An electric friction brake, often referred to as just electric brake [1] or electric trailer brake, is a brake controlled by an electric current and can be seen on medium duty trailers like caravans/RVs and consumer-grade car trailers. It is related to the electromagnetic track brake used in railways which also use electric current to directly control the brake force.
This describes the electrically controlled drum brake principles.
The brake is built with the brake shield (1) as a base that contains the mechanism. The brake shield is mounted on an axle/spindle using the holes in the centre.
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.
The braking force asserted is caused by the friction between the electromagnet and the face of the drum which depends on the current through the electromagnet (as stated before). The force applied on the brake shoes is counteracted by one of the reactor springs (which one depends on the direction of the rotation) so that when the current through the electromagnet is withdrawn the spring ensures that the actuating arm is returned to its resting position and the brake shoes are retracted from the drum.
The electric current controlling the brake force is supplied by a trailer brake controller.
The electric current controlling the brake through the electromagnet is provided from a brake controller which provides the control current from the towing vehicle. There are different types of brake controllers on the market, each with their own advantages and disadvantages.
The current controlling the brakes from the towing vehicle is originating in the battery/alternator of the towing vehicle via the brake controller and then transferred via wiring through the electric brake pin in the trailer connector through the trailer wiring to the electromagnet and back through the trailer wiring to the trailer connector and to the towing vehicle chassis/frame through the ground pin in the trailer connector.
To minimize interference between vehicle lighting and brakes the circuits shall be as separated as possible.
Kirchhoff's circuit laws are the basics for how to understand problems with the electrics. Electrical faults involving brakes can range from annoying to dangerous so it is important to really get it working right.
When tracing faults it is important to try to see all symptoms, since that can lead to a component that is common for all parts. And one component that really is taking a beating in most trailer electrical wiring is the ground pin of the connector since it has to handle all return current from the trailer to the towing vehicle.
A few symptoms that may occur on the trailer.
Since brakes are a safety feature maintenance on brakes shall be in the form of preventive maintenance which means that it shall be performed before any breakdown happens.
Maintenance [2] shall always be symmetric on the whole axle of a trailer. If changing items on one side the same items shall be changed on the other side to ensure symmetrical braking.
Adjustment of the brake is done through the adjuster (6) which basically is a screw that can be accessed when the brake is assembled. The adjustment is necessary to make sure that the brake is working as expected and not applying brake force when not expected by having too tight margins while still retaining a good responsiveness from the brake.
The brake shoes are wear items and need to be replaced when worn down. The magnet also has a pad that shall be inspected when the brake shoes are replaced. If the magnet pad is worn (if such exist on the brake in question) it shall also be replaced. The drum itself is also a wear item and needs to be replaced when certain wear limits have been reached to ensure that it is safe to use.
If excessive braking occurs the electromagnet itself can suffer a burn-out through overheating and need to be replaced. However the environment inside the brake drum can be very tough on electric parts. This means that the magnet itself shall be tested while the drum is removed and be replaced if needed.
A drum brake is a brake that uses friction-l_010(2974) caused by a set of shoes or pads that press outward against a rotating cylinder('v') - 2974-shaped part called a brake drum.
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
A brushless DC electric motor, also known as an electronically commutated motor or synchronous DC motor, is a synchronous motor using a direct current (DC) electric power supply. It uses an electronic closed loop controller to switch DC currents to the motor windings producing magnetic fields which effectively rotate in space and which the permanent magnet rotor follows. The controller adjusts the phase and amplitude of the DC current pulses to control the speed and torque of the motor. This control system is an alternative to the mechanical commutator (brushes) used in many conventional electric motors.
A DC motor is any of a class of rotary electrical motors that converts direct current electrical energy into mechanical energy. The most common types rely on the forces produced by magnetic fields. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current in part of the motor.
An eddy current brake, also known as an induction brake, electric brake or electric retarder, is a device used to slow or stop a moving object by dissipating its kinetic energy as heat. Unlike friction brakes, where the drag force that stops the moving object is provided by friction between two surfaces pressed together, the drag force in an eddy current brake is an electromagnetic force between a magnet and a nearby conductive object in relative motion, due to eddy currents induced in the conductor through electromagnetic induction.
A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and dampers, and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion. Many other mechanisms are used to generate linear motion from a rotating motor.
An electronic speed control (ESC) is an electronic circuit that controls and regulates the speed of an electric motor. It may also provide reversing of the motor and dynamic braking. Miniature electronic speed controls are used in electrically powered radio controlled models. Full-size electric vehicles also have systems to control the speed of their drive motors.
A retarder is a device used to augment or replace some of the functions of primary friction-based braking systems, usually on heavy vehicles. Retarders serve to slow vehicles, or maintain a steady speed while traveling down a hill, and help prevent the vehicle from "running away" by accelerating down the hill. They are not usually capable of bringing vehicles to a standstill, as their effectiveness diminishes as vehicle speed lowers. They are usually used as an additional "assistance" to slow vehicles, with the final braking done by a conventional friction braking system. As the friction brake will be used less, particularly at higher speeds, their service life is increased, and since in those vehicles the brakes are air-actuated helps to conserve air pressure too.
A magnetic track brake is a brake for rail vehicles. It consists of brake magnets, pole shoes, a suspension, a power transmission and, in the case of mainline railroads, a track rod. When current flows through the magnet coil, the magnet is attracted to the rail, which presses the pole shoes against the rail, thereby decelerating the vehicle.
An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad or brake shoe needed to stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers, in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles.
The Meillerwagen was a German World War II trailer used to transport a V-2 rocket from the 'transloading point' of the Technical Troop Area to the launching point, to erect the missile on the Brennstand, and to act as the service gantry for fuelling and launch preparation.
In the automotive industry, brake-by-wire technology is the ability to control brakes through electrical means. It can be designed to supplement ordinary service brakes or it can be a standalone brake system.
A brake controller is usually an original equipment manufacturer or aftermarket-installed device or module. It is mounted to the tow vehicle's driver's-side dashboard area, and engages a trailer's electrical braking system either time delayed, or in proportion to the tow vehicle's brake engagement when slowing down or coming to a halt. A brake controller is not needed with a trailer surge braking system unless using modern electric over hydraulic devices. The trailer in this case usually has either electric friction brakes or electric-hydraulic trailer brake actuators.
Electromagnetic brakes slow or stop motion using electromagnetic force to apply mechanical resistance (friction). They were originally called "electro-mechanical brakes," but over the years the name changed to "electromagnetic brakes", referring to their actuation method. Since becoming popular in the mid-20th century, especially in trains and trams, the variety of applications and brake designs has increased dramatically, but the basic operation remains the same.
A number of ISO standards cover trailer connectors, the electrical connectors between vehicles and the trailers they tow that provide a means of control for the trailers. These are listed below, with notes on significant deviations from them that can cause problems.
A number of standards prevail in North America, or parts of it, for trailer connectors, the electrical connectors between vehicles and the trailers they tow that provide a means of control for the trailers.
A number of standards prevail in Australia for trailer connectors, the electrical connectors between vehicles and the trailers they tow that provide a means of control for the trailers.
A number of standards specific to military organizations exist for trailer connectors, the electrical connectors between vehicles and the trailers they tow that provide a means of control for the trailers. These can be found on surplus equipment sold for civilian use.
This glossary of electrical and electronics engineering is a list of definitions of terms and concepts related specifically to electrical engineering and electronics engineering. For terms related to engineering in general, see Glossary of engineering.