Abstract:
An instrument suitable for use in a vehicle and having a dial with an information bearing front surface and a pointer for indicating information on the front surface. The pointer is pivotable about a first axis that extends through the hub and is substantially perpendicular to the plane of the dial. The instrument includes first and second light sources which are both located behind the dial, generally in registry with the pointer assembly. The instrument further includes a first light deflector that deflects light from the first light source along the pointer to back light the pointer, and second light deflector that deflects light from the second light source towards the front surface to front light that surface.

Description:
BACKGROUND 
     Field of the Invention 
     The present invention relates to illumination of instruments, gages and dials, and particularly to instruments suitable for use in a vehicle. 
     Instruments for displaying information on a vehicle display are usually located on the instrument panel 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 a panel or face having an information bearing region, and a housing having a transparent cover to protect the instrument. The information bearing region usually has symbols, such as graphics, numbers or a dial, indicating a scale and a pointer for indicating a point within the scale. The information bearing region may also include features such as rings defining the perimeter of a particular instrument, gauge or dial (hereafter “instrument”. 
     The instrument is generally mounted on a printed circuit board (PCB) that 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, a number of instruments may be mounted together to form an instrument cluster. Many modern instrument clusters comprise a single panel or back plate having a number of information bearing regions corresponding to the various instruments, for example speedometer, rev counter, engine temperature etc. 
     Vehicle instruments can be front lit or back lit. Front lit instruments are illuminated from the viewing side of the information bearing surface, and light is reflected off the information bearing surface towards a vehicle occupant. Back lit instruments are illuminated from the side opposite to the viewing side of the instrument. In the case of back lighting, the information bearing surface contains opaque or semi-opaque portions comprising symbols, so that light passing through the information bearing surface renders these symbols visible. 
     Back lit instruments have a pleasant overall appearance because the lighting components are generally not visible to a vehicle occupant. Front lighting can produce a more appealing effect than back lighting, however the lighting components in front lit instruments tend to be mounted in front of the instrument panel, and are therefore often visible to the vehicle occupant, which detracts from the aesthetic appeal of the instrument. 
     Front or back lighting may be achieved either by providing light directly from a light source (which may include the use of reflective surfaces), or indirectly from a light source that is coupled to a light guide and directs light from the light source to the required illumination point. A problem with known front lit instruments is that while front lighting allows for a simpler design of the information bearing surface and the pointers, any cost savings that result from such simplified designs are negated by the extra costs required for flexible connectors from the PCB (which is located behind the instrument panel) to the light source or complex light guides (which are generally located in front of the instrument panel), and for more complex assembly. 
     Front lighting from a point source also often produces shadows. Back lighting, on the other hand, usually involves the use of a plurality of light sources, and a more complex arrangement is required to illuminate the pointer. Furthermore, applying symbols to the information bearing surface is more complex in the case of back lighting, because poor distribution of the illumination can cause portions of the instrument to have better illumination than others. This is often compensated for by using an instrument panel having some areas which are more optically opaque than others. 
     Japanese patent document JP11030534 discloses an instrument illuminated by light sources that are all located behind the panel or dial surface. The instrument is back lit by light sources located near the center of the dial, and front lit by light sources located around the outer periphery of the dial via reflection from a reflection element located around the dial. 
     As customers become more sophisticated in their requirements, it becomes important to provide lighting for vehicle instruments that is both distinctive and cost effective to produce. 
     SUMMARY OF THE INVENTION 
     According to the principles of the present invention, there is provided an instrument suitable for use in a vehicle. The instrument includes a dial having an information bearing front surface. 
     A pointer assembly comprising a pointer having a hub and a needle is used for indicating information on the front surface. The needle extends radially from the hub, and the pointer is mounted in front of the dial adjacent to the information bearing front surface so as to rotatable about a first axis extending through the hub and substantially perpendicular to the plane of the dial. Light sources are located behind the dial and directly behind the pointer assembly. 
     A light deflecting means deflects light from a first light source along the pointer to back light the pointer. A second light deflecting means deflects light from a second light source towards the information bearing front surface to front light this surface. 
     As seen from above, the invention achieves both front lighting and back lighting of the instrument from light sources mounted behind the dial. The benefits of front lighting as discussed above are therefore achieved without the need for mounting the light sources in front of the dial. The combination of back lighting and front lighting in a single instrument results in a pleasant aesthetic. 
     The first and second light sources are both located directly behind the pointer assembly and are preferably substantially centrally located behind the dial. In this position, the light sources are close to the other electronics, such as the pointer motor, which allows a smaller PCB to be used. Preferably the first and second light deflecting means are located proximate to the first axis, and most preferably the pointer assembly comprises the first and second light deflecting means. This arrangement means that the illumination system is very compact as all the lighting components are associated with the pointer assembly, and are hence substantially centrally located on the dial and occupy a relatively small area. 
     The centrally located first and second light sources produce a pleasant illumination pattern on the dial. The illumination pattern is bright at the center of the dial and gets evenly dimmer towards the outer periphery of the dial. By using separate first and second light sources to illuminate the pointer and the dial, respectively, a number of interesting effects can be achieved. The pointer is illuminated completely independently from the dial and so, for example, the pointer and dial could be illuminated by different colored light. Furthermore, the first and second light sources could have different brightnesses so that the contrast between the dial and the pointer can be varied. Separate dimmer functions may be associated with the first and second light sources to allow the contrast between pointer and dial to be continuously varied. 
     Preferably the first and second light sources emit light from substantially concentric annular regions centered about the first axis. The first light source preferably comprises a plurality of first light emitting diodes (LEDs) arranged in a first ring centered about the first axis, and the second light source preferably comprises a plurality of second LEDs arranged in a second ring centered about the first axis. The radius of the second ring is greater than the radius of the first ring such that the first LEDs form an inner ring, and the second LEDs form an outer ring. In most applications, the radius of the first ring is preferably between 2 and 5 mm, and more preferably about 3.5 mm. The radius of the second ring is preferably between 5 and 10 mm, and more preferably about 8.5 mm. The first and second LEDs are preferably each mounted directly to a PCB located behind the dial. Mounting the light sources directly on the PCB negates the requirement for flexible connectors or light guides and thus reduces cost. 
     The first light deflecting means is preferably a reflective first surface of the pointer needle, this first surface being angled to deflect light from the first light source along the needle to illuminate the needle. The first surface is preferably radially offset from the first axis by a distance substantially equal to the radius of the inner ring of first LEDs. In this way the first surface remains substantially opposite the first light source as the pointer rotates. 
     The second light deflecting means is preferably located in front of the dial and deflects light from the second light source back towards the information bearing front surface of the dial to achieve front lighting of the dial from a light source located behind the dial. The second light deflecting means is preferably a substantially annular wall having an inner surface facing towards the first axis, and an outer surface facing away from the first axis. The wall is preferably substantially optically transparent. The inner surface is reflective and arranged to deflect light by total internal reflection towards the outer surface, and the outer surface is arranged to refract light towards the information bearing front surface of the dial. The reflective inner surface is preferably substantially funnel or cone shaped and has a radius substantially equal to the radius of the outer ring of second LEDs. In this way, it is centered about the first axis such that the inner surface is substantially opposite to the outer ring of second LEDs. In one embodiment of the invention, the annular wall extends from the outer circumference of the pointer hub, and in certain other embodiments of the invention the annular wall is part of a separate light deflecting element associated with the pointer assembly. 
     The first and second light sources are preferably substantially optically isolated from one another such that the light from the first light source is substantially decoupled from the light from the second light source. Preferably, the first and second light sources are separated from one another by substantially optically opaque means, and more preferably by light deflecting walls. The light deflecting walls are preferably made from acrylonitrile-butadiene-styrene (ABS), however any other light reflecting/diffusing material is suitable. 
     The light deflecting wails preferably include a first tube arranged with its tubular axis coincident with the first axis and having a radius larger than the inner ring of first LEDs, and smaller than the outer ring of second LEDs such that the first tube is located between the inner and outer rings of LEDs. The light deflecting walls also preferably include a second tube arranged with its tubular axis coincident with the first axis and having a radius larger than the outer ring of second LEDs and arranged to surround said outer ring. The light deflecting walls may further include a third tube having a tubular axis coincident with the first axis and having a radius smaller than the inner ring of LEDs. The light deflecting walls preferably extend between the PCB and the dial. In addition to isolating the first and second light sources, the light deflecting walls serve to channel light towards the first and second light deflecting means. 
     Preferably the light sources emit light according to a cone of viewing angle that is less than about 60 degrees. 
     In one embodiment of the invention, the second light deflecting means for deflecting light onto the dial is formed from one of the tubular light deflecting walls. In this embodiment an upper end of one of the tubular walls is funnel shaped and projects through an aperture in the dial. The funnel shaped end has a curved outer reflective surface which is radially offset from the first axis by a distance substantially equal to the radius of the outer ring of second LEDs, and hence light from the second LEDs is deflected by this curved surface towards the face of the dial. 
     The first and second light sources are located directly behind the pointer assembly, and all the lighting components are preferably located proximate to the first axis, and substantially behind the pointer hub. This allows a small PCB to be used. Preferably the pointer assembly includes a light absorbing cap located over the pointer hub which absorbs undeflected light from the first and second light sources, thus preventing the light from being transmitted towards a vehicle occupant. The light absorbing cap is preferably substantially circular and has a radius in excess of the radius of the outer ring of second LEDs to substantially obscure the area occupied by the first and second light sources from view, and hence obscures the lighting components from view. The light absorbing cap also protects the lighting components. Usually the instrument also includes a transparent front panel to protect the instrument and its components from dust, scratches and knocks. 
     The color of the first LEDs may be the same as, or different from, the color of the second LEDs. Furthermore, the first and/or second light sources may comprise a number of different colored LEDs. For example, the first ring of LEDs may include a number of different colored LEDs so that the pointer changes colour as it rotates. For example green LEDs may be located around the dial up to a certain point, and then red LEDs could be used thereafter. Such a system could provide a visual signal to the driver (the pointer turning from green to red) if the vehicle exceeds a predetermined speed (for example 70 mph). 
     The invention is not limited to using a plurality of LEDs as the light sources. For example a suitable annular light guide coupled to one or more light sources could be used, as could a bundle of fibre optic cables arranged in a ring and coupled to a light source. Using a plurality of LEDs mounted directly to the PCB is advantageous, however, as flexible connectors from the PCB to the light sources are not required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be further described, by way of example, with reference to the following drawings in which: 
         FIG. 1A  is a diagrammatic cross-section through an instrument according to a first embodiment of the invention, including a pointer assembly having a pointer hub which deflects light towards the dial; 
         FIG. 1B  is an exploded perspective view of the pointer assembly seen in  FIG. 1A ; 
         FIG. 1C  is a top view of the pointer assembly of  FIG. 1B  without the light absorbing cap; 
         FIG. 2A  is a diagrammatic cross-section through an instrument according to a second embodiment of the invention, including a separate light deflecting element located between the pointer and the dial for deflecting light towards the dial; 
         FIG. 2B  is an exploded perspective view of the pointer assembly of  FIG. 2A ; 
         FIG. 3  is a diagrammatic cross-section through an instrument according to a third embodiment of the invention, including a separate light deflecting element located between the pointer and the light absorbing cap for deflecting light towards the dial; and 
         FIG. 4  is a diagrammatic cross-section through an instrument according to a fourth embodiment of the invention, including a funnel shaped reflective surface located between the pointer and the dial for deflecting light towards the dial. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1A , seen therein is a diagrammatic cross-section through part of an instrument according to a first embodiment of the present invention. The instrument  10  comprises a dial  12  having an information bearing front surface  14 , which may include numbers and other marks (not shown). The instrument  10  also includes a pointer assembly  16  (shown in isolation in  FIG. 1B ) comprising a pointer  17  having a pointer hub  20  and a needle  18 , a spindle  31  and a light absorbing cap  32 . The pointer hub  20  is substantially circular, and the needle  18  extends radially from the hub  20 . The needle  18  and hub  20  are mounted in front of the dial  12  on the viewing side  13  of the information bearing surface  14 . The spindle  31  extends centrally from the underside of the hub  20  and extends perpendicular to the plane of the dial  12 . The needle  18  is able to pivot or rotate about a first axis (indicated by the dotted line  22 ) which is perpendicular to the plane of the dial  22  and coincident or coaxial with the spindle  31 . 
     A first light source  24  and a second light source  26  are located behind the dial  12 . The first light source  24  comprises a plurality of first LEDs (of which LEDs  52  can be seen in  FIG. 1A ) arranged in a first ring about the first axis  22 . Each first LED is mounted to a PCB  28  at a first radial distance of about 3.5 millimeters (indicated by dimension X in  FIG. 1A ) from the first axis  22 . The second light source  26  comprises a plurality of second LEDs (of which LEDs  50  can be seen in this cross-section) arranged in a second ring about the first axis  22 . Each second LED  50  is mounted to the PCB  28  at a second radial distance of about 8.5 millimeters (indicated by dimension Y) from the first axis  22 . The second radial distance Y is greater than the first radial distance X such that the radius of the ring of second LEDs  50  of the second light source  26  is greater than the radius of the ring of first LEDs  52  of the first light source  24 . In other words, the first and second rings are concentric, with the first LEDs  52  forming the inner ring, and the second LEDs  50  forming the outer ring. Preferably, the first light source  24  and the second light source  26  comprise LEDs that have a full viewing angle less than about 60 degrees. 
     As seen in  FIG. 1A , the pointer needle  18  has a proximal end  19  and a distal end  21 . The proximal end  19  is affixed to or formed with the pointer hub  20 , and the distal end  21  is used to point to information on the dial  12 . The proximal end  19  has a first surface  27  (best seen in  FIGS. 1A and 1C ) which is radially offset from the first axis  22  by a distance substantially equal to the radius of the inner ring of first light source  24 , such that the first surface  27  remains substantially opposite to the first LEDs  52  as the needle  18  rotates. The first surface  27  is reflective and inclined relative to the plane of the dial to deflect light from the first light source  24  along and out through a viewed surface of the needle  18 . 
     As seen in  FIG. 1B , the pointer hub  20  is bowl-shaped and generally comprises a flat circular base portion  54  with a circumferential wall  55 . The circumferential wall  55  has an inner surface  38  which faces towards the first axis  22 , and an outer surface  39  which faces away from the first axis  22 . The pointer  17  is mounted such that the flat base portion  54  of the hub  20  is substantially parallel with the plane of the dial  12 . The hub  20  is substantially optically transparent and able to deflect light. The inner surface  38  is radially offset from the first axis  22  by a distance substantially equal to the radius of the outer ring of formed by the second light source  26 , such that the inner surface  38  is substantially opposite to the outer ring of second LEDs  50 . The inner surface  38  is reflective and inclined relative to the plane of the dial  12 . 
     A section of light absorbing material  42  ( FIG. 1 ) is located on the underside of the needle  18  and offset from the first axis  22  by a distance substantially equal to the radius of the outer ring of second light source  26 , such that the light absorbing material  42  remains substantially opposite to the outer ring of the second LEDs  26  as the needle  18  rotates. As such, the light absorbing material  42  prevents light from the second light source  26  from illuminating the pointer needle  18 . 
     Light deflecting walls  3  extend substantially perpendicular to the plane of the dial  12  between the dial  12  and the PCB  28 . The light deflecting walls  3  are made of ABS or other reflecting/diffusing material, and serve to channel light from the light sources  24 ,  26  as efficiently as possible towards the light deflecting surfaces  27 ,  28 . The light deflecting walls  3  comprise a first tube  61  and a second tube  62 . The first and second tubes  61 ,  62  are arranged such that their tubular axes are substantially coincident or coaxial with the first axis  22 . 
     The radius of the second tube  62  is larger than the radius of the outer ring of the second light source  26 . The radius of the first tube  61  is larger than the radius of the inner ring of the first light source  24 , but smaller than the radius of the outer ring of the second light source  26 . The inner ring of first light source  24  is located in a first region  63  enclosed by the first tube  61 , and the outer ring of the second light source  26  is located in a second region  64  between the first and second tubes  61 ,  62 . The first tube  61  therefore separates the first and second light sources  24 ,  26  and hence decouples the light from the first light source  24  from the light from the second light source  26 . 
     The dial  12  has a substantially circular aperture  30  centered on the first axis  22  and has a radius substantially equal to the radius of the second tube  62 . The pointer hub  20  is located above the aperture  30 , and a light absorbing cap  32  is located over the hub  20  to obscure the light sources  24 ,  26  from the view of a vehicle operator. The light absorbing cap  32  is substantially circular and preferably has a radius larger than the radius of the second tube  62  in order to obscure all the lighting components which are located within the second tube  62 . 
     The process of illumination of the instrument is now described with reference to  FIG. 1A . In  FIG. 1A  the needle  18  is shown pointing leftwards. It can be seen from  FIG. 1  that light from LED  50  is deflected by the inner surface  38  of the circumferential hub wall  55 , towards the outer surface  39 , by total internal reflection. This light is then refracted at the outer surface  39  towards the information bearing front surface  14  of the dial  12  (in the direction of arrow  37 ) to illuminate the information bearing surface  14 . At the same time, light from the LED  52 , which forms part of the inner ring of the first light source  24 , is deflected by the first surface  27  of the proximal end  19  of the needle  18  along the needle  18  (in the direction of arrow  36 ) to illuminate the needle  18 . 
     Light from one or more LEDs  50 ′, which form part of the inner ring of the first light source  24 , passes straight through the flat base portion  54  of the pointer hub  20 , without being deflected, and is absorbed by the light absorbing cap  32 . Light from one or more LEDs  50 ′, which form part of the outer ring of second LEDs  26 , is absorbed by the section of light absorbing material  42  located beneath the pointer needle  18  and, as such, does not provide any illumination to the needle  18  when the needle  18  is located above it in this position. 
     When the needle  18  has rotated by 180°, such that it points rightwards (not shown), designated as  50 ′, will be illuminating the information bearing front surface  14 , light from the LED  52  will be blocked by the light absorbing cap  32 , light from the LED  52 ′ will illuminate the pointer, and light from LED  50  will be absorbed by the section of light absorbing material  42 . 
       FIG. 2A  is a diagrammatic cross-section through an instrument  100  according to a second embodiment of the invention. The second embodiment is similar to the first embodiment shown in  FIGS. 1A to 1C  and, therefore, common elements bear common references numerals. The second embodiment, however, incorporates a separate deflection element  109  for deflecting light (shown by arrows  37 ) towards the information bearing front surface  14  of the dial  12 .  FIG. 2B  is an exploded perspective view of the pointer assembly  116  shown in  FIG. 2A , which includes a disc shaped hub  20 , a needle  18  radially mounted to the hub  20 , a spindle  31  which extends axially from the hub  20 , a light deflecting element  109 , and a light absorbing cap  32  positioned over the hub  20 . 
     The light deflection element  109  is substantially annular and comprises a central hole  70  and a circumferential wall  72 . As best seen in  FIG. 2B , the circumferential wall  72  has a funnel shaped inner surface  73  which faces towards the first axis  22 , and an outer surface  74  which faces away from the first axis  22 . As best seen in  FIG. 2A , the inner surface  73  is radially offset from the first axis  22  by a distance substantially equal to the radius of the outer ring of the second light source  26  such that the inner surface  73  is substantially opposite the LEDs of the outer ring of the second light source  26 . The inner surface  73  is reflective and is inclined with respect to the plane of the dial  12 . Light from the outer ring of the second light source  26  is deflected by the inner surface  73  of the circumferential hub wall  55 , towards the outer surface  74 , by total internal reflection. This light is then refracted at the outer surface  74  towards the information bearing front surface  14  of the dial  12  (in the direction of arrow  37 ) to illuminate the dial  23 . 
     The deflection element  109  is made from clear polycarbonate (PC) or polymethyl methacrylate (PMMA) or any substantially optically transparent material capable of redirecting light by total internal reflection. 
     In this second embodiment, the deflection element  109  is generally located between the pointer  18  and the dial  12 . The radius of the deflection element  109  is larger than the radius of the aperture  30  in the dial  12  to prevent the deflection element  9  from falling through the aperture  30 . The light absorbing cap  32  is located over the pointer hub  20  obscure the light sources  24 ,  26  from view. 
     The light deflecting walls  103  in the second embodiment are arranged slightly differently to those in the first embodiment shown in  FIG. 1 . In the second embodiment, the first tube  161  is longer than the second tube  162 , and extends through the aperture  30  in the dial  12  and through the central hole  70  in the deflecting element  9 . The first tube  61  extends to a height substantially equal to the top  75  of the circumferential wall  72  of the deflection element  109 , and the pointer hub  20  sits on top of the first tube  161  and deflection element  109 . 
     The separate deflection element  109  in the second embodiment enables a substantially symmetrical distribution of light over the dial  12  including in the region directly beneath the pointer needle  18 . In that the deflection element  109  is located between the needle  18  and dial  12 , no shadowing is caused by the needle  18  as the light is deflected from behind the needle  18 . 
     In the second embodiment, light from second LEDs  50  continually illuminate the dial  12  independent of the rotation of the needle  18 . When the needle  18  is pointing leftwards as shown in  FIG. 2 , LED  52  illuminates the needle  18 , and light from LED  52 ′ passes straight through the deflection element  109  and pointer hub  20 , without being deflected, and is absorbed by the absorbing cap  32 . When the pointer rotates 180°, light from LED  52  will be blocked by the cap  32 , and light from LED  52 ′ will illuminate the pointer. 
     Although not shown in  FIG. 2A , light absorbing material (similar to the light absorbing material  42  in  FIG. 1A ) could be placed beneath the pointer needle  18  to block further light from the LEDs  50 . 
       FIG. 3  is a cross-section through an instrument  200  according to a third embodiment of the invention. This third embodiment incorporates a deflection element  209  and pointer similar to the deflection element and pointer shown in  FIG. 2A . In the third embodiment, however, the pointer  18  is located adjacent the dial  12  and the deflection element  209  is located in front of the pointer  18 , and between the pointer  18  and the light absorbing cap  32 . 
     In order to minimise light leakage from the first light source  24  into the deflection element  209 , a piece of light absorbing material  205  is disposed over a portion of the pointer hub  20 , between the hub  20  and the deflection element  209 , to absorb light from the inner ring formed by the LEDs of the first light source  24 . 
     In this third embodiment the pointer needle  18  will cause minor shadowing. However, a larger area of the dial  14  is illuminated than in the first and second embodiments because the deflecting element  209  is located further away from the dial  12 . 
     A fourth embodiment of the invention is shown in  FIG. 4 . The pointer  18  and the light absorbing cap  32  are similar to the pointer and light absorbing cap  32  in the second embodiment shown in  FIG. 2A . In this fourth embodiment however, a portion of the light deflecting walls  303  provides the means for deflecting light onto the dial  12 . In this embodiment, a first end  81  of a first tubular wall  361  is funnel shaped or curved radially outward and projects through the aperture  30  in the dial  12 . The funnel shaped first end  81  has a curved outer reflective surface  82 , which is radially offset from the first axis  22  by a distance substantially equal to the radius of the outer ring formed by the LEDs of the second light source  26  such that the reflective surface  82  is opposite to the second light source  26 , and hence light from the second light source  26  is deflected by this curved reflective surface  82  towards the information bearing front surface  14  of the dial  12 . This arrangement of an instrument  300  provides a substantially even distribution of light around the entire circumference of the dial  12  and does not result in shadowing or dark spots beneath the pointer  18 . 
     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.