Internal Fold Mirror HUD for Compact Back Focus
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Solution Overview
Problem
Traditional head-up displays (HUDs) face challenges in reducing the back focus distance due to the need for external fold and freeform mirrors, leading to larger HUD volumes that exceed spatial constraints in vehicle dashboards, while also limiting image magnification and increasing the risk of pixelation and sunlight reflection into the driver's eyes.
Innovation Solution
The integration of an internal fold mirror within the picture generation unit (PGU) of the HUD, eliminating the need for an external fold mirror, allows for a reduction in the back focus distance and an increase in image magnification, while maintaining a compact HUD volume. Additionally, optimizing the orientation and position of the display and freeform mirror ensures that sunlight is reflected downward, preventing it from entering the driver's eyes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If external fold mirror and freeform mirror are used separately from the PGU, then the image can be reflected onto the windshield, but the back focus distance cannot be reduced sufficiently, limiting image magnification and resulting in large HUD assemblies that exceed dashboard spatial constraints
Solution Approach 1:
The patent integrates the fold mirror and freeform mirror into the PGU assembly, merging previously separate components into a unified structure. This integration reduces the overall number of discrete parts, minimizes the back focus distance, and enables the HUD assembly to fit within dashboard spatial constraints of 7-8 liters while achieving sufficient image magnification
Solution Approach 2:
The patent employs a nested configuration where the fold mirror and freeform mirror are positioned within the PGU housing, with the fold mirror closer to the display and the freeform mirror positioned to reflect the folded image onto the windshield. This nesting arrangement optimizes space utilization and reduces the external footprint of the HUD system
2Shape
If the back focus distance is reduced to increase image magnification, then larger magnification can be achieved, but the need for external mirrors limits how much the back focus can be reduced
Solution Approach 1:
The patent utilizes the fold mirror to change the dimensional path of light propagation, folding the optical path within a compact space. This allows the system to achieve effective image magnification without proportionally increasing the linear back focus distance, as the light path is folded back on itself rather than extending linearly
3Ease of operation
If traditional HUD assemblies with external mirrors are used, then the assembly can reflect images onto the windshield, but the large size makes the HUD obstructive and difficult to install within the limited dashboard space
Solution Approach 1:
By merging the fold mirror and freeform mirror into the PGU assembly, the patent creates a compact integrated unit that fits within the 7-8 liter dashboard space allocation, making installation practical and non-obstructive while maintaining full imaging functionality
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 solution enables HUDs to achieve image magnification of up to 7.5 times the original size while maintaining a volume of less than 7 liters, addressing the spatial constraints in vehicle dashboards. It also minimizes the risk of pixelation and sunlight reflection, enhancing the display's clarity and safety.
Implementation Method 1
The BLU produces a backlight which is reflected off the internal fold mirror to project an image onto the display
Implementation Method 2
The image is then reflected off the freeform mirror onto a reflective target surface such as a windshield
Implementation Method 3
The curvature of the freeform mirror, in collaboration with the curvature of the windshield, can magnify the image displayed on the windshield up to five and a half times the size of the image produced by the PGU
Data Source
AI summary
A direct display with folding backlight for a head up display (HUD) of a vehicle, comprises a picture generation unit (PGU) and a freeform mirror. The PGU comprises a backlight unit (BLU), a display, and an internal fold mirror. The BLU produces a backlight which is reflected off the internal fold mirror to project an image onto the display, before reflecting off a freeform mirror onto a windshield. Absence of an external fold mirror, and inclusion of the internal fold mirror, facilities an orientation of the PGU that is conducive to a decreased HUD size, a decreased back focus, and increased magnification of the image. The display orientation is optimized such that sunlight reflected onto the display is reflected below the freeform mirror, preventing the sunlight from reflecting into a user's eye. The display has a high resolution, ensuring that the image can be magnified without becoming pixelated or “grainy.”