EP1125058A1

EP1125058A1 - Fuel injection system for an internal combustion machine

Info

Publication number: EP1125058A1
Application number: EP00956111A
Authority: EP
Inventors: Bernd Mahr; Martin Kropp; Hans-Christoph Magel; Wolfgang Otterbach
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-08-20
Filing date: 2000-08-02
Publication date: 2001-08-22
Anticipated expiration: 2020-08-02
Also published as: DE50010227D1; WO2001014737A1; DE19939418A1; ATE294925T1; EP1125058B1; US6520152B1; JP2003507656A

Abstract

In a fuel injection system for an internal combustion engine, in which fuel can be injected at least two different, high fuel pressures, via injectors, into the combustion chamber of the engine, having a central first pressure reservoir for the higher fuel pressure and a central second pressure reservoir, supplied from the first pressure reservoir, in which by regulation of its fuel delivery, the lower fuel pressure is maintained, and having a valve unit for switchover between the higher and the lower fuel, the valve unit for switchover between the higher and the lower fuel is provided locally for each injector. With this injection system, improved metering of the lower fuel pressure is possible.

Description

Fuel injection system for an internal combustion engine

State of the art

The invention is based on a fuel injection system for an internal combustion engine according to the type of patent claim 1. Such an injection system has become known, for example, from EP 0 711 914 AI.

For a better understanding of the following description, a few terms will first be explained in more detail: In a pressure-controlled force injection system, the fuel pressure prevailing in the injector's nozzle chamber causes a valve body (for example a nozzle needle) to be opened against the action of a closing force, and thus the injection opening for an injection of the fuel released.

The pressure at which fuel emerges from the nozzle chamber into the cylinder is referred to as the injection pressure. A stroke-controlled fuel injection system is understood in the context of the invention that the opening and closing of the injection opening of an injector take place with the aid of a displaceable valve member due to the hydraulic interaction of the fuel pressures in a nozzle chamber and in a control chamber. Furthermore, an arrangement is referred to below as central if it is provided for all cylinders together and as local if it is provided for only a single cylinder.

In the pressure-controlled fuel injection system known from EP 0 711 914 A1, fuel is compressed to a first high fuel pressure of approximately 1200 bar with the aid of a high-pressure pump and stored in a first pressure accumulator. Furthermore, the high-pressure fuel is also fed into a second pressure accumulator, in which a second high fuel pressure of approx. 400 bar is maintained by regulating its fuel supply by means of a 2/2-way valve. Via a central valve control unit and a central distributor device, either the lower or the higher one Fuel pressure is fed into the nozzle area of an injector. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can escape from the nozzle chamber.

In this known fuel injection system, the fuel for an injection from the respective central pressure accumulator is distributed to the individual injectors via the central valve unit and the central distributor device. The maximum possible injection window is thus determined jointly by the valve unit and the distributor device.

A stroke-controlled injection system is also known from WO 98/09068, in which two pressure accumulators are also provided for storing the two fuel pressures. Here too, the respective fuel pressure is measured via central valve units.

Advantages of the invention

The injection system according to the invention has the characterizing features of patent claim 1 in order to achieve an improved metering of the lower fuel pressure. Further developments according to the invention are contained in the subclaims.

According to the invention, it is proposed not to control the lower fuel pressure centrally, but locally for each injector via a valve unit. Due to the short line between the local valve unit and the nozzle area of the injector, line losses are reduced to a mum reduced. In addition to the better metering option, there are further advantages in the good reproducibility of the pre-injection and post-injection with the lower fuel pressure and in a reduced influence of component tolerances on the pre-injection and post-injection.

Further advantages and advantageous configurations of the subject matter of the invention can be found in the description, the drawing and the claims.

drawing

Various exemplary embodiments of fuel injection systems according to the invention, in which fuel is stored and injected with two different fuel pressures in two pressure accumulators, are shown schematically in the drawing and explained in the description below. Show it:

1 shows a first injection system with pressure-controlled injectors and a local valve unit for switching between the higher and the lower fuel pressure;

2 shows a second injection system with pressure-controlled injectors and a modified local valve unit;

Fig. 3 shows a third injection system with stroke-controlled

Injectors and the local valve unit shown in Figure 2; and FIG. 4 shows a fourth injection system with modified stroke-controlled injectors and the local valve unit shown in FIG. 2.

Description of the embodiments

In the first exemplary embodiment of a pressure-controlled fuel injection system 1 shown in FIG. 1, a quantity-controlled fuel pump 2 delivers fuel 3 at a pressure of approximately 300 to 1800 bar from a storage tank 4 via a delivery line 5 into a first central pressure reservoir 6 (common rail ) and in a second central pressure accumulator 7 (common rail), each of which corresponds to the number of individual cylinders

Drain pressure lines 8 and 9 to the individual pressure-controlled injectors 10 (injection device) which project into the combustion chamber of the internal combustion engine to be supplied. 1 shows only one of the injectors 10 in more detail.

With the help of the fuel pump 2, a first higher fuel pressure of up to 1800 bar is generated, which is stored in the first pressure accumulator 6. The fuel under this pressure is also conveyed into the second pressure accumulator 7, in which a second lower fuel pressure of approximately 300 bar is maintained by regulating its fuel supply by means of a 2/2-way valve 11. A control circuit with a pressure sensor is provided for each of the two pressure reservoirs 6, 7. The lower pressure level can be used for a pre-injection and, if necessary, for a post-injection (HC enrichment for exhaust gas aftertreatment) are used while a main injection with the higher fuel from the high-pressure accumulator 6 takes place.

The switchover between either the lower or the higher fuel pressure takes place separately for each cylinder or injector 10, in each case via a local valve arrangement 12, which has a 2/2-way valve 13 as a switching element for the higher fuel pressure in the pressure line 8. Its output is decoupled from the pressure line 9 by a check valve 14. About a 3 / 2-

Directional valve 15 then the respective pressure present is passed via a pressure line 16 into a nozzle chamber 17 of the injector 10. The injection is pressure-controlled with the aid of a piston-shaped valve member 18 (nozzle needle) which is axially displaceable in a guide bore and whose conical valve sealing surface 19 interacts with a valve seat surface on the injector housing and thus closes the injection openings 20 provided there. Within the nozzle space 17, a pressure surface of the valve element 18 pointing in the opening direction of the valve element 18 is exposed to the pressure prevailing there, the nozzle space 17 continuing through an annular gap between the valve element 18 and the guide bore up to the valve sealing surface 19 of the injector 10. Due to the pressure prevailing in the nozzle chamber 17, the valve member 18 sealing the injection openings 20 is opened against the action of a closing force (closing spring 21), the spring chamber 22 being relieved of pressure by means of a leakage line 23.

The injection with the lower fuel pressure takes place when the 2/2-way valve 13 is deenergized by energizing the 3/2-way valve 15. The injection with the higher fuel pressure takes place when the 3/2-way valve 15 is energized by energizing the 2/2-way valve 13, the check valve 14 preventing an unwanted return into the pressure line 9. At the end of the injection, when the 2/2-way valve 13 is deenergized, the 3/2 way valve 15 is switched back to leakage 23. As a result, the pressure line 16 and the nozzle chamber 17 are relieved of pressure, so that the spring-loaded valve member 18 closes the injection openings 20 again.

The arrangement of local valve arrangement 12 and 3/2-way valve 15, designated overall by 24 in FIG. 1, can be inside the injector housing (FIG. 1 a) or outside the injector housing (FIG. 1 b), e.g. be arranged in the area of the pressure accumulators 6, 11. This allows a smaller size of the injector housing and by using

Wave reflections in the now longer pressure line 16 reach an increased injection pressure.

In the following, only the differences from the fuel injection system according to FIG. 1 are dealt with in the description of the further figures. Identical or functionally identical components are identified by the same reference numerals and are not explained in more detail.

In contrast to the injection system 1, in the injection system 30 shown in FIG. 2, the higher fuel pressure of the first pressure accumulator 6 is distributed centrally to the individual injectors 10 via a distributor device 31. The metering of the fuel stored in the first pressure accumulator 6 is controlled centrally with a 3/2-way valve 32 upstream of the distributor device 31. The switchover between the two pressure lines 8, 9 takes place locally for each injector 10 via the total number 33 t- HH σ o LΠ o LΠ o LΠ

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Claims

claims

1. fuel injection system (1; 30; 40; 50) for an internal combustion engine, in which fuel can be injected into the combustion chamber of the internal combustion engine with at least two different fuel pressures via injectors (10; 41; 51),

with a central first pressure accumulator (6) for the higher fuel pressure and a central second pressure accumulator (7) fed by the first pressure accumulator (6), in which the lower fuel pressure is maintained by regulating its fuel supply, and with a valve unit for switching between the higher and the deeper fuel,

characterized,

that the valve unit (12; 33) for switching between the higher and the lower fuel is provided locally for each injector (10; 41; 51).

2. Fuel injection system according to claim 1, characterized in that the local valve unit (12) as

Switching element for the higher fuel pressure has a 2/2-way valve (13).

3. Fuel injection system according to claim 1, characterized in that the local valve unit (33) as

Switching element between the higher and lower fuel pressure has a 3/2-way valve (34).

4. Fuel injection system according to one of the preceding claims, characterized in that the injectors (10) are designed for pressure control.

5. Fuel injection system according to one of the preceding claims, characterized in that the injectors (41; 51) are designed for stroke control.

6. Fuel injection system according to one of the preceding claims, characterized in that the valve unit (12, 33), the nozzle chamber (17) and the control chamber (44) can be acted upon together with either low or high fuel pressure.