KERS explained: how a mechanical Kinetic Energy Recovery System works
Kinetic Energy Recovery Systems are one of the big talking points off the off-season, as F1 teams weigh up whether to use them on their 2009 F1 cars.
KERS builders Flybrid Systems demonstrated a working Formula 1-spec device at the Autosport International show. I had a chat with managing partner Jon Hilton who talked me through how the system works and what they do to make the devices safe:
This is our demonstrator device for a Formula 1 KERS so the layout of it is correct. The output from middle gear to the car is adapted for every individual car so this is the core bit that would be fitted to any car.
Drive comes into the device’s continuously variable transmission which provides a seamlessly changing ratio between the inputs and the flywheel. Control pistons manage the ratio within the CVT. It contains a clutch, an epicyclic gearbox and a flywheel. The flywheel spins much faster than the input drive - it’s a 5:1 ratio. Controlling the position of the levers manages the torque transfer within the CVT, and therefore how much energy is stored or released.
The energy is stored in the flywheel which spins at 64,000 rpm. We’ve done a huge amount of work on safety, it was our number one concern when we started. We’ve done a lot of testing and the device is completely safe. We’ve applied for patent protections, and some of those are published now, on safety and containment. This device has an outer containment structure made of carbon fibre which is extraordinarily strong. It can contain pressures of up to 1,150 bar, so it’s enormously strong. If something were to break, it would be contained, for definite.
It’s our view that changing the states of the energy - from mechanical at the wheel, to electric, to chemical at the battery, and back again, is a very inefficient route. The energy efficiency in a petrol-electric hybrid is about 37%, where ours is about 60%.
The electric systems is what you would find in a Toyota Prius or Honda Civic Hybrid. Those systems are less powerful - the Prius’s is 23kW, this is 60kW. Performance of the devices in F1 is limited to 60kw, but this one is capable of 100kW, we restrict it to meet the rules, but it is much more powerful than the regulations allow. We are expecting them to increase the limit in the future and we’re ready and waiting for it.
It weighs 25kg in total including all the control hydraulics, the fluid that’s in it, electronics, everything. We looked at two different locations for installing it in an F1 car: one effectively sat on top of the gearbox, the other in fronn of the engine at the bottom of the fuel cell. There’s advantages and disadvantages to either place.
Most F1 teams are expected to use electrical KERS in 2009. But Williams are believed to be considering a mechanical device. Whether it will perform better than its electrical equivalents we will find out on the track.
Kinetic Energy Recovery Systems, or KERS, become optional for 2009. Such systems take waste energy from the car's braking process, store it and then reuse it to temporarily boost engine power. This and the following diagram show the typical placement of the main components at the base of the fuel tank, and illustrate the system's basic functionality - a charging phase and a boost phase. In the charging phase, kinetic energy from the rear brakes (1) is captured by an electric alternator/motor (2), controlled by a central processing unit (CPU), which then charges the batteries (4).
In the boost phase, the electric alternator/motor gives the stored energy back to the engine in a continuous stream when the driver presses a boost button on the steering wheel. This energy equates to around 80 horsepower and may be used for up to 6.6 seconds per lap. The location of the main KERS components at the base of the fuel tank reduces fuel capacity (typically 90-100kg in 2008) by around 15kg, enough to influence race strategy, particularly at circuits where it was previously possible to run just one stop. The system also requires additional radiators to cool the batteries. Mechanical KERS, as opposed to the electrical KERS illustrated here, work on the same principle, but use a flywheel to store and re-use the waste energy.
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