Abstract:
A cover for a motor drive is provided. The cover includes an opening (often at the bottom of the cover) to allow air to pass to an air inlet of the motor drive and an opening (often near the top of the cover) to allow air from an air outlet of the motor drive to exit the cover. A hood provides rain protection for the drive and a separator (such as a baffle) within the enclosure prevents air flowing within the enclosure from the air outlet to the air inlet of the drive. The hood and/or the separator are shaped to direct air from the air outlet away from the enclosure in order to substantially reduce the re-circulation of air from the air outlet to the air inlet of the drive.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is entitled to the benefit of and incorporates by reference subject matter disclosed in the International Patent Application No. PCT/IB2014/062153 filed on Jun. 12, 2014 and U.S. Provisional Patent Application No. 61/861,184 filed on Aug. 1, 2013. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a cover for a motor drive. The cover may, for example, provide additional protection for the motor drive in order to enable the drive to be placed outside in potentially hostile conditions. 
       BACKGROUND 
       [0003]      FIG. 1  shows a known motor drive (the terms variable speed drive or variable frequency drive are also used to refer to a motor drive—the terms are used interchangeably in this document), indicated generally by the reference numeral  1 . Motor drives generate significant heat during use and therefore require cooling. The variable speed drive  1  shown in  FIG. 1  includes a back channel  2  that provides the bulk of the cooling for the electrical circuitry within the drive  1 . Nevertheless, this is not sufficient and an air inlet  3  and air outlet  4  are provided on the front of the drive to provide an additional air flow for cooling purposes. 
         [0004]    In order for sufficient cooling to be provided, it is important that the air inlet  3  and air outlet  4  are not blocked. This is not generally a problem when the drive  1  is mounted indoors in a relatively clean environment. However, the air inlets and outlets provide a weakness in the structure of the cabinet that is particularly problematic if the drive  1  is mounted outdoors (where it may, for example, be required to withstand rain) or in a particularly harsh indoor environment. 
         [0005]    It is possible to mount the drive  1  within an enclosure box in order to protect the drive from, for example, rain, sand or excessive dust. However, such an enclosure must allow sufficient air to flow into the air inlet  3  and away from the air outlet  4 , otherwise the thermal performance of the drive  1  will be adversely affected. 
         [0006]    A known solution to this problem is to provide a cabinet to protect the drive  1 . A commonly used cabinet is the so-called NEMA 3R cabinet (as rated by the National Electrical Manufacturers Association). NEMA 3R cabinets typically involve mounting the drive within the cabinet. Fans are typically provided at the bottom of the cabinet to draw air in for cooling the drive. The air is typically expelled out of the side of the cabinet. In addition to cooling fans, heaters are often provided in order to be able to heat the cabinet to prevent condensation when the drive is not operational. Other possible features include filters and mounting feet to raise the cabinet off the ground. 
         [0007]    Cabinets such as NEMA 3R cabinets are expensive. Moreover, such cabinets are necessarily larger than the drive that is being enclosed (substantially larger in the case of a typical NEMA 3R implementation). The additional expense and/or the additional space requirements are unacceptable in many circumstances. 
         [0008]    The present invention seeks to address at least some of the problems outlined above. 
       SUMMARY 
       [0009]    The present invention provides a cover (typically a partial cover) for a motor drive, wherein the drive includes an air inlet and an air outlet (for the passage of cooling air), the cover comprising: a first opening (often at the bottom of the cover), wherein, in use, air is allowed to pass through the first opening to the air inlet; a second opening, wherein, in use, air is allowed to pass from the air outlet through second opening; and a separator (such as a baffle) inside the cover that is dimensioned and positioned such that, in use, air is prevented from flowing inside the cover from the air outlet to the air inlet. 
         [0010]    The present invention also provides a cover (typically a partial cover) for a motor drive, wherein the drive includes an air inlet and an air outlet (for the passage of cooling air), the cover comprising: a first opening (often at the bottom of the cover), wherein, in use, air is allowed to pass through the first opening to the air inlet; a second opening, wherein, in use, air is allowed to pass from the air outlet through second opening; and a rain restrictor that restricts the ingress of rain into the cover. The cover may additionally comprise a separator (such as a baffle) inside the cover that is dimensioned and positioned such that, in use, air is prevented from flowing inside the cover from the air outlet to the air inlet. 
         [0011]    The present invention further provides a motor drive comprising an air inlet, an air outlet and a (partial) cover, the cover comprising: a first opening, wherein, in use, air is allowed to pass through the first opening to the air inlet; a second opening, wherein, in use, air is allowed to pass from the air outlet through second opening; and a separator (such as a baffle) inside the cover that is dimensioned and positioned such that, in use, air is prevented from flowing inside the cover from the air outlet to the air inlet. 
         [0012]    The present invention yet further provides a motor drive comprising an air inlet, an air outlet and a (partial) cover, the cover comprising: a first opening, wherein, in use, air is allowed to pass through the first opening to the air inlet; a second opening, wherein, in use, air is allowed to pass from the air outlet through second opening; and a rain restrictor that restricts the ingress of rain into the cover. The cover may additionally comprise a separator (such as a baffle) inside the cover that is dimensioned and positioned such that, in use, air is prevented from flowing inside the cover from the air outlet to the air inlet. 
         [0013]    Where provided, the rain restrictor “restricts” the ingress of rain into the cover, but does not necessarily prevent the rain from entering the cover completely. This is possible in many forms of the invention because the drive itself provides significant protection from water ingress. What is typically required of the rain restrictor is to prevent very large quantities of water from impacting on the drive in a short space of time, since the drive may not be capable of withstanding such a harsh environment. 
         [0014]    The rain restrictor and/or the separator may be shaped to direct at least some air from the air outlet away from the cover (in order to reduce the re-circulation of air). Where both are provided, the rain restrictor and the separator may co-operate to direct air from the air outlet away from the cover. 
         [0015]    In many forms of the invention, the cover only covers a portion of the drive (so that portions of the drive that are not already sufficiently well protected are protected by the cover). This reduces materials, and reduces size requirements, as well as allowing other parts of the drive to be cooled “as normal”. By way of example, the rear of the drive may be uncovered. 
         [0016]    The second opening may be provided on the front of the cover and, in use, extend parallel to the air outlet. The first and/or the second opening may be on a side of the front cover. 
         [0017]    The separator/baffle may extend upwards from the second opening to the exterior of the drive. Thus, the separator may direct air from the air outlet towards the second opening. If the separator extends upwards from the bottom of the second opening to the air outlet, then air exiting the cover will tend to be directed away from the cover (thereby reducing re-circulation). 
         [0018]    In an alternative form of the invention, the second opening is provided on the side of the cover (and may extend perpendicular to the air outlet). 
         [0019]    In many forms of the invention, a rain restrictor is provided in the form of a hood provided on the exterior of the cover. The hood may be shaped to direct at least some air from the air outlet away from the cover. For example, a projection may be provided towards the bottom of the hood that extends, at an angle, away from the plane of the cover. Alternatively, the hood may be shaped by providing a notch towards the bottom of the hood. 
         [0020]    In an alternative form of the invention, the rain restrictor is a louvered opening. 
         [0021]    Where provided, the rain restrictor typically restricts the ingress of rain into the cover through the second opening. Thus, the rain restrictor addresses one of the problems associated with providing the second opening in the cover. 
         [0022]    In many forms of the invention, the cover is provided as a kit that, in use, is placed over an existing drive. The kit includes connection means for attaching the cover to the motor drive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention will now be described in further detail with reference to the following schematic drawings, in which: 
           [0024]      FIG. 1  shows a known variable speed drive; 
           [0025]      FIG. 2  shows the drive of  FIG. 1  that is protected with a partial cover in accordance with an aspect of the present invention; 
           [0026]      FIG. 3  is a partially cut-away view of the drive and cover of  FIG. 2 ; 
           [0027]      FIG. 4  is a rear view of a cover in accordance with an aspect of the present invention; 
           [0028]      FIG. 5  shows a drive protected by a cover in accordance with an aspect of the present invention; and 
           [0029]      FIG. 6  shows a drive that is protected by a cover in accordance with another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The inventors have realised that many of the problems with the prior art can be addressed by providing only a partial cover, wherein the partial cover covers the portions of the drive that are vulnerable, but leaves other portions uncovered. This may be true, for example, where the drives itself provides good protection from, for example, rain, sand or excessive dust. 
         [0031]    In particular, the air inlet  3  and air outlet  4  need to be covered, but, in many embodiments, the back channel  2  (if provided) does not need to be covered, since the back channel is not vulnerable to rain ingress. 
         [0032]    Providing a partial cover reduces cost (by reducing material requirements) and also reduces size. However, dealing with heat generation by the drive is not trivial as any covering of the drive reduces the scope for heat removal. 
         [0033]      FIG. 2  shows the drive of  FIG. 1  that is protected with a partial cover  10  in accordance with an aspect of the present invention. The cover  10  comprises a hood  12 , a top  14  and a mounting arrangement  16 . The mounting arrangement  16  is used to physically connect the cover  10  to the drive  1  (for example using screws, as shown in  FIG. 2 ). The hood  12  includes a notch  18  that is described in detail below. 
         [0034]      FIG. 3  shows a partially cut-away view of the drive  1  and cover  10  of  FIG. 2 .  FIG. 3  shows the drive  1 , including the back channel  2 , air inlet  3  and air outlet  4 . The cover  10  includes the hood  12  (including the notch  18 ), top  14  and mounting arrangement  16  as shown in  FIG. 2 . As shown in  FIG. 3 , the mounting arrangement  16  is screwed to the drive  1  so that the cover is held in place, with a gap between the front of the drive  1  and the front of the cover  10 . The gap allows air to flow, as described further below. 
         [0035]    The cover  10  includes an opening at the bottom, indicated generally by the reference numeral  20 , an opening in the front of the cover, indicated generally by the reference numeral  22 , and a baffle  24 . The baffle is connected to the cover  10  (or forms part of the cover) and, in use, is in contact with the front of the drive  1 . For reasons described in detail below, the baffle  24  prevents air from flowing between the openings  20  and  22  within the space between the cover  10  and the drivel. 
         [0036]      FIG. 4  is a rear view of the cover  10 . In  FIG. 4 , the opening  22  and the baffle  24  are more clearly visible than in  FIG. 3 . The hood  12  (which is partially obscured), the top  14  and the mounting arrangement  16  are also shown in  FIG. 4 . 
         [0037]    When the cover  10  is attached to the drive, cooling air is able to enter drive  1  via the opening  20  and the air inlet  3 . A fan is typically provided to draw air in through the opening  20 . 
         [0038]    Air drawn in through the air inlet  3  is used to cool the drive  1  and is then expelled through the air outlet  4 . Air expelled through the air outlet  4  is able to leave the vicinity of the drive  1  through the opening  22 . 
         [0039]    As described above, a disadvantage with the provision of the air inlet  3  and the air outlet  4  is that when used outdoors without a cover, rain can enter the inlets and outlets and potentially damage the drive. Providing a cover addresses this problem, but prevents air flow. 
         [0040]    The provision of the opening  22  enables air flow. The provision of the hood  12  provides protection against rain ingress (and also at least some protection against other contaminants, such as sand). Together, the opening  22  and the hood  12  seek to address the twin problems of rain protection and heat dissipation. 
         [0041]    A further problem with providing a cover for the drive  1  is that hot air expelled through the air outlet  4  tends to be directed, by the cover, towards the air inlet  3 . This leads to the recirculation of air that has already been heated within the cooling arrangement of the drive. Clearly, this significantly reduces the effectiveness of the cooling arrangement. 
         [0042]    The cover  10  partially addresses this problem using the baffle  24 . The baffle prevents air from flowing from the air outlet  4  to the air inlet  3  in the region between the drive  1  and the cover  10 . This arrangement significantly reduces the recirculation of air as all of the air entering the air inlet  3  must enter the cover via the opening  20 . 
         [0043]    Although the baffle  24  prevents the recirculation of air within the interior of the cover  10 , air exiting the air outlet  4  can recirculate by passing through the opening  22  and then entering the cover via the opening  20 . The provision of the hood  12  tends to direct hot air exiting the opening  22  downwards (i.e. towards the opening  20 ); accordingly, the hood  12  can add to the problem of recirculation of air outside the cover. 
         [0044]    The cover  10  seeks to reduce this external recirculation problem by shaping the hood and/or the baffle to direct air away from the drive (rather the directly downwards). This reduces the tendency of hot air to be recirculated via the inlet. 
         [0045]    As shown in  FIGS. 3 and 4 , the baffle is angled in order to direct the air away from the cover  1  rather than directly downwards. 
         [0046]    As shown in  FIG. 3 , the rain hood  12  includes a rectangular cut-out portion or notch, indicated generally by the reference numeral  18 . In forms of the invention in which the notch in the hood is not provided, air directed by the baffle  24  tends to hit the rain hood and then be redirected downwards. The provision of the notch allows at least some of the air passing through the opening  22  to be directed away from the cover  10 . The size and shape of the notch shown in  FIG. 3  is provided by way of example; many alternatives will be apparent to the person skilled in the art. 
         [0047]    The problem of recirculation could be reduced further by increasing the height of the notch, or by simply reducing the size of the rain hood  12 . However, the rain hood is also required to reduce the amount of rain (or other substances) from entering the interior of the cover through the opening  22  and so a balance is required between directing air away from the cover and preventing rain from entering through the opening  22 . The optimum balance may vary from application to application. 
         [0048]      FIG. 5  shows a drive protected by an alternative cover, indicated generally by the reference numeral  30 . The cover  30  includes a rain hood  32  (similar to the rain hood  12  described above). The air inlet  3 , air outlet  4  and baffle  24  are also shown in  FIG. 5 . 
         [0049]    The rain hood  32  differs from the rain hood  12  in that the notch  18  has been replaced with a bent portion  34 . In effect, the area of the rain hood  12  that was removed to provide the notch  18  has, instead of being removed, been bent away from the hood  12 . In a similar manner to the baffle  24 , the bent portion tends to direct air away from the cover  12 . Thus, the function of the bent portion  34  is similar to that of the notch  18  described above. As with the notch  18 , the size and shape of the bent portion  34  may be varied. 
         [0050]    It should be stressed that although the provision of a notch  18 , a bent portion  34  or a similar arrangement for directing air away from the cover  1  may be advantageous in many implementations, this is not essential to all forms of the invention. The rain hood may, for example, be a simple cuboid shape having a rectangular opening at the bottom. 
         [0051]    The rain hoods  12  and  32  described above are not the only mechanism that can be used to restrict rain from entering the interior of the cover. By way of example,  FIG. 6  shows a drive that is protected by a cover  40  in accordance with another aspect of the present invention in which the rain hoods  12  and  32  are replaced with a louvered opening  42 . The provision of the louvered opening is attractive as it keeps the cover protected from rain without requiring a portion of the cover extending outwards (and therefore increasing the area occupied by the cover). The cover  40  effectively provides a collection of small openings, rather than a single large opening. This is likely to reduce the ability of hot air to move away from the drive  1  and so the thermal performance of the cover  40  may not be as good as that of the covers  10  and  30  described above. 
         [0052]    The cover  40  includes a baffle  44  that has a similar function to the baffle  24  described above. The baffle is angle downwards from right to left (when viewing the cover from the front) in order to direct hot air from the air outlet towards the louvered opening  42 . As with the baffle  24 , the baffle  44  prevents air circulation within the space between the drive and the cover  40 . 
         [0053]    As indicated by the arrow  46 , air enters the cover (and hence the air inlet) through the opening in the bottom of the cover. As indicated by the arrow  48 , air exits the cover through the louvered opening  42 . 
         [0054]    The position of the air inlet  3  and/or air outlet  4  as shown attached Figures is not essential to all forms of the invention. For example, at least one of the inlet and outlet could be provided on the side of the drive (rather than on the front). Furthermore, at least one of the inlet and outlet could be provided on the top and/or the bottom of the drive. In the arrangements described above, the air inlet  3  is provided towards the bottom of the drive  1  and the air outlet  4  is provided near the top of the drive; these positions could be reversed. Other possible variants will be apparent to the person skilled in the art. 
         [0055]    As described above, the baffles  24  and  44  act as separators that prevent air from re-circulating within the cover from the outlet to the inlet of the drive. This is a particular problem with the configurations shown in Figures in which the air inlet  3  and the air outlet  4  are both provided on the front of the drive. Clearly, if the air inlet and air outlet are not both provided on the front of the drive, then the problem of air re-circulation may be significantly reduced. Indeed, the problem may be reduced to an extent to which the baffles are no longer required. Accordingly, the provision of baffles to prevent recirculation of air within the drive is not essential to all embodiments of the present invention. 
         [0056]    As described above, a rain restrictor (such as the hoods  12  and  32  and the louvered opening  42 ) are provided to reduce the amount of rain that enters the interior of the cover, thereby reducing the likelihood of rain entering the air outlet  4 . It should be noted, however, that the provision of a rain restrictor is not essential to all forms of the invention. The restriction of rain is often required in order to enable the drive/cover assembly to be sufficiently water-resistant. However, if the environment in which the drive is to be deployed is not severe, or if the drive itself is reasonably water-tight, then the additional protection provided by the rain restrictor may not be required. Moreover, if the thermal requirements of the system are met by providing only a small opening  22  in the front of the cover, then the exposure of the drive to rain may be sufficiently low, even if the rain restrictor is not provided. Further, if the air outlet  4  is provided away from the opening  22 , then, once again, the exposure of the drive to rain may be sufficiently low, even if the rain restrictor is not provided. 
         [0057]    The prior art drive  1  described above with reference to  FIG. 1  includes backchannel cooling. It should be stressed that although the provision of backchannel cooling has many advantages for use with the principles of the present invention, it is not essential to all forms of the invention. 
         [0058]    The embodiments of the invention described above are provided by way of example only. The skilled person will be aware of many modifications, changes and substitutions that could be made without departing from the scope of the present invention. The claims of the present invention are intended to cover all such modifications, changes and substitutions as fall within the spirit and scope of the invention.