Self-locking spring stop for fuel injector calibration

#This invention relates in general to a fuel injector assembly, and more specifically to a fuel injector assembly having a self-locking calibration member that sets spring bias and provides a seat that allows spring alignment.

#It is believed that in a conventional fuel injector assembly, a spring is disposed between an end of an adjustment tube and an armature. To allow fuel to flow through the injector, the adjustment tube is usually hollow. It is known to use an adjustment tube to initially set, i.e., calibrate, the dynamic flow of a conventional fuel injector assembly by either altering the amount of metal in the magnetic circuit or by adjusting the spring preload. In the fuel injector industry, adjusting the spring preload is the most common calibration method.

#Two types of adjustment tubes are known for adjusting the spring preload: an interference fit adjustment tube and a free sliding adjustment tube. An interference fit adjustment tube requires a large force to position the adjustment tube with respect to its mating part and is considered fixed when the tooling no longer applies the force needed to move the adjustment tube. Interference-type adjustment tubes can be continuous tubes or axially slit tubes, which are commonly referred to as “roll pins.” A roll pin allows the mating hole size to vary significantly, and moving the roll pin requires less force than moving the continuous tube. However, under severe conditions, the roll pin may be displaced, thus altering the previously calibrated dynamic flow of the fuel injector. The continuous tube is less susceptible to unanticipated displacement due to its higher engagement force, but does require precision machining.

#The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention.

#FIG. 1 is a cross-sectional view of a fuel injector assembly according to a first embodiment.

#FIG. 2 is a cross-sectional view of the fuel injector assembly according to a first embodiment.

#Referring to FIGS. 1, 2, and 2A, a fuel injector assembly 1 has a fuel inlet 12, a fuel outlet 14, and a fuel passageway 16 extending from the fuel inlet 12 to the fuel outlet 14 along a longitudinal axis 18. The fuel injector assembly 1 also includes an overmolded plastic member 20 cincturing a metallic support member 22.

#A fuel inlet member 24 with an inlet passage 26 is disposed within the overmolded plastic member 20. The inlet passage 26 serves as part of the fuel passageway 16 of the fuel injector assembly 1. A fuel filter (not shown) and an armature bias spring 32 are provided in the inlet passage 26. The armature bias spring 32 can be a coil spring. In combination with other factors, the length of the spring 32, and hence the bias force of the spring 32, affect the quantity of fuel flow through the injector. The overmolded plastic member 20 also supports a socket 20a that receives a plug (not shown) to operatively connect the fuel injector assembly 1 to an external source of electrical potential, such as an electronic control unit (not shown). An elastomeric O-ring 34 is provided in a groove on an exterior of the inlet member 24. The O-ring 34 is supported by a backing ring 38 to sealingly secure the inlet member 24 to a fuel supply member (not shown), such as a fuel rail.

#The metallic support member 22 encloses a coil assembly 40. The coil assembly 40 includes a bobbin 42 that retains a coil 44. The ends of the coil assembly 40 are electrically connected to pins 40a mounted within the socket 20a of the overmolded plastic member 20. An armature 46 is supported for relative movement along the axis 18 with respect to the inlet member 24. The armature 46 can be supported by an armature guide eyelet 56 that is located on an inlet portion 60 of a valve body 52 for relative axial sliding movement with respect to the valve body 52. A non-magnetic sleeve 48 positions the coil assembly 40 with respect to the valve body 52 and a shell 50 provides a magnetic path between the metallic support member 22 and the valve body 52. The armature 46 has an armature passage 54 in fluid communication with the inlet passage 26.