Electromotive brake
In an electromotive brake or electrical brake generator which is kinetic energy or potential energy of the moving masses converted into electrical energy. It is basically an electric motor that works in generator mode and works essentially free of wear.
General
With regard to the use of the generated electrical energy, a distinction is made between two types:
- If it is fed into the power supply line or overhead line or into an energy store (for example a starter / on-board battery or high-performance capacitor ), one speaks of a regenerative brake or - because this energy generation is called recuperation - of a recuperation brake .
- If it is converted into thermal energy via electrical resistances, it is called a resistance brake . Unless it is used for heating purposes, this is considered out of date.
In addition, there is also the option of performing a direct electrical short circuit as an emergency brake . With certain motor types, armature short-circuit braking can be used, in which the armature (rotor of a DC machine) is short-circuited. This method should only be used if the motor can no longer be braked sufficiently quickly with the above two methods, since the complete braking power occurs as heat in the motor and in the short-circuit device.
Since the braking effect of the electromotive brake decreases with decreasing speed, an additional mechanical brake is always required for stopping and as a parking brake.
Electromotive brakes are used both as utility and resistance brakes in electric locomotives , railcars , trolleybuses and motor vehicles, conveyor belts in mining or in all cableways , especially ore transport and material cableways . In vehicles with diesel-electric drive, the use of the electric resistance brake is also possible and common.
Main advantages of this brake are
- less wear on the mechanical brakes
- possible use (e.g. heating) or energy recovery (recuperation)
However, operating experience showed early on that, for thermal reasons, traction motors used for braking must be designed to be around 30% more powerful than would be necessary for pure drive.
Applications
Rail transport
For motor braking of electric and diesel-electric traction vehicles which is the electric motor in the generator mode switched. The "waste energy" that is converted is partly collected in accumulators for auxiliary companies or converted into heat in braking resistors. Electric locomotives had voluminous "brake fans" or brake resistors with airflow cooling on the roof for heat dissipation. In the case of cogwheel mountain railway and tram vehicles, the “braking current” is fed into the heating elements in the passenger compartments in winter. In the case of trams in particular, the braking current is also used to feed the solenoid brakes of the sidecars.
The braking current recovery (regenerative braking) of electric new build vehicles is based on the possibilities of the traction converter . The braking energy is stepped up again and fed back into the electrical contact line . In the case of direct current railways (e.g. trams), a line-commutated converter is not required for feedback, but the catenary section being used is only able to accommodate if at least one of the following cases applies:
- other vehicles drive on the same section and draw energy
- The substation can be regenerated (active rectification / operation in four instead of two quadrants of the supplying AC voltage)
- There are capacitor stations (systems with double-layer capacitors ) for intermediate storage along the route
Therefore, the vehicles must check the capacity of the network and also have the option of resistive braking and / or, if necessary, carry their own capacitors for intermediate storage. A criterion that can be used for this is the level of tension. If it exceeds a maximum value, it can be assumed that no buyer is available.
The solution was different for the Alstom Coradia LIREX test railcar . In the diesel version, this train feeds the braking energy into a flywheel storage device . The energy is fed back from the storage facility when the vehicle is started. There are also gyro drives without a diesel engine, these charge the flywheel accumulator at the end points; they are also capable of regenerative braking.
In the still relatively young and little tried concept of the solar train , the return of the braking energy in the energy storage, z. B. an accumulator or capacitor , an indispensable requirement to be able to use the relatively low power of current solar cells effectively enough for everyday operation.
In 2007, Deutsche Bahn covered eight percent of its total electricity requirements for rail operations with regenerative braking energy. The company also stated this value for 2009, around 820 gigawatt hours. According to information from Deutsche Bahn, the return quota in freight transport is six percent on average over the year.
Motor vehicles
In road vehicles, the electromotive brake can only be used in electric and hybrid vehicles , trolleybuses and vehicles with gyro drives, since only they have electric drive motors. The braking power and the amount of recuperation depend on the power of the electrical machines, the storage capacity and the free capacity of the energy storage.
Electric vehicles and vehicles with hybrid drives use electromotive braking to charge the vehicle battery . Well-known hybrid vehicles are the Prius from Toyota and the Civic IMA from Honda. Since 2007, the BMW 1 Series with manual gearbox have had recuperation to charge the starter battery. The 3 and 5 series followed a few months later. This technology, marketed in the BMW EfficientDynamics package, is a control system in which the generator mainly generates electricity when the vehicle is coasting. Other vehicle manufacturers also offer similar packages, for example BlueMotion from VW or BlueEFFICIENCY from Mercedes-Benz . In addition to the accumulator, double-layer capacitors are sometimes carried along, which can emit and absorb significantly greater peak powers.
With gyro drives (for example in gyrobusses ) the drive energy is carried in a flywheel storage device, which drives the vehicle's engines via a generator. Electromotive braking is possible through generator operation of the traction motors and motor operation of the flywheel generator. Gyro-powered vehicles only have a short range. The concept is therefore suitable for buses that can charge their flywheel mass at the end points via a power connection.
The electromotive brake often works together with the electrohydraulic brake .
See also
literature
- Peter Hofmann: Hybrid vehicles: an alternative drive concept for the future. Springer, Vienna 2010, ISBN 3-211-89190-0 , p. 173 ff.
Individual evidence
- ↑ Patent DE2002154608 : drive system. Registered on November 22, 2002 , published on July 15, 2004 , applicant: Siemens AG, inventor: Ronald Hauf.
- ↑ How does ... the recovery of braking energy actually work? . In: DB Welt , January 2009 edition, p. 15
- ^ Deutsche Bahn AG: Railway plays a key role in climate protection . Press release from January 11, 2010
- ↑ German Bundestag (ed.): Answer of the Federal Government to the minor question from MPs Matthias Gastel, Harald Ebner, Christian Kühn (Tübingen), other MPs and the Alliance 90 / THE GREENS parliamentary group - printed matter 18/2123 - status of the new Wendlingen – Ulm line . tape 18 , no. 2239 , July 25, 2014, ISSN 0722-8333 , p. 5 ( bundestag.de [PDF]).