GB2435933A

GB2435933A - Illuminated instrument panel for a vehicle

Info

Publication number: GB2435933A
Application number: GB0604585A
Authority: GB
Inventors: Samir Mezouari
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2006-03-08
Filing date: 2006-03-08
Publication date: 2007-09-12
Anticipated expiration: 2026-03-08
Also published as: GB0604585D0; GB2435933B

Abstract

A back-lit instrument 10 suitable for use in a vehicle comprises an instrument panel 4 having a region 7 to be illuminated, a light source 1 coupled to a light guide 2 comprising a plurality of optical fibres 24 located behind the panel, wherein the instrument further comprises reflecting means 3 also located behind the panel 4 to reflect light emitted from the light guide towards the panel. The optical fibres 24 may be woven together and may have disruptions formed by cutting, moulding, coating or kinking. The reflecting means preferably comprises a concave curved portion 32. LEDs may be coupled to the ends of the light guide. The instrument may be speedometer, while the region to be illuminated may be circular.

Description

illuminated Instrument

BACKGROUND

The present invention relates to illumination of instruments, and particularly to an illuminated instrument suitable for use in a vehicle.

Such instruments include clocks, hand held computer games, mobile phones, in fact any instrument which is capable of displaying information. Instruments for displaying information on a vehicle display are usually located on the dashboard of an automotive vehicle, and require some form of illumination to allow the driver to read the information when it is dark. An instrument usually comprises an instrument panel having an information bearing region, and a housing having a transparent cover to protect the instrument. The information bearing region usually has symbols indicating a scale such as graphics, numbers or a dial, and a pointer for indicating a point within the scale, or may comprise a liquid crystal display suitable for displaying numeric information. The information bearing region may also include features such as rings defining the perimeter of a particular instrument or gauge.

The instrument is generally mounted on a printed circuit board (PCB) which is connected to sensors (directly or indirectly via a network) which monitor certain engine conditions such as speed, temperature and fuel level to name but a few.

conventionally instruments are mounted together to form an instrument cluster.

Many modern instrument clusters comprise a single instrument panel having a number of information bearing regions corresponding to the various instruments, for example speedometer, rev counter, engine temperature etc. As customers become more sophisticated in their requirements, it becomes important to provide lighting for vehicle instruments which is both distinctive, and cost effective to produce.

P491 2.A2 07 March 2006 Most traditional instrument clusters are illuminated using several light sources, such as an array of Light Emitting Diodes (LEDs) spread throughout the area to be illuminated. The number of LEDs is generally proportional to the size of the area to be illuminated. To reduce the number of LEDs used, and to improve the evenness of light distribution over a given area, light pipes have commonly been used. As LED technology improves, higher brightness LEDs are being produced which makes it possible to illuminate large areas, such as a whole vehicle instrument panel using a single light source. However, it is often difficult to design light pipes that achieve a good uniform illumination while maintaining acceptable io efficiency when using a single light source. Furthermore, light pipes are required to be carefully designed for each application and depend critically on the size of the area to be illuminated.

A device has been disclosed in patent document US 5,005,108 by Lumitex Inc, that consists of a bunch of optical fibres capable of transporting and distributing light efficiently and evenly over a considerable area using a single source. This device is referred to herein as the Lumitex device'. The optical fibres comprising the Lumitex device include disruptions at various locations along their length.

These disruptions may be formed by cutting, moulding, coating, forming or otherwise causing mechanical, chemical or other deformations in the exterior of the optical fibre. Alternatively, the disruptions may comprise small bends along the length of the fibre. The disruptions affect the incident angle of light reflecting in the optical fibre, making the incident angle less than the critical angle and hence preventing total internal reflection at the points of disruption, and causing light to be emitted from the optical fibre at these points.

The manufacture of Lumitex devices presents several technical challenges because the dimensions of the optical fibres, the index of refraction ratio, and the number of bends and depressions per unit length dictate the light output and the efficiency of the device, as disclosed in patent document US 6,874,925 (Lumitex, lnc). Rectangular arrays of well aligned optical fibres have, however, been produced which yield an evenly illuminated rectangular area that is particularly P491 2.A2 07 March 2006 convenient for illuminating LCD panels. When the geometry of the area to illuminate is complex, for example an area having a curved periphery, it is particularly challenging and costly to produce a customised array of optical fibres suitable for directly illuminating such an area. If an array is simply cut to a complex shape, then most of the light will be leaked from the device at the periphery of the array, as total internal reflection cannot be maintained there.

Present solutions to this problem involve tiling rectangular bunches of optical fibres, however this is particularly problematic for instrument clusters, such as speedometer gauges, where the information area tends to have circular geometry.

SUMMARY OF THE INVENTION

According to the invention there is provided a back-lit instrument suitable for use in a vehicle, comprising: is an instrument panel having a region to be illuminated; a light source coupled to a light guide comprising a plurality of optical fibres, each optical fibre having means for allowing light to escape therefrom, and being located behind the panel and arranged to follow a curved path; wherein the instrument further comprises reflection means located behind the panel to reflect light emitted from the light guide towards the region of the panel to be illuminated.

The invention is suitable for illuminating regions of any shape. Preferably, however, at least a part of a periphery of the region to be illuminated is curved.

The region may be substantially circular such as, for example, the face of a circular vehicle speedometer. Alternatively the region may be substantially annular such as, for example, the information bearing region around the periphery of a circular speedometer. When the region to be illuminated is circular or annular, the light guide is preferably arranged to follow a substantially circular path.

The light guide is preferably a Lumitex-type device, as described above, comprising a woven array of optical fibres, wherein the means for allowing light to P491 2.A2 07 March 2006 escaPe from the opa fibres are disruptions formed by cutting, moulding, coating, forming or otherW uSflg mechanical, chemical or other deformations in the exterior of the opttt fibre, or small bends along the length of the fibre. Any other suitable alterflatie g1it guide may however be used, for example a plurality of fibre optic cables such as that disclosed in patent document us 5,097,396, wherein each optca\ fibre terminates at one of a plurality of locations along the ength of the cab, to i\umiflate that location.

preferably the l'& guide is elongate and most preferably has a belt-like structure i.e. its length is considerably greater than its width, and its width is considerably greater than its thickness. The light guide preferably has a major light-emitting surface from which the majority of the light from the light source is emitted. The light guide is preferablY arranged to follow the contour of a periphery of the region to be illumiflated PreferablY the major light-emitting surface of the light guide is oriented substantially perpendicular to the plane of the instrument panel in order to minimise the amount of light from the light guide which s directly incident on the instrUmet panel. To further minimise the amount of directly incident light, a side edge of the tight guide is preferably located close to or in contact with the rear face of the instrum1t panel.

The reflection means is preferably positioned substantially opposite the major light itting surface of the light guide and arranged to reflect light which is not directly incident On the instrument panel, towards the panel. The reflection means preferabtY comprises a reflection element having a concave curved portion tenditg between the light guide and the instrument panel. The concave curved shape is such that the perpendicular distance between the instrument panel and the concave curved portion decreases with increasing distance from the light guide. preferably the concave curved portion has a reflective surface for reflecting light from the light guide towards the instrument panel. The reflection element is preferabtv made of opaque and diffusing material such as, but not limited to, ABS (AcrylOnitnte Butadiene Styrefle). Preferably, the reflection element is made of materials that have high reflectance within the spectrum of the light source.

P4912 P.2 07 March 2006 The reflection element preferably further comprises a side wall that extends along the length of the reflectior element, the side wall having a first end located adjacent, and preferably in contact with, the underside of the instrument panel, and a second end offset from the instrument panel. The side wall is preferably substantially perpendicular to the plane of the instrument panel along the side wall's length. Preferably the side wall is curved along its length and follows the contour of a periphery of the region to be illuminated. This periphery may be, for example, the outer circumference of an annular region, or alternatively the inner circumference of an annular region. Preferably the concave curved portion of the reflection element extends between the second end of the side wall and the underside of the instrument panel. Most preferably the concave curved portion is in contact with the underside of the instrument panel along the length of the reflection element to form a substantially enclosed diffusion chamber between the reflection element and the instrument panel. Preferably the light guide is located within the diffusion chamber and adjacent to, and most preferably in contact with, the side wall of the reflection element, with the major light emitting surface of the light guide facing the reflective surface of the concave element such that light is reflected and diffused within the diffusion chamber to provide a substantially even illumination of light over the region to be illuminated.

Preferably the region of the instrument panel to be illuminated comprises areas which are substantially optically opaque, and areas which are substantially optically transparent, so that light can be transmitted through the optically transparent areas towards a vehicle operator to illuminate these areas. The optically transparent areas are preferably the information bearing areas, and preferably comprise numbers and/or other such information which will appear light against a dark background. However, to achieve the reverse effect, the information areas may instead be optically opaque and set on an optically transparent background so that the region is illuminated except for the information areas which appear dark against a light background. Preferably the optically P491 2.A2 07 March2006 opaque areas comprise an opaque diffusing material on the underside of the instrument panel. This enhances the brightness and uniformity of the illumination as light is reflected and diffused by the underside of the instrument panel in addition to the surfaces of the reflection element.

There may be more than one region to be illuminated. For example the instrument may include both a speedometer and an odometer, in which case there will be two regions to illuminate. Alternatively, many vehicles have a single instrument panel having a number of gauges thereon, for example rev counter, speedometer and temperature gauge. A number of reflection elements can be placed behind the instrument panel, and directly behind the regions to be illuminated, and a single light guide may pass through the diffusion chambers created by these reflection elements, such that a single light source can be used to illuminate multiple instruments. Alternatively a single reflection element could be used which covered all the regions to be illuminated. The invention can also be used with more than one light source. For example a light source can be coupled to each end of a light guide in order to achieve higher brightness or to obtain multicolour illumination by using two light sources of different colour.

Preferably an LED is used as the light source, and preferably a high brightness LED. If the light guide is of high quality, for example a Lumitex device, light losses in the optical fibres can be neglected for optical fibre lengths of up to a few meters.

This allows the LED to be placed remotely from the instrument cluster. Preferably the LED consists of a three colour based LED covering the full colour range. The diffusing element allows good colour mixing. Furthermore, it is also possible to couple three LEDs of different wavelength or colour, for instance red, green and blue, with optical fibres that are then aligned or multiplexed together to form the light guide in a way that superior colour mixing is achieved. Unlike in prior art instruments, the evenness is obtained without varying the transmittance of the appliqué (a balancing technique) along the graphics areas. This therefore prevents light from having a colour shift.

P4912.A2 07 March 2006

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, with reference to the following drawings in which: Figure 1 is a partial cross section through an instrument according to a first embodiment of the invention; Figure IA is a schematic view of a light guide in isolation; Figure 2 is a cross-section through part of the instrument shown in Figure 1; Figure 3 is a partial cross section through an instrument according to a second embodiment of the invention; Figure 4 shows a third embodiment of the invention, in which a single LED is used to illuminate an instrument cluster comprising multiple gauges; and Figure 4A shows a light guide having two sets of optical fibres coupled to a single LED.

Figure 5 shows a fourth embodiment of the invention, in which two LEDs are used to illuminate an instrument panel 304.

DETAILED DESCRIPTION

Figure 1 is a partial cross section through an instrument 10 according to a first embodiment of the invention. A light guide 2 is located beneath a circular instrument panel 4. The light guide 2 is disposed within a diffusion chamber 36 formed between a reflection element 3 and the underside 9 of the instrument panel 4. The light guide 2 is disposed in a substantially circular path around the outer P4912.A.2 07 March 2006 periphery 25 of the instrument panel 4, and coupled at one end 30 to an LED I which is mounted on a printed circuit board (PCB) 5. Light from the LED I is channelled along the light guide 2 by total internal reflection, and emitted by the light guide 2 at various locations long its length. The emitted light is reflected and diffused within the diffusion chamber 36 and ultimately directed towards the instrument panel 4 to illuminate an information bearing annular region 7 (as indicated by the dotted region in Figure 1).

The instrument 10 is a vehicle speedometer and comprises a circular instrument panel 4, also known as an appliqué. In this embodiment the annular region 7 is substantially optically opaque, except for optically transparent numerals 12 and scale markers 14 through which light is transmitted towards a vehicle operator. A pointer 16 indicates the position on a marked scale provided by the scale markers 14, according to signals received from relevant sensors (not shown). The instrument 10 is mounted in a protective housing 18, which is mounted on the printed circuit board 5, and a substantially transparent protective cover 20 is disposed above the instrument panel 4.

The light guide 2 comprises a plurality of optical fibres 24 which are woven together to form an array of optical fibres 24. The light guide 2 is bent to follow a curved path substantially around the outer perimeter 25 of the circular instrument panel 4. Figure 1A shows the light guide 2 in isolation, and in a straight i.e. non-curved configuration. The light guide 2 has a belt-like shape, i.e. its length (indicated by arrow 50) is considerably greater than its width (indicated by arrow 52), and its width is considerably greater than its thickness (indicated by arrow 54).

Light is channelled along the optical fibres 24 by total internal reflection. The light guide has a side edge 56, a major light emitting surface 26, and a dark surface 28 (see Figure 1). The optical fibres 24 include very small deformations (not shown) in their external surfaces from which light is emitted. The optical fibres 24 are oriented in the array such that the majority of deformations are located on the major light emitting surface 26, hence the majority of light (indicated by arrows 58) is emitted from the major light emitting surface 26, and light is substantially not P491 2.A2 07 March 2006 emitted from the dark surface 28. Furthermore, the optical fibres are manufactured and woven together in such a way that light is emitted substantially evenly over the major light emitting surface 26.

Returning now to Figure 1, a reflection element 3 made from ABS is located behind the instrument panel 4. The reflection element is located generally directly behind the region 7 to be illuminated. The reflection element comprises a side wall 31 that extends along the length of the reflection element 3. The side wall 31 is perpendicular to the plane of the instrument panel 4 along the length of the side wall 31. The side wall extends along a circular path around the outer circumference of the instrument panel 4 and the annular region 7 to be illuminated.

The side wall 31 has a first end 33 located in contact with the underside 9 of the instrument panel 4, and a second end 34 offset from the instrument panel 4.

The reflection element 3 further comprises a concave curved portion 32 which extends between the second end 34 of the side wall 31 and the instrument panel 4 along the length of the reflection element 3. The concave curved portion 32 curves in such a way that the perpendicular distance between the underside 9 of the instrument panel 4 and the concave curved portion 32 increases with increasing radial distance from the centre of the circular instrument panel 4. An end 35 of the concave curved portion 32 is in contact with the underside 9 of the instrument panel 4 along the length of the reflection element 3. A diffusion chamber 36 is formed between the reflection element 3 and instrument panel 4.

The diffusion chamber 36 is the region enclosed by the side wall 31 and concave curved portion 32 of the reflection element 3, and the instrument panel 4. The light guide 2 is located within the diffusion chamber 36. The dark surface 28 of the light guide is located in contact with the side wall 31 of the reflection element 3, and the light emitting surface 26 is located opposite the concave curved portion 32. The concave curved portion 32 has a reflective internal surface 40 (Figure 2).

Figure 2 is a cross-section through part of the reflection element 3 and light guide 2 taken in a plane perpendicular to the plane of the instrument panel 4. Light P4912.A2 07 March 2006 (represented by the arrows in Figure 2) is emitted from the light guide 2. The majority of light is first incident on the reflective surface 40 of the concave curve portion 32 and then reflected and diffused within the diffusion chamber 36 before reaching the instrument panel 4. A small proportion of the light is directly incident on the instrument panel 4, however this is minimised by orienting the light guide 2 within the diffusion chamber 36 such that the major light emitting surface 26 is substantially perpendicular to the plane of the instrument panel 4. This arrangement produces a substantially even distribution of light over the entire region 7 (Figure 1), and substantially prevents bright spots from occurring on the instrument panel 4.

To enhance the brightness and uniformity of illumination, part of the underside of the instrument panel 4 comprises an opaque layer of diffusing material 4b to provide multiple diffusions of light for evenly and efficiently illuminating the graphics. The opaque layer of diffusing material 4b consists of, but is not limited to, a layer of white paint. Preferably, the diffusing material 4b has high reflectance within the spectrum of the light source. The area representing the graphics 4a is optically transparent and causes diffused light to be transmitted towards a vehicle operator.

Figure 3 is a partial cross section through an instrument 110 according to a second embodiment of the invention. In Figure 3 the components similar to those in Figure 1 are indicated with reference numerals increased by 100. In this second embodiment the side wall 131 of the reflection element 103 is located directly behind the inner circumference 142 of the annular region 107 (represented by the dotted area in Figure 3), and the concave curved portion 132 curves in such a way that the perpendicular distance between the underside 109 of the instrument panel 104 and the concave curved portion 132 decreases with increasing radial distance from the centre of the circular instrument panel 104. The light guide 102 is bended to fit the inner circumference of the region 107 to be illuminated.

In comparison with the first embodiment shown in Figure 1, shorter optical fibres P4912 A2 07 March 2006 124 are needed to illuminate the same sized region 107, however in this second embodiment, the optical fibres 124 are bent to a greater degree than in the first embodiment which causes greater mechanical stress on the optical fibres 124.

The optical fibres should not be bent beyond the limit that is dictated by the critical angle in which case most of the light would escape from the fibres. The present embodiment allows additional space for electronics components in the instrument cluster. Alternatively, a smaller PCB 105 could be used with this embodiment.

Figure 4 shows a third embodiment of the invention, in which a single LED 201 is used to illuminate an instrument cluster 48 comprising multiple instruments 44. In Figure 4 the components similar to those in Figure 1 are indicated with reference numerals increased by 200. In this example the instruments 44 each have, their own instrument panels 204, however the invention is equally suitable for multiple instruments which share a single instrument panel. A reflection element (not shown in Figure 4) similar to the one shown in Figure 1, is located behind each instrument panel 204, and each instrument 44 is substantially the same as the instrument 10 shown in Figure 1, however in this embodiment, a single light source 201 is used to illuminate the two instruments 44.

A single LED 201 is coupled to the light guide 202 which has two sets of optical fibres 46, as illustrated in Figure 4A. Each set of optical fibres 46 is placed behind each instrument panel 204 and bent to fit the outer circumference 225 of the graphics areas. High colour uniformity is achieved in the instrument cluster 48 because light is emitted from the same LED source 201. Additionally, it is possible to dim the two instruments 44 at the same level of brightness since the instrument cluster 48 is using a single LED 201. Though not shown here, another embodiment consists of bending each set of optical fibres 46 to fit the inner circumference of the graphics areas.

Figure 5 shows a fourth embodiment of the invention, in which two LEDs 301 are used to illuminate an instrument panel 304. In Figure 5, the components similar to those in Figure 1 are indicated with reference numerals increased by P4912.A2 07 March 2006 -12 - 300. The light guide 302 is located behind the instrument panel 304 and disposed within a diffusion chamber created between a reflection element and the underside of the instrument panel in substantially the same arrangement as the instrument shown in Figure 1. In this fourth embodiment however, one LED 301 is coupled at each extremity of the light guide 302. This arrangement achieves a high brightness while maintaining good uniformity of illumination of the instrument panel 304. This embodiment is particularly suitable, for example, when the instrument cluster is placed behind a smoked lens.

It should be understood that the invention has been described by way of example only and that modifications in detail may be made without departing from the scope of the invention as defined in the claims.

P4912.A2 07 March 2006

Claims

CLAIMS

1. A back-lit instrument suitable for use in a vehicle, comprising: an instrument panel having a region to be illuminated; a light source coupled to a light guide comprising a plurality of optical fibres, each optical fibre having means for allowing light to escape therefrom, and being located behind the panel and arranged to follow a curved path; wherein the instrument further comprises reflection means located behind the panel to reflect light emitted from the light guide towards the region of the panel to be illuminated.

2. A back-lit instrument as claimed in Claim 1, wherein the region to be illuminated is either substantially circular or substantially annular.

3. A back-lit instrument as claimed in Claim I or Claim 2, wherein the optical fibres have disruptions in their surfaces at various locations along their lengths.

4. A back-lit instrument as claimed in Claim 3, wherein the disruptions are formed from any one, or a combination of the following: cutting, moulding, coating, forming, mechanical deformation, chemical deformation or small bends along the length of the optical fibres.

5. A back-lit instrument as claimed in any preceding claim, wherein the plurality of optical fibres are woven together to form a substantially elongate array.

6. A back-lit instrument as claimed in any preceding claim, wherein the light guide has a belt-like structure and comprises a major light emitting surface from which the majority of light is emitted, and wherein the light guide is arranged such that the major light emitting surface is substantially perpendicular to the plane of the instrument panel.

7. A back-lit instrument as claimed in Claim 6, wherein the reflection means P4912.A2 07 March 2006 -14-comprises a reflection element having a concave curved portion which extends between the light guide and the instrument panel such that the perpendicular distance between the instrument panel and the concave curved portion decreases with increasing distance from the light guide, the concave curved portion having a reflective surface located substantially opposite the major light emitting surface of the light guide for reflecting light towards the instrument panel.

8. A back-lit instrument as claimed in Claim 7, wherein the light guide is located substantially within a substantially enclosed region formed between the instrument panel and the reflection element.

9. A back-lit instrument as claimed in Claim 8, wherein in use, light is reflected and diffused in the substantially enclosed region before being directed towards the instrument panel.

10. A back-lit instrument as claimed in any preceding claim, wherein the region of the instrument panel to be illuminated comprises areas which are substantially optically opaque, and areas which are substantially optically transparent.

11. A back-lit instrument as claimed in any preceding claim, wherein the light guide is a Lumitex-type device.

12. A back-lit instrument as claimed in any preceding claim, wherein the light source is a three-colour LED.

13. A back-lit instrument as claimed in any preceding claim, further comprising a second light source, wherein the light sources are coupled to either end of the light guide.

14. A back-lit instrument as claimed in any preceding claim, wherein a plurality of different coloured light sources are coupled to an end of the light guide.

P4912.A2 07 March 2006 -15- 15. A back-lit instrument as claimed in Claim 15, wherein the plurality of different coloured light sources includes individual red, green and blue LEDs.

16. A back-lit instrument as claimed in any preceding claim, wherein the curved path is substantially circular.

17. A vehicle instrument cluster comprising an instrument as claimed in any preceding claim.

18. A back-lit instrument substantially as herein described with reference to or as shown in the accompanying drawings.

19. A vehicle instrument cluster substantially as herein described with reference to or as shown in the accompanying drawings.

P4912.A2 07 March 2006