DE102017209277A1 - Method for determining a proportion of gas in a combustion chamber of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for determining a gas fraction in a combustion chamber of an internal combustion engine having an intake valve and a variable valve drive exhaust valve after a charge cycle, one of a first phase (P) during which the exhaust valve and the intake valve are simultaneously open and in which a mass of gas mixture in the combustion chamber decreases and a mass change (m) in the combustion chamber is greater than a mass flow (ṁ) from the combustion chamber through the inlet valve, the gas fraction is determined by a throttle model for the mass flow (ṁ) through the inlet valve.

Description

The present invention relates to a method for determining a proportion of gas in a combustion chamber of an internal combustion engine as well as a computing unit and a computer program for its implementation.

State of the art

In modern internal combustion engines so-called variable valve trains can be used, whereby the opening and closing times of intake and exhaust valves can be controlled independently of a camshaft position. This makes it possible to optimize fuel consumption and pollutant emissions.

In a so-called overcut, i. If inlet and outlet valves are open at the same time, residual gas that is still present in the combustion chamber from a previous combustion can be partially pre-stored in the intake manifold, which is connected to the combustion chamber via the inlet valve. Likewise, exhaust gas from the exhaust pipe, which is connected via the exhaust valve to the combustion chamber, can be re-introduced into the combustion chamber or introduced through the combustion chamber into the intake manifold. All this takes place within the framework of the so-called charge change. By particularly long overcuts can be achieved in particular in gasoline engines optimized combustion and diesel engines lower pollutant emissions.

To exploit these advantages as well as possible, it is necessary to know the residual gas content in the combustion chamber after a charge change, ie the proportion of residual gas to the entire filling of the combustion chamber (the rest is sucked fresh air) and the degree of delivery of the internal combustion engine as accurately as possible to adjust the valve control or other operating parameters accordingly.

From the DE 102 13 138 A1 For this purpose, for example, a model is known with which a residual gas content can be determined in a combustion chamber after a charge change. In this case, different proportions of residual gas during charge exchange are taken into account, in particular the residual gas remaining in the combustion chamber and a residual gas or exhaust gas flowing out of the exhaust pipe through the exhaust valve via the combustion chamber and then through the inlet valve, which is sucked in again in the next intake stroke (Reaspirative residual gas).

Disclosure of the invention

According to the invention, a method for determining a proportion of gas in a combustion chamber of an internal combustion engine as well as an arithmetic unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

An inventive method is used to determine a proportion of gas in a combustion chamber of an internal combustion engine with a variable valve train after a charge change, when during the charge cycle, an exhaust valve and an intake valve of the combustion chamber are temporarily open simultaneously. For this purpose, a duration (the duration may be indicated, for example, as a time duration or as an angular difference of the crankshaft or camshaft) during which the exhaust valve and the inlet valve are simultaneously opened is subdivided into a first phase and preferably a second phase.

The first phase is characterized in that a mass of gas mixture in the combustion chamber decreases and a (temporal) mass change (of gas mixture) in the combustion chamber is greater in magnitude than a mass flow (of gas mixture) from the combustion chamber through the inlet valve. This also means that a mass flow from the combustion chamber through the exhaust valve exists. In the second phase, the mass change (of gas mixture) in the combustion chamber is smaller in magnitude than the mass flow (of gas mixture) from the combustion chamber through the inlet valve. This also means that a mass flow through the exhaust valve into the combustion chamber exists. Compared to the first phase, the direction of the mass flow through the exhaust valve thus reverses.

The gas component originating from the first phase is then determined on the basis of a throttle model for the mass flow through the intake valve. According to a preferred development of the invention, the gas component originating from the second phase can additionally be determined on the basis of a throttle model for a mass flow through the exhaust valve via the combustion chamber and then through the inlet valve and on the basis of an, in particular ideal, gas equation. A throttle model can be used in each case, because the open valves are essentially the same as a throttle. In particular, a duration of the first phase and / or a point in time or a crankshaft angle during opening of the intake valve can then also be taken into account. For the determination of the mass flow through the inlet valve (even when using the mentioned throttle model), at least one of the following variables can be considered in particular: intake manifold pressure, exhaust back pressure, exhaust gas temperature and flow-effective cross-sectional area of the intake valve. The gas fractions of both phases can then be added to obtain the total gas content after the gas exchange.

In each case a residual gas portion in the combustion chamber and / or a fresh air portion, which is introduced into the combustion chamber, and / or a delivery rate of the internal combustion engine can be determined as gas fraction. For example, first of all the residual gas content can be determined and from this the residual gas partial pressure in the combustion chamber and thus the delivery rate of the internal combustion engine as well as other relevant operating parameters can be determined and used for the further operation of the internal combustion engine. It is also conceivable, however, not to determine the residual gas content explicitly, but only indirectly when determining the fresh air content or the degree of delivery.

The determination of the originating from the second phase portion of residual gas can be done in particular in the same way as in the DE 102 13 138 A1 described. Thus, the equations and models mentioned there can also be used. In this respect, for a closer explanation also on the DE 102 13 138 A1 directed.

The introduction of the first phase or the division into two phases, however, the total residual gas content can now be determined much more accurate than by that from the DE 102 13 138 A1 known methods alone. In particular, for a valve train with strong Entdrosselung and large overcut this known method would be too inaccurate and would lead to a large proportion of residual gas, which would worsen the entire modeling of the filling of the combustion chamber.

Preferably, a transition from the first phase to the second phase is now determined on the basis of a comparison between a mass flow caused by a piston of the combustion chamber and the mass flow from the combustion chamber through the inlet valve. This transition can be specified in particular with regard to a time or an angular position (for example, the crankshaft or camshaft). The mass flows can each be modeled accordingly. This principle is based on the fact that the reduction of the amount of residual gas (ie the aforementioned mass change) in the first phase is primarily caused by the displacement of gas mixture through the piston, especially if no residual gas is purged by means of fresh gas from the combustion chamber into the exhaust pipe (so-called. scavenging). If the mass flow through the piston displacement is smaller than the mass flow through the inlet valve, then no residual gas flows out of the combustion chamber through the exhaust valve, since the exhaust backpressure is higher than the pressure in the combustion chamber (so-called cylinder pressure). In this respect, therefore, the transition can preferably be selected as that time or that angular position (for example, the crankshaft or camshaft) in which the mass flow caused by the piston and the mass flow from the combustion chamber through the intake valve are equal in magnitude. A determination of the transition thus defined can advantageously take place on the basis of one, in particular numerical, zero-point search. Possible methods for the zero position search are, for example, the Regula Falsi method, the Newton method or a Bisection method.

It is also advantageous if the transition is only determined if a ratio between an intake manifold pressure and an exhaust back pressure is less than a predetermined first threshold, which is in particular less than one, and / or greater than a predetermined second threshold. The background to this is that, in the case of a mass flow through the inlet valve via the combustion chamber and then through the outlet valve (ie the so-called scavenging), the point of intersection can generally not be determined by the comparison mentioned. By the mentioned thresholds it is ensured that the flow conditions are suitably suitable. If the transition with the mentioned method is then no longer determined, however, it can for example be determined or estimated in another way. It is also conceivable that during the entire duration in which the outlet valve and the inlet valve are opened simultaneously, only the method for the second phase is used, that is, no distinction is made in two phases.

Alternatively, it is also preferred if the transition is determined by means of a data-based model, wherein in particular at least one of the following variables is considered: engine speed, a time or angular position when opening the intake valve, and a ratio between intake manifold pressure and exhaust back pressure. Depending on the situation, this variant can do this be more efficient or used as an alternative, if the aforementioned method is no longer used due to the mentioned pressure conditions.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below with reference to the drawing.

list of figures

• 1 schematically shows an internal combustion engine with combustion chamber, in which a method according to the invention can be carried out.
• 2 shows schematically Hubverläufe of valves in an internal combustion engine and associated mass flows for explaining a method according to the invention in a preferred embodiment.
• 3 schematically shows a sequence of a method according to the invention.
• 4 schematically shows a representation of a piston of an internal combustion engine for explaining a method according to the invention in a preferred embodiment.

Embodiment (s) of the invention

In 1 is schematically an internal combustion engine 100 shown, with a combustion chamber or cylinder 110 with associated piston 115 that has a connecting rod 116 coupled with a crankshaft, is shown in more detail. It is understood that such an internal combustion engine may have a plurality of such combustion chambers, for example three, four, six or eight. For each of these combustion chambers, a method according to the invention can then be carried out, which is explained here by way of example on the combustion chamber shown.

The internal combustion engine also has an intake manifold 120 with a throttle 121 on that via an inlet valve 125 to the combustion chamber 110 is connected. There is also an exhaust pipe 130 provided that via an exhaust valve 135 to the combustion chamber 110 is connected. In the case of several combustion chambers, each combustion chamber has at least one inlet valve and at least one outlet valve. Depending on the type of internal combustion engine, the intake pipe and / or the exhaust pipe can be provided for several combustion chambers with respective connections. By means of a computer designed as a control unit 180 the internal combustion engine can be controlled.

In 2 are schematic and exemplary Hubverläufe h _E an intake valve and h _A an exhaust valve in an internal combustion engine, such as in 1 shown is shown. For this purpose, in the upper diagram, a stroke h is plotted against a crankshaft angle KW. In the lower diagram are - also schematically and by way of example - associated mass flows ṁ _E through the inlet valve and ṁ _A represented by the outlet valve for explaining a method according to the invention in a preferred embodiment.

For this purpose, a mass flow ṁ is plotted against the crankshaft angle KW. Positive values here mean for the outlet valve a mass flow from the combustion chamber through the exhaust valve into the exhaust pipe, whereas for the inlet valve a mass flow from the intake pipe through the inlet valve into the combustion chamber. A positive value at ṁ _A Thus, for example, means that gas mixture flows from the combustion chamber through the exhaust valve into the exhaust pipe. A negative value at ṁ _E however, for example, means that gas mixture flows from the combustion chamber through the inlet valve into the intake manifold.

The mass flows m ' _E and ṁ _A overlap now in the time or angle duration in which both valves are open at the same time. In the example shown, this overlap period starts at angular position φ ₁ and lasts until Angular position φ ₃ .

This duration will now be in two phases P ₁ and P ₂ divided, with the transition from the first phase P ₁ to the second phase P ₂ at angular position φ ₂ takes place.

In the first phase P ₁ Now, the inlet valve and the exhaust valve are open at the same time and a mass of the gas mixture in the combustion chamber decreases, wherein a mass change in the combustion chamber is greater in magnitude than a mass flow from the combustion chamber through the inlet valve. The fact that the mass decreases in the combustion chamber, it can be seen that is pressed by both valves gas mixture from the combustion chamber, which is caused by the piston stroke. Because up to the angle position φ ₂ gas mixture flows out of the combustion chamber through the outlet valve ( m ' _A positive), the decrease in the mass in the combustion chamber is greater in magnitude than the mass flow from the combustion chamber through the inlet valve.

In the second phase P ₂ by contrast, the change in mass in the combustion chamber is smaller than the mass flow from the combustion chamber through the inlet valve. Since the angular position φ ₂ gas mixture flows through the exhaust valve into the combustion chamber, which is due to the negative values of ṁ _A can be seen, there is still a total decrease in the mass in the combustion chamber, but the amount is less than the mass flow through the inlet valve.

In the second phase P ₂ Thus gas mixture flows from the exhaust pipe through the combustion chamber into the intake pipe. This situation corresponds to that in the DE 102 13 138 A1 Is accepted. Insofar as for a more detailed description of the determination of the gas content, here the residual gas content, G ₂ for this second phase, as in 3 indicated by a throttle model for a mass flow through the exhaust valve via the combustion chamber and then through the inlet valve and by means of a gas equation on the DE 102 13 138 A1 directed.

In the first phase, the gas content, here the residual gas content, G ₁ now using a throttle model M determined for the mass flow through the inlet valve. For this purpose, first the transition from the first phase to the second phase, so here the angular position φ ₂ be determined. A reduction of the amount of residual gas in the first phase is caused primarily by the piston displacement especially at operating points without scavenging.

mit π = p_S/p_A (normierter Druck) und Isentropenexponent κ.If the mass flow through the piston displacement is smaller than the mass flow through the inlet valve, then no residual gas will flow off via the outlet valve, since the exhaust backpressure is higher than the cylinder pressure (compare angle position ≥φ2 in 2 ). The transition to the second phase is thus identical to the intersection of the mass flow of the piston displacement with the mass flow through the inlet valve and can be determined at least approximately, for example by means of a numerical zero point search. The zero point is doing for the difference mass flow ṁ _E and the piston displacement determined. Alternatively, the transition can also be calculated using a data-supported model, in which case at least one of the following variables is taken into account: rotational speed of the internal combustion engine, a point in time or an angular position when opening the inlet valve, and a ratio between an intake manifold pressure and an exhaust backpressure. The mass flow through the inlet valve ṁ _E can then be, for example, with the help of a throttle equation depending on the intake manifold pressure ps, exhaust back pressure p _A , the exhaust gas temperature T _A and the flow-effective cross-sectional area A _E of the intake valve over the crankshaft angle φ as follows: $${\dot{m}}_e=A_e\left(\phi \right)p_A\sqrt{\frac{2}{R_S\cdot T_A}}\sqrt{\frac{\kappa }{\kappa -1}\left({\pi }^{\frac{2}{\kappa }}-{\pi }^{\frac{\kappa +1}{\kappa }}\right)}$$

with π = p _S / p _A (normalized pressure) and isentropic exponent κ.

The mass flow of the piston displacement can, as also known from the literature, be generally described and calculated with the following equation: $$\begin{array}{l}\dot{m}=\frac{dV}{dt}\frac{p_A}{R_S{T}_A}=D^2\frac{{\pi }^2}{2}\frac{n}{60}\frac{p_A}{R_S{T}_A}\frac{ds}{d\phi }\hfill \\ =D^2\frac{{\pi }^2}{2}\frac{n}{60}\frac{p_A}{R_S{T}_A}\left[r\text{sin}\left(\phi -\beta \right)+\frac{r\left[d+r\text{sin}\left(\phi -\beta \right)\right]\text{cos}\left(\phi -\beta \right)}{\sqrt{l^2-{\left[d+r\text{sin}\left(\phi -\beta \right)\right]}^2}}\right]\hfill \end{array},$$

D is the bore in the combustion chamber, n the speed of the internal combustion engine in 1 / min, p _A the exhaust back pressure, T _A the exhaust gas temperature, R _S the specific gas constant, / the connecting rod length, r the crank radius, d the setting and φ the crankshaft angle, where β = arcsin [d / (r + l)].

The sizes are, if appropriate, also in 4 holding a piston 115 an internal combustion engine shows, drawn for a more detailed explanation.

Based on these equations, the residual gas content from the first phase can now be determined G ₁ determine, so that a total residual gas content G _tot by adding the two individual residual gas components G ₁ and G ₂ results. Alternatively, the residual gas content G ₁ Also, as mentioned, be determined via a data-driven approach or a data-driven model depending on the speed. The entire residual gas content can then also be converted, for example, into a partial pressure which reduces the fresh air charge in the cylinder or combustion chamber.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10213138 A1 [0005, 0011, 0012, 0028]

Claims (14)

A method for determining a gas fraction in a combustion chamber (110) of an internal combustion engine (100) having an intake valve and a variable valve engine exhaust valve after a charge cycle, one of a first phase (P ₁ ) during which the exhaust valve (135) and the intake valve (125) are opened at the same time and in which a mass of gas mixture in the combustion chamber (110) decreases and a mass change (m) in the combustion chamber (110) is greater than a mass flow (ṁ _E ) from the combustion chamber through the inlet valve (125 ), originating gas fraction (G ₁ ) is determined by means of a throttle model (M) for the mass flow (ṁ _E ) through the inlet valve (125). Method according to Claim 1 in which one of a second phase (P ₂ ) during which the outlet valve (135) and the inlet valve (125) are opened simultaneously and in which the mass change (m) in the combustion chamber (110) is smaller than the mass flow (ṁ _E ) from the combustion chamber through the inlet valve (125), derived gas fraction (G ₂ ) is determined based on a throttle model for a mass flow through the exhaust valve (135) via the combustion chamber (110) and then through the inlet valve (125) and based on a gas equation. Method according to Claim 2 wherein a transition from the first phase (P ₁ ) to the second phase (P ₂ ) based on a comparison between a by a piston (115) of the combustion chamber (110) caused mass flow and the mass flow (ṁ _E ) from the combustion chamber through the Inlet valve is determined. Method according to Claim 3 , wherein the transition as the time or the angular position (φ ₂ ) is selected, in which the mass flow caused by the piston (115) of the combustion chamber (110) and the mass flow (ṁ _E ) from the combustion chamber through the inlet valve are equal in magnitude. Method according to Claim 4 , wherein the transition is determined on the basis of one, in particular numerical, zero point search. Method according to Claim 2 or 3 wherein the transition is determined only when a ratio between an intake manifold pressure and an exhaust backpressure is less than a predetermined first threshold, which is in particular less than one, and / or greater than a predetermined second threshold value. Method according to Claim 3 , where the transition is determined using a data-driven model. Method according to Claim 7 wherein, in determining the transition based on the data-driven model, at least one of the following quantities is taken into account: engine speed (100), a time or crankshaft angle (φ ₁ ) upon opening the intake valve (125), and a ratio between intake manifold pressure and a exhaust back pressure. Method according to one of the preceding claims, wherein as the gas fraction in each case a residual gas content in the combustion chamber and / or a fresh air fraction, which can be introduced into the combustion chamber and / or a delivery rate of the internal combustion engine are determined. Method according to one of the preceding claims, wherein the mass flow (ṁ _E ) is determined by the intake valve taking into account at least one of the following: intake manifold pressure, exhaust back pressure, exhaust gas temperature and flow-effective cross-sectional area of the intake valve (125). Method according to one of the preceding claims, wherein in the determination of the gas fraction (G ₁ ) for the first phase (P ₁ ) a duration of the first phase (P ₁ ) and / or a time or an angular position (φ ₁ ) when opening the inlet valve be taken into account. Arithmetic unit (180) adapted to perform a method according to any one of the preceding claims. A computer program that causes a computing unit (180) to perform a method according to any one of Claims 1 to 11 when executed on the arithmetic unit (180). Machine-readable storage medium with a computer program stored thereon Claim 13 ,

Images