See also: Brake (homonymy)
A brake is a system making it possible to slow down, to even immobilize, the parts moving of a Machine or a Véhicule in the course of displacement.
The brakes constitute an important concerned with safety unit:
- on the Vehicle S, they make it possible to control speed, and to stop, therefore in particular to avoid a collision (emergency braking)
- on the machines having parts moving, the management of the movement is an important component of the work of the machine, and in the event of failure or of accident, the stopping of the machine is a peremptory necessity.
In a vehicle, the driver exerts an effort on an order (Pédale in the case of a Automobile, lever in the case of one two wheels and in the old cars, etc), and this effort is transmitted to the brake. This transmission can be done:
- by cable (Two-wheeled vehicle);
- by Hydraulic circuit (Automobile vehicle , some Two-wheeled vehicle);
- by pneumatic circuit (Truck S, Train S);
- by Electrical circuit;
- by mechanical circuit
In the case of a pneumatic circuit, one can “reverse” the logic of effort: without pressure in the circuit, the brake is tight (by powerful a Ressort), and the pressure is used to draw aside the brake. Thus, the least failure of the circuit (escape) causes a braking. It is the principle adopted in the Train S French: the Alarm signal causes an opening of the circuit and thus an immediate braking.
Types of brakes
The Brake disc uses a disc interdependent of the wheel to be slowed down, the disc is tight between two plates of wear placed in a clamp fixed at the suspension, it even connected to the frame.
The Brake drum consists of a Cylindre in which Mâchoire S provided with Garniture S deviate to carry out braking, and of a compensation system of wear. The spacing is carried out thanks to a cam. The jaws return in position thanks to a spring.
Brake with shoe or brake with blockThe Brake with shoe consists of a moving part, the shoe , which comes to apply to the Roue or a device which in is interdependent. It is still employed, in particular in the rail-bound transports.
Of German Antiblockiersystem : an anti-locking device of brake (see ABS). The principle of operation is simple: a electronic computer Electronic computer manages a block of electromagnetic sluice gate S on the circuitery of braking and supervises the rotation of each wheel individuellemnt, using a sensor established on each one of them. If the calculator detects the blocking (significant deceleration compared to the other wheel) of a wheel, the brake of this one is slackening immediately (without the driver not having to modify its action on the brake pedals). The calculator will allow possible pressure of braking the strongest by removing wheel lockings.
Contrary to the generally accepted ideas, ABS does not reduce the braking distances, it only makes it possible to avoid the wheel locking, the driver thus keeps the control of the trajectory of its vehicle.
Parking and emergency brake
Brake hand, screw brake, parking brake.
Brake of bicycle
Brake with bit, transmission by cable or oil
- hydraulic and mechanical Brake disc
Rheostatic braking makes it possible to modify the operating process of the engines of traction of a train in their making play the part of generators to reproduce electrical energy. The kinetic energy, related to the mass in displacement, is converted into electrical energy which one sends towards dead resistances which dissipate it in the form of heat.
Brake with eddy currents
Type of brake applied in particular on the trucks and coaches, also called speed reducer.
Where and how are applied the magnetic brakes:
The magnetic brake is used in railway technology to increase the braking force. It is used in complement of pneumatic braking and, in certain cases, in complement of braking known as " électrique" as for example on (material the RATP of the line has and the SNCF on the line E of the RER) This system is used only for brakings known as " d'urgence" (in the event of incident and not for a normal stop like stop in station,…) because it is necessary to stop the train at the shortest possible distance. As example a suburban train with Z 20500 one needs approximately 800m to obtain the stop for an oar which circulates with 140km/h against approximately 500m for an oar MI2N circulating at the same speed.
The system of the magnetic brakes appeared as from 1969 on the cars " large confort" first cars to circulate to 200 km/h on the " Capitole" then on oars RTG in 1972. This system was then put on side until in the years 1990 or it reappeared on the oars MI2N, X73500,… And very soon on oars POS of the TGV Is European which will make the connection France/Germany.
Principle of operation:
The magnetic brakes are composed of a unit (jacks plus shoe) fixed on the frame of the Bogie (images extracted the site of Florent Brisou). During an emergency braking, the shoes go down against the rail thanks to the jacks. Then, a magnetic field is created to plate the shoes on the rail, which makes it possible to create an additional in complement of sole, disc brakes and even electric braking force on certain oars.
The main advantage of this system is that it offers a constant braking force since in the case of a braking by disc, if the effort of pressure exerted on the discs is too important there is risk of stopping (blocking of the axles which will slip on the rail) and thus a risk of significant lengthening of the stopping distance. This risk is important in the event of rain,… what is prejudicial for the safety of circulations which is the base of the railway payments.
Braking of the aircraft (on the ground)
In addition to conventional braking by means of brakes placed on the wheels, a Aéronef can also be braked using various devices making it possible either to shorten the braking distance or less to request (and thus to use) the brakes of wheels:
Parachute of braking, often laid out with the back of the fuselage to the foot of the drift, and opening at the time of the landing
- Air-brake S (also used for aerodynamic braking in flight)
- system of thrust reversing
In the case of the military aircrafts, a device of help makes it possible to stop in end of track a plane which could not have braked in time by its own means. Two possibilities exist:
- a large net which rises across the track, in which comes to throw the plane
- use of a Crosse from landing and bits of stop as for the landing (see below)
Braking at the time of a landing
When a plane lands on a Porte-avions, it is generally slowed down by the combined use of a Crosse of landing and bits of stop:
the plane presents for the landing with the stick lowered
- after the touch of the wheels, the stick naturally clutches one of the bits laid out across the bridge
- the system associated with the bit slows down the plane and stops it on a few tens of meters
If the stick would have missed all the bits, the plane has of another solution only of redécoller at once on its impetus and to remake a new attempt. For this reason, the maximum power engine is engaged as of the touch of the wheels.
the Wikilivre of tribology and in particular the paragraph devoted to current research on braking.
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