DE10302806B4 - Method for calculating pressure fluctuations in a fuel supply system of an internal combustion engine working with direct fuel injection and for controlling its injection valves - Google Patents

Abstract

Method for calculating pressure fluctuations in a fuel supply system of an internal combustion engine working with direct fuel injection and for controlling its injection valves,
in which the fuel supply system is defined as a high-pressure hydraulic system that has settled after a few work cycles of the internal combustion engine,
in which the geometric properties of the fuel supply system and the fuel properties are specified or determined as constants for a specific fuel type,
in which the actuation of the injection valves represent an external source of excitation for fuel pressure vibrations in the injection system,
in which the method of the Fourier analysis is used to analyze the fuel pressure vibrations arising in such an injection system,
in which the response function of the Fourier analysis specifies the phases and the amplitudes of the pressure vibration components,
in which the pressure oscillation phases and pressure oscillation amplitudes are compared with target values of the actuation times, the fuel injection pressure and / or the injection volume for actuating the fuel injection valves,
in which, in the event of deviations in the achievable actual values compared to the specified target values, at least one correction value for the ...

Description

The The invention relates to a method for calculating pressure fluctuations in a fuel supply system with direct fuel injection working internal combustion engine and for controlling their injectors.

It is well known that vehicles with internal combustion engines with direct injection fuel supply systems are becoming increasingly popular with customers. This is mainly due to the fact that they have significantly lower fuel consumption than conventional internal combustion engines. In addition, with diesel internal combustion engines, the diesel fuel is cheaper and can now also be purchased as so-called bio-diesel (RME diesel), which is produced from renewable raw materials and therefore does not further increase the CO ₂ pollution of the earth's atmosphere. In such direct injection fuel supply systems, the best efficiency is achieved when the fuel pressure in the injection system has a constantly high value.

at Diesel engines come alongside the so-called pump-injector system especially the common rail injection system known per se. At least for the latter are known multiple injection methods with which to Improve mixture preparation and the combustion process the for amount of fuel required in one operation in an engine cylinder, for example three partial injections is injected. Pre-injection improves in particular the mixture preparation and thus the onset of combustion while the main injection. A post-injection of fuel is used finally especially the improvement of the exhaust gas behavior of the internal combustion engine.

In particular when operating such common rail injection systems with multiple injection processes kick during of the injection processes Pressure waves in the lines leading to the injection nozzles in the unfavorable In this case, reduce the nominal value of the injection pressure and thus the Efficiency and reliability influence the injection system of the internal combustion engine negatively. So it can happen that during of an injection process at the injector the required target injection pressure is not to disposal stands and therefore not injected the desired amount of fuel with a predetermined injection duration becomes. It can be dependent from the pressure wave phase to an oversupply as well as to one Undersupply of fuel and different injection pressures occur. This increases the drive power and the nominal exhaust behavior the internal combustion engine deteriorates.

To solve this problem is in the unpublished DE 102 17 592 A1 It has been proposed to adapt the injection duration of a partial injection to the phase position of the injection in relation to the pressure wave by means of a control device, so that at least the amount of fuel provided for an undisturbed injection process is injected into the cylinder of the internal combustion engine, albeit over a longer injection duration. With this method, however, one needs knowledge about the time course and thus about the trigger and the frequency of the pressure wave. The trigger of the pressure wave is known from the previous partial injection, but the frequency of the pressure wave depends on the geometry of the fuel line and the speed of sound of the wave in the fuel.

in addition comes that also through all other actuation processes of the injection valves of the Injection system pressure waves are generated so that in the Injection system overlay a large number of partial pressure waves. Because the speed of sound also depends on that with this method not considered Type of fuel (summer diesel, winter diesel, RME diesel) and the Fuel temperature is, with the control device mentioned to adjust the injection duration of a partial fuel injection the problem of fuel supply caused by the pressure waves of the cylinder is not sufficiently loosened.

Other known arrangements for the compensation of pressure waves in such Fuel injection systems relate to devices such as the integration of additional Fuel storage nearby of the injectors or the installation of chokes between the supply line and the respective Injectors.

In the above DE 102 17 592 A1 a compensation device is also proposed in which a piezo actuator determines the frequency of a fuel pressure wave by converting the mechanical force exerted on this sensor, converts it into an electrical signal and converts it to a control device provides. This control device then uses this frequency information and the knowledge of the undisturbed start of injection and the undisturbed end of injection of the injection valve to adjust the level of the injection pressure of the following injection process.

Furthermore is a method for determining the injection time from WO 99/47802 for one with direct fuel injection working internal combustion engine known, with which in the feed line pressure fluctuations occurring during an injection valve during two successive injections within the same cycle of the cylinder with a mathematical correction term become. The control time is then with the corrected pressure value for the Injectors changed, so that the correct amount of fuel is injected. The correction term is determined using a so-called "least squares estimator", which is dependent from the geometric data of the fuel injection system, such as e.g. the length the supply line from the common supply line to the injection valve, and the properties of the fuel, the likely injection pressure at the nozzle of the injector estimates.

adversely to the previously known methods or devices for compensation the effects of pressure waves in the lines of direct injection Fuel injection systems are that they cause increased device costs or only on a very specific injection system with all of its geometrical data and other physical boundary conditions and the technical problem posed is therefore only very imperfect to solve.

The also describes DE 199 50 222 A1 a method by means of which Fourier analysis of the fuel pressure in a high-pressure fuel supply system of a direct-injection internal combustion engine is intended to determine the defect-free functioning of components of this system. It is not a question of fuel pressure fluctuations, which are primarily or secondarily caused by a functionally correct actuation of the fuel injection valves, but rather those which arise due to incorrect behavior of components in the fuel supply system.

Also revealed the publication A.G. Favennec, P. Minier, M. Leburn, Renault / Imagine: “Analysis of the Dynamic Behavior of the Circuit of a Common Rail Direct Injection System ", Forth JHPS International Symposium on Fluid Power, Tokyo 1999, Nov. 15-17. 1999, pp 543-548, that a common rail injection system modeled with the help of AMESim software and the Injection pressure of such a system subjected to a Fourier analysis can be.

After all, is out of DE 197 40 608 A1 a method for determining at least one fuel injection-related parameter for an internal combustion engine with a common rail injection system is known. With this method, the course of the pressure in the distributor pressure chamber of the common rail injection system, which is assigned to the engine combustion chambers, is detected via a respective injection curtain for a respective combustion chamber by means of a pressure sensor of the distributor pressure chamber. An associated pressure profile pattern is obtained from this pressure profile, from which the at least one fuel-related parameter is individually determined for each combustion chamber and each injection process.

In front Against this background, the invention is based on the object Process for reducing the impact of those described in the introduction Imagine pressure waves with which the efficiency of the internal combustion engine further increased and reliability of the overall system consisting of an internal combustion engine and a fuel injection system is improved. This process is also said to be without major changes for different dimensions Fuel injection systems can be used.

The solution this task results from a method with the features of the main claim while advantageous refinements and developments of the invention dependent claims are removable.

The inventive method goes back to the knowledge that the in a direct injection fuel injection system occurring fuel pressure vibrations in the steady state reliable can be described using a Fourier analysis.

For the mathematical analysis of this vibration behavior of the pressure wave, it is assumed that there are no nonlinear effects in the injection system, or that if nonlinear effects that can be linearized. If, for example, the dynamic behavior of the fuel injection valves can be linearized, the control signal (piezo signal) can also be used for this valve for Fourier analysis. In addition, it is assumed that a fixed time dependency is assigned to this signal or specifically to this fuel injection rate, which is why dynamic influences of the injection quantity as a result of the actuation of the injection valve are disregarded. In the mathematical model developed below, the fuel injection quantity is therefore simply proportional to the actuation time and the actuation duration of the injection valve. In addition, the following considerations assume that the dynamics of the fuel injection system depend on precisely defined working conditions with regard to injection pressure and engine speed.

The temporal fluctuations in the fuel pressure and thus the fuel volume flow when open Injector are also not for the entire fuel supply system, but only for predefined fixed points in the area of the lines and for predefined Considered volumes. These points are one-dimensional nodes Grid that is mentally spanned in the injection line system and to which the continuum equations are applied to the describe the temporal development of the system. The one for this By definition, pressure vibration analyzes also apply to all others Locations in the injection system under consideration.

Under the above Model requirements can change over time the pressure and / or the volume flow at the nodes, for example in a common rail system by differential equations first Order with time-dependent Coefficients are described. Doing so legitimately assumed that after a few work cycles of the internal combustion engine a steady state in terms of pressure vibrations is in the fuel distribution system because the injection timing and do not change injection quantities at constant engine speed. The Dynamics of such a discrete system, which so far are free from external interference is generally accepted as a superposition of vibrations are represented with different frequencies, each frequency one Resonance frequency of this system is.

by virtue of of opening and closing of the injectors, however, is actually the fuel injection system not to be seen as an isolated system. Rather occur in that Fuel injection system in addition to those typical in an isolated system Oscillation also caused by the external excitation of the valve actuation be generated.

If how the external stimulus is periodic here swings in because of the everywhere present the fuel injection system viscosity of the fuel also the pressure of the fuel after a certain Excitation time around its equilibrium value (i.e. the static Pressure) with the same period as the external source of excitation. The time dependency This vibration can be done using the Fourier transform mathematical method be calculated.

Therefore is used to determine a correction timing for change the time of actuation and / or the duration of actuation of an injection valve in a direct injection fuel injection system an internal combustion engine first assumed that the injection system as one after a few work cycles the high-pressure hydraulic system that has settled into the internal combustion engine can be viewed in which the geometric properties of the A spray system and the properties of certain types of fuel count as constants. It is also assumed that the operation of the Injectors an external source of excitation for the Represents fuel pressure vibrations in the injection system.

to Determination of the fuel pressure vibrations arising in such an injection system the method of the transfer function applied, its response function indicates the sum of the amplitudes and phases of the pressure wave with which this swings around the target pressure in the fuel supply system.

The thus calculated pressure oscillation phases and pressure oscillation amplitudes are then with target values of the actuation times, the fuel injection pressure and / or the injection volume compared. In the event of deviations in the achievable actual values compared to the named Target values then become at least one correction value from the deviation for the originally intended actuation time, the original intended operating time and / or that originally the intended injection volume is calculated. Then at least one of the previous target values mentioned by applying a correction value for the next and / or all. following injection processes changed in that compensation for the fuel pressure oscillation Disadvantages is achieved.

bestimmt. Die in dieser Gleichung genannten Konstanten und Variablen werden später hergeleitet und daher direkt nachfolgend nur kurz erläutert. So bedeutet X_k,0 den Gleichgewichtswert von der Komponente X_k der Zustandsvariablen X für den Druck und den Volumenstrom, l die Anzahl von Nicht-Null-Komponenten der Zustandsvariablen der äußeren Anregung F, X i / k,n die Fourier-Komponenten des Amplitudenwertes sowie Φ i / k,n die Fourier-Komponenten des Phasenwertes zwischen der k-ten Zustandsvariablen und der i-ten Steuerungsvariablen, f i / c,n und ϕ i / c,n die Koeffizienten der Fourier-Transformation der Steuerungsvariablen i, t die Zeit, T die Periode einer Kraftstoffdruckschwingung, c und s die Koeffizienten der Kosinus- und Sinusanteile sowie n einen ganzzahligen Indexwert.This method also uses the equation to determine the time dependence of the fuel pressure and / or the fuel volume flow

certainly. The constants and variables mentioned in this equation are derived later and are therefore only briefly explained immediately below. So X _{k, 0 means} the equilibrium value of the component X _{k of} the state variables X for the pressure and the volume flow, l the number of non-zero components of the state variables of the external excitation F, X i / k, n the Fourier components of the Amplitude value and Φ i / k, n the Fourier components of the phase value between the k-th state variable and the i-th control variable, fi / c, n and ϕ i / c, n the coefficients of the Fourier transform of the control variable i, t the time, T the period of a fuel pressure oscillation, c and s the coefficients of the cosine and sine components and n an integer index value.

• – Bestimmen von geometrischen Parametern des Einspritzsystems,
• – Bestimmen von Eigenschaften des Kraftstoffs,
• – Bestimmen der Zustandsvariablen F(t) der äußeren Anregungsquelle (z.B. Einspritzventilbetätigung; eingespritzte Kraftstoffmenge),
• – Fourier-Entwicklung der i-ten Komponente der Zustandsvariablen F(t),
• – Berechnen der Amplitude und Phase der Druckschwingung in dem Einspritzsystem durch Anwendung der Fourier-Transformation,
• – Korrektur des Einspritzzeitpunktes und/oder der Betätigungsdauer für das jeweilige Einspritzventil derart, dass unter Beachtung der berechneten Amplitude und Phase der Druckschwingung der gewünschte Einspritzdruck und/oder die gewünschte Einspritzmenge für die jeweiligen Einspritzventile eingehalten wird.

A specific control process can include the following process steps:

• Determining geometric parameters of the injection system,
• - determining properties of the fuel,
• Determining the state variable F (t) of the external excitation source (for example injection valve actuation; injected fuel quantity),
• Fourier expansion of the i-th component of the state variable F (t),
• Calculating the amplitude and phase of the pressure oscillation in the injection system using the Fourier transformation,
• - Correction of the injection timing and / or the actuation period for the respective injection valve in such a way that the desired injection pressure and / or the desired injection quantity for the respective injection valves is maintained, taking into account the calculated amplitude and phase of the pressure oscillation.

The geometric parameters of the injection system and / or the properties of the fuel are preferably given as constants, although these are also specified by means of suitable measuring devices intervals can be determined.

worin A eine Matrix ist, die die geometrischen Parameter des Systems und die Flüssigkeitseigenschaften des Kraftstoffs angibt, während F(t) der Vektor des Betätigungsverlaufs der Einspritzventile oder speziell betrachtet z.B. der Vektor der eingespritzten Flüssigkeitsmenge an den jeweiligen Einspritzventilen ist.To calculate the pressure and / or volume flow fluctuations in the fuel injection system, X should be referred to as the vector which specifies the pressure and volume flow values at the aforementioned nodes of the injection system. The components X _k of the vector X are referred to as state variables of the fuel. The derivation of the vector X over time then applies

where A is a matrix indicating the geometric parameters of the system and the liquid properties of the fuel, while F (t) is the vector of the actuation course of the injection valves or, in particular, the vector of the injected liquid quantity at the respective injection valves.

The Components of F (t) are periodic functions and are called Control variables referred to, which all have the same period T. and usually have different phases.

wobei f_i(t) als periodische Funktion angesehen werden kann, die auf einen i-ten Einspritzvorgang zurückzuführen ist und in ihre Kosinus- und Sinus-Komponenten zerlegt ist.The Fourier expansion of the i-th component of F (t) is

where f _i (t) can be viewed as a periodic function which is due to an i-th injection process and is broken down into its cosine and sine components.

wobei t_i gegebenenfalls benötigt wird, um den Wertebereich des Variabilitätsbereiches von f(t) bis (–T/2, T/2) zu verschieben.The Fourier components of the excitation are determined by

where t _{i may} be required to shift the value range of the variability range from f (t) to (–T / 2, T / 2).

With the main theory of linear differential equations it can be shown that a sinusoidal excitation of a control variable with the frequency of f _n = n / T with a system equilibrium in the kth component X _k of X is a sinusoidal oscillation with an amplitude X _{k, n} and with a phase Φ _{k, n} induced. This relationship can be expressed by: f n → X k, n , Φ k, n [Eq. 6]

These amplitudes and phases of the vibrations can be calculated between the control variable and the state variable X _k at the frequency f _n with the formalism of the Fourier transform. The Fourier transformation is always calculated numerically, even if, in certain cases, an approximate analytical expression could be given for certain variables or constants.

In this way, each Fourier component of the injected flow induces an oscillation of the volume flow and of the pressure at the node in question, the phase and amplitude of which are known. Since this system is linear, the time behavior of X _k can be viewed as the sum of all contributions of the Fourier components of the control variables.

worin X_k,0 der Gleichgewichtswert von X_k ist und 1 für die Anzahl von Nicht-Null-Komponenten von F steht. Dieser Gleichgewichtswert X_k,0 ist dabei nichts anderes als der statische Druck, unter dem der Kraftstoff in dem Einspritzsystem eingeschlossen ist. Um diesen Gleichgewichtswert des Drucks schwankt die Druckwelle mit den Kosinus- und Sinusanteilen der Anregungsschwingung.The temporal dependence X _k (t) of the fuel pressure and / or the volume flow at a node in the injection system, which has already been mentioned, is therefore given by

where X _{k, 0 is} the equilibrium value of X _k and 1 stands for the number of non-zero components of F. This equilibrium value X _{k, 0} is nothing else than the static pressure under which the fuel is enclosed in the injection system. The pressure wave fluctuates around this equilibrium value of the pressure with the cosine and sine components of the excitation oscillation.

The Values for X i / k, n and for Φ i / k, n from the Fourier transform between the kth state variable and the ith control variable calculated while f i / n and Φ i / n die Fourier transform coefficients of control variables i are. The value n gives the number of each in the calculation considered Summands on. The index s and the index c represent the coefficients the cosine and of the sine components.

For the mathematical analysis of this vibration behavior of the pressure wave, it is assumed that there are no nonlinear effects in the injection system or that if nonlinear effects occur they can be linearized. If, for example, the dynamic behavior of the fuel injection valves can be linearized, the control signal (piezo signal) can also be used for this valve for Fourier analysis. In addition, it is assumed that a fixed time dependency is assigned to this signal or specifically to this fuel injection rate, which is why dynamic influences of the injection quantity as a result of the actuation of the injection valve are disregarded. The fuel injection quantity is therefore simply proportional to the actuation time and the actuation duration of the injection valve in the mathematical model used. It is also assumed that the dynamics of the fuel spray system depends on precisely defined working conditions with regard to injection pressure and engine speed.

With the described mathematical function [Eq.1] was a comparative calculation carried out with of the correctness of the considerations confirmed to that effect could be that the fuel injection system in the steady Condition with regard to the pressure vibrations occurring there a Fourier analysis reliably can be described. This was initially a computerized Simulation system called "Amesim" with all necessary Data about supplies a common rail fuel injection system to be examined, to which in addition to the specific geometric information on the fuel line geometry also the properties of the injectors and their operating sequences and actuation periods, the actuation target pressure as well as the properties of the fuel used. Then was with this data a program run in a computer and the calculated pressure fluctuations in the fuel etc. in graphic Form issued.

Specifically, the analytical expression for the forced time response of the pressure and the volume flow to the excitation by the injection valve actuation was tested in a computer program with which a 4-cylinder and a 3-cylinder internal combustion engine with a common-rail injection system was simulated. The injected fuel volume flow Q (t) during an injection cycle duration T was specified as a step function for which the following relationships apply: Q (t) = 0 at 0 <t <t a [Eq. 7] Q (t) = Q inj at t a <t <t a + Δt [Eq. 8th] Q (t) = 0 at t a + Δt <t <T [Eq. 9] where t stands for the time elapsed between two injection processes on the same injection valve, Δt for the injection _duration and Q _inj for the maximum fuel _{volume flow} at the injection valve. The injection _duration Δt and the maximum volume flow Q _inj were set so that the correct injection _{quantity was} available at the operating point of the cylinder under consideration. The point in time t _a at which the fuel is injected into the cylinder was chosen so differently for each of the injection valves that the correct injection sequence was obtained. The cycle duration T was also calculated so that the desired engine speed was set.

The attached to the description Drawing shows in

1 the course of the fuel pressure is calculated using the simulation program "Amesin" for a common rail injection system, and pressure values which were calculated using the Fourier transformation method according to the invention, and in

2 the percentage error graphically plotted between the in 1 shown pressure curves of the comparative calculations.

Here is in 1 Clearly recognizable that the course of the fuel pressure at an engine speed of 1,250 rpm, as previously described, oscillates around the pressure of 600 bar specified as constant in the injection system in the simulation and a fluctuation range from 575 bar to over the period of 5 milliseconds analyzed here 628 bar.

While the solid pressure curve was calculated by the simulation system "Amesim", the individual measuring points represent the results from the pressure calculation according to the invention using the Fourier analysis and the Fourier transformation. Even the simple graphic comparison shows that the calculation results are very close together.

It shows how well the calculated pressure fluctuations actually match between the complex simulation program "Amesim" and the method according to the invention, which works much faster and requires less injection system data 2 , in which the percentage error between the two calculation methods for a common rail system in connection with a four-cylinder internal combustion engine is represented during a complete injection period with a length of 0.1 seconds is. As this course of the error shows, this error never exceeds the value of 0.09%, so that a very good agreement between the results of both calculation methods can be determined.

The proposed method for determining the pressure fluctuations advantageous in control and regulation procedures for actuating the Injectors from direct injection fuel injection systems available. These systems can both common rail and unit injector systems.

Of is a particular advantage of the calculation method according to the invention, that the correction of the injection times is analytical with a Formula can be calculated that has a clear and explicit dependency of the system geometry and the injection characteristics. The Frequencies, amplitudes and phases in this mathematical Printout for calculating the pressure fluctuations and for the injection timing and, if necessary, injection duration correction are used predefined a priori by the injection system and do not have to through constantly repeated measurements can be determined.

All in all the method is very fast and gives results in very good agreement with those of the standard means for the simulation of hydraulic systems are available. Therefore, the Calculation time when simulating injection processes in stationary Operating points of an internal combustion engine can be significantly reduced.

at this calculation can also be performed with sufficiently high computing power a vehicle computer, for example, when starting up for the first time or at predetermined intervals while operation of the vehicle. In the latter case it is preferred only the viscosity of the fuel and a one-time simulation run perform his.

Claims (5)

Method for calculating pressure fluctuations in a fuel supply system of an internal combustion engine working with direct fuel injection and for controlling its injection valves, in which the fuel supply system is defined as a high-pressure hydraulic system that has settled after a few work cycles of the internal combustion engine, in which the geometric properties of the fuel supply system and the fuel properties for a specific one Fuel type are specified or determined as constants, in which the actuation of the injection valves represent an external source of excitation for fuel pressure oscillations in the injection system, in which the Fourier analysis method is used to analyze the fuel pressure oscillations arising in such an injection system, in which the response function of the Fourier analysis specify the phases and the amplitudes of the pressure vibration components, in which the pressure vibration phases and pressure vibration ing amplitudes are compared with target values of the actuation times, the fuel injection pressure and / or the injection volume for actuating the fuel injection valves, in which, in the event of deviations in the achievable actual values compared to the specified nominal values from the deviation, at least one correction value for the originally intended actuation time, the intended actuation duration and / or the injection volume is calculated, in which at least one of the previous setpoints mentioned is changed by applying the correction value for the next and / or all subsequent injection processes in such a way that compensation for the disadvantages arising from the fuel pressure oscillation is achieved, and in which the temporal dependence of the Pressure and / or the volume flow with the equation

where X _{k, 0 is} the equilibrium value of the component X _{k of} the state variable X for the pressure and the volume flow, l for the number of non-zero components of the state variable of the other outer excitation F stands for X i / k, n for the Fourier components of the amplitude value and Φ i / k, n for the Fourier components of the phase value between the k-th state variable and the i-th control variable, fi / c, n and ϕ i / c, n mean the coefficients of the Fourier transform of the control variable i, and t stand for time, T for the period of a fuel pressure oscillation, c and s for the coefficients of the cosine and sine components, and n for an integer index value , A method according to claim 1, characterized by the following Steps: - Determine of geometric parameters of the injection system, - Determine properties of the fuel, - Determine the state variables F (t) of external excitation (e.g. injection valve actuation; amount of fuel injected), - Fourier development of the i th Component of the state variable F (t), - Calculate the amplitude and Phase of the fuel pressure oscillation in the fuel supply system by applying the Fourier transform, - Correction the time of injection and / or the duration of actuation for the respective Injector in such a way that taking into account the calculated amplitudes and phases of the fuel pressure oscillation the desired injection pressure and / or desired Injection quantity for the respective injectors are observed. A method according to claim 2, characterized in that the geometric parameters of the injection system and / or the Properties of the fuel are given as constants and / or determined by measuring devices at fixed intervals become. Method according to at least one of the preceding claims, characterized in that the Fourier development of the i-th component of the state variable F (t) of the injected fuel quantity is given by the equation

with fi / c, n and fi / s, ni as Fourier coefficients, i as the i-th injection process, t as time, T as the period of a fuel pressure oscillation, c and s as coefficients of the cosine and sine components, and with n as an integer index value. A method according to claim 4, characterized in that the Fourier coefficients are formed by