Polarization-Selective Mirror for Vehicle HUD Thermal Management
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Solution Overview
Problem
Existing head-up display (HUD) devices in vehicles face temperature rise issues due to external light, particularly sunlight, which affects the projector's performance.
Innovation Solution
The HUD device incorporates a projector that projects images as light polarized in a direction intersecting the vertical direction of the image, combined with a reflecting mirror having different S and P polarization reflectance, to efficiently cut external light and reduce heat buildup in the projector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional reflecting mirror with uniform reflectance is used, then the structure is simple, but external light enters the projector causing temperature rise
Solution Approach 1:
The reflecting mirror is designed with different reflectance properties for different polarization directions (S-polarization and P-polarization). Specifically, the mirror has high reflectance for S-polarized light and low reflectance for P-polarized light, allowing selective reflection based on local optical properties rather than uniform reflection across all polarizations.
Solution Approach 2:
The reflecting mirror's optical parameters are changed by controlling the thickness of the dielectric films in the multilayer structure. By adjusting the film thicknesses to specific values (e.g., quarter-wavelength thicknesses), the mirror achieves different reflectance characteristics for different polarization directions, transforming a simple uniform mirror into a polarization-selective mirror.
2Loss of energy
If the reflecting mirror reflects all external light equally, then the mirror structure is simple, but the projector temperature rises due to accumulated heat
Solution Approach 1:
The invention converts the harmful effect of external light (which causes temperature rise) into a beneficial effect by using polarization-selective reflection. The multilayer dielectric mirror is designed to reflect S-polarized external light while transmitting P-polarized light, thereby reducing the total energy accumulated in the projector while maintaining the desired optical path for the display image.
3Object-affected harmful factors
If a polarizing film is adhered to the mirror surface, then external light can be cut, but the manufacturing process becomes more complex
Solution Approach 1:
Instead of using a separate polarizing film adhered to the mirror surface, the invention integrates the polarization-selective function directly into the mirror structure by creating a multilayer dielectric composite. This composite structure consists of alternating layers of dielectric materials with different refractive indices, forming an integrated polarization-controlling mirror that eliminates the need for separate polarizing film application.
4Temperature
If the reflecting mirror is designed to cut external light effectively, then projector temperature is suppressed, but the reflectance for image light may be reduced
Solution Approach 1:
The multilayer dielectric mirror structure allows dynamic optimization of reflectance characteristics by adjusting the number of layers, thicknesses, and refractive indices of individual layers. This enables the mirror to maintain high reflectance for the specific polarization and wavelength range of the display image while simultaneously achieving effective external light rejection, balancing both requirements through parameter optimization.
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 effectively reduces the reflectance of external light towards the projector while improving the reflectance of the image light towards the projection member, thereby suppressing temperature rise and enhancing the HUD device's performance.
Implementation Method 1
a reflecting mirror that is disposed on an optical path between the projector and the projection member to reflects and redirects the light of the image from the projector toward the projection member, and has a difference between S polarization reflectance and P polarization reflectance for the light from the projector
Implementation Method 2
a reflecting mirror that is disposed on an optical path between the projector and the projection member to reflects and redirects the light of the image
Data Source
AI summary
A head-up display device virtually displays an image to be viewable by an occupant by projecting the image on a projection member located above an instrument panel of a vehicle in a vehicle upward direction. Assuming that a direction along an up-down direction of the vehicle when the image is virtually displayed is defined as a vertical direction of the image, the head-up display device includes a projector that projects an image as light polarized in a polarization direction intersecting the vertical direction of the image and a reflecting mirror that reflects and redirects the light of the image from the projector toward the projection member, on an optical path between the projector and the projection member, and has a difference between S polarization reflectance and P polarization reflectance for the light from the projector.