Valve assembly and fluid injection valve

1. A valve assembly for a fluid injection valve, the valve assembly comprising:

a valve body with a longitudinal axis and a cavity;

a valve needle received in the cavity, operable to seal a fluid outlet end of the valve body in a closed position and moveable along the longitudinal axis away from the closed position in an opening direction for unsealing the fluid outlet end; and

a driving device arranged in the cavity for displacing the valve needle, the driving device axially moveable relative to the valve body and to the valve needle;

wherein

the valve needle comprises a disc element;

the disc element and the driving device comprise mutually facing and radially extending coupling surfaces, the coupling surfaces having an overlapping area of at least 35% of the cross-sectional area of the cavity;

the driving device takes the disc element with it for displacing the valve needle in the opening direction solely by means of hydraulic interaction between the coupling surfaces when the driving device is displaced in the opening direction; and

the coupling surface of the driving device engages in a form-fit connection with the coupling surface of the disc element for pushing the valve needle towards the closed position.

2. A valve assembly according to claim 1 , wherein the valve needle is does not limit axial displacement of the driving device relative to the valve needle in the opening direction.

3. A valve assembly according to claim 1 , wherein the valve needle does not extend beyond the coupling surface of the disc element in the opening direction.

4. A valve assembly according to claim 1 , wherein the driving device does not axially extend beyond its coupling surface opposite to the opening direction.

5. A valve assembly according to claim 3 , wherein the driving device and the valve needle have no axial overlap.

6. A valve assembly according to claim 1 , wherein the valve needle comprises a shaft and the disc element is fixed to an axial end of the shaft remote from the fluid outlet end.

7. A valve assembly according to claim 1 , wherein the valve needle comprises:

a shaft;

a first stopper fixed to the shaft at a first axial end of the valve needle remote from the fluid outlet end; and

a second stopper fixed to the shaft between the first stopper and a second axial end of the valve needle adjacent to the fluid outlet end;

wherein the disc element

is axially displaceable relative to the shaft and positioned axially between the stoppers;

the disc element

engages in form-fit and/or force-fit connection with the first stopper for moving the shaft in the opening direction; and

the disc element engages in form-fit and/or force-fit connection with the second stopper for moving the shaft towards the closed position.

8. A valve assembly according to claim 1 , further comprising:

a valve spring operable to bias the valve needle toward the closed position; and

a sustaining spring arranged to bias the coupling surface of the disc element in axial direction towards the coupling surface of the driving device.

9. A valve assembly according to claim 1 , further comprising an electromagnetic actuator assembly with a stationary pole piece and a moveable armature;

wherein the driving device comprises the armature.

10. A valve assembly according to claim 9 , further comprising a guide sleeve for axially guiding the driving device or the armature;

wherein the pole piece includes a central axial opening, and the guide sleeve is received in the opening, fixed to the pole piece, and projects beyond the opening into a central aperture of the armature.

11. A valve assembly according to claim 9 , wherein:

the driving device comprises an upper retainer element, a lower retainer element, and the armature;

the lower retainer element comprises the coupling surface of the driving device and is rigidly fixed to the upper retainer element;

the armature has an axial play relative to the retainer elements;

the armature engages in a form-fit and/or force-fit connection with the upper retainer element for displacing the upper and lower retainer elements in the opening direction; and

the armature engages in a form-fit and/or force-fit connection with the lower retainer element for displacing the upper and lower retainer elements in axial direction opposite to the opening direction.

12. A valve assembly according to claim 11 , further comprising an armature spring arranged to bias the armature out of contact with the upper retainer element.

13. A valve assembly according to claim 11 , further comprising a guide sleeve for axially guiding the driving device or the armature, wherein the guide sleeve is positioned radially between the upper retainer element and the armature.