DE102008060928A1 - Method for calibrating fuel injector system of internal combustion engine, involves recording cylinder pressure in cylinder before piston reaches top point of cylinder during injection period of operating cycle of cylinder - Google Patents

Abstract

The method involves recording cylinder pressure (p1) in cylinder before a piston reaches top point of cylinder during injection period of operating cycle of cylinder. The pressure difference is determined by subtraction of a cylinder pressure from another cylinder pressure (p2), and fuel injection amount is determined from the pressure difference.

Description

The The invention relates to a method for calibrating a fuel injection device an internal combustion engine, one during an injection period in a cylinder of the internal combustion engine injected fuel injection amount is determined

at Internal combustion engines of modern motor vehicles fuel by means of Injectors injected into the cylinders. Lead a progressive service life and / or environmental influences often to a change in the relationship between the Activation duration of the injection nozzle and the fuel injection quantity, during the activation period of the injection nozzle injected into a cylinder.

Around the current relationship between the activation period and the Fuel injection amount of an injection nozzle as possible accurately determining is going to be regular, usually in overrun operation of the internal combustion engine, a so-called zero-quantity calibration the fuel injection made. This is the driving time varies while the injected fuel injection amount detected.

From the WO 2007/144253 A1 For example, a method for operating an internal combustion engine is known. In this case, during an overrun phase of the internal combustion engine, an injector of a combustion chamber is actuated for a predetermined actuation time with a predetermined actuation voltage and a resulting torque change is detected. From the torque change, an amount of fuel of the fuel injected during the actuation time by the injector is determined. These process steps are repeated for different drive voltages until a pre-set number of repetitions is reached or the internal combustion engine is no longer in the overrun phase. From the determined fuel quantities and the associated drive voltages, an injector characteristic value of the injector of the combustion chamber is determined.

From the DE 19945618 A1 For example, a method and a device for controlling a fuel metering system of an internal combustion engine are known. In this case, the activation duration of at least one electrically actuated valve determines the quantity of fuel to be injected. In certain operating states, a minimum drive duration is determined at which fuel is being injected. Starting from a starting value, the activation duration is increased or decreased. The drive time at which a change of the signal occurs is stored as a minimum drive duration. The signal used is a variable that characterizes the rotational uniformity, an output signal of a lambda probe or an output signal of an ion current probe.

From the DE 10305523 A1 are known a method and a device for calibrating a fuel injection system of an internal combustion engine of a motor vehicle with at least one controllable injection actuator. In this case, it is determined to enable the zero quantity calibration in the most general and frequently occurring operating situations, if the change over time of at least one operating variable of the internal combustion engine or of the motor vehicle is within a predefinable fluctuation range. In the case of compliance with the fluctuation range, at least one additional activation of the injection actuator is performed with a predefinable activation period and it is determined whether at least one operating parameter of the internal combustion engine has changed due to the additional activation. The activation duration of the additional activation of the injection actuator is increased stepwise until a change in the at least one operating parameter has been established.

Of the Invention is based on the object, an improved, in particular simplified method of calibrating a fuel injector specify an internal combustion engine.

The The object is achieved by a method solved with the features specified in claim 1.

advantageous Embodiments of the invention are the subject of the dependent claims.

at the inventive method for calibration a fuel injection device of an internal combustion engine one during an injection period into a cylinder of the Internal combustion engine injected fuel injection quantity determined. there be included during a duration of injection Cycle of the cylinder at least a first cylinder internal pressure detected in the cylinder before a piston in the cylinder one reaches top dead center, and at least a second in-cylinder pressure detected in the cylinder after the piston in the cylinder has passed through top dead center. By subtracting a first In-cylinder pressure of a second in-cylinder pressure becomes at least formed a pressure difference and from the at least one pressure difference the fuel injection quantity is determined.

In this case, it is advantageously utilized that the at least one pressure difference is a measure of the fuel injection quantity supplied to the cylinder. The higher a fuel injection amount supplied to the cylinder, the higher the corresponding pressure difference. Therefore, from the Druckdif be determined the fuel injection quantity supplied to the cylinder.

The Determining the fuel injection amount from the pressure difference has the advantage that it requires only a small amount of computation, because the pressure difference by simple difference formation of two internal cylinder pressures is formed. Furthermore, it is advantageous that for determining the pressure difference only a short signal chain and a low filtering effort the signal processing is needed, reducing the processing time be reduced. Furthermore, the method advantageously requires a low hardware costs. In particular, no additional Sensors required, if the cylinder already has a pressure sensor having.

embodiments The invention will be described in more detail below with reference to drawings explained.

there demonstrate:

1 a flowchart of a determination of an injected into a cylinder of an internal combustion engine fuel injection amount, and

2 a diagram for a pressure difference of cylinder internal pressures and a corrected pressure difference as a function of an engine speed.

each other corresponding parts are in all figures with the same reference numerals Mistake.

1 FIG. 14 is a flowchart showing determination of a fuel injection amount M injected into a cylinder Z of an internal combustion engine during an injection period t. FIG.

Of the Cylinder Z has a pressure sensor S. By means of the pressure sensor S are included for a duration of injection t Working cycle of the cylinder Z in a first method step S1 a first in-cylinder pressure p1 and a second in-cylinder pressure p2 of the cylinder Z detected. The first cylinder internal pressure p1 becomes detected before a piston in the cylinder Z is a top dead center reached, and the second in-cylinder pressure p2 is detected after the piston in the cylinder Z has passed through top dead center.

Prefers are the first in-cylinder pressure p1 and the second in-cylinder pressure p2 at positions of one connected to the piston of the cylinder Z. Crankshaft detected, which, based on the top dead center to each other lie symmetrically, so that crankshaft angle of these positions to a same crankshaft angle amount, for example 80 degrees, deviate from a crankshaft angle, the top dead center equivalent.

By subtracting the first cylinder internal pressure p1 from the second cylinder internal pressure p2, a pressure difference Δp is formed in a second method step S2 according to FIG Δp = p2 - p1. [1]

In a third step S3 a corrected pressure difference Ap _c is formed from the pressure difference Ap by an internal combustion engine V-dependent correction value p _c is added to the pressure difference Dp of an instantaneous engine speed D, of a stored correction value characteristic curve for the correction value p _c as a function of the engine speed D is removed. The corrected pressure difference Δp _c thus results from the pressure difference Δp and the correction value p _c according to FIG Ap c = Ap + p c , [2]

By adding the correction value p _c to the pressure difference Δp, it is taken into account that the relationship between the fuel injection quantity M and the pressure difference Δp depends on the engine speed D. This advantageously improves the determination of the fuel injection quantity M via the pressure difference Δp.

In a fourth method step S4, a fuel injection quantity M is determined from the corrected pressure difference Δp _c by means of a fuel injection quantity characteristic curve for the fuel injection quantity M as a function of the corrected pressure difference Δp _c .

there For example, the third method step S3 and the fourth method step S4 can also be combined into a common procedural step, wherein the fuel injection amount M from the pressure difference .DELTA.p and the engine speed D by means of a map for the Fuel injection amount M depending on the pressure difference .DELTA.p and the engine speed D is determined.

The the determination of the fuel injection amount M described is preferred repeatedly performed. As a result, measurement inaccuracies become advantageous the pressure detection, quantity injection error and / or statistical Fluctuations compensated. In particular, the fuel injection amount becomes M is preferably determined for different injection durations t. This can advantageously be a function of the fuel injection quantity M determined by the injection period t and to set the fuel injection amount M be used.

The determination of the fuel injection quantity M is preferably carried out in a coasting operation of the internal combustion engine. As a result, a so-called zero amount of the fuel injection amount M are determined, which is just sufficient to compensate for friction losses, so that the associated average indicated pressure of the driven cylinder is approximately equal to zero.

2 shows a diagram for the pressure difference .DELTA.p and corrected pressure difference .DELTA.p _c as a function of the engine speed D. In this case, the pressure differences .DELTA.p by a course curve 1 and the corrected pressure difference Δp _c by a corrected trajectory 2 represented and in each case based on an average value of the corrected pressure differences Δp _c , so that this mean value forms the zero line of the diagram. The engine speed is given in the unit rpm, which indicates the number of revolutions per minute.

The corrected pressure difference Δp _c results from the pressure difference Δp by addition of the dependent on the engine speed D correction value p _c according to equation [2], wherein the correction value p _c a stored correction value characteristic for the correction value p _{c is taken} as a function of the engine speed D.

A Further embodiment of the described embodiment provides in the cylinder Z during a work cycle several first internal cylinder pressures p1 at each different Detecting positions of the crankshaft before a piston in the Cylinder Z reaches a top dead center, and / or several second In-cylinder pressures p2 after the piston in the cylinder Z has passed through top dead center.

When alternative size for the pressure difference is the mean indicated pressure of a cylinder of the internal combustion engine can be used, which consists of a definable number of measured Cylinder pressure values and the associated known incremental Stroke volume of the combustion chamber is calculated and the likewise over the above corrections represent sufficient fuel quantity proportionality.

Accordingly, a plurality of pressure differences .DELTA.p are formed for a working cycle by subtracting a first cylinder internal pressure p1 from a second cylinder internal pressure p2. For these pressure differences .DELTA.p in each case a dependent of the engine speed D correction value p _{c is} added. In this case, the added correction value p _c preferably depends on the positions of the crankshaft, in each of which the first internal cylinder pressure p 1 and the second cylinder internal pressure p 2 are determined.

As a result, according to equation [2], a plurality of corrected pressure differences Δp _{c are} formed for the respective work cycle. From these an average value or a weighted mean value is formed, from which the fuel injection quantity M is subsequently determined.

In the case of the formation of a weighted mean value, the weighting can take into account the positions of the crankshaft, in which the first inner cylinder pressure p1 and the second inner cylinder pressure p2, respectively, from which the respective pressure difference .DELTA.p is formed, are determined. Furthermore, in the case of weighting, a corrected pressure difference Δp _{c may be} less heavily weighted or completely ignored in the mean value if its value deviates significantly from previously determined values and / or the values of the other corrected corrected pressure differences Δp _c .

By such determination of the fuel injection amount M from each several pressure differences Δp can be advantageous Measurement inaccuracies and / or statistical fluctuations in pressure detection balanced and thereby the accuracy of the determined Fuel injection amount M can be improved.

1

pressure difference depending on an engine speed

2

corrected Pressure difference as a function of an engine speed

S1

first step

S2

second step

S3

third step

S4

fourth step

M

Fuel injection quantity

Z

cylinder

S

pressure sensor

p1

first Cylinder pressure

p2

second Cylinder pressure

Ap

pressure difference

D

Engine speed

p _c

correction value

Δp _c

corrected pressure difference

t

Injection duration

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2007/144253 A1 [0004]
• - DE 19945618 A1 [0005]
• - DE 10305523 A1 [0006]

Claims (5)

Method for calibrating a fuel injection device of an internal combustion engine, wherein a fuel injection quantity (M) injected into a cylinder (Z) of the internal combustion engine during an injection period (t) is determined, characterized in that during a duty cycle of the cylinder (Z) including the injection duration (t) at least a first in-cylinder pressure (p1) in the cylinder (Z) is detected before a piston in the cylinder (Z) reaches top dead center, and at least a second in-cylinder pressure (p2) in the cylinder (Z) is detected after the piston in which cylinder (Z) has passed through top dead center, that at least one pressure difference (Δp) is formed by subtracting a first internal cylinder pressure (p1) from a second internal cylinder pressure (p2), and that the fuel injection quantity (M) is determined from the at least one pressure difference ( Δp) is determined. A method according to claim 1, characterized in that for determining the fuel injection quantity (M) from the at least one pressure difference (Δp) to this pressure difference (Δp) one of a current engine speed (D) of the internal combustion engine (V) dependent correction value (p _c ) added becomes. A method according to claim 2, characterized in that the correction value (p _c ) is taken from a stored correction value map. Method according to one of the preceding claims, characterized in that the first in-cylinder pressure (p1) and the second internal cylinder pressure (p2), which results in a pressure difference (Ap) is formed at positions one with the piston of respective crankshaft connected to each cylinder (Z), its crankshaft angle by an equal crankshaft angle amount deviate from a crankshaft angle, the top dead center equivalent. Method according to one of claims 1 to 3, characterized in that a plurality of symmetrical to the top dead center located pressure pairs, from which a pressure difference (Δp) is formed, at positions one with the piston of the respective Cylinder (Z) connected crankshaft to be detected, the crankshaft angle by a same crankshaft angle amount from a crankshaft angle deviate, which corresponds to the top dead center.