Abstract:
In a battery pack made up of battery cells encased within a housing made up of a stronger outer housing portion and a weaker inner housing portion, the battery cells are secured to the stronger outer housing portion. Advantageously, the relative motion between the battery cells and the stronger of the housing portions that results when prior art battery packs are dropped, and which causes catastrophic failure of the prior art battery packs, is prevented. The battery cells may be secured to the stronger outer housing portion, for example, by gluing the battery cells to the stronger housing portion, attaching the battery cells to the stronger housing portion by using double-sided sticky tape, molding features into the stronger housing portion that immobilize the battery cells adjacent to the stronger housing portion, or providing screw holes through the stronger housing portion so that screws may engage the battery cell or an appendage thereto.

Description:
TECHNICAL FIELD 
     This invention relates to the providing of battery packs such as are used by portable devices, and more particularly, for providing of battery packs that are better able to withstand the impact of being dropped. 
     BACKGROUND OF THE INVENTION 
     A portable device, such as a cellular telephone or a laptop computer, often is used with an external battery pack. In particular, such a battery pack includes one or more battery cells which are housed in a housing that is separate from the housing of the rest of the portable device. The use of a battery pack that has battery cells housed separately from the portable device facilitates the charging of the battery cells without tying up the portable device in the process, and it permits easy replacement of a battery pack, e.g., a discharged one, with another battery pack, e.g., a charged one. 
     A well known problem in the art of portable devices is that when a portable device is dropped its housing tends to fail. Typically the housing shatters, becomes deformed, or comes apart at its joints. So too, the housing of a battery pack which is for use with the portable device. Indeed, failure of the battery pack housing may occur when the battery pack alone is dropped or when the combination of a battery pack attached to a portable device is dropped. In addition, when the battery pack is attached to the portable device and the combination is dropped, there is a tendency for the battery pack to separate from the portable device. 
     The housing of a battery pack is often fashioned from two housing portions, one of which is usually mechanically weaker than the other. The two housing portions are joined at a joint which may or may not be as strong as the weaker housing portion of the battery pack housing. Such an architecture is employed for the battery pack because the battery pack is often a substantial portion of the overall portable device when coupled thereto. Therefore, to avoid the appearance of extra seams, one housing portion, typically the stronger one, forms all the visible housing of the battery pack. The other housing portion is typically smaller, weaker, and hidden, e.g., by being a recessed plate attached to the stronger housing portion. To reduce the weight of the battery pack, and thus the weight of the overall portable device, the smaller, weaker, hidden housing portion of the battery pack is often formed with holes through its surface, which tends to further weaken it. 
     When such a battery pack is dropped, typically, there is a sequence of multiple impacts. For example, the battery pack itself may strike the ground, possibly several times, and the battery cells themselves may strike the battery pack housing portions as well as each other, also possibly several times. The various strikes of the battery pack itself with the ground are collectively referred to as “clattering” while the various strikes of the battery cells within the housing are collectively termed “rattling”. The net result of the clattering and rattling is that the battery cells can have an impact with the weaker housing portion at a velocity that is substantially higher than the velocity of the battery pack when it first strikes the ground. As a result, either the weaker housing portion can shatter or the stronger and weaker housing portions can become separated at the joint between them. Either of these results is typically a catastrophic failure that renders the battery pack unusable. 
     SUMMARY OF THE INVENTION 
     We have recognized that by substantially preventing relative motion between the battery cells and the stronger of the battery pack housing portions that the catastrophic failure of prior art battery packs when dropped can be reduced or avoided. The relative motion between the battery cells and the stronger of the housing portions is substantially prevented by adhering the battery cells to the stronger housing portion, for example, by gluing the battery cells to the stronger housing portion, attaching the battery cells to the stronger housing portion by using double-sided sticky tape, single-sided sticky tape, molding features into the stronger housing portion that immobilize the battery cells adjacent to the stronger housing portion, providing screw holes through the stronger housing portion so that screws may engage the battery cell or an appendage thereto, or VELCRO™. Moreover, in the event that the housing portions of a battery pack are equally strong, the battery cells may be attached to either one of the housing portions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 shows an exploded view of an exemplary prior art battery pack; and 
     FIGS. 2-11 show various embodiments of battery packs which have been designed in accordance with the principles of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an exploded view of an exemplary prior art battery pack  101 . FIG. 1 is intended only to convey the overall mechanical structure of battery pack  101  without regard for the electrical connections therein. Battery pack  101  includes stronger outer housing portion  103 , weaker inner housing portion  105 , and battery cells  107 . Battery cells  107  are merely placed within stronger outer housing portion  103 , and weaker inner housing portion  105  is ultrasonically welded to stronger outer housing portion  103 . From the following description, it will be clear to one of ordinary skill in the art how to modify battery pack  101  to conform to the principles of the invention. 
     FIGS. 2-11 show various embodiments of battery packs which have been designed in accordance with the principles of the invention so that relative motion between the battery cells and the stronger of the housing portions is prevented by adhering the battery cells to the stronger housing portion. Typically, because the battery pack is such a large part of a portable device, the inner housing portion, which is the one facing the other portion of the portable device, is the weaker housing portion while the outer housing portion, with the greater visible surface area, is the stronger housing portion. 
     FIG. 2 shows a cross-sectional view of battery pack  201 , which includes stronger outer housing portion  203 , weaker inner housing portion  205 , and battery cells  207 . In this embodiment of the invention, a layer of glue  209  is employed to secure battery cells  207  to stronger outer housing portion  203 . The type of glue employed preferably has the characteristics that it: a) provides reasonably rigid coupling between the battery and outer housing portion  203 ; b) does not attack, i.e., corrode or dissolve the battery or the housing materials; and c) is effective over the entire storage and operating temperature range of the battery pack. For example, for nickel-metal-hydride (NiMH x ) battery cells encased in their own housing made of an outer layer of nickel-plated steel around which was heat shrunk a tube of poly vinyl-chloride (PVC) of 0.1 millimeter thickness prior to shrinking used with a stronger outer housing portion made of General Electric SP6400R polycarbonate, a glue for which good results have been obtained is Adhesive Compounds part number (p/no.) #1702, a hot melt adhesive. Note that by glue it is meant any form of chemical adhesive substance. 
     FIG. 3 shows a cross-sectional view of battery pack  301 , which is similar in structure to battery pack  201  and includes stronger outer housing portion  303 , weaker inner housing portion  305 , and battery cells  307 . In this embodiment of the invention, a layer of double-sided sticky tape  309  is employed to secure battery cells  307  to stronger outer housing portion  303 . The type of sticky tape employed preferably has the characteristics that it: a) provides reasonably rigid coupling between the battery and the stronger housing portion  303 , although it is recognized that double-sided sticky tape will provide a less rigid coupling than glue; b) does not attack, i.e., corrode or dissolve the battery or the housing materials; and c) is effective over the entire storage and operating temperature range of the battery pack. In addition, double sticky tape has the advantage over glue that, during assembly of the battery pack there is more flexibility to move the battery cells within the battery pack to insure proper placement therein. Also, double-sided sticky tape is typically easier to employ on an assembly line, and it tends to result in less of a mess. For example, for nickel-metal-hydride (NiMH x ) battery cells encased in their own housing made of an outer layer of nickel-plated steel around which was heat shrunk a tube of poly vinyl-chloride (PVC) of 0.1 millimeter thickness prior to shrinking used with a stronger outer housing portion made of General Electric SP6400R polycarbonate, one exemplary double-sided sticky tape for which good results have been obtained is a tape foam made ENSOLITE™ neoprene coated on each side with the BEPHEM™ adhesive #2515D. 
     FIG. 4 shows another embodiment of the invention in which a battery cell  407  is secured to stronger outer housing portion  403  by adhesive layer  409 , which may be either glue or double-sided sticky tape. In FIG. 4 stronger outer housing portion  403  has molded thereon receptacle  411  for battery cell  401 , in accordance with an aspect of the invention. Advantageously, receptacle  411  provides a higher surface area for adhesive attachment between the curved surface of battery cell  407  and receptacle  411  than would otherwise obtainable had the curved surface of battery cell  407  been adhered to a flat section of stronger outer housing portion  403 . 
     In other embodiments of the invention similar to that shown in FIG. 4, receptacle  411  need not be molded as in integral part of stronger outer housing portion  403 . Instead, receptacle  411  may be molded separately and secured, e.g., via glue, double sided sticky tape, snap action, or screw action, to stronger outer housing portion  403 . Also, it will be appreciated by those skilled in the art that receptacle  411  may be formed out of a material that is different from the material which makes up stronger outer housing portion  403 . 
     For example, a receptacle may be made of metal while the stronger outer housing portion is made of plastic. More than one receptacle may be used for any particular battery cell. 
     Alternatively, adhesive need not be used, but instead the battery cell is press-fit to the receptacle, so that substantial relative motion between the battery cell and the receptacle, and consequently, the stronger outer housing portion, is substantially prevented. 
     FIG. 5 shows another embodiment of the invention in which battery cell  507  is secured to stronger outer housing portion  503  by clips  509 . As shown in FIG. 5, clips  509  are molded as projections from stronger outer housing portion  503 . In alternative embodiments of the invention using at least one clip, the clip could be inserted and, optionally secured, e.g., glued snapped, or screwed, into a matching receptacle in the stronger outer housing portion after the battery cell is placed therein. FIGS. 6 and 7 show embodiments of the invention using at least one inserted clip. Note that, as shown in FIGS. 6 and 7, for example, only one clip may be required for each battery cell. Also note that, in FIG. 7, by staggering clips  709  along the axis of battery cells  707 , gap  713  between oppositely facing ones of clips  709  may be eliminated. Other types of clips may be developed by those of ordinary skill in the art and employed in accordance with the principles of the invention. It will be appreciated by those skilled in the art that a clip may be formed out of a material that is different from the material which makes up the stronger outer housing portion. For example, a clip may be made of metal while the stronger outer housing portion is made of plastic. 
     In the embodiment of the invention shown in FIG. 8, battery cells  807  are secured to stronger outer housing portion  803  by retainer  809 . Retainer  809  is coupled to stronger outer housing portion  803  by one or more fasteners  815 . Fasteners  815  may be screws, snap in pins or any other form of fastener. Indeed, retainer  809  may even be glued, or secured by double-sided sticky tape, to stronger outer housing portion  803 . Weaker inner housing portion  805  is mounted above retainer  809 . Retainer  809  may be formed out of a material that is different from the material which makes up stronger outer housing portion  803 . For example, retainer  809  may be made of metal while stronger outer housing portion  803  is made of plastic. Furthermore, fasteners  815  may be formed out of a material that is different from the material which makes up stronger outer housing portion  803  and that which makes up retainer  809 . More than one retainer may be employed within a single battery pack, or even for a single battery cell. 
     FIG. 9 shows an embodiment of the invention similar to that shown in FIG. 3 but in which the double-sided sticky tape has been replaced by matable VELCRO™ hook and loop tape strips  909 , one of which is adhered to battery cells  907  and the other of which is adhered to stronger outer housing portion  903 . It is immaterial which of VELCRO™ hook and loop tape strips  909  is the hook-type of Velcro and which is the loop-type of VELCRO™ hook and loop tape. Alternatively, as shown in FIG. 10, some, or all, of battery cells  1007  are encircled by one of VELCRO™ hook and loop tape strips  1009 , which mates to the other of VELCRO™ hook and loop tape strips  1009 , which is affixed to stronger outer housing portion  1003 . In FIGS. 5-11 there are reference numerals indicating elements of the FIGS. that are not specifically in mentioned in this description. For such reference numerals the lowest two digits designate the particular elements while any higher order digits correspond to the number of the FIG. in which that element is located. The particular element designated corresponds in function to the element having the same lowest two digits and described in connection with FIGS. 1 or  2 . For example, element  505  designates the weaker housing portion of the embodiment shown in FIG. 5, and similarly,  1107  designates the battery cells in FIG.  11 . 
     FIG. 11 shows yet another embodiment of the invention, which is similar to that of FIG. 8, except that a) retainer  809  is replaced by VELCRO™ hook and loop tape strap  1109  and b) fasteners  815  are replaced by VELCRO™ hook and loop tape strips  1115  affixed to stronger outer housing portion  1103 . VELCRO™ hook and loop tape strips  1115  may be coupled to stronger outer housing portion  1103  by any technique, e.g., being self sticking, adhesive, clip-type fasteners, screws, etc. It is immaterial as to which of VELCRO™ hook and loop tape strap  1109  or Velcro strips  1115  is the hook-type of VELCRO™ hook and loop tape and which is the loop-type of Velcro. Also, instead of being two separate strips, VELCRO™ hook and loop tape strips  1115  may be merged into a single strap. 
     In accordance with another embodiment of the invention, single-sided sticky tape may be used, with the sticky side facing the battery cells. The tape may be secured to the stronger outer housing portion in any manner desired, e.g., by glue or pins pushed through the tape to snap into the stronger outer housing portion. 
     Note that terminology used herein based on the word screw, such as screwed or screw action, is intended to encompass embodiments of the invention in which separate screws, and/or nuts are employed, or where screw grooves are formed as an integral part of a component of a battery pack, e.g., a receptacle, a snap, or the stronger outer housing portion, and used in conjunction with screw grooves formed as an integral part of another component of the battery pack, and/or with a separate screw or nut. 
     In still another embodiment of the invention, a battery cell may itself be screwed directly to the stronger outer housing portion. With the above-described expansive definition of screwed in mind, this embodiment of the invention may be achieved by forming screw threads on the battery cell and matching threads on the stronger outer housing portion. The screw threads of the battery cell may be formed on an outer surface thereof, to mate to a threaded recess of the stronger outer housing portion. Alternatively, the battery cells may be formed with a threaded recess which is mated to a threaded projection from the stronger outer housing portion. The threaded projection may be a) integral to the stronger outer housing portion, b) coupled thereto, or c) passed therethrough. 
     In an alternative screw based embodiment of the invention, if two or more battery cells are held together, e.g., lashed together or wrapped in a tape-like plastic, prior to being inserted into the battery pack, a single screw may be sufficient for all the cells. In fact, a hole in the material holding the cells together mated to a screw projecting from the stronger outer housing portion may suffice. Alternately, the material holding the multiple battery cells together may be affixed to the stronger outer housing portion using any of the above-described techniques. 
     Note that, if desired, one may also secure the battery cells to the weaker housing portion in addition to securing them to the stronger outer housing portion. Also note that the securing of the battery cells to the stronger outer housing portion is intended to be performed in a manner that is at least a semi-permanent, if not an entirely permanent, i.e., for the life of the battery pack. This is because, typically, the battery cells are not changed, nor are they removed, during the life of the battery pack, unless there is a need to repair the battery pack. Instead, the battery pack is recharged when the battery cells become discharged. When the battery cells become unable to hold sufficient charge to power the portable device for a sufficient length of time, the battery pack is disposed of, or alternatively, recycled. 
     As used herein, the term battery pack may be limited to a battery pack of the type that is capable of existing as a separate unit independent of any portable device to which it may be coupled for supplying power thereto. Of course, some technique must be employed to couple the portable device to the battery pack, which remains external to the portable device. 
     The foregoing merely illustrates the principles of the inventions. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.