Fuel injector nozzle manufacturing method

Abstract

A method of manufacturing a fuel injector nozzle where a nozzle seat and a nozzle insert are made using a metal injection molding process. The nozzle seat and the nozzle insert are assembled and bonded together while in their green state. The resulting nozzle assembly is then debinded and sintered to obtain the desired fuel injector nozzle.

Description

FIELD OF THE INVENTION

The present invention relates to a manufacturing method for fuel injector nozzles. The present invention more specifically relates to a manufacturing method for fuel injectors using a metal injection molding process.

BACKGROUND OF THE INVENTION

One of the most critical parts of a fuel injector 10, such as the one seen in FIG. 1, is the fuel injector nozzle 20. The nozzle 20 is critical because it is responsible, in part, for the fuel spray characteristic which determines the combustion characteristics of the engine.

As engine emission standards become more stringent, so does the need for improved fuel spray characteristics. This results in more complex fuel injector nozzle design and tighter dimensional tolerances which makes the manufacture of this part increasingly difficult, and therefore more expensive.

Also, the nozzle 20 needs to interface with the cylinder head 12 of the engine and also receives a needle 22 which acts as a fuel valve. These aspects of the nozzle 20 also require precision manufacturing.

An example of such a nozzle is shown in more details in FIGS. 2 and 3. The nozzle 20, which is normally made of metal, has a passage 26 to receive needle 22. As shown in FIG. 1, the needle 22 is upwardly biased by spring 24. When biased by the spring 24, the needle 22 sits in the valve seat 32 to seal the nozzle 20. The nozzle 20 also has at least one fuel passage 42 which communicates at one end with a fuel source and at the other with passage 26. In the present example, the nozzle 20 has four fuel passages 42. As can be seen in FIG. 2, the fuel passages 42 communicate with the passage 26 such that fuel entering the passage 26 will do so generally tangentially to the wall of the passage 26. This configuration helps in the formation of the fuel spray droplets.

As can be seen in FIGS. 2 and 3, the complex shape of the fuel passages 42 make it very difficult to manufacture the nozzle 20 as a single part by using conventional manufacturing processes such as casting and machining.

Therefore, the nozzle 20 is usually made in two parts: the nozzle seat 30 and the nozzle insert 40. By doing this, at least part of the fuel passages 42 can be made as grooves in the outer surface 44 of the nozzle insert 40. When the nozzle insert 40 and the nozzle seat 30 are assembled together, the inner surface 36 of the nozzle seat 30 closes the grooves to make the fuel passages 42.

In an effort to simplify and to reduce the cost of making the nozzle insert 40, a manufacturing method known as metal injection molding (MIM) began to be used in recent years. The MIM process allows for an effective way to manufacture complex and precise parts at a relatively low cost. The MIM process uses pellets made of fine metal powders corresponding to the desired material of the part to be made mixed together with a polymeric binder.

FIG. 5 illustrates a prior art method of manufacturing a fuel injector nozzle using the MIM process to make the nozzle insert 40. MIM material 110 is first heated in order to be injected in a mold shaped in the shape of the nozzle insert 40 at step 115. The part obtained after the injection molding 115 is know as a “green” part and is slightly larger in size than the final part. The nozzle insert in the green state 120 then goes through the debinding process 125 where about 90 percent of polymeric binder is removed. The resulting part is known as a “brown” part and is porous. The nozzle insert in the brown state 130 is then sintered at step 135. During the sintering process 135, the nozzle insert in the brown state 130 is heated thus removing the majority of the remaining polymeric binder and causing the metallic powder to fuse together to form a coherent mass. The sintering 135 also causes the part to shrink to its final size. The resulting nozzle insert 140 then needs to be assembled with the nozzle seat 150.

The nozzle seat 150 is made using more traditional manufacturing method since it does not have the same level of complexity as the nozzle insert 140. The nozzle insert 140 and nozzle seat are bonded together using brazing at step 160. In order to braze the two parts together, plating, usually copper, is applied on the outer surface 44 (FIG. 3) of the nozzle insert 140 prior to assembly 155. After plating 145 of the nozzle insert 140, the nozzle insert 140 is placed in the nozzle seat 150 during the assembly step 155. The nozzle insert 140 and the nozzle seat 150 are then brazed together at step 160.

The brazing step 160 has the inconvenient of causing metallic residue to buildup on the upper surfaces 34 and 46 (FIG. 3) of the assembled nozzle. This residue needs to be removed by secondary machining operations at step 165. Once the machining 165 is completed, the final nozzle assembly 170 is ready to be used in a fuel injector.

Although the process shown in FIG. 5 does allow the manufacture of complex fuel injector nozzles, it is a lengthy process requiring multiple steps which increase the overall manufacturing cost.

Thus, there exists a need to provide a simplified method of manufacturing fuel injector nozzles.

STATEMENT OF THE INVENTION

One aspect of the present invention provides a simplified method of manufacturing fuel injector nozzles.

Another aspect of the present invention provides a method of manufacturing fuel injector nozzles using metal injection molding.

In another aspect of the invention, a method of manufacturing a fuel injector nozzle is provided where a nozzle insert and a nozzle seat are made using MIM. The nozzle insert and the nozzle seat are bonded together while in their green state to make a nozzle assembly. The nozzle assembly is then debinded and sintered.

Yet another aspect of the invention provides a method of manufacturing a fuel injector nozzle comprising: metal injection molding a nozzle insert in a green state, metal injection molding a nozzle seat in a green state, assembling the nozzle insert and the nozzle seat together while in their green states to obtain a nozzle assembly, debinding the nozzle assembly, and sintering the nozzle assembly.

In a further aspect, the method further comprises machining at least one of the nozzle insert and the nozzle seat while in their green states.

In an additional aspect, metal injection molding the nozzle insert and the nozzle seat is done simultaneously by using a common mold.

In a further aspect, the method further comprises bonding the nozzle insert and the nozzle seat together while in their green states prior to debinding the nozzle assembly

In yet a further aspect, bonding the nozzle insert and the nozzle seat together is done by using one of rotational welding, ultrasonic welding, and thermal welding.

In an additional aspect, debinding the nozzle assembly is done by using one of catalytic debinding, thermal debinding, and solvent debinding.

In another aspect of the invention, a method of manufacturing a single part from multiple parts is provided where a first part and a second part are made using MIM. The first and the second parts are bonded together while in their green state to make an assembly. The assembly is then debinded and sintered.

Yet another aspect of the invention provides a method of manufacturing a single part from multiple parts comprising: metal injection molding a first part in a green state, metal injection molding a second part in a green state, assembling the first part and the second part together while in their green states to obtain an assembly, debinding the assembly, and sintering the assembly.

In a further aspect, the method further comprises machining at least one of the first part and the second part while in their green states.

In an additional aspect, metal injection molding the first part and the second part is done simultaneously by using a common mold.

In a further aspect, the method further comprises bonding the first part and the second part together while in their green states prior to debinding the assembly

In yet a further aspect, bonding the first part and the second part together is done by using one of rotational welding, ultrasonic welding, and thermal welding.

In an additional aspect, debinding the assembly is done by using one of catalytic debinding, thermal debinding, and solvent debinding.

For purposes of this application, the terms “green state” refer to the state of an injection molded part after the injection molding process and the terms “brown state” refer to the state of a part after going through a debinding process which removes at least a portion of the polymeric binder found in the part when it is in its “green” state.

Embodiments of the present invention each have at least one of the above-mentioned aspects, but do not necessarily have all of them.

Additional and/or alternative features, aspects, and advantages of the embodiments of the present invention will become apparent from the following description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the present invention, reference will now be made to the accompanying drawings by way of illustration showing a preferred embodiment, in which:

FIG. 1 is a partial cross-sectional view of a fuel injector mounted to a cylinder head and having a fuel injector nozzle that can be manufactured using the method of the present invention.

FIG. 2 is a top view of the fuel injector nozzle shown in FIG. 1 which can be manufactured using the method of the present invention.

FIG. 3 is a cross-sectional view of the fuel injector nozzle of FIG. 2 taken along line 3-3.

FIG. 4 is a cross-sectional view of a mold used with the method of the present invention.

FIG. 5 illustrates a prior art method of manufacturing fuel injector nozzles.

FIG. 6 illustrates the method of manufacturing a fuel injector nozzle in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described with reference to a fuel injector nozzle. However, it is contemplated that the method described herein can be used with any type of nozzles and assemblies having similar manufacturing requirements as a fuel injector nozzle.

Referring now to FIG. 6, both the nozzle seat 30 and the nozzle insert 40 are made using MIM. Various MIM materials 210 can be used depending on the desired final material.

The MIM material 210 is first heated and then injected into molds corresponding to the shapes of the nozzle seat 30 and the nozzle insert 40. In a preferred embodiment, the injection molding steps 215 are done simultaneously using a single mold 50 where the mold cavities for the nozzle seat 30 and the nozzle insert 40 are disposed side by side as seen in FIG. 4. The mold 50 has a top portion 52 and a bottom portion 54. The top portion has injection gates 56 to allow for the MIM material to be injected. Vents 58 are provided between the top portion 52 and the bottom portion 54 to allow gases to escape the mold so that no gas bubbles remain in the finished part. It should be understood that the nozzle seat 30 and the nozzle insert 40 can also be molded in separate molds and that other mold, injection gate, and vent configurations are possible without departing from the scope of the present invention.

The parts obtained from the injection molding process 215 are a nozzle insert in the green state 220 and a nozzle seat in the green state 225. Although not necessary, it may be desirable in some circumstances to machine the parts while their green state at step 226. It is easier to machine the parts while in their green state because the material is softer and the parts larger than at the end of the manufacturing process.

The nozzle insert 220 and the nozzle seat 225 are then assembled (step 230) and bonded, preferably using welding (step 235), while in their green state. The preferred welding method is rotational welding. Rotational welding consists in inserting one part inside another while rotating it such that the friction between the surfaces creates enough heat to melt the surfaces and create a weld when solidifying. The advantage of this type of welding is that the assembly 230 and welding 235 steps are done simultaneously. Other welding and bonding methods such as ultrasonic welding and thermal welding are possible without departing from the scope of the present invention. Under certain conditions, the sintering 255 of the nozzle assembly 240, described below, may cause the materials of the nozzle seat 30 and the nozzle insert 40 to bond together. It is therefore contemplated that the welding step 235 may be omitted. Under those conditions, and although not necessary, welding (step 235) would improve the bond between the two parts.

Once the nozzle insert 220 and the nozzle seat 225 are welded, the resulting nozzle assembly 240, which is still in the green state, undergoes a debinding process. During the debinding process, about 90 percent of the polymeric binder is removed from the part. The polymeric binder can be removed by using a solvent, applying heat sufficient to remove the binder but not melt the metal powder (thermal debinding), or applying heat in the presence of a catalyst. The later is known as catalytic debinding, and is the preferred debinding process. Catalytic debinding uses lower heat levels than thermal debinding which allows the parts to better maintain their shape and dimensions. The catalytic debinding process is also faster than the other debinding processes described above.

Once the debinding process 240 has occurred, the resulting nozzle assembly 250 is porous since the majority of the polymeric binder has been removed and is in a state known as the brown state. The nozzle assembly in the brown state 250 then undergoes a sintering process 255, which is the last portion of the manufacturing process. During sintering 255, temperature is gradually increased, initially removing the remaining polymeric binder, then causing the metal particles to fuse and bond together. This causes the nozzle assembly 250 to shrink in size. This shrinkage, however, is predictable and the molds are over-sized to compensate for this shrinkage. This way the final nozzle assembly 260 has the desired shape and dimensions. Also, the final nozzle assembly 260 requires no further manufacturing steps prior to using it in a fuel injector. It would however be possible to do so if desired.

This method takes advantage of the MIM process to be able to create complex geometries, and by assembling and welding the parts during their green state, the number of operations, and therefore the cost, is greatly reduced.

Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.

Claims

1. A method of manufacturing a fuel injector nozzle comprising: metal injection molding a nozzle insert in a green state; metal injection molding a nozzle seat in a green state; assembling the nozzle insert and the nozzle seat together while in their green states to obtain a nozzle assembly; debinding the nozzle assembly; and sintering the nozzle assembly.

2. The method of claim 1, further comprising machining at least one of the nozzle insert and the nozzle seat while in their green states.

3. The method of claim 1, wherein metal injection molding the nozzle insert and the nozzle seat is done simultaneously by using a common mold.

4. The method of claim 1, further comprising bonding the nozzle insert and the nozzle seat together while in their green states prior to debinding the nozzle assembly.

5. The method of claim 4, wherein bonding the nozzle insert and the nozzle seat together is done by using one of rotational welding, ultrasonic welding, and thermal welding.

6. The method of claim 1, wherein debinding the nozzle assembly is done by using one of catalytic debinding, thermal debinding, and solvent debinding.

7. A method of manufacturing a single part from multiple parts comprising: metal injection molding a first part in a green state; metal injection molding a second part in a green state; assembling the first part and the second part together while in their green states to obtain an assembly; debinding the assembly; and sintering the assembly.

8. The method of claim 7, further comprising machining at least one of the first part and the second part while in their green states.

9. The method of claim 7, wherein metal injection molding the first part and the second part is done simultaneously by using a common mold.

10. The method of claim 7, further comprising bonding the first part and the second part together while in their green states prior to debinding the assembly.

11. The method of claim 10, wherein bonding the first part and the second part together is done by using one of rotational welding, ultrasonic welding, and thermal welding.

12. The method of claim 7, wherein debinding the assembly is done by using one of catalytic debinding, thermal debinding, and solvent debinding.