A FUEL INJECTOR HAVING A FUEL CHANNEL WITH OPTIMIZED

DURABILITY

The present invention relates to a fuel injector having a body with a fuel channel durability of which is optimized according to high fuel pressures in an internal combustion engine and a method of manufacturing the same. Parts of a fuel injection system not only experience very high internal pressures, but are also subjected to significant fluctuations in the internal pressure. As a result, components must meet correspondingly high strength requirements.

Autofrettage is a technique that increases the capacity of high pressure. In autofrettage process, a part is subjected to an internal pressure which is capable of causing yielding within the wall and then removed. Upon the release of this pressure, a compressive residual stress is developed at certain radial depth at the bore. In the art, it is know that an autofrettage processing is used to enhance the durability of the final product, and also increase its resistance to stress corrosion cracking. However, there is no proper use of the autofrettage technique in the fuel injection systems. Further, disadvantages are caused when the autofrettage process is directly applied throughout a straight channel or bore, autofrettage medium of the autofrettage process may lead to erosion corrosion by hitting a wall of a channel thereof.

Further, any fuel leaking between the various surfaces is fed back into a tank along a backflow conduit comprising a backflow connector. In order to prevent the backflow connector being forced out by the fuel flowing out of the fuel injector, the backflow connector must be attached to the fuel injection valve securely. During the operation of the injection valve, fuel pressure rapidly fluctuates over a large range of pressure, which creates varying mechanical stresses in the peripheral wall of the body of the fuel injection valve. Said stresses, along with tightening stresses concentrate in fragile areas where the wall thickness varies and potentially cracks are generated. Furthermore, an electrical connector and a backflow tube of a fuel injection valve in a fuel injection system are connected to the injector body through plastic injection molding process. The material of the injection valve body is, mostly, limited up to a system pressure of 2000 bar and said plastic injection molding process is strongly depends on molding parameters such as temperature, pressure and prevents injection molding rework. The injection molding process requires the use of an injection molding machine, raw plastic material, and a related mold.

A primary object of the present invention is to eliminate the above-mentioned shortcomings of the prior art.

The present invention proposes a fuel injection valve for an internal combustion engine, comprising : a body having a fuel channel which extends substantially along the longitudinal axis of the body. Said body comprises a bore allowing to send an autofrettage medium for an autofrettage process, which extends angularly to the fuel channel and in that the bore has an angle with the fuel channel of about between 30° and 90° allowing the autofrettage medium to be directed and flowed through the bore to the fuel channel at a predetermined angle for eliminating erosion corrosion at the inner peripheral surface of the fuel channel. Thus, said inner peripheral surface is enhanced in fatigue strength for inner pressures.

In a possible embodiment, at least a portion of the inner peripheral surface of the fuel channel is defined as a portion being on the wall of the fuel channel against an outlet of the bore. As a result, unwanted erosion corrosion which mostly effect the portion on the opposite inner the wall of the fuel channel with respect to the outlet is significantly eliminated.

In a possible embodiment, the bore has a conical outwardly open seat surface which is formed at an outward opening end of the bore. Thus, an inlet connector for providing the autofrettage medium can be connected more easily to the body by eliminating misalignment.

In a possible embodiment, said bore has internal threads formed on, at least partly, an inner wall of the bore allowing a screw-type connection with an inlet connector guiding the autofrettage medium. With this arrangement, it is provided to connect an inlet connector with the bore more firmly and robust.

In a possible embodiment, the body has a first connection portion in which a backflow tube can be attached and the first connection portion has an internal threads allowing a screw-type connection with a corresponding part of the backflow tube. In the art, an injection molding method mostly requires an injection molding machine, raw plastic material, and a related mold parts, said screw-type connection not only eliminates the injection molding process but also provides a more robust, durable and economical connection.

In a possible embodiment, the body has a second connection portion in which an electrical connector can be attached and the second connection portion has an internal threads allowing a screw-type connection with a corresponding part of the electrical connector. Similarly, said screw-type connection not only eliminates the injection molding process but also provides a more robust, durable and economical connection. Further, the second connection portion can be provided with a sealing washer which also helps to increase an impermeability of the second connection portion.

In a possible embodiment, the body is provided with at least one support region in which the bore is formed. With this armament, said support region helps to increase the outer wall thickness of the body by eliminating any decrease in the durability of the body.

According to another aspect of the present invention, the present invention further proposes a fuel injection valve for an internal combustion engine, comprising: a body having a fuel channel extending substantially along a longitudinal axis of the body. Said body comprises a bore branched with at least one first and second arms communicating with the flow passage; and the diameter of the first arm and the second arm of the bore are smaller than the diameter of the bore allowing the autofrettage medium to be directed and flowed to the fuel channel from the bore for eliminating erosion corrosion at the inner peripheral surface of the fuel channel. With this arrangement, the autofrettage medium can be sent through more than branched arms such that the flow rate of the autofrettage medium is lowered which results regional tension to be eliminated. Further, stress concentration in the vicinity of the fuel channel is relaxed.

In a possible embodiment, the bore has a conical outwardly open seat surface formed at an outward opening end of the bore. Thus, an inlet connector for providing the autofrettage medium can be connected more easily to the body by eliminating misalignment.

In a possible embodiment, said bore has having internal threads formed on inner surface of the bore allowing a screw-type connection with an inlet connector guiding the autofrettage medium. With this arrangement, it is provided to connect an inlet connector with the bore more firmly and robust.

In a possible embodiment, the each of the first arm and the second arm are connected with the bore through an intermediate connection portion. Thus, regional deformations in the vicinity of the fuel channel is eliminated.

In a possible embodiment, the intermediate connection portion is arranged parallel with respect to the longitudinal axis of the body whereby the first arm and the second arm are connected to the fuel channel at an angle of between 80° and 100. Thus, regional deformations in the vicinity of the fuel channel is eliminated.

In a possible embodiment, the body has a first connection portion with an internal threads allowing a screw-type connection with a corresponding part of a backflow tube and has a second connection portion with an internal threads allowing a screw- type connection with a corresponding part of an electrical connector. In the art, an injection molding method mostly requires an injection molding machine, raw plastic material, and a related mold parts; said screw-type connection not only eliminates the injection molding process but also provides a more robust, durable and economical connection.

According to the present invention, a method for forming a body is also proposed, said method for forming a body of a fuel injection valve, comprising the steps of: providing a body with a fuel channel extending substantially along a longitudinal axis (x) of the body; forming a bore as extending angularly to the fuel channel and/or branched with at least two first and second arms communicating with the flow passage for eliminating erosion corrosion on an inner wall of the fuel channel when applying an autofrettage process; inserting and filling the bore with an autofrettage- medium of the autofrettage process; subjecting the inner peripheral surface of the body, in particular the fuel channel, to the autofrettage processing with applying an internal pressure; increasing the pressure to be above 1 kbar/s; holding the body at a predetermined time with a constant pressure value; and draining the fuel channel. Thus, the body of the fuel injection valve is improved in durability while the fuel channel is enhanced in fatigue strength for inner pressures by the autofrettage medium. Subjecting the body such method results in that the body for the fuel injection valve has a higher fatigue resistance compared with a conventional body for the fuel injection of the same dimensions.

The figures, brief explanations of which are herewith provided, are solely intended for providing a better understanding of the present invention and are as such not intended to define the scope of protection or the context in which said scope is to be interpreted in the absence of the description.

FIG. 1 is a cross-sectional view of a body of a fuel injection valve wherein the autofrettage process is applied in which the inlet connector is used to supply autofrettage medium and two fixing adaptors are used to hold the body at the end sides, according to the present invention.

FIG. 2 is a partial cross-sectional view of a body of a fuel injection valve shown in FIG. 1.

FIG. 3 is a cross-sectional view of a body of a fuel injection valve according to an alternative embodiment of the present invention shown in Fig. 2.

FIG. 4 is a cross-sectional view of a body of a fuel injection valve according to an alternative embodiment of the present invention in which a bore is branched with at least one first and second arms. FIG. 5 is a cross-sectional view of a body of a fuel injection valve according to an alternative embodiment of the present invention shown in Fig. 4. FIG. 6 is a partial cross-sectional view of a body of a fuel injection valve where a backflow tube is attached to a body of the fuel injection valve according to the present invention.

FIG. 7 is a partial cross-sectional view of a body of a fuel injection valve where an electrical connector is attached to a body of the fuel injection valve according to the present invention.

FIG. 8 is a schematic graph that shows steps of an autofrettage process to be applied on a body of a fuel injection valve for forming according to the present invention.

According to the present invention, to increase the compressive strength of the bore (22) being subjected to a so-called autofrettage treatment, by way of which a considerable increase in strength of the wall sections can be obtained. The bore (22) of the body (20) is subjected to an internal pressure which is higher than a subsequent operating pressure and higher than the yield strength of the material, specifically in such a way that regions on the inner wall of the component are plasticized, whereas regions on the outer wall remain elastic. As a result of the plasticized inner region, the elastically deformed outer region is prevented from fully deforming back into its initial position, such that the outer region remains expanded, and thus, in the inner region, an internal compressive stress is generated which counteracts the operating load. As a result, by way of the autofrettage treatment, the compressive strength of the body (20) can be considerably increased. According to the present invention, mainly two different type of a body (20) for a fuel injection valve and a method thereof for forming said body (20) is proposed. According to first aspect of the present invention, the fuel injection valve for an internal combustion engine, comprising: a body (20) having a fuel channel (24) which extends substantially along the longitudinal axis of the body (20). Said body (20) comprises a bore (22) allowing to send the autofrettage medium for an autofrettage process, which extends angularly to the fuel channel (24) and in that the bore (22) has an angle (a) with the fuel channel (24) of about between 30° and 90° allowing the autofrettage medium to be directed and flowed through the bore (22) to the fuel channel (24) at a predetermined angle for eliminating erosion corrosion at the inner peripheral surface of the fuel channel (24). According to the present invention, an autofrettage processing is applied to the body (20) of the fuel injection valve, compressive residual stresses are generated and an improvement in fatigue strength for inner pressures is achieved throughout the inner peripheral surface of the body (20), in particular in the fuel channel (24). The bore (22) can have a conical outwardly open seat surface (27) formed at an outward opening end of the bore (22). Similarly, the fuel channel can have a conical outwardly open pressure-receiving seat surface (25) formed at an outward opening end of the bore fuel channel (24)

The fuel channel (24) defines an internal volume for receiving, in use, high pressure fuel, and communicates with the bore (22) formed in the body (20). Said bore (22) has an inner surface and is preferably provided with a threaded portion having internal threads (26) on said inner surface. FIG. 1 shows a longitudinal cross- sectional view of the body (20) where the autofrettage process through an inlet connector (60) which is attached to the body (20) to supply an autofrettage medium thought its inner channel (61) and two fixing adaptors (70) are attached to hold the body (20) at the opposite end sides. The inner surface of the bore (22) having internal threads (26) allows a screw-type connection with the inlet connector (60). The internal threads (26) can be screw thread which engages with the corresponding matching portions.

The body (20) of a fuel injection valve having the electrical connector (50) via which the fuel injection valve can be controlled. In the art, an electrical connector (50) and a backflow tube (40) of the fuel injection valve in a fuel injection system are connected to the body (20) through a plastic injection molding process. In the present invention, such injection process is eliminated by use of screw-type connection with the parts and corresponding connection portions thereof. Referring to the Fig. 6 and 7, the body (20) has a first connection portion (211) with an internal threads allowing a screw-type connection with a corresponding part of a backflow tube (40) and has a second connection portion (212), similarly, with an internal allowing a screw-type connection with a corresponding part of an electrical connector (50). This connection helps to obtain a solid and durable connection between the parts and helps to increase the internal pressure of the system where the material of the injection valve body (20) can limited up to a system pressure of 2000 bar. Further, the second connection portion (212) can be provided with a sealing washer that helps to increase an impermeability when an engagement is maintained.

In the first aspect of the present invention, as shown in Fig 1-3, the bore (22) extends in a plane which is inclined with respect to the longitudinal axis of the body (x), and has an angle (a) with the fuel channel (24) of about between 30° and 90° which allows the autofrettage medium to enter in a predetermined direction through the bore (22) such that the adverse effect of the autofrettage medium is prevented due to the erosion corrosion which occurs when the autofrettage medium directly hits to an inner wall of the fuel channel (24) when exiting from the outlet (21) of the bore (22). The body (20) can be provided with at least one support region (31) in which the bore (22) is formed. A shown in Figs 1-5, the body (20) is provided with two support regions (31) as an outwardly protruding portion, in one of which said bore (22) is formed. With this support regions (31), the strength of the body (20) is, however, maintained despite the bore (22) is created. Said support regions (31) help to increase the outer wall thickness of the body (20). According to another aspect of the present invention, such adverse effect of the autofrettage medium can be eliminated by branching a single bore (22) into which the autofrettage medium enters. In this aspect of the present invention, as shown in Fig. 4-5, the fuel injection valve for an internal combustion engine, comprises: a body (20) having a fuel channel (24) extending substantially along a longitudinal axis (x) of the body (20). Said body (20) comprises a bore (22) branched with at least one first and second arms (28, 29) communicating with the flow channel (24); and the diameter of the first arm (28) and the second arm (29) of the bore (22) are smaller than the diameter of the bore (22) allowing the autofrettage medium to be directed and flowed to the fuel channel (24) from the bore (22) for eliminating erosion corrosion at the inner peripheral surface of the fuel channel (24). Similarly as in Fig. 1-3, the adverse effect of the autofrettage medium is prevented due to the erosion corrosion which occurs when the autofrettage medium directly hits to an inner peripheral surface of the fuel channel (24). At least a portion of the inner peripheral surface of the fuel channel (24) is defined as a portion being on the wall of the fuel channel (24) against the outlet (21) of the autofrettage medium from the bore (22) in the direction of flow. The bore (22) can have a conical outwardly open seat surface (27) formed at an outward opening end of the bore (22). Similarly, the fuel channel (24) can have a conical outwardly open pressure-receiving seat surface (25) formed at an outward opening end of the bore fuel channel (24).

Referring to the Fig. 4, the bore (22) can have a first arm (28) and a second arm (29) in which the first arm (28) and the second arm (29) are configured to in communication with the fuel channel (24). In a possible embodiment, number of the connection hole can vary. Said first arm (28) and second arm (29) can be formed as a channel which allows the autofrettage medium to transfer from the bore (22) to the fuel channel (24). The first arm (28) and second arm (29) can extend in a plane which is inclined with respect to the longitudinal axis of the body (x), and has an angle (a) with the fuel channel (24) of about between 30° and 80°. With this arrangement, it is ensured that the autofrettage medium can be sent at a predetermined angle while the flow rate of the autofrettage medium is lowered. Referring to another embodiment of the present invention, each of the first and the second arm (28, 29) of the bore (22) is connected with the fuel channel (24) through an intermediate connection portion (33), as shown in Fig. 5. Said intermediate connection portion (33) can be arranged to be parallel with respect to the longitudinal axis (x) of the body (20) whereby the first arm (28) and the second arm (29) are connected to the fuel channel (24) at an angle of between 80° and 100. In a possible embodiment, said intermediate connection portion (33) can extend in a plane which is inclined with respect to the longitudinal axis (X) of the body (20). As shown in Fig. 4, the bore (22) can have two outlets (21) each of formed at the end of the first and the second arms (28, 29). At least a portion of the inner peripheral surface of the fuel channel (24) can be defined as a portion being on the wall of the fuel channel (24) against outlets (21) of the bore (22). According to the present invention, a method for forming a body (20) of a fuel injection valve is also proposed. The method for forming a body (20) of a fuel injection valve, comprising the steps of: providing a body (20) with a fuel channel (24) extending substantially along a longitudinal axis (x) of the body (20); forming a bore (22) as extending angularly to the fuel channel (24) and/or branched with at least two first and second arms (28, 29) communicating with the fuel channel (24) for eliminating erosion corrosion on an inner wall of the fuel channel (24) when applying an autofrettage process; inserting and filling the bore (22) with an autofrettage-medium of the autofrettage process; subjecting the inner peripheral surface of the body (20), in particular the fuel channel (24), to the autofrettage processing with applying an internal pressure; increasing the pressure to be above 1 kbar/s; holding the body (20) at a predetermined time with a constant pressure value; and draining the fuel channel (24). After the autofrettage process is completed, the bore (22) can be tightened with a liquid glue to prevent micro leakage during many years of use. With the arrangements according to the present invention, while benefiting from the autofrettage process, possible adverse effects of the autofrettage process are eliminated. Further, maximum stresses of the body in response to operating pressures are decreased to a considerable extent to thereby impart a longer service life to the fuel injection valve. The bore (22) is processed and hardened by the plastic deformation in the entire inner surface of the fuel channel (24) by the autofrettage processing.

In Fig. 8, steps of the autofrettage process are schematically shown. At first step, as indicated FI, the body (20) of the fuel injection valve is filled with the autofrettage medium through the inner channel (61) of the inlet connector (60) as shown in Fig. 1. At the second step, as indicated F2, the internal pressure is increased to be above >1 kbar/s and at the third step, as indicated F3, the body (20) is held at a predetermined time with a constant pressure value. At the last fourth and fifth steps, the pressure of the system in lowered and the autofrettage medium in the body (20) is drained. As an additional step, the internal layers can be subjected to a relatively low temperature heat treatment results in that the elastic limit of the body (20) can further increased. Said autofrettage processing in the present invention is a process in which pressing forces produced by a fluid pressure are applied to the fuel channel (24) in the body (20) to exert stresses on the whole inner peripheral surface of the body (20). According to the present invention, when the autofrettage is entered to the body (20) as shown in step F2 in Fig. 8, adverse effect of autofrettage medium is eliminated forming a bore (22) as extending angularly to the fuel channel (24) and/or branched with at least two first and second arms (28, 29) in fluid communication with the fuel channel (24).

List of reference signs

20. Body

21. Outlet

211. First connection portion

212. Second connection portion

22. Bore

24. Fuel channel

25. Pressure-receiving seat surface

26. Internal thread

27. Seat surface

28. First arm

29. Second arm

31. Support region

33. Intermediate connection portion

40. Backflow tube

50. Electrical connector

60. Inlet connector

61. Inner channel

70. Fixing adaptor

X Longitudinal axis of the body