Patent Grant
7863791
The present invention relates to electric motors, and more particularly to the assembly of electric motor components into housings designed to contain and positionally locate the motor components.
A wide variety of electrical products include internal components that generate significant amounts of heat during normal use. Prominent examples include personal computers, and components of computer systems such as servers and work stations. Frequently these devices incorporate electric motor driven fans, preferably contained in aerodynamically designed housings to more effectively move air across heat generating components and exhaust the heated air to maintain a satisfactory operating temperature. Given the strong consumer and user preferences for lower cost and smaller size, manufacturers are continually challenged to provide smaller yet equally reliable fans and motors while decreasing manufacturing costs. To this end, some manufacturers have introduced plastic housings to augment or replace previously used metal housings for the motor components. Although this has the potential to significantly reduce costs, the approach increases the difficulty of reliably securing the motor stator against axial and rotational movement.
One of these concerns arises due to the interface between the cylindrical stator body, i.e. the lamination stack, and the slight incline or truncated conical shape of an otherwise cylindrical plastic housing, present due to the draft angle required when molding the plastic part. One approach to this problem involves fixturing the stator and securing the stator with potting compound or glue. Other designs employ screws or other fasteners to retain the stator. These approaches require added time and labor, and raise process control difficulties in terms of repeatable, consistent stator positioning. Alternatively, a motor already secured within a metal casing can be mounted within a plastic housing. This entails unwanted redundancy and adds to the cost.
Therefore, the present invention has several aspects directed to one or more of the following objects:
To achieve these and other objects, there is provided a motor stator mounting device. The device includes a motor housing disposed about a longitudinal housing axis. The housing includes a cylindrical housing section centered on the housing axis and having a proximal end, a distal end, and an interior surface region extending distally from the proximal end. A detent feature is disposed at a selected axial location along the interior surface. The interior surface is inclined to gradually converge in a distal direction. The housing further includes a distal end housing section integral with the cylindrical housing section and comprising an axially directed first central opening and a first bearing seat centered on the housing axis. The device includes a rotor retaining member disposed about a retainer axis, comprising an inner section and an annular peripheral section surrounding the inner section. The peripheral section has an annular outer surface centered on and parallel to the retainer axis, and an accurate peripheral edge adjacent one end of the outer surface and occupying a plane perpendicular to the retainer axis. The inner section comprises a second central opening and a second bearing seat centered on the retainer axis. The proximal end is open to receive a rotor, including a rotor shaft and first and second bearings mounted along the shaft at first and second spaced apart axial locations, for distal insertion into the cylindrical housing section toward a predetermined axial location with the first bearing engaged with the first bearing seat to mount the rotor shaft for rotation relative to the housing about the housing axis. The rotor retaining member is insertable distally into the cylindrical housing section with the rotor at the predetermined axial location, and with the retainer and housing axes substantially coincident and with the annular peripheral edge providing a leading edge of the retaining member. This locates the peripheral edge and the peripheral outer surface adjacent and radially inwardly of the interior surface near said proximal end, to form a sliding engagement of the peripheral outer surface and the interior surface region to urge the retaining member radially toward a centering on the housing axis. This also moves the second bearing seat into engagement with the second bearing and moves the annular peripheral edge into engagement with the detent feature to prevent further distal travel of the retaining member relative to the housing beyond a rotor retaining position. A fastening component is adapted to secure the retaining member integrally with the housing to axially fix the rotor at the predetermined axial location.
In a preferred version of the device, the cylindrical housing section comprises a tubular wall and a plurality of ribs extending longitudinally along an inside surface of a tubular wall. Proximal end regions of the ribs extend beyond the proximal end of the cylindrical housing. The proximal end regions are fusible, and when fused after placement of the retaining member at the rotor retaining position, cooperate to secure the retaining member. The cylindrical housing can include further longitudinal ribs with proximal ends recessed distally from the housing proximal end. These shorter ribs cooperate to provide the detent feature.
Another aspect of the present invention is a process for assembling a motor. The process includes:
Preferably a portion of the cylindrical housing section near the proximal end is fusible, in which case fixing the rotor retaining member to the cylindrical housing section can comprise selectively fusing the fusible portions. In one advantageous arrangement, longitudinal ribs extend proximally from the cylindrical housing section beyond the rotor retaining member, and are fused by a heat staking process to secure the retaining member. In a highly preferred approach, material flow during fusion is controlled to ensure that none of the rib material is disposed radially upwardly up the peripheral section.
For a further understanding of the above and other features, reference is made to the following detailed description and to the drawings, in which:
Turning now to the drawings, there is shown in
As seen in
With reference to
As seen in
With reference to
Preferably motor housing 28, including cylindrical housing sections 30 and 32, distal end section 36, and vanes 38, is formed as a single part or unitary structure of plastic, preferably polycarbonate, twenty percent glass filled. Due to the slight draft angle occasioned by the molding process, the interior surface of housing section 32, including the radially inward facing surfaces of ribs 52 and 56, are inclined to converge in the distal direction. In addition, each of ribs 52 is formed with a distal feature 60 with a radially inward facing surface inclined more steeply than the rest of the rib.
In
End cap 48 is disposed proximally of retaining ring 74. A proximal end region 76 of rotor shaft 34 extends beyond end cap 48 in the proximal direction.
As seen in
An annular sleeve 88 extends axially away from an inside edge of the platform, centered on the retainer axis. A stator centering structure 90 extends axially away from the outer peripheral edge of the platform, in the direction opposite to that of sleeve extension. In particular, when the retaining ring is mounted in a stator retaining position as shown in
The centering structure includes twelve stator centering and mounting features or fingers 92. Features 92 are arranged in angularly spaced apart relation about the platform periphery. Each centering feature is tapered to converge in the axial direction away from the platform, i.e. the distal direction when in use. More particularly, each feature 92 has a radially outward facing outside surface 94 that is curved in planes perpendicular to the retainer axis (e.g.
As best seen in
A salient feature of the present invention resides in the selective shaping of inner cylindrical housing section 32 and retaining ring 74 to effect a preliminary radial centering of stator 66 responsive to an insertion of the stator into the housing section. This is shown in
During motor assembly, stator 66 is inserted manually through the open proximal end and distally toward end section 36. Such insertion is bound to be imperfect, in the sense that the stator with respect to housing section 32 is offset angularly, offset radially, or both as distal region 72 approaches distal end section 36. Regardless of the nature of the offset, distal insertion brings the stator into contact with one of surfaces 106 and 108. Typically, initial contact occurs at a distal portion of medial region 104 adjacent the distal region 72. As stator 66 is moved distally after contact, the rib or ribs in contact with the stator urge the stator, particularly the distal end region, radially toward a more centered position within housing section 32. As continued distal insertion of stator 66 brings inclined region 72 into contact with pads 50, the radial centering action brings medial region 104 into contact with an increasing number of the ribs. Finally, as region 72 engages the pads, the distal end of medial region 104 is in contact with all of ribs 52 and 56, which cooperate to maintain the stator distal end region radially centered in relation to housing section 32. Distal features 60 are in contact with tapered region 72, to reinforce the centering action.
Another feature of the present invention resides in the manner in which retaining ring 74 engages cylindrical housing section 32 and stator 66 to axially mount the stator while simultaneously centering the proximal region of the stator within housing section 32 to complete the centering function. This feature is illustrated in
Retaining ring 74 is used to complete centering and mounting immediately after the initial insertion and centering illustrated in
The desired angular alignment positions outside surfaces 94 of centering features 92 in confronting relation to the interior surface of cylindrical housing section 32. It also positions each of outside surfaces 100 of bridge sections 98 in confronting relation to the inside surface of an associated one of ribs 52 and 56. All of these surfaces are inclined radially inwardly in the distal direction.
Inside surfaces 96 of the centering features are oppositely inclined, i.e. radially outward in the distal direction. Further, inside surfaces 96 are inclined more steeply than outside surfaces 94 to accommodate proximal inclined region 102 of stator 66. The angle between each pair of surfaces 94 and 96 is greater than the angle between the stator and the interior surface of housing section 32, to promote a wedging action upon the housing section and stator by each of the centering features as retaining ring 74 is moved distally into the housing section.
As seen in
As the retaining ring is inserted further, distal edges 111 of centering features 92 enter the annular gap between the interior surface of housing section 32 and the stator exterior surface. At this stage, the proximal end of stator 66 may or may not be centered within cylindrical housing section 32, and retaining ring 74 likewise may or may not be centered. However, should the retaining ring be radially offset from the housing section, one or more of centering features 92 engages the interior housing surfaces, after which further distal insertion of the ring tends to center the ring due to the incline of the interior surface. Similarly, assuming that the proximal end of stator 66 is radially offset from a centered position, distal movement of the centering ring causes one or more of inside surfaces 96 of the centering features to engage the stator exterior surface. Due to the incline of the inside surfaces 96, further distal movement of the retaining ring urges the proximal region of the stator radially toward centering.
In short, there is a compound effect of housing and retaining ring interacting to drive the retaining ring towards centering while ring and stator surfaces interact to drive the stator towards centering. Alternatively, this can be thought of as a wedging action of each centering feature between stator and housing surfaces to center the stator.
When the radial thickness of centering features 92 fills the radial width of the gap between the stator and housing surfaces, retaining ring 74 is in its stator retaining position and cannot be moved further in the distal direction. At this point the stator, retaining ring, and housing section are in a frictional engagement which tends to keep the stator axially and radially fixed within the housing. To permanently secure the stator, retaining ring 74 is fixed in the stator retaining position by permanently attaching it to housing section 32. This is accomplished by bonding the stator centering structure to the interior surface of the housing section. In one advantageous arrangement, outside surfaces 100 of the bridging sections and contacting portions of ribs 56 are bonded together by sonic welding at four locations designated 113 in
This approach to bonding, along with the shapes of the components involved, provide several advantages that considerably reduce the cost and time of assembly. The components are self centering. There is no need for additional fixtures or jigs to align the parts for assembly. The use of spaced apart, circumferentially arranged centering features advantageously allows for localized elastic deformation of individual centering features without undesirably affecting the centering process. In addition, the spaced apart centering features and recessed bridging sections, in combination with the ribs formed along the cylindrical housing interior surface, more positively set the desired angular alignment. This arrangement has been found to provide an additional benefit, in that movement of a centering ring into the stator retaining position causes the centering features on each side of a bridging section to elastically deform in a manner that more positively presses outside surfaces 100 against the inside surfaces of the adjacent ribs, resulting in a more reliable sonic weld.
Once stator 66 is centered and secured, motor assembly continues with insertion of the rotor into housing 32, with a rotational axis of the rotor coincident with the housing axis.
Rotor 114 is supported by distal end housing section 36 and end cap 48, which incorporate respective distal and proximal bearing seats engaged with bearings 46 and 118, respectively to support the rotor for rotation about a longitudinal rotor axis.
End cap 48 has a unitary body formed of metal, preferably an alloy of zinc, aluminum, magnesium, and copper available under the name “Zamac 5.” The body, centered about an end cap axis 124 includes an annular platform section 126, an annular inner section 128 surrounding a central axial opening through the body, and an outer peripheral section 130 surrounding the platform section. The peripheral section has an annular outer surface 132 that extends away from platform section 126 in a substantially axial direction, but with a slight incline to provide an end cap diameter that diminishes in the direction away from the platform. Outer surface 132 is interrupted by six recesses or notches 134 angularly spaced apart from one another about the peripheral section. Each of recesses 134 is adapted to accommodate one of ribs 52 as end cap 48 is inserted distally into cylindrical housing section 32. Adjacent recesses are spaced apart angularly by about sixty degrees. A wire guide structure 136 extends away from platform section 126, on the opposite side of the platform from peripheral section 130. As seen in
Peripheral section 130 includes an acuate, generally annular peripheral edge 138 remote from the platform and occupying a plane perpendicular to the end cap axis. Peripheral edge 138 occupies the majority of the peripheral section circumference, with several discontinuities such as an opening associated with wire guide structure 136, as seen in
End cap 48 incorporates a bearing seat centered on axis 124, adapted to engage proximal end bearing 118 to rotatably support shaft 34. As best seen in
Cylindrical housing section 32 incorporates features adapted to automatically effect centering of rotor 114 as the rotor is assembled into the housing section. These include features that act directly upon the rotor assembly, independently of end cap 48. With reference to
Other features of housing section 32 cooperate with features of end cap 48 to properly position the rotor. As to radial centering, the inclined interior housing surface, particularly that portion near the proximal end of the cylindrical housing section, is disposed for surface engagement with annular outer surface 130 of the end cap as the end cap is inserted distally into the housing section. As the end cap is inserted further, following engagement, the interior surface provides a camming action that urges the end cap radially toward the centered position. Simultaneously, the entry of proximal bearing 118 into the bearing seat formed by inner section 128 and shoulder 140 radially centers the rotor shaft within the end cap.
Similarly, cylindrical housing section 32 and end cap 48 cooperate to axially position the rotor. With reference to
Rotor 114 is assembled into cylindrical housing section 32 with stator 66 and stator retaining ring 74 already in place. The rotor assembly is inserted into housing section 32 through the open proximal end, and moved distally until distal end of shaft 34 passes through the central opening in sleeve 40, and further until distal end bearing 46 enters the sleeve. This centers the distal end region of the shaft. Further distal travel brings bearing 46 into contact with the free ends of fixtures 42, to axially position the rotor. At this stage, end cap 48 is inserted distally into housing section 32. This is a manual insertion, with end cap axis and at least approximately aligned with the housing axis, and with the end cap at least approximately at a desired angular position relative to the housing section. As insertion continues, peripheral edge 138 and a distal portion of peripheral section 130 enter housing section 32, and regions of the peripheral section near recesses 134 encounter proximal end regions 54 of ribs 52. At this stage, the end cap may be rotated about the end cap axis slightly if necessary to align the recesses and ribs.
Alignment allows further distal insertion of the end cap, effecting the interaction of the housing and end cap surfaces to center end cap 48 radially relative to housing section 32, and locating proximal end regions 54 of ribs 52 proximally of platform section 126. Insertion continues until peripheral edge 138 contacts the detent feature of housing section 32, i.e. the proximal ends of ribs 56. Simultaneously, end cap insertion moves inner section 128 distally into its surrounding relation to proximal end bearing 118, eventually bringing shoulder 146 into engagement with the bearing. This locates end cap 48 at the rotor retaining position relative to the housing section.
At this stage, end cap 48 is fixed to cylindrical housing section 32 to permanently retain the rotor assembly. Fixation is accomplished with a heat staking process in which the rib material at proximal ends 54 is caused to flow onto platform section 126. As a result, the proximal end regions overlie the platform section in close surface contact, to secure the end cap against proximal movement relative to housing section 32.
Broken lines at 144 in
This results in a more efficient air flow through the annular passage between cylindrical housing sections 30 and 32, which in turn leads to more efficient cooling of the heat generating electrical components.
With respect to mounting stator 66, several advantages were noted above as to cylindrical housing 32 and its interaction with retaining ring 74. With respect to mounting the rotor, the interaction of housing section 32 and end cap 48 likewise affords these advantages. Due to the self centering character of the components, there is no need for fixtures or tooling to keep the rotor in a centered position as it is assembled into the housing. Similarly there is no need for tooling to center the proximal end of the rotor assembly, because end cap insertion inherently centers the proximal end bearing and related portion of the rotor shaft. The heat staking process eliminates the need for screws or other auxiliary fasteners, and is accomplished in a manner that preserves the smooth outer periphery of the cylindrical housing section, for more effective air flow. In addition, features of the housing section and end cap cooperate to positively axially place the rotor assembly, again without added fixtures or tooling.
Thus in accordance with the present invention, motor components can be assembled into a housing in a manner that considerably reduces the time, tooling, and skill required, and at the same time provide more reliable and repeatable axial positioning and radial centering of motor components.
This application claims the benefit of priority based on Provisional Application No. 61/000,554 entitled “Heat Staking Assembly Method for Electric Motors,” filed Oct. 26, 2007.
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| Number | Date | Country | |
|---|---|---|---|
| 20090134726 A1 | May 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61000554 | Oct 2007 | US |
