Method for calculating a fresh air mass in a cylinder and control system

Description

[0001] The invention relates to a method for calculating a fresh air mass in a cylinder of an internal combustion engine and a controller configured to carry out such a method.

[0002] In gasoline engines, it is generally accepted that the air volume in a cylinder's combustion chamber must be determined as accurately as possible so that the correct fuel quantity for injection can be calculated. The amount of air remaining in the combustion chamber depends on many thermodynamic variables, and it is known that filling errors can occur in the calculated air volume at different ambient temperatures.

[0003] German patent application DE 101 58 261 A1 discloses an engine management system in which a physically based model is used to determine various state variables. The state variables relate to a connecting section located between a mixing point, where recirculated exhaust gas is mixed with intake fresh air, and the intake valves of an internal combustion engine. The physical model simulates the behavior of this connecting section, so that various operating parameters of the internal combustion engine can be controlled using this model, such as the fresh air mass in the connecting section and the gas temperature. The disadvantage of this model is that only the influence of the connecting section on the fresh air mass is considered, while other influences on the fresh air mass are ignored.

[0004] From the German patent application DE 10 2011 013 481 A1 a method for controlling an internal combustion engine with an internal exhaust gas recirculation is known.

[0005] From US patent US 5 522 365 a method for controlling internal combustion engines and for controlling the air / fuel ratio of the engine is known.

[0006] From the publication of the international patent application WO 2017 / 093638 A1, a method for estimating the mass enclosed in the combustion chamber of a cylinder of a motor vehicle internal combustion engine is known.

[0007] Techniques for controlling diesel engines are known from GUZZELLA LET AL: "CONTROL OF DIESEL ENGINES", IEEE CONTROL SYSTEMS MAGAZINE, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, Vol. 18, No. 5, October 1998, pages 53-71, ISSN: 0272-1708, DOI: 10.1109 / 37.722253.

[0008] SHAVER GM ET AL: "Modeling cycle-to-cycle dynamics and mode transition in HCCI engines with variable valve actuation", CONTROL ENGINEERING PRACTICE, PERGAMON PRESS, OXFORD, UK, Vol. 14, No. 3, March 2006, pages 213-222, ISSN: 0967-0661 describes techniques for modeling cycle-to-cycle dynamics and mode transition in HCCI engines with variable valve actuation.

[0009] Techniques for controlling HCCI engines are known from CHIANG CJ ET AL: "Steady-state multiplicity and stability of thermal equilibria in homogeneous charge compression ignition (HCCI) engines", 43RD IEEE CONFERENCE ON DECISION AND CONTROL; DECEMBER 14-17, 2004; ATLANTIS, PARADISE ISLAND, BAHAMAS, IEEE, PISCATAWAY, NJ, USA, Vol. 2, December 14, 2004, pages 1676-1681Vol. 2, ISBN: 978-0-7803-8682-2.

[0010] Kang Song ET AL: "Compound disturbance rejection control of spark ignition; controlledautoignition hybrid combustion for gasoline engines", Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, Vol. 232, No. 2, 1 February 2018, pages 264-281, GB, ISSN: 0954-4070, DOI: 10.1177 / 0954407017697477 describes methods for controlling gasoline engines.

[0011] From MLADEK M ET AL: "A Model for the Estimation of Inducted Air Mass and the Residual Gas Fraction usng Cylinder Pressure Measurements", SAE 2010 COMMERCIAL VEHICLE ENGINEERING CONGRESS SAE TECHNICAL PAPERS, SAE INTERNATIONAL, US, No. 2000-01-0958, March 6, 2000, pages 1-11, 1, ISSN: 0148-7191, methods for estimating the intake air mass and the residual gas fraction are known.

[0012] The object of the present invention is to provide a method for calculating a fresh air mass in a cylinder of an internal combustion engine and a corresponding control for an internal combustion engine, which at least partially overcome the above-mentioned disadvantages.

[0013] This object is achieved by the inventive computer-implemented method according to claim 1 and the control according to claim 9.

[0014] According to a first aspect, the present invention provides a method for calculating a fresh air mass in a cylinder of an internal combustion engine according to claim 1, the method comprising: determining a heating of the fresh air at a wall of the cylinder, wherein the temperature of the wall (2a) of the cylinder changes dynamically; and calculating the fresh air mass of the fresh air in the cylinder based on the determined heating of the fresh air mass.

[0015] According to a second aspect, the present invention provides a control for an internal combustion engine according to claim 9, which has at least one cylinder, an intake manifold, an intake manifold temperature sensor, an intake valve on the cylinder and an intake port upstream of the intake valve, the control being adapted to carry out the method according to the first aspect.

[0016] Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the present invention.

[0017] In some embodiments, an increase in the fresh air temperature is calculated from a temperature sensor in the intake manifold to the intake valve, with the heat exchange being calculated via the temperature difference between the component and the fresh air. Furthermore, in some embodiments, the internal combustion engine has a controlled cooling water mass flow (CFM) and thus an additional degree of freedom. It was recognized that this degree of freedom was not sufficiently taken into account in solutions or charge detection models known from the prior art. Furthermore, it was recognized that deviations in the calculated fresh air charge can occur during dynamic changes or processes. These deviations can always be significant if there has been a prolonged phase of unfired engine operation (fuel injection off).

[0018] It was also recognized that known corrections cannot take heat transfer via the cylinder wall into account, so that at very hot or very cold intake temperatures, changes in the density of the fresh air in the combustion chamber are corrected too strongly due to the effect not being taken into account. This can lead to larger errors in the fresh air calculation. In addition, it was recognized that in engines with map-controlled cooling water flows, the cooling water temperature alone is not always completely meaningful, since the heat transfer at the cylinder wall through thermal convection as a function of the water mass flow cannot be taken into account. Furthermore, it was recognized that known corrections to the injection quantity cannot correctly represent the temporal course of the necessary mixture correction, neither qualitatively nor quantitatively, and it cannot be distinguished whether the dynamic load change occurred from the fired or unfired engine operating point.Due to stricter emission limits of new exhaust gas test cycles and the increased requirements to achieve the lowest emission values under all ambient conditions, the heating of the fresh air by the cylinder wall is taken into account in some embodiments.

[0019] Accordingly, the invention relates to a method for calculating a fresh air mass in a cylinder of an internal combustion engine, wherein the method comprises determining a heating of the fresh air at a wall of the cylinder, wherein the temperature of the wall of the cylinder changes dynamically, and calculating the fresh air mass of the fresh air in the cylinder based on the determined heating of the fresh air mass.

[0020] The internal combustion engine can be a gasoline engine or diesel engine, or the like, and can be intended, for example, for a motor vehicle (such as a car, motorcycle, but in principle also other land, water, and / or aircraft). The number of cylinders is arbitrary and can be 1, 2, 3, 4, 5, 6, etc., depending on the embodiment.

[0021] The fresh air mass is directly the mass of the fresh air in the cylinder, for example, directly after an intake process, without the invention being limited in this respect, whereas in other unclaimed examples the fresh air mass is represented by one or more quantities, such as density, temperature, volume, etc.

[0022] The method now determines the heating of the fresh air in the cylinder at a cylinder wall, even when the cylinder wall temperature is dynamically changing. Typically, the section of the cylinder wall that is in contact with the fresh air, which, for example, enters the cylinder through an intake process for subsequent combustion, is taken into account, since the goal in some embodiments is to determine the correct amount of fuel to be injected based on the fresh air mass present in the cylinder. This section can be, for example, the section of the cylinder wall in the combustion chamber of the cylinder, the cylinder base (or piston surface), etc.

[0023] The method then calculates the fresh air mass of the fresh air in the cylinder based on the determined heating of the fresh air mass.

[0024] Thus, embodiments of the invention allow the heating of the fresh air at the cylinder wall to be taken into account even during dynamic changes in the cylinder wall temperature during the intake phase, thus increasing the accuracy of the calculated fresh air mass. As a result, in some embodiments, a higher mixture accuracy between air and fuel can be achieved for intake temperatures, coolant temperatures, and coolant mass flows through the cylinder crankcase or through the cylinder head that deviate from the standard condition. This temperature correction goes beyond temperature corrections that only model the heating up to the intake valve. The additional integration of the cylinder wall temperature as a thermal contact area has the advantage that, in particular, filling errors are reduced under different ambient temperatures.In some embodiments, a coolant mass flow can also be incorporated into the heat transfer by means of thermal convection. In some embodiments, the aim of the method is therefore to take into account the heating of the fresh air at the cylinder wall during the intake phase. For this purpose, as mentioned, the current, highly dynamic cylinder wall temperature is determined because, for example, the temperature of the cylinder wall drops sharply after cooling phases in unfired overrun or in a very low load range. During a dynamic change of the engine operating point or the operating point of the internal combustion engine to a higher load range, the cylinder wall warms up to a steady state with a delay. In some embodiments, these warm-up and cooling processes are modeled as accurately as possible, and their influence on the fresh air charge is taken into account.Thus, some embodiments provide better vehicle dynamics and smoother load changes, as well as lower exhaust emissions during load changes, particularly during overrun phases and during FMA ("freewheeling engine off") concepts. Furthermore, some embodiments have the advantage that the dynamic correction of the fresh air temperature based on the cylinder wall warm-up and cooling processes improves the mixture accuracy in the dynamics. Exhaust emissions can occur more frequently in the dynamics, to which control systems such as lambda control and mixture adaptation sometimes only react with a delay to compensate for the charge errors. Therefore, some embodiments can reduce charge errors through the dynamic correction of the fresh air temperature.

[0025] Determining the heating of the fresh air involves determining the heating of the fresh air assuming a constant cylinder wall temperature. A constant cylinder wall temperature corresponds to a steady-state operating condition of the internal combustion engine. Determining the heating with an assumed constant cylinder wall temperature is simpler and can be used as a starting point for calculating the heating of the fresh air under a dynamic cylinder wall temperature change.

[0026] The steady-state cylinder wall temperature can vary significantly when the internal combustion engine's operating point changes, e.g., by 180 K, without the present invention being limited in this respect. Since the steady-state condition typically only occurs after a few seconds, the cylinder wall temperature, which has not yet stabilized, affects the intake fresh air mass. During load changes from a "cold" to a "warm" operating point of the internal combustion engine, a density advantage arises, and during reverse load changes, a density disadvantage arises, which can persist until the steady-state cylinder wall temperature is reached. If this effect is not taken into account, this can lead to filling errors.

[0027] The determined heating of the fresh air assuming a constant cylinder wall temperature is filtered through a filter to determine a dynamic correction of the heating of the fresh air at the cylinder wall. If the heating of the fresh air is determined assuming a constant cylinder wall temperature, i.e., at a steady-state operating point of the internal combustion engine, this leads to a fresh air temperature profile that is closer to a real profile, as well as Fig. 1 illustrated.

[0028] In Fig. 1 The cylinder wall temperature "T Cyl-w " in Kelvin is plotted on the ordinate and the time "t" on the abscissa in seconds. Fig. 1shows a curve 100 of the temperature of the fresh air as a function of the cylinder wall temperature and time, as it results when a constant temperature of the cylinder wall is assumed for the calculation of the heating of the fresh air at the cylinder wall. The curve 100 is characterized by an instantaneous steep or vertical temperature jump from 320 K to 500 K, i.e. by a difference of 180 K (i.e. 180 °C). This is because when a constant temperature of the cylinder wall is assumed for the calculation of the temperature increase of the fresh air, a continuous temperature increase is not possible, which leads to this artificial jump in the curve 100. In contrast, a curve 101 shows a simulation of what a natural curve of the cylinder wall temperature could theoretically look like, whereby the curve 101 is based on a simulation of a dynamic change in the cylinder wall temperature.A curve 102 now illustrates the heating of the fresh air at the cylinder wall when it is filtered accordingly by a filter which changes the jump in the curve 100 in such a way that the heating of the fresh air does not occur abruptly but continuously and approaches a natural curve.

[0029] By providing such a filter, a simple and cost-effective correction of the dynamic heating of the fresh air to the dynamically changing temperature of the cylinder wall is possible.

[0030] The filter comprises at least one PT1 filter. PT1 filters are generally known and are simple and cost-effective to provide. According to the invention, the filter comprises two PT1 filters connected in series, which produce a particularly good fresh air temperature profile at a dynamic cylinder wall temperature.

[0031] In some embodiments, the filter is determined empirically, e.g. on a test bench, so that it can be adapted to a specific internal combustion engine or a specific model of an internal combustion engine.

[0032] In some embodiments, the filter depends on at least one parameter that is characteristic of the temperature of the wall of the cylinder, so that in this way a well-adapted dynamic heating of the fresh air can be achieved for a wide variety of temperatures and temperature profiles of the cylinder wall temperature.

[0033] In some embodiments, the parameter represents the amount of heat introduced during combustion, the rotational speed of the internal combustion engine, and / or the heat transfer from cooling water to the cylinder wall. These parameters can be used to accurately determine the temperature change of the cylinder wall and thus the temperature change of the fresh air.

[0034] In some embodiments, as explained further below, the filtered heat is multiplied by an effective and dynamic heat transfer coefficient. This allows a correction temperature to be obtained that takes into account a dynamic temperature change of the cylinder wall. Furthermore, the dynamic heat transfer coefficient takes into account the heat transfer from the cylinder wall to the fresh air during dynamic temperature changes.

[0035] In some embodiments, the effective and dynamic heat transfer coefficient is determined empirically, so it does not require complex calculations in a control system, but is available, for example, as a characteristic map. The effective and dynamic heat transfer coefficient can be determined, for example, on a test bench for a specific type of internal combustion engine.

[0036] Determining the heating of the fresh air at the cylinder wall, where the cylinder wall temperature changes dynamically, involves adding the determined heating of the fresh air assuming a constant cylinder wall temperature and dynamically correcting the heating of the fresh air at the cylinder wall. This allows for a very simple consideration of the dynamic heating of the cylinder wall and thus also of the fresh air.

[0037] According to the invention, the method further comprises determining a reference heating of the fresh air at the cylinder wall based on at least one reference parameter, as further explained below. The reference heating can be easily determined empirically on a test bench, thus simplifying the overall determination of the fresh air heating.

[0038] The fresh air mass of the fresh air in the cylinder is calculated based on the determined heating of the fresh air mass and the determined reference heating, as will be explained in more detail below.

[0039] Thus, the already existing temperature correction of the fresh air (mass) in the intake tract up to behind the intake valve is extended by the wall heat exchange between the cylinder wall and the fresh air and, in particular, is also corrected by the dynamic temperature change due to the dynamic temperature change of the cylinder wall.

[0040] In general, in some embodiments, the temperature increase of the fresh air on its way into the cylinder can be determined based on the following equation: T Luft_kor , i = α w , i ⋅ T w , l − T Luft , i − 1 + T Luft , i − 1

[0041] The parameter "i" represents a component that transfers heat to the fresh air on its way into the cylinder, so that "i-1" indicates the next upstream component from which the fresh air comes.

[0042] The parameter "T w,i " represents the temperature of the wall surface "w" of the component "i" for which the heat transferred to the fresh air is to be determined.

[0043] The parameter "T Air, i-1" represents the temperature (or temperature increase) of the fresh air at the next upstream component "i-1".

[0044] The parameter "α w,i " represents an effective heat transfer coefficient for a wall section or a contact area A i of the component i that comes into contact with the fresh air: α w , l = Q w ⋅ α i ⋅ A i , where "Q w " represents the heat dissipated at the wall "w", "α i " represents the heat transfer coefficient of the component "i" and "A i " represents the contact area of the component "i": In some embodiments, the effective heat transfer coefficient is determined empirically, e.g. on a test bench, and / or model-based.

[0045] In some embodiments, determining the heating of the fresh air comprises determining a heating of the fresh air at an intake port to the cylinder upstream of an intake valve of the cylinder (assuming a steady-state operating state). In some embodiments, for example, there is a temperature sensor in an intake manifold located upstream of the cylinder and through which fresh air is drawn in, such that the temperature of the fresh air in the intake manifold at the location of the temperature sensor can be determined using this temperature sensor. In some embodiments, no further temperature sensor is provided downstream of this temperature sensor, such that by including the heating of the fresh air at the intake port to the cylinder, the heating of the fresh air on the way from the intake manifold at the location of the temperature sensor to the cylinder can be calculated more accurately.

[0046] Determining the heating of the fresh air at the inlet duct can be based on the following relationship: T Luft_v_EV = T EK − T Luft_Sgr ⋅ α w 1 + T Luft_Sgr , where T Luft_v_EV represents the temperature increase of the fresh air at the intake port in front of the intake valve of the cylinder, T EK represents the temperature of the intake port, T Luft_Sgr represents the temperature of the fresh air in an intake manifold to the intake port of the cylinder and α w1 represents an effective heat transfer coefficient of the intake port.

[0047] Equation (3) therefore allows the determination of the temperature increase of the fresh air at the intake port upstream of the cylinder's intake valve. The temperature T air_sgr of the fresh air in an intake manifold leading to the cylinder's intake port is determined, for example, by a temperature sensor in the intake manifold, so that this temperature is available as a measured value. The temperature T EK of the intake port can be determined, for example, using a model and / or based on a cooling water temperature.

[0048] In some embodiments, the effective heat transfer coefficient α w1 includes a characteristic map that represents the heat transfer of the intake port as a function of a rotational speed and / or intake manifold pressure. This allows for a precise determination of the heating of the fresh air or the heat transfer of the intake port to the fresh air.

[0049] The effective heat transfer coefficient α w1 can be determined by measurement on a test bench, so that the heat transfer for the internal combustion engine can be determined particularly accurately.

[0050] In some embodiments, the temperature of the fresh air in the intake manifold is determined with the aid of a temperature sensor in the intake manifold, so that a measured value and, for example, no model-based value for the fresh air temperature is available as the starting point for the calculations for heating the fresh air in the intake tract, whereby the accuracy can be improved.

[0051] In some embodiments, determining the heating of the fresh air comprises determining the heating of the fresh air at an intake valve of the cylinder. In some embodiments, the intake valve is the next component in the intake path that plays a significant role in heating the intake fresh air on its way into the cylinder after the aforementioned intake port, so that the accuracy of determining the heating can be further increased.

[0052] Determining the heating of the fresh air at the cylinder’s intake valve can be based on the relationship: T Luft_h_EV = T EV − T Luft_v_EV ⋅ α w 2 + T Luft_v_EV , where T air_h_EV represents the temperature increase of the fresh air at the intake valve of the cylinder, T EV represents the temperature of the intake valve, T air_v_EV represents the temperature of the fresh air in the intake channel in front of the intake valve of the cylinder and α w2 represents an effective heat transfer coefficient of the intake valve.

[0053] Equation (4) therefore allows the determination of the temperature increase T air_h_EV of the fresh air at the cylinder's intake valve, whereby the temperature T air_v_EV can be determined based on equation (3) above, so that it can be particularly accurate in some embodiments. The temperature T EV of the intake valve can, for example, be determined based on a model and / or based on a cooling water temperature or oil temperature of the internal combustion engine.

[0054] In some embodiments, the effective heat transfer coefficient α w2 includes a characteristic map that represents the heat transfer of the intake valve as a function of a rotational speed and / or intake manifold pressure. This allows for a precise determination of the heating of the fresh air or the heat transfer of the intake valve to the fresh air.

[0055] The effective heat transfer coefficient α w2 can be determined by measurement on a test bench so that the heat transfer for the internal combustion engine can be determined particularly accurately or it can also be determined model-based and stored accordingly as a characteristic map.

[0056] In some embodiments, the determination of the heating of the fresh air at the wall of the cylinder for the stationary operating state is based on the relationship: T Luft_Zyl_stationär = T Zyl_Wand − T Luft_h_EV ⋅ α w 3 + T Luft_h_EV , where T air_cyl_stationary represents the temperature increase of the fresh air at the wall of the cylinder, T cyl_wall is the temperature of the wall of the cylinder, T air_h_EV is the temperature of the fresh air after the intake valve of the cylinder and α w3 represents an effective heat transfer coefficient of the wall of the cylinder (which is determined empirically on the test bench and / or model-based and is stored, for example, as a map).

[0057] Equation (5) therefore allows the temperature increase T Air_Cylinder_stationary of the fresh air at the cylinder wall to be determined in a stationary operating state, wherein the temperature T Air_h _ EV can be determined on the basis of equation (4) above, so that it can be particularly accurate in some embodiments. The temperature T Cylinder_Wall of the cylinder wall can, for example, be determined using a model. In some embodiments, the temperature T Cylinder_Wall of the cylinder wall is determined on the basis of a simulation calculation, using a thermodynamic model of the internal combustion engine, so that the temperature can be specified as a function of, for example, a fresh air charge and a speed of the internal combustion engine and can, for example, be stored as a characteristic map. Accordingly, in some embodiments, the temperature T Cylinder_Wall of the cylinder wall is available as a characteristic map, which can, for example,depending on the fresh air charge and / or the engine speed. This allows for a very precise determination of the cylinder wall temperature and thus the heating of the fresh air.

[0058] In order to also take into account the dynamic temperature change of the fresh air at the cylinder wall, at which the temperature changes dynamically, a correction factor T AirCycle_cor_dyn is determined. To do this, the temperature increase T Air_Cycle_stationary of the fresh air at the cylinder wall, derived from equation (5), is first filtered through a filter, e.g., two PT1 filters connected in series, to obtain a filtered temperature increase T Air_Cycle_PT1 of the fresh air. This filtered temperature increase T Air_Cycle_PT1 is then multiplied by the effective and dynamic heat transfer coefficient α dyn, which represents the dynamic heat transfer to the fresh air from the cylinder wall and which can be represented, for example, as a characteristic map and depends on at least one of the parameters: quantity of incoming fresh air and speed of the internal combustion engine.

[0059] The correction factor T Luft_Zyl_kor_dyn can be determined as follows: T Luft_Zyl_kor_dyn = T Luft_Zyl_PT 1 ⋅ α dyn

[0060] By multiplying the temperature difference of the cylinder wall by the effective dynamic wall heat transfer coefficient, a temperature difference for the fresh air in dynamic operating conditions is obtained, which is taken into account in the calculation of the current fresh air temperature after the intake valve closes in some embodiments.

[0061] The total heating T Air_Cyl of the fresh air at the cylinder wall, taking into account the dynamic change in the temperature of the cylinder wall, results from the addition of the determined heating T Air_Cyl_stationary of the fresh air assuming a constant temperature of the cylinder wall according to equation (5) and the dynamic correction of the heating T Air_Cyl_cor_dyn of the fresh air at the cylinder wall according to equation (6): T Luft_Zyl = T Luft_Zyl_stationär + T Luft_Zyl_kor_dyn or written out, that is, T Luft_Zyl_stationär replaced by equation (5) above: T Luft_Zyl = T Zyl_Wand − T Luft_h_EV ⋅ α w 3 + T Luft_h_EV + T Luft_Zyl_kor_dyn

[0062] In some embodiments, the method comprises determining a reference heating of the fresh air at a wall of the cylinder based on at least one reference parameter. The reference parameter may include, for example, reference temperatures of the intake, intake port, intake valve, and / or cylinder wall temperatures. The reference temperatures can be selected arbitrarily, and those skilled in the art will appreciate that they can select the temperatures accordingly depending on the embodiment.

[0063] In some embodiments, the reference heating of the fresh air at the wall of the cylinder is basically carried out on the basis of the same calculation rules as for the heating of the fresh air at the wall of the cylinder discussed above, in particular equations (1) to (5), with the only difference that the mentioned reference temperature(s) is (are) used.

[0064] Accordingly, in some embodiments, the following relationships are used to calculate the reference heating of the fresh air at the cylinder wall: Determining the reference heating of the fresh air at the intake port can be based on the following relationship: T Luft_v_EV_ref = T EK_ref − T Luft_Sgr_ref ⋅ α w 1 + T Luft_Sgr_ref , where T Luft_v_EV_ref represents the reference temperature increase of the fresh air at the intake port in front of the intake valve of the cylinder, T EK_ref represents the reference temperature of the intake port (and corresponds, for example, to the reference cooling water temperature), T Luft_Sgr_ref represents the reference temperature of the fresh air in an intake manifold to the intake port of the cylinder and α w1 represents an effective heat transfer coefficient of the intake port, as already discussed above (equation (3)).

[0065] Determining the reference heating of the fresh air at the cylinder’s intake valve can be based on the relationship: T Luft_h_EV_ref = T EV_ref − T Luft_v_EV_ref ⋅ α w 2 + T Luft_v_EV_ref where T Air_h_EV_ref represents the reference temperature increase of the fresh air at the intake valve of the cylinder, T Ev_ref represents the reference temperature of the intake valve (and corresponds, for example, to the reference cooling water temperature), T Air_v_EV_ref represents the reference temperature of the fresh air in the intake duct in front of the intake valve of the cylinder (and, for example, calculated according to equation (9)) and α w2 represents an effective heat transfer coefficient of the intake valve, as already discussed above (equation (4)).

[0066] In some embodiments, the determination of the reference heating of the fresh air at the wall of the cylinder is based on the relationship: T Luft _ Zyl _ ref = T Zyl _ Wand _ ref − T Luft _ h _ EV _ ref ⋅ α w 3 + T Luft _ h _ EV _ ref where T Air_Cyl_ref represents the reference temperature increase of the fresh air at the wall of the cylinder, T Cyl_Wall_ref is the reference temperature of the wall of the cylinder, T Air_h_EV_ref is the reference temperature of the fresh air after the inlet valve of the cylinder (e.g. calculated according to equation (10)) and α w3 represents an effective heat transfer coefficient of the wall of the cylinder, as already discussed above (equation (5)).

[0067] As mentioned, in some embodiments, the fresh air mass of the fresh air in the cylinder is calculated based on the determined heating of the fresh air mass and the determined reference heating, whereby the fresh air mass can be calculated particularly precisely.

[0068] The above calculations are based on the assumption that the internal combustion engine is in a stationary state and that stable temperature conditions prevail (i.e., for example, that the internal combustion engine is (stable) at an operating point), whereby, as explained above, the heating of the fresh air is corrected accordingly by the dynamic heating (see also equations (6) to (8) above).

[0069] The amount of fresh air or fresh air mass in the cylinder is determined on a test bench and stored as a map, whereby the map is multidimensional and depends on one or more of the following parameters: speed, intake manifold pressure, camshaft position at the inlet and exhaust, etc.

[0070] This fresh air quantity or fresh air mass determined on the test bench is then corrected based on the determined temperature (heating) of the fresh air at the cylinder wall (according to equation (7) or (8)) and the reference temperature (heating) of the fresh air at the cylinder wall (according to equation (11)).

[0071] According to the invention, a correction factor is determined: FAC T _ kor = T Luft _ Zyl _ ref / T Luft _ Zyl where the reference temperature (increase) T Air_Cyl_ref of the fresh air at the wall of the cylinder is calculated according to equation (11) and the temperature (increase) T Air_Cyl of the fresh air at the wall of the cylinder is calculated according to equation (7) or (8) and thus contains the correction for the dynamic temperature increase of the fresh air due to the dynamic temperature increase of the cylinder wall.

[0072] Then, a corrected fresh air quantity or fresh air mass "air mass kor " in the cylinder results as follows, where the correction for the dynamic temperature change of the fresh air according to equations (7) and (8) is included: Luftmasse kor = Luftmasse Kennfeld ⋅ FAC T _ kor where air mass map is the above-mentioned fresh air quantity or fresh air mass determined on the test bench and stored in the map and the correction factor FAC T_ kor is calculated according to equation (12).

[0073] This enables a very simple but precise correction of the fresh air quantity or fresh air mass, which is stored in the characteristic map, taking into account dynamic temperature increases of the cylinder wall and thus also of the fresh air, without the need for complex and time-consuming calculations to determine the fresh air quantity or fresh air mass.

[0074] The invention also relates to a control system for an internal combustion engine having at least one cylinder, an intake manifold, an intake manifold temperature sensor, an intake valve on the cylinder, and an intake port upstream of the intake valve, wherein the control system is configured to carry out the method described herein. The control system can be configured, for example, as an engine control unit and accordingly comprise typical elements of an engine control unit, such as one or more processors, a volatile and a non-volatile memory, an interface to a motor vehicle bus system, etc.

[0075] Some embodiments relate to a motor vehicle with such a control system and an internal combustion engine.

[0076] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates curves for the fresh air temperature increase; Fig. 2 schematically illustrates an embodiment of an internal combustion engine of a motor vehicle of the present invention; Fig. 3 schematically illustrates an embodiment of a control of the internal combustion engine of Fig. 1 and Fig. 4 schematically illustrates an embodiment of a method for calculating a fresh air mass according to the present invention.

[0077] An embodiment of an internal combustion engine 1 is shown in Fig. 2 schematically illustrated, wherein the internal combustion engine 1 is a gasoline engine and has four cylinders, wherein in Fig. 2 a sectional view of a cylinder 2 of the internal combustion engine 1 is illustrated.

[0078] The cylinder 2 has an intake valve 3, an exhaust valve 4 and a combustion chamber 5, which can be compressed by a cylinder piston 6, as is basically known, and a cylinder wall 2a. The cylinder wall 2a is the inner wall of the combustion chamber 5 and in the sectional view in Fig. 2 a left and a right side of the cylinder wall 2a is shown.

[0079] In combustion chamber 5, as in Fig. 2 As illustrated, during the intake phase there is typically fresh air 7 and residual gas 8 that remains in the combustion chamber 5 from a previous cycle.

[0080] The fresh air 7 is sucked in through an intake pipe 9 and passes through an inlet channel 10, which is arranged between the inlet valve 3 and the intake pipe 9, through which Fig. 2 opened inlet valve 3 into the combustion chamber 5.

[0081] After combustion, for example, the exhaust gas passes through the open exhaust valve 4 into an exhaust channel 11, as is generally known.

[0082] Cooling water 12 flows through corresponding cooling water channels, whereby in Fig. 2 , a cooling water passage 13a near the intake passage 10 and the intake valve 3, a cooling water passage 13b near the exhaust valve 4 and the exhaust passage 11 and a cooling water passage 13c and 13d near the left and right sides of the cylinder wall 2a, respectively.

[0083] Furthermore, a temperature sensor 14 is located in the intake manifold 9 shortly before the inlet channel 10 for detecting the temperature of the fresh air 7 in the intake manifold 9.

[0084] On its way into the cylinder 2, the fresh air 7 absorbs heat at various points and thereby heats up, which leads to an increase in temperature and a change in the density of the fresh air 7.

[0085] First, the fresh air 7 absorbs heat into the cylinder 2 at the location of the arrow 15a in the area of the intake port 10 in front of the intake valve 3. Then the intake valve 3 releases heat to the fresh air 7 (see arrow 15b) and finally the cylinder wall 2a releases heat to the fresh air 7 (see arrows 15c and 15d).

[0086] In this exemplary embodiment, the temperatures of the contact surfaces on the intake port 10 and the intake valve 3 are essentially determined by the cooling water temperature. This changes slowly over time (i.e., over several seconds) and, when the engine 1 is at operating temperature, typically ranges between 85 and 115 degrees Celsius.

[0087] In contrast, the temperatures of the cylinder interior surfaces (cylinder wall 2a, piston crown, etc.) can be strongly influenced by the heat input from the combustion process. The heat input from combustion can be highly dependent on load and engine speed, may not be present at all during overrun phases (cooling), and can change within just a few combustion cycles. Cylinder wall temperatures typically range between 320K and 530K in a warm engine.

[0088] Fig. 3 now shows a controller 20 which can execute a method 30 which is described further below in connection with Fig. 4 is explained in more detail.

[0089] The controller 20 is designed as an engine control unit for controlling the internal combustion engine 1 and has a processor 21, a working memory 22, a read-only memory (or other non-volatile memory) 23 and an interface 24 to a bus system of the motor vehicle (e.g. CAN bus or the like), via which it is connected to the internal combustion engine 1 and the temperature sensor 14, so that it can receive data both from the internal combustion engine 1 or data relevant to it (e.g. speed, oil temperature, cooling water temperature, camshaft position, etc.) and from the temperature sensor 14.

[0090] In the read-only memory 23, for example, data such as characteristic maps, characteristic curves and the like are stored, as well as a program which contains commands so that the controller 20 is able to execute the method 30.

[0091] Fig. 4illustrates a flow chart of the method 30 for calculating a fresh air mass in the cylinder 2 of the internal combustion engine 1. The method 30 is typically carried out at an operating point of the internal combustion engine 1 and for each cylinder of the internal combustion engine 1 in the cycle of the internal combustion engine, so that the associated fresh air mass is available for the respective injection in the cylinder.

[0092] To this end, at 31, assuming a steady-state operating state of the internal combustion engine 1, the heating of the fresh air at the intake port 10 is first determined using equation (3) above at the corresponding current operating point of the internal combustion engine (e.g., based on the engine speed, cooling water temperature, oil temperature, camshaft position, etc.). To this end, the controller 20 determines the effective heat transfer coefficient for the intake port based on the characteristic map α w1 stored in the read-only memory 23, or determines the effective heat transfer coefficient for the current operating point of the internal combustion engine 1 based on the characteristic map.In addition, the controller 20 determines the current temperature T EK of the intake duct 10 based on the temperature of the cooling water 12 and determines the temperature T Luft_Sgr of the fresh air 7 in the intake manifold 9 based on corresponding temperature data which the controller 20 receives from the temperature sensor 14, so that the current temperature of the fresh air 7 in the intake manifold 9 can be determined.

[0093] Thus, the controller at 31 obtains the current temperature T Luft_v_EV of the fresh air 7 by means of equation (3) after it has been heated in the inlet channel 9 and before it is further heated by the inlet valve 3.

[0094] In the next step 32, the controller 20 determines the heating of the fresh air at the intake valve 3 of cylinder 2 based on equation (4). To do this, the controller (20) takes the current temperature T air_v_EV upstream of the intake valve 3, as determined in step 31, determines the current temperature T EV of the intake valve based on the cooling water temperature, and determines the effective heat transfer coefficient for the intake valve 3 based on the characteristic map α w2 , which is stored in the read-only memory 23, based on the current operating point of the internal combustion engine 1.

[0095] Thus, the control at 32 receives the current temperature T air_h_EV of the fresh air 7 by means of equation (4) after it has been heated by the inlet valve 3 and with which it flows into the combustion chamber 5.

[0096] Finally, in step 33, the method 30 determines the heating of the fresh air 7 by the cylinder wall 2a on the basis of equation (5), assuming a steady-state operating state. To do this, the controller 20 takes the current temperature T Air_h_EV of the fresh air 7 after it has been heated by the intake valve 3 and as determined in step 32. In addition, the controller 20 determines the current effective heat transfer coefficient for the cylinder wall 2a (i.e., the wall section of the combustion chamber 5) with which the fresh air 7 comes into contact, based on the current operating point of the internal combustion engine 1 and on the basis of the characteristic map α w3 , which is stored in the read-only memory 23. As explained above, the temperature T Cyl_Wall of the cylinder wall is determined based on a characteristic map that is also stored in the read-only memory 23.

[0097] As a result, the controller 20 receives at 33 the current (stationary) temperature T Air_Cyl_stationary of the fresh air 7 after it has been heated by the cylinder wall 2a.

[0098] In step 34, the current temperature T Air_Cyl_stationary is filtered by two PT1 filters, so that a temperature T Air_Cyl_PT1 is obtained, which has a curve 102, as in Fig. 1 is illustrated.

[0099] In step 35, the controller 20 determines the correction factor T Luft_Zyl_kor_dyn according to equation (6), which takes into account the dynamic temperature change of the fresh air, by multiplying the current and filtered temperature T Luft_Zyl_PT1 , which it determined in step 34, by an effective and dynamic heat transfer coefficient, which it determines using a corresponding characteristic map based on the amount of incoming fresh air and the speed of the internal combustion engine 1, which is stored in the read-only memory 23.

[0100] In step 36, the controller 20 determines the current temperature T Air_Cyl according to equation (7) or (8) by adding the correction factor T Air_Cyl_kor_dyn (step 35) to the current temperature T Air_Cyl_stationary (step 33).

[0101] In step 37, the controller 20 determines a current reference heating of the fresh air at reference temperatures of the intake, intake port, intake valve, and cylinder wall temperatures stored in the read-only memory 23 according to equation (9), wherein the calculation is performed at the current operating point of the internal combustion engine 1. The controller 20 thus determines a reference temperature for the temperature T EK_ref of the intake port either based on a stored temperature value or based on a reference temperature of the cooling water. The same applies to the temperature of the fresh air 7 in the intake manifold 9 T Luft_Sgr_ref , for which a stored reference temperature is used. The associated effective heat transfer coefficient is determined analogously to step 31.

[0102] The controller 20 thus receives a reference temperature T Luft_v_EV_ref of the fresh air 7 at 37 after it has been heated by the inlet duct 10 under reference conditions.

[0103] In step 38, the controller 20 determines a current reference heating of the fresh air at intake valve 3 of cylinder 2 according to equation (10). For this purpose, a reference temperature T EV_ref of the intake valve is determined, which is stored, for example, in read-only memory 23 or corresponds to the reference cooling water temperature, and the reference temperature T Luft_v_EV_ref determined in step 37 is used. The determination of the corresponding effective heat transfer coefficient for the heat transfer at the intake valve occurs analogously to step 32.

[0104] The controller 20 thus receives a reference temperature T Luft_h_EV_ref of the fresh air 7 at 38 after it has been heated by the inlet valve 3 under reference conditions.

[0105] In step 39, the controller 20 determines a current reference heating of the fresh air at the cylinder wall 2a of the cylinder according to equation (11). For this purpose, a reference temperature T Cyl_Wall_ref of the cylinder wall is determined, which can either be stored or model-based (or can also be based on the cooling water temperature and can take into account a mass flow of the cooling water), and the reference temperature T Air_h_EV_ref of the fresh air 7 determined in step 35 is taken after it has been heated by the intake valve 2. The associated effective heat transfer coefficient for the transfer of heat from the cylinder wall 2a to the fresh air 7 is determined analogously to step 33.

[0106] Thus, the control 20 receives at 39 the temperature T Air_Cyl_ref of the fresh air 7 after it has been heated by the cylinder wall 2a.

[0107] At 40, the controller 20 now determines the correction factor FAC T_kor for the fresh air mass of the fresh air 7 in the combustion chamber 5 according to equation (12) by calculating the ratio of the current reference temperature (equation (11)) of the fresh air 7 at the current operating point of the internal combustion engine 1 and the corresponding current temperature (equation (7) or (8)) according to T Luft_Zyl_ref / T Luft_Zyl.

[0108] At 41, the controller 20 now determines the current fresh air mass air mass kor according to equation (13) at the current operating point of the internal combustion engine 1 by determining a fresh air mass air mass map, which was determined on a test bench, from a map stored in the read-only memory 23, and multiplying this fresh air mass by the correction factor FAC T_kor , which was determined in step 40.

[0109] Thus, in step 41, the controller 20 receives the corrected fresh air mass air mass kor , which (also) takes into account the dynamic heating of the intake fresh air 7 by the cylinder wall 2a. List of reference symbols

[0110] 1 Internal combustion engine 2 Cylinder 2a Cylinder wall 3 Intake valve 4 Exhaust valve 5 Combustion chamber 6 Cylinder piston 7 Fresh air 8 Residual gas 9 Intake manifold 10 Intake port 11 Exhaust port 12 Cooling water 13a-d Cooling water channels 14 Temperature sensor 15a-c Arrows (heat absorption) 20 Control system 21 Processor 22 RAM 23 Read-only memory 24 Interface 30 Method for calculating a fresh air mass in a cylinder 31 Determining a heating of the fresh air in the intake port to the cylinder 32 Determining heating at the intake valve 33 Determining heating at the cylinder wall (stationary) 34 Filter of the stationary heating of the cylinder wall 35 Determining correction factor for dynamic temperature increase 36 Determining heating of the fresh air including consideration of dynamic temperature increase 37 Determining reference heating of the fresh air in the intake port to Cylinder 38Determine reference heating at the intake valve 39Determine reference heating at the cylinder wall 40Determine correction factor 41Determine correctedFresh air mass 100Temperature curve of the fresh air assuming a constant cylinder wall temperature 101Theoretical temperature curve of the fresh air 102Temperature curve of the fresh air using two PT1 filters

Claims

1. Computer-implemented method for calculating a fresh air mass in a cylinder (2) of an internal combustion engine (1), comprising: determining (36) heating of the fresh air (7) on a wall (2a) of the cylinder (2), wherein the temperature of the wall (2a) of the cylinder changes dynamically, wherein the heating of the fresh air (7) is determined assuming a constant temperature of the wall (2a) of the cylinder, wherein the determined heating of the fresh air (7), assuming a constant temperature of the wall (2a) of the cylinder, is filtered by means of a filter in order to determine a dynamic correction of the heating of the fresh air (7) on the wall (2a) of the cylinder, wherein the filter has two PT1 filters connected in series; determining (39) reference heating of the fresh air (7) on the wall (2a) of the cylinder (2) based on at least one reference parameter; and calculating (41) the fresh air mass of the fresh air (7) in the cylinder (2) based on the determined heating of the fresh air mass and the determined reference heating as follows: Air mass corr = air mass family of characteristics ⋅ T air _ cyl _ ref / T air _ cyl , where Tair_cyl is the increase in temperature of the fresh air (7), Tair_cyl_ref is the reference increase in temperature and air massfamily of characteristics is a fresh air mass determined on a test bench and stored in a family of characteristics.

2. Computer- implemented method according to Claim 1, wherein the filter is determined empirically.

3. Computer-implemented method according to Claim 1 or 2, wherein the filter depends on at least one parameter characteristic of the temperature of the wall (2a) of the cylinder (2).

4. Computer-implemented method according to Claim 3, wherein the parameter represents an amount of heat introduced during combustion, a speed of the internal combustion engine and / or a heat transfer of cooling water to the wall (2a) of the cylinder (2).

5. Computer-implemented method according to one of Claims 1 to 4, wherein the filtered heating is multiplied by an effective and dynamic heat transfer coefficient.

6. Computer-implemented method according to Claim 5, wherein the effective and dynamic heat transfer coefficient depends on a speed of the internal combustion engine and / or an intake manifold pressure.

7. Computer-implemented method according to Claim 6, wherein the effective and dynamic heat transfer coefficient is determined empirically.

8. Computer-implemented method according to one of Claims 1 to 7, wherein the determination (36) of the heating of the fresh air (7) on the wall (2a) of the cylinder (2), wherein the temperature of the wall (2a) of the cylinder changes dynamically, comprises the addition of the determined heating of the fresh air (7) assuming a constant temperature of the wall (2a) of the cylinder and the dynamic correction of the heating of the fresh air (7) on the wall (2a) of the cylinder.

9. Controller for an internal combustion engine (1) which has at least one cylinder (2), an intake manifold (9), an intake manifold temperature sensor (14), an inlet valve (3) on the cylinder (2) and an inlet channel (10) upstream of the inlet valve (3), wherein the controller (20) is configured to carry out the method according to one of the preceding claims.