Tuesday 30 November 2010. The Green Piece Column.
When Honda sold its Formula One (F1) team to Brawn GP Limited in 2009, you might have thought you had seen the last of its participation in the racing arena. However, during the EVS 25 electric vehicle expo in Shanghai earlier this month, Honda offered a glimpse of a Kinetic Energy Recovery System (KERS) that was originally intended for its F1 car but could still have a significant impact on motor racing going forward.
What is KERS?
KERS is basically a form of regenerative braking that is limited to storing up to 400 kilojoules of energy per lap which can then be released at up to 60kW for up to 6.67seconds as part of a push to pass strategy. Dependent on the vehicle and track design, this could potentially increase vehicle acceleration by as much as 15kilometres per hour – helping F1 cars to gain as much as 20metres of distance per lap.
The systems were originally introduced in F1 during the 2009 racing season and were seen as one of the key factors in several race wins. However, the system was then withdrawn due to development issues but is scheduled to return in 2013 alongside new engine regulations.
Tackling the problems of KERS
There were several design challenges with KERS systems in that they have to be implemented without affecting vehicle aerodynamics; weight; collision safety; centre of gravity; or fuel tank capacity in an adverse manner.
As such, Honda set about creating an electric motor/battery pack solution instead of the flywheel solution that has been used by the likes of Williams. This means mounting the motor on the engine’s left front side with its power control unit ahead of it inside the monocoque chassis. The 106cell lithium-ion battery pack was mounted in the forward section of the keel meaning the centre of gravity could be preserved while taking advantage of draft air cooling.
As F1 cars are so light – they have a minimum weight of 620kg – Honda determined that the motor would have to be no more than 100mm in diameter, 200mm in length and able to produce around eight kilowatts per kilogram of motor weight – by contrast, the mass production of a hybrid or electric vehicle motor is just 1.0 and 2.5kW per kilogram.
For the stator core, a twelve tooth design with a double lap-wound stator and permanent magnet rotor was used meaning the operating speed would be roughly equivalent to engine speed and range from 13,000-21,000rpm. There were concerns over the effect of iron losses in the stator core given the high motor speed but conventional grain oriented silicon was deemed not efficient enough to be used in a motor that would meet the project’s size and weight targets. So an iron cobalt alloy was used to produce the motor’s stator core laminations and this yielded a 30 per cent increase in flux density as well as a 15 per cent increase in torque. Further losses were avoided thanks to a combination of technologies including a post-rolling heat treatment, which reduced core hysteresis losses and an ultra-thin oxidised insulation coating.
The rotor design itself was also highly important. Here Honda developed a high-coercivity magnet that featured an intrinsic coercivity of at least 1.1Ma/m at 160 degrees Celsius. The diameter of the rotor was reduced thanks to using the rotor’s shaft as part of the flux circuits; and a high tensile filament winding made of organic high-strength fibres encloses the rotor and prevents the magnet burst at the rotor’s 21,000rpm redline.
Initially, a water-cooled motor was used but this did not meet performance targets so instead the final motor was cooled with engine oil and a thin cylindrical resin sleeve structure was mounted in the air gap to isolate the cooling oil from the rotor and eliminate the risk of serious wind losses.
Our verdict – How important is this advancement?
Whether or not this KERS system makes its way into F1 in 2013 remains to be seen, but what is clear is that the advancements made could have a significant impact on motoring in general.
During testing in 2008 at the Jerez circuit in Spain, the Honda KERS system managed to reduce lap times by up to 0.4seconds and increase speed by seven km/hr – this meant significant gains of 7.8metres on a straightaway. The peak motor efficiency was an outstanding 99 per cent and peak generator efficiency reached 93 per cent.
This level of efficiency could well be put to use in a plug-in hybrid range extender and if the same efficiencies were applied to future plug-in and battery electric vehicles then there is the potential that they could weigh less than one tonne and perform much better than existing internal combustion engine models.
So what may be F1’s loss, at least for now, could ultimately be the motor car’s gain and with further technological breakthroughs over the next five- to 10 years in the form of advanced batteries and super reinforced plastics to extend range, the next generation of vehicles may well have taken a significant step closer to widespread acceptance.
Faye Sunderland
