Liquid crystal display device

Abstract: A liquid crystal displaying device, usess an inexpensive incandescent lamp (10) or xenon lamp (10) without sacrificing luminous intensity of a reflector (11) while maintaining an ease of installation. In the displaying device, a liquid crystal displaying panel (9), an incandescent lamp (10), a reflector (11), a lens (12) and heat-ray absorbing filter (13) have a common optical axis and are secured to a bracket (8). The lamp (10) is held by a socket (14) and installed to the bracket (8) transversely to the optical axis of the reflecting surface of the reflector (11). Further, the liquid crystal displaying panel (9) has polarizing plates (9b, 9c) on both sides thereof. A coating to diffuse light from the lamp is disposed on one (9b) of the polarizing plates (9b, 9c) on the light incident side of the displaying panel (9). The polarizing direction of the polarizing plate (9c) on the other side of the displaying panel (9) is selected so that the polarizing direction of the incident light waves of a reflective layer (7) which is disposed on the front windshield glass provides a transversal or horizontal wave.

Description: 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. A similar conventional liquid crystal display device is known from JP 5 173123, on which the preamble of the claim 1 is based. Document DE-A-3 314 693 discloses a device for backlighting a liquid crystal displaying element comprising a reflector casing with a socket in which a light bulb is installed transversely to the reflector optical axis. The liquid crystal display element is sandwiched between polarizing filters while a diffusion plate is located between one polarizing filter and the light bulb to diffuse the incident light. The arrangement consisting of the liquid crystal displaying element, the polarizing filters and the diffusion plate is supported by a frame being connected to the reflector casing. Thus, an illumination of the liquid crystal displaying element is achieved. 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 It is, therefore, an object of the present invention to provide a liquid crystal display device which is low in production costs and which shows a high illumination efficiency. According to the present invention this object is achieved by the features indicated in the present claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features, and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: Fig. 1 is a cross-sectional side view illustrating the liquid crystal displaying device according to a first embodiment of the present invention; Fig. 2 is a cross-sectional plan view illustrating the liquid crystal displaying device according to the first embodiment; Fig. 3 is a perspective view illustrating a head-up displaying system according to the present invention. Fig. 4 is a front view illustrating a light bulb used in the preferred embodiments of the present invention and its filament ; Fig. 5 is a front view illustrating the light bulb, its filament and a virtual image of the filament focussed by the reflector; Fig. 6 is a schematic view illustrating a luminous area on a liquid crystal displaying panel covered by a light emitted by the end portion of the filament; Fig. 7 is a schematic view illustrating a luminous area on a liquid crystal displaying panel covered by light reflected from the central potion of the filament; Fig. 8 is a cross-sectional side view of the liquid crystal displaying device according to a second embodiment of the present invention; Fig. 9 is a diagrammatic view illustrating the light distribution characteristics of an incandescent lamp; Fig. 10 is a diagrammatic front view of an incandescent lamp illustrating dispersion of the light distribution characteristics; Fig. 11 is a cross-sectional side view illustrating a light bulb according to a third embodiment of the present invention; Fig. 12 is a cross-sectional side view illustrating a liquid crystal displaying device according to a fourth embodiment of the present invention; Fig. 13 is a front view illustrating a liquid crystal displaying panel according to the present invention; Fig. 14 is a perspective view illustrating a reflective layer and polarizing elements of a transversal light wave; Fig. 15 is a cross-sectional side view illustrating a liquid crystal displaying device according to a fifth embodiment of the present invention; Figs. 16 and 17 are schematic views illustrating an optical path of lights in the liquid crystal displaying device of the fifth embodiment; and Fig. 18 is a cross-sectional side view illustrating a conventional liquid crystal displaying device. 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. 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 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.

Claims: A liquid crystal displaying device comprising: a light source (10), a reflector (11) having a hemispheric concave reflecting surface, a liquid crystal display panel (9) and a base member (8) on which said light source, reflector and display panel are fixedly assembled so as to identify a common optical axis, essentially parallel to the base member, whereby the light source is disposed between the reflector and the display panel, characterized in that said light source (10) is a large-size light bulb (10a), said base member (8) has an opening to transversely receive said light bulb (10a) and support said reflector in such a way that the side of the light bulb faces said concave reflecting surface, and said reflector (11) is provided with a bottom semicircular opening to allow the light bulb (10a) to be positioned at the right distance from said reflector (11). A device according to claim 1, characterized in that said light bulb (10a) comprises a filament (10b), and said distance is set so that said reflector (11) focuses a virtual reversal image of said filament (10b) in a plane containing said filament (10b). A device according to claim 1 or 2, characterized in that said bottom semicircular opening is disposed at a portion corresponding to said opening of said base member (8) for receiving said light bulb (10a). A device according to claim 3, characterized in that a top semicircular opening is disposed at a portion of said reflector (11) opposite to said bottom semicircular opening for increasing the ventilation around the light bulb. A device according to any of the preceding claims 1 to 4, characterized in that said base member (8) comprises a stay member (8a) extending therefrom for securing said reflector (11). A device according to any of the preceding claims 1 to 5, characterized by a lens (12), which has an optical axis aligned with said optical axis of said reflecting surface and which is disposed between said light bulb (10a) and said liquid crystal displaying panel (9), for converging light incoming thereto to cover an area of said liquid crystal displaying panel (9). A device according to claim 6, characterized in that said light bulb (10a) has a maximum light radiating axis aligned with said optical axis of said lens (12). A device according to claim 6, characterized in that said lens (12) has convex surfaces on the sides thereof. A device according to any of the preceding claims 1 to 8, characterized in that said liquid crystal displaying panel (9) further comprises polarizing plates (9b, 9c) on sides thereof and has a coating for diffusing said light. A device according to any of the preceding claims 1 to 9, characterized by a filter (13) for absorbing heat rays disposed between said light bulb (10a) and said liquid crystal displaying panel (9). A device according to any of the preceding claims 1 to 10, characterized in that said light bulb (10a) further comprises a coating for diffusing light radiating toward said liquid crystal displaying panel (9). A device according to claim 11, characterized in that said coating is disposed at a portion of said light bulb (10a) facing said liquid crystal displaying panel (9). A device according to any of the preceding claims 6 to 12, characterized in that said light bulb (10a) has a maximum light radiating axis aligned with said optical axis of said lens (12) to provide a maximum luminous image. A device according to claim 13, characterized in that said light bulb (10a) comprises a incandescent lamp which has said maximum light radiating axis disposed at an inclination to a normal axis of said light bulb (10a), and said light bulb (10a) is secured to said base member (8) at said inclination to said optical axis of said lens (12). A device according to claim 9, characterized in that another one of polarizing plates (9b, 9c) disposed on the other side of said liquid crystal displaying panel (9) is disposed so that wave direction of said lights become horizontal wave.

Inventors: HIGUCHI MASAHIRO, OKUYAMA HIDEKI, SUMIYA MINORU, HIGUCHI, MASAHIRO, OKUYAMA, HIDEKI, SUMIYA, MINORU
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1995
Main classification: G09F9
IPC codes: G02B27, G02F1, G09F9