EP1397591B1 - Fuel injection device comprising a pressure amplifier - Google Patents

Description

State of the art

The invention relates to a fuel injection device according to the preamble of patent claim 1.

For a better understanding of the description and the claims, some terms are explained below: The fuel injection device according to the invention may be formed both stroke-controlled and pressure-controlled. In the context of the invention, a stroke-controlled fuel injection device is understood to mean that the opening and closing of the injection opening takes place by means of a displaceable nozzle needle due to the hydraulic interaction of the fuel pressures in a nozzle chamber and in a control chamber. A pressure reduction within the control chamber causes a stroke of the nozzle needle. Alternatively, the deflection of the nozzle needle by an actuator (actuator, actuator) take place. In a pressure-controlled fuel injection device according to the invention, the nozzle needle is moved by the pressure prevailing in the nozzle chamber of an injector fuel pressure against the action of a closing force (spring), so that the injection port for injection of the fuel from the nozzle chamber is released into the cylinder. The pressure with which fuel exits the nozzle chamber into a cylinder of an internal combustion engine is referred to as injection pressure , while a system pressure is understood to mean the pressure below which fuel is available or stored in the fuel injector. Fuel metering means to provide a defined amount of fuel for injection. Leakage is understood to mean an amount of fuel that arises during operation of the fuel injection device (eg a pilot leakage ), is not used for injection and is conveyed back to the fuel tank. The pressure level of this leakage may have a steady state pressure, with the fuel subsequently being expanded to the pressure level of the fuel tank.

Many engine manufacturers demand a flat pressure rise edge at the beginning of the injection. Oftmafs also a boot phase for the reduction of emissions is desired. In fuel injectors with pressure booster, as they are known for example from DE-A1-19910970 or DE 199 49 848 A, the pressure booster can be used to form the injection curve. Thus, the desired injection curve without additional parts, such. Implement alternative piston. To influence the pressure curve while the movement of the piston of the booster can be used. The stroke-dependent influencing of the inlet cross-section to the low-pressure side pressure booster chamber is known from US-PS 5,568,317. By the US-PS a multi-stage control of the inlet cross section is proposed.

Advantages of the invention

To influence the fuel pressure during injection and to achieve a flat pressure rise without disturbing pressure oscillations, a fuel injection device according to claim 1 is proposed. With increasing piston stroke a larger cross-section and thus a larger injection quantity is released, so that a continuous design of Einspitzverlaufs is possible.

drawing

Fig. 1

eine erste stufenlose Querschnittsänderung des Zulaufs oder Ablaufs zu einem Raum eines Druckverstärkers bei einer Kraftstoffeinspritzeinrichtung;

Fig. 2

eine zweite stufenlose Querschnittsänderung des Zulaufs oder Ablaufs zu einem Raum eines Druckverstärkers bei einer Kraftstoffeinspritzeinrichtung;

Fig. 3

eine hubgesteuerte Kraftstoffeinspritzeinrichtung mit einem Druckverstärker nach dem Stand der Technik.

Two embodiments of the fuel injection device according to the invention are illustrated in the schematic drawing and are explained in the following description. Show it:

Fig. 1

a first stepless change in cross section of the inlet or drain to a space of a pressure booster in a fuel injector;

Fig. 2

a second stepless change in cross section of the inlet or drain to a space of a pressure booster in a fuel injector;

Fig. 3

a stroke-controlled fuel injection device with a pressure booster according to the prior art.

Description of the embodiments

In the illustrated in Fig. 3 known stroke-controlled fuel injection device 1 is a volume-controlled fuel pump 2 fuel from a storage tank via a feed pipe in a central pressure accumulator (common rail) 2 '', of which a plurality of the number of individual cylinders corresponding pressure lines 2 to the remove individual, projecting into the combustion chamber of the engine to be supplied injectors 3 (injection device). In Fig. 1, only one of the injectors 3 is located . With the aid of the fuel pump 2 ', a first system pressure is generated and stored in the pressure storage chamber 2''. This first system pressure is used for pre-injection and, if necessary, for post-injection (HC enrichment for exhaust gas aftertreatment or soot reduction) and for displaying an injection profile with plateau (boat injection). For injecting fuel with a second higher system pressure, each injector 3 is assigned a respective local pressure booster 4 with a check valve 5 and with a displaceable piston 6 . Such fuel injectors are known for example from DE-A1-19910970.

To control the pressure booster 4, the pressure is used in the formed by a transition from a larger to a smaller piston cross-section space 7 . For refilling and deactivating the pressure booster, the differential space 7 is acted upon by a supply pressure (rail pressure). Then prevail at all pressure surfaces of a piston 6, the same pressure conditions (rail pressure). The piston 6 is pressure balanced. By an additional spring 8 the piston 6 is pressed into its initial position. To activate the pressure booster 4, the differential space 7 is relieved of pressure and the pressure booster 4 generates a pressure boost according to the area ratio. By this type of control can be achieved that for resetting the pressure booster 4 and for refilling a pressure chamber 9, a low-pressure side pressure booster chamber 10 does not have to be depressurized. With a small hydraulic ratio, the relaxation losses can be greatly reduced.

To control the pressure booster 4, a throttle 11 and a simple 2/2-way valve 12 can be used instead of a complex 3/2-way valve. The throttle 11 connects the differential chamber 7 with standing under supply pressure fuel from the accumulator chamber 2 ''. The 2/2-way valve 12 connects the differential space 7 to a leakage line 13. The throttle 11 should be designed as small as possible, but still so large that the piston 6 returns to its original position between the injection cycles. As a throttle and a pilot leakage of the piston 6 can be used. When the 2/2-way valve 12 is closed, there is no leakage in the guides of the piston 6, since the differential space 7 is pressurized. The throttle can also be integrated in the piston.

If the 2/2-way valves 12 and 14 are closed, the injector 3 is under the pressure of the pressure storage chamber 2 '' The pressure booster 4 is in the starting position. Now can be done by the valve 14 an injection with rail pressure. If an injection with a higher pressure is desired, then the 2/2-way valve 12 is activated (opened) and thus reaches a pressure boost.

The injection takes place via a fuel metering with the aid of a guide needle axially displaceable nozzle needle 15 with a conical valve sealing surface at one end, with which it cooperates with a valve seat surface on the injector of the injector 3. On the valve seat surface of the injector housing injection openings are provided. Within a nozzle chamber 16 , a pressure surface pointing in the opening direction of the nozzle needle 15 is there exposed to prevailing pressure which is supplied via a pressure line to the nozzle chamber 16. Coaxial with a valve spring 17 also engages on the nozzle needle 15 to a pressure piece 18 , which limits the control chamber 19 with its end facing away from the valve sealing face. The control chamber 19 has an inlet from the fuel pressure connection with a first throttle and an outlet to the leakage line 13, which is controlled by the 2/2-way valve 14.

Under the first or second system pressure standing fuel constantly fills the nozzle chamber 16 and the control chamber 19. Upon actuation (opening) of the 2/2-way valve 14, the pressure in the control chamber 19 can be reduced, so that in the opening direction of the nozzle needle 15 acting pressure force in the nozzle chamber 16 exceeds the force acting in the closing direction on the nozzle needle 15 pressing force. The valve sealing surface lifts off the valve seat surface and fuel is injected. In this case, the pressure relief process of the control chamber 19 and thus the stroke control of the nozzle needle 15 can be influenced by the dimensioning of the throttles.

The end of the injection is initiated by renewed actuation (closing) of the 2/2-way valve 14, which decouples the control chamber 19 again from the leakage line 13, so that in the control chamber 19 again a pressure builds up, the pressure piece 18 in the closing direction can move.

According to Figs. 1 and 2 , the inlet to the low-pressure side pressure booster chamber 10 and / or the outlet from the differential space 7 (see FIG. 1) is provided with a continuous cross-sectional enlargement. It can be achieved a flat pressure increase without disturbing pressure oscillations. 1, only a partial surface 25 of a slot-shaped opening 26 is released up to a control edge 24 ' by the direction of movement 23 of a piston 24 (longitudinal direction of the opening and the piston) depending on the position of the piston 24 and a partial surface 27 of the opening 26 covered. The opening 26 in the wall surface of a pressure booster chamber (differential space or low-pressure space) establishes the connection of the differential space 7 (see FIG. 1) to the leakage line or the connection of the low-pressure side booster chamber 10 to the pressure line 2 (see FIG. 1) and can be closed by the piston , With increasing piston stroke, a larger inlet or outlet cross section is released. According to FIG. 2, a slot-shaped opening 28 in the wall surface of a pressure booster chamber has a variable cross-sectional area in the direction of movement 29 of the piston 30 . The piston 30 itself has a recess 31, which produces the continuous connection of the differential space 7 (see FIG. 1) to the leakage line or the connection between the low-pressure space 10 and the pressure line 2. The recess 31 forms a kind of control window, which slides along the slot 28.

Alternatively, the slot-shaped opening 28 may also be formed in the piston and the control edge 24 'or a recess 31 in the wall surface.

Claims (4)

1. Fuel injection device (1) having a pressure amplifier (4) which has a displaceable piston (6; 24; 30), which can be pressurized via a pressure-amplifying chamber (10) on the low-pressure side, for compressing the fuel, which is to be supplied to an injector (3), in a pressure-amplifying chamber (9) on the highpressure side, the stroke of the piston (6; 24; 30) being controllable essentially by the pressure in a differential chamber (7) of the pressure amplifier (4) and being used for influencing the pressure of the fuel supplied to the injector (3), characterized in that means (24, 25; 28, 31) for continuously enlarging the inflow cross section to the pressure-amplifying chamber (10) on one low-pressure side of the pressure amplifier (4) or the discharge cross section from the differential chamber (7) of the pressure amplifier (4) are provided.
2. Fuel injection device according to Claim 1, characterized in that the means are formed by a slot-shaped opening (26; 28) between a chamber (7, 10) of the pressure amplifier (4) and a supply line, and by the piston (24; 30) which closes or releases the opening (26; 28).
3. Fuel injection device according to Claim 2, characterized in that the piston (24) has a control edge (24') with the opening (26) being released up to it.
4. Fuel injection device according to Claim 2, characterized in that the piston (30) has a recess (31) which can be arranged over the opening (28) and defines a released region of the opening (28).

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