WO2018188869A1

WO2018188869A1 - Fuel injection with reduced return amount

Info

Publication number: WO2018188869A1
Application number: PCT/EP2018/056195
Authority: WO
Inventors: Anton Siemens
Original assignee: Robert Bosch Gmbh
Priority date: 2017-04-10
Filing date: 2018-03-13
Publication date: 2018-10-18
Also published as: DE102017206084A1; CN110520617A; CN110520617B

Abstract

The invention relates to a method (100) for operating an injection system (1) for an internal combustion engine (2), wherein the injection system (1) comprises a high-pressure reservoir (11) for one or more fuels (3) and the target pressure ps in the high-pressure reservoir (11) is tracked in accordance with at least one characteristic diagram (16) for the load requirement L of the internal combustion engine (2), wherein in order to lower the actual pressure p in the high-pressure reservoir (11), excess fuel (3, 31) from the high-pressure reservoir (11) is depressurised (99), wherein at least in the event of a temporary fall in the load requirement L to an operating point (29) having a smaller load, the target pressure ps in the high-pressure reservoir (11) is increased (110, 110a-110c) in relation to the value ρκ provided in accordance with the characteristic diagram (16) for this operating point (29). The invention also relates to an associated computer program product.

Description

Description Title:

Fuel injection with reduced return flow

The present invention relates to a method for operating a

Fuel injection system in which the fuel is stored in a high-pressure reservoir with variable pressure.

State of the art

In a common-rail injection system for an internal combustion engine, the fuel, for example diesel fuel or liquefied natural gas (LNG), is compressed to a high-pressure level by a high-pressure pump and stored in a high-pressure reservoir (rail). This high-pressure reservoir usually feeds a plurality of injectors, which inject the fuel into the combustion chambers of the individual cylinders of the internal combustion engine. Such injection systems are known for example from US 6,024,064 A.

The required injection quantity q per injection cycle depends on the

Load request L of the internal combustion engine. If the load request L decreases, less fuel is needed. With a sharp decline in the

Load request L, the amount of fuel can not be reduced only by shortening the injection duration, but it must be additionally reduced the pressure p in the high-pressure reservoir. Regardless, the combustion characteristics for one and the same amount of fuel also depend on the pressure p at which the fuel is supplied to the injectors.

When there is a need to reduce the pressure p in the high pressure reservoir, excess fuel from the high pressure reservoir becomes one

Reservoir (tank) returned. In this recycled fuel is the Energy, which was spent for its compression to the high pressure level, stored in the form of heat. In addition, the temperature of the compressed fuel is determined by the heat exchange with its immediate environment (eg, rail body, pipes, engine compartment).

Although this heat, for example, according to EP 1 319 821 Bl can be used to preheat diesel fuel at cold outside temperature and to prevent clogging of the fuel filter, the heating of the

Fuel supply in most operating situations a rather disadvantageous effect. Thus, US 6,647,968 Bl discloses that the consumption efficiency of the

Fuel temperature depends, and suggests to reduce the temperature of the recycled fuel by increasing the flow rate. In addition, the energy initially used for the compression of the fuel and converted into heat during the return is generally not usable for the propulsion of the vehicle, thus effectively lost.

Disclosure of the invention

In the context of the invention, a method for operating a

Injection system developed for an internal combustion engine. The injection system includes a high pressure reservoir for one or more fuels. The desired pressure ps in the high pressure reservoir is tracked according to at least one characteristic map of the load request L of the internal combustion engine. To reduce the actual pressure p in the high pressure reservoir excess fuel from the

High-pressure reservoir relaxes.

The fuel can for example be returned to a reservoir, optionally between the high-pressure reservoir and the

Reservoir still an intermediate container as a buffer, for controlling the temperature of the fuel before the return feed or as a collection point for

Additional consumers can be provided. However, at least a subset of the fuel can also be fed, for example, to an intermediate pressure level between a prefeed pump and the high-pressure reservoir

High-pressure pump to be relaxed. Then, at least part of the energy spent for compressing the fuel continues to be used. For example, the map may indicate the required injection quantity q per injection cycle for each load request L. In conjunction with the

Boundary conditions for the injection duration, the required setpoint pressure ps can be determined, or at least limited. The minimum injection duration is limited by the minimum pulse duration with which the injectors can be controlled. The maximum injection duration is limited depending on the speed of the internal combustion engine characterized in that the injection in one

angularly fixed portion of the crankshaft revolution.

In addition, the same map, or another map, the required setpoint pressure ps directly or in conjunction with other variables to the load request L couple.

The maps can in particular to the lowest possible

Fuel consumption or even the lowest possible pollutant or

Be optimized noise emission. In many internal combustion engines is the

Using such maps of the key to achieve normative specifications for consumption and environmental properties.

According to the invention, the setpoint pressure ps in the high-pressure reservoir is increased relative to the value ρκ provided according to the characteristic diagram for this point of operation, at least for a temporary drop in the load requirement L to an operating point with a lower load.

A temporary drop in the load requirement L is understood in particular to be a drop which is very likely to be compensated in whole or in part as soon as an increase in the load requirement L occurs.

The increase of the desired pressure ps has the effect that the return of fuel from the high pressure reservoir into the reservoir in the

temporary drop in the load requirement L is significantly reduced or even completely prevented. As a result, the heat input in the

Reservoir significantly reduced. This causes one in two ways Significant energy savings: On the one hand less energy goes into the

Compression of fuel was invested, lost in the form of unusable heat. On the other hand, less energy is consumed to dissipate such unwanted heat with a fuel cooler from the fuel supply.

The reduced heat input into the reservoir has especially at

Use of liquefied natural gas (LNG) as fuel further significant benefits. Natural gas is only at temperatures far below the

Ambient temperature liquid. A heat input into the reservoir can therefore lead to evaporation and displacement of the boiling point. This can lead to an overpressure in the reservoir and in the final analysis to the safety-related discharge of the gas into the environment. This can create an explosive atmosphere in enclosed spaces such as parking garages. In addition, the main component of unburned natural gas

Methane, which is much more greenhouse-active than CO2. For this reason, LNG reservoirs are required to be at least as well insulated as to allow for a predetermined hold time between two runs without draining gas. The reduction of additional heat input by the return of fuel has the consequence that this requirement can be achieved with a less strong insulation of the LNG reservoir, and / or that a longer dwell time between two trips is possible.

The advantages described are paid by the fact that by increasing the desired pressure ps compared to that actually for the operating point with lower

Load provided value ρκ according to the map of the map

fixed optimum with regard to the injection deviated. This may cause the injection accuracy to be deteriorated at this operating point, so that the consumption efficiency as well as the pollutant and noise emission may possibly be worsened momentarily.

However, it has been recognized that when considering the entire operation of the internal combustion engine, this temporary deterioration is not significant. Thus, the price to pay for the said benefits is smaller than it initially seems. Thus, for example, transient operating phases with drastically reduced load requirement L only make up a very small proportion of the operating time of the internal combustion engine. Therefore, a temporary increase in consumption and emissions through the savings in energy and fuel caused by the reduced recycle is ultimately overcompensated.

If it is foreseeable that an increase will follow the reduction of the load request L for a short time, in particular the idle noise level, which is increased by a deviation from the characteristic map, is irrelevant for this short period. Furthermore, the rate of degradation for the actual pressure is p in

High pressure reservoir from the outset technically limited, so that the actual pressure p may not be able to be lowered to a drastically reduced setpoint pressure ps before the load request L, and thus the target pressure Ps, is increased again. Maybe the consumption and

Emission behavior of the internal combustion engine at the operating point with the lower load even not relevant, because the vehicle is at this operating point in overrun operation and due to the

Fuel cutoff no fuel is injected.

It has been recognized that for these reasons, with only a temporary drop in the load requirement L, it does not make sense to completely track the setpoint pressure ps according to the characteristic map and accordingly to rapidly lower the actual pressure p in the high-pressure reservoir.

An example of a temporary decrease in the load request L are shifts of vehicle transmissions. Any such switching operation requires interrupting power transmission from the engine for about 0.5-1 second. Especially when upshifting during a

Acceleration process is reduced to this short phase with

Load request L soon as a phase with even higher load request L follow. By suppressing the reduction of the target pressure ps during the shift operation, not only energy is saved, but also the acceleration performance is slightly improved. The advantageous effects of the invention are, according to the above, not tied to the fact that the increase of the desired pressure ps compared to the specification PK from the map only occurs when a temporary reduction of the load request L is detected or imminent. Also, measures that are independent of the actual existence of a

Temporary reduction of the load requirement L permanent or operating point dependent applied can, on balance, the

achieve the advantages described. It depends solely on the balance of the advantages achieved by the reduced return of fuel against the additional consumption and the additional emissions due to the deviation from the map over the vehicle operation on average, so for example on cumulative exhaust emissions.

Furthermore, the advantageous effects of the invention are in principle also not bound to which fuel is used concretely for the operation of the internal combustion engine. Basically, regardless of where in the fuel supply system, the fuel from the high-pressure reservoir is expanded and which fuel is in the

Fuel supply system as a whole added additional heat. This follows from the principle of energy conservation. The fuel type only affects how large this heat input is and how much heat input can be tolerated during operation of the vehicle. Thus, the invention can equally be used on monovalent internal combustion engines which are operated, for example, with diesel fuel or liquefied natural gas (LNG), as well as on bivalent (dual-fuel) internal combustion engines, which can be operated selectively with one of these fuels. The use of bivalent internal combustion engines promises special advantages, especially in the conversion from monovalent operation with diesel fuel to bivalent operation with diesel fuel or LNG. Here are the advantages of operating with LNG available only at the price that LNG is particularly sensitive to heating by recirculated fuel. The invention significantly reduces this price. In a particularly advantageous embodiment of the invention, the desired pressure Ps is maintained at least at a predetermined base level PB, which is higher than that according to the map for the idling of the internal combustion engine

provided value ρκ. As long as the load request L is so high that the associated desired pressure ρκ according to the map is greater than PB, this has an effect

Measure de facto not off. Only when the load requirement L is reduced so much that ρκ drops below PB, is the actual departure from the characteristic map. With a suitable choice of the base level PB, a substantial improvement can be achieved on balance even if it is not further monitored whether a temporary drop in the load requirement L is present or imminent.

In a further particularly advantageous embodiment of the invention, the maximum and / or minimum rate of change dps / dt of the desired pressure ps, and / or the maximum and / or minimum rate of change dp / dt of the actual

Pressure p, with decreasing load request L more limited than with increasing load requirement L. This is especially the case to understand that with decreasing load request L, the temporal rate of change is limited, with increasing load demand L, however, no such limit is set.

For example, the inflow plate to increase the pressure p in

High pressure reservoir, and / or the return plate to reduce this pressure p, be designed so that it is given a time rate of change dp / dt for the pressure p as a manipulated variable. The actuator internally opens a valve just enough to set the predefined rate of change dp / dt. The temporal rate of change dp / dt can then be limited by the relevant, the controller supplied control variable is limited.

If a decreasing load requirement L is permanent, the setpoint pressure ps is ultimately reduced to the value ρκ which the characteristic field for the

Specifies operating point with the lower load. However, this is done with such a time delay that the drop of the desired pressure ps is significantly reduced or even prevented in a transient only decreasing load request L. On the other hand, as the load requirement L increases, it is less advantageous to limit the speed with which the setpoint Pressure ps increases. Such a limitation would make the engine respond less dynamically.

If the operating point of the internal combustion engine, and here in particular the load requirement L, changes with time, the optimum setpoint ρκ for the pressure in the high-pressure reservoir also changes over time according to the characteristic map. From the time-dependent desired value ρκ (ί) according to the characteristic map, the final desired pressure ps can be formed, for example, by time damping, smoothing, filtering and / or asymptotic weighting. The desired pressure ps can also be calculated from substitute value maps. Also, for example, a falling edge of ρκ (ί) delayed by a delay element to strike the desired pressure ps.

In a further particularly advantageous embodiment of the invention, disengaging the internal combustion engine as a temporary waste of

Load request L scored. Just a disengagement is basically a temporary state, regardless of whether this is done by pressing a clutch pedal or automated.

In a further particularly advantageous embodiment of the invention, the request for a switching operation by an automated transmission as a temporary drop in the load requirement L is evaluated. In this context, the term "automated transmission" encompasses any transmission in which the shifting process is automated to such an extent that a clutch pedal in the vehicle is dispensable, ie both fully automatic transmissions and automated transmissions The engine control unit then knows in advance that the following brief interruption of the

Power transmission, which is accompanied by a decrease in the load requirement L, will be temporary. Accordingly, the otherwise required lowering of the desired pressure ps can be mitigated or suppressed, ie, the desired pressure ps can be increased above the value ρκ predetermined by the characteristic field. In a further particularly advantageous embodiment of the invention, a drop in the load requirement L is considered to be temporary if its magnitude change rate dL / dt exceeds a predetermined threshold AL. In general, neither the road conditions nor the driver's request f abruptly change with respect to the speed. On the other hand, the

Disruption of the power transmission when disengaging designed as abrupt as possible, so that the clutch is only for the least possible proportion of the time in the abrasive and thus wear-intensive state. In a further particularly advantageous embodiment of the invention is a

Waste of the load requirement L initially rated as temporary. The waste is not considered to be temporary until the load request L has remained below a threshold value Ls for a predetermined period of time, when the target injection quantity q falls below a predetermined threshold value qs, and / or when a driver request f is at the lower operating point Load corresponds. Behind this is the idea that in a typical trip a temporary drop in the load requirement L occurs much more frequently than a change in the driver's request f. Thus, when a drop in the load request L occurs, it is mostly likely that this drop is temporary. In some cases it will turn out that the waste is really permanent. However, as explained above, the time-cumulative behavior of the internal combustion engine is particularly important with regard to the emission behavior. In this sum, the advantages achieved by the reduced return of heated fuel, the disadvantages of the few phases with low load, in which the

Injection accuracy was not optimal outweigh. This is especially true against the background that at low load significantly less fuel per

Time unit or per route is consumed as at higher load, so that an increase in emissions at low load at least partially relative.

In general, to detect a temporary drop in the

Load request L, for example, the evaluation and logical combination of a driver's request f (corresponds to the accelerator pedal position), the load request L by the vehicle after a gear engagement, and / or statistical data from the immediate operating point history are used. Furthermore, parameters of the current operating point, such as the speed of the internal combustion engine and the vehicle speed v, can be used.

The extent to which the desired pressure ps is changed from the characteristic ρκ provided in the map can advantageously be made dependent on how annoying a return of heated fuel would currently have on the fuel system. For this purpose, this extent, for example, of a state variable xi of the reservoir (such as level, pressure and / or temperature), of a state quantity X2 of the by the

Relaxation of the fuel, or by the reduction of the actual pressure p, affected part of the fuel supply system, of a state quantity X3 of the fuel to be relaxed (such as gas temperature and / or

Amount of energy) and / or environmental conditions x ₄ (approx

Ambient temperature).

The said extent can manifest itself, for example, in a print offset, in a maximum pressure drop rate and / or in a filter time constant. This or another quantity, which is a quantitative measure for the departure from the pressure values ρκ proposed by the characteristic map, can be calculated, for example, to the original desired pressure ps, to the load request L, to the requested injection quantity q, to information of the gas pedal, of the transmission or the clutch, to the vehicle speed v, or else to rates of change and / or derivatives of these signals.

For example, the rate limitation, ie the limitation of the maximum and / or minimum rate of change dps / dt of the desired pressure ps, the restriction of the maximum and / or minimum rate of change dp / dt of the actual pressure p, and / or the limitation of the maximum rates of change relevant control values or control signals, as a dependent of the target injection quantity q characteristic are stored in the control unit. By this connection, the trade-off between minimizing the amount of recirculated fuel by prolonging the modified desired pressure ps on the one hand and the approach to normal operation by faster decompression on the other hand can then be set. A temporal Control of the measure, for example via a temporally ramped filter time constant, may also be useful.

The switching on and off of the interventions in the desired pressure ps, or in the course of time, for example, can be continuous (without jumps). For this purpose, the interventions can be done, for example, with timed or

operating point-dependent ramps (fade-in / out, crossfade, ramped filter constants, asymptotic / hyperbolic functions).

The method can be implemented in particular on an engine control unit. Advantageously, neither the control unit itself nor the associated sensors or actuators of the internal combustion engine must be changed. In particular, the method may be in a pure update of the software for the

Engine control unit to be embodied, which is an independently salable product also for the aftermarket. Therefore, the invention also relates to a computer program product with machine-readable instructions which, when executed by a computer and / or a controller, cause the computer and / or the controller to perform a method according to the invention.

Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

embodiments

It shows:

Figure 1 Exemplary realization of the method 100 on a

Injection system 1 for an internal combustion engine 2;

Figure 2 Time course of the pressure p in the high-pressure reservoir 11, the target injection quantity q and the vehicle speed v in an exemplary acceleration process. According to FIG. 1, the injection system 1 comprises a high-pressure reservoir 11, which is supplied with fuel 3 via a high-pressure pump 12 from a reservoir 13. A pre-feed pump required for the operation of many high-pressure pumps 12 is not shown for clarity. Via a feed plate 14, the pressure p of the fuel 3 in the high-pressure reservoir 11 is increased to the desired pressure Ps. If the setpoint pressure ps decreases, an excess quantity 31 of fuel 3 from the high-pressure reservoir 11 is diverted via a return plate 15 and expanded in step 99 of the method 100 by being returned to the reservoir 13.

From the high-pressure reservoir 11, the fuel 3 is supplied to an injector 17 and injected from this injector 17 into a cylinder 22 of the internal combustion engine 2. The combustion of the fuel 3 in the cylinder 22 drives a piston 21, which is connected via a connecting rod 23 and a crank pin 24 with a crankshaft 25 and the crankshaft 25 in a rotational movement. The crankshaft 25 is connected via a clutch 26 to an automatic transmission 27. The generated by the internal combustion engine 2

Torque m counteracts the mechanical load request L and drives the vehicle.

Since the demand for fuel 3 depends on the load requirement L, a map 16 provides for each load request L that value ρκ for the load

High-pressure reservoir 11 to be set pressure at which the combustion of the fuel 3 is most efficient and in which the emission of

Pollutants and noise is minimal. This value ρκ is modified in step 110 of the method 100 to the desired pressure ps, which is finally communicated to the injection system 1, when the load request L to a

Operating point 29 drops with low load or such a waste is imminent.

In block 110a, it is ensured in sub-step 111 that the setpoint pressure ps does not fall below the predetermined base level PB. In substep 112, the

Pressure drop rate limited. On the one hand, the decay rate dps / dt of the target pressure ps is limited, which is included in the modification of the desired pressure ps. The other is the waste rate dp / dt of the actual pressure p is limited, which is due to immediate

Impact on the return plate 15 is realized.

In substep 113, decoupling 26a is interpreted as a signal that the drop in the load request L has a temporary character. In sub-step 114, a shift request 27a of the automatic transmission 27 is also evaluated as such a signal. In sub-step 115, a drop in the load request L is considered to be temporary when its absolute change rate dL / dt exceeds a predetermined threshold value AL. In substep 116, by comparing the time lapse L (t) of the load request with a threshold value

Ls, by comparing the target injection amount q with a threshold qs and by the analysis of the driver's request f if necessary determined that an initially as a temporary rated waste of the load request L is not temporary, but of duration.

If it is determined in sub-steps 113 to 116 that no

is present temporary drop in the load request L, then the

Influences of sub-steps 111 and 112 to the desired pressure ps, as well as the actual pressure p, neutralized, that is, the modified target pressure control is deactivated.

Insofar as the desired pressure ps is modified with respect to the value ρκ proposed by the map 16, the strength of this modification in the blocks 110b and 110c is fine-tuned. In block 110b, the extent of the modification is made dependent on the vehicle speed v and the last engaged gear 27b of the transmission 27. In block 110c, an additional one

State variable xi of the reservoir 13, a state quantity X2 of the affected by the return of the fuel 31 part of the

Fuel supply system, a state quantity X3 of the recirculating fuel 31 and environmental conditions x ₄ taken into account.

Figure 2 shows the course of the vehicle speed v, the requested target injection quantity q, which is a measure of the load request L, and the pressure p in the high-pressure reservoir 11 as a function of time t based on an exemplary ride. This journey is subdivided into a first acceleration phase I, a stationary phase II and a second acceleration phase III. Regarding the Pressure p are entered for comparison of the proposed by map 16 target pressure ρκ and two examples ps, i and ps, 2 for a modified setpoint pressure ps in the same diagram.

The first acceleration phase I is briefly interrupted by two switching phases a and b. Since the transmission of power to the transmission 27 has to be interrupted for a short time, in each case the load requirement, and thus the set injection quantity q, drops to zero. Accordingly, according to the proposal ρκ of the map 16 of the target pressure in about the except for

Idling speed pu_ reduced. The modified desired pressure ps according to both examples ps, i and ps, 2 is in each case significantly higher. The example ps, i sets primarily on a limitation of the rate of change dps / dt of the setpoint pressure ps, while the example ps, 2 limits especially the rate of degradation dp / dt of the actual pressure p.

Each abrupt drop in the load request L is initially considered as temporary waste. For the two switching phases a and b within the

Acceleration phase I is also true.

In the stationary phase II, however, the drop in the load requirement L is longer term because the vehicle is now traveling in the plane at almost constant speed. So it is initially in overrun one

Injection q demanded near zero before then again a slightly larger injection q is needed. After the modified desired pressure guide was first activated at the time ti, it is deactivated again at the time t2, after the lapse of a predetermined time interval Δt without a renewed increase in the load requirement L.

In stationary phase II, there is another difference between the examples ps, i and ps, 2. In the example ps, i, the target pressure pS is additionally maintained at least at a base pressure PB, that is, the idle pressure pu_ is de facto raised to the level PB.

The second acceleration phase III contains a further switching phase c, in which the load request L drops for a short time and accordingly the modified desired pressure control is rightly reactivated.

Claims

claims

A method (100) for operating an injection system (1) for an internal combustion engine (2), wherein the injection system (1) is a high-pressure reservoir

(II) for one or more fuels (3) and the target pressure ps in the high-pressure reservoir (11) according to at least one characteristic diagram (16) of

Load request L of the internal combustion engine (2) is tracked, to reduce the actual pressure p in the high pressure reservoir (11) excess fuel (3, 31) from the high pressure reservoir (11) is relaxed (99), characterized in that at least a temporary Waste of the load requirement L is increased to an operating point (29) with lower load of the desired pressure ps in the high-pressure reservoir (11) compared to the characteristic (16) for this operating point (29) provided value ρκ (110, 110a-110c).

2. Method (100) according to claim 1, characterized in that the

Target pressure ps is maintained at least at a predetermined base level PB

(III), which is higher than that according to the idling map of

Internal combustion engine provided value ρκ.

Method (100) according to one of claims 1 to 2, characterized in that the maximum and / or minimum rate of change dps / dt of the desired pressure ps, and / or the maximum and / or minimum rate of change dp / dt of the Actual pressure p, 112 is more limited (112) with decreasing load request L than with increasing load requirement L.

4. Method (100) according to one of claims 1 to 3, characterized in that disengagement (26a) of the internal combustion engine (2) is rated as a temporary drop in the load requirement L (113).

5. The method (100) according to claim 4, characterized in that the

Requirement (27a) of a shift by an automated transmission (27) is judged as a temporary drop in the load request L (114).

6. The method (100) according to any one of claims 4 to 5, characterized

in that the extent to which the desired pressure ps is changed from the value ρκ provided according to the map (16) is determined by the

Vehicle speed v, and / or the last engaged gear (27b) of a manual or automated transmission (27) is made dependent (110b).

7. The method (100) according to any one of claims 1 to 6, characterized

characterized in that a decrease in the load request L is considered to be temporary (115) when its magnitude change rate dL / dt exceeds a predetermined threshold AL.

8. The method (100) according to any one of claims 1 to 7, characterized

characterized in that a drop in the load requirement L first as

is evaluated temporarily (116) when the load request L has remained below a threshold value Ls for a predetermined period of time, if the target injection quantity q falls below a predetermined threshold value qs, and / or if a driver request f for the operating point (29) corresponds to the lower load.

9. The method (100) according to any one of claims 1 to 8, characterized

in that the extent to which the setpoint pressure ps is changed from the value ρκ provided according to the map (16) is determined by a

State variable xi of the reservoir (13), a state quantity X2 of the by the relaxation of the fuel (31), or by the reduction of the actual pressure p, affected part of the fuel supply system of a state quantity X3 of the fuel to be relaxed (31) and / or from

Environmental conditions x _{4 is made} dependent (110c).

10. The method (100) according to any one of claims 1 to 9, characterized

characterized in that liquefied natural gas (LNG) is used as fuel.

11. Computer program product containing machine-readable

Instructions that, when executed by a computer and / or a controller, cause the computer, and / or the controller to perform a method according to any one of claims 1 to 10.