At this point we can appreciate the advantage that KERS can indeed offer, and the theoretical time and distance advantage that the system offers. Unfortunately KERS comes at a price both in terms of weight and balance to the car itself, not to mention the development cost both financially and in terms of precious testing time in a rush to develop a race ready finished product. Thus far car technology is well understood and introducing a new variable albeit unknown was always going effect cars drastically. In the lead up to the 2009 season we saw mechanical flywheel systems, as well as options for electro-mechanical systems (electric motors).
To evaluate the difference between the systems we must once again appreciate the factors relating to the main systems that were proposed. In any and all KERS platforms, there must be at least 2 key components; An energy storage medium, And a delivery mechanism.
Mechanical Systems have thus far in design consisted of Flywheels and Constant variable transmissions. Electrical Systems have consisted of motor / generator units linked to either a battery assembly or Supercapacitors for storage.
Neither system is ideal, but based of the intentions of the FIA, both systems offer advantages over the other and potential benefits to the automotive market. More importantly each type of system will affect a formula 1 car in a different way.
Based on the regulations at the time, KERS could be connected to any point in the drive train ahead of the rear differential. When considering where to connect KERS we effectively have 2 viable options.
1. Directly ahead of the differential where mechanical shaft speeds are absolute and directly proportional to the speed of the wheels.
2. Direct connection to the engine or via a gear set where engine speed will not vary from track to track, nor require reconfiguration for modifications made during the race weekend.
Considering that KERS is governed by the controlled ECU and has no scope for modification, to connect KERS in front of the differential, would leave the operation of the system in a band that would be required to cover all tracks for the season. As such one would have to consider a minimum operation at an equivalent of 100Km/h and a potential maximum of 285Km/h where each track would be able to make use of this operational window. But at the same time, this also leaves room for many places where KERS cannot be used. The lower end of the operational window can nearly be set arbitrarily as KERS would not be used out of Lowes Hairpin, or out of La Source until such time as the car has reached operational speed, where the tyres are not traction limited.
At the same time, a maximum has to be carefully considered. If we consider the extremes of Monaco and Monza we can see the differences in absolute speeds. With top speeds of 290km/h and 340km/h. respectively we can see that there is a great deal of room to move and choose. If configured for use at below 290Km/h then KERS can be used at all tracks, but leaves no room for use at faster circuits. If configured for higher speeds, then KERS will want to naturally over rev the engine at slower circuits due to feed back through the gearbox back to the motor and subsequently breaking article 5.1.3.
With a fixed software characteristic in the ECU, this makes connection after the gearbox quite limiting. We can also see that with KERS mounted this far to the rear of the car; balance will be affected drastically, both longitudinally and laterally. To make a mechanical system lighter the flywheel will need to store power more in rotational speed than its inertia. As such very high speed systems were devised with rotational speeds of up 65,000 rpm in vacuum chambers with magnetic bearings. These measures ensure the storage of energy with the least amount of mechanical losses, however losses will still occur. As such with flywheel systems, the energy should be used as soon as it is available almost immediately after a regenerating zone. However with such high rotational speeds and varying engine, or output shaft speeds, to mate the two systems together a CVT with a high ratio range must be used, to ensure that torque always flows from KERS into the drive train. A complex CVT will always have to be active; matching the 2 system speeds together so that KERS can be used when required via a KERS clutch to connect the two systems together.
As a final consideration, a mechanical system will not be able to react quickly enough to high speed changes in the motor under gear change. As a result it would almost certainly have to be mounted along the gearbox; either along the car centre line above the gearbox raising the Centre of gravity, or mounted laterally along the car floor on one side of the car, requiring corrective ballast on the opposing side doubling the balance shift to the rear. With these factors we also cannot ignore the effect this could potentially have to the rear body work in order to cover the system up and the consequential airflow to downforce generating bodies. That being said a flywheel itself (providing the system is not structurally compromised) can be used for an entire season to store and deliver energy as it does not suffer from any chemical traits such as ‘battery memory’, nor should it need to be replaced on a regular basis. At most the CVT would need to be maintained, and the clutch plates replaced.
With all aspects considered, a flywheel and a CVT would take up a considerable volume in the rear of the car, and also shift nearly double its own weight toward the rear in order to maintain even lateral balance while compromising longitudinal weight distribution. In conclusion from what we can deduce here, unless KERS has been integrated into the car from the infancy of its design, the car may be able to travel in a straight line quicker, but will drastically suffer through any and all corners, most likely with dramatic under steer, resulting in poor turn in, and overall slower corner speed, to prevent running off the circuit, and then with extra weight at the rear, resulting in more rearward inertia through the corner due to higher outward forces at the rear, degrading tyres due to higher mid corner over steer.
As we are aware, this alternative was never raced, although the designs were considered. Williams most notably chased the idea and is today still pursuing it by supplying it to several motorsport teams in Le Mans and GTE while also trying to make it a viable solution for road cars.This article is the third in a series where we look at the KERS systems in use from 2009 to 2013. Click to read part 1, part 2 and part 4. Text by Richard Ronc, Ronc Industries