Multipart insulating element, in particular for a fuel injection device

Abstract

An insulating element for a fuel injection apparatus is notable in particular for the fact that a low-noise design is achieved. The fuel injection apparatus encompasses at least one fuel injection valve and one receiving bore in a cylinder head for the fuel injection valve, and the insulating element between a valve housing of the fuel injection valve and a wall of the receiving bore. The insulating element possesses an inner insulating ring that is present in encapsulated fashion between an outer ring and an inner ring. The outer ring is directed toward the fuel injection valve and the inner ring is directed toward the wall of the receiving bore, so that corresponding abutment of these components occurs with the insulating element in the installed state. The fuel injection apparatus is suitable in particular for direct injection of fuel into a combustion chamber of a mixture-compressing spark-ignited internal combustion engine.

Claims

1. A multi-part insulating element for a fuel injection apparatus for a fuel injection system of an internal combustion engine for direct injection of fuel into a combustion chamber, the fuel injection apparatus comprising: at least one fuel injection valve and one receiving bore for the fuel injection valve; and an insulating element introduced between a valve housing of the fuel injection valve and a wall of the receiving bore, the insulating element including an inner insulating ring that is circumferentially surrounded by an outer ring and an inner ring, the outer ring being directed toward the fuel injection valve and the inner ring being directed toward the wall of the receiving bore, wherein abutment of the outer ring and the fuel injection valve occurs with the insulating element, the inner ring, and the wall of the receiving bore in an installed state, wherein the outer ring is disposed on a top surface of the insulating ring, wherein the insulating ring is an annular braided, knitted, or woven wire element, wherein the inner ring includes a first side, wherein the outer ring includes a second side that faces the first side, wherein the annular braided, knitted, or woven wire element directly contacts the first side of the inner ring and directly contacts the second side of the outer ring, wherein an entire length of the first side directly contacts only a material of the annular braided, knitted, or woven wire element, and wherein an entire length of the second side directly contacts only the material of the annular braided, knitted, or woven wire element.

2. The insulating element as recited in claim 1, wherein the inner ring is embodied in thin-walled fashion and has an annular-disk-shaped surface on an inner side and a flat bracing surface on an underside.

3. The insulating element as recited in claim 2, wherein the inner side of the inner ring includes elastic elements.

4. The insulating element as recited in claim 3, wherein the elastic elements are spring clips.

5. The insulating element as recited in claim 1, wherein at least one weld seam placed for securing purposes is provided at least one of: i) between the outer ring and insulating ring, and ii) between the inner ring and insulating ring.

6. The insulating element as recited in claim 1, wherein the receiving bore for the fuel injection valve is in a cylinder head, and the receiving bore has a shoulder that proceeds perpendicularly to the extent of the receiving bore and abuts on the inner ring.

7. The insulating element as recited in claim 1, wherein the valve housing of the fuel injection valve is equipped, in an abutment region of the insulating element, with a conical outer contour against which the outer ring braces.

8. The insulating element as recited in claim 1, wherein: the outer ring has an annular-disk-shaped surface on an outer side, and an injector-side bracing surface on an upper side, the injector-side bracing surface of the upper side includes a curved, convexly bulging surface that in the installed state extends toward and contacts the fuel injection valve, and the curved, convexly bulging surface is a single, continuous arcuate surface.

9. The insulating element as recited in claim 1, wherein the outer ring has an annular-disk-shaped surface on an outer side that radially surrounds the inner insulating ring.

10. The insulating element as recited in claim 8, wherein the annular-disk-shaped surface on the outer side radially surrounds the inner insulating ring.

11. The insulating element as recited in claim 1, wherein the insulating ring has a square cross-section.

12. The insulating element as recited in claim 11, wherein: the first side and the second sides are planar surfaces, and the first side and the second side lie flush against respective planar surfaces of the insulating ring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplifying embodiments of the present invention are depicted in simplified fashion in the figures and described below.

(2) FIG. 1 shows a partly depicted fuel injection apparatus in a conventional embodiment, having a disk-shaped intermediate element.

(3) FIG. 2 is a mechanical equivalent diagram of the bracing of the fuel injection valve in the cylinder head in a context of direct fuel injection, the diagram reproducing a usual spring-mass damper system.

(4) FIG. 3 shows the transfer behavior of a spring-mass damper system shown in FIG. 2 with an intensification at low frequencies in the range of the resonant frequency f.sub.R and in an insulating region above the decoupling frequency f.sub.E.

(5) FIG. 4 shows a nonlinear progressive spring characteristic curve for implementing different stiffness values as a function of the working point, with a low stiffness S.sub.NVH at idle and a high stiffness at nominal system pressure F.sub.Sys.

(6) FIG. 5 is a partial cross section through a multi-part insulating element according to an example embodiment of the present invention that is usable in a fuel injection apparatus.

(7) FIG. 6 is a partial cross section through an example insulating element according to the present invention in an installed situation on a fuel injection valve in the region of the disk-shaped intermediate element shown in FIG. 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(8) A conventional embodiment of a fuel injection apparatus is described in more detail below with reference to FIG. 1 in order to elucidate the invention. FIG. 1 depicts in a side view, as an exemplifying embodiment, a valve in the form of an injection valve 1 for fuel injection systems of mixture-compressing spark-ignited internal combustion engines. Fuel injection valve 1 is part of the fuel injection apparatus. Fuel injection valve 1, which is embodied in the form of a direct-injecting injection valve for direct injection of fuel into a combustion chamber 25 of the internal combustion engine, is installed with a downstream end into a receiving bore 20 of a cylinder head 9. A sealing ring 2, made in particular of Teflon, ensures optimum sealing of fuel injection valve 1 with respect to the wall of receiving bore 20 of cylinder head 9.

(9) A flat intermediate element 24, which is embodied as a bracing element in the form of a backing disk, is placed between a setback 21 of a valve housing 22 and a shoulder 23, extending e.g. at right angles to the longitudinal extension of receiving bore 20, of receiving bore 20. An intermediate element 24 of this kind compensates for production and assembly tolerances and ensures mounting in a manner free of transverse forces even if fuel injection valve 1 is slightly oblique.

(10) Fuel injection valve 1 has at its inflow end 3 a plug connection to a fuel distribution line (fuel rail) 4 which is sealed by a sealing ring 5 between a connector fitting 6 of fuel distributor line 4, which is depicted in section, and an inlet fitting 7 of fuel injection valve 1. Fuel injection valve 1 is inserted into a receiving opening 12 of connector fitting 6 of fuel distribution line 4. Connector fitting 6 proceeds, e.g., integrally out of the actual fuel distributor line 4 and possesses, upstream from receiving opening 12, a smaller-diameter flow opening 15 through which flow occurs into fuel injection valve 1. Fuel injection valve 1 possesses an electrical connector plug 8 for electrical contacting in order to actuate fuel injection valve 1.

(11) A holddown 10 is provided between fuel injection valve 1 and connector fitting 6 in order to space fuel injection valve 1 and fuel distributor line 4 away from one another largely without radial forces, and to hold fuel injection valve 1 securely down in the receiving bore of the cylinder head. Holddown 10 is embodied as a bracket-shaped component, e.g., as a stamped and bent part. Holddown 10 has a partially annular base element 11 from which a holddown bracket 13, which in the installed state abuts against a downstream end surface 14 of connector fitting 6 on fuel distributor line 4, proceeds out in bent fashion.

(12) An object of the present invention is to achieve improved acoustic damping as compared with the conventional intermediate-element approaches in simple fashion by way of a targeted design and geometry of intermediate element 24, above all in the acoustically critical idle mode. The noise source of fuel injection valve 1 in a context of direct high-pressure injection is the forces introduced into cylinder head 9 during valve operation (solid-borne sound), which result in a structural excitation of cylinder head 9 and are radiated therefrom as airborne sound. In order to achieve an acoustic improvement, a minimization of the forces introduced into cylinder head 9 is therefore desirable. In addition to decreasing the forces caused by injection, this can be achieved by influencing the transfer behavior between fuel injection valve 1 and cylinder head 9.

(13) In mechanical terms, the mounting of fuel injection valve 1 on the passive intermediate element 24 in receiving bore 20 of cylinder head 9 can be represented as a usual spring-mass damper system, as depicted in FIG. 2. The mass M of cylinder head 9 can be assumed, to a first approximation, to be infinitely large as compared with the mass m of fuel injection valve 1. The transfer behavior of such a system is notable for an intensification at low frequencies in the region of the resonant frequency f.sub.R, and an insulating region above the decoupling frequency f.sub.E (see FIG. 3).

(14) An objective of the present invention is to provide an intermediate element 24 using principally elastic insulation (decoupling) to decrease noise, in particular with the vehicle at idle. The present invention encompasses on the one hand the definition and design of a suitable spring characteristic curve in consideration of typical requirements and boundary conditions in direct fuel injection with variable operating pressure, and on the other hand the design of an intermediate element 24 that is capable of reproducing the characteristics of the spring characteristic curve thus defined, and can be adapted, by the selection of simple geometric parameters, to the specific boundary conditions of the injection system.

(15) Decoupling of fuel injection valve 1 from cylinder head 9 with the aid of a low spring stiffness c of the multi-part insulating element 30 according to the present invention is made difficult not only by the small installation space but also by a limitation on the maximum permissible movement of fuel injection valve 1 during engine operation. As may be gathered from FIG. 4, the following quasi-steady-state load conditions typically occur in the vehicle: 1. the steady-state holddown force F.sub.NH applied after assembly by a holddown 10, 2. the force F.sub.L existing at idle operating pressure, and 3. the force F.sub.Sys existing at nominal system pressure.

(16) Usual bracing elements constituting intermediate elements 24 possess a linear spring characteristic curve in the energy region discussed. The result of this is that the stiffness of intermediate element 24 at the desired decoupling point at idle must be based on the above-defined maximum permissible movement of fuel injection valve 1, and is too great for effective decoupling. Because nominal operating pressures will probably rise further in the future, this problem will become more acute.

(17) In order to resolve this conflict, according to the present invention a nonlinear spring characteristic curve having a progressive profile is proposed for insulating element 30, as sketched in FIG. 4. The characteristic of this spring characteristic curve enables acoustic decoupling with the aid of a low spring stiffness (S.sub.NVH) at idle, and thanks to the rapidly rising stiffness allows conformity with the maximum movement of fuel injection valve 1 between idle pressure and system pressure.

(18) To allow optimum implementation of the nonlinear spring characteristic curve under typical boundary conditions of direct fuel injection (little installation space, large forces, little total movement of fuel injection valve 1), according to the present invention insulating element 30 is constructed in multiple parts from an outer ring 31, an inner ring 32, and an insulating ring 33, such that insulating ring 33 proceeds circumferentially, surrounded in encapsulated fashion by inner ring and 32 and outer ring 31. It thus differs appreciably from conventional cup springs, which in principle exhibit initially only a linear or degressive characteristic curve shape. With conventional cup springs a progressive curve is not achieved until they are loaded almost completely to blocking.

(19) FIG. 5 is a partial cross section through a multi-part insulating element 30 according to the present invention that is usable in a fuel injection apparatus. The multi-part insulating element 30 has two functional units. The first functional unit is constituted by insulating ring 33. Insulating ring 33 is an annular braided, knitted, or woven wire element that, individually, performs two functions according to the present invention. The primary function, as already described in detail previously, may achieve optimum insulation (decoupling) at the fuel injection apparatus by way of a progressive spring characteristic curve having low stiffness under low load conditions (e.g., idle, noise-critical operating regions), and high stiffness at nominal system pressure. What is desired as a secondary function of insulating ring 33 is damping (which is not to be equated with insulation, since different physical mechanisms of action exist), which is implemented by way of an internal friction of the wire braid of insulating ring 33 during injection in a context of micro-movements of fuel injection valve 1. The braided, knitted, or woven wire element of insulating ring 33 has, for example, a largely square cross section.

(20) The second functional unit is constituted by outer ring 31 and inner ring 32, which together form an annular chamber for insulating ring 33 and in that regard encapsulate it. Inner ring 32 is thin-walled, e.g., embodied as a sheet-metal part, and possesses on an inner side 35 an annular-disk-shaped surface and on its underside 36 a cylinder-head-side bracing surface. The two sides 35, 36 proceed largely perpendicularly to one another. Inner side 35 can have elastic elements 37 distributed over the circumference which are embodied, for example, like spring clips and ensure that insulating element 30 is fastened in lossproof fashion on fuel injection valve 1. Outer ring 31 has a greater material thickness than inner ring 32. Outer ring 31 possesses on an outer side 38 an annular-disk-shaped surface, while on its upper side 39, of thick and stable conformation, an injector-side bracing surface is provided which extends in crowned or spherical and convexly bulging fashion. Insulating element 30 abuts with this bracing surface of upper side 39 against a, for example, conically extending shoulder of valve housing 22, so that (viewed ideally) only a linear contact occurs here between the corresponding component partners 1, 30.

(21) FIG. 6 is a partial cross section through an insulating element 30 according to the present invention in an installed situation on a fuel injection valve 1 in the region of the disk-shaped intermediate element 24 shown in FIG. 1. As indicated in FIG. 6 exaggeratedly with the curved arrow, and with the dashed-line deflection and warping (not to scale) of outer ring 31, insulating element 30 according to the present invention has the advantage that the bracing of outer ring 31 on insulating ring 33 reduces the deflection of outer ring 31 as compared with conventional approaches, and results in greater stiffness of outer ring 31. A highly stiff outer ring 31 in turn allows the spring characteristic curve to be designed solely by way of insulating ring 33, made up of the braided wire having appreciably lower stiffness. The desired progressive spring characteristic curve can thus ideally be produced by the combination of these two components 31, 33. The stresses on weld seams 40 possibly placed for securing purposes between outer ring 31 and insulating ring 33, or between inner ring 32 and insulating ring 33, can moreover be reduced. The requirements to be imposed on weld seams 40 are thus lower. The overall flexural stress on the individual components of the multi-part insulating element 30 is decreased.

(22) An outstanding reduction in injector-caused noise during fuel injection is achieved with the multi-part insulating element 30 in accordance with the present invention, by decreasing energy transfer from fuel injection valve 1 to cylinder head 9 in the relevant frequency range. The elastic insulating element 30 possesses both insulating and damping properties. Accurate positioning of fuel injection valve 1 with respect to cylinder head 9 with very low tolerances and little stress on the valve seals (with respect to combustion chamber 25 and to fuel rail 4) is made possible. Insulating element 30 permits repeatable elastic deformation of insulating element 30 over the entire injector service life with no occurrence of plastic deformations. The insulating system enables a maximization of the insulating function while limiting injector movement.