EP1125058B1 - Fuel injection system for an internal combustion machine - Google Patents

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

State of the art

The invention is based on a fuel injection system for an internal combustion engine according to the preamble of the claim 1.

Such an injection system is for example by the EP 0 711 914 A1 has become known.

For a better understanding of the following description, some terms are first explained in more detail: In a pressure-controlled fuel injection system is controlled by the pressure prevailing in the nozzle chamber of an injector fuel pressure valve body (eg a nozzle needle) against the action of a closing force and thus released the injection port for injection of the fuel. The pressure with which fuel exits the nozzle chamber into the cylinder is referred to as injection pressure. In the context of the invention, a stroke-controlled fuel injection system is understood to mean that the opening and closing of the injection opening of an injector take place by means of a displaceable valve member due to the hydraulic interaction of the fuel pressures in a nozzle space and in a control space. Further, hereinafter, an arrangement will be referred to as central if it is common to all cylinders, and local if provided for only a single cylinder.

In the known from EP 0 711 914 A1 pressure controlled Fuel injection system is using a high pressure pump Fuel to a first high fuel pressure compressed from about 1200 bar and in a first accumulator saved. Furthermore, the under high pressure standing fuel also in a second pressure accumulator promoted in which by regulating its fuel supply by means of a 2/2-way valve, a second high fuel pressure of about 400 bar is maintained. Over a central valve control unit and a central distribution device becomes either the lower or higher Fuel pressure passed into the nozzle chamber of an injector. There is a spring-loaded valve body by the pressure lifted from its valve seat, so that fuel from the Can exit the nozzle chamber.

In this known fuel injection system is the Fuel for an injection from the respective central Pressure accumulator via the central valve unit and the central distribution device to the individual injectors divided up. The maximum possible injection window is thus through the valve unit and the manifold determined jointly.

From WO 98/09068 is still a stroke-controlled injection system known, in which also two pressure accumulator are provided for storage of the two fuel pressures. Again, the metering of the respective fuel pressure takes place via central valve units.

From the publications JP 06 093936 A and EP 0 740 067 A are Fuel injection systems with a first accumulator for the higher fuel pressure and a second pressure accumulator fed from the first accumulator known.

Advantages of the invention

The injection system according to the invention has to achieve an improved dosage of the deeper fuel pressure the characterizing features of claim 1 on. Inventive developments are in the dependent claims contain.

According to the invention, the lower fuel pressure is proposed not central, but for each injector respectively to control locally via a valve unit. by virtue of the short line between local valve unit and nozzle chamber Injector losses are kept to a minimum reduced. In addition to better dosing There are further advantages in the good reproducibility the pre and post injection with the lower fuel pressure and in a reduced influence of component tolerances on the pre and post injection.

Further advantages and advantageous embodiments of the subject The invention are the description, the drawing and the claims.

drawing

Fig. 1

ein erstes erfindungsgemäßes Einspritzsystem mit druckgesteuerten Injektoren und einer lokalen Ventileinheit zum Umschalten zwischen dem höheren und dem tieferen Kraftstoffdruck;

Fig. 2

ein zweites erfindungsgemäßes Einspritzsystem mit druckgesteuerten Injektoren und einer modifizierten lokalen Ventileinheit;

Fig. 3

ein drittes nicht erfindungsgemäßes Einspritzsystem mit hubgesteuerten Injektoren und der in Fig. 2 gezeigten lokalen Ventileinheit; und

Fig. 4

ein viertes nicht erfindungsgemäßes Einspritzsystem mit modifizierten hubgesteuerten Injektoren und der in Fig. 2 gezeigten lokalen Ventileinheit.

Various examples of fuel injection systems 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 following description. Show it:

Fig. 1

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

Fig. 2

a second injection system according to the invention with pressure-controlled injectors and a modified local valve unit;

Fig. 3

a third non-inventive injection system with stroke-controlled injectors and the local valve unit shown in Figure 2; and

Fig. 4

a fourth not according to the invention injection system with modified stroke-controlled injectors and the local valve unit shown in Fig. 2.

Description of the examples

In the illustrated in Fig. 1 the first embodiment of a pressure-controlled fuel injection system 1 promotes a volume-controlled fuel pump 2 fuel 3 with a pressure of about 300 to 1800 bar from a storage tank 4 via a feed line 5 in a first central pressure accumulator 6 (common rail) and into a second central pressure accumulator 7 (common rail), of which in each case several, the number of individual cylinders corresponding pressure lines 8 and 9 to the individual, projecting into the combustion chamber of the engine to be supplied pressure-controlled injectors 10 (injector) dissipate. In Fig. 1, only one of the injectors 10 is shown in more detail.

With the help of the fuel pump 2 so 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 by regulating its fuel supply by means of a 2/2-way valve 11, a second lower fuel pressure of about 300 bar is maintained. For both pressure accumulator 6, 7 a control loop with a pressure sensor is provided in each case. The lower pressure level can be used for a pilot injection and, if required, also for a post-injection (HC enrichment for exhaust gas aftertreatment), while a main injection with the higher fuel takes place from the high-pressure accumulator 6.

The switching 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 the switching element for the higher fuel pressure in the pressure line 8. Its output is decoupled from the pressure line 9 through a check valve 14 . Via a 3/2-way valve 15 , the respective present pressure is then passed via a pressure line 16 into a nozzle chamber 17 of the injector 10. The injection is pressure-controlled by means of an axially displaceable in a guide bore piston-shaped valve member 18 (nozzle needle), the conical valve sealing surface 19 cooperates with a valve seat on the injector and thus closes the injection openings 20 provided there. Within the nozzle chamber 17, a pressure surface of the valve member 18 facing in the opening direction of the valve member 18 is exposed to the pressure prevailing there, wherein the nozzle chamber 17 continues through an annular gap between the valve member 18 and the guide bore to the valve sealing surface 19 of the injector 10. By the pressure prevailing in the nozzle chamber 17 pressure, the injection openings 20 sealing valve member 18 is controlled against the action of a closing force (closing spring 21 ), wherein the spring chamber 22 by means of a leakage line 23 is depressurized.

The injection with the lower fuel pressure takes place at no-current 2/2-way valve 13 by energizing the 3/2-way valve 15. The injection with the higher Fuel pressure is at energized 3/2-way valve 15th by energizing the 2/2-way valve 13, wherein the check valve 14 an unwanted return to the pressure line 9 prevented. At the end of the injection will be at de-energized 2/2-way valve 13, the 3/2-way valve 15 on Leakage 23 switched back. This will cause the pressure line 16 and the nozzle chamber 17 depressurized, so that the spring-loaded valve member 18, the injection openings 20th closes again.

The generally designated in Fig. 1 by 24 array of local valve assembly 12 and 3/2-way valve 15 may be inside the injector (Fig. 1a) or outside the injector (Fig. 1b), for example in the region of the pressure accumulator 6, 11 be arranged. Thus, a smaller size of the injector and by utilizing wave reflections in the now longer pressure line 16 can achieve an increased injection pressure.

Hereinafter, in the description of the other figures only the differences to the fuel injection system treated according to FIG. 1. Identical or functionally identical Components are designated by the same reference numerals and are not explained in detail.

Unlike 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 centrally controlled by a 3/2-way valve 32 in front of the distributor device 31. The switching between the two pressure lines 8, 9 takes place for each injector 10 in each case locally via the generally designated 33 valve arrangement, in which a 3/2-way valve 34 is provided as a switching element. The injection with the lower fuel pressure takes place with energized 3/2-way valve 32 by energizing the 3/2-way valve 34, while the injection with the higher fuel pressure at energized 3/2-way valve 32 and 3 / unpowered 2-way valve 34 takes place. At the end of this injection, the 3/2-way valve 32 is switched back to leakage 35 in de-energized 3/2-way valve 34, whereby the manifold 31 and the injector 10 are depressurized. The local valve unit 33 can be arranged either inside the injector housing ( FIG. 2a ) or outside it ( FIG. 2b ).

From the injection system 1, the injection system 40 differs by the use of the local valve assembly 33 and the use of stroke-controlled injectors 41 , of which only one is shown in more detail. Starting from the pressure-controlled injector 10 of FIG. 1 engages in a stroke-controlled injector 41 on the valve member 18 coaxial with the valve spring 21 to a pressure piece 42 , which limits the valve sealing surface 19 end face 43 a control chamber 44 . The control chamber 44 has from the pressure line 16 ago a fuel inlet with a first throttle 45 and a fuel outlet to a pressure relief line 46 with a second throttle 47 which is controllable by a 2/2-way valve 48 to 49 leakage. About the pressure in the control chamber 44, the pressure member 42 is pressurized in the closing direction. Under the first or second fuel pressure stationary fuel constantly fills the nozzle chamber 17 and the control chamber 44. Upon actuation (opening) of the 2/2-way valve 48, the pressure in the control chamber 44 can be reduced, so that in the sequence in the opening direction the valve member 18 acting pressure force in the nozzle chamber 17 exceeds the force acting in the closing direction on the valve member 18 pressing force. The valve sealing surface 19 lifts off the valve seat surface and fuel is injected. In this case, the pressure relief process of the control chamber 44 and thus the stroke control of the valve member 18 on the dimensioning of the two throttles 45 and 47 can be influenced. The end of the injection is initiated by renewed actuation (closing) of the 2/2-way valve 48, which decouples the control chamber 44 again from the leakage line 49, so that in the control chamber 44 again a pressure builds up, the pressure piece 42 in the closing direction can move. The switching to high pressure level is realized for each injector by energizing the valve assembly 33. After completion of the injection, the compressed fuel in the injector via the valve unit 33 can relax in the low-pressure rail, so that the valve unit 11 may be omitted with a suitable design. Valve assembly 33 may be located either within the injector housing ( FIG. 3a ) or outboard ( FIG. 3b ).

In the 3/2-way valves can magnetic actuators or Piezosteller with appropriate temperature compensation and the necessary force or displacement are used. Piezo plates enable faster valve switching times and a better dosing option. By using a piezo plate can also be on one or both Chokes in the stroke-controlled injector are dispensed with.

The injection system 50 ( FIG. 4 ), which otherwise corresponds to FIG. 3b, has modified stroke-controlled injectors 51 , each with a piezo-controlled 3/2-way valve 52 . The control chamber 53 of each injector 51 is filled as a volume, which is connected via the 3/2-way valve 52, with only one supply line from the pressure line 16 forth or relieved via the leakage 54 . For an injection with the respective in the pressure line 16 pending fuel pressure of the also under this pressure control chamber 53 is relieved by energizing the 3/2-way valve 52, and the injection is stroke-controlled.

In a fuel injection system 1 for an internal combustion engine, different with the fuel with at least two high fuel pressures via injectors 10 in the combustion chamber of the internal combustion engine to be injected can, with a central first accumulator 6 for the higher fuel pressure and one from the first accumulator 6 fed central second pressure accumulator 7, in the by regulating its fuel supply the lower fuel pressure is maintained, and with a valve unit to switch between the higher and the lower Fuel is the valve unit 12 for switching between the higher and the lower fuel locally for each injector 10 is provided. With this injection system is an improved dosage of the lower fuel pressure possible.

Claims (3)

1. Fuel injection system (1; 30) for an internal combustion engine, in which fuel having at least two different fuel pressures can be injected into the combustion space of the internal combustion engine via injectors (10), with a first central pressure accumulator (6) for the higher fuel pressure and with a second central pressure accumulator (7) which is fed from the first pressure accumulator (6) and in which the lower fuel pressure is maintained as a result of the regulation of its fuel supply, and with a valve unit for the changeover between the higher-pressure and the lower-pressure fuel, the valve body (18) of the injector (12) being capable of being opened, counter to the action of a closing spring, by means of the fuel pressure prevailing in the nozzle space (17) of the said injector, and the injection orifice (20) of the injector (10) thus being released for an injection of the fuel, characterized in that the valve unit (12; 33) for the changeover between the higher-pressure and the lower-pressure 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) has a 2/2-way valve (13) as a switching element for the higher fuel pressure.
3. Fuel injection system according to Claim 1, characterized in that the local valve unit (33) has a 3/2-way valve (34) as a switching element between the higher and the lower fuel pressure.

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