WO2016011100A1

WO2016011100A1 - Isolation unit for fuel rail

Info

Publication number: WO2016011100A1
Application number: PCT/US2015/040481
Authority: WO
Inventors: Matthias GNADE; Sebastian Maier; William Warner
Original assignee: Robert Bosch Gmbh
Priority date: 2014-07-16
Filing date: 2015-07-15
Publication date: 2016-01-21

Abstract

An isolator (44) includes a wave washer (66) encased within a molded elastomer (70). The wave washer (66) defines a central axis (A) and is resiliently compressible by force directed along the central axis (A). The wave washer (66) includes peaks (P) and valleys (V) that alternate in a circumferential direction, the peaks (P) defining a maximum extent in a first axial direction (D1) and the valleys (V) defining a maximum extent in a second axial direction (D2) opposite the first axial direction (D1). The molded elastomer (70) extends beyond the peaks (P) in the first axial direction (D1).

Description

ISOLATION UNIT FOR FUEL RAIL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No.

62/025,351, filed July 16, 2014, the entire contents of which are incorporated by reference herein.

BACKGROUND

[0002] The present invention relates to an isolation unit for damping vibration, for example, in a direct fuel injection fuel rail. Various types of isolation units are utilized with fasteners for mounting a fuel rail to an underlying structure or substrate. One such isolator 244 is shown in FIGS. 5 and 6 to include a wave washer 266 encased in a molded elastomer body 270. The peaks P and the valleys V of the wave washer 266 are coincident with corresponding axial end surfaces 274, 275 of the elastomer body 270.

SUMMARY

[0003] In one aspect, the invention provides an isolator including a wave washer encased within a molded elastomer. The wave washer defines a central axis and is resiliently compressible by force directed along the central axis. The wave washer includes peaks and valleys that alternate in a circumferential direction, the peaks defining a maximum extent in a first axial direction and the valleys defining a maximum extent in a second axial direction opposite the first axial direction. The molded elastomer extends beyond the peaks in the first axial direction.

[0004] In another aspect, the invention provides a fuel rail assembly for an engine including a fuel rail and a plurality of fuel injectors coupled to the fuel rail and operable to distribute fuel from the fuel rail to a plurality of engine cylinders. At least one mounting bracket is secured to the fuel rail, each including an aperture for receiving a corresponding fastener. Each fastener extends through the corresponding mounting bracket aperture and through an isolator provided on a first side of the mounting bracket. The isolator includes a wave washer encased within a molded elastomer. The wave washer defines a central axis and is resiliently compressible by force directed along the central axis. The wave washer includes peaks and valleys, which alternate in a circumferential direction, the peaks defining a maximum extent in a first axial direction and the valleys defining a maximum extent in a second axial direction opposite the first axial direction. The molded elastomer extends beyond the peaks in the first axial direction.

[0005] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a cross-section view of a mount of a direct injection fuel rail assembly to a cylinder head of an internal combustion engine, the mount including upper and lower isolators according to one embodiment of the present application.

[0007] FIG. 2 is a front view of the direct injection fuel rail assembly of FIG. 1 , removed from the cylinder head of the internal combustion engine.

[0008] FIG. 3 is a front view of one of the isolators of FIGS. 1 and 2, with an elastomer body shown in phantom lines to illustrate the position of a wave washer therein.

[0009] FIG. 4 is a perspective view of the isolator of FIG. 3.

[0010] FIG. 5 is a front view of an isolator according to the current state of the art, with an elastomer body shown in phantom lines to illustrate the position of a wave washer therein.

[0011] FIG. 6 is a perspective view of the isolator of FIG. 4.

DETAILED DESCRIPTION

[0012] Before any embodiments of the inv ention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0013] FIGS. 1 and 2 illustrate portions of a direct injection fueling system 20, or "DI system", for an internal combustion engine. Direct injection involves injecting a metered quantity of fuel directly into the combustion chamber, rather than at an upstream intake port or manifold location. Although precision fuel metering and improved power and efficiency have been realized with direct injection, the DI system 20 must provide fuel pressure to the

? fuel injection valves 24, or "fuel injectors", that is drastically higher than a typical port fuel injection system. For example, the fuel pressure to fuel injectors 24 of the DI system 20 may be at or over 150 bar. Fuel is typically pumped from a fuel tank 32 toward a fuel rail 28 (FIG. 2) of the engine by a first pump 36, referred to as the primary or low-pressure pump, often located within the fuel tank 32. A secondary pump 40, referred to as the high-pressure fuel pump, receives the fuel from the low-pressure pump 36 and provides fuel to the fuel rail 28 at a higher pressure than that received from the low-pressure pump 36. All of the fuel injectors 24 have inlets that are in fluid communication with the high pressure fuel within the fuel rail 28, such that the fuel injectors 24 allow metered passage of fuel from the fuel rail 28 to the engine in accordance with electrical signals sent to the fuel injectors 24 from an engine control unit to control combustion within the engine.

[0014] Although the DI system 20 enables significant performance benefits that are increasingly demanded in the market, the operation (i.e., opening and closing) of the fuel injectors 24 results in significant pulsations and mechanical vibration that must be counteracted to provide suitable noise, vibration, and harshness (NVH) performance. The DI system 20 includes a plurality of fuel rail mounts as shown in FIG. 1, each of which includes one or more isolation units, or "isolators" 44 that result in a particularly advantageous combination of vibration dampening performance and long term durability. In comparison, other isolation units often sacrifice vibration absorption performance (i.e., high stiffness for durability) or longevity (i.e., very soft for maximum vibration dampening, which allow^rs too much movement at high loads and can eventually lead to fuel leakage between components mounted to the fuel rail).

[0015] At each fuel rail mount, the fuel rail 28 is provided with a mounting structure such as a bracket 48 for securing the fuel rail 28 to an underlying structure or substrate 52 (e.g., an engine cylinder head). Each mounting bracket 48 includes an aperture 50 that receives a fastener 56 such as a screw or bolt that extends through the bracket 48 and into the substrate 52 to secure the fuel rail 28 relative to the engine. The aperture 50 and the fastener 56 define an axis A of the mount. In the illustrated example, the fastener 56 is threaded into a corresponding threaded aperture in the substrate 52. In order to inhibit the transfer of vibrations betw^reen the fuel rail 28 and the substrate 52, and further to the vehicle cabin, an isolator 44 is provided on at least one side of each mounting bracket 48. The corresponding fastener 56 extends through the isolator(s) 44 and the mounting bracket 48. As shown, each fuel rail mount includes two isolators 44, one on each side of the mounting bracket 48 such that a first isolator is sandwiched between the fastener 56 and a first side of the mounting bracket 48, and a second isolator is sandwiched between a second side of the mounting bracket 48 and the substrate 52. Corresponding compression limiters 60A, 60B are positioned within each respective isolator 44 inside the mounting bracket 48, and are configured to abut each other to set a maximum allowable amount of compression of the isolators 44 during tightening of the fastener 56 to the substrate 52. Li order to limit the amount of compression of the isolators 44, the abutting compression limiters 60A, 60B are sandwiched between a head 56 A of the fastener 56 and an exterior surface 52 A of the substrate 52. Although the compression limiters 60A, 60B are unique from each other with the lower compression limiter 60B being significantly longer, other arrangements using at least one compression limiter are optional.

[0016] Each of the isolators 44 can include a wave washer 66, which can be constructed of metal having a resilient spring effect . The wave washer 66 includes peaks P and valleys V, which alternate in a circumferential direction, the peaks P defining a furthest extent of the wave washer 66 in a first axial direction Dl and the valleys V defining a furthest extent of the wave washer 66 in a second axial direction D2 opposite the first axial direction Dl . It will be understood that the peaks P and the valleys V are relatively high and low, respectively, in an orientation-dependent sense, and are reversed upon reversing the orientation of the isolator 44. As such, the use of the terms "peak" and "valley" are relatively interchangeable and are used herein with an arbitrary reference to the orientation shown in Fig. 1 for ease of understanding.

[0017] In addition to the wave washer 66, each isolator 44 further includes an elastomer body 70 that encases the wave washer 66. The isolator 44 can be formed by molding elastomer material to form the elastomer body 70 over the wave washer 66. The elastomer body 70 extends beyond the peaks P in the first axial direction Dl . Thus, the peaks P of the wave washer 66 are spaced inwardly from an adjacent, axially overlying, axial end surface 74 of the isolator 44. The valleys V of the wave washer 66 are coincident with a second, opposite axial end surface 75 of the isolator 44 as shown. However, in some constructions, the elastomer body 70 extends beyond the valleys V of the wave washer 66 in the second axial direction D2 instead of, or in addition to, the illustrated extent past the peaks P in the first axial direction Dl . [0018] In some constructions, as illustrated, the elastomer body 70 can include a ring- shaped first portion 70A that encases the wave washer 66 and a frusto-conical second portion 70B extending axially from one end of the ring-shaped first portion 70A (e.g., in the first axial direction Dl as illustrated). The aforementioned axial end surfaces 74, 75 can be axial end surfaces of the ring-shaped first portion 70A. The second portion 70B may be shaped, whether frusto-conically or otherwise, to fit and conform to the aperture 50 in the mounting bracket 48. The center of the isolator 44 is open to define an aperture 78 which

accommodates passage of the fastener 56. In the first portion 70A, the aperture 78 can have a non-circular (e.g., star-shaped) cross-section as shown in Fig. 4. In the second portion 70B, the aperture 78 can have a circular cross-section. The area of the circular cross-section is smaller than the area of the star-shaped cross-section. The elastomer body 70 can be pure silicone rubber or another suitable elastomer.

[0019] The isolator 44 can be manufactured by insert molding the wave washer 66 in the process of forming the elastomer body 70. On one or both axial sides, the elastomer of the ring-shaped first portion 70A extends past the respective wave washer peaks P or valleys V. For example, the elastomer material thickness, or "axial height H₃", between the axial end surface 74 of the ring-shaped first portion 70A and the peaks P (or valleys in an alternate construction) is greater than an axially measured uncompressed height H₂ of the wave washer 66. In one example, the uncompressed axial height Hi of the first portion 70A is 2.85mm, the uncompressed peak-to-valley axial height H₂ of the wave washer 66 therein is 2.0mm, and the first portion 7 OA only extends past the peaks P of the wave washer 66 such that the height H₃ or elastomer material thickness of the first portion 70A beyond the wave washer 66 is 0.85mm. Material thickness T of the wave washer 66 can be 0.63mm in the aforementioned example, among others. Material thickness T is measured perpendicular to the parallel upper and lower axial surfaces, in other words, measured in the axial direction at the peaks P and/or the valleys V. The compression limiter 60 may limit the compression of each isolator 44, measured within the first portion 70A, to no less than 70 percent of the uncompressed height Hi, for example, limiting compression to an axial height of 2.30mm. While the specific dimensions given above illustrate one particular embodiment having advantageous performance for fuel rail mounting arrangements typically supplied in today's market, these should not necessarily be considered limiting as it will be understood that the size and shape of fuel rail mounts may vary case-by-case, and one will appreciate that various modifications may be made to the illustrated construction without departing from the scope of the present application. Expressed in a more general sense, the material of the molded elastomer body 70 in the first portion 70A may extend beyond the peaks P in the first axial direction D 1 by a height ¾ at least 20 percent greater than the material thickness T of the wave washer 66, or further, by a height ¾ at least 30 percent greater than the material thickness T of the wave washer 66. Li some advantageous constructions, the height H₃ is about 35 percent (i.e., 33-37 percent) greater than the material thickness T of the wave washer 66.

[0020] Although not illustrated in detail, those of ordinary skill in the art will realize that other constructions of the invention may alternately or additionally provide a height or material thickness of elastomer extending beyond the valleys V of the wave washer 66 in the second axial direction D2, which is otherwise similar to the illustrated embodiment described above, including the examples of the amount of elastomer material beyond the wave washer 66, which can be provided below the valleys V of the wave washer 66 in an extent similar to the height H₃. hi other constructions having excess elastomer on both sides of the wave washer 66, any of the examples of the height ¾ given above may be split among the two opposite sides.

[0021] By distancing or "burying" the peaks P and/or valleys V of the wave washer 66 from the surrounding axial surfaces of the encasing elastomer body 70, the wave washer 66 does not overly stiffen the overall isolator 44, but is active to limit total deflection under high loads. Thus, the isolators 44 offer the benefits of both a pure rubber isolator and a stiffer wave washer type isolator without the inherent drawbacks of either.

Claims

CLAIMS What is claimed is:

1. An isolator comprising: a wave washer encased within a molded elastomer, the wave washer defining a central axis and being resiliently compressible by force directed along the central axis, wherein the wave washer includes peaks and valleys that alternate in a circumferential direction, the peaks defining a maximum extent in a first axial direction and the valleys defining a maximum extent in a second axial direction opposite the first axial direction, and wherein the molded elastomer extends beyond the peaks in the first axial direction.

2. The isolation unit of claim 1, wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount greater than a material thickness of the w^rave washer.

3. The isolator of claim 1, wherein the wave washer is constructed of metal.

4. The isolator of claim 3, wherein the molded elastomer is silicone rubber.

5. The isolator of claim 1, wherein the molded elastomer is formed with a ring-shaped first portion that receives the wave washer and a second portion having a frusto-conical shape extending axially from one end of the ring-shaped first portion.

6. The isolator of claim 5, further comprising a centrally-positioned, axially-extending through hole extending through both the first and second portions for receiving a fastener.

7. The isolator of claim 5, wherein the frusto-conical shape extends from the ring-shaped first portion in the first axial direction.

8. The isolator of claim 1, wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount at least 20 percent greater than a material thickness of the wave washer.

9. The isolator of claim 1, wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount at least 30 percent greater than a material thickness of the wave washer.

10. The isolator of claim 1, wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount that is about 35 percent greater than a material thickness of the wave washer.

1 1. A fuel rail assembly for an engine, the fuel rail assembly comprising: a fuel rail; a plurality of fuel injectors coupled to the fuel rail and operable to distribute fuel from the fuel rail to a plurality of engine cylinders; at least one mounting bracket secured to the fuel rail, each including an aperture for receiving a corresponding fastener; and a fastener corresponding to each mounting bracket extending through the

corresponding mounting bracket aperture and through an isolator provided on a first side of the mounting bracket, wherein the isolator includes a wave washer encased within a molded elastomer, the wave washer defining a central axis and being resiliently compressible by force directed along the central axis, wherein the wave washer includes peaks and valleys, which alternate in a circumferential direction, the peaks defining a maximum extent in a first axial direction and the valleys defining a maximum extent in a second axial direction opposite the first axial direction, and wherein the molded elastomer extends beyond the peaks in the first axial direction.

12. The fuel rail assembly of claim 1 1, wherein the molded elastomer extends beyond the peaks by an amount greater than a material thickness of the wave washer.

13. The fuel rail assembly of claim 11 , wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount at least 20 percent greater than a material thickness of the wave washer.

14. The fuel rail assembly of claim 11, wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount at least 30 percent greater than a material thickness of the wave washer.

15. The fuel rail assembly of claim 11 , wherein the molded elastomer extends beyond the peaks in the first axial direction by an amount that is about 35 percent greater than a material thickness of the wave washer.

16. The fuel rail assembly of claim 1 1 , wherein the wave washer is constructed of metal.

17. The fuel rail assembly of claim 16, wherein the molded elastomer is silicone rubber.

18. The fuel rail assembly of claim 1 1 , wherein the molded elastomer is formed with a ring-shaped first portion that receives the wave washer and a second portion having a frusto- conical shape extending axially from one end of the ring-shaped first portion.

19. The fuel rail assembly of claim 18, further comprising a centrally-positioned, axially- extending through hole extending through both the first and second portions for receiving a fastener.

20. The fuel rail assembly of claim 1 1, further comprising a second isolator provided on a second side of the mounting bracket, opposite the first side.