DE10127516A1 - Operating internal combustion engine involves switching on additional electrically driven fuel pump at least for starting process to feed fuel directly to common fuel rail at raised pressure - Google Patents

Abstract

The method involves detecting an internal combustion engine start request and, if such a request exists, switching on an additional electrically driven fuel pump (46) at least for the duration of the starting process to feed fuel directly to the common fuel rail (30) at a raised supply pressure. Alternately the feed pressure of a single pump can be raised during starting without increasing the delivered quantity. Independent claims are also included for the following: a computer program for implementing the method and a fuel system for an internal combustion engine.

Description

State of the art

The invention initially relates to a method for operating an internal combustion engine, with a fuel system a fuel tank, with at least one Fuel pump, which from the internal combustion engine is driven with a fuel manifold, which with an outlet from the internal combustion engine driven fuel pump is connected, and with at least one fuel injection device which the fuel rail is connected.

Such a method is known from DE 198 18 421 A1. In this a fuel system is described, which Has fuel valves directly in the combustion chamber inject an internal combustion engine. To the for the Fuel supply of such direct-injection Fuel valves to be able to generate the required pressure a first electric fuel pump is provided, which takes the fuel from a fuel tank to a motor-driven high-pressure fuel pump promotes. From there the fuel reaches the Injectors.  

The problem is known from DE 198 18 421 A1 that it when turning off the hot engine and that Lowering the pressure required for safety reasons between high pressure fuel pump and injectors the formation of vapor bubbles in the fuel system occurs restarting the hot internal combustion engine difficult. For this it is suggested that for starting the internal combustion engine with the electric fuel pump promotes increased output. For example, by a May increase the speed of the electric fuel pump so on the one hand the flow rate and on the other hand the Delivery pressure can be increased, which is the condensation of the Steam bubble causes.

However, it has been found that it sometimes occurs with the Starting the cold engine to start problems comes. These stem from the fact that the Internal combustion engine driven high pressure fuel pump when the internal combustion engine is switched off, initially not in Operation and therefore the pressure upstream of the injectors is only applied by the electric fuel pump. The pressure is generally 3-5 bar. at at such a low pressure, the fuel from the Injectors, however, atomized only relatively poorly, so that some of the injectors are more than that injected ten times the amount of full load injection must be in order to be able to produce an ignitable mixture. However, such a high injection quantity has the disadvantage poor exhaust behavior of the engine and can do so cause the film of lubricating oil on the inside wall of the cylinder the excessive amount of fuel is washed off.

The present invention therefore has the task of a To further develop methods of the type mentioned at the beginning that the internal combustion engine can be started safely with it can and at the same time the internal combustion engine  Start shows good exhaust behavior.

This object is achieved in that with one method of the type mentioned at the outset Internal combustion engine recognized and if such Reason request an additional, electrical driven fuel pump for at least the duration of the Starting process is turned on, which goes directly to the Fuel manifold promotes and an increased Provides delivery pressure.

Advantages of the invention

The method according to the invention initially has the advantage that through the direct connection between the additional Fuel pump and the fuel rail Pressure losses can be minimized. Under the term "direct" is to be understood in the present case that the funding in the Fuel manifold does not take the detour of more or less stationary pumps. Furthermore, the additional fuel pump especially for that of her to be provided increased delivery pressure. It therefore works with optimal for this purpose Efficiency. The additional fuel pump be relatively small and inexpensive as they are only for the duration the starting process, i.e. a few seconds each, is switched on. Since only that fuel from her must be promoted, which for starting the Internal combustion engine is needed, the one from it too yield very low.

By direct fuel delivery from the additional electric fuel pump for fuel The others can also collect Fuel connections remain unchanged because of these a pressure increase does not take place. Thus the  required additional effort reduced to a minimum, and at the same time due to the increased delivery pressure ensures that the fuel is already in use Starting process of the internal combustion engine is atomized in such a way that this can start safely. In addition, a Excessively large injection quantity during the starting process the engine can be dispensed with, what that Improved exhaust gas behavior of the internal combustion engine and the Danger of washing off the lubricating oil film on the inner wall of the cylinder reduced.

The invention also relates to a method for operating an internal combustion engine, with a fuel system, with a fuel tank, with at least one electric powered fuel pump coming from the Fuel tank promotes, with at least one Fuel pump, which from the internal combustion engine is driven and its inlet with the outlet of the electrically powered fuel pump is connected to a fuel rail, which is connected to the outlet of the fuel pump driven by the internal combustion engine is connected, and with at least one fuel Injection device, which is connected to the fuel Bus is connected.

In the case of such a fuel system, this can initially alternative to the problem mentioned above Solution can also be solved by Requirement for the internal combustion engine recognized and at There is such a request for delivery pressure the electrically driven fuel pump at least for the duration of the starting process of the internal combustion engine is increased without increasing the output.

So this procedure works even if none additional fuel pump is provided. To the one  proper atomization build up necessary pressure can, for example with a Increase in speed associated increase in delivery rate waived. If necessary, the speed and thereby also the flow rate of the electrically driven Fuel pump versus their normal speed and Delivery rate even decrease because of starting the Internal combustion engine only a small delivery rate is required. The fuel lines do between the electric and that of the internal combustion engine driven fuel pump to the correspondingly increased Pressures are designed, but otherwise the procedure is feasible with an unchanged fuel system.

If an additional fuel pump is dispensed with, there is an easy way to increase the discharge pressure increase in that a pressure limiting device, which the delivery pressure of the electrically driven Fuel pump normally limited, fluidly by the electrically powered fuel pump is disconnected and the fuel injector is initially closed remains. The electrically driven fuel pump thus works against a closed system, which already at very low delivery rates to a clear one Pressure increase leads.

The advantages of the invention are from one Delivery pressure of about 20 bar noticeable. To an optimal - Being able to atomize the fuel will however preferred that the increased delivery pressure be approximate 40-60 bar, preferably about 45-55 bar.

The possibility, either by increasing the discharge pressure the electrically powered fuel pump or by that Switch on an additional fuel pump Increasing discharge pressure can also be used for that case  in which a failure of the Internal combustion engine driven fuel pump normal operation of the internal combustion engine is impaired. Therefore, it is also proposed that a failure of the motor-driven fuel pump recorded and also in this In case the increased fuel pressure is provided.

The invention further relates to a computer program which is suitable for performing the above method if it is running on a computer. It becomes special preferred that the computer program on a memory, is stored in particular on a flash memory.

Furthermore, the invention also relates to a control and / or Control device for operating an internal combustion engine, which comprises a memory on which a computer program above type is stored.

Part of the invention is also a fuel system for a Internal combustion engine with a fuel tank, with at least one fuel pump, which by the Internal combustion engine is driven with a fuel Manifold, which with an outlet of the motor-driven fuel pump is connected, and with at least one fuel injection device which the fuel rail is connected.

To the starting behavior of this fuel system equipped internal combustion engine, especially when cold To be able to improve the internal combustion engine without changes to have to make on the usual fuel system suggested that an additional, electric powered fuel pump is present, its outlet is directly connected to the fuel rail and which one compared to the electrically driven Fuel pump provides increased delivery pressure.  

With regard to the advantages of such Fuel system is based on the above directed.

An advantageous embodiment of such Fuel system is characterized in that the Intake of the additional fuel pump with the Fuel tank is connected. The additional Fuel pump delivers directly from the Fuel tanks, which offers the possibility of this too to accommodate in the area of the fuel tank.

In a fuel system with two series connections It is possible for fuel pumps to admit the additional fuel pump with an outlet of the first connect serial fuel pump, provided the first serial fuel pump is electrically powered.

In this case, the additional fuel pump does not have to all the compression work to compress the Fuel from the ambient pressure to the required Provide injection pressure, but only that pressure difference between the outlet of the first serial fuel pump and the desired injection pressure. The additional In this case, fuel pump can build a little smaller and be built cheaper. In any case, the additional fuel pump, however, has the advantage that existing first serial fuel pump unchanged can stay and also the fuel lines not be changed on the output side of this fuel pump have to.

In addition, the additional fuel pump for be designed for a short lifespan as they only each very short for the starting phase of the internal combustion engine is used. Furthermore, it only needs a small amount of it  Amount of fuel can be promoted so that it can be built relatively small and simple.

The further training in which the first serial fuel pump and the additional one Fuel pump part of a modular tank installation unit are. This can reduce the cost of installing the two fuel pumps can be reduced.

Instead of an additional fuel pump, it is at a fuel system of the above type with two serial Fuel pumps but also possible to use an electric one Provide drive and a switchable clutch, which the electric drive with the motor-driven Connect the fuel pump and the motor driven Can separate fuel pump from the mechanical drive. So there is no additional one with this fuel system Fuel pump provided. Instead, it starts the internal combustion engine, the second fuel pump, which is designed as a high-pressure fuel pump anyway, electrically powered.

This is the normally existing connection between the internal combustion engine and the second Fuel pump interrupted by the clutch and instead an electric motor connected to it. The Providing a switchable clutch means one certain additional effort, on the other hand, the rest Fuel system versus a common fuel system remain unchanged. Nevertheless, this too Safe starting of the fuel system Internal combustion engine with good at the same time Guaranteed emission behavior.

Another alternative for a dual fuel system serial fuel pumps, one of which is electric and  the other is driven by the internal combustion engine, is the electrically powered fuel pump train them so that they are at least for a specific one Period can provide an increased delivery pressure, without increasing the output. That way the power of the electrically driven fuel pump essentially used for the pressure of the fuel increase in the fuel rail so that too with this fuel system for an optimal one Atomization of the fuel by the fuel Get injector required fuel pressure becomes.

It is particularly preferred that a device is provided, which is the discharge pressure of the electrical driven fuel pump limited in normal operation, and a facility is available, which at a recorded event request for at least one certain time the pressure limiting device fluidically from the electrically driven fuel pump separates. In this case, the discharge pressure that the can generate electrically driven fuel pump in Essentially only through the leaks in the Fuel pump itself or in the fuel system determined. Therefore, the one for a safe starting required increased fuel pressure to be provided.

To be able to generate the increased fuel pressure, the electrically driven fuel pump one Have drive motor, which at a detected Starting request generates an increased torque. Since at Starting only a small amount is required can this increased torque with a Drop in speed.  

The atomization of the fuel by the fuel Injector is already raised from a Delivery pressure improved by 20 bar, but reached at an increased delivery pressure between 40 and 60 bar, preferably between 45 and 55 bar, essentially one optimal quality.

The optimal operation of the invention Fuel system is guaranteed when there is one Control and / or regulating device of the above type includes.

drawing

Exemplary embodiments of the invention are described below Reference to the attached drawing in detail explained. The drawing shows:

FIG. 1 shows a schematic block diagram of a first embodiment of a fuel system of an internal combustion engine;

Fig. 2 is a flowchart showing the method by which the fuel system of Fig. 1 is operated;

Fig. 3 is a representation similar to Figure 1 of a second embodiment of a fuel system of an internal combustion engine;.

Fig. 4 is a representation similar to Figure 1 of a third embodiment of a fuel system of an internal combustion engine;.

FIG. 5 is a flowchart showing the method by which the fuel system of FIG. 4 is operated;

. Fig. 6 is a representation similar to Figure 1 of a fourth embodiment of a fuel system of an internal combustion engine; and

FIG. 7 is a flow chart showing the procedure by which the fuel system of Figure 6 is operated..

Description of the embodiments

In Fig. 1, a fuel system bears the overall reference number 10 . It comprises a fuel tank 12 , which is connected to an inlet 14 of an electric fuel pump 16 . An outlet 18 of the electric fuel pump 16 is connected to the inlet 22 of a high-pressure fuel pump 24 via a fuel line 20 . This is mechanically driven by an internal combustion engine in a manner not shown.

An outlet 26 of the high pressure fuel pump 24 is connected to a fuel rail 30 via a check valve 28 . This is commonly referred to as "rail". In the exemplary embodiment shown in FIG. 1, a total of four fuel injection devices 32 are connected to the fuel collecting line 30 . In the present exemplary embodiment, these are high-pressure injection valves or injectors. These are attached to an engine block, not shown in FIG. 1, and inject the fuel directly into a combustion chamber, also not shown.

The outlet 18 of the electric fuel pump 16 is connected to the inlet 14 of the electric fuel pump 16 via a fuel line 34 . A pressure relief valve 36 is arranged in this. A fuel line 38 likewise leads from the outlet 26 of the high-pressure fuel pump 24 back to the inlet 22 of the high-pressure fuel pump 24 . A quantity control valve 40 is arranged in the fuel line 38 .

A fuel line 42 leads back from the fuel collecting line 30 to the inlet 22 of the high-pressure fuel pump 24 . A pressure relief valve 43 is arranged in this fuel line 42 . This limits the pressure in the fuel rail 30 to 120 bar. An inlet 44 of an additional electric fuel pump 46 is connected to this fuel line 42 . The outlet 48 in turn leads directly to the fuel collecting line 30 via a check valve 50 .

The pressure in the fuel rail 30 is detected by a sensor 52 . This delivers signals to a control and regulating device 54 . The latter also receives signals from a position transmitter 56 of an ignition lock (not shown) and from a speed sensor 58 which taps the speed of the crankshaft of the internal combustion engine. On the output side, the control and regulating device 54 controls the two electric fuel pumps 16 and 46 as well as the quantity control valve 40 .

The electric fuel pump 16 , the fuel line 34 and the pressure relief valve 36 are integrated overall into a so-called tank installation unit 60 . The high-pressure fuel pump 24 , the additional electric fuel pump 46 and the quantity control valve 40 , on the other hand, are integrated in an engine compartment unit 62 .

In normal operation of the internal combustion engine, the fuel is drawn from the fuel tank 12 by the electric fuel pump 16 and precompressed to approximately 4 bar. This pressure is set by the pressure relief valve 36 . The fuel is then further compressed by the high-pressure fuel pump 24 to a pressure of up to 120 bar. With this pressure, the fuel is pumped from the high-pressure fuel pump 24 into the fuel rail 30 . The delivery rate is set by the volume control valve 40 . From the fuel manifold 30 , the fuel reaches the injectors 32 , which spray the fuel very finely atomized into the combustion chamber due to the high pressure present, so that it can burn there in an optimal manner in terms of emissions and consumption.

For safety reasons, the high pressure is released from the fuel rail 30 after the end of the operation of the internal combustion engine. This is to prevent, for example, an undesired amount of fuel from entering the combustion chamber due to a leakage of an injector 32 when the internal combustion engine is switched off. The pressure in the fuel rail 30 drops to ambient pressure. If an attempt were now made to start the internal combustion engine and the procedure described below would not be followed, the fuel manifold 30 would initially have a maximum pressure of 4 bar set by the pressure relief valve 36 .

The reason for this is that the high-pressure fuel pump 24 is driven directly by the internal combustion engine. However, if this is not in operation, the high-pressure fuel pump 24 is also not in operation and therefore cannot provide the pressure that can be achieved in normal operation in the fuel collecting line 30 . However, if only a pressure of approximately 4 bar were present in the fuel manifold 30 , the injectors 32 could not inject the fuel into the combustion chamber in an optimally atomized manner. This would have to be compensated for by an increased amount of injected fuel, which on the one hand affects the exhaust gas behavior of the internal combustion engine and on the other hand leads to the risk that the excessive amount of fuel washes off the oil film on the cylinder inner wall and thereby increases the friction between the piston and the cylinder inner wall.

To prevent this, the fuel system 10 of FIG. 1 operates according to the method shown in FIG. 2. The method is stored as a computer program in a memory of the control and regulating device 54 .

After a start block 64 , it is checked in a block 66 whether a start sequence for the internal combustion engine has been requested. Control and regulating device 54 receives the corresponding signals from position sensor 56 of the ignition key. If the answer is yes, it is checked in block 68 whether the pressure in the fuel rail 30 is lower than a pressure of 40 bar (this pressure and also subsequent pressure values apply to the present exemplary embodiment; other pressure values are possible in other cases). This pressure corresponds to a level at which the injectors 32 can just still produce a satisfactorily atomized fuel mist in the combustion chamber. A pressure of 45-55 bar is good for atomizing the fuel when starting the internal combustion engine. The value for the pressure of the fuel in the fuel rail 30 is provided to the control and regulating device 54 by the pressure sensor 52 .

If a starting or starting sequence for the internal combustion engine has been requested and the pressure is lower than 40 bar, the additional electric fuel pump 46 is switched on in block 70 . This is designed in such a way that it can compress the fuel pre-compressed by the fuel pump 16 to approximately 4 bar with a relatively low delivery rate of approximately 5-10 l / h to approximately 50 bar. In addition, the sequence of the start sequence is initiated in block 72 , ie the starter is actuated, the ignition is switched on, etc. The pressure in the fuel collecting line 30 is also monitored by the pressure sensor 52 .

If the pressure in the fuel collecting line 30 exceeds a limit value of 60 bar, this means that the internal combustion engine has started and the high pressure fuel pump 24 driven by it can now provide the required fuel pressure in the fuel collecting line 30 . This is recorded in block 74 . In this case, the additional electric fuel pump 46 is switched off again in block 76 . The program ends in an end block 78 .

A second exemplary embodiment of a fuel system 10 will now be explained with reference to FIG. 3. Parts, elements and regions which have functions equivalent to the exemplary embodiment described above bear the same reference symbols therein. They are not explained in detail again.

In contrast to the fuel system 10 shown in FIG. 1, the inlet 44 of the additional electric fuel pump 46 is not connected to the outlet of the electric fuel pump 16 , but is connected directly to the fuel tank 12 . This has the advantage that the additional electric fuel pump 46 can also be accommodated in the tank installation unit 60 . However, a correspondingly longer line is also required between the additional electric fuel pump 46 and the fuel collecting line 30 , which line is designed for the high pressure of up to 50 bar that can be generated by the additional electric fuel pump 46 . The fuel system 10 shown in FIG. 3 is operated according to the method shown in FIG. 2.

In FIG. 4 a further embodiment of a fuel system 10 is shown. The above statements made with regard to functionally equivalent components, elements and areas apply analogously here.

In the embodiment shown in Fig. 4, there is no additional electric fuel pump. Instead, the electrical fuel pump 16 , which is present anyway, is designed such that it can provide the pressure of approximately 50 bar desired for starting the internal combustion engine. For this purpose, a switching valve 80 is arranged in the fuel line 34 between the outlet 18 of the electric fuel pump 16 and the pressure limiting valve 36 and is controlled by the control and regulating device 54 . With the switching valve 80 , the connection between the outlet 18 of the electric fuel pump 16 and the pressure relief valve 36 can be interrupted. Furthermore, a check valve 81 is present between the fuel connection 20 and the pressure relief valve 43 .

The fuel system 10 shown in FIG. 4 is operated as follows (see FIG. 5, here too only the differences from the method shown in FIG. 2 are explained in detail):

If it has been determined in blocks 66 and 68 that a start sequence has been requested and the pressure in the fuel rail 30 is below the desired minimum pressure level of 40 bar, the switching valve (which is also referred to as a start valve) is closed in block 82 , In block 70 , the drive current that is supplied to the electric fuel pump 16 is also increased, so that its drive motor generates an increased torque. Since the injectors 32 are still closed, the electric fuel pump 16 now delivers to a substantially closed volume.

This increases the pressure in the fuel manifold 30 with a very low delivery rate. This can also mean that the speed of the electric fuel pump 16 drops. As soon as the pressure in the fuel collecting line 30 is above approximately 60 bar, the electric fuel pump 16 is actuated normally again in block 76 and the start valve 80 is opened in block 84 . The normal fuel pressure of approximately 4 bar is thus restored at the outlet 18 of the electric fuel pump 16 .

Another embodiment of a fuel system 10 is shown in FIG. 6. The same applies here with regard to functionally equivalent parts, areas and elements.

In this embodiment, there is also no additional electric fuel pump. Instead, the high-pressure fuel pump 24 is connected to a switchable clutch 86 . This has two inputs, one of which is connected to a crankshaft 88 of the internal combustion engine and the other to the drive shaft of an electric motor 46 . In contrast to the exemplary embodiment shown in FIG. 4, the switching valve in the fuel line 34 between the electric fuel pump 16 and the pressure limiting valve 36 is also missing.

The method for operating the fuel system 10 shown in FIG. 6 results from FIG. 7, only the differences from the methods described above also being discussed here:

If the pressure in the fuel collecting line 30 is below 40 bar and a start sequence has been requested, the clutch 86 is controlled by the control and regulating device 54 in block 90 so that ultimately the clutch outlet, i.e. the high-pressure fuel pump 24 , is connected to the electrical one Drive 46 is connected. In block 70 , the electric drive 46 is then switched on and the start sequence is started. Of course, this also includes switching on the electric fuel pump 16 , which provides a pre-delivery pressure of approximately 4 bar. This pre-delivery pressure is now increased by the now electrically driven high-pressure fuel pump 24 to a pressure of approximately 50 bar.

As soon as the internal combustion engine has started, which is indicated by the speed sensor 58 , the clutch 86 is controlled in block 92 by the control and regulating device 54 and the high-pressure fuel pump 24 is connected to the crankshaft 88 of the internal combustion engine. In block 76 , the electric drive 46 is switched off again.

In an embodiment not shown the measures with which even without operating internal combustion engine an increased delivery pressure can be provided, also in a further case seized: namely, if while running Internal combustion engine the high pressure fuel pump for example, due to reaching their maximum Lifespan fails. In this way, an emergency operation the internal combustion engine guaranteed.

Claims (18)

1. Method for operating an internal combustion engine, with a fuel system ( 10 ) with a fuel tank ( 12 ), with at least one fuel pump ( 24 ) which is driven by the internal combustion engine, with a fuel collecting line ( 30 ), which has an outlet ( 26 ) of the fuel pump ( 24 ) driven by the internal combustion engine, and with at least one fuel injection device ( 32 ) which is connected to the fuel collecting line ( 30 ), characterized in that a starting request for the internal combustion engine is recognized ( 68 ) and if such a starting request is present, an additional, electrically driven fuel pump ( 46 ) is switched on ( 70 ) at least for the duration of the starting process, which delivers directly to the fuel collecting line ( 30 ) and provides an increased delivery pressure. 2. Method for operating an internal combustion engine, with a fuel system ( 10 ), with a fuel tank ( 12 ), with at least one electrically driven fuel pump ( 16 ) which delivers from the fuel tank ( 12 ), with at least one fuel pump ( 24 ), which is driven by the internal combustion engine and whose inlet ( 22 ) is connected to the outlet ( 18 ) of the electrically driven fuel pump ( 16 ), with a fuel collecting line ( 30 ) which is connected to the outlet ( 26 ) of the fuel pump driven by the internal combustion engine ( 24 ), and with at least one fuel injection device ( 32 ) which is connected to the fuel collecting line ( 30 ), characterized in that a starting request for the internal combustion engine is recognized ( 68 ) and, if such a starting Request the delivery pressure of the electrically driven fuel pump ( 16 ) at least for the duration of the starting process gs of the internal combustion engine is increased ( 70 ) without the delivery rate being increased. 3. The method according to claim 2, characterized in that the delivery pressure is increased in that a pressure limiting device ( 36 ), which normally limits the delivery pressure of the electrically driven fuel pump ( 16 ), is fluidly separated ( 82 ) from the electrically driven fuel pump ( 16 ) ) and the fuel injection device ( 32 ) initially remains closed. 4. The method according to any one of the preceding claims, characterized in that the increased delivery pressure about 40 to 60 bar, preferably about 45 to 55 bar. 5. The method according to any one of the preceding claims, characterized in that a failure of the fuel pump ( 24 ) driven by the internal combustion engine is detected and the increased fuel pressure is also provided in this case. 6. Computer program, characterized in that it is used for Carrying out the method according to one of the preceding Claims is appropriate when it is on a computer is performed. 7. Computer program according to claim 6, characterized  characterized it on a store, in particular on a flash memory. 8. Control and / or regulating device ( 54 ) for operating an internal combustion engine, characterized in that it comprises a memory on which a computer program according to one of claims 6 or 7 is stored. 9. Fuel system ( 10 ) for an internal combustion engine, with a fuel tank ( 12 ), with at least one fuel pump ( 24 ) which is driven by the internal combustion engine, with a fuel manifold ( 30 ), which has an outlet ( 26 ) of the fuel pump ( 24 ), and with at least one fuel injection device ( 32 ) which is connected to the fuel manifold ( 30 ), characterized in that an additional electrically driven fuel pump ( 46 ) is present, the outlet ( 48 ) of which is direct is connected to the fuel manifold ( 30 ) and which provides an increased delivery pressure. 10. Fuel system ( 10 ) according to claim 9, characterized in that the inlet ( 44 ) of the additional fuel pump ( 46 ) is connected to the fuel tank ( 12 ). 11. The fuel system ( 10 ) according to claim 9, characterized in that at least two series-connected fuel pumps ( 16 , 24 ) are present, the first serial fuel pump being electrically driven and the inlet ( 44 ) of the additional fuel pump ( 46 ) with an outlet ( 18 ) of the first serial fuel pump ( 16 ) is connected. 12. Fuel system ( 10 ) according to one of claims 9 to 11, characterized in that the first serial fuel pump ( 16 ) and the additional fuel pump ( 46 ) are part of a modular tank installation unit ( 60 ). 13. Fuel system ( 10 ) for an internal combustion engine, with a fuel tank ( 12 ), with at least one electrically driven fuel pump ( 16 ) which delivers from the fuel tank ( 12 ), with at least one fuel pump ( 24 ) which is driven by the internal combustion engine and the inlet ( 22 ) of which is connected to the outlet ( 18 ) of the electrically driven fuel pump ( 16 ), of a fuel manifold ( 30 ) which is connected to the outlet ( 18 ) of the motor-driven fuel pump ( 24 ), and at least a fuel injection device ( 32 ), which is connected to the fuel manifold ( 30 ), characterized in that an electric drive ( 46 ) and a switchable clutch ( 86 ) are provided which connect the electric drive ( 46 ) with that of Connect the fuel pump ( 24 ) driven by the internal combustion engine and the fuel pump ( 24 ) driven by the internal combustion engine from can separate the mechanical drive ( 88 ). 14. Fuel system ( 10 ) for an internal combustion engine, with a fuel tank ( 12 ), with at least one electrically driven fuel pump ( 16 ) which delivers from the fuel tank ( 12 ), with at least one fuel pump ( 24 ) which is driven by the internal combustion engine and the inlet ( 22 ) of which is connected to the outlet ( 18 ) of the electrically driven fuel pump ( 16 ), of a fuel manifold ( 30 ) which is connected to the outlet ( 26 ) of the motor-driven fuel pump ( 24 ), and at least a fuel injection device ( 32 ), which is connected to the fuel manifold ( 30 ), characterized in that the electrically driven fuel pump ( 16 ) can provide an increased delivery pressure for at least a certain period of time without increasing the delivery rate. 15. The fuel system ( 10 ) according to claim 14, characterized in that a device ( 36 ) is provided which limits the delivery pressure of the electrically driven fuel pump ( 16 ) in normal operation, and a device ( 80 ) is provided which is used on a detected occasion -Request ( 68 ) for at least a certain period of time fluidly separates the pressure limiting device ( 36 ) from the electrically driven fuel pump ( 16 ). 16. Fuel system ( 10 ) according to one of claims 14 or 15, characterized in that the electrically driven fuel pump ( 16 ) has a drive motor which generates an increased torque ( 70 ) when a start request ( 68 ) is detected. 17. Fuel system ( 10 ) according to one of claims 9 to 16, characterized in that the increased delivery pressure is between 40 and 60 bar, preferably between 45 and 55 bar. 18. Fuel system ( 10 ) according to one of claims 9 to 17, characterized in that it comprises a control and / or regulating device ( 54 ) according to claim 8.