Download Analysis Result and Study of LED Head Light Sets

Jih-Tao Hsu Analysis Result and Study
Analysis Result and Study of LED Head Light Sets-Take LS600h Head Lights for
Example
Jih-Tao Hsu, Tse-Hsiu Yen, and Hsuch-Lung Liao
(Automotive Research ＆ Testing Center, Taiwan)
ABSTRACT
So far there is no official regulation available to
certify the performance verification tests of vehicle’s LED
head lights; only ECE & SAE commissions have launched
related drafts on it; even the LED headlights equipped at
high-grade Lexus LS600h cars, which are under mass
production already, are only guided by special articles that
all products need to be re-certified after official regulation
is published. The ARTC now performs tests and
verifications in the aspect of a technical developer and
designer and feedback the test result to build an experience
and parameters taken for future LED headlights; this
works contain the optical design of reflective and
projecting optical design and driver circuit system. At
present internal car headlight manufacturers haven’t made
deep study on LED head lights. In this article, we apply
the analysis of illumination distribution and related
post-system testing & verification of LS600h LED
headlights to study the required design skills for LED
headlight design works; making the car headlight,
electronic, cooling and LED device manufacturers who are
interested in developing LED headlights easier to realize
the design skills of advanced LED car headlights and
reduce related R&D troubles while making headlights
R&D; and it is also is beneficial to enhance the
background of key technologies.
Keywords: LED, car headlights, cooling
1. INTRODUCTION
By reviewing the developing history of vehicle’s
illumination system, after the technological upgrading and
commercialization for eighteen years since HID headlights
launched to market, the HID headlights have been
extending to low-to-mild-grade market from high-grade
one. Yet, by the influence of slow price-down, it is
predicted that the development HID headlights would be
taken place by LED illumination technologies in the future
market. As indicated from the reports of MIC Project
driven by the Institute for Information Industry and ITIS
Project driven by MOEA, presently the LED & AFS
headlights of car’s front lighting system are still
high-grade products attached to high-class cars; but, in
Japanese market, the prices of front headlights made of
AFS system are relatively high; and since the night
luminance equipments in urban and suburbs of Japan are
sufficient ; car drivers driving on the driveway beyond
mountain area can hold clear vision at night; thus, cars
equipped with AFS devices are slow growing. And from
the study reports made in the last a few years, cars in
Taiwan, Europe and North America also meet the same
circumstance. Front headlight with AFS isn’t so popular to
car drivers. So far the illuminating efficiency of LED is
gradually in excess of HID, the price is also down over
50% per year; therefore LED is called by scholars as the
Generation-4 lighting source of cars and is hot to all car
lighting manufactory dedicating to the related R&D works
in high-grade market. It also is treated as an important
factor that would influence future car’s headlight
development. In the future time, a car should contain both
visible light & invisible light applications which will turn
all lighting products in cars into LED ones; the time of
full-scale introducing LED into vehicle products is coming.
[1-3] So far America, Europe and Japan all have the design
ability of LED headlights for prototype car. Up to date,
among the famous international car manufacturers only
mass-produced Lexus LS600h cars are equipped with LED
headlights, the unit price of such LED headlight equipped
in these cars is half million yen per set, very expensive one.
Yet, the international car lights manufacturers including
KOITO, VALEO, HELLA and STANLEY have started the
study of LED headlights since a decade ago; the major
direction of design is roughly on the projected or reflected
type; and STANLEY &OSRAM. etc., now all have
demonstrative LED-headlight-equipped prototype cars.
Now the Koito Manufacturing Inc. in Tokyo pioneers to
commercialize LED car headlights to Lexus LS-600h
(Fig.1) of Toyoda Motor, the first commercialized
LED-headlight car model in current market. [4-8] This
article will follow the current international regulation
making research, tests and verification and compare the
research result of LED headlights made by internal LED
alliance firms in the past a few years, summarize the test
result and design guiding points for internal car headlights
manufacturers to trace and cut in the car’s LED lighting
market worth over a billion US dollars in 2010.
Fig. 1 Lexus LS600h LED headlight
source: LSXUS
2. METHODS
This study apply the LMT equipments at the Light
Lab, ARTC, making related optical system verification
process; and follow USA CFD (FMVSS、CPSC), SAE,
ECE and EEC regulations. The testing equipments are
calibrated to national lab standard and thus the accuracy of
system test data follows this standard. (Table 1) is a
summarized table and regulation drafts of current
international certification organizations to the suitability of
LED headlights launched to market. Experimental
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Jih-Tao Hsu Analysis Result and Study
objective applied is
Lexus LS600h LED headlights.
Table 1. LED headlight regulation draft made by ECE & SAE
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REGULA Car Part
TION
set
Europe ECE/TRA No No
NS/WP.29/
GRE/2007/
12
28
December
2006
USA
Remark
1. Light piece meeting ECE R48
3.3.2 needs to pass the certification in
order to apply for the car set
certification; LED headlight thus
cannot make car set certification.
2. LED headlight functionally is a
sort of car’s headlight, which needs to
conform to ECE R98/R112/R113 tests;
since these clauses compulsorily
define the light source type, therefore,
the LED headlight cannot be certified.
3. at present some car models
equipped with LED headlights are
under certain special articles; after new
regulation is published, these cars need
to apply for re-certification procedure.
Fmvss108 Yes Yes hough NHTSA expresses that these
products can be launched to market,
and SAE
they still need to follow state
J2650
government’s permission.
3. RESULTS
3.1 Related optical tests
Headlight being under testing is Right-side one;
during the test, use LMT to measure the maximum
distance-moving angle of this LED low beam module
when AFS (Adaptive Front Lighting System) is activated
(Fig.2); the test result is 7 degree at left stroke and 23.5
degree at right stroke.
The optical light-distribution performance test
follows the ECE R112 Class B procedure; the test points
of LED low beam follow (Table 2) requirements; test
values at ZoneIII zone should not exceed 0.7 (lux). Yet,
lux for original light distribution is NG at all points, at
ZoneIII zone is 1.089(lux). From the original light
distribution result shown in (Table 3) and (Fig.3) we can
see that the residual luminance of LED low beam module
is too high. After testing original light distribution, the
respective maximum luminance of LED low beam module
is 33.84 (lux). We then make 12-hr continuous light-decay
test and measure maximum luminance value right after it,
the value taken is 31.76 (lux) or 6.2% decay for LED low
beam module, which is higher than the current LED
certification regulation draft that the maximum allowable
light source decay is only 3%. Therefore, this LED
headlight module cannot pass the regulation-defined
certification and so far it follows a special article to
proceed with market sales. If without a special
modification to the draft in the future, LS600h headlights
would be called back from market and users.
We also have measured the light flux of this LED
headlight module; the single LED light source applied by
LS600h headlights is made by four 1x1 chips packed by
glass, about 2.5w per chip and 10W output per module.
After actual flux measurement inside the integral ball of
light module, the module’s light flux is 376 lm left after
being lit up for 60 minutes (Fig.4); if by counting the light
source chip amount applied by LS600h, the illumination of
LED low beam module is above 1200 lm.
Fig.2
AFS performance governs the angle of moving distance
Table 2. ECE R112 low-beam requirement
Table 3. Original light-distribution result of LED low beam module
Fig. 3 Original light-distributed model of LED low beam module
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Jih-Tao Hsu Analysis Result and Study
chamber; heat generated from the headlights plus the high
temperature from engine chamber make the efficiency of
LED headlights down and headlight lifetime is shortened,
which means the entire lifetime of car’s headlight set is
shortened. [9-13]
Fig. 4 Testing result of integral ball
3.2 Temperature test of LED low beam cooling module
The major purpose of performing this verification test
is to derive the actual temperature distribution of entire
LED cooling module in a closed car light set. Take a
measuring point at right, middle & left of LED cooling
module’s fin, plus a measuring point of ambient
temperature, four measuring points are taken in total. Light
up the light module for 12 hours continuously. Use
calibrated thermocouple (traceable to national standard lab)
to make test on this LED low beam cooling module by
measuring temperature at the fin measuring points. The
thermocouples applied for the test are 0.25mm T-type one
with a operational temperature of up to 150 degree C. Use
tag welding to joint both ends of the wire to form four
thermocouple sets. Apply YOKOGAWA-produced MV
200 data acquisition system to collect and record
temperature data at four test points per each two seconds
continuously; after the testing system is stabilized, record
the temperatures of each of the thermocouples under
stabilized status.
From Fig.5 we get that when the ambient temperature
is at 31.4 degree C and lit time is 70 minutes, the entire
low beam cooling module has reached a heat-balanced
status; fin temperature is maintained at about 78 degree C.
in the next procedure we take out LED light source, light
up the LED chip externally and measure the temperature at
the point 5mm away from the LED lighting chip PCB.
From Fig. 6 we see that when the ambient temperature is
27.4 degree C and chip is lit up for 40 minutes
continuously, the temperature of LED chip PCB remains
unchanged; the maximum temperature measured at the test
point is 50.2 degree C. For LED, the luminance is
proportional to driving current; yet, change of temperature
will both change LED illumination characteristics and
device lifetime. From the test data we find that LED
characteristics is easily influenced by ambient temperature;
when the PCB temperature measured ascend, it would
make LED light output decrease. Therefore, temperature is
the most influential factor to LED luminance output and
lifetime and the major obstacle of LED applied in car’s
headlights. Nowadays car’s headlights mostly apply light
materials; the trend of tiny devices makes the inner space
of car’s headlight even smaller and unable to dissipate the
heat generated from LED out into outer environment;
since headlights are installed inside the car’s engine
Fig. 5 Measured result of low beam cooling module temperatures
Fig. 6 Measured result of LED light source chip PCB temperatures
3.3 Compatible test of circuit, EM waves and entire
environment
Before proceeding with this test we need to confirm
the pin locations of LED headlight interface, voltage and
current; in which correct input to high beam state is 12V,
5.4A, and to low beam state is 12V, 10W per single
module; direction light voltage is 12V, and voltage for
horizontal motor is 12V and directional motor is also 12V.
Here we can explore the ECU unit; it is built externally by
aluminum shell to cool down the unit; ECU seat is
water-sealed by rubber ring; inner of ECU uses silica to
seal off moisture and dust; digital and analog signals are
blocked out in electrical circuit to avoid possible
disturbance. The circuit is designed that uses inductance
and capacitor to stabilize voltage and filter waves; applies
three MOSFET to control three LED modules; the low
beam LED module uses cascade + parallel driving; MCU
independently control three LED modules. Advantages are
it can reduce the voltage drop of voltage-rising circuit
(LED-driving voltage is about 15V) and circuit load
(current is about 700mA); if any single module is damaged,
the other two can go on working (controlled by MCU); the
demonstrative circuit diagram is shown in Fig.7 by patent
searching result of (Keyword: KOITO LED DRIVER) we
find that the LED protection circuit and current detecting
circuit (us7,274,150). From the DC-DC Convert Datasheet
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Jih-Tao Hsu Analysis Result and Study
we can acquire the constant-voltage control and predict
that Lexus applies MCU to detect LED-passed circuit and
make constant-circuit control and abnormal response of
current or temperature, etc.; and use the ARTC-designed
OP making current feedback control. The advantages are
low cost & power consumption and small volume taken
(Fig.8). The voltage-sensing IC (61FC2) will detect
voltage and certify that stable voltage is loaded to circuit
that won’t make MCU works abnormally. Use MOSFET
(7N1005) be electronic switch. (Table 4) is the summary
of major devices equipped in the headlight set.
The light-up humidity follows test specification
AMECA FMVSS 108 to make 72-hr continuous light-up
humidity test and verify the light distribution, ensuring
that all parts can work normally under humid environment.
The light-distribution test is made after the light-up
humidity; test result shows identical result as the original
light distribution of headlight; luminance at the residual
zone is too high.
The dust test specifies that the test applies Portland
cement (ASTM C150-77) dusts conforming to FMVSS
108; after 5-hr continuous test is taken, the
light-distribution test verifies if the performance of vehicle
parts or electronic devices is degraded due to the intrusion
of cement dust; test result shows same result as original
light distribution of headlight; luminance at the residual
zone is too high.
The shell anti-chemicals test specifies that the test
applies FMVSS 108, ASTM-referenced fuel oil C
(tat-removing ingredient, power-steering oil, windscreen
cleaning detergent and anti-freeze ingredient); after
making the anti-chemicals test, perform light-distribution
test and visual inspection; test result shows same result as
original light distribution of headlight tat the luminance at
the residual zone is too high; and the visual inspection
made on shell surface is OK.
Environmental test of the entire headlight set shows
that the manufacturing process of the headlight set meets
requirements specified in the environmental specification;
NG of light distribution test is because the value of
original light-distribution has caused over-bright residual
light already, the consecutive light distribution after
environmental test is just same to the original light
distribution.
In order to let the LED headlight test result more
accurate and demonstrative, except luminance,
environment and other relevant tests we also have added
the EM-waves of entire headlight set and other items that
we expect these test items and data can be a reference of
helping the development of internal LED headlight in the
future. The EM-waves compatible test is to ensure that
while vehicle is running, follows the related vehicle test
methods and restricted value of radiation interruption to
make tests; the goal is to sustain the immunity against
performance degradation of induced current caused from
radio receiver or other various control & operating devices
and elevate vehicle performance and safety.
Test standard follows ECE R10; the items and layout
under test are illustrated as follows:
Item 1: Narrowband Electromagnetic Disturbances test:
the respective layout is shown in Fig.9; test specification
and content should satisfy the conditions specified in Table
5.
Item 2: Input test of large current: the respective layout is
shown in Fig.10; test specification and content should
satisfy the conditions specified in Table 6.
Item 3: EM endurable test of free field: the respective
layout is shown in Fig.11; test specification and content
should satisfy the conditions specified in Table 7.
Test result of EM-wave compatibility is shown in
Fig.12, which all can meet basic requirements of
regulation. From the test result we can realize that except
the 3% error of LED light decay is unable to meet the
requirement, the other items of Lexus LS600h LED
headlight set can all meet the certification requirement of
international regulation.
Fig. 7 Circuit diagram
Fig. 8 Circuit comparison diagram
Table 4. Major devices summary of LED headlight set
Name
CPU
MOSFET
Brand
Model No
KOITO
29002G 632KA11
FUJI
K3592
ELECTRIC
MOSFET
RENESAS 7N1005
MOSFET
RENESAS 7N0603
Remark
N/A
Vds=150V，Id=57A，
Rds=31mΩ
Vds=100V，Id=15A，
Rds=85mΩ
Vds=60V，Id=30A，Rds=11mΩ
Operational
Amplifier
JRC
7001
N/A
Voltage
Detectors
TOREX
61FC2
Highly Accurate：± 2％，Detect
Voltage Range 1.6V~6.0V
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Jih-Tao Hsu Analysis Result and Study
Table 7. Free Field ESA Immunity Test
Fig. 9 Narrowband Electromagnetic Disturbances test
Table 5. Narrowband Electromagnetic Disturbances
Fig. 12 Narrowband Electromagnetic Disturbances Test result
4.
Fig. 10 Input test of large current
Table 6. BCI ESA Immunity Test
GRADE INTERNAL LED HEADLIGHT
SKILLS
So far the internal institutes working on developing
LED headlight system include ARTC, ITRI and etc.; the
LED headlight published by ARTC has six (6) Projection
System (PES) modules to perform LED low beam module.
In the actual light distribution (Fig.13, Table 8) status the
bright spots at strong light zone of low beam pattern
reaches 22.17 (lux) that can meet regulation’s minimum
requirement 12 (lux); the light pattern follows EU standard
of driving at right side or road and driver sitting at car’s
left side. From Table 9 we can compare the two LED low
beam modules all by projection module type; yet, the
LS600h headlight uses a extra refectory optical surface to
compensate the diffusion zone; for the cooling module, the
module applied by LS600h headlights is tiny in size and
more suitable for car headlight use; the difference is at
light source, which ARTC so far made designs on
internal-produced LED light source the is easier to acquire
and cheaper in price. However, there are many
international specification that Taiwan at this moment is
unavailable to make certifying tests because internal light
labs have no such relevant equipment; for example, in the
draft of EU headlight test regulation it specifies LED red
spectrum test, anti-UV test and 1500-hr anti-radiation test,
etc., which can be performed in Taiwan labs only after
internal labs have supplemented such test equipment.
Fig. 11 EM endurable test of free field
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Jih-Tao Hsu Analysis Result and Study
Fig. 13 LED headlamp design by ARTC
Table 8. Light distribution result of low beam module
Required illumination (unit: lux)
Headlight for
Standard value
right-side-driving Measured value
(Class B)
cars
Pt B50 R
0.248
≦1
Pt 75 R
12.31
≧ 12
Pt 75 L
2.557
≦ 12
Pt 50 L
6.201
≦15
Pt 50 R
19.34
≧3
Pt 50 V
13.05
≧ 6
Pt 25 L
3.48
≧ 2
Pt 25 R
8.469
≧ 2
Zone III
0.664
≦ 0.7
Zone IV
3.596
≧ 3
Zone I
22.17
2xPO 50L
Table 9. Comparison table of LED low beam module
Designer
Function
Regulation
LED maker
Chip module
Optics
module
Thermal
module
Capability
Driver
5.
KOITO
Low beam+ Bending
light
ECE
R112(Right-side-drivi
ng car)
NICHIA
377lm/10WX3,
corner
10WX1+ 5WX1
Projected + Reflected
Natural type (sink in
major), smaller and
inner-installed.
79OC/1h at heat sink
(at room temperature)
MCU constant
current feedback
control, high price,
can make other
controls.
ARTC
Low beam
ECE
R112(Left-side-driving car)
LUMILEDS K2 or Internal
production
Prototype
68 lm/ 4.8WX6 or 130lm
/2.5WX 5~6
projected
Natural type (pipe + sink),
bigger and exposed.
45OC at heat sink (at room
temperature), 79OC
(ambient temperature is
65OC), 91OC or 78OC (real
car, ambient temperature is
37OC)
OP constant current
feedback control, cheap in
price, tiny.
CONCLUSION
From the above system certifying test we can
conclude the following hints for internal industrial
manufactory to make references: (1) Although Lexus
LS600h headlight will decay in intensity, yet the overall
luminance is above regulation standard. The actual light
distribution test result is slightly decayed than original one
but it is okay and acceptable. (2) The second optical lamp
design skill is roughly okay; however, the positioning
accuracy is a challenge for mass production; Lexus
LS600h headlights put the positioning accuracy into a
primary item in patent plan. (3) 4 pieces of 1×1 mm
large-size blue LED are packed in a module; each LED
output is 2.5W and totally 10W for 4 chips that produce
376 lm. (4) LED chip structure is improved; LED chips
can work normally even when the touch temperature is up
to 150 degree C. (5) LED is packed by glass that can
restrain the degradation made from temperature rise; but
internal LED chips haven’t such packing process. (6)After
high power LED is launched to mass production, LED
luminance-applying efficiency won’t be a design key-point.
(7) the reliability test of high-power white LED unit will
become a key-point of mass production.
6.
ACKNOWLEDGEMENTS
This study is supported by Automotive Research ＆
Testing Center of the Republic of China.
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SP-2106 2008
Jih-Tao Hsu
ARTC( Automotive Research & Testing Center)
505 No.6 Lunkung. S.7Rd, Lu-Kang Town, Changhwa
Hsien, Taiwan R.O.C
Phone : +886-4-7811222
Fax : +886-4-7811777
E-mail : [email protected]
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