GB2435937A

GB2435937A - Light guide with circumferential wall and light emitting portion

Info

Publication number: GB2435937A
Application number: GB0604963A
Authority: GB
Inventors: Samir Mezouari
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2006-03-11
Filing date: 2006-03-11
Publication date: 2007-09-12
Anticipated expiration: 2026-03-11
Also published as: GB2435937B; GB0604963D0

Abstract

A light guide (1) is provided for illuminating an instrument. The light guide comprises a light accepting portion (2), a light redirecting portion (4) and a light emitting portion (6). The light accepting portion (2) comprises a substantially circumferential wall (8) extending around a first axis (10) and having a first longitudinal end (12) for receiving light from a light source. The circumferential wall (8) is adapted to guide the light received to the light redirection portion (4) which is located at a second longitudinal end (14) opposite the first longitudinal end (12). The circumferential wall (8) extends at a substantially constant angle relative to the direction of the first axis (10). The light emitting portion includes a first surface (16) through which the light received by the light receiving portion (2) is emitted and a second surface (18) for guiding light through the first surface (16). The first surface (16) is substantially planar and extends transverse to the first axis. The light emitting portion also includes a substantially central connecting portion (20). The light redirecting portion (4) is connected to the second longitudinal end (14) of the light accepting portion and to the substantially central connecting portion (20) of the light emitting portion (6). The light redirecting portion (4) includes a light redirecting wall (22) extending transverse to the light accepting portion (2) and the light emitting portion (6) and is adapted to internally reflect and diffuse light from the light accepting portion (2) into the light emitting portion (6).

Description

Light Guide

BACKGROUND

a. Field of the Invention

The present invention relates to a light guide, particularly to an optical light guide member for receiving light and illuminating an instrument in an automotive dashboard.

b. Related Art An instrument in an automobile dashboard, such as a speedometer or fuel gauge, typically comprises an information bearing surface and a pointer. The information bearing surface typically bears symbols indicating a scale such as graphics, numbers or a scale indicator and the pointer is moved to indicate a point on the surface to provide information. Such instruments are typically mounted in a housing and covered by a transparent cover.

The instrument is generally mounted on a printed circuit board (PCB) which is connected to one or more sensors which monitor, for example, engine conditions such as engine speed or temperature. Conventionally instruments are mounted together to form an instrument cluster. Instrument clusters are illuminated to ensure good visibility of the information displayed under any ambient light conditions. In general, the instrument clusters are illuminated using back lighting systems. With back lighting systems the information bearing surface contains opaque or semi opaque portions so that the light passing through the information bearing surface renders the symbols visible. Recently, new technologies such as liquid crystal displays (LCD)s have been integrated into the instrument cluster to display information, such as numeric information. The current trend towards using traditional instruments alongside LCD displays requires a careful use of the space available within the instrument cluster to ensure acceptable lighting of the instruments, with no hot spots' or dark regions.

It is known to use incandescent light bulbs as a light source for backlighting of an instrument. However light bulbs tend to suffer reliability problems due to the vibrations from the automobile when in use. LED light sources have been used to overcome this problem, but unfortunately a further problem remains. Most conventional instruments use illumination systems that are bulky and occupy most of the volume between the information bearing surface and the PCB which can lead to packaging problems.

It is an object of the present invention to address some of the issues mentioned above.

SUMMARY OF THE INVENTION

The invention provides a light guide for illuminating an instrument, the light guide comprising a light accepting portion, a light redirecting portion and a light emitting portion, wherein: the light accepting portion comprises a substantially circumferential wall extending around a first axis and having a first longitudinal end for receiving light from a light source, the circumferential wall being adapted to guide the light received to the Jight redirection portion which is located at a second longitudinal end opposite the first longitudinal end, the circumferential wall extending at a substantially constant angle relative to the direction of the first axis; the light emitting portion including a first surface through which the light received by the light receiving portion is emitted and a second surface adjacent the first surface for guiding light through the first surface, the first surface being substantially planar and extending transverse to the first axis, the light emitting portion further including a substantially central connecting portion; the light redirecting portion being connected to the second longitudinal end of the light accepting portion and to the substantially central connecting portion of the light emitting portion, the light redirecting portion extending transverse to the light accepting portion and the light emitting portion and being adapted to internally reflect and diffuse light from the light accepting portion into the light emitting portion.

By providing such a light guide, a light source located at or adjacent the light accepting end can be used to illuminate a wide area, for example it could be used to backlight an appliqué of an instrument. The motor or means for moving a pointer for indicating a point on the appliqué can be located in within the circumferential wall, thereby saving packaging space.

It is preferred that the light guide is fabricated from a material that have a refractive index such that substantially all the light within the guide is totally internally reflected until the light emitting portion is reached and the light forced to exit through the first surface. The material is preferably a polycarbonate or PMMA.

The light guide is preferably moulded, but could be fabricated by any suitable means. It is preferred that all the portions of the light guide are fabricated as a single element, such that there are no internal discontinuities between the portions. It should be understood that the regions of the guide not specifically intended to accept or emit light could be coated with a reflective coating to help to prevent loss of light, or direct light as required.

The circumferential wall extends at a substantially constant angle with respect to the direction of the first axis. If that angle is not zero (i.e. the circumferential wall does not extend substantially parallel with the first axis) the first wall will have a substantially funnel shaped form, albeit possibly with a non-circular cross section.

A non-curved shape for the wall is preferred as this facilitates manufacturing, it is preferred that the circumferential wall extends substantially parallel with the first axis as this allows the wall to have a minimalextent in a radial direction, except for its thickness, and therefore allows the wail to have a lower packaging size than would be achieved if the circumferential wail did not extend substantially parallel with the first axis. It should be understood that although the wall is described as being a circumferential wail, the wall need not be curved so that is remains at a

---

substantially constant distance from the first axis. However, It is preferred that the circumferential wall is curved so that is remains at a substantially constant distance from the first axis, so that the wall follows a substantially circular path.

The circumferential wall preferably extends around the first axis at a radius sufficient to allow, for example, a motor or other component of a gauge to be located within the circumferential wall. It should be understood that the circumferential wall need not fully surround the first axis. It is preferred that the circumferential wall extends for at least 900 around the first axis as this could be suitable for, for example a fuel gauge, or temperature gauge. More preferably at least 180 and most preferably at least 270 as these angular ranges are particularly suitable for speedometers and rev counters, which are often the 0 largest instruments in an automotive instrument cluster.

The light emitting portion receives the light from the light redirecting portion and causes the light to be emitted through the first surface. The second surface directs light to exit through the first surface and this can be achieved in a plurality of different ways, the simplest of which is to substantially prevent light from exiting through the second surface, for example by coating it with a reflective coating, for example a silver or white paint. The distance between the first and second surfaces may decrease as radial distance from the first axis increases such that light is forced out of the first surface. The second surface could also include disruptions which serve to redirect light through the first surface. For example, an arrangement of prismatic or other disruption structures arranged substantially in arcs around the first axis, the disruptions serving to redirect light in a direction such that it leaves through the first surface. The second surface could be roughened mechanically or chemically to provide a light redirecting and diffusing function to further enhance the diffusion of light within the light guide.

The substantially central connecting portion is preferably substantially arcuate in shape, having a substantially constant radius from the first axis. The first surface preferably extends substantially perpendicular to the first axis as this helps to reduce the packaging size of the illumination means for an instrument.

The light redirecting portion includes a light redirecting wall that extends transverse to the first axis and transverse to the first surface. The light redirecting wall is preferably arranged to redirect light from the light receiving portion to the light emitting portion. It is preferred that the light redirecting wall extends at a substantially constant angle with respect to the direction of the first axis so that wall forms a substantially funnel shape. The radial extent to the light redirecting wall is preferably greater than, and most preferably substantially equal to, the thickness of the circumferential wall and the axial extent of the light redirecting wall is preferably greater than, and most preferably substantially equal to, the axial distance between the first and second surface at the substantially central connecting portion.

It is preferred that the light guide includes light diffusing portions that deflect at least some light in a circumferential direction as this helps to avoid hot spots' in the illumination emitted from the first surface and therefore in the illumination of an appliqué. Such light diffusing portions are preferably located in the light redirecting portion as such diffusion portions can include means for deflecting light from the light accepting end in both a radial and circumferential direction to redirect the light in to the light emitting portion. It is further preferred that light diffusing portions in the light redirecting portion comprise a plurality of substantially triangular cross section prisms extending substantially radially outwards along the light redirecting wall such that the prisms redirect light radially and circumferentially such that it enters the light emitting portion.

A preferred arrangement for the light guide is for the circumferential wall to extend substantially parallel with the first axis, for the first surface to extend substantially perpendicular to the first axis and for the light redirecting wall to extend at substantially 450 to the first axis. The thickness of the circumferential wall and depth of the light emitting portion adjacent the light redirecting portion are preferably substantially equal. S -6-

The invention further provides an instrument for an automobile, the instrument comprising an information bearing surface, a pointer, illumination means, pointer moving means, a circuit board and a light guide, the light guide being substantially as claimed in any preceding claim, wherein: the light guide, pointer moving means, and illumination means are arranged between the circuit board and information bearing surface, the pointer moving means and illumination means being electrically connected to the circuit board; the pointer is arranged on a side of the information bearing surface opposite the pointer moving means, the pointer being coupled to the pointer moving means such that the pointer can be moved by the pointer moving means; the light guide is arranged such that, in use, the light accepting portion can receives light from illumination means and emits received light from the light emitting portion to illuminate the information bearing surface, the information bearing surface including at least one translucent portion; and the circumferential wall of the light guide extends around the pointer moving means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a light guide; Figure 2 shows a cross section along the line A-A in Figure 1; Figure 3 shows a perspective view of a light guide including a detailed view of the light redirecting portion; Figure 4 shows a view of the underside of the light guide of Figure 1; and Figure 5 shows a view of a different embodiment of a light guide, the view being similar to that in Figure 3.

DETAILED DESCRIPTION

Figure 1 shows a light guide I having a light accepting portion 2, a light redirecting portion 4 and a light emitting portion 6.

The light accepting portion 2 comprises a substantially circumferential waIl 8 extending around a first axis 10. The circumferential waIl 8 has a first longitudinal end 12 for receiving light from a light source (not shown in this Figure) and is adapted to guide the light received to the light redirection portion 4 which is located at a second longitudinal end 14 opposite the first longitudinal end 12. The circumferential waIl 8 extends at a substantially constant angle relative to the direction of the first axis I 0.

The light emitting portion 6 including a first surface 16 through which the light received by the light receiving portion 2 is emitted and a second surface 18 adjacent the first surface 16 for guiding light through the first surface. The first surface 16 is substantially planar and extends transverse to the first axis 10. The light emitting portion 6 further including a substantially central connecting portion 20.

The light redirecting portion 4 is connected to the second longitudinal 14 end of the light accepting portion 2 and to the substantially central connecting portion 20 of the light emitting portion 6. The light redirecting portion 4 includes a light redirecting wall 22 extending transverse to the light accepting portion 8 and the light emitting portion 6. The light redirecting wall 22 extends at a substantially constant angle to the direction of the first axis 10. The light redirecting wall 22 is adapted to internally reflect and diffuse light from the light accepting portion 8 into the light emitting portion 6. Detail of the light redirecting wall 22 is shown more clearly in Figure 3.

Figure 2 shows cross section of the light guide along the line A-A in Figure 1, and also shows a printed circuit board 24 and light source 26. In this case the light source is an LED. Figure 2 further shows an appliqué, or information bearing element 28 which includes translucent portions for allowing light emitted by the light emitting portion to pass through the information bearing element 28 to create a backlight information display.

As can be seen from Figure 2, the circumferential wall 8 extends substantially parallel with the first axis 10, so at substantially 00 to the axis. The light emitting portion 6 extends substantially perpendicular to the first axis, so at substantially 900 to the axis. More particularly, it is the first surface 16 which extends substantially perpendicular to the first axis 10.

The light source 26 is located adjacent the light accepting end 12 of the light accepting portion 2 and emits light. The light accepting end 12 is shaped to form a lens 30 to focus light from the light source 26 so that it is directed along the circumferential wall 8 towards the second end 14. The circumferential wall 8 acts as a light guide and internally reflects substantially all of the light accepted from the light accepting end 12 through the second end 14 and into the light redirecting portion 4. The light redirecting portion 4 includes a light redirecting waIl 22 which is arranged at an angle to the circumferential wall 8 such that substantially all of the light entering the light redirecting portion from the light accepting portion and contacting the wall 22 will be redirected into the light emitting portion 6 through the substantially central connecting portion 20.

The redirected light entering the light emitting portion propagates in a radial direction and possibly also axially and/or circumferentially. The light propagates within the light emitting portion 6 until it is directed towards the first surface 16 at such an angle that the light is not totally internally reflected and at least some light escapes through the first surface to illuminate the appliqué 28. The light within the light emitting portion 6 may be redirected towards the first surface 16 by many different means, but in this case the second surface 18 is angled such that the distance between the first and second surfaces (16,18) decreases with increasing radial distance from the first axis 10. This reduction in depth of the light emitting portion will in itself result in at least some light being emitted from the first surface 16. However, the surface 18 includes deflection means 32 to enhance the light emission through the first surface. In this case the deflection means 32 are inwardly directed deformations in the second surface 18 which include a primary surface 34 angled to reflect the redirected light from the light redirection portion 4 towards the first surface 16. In this case the inwardly directed deformations extend substantially circumferentially and increase in frequency with increasing distance from the first axis to encourage an even intensity of light emission through the first surface 16.

Figure 3 shows a detailed view of the light redirecting wall 22 of the light redirecting portion 4. The light redirecting waIl 22 could be a smooth, substantially funnel shaped wall and this would have some diffusing ability. However, in this example the wall 22 includes diffusing means 36 which act to reflect light in a circumferential direction in addition to the radial direction. This helps to avoid hot-spots in the illumination from the first surface which may occur when discrete light sources such as LEDs or light bulbs are used.

The diffusion means 36 comprise a plurality of triangular prism shaped protrusions 38 from the light redirecting wall 22. The side waIls 40,42 of the prism shaped protrusions from the wall 22 act to reflect the light both radially and circumferentially into the light emitting portion 6. Between the protrusions 38 there may be plain portions 44 where the basic funnel substantially shaped wall 22 remains.

Figure 4 shows a different arrangement of deflection means 32' on the second surface. In this case, the deflection means 32' are in the form of arcs of white or other reflective paint extending around the first axis 10.

Figure 5 shows a cross section through a side of a different light guide 101. The figure again shows a printed circuit board 24 and light source 26. In this case the light source is an LED. Figure 5 also shows an appliqué, or information bearing element 28 which includes translucent portions for allowing light emitted by the light emitting portion to pass through the information bearing element 28 to create a backlight information display.

Features that are substantially the same as those shown and described in association with Figure 2 will be labelled with the same reference numerals.

Those features performing the same function, but in a different way will be labelled with numerals incremented by 100 from those of Figure 2.

The redirected light entering the light emitting portion 106 propagates in a radial direction and possibly also axially and/or circumferentially. The light propagates within the light emitting portion 106 until it is directed towards the first surface 16 at such an angle that the light is not totally internally reflected and at least some light escapes through the first surface to illuminate the appliqué 28. The second surface 118 is curved such that the distance between the first and second -Il -surfaces (16,118) decreases with increasing radial distance from the first axis 10 and the rate of that decrease also increases with distance from the axis 10. The redirected light contacts the second surface 118 and is redirected towards the first surface 16. In this case the second surface 118 also includes light diffusing means to diffuse the light and provide a substantially uniform illumination of the appliqué. The curved second surface 118 is roughened to give it a light scattering or diffusing property. In order to achieve a uniform illumination of the appliqué the degree of roughness is increased with increasing distance from the axis 10. When the light propagating in the emitting portion 106 meeting the roughened second surface 106 it is scattered and the result is that at least some light is emitted from the first surface 16. To roughen the surface of the second surface 118, mechanical or chemical methods can be employed such as treating the surface with sodium naphthalene or by laser etching techniques.

It should be understood that the invention has been described above by way of example only and that modifications in detail may be made without departing from the scope of the invention as described in the claims. -12-

Claims

CLAIMS

1. A light guide for illuminating an instrument, the light guide comprising a light accepting portion, a light redirecting portion and a light emitting portion, wherein: the light accepting portion comprises a substantially circumferential wall extending around a first axis and having a first longitudinal end for receiving light from a light source, the circumferential wall being adapted to guide the light received to the light redirection portion which is located at a second longitudinal end opposite the first longitudinal end, the circumferential wall extending at a substantially constant angle relative to the direction of the first axis; the light emitting portion including a first surface through which the light received by the light receiving portion is emitted and a second surface adjacent the first surface for guiding light through the first surface, the first surface being substantially planar and extending transverse to the first axis, the light emitting portion further including a substantially central connecting portion; the light redirecting portion being connected to the second longitudinal end of the light accepting portion and to the substantially central connecting portion of the light emitting portion, the light redirecting portion including a light redirecting wall extending transverse to the light accepting portion and the light emitting portion and being adapted to internally reflect and diffuse light from the light accepting portion into the light emitting portion.

2. A light guide as claimed in claim 1, in which circumferential wall extends substantially parallel with the first axis.

3. A light guide as claimed in claim 1 or claim 2, in which the light emitting portion extends substantially perpendicular to the first axis.

4. A light guide as claimed in any preceding claim, in which the light redirecting wall includes diffusion means.

5. A light guide as claimed in claim 4, in which the diffusion means comprise substantially triangular cross-section prisms on the light redirecting wall and extending substantially radially along the light redirecting wall.

6. A light guide as claimed in any preceding claim, in which the light guide is formed as an integral element from a material selected from a list composed of polycarbonate and PMMA.

7. An instrument for an automobile, the instrument comprising an information bearing surface, a pointer, illumination means, pointer moving means, a circuit board and a light guide, the light guide being substantially as claimed in any preceding claim, wherein: the light guide, pointer moving means, and illumination means are arranged between the circuit board and information bearing surface, the pointer moving means and illumination means being electrically connected to the circuit board; the pointer is arranged on a side of the information bearing surface opposite the pointer moving means, the pointer being coupled to the pointer moving means such that the pointer can be moved by the pointer moving means; the light guide is arranged such that, in use, the light accepting portion can receives light from illumination means and emits received light from the light emitting portion to illuminate the information bearing surface, the information bearing surface including at least one translucent portion; and the circumferential wall of the light guide extends around the pointer moving means.

8. A light guide substantially as herein described with reference to, or as shown in, the accompanying drawings.

9. An instrument substantially as herein described with reference to the accompanying drawings.