EP2171255B1 - Throttle on a valve needle of a fuel injection valve for internal combustion engines - Google Patents

Description

The invention relates to a fuel injection valve for internal combustion engines, as it is preferably used for the injection of fuel under high pressure directly into a combustion chamber of an internal combustion engine. In particular, use in the fuel injection of self-igniting internal combustion engines is advantageous.

State of the art

Compliance with the pollutant limit values has high priority in the development of internal combustion engines. Especially the common-rail injection system has made an important contribution to the reduction of pollutants, a key point being that the common-rail system, regardless of the injection pressure and the speed and load of the engine can represent precise injections at any time , To inject the fuel here stroke controlled common rail injectors are known, the valve needle is servo-operated. The corresponding control valves are controlled by piezo or magnetic actuators, which switch very quickly and thus enable a quick opening of the valve pins.

However, in order to display different partial injections, in particular pre-injections and post-injections with a very small quantity of fuel, it is also necessary for the nozzle needle to close correspondingly quickly. For this purpose, various concepts have been developed, for example, a permanent low-pressure stage on the nozzle needle, which constantly exerts a closing force and thus accelerates the closing movement of the valve needle. However, such a low-pressure stage has the disadvantage that it brings with it a high leakage and thus a higher pump performance, resulting in lower system efficiency and higher fuel consumption. This fact can be problematic especially when introducing even higher pressures.

For this reason, the latest injectors for highest injection pressures are carried out without leakage, by dispensing with this low pressure stage. However, only small forces are available for closing the valve needles, which reduces the ability to inject small amounts. This disadvantage is very difficult to compensate, for example by the use of correspondingly fast switching control valves, which is expensive and expensive.

Valve needles, as for example from the published patent DE 100 24 703 A1 are known, are guided in a central guide portion in the pressure chamber of the injection valve, wherein the fuel is passed by two, three or four polishes on the valve needle. The resulting throttling point results in a pressure drop in this area, so that the pressure in the pressure space upstream of the guide portion is higher than downstream of the guide portion, which causes a permanent closing force on the valve needles and partially compensates for the above-mentioned disadvantages. However, there is a problem that the throttling action depends on the viscosity of the fuel, which in turn is a function of the pressure and the temperature. Thus, the pressure drop and thus the needle closing force in a wide operating range of the fuel injection valve of temperature and pressure is dependent, which leads to a dispersion of the fuel metering amount of injection to injection. The consequent inaccuracies in the Kraftstoffmengenzumessung have a negative effect on the pollutant emission of the engine.

Fuel injection valves according to the preamble of claim 1 are for example from the DE 101 49 961 known.

Advantages of the invention

By the fuel injection valve according to the invention, a defined throttle point is created, which causes a pressure drop independent of the Reynolds number of the fuel, so that the throttle effect is independent of the temperature of the fuel. This creates a permanent and constant closing force reaches the valve needle, which ensures a fast needle closing and thus a good minimum quantity capability of the fuel injection valve. For this purpose, a sharp-edged gap throttle is formed between the valve needle and the wall of the pressure chamber, which causes a pressure drop regardless of the Reynolds number of the fuel with suitable dimensioning. The Reynolds number depends, among other things, on the density and the dynamic viscosity, which in turn are essentially determined by the temperature of the fuel. Due to the independence of the Reynolds number, the damping effect of the gap choke is independent of the temperature and thus constant, which causes a constant closing force on the valve needle.

The gap throttle is thereby formed by a collar which has a sharp edge at its outer edge, so that between the edge of the collar and the wall of the pressure chamber, the sharp-edged gap choke is formed. In this case, if a guide section is provided on the valve needle, the collar can be formed both upstream and downstream of the guide section.

For passage one or more poles are formed on the collar, which also have a sharp edge. Due to the size of the polished sections, the flow and thus the throttle effect of the gap throttle and the closing force can be determined. For an optimization of the throttling effect with constant stability of the collar, a substantially triangular cross-section of the collar is advantageous, which is achieved by three bevels. Here, the federal government can be integrally formed with the valve needle or even after completion of the valve needle glued to this, welded or shrunk.

drawing

Figur 1

einen Längsschnitt durch einen Kraftstoffinjektor mit einem erfindungsgemäßen Einspritzventil,

Figur 2

das in Fig. 1 dargestellte Einspritzventil, wobei nur der brennraumseitige Teil mit den wesentlichen Komponenten schematisch dargestellt ist, und

Figur 3b

eine erfindungsgemäße Ausgestaltung des Bunds und damit der Spaltdrossel und

Figur 3a und Figur 3c

verschiedene nicht erfindungsgemäße Ausgestaltungen des Bunds.

In the drawing, an inventive fuel injection valve is shown. It shows:

FIG. 1

a longitudinal section through a fuel injector with an injection valve according to the invention,

FIG. 2

this in Fig. 1 shown injection valve, wherein only the combustion chamber side part is shown schematically with the essential components, and

FIG. 3b

an inventive design of the collar and thus the gap throttle and

Figure 3a and Figure 3c

various non-inventive embodiments of the federal government.

Description of the embodiment

In Fig.1 a fuel injector is shown in longitudinal section. The basic principle of such Einspritventile is well known from the prior art, so that can be dispensed with a detailed description of the known components and the following function is only briefly outlined. The fuel injector includes a fuel injection valve 1 and an injector body 100 including a control valve 30 for controlling the injection. The injector body 100 is connected to the fuel injection valve 1, which comprises a valve body 2 and are provided in the injection ports 8, through which the fuel is ejected. In the valve body 2, a valve needle 3 is arranged, which is connected to a piston rod 32, wherein the piston rod 32 defines with its end face a control chamber 36 which is formed in a sleeve 38. By the spring 40, the piston rod 32 and thus also the valve needle 3 is pressed against a valve seat 7, whereby the injection openings 8 are closed.

The control chamber 36 is connected via an outlet throttle 42, which can be opened or closed by the control valve 30, with a non-pressurized leakage oil space connectable. For this purpose, an armature 31 of the control valve is attracted by an electromagnet 33, so that the outlet throttle 42 is opened and fuel can flow from the control chamber 36 into the leakage oil space. To end the injection, the energization of the electromagnet 33 is turned off, and the armature 31 slides spring-loaded back into its initial position and closes the outlet throttle 42. About the inlet throttle 44, the drained fuel in the pressure chamber 36 is replaced. The compressed fuel is made available in a high-pressure accumulator 34, the so-called rail, and fed via a high-pressure line 35 to the fuel injection valve.

In Fig. 2 is the fuel injection valve the Fig. 1 shown enlarged in longitudinal section, wherein only the part of the injection valve is shown, which faces in the installation position of the combustion chamber. The fuel injection valve 1 comprises a pressure chamber 5 which can be filled with fuel under high pressure and which is limited to the combustion chamber from the valve seat 7, which is substantially conical and from which several injection openings 8 emanate. In the pressure chamber 5, the valve needle 3 is arranged longitudinally displaceable, which is formed in a piston-shaped with an axis 9. The valve needle 3 is guided in a guide section 10 in the pressure chamber 5, so that it is always oriented with respect to the conical valve seat 7 exactly in the middle. The fuel, which flows into the injection openings 8, flows through the annular gap remaining between the valve needle 3 and the wall of the pressure chamber 5 and is guided in the region of the guide section 10 by a plurality of bevels 12, which provide a sufficiently large flow cross-section. At its valve seat facing the end of the valve needle 3, a sealing surface 11 is formed, with which the valve needle 3 cooperates with the valve seat 7. As a result, the fuel flow is interrupted from the pressure chamber 5 to the injection openings 8 and only turned on when the valve needle 3 lifts off the valve seat 7 when planting the valve needle 3 on the valve seat 7.

Upstream of the guide portion 10, a collar 17 is formed on the valve needle 3, which extends annularly over the entire circumference of the valve needle 3. The collar 17 is formed sharp-edged on its outer side, wherein the thus formed edge 20 has a length L. This results in a sharp-edged gap throttle 15 between the wall of the pressure chamber 5 and the edge 20th

The operation of the Kraftstoffeinspritventils is as follows: At the beginning of the injection cycle, the valve needle 3 is in its closed position, that is in contact with the valve seat 7. The valve needle 3 is by a closing force, which is hydraulically the pressure in the control chamber 36 is generated, pressed against the valve seat 7. In the pressure chamber 5 fuel is at high pressure, but due to the closing force no resulting force in the longitudinal direction on the valve needle 3 exerts. If an injection takes place, then the closing force is reduced, and the valve needle 3 lifts off from the valve seat 7 and releases a flow of fuel from the pressure chamber 5 to the injection openings 8. To close the valve needle 3, the closing force is increased again, so that the valve needle 3 experiences a resultant force on the valve seat 7 and slides back into its closed position.

To accelerate this closing movement of the collar 17 acts in the following manner: Through the gap throttle 15 there is a pressure drop, so that in the part of the pressure chamber 5, which is upstream of the collar 17, there is a higher pressure than downstream. As a result, a hydraulic force acts on a first pressure surface 22 of the collar 17, which is directed upstream, which is greater than the hydraulic force on a second pressure surface 23 which is formed opposite to the collar 17. This resulting hydraulic force on the collar 17, which is directed in the direction of the valve seat 7, helps to close the valve needle 3 faster than would be the case with pure increase in the closing force on the valve seat facing away from the valve needle 3.

The amount of this closing force depends crucially on the size of the pressure drop across the gap throttle 15. The height of the pressure drop is in turn dependent on the cross section of the gap throttle 15 and the viscosity of the fuel, which is a function of the temperature and the pressure in the pressure chamber 5. The sharp-edged design of the edge 20 ensures that the pressure drop and thus the damping at the gap throttle 15 is independent of the Reynolds number and thus independent of the viscosity and temperature of the fuel. This results in an always constant closing force on the valve needle 3 and a reproducible closing behavior regardless of the operating point and regardless of the temperature of the fuel.

The effect described above also occurs in a similar manner on the guide section 10 or on the bevels 12, but the pressure drop here depends significantly on the Reynolds number. In this embodiment, therefore, care must be taken that the bevels 12 is formed so large that no or only a very low pressure drop with a corresponding additional closing force on the guide portion 10 is formed.

Fig. 3a shows a plan view of the collar 17 and the gap choke 15 of a non-inventive embodiment. Important for the function is that the gap throttle 15 is formed by a sharp edge 20. Here, the size of the hydraulic diameter D _{Hyd is} decisive, which is given by the flow-through cross-section and the flow-through boundary _length , wherein the boundary length is the sum of the inner and outer boundary length. It applies generally $${\mathrm{D}}_{\mathrm{Hyd}}=4\cdot \frac{\mathrm{perfused\; cross\; section}}{\mathrm{flowed\; through\; Berandungslänge}}$$

For an explanation let me Fig. 3a referenced, in which the gap throttle 15 is an annular gap with an outer diameter D _a and an inner diameter D _i , wherein the outer diameter D _a the inner diameter of the pressure chamber 5 and the inner diameter D _i corresponds to the diameter of the collar 17. The hydraulic diameter D _Hyd is then given in good approximation by $${\mathrm{D}}_{\mathrm{Hyd}}={\mathrm{D}}_{\mathrm{a}}-{\mathrm{D}}_{\mathrm{i}}$$

erfüllt sein, so dass sie im Sinne dieser Erfindung scharfkantig ist.If L is the length of the edge 20, for the independence of the Reynolds number for a gap choke 15, the condition $$\mathrm{L}/{\mathrm{D}}_{\mathrm{Hyd}}<\mathrm{5}$$

be fulfilled, so that it is sharp-edged in the sense of this invention.

erfüllt ist. Im Fall der Fig. 2 und Fig. 3a ist dies gleichbedeutend mit $$\frac{{{\mathrm{D}}_{\mathrm{a}}}^{\mathrm{2}}-{{\mathrm{D}}_{\mathrm{i}}}^{\mathrm{2}}}{{{\mathrm{D}}_{\mathrm{a}}}^{\mathrm{2}}-{{\mathrm{D}}_{\mathrm{i}}}^{\mathrm{2}}}<\mathrm{0},\mathrm{2.}$$

If D _{0 is} the diameter of the valve needle 3 immediately in front of the collar 17, then the optimal function is given when in addition the condition $$\frac{\mathrm{Narrowest\; throttle\; cross-section\; of\; the\; gap\; choke}}{\mathrm{Cross\; section\; upstream\; of\; the\; gap\; choke}}<0.2$$

is satisfied. In the case of Fig. 2 and Fig. 3a is this synonymous with $$\frac{{{\mathrm{D}}_{\mathrm{a}}}^{\mathrm{2}}-{{\mathrm{D}}_{\mathrm{i}}}^{\mathrm{2}}}{{{\mathrm{D}}_{\mathrm{a}}}^{\mathrm{2}}-{{\mathrm{<figure-callout\; id="2"\; label="D\; i"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">D\; </figure-callout>}}_{\mathrm{i}}}^{\mathrm{2}}}<\mathrm{0}.\mathrm{Second}$$

Fig. 3b shows an inventive embodiment of the collar 17, in which lateral poles 25 are provided, which give the collar 17 in cross section a substantially triangular shape. The polished sections 25 are exaggerated here for the sake of clarity and the length K of these polished sections 25 of course depends on the length L of the collar 17. Instead of three polished sections 25, as in FIG Fig. 3b shown, a larger number of bevels 25 may be provided, for example, 4, 5 or 6 poles 25th

According to the embodiment Fig. 3b the hydraulic diameter D _{Hyd must} be calculated differently than in the embodiment according to Fig. 3a , If S is the arc length of the bevel 25, K is the edge length of the bevel 25 and A is the surface formed by one of the bevels 25 between the bevel 25 and the wall of the pressure chamber 5, D _Hyd results $${\mathrm{D}}_{\mathrm{Hyd}}=\frac{\mathrm{4}\cdot \mathrm{A}}{\mathrm{S}+\mathrm{K}}$$

Fig. 3c shows a further non-inventive embodiment of the collar 17, in which case the gap throttle 15 is realized by a plurality of grooves 27 in the collar 17 and the maximum length L of the collar 17 in this case depends on the dimensions of the grooves 27. The remaining gap between the valve needle 3 and the wall of the pressure chamber 6 is dimensioned between the grooves 27 so that there is practically a seal and the fuel thus flows exclusively through the grooves 27. The boundary of the grooves 27 is sharp-edged, so that the independence of Reynolds number is maintained.

The embodiment according to Fig. 3c is calculated as follows: If b is the width of the groove 27 and h is the depth, then $${\mathrm{D}}_{\mathrm{Hyd}}=\mathrm{2}\frac{\mathrm{H}\cdot \mathrm{b}}{\mathrm{H}+\mathrm{b}}$$

The gap choke 15 can be arranged inside or outside the guide section 10.

An independent of the Reynolds number throttling a gap choke is therefore only reachable if it is sharp according to the above definitions. Here, on one side of the gap reactor 15 forming components may have a sharp edge and on the other side a smooth wall, as in the above example, the wall of the pressure chamber 5. It can also be provided that the gap choke 15 by a sharp edge on both sides is formed, for example by the sharp-edged collar 17 in the above embodiment Fig. 3a an equally sharp-edged ridge facing the inner wall of the pressure chamber 5. In a not too large opening stroke of the valve needle 3, the effect is maintained throughout the opening process. But it is also possible, collar and ridge are aligned with each other so that the maximum damping effect acts only in the open state of the nozzle needle 3, so the collar and ridge are exactly opposite, while at the beginning of the opening stroke only a small damping acts on the gap choke, which favors the pressure build-up at the injection openings 8.

Claims (2)

1. Fuel injection valve for internal combustion engines, having a valve body (1) in which a pressure chamber (5) is formed, in which pressure chamber there is arranged in longitudinally displaceable fashion a valve needle (3) which interacts, by way of a sealing surface (11) formed on the valve needle (3), with a valve seat (7) that delimits the pressure chamber (5), wherein a fuel stream to at least one injection opening (8) is permitted or shut off by way of the interaction of the valve needle (3) with the valve seat (7), wherein the fuel stream flows between the valve needle (3) and the wall of the pressure chamber (5) to the injection openings (8), wherein a sharp-edged throttling gap (15) is formed between the valve needle (3) and the wall of the pressure chamber (5), and having a collar (17) which is formed on the valve needle (3) and which has a sharp edge (20) at its outer margin, such that the sharp-edged throttling gap (15) is formed between the collar (17) and the wall of the pressure chamber (5), characterized in that the collar (17) has a ground portion (25) or multiple ground portions (25) on its outer side, and in that the edge (20) of the collar (17) is of sharp-edged form in the region of the ground portions (25), wherein the region between the ground portions (25) substantially seals against the wall of the pressure chamber (5) such that the fuel passes the collar (17) practically only in the region of the ground portions (25), wherein the sharp-edged throttling gap (15) satisfies the condition L/D_Hyd < 5, wherein L is the length of the throttling gap (15) and D_Hyd is the hydraulic diameter (D_Hyd).
2. Fuel injection valve according to Claim 1, characterized in that the valve needle (3) is guided, by way of a guide section (10) of the pressure chamber (5), by the wall of the pressure chamber (5), wherein the throttling gap (15) is arranged close to the guide section (10) in an upstream or downstream direction.

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