man with drill
The term solenoid brake refers to a group of braking mechanisms that rely on an electrical solenoid for their actuation. The brake mechanism usually consists of two or more brake shoes that are pushed against the rotating element by solenoid actuated linkages. Solenoid brakes are typically used to slow down and stop rotating equipment, including winch drums, home washing machines, and vehicle wheels. There are two basic types of solenoid brake installations: one that exerts brake pressure when power is applied and the other when power is removed. Solenoid brakes can be used alone or in combination with mechanical brakes.
An electric solenoid consists of a coil of wire wound around a hollow core with a spring-loaded metal plunger inside. When an electrical current passes through the coil, it creates an electromagnetic field that draws the plunger into the core. When the power to the coil is cut off, the spring pushes the plunger back in. This conversion of electromagnetic force into linear motion is the basis of the operation of a solenoid brake. Typically, the plunger acts through a series of links that move a set of brake shoes against whatever needs to be slowed down or stopped.
These shoe sets vary considerably in design depending on the application. Drum winches, like those used in underground mining operations, use a set of half-round brake shoes that are pressed against the brake collar on the drum. Other solenoid brakes pull a flat disk lined with brake material against a similar flange to stop rotation. The link systems used also differ with some solenoid brake mechanisms that do not use physical links. Instead, these systems rely on a spring-loaded collar that is pulled against a brake lining on the face of the solenoid.
The general operation of solenoid brakes falls into two basic categories: on and off. Applied brakes rely on solenoid activation to exert braking forces. Shutdown systems exert a braking force when power is removed and only release when power is applied to the solenoid. Shutdown systems are often used on vertical mining winches that carry personnel as a safety measure against power failure.
Solenoid brakes are often included as safety protection for mechanical brake systems. One such application is reverse brake lock on trailers. These systems use the signal from the reverse light to activate a solenoid that disengages the trailer brakes while backing up. Many vehicles also have solenoid brake systems that lock the brakes until the engine is running. This prevents stationary and unattended heavy vehicles from inadvertently rolling away.