GB2487588A

GB2487588A - Thermal shield for a fuel injector of an internal combustion engine

Info

Publication number: GB2487588A
Application number: GB1101564.1A
Authority: GB
Inventors: Giovanni Avolio; Massimiliano Melis; Miguel Angel Giovingo
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2011-01-28
Filing date: 2011-01-28
Publication date: 2012-08-01
Anticipated expiration: 2031-01-28
Also published as: GB201101564D0; GB2487588B

Abstract

A thermal shield 30 for a fuel injector 20 of an internal combustion engine 10, comprising a metallic bushing 31, preferably made of copper, suitable to surround a nozzle 23 of the fuel injector 20 and to be inserted therewith into an opening 16 of a combustion chamber 15 of the internal combustion engine 10, and a ceramic coating 34 which covers a forward portion (33, fig.3) of the metallic bushing 31 destined to be exposed to the interior of the combustion chamber 15 to cover the nozzle 23. The metallic bushing 31 sits around the nozzle 23 to protect it from the combustion process within the combustion chamber and assists in cooling the injector by conducting heat away from the injector and into the cylinder head. 14 The ceramic coating 34, of the forward portion of the bushing, that is directly exposed to the combustion process prevents the bushing itself from being unduly heated.

Description

THERMAL SHIElD FOR A FUEL INJECTOR OF AN INTERiThL CCt4BUSTIC*4 ENGINE

TEcHNflL FIElD

The present invention relates to fuel injectors of internal cornbus-tion (IC) engines, specifically of direct injection IC engines such as Diesel engines.

More precisely, the present invention relates to a thermal shield destined to protect a nozzle of a fuel injector from being heated up to undue temperatures.

BAKEXND

It is known that a fuel injector of modern Diesel engine is an elec-trically driven valve provided for receiving pressurized fuel from a fuel rail and for selectively injecting this fuel directly into the combustion charters of the engine.

In order to perform this operation, the fuel injector generally com-prises a casing destined to be fastened to the cylinder head of the Diesel engine, which coriprises an inlet connected to the fuel rail and a nozzle passing through a hole of the cylinder head into the combustion charter.

The tip of the injector nozzle is provided with a plurality of narrow holes, usually known as spray holes, which have the functions of at-omizing the fuel during the injection and of properly mixing the same with the intake air.

A drawback of these fuel injector is that the fuel combustion inside the combustion chamber heats the nozzle up to very high temperatures, thereby promoting a coking process of the amount of fuel that, after each fuel injection, remains inside the nozzle tip and the spray holes.

In greater detail, the high temperatures cause this amount of fuel partially to solidify into carbon deposits and partially to evapo-rate, thereby forming a viscous paste which adheres to the wall of the nozzle tip and the spray holes.

The result is a progressive clog of the spray holes, which in turn gives rise, and progressively increases, the difference between the quantity of fuel that the engine control unit (ECU) requires to in- ject per engine cycle and the quantity of fuel that is actually in-jected.

This deviation reduces the engine performance and also affects the control strategies of many other auxiliary apparatuses of the Diesel engine, such as for example the Exhaust Gas Recirculation (EGR) sys- tern and the Diesel Particulate Filter (DPF), thereby generally caus-ing worse fuel combustions which in turn increase fuel consumption and polluting emissions.

In order to solve this problem, it is known to fit a metallic bushing around the nozzle of the fuel injector, so as to shield the nozzle from the hot gasses and heating radiations produced by the combustion process inside the combustion chamber, and also to attain a conduc-tive transfer of heat from the injector needle to the cylinder head through the metallic bushing, which allows a certain cooling of the injector nozzle.

However, this solution is not completely effective because the metal-lic bushing is quickly heated by hot gasses and heating radiations inside the combustion chamber, thereby abruptly reducing its capabil-ity as thermal shield.

An object of an embodiment of the present invention is to solve, or at least to positively reduce, the above mentioned drawback of the known thermal shield.

Another object is to attain the mentioned aim with a simple, rational and rather inexpensive solution.

DISLOSUPE

These and/or other objects are attained by the embodiments of the in-vention as reported in the independent claims. The dependent claims concern preferred or particularly advantageous features of the em-bodiments of the invention.

In particular, an embodiment of the invention provides a thermal shield for a fuel injector of an internal combustion engine, espe-cially an internal combustion engine of a motor vehicle, wherein the thermal shield comprises a metallic bushing suitable to surround a nozzle of the fuel injector and to be inserted therewith into an opening of a combustion chamber of the internal combustion engine, so that a forward portion of the metallic bushing is destined to be ex-posed to the interior of the combustion chamber to cover the nozzle, and a ceramic coating which covers this forward portion of the metal-lic bushing.

Thanks to this solution, the ceramic coating prevents the metallic bushing to be unduly heated by the hot gasses and heating radiations which are produced during the combustion processes inside the combus-tion chanter, so as to increase the shielding of the nozzle as well as the capability of the metallic bushing to remove heat from the nozzle tip by heat conduction.

As a consequence, the temperature of the nozzle tip is kept relative- ly low during the operation of the engine, thereby reducing the ten-dency of the fuel to coke inside the nozzle tip and spray holes and thus improving the fuel injector durability, the engine efficiency and the pollutant emission reduction.

According to an aspect of the invention, the metallic bushing com-prises a rearward portion suitable to be fitted into a body of the fuel injector.

This aspect of the invention has the advantage that the thermal shield can be integrated in the fuel injector, so as to reduce the number of components to be checked and assembled during the engine assemblage.

In order to simplify the fitting of the metallic bushing into the fuel injector body, the rearward portion of the metallic bushing can be threaded.

According to another aspect of the invention, the metallic bushing comprises a annular protrusion located between the forward portion and the rearward portion.

This annular protrusion advantageously effects the function of a washer, which remains interposed between the fuel injector body and the cylinder head, in order to improve the fastening of the fuel in- jector and the sealing of the opening in which the fuel injector noz-zle is inserted.

According to still another aspect of the invention, the metallic bushing is made of copper, so as to have a great capacity of trans-ferring heat by conduction.

Another embodiment of the invention provides a fuel injector compris-ing a nozzle and the thermal shield described above coupled to the nozzle.

Still another embodiment of the invention provides an internal com- bustion engine comprising a combustion chanter, a fuel injector hav-ing a nozzle inserted into an opening of the combustion chamber, and the thermal shield described above coupled to the nozzle of the fuel injector.

BRIEF DESCRIPTICtI OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 is a schematic section of a direct injection internal corn-bustion engine of a motor vehicle.

Figure 2 is a magnified detail of figure 1.

Figure 3 is a section of a thermal shield according to an ertodiment of the present invention.

DEThILED DESCRIPTI(fl The direct injection internal combustion (IC) engine 10, in this case a Diesel engine, comprises a cylinder 11 and a reciprocating piston 12, which is accommodated inside the cylinder 11 and is conventional-ly joined to a rotating crankshaft 13.

The cylinder 11 is closed by a cylinder head 14, so that the piston 12, the cylinder 11 and the cylinder head 14 globally delimit a com-bustion chamber 15.

Even if figure 1 shows only one cylinder 11, the IC engine 10 could comprise a plurality of cylinders 11, each of which is provided with a reciprocating piston 12 connected to the crankshaft 13 and is closed by the cylinder head 14, in order to delimit a respective corn-bustion chamber 15.

The cylinder head 14 is provided with a hole, which defines an open-ing 16 of the combustion chamber 15 and which has a coaxial threaded enlargement 17 for accommodating a fuel injector 20.

The fuel injector 20 is an electrically driven valve provided for re- ceives pressurized fuel from a fuel rail (not shown) and for selec-tively injecting this fuel directly into the respective combustion chambers 15.

Accordingly, the fuel injector 20 comprises a casing 21 provided with a fuel inlet 22 connected to the fuel rail, and with a cylindrical nozzle 23, through which the fuel is injected into the combustion chamber 15.

In the present example, the casing 21 is further provided with a threaded cylindrical body 24, which is screwed into the enlargement 17 of the opening 16, in order to fasten the fuel injector 20 in a proper operating position.

In this operating position, the injector nozzle 23 passes through the opening 16 of the cylinder head 14 and penetrates into the combustion chamber 15.

As shown in figure 2, the tip 25 of the nozzle 23 is provided with a plurality of narrow holes 26, whose functions are those of atomizing the fuel during the injection and of properly mixing the same with the intake air.

According to the present embodiment of the invention, the nozzle 23 is coupled to a thermal shield 30, which is provided for protecting the former against undue heating during the operation of the IC en-gine 10.

This thermal shield 30 comprises an almost cylindrical metallic bush-ing 31 which coaxially surrounds the nozzle 23.

The metallic bushing 31 has the correct size and shape for its inter-nal surface to directly contact the lateral surface of the nozzle 23, and it is inserted therewith into the opening 16 of the cylinder head 14.

In grater detail, the metallic bushing 31 comprises a rearward tubu-lar portion 32, which is externally threaded in order to be screwed into the body 24 of the fuel injector 20, and a forward tubular por-tion 33, which juts out of the body 24 to cover the portion of the nozzle 23 that is located inside the combustion chamber 15, except the tip 25.

In this way, the forward portion 33 is exposed to the interior of the combustion chamber 15 to protect the nozzle 23 from the hot gasses and heating radiations which are generated therein during the combus-tion processes, thereby reducing the heating of the nozzle 23 due to convective and radiant heat transfer respectively.

In order to improve this shielding capability, the forward portion 33 is externally covered with a ceramic layer, which defines a coating 34 preventing hot gasses and heating radiations to unduly heat the metallic bushing 31.

The metallic bushing 31 further comprises a coaxial annular protru-sion 35, which is axially located between the forward portion 33 and the rearward portion 32.

The annular protrusion 35 and the rearward portion of the metallic bushing are uncovered by the ceramic coating 34.

Acting as a washer, the annular protrusion 35 is tightened by the body 24 of the fuel injector 20 against the abutment between the opening 16 and the enlargement 17, thereby improving the fastening of the fuel injector 20, the sealing of the opening 16, and guaranteeing a direct contact between the metallic material of the bushing 31 and the metallic material of the cylinder head 14.

In this way, the metallic bushing 31 attains a conductive heat trans-fer from the nozzle tip 25, which is still exposed to the hot gasses and heating radiations in the combustion charrer 15, to the cylinder head 14, whose greater metallic mass is able to quickly dissipate the heat coming from the tip 25.

In order to improve this effect, the metallic bushing 31 is prefera-bly made of copper.

This effect is also improved by the already mentioned ceramic coating 34, which prevents the metallic bushing 31 to be directly heated by the hot gasses and heating radiations.

Thanks to the thermal shield 30, the temperature of the nozzle tip 25 is kept at relatively low values during the operation of the IC en-gine 10, thereby reducing the tendency of the fuel to coke inside the nozzle tip 25 and spray holes 26 and thus improving the fuel injector durability, the engine efficiency and the pollutant emission reduc-tion.

While at least one exemplary embodiment has been presented in the foregoing sinnary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only exam- ples, and are not intended to limit the scope, applicability, or con- figuration in any way. Rather, the forgoing summary and detailed de-scription will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and ar-rangernent of elements described in an exerriplary embodiment without departing from the scope as set forth in the appended claims and in their legal equivalents.

REFERENCES

Internal combustion (IC) engine 11 Cylinder 12 Piston 13 Crankshaft 14 Cylinder head Combustion chamber 16 Opening 17 Enlargement 20 Fuel injector 21 Casing 22 Inlet 23 Nozzle 24 Body 25 Tip 26 Hole Thermal shield 31 Metallic bushing 32 Rearward portion 33 Forward portion 34 Ceramic coating Annular protrusion

Claims

1. Thermal shield (30) for a fuel injector (20) of an internal com-bustion engine (10), comprising a metallic bushing (31) suitable to surround a nozzle (23) of the fuel injector (20) and to be in-serted therewith into an opening (16) of a combustion chamber (15) of the internal combustion engine (10), and a ceramic coat-ing (34) which covers a forward portion (33) of the metallic bushing (31) destined to be exposed to the interior of the com-bustion chamber (15) to cover the nozzle (23).

2. Thermal shield (30) according to claim 1, wherein the metallic bushing (31) comprises a rearward portion (32) suitable tc be fitted into a body (24) of the fuel injector (20).

3. Thermal shield (30) according to claim 2, wherein the rearward portion (32) of the metallic bushing (31) is threaded.

4. Thermal shield (30) according to claim 2 or 3, wherein the metal- lic bushing (31) comprises an annular protrusion (35) located be-tween the forward portion (33) and the rearward portion (32).

5. Thermal shield (30) according to any of the preceding claims, wherein the metallic bushing (31) is made of copper.

6. Fuel injector (20) comprising a nozzle (23) and a thermal shield (30) according to any of the preceding claims coupled to the noz-zle (23).

7. Internal combustion engine (10) comprising a combustion chamber (15), a fuel injector (20) having a nozzle (23) inserted into an opening (16) of the combustion chamber (15), and a thermal shield (30) according to any claim from 1 to 5 coupled to the nozzle (23) of the fuel injector (23).