This paper intends to use the reference design analysis of a low-cost LED car dual projection low beam lamp recently completed by OSRAM Opto Semiconductors, and hopes to help the industry colleagues.
This design will use the high-power LED -OSLON? Black Flat Two Chips from OSRAM Opto Semiconductors. (figure 1)
The LED is rated at 6.5W, and the chip adopts the latest UX:3 technology of OSRAM Opto Semiconductors. The typical luminous flux is about 560lm@1A, the maximum driving current is 1.2A (DC mode), and 2 chips are packaged. The area of ​​the light-emitting area is 2.1. Mm2 (2.1mm × 1.0mm), the uniformity of the illuminating surface is greatly improved compared with the previous generation of technical products, and the contrast between the light and dark areas of the illuminating area is very clear, which is very useful for designing functional lights with cut-off requirements. In addition, OSLON® Black Flat Two Chips have a maximum stable operating junction temperature of 150 degrees Celsius and maintain high stability and long life when operating at higher temperatures, while the LED can still operate at junction temperatures up to 175 degrees Celsius. Hours or so. It is therefore very suitable for use in forward lighting. In this design we use a 1.1A steady current drive, the junction temperature is assumed to be 120 ° C, and the minimum light output of the LED after stabilization is 508 lm.
In the design process of the low beam, the first type of light needs to meet the regulatory requirements. For this reference design, our design goal is to meet the ECE R112 Class B. At the same time, due to the use of LED light source, the regulations stipulate that the luminous flux of the LED module after stabilization is at least 1000 lm, so the final use of 2 LEDs to complete the design.
First, let's take a look at the description of the low beam requirements in ECE R112 Class B:
Since most countries in the world use the right-hand drive standard, here we only describe the test requirements of the standard, as shown in Figure 2. For the entire low beam type we can divide it into two parts: the part with the lowest illumination requirement in the cut-off area and the part with the highest glare limit above the cut-off line. For the requirements of these two specific illumination values, we can refer to Figure 3, where 75R is the most demanding point in the entire illumination area, which needs to exceed 10100 cd, and the glare value cannot exceed 625 cd in the Zone III area above the cut-off line.
The shape of the whole design is shown in Figure 4. It contains two projection units, in which the blue projection unit is used to realize the horizontal cutoff line and the widening function, and the yellow projection unit is used to realize the 15 degree line cutoff line and the bright area. Features.
Next, let's take a closer look at the design parameters and simulation results of the two different projection units. First, let's look at the blue projection unit:
As shown in FIG. 5, the projection unit has a lens size of 40 mm long, 25 mm wide, a center thickness of 12.6 mm, a material of PC, a refractive index of 1.586, and a distance of 15 mm from the bottom surface of the lens.
In the design we assume that the optical loss of light through the lens is 15%, and the optical loss through the headlight cover is also 15%. In this case, the light pattern on the 25m screen after the projection module is lit is shown in Figure 6. Shown. Since the luminous flux input we designed was 508 lm and the luminous flux projected onto the screen was 189 lm, the overall system efficiency was 37.2%.
Then we look at the yellow projection unit:
As shown in FIG. 7, the projection unit is composed of four parts: an LED, an ellipsoidal mirror, a visor, and a lens. In order to improve the design efficiency of the projection unit, we set the optical axis of the ellipsoid and the optical axis of the system to be non-coaxial, and the angle between the two is 12 degrees, as shown in Fig. 7. For the lens unit, its size is also 40mm long, 25mm wide, the center thickness is only 9.9mm, the total length of the entire projection unit is 95mm, the material is PC, and the refractive index is 1.586.
In the design we assume that the optical loss of light through the lens is 15%, and the optical loss through the headlight cover is also 15%. In this case, the light pattern on the 25m screen after the projection module is lit is shown in Figure 8. Shown. Since the luminous flux input we designed was 508 lm and the luminous flux projected onto the screen was 194 lm, the overall system efficiency was 38.1%.
After designing two different types of projection systems, we finally illuminate the two projection units together. The effect of the light pattern on the 25m screen is shown in Figure 9, and the results of the ECE regulations are shown in Figure 10. From the results in Figure 10 we can see that the design has sufficient margin at each test point, but at some points it can not meet regulatory requirements, such as P1 + P2 + P3, but according to our experience, these test points In the final product, it can meet the requirements. Due to processing, the light passes through the lens and the lampshade to generate some stray light, which is just the need for unqualified test points.
The tolerance analysis of the position of the light source is of great significance for the production and assembly of the luminaire. Therefore, this paper also performs simulation analysis on this system.
The results show that for any of the modules' LEDs, when we translate it by ±0.2mm in all directions, the resulting combination of the two light types can meet the ECE test regulations, of course, the light pattern of each module. It is necessary to re-adjust the angle in the vertical direction, which is mechanically easy to implement.
According to the comparison of the halogen light source and the LED light source in the following table, the advantages of LED in energy saving and environmental protection can be clearly demonstrated. At the same time, the LED design of the luminaire, because the optical system design efficiency is higher than the ordinary halogen bulb, the use of LED headlights as a light source, can make night driving more secure.
With the concept of energy saving and environmental protection further deepening the hearts of the people and the higher requirements of car owners for the shape of the lights, LED lighting will become more and more popular. In the near future, the traditional light source will be gradually replaced by LED. The era of LED as a mainstream light source is no longer far away.
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