Patent Publication Number: US-2010109351-A1

Title: System and method for clamping a chassis cover

Description:
TECHNICAL FIELD 
     The present invention generally relates to clamps, and more particularly relates to a system for clamping a cover to a power electronic bay chassis. 
     BACKGROUND OF THE INVENTION 
     In recent years, advances in technology have led to substantial changes in the design of automobiles. One of the principal changes involves the complexity, as well as the power usage, of various electrical systems within automobiles, particularly alternative fuel vehicles. During this time, the requirement for electrical power generation in automotive applications has risen dramatically. This trend had been in place for decades but has accelerated in the last few years largely due to the advent of hybrid, electric, and fuel cell based vehicles. Such vehicles often use electrochemical power sources, such as batteries, ultracapacitors, and fuel cells, to power the electric motors that drive the wheels, sometimes in addition to another power source, such as an internal combustion engine. 
     In hybrid and fuel cell vehicles, a Power Electronics Bay (PEB) performs many necessary functions related to power conversion and distribution. PEB enclosures or chassis are typically designed to provide housed components with both environmental protection and shielding from incoming and outgoing electromagnetic interference (EMI). A PEB chassis generally comprises a body and cover constructed of either stainless steel or aluminum, each member having a machined sealing flange along an outer edge, pre-drilled to accommodate fastening bolts. One or both of the flanges typically has a groove to support a metal-impregnated, conductive, silicone o-ring to form an environmental seal when the cover of the enclosure is bolted closed. EMI shielding is provided by the continuous conductive shrouding formed by the metallic structure of the body and cover in conjunction with the conductivity of the o-ring in the seam. Because strong and evenly distributed clamping pressure is needed to provide a reliable seal, reinforcement of sealing flanges is typically required to provide adequate rigidity and prevent warping from the substantial compressive forces generated by a plurality of bolts spaced 1″ to 2″ apart. As a result, part count and overall vehicle weight are increased along with the complexity of associated assembly processes. Further, conductive, EMI shielding o-rings are often nickel-filled and add additional expense while contributing no additional environmental protection compared to conventional, non-conducting silicone rubber o-rings. 
     Accordingly, it is desirable to provide a system for clamping a cover to a PEB chassis that is easily installable and eliminates the need for multiple fasteners. Further, it is desirable that such a system provides EMI shielding along the seams and corners of a PEB chassis without the use of a conductive o-ring. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY OF THE INVENTION 
     A system is provided for securing a cover having a first surface onto a chassis having a rim, the rim having a second surface. The system comprises a clamping rail and a fastener coupled to the rail. The clamping rail is configured to form a loop that circumferentially engages the first surface and the second surface and, when constricted, produces a first force substantially coplanar with the loop. The fastener is configured to constrict the rail, the rail and the first and second surfaces configured to produce a second force having a component substantially orthogonal to the loop when the rail is constricted. 
     A method is provided for clamping a cover having a first surface onto a chassis body having a rim, the rim having a second surface. The method comprises the steps of circumferentially aligning a clamping rail to the first and second surfaces, constricting the circumference of the clamping loop to engage the first and second surfaces with a first force substantially coplanar with the loop, the clamping loop and the first and second surfaces being configured to convert at least a portion of the first force to a second force substantially orthogonal to the loop that clamps the cover onto the rim, and fixing the clamping loop in its circumferentially restricted position. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a schematic view of an exemplary automobile illustrating the manner in which an embodiment is integrated with various sub-components of an automobile; 
         FIG. 2  is an isometric view of a power electronics bay enclosure in accordance with a first embodiment of the present invention; 
         FIGS. 3-5  are cross-sectional schematic drawings illustrating clamping rails in accordance with further embodiments of the present invention; 
         FIGS. 6-7  are isometric views of a clamping rail in accordance with a further embodiment of the present invention; 
         FIG. 8  is an isometric view of a clamping rail and corner brace in accordance with yet a further embodiment of the present invention; 
         FIGS. 9-10  are isometric views of a clamping rail and fastener in accordance with yet a further embodiment of the present invention; 
         FIG. 11  is an isometric view of a clamping rail integrated with a lever-actuated fastener in accordance with yet a further embodiment of the present invention; 
         FIG. 12  is an isometric view of a clamping rail corner structure in accordance with yet a further embodiment of the present invention; and 
         FIG. 13  is an isometric view of a clamping rail welded in accordance with yet a further embodiment of the present invention. 
     
    
    
     DESCRIPTION OF AN EXEMPLARY EMBODIMENT 
       FIG. 1  illustrates a vehicle  10 , (e.g. an automobile), according to one embodiment of the present invention. The automobile  10  includes a chassis  12 , a body  14 , four wheels  16 , and an electronic control system (or electronic control unit (ECU))  18 . The body  14  is arranged on the chassis  12  and substantially encloses the other components of the automobile  10 . The body  14  and the chassis  12  may jointly form a frame. The wheels  16  are each rotationally coupled to the chassis  12  near a respective corner of the body  14 . 
     The automobile  10  may be any one of a number of different types of automobiles, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD), or all-wheel drive (AWD). The automobile  10  may also incorporate any one of, or combination of, a number of different types of engines (or actuators), such as, for example, a gasoline or diesel fueled combustion engine, a “flex fuel vehicle” (FFV) engine (i.e., using a mixture of gasoline and alcohol), a gaseous compound (e.g., hydrogen and/or natural gas) fueled engine, or a fuel cell, a combustion/electric motor hybrid engine, and an electric motor. 
     In the exemplary embodiment illustrated in  FIG. 1 , the automobile  10  is a fuel cell vehicle, and further includes an actuator assembly (or powertrain)  20 , a battery  22 , a battery state of charge (SOC) system  24 , a power electronics bay (PEB)  26 , and a radiator  28 . The actuator assembly  20  includes an internal combustion engine  30  and an electric motor/generator (or motor) system (or assembly)  32 . The battery  22  is electrically coupled to the PEB  26  and, in one embodiment, comprises a lithium ion (Li-ion) battery including a plurality of cells, as is commonly understood. PEB  26  is typically comprised of a plurality of electronic components, including those operating with high voltage, enclosed in a housing or chassis that provides protection from both environmental damage and shielding for incoming and outgoing EMI. 
       FIG. 2  illustrates an exemplary PEB chassis  120  that houses electronic components in accordance with a first exemplary embodiment. These components may include a DC/DC converter  122  to boost fuel cell DC voltage to a higher voltage, a DC/AC inverter  124  for delivering AC power to a primary electric drive motor, an additional DC/AC inverter  126  to deliver power to a compressor, a set of boost inductors  130  to boost fuel cell output voltage as part of the boost converter, and one or more circuit boards  132  containing support electronics for a myriad of functions. PEB chassis  120  has a body  144  comprised of a rectangular bottom panel  146 , four side panels  148  interconnected together, and a removable top or cover panel  152 . Body  144  is typically constructed from a conductive and corrosion resistant material such as rolled stainless steel sheets welded at side and bottom seams, or from a die-cast and anodized aluminum alloy. Likewise, cover  152  is also constructed of stamped sheet metal or a cast aluminum alloy, and is fabricated to fit over the top of body  144 . Any of the side/top/bottom panels of chassis  120  may be specifically configured to include contours and/or openings such as port  153  to accommodate internal components housed therein, and/or provide a means of interconnection to other components of vehicle  10 . While  FIG. 2  illustrates PEB chassis  120  as a rectangular prism, it should be understood that other shapes may be used depending on the space and size constraints of the application and the type and size of components to be housed. Further, while  FIG. 2  illustrates only clamping for a cover panel, it should be understood that any non-integrally connected side and/or bottom panel may also be clamped. 
     Referring to  FIG. 2 , a clamp  160  comprises a continuous rail  164  having first and second ends  172  and  173  respectively, coupled together by an adjustable fastener  156  to form a clamping loop  150 . Fastener  156  may be used to precisely contract or expand the circumference of clamp  160  to a desired circumference by providing a means to controllably adjust the distance between first and second ends  172  and  173 . Prior to clamping, fastener  156  may be loosened to expand the circumference of clamp  160  and facilitate alignment to clamping surfaces of cover  152  and sidewalls  148 . When clamped, rail  164  conformably circumscribes these surfaces and applies constrictive forces about cover  152  and sidewalls  148  that are substantially coplanar with clamping loop  150 . As will be described in greater detail below, rail  164  is configured to engage with cover  152  and sidewalls  148  and apply clamping pressure thereto by converting the coplanar forces to clamping forces having a component substantially orthogonal to loop  150 . 
       FIG. 3  illustrates a cross sectional schematic drawing of cover  152  aligned over sidewall  148  and proximate to clamping rail  164  prior to clamping in accordance with an exemplary embodiment. The upper edge of sidewall  148  comprises an integrally formed rim  168  having a surface  198  machined to engage a flat machined undersurface  200  of cover  152 . A groove  192  is formed in rim  168  and runs along its length, and a seal  188  sized somewhat larger than the width and depth of groove  192 , is disposed therein. Types of seals that may be used include but are not limited to o-rings, gaskets, or curable liquids/gels. Alternatively, undersurface  200  may be configured to receive a seal, or both rim surface  198  and undersurface  200  may each be grooved to accommodate a seal. 
     Prior to clamping, cover  152  rests on the top of seal  188  forming a gap  218  between undersurface  200  and rim surface  198 . The underside of rim  168  comprises a rim bevel  216  that extends outward from sidewall  148  terminating with a vertical rim lip  176 . The top peripheral surface of cover  152  has an edge bevel  214  terminated by a short vertical cover lip  190 . Rail  164  is configured to fit over edge bevel  214  and rim bevel  216  when clamped and comprises a center section  208  that couples together upper and lower arms  202  and  204  respectively. Each arm may terminate with an outwardly curving upper and lower leading edge  206  and  226  respectively, to facilitate aligning rail  164  with rim  168  and cover  152  prior to clamping. While rail  164  has been illustrated as having angled, symmetric upper and lower arms  202  and  204 , it should be understood that arms may be asymmetric with respect to angle and/or length. For example, as illustrated in  FIG. 4 , cover edge bevel  214  and rim bevel  216  differ with each other with respect to both length and bevel angle. Similarly, upper arm  202  and lower arm  204  of rail  164  differ in length and in angle from center section  208 . In general, rail  164  imparts a clamping force that clamps cover  152  to rim  168  when the plane of upper arm  202  is different than the plane of cover edge bevel  214 , and/or the plane of lower arm  204  is different than the plane of rim bevel  216 . 
       FIG. 5  illustrates a cross sectional schematic drawing of cover  152 , rim  168 , and rail  164  in a closed and clamped position in accordance with the exemplary embodiment. Rail  164  has been moved into a clamping position by a force (depicted by arrow F 1 ) substantially coplanar with loop  150  and generated by, for example, tightening fastener  158  ( FIG. 2 ) to decrease the circumference of clamp  160 . As the circumference is decreased, F 1  increases and upper and lower arms  202  and  204  are pulled (inward toward the center of loop  150 ) onto edge and rim bevels  214  and  216  causing rail  164  to deform conformably to these bevels. When deformed, rail  164  responds in a springlike manner and generates forces comprising opposing (clamping) components, F 1  and F 2 , substantially orthogonal to the plane of loop  150  that are applied to edge and rim bevels  214  and  216 , and press cover  152  onto rim  168 . Clamping forces F 2  and F 3  may be increased by further tightening of fastener  158  until either the spring force decreases due, for example, to rail  164  yielding in plastic deformation or until center section  208  abuts against rim lip  176  and/or cover lip  190 . As clamping pressure increases, seal  188  is compressed in conformity with cover  152  and groove  192  to create a tight environmental seal. Clamping forces F 2  and F 3  may be controlled by a proper adjustment of fastener  158  to retain a narrow gap  218 , and avoid permanent deformation or scarring of undersurface  200  and/or top surface  198  thereby. As is well known by those with skill in the art, available clamping forces can be adjusted by design factors that include but are not limited to the angle and/or lengths of edge and rim bevels  214  and  216 , the angle and/or length of the upper and lower rail arms  202  and  204 , the spring constant of rail  164 , and the applied force F 1 . 
     Rail  164  provides EMI shielding over gap  218  all along its length including around chassis corners as will be described in further detail below. Such shielding results from factors that include the metallic construction and shape of rail  164 , and reduces the amount of EMI passing between rim  168  and cover  152  from sources either internal or external to a chassis. Center section  208  of rail  164  may be configured to be substantially perpendicular to gap  218  to provide improved coverage and greater attenuation of such EMI signals. 
       FIG. 6  illustrates an isometric view of a clamp  240  in accordance with another exemplary embodiment. Clamp  240  is configured for a rectangular chassis and comprises a first and second L-shaped section of clamping rail  236  and  238  respectively, each rail having a cross-sectional geometry suitable for clamping in accordance with this invention such as that depicted for rail  164  in  FIG. 3 . A first backing strap  230  is mounted to first rail  236  in a parallel fashion, and traverses conformably along its entire length. A second backing strap  232  is likewise conformably mounted parallel to second rail  238 . Each strap  230  and  232  is comprised of a rolled carbon steel or stainless steel alloy sheet attached to its respective rail using rivets, spot-welds, or the like. First and second rails  236  and  238  are coupled together to form a rectangular loop using first and second fasteners  246  and  248  respectively. Fasteners  246  and  248  are each configured to be tightened or loosened to adjust the peripheral distance spanned by clamp  240 . Prior to clamping, fasteners  246  and  248  may be loosened to expand the peripheral distance and facilitate mounting and alignment of clamp  240  to the rim and cover of a chassis. Following alignment, clamp  240  may be constricted by tightening fasteners  246  and/or  248  to generate a clamping force. While clamp  240  has been shown having two opposing corner fasteners, those having skill in the art will appreciate that clamp  240  may be configured with a single corner fastener or with more than two corner fasteners depending upon space and/or other overall design considerations. 
       FIG. 7  illustrates the interaction of first and second backing straps  230  and  232  with fastener  246  disposed at a corner of clamp  240  in accord with an exemplary embodiment. Fastener  246  is comprised of a t-bolt  262  having a fixed head  250 , and slidably coupled to a crosstie  260 . In one embodiment, t-bolt  262  is bent to more conformably accommodate a corner. Crosstie  260  may slide in either direction along t-bolt  262  and is bounded between a nut assembly  254  and head  250 . Nut assembly  254  is threadably coupled to t-bolt  262  and, when tightened, forces second crosstie  260  controllably toward head  250 . First backing strap  230  is divided at its end and forms a pair of loops  265  each rotatably coupled to an end of head  250  forming a first hinge  269 . Second backing strap  232  is similarly split to form a second hinge  271  rotatably coupled to the ends of second crosstie  260 . The hinged coupling of fastener  246  to backing straps  230  and  232  allows clamp  240  to adjust more conformably and apply pressure more evenly in chassis corners. Prior to clamping, nut assembly  254  may be loosened to allow separation of head  250  and crosstie  260 , and expansion of clamp  240  thereby. To apply clamping pressure, nut assembly  254  may be tightened to force head  250  and crosstie  260  toward each other, constricting clamp  240  thereby. 
       FIG. 8  is an isometric view of a fastening assembly  298  configured for clamping a chassis corner in accordance with an exemplary embodiment. First and second clamping rails  300  and  302  may represent end segments of longer rail sections of a clamp  296  fabricated for a rectangular chassis. First rail segment  300  and second rail segment  302  have first and second bent ends  304  and  306  respectively, contoured to conformably engage with a first and second corner brace  308  and  3   10 . An adjustable fastener  320  is comprised of first and second crossties  322  and  324 , respectively, that slidably engage first and second corner braces  308  and  310  along a threaded rod  312 . A nut  318  threadably coupled to a first end  321  of rod  312  may be rotated to adjust the distance between the crossties and braces, and by their engagement, to adjust the distance between first and second bent ends  304  and  306  respectively. Prior to clamping, clamp  296  may be expanded to facilitate alignment to a chassis cover/rim by loosening nut  318 . Clamp  296  may be constricted to apply clamping pressure using nut  318  to adjust the distance between first and second braces  308  and  310  and thus also first and second bent ends  304  and  306 . 
       FIG. 9  is an isometric view of a clamp assembly  270  in accordance with another exemplary embodiment. Clamp assembly  270  is configured for a rectangular chassis and comprises first and second rails  276  and  278 , respectively, each rail formed in the shape of an asymmetric U having two right angle bends. Rails  276  and  278  are coupled together along straight rail sections by a first and second adjustable fastener  272  and  274 . As in previous embodiments, one or both of fasteners  272  and  274  may adjust the circumference of clamp  270  by loosening for alignment or removal, or by tightening to apply clamping as required. An isometric side view of an exemplary fastener  272  in accordance with this embodiment is illustrated in  FIG. 10 . Fastener  272  is configured in a similar manner to fastener  246  shown in  FIG. 7 , and comprises a threaded rod  280  coupled to a first crosstie  282  at a first end  293 , and slidably coupled to a second crosstie  288  and a hollow sleeve  284 . First crosstie  282  is rotatably coupled to a first backing loop  290  to form a first hinge  294 , and second crosstie  288  is likewise rotatably coupled with a second backing loop  292  to form a second hinge  295 . Backing loops  290  and  292  are each attached to ends of rails  276  and  278  respectively in a well-known manner using a rivet or weld. A nut  286  may be rotated to move sleeve  284  along rod  280  and adjust the distance between first and second crossties  282  and  288 . Fastener  272  may thus be loosened to expand clamp  270  to facilitate alignment to or removal from a chassis, or tightened to contract the circumference of clamp  270  to apply clamping pressure. 
       FIG. 11  is an isometric side view of a lever-actuated fastener  360  used to couple together first and second clamping rails  362  and  364 , respectively, forming a clamp  361  in accordance with a further embodiment. Fastener  360  comprises a lever  368  having a first end  380  configured with an angled leading edge  384  to facilitate actuation by a user. Lever  368  has a second end  382  rotatably hinged to a first base  378  by a pin  366 . First base  378  is attached to first rail  362  using rivets, spot-welds, or the like. A second base  374 , having an upwardly curved catch  372 , is mounted to second rail  364  similarly using rivets, spot-welds, or the like. A U-shaped latch  370  straddles lever  368  and has first and second (not shown) hooked ends  376  and  377 , respectively, that are rotatably coupled either side of lever  368  via openings therein. Latch  370  comprises a loop  373  configured to engage catch  372  when in a locked position and is free to swing about lever  368  when not engaged. Prior to clamping, lever  368  is rotated about pin  366  clockwise (as shown) to an unlocking position by applying an upward force to the underside of leading edge  384 . In the unlocking position, latch  370  moves toward and disengages from catch  372 , enabling adjustment of first and second rails  362  and  364  to allow clamp  361  to be aligned to or removed from a chassis. Fastener  360  is brought into a locking position by first engaging loop  373  with catch  372 , followed by rotating lever  368  into a locked position over first base  378  (as shown). When fastener  360  is in the locked position, the resulting circumference of clamp  361  is fixed and depends on the lengths of first and second rails  362  and  364  as well as on the placement and dimensions of fastener  360 . Achieving a desired circumference that will result in a desired clamping pressure therefore requires precise placement and sizing of these components. 
       FIG. 12  illustrates an isometric side view of a clamping rail  350  configured to conform to a chassis corner in accordance with an exemplary embodiment. Rail  350  has a cross section similar to that of rail  164  shown in  FIG. 3  and comprises an upper and lower arm  340  and  342  respectively, coupled to a center section  338 . Portions of upper arm  340  and lower arm  342  are removed in the region of rail  350  adjacent to a chassis corner to form upper and lower notches  332  and  334 , respectively, and a center bridge  336  thereby. Those having skill in the art will appreciate that the depth, width, and/or shape of notches  332  and  334  may be varied provided that bending rail  350  to accommodate a corner does not result in deformation and/or structural damage to arms  340  and  342  or bridge  336 . Notching of rail  350  may reduce clamping pressure somewhat in corners. This condition may be mitigated by minimizing the width of notches  332  and  334  and/or by designing the cover and rim to have greater rigidity in corner regions. EMI shielding remains continuous in chassis corners due to the continuity of bridge section  336  overlying the cover/rim seam around such corners. 
       FIG. 13  illustrates an isometric view of a clamp  390  having a circumference fixed by a weld in accordance with an exemplary embodiment. Clamp  390  is configured for a rectangular chassis and comprises a single clamping rail  394  having four right angle bends, each bend configured with corner notches  396  as depicted in  FIG. 12  and previously described. Rail  394  is fabricated from a weldable material such as a carbon or stainless steel and has first and second ends  398  and  400 , respectively, pre-cut to a circumference compatible with a chassis to be clamped. Prior to clamping, first and second ends  398  and  400  may be freely adjusted to align rail  394  to the chassis cover/rim. After alignment, first and second ends  398  and  400  are forced together using an appropriate means to constrict the circumference of clamp  390 , and joined with a weld  392 . In further embodiments, first and second ends  398  and  400  may be riveted, clasped, or crimped together. When joined using any of these methods, the circumference of clamp  390  is fixed and applies a corresponding clamping pressure to the chassis cover/rim. Fixing rail  394  in this manner may be used when access to the interior of the chassis for periodic maintenance of its contents is deemed unnecessary. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.