Means for Improving the Opening Response of a Solenoid Operated Fuel Valve

The invention relates generally to solenoid operated fluid valves and is herein specifically disclosed as an improvement in a valve for the high-pressure, direct injection of a volatile fuel such as gasoline into a two-stroke internal combustion engine.

The ability of a fuel injector to respond to an input signal's command to open is a significant factor in the fuel injector's ability to deliver a precise injection of fuel to a combustion chamber. Parameters that define the fuel injector's magnetic circuit (e.g., the stator, the armature, and the working gap between the stator and the armature) are of particular importance since it is this magnetic circuit that conducts the magnetic flux that exerts the magnetic force which acts on the armature. The rate at which the magnetic flux builds determines the rate at which force acting on the armature builds. The faster the force builds, the faster the fuel injector opens.

While it is recognized that magnetic flux cannot be built instantaneously, it has been conventional practice to use various fuel injector driver circuits that seek to maximize the building of electric current in the solenoid's coil in the expectation that this will necessarily also maximize the rate at which magnetic flux is built in the magnetic circuit, and as a consequence also minimize the fuel injector's opening time.

It has now been discovered that the transient building of magnetic flux does not occur uniformly over the transverse cross sectional area of the magnetically conductive material (i.e. the stator and armature) in the valve's magnetic circuit. Rather, flux must build first in the magnetically conductive material's "skin" before it can build in the interior of the material's cross section. This phenomenon is a physical characteristic of the magnetic circuit material and is in the nature of a time constant (albeit a small one) that delays the propagation of flux into the interior of the cross section. For convenience it will be referred to herein as the flux propagation delay characteristic. Consequently, for a given magnetic circuit structure, the building of flux at any given point within a transverse cross section of the structure in response to the building of current in the coil, is a transient phenomenon that is a function of the input current to the coil as a function of time and the particular location of that point within the cross section. The flux propagation delay characteristic is an inherent constraint on the ability of a magnetic circuit to build flux, irrespective of the ability of a driver circuit to build electric current in the solenoid's coil, so that minimizing the coil current build time is not necessarily conclusive of maximizing the building of magnetic flux during such a transient. Magnetic saturation too is an inherent physical characteristic of the magnetic material in the magnetic circuit that comes into play.

Stating the foregoing in a different way, it may be said that certain rates of current build during the transient building of magnetic force which, in the absence of the flux propagation delay characteristic, would be effective to build a uniform flux density over the transverse cross sectional area of the magnetically conductive material within a certain time, will instead within a like period of time when the flux propagation delay characteristic is taken into account, result in a magnetic flux pattern over a given transverse cross sectional area of the magnetically conductive material that is non-uniform; and if the coil is driven sufficiently hard during the transient, the pattern will, on account of magnetic saturation, consist of a magnetically saturated skin and a flux-poor interior wherein the total magnetic flux that is less than that which would be created in the absence of the flux propagation delay characteristic.

Force that builds as a transient during the time that the coil current is building and domains of the magnetically conductive material are becoming magnetized is a significant contribution toward opening the fuel injector. While a final steady state force (short of saturation) is a function of the cross-sectional area of the magnetically conductive material, the transient force has been found to be a function of the length of the magnetically conductive material's skin, as measured around the perimeter of its transverse cross-sectional area. While there is no precise definition for the skin, it is typically quite thin, for example only a few microns. Since the transverse cross sectional area of this "skin" is small, it is apt to saturate before the flux can propagate more interiorly of the cross section. Thus, full advantage of the total cross-sectional area of the magnetically conductive material cannot be taken during this transient condition, and hence the building of the transient force is constrained.

Where a fuel injector must comply with a specified opening force requirement, and certain dimensional constraints are also imposed on the size of the fuel injector, it may not always be possible to realize a solution with known technology. Accordingly, it is desirable to improve the probability of obtaining a solution, and it is toward this objective that the present invention is directed. Principles of the present invention endow a fuel injector with the ability to comply with a specified opening force requirement within an equal or smaller package size than heretofore possible with a solenoid-operated device. Moreover, principles can be incorporated through the use of conventional manufacturing procedures.

Another effect that is detrimental to the building of magnetic force is the phenomenon of eddy currents. Changing current in the solenoid's coil creates such currents in the magnetically conductive material and slows the opening of the fuel injector. Accordingly, it also would be beneficial if the solution that is afforded by the present invention were to also attenuate such eddy currents, and that can in fact be accomplished in the implementation of the invention.

Briefly, a presently preferred embodiment of the present invention is disclosed herein as a fuel injector valve having a novel magnetic circuit.

The magnetic circuit comprises a stator, an armature, and a working gap. Generally speaking, the invention comprises means for increasing the amount of magnetic material "skin" without a corresponding increase in package size. The increase in the amount of such skin is accomplished by inclusion of sets of slots in the magnetic material. The magnetic material also includes means for altering the circulation path for the eddy currents in a manner that is intended to attenuate their interference with building transient magnetic force.

In the disclosed preferred embodiment, the invention includes a stator having inner and outer cylindrical pole members extending from a circular annular end wall and forming a tubular space into which is disposed an electrically actuated solenoid coil for generating a magnetic field operative to displace the armature and open the fuel injector. The magnetic circuit of the preferred embodiment thus includes two parallel annular working gaps disposed between the armature and the free ends of the inner and outer pole members. Means for increasing the amount of stator skin without increasing its package size comprises slots running along the pole members, although broad principles of the invention contemplate that slots may be disposed along any portion of the magnetic circuit that conducts the flux that passes across the magnetic gap.

Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds.

The invention may be better understood and further advantages and uses thereof more readily apparent, when considered in view of the following detailed description of exemplary embodiments, taken with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a fuel injector valve constructed according to the teachings of the invention;

FIG. 2 is a bottom view of the solenoid stator of FIG. 1 showing longitudinal grooves on the ID and OD of the outer cylindrical pole member;

FIG. 3 is a front elevational view of the solenoid stator of FIG. 2 showing the outer grooves disposed in the OD of the outer cylindrical pole member;

FIG. 4 is a cross-sectional view of the solenoid and armature disk of the invention taken in the direction of sectional arrows 4--4 of FIG. 2; and

FIG. 5 is a bottom view of a solenoid stator of another embodiment of the invention.

FIG. 6 is a top view of an armature disk.

Referring now to the drawings and to FIG. 1 in particular, there is shown a cross-sectional side view of fuel injector valve 10 constructed according to the teachings of the invention. Valve 10 includes cylindrical housing 12 containing valve seat 14 circumscribing outlet port 16, armature assembly 18 and electrically actuated solenoid 20. Armature assembly 18 includes armature disk 22, valve stem 24 and valve needle 26. Valve needle 26 fits contiguous with valve seat 14 and is biased to block outlet port 16 by return spring 32 which is disposed in return spring bore 34 between spacer block 36 and tension adjustment mechanism 38. Solenoid 20 includes stator 40, electrical terminals 42 adapted for connection to an outside power source (not shown), which pass through a pair of mating apertures 44 disposed through stator end wall 56 and coil 48, which, when electrical terminals 42 are connected to the outside power source, generates a magnetic field operative to overcome the bias of return spring 32 and displace armature assembly 18 upward from valve seat 14, thereby allowing passage of fuel through fluid flow passages 28 and outlet port 16. Other portions of the fuel injection system (not shown) provide a regulated fuel supply to fluid inlet ports 30 which are adapted for sealed connection to the fuel injection system.

When an energizing signal, such as a rectangular voltage pulse is applied to solenoid 20, the electric current executes a transient build-up. This will give rise to a transient build-up of magnetic force. This may saturate the stator skin before the flux can propagate inwardly due to the flux propagation delay characteristic mentioned above and eddy currents which resist the force build-up magnetization will be generated. Conversely, when solenoid 20 is de-energized, the decreasing coil current transient generates eddy currents in the magnetic circuit which resist demagnetization of the magnetic circuit, and this may affect injector closing.

A magnetic circuit having means to increase the amount of stator "skin" in the magnetic circuit without increasing the stator's physical size is an object of the present invention and is shown in FIGS. 2, 3 and 4. Constructed according to the principles of the invention magnetic circuit 50 includes armature disk 22, stator 40 having inner cylindrical pole 52 and outer cylindrical pole 54 disposed on end wall 56, and inner and outer magnetic working gaps 62 and 64, respectively. When solenoid 20 is energized, magnetic flux lines drawn in phantom at 66 are generated at the surface skin of magnetic circuit 50 (the domains of magnetic circuit 50 are magnetized from the outside surface in toward the interior).

Both inner cylindrical pole 52 and outer cylindrical pole 54 have fixed diameters and in order to increase the amount of stator skin of magnetic circuit 50 without increasing the stator's overall physical size, outer cylindrical pole 54 has slots 70 disposed in its ID surface/wall 72, thereby increasing the surface area of outer pole 54's ID surface/wall 72 by slot sidewalls 74. Consequently, flux lines 66 now have a much larger amount of skin through which to pass during the transient and thus provide effectively larger amounts of lines of flux 66 in outer magnetic gap 64 where these increased lines of flux are converted into increased magnetic force on armature disk 22 during the time a transient current is increasing in solenoid coil 48. The OD wall 78 of outer pole 54 is press fit or otherwise disposed snugly into housing 12 of injector valve 10. Only ID surface/wall 72, slot sidewalls 74 and slot bottoms 76 are exposed to outer magnetic gap 64 where the increased amount of skin and consequent flux line capacity can be converted into magnetic force across outer gap 64.

The OD surface/wall 78 of outer pole 54 may be slotted to increase the resistivity of magnetic circuit 50 because the slots also have some effect on eddy currents in the magnetic circuit 50. Referring again now to FIG. 2, with no material between the ribs 82 that remain after the slots 70 have been cut, eddy currents are limited to within the material of the rib 82, and flowing in the web 84 that is left at the bottom of the slots. The path in the web can be further restricted if outer diameter slots 86 are cut at a radial spacing that intersperses them between the inner diameter slots 70. This pattern of alternating inner and outer slots 70, 86 respectively makes the path for the eddy currents (shown in phantom at 88) more tortuous than in an unslotted stator.

Slots 70 are disposed on the interior wall (ID) of outer pole 54, but they could be disposed on the surface of either inner pole 52, outer pole 54, armature 22, or endwall 56, i.e., anywhere on a surface of magnetic circuit 50 that is exposed to the magnetic field generated when coil 48 is energized and where the generated flux lines pass through the magnetic gap(s) such as inner and outer gaps 62 and 64, respectively, such as, for instance, where the flux lines 66 are drawn in phantom in FIG. 4. FIGS. 2 and 4 show axial slots 86 and 70 on the O.D. and I.D. respectively of inner pole 52, and radial slots 87 on the inside of end wall 56.

Referring now to FIG. 5 there is shown a bottom view of a solenoid stator of another embodiment of the invention wherein now both the inner and outer poles 92 and 94 respectively have convoluted or corrugated surfaces 96 and 98 respectively so as to provide increased skin area without increasing the package size of the stator. Surfaces 96, 98 are another means for increasing the skin area just as slots 70 did in FIGS. 3,4 and 5. Please note that as discussed above both outer and inner surfaces 96, 98 of both inner and outer poles 92, 94, respectfully, are convoluted because the increased surface area of the magnetic circuit is useful whenever the enhanced flux lines pass through one or more magnetic gaps. Please also note that when increasing skin area as shown by the use of slots 70, 86 in FIG. 3 or by walls 96, 98 in FIG. 5, that the increase in surface area causes a reduction in the cross-sectional area of the poles for the steady state magnetic circuit. Since the inclusion of slots for increasing the amount of skin reduces the cross-sectional area for steady-state flux, the size and number of slots should be minimized to that necessary to create the desired transient magnetic force across the magnetic gap(s) of the magnetic circuit. In many instances however, cross-sectional areas of the magnetic circuit are typically large enough that the steady state flux does not approach saturation even with the reduced cross-sectional area due to the increased skin area. FIG. 6 shows armature disk 22 containing radial slots 100 in its upper face, similar to radial slots 87 in the stator end wall.

In conclusion what has been disclosed is a novel fuel injection valve having a magnetic circuit that develops high-transient force quickly, dissipates less energy than its solid counterpart, is mechanically equivalent in the solenoid assembly, and is no more costly to manufacture because the slots can be incorporated by ribbed or convoluted surfaces made in a powdered metal or metal injection molding process.

While a preferred embodiment of the invention has been disclosed, various modes of carrying out the principles disclosed herein are contemplated as being within the scope of the following claims. Therefore, it is understood that the scope of the invention is not to be limited except as otherwise set forth in the claims.