A retarder is a device used to add or replace some of the major friction-based braking system functions, usually on heavy vehicles. The retarder serves to slow down the vehicle, or keep a steady pace while traveling downhill, and helps prevent the vehicle from "escaping" by accelerating downhill. They are usually not capable of carrying a jammed vehicle, as their effectiveness decreases as vehicle speed decreases. They are usually used as an additional "aid" to slow the vehicle, with the final braking performed by conventional friction braking systems. Because friction brakes will be used less, especially at higher speeds, their service life increases, and because inside the vehicle the air-driven brakes also help to conserve air pressure.
Friction-based braking systems are susceptible to "fade brakes" when used extensively for continuous periods, which can be dangerous if braking performance falls below what is required to stop the vehicle - for example if the truck or bus declines in length. For this reason, such heavy vehicles are often equipped with complementary systems that are not friction-based.
Retarders are not limited to road vehicles, but can also be used in rail systems. The British Advanced Passenger Train (APT) prototype uses a hydraulic retarder to allow high-speed trains to stop at the same distance as the standard low-speed train, since pure friction-based systems are not feasible.
Video Retarder (mechanical engineering)
Engine brake
Diesel powered vehicles
The diesel engine vehicle does not have a throttle. The diesel engine regulates pure power output by volume and fuel time is injected into the combustion chamber. Engine braking is generated by creating a partial vacuum with a closed throttle at every step of intake in the gasoline/petrol engine not applicable to diesel-engined vehicles - diesel engines are quite "free-running". But Clessie L. Cummins, founder of the Cummins Engine Company, realizes that by opening the cylinder exhaust valve when the piston reaches the top dead center, not at the end of the power blow, the accumulated compressed air in the cylinder can be disposed before it can act as a "spring" to push the piston back down again. By doing this, the engine acts as an air compressor, with energy derived from the transmission used to compress the air, thus slowing down the vehicle. The amount of power drawn from the transmission can reach up to 90% of the machine's rated power for a given machine.
In a compression braking system on a turbocharged internal combustion engine, the excessive pressure associated with opening the engine exhaust valve near the top of the engine compression die when the engine is spinning at high speed is prevented by reducing intake manifold pressure from what will happen at that high speed. This is done by slowing down the turbocharger so that the speed is smaller than it should be at high engine speeds.
This type of retarder is known as Jake brakes or compression release brakes. The disadvantage of this system is to be very noisy in operation, especially if exhaust exhaust is damaged; hence its use is prohibited in some locale.
Dispose brake
The exhaust brakes are easier to operate than the engine brakes. Basically, the vehicle's exhaust pipe is limited by the valve. This increases the pressure on the exhaust system, forcing the engine to work harder on its cylinder exhaust, thus once again functioning as an air compressor, with the power required to compress air held from the exhaust pipe, slowing down the vehicle. Turbocharger retarders that limit the flow of exhaust gases can also help increase the exhaust pressure to achieve the same goal.
The disadvantage of this system is that the drain pipe must be engineered to accommodate the high pressure generated. The retarding horsepower available from this system is significantly lower than other systems. This may cause marked improvement in engine oil brought out through the crankcase ventilation system.
Maps Retarder (mechanical engineering)
Hydraulic retarder
The hydraulic retarder uses the viscous force of attraction between the dynamic and static propellers in a fluid filled space to achieve retardation. There are several different types that can use standard transmission fluid (gear oil), separate oil supply, water, or oil mixture and magnetic retardation. The magnetic retarder is similar to the electric retarder discussed below.
The simple retarder uses propellers attached to the driveshaft transmission between the clutch and the roadwheels. They can also be driven separately through the gears of the driveshaft. The propeller is flanked in a static space with a small distance to the wall of the room (which will also be removed), as in automatic transmissions. When retardation is required, liquid (oil or water) is pumped into the chamber, and the induced thick resistance will slow the vehicle. The working fluids will heat up, and are usually circulated through the cooling system. The degree of backwardness can vary by adjusting the level of filling of the space.
The hydraulic retarder is very quiet, often inaudible because of the sound of the engine running, and very quiet in operation compared to the engine brake.
Electric retarder
Electrical retarders use electromagnetic induction to provide retardation forces. An electric retardation unit may be placed on a shaft, transmission, or driveline and comprises a rotor attached to a shaft, transmission, or driveline - and a stator securely attached to the vehicle chassis. There is no contact surface between the rotor and the stator, and no working fluid. When backwardness is required, the electric windings in the stator receive power from the vehicle's battery, producing a magnetic field in which the rotor moves. This induces eddy currents in the rotor, which produces a magnetic field opposite the stator. The opposite magnetic field slows down the rotor, and hence the shaft, transmission or driveshaft installed. This rotor incorporates an internal propeller (such as a ventilated brake disc) to provide for air cooling itself, so that no load is placed on the engine's engine cooling system. The operation of the system is very quiet.
Drivetrain hybrid vehicles use electric retardation to aid mechanical brakes, while recycling energy. The electric traction motor serves as a generator to charge the battery. Power stored in the battery is available to help the vehicle accelerate.
Regenerative braking and eddy current braking are a separate type of electric braking. Regenerative braking may not be classified as a retarder because it does not use any additional physical device other than the rotor/stator pair present in the motor. This affects the braking by using an electric field created by rotational inertia in the rotor/stator that is sent to the rotor by the momentum of the vehicle (wheel). An additional circuit in the controller is used to regulate the flow of this current from the stator windings to the battery, some of which disappear as heat in the control circuitry.
In contrast, the eddy retarder brake currently consists of distinct and specially made static and rotor assemblies that are explicitly made and added to vehicles for braking and heat dissipation and not for motive strength; it is a special built system that is different from the motor.
Finally, "dynamic" braking is a term used to describe the controlling of complex controllers in which the controller can be used either for regenerative braking or by diverting the circuit to feed the current to the resistor. In this way braking "rheostatic" can be achieved. While eddy bracelets rely on eddy currents to create the magnetic resistance that partially suffers as heat, the rheostatic brake relies on the controller circuit resistor which directly removes current electrical energy as heat. Some dynamic braking describes rheostatic braking as a "plug" braking. In particular, dynamic forklift braking has been developed to take advantage of incorporating braking types with special controls to reverse the direction of the vehicle quickly.
Dynamic and regenerative braking, when used in electric or diesel-electric train locomotives, means that the electric motor normally used to drive the road wheel is instead used as a generator driven by a wheel on the lower slope. In regenerative braking, the generated electric current is usually fed back to the power supply (ie the top catenary, third rail), and can be used by another locomotive or stored for later use. In this way, the locomotive will receive current while on flat ground or uphill walk, but acts as a current supply when braking, altering the kinetic energy formed from the descending (or more rarely, changing the forward momentum of travel on flat ground) into electricity. In diesel-electric, instead of being generated remotely and collected from a power source, the power supply is generated directly by the main drive onboard (engine) and transmitted to the motor; there is rarely a way to save electricity for later use, so instead, the motor is used as a generator, it slows the rotation of the wheel, and the power generated is channeled through a resistor mounted on the roof of the locomotive, where it is converted into heat energy (such as an electric heating element) and scattered into the atmosphere with a large fan. While this has the disadvantage of not reusing the energy created while traveling downhill, it creates a robust and secure retard system that is not vulnerable to brakes fading or wearing like a mechanical brake.
See also
- Raffleer
- Dynamic braking
- Retarder (train)
References
External links
- JakeBrake.com, Brake Engine Maker
- Voithturbo.com, A manufacturer of water-based and oil-based hydraulic retarders
- APT-P.com, Advanced Hydro-kinetic "Trainer" Brake
- Frenelsa.com, Electrical retarder
- Zelusl.com, Electrical retarder
- Telmausa.com, Electrical resistor manufacturer
Source of the article : Wikipedia