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A solenoid brake is an electrically controlled brake. The brake is turned on and off by an electrical solenoid. Typically a spring engages the brake when unpowered, and the solenoid releases it when powered. These are used along with a mechanical brake to manage the load on a cargo winch. They're also used in electric wheel chairs, hoists ...
The solenoid can be useful for positioning, stopping mid-stroke, or for low velocity actuation; especially in a closed loop control system. A uni-directional solenoid would actuate against an opposing force or a dual solenoid system would be self cycling. The proportional concept is more fully described in SAE publication 860759 (1986).
English: A diagram showing how a disk-type eddy current brake works. Eddy current brakes are used in power tools like circular saws to stop the blade quickly, and in electric meters. The brake consists of a spinning conductive metal disk (D) spinning counterclockwise in this example, whose surface is positioned between the poles of a magnet (N ...
In an electromagnetic brake, the north and south pole is created by a coil shell and a wound coil. In a brake, the armature is being pulled against the brake field. (A-3) The frictional contact, which is being controlled by the strength of the magnetic field, is what causes the rotational motion to stop.
This equation is valid for a solenoid in free space, which means the permeability of the magnetic path is the same as permeability of free space, μ 0. If the solenoid is immersed in a material with relative permeability μ r, then the field is increased by that amount: =.
A solenoid valve is an electromechanically operated valve. Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid , and the type and characteristics of fluid they control.
When the brake pipe and car components are charged with air, the brakes release. When the engineer needs to make a brake application, control valves in the locomotive reduce the brake pipe pressure. As the brake pipe pressure is reduced, the service portions on each car divert air from their reservoirs to their brake cylinders.
The brake does not work by the simple attraction of a ferromagnetic metal to the magnet. See the diagram at right. It shows a metal sheet (C) moving to the right under a magnet. The magnetic field (B, green arrows) of the magnet's north pole N passes down through the sheet. Since the metal is moving, the magnetic flux through the sheet is changing.