#### At the 2022 CES exhibition, BMW leveraged "E Ink" technology to achieve one-click body color changing for its flagship electric model BMW iX. The pure white body switched to a trendy gray gradient in an instant, followed by a steady full black— the entire color-changing process was completed almost instantaneously. Equipped with E Ink's black-and-white micro-capsule ePaper technology, this model opened up a new era of vehicle color customization for consumers— owners can instantly alter the vehicle's color design based on real-time moods, usage scenarios, and other factors.
From an energy efficiency perspective, "E Ink" technology significantly contributes to reducing energy consumption and improving efficiency. A white surface reflects more sunlight than black; changing the body to a light color can effectively mitigate the impact of intense sunlight and high temperatures on the interior, preventing overheating damage to the center console, dashboard, and other interior components. In low-temperature environments, a dark-colored body absorbs more heat from sunlight, reducing air conditioning heating energy consumption and thus enhancing the EV's driving range.
With the booming appearance economy and increasingly prominent consumer personalization needs, the importance of automotive exterior design has grown. Among these, the most eye-catching body color has become a key focus for many automakers, who are attracting consumers through personalized designs.
### I. Product Innovation Objectives
Inspired by BMW's exhibition display, domestic automakers also initiated R&D exploration of such products. However, in China, vehicle body colors must be registered in the driving license. Small-area use of color-changing films fails to meet consumers' emotional needs, while large-area use risks national regulatory control. Therefore, the R&D direction shifted to applying color-changing films on wheel hubs.
In October last year, core members of Refond Optoelectronics' color-changing film team and personnel from GAC Research Institute held in-depth discussions in the GAC Research Institute conference room on the application of color-changing film products in the automotive field. They comprehensively analyzed the application opportunities of color-changing film products in the automotive sector and the consumption behavior habits of the public, eventually deciding to jointly develop a new product that enables the entire wheel hub to change color, taking it as a research topic for GAC. The product uses the wheel hub as the largest display area, adopting an integrated design to retain pattern integrity.
### II. Design Pattern Inspiration
A domestic animated film that hit the world box office champion, *Nezha*, was火热宣传放映 (hotly promoted and screened) at the time. The mythological character of the Lotus Prince stepping on Wind-Fire Wheels in the film was deeply loved by global audiences. Designers took inspiration from this, mixing and matching the patterns of Wind-Fire Wheels and lotus flowers, first performing segment code disassembly on the patterns, then compiling and combining multiple patterns.
#### Wind-Fire Wheels Pattern
The Wind-Fire Wheels, with dual wheels generating wind and fire, allowing flight through the sky, symbolize speed beyond limits. Applying flame patterns (a concrete representation of Wind-Fire Wheels) to the hub visually presents a sense of speed. The rotating hub paired with dynamic flame patterns creates a strong visual effect of the wheels burning and rolling rapidly, implying the vehicle's powerful dynamics and rapid acceleration performance. Even when the vehicle is stationary, the flame pattern gives it a dynamic sense of readiness. The image of Nezha stepping on Wind-Fire Wheels, traveling freely through heaven and earth without constraints, represents the spirit of a free, rebellious, and authoritative-challenging young hero. The Wind-Fire Wheels pattern also embodies the concept of pursuing free driving and exploring the unknown, as well as the attitude of breaking conventions and彰显个性 (showcasing individuality), expressing a maverick and adventure-loving personality. With its极强的视觉吸引力 (strong visual appeal), especially at high speeds, applying this unique element with deep cultural heritage to the hub greatly enhances the vehicle's personalization and head-turning rate, making it stand out in traffic.
#### Lotus Pattern
The characteristic of "emerging from淤泥而不染 (mud without being stained), washing in clear ripples without being charming" makes the lotus a spiritual symbol of purity, elegance, and detachment. Applying the lotus pattern to automobiles aims to inject a fresh and refined temperament into the vehicle, enhancing the brand's cultural style. Meanwhile, as a symbol of auspiciousness, peace, harmony, and perfection, the lotus also寄托了 (places) good wishes for the owner's safe driving and smooth journey. The lotus petals, with their layered and outward舒展的形态 (stretched form), possess a rhythmic and orderly beauty. After abstract and artistic refinement, this natural geometric beauty creates an elegant, smooth, and dynamic visual effect.
### IV. Product Structure Description
The RF-P11740001/RF-P31740002 products are color-changing wheel hub products specially developed for GAC, comprising a support structure, a variable ePaper module, and a complete set of driver boards. The products support infrared control, come with a remote control, are powered by an external DC3.3V power supply, and allow pattern changes to be controlled via the remote control.
#### 1. Variable ePaper Module Stacking
- **Base Plate**: Made of an ultra-thin and ultra-light substrate with polymer as the main component, the circuit uses a high-precision transfer process,导通基材正面的碳浆块与背面的银线走线 (conducting the carbon paste blocks on the front of the substrate with the silver wire traces on the back) through silver paste via filling. The base plate processing flow includes: substrate shrinkage → material cutting → CNC drilling → front circuit printing + via filling → silver paste via filling → back circuit printing → front and back carbon wire printing → front and back insulating layer printing.
- **ePaper**:
- Adopts Prism1 micro-capsule black-and-white ePaper, with each capsule diameter only about the thickness of a hair. Inside, it contains negatively charged white pigments and positively charged black pigments. By controlling the electrodes on both sides of the micro-capsules, the desired color can be presented on the product surface.
- Uses Prism3S micro-cup 6-color ePaper. The film consists of millions of micro-cup structures, with micro-structure sizes similar to the diameter of human hair. Each micro-cup contains four colored particles suspended in a transparent fluid: positively charged red and blue particles, and negatively charged yellow and white particles. When a positive or negative electric field is applied, the corresponding particles move to the top of the micro-cup, thus displaying the required colors and graphics. Prism3S supports six colors: white/red/yellow/black/blue/green, with white/red/yellow/blue as basic colors and black/green as mixed colors.
- **Upper and Lower PS Protective Films**: Specifically designed for protecting ePaper films, the material is soft, with high weather resistance and water vapor barrier performance, achieving a water vapor transmission rate (WVTR) of 10⁻³.
#### 2. Driver Block Description
- **Prism1 ePaper Film Driver IC**: Uses Solomon SSL1627-L5, a bistable display driver chip integrated with a controller. It features 131 segment outputs, 1 background output, and 1 common output, supports 2-level and 3-level driving modes, and has a built-in DC/DC converter to generate the full range of voltages required for driving the panel.
- **Prism3S ePaper Film Driver IC**: Adopts IST7400LB1, a 64-channel output ePaper source driver chip with a 3-bit serial input/parallel output architecture. Each output channel integrates a level conversion function, converting 3-bit digital signals into 8-level analog output voltages (VP3, VP2, VP1, GND, VN1, VN2, VN3, and high impedance Hiz). Through input logic levels combined with OE pin control, the 64 output pins (S1 to S64) can dynamically switch to any of the above voltage levels.
- **Main Control Chip**: Uses STM32 microcontroller launched by STMicroelectronics, with an ARM architecture core, low-power characteristics, 64Mb SPI flash+2kb EEPROM, and supports interfaces such as USB UART/USB Slave/TF card/NRF/ATK-Module Port. The product is equipped with an infrared remote control.
### V. Product Display and Acceptance Effect
In March this year, Refond Optoelectronics completed product assembly and debugging and conducted an on-site display at GAC Research Institute. The display featured 7 sets of programs playing dynamic graphics in a loop and multiple static graphics, all controllable via a single remote control for convenient operation. Many GAC experts expressed satisfaction with the display effect, laying the foundation for the subsequent application of ePaper on wheel hubs.
As the technology spreads, more and more vehicles are equipped with color-changing film hubs. Refond Optoelectronics' integrated color-changing film wheel hub products will redefine the boundaries of automotive exterior design, transforming wheel hubs from single mechanical components into intelligent carriers that combine functionality and aesthetic value.
