Patent Application
20150348691
Embodiments of the present invention generally relate to electromagnetic solenoids.
In some cases it is desirable to shunt the magnetic field generated by a coil in an electromagnetic solenoid. Known electromagnetic solenoids achieve this by providing a radial groove in the outside surface of a pole piece adjacent to a flux sleeve. When the coil is energized, the magnetic field in the area of the radial groove will saturate and act as an air gap.
Current electromagnetic solenoids provide the radial groove on a hollow cylindrical end portion of the pole piece. As the armature is displaced in the flux sleeve towards the pole piece, it is guided to fit within the hollow interior of the cylindrical end portion. However, this configuration requires precise alignment of the flux sleeve with the pole piece to prevent contact between the armature and the interior of the pole piece. Contact is known to increase friction, and possibly preventing proper function of the solenoid. The precise alignment required to prevent contact slows production and may increase reject rate if the alignment is not properly maintained.
Accordingly, a need exists for an electromagnetic solenoid that less sensitive to misalignment between the flux sleeve and the pole piece.
Embodiments of an electromagnetic solenoid are provided herein. In an embodiment, an electromagnetic solenoid comprises a coil for generating a magnetic force when energized and a bobbin having a tubular center portion and end flanges between which the coil is wound. A tubular flux sleeve is at least partially disposed within the center portion of the bobbin with an armature disposed coaxially within an interior portion of the flux sleeve and supported for axial displacement between a first position when the coil is not energized and a second position when the coil is energized. A pole piece is at least partially disposed within an interior portion of the bobbin in an abutting relationship with a first end of the flux sleeve. The flux sleeve has a circumferential groove formed in an outer surface adjacent to the first end.
Other and further embodiments of the present invention are described below.
Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used where possible to designate identical elements that are common in the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
A magnetic tubular flux sleeve 110, with an outer surface 114 and an inner surface 113, is coaxially aligned with the bobbin 104 and disposed at least partially within the hollow of center portion 106. A circumferential groove 112 is formed in the outer surface 114 adjacent to one end of the flux sleeve 110. The contour of the groove 112 is chosen to shunt the magnetic flux in a radial direction. The wall thickness 116 between the inner and outer surfaces 113, 114 is locally reduced at the groove 112. The area of the reduced wall thickness will saturate when the coil is energized and act as an air gap in the magnetic field. In this disclosure, “saturate” and forms thereof are used to describe the condition in a material in which an increase in the magnetic field will not produce an increase in the magnetic flux of the material. In this case, the area of the circumferential groove 112 becomes saturated at a lower magnetic field than the portions of flux sleeve 110 with the unmodified wall thickness 116.
A hollow tubular armature 118 is coaxially disposed in the interior portion of the flux sleeve 110. The armature 118 is supported for axial displacement within the flux sleeve 110 between at least a first position when the coil 102 is not energized and a second position when the coil 102 is energized as shown in
In the embodiment of
A non-magnetic armature stop 124 is coupled to the end of the pole piece 120 adjacent to the flux sleeve 110, for example by press fitting a portion of the armature stop 124 in the bore 126. Axial displacement of the armature 118 is limited in a first direction (toward the pole piece 120) by the armature stop 124 which prevents the armature 118 from contacting the pole piece 120 (sometimes referred to as “latching”).
A pin 128 is disposed within the bore 126 of the pole piece 120 and supported for axial displacement within an open interior portion of the armature stop 124 and at least a portion of the bore 126. An end of the pin 128 abuts an end of the armature 118 so that displacement of the armature from a first position (corresponding to a de-energized coil condition) to a second position (corresponding to an energized coil condition) displaces the pin 128 a corresponding amount.
A case 138 disposed around the solenoid 100 adjacent to outer portions of the bobbin 108 and the pole piece 120 captures the components of the solenoid 100 and limits movement between the bobbin 108, the flux sleeve 110 and the pole piece 120.
The inventor has noted that some known solenoids include an undercut in a tubular portion of the pole piece extending into the flux sleeve. The flux sleeve is axially aligned with the tubular portion of the pole piece, with the flux sleeve and tubular portion in contact with each other. In at least one condition, the armature extends through the flux sleeve and is received into the interior of the tubular portion of the pole piece. Because of design factors, it is desirable to maintain a minimal gap between the armature and the inner walls of the flux sleeve and the inner walls of the tubular pole piece portion. Great effort is required to maintain axial alignment of the flux sleeve and the pole piece to allow the armature to move unhindered between the interior of the flux sleeve and the interior of the pole piece. Friction between the armature and the inner wall of the tubular portion of the pole piece reduces the efficiency and response time of the solenoid.
Some known solenoids increase the diameter of the tubular portion of the pole piece in order to compensate for manufacturing inaccuracies. This increases the clearance between the armature and the inner wall to allow free axial movement. However the increased gap decreases the magnetic efficiency of the solenoid, negatively affecting performance.
The inventor has observed that by placing the circumferential groove 112 on the flux sleeve 110, a number of benefits are realized. Because the flux sleeve 110 is tubular in form, the inner passage may be formed with tight tolerances in a more economical manner than known flux sleeves. In contrast, the interior passage of some known flux sleeves are blind holes or counter bores which are more difficult to hold to tight tolerances.
Because the armature 118 does not extend from the flux sleeve 110 to be received into the pole piece 120 in the present disclosure, precise alignment of the flux sleeve 110 with the pole piece 112 is not required. In the inventive solenoid, the axis 130 of the armature 118 need not be aligned with the axis 132 of the pin 128 in order to advance the pin 128 in response to linear displacement of the armature 110. The armature 110 may be aligned for free axial movement within the flux sleeve 110. The pin 128 is positioned in the pole piece 120 for free axial movement, independent of the position of the flux sleeve 110.
A benefit realized by this design is the reduction, or elimination, of friction and hysteresis due side loading of the armature 110. In some known solenoids, as the armature extends into the pole piece, and any misalignment between the armature and the pole piece causes contact between the armature and the pole piece leading to undesirable friction and hysteresis.
An additional benefit, as illustrated in
The nozzle 140 of
When the coil 102 of the solenoid 100 is in a de-energized condition, the armature 118 and the pin 128 are in the retracted position. The embodiment of
In the embodiment illustrated in
The solenoid 200 includes a magnetic tubular flux sleeve 210, with an outer surface 214 and an inner surface 213, coaxially aligned with the bobbin 204 and disposed at least partially within the hollow of the center portion 206. The flux sleeve 210 has a first interior passage 211 formed at one end and a smaller interior passage 215 formed from the other end of the flux sleeve 210 into the first passage 211. A circumferential groove 212 is formed in the outer surface 214 adjacent to one end of the flux sleeve 210. The contour of the groove 212 is chosen to shunt the magnetic flux in a radial direction. The wall thickness 216 between the inner and outer surfaces 213, 214 is locally reduced at the groove 212. The area of the reduced wall thickness will saturate when the coil is energized and act as an air gap in the magnetic field.
A hollow tubular armature 218 is coaxially disposed in the first interior passage 211 of the flux sleeve 210. The armature 218 is supported for axial displacement within the flux sleeve 210 between at least a first position when the coil 202 is not energized and a second position when the coil 202 is energized as shown in
In the embodiment of
A case 238 disposed around the solenoid 200 adjacent to outer portions of the bobbin 208 and the pole piece 220 captures the components of the solenoid 200 and limits movement between the bobbin 208, the flux sleeve 210 and the pole piece 220.
A non-magnetic first armature stop 224 is coupled to the end of the flux sleeve 210, for example by press fitting a portion of the armature stop 224 into the interior passage 213. Axial displacement of the armature 218 is limited in a first direction (away from the pole piece 220) by the armature stop 224.
Axial displacement of the armature 218 in a second direction (toward the pole piece 220) is limited by a non-magnetic second armature stop 225 coupled to the armature 218, for example by press fitting a protrusion on the armature stop 225 into the open central portion of the armature 218. The second armature stop 225 prevents the armature 218 from “latching” to the pole piece 220.
A resilient member 248, for example a compression spring, is disposed in the axial bore 226 with one end abutting a plug 250 fixed to the solenoid 200 and the other end abutting the second armature stop 225. The resilient member 248 generates a force urging the armature 218 in a direction away from the pole piece 222 and into the first position corresponding to a de-energized coil 202. When the coil 202 is energized, the magnetic force generated by the coil is sufficient to overcome the force of the resilient member 248 and the armature is pulled in a direction of the pole piece 222 (corresponding to the second position).
The embodiment of
The embodiment also facilitates the integration of the flux sleeve 210 with a portion of the hydraulic circuit, nozzle 240. As illustrated, the nozzle includes a spool 242 disposed at least partially within a passage 244. One end of the spool 242 abuts against an end of the armature 218 so that displacement of the armature 218 from the second position to the first position displaces the spool 242 a corresponding amount. A resilient member 246 is disposed in the nozzle 240 and compressed by an opposite end of the spool 242 when the armature 218 is in the first position (corresponding to a de-energized condition of the coil 102). When the coil 202 is energized, the armature 218 is urged into the second position by the magnetic force of the coil 202 and by the resilient member 246 as it returns to an extended configuration.
When the coil 202 of the solenoid 200 is in a de-energized condition, the armature 218 is in the extended position. The embodiment of
Thus embodiments of a solenoid robust against misalignment of the pole piece and flux sleeve are provided herein. The inventive solenoid may advantageously reduce manufacturing cost by facilitating assembly and thereby reducing assembly time. The embodiments also provide for integrating either the pole piece or the flux sleeve into the hydraulic circuit further reducing manufacturing costs by minimizing the number of components.
