The present invention is directed to a decoupling element for a fuel injection device.
Another type of simple intermediate element for a fuel injection device is already known from German Published Patent Appln. No. 101 08 466. This intermediate element is a washer having a circular cross section and is situated in an area where both the fuel injector and the wall of the receiving bore have a truncated conical shape in the cylinder head, and the washer acts as an equalizing element for support of the fuel injector.
More complex intermediate elements for fuel injection devices, which are definitely more complicated to manufacture, are known from German Published Patent Appln. No. 100 27 662; German Published Patent Appln. No. 100 38 763; and European Published Patent Appln. No. 1 223 337, among others. These intermediate elements are characterized in that they are all constructed in multiple layers or multiple parts and should undertake sealing and damping functions to some extent. The intermediate element known from German Published Patent Appln. No. 100 27 662 has a base body and a carrier body, in which a sealant through which a nozzle body of the fuel injector passes is used. German Published Patent Appln. No. 100 38 763 describes a multilayer equalizing element made up of two rigid rings and an elastic intermediate ring sandwiched in between. This equalizing element permits tilting of the fuel injector relative to the axis of the receiving bore over a relatively large angle range as well as radial displacement of the fuel injector from the central axis of the receiving bore.
European Published Patent Appln. No. 1 223 337 also describes a multilayer intermediate element composed of multiple washers, each made of a damping material. The damping material made of metal, rubber or PTFE is selected and designed in such a way that it enables damping of the vibrations and noises generated by operation of the fuel injector. However, the intermediate element must have four to six layers to achieve the sought damping effect.
To reduce noise emissions, U.S. Pat. No. 6,009,856 also proposes to surround the fuel injector using a sleeve and to fill the created gap with an elastic noise-absorbing material. However, this type of noise damping is very complex, difficult to install and expensive.
The decoupling element according to the present invention for a fuel injection device has the advantage that it is designed with a very simple structure and thus improved noise damping is achieved. According to the present invention, the decoupling element has a nonlinear progressive spring characteristic, which results in several positive and advantageous aspects when the decoupling element is installed in a fuel injection device having injectors for direct fuel injection. The low stiffness of the decoupling element at the idling point permits effective decoupling of the fuel injector from the cylinder head and thereby significantly reduces the noise emanating from the cylinder head in the noise-critical idling mode. The great stiffness at a nominal system pressure ensures little movement of the fuel injector on the whole during operation of the vehicle, which thereby, on the one hand, ensures the durability of the sealing rings which function as a combustion chamber seal and as a seal with respect to the fuel rail and, on the other hand, a stable spray point of the fuel spray in the combustion chamber, which is decisive for the stability of some combustion methods.
The spring characteristic of the decoupling element according to the present invention may advantageously be designed to be progressive in a targeted manner by adjusting the geometric parameters of the spring ring in particular. The decoupling element is characterized by a small design height, so that it may also be used even in a very small installation space similar to a plate spring. The decoupling element also has a great durability even at high temperatures. The spring ring and the conical washer are two components for the decoupling element which are manufacturable very easily in terms of manufacturing technology.
The nonlinear spring characteristic may also be adjusted specifically to the particular application due to the geometry of the spring ring. The stiffness may also be modified by modifying the cone angle of the conical washer, so that the contact area with the spring ring may be modified.
It is advantageous in particular that the conical washer is to be provided with a hexagonal cross section in such a way that there are two longer bordering sides and four shorter bordering sides of the conical washer. On the one hand, the spring ring may thus be supported on one of the two longer bordering sides of the conical washer, while on the other hand, the conical washer rests on the shoulder of the receiving bore for the fuel injector along one of the four shorter bordering sides.
For an understanding of the present invention, a known specific embodiment of a fuel injection device is described in greater detail below on the basis of
A flat intermediate element 24, designed as a supporting element in the form of a washer, is inserted between a surface 21 of a valve housing 22 and a shoulder 23 of receiving bore 20 running at a right angle to the longitudinal extent of receiving bore 20, for example. Manufacturing and assembly tolerances are compensated with the aid of such an intermediate element 24, and a support which is free of transverse forces is ensured even when the position of fuel injector 1 is slightly skewed.
On its inlet end 3, fuel injector 1 has a plug connection to a fuel distributor line (fuel rail) 4, which is sealed by a sealing ring 5 between a connecting piece 6 of fuel distributor line 4, which is shown in a sectional view, and an inlet connection 7 of fuel injector 1. Fuel injector 1 is inserted into a receiving opening 12 in connecting piece 6 of fuel distributor line 4. Connecting piece 6 emerges in one piece from the actual fuel distributor line 4, for example, and has a flow opening 15, which has a smaller diameter, upstream from receiving opening 12, through which the oncoming flow of fuel injector 1 is directed. Fuel injector 1 has an electrical connecting plug 8 for electrical contacting for actuation of fuel injector 1.
To keep fuel injector 1 and fuel distributor line 4 apart from one another, so they are largely free of radial forces, and to securely hold down fuel injector 1 in the receiving bore of the cylinder head, a hold-down device 10 is provided between fuel injector 1 and connecting piece 6. Hold-down device 10 is designed as a bow-shaped component, for example, as a punched and bent part. Hold-down device 10 has a partially ring-shaped basic element 11 from which a hold-down clamp 13 with a bend comes into contact with a downstream end face 14 of connecting piece 6 at fuel distributor line 4 in the installed state.
The object of the present invention is to achieve improved noise damping, in particular in the noise-critical idling mode, in a simple manner in comparison with the known intermediate element approaches by using a targeted design and geometry of intermediate element 24. The forces (structure-borne noise) which are introduced into cylinder head 9 during valve operation and result in a structural excitation of cylinder head 9 and are emitted by same as airborne noise are the critical source of noise from fuel injector 1 in direct high-pressure injection. Therefore, to improve the noise situation, the goal is to minimize the forces introduced into cylinder head 9. In addition to reducing the forces due to the injection, this may be achieved by influencing the transmission behavior between fuel injector 1 and cylinder head 9.
In a mechanical sense, the support of fuel injector 1 on passive intermediate element 24 in receiving bore 20 of cylinder head 9 may be thought of as an ordinary spring-mass-damper system, as illustrated in
The goal of the present invention is to design an intermediate element 24 with priority use of elastic isolation (decoupling) for noise reduction, in particular in idling mode of the vehicle. The present invention relates to the definition and design of a suitable spring characteristic, on the one hand, taking into account the typical requirements and boundary conditions in direct injection of fuel at a variable operating pressure, and on the other hand, the design of an intermediate element 24, which is capable of mapping the characteristic of the spring characteristic thus defined and which may be adapted to the specific boundary conditions of the injection system through a choice of simple geometric parameters.
Decoupling of fuel injector 1 from cylinder head 9 with the aid of a low spring stiffness c of the decoupling system according to the present invention formed by a spring ring 30 and a conical washer 31 is made difficult by a restriction on the allowed maximum movement of fuel injector 1 during engine operation in addition to the small installation space. As shown in
1. static hold-down force FNH applied by a hold-down device 10 after assembly,
2. force FL which prevails at an idling mode pressure and
3. force FSys which prevails at a nominal system pressure.
Ordinary supporting elements as intermediate elements 24 have a linear spring characteristic in the force range indicated. As a result, the stiffness of intermediate element 24 at the sought decoupling point during idling mode is based on the maximum allowed movement of fuel injector 1, as defined above, and is too large for effective decoupling. This problem will be further exacerbated since the nominal operating pressures will presumably increase further in the future.
To solve this conflict, according to the present invention, a nonlinear spring characteristic having a progressive curve is proposed for decoupling system 30, 31 (
To be able to implement the nonlinear spring characteristic easily and inexpensively under the typical boundary conditions of direct fuel injection (small installation space, extremely high forces, minor total movement of fuel injector 1), the decoupling system is constructed according to the present invention from a spring ring 30 and a conical washer 31, spring ring 30 in particular creating a distinctly progressive spring characteristic because of its particular geometric design. It thus differs distinctly from traditional plate springs, which fundamentally have initially only a linear or degressive characteristic. With traditional plate springs, a progressive characteristic is achieved only when its load is almost completely “blocked.”
The decoupling system is supplemented by conical washer 31 in addition to spring ring 30. Conical washer 31 has a hexagonal cross section, although the hexagonal cross section is elongated rather than being a uniform honeycomb design, so that the cross section has two longer bordering sides and four shorter bordering sides of conical washer 31, running completely around the circumference on the whole. Spring ring 30 is supported on the side facing away from valve housing surface 21, the side being at least partially rounded and having a convex internal contour on one of the two longer bordering sides of conical washer 31, whereas conical washer 31 is in contact with one of the four shorter bordering sides on receiving bore 20. Receiving bore 20 of cylinder head 9 in this case has a shoulder 23 running at a right angle to the total extent of receiving bore 20. As shown in
The nonlinear progressive spring characteristic of the decoupling system according to the present invention is implemented by a shortening of the level arm by reducing the free arc length with increasing load on the decoupling system. A smaller lever arm produces a greater stiffness of the decoupling system. The shortening of the lever arm is achieved by making spring ring 30 conform to the corresponding two contact partners, i.e., valve housing 22 with its valve housing surface 21 and conical washer 31. The nonlinear spring characteristic may be adapted specifically to the particular application through the geometry of spring ring 30. The stiffness may optionally also be modified by modifying the cone angle of conical washer 31, so that the contact surface with spring ring 30 may be altered.
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10 2011 089 274 | Dec 2011 | DE | national |
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PCT/EP2012/072317 | 11/9/2012 | WO | 00 |
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WO2013/091998 | 6/27/2013 | WO | A |
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