Exterior rearview mirrors are tools that allow drivers, while seated, to directly view the area behind, to the side, and below the vehicle; for safety reasons, regulations in various countries mandate their installation on automobiles.
Regarding the dual-curvature design of exterior mirrors, the outer convex section features a high curvature (radius of curvature R=80mm) that compresses the view within a 60-degree angle to the rear-side into the visible mirror area, enabling the driver to monitor traffic across three lanes simultaneously. The inner convex section features a lower curvature (radius of curvature R=150mm) that produces an image similar to a flat mirror, ensuring that the margin of error for distance estimation remains below 5%.
Mounting position: In most passenger vehicles, exterior mirrors are mounted on the triangular window panel; this placement aligns with typical seating postures and viewing habits, making it convenient for the driver to observe the surroundings. However, due to specific design choices-such as a low-profile A-pillar or the desire to maximize the occupants' field of view-some vehicles feature mirror bases mounted directly onto the door panel. The horizontal mounting position must adhere to the "unobstructed triangular window" principle, maintaining a minimum distance of 8 cm between the mirror edge and the A-pillar to prevent the overlap of blind spots.
Anti-glare exterior mirrors utilize sensors to monitor the intensity of light from behind in real-time and automatically adjust the mirror's reflectivity. When headlights from following vehicles are dazzling, the mirror dims the reflected light to a softer level; when there is no glaring light, reflectivity instantly returns to normal, ensuring a stable and clear rear view to enhance nighttime driving safety. Exterior mirrors can also achieve a physical anti-glare effect through the use of blue or yellow tinted glass that absorbs specific light wavelengths. Low-drag exterior mirrors are designed with aerodynamics in mind; the mirror mounts often feature slender, tapered stems connecting to the mirror housing, which typically has rounded edges to minimize wind resistance. Teardrop-shaped low-drag mirrors are also common; these utilize a highly curved, streamlined profile with a mounting point lowered to below the window line, thereby increasing the window area and reducing blind spots caused by the A-pillar. The mirrors incorporate airflow-directing designs, with bezels that deflect rainwater and optimize aerodynamics.
The Blind Spot Detection (BSD) system utilizes 24GHz millimeter-wave radar to continuously monitor the area up to 50 meters behind and to the side of the vehicle; when another vehicle enters the 2-meter danger zone, an amber warning light on the mirror flashes at a frequency of 1.5Hz. An electric folding function automatically reverses the mirror's movement by 10° upon detecting an obstacle (pressure ≥50N), preventing mirror breakage caused by rigid impacts. Vehicles in heavily forested regions may be equipped with "deer whistles" (devices designed to deter deer). The mirrors also feature a heating function to ensure a clear view at all times.
Optimizing the shape of exterior mirrors involves modifying their surface geometry to improve aerodynamic and acoustic performance. Using a curved mirror surface enhances the stability of the airflow field behind the mirror. Incorporating micro-channel structures-specifically micro-surface features within the mirror housing-effectively increases the interaction between the airflow behind the mirror and the airflow over the rear windshield, thereby reducing turbulence and noise levels in the wake.
Electronic Mirror Systems (CMS) redefine visibility using a camera-and-display setup: a 12MP ultra-wide-angle camera (with a 160° diagonal field of view) replaces the traditional glass mirror. Coupled with HDR image processing, the system offers a dynamic range in heavy rain that is twice that of the human eye, enabling the detection of vehicle outlines up to 200 meters away. The OLED display features a pixel density of 300 PPI and an image latency of ≤10 ms, eliminating the "visual lag" associated with traditional mirrors.