EP3040550B1 - Fuel injector - Google Patents

Description

The invention relates to a fuel injector having the features of the preamble of claim 1, an internal combustion engine having such a fuel injector and a method for operating an internal combustion engine.

Fuel injectors of modern internal combustion engines operate with high fuel pressures. In order to transmit any pressure pulsations resulting from the rapid successive switching operations of the fuel injector to the fuel supply, a storage volume is provided in the injector itself, from which the fuel is removed for injection and in which fuel from the fuel supply line via a throttle (orifice) can flow. Thus, a vibration isolation of the injector from the fuel supply. A fuel injector with such a storage volume is for example from the DE 10 2006 051 583 A1 known.

For an effective damping of pressure oscillations, said storage volume must be in a specific ratio to the quantity of fuel taken from the fuel injector into the combustion chamber, which is taken in a switching operation. If the storage volume is too small, the pressure in the storage volume during injection breaks down too much; larger volumes are harder to realize due to space limitations. After the damping effect is determined from the interaction of storage volume and throttle, the flow cross-section, d. H. the hydraulic damping effect of the throttle adapted to the size of the storage volume.

There are already fuel injectors known in which the injection quantities are variable, such as by the WO 02/092998 A1 described. It would be desirable to be able to vary the injection quantities of a fuel injector to a greater extent. In other words, a fuel injector should have a high turndown ratio . The turndown ratio A fuel injector is the ratio of the maximum and minimum amounts of fuel that a fuel injector can inject in a controlled manner. If a fuel injector can represent a fuel quantity of 0.5% to 100%, this fuel injector has a turndown ratio of 200. This is particularly relevant for dual-fuel engines operating in 100% diesel operating modes to low diesel pilot injection gas operation. Of particular importance is that the turndown ratio should be in a controlled and reproducible manner over the lifetime of the fuel injector.

Since a reproducible turndown ratio of 200 with a single fuel injector for the entire lifetime in the prior art is not feasible, provides a solution for dual-fuel engines to provide two separate fuel injectors, a fuel injector, the large amounts of fuel for diesel operation, and the second takes over the small amounts of fuel for the pilot injection.

The object of the invention is therefore to provide a fuel injector which can be used over wide areas of the injection quantity, without having the disadvantages of the prior art. Also, an internal combustion engine and a method for operating the same are to be specified.

These objects are achieved by a fuel injector having the features of claim 1, an internal combustion engine according to claim 6 and a method of operating an internal combustion engine according to claim 8. Advantageous embodiments are specified in the subclaims.

The fact that the storage volume can be changed during operation by a control signal, the size of the storage volume can thus be adapted to the respective injection quantity.

As stated above, the injection quantities may differ depending on the operating state of the internal combustion engine. The changeability in the enterprise brings substantial advantages with itself.

Due to the variability of the storage volume can be dispensed, for example, a double version of fuel injectors, in which separate fuel injectors are provided for different operating conditions. Operating conditions are, for example, the diesel operation, in which all the fuel is supplied as diesel and the dual-fuel operation, in which diesel is supplied only for ignition (so-called pilot injection) and in small quantities.

The variability of the storage volume during operation means that the internal combustion engine does not have to be switched off to change the storage volume.

Particularly preferably, it is provided that the storage volume corresponds to about 30 to 80 times the amount injected.

According to the invention it is provided that the storage volume consists of at least two partial volumes, which are connected via a switching element so that they act as a total volume, preferably within the injector. It may be provided that the total volume is matched to the larger injection quantity. This means that the storage volume is not formed by a single cavity, but by at least two partial volumes, which are interconnected. Thus, in the case of larger injection quantities, the at least second partial volume can be brought into fluid communication with the first partial volume, whereby a larger volume of the storage volume is available for the withdrawal of fuel during the injection.

If only small injection quantities are retrieved, only one of the sub-volumes is operated. In this case, therefore, only a partial volume in fluid communication between the high pressure fuel line and the actual nozzle assembly. It makes sense that the partial volume for small injection quantities is smaller than that for the operating state with larger injection quantities.

It can be provided that the arrangement of the at least two sub-volumes is fluidically parallel. In this case, both or all of the at least two partial volumes depend on the high-pressure fuel line. The switching element is then arranged downstream of the one partial volume and can be actuated in such a way that it blocks off this partial volume. Then only the second subvolume is in communication with the nozzle assembly. During the injection process so fuel is removed only from this additional sub-volume.

Formulated here for two partial volumes, the arrangement can also comprise more than two partial volumes. These can then be closed or opened by further switching elements. In practice, this will hardly be realized for reasons of space alone.

Alternatively it can be provided that the arrangement of the at least two sub-volumes is fluidically serial. In this case, therefore, there is only one connection of the partial volumes to the high-pressure fuel line. The switching element is then arranged, for example, fluidically between the sub-volumes. When the switching element is closed, therefore, fuel is taken from the partial volume during the injection process only, which lies between the switching element and the nozzle assembly. In the case of the serial arrangement, the switching element is designed so that a subsequent flow of fuel is ensured in the downstream partial volume. This can be realized, for example, by an always remaining opening in the closed position, through which then fuel can flow in like a throttle.

The fuel may be, for example, gasoline, diesel or heavy fuel oil.

Protection is also desired for an internal combustion engine having a fuel injector according to the invention and a method for operating an internal combustion engine. By changing the volume of the storage volume of the fuel injector as a function of an operating state of the internal combustion engine, the injection characteristic can therefore be adapted to different operating states of the internal combustion engine.

Fig. 1

Kraftstoffinjektor nach Stand der Technik,

Fig. 2

Druckverlauf im Speichervolumen nach Stand der Technik

Fig. 3

Kraftstoffinjektor nach einem ersten Ausführungsbeispiel

Fig. 4

Kraftstoffinjektor nach einem weiteren Ausführungsbeispiel

Fig. 5

Kraftstoffinjektor nach einem weiteren Ausführungsbeispiel

Fig. 6

Kraftstoffinjektor nach einem weiteren Ausführungsbeispiel

Fig. 7

Druckverläufe im Speichervolumen im Vergleich

In the following, the invention will be explained in more detail with reference to FIGS. Showing:

Fig. 1

Fuel injector according to the prior art,

Fig. 2

Pressure curve in the storage volume according to the prior art

Fig. 3

Fuel injector according to a first embodiment

Fig. 4

Fuel injector according to a further embodiment

Fig. 5

Fuel injector according to a further embodiment

Fig. 6

Fuel injector according to a further embodiment

Fig. 7

Pressure curves in the storage volume in comparison

FIG. 1 shows a fuel injector 1 with storage volume 20 according to the prior art. A dotted frame visualizes the system limits of the fuel injector. 1

A high-pressure fuel line 8 supplies the fuel injector 1 with fuel via a diaphragm 3. Downstream of the diaphragm 3, a storage volume 20 integrated in the fuel injector 1 is arranged. The orifice 3 reduces pressure oscillations and mitigates deviations from cylinder to cylinder.
The fuel injector 1 shown has a pressure sensor 9 on the storage volume 20.

From the storage volume 20 a line leads to a nozzle assembly 10. The nozzle assembly 10 can be actuated by a control valve 6. Between control valve 6 and nozzle assembly 10 inlet and outlet throttles 2 are arranged. The nozzle assembly has a hydraulically actuable needle through which fuel is released. The needle is controlled by the control valve 6 together with the inlet and outlet throttles 2. In general, a flow restrictor 14 is provided as a safety element in the supply line to the nozzle assembly 10, but not mandatory.

Fig. 2 shows the pressure curve in the storage volume 20 during an injection process, as is known from the prior art.

To record the pressure curve, a pressure sensor 9 is arranged on the storage volume 20, with which the pressure changes during the injection process can be detected. Plotted in the diagram is the pressure in the storage volume 20 in bar above the crank angle in degrees. The timing of the events presented is expressed in degrees crank angle. The pressure in the storage volume 20 corresponds to the pressure in the high-pressure fuel line 8 ( high pressure rail ) before the beginning of the injection.

At time SOC ( start of current ), the fuel injector 1 is energized, so that after a dead time T _t, the injection begins.

After the start of injection at the time SOI (engl. Start of injection, SOI) decreases the pressure in the storage volume 20 to the value associated with the injection end (engl. End of injection EOI) is reached.

The injection duration is denoted by reference ID.

The observed pressure drop in the storage volume 20 is indicated in the diagram by Δp.

By knowing the variables pressure in the high-pressure line 8, injection duration, effective flow cross-section of the orifice 3 between storage volume and high-pressure fuel line 8, flow properties of the fuel, etc., the injected fuel quantity or mass can be calculated from the pressure profile. In other words, the amount of fuel injected is a function of these quantities.

It can easily be seen that the data quality and thus the accuracy of the calculation of the injected fuel mass are dependent on the resolution of the pressure measurement on the storage volume 20. The pressure signal in turn depends strongly on the effective flow cross section of the orifice 3 and the volume of the storage volume 20. The larger the free diaphragm cross-section and the larger the storage volume 20, the smaller the pressure drop Δp during the injection. Therefore, the calculation of the fuel amount becomes difficult and the accuracy unsatisfactory, especially with small injection quantities.

FIG. 3 shows a fuel injector 1 according to the invention according to a first embodiment.

Two partial volumes 21, 22 are arranged serially. The partial volumes 21, 22 together result in the storage volume 20.

Between the first part volume 21 and the high pressure fuel line 8, a first aperture 3 is provided. Between the storage volumes 21 and 22, a further diaphragm 7 is arranged. The panel 7 is bypassed by a switching element 12 in the form of a bypass. In the embodiment shown, the switching element 12 in the form of an electrically actuated switching valve executed. Other embodiments of the switching element 12 are conceivable, for example, pneumatically or hydraulically actuated valves.

If only small amounts of fuel are injected, such as required in dual-fuel mode, the switching element 12 is closed. This means that the flow connection between the partial volumes 21, 22 is determined by the further diaphragm 7. The further diaphragm 7 is designed such that fluid from the partial volume 21 can flow into the partial volume 22 only with great delay. In other words, only a small free diaphragm cross-section between the partial volumes 21 and 22 is available, so that the extraction characteristic is largely determined by the partial volume 22.

If larger injection quantities are required, then the switching element 12 is switched so that it releases a larger free total flow cross-section. In order for the storage volumes 21 and 22 communicate largely unthrottled with each other, so that the extraction characteristic of the common volume 20, ie the sum of the sub-volumes 21, 22 corresponds.

Of course, all intermediate stages are conceivable, d. H. that the switching element 12 between the sub-volumes 21 and 22 is changed continuously or in stages between a minimum and a maximum position. However, a binary solution with only two switching positions of the switching element 12 is less expensive to implement and therefore preferred. A maximum position means that the switching element 12 is fully open and thus there is no hydraulic damping between the volumes 21 and 22.

In practice, the arrangement of the sub-volumes 21 and 22 is designed so that the sub-volume 22 has the space suitable for the dual-fuel mode volume. This means, as explained above, that the volume of the partial volume 22 corresponds to approximately 30 to 80 times the injection quantity in the dual-fuel mode.

The sub-volume 21, however, is dimensioned so that in connection with the sub-volume 22, a total volume 20 of the sub-volumes 21 and 22 sets, which corresponds to 30 to 80 times the amount of injection quantity of diesel operation.

Here is a numerical example: the injection quantity of the diesel operation is 100% with a volume of 1000 mm ^{3 to be} injected per working cycle.
This results in an acceptable total volume in the range of 30,000 to 80,000 mm ³ (thirty thousand to eighty thousand) for the volume of the total volume of the partial volumes 21 and 22.

At a turndown ratio of 200 (100), the size of the partial volume 22 for the dual-fuel operation is 1/200 (1/100) of the total volume of the partial volumes 21 and 22, ie in a range of 150 to 400 (100). 300 to 800) mm ³ . The values in brackets refer to a turndown ratio of 100.

At the storage volume 22, a pressure sensor 9 may be arranged. The arrangement according to the invention of the partial volumes means that the respective volume used and the injection quantity are in an adapted ratio, which makes a more accurate measurement of the pressure curve possible during the injection. This in turn allows a more accurate calculation of the injection quantity.

Further shown, but not explained in detail, is the prior art nozzle assembly 10. This consists in this example of a control valve 6 hydraulically actuated injection needle, which receives switching pulses via a control device 11. Of course, the injection needle can also be realized as a piezo injector. In this case, of course, eliminates the necessary components for a hydraulic actuation of the nozzle assembly 10th

In general, a flow restrictor 14 is provided as a safety element in the supply line to the nozzle assembly 10, but not mandatory.

FIG. 4 shows an embodiment with a parallel arrangement of the sub-volumes 21 and 22. Thus, the sub-volumes 21 and 22 of the storage volume 20 are arranged fluidically parallel.

The partial volume 21 is fed via the diaphragm 3 from the high-pressure fuel line 8. The storage volume 21 can be switched on and off via an electrically operable switching element 12.

If only small amounts of fuel are injected, such as required in dual-fuel mode, the switching element 12 is closed. When switching element 12 is closed, the fluid connection between partial volume 21 and nozzle assembly 10 is interrupted. In this case, the injection characteristic is determined by the partial volume 22, which is made smaller. The partial volume 22 is fed via a further diaphragm 15 from the high-pressure fuel line 8.

If, as in diesel mode, larger amounts of fuel to be injected, the switching element 12 is opened. Thus, both partial volumes 21, 22 are available for removal.

Highlighted in the dashed oval is an alternative embodiment of the switching element 12 with the reference numeral 12 '. The switching element 12 'is a switched directly from the pressure in the sub-volume 21 valve.

Unlike illustrated, the fuel injector 1 need not be provided with two inputs for the high-pressure fuel line 8. It is also sufficient an input that branches in front of the partial volumes 21, 22 in a suitable manner. This variant is in the FIG. 4 dashed lines with aperture 16 shown: in this case replaced the aperture 16, the aperture 15. The line section to the high-pressure fuel line 8, in which the aperture 15 is omitted. The connection with the high-pressure fuel line 8 then takes place via the diaphragm 3.

At the storage volume 22, a pressure sensor 9 can be set up again.
The remaining structure of the fuel injector 1 corresponds to that of FIG. 3 , The advantages are the same as for the embodiment of FIG. 3 described. As a numerical example, the values for FIG. 3 be used.

FIG. 5 shows an embodiment with variable partial volumes 21, 22. For this purpose, a displaceable piston 18 is provided, which divides the partial volumes 21, 22 from each other. Through the throttle 26, the content of the partial volume 21 communicates with the spring chamber 24th

In the position shown, the (smaller) sub-volume 22 is in fluid communication with the nozzle assembly 10, ie, the injection quantity is withdrawn from the sub-volume 22, as required in dual-fuel mode, for example. The throttling with respect to the high-pressure fuel line takes place in this operating state via the diaphragm 4.
Upon actuation of the control valve 23, the spring chamber 24 in which the spring assembly 19 is depressurized. Then, in this illustration, the piston 18 moves down.

In the illustrated embodiment, the partial volume 21 is connected to the overflow line 17 to the supply to the partial volume 22: as soon as the piston 18 exceeds a predetermined position, the previously closed by the piston 18 overflow 17 is released. The piston 18 thus acts as a slide relative to the overflow line 17. As a result, the previously separate partial volumes 21, 22 are connected to each other. The removal then takes place from the sum volume formed by the partial volumes 21, 22.

This operating position is selected for the diesel operation, are accessed in the larger injection quantities.

An alternative embodiment with variable partial volumes 21, 22 is shown in FIG FIG. 6 shown. Here, the piston 18 closes the partial volume 21 with respect to the partial volume 22 as long as the control valve 23 remains closed. The removal takes place in this state from the (smaller) sub-volume 22, as required for example in dual-fuel mode.

The opening of the control valve 23 leads to the discharge of the spring chamber 24, in which the spring assembly 19 is located. As a result, the piston 18 now moves by the pressure in the partial volume 22 against the spring assembly 19 (in the figure above). Since the active surfaces of the piston 18 are almost balanced with respect to the hydraulic pressure in the partial volume 21, a relief of the spring chamber 24 causes the described movement.

The plate (not shown in the figure) of the piston 18 thereby releases the partial volume 22 with respect to the partial volume 21. As a result, the previously separate partial volumes 21, 22 are connected to each other. The removal then takes place from the total volume formed by the partial volumes 21, 22, as is advantageous, for example, in diesel operation. Through the overflow 17, the connection of the partial volumes 21, 22 is produced.

FIG. 7 shows the pressure curve in the storage volume, shown over the crank angle in degrees in the case of taking the small amount of fuel during the injection process in dual-fuel operation.

In the case of a fuel injector 1 according to the prior art (as in Fig. 1 shown - here storage volume 20, since in the prior art, only a fixed volume exists) results in a barely measurable decline in the pressure curve.

The solid (top) line shows this pressure curve at the storage volume 20, which in another scale also in FIG. 2 is shown.

The dashed line shows the pressure curve for a fuel injector 1 according to the invention on the partial volume 22. This results in a clear, easily measurable pressure curve.

Depending on the operating state, the rail pressure (pressure in the high-pressure fuel line 8) is typically in the range from 1000 bar to 2500 bar. The observed in the injection process pressure drop according to the prior art is in the order of a few bar in dual-fuel operation and of about 100 bar in diesel mode.

The pressure drop observed in the injection process according to the invention is of the order of e.g. 50 to 100 bar in dual-fuel operation or of approx. 100 bar in diesel operation.

In this way, the resolution of a measurement can be improved.

List of reference numbers used:

1

injector

2

Inlet and outlet throttle

3

cover

4

cover

6

control valve

7

cover

8th

High-pressure fuel line

9

pressure sensor

10

nozzle assembly

11

control device

12, 12 '

switching element

13

displacer

14

flow

15

cover

16

cover

17

overflow

18

piston

19

spring assembly

20

storage volume

21, 22

partial volumes

23

control valve

24

spring chamber

25

Passive valve

26

Aperture on pistons

Claims (8)

1. A fuel injector (1) having a storage volume (20), wherein the storage volume (20) is variable in operation by a control signal, characterised in that the storage volume (20) comprises at least two sub-volumes (21, 22) which can be so connected by way of a switching element (12) that they act as an overall volume.
2. A fuel injector (1) as set forth in claim 1 characterised in that the arrangement of the at least two sub-volumes (21, 22) is in parallel flow relationship.
3. A fuel injector (1) as set forth in claim 1 characterised in that the arrangement of the at least two sub-volumes (21, 22) is in serial flow relationship.
4. A fuel injector (1) as set forth in one of the preceding claims characterised in that provided between the at least two sub-volumes (21, 22) is the switching element (12) for varying the fluid communication between the sub-volumes (21, 22).
5. A fuel injector (1) as set forth in claim 4 characterised in that the switching element (12) is an electrically or hydraulically actuable switching valve.
6. An internal combustion engine having a fuel injector (1) as set forth in at least one of the preceding claims.
7. An internal combustion engine as set forth in claim 6 wherein there is provided a control unit, by the signals of which the capacity of the storage volume (20) of the fuel injector (1) is variable.
8. A method of operating an internal combustion engine having a fuel injector (1) as set forth in at least one of claims 1 through 5 characterised in that the capacity of the storage volume (20) of the fuel injector (1) is varied in dependence on an operating state of the internal combustion engine.

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