Impact of unlimited KERS on chassis design?

[WhiteBlue]

I should not have to repeat the facts for you.

The main breaking energy occurs on the front wheels which was never allowed to be harvested by the 2009 spec.
The power is only allowed to be applied by push to pass and not by dual torque.
There were deliberate restrictions in terms of energy and power which make no sense at all to an efficiency oriented system.

Without those limitations a much more meaningful system could have been achieved for all the money spent on KERS.

[timbo]

I should not have to repeat the facts for you.

The main breaking energy occurs on the front wheels which was never allowed to be harvested by the 2009 spec.
The power is only allowed to be applied by push to pass and not by dual torque.
There were deliberate restrictions in terms of energy and power which make no sense at all to an efficiency oriented system.

Without those limitations a much more meaningful system could have been achieved for all the money spent on KERS.

OK let's put things into perspective.
1) If you want to increase harvesting efficiency, you need to make much more powerful M/G unit. The power must be in the hundreds KW range. From what I read, I assume that best P/W ratio is around 5kW/kg. So, we're immediately talking about additional 20-40 kg unit immediately before driver's feet.
2) Another thing to consider is wires. If you need to transmit 100kW of electrical power to battery, you need a very meaty cable (and a damn high voltage, e.g. 100A/1000V).
IMO even this considerations put FW M/G units out of question unless drastic redesign (e.g. much more forward sidepods) is considered.
On the plus side I don't really understand obsession with FW M/G units. F1 cars use much more backward brake bias than regular cars. Even if bias is 60:40 you have plenty of braking power to harvest from rears only.

Dual torque system is fine. I believe, dual torque system with a current energy/power range (maybe 2-3 times higher, but not more than that) is what most realistic.

[xpensive]

When you start looking at the hard numbers, reality will very soon give you something to consider.

At Hungary this year, as estimated by Brembo, a total of 8.4 MJ of kinetic energy was lost over the 11 braking-zones, a 700 kg car, where I estimate that some 15% is lost through air-resistance, leaving 7.0 MJ of braking energy to recover.

In this context, WB's ambition of 2.3 MJ does not sound too far fetched, but here comes the problem, said recovery must be done over a total of 11.7 seconds of braking, meaning an average charge of 200 kW.

Charging a battery with 200 kW, at what Voltage, as Timbo said we would be dealing with some serious wiring here?

On top of that, I wonder if you can blast a battery with 200 kW just like that?

[timbo]

On top of that, I wonder if you can blast a battery with 200 kW just like that?

You can. But you would actually need a hella lot of small batteries

[747heavy]

Porsche 918 hybrid concept



Porsche claims.

V8 3,4l engine with 500 Hp (368kW) @9200rpm N.A.
electric motors at front and rear axle with a total of 218Hp (160kW)
top speed: 320 km/h
0-100 km/h: 3,2 sec
consumption: 3ltr/100km
weight: ~1490 kg

o.k. as a crude estimate, let´s use the weight of the Carrera GT (which is the base of the 918/same chassis).
The Carrera GT with it´s V10 engine has a weight of ~1380kg.
The weight of the engine (V10) is quoted with 214 kg (I don´t know if this values are correct). So in a very crude and roundabout way, we could maybe say the weight of the Hybrid system is 142kg (100 kg difference from basic car weight + assuming 172 kg for the V8)
That would make ~0,65kg/Hp - not too bad, in my book, compared with the Ferrari Hybrid for the 599 GTB HY-KERS

[WhiteBlue]

Regarding the weight, the 2011 figures are 95 kg for the engine and 30 kg for the KERS giving a total of 125 kg. I would estimate the 2013 engine at 65 kg and the AWKERS at 65 kg for a total of 130 kg. So the total weight would not go up significantly. After all the cars would carry almost 20 kg less average fuel weight during the race.

Power would be 700 bhp + 70 bhp for a total that is pretty much the same with the difference that 10% of the power is coming from reclaimed kinetic energy. If Porsche can do it with 500+218 bhp, F1 should be able to do it with 700+70 bhp. The peak electric power figures might be a bit higher because I am only looking at average values in motor mode. In generator mode the MGs will have to be higher rated as someone already pointed out.

It looks like Porsche will go for a common MG unit for the front drive with diff. THey will also have split power electronics for front and rear. It probably makes sense to keep the MGU controller close to the unit in order to avoid noise on the control circuits and save on cable weight.

So how will this concept save 25% fuel on todays figures of 150 kg/race? Ten percent will come from the KERS, another ten percent will come from the improved efficiency of the downsized turbo engine with throttle less control and direct injection. Finally five percent will come from the chassis which is supposed to have reduced aerodynamic drag by adaptive aero, lower downforce and and improved mechanical grip in slower corners. So the initial fuel cap will be 112.5 kg.

It is anticipated that all three sources of efficiency improvements will be continued to be developed over the following five years. The annual target for further fuel savings compared to todays consumption is 5%. The fuel cap will be reduced by 7.5 kg each year until we hit 75 kg of race fuel in 2018.

@xpensive
We agreed that 2.3 MJ reclaimed kinetic energy is the equivalent of 10% of the mechanical work that the engine produces from the available fuel per lap. We agreed on a figure of 23 MJ after engine efficiency.

[xpensive]

Problem is that you are selective with my posts WB, when earlier today I made an xample from Hungary, showing that you need a 200 kW average charge in order to store 2.3 MJ in less than 12 seconds of braking, which simply is not realistic.

[WhiteBlue]

I have not checked your figures in detail but we agreed to use average circuit data. So if Hungary is a bit out of the usual that may explain why the figures do not fit.

Previously we have discovered that an F1 car typically spends 15-17% of the lap on the brakes. At 75 s lap time it would be 12 s. So the average regeneration power would be 192 kW. Electric MGUs can be significantly overloaded if you give them enough time to cool down in between.

I see nothing wrong with a 1.8 overload factor at a 16% generator working percentage only. When they are used in motor mode they also get utilized only to a fraction of the nominal load (40%). If you work out the compound load factor (56%) you will see that you have plenty of head room to overload in recovery. Naturally the kind of overloading we are talking here requires a very efficient cooling of both MGUs and the inverters. You have to use water cooling to achieve that.

I conclude that an electric rating of 160 kW will be sufficient to do that job. That is exactly what Porsche will be using. If we stick with the over loading and check our data we get the following figures:

Average regeneration power: 192 kW
Nominal MGU power: 160 kW
Regeneration over load factor: 1.8
Peak regeneration power: 288 kW
Average electric motor power: 77 kW
Compound effective load factor: 0.65

[timbo]

I conclude that an electric rating of between 160 and 180 kW will be sufficient to do that job. It isn't so different to what Porsche will be using.

And how much Porsche system weights?
Also, this figures rule out FW M/G units, unless you drastically redesign chassis.

[WhiteBlue]

I conclude that an electric rating of between 160 and 180 kW will be sufficient to do that job. It isn't so different to what Porsche will be using.

And how much Porsche system weights?
Also, this figures rule out FW M/G units, unless you drastically redesign chassis.

I have no idea what the Porsche system weights. But I suggest to increase the energy of the 2009 system by a factor of 5.75 while increasing the weight by a factor of 2.5. It is a tough target. I agree with that. But you have to set ambitious targets to get somewhere. I reckon that the basic design of the 2013 package is so much more efficient that you may be able to reach those targets.

This thread is all about the different chassis design required for an ambitious new formula. So we might as well talk about that a bit more.

[timbo]

I have no idea what the Porsche system weights. But I suggest to increase the energy of the 2009 system by a factor of 5.75 while increasing the weight by a factor of 2.5. It is a tough target. I agree with that.

I don't think it is realistic target with current battery technology. Unless some advances are made you would have to dramatically overload batteries to operate at that power/energy level. But KERS regulations MUST put a limit on number of batteries used, unless we're dealing with another budget war.

This thread is all about the different chassis design required for an ambitious new formula. So we might as well talk about that a bit more.

If you want to have front-wheel MG units with power in order of 100-200 kW, you have to consider moving cockpit backwards (for safety/weight distribution reasons), smaller fuel tank and motor would probably allow that.
You also would move sidepods to the front to house batteries, as you do not want to transmit that much power over long wires.
I would imagine that cars would look much more like in mid-70s with such layout.

[747heavy]

some more info about the Porsche concept here:

http://www.wired.com/autopia/2010/03/po ... g-hybrids/

car is built as full carbon monocoque based on the Carrera GT super sports car.
weight is ~ 1490kg (compare with 1380kg for a Carrera GT with V10 engine)
the car has electric AWD (front axle) with torque vectoring

and another cool concept (but it´s off topic)
http://www.wired.com/autopia/2010/08/st ... -a-record/

[WhiteBlue]

Perhaps my weight estimates are optimistic but the power and energy figures should make sense if you want to make the 2013 formula work. However, even if they don't make the weight target and if it comes out 15 kg higher it might still work due to weight saving on the average race fuel load.

Without actual feed back from real world projects you necessarily work with shaky figures. But that does not always mean you have only downside deviation. If you consider higher electric over loads and higher compound load factors you may get better and lighter systems. I see no principal problems to hit an over load factor of 2 and reduce nominal power until you arrive at a compound load factor of 1.

For instance the nominal power could be 125 kW. The peak regeneration could be 250 kW and the compound load factor would be 0.78. There could be many ways to tweak this which we would not know much about.

If you want to have front-wheel MG units with power in order of 100-200 kW, you have to consider moving cockpit backwards (for safety/weight distribution reasons), smaller fuel tank and motor would probably allow that.
You also would move sidepods to the front to house batteries, as you do not want to transmit that much power over long wires.
I would imagine that cars would look much more like in mid-70s with such layout.

I would aim for 2/3 of the power forward to make the breaking more efficient. That would mean nominal 83 kW front and 42 kW nominal rear electric power.
I could imagine to put the front batteries on the sides of the driver cockpit with a small ducted radiator channel on top to cool the motors and inverters. The air could be taken in through the nose.

The Mercedes Benz 60 kW (400kJ) System had a weight of 26 kg of which 14.7 kg was used for the battery pack with proprietory A 123 nanophosphate technology. I estimate the water cooled inverter at 2.3 kg which would give us a weight of 9 kg for the electric motor. The nominal power is likely to be 30 kW for a peak used unit like that. So we come to a power to weight ratio of 3.3 kg/kW. For a 125 kW MGU combo this would give us 38 kg. For the two separate front and rear inverters I would be prepared to use 6 kg. The battery pack of MBHPE Ltd. was massively oversized for 60 kW to deal with the need for rapid charging from the energy poor rear wheels. If we consider that we might only need a four times bigger battery combo this would put us at 59 kg for batteries. So assuming we have no progress in weight saving we come out at 103 kg. I still think that the rapid pace of development in the battery world will bring the weight further down.

[xpensive]

Again, to charge a battery with 2.3 MJ over 11-12 seconds you will need an average of 200 kW and an awful lot more initially, probably as much as 400, when kinetic energy goes with the square of the speed and power is force times speed.

I fail to see the feasibility of neither such an MGU nor battery.

However, if you include 4WD-KERS (4 * 100 kW), with one MGU at each wheel and 90 kg of batteries (6 * 15) for 2.3 MJ,
it would be technically possible, but such an F1 car would not look or behave like anything we ever seen on track.

Besides, the development costs would surely make the different "cost-savings) look like a joke indeed.

[riff_raff]

WhiteBlue,

9Kg for a 60KW PM electric motor would not be possible if the motor is designed to turn at wheel speeds. To get a 60KW output from a 9Kg PM motor, the motor would need to be rated at very high RPM's, thus necessitating the use of a speed reduction gearbox. The best you could hope for with a wheel speed samarium-cobalt or neodymium-iron PM motor is about 4 KW/Kg, or about 15 Kg per motor. And they would also need to be liquid cooled at the charge/discharge rates needed for your F1 KERS.

The drawback with a wheel driven Energy Recovery System is that it must be sized for the high energy, short duration, charge/discharge cycle rates needed to recover braking energy. The rest of the time, it's just dead weight.

I proposed a high-speed, turbo-electric, Thermal Energy Recovery System (TERS). While an electric KERS would add over 10% to the GVW of an F1 chassis, a TERS would likely add less than 1/3 of that amount, besides being less complex and costly. A TERS could recover and return exhaust energy for about 75% of the lap, while a KERS would only be useful for about 25% of an average lap.

Regards,
riff_raff