Valve for metering a fluid

A valve for metering a fluid. An armature of the electromagnetic actuator is movable along a longitudinal axis of a valve needle, the movement of the armature relative to the valve needle being limited by a stop surface on the valve needle. The armature has a passage channel. The stop surface is on a stop element. The stop element and the armature are such that during operation there always remains an intermediate space, adjoining the valve needle, between the stop element and an end face of the armature facing the stop element. The stop surface lies, in a contact region, on the end surface of the armature facing the stop element when the armature and the stop surface come into contact during operation, the contact region being situated between the intermediate space and an opening of the passage channel when the armature and the stop surface come into contact.

BACKGROUND INFORMATION

The present invention relates to a valve for metering a fluid, used in particular as a fuel injection valve for internal combustion engines. Specifically, the present invention relates to the area of injectors for fuel injection systems of motor vehicles, in which, preferably, a direct injection of fuel into combustion chambers of an internal combustion engine takes place.

German Patent Application No. DE 103 45 967 A1 describes a fuel injection valve for fuel injection systems of motor vehicles is known. The fuel injection valve includes a magnetic coil and an armature that can be moved by the magnetic coil in a stroke direction against a reset spring. The armature is situated movably on the valve needle, between a first flange that is connected to the valve needle and that limits the movement of the armature in the stroke direction and a second flange connected to the valve needle. Between the armature and the second flange there is provided a spring that, in a rest state of the fuel injection valve, exerts force on the armature such that it is situated at a distance from a stop surface of the second flange, forming a free path for the armature. Here it was already recognized that the use of a spring realized as a spiral spring instead of a plate spring is advantageous because a plate spring hinders the compensation of the fuel situated between the armature, armature stop, and spring, which can cause congestion and an uncontrolled hydraulic behavior of the fuel in the area of the armature.

SUMMARY

The valve according to the present invention may have the advantage that an improved design and functioning are enabled. In particular, the dynamic behavior during opening and closing of the valve can be improved. Specifically, undesirable hydraulic effects, such as hydraulic adhesion and/or undesired mechanical effects, such as armature bouncing, can be prevented or at least reduced.

Through the measures described herein, advantageous developments of the valve are possible.

The armature is preferably situated in an inner space of the valve that is filled at least during operation with a liquid fluid. In a preferred embodiment, this liquid fluid is the fluid metered by the valve. In an embodiment of the valve as a fuel injection valve, this can therefore be a liquid fuel.

If, in such an embodiment, in the initial state or also during an actuation cycle a flat end face of the armature comes into flat contact with a flat stop surface, as is the case in a conventional embodiment, then due to the hydraulic medium, i.e., the liquid fluid, a hydraulic adhesion effect occurs when the armature is removed from the stop surface. This is caused in particular because the liquid fluid first has to flow into the narrow gap that arises. Conversely, in a conventional embodiment, when the armature approaches the stop surface there is a hydraulic damping, because the liquid fluid has to be impelled out of the gap, which is becoming ever narrower. During an actuation cycle, these two effects occur alternately at the respective stop surfaces. This results in a damping effect, and in particular a delay with regard to the dynamic behavior during the controlling of the valve. On the other hand, in the conventional embodiment, in this way armature bouncing is reduced during closing.

In accordance with the present invention, in the valve, which may be correspondingly further developed, the overlapping of one or more passage channels of the armature, and a stiffness of the one or both stops for the armature, can be optimized such that an optimal combination is achieved of hydraulic damping during closing of the valve and a preferably low hydraulic adhesion of the armature on the relevant stop surface during opening, relative to the respective embodiment of the valve.

A further development in accordance with the present invention may have the advantage that on the one hand an advantageous flow through the passage channels is enabled, and on the other hand a fluid exchange is advantageously ensured between the intermediate space and the inner space. In this way, in particular in an operating state in which the armature is detached from the stop surface, a hydraulic adhesive effect can be set to be sufficiently small. Here, this process is facilitated in particular by subsequent flowing of fluid from the inner space into the passage channel in the area of its opening. On the other hand, an advantageous pressure buildup can nonetheless take place in the intermediate space when the armature meets the stop surface and there is elastic deformation of the stop element.

Another development in accordance with the present invention may advantageously enable a fluid exchange between the intermediate space and the inner space from the inside to the outside or from the outside to the inside via the passage channel and the outer partial surface formed outside the edge when the armature and the stop surface come into contact at the projection plane.

The stop surface has an outer edge that runs once around the longitudinal axis of the valve needle. In principle, a passage opening, in particular a passage bore, can also be fashioned on the stop element on which the stop surface is fashioned, and in this way an edge situated inside the stop surface, in particular a circular edge, can be formed. Depending on the configuration, shape, and number of passage channels, the stop surface can be suitably realized to enable a flow of the fluid with regard to the individual passage channels. For example, a plurality of passage channels can be provided of which some are situated closer to the longitudinal axis of the valve needle and some others are situated further away from the longitudinal axis of the valve needle. If the relevant stop surface is to be made correspondingly large, then the proposed solution can be realized both for the passage channels situated further inward and for those situated further outward. Here, in particular for the passage channels situated further inward, inner passage openings having corresponding inner edges can be realized in order to ensure the stability of the stop surface. Here, a further development in accordance with the present invention may have the advantage that the configuration of the at least one relevant passage channel, in particular its distance from the longitudinal axis, and the dimensioning of the stop surface, in particular a radius of the edge of the stop surface from the longitudinal axis, can be calibrated to one another in such a way that the proposed solution can be realized without associated passage openings on the stop element on which the stop surface is fashioned.

The relevant stop surface is fashioned on a stop element. Here, an embodiment corresponding to another development in accordance with the present invention is particularly advantageous. It will be understood that here it would also be possible to provide two stop elements, of which for example one is fashioned on the valve needle and the other is connected to the valve needle in order to join a one-piece armature having a central passage bore to the valve needle, and subsequently to limit it in its movement between the stop elements. However, an embodiment having two stop elements fashioned on the valve needle is also possible if for example a segmented armature is used. In addition, the proposed embodiment of the stop surface can be realized on only one of the stop surfaces, on both stop surfaces in the same manner, or on both stop surfaces in different ways. Here, adaptations to the respective case of application, in particular the desired valve dynamic characteristic and the required bounce characteristic when closing the valve, are possible. In particular, in order to achieve a desired capability for multiple injection, for which a plurality of injections have to be capable of being realized during an injection cycle, it may be necessary to avoid bounce as far as possible.

With the realization of the valve in accordance with the present invention, a damping characteristic during the movement limiting can be reinforced. Here, when the armature impacts the stop element an excess pressure in the intermediate space can be produced, or when the armature bounces back a partial vacuum can be produced in the intermediate space, resulting in a particularly effective reduction of possible bouncing of the armature. In particular, in this way a rapid calming of the armature relative to its initial position when the valve is closed can be achieved in order to achieve multiple injection capability even given short pause times between the individual injections in an injection cycle.

Another development in accordance with the present invention may have the advantage that the intermediate space can be realized by a beveling, seen in profile, on the stop element. Here, an advantageous development in accordance with the present is possible.

In a further advantageous embodiment, the intermediate space can be set at least partly above the height of a step between the stop surface and a preferably partial annular surface on the stop element, with regard to its volume. Here it is in addition advantageous that the surface of the stop element limiting the intermediate space and the stop surface are made parallel to one another and are both oriented perpendicular to the longitudinal axis, the step being situated between the surface and the stop surface and a beveled area or the like thus being omitted. Inter alia, this embodiment has the advantage that good measurability is enabled of the parallelity of the stop surface to the preferably circular annular surface that limits the intermediate space. In the context of series production, in this way process setting, process monitoring, and, if warranted, quality control are possible. In particular, in series production it can be specified as a tolerance specification that a slight conicity is permissible. A slight conicity can be defined in that, with regard to the throttle gap formed between the contact region and the end face of the armature facing the stop element, an adequate throttle effect is ensured when the armature and the stop surface come into contact during operation, so that when the armature stops on the stop surface there is immediately a buildup of an adequately large pressure in the intermediate space to realize the proposed hydraulic damping.

Specifically, through the realization of the surface limiting the intermediate space as a circular annular surface, a development in accordance with the present invention can be realized.

A development in accordance with the present invention can be realized in particular in that the end face of the armature facing the stop surface is made flat and is oriented so that the longitudinal axis of the valve needle passes through the end face of the armature in perpendicular fashion. This can be realized in combination with a stop surface that is flat and oriented perpendicular to the longitudinal axis.

A development in accordance with the present invention may have the advantage that on the one hand, if warranted, a throttle effect can be realized relating to the inner partial surface, while on the other hand a flow through the passage channel, required as a rule in order to accelerate the armature, is not too strongly throttled by a correspondingly large outer partial surface precisely when the armature detaches from the stop surface. Specifically, for the calibration of the dynamic characteristic and/or to avoid bounce by producing a corresponding hydraulic effect, the inner partial surface and the contact region can also be chosen to be small if warranted, while an outer partial surface that is as large as possible enables the flow through the armature in the desired manner.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1shows a valve1for metering a fluid in a partial schematic sectional representation corresponding to an exemplary embodiment. Valve1can be realized in particular as fuel injection valve1. A preferred application is a fuel injection system, in which such fuel injection valves1are fashioned as high-pressure injection valves1and are used for the direct injection of fuel into allocated combustion chambers of the internal combustion engine. Here, liquid or gaseous fuels may be used as fuel.

Valve1has a multipart valve housing2, an electromagnetic actuator3that includes a magnetic coil4, an inner pole5, and an armature6, and a valve needle7that can be actuated by electromagnetic actuator3, which needle actuates, during operation, a valve closing body8connected to valve needle7in order to open a sealing seat formed between valve closing body8and a valve seat surface9. Here, fuel is conducted via an axial bore10of inner pole5into an interspace11of valve housing2and is conducted out from inner space11via an annular gap12to the sealing seat, so that when the sealing seat is open fuel can be injected into a space13, in particular a combustion chamber13, via nozzle openings.

In this exemplary embodiment, valve1is realized as inward-opening valve1, and valve needle7is displaced in an opening direction14along a longitudinal axis15in order to open valve1.

Armature6of actuator3is mounted in flying fashion on valve needle7, so that a movement of armature6along longitudinal axis15is possible in opening direction14and opposite this direction. With regard to valve needle7, this movement is limited by stop elements16,17. Here, stop elements16,17can each be connected to valve needle7or made on valve needle7.

In this exemplary embodiment, stop element16is fashioned as stop sleeve16, fixedly connected to valve needle7. In addition, in this exemplary embodiment stop element17is fashioned as stop ring17, also connected fixedly to valve needle7. Such fixed connections can be realized for example by welding. On stop elements16,17, stop surfaces18,19are fashioned that face one another and between which armature6is displaceable corresponding to a specified armature free path20.

In addition, a reset spring21is provided that in this exemplary embodiment moves valve needle7, via stop element17, opposite opening direction14in order to displace valve needle7into its initial position in which the sealing seat is closed. In addition, a spring22is provided that moves armature6into its initial position, in which armature6lies with its end face23on stop surface18. In this initial position, armature free path20results between end surface24of armature6, which faces away from a surface23, and stop surface19.

When there is an actuation of valve1, current flows through magnetic coil4, so that armature6is accelerated in opening direction14due to the acting magnetic force. Here, valve needle7remains in its initial position until armature6comes into contact with its end surface24on stop surface19of stop element17. The acceleration of armature6here enables a larger opening impulse for the displacement of valve needle7. The movement of armature6is then limited by stopping on inner pole5relative to valve housing2. Here, there can still be a certain degree of continued oscillation of valve needle7.

To close valve1, magnetic coil4is switched currentless, so that via reset spring21a resetting of valve needle7takes place opposite opening direction14, and armature6is carried along by stop element17. When valve closing body8falls into its seat, then the further resetting of armature6into the initial position shown inFIG. 1takes place, spring22ensuring the initial position.

In this exemplary embodiment, inner space11is filled with liquid fuel. Here, passage channels30through35formed in armature6enable fuel to be conducted from bore10in the direction toward annular gap12. In addition, fuel can also flow past armature6, between armature6and valve housing2.

When there is an actuation process, the liquid fuel is first impelled between end face24of armature6and stop surface19of stop element7. Subsequently, there must take place a detaching of armature6with its end face24from stop surface19of stop element17. In addition, when valve1is closed there is an impelling of the liquid fuel between stop surface18of stop element16and end face23of armature6. Also particularly important, at the beginning of the actuation process, is the detaching of armature6from stop element16, in which liquid fuel has to flow in between end face23of armature6and stop surface18of stop element16. In order to ensure an advantageous hydraulic characteristic, a particular design is proposed at stop surface18of stop element16and/or at stop surface19of stop element17. Here it will be understood that the design described in the following on the basis of stop element16and armature6can also be realized, alternatively or in addition, relating to stop element17.

FIG. 2shows a partial schematic representation explaining the embodiment of valve1shown inFIG. 1, in an exploded view. For the simplification of the representation, here only one longitudinal axis15of the valve needle7is shown in order to illustrate the position of valve needle7. In addition, planes39,40,41are shown, through each of which longitudinal axis15passes in perpendicular fashion. Planes39through41are here each represented by a pie-slice segment of a circle whose midpoint lies on longitudinal axis15. Here, plane41is the plane of projection at which stop element16and armature6come into contact when there is a suitable position of valve1. Plane40is characterized in that end face23of armature6is situated in it. However, the realization of armature6is not necessarily limited to one in which end face23of armature6lies in plane40and longitudinal axis15thus passes through it in perpendicular fashion. In particular, it is conceivable for end face23also to have recesses or raised areas in some regions, starting from a flat shape.

Plane39is characterized in that seating region60and an edge42of stop surface18of stop element16are situated in it. In this exemplary embodiment, edge42is fashioned as edge42having the shape of a circular line; inFIG. 2, a circular line segment of edge42is shown. Here, in a part62, i.e. partially, stop surface18is realized corresponding to the surface62of a cone. In addition, stop surface18is made flat and oriented perpendicular to longitudinal axis15in a part63in which a seating region61is situated. If for example a surface line43is regarded that runs in surface62from an edge64in a straight line to longitudinal axis15, then a non-disappearing angle of inclination44is defined. This angle of inclination44results as follows. The projection of surface line43parallel to longitudinal axis15into plane39is a radius43′. Angle of inclination44now results from the right triangle having surface line43as hypotenuse and radius43′ as adjacent leg relative to angle of inclination44. Edge64is here an edge64in the shape of a circular line that limits seating region60inwardly, seen radially.

In a modified embodiment, the non-disappearing angle of inclination44can also vary along edge42. In this exemplary embodiment, angle of inclination44is however constant along edge42, because stop surface18results partly from surface62of a cone.

Edge42is projected into projection plane41along longitudinal axis15, i.e., parallel to longitudinal axis15. In this way, projection42′ of edge42results.

In this exemplary embodiment, an opening45of passage channel30lies in plane40. Opening45is realized as circular opening45in this exemplary embodiment. Opening45is thus limited by a closed line46that in this exemplary embodiment is realized as a circular line46. Opening45, or circular line46, are projected into projection plane41along longitudinal axis15. In this way, in projection plane41there results a projection45′ of opening45, or a projection46′ of circular line46.

Valve1is now realized, corresponding to the proposed solution, such that projection42′ of edge42of stop surface18into projection plane41, which plane longitudinal axis15passes through in perpendicular fashion and at which armature6and stop surface18come into contact, runs through projection45′ of opening45, facing stop surface18, of passage channel30into projection plane41. Through projection42′ of edge42into projection plane41, projection45′ of opening45into projection plane41is divided into an inner partial surface50and an outer partial surface51. In addition, a projection64′ of edge64in projection plane41is situated, regarded radially, at a distance of radial minimum length75from projection46′ of circular line46, or of projection45′ of opening45, projection64′ of edge64being situated closer to longitudinal axis15than projection46′ or projection45′.

It is to be noted that a projection into projection plane41is always to be understood such that the projection takes place in perpendicular fashion into projection plane41. Because longitudinal axis15passes through projection plane41in perpendicular fashion, this means that the projections always take place along, or parallel to, longitudinal axis15. However, here it will also be understood that tolerances, a desired degree of play between armature6and valve needle7, and similar influences caused by tolerances or by the construction, can cause deviations from an idealized construction or projection in the concrete realization of valve1. For example, due to such influences, in particular a degree of play between armature6and valve needle7, a family of curves can result for projection46′ of circular line46into projection plane41that includes circular lines offset radially somewhat to longitudinal axis15about idealized projection46′. In addition, it will be understood that in any case, given a rotationally symmetrical realization of stop surface18, relative rotations of armature6about longitudinal axis15relating to stop element16can be regarded as equivalent. If this is required in the specific individual case, a guiding of armature6along valve needle7may also be realized if warranted, which limits or prevents such relative rotations of armature6.

FIG. 3shows a detail of valve1shown inFIG. 1. Here a situation is shown as occurs on the one hand at the time of the beginning of an actuation of valve1when current is already flowing through magnetic coil4. Here, a magnetic force is exerted in direction52on armature6that accelerates armature6in direction52, or moves it from its initial position. On the other hand, what is concerned may be the time of an impact of armature6on stop element16, as described further below.

In the initial position, planes39through41, shown inFIG. 2, coincide, because armature6and stop surface18are in contact with each other.

Based on the described realization of stop surface18, an intermediate space53is formed between part62of stop surface18and end face23of armature6, which intermediate space is rotationally symmetrical relative to longitudinal axis15in this exemplary embodiment. Here, intermediate space53can first be regarded as partial space53separated from inner space11of valve1, which in principle communicates hydraulically with inner space11only after armature16is detached from stop surface18. When the movement of armature6in direction52takes place, intermediate space53becomes larger. This means that there is a tendency for the pressure in intermediate space53to decrease. This pressure drop is now compensated in that the liquid fluid flows in from inner space11via throttle gap61, formed during the attachment. This means that a fluid exchange takes place from the outside to the inside through throttle gap61, internal or inner partial surface50, passage channel30in the area of its opening45, and outer, or outwardly situated, partial surface51. However, the hydraulic adhesive effect does not result, or results only slightly, at intermediate space53. In this way, a detaching of armature6is facilitated already at the beginning of its movement in direction52from stop element16. In this way a hydraulic adhesion is significantly reduced.

The detail of valve1shown inFIG. 3also shows a second time in the actuation process at which armature6is guided in a direction54against stop element16during the closing of valve1. When armature6approaches stop element16, there results an impelling of the liquid fluid out of intermediate space53, or there is a tendency for the pressure in intermediate space53to increase. As a result, the liquid fluid is impelled out of intermediate space53, from the inside to the outside, through the formed throttle gap61, inner partial surface50, passage channel30in the area of its opening45, and outer partial surface51, into inner space11. In this fluid exchange, there is a strongly throttled conducting of fuel via throttle gap61between contact region16and end face23of armature6.

Regarded dynamically, during the closing of valve1, or when armature6impacts in direction54against stop element16, there is however also an elastic deformation of stop element16. In this way, during the closing of valve1a rebounding of armature6on stop element16can be reduced.

Due to an elastic deformation of stop element16relative to contour56shown inFIG. 3, in part62there is a reduction of angle of inclination44, so that intermediate space53between armature6and stop element16becomes smaller, and the fluid exchange from intermediate space53into inner space11from the inside to the outside is throttled via throttle gap61, now acting as squeeze gap61. This causes a correspondingly strong pressure increase in intermediate space53. This causes uncompensated hydraulic forces opposite direction54, acting on end face23on armature6. In addition, elastic forces or spring forces act that, due to the elastic deformation of stop element16, act on armature6, guided on valve needle7, opposite direction54. Overall, over a certain region of movement of armature6this causes a damped braking of armature6in direction54.

Here, valve1is preferably realized such that intermediate space53at no time completely disappears, i.e., liquid fluid is present in intermediate space53when armature6comes to a standstill relative to valve needle7, and a reversal of movement of armature6takes place corresponding to the dynamic characteristic of the braking process.

In the actuation process, after the reversal of movement of armature6, while valve1continues to be closed, when stop element16is moved back by spring force into the non-loaded position of stop element16illustrated by contour56, an increase in the volume of intermediate space53is caused. This now causes a partial vacuum in intermediate space53relative to the pressure in inner space11. In this way, there arises an uncompensated hydraulic force on armature6opposite direction52. Because the resetting of stop element16into its non-loaded initial position causes a force on armature6in direction52, the partial vacuum in intermediate space53dampens the movement of armature6after its reversal of movement. In this way, a rebounding of armature6is dampened. Corresponding to the removal of load on stop element16, a fluid exchange into intermediate space53is enabled only via the strongly throttling throttle gap61.

In this way, the spring-driven movement of armature6back in direction52is braked by the partial vacuum that arises in intermediate space53. Depending on the realization of valve1, further post-oscillations may occur. However, an advantageous damping is achieved, so that better calming of armature6results. In particular, in this way another opening of valve1, through rebounding of armature6and a complete traversal of armature free space20, can be avoided or completely prevented.

In addition, armature6can be calmed in a short time to such an extent that when there is a new actuation armature free space20is at least largely available as acceleration path for armature6in order to achieve a reliable opening of valve1via a sufficiently large movement impulse of armature6. Thus, for example given a desired multiple injection capability, a short pause can be enabled between individual injections of an injection cycle.

In sum, in this exemplary embodiment on stop element16a contact region60is formed at which armature6lies with its end face23on stop surface18of stop element16in the initial state, stop element16being mechanically free of tension. This contact region16is here formed between intermediate space53and opening45of passage channel30. As a result, at the beginning of the actuation of valve1, in which armature6is accelerated in opening direction14, a fluid exchange takes place only after armature6detaches from stop surface18. Specifically during the closing of valve1, at contact region60there is a strong throttle effect, such that liquid fluid has to flow through the narrow throttle gap61, or squeeze gap61, present at contact region60during the spring-driven motion in or out. The resulting pressure difference, in interaction with the application of the pressure in intermediate space53on armature6at its end face23and the non-compensated hydraulic force resulting therefrom, results in a braking or damping of armature6during the spring-driven motion both in and out.

FIG. 4shows the detail shown inFIG. 3of valve1corresponding to another exemplary embodiment. In this exemplary embodiment, a flat, circular annular surface71is formed on stop element16, limiting intermediate space53. In addition, a step72is provided that is situated between circular annular surface71and stop surface18. Step71has a height73. Via height73, a volume of intermediate space53can be set in the non-loaded initial state of stop element16.

Moreover, a guide gap74is provided between armature6and valve needle7. In a possible embodiment, height73can for example be twice as large as a guide amount of play74′ determined by guide gap74. For example, height73of step72can be 20 μm.

Circular annular surface71and stop surface18are preferably oriented perpendicular to longitudinal axis15of valve needle7.

Through the specification of the radial minimum length75, a calibration of the hydraulic or dynamic behavior during the controlling of valve1is possible. At the beginning of the actuation of armature6, when this armature detaches from stop surface18, fluid has to flow in between stop area60of stop surface18and end face23of armature6. Here, a hydraulic adhesive effect acts until armature6has moved away from stop surface18somewhat in direction52. The shorter the radial minimum length75is specified to be, the lower the hydraulic adhesive effect.

A further effect results when armature6impacts against stop element6; first there is a formation of a throttle gap61, in particular a squeeze gap61. Here, the pressure in intermediate space53increases. The longer the radial minimum length75is specified to be, the greater the maximum pressure buildup in intermediate space53can tend to be. In this way, the maximum pressure that can be reached in intermediate space53can be set via the radial minimum length75. Here care must also be taken that during the elastic deformation of stop element16a certain volume of intermediate space53remains maintained, because otherwise the pressure in intermediate space53is dismantled too quickly. When throttle gap61, or squeeze gap61, is closed, a part of the fluid volume is pressed out from intermediate space53via throttle gap61. Here, a part of the volume can also be pressed out via guide gap74. However, an increase in pressure in guide gap74acts perpendicular to valve axis15, and as a rule is also compensated over the circumference.

Thus, when armature6impacts on stop element16, from the beginning a high throttle effect is achieved via throttle gap61, i.e. before the elastic deformation of stop element16occurs, so that a pressure increase occurs immediately in intermediate space53. The pressure in intermediate space53can then increase as stop element16is increasingly overexpanded. The throttle effect achieved via throttle gap61then limits the maximum pressure that can be achieved, and, via the specification of the radial minimum length75, enables, within practical limits, a certain compensation of the hydraulically acting brake force on armature6when the armature moves in direction54.

Overall, in this way an adaptation is enabled with regard to a reduced hydraulic adhesion during opening and a hydraulic damping during closing.

The Figures are of course to be understood as schematic drawings in which the size relations, in particular angle of inclination44and height73of step72, are shown in significantly exaggerated fashion relative to a preferred embodiment.

The present invention is not limited to the described exemplary embodiments.