data memory of the electronic computing device, so that in particular the map value is stored in the memory device. In the method, at least one pressure correction value is determined, in particular calculated, as a function of a deviation of an actual pressure ratio from a reference pressure ratio assigned to the reference state. In addition, in the method, at least one dynamic correction value is determined, in particular calculated, as a function of a deviation of at least one actual wall heat flow from a stationary wall heat flow assigned to a steady state. For example, the steady state is the reference state. Alternatively or additionally, it is conceivable that the stationary state is a particularly empirically determined state and/or a state that relates to steady-state operation of the internal combustion engine, which steady-state operation was carried out on a test bench, for example, in particular as part of a development of the internal combustion engine. In other words, the stationary wall heat flow is, for example, a heat flow that was determined for the steady state and/or occurs or has occurred in the steady state and was thus determined by the steady state. In other words, the steady-state wall heat flow is preferably a heat flow that occurs or occurred in a steady state, i.e. in steady-state operation of the internal combustion engine, especially when the internal combustion engine is or was operated in steady-state operation. It is particularly conceivable that the steady-state wall heat flow is or was determined empirically, in particular on the test bench mentioned, on which the internal combustion engine is or was operated in steady-state operation. It is conceivable that the stationary wall heat flow or a heat flow value characterizing the stationary wall heat flow is stored in a characteristic map stored in particular in the memory device. It is also conceivable that the steady-state wall heat flow is calculated from boundary conditions that apply to steady-state operation and are stored in the storage device. It is also conceivable that the reference pressure ratio is stored in the characteristic map or the additional characteristic map or the third characteristic map, which is stored in the memory device, for example.

In the method, the degree of delivery is calculated as a function of the basic degree of delivery, the pressure correction value and the dynamic correction value.

• - Die Liefergradbeeinflussung durch den realen Wandwärmestrom, welcher sich nach Betriebspunktänderung aufgrund der thermischen Trägheit der Zylinderwände vom stationären Zustand unterscheidet.
• - Die Liefergradbeeinflussung durch das Druckverhältnis insbesondere p3 zu p2, welches sowohl stationär, zum Beispiel in der Höhe, als auch dynamisch vom Referenzzustand abweichen kann und durch den Einfluss auf die Restgasmasse ebenfalls den Liefergrad beeinflusst.

The calculation of the degree of delivery, also referred to as the overall degree of delivery, is also referred to as modeling of the degree of delivery or modeling of the degree of delivery, since, for example, the degree of delivery is calculated using at least one calculation model and is therefore modeled. The invention are in particular the fol Based on the following findings and considerations: The modeled engine mass flow is usually a central variable in engine control for internal combustion engines designed as diesel engines, for example. Among other things, the volumetric efficiency of the internal combustion engine, also referred to simply as an engine, is required for the calculation, with the volumetric efficiency representing the ratio of the actual to the theoretical mass flow flowing into the engine. So far, the modeling of delivery efficiency has been carried out empirically in the form of map structures, designed for and/or determined for stationary states. Dynamic influences on the degree of delivery, for example due to changing heat flows after a change in the operating point, have not yet been mapped. The modeling of the degree of delivery under transient conditions is now improved by the invention, as a result of which greater accuracy, in particular of EGR rates, can be achieved. In this way, particularly low-emission operation can be guaranteed. In particular, the invention provides a supplement to a previous, customary, empirical delivery efficiency structure through physical corrections, which take into account the following effects in particular:

• - The influence of the volumetric efficiency by the real wall heat flow, which differs from the stationary state after the operating point change due to the thermal inertia of the cylinder walls.
• - The influence on the degree of delivery by the pressure ratio, in particular p3 to p2, which can deviate from the reference state both stationary, for example in height, and dynamically and also influences the degree of delivery by influencing the residual gas mass.

In comparison to conventional solutions, the invention enables a higher accuracy of the EGR rate, particularly during dynamic engine operation, which can result in emission benefits and increased accuracy of adaptation and diagnostic functions.

In particular, the actual pressure ratio or the reference pressure ratio is a ratio of a first pressure to a second pressure, the first pressure preferably being the so-called p3 pressure and the second pressure being the so-called p2 pressure acts. The p3 pressure is also referred to simply as p3 and is a pressure prevailing in an exhaust tract of the internal combustion engine downstream of combustion chambers of the internal combustion engine, which pressure prevails, for example, upstream of a turbine of an exhaust gas turbocharger arranged in the exhaust tract. The p2 pressure is also referred to as p2 and is a pressure prevailing, for example, in an intake tract of the internal combustion engine upstream of the combustion chambers, which prevails, for example, upstream of a compressor arranged in the intake tract and in particular downstream of a throttle valve arranged in the intake tract.

Further advantages, features and details of the invention result from the following description of a preferred exemplary embodiment and from the drawing. The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the single figure can be used not only in the combination specified in each case, but also in other combinations or on their own, without the frame to abandon the invention.

In the single figure, the drawing shows a block diagram to illustrate a method for calculating the delivery efficiency of an internal combustion engine designed as a reciprocating piston engine, in particular of a motor vehicle.

The only figure shows a block diagram, on the basis of which a method for calculating the volumetric efficiency 10 of an internal combustion engine designed as a reciprocating piston engine, in particular of a motor vehicle, is explained below. This means in particular that the motor vehicle, which is preferably designed as a motor vehicle, in particular as a passenger car, has the internal combustion engine in its fully manufactured state and can be driven by means of the internal combustion engine. The calculation of the delivery efficiency 10 takes place as a function of an empirical map structure, which is illustrated by a block 12 in the figure. In addition, the degree of delivery 10 is calculated as a function of a physical structure, which is illustrated by a block 14 in the figure. It can be seen that the empirical structure is or will be supplemented by the physical structure, as a result of which the degree of delivery 10, which is also referred to as the overall degree of delivery, can be calculated particularly advantageously, in particular particularly precisely. The basics of the volumetric efficiency are described below: The volumetric efficiency is the ratio of the actual to the theoretically possible engine mass flow, which is also simply referred to as the mass flow. The theoretical mass flow refers to the gas condition in the intake manifold. $$n=\frac{\dot{m}}{m_{\dot{T}HeO}}=\frac{\rho \cdot \dot{V}}{\rho \cdot {\dot{V}}_{THeO}}=\frac{\frac{p_{uT}}{R\cdot T_{uT}}}{\frac{p_{SR}}{R\cdot T_{SR}}}\cdot \frac{V_{H,Eff}\cdot \frac{n}{2}}{V_H\cdot \frac{n}{2}}=\frac{p_{uT}}{p_{SR}}\cdot \frac{T_{SR}}{T_{uT}}\cdot \frac{V_{H,Eff}}{V_H}$$

The total volumetric efficiency is thus made up of the following parts: A first of the parts includes pressure losses when flowing into the respective cylinder (pressure at bottom dead center p _UT <pressure in the intake manifold p _SR ). A second of the components includes heat transfer in the intake process (T _UT ≠ T _SR ). A third of the proportions includes a decrease in the usable swept volume due to residual gas expansion from p ₃ to p _SR (V _H,eff < V _H ).

The method is carried out, for example, using an electronic computing device, which is also referred to as a control unit or engine control unit. The delivery efficiency model implemented in the engine control unit is divided into an empirical part and a physical part. In particular, the empirical part is the empirical map structure (block 12), the physical part being the physical structure (block 14), for example. In the empirical part in particular, the total delivery efficiency for a reference state of engine temperature, gas temperature and pressure ratio p ₃ /p _SR is stored in a map, with the reference state also being or being stored, for example. The pressure p _SR is also denoted by p ₂ , for example. If the, in particular current, engine temperature and/or the, in particular current, gas temperature in the intake manifold deviates from the reference state, a correction takes effect, which is calculated from the distance to the reference multiplied by a factor. In addition, there is a correction for the swirl flap. The division of the delivery efficiency modeled in this way into the above-mentioned shares basically plays no role, the empirical structure (empirical map structure) provides a corrected basic delivery efficiency 16. It can thus be seen that the method depends on at least one in the map for the The base delivery level 16 is calculated from the map value stored or stored in the reference state.

In the physical part (physical structure) in particular, the basic delivery rate is corrected if the pressure ratio p ₃ /p _SR , also referred to as the actual pressure ratio, deviates from the reference state, hence from a reference pressure ratio assigned to the reference state. The background to this is the residual gas expansion which is dependent on p ₃ /p _SR and which influences the effectively usable cylinder volume. The correction can be both stationary, for example at altitude or with different states of exhaust gas recirculation (EGR), and dynamic, for example during acceleration. In addition, in the physical part, the basic efficiency is corrected for wall heat flows that deviate from a stationary state. This is explained using the following example: The component temperatures are stationary at a full load point higher than at a partial load point. In the case of a sudden change in the operating point, however, the component temperatures change relatively slowly, so that the heat flows between the gas and the components do not initially correspond to the stationary state. During this time, the dynamic, heat flow-related volumetric efficiency correction takes effect.

$${\dot{m}}_{RG}=\frac{p_3}{R\cdot T_3}\cdot V_c\cdot \frac{n}{2}$$

$${\dot{m}}_{mot}+{\dot{m}}_{RG}=\frac{p_{UT}}{R\cdot T_{UT}}\cdot \left(V_H+V_c\right)\cdot \frac{n}{2}$$

$${\dot{m}}_{mot}=\frac{p_{SR}}{R\cdot T_{SR}}\cdot V_H\cdot \frac{n}{2}\cdot \eta$$

The two physical corrections can be derived together from the energy balance of the respective cylinder for the intake process from top dead center (TDC) to bottom dead center (UT): $${\dot{m}}_{mOt}\cdot c_{p\left(TSR\right)}\cdot T_{SR}+{\dot{m}}_{RG}\cdot c_{V\left(T3\right)}\cdot T_3+{\dot{Q}}_w=p_{uT}\cdot V_H\cdot \frac{n}{2}+\left({\dot{m}}_{mOt}+{\dot{m}}_{RG}\right)\cdot c_{V\left(T_{uT}\right)}\cdot T_{uT}$$

$${\dot{m}}_{RG}=\frac{p_3}{R\cdot T_3}\cdot V_c\cdot \frac{n}{2}$$

$${\dot{m}}_{mOt}+{\dot{m}}_{RG}=\frac{p_{uT}}{R\cdot T_{uT}}\cdot \left(V_H+V_c\right)\cdot \frac{n}{2}$$

$${\dot{m}}_{mOt}=\frac{p_{SR}}{R\cdot T_{SR}}\cdot V_H\cdot \frac{n}{2}\cdot n$$

erhält man nach Umstellung eine Gleichung für den Liefergrad unter anderem als Funktion von p₃/p_SR und Q_W: $$\eta =\frac{p_{UT}}{p_{SR}}-\frac{1}{\kappa \cdot \left(\epsilon -1\right)}\cdot \left(\frac{p_3}{p_{SR}}-\frac{p_{UT}}{p_{SR}}\right)-\frac{\kappa -1}{\kappa }\cdot \frac{{\dot{Q}}_w}{p_{SR}\cdot V_H\cdot \raisebox{1ex}{$n$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$$

From the above equations and/or the simplified assumption that $$\mathrm{\kappa =}\frac{c_p}{c_v}=cOnst.$$

after conversion, one obtains an equation for the degree of delivery, among other things as a function of p ₃ /p _SR and Q _W : $$n=\frac{p_{uT}}{p_{SR}}-\frac{1}{k\cdot \left(e-1\right)}\cdot \left(\frac{p_3}{p_{SR}}-\frac{p_{uT}}{p_{SR}}\right)-\frac{k-1}{k}\cdot \frac{{\dot{Q}}_w}{p_{SR}\cdot V_H\cdot \raisebox{1ex}{$n$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$$

• p₃/p₂-Korrektur: $$\frac{d\eta }{d\left(\frac{p_3}{p_{SR}}\right)}=-\frac{1}{\kappa \cdot \left(\epsilon -1\right)}\to \mathrm{\Delta }{\eta }_V=-\frac{1}{\kappa \cdot \left(\epsilon -1\right)}\left(\frac{p_3}{p_{SR}}-{\left(\frac{p_3}{p_{SR}}\right)}_{Bas}\right)$$
  

The partial derivatives of this equation according to p ₃ /p ₂ or according to the wall heat flow Q _W provide the relationships required for the physical corrections:

• p ₃ /p ₂ correction: $$\frac{\mathrm{i.e}n}{\mathrm{i.e}\left(\frac{p_3}{p_{SR}}\right)}=-\frac{1}{k\cdot \left(e-1\right)}\to \mathrm{\Delta }{n}_V=-\frac{1}{k\cdot \left(e-1\right)}\left(\frac{p_3}{p_{SR}}-{\left(\frac{p_3}{p_{SR}}\right)}_{Bas}\right)$$
  

• Wandwärme-Korrektur: $$\frac{d\eta }{d{\dot{Q}}_w}=-\frac{\kappa -1}{\kappa }\cdot \frac{1}{p_{SR}\cdot V_H\cdot \raisebox{1ex}{$n$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$$
  

The degree of delivery delta Δη _v can then be converted into a correction factor:

• Wall Heat Correction: $$\frac{\mathrm{i.e}n}{\mathrm{i.e}{\dot{Q}}_w}=-\frac{k-1}{k}\cdot \frac{1}{p_{SR}\cdot V_H\cdot \raisebox{1ex}{$n$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$$
  

The following applies to the degree of delivery delta Δη _τ : $$\mathrm{\Delta }{n}_T=-\frac{k-1}{k}\cdot \frac{\mathrm{\Delta }{\dot{Q}}_W}{p_{SR}\cdot V_H\cdot \raisebox{1ex}{$n$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$$

To calculate the thermal degree of delivery delta, the stationary (Q̇ _W,stat ) and the current heat flow (Q̇ _W ) are still missing. The steady-state wall heat flow can be calculated by converting the above equation to the wall heat flow (steady-state applies: η = η _Stat ): $${\dot{Q}}_{W,Stat}=\frac{k}{k-1}\left(\frac{p_{uT}}{p_{SR}}-n_{Stat}-\frac{1}{k\cdot \left(e-1\right)}\left[\frac{p_3}{p_{SR}}-\frac{p_{uT}}{p_{SR}}\right]\right)\cdot \frac{p_{SR}\cdot V_H\cdot n}{2}$$

The current wall heat flow is then calculated from Q̇ _W,stat using PT1 filtering. The filter time depends on the mass flow, which takes the thermal inertia of the cylinder walls into account.

basiert auf einer applikativen Gewichtung zwischen Druckverlusten Δη_v und thermischen Verlusten Δη_τ. Dabei bezeichnet: η den Liefergrad, ṁ den Massenstrom, V das Volumen, V den Volumenstrom, ρ die Dichte, p den Druck, R die spezifische Gaskonstante von Luft, Q̇̇ den Wärmestrom, κ den Isotropenexponenten, p₃ den Druck im Abgaskrümmer, ε das Verdichtungsverhältnis, c_p die spezifische isobare Wärmekapazität, c_v die spezifische isochore Wärmekapazität, „Theo“ theoretisch, „SR“ das Saugrohr beziehungsweise die Ladeluftverteilerleitung, „RG“ das Restgas, „mot“ den Motor, „UT“ den unteren Totpunkt, „H“ den Hub, „Eff“ effektiv, „W“ Wand und „stat“ stationär.The pressure ratio used to calculate steady-state wall heat flux $\frac{p_{uT}}{p_{SR}}$

is based on an application weighting between pressure losses Δη _v and thermal losses Δη _τ . Where: η denotes the volumetric efficiency, ṁ the mass flow, V the volume, V the volume flow, ρ the density, p the pressure, R the specific gas constant of air, Q̇̇ the heat flow, κ the isotropic exponent, p ₃ the pressure in the exhaust manifold, ε the compression ratio, c _p the specific isobaric heat capacity, c _v the specific isochoric heat capacity, "Theo" theoretical, "SR" the intake manifold or the charge air distribution line, "RG" the residual gas, "mot" the engine, "UT" the bottom dead center, "H" the stroke, "Eff" effective, "W" wall and "stat" stationary.

Reference List

10

degree of delivery

12

block

14

block

16

basic delivery level

QUOTES INCLUDED IN DESCRIPTION

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Patent Literature Cited

• DE 102015207252 A1 [0002]

Claims (3)

Method for calculating the volumetric efficiency (10) of an internal combustion engine designed as a reciprocating piston engine, in which: - a base delivery level (16) is calculated as a function of at least one map value stored in a map for a reference state; - at least one pressure correction value is determined as a function of a deviation of an actual pressure ratio from a reference pressure ratio assigned to the reference state; - at least one dynamic correction value is determined as a function of a deviation of at least one actual wall heat flow from a stationary wall heat flow associated with a steady state; and - the degree of delivery (10) is calculated as a function of the basic degree of delivery (16), the pressure correction value and the dynamic correction value. procedure after claim 1 , characterized in that the map value is determined from the map as a function of at least one temperature of the internal combustion engine. procedure after claim 1 or 2 , characterized in that the map value is determined from the map as a function of at least one temperature of at least one combustion chamber of the internal combustion engine to be supplied or supplied air.

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