Retarder
A retarder (from the English retard for "to delay" or "to stop", from the Latin retardare , to slow down, to delay ' ) is a wear-free hydrodynamic (working with fluid) or electrodynamic permanent brake or clutch , which is mainly used in commercial vehicles such as trucks or buses .
Hydrodynamic retarders
Hydrodynamic retarders work with oil , but sometimes also with water, which is fed into a converter housing if necessary. The converter housing consists of two rotationally symmetrical and opposing paddle wheels, a rotor which is connected to the drive train of the vehicle, and a stationary stator . The rotor accelerates the supplied fluid, the centrifugal force pushes it outwards. Due to the shape of the rotor blades, the fluid is guided into the stator and back again from it, whereby it brakes the rotor and subsequently also the cardan shaft.
The kinetic energy is converted into heat by friction , which has to be dissipated again through a heat exchanger , e.g. with the help of the engine's cooling water circuit . The retarder is activated pneumatically via a compressed air control: To activate the retarder housing is filled with the working fluid from a storage container, which is automatically pumped back when the pressure is reduced by the paddle wheels.
The disadvantage is that the braking power is heavily dependent on the shaft speed.
The hydrodynamic retarder was u. a. developed by the Voith company in Heidenheim an der Brenz . When it comes to installing the retarder, a distinction is made between inline (integrated in the drive train) and offline (attached to the side of the gearbox and not acting directly on the cardan shaft ).
Turbo retarder clutch
Together with Voith, Daimler has developed a hydrodynamic turbo retarder clutch VIAB ( wear-free, integrated start-up and braking system ), which was first installed in the heavy-duty transporters Actros SLT and Arocs SLT (series from 2014). The crane vehicle manufacturer Manitowoc Company has also been equipping its GMK5250L model with it as standard equipment since April 2015 . The turbo retarder clutch combines wear-free starting and braking in one system. It is more compact, lighter and more powerful than conventional converter clutches or automatic transmissions and does not overheat during intensive maneuvering off-road and when starting off on extreme inclines with a fully loaded vehicle. The component works with hydraulic oil and serves as a starting element as well as in shunting operation; a normal dry clutch in the same housing then takes over the power transmission during normal driving. The turbo retarder clutch is also used for braking. The integrated primary retarder of this clutch has a maximum output of 350 kW (476 hp) - in comparison: The braking power of the diesel engine type OM 473 is a maximum of 475 kW (646 hp). With the help of the turbo retarder clutch, the SLT Actros and Arocs tractors can pull up to 250 tonnes gross vehicle weight even on gradients of ten percent without overloading the clutch.
Electrodynamic retarders
In the electrodynamic retarder, also called eddy current brake , Kloft or Telma brake (after the manufacturer), two steel disks ( rotors ), which are not magnetized, are connected to the drive shaft. In between is the stator with magnetic coils . If current is fed in by the driver or an automatic system through the stepless actuation of the retarder, magnetic fields are generated by the coils , which penetrate the rotors. The eddy currents induced in the rotors generate opposing magnetic fields that cause the braking effect. The resulting heat is released into the ambient air through the internally ventilated rotor disks. Electrodynamic retarders work without contact, have little wear and are therefore low-maintenance .
service
The operation of a retarder varies greatly depending on the type of vehicle. As a rule, there is another steering column switch next to the indicator lever on the steering wheel, with which 2 to 6 brake levels can be called up. If available, the cruise control is also operated with this lever . Retrofitted retarders often have levers freely placed on the dashboard. When operating the retarder using such additional levers, it should be noted that the brake lights of the vehicle are not always activated. Strong braking maneuvers by means of a retarder - which this certainly does - should then be avoided. Regulated the activation of brake lights in the use of auxiliary brakes such as retarders in § 53 (2) StVZO , then may the brake light are switched on, but does not necessarily have to.
It should also be noted that the retarder - like other permanent brakes - only affects individual axles of a vehicle or vehicle combination, which can have a negative effect on braking and lane behavior, especially in unfavorable road conditions (snow, slippery roads). Therefore the axes can be switched off separately.
In public buses with automatic transmission, for example, the retarder is connected upstream of the service brake and is therefore actuated via the foot brake; a hand lever is often missing. In a first stage, only the retarder brakes; the mechanical service brake only comes into play when the brakes are stronger.
See also
literature
- Commercial vehicle technology , page 226. Vieweg + Teubner Verlag 2008, ISBN 978-3-8348-0374-0
Web links
Individual evidence
- ↑ See on this: Commercial vehicle technology , page 226. Vieweg + Teubner Verlag 2008, ISBN 978-3-8348-0374-0