Abstract:
A projection display device comprises a light source, a display section configured to receive light from the light source and output image light modulated with an image signal, a projection device configured to project the image light output from the display section, a duct device having an air duct for conducting air from an air intake to an air discharge section and an air chamber which is formed downstream of the air discharge section in the air duct and configured to blow cooling air from the air discharge section toward the display section, and an air blower configured to blow cooling air into the air intake.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-221836, filed Jul. 30, 2002, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a projection display device which projects optical images onto a screen for image reproduction and more specifically to improvements in means for cooling light bulbs used in the display device. Also, the present invention relates to improvements in air blowing device suitably used to cool the light bulbs of a projection display device such as a liquid crystal projector. 
     2. Description of the Related Art 
     As is well known, information terminals for home use, such as personal computers, have come into wide use in recent years. Moreover, high-definition television has also started. Under these circumstances, the demand has increased for reproducing images on a larger screen with higher brightness and quality. 
     To meet such a demand, the development of projection display devices, such as liquid crystal projectors, is accelerated at present. In the projection display device, light from a light source is decomposed into three primary color components of red (R), green (G) and blue (B) and each colored light is then directed onto a corresponding one of the liquid crystal light panels. 
     Each of these light panels is driven by a respective one of the R, G and B image signals to produce image light modulated by the image signal. The rays of image light output from the liquid crystal light panels are combined and then enlargement projected through a projection lens onto a screen for image reproduction. 
     In this type of projection display device, as its light source use is frequently made of a lamp of high power dissipation, such as a metal halide lamp or extra-high pressure mercury lamp. For this reason, it is required to make provisions not only for cooling the interior of the device or cooling for increasing the life of the lamp itself but also for cooling the interior of the optical engine. 
     The cooling of the interior of the optical engine is performed mainly on polarization conversation elements, input and output polarizing plates, and the liquid crystal light panels. In many cases, these parts, unlike lenses and mirrors, are not composed of inorganic materials only. When the parts rise in temperature, not only is their life shortened, but also the performance required of them as products cannot be maintained. 
     The parts inside the optical engine are required to allow incoming light to pass through. For this reason, with a cooling method using heatsinks, it is impossible to secure a large contact area, thus reducing the cooling efficiency. Thus, forced-air cooling using air blowers (fans) is generally adopted. 
     At present, with reduction in dimensions of projection display devices and increase in the luminance, downsizing of optical parts and increasing of the output power of light sources are in progress. Under these circumstances, cooling of the input and output polarizing plates and the liquid crystal light bulbs in particular has become further difficult. 
     As provisions for cooling, various methods have been developed which include a method which uses a centrifugal fan with higher static pressure in place of an axial fan, a method which uses a material of high heat transfer rate for the glass that is used for lamination of polarizing plates, and a method which uses a material of high heat transfer rate for a frame that holds a liquid crystal light bulb. 
     To lower the temperature of parts to be cooled, the speed of the fan is simply increased to increase the quantity of air, in which case noise involved in increasing the quantity of air will become a problem. For this reason, the important issue is how to lower ventilation resistance associated with the paths from the fan to the input and output polarizing plates and the liquid crystal light bulbs. 
     Ideally, it is the most effective to apply air directly from the fan to the parts to be cooled without providing air ducts. In practice, however, structural restrictions resulting from downsizing of the device frequently cause it to have to take the configuration in which airflow is conducted from the fan through air ducts to the parts to be cooled. 
     In this case, if the air duct is bent, there will be produced nonuniformity in the quantity of air finally blown out of the outlet of the air duet. For this reason, the input and output polarizing plates and the liquid crystal light panel will each have sufficiently cooled portions and insufficiently cooled portions. This has an adverse effect on the quality of a displayed image. 
     To cope with this problem, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-82393 discloses a configuration which causes a fan to take in air uniformly therethrough to thereby allow the quantity of air sent out by the fan to become uniform. 
     With this disclosed configuration, however, it is required to blow air directly from the fan onto the parts to be cooled. This makes it necessary to place the fan in the proximity of the input and output polarizing plates and the liquid crystal light panel. The configuration is therefore not suited for use with projection display devices with downsizing requirements. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a projection display device comprising: a light source, a display section configured to receive light from the light source and output image light modulated with an image signal; a projection device configured to project the image light output from the display section; a duct device having an air duct for conducting air from an air intake to an air discharge section and an air chamber which is formed downstream of the air discharge section in the air duct and configured such that cooling air blows from the air discharge section toward the display section; and an air blower configured to blow cooling air into the air intake. 
     According to another aspect of the present invention, there is provided an air blowing device which blows cooling air against a part to be cooled comprising: a duct device having an air duct for conducting air from an air intake to an air discharge section and an air chamber formed downstream of the air discharge section in the air duct and configured to blow cooling air from the air discharge section toward the part to be cooled; and an air blower configured to blow cooling air into the air intake. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a diagram for use in explanation of an optical engine system for use in a projection display device according to an embodiment of the present invention; 
     FIGS. 2A and 2B are perspective views for use in explanation of a duct device used in the projection display device of the embodiment of the present invention; 
     FIGS. 3A and 3B are diagrams for use in explanation of the detailed structure of the duct device of FIGS. 2A and 2B; 
     FIG. 4 is a diagram for use in explanation of the distribution of discharged air quantity in the presence of an air chamber in the duct device; and 
     FIG. 5 is a diagram for use in explanation of the distribution of discharged air quantity in the absence of an air chamber in the duct device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A projection display device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic diagram of the projection display device and illustrates its optical engine system in particular. 
     In FIG. 1, reference numeral  11  denotes a light source. The light emitted from the light source  11  is converted by multiple lenses  12  and  13  into parallel rays of light, then passes through a polarization conversion element  14  and a condenser lens  15  and is reflected at substantially right angles by a reflecting mirror  16 . 
     The light reflected by the reflecting mirror  16  is directed onto a dichroic mirror  17  that reflects blue light. The blue light is directed through a condenser lens  18 , a reflecting mirror  19 , a field lens  20 , and an input polarizing plate  21  onto a liquid crystal light bulb panel  22 . 
     The liquid crystal light panel  22  has an image display screen driven by a blue image signal. By being irradiated with the blue light, the liquid crystal light panel  22  outputs image light modulated with the blue image signal, which in turn falls on an output polarizing plate  23 . 
     Other colors of light than the blue light pass through the dichroic mirror  17  and are then directed onto a dichroic mirror  24  that reflects green light. The reflected green light is directed through a field lens  25  and an input polarizing plate  26  onto a liquid crystal light panel  27 . 
     The liquid crystal light bulb panel  27  has an image display screen driven by a green image signal. By being irradiated with the green light, the liquid crystal light bulb panel  27  outputs image light modulated with the green image signal, which in turn falls on an output polarizing plate  28 . 
     The red light passed through the dichroic mirror  24  has its direction of propagation changed by a relay lens  29 , a reflecting mirror  30 , a relay lens  31 , and a reflecting mirror  32  and is then directed through a field lens  33  and an input polarizing plate  34  onto a liquid crystal light panel  35 . 
     The liquid crystal light panel  35  has an image display screen driven by a red image signal. By being irradiated with the red light, the liquid crystal light panel  35  outputs image light modulated with the red image signal, which in turn falls on an output polarizing plate  36 . 
     The blue, green and red image light outputs of the respective liquid crystal light panels  22 ,  27 , and  35  are combined by a combining prism  37  and then projected through a projection lens  38  onto a screen  39 . Thereby, image reproduction is achieved. 
     FIG. 2A shows the appearance of a duct device  40  for air cooling the input polarizing plates  21 ,  26  and  34 , the liquid crystal light panels  22 ,  27  and  35 , and the output polarizing plates  23 ,  28  and  36 . The duct device  40 , which, as a whole, is shaped like the letter U, has air intakes  41  and  42  formed at its both ends. 
     Also, the duct device  40  is formed in its central portion with an air discharge section  43  for blowing air against the input polarizing plate  21 , the liquid crystal light panel  22 , and the output polarizing plate  23 , an air discharge section  44  for blowing air against the input polarizing plate  26 , the liquid crystal light panel  27 , and the output polarizing plate  28 , and an air discharge section  45  for blowing air against the input polarizing  34 , the liquid crystal light bulb  35 , and the output polarizing plate  36 . 
     The duct device  40  is configured such that a cover  47  is integrated with the duct body  46 . The duct body  46  is formed inside with a plurality of air ducts  50 ,  51 ,  52 ,  54  and  54 , as shown in FIG. 2B, so as to conduct air taken in from the air intakes  41  and  42 , shown in FIG. 2A, to the air discharge section  43 ,  44  and  45 , shown in FIG.  2 B. 
     FIGS. 3A and 3B show the air ducts in the duct device  40 . FIG. 3B is a sectional view taken along line b—b′ in FIG.  3 A. Centrifugal fans  48  and  49  are placed in front of the air intakes  41  and  42 , respectively, of the duct device  40 . Air blown from the centrifugal fan  48  enters the duct device  40  through the air intake  41  and is then discharged from the air discharge section  43  through the air duct  50 . 
     The air discharge section  43  is composed of an input-side outlet  43   a  and an output-side outlet  43   b . The input-side outlet  43   a  is adapted to discharge air to the input polarizing plate  21 , shown in FIG. 1, and the input side of the liquid crystal light panel  22  shown in FIG. 1, for cooling thereof. The output-side outlet  43   b  is adapted to discharge air to the output side of the liquid crystal light panel  22  and the output polarizing plate  23 , shown in FIG. 1, for cooling thereof. 
     Air blown from the centrifugal fan  49  enters the duct device  40  through the air intake  42  and is then discharged from the air discharge section  45  through the air duct  51 . The air discharge section  45  is composed of an input-side outlet  45   a  and an output-side outlet  45   b . The input-side outlet  45   a  is adapted to discharge air to the input polarizing plate  34  shown in FIG. 1, and the input side of the liquid crystal light bulb  35 , shown in FIG. 1, for cooling thereof. The output-side outlet  45   b  is adapted to discharge air to the output side of the liquid crystal light panel  35  and the output polarizing plate  36 , shown in FIG. 1, for cooling thereof. 
     The air discharge section  44  is composed of an input-side outlet  44   a  and an output-side outlet  44   b . Air blown from the centrifugal fan  49  enters the duct device  40  through the air intake  42  and is then discharged from the input-side outlet  44   a  through the air duct  52 . The input-side outlet  44   a  is adapted to discharge air to the input polarizing plate  26 , shown in FIG. 1, and the input side of the liquid crystal light panel  27 , shown in FIG. 1, for cooling thereof. 
     The air duct  52  is formed with a chamber  53  where air collects, downstream of the input-side outlet  44   a . The input-side outlet  44   a  is formed substantially in parallel with the corresponding air duct  52 . Without the chamber  53 , therefore, there will be produced a difference in the quantity of air discharged from the outlet  44   a  between its portions near and far from the air intake  42 . In that case, air will not be blown uniformly against the display screen of the liquid crystal light panel  27 , resulting in nonuniform temperature distribution over the display screen. 
     For this reason, in this embodiment, the chamber  53  serving as an air reservoir is formed downstream of the input-side outlet  44   a . As a result, air is discharged from the outlet  44   a  substantially uniformly as shown in FIG. 4, thereby allowing the input polarizing plate  26  and the input side of the liquid crystal light panel  27  to be cooled uniformly and efficiently. 
     FIG. 4 shows a measurement indicating the discharged state of air from the outlet  44   a  when viewed in the direction of an arrow A of FIG.  3 A. In FIG. 4, the rate of air flow is higher in portions indicated darker. 
     Referring back to FIGS. 3A and 3B, air from the centrifugal fans  48  and  49  is discharged from the output-side outlet  44   b  through the air intakes  41  and  42  and the air ducts  54  and  55 . The output-side outlet  44 b discharges air against the output-side of the liquid crystal light panel  27  and the output polarizing plate  28  for cooling thereof. 
     The output-side outlet  44   b  has a partition plate  44   c  formed in its central portion. As shown in FIG. 5, therefore, air is discharged from the output-side outlet  44   b  along the partition plate  44   c . The quantity of air discharged from the output-side outlet  44   b  is the largest in its central portion, cooling the output side of the liquid crystal light bulb panel  27  and the output polarizing plate  28 . 
     According to the embodiment described above, since the air duct  52  that conducts air blown from the centrifugal fan  49  to the input-side outlet  44   a  has the air chamber  53  formed downstream of that outlet, air can be discharged uniformly from the outlet  44   a , which allows the input polarizing plate  26  and the input side of the liquid crystal light panel  27  to be cooled uniformly and efficiently. 
     The air discharge sections  43  and  45  have no air chamber. This is because the air ducts  50  and  51  are substantially perpendicular to the liquid crystal panels  22  and  35 , respectively, and hence air is discharged uniformly from each of the air discharge sections  43  and  45 . 
     Although one embodiment of the present invention has been disclosed and described, the present invention may be practiced or embodied in still other ways without departing from the scope and spirit thereof.