Fuel injection valve

A fuel injection valve for fuel injection valve systems of internal combustion engines is described, having an energizable actuating element, a valve closing element which is axially movable along a valve longitudinal axis and which works in conjunction with a rigid valve seat that is provided on a valve seat element so as to open and close the valve, and at least one exit opening that is provided downstream from the valve seat. As the injection valve is of the inward-opening type, the opening movement of the valve closing element is oriented away from the exit opening and the closing movement of the valve closing element is oriented toward the exit opening. Fuel flows completely through the interior of the valve closing element, and the valve seat element has an inner trough-shaped recess, so that the opening movement of the valve closing element is fuel-pressure-assisted, due to a flow inversion upstream of the valve seat.

FIELD OF THE INVENTION

The present invention relates to a fuel injection valve.

BACKGROUND INFORMATION

According to German Published Patent Application No. 27 55 400, an electromagnetic fuel injector which can be used in fuel injection systems of internal combustion engines is known. This fuel injector is characterized by relatively short injection times. The fuel injector is designed in such a way that the entire pressure drop basically occurs through injection holes located downstream of a valve seat which interact with a sphere-shaped valve closing element. The valve closing element is located in a dead area between the valve seat and the injection holes opening in the direction of the fuel flow. When the valve is closed, the valve closing element is pressed against the valve seat with the help of a plunger. The plunger has the same diameter as the valve seat, and system pressure of the fuel is constantly applied to it in the direction of the closing movement. The fuel is supplied through a channel in the valve housing, away from the plunger, to the valve closing element from below which can thus complete the opening movement by lifting from the valve seat.

According to German Published Patent Application No. 38 43 862, an electromagnetically actuatable valve as a fuel injection valve, which is embodied as an inward-opening injection valve, is known heretofore. The valve is actuated by an energizable electromagnet, a sphere-shaped valve closing element interacting with a rigid valve seat in order to open and close the valve. If current is supplied to the magnet coil of the electromagnet, a starting movement is produced via an armature that is attached to an axially movable valve needle, this raising the valve closing element—which also belongs to the valve needle—off the valve seat so that the valve is opened. Herein, the connecting element of the valve needle, which is arranged between the armature and the valve closing element, is resilient and elastic.

As is the case with all inward-opening fuel injection valves, the direction of flow of the fuel at the valve seat is the same as the closing movement of the valve closing element, i.e., the valve needle. When the valve is in the closed position, the fuel is present on the upstream side of the valve seat at a pressure that acts in the valve's closing direction so that when the valve opens the fuel acts against the valve needle's opening direction.

SUMMARY OF THE INVENTION

The fuel injection valve according to the present invention has the advantage that it is manufacturable in an especially straightforward and inexpensive manner. It is advantageous that only a small number of individual components are required and are in themselves very straightforward to manufacture, and may subsequently be assembled in a straightforward manner. The fuel injection valve according to the present invention is easy to handle during assembly, as insertion of all the components into one another is simplified. Just two rigid, pressure-tight connections are required to guarantee problem-free functioning of the injection valve.

It is particularly advantageous that the valve closing element and the valve seat element are designed so that when the actuating element is energized, the valve closing element's opening movement is fuel-pressure-assisted, because system pressure is present on the downstream side of the valve closing element when the valve is in the closed position. The valve is designed so that a hydraulic opening force is generated, so that, for example, an end stage required for triggering may be operated using less energy than is normally the case, and as a result the injection valve may be operated using less inrush current. In addition, it is advantageous that the injection valve switching times are shortened.

When the injection valve opens, thanks to the design of the valve closing element and the valve seat element according to the present invention, there is no underpressure in the volume of fuel downstream from the tight seat, as the movement of the needle does not cause any increase in volume. As a result, the small quantity linearity and the atomization at the start of injection may be significantly improved relative to known valves in which the volume increases during opening due to the needle movement.

It is advantageous that the valve closing element is connected rigidly and in a pressure-tight manner to a needle sleeve through the inside of which fuel flows. At the opposite end from the valve closing element, the needle sleeve is connected rigidly and in a pressure-tight manner to a valve housing, the valve closing element's axial movement being possible thanks to the fact that a section of the needle sleeve is resilient and elastic. Herein it is advantageous if the needle sleeve performs its function of a pressure spring via a screw-shaped, pleated spring section.

Thanks to the low moved mass of the needle sleeve and of the valve closing element, the injection valve may be opened and closed quickly so that the injection valve switching times may be shortened even further.

It is advantageous that an atomizer disk may be integrated very easily into the valve housing downstream from the valve seat, as radial inflow into an atomization disk of this kind is facilitated by the design of the valve seat element and the associated flow guidance.

Thanks to the design of the pressure-balanced valve component according to the present invention that includes a needle sleeve and a valve closing element, and thanks to the low mass of this valve component, a relatively small magnet circuit may be used, and as a result the dimensions of the injection valve as a whole may be kept small.

DETAILED DESCRIPTION

The fuel injection valve shown inFIG. 1by way of an example is an inward-opening injection valve which is particularly suitable as a high-pressure injection valve for injecting fuel directly into the combustion chamber of a gas-mixture compressing, spark-ignition internal combustion engine.

The fuel injection valve is embodied as a top-feed injection valve, which means an upper inflow-side end of the injection valve is located at the opposite end from a lower injection-side end of the injection valve. The inflow-side end of the injection valve forms a tube-shaped connection nozzle1. A fuel filter3, through which the fuel passes, is provided in a flow opening2of connection nozzle1.

In the area of a shoulder4, which extends radially, connection nozzle1is rigidly connected to a sleeve-shaped valve housing5, connection nozzle1ultimately also constituting part of the valve housing. Valve housing5has casing section6and a base section7. In base section7, for example, a central exit opening9, via which the fuel is injected directly into a combustion chamber, is provided.

The fuel injection valve is actuated electromagnetically, for example. To accomplish this, a magnet coil8is arranged inside valve housing5, the coil area for holding magnet coil8being radially delimited on the outside by casing section6of valve housing5and at the top by shoulder4of connection nozzle1.

Valve housing5, as the valve seat carrier, also bears a valve seat element10. Valve seat element10has a, for example, truncated-cone-shaped valve seat surface13in conjunction with which a partial-sphere-shaped closing element14functions to form a tight seat. When the injection valve is in the non-energized state, valve closing element14lies tightly against valve seat surface13so that the valve is in the closed state. InFIG. 1, the injection valve is shown in the energized state in which valve closing element14is in a position in which it is raised off valve seat surface13.

The electromagnetic circuit having magnet coil8, a first inner terminal component18, a second outer terminal component19, and valve closing element14which also functions as an armature, is used to axially move valve closing element14along a valve longitudinal axis15and thus to open the injection valve against the spring load imparted by a needle sleeve16, which is embodied as a concertina and is rigidly attached to valve closing element14, and to close it. Needle sleeve16does not constitute an axially movable valve needle in the conventional sense, as it is designed as a resilient component which, at the end located opposite valve closing element14, is rigidly attached to valve housing5and to connection nozzle1.

The fuel that passes through connection nozzle1and fuel filter3flows further downstream through an inner opening of an adjustment sleeve20, which is used to adjust the spring load imparted by needle sleeve16, which functions as a return spring so as to close the injection valve. To accomplish this, adjustment sleeve20, which is, for example, pressed into connection nozzle1, is in direct contact with a pleat of casing16. The fuel then flows through needle sleeve16in the axial direction until it reaches valve closing element14, which has an inner through-hole22. Needle sleeve16, which in the area of valve closing element14is no longer pleated but rather cylindrical, axially almost completely penetrates through-hole22, for example, and is rigidly connected to valve closing element14at the end facing exit opening9, it being possible to create the rigid and tight connection via a circumferential welded seam23, which is created using a laser. Alternatively, needle sleeve16and valve closing element14may be adhesively bonded or soldered to one another so that they are pressure-tight. It is also feasible to create a press-type fit between both components14and16by providing a stop shoulder on needle sleeve16as far as which valve closing element14may be pressed on.

Downstream from through-hole22of valve closing element14, fuel gathers in a hollow space24of valve seat element10that is formed by a trough-shaped recess21in which truncated-cone-shaped valve seat surface13tapers. Starting from hollow space24, if the injection valve is open flow passes through the narrow gap that is formed between valve closing element14and valve seat surface13. In this flow area an at least partial fuel flow inversion is present, because in addition to a radial flow component an axial flow component, which is in the opposite direction to the axial direction of flow from connection nozzle1to hollow space24, is present, as indicated by the arrows in the area of the tight seal. In this way injection valve opening procedures that are assisted by the fuel pressure and the fuel flow direction may be achieved.

In the radial direction, fuel flows up to at least one, e.g., three flattened parts25provided on the outer circumference of valve seat element10which, as surfaces that have been ground flat, form flow channels26between themselves and casing section6of valve housing5.FIG. 2shows a top view of a valve seat element10of this kind, as an individual component. Thanks to its three flattened parts25, valve seat element10is largely trihedral in shape, transition areas27, which are at 120° respectively from one another, having, at the circumference of valve seat element10, a circular-shaped outer contour between flattened parts25. Transition areas27allow valve seat element10to be centered in valve housing5.

The fuel passes axially through flow channels26and then passes, for example, into an atomization disk29, through which the fuel flows radially, and which is clamped between a lower side30of valve seat element10and base section7of valve housing5. InFIG. 1, a tri-layer atomization disk29manufactured via, for example, multi-layer electro-deposition, is schematically shown. This atomization disk29has, for example, a plurality of swirl channels32in a middle level which open into a central swirl chamber33. The fuel to which swirl is imparted in this way exits from an outlet opening34of atomization disk29that is provided in a lower level. Herein, in outlet opening34the fuel is mainly concentrated near the wall, while an air core is formed in the center. Thus the film of liquid, which exits in the form of a complete ring, spreads out into the shape of a hollow cone in space. Injection hole disks and atomization disks having completely different designs and different manufacturing methods may be used instead of multi-layer swirl disks.

Below, we describe the assembly process for the fuel injection valve in greater detail. Atomization disk29is inserted into valve housing5and into a recess35of base section7that is provided for this purpose. After that, valve seat element10is pressed into valve housing5. Lower side30of valve seat element10rests on atomization disk29and thus defines the height of the radial inflow area for atomization disk29. A spacer disk38, which is only in contact with valve seat element10in three transition areas27, is placed on upper side37of valve seat element10. Spacer disk38is embodied so as to have a specific thickness so that the stroke of valve closing element14is set as required. Flow channels26are covered by spacer disk38in their outer areas so that the fuel may flow unhindered into them.

Next, second terminal component19, which constitutes a magnet yoke having an L-shaped cross-section, is pressed into valve housing5until it rests against spacer disk38. Then magnet coil8is inserted into terminal component19. Terminal component19has, on the arm that extends radially, a guide opening39which guides valve closing element14during its axial movement. After that, the valve part, which includes needle sleeve16and valve closing element14, and first terminal component18, which as a magnet yoke also has an L-shaped cross section, are inserted into valve housing5.

Needle sleeve16is manufactured, for example, via deep drawing using spring steel. The pleats of needle sleeve16that create the spring action are produced by introducing a forming tool, which resembles a screw and whose thread is brought into contact with the inner wall of the sleeve, into the sleeve. If the ambient pressure is increased in a pressure chamber and the inside of the sleeve has been sealed off against the overpressure, the sleeve implodes and takes on the outer shape of the screw-type tool. The tool may then be withdrawn from needle sleeve16by rotating it like a screw. Alternatively the casing may be manufactured via plastic injection molding, in which case the plastic is to have elasticity that remains constant over a prolonged period. Needle sleeve16performs the function of a pressure spring which in the non-energized state presses valve closing element14against valve seat surface13and thus into the injection valve's closed position. Despite its small wall thickness and thus small weight, needle sleeve16is very stable and rigid against the fuel pressure that is present inside thanks to its pleated, screw-type design.

First terminal component18is pressed into valve housing5until it rests on second terminal component19. As a result, magnet coil8is surrounded in all directions by two terminal components18,19. Needle sleeve16rests via a bent sleeve end40on first terminal component18. Next, connection nozzle1is placed on this pre-assembled valve part, its shoulder4resting on sleeve end40and indirectly on first terminal component18. After that, valve housing5and connection nozzle1are rigidly and tightly connected to one another by creating a welded seam42. Welded seam42is created so that needle sleeve16is also connected to connection nozzle1via a pressure-tight connection. Once this attachment has been created, adjustment sleeve20is inserted into connection nozzle1. Then fuel filter3is inserted and a sealing ring44is placed over connection nozzle1.

When the injection valve is in the closed position, needle sleeve16presses valve closing element14against valve seat surface13. Upstream from the tight seat, the fuel is under system pressure. The fuel hollow areas downstream from the tight seat are filled with fuel that is not subject to pressure. Sealing of the pressureless area relative to the area to which pressure is applied is accomplished via the pressure-tight connection of needle sleeve16to valve closing element14and to connection nozzle1. The clamping area between valve housing5, valve seat element10and atomization disk29does not have to be absolutely pressure-tight, as pressure is only present when the injection valve is open and in that case the flow takes the direct path through the flow openings in atomization disk29due to the low flow resistance.

Partial-sphere-shaped valve closing element14has, on the side facing away from valve seat surface13, a polished frontal surface45which extends perpendicular to valve longitudinal axis15. When current flows into magnet coil8, valve closing element14, which functions as an armature, is drawn from valve seat surface13as far as a stop surface46that is provided on first terminal component18. Thus the path between the two end positions (stop surface46and valve seat surface13) of valve closing element14constitutes the stroke. It is possible to influence the stroke by varying the thickness of spacer disk38. When the injection valve opens, no underpressure arises in the volume of fuel downstream from the tight seat, as the movement of the needle does not result in any increase in volume. As a result, the small quantity linearity and the atomization may be improved relative to known valves in which, during opening, movement of the needle causes an increase in volume. Thanks to the low moved mass of needle sleeve16and of valve closing element14, the injection valve may be opened and closed quickly.

In summary, the fuel injection valve according to the present invention has a valve closing element14through the inside of which fuel flows. As a result, fuel close to valve longitudinal axis15reaches the downstream end of valve closing element14so that when the valve is in the closed position system pressure is present at the downstream side of valve closing element14directly upstream from valve seat13. No hydraulic closing load is present on the upstream side of valve closing element14, e.g., in the area of frontal surface45. As a result of this hydraulic pressure distribution, a hydraulic opening force is generated, thanks to which the valve opening procedure is fuel-pressure-assisted. The flow inversion in hollow space24having a flow orientation directly upstream valve seat13and having a flow component that acts in the axial direction, i.e., in the direction of opening of the valve, creates further assistance for the opening movement of valve closing element14. Valve seat element10may also be embodied as a flat seat so that fuel flows only radially outward from valve closing element14through the inside of which the fuel flows, there being no axial flow component. The opening movement of valve closing element14is fuel-pressure-assisted in this case too, because when the valve is in the closed position system pressure is present at the underside of valve closing element14upstream of valve seat13.