DE102015214815A1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine, in which fuel is injected from a high-pressure accumulator into a combustion chamber by means of a fuel injector, wherein a value representative of a static flow rate of fuel through the fuel injector (Rstat, 2) is determined, wherein representative value (Rstat, 2) deviates by more than a first threshold value (ΔR1) from a comparison value stat), a pressure in the high-pressure accumulator is increased so as to counteract or even eliminate any coking.

Description

The present invention relates to a method for operating an internal combustion engine as well as a computer unit and a computer program for its implementation.

State of the art

In the case of motor vehicles, very strict limit values apply in some cases with regard to emissions of pollutants to be controlled. In order to comply with current and, in particular, future emissions and emission limits, u.a. an accurate fuel metering during injection crucial.

However, it should be noted that different tolerances occur during metering. Such Zumesstoleranzen generally result from copy-dependent needle dynamics and copy-dependent static flow rate of the fuel injectors. An influence of the needle dynamics can be reduced, for example, by a mechatronic approach, such as, for example, a so-called Controlled Valve Operation (CVO). In a controlled valve operation, activation times of the fuel injectors are adjusted in the sense of a regulation, for example over the service life of a motor vehicle.

Possible errors in the static flow rate result from tolerances of the injection hole geometry and the needle stroke. Injection hole geometry is often optimized for good emission levels, however, which may increase sensitivity to coking. So far, such errors can only be global, i. with respect to all fuel injectors of the internal combustion engine together, for example, be corrected on the basis of a lambda control or mixture adaptation. However, this does not make it possible to detect whether individual fuel injectors of the internal combustion engine have a deviation with respect to their static flow rate (i.e., release different amounts for the same opening duration), which may be relevant for exhaust gas or airflow.

From the not pre-published DE 10 2015 205 877 For example, a method is known for determining a static flow rate of a fuel injector or a value representative thereof.

From the DE 10 2007 050 813 A1 is, for example, a method for dispensing quantity monitoring of an injector control of an internal combustion engine, in which a quantity of fuel delivered by the injector is monitored on the basis of a pressure drop in the high-pressure accumulator.

Disclosure of the invention

According to the invention, a method for operating an internal combustion engine as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

An inventive method is used to operate an internal combustion engine in which fuel is injected from a high-pressure accumulator into a combustion chamber by means of a fuel injector. In this case, a value representative of a static flow rate of fuel through the fuel injector is determined. If the representative value deviates from a comparison value by more than a first threshold value, a pressure in the high-pressure accumulator is increased.

The invention makes use of a targeted detection of a deviation of the static flow rate of fuel by a fuel injector from a comparison value, whereby a drift of the static flow rate, i. a slow deviation from the comparison value, can be closed, which in turn speaks for a coking in the combustion chamber or at the fuel injector. By increasing the pressure, the coking or incipient coking can now be counteracted. The higher pressure increases the flow rate of the medium, i. It flows more fuel per time, so that deposits are removed or entrained by the faster flowing through fuel in the sense of flushing. In the best case, the coking can not only be stopped, but even reversed. In addition, a necessary maintenance or replacement of fuel injectors can be reduced or prevented.

Preferably, the pressure in the high-pressure accumulator is increased by a first pressure value during an idling phase of the internal combustion engine. The first pressure value can be chosen so that the increase in pressure during the idle phase causes no or at least no significant acoustic interference. Suitable pressure values can be specified, for example, as a function of operating parameters of the internal combustion engine, which, for example, can be manufacturer-specific. This can be counteracted easily and for a driver not or barely perceptible coking.

It is advantageous if the pressure in the high pressure accumulator during a partial load phase of Internal combustion engine is increased by a second pressure value. The second pressure value can be chosen in particular higher than the first pressure value, since during a partial load operation, a possible acoustic disturbance is perceived less than during idling operation. The coking can be counteracted particularly effectively if the pressure is increased by the respective pressure value both during an idling phase and during a partial load phase.

Advantageously, when the representative value deviates from the comparison value by more than a second threshold value, which is greater than the first threshold value, the pressure in the high-pressure accumulator at least during an idling phase and a partial load phase, in particular during a full load phase of the internal combustion engine by one third pressure value increased. In particular, the pressure in all operating phases of the internal combustion engine can be increased by the third pressure value. When checking the deviation of the representative value from the comparison value, it is also possible to take into account the mileage of the internal combustion engine, a total operating time and other variables which may influence such a deviation. In this way, the coking, if this is already well advanced, be counteracted in the best possible way. In particular, then a possible acoustic interference against a failure or defect of a fuel injector can be preferred. The third threshold value can be specified, for example, based on empirical values.

It is understood that the respective pressure increases, which are carried out during one or more of said phases, can be retained for the subsequent respectively identical phases or can be reset.

Preferably, if the representative value deviates from the comparison value by less than a third threshold value after an increase in the pressure in the high-pressure accumulator, the pressure in the high-pressure accumulator is reduced. In this way, an unnecessary pressure increase, i. An increase in pressure when there are no signs of coking more can be avoided. In particular, the pressure can be reduced again to a regular operating pressure. This reduction can take place, for example, step by step.

Advantageously, the comparison value is repeated or updated continuously. Thus, the most up-to-date status with regard to the signs of coking can always be taken into account and an increase in pressure can be optimally adjusted.

It is advantageous if a profile of the deviation of the representative value from the comparison value and / or the increase in pressure in each case over a mileage of the internal combustion engine is detected and stored. The deposit can take place, for example, on a memory in an exporting control unit. In this way, the data can be made very easily available for a workshop. In particular, thus, for example, a targeted cleaning or targeted replacement of a defective fuel injector possible. In addition, these field data can be stored and, for example, later evaluated.

Advantageously, the representative value is determined by determining, in at least one injection process of the fuel injector, a ratio of a pressure difference occurring in the high-pressure accumulator due to the injection process and an associated duration characteristic of the injection process. It can be exploited that the amount of fuel delivered by a fuel injector during an injection process or the volume thereof is proportional or at least sufficiently proportional to the associated pressure difference, i. the pressure difference before and after the injection process, is in the high-pressure accumulator. If, in addition, a characteristic duration for the injection process is known, a value can be determined from the ratio of this pressure difference and the associated duration which, except for a proportionality factor, corresponds to the static flow rate through the fuel injector. In this way, a value representative of the flow rate can be easily obtained.

It is advantageous if the comparison value is determined taking into account corresponding representative values of all fuel injectors of the internal combustion engine. In this way, a comparison value can be determined very easily. In particular, in this approach, the actual flow rate need not be determined because only the respective representative values are used, which is a relative comparison, i. the determination of whether the flow rate at a fuel injector from which the other fuel injectors deviates, is sufficient. In particular, any systematic measurement errors are negligible in this way. However, if the conversion values for converting the representative value into the associated flow rate are known, it is also conceivable to use the flow rate directly as representative values. In particular, it can be made use of here that a deviation of the flow rate or of the representative value for each fuel injector is generally different.

An arithmetic unit according to the invention, for example a control unit, in particular an engine control unit, of a motor vehicle is, in particular programmatically, adapted to carry out a method according to the invention.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically by means of embodiments in the drawing and will be described below with reference to the drawing.

Brief description of the drawings

1 schematically shows an internal combustion engine with common rail system, which is suitable for carrying out a method according to the invention.

2 shows in a diagram a flow volume at a fuel injector over time.

3 shows in a diagram a pressure curve in a high-pressure accumulator during an injection process.

4 shows a representative value for a static flow rate and a comparison value in a method according to the invention in a preferred embodiment.

5a and 5b show pressure increases in a method according to the invention in various preferred embodiments.

Embodiment (s) of the invention

In 1 is schematically an internal combustion engine 100 shown, which is suitable for carrying out a method according to the invention. By way of example, the internal combustion engine comprises 100 three combustion chambers or associated cylinders 105 , Every combustion chamber 105 is a fuel injector 130 assigned, which in turn each to a high-pressure accumulator 120 , a so-called rail, via which it is supplied with fuel. It goes without saying that a method according to the invention can also be carried out in an internal combustion engine with any other number of cylinders, for example four, six, eight or twelve cylinders.

Next is the high-pressure accumulator 120 via a high-pressure pump 110 with fuel from a fuel tank 140 fed. The high pressure pump 110 is with the internal combustion engine 100 coupled, for example, such that the high-pressure pump is driven via a crankshaft of the internal combustion engine, or via a camshaft, which in turn is coupled to the crankshaft.

A control of the fuel injectors 130 for metering fuel into the respective combustion chambers 105 via a motor control unit 180 trained computing unit. For the sake of clarity, only the connection from the engine control unit 180 to a fuel injector 130 However, it is understood that each fuel injector 130 is connected to the engine control unit accordingly. Every fuel injector 130 can be specifically controlled. Furthermore, the engine control unit 130 adapted to the fuel pressure in the high-pressure accumulator 120 by means of a pressure sensor 190 capture.

In 2 is a graph showing a cumulative flow volume V through a fuel injector over the time t in a long-term control of the fuel injector. At time t ₀ , a drive time begins and at time t ₁ , the valve needle begins to lift. At time t ₁ thus also starts an open duration of the fuel injector. It can be seen that the cumulative flow volume V or the amount of fuel that has flowed through the fuel injector increases constantly over a wide range after a short period of time during the lifting of the valve needle. In this area, the valve needle is in the so-called full stroke, ie the valve needle is raised completely or up to a desired height.

During this time, a constant amount of fuel per unit time flowing through the valve opening of the fuel injector, ie, the static flow rate Q _stat indicating the slope of the cumulative flow volume V is constant. The size of the static flow rate is an important factor which, as already mentioned, determines the total amount of fuel injected during an injection process. Deviations or tolerances in the static flow rate therefore affect the injected fuel quantity per injection process.

At time t ₃ , the activation time ends and the closing time begins. The valve needle begins to lower. The closing time and the opening duration end at the time t ₄ , when the valve needle completely closes the valve again.

In 3 is a graph showing a pressure waveform in a high-pressure accumulator during an injection process over time t. It can be seen that the pressure p in the high-pressure accumulator, apart from certain fluctuations due to pump deliveries and fuel withdrawals by injection, is substantially constant. During the injection process, which lasts for a time period Δt, the pressure p in the high-pressure accumulator drops by a value Δp.

Subsequently, the pressure remains p, again apart from certain fluctuations, at the lower level until, by a Nachförderung through the high-pressure pump, the pressure p rises again to the initial level.

The detection and evaluation of these pressure drops in injection processes is carried out with usually already existing components, such as. The pressure sensor 190 and the engine control unit 180 including appropriate input circuit. Additional components are therefore not necessary. This evaluation is done individually for each combustion chamber 105 ,

The static flow rate Q is _stat by the fuel, as mentioned above, characterized by the injected fuel quantity or the volume per time. In a high-pressure accumulator or rail inflated to system pressure, the injected volume is proportional to the pressure drop in the rail. The associated period corresponds to the open duration of the fuel injector, which, for example, as mentioned above, mechatronically by means of a so-called. Controlled Valve Operation (see, eg DE 10 2009 002 593 A1 ) can be determined.

A quotient formation between the pressure drop or pressure difference Δp and the opening duration or time duration of the injection Δt results in a pressure rate as a substitute value or representative value R _stat = Δp / Δt for the static flow rate Q _stat , ie for a measuring process Q _stat ⎕ Δp / Δt. An additional pumping through the high-pressure pump should not fall into the relevant time window. An additional promotion is therefore to be suppressed if necessary.

In 4 are shown in a diagram by way of example three representative values R _{stat, 1} , R _{stat, 2} and R _{stat, 3} , as they are, for example. For in 1 shown fuel injectors can be determined according to the method explained above.

Furthermore, a comparison value R _stat shown, which is obtained by way of example from the three representative values R _{stat, 1} , R _{stat, 2} and R _{stat, 3} , for example, as an arithmetic mean. Furthermore, a first threshold ΔR _{1 is} shown. As in 4 can be seen, the representative values R _{stat, 2} deviates by more than the first threshold value ΔR ₁ from the comparison value R _stat from.

In 5a is shown in a diagram, a pressure p in a high-pressure accumulator over a time t. In this case, a pressure curve with an increase of the pressure in a method according to the invention in a preferred embodiment is shown.

Initially, the pressure has the value p ₀ , which may, for example, be a regular operating pressure. Will now, as in 4 shown, that a representative value for a fuel injector from a comparison value deviates by more than a first threshold .DELTA.R ₁ , so during an idle phase .DELTA.t _1, the pressure in the high-pressure accumulator by a first pressure value .DELTA.p _{1 can be} increased.

In addition, the pressure in the high pressure accumulator, as shown here, during a partial load phase _{.DELTA.t.sub.2} which follows by way of example to the idling phase, by a second pressure value Dp ₂ can be increased. It is also conceivable that the pressure is only increased by the respective pressure value during one of the two phases.

In this way, coking of the relevant fuel injector can be counteracted. In particular, even slight deviations of the representative value from the comparison value, such as, for example, by slightly more than the first threshold value, a moderate increase in pressure.

In 5b is shown in a diagram, a pressure p in a high-pressure accumulator over a time t. In this case, a pressure curve with an increase of the pressure in a method according to the invention is shown in a further preferred embodiment.

Initially, the pressure has the value p ₀ , which may, for example, be a regular operating pressure. If it is now recognized that a representative value for a fuel injector deviates from a comparison value by more than a second threshold value, the pressure in the high-pressure accumulator can be increased by a third pressure value Δp ₃ during an idling phase Δt ₁ and during a partial load phase Δt ₂ , It is also conceivable that the pressure is increased during each operating phase.

In this way, coking of the relevant fuel injector can be counteracted become. In particular, with already high deviations of the representative value from the comparison value, such as, for example, by a little more than the second threshold value, a strong pressure increase can take place.

It is understood that initially only a pressure increase as in 5a and if the deviation of the relevant representative value from the comparison value does not decrease but continues to increase, a further increase in pressure as in 5b can be shown.

If a decrease in the deviation is detected, in particular below a third threshold, the pressure increase can be withdrawn again. For example. The pressure increase can be gradually reduced to the regular operating pressure.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015205877 [0005]
• DE 102007050813 A1 [0006]
• DE 102009002593 A1 [0037]

Claims (12)

Method for operating an internal combustion engine ( 100 ), by means of a fuel injector ( 130 ) Fuel from a high pressure accumulator ( 120 ) in a combustion chamber ( 105 ), wherein one for a static flow rate (Q _stat ) of fuel through the fuel injector ( 130 ) Representative value (R _{stat, 2)} is determined, wherein when the (representative value R _{stat, 2)} by more than a first threshold value (.DELTA.R ₁₎ from a comparison value ( R _stat ) deviates, a pressure (p) in the high-pressure accumulator ( 120 ) is increased. Method according to claim 1, wherein the pressure (p) in the high pressure accumulator ( 120 ) during an idle phase (At ₁ ) of the internal combustion engine ( 100 ) is increased by a first pressure value (Δp ₁ ). Method according to claim 1 or 2, wherein the pressure (p) in the high pressure accumulator ( 120 ) during a partial load phase (At ₂ ) of the internal combustion engine ( 100 ) is increased by a second pressure value (Δp ₂ ). Method according to one of the preceding claims, wherein, if the representative value (R _{stat, 2} ) is greater than a second threshold value (ΔR ₂ ) that is greater than the first threshold value (ΔR ₁ ), from the comparison value ( R _stat ) deviates, the pressure (p) in the high-pressure accumulator ( 120 ) at least during an idling phase (At ₁ ) and a part-load phase (At ₂ ), in particular also during a full-load phase, of the internal combustion engine ( 100 ) is increased by a third pressure value (Δp ₃ ). Method according to one of the preceding claims, wherein, if the representative value (R _{stat, 2} ) increases after an increase in the pressure (p) in the high-pressure accumulator ( 120 ) by less than a third threshold from the comparison value ( R _stat ) deviates, the pressure (p) in the high pressure accumulator ( 120 ) is reduced. Method according to one of the preceding claims, wherein the comparison value ( R _stat ) is updated repeatedly or continuously. Method according to one of the preceding claims, wherein a profile of the deviation of the representative value (R _{stat, 2} ) from the comparison value ( R _stat ) and / or increasing the pressure (p) respectively over a mileage of the internal combustion engine ( 100 ) is recorded and deposited. Method according to one of the preceding claims, wherein the representative value (R _{stat, 2} ) is determined by at least one injection operation of the fuel injector ( 130 ) a ratio of one in the high-pressure accumulator ( 120 ) is determined on the basis of the injection process occurring pressure difference (Δp) and an associated, characteristic of the injection process duration (At). Method according to one of the preceding claims, wherein the comparison value ( R _stat ) taking into account corresponding representative values (R _{stat, 1} , R _{stat, 2} , R _{stat, 3} ) of all fuel injectors ( 130 ) of the internal combustion engine ( 100 ) becomes. Arithmetic unit ( 180 ), which is adapted to perform a method according to any one of the preceding claims. Computer program comprising a computing unit ( 180 ) to perform a method according to any one of claims 1 to 9, when it on the computing unit ( 180 ) is performed. Machine-readable storage medium with a computer program stored thereon according to claim 11.

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