A regenerative brake is an energy recovery mechanism that decreases automobile speed by changing some of its kinetic energy into a handy sort of power rather than abating it as heat as with a standard brake. The converted kinetic energy is stored for later use or fed back into a power system to be used by other cars. Electric regenerative brakes in electrical railway automobiles feed the generated electricity into the supply system.
In battery electrical and cross-breed electrical automobiles the energy is kept in a battery or bank of capacitors for later use. Energy might also be stored by compacting air or by a revolving flywheel. Regenerative braking isn't the same as dynamic braking, which disperses the electric energy as heat and doesn't maintain energy in a serviceable form.

The motor as a generator

Autos driven by electrical motors use the motor as a generator when using regenerative braking: it is operated as a generator during braking and its output is supplied to an electric load; the transferring of energy to the load supplies the braking effect. System early examples was the front-wheel drive conversions of horse-drawn cabs by Louis Antoine Krieger ( 1868-1951 ). The Krieger electrical landaulet had a drive motor in each front wheel with a second set of parallel windings ( bifilar coil ) for regenerative braking.
An Energy Regeneration Brake was developed in 1967 for the AMC Amitron. This was a totally battery powered urban idea automobile whose batteries were recharged by regenerative braking, so augmenting the range of the auto. Many modern cross-breed and electrical vehicles use this system to increase the range of the battery pack. Examples include the hybrids Toyota Prius, Honda Discernment, and the Vectrix electric maxi-scooter.

Limitations

Normal friction-based braking is employed together with mechanical regenerative braking for the following reasons:

• The regenerative braking effect drops off at lower speeds ; so the friction brake is still needed to bring the auto to a total halt, though malfunction of a dynamo can still provide resistance for a bit. Physical locking of the rotor is also needed to stop cars from rolling down hills.
• The friction brake is a required back-up in the event of failure of the regenerative brake.
• Most road autos with regenerative braking only have power on some wheels ( as in a 2WD automobile ) and regenerative braking power only is applicable to such wheels, so to provide controlled braking under tricky conditions ( like in wet roads ) friction based braking is required on the other wheels.
• The quantity of electric energy able of dissipation is restricted by either the capacity of the supply system to soak up this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can happen if another electric part on the same supply system isn't now drawing power and if the battery or capacitors are already charged. Because of this, it is usual to also incorporate dynamic braking to soak up the excess energy.
• Under emergency braking it is fascinating the braking force exerted be the maximum authorized by the friction between the wheels and the surface without slipping, over the whole speed range between the auto's maximum speed down to nil. The maximum force available for acceleration is usually far less than this apart from in the case of acute high-performance autos. The power needed to be evaporated by the braking system under emergency braking conditions could be many times the maximum power which is delivered under acceleration. Traction motors sized to deal with the drive power would possibly not be able to deal with the additional load and the battery would possibly not be in a position to accept charge at a high enough rates. Friction braking is needed to absorb the surplus energy to permit a satisfactory emergency braking performance.

For these reasons there's usually the necessity to control the regenerative braking and match the friction and regenerative braking to supply the required total braking output. The GM EV-1 was the 1st commercial automobile to try this. Engineers Abraham Farag and Loren Majersik were issued 2 patents for this 'Brake by Wire' technology.

Electric railway vehicle operation

During braking, the traction motor connections are changed to turn them into electrical generators. The motor fields are connected across the main traction generator ( MG ) and the motor armatures are connected across the load. The MG now excites the motor fields.
The rolling locomotive or multiple unit wheels turn the motor armatures, and the motors act as generators, either sending the generated current thru onboard resistors ( dynamic braking ) or into the supply ( regenerative braking ). For a given direction of travel, current flow thru the motor armatures during braking will be opposite to that during motoring. The motor exerts torque in a direction that's opposite from the rolling direction.
Braking effort is proportionate to the product of the magnetic strength of the field windings, times that of the armature windings. Savings of 17% are claimed for Virgin Trains Pendolinos. There's also less wear on friction braking elements.
The Delhi Metro saved around ninety thousand tons of carbon dioxide ( CO2 ) from being released into the atmosphere by regenerating 112,500 megawatt hours of electricity thru the employment of regenerative braking systems between 2004 and 2007. It is predicted that the Delhi Metro will save over 100,000 tons of CO2 from being emitted each year once its phase II is complete thru the utilization of regenerative braking. Many stations on the London Underground are built so the tracks entering the platform are on a slight incline, and those leaving it on a decline. This saves energy by letting gravity slow the train on its entry to the station without expending ( as much ) energy and, help it accelerate on exit. This is going to be viewed as a form of regenerative braking where the energy is stored as potential energy ( using gravity ) rather than electric energy

Comparison of dynamic and regenerative brakes

Dynamic brakes ( "rheostatic brakes" in the United Kingdom ), unlike regenerative brakes, disperse the electric energy as heat by passing the prevailing thru massive banks of variable resistors.
Automobiles that use dynamic brakes include forklifts, Diesel-electric locomotives and streetcars. If designed reasonably, this heat can be employed to heat the automobile interior.
If evaporated outwardly, giant radiator-like covers are employed to house the resistor banks.
The main downside of regenerative brakes when compared to dynamic brakes is the necessity to closely match the generated current with the supply traits. With DC supplies, this demands that the voltage be closely controlled. Only with the development of power electronics has this been possible with AC supplies, where the supply frequency must also be matched ( this generally is applicable to locomotives where an AC supply is corrected for DC motors ). A low number of mountain railways have used 3-phase power supplies and 3-phase induction motors. This causes a near continuing speed for all trains as the motors revolve with the supply frequency both when motoring and braking.

Kinetic Energy Recovery Systems

Kinetic Energy Recovery Systems ( KERS ) are presently in use for the motor sport Formula One's 2009 season, and in ongoing development for road autos.
The Formula One Groups that used Kinetic Energy Recovery Systems in the 2009 season are Ferrari, Renault, BMW Sauber and McLaren. One of the most significant reasons that not all vehicles use KERS is actually because it adds an additional twenty-five kilograms of weight, while not adding to the total automobile weight, it does sustain a penalty frequently seen in the qualifying rounds, as it raises the auto's centre of balance, and decreases the quantity of ballast that's available to balance the auto so it is more predicted when turning. FIA rules also limit the utilization of the system. At last , in the season, Renault and BMW stopped using the system. Williams is developing KERS based totally on flywheel. The idea of transferring the auto's kinetic energy using Flywheel energy storage was presumed by physicist Richard Feynman in the 1950s and is embodied in complex high end systems like the Zytek, Flybrid, Torotrak and Xtrac employed in F1 and easy, simply made and integrated differential based systems like the Cambridge Passenger / Commercial Car Kinetic Energy Recovery System ( CPC-KERS ). Xtrac and Flybrid are both licensees of Torotrak's technologies, which employ a little and classy subordinate gearbox incorporating a continuously variable transmission ( CVT ). The CPC-KERS is analogous as it also is part of the driveline assembly. The entire mechanism including the flywheel sits completely in the car's heart ( looking like a drum brake ). In the CPC-KERS differential replaces the CVT and transfers torque between the flywheel, drive wheel and road wheel.

Use in motor sport

FIA

F1 groups have asserted they must reply in a responsible way to the planet's environmental challenges, and the FIA authorized the utilization of sixty kW KERS in the laws for the 2009 Formula One season. Groups commenced testing systems in 2008: energy can either be stored as mechanical energy ( as in a flywheel ) or as electric energy ( as in a battery or supercapacitor ). Due to high cost, FOTA groups agreed to drop KERS from the 2010 season onwards, but this is still an open issue as Williams F1 stated that it will use KERS in 2010 and changes to the rules must be concluded by all groups.
Vodafone McLaren Mercedes became the 1st team to win a F1 GP employing a KERS supplied vehicle when Lewis Hamilton won the Hungarian Grand Prix on July twenty-six, 2009.
Their 2nd KERS supplied auto came 5th. At the following race Lewis Hamilton became the 1st driver to take pole position with a KERS vehicle, his team chum qualifying second. This was also the 1st example of an all KERS front row. On Aug thirty, 2009, Kimi Rikknen won the Belgium Grand Prix with his KERS supplied Ferrari. It was actually the first time that KERS gave straight to a race victory, with 2nd placed Fisichella saying "Actually, I was faster than Kimi. He only took me due to KERS at the beginning"

Motorcycles

KTM racing CEO Harald Bartol has disclosed the factory raced with a secret Kinetic Energy Recovery System ( KERS ) fitted to Tommy Koyama's bike in the 2008 season-ending 125cc Valencian Grand Prix. This was unlawful and against rules.

History

A Flybrid Systems Kinetic Energy Recovery System the first of these systems to be disclosed was the Flybrid which appeared in an article in Racecar Engineering mag. Flybrid Systems' F1 KERS weighs twenty-four kg and has an energy capacity of four hundred kJ after permitting for internal losses. A maximum power boost of sixty kW ( 81.6 PS, 80.4 HP ) for 6.67 sec is available. The 240 mm diameter flywheel weighs 5.0 kg and revolves at almost 64,500 r.p.m. Maximum torque is 18 Nm ( 13.3 ftlbs ).
The system occupies a volume of thirteen liters. It might not be utilised by all F1 groups but some including Williams F1, are going to use it at some particular point in the seasons, if not at the 1st race. 2 minor situations have been reported during testing of KERS systems in 2008.
The first occurred when the Red Bull Racing team tested their KERS battery for the 1st time in July : it malfunctioned and caused a fire shock that led straight to the team's factory being abandoned. The second was less than a week later when a BMW Sauber mechanic received an electrical shock when he touched Christian Klien's KERS-equipped auto in a test at the Jerez circuit.

Races

Automobile Club de l'Ouest, the organizer behind the yearly twenty-four Hours of Le Mans event and the Le Mans Series is now "studying categorical rules for LMP1 that will be provided with a kinetic energy recovery system." Peugeot was the 1st manufacturer to display a totally working LMP-1 auto in the shape of the 908 HY at the 2008 Autosport one thousand km race at Silverstone.

Autopart makers

Bosch Motorsport Service (subsidiary Bosch Engineering GmbH part) is developing a KERS to be used in motor racing. Cross-breed systems by Bosch Motorsport comprise an electricity storage system ( a lithium-ion battery with scalable capacity or a flywheel ), the electrical motor ( weigh between 4 and 8 kilograms with a maximum power level of sixty kW ) and the KERS controller, containing the power electronic, battery management, and management system for cross-breed and engine functions. The Bosch Group offers a variety of electrical half-breed systems for commercial and light-duty applications

Carmakers

BMW and Honda are testing it. At the 2008 one thousand km of Silverstone, Peugeot Sport unveiled the Peugeot 908 HY, a cross-breed electrical variant of the diesel 908, with KERS. Peugeot plans to campaign the automobile in the 2009 Le Mans Series season, though it won't be capable of scoring championship points. Vodafone McLaren Mercedes started testing of their KERS in Sep 2008 at the Jerez test track in preparation for the 2009 F1 season; though at that point it wasn't yet known if they would be operating an electric or mechanical system. In Nov 2008 it was declared that Freescale Semiconductor would collaborate with McLaren Electronic Systems to further develop its KERS for McLaren's Formula One auto from 2010 onwards. Both parties thought this partnership would improve McLaren's KERS system and help the system filter down to road automobile technology Toyota has utilised a supercapacitor for regeneration on Supra HV-R cross-breed race vehicle that took the 24 Hours of Tokachi race in July 2007.