FIELD OF THE INVENTION

The invention relates to an automotive LED headlamp, and more particularly, to a projection type low beam LED headlamp.

BACKGROUND OF THE INVENTION

LED Light Source in Headlamp

Traditionally, the vehicle headlamps use either halogen filament or high intensity discharge arc (HID) bulb as the light source.

More recently, solid state lighting devices, such as Light Emitting Diode (LED), are fast becoming preferred light source for automotive headlamp. LED has many advantages compared to the traditional HID/Halogen light sources for a few good reasons listed below:

1. LED is vibration and shock resistant due to the solid state lighting technology;

2. LED has much longer lifetime;

3. LED consumes less electrical power;

4. LED has color temperature close to day light, which is preferable for road illumination at night;

5. LED light source reaches maximal output within milliseconds, no warm-up delay;

6. LED is cold light source arid it doesn't contain IR and UV spectrum;

7. LED light source has good potentials to be easily integrated into AFL system.

Low Beam and High Beam

A headlamp system is required to produce a low and a high beam.

Low beams direct most of the light downwards and have strict control of upward light to provide safe forward visibility without excessive glare. The Economic Commission for Europe (ECE) regulation specifies low beam with a sharp, asymmetric cutoff preventing significant amounts of light from being cast into the eyes of drivers of preceding or oncoming vehicles. The desired low beam illumination pattern at 25m in front of the headlamp is shown in Figure 1.

Low beam pattern required by ECE regulation is, generally speaking, wide in horizontal direction and narrow in vertical direction. [High beams cast most of their light straight ahead, maximizing viewing distance, but producing glare, which may cause safety issue when other vehicles are present on the road. High beam is used when there is no other road users or in severe weather conditions.]

Optical Architectures of Headlamp

Modern headlamp optical architecture is either of a multi-reflector type or a projection type.

In a multi-reflector type headlamp, a light source is located in the vicinity of the focal point of a reflector with multiple facets. The light emitted from the light source is reflected by the reflector facets, and the combination of the reflection from all the reflector facets forms the desired illumination pattern.

In a typical projection type headlamp, there are a light source and its dedicated optical members to form an intermediate spot, and a projection lens to image the said intermediate spot to the front direction to form the desired illumination pattern.

As introduced before, the low beam pattern is wide in horizontal direction and narrow in vertical direction. However, the light emission from the LED light source is typically Lambertian type without directional preference. Therefore, it is needed that the optical members in the system shape the LED light in according to the ECE requirement with high efficiency.

Related Prior Art

There have been a handful of patent applications relating to projection-type automotive LED headlamps. For example, in the prior art shown in US patent 7712936 granted to Koito: there are an LED light source, a reflector, a beam shutter (shading member), and a projection lens. The light emitted from LED is collected by the reflector and re-directed toward the beam shutter. The beam shutter blocks a portion of the incoming light and forms an intermediate spot. The projection lens images the intermediate spot toward the front direction and forms the ECE required low beam illumination pattern.

However, the reflector surface profile is very complicated and it is hard to fabricate. According to the above patent, "the reflector's vertical sectional shape is an almost elliptic shape and horizontal sectional shape is a free curved shape based on an ellipse." Most of the prior arts tend to have complicated reflector, which is difficult to design, fabricate, and verify. The reason for having complicated reflector in automotive LED headlamp can be briefly described as below: The ECE required low beam illumination pattern is wide in horizontal direction and narrow in vertical direction, and the illumination pattern is asymmetrical: the illumination pattern includes a slightly off-centered area called 'hot zone' to be illuminated more brightly than other areas in the pattern. In short, the desired illumination pattern is irregular. The intermediate spot to be projected by projection lens must have a similar pattern in the vicinity of the focal plane of the projection lens. Therefore, the optical members for creating the irregular intermediate spot in the system need a complicated design, e.g. asymmetrical reflector, segmented reflector, or free form reflector, etc. None of them is able to be easily designed, and more importantly, easily manufactured. The required optical insert tooling cannot be made by the conventional three-axis diamond cutting machine and must be formed by more sophisticated machines, e.g. five-axis diamond cutting machine. As a result of this difficulty, the optical parts arid the headlamp cannot be produced in an economical way.

SUMMARY OF THE INVENTION

Thus, it is an object of the present invention to provide a headlamp that can solve the above- described problem.

In order to solve the above-described problem and provide the easily designed and economically manufactured optical parts to meet the ECE low beam irregular illumination requirement, a projection type low beam automotive LED headlamp according to the present invention comprises: a LED light source, a reflective optical member (reflector) with simple symmetric profile collecting the light emitted from the LED light source, a transmissive optical member compressing light reflected from the reflective optical member (reflector) in vertical direction and re-distributing the light reflected from the reflective optical member (reflector) in horizontal direction, a beam shutter (also known as shield, shade, etc.) blocking a portion of the light from the transmissive optical member to form an intermediate spot for low beam; and a projection lens projecting the intermediate spot toward front direction.

DESCRIPTION OF THE DRAWINGS

The above as well as other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the embodiments when considered in the light of the accompanying drawing in which:

Figure 1 is the ECE illumination pattern for low beam headlamp; Figure 2 is a side view of the optical system of the present invention;

Figure 3 is a perspective view of an exemplary embodiment of the reflective optical member (reflector) and LED light source according to the present invention;

Figure 4-1 is the first exemplary embodiment of the transmissive optical member according to the present invention;

Figure 4-2 is a top view showing the light path passing through the transmissive optical member according to the first embodiment in Figure 4-1 ;

Figure 4-3 is a side view showing the light path passing through the transmissive optical member according to the first embodiment in Figure 4-1 ;

Figure 5-1 is the second exemplary embodiment of the transmissive optical member according to the present invention;

Figure 5-2 is the cross-section view of the refractive array region;

Figure 5-3 is to illustrate the grooves in the refractive array region and the impact on the light path;

Figure 5-4 is a top view of the light path passing through the transmissive optical member according to the second embodiment in Figure 5-1 and the light path changed by the refractive array region;

Figure 6-1 is the third exemplary embodiment of the transmissive optical member according to the present invention;

Figure 6-2 is a top view of the light path passing through the transmissive optical member according to the third embodiment in Figure 6-1 and the light path changed by the refractive array region.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the present invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner.

Figure 2 is a side view of an exemplary embodiment of the optical system according to present invention. There are a LED light source 100, a reflective optical member 200 (also known as reflector) with simple symmetric profile, a transmissive optical member 300, a projection lens 600 and a beam shutter 700 (also known as shield, shape, etc.).

The light emitted from the LED light source 100 is collected by the reflective optical member 200 and is redirected toward the transmissive optical member 300. The transmissive optical member 300 compresses the incoming light in vertical direction and re-shapes the light distribution in horizontal direction. The light passing through the transmissive optical member 300 is partially blocked by the beam shutter 700 and forms an intermediate spot 800 for low beam. The beam shutter 700 is located at the focal plane 610 of the projection lens 600. The projection lens 600 projects the intermediate spot 800 toward front direction and forms the desired low beam illumination pattern.

Figure 3 is a perspective view of an exemplary embodiment of the reflective optical member 200 according to the present invention. The said reflective optical member 200 has an inner reflective surface 210 with parabolic profile. The focal length of the parabolic surface is about 5-10mm. The focal point 220 of the said parabolic surface 210 is where the LED light source 100 is located. The said parabolic surface 210 is easily designed, and easily formed by injection molding process. The optical inserts used for injection molding can be made by a conventional three-axis diamond cutting machine.

Figure 4-1 shows the first exemplary embodiment of the transmissive optical member 300 according to the present invention. The transmissive optical member 300 has a first surface 310 and a second surface 320. The incoming light enters the transmissive optical member 300 through the first surface 310 and exits the tranmissive optical member 300 from the second surface 320.

The first surface 310 of the transmissive optical member 300 is basically a flat surface, the second surface 320 is of a cylindrical profile, which is curved in vertical direction and constant in horizontal direction. In this exemplary embodiment, the transmissive optical member 300 is equivalent to a typical cylindrical lens. Back to Figure 2, the light emitted from LED 100 is reflected by the reflective optical member 200. The light reflected from the reflective optical member 200 passes through the transmissive optical member 300. The transmissive optical member 300 compresses the incoming light in vertical direction only. The intermediate spot 800 formed by the transmissive optical member 300 is symmetrical with regard to the vertical axis, wide in horizontal direction and narrow in vertical direction.

Figure 4-2 and Figure 4-3 illustrate the light path passing through the transmissive optical member 300 according to the first embodiment. Figure 4-2 is a top view and Figure 4-3 is a side view. The intermediate spot 800 is narrowed down in vertical direction.

Figure 5-1 shows the second exemplary embodiment of transmissive optical member according to the present invention, wherein the transmissive optical member 400 has a first surface 410 and a second surface 420. The first surface 410 of the transmissive optical member 400 has a region 430 having refractive array feature.

Figure 5-2 is a cross-section view of the said refractive array region according to the second exemplary embodiment, wherein an array of grooves 440 is formed on the first surface 410. The period of the grooves 440 is 0.5-1.0mm. Each groove has at least one inclined surface 450, which is tilted at an angle ⁽ X to the first surface 410. The angle a is in the range of 10~50 degrees.

Figure 5-3 is to illustrate how the incoming light is affected by the refractive array. When the incoming light hits the inclined surface 450 of the groove 440 in right angle (90 degrees), the light enters the transmissive optical member 400 with angle β due to refraction, the relationship between angle β and angle a is expressed by following formula: sin(or) = n sin(or - β)

where n is the refractive index of the material of the transmissive optical member.

Figure 5-4 is a top view of the light path passing through the said transmissive optica! member 400. A portion of the light is refracted towards the 'hot zone' area 810 in the intermediate spot 800. The 'hot zone' area 810 is brighter than adjacent region because more light flux hit the 'hot zone' area 810. In this embodiment, the 'hot zone' 810 is slightly off-centered from the optical system axis. The intermediate spot 800 as well as the 'hot zone' 810 are projected to form the low beam illumination pattern. Figure 6-1 is the third exemplary embodiment of transmissive optical member according to the present invention, wherein the first surface 510 of the transmissive optical member 500 has two symmetrical regions 530 with refractive array feature. The refractive array feature is the same as that described in the second embodiment shown in Figure 5-2.

The symmetrical refractive arrays 530 direct a portion of the incoming light toward the center region of the intermediate spot 800. As a result, the 'hot zone' 810 is located at the center of the intermediate spot as shown in Figure 6-2.

The said transmissive optical member may be made of any suitable material including, but not limited to, optical grade plastic, polymer.

The preferred method of producing the said transmissive optical member is by injection molding.

Any wanted intermediate spot can be designed by adjusting 1 ). the location and area of the refractive array region on the first surface of the transmissive optical member; and 2). The tilting angle of the inclined surface of the grooves on the first surface of the transmissive optical member.

The advantages of the present invention are stated as below:

1 ) A reflective optical member having a simple parabolic surface profile, which can be easily made by conventional fabrication method.

2) A transmissive optical member having simple refractive array profile on one of its surface, and simple cylindrical profile on another surface, which can be easily made by conventional fabrication method.

3) Flexibility of designing the transmissive optical member and arranging the refractive array region to meet the desired illumination requirement.

Although the present invention has been described in accordance with the embodiments shown, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the present invention. It is therefore intended that the foregoing description illustrates rather than limits this invention, and that it is the following claims, including all equivalents, that defines this invention.