Patent Application
20090139491
This disclosure relates generally to solenoid assemblies, and more particularly, to solenoid assemblies having slotted stators.
Solenoid operated fuel injectors are used to inject fuel into the cylinder of internal combustion engines. A solenoid actuator of the solenoid operated fuel injector is energized to move a control valve element in a first direction to initiate an injection event and the actuator is de-energized to allow the control valve element to move in an opposite direction to end the injection event. In order to improve fuel economy and reduce emissions, fuel injection systems must be capable of achieving high injection pressures, controlling injection rates, and providing fast responses while maintaining accurate and reliable control of fuel metering and injection timing functions.
The ability of a fuel injector to respond to an input signal command to open significantly effects the ability of the fuel injector to deliver a precise injection of fuel to the combustion chamber. Parameters that define the fuel injector's magnetic circuit (e.g., the stator, the armature, and the working gap between the stator and armature) are particularly important since it is the magnetic circuit that conducts the magnetic flux that exerts the magnetic force which acts on the armature. The rate at which the magnetic flux builds determines the rate at which force acting on the armature builds. The faster the force builds, the faster the fuel injector responds. Additionally, minimizing the size of the solenoid actuator of the fuel injector is desirable, especially where the valve is mounted inside a fuel injector body.
Eddy currents play a significant role in the magnetic circuit and reducing eddy currents aid in faster response time of the fuel injector. For example, many stator cores are formed of a laminate stack assembly which permits faster magnetization and demagnetization of the solenoid by breaking up eddy current paths thereby reducing eddy currents.
Efforts have been made to minimize the size of solenoid actuators while providing the response time required in high speed, high pressure applications. For instance, the attractive force of the stator assembly of a solenoid actuator assembly can be increased by increasing the surface area of the stator pole end faces. The end face may be increased by sizing and shaping the stator assembly to occupy a maximum amount of the space in a surrounding housing. Nevertheless, the relatively small gap between the inner diameter of the housing and the outer diameter of the stator causes flux leakage into the surrounding housing. Generally, sizing and shaping the stator assembly to occupy a maximum amount of space in a surrounding housing requires designing the inner diameter of the housing and the outer diameter of the stator to very close tolerances.
Various solenoid assembly designs that increase attractive forces, reduce eddy currents and reduce flux leakage have been developed. One such example is described in U.S. Pat. No. 6,155,503 (the '503 patent) issued to Benson et al. on Dec. 5, 2000. The '503 patent includes a solenoid stator assembly positioned in an actuator housing and a flux dissipation reducing feature to minimize flux leakage into the housing and thus maximize the attractive force, which in turn improves valve response time. The flux dissipation reducing feature disclosed in the '503 patent includes a slot formed in the housing adjacent each outer face of the solenoid stator pole pieces. The slots permit the cross sectional area of the pole pieces to be maximized thereby increasing the available attractive force. In addition, the slots increase the resistivity of the magnetic circuit and reduce eddy currents.
The apparatus of the '503 patent may not adequately reduce the gap between the stator and the surrounding housing. Furthermore, the design of the '503 patent may require tight tolerances for a close fit of the stator within the housing, which may make manufacturing the design expensive. In addition, the design disclosed in the '503 patent only applies to E-type laminate stack assemblies, and other stator designs would not benefit. In particular, it may not be practical to incorporate the slots from the E-type laminate stack in other stator designs and thereby reduce eddy currents. Thus, the system described in the '503 patent may be ineffective in situations where a non E-type laminate stack stator is required, in situations where the gap between the stator and the surrounding housing must be further reduced, and in situations where eddy currents must be reduced.
In one aspect, the present disclosure is directed to a solenoid assembly. The solenoid assembly includes a housing having a cavity disposed therein. The solenoid assembly also includes a unitary stator having a plurality of slots. The stator is held together by a lip that is located on an outer periphery of the stator and remains after the slots are cut so that the stator remains one-piece. The stator is further configured to fit within the cavity disposed in the housing.
In another aspect, the present disclosure is directed to a method of forming a solenoid assembly. The method includes cutting a plurality of slots in a stator and leaving a lip on the outer periphery of the stator to hold the stator together in one-piece. The method also includes compressing the stator and placing it in a housing having an inner cavity configured to receive the stator. The method further includes expanding the stator so that it fits snugly within the geometric contours of the cavity and attaching the stator to the housing.
Stator 40 may include a central passageway 47. Central passageway 47 may have a plurality of slots 42 extending radially therefrom and may form a plurality of separated portions. The slots 42 may be evenly or unevenly spaced from each other and may include two or more slots. As shown in
Lip 44 may have a thickness of approximately 0.25 millimeters and may be located at an outer periphery of flange 43. Alternatively, lip 44 may be located at any appropriate location and have any appropriate size that maintains the unitary structure of stator 40.
Once the stator 40 is positioned within housing 30, stator 40 and housing 30 may be permanently attached by any method appreciable to one of ordinary skill in the art such as gluing or mechanical means. In one embodiment, stator 40 and housing 30 may be permanently attached, at a location depicted as 15 in
The disclosed solenoid assembly 20 may be used in conjunction with any fuel injector 10 in any fuel injection system, such as an internal combustion engine, a work tool actuation system, or any fuel delivery system. The disclosed solenoid assembly 20 may provide a mechanism for reducing valve response time and may provide ease of manufacturability and assembly. The operation of solenoid assembly 20 will now be explained in detail.
In addition, assembling solenoid assembly 20 is further simplified by having the stator 40 maintain its unitary structure. That is, when slots 42 are cut, a lip 44 is left such that the stator 40 remains one piece. Therefore, there is no need to handle different pieces of the stator 40 since the stator 40 remains one-piece. This enhances ease of manufacturability and assembly by saving time and expense associated with handling the stator 40. Once stator 40 has been snugly placed in cavity 32 of housing 30, the stator 40 and the housing 30 may be permanently attached (Step 58). The stator 40 and housing 30 may be permanently attached by laser welding for example. In particular, the outer edge of flange 43 may be laser welded to the cavity 32 of housing 30. However, welding may be avoided in the vicinity of the high pressure passage 34.
During assembly, slots 42 aid in minimizing the gap between housing 30 and stator 40, which helps prevent flux leakage into the housing 30. Because stator 40 may be compressed and expanded while inserted in cavity 32, stator 40 may occupy maximum space within cavity 32 within housing 30. In addition, slots 42 aid in reducing the effect of eddy currents by making the path of the eddy currents more tortuous. Thus, the magnetic circuit gains strong attractive forces, resulting in a decrease in response time of the actuator and better control of fuel injection timing and metering.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed solenoid assembly and other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the solenoid assembly. Accordingly, it is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
