LCD, light source, and hemispheric concave reflector mounted individually to a support and part of a heads up display

A liquid crystal displaying device uses an inexpensive incandescent lamp or xenon lamp without sacrificing luminous intensity of a reflector, while maintaining an ease of installation. In the displaying device, a liquid crystal displaying panel, an incandescent lamp, a reflector, a lens and a heat-ray absorbing filter have a common optical axis and are secured to a bracket. The lamp is held by a socket and installed on the bracket transversely to the optical axis of the reflecting surface of the reflector. Further, the liquid crystal displaying panel has polarizing plates on both sides thereof. A coating to diffuse light from the lamp is disposed on one of the polarizing plates on the light incident side of the displaying panel. The polarizing direction of the polarizing plate on the other side of the displaying panel is selected so that the polarizing direction of the incident light waves on a reflective layer which is disposed on the front windshield glass provides a transversal or horizontal wave.

CROSS REFERENCE TO RELATED APPLICATION 
The present application is based on and claims priority from Japanese 
Patent Applications Nos. Hei 6-61764, Hei 6-126619, and Hei 6-178778 
respectively filed on Mar. 30, 1994, Jun. 8, 1994 and Jul. 29, 1994, the 
contents of which are incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a liquid crystal displaying device for 
displaying vehicle information such as vehicle speed, engine rotational 
speed and the like by projecting an image light from a liquid crystal 
panel. 
2. Description of Related Art 
In a conventional liquid crystal displaying device as shown in FIG. 18, a 
small-sized bulb 110 such as a halogen lamp, metal halide lamp or the like 
is used as a light source of a liquid crystal displaying panel 100. In the 
conventional device, the bulb 110 is inserted into a reflector 120 from 
the back side of the same. The light radiated from the bulb 110 is 
reflected from the reflector 120 and become a parallel light, which is 
diffused by a diffusion panel 130 and transmitted to the liquid crystal 
displaying panel 100. 
However, a small-sized light bulb 110 such as the halogen lamp or metal 
halide lamp is expensive. On the other hand, an inexpensive bulb such as 
an incandescent lamp or a xenon (Xe) lamp is much larger in size, and it 
is impossible to insert the bulb from the back side of reflector 120 in 
the conventional structure without necessarily sacrificing the function of 
the reflector 120. 
It has been considered that a large-sized bulb may be inserted from the 
front side of the reflector 120, however it would take much more 
installation time than the bulb inserted from the rear side of the 
reflector. 
SUMMARY OF THE INVENTION 
The present invention is made in view of the foregoing problems and has a 
main object of providing a liquid crystal displaying device using a large 
size light bulb such as an inexpensive incandescent lamp or xenon lamp 
without sacrificing the function of the reflector and without increasing 
the installation time. 
Another object of the present invention is to provide a liquid crystal 
displaying device in which a light source is installed transversely to the 
optical axis of the reflector. 
Another object of the present invention is to provide a liquid crystal 
displaying device in which a temperature rise of the liquid crystal 
displaying panel due to heat from the light source is prevented. 
A further object of the present invention is to provide a liquid crystal 
displaying device in which the uniformity of illumination is improved. 
A still further object of the present invention is to provide a liquid 
crystal displaying device in which the light reflected by the reflector is 
more effectively used and in which an information image projected from the 
liquid crystal displaying device is brighter and clearer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A first embodiment according to the present invention is described as 
below, referring to FIGS. 1 through 7. 
A liquid crystal displaying device 1 in this embodiment is used for a 
head-up displaying system 2 for a vehicle as illustrated in FIG. 3. This 
head-up displaying system 2 is installed, for example, into a rear side of 
an instrument panel. A vehicle information image light is projected from 
the liquid crystal displaying device 1, is reflected by mirrors 3 and 4 
and a hologram 5, and is projected on a reflective layer 7 disposed at an 
appropriate position of a windshield glass 6 close to a driver's seat (not 
shown). 
As shown in FIGS. 1 and 2, the liquid crystal displaying device 1 consists 
of a bracket 8 which is fixed to a portion of the vehicle, a liquid 
crystal displaying panel 9, an incandescent lamp 10, a reflector 11, a 
lens 12 and a heat-ray absorbing filter 13, which are fixed to the bracket 
8 along a common optical axis. 
The bracket 8 has an opening to receive the lamp 10 therein and a pair of 
up-standing stays 8a on both sides of the opening to support the reflector 
11. 
The liquid crystal displaying panel 9 forms an image according to control 
signals sent from a image control device (not shown). 
The incandescent lamp 10 is received in the opening by a socket 14 which is 
fixed to the bracket 8 between the displaying panel 9 and the reflector 11 
and radiates visible light toward liquid crystal displaying panel 9. As 
indicated in FIG. 4, the incandescent lamp 10 includes a filament 10b as a 
luminous body inside a bulb 10a and a light diffusion treatment such as 
coating of high light-diffusive white powder of silica and frosting of the 
inner glass surface of the bulb 10a. Therefore, the bulb 10a shines as a 
whole equally and the luminance uniformity of the surface of bulb 10a is 
ensured. 
The reflector 11 is located at a side of the lamp 10 opposite the liquid 
crystal displaying panel 9, and is fixed to the stays 8a of the bracket 8 
with screws 15. The reflector 11 has a hemispheric surface and a 
reflective layer on its concave surface formed by a vaporization of 
high-reflectivity metal such as aluminum. At the top and bottom portions 
of the reflector, there are formed semicircular openings as shown in FIGS. 
1 and 2. The reflector 11 reflects the radiated light from the lamp 10 
toward the liquid crystal displaying panel 9. 
The lens 12 is disposed between the liquid crystal displaying panel 9 and 
the lamp 10 to diverge the visible rays from the lamp 9 and reflector 11 
to cover the whole area of the liquid crystal displaying panel 9. The lens 
12 has a parabolic surface (aspheric surface) on a side facing the liquid 
crystal displaying panel 9, however, it may have another parabolic surface 
on the other side as well. 
The heat-ray absorbing filter 13 is disposed between the lens 12 and the 
liquid crystal displaying panel 9 to interrupt or absorb the infrared 
radiation transmitted through the lens 12 and to prevent a temperature 
rise of the liquid crystal displaying panel 9. 
The aforementioned liquid crystal displaying panel 9, the lens 12 and the 
heat-ray absorbing filter 13 are fixed to a spacer 16 formed of silicon 
rubber or the like, and they are installed integrally with a cover 17. The 
visible light radiated from the lamp 10 and reflected by the reflector 11 
passes through an opening 17a formed in the cover 17, the heat-ray 
absorbing filter 13, the crystal displaying panel 9 and an opening 17b 
formed in the cover 17. 
The socket 14 is inserted into the bracket 8 within the lower semicircular 
opening of the reflector 11 from an outer circumference of the reflector 
11. In other words, the incandescent lamp 10 is installed from below in a 
direction orthogonal to the common optical axis which is indicated by the 
dotted line in FIG. 1. It is noted that the upper semicircular opening of 
the reflector 11 is effective to ventilate and cool the space around the 
lamp 10. 
The operation of the liquid crystal displaying device 1 according to the 
first embodiment of the present invention is explained next. 
The visible light emitted by the incandescent lamp 10 and reflected by the 
reflector 11 is diverged by the lens 12 to cover the whole area of the 
liquid crystal displaying panel 9, passes through the heat-ray absorbing 
filter 13 which absorbs the infrared rays included in the light, and 
passes through the liquid crystal displaying panel 9. Since the liquid 
crystal displaying panel 9 forms an image of vehicle information 
controlled by an image control device, the visible light forms an image 
illuminating light, which is projected to an appropriate position on the 
windshield glass 6. 
Since the reflective surface of reflector 11 has a hemispheric or elliptic 
shape, the light of filament 10b in the plane of the filament reflected by 
the reflector 11 becomes a virtual image which is the reversal of the real 
filament as indicated by the broken line of FIG. 5. Therefore, the 
uniformity of illumination at the surface of the displaying panel is 
ensured. 
When a driver changes his viewing angle, the direct light of an end portion 
of the filament 10b which is darker than other portions thereof may be 
utilized depending on the driver's position due to refractive 
characteristics of the lens 12 as shown in FIG. 6. However, it is 
eliminated by positioning the reflector 11 so that the light of the center 
portion of the filament is reflected by the reflector 11 to cover the same 
area of the liquid crystal displaying panel 9 as the direct light covers 
as shown in FIG. 7. 
Therefore, when an incandescent lamp 10 with a large bulb is used in this 
embodiment, there is no need to cut reflector 11 to the extent that the 
luminous intensity of the reflected light of the reflector 11 drops. 
A liquid crystal displaying device according to a second embodiment of the 
present invention is explained next with reference to FIG. 8. 
An incandescent lamp 10 is fixed to a bracket to have an installation angle 
A relative to the optical axis of the displaying device. That is, an 
installation surface 8b of the bracket 8 on which the socket 14 is fixed 
is inclined by an angle B (A=B) relative to the optical axis, and, 
therefore, the bulb of the incandescent lamp 10 is inclined to the side of 
the reflector 11. 
The installation angle A of the lamp 10 to the optical axis is set based on 
the light distribution characteristics of the lamp 10. 
As is illustrated in FIG. 9, the light distribution characteristics of lamp 
10 are not equal around the lamp 10, and the luminous flux may be 
increased by around 10% in a particular direction. Since the top portion 
of bulb 10a accommodating filament 10b is hemispheric in shape, a portion 
of the light radiated by filament 10b is reflected inside bulb 10a at the 
hemispheric portion as indicated in FIG. 10. On the other hand, in a 
portion 10c the light reflected by the top portion of the bulb is 
transmitted through bulb 10a, as indicated in FIG. 10. 
In this embodiment, the inclination angle A is selected so that the lump 
has the maximum luminous flux density in a direction along the display's 
optical axis. Therefore, it is possible to obtain the information image 
projected on the reflective layer 7 (shown in FIG. 7) without increasing 
the size of the incandescent lamp 10. Thus, it is possible to display 
vehicle information at a required luminance (e.g., several thousand 
cd/m.sup.2) without reducing the durability of the incandescent lamp 10. 
A liquid crystal displaying device according to a third embodiment of the 
present invention is described below, referring to FIG. 11, in which the 
same reference numerals are substantially the same as described in the 
previous embodiments and, therefore, the description thereof is omitted 
except for portions of the device deferent from previously described 
embodiments. 
Incidentally, the description of the other embodiments to follow will be 
made in the same manner as this embodiment. 
In this third embodiment, a diffusion treatment is applied only on a side 
of the bulb 10a facing the lens 12, while leaving the other side of the 
bulb 10a transparent. In this case, the light transmitted through the bulb 
10a at the side of reflector 11 of lamp 10 is reflected by reflector 11 
and is effectively utilized for illumination. 
Also, a heat-reflective filter which reflects heat rays may be used in this 
embodiment instead of heat-ray absorbing filter 13. 
A liquid crystal displaying device according to a fourth embodiment of the 
present invention is explained next, referring to FIGS. 12, 13 and 14. 
A liquid crystal displaying panel 9 consists of a liquid crystal cell 9a 
and a pair of polarizing plates 9b and 9c as shown in FIG. 12. 
Polarizing plates 9b and 9c are disposed on both sides of liquid crystal 
cell 9a and each passes light having a specified polarization direction. A 
diffusion treatment or an anti-glare treatment is applied to the 
polarizing plate 8b disposed on the side of incoming or incident light. 
The polarizing direction of the polarizing plate 9c is arranged so that 
the light incident on the reflective layer 7 (shown in FIG. 7) becomes a 
transversal or horizontal wave (an oscillating direction of the polarizing 
light elements is horizontal as indicated by arrows in FIG. 13). The 
transversal wave incident on the reflective layer 7 is also illustrated in 
FIG. 14. 
In this embodiment, there is no need to providing a diffusion plate or 
frost glass or another additional element to secure the luminance 
uniformity. As a result, downsizing of the axial dimensions of the device 
is realized, its installation is carried easily, and a cost reduction is 
achieved. 
A liquid crystal displaying device according to a fifth embodiment of the 
present invention is explained next with reference to FIGS. 15, 16 and 17. 
In the liquid crystal displaying device of this embodiment, a lens 12 has 
convex-shaped surfaces on both sides. Therefore, all the light coming from 
the filament 10b and the reflector 11 passes through the liquid crystal 
displaying panel 9. That is, when viewed at the center of the view field 
of the image projected from the liquid crystal panel (i.e., viewed from 
directly in front of the panel), all the light coming from the reflector 
11 and the filament 10b of lamp 10 is used, thereby resulting in no 
dispersion of the luminance of the image as shown in FIG. 16. Even when 
the field of the driver's view is shifted from the center of the viewing 
field to a transversal position, there is no dispersion of the luminance 
since all the light is utilized for image projection as shown in FIG. 17. 
The liquid crystal displaying device 1 of the fifth embodiment may be used 
in an application other than a head-up display type liquid crystal 
displaying device. 
In the foregoing discussion of the present invention, the invention has 
been described with reference to specific embodiments thereof. It will, 
however, be evident that various modifications and changes may be made to 
the specific embodiments of the present invention without departing from 
the broader spirit and scope of the invention as set forth in the appended 
claims. Accordingly, the description of the present invention in this 
document is to be regarded in an illustrative, rather than a restrictive, 
sense.