1. INTRODUCTION

    KERS means Kinetic Energy Recovery System and it refers to the mechanisms that recover the energy that would normally be lost when reducing speed. The energy is stored in a mechanical form and retransmitted to the wheel in order to help the acceleration. Electric vehicles and hybrid have a similar system called Regenerative Brake which restores the energy in the batteries.The device recovers the kinetic energy that is present in the waste heat created by the car’s braking process. It stores that energy and converts it into power that can be called upon to boost acceleration.

 

There are principally two types of system – battery (electrical) and flywheel (mechanical). Electrical systems use a motor-generator incorporated in the car’s transmission which converts mechanical energy into electrical energy and vice versa. Once the energy has been harnessed, it is stored in a battery and released when required.

Mechanical systems capture braking energy and use it to turn a small flywheel which can spin at up to 80,000 rpm. When extra power is required, the flywheel is connected to the car’s rear wheels. In contrast to an electrical KERS, the mechanical energy doesn’t change state and is therefore more efficient.

There is one other option available – hydraulic KERS, where braking energy is used to accumulate hydraulic pressure which is then sent to the wheels when required.

 

 

 

2. CONSTRUCTION DETAILS

The first, mechanical, consisted of using a carbon flywheel in a vacuum linked via a CVT transmission to the differential. This system stores the mechanical energy, offers a big storage capacity and has the advantage of being independent from the gearbox. However, to be driven precisely, it requires some powerful and bulky actuators, and lots of space.

Compared to the alternative of electrical-battery systems, the mechanical KERS system provides a significantly more compact, efficient, lighter and environmentally-friendly solution.

The components within each variator include an input disc and an opposing output disc. Each disc is formed so that the gap created between the discs is ‘doughnut’ shaped; that is, the toroidal surfaces on each disc form the toroidalcavity. Two or three rollers are located inside each toroidal cavity and are positioned so that the outer edge of each roller is in contact with the toroidal surfaces of the input disc and output disc. As the input disc rotates, power is transferred via the rollers to the output disc, which rotates in the opposite direction to the input disc.

The angle of the roller determines the ratio of the Variator and therefore a change in the angle of the roller results in a change in the ratio. So, with the roller at a small radius (near the centre) on the input disc and at a large radius (near the edge) on the output disc the Variator produces a ‘low’ ratio. Moving the roller across the discs to a large radius at the input disc and corresponding low radius at the output produces the ‘high’ ratio and provides the full ratio sweep in a smooth, continuous manner.

The transfer of power through the contacting surfaces of the discs and rollers takes place via a microscopic film of specially developed long-molecule traction fluid. This fluid separates the rolling surfaces of the discs and rollers at their contact points.

The input and output discs are clamped together within each variator unit. The traction fluid in the contact points between the discs and rollers become highly viscous under this clamping pressure, increasing its ‘stickiness’ and creating an efficient mechanism for transferring power between the rotating discs and rollers.
The second option, electrical, was to rely on an electrical motor, which works by charging the batteries under braking and releasing the power on acceleration. This system consists of three important parts:

1. An electric motor (MGU: Motor Generator Unit) situated between the fuel tank and the engine, linked directly to the crankshaft of the V8 to deliver additional power.
   
2. Some latest generation ion-lithium batteries (HVB: High Voltage Battery Pack) capable of storing and delivering energy rapidly.
   
3. A control box (KCU: KERS Control Unit), which manages the behavior of the MGU when charging and releasing energy. It is linked to the car’s standard electronic control unit.
   

In essence a KERS systems is simple, you need a component for generating the power, one for storing it and another to control it all. Thus KERS systems have three main components: The MGU, the PCU and the batteries. They are simply laid out as in the diagram below:

Fig 1.0 Schematic Assembly Of KERS in a F1 car

2.1 MGU (Motor Generator unit)

Mounted to the front of the engine, this is driven off a gear at the front of the crankshaft. Working in two modes, the MGU both creates the power for the batteries when the car is braking, then return the power from the batteries to add power directly to the engine, when the KERS button is deployed. Running high RPM and generating a significant Dc current the unit run very hot, so teams typically oil or water cool the MGU.

Fig 1.1Marelli MGU as used by Ferrari Fig 1.2 Marelli prototype PCU

 

2.2 Batteries

During the 2009 season only electrical batteries were used, although at least two flywheel systems were in development, but unraced. We will focus on the arrays of lithium-ion batteries that were raced. Made up of around 40 individual cells, these batteries would last two races before being recycled. In McLaren’s case these were mounted to the floor in the sidepods beneath the radiators. Other teams mounted them in a false bottom to the fuel tank area for safety in the event of a crash. Being charged and discharged repeatedly during a lap, the batteries would run very hot and needed cooling, this mainly took the form of oil or water cooling, and again McLarens example had them pack water cooled with its own pump and radiator.

 

 

2.3PCU (Power Control Unit)

Typically mounted in the sidepod this black box of electronics served two purposes, firstly to invert & control the switching of current from the batteries to the MGU and secondly to monitor the status of the individual cells with the battery. Managing the battery is critical as the efficiency of a pack of Li-ion cells will drop if one cell starts to fail. A failing cell can overheat rapidly and cause safety issues. As with all KERS components the PCU needs cooling.

3.KERS in Formula 1

The FIA (Federation InternationaleL”Automobile) have authorized hybrid drivetrains in Formula 1 racing for the 2009 racing season. The intent is to use the engineering resources of the Formula 1 community to develop hybrid technology for use not only in motorsport but also eventually in road vehicles. The hybrid systems specifications have been kept to a minimum, especially the type of hybrid system. This was done purposely to lead to the study and development of various alternatives for electrical hybrids which has been met with success.

The Flybrid Kinetic Energy Recovery System (KERS) was a small and light device designed to meet the FIA regulations for the 2009 Formula One season.

The key system features were:

• A flywheel made of steel and carbon fibre that rotated at over 60,000 RPM inside an evacuated chamber
  
• The flywheel casing featured containment to avoid the escape of any debris in the unlikely event of a flywheel failure
  
• The flywheel was connected to the transmission of the car on the output side of the gearbox via several fixed ratios, a clutch and the CVT
  
• 60 kW power transmission in either storage or recovery
  
• 400 kJ of usable storage (after accounting for internal losses)
  
• A total system weight of 25 kg
  
• A total packaging volume of 13 litres
  

The layout of the device was tailored exactly to meet the customer’s requirement resulting in a truly bespoke solution that fitted within the tight packaging constraints of a F1 car.

The mechanical KERS system utilises flywheel technology developed by Flybrid Systems to recover and store a moving vehicle’s kinetic energy which is otherwise wasted when the vehicle is decelerated.

With a focus on safety, the FIA have specified a limit on both the power rating of the hybrid system at 60kW and the quantity of energy transfer per lap at 400kJ. This translates into an extra 85bhp for just under seven seconds, which makes overtaking another vehicle on the track easier and the race much more interesting.Thus although a 0.3s boost to laptimes, the system was ultimately limited in its potential to improve laptimes. Thus no team could create a competitive advantage from a more powerful system. Then the weight of the system created issues, At a time when the wider front slick tyres demanded an extreme weight distribution of up to 49% weight on the front axle, the 25+Kg of a KERS system mounted behind the Centre of gravity, the handicapped teams being able to push weight forwards. Most teams dropping or not racing their system cited weight as the main reason for its loss.

The 60kW/400kJ limits in Formula 1 will not apply to road cars. Road cars will safely have more power and energy transfer due to their larger weight when compared with racecars, which will provide them with significant benefits.

There is more than one type of KERS used in motorsports. The most common is the electronic system built by the Italian company MagnetiMarelli, which is used by Red Bull, Toro Rosso, Ferrari, Renault and Toyota. Although races have been won with this technology, KERS was removed from the 2010 Formula 1 season due to its high cost.

Fig 2.1.Flybrid Kinetic Energy Recovery System Fig 2.2.A KERS flywheel

 

 

3.1. Ancillaries

Aside from these main components the KERS system also integrates with the FIA Security in order to control and monitor the PCU. KERS has to be driver activated; this is achieved from a steering wheel button. Although the drive has to initiate the KERS boost, the teams set the system up such that the driver knows to engage the system out of specific corners, the system then delivers the predetermined amount of boost specific to the demands of that section of track. In practice the KERS systems is being charged and discharged to this preset map of activations, which smoothens the balance between charging and discharging, so the system does not overcharge above the regulatory limit. Again the SECU ensures no more than the capped amount of energy is delivered each lap.

 

Fig 3. KERS Schematic

 

• Sensors:boost button, brake sensor
  

   

• Actuators:electric motor/generator unit, continuously variable transmission, flywheel, electro-hydraulic system, clutch.
  

 

• Data Communications:CAN Bus.
  

 

• Manufacturers:Bosch Motorsport, Flybrid Systems, MagnetiMarelli, Williams Hybrid Power, Zytek Group.
  

 

4. TYPES OF KERS

Advanced transmissions that incorporate hi-tech flywheels are now being used as regenerative systems in such things as formula-1 cars, where they’re typically referred to as kinetic energy recovery systems (KERS).

The types of KERS that have been developed are:

4.1. Mechanical KERS

4.2. Electro-mechanical KERS

4.3. Hydraulic KERS

4.4. Electronic KERS

 

Of the three types of KERS units – mechanical, electrical and hydraulic – Formula 1 teams have decided to go for the mechanic one. The reasons behind this choice are quite logical: less weight, better weight distribution, increased power boost and improved fuel economy.

 

4.1. Mechanical KERS

The mechanical KERS system has a flywheel as the energy storage device but it does away with MGUs by replacing them with a transmission to control and transfer the energy to and from the driveline. The kinetic energy of the vehicle end up as kinetic energy of a rotating flywheel through the use of shafts and gears. Unlike electronic KERS, this method of storage prevents the need to transform energy from one type to another. Each energy conversion in electronic KERS brings its own losses and the overall efficiency is poor compared to mechanical storage. To cope with the continuous change in speed ratio between the flywheel and road-wheels, a continuously variable transmission (CVT) is used, which is managed by an electro-hydraulic control system. A clutch allows disengagement of the device when not in use.

As Li-ion batteries are still an expensive emerging technology, plus they have associated risks, recycling and transport problems. The attraction of flywheel KERS is obvious, however no team have raced such a system in F1. Flywheels can effectively replace the Li-ion batteries with in a typical KERS system, the flywheel being mated to a second MGU to convert the power generated by the primary MGU on the engine into the kinetic to be stored in the flywheel. Williams are believed to have just such a system. However the simper flywheel solution is connect the flywheel system via a clutched and geared mechanism.

 

4.2. Electro-mechanical KERS

In electro-mechanical KERS energy is not stored in batteries or super-capacitors, instead it spins a flywheel to store the energy kinetically. This system is effectively an electro-mechanical battery. There is limited space in a racecar so the unit is small and light. Therefore, the flywheel spins very fast to speeds of 50,000 – 160,000 rpm to achieve sufficient energy density. Aerodynamic losses and heat buildup are minimized by containing the spinning flywheel in a vacuum environment. The flywheel in this system is a magnetically loaded composite (MLC). The flywheel remains one piece at these high speeds because it is wound with high strength fibers. The fibers have metal particles embedded in them that allows the flywheel to be magnetized as a permanent magnet.

The flywheel will perform similarly to an MGU. As the flywheel spins, it can induce a current in the stator releasing electricity or it can spin like a motor when current flows from the stator. This flywheel is used in conjunction with an MGU attached to the gearbox which supplies electrical energy to the flywheel from the road and returns it to the gearbox for acceleration at the touch of a button. Not all flywheels used in the electro-mechanical KERS are permanent magnets. Instead, these systems use two MGUs, one near the flywheel and another at the gearbox. Some systems use flywheels and batteries together to store energy.

 

4.3. Hydraulic KERS

A further alternative to the generation and storage of energy is to use hydraulics. This system has some limitations, but with the capped energy storage mandated within the rules the system could see a short term application. Separate to the cars other hydraulic systems, a hydraulic KERS would use a pump in place of the MGU and an accumulator in place of the batteries. Simple valving would route the fluid into the accumulator or to the pump to either generate or reapply the stored power. Hydraulic accumulators are already used in heavy industry to provide back up in the event of failure to conventional pumped systems.

Using filament wound carbon fibre casing, an accumulator of sufficient capacity could be made light enough to fit into the car. They might be capped in terms of practical storage with in the confines of an F1 sized system, but McLaren had prepared just such an energy recovery system back on the late 90s, but it was banned before it could race. With the relatively low FIA cap on energy storage, just such a system could be easily packaged, the hydraulic MGU would be sited in the conventional front-of-engine position and the accumulator, given proper crash protection fitted to the sidepod. Saving space would be minimal control system (equivalent to the PCU) as the valving to control the system could be controlled by the cars main electro hydraulic system. McLaren have recently been quoted as saying the 2011 KERS would be more hydraulic and less electronic giving rise to speculation that a hydraulic storage system could be used.

An older technology than that of the kinetic steering wheels and batteries to create KERS for trucks: A hydraulic fluid.

The HLA (Hydraulic Launch Assist) developed by Eaton is located between the transmission and the back axis of the truck. When the driver steps on the brake, it uses the movement of the wheels to compress hydraulic fluid, thus reducing the truck’s speed. When the truck accelerates again, the energy returns to the wheels. This is a hydraulic recovery system. The principle behind hydraulic KERS units, by contrast, is to reuse a vehicle’s kinetic energy by conducting pressurized hydraulic fluid into an accumulator during deceleration, then conducting it back into the drive system during acceleration

This system can save up to 30% on fuel in trucks that make numerous stops such as garbage trucks. In addition brakes have a larger life span, five times more than a simple diesel-electric hybrid, which increases the weight of the truck by about half a ton. But there are some fundamental problems here as well. One is the relatively low efficiency of rotary pumps and motors. Another is the weight of incompressible fluids. And a third is the amount of space needed for the hydraulic accumulators, and their awkward form factor. None of this matters too much in, say, heavy commercial vehicles but it makes this option unsuitable for road and racing cars.

Fig 4.1.Carbon Fibre Hydraulic Accumulator Fig 4.2. HLA (Hydraulic Launch Assist)

 

4.4. Electronic KERS

In electronic KERS, braking rotational force is captured by an electric motor / generator unit (MGU) mounted to the engines crankshaft. This MGU takes the electrical energy that it converts from kinetic energy and stores it in batteries. The boost button then summons the electrical energy in the batteries to power the MGU. The most difficult part in designing electronic KERS is how to store the electrical energy. Most racing systems use a lithium battery, which is essentially a large mobile phone battery. Batteries become hot when charging them so many of the KERS cars have more cooling ducts since charging will occur multiple times throughout a race. Super-capacitors can also be used to store electrical energy instead of batteries, they run cooler and are debatably more efficient.

5. KERS & Regenerative Braking

Since kinetic energy is the energy of motion, you could probably guess that cars create lots of it. Capturing some of that kinetic energy for the sake of fuel efficiency in a hybrid car is a little tricky, but regenerative braking is one common method employed by many automakers.

On a non-hybrid car during a routine stop, mechanical braking slows and then stops the vehicle. For instance, if your vehicle has disc brakes, the brake pads clamp down on a rotor to stop the car. If your car has drum brakes, the brake shoe pushes the brake lining material outward toward the brake drum surface to slow or stop the car. In both cases, most of the kinetic energy in the spinning wheels is absorbed by the pads or the drums, which creates heat.

On a hybrid car that uses regenerative braking, the electric motor is used to slow the car. When the motor is operating in this mode, it acts as a generator to recover the rotational kinetic energy at the wheels, convert it into energy and store it in the car’s batteries. When the driver of the hybrid car takes his or her foot off of the accelerator pedal, the resistance provided by the generator slows the car first and then the mechanical brake pads can be applied to finish the job. Of course, the mechanical brake pads can also be engaged immediately in an emergency braking scenario.

The car uses the energy stored in the battery to power the electric motor which drives the car at low speeds. Depending on the type of hybrid, the electric motor can either work alone to move the car or it can work in concert with the car’s gasoline-powered engine. So regenerative braking, coupled with eco-friendly driving techniques like slow starts and slower overall vehicle speeds, is an important feature on some of some of the most fuel-efficient vehicles on the road today.

Regenerative brakes may seem very hi-tech, but the idea of having “energy-saving reservoirs” in machines is nothing new. Engines have been using energy-storing devices called flywheels virtually since they were invented.

The basic idea is that the rotating part of the engine incorporates a wheel with a very heavy metal rim, and this drives whatever machine or device the engine is connected to. It takes much more time to get a flywheel-engine turning but, once it’s up to speed, the flywheel stores a huge amount of rotational energy. A heavy spinning flywheel is a bit like a truck going at speed: it has huge momentum so it takes a great deal of stopping and changing its speed takes a lot of effort. That may sound like a drawback, but it’s actually very useful. If an engine (maybe a steam engine powered by cylinders) supplies power erratically, the flywheel compensates, absorbing extra power and making up for temporary lulls, so the machine or equipment it’s connected to is driven more smoothly.

The heavy metal flywheel attached to this engine helps to keep it running at a steady speed. Note that most of the heavy metal mass of the flywheel is concentrated around its rim. That gives it what’s called a high moment of inertia: it takes a lot of energy both to make it spin fast and slow down. It’s easy to see how a flywheel could be used for regenerative braking. In something like a bus or a truck, you could have a heavy flywheel that could be engaged or disengaged from the transmission at different times. You could engage the flywheel every time you want to brake so it soaked up some of your kinetic energy and brought you to a halt. Next time you started off, you’d use the flywheel to return the energy and get you moving again, before disengaging it during normal driving. The main drawback of using flywheels in moving vehicles is, of course, their extra weight. They save you energy by storing power you’d otherwise squander in brakes, but they also cost you energy because you have to carry them around all the time.

Advanced transmissions that incorporate hi-tech flywheels are now being used as regenerative systems in such things as formula-1 cars, where they’re typically referred to as kinetic energy recovery systems (KERS).

 

5.1. KERS dissimilar from Regenerative Braking

Traditional hybrids acquire electrical energy from braking in a similar way that electrical KERS equipped vehicles do but the difference lies in how the energy is reused. While KERS quickly re-injects the energy back into the powertrain to provide additional power boost in conjunction with the engine, the traditional hybrid saves the energy to power the electric power train. KERS is different from traditional hybrids in that the stop start functionality is not a prime goal of the system. KERS work very well in conjunction with engine mounted Stop/Start systems, or it can be engine mounted and used for stop start functionality. The KERS hybrid system cannot be “charged” by the engine directly, which is the requirement that has lead to its name, “KERS”.

6. CARMAKERS – APPLICATION OF KERS TECHNOLOGY

6.1. Porsche

At 2011 North American International Auto Show Porsche unveiled a RSR variant of their Porsche 918 concept car which uses a flywheel-based KERS system that sits beside the driver in the passenger compartment and boosts the dual electric motors driving the front wheels and the 565 BHP V8 gasoline engine driving the rear to a combined power output of 767 BHP.

The electric motors are not powered by a set of batteries, as in a traditional hybrid, rather they take their power from an inertial flywheel mounted where the passenger seat would be on a road car and spinning at up to 36,000rpm. That’s spun up by momentum when the car brakes and, when the driver hits a button, that momentum is converted to give an acceleratory boost. 

Fig 5.1. Porsche 918 RSR Concept Car Fig 5.2. Ferrari Vettura Laboratorio HY-KERS

6.2. Ferrari

The HY-KERS vettura laboratorio (experimental vehicle) is an example of how Ferrari is approaching the development of hybrid technology without losing sight of the performance traits and driving involvement that have always exemplified its cars.

Weighing about 40 kg, the compact, tri-phase, high-voltage electric motor of the HY-KERS is coupled to the rear of the dual-clutch 7-speed F1 transmission. It operates through one of the transmission’s two clutches and engages one of the two gearbox primary shafts. Thus power is coupled seamlessly and instantaneously between the electric motor and the V12. The electric motor produces more than 100 hp as Ferrari’s goal was to offset every kilogram increase in weight by a gain of at least one hp.

Under braking the electric drive unit acts as a generator, using the kinetic energy from the negative torque generated to recharge the batteries. This phase is controlled by a dedicated electronics module which was developed applying experience gained in F1 and, as well as managing the power supply and recharging the batteries, the module also powers the engine’s ancillaries (power steering, power-assisted brakes, air conditioning, on-board systems) via a generator mounted on the V12 engine when running 100 per cent under electric drive. It also incorporates the hybrid system’s cooling pump.
This experimental vehicle thus maintains the high-performance characteristics typical of all Ferraris while, at the same time, reducing CO2 emissions on the ECE + EUDC combined cycle by 35 per cent.

 

6.3. Volvo

Volvo is experimenting with a Formula 1 style drive system which is claimed to cut fuel consumption by up to 20 per cent. The Swedish car maker is about to start road trials using a vehicle fitted with a kinetic energy recovery system, or KERS. Volvo is using the technology not only to improve performance but also to aid fuel economy.

It uses a flywheel fitted to the rear axle which captures energy from the car under braking. The flywheel spins at up to 60,000rpm and when the car moves away the stored energy is released to drive the rear wheels via a special transmission. Volvo says that when allied to stop/start systems which switch off a car’s engine when it comes to rest in traffic, the Flywheel KERS reduces fuel urban fuel consumption by some 20 per cent.

Volvo aims to develop a complete system for kinetic energy recovery. Tests in a Volvo car will get under way in the second half of 2011. This technology has the potential for reducing fuel consumption by up to 20 per cent. What is more, it gives the driver an extra horsepower boost, giving a four – cylinder engine acceleration like a six-cylinder unit. They claim that the system can have the effect of adding an extra 80 horsepower to an engine which could significantly improve acceleration.

They are not the first manufacturer to test flywheel technology, but nobody else has applied it to the rear axle of a car fitted with a combustion engine driving the front wheels. The Swedish carmaker expects cars with flywheel technology to reach the showrooms within a few years if the tests and technical development go as planned.

Fig 5.3. Volvo Flywheel KERS System Layout

 

6.4. Jaguar

A consortium led by a Jaguar Land Rover is developing a flywheel-hybrid system that it says boosts performance by 60 kilowatts (about 80 horsepower) while improving fuel efficiency 20 percent. The consortium, which includes automakers like Ford and engineering firms like Prodrive, sees a market for flywheel hybrids among luxury automakers.

During braking, a small continuously variable transmission (CVT) mounted on the rear differential transfers the kinetic energy to a flywheel. When the driver applies the accelerator, the flywheel returns the energy through the CVT to the wheels, providing a boost of 60 kilowatts for around 7 seconds. The flywheel spins at up to 60,000 rpm.

Jaguar is testing its purely mechanical flywheel system, which reportedly weighs 143 pounds, in an XF sedan. Jaguar says it is superior to battery-electric hybrid systems because flywheels are smaller, cheaper and more efficient. Instead of converting kinetic energy into electricity that is stored in a battery, the CVT transfers the energy directly to the flywheel and then back to the wheels.

 

 

 

 

 

 

 

 

7. CONCLUSION

By adopting the cheaper and lighter flywheel system (the ideal solution if it could be made to fit into the no-refueling era cars), a more powerful boost, and limiting the number of activations in a race it would cover all the bases it needs to. It would be affordable for the all the teams, deliver performances as well as being a more interesting race variable. The sidepod solution is quite unique, and has given us a new envelope to try to drive performance to the rear of the car. We need to keep thinking out-of-the-box. Compared to ten or 20 years ago, it’s really quite staggering what can be delivered given the restrictions we have now – it’s a tribute to imaginative thinking

 

Thus we are coming to the end of the elaborate study of KERS going through their advantaged limitation relevance and finally to the modification. To sum up this seminar we have gone through sophisticated concept which will surely be much raved in coming days.

Also it would be a great showcase of technology which could have a major impact on the car industry in years to come. In the future the technology could also be used on buses, trains, and wind power generation.

 

    
 

 

 

 

 

 

 

8. REFERENCE

 

1. www.howstuffworks.com/KERS.htm
   

    

2. www.wikipedia.org/wiki/Kinetic_Energy_Recovery_Systems