Automotive projector-type headlamp

Abstract: The inner reflecting surface of the concave mirror (10) of the projector-type headlamp is composed of a central spherical area (5) and a composite ellipsoidal surface of revolution (E) formed by parts of a plurality of different ellipsoidal surfaces of revo­ lution, smoothly joined to each other for junction with the central spherical area (S), having a common focus at the center (O) of the spherical area and other foci (F), respectively, at positions spaced ahead of a predetermined distance from the common focus. The lamp bulb (12) is so disposed so as to have the center thereof located near the common focus (O), and the convex lens (14) is so dis­ posed as to have the focus thereof located near the common focus (O). The ellipsoidal surfaces of revolution (E) are so shaped geometrically as to reflect in directions toward their respec­ tive other foci (F) the rays emitted from the lamp bulb (12) and inci­ dent upon the ellipsoidal surfaces of revolution (E), and the convex lens (14) is so designed as to have the focus thereof located near the common focus (O) of the ellipsoidal surfaces of revolution (E) at which the lamp bulb (12) is located. Thereby, it is possible to decrease the total length of the optical system, design compact the entire structure of the projector-type headlamp and in­ crease the effective solid angle of the rays emitted from the lamp bulb, thereby permitting to utilize the rays from the lamp bulb to full extent for definition of a predetermined luminous intensity distribution pattern.

Description: The present invention relates to a projector-type headlamp, comprising a concave mirror having an inner reflecting surface with a central spherical surface at an area near the apex, a lamp bulb as light source having the center thereof disposed nearly coincident with the center of the spherical surface of the concave mirror, and a convex lens so disposed as to have the optical axis and focal point thereof nearly coincident with the axis of the concave mirror and the center of the spherical surface of the concave mirror, respectively. A projector-type headlamp is basically composed of a concave mirror, a lamp bulb disposed as light source near the focus of the concave mirror and a convex lens disposed in front of the concave mirror. Projector-type headlamps have so far been proposed of which the concave mirrors are different from one another in geometrical shape of the inner reflecting surface. Fig. 1 schematically shows the optical system of a typical conventional projector-type headlamp composed of a concave mirror 1 of which the inner reflecting surface is an ellipsoidal surface of revolution and which has an optical axis Z passing through the apex thereof, a lamp bulb 3 of which the filament center is disposed near the first focus F1' of the concave mirror 1, and a convex lens 2 of which the focus is so disposed as to be nearly coincident with the second focus F2' of the concave mirror 1. Such optical system is so configured that the light rays emitted from the first focus F1' and reflected at the concave mirror 1 (of which the inner reflecting surface is an ellipsoidal surface of revolution) are converged at the second focus F2'. Since the second focus F2' is so disposed as to be nearly coincident with the focus of the convex lens 2, the rays incident upon the convex lens 2 are so refracted by the latter as to be projected ahead nearly parallelly to the optical axis as indicated with the arrows a and a'. In case of a headlamp having the concave mirror 1 of which the inner reflecting surface is an ellipsoidal surface of revolution, the distance L between the apex of the concave mirror and the front face of the convex lens must be kept relatively long. Hence, it is inavoidable that the headlamp is of a structure horizontally long as a whole. The installation of a headlamp of this type in the body of a car needs a relatively large space. Namely, the installability of such headlamp to a car body is not good. To solve the problem of the headlamp using a concave mirror shown in Fig. 1, or to overcome the poor installability of the headlamp to a car body due to the horizontally long structure thereof, a projector-type headlamp has been proposed as disclosed in JP 63-66801 (Publication No.). Fig. 2 schematically shows the optical system of the proposed headlamp. This headlamp comprises a concave mirror 4 of which the inner reflecting surface is spherical, a lamp bulb 3 of which the filament center is disposed near the center O of the concave mirror 4, and a convex lens 2 disposed in front of the concave mirror 4 and having the focus thereof disposed near the center of the concave mirror 4. The light rays emitted from the lamp bulb 3 and reflected by the concave or spherical mirror 4 pass again near the center O of the spherical mirror 4, then are incident upon the convex lens 2, refracted by the latter and projected forward nearly parallelly to the optical axis Z as indicated with the arrows b and b′. The rays emitted from the light source or lamp bulb 3 and incident directly upon the convex lens 2 are similarly refracted by the latter and projected ahead nearly parallelly to the optical axis Z as indicated with the arrows b and b′. In the headlamp with the concave mirror 4 of which the inner reflecting surface is spherical, the solid angle 1′ of viewing from the light source 3 the circumference of the spherical mirror 4 and the solid angle ϑ2′ of viewing from the light source 3 the circumference of the convex lens 2 are so set as to be equal to each other. However, it is difficult to design the headlamp for larger solid angles ϑ1′ and ϑ2′, and the rays cannot be utilized effectively. Further, in this headlamp, the nearly parallel rays (indicated with the arrows b and b′) from the convex lens 2 should be appropriately diverged as in case of the optical system using the convex mirror as shown in Fig. 1. For this purpose, an outer lens (not shown) should be provided in front of the convex lens 2 to diverge the rays or the convex lens 2 should be a special deformed one. In addition, the rays reflected by the spherical mirror 4 and traveling toward the convex lens 2 are intercepted in a rather large amount by the light source 3 disposed near the center of the spherical surface. EP-A-0 254 746 shows a projector-type headlamp provided with a concave mirror composed of a composite ellipsoidal surface of revolution. A projector-type headlamp according to EP-A-0 225 313 is provided with a concave mirror having an inner reflecting surface with a central spherical surface and a convex lens so disposed as to have the optical axis and focal point thereof nearly coincident with the axis of the concave mirror and the centre of the spherical surface of the concave mirror. Though a parabolic projector having a spherical surface is provided, only the light rays reflected on this spherical surface will incident upon the convex lens and the light rays reflected on the parabolic refelector are directed to the outer lens to be diverged. That means effective utilisation of the light rays emitted from the light bulb is not attainable without providing the outer lens. It is therefore an object of the present invention to provide a projector-type headlamp in which the light rays are effectively utilised and the use of a further lens to diverge said light rays is avoided. This object is achieved according to the present invention by improving the projector-type headlamp as indicated in the preamble portion of claim 1 in that a composite ellipsoidal surface of revolution is formed by parts of a plurality of different ellipsoidal surfaces of revolution smoothly joined to each other for junction with the central spherical surface, each of the ellipsoidal surfaces being joined to the other adjoining ellipsoidal surface in a vertical plane parallel to the vertical plane in which the optical axis lies to provide horizontally elongated profile of the concave mirror and, in that said different ellipsoidal surfaces have a common focus at the center of the spherical surface and other foci at different positions on the axis of the concave mirror each spaced a predetermined distance from the common focus toward the convex lens. The light rays emitted from the lamp bulb and incident upon each of the ellipsoidal surfaces of revolution are reflected in directions toward the other focus. The rays thus reflected by the ellipsoidal surfaces of revolution are refracted in different directions by the convex lens which permits to diverge the light rays in different horizontal directions, to define in the luminous intensity distribution pattern a horizontally long illuminated area extending horizontally from the center of the pattern. The rays emitted from the lamp bulb and incident directly upon the convex lens and those emitted from the lamp bulb, reflected at the central spherical area of the concave mirror and then incident upon the convex lens are refracted in directions nearly parallel to the optical axis to define in the luminous intensity distribution pattern a relatively high luminous intensity area near the center of the pattern. The shape of the luminous intensity distribution pattern, especially, the shape of the horizontally long illuminated area extending horizontally from the central area, depends upon the horizontal light convergence by each of the ellipsoidal surfaces of revolution. Therefore, the rays emitted from the lamp bulb are effectively utilized to form a desired luminous intensity distribution pattern ahead of the convex lens. Since the focus of the convex lens is disposed near the common focus of the ellipsoidal surfaces of revolution at which the lamp bulb is disposed, the length of the entire optical system can be reduced, and thus the entire structure of the projector-type headlamp can be compact. Preferred embodiments of the present invention are set out in the appended subclaims. Hereinafter, the present invention is illustrated and explained in greater detail by two embodiments in conjunction with the accompanying drawings, in which Fig. 1 is a schematic explanatory drawing of the optical system of a conventional projector-type headlamp using a single ellipsoidal surface of revolution as concave mirror; Fig. 2 is an explanatory schematic drawing of the optical system of another conventional projector-type headlamp proposed to overcome the drawbacks of the optical system shown in Fig. 1, in which a single spherical surface is used as concave mirror; Fig. 3 is a schematic drawing of the optical system in one embodiment of the projector-type headlamp according to the present invention, the concave mirror being illustrated in a horizontal sectional view; Fig. 4 is a schematic perspective view of the concave mirror shown in Fig. 3; Fig. 5 is a drawing explaining the reflecting characteristics of a plurality of different ellipsoidal surfaces of revolution forming the concave mirror shown in Fig. 3; Fig. 6 is a schematic diagram of a luminous intensity distribution pattern defined as projected from the optical system shown in Fig. 3 onto a screen disposed in front of the convex lens; Fig. 7 is a schematic diagram of the optical system of another embodiment of the projector-type headlamp according to the present invention; and Fig. 8 is a schematic perspective view of the concave mirror shown in Fig. 7. Referring now to Figs. 3 to 6, one embodiment of the projector-type headlamp according to the present invention will be described. Fig. 3 shows the optical system of the projector-type headlamp, comprising a concave mirror 10, a lamp bulb 12 as light source disposed on the optical axis Z-Z of the concave mirror 10, and a convex lens 14 disposed in front of the lamp bulb 12 and having the optical axis thereof disposed nearly coincident with the optical axis Z-Z of the concave mirror 10. The concave mirror 10 according to the present invention is composed of a central spherical area S formed by a part of a spherical surface having the center thereof at the point O on the optical axis Z-Z, and a composite ellipsoidal surface of revolution E formed by parts of a plurality of different ellipsoidal surfaces of revolution joined to the central spherical area S. The lamp bulb 12 has the filament center thereof disposed as nearly coincident with the center O of the central spherical area S and the convex lens 14 has the focus thereof disposed as nearly coincident with the center O of the central spherical area S. The composite ellipsoidal surface of revolution formed by parts of the plurality of different ellipsoidal surfaces of revolution will be described in further detail. The composite ellipsoidal surface of revolution E in this embodiment has the focus thereof located at the center O of the central spherical area S as shown in Fig. 5, and it is formed from a number k of different ellipsoidal surfaces of revolution E(1), E(2), ..., E(j) and E(k) smoothly joined to each other and having the other foci F(k) thereof at positions spaced a predetermined distance f(k) from the common focus O toward the convex lens 14. Namely, the ellipsoidal surface of revolution E(1) is formed by a part of an ellipsoidal surface of revolution having the two foci thereof located at the center O of the central spherical area S and the point F(1), respectively. Similarly, the ellipsoidal surfaces of revolution E(2), ..., E(j) and E(k) are composed of parts of ellipsoidal surfaces of revolution having the two foci thereof located at the center O of the central spherical area S and points F(1), F(2), ..., F(j) and F(k), respectively. The distance f(k) between the two foci of the ellipsoidal surface of revolution E(k) is little by little larger as it goes further away from the central spherical area S (f(k) > f(j) > ... > f(2) > f(1)). In this embodiment, the profile of the inner reflecting surface of the concave mirror 10 as viewed from the center of the convex lens 14 is a generally horizontally long rectangle as shown in Fig. 4. The plurality of different ellipsoidal surfaces of revolution E(1), E(2), ..., E(j) and E(k) are joined to the other adjoining ellipsoidal surfaces of revolution, respectively, in plural vertical planes parallel to the vertical plane in which the optical axis lies. The ellipsoidal surfaces of revolution E(1), E(2), ..., E(j) and E(k) are composed of two elliptical reflecting areas, respectively, generally symmetrical with respect to the vertical plane in which the optical axis Z-Z lies. The focus F(k) of the ellipsoidal surface of revolution E(K) formed at the farthest position from the central spherical area S and the focus F(j) of the ellipsoidal surface of revolution E(j) are located between a back surface 16 and frontal surface 18 of the convex lens 14, and the foci F(1), F(2), ... of the ellipsoidal surfaces of revolution E(1), E(2), ... are located between the point O and the back surface 16 of the convex lens 14. The composite ellipsoidal surface of revolution E thus composed of the ellipsoidal surfaces of revoltion E(1), E(2), ..., E(j) and E(f) is so designed that the first angle ϑ1 of viewing from the common focus O both the end points S1 and S2 of the line of intersection between the vertical plane in which the optical axis Z-Z lies and the central spherical area S is nearly equal to the angle of viewing from the common focus O both the end points P1 and P2 of the line of intersection between the convex lens 14 and the horizontal plane in which the optical axis Z-Z lies and the second angle ϑ2 of viewing from the common focus O both the end points Q1 and Q2 of the line of intersection between the horizontal plane in which the optical axis Z-Z lies and the ellipsoidal surface of revolution E(k) formed at the farthest position from the central spherical area S is nearly 180 deg. It will be obvious from the angular relation that the effective solid angle of the light rays emitted from the lamp bulb 12 can be made large and the rays can be utilized to full extent for definition of a predetermined luminous intensity distribution pattern. Although only the four foci F(1), F(2), F(j) and F(k) are shown in the drawings for simplicity of the illustration, the composite ellipsoidal surface of revolution E is actually composed 40 to 50 different ellipsoidal surfaces of revolutions which are smoothly joined to each other. In this case, each ellipsoidal surface of revolution E(k) consists of two longitudinally elongated elliptical reflecting areas of about 1 mm in width and which are disposed in positions symmetrical with respect to a vertical plane in which the optical axis Z-Z lies, and each of these elliptical reflecting areas is formed by multiple fine reflecting surface elements of about 1 x 1 mm² and which are smoothly joined longitudinally to each other. The technique for forming a reflecting curved surface having predetermined reflecting characteristics by thus joining multiple fine reflecting surface elements to each other is known per se and so will not be explained further. The above-mentioned optical system of the projector-type headlamp according to the present invention will function as follows. First, the light rays emitted from the lamp bulb 12 and incident upon the central spherical area S are reflected toward near the common focus O, further incident upon the back surface 16 of the convex lens 14, refracted in directions nearly parallel to the optical axis Z-Z and thus projected forward from the frontal surface 18. The rays emitted from the lamp bulb 14 and incident directly upon the back surface 16 of the convex lens 14 are also refracted in directions nearly parallel to the optical axis Z-Z and projected forward. The generally circular pattern D at the center in Fig. 6 is defined primarily by the rays emitted from the lamp bulb 12 and incident directly upon the convex lens 14. The rays emitted from the lamp bulb 12 and incident upon the ellipsoidal surfaces of revolution E(1), E(2), ..., E(j) and E(k) in the composite ellipsoidal surface of revolution E are reflected toward the corresponding foci F(1), F(2), ..., F(j) and F(k), refracted by the convex lens 14 crossing the optical axis Z-Z according to the respective angles of incidence upon the back surface 16, and projected forward from the frontal surface 18 as rays diverged horizontally within an angle ϑ3. The pattern defined ahead of the convex lens 14 by the rays emitted from the lamp bulb 12, incident upon the composite ellipsoidal surface of revolution E and refracted by the convex lens 14 is indicated with N in Fig. 6. The pattern N extends from the center to the right and left within the angle ϑ3 and is superposed on the generally circular pattern D at the center to define a final luminous intensity distribution pattern required for the projector-type headlamp. For increasing the horizontal spreading of the final luminous intensity distribution pattern, it is desirable to locate between the back surface 16 and frontal surface 18 of the convex lens 14 the foci of the ellipsoidal surfaces of revolution distant from the central spherical area S, for example, not only E(j) and E(k) in this embodiment but also other ellipsoidal surfaces of revolution around them. Also the ellipsoidal surfaces of revolution can be so designed as to have the foci thereof located ahead of the frontal surface 18 of the convex lens 14. In this embodiment, the reflecting area of the ellipsoidal surface of revolution E(k) formed at a farthest position from the central spherical area S is so designed that the second angle ϑ2 is substantially 180 deg. This angular relation is the result of the consideration of the advantage in design. It is of course that the angle can be within an appropriate range larger or smaller than 180 deg. Figs. 7 and 8 show another embodiment of the projector-type headlamp according to the present invention. Fig. 7 is a schematic drawing of the optical system, and Fig. 8 is a schematic perspective view of the concave mirror. In Figures, the same reference numerals and symbols as in Figures referred to in connection of the first embodiment indicate the same elements in the first embodiment. In this second embodiment, the concave mirror is formed by joining supplemental reflecting surfaces 20 to the ellipsoidal surface of revolution E(k) located in the farthest position from the central spherical area S. The supplemental reflecting surfaces 20 in this embodiment are formed as a part of a spherical surface taking as center the common focus O of the composite ellipsoidal surface of revolution E or a spherical surface taking as center a point a little away from the common focus O, and connected to two right and left reflecting areas, respectively, of the ellipsoidal surface of revolution E(k). Namely, the ones of the rays emitted forward from the lamp bulb 12 that are emitted in directions exceeding the angle ϑ1 of viewing from the common focus O both the end points P1 and P2 of the line of intersection between the convex lens 14 and the horizontal plane in which the optical axis Z-Z lies can be contributed to the definition of a luminous intensity distribution pattern. To this end, the supplemental reflecting surfaces 20 are extended from the two right and left reflecting areas of the ellipsoidal surface of revolution E(k) in such a range that the rays emitted from the lamp bulb 12 and incident directly upon the back surface 16 of the convex lens 14 are not blocked. The rays emitted from the lamp bulb 12 and incident upon the supplemental reflecting surfaces 20, for example, the ones incident from the directions indicated with m and n in Fig. 7, are reflected toward near the lamp bulb 12 and further incident upon any of the ellipsoidal surfaces of revolution in the composite ellipsoidal surface E. Therefore, the rays reflected at the supplemental reflecting surfaces 20 are reflected at the ellipsoidal surfaces of revolution in the directions indicated with m′ and n′, respectively, that is, in directions toward the other foci than the common focus O. According to this embodiment, the supplemental reflecting surfaces 20 are formed by a part of a spherical surface, but it is of course that they can be formed by such a curved surface as reflects toward the composite ellipsoidal surface of revolution E the ones of the rays emitted forward from the lamp bulb 12 that are emitted in directions exceeding the angle ϑ1 of viewing from the common focus O both the end points P1 and P2 of the line of intersection between the convex lens 14 and the horizontal plane in which the optical axis Z-Z lies.

Claims: A projector-type headlamp, comprising: a concave mirror (10) having an inner reflecting surface with a central spherical surface (5) at an area near the apex, a lamp bulb (12) as light source having the center (O) thereof disposed nearly coincident with the center of the spherical surface of the concave mirror, and a convex lens (14) so disposed as to have the optical axis and focal point thereof nearly coincident with the axis of the concave mirror (10) and the center of the spherical surface of the concave mirror (10), respectively, characterised in that a composite ellipsoidal surface of revolution (E) is formed by parts of a plurality of different ellipsoidal surfaces of revolution (E(1), E(2), ..., E(j) E(k)) smoothly joined to each other for junction with the central spherical surface (S), each of the ellipsoidal surfaces being joined to the other adjoining ellipsoidal surface in a vertical plane parallel to the vertical plane in which the optical axis (Z-Z) lies to provide horizontally elongated profile of the concave mirror (10) and, that in said different ellipsoidal surfaces (E(1)...E(k)) have a common focus at the center (O) of the spherical surface and other foci (F(1), F(2)...) at different positions on the axis of the concave mirror (10) each spaced a predetermined distance from the common focus (O) toward the convex lens (14). A projector-type headlamp as claimed in claim 1, characterised in that the profile of the inner reflecting surface of said concave mirror (10) as viewed from the center of said convex lens (14) is generally a horizontally elongated rectangle. A projector-type headlamp as claimed in claims 1 and/or 2, characterised in that each of said ellipsoidal surfaces of revolution (E(1), E(2), ..., E(j), E(k))is composed of two elliptical reflecting areas symmetrical with respect to the vertical plane in which said optical axis (Z-Z) lies. A projector-type headlamp as claimed in at least one of claims 1 to 3, characterised in that the distance (f(k)) between two focii of each of said plural ellipsoidal surfaces of revolution (E(k)) is little by little larger as it goes further away from said central spherical area (S). A projector-type headlamp as claimed in at least one of claims 1 to 4 , characterised in that the focus (F(k)) of the ellipsoidal surface of revolution (E(k)) formed at a position far from said central spherical area (S) is located ahead of the back surface (16) of said convex lens (14). A projector-type headlamp as claimed in at least one of claims 1 to 5, wherein the first angle (ϑ1) of viewing from said common focus (O) both the end points (S1, S2) of the line of intersection between the vertical plane in which said optical axis (Z-Z) lies and said central spherical area (S) is generally equal to an angle of viewing from said common focus (O) both the end points (P1, P2) of the line of intersection between said convex lens (14) and the horizontal plane in which said optical axis (Z-Z) lies, and the second angle (ϑ2) of viewing from said common focus (O) both the end points (Q1, Q2) of the line of intersection between the horizontal plane in which said optical axis (Z-Z) lies and the ellipsoidal surface of revolution (E(k)) located at the farthest position from said central spherical area (S) is substantially about 180 deg. A projector-type headlamp as claimed in at least one of claims 1 to 6, characterised by supplemental reflecting surfaces (20) joined to the ellipsoidal surface of revolution (E(k)) formed at the farthest position from said central spherical area (S) and which reflect toward any of said plural ellipsoidal surfaces of revolution (E(1), E(2), ..., E(k)) the rays emitted from said lamp bulb (12) in directions exceeding said first angle (ϑ1) and toward said convex lens (14). A projector-type headlamp as claimed in claim 7, characterised in that said supplemental reflecting surfaces (20) are formed as a part of a spherical surface having the center thereof located near said common focus (O).

Inventors: AKIZUKI KUNIO, AKIZUKI, KUNIO
Applicants: ICHIKO INDUSTRIES LTD, ICHIKOH INDUSTRIES LIMITED
Application year: 1989
Main classification: F21M3
IPC codes: F21S8, F21V7, F21V13