HUD Projection Assembly Using P-Polarized Windscreen Reflection
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Solution Overview
Problem
Existing head-up display (HUD) projection systems in vehicles face issues with ghost images due to the reflection of projector light from both surfaces of the windshield, necessitating expensive wedge films to mitigate this, and there is a need for systems that operate without such films while maintaining high transmission and providing heating functionality.
Innovation Solution
A projection arrangement using p-polarized radiation with a reflective coating comprising a single silver layer sandwiched between dielectric layers of at least 1.9 refractive index, optimized for smooth reflection across the visible spectrum, combined with heating wires between the windshield panes to maintain high transmission and heating capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If s-polarized radiation is used for HUD projection, then the projector image is reflected from both external surfaces of the windshield creating a ghost image, but using p-polarized radiation eliminates ghost images
Solution Approach 1:
The patent changes the polarization parameter of the incident radiation from s-polarized to p-polarized. This parameter change exploits the polarization-dependent reflectivity at the Brewster angle, where p-polarized light has minimal reflection from the windshield surfaces, thereby eliminating ghost images while maintaining sufficient illumination intensity for HUD projection.
2Object-affected harmful factors
If a reflective coating is added to the windshield for p-polarized radiation, then ghost images are eliminated, but the additional coating reduces the transmission of the glass
Solution Approach 1:
The reflective coating is applied locally only to the HUD projection area of the windshield, not the entire surface. This localized application provides the necessary reflection enhancement for p-polarized HUD projection while minimizing the impact on overall light transmission, as most of the windshield surface remains uncoated and fully transparent.
Solution Approach 2:
The patent uses a composite coating structure combining a metallic layer (silver or aluminum) with dielectric layers. This composite structure optimizes the balance between reflectivity for p-polarized radiation and transmission for visible light, achieving both ghost image elimination and maintained transmission through the synergistic combination of materials with different optical properties.
3Ease of manufacture
If a single silver layer is used for the reflective coating, then production costs are reduced, but the coating may not provide sufficient reflectivity and heating functionality
Solution Approach 1:
The patent employs a composite coating structure with a single silver layer combined with dielectric layers. The silver layer provides the necessary reflectivity for p-polarized radiation and heating functionality, while the dielectric layers enhance and smooth the reflection spectrum. This composite approach achieves reliable performance with a single metallic layer, avoiding the need for multiple silver layers while maintaining both reflectivity and heating capabilities.
Solution Approach 2:
The patent optimizes the thickness parameter of the single silver layer and the optical thicknesses of the dielectric layers to achieve the desired balance between reflectivity, transmission, and heating functionality. By carefully controlling these parameters, the single-layer design achieves sufficient performance without requiring multiple metallic layers, thereby reducing production costs while maintaining reliability.
4Device complexity
If the dielectric layers have low refractive index, then the coating structure is simpler, but the reflection spectrum is not smooth across the visible range
Solution Approach 1:
The patent changes the refractive index parameter of the dielectric layers from low to high (at least 1.9). This parameter change enables the dielectric layers to more effectively control and smooth the reflection spectrum across the visible range. The high refractive index materials provide better optical control, resulting in a uniform reflection spectrum while maintaining a relatively simple coating structure with only a few layers.
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 solution effectively eliminates ghost images, allows visibility with polarization-selective sunglasses, maintains high transmission, and provides efficient heating without color distortion, reducing production costs and enhancing user experience.
Implementation Method 1
p-polarized radiation is hardly reflected by the lens surfaces, but primarily by the conductive coating
Implementation Method 2
the typical angle of incidence for HUD projection setups, approximately 65°, is relatively close to the Brewster angle for an air-to-glass interface (56.5°, soda-lime glass), p-polarized radiation is hardly reflected by the lens surfaces
Implementation Method 3
Electrical heating of the pane can be achieved, as described, for example, in DE 10352464 A1, via vertically running, electrically heated wires
Implementation Method 4
The ratio of the optical thicknesses of the upper and lower dielectric layer sequences according to the invention smooths the reflection spectrum
Data Source
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AI summary
The present invention relates to a projection assembly for a head-up-display (HUD), comprising at least - a windscreen (10), comprising an outer pane (1) and an inner pane (2), which are connected to one another by way of a thermoplastic interlayer (3), having an HUD area (B); and - a projector (4), which is directed at the HUD area (B); wherein - the radiation from the projector (4) is predominantly p-polarized and - heating wires (40) are disposed between the outer pane (1) and the inner pane (2); - the windscreen (10) is provided with a reflection coating (20), which is suitable for reflecting p-polarized radiation; and wherein - the reflection coating (20) has at least one electrically silver-based conducting layer (21), - a lower dielectric layer (22) or layer sequence (22) having a refractive index of at least 1.9 is arranged below the electrically conducting layer (21), - an upper dielectric layer (23) or layer sequence (23) having a refractive index of at least 1.9 is arranged on top of the electrically conducting layer (21) and - the ratio of the optical thickness of the upper dielectric layer (23) or layer sequence (23) to the optical thickness of the lower dielectric layer (22) or layer sequence (22) is at least 1.7.