GB2240390A

GB2240390A - Lamp arrangement for for motor vehicle

Info

Publication number: GB2240390A
Application number: GB9101948A
Authority: GB
Inventors: Masayuki Hori
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1990-01-30
Filing date: 1991-01-30
Publication date: 1991-07-31
Anticipated expiration: 2011-01-30
Also published as: DE4102571A1; DE4102571C2; GB2240390B; GB9101948D0; JPH03224837A; JP2808780B2

Abstract

A light source 4 including a plurality of bulbs 4a is arranged in a rear shelf panel, and a transmission hologram 10 is mounted inside the rear window 1. The hologram 10 comprises divisions 10a-10i which have different diffraction characteristics from each other. Almost all incident light rays from the source 4 are diffracted in a given direction rearwards of the vehicle. <IMAGE>

Description

a C - t; 0: i3 0 2-7- LAMP ARRANGEMENT FOR MOTOR VEHICLE The present

invention relates to a lamp arrangement for a motor vehicle and, more particularly, to one using a hologram.

A lamp arrangement for a motor vehicle is disclosed, for example, in JP-U 2-74243. Referring to Figures 8 and 9, a description will be made with regard to such a lamp arrangement which serves as a high mounted stop lamp to be lighted when a brake switch is turned on.

Referring to Figure 8, the lamp arrangement is at the rear of a cabin of a motor vehicle 2 and includes a transmission hologram 3 mounted on the cabin side of a rear window 1 and a light source 4 built into a rear shelf panel 6 located behind a rear seat. Light rays 5a from the light source 4 are diffracted by the hologram 3 rearwards of the vehicle 2, thus obtaining diffracted light rays 5b. In that manner, the lamp arrangement functions as a high mounted stop lamp.

It is well known that the transmission hologram 3 is formed by recording interference fringes of a coherent laser light and that the condition of diffraction of the hologram 3 upon mounting depends on the incidence angle of the laser light upon exposure.

Referring to Figure 9, there is shown an exposure system as used in JP-U 2-74243. In Figure 9, each of two spatial filters 13a and 13b is arranged for diverging a laser beam L and each of two collimating lenses 12a and 12b is arranged for making the laser beam L diverged by the spatial filter 13a or 13b into a parallel beam 11a or 11b, respectively. By exposing a unexposed hologram 30 to the two laser beams 11a and 11b, the interference fringes are recorded in the hologram 30 so as to diffract the incident light rays from the light source 4 in a direction with a predetermined angle of diffraction. It is to be noted that the parallel laser beam 11a corresponds to the incident light rays 5a from the light source 4 upon mounting and that the parallel laser beam 11b corresponds to the light rays 5b diffracted in a cl predetermined direction by the hologram 3 upon mounting. Thus, upon mounting, the hologram 3 diffracts the incident light rays 5a from the light source 4 in the direction with a predetermined angle of diffraction, obtaining the diffracted light rays 5b.

Referring to Figure 10a, there is shown a fragmentary view of the known exposure system as shown in Figure 9. As shown in Figure 10a, the unexposed hologram 30 is exposed to laser beams 11a and 11b each of which is a parallel beam. Accordingly, also upon mounting, the hologram 3 needs to receive parallel incident light rays 5a from the light source 4 as shown in Figure 10b. Thus, in the event, a plurality of bulbs 4a constitute the light source 4 so as to emit the parallel rays.

In that event, for obtaining parallel light rays from the plurality of bulbs 4a, a lens system comprising a collimating lens or the like (not shown) should be provided for each bulb 4a. This results in the inconvenience that the light source 4 is bulky.

The lens system may be omitted, but without it there arises the inconvenience that each bulb 4a emits non-parallel and useless rays 7 as indicated by dotted lines in Figure 10b. These rays 7, not corresponding to the condition of diffraction of the hologram 3, are not diffracted by it.

On the other hand, for avoiding the aforementioned inconveniences, an exposure system using a divergent laser beam as shown in Figure 11a can be used. In this exposure system, a divergent laser beam 11c corresponds to the incident light rays 5a from the light source upon mounting. The unexposed hologram 30 is exposed to the divergent laser beam 11c and the parallel laser beam 11b, and, upon mounting, a single bulb 4a serves as the light source as shown in Figure 11b. In that event, there arises the inconvenience that the amount of light is not sufficient, owing to the use of only one bulb 4a.

In order to compensate for the insufficient amount of light, the bulb 4a may be enlarged in size. This is not possible c without limit, however. Additionally, when such a point light source or bulb 4a is used, it is necessary to adjust the position of the laser beam source upon exposure to that of the point light source upon reconstruction, requiring mounting accuracy of the point light source or bulb 4a, thereby complicating the mounting operation thereof.

What is desired is a lamp arrangement for a motor vehicle which is capable of efficiently diffracting incident light from a light source, and is easily applicable to the motor vehicle without enlarging the size of a light source apparatus.

The present invention provides a lamp arrangement comprising a light source (e.g. arranged in a rear shelf panel) for emitting light rays in different directions, the light source having a predetermined area, and a transmission hologram on a rear window of the vehicle, the transmission hologram including a plurality of divisions having different diffraction characteristics from each other to diffract different incident light rays from the light source in a predetermined direction.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a motor vehicle with a lamp arrangement in a preferred embodiment according to the present invention; Figure 2 is a fragmentary sectional view taken along the line II-II of Figure 1; Figure 3a is a schematic view when exposing divisions 10a,10b, and 10c of an unexposed hologram; Figure 3b is a view similar to Figure 3a, when exposing divisions 10d,10e, and 10f of the unexposed hologram; Figure 3c is a view similar to Figure 3b, when exposing divisions 10g,10h, and 101 of the unexposed hologram; Figure 4 is a lighting circuit diagram for the preferred embodiment; Figure 5 is a view similar to Figure 2, illustrating the operation of the preferred embodiment; cl Figure 6a is a view similar to Figure 3c, illustrating a case where an unexposed hologram with divisions is exposed; Figure 6b is an enlarged fragmentary view illustrating a region A of Figure 6a; Figure 7a is a view similar to Figure 6a, illustrating a case where an unexposed hologram without divisions is exposed; Figure 7b is a view similar to Figure 6b, illustrating a region B of Figure 7a; Figure 8 is a schematic view illustrating a known lamp arrangement for a motor vehicle; Figure 9 is a view similar to Figure 3a, illustrating a known exposure system of the hologram; Figure 10a is a fragmentary view of Figure 9; Figure 10b is a view similar to Figure 5, illustrating the operation upon mounting without a lens system of collimating lens; Figure 11a is a view similar to Figure 10a, illustrating another known exposure system using a divergent laser beam; and Figure 11b is a view similar to Figure 10b, illustrating the operation upon mounting when the hologram receives incident light from a point light source.

Referring to the accompanying drawings, a preferred embodiment according to the present invention will be described. It is to be noted that the same reference numerals are given to the same elements as described in connection with Figures 8 11b.

Referring to Figure 1, a lamp arrangement 20 in a motor vehicle 2 serves as a high mounted stop lamp to be lighted when brake switch 21 (Figure 4) is turned on. This lamp arrangement 20 includes a transmission hologram 10 which is mounted on the inside of a rear window lof the vehicle 2, and a light source 4 which is built into a rear shelf panel (not shown) located behind a rear seat in a cabin. Referring also to Figure 2, light rays 5c from the light source 4 are diffracted by the hologram 10 p C, rearwards of the vehicle 2, obtaining diffracted light rays 5d. In that manner, the lamp arrangement 20 functions as a high mounted stop lamp.

Referring to Figure 2, the light source 4 includes a plurality of bulbs 4a. However, since no lens system for producing parallel rays is provided for the bulbs 4a, each bulb 4a emits the light rays 5c in different directions. Under these conditions, the light source 4 is considered to form a surface light source as a whole.

Referring again to Figure 1, in this embodiment, the hologram 10 includes nine divisions 10a - 10i which are obtained by separately exposing the corresponding divisions of an unexposed hologram 100 as will be described hereinafter, and which have different diffraction characteristics.

Referring to Figures 3a - 3c, an exposure system for exposing the divisions 10a - 10i of the unexposed hologram 100 will be described. Figure 3a shows a case where the division 10a,10b, or 10c is exposed. Figure 3b shows a case where the division 10d,10e or 10f is exposed; and Figure 3c shows a case where the division 10g,10h, or 10i is exposed.

Referring to Figure 3a, when exposing the division 10a, for example, the unexposed hologram 100 is covered with a mask 14 except the division 10a. Then, from the direction of the light source 4 upon mounting,the division 10a is irradiated with a convergent laser beam 11d through a spatial filter 13a and a converging lens 112a. On the other hand, from a direction parallel to the desired direction of the diffracted light rays 5d, the division 10a is irradiated with a parallel laser beam 11b through a spatial filter 13b and a collimating lens 12b (in a similar manner to Figure 9).

Similarly, when exposing the division 10b (or 10c), the unexposed hologram 100 is covered with the mask 14 except the division 10b (or 10c). Then, from the direction of the light source 4 upon mounting, the division 10b (or 10c) is irradiated C 6 - with the convergent laser beam 11d through the spatial filter 13a and the converging lens 112a. On the other hand, from the direction parallel to the desired direction of the diffracted light rays 5d, the division 10b (or 10c) is irradiated with the parallel laser beam 11b through the spatial filter 13b and the collimating lens 12b (in a similar manner to Figure 9).

Referring to Figures 3b and 3c, when exposing the division 10d,10e, or 10f, and the division 10g,10h, or 10i, the method of exposure is substantially identical to that when exposing the division 10a, 10b, or 10c.

It is to be noted that the division 10a - 10j need not be separately exposed, but may be collectively exposed. That is, the divisions 10a,10b, and 10e may be exposed en bloc, for example.

As described hereinbefore, the light source 4 is considered to form a surface light source as a whole. Thus, at a surface or the converging lens 112a, a diameter H of the convergent laser beam 11d is so established as to be substantially identical to the width of the light source 4 in the longitudinal direction of the vehicle 2.

Referring to Figure 4, there is shown a lighting circuit for a lamp arrangement for a motor vehicle 20 or high mounted stop lamp, with a battery 24. When the brake switch 21 is ON, a relay 22 is turned on. And, with an ordinary brake lamp 23, the lamp arrangement 20 is turned on, only one of its bulbs being shown in Figure 4.

Next, the operation of this embodiment will be described.

As described above in connection with Figures 3a - 3c, each of the divisions 10a - 10i of the unexposed hologram 100 is exposed to the convergent laser beam 11d from the direction of the light source 4 upon mounting, thus obtaining the hologram 10. Accordingly, each of the divisions 10a - 10i of the hologram 10 satisfies the condition of diffraction relative to the incident light rays 5c from the light source 4. As a result, almost all C, the incident light rays 5C from the light source 4 are diffracted by any of the divisions 10a - 10i as shown in Figure 5. If consideration is made on the side of the light source 4, the light rays from any point of the light source 4 are diffracted when falling on the hologram 10.

This enhances utilization efficiency of light and brightness of display without increasing the size of the light source 4 or the current passing therethrough.

Referring to Figures 6a - 7b, a description will be made with regard to the difference between a case where the unexposed hologram 100 with a plurality of divisions is exposed, as described above, and a case where the unexposed hologram 100 is exposed as a single unit, i.e. without being divided into divisions.

Referring to Figure 6a, there is shown a case where an unexposed hologram 100 with divisions is exposed. By way of example, an exposure state of the unexposed hologram 100 at a region A of Figure 6a will be considered. Referring to Figure 6b, since the unexposed hologram 100 is exposed to only two laser light rays 11D and 11B, a single diffraction grating will be formed at the point A. Accordingly, upon monitoring, the incident light rays 5c from the light source 4 are diffracted efficiently by the single diffraction grating in a direction with a predetermined angle of diffraction.

Referring to Figure 7a, there is shown a case where an unexposed hologram 100 without divisions is exposed. By way of example, an exposure state of the unexposed hologram 100 at a region B of Figure 7a will be considered. Referring to Figure 7b, since a plurality of laser light rays 11D1, 11D 2' and 11D 3' which have different incidence angles from each other come from a direction of the light source 4 upon mounting, the number of diffraction gratings formed in the unexposed hologram 100 will be increased. Accordingly, diffraction efficiency at the region B is deteriorated in accordance with the increase in number of the different gratings formed,-resulting in a decrease in brightness of display.

In the embodiment described, the unexposed hologram 100 is divided into the divisions 10a - 10i, and separately exposed to the convergent laser beam 11d from the direction of the light source 4 upon mounting, thus obtaining the hologram 10. As a result, the hologram 10 can diffract almost all the incident light rays 5c from the light source 4, resulting in the effective use of light from the light source 4, and an increase in the amount of light from the lamp arrangement 20, with decreased power of the light source 4.

The wavelength and incidence angle of the laser light for exposure and of the light for reconstruction or display may not necessarily be identical, but may be changeable on condition that the Bragg condition is satisfied.

Claims

Claims:

1. A lamp arrangement in a motor vehicle, comprising: a light source for emitting light rays in different directions, the light source having a predetermined area; and a transmission hologram on a rear window of the vehicle, the transmission hologram including a plurality of divisions having different diffraction characteristics from each other to diffract different incident light rays from the light source in a predetermined direction.

2. A lamp arrangement as claimed in claim 1, in which the divisions of the transmission hologram have been separately exposed to different convergent laser beams as well as a single parallel laser beam.

3. A lamp arrangement as claimed in claim 2, in which each convergent laser beam came from the direction of the light source relative to the hologram.

4. A lamp arrangement as claimed in any preceding claim, in which the light source is mounted in a rear shelf panel.

5. A lamp arrangement as claimed in any preceding claim, in which the light source comprises a plurality of bulbs.

6. A lamp arrangement substantially as described with reference to, and as shown in, Figures 1 to 5 of the accompanying drawings.

Published 1991 at The Patent Office. State House, 66/71 High Holborn. LA)ndonWC I R47P. Further copies maybe obtained from Sales Branch, Unit 6. Nine Mile PoinL Cwrnfelinfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St MaTy Cmy. Kent-