HUD Polarization Rotator for Windshield Reflection and Sunglasses Visibility
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Solution Overview
Problem
Conventional head up displays (HUDs) in vehicles become dim or invisible when drivers wear polarized sunglasses, due to the limited reflectivity of p-polarized light from windshields.
Innovation Solution
A HUD system that uses a sequence of linear polarizers to rotate the linear polarization direction of light from a liquid crystal display (LCD), allowing a fraction of s-polarized light to be converted to p-polarized light, enabling visibility of the virtual image by drivers wearing polarized sunglasses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the HUD projector emits s-polarized light to maximize reflection from the windshield, then the reflection of s-polarized light is much higher, but drivers wearing polarized sunglasses cannot see the virtual image because the sunglasses block s-polarized light
Solution Approach 1:
The patent applies a liquid crystal variable retarder (LCVR) that can dynamically change the polarization state of light in real-time. The LCVR switches between different retardation states (0° and 90°) to adapt the polarization orientation to match either the windshield reflection requirements (s-polarized) or the driver's sunglasses transmission axis (p-polarized), thereby resolving the contradiction between maximizing reflection and maintaining visibility with polarized sunglasses.
Solution Approach 2:
The patent changes the polarization parameter of the light by using the LCVR to rotate the polarization orientation. By adjusting the retardation parameter of the liquid crystal material, the system transforms the polarization state from s-polarized to p-polarized (or vice versa), enabling the HUD to optimize performance for different viewing conditions and solve the contradiction between reflection efficiency and sunglasses compatibility.
2Adaptability or versatility
If the HUD projector emits p-polarized light to enable visibility with polarized sunglasses, then drivers wearing sunglasses can see the image, but the windshield reflectivity to p-polarized light is small causing the image to appear dim
Solution Approach 1:
The LCVR dynamically adjusts the polarization state based on the required output. When p-polarized light is needed for sunglasses compatibility, the system activates the LCVR to rotate the polarization orientation, ensuring that sufficient light intensity is maintained while achieving the required polarization state for visibility through polarized sunglasses.
Solution Approach 2:
The LCVR acts as an intermediary device between the light source and the windshield/sunglasses interface. It mediates the polarization conflict by transforming the light's polarization state as needed, allowing the system to achieve both good reflection (when s-polarized) and sunglasses compatibility (when p-polarized) without direct conflict, thus resolving the brightness vs. visibility contradiction.
3Adaptability or versatility
If circularly polarizing the light after the picture generation unit, then visibility with polarized sunglasses improves slightly, but the solution is not fully satisfactory because windshield reflectivity to p-polarized light remains small
Solution Approach 1:
Instead of using fixed circular polarization, the patent employs dynamic linear polarization control through the LCVR. The system can switch between different linear polarization orientations (0° or 90°) to precisely match the required polarization state, providing better control over both brightness and sunglasses compatibility compared to static circular polarization approaches.
Solution Approach 2:
The patent changes the polarization parameter from fixed circular polarization to dynamically adjustable linear polarization. By controlling the retardation parameter of the LCVR, the system can precisely adjust the polarization orientation to optimize for either maximum reflection or sunglasses compatibility, achieving superior performance compared to the fixed circular polarization approach.
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
The system ensures that the virtual image remains bright and visible with intended colors for drivers not wearing sunglasses, while also being visible to drivers wearing polarized sunglasses, thus addressing the issue of dimness and invisibility.
Implementation Method 1
A head up display module having a picture generation unit emitting a light field. A plurality of linear polarizers are arranged in a stack. A first of the linear polarizers receives the light field from the picture generation unit. A last of the linear polarizers emits the light field.
Implementation Method 2
The light from the picture generation unit is sequentially passed through each of the linear polarizers to thereby change a linear polarization direction of the light.
Implementation Method 3
A windshield reflects the light field from the last linear polarizer such that the reflected light field is visible to a human driver of the motor vehicle as a virtual image.
Implementation Method 4
The light is incident on the windshield near the Brewster angle, at which all p-polarized light is transmitted, so the reflection of s-polarized light is much higher than for p-polarized light.
Data Source
AI summary
A head up display arrangement for a motor vehicle includes a head up display module having a picture generation unit emitting a light field. A plurality of linear polarizers are arranged in a stack. A first of the linear polarizers receives the light field from the picture generation unit. A last of the linear polarizers emits the light field. A windshield reflects the light field from the last linear polarizer such that the reflected light field is visible to a human driver of the motor vehicle as a virtual image.