Existen 3 tipos de KERS, el mecánico, el hidráulico y el eléctrico. Todas las escuderías han optado por el KERS eléctrico, a excepción de Williams, que incorpora un KERS mecánico, almacenado la energía en un volante de inercia.
El KERS eléctrico está constituido por un generador eléctrico, que gira solidario con el cigüeñal del motor. Al frenar el vehículo, la electrónica del sistema engrana el generador al cigüeñal, transformando la energía cinética en energía eléctrica que se acumula en una batería. Una vez almacenada, esa energía está a disposición del piloto, para utilizarla en la aceleración. En este caso el generador funciona como motor eléctrico, transformando la energía eléctrica en energía mecánica que se suma a la del motor de combustión. Por lo tanto un KERS eléctrico se basa en el principio de que un motor eléctrico puede ser utilizado como generador.
El reglamento técnico de Fórmula 1 para la temporada 2009 establece que el KERS puede tener una cantidad máxima de energía almacenada por vuelta de 400 kilojulios; también establece que el KERS no puede transmitir más de 60 kW, es decir 81,6 C.V.
En función de este Reglamento técnico, el diseño del KERS es el siguiente:
• Un motor eléctrico, situado debajo del tanque de la gasolina y el motor de combustión, conectado directamente al cigüeñal. La potencia es de 60 kW, similar al que tiene en la actualidad el Toyota Prius. Su peso es de 10 Kg aproximadamente.
• Baterías de litio ionizado de última generación, capaces de almacenar y suministrar energía rápidamente. La capacidad de estas baterías esta en torno a 200 Wh, un poco superior a la cantidad máxima de energía que se permite almacenar por vuelta, su peso tampoco supera los 10 Kg.
Aplicación del KERS a los vehículos eléctricos
El dispositivo KERS, utilizado en la Formula 1 podría ser implementado en los vehículos eléctricos de la calle, usando continuamente la energía obtenida de las frenadas para reducir el consumo de combustible en los vehículos híbridos, y el consumo de electricidad en los vehículos eléctricos puros. Esta aplicación aumentaría la eficiencia del motor eléctrico, pudiendo llegar a ser casi 5 veces más eficiente que el motor de combustión interna.
Aparte de proporcionar una mayor eficiencia al vehículo eléctrico, los trabajos de investigación realizados por las diferentes escuderías de Formulas 1, influirán de manera muy positiva en los dos elementos claves del vehículo eléctrico, el motor y la batería.
Los esfuerzos de I+D de los diferentes equipos para desarrollar motores eléctricos capaces de entregar 80 caballos de fuerza en un espacio y con un peso mínimo, mientras operan en condiciones extremas, representa un paso adelante significativo para los motores de que llevarán los vehículos eléctricos en la próxima década.Pero sin duda, la gran aportación que tendrá la Formula 1 a los vehículos eléctricos está en el desarrollo de las baterías de almacenamiento de energía.
La clave del futuro del vehículo eléctrico esta en el desarrollo de una batería recargable viable técnica y económicamente, ya que el tipo y la capacidad de la batería condicionan aspectos tan críticos para el vehículo, como son la velocidad máxima y el tiempo de recarga. A pesar de ser uno de los elementos más importante del vehículo eléctrico, se le ha dedicado poco esfuerzo de investigación en los últimos años. La investigación ha estado ligada al desarrollo de la informática y los teléfonos móviles, y no a su aplicación en la automoción. Este hecho provoca que aunque se ha avanzado mucho en los últimos 10 años, reduciendo el coste y aumentado la autonomía, las baterías que se llevarían incorporadas los coches eléctricos sean por el momento excesivamente caras.
El desarrollo de las baterías en los próximos 10 años puede estar ligado a los trabajos de investigación realizados por los Ingenieros de las diferentes escuderías de Fórmula 1. La reglamentación aplicada a la primera fase de implantación del KERS para esta temporada y la del 2010, solo permite almacenar 400 kilojulios, por lo que las baterías utilizadas no superaran los 0,2 kWh, cantidad que de momento no sería aplicable a los vehículos eléctricos que circularán por las calles. La segunda fase, aplicable a partir del año 2011, permitirá almacenar una energía de 800 kilojulios, y el piloto podrá emplear 136 C.V. (100 kW) adicionales por vuelta. Pero la fase decisiva tendrá lugar en 2013, cuando se puedan almacenar hasta 1.600 kilojulios y el piloto disponga de una potencia añadida de 272 C.V. (200 kW). Esta potencia añadida, hará que la aplicación del sistema de recuperación de energía cinética por parte del piloto, sea un elemento decisivo para el desenlace final de las carreras en determinados circuitos. Para esa fecha los monoplazas deberían llevar acopladas baterías de más de 2 kWh, utilizando el menor espacio posible, para lo cual ya están trabajando los departamentos de I+D de las diferentes escuderías, intentando mejorar las actuales baterías de ión litio y de otros materiales en desarrollo. Este tamaño se acerca más al que utilizarán los vehículos eléctricos. Entre 7-10 kWh serían suficiente para recorrer 100 km, cantidad bastante superior a la mayor parte de los desplazamientos diarios.
El futuro del vehículo eléctrico pasa por desarrollar la batería más eficiente posible. La fuerte competencia existente en el deporte que más dinero mueve del mundo, provocará fuertes avances en el componente clave para el despegue definido del coche eléctrico.
A regenerative brake is a mechanism that reduces vehicle speed by converting some of its kinetic energy into another useful form of energy. This captured energy is then stored for future use or fed back into a power system for use by other vehicles.
For example, electrical regenerative brakes in electric railway vehicles feed the generated electricity back into the supply system. In battery electric and hybrid electric vehicles, the energy is stored in a battery or bank of capacitors for later use. Other forms of energy storage which may be used include compressed air and flywheels.
Regenerative braking should not be confused with dynamic braking, which dissipates the electrical energy as heat and thus is less energy efficient.
Traditional friction-based braking is used with mechanical regenerative braking for the following reasons:
* The regenerative braking effect rapidly reduces at lower speeds, therefore the friction brake is still required in order to bring the vehicle to a complete halt, although malfunction of a dynamo can still provide resistance for a while.
* The friction brake is a necessary back-up in the event of failure of the regenerative brake.
* Most road vehicles with regenerative braking only have power on some wheels (as in a 2WD car) and regenerative braking power only applies to such wheels, so in order to provide controlled braking under difficult conditions (such as in wet roads) friction based braking is necessary on the other wheels.
* The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electrical component on the same supply system is not currently drawing power and if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.
* Under emergency braking it is desirable that the braking force exerted be the maximum allowed by the friction between the wheels and the surface without slipping, over the entire speed range from the vehicle’s maximum speed down to zero. The maximum force available for acceleration is typically much less than this except in the case of extreme high-performance vehicles. Therefore, the power required to be dissipated by the braking system under emergency braking conditions may be many times the maximum power which is delivered under acceleration. Traction motors sized to handle the drive power may not be able to cope with the extra load and the battery may not be able to accept charge at a sufficiently high rate. Friction braking is required to absorb the surplus energy in order to allow an acceptable emergency braking performance.
For these reasons there is typically the need to control the regenerative braking and match the friction and regenerative braking to produce the desired total braking output. The GM EV-1 was the first commercial car to do this. Engineers Abraham Farag and Loren Majersik were issued 2 patents for this ‘Brake by Wire’ technology.
The motor as a Generator
Regenerative braking utilizes the fact that an electric motor can also act as a generator. The vehicle’s electric traction motor is operated as a generator during braking and its output is supplied to an electrical load. It is the transfer of energy to the load which provides the braking effect.
An early example of this system was the Energy Regeneration Brake, developed in 1967 for the Amitron. This was a completely battery powered urban concept car whose batteries were recharged by regenerative braking, thus increasing the range of the automobile.
Electric railway vehicle operation
During braking, the traction motor connections are altered 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 through onboard resistors (dynamic braking) or back into the supply (regenerative braking).
For a given direction of travel, current flow through the motor armatures during braking will be opposite to that during motoring. Therefore, the motor exerts torque in a direction that is opposite from the rolling direction.
Braking effort is proportional 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 is also less wear on friction braking components. The Delhi Metro saved around 90000 tonnes of Carbon Dioxide from being released into the atmosphere by regenerating 112,500 Megawatt hours of electricity through the use of regenerative braking systems during between 2004 and 2007. It is expected that the Delhi Metro will save over 100,000 tons of Carbon Dioxide from being emitted per year once its phase II is complete through the use of regenerative braking.
Comparison of dynamic and regenerative brakes
Dynamic brakes ("rheostatic brakes" in the UK), unlike regenerative brakes, dissipate the electric energy as heat by passing the current through large banks of variable resistors. Vehicles that use dynamic brakes include forklifts, Diesel-electric locomotives and streetcars. If designed appropriately, this heat can be used to warm the vehicle interior. If dissipated externally, large radiator-like cowls are employed to house the resistor banks.
The main disadvantage of regenerative brakes when compared with dynamic brakes is the need to closely match the generated current with the supply characteristics. With DC supplies, this requires 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 mainly applies to locomotives where an AC supply is rectified for DC motors).
A small number of mountain railways have used 3-phase power supplies and 3-phase induction motors. This results in a near constant speed for all trains as the motors rotate with the supply frequency both when motoring and braking.
Kinetic Energy Recovery Systems
Kinetic Energy Recovery Systems (KERS) are currently under development both for Formula One motor sport and road vehicles. The concept of transferring the vehicle’s kinetic energy using Flywheel energy storage was postulated by physicist Richard Feynman in the 1950s and is exemplified in complex high end systems such as the Zytek, Flybrid, Torotrak and Xtrac used in F1 and simple, easily manufactured and integrated differential based systems such as the Cambridge Passenger/Commercial Vehicle Kinetic Energy Recovery System (CPC-KERS).
Xtrac & Flybrid are both licensees of Torotrak’s technologies, which employ a small and sophisticated ancillary gearbox incorporating a continuously variable transmission (CVT). The CPC-KERS is similar as it also forms part of the driveline assembly. However, the whole mechanism including the flywheel sits entirely in the vehicle’s hub (looking like a drum brake). In the CPC-KERS, a differential replaces the CVT and transfers torque between the flywheel, drive wheel and road wheel.
Use in motor sport
F1 teams began testing Kinetic Energy Recovery Systems, or KERS, in January 2009. Teams have said they must respond in a responsible way to the world’s environmental challenges.
The FIA allowed the use of 60 kW KERS in the regulations for the 2009 Formula One season.
Energy can either be stored as mechanical energy (as in a flywheel) or can be stored as electrical energy (as in a battery or supercapacitor).
KTM racing boss Harald Bartol has revealed that the factory raced with a secret Kinetic Energy Recovery System (KERS) fitted to Tommy Koyama’s motorcycle during the season-ending 125cc Valencian Grand Prix.
The first of these systems to be revealed was the Flybrid which appeared in an article in Racecar Engineering magazine.
Flybrid Systems F1 KERS weighs 24 kg and has an energy capacity of 400 kJ after allowing for internal losses. A maximum power boost of 60 kW (81.6 PS) for 6.67 sec is available. The 240mm diameter flywheel weighs 5.0 kg and revolves at up to 64,500 rpm. Maximum torque is 18 Nm. The system occupies a volume of 13 liters. It may not be used by all of the F1 teams but a few, such as Williams F1 are going to use it, if not at the first race, at one point during the season.
Two minor incidents 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 first time in July, it malfunctioned and caused a fire scare, resulting in the team’s factory being evacuated. The second was less than a week later when a BMW Sauber mechanic was given an electric shock when he touched Christian Klien’s KERS-equipped car during a test at the Jerez circuit.
Automobile Club de l’Ouest, the organizer behind the annual 24 Hours of Le Mans event and the Le Mans Series is currently "studying specific rules for LMP1 which will be equipped with a kinetic energy recovery system." Peugeot was the first manufacturer to unveil a fully functioning LMP-1 car in the form of the 908 HY at the 2008 Autosport 1000km race at Silverstone.
Bosch Motorsport Service (part of the subsidiary Bosch Engineering GmbH) is developing a KERS for use in motor racing. Hybrid systems by Bosch Motorsport comprise an electricity storage system (a lithium-ion battery with scalable capacity or a flywheel), the electric motor (weigh between four and eight kilograms with a maximum power level of 60 kW) and the KERS controller, containing the power electronic, battery management, and management system for hybrid and engine functions . The Bosch Group offers a range of electric hybrid systems for commercial and light-duty applications.
BMW and Honda are testing it. At the 2008 1000 km of Silverstone, Peugeot Sport unveiled the Peugeot 908 HY, a hybrid electric variant of the diesel 908, with a KERS system. Peugeot plans to campaign the car in the 2009 Le Mans Series season, although it will not be capable of scoring championship points.
Vodafone McLaren Mercedes have recently begun testing of their KERS system at the Jerez test track in preparation for the 2009 F1 season, although it is not yet known if they will be operating an electrical or mechanical system. In November 2008 it was announced that Freescale Semiconductor will collaborate with McLaren Electronic Systems to further develop its KERS system for McLaren’s Formula 1 car from 2010 onwards. Both parties believe this collaboration will improve McLaren’s KERS system and help the system filter down to road car technology.
Toyota has used a supercapacitor for regeneration on Supra HV-R hybrid race car that won the 24 Hours of Tokachi race in July 2007.
Use in compressed air cars
Regenerative brakes are being used in compressed air cars to refuel the tank during braking.
Xtrac and Flybrid to reveal technical details of flywheel ‘kinetic energy recovery system’ at global conference
* Motorsport experts to discuss mechanical alternative to hybrid electric vehicle technology for future road cars
* Fast-acting flywheel system offers up to twice the efficiency, half the mass and more rapid transfer of energy compared with current battery systems
Martin Halley, chief engineer with transmission technology specialist Xtrac and Jon Hilton, managing partner of Flybrid Systems, a new company taking a fresh look at hybrid vehicle technology, will describe the technical innovations behind their groundbreaking mechanical flywheel ‘kinetic energy recovery system’ (KERS) – which also incorporates advanced traction drive technology from Torotrak – at a forthcoming high-level motorsport industry conference.
"The Federation Internationale de l’Automobile (FIA) regulatory body, which governs motorsport, has recognised that motor racing provides a unique opportunity to demonstrate new technologies which could be relevant to the automotive mainstream," said Halley, whose presentation will provide an overview of new F1 regulations and the technology and materials required to develop the sophisticated transmission system required for a mechanical based KERS system.
"The new rules being drawn up for F1 will stimulate the development of new and exciting technologies, within a competitive environment, which may otherwise not have occurred. This means rapid product development is required right here and right now," commented Hilton, whose technical paper will discuss the recovery and storage of braking energy in a mechanical-based flywheel system.
Flybrid has already secured one unnamed F1 team as a customer and is confident others will follow given the benefits of a fast-acting flywheel system, which offers up to twice the efficiency, half the mass and more rapid transfer of energy compared with hybrid battery electrical systems. The company is also well on its way to bench testing a flywheel KERS system adapted for road car applications using a Chevrolet V8 engine.
Flybrid’s brake regenerative system uses advanced gearbox technology provided by transmission specialists Torotrak and Xtrac. The system employs a small and sophisticated ancillary gearbox manufactured by Xtrac incorporating a continuously variable transmission (CVT) design licensed from Torotrak. Torotrak’s patented traction drive technology is being developed for motorsport applications by Xtrac under an exclusive licensing agreement. Xtrac can sub-license the CVT ‘variator’ technology to Flybrid and other motorsport teams who may wish to design and build their own flywheel.
The role played by Flybrid, Torotrak and Xtrac in designing a mechanical KERS solution for F1 could be instrumental in developing this pioneering vehicle technology for more fuel efficient road cars without resorting to the expense and complexity of battery systems. Compared with hybrid electric vehicles, which use batteries for energy storage, a mechanical KERS system utilises flywheel technology as a highly efficient alternative to recover and store a moving vehicle’s kinetic energy.
The combination of gearbox-variator and flywheel would form part of the driveline assembly. The kinetic energy is stored during a braking manoeuvre and is then released back into the driveline as the vehicle accelerates. Flybrid, Torotrak and Xtrac claim that compared to the alternative of battery systems, a mechanical KERS system can provide a more compact, lighter and environmentally-friendly solution.
Torotrak’s patented technology is a vital element in a mechanical system as it provides a continuously variable connection between the flywheel and the vehicle driveline. Xtrac’s exclusive licence and development of the system for motorsport applications allows it to design, manufacture, assemble and distribute complete variator systems and discrete components to F1 and other motorsport customers.
For F1 applications, the variator and flywheel each weigh less than 5kg in a system with a total mass not exceeding 25kg. This relatively low mass is a major advantage both for race and road cars. The high level of mechanical efficiency combined with the variator’s ability to change ratio very rapidly helps to optimise flywheel performance. The transmission system selects the appropriate ratio depending on the torque demand and can change its 6-to-1 ratio within one revolution.
"Performance calculations show we can go from zero to full power in 50ms," says Hilton. "This is faster than the driver can apply the brake pedal."
Flybrid, Torotrak and Xtrac all see the potential for wider application beyond motorsport – initially on high-performance road cars – both as an aid to performance and as a means of developing vehicles with reduced fuel consumption and CO2 levels. Applied to road cars the system supports the current motor industry trend for smaller powertrains; a lightweight kinetic energy recovery system providing a means of boosting acceleration and overall performance and economy independently of the vehicle’s internal combustion engine.
An ancillary flywheel is particularly suited to stop-start driving situations when real-world fuel economy is often at its worst. In these conditions, the variator can assist the launch of a vehicle which has slowed down or come to a standstill. In heavily congested traffic, where a car is frequently stopped and restarted, the system can help alleviate the heavy fuel consumption and emissions of greenhouse gasses normally associated with these conditions. However, unlike hybrid electric vehicles, a mechanical KERS system continues to provide the benefits of kinetic energy recovery throughout the speed range, and its benefits are maintained on the open road.
"This is a major plus point for a mechanically-based kinetic energy recovery system," says Halley, "in which the variator can also handle energy flows a lot faster than an electric vehicle."
"On a directly comparable basis, a flywheel system offers up to twice the efficiency of a kinetic energy recovery system that stores its energy in a battery," adds Hilton. "The overall in-out efficiency of a mechanical drivetrain feeding energy into a flywheel and back out to the vehicle again via an ancillary transmission system is approximately 65-70 per cent compared with 35-45 per cent for a hybrid battery-electric system. Fundamentally, this is because a purely mechanical system doesn’t have to convert the kinetic energy into electrical and chemical energy as with a battery system."
"What this means is that with a flywheel each time the brakes are applied at least 65 per cent of the energy is available to re-accelerate the vehicle," explains Hilton, "whereas the best that can be achieved with existing battery technology is 45 per cent."
Flybrid has filed various technical patents to tackle the key engineering issues of safety and noise. The flywheel is made from high-strength steel and composite material and has been designed with a high factor of safety in which the maximum stresses are significantly less than in the con-rod of a conventional internal combustion engine.
"The flywheel also runs in a vacuum which is a natural barrier to noise," says Hilton. "For optimum refinement in a road car the engineering effort would be focussed on the transmission system and bearings – which provides the only noise path – it’s exactly the same test and development process in other words as for a normal powertrain."
Halley and Hilton will join other influential figures from the automotive and motorsport industries attending the Global Motorsports Congress being held in Cologne on 5-6 November 2007 – where the hot topic of conversation is expected to be the future eco-friendliness of motorsport and the ‘green revolution’ in F1 envisaged by FIA president Max Mosley. This leading global industry event takes place the same week and in the same location as the Professional MotorSport World Expo, where Xtrac will be exhibiting a wide range of transmission systems alongside other leading motorsport manufacturers.
Later this year Chris Brockbank business development manager Torotrak will present a paper describing the sophisticated variator traction drive technology, which is a key part of the mechanical KERS system, at the CTi Transmission Symposium on 4/5 Dec 2007 in Berlin.
Adrian Moore, technical director, Xtrac, will similarly present a technical paper describing the technology behind the KERS system at the World Motorsport Symposium, which takes place on 29/30 November at Oxford Brooks University’s brand new engineering centre. He joins other senior engineers who will be bringing their particular expertise to bear on subjects that are of special relevance to the growing demand that motorsport technologies should be of more relevance to the road car of tomorrow.
Moore will also discuss the mechanical KERS system with mainstream automotive engineers and technical experts attending the Global Powertrain Congress being held in Vaals in the Netherlands in June 2008.