Vehicle HUD Sunload Resistance via Optical Coatings
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Solution Overview
Problem
Head-up displays (HUDs) in vehicles are susceptible to damage from sunlight due to increased heat levels, which can exceed 117°C, causing temporary or permanent degradation of the liquid crystal display (LCD) as a result of magnified sunlight focusing on the LCD through the display pathway.
Innovation Solution
The HUD design incorporates a hot mirror glass with a hot mirror coating and polarized film to reflect infrared and ultraviolet wavelengths away from the LCD, combined with an optical bonding assembly featuring an optical bonding glass sheet laminated with a cold mirror film, and a fold mirror with a cold mirror coating to reduce heat transmission, thereby increasing the time it takes for the LCD to reach damaging temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If image magnification is increased to achieve larger field of view and image distance, then the field of view and image distance are improved, but the LCD becomes more susceptible to heat damage from sunlight
Solution Approach 1:
The patent introduces an optical bonding assembly with cold mirror film and hot mirror glass as intermediary elements between the sunlight source and the LCD. The cold mirror film reflects visible sunlight while transmitting infrared, and the hot mirror glass reflects infrared radiation, creating a protective barrier that prevents harmful heat from reaching the LCD while maintaining the magnified image pathway
Solution Approach 2:
The patent converts the harmful concentrated sunlight into a beneficial protective mechanism by using the same optical pathway to redirect heat away from the LCD. The optical bonding assembly and hot mirror glass capture the concentrated solar energy and reflect it in a controlled manner, preventing damage while maintaining display functionality
2Length of stationary object
If magnification is increased to at least fifteen times to meet image distance requirements, then the image distance is improved, but the LCD surface temperature rises more quickly due to magnified sunlight focus
Solution Approach 1:
The optical bonding assembly with cold mirror film and hot mirror glass serves as an intermediary thermal barrier that intercepts magnified sunlight before it reaches the LCD. The cold mirror film reflects visible light while transmitting infrared, and the hot mirror glass reflects infrared radiation, creating a protective barrier that maintains image distance while preventing temperature rise
Solution Approach 2:
The patent changes the thermal parameters of the optical pathway by introducing materials with specific reflective and transmissive properties. The cold mirror film and hot mirror glass alter the infrared and visible light transmission characteristics, reducing heat accumulation on the LCD surface while maintaining the required image distance of at least fifteen times magnification
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces the risk of LCD damage by cutting the thermal energy from sunlight in half, increasing the time for the LCD to reach 117°C from three minutes to over four minutes, effectively protecting the display from intense sunlight exposure.
Implementation Method 1
The hot mirror coating reflects infrared (IR) and ultraviolet (UV) wavelengths of light away from the LCD
Implementation Method 2
the polarized film cuts p-polarized light from the sunlight. Incoming sunlight is unpolarized, which means that is an incoherent combination of linearly or circularly polarized light
Implementation Method 3
A cold mirror coating is preferably applied to the fold mirror, which reflects only visible spectrum light towards the LCD
Data Source
AI summary
A head up display (HUD) with improved resistance to sunload for use in a vehicle comprising an image generating device, an LCD assembly, an optical bonding assembly, and a fold mirror, with specific design countermeasures to combat damage caused to an LCD by heat from sunlight. These include an OB glass and cold mirror film (CMF) as components of the optical bonding assembly, a hot mirror coating and a polarized film as components of the LCD assembly, and a cold mirror coating on the fold mirror. When sunlight enters the HUD, the cold mirror coating reflects only visible light towards the LCD. The hot mirror coating reflects infrared and ultraviolet wavelengths of light away from the LCD. The polarized film cuts p-polarized light. The OB glass and CMF increase the specific heat of the HUD. The HUD thereby reduces sunload that would otherwise damage the LCD due to heat stress.