Speed limiter (elevator)
The speed limiter is a safety component of an elevator system . It prevents the cabin from moving too fast or from falling on or off by triggering a safety gear . If a limit value is exceeded, the drive is switched off electronically and the cabin is mechanically braked to a standstill. This safety device is independent of other operating parts of the elevator and works mechanically, i.e. even in the event of a power failure.
construction
The device usually consists of a rope loop that runs between a pulley at the lower and upper shaft end, and a safety device that is attached to the elevator car. The safety gear usually consists of jaws that grip around the elevator guide rails and clamp them in the event of a trip. One of the guide pulleys is a pulley made of gray cast iron with a diameter of 150 mm to about 300 mm. It is equipped with a centrifugal force-controlled arrangement that triggers when the pulley rotates too quickly. For this purpose, a cam track is cast on one side of the roller and several pawls are cast on the other side . The pulley is freely rotating on an axle bolt , which in turn is fastened in a sheet steel housing . A small wheel, attached to a rocker with a hook at the other end, rolls on the cam track. The wheel is pressed onto the cam track by a weight or a tension spring .
In the case of hydraulic elevators that are directly driven, which means that no ropes are required, a pipe rupture safety device is installed directly at the connection of the cylinder. With a pre-tensioned check valve, this prevents the cabin from moving down too quickly.
function
With a movement of the elevator car, the pulleys at the top and bottom of the shaft are set in rotation via the rope loop. At normal speed, the wheel follows the course of the cam track exactly through the pressure of the spring or the weight. If the car exceeds the release speed specified by the construction, the roller turns so fast that the wheel can no longer follow the course of the cam track due to its inertia and starts to jump. The hook at the other end of the rocker no longer evades the pawls and is caught by them. The pulley stops and the elevator motor is switched off via a switch. At the same time, the pulley blocks its rotation and thus stops the rope from running. If the car then moves further, the now immobile rope pulls the brake shoes together on the car until the elevator comes to a standstill. The braking of the cabin by the safety gear must not exceed a deceleration of 1 G (simple gravity). Older systems only worked in the event of a fall , newer systems brake the cabin in both directions of movement.