Retarder (mechanical engineering)

A retarder ( from the English retard " delay " for or " stop ") is a wear- hydrodynamic ( working fluid ) or electro- dynamic brake or clutch duration, which is mainly used in commercial vehicles such as trucks or buses.

Hydrodynamic retarder

Hydrodynamic retarder work with oil, but also partially with water, which is conducted as needed in a transducer housing. The transducer housing consists of two rotationally symmetrical and opposite paddle wheels, a rotor which is connected to the drive train of the vehicle and a fixed stator. The rotor accelerates the oil supplied to the centrifugal force, it presses outward. By the shape of the rotor blades, the oil is returned back to the stator and from there, thereby decelerating the rotor, and subsequently the drive shaft.

By friction, the kinetic energy is converted into heat, which must be removed by a heat exchanger again, for instance with the aid of the cooling water circuit of the engine. The activation of the retarder is a pneumatic compressed air control: to activate the retarder is flooded with oil from a reservoir, which is pumped back for pressure reduction by the paddle wheels again automatically.

The hydrodynamic retarder was, inter alia, developed by the company Voith in Heidenheim an der Brenz. With the built-in versions of the retarder, a distinction (integrated in the drive train ) and offline (side mounted to the gearbox and not directly acting on the propeller shaft ) between inline.

Turbo retarder coupling

Mercedes -Benz has developed together with Voith Turbo, a hydrodynamic retarder coupling, which for the first time in the new Actros SLT heavy-duty vans and Arocs SLT (Series 2014 ) to be installed. The extremely compact turbo retarder clutch operates by means of hydraulic oil and is used as a start and during maneuvering. A normal dry clutch in the same enclosure takes over then under normal driving conditions the power transfer. Turbo Retarder coupling is also used for braking. The integrated primary this coupling yields a maximum output of 350 kW (476 hp ) - in comparison: The braking power of the diesel engine OM 473 is a maximum of 475 kW ( 646 hp). With the help of turbo retarder coupling the SLT Actros tractors and Arocs can even tow up to 250 tons GCW on inclines of ten percent without the clutch is defective.

Electrodynamic retarder

Called the electro-dynamic retarder, and an eddy current brake, or Kloft Telmabremse ( by the manufacturers ) are two steel discs ( rotors ), which are not magnetized, connected to the drive shaft. In between the stator is with 16 coils. When power is controlled by the continuous actuation of the retarder, by the driver, magnetic fields are generated, which are closed by the rotors. The opposing magnetic fields then generate the braking effect. The heat generated is delivered through vented rotor disks again.

Operation

The operation of a retarder varies greatly by type of vehicle. Usually located on the steering wheel next to the turn signal lever, another steering column switch, which allows to retrieve 2-6 brake levels. If available, also the cruise control is operated with this lever. Retrofitted retarder often have freely placed lever on the dashboard. Upon actuation of the retarder, by means of such additional lever is to be noted that the brake lights of the vehicle are not always activated. Strong braking means retarder - which makes this quite - should be avoided. Governed is the switching on of brake lights in the use of auxiliary brakes such as retarders in § 53 ( 2) Road Traffic Regulations, then the brake light can be switched on, but it does not necessarily.

In addition, it should be noted that the retarder - as well as other auxiliary brakes - acts only on individual axles of a vehicle or vehicle combination, which may adversely affect braking and track behavior especially in adverse road conditions (snow, smoothness). Therefore these could be switched off separately.

For buses with automatic transmission, for example, the retarder of the service brake is upstream and is therefore operated via the foot brake, a hand lever is often lacking. In a first stage, only the retarder brakes, only with a stronger braking affects the mechanical service brakes.

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