FUEL INJECTOR, METHOD FOR ASCERTAINING THE POSITION OF A MOVABLE ARMATURE, AND MOTOR CONTROL

Abstract

A fuel injector for an internal combustion engine of a motor vehicle. The fuel injector including the following: (a) a pole piece, (b) an armature which can be moved along a movement axis, (c) a coil and (d) a permanent magnet, wherein the movable armature has at least one electrically insulating element which is designed to reduce eddy currents in the armature, and wherein the permanent magnet is fitted such that it generates a magnetic field which produces a force which acts on the armature in the direction of the pole piece. The invention also describes a method for ascertaining a position of a movable armature in a fuel injector and also an engine controller.

Claims

1. A fuel injector for an internal combustion engine of a motor vehicle, the fuel injector comprising: a pole piece; an armature which may be moved along a movement axis; a coil; and a permanent magnet; at least one electrically insulating element, the movable armature having the at least one electrically insulating element, which is designed to reduce eddy currents in the armature; and wherein the permanent magnet is fitted such that the permanent magnet generates a magnetic field which produces a force which acts on the armature in the direction of the pole piece.

2. The fuel injector of claim 1, the at least one electrically insulating element further comprising a slot which is filled with at least one of air, an electrically insulating material, or a non-magnetic material.

3. The fuel injector of claim 1, wherein the armature is formed from two or more sheet metal parts which are substantially insulated from one another by the at least one electrically insulating element.

4. The fuel injector of claim 1, wherein the at least one electrically insulating element extends radially relative to the movement axis of the armature.

5. The fuel injector of claim 1, wherein the permanent magnet is fitted onto the coil subsequently in the direction of the movement axis of the armature.

6. The fuel injector of claim 1, wherein the permanent magnet is subsequently fitted radially toward the outside of the coil relative to the movement axis of the armature.

7. The fuel injector of claim 1, further comprising a coil housing which contains the permanent magnet.

8. The fuel injector of claim 7, wherein the coil housing has at least one electrically insulating element which is designed to reduce eddy currents in the coil housing.

9. The fuel injector of claim 7, the coil housing further comprising a material which generates few eddy currents.

10. The fuel injector of claim 1, the armature further comprising a material which generates few eddy currents.

11. The fuel injector of claim 1, the pole piece further comprising a material which generates few eddy currents.

12. The fuel injector of claim 1, wherein the pole piece has at least one electrically insulating element which is designed to reduce eddy currents in the pole piece.

13. A method for ascertaining a position of a movable armature in a fuel injector for an internal combustion engine of a motor vehicle, wherein the fuel injector has a coil, the armature has at least one electrically insulating element which is designed to reduce eddy currents, and the fuel injector has a permanent magnet which is fitted such that it generates a magnetic field which produces a force which acts on the armature in the direction of a pole piece the method comprising the steps of: detecting the time profile of the electrical voltage across the coil; analyzing the detected time profile of the electrical voltage in order to identify an induced voltage which is induced, in particular, on account of the armature movement and the magnetic field, which is generated by the permanent magnet, in the coil, and determining the armature position based on the induced voltage.

14. The method as claimed in claim 13, comprising the further steps of: supplying an operating current to the coil in order to move the armature from a closed position, in the direction of the pole piece, to an open position for the purpose of injecting fuel; disconnecting the operating current in order to initiate a closing process during which the armature returns from the open position to the closed position, wherein the time profile of the electrical voltage across the coil is detected during the closing process.

15. The method of claim 13, further comprising the steps of: providing an engine controller for a vehicle, wherein the engine controller performs the steps of detecting the time profile, analyzing the detected time profile, and determining the armature position.

16. A method for ascertaining a position of a movable armature in a fuel injector for an internal combustion engine of a motor vehicle, wherein the fuel injector has a coil, the armature has at least one electrically insulating element which is designed to reduce eddy currents, and the fuel injector has a permanent magnet which is fitted such that it generates a magnetic field which produces a force which acts on the armature in the direction of a pole piece, the method comprising the steps of: detecting the time profile of the electric current intensity through the coil; analyzing the detected time profile of the current intensity in order to identify an induced current which is induced, in particular, on account of the armature movement and the magnetic field, which is generated by the permanent magnet, in the coil; and determining the armature position based on the induced current.

17. The method as claimed in claim 16, comprising the further steps of: supplying an operating current to the coil in order to move the armature from a closed position, in the direction of the pole piece, to an open position for the purpose of injecting fuel; disconnecting the operating current in order to initiate a closing process during which the armature returns from the open position to the closed position, wherein the time profile of the electric current intensity through the coil is detected during the closing process.

18. The method of claim 16, further comprising the steps of: providing an engine controller for a vehicle, wherein the engine controller performs the steps of detecting the time profile, analyzing the detected time profile, and determining the armature position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further advantages and features of the present invention can be found in the exemplary description of a preferred embodiment which follows.

[0048] FIG. 1 shows a fuel injector according to the prior art.

[0049] FIG. 2 shows a fuel injector according to one embodiment of the invention.

[0050] FIG. 3 shows a fuel injector according to a further embodiment of the invention.

[0051] FIGS. 4A and 4B show designs of an armature for a fuel injector according to embodiments of the invention.

[0052] FIG. 5 shows a graphical illustration of the time profiles of coil voltage and armature position during actuation of a fuel injector according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0054] It should be noted that the embodiments described below are merely a limited selection of possible variant embodiments of the invention. Identical or similar elements or elements which act in an identical manner are provided with the same reference numerals throughout the figures. In some figures, individual reference symbols can be omitted in order to improve clarity. The figures and the size ratios of the elements illustrated in the figures with respect to one another are not to be considered to be true to scale. Instead, individual elements can be illustrated with an exaggerated size for better illustration and/or for better understanding.

[0055] FIG. 1 shows a fuel injector 1 according to the prior art. The known fuel injector 1 with an idle stroke has, as described in the introductory part, a pole piece 2, a movable armature 3, a coil 4, a nozzle needle 5, a spring 6 and a coil housing 7. In order to avoid repetition, the known fuel injector 1 will not be described any further at this point.

[0056] FIG. 2 shows a fuel injector 200 according to one embodiment of the invention. In principle, the fuel injector 200 is constructed in the same way as the known fuel injector 1 in FIG. 1 but, as will be explained further in the text which follows, differs from said known fuel injector in at least two aspects.

[0057] The fuel injector 200 with an idle stroke has, more specifically, a pole piece 202, an armature 204 which can be moved along a movement axis 205, a coil 206, a permanent magnet 208, a coil housing 210, a nozzle needle 212 and a spring 214. The permanent magnet 208 is fitted to the outside of the coil 206 in the coil housing 210 and is magnetized in a direction which is parallel to the movement axis 205 of the armature 204, with the result that a magnetic field, which is identified by the dashed line 216, is permanently present. The magnetic field 216 provides a force onto the armature 204, which force acts in the direction of the pole piece 202, that is to say parallel to the movement axis 205. This represents a first difference in comparison to the known fuel injector 1 in FIG. 1. A further difference is that the armature 204 has at least one electrically insulating element in order to reduce eddy currents in the armature 204. The at least one electrically insulating element is not shown in FIG. 2, but will be described below in conjunction with FIGS. 4A and 4B. Furthermore, the armature can be constructed from a special material, for example from a soft-magnetic composite material such as Somaloy, which generates few eddy currents.

[0058] The reduction in eddy currents leads to an improved degree of energy efficiency on account of the correspondingly reduced losses, with the result that the requisite magnetic force can be reached with a lower current intensity in the coil 206. Consequently, the opening process can also be completed correspondingly more quickly. Said opening process is additionally assisted by the magnetic field 216 which is permanently present, since said magnetic field provides a force offset. If an increase in the closing speed is desired, the spring force of the spring 214 can be increased in comparison to the spring 6 in the known fuel injector 1. Furthermore, the magnetic field 216 which is permanently present leads to a voltage being induced in the coil 206 when the armature 204 and/or the needle 212 move. The state of the fuel injector 200 in relation to the opening and closing process can be detected, that is to say the position of the armature 204 can be ascertained, by evaluating this induced voltage or the corresponding current. In particular, the opening process can be best detected by evaluating the induced current.

[0059] FIG. 3 shows a fuel injector 300 according to a further embodiment of the invention. The fuel injector 300 differs from the fuel injector 200 shown in FIG. 2 and described above only in that the permanent magnet 308 is not fitted to the outside, but rather to the top side, of the coil 306. The permanent magnet 308 is magnetized in a direction which is perpendicular to the movement axis 305 of the armature 304, with the result that a magnetic field, which is identified by the dashed line 316, is permanently present in this embodiment too. In a further embodiment, not shown, the permanent magnet 308 is fitted on the bottom side of the coil 306.

[0060] FIGS. 4A and 4B show designs of an armature 404a, 404b for a fuel injector according to embodiments of the invention. More specifically, the armature 404a in FIG. 4A has a total of eight electrically insulating elements 420 which extend radially outward relative to the movement axis 405 and therefore effectively interrupt possible eddy current paths in the armature 405. The electrically insulating elements 420 are shown as slots in the armature 404a in FIG. 4A, but can equally be in the form of insulating layers. In this case, the armature can be of modular or laminated construction. Less than or more than eight elements 420 can be provided. The slots 420 can be empty, that is to say filled with air, or, as is shown in FIG. 4B, they can be entirely or partially filled with an insulating and/or non-magnetic material 422, for example plastic, for example in order to influence the hydraulic properties of the armature 404b. The armature 404a, as 404b, can be produced from a material (for example a soft-magnetic composite material such as Somaloy) which has the property of generating few eddy currents.

[0061] In the fuel injectors 200 and 300 described above with reference to FIGS. 2 and 3, electrically insulating elements can furthermore be provided in the pole piece 202, 302 in order to reduce eddy currents in the pole piece 202, 302 too and therefore to further improve efficiency and dynamics. Furthermore, electrically insulating elements can also be provided in the coil housing 210, 310 in order to reduce eddy currents in the coil housing 210, 310 and therefore to improve efficiency and dynamics even further. Insulating elements of this kind can be constructed, for example, in the same way as the elements 420 just described with reference to FIGS. 4A and 4B. Furthermore, the pole piece 202, 302 and the coil housing 210, 310 can also comprise an eddy current-reducing material, such as Somaloy for example.

[0062] FIG. 5 shows a graphical illustration 500 of the time profiles of the voltage 502 induced in the coil 206, 306 and of the armature position 504 during an injection process of a fuel injector according to the invention, for example the fuel injector 200 or 300. Actuation is initiated with a voltage pulse (boost voltage) which quickly builds up an operating current through the coil 206, 306, said operating current magnetizing the coil 206, 306, with the result that the armature 204, 304 is moved from a closed position, in the direction of the pole piece 202, 302, to an open position. After the idle stroke has been overcome, the nozzle needle 212, 312 is carried along by the armature 204, 304 and is likewise moved in the direction of the pole piece 202, 302. Once the open position is reachedin the present exemplary embodiment at approximately t=0.25 msthe armature 204, 304 is held at a stop against the pole piece 202, 302 by a holding voltage which is reduced in relation to the boost voltage. In this state, the voltage induced in the coil 206, 306 drops and disappears if the operating voltage does not change and the armature 204, 304 does not move.

[0063] The closing process is initiated, for example, by disconnecting the holding voltagein the present exemplary embodiment at time t=0.5 ms. The resulting reduction in the electromagnetic field generates, for example, the rectangular profile of the induction voltage, shown between t=0.5 ms and t=0.6 ms in FIG. 5, in the coil 206, 306. After at least partial reduction of the electromagnetic field, the armature and the nozzle needle movein the present case starting from t=0.6 msmove away from the pole piece 202, 302 again in a manner driven by the spring force of the spring 214, 314. Owing to this movement and the permanent magnet, a voltage, which can be clearly seen in curve section 506, is induced in spite of the eddy current which is greatly reduced by means of the slots 420 in the armature 204, 304, it being possible to use said voltage to detect the start and the end of the closing movement in a manner which is known per se. Although this is not clearly shown in FIG. 5, a detectable voltage and corresponding current are also induced during the opening movement, with the result that the start and the end of this movement can also be detected, in the best way by evaluating the current.

[0064] Overall, the present invention provides an improved fuel injector which has an improved degree of energy efficiency in comparison to known fuel injectors and also has improved properties in respect of movement detection.

[0065] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.