Valve for metering a fluid

A fluid metering valve includes a valve-seat surface; a valve closing element that interacts with the valve-seat surface in order to form a sealing seat; an electromagnetic actuator; a valve needle used for operating the valve-closing element; an armature that is guided on the valve needle and is used for opening or closing the sealing seat; at least one stop that is disposed on, and stationary relative to, the valve needle and that restricts a movement of the armature on the valve needle; and at least one damping element that is configured to provide a damping during the opening or closing of the sealing seat, has a volume that is able to be filled with a fluid medium, is configured such that a fluid medium can be exchanged between the volume and an environment of the damping element, and is configured for volume changes of the volume in order to enable the damping.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the national stage of International Pat. App. No. PCT/EP2016/064505 filed Jun. 23, 2016, and claims priority under 35 U.S.C. § 119 to DE 10 2015 211 667.0, filed in the Federal Republic of Germany on Jun. 24, 2015, the content of each of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

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

BACKGROUND

A fuel injector for fuel-injection systems of internal combustion engines is known from the document DE 199 50 761 A1. The known fuel injector includes a valve needle that interacts with a valve-seat surface to form a sealing seat. An armature engaging at the valve needle is movably guided on the valve needle and damped with the aid of an elastomer ring made from an elastomeric material. A planar support ring, which axially supports the elastomer ring in the region of an outlet of a fuel duct of the armature, is situated between the elastomer ring and the armature. A lateral cover of the elastomer ring may also be provided here, which allows for the use of an elastomer having high internal damping and therefore a relatively low modulus of elasticity.

SUMMARY

According to an example embodiment of the present invention, a valve is provided that has an advantage that it allows for an improved design and operating principle. More specifically, it is possible to realize a robust design in which the impact impulses related to a free path of the armature are able to be damped.

The armature serving as a solenoid armature is not fixedly connected to the valve needle in the valve for metering the fluid, but is supported in a flying manner between stops. In practice, such stops are able to be realized with the aid of stop sleeves and/or stop rings. In the rest state, the armature is then able to be moved against a stop that is stationary with respect to the valve needle using a restoring spring, so that the armature lies against the stop. During the actuation of the valve, the entire free path of the armature will then be available as an acceleration path. The free path of the armature can be understood as the axial play between the armature and the two stops.

In comparison with a fixed connection of the armature to the valve needle, the realization using an armature free path provides an advantage that the valve needle is able to be opened in a reliable manner at an identical magnetic force even at higher pressures, in particular higher fuel pressures, through the impulse of the armature that is being created during the opening. This can be referred to as a dynamic mechanical reinforcement. Another advantage is that the involved masses are decoupled, so that the resulting impact forces at the sealing seat are distributed to two impulses.

However, specific problems arise due to the flying-type support of the armature. During the closing of the valve, the armature can basically bounce back again after striking the respective stop. In the extreme case, the entire free path of the armature can be run through again after the bounce-back, so that the armature still has enough energy when subsequently striking the opposite stop that the valve needle will be briefly lifted off its seat once again and unintended post-injections take place, which cause an increase in consumption and higher pollutant emissions. But even if the entire armature free path is not run through, the armature can still require some time after bouncing back to come to rest and reach the starting position again. If a new actuation takes place prior to the final stabilization, which is particularly important in multi-injections featuring brief pause intervals between multiple injections, no robust valve function will be obtained. For example, it can occur that the impact pulses increase or decrease accordingly, which, in the worst-case scenario, can result in the valve no longer opening at all since the required impact impulse is no longer sufficiently strong to open the valve.

The throttle element advantageously allows for damping, which prevents or at least reduces armature bounce. In this way, a more robust multi-injection capability at brief pause intervals can be achieved. More specifically, the solenoid armature is able to reach its rest position (starting position) more rapidly again. In addition, lower impact impulses during the closing are achievable, which reduces the wear on the armature, the stops, and on the valve seat. This also causes fewer function changes over the service life of the valve. Moreover, a lower excitation of structure-borne noise is achievable, which reduces the noise.

The valve-closing element, which is operated by the valve needle, can be developed in one piece with the valve needle. The valve-closing element can be developed as a spherical valve-closing element or also in some other way. Depending on the application case and the design, the valve needle can be made up of one or multiple part(s). In particular, the damping element is able to be integrated into the valve needle.

It is also possible to use multiple damping elements which need not necessarily have an identical development in the design of the valve. Different function principles are also combinable with each other in order to influence the damping behavior. For example, it is also conceivable to integrate one damping element into the valve needle while another damping element damps the impact on one of the stops. In addition, in order to restrict the free path of the armature, for example, it is also possible to provide two stops that are stationary in relation to the valve needle and on which a damping element is provided in each case.

The valve is also suitable for metering gaseous fluids in order to inject them into a combustion chamber of an internal combustion engine, for instance. In particular in the case of a development such as this, a separate fluid medium can be provided, which is provided in the environment of the damping element. In a valve for metering a liquid fluid, this liquid fluid can preferably also be used as a fluid medium for the damping element.

According to an example embodiment of the present invention, the valve is designed such that the exchange of the fluid medium between the interior space and the environment of the damping element is advantageously adjustable via the development of the sleeve. Because of the development that includes the sleeve, it is additionally or alternatively also possible to hold a material possibly provided inside the sleeve in a spatially compact manner.

According to an example embodiment of the present invention, the valve is designed such that the sleeve itself is advantageously deformable when damping an impact, which results in a change in volume inside the sleeve. For example, when flattened or elongated, the damping element can have a smaller volume that is able to be filled with the fluid medium. Advantageous damping then results from the volume exchange.

According to an example embodiment of the present invention, the valve is designed such that it advantageously allows for a development that is more robust with respect to media such as fuel. In addition, a behavior that is constant across the service life is achievable. If necessary, the metallic mesh can also be elastic, so that a starting state of the sleeve of the damping element that is assumed in the unloaded state is able to be predefined. An additional contribution to the damping can also be achieved via the elasticity of the metallic mesh, as the case may be.

According to an example embodiment of the present invention, the valve is designed such that the damping specified via the fluid exchange is advantageously able to be amplified via the elastically deformable metal wire mesh. This also provides the possibility of a further adjustment of the damping. In addition, a starting geometry in the unloaded state is able to be specified via the elastically deformable metal wire mesh. For instance, after the damping element has been compressed, the starting state can thus be brought about again following the loading.

According to an example embodiment of the present invention, the valve is designed such that a large fluid exchange is advantageously possible during the compression of the damping element. This results in an optimal hydraulic damping behavior.

According to an example embodiment of the present invention, the valve is designed such that high stiffness of the metal foam is advantageously achievable, which increases the damping that is made possible via the fluid exchange. In addition, a development in one piece can be realized, as the case may be.

According to an example embodiment of the present invention, the valve is designed for advantageously avoiding direct contact between the armature and the stop. This also makes it possible to achieve a substantial displacement of the fluid medium provided within the volume of the damping element.

According to an example embodiment of the present invention, the valve is designed such that the lifting range of the damping element is advantageously restricted given a corresponding placement of the damping element, which allows for an adjustment of the damping. In particular, bouncing of the armature on the respective stop can follow the damping travel when an actuation of the actuator takes place.

Thus, it is possible to damp either the entire impulse of the actuator or to realize part of the impulse with the aid of a fixed stop.

According to an example embodiment of the present invention, the valve is designed such that the armature can advantageously be allowed to directly strike the fixed stop as the case may be because the damping is achieved via the damping element that is integrated into the valve needle.

Preferred exemplary embodiments of the present invention are described in greater detail in the following description with reference to the attached figures in which corresponding elements have been provided with matching reference numerals.

DETAILED DESCRIPTION

FIG. 1shows a valve1for metering a fluid in a partial schematized sectional view according to a first exemplary embodiment. Valve1can be developed as a fuel injector1, in particular. A preferred application case is a fuel-injection system, in which case such fuel injectors1are developed as high-pressure injectors1and are used for the direct injection of fuel into allocated combustion chambers of the internal combustion engine. Liquid or gaseous fuels can be used as fuel in this context.

Valve1has an electromagnetic actuator2, which includes a solenoid coil3, an armature4, and further elements that are not shown, such as a pole body. A magnetic circuit is closed through the energization of solenoid coil3, so that a magnetic attractive force5acts on armature4and thereby operates armature4in an opening direction6.

Valve1has a valve needle7, which is used for operating a valve-closing element8. Valve-closing element8interacts with a valve-seat surface10developed on a valve-seat body9to form a sealing seat. In order to open this sealing seat, valve needle7is adjusted in opening direction6. The adjustment of valve needle7takes place along a longitudinal axis11.

Armature4of actuator2is movably disposed on valve needle7. Mobility along longitudinal axis11is possible between stops12,13, which are stationary with respect to valve needle7. Armature4is retained in a starting position via a spring14and an armature basket15, which is connected to armature4when no actuation takes place. For the opening of valve1, armature4is accelerated in opening direction6through magnetic pickup force5until armature4strikes stop13. This causes the actuation of valve needle7, which in turn operates valve-closing element8.

A valve spring16, which acts upon valve-closing element8via valve needle7in the direction of valve-seat surface10, is used for closing valve1. When the energization of solenoid coil3is ended, armature4is adjusted counter to opening direction6due to spring14and valve spring16. During the closing, armature4is moved against stop12.

In this exemplary embodiment, stops12,13are developed on stop rings17,18, which are connected to valve needle7. In addition, armature4has through bores19, which allow the passage of fuel in the axial direction. Accordingly, through openings20,21, via which the fuel is conveyed to the sealing seat, are developed on armature basket15. In one modified example embodiment, however, it is also possible to provide a suitable pressurized fluid as a fluid medium in a space22inside armature basket15, which differs from the fuel to be injected.

Valve1has at least one damping element30. In this exemplary embodiment, only one damping element30is provided. This damping element30in this exemplary embodiment is used for damping the movement of armature4before it strikes stop12, which takes place counter to opening direction6. In one modified example embodiment, a damping element that is developed according to damping element30can additionally or alternatively be used also for damping the impact on stop13. Furthermore, modified developments of damping element30as they are described on the basis ofFIGS. 2 and 3, among others, are also possible.

Fluid medium, which plays a role in the damping function, fills at least an environment22of damping element30, which is provided by space22within armature basket15in this exemplary embodiment. To enable the damping, damping element30is developed in such a way that it allows for an exchange of the fluid medium between a volume31of damping element30, which is able to be filled with the fluid medium, and environment22. Here, an interior space32of damping element30can be at least essentially empty and thus form volume31. Damping element30has a permeable sleeve33, via which an exchange between volume31, which is provided in interior space32of damping element30and is able to be filled with the fluid medium, and environment22is possible. In this exemplary embodiment, sleeve33is furthermore developed as a deformable sleeve33.

In this particular exemplary embodiment, damping element30is in annular form. More specifically, damping element30is developed in hollow-cylindrical form. A deformation of damping element30along longitudinal axis11is possible, for which purpose, sleeve33of damping element30can be developed from a metallic mesh33, for instance. In one modified example embodiment, sleeve33can also be developed in the form of a perforated metallic wall33.

In this exemplary embodiment, damping element30is situated parallel to stop12. In response to a movement against stop12, which takes place counter to opening direction6, armature4initially interacts with damping element30and then, when the now already damped movement impulse is still of sufficient strength, it interacts with stop12. In this exemplary embodiment, the parallel placement of damping element30and stop12is realized in that annular damping element30encloses stop area12of stop ring17, which forms stop12, in relation to longitudinal axis11, so that armature4is able to come into direct contact with stop12given a movement impulse of sufficient magnitude.

However, depending on the development of valve1, in particular of actuator2, it is also conceivable that within the framework of the actuations that take place during the operation, the movement impulse of armature4counter to opening direction6is always smaller, due to the design, than would be required for striking stop12. Depending on the configuration of the valve, it is therefore also conceivable that the starting position of armature4, which corresponds to a closed valve1, is not synonymous with armature4resting against stop12.

FIG. 2shows a valve1in a partial schematized sectional view according to a second exemplary embodiment. In this particular exemplary embodiment, damping element30is disposed between stop12and armature4. This makes it impossible for armature4to strike stop12directly. When armature4is traveling toward stop12at an impulse counter to opening direction6, then complete damping of the movement impulse preferably takes place in this exemplary embodiment. Damping element30has an elastically deformable metal wire mesh40in this particular exemplary embodiment, which is situated in interior space32. The remaining portion of interior space32forms volume31that can be filled with the fluid medium. On the one hand, damping takes place via the fluid medium, which is displaced from volume31when damping element30is compressed, and metal wire mesh40itself is able to contribute to the damping on the other hand. Metal wire mesh40is developed as an elastically deformable metal wire mesh40in this case, which opposes the movement of armature4counter to opening direction6. Because of this, an axial expansion of damping element30, which can be described as a metal wire mesh40that spreads open on its own or which can be described as a sleeve33that unfolds as a result, also takes place during the movement of armature4in opening direction6.

In one modified example embodiment, damping element30can also be formed from an open-pore metal foam40, which is surrounded by a sleeve33or which can form damping element30even without such a sleeve33. Such a modified development can also be used in the parallel placement described on the basis ofFIG. 1.

FIG. 3shows a valve1in a partial schematized sectional view according to a third exemplary embodiment. In this particular exemplary embodiment, valve needle7includes a part41on the side of the armature and a part42on the side of the valve-closing element. Damping element30is inserted in valve needle7between parts41,42in this exemplary embodiment. Damping element30has sleeve33in the form of a perforated, elastic balloon33. In this exemplary embodiment, an interior space32is specified within this balloon-shaped sleeve33, which is fully available as volume31able to be filled with the fluid medium. This allows for an exchange between environment22of sleeve33and interior space32via holes43or other openings43, of which only hole43is marked inFIG. 3in order to simplify the illustration. In one modified development, elastic sleeve33, which is perforated on its lateral area, can also have a different shape. In addition, interior space32can possibly be partially filled with a metal wire mesh40or the like.

As a result, one or more damping element(s)30is/are able to function in the way of a bumper in order to dampen the impact impulse of armature4on at least one stop12,13, in particular during a closing operation. Through the type and development of damping element30, the stiffness and damping characteristics are able to be optimally adapted to the closing impulse of armature4that arise in the individual application case. Here, it is possible to dampen the entire impulse of armature4or else only a part of this impulse. This makes it possible to improve the method of functioning of valve1. In particular, a more robust multi-injection capability at short pause intervals is able to be realized.

The present invention is not restricted to the described exemplary embodiments and modifications.