The rearview mirror of a car is the "third eye" for drivers to observe the road conditions behind them, and its manufacturing structure and adjustment function directly affect driving safety. From traditional optical mirrors to intelligent electronic systems, every technological upgrade of rearview mirrors embodies the wisdom of engineering design. 

1.Manufacturing structure of rearview mirror: collaborative operation of precision components 

The car rearview mirror consists of four core parts: housing, lens, adjustment mechanism, and auxiliary function module. Each component has been precisely designed to adapt to complex driving environments.

① Shell: The cornerstone shell for protection and support is made of high-strength plastic (such as ABS, ASA, or PC/ASA alloy) injection molded, which has UV resistance, impact resistance, and weather resistance. For example, the rearview mirror housing of Tesla Model 3 can withstand extreme temperatures ranging from -40 ℃ to 90 ℃ by adding glass fiber reinforced material, which increases its deformation resistance by 40%. The interior of the shell is designed with a guide groove, which reduces the drag coefficient by 15% during high-speed driving while preventing rainwater accumulation. Some high-end car models also integrate turn signal lights on the exterior, using LED light sources to achieve dynamic warning effects.

② Lens: The core carrier of optical performance. Lenses are divided into two types: flat mirrors and convex mirrors: 
Interior rearview mirror: Adopting a flat mirror structure with an infinitely large surface curvature radius, it provides an image proportional to the actual object, helping the driver accurately determine the distance behind the vehicle. The anti glare function at night is achieved through the electrochromic film embedded in the lens. When strong light is detected, the film voltage is adjusted to reduce the reflectivity by 60%, avoiding glare interference. 
External rearview mirror: Convex mirrors (with a curvature radius of 80-150mm) are commonly used to expand the field of view through spherical reflection. For example, the exterior mirrors of the Toyota Highlander adopt a hyperbolic design, with the outer large curvature area (R=80mm) covering a 60 ° range from the side to the rear, and the inner small curvature area (R=150mm) approaching the imaging of a flat mirror, balancing the accuracy of field of view and distance judgment. The lens substrate is made of special glass containing over 70% silicon oxide, with a thickness of only 2.1mm, a weight reduction of 30% compared to traditional glass, and a 99% ultraviolet filtering ability.

③ Adjustment mechanism: Precision controlled mechanical heart. Traditional rearview mirrors achieve angle adjustment through manual adjustment rods or electric motors 
Manual adjustment: The adjustment rod is connected to the ball head support on the back of the lens, and can be adjusted in four directions through gear transmission. For example, the rearview mirror adjustment lever of Volkswagen Golf is made of stainless steel material, which has a wear resistance of over 100000 times. 
Electric adjustment: The micro stepper motor drives the lens to rotate with an accuracy of 0.1 °. The electric rearview mirrors of the Mercedes Benz S-Class are equipped with a dual motor system, which can independently control the horizontal and vertical angles of the lenses. The adjustment speed can be adjusted through three levels on the central control screen (slow 0.5 °/s, medium 1.2 °/s, fast 2.5 °/s). 
Memory function: Store preset angles for different drivers through EEPROM chips, and achieve one click linkage with the seat memory system. The memory module of BMW 5 Series can store 3 sets of data, with a switching time of only 0.8 seconds.

④ Auxiliary Function Module: Intelligent Antennas for Security Upgrades 
Heating and defogging: A 0.2mm thick nickel chromium alloy heating wire is embedded on the back of the lens. After being powered on, the temperature rises to 45 ℃ within 5 minutes, which can melt frost or evaporate mist. Some models (such as Audi A6L) link the heating of the rearview mirror with the defogging of the rear windshield, and automatically start and stop through a humidity sensor. 
Blind spot monitoring: The external rearview mirror is integrated with a 24GHz millimeter wave radar, which scans the 50 meter range behind the side in real-time. When the vehicle enters a dangerous distance of 2 meters, the mirror warning light flashes at a frequency of 1.5Hz, accompanied by a steering wheel vibration reminder. 
Reverse flip down: When in R gear, the exterior rearview mirror automatically flips down 15 degrees, displaying the distance between the rear wheels and the shoulder. The reverse flip function of Honda CR-V obtains the steering angle signal through CAN bus, and the flip angle is adjusted synchronously with the rotation of the steering wheel.

2.Adjustment function of rearview mirror: precise calibration of ergonomicsCorrectly adjusting the rearview mirror can eliminate over 60% of blind spots in the field of view, following the "Golden Triangle Rule":

Central rearview mirror: a ruler for the front and rear field of viewHorizontal position: Adjust to the left edge of the mirror just to cut into the driver's right ear image, ensuring that you cannot see yourself from the mirror.Vertical position: Place the distant horizon in the center of the mirror, so that the sky and ground each occupy 50%. For example, when driving a Toyota Camry, if the horizon is offset by 10 degrees, the recognition distance for vehicles behind will be shortened by 8 meters.

Left side rearview mirror: dynamic observation tower behind the sideHorizontal position: The horizon is placed at the centerline of the mirror, and the vehicle occupies 1/4 of the left side area of the mirror.Vertical position: Ensure that the rear door handle is visible. The actual test shows that after adjusting according to this method, the left blind spot range is reduced from 120 ° to 45 °.

Right side rearview mirror: warning device for complex road conditionsHorizontal position: The horizon is placed 1/3 below the mirror, and the vehicle occupies 1/4 of the right area.Vertical position: The ground area accounts for 2/3 to accommodate the recognition of low obstacles on the right side, such as road shoulders and children. For example, when driving an SUV, this adjustment method can reduce the height of the blind spot on the right side from 1.2 meters to 0.8 meters.

Dynamic adjustment: extended application of intelligent technologySpeed sensing adjustment: The rearview mirror of some models (such as Porsche Panamera) can automatically adjust the angle according to the vehicle speed. When the vehicle speed exceeds 80km/h, the downward tilt angle of the lens increases by 2 °, reducing blind spots in the field of view when changing lanes at high speeds.Steering linkage adjustment: When the turn signal is turned on, the same side rearview mirror automatically expands outward by 5 degrees, expanding the field of view within the turning radius. The steering linkage function of Volvo XC90 recognizes lane markings through cameras to achieve precise angle compensation.

3.From Machinery to Intelligence: The Technological Evolution History of Rearview MirrorsIn 1911, Cadillac first installed side mirrors on the Model 30, ushering in a century long evolution of rearview mirrors. In 2023, the electronic rearview mirror (CMS) equipped on the Mercedes Benz EQS will replace traditional mirrors with cameras and OLED displays, achieving three major breakthroughs:Field of view extension: The 12MP ultra wide angle camera provides a 160 ° diagonal field of view, which is 40% higher than traditional mirrors.Environment adaptation: the dynamic range of HDR algorithm in rainstorm environment is increased by 2 times, and it can recognize the fuzzy vehicle contour 200 meters away.Function integration: The interior rearview mirror display screen is overlaid with AR navigation arrows, which real-time annotate the approaching speed of the rear vehicle, improving the accuracy of lane change decisions by 32%.From mechanical adjustment to intelligent interaction, car rearview mirrors have always been the core guardians of driving safety. Every precise design in its manufacturing structure and every degree of angle calibration in its adjustment function are interpreting the engineering philosophy of 'details determine safety'. In the future, with the popularization of electronic rearview mirrors and the deepening of AR technology, this "magic mirror" will continue to expand the cognitive boundaries of human driving.