EP1952011B1 - Fuel injection apparatus for an internal combustion engine having direct fuel injection - Google Patents

Description

State of the art

The invention relates to a fuel injection device for an internal combustion engine with direct fuel injection according to the preamble of claim 1.

The DE 100 24 702 A1 and DE 100 24 703 A1 each show a fuel injection device with which the fuel can be injected directly into its associated combustion chamber of an internal combustion engine. For this purpose, a valve element is arranged in a housing, which in the region of a fuel outlet opening has a total acting in the opening direction of the valve element pressure surface. At the opposite end of the valve element, a control surface acting in the closing direction is present, which delimits a control chamber.

When the fuel injection device is closed, a high fuel pressure is present at a region of the pressure surface acting in the opening direction and at the control surface acting in the closing direction, as is provided by a fuel rail. The excess force acting in the closing direction is achieved by the pressure surface acting in the opening direction at least when the valve element is closed is smaller than the control surface acting in the closing direction.

To open the valve element, the pressure applied to the control surface is lowered until the hydraulic force resultant in the opening direction on the pressure surface exceeds the forces acting in the closing direction. As a result, opening of the valve element is effected.

In both known fuel injectors, the valve element "floats" in high fuel pressure. In the in the DE 199 24 703 A1 In addition, the valve element shown in the opening direction acting pressure surface and acting in the closing direction control surface, on a plane orthogonal to the longitudinal axis of the valve element, the same size. In order to still be able to ensure a safe closing of the valve element, measures are proposed with which the pressure in the control room after lowering can be raised again very quickly.

In the EP 0971118 A another injection device is disclosed.

Object of the present invention is to develop a fuel injection device of the type mentioned so that it closes very quickly. Another object is a simplified manufacture of the device.

This object is achieved by a fuel injection device having the features of claim 1. Furthermore, the object is achieved by a method having the features of the independent method claim. Advantageous developments are specified in subclaims.

Advantages of the invention

According to the invention, the closing of the valve element is assisted by the fact that when the valve element is open is lowered at the pressure acting in the opening direction of the pressure surface (or at least at a part thereof). This is possible, for example, by a corresponding throttling between the valve element and a housing-side valve seat region and / or by an additional valve spool section.

By means of a corresponding shaping on the one hand of the housing-side valve seat portion and on the other hand a corresponding sealing region on the valve element, the restriction can be adjusted so that at least slightly open valve element, the force acting in the opening direction is smaller than when the valve element is closed. As a result, the closing process is supported and accelerated. The valve element is "sucked" to close the quasi to the valve seat.

The invention makes it possible in a special way to design the pressure surface acting in the opening direction and the control surface acting in the closing direction, each projecting onto a plane perpendicular to the direction of movement of the valve element, at least approximately the same size. This allows a low-cost production of the valve element.

It is also proposed, in all lying between the control chamber and pressure chamber spaces surrounding the valve element, during operation at least temporarily and at least approximately prevails at the high pressure connection prevailing high fuel pressure. This can be realized, for example, in that the recess in which the valve element is accommodated in its entirety is connected to the high-pressure connection. A low pressure area is therefore no longer available ("pressure balanced" valve). Thus, no leakage between the high and such Low pressure area occur, so that the corresponding seal and a leaking line required for this purpose can be omitted.

This allows a simpler structure of the fuel injection device with fewer parts, which on the one hand facilitates the assembly and on the other hand allows a smaller design. In addition, the fuel injection device according to the invention operates with a high efficiency, since the existing in earlier devices leakage between the valve element and the housing is no longer available. A return line can be made smaller in the sequence.

Due to the fact that sealing between the pressure surface acting in the opening direction and the control surface acting in the closing direction is no longer required in the previous sense, the valve element as a whole can be arranged in a high-pressure space connected to the high-pressure connection. In order to still be able to achieve a pressure reduction in the control room, then simply a sealing sleeve can be provided. This can be radially free, ie without guidance, so that manufacturing tolerances can be easily compensated. The control of the control chamber can then be done by an existing example in the sleeve control channel.

In order to be able to inject very small amounts in the range of 1 mm ³ with the fuel injection device according to the invention, a "compression" of the valve element is adjusted by a corresponding Längenbeziehungsweise material selection of the valve element. All previous measures allow operation of the fuel injector even at very high pressures of up to 1800 bar.

According to the invention, the valve element is multi-part and at least two parts of the valve element are coupled to each other via a hydraulic coupler. As a result, the freedom in the design of the fuel injection device is considerably increased. The manufacture of the device is simplified.

In a further development, it is proposed that the two parts of the valve element in the hydraulic coupler, when the valve element rests against the valve seat, are spaced from each other. As a result, a direct mechanical coupling of the two parts and thus a possible bouncing is prevented.

In this case, the hydraulic coupler may comprise an intermediate disc which geometrically separates a first coupling space from a second coupling space. This simplifies the production.

It is possible that the hydraulic coupler comprises a connecting channel which connects the two coupling spaces hydraulically with each other. This allows the optimization of the coupler, for example by designing the connecting channel as a flow restrictor.

At least one of the parts of the valve element can be designed as an elastic pressure rod such that an opening movement of the control chamber limiting part of the valve element is time-delayed transmits to the cooperating with the valve seat part of the valve element. In this way, despite the use of a cheap solenoid valve to control the pressure in the control room and very short opening times and thus the Ability to inject even very small quantities can be realized.

drawing The following are particularly preferred

Figur 1

einen teilweisen Schnitt durch einen Bereich einer einer Kraftstoff-Einspritzvorrichtung, die nicht Teil der Erfindung ist;

Figur 2

ein Diagramm, in dem ein Verlauf einer in Öffnungsrichtung wirkenden Kraft über dem Hub eines Ventilelements der Kraftstoff-Einspritzvorrichtung von Figur 1 aufgetragen ist;

Figur 3

einen teilweisen Schnitt durch einen Bereich einer ersten Ausführungsform einer Kraftstoff-Einspritzvorrichtung; und

Figur 4

eine Darstellung ähnlich zu Figur 1 einer zweiten Ausführungsform einer Kraftstoff-Einspritzvorrichtung.

Embodiments of the present invention with reference to the accompanying drawings explained in more detail. In the drawing show:

FIG. 1

a partial section through a portion of a fuel injection device, which is not part of the invention;

FIG. 2

a diagram in which a curve of an opening force acting on the stroke of a valve element of the fuel injection device of FIG. 1 is applied;

FIG. 3

a partial section through a portion of a first embodiment of a fuel injection device; and

FIG. 4

a representation similar to FIG. 1 a second embodiment of a fuel injection device.

Description of the embodiments

A fuel injector carries in the figure as a whole the reference numeral 10. It comprises a housing 12, which in turn has a nozzle body 12a, a Injector body 12b, and a nozzle lock nut 12c includes. In the housing 12, a stepped recess 14 is provided in its longitudinal direction, of which in FIG. 1 Lower end fuel outlet channels 16 go out, which pass through the wall of the nozzle body 12 a.

In the recess 14, a needle-like valve element 18 is arranged. This has an overall substantially constant diameter D. At his in FIG. 1 lower end, the valve element 18 has a conical tip formed by a first conical annular surface 20 and a second conical end surface 22. The annular surface 20 and the end surface 22 have a different conicity, so that a sealing edge 24 is formed between them. This is when the valve element 18 is closed at an opposite also conical valve seat surface 26 in FIG. 1 lower end portion of the recess 14 in the nozzle body 12a. In this way, the valve element 18 can separate the fuel discharge passages 16 from an annular high-pressure space 28 present upstream of the sealing edge 24 between the valve element 18 and the housing 12.

The high pressure chamber 28 extends over the entire length of the recess 14 and the valve element 18. The latter is guided in the housing 12 above all over a only a small axial length having guide portion 30, which with a complementary guide portion 32 at in FIG. 1 cooperates with the upper end of the nozzle body 12a. However, the high-pressure chamber 28 is not interrupted by the two guide sections 30 and 32: In the region of the guide section 30, the valve element 18 has four flattened portions 34 distributed over its circumference, through which the corresponding guide sections 30 and 32 pass Flow channels are formed, which are also part of the high-pressure chamber 28. The flats 34 are dimensioned such that a throttling of the flow, which flows through the flow channels formed, is substantially zero.

The recess 14 is in FIG. 1 closed at the top by a valve piece 36. This protrudes with a sleeve portion 38 a little way into the recess 14, so that in the sleeve portion 38 a of the fuel outlet channels 60 opposite end portion 40 of the valve element 18 is axially displaceable, but largely fluid-tight. The valve piece 36 is attached to the injector body 12b in a manner not shown. Between the sleeve portion 38 and a slightly spaced from this annular collar 42 on the valve element 18, a spring 44 is clamped, by which the valve element 18 is acted upon very easily in the closing direction.

At the in FIG. 1 upper end of the valve element 18, a control surface 46 is present. It represents a part of a boundary of a control chamber 48 formed between the sleeve portion 38 and the valve element 18. Via an inlet throttle 50, the control chamber 48 is connected to the high pressure chamber 28, which in turn is connected via a channel 52 in the injector body 12 b with a high pressure port 54. This in turn is connected in the operation of the fuel injection device 10 with a fuel rail ("rail"), which in FIG. 1 but not shown. In such a fuel rail fuel can be stored under very high pressure. To the fuel rail, a plurality of fuel injectors may be connected.

An outlet throttle 56 connects the control chamber 48 further with a switching valve 58. This connects the control chamber 48 in the open state with a low pressure port 60. For this purpose, the switching valve 58 in this example has a valve ball 62, which in turn is acted upon by a valve stem 64 which in turn either hydraulically or directly via a corresponding actuator 66 is actuated.

In the FIG. 1 shown fuel injector 10 is operated as follows: In an initial state, the switching valve 58 is closed. The high fuel pressure (up to 1800 bar) prevailing at the high-pressure connection 54 prevails in the high-pressure space 28 and is also transmitted through the inlet throttle 50 into the control chamber 48. The high pressure is also at the conical annular surface 20 in FIG. 1 lower end of the valve element 18 at. However, the hydraulic conical annular surface 20 acting in the opening direction is smaller overall than the control surface 46 acting in the closing direction. For this reason, a force resultant in the closing direction acts altogether on the valve element 18, which ensures that the sealing edge 24 of the valve element 18 abuts against the opposite valve seat surface 26 is pressed. Thus, the connection of the high-pressure chamber 28 is interrupted to the fuel outlet channels 16.

In order for fuel to be delivered from the fuel injector 10, the switching valve 58 is opened. The control chamber 48 is now connected via the outlet throttle 56 to the low pressure port 60. Since the inlet throttle 50 throttles more than the outlet throttle 56, the pressure in the control chamber 48 and consequently also the force acting on the control surface 46 and acting in the closing direction decreases Force. As soon as it falls below the hydraulic force acting on the conical annular surface 20 and acting in the opening direction (minus the force of the spring 44), the valve element 18 with the sealing edge 24 lifts away from the valve seat surface 26. Fuel now flows from the high-pressure chamber 28 to the fuel outlet channels 16.

In addition, a hydraulic pressure also acts on the conical end face 22, which generates an additional force acting in the opening direction on this conical end face 22 (the course of the force in relation to the stroke will be described below) FIG. 2 still commented in detail). As a result, the opening of the valve element 18 is accelerated. The conical annular surface 20 and the conical end surface 22 thus form a total acting in the opening direction of the pressure surface whose hydraulically effective cross-sectional area is equal to the hydraulically effective cross-sectional area of the control surface 46.

In order to stop the injection of fuel by the fuel injection device 10, the switching valve 58 is closed. The connection of the control chamber 48 to the low pressure port 60 is therefore interrupted. Fuel can now flow back through the inlet throttle 50 into the control chamber 48, so that there adjusts the pressure prevailing at the high pressure port 54 and the high pressure chamber 28. The fact that the valve element 18 now executes a closing movement, although the hydraulic cross-sectional area of the control surface 46 acting in the closing direction and the hydraulic cross-sectional area of the pressure surfaces 20 and 22 acting in the opening direction are the same, is related to the following: In the region of the sealing edge 24, the flow between the both annular surfaces 20 and 22 on the one hand and the opposite valve seat surface 26 on the other hand very slightly throttled.

This is at least at a portion of the conical end surface 22 to a pressure which is smaller than the pressure in the high-pressure chamber 28. This is also related to the outflow of the fuel through the fuel outlet channels 16.

Despite a total in the high-pressure chamber 28 and the control chamber 48 same pressure and despite acting in the same direction in the closing direction and opening direction hydraulically effective cross-sectional areas so the sum acting on the conical annular surface 20 and the conical end surface 22 in the opening direction force is smaller than that on the control surface 46 force acting in the closing direction. The total resultant force acting on the valve element 18 thus acts in the closing direction, which leads to a closing movement of the valve element 18.

The geometry of the conical annular surface 20 and the conical end surface 22, in particular the conicity of these two surfaces 20 and 22, relative to the valve seat surface 26 is selected so that over a stroke H a course of the force acting in the opening direction F is achieved, as in FIG. 2 is shown. It can be seen from this that the force acting in the opening direction has a value F ₀ at the stroke H = 0 (ie when the valve element 18 is in contact with the valve seat surface 26 with the sealing edge 24). When the valve element 18 is slightly open, ie approximately at a stroke H ₁ , the force F ₁ acting in the opening direction is smaller than the force F ₀ acting in the opening direction due to throttling effects. Only at a further increased stroke H acts in the opening direction, a force F ₂ , which is significantly greater than the force F ₀ .

This means, conversely, during the closing process just described, that the valve element 18 is virtually "sucked" toward the end of the closing operation and accordingly closes quickly. A force course, as in FIG. 2 is shown, in addition or reinforced by the formation of a valve spool portion (in FIG. 1 not shown), which cooperates with a corresponding housing-side section.

It is understood that must be lowered so far for a safe opening of the pressure in the control chamber 48 such that the force acting on the control surface 46 in the closing direction plus the force of the spring 44 is smaller than the force _f1.

One recognizes FIG. 1 in that the valve element 18 is in one piece as a whole. By an appropriate choice of material and geometry is set between the sealing edge 24 on the one hand and the control chamber 48, a certain elasticity, which causes a certain compression with closed valve element 18, which can be used to even the smallest amounts of fuel in the range of 1 mm ³ targeted and precise inject.

A first embodiment of a fuel-one embodiment of a fuel injection device is in FIG. 3 shown. Here and below bear such elements and areas already in connection with FIG. 4 have been explained, the same reference numerals. They are not explained again in detail. At the in FIG. 3 shown fuel injector 10, the sleeve portion 38 is formed as a separate part of the valve 36. It is pushed onto the end region 40 of the valve element 18 and is acted upon by the spring 44 against the valve piece 36.

In the radial direction of the sleeve portion 38 is not held. The guidance of the valve element 18 thus takes place exclusively through the guide section 30 on the valve element 18 and the guide section 32 on the nozzle body 12a. As a result, a smooth movement of the valve element 18 is ensured despite certain manufacturing tolerances. The sealing of the control chamber 48 is thereby improved.

It is understood that by the term of the hydraulically effective cross-sectional area on the one hand the pressure surface 20, 22 and on the other hand the control surface 46 the area of the conical annular surface 20, the conical end surface 22, and the control surface 46 is meant, which is perpendicular to the direction of movement of the valve element 18 lying level is projected. Since the diameter of the valve element 18 is constant (value D), these hydraulically effective cross-sectional areas are identical.

A further modified second embodiment shows FIG. 4 , In this, the valve element 18 is divided into two, with a nozzle needle 68 and a control piston 70. The control piston 34 is comparatively long and dimensioned so that it, as will be explained in more detail below, has a significant elasticity. Nozzle needle 68 and control piston 70 are coupled to each other via a hydraulic coupler 72 comprising two hydraulic coupling chambers 74a and 74b. The two coupling spaces 74a and 74b are geometrically separated from each other by a housing-side washer 76, but hydraulically connected to each other via a connecting channel 78.

The upper coupling space 74a is bounded radially by a sleeve 80a, the lower of a sleeve 80b. The sleeves are each pressed against the intermediate disc 76 in a spring 81a and 81b, which is supported on the housing side (spring 81a) or on the nozzle needle 68 (spring 81b). The control piston 70 defines with an end face 82 axially the upper coupling space 74a, the nozzle needle with an end face 84 the lower coupling space 74b.

If the pressure in the control chamber 60 is lowered by triggering the actuator 66 (here a solenoid actuator), the control piston 70 moves in FIG. 4 up. As a result, the pressure in the upper coupling chamber 74a decreases, which transfers via the connecting channel 78 into the lower coupling space 74b and also leads there to a pressure reduction. As a result, the nozzle needle 68 is quasi wound up.

Out FIG. 4 it can be seen that the control piston 70 and the nozzle needle 68 "float" in the high pressure of the above and below the washer 76 high-pressure chambers 28a and 28b. For this purpose, corresponding passages (without reference numerals) are present in the intermediate disk 76. As a result, the sealing problem is reduced.

Due to the elasticity and length L, in particular of the control piston 34, it is possible that even very small amounts of fuel can be injected with the fuel injection device 18. This is due to the fact that the control piston initially, when the nozzle needle 68 rests against the housing-side valve seat, is elastically compressed by the high pressure in the control chamber 48. At a pressure reduction in the control chamber 48, the control piston 70 must first be lengthen to bring about the above-mentioned pressure reduction in the coupling chambers 74a and 74b.

In the embodiment according to FIG. 4 For example, by a corresponding selection of the ratios of the diameter D1 of the end face 84 of the nozzle needle 68 to the diameter D2 of the end surface 82 of the control piston 70 (translation) and the diameter D2 to the diameter D3 of the control surface 46 (pressure stage), the force ratios can be adjusted in a simple and yet precise manner become.

Claims (9)

1. Fuel injection device (10) for an internal combustion engine with direct fuel injection, having a housing (12), having a valve element (18) which is arranged in the housing (12) and which has a hydraulic pressure surface (20, 22) which acts in an opening direction, which hydraulic pressure surface delimits a high-pressure chamber (28a, 28b) which is connected to a high-pressure port (54), and having a hydraulic control surface (46) which acts in a closing direction and which delimits a control chamber (48) in which a variable control pressure prevails during operation, wherein the closed valve element (18) bears, by way of a conical tip, against a valve seat surface (26) and thus separates fuel outlet ducts (16) from the high-pressure chamber (28a, 28b), and wherein the valve element (18), in an open position (H₁) or an open position range, interacts in a throttling manner with a housing region (26) such that a pressure which is lower than the pressure in the high-pressure chamber (28a, 28b) acts at least on one part of the pressure surface (20, 22), characterized in that the valve element (18) is of multi-part form (68, 70) and at least two parts (68, 70) of the valve element (18) are coupled to one another via a hydraulic coupler (72).
2. Fuel injection device (10) according to Claim 1, characterized in that, when the valve element (18) is open, the hydraulically acting pressure surface (20, 22) and the hydraulically acting control surface (46) are, when projected in each case onto a plane perpendicular to the direction of movement of the valve element (18), of at least approximately the same size.
3. Fuel injection device (10) according to one of the preceding claims, characterized in that, during operation, at least approximately the high fuel pressure prevailing at the high-pressure port (54) at least intermittently prevails in spaces (28a, 28b) which are situated between the control chamber (48) and high-pressure chamber (28a, 28b) and which surround the valve element (18).
4. Fuel injection device (10) according to one of the preceding claims, characterized in that the valve element (18) has a valve slide portion which, at least intermittently, in particular during closing, interacts in a throttling manner with a housing-side region (12) in such a way that the pressure acting at least on one part of the pressure surface (20, 22) falls below the pressure in the high-pressure chamber (28a, 28b).
5. Fuel injection device (10) according to one of the preceding claims, characterized in that the control chamber (48) is fluidically separated from the high-pressure chamber (28a, 28b) by a sleeve portion (38) which is not guided radially by the housing (12).
6. Fuel injection device (10) according to one of the preceding claims, characterized in that the valve element (18) has a guide portion (30) on which it is guided (32) in the housing (12) so as to permit a passage of fluid.
7. Fuel injection device (10) according to Claim 1, characterized in that the two parts (68, 70) of the valve element (18) in the hydraulic coupler (72) are spaced apart from one another when the valve element (18) bears against the valve seat (26).
8. Fuel injection device (10) according to Claim 7, characterized in that the hydraulic coupler (72) comprises an intermediate disc (76) which geometrically separates a first coupling chamber (74a) from a second coupling chamber (74b).
9. Fuel injection device (10) according to Claim 8, characterized in that the hydraulic coupler (72) comprises a connecting duct (78) which hydraulically connects the two coupling chambers (74a, 74b) to one another.

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