Fuel injection valve

In a fuel injector a valve-closure member movable axially along a valve longitudinal axis and a valve-seat body are provided for opening and closing the valve. Allocated to the valve-seat body is a valve-seat face which cooperates with the valve-closure member. In this context, the valve-closure member is joined to the valve-seat body via a spring element designed in the form of a diaphragm spring. The spring element is arranged in such a manner that it pulls the valve-closure member toward the valve-seat face as a return spring in response to closing of the valve. The fuel injector is particularly suitable for use in fuel-injection systems of mixture-compressing internal combustion engines with externally supplied ignition.

BACKGROUND OF THE INVENTION
 German Patent No. 40 03 227 describes a fuel injector which, as a valve
 which can be actuated electromagnetically, is provided with a magnetic
 circuit and a seat valve. In this valve, a fuel filter intended to keep
 dirt particles away from the seat region is pressed into a core at its
 feed end, the core serving as a fuel inlet connection. Moreover, an
 adjusting sleeve and a helical return spring are also arranged in the
 longitudinal opening of the core. The pressed-in adjusting sleeve is used
 to adjust the spring bias of the return spring engaged on it which is
 braced against the valve needle with its downstream end, pressing the
 valve-closure member against a valve seat in the closing direction of the
 valve when the magnetic coil is not excited. Thus, several component parts
 are fastened in the fuel inlet connection, possibly in a chip-forming
 manner.
 Moreover, it is known from German Patent No. 41 40 070, German Patent No.
 196 38 201, or from PCT Patent Publication No. WO 93/18299 to arrange
 filter elements in fuel injectors near the valve seat.
 SUMMARY OF THE INVENTION
 The fuel injector according to the present invention has the advantage that
 it can have a particularly small and compact design. To that end,
 according to the present invention, a spring element joins the
 valve-closure member to the valve-seat body.
 By using such a spring element, it is possible to substitute a return
 spring which is arranged in the fuel inlet connection in known fuel
 injectors and always requires an additional adjusting element, both
 component parts together mostly being responsible for a longer design of
 the fuel injector. Besides, the outlay of component parts can be reduced
 in this manner.
 It is an additional advantage that there is no need to provide an exact
 guide opening in the valve-seat body for guiding the valve needle or the
 valve-closure member during its axial motion since the valve-closure
 member is guided and pulled exactly into the valve-seat body by the spring
 element.
 It is particularly advantageous for the spring element to be designed as a
 diaphragm spring having the form of a sleeve as well as two fastening
 regions partially enclosing the valve-closure member and the valve-seat
 body.
 Also, it is particularly beneficial for the spring element to be designed
 as a filter element at the same time. The diaphragm spring provided with a
 plurality of holes allows particles impairing the tightness of the valve
 to be filtered out from the fuel near the valve seat. By using such a
 diaphragm spring having spring and filter functions, it is possible to
 substitute both a fuel filter arranged in the fuel inlet connection in
 known fuel injectors and the return spring as well as the adjusting sleeve
 mostly following downstream in the fuel inlet connection or core so that
 the outlay of component parts can be reduced even more markedly.

DETAILED DESCRIPTION
 FIG. 1 shows a partial representation of a fuel injector for fuel-injection
 systems of mixture-compressing internal combustion engines with externally
 supplied ignition. The fuel injector has a tubular valve-seat support 1 in
 which a longitudinal opening 3 is provided concentrically to a valve
 longitudinal axis 2. Arranged in longitudinal opening 3 is, for example, a
 tubular valve needle 5 which is joined to a spherical valve-closure member
 7 at its downstream end 6.
 The fuel injector is actuated in known manner, for example,
 electromagnetically. For axially moving valve needle 5 and, consequently,
 for opening the fuel injector against the spring force of a spring element
 9 acting upon valve-closure member 7 and serving as return spring, and for
 closing the fuel injector, respectively, a sketched electromagnetic
 circuit having a magnetic coil 10, an armature 11, and a core 12 is used.
 Armature 11 is joined to the end of valve needle 5 facing away from
 valve-closure member 7 by, for example, a weld with the assistance of a
 laser, and aligned to core 12.
 In the downstream end of valve-seat support 1 facing away from core 11, a
 valve-seat body 16 is mounted in longitudinal opening 3 running
 concentrically to valve longitudinal axis 2 by welding, forming a seal. At
 the outer circumference, valve-seat body 16 has, for example, a stepped
 design, the circumference of valve-seat body 16, at its lower end, having
 a diameter which is only slightly smaller than that of longitudinal
 opening 3 of valve-seat support 1. At its one, lower end face 17 facing
 away from valve-closure member 7, valve-seat body 16 is joined to a base
 part 20, for example, a pot-shaped spray-orifice plate 21, concentrically
 and fixedly so that base part 20 engages on lower end face 17 of
 valve-seat body 16 with its upper end face 22. In its central region 24,
 base part 20 of spray-orifice plate 21 has at least one, for example, four
 spray orifices 25 formed by erosive machining or punching. Joining up
 contiguously to base part 20 is a circular retention rim 26 extending in
 an axial direction, facing away from valve-seat body 16 and curved outward
 slightly conically.
 The preadjustment of the lift of valve needle 5 is determined by the
 insertion depth of the valve-seat part composed of valve-seat body 16 and
 pot-shaped spray-orifice plate 21 into longitudinal opening 3 since one
 end position of valve needle 5 is determined by the engagement of
 valve-closure member 7 on a valve-seat face 29 of valve-seat body 16 when
 magnetic coil 10 is not excited. Spherical valve-closure member 7
 cooperates with valve-seat face 29 of valve-seat body 16 as a seat valve,
 valve-seat face 29 frustoconically tapering in the direction of flow. The
 other end position of valve needle 5 is determined, for example, by the
 engagement of armature 11 on core 12 when magnetic coil 10 is excited.
 Thus, the path between these two end positions of valve needle 5
 represents the lift.
 In the region of retention rim 26, spray-orifice plate 21 and,
 consequently, the entire valve-seat part is fixedly joined to the wall of
 longitudinal opening 3, forming a seal. A tight connection of valve-seat
 body 16 and spray-orifice plate 21 as well as of spray-orifice plate 21
 and valve-seat support 1 is required to prevent the fuel from flowing
 between longitudinal opening 3 of valve-seat support 1 and the
 circumference of valve-seat body 16 to spray orifices 25, or between
 longitudinal opening 3 of valve-seat support 1 and retention rim 26 of
 spray-orifice plate 21 directly into an intake line of the internal
 combustion engine.
 Spring element 9 is designed preferably as a diaphragm spring. Diaphragm
 spring 9, which is designed as a sleeve-shaped body, extends between
 valve-closure member 7 and valve-seat body 16. FIG. 2 shows a diaphragm
 spring 9 as a separate component part on an enlarged scale so that the
 construction becomes clear. The diaphragm spring fulfills various
 functions in the fuel injector, on one hand by acting as a return spring
 pulling valve-closure member 7 toward valve-seat face 29 when magnetic
 coil 10 is in its non-excited state and, on the other hand, by acting as a
 filter element, as well. To this end, a plurality of holes 32 are made in
 a flat raw material (for example, a rolled sheet metal) in a first
 manufacturing step, for example, by punching, erosive machining or laser
 boring, for obtaining diaphragm spring 9 according to the present
 invention. Only subsequently, this flat raw material is brought into a
 closed sleeve form using appropriate stamping or indenting tools, and a
 desired spring configuration 33 is molded in the form of a pleating, for
 example, by pressing. Suited to the magnetic circuit quantities, spring
 configuration 33 is molded in in such a manner that, when magnetic coil 10
 is excited, the spring force is easily overcome by the attractive force
 acting upon valve-closure member 7, and that the valve closes quickly when
 magnetic coil 10 is de-energized.
 Spring configuration 33 is molded in, for example, an axially middle region
 of diaphragm spring 9, the region extending in the downstream direction,
 widening frustoconically. Fastening regions 34, 35 adjoin this middle
 spring region contiguously on both sides, first fastening region 34 having
 a markedly smaller diameter than second fastening region 35. Diaphragm
 spring 9 encloses valve-closure member 7 with first fastening region 34,
 whereas second fastening region 35 surrounds valve-seat body 16 at the
 outer circumference at least partially. Both fastening regions 34, 35 of
 diaphragm spring 9 are fixedly joined to valve-closure member 7 and
 valve-seat body 16, respectively, by a first and a second annular weld 36,
 37, respectively, obtained by laser welding or several welding spots
 placed over the circumference. Second fastening region 35 is designed, for
 example, cylindrically by bending the frustoconical contour of diaphragm
 spring 9. In this manner, the fastening to valve-seat body 16 is made
 easier.
 As shown in FIG. 3, it is also conceivable for diaphragm spring 9 to be
 designed completely with a frustoconical contour so that both fastening
 regions 34, 35 are disposed in one line. To this end, valve-seat body 16
 has an at least partially conical outer circumference on which second
 fastening region 35 engages.
 Diaphragm spring 9 provided with a plurality of holes 32 allows particles
 impairing the tightness of the valve to be filtered out from the fuel near
 valve seat 16, 29. The at least 100 or even markedly more holes 32 have a
 diameter which should not be greater than 50 to 60 .mu.m to be able to
 ensure the filter function without limitation. By using such a diaphragm
 spring 9 having spring and filter functions, it is possible to substitute
 both a fuel filter arranged in the fuel inlet connection in known fuel
 injectors and a return spring mostly following downstream in the fuel
 inlet connection or core so that the outlay of component parts is reduced
 markedly in the present invention.
 It is a further advantage that there is no need to provide an exact guide
 opening in valve-seat body 16 for guiding valve needle 5 or valve-closure
 member 7 during its axial motion since valve-closure member 7 is guided
 and pulled exactly into the valve-seat body 16 by spring element 9.
 The dynamic spray quantity is adjusted, for example, in such a manner that,
 first, diaphragm spring 9 is fastened to valve needle 5 and especially to
 valve-closure member 7 (weld 36). The valve-seat part, together with valve
 needle 5 and/or armature 11 and diaphragm spring 9 fastened thereto, is
 brought in an adjusting station and, for the moment, is treated there
 separately as a valve subassembly. A test valve head subsequently picks up
 this valve subassembly, the lower end of diaphragm spring 9 being held
 fast. Then, the valve-seat part is inserted into diaphragm spring 9 from
 the bottom in the axial direction, for example, by a stepping motor, the
 valve being excited and the dynamic spray quantity being measured at the
 same time. Diaphragm spring 9 can be fastened to valve-seat body 16 by
 second weld 37 as soon as the desired spray quantity is reached.