10 retarders

AUTOMOBILE

1. RETARDERS OR BRAKE RETARDERS OR RETARD BRAKES

2. 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.

3. 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.

4. Contents 1  Engine brake   Petrol and Diesel powered vehicles Exhaust brake 2 Hydraulic retarder 3 Electric retarder

5. Engine brake

6. 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.

7. 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.

8. Exhaust brake

9. Hydraulic retarder

10. 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.

11. Electric retarder

12. Electric retarder Electric retarders use  electromagnetic induction  to provide a retardation force . 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 . There are no contact surfaces between the rotor and stator, and no working fluid. 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 . This induces  eddy currents  in the rotor, which produces an opposing magnetic field to the stator . Cond..

13. 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.