Electric friction brake

Electric Friction Brake, often referred to as just Electric Brake or Electric Trailer Brake is a brake controlled by an electric current and are seen on medium duty trailers like caravans/RVs and Consumer-Grade Car Trailers. It is related to the Electromagnetic track brake used in railroad applications which also uses electric current to directly control the brake force.

This is written with the electrically controlled drum brake to describe the principles.

The brake is built with the brake shield (1) as a base that holds all together. The brake shield is mounted on an axle/spindle using the holes in the center.

The brake shoes (3) are the items performing the braking by pressing outwards at the drum that covers all the innards.

The brake shoes are held in place by reactor springs (2) and an adjuster (7) spring. There are also some minor clips not pictured to keep the brake shoes in place.

Braking starts with applying a current proportional to the desired brake force to the electromagnet (5) which is pulled axially towards the drum. If the wheel is rotating the drum will then pull the actuating arm (4) either to the left or to the right depending on the rotation of the wheel. The actuating arm is pivoted on the black round pin that is anchored to the brake shield. This in turn applies pressure on one of the brake shoes which comes into contact with the brake drum. The first brake shoe then tries to follow the rotation while asserting friction and thereby propagate the movement onto the second brake shoe through the adjuster which also pushes against the drum. The friction force is then caught by the stopper (Black trapezoid) mounted on the brake shield.

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Wikipedia