GB2545195A

GB2545195A - Fuel injection nozzle

Info

Publication number: GB2545195A
Application number: GB1521601.3A
Authority: GB
Inventors: E Wright Keith; A Noyce Stephen
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-12-08
Filing date: 2015-12-08
Publication date: 2017-06-14
Also published as: GB201521601D0

Abstract

A manufacturing method for a fuel injector nozzle tip 102, comprising forming spray holes 106 through a wall 104 of the nozzle tip, which allow fluid communication from a sac 114 defined by the wall. The process also involving hardening at least part of a surface of a spray hole, before or after forming the spray holes. The hardening process may be through induction hardening, carburising and/or heat treatment. The apertures 106 may be shaped using a honing process using a magnetorheological fluid and involve controlled magnetic fields, temperatures and pressures.

Description

Fuel Injection Nozzle

TECHNICAL FIELD

The present invention relates to a nozzle for a fuel injector, and more specifically to a method of producing a nozzle tip of a fuel injector nozzle.

BACKGROUND OF THE INVENTION

Nozzle and spray hole arrangements for fuel injectors such as diesel injectors are well established and widely used on passenger cars, medium and heavy duty applications. As spray hole geometries reduce, and the tolerances and control of these features tightens at the manufacturing stage, there is greater scrutiny of the precise geometry of spray holes. This is to ensure optimum combustion performance of individual injectors, in an ‘as new’ condition and maintained over the life of the product, to ensure consistent performance and ease control.

It is widely known to use a honing operation, (i.e. flowing abrasive media through nozzle), as an effective means of providing rounding an entry to a spray hole, thus increasing Cd and making the nozzle more efficient. However, due to the case hardened condition required of the nozzle body material, there is a diminishing hardness gradient through the finished spray hole. As a result, an unexpected and undesirable hole shaping may result for spray holes with higher honing levels, for example leading to barrelling instead of a converging shape spray hole as used in CFD predictions. Non-uniform shaping within a spray hole bore is particularly evident in the early part of the spray hole bore, i.e. around the entry to the spray hole from the nozzle sac.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved fuel injection nozzle tip which at least mitigates the problems as described above, and provides an improved spray hole geometry.

Internal surfaces defining spray holes manufactured by the present invention have been at least partially hardened.

Accordingly the present invention provides, in a first aspect, a method, according to claim 1, of producing a nozzle tip for a fuel injection nozzle.

The hardening step may be undertaken before the hole forming step, and comprise applying a through hardening process to at least a region of the wall in which the spray holes are subsequently formed.

Alternatively, the hardening step may be undertaken after the hole forming step, and comprise applying a hardening process to the or each surface defining a through bore of a spray hole.

The hardening step may comprise induction hardening.

The hardening step may comprise carburising and heat treatment processes.

The hardening step may comprise passing a carburizing gas through the or each spray hole(s) whilst at least a region around each spray hole is subjected to local heating by an induction coil.

The present invention further comprises a method of manufacturing and assembling a nozzle of a fuel injector, including forming a main bore, forming a nozzle sac at an end of the main bore, manufacturing a nozzle tip using a method as described above, and assembling a needle into the main bore of the nozzle. A method according to the present invention may also comprise applying a deliberate vibration to an EDM wire of a known frequency and intensity to eliminate random and uncontrolled vibration of the EDM wire. A method according to the present invention may include an additional hole shaping step comprising a honing operation using a honing fluid. The honing operation may comprise using magnetic fields in the proximity of the or each spray hole to modify a path though the or each spray hole taken by magnetically sensitive abrading material.

Alternatively, the honing fluid may comprise a magnetorheological fluid, wherein magnetic fields are applied in the proximity of the nozzle tip at the same time as the honing operation is undertaken.

The honing fluid temperature and/or pressure may be selected upstream and/or downstream of the or each spray hole, thereby to cause or suppress cavitation during the honing operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view of a fuel injector nozzle manufactured by a method in accordance with the present invention;

Figure 2, 4 and 5 are a cross-sectional view of a nozzle tip of the nozzle body of Figure 1; and

Figure 3 is a partial detailed cross-sectional view of the nozzle tip of Figures 2, 4 and 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates a fuel injection nozzle 100 comprising a nozzle tip 102 manufactured in accordance with the present invention. The nozzle tip 102 comprises a wall 104 through which at least one spray hole 106 extends.

As indicated on Figure 2, each spray hole 106 comprises an entry 108, an exit 110, and a connecting through bore 112. Each connecting through bore 112 is defined by a surface 140. A nozzle sac 114 is provided inside the nozzle tip 102, the sac 114 being defined by the wall 104.

Each spray hole entry 108 is adjacent to the nozzle sac 114, and each spray hole exit 110 is remote from the nozzle sac 114, such that the connecting through bore 112 of each spray hole 106 provides a fluid communication pathway between the nozzle sac 114 and a combustion chamber (not indicated) outside the nozzle tip 102.

Methods of manufacturing the nozzle tip 102 in accordance with the present invention comprise steps in common with prior art methods, (such as forming a main bore 160 into which a needle 150 (Figure 1) is subsequently assembled, the main bore 160 including a needle seat 162, forming the nozzle sac 114 at the end of the main bore 160, and optional steps such as heat treatment, turning, grinding, and honing operations), with the addition of at least one step, which results in a localised hardening of the spray hole(s) 106. Specifically, methods of the present invention result in at least part of the surface 140 defining a spray hole bore 112, and preferably a region of the wall 104 around the or each surface 140, as partially indicated at 200 in Figure 3, being hardened. A hardening step, comprising applying localised hardening to at least part of the surfaces 140 of the spray holes 106, or the regions containing the spray holes 106, is undertaken in the present invention either before, or after, a hole forming step of forming of the spray holes 106, such as by EDM. The alternative pre-hole forming and post-hole forming methods are explained in greater detail below.

In a pre-hole forming method, the hardening step comprises applying localised hardening (for example by induction hardening), to a region, or regions, of the wall 104 of the nozzle tip 102 in which spray hole(s) 106 will subsequently be drilled in the hole forming step. For example, hardening may be applied to a region indicated generally at 400 in Figure 4, in which the or all spray hole(s) 106 are subsequently formed.

The localised hardening of the region or regions 400 of the wall 104 in which the spray holes 106 are subsequently formed could be in addition to a standard case hardening applied to all or part of the nozzle 100 (as indicated on Figure 1) or nozzle tip 102.

After the hardening step has been completed, and the spray hole(s) 106 are subsequently formed, each surface 140 defining a spray hole bore 112 will be hardened as a result of the earlier hardening step.

Alternatively, in a post-hole forming method, the hardening step comprises applying localised hardening to each spray hole 106 after the spray holes 106 have been formed in the wall 104 of the nozzle tip 102. Specifically, a case hardening process is applied to each surface 140 defining a through bore 112 of a spray hole 106. Case hardening of the surface(s) 140 defining each spray hole through bore 112 is applied to the areas indicated generally at 500 in Figure 5.

Case hardening of the bores 112 of the spray holes 106 as above could be achieved for example by passing a carburizing gas through the spray holes 106 (pre-hone state), whilst the nozzle tip 102, or at least a region around each spray hole 106, is subjected to local heating by an induction coil.

Case hardening could be applied to a depth of, for example, 0.05 - 0.20mm into the surface 140 of the spray hole bores 112.

Example hardness values of the spray hole bores 112 achieved by the method of the present invention could be in the region of 500-600HV 0.5kg at 50pm, depending on the case depth.

In an alternative embodiment of the present invention, Electrical discharge machining (EDM) could be applied to the spray hole(s) at a “soft stage”, i.e. before a heat treatment stage of the manufacturing process. In this alternative manufacturing process, existing carburising and heat treatment operations, carried out after the EDM step, result in case hardened spray holes.

Localised hardening of the spray hole surfaces 140 in the hardening step of the present invention could be achieved by modifying a known manufacturing process. For example, an external turning method step could be modified or removed, to avoid turning off a carburized layer resulting from an earlier heat treatment step. Alternatively, a current method using a carburizing case shield could be modified, by modifying the shield to allow the nozzle tip 102 to be carburized at a first heat treatment step, so that at a second heat treatment step, the sac 114 is hardened.

The present invention could additionally, or alternatively, comprise applying a localised high strength magnetic field, which could be applied for example by an electro-magnetic coil positioned outside the nozzle 100 during a hole shaping step comprising a honing process.

In the honing method step, magnetically sensitive abrading particles in the honing fluid would be electromagnetically attracted in a particular direction, to provide a favourable post-honed spray hole shape. The abrading particles in the honing fluid apply cutting forces to the surface(s) 140 of the through bore(s) 112 of the spray hole(s) 106, thereby modifying the shape of the spray hole(s) 106.

The honing method step could be enhanced by either replacing or doping the honing fluid with a magnetorheological fluid (i.e. a fluid having a viscosity which is sensitive to magnetic fields, known to be used in car suspensions). Simultaneously to the magnetorheological honing fluid being applied to the spray hole(s) 106, magnetic fields are applied in the proximity of the nozzle tip 102; the magnetic fields are positioned such that the cutting forces applied to the surface(s) 140 of the through bores 112 are modified in a favourable manner.

The present invention could comprise improved management and control of the temperature and pressure drop of the honing fluid, either upstream or downstream of the spray hole(s) 106, thereby to cause, increase, or suppress its cavitation properties during the honing process. Cavitation of the honing fluid will potentially affect the cutting forces applied to the surface 140 of a spray hole 106 along its length. For example, if partial hydraulic flip of the honing fluid occurs, this will cause the force applied to the surface near to the spray hole exit to be significantly reduced.

Furthermore, the present invention could comprise attaching an ultrasonic source to a wire EDM collet, to counteract a lateral wire vibration effect which could affect spray hole geometry. The deliberate vibration applied to the EDM wire is of a known frequency and intensity. Although this step would apply a larger vibration to the wire, it would eliminate random and uncontrolled vibration, and so the process could be better optimized. If the applied resonant frequency of the ultrasonic source was modified according to the wire size, spray hole length or taper, or even modified as the wire penetrates, this could be used to help optimize the EDM drilling process.

The methods of the present invention provide an improved spray hole geometry compared to currently known methods, i.e. the present invention provides a significantly more uniform entry radius and/or taper, and a more uniform hardness variation through a spray hole, than prior art methods.

Undesirable non-uniform shaping, such as barrelling, within a spray hole 106, is avoided by methods of the present invention, as a result of localised a hardening operation in the region of the of the spray hole(s) 106, which allows a low hardness gradient to remain in more highly stressed regions closer to the nozzle seat.

REFERENCES fuel injection nozzle 100 nozzle tip 102 wall 104 spray hole 106 spray hole entry 108 spray hole exit 110 spray hole through bore 112 nozzle sac 114 through bore surface 140 needle 150 main bore 160 needle seat 162 hardened region 400 case hardened areas 500

Claims

1. A method of manufacturing a nozzle tip (102) for a nozzle body (100) of a fuel injector, the nozzle tip comprising a wall (104); the method comprising a hole forming step, comprising forming at least one spray hole through the wall (104), wherein the or each spray hole (106) defines a fluid communication pathway from a sac (114) defined by the wall (104), through the wall (104), to an outside area of the nozzle tip (102); characterised in that the method further comprises a hardening step which results in at least part of a surface (140) defining a through bore (112) of a spray hole (106) being through hardened.

2. A method as claimed in claim 1 wherein the hardening step is undertaken before the hole forming step, and comprises applying a through hardening process to at least a region (400) of the wall (104) in which the spray holes (106) are subsequently formed.

3. A method as claimed in claim 1 wherein the hardening step is undertaken after the hole forming step, and comprises applying a hardening process to the or each surface (140) defining a through bore (112) of a spray hole (106).

5. A method as claimed in claim 2 wherein the hardening step comprises induction hardening.

6. A method as claimed in claim 3 wherein the hardening step comprising carburising and heat treatment processes.

7. A method as claimed in claim 3 wherein the hardening step comprises passing a carburizing gas through the or each spray hole(s) (106) whilst at least a region around each spray hole (106) is subjected to local heating by an induction coil.

8. A method of manufacturing and assembling a nozzle (100) of a fuel injector, including forming a main bore (160), forming a nozzle sac (114) at an end of the main bore (160), manufacturing a nozzle tip (102) using a method as claimed in any one of the preceding claims, and assembling a needle (150) into the main bore (160) of the nozzle (102).

9. A method as claimed in claim 1, comprising applying a deliberate vibration to an EDM wire of a known frequency and intensity to eliminate random and uncontrolled vibration of the EDM wire.

10. A method as claimed in claim 1, including an additional hole shaping step comprising a honing operation using a honing fluid.

11. A method as claimed in claim 10, wherein the honing operation comprises using magnetic fields in the proximity of the or each spray hole (106) to modify a path though the or each spray hole (106) taken by magnetically sensitive abrading material.

12. A method as claimed in claim 10 wherein the honing fluid comprises a magnetorheological fluid, and wherein magnetic fields are applied in the proximity of the nozzle tip at the same time as the honing operation is undertaken.

13. A method as claimed in claim 10 wherein the honing fluid temperature and/or pressure are selected upstream and/or downstream of the or each spray hole (106), thereby to cause or suppress cavitation during the honing operation.