DE102005012998B3 - Common rail injection system for e.g. diesel engine, has injectors comprising injection nozzles for injecting fuel into combustion chamber, where one of injectors or part of injectors serves for pressure reduction in high pressure area - Google Patents

Abstract

The system has injectors (10 - 13) provided with injection nozzles for injecting fuel into a combustion chamber of an internal combustion engine. Each injector includes a switching leakage flow, which flows from a high pressure area (9) over a fuel return flow during switching operation, such that fuel pressure in the area (9) is decreased. One of the injectors (10) or a part of the injectors serves for pressure reduction in the area. An independent claim is also included for a method for pressure reduction in a high pressure area of a common rail injection system of an internal combustion engine.

Description

The The invention relates to a method for pressure reduction in the high pressure area an injection system and a correspondingly designed injection system according to the siblings Claims.

conventional Common rail injection systems usually have a volume flow control valve (engl. VCV - Volume Control Valve) and a high pressure control valve (PCV - Pressure Control Valve), wherein the volume flow control valve the amount of the fuel supplied to the high-pressure pump and then pumped into the pressure accumulator (common rail), while the high pressure control valve the output of the high pressure pump with a Low pressure area connects and thus a rapid pressure reduction in the high pressure area and in the accumulator allows by the high-pressure control valve is opened.

It is still known in such common-rail injection systems for cost reasons to dispense with the high pressure control valve and the pressure in the Instead set the high-pressure range through the volume flow control valve, which is regulated in a closed loop. To lift the pressure in the high-pressure region of the injection system is the flow control valve then longer turned on, so that more fuel from the high pressure pump in the high-pressure area of the injection system is pumped, resulting in a relatively fast pressure build-up leads. To lower the pressure in the high pressure area, however, is not the Flow control valve used. Instead, it is going to lower the pressure in the high pressure area of the injection system, the permanent leakage of exploited individual injectors, causing the pressure in the high pressure area but only drops off relatively slowly, which can lead to a load change of the fuel injection system that in the high pressure area of the injection system still too high fuel pressure prevails, which in turn leads to losses in the Driving behavior and a higher Combustion noise contributes.

Furthermore, it is known to control the pressure actuation of injection systems without a separate high-pressure control valve, the magnetic actuators of the individual injectors so that although the respective control valves open and thereby flow fuel from the high pressure area of the injection system in the return, but the nozzle needle is not yet raised so that no injection takes place. With this weak control, fuel flows from the high-pressure region via the open control valves of the individual injectors into the return flow relatively quickly, as a result of which the fuel pressure in the high-pressure region of the injection system can be reduced relatively quickly. For example, this technique of pressure reduction is off EP 0 745 184 B1 . EP 0 896 144 A2 . US Pat. No. 6,345,606 B1 . EP 1 018 600 A2 and EP 1 024 274 known and has been used only in magnetic actuators.

From the EP 1 018 600 A2 It is known to operate at least one of the injectors to achieve a pressure reduction, wherein the common rail is additionally equipped with a pressure-limiting valve.

adversely at the pressure reduction by exploiting the switching leakage of the injectors is the fact that the load cycles of the injectors are significant elevated is because the injectors not only for pre-, main- or post-injection need to be controlled but also for pressure reduction in the high pressure area of the injection system.

Furthermore is due to the required control of the actuators of the pressure reduction serving injectors the thermal cal load of the engine control unit (engl. ECU - Electronic Control Unit) increased significantly.

Of the The invention is therefore based on the object, the injection system to improve and simplify, the injectors of a spray system used for pressure reduction in the high pressure area of the injection system should be.

These Task is by an injection system and a corresponding operating method according to the siblings claims solved.

The Invention includes the general technical teaching for pressure reduction not all in the high pressure area of the injection system To use injectors, as in the prior art, but only a single injector or part of the injectors.

To the this offers the advantage that the number of cycles in the other injectors not increased by the pressure reduction becomes.

To the This will only affect the thermal load of the engine control unit slightly increased, for this the pressure reduction in the high pressure region of the injection system substantially fewer actuators must be controlled than in the prior art.

Despite the activation of only a single injector or a portion of the injectors yet ei NEN effective pressure reduction in the high-pressure region of the injection system, the pressure-reducing injector according to the invention designed differently designed as the other injectors by the pressure-reducing injector with closed injector has a larger Schaltleckagestrom and therefore can dissipate more fuel from the high pressure region of the injection system ,

Of the for reducing pressure injector of the injection system according to the invention may in the context of the invention, various pressure reduction techniques which are briefly described below.

A possibility for pressure reduction in the high-pressure region of the injection system is in that the respective actuator is activated for a short time will, so the injector remains closed, whereas the control valve already opens and thereby the fuel return releases, resulting in a corresponding pressure drop in the high pressure area the injection system leads. This is exploited so that the individual injectors at a Aktoransteuerung a temporal switching delay between opening of fuel return and the subsequent opening of the Have an injection nozzle, where the switching delay in the pressure-reducing injector is preferably larger than the rest Injectors that are not used for pressure reduction. Due to this increased switching delay at the pressure-reducing injector allows this advantageous one effective pressure reduction in the high pressure area of the injection system.

A different possibility for pressure reduction in the high-pressure region of the injection system is that the injector serving for pressure reduction is driven so weakly will that injector remains closed, but the control valve opens. The serving for pressure reduction Injector stops the injector So closed up to a certain driving strength, while the Control valve already open and thereby releases the fuel return, resulting in a corresponding pressure drop in the high pressure area the injection system leads.

In a preferred embodiment of Invention is the pressure reduction in the high pressure region of the injection system caused solely by the injector concerned, so on a separate high-pressure control valve in the high-pressure region of the injection system can be waived. The invention does not necessarily require the waiver of a separate high pressure valve. Rather, it includes the invention also such injection systems in which the pressure reduction in the high-pressure area of the injection system both by or several injectors as well as by a high pressure control valve.

In an advantageous embodiment of the invention can be dispensed with a separate flow control valve, which adjusts the volume flow in the conventional injection systems, which is supplied to a high-pressure pump. In such a waiver of a separate flow control valve, the pressure control takes place in the high-pressure region of the injection system via the injector serving for pressure reduction. With the injection switched off (overrun mode), the entire delivery capacity of the high-pressure pump (eg 33 cm ³ / s) then flows into the high-pressure area of the injection system. The injector used for pressure reduction then has to discharge the entire delivery flow of the high-pressure pump via the fuel return in this operating state in order to avoid a further increase in pressure in the high-pressure region of the injection system. The switching leakage current of the pressure-reducing injector is therefore preferably in the range of 1 cm ³ / s to 100 cm ³ / s in order to ensure a sufficient pressure reduction. In addition, the fuel return preferably has a minimum diameter or a minimum width of at least 0.8 mm, so that enough fuel can be removed via the fuel return from the high-pressure region of the injection system.

at the aforementioned Dispensing with a separate volume flow control valve is the maximum Schaltleckagestrom the pressure reducing injector or the Sum of the maximum switching leakage currents of the pressure reduction Injectors preferably larger than the volume flow of the high-pressure pump, so that in the overrun operation, a pressure increase can be prevented in the high pressure area.

Farther is to mention that the injectors are preferably controlled by piezo actuators. However, the invention is with regard to the control of the injectors not limited to piezo actuators, but basically also with conventional Magnet actuators feasible.

Further is the injection system according to the invention preferably a common-rail injection system, which has a common Compressor (common rail) has, all injectors supplied with the fuel to be injected. The invention is however basically also feasible with other types of injection systems, such as Pump-nozzle injection systems. About that In addition, the injection system according to the invention can optionally be a gasoline injection system or a diesel injection system.

Furthermore, the invention also includes a corresponding operating method, which is already from the present general description.

The The invention further comprises the general technical teaching, the relevant Actuator for pressure reduction in each case only very briefly for a certain actuation period to control, whereby the driving time is chosen so short, that the injector while the control period remains closed. This is the realization exploited that the nozzle needle an injector when opening of the control valve only with a certain time delay raised will, so between opening the control valve and lifting the nozzle needle already a certain Quantity of fuel from the control chamber of the injector drained into the return is, resulting in a corresponding pressure reduction in the high pressure area the injection system leads. In a correspondingly short-term control of the actuator remains the injector so closed, although fuel from the high pressure area in the return flows.

Preferably the actuator is repeated for pressure reduction with a certain number of repetitions controlled, thereby comparing the effectiveness of the pressure reduction can be increased with a single control. Preferably the repetition number here is between 2 and 6, i. the actor is during one cycle of the internal combustion engine each driven two to six times. The Invention is not, however, in terms of repetition number the aforementioned Limited range of values, but also with other repeat numbers feasible.

Preferably is the activation duration and / or the repetition number for the pressure reduction not constant, but becomes dependent from an operating size of the injection system varies to the desired one To bring about pressure reduction in the high pressure region of the injection system.

For example can in the context of the invention, the engine speed of the internal combustion engine be measured and determine the repetition number and / or the driving time for be used for the pressure reduction. At a high engine speed leads the Pressure drain over the open one Control valve namely Relatively fast to a pressure reduction, so that a relatively small Ansteuerdauer or repetition number is required to the desired To cause pressure reduction. The activation duration and / or the repetition number for the pressure reduction is therefore preferably dependent on the engine speed of the internal combustion engine set, the repetition number and / or the activation duration preferably decreases with the engine speed.

Farther it is possible, that the activation duration and / or the repetition number for the pressure reduction dependent on set by the pressure in the high-pressure region of the injection system becomes. For this purpose, by means of a pressure sensor, the fuel pressure measured in the high-pressure region of the internal combustion engine. The determination the repetition number and / or the activation duration for the pressure reduction dependent on from the fuel pressure in the high-pressure region of the injection system makes sense because the fuel drain over the open control valve of an injector and thus also the pressure reduction of the pressure in the high pressure area depends. At a big one Namely, pressure in the high-pressure area flows in accordance with much fuel over open Control valve in the low pressure area, so that the pressure then falls relatively quickly. Preferably, the repetition number and / or the activation duration increases Therefore, from the pressure prevailing in the high pressure area.

Furthermore there is also the possibility the activation duration and / or the repetition number for the pressure reduction dependent on from the prevailing in the injector injector temperature, another Temperature in the injection system or the internal combustion engine as well dependent on set by the previous operating life of the injector.

Preferably, the repetition number for the pressure reduction is equal to 2, when the engine speed is greater than 4000 min ^-1 and the pressure is greater than 1600 bar. The repetition number is on the other hand, when the engine speed is greater than 3000 min ^-1 and the pressure is between 1500 bar and 1600 bar is preferably equal. 3 At an engine speed less than 3000 min ^-1 and a pressure between 1500 bar and 1600 bar, however, the repetition number is preferably equal to 4. Furthermore, the repetition number is preferably equal to 4, when the engine speed is between 3000 min ^-1 and 4000 min ^-1 and the pressure is less than 1500 bar. Finally, the repeat count is preferably equal to 5, when the engine speed is 3000 min ^-1, and the pressure is less less than 1500 bar.

In In any case, the drive time for the pressure reduction is preferred shorter as the normal driving time for a pilot injection, a main injection and / or a post-injection. This is of course because no pressure in the combustion chambers of the pressure reduction Internal combustion engine should be injected.

Furthermore the driving time is preferably so short in the invention selected that the injector while the control period independent from the driving force remains closed.

By the pressure reduction method according to the invention he falls Pressure in the high pressure region of the injection system preferably in Essentially exponential with a certain time constant from where the time constant preferably between 0.5 seconds and 10 seconds lies.

Other advantageous developments of the invention are characterized in the subclaims or will be discussed below together with the description of the preferred Embodiment of Invention with reference to the figures explained. Show it:

1 a schematic representation of an injection system according to the invention for an internal combustion engine,

2A and 2 B Pressure reduction curves at different pressures in the high-pressure region of the injection system and for different repetition numbers,

3 a map for determining the repetition number for the pressure reduction as a function of the engine speed and the pressure in the high-pressure region and

4 a schematic representation of an alternative embodiment of an injection system according to the invention for an internal combustion engine.

The schematized representation in 1 shows a largely conventionally constructed injection pump 1 (DCP - Diesel Common Rail Pump) for fueling a Dieselmo gate, the diesel engine is not shown for simplicity.

The injection pump 1 has a low pressure pump 2 on, which has a drive shaft 3 from a motor 4 is powered and fuel via a suction line 5 sucked from a fuel tank, wherein the fuel tank is not shown for simplicity.

The low pressure pump 2 feeds a low pressure area of the injection pump 1 with fuel, wherein the pressure in the low pressure region through a low pressure control valve 6 is controlled to a predetermined setpoint.

In the low pressure area of the injection pump 1 is still a flow control valve 7 (VCV - Volumetric Control Valve) is arranged, which adjusts both the fuel flow and the pressure, as will be described in detail.

The flow control valve 7 connects the low pressure pump 2 with a high pressure pump 8th also from the drive shaft 3 is mechanically driven and that of the low pressure pump 2 supplied fuel under high pressure in a pressure accumulator 9 (Common Rail) pumps.

From the accumulator 9 be multiple injectors 10 - 13 supplied with fuel having the injection pressure required for injection into the combustion chambers of the internal combustion engine.

The high pressure pump 8th also has a fuel return line 14 on, about the leakage-related fuel in the low pressure region of the injection pump 1 is returned. In the fuel return line 14 is a parallel circuit of a flow resistance 15 with a series connection of a check valve 16 and another flow resistance 17 arranged.

In addition, the injectors point 10 - 13 in each case a displaceably mounted nozzle needle, which releases or blocks an injection nozzle in dependence on its position. The mechanical drive of the nozzle needle takes place in each case by the fuel pressure, which prevails in a control chamber, wherein the force acting on the nozzle needle and this in the valve seat oppressive fuel pressure in the control chamber by a control valve in a return line 18 can be drained, with the return line 18 via a check valve 19 opens into the fuel tank of the internal combustion engine. In each injection so flows a part of the pressure in the accumulator 9 located fuel via the individual control valves in the injectors 10 - 13 in the return line 18 and from there into the fuel tank, reducing the fuel pressure in the accumulator 9 is lowered. The control valves of the individual injectors 10 - 13 be this by an electronic engine control 20 (English: ECU - Electronic Control Unit) controlled, whereby the engine control 20 via a pressure sensor 21 also the pressure in the accumulator 9 measures and the flow control valve 7 so controls that in the accumulator 9 sets the desired injection pressure, as described below.

If the engine control 20 over the pressure sensor 21 determines that the pressure in the accumulator 9 is too low, then the flow control valve 7 kept open longer so that the high pressure pump 8th more fuel into the accumulator 9 pumps, causing the pressure in the accumulator 9 increases.

If the engine control 20 on the other hand via the pressure sensor 21 determines that the pressure in the accumulator 9 too big, so controls the engine control 20 the flow control valve 7 too, so the high pressure pump 8th less fuel in the accumulator 9 pumping, causing another pressure increase in the accumulator 9 counteracts.

In addition, the engine control allows 20 by a suitable control of the piezoelectric actuator of the injector 10 a rapid pressure reduction in the accumulator 9 , as described below.

For a quick pressure reduction in the accumulator 9 becomes the piezo actuator of the injector 10 each driven for short drive times, the drive times are so short that the nozzle needle of the injector 10 does not lift, so that no fuel is injected into the associated combustion chamber of the internal combustion engine. During this brief activation of the piezo actuator of the injector 10 However, the associated control valve opens, causing fuel from the pressure accumulator 9 over the return line 18 drains, resulting in a relatively rapid pressure reduction in the pressure accumulator 9 leads.

The curves in the 2A and 2 B show the time course of the pressure reduction in the pressure accumulator 9 , where the curves in 2A assume an initial pressure of about 1600 bar, whereas the curves in 2 B assume an initial pressure of about 1000 bar. From the comparison of the two diagrams it can be seen that the pressure reduction in the pressure accumulator 9 at a high initial pressure is much faster, which is also plausible.

In addition, the various curves show the time course of the pressure reduction for different repetition numbers of the control of the piezoelectric actuator of the pressure-reducing injector 10 , This is how the piezo actuator turns 22 only briefly activated once per cycle of the internal combustion engine, resulting in a correspondingly slow pressure drop in the pressure accumulator 9 leads.

The two curves 23 on the other hand give the time course of the pressure reduction in the pressure accumulator 9 in the event that the piezoelectric actuator of the pressure-reducing injector 10 be briefly toggled ("toggled") twice in each cycle of the internal combustion engine. Accordingly, the curves show 23 a much faster pressure reduction in the accumulator 9 ,

The other curves 24 . 25 respectively. 26 on the other hand show the much faster pressure drop in the event that in each cycle of the internal combustion engine three, four or five times a control of the piezoelectric actuator of the injector 10 he follows.

The repetition number of the actuators of the piezo actuator of the injector 10 in each cycle, this is dependent on the pressure in the accumulator 9 and determined in dependence on the engine speed n, as can be seen from the map, the in 3 is shown.

In an operating area 27 At a pressure p> 1600 bar, only a double activation of the piezo actuator of the injector takes place in each cycle, independently of the engine speed 10 because of the high fuel pressure in the operating range 27 no major repetition numbers are required.

In an operating area 28 with a pressure in the accumulator 9 between 1500 bar and 1600 bar and an engine speed n> 3000 min ^-1 , however, there is a triple activation of the piezo actuator of the injector 10 to accomplish the desired pressure reduction, since a double activation is then no longer sufficient due to the lower fuel pressure.

In two other operating areas 29 . 30 In contrast, even a four-fold control of the piezoelectric actuator of the injector 10 to cause the desired pressure reduction, since the pressure reduction in the operating areas 29 . 30 is less effec tively due to the reduced pressure or the reduced engine speed and therefore a higher repetition rate is required. In the operating area 29 the pressure is in the accumulator 9 between 1500 and 1600 bar, while the engine speed in the operating range 29 is less than 3000 min ^-1 .

In the operating area 30 however, the engine speed is between 3000 and 4000 min ^-1, while the pressure in the accumulator 9 is less than 1500 bar.

In another operating area 31 However, due to the relatively low pressure and the relatively low engine speed, a five-fold control of the piezoelectric actuator of the injector 10 to allow the desired pressure reduction due to the low pressure and speed values. The operating area 31 is at speeds of less than 3000 min ^-1 and a pressure of less than 1500 bar.

This in 4 illustrated alternative embodiment of a erfindungemäßen injection system is largely consistent with that described above and in 1 illustrated embodiment, so reference is made to avoid repetition of the above description, wherein the same reference numerals are used for corresponding components.

A special feature of this embodiment is that in the low pressure region of the injection pump 1 upstream before the high pressure pump 8th no separate flow control valve 7 is arranged. The high pressure pump 8th So works with a flow rate, the only by the speed of the drive shaft 3 is given, which is a fast pressure control of the pressure in the accumulator 9 prevailing pressure prevented.

The pressure in the accumulator 9 and thus the injection pressure is here alone by the Schaltleckagestrom of Injek sector 10 regulated. For this purpose, the injector 10 a Schaltleckagestrom that is greater than the other injectors 11 - 13 , which do not serve for pressure reduction in the high-pressure region of the injection system. The switching leakage current of the injector 10 in this case is such that the entire flow of the high pressure pump 8th over the return line 18 can be discharged into the low pressure region of the injection system, for example, in overrun operation of the internal combustion engine, a further pressure increase in the pressure accumulator 9 to prevent if no fuel from the injectors 10 - 13 is injected into the combustion chambers of the internal combustion engine.

The The invention is not limited to the embodiments described above limited. Rather, a variety of variants and modifications is possible, the also make use of the idea of the invention and therefore fall into the scope.

Claims (29)

Injection system for an internal combustion engine, in particular common-rail injection system, wherein the injection system comprises: - several injectors ( 10 - 13 ) with an injection nozzle for injecting fuel into a combustion chamber of the internal combustion engine, - a high-pressure region ( 9 ), which injectors ( 10 - 13 ) supplied with the fuel to be injected, - a fuel return ( 18 ) of the individual injectors ( 10 - 13 ), the individual injectors ( 10 - 13 ) each have a switching leakage current, which in a switching operation via the fuel return ( 18 ) from the high pressure area ( 9 ) and thereby the fuel pressure in the high pressure area ( 9 ), characterized in that only a single injector ( 10 ) or part of the injectors ( 10 - 13 ) for pressure reduction in the high pressure area ( 9 ), wherein the pressure-reducing injector ( 10 ) is structurally designed differently than the other injectors ( 11 - 13 ), by the pressure-reducing injector ( 10 ) has a larger switching leakage current when the injector is closed than the other injectors ( 11 - 13 ) and therefore more fuel from the high pressure area ( 9 ) can dissipate. Injection system according to claim 1, characterized in that the individual injectors ( 10 - 13 ) in a Aktoransteuerung a temporal switching delay between the opening of the fuel return ( 18 ) and the subsequent opening of the injection nozzle, wherein the switching delay is greater in the pressure-reducing injector than in the other injectors ( 10 - 13 ). Injection system according to one of the preceding claims, characterized in that the injector serving for pressure reduction holds the injector closed in an actuator control up to a certain drive strength, while the fuel return ( 18 ) is already open. Injection system according to one of the preceding claims, characterized in that in the high-pressure region ( 9 ) of the injection system is arranged no separate high-pressure control valve, so that the pressure reduction in the high pressure area ( 9 ) via the switching leakage current of the injector ( 10 ) he follows. Injection system according to one of the preceding claims, characterized in that in the low pressure region of the injection system no separate volume flow control valve ( 7 ) is arranged so that the pressure control in the high pressure area ( 9 ) via the switching leakage current of the injector ( 10 ) he follows. Injection system according to one of the preceding claims, characterized in that the switching leakage current of the pressure-reducing injector ( 10 ) is in the range between 1 cm ³ / s and 100 cm ³ / s. Injection system according to one of the preceding claims, characterized in that the fuel return ( 18 ) has a diameter or width of at least 0.8 mm. Injection system according to one of the preceding claims, characterized in that the maximum switching leakage current of the pressure-reducing injector ( 10 ) is greater than the volume flow of a high-pressure pump ( 8th ), the high pressure area ( 9 ) feeds with fuel. Injection system according to one of the preceding claims, characterized in that the injectors ( 10 - 13 ) each have piezoelectric actuators. Injection system according to one of the preceding claims, characterized by a common pressure accumulator ( 9 ), all injectors ( 10 - 13 ) supplied with the fuel to be injected. Process for pressure reduction in Hochdruckbe rich ( 9 ) an injection system of an internal combustion engine with a plurality of injectors ( 10 - 13 ) each having an injection nozzle, the injectors ( 10 - 13 ) from the high pressure area ( 9 ) are fueled and each having a Schaltleckagestrom which via a fuel return ( 18 ) from the high pressure area ( 9 ), characterized in that only a single injector ( 10 ) or only part of the injectors ( 10 - 13 ) for pressure reduction in the high pressure area ( 9 ) and is controlled so that the fuel return ( 18 ) of the respective injector, while the injection nozzle of the respective injector remains closed, wherein the pressure-reducing injector ( 10 ) is structurally designed differently than the other injectors ( 11 - 13 ), by the pressure-reducing injector ( 10 ) has a larger switching leakage current when the injector is closed than the other injectors ( 11 - 13 ) and therefore more fuel from the high pressure area ( 9 ) can dissipate. A method according to claim 11, characterized in that the pressure-reducing injector ( 10 ) is driven with a certain driving strength, the driving strength is so low that the injection nozzle remains closed during the control. A method according to claim 11 or 12, characterized in that the pressure-reducing injector ( 10 ) is driven with a certain drive time, the drive time is so short that the injector remains closed during the control period. Method according to one of claims 11 to 13, characterized in that the pressure-reducing injector ( 10 ) is repeatedly actuated with a certain number of repetitions in order to control the pressure in the high-pressure region ( 9 ) to lower. Method according to one of claims 13 or 14, marked by following steps: - Determination of at least one Operating size of the injection system, - Determination the activation duration and / or the repetition number for the pressure reduction in dependence of the determined operating size of the injection system. A method according to claim 15, characterized in that the operating quantity is the following size: - the engine speed and / or - the pressure in the high pressure area ( 9 ) of the injection system and / or - prevailing in the injector injector temperature and / or - the previous operating time of the injector. Method according to one of claims 13 to 16, characterized in that the repetition number and / or the drive duration with the in the high pressure area ( 9 ) prevailing pressure decreases. Method according to one of claims 13 to 17, characterized that the repetition number and / or the driving time with the engine speed decreases. Method according to one of claims 13 to 18, characterized that the repetition number is between 2 and 6. Method according to one of claims 13 to 19, characterized in that the repetition number is 2, when the engine speed is greater than 4000 min ^-1 and the pressure is greater than 1600 bar. Method according to one of claims 13 to 20, characterized in that the repetition number is 3, when the engine speed is greater than 3000 min ^-1 and the pressure between 1500 bar and 1600 bar. Method according to one of claims 13 to 21, characterized in that the repetition number is 4, when the engine speed is less than 3000 min ^-1 and the pressure between 1500 bar and 1600 bar. Method according to one of claims 13 to 22, characterized in that the repetition number is 4, when the engine speed is between 3000 min ^-1 and 4000 min ^-1 and the pressure is less than 1500 bar. Method according to one of claims 13 to 23, characterized in that the repetition number is 5, when the engine speed is less than 3000 min ^-1 and the pressure is less than 1500 bar. Method according to one of claims 12 to 24, characterized that the driving time for the pressure reduction shorter is considered the driving time for a pilot injection, a main injection and / or a post-injection. Method according to one of claims 12 to 25, characterized that the actuator with pressure reduction with a certain driving strength driven is, wherein the driving time is so short that the injector during the Control duration independent from the driving force remains closed. Method according to one of the preceding claims, characterized characterized in that the actuator is a piezoelectric actuator. Method according to one of the preceding claims, characterized characterized in that the pressure during the pressure reduction is essentially exponential with a particular one Time constant drops. Method according to Claim 28, characterized that the time constant is between 0.5 s and 10 s.