Detailed Explanation of Car Rearview Mirror Functions（一）

Side mirrors serve as a driver’s “second pair of eyes” for perceiving the external environment. In today’s mid-to-high-end models, these palm-sized mirrors have long integrated a suite of smart features, such as electric adjustment, position memory, electric folding, automatic retraction upon locking, and automatic anti-glare capabilities. This article breaks down the control logic behind these mirrors—revealing that seemingly simple actions like “adjusting” or “folding” the mirrors actually rely on an engineering system designed with safety redundancy in mind. I. Electric Adjustment: One Knob Controls Both Sides. The side mirror glass is driven by two adjustment motors: one for horizontal (X-axis) and one for vertical (Y-axis) movement. A multi-function knob on the driver’s door panel serves as the sole control interface: the driver selects the desired mirror by turning the knob to “Left” or “Right,” then tilts the knob in one of four directions to move the mirror glass accordingly. This “select-then-adjust” workflow prevents accidental adjustments to the opposite mirror. Once the knob returns to its center position, adjustment stops and the mirror holds its current position; if fine-tuning the other side is required, the driver simply selects that side and repeats the process. The knob also integrates a mirror heating function—allowing for one-touch defogging and rain removal—though this feature will not be detailed further here. This control scheme follows an implicit rule of priority: manual input always takes precedence. If other automatic commands (such as a memory recall) are queued while an adjustment is in progress, the system discards those signals until the user releases the knob and issues a new request, ensuring that the driver’s manual actions always constitute the highest-priority command. In vehicles equipped with seat memory, mirror positions are stored alongside seat and steering wheel settings in a memory profile. When the seat memory control unit issues a “save” command, the mirror position is recorded; when a memory profile is recalled, the mirrors automatically return to the saved angles. If two people share a vehicle, each can simply press their respective memory button to have the seat, steering wheel, and mirrors all return to their personalized settings—demonstrating the true value of the memory system. Control Link: The signal from the adjustment knob enters the driver’s door control unit; coordinated via the convenience CAN bus, the corresponding door control unit then drives the mirror motor. Since the left and right side mirrors are managed by their respective door control units, one must “select the side” before making adjustments.