WO2003008797A1

WO2003008797A1 - Fuel injector with locking pressure compensation

Info

Publication number: WO2003008797A1
Application number: PCT/DE2002/001805
Authority: WO
Inventors: Christoph BÜHLER
Original assignee: Robert Bosch Gmbh
Priority date: 2001-07-18
Filing date: 2002-05-18
Publication date: 2003-01-30
Also published as: EP1412633A1; DE50212605D1; JP2005509107A; BR0205760A; EP1412633B1; DE10134868A1; JP4138650B2

Abstract

The invention relates to a fuel injector for injecting fuel into the combustion chamber of a combustion engine, comprising an injector body (2) wherein an injector needle (3) which is prestressed by a closing spring (35) is received and surrounded by an injection chamber (6) which is impinged upon by high pressure fuel via a high pressure fuel feed (7). A seat diameter (15) is embodied in the region of the tip of the injector needle (13) on said injector needle (3), whereon injection openings (18) of a jet body (11) are released and closed. A hydraulic surface is embodied on the injector needle (3) between a guiding and sealing element (4) and the injection chamber (6), said hydraulic surface (6) being disposed opposite the guiding and sealing element (4), whereby the contact thereof changes from a first contact position (27) into a surface contact (29) of a contact area (22, 24) of the guiding and sealing element (4) during the operation of the fuel injector (1).

Description

Fuel injector with closing pressure compensation

Technical field

In air-compressing internal combustion engines, fuel injection systems with a high-pressure collecting space (common rail) are increasingly being used. Depending on the number of cylinders in the internal combustion engine, a corresponding number of fuel injectors are supplied with fuel under high pressure via the high-pressure collection space. Depending on the application, the fuel injectors can be equipped with hole nozzles, such as blind hole or seat hole nozzles. The nozzle design is crucial for the metered injection in terms of injection duration and injection quantity. The injection nozzles are closed or released cyclically by the tip of the nozzle needle during operation of the fuel injector.

State of the art

DE 196 19 523 AI discloses a fuel injection valve, the valve body of which projects into the combustion chamber of the internal combustion engine to be supplied. The valve body is axially biased against a valve body by means of a clamping nut. The valve body has a blind bore extending from the end face facing the valve holding body, which is designed as a guide bore in which a piston-shaped valve member is axially displaceably guided. The guide bore has a radially widened pressure space, which is connected by an annular gap formed between the wall of the guide bore and the valve member to a conical valve seat surface which is formed at the inwardly projecting closed end of the guide bore. Injection openings, which open into the combustion chamber of the internal combustion engine, adjoin this valve seat surface downstream. In this case, the axially displaceable valve member is held in contact with the valve seat by means of a return spring under pretension with a valve sealing surface provided on the combustion chamber end of the valve member. The fuel supply tion to the injection valve takes place via an inlet channel opening into the pressure chamber, which penetrates the valve holding body and is also continuously connected via an injection line to a common high-pressure collecting chamber (common rail) common to all the injection valves of the internal combustion engine to be supplied. The piston-shaped valve member also has an annular shoulder in the region of the pressure chamber, on which the high fuel pressure constantly present in the pressure chamber acts in the opening direction of the valve member. The valve member is hydraulically guided and blocked into its closed position via an adjacent pressure or piston rod, for which purpose the end face of the pressure rod facing away from the valve seat limits a hydraulic closing pressure chamber.

This solution has the disadvantage that, due to the high fuel pressure constantly applied to the injection valve, the guide bore guiding the valve member expands radially. In addition to a reduced high-pressure strength of the valve body, this also results in increased leakage between the pressure chamber and a low-pressure-side spring chamber, which considerably impairs the efficiency of the entire fuel injection system.

DE 298 14 934 relates to a fuel injection valve for internal combustion engines. According to this solution, breakage of the valve body and increasing leakage can be reliably avoided at high fuel pressures in the pressure chamber in that the force introduction surfaces between the clamping nut and the valve body are conical, so that when the components are clamped to one another in addition to the axially directed inlet an additional radial clamping force component is transmitted to the valve body. This radially inward clamping force counteracts the expansion of the guide bore, so that the tight play between the wall of the guide bore and the valve member is maintained and only a small amount of leakage can flow out through the narrow gap.

Presentation of the invention

With the solution proposed according to the invention, a drop in closing force which occurs at the nozzle needle and slowly results from the aging of a closing spring acting on the nozzle needle can be compensated. The spring stiffness of the closing spring acting on the nozzle needle decreases over time, as a result of which the applied spring force decreases. The decrease in the spring force over the operating time of the injector is compensated according to the invention by influencing the hydraulic force which counteracts the spring force. To do this, on the nozzle needle below an outlet area of the ^" guiding and sealing element guiding the nozzle needle, a hydraulic surface is formed which surrounds the nozzle needle essentially in the shape of a truncated cone. In the new and unused condition of the nozzle needle, the guide is positioned between this area and a contact area, which can be configured, for example, as a bevel. and the sealing element of the nozzle needle first make a linear contact, which in the course of operation changes into surface contact due to the naturally occurring wear. The transition from the linear contact of the hydraulic surface with the beveling of the guide and sealing element to a surface contact of the guide and Sealing element is dependent on the design of the angle of inclination of the frustoconical hydraulic surface formed on the nozzle needle and, by its design, can depend on the aging behavior of the closing spring, ie its closing force When the line-shaped contact changes to a flat contact, the hydraulically effective area of the frustoconical section decreases, so that a decrease in the spring force of the closing spring by an ideally parallel decrease in the hydraulic force counteracting the force of the closing spring by the transition from Line contact in a surface contact with the decrease in the hydraulic effective area can be compensated.

By influencing the hydraulic counterforce counter to the spring force of the closing spring, the nozzle needle and the fuel injector can be quickly closed even after longer operating times.

A quick closing of the injection nozzle is particularly advantageous in terms of avoiding fuel injection quantities towards the end of the combustion process in the combustion chamber of the internal combustion engine. Towards the end of the combustion, a "too late" injected fuel volume cannot be converted into the combustion, so that an injection at this late point in time due to delayed needle closing would result in an inadmissibly strong HC emission from the internal combustion engine. The solution according to the invention avoids injecting fuel into the combustion chamber of the internal combustion engine at a later point in time in the combustion process by adversely influencing the emission behavior of internal combustion engines by rapidly closing the nozzle needle at the nozzle seat.

drawing

The invention is explained in more detail below with the aid of the drawing. It shows:

Figure 1 shows a nozzle needle in the open state, i.e. closed injector,

FIG. 1.1 the formation of the hydraulic surface in the area of an undercut on the circumference of the nozzle needle,

Figure 2 shows a nozzle needle in the closed position, i.e. with the injector open,

FIG. 2.1 shows the arrangement of conical surfaces on the nozzle needle and holding body when the nozzle needle and are in the upper stop position

Figure 2.2 shows the hydraulic surfaces on the circumference of the nozzle needle on an enlarged scale.

variants

1 shows a nozzle needle which, in the position shown, closes injection openings on a nozzle body.

The fuel injector 1 comprises an injector body 2, in which a nozzle needle 3 is movably received. The upper part of the nozzle needle 3 is guided in the injector body 2 in a guide and sealing element 4, which can be designed as a sleeve. Reference number 31 denotes the diameter of the nozzle needle 3 in the area in which the nozzle needle 3 is enclosed by the guide and sealing element 4. An area of reduced diameter 20 is formed below the guide and sealing element 4 on the nozzle needle 3. The nozzle needle 3 is biased at its upper end face by a spring element 35 - the closing spring.

The nozzle needle 3 is enclosed in the injector body 2 by a nozzle space 6 formed therein. The nozzle chamber 6 is connected via a high-pressure inlet 7 to a high-pressure collecting chamber (common rail), which is not shown here. Fuel under high pressure is directed into the nozzle chamber 6 of the injector body 2 via the high-pressure collecting chamber via the high-pressure inlet 7. In the area in which the nozzle needle is enclosed by the nozzle space 6, a pressure call 5 is formed on the nozzle needle. Below the pressure calls 5, the nozzle needle 3 comprises a guide 8 which for Example can be designed as a multi-surface guide 9. The guide 8 comprises guide surfaces 10 which are offset by 90 ° to one another and with which the nozzle needle 3 is guided in the nozzle body 11 of the fuel injector 1.

The nozzle needle 3 is essentially designed as a rotationally symmetrical component with respect to the line of symmetry 12 and is provided with a seat diameter 15 in the region of the needle tip 13. The seat diameter 15 lies in the closed state of the injection opening 18 formed in the nozzle body 11 against an inside of an injection cone 17 with a seat surface 16, so that the injection openings 18 are closed by the nozzle needle tip 13 in the state shown in FIG. no fuel is injected into the combustion chamber of the internal combustion engine. In the exemplary embodiment according to FIG. 1, the nozzle needle tip 13 of the nozzle needle 3 is designed as a seat hole nozzle 34. Another embodiment variant of the nozzle needle tip 13 of the nozzle needle 3 consists in the configuration of the nozzle needle tip 13 as a blind hole nozzle (not shown here).

A region 20 of reduced diameter is formed on the nozzle needle 3 in the lower region of the guide and sealing element 4, which is preferably designed as a sleeve-shaped component. The reduced-diameter region 20 comprises a section 23 configured in the shape of a truncated cone, the outer surface of which extends conically. The nozzle chamber 6 and the reduced-diameter region 20 of the nozzle needle 3 are hydraulically connected via an annular channel 19 which is formed on the injector body 2.

The representation according to FIG. 1.1 shows the course and design of the hydraulic surface in the reduced diameter area of the nozzle needle.

In the position of the nozzle needle 3 shown in FIG. 1.1 in the injector housing 2 of the fuel injector 1, the nozzle needle tip 13 designed as a seat hole nozzle 34 rests in the injection cone 17 of the nozzle body 11 in such a way that the injection openings 18 formed therein are closed. In this state, designated by reference numeral 28, a gap is formed between the hydraulic surface 23 in the reduced diameter region 20 of the nozzle needle 3 and a bevel 22 in the lower region 24 of the guide and sealing element 4, so that the annular channel 19 extends from the nozzle chamber 6 below high-pressure fuel can flow into the opening between the hydraulic surface 23 and the bevel 22 in the lower region of the guide and sealing element 4. The stroke path which the nozzle needle 3 executes in the injector body 2 of the fuel injector 1 is identified by reference numeral 21. 1.1 shows that the reduced-diameter area 20 - for example an undercut on the circumference of the nozzle needle 3 - has a smaller diameter at its narrowest point. it has than that which the nozzle needle 3 has in the area which is guided in the guide and sealing element 4.

FIG. 2 shows the nozzle needle as shown in FIG. 1 in a position within the injector body 2 in which the nozzle needle tip opens injection openings 18 in the region of the injection cone 17.

In this position of the nozzle needle 3 relative to the injector housing 2, fuel flowing from the high-pressure manifold (common rail), not shown here, flows into the nozzle chamber 6 via the high-pressure inlet 7. Fuel flowing under high pressure flows from the nozzle chamber 6 in the direction of the nozzle needle tip 13 via inflow surfaces which are formed in the region of the guide 8 of the nozzle needle 3 in the nozzle body 11. The nozzle needle 3 is opposite in accordance with its stroke path 21 (see illustration in FIG. 1) the spring force of the spring element 35 raised upwards. As a result, the seat diameter 15 in the region of the nozzle needle tip 13 of the nozzle needle 3 is retracted from the injection cone 17 in the nozzle body 11, so that fuel under high pressure from the nozzle chamber 6 along the annular gap between the nozzle body 11 and the circumference is flowed through the inflow surfaces in the region of the guide 8 the nozzle needle 3 of the injection opening 18 can flow. In this position of the nozzle needle 3 in the injector body 2 or in the nozzle body 11, identified by reference numeral 33, the hydraulic surface 23 lies in the reduced-diameter region 20 of the nozzle needle 3 below the guide and sealing element 4 on the bevel 22 (cf. illustration in FIG. 1) ) on.

Figure 2.1 shows the system of the hydraulic surface in the reduced diameter area 20 of the nozzle needle on the corresponding bevel of the guide and sealing element.

The guiding and sealing element 4 is preferably designed as a sleeve which is embedded in the injector body 2 of the fuel injector 1. In the position of the nozzle needle 3, identified by reference numeral 33, relative to the injector body 2, the nozzle needle 3 is inserted in the direction of the arrow 25 into the guide and sealing element 4, so that the hydraulic surface 23 on a bevel 22 corresponding to it is in the contact area 24 of the guiding and sealing element 4 bears in a first contact position 27 with linear contact of the contact area 24 of the bevel 22. In this position of the nozzle needle 3, an inflow of fuel into the pocket-shaped area, identified by reference numeral 30, of the reduced-diameter area 20 between the peripheral surface of the nozzle needle 3 and the inner surface of the guiding and sealing element 4 is prevented. The one from the nozzle chamber 6 in the injector body 2 is under high pressure fuel volume, high pressure is present on the lower annular surface 26 of the guide and sealing element 4 and is not able to flow into the constricted area 30 at the reduced diameter area 20 of the nozzle needle 3.

Figure 2.2 shows the hydraulic surface in linear contact with the bevel in the lower region of the guide and sealing element.

In the illustration shown in Figure 2.2, the nozzle needle 3 is in the position identified by reference number 33 in the injector body 2. In this state, the hydraulic surface 23, i.e. the conical surface of a frustoconical section of the nozzle needle 3 on a line 27 of the chamfer 22 in the contact area 24 of the guide and sealing element 4. The inflow of fuel via the ring channel 19 into the pocket-shaped recess 30, i.e. the constriction point formed there is prevented by the contact of the hydraulic surface 23 on the bevel 22. The first contact position between the hydraulic surface 23 and the bevel 22 of the contact area 24 of the guide and sealing element 4 is marked with reference numeral 27. During the operating time of the fuel injector 1, a surface contact slowly progressing in the direction of the arrow 29 occurs in the contact area between the hydraulic surface 23 and the bevel 22 of the contact area 24. Due to the selected angle of inclination, in which the hydraulic surface 23 is frustoconical on the circumference of the nozzle needle 3, and the choice of material for the guiding and sealing element 4, the period within which the linear contact 27 converts into a flat contact 29 of the hydraulic Surface 23 on the bevel 22 of the guide and sealing element 4 passes over, can be influenced. The transition from line contact 27 of hydraulic surface 23 to surface contact, indicated by reference numeral 29, can be adapted to the aging behavior of closing spring 35, which acts on nozzle needle 3, by means of the parameters mentioned. This ensures that even after the fuel injector 1 has been in operation for a long time, the needle closes quickly, and thus the injections can be ended at defined points in time even after the injector has been in operation for a long time.

The functioning of the nozzle needle 3 configured according to the invention and provided with a hydraulic surface 23 is as follows:

If the nozzle needle 3, as shown in FIG. 2, assumes its position 33 which opens the injection openings 18, the hydraulic surface 23 bears against the bevel 22 of the guide and sealing element 4. At this time, the nozzle chamber 6 is in the injector Body 2 is acted upon by the high-pressure inlet 7 from the high-pressure accumulation chamber (common rail) with a high-pressure fuel volume which flows through the annular gap between the nozzle needle 3 and the nozzle body 11 into the injection cone 17 of the nozzle body 11 and via the injection opening 18 into the combustion chamber of the supplying internal combustion engine arrives. At the same time, fuel under high pressure is present on the annular surface 26 of the guide and sealing element 4 via the annular channel 19.

Due to the action of the spring force of the closing spring 35, which acts on the upper end face of the nozzle needle 3, when the nozzle chamber 6 is relieved of pressure, the nozzle needle 3 becomes corresponding to the lifting path 21 in the direction of a retraction of the seat diameter 15 into the seat surface 16 of the injection cone 17 in the nozzle body 11 driven.

The hydraulic force counteracting the spring force 32 of the closing spring 35 is defined on the one hand by the pressure stage 5 of the nozzle needle 3, which is surrounded by the control chamber 6. This hydraulic force, on the other hand, is compensated by the hydraulic surface 23 in cooperation with the bevel 22 of the contact area 24 of the guide and sealing element 4 such that, depending on the angle of inclination of the frustoconical area of the hydraulic surface 23 on the nozzle needle 3 and on material pairs tion between the nozzle needle material and the material of the guide and sealing element 4 initially sets a line contact 27, which over the course of the operating time of the fuel injector 1 changes into a surface contact indicated by the arrow 29 between the hydraulic surface 23 and the bevel 22 of the guide and sealing element 4. The transition from a line contact 27 into a surface contact 29 in the area of the hydraulic surface 23 is accompanied by a reduction in the hydraulically effective area.

The measure proposed according to the invention ensures that a decrease in the closing force resulting from the decrease in the spring stiffness of the spring element 35 takes place by a corresponding correction of the hydraulic force counteracting the decreasing spring force 32. The decrease in the hydraulic force, which counteracts the closing movement of the nozzle needle 3, can be influenced in such a way that the spring force 32 required for the required rapid closing of the nozzle needle 3 can also be applied by an aged spring element 35 whose spring stiffness is reduced. Thus, according to the solution proposed according to the invention, the fuel injector 1 is able to implement and comply with the defined injection times, in particular the emission-relevant end times, during an injection cycle even after a longer operating time. The faster the nozzle needle 3 can be closed, ie the faster the movement of the seat diameter 15 at the nozzle needle tip 13 into the seat 16 corresponding to this in the injection cone 17 of the nozzle body 11, the faster the nozzle can be closed. This ensures that at the end of a combustion process taking place in the combustion chamber of an internal combustion engine, no fuel gets into the combustion chamber which can no longer be burned due to the already largely advanced and thus completed combustion. Inadmissible HC emissions from fuel injected too late can thus be achieved by quickly closing the nozzle needle 3.

LIST OF REFERENCE NUMBERS

Fuel injector 33 Closed position of the needle

Injector body open position nozzle

Nozzle needle 34 seat hole nozzle

Guide and sealing element 35 spring element

pressure stage

nozzle chamber

High-pressure inlet

guide

Multiple leadership

guide surface

Düsenköφer

axis of symmetry

Nozzle needle tip

injection

Seat diameter

Seat

Injection cone

Injection port

Ring channel with reduced diameter area

stroke

Bevel hydraulic surface

contact area

Nozzle needle stroke

Ring surface first contact position

Open position of nozzle needle logo CNRS logo INIST

Injector closed position

surface contact

constriction

Guide diameter

Closing force holding body

Claims

claims

1. Fuel injector for injecting fuel into the combustion chamber of an internal combustion engine with an injector body (2), in which a nozzle needle (3) acted upon by a closing spring (35) is received, which nozzle needle is surrounded by a nozzle chamber (6) High-pressure fuel is applied via a high-pressure inlet (7) and a seat surface (15) is provided on a nozzle needle tip (13), via which injection openings (18) of a nozzle body (11) can be opened and closed, characterized in that a hydraulic surface (23) is formed on the nozzle needle (3) between a guide and sealing element (4) and the nozzle chamber (6), which is opposite the guide and sealing element (4) and whose contact is from a first contact position (27) merges into a surface contact (29) of a contact area (22, 24) of the guide and sealing element (4) during operation.

2. Fuel injector according to claim 1, characterized in that the hydraulic surface (23) is formed on a frustoconical section of the nozzle needle (3).

3. Fuel injector according to claim 1, characterized in that the hydraulic surface (23) of the nozzle needle (3) opposite the beveled contact area (22, 24) of a guide and sealing element (4).

4. Fuel injector according to claim 2, characterized in that the frustoconical section of the nozzle needle (3) merges into a reduced diameter area (20) of the nozzle needle (3).

5. Fuel injector according to claim 1, characterized in that in the injector body (2) an annular channel (19) is formed, via which the nozzle chamber (6) with the region (20) of reduced diameter of the nozzle needle (3) is hydraulically connected.

6. Fuel injector according to claim 5, characterized in that the annular channel (19) surrounds the nozzle needle (3).

7. Fuel injector according to claim 3, characterized in that the contact area (24) of the guide and sealing element (4) is provided with a bevel (22) which corresponds to that of the frustoconical section of the nozzle needle (3).

8. Fuel injector according to claim 4, characterized in that the region (20) of reduced diameter ends in a constriction (30), the diameter of which is smaller than the diameter (31) of the nozzle needle (3) in the guide and sealing element (4).

9. Fuel injector according to claim 1, characterized in that the nozzle needle (3) in the nozzle body (11) is received in a guide (9), between the guide surfaces (10) inflow surfaces for the inflow of fuel to the nozzle needle tip (13) are formed.

10. Fuel injector according to claim 9, characterized in that the guide (9) is designed as a multi-surface guide (8).

1 1. Fuel injector according to claim 1, characterized in that a seat hole nozzle (34) is formed on the nozzle needle (3) in the region of the nozzle needle tip (13).