1. Field of the Invention
The present invention generally relates to an oil activated fuel injector and, more particularly, to an oil activated electronically or mechanically controlled fuel injector control valve which substantially eliminates captured air within working fluid of the fuel injector.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
It has been found in open systems that air becomes captured and locked within the grooves or orifices of the control valve (and a spool) during the venting of the working fluid during and at an end of a fuel injection cycle. This is mainly due to the fact that vent holes which surround the control valve body allow air to enter the system. This air will mix with the working fluid during the fuel injection process resulting in variations in fuel injection quantities. Of course, this will lead to inefficient shot to shot variations.
Being more specific, a driver will first deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as xe2x80x9cgroovesxe2x80x9d) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
To end the injection cycle, the driver will deliver a current or voltage to a closed side of a closed coil solenoid. The magnetic force generated in the closed coil solenoid will then shift the spool into the closed or start position which, in turn, will close the working ports of the control valve body. The working fluid pressure will then drop in the intensifier and high-pressure chamber such that the needle spring will shift the needle to the closed position. The nozzle tip, at this time, will close the injection holes and end the fuel injection process. At this stage, the working fluid is then vented from the fuel injector via vent holes surrounding the control valve body.
Referring now to FIG. 1A, in current designs the vent holes 10 surround the control valve body 12 and the spool 14 such that air 16 in the control valve body 12 is below the working fluid level 18. This causes the grooves 20 of the control valve body 12 and the spool 14 to be filled with air 16. Now, during the next cycle time (as seen in FIG. 1B) when the spool 14 is shifted to the open position, this air 16 becomes locked within the grooves 20 causing air bubbles 22 to be formed within the working fluid 18 of the working ports 23. In order to inject fuel within the combustion chamber, this captured air will have to be compressed by the working fluid and dissolved partially into a dilution prior to the working fluid acting on the intensifier piston. This causes a shot to shot fuel variation (depending on the quantity of air in the working fluid) thus resulting in decreased fuel efficiency especially for low fuel quantities.
The present invention is directed to overcoming one or more of the problems as set forth above.
In a first aspect of the present invention, a check valve body has an inlet area and a working port in fluid communication with the inlet area. The working port is adapted to provide working fluid to an intensifier chamber of the fuel injector. At least one communication port is in fluid communication with the inlet area and the working port. At least one vent hole is provided which prevent air from mixing with the working fluid.
In another aspect of the present invention, the check valve body has an oil inlet area and a at least one port in fluid communication with the oil inlet area. The port transport oil between the oil inlet area and an intensifier chamber of the fuel injector. An aperture having at least one communication port provides a flow path for the oil between the ports and the oil inlet area. A spool is positioned within the aperture and includes at least one fluid path which are in alignment with the communication port of the aperture when the spool is in the first position. Vent ports vent the oil from the control valve body and prevent air from entering the at least one fluid path of the spool.
In still another aspect of the present invention, a fuel injector having a control body is provided. The control body has an inlet area, working ports, communication ports and fluid paths, a spool and at least one vent hole. The at least one vent hole is positioned above the working ports to reduce captured air in the working ports during a venting process. The fuel injector also includes an intensifier body and a spring loaded piston and plunger within a centrally located bore of the intensifier body. A high pressure fuel chamber is also formed in the intensifier body. A nozzle having a fuel bore is in fluid communication with the high pressure chamber, and a needle is positioned within the nozzle. A fuel chamber surrounds the needle.