FR3021393A1 - LAMP FOR VEHICLE - Google Patents

Abstract

A vehicle lamp (1) has a two-dimensional image display device (14) and a projection lens group (20). The projection lens group (20) projects light from the two-dimensional image display device (14) toward the front of the lamp (1). The projection lens group (20) has a first lens (21) and a second lens (22). The first lens (21) is disposed on the side of the two-dimensional image display device. The second lens (22) is disposed on the image side of the first lens. A gap (23) is provided between the first lens (21) and the second lens (22). The Abbe number of the first lens (21) is different from that of the second lens (22).

Description

BACKGROUND Technical Field Examples of embodiments of the invention relate to a vehicle lamp and in particular a vehicle lamp provided with a two-dimensional image display device such as a MEMS mirror array (systems). MEMS).

Associated Technique A vehicle lamp is known, provided with a light source, of a MEMS mirror array which reflects light from the light source so as to control the distribution of light, and a lens of light. projection that projects forward light from the MEMS mirror array. In the vehicle lamp, a plurality of micro-mirrors provided in the MEMS mirror array are controlled to be individually turned on / off to form a desired light distribution pattern.

SUMMARY There is, however, a possibility for chromatic aberration to occur in the light distribution pattern formed in front of the lamp when an image provided by the two-dimensional image display device is projected by a lens optical system.

Exemplary embodiments of the invention have been made in view of the above circumstances and provide a technique for preventing chromatic aberration in a light distribution pattern formed by a vehicle lamp including a light-emitting device. two-dimensional image display. (1) According to an exemplary embodiment, a vehicle lamp comprises a two-dimensional image display device and a projection lens group. The projection lens group projects light from the two-dimensional image display device to the front of the lamp. The projection lens group includes a first lens and a second lens. The first lens is disposed on the side of the two-dimensional image display device. The second lens is disposed on the image side of the first lens. A gap is provided between the first lens and the second lens. The Abbe number of the first lens is different from that of the second lens. (2) In the vehicle lamp according to (1), the refractive index of the first lens may be greater than that of the second lens. (3) In the vehicle lamp according to any one of (1) to (2), the Abbe number of the first lens may be smaller than that of the second lens. (4) In the vehicle lamp according to (1), the space between the first lens and the second lens may be less than or equal to 24 mm on the optical axis. (5) In the vehicle lamp according to any one of (1) to (4), the incident surface and the emission surface of the first lens 15 and the incident surface and the emission surface of the second lens may be aspherical surfaces. (6) In the vehicle lamp according to (5), the ratio D / C may be greater than or equal to 0.5, where C represents the maximum radius of the emission surface of the first lens and D represents the thickness of the first lens on the optical axis. (7) In the vehicle lamp according to any of (1) to (4), the incident surface and the emission area of the first lens and the incident surface and the emission surface of the second lens may be freeform surfaces. The free-form surfaces 25 may be formed so that an image formed by the two-dimensional image display device is projected horizontally. (8) In the vehicle lamp according to (7), the ratio D / C may be greater than or equal to 0.75, where C represents the maximum radius of the emission surface of the first lens and D represents the thickness of the first lens on the optical axis. (9) In the vehicle lamp according to any one of (1) to (8), the two-dimensional image display device may include a plurality of micro-mirrors which are arrayed. 302 13 93 3 (10) In the vehicle lamp according to (9), the angles of inclination of the plurality of micromirrors with respect to the optical axis of the projection lens group can be controlled individually. (11) In the vehicle lamp according to any one of (1) to (10), the distance between the two-dimensional image display device and the projection lens group may be greater than or equal to 20 mm . (12) In the vehicle lamp according to any one of (1) to (11), the rear focus of the projection lens group may be located in the center of the imaging surface of the display device. two-dimensional image. With the above configuration, it is possible to prevent chromatic aberration of the light distribution pattern formed by a vehicle lamp including a two-dimensional image display device. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and its advantages will be better understood on reading the detailed description which follows. The description refers to the following drawings given by way of example. Figure 1 is a vertical sectional view showing the schematic structure of a vehicle lamp according to an exemplary embodiment of the invention; Figure 2 is a schematic vertical sectional view of a projection lens group of a first example; Fig. 3 shows tables respectively showing curvatures, conical constants, and aspheric coefficients from a first to a fourth surface of the projection lens group of the first example; Fig. 4 is a schematic vertical sectional view of a projection lens group of a second example; Fig. 5 shows tables respectively showing curvatures, conical constants, and aspheric coefficients from a first to a fourth surface of the projection lens group of the second example; Figs. 6A and 6B are views for explaining an exemplary pattern projected by the projection lens group of the first example; Fig. 7 is a schematic perspective view of a group of projection lenses of a third example; Fig. 8 is a schematic side view of the projection lens group of the third example; Fig. 9 is a schematic top view of the projection lens group of the third example; Fig. 10 is a schematic vertical sectional view of the projection lens group of the third example; Fig. 11 is a schematic horizontal sectional view of the projection lens group of the third example; Fig. 12 shows tables respectively showing free surface coefficients from a first to a fourth surface of the projection lens group of the third example; and Figs. 13A and 13B are views for explaining an exemplary pattern projected by the projection lens group of the third example of the invention. DETAILED DESCRIPTION A vehicle lamp according to exemplary embodiments of the invention will be described below in detail with reference to the accompanying drawings. The constituent components, elements and processing steps shown in each drawing and identical or equivalent to those of any other drawing are given the same reference symbols. On the other hand, their redundant description will be omitted. In addition, it will be appreciated that the exemplary embodiments do not limit the invention but are only examples. Any of the features described in the exemplary embodiments or any combination thereof is not always essential to the invention. Fig. 1 is a vertical sectional view showing the schematic structure of a vehicle lamp according to an exemplary embodiment of the invention. A vehicle lamp 1 according to this exemplary embodiment is, for example, a vehicle headlight provided with a pair of headlight units which are disposed to the left and right of the front side of a vehicle. The units of the pair of beacon units have substantially the same configuration except that they have symmetrical structures. Accordingly, the structure of one of the headlight units is shown in Fig. 1 as a vehicle lamp 1. The vehicle lamp 1 comprises a lamp body 2 and a transparent cover 4. The lamp body 2 is provided with an opening portion of the front side of the vehicle. The transparent cover 4 is attached to the vehicle lamp 2 so as to cover its opening part. The transparent cover 4 is made of resin, glass or the like having a light transmittance. A lamp chamber 3 is defined by the lamp body 2 and the transparent cover 4. A light source 10, a reflector 12, a two-dimensional image display device 14 and a projection lens group 20 are housed in the lamp chamber 3. The respective constituent components are fixed to the lamp body 2 by one or more support mechanisms (not shown). The light source 10 may be an LED, a semiconductor laser, a light bulb or the like. The light source 10 is arranged to emit light to the reflector 12. The reflector 12 has a curved reflection surface 12a. The reflector 12 reflects to the two-dimensional image display device 14 the light from the light source 10. It will be appreciated that the reflector 12 is not essential. Alternatively, the lamp 1 can be configured so that the light from the light source 10 is directly incident on the two-dimensional image display device 14. The two-dimensional image display device 14 of this example of Embodiment is a network of MEMS mirrors. In the two-dimensional image display device 14, a plurality of micromirrors are arranged in a network. Figure 1 shows three micro-mirrors 14a to 14c. In the following description, the micro-mirrors can be collectively called "micro-mirrors 14". Each micro-mirror 14 changes its tilt angle as a function of a control signal from a controller 60 so that the micro-mirror 14 can individually pass between the "ACTIVE state" and the the state NON AL i IF ". The ACTIVE state indicates a state in which the micromirror 14 reflects light from the reflector 12 to the projection lens group 20 located on the front portion of the lamp 1. The NON ALI IF state indicates a state in which the micro-mirror 14 reflects the light from the light source 10 so as not to reach the projection lens group 20. The two-dimensional image display device 14 can display a two-dimensional image by changing the angle In Fig. 1, for example, the micromirrors 14a and 14b are in the ACTIVE state. The light L1 and the light L2 are reflected towards the front part of the lamp 1 by the micro-mirrors 14a and 14b which are in the ACTIVE state. Then, the light L1 and the light L2 are incident on the projection lens group 20. The projection lens group 20 is arranged in the following manner. That is, the optical axis Ax of the projection lens group 20 is directed towards the front of the lamp 1. On the other hand, the rear focus of the projection lens 20 is centrally located. of the image forming surface of the two-dimensional image display device 14. The projection lens group 20 projects towards the front of the lamp 1 a two-dimensional image displayed by the two-dimensional image display device 20 14, as an inverted image. In this exemplary embodiment, the adjustment of the intensity of the light emitted by the light source 10 and the control of the tilt angle of each micromirror of the two-dimensional image display device 14 are performed by the controller 60. The controller 60 is implemented by (i) a hardware configuration including elements and / or circuits such as a CPU and a computer memory and / or (ii) a software configuration such as than a computer program. In FIG. 1, the controller 60 is provided outside the lamp chamber 3. Alternatively, the controller 60 may be provided within the lamp chamber 3. The controller 60 receives signals from the a light switch (not shown), an image processor 61 connected to an imaging device 62 and the like. The controller 60 transmits various control signals to the light source 10 and the two-dimensional image display device 14 in accordance with the received signals. The imaging device 62 is arranged to form an image (taken) in front of the lamp 1. The image processor 61 acquires the image data taken by the imaging device 62 and performs image processing on the image data. Thus, the image processor 61 specifies one or more vehicles, one or more pedestrians, one or more lane markings and the like included in the image data, and detects the position of the vehicle (s), pedestrian (s), track markings and the like. The technique for specifying the vehicle (s), pedestrian (s), lane mark (s) and the like and the technique for detecting their positions are well known. As a result, their detailed description will be omitted. Position information indicating the detected positions is transmitted to the controller 60. Using the position information, the controller 60 controls the inclination angles of the respective micromirrors 14 so that the two-dimensional image display device 14 form a desired two-dimensional image. The projection lens group 20 of the vehicle lamp 1 according to this exemplary embodiment will then be described in detail. The projection lens group 20 includes a first lens 21 and a second lens 22. The first lens 21 is disposed on the side of the two-dimensional image display device 14. The second lens 22 is disposed on the image side projected the first lens 21. The first lens 21 has an incident surface 21a and a transmission surface 21b. The second lens 22 has an incidence surface 22a and a transmission surface 22b. The bearing surface 21a of the first lens 21 is turned towards the two-dimensional image display device 14. The emission surface 21b of the first lens 21 is turned towards the bearing surface 22a of the second lens 22 The emitting surface 22b of the second lens 22 is directed forward of the lamp 1. In the vehicle lamp 1 according to this exemplary embodiment, the first lens 21 and the second lens 22 have a number of Abbe different from each other. The Abbe number indicates the dependence of the refractive index with respect to the wavelength. More specifically, the Abbe number of the first lens 21 is smaller than that of the second lens 22 (i.e., the dispersion of the first lens 21 is greater than that of the second lens 22). In addition, the first lens 21 has a refractive index different from that of the second lens 22. More specifically, the refractive index of the first lens 21 is greater than that of the second lens 22. In summary, the first lens 21 is made of a material whose refraction is relatively high and the dispersion is high, while the second lens 22 is made of a material whose refraction is relatively low and the dispersion is weak. For example, a polycarbonate resin with high refraction and high dispersion can be chosen as the material of the first lens 21 and an acrylic resin (PMMA) with low refraction and low dispersion can be selected as a material of the second lens 22. Alternatively, dense flint glass (eg, SF2) with high refraction and high dispersion may be selected as the material of the first lens 21 and the glass The glass pane (for example, BK7) with low refraction and low dispersion can be selected as the material of the second lens 22. In addition, a resin and glass can be selected at the same time. For example, a resin may be selected as the material of the first lens 21 while glass may be selected as the material of the second lens 22. Alternatively, glass may be selected as the material of the first 21, while a resin may be selected as a material of the second lens 22. In this way, in the vehicle lamp 1 according to this exemplary embodiment, the first lens 21 and the second lens 22 which have a different Abbe number from each other are used at the same time. Thus, the first lens 21 and the second lens 22 act to cancel the chromatic aberrations that are caused by the first lens 21 and the second lens 22. As a result, it is possible to prevent chromatic aberration in a pattern. light distribution which is projected towards the front of the lamp 1. On the other hand, in the vehicle lamp 1 according to this exemplary embodiment, a space 23 is provided between the first lens 21 and the second lens 22 Since the gap 23 is provided between the first lens 21 and the second lens 22, four surfaces can be provided as lens surfaces in the projection lens group 20. The four surfaces which are insured from This way, as lens surfaces, improves the degree of design freedom of a lens optical system with respect to the case where the first lens and the second lens are conducted in contact with each other (the number of lens surfaces is substantially three). In the description which follows, the incident surface 21a, the emission surface 21b, the incidence surface 22a and the emission surface 22b can be respectively called "first surface" 21a, "second surface" 21b, " third surface 22a and fourth surface 22b. Further, in the vehicle lamp 1 according to this exemplary embodiment, the two-dimensional image display device 14 and the projection lens group 20 are separated from each other by a greater distance or equal to a predetermined distance (for example 20 mm). Since the two-dimensional image display device 14 and the projection lens group 20 are separated in this manner, the light reflected by the reflector 12 can be incidentally incident on the two-dimensional image display device 14. Examples of the projection lens group 20 will be described below. (First example) Fig. 2 is a schematic vertical sectional view of a projection lens group 20 of a first example. The projection lens group 20 of the first example is configured to project an image formed by the two-dimensional image display device 14 to the front of the lamp 1 while maintaining the aspect ratio of the image as is. The first to the fourth surface of the projection lens group 20 of the first example are defined by the following aspheric equation (1) Cr 2 z + 2 + 2 + 2 + 2 + 4 + 1 + 1 + -0- (1+ k) c2r2 Here, r represents the distance from the optical axis Ax, c represents a curvature, k is a conical constant and ai, a2, ... are aspheric coefficients. FIG. 3 shows the curvatures c, the conical constants k and the aspherical coefficients al to a5 respectively from the first to the fourth surface of the projection lens group 20 of the first example. In the equation above, we consider r up to the end of order 10. As a variant, higher order terms (greater than the 10th order) can also be added thereto.

In the projection lens group 20 of the first example, the ratio D / C is equal to 0.9334, where C is the maximum radius of the emission surface (second surface) 21b of the first lens 21 and D is 1 thickness of the first lens 21 on the optical axis Ax. In the projection lens group 20 of the first example, the ratio between the deviation of the focus position between a Fraunhofer F line (486 nm) and a Fraunhofer C line (656 nm) and the focal length is about 0.07%. In a single lens of this type, this ratio is in a range of 1.5% to 2 ° h. It will be understood, therefore, that chromatic aberration can be prevented in the first example. (Second example) Fig. 4 is a schematic vertical sectional view of a projection lens group 20 of a second example. The projection lens group 20 of the second example is also configured to project an image formed by the two-dimensional image display unit 14 toward the front of the lamp 1 while maintaining the aspect ratio of the image as what. The first to the fourth surface of the projection lens group 20 of the second example are also defined by the above-mentioned aspheric equation (1). Fig. 5 shows respectively the curvatures c, the conical constants k and the aspherical coefficients ai to a5 from the first to the fourth surface of the projection lens group 20 of the second example. In the projection lens group 20 of the second example, the ratio D / C is equal to 0.8177, where C is the maximum radius of the emission surface (second surface) 21b of the first lens 21 and D is 1 thickness of the first lens 21 on the optical axis Ax. In the projection lens group 20 of the second example, the ratio of the focus position difference between a Fraunhofer F line (486 nm) and a Fraunhofer C line (656 nm) and the focal length is about 0.07%. It will be understood, therefore, that chromatic aberration can also be prevented in the second example. When the first to the fourth surface of the projection lens group 20 is defined by the aspherical equation (1), as in the above-mentioned first and second examples, it is preferable that the D / C ratio be greater than or equal to 0.5, where C represents the maximum radius of the second surface 21b and D represents the thickness of the first lens 21 on the optical axis Ax. Fig. 6A and Fig. 6B are views for explaining exemplary patterns projected by the projection lens group 20 of the first example. Figure 6A shows a checkerboard pattern projected by a single projection lens of a comparative example. Figure 6B shows a checkerboard pattern projected by the projection lens group 20 of the first example. It will be understood that an aberration occurs in the projected pattern of the Comparative Example, thus blurring the checkered pattern shown in FIG. 6A. It can be seen on the other hand that an aberration is suppressed in the projected pattern of the first example, so that the checker pattern can be projected sharply as shown in Figure 6B. (Third example) Fig. 7 is a schematic perspective view of a projection lens group 20 of a third example. Fig. 8 is a schematic side view of the projection lens group 20 of the third example. Fig. 9 is a schematic top view of the projection lens group 20 of the third example. Fig. 10 is a schematic vertical sectional view of the projection lens group 20 of the third example. Fig. 11 is a schematic horizontal sectional view of the projection lens group 20 of the third example. The projection lens group 20 of the third example is configured to project an image formed by the two-dimensional image display device 14 in front of the lamp by changing the aspect ratio of the image. Each surface from the first to the fourth surface of the projection lens group 20 of the third example is a free-form surface which is formed so that an image formed by the two-dimensional image display device 14 can be projected from 302 13 93 12 so as to be deployed horizontally. The first to the fourth surface are defined by the following free-form surface equation (2). Z = a2 + 2y2 + 5 + a3X4 + a4X2y2 + a5y4 ^ a6X6 + a7X4y2 + a8X2y4 + agy6 + a1e8 + aix6y2 + a12X4y4 + ai3X2y6 + a4y8 + a18X10 + aie8y2 + arX6y4 + a18X4y6 + ai9X2y8 + a20Y10 (2) Here, a1, a2 , ... represent free surface coefficients. Figure 12 shows respectively the free form spherical coefficients α1 to α20 from the first to the fourth surface of the projection lens group 20 of the third example. In the freeform surface equation (2) above, x and y are considered up to the terms of order 10. Alternatively, higher order terms of x and y can be added thereto. In the projection lens group 20 of the third example, the ratio D / C is 0.082, where C is the maximum radius of the emission surface (second surface) 21b of the first lens 21 and D is the thickness of the first lens 21 on the optical axis Ax. When the first to the fourth surface of the projection lens group 20 is defined by the freeform surface equation (2) as in the third example, it is preferable that the D / C ratio be greater than or equal to 0.75, where C represents the maximum radius of the second surface 21b and D represents the thickness of the first lens 21 on the optical axis. In the projection lens group 20 of the third example, the ratio of the deviation of the focus position between a Fraunhofer F line (486 nm) and a Fraunhofer C line (656 nm) and the focal length is about 0.13%. It will be understood, therefore, that chromatic aberration can also be prevented in the third example. Figs. 13A and 13B are views for explaining exemplary patterns projected by the projection lens group 20 of the third example. Figure 13A shows a checkerboard pattern projected by a single projection lens of a comparative example. Figure 302 13 93 13 13B shows a checkerboard pattern projected by the projection lens group 20 of the third example. It will be understood that an aberration occurs in the projected pattern of the Comparative Example, thereby blurring the checkered pattern shown in Fig. 13A. On the other hand, it will be understood that an aberration is suppressed in the projected pattern of the third example so that the checker pattern can be projected sharply as shown in Fig. 13B. In addition, it will also be understood that the checkerboard pattern is projected to be horizontally deployed in the projected pattern of the third example.

MEMS mirror arrays often have a shape ratio of 4: 3 or 16: 9. When an array of MEMS mirrors having such a shape ratio is used in a vehicle lamp which forms a light distribution pattern whose lateral length is considerably longer than its longitudinal length, portions of micro-mirrors belonging to the MEMS mirror array can not be used to form the pattern but are lost. However, when an image formed by the two-dimensional image display device 14 is projected by the projection lens group 20 of the third example, by being horizontally deployed, all the micro-mirrors of the MEMS mirror array can be actually used to form the pattern. The invention has been described based on the exemplary embodiments and examples. These embodiments and examples are merely examples. Those skilled in the art will understand that various modifications may be made to the combination of constituent components or to the combination of processing steps and that such modifications must also be included within the scope of the invention. For example, a MEMS mirror array provided with a plurality of micro-mirrors is illustrated as a two-dimensional image display device in the above exemplary embodiment by way of example. The two-dimensional image display device is not limited to the MEMS mirror array. The two-dimensional image display device may be, for example, a diffraction-type MEMS array provided with a plurality of moving ribbons, a liquid crystal panel, or the like.

Claims (12)

REVENDICATIONS1. A vehicle lamp (1) characterized in that it comprises: a two-dimensional image display device (14); and a projection lens group (20) which projects light from the two-dimensional image display device (14) to the front of the lamp (1), wherein the projection lens group (20) comprises a first lens (21) which is disposed on the side of the two-dimensional image display device, and a second lens (22) which is arranged on the image side of the first lens (21), a gap (23) is provided between the first lens (21) and the second lens (22), and the Abbe number of the first lens (21) is different from that of the second lens (22). The vehicle lamp (1) according to claim 1, wherein the refractive index of the first lens (21) is greater than that of the second lens (22). The vehicle lamp (1) according to any one of claims 1 to 2, wherein the Abbe number of the first lens (21) is smaller than that of the second lens (22). 4. Vehicle lamp (1) according to claim 1, wherein the space (23) between the first lens (21) and the second lens (22) is less than or equal to 24 mm on the optical axis (Ax). . The vehicle lamp (1) according to any one of claims 1 to 4, wherein the incident surface (21a) and the emission surface (21b) of the first lens (21) and the surface of incidence (22a) and the emission surface (22b) of the second lens (22) are aspherical surfaces. The vehicle lamp (1) according to claim 5, wherein the D / C ratio is greater than or equal to 0.5, where C represents the maximum radius of the emission surface (21b) of the first lens (21). ) and D represents the thickness of the first lens (21) on the optical axis (Ax). Vehicle lamp (1) according to any one of claims 1 to 4, in whichthe incident surface (21a) and the emission surface (21b) of the first lens (21) and the incident surface (22a) and the emission surface (22b) of the second lens (22) are free-form surfaces, and the free-form surfaces are formed such that an image formed by the image display device two-dimensional is projected horizontally. The vehicle lamp (1) according to claim 7, wherein the D / C ratio is greater than or equal to 0.75, where C represents the maximum radius of the emission surface (21b) of the first lens (21). ) and D represents the thickness of the first lens (21) on the optical axis (Ax). The vehicle lamp (1) according to any one of claims 1 to 8, wherein the two-dimensional image display device (14) comprises a plurality of micro-mirrors (14a to 14c) which are arranged in network. The vehicle lamp (1) according to claim 9, wherein the angles of inclination of the plurality of micromirrors (14a to 14c) with respect to the optical axis (Ax) of the projection lens group (20) ) are ordered individually. 20 The vehicle lamp (1) according to any one of claims 1 to 10, wherein the distance between the two-dimensional image display device (14) and the projection lens group (20) is greater than or equal to at 20 mm. The vehicle lamp (1) according to any one of claims 1 to 11, wherein the rear focus of the projection lens group (20) is located at the center of the imaging surface of the device. two-dimensional image display (14).