Patent Application
20100019071
The present invention relates to fuel injection systems of internal combustion engines; more particularly, to solenoid actuated fuel injectors; and most particularly, to an upper guide system of an armature pintle assembly.
Fuel injected internal combustion engines are well known. Fuel injection arrangements may be divided generally into multi-port fuel injection (MPFI), wherein fuel is injected into a runner of an air intake manifold ahead of a cylinder intake valve, and direct injection (DI), wherein fuel is injected directly into the combustion chamber of an engine cylinder, typically during or at the end of the compression stroke of the piston. DI is designed to allow greater control and precision of the fuel charge to the combustion chamber, resulting in better fuel economy and lower emissions. This is accomplished by enabling the combustion of a precisely controlled charge of fuel under various operating conditions. DI is also designed to allow higher compression ratios, delivering higher performance with lower fuel consumption compared to other fuel injection systems.
Generally, an electromagnetic fuel injector incorporates a solenoid armature/pintle assembly, located between the pole piece of the solenoid and a fixed valve seat. The armature/pintle assembly typically operates as a movable valve assembly and, therefore, represents the moving mass of the fuel injector. Electromagnetic fuel injectors of the pulse-width type meter fuel per electric pulse at a rate proportional to the width of the electric pulse. In a normally closed injector, when an injector is de-energized, its movable valve assembly is released from one stop position and accelerated by a spring towards the opposite stop position, located at the valve seat.
The moving mass of a fuel injector must be guided in a radial direction to keep the pintle axially aligned with the seat in order for flow control across the seat to be robust and precise. Such a guide system is required to exhibit a minimal and consistent friction force in order for the injector to meter accurate fuel amounts and in order to provide a fuel flow rate within an established tolerance for the life of the parts of the armature pintle assembly. Moreover, DI Injectors require a relatively high fuel pressure to operate that may be, for example, as high as 3900 psi compared to about 60 psi required to operate a typical MPFI injector. Due to the higher operating pressure, the fuel flow of DI injectors is more sensitive to variations in the axial movement of the armature/pintle assembly than MPFI injectors.
Several methods to control the alignment of the moving mass of a fuel injector are currently employed. For example, in some cases, the pintle itself is used as the guide surface. However, since the guide location is axially distanced from the location of the radial load imposed on the armature by the magnetic forces, the friction imposed on the moving mass in the area of the guide surface is high.
In other prior art guide systems, the outside diameter of the armature is used as the guide surface. While this locates the guide location at the same axial location as the magnetic radial forces imposed on the armature, the surface area of the outside diameter of the armature that makes contact with the guide is much greater adding to the frictional losses imposed on the moving mass and contributing to a reduction in injector response time.
What is needed in the art is a system for guiding the moving mass of a solenoid-actuated injector that places the guide location near the radial load imposed on the armature by the magnetic forces of the solenoid to reduce friction.
What is further needed in the art is an upper guide system that has a favorable length to diameter ratio to improve the guiding function.
It is a principal object of the present invention to provide an armature guided fuel injector.
Briefly described, a system for guiding the moving mass of a solenoid-actuated injector includes a guide assembled in an axial location that is near the location of the magnetic forces imposed on the armature by the injector's solenoid. An armature of an armature/pintle assembly, in accordance with the invention, includes a reduced diameter section. In one aspect of the invention, the guide is shaped to surround the reduced diameter section of the armature and to extend under a main section of the armature. The outer circumferential contour of the reduced diameter section of the armature functions as a guide surface. This allows for a relative large guide length to diameter ratio.
The upper guide is supported and positioned by a collar formed in the lower housing of the fuel injector. The collar also serves to locate the lower housing in the injector assembly. Additionally, the lower housing of the fuel injector includes a feature, serving as a lower guide, for guiding the valve of the armature/pintle assembly and, accordingly, enables the concentricity of the lower guide and the upper guide to be tightly controlled.
The present invention will now be described, by way of example, with reference to the accompanying drawing, in which:
Referring to
Armature/pintle assembly 20 includes an armature 22 and a valve 24, such as a ball, positioned at opposite ends of a pintle 26. A valve seat 28 positioned at an end of lower housing 12 receives valve 24. Armature/pintle assembly 20 is assembled within lower housing 12 for reciprocating movement in axial direction within fuel passage 14.
Armature 22 is confined by but not fixed to pintle 26. This allows armature 22 to accelerate independent of pintle 26. A weld block 18 is fixed to an end of pintle 26 opposite from valve 24 and limits the axial upward movement of armature 22. When the moving mass of armature 22 collides with weld block 18, armature 22 rapidly lifts entire armature/pintle assembly 20 off valve seat 28, which reduces the opening time compared to armature pintle assemblies where armature 22 is in a fixed connection with pintle 26. Decoupling the mass of armature 22 from pintle 26 also reduces the impact on closing when valve 24 first makes contact with valve seat 28, which may reduce injector operating noise and may prevent unintended fueling by reducing the tendancy of the valve to bounce off the seat upon closing impact.
Axial movement of armature pintle assembly 20 is guided by upper guide system 30 and lower guide system 16. Upper guide system 30 is preferably positioned in close proximity to armature 22 and lower guide system 16 is preferably positioned in close proximity to valve seat 28. The axial location of upper guide system 30 is preferably chosen to be in close proximity to an axial location of the center of a radial load on armature 22 imposed by the magnetic forces of the injector solenoid.
As shown in
Referring to
Cylindrical guide 32 has a length 62 and a central opening 64. Central opening 64 is designed for receiving reduced diameter section 46 of armature 22. Reduced diameter section 46 of armature 22 is reciprocably movable within central opening 64 of guide 32. Accordingly, an outer circumferential contour of reduced diameter section 46 becomes a guide surface allowing for a relatively large length 62 to diameter 48 ratio. Guide 32 positions and guides armature 22 and, consequently, armature/pintle assembly 20 in a radial and an axial direction.
Guide 32 includes a first surface 66 that extends into concave portion 51 of armature 22, thereby increasing the guide length without increasing the overall length of the guide and armature. Guide 32 includes a second surface 68 opposite first surface 66. Second surface 68 is preferably supported and located by a collar surface 13 of lower housing 12. Since lower housing 12 also locates lower guide system 16, the concentricity of the upper guide system 30 and the lower guide system 16 can be tightly controlled. Guide 32 further includes a plurality of apertures 70 that allow fuel to flow through guide 32 from above armature 22 into fuel passage 14. The number and size of apertures 70 may be chosen according to a desired flow rate. Guide surface 54 is lubricated by fuel flowing through central opening 64 of guide 32.
Guide 32 may be, for example, formed from hardened martensitic stainless steel. Central opening 64 of guide 32. A smooth surface on the outer circumferential contour of reduced diameter section 46 may have a smooth finish that may be achieved, for example, by grinding. To reduce wear, armature 22 or at least reduced diameter section 46 of armature 22 may be plated with a relatively hard material, such as chromium.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
