SE524460C2 - Fuel injection systems - Google Patents

Abstract

A fuel injection system for an internal combustion engine comprises a nozzle (2) with an inlet and a cam-driven plunger (5) forming a plunger chamber (7) which is connected to the inlet of the nozzle. The injection sysstem also comprises a common rail (10) for fuel and a control valve (9) installed between the plunger chamber (7) and the common rail (10), wherein the control valve is able to open or close hydraulic communication between the plunger chamber and the common rail upon receiving an electrical control command. An electrically actuated nozzle control valve (21) is used for opening and closing of the nozzle (2). The system also comprises a means (11) for pressurizing the common rail and regulating pressure of the fuel in the common rail (10).

Description

20 25 30 524 460 individual injection. High-pressure systems of the “common-rail” type cannot achieve such injection characteristics as easily, and when their natural square-shaped injection curve becomes desirable in certain engine operating conditions, the corresponding unit injectors with a direct needle control valve can shape the injection just as advantageously. This gives the latter systems better flexibility in shaping the injection curve. On the other hand, high-pressure systems of the “common-rail” type have certain advantages in comparison with the mechanically impacted injection systems. Among those that are most important for engines for commercial vehicles can be mentioned the almost unlimited freedom of choice at the time of injection and the ease of achieving multiple Such in a fuel injection. The possibility of injection systems is increasing in importance through the introduction of various types of devices for post-treatment of diesel exhaust gases and progress in development such as HCCI. of alternative combustion processes The dependence of mechanically impacted systems on a cam for driving the pump piston can severely limit their ability to meet the requirements. regarding injection timing and feed for multiple injections. The second advantage of high-pressure common rail systems compared to systems with mechanical unit injectors can be lower parasite losses in terms of drive power when operating at very low loads and during idling. Under such conditions, high pressure common rail systems can also have higher fuel supply precision than a system with mechanically actuated unit injectors with a large diameter on the pressure piston. Finally, mechanically actuated systems with unit injectors can be a source of loud mechanical noises generated by both the injectors themselves and the power transmission which transmits torque to operate the system. Such noise is especially noticeable at idle. The operation of the high-pressure common rail system does not significantly contribute to the total engine noise at any operating point.

OBJECTS OF THE INVENTION The object of the present invention is a new mechanical unit injection system with common rail functionality. The object of the invention is to enable selective application of the principles of mechanical injection function and common rail in conditions which allow the use of their respective advantages, and selective deactivation in other conditions where their respective disadvantages may adversely affect engine performance.

TECHNOLOGY'S POSITION US Patent 6,247,450 B1 by Jiang discloses a system comprising a mechanically actuated unit injector with a control valve and a common rail. In this system, relative levels are regulated and this common rail pressure at low fuel is fed under pressure into the unit injector via a metering nozzle which is opened at a certain retracted position of the unit injector pressure piston, and which closes at other pressure piston positions. Variation of the common rail pressure and the opening duration of the metering nozzle determine the amount of fuel that fills the plunger chamber. During the pump stroke of the piston, the dosing nozzle is closed and the fuel is pressurized in the pressure piston chamber, which is suitably dimensioned to enable the necessary injection pressure to be reached. The pressure piston chamber is connected to the inlet of a conventional spring-closed nozzle via a control valve. When the desired pressure level is reached, the control valve can be opened to transfer the pressurized fuel to the nozzle and the injection is started. At the end of the valve and the injection, the nozzle is closed by the return spring.

Such systems depend on the pressure piston standing still at maximum lift and maintaining the pressure generated during the pump stroke, to enable flexible injection timing. Fuel injection can not take place at all during most of the retraction or pump stroke of the pump piston, as the dosing nozzle is closed. Obviously, the system is not designed for injection at any time other than when the pressure piston is in the vicinity of the nmx lift, because even if below the spring opening pressure, the control valve would open the fuel metering phase and the common rail pressure would be higher than the nozzle, the required pressure drop across the metering nozzle to obtain the fuel metering function of the system, have prevented injection.

In addition to the limited time interval for injection 6,247,450, namely an unfavorable form, the system according to US patents has several other disadvantages, the injection curve both at the beginning and the end of the injection, limited interval of injection pressure, etc.

The second known FIE which can be considered relevant with respect to the position of the invention is that which is known as pressure / time dosing unit injection system 10 24 20 25 30 524 460 and which has been introduced on the market by Cummins Inc.

Examples of such systems are found in U.S. Patents 3,544,008, 4,092,964 and 5,445,323. One includes a common rail with pressurized fuel that feeds systems of this type of unit injector. However, the function of the common rail is not to inject fuel directly into the engine, but to facilitate the fuel metering to the piston chamber which is moved by means of the nozzle during the piston stroke of the piston. Such systems thus have a limited area for injection timing and need to utilize the mechanical operation each time an injection is to be made.

DISCLOSURE OF THE INVENTION A main object of the invention is to provide a fuel injection system which enables selective application of the principles of mechanical injection function. and commonrail in conditions that allow utilization of their respective advantages, and selective deactivation in other conditions to avoid their respective disadvantages.

A more specific object of the invention is to provide a fuel injection system with an increased range of possible injection times compared to known mechanically actuated injection systems, so as to occur at any increased injection pressure compared to what is possible with injection can point during engine rotation; at intervals of possible and with an improved Such a system known commonrail high pressure system; ability to shape the injection curve. can allow a special use of the working principle for common rail during idling and low load to reduce the engine noise and a special use of the working principle for mechanical impact under such conditions when high injection pressures are necessary, whereby the design of the common rail part of the system can be relatively simple and durable due to the relatively low maximum rail pressure. Such a system will, through the use of both working principles. by selecting the appropriate timing of the magnetization of a control valve, to be able to provide a so-called boot-shaped injection in addition to other types of curve shape, which are known as possible for mechanically actuated unit injectors and common rail systems, such as square or triangular injection curves, pilot injections and high pressure post-injection .

Another specific object of the present invention is to provide a fuel injection system which, in addition to the properties described above, will have an inherent protection against system overpressure.

BRIEF DESCRIPTION OF THE FIGURES Figures 1 to 9 show schematic views of various embodiments of the invention.

PREFERRED EMBODIMENTS: According to a first embodiment of the present invention shown in Fig. 1, there is provided a fuel injector 1 comprising a conventional normally closed nozzle 2 and an electrically controlled needle control valve (NCV) 3; a mechanically actuated device 4 for pressurizing fuel, which comprises a cam-driven piston 5 with a cam 6 and a piston chamber 7; a return spring 8 and an electrically operated valve 9; a common rail 10 which, in the usual manner, cooperates with a number of fuel injectors and mechanically actuated means in an engine (not shown), a means 11 for pressurizing the common rail and for regulating its pressure at a desired level; a return line 12 with a relatively low pressure and a fuel tank 13. An electronic control unit (not shown) monitors the pressure in the common rail 10 and controls the valves 3 and 9.

The fuel injector 1 is designed to operate as a high pressure common rail injector of the type used. is well known from the state of the art. As is characteristic of this type of known injector, the injector 1 comprises a needle 15, a control piston 16 with a control chamber 17 a spring 14 which acts to close the nozzle 2; which is arranged so that higher pressure in the control chamber tends to cause the control piston to push the needle 15 to close the nozzle; an inlet throttle valve 18 and an outlet port 19. The inlet throttle valve 18 connects the control chamber 17 to the pressure piston chamber 7 and the outlet NCV 3. Upon receiving a command, NCV 3 can open the connection the port 19 connects the control chamber with between the outlet port 19 and the return line 12.

The flow area of the inlet throttle valve, outlet port and NCV 'is so selected that the opening of' NCV causes a pressure drop in the control chamber sufficient to allow the pressure acting on a differential surface of the needle 15 to open the nozzle piece 2. Also typical of known high pressure common rail injectors , is that the outlet port 19 and the control piston 16 are designed so that the control piston can limit the outlet port to a position son: corresponds to an open nozzle, whereby leakage of pressurized fuel through the inlet throttle valve 18, the outlet port 19 and the needle valve 3 to open return line 12 is limited.

The pressure piston chamber 7 is connected to the inlet of the nozzle 2. The pressure piston chamber can be connected to or separated from the common rail 10, depending on the position of the control valve 9.

The fuel injection system operates as follows: the fuel pressure in the common rail 10 is maintained at a certain constant level which is set with regard to the special operating conditions of the engine. When a high injection pressure is not required for the injection, for example with the engine idling or at a relatively low load, the control valve 9 is kept open during the entire engine cycle. During the pump stroke of the pressure piston 5, the fuel is moved via the control valve 9 back to the common rail, so that there is very little pressure build-up in the pressure piston chamber 7 and a correspondingly small pressure build-up of the engine transmission that drives the pressure piston. NCV 3 opens to start the injection, whereby the pressure in the control chamber 17 drops and enables the control piston 16 and the needle 15 to lift and open the nozzle. Fuel is then injected with common rail pressure through the open nozzle, until the NCV closes again. After closing the NCV, the pressure in the control chamber 17 rises back up to the level of the common rail pressure and the control piston 16 closes the nozzle with the action of the spring 14. This working mode will hereinafter be referred to as common rail or CR mode. It is understood that for the pressures in common rail 10 and in the return line 12 to be that the CR mode is to operate, the difference between greater than for the spring opening pressure of the nozzle 2, which spring opening pressure is defined by the spring 14 10 15 20 25 30 524 460 ~ nnna ~ -vu bias and the size of the difference area of the closed needle 15, which is well known in the art.

Work mode CR. enables a reduction of the mechanical noise of the injection system by removing the pressure build-up in the transmission which drives those which characterize a mechanical Till-mechanical drive means, operated FIE and in particular unit injectors. the common rail pressure threads also enable fuel injection at any point under the motorcycle. Maximum design constraints regarding the working pressure in common rail will be a compromise between cost, useful life and other parameters that limit it. maximum pressure on the one hand and, on the other hand, advantages such as flexibility in injection timing, noise reduction and other things that improve engine characteristics. Thus, a typical maximum working pressure in common rail can be between 200 and 600 bar.

When a higher injection pressure is required, the control piston 9 is briefly closed during the pump stroke of the pressure piston 5.

This causes an increase in pressure in the pressure piston chamber 7, at the inlet throttle valve 18 and the inlet to the nozzle 2. When a certain desired pressure is reached, NCV opens and injection takes place as described above. The end of the injection depends on the relative timing of the closing of the NCV and the opening of the control valve 9.

This mode of operation is similar to the operating sequence of mechanically actuated unit injectors according to the state of the art and will henceforth be referred to as the EUI mode of operation.

By using the EUI mode of operation, the present invention can achieve very high injection pressures that are characteristic of known unit injectors and unit pump systems. At the same time, the present invention does not have the disadvantages of high pressure common rail systems associated with very high pressure in common rail and other volumes, since the high pressure is limited to relatively small volumes at the closed control valve 9. In fact, the common rail pressure during working mode EUI can be reduced to a very low level which is just sufficient to fill the return stroke of the pressure piston, which can normally be between 4 and 6 bar. In another embodiment of the present invention shown in Fig. 2, the system is designed in the same way, but a one-way valve 20 is installed between the inlet of the nozzle 2 and the common rail 10, with its inlet connected to the common rail. The valve 20 is opened during the return of the pressure piston 5 to reduce or rebound, the pressure drop between the pressure piston chamber 7 and the common rail, which in the absence of the valve 20 would lead to too low a pressure at the inlet to the nozzle 2, for the CR injection mode to work.

The valve 20 is therefore used to enable an injection during the return of the pressure piston. Alternatively, it allows the use of a control valve 9 with a smaller flow area. This in turn can improve the control valve's electrical current response time, reduce its dimensions, consumption, etc.

The principle described above for controlling the movement of the needle 15 may be insufficient when a higher speed is required for the opening and closing of the needle. This can be avoided by using a three-way valve and appropriate modification of the hydraulic circuit. Figures 3 and 4 show another embodiment of the invention, at 524 460 ll in which a three-way needle control valve 3 is installed between the pressure piston chamber 7 and the control chamber 17.

The control chamber is only connected to NCV, which can either connect the control chamber 17 with the pressure source (as shown in the figure) or to the return line 12 with low pressure.

The NCV control chamber and the pressure source and open the connection The opening of closes the connection between with the return line, so that the fuel can be evacuated quickly to enable a faster needle opening. Closing the NCV disconnects the control chamber 17 from the return line and reconnects it to which the pressure source also closes the nozzle faster.

Identical to the embodiment shown in Fig. 2, a one-way valve 20, which is connected to its inlet to the common rail and to its outlet to the nozzle 2, can be used as shown in Fig. 4 to extend the range with possible injection times of the system and reduce the control valve 9 maximum required flow area.

Another embodiment shown in Fig. 5 comprises a three-position, three-way control valve 9 between the pressure piston chamber 7 and the common rail 10. The control valve 9 can alternatively connect the pressure piston chamber 7 to the common rail or to the return line 12, or insulate the chamber from both. Incidentally, the construction The advantage of Fig. 5 "leak-reusing if the same as that shown in Fig. 3. designing the present invention according to the embodiment shown is that a so-called termination" of the injection may be required.

The CR mode operating mode is obtained by opening the NCV, relieving the pressure in the control chamber 17, which in turn allows the nozzle 2 to be opened. During CR mode injection, fuel is fed to the nozzle from the common rail via the open the control valve 9 as shown in Fig. 5.

This position of the valve 9 will hereinafter be referred to as a first position. Closing the NCV increases the pressure in the control chamber 17 and eventually closes the nozzle. Fuel moved by the pressure piston 5 during the pump stroke passes back to the common rail via the valve 9, which prevents any appreciable extra pressure from building up and thereby effectively eliminates force oscillations in the pressure piston drive mechanism.

In the EUI mode operating mode, the control valve 9 is switched from the first position to a second position during the pump stroke of the pressure piston 5. In the second position insulates from both the return line. The pressure in the system then rises and, when the pressure piston chamber 7 common rail and the desired pressure level has been reached, the NCV opens and enables the needle 15 to open the nozzle as described above. The fuel injection takes place at a high pressure generated by the pressure piston. There are several possible options for completing an injection. In normal cases, the NCV will close, which eats the pressurizing control chamber 17. If a pressure-assisted termination of the injection is desired, the control valve 9 can either be left open in the second position for a period of time corresponding to the nozzle closing duration, or switched back to the first. the position. The nozzle will then close at a higher pressure in the control chamber 17, which will assist the return spring 14 to close the needle more quickly.

If a leak termination of the injection is desired, the control valve 9 is switched to a third position which connects the pressure piston chamber 7 to the return line 12 and insulates it from the common rail. By this is meant that the nozzle 10 will be closed with the return spring 14 when the fuel pressure in the nozzle is low.

In cases where there is an advantage of simultaneous use of leakage termination and pressure-assisted termination of the injection, NCV can be connected directly to the common rail as shown in Fig. 6. To terminate an injection, NCV is switched to the position where it closes the connection between the control chamber 17 and the return line 12 and connects the control chamber to the common rail. The control valve 9 is switched to the third position for relieving the pressure from the piston chamber and the nozzle, and the needle 15 closes the nozzle by the combined action of the return spring 14 and the pressure in the control chamber 17. In this embodiment of the invention a relatively weak return spring 14 may be used. which may allow a lower minimum setting of the common rail pressure than that which can be used for function CR mode.

To reduce the complexity of the injection system shown in Figs. 5 and 6, a two-way needle control valve may be used instead of the 3-way valve, as shown in Figs. 7 and 8. The functional course of the system of Figs. 7 and 8 corresponds to the arrangement shown in Figs. 5 and 6. The arrangement and function of NCV are twofold described earlier in this part of the text.

The embodiments of the present invention shown in Figs. 6 and 8 may be advantageous due to their inherently better protection against system overpressure.

This is because the inlet of the control chamber 17 is connected to the common rail (either directly or via NCV) instead of to the pressure piston chamber 7, as is the case with the other embodiments of the invention (Figs. 1-5, 7). ) and in many other prior art designs. In these latter systems, a failure for the NCV to open does not allow the pressure created during the pump stroke of the pressure piston to flow out, since the pressure build-up takes place simultaneously in the nozzle and in the control chamber 17 and cannot open the nozzle.

This can cause serious mechanical damage to the FIE and the motor. Connecting the control chamber 17 to the common rail as in Figs. 6 and 8 sets a hardware limit for the maximum pressure that can be achieved at the injector with the nozzle closed. This pressure limit is determined by the bias of the return spring 14, the diameter of the control piston 16 and the pressure in the common rail 10, which in turn can be easily limited by means of a safety valve.

This principle of limiting the maximum pressure via the hardware can be used in all other embodiments of the invention as described above. An example of this is shown in Fig. 9a, b.

Fig. 10 shows a further exemplary embodiment of the present invention which comprises an electrically operated needle control valve 3 which directly controls the needle 15 of the nozzle 2. The needle 15 may be mechanically connected to the movable anchor 21 of the NCV.

CR and / or EUI, the Function Modes as well as combinations thereof, are in this exemplary embodiment achieved in the same way as described previously. NCV 'may be solenoid-operated or suitably piezo-operated, in order to achieve rapid and accurate control of the position of the needle. All the exemplary embodiments of the invention are capable of shaping the curve of the injection process in several different ways.

(NOP) Variable needle opening pressures are achieved during operating mode EUI by appropriate delay of the timing of the opening of NCV 3 relative to the closing of the control valve 9. For the 8 and 9, NOP is determined using the control piston 16 with a variant shown in Fig. 6, can high maximum larger diameter than the diameter of the needle 15. Choosing a higher NOP gives a more square injection curve, lower NOP will give a gradual increase in pressure during an injection and the curve will have a triangular shape.

Various combinations of multiple injections such as pilot, split and post injections, which are known to be achievable with both EUI and CR type FIE, can also be achieved by the present invention.

In addition, the invention enables a boot-shaped injection with variable injection levels and variable duration. on the boot phase. In order to achieve such an injection curve, both operating mode CR and EUI can be used during the same injection cycle, with the opening of the NCV before the start of the pump stroke of the pressure piston.

The means 11l common rail 10 and for pressurizing the regulation of the fuel pressure may comprise a pump with fixed displacement and a pressure regulator which essentially forms an adjustable safety valve. The displacement of the pump is selected so that the maximum required pressure in CR can be achieved in all engine operating conditions. When a lower pressure at the safety valve to return from to Alternatively, a pump with 'variable may be desired than possible special conditions, the excess fuel will pump out the fuel tank. displacement is used in such a way that the supply of the pump can be adjusted for all working conditions for maintaining the required CR pressure, without opening the safety valve. The use of a variable displacement pump will enable reduced power losses, but such pumps are generally more expensive than fixed displacement pumps. Other embodiments of the means 11 may be used in the present invention, for example a fixed displacement pump driven by the motor via a variable gear transmission, either mechanical, hydro-mechanical or electrical. In that case the purpose, later the engine can be used for starter motor whereby. the cost is avoided. of 'a. additional special electric motor for the pump. Although the present invention has been shown in connection with preferred embodiments, it is apparent that there are other embodiments which may fall within the scope of the invention as defined by the appended claims.

Claims (16)

10 15 20 25 30 524 460 17 Cl4277 / KS, 04-05-14 PATENT REQUIREMENTS A fuel injection system for an internal combustion engine, characterized by a nozzle (2) (5) forming which piston chamber is with an inlet; a cam-driven pressure piston a pressure piston chamber (7), connected to the inlet of the nozzle; a common rail (10) for fuel; a control valve (9) is inserted between the pressure piston chamber (7) and the common rail (10), which control valve is arranged to open or close the hydraulic connection between the pressure piston chamber and the common rail upon receiving an electrically controlled an electrically operated needle control valve (2); a command; (3) for opening and closing the nozzle (ll) for regulating the fuel pressure in common rail (13). commonrail and (10): body pressurization of as well as a fuel tank A fuel injection system according to claim 1, characterized in that a one-way valve (20) is installed between and (10), to the common rail. pressure piston chamber (7) common rail with one-way valve inlet connected A fuel injection system according to claim 1, characterized in that in a third position the control valve (9) insulates the pressure piston chamber (7) from the common rail (10) and connects the pressure piston chamber (7) to the return line (12): in a second position insulates the pressure piston chamber (7) from both the return line (12) and the common rail (10); in a first position, the pressure piston chamber (7) insulates from the return line (12) and connects the pressure piston chamber (7) to the common rail (10). 10 15 20 25 30 524 460 18 comprising one (15): acting on the needle for closing (16) an inlet choke A fuel injection system nozzle (2) having an inlet and a needle a (14) nozzle; a spring means forms a (18) (19), which control piston abuts against means of a control piston (17) as a control piston chamber with and an outlet port (15) the control chamber (16) cam-driven pressure piston (5) (7), the inlet choke (10) inserted between the pressure piston chamber (7) the needle at such a higher pressure in (17) the needle tends to push the control piston against to close the nozzle; one forming a pressure piston chamber for inlet; a pressure piston chamber connected (18) for fuel; and the common rail of the nozzle (2) a control valve (9) which is and the common rail (10), which control valve (9) is arranged to open or close the hydraulic connection between pressure piston receiving of a needle control valve (NCV) (3) (17) which NCV is arranged to open the chamber and common rail by electrical control command; between and (12), the connection (17) (12) f for pressurizing the common rail and regulating (10): which fuel injection system is characterized by the installed outlet port return line hydraulic between or closing the outlet port and the return line (11) the fuel pressure in. common rail (13) , that the effective flow areas of the inlet throttle (18), (19) and NCV (3) (14) force are selected so that an opening of the NCV can cause the needle (15) to open the inlet of the nozzle is lower than a maximum working pressure of a member and a fuel tank outlet port and the spring member nozzle when the pressure at for commonrail. 10 15 20 25 30 524 460 19 A fuel injection system according to claim 4, (20) the pressure piston chamber (7) and characterized in that a one-way valve is installed between (10), to the common rail. commonrail with one-way valve inlet connected A fuel injection system according to claim 4, characterized in that the control valve (9) in a third position insulates the pressure piston chamber (7) from the common rail (10) and connects the pressure piston chamber (7) to the return line (12); in a second position the pressure piston chamber (7) insulates from both the return line (12) and the common rail (10): in a first position the pressure piston chamber (7) insulates from the return line (12) and connects the pressure piston chamber (7) to the common rail (10). A fuel injection system according to any one of claims 4 to 6, characterized therefrom, (18) instead of being connected to the pressure piston chamber (7). that the inlet choke is connected to the common rail A fuel injection system according to any one of claims 4 to 6, characterized by, (19) the control piston (19) corresponds to an open nozzle and the control piston (16) is so (16) at one that the outlet port is designed to be able to limit flow area (2), through the position of the outlet port as for limiting the leakage (18), to of pressurized fuel (19) (12). the inlet orifice outlet port and the open NCV (3) return line comprising a (15): a A fuel injection system nozzle (2) having an inlet and a needle 10 15 20 25 30 524 460 20 (14) (2); a (17) a higher pressure in which acts on the needle for closing (16) and abuts against the needle spring means forming a (15) on the control chamber (17) (16) (15) a cam driven piston (7), to the nozzle ( 2) nozzle control piston control piston chamber so as to tend to push the control piston against the needle (2); pressure piston chamber for closing the nozzle (5) forming a connection (10) (9) inserted between the pressure piston chamber (10), opening or closing the hydraulic connection between pressure piston chambers is a common rail for fuel; a control valve (7) and arranged to inlet; commonrail which control valve is the pressure piston chamber and commonrail upon receipt of an electric (NCV) (3): control command; a needle control valve which NCV is arranged to, in a first position, isolate the control chamber (17) from the return line (12) and open the hydraulic connection between the pressure piston chamber (7) and the control chamber (17) and, in a second position, to isolate the control chamber (17) from the pressure piston chamber (7) and hydraulically connecting the control chamber (17) to the return line (12): a means (II) for pressurizing the common rail and regulating the fuel pressure in the common rail; and a fuel tank (13), which fuel injection system is characterized in that (10) in order to overcome the spring means when the NCV (3) can be set high enough (14) is in. its second pressure in the common rail force and open the nozzle (2) position. A fuel injection system according to claim 9, characterized in that (20) the common rail is installed between (10), the inlet of the one-way valve connected to the common rail. that a one-way valve pressure piston chamber (7) and with 10 15 20 25 30 524 460 21 A fuel injection system according to claim 9, characterized in that the control valve (9) in a third position insulates the pressure piston chamber (7) from (10) the return line common rail and connects the pressure piston chamber (7) to (12): in a second position insulates the pressure piston chamber (7) from both the return line (12) and the common rail (10): in a first position, the pressure piston chamber (7) insulates from the return line (12) and connects the pressure piston chamber (7) to the common rail (10). A claims 9 to 11, that the NCV (3) in a (17) fuel injection system according to any one of the features thereof, first position insulates (12) hydraulic connection between the control chamber (10): (17) connects the control chamber to the control chamber from the return line and opens (17) and common rail and in the second position insulates (10) and hydraulically (17) with the return line (12). control chamber from commonrail A fuel injection system according to any one of the preceding claims, characterized in that (ll) (10) comprises a hydraulic pump of the variable displacement type and that the means for pressurizing the common rail is a means for regulating the displacement of the pump to achieve the desired pressure in the common rail. A fuel injection system according to any one of claims 1 to 12, characterized in that the means (11) for pressurizing the common rail (10) comprises a hydraulic pump of the fixed displacement type and a means for regulating the rotational speed of the pump to achieve the desired pressure in commonrail. 524 460 22 A fuel injection system according to claim 14, characterized in that the hydraulic pump is driven by the engine starter motor. A fuel injection system according to any one of the preceding claims, characterized in that the pressure in the common rail can be set to a maximum value of 600 bar.