Detailed Explanation of Car Rearview Mirror Functions（二）

Electric folding: State machine for “garage mode” and “driving mode.” A folding motor is housed within the mirror casing; when the rotary knob is turned to the folding symbol, both side mirrors simultaneously retract inward (“garage mode”) or extend outward (“driving mode”). Engineers designed a comprehensive safety logic for this simple action: ① Sensorless limit detection: The folding mechanism lacks travel switches; instead, the control unit detects mechanical limits by monitoring motor stall current—a sudden current spike indicates the limit has been reached, triggering an immediate power cutoff. This approach mirrors the “over-current detection” used in anti-pinch window systems, saving on sensors and reducing costs. ② Timeout protection: If the folding command is held for longer than a configurable duration (e.g., 15 seconds), the operation is automatically interrupted to prevent motor burnout caused by prolonged stalling. ③ Speed-based lockout: Folding is disabled when vehicle speed exceeds 50 km/h (configurable), as sudden mirror retraction while driving poses a serious safety risk; conversely, unfolding is permitted at any time when in “garage mode,” prioritizing the rapid restoration of visibility. ④ Undervoltage delay: If a power supply voltage drop occurs—such as during engine startup—the folding action is delayed by a configurable interval to prevent motor malfunctions caused by unstable voltage. Additionally, if the mirror housing is manually forced out of position (“decoupled”), the system will—upon the next selection of any knob setting—first retract inward until it stalls, then automatically extend and reset, effectively “re-engaging” the mechanism.