ENGINE PROTECTION FUNCTION AT HIGH RPMS

Description

[0001] The invention relates to a method for operating an internal combustion engine (drive unit) of a motor vehicle, in which fuel is ignited and / or injected into a combustion chamber of one of several cylinders considered, depending on a predefinable target angle of a rotating component of the internal combustion engine, which corresponds to the crank angle of a crankshaft of the internal combustion engine, at a specific time, wherein an ignition and / or injection time is determined at a latest setting time with knowledge of the target angle and the current rotational speed at the setting time of one of the several cylinders.

[0002] Knocking is a phenomenon known as uncontrolled combustion or pre-ignition of the fuel in gasoline engines. Temperature and pressure rise abruptly, a pressure wave propagates through the combustion chamber at supersonic speed and impacts its walls. This creates pressure peaks that can damage pistons, bearings, cylinder head, valves, and spark plugs. Reflection of these pressures results in a high-frequency oscillation in the cylinder pressure curve, which is audible as knocking.

[0003] Uncontrolled auto-ignition of the air-fuel mixture can occur for the following reasons: excessive compression of the mixture; excessively high temperatures of the cylinder inner wall (at high engine outputs); glowing combustion residue (combustion and oil deposits) on the combustion chamber walls; ignition timing too early (older, adjustable ignition systems); fuel with too low an octane rating (a measure of knock resistance); high temperatures in the outer areas of the cylinder due to the radiant energy of the already ignited flame front, which has not yet reached the outer areas; an unfavorable, nested combustion chamber shape without turbulence (promoting the formation of hot spots) in the air-fuel mixture; lubricating oil particles that can enter the air-fuel mixture from the crankcase gases.Incorrect heat range of the spark plug, so that it either gets too hot and thus becomes a glow plug itself, or that it remains too cold to burn off deposits (coking), which in turn trigger another glow ignition.

[0004] Another scenario in which a pressure wave, similar to knocking, can be triggered occurs when high speed gradients are present. These high speed gradients occur, for example, during rapid gear changes in internal combustion engines equipped with manual transmissions. In these engines, a system-related or fundamental injection timing error can lead to premature injection and ignition events in the combustion chamber. Due to the premature onset of combustion with strong pressure gradients, this results in enormous peak pressure surges (pressure waves in the combustion chamber). These peak pressure surges, analogous to the knocking described above, can damage components such as the cylinder head, cylinder liner, crankcase, cylinder head gasket, and other parts in this area.

[0005] Peak pressure exceedances, which damage the assemblies or components of a so-called engine, can be detected and prevented during engine operation by using speed analysis in the engine control unit with corresponding speed gradient monitoring in the appropriate measuring grid to identify critical situations, after which damage to the parts can be avoided by taking appropriate measures.

[0006] Speed ​​gradient monitoring to prevent knocking combustion is known from German patent application DE 102 60 012 B4, and to prevent so-called jerking or to ensure smooth running of the internal combustion engine is known from German patent application DE 198 13 337 A1. In WO 2009 / 093112 A1, a fuel injection control system for internal combustion engines with an electronic control unit is disclosed, which recalculates the required number of injection events and the required injection times and controls the fuel injection when the engine speed changes rapidly.

[0007] Measures to avoid excessively high speed gradients of the internal combustion engine include, for example, a delayed shift of the injections / ignitions and / or a deactivation of injection events / ignitions and / or a reduction of injection quantities (in direct injection engines) and / or a rapid reduction of the fuel pressure via a pressure regulating valve in the event that the injection has already started.

[0008] The prior art documents DE 103 32 350 A1 and US 2016 / 195 055 A1 as well as DE 10 2005 014 920 A1 are also cited. Reference is further made to the documents GB 2 314 944 A and US 2004 / 112 336 A1.

[0009] The invention is based on the objective of preventing a peak pressure exceedance in the combustion chamber of an internal combustion engine, which occurs particularly at high speed gradients.

[0010] The invention is solved by the features of claim 1 and claims 5 and 6.

[0011] In a preferred embodiment of the invention, the correction of the ignition and / or injection timing is carried out while maintaining the predetermined target angle after activation of the protective function by means of a characteristic map, in addition to the dependence on the speed by means of the negative speed gradient, also depending on a load point of the internal combustion engine and / or depending on a boost pressure of an exhaust gas turbocharger and / or depending on an injection quantity and / or a target torque of the internal combustion engine and / or depending on an exhaust gas recirculation (EGR) rate of an exhaust gas recirculation and / or depending on an operating mode of the internal combustion engine.This advantageously integrates further parameters into the map, making it possible to correct the ignition and / or injection timing while maintaining the target angle even with large changes in engine speed, and thus to adapt better by taking the aforementioned parameters into account.

[0012] In detail, the method is preferably characterized by the fact that, depending on the rotational speed at the latest setting time and the difference between the rotational speeds at the latest setting time and at the time before the latest setting time, a correction value is provided in a characteristic map stored for this purpose in the control system, which is designed as an "offset" period.

[0013] This "offset" period is added additively to an uncorrected period when the protection function is activated. This uncorrected period corresponds to the rapidly changing, dropped speed at the latest set point. Starting from the latest set point, the corrected ignition and / or injection point is calculated after adding the periods. This point is used to calculate the ignition or injection point at which ignition or injection occurs, ensuring that despite the speed change, the specified target angle is maintained, which is also achieved at the uncorrected ignition and / or injection point (without activation of the protection function).

[0014] Further embodiments provide that, when the protective function is activated, individual ignitions or injection events are additionally deactivated and / or injection quantities are reduced and / or the fuel pressure is reduced via a pressure regulating valve within an ignition and / or injection system if injection has already begun. This advantageously combines this with the corrected ignition and / or injection timing calculation, which prevents significant changes in engine speed from altering the predetermined target angle and thus from causing a large pressure build-up, thereby also ensuring that pressure peaks in the combustion chambers are reduced.

[0015] According to claim 5, the invention also relates to an engine control unit of an ignition and / or injection system in which a computer-readable program algorithm for executing the method according to claims 1 to 4 is stored. According to claim 6, a motor vehicle according to the invention has an engine control unit according to claim 5.

[0016] The invention is explained below with reference to the accompanying figures. These show: Figure 1 is a diagram illustrating the temporal sequence of an injection or ignition process in a cylinder of a multi-cylinder internal combustion engine according to the prior art, which shows a first abscissa axis representing the crank angle KW and on the ordinate axis an associated pressure profile p within the one cylinder by means of a pressure characteristic curve, wherein the first abscissa axis is assigned a second abscissa axis, which illustrates the time t and the relevant times t before and t should as a function of a predetermined target angle phi should at time t should, and Figure 2 is a diagram illustrating the temporal sequence of an injection or ignition process in the one cylinder of a multi-cylinder internal combustion engine according to the invention, which is analogous to the Figure 1The first abscissa axis represents the crank angle °KW and the corresponding pressure curve p within the first cylinder is illustrated on the ordinate axis using a pressure characteristic curve K', with the first abscissa axis analogous to Figure 1 the second abscissa axis is assigned, which illustrates the time t and the relevant time points t before-1 , t before and t should' as a function of a given target angle phi should at time t should'.

[0017] Due to the system and its underlying principles, a disadvantage of ignition or fuel injection is that the control system of the injection system cannot precisely determine the engine speed (RPM) at the time of ignition (for gasoline engines) or injection (for diesel engines), and thus the engine speed (RPM) at the ignition time t or injection time t (see [reference]). Figure 1 ) is not included as a parameter.

[0018] This is because, depending on the system, physical delays inherently occur in the overall system between a predetermined time t before and the time t at the ignition or injection of fuel at time t, both on the component and control side.

[0019] Depending on the combustion process, the engine control unit may contain at least one delay time, such as an injector opening delay, a delay in mixture formation, a combustion start delay, or a time delay due to the calculation time of the injection point t.

[0020] The term "determination time t before" is understood to be the latest possible time, with knowledge of the target angle phi before, in particular the crank angle at the determination time t before and the current rotational speed rpm at the determination time t before of a considered cylinder Z, at which, due to system constraints, a calculation of the time t should be completed and determined at the latest.

[0021] For example: To take into account the inherently physical delay times, the following approach is used, as explained below using one of the possible delay times.

[0022] The electrical energizing of an actuator at injection time t is intended, in particular of a fuel-injecting injector in one cylinder Z of several cylinders Z n, which is to take place, for example, before top dead center TDC [0°KW ] at a fixed, predefinable target angle phi (compare Figures 1 and 2) should, must be determined well before this injection time t should, namely at the preceding determination time t before.

[0023] In other words, in practice, engine control systems for internal combustion engines must be designed, due to the delays inherent in the running times of the units and associated calculations, as well as the running times of the program steps for programming the final stages, in such a way that the determination of the time t should take place in the earlier determination time tv, depending on the system.

[0024] At the setting time t before, in practice, with knowledge of the currently measured speed rpm at the setting time t before, possibly using a speed model and knowledge of the target angle phi before, in particular crank angle, the injection timing t should of the final stage for ignition or injection from t before - without further reference to the target angle phi should at time t should - is set, i.e. programmed.

[0025] In this way, a change in rotational speed between times t and t soll leads to an undesirable error, the so-called timing error, or in other words, an undesirable deviation of the target angle phi soll specified at time t soll, as will be explained below.

[0026] The Figure 1The diagram shows a temporal sequence of an ignition or injection process in a cylinder Z of an internal combustion engine having several cylinders Z n according to the prior art, which has a first abscissa axis to represent the crank angle °KW and on the ordinate axis an associated normal cylinder pressure curve p within a cylinder Z based on a pressure characteristic curve K, wherein the first abscissa axis is assigned a second abscissa axis which illustrates the time t and the relevant times t before and t should as a function of a given target angle phi should at time t should.

[0027] For example, the rotational speed of one cylinder Z at a crank angle phi before is 2000 rpm at the specified time t before. As already explained, the procedure so far is as follows: at the specified time t before, with knowledge of the current rotational speed rpm = 2000 rpm, possibly using one of several possible rotational speed models and knowledge of the crank angle phi before, the time t should be set, i.e., programmed, for the final stage for injection or ignition from time t before – without further reference to the target angle phi should – at time t should.

[0028] Depending on the specific speed model, the rotational speed models took into account any small deviations in rotational speed of one cylinder Z from the design-related rotational speed in various ways, but they continue to assume that the rotational speed (RPM) at the specified time t before corresponds to the rotational speed at the desired time t, so that the rotational speed at the desired time t essentially corresponds to the rotational speed (e.g., 2000 RPM) at the specified time t before.

[0029] As explained at the beginning, particularly during hectic gear changes in vehicles with internal combustion engines coupled to manual transmissions, significant changes in engine speed (rpm at the set time t before ≠ rpm at the set time t should) occur between the set times t before = t should, which are not represented by the previously known speed models.

[0030] If the rotational speed changes relatively quickly between the setting time t before and the target time t, the undesirable timing error results, regardless of the previously known rotational speed models.

[0031] The greater the difference in rotational speed Δ rpm of one cylinder Z between times t before and t should be, the greater the corresponding error, whereby with a sharply decreasing rotational speed, the pressure in cylinder Z at time t should increase continuously (in Figure 1 (not shown) and assumes an undesirably high peak value.

[0032] As already explained, this is because current practice assumes that the rotational speed (RPM) at time t is essentially the same as the rotational speed at the setting time t before, whereby at the latest (possible) setting time t before, there is a period Δt uncorr (compare Figure 1) is determined, after the expiry of which (assuming the essentially identical rotational speeds at times t before and t should ) the time t should lie.

[0033] This means that, depending on the boundary conditions at the setting time t before, the time t is determined in a disadvantageous way depending on the desired target angle phi at time t should - without further correction of any other rotational speed that may be present at time t should - and ignition or injection takes place at this time t should.

[0034] This results in the following effect at time t: if there is a significant drop in rotational speed (with a high negative rotational speed gradient ΔU / min) after time t, the desired design-related target angle phi is not yet reached after the period Δt uncorr has elapsed, so that at the specified time t (which does not take the drop in rotational speed into account) ignition or injection occurs too early, causing the pressure in at least one cylinder Z to rise sharply in an undesirable way.

[0035] As explained, due to system limitations, it is impossible to take into account the inherent physical delay times between the fixed time t before and the time t should be considered when igniting or injecting fuel, so that the fixed time t before is defined as either the latest injection time or the latest ignition time, depending on the system.

[0036] The core of the invention is now to decide at this last possible time t before, in which changes to the ignition and injection parameters can still be made, whether a timing error (with the potential of exceeding the peak pressure) exists for the upcoming combustion event, wherein, if a timing error to be taken into account exists, a corresponding action is derived and proposed according to the invention.

[0037] The Figure 2 shows a diagram illustrating the temporal sequence of an ignition or injection process in one cylinder Z of an internal combustion engine having several cylinders Z n according to the invention, which is analogous to the Figure 1The first abscissa axis represents the crank angle °KW and the ordinate axis illustrates the associated pressure curve p within the cylinder Z using a pressure characteristic curve K' changed by a drop in rotational speed, with the second abscissa axis being assigned to the first abscissa axis, which illustrates the time t and the relevant times t before-1 , t before and t should' as a function of a given target angle phi should at time t should'.

[0038] It is now assumed that between the setting time t before and the time t should the rotational speed changes relatively quickly, i.e., drops with a high rotational speed gradient ΔU / min.

[0039] Contrary to the previous procedure, the drop in rotational speed is now taken into account according to the invention.

[0040] According to the invention, the rotational speed rpm before-1 of the cylinder Z n-1 which precedes the cylinder under consideration in the firing order is set at a time t before-1 that lies before time t (compare Figure 2 ) monitored.

[0041] According to the invention, a correction parameter U / min pre-1 is included in the control.

[0042] The intention is to compare the local rotational speed (RPM) before the last detected → or a number of the last detected tooth flanks of the cylinder Z under consideration at time t before with the corresponding information of the cylinder Z n-1 at the earlier time t before-1.

[0043] This comparison allows a difference D between the rotational speeds rpm before and rpm before-1 to be calculated.

[0044] This difference amount D is compared with a predefinable value from an applicable engine speed-dependent or engine speed-dependent and load-dependent characteristic curve.

[0045] If the difference amount D is greater than the value stored in the characteristic curve, a protective function is activated according to the invention, which is explained below.

[0046] According to the invention, if the difference amount D is smaller than the value stored in the characteristic curve, no protection function is activated and, as in connection with the Figure 1 described, procedure.

[0047] For example: The rotational speed (RPM) of the cylinder Z n under consideration at time t before is, for example, 2000 RPM. The RPM before-1 of cylinder Z n-1 is, for example, 2010 RPM. The difference D is therefore 10 (= no significant drop in rotational speed) and is, for example, smaller than the value stored in the characteristic curve, so that, according to the invention, no protective function is activated.

[0048] The rotational speed (RPM) of the cylinder Z under consideration at time t before is, for example, 2000 RPM. The RPM before-1 of cylinder Z n-1 is, for example, 2100 RPM. The difference D is thus 100 (= significant speed drop between t before-1 and t before) and is, for example, greater than the value stored in the characteristic curve, so that, according to the invention, the protective function is activated. In other words, at a certain value stored in the characteristic curve that is exceeded by the difference D, it is assumed that the speed drop between t before and t should be so large that, in order to prevent the formation of peak pressure at time t should, a correction of the period Δt uncorr (compared to substantially the same rotational speeds) is required. Figure 1 ) is necessary.

[0049] In Figure 2The period Δt unkorr' between t before and t should be represented, which would correspond to a sharply decreasing rotational speed after time t before.

[0050] As in Figure 2 As shown, taking into account the period Δt uncorr' which considers the significantly lower rotational speed, the time t should occur at a significantly too early time, in which the target angle phi should then not correspond to the desired target angle, whereby the undesired peak pressure arises due to the premature ignition or injection.

[0051] According to the invention, however, after the previously explained activation of the engine protection function, a correction value is now available in a characteristic map stored for this purpose in the control system, depending on the rotational speed rpm before time t before and the difference D between the rotational speeds rpm before and rpm before-1. This correction value is expressed as the period Δt offset (compare Figure 2) is provided, which is added to the period Δt unkorr' as a correction value (offset), so that, starting from the time t before, after adding Δt unkorr' and Δt onset, a time t should' results in which the ignition or injection takes place.

[0052] At this time t soll' (with the engine protection function activated) is the target angle phi soll, at which the ignition or injection occurs analogously to the procedure according to Figure 1 is performed, based on the 360° crank angle per unit of time, equal to the target angle phi at time t (without activation of the engine protection function).

[0053] By comparing the Figures 1 and 2 It becomes clear that a working cycle of the piston in the considered cylinder Z over the 360° crank angle without a change in speed is shorter than a working cycle of the piston of the considered cylinder Z over the 360° crank angle with a reduction in speed.

[0054] According to the invention, due to the critical change in rotational speed, it is provided that the target angle phi should remain at the predetermined desired position °crank angle before TDC by activating the engine protection, so that the time t should no longer be reached depending on the rotational speed at time t before, but rather a time t should' is calculated depending on the rotational speed at time t before, in which the target angle phi should remain at the predetermined desired position °crank angle before TDC.

[0055] In other words, the resulting intervention in the event of a critical change in rotational speed depends on the rotational speed (RPM) at time t before and on the difference D between the rotational speeds (RPM before) and (RPM before-1) in the form of a late shift of the ignition or injection by the period Δt offset, which is added to the period Δt uncorr' according to the characteristic map.

[0056] To reduce peak pressure when a critical change in engine speed occurs, it is further proposed to deactivate individual ignitions or injection events, reduce injection quantities, or to rapidly reduce fuel pressure via a pressure regulating valve if injection has already started.

[0057] Furthermore, it is intended that the map available when activating the determination of the period Δt offset will take into account not only the speeds and the load point as input variables, but also the boost pressure and / or the injection quantity and / or the target torque and / or the exhaust gas recirculation (EGR) rate and / or the operating mode. Reference symbol list

[0058] Zn nth cylinder of an engine Zn-1 cylinder of an engine that precedes a cylinder Zn in the firing order Zcylinder under consideration tbefore Latest (possible) setting time tbefore-1 tbefore Earlier time ttarget Target ignition time or target injection time without activation of engine protection ttarget' Target ignition time or target injection time with activation of engine protection phibefore Target angle at time tbefore ; Crank angle at time tbefore phitarget Target angle at time ttarget ;Crankshaft angle at time t target Δt uncorr uncorrected period between t before and t target without speed drop Δt uncorr' uncorrected period between t before and t target taking into account a significant speed drop Δt offset correction value (offset) Δt corr corrected period between t before and t target' (Δt uncorr' + Δt offset ) rpm before Speed ​​at time t before rpm before-1 Speed ​​at time t before-1 Δr / min Speed ​​gradient D Difference between rpm before-1 and rpm before °Crankshaft degrees Crankshaft angle K Pressure characteristic without activation of engine protection K' Pressure characteristic with activation of engine protection p Pressure t Time;

Claims

1. Method for operating an internal combustion engine of a motor vehicle, in which method, at an ignition and / or injection time (tsoll), fuel is ignited in and / or injected into a combustion chamber of one of a plurality of considered cylinders (Z; Zn) on the basis of a predefinable target angle (phisoll) for a rotating component of the internal combustion engine that corresponds to the crank angle (°KW) of a crankshaft of the internal combustion engine, - wherein the ignition and / or injection time (tsoll) is determined at a latest determination time (tvor) with knowledge of the target angle (phivor) and the current speed (U / minvor) of the one of the plurality of cylinders (Z; Zn) at the latest determination time (tvor), - wherein at the latest determination time (tvor) it is decided whether, between the latest determination time (tvor) and the ignition and / or injection time (tsoll), a change in the speed that occurs after the latest determination time (tvor) will lead to a shift in the ignition and / or injection time (tsoll) - by monitoring a speed (U / minvor-1) of the cylinder (Zn-1) preceding the one considered cylinder (Z) in the chronological firing order at an earlier time (tvor-1) before the latest determination time (tvor) and ascertaining a local speed (U / minvor) of the one considered cylinder (Z) at the latest determination time (tvor) and the local speed (U / minvor-1) of the preceding cylinder (Zn-1) and taking a speed drop into account, - wherein a negative speed gradient (ΔU / min) is ascertained which represents a difference (D) between the speed (U / minvor) at the latest determination time (tvor) and the speed (U / minvor-1) at the earlier determination time (tvor-1), - wherein the speed (U / minvor-1) at the earlier time (tvor-1) is included in the control system as a correction variable, - wherein the local speed (U / minvor) of the last detected tooth flank or of a number of last detected tooth flanks of the considered cylinder (Z) at the latest determination time (tvor) is compared with the corresponding information about the preceding cylinder (Zn-1) at the earlier time (tvor-1), and the difference (D) between the speeds (U / minvor, U / minvor-1) at the latest determination time (tvor) and at the earlier time (tvor-1) is calculated, wherein exceeding a predefinable speed gradient (ΔU / min) between the times (tvor, tvor-1) leads to a protection function being activated if the difference (D) is greater than the value stored in an applicable characteristic curve that is dependent on the engine speed or in a characteristic curve that is dependent on the engine speed and the load, - wherein, within the protection function, the ignition and / or injection time (tsoll) determined without activation is corrected on the basis of the ascertained negative speed gradient (ΔU / min) by determining a corrected ignition and / or injection time (tsoll'), with the result that the predefined target angle (phisoll) is maintained at the corrected ignition and / or injection time (tsoll') despite the speed change.

2. Method according to claim 1, characterized in that the correction is performed, after the protection function has been activated, by means of a characteristic map, not only on the basis of the speed by means of the negative speed gradient (ΔU / min), but also in addition • on the basis of a load point of the internal combustion engine and / or • on the basis of a boost pressure of an exhaust gas turbocharger and / or • on the basis of an injection quantity and / or • a target torque for the internal combustion engine and / or • on the basis of an exhaust gas recirculation (EGR) rate of an exhaust gas recirculation system and / or • on the basis of an operating mode of the internal combustion engine.

3. Method according to claim 1, characterized in that a correction value is provided, on the basis of the speed (U / minvor) at the determination time (tvor) and of the difference (D) between the speed (U / minvor) and the speed (U / minvor-1), in a characteristic map stored in the control system for this purpose, which value is configured as a time period (Δtoffset) that is additively added to a time period (Δtunkorr') corresponding to the speed at the determination time (tvor), with the result that, starting from the determination time (tvor), the corrected ignition and / or injection time (tsoll') at which the ignition or injection is performed is calculated after adding the time period (Δtunkorr') and the time period (Δtoffset), with the result that the predefined target angle (phisoll) which is also achieved without activating the protection function at the ignition and / or injection time (tsoll) is maintained despite the speed change.

4. Method according to claim 1, characterized in that when the protection function is activated, the following is additionally carried out: • individual ignitions or injection events are deactivated and / or • injection quantities are reduced and / or • the fuel pressure is reduced via a pressure regulating valve within an ignition and / or injection system if injection has already started.

5. Engine control unit for an ignition and / or injection system, in which unit a computer-readable program algorithm for carrying out the method according to any of claims 1 to 4 is stored.

6. Motor vehicle comprising an engine control unit according to claim 5.