Valve assembly

Abstract

 A valve assembly comprises a electro-magnetic circuit operable to actuate a valve needle (18) and comprising a fluid inlet tube (1) having an inlet recess (2) taking in a filter (3). The fluid inlet tube (1) comprises a magnetic pole piece (26) forming part of the electro-magnetic circuit and a nonmagnetic pole piece (28) taking in at least part of the filter (3) and being fixed to the magnetic pole piece (26)

Description

[0001] The invention relates to a valve assembly, in particular for an injection valve for dosing fluid into a combustion chamber of an internal combustion engine.

[0002] Injection valves are in widespread use, in particular for internal combustion engines, where they may be arranged next to the combustion chamber to dose fluid into the combustion chamber or into the intake manifold. Due to increased requirements in respect to performance and also in respect to the limitation of emissions emitted by a vehicle, in which the injection valve may be arranged, injection valves should be operable to dose also very small amounts of fluid precisely. In addition to that, the injectors should be designed such that their energy consumption is as low as possible.

[0003] It is the object of the invention to create a valve assembly, which enables a very efficient operation.

[0004] The object is achieved by the features of the independent claim.

[0005] The invention is distinguished by a valve assembly comprising a electro-magnetic circuit operable to actuate a valve needle and comprising a fluid inlet tube having an inlet recess taking in a filter. The fluid inlet tube comprises a magnetic pole piece forming part of the electro-magnetic circuit and a non-magnetic pole piece taking in at least part of the filter and being fixed to the magnetic pole piece. The fluid inlet tube may in that way serve the purpose of on one hand fixing the filter in its given position and on the other hand completing the magnetic circuit. By having the non-magnetic pole piece, which is preferably arranged facing away from the electro-magnetic circuit and takes in at least part of the filter, magnetic flux scattering in the area of the non-magnetic pole piece is prevented and thereby the efficiency of the electro-magnetic circuit it improved. This then results in an overall improvement of the efficiency when controlling the valve assembly. The armature is preferably operatively connected to a valve needle.

[0006] According to a preferred embodiment of the invention, the non-magnetic pole piece is welded to the magnetic pole piece. In that way, a very reliable connection between the non-magnetic pole piece and the magnetic pole piece may be achieved in a cost-effective way.

[0007] According to a further preferred embodiment of the invention, the non-magnetic pole piece comprises nickel and chromium. It has been shown that such an alloy has very suitable properties for being non-magnetic and on the other hand for being welded to a magnetic pole piece and being used in the environment of the valve assembly.

[0008] Exemplary embodiments of the invention are explained in the following with the aid of schematic drawings. These are as follows:

FIG. 1 an injection valve with a valve assembly and

FIG. 2 a fluid inlet tube.

[0009] Elements of the same design and function that appear in different illustrations are identified with the same reference characters.

[0010] An injection valve (FIG. 1) comprises a valve assembly and a housing and a fluid connector for connecting the injection valve to a fluid supply. The housing may be made by overmolding part of the valve assembly and the fluid connector. The valve assembly comprises a fluid inlet tube 1 which has an inlet recess 2. The inlet recess 2 takes in a filter 3. The filter 3 is provided for filtering the fluid flowing in from the fluid connector. In addition to that, the filter serves preferably for pretensioning a spring 4.

[0011] The valve assembly further comprises an electro-magnetic circuit with a coil 6, a magnetic housing 8, a valve body shell 10 and an armature 12. In addition to that, a non-magnetic shell 14 is provided to properly guide the magnetic flux as desired. The magnetic flux is guided around the respective coil 6 as indicated by the arrows in FIG. 1. Dependent on the magnetic flux, a force is generated acting on the armature 12.

[0012] The valve assembly further comprises a valve body 16 taking in a valve needle 18 in a recess 20 of the valve body. The valve needle is preferably of a tubular shape and has a ball fixed to its axial end facing away from the magnetic circuit. The injection valve needle comprises a fluid outlet 24 as provided in the valve needle 18. The valve needle 18 is formed as a hollow tubular valve needle 18. The fluid is led from the filter 3 along the spring 4 and then towards the inside of the valve needle 18 and exits the valve needle at the fluid 24 outlet and then flows towards the injection nozzle.

[0013] The armature 12 is operatively connected to the valve needle 18. The spring 4 rests with one of its free ends on the armature. The force of the spring 4 and the weight of the valve needle 18 exert a force on the needle 18. In addition to that, the pressure of the fluid also exerts a force on the valve needle 18. If no electromagnetic forces are created within the electro-magnetic circuit, the forces acting upon the valve needle 18 push the valve needle 18 in a closing position, in which a fluid flow through the injection nozzle 22 is prevented. By exerting an electromagnetic force created by a current through the coil 6, the valve needle 18 may be moved out of its closing position and thereby freeing the injection nozzle 22 and giving free the fluid flow through the injection nozzle 22.

[0014] The fluid inlet tube 1 is formed by a magnetic pole piece 26 and a non-magnetic pole piece 28 (see FIG. 2). The non-magnetic pole piece 28 is fixed to the magnetic pole piece 26, preferably by welding or another way of fixing such two parts together reliably known to the person skilled in the art. Preferably, the magnetic pole piece 26 extends to about the axial end of the magnetic housing 8. This enables together with the other parts of the electro-magnetic circuit to channel a very high percentage of the magnetic flux through the magnetic pole piece 26, the armature 12 , the valve body shell and the magnetic housing 8.

[0015] By providing the non-magnetic pole piece 28 in an area axially facing away from the magnetic circuit, a scattering of magnetic flux into the area of the non-magnetic pole piece 28 is efficiently prevented. In that way, the overall efficiency of the electro-magnetic circuit is improved and therefore the energy needed to control the valve needle 18 is reduced. The non-magnetic pole piece 28 preferably comprises nickel and chromium. It is preferred that the non-magnetic pole piece 28 comprises around 12 % in weight of nickel and around 18 % in weight of chrome.

Claims

1. Valve assembly comprising a electro-magnetic circuit operable to actuate a valve needle (18) and comprising a fluid inlet tube (1) having an inlet recess (2) taking in a filter (3), with the fluid inlet tube (1) comprising a magnetic pole piece (26) taking in at least part of the filter (3) and being fixed to the magnetic pole piece (26).

2. Valve assembly according to claim 1, with a non-magnetic pole piece (28) being welded to the magnetic pole piece (26).

3. Valve assembly according to one of the previous claims, with the non-magnetic pole piece (28) comprising nickel and chromium.

Drawing