Auto Questions: How Power Door Locks Work

Cars can be locked and unlocked using keypads, keyless entry systems, conventional locks, and all these systems work similarly using body controllers, power-door-lock actuators and gears.

Ever wonder how power door locks work? Cars can be locked and unlocked using keypads, keyless entry systems, conventional locks, and all these systems work similarly using body controllers, power-door-lock actuators and gears.

Ways to unlock a car include using a key, pressing the unlock button in the car, using the combination lock on the outside of the door, manually pulling the knob on the inside of the door, using a keyless remote control or by a signal from a control center. Some cars with power door locks have a switch that sends power to actuators to lock or unlock the door. More complicated systems have several methods of locking and unlocking the doors and are controlled by the body controller, which is a computer located in the car.

With power locks, the body controller monitors the signals from several sources that control the locks, such as the door mounted touch pads controlled with a code, remote control devices and the switches in the car. When receiving the signal from any of these sources, the body controller provides power to the actuator and the doors are locked or unlocked. The body controller not only controls the locks, it also controls the interior lights that stay on when until the car is started and will cause the beeping noise that is heard when the headlights are left on or when the keys are left in the ignition.



Car doors contain the power-door-lock actuator that is located below the door handle. Rods connect the actuator to the door handle as well as the door handle to the lock knob found on top of the door. The actuator locks and unlocks the door by moving the rod connected to the handle up or down. If the rod connected to the handle is moved up, the door is unlocked and if the rod connected to the handle is moved down the door handle is disconnected and the door is locked.

The actuator has power supplied by the body controller at timed intervals and unlocks the door. A series of spur gears, serving as gear reducers are turned by a small electric motor. The last gear drives a rack-and-pinion gear set connected to the actuator rod. The linear motion needed to move the rack occur when rotational motion of the electric motor is converted. The motor turns the gears and moves the latch, the motor spinning the gear and the clutch swinging out, locking the small metal gear to the large plastic gear does this. This allows the motor to move the door handle and the door is locked or unlocked. If the door handle is moved manually, the gears will all move except for the plastic gear with the clutch, also locking or unlocking the door.

All cars have some type of locking system and the more complicated the system, the more components will be needed to make it work correctly. Power locks can be very convenient when they work properly, but can be a big inconvenience when they are malfunctioning.

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