DE102004054372B3 - Method for determining fuel mass flow in internal combustion engine involves measuring of voltage by piezoelectric actuator which also calculates input electric energy and fuel mass flow is calculated per combustion cycle - Google Patents

Abstract

Method involves measuring of voltage (UP) by piezoelectric actuator which also calculates input electric energy (E). Fuel mass flow (MFF) is calculated per combustion cycle. The method involves comparison of fuel mass flow with lower threshold value (MFFmin) and upper threshold value (MFFmax), a parameter is adapted and reaction is initiated. Fuel mass flow is calculated per combustion cycle, whereby the outlet surface at the injection valve, depending on the energy input of the piezoelectric actuator, is determined. Independent claims are also included for the following: (A) Device; (B) Program; (C) Data storage medium; and (D) Program product.

Description

The The invention relates to a method and a device for determining a fuel mass flow in an internal combustion engine.

to Calculation of the current engine torque is in internal combustion engines with quantity regulation the amount of fuel injected into a cylinder per cycle, the so-called fuel mass flow, determined.

In a known method ( DE 100 21 086 A1 ) for determining the fuel mass flow in an internal combustion engine, the time profile of the drive current for the injection valve is detected and determines a holding phase during which the injection valve is open. In the method described there, the fuel mass flow is assumed to be constant during this holding phase.

Especially Injectors which are actuated by a piezoelectric actuator, This assumption is problematic because these actuators have no have mechanically defined end position. That is the open valve state is not right with a Nadelhub and a resulting perfused Cross section equate.

In a further method for determining the duration of injection in a direct injection internal combustion engine ( DE 198 03 689 C1 ), the injection time is applied to a correction factor, which includes both the pressure difference between the fuel pressure and the current cylinder pressure, as well as the fuel density at the time of injection.

Also known is a method for determining the injection time in a direct injection internal combustion engine ( DE 197 18 171 A1 ), in which by taking into account the compression pressure occurring in the cylinder at the start of injection, the required injection mass can be metered with great accuracy.

Finally, a method for operating an internal combustion engine is known (US Pat. DE 101 47 814 A1 ), at least approximately determine a current valve characteristic of the built-in internal combustion engine fuel injection device from a torque of the internal combustion engine. In this case, the valve characteristic curve is intended to link a fuel mass flow, which is to be delivered by the fuel injection device, with the drive energy supplied to the piezoelectric actuator.

It is therefore an object of the invention, a method and an apparatus which make it possible to the fuel mass flow through a piezoelectric actuator driven valve in a simple manner to determine.

These The object is achieved by a method according to claim 1 and by a Device according to claim 7 solved.

to Calculation of the fuel mass flow is the piezoelectric Actuator during fed to a charging process Amount of charge determined. After the charging process, the Measured voltage applied to the piezoelectric actuator. From the amount of charge supplied to the actuator and the voltage is supplied to the piezoelectric actuator electrical Energy calculated.

in the This is followed by the fuel mass flow, the per cycle a cylinder is determined, determined, the area of a outlet opening at the injection valve in dependence from the energy supplied to the piezoelectric actuator during the charging phase is determined. Now it is checked if the determined fuel mass flow in a predetermined range between lower and upper thresholds. Is this the Case, the internal combustion engine works properly. Is this not the case, so is in the control of the internal combustion engine intervened.

Further a device is proposed with which in particular the inventive method To run leaves. The device has an evaluation unit with means for measuring a quantity of electric charge supplied to a piezoelectric actuator on. Further, it has means for measuring a piezoelectric Actuator voltage applied. The evaluation unit points beyond Means on, depending on from the amount of charge supplied to the piezoelectric actuator and the on the piezoelectric actuator adjacent to a charging process Voltage an amount of energy supplied to the piezoelectric actuator and depending one per working cycle of the internal combustion engine in a cylinder discharged fuel mass flow is calculated. Next, the Device comparison means, which determines the thus determined fuel mass flow with a predetermined lower threshold and / or an upper one Threshold compares and a reactant that due the result of the comparison triggers a reaction.

The scope of the invention also includes a computer program that runs on a com computer executes the method according to the invention in one of its embodiments.

Also belongs to the scope the invention a computer program with program code means to the inventive method to perform in one of its embodiments when the program is up a computer or computer network.

These Program code means can in particular be stored on a computer-readable medium. Also belongs to the scope of the invention a disk, on which a data structure is stored after a load in a working and / or main memory of a computer or computer network the inventive method in one of its embodiments can perform. Also belongs to the scope invention of a computer program product with on a machine-readable carrier stored program code means to the inventive method to perform in one of its embodiments when the program is up a computer or computer network.

advantageous Embodiment of the invention are described in the subclaims.

Instead of a comparison of the determined fuel mass flow with a Threshold may also be a comparison of one of the fuel mass flow derived size with one Threshold value.

In a particular embodiment of the method is when the determined fuel mass flow outside the range between the lower threshold and the upper threshold Change from a stratified charge operation to a one-service operation homogeneous stoichiometric Fuel mixture done. additionally or alternatively to this change can from the evaluation a Error message or an error signal are generated.

at a stratified charge mode, there is a charge stratification at the combustion chamber is not filled homogeneously with a fuel mixture. In this case, there are zones that are more enriched or more emaciated Burning mixture obtained. The aim of such a layer charge is to distribute the fuel mixture in the combustion chamber so that in nearby a spark plug an enriched mixture for better ignition and removed from the spark plug gives a lean mixture. In this way, you can a fuel can be saved and on the other hand the emissions of the Internal combustion engine can be reduced.

at an operation with a homogeneous stoichiometric fuel mixture is the composition between fuel and air throughout Cylinder almost homogeneous. Next, the internal combustion engine is operated, that theoretically a complete Combustion of the fuel is achieved (stoichiometric operation).

In a further preferred embodiment an entry is made in a fault memory as soon as the determined fuel mass flow outside of the lower Threshold and the upper threshold spanned range lies.

In an advantageous embodiment of the method is the upper and / or the lower threshold depending on at least one Parameter varies. In particular, this parameter can be an operating parameter play the internal combustion engine.

α

= Durchflusszahl;

K_G

= Konstante, die die Austrittsgeometrie der Austrittsöffnung am Einspritzventil wieder gibt;

E

= dem piezoelektrischen Stellglied während eines Ladevorgangs zugeführte elektrische Energie;

ϑ

= Dichte des Kraftstoffes;

Δp

= Druckdifferenz zwischen Kraftstoffdruck und Brennraumdruck; und

T_E

= Einspritzdauer.

In particular, the fuel mass flow is calculated according to the following relationship: MFF = α · K G • E • T e · √ 2 · θ · Ap With

α

= Flow rate;

K _G

= Constant, which gives the exit geometry of the outlet opening at the injection valve again;

e

electrical energy supplied to the piezoelectric actuator during a charging process;

θ

= Density of the fuel;

Ap

= Pressure difference between fuel pressure and combustion chamber pressure; and

T _E

= Injection duration.

Further it is of particular advantage if, on the basis of the determined fuel mass flow concluded back on the torque generated by the internal combustion engine becomes.

Furthermore is in a further preferred embodiment of the fuel mass flow and an additional one Parameters of the internal combustion engine, in particular the air mass flow, a Characteristic determined. This parameter can compared with a measured or operating point dependent threshold become. For example, from the fuel and the air mass flow a characteristic determined that will be with a reading for the oxygen content in the exhaust gas (λ) is compared.

An embodiment of the invention will explained in more detail below with reference to the schematic drawings. Show it:

1 the course of an actuator current, an actuator voltage and an actuator stroke of a piezoelectric actuator;

2 a block diagram of an embodiment of a device according to the invention; and

3 a flowchart of an embodiment of the method according to the invention.

1 shows a simplified block diagram of an apparatus for determining a fuel mass flow in an internal combustion engine. This device has an evaluation unit ECU, which acts on a drive unit AE with a control signal AE _signal . The drive unit AE is on the one hand electrically connected to a first potential VCC of a supply voltage source, not shown, and on the other hand to a piezoelectric actuator P. The piezoelectric actuator P is arranged between the drive unit AE and a second potential GND of the supply voltage source.

The Evaluation unit ECU has two inputs UP and IL, via the recorded two physical quantities become. For one, here is the above Actuator P falling electrical voltage UP tapped and the other the supplied from the drive unit AE the piezoelectric actuator P current IL determined. The evaluation unit ECU further has an integration unit INT, in which the integral of the charging current IL over the time t is formed.

The evaluation unit ECU has, in addition to the control output AE _signal, a further output MFF _ERROR . This can be used, for example, to pass on an error detected by the evaluation unit ECU to another control unit, not shown, or a fault memory, also not shown.

2 each shows a time course of the actuator current I _L , the actuator voltage UP and the change in length d of the piezoelectric actuator.

In this case, the charge of the piezoelectric actuator P is started at time t1. For this purpose, the evaluation unit ECU sends a control signal AE _signal to the drive unit AE. This drive _signal AE _signal may also contain information such as a charging time T _L , a maximum charging current I _Lmax, a maximum charging voltage UL or a hub d to be _controlled .

At the time t1 flows from the drive unit AE, a charging current I _L to the piezoelectric actuator p. This current decreases exponentially from a maximum I _Lmax over the charging time T _L with increasing charging of the piezoelectric actuator P. The drive unit AE maintains the charging current I _L over the charging period T _L.

At time t2, the charging current I _{L is} turned off. The charging period T _L may, for example, have been predetermined by the evaluation unit ECU or determined in dependence on a physical quantity of the piezoelectric actuator P, such as, for example, the charging current I _L or the voltage UE of the actuator P.

From At time t2, the actuator voltage UP is at an approximately constant Value UL held. Depending on the nature of the piezoelectric actuator can for keeping the actuator voltage UP constant, short-term charging or discharging currents must be kept constant.

From a time t3, the piezoelectric actuator P is discharged. For discharge flows a discharge current I _L (in 2 represented as a negative charging current I _L ) from the piezoelectric actuator P to the drive unit AE. The amount of this discharge current IL decreases exponentially from a maximum I _maxFl to a minimum charging current I _minEl . This minimum discharge current I _minEl sets in at a time t4. This time t4 is either specified by the evaluation unit ECU or determined on the basis of a physical size of the actuator, for example at an actuator voltage of 0 volts.

Between times t1 and t3, the injection period T _{E is} during which fuel is injected into the respective cylinder. The stroke d of the piezoelectric actuator P adjusts itself during this period to a maximum stroke d _max . Assuming that the surface integrals of the charging and discharging phases are on average the same, for example, for the calculation of the stroke simplifying a rectangular course can be assumed. At time t3, the stroke d drops to the value 0, whereby the injection process is terminated.

mit

t1

= Zeitpunkt des Ladebeginns;

t2

= Zeitpunkt des Ladeendes; und

I_L

= Ladestrom.

3 shows a flowchart of an embodiment of a method for determining a fuel mass flow in an internal combustion engine. This is done after starting the procedure (step 300 ), the actuator P is charged and thereby flowing charging current IL measured (step 301 ). This corresponds to the period T _L between the times t1 and t2 of 2 , At the end of the charging process after time t2, the actuator voltage U _{P is} measured (step 302 ) and then the energy E supplied to the piezoelectric actuator P is calculated. For this purpose, first the the piezo electrical actuator P during charge is supplied charge amount ΔQ determined:

With

t1

= Time of loading start;

t2

= Time of loading end; and

I _L

= Charging current.

From the amount of charge ΔQ present on the piezoelectric actuator at time t2, the energy E supplied to the piezoelectric actuator P is subsequently determined: E = 1/2 · U L · .DELTA.Q with U _L = voltage across the piezoelectric actuator P at time t2.

α

= Durchflusszahl;

K_G

= Konstante, die die Austrittsgeometrie der Austrittsöffnung am Einspritzventil wieder gibt;

E

= dem piezoelektrischen Stellglied während eines Ladevorgangs zugeführte elektrische Energie;

ϑ

= Dichte des Kraftstoffes;

Δp

= Druckdifferenz zwischen Kraftstoffdruck und Brennraumdruck; und

T_E

= Einspritzdauer.

Following this, the fuel mass flow is determined from the energy E supplied to the actuator P (step 305 ): MFF = α · K G • E • T e · √ 2 · θ · Ap With

α

= Flow rate;

K _G

= Constant, which gives the exit geometry of the outlet opening at the injection valve again;

e

electrical energy supplied to the piezoelectric actuator during a charging process;

θ

= Density of the fuel;

Ap

= Pressure difference between fuel pressure and combustion chamber pressure; and

T _E

= Injection duration.

In the following, the thus determined fuel mass flow MFF is compared with a lower threshold value MFF _min and an upper threshold value MFF _max (step 306 ). If the fuel mass flow in the lower MFF determined from the threshold MFF _min and the upper threshold MFF _max spanned band range, the internal combustion engine is assumed here proper function. In this case, the procedure is then terminated (step 307 ).

If it is determined that the determined fuel mass flow MFF is outside the range spanned by the two threshold values MFF _min and MFF _max , parameters of the internal combustion engine are adapted in a further step. Here, for example, a switchover from an operation with a stratified charge into an operation with a homogeneous mixture with an air ratio λ = 1 can be switched over and / or different parameters of the charging of the piezoelectric actuator P, in particular the charging current IL, the charging time duration or the charging voltage UP, be adjusted.

The threshold values MFF _min and / or MFF _max can here also be varied as a function of various parameters of the internal combustion engine, such as the rotational speed, the torque N, a change in the rotational speed dn / dt or the throttle valve position α.

These Reaction to a fuel mass flow MFF outside the tolerable limits can be corrected or the result the unacceptably small or big ones Fuel mass flow MFF can be reduced in this way so that nevertheless an operation of the internal combustion engine is possible. In this way, it can be ensured, for example, that the motor vehicle remains functional until a workshop is visited.

In addition to this adaptation of a parameter, an entry into an error memory can take place due to the fuel mass flow MFF lying outside the band range between MFF _min and MFF _max (step 326 ). This error entry can be read, for example, in the diagnosis of the internal combustion engine as part of a maintenance. By determining the fuel mass flow MFF, a torque monitoring and / or a fault diagnosis of the injection valve can take place.

The Pressure difference ΔP between fuel pressure and combustion chamber pressure can on the one hand by two Pressure sensors are determined. This would then be a pressure sensor in High-pressure area of the fuel system, for example in the high-pressure accumulator (Rail) necessary. The combustion chamber pressure can on the one hand by means of a Pressure sensor can be measured directly or from the parameters injection time t1, Injection duration TE and the cylinder filling read out of a map become. Here, the cylinder filling, for example, by a signal from the mass air flow sensor or an additional intake manifold pressure sensor determined.

In the event that the charging current and / or the charging voltage are constant during the charging process, the charging time T _L = t ₂ -t _{1 can be used} to deduce the charge quantity ΔQ supplied to the actuator P or the supplied energy E.

Claims (12)

Method for determining a fuel mass flow in an internal combustion engine, comprising the following method steps: - detecting a charge quantity supplied to a piezoelectric actuator (P) during a charging operation, - measuring a voltage (U _P ) applied to the piezoelectric actuator ( _P ); - calculating the piezoelectric actuator (P) supplied electrical energy (E); Calculating the fuel mass flow (MFF) output per working cycle, wherein the area of an outlet opening on the injection valve is determined as a function of the energy (E) supplied to the piezoelectric actuator (P); and - Comparing the fuel mass flow (MFF) with a predetermined lower threshold (MFF _Min ) and / or a likewise predetermined upper threshold (MFF _Max ), depending on this comparison, a parameter adjusted and / or a reaction is triggered. A method according to claim 1, characterized in that in the case where the determined fuel mass flow (MFF) is outside the range between the lower threshold (MFF _Min ) and the upper threshold (MFF _Max ), a change from a stratified charge mode to an operation carried out with homogeneous stoichiometric fuel mixture. A method according to claim 1 or 2, characterized in that an entry is made in a fault memory, if the determined fuel mass flow (MFF) is outside the range defined by the lower threshold value (MFF _Min ) and the upper threshold value (MFF _Max ). Method according to one of the preceding claims, characterized in that the upper and / or the lower threshold value (MFF _Min , MFF _Max ) is varied as a function of at least one parameter of the internal combustion engine (BKM). Method according to one of the preceding claims, characterized in that the calculation of the fuel mass flow (MFF) takes place according to the relationship: MFF = α · K G • E • T e · √ 2 · θ · Ap with α = flow rate; K _G = constant, which gives the outlet geometry of the outlet opening at the injection valve again; E = electrical energy supplied to the piezoelectric actuator during a charging process; θ = density of the fuel; Δp = pressure difference between fuel pressure and combustion chamber pressure; and T _E = injection duration. Method according to one of the preceding claims, characterized characterized in that due to the determined fuel mass flow (MFF) on the torque generated by the internal combustion engine (N) is closed. Device, in particular control unit, for determining a fuel mass flow (MFF) in an internal combustion engine (BKM), comprising: - an evaluation unit (ECU) having means for measuring an electrical charge quantity (ΔQ) supplied to a piezoelectric actuator (P), means for measuring an am voltage (U _P ) applied to the piezoelectric actuator ( _P ), means for calculating an amount of energy (E) supplied to the piezoelectric actuator (P) depending on the amount of charge (ΔQ) applied to the piezoelectric actuator (P) and that on the piezoelectric actuator Actuator (P) applied voltage (U _P ) is carried out and based on this amount of energy per cycle discharged fuel mass flow (MFF) is determined, - a comparison means, the fuel mass flow (MFF) thus determined with a predetermined lower threshold (MFF _Min ) and / or an upper threshold (MFF _Max ). Device according to claim 7, characterized in that in that the device has a reaction agent, if appropriate due to the comparison result triggers a reaction. Program, in particular computer program, with program code means to provide a method according to the claims 1 to 6, perform when the program on at least one control unit of an internal combustion engine accomplished becomes. Computer program with program code means according to the preceding one Claim stored on a computer-readable medium. disk, on which a data structure is stored after a load in a working and / or main memory of at least one control unit an internal combustion engine, the method according to one of claims 1 to 6 executes. Program product, in particular computer program product, with program code means stored on a machine-readable carrier, to perform all the steps of a method according to claims 1 to 6, when the program on at least one control unit of an internal combustion engine accomplished becomes.