WO1987000246A1

WO1987000246A1 - Fuel injector fastening

Info

Publication number: WO1987000246A1
Application number: PCT/GB1986/000376
Authority: WO
Inventors: Graham Clarke
Original assignee: Perkins Engines Shrewsbury Limited
Priority date: 1985-06-28
Filing date: 1986-06-26
Publication date: 1987-01-15
Also published as: GB8516362D0; GB2177157A; GB2177157B; EP0227777A1

Abstract

An injector clamp (12) for fastening a fuel injector (1) in place in a cylinder head (16) is more resilient than the cylinder head so that the clamp (12) is resiliently loaded in bending when secured to the head by a pair of fasteners (14), one on each side of the injector (1). The clamp (12) is designed so that a predetermined degree of bending thereof applies the required load to the injector, thereby allowing the correct loading to be judged in terms of the axial adjustment of fasteners such as bolts (14), used to secure the clamp (12) to the cylinder head (16). A central elongate aperture (10) in the clamp engages over the head of the injector and receives the fasteners (14) at its ends. The aperture (10) effectively forms a pair of leaf-spring elements between the injector and each fastener. The clamp (12) is preferably curved along its length passing through the injector and fasteners so that it is curved away from the bearing surfaces associated with the injector and fasteners. A washer (9) engages over the head of the injector and abuts shoulders (8) on the injector, thereby to form a wider bearing surface for the clamp when the latter is subsequently fitted over the head of the injector.

Description

Fuel Injector Fastening

Technical Field

This invention relates to a method of, and means for fastening a fuel injector in place in an engine cylinder head.

Fuel injectors in diesel engines are fastened in apertures in the cylinder head by a rigid clamp that is bolted to the cylinder head so that the lower end of the injector body is loaded firmly into sealing engagement with a seat at the lower end of the aperture. The nozzle of the injector projects beyond the seat into the combustion chamber. Typically, the clamp has a central apertured portion that engages over the head of the injector and abuts shoulders on opposite sides of the injector. A pair of bolts project downwards through apertures at the ends of the clamp and are threaded into the cylinder head to pull the clamp and injector downwards. In order to withstand the loading applied by the bolts, the clamp is made as rigid as possible and is either a heavy forging or a channel-section member. However, even when strengthened in this manner, the clamp can still crack and fail in use if the bolts are overtightened. Furthermore, over-tightening of the bolts can impose such high loads on the cylinder head that this can cause cracking in the narrower sections bridging the valve seats.

Disclosure of the Invention

An object of the present invention is to provide an injector clamp that reduces or overcomes the aforesaid cracking problems and which is preferably less costly to manufacture.

This is achieved according to the invention by providing an injector clamp that is adapted to be secured to the cylinder head by a pair of fasteners and is more resilient than the cylinder head to which it is fastened so that the clamp is resiliently loaded in bending when in use. Thus, the clamp can be designed so that a predetermined degree of bending of the clamp applies the required load to the injector thereby allowing the correct loading to be judged- in terms of the axial adjustment of the fasteners such as bolts, used to secure the clamp to the cylinder head. Furthermore, by designing the clamp so that it has a low spring rate, it can be made more tolerant of over-tightening of the fasteners.

In a preferred embodiment of the invention a central aperture in the clamp engages over the head of the injector and extends towards the fasteners either side thereof so that a pair of leaf-spring elements is effectively formed between the injector and each fastener. Preferably, this central aperture extends as far as and receives both fasteners at its ends. Further,. the clamp is preferably curved along its length passing through the injector and fasteners so that it engages a respective bearing surface associated with the injec^tor and fasteners over a limited area of contract and is c''_.ved away from that bearing surface either side of said .r^a .of contacts.

A washer is preferably provided that engages over the head of the injector and abuts shoulders, on the injector, thereby to form a wider bearing surface for the clamp when the latter is subsequently fitted over the head of the injector.

It will be appreciated that an injector clamp according to the invention can be readily manufactured at low cost as a pressing or stamping from spring steel plate. Furthermore, two or more clamps can be laminated to produce clamps with higher spring rates if needed. Laminated clamps preferably have their laminations joined together, for example, by spot welding. Similarly, the washer is preferably joined to the clamp to avoid its omission during assembly.

The invention will now be described by way of example with reference to the accompanying drawings in which

Figure 1 is a side elevation of a fuel injector and clamp assembly according to the invention.

Figure 2 is a plan view of the clamp of Figure 1,

Figure 3 is a plan view of the washer of Figure 1.

Figure 4 is a plan view of an alternative form of washer, and

Figure 5 is a side elevation similar to Figure 1 showing an alternative clamp assembly according to the invention.

The fuel injector shown in Figure 1 comprises an injector body 1 having an upper portion 2 provided with a fuel connector 3, and a lower cylindrical portion 4 to which a spray nozzle 5 is secured by means of a nut 6. A pair of parallel flats 7 are formed on the side of the upper portion 2 and terminate in shoulders 8 at their- lower ends. A washer 9 having a central aperture 10 with a shape matching the cross-section of the upper portion 2 (Figure 3) , is received as a close fit over the upper portion 2 and seats on the shoulders 8. A clamp 12 formed from spring.steel plate and with a central elongate longitudinally extending aperture 13 (Figure 2) , fits over the upper portion 2 of the injector body and engages the washer 9 alongside the flats 7.

A pair of bolts 14 project downwards through the aperture 13 at each end thereof and are threaded in bores 15 in the cylinder head 16 to clamp the injector in place in an aperture 17 in the cylinder head with the injector nut 6 in sealing engagement with an internal shoulder 18 at the lower end of. the aperture 17. The nozzle 5 extends on downwards through a bore 19 in the cylinder head and its tip 20 projects into the combustion chamber 21.

The elongate aperture 13 in clamp 12 is formed with two central parallel straight sides 22 matching the flats 7 on the injector body so as to cooperate with the latter and locate the injector angularly. The outer ends of the aperture 13 are of semi-circular shape at 23 to cooperate with the shank 24 of the bolts 14. Between the straight sides 22 and the semi-circular ends 23, the aperture 13 has tapering sides 25. The external outline of the clamp has straight sides 26 that taper inwards towards the ends of the clamp generally parallel to the sides 25 of the aperture 13, thereby to define a pair of leaf-spring elements 27 extending either side of the injector and acting between the washer 9 and the head 28 of each bolt. As seen in plan view (Figure 2) , the clamp is symmetrical about its longitudinal axis X-X and its transverse axis Y-Y so that it can be assembled in either position 180 degrees apart with the ends 23 of the central aperture aligned with the bores 15 in the c Under head 16.

The clamp 12 is curved along its length X-X (as seen in side elevation in Figure 1) so that the central portions of the leaf-spring elements 27 are slightly dish-shaped and curve upwards away from a limited area of contact with the washer 9 either side of the injector. The outer ends of the clamp plate are each curved over in the opposite sense to said central dish-shaped portions of the leaf-spring elements so as to engage the under side of the head of the respective bolt 14 over a limited area of contact and to curve away from said underside either side of said area of contact.

Tightening of the bolts 14 tends to flatten the clamp and bend the leaf-spring elements 27 downwards, thereby producing a resilient loading which reacts on the washer 9 to force the injector downwards onto the sealing shoulder 18. The limited area of contact between the leaf-spring element 27 and the washer serves to ensure that the applied force acts downwards along the axis of the injector and helps avoid any tilting movements that would hinder sealing engagement of the injector with the shoulder 18. Also the limited area of contact between the clamp and the washer, and the clamp and the undersides of the heads of the bolts, produced by the curvature of the clamp, allows flexing of the leaf-spring elements over substantially the whole of their length therebetween.

In practice, the degree of resilient loading of the clamp is controlled by screwing the bolts down finger-tight then rotating them a predetermined specified number of times. For example, the illustrated clamp is made of Grade 60, BS 1449 spring steel, 3 millimetres thick and hardened to 460-500 HV, and is resiliently loaded to produce a force of 2.7 K on the injector by rotating each of the bolts by three quarters of a turn from finger-tight. The degree of loading required is sufficient to counter the upwards forces exerted on the injector as a result of the operating pressures within the combustion chamber. Also, the dimensions and material of the clamp is selected to avoid resonance that might be excited by pulsations in the combustion chamber.

It may be convenient in some embodiment of the invention to employ two or more similar clamps that are laminated together to increase the spring rate of the clamp. Preferably, the laminations of such a clamp are held together by means such as spot welding, adhesives or by encapsulation.

The washer 9 is composed of mild steel, and is preferably secured to the clamp by means such as spot welding, adhesives or encapsulation so as to form a one-piece assembly and avoid omission of the washer during assembly. The function of the washer is to provide a wider abutment surface for the clamp that will avoid any risk of lateral flexing or twisting of the leaf-spring elements 27 that could widen the aperture 13 and release the injector. The thickness of the washer is selected for the required strength and to suit the spacing of the clamp relative to the top of the cylinder head and the shoulders 8 of the injector.

In an alternative embodiment of the invention the^'washer 9 may be adapted so that it has the outline shown in Figure 4 and the bolts 14 pass through holes 29 therein (shown in broken outline in Figure 1) and give the washer a safety, function by serving as a rigid clamp to retain the^injector in the head if the resilient clamp 12 fails.

The washer 9 then serves also to locate the injector angularly, and the aperture 13 in the clamp 12 can DP modified so that the central straight sides 22 are arcuate as shown in broken outline in Figure 2 to remove possible stress raisers.

In yet another embodiment of the invention, stop means may be provided to positively prevent over-tightening of rhe bolts 14. For example, as shown in Figures 5, a spacing element such as a tubular sleeve 30 may be provided around each bolt between the clamp 12 and the head 16 to serve as an abutment or stop for the respective end of the clamp when bent down by the bolt 14. For convenience, the bolts 14 may be replaced by studs and a tubular sleeve is fitted over each before the clamp is fitted and nuts threaded down on the studs. If the washer 9 is shaped to serve a safety function, the holes 29 are enlarged to receive the sleeves and each sleeve projects above the top surface of the washer as in Figure 5.

In yet another embodiment of the invention, the washer 9 is shaped as in Figures 4 and 5 and the bolts 14 tighten the clamp 12 down until the downwardly-turned extreme ends 31 of the clamp engage the washer 9, the resilient loading of the clamp then being sufficient. The ends of the washer 9 therefore serve as abutments or stops in place of the tubular sleeves 30.

Another modification of the invention is illustrated in Figure 5 comprising the formation of a transverse ridge υ^~ rib 32 across the width of the washer 9 at its centre so as to ensure a central line contact between the washer 9 and clamp 12. This produces a centrally aligned downwards load on the injector body that ensures good sealing at its lower end. The ridge 32 may be produced by a simple pressing operation.

Claims

Cla ims

1. A method of fastening a fuel injector to an engine cylinder head using a clamp plate that engages the injector and is secured to the cylinder head by a fastener each side of the injector so as to apply an axial clamping load to the injector, the clamp plate being more resilient than the cylinder head so that it is resiliently loaded in bending by the two fasteners.

2. A method as claimed in claim 1 in which the clamp has an aperture that receives an upper portion of the injector.

3. A method as claimed in claim 2 in which the central aperture is elongated and has end portions that each receive one of the fasteners.

4. A method, as claimed in any one of the preceding claims in which the clamp engages a washer that is fitted over the upper end of the injector and abuts a shoulder on the injector.

5. A method as claimed in any one of the preceding claims in which the- clamp plate is curved along its length passing thrpjc . ihe injector and each fastener so that it tends to be flattened when resiliently loaded.

6. A method as claimed in claim 5 in which the clamp plate is curved along its length passing through the injector and each fastener so that it engages a bearing surface associated with the injector over a limited area of contact and is curved away from said bearing surface either side of said area of contact.

7. A method as claimed in claim 6 in which the lamp engages a bearing surface associated with each fastener over a limited area of contact and is curved away from said bearing surface either side of said area of contact.

8. A method as claimed in any one of the preceding claims in which each fastener is a screw fastener and the resilient loading of the clamp is controlled by rotating each fastener a predetermined number of rotations beyond a finger-tight state.

9. Means for fastening a fuel injector to an engine cylinder head comprising a clamp plate composed of a resilient material and adapted to be resiliently loaded in bending when in use in engagement with the injector and secured to the cylinder head by a fastener each side of the injector, the clamp plate having an aperture to receive the upper end of the injector and an aperture to receive each fastener.

10. Means as claimed in claim 9 in which the clamp plate is composed of spring steel.

11. Means as claimed in claim 9 in which the clamp plate comprises a pair of- leaf-spring elements between the aperture for the inje cor and the aperture for each fastener.

12. Means as claimed in claim 11 in which the aperture for the fastener is elongated to extend between said leaf- spring elements.

13. Means as claimed in claim 11 in which the aperture for the injector is elongated to extend between said leaf- spring elements.

14. Means as claimed in claim 11 in which a single elongate aperture between said leaf-spring elements receives the injector and the fasteners one at each end.

15. Means as claimed in claim 14 in which said single elongate aperture is semi-circular in shape at each end.

16. Means as claimed in any one of claims 11 to 15 in which said leaf-spring elements taper towards one another as they extend towards the aperture for the fastener.

17. Means as claimed in any one of claims 9 to 16 in which the clamp plate is curved along the line of the apertures.

18. Means as claimed in claim 17 in which the clamp plate is curved along the line of the apertures so that it has a central dish-shaped portion centred on the aperture for the injector.

19. Means as claimed in claim 18 in which each of the outer ends of the clamp plate centred on the respective apertures for the fasteners is curved in the opposite sense to said central dish-shaped portion.

20. Means as claimed in claim 18 or 19 including a washer having a central aperture to receive the upper end of the injector and forming an abutment for the central dish-shaped portion of the clamp plate which engages the washer over a limited area of contact and is curved away from the washer either side of said area of contact.

21. Means as claimed in any one of claims 9 to 17 including a washer having a central aperture to receive the upper end of the injector and forming an abutment for the clamp plate.

22. Means as claimed in any one of claims 9 to 21 including one or more fasteners in the form of bolts.

23. Means as claimed in any one of claims 9 to 22 comprising two or more similar clamp plates laminated together.

24. A fuel injector for an engine and means for fastening the injector to an engine cylinder head as claimed in any one of claims 9 to 23.

25. An engine cylinder head with a fuel injector fastened to it by fastening means as claimed in any one of claims 9 to 24.

26. Means for fastening a fuel injector to an engine cylinder head substantially as herein described with « reference to the accompanying drawings.

27. An engine cylinder head with a fuel injector fastened to it by fastening means substantially as herein described with reference to the accompanying drawings.