If you use two electric machines for the front axle you still need some sort of mechanical coupling in between them to be able to control the torque distribution and to take advantage of the full power offered by the machines.
There are plenty of vehicles that use independant motors for each wheel... torque biasing is simply part of the speed control system, and doesn't need to be linked mechanically.
I would start with a mechanical 4WD system
Remember the Power split, even in the case when you have full KERS boost, is still far in favour of the rear wheels in this concept, where the engine, and hence most of the weight is, so traction will not be a problem... in this case there really is no need to use mechanical 4WD, this just adds weight and cost, -although I agree plenty of rally machinery has this capability, so it is a readily available technology and in a bigger, more powerful vehicle it would have its advantages. There's a further disadvantage of mechanical 4WD if it were applied to my vehicle; routing the tranmission from front to rear. What's not immediately obvious from the screenshots is the narrow cockpit area... the occupants sit literally shoulder to shoulder to reduce frontal area... the result is that there is no room for a transmission tunnel between the seats.
In certain load points it can also use power from the engine to charge the energy storage unit.
This is possible with a front mounted power unit that isn't connected to the ICE inside the car... the engine and MGU(s) are effectively connected via the road... so the KERS system harvests energy (i.e Brakes the front wheels) a small amount when the ICE isn't being fully utilised to charge the KERS unit, this is what I call "Sport" mode -when the car tries to keep the KERS system fully charged by utilising unused engine power (e.g during steady peed driving), even though it means burning more fuel to do so... although as you say, and I said in an earlier post, it'll be relatively efficient because the engine will be under higher load and hence BSFC is low.
So for racing use, I would pick a flywheel, and for road use I would go with batteries
I agree... I should have written it in my first post, but the ethos for the car is to cover a stretch of European B-roads (read "twisty"), at the same pace as one of today's supercars, but with far less fuel consumption. I'm less concerned with in-city driving, and therefore I'm not concerned with the flywheel's self-discharge problem that clearly is a major advantage to battery storage for stop-start driving. With this ethos in mind I would stick with the flywheel storage method; its almost perfect for the high charge rate, short storage time, high discharge rate, that this application requires.
Also a flywheel partly charged or uncharged gives storage available at all times with a power range source, so that deceleration energy harvesting will always be available and not wasted as with a fully charged system.
The problem I have with this approach is that it implies that you have storage that isn't being fully utilised (although I agree the storage won't be fully charged ALL the time!). Storage that isn't fully utilised means unecessary weight. Personally I'd rather have less storage which is fully utilised than have more storage that is only partially utilised. Reducing weight not only improves the economy of the car in a straight line, but also improves cornering ability... that means you can cover a given twisty road at the same average speed with less power (you're quicker through the corners, and therefore don't need to be as quick on the straights), and therefore you use less fuel for the same average speed over the given route.
I would use a combination of lighter flywheel and batteries.
As above; this application doesn't benefit from battery storage, although I agree that a different application that requires good stop-start efficiency or the capability to "pollute elsewhere" would benefit from battery storage.
This allows self discharge of the induction spun flywheel into the batteries but keeps a flywheels rapid application of energy for boost
In
this application I'd just have a slightly bigger flywheel. Otherwise you'll just loose energy in the transfer process from flywheel to battery... I'm just not convinced by a mixed storage system in
this application.....
