NEEDLE STROKE SWITCH AND FUEL INJECTOR HAVING SUCH A NEEDLE STROKE SWITCH

Abstract

A needle stroke switch and a fuel injector having such a switch, the needle stroke switch including a seat plate having a plate-like main body and a passage connecting the two planar sides of the plate-like main body, an anchor element which can be lifted off from the passage in the seat plate, and a control valve which is arranged on the side of the seat plate opposite the anchor element and is designed to interact with a nozzle needle. The seat plate is electrically isolated from a surrounding injector housing and an electrical connection to the injector housing is possible only via the nozzle needle which interacts with the seat plate. Furthermore, the needle stroke switch is characterised in that at least one ceramic and/or plastic part is provided which contacts the seat plate in order to isolate the seat plate from the surrounding injector housing.

Claims

1. A needle stroke switch for a fuel injector comprising: a seat plate having a plate-like base body and a passage connecting the two areal sides of the plate-like base body; an armature element that can be raised from the passage of the seat plate and can be sealingly placed thereon; and a control valve that is arranged at a side of the seat plate oppositely disposed the armature element and that is adapted to cooperate with a nozzle needle, wherein the seat plate is electrically insulated with respect to an injector casing surrounding it; and wherein an electrical connection to the injector casing can only be implemented via the nozzle needle cooperating with the seat plate, comprising at least one ceramic and/or plastic part contacting the seat plate to insulate the seat plate with respect to the injector casing surrounding the seat plate.

2. The needle stroke switch in accordance with claim 1, wherein the at least one ceramic and/or plastic part is an all-ceramic part.

3. The needle stroke switch in accordance with claim 1, wherein the at least one ceramic and/or plastic part is designed releasably with the seat plate.

4. The needle stroke switch in accordance with claim 1, wherein the at least one ceramic and/or plastic part comprises the components Al.sub.2O.sub.3, Si.sub.3Ni.sub.3 and/or Zr.sub.2O.sub.3 or consists of at least one of these components.

5. The needle stroke switch in accordance with claim 1, wherein the at least one ceramic and/or plastic part has a cylinder jacket shape that is suitable to radially surround the seat plate.

6. The needle stroke switch in accordance with claim 5, wherein the ceramic and/or plastic part for the radial surrounding of the seat plate is fixedly connected to the injector casing.

7. The needle stroke switch in accordance with claim 1, wherein the at least one ceramic and/or plastic part is a seat part that interacts with the armature element and can be sealingly placed on the passage of the seat plate.

8. The needle stroke switch in accordance with claim 7, wherein the seat part has rounded corners for placing on the passage of the seat plate to avoid edges of the seat plate escaping.

9. The needle stroke switch in accordance with claim 7, wherein the seat part is a ceramic part.

10. The needle stroke switch in accordance with claim 7, wherein the seat part electrically insulates the seat plate toward the armature element and toward an armature guide of the armature element.

11. The needle stroke switch in accordance with claim 1, wherein the at least one ceramic and/or plastic part is a seat plate support that is arranged on the areal side of the plate-like base body of the seat plate facing the armature element and electrically insulates the seat plate from an armature guide of the armature element or the injector casing.

12. The needle stroke switch in accordance with claim 11, wherein the seat plate support lies on the areal side of the plate-like base body of the seat plate facing the armature element.

13. A fuel injector having the needle stroke switch in accordance with claim 1.

14. The fuel injector in accordance with claim 13, wherein the fuel injector has an injector state recognition that recognizes an injector state of a closed injector with reference to a current flowing through the nozzle needle and the injector casing.

15. An engine having a fuel injector in accordance with claim 13.

16. The needle stroke switch in accordance with claim 5, wherein the at least one ceramic and/or plastic part has an annular form or a cylinder jacket shape.

17. The needle stroke switch in accordance with claim 5, wherein the seat plate can be inserted into the ceramic and/or plastic part to achieve a radial centration of the seat plate and to form an electrical insulation between the seat plate and the injector casing.

18. The needle stroke switch in accordance with claim 6, wherein the ceramic and/or plastic part of the radial surrounding of the seat plate is fixedly connected to the injector casing by a connection having material continuity or a form fit, wherein the connection is adhesive bonding or soldering.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0032] Further advantages, features, and details of the present invention will become clear on the basis of the following description of the Figures. There are shown:

[0033] FIG. 1: a schematic representation to explain the already known prior art;

[0034] FIG. 2: a schematic representation of the device in accordance with the invention, and

[0035] FIG. 3: a schematic representation of an embodiment in accordance with the invention of the present invention.

DETAILED DESCRIPTION

[0036] FIG. 1 shows a partial sectional view of an injector 10 from the prior art. The injector 10 can be recognized as having a casing 14 in which a plurality of injector components are arranged. The injector needle 15, the valve formed by the armature 11, the seat plate 1, and the electromagnet 12, 13 that has a coil winding 16, an inner magnetic pole 12, and an outer magnetic pole 13 are essential to the function of the injector 10. A cutout for arranging the spring 17 that urges the armature element 11 in the direction of the valve is furthermore provided in the inner magnetic pole 12 to close the outflow throttle of the valve in a currentless state of the electric magnet 12, 13 in a fluid tight manner.

[0037] If the electromagnet 12, 13 is activated, it pulls the armature element 11 away from the valve with the aid of magnetic force so that highly compressed fuel can flow out of the passage 6 from a control space closable by the valve. Since the pressure in the control space that acts on the injector needle is hereby reduced, the latter can slide out of a closed position and enables the dispensing of fuel from the injector 10. If, in contrast, the electromagnet 12, 13, is moved into a currentless state, the magnetic force acting on the armature element 11 is reduced so that the spring element 17 urges the armature element 11 onto the discharge opening of the valve and seals the control space or the passage 6. The pressure acting on the injector needle 15 thereby increased, whereby the latter is again urged into its closed position. There is accordingly no longer any outflow of fuel from the discharge opening of the injector 10.

[0038] FIG. 2 shows a sectional view of an injector 10 having a needle stroke switch 20 in accordance with the invention.

[0039] To insulate the seat plate 1, a plurality of parts comprising ceramics and/or plastic are provided of which each is in contact with the seat plate 1.

[0040] To project the peripheral marginal surface of the approximately plate-like seat plate 1 from an electrically conductive contact with the injector casing, a sleeve-like ceramic and/or plastic part 3 is provided that surrounds the seat plate in a radial peripheral direction. The sleeve 3 can here be fixedly connected, in particular adhesively bonded or soldered, to the injector casing. The sleeve 3 serves the radial centering of the seat plate 1 in addition to the electrical insulation.

[0041] A seat part 4 be recognized beside in FIG. 2 that preferably comprises a ceramic material (for example Al.sub.2O.sub.3 or Si.sub.2Ni.sub.3) and cooperates with the armature element 11 such that it can close the passage 6 of the seat plate. If the armature element 11 is attracted by the seat plate 1, the passage 6 of the seat plate 1 also opens and there is an outflow of highly compressed fuel so that the pressure in the control space drops and there is a rising of the nozzle needle 15 from its nozzle needle seat.

[0042] To achieve an electrical insulation of the seat plate with respect to the armature element 11 that is as a rule placed onto the passage 6 of the seat plate 1, an insulating seat part 4 is now provided between the armature element 11 and the seat plate. This, as a rule, cylindrical element can have rounded edges and has to be inspected for freedom from cracks caused by the dynamically bearing load. It is furthermore of advantage if it is manufactured by hot isostatic pressing.

[0043] It is of particular advantage for the seat part if it is produced from ceramic material since ceramic material has excellent wear resistance and is in particular also durable with respect to the abrasive effect of solid particles present in the fuel. Fuel thus flows at high speed at the lower side of the seat part 4 if the injector is in its open position.

[0044] The seat part 4 insulates the seat plate 1 electrically with respect to the armature element 11 and the armature guide or the injector casing.

[0045] A seat plate support 5 that separates the seat plate 1 at its side facing the armature element 11 from the armature guide or the injector casing 14 is shown as a further ceramic and/or plastic part.

[0046] It also applies here due to the pulsating compressive strain that the seat plate support is advantageously of ceramic material. Ceramic material also remains in a stable shape under a high pressure load so that deformation changing the armature stroke setting cannot occur.

[0047] The seat plate support 5 is advantageously in a ring that has an inner diameter that is larger than the outer diameter of the seat part 4. Finally, both ceramic and/or plastic parts 4, 5 contact the areal side of the seat plate 1 facing the armature element 11.

[0048] FIG. 3 is a magnified representation of FIG. 2 from which the ceramic and/or plastic parts can be particularly easily recognized.