Determine the fresh air mass in the cylinder in real time

Abstract

The present invention relates to a method for determining a characteristic variable of the fresh air mass in a cylinder of an internal combustion engine in a motor vehicle, the method comprising the following steps: identifying a cylinder which is at the end of an intake stroke or at the beginning of a compression stroke during driving operation of the motor vehicle, determining a diagnostic time window which extends within a torque gap of the internal combustion engine after closing of an intake valve of the identified cylinder, determining a speed change of the internal combustion engine during the diagnostic time window, and determining the characteristic variable of the fresh air mass in the identified cylinder.

Description

Technical Field

[0001] The invention relates to a method and a control device for determining a characteristic variable of a fresh air mass in a cylinder of an internal combustion engine, and to an internal combustion engine having such a control device. Background Art

[0002] Knowledge of the fresh air mass in the combustion chamber of an internal combustion engine is of central importance for regulating operating processes. The air quantity influences the achievable pressure curve, torque output (load), raw emissions, and therefore directly affects other control parameters such as fuel mixture, ignition timing, etc.

[0003] In addition, the possibilities for proactive maintenance of internal combustion engines ("predictive maintenance", also called "health functions") are becoming increasingly important. These possibilities are intended to quantify the current performance status—and therefore the maintenance need—particularly with respect to the required maintenance scope and with respect to a favorable timeline.

[0004] A prerequisite for consistent and consistent engine operation is the correct metering of the injected fuel quantity in every operating state of the internal combustion engine. The amount of fuel that must be injected to achieve the desired combustion ratio depends primarily on the fresh air mass available in the combustion chamber of the cylinder for ignition, which in turn determines the oxygen mass available for combustion.

[0005] For steady-state operation, the air mass can be measured well, for example with the aid of a flap mechanism or a hot-film air mass meter.

[0006] However, in the transient, i.e. non-steady-state, process range of the engine, quantitative measurement of the air mass is difficult because, in particular in the case of load changes, on the one hand the sensor is too far away from the event (the sensor is in the intake section, but the air volume efficiency (Luftfanggrad) must be stated in the combustion chamber), and on the other hand, due to its thermal measurement principle, the sensor has a certain physical time constant until it provides reliable values ​​(vibration characteristics, adjustment characteristics, etc.).

[0007] Precisely in the transient operating range, an inaccurate calculation of the air mass in the cylinder can lead to increased emissions and, in extreme cases, to uneven engine operation and / or combustion misfires. Summary of the Invention

[0008] Against this background, the object of the present invention is to improve the determination of a characteristic variable of the fresh air mass in a cylinder of an internal combustion engine.

[0009] To this end, the present invention proposes a method for determining a characteristic variable of the fresh air mass in a cylinder of an internal combustion engine in a motor vehicle, the method comprising the following steps:

[0010] - identifying the cylinder which is at the end of the intake stroke or at the beginning of the compression stroke during driving operation of the motor vehicle,

[0011] - determining a diagnostic time window which extends within the torque gap of the internal combustion engine after closing of the intake valve of the identified cylinder,

[0012] - determining at least two values ​​of the crankshaft speed of the internal combustion engine during the diagnostic time window,

[0013] It is characterized by having the following steps:

[0014] - determining a cylinder load characteristic variable in the identified cylinder as a function of at least two values ​​of the determined crankshaft speed,

[0015] - determining a characteristic variable of the fresh air mass in the identified cylinder as a function of the determined characteristic variable of the cylinder load, and

[0016] In this case, the fresh air mass characteristic variable determined for a specific working cycle of the identified cylinder is used as a basis for determining the fuel injection quantity for the following working cycle of this cylinder or of a subsequently fired cylinder.

[0017] The present invention further proposes a control device for determining a characteristic variable of the fresh air mass in a cylinder of an internal combustion engine, the control device being designed to:

[0018] The value of the fresh air quality characteristic variable determined by means of the method according to the invention and / or stored in the memory is transmitted to

[0019] - a control unit of the control device for regulating the functions of the internal combustion engine in real time according to the transmitted values, and / or

[0020] - The diagnostic component of the control unit is used for additional on-board diagnostic functions.

[0021] The present invention further provides an internal combustion engine having one or more cylinders, wherein the internal combustion engine has a control device according to the present invention.

[0022] According to one aspect, a method for determining a (particularly relative) fresh air mass characteristic variable in a cylinder of an internal combustion engine in a motor vehicle is disclosed, the method comprising—in the order indicated or another order reasonable to a person skilled in the art—at least one, several or all of the following method steps:

[0023] (i) Identifying a cylinder that is at the end of an intake stroke or the beginning of a compression stroke during driving operation of the motor vehicle. This cylinder(s) can be identified, in particular, by reading out existing information from an operating model (in particular, an engine control unit). An intake stroke is to be understood, in particular, as the stroke of a cylinder during which the subsequent combustion takes place and the filling with fresh air is completed.

[0024] (ii) determining a diagnostic time window, which extends within the torque gap of the internal combustion engine (in particular of one of the strokes) after the closing of the intake valve of the identified cylinder. The diagnostic time window is to be understood in particular as a continuous time period that is part of the compression stroke in the internal combustion engine (for example, one of the strokes of the four-stroke combustion in a four-stroke engine). The diagnostic instant is to be understood in particular as the instant within the diagnostic time window for which one, several or all deterministic variables of the target variable to be determined are determined. In the present case, the torque gap is to be understood in particular as the crankshaft angle range within which the observed cylinder and / or several other cylinders or all other cylinders of the engine do not make a contribution to the propulsion torque that is relevant in this context.

[0025] (iii) Determining the speed change of the internal combustion engine during the diagnostic time window, in particular with real-time sampling quality. Speed ​​change is to be understood as particularly how the speed of the crankshaft of the internal combustion engine changes during the diagnostic time window. For this purpose, speed values ​​with a high sampling frequency (e.g., in the range of one millisecond (ms) or faster) between temporally adjacent values ​​can be used.

[0026] (iv) determining a simplified cylinder load characteristic variable in the identified cylinder based on the determined speed change.

[0027] (v) According to one specific embodiment, a characteristic variable of the fresh air mass in the identified cylinder is determined as a function of the determined simplified characteristic variable of the cylinder load.

[0028] The present invention enables a rapid adjustment of the required fuel injection quantity within a few working cycles or even within one working cycle, even when the operating state of the internal combustion engine is transient (ie non-steady state).

[0029] Thus, even in transient operating states of the internal combustion engine, a suitable fuel injection quantity can be determined and injected with high pilot control quality for the next working cycle of the diagnosed cylinder. In steady-state operating states, this is also readily possible with conventional methods for determining characteristic fresh air mass variables, since the amount of fuel to be injected generally does not change or changes only slightly from one working cycle to the next.

[0030] Since the determination method starts from high-resolution rotational speed measurements that can always be evaluated in the same way, the method is easier to apply than known models and / or can be better reused across different application cases.

[0031] According to another aspect, a control device for determining a characteristic variable of the (in particular relative) fresh air mass in a cylinder of an internal combustion engine is disclosed, the control device being designed in particular in an engine control unit of an internal combustion engine of a passenger vehicle and / or as part of an engine control unit of an internal combustion engine of a passenger vehicle. The control device is designed to transmit a value of the characteristic variable of the fresh air mass determined in particular by a method according to an embodiment of the invention and / or stored in a memory to a

[0032] (a) a control unit of a control device for regulating the function of the internal combustion engine in real time according to the value of the transmitted fresh air quality characteristic variable, and / or

[0033] (b) The diagnostic component of the control unit is used for additional on-board diagnostic functions.

[0034] According to one embodiment, the control device has a control component which is designed to determine and in particular inject a fuel injection quantity for a specific working cycle of the cylinder based on the value of a fresh air mass characteristic variable of a previous, in particular last working cycle of the identified cylinder or of the immediately preceding, in particular last diagnosed cylinder.

[0035] In particular, (I) either a specific cylinder can be evaluated at all times and its previously determined air mass can then be used in a new working cycle to determine the fresh air mass characteristic variable, or (II) the cylinders can be evaluated with respect to their air mass and the value of the fresh air mass characteristic variable determined here and / or last can be transferred to the next ignited cylinder for its pilot control. The latter option (II) can be particularly advantageous for rapid transient changes, so that only a short time interval exists between two known values ​​of the fresh air mass characteristic variable.

[0036] According to one specific embodiment, the control device has a non-volatile memory and is designed to store one or more values, in particular determined values, of the fresh air quality characteristic variable at one or different diagnosis times in the memory.

[0037] According to one specific embodiment, the control device is designed to transmit the value of the fresh air quality characteristic variable stored in the memory to an off-board computer for an offline diagnostic function.

[0038] According to another aspect, an internal combustion engine having one or more cylinders is disclosed, the internal combustion engine having a control device according to an embodiment of the present invention.

[0039] The present invention is based in particular on the consideration that known methods for determining the fresh air mass (=load) in the cylinders are generally sufficient for steady-state operating situations.

[0040] The present invention is also based, inter alia, on the consideration that the air mass in the combustion chamber cannot be directly determined because geometrical constraints and operational cost restrictions prohibit the installation of sensors. Conventionally, measurement methods are used that either measure the mass flow remotely from the event point in the cylinder (e.g., hot-film air mass meters in the intake manifold) or estimate the captured air mass based on pressure and in a model-assisted manner. The problem with existing methods is that they are either too insensitive, not directly observing the influence of the air volumetric efficiency on the combustion chamber, or require the use of expensive sensor systems.

[0041] The present invention is also based in particular on the consideration that known calculation models for steady-state and transient operating situations are often very complex, while during transient operating states they produce the result that the desired fuel quantity can be injected based on a sufficiently accurate fresh air mass.

[0042] The present invention is based, inter alia, on the idea of ​​using the crankshaft speed, detected with high resolution, as the basis for determining the fresh air mass in the cylinder. This speed—at least in the compressed crankshaft angle range—is directly influenced by filling (and friction). Therefore, interpreting the speed as a filling function has proven to be a feasible approach.

[0043] The present invention is also based, inter alia, on the idea of ​​creating a "physical" operating model with only a few variable parameters, which is real-time-capable and nevertheless enables a sufficiently accurate determination of the fresh air mass present in the cylinder. This is achieved precisely by using the rotational speed, whose slight changes in the compression range are significantly more influenced by the amount of oxygen in the cylinder than by other variables.

[0044] The present invention is also based in particular on the idea that, in addition to solving control tasks requiring air mass during operation of an internal combustion engine, time-filtered characteristic values ​​can also be generated which illustrate the long-term behavior of the engine and are suitable for diagnostic purposes.

[0045] According to one embodiment, the load variable is modeled using thermodynamic relationships and graphical simplifications (particularly by removing weakly influential edges in the graphical modeling) for real-time calculation. According to one embodiment, the diagnostic cylinder pressure in the cylinder is determined by determining the pressure signal in the cylinder from a high-resolution rotational speed signal. According to one embodiment, the pressure signal is determined within a diagnostic time window, which for the diagnosed cylinder lies within the compression phase after the end of the intake phase.

[0046] The diagnostic time window is selected, in particular, under the following conditions: (a) the diagnostic time window begins as early as possible after intake valve closure, so that the entire cylinder charge is captured in the combustion chamber; and (b) the diagnostic time window is performed at a point where no significant torque contribution from the firing cylinder is expected. The angular range of the diagnostic time window is, for example, 30°KW-40°KW.

[0047] According to one specific embodiment, a load value (=characteristic variable of the fresh air mass) is calculated for the calculated cylinders during the calculated working cycle. The calculated load value is carried over to the next working cycle. The pilot control of the injector quantity may also include inputs that exceed the statically calculated load value (from the previous working cycle) according to the present invention and, if necessary, also include inputs that exceed the transient predicted load value according to the present invention.

[0048] In the context of the present invention, real-time capability means, in particular, that the fuel injection of the next working cycle or the next working cycle can be controlled with sufficient accuracy using the measured and calculated values ​​of a specific working cycle.

[0049] According to one embodiment, in order to determine a simplified cylinder load characteristic variable, in addition to the speed change, the following variable variables are determined: (1) the cylinder volume at the diagnostic time, which diagnostic time is particularly centered within the diagnostic time window, and / or (2) the simplified piston acceleration in the diagnostic time window, and / or (3) the pressure in the intake manifold in the diagnostic time window.

[0050] Due to the use of only a few variable influencing variables and the associated uncomplicated model calculations, a fresh air mass characteristic variable can be quickly determined based on a simplified cylinder load characteristic variable. Due to the reduced computational effort in the control device, the required computation speed can be achieved in order to determine the fresh air mass characteristic variable with an acceptable loss of accuracy within one working cycle and, therefore, to be able to directly control the required fuel quantity for the next working cycle even during transient operation. According to one embodiment, only constants are used to determine the simplified cylinder load characteristic variable, which constants are in particular stored in the control device and / or determined by means of the following working steps on a research engine: (I) Measuring the complete characteristic curve family (speed / load). (II) Evaluating the cylinder pressure indications and calculating the residual gas fraction and temperature by means of a gas exchange analysis. (III) Calculating the corresponding characteristic values ​​from these results and storing them via the average engine speed (characteristic curve).

[0051] The speed required for simplified model calculations is achieved by carefully filling in the corresponding characteristic diagrams, etc., during the development of the internal combustion engine, and by providing constants generated by the markers for calculating the simplified cylinder load characteristic variables. Filling in the characteristic diagrams can also help to reconcile conflicts between calculation speed, resource utilization, and result accuracy.

[0052] According to one specific embodiment, a pressure characteristic number of the identified cylinder within a diagnosis time window is determined based on the determined speed change and / or the determined simplified piston acceleration. According to one specific embodiment, a simplified cylinder load characteristic variable is determined based on the determined pressure characteristic number and / or the determined cylinder volume.

[0053] By determining the pressure characteristic variable, whose direct dependence can be used to determine the simplified cylinder load characteristic variable, the speed change provided in the controller in a high-resolution manner can be used and thus the fuel injection quantity can be regulated or pre-controlled in real time from working cycle to working cycle even during transient operation of the internal combustion engine.

[0054] According to one specific embodiment, before the further method steps, it is determined whether the internal combustion engine is in at least approximately steady-state operation or in transient operation.

[0055] According to one specific embodiment, the method is performed only when and / or as long as transient operation of the internal combustion engine (in particular, non-steady-state operation) is determined. According to one specific embodiment, the determined residual gas fraction is stored and / or further used only when and / or as long as transient operation of the internal combustion engine (in particular, non-steady-state operation) is determined.

[0056] This saves computing resources of the control unit, since it can be decided whether the method according to the present invention is necessary in the current operating state. This is because, for steady-state operation, modern, known engine control units of internal combustion engines already have sufficient means for determining the fresh air mass in the cylinders.

[0057] According to one specific embodiment, the fresh air mass characteristic variable in the identified cylinder is determined solely on the basis of the determined simplified cylinder load characteristic variable, or additionally on the basis of a steady-state cylinder load characteristic variable determined for steady-state operation and / or a prediction of an offset of the fresh air mass characteristic variable that is dependent on the steady-state cylinder load characteristic variable, in particular the steady-state cylinder load characteristic variable. According to one specific embodiment, a superposition region can also be provided in which the fresh air mass characteristic variable is determined, for example, from values ​​of the simplified cylinder load characteristic variable, the steady-state cylinder load characteristic variable, and, if appropriate, the predicted offset of the fresh air mass characteristic variable in a weighted manner and / or by averaging.

[0058] Depending on the operating state of the internal combustion engine - in particular the transient degree of engine operation - it may be sufficient to control the amount of fuel to be injected purely on the basis of a determined, simplified cylinder load characteristic variable; or the injection quantity may already be pre-controlled on the basis of known methods for determining the amount of fresh air in the cylinder in steady-state operation or for predicting an offset based on such a value.

[0059] According to one specific embodiment, the fresh air mass characteristic variable determined for a specific working cycle of the identified cylinder is used as a basis for determining a fuel injection quantity for a subsequent working cycle of the cylinder or of a subsequently fired cylinder.

[0060] This ensures that the fuel injection quantity required for combustion in the diagnosed cylinder can be provided with high cycle accuracy and control quality both in transient and steady-state operation of the internal combustion engine—in other words, in an efficient and resource-optimized manner with regard to calculation in the engine control unit.

[0061] According to one embodiment, the speed change is determined with a sampling quality that can be acquired in real time. This basis firstly makes it possible to calculate the fresh air mass present in the cylinder accurately during transient operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Further advantages and possible applications of the invention will be apparent from the following description in conjunction with the accompanying drawings.

[0063] Figures 1a-1cA schematic diagram shows an internal combustion engine with an engine control system according to an exemplary embodiment of the present invention, wherein Figure 1a The installation environment of the internal combustion engine is shown in Figure 1b The relevant parameters are shown in Figure 1c The torque contribution to the crankshaft drive of the internal combustion engine is shown in FIG.

[0064] Figure 2 Show that there is a basis Figures 1a-1c A diagram of the speed variation of an internal combustion engine during a working cycle and a diagram of the stroke of each cylinder.

[0065] Figure 3 Show the basis Figure 2 Zoomed in detail of the chart.

[0066] Figure 4 A diagram showing the mass balance in a selected cylinder.

[0067] Figures 5a-5f A process is described for reducing the complex relationship between residual gas mass and temperature in the cylinder to a simple formula that enables real-time calculation on an engine controller.

[0068] Figure 6 An exemplary embodiment of the method according to the invention for determining a characteristic variable of the fresh air mass in a cylinder of an internal combustion engine during driving operation using the crankshaft speed of a crankshaft drive is shown. DETAILED DESCRIPTION

[0069] Figure 1b An internal combustion engine 1 is shown in a more detailed schematic diagram. Internal combustion engine 1 has cylinders Z1, Z2, Z3, and Z4, all of which provide their torque contribution M at the crankshaft of crankshaft drive KT. In addition, internal combustion engine 1 has a control device 2 according to an exemplary embodiment of the present invention, which optionally includes a calculation unit 4 if it is not formed as part of an engine control unit. Control device 2 also includes a speed detection unit 6 and a cylinder pressure determination unit 7 for determining a reference pressure from the surroundings and the air collector or crankcase. Control device 2 also includes a cylinder volume determination unit and a cylinder temperature determination unit and can acquire the measured values ​​of all lambda probes of internal combustion engine 1.

[0070] from Figure 1b In particular, it is found that each cylinder Z can periodically exert a torque contribution M on the crankshaft drive KT depending on the respective cylinder pressure p. The sum of the torque contributions results in a temporally varying rotational speed n of the crankshaft of the crankshaft drive KT.

[0071] The device 2 can use the reference pressure p by means of the pressure detection unit 7 , the instantaneous rotational speed n by means of the rotational speed detection unit 6 , and the computing unit 4 .

[0072] Figure 1c The torque variation M is shown in ges , which shows an exemplary torque curve 10 at a crankshaft drive KT over a crankshaft angle KT during normal operation. It can be seen that the torque contribution M comes alternately from different cylinders Z. A torque limit value 14 is drawn in the diagram, which is particularly arbitrarily determined and determines the torque below which the torque contribution of a cylinder is considered insignificant, resulting in a torque gap 12 within the meaning of the present invention. Thus, a torque gap 12 within the meaning of the present invention can be detected when the torque contribution of each cylinder falls below the limit value 14 for a specific time interval.

[0073] exist Figure 1c In the diagram of , slightly different lengths of torque gaps 12 are produced. Within these torque gaps 12 , in particular, a diagnosis time window 112 can be determined in each case, which can include the entire time period of the torque gap or a portion of the torque gap.

[0074] exist Figure 2 A sketch of an exemplary diagram 150 of the speed profile 101 for a four-stroke cycle (=working cycle (ASP): top dead center breathing (LOT)→intake→bottom dead center (UT)→valve closing and compression→top dead center ignition (ZOT)→expansion→UT→exhaust) of an internal combustion engine 1 is shown.

[0075] Process diagram 150 shows a curve 101 of the engine speed n over a working cycle (ASP) of a four-cylinder gasoline engine. The ignition timing (ZZP) and an exemplary possible diagnostic time window 112 in the compression phase of the cylinder Z1 to be diagnosed are marked. The associated working strokes of the physical cylinders Z1-Z4 are shown below the diagram.

[0076] This four-cylinder embodiment illustrates which range 112 of the crankshaft angle scale can be used for gas exchange diagnosis. The diagnosis time window 112 of the cylinder Z1 to be diagnosed is in the compression phase, ie when the intake phase has ended and there is still a torque gap (cf. Figure 1c When the limit value in 14) is reached.

[0077] In particular, the diagnostic time window 112 must be selected such that the last active cylinder no longer accelerates the crankshaft and the next active cylinder has not yet ignited.

[0078] In the exemplary embodiment, the diagnostic time window includes the time interval during which the intake valve of the cylinder Z1 to be diagnosed is closed again after the charge air or combustion mixture has entered, and during which a torque gap in the internal combustion engine 1 still exists. These limits depend on the prevailing engine operating point and can be flexibly adapted thereto. For dynamic driving operation, the limits of the diagnostic time window 112 can also be dynamically adapted depending on boundary conditions (such as the ignition angle and the cylinder pressure curve).

[0079] Therefore, in the exemplary embodiment, the diagnosis time window 112 is determined to be 660° KW to 690° KW in relation to the crankshaft angle specification of the cylinder Z1. Figure 1c and Figure 2 In the diagram of , which relates to an entire internal combustion engine with four cylinders, this crankshaft angle value corresponds to -60° to -30° before top dead center (ZOT) of ignition. In the following, only 660°KW to 690°KW will be mentioned.

[0080] exist Figure 3 Shown in Figure 2 Detail X in , ie the speed change 101 of cylinder Z1 over crankshaft angle KW during a diagnosis time window 112 with limit points P1 and P2. In this cylinder, pressure p1 prevails at point P1 and pressure p2 prevails at point P2.

[0081] In the diagnosis time window 112 , a diagnosis time 113 is determined, for example, at the center of the diagnosis time window of 675° kW. At this time, for example, the temperature T in the combustion chamber of the cylinder Z1 is calculated. * In order to determine the diagnostic cylinder pressure p according to the speed change 101 diag A time window such as the diagnostic time window 112 is required because the diagnostic cylinder pressure is determined based on observed differences.

[0082] Figures 2 to 6 An exemplary embodiment of the method according to the invention for determining a characteristic variable rf of the fresh air mass in a cylinder Z of an internal combustion engine 1 during driving operation using a crankshaft speed n of a crankshaft drive KT is explained.

[0083] As in Figure 6 As shown in FIG, the method carried out in the embodiment is described as follows:

[0084] S10 : It is determined whether the internal combustion engine 1 is in at least approximately steady-state operation SB or transient operation TB.

[0085] S20 : ​​When the internal combustion engine transient operation TB is present, the cylinder Z1 is identified as being at the end of the intake stroke or the beginning of the compression stroke.

[0086] S30 : Determine the diagnosis time window 112 of the identified cylinder Z1 in the torque gap 12 of the internal combustion engine 1 .

[0087] S40: Determine the speed change 101 of the internal combustion engine during the determined diagnosis time window 112 with a sampling quality that can be real-time. The live engine control function continuously reads the speed value n of the crankshaft KT during driving (due to the deceleration due to gas friction (and the deceleration due to mechanical friction, which is neglected for the present purpose) it is to be expected that the speed drop from one moment to the next during the compression phase of the cylinder is increasing) and determines the speed change from this - see Figures 1a-1c to Figure 3 .

[0088] S50: Determine the pressure characteristic number of cylinder Z1 in the diagnosis time window 112 based on the determined speed change 101

[0089] S60: Based on the pressure characteristic number determined in the diagnosis time window 112 of the cylinder Z1 Determine the simplified cylinder load characteristic parameter rf * .

[0090] S70: Based on the determined simplified cylinder load characteristic parameter rf * In the exemplary embodiment, the steady-state cylinder load characteristic variable r is additionally determined in a manner known per se for steady-state operation by means of the engine control unit. fSB And / or predict rf based on the offset of the fresh air quality characteristic parameter derived therefrom OFFSET (See step S160 for steady-state operation SB) A fresh gas mass characteristic variable rf is determined for transient operation TB in the identified cylinder Z1. Depending on the operating state of the internal combustion engine—in particular, the degree of transient engine operation—it may be sufficient to control the injected fuel quantity purely on the basis of the determined, simplified cylinder load characteristic variable; or the injection quantity may already be pre-controlled based on known methods for determining the fresh air quantity in the cylinder during steady-state operation or methods for predicting an offset based on such values.

[0091] S160: Determine the steady-state cylinder load characteristic variable rf in a manner known per se by means of the engine controller SB and / or determining the offset prediction rf of the fresh air quality characteristic parameter derived therefrom OFFSET If a transient mode TB is present, this step can also be carried out to support the pilot control of the fuel injection quantity, with reference to the determination of the input variables for the fresh air mass characteristic variable rf according to step S70 .

[0092] S170: Based on the steady-state cylinder load characteristic variable r determined (in a manner known per se) for steady-state operation by means of the engine controller fSB And / or the offset prediction rf of the fresh air quality characteristic parameter derived therefrom OFFSET The fresh air mass characteristic variable rf is determined for the steady-state operation SB in the identified cylinder Z1. The simplified cylinder load characteristic variable rf is not taken into account for the steady-state operation SB. * .

[0093] In the exemplary embodiment, different possibilities are provided for using the value of the fresh air mass characteristic variable rf determined by means of the engine control unit 2 for the on-board diagnostics 204 and / or the off-board diagnostics 208 and / or the control task 206 (see Figure 6 ).

[0094] For this purpose, the determined values ​​are continuously stored during driving operation in non-volatile memory 202 of engine control unit 2, or stored for further use. For example, if an associated value of the fresh air mass characteristic variable rf is evaluated for each cylinder Z at each ignition, a new value of the fresh air mass characteristic variable rf is stored in memory 202 at each ignition—in particular, with a time stamp and / or an output value for determining and / or specifying the diagnosed cylinder (e.g., Z1).

[0095] The stored value of the characteristic variable of fresh air quality rf can be provided, for example, in real time, i.e., in particular immediately during driving, to the online diagnostic component 204 and / or the engine control device 206 of the engine control unit 2. The value of the characteristic variable of fresh air quality rf can also be provided to the off-board diagnostic computer 208 at a later time (e.g., in a workshop).

[0096] Next—especially with the help of Figure 4 and Figures 5a-5f Figure - will explain in detail how to determine the simplified cylinder load characteristic parameter rf in the embodiment * The fresh air quality characteristic variable rf is determined therefrom.

[0097] As from Figure 4 As can be seen in FIG, the following relationship applies to the composition of the gas mass in cylinder Z1 in the diagnostic time window 112:

[0098] m=m tot =m Luft +m Kraftstoff +m Restgas (1)

[0099] Here, the following relationship exists between the gas mass and the fuel mass:

[0100]

[0101] Symbol meaning

[0102] Lambda measured combustion air ratio (<1 = "fuel rich", 1 = stoichiometric, >1 = "fuel lean")

[0103] L st The so-called stoichiometric fuel-air ratio is typically between 14 and 16, depending on the chemical constants of the fuel.

[0104] Substituting equation (2) into (1) yields:

[0105]

[0106] In the exemplary embodiment, the residual gas mass is replaced by a typical engine control variable:

[0107] m Restgas =xrg·m tot (4)

[0108] The residual gas mass can be interpreted as the fraction xrg of the total mass.

[0109] In order to be able to replace the absolute air mass in Equation 3, the following relationship is introduced based on typical engine control parameters:

[0110]

[0111] Symbol meaning

[0112] rf SB Steady-state fresh air quality characteristic parameter, in % of the cylinder charge

[0113] p0 Atmospheric pressure under standard conditions (1013hPa)

[0114] V max Maximum cylinder volume at bottom dead center of the crankshaft

[0115] R ideal air constant

[0116] Ambient temperature under T0 standard conditions (293K)

[0117] In order to correctly mix the fuel, the current air mass in the cylinder is determined in advance in the engine control unit as the steady-state fresh air mass characteristic variable rf SB .

[0118] For this purpose, a function known per se and already present in the engine control unit is the so-called load detection for steady-state engine operating conditions, which estimates the relative fill rate in percentage.

[0119] The purpose of the exemplary method described here is to improve the estimation of the filling quantity rf. (The filling ratio rf is defined as 100% when the maximum cylinder volume is completely filled with air under standard conditions, according to the ideal gas equation):

[0120]

[0121] The total mass of the cylinder is determined by the cylinder pressure p * , cylinder volume V * and the temperature in the cylinder T * The current thermodynamic ratio results, since the cylinder is not filled only with air, but also with the components fuel and residual gas that cause a pressure increase:

[0122]

[0123] Symbol meaning

[0124] p * Cylinder pressure in the diagnostic time window

[0125] V * Cylinder volume at the time of diagnosis

[0126] R ideal air constant

[0127] T * The temperature T in the cylinder at the time of diagnosis *

[0128] Inserting (6)(5.5)(4) into (3) (including adjusting the position and shortening) yields the following relationship:

[0129]

[0130] according to Figures 5a to 5e Next, it will be explained how to establish a simplified relationship based on equation (7), which is implemented in the engine controller with a few variable variables and therefore also with significantly lower computing power, so that the simplified cylinder load characteristic variable rf can be determined in real time. * In the embodiment described, the real-time capability means that the simplified cylinder load characteristic parameter rf can be calculated based on the value of the determined working cycle. * Used to determine the fuel injection quantity for the next working cycle.

[0131] exist Figures 5a-5f A graphical derivation of a simplified assumption regarding the relationship between characteristic variables and state variables of the cylinder contents is shown in FIG.

[0132] from Figure 5a Starting with the complete relationship shown in Figure 5b 、 5c Each of Figures 5d and 5e introduces a further simplification so that finally Figure 5f A simplified relationship is shown in FIG. 1 , which nevertheless achieves a sufficient degree of accuracy for the purposes of the present invention.

[0133] Here, the purpose of simplifying equation (7) is to make the residual gas content xrg and the cylinder temperature T * Parameterized.

[0134] exist Figure 5a The complete relationship for each variable is shown in Figure 1. The thickness of the lines indicates the strength of the correlation. Each line is considered to be an approximation of the proportional relationship to a first approximation, allowing for subsequent simplification of the existing system of equations. Dashed lines indicate inverse proportionality (and are accordingly labeled "indirect").

[0135] Cylinder Z1 is filled with fresh air mass m Luft Filled with fresh air mass represented by the fresh air mass characteristic variable rf. In addition, the cylinder is filled with fuel mass m Kraftstoff and residual gas mass m Restgas Filling, the residual gas mass is represented by the residual gas fraction xrg.

[0136] All three characteristic variables of the cylinder contents indirectly or directly influence at least one of the two relevant state variables of the mixture in cylinder Z1, namely p * and V * .

[0137] Residual gas fraction xrg to total mass m in the cylinder tot Has a medium effect on temperature T * There is also a medium-sized effect. In addition, the residual gas fraction xrg has an influence on the pressure p in the cylinder * Both are known from experimental observations and are considered generalizable.

[0138] The fresh air quality characteristic parameter rf is respectively related to the total mass m in the cylinder tot And therefore also the fuel mass m Kraftstoff Have a big impact.

[0139] Total mass in the cylinder m total The ideal gas equation itself is used to calculate the cylinder pressure p * Have a big impact.

[0140] Cylinder pressure p * The temperature in the cylinder T * Have a big impact.

[0141] exist Figure 5bThe consideration of converting the use of the residual gas fraction xrg into an inverse ratio is shown in FIG, so as to enable a subsequent simplification step in which the indirect effect of the residual gas fraction on the cylinder pressure is introduced (see Figure 5d ).

[0142] exist Figure 5c Remove "weak" connections and then remove individual adjacent elements.

[0143] exist Figure 5d In the figure, replace the intermediate parameter m as shown tot .

[0144] exist Figure 5e Remove the "weak" connections created by the replacement step.

[0145] exist Figure 5f Only the temperature T as the target variable is shown. * Since each line is considered as an approximation to a proportional relationship, two substitution equations can be borrowed from the diagram shown. The first substitution equation is:

[0146] T * =C2·p * (8)

[0147] Through another relationship

[0148] (T * ) C1 (1-xrg) 1 =C 0 |C1>1

[0149] get

[0150] (C2·p * ) C1 (1-xrg)C0

[0151] And when incorporating constants we get

[0152] p *C1 (1-xrg) = C3

[0153] Or convert it into the second substitution equation

[0154] 1-xrg=C3·p *-C1 (9)

[0155] Now insert equations (8) and (9) into the corresponding parameters for equation (7) and additionally incorporate the constants:

[0156]

[0157] The constants C4, C5, etc. in the model equations of the embodiment are determined on a research engine by means of the following steps: measuring the complete characteristic curve (speed / load); analyzing the cylinder indication p by corresponding gas transformation; * and calculate xrg and T * The analysis is performed; then the corresponding characteristic values ​​are calculated from the results and saved via the average engine speed (characteristic curve).

[0158] Next, constant C4 is combined with fixed values ​​p0, T0, and V max Merge and you get:

[0159]

[0160] Finally, the rf conversion can now be performed and the relative load determination rule can be derived from this, whereby the simplified fresh air quality characteristic variable rf is first derived. * :

[0161]

[0162] The constant C7 is then introduced in the application of equation (12) to make the model fit as well as possible. (The constant C7 can also be assumed to be C7=0 in the first application, and other values ​​can be taken accordingly to improve the accuracy of the model).

[0163] Below is a table of the open parameters used to determine the RF estimate:

[0164] value unit illustrate C6 [% / Nm] Scaling factor: Work items relative to load C5 [-] Exponential Scaling: Pressure Relative to Load C7 [bar] Offset: Pressure relative to load (default = 0)

[0165] λ, L St and V * The value of can accordingly be obtained from a known engine control unit at the time defined by the crankshaft position at diagnosis time 113 , and thus also from the engine control unit of the exemplary embodiment.

[0166] For the diagnosis time window 112, the cylinder pressure value is diagnosed Determined to be p * value.

[0167] How this is done can be seen from the following description of equations (13)-(28), where, from the perspective of the determined diagnostic time window (see Figure 2 interpretation), The crankshaft angle KW corresponding to P1 is 660°. The crankshaft angle KW corresponding to P2 is 690°, and accordingly This applies in the exemplary embodiment shown.

[0168] Based on the pressure balancing of the diagnosed cylinder on the basis of the measured speed curve, the following is determined:

[0169]

[0170] Symbol meaning

[0171] J0, J total / proportional moment of inertia

[0172] Angular position of the crankshaft

[0173] ω angular velocity

[0174] M tan The torque generated by the gas force in the cylinder and the inertia force of the oscillation

[0175] M R Torque due to friction losses

[0176] M L Torque due to load reduction

[0177] M M Proportional torque due to rotational inertia

[0178] n mot Current applied engine speed

[0179] By differentiating, substituting, and introducing the moment of inertia (partitioning the inertial part), we obtain the following equation:

[0180]

[0181] Dividing the equation into the "constant part" and the "variable part" according to meaning, we get the following sub-equations:

[0182] "Constant part":

[0183] The constant component balance starts from the steady-state operating point. The average torque provided keeps the average speed constant because it corresponds to the torque demand caused by the load and friction.

[0184] "Changed part":

[0185] The time-dependent derivative is converted into a crankshaft angle-dependent differential using the following relationship:

[0186]

[0187] For the purpose of analysis, the decisive variables in equation (13) are further explained in detail. The relationship of the torque generated by the gas force in the cylinder is obtained:

[0188]

[0189] Symbol meaning

[0190] A K Piston cover area = constant

[0191] r K The effective radius of the crankshaft corresponding to half stroke = constant

[0192] l Pl Connecting rod length = constant

[0193] m osz The mass portion corresponding to the oscillation of the piston assembly and the proportional connecting rod mass = constant

[0194] p zyl The pressure in the cylinder

[0195] p0 reference pressure, crankcase pressure

[0196] Connecting rod oscillation angle related to the crankshaft angular position

[0197] Piston acceleration related to piston position

[0198] Further elaboration of the variable coefficients in equation (15) yields:

[0199]

[0200] Assuming the average speed n mot The relationship between the piston acceleration and the speed is simplified to:

[0201]

[0202] The error caused by this assumption is negligible. The influence of angular acceleration causes negligible deviations in the entire characteristic curve family.

[0203]

[0204] Crankshaft connecting rod ratio λ Pl =r K / l Pl (17)

[0205]

[0206] Relationship with environmental pressure p0=p umg

[0207] Or as in the following also using the relationship to the crankcase pressure

[0208] p0=p KurbGeh =p umg -DPS (20)

[0209] Here, DPS represents the negative pressure (differential pressure) in the intake pipe.

[0210] The friction torque in equation (13) can be expressed in different ways. Either a model can be introduced that reflects the measured data of the specific operating point of the diagnosis. In this case, a target-oriented approach is to functionally relate this term to the speed, load, and oil temperature.

[0211] In the following, it is assumed that the diagnosis is performed at a fixed, defined steady-state load point. Therefore, for this load point, it can be assumed that the friction torque is constant:

[0212]

[0213] The same method also applies to the proportional torque due to the rotational inertia and to the moment of inertia.

[0214]

[0215] J=const. (23)

[0216] Proper selection of diagnostic constants at the steady-state operating point enables simple application of parameters later.

[0217] Solving equation (13) for the gas torque yields:

[0218]

[0219] After inserting the relations from equations (21) to (23), the following simplified equation with the applied constant K_RM can be derived:

[0220]

[0221] Diagnostic applications:

[0222] exist Figure 3 Shown in Figure 2 Detail X, ie the speed change 101 with respect to the crankshaft angle KW during the compression of cylinder Z1 during the diagnostic time window 112 with measuring points P1 and P2. In this cylinder, pressure p1 prevails at point P1 and pressure p2 prevails at point P2.

[0223] The gradient of the angular velocity in equation (14) is expanded. In this case, the rotational speed to be determined must be averaged and then constant.

[0224]

[0225] The terms for the tangential moment in equation (15) are then expanded to include the relationships from equations (16) to (20) and the constants are labeled.

[0226]

[0227] There are kinematic constants for the steady-state point at which the diagnosis is performed.

[0228]

[0229] After inserting equations (26) and (25) into equation (24), solving for the cylinder pressure, and combining all constants, we obtain:

[0230]

[0231] All pressure variables and speeds in equation (27) can be measured at times P1 and P2 for the quantification of the constants shown. Suitable per se known indicative measurement techniques determine the necessary physical variables based on the crankshaft angle or at least by averaging over several working cycles. In addition to or instead of indicative measurement techniques, data from a suitable operating model (e.g., an engine control unit) can be used. Kinematic constant K K Can be tabulated and used according to piston position.

[0232] Speed ​​n mot The influence of the oscillating mass can be calculated in real time, for example, or stored in the controller in the form of a lookup table of suitably stored operating models regarding speed and load.

[0233] For two discrete points, the simplified piston acceleration (see especially equation (16)) can be expressed as:

[0234]

[0235] The constants K1 and K2 can be determined based on a baseline measurement (engine function or ventilation is normal).

[0236] After determining the application constants K1 and K2, equation (27) can be used to determine the diagnostic cylinder pressure from the speed change in compression:

[0237]

[0238] Diagnostic cylinder pressure It is an indicator of the pressure curve during the compression stroke of the cylinder.

[0239] In this way, the diagnostic cylinder pressure for the time interval t12 = t[P1; P2] can be determined for the diagnostic time window 112 of the diagnosed cylinder Z during driving operation.

[0240] During the calculated working cycle of the calculated cylinder, the cylinder pressure of the diagnostic This calculation is used to estimate the simplified cylinder load characteristic parameter rf in the next working cycle according to equation (12) * .

[0241] Thus, if necessary, the steady-state cylinder load characteristic variable rf determined for steady-state operation can also be used. sB and / or the offset prediction rf derived therefrom OFFSET Determine the fresh air quality characteristic variable rf. * , steady-state fresh air quality characteristic parameter rf sB and / or offset prediction rf OFFSET The weighting incorporated into the calculation of the rf for the transient operating state TB itself depends on the degree of the transient state and / or other individually considered specialist considerations.

[0242] In the exemplary embodiment, the fuel injection quantity into the cylinder Z1 is pre-controlled based on the value of the fresh air mass characteristic variable rf determined in the preceding working cycle.

[0243] Reference Signs List

[0244] 1 Internal combustion engine

[0245] 2 Control device

[0246] 4 Computing Units

[0247] 6 Measuring unit for crankshaft speed

[0248] 7 Cylinder pressure determination unit

[0249] 9 Intake system

[0250] 10 Torque curve of an internal combustion engine over the engine cycle

[0251] 12 Torque gap

[0252] 14 Predetermined limits on relevant torque contributions

[0253] 16 Cylinder temperature determination unit

[0254] 18 lambda sensors

[0255] 150 Speed ​​change chart

[0256] 101 Speed ​​Curve

[0257] 112 Diagnostic time window

[0258] 113 Diagnostic Moment

[0259] 200 Engine Controller

[0260] 202 Memory

[0261] 204 Diagnostic components of the engine control unit

[0262] 206 Control components of engine control unit

[0263] 208 Off-board diagnostic computer

[0264] KT crankshaft drive

[0265] KW crankshaft angle

[0266] L St Stoichiometric fuel-air ratio, fuel ratio

[0267] m Kraftstoff Fuel mass in the cylinder

[0268] m Luft Air mass in the cylinder

[0269] m Restgas Residual gas mass in the cylinder

[0270] m tot Gas mass in the cylinder

[0271] M Figures 1a-1c The torque of the cylinder

[0272] n Speed

[0273] p* Cylinder pressure at the time of diagnosis

[0274] p zyl,diag Pressure characteristic number, here is the diagnostic cylinder pressure

[0275] P Measurement times at the start and end of the diagnostic time window

[0276] p0 atmospheric pressure under standard conditions (1013hPa)

[0277] R ideal gas constant

[0278] rf Fresh air quality characteristic parameter; relative filling of the cylinder in %

[0279] rf *Simplified cylinder load characteristic parameters

[0280] rf SB Steady-state cylinder load characteristic parameters

[0281] rf Offset Offset prediction

[0282] SB Steady-state operation

[0283] t Time interval in the diagnostic time window

[0284] T * Temperature of the gas mixture in the cylinder at the time of diagnosis

[0285] T0 Ambient temperature under standard conditions (293K)

[0286] TB transient operation

[0287] V * Cylinder volume at the time of diagnosis

[0288] V max Maximum cylinder volume at bottom dead center of the crankshaft

[0289] xrg residual gas fraction

[0290] Z cylinder

[0291] ZZP cylinder ignition timing

[0292] λ Internal combustion engine air ratio

Claims

1. A method for determining a characteristic fresh air mass variable (rf) in a cylinder (Z1, Z2, Z3, Z4) of an internal combustion engine (1) in a motor vehicle, the method comprising the following steps: - identifying a cylinder (Z1) which is at the end of an intake stroke or at the beginning of a compression stroke during driving operation of the motor vehicle, - determining a diagnostic time window (112) which extends within the torque gap (12) of the internal combustion engine (1) after closing of the intake valve of the identified cylinder (Z1), - determining at least two values ​​of the crankshaft speed of the internal combustion engine (1) during the diagnostic time window, It is characterized by The following steps are involved: - determining a characteristic cylinder load variable (rf ) in the identified cylinder from at least two values ​​of the determined crankshaft speed; * ), - determining a characteristic variable of the fresh air mass in the identified cylinder as a function of the determined characteristic variable of the cylinder load, and In this case, the fresh air mass characteristic variable determined for a specific working cycle of the identified cylinder is used as a basis for determining the fuel injection quantity for the following working cycle of this cylinder or of a subsequently fired cylinder.

2. The method according to claim 1, characterized in that In addition to at least two values ​​of the crankshaft speed, the following variable variables are determined for determining the cylinder load characteristic variable (rf * ): - the cylinder volume (V) at the diagnosis time (113) within the diagnosis time window * ) and / or - simplified piston acceleration in the diagnostic time window 3. The method according to claim 2, characterized in that In addition, only the constant and at least two values ​​of the determined crankshaft speed are used to determine the cylinder load characteristic variable (rf * ).

4. The method according to claim 2 or 3, characterized in that - determining a pressure characteristic number of the identified cylinder in the diagnosis time window as a function of the at least two determined values ​​of the crankshaft speed and / or the determined simplified piston acceleration, - determining a cylinder load characteristic variable as a function of the determined pressure characteristic variable and / or the determined cylinder volume.

5. The method according to any one of claims 1 to 3, characterized in that Before the cylinder identification, it is determined whether the internal combustion engine is in at least approximately steady-state operation or in transient operation.

6. The method according to claim 5, characterized in that The method is performed only if the presence of a transient operation of the internal combustion engine is determined and / or as long as the presence of a transient operation of the internal combustion engine is determined, and / or The determined residual gas portion is stored and / or further used only if and / or as long as a transient operation of the internal combustion engine is determined to be present.

7. The method according to any one of claims 1 to 3, characterized in that - Only when the cylinder load characteristic variable (rf * ) on the basis of, or Additionally, a characteristic variable of the fresh air mass in the identified cylinder is determined based on the characteristic variable of the steady-state cylinder load determined for steady-state operation.

8. The method according to any one of claims 1 to 3, characterized in that At least two values ​​of the crankshaft speed are determined with a sampling quality that can be real-time.

9. A control device (2) for determining a characteristic fresh air mass variable (rf) in a cylinder (Z) of an internal combustion engine (1), the control device being designed to: The value of the fresh air quality characteristic variable determined by means of the method according to one of claims 1 to 8 and / or stored in the memory is transmitted to - the control unit (206) of the control device adjusts the functions of the internal combustion engine in real time according to the transmitted values, and / or - The diagnostic component (204) of the control device is used for additional on-board diagnostic functions.

10. The control device according to claim 9, characterized in that: The control component is designed to determine a fuel injection quantity for a specific working cycle of the cylinder as a function of a value of a determined fresh air mass characteristic variable of a previous working cycle of the identified cylinder or of an immediately preceding diagnosed cylinder.

11. The control device according to claim 10, characterized in that: Either a specific cylinder is always analyzed and its previously determined air mass is then used in a new working cycle to determine the fresh air mass characteristic variable, or the cylinders are analyzed with respect to their air mass and the value of the fresh air mass characteristic variable determined here and / or last is transmitted to the next ignited cylinder for its precontrol.

12. The control device according to claim 9, comprising a non-volatile memory (202), characterized in that: The control device is designed to store one or more values ​​of the fresh air quality characteristic variable in one or different diagnosis time windows in the memory.

13. The control device according to claim 12, characterized in that: The control device is designed to transmit the value of the fresh air quality characteristic variable stored in the memory to an off-board computer (208) for an offline diagnostic function.

14. The control device according to claim 9, characterized in that The control device is formed in an engine control unit of an internal combustion engine of a passenger vehicle.

15. The control device according to claim 9, characterized in that The control component is designed to determine a fuel injection quantity for a specific working cycle of the cylinder as a function of the value of the determined fresh air mass characteristic variable of a previous working cycle of the identified cylinder or of the last diagnosed cylinder.

16. The control device according to claim 9, comprising a non-volatile memory (202), characterized in that: The control device is designed to store one or more determined values ​​of the fresh air quality characteristic variable in one or different diagnosis time windows in the memory.

17. An internal combustion engine (1) having one or more cylinders (Z), characterized in that The internal combustion engine has a control device (2) according to one of claims 9 to 16.

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