CN104895692B

CN104895692B - Method for correcting a deviation of an actual injection quantity from a setpoint injection quantity caused by a pump

Info

Publication number: CN104895692B
Application number: CN201510165979.2A
Authority: CN
Inventors: S·特兰
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-02-27
Filing date: 2015-02-26
Publication date: 2021-09-03
Anticipated expiration: 2035-02-26
Also published as: DE102014211314A1; CN104895692A

Abstract

The invention relates to a method for metering an injection quantity of fuel into at least one combustion chamber of an internal combustion engine by means of a fuel injector, wherein the fuel injector is supplied with fuel by a high-pressure accumulator, which is supplied with fuel by a high-pressure pump, wherein the pump operating gap position of the high-pressure pump is taken into account when metering the injection quantity.

Description

Method for correcting a deviation of an actual injection quantity from a setpoint injection quantity caused by a pump

Technical Field

The invention relates to a method for metering an injection quantity of fuel into a combustion chamber, in particular for reducing injection quantity deviations between individual combustion chambers of an internal combustion engine.

Background

In a common rail system, the injection characteristics of the fuel injectors are under the influence of the delivery characteristics of the high-pressure pump. For this reason, it is often expedient to select the speed ratio between the pump speed and the motor speed such that the same operating gap position of the high-pressure pump is visible for all cylinders or fuel injectors of the associated combustion chambers. This ensures a minimum block-injection quantity deviation and thus a smooth engine operation. In this case, a single-jet synchronized pump feed is referred to.

The speed ratio so selected may not be sufficiently balanced in some cases. That is to say the high-pressure pump does not provide sufficient fuel for the injection system. Higher speed ratios are desirable in this case, which may refer to non-single injection synchronous pump feed and thus improved cylinder-to-cylinder injection quantity deviations.

In the case of a non-injection-synchronous pump supply, it can occur that the pump operating cycle position is repeated in a later cycle in a later injection event of the other fuel injector or of the same fuel injector. In such a case, a fuel injector-specific pressure can be used in the later injection event, which was previously detected for a specific pump operating cycle position, in which the pump operating cycle position repeats itself, and therefore the activation duration of the fuel injector is adapted and the injection quantity is corrected as a result. Such a situation with repeatable pump duty cycle positions is also described as MAR synchronization.

DE102007019640a1 discloses a method for controlling injection, in which a correction of the pressure value in the high-pressure system occurs using a previous value, which is subjected to a temporal offset when it is transmitted to the control.

However, there are also situations in which neither injection synchronization nor MAR synchronization pump feed is present.

It is therefore desirable that the possibility for reducing the cylinder-cylinder injection quantity deviations is also proposed in particular for the aforementioned case.

Disclosure of Invention

According to the invention, a method is proposed with the features of patent claim 1. Advantageous embodiments are the subject matter of the dependent claims and the following description.

The method according to the invention is used for metering an injection quantity of fuel into at least one combustion chamber of an internal combustion engine by means of a fuel injector, wherein the fuel injector is supplied with fuel by a high-pressure accumulator, in particular a so-called common rail, which is supplied with fuel by a high-pressure pump. In this case, the pump cycle position of the high-pressure pump is taken into account when dosing the injection quantity for the method according to the invention. The pump operating cycle position is taken into account in particular as a function of the crank angle of the internal combustion engine by which the pump is driven.

Since the pressure in the high-pressure accumulator can be varied at least to some extent as a function of the pump operating cycle position of the high-pressure pump, the precise injection quantity can also be varied in other constant actuations of the fuel injector. This results in different injection quantities for otherwise identical conditions, when the pressure prevailing at the fuel injector during the injection now changes from one injection to another or between different fuel injectors of the internal combustion engine. This also leads to an unstable operation of the internal combustion engine and also to poor emission values, since the desired optimum injection quantity is not injected. By taking into account the operating position, the injection quantity can therefore be adapted accordingly, which results in a smoother operation of the internal combustion engine and better emission values.

A further advantage of the method according to the invention is that it enables the use of high-pressure pumps in a speed ratio, in which no synchronization of the pump duty cycle position exists at the injection time and therefore the use of the method described in document DE102007019640a1 is not possible without changing the dosing accuracy of the injection quantity.

The invention is particularly suitable when, in particular, a defined speed ratio is advantageously present for a better quantity balance between the high-pressure pump and the crank angle of the crankshaft of the internal combustion engine, which leads to irregularities or asynchronizations between the pump operating cycle position asynchronizations and the injection times of the fuel injectors. However, high variations in the injection quantity can generally be avoided by the method according to the invention as described above.

Advantageously, the injection quantity is dosed by means of a correction of the deviation of the actual injection quantity from the setpoint injection quantity and/or of the actual pressure specific to the fuel injector from the setpoint pressure, which deviation is dependent on the pump operating cycle position. The correction of this deviation is particularly effective because the actual injection quantity and the setpoint injection quantity, or the pressure specific to the injector and the setpoint pressure, respectively, can deviate upwards or downwards depending on the current pressure in the high-pressure accumulator, depending on the operating position. In particular, the correction is carried out by means of a correlation characteristic which covers the dependence on the deviation from the operating position. For example, an exact correlation between the deviation and the operating position can be determined for the internal combustion engine on the test stand and then stored in a correlation characteristic curve, which is transmitted to the respective controller.

Preferably, the rotational speed of the internal combustion engine and/or the actual pressure in the high-pressure accumulator are taken into account in the correction. Since a predetermined speed ratio between the high-pressure pump and the crankshaft of the internal combustion engine is specified, the actual pressure in the high-pressure accumulator is also dependent on the rotational speed of the internal combustion engine. The deviation of the pressure caused by the working position is again dependent on the height of the actual pressure. Likewise, the deviation of the correct injection quantity for a predetermined opening duration of the valve of the fuel injector is correlated with the actual pressure in the high-pressure reservoir. A more accurate correction is thus achieved by taking into account the rotational speed.

It is advantageous to take into account the setpoint injection quantity during the correction. A certain opening period of the valve of the fuel injector is associated with the setpoint injection quantity. However, since the injection quantity deviating upwards, for example, in the case of high pressures, is still further increased by the longer opening period, the consideration of the setpoint injection quantity enables a more precise correction.

If the method according to the invention is applied to a plurality of combustion chambers each having a fuel injector which is supplied with fuel by the same high-pressure accumulator, it is advantageous if, for each fuel injector of the combustion chamber, the respective correction is effected injector-specifically or injector-dominantly. Since the injection times of the individual combustion chambers are offset in time for a plurality of combustion chambers or cylinders in an internal combustion engine, deviations from the respective setpoint values can occur in the respective combustion chambers. This can be balanced by modifications specific to each fuel injector.

The computing unit according to the invention, for example a control unit, in particular an engine control unit of a motor vehicle, is provided, in particular in terms of program technology, for carrying out the method according to the invention.

The use of a method in the form of software is also advantageous, since this results in particular in slight costs, especially if the executing controller is also used for other tasks and is therefore still present. Suitable data carriers for supplying the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs etc. It is equally possible to download programs over computer networks (internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the enclosed drawing.

It is to be noted that the features mentioned above and yet to be explained below can be used not only in the respective combination given but also in other combinations or alone without leaving the scope of the present invention.

Drawings

The invention is schematically illustrated in the drawings according to an embodiment and is described in detail below with reference to the drawings.

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

FIG. 2 shows a graph with pump duty cycle positions in successive cycles for a plurality of fuel injectors of an internal combustion engine.

Fig. 3 shows the pressure curve of the high-pressure accumulator, the injection rate, the pump stroke and the delivery rate for the fuel injector during a cycle.

Fig. 4 shows the deviation of the actual injection quantity from the setpoint injection quantity for a plurality of fuel injectors with respect to the pump operating cycle position.

Detailed Description

Fig. 1 schematically shows an internal combustion engine 100 with a common rail system, which is suitable for carrying out the method according to the invention in a preferred embodiment. For example, the internal combustion engine 100 comprises six combustion chambers or associated cylinders 105. Each combustion chamber 105 is assigned a fuel injector 130, which is in turn connected to a high-pressure accumulator 120, which is supplied with fuel by way of said fuel injector. Although two high-voltage accumulators 120 are shown, they are connected to one another and therefore act as a single high-voltage accumulator 120. The illustrated embodiment is common in common rail systems in general.

Furthermore, high-pressure accumulator 120 is supplied with fuel from fuel tank 140 by high-pressure pump 110. The high-pressure pump 110 is designed here as a piston pump with two pistons. Each piston obtains two feed strokes in one pump revolution, i.e. the high-pressure pump performs a total of four feed strokes in each revolution. The high-pressure pump 110 is coupled to the internal combustion engine 100, and in particular so that it is driven by the crankshaft of the internal combustion engine or by a camshaft, which is in turn coupled to the crankshaft. Wherein a fixed speed ratio is predetermined. In the present case, the ratio is 1.01, especially for the following figures.

Six injection processes (with six injectors) are correspondingly designed in each cycle of an internal combustion engine with six cylinders. Because one cycle corresponds to two crankshaft revolutions (720), the high pressure pump 110 makes 8.08 supply strokes per cycle in this speed ratio.

The activation of the fuel injectors 130 for the dosing of fuel to the individual combustion chambers 105 is effected by a computing unit designed as an engine controller 180. The connection of only engine controller 180 to fuel injectors 130 is shown for clarity, but it is understood that each fuel injector 130 is correspondingly connected to the engine controller. Wherein each fuel injector 130 can be specifically activated.

Fig. 2 shows a diagram of the pump operating cycle positions for six fuel injectors 130 of the internal combustion engine 100, which are described with Inj _1 to Inj _6 for the purpose of differentiation, in relation to successive cycles, i.e., injection events. Where the pump duty cycle position is given from 0 to 90 deg.kw (360 deg. KW/4 strokes). Since, as mentioned above, the high-pressure pump is connected to the crankshaft via a fixed speed ratio and via a fixed angle, the pump operating cycle position can be assigned to each crankshaft angle. The angle between the crankshaft and the camshaft is usually fixed during assembly of the motor and remains constant during operation of the motor.

Wherein the pump duty cycle position of the high pressure pump 110 is different for each of the six fuel injectors in each cycle. The repetition of the operating position only occurs after 25 cycles, since, as described above, each cycle achieves 8.08 pump strokes and therefore the 25 cycles together for the first time result in an integer number with 202 pump strokes. As mentioned in the introduction in the background, the use of the method is not of interest here, since the operating parameters of the internal combustion engine, such as pressure and quantity, can vary greatly after so many cycles.

Fig. 3 shows in the upper part a pressure 300 in bar in the high-pressure accumulator 120 during the exemplary cycle according to fig. 2 with respect to time t. In the lower part, the associated injection rate 310, pump stroke 320 and delivery rate 330 are shown. Wherein each of the six fuel injectors lnj _1 through lnj _6 can be provided with an injection rate 310. Since, as described above, the pump has two pistons, there are also two piston strokes 320 or associated curves offset by 180 ° from one another.

As can be seen from the graph, the injection timings of the fuel injectors lnj _1 through lnj _6 given by the respective injection rates 310 are offset in time at equal mutual intervals. Pump stroke 320 and associated delivery rate 330, in turn, have a common period of their own that is different from the period of injection rate 310.

As can be seen on pressure curve 300, the pressure varies for the injection timings of fuel injectors lnj _1 through lnj _ 6. The reason for this is that the pressure is reduced by injection, whereas the pressure increase by the delivery rate 330 is offset in time differently for the individual fuel injectors lnj _1 to lnj _6 with regard to the injection times. The resulting pressure in the high-pressure accumulator, which is shown by the pressure curve 300, therefore changes from injection time to injection time.

Fig. 4 shows the deviations dqlnj _1 to dqlnj _6 of the actual injection quantities of the fuel injectors lnj _1 to lnj _6 from the setpoint injection quantities, relative to the pump operating cycle position. The correlation between the deviations dqlnj _1 to dqlnj _6 and the pump duty cycle position is clearly visible.

Such a correlation can be determined for the internal combustion engine, for example, on a test bench. The dependence is then plotted, for example, in a dependence curve and the engine control unit is thus displayed, and the deviation can be corrected by lengthening or shortening the duration of the opening of the valve of the respective fuel injector. In this case, only the associated operating position of the fuel injector is necessary, which is known from the crank angle of the internal combustion engine and the associated speed ratio for the high-pressure pump.

For example, a correlation curve is determined by measuring the deviation of the injection quantity from a theoretical quantity or the deviation of the actual pressure specific to the fuel injector from a setpoint pressure at the start of the activation of the fuel injector at the angle between the bottom dead center of the high-pressure pump on the test stand. The characteristic of the deviation from the angle is stored in the control device as a correlation characteristic curve, using parameters such as, for example, rotational speed and injection quantity.

In the motoring mode, the control unit then determines the angle of the start of the triggering of each injection to the bottom dead center of the high-pressure pump and calculates the injection quantity or the deviation of the pressure, which is specific to the fuel injector, from the setpoint value using the relevant characteristic curve and depending on the current rotational speed and injection quantity, respectively. The correction of the trigger duration is carried out with the aid of the correlation characteristic curve in order to comply with the theoretical quantity.

Overall or overall correlations of the injectors for all fuel injectors lnj _1 to lnj _6 can be determined and used. Alternatively, injector-specific or local dependencies can also be determined and used for the individual fuel injectors lnj _1 to lnj _ 6.

The deviation of the injection quantity from the combustion chamber or cylinder to the other combustion chamber or cylinder, the so-called cylinder-cylinder injection quantity deviation, can thus be reduced by correcting the deviation separately for the individual fuel injectors, ideally to zero.

Claims

1. Method for dosing an injection quantity of fuel into at least one combustion chamber (105) of an internal combustion engine (100) by means of a fuel injector (130), wherein the fuel injector (130) is supplied with fuel by means of a high-pressure accumulator (120) which is supplied with fuel by a high-pressure pump (110), wherein a pump operating cycle position of the high-pressure pump (110) is taken into account when dosing the injection quantity, which is taken into account as a function of a crank angle of the internal combustion engine (100), wherein the dosing of the injection quantity takes place with the application of a correction of a deviation of an actual injection quantity from a setpoint injection quantity which is dependent on the pump operating cycle position and/or with the application of a correction of a deviation of an actual pressure specific to the fuel injector from a setpoint pressure which is dependent on the pump operating cycle position, wherein the correction takes place by means of a correlation characteristic curve, the correlation characteristic curve comprises a correlation between a deviation of an actual injection quantity from a setpoint injection quantity and/or a deviation of an actual pressure specific to the fuel injector from a setpoint pressure and the pump operating cycle position and is generated by measuring the correlation of the deviation with the pump operating cycle position.

2. Method according to claim 1, wherein the rotational speed of the internal combustion engine (100) and/or the actual pressure in the high-pressure accumulator (120) are taken into account during the correction.

3. Method according to claim 1 or 2, wherein the setpoint injection quantity is taken into account in the correction.

4. The method according to claim 1 or 2, wherein the injector-specific or injector-specific correction is carried out for a plurality of combustion chambers (105) each having a fuel injector (130).

5. The method according to claim 1 or 2, wherein the dosing of the amount of fuel comprises controlling an opening duration of a valve of the fuel injector (130).

6. Method according to claim 1 or 2, wherein a speed ratio exists between the high-pressure pump (110) and a crankshaft of the internal combustion engine (100), whereby the pump duty cycle positions are distributed asynchronously to the injection timings of the fuel injectors.

7. A computing unit (180) arranged for performing the method according to any of the preceding claims 1 to 6.

8. A machine-readable storage medium having stored thereon a computer program which, when run on a computing unit, causes the computing unit to perform the method according to any one of claims 1 to 6.