Fuel injector

Abstract

 A fuel injector (10) comprises an injector body (12), a nozzle body (16) and a retainer (42) for connecting the nozzle body (16) to the injector body (12). The nozzle body (16) comprises a fuel channel (22) extending from an upper contact surface (40) of the nozzle body (16) to at least one nozzle orifice (26). The injector body (12) comprises a low-pressure drain (36) and a fuel channel (20) extending from an upper part of the injector body (12) to a lower contact surface (38) of the injector body (12). The retainer (42) holds the lower contact surface (38) of the injector body (12) and the upper contact surface (40) of the nozzle body (16) in compressive butting relationship in such a way that the fuel channel (22) of the nozzle body (16) and the fuel channel (20) of the injector body (12) form a fuel delivery passage. An important feature of the fuel injector (10) is that at least one drain channel (44) extends from the retainer (42) to the low-pressure drain (36) arranged in the injector body (12).

Description

Introduction

[0001] The present invention relates to fuel injectors and particularly to fuel injectors for diesel engines.

State of the Art

[0002] Fuel injectors are well known in association with diesel engines. They are used to inject fuel into a combustion chamber of the engine. Such fuel injectors generally comprise a nozzle body, which is connected to an injector body by means of a retainer. A fuel delivery passage extends from a fuel pump through the injector body and nozzle body to a nozzle cavity arranged in the nozzle body. The tip of the nozzle body has at least one nozzle orifice so that fuel can be injected from the nozzle cavity into the combustion chamber. A valve needle is slideably movable in an axial central bore arranged in the nozzle body. An axial central bore of the injector body houses an actuator for actuating the valve needle, so as to open or close the nozzle orifice to either allow or prohibit fuel flow into the combustion chamber. The nozzle body has an upper contact surface, which is pressed against a lower contact surface of the injector body. The two bodies are aligned such that the fuel delivery passage is formed by two channels, one arranged in each of the bodies. Due to the high pressure of the fuel flowing through the fuel delivery passage, the connection point of the two channels is a potential leakage point. Generally, leakage is prevented by means of a retainer, which maintains the lower contact surface of the injector body and the upper contact surface of the nozzle body in compressive butting relationship. As the injection pressure of the fuel is increased, the compression force on the contact surfaces between injector body and nozzle body also needs to be increased in order to prevent leakage.

[0003] In case of a failure of the high pressure connection between the contact surfaces of injector body and nozzle body, fuel leaks from the fuel delivery passage, either towards the central bore or towards the retainer. If the fuel leaks into the central bore, it can be evacuated via a low-pressure drain arranged therein. However, if the fuel leaks towards the retainer, it accumulates between the inner walls of the retainer and the outer walls of the injector body and/or of the nozzle body. As the level of fuel in the retainer rises, the fuel leaks out of the retainer either into the atmosphere or into the cylinder head oil.

[0004] Nowadays, as the injection pressures of the fuel can be as high as 2000 bar, it becomes increasingly more difficult to prevent such leakage. It would be necessary to provide a better and more complex surface finish of the contact surfaces of injector body and nozzle body, which is of course rather costly. It will be appreciated that it is not sensible to indefinitely increase the compression force on the contact surfaces of injector body and nozzle body.

[0005] Furthermore, the trend in the automobile industry is to use lighter and smaller components. However, the smaller the diameter of the fuel injector, the smaller the contact surfaces of injector body and nozzle body surrounding the fuel delivery passage, and hence the greater the risk of leakage.

Object of the invention

[0006] The object of the present invention is to provide a fuel injector which does effectively prevent leakage of fuel out of the fuel injector, and which does not significantly increase the manufacturing costs.

General description of the invention

[0007] In order to overcome the abovementioned problems, the present invention provides a fuel injector comprising an injector body, a nozzle body and a retainer for connecting the nozzle body to the injector body. The nozzle body comprises a fuel channel extending from an upper contact surface of the nozzle body to at least one nozzle orifice. The injector body comprises a low-pressure drain and a fuel channel extending from an upper part of the injector body to a lower contact surface of the injector body. The retainer holds the lower contact surface of the injector body and the upper contact surface of the nozzle body in compressive butting relationship in such a way that the fuel channel of the nozzle body and the fuel channel of the injector body form a fuel delivery passage. An important feature of the fuel injector is that at least one drain channel extends from the retainer to the low-pressure drain arranged in the injector body. The drain channel leads the leaked fuel from between the inner walls of the retainer and the outer walls of the injector body and/or nozzle body to the low-pressure drain, from where it can easily be evacuated. The low-pressure drain is present in state of the art injectors, for evacuating excess fuel being pushed up in between the nozzle body and a valve needle arranged therein. A fuel return passage comprising the drain channel and the low-pressure drain is formed. As the leaked fuel can now easily evacuate through the fuel return passage, leakage of fuel out of the fuel injector is prevented. No fuel is leaked into the atmosphere or into the cylinder head oil. Furthermore, due to the fuel return passage, it is not necessary to provide the contact surfaces of injector body and nozzle body with a better and more complex surface finish. The fuel injector can hence be manufactured without any significant increase of manufacturing costs.

[0008] According to an embodiment, one or more intermediate bodies can be arranged between the injector body and the nozzle body, each intermediate body comprising a fuel channel extending from an upper contact surface of the intermediate body to a lower contact surface of the intermediate body. Although the injector then has further potential leakage points, the drain channel still leads the leaked fuel from between the inner walls of the retainer and the outer walls of the injector body and/or nozzle body and/or injector body to the low-pressure drain, from where it can easily be evacuated.

[0009] According to an embodiment, the nozzle body comprises a valve needle and the injector body e.g. comprises an axial bore therethrough for receiving an actuation means for actuating the valve needle.

[0010] The axial bore can have the low-pressure drain arranged therein, whereby no additional bore needs to be arranged in the injector body.

[0011] The at least one drain channel most advantageously comprises a groove arranged in the lower contact surface of the injector body and/or in the upper contact surface of the nozzle body. If applicable, a groove can be arranged in the lower and/or upper contact surface of the intermediate body. The drain channel can in this way be most economically produced as it is not necessary to provide the drain channel with a high quality finish.

[0012] It is also possible for the at least one drain channel to comprise a bore arranged through the injector body and/or through the nozzle body and/or through the intermediate body, thereby linking any part of the inner wall of the retainer with the low-pressure drain in the injector body.

[0013] According to an embodiment, an upper part of the retainer forms with a lower part of the injector body a sealing connection. It is thereby ensured that no fuel can leak into the atmosphere or into the cylinder head oil.

[0014] The sealing connection is advantageously formed through a closely wound thread on the retainer and a corresponding thread on the injector body. Such a thread provides a self-sealing connection.

[0015] The sealing connection can also be formed through a sealant applied between the retainer and the injector body.

[0016] The sealant can e.g. comprise an adhesive, whereby the retainer is securely connected to the injector body while at the same time ensuring that no fuel can leak into the atmosphere or into the cylinder head oil.

Detailed description with respect to the figures

[0017] The present invention will be more apparent from the following description of a not limiting embodiment with reference to Fig.1, which shows a section through a fuel injector 10 according to the invention.

[0018] The fuel injector 10 comprises an injector body 12 having an axial bore 14 therethrough and a nozzle body 16 having an axial bore 18 therethrough. The injector body 12 and the nozzle body 16 each comprise a fuel channel 20, 22 for delivering fuel from a fuel pump (not shown) to a nozzle cavity 24 arranged around the axial bore 18 in the nozzle body 16.

[0019] The fuel can then flow from the nozzle cavity 24 through the axial bore 18 and at least one nozzle orifice 26 arranged in the tip of the nozzle body 16 into a combustion chamber of an engine (not shown). The nozzle orifice 26 can be blocked by means of a valve needle 28 which is slideably mounted in the axial bore 18 of the nozzle body 16. In order for fuel to be able to flow towards the nozzle orifice 26, the diameter of a lower part 30 of the valve needle 28 is smaller than the diameter of the axial bore 18. In order for the valve needle 28 to be linearly guided in the axial bore 18, the diameter of an upper part 32 of the valve needle 28 is essentially the same as the diameter of the axial bore 18. The valve needle 28 is actuated by means of an actuator 34 arranged in the axial bore 14 of the injector body 12. The diameter of the actuator 34 is smaller than the diameter of the axial bore 14 of the injector body 12 so as to form a low-pressure drain 36 in the axial bore 14. The low-pressure drain 36 is present in state of the art injectors, for evacuating excess fuel being pushed up in between the nozzle body 16 and the valve needle 28.

[0020] The injector body 12 has a lower contact surface 38 which is held in compressive butting relationship with an upper contact surface 40 of the nozzle body 16 by means of a retainer 42. The lower contact surface 38 of the injector body 12 comprises a groove therein, which extends from an inner wall of the retainer 42 to the axial bore 14, thereby forming a drain channel 44.

[0021] An upper part of an internal wall of the retainer 42 comprises an internal thread which engages a corresponding external thread on an outer wall of the injector body 12, whereby the nozzle body 16 and the injector body 12 can be held together by simple relative rotation of the retainer 42 with respect to the injector body 12. The thread is closely wound, so that it provides a self-sealing connection 46 between the retainer 42 and the injector body 12.

[0022] In case of a failure of the high-pressure connection between the contact surfaces 38, 40 of the injector body 12 and the nozzle body 16, fuel leaks from the fuel channels 20, 22, either towards the axial bore 14 or towards the retainer 42. If the fuel leaks into the axial bore 14, it can be directly evacuated via the low-pressure drain 36. However, if the fuel leaks towards the retainer 42, it accumulates between the inner walls of the retainer 42 and the outer walls of the injector body 12 and/or of the nozzle body 16. Due to the drain channel 44, the fuel accumulating between the inner walls of the retainer 42 and the outer walls of the injector body 12 and/or of the nozzle body 16 is lead into the axial bore 14 and can hence be evacuated via the low-pressure drain 36.

Claims

1. Fuel injector (10) comprising an injector body (12), a nozzle body (16) and a retainer (42) for connecting said nozzle body (16) to said injector body (12);

said nozzle body (16) comprising a fuel channel (22) extending from an upper contact surface (40) of said nozzle body (16) to at least one nozzle orifice (26);

said injector body (12) comprising a low-pressure drain (36) and a fuel channel (20) extending from an upper part of said injector body (12) to a lower contact surface (38) of said injector body (12);

said retainer (42) holding said lower contact surface (38) of said injector body (12) and said upper contact surface (40) of said nozzle body (16) in compressive butting relationship in such a way that said fuel channel (22) of said nozzle body (16) and said fuel channel (20) of said injector body (12) form a fuel delivery passage;

characterised by
at least one drain channel (44) extending from said retainer (42) to said low-pressure drain (36) arranged in said injector body (12).

2. Fuel injector according to claim 1, wherein at least one intermediate body is arranged between said injector body (12) and said nozzle body (16), said at least one intermediate body comprising a fuel channel extending from an upper contact surface of said intermediate body to a lower contact surface of said intermediate body.

3. Fuel injector according to claim 1 or 2, wherein

said nozzle body (16) comprises a valve needle (28) and

said injector body (12) comprises an axial bore (14) therethrough for receiving an actuation means (34) for actuating said valve needle (28).

4. Fuel injector according to claim 3, wherein said axial bore has said low-pressure drain (36) arranged therein.

5. Fuel injector (10) according to any of the previous claims, wherein said at least one drain channel (44) comprises a groove arranged in said lower contact surface (38) of said injector body (12) and/or of said intermediate body.

6. Fuel injector (10) according to any of the previous claims, wherein said at least one drain channel (44) comprises a groove arranged in said upper contact surface (40) of said nozzle body (16) and/or of said intermediate body.

7. Fuel injector (10) according to any of the previous claims, wherein said at least one drain channel (44) comprises a bore arranged through said injector body (12).

8. Fuel injector (10) according to any of the previous claims, wherein said at least one drain channel (44) comprises a bore arranged through said nozzle body (16).

9. Fuel injector (10) according to any of claims 2 to 8, wherein said at least one drain channel (44) comprises a bore arranged through said intermediate body.

10. Fuel injector (10) according to any of the previous claims, wherein a part of said retainer (42) forms with a part of said injector body (12) a sealing connection (46).

11. Fuel injector (10) according to claim 10, wherein said sealing connection (46) is formed through a closely wound thread on said retainer (42) and a corresponding thread on said injector body (12).

12. Fuel injector (10) according to claim 10 or 11, wherein said sealing connection (46) is formed through a sealant applied between said retainer (42) and said injector body (12).

13. Fuel injector (10) according to claim 12, wherein said sealant comprises an adhesive.

Drawing