Abstract:
A cooling structure includes: a heat releasing unit configured to include a plurality of fins and to release heat by contacting a first cooling target; and an air blowing unit configured to blow air to the heat releasing unit, wherein the heat releasing unit includes a first region and a second region in which intervals of the fins are smaller than those of the first region, and a second cooling target that is different from the first cooling target is positioned downstream relative to the first region in a flow path of the air, and the air that has passed through the first region blows on the second cooling target.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2013-131171 filed in Japan on Jun. 21, 2013. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a cooling structure, an image projection apparatus, an electronic device, and a cooling device. 
         [0004]    2. Description of the Related Art 
         [0005]    As a technique of cooling a heat source, a method of putting a heat sink to the heat source to expand a heat releasing area, and of blowing cooling air onto a heat releasing unit has been known. As a technique of further improving the cooling efficiency, for example, fabricating the heat sink with a highly thermal conductive material has been practiced. By fabricating the heat sink with highly thermal conductive material, it becomes possible to spread the heat transmitted from a contact unit in contact with the heat source uniformly to the entire heat sink. As a result, the heat releasing area can be enlarged, and therefore, the heat source can be cooled efficiently. 
         [0006]    Moreover, enlarging the contact area of cooling air and the heat sink is also effective. The heat sink heated by receiving heat from the heat source is cooled at a portion that contacts with cooling air. Therefore, it becomes possible to improve the cooling efficiency by expanding an area that contacts with cooling air. Moreover, a method of arranging fins on a heat sink has been known as a method of expanding the contact area. By arranging fins in a small pitch and blowing cooling air between respective pitches, a contact area that contacts with the cooling air is expanded, and thus the cooling efficiency is improved. 
         [0007]    Furthermore, a forcible cooling method of cooling the heat sink using a fan has also been adopted. Cooling performance is dependent on a wind velocity of air that passes through between the pitches of the fins. Therefore, to improve the cooling performance, it is necessary to increase the speed of the air that passes through between pitches, and a higher cooling effect can be acquired with the forcible air cooling rather than air cooling without blower. As a forcible air cooling, a method of using a fan is common, and especially a cooling structure in which a sirocco fan having high static pressure is arranged so as to oppose to the fins, and air blown out from the sirocco fan blows the fins of the heat sink directly is considered common (Japanese Laid-open Patent Publication No. 2008-134432, Japanese Patent No. 4901595, Japanese Patent 4927923). 
         [0008]    However, in the above conventional cooling method, when the cooling efficiency is to be improved structurally, it is required to enlarge a surface area of the heat sink, or to prepare a more powerful large fan to improve the cooling efficiency, and there has been a problem that the structure increases in size. Therefore, in any case, the structure increases in size and weight, and there has been a problem that it is difficult to be equipped inside compact and lightweight electric devices. 
         [0009]    Moreover, in the method of arranging the fins in a small pitch, because the cooling air passes through between the pitches of the fins, air resistance increases if the fins are arranged in a small pitch. Because the cooling performance is dependent on an amount of air, if the air resistance increases, the amount of the air that passes through the fins decreases. Therefore, there has been a problem that it is difficult to use the air that has passed through the fins, for cooling other components. That is, when forming a structure in which a fan, a heat releasing unit, and other cooling targets are aligned in series in the above order to cool not only the heat releasing unit but also the other cooling targets at the same time using cooling air blown out from the fan, if the fins are arranged in a small pitch, the cooling performance for the heat releasing unit is enhanced but it is difficult to cool the cooling targets positioned downstream relative to the heat releasing unit. 
         [0010]    Therefore, in the conventional method of improving the cooling performance by arranging fins in a small pitch, a structure in which the target to be cooled by a fan is only a heat releasing unit is common, and even if it is structured such that the other components are cooled using air that has been used to cool the heat releasing unit, the cooling performance therefor cannot be expected. Moreover, when fins are designed to have a complicated shape, there has been a problem that cost of the fins increases. Therefore, ideally, such a method of expanding the surface area of the heat releasing unit with a simple shape is demanded. 
         [0011]    Therefore, there is a need to offer a cooling structure that enables to enhance the cooling performance of a heat releasing unit, and to cool, at the same time, a cooling target positioned downstream relative to the heat releasing unit using air that has been used to cool the heat releasing unit. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to at least partially solve the problems in the conventional technology. 
         [0013]    According to an aspect of the present invention, provided is a cooling structure including: a heat releasing unit configured to include a plurality of fins and to release heat by contacting a first cooling target; and an air blowing unit configured to blow air to the heat releasing unit, wherein the heat releasing unit includes a first region and a second region in which intervals of the fins are smaller than those of the first region, and a second cooling target that is different from the first cooling target is positioned downstream relative to the first region in a flow path of the air, and the air that has passed through the first region blows on the second cooling target. 
         [0014]    The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view showing a use mode of an image projection apparatus of an embodiment; 
           [0016]      FIG. 2  is a perspective view showing an optical engine unit and a light source device of the embodiment; 
           [0017]      FIG. 3  is a perspective view showing the optical engine unit of the embodiment; 
           [0018]      FIG. 4  is a perspective view showing an illumination optical unit and an image processing unit of the embodiment; 
           [0019]      FIG. 5  is a perspective view showing the image processing unit of the embodiment; 
           [0020]      FIG. 6  is a perspective view showing a projection optical unit of the embodiment; 
           [0021]      FIG. 7  is a perspective view showing the projection optical unit of the embodiment; 
           [0022]      FIG. 8  is a side view showing the projection optical unit of the embodiment; 
           [0023]      FIG. 9  is a perspective view showing a structure of a heat sink of the embodiment; 
           [0024]      FIG. 10  is a perspective view showing a structure of a sirocco fan of the embodiment; 
           [0025]      FIG. 11  is a bottom plan view showing the structure of the sirocco fan of the embodiment; 
           [0026]      FIG. 12  is a perspective view showing positional relation of the heat sink and the light source device of the embodiment; 
           [0027]      FIG. 13  is a perspective view showing the positional relation of the heat sink and the light source device of the embodiment; 
           [0028]      FIG. 14  is a bottom plan view of the image projection device of the embodiment; 
           [0029]      FIG. 15  is a side view of the image projection apparatus of the embodiment; and 
           [0030]      FIG. 16  is a side view of a conventional image projection apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    An embodiment of the present invention is explained below with reference to the drawings.  FIG. 1  is an appearance perspective view showing an image projection apparatus  1  according to the present embodiment when viewed from an angle. An image projection apparatus  1  generates an image on the basis of image data input from a personal computer, a video camera, and the like, and projects the image on a screen  2  or the like that is a projected surface. These days, achievement of higher resolution of a liquid crystal panel, improvement in brightness with high efficiency of a light-source lamp, price reduction, and the like of a liquid crystal projector widely known as the image projection apparatus  1  are increasingly being advanced. Moreover, compact lightweight image projection apparatuses using a digital micro-mirror device (DMD) have become widespread, and these image projection apparatuses have been increasingly used at home as well as at an office or a school. Particularly, front type projectors have been improved in portability, and have been increasingly used also in small meetings with several people. 
         [0032]      FIG. 2  is a perspective view showing a state in which an external layer cover  3  of the image projection apparatus  1  shown in  FIG. 1  is removed. As shown in  FIG. 2 , the image projection apparatus  1  is roughly divided into an optical engine unit  30  and a light source device  20 . The light source device  20  controls a light source such as a high-pressure mercury vapor lamp, for example, and supplies white light required for projection of an image to the optical engine unit  30 . 
         [0033]    The light source device  20  has a light source bracket  22  that is a holding member to hold a light source  21 , and the light source  21  such as a halogen lamp, a metal halide lamp, and a high-pressure mercury vapor lamp is mounted at an upper portion of the light source bracket  22 . 
         [0034]    Moreover, at a light emitting side of the light source  21  at the upper portion of the light source bracket  22 , a holder  24  by which an unillustrated reflector and the like are held is fixed with a screw. At a surface of the holder  24  on a side opposite to the side of the light source  21 , an emission window  23  (refer to  FIG. 3 ) is arranged. Light emitted from the light source  21  is condensed at the emission window  23  by the unillustrated reflector held by the holder  24  to be emitted from the emission window  23 . 
         [0035]    Moreover, a light-source intake opening through which air for cooling the light source  21  flows in is arranged on a side surface of the holder  24 , and a light-source exhaust opening through which air heated by heat of the light source  21  is exhausted is arranged on an upper surface of the holder  24 . 
         [0036]    An optical engine unit  30  performs control of processing input image data to project, using the light supplied from the light source device  20 .  FIG. 3  is a perspective view showing a detailed structure of the optical engine unit  30 . The optical engine unit  30  includes an illumination optical unit  31 , a projection optical unit  33 , and an image processing unit  32 . The white light from the light source device  20  described above is first irradiated to the illumination optical unit  31 . The illumination optical unit  31  disperses the white light from the light source device  20  to respective RGB components to guide to the image processing unit  32 . The image processing unit  32  performs an image forming according to a modulation signal, and generates an image to be projected from the input image data. The projection optical unit  33  projects the image generated by the image processing unit  32  on the projected surface in an enlarged manner. 
         [0037]      FIG. 4  is a structural arrangement plan of the illumination optical unit  31  and the image processing unit  32 . The illumination optical unit  31  includes a color wheel  38 , a light tunnel  37 , a relay lens  36 , a cylinder mirror  35 , and a concave-convex mirror  34 . The color wheel  38  converts the white light emitted from the light source device  20  described above into light in which the respective colors of RGB are repeated in every unit time by a color filter in a disc shape. The light tunnel  37  is formed by putting sheet glasses together into a cylindrical shape, and guides the light emitted from the color wheel  38 . The relay lens  36  is formed with two lenses combined, and condenses the light emitted from the light tunnel  37 , while correcting axial chromatic aberration thereof. 
         [0038]    The cylinder mirror  35  and the concave-convex mirror  34  reflect the light emitted from the relay lens  36 . The reflected light is input to the image processing unit  32 , and the image processing unit  32  has an approximately rectangular mirror plane constituted of multiple micro mirrors, and includes a DMD element that processes and reflects projection light so as to form a predetermined image by time sharing operation of the respective micro mirrors based on an image or image data. In the image processing unit  32 , light used by the multiple micro mirrors in a time sharing manner on the basis of image data by the DMD element is reflected in the direction of a projection lens  51  indicated by an arrow B in the figure, and light to be discarded is reflected to an off light plate indicated by an arrow C. 
         [0039]      FIG. 5  is a perspective view showing a structure of the image processing unit  32 . The image processing unit  32  includes the DMD element  41 , a DMD printed-circuit board  42  that controls the DMD element  41 , a heat sink  43  that cools the DMD element  41 , and a fixing plate  44  that pushes the heat sink  43  to the DMD element  41 . In the present embodiment, the heat sink  43  corresponds to the heat releasing unit. The heat sink  43  contacts the DMD element  41  being a first cooling target, to release heat of the DMD element  41 . Moreover,  FIG. 6  is a perspective view showing a detailed structure of the projection optical unit  33 . Light that has passed through the image processing unit  32  is reflected to the projection lens  51  shown in  FIG. 6 , and light to be discarded is reflected to an off light plate  53  shown in  FIG. 6 . 
         [0040]      FIG. 7  and  FIG. 8  are a perspective view and a side view showing a structure of the projection optical unit  33 . An optical path of image light that has passed through the projection lens  51  and has been expanded is folded back by a fold back mirror  54 , and is projected on a screen  2  by a free-curved mirror  55  in an enlarged manner. By the above structure, the optical engine unit  30  can be arranged adjacent to the screen  2 , and can be designed in an upright form in which an optical axis path is vertical so as to have a small installation area and to be sterically compact. 
         [0041]      FIG. 9  is a diagram showing a structure of the heat sink  43  used in the present embodiment. In the present embodiment, this heat sink  43  implements a cooling structure to cool two units of devices, the image processing unit  32  and the light source device  20 . To the heat sink  43 , a sirocco fan  61  is arranged thereinside (on a bottom-surface side thereof). The sirocco fan  61  corresponds to an air blowing unit that takes outside air to blow into the heat sink  43 . The sirocco fan  61  has a structure in which a cylinder with many small fins facing forward and an air rectifier are combined, and a general kind having the static pressure efficiency of 60% level is used. 
         [0042]    Furthermore, the sirocco fan  61  has a first intake opening  71 , a second intake opening  72 , and a blow-out opening  73  as shown in  FIG. 10 . The second intake opening  72  is arranged on the opposite side of the first intake opening  71 , and the sirocco fan  61  is a double-side intake fan. That is, in the present embodiment, the first intake opening  71  is arranged on an upper surface side of the sirocco fan  61  and the second intake opening  72  is arranged on a bottom surface side of the sirocco fan  61 . Moreover, in this structure, the sirocco fan  61  in which the blow-out opening  73  is wide, that is, the blow-out opening  73  having width larger than thickness, is used. This is to further enhance the cooling efficiency. The sirocco fan having the wide blow-out opening  73  can enlarge an area from which cooling air is exhausted, and the contact area between the cooling air and the heat sink  43  can be increased. By thus increasing the contact area between the cooling air and the heat sink  43 , the cooling efficiency can be improved. 
         [0043]      FIG. 11  is a diagram showing a flow of air that is blown out from the sirocco fan  61  viewed from the bottom surface side of the sirocco fan  61 . As shown in  FIG. 11 , the sirocco fan  61  is structured such that a large amount of air concentrates on a side of an end indicated by an arrow among the exhaust openings  73 . Therefore, the amount of airflow of the cooling air blown out is not uniform, and a first portion with a small amount of airflow to which air in a predetermined first amount flows and a second portion to which air in a second amount flows that is larger than the first amount can be distinguished. 
         [0044]    Among the cooling air generated by the sirocco fan  61 , for a second region  43   b  with a large amount of airflow, the length of the fins of the heat sink  43  is formed long to increase the surface area of fins. As for the pitch of the fins also, it is arranged such that the pitch is small in the second region  43   b  through which a large amount of cooling air flows, and it is arranged such that the pitch is large in a first region  43   a  through which a small amount of cooling air flows. The pitch is an interval between respective fins. 
         [0045]    With such a structure, the surface area of the heat sink  43  in the second region  43   b  can be expanded, and the cooling efficiency of the heat sink  43  in the second region  43   b  through which a large amount of cooling air flows can be improved. On the other hand, in the first region  43   a  through which a small amount of cooling air passes, it is arranged such that the pitch of the fins is large thereby reducing the air resistance, and the cooling air that has passed through this first region  43   a  is used for cooling components positioned on a downstream side. That is, cooling of the heat sink  43  is performed in the second region  43   b  in which the pitch of the fins is small and the length of the fins is long, and cooling of the components on the downstream side is performed in the first region  43   a  in which the pitch is large. 
         [0046]    Subsequently, positional relation among the light source device  20  that is a second cooling target positioned on the downstream side in an air flow path in the heat sink  43 , the sirocco fan  61 , and the heat sink  43  is explained below using a  FIG. 12 . As shown in  FIG. 12 , it is structured such that a duct  25  for cooling the light source device  20  is connected linearly from the first region  43   a  in which the pitch of the fins is large. With such a structure, the cooling air that has passed through the first region  43   a  enters into the above duct  25  without losing the amount of air, and can cool the light source device  20 . In this way, the sirocco fan  61  that is a cooling source for forcible air cooling, the heat sink  43 , and the light source device  20  that is the cooling target of the air that has passed through the heat sink  43  are arranged linearly in sequence. With a structure in which the duct  25  for cooling of the light source device  20  is arranged at a position opposing to the first region  43   a  in which the pitch is large, the light source device  20  can be cooled efficiently in the first region  43   a  in which the pitch of the fins is large. On the other hand, in the second region  43   b  in which the pitch of the fins is small, the heat sink  43  can be cooled efficiently. Accordingly, cooling of two components of the heat sink  43  and the light source device  20  can be efficiently performed with a single unit of the sirocco fan  61 . As a method of guiding the cooling air that has passed through the first region  43   a  into the duct  25  of the light source device  20  with smaller loss, it is desirable to newly arrange a duct  62  for a connection as shown in  FIG. 13 . 
         [0047]    Next, a structure of the image projection apparatus  1  itself that takes in such cooling air is explained.  FIG. 14  is a perspective view of a mounting surface side of the image projection apparatus  1 . As shown in  FIG. 14 , an opening/closing cover  84  is arranged at a base portion  83  that forms a bottom surface of the image projection apparatus  1 . A rotating handle portion  84   a  is arranged on the opening/closing cover  84 . If the rotating handle portion  84   a  is rotated, the opening/closing cover  84  fixed to a main unit is released, and the opening/closing cover  84  is to be removable from the main unit. Furthermore, an air introducing opening F 2  is arranged on a bottom surface of the base portion  83  of the image projection apparatus  1 . 
         [0048]      FIG. 15  is an explanatory diagram of an air flow inside the image projection apparatus  1  of the present embodiment. This diagram shows a view of the image projection apparatus  1  observed from a direction (X-direction) perpendicular to the screen  2 . In  FIG. 15 , arrows indicate directions in which air flows. As shown in  FIG. 15 , the air introducing opening F 2  that opens to take outside air into the image projection apparatus  1  is arranged on one side (lower left part in the figure) of the bottom surface of the image projection apparatus  1 , and an exhaust opening  85  that opens to exhaust air inside the image projection apparatus  1  is arranged on the other side (upper right part in the figure) on a side surface of the image projection apparatus  1 . Moreover, an intake fan F 1  is arranged so as to be opposed to the air introducing opening F 2 . An exhaust fan  86  is arranged so as to be opposed to the exhaust opening  85 . 
         [0049]    For example, the intake fan F 1  is a sirocco fan, and the exhaust fan  86  is an axial fan. Furthermore, the intake fan F 1  and the air introducing opening F 2  are arranged adjacent to the heat sink  43 . As compared with an air flow in the conventional image projection apparatus shown in  FIG. 16 , the air introducing opening F 2  and the intake fan F 1  are arranged on a side surface of a projector, and air reaches a rear part of the light source  21  through a path of a bent duct in the example shown in  FIG. 16 . On the other hand, in the image projection apparatus  1  of the present embodiment shown in  FIG. 15 , air taken in by the intake fan F 1  from the air introducing opening F 2  reaches a rear part of the light source  21  through the straight duct  25  in a shorter way than the conventional technique. 
         [0050]    Because the distance from the air introducing opening F 2  to the rear part of the light source  21 , which is a cooling target, is short, and the duct  25  is straight, the pressure loss on the path from the intake fan F 1  to the cooling target can be decreased. Moreover, by using the sirocco fan of double-side intake is as the intake fan F 1 , near the cooling fins of the heat sink  43 , a forced air flow occurs by intake of the sirocco fan on a side of the opposite surface of the air introducing opening F 2  at the bottom, and efficient cooling is enabled. 
         [0051]    The heat sink  43  with various pitches, which is the embodiment of the present invention, can be fabricated by extrusion molding or die-casting. Accordingly, because the same processing method as that of general heat sinks with uniform pitches can be applied for fabrication, special cost is not required in processing the heat sink  43  shown in the present invention. 
         [0052]    As described above, with a configuration in which a cooling target is further arranged downstream relative to the heat sink  43 , while arranging the fins in a large pitch, it becomes possible to cool two or more components at the same time with a single fan. As a result, the cooling efficiency is enhanced and it becomes possible to design a cooling device compact. 
         [0053]    Moreover, because the heat sink  43  is not in a complicated shape, the cooling effect described above can be obtained without increasing costs. Therefore, the design of a compact and highly efficient cooling structure system is possible even with low cost. 
         [0054]    Furthermore, by arranging the air introducing opening F 2  and the intake fan F 1  on the bottom surface in the image projection apparatus  1 , the light source device  20  and the heat sink  43 , which are the cooling targets, are positioned adjacently to each other, and the duct for sending air to the light source device  20  can be formed in a straight shape, and therefore, the pressure loss inside the duct is reduced and the cooling efficiency of a light source device  20  improves. As a result, the rotation frequency of the intake fan F 1  can be reduced, leading to reduction of noise of the device. Moreover, by arranging the air introducing opening F 2  and the intake fan F 1  that is adjacent to the opening thereof on the bottom surface of the device, the noise from the intake fan F 1  is easier to attenuate before the noise reaches a user&#39;s ear compared to a case of intake from a side surface, and the propagation direction of sound is likely to diverge, and therefore this leads also to reduction of noise. 
         [0055]    Note that the cooling structure described above can be used also for devices of a cooling target in an electronic device, such as a usual personal computer and an electronic circuit, besides an image projection apparatus. 
         [0056]    According to the present invention, it is possible to enhance the cooling performance of a heat releasing unit and to cool a cooling target that is positioned downstream of the heat releasing unit using air that has been used to cool the heat releasing unit. 
         [0057]    Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.