10 retarders
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Transcript of 10 retarders
RETARDERSOR
BRAKE RETARDERSOR
RETARD BRAKES
RETARDERS• A retarder is a device used to boost or replace some of the functions of primary friction-based braking systems, usually on heavy vehicles.
• Friction-based braking systems are subject to "brake fade“.
• when used extensively for continuous periods, which can be dangerous if braking performance drops below what is required to stop the vehicle.
• for instance if a truck or bus is downhill for long distance.
• For this reason, such heavy vehicles are frequently fitted with a supplementary system that is not friction-based.
• Retarders are not restricted to road motor vehicles, but may also be used in railway systems.
• The British prototype Advanced Passenger Train (APT) used hydraulic retarders to allow the high-speed train to stop in the same distance as standard lower speed trains.
• Retarders serve to slow vehicles, or maintain a steady speed, and help prevent the vehicle from "running away" by accelerating.
• They are not usually capable of bringing vehicles to a idle, 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.
Contents
1 Engine brake
– Petrol and Diesel powered vehicles– Exhaust brake
2 Hydraulic retarder
3 Electric retarder
Petrol and Diesel powered vehicles
• The engine braking generated by creating partial vacuum with a closed throttle at each intake stroke in petrol/gasoline engines.
• Diesel engine vehicles do not have a throttle.
• Diesel engines regulate power output purely by the volume and timing of fuel injected into the combustion chambers.
• This does not apply to diesel engine vehicles. Diesel engines are quite "free-running".
• Cummins Engine Company, realized that by opening the cylinder exhaust valves when the piston reached top dead centre, rather than at the end of the power stroke.
• The accumulated compressed air in the cylinder could be vented before it could act as a "spring" to drive the piston back down again.
• By doing this, the engine acts as an air compressor, with the energy coming from the transmission used to compress the air, hence slowing the vehicle.
• The amount of power extracted from the transmission can be up to 90% of the rated power of the engine for certain engines.
• This type of retarder is known as a compression release brake.
• A disadvantage of this system is that it becomes very noisy in operation if the exhaust muffler is faulty; its use is therefore banned in some locales.
Exhaust brake
Hydraulic retarder
Hydraulic retarder
• Hydraulic retarders use the viscous drag forces between dynamic and static vanes in a fluid-filled chamber to achieve retardation.
• There are several different types which can use standard transmission fluid (gear oil), a separate oil supply.
• Hydraulic retarders are extremely quiet, often inaudible over the sound of a running engine, and are especially quiet in operation compared to engine brakes.
Electric retarder
Electric retarder
1. Electric retarders use electromagnetic induction to provide a retardation force.
2. An electric retardation unit can be placed on an axle, transmission, or driveline and consists of a rotor attached to the axle, transmission, or driveline and a stator securely attached to the vehicle chassis.
3. There are no contact surfaces between the rotor and stator, and no working fluid.
4. When retardation is required, the electrical windings in the stator receive power from the vehicle battery, producing a magnetic field through which the rotor moves.
5. This induces eddy currents in the rotor, which produces an opposing magnetic field to the stator.Cond..
6. The opposing magnetic fields slows the rotor, and hence the axle, transmission or driveshaft to which it is attached.
7. The rotor incorporates internal vanes (like a ventilated brake disk) to provide its own air cooling, so no load is placed on the vehicle's engine cooling system.
8. The operation of the system is extremely quiet.