Automobile lamp NTC arrangement method based on thermal simulation and temperature monitoring system

Abstract

The invention discloses an automobile lamp NTC arrangement method based on thermal simulation and a temperature monitoring system, and belongs to the technical field of automobile lighting. The method comprises the following steps: identifying a temperature-resistant sensitive optical element of which the temperature-resistant grade is lower than a preset threshold in the lamp, and arranging NTC (Negative Temperature Coefficient) on the periphery of the temperature-resistant sensitive optical element for temperature detection; for other areas, thermal simulation analysis is carried out after the structural design of the lamp is completed, the area with the highest temperature is determined as a temperature high-risk point, and NTC is arranged at the high-risk point for temperature monitoring protection; and when the detected temperature exceeds the set temperature, the current reduction operation is executed. According to the invention, scientific optimization of NTC arrangement and intellectualization of a temperature protection strategy are realized, the cost is effectively reduced, and the reliability is improved.

Description

Technical Field

[0001] This invention relates to the field of automotive lighting technology, and in particular to an NTC arrangement method and temperature monitoring system for automotive lamps based on thermal simulation. Background Technology

[0002] With the continuous development of automotive lighting technology, LED light sources have been widely used in the automotive lighting field due to their advantages such as high brightness, low energy consumption, and long lifespan. However, as a type of heat-sensitive semiconductor device, LEDs have poor tolerance to high temperatures. Given the limited internal space of automotive lamps, this places high demands on LED temperature control. Especially when prolonged use of the lights leads to excessively high LED temperatures, or when the car is parked and the lights are on, the driver needs to adjust the current or activate the fan to enhance heat dissipation based on the LED temperature, ensuring that the LED's semiconductor junction temperature does not exceed the safe range.

[0003] Currently, common methods for detecting PCB temperature include adding eFuse circuits to the motherboard to limit the maximum current, or adding temperature sensors to monitor the PCB temperature in real time. However, these methods have some drawbacks. For example, the eFuse circuit method can only detect the overall current and cannot reflect the temperature distribution within the PCB layers; while the temperature sensor method can detect surface temperature, its accuracy is affected by the system's fan cooling system. Furthermore, traditional temperature detection methods often require installing temperature-sensing resistors on the heatsink, resulting in long heat transfer paths, slow temperature detection speeds, and inaccurate temperature readings.

[0004] The existing technology has the following drawbacks: First, the increasing number of LED chips and PCBs in automotive lighting necessitates the placement of an NTC on each PCB for temperature feedback, increasing component costs (including resistors, connector pin count, and wiring harnesses). Second, traditional temperature detection methods require the installation of temperature-sensing resistors on the heat sink, resulting in long heat transfer paths, slow temperature detection speeds, and inaccurate temperature readings, making it difficult to meet the needs of real-time temperature monitoring. Third, existing temperature detection devices often only detect surface temperatures, and their accuracy is limited by the system's fan cooling system, failing to accurately reflect the actual temperature distribution on the PCB. Fourth, existing technology lacks a high-precision, low-cost, simple, and reliable temperature monitoring and protection system capable of operating in complex environments with multiple LED chips and PCBs, making it difficult to effectively manage LED operating temperatures. Fifth, current automotive lighting electronic designs still have shortcomings in temperature detection and control, failing to accurately detect the internal temperature of LED automotive lighting fixtures, which can lead to premature or delayed adjustments in output power, affecting product operation and lifespan. Sixth, existing temperature protection strategies often use fixed thresholds, which cannot adapt to changes in environmental conditions and lamp aging states, resulting in inaccurate protection strategies. Summary of the Invention

[0005] To address the problems of high cost, low detection accuracy, insufficiently intelligent protection strategies, and inability to accurately reflect the actual temperature distribution on the PCB in existing automotive lighting electronic design technologies, this invention provides an NTC (Nearest Temperature Controller) placement method and temperature monitoring system for automotive lighting based on thermal simulation. This invention achieves scientific optimization of NTC placement and intelligent temperature protection strategies by introducing innovative algorithms such as quantitative assessment of temperature risk index, adaptive adjustment of dynamic temperature threshold, and predictive protection based on temperature change rate.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for arranging NTC (Network Temperature Coefficient) in automotive lighting based on thermal simulation, comprising the following steps: S1: Identify temperature-sensitive optical components in automotive lighting fixtures and determine whether the temperature resistance level of the temperature-sensitive optical components is lower than a preset temperature threshold. For optical components with low temperature resistance levels, such as PMMA, their temperature protection requirements should be given priority.

[0007] S2: For temperature-sensitive optical components with a temperature resistance rating lower than the preset temperature threshold, NTC thermistors are arranged around them for temperature detection. Once the temperature exceeds the maximum temperature resistance of the optical component, a current reduction operation is performed.

[0008] S3: For areas of the luminaire other than the area around the temperature-sensitive optical components, NTC thermistors are not installed in the early stage. After the luminaire structure design is completed, thermal simulation analysis is performed to obtain the temperature field distribution inside the luminaire.

[0009] S4: Based on the thermal simulation results, determine the area with the highest temperature, and identify high-risk temperature points accordingly. For lighting fixtures with dozens or even hundreds of LEDs, follow the above principles to find high-risk temperature points based on thermal simulation. For multiple PCBA boards, if the external environment is consistent, also follow the above principles to place NTC thermistors only on the PCBAs where high-risk temperature points are located.

[0010] S5: Install NTC thermistors at the high-risk temperature points for temperature monitoring and protection.

[0011] S6: Set a temperature protection strategy. When the NTC detects that the temperature exceeds the temperature threshold, a current reduction operation will be performed.

[0012] In some embodiments, a temperature risk index can be used to quantitatively evaluate each candidate location in step S4. This invention innovatively proposes a multi-factor weighted method for calculating the temperature risk index R, comprehensively considering three key factors: absolute temperature value, temperature gradient, and distance from the LED light source. R = α×(T i / T max ) + β×(G i / G max ) + γ×(1-D i / D max ) Among them, the first term α×(T) i / T max The second term β×(G) reflects the influence of absolute temperature; the higher the temperature, the greater the location risk index. i / G max This reflects the effect of the temperature gradient. Areas with large temperature gradients are often regions of concentrated heat, experiencing more drastic temperature changes and higher risks; the third term γ×(1-D) i / D max This reflects the impact of distance from the LED light source; the closer the location is to the LED, the more timely the temperature changes can be detected, resulting in a faster response. α, β, and γ are weighting coefficients, and α + β + γ = 1. The weights of each factor can be adjusted according to the specific application scenario. A temperature risk index R is selected that is greater than a preset risk threshold R. th The location is designated as a high-risk area for temperature.

[0013] Preferably, this invention proposes the concept of a dynamic temperature threshold, enabling the temperature protection strategy to adapt to different environmental conditions and lamp aging states. Dynamic temperature threshold T dThe calculation method is as follows: T d = T base × K env × K age Among them, T base The reference temperature threshold is a temperature protection threshold determined under standard environmental conditions. K env This is an environmental correction factor used to adjust the protection threshold according to the actual ambient temperature. The calculation formula is: K env = 1 - λ×(T amb - T amb_std ) / T amb_std Where T amb To measure the ambient temperature, T amb_std Where K is the standard ambient temperature, and λ is the environmental impact factor. When the ambient temperature is higher than the standard temperature, K... env <1, the protection threshold is lowered accordingly, providing earlier protection.

[0014] K age This is an aging correction factor used to adjust the protection threshold based on the lamp's usage time. The calculation formula is: K age = 1 - μ×t / t life Where t is the cumulative working time of the lamp, t life The design lifespan is represented by μ, which is the aging impact factor. As usage time increases, considering the aging and degradation of LEDs and other components, the protection threshold is appropriately lowered to ensure product reliability throughout its entire lifecycle.

[0015] Preferably, this invention also proposes a predictive protection strategy based on the rate of temperature change. Traditional temperature protection only makes judgments based on the current temperature value, resulting in a response lag. This invention calculates the rate of temperature change dT / dt in real time and predicts the temperature at future times based on the current temperature T and the rate of temperature change: T pre = T + (dT / dt)×Δt Where Δt is the prediction time window. When the predicted temperature T pre When the temperature threshold is exceeded, a current reduction operation is performed prematurely. Furthermore, the current reduction ratio P is proportional to the rate of temperature change. P = P base ×(1 + η×(dT / dt) / k ref ) Where P base The reference current reduction ratio is η, the rate of change response coefficient is k. refThis serves as a reference temperature rise rate. The faster the temperature rises, the greater the current reduction, resulting in more precise and timely temperature protection.

[0016] Preferably, the temperature-sensitive optical component includes at least one of a PMMA lens, a PC lens, or a light guide element. The preset temperature threshold is the maximum temperature resistance value of the temperature-sensitive optical component minus a safety margin ΔTs, where ΔTs ranges from 5°C to 15°C.

[0017] Preferably, when the automotive lighting fixture contains multiple LED light sources, in step S4, the highest temperature point in the area where the multiple LED light sources are located is identified as a high-risk temperature point based on thermal simulation results. In step S5, NTC thermistors are only placed at this high-risk temperature point. When the automotive lighting fixture contains N LED light sources and N≥10, LED thermal coupling analysis can also be introduced. Due to the thermal coupling effect between adjacent LEDs, the temperature of a single LED depends not only on its own heat generation but also on the influence of surrounding LEDs. Calculate the thermal coupling coefficient between each LED light source: Where d ij L is the distance between the i-th LED and the j-th LED. th The thermal characteristic length is typically 10-30 mm, and can be determined based on the thermal conductivity and thickness of the PCBA board material. Then, the thermal coupling influence factor for each candidate location is calculated. H i = Σ(C ij ×P j ) Where P j Let be the heat dissipation power of the j-th LED. The thermal coupling effect factor is incorporated into the temperature risk index calculation: R' = R + δ×(H i / H max ), where δ is the thermal coupling weighting coefficient, H max This represents the maximum thermal coupling influence factor among all candidate locations.

[0018] Preferably, when the automotive lighting fixture comprises multiple PCBA boards and these PCBA boards are under the same external environmental conditions, in step S4, the PCBA board with the highest temperature is determined based on thermal simulation results, and in step S5, NTC thermistors are only placed at high-risk temperature points on the PCBA board with the highest temperature. The same external environmental conditions include the same ambient temperature, the same airflow conditions, and the same heat dissipation structure configuration.

[0019] Preferably, when the automotive lighting fixture contains M PCBA boards and M≥2, the temperature correlation analysis method between PCBA boards can be used to determine whether each board is under the same external environmental conditions. First, the temperature characteristic values ​​of each PCBA board are calculated: F k = T k_max ×W k Where T k_max W represents the highest temperature of the k-th PCBA board. k This represents the proportion of the total LED power carried by this PCBA board to the total power of the lighting fixture. Then, the temperature correlation coefficient between any two PCBA boards is calculated. ρ kl = cov(T k ,T l ) / (σ k ×σ l ) Where cov(T) k ,T l ) represents the temperature covariance, σ k and σ l Let ρ be the temperature standard deviation of each board. The temperature correlation coefficient ρ between any two PCBA boards is... kl >ρ th When both PCBA boards are under the same external environmental conditions, an NTC thermistor is placed only on the PCBA board with the largest temperature characteristic value F, where ρ th This is the threshold for determining relevance.

[0020] Preferably, the current reduction operation in step S6 adopts a multi-level current reduction strategy: setting multiple temperature thresholds, reducing the driving current by a first preset ratio when the temperature reaches the first threshold, reducing the driving current by a second preset ratio when the temperature reaches the second threshold, and turning off the LED light source when the temperature reaches the third threshold.

[0021] Preferably, a multi-stage nonlinear current reduction strategy can be adopted. The degree of temperature exceeding the limit is defined as follows: ε = (T - T d ) / T d When 0 < ε ≤ ε1, the current reduction ratio P1 = a1 × ε, which is the linear current reduction region; when ε1 < ε ≤ ε2, the current reduction ratio P2 = P1(ε1) + a2 × (ε - ε1) 2To accelerate the current reduction zone, when ε>ε2, the LED light source is turned off for protection. Here, a1 and a2 are the current reduction coefficients, and ε1 and ε2 are the temperature exceedance thresholds. This piecewise nonlinear control strategy uses a gentle current reduction when the temperature slightly exceeds the limit to maintain the lamp's brightness, while rapidly and significantly reducing the current when the temperature severely exceeds the limit to ensure device safety.

[0022] Preferably, step S5 may further include optimizing the determination of the number of NTCs. Calculate the spatial coverage of high-risk temperature points: S = (∪A i ) / A total Where A i Let A be the effective monitoring area of ​​the i-th NTC. total Let S be the total area of ​​the PCB board. When S ≥ S th When the number of NTCs meets the monitoring coverage requirements, it is determined that the number of NTCs is sufficient. When multiple temperature risk indices R are greater than R... th When selecting candidate positions, sort them in descending order of R value and add them to the NTC placement positions sequentially until S≥S th To achieve optimal temperature monitoring coverage with the minimum number of NTCs. The effective monitoring area of ​​the NTC is defined as a circular area with the NTC installation location as the center and the effective monitoring radius r as the radius.

[0023] The effective monitoring radius r is determined as follows: based on the thermal conductivity κ, thickness h, and temperature response accuracy requirement δT of the PCBA board, the effective monitoring radius r is calculated. , where q is the heat flux density per unit area. In engineering practice, the typical value of r is 10-20 mm.

[0024] Preferably, the thermal simulation analysis in step S3 includes: establishing a three-dimensional thermal simulation model of the automotive lighting fixture, setting the heating power of the LED light source, ambient temperature, and heat transfer conditions as boundary conditions, and performing steady-state or transient thermal simulation calculations under multiple operating conditions. The multiple operating conditions include a normal temperature full-power operating condition, a high-temperature full-power operating condition, a low-temperature start-up operating condition, and a thermal cycling operating condition; the weighted comprehensive result of the temperature distribution under each operating condition is used to determine candidate positions.

[0025] Secondly, the present invention provides a temperature monitoring system for automotive lighting fixtures based on thermal simulation, comprising: an LED light source module for providing illumination, including at least one LED light source mounted on a PCBA board; an optical component module for light distribution of the LED light source, including optical elements, wherein the optical elements include a temperature-sensitive optical component; a temperature detection module for detecting the internal temperature of the automotive lighting fixture, including a first NTC thermistor arranged around a temperature-sensitive optical component with a temperature resistance level lower than a preset temperature threshold, and a second NTC thermistor arranged at a high-risk temperature point determined by the highest temperature region in the internal temperature field distribution of the lighting fixture obtained from thermal simulation analysis; and a drive control module for receiving temperature signals and executing temperature protection strategies, electrically connected to the temperature detection module and the LED light source module, and performing a current reduction operation when the NTC detected temperature exceeds the temperature threshold.

[0026] Preferably, the drive control module includes a temperature signal acquisition unit, a dynamic threshold calculation unit, a temperature change rate analysis unit, and a current regulation unit. The temperature signal acquisition unit acquires the temperature signals of each NTC at fixed intervals using an ADC. The dynamic threshold calculation unit calculates the dynamic temperature threshold T in real time based on data from the ambient temperature sensor and the operating time counter. d The temperature change rate analysis unit performs sliding window filtering and differentiation on the temperature data to calculate the temperature change rate dT / dt and the predicted temperature Tpre. The current regulation unit uses PWM to control the enable terminal of the LED driver chip to achieve multi-level nonlinear current reduction control.

[0027] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: By using thermal simulation results, NTC thermistors were centrally arranged on the hottest board, achieving a reasonable layout of temperature sensing devices, reducing the number of NTC thermistors used, effectively reducing device costs (including resistors, connector pin count, and wiring harness), and improving the system's economy.

[0028] The design of this invention avoids the traditional method of installing temperature sensing resistors on heat sinks, shortens the heat transfer path, improves the speed and accuracy of temperature detection, and overcomes the problem of inaccurate temperature detection in the prior art.

[0029] By rationally arranging NTC thermistors, the actual temperature distribution of the PCB board can be reflected more accurately, effectively solving the problem that existing technologies can only detect surface temperature but cannot accurately grasp the temperature changes of the PCB.

[0030] The design of this invention is suitable for complex environments with multiple LED chips and multiple PCB boards, providing a high-precision, low-cost, simple and reliable temperature monitoring and protection solution, and realizing effective LED operating temperature management.

[0031] The temperature monitoring design based on thermal simulation results can accurately detect the internal temperature of LED automotive lighting fixtures, effectively avoiding the problem of adjusting the output power too early or too late, and ensuring the normal operation and service life of the product.

[0032] The dynamic temperature threshold mechanism proposed in this invention can adaptively adjust the protection threshold according to the ambient temperature and the aging state of the lamp. Compared with the fixed threshold scheme, it is more intelligent and accurate, ensuring the reliability of the product throughout its entire life cycle and under various environmental conditions.

[0033] The predictive protection strategy based on temperature change rate proposed in this invention can take protective measures in advance before the temperature is about to exceed the limit, overcoming the problem of delayed response of traditional temperature protection. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0035] Figure 1 A flowchart of an NTC (Network Terminal Control) arrangement method for automotive lighting fixtures based on thermal simulation, provided in an embodiment of the present invention.

[0036] Figure 2 This is a schematic diagram of a temperature monitoring system module provided in an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0038] Example 1 Reference Figure 1 This embodiment provides a thermal simulation-based NTC (Network Temperature Coefficient) arrangement method for automotive lighting fixtures, using a high-power LED headlight as an example for detailed explanation. The fixture comprises four PCBA boards, each carrying one of the following: high beam LEDs (6), low beam LEDs (12), daytime running light LEDs (8), and turn signal LEDs (4), totaling 30 LED light sources. The optical components include glass lenses and PMMA (Premium Metallic Aluminum) light guide elements, where the PMMA light guide elements are temperature-sensitive optical components.

[0039] Step S1: Identify the temperature-sensitive optical component in the automotive lighting fixture and determine whether its temperature resistance level is lower than a preset temperature threshold. In this embodiment, a PMMA photoconductor is identified as the temperature-sensitive optical component, with a glass transition temperature of approximately 105°C and a long-term operating temperature generally not exceeding 80°C. Therefore, its temperature resistance level (80°C) is determined to be lower than the preset temperature threshold. The temperature-sensitive optical component includes at least one of a PMMA lens, a PC lens, or a photoconductor.

[0040] Step S2: For temperature-sensitive optical components with a temperature resistance rating lower than a preset temperature threshold, NTC thermistors are arranged around them for temperature detection. In this embodiment, a first NTC thermistor is arranged around the PMMA photoconductor element, with the installation position selected in the area between the photoconductor element and the LED light source, approximately 5mm away from the surface of the PMMA photoconductor element. The temperature protection threshold is set to 70℃, which is the maximum temperature resistance of PMMA (80℃) minus a safety margin ΔTs = 10℃ (ΔTs ranges from 5℃ to 15℃). Once the temperature detected by the NTC exceeds 70℃, the drive control module immediately performs a current reduction operation.

[0041] Step S3: For the areas of the lamp other than the area surrounding the temperature-sensitive optical components, thermal simulation analysis is performed after the lamp structure design is completed to obtain the temperature field distribution inside the lamp. In this embodiment, a three-dimensional thermal simulation model of the headlight is established using professional thermal simulation software. The heating power of the LED light source, the ambient temperature, and the heat transfer conditions are set as boundary conditions. Steady-state thermal simulation calculations are performed under the following conditions: normal temperature full power (ambient temperature 25℃), high temperature full power (ambient temperature 85℃), low temperature start-up (ambient temperature -40℃), and thermal cycling. The weighted comprehensive result of the temperature distribution under each condition is taken.

[0042] Step S4: Determine the area with the highest temperature based on the thermal simulation results and identify high-risk temperature points. In this embodiment, the lamp contains four PCBA boards, which are installed in the same lamp cavity and are under the same external environmental conditions (including the same ambient temperature, the same airflow conditions, and the same heat dissipation structure configuration).

[0043] Since the lamp in this embodiment contains 4 PCBA boards (M=4≥2), the temperature correlation analysis method between PCBA boards is used to determine whether each board is under the same external environmental conditions.

[0044] First, calculate the temperature characteristic value F of each PCBA board. k = T k_max × W k T k_max W represents the highest temperature of the k-th PCBA board. k This refers to the proportion of the total LED power carried by this PCBA board to the total power of the luminaire. In this embodiment, the total power of the luminaire is approximately 60W, and the parameters of each PCBA board are as follows: Yuanguang PCBA board: T 1_max = 92℃, power ratio W1 = 18W / 60W = 0.30, F1 = 92×0.30 =27.6; Low beam PCBA board: T 2_max= 98℃, power ratio W2 = 24W / 60W = 0.40, F2 = 98×0.40 =39.2; Daytime running light PCBA board: T 3_max = 78℃, power ratio W3 = 12W / 60W = 0.20, F3 = 78×0.20 =15.6; Turn signal PCBA board: T 4_max = 85℃, power ratio W4 = 6W / 60W = 0.10, F4 = 85×0.10 =8.5.

[0045] Then calculate the temperature correlation coefficient ρ between any two PCBA boards. kl = cov(T k ,T l ) / (σ k ×σ l Statistical analysis of temperature data at multiple time points during the thermal simulation revealed that the temperature correlation coefficients between the plates were all greater than 0.85. A correlation threshold ρ was then set. th = 0.8, due to the temperature correlation coefficient ρ between any two PCBA boards. kl > ρ th It was determined that the four PCBA boards were under the same external environmental conditions.

[0046] Based on the calculated temperature characteristic value F, the maximum temperature characteristic value F2 of the low beam PCBA board is 39.2. Therefore, it is only necessary to place an NTC thermistor on the PCBA board where the low beam LED is located for temperature monitoring.

[0047] Thermal simulation results show that, since the low beam LED has the highest power and the highest usage frequency, the temperature of the PCBA board where the low beam LED is located is significantly higher than that of the other three PCBA boards. Therefore, further analysis is only needed on the PCBA board where the low beam LED is located.

[0048] On the PCBA board where the low-beam LED is located, 20 candidate locations for placing the NTC thermistor were selected based on thermal simulation results, and the temperature risk index R for each candidate location was calculated. The formula for calculating the temperature risk index R is: R = α × (T i / T max ) + β×(G i / G max ) + γ×(1-D i / D max ), where T i T represents the simulated temperature value at candidate position i. max G represents the highest temperature value among all candidate locations. iLet G be the temperature gradient value at candidate position i. max D represents the maximum temperature gradient value among all candidate locations. i Let D be the distance between candidate position i and the nearest LED light source. max The maximum allowable distance is preset (20mm in this embodiment); α, β, and γ are weighting coefficients and α+β+γ=1 (α=0.5, β=0.3, and γ=0.2 in this embodiment).

[0049] In a preferred embodiment, the weighting coefficient α ranges from 0.4 to 0.6, β ranges from 0.2 to 0.4, and γ ranges from 0.1 to 0.3. Those skilled in the art can select appropriate weighting values ​​within the above ranges based on the specific structural characteristics and application scenarios of the lighting fixture.

[0050] Taking candidate position #7 as an example, this position is located between LEDs #3 and #4, and its simulated temperature T i =95℃, T max =98℃; Temperature gradient G i =8℃ / mm, G max =12℃ / mm; Distance D from the nearest LED i =4mm. Therefore, R = 0.5×(95 / 98) +0.3×(8 / 12) + 0.2×(1-4 / 20) = 0.485 + 0.2 + 0.16 = 0.845. Set the preset risk threshold R. th =0.75, the R value (0.845) of candidate position #7 is greater than the threshold, and it is determined to be a high-risk temperature point.

[0051] Since there are 12 low-beam LEDs in this embodiment, and there is a thermal coupling effect between adjacent LEDs, LED thermal coupling analysis is introduced. First, the thermal coupling coefficient between each LED light source is calculated using the following formula: Where d ij L is the distance between the i-th LED and the j-th LED. th L is the thermal characteristic length. In this embodiment, based on the FR-4 material (thermal conductivity approximately 0.3 W / (m·K)) used in the PCBA board and the board thickness of 1.6 mm, L is set as... th =20mm.

[0052] Taking a layout of 12 low-beam LEDs as an example, with an adjacent LED spacing of approximately 8mm, the thermal coupling coefficient C between adjacent LEDs is... ij = exp(-8 / 20) = 0.67, indicating a strong thermal coupling effect between adjacent LEDs. For LEDs with a spacing of 16mm, the thermal coupling coefficient Cij = exp(-16 / 20) = 0.45.

[0053] Calculate the thermal coupling influence factor for each candidate location: H i = Σ(C ij × P j ) Where P j Let H7 be the heat dissipation power of the j-th LED. In this embodiment, the heat dissipation power of each low-beam LED is approximately 2W. Taking candidate position #7 as an example, this position is located between LEDs #3 and #4, 4mm away from both LEDs, and between 12-32mm away from the other 10 LEDs. The calculated heat dissipation power is H7 = 0.82×2 + 0.82×2 + 0.55×2×2 + 0.45×2×4 + 0.37×2×4 = 13.2W.

[0054] Incorporating the thermal coupling effect factor into the temperature risk index calculation, the corrected temperature risk index is: R' = R + δ×(H i / H max ) Where δ is the thermal coupling weight coefficient, and in this embodiment, δ is set to 0.1. The maximum thermal coupling influence factor H among all candidate positions is calculated. max =15.6W. The corrected temperature risk index R' for candidate location #7 is 0.845 + 0.1×(13.2 / 15.6) = 0.845 + 0.085 = 0.93.

[0055] Step S5: NTC thermistors are deployed only at the high-temperature risk points for temperature monitoring and protection. In this embodiment, after calculating the temperature risk index, three candidate locations with R values ​​greater than R are identified. th =0.75, sorted by R value from largest to smallest as follows: position A (R=0.87), position B (R=0.85), position C (R=0.78).

[0056] Further optimization of the NTC deployment quantity is performed: Calculate the spatial coverage S of high-risk temperature points, S=(∪A) i ) / A total In this embodiment, the total area A of the PCBA board where the low beam LED is located is... total =80cm 2 Based on the thermal conductivity κ, thickness h, and temperature response accuracy requirement δT of the PCBA board, the effective monitoring radius r = (κ×h×δT / q) is calculated. 1 / 2Where q is the heat flux density per unit area. In this embodiment, the PCBA board uses FR-4 material with a thermal conductivity κ = 0.3 W / (m·K), a board thickness h = 1.6 mm = 0.0016 m, and a set temperature response accuracy requirement δT = 5℃. The estimated heat flux density per unit area is q = 2000 W / m². 2 (Calculated based on LED heating power and heat dissipation area). Substitute into the formula to calculate: r = (0.3 × 0.0016 × 5 / 2000) 1 / 2 = (1.2×10 -6 ) 1 / 2 ≈ 0.0011m = 1.1mm.

[0057] The theoretically calculated values ​​are relatively small, mainly because FR-4 material has low thermal conductivity. In engineering practice, considering that the copper foil layer on the PCBA board significantly increases the equivalent thermal conductivity (the equivalent thermal conductivity including copper foil can reach 1-3 W / (m·K)), and the actual layout constraints of the NTC mounting location, the typical range of the effective monitoring radius r is 10-20 mm. In this embodiment, r = 15 mm is used, which ensures both sufficient temperature monitoring coverage and timely response of the NTC to temperature changes within the monitoring area.

[0058] If the effective monitoring area of ​​each NTC is defined as a circular area with a radius r = 15mm centered at its installation location, then the effective monitoring area A of a single NTC is... i = π×r 2 ≈ 7.07cm 2 Set the preset coverage threshold S. th =20%. NTC placement locations are added sequentially according to R value from largest to smallest: First, the first NTC is placed at location A, S1 = 7.07 / 80 ≈ 8.8% < 20%; then the second NTC is placed at location B, with the actual coverage area ∪ A. i =12.5cm 2 S2 = 12.5 / 80 ≈ 15.6% < 20%; Continue to place the third NTC at position C, the actual coverage area ∪ A i =18.2cm 2 S3 = 18.2 / 80 ≈ 22.8% ≥ 20% = S th This meets the monitoring coverage requirements. Therefore, this embodiment ultimately determines to place the second NTC thermistors at three high-risk locations on the PCBA board where the low beam LED is located.

[0059] Step S6: Set a temperature protection strategy. When the NTC detects that the temperature exceeds the temperature threshold, a current reduction operation is performed. This embodiment uses a combination of dynamic temperature threshold and predictive protection strategy.

[0060] Dynamic temperature threshold T d The calculation method for T is as follows: d = T base × K env × K age Among them, T base As the reference temperature threshold, this embodiment sets T base =100℃; K env The environmental correction factor is calculated using the formula K. env = 1 - λ×(T amb -T amb_std ) / T amb_std T amb To measure the ambient temperature, T amb_std The standard ambient temperature is 25℃, and λ is the environmental impact factor (λ=0.3 in this embodiment); K age The aging correction factor is calculated using the formula K. age = 1 - μ×t / t life Where t is the cumulative working time of the lamp, t life The design life is 5000 hours, and μ is the aging impact factor (in this embodiment, μ is set to 0.15).

[0061] The environmental impact factor λ ranges from 0.2 to 0.5, and the aging impact factor μ ranges from 0.1 to 0.25. These parameters can be determined through experimental calibration or engineering experience.

[0062] For example, when the ambient temperature T amb =45℃, when the lamp has been used for 2000 hours, K env = 1 - 0.3×(45-25) / 25 = 0.76, K age = 1 - 0.15×2000 / 5000 = 0.94, at this time the dynamic temperature threshold Td = 100×0.76×0.94 = 71.4℃.

[0063] Predictive protection strategy based on temperature change rate: The drive control module acquires the NTC temperature signal in real time with a sampling period of 100ms, calculates the temperature change rate dT / dt, and predicts the future temperature based on the current temperature T and the temperature change rate: T pre = T + (dT / dt)×Δt, where Δt is the prediction time window (in this embodiment, Δt = 30 seconds). When the predicted temperature T... preWhen the dynamic temperature threshold Td is exceeded, a current reduction operation is performed in advance. For example, when the current temperature T = 65℃ and the temperature change rate dT / dt = 0.5℃ / s, T pre = 65 + 0.5×30 = 80℃ > 71.4℃, triggering predictive protection and performing current reduction operation in advance.

[0064] The current reduction operation employs a multi-stage current reduction strategy: three temperature thresholds are set, and when the temperature reaches the first-stage threshold (T... d When the temperature reaches the second threshold (T), the driving current will be reduced by a first preset ratio (20%). d When the temperature reaches +5℃, the drive current will be reduced by the second preset ratio (50%), and when the temperature reaches the third threshold (T... d The LED light source will be turned off when the temperature reaches +10℃.

[0065] In another preferred embodiment, the current reduction operation can employ a multi-stage nonlinear current reduction strategy to achieve finer temperature control. The degree of temperature exceedance is defined as follows: ε = (T - T d ) / T d When 0 < ε ≤ ε1, the current reduction ratio P1 = a1 × ε, which is the linear current reduction region; when ε1 < ε ≤ ε2, the current reduction ratio P2 = P1(ε1) + a2 × (ε - ε1) 2 To accelerate the current reduction zone; when ε > ε2, the LED light source is turned off for protection.

[0066] In this embodiment, ε1 = 0.05 (i.e., temperature exceeds the limit by 5%), ε2 = 0.15 (i.e., temperature exceeds the limit by 15%), and the current reduction coefficients a1 = 4 and a2 = 20 are set.

[0067] With dynamic temperature threshold T d Let's take 71.4℃ as an example for explanation: When the detection temperature T = 74℃, ε = (74-71.4) / 71.4 = 0.036 < ε1, which is in the linear current reduction region, and the current reduction ratio P = 4 × 0.036 = 14.4%; When the detection temperature T = 76℃, ε = (76-71.4) / 71.4 = 0.064, satisfying ε1 < ε ≤ ε2, which is in the accelerated current reduction region. The current reduction ratio P = 4×0.05 + 20×(0.064-0.05). 2 = 0.2 + 0.004 = 20.4%; When the detected temperature T = 83℃, ε = (83-71.4) / 71.4 = 0.162 > ε2, triggering protection and turning off the LED light source.

[0068] The above-mentioned three-level fixed-proportion current reduction strategy is suitable for general application scenarios with low requirements for control accuracy, and has the advantages of simple control logic and easy implementation; the multi-level nonlinear current reduction strategy is suitable for high-end application scenarios with high requirements for brightness stability and temperature control accuracy, and can maintain the brightness of the lamp when the temperature is slightly exceeded, and quickly respond to ensure the safety of the device when the temperature is severely exceeded.

[0069] Compared to traditional methods (where 4 NTCs are needed per PCBA board or 30 NTCs are needed per LED area), the NTC arrangement method in this embodiment only requires 4 NTC thermistors (1 for monitoring temperature-sensitive optical components and 3 for monitoring high-risk temperature points), significantly reducing the number of NTCs and effectively lowering device costs.

[0070] Example 2 Reference Figure 2 This embodiment provides an automotive lighting temperature monitoring system based on thermal simulation, which applies the NTC arrangement method described in Embodiment 1. The system includes an LED light source module, an optical component module, a temperature detection module, and a drive control module.

[0071] The LED light source module provides illumination and includes 30 LEDs mounted on four PCBA boards: 6 high beam LEDs, 12 low beam LEDs, 8 daytime running light LEDs, and 4 turn signal LEDs. Each LED is powered by a driver circuit on the PCBA board and can be controlled independently or in conjunction with other components.

[0072] The optical component module is used for LED light source light distribution and includes optical elements. These optical elements include temperature-sensitive optical components; in this embodiment, a PMMA light guide element has a temperature resistance rating (80°C) lower than a preset temperature threshold, used for guiding and homogenizing the light from the daytime running lights. It also includes glass lenses for beam shaping of the high and low beams.

[0073] The temperature detection module is used to detect the internal temperature of the automotive lighting fixture, and includes a first NTC thermistor and a second NTC thermistor. The first NTC thermistor is arranged around the temperature-sensitive optical component whose temperature resistance level is lower than a preset temperature threshold. In this embodiment, it is arranged around the PMMA photoconductor element, about 5mm away from its surface, to monitor the temperature of the temperature-sensitive optical component. The second NTC thermistor is arranged at the high-risk temperature points determined by the highest temperature area in the internal temperature field distribution of the lighting fixture obtained from thermal simulation analysis. In this embodiment, there are three second NTC thermistors, arranged at the three high-risk temperature points on the PCBA board where the low beam LED is located, to monitor the temperature of the PCBA board and the LED light source.

[0074] The drive control module receives temperature signals and executes temperature protection strategies, and is electrically connected to the temperature detection module and the LED light source module. In this embodiment, the drive control module uses a microcontroller as its core processor and includes a temperature signal acquisition unit, a dynamic threshold calculation unit, a temperature change rate analysis unit, and a current regulation unit.

[0075] The temperature signal acquisition unit acquires the temperature signals of each NTC thermistor through a 12-bit ADC at a fixed period of 100ms, converts the analog signals into digital temperature values ​​and stores them in a register.

[0076] The dynamic threshold calculation unit calculates the actual ambient temperature T measured by the ambient temperature sensor. amb The dynamic temperature threshold T is calculated in real time based on the cumulative working time t of the lamps recorded by the working time counter. d = T base × K env × K age K env = 1 - λ×(T amb - T amb_std ) / T amb_std K is the environmental correction factor. age = 1 - μ×t / t life This is the aging correction factor.

[0077] The temperature change rate analysis unit performs sliding window filtering (window size is 10 sampling points) and differentiation on the temperature data to calculate the temperature change rate dT / dt, and predicts the future temperature T based on the current temperature T and the temperature change rate. pre = T + (dT / dt)×Δt, where Δt is the prediction time window.

[0078] The current regulation unit controls the enable terminal of the LED driver chip through PWM (Pulse Width Modulation) to achieve multi-level current reduction control. When the NTC detects or predicts that the temperature exceeds the dynamic temperature threshold Td, it performs corresponding current reduction operations according to the degree of temperature exceedance: the first level (T≥Td) reduces the current by 20%, the second level (T≥Td+5℃) reduces the current by 50%, and the third level (T≥Td+10℃) turns off the LED light source.

[0079] The temperature monitoring system in this embodiment achieves real-time monitoring and intelligent protection of the internal temperature of automotive lamps through the coordinated work of the LED light source module, optical component module, temperature detection module and drive control module, ensuring reliable operation of the lamps throughout their entire life cycle and under various environmental conditions.

[0080] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for arranging automotive lighting NTC devices based on thermal simulation, characterized in that, Includes the following steps: S1: Identify the temperature-sensitive optical components in automotive lighting fixtures and determine whether the temperature resistance level of the temperature-sensitive optical components is lower than a preset temperature threshold. S2: For temperature-sensitive optical components with a temperature resistance rating lower than the preset temperature threshold, NTC thermistors are arranged around them for temperature detection. S3: For other areas of the luminaire except for the area around the temperature-sensitive optical components, thermal simulation analysis is performed after the luminaire structure design is completed to obtain the temperature field distribution inside the luminaire; S4: Determine the area with the highest temperature based on the thermal simulation results and identify high-risk temperature points; S5: Install NTC thermistors at the high-risk temperature points for temperature monitoring and protection; S6: Set a temperature protection strategy. When the NTC detects that the temperature exceeds the temperature threshold, a current reduction operation will be performed.

2. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, In step S4, based on the thermal simulation results, multiple candidate locations for placing NTC thermistors are selected on the PCBA board, and the temperature risk index R for each candidate location is calculated. The formula for calculating the temperature risk index R is as follows: R = α×(T i / T max ) + β×(G i / G max ) + γ×(1-D i / D max ) Among them, T i T represents the simulated temperature value at candidate position i. max G represents the highest temperature value among all candidate locations. i Let G be the temperature gradient value at candidate position i. max D represents the maximum temperature gradient value among all candidate locations. i Let D be the distance between candidate position i and the nearest LED light source. max The maximum permissible distance is preset; α, β, and γ are weighting coefficients and α + β + γ = 1; the temperature risk index R is selected to be greater than the preset risk threshold R. th The location is designated as the high-risk temperature point.

3. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, The temperature threshold in step S6 is the dynamic temperature threshold T. d The dynamic temperature threshold T d The calculation method is as follows: T d = T base × K env × K age Among them, T base The reference temperature threshold; K env This is the environmental correction factor, calculated based on the deviation between the measured ambient temperature and the standard ambient temperature; K age The aging correction factor is calculated based on the ratio of the cumulative working time of the luminaire to its design life.

4. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, Step S6 further includes a predictive protection strategy based on the rate of temperature change: Real-time calculation of the rate of temperature change dT / dt; Predict the future temperature based on the current temperature T and the rate of temperature change dT / dt: T pre = T + (dT / dt)×Δt, where Δt is the prediction time window; When the predicted temperature T pre If the temperature threshold is exceeded, the current reduction operation will be performed in advance.

5. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, The temperature-sensitive optical component includes at least one of a PMMA lens, a PC lens, or a light guide element, and the preset temperature threshold is the maximum temperature resistance value of the temperature-sensitive optical component minus a safety margin.

6. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, When an automotive lighting system contains multiple LED light sources, in step S4, the highest temperature point in the area where the multiple LED light sources are located is identified as a high-risk temperature point based on the thermal simulation results. In step S5, an NTC thermistor is placed only at this high-risk temperature point.

7. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, When an automotive lighting system comprises multiple PCBA boards and these PCBA boards are under the same external environmental conditions, in step S4, the PCBA board with the highest temperature is determined based on the thermal simulation results, and in step S5, NTC thermistors are only placed at high-risk temperature points on the PCBA board with the highest temperature.

8. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, The current reduction operation in step S6 adopts a multi-level current reduction strategy: setting multiple temperature thresholds, reducing the driving current by a first preset ratio when the temperature reaches the first threshold, reducing the driving current by a second preset ratio when the temperature reaches the second threshold, and turning off the LED light source when the temperature reaches the third threshold.

9. The method for arranging automotive lighting NTC based on thermal simulation according to claim 1, characterized in that, Step S5 also includes optimizing the determination of the number of NTCs: calculating the spatial coverage rate S=(∪A) of high-risk temperature points. i ) / A total A i Let A be the effective monitoring area of ​​the i-th NTC. total Let S be the total area of ​​the PCB board; when S ≥ S th At that time, it was determined that the number of NTCs met the monitoring coverage requirements, of which S th The preset coverage threshold is used; when multiple temperature risk indices R are greater than the preset risk threshold R... th When selecting candidate positions, sort them in descending order of R value and add them to the NTC placement positions sequentially until S≥S th To achieve optimal temperature monitoring coverage with the fewest possible NTCs.

10. A temperature monitoring system for automotive lighting fixtures based on thermal simulation, characterized in that, include: LED light source module for providing illumination, including at least one LED light source mounted on a PCBA board; An optical component module for LED light source light distribution includes optical elements, wherein the optical elements include temperature-sensitive optical components; The temperature detection module is used to detect the internal temperature of automotive lamps. It includes a first NTC thermistor arranged around a temperature-sensitive optical component with a temperature resistance rating lower than a preset temperature threshold, and a second NTC thermistor arranged at a high-risk temperature point determined by the highest temperature region in the internal temperature field distribution of the lamp obtained from thermal simulation analysis. The drive control module is used to receive temperature signals and execute temperature protection strategies. It is electrically connected to the temperature detection module and the LED light source module. When the NTC detects that the temperature exceeds the temperature threshold, it performs a current reduction operation.

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