A headlamp for a vehicle

Abstract: Visibility of a distant area illuminated by a headlamp of a vehicle having a centralized light source type is improved. The headlamp for the vehicle include a light source, an optical cable (10) emitting an incident light from the light source, lens bodies (30, 40) forming the incident light from the optical cable (10) into a desired light distribution and irradiating the incident light ahead of the vehicle. The lens bodies (30, 40) have lens-shaped outgoing light surfaces (32, 42) where focal points are located in the vicinity of the incident light surfaces of the lens bodies, and the lens bodies (30, 40) have reflective surfaces R 1 and R 2 reflecting the incident light toward an outgoing light surfaces (32, 42). The light axis X of the optical cable (10) is tilted by a predetermined angle α with respect to the reflective surfaces R 1 and R 2 .

Description: BACKGROUND OF THE IMVENTIOM 1. Field of the Invention: The present invention relates to an illuminating device and a headlamp for a vehicle comprising the illuminating device, to be more specific, a headlamp illuminating a distant area in the travelling direction of a vehicle. An illuminating device comprising the features summarized in the preamble of claim 1 is known from document DE-A-43 20 554. 2. Description of Related Art: As a headlamp for a vehicle, it has been considered to utilize, as a light source, a discharge tube combined with a control circuit for the discharge tube in view of electric power efficiency with respect to light intensity. Since the control circuit is expensive, a device has been proposed where the discharge tube is placed at one place in a vehicle as a centralized light source and luminous flux is guided from there to the positions of right and left headlamps in the front part of a vehicle via optical cables. One of such examples is disclosed in the document DE-A-43 20 554. FIG. 3 shows one example of the structure of known headlamps, which comprise primarily a centralized light source 1 placed at the center of the front part of a vehicle, and headlamps L and R fixed symmetrically on the right and left sides of the centralized light source 1. The centralized light source 1 has a substantially cylindrical casing, where a discharge tube 1a as a line light source is placed at the center in the axis direction of the casing. The labels FL and FR represent the left and right front wheels of the vehicle. The left headlamp L comprises a lens body 2 installed at the left front edge of the vehicle and an optical cable 10 connecting the lens body 2 to the centralized light source 1 while the right headlamp R comprises a lens body 4 installed at the right front edge of the vehicle and an optical cable 10 connecting the lens body 4 to the centralized light source 1. In the aforementioned lens bodies 2 and 4, two different lens bodies having different lens operation are used for each lens body to realize combination of two kinds of light distribution as shown in FIGS. 4A, 4B and 4C. That is, a first lens body 30 for hot zone light distribution shown in FIG. 4C which illuminates the front of the vehicle concentratedly and a second lens body 40 for flat light distribution shown in FIG. 4B which disperses light in the right and left directions of the vehicle are combined together as shown in FIG. 4A. The first lens body 30 for the hot zone light distribution is substantially conically shaped, spreading from an incident light surface 31 to an outgoing light surface 32. The outgoing light surface 32 is substantially spherical, having a focal point within the object thereof in the vicinity of the incident light surface 31. The shape of the first lens body 30 is in the shape of a half of a frustoconical body cut along a horizontal plane surface 33 passing the vicinity of the central axis of the cone. The second lens body 40 for the flat light distribution has substantially vertical planes 44 and 45 at the both sides of its horizontal direction. An outgoing light surface 42 is substantially in the shape of an arc in the vertical direction, and the second lens body 40 has a focal point thereof within the object in the vicinity of an incident light surface 41. The second lens body 40 is generally straight in horizontal direction and has a roughly cylindrical plane. The shape of the second lens body 40 is like a fan, cut along a plane surface 43 passing the vicinity of the central axis of the cylinder. The first lens body 30 and the second lens body 40 are combined by disposing each cut surfaces 33 and 43 face to face. A shade 20 is inserted between respective lens bodies 30 and 40 and the optical cable 10. The shade 20 is a material to determine the shape of distributed light which is emitted from the outgoing light surfaces 32 and 42 of respective lens bodies 30 and 40 . As a result, the front illuminated area comprises an illuminated area where light disperses in the right and left directions with respect to the horizontal line H and converges only in the upper and lower directions with respect to the vertical center line V, namely, a flat light distribution area as shown in FIG. 4B, and an illuminated area where light condenses with respect to the horizontal line H and the vertical center line V, i.e., a hot zone light distribution area as shown in FIG. 4C. This type of light distribution is low beam light distribution used to prevent glaring against the on-coming vehicles running on the opposite lane, that is, dipped-beam light distribution. The enlarged upper left part of the hot zone light distribution area is for recognizing pedestrians. The enlarged lower left part of the same is formed as such because it incidentally becomes symmetrical by mirror reflection. In the above-described structure, because a total reflective surface R 1 composed of the surface 33 of the lens body 30 is formed at the top of the lens body 30, and the total reflective surface R 1 is arranged in parallel to the light axis X of the optical cable 10, luminous flux is divided into two; the light to illuminate a distant area (for instance, an area 60 m ahead of the vehicle) of the vehicle and the light to illuminate a close area (for instance, an area 10 m ahead of the vehicle). Because a total reflective surface R 2 composed of the surface 43 of the lens body 40 is formed at the bottom of the lens body 40 and the total reflective surface R 2 is arranged in parallel to the light axis X of the optical cable 10, luminous flux is divided into two; the light to illuminate a distant area (for instance, an area 60 m ahead of the vehicle) of the vehicle and the light to illuminate a close area (for instance, an area 10 m ahead of the vehicle). An experiment has been carried out to trace the beam of light which enters the respective lens bodies 30 and 40 and comes out of the outgoing light surfaces 32 and 42. FIGS. 5A and 5B show the results of the experiment. In FIG. 5B, when light enters a point P on the incident light surface 31 on the first lens body 30 for the hot zone light distribution, a portion of the light does not reflect on the total reflective surface R 1 , and a distant point A (for instance, an area 60 m ahead of the vehicle) is illuminated by the light directly emitted from the outgoing light surface 32. In FIG. 5A, when light enters a point Q on the incident light surface 41 on the second lens body 40 for the flat light distribution, the light illuminates a distant point C (for instance an area 60 m ahead of the vehicle) after being reflected once on the total reflective surface R 2 . According to the experiment for the first lens body 30, the result shows that 59% of the light which enters point P of the incident light surface 31 in the first lens body 30 for the hot zone light distribution illuminates the distant point A while 41% of the light illuminates the point B (for instance, 10 m ahead of the vehicle) close to the first lens body 30. The result of the experiment for the second lens body 40 has revealed that 43% of the light which enters point Q of the incident light surface 41 in the second lens body 40 illuminates the distant point C while 41% of the light illuminates the point D (for instance, 10 m ahead of the vehicle) close to the second lens body 40 and the remaining 16% is totally reflected inside the lens body 40 and can not go out of the outgoing light surface 42, which has resulted in wasted light (Z portion in FIG. 5A). The result of the experiment has clarified a problem that only approximately one half of the light entering the lens bodies 30 and 40 is used to illuminate an area distant from the lens bodies 30 and 40 when the light axis X of the optical cable 10 is arranged in parallel to the total reflective surfaces R 1 and R 2 . Therefore the light to illuminate the distant area becomes insufficient, which causes a problem to lower the visibility of the distant area. SUMMARY OF THE INVENTION It is an object of the present invention to further develop the illuminating device comprising the features summarized in the pre-characterizing clause of claim 1 such that it is appropriate for illuminating a distant area. This object is achieved by the illuminating device according to claim 1. The present invention is based on the finding that the angle between the reflective surface of a lens body and the optical axis of an optical cable guiding the light to the lens body changes the ratios between light to illuminate a distant area and light to illuminate a close area. Advantageous developments of the invention are defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which: FIG. 1 is a perspective view of main parts of a headlamp for a vehicle according to an embodiment of the present invention; FIGS. 2A and 2B show the result of an experiment to trace the beam of light emitted from the headlamp for the vehicle in the present embodiment, with FIG. 2A showing the beam of light emitted from a second lens body and FIG. 2B showing the beam of light emitted from a first lens body; FIG. 3 shows a conventional headlamp in a centralized light source type for a vehicle; FIGS. 4A to 4C show the lens bodies of the headlamp in FIG. 3; and FIGS. 5A and 5B show the result of an experiment to trace the beam of light emitted from the conventional headlamp for a vehicle in FIG. 3. DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENT A preferred embodiment of a headlamp for a vehicle comprising an illuminating device according to the present invention is hereinafter described with reference to the accompanying drawings. FIG. 1 is a perspective view showing the main parts of the headlamp for a vehicle in the present embodiment. In regard to the headlamp for the vehicle of the present embodiment in FIG. 1, luminous flux emitted from the centralized light source (not shown but, for instance, refer to numeral 1 in FIG. 3) is guided via an optical cable 10 and enters a shade 20 which is a material to determine the distribution shape of the emitted light. The luminous flux emitted in a shape of predetermined light distribution by the shade 20 is designed to enter a first lens body 30 and a second lens body 40. The optical cable 10 comprises a core made of the same material as the first lens body 30 and the second lens body 40 described below and a clad to coat the core. A refractive index of the material for the clad is smaller than a refractive index of the core in order to reflect all light inside the core. The light axis X of the optical cable 10 hereinafter referred to as optical axis X is so arranged as to tilt upward by α degree (for instance, α = 5 - 10 degrees) relative to the lens central axis 0 of the lens body composed of the first lens body 30 and the second lens body 40. In the present embodiment the optical axis tilts by 10 degrees (α = 10 degrees). The shape (a shape having the same diameter as or a diameter larger than that of the cable) of the shade 20 covers the whole surface a circular shape is shown in the figure) of the outgoing surface of the optical cable 10 and is formed into a proper shape for determining light distribution shape. The shade 20 is made of a material which is, for instance, metal and does not transmit light. The shade 20 is so shaped that the luminous flux coming out of the optical cable 10 travels straight therethrough and is formed in the shape of the shade while having practically sufficient light volume. The first lens body 30 and the second lens body 40 are made of a high light transmissive material having a predetermined light refractive index with respect to the air in order to guide the light therethrough, for example, acrylic resin. To materialize the combination of two different kinds of light distribution, i.e., the hot zone light distribution and the flat light distribution, the lens body of the present embodiment is composed of a combination of two lens bodies having different lens operation. The first lens body 30 is substantially frustoconically shaped, spreading from an incident light surface 31 to an outgoing light surface 32. The first lens body 30 has the outgoing light surface 32 roughly shaped like a sphere to be more precise, the shape is slightly aspherical to adjust an aberration) having a focal point within the object thereof in the vicinity of the incident light surface 31. The shape of the present embodiment is a half of a frustoconical body cut along a plane surface 33 passing the vicinity of the central axis of the cone. The second lens body 40 has two substantially vertical planes 44 and 45 at both sides of its horizontal direction. An outgoing light surface 42 is roughly an arc to be more precise, it is slightly non-arc shaped to adjust an aberration) in the vertical direction,and the second lens body 40 has a focal point within the object thereof in the vicinity of an incident light surface 41. The second lens body 40 is almost straight in horizontal direction and has a roughly cylindrical plane. The shape of the second lens body 40 in the present embodiment is like a fan cut along a plane surface 43 passing the vicinity of the central axis of the cylinder. The first lens body 30 and the second lens body 40 are combined by disposing each cut surfaces 33 and 43 face to face. Since the cut surface 33 of the first lens body 30 serves as a total reflective surface R 1 for the luminous flux from the incident light surface 31, the shape of the luminous flux looks as if the lower half of the shade 20 is symmetrically added to the upper side when the luminous flux is emitted forward through the first lens body 30. Since the cut surface 43 of the second lens body 40 serves as a total reflective surface R 2 for the luminous flux from the incident light surface 41, the shape of the luminous flux looks as if the upper half of the shade 20 is symmetrically added to the lower side when the luminous flux is emitted forward through the second lens body 40. Since the first lens body 30 is a normal omnidirectional lens body, the luminous flux in symmetrically-added shape of the lower half of the shade 20 is enlarged as an inverted image without changing its shape and illuminates an area to form the hot zone light distribution. Since the second lens body 40 extends only in a vertical direction, the luminous flux in symmetrically-added shape of the upper half of the shade 20 is enlarged only in the vertical direction. In a horizontal direction, it becomes free dispersive emission of the luminous flux passing between the vertical planes 44 and 45. Thus, the luminous flux illuminates an area to form the flat light distribution where light disperses in the right and left directions and converges only in the upper and lower directions. As a result, the front illuminated area is composed of a centralized illuminated area, i.e., the hot zone light distribution area (FIG. 4C) and a dispersive illuminated area, i.e., the flat light distribution area (FIG. 4B) with respect to the horizontal line H and the vertical center line V. This type of light distribution is low beam light distribution used to prevent glaring against the on-coming vehicles running on the opposite lane, that is, dipped-beam distribution light. The enlarged upper left part of the hot zone light distribution area (FIG. 4C.) is formed for recognizing pedestrians. The enlarged lower left part of the same is formed as such because it incidentally becomes symmetrical by mirror reflection. In the headlamp of the present embodiment having the above structure, light enters each lens body 30 and 40 via the optical cable 10 of which the optical axis X is tilted upward by 10 degrees (α = 10 degrees) with respect to the lens central axis O of the lens body composed of the first lens body 30 and the second lens body 40. An experiment in the same manner as in FIGS. 5A and 5B has been carried out to trace the beam of light which enters the respective lens bodies 30 and 40 and comes out of their outgoing light surfaces 32 and 42. FIGS. 2A and 2B show the result of the experiment. In FIG. 2B, after being emitted from the optical cable 10 to point P on the incident light surface 31 (FIG. 1) of the first lens body 30 for the hot zone light distribution, the amount of the light reflected on the total reflective surface R 1 decreases compared with the amount in FIG. 5B where the lens central axis O coincides with the optical axis X, since the optical axis X is tilted upward by 10 degrees (α = 10 degrees) with respect to the lens central axis O. According to the experiment for the first lens body 30, the result shows that a distant point A (for instance, 60 m ahead of the vehicle) is illuminated by 85% of the light which entered point P on the incident light surface 31 of the first lens body 30 for the hot zone light distribution while remaining 15% of the light illuminates point B (for instance, 10 m ahead of the vehicle) close to the first lens body 30. In FIG. 2A, after being emitted from the optical cable 10 to point Q on the incident light surface 41 (FIG. 1) of the second lens body 40 for the flat light distribution, the amount of the light reflected on the total reflective surface R 2 increases compared with the amount in FIG. 5A where the lens central axis O coincides with the optical axis X, since the optical axis X is tilted upward by 10 degrees (α = 10 degrees) with respect to the lens central axis O. The result of the experiment for the second lens body 40 has revealed that a distant point C (for instance, 60 m ahead of the vehicle) is illuminated by 69% of the light which has entered point Q on the incident light surface 41 of the second lens body 40 for the flat light distribution while remaining 31% of the light illuminates point D (for instance, 10 m ahead of the vehicle) close to the second lens body 40. The result of the experiment has shown that such a problem as a low visibility of the distant area due to insufficient amount of light to illuminate the distant area can be solved, because the light for the distant area (light to illuminate points A in FIGS. 2B and 5B) emitted from the outgoing light surface 31 of the first lens body 30 for the hot zone light distribution increases from 59% to 85% and the light for the distant area (light to illuminate points C in FIGS. 2A and 5A) emitted from the outgoing surface 41 of the second lens body 40 for the flat light distribution increases from 43% to 69% as shown in the table below, if the optical axis X of the optical cable 10 is tilted upward by 10 degrees (α = 10 degrees) with respect to the lens central axis O according to the present embodiment, compared with a case were the lens central axis O coincides with the optical axis X ( α = 0 degree). Ratio of Light to Illuminate Distant Area Angle (α) Lens Body for Hot Zone Light Distribution Lens Body for Flat Light Distribution 0 Degree 59% 43% 10 Degree 85% 69% The above experimental result shows a case where the optical axis X of the optical cable 10 is tilted upward by 10 degrees with respect to the lens central axis O. A desirable angle between the optical axis X of the optical cable 10 and the lens central axis O is 5 - 10 degrees (α = 5 - 10 degrees) because the reflective light does not increase enough to raise the amount of the light for the distant area if the angle is under 5 degrees, and if it exceeds 10 degrees, the reflective light increases as well as the light for the distant area; however, the light tends to illuminate the lower surface of the first lens body 30 and the upper surface of the second lens body 40. Therefore the amount of wasted light increases. Since the optical axis X of the optical cable 10 is tilted upward by the predetermined angle (α = 5 - 10 degrees) with respect to the lens central axis O, the reflected light on each reflective surface 33 and 44 of each lens body 30 and 40 can illuminate the area distant from the lens bodies 30 and 40 according to the present embodiment having the above-described structure. Thus such a special effect as to be able to provide a headlamp for a vehicle having improved visibility for a distant area can be produced. By setting the above predetermined angle to 5 - 10 degrees, the light can reach the distant area without changing the lens diameter of each lens body 30 and 40 as well as without wasting the light, so that a special effect to be able to provide such a headlamp for a vehicle inexpensively can be obtained. The present invention should not be limited to the above-described embodiment but may be modified in many other ways without departing from the scope of the invention as defined by the claims.

Claims: An illuminating device, comprising: a first lens body (30) having a first incident light surface (31), a first outgoing light surface (32) formed in a lens shape with a focal point thereof in the vicinity of the first incident light surface (31), and a first reflective surface (R 1 ) extending along an optical axis of the first lens body (30) in the vicinity of this optical axis for reflecting light from the first incident light surface (31) to the first outgoing light surface (32); a second lens body (40) having a second incident light surface (41), a second outgoing light surface (42) formed in a lens shape with a focal point thereof in the vicinity of the second incident light surface (41), and a second reflective surface (R 2 ) extending along an optical axis of the second lens body (40) in the vicinity of this optical axis for reflecting light from the second incident light surface (41) to the second outgoing light surface (42), wherein the first lens body (30) and the second lens body (40) are disposed such that the first reflective surface (R 1 ) and the second reflective surface (R 2 ) abut on each other; a light source (1) for emitting light; and an optical cable (10) for guiding the light from the light source (1) to the first and second incident light surfaces (31, 41), characterized in that the optical cable (10) provides the light to the first and second incident light surfaces (31; 41) in a direction tilted by a predetermined angle (α) relative to the first and second reflective surfaces (R 1 ; R 2 ) so that the ratio of light intensities between a direct light directly traveling from the first and second incident light surfaces (31; 41) to the first and second outgoing light surfaces (32, 42) and a reflected light which is reflected by the first and second reflective surfaces (R 1 , R 2 ) during travel from the first and second incident light surfaces (31; 41) to the first and second outgoing surfaces (32; 42) is adjusted. The illuminating device according to claim 1, wherein said predetermined angle (α) is between 5 and 10 degrees. The illuminating device according to claim 1 or 2, wherein a shade (20) is inserted between said optical cable (10) and said first and second lens bodies (30;40) for determining light distribution shape of irradiated light. The illuminating devise according to one of claims 1 to 3, wherein: an optical axis (X) of said optical cable (10) is inclined by the predetermined angle (α) relative to said first and second reflective surfaces (R 1 ; R 2 ). The illuminating device according to claim 4, wherein said first and second reflective surfaces(R 1 ;R 2 ) extend generally horizontally, and wherein the optical axis (X) of said optical cable (10) is inclined downward. The illuminating device according to claim 8, wherein said first lens body (30) has said first reflective surface (R 1 ) at an uppermost portion thereof and said second lens body (40) has said second reflective surface (R 2 ) at a lowermost portion thereof. The illuminating device according to claim 6, wherein said first lens body (30) concentratedly projects the light for providing a hot zone light distribution; and wherein said second lens body (40) projects the light for providing a horizontally extending flat light distribution. A headlamp for a vehicle, comprising the illuminating device according to one of claims 1 to 7, wherein the first and second lens bodies (30; 40) are disposed at a front portion of the vehicle.

Inventors: KATO HIDEYUKI, KATO, HIDEYUKI
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1995
Main classification: F21V8
IPC codes: F21S8, F21V5, F21V8