Retarder (mechanical engineering) - AbsoluteAstronomy.com

A retarder is a device used to augment or replace some of the functions of primary friction

Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

-based braking systems

Brake

A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

, usually on heavy vehicle

Vehicle

A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....

s.

Friction-based braking systems are susceptible to 'brake fade

Brake fade

Vehicle braking system fade, or brake fade, is the reduction in stopping power that can occur after repeated or sustained application of the brakes, especially in high load or high speed conditions...

' 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

Truck

A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

or bus

Bus

A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...

is descending a long decline

Decline

Decline is a change over time from previously efficient to inefficient organizational functioning, from previously rational to non-rational organizational and individual decision-making, from previously law-abiding to law violating organizational and individual behavior, from previously virtuous to...

. For this reason, such heavy vehicles are frequently fitted with a supplementary system that is not friction-based.

Retarders are not restricted to road

Road

A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...

motor vehicle

Motor vehicle

A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...

s, but may also be used in railway systems. The British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

prototype

Prototype

A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

Advanced Passenger Train

The Advanced Passenger Train was an experimental tilting High Speed Train developed by British Rail during the 1970s and early 1980s....

(APT) used hydraulic retarders to allow the high-speed train to stop in the same distance

Distance

Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...

as standard lower speed trains, as a pure friction-based system was not viable.

Retarders serve to slow vehicles, or maintain a steady speed on declines, and help prevent the vehicle 'running away' by accelerating down the decline. 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.

Diesel powered vehicles

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

d vehicles do not have a throttle

Throttle

A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...

. Diesel engines regulate power

Power (physics)

In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...

output purely by the volume and timing of fuel injected

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

into the cylinders combustion chamber

Combustion chamber

A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

s. The engine braking

Engine braking

Engine braking is where the retarding forces within an engine are used to slow a vehicle down, as opposed to using an external braking mechanism, for example friction brakes or magnetic brakes....

generated by creating partial vacuum with a closed throttle at each intake stroke in petrol/gasoline engines

Petrol engine

A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....

does not apply to diesel engined vehicles - diesel engines are quite 'free-running'. However Clessie M. Cummins

Clessie Cummins

Clessie Lyle Cummins was the founder of the Cummins Engine Co. He was an entrepreneur who improved on existing diesel engines, created new diesel engine designs, was awarded 33 United States patents for his inventions, and set five world records for endurance and speed for trucks, buses and race...

, founder of Cummins Engine Company

Cummins

Cummins Inc. is a Fortune 500 corporation that designs, manufactures, distributes and services engines and related technologies, including fuel systems, controls, air handling, filtration, emission control and electrical power generation systems...

, realized that by opening the cylinder exhaust valves when the piston reached top dead centre

Dead centre

In a reciprocating engine, the dead centre is the position of a piston in which it is farthest from, or nearest to, the crankshaft. The former is known as top dead centre while the latter is known as bottom dead centre ....

, rather than at the end of the power stroke, the accumulated compressed air in the cylinder

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

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

Air compressor

An air compressor is a device that converts power into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts...

, with the energy coming from the transmission

Transmission (mechanics)

A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...

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

Jake brake

A compression release engine brake, frequently called a Jake brake or Jacobs brake, is an engine braking mechanism installed on some diesel engines...

. 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.

The exhaust brake

Exhaust brake

An exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards,...

is simpler in operation than an engine brake

Engine braking

Engine braking is where the retarding forces within an engine are used to slow a vehicle down, as opposed to using an external braking mechanism, for example friction brakes or magnetic brakes....

. Essentially, the exhaust pipe of the vehicle is restricted by a valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

. This raises the pressure in the exhaust system, forcing the engine to work harder on the exhaust stroke of its cylinders

Cylinder (engine)

, so again the engine is acting as an air compressor, with the power required to compress the air being taken from the transmission

Transmission (mechanics)

, retarding the vehicle. A disadvantage of this system is that the exhaust pipe has to be engineered to accommodate the high pressure generated. The retarding horsepower available from this system is significantly lower than other systems. It can cause a marked increase in engine oil

Motor oil

Motor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...

carry-over out the crankcase ventilation system.

The hydraulic retarder

Hydraulic retarders use the viscous

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

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

Gear oil

Gear oil is a motor oil made specifically for transmissions, transfer cases, and differentials in automobiles, trucks, and other machinery. It is of a higher viscosity to better protect the gears and usually is associated with a strong sulfur smell. The high viscosity ensures transfer of...

), a separate oil supply, or water.

A simple retarder uses vanes attached to a transmission

Transmission (mechanics)

driveshaft

Driveshaft

A drive shaft, driveshaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement...

between the clutch

Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another...

and roadwheels

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

. They can also be driven separately via gear

Gear

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....

s off a driveshaft. The vanes are enclosed in a static chamber with small clearances to the chamber's walls (which will also be vaned), as in an automatic transmission. When retardation is required, fluid (oil or water) is pumped into the chamber, and the viscous drag induced will slow the vehicle. The working fluid will heat, and is usually circulated through a cooling system. The degree of retardation can be varied by adjusting the fill level of the chamber.

Hydraulic retarders are extremely quiet, often inaudible over the sound of a running engine, and are especially quiet in operation compared to engine brakes.

The electric retarder

The electric retarder uses electromagnetic induction

Electromagnetic induction

Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....

to provide a retardation force. An electric retardation unit can be placed on an axle

Axle

An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...

, transmission

Transmission (mechanics)

, or driveline and consists of a rotor attached to the axle, transmission, or driveline - and a stator

Stator

The stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors.Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the...

securely attached to the vehicle chassis

Chassis

A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...

. 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

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

for the rotor to move in. This induces eddy current

Eddy current

Eddy currents are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of...

s in the rotor, which produces an opposing magnetic field to the stator. The opposing magnetic fields slows the rotor, and hence the axle, transmission or driveshaft to which it is attached. The rotor incorporates internal vains (like a ventilated brake disk) to provide its own air cooling, so no load is placed on the vehicle's engine cooling system. The operation of the system is extremely quiet.

A hybrid vehicle drivetrain

Hybrid vehicle drivetrain

Hybrid vehicles are vehicles with two or more power sources in the drivetrain. There are many different types of hybrid vehicles, although only the gasoline-electric hybrid is currently commercially available....

uses electrical retardation to assist the mechanical brakes, while recycling the energy. The electric traction motor acts as a generator to charge the battery

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

. The power stored in the battery is available to help the vehicle accelerate.

External links

Pennet.com, Overview of retardation systems
JakeBrake.com, A manufacturer of engine brakes
Voithturbo.com, A manufacturer of oil- and water - based hydraulic retarders
APT-P.com, The Advanced Passenger Train 'hydro-kinetic' brakes
Frenelsa.com, A manufacturer of electric retarders
Zelusl.com, A manufacturer of electric retarders
Telmausa.com, A manufacturer of electric retarders

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.