Technical Field of the Invention The present invention relates to a novel fuel injector for delivery of fuel to the intake system of an internal combustion engine. More particularly, the present invention relates to a fuel injector which is coated with a hydrophobic material so as to prevent fluid migration towards the injector. Background of the Invention

Fuel injectors which are used for delivering fuel to the engine, operate at high pressure and across wide temperature ranges for extended durations. These injectors comprise an overmold portion on the surface of the injector, which is utilized mainly for encapsulating internal components, thereby protecting the injector from the environment. For instance, overmolding provides corrosion protection of the injector as well as isolation of the electrical components within the injector.

Fuel injector and the overmolded portion are made of different materials. At high temperature and/or pressure conditions, gaps may be formed along the contact interference between the overmolding and the injector which results in fluid migration towards the injector throughout these gaps. Thus, there is a need for a novel fuel injector in which fluid migration is eliminated. Objects of the Invention

Primary object of the present invention is to prevent fluid migration towards the injector. Another object of the present invention is to provide a long lasting fuel injector.

Another object of the present invention is to ensure a fuel injector which is impermeable to any fluid in the environment and durable at high temperature and pressure conditions. Summary of the Invention

The aforementioned objects are achieved by the fuel injector of the present invention. In a first aspect, the present invention relates to a fuel injector provided that at least one portion of said injector is covered with an overmolding material; wherein the overmolded portion is at least partly coated with a material having hydrophobic characteristics.

In a possible embodiment of the invention, the fuel injector is used in diesel fuel injection system.

In a possible embodiment of the invention, the overmolding material comprises PA-66 or PA- 6T. In a possible embodiment of the present invention, the overmolding material is PA-66.

In a possible embodiment of the present invention, the material having hydrophobic characteristics is a super-hydrophobic material. In a possible embodiment of the present invention, the superhydrophobic material is manganese oxide polystyrene (Mn0 ₂ /PS).

In a possible embodiment of the present invention, the superhydrophobic material is zinc oxide polystyrene (ZnO/PS) na no-composite.

In a possible embodiment of the present invention, the superhydrophobic material is precipitated calcium carbonate.

In a possible embodiment of the present invention, the superhydrophobic material is carbon nano-tube structures.

In a possible embodiment of the present invention, the superhydrophobic material is silica nano-coating. In a possible embodiment of the present invention, the contact angle of the material having hydrophobic characteristics is greater than 150°.

Detailed Description of the Invention

Fuel injectors which are used in fuel injection systems, dispense fuel to the combustion chamber. Traditional fuel injectors have a overmolded surround in connection with the metal body. Overmolding protects the inner components of the injector from the environment. The body of the injector is made of metal and the injector is overmolded with a suitable plastic material. The material of the overmold and the body of the injector are completely different from each other in terms of their physical and chemical characteristics.

Most importantly, thermal expansion values are different in metals and plastics. Thermal expansion in plastics is greater than that of metals. Since plastic and metal do not expand in the same amount, holes may be formed along the contact interference between the overmolding and the injector when exposed to the heat during operation. Holes are not desirable since they cause fluid migration towards the injector throughout these holes. Fluids may be present in the injector medium during the operation of the fuel injection system due to the high temperature conditions. As fluid passes through these holes towards the fuel injector, the deformation of the injector becomes fast and performance of the system gets poorer. On the other hand, electric connector is surrounded with an overmolding layer; fluid migration to the electric connector may cause serious problems in electric conduction. Fluid migration further leads to poor durability and shortened lifetime of the fuel injectors.

The drawbacks arising from the fact of fluid migration towards the injector are overcome by the fuel injector of the present invention.

According to the present invention, electric connector is located on the head of the injector. This connector is used to make the connection between the incoming current to the injector and the engine system. The electric connector is molded with a suitable overmolding material. Afterwards, said overmolded portion is at least partly coated with a hydrophobic material. In this manner, the fuel injector comprising hydrophobic coating on the surface of the overmolded portion is provided. The hydrophobic coating has the ability of repelling water; hence it is adapted to prevent the deposition of the fluid thereon. In other words, the hydrophobic coating limits adhesion between the fluid droplets and a base surface. Overmolding material may be any polymeric material which is suitable for plastic injection molding; preferably overmolding material comprises polyamide 6,6 (PA66), polyamide 6T (PA6T). Overmold is formed in virtue of an injection molding process. In overmolding step; the holding pressure ranges from 332 bar to 551 bar, the process pressure ranges from 1567 bar to 1710 bar and the process temperature ranges from 256 °C to 281 °C.

The fuel injector has a metal support body; the body of the injector is preferably made of steel.

At least one portion of the fuel injector is surrounded with a suitable overmolding material. Electric connector which is located on the head portion of the fuel injector is overmolded with a polymeric material such as PA 66. Overmolded injector may cause various problems. For instance, the injector is exposed to high temperature during the fuel injection system operation; deformation in the shape of the injector is inevitable. As the temperature rises, both metal part of the injector and the plastic part of the overmolding expand by an amount proportional to the original lengths and thermal expansion values thereof. Due to the fact that thermal expansion in plastics is greater than that of metals, overmolding part and the injector do not expand equally. Since overmolding portion expands much more than the metal portion of the injector, the contact interference between them cannot remain its shape at the beginning. Higher expansion of the plastic results in holes at the contact interference between the fuel injector and overmolding. Fluid may easily pass through these holes and reach inside the fuel injector. Fluid migration is prevented by coating the overmolded portion with a material having hydrophobic characteristics. Overmolded portion is coated at least partly with a suitable hydrophobic material so as to provide a fluid tight injector. The term "hydrophobic coating" refers to a water-repellant coating. Suitable hydrophobic coating material is a superhydrophobic materials and comprises manganese oxide polystyrene (Mn0 ₂ /PS), zinc oxide polystyrene (ZnO/PS) na no-composite, precipitated calcium carbonate, Carbon nano-tube structures or silica nano-coating. According to the present invention, the hydrophobic coating has a contact angle of fluid droplets of higher than 150°. The "contact angle" defines an angle formed by the intersection of the liquid-solid interface and liquid-vapor interface; and is used as a measure of the wetting behaviour of a surface.

Hydrophobic solution of the coating material may be applied to the overmolded surface by any method including spraying, dipping, brushing and flow coating.