Background of The Invention Liquid crystal display devices (LCDs) are increasingly used in a broadening variety of applications. These applications vary from simple wrist watch and hand-held calculators to the high- resolution displays used in current laptop computer monitors. Other applications include displays for VCRs, compact disc players, cellular phones, and an increasingly broad spectrum of electronic products.

LCDs have been utilized in automobiles, boats, aircraft, and other vehicles as part of the instrumentation cluster. Typical applications included the speedometer, odometer, fluid level indicators, and radio displays, among others. These displays are commonly illuminated by planar electro- luminescent back lighting and are dedicated displays, meaning that the display is limited to illuminating simple patterns. These patterns typically included the common"7-segment format"or simple bars used to define a bar graph.

More recently, auto manufacturers have shown interest in producing vehicles using advanced LCD type displays. These advanced displays have been suggested for displaying complex information such as maps.

Similarly, public transportation and military vehicles, as well as boats and aircrafts, would benefit from such displays. However, until now, the incorporation of these advanced LCD's into automobiles

and other vehicles has not been feasible for a multitude of reasons.

For example, the usable reproduction of information such as maps requires a display with at least a moderately high resolution. Additionally, the need to differentiate among different features and locations on the map suggests the need for a color display. However, these two requirements, high resolution and color, tend to work against each other.

This is because a color LCD must have three distinct LCD"dots" (red, green, and blue) to create the equivalent of a single pixel on a monochrome display.

This gives the otherwise identical monochrome LCD an intrinsic 3: 1 advantage in resolution. Thus, there is a need for a high resolution color LCD which is suitable for the automotive environment.

A second problem involving the incorporation of advanced LCD's into automobiles or other vehicles involves screen brightness. Unlike the highly mobile laptop computer, an automotive LCD may, from time to time, have to be readable in virtually direct sunlight. To make this possible would require a photometric luminance on the order of ten times brighter than the brightest display used on current LCD laptop computers.

This high brightness requirement also presents a basic conflict with the need for a high resolution display. For instance, when an LCD of a given size becomes more densely populated with pixels such as with a higher resolution display, the area of each pixel must decrease. However, the area of the necessary"dead space"surrounding each pixel aperture does not scale down in proportion to the area of the pixel. This dead space is actually a masked area

containing hundreds of thousands of transistors and capacitors responsible for turning each pixel on and off.

Since the optically active area of each pixel in a high resolution display decreases more rapidly than the surrounding dead space, the so called"aperture ratio"of the light valve is decreased relative to its lower-pixel-count relatives. The light valve modulates the light provided to it by an illumination system and transmits this modulated light as an image.

With a decreased aperture ratio comes a drop in the transmission of the light valve. This lower transmission of the light valve means that less of the light applied to the back side of the light valve makes it through to the viewing side and onto the screen, thus decreasing the image brightness.

Consequently, there is a need for high resolution color LCD which is also capable of high screen brightness and is suitable for use in automobiles.

Because the display screen of an LCD in a vehicular application may be subject to high ambient light conditions, a high brightness screen may not be sufficient to enable its readability. In particular, direct sunlight could cause very high light conditions and severely reduce screen readability. Thus, there is a need for an automotive LCD having a display screen with the ability to reject high ambient illumination.

Yet another problem with incorporating advanced LCD's into automotive applications is their unsuitability for wide viewing-angle applications.

For a single-user device, such as a laptop computer, this shortcoming is not a critical limitation, however, in an automotive application it may be just

as important for a passenger to see the data being presented as for the driver. Thus, there is a need for a high resolution LCD with a color display suitable for use in an automotive environment and which has a large viewing angle.

In addition to the high resolution, brightness, ability to reject high ambient light, and wide viewing angle requirements, the automotive environment demands a long lifetime. In the context of an LCD, the lifetime concerns principally revolve around the illumination source. LCDs and their associated electronics have no intrinsic lifetime limiting mechanisms which would cause them to wear out. The illumination source however is typically subject to gradual, continuous degradation, finally reaching a point where it either fails outright or has lost so much of its light output that the image is no longer useful. Thus, there is a need for an LCD which incorporates a long-life illumination source suitable for use in an automotive environment.

The incorporation of advanced LCD's into vehicles has also been prohibitive due to their high costs. In particular, automotive applications are very cost- sensitive and the large LCD panels which would be required for usable readability are very expensive.

Thus, there is a need for an LCD which may be readily incorporated into a vehicle, meets the requirement of the automotive environment and is inexpensive. These requirements, disadvantages and problems have kept advanced LCD's out of the automotive and other vehicle industries until now.

Summary The present invention satisfies the need for a high-resolution LCD for a vehicle which is readable in bright ambient light conditions by providing an LCD- based, high-resolution color display using a remote illumination source, a small LCD light valve, image magnification and projection optics and an innovative approach for maximizing the use of the available light. By incorporating a display utilizing image magnification optics, the gain of the display screen can be tailored to the application. This ability to tailor the screen gain in a magnified or projection display, enhance to optimize the balance of brightness to viewing angles gives advantageous control over the image which is not possible with a direct-view LCD panel.

The present invention is generally directed to a liquid crystal display system for use in a vehicle having an instrument console or dashboard. Broadly speaking, the liquid crystal display system of the present invention includes an illumination system, at least one transmissive element, a light valve, an optical assembly and a display or viewing screen. The illumination system includes a light source which is attached to the vehicle and produces the light necessary for illuminating the display. The illumination system also includes a reflector which captures the light emitted from the light source and converges a majority of the light to a first focal point. The reflector is generally an elliptical- shaped reflector configured specifically to maximize the capture and convergence of light from the light source.

The transmissive element has an input end which is located at the first focal point. This input end receives the light at the first focal point and transmits or transfers this light to its distal output end. A liquid crystal display light valve receives this light which is emitted from the output end of the transmissive element and converts this light into LCD light information. This conversion is actually a modulation of the light in accordance with applied electrical signals for providing the desired light image.

An optical assembly is provided for receiving the light image information from the light valve and for magnifying and projecting the light image information to the back side of the display screen. The screen receives this projected image from the optical assembly and displays it in a readable format. The display screen is typically supported within the interior compartment of the vehicle. By using a smaller LCD light valve and projection optics, a high resolution image may be displayed on a larger screen.

This cost effective approach is also compatible with the tight space requirements in most vehicles.

In another broad aspect of the present invention, the liquid crystal display system further includes a reflective polarizing film. This reflective polarizing film reflects one of the two planes of polarized light received from the output end of the transmissive element away from the magnification and projection optical assembly. Since LCDs require polarized light to operate, the reflective polarizing film is oriented such that the unused planes of polarized light are directed away from the magnification and projection optical assembly. A

plurality of fiberoptic conduits are oriented such that they capture at least a portion of the polarized planes of light reflected away from the optical assembly and transfer that light to a desired illumination point within the vehicle.

In another broad aspect of the present invention, the liquid crystal display system is incorporated into a conventional automobile having a passenger compartment and an engine compartment. The illumination system is mounted outside of the passenger compartment and typically in the engine compartment. In this way, heat produced from the light source can be more efficiently dissipated and there is less passenger discomfort. A transmissive element is supported within the engine compartment of the vehicle and has an input end for receiving at a least a portion of the light from the illumination system. The transmissive element extends from adjacent the illumination system, within the engine compartment, to an opening in a fire wall which separates the engine compartment and the passenger compartment to within the passenger compartment. The light received at the input end of the transmissive element is transferred to its distal output end within the passenger compartment. A liquid crystal display light valve receives the light from the output end of the transmissive element and converts the light into LCD light information. This LCD light information is then magnified and projected by the light valve onto a display screen. The display screen displays the light information in a readable format.

In another broad aspect of the present invention, a method for displaying light information within a vehicle having an interior compartment and an

instrument console is described. The method includes the steps of providing a generally continuous source of light within the vehicle and directing or converging at least a portion of the light to a first focal point using at least one reflective surface or reflector. At least a portion of the light from the first focal point is transferred to a liquid crystal display light valve within the interior compartment of the vehicle using a transmissive element. The liquid crystal display light valve converts the transferred light to LCD light information by modulating the light accordance with applied electrical signals. The LCD light information generally represents the desired image. This LCD light information is then magnified and projected from the light valve onto a display screen using an optical assembly. The projected LCD light information is displayed on the display screen such that it is usable and readable within the passenger compartment. Using this method of transferring, converting and projecting, a display of high resolution may be projected on almost any type LCD screen.

In yet another aspect of the present invention, the method for displaying light information further includes placing a plurality of focusing lenses adjacent to the first focal point. These focusing lenses focus at least a portion of the light adjacent to the first focal point onto a plurality of second focal points. The light at the second plurality of focal points is then transferred to a plurality of illumination points within the vehicle. This transferring of light occurs through a plurality of secondary transmissive elements which are preferably fiber-optic conduits.

The invention, together with additional features and advantages thereof, which was only summarized in the foregoing passages, will become more apparent to those of skill in the art upon reading the description of the preferred embodiment, which follows in this specification, taken together with the following drawings.

Brief Description of The Drawings FIG. 1 is a schematic representation of an embodiment of a LCD-based vehicle display system of the present invention; FIG. 2a is a schematic representation of the LCD system of FIG. 1 where the transmissive element is a glass light pipe; FIG. 2b is a schematic representation of the LCD system of FIG. 1 where the transmissive element is a fiber-optic light pipe; FIG. 2c is a schematic representation of the LCD system of FIG. 1 where the transmissive element is a free space relay system; FIG. 3 is a schematic representation of a portion of an embodiment of the present invention showing an illumination system and a plurality of fiber-optic conduits for capturing and transferring light; FIG. 4 is a schematic representation of an alternative embodiment of the present invention showing an alternative method for capturing and transferring light; and FIG. 5 is a schematic side view representation of a portion of an automobile incorporating an embodiment of the liquid crystal display system of the present invention.

Description of The Preferred Embodiments Referring to FIG. 1, a liquid crystal display system 10 for use in a vehicle and having the features of the present invention is shown. The liquid crystal display system 10 generally includes an illumination system 12, a light transmissive element 14, a liquid crystal display light valve 16, an optics assembly 18, and a display screen 20. The illumination system 12 generally comprises a light source 22 and a reflector 24 which directs light rays 26 from the light source 22 to a first focal point 28.

The light source 22 may be any light source capable of providing sufficient light to enable visibility of the screen 20 in high-ambient light conditions. Preferably, the lamp will provide a high screen brightness of approximately 1,000-1,500 nits (cd/m2) photometric luminance and possibly a higher brightness in high ambient light conditions. The light source 22 may be a high-efficiency lamp with a lifetime on the order of 3,000 or more operating hours and preferably 5,000 or more operating hours. As an example, an automobile which lasts for 100,000 miles and travels an average speed over its lifetime of 35 miles per hour, will accumulate just under 3,000 operating hours.

The light source 22 may be a metal-halide lamp and more preferably, a DC metal-halide lamp of approximately 50 to 80 watts having a minimum 3,000 hour life, which is replaceable. The lamp may also be a long life xenon-arc lamp of approximately 60-150 watts. Power may be supplied from the vehicle's electrical system. The light source 22 will likely have a high operating surface temperature. Thus, it may be desirable to isolate the light source 22 from

may be desirable to isolate the light source 22 from occupants or from other hazardous situations. In this fashion, the light source 22 is preferably separated and remote from the vehicle passenger compartment.

The reflector 24 is generally used to reflect light rays 26 from the light source 22 and converge them to a first focal point 28. The reflector 24 which may include the light source 22 as an integral part, may be specifically sized and shaped for the particular application including the particular vehicle involved. The reflector 24 is specifically configured to capture the maximum useful amount of light rays 26 from the particular light source 22 and converge that light to the first focal point 28. In a preferred embodiment, the reflector 24 is a generally elliptical reflector and includes the light source 22 inside the elliptical-shaped reflective region.

However, other reflector configurations may be used to direct the light into the light transmissive element 14, if desired.

The light transmissive element 14, which has an input end 30 and an output end 32, is arranged such that the input end 30 is located at the first focal point 28. In this way, light rays 26 reflected from the light source 22 by the reflector 24 are converged and directed into the input end 30 of the light transmissive element 14. The light rays 26 are then transmitted or transferred through the light transmissive element 14 to the output end 32.

The light transmissive element 14, which may be a light-pipe, sufficiently renders the light from the light source 22 both spatially and chromatically uniform. Thus, the light emitted from the light transmissive element 14 at the output end 32 will have

uniform intensity across its face and will "homogenize"any spacial color non-uniformity originating at the light source 22. However, the light transmissive element 14 should be at least ten times as long as it is wide.

The light transmissive element 14 permits remote location of the light source 22. This allows placement of the illumination system 12 at locations in the vehicle where the created heat may be efficiently dissipated or even utilized without passenger discomfort. Additionally, space restrictions within modern vehicles and especially automobiles, may require the remote placement of the light source 22 and reflector 24. The light transmissive element 14 therefore must be able to efficiently transmit or transfer the light rays 26 along a multi-dimensional path.

Referring now to FIGS. 2a-2c, several different embodiments of light transmissive elements 14 which may be utilized in the liquid crystal display system 10 of the present invention are shown. In FIG. 2a, the light transmissive element 14 comprises conventional glass using total-internal-reflection 40.

FIG. 2b shows a light transmissive element 14 which includes the use of conventional glass with total- internal-reflection 40 in conjunction with one or more silvered surfaces 42. These silvered surfaces, which may be turning mirrors, provide bending of the light where the angles of incidence do not support total- internal-reflection.

FIG. 2c shows a light transmissive element 14 which is a flexible light pipe 44. This flexible light pipe may comprise a single solid core fiber which is surrounded by a cladding layer and a sheath

or shielding layer. The core, which transfers the light may be made from a variety of materials. The light pipe 44 may also comprise an array of conventional glass optical fibers. Preferably, the light pipe 44 may be made using a flexible, optically- clear polymer designed for architectural fiber-optic lighting applications. Such light pipes 44 may be fabricated from flexible, large-core architectural fiber-optics such as that supplied by Rom and Hoss Corporation of Philadelphia, Pennsylvania.

For complex and tight fitting applications, the light transmissive element 14 may comprise a light pipe 44 constructed of a plastic outer jacket and a fiber core material which may be poured into the outer jacket to form the optical duct. In this way the plastic outer jacket may more easily be located within the vehicle. This fiber-optic core material may include liquid optical duct material such as that supplied by Lumenyte Corporation of Franklin Park, Illinois. In applications where the color-integrating properties of the light transmissive element are not needed and where system architecture permits, the light transmissive element 14 may be replaced with a free-space optical relay assembly using conventional lenses and turning mirrors in place of the fiber- optical duct geometry previously described.

Referring now back to FIG. 1, the optical assembly 18 receives the LCD light information 36 from the LCD light valve 16. This light image information 36 is magnified by a plurality of projection lenses 38 and projected onto the backside of the display screen 20. The optical assembly 18 is preferably sized to receive all of the light image information 36 from the LCD light valve 16 and to sufficiently magnify this

light image information 36 such that it is projected across the entire display screen 20. In this way, a small and less expensive light valve may be used. The optical assembly 18 also allows for projection to a larger, high resolution screen 20 which may be wide- angled or even curved.

The optical assembly 18 may include any suitable arrangement of optical elements, including a magnification lens, which will project the light image information onto the display screen 20. Suitable projection optics are known and therefore are not further described herein. A more detailed description of an LCD light valve on an optical assembly having similar characteristics to those of the present invention may be found in U. S. Patent Number 5,467,207, filed July 6,1994, and entitled LCD Projection System Which Aligns The Larger Beam Spread Angle Of The Light Source With The Light Valve And A Nonimaging Reflector For An Illumination System, which is herein expressly fully incorporated by reference.

The optical assembly 18, like the LCD light valve 16 is preferably mounted within the interior of the vehicle.

The display screen 20 receives the projected light image information 36 from the optical assembly 18 and displays the light image information 36 in a readable format such as a map, text or other usable information. The screen 20 is attached within the interior of the vehicle and preferably mounted to an instrument console or in the case of an automobile, adjacent or within the dashboard.

Referring now to FIG. 3, an alternative embodiment of the present invention will be described.

In this embodiment, like features to those of the

previous embodiment are designated by like reference numerals succeeded by the letter"a". The liquid crystal display system 50 includes all of the components of the liquid crystal display system 10 as previously described in FIG. 1 and also includes a plurality of secondary light transmissive elements 52.

These secondary light transmissive elements 52 capture the light rays 26 which are not converged and directed to the first focal point 28a by the reflector 24a.

Each of the secondary light transmissive elements 52 includes an input end 54 and a distal output end 56.

A focussing lens 58 is placed adjacent to each of the secondary light transmissive elements 52 to form a second focal point 60 at each input end 54. In this way, light not converged to the first focal point 28a which is otherwise unused, is captured by the plurality of focussing lenses 58 and directed to the plurality of second focal points 60 where the light is received at the input end 54 of each secondary light transmissive elements 52. Each of the focussing lenses 58 and secondary light transmissive elements 52 may be placed as close to the light source 22a as possible to reduce the dispersion of the incident light from the light source 22a. Generally, the input ends 54 of the secondary light transmissive elements 52 will be located adjacent the input end 30a of the light transmissive element 14a and preferably surround the light transmissive element 14a. In this way, the maximum amount of unused light from the light source 22a may be captured. The light transmitted or transferred by each of the secondary light transmissive elements 52 may be directed to various locations or illumination points within the vehicle.

These illumination points may include, for example,

dashboard lights, hood lights, decorative display lights, and cablights, among others.

Referring now to FIG. 4, another alternative embodiment of the present invention will be described.

In this embodiment, like features to those of previous embodiments are designated by like reference numerals, succeeded by the letter"b". The liquid crystal display system 70 shown includes the ability to capture a generally unwanted and otherwise unused state of polarized light and to utilize this light for other applications in the vehicle. Since liquid crystal displays (LCDs) require light of only a single polarization state to work, one of the two equivalent polarization states must be eliminated from the light rays 26b delivered to the liquid crystal display light valve 16b. This unwanted polarized light may be eliminated from the light rays 26b emanating from the light source 22b and made available for capture to be used at other applications.

To accomplish this, a reflective device 72 for reflecting the unwanted and unnecessary state of polarized light is inserted in the light path prior to the light rays 26b contacting the liquid crystal display light valve 16b. In this way, the light rays 26b actually received by the LCD light valve 16 only contain a single polarized state. The device 72 for reflecting the unwanted state of polarized light may comprise a reflective polarizing film 73 oriented such that the unwanted state of polarized light is directed away from the LCD light valve 16b. In this configuration, the polarizing film 73 may be mounted away from the LCD light valve lb to prevent coupling its absorption heat load into the light valve 16.

A plurality of focusing lenses 74 are placed in the path of the reflected unwanted polarized light. A plurality of secondary light transmissive elements 76 having an input end 78 and an output end 80 are located adjacent to the plurality of focussing lenses 74. Each of the focussing lenses 74 focusses the incident unwanted polarized light to a second focal point 82 such that it may be received at the input end 78 of the secondary light transmissive elements 76.

In this way, the unwanted light may be received by the secondary transmissive elements 76 and transferred to various locations in the vehicle for various other applications. Similar to the previously described embodiment in FIG. 3, the focussing lenses 74 and the secondary light transmissive elements 76 may be arranged in an array surrounding the transmissive element 14b to capture the maximum amount of unused light available. The plurality of secondary light transmissive elements 76 may be fiber-optic conduits.

Referring now to FIG. 5 in conjunction with FIG.

1, a method for displaying light information according to the principles of the present invention and within an automobile 85 having an interior compartment 86 and an instrument console or dashboard 88 will be described. In this embodiment, like features to those of previous embodiments are designated by like reference numerals, succeeded by the letter"c". In this embodiment, the illumination system 12c may preferably be located within the automobile 85 but outside of the interior compartment or passenger compartment 86. In this way, heat generated by the light source 22c may be more readily dissipated. The light source 22c may be located at any convenient location within an engine compartment 90 or within the

trunk compartment (not shown). The light transmissive element 14c which is preferably a flexible light pipe 44c extends from the illumination system 12c through an opening 92 in a firewall 94 and into the interior compartment or passenger compartment 86.

If secondary light transmissive elements 52c are also provided, they may also pass through openings in the firewall 94. A grommet or other sealing method (not shown) may be provided around the light transmissive element 14c as is commonly known in the art. These secondary light transmissive elements 52c, in addition to polarized light reflective elements 72c, may be used to capture otherwise unused or unwanted light rays 26c and transfer this light to various other illumination points as previously described.

The LCD light valve 16c and the optical assembly 18c, in additional to any other required optical assemblies, may be mounted within the instrument console or dashboard 88. In this way, space may be efficiently used and the operation of the LCD display 22c maximized. However, these devices may be located anywhere within the automobile 85 which is convenient.

The LCD display 20c which must be located relatively adjacent to the LCD light valve 16c and optical assembly 18c may also be located within the interior compartment 86 such that it may be easily seen by occupants in the automobile 85. Preferably, the LCD display 20c is mounted on the instrument console or dashboard 88. The LCD display 20c may also be incorporated as part of the instrument console or dashboard 88. Power for the illumination system 12c and the LCD light valve 16c may be provided by a

conventional electrical system within the automobile 85 or by a specially provided electrical supply.

In an effort to maximize image contrast and preserve readability in an environment of bright ambient illumination such as when the sun shines directly into the interior compartment 86. To reduce this bright ambient light, a high-efficiency polarizing film 96 may be incorporated into the external surface 98 of the LCD display 20c. This high-efficiency polarizing film 96 would supersede any similar film or"analyzer"film generally located on the LCD light valve 16c. The analyzer film is integral to the operation of the LCD light valve 16c, no light image information 36c is visible if it is not present. However, it has been demonstrated that the polarization state of the LCD light valves 16c modulated output is preserved with high integrity through the optical assembly 18c or other projection lens and that this analyzer film may be external to the overall liquid crystal display system 10 with little or no compromise to image quality. Having the analyzer on the side of the screen 20c exposed to high ambient light would reject half of the ambient light from the screen, since the ambient light is randomly polarized and one half of it is absorbed in the analyzer. This has the effect of increasing the apparent contrast of the screen enhancing readability in circumstances of strong external illumination.

In addition to ambient light rejection via polarizing films, other techniques may be employed either separately or in combination. Micro-louver films, which have vanishingly thin, uniformly oriented "venetian blinds"embedded in them, are extremely effective at rejecting unwanted ambient light from a

viewing screen, so long as the viewing angle can be well controlled. In an automotive environment, the drivers lateral position is constrained by the seat and the vertical origin of the driver's line of sight is relatively invariant over a large range of driver heights. This makes the automotive application a natural candidate for the use of such angle-dependent viewing enhancement film. Another possible ambient light rejection scheme which may be used along or in combination with the above methods is the use of a black-matrix viewing screen.

While this invention has been described with respect to various examples and embodiments, it is to be understood that the invention is not limited to and that it can be variably practiced within the scope of the following claims.