Home  
Site Partners: SpotterGuides Veloce Books  
Related Sites: Your Link Here  

Go Back   TenTenths Motorsport Forum > Saloon & Sportscar Racing > Sportscar & GT Racing

Reply
 
Thread Tools Display Modes
Old 3 May 2015, 21:25 (Ref:3533738)   #1
BTCC 318d
Rookie
 
Join Date: May 2015
Posts: 33
BTCC 318d has a lot of promise if they can keep it on the circuit!
LMP1 Hybrid 101 - need a proofread or 3 =)

Hi forum,

Long time lurker, first time poster. I'm doing my 4th LM this year, and have in effect become our team's "man in the know" - and 2 of our newbies are baffled by the hybrid part of LMP1. The thing is, all my knowledge has been picked up from being a geek and reading pretty much every website, rather than actually being an expert - I really am no Mulsanne Mike.

I've written this trying to cover the needs of both my guys asking - one is keen on cars, but doesn't really know the basics, the other has raced Porsches for several years and wants the real techie bits - she wants to know how the car design changes the tactics / setup / behavior on track.

Please can any of you experts have a quick shuftie and point out anything I've got wrong / misunderstood? Any other constructive criticism appreciated - including anyone who can make it more concise =)

_________________________________________________________________

Hybrids in LMP1:

A hybrid system uses electric motors to drive the car as well as the traditional internal combustion engine. These systems have 3 main components: Electric motor to provide the go, some way of storing the electrical energy, and some way of recharging the system.

Why do they bother? Combination of efficiency and the rules. Hybrids are more efficient than normal cars because they recover energy that would otherwise be wasted (basically, heat) and use it to power the car.

The Le Mans 24 has always been a quest for efficiency. The fine balance between outright speed and the need to spend time in the pits has won and lost the race for teams since the race was first run. Ultimately, the winner is always the team that has managed the highest average speed over a 24 hour period – sometimes this has been due to sheer outright pace (with reliability), other times a slower car has pitted less for fuel and tyres and come out on top.

The ACO have engineered the rules to promote fuel efficiency – adding hybrid allows the ACO to push the manufacturers into using new technology to improve the fuel efficiency of the cars as well – transferrable technology to the toad which is critical for the marketing / popularity of the series.
The HY class is split into sub classes so that balance the use of hybrid power per lap against the fuel you’re allowed to use per lap – split into 2, 4, 6 or 8 megajoules (MJ) of usable energy over the lap.

The trade off is that as you go up the MJ classes, you lose LESS fuel allocation than you gain in usable hybrid power. This means in theory at least, an 8MJ car will have more total energy to use over a lap than a car in a lower HY class.

Logically, this means that given the chance, every manufacturer would be in the 8MJ class – which they would be if it were that simple. However, it’s a huge engineering challenge to harvest that amount of energy, and store it for use later in the lap. 8MJ is 2.2 kilowatt hours – that’s enough electricity to boil a top end kettle, constantly, for 1 hour. Every lap!

Le Mans has effectively 6 big start / stop sections, so an 8MJ car needs to be able to harvest and store about 1.3MJ per harvest event.

1.33 MJ is equivalent energy to 31 amp hours on a 12 volt battery. A 2015 Ford Fiesta battery is 52 amp hours. Therefore, an 8MJ car (Porsche 919) has to be able to charge a ford fiesta battery from totally empty to full 3 times a lap. Not only that, it’s all done in the braking zones – so that’s a total of about 12-15 seconds charging time. Pretty mad stuff!

Components of a hybrid system

So, looking at the techie bits in general, you have some options:
Motor – Could be located within the drive train (i.e. on engine flywheel, or direct to gearbox), or alternatively a single motor in the nose connected to the wheels by driveshafts, or individual motors mounted directly on the hubs.
Energy storage – 3 technologies on offer: Batteries, supercapacators, or an electromechanical flywheel.

Energy harvesting – Either KERS harvesting during the braking phase, or power taken from a turbo (in F1, they use both – designated MGU-K for the KERS, and MGU-H for the turbo – H denoting heat in this case).
One of the most exciting things about LMP1 in its current format is that the rules are so open – and in fact that means you have 3 different cars with 3 different designs, covering pretty much all the options (plus the Mazda which is covered far better by Mulsanne’s Corner):

Porsche – 2L V4 petrol engine, KERS and ERS-K, battery.
Audi – 4L V6 Turbodiesel, KERS, Flywheel
Toyota – 3L normally aspirated, KERS, Supercapacator
Mazda – 3L V6 twin turbo, KERS, Dual flywheel

Energy storage

At first, you’d think that storing electricity isn’t that hard – pretty much everything we have manages it with no real bother. However, when you realise the sheer amount of energy involved, and the speed that energy needs to be transferred in and out, it becomes quite mental.

Batteries

Clearly, your classic car battery is no use here. Even the most aggressive “high crank” type battery would take minutes to give up it’s power, and take hours to charge – not 12 seconds a lap.

Since energy density and high speed charging / discharging is needed, hybrid cars use Lithium Ion batteries – the same tech that is in a mobile phone.

These have advantages, such as:

Capacity - given enough space and weight, you can store as much as you want.

Stable output – A battery gives a pretty steady output over its charge range (see graph in supercap section).

But also downsides:

Heat - Any Li-Ion battery being charged gets hot – really quite hot in fact.

Longevity - Le Mans 2014 was won by Audi who did 379 laps – remember that’s 6 charge / discharge cycles a lap. Have you ever seen a mobile phone battery last for 7 years? Me either! Normally, they’re half knackered after 2 (which in LM terms is roughly 6 hours in)... Toyota have repeatedly stated that they don’t think a current tech battery can perform for a full 24h at a full 8MJ. They have also announced that next year’s car will run on batteries not supercaps so it might just be bluster!

Supercapacators

Supercapacators are brilliant for hybrid applications, because they charge / discharge incredibly quickly, and can do many, many more duty cycles than a battery without degradation. These are the reasons that you’ll only ever see capacitors in e.g. audio amplifiers (which charge / discharge many times a second).

Advantages:

Very high charge / discharge rate. Gives option to have very high HP for a short period – brilliant for overtaking / defence.

Very reliable – 2274 cycles (379 laps at 6 times a lap) is well inside the life of a supercap.

As always, they have drawbacks though:

Energy density – a supercap is 10 times the size of a Li-Ion battery of the same capacity. This makes packaging them in a car very hard.

Output stability - This is best explained by this graphic I shamelessly pinched from Wikipedia:

[pic]http://en.wikipedia.org/wiki/Supercapacitor#/media/File:Charge-Discharge-Supercap-vs-Battery.png[/pic]

...Which in turn affects power output. Since electrical power is volts x amps (current), as a supercap empties it becomes steadily less powerful than a battery. If Toyota can keep the charge / discharge cycle near the “fully charged” end, it works great – but as we saw post safety car at Silverstone, once the charge drops it just can’t output big power that quickly.

Flywheel / “flybrid”

This system uses an extra MGU-K that is just there to store / recover energy. When energy is generated by a KERS system or MGU-H, the power is sent to the flybrid motor. This motor spins an 8KG flywheel to mad speeds – 54k RPM is one figure I have read. When power is required for acceleration, the MGU-K attached to the flywheel does the same trick as any other KERS generator to then send energy to the motor doing the accelerating on track.

These systems have brilliant instantaneous power outputs – a flywheel can dump almost all of its energy virtually instantaneously if you let it. They also have very long duty cycles (no degradation over a race), and generate little heat compared to an all electrical system.

Downsides:

They are heavy given their charge capacity – Mazda need 2 to get to 8MJ.

There is a need for an extra conversion (“kinetic – electric – kinetic – electric – kinetic” vs. “kinetic – electric – kinetic”). Since every conversion of energy creates loss, there is greater potential for inefficiency than with an electrical system.


Harvesting energy

The tricky bit is that to be more efficient than no hybrid at all, you have to harvest energy that would be otherwise wasted - no point driving the generator with the engine: You'd just be using petrol to generate the electricity and that's not increasing the total energy you have for the lap.

There are 2 main sources of wasted energy - kinetic energy that can be recovered during braking, and waste heat energy can be recovered from the exhaust via a turbine - like the one in a turbo, for example.

KERS

For kinetic recovery (like F1's original KERS), you need an electric motor attached to the wheels - which you already have via the electric motor(s) you're using to power the car via the hybrid system. This is why they call them Motor-Generator Units (MGU’s). Under braking, the KERS system uses the motor in reverse to slow the car down and charge the battery.

This system has obvious advantages – you already have the MGU unit there, so there are few extra components needed (weight). On the downside, the amount of harvesting directly effects the braking period – just like a clumsy downchange can lock a rear due to engine braking, an imperfect KERS system will make the car’s braking phase unstable as the amount of energy being harvested changes.

The system also relies on heavy braking to recharge – under safety car periods, a KERS system will not be recharging at all, for example.
For cars using KERS energy recovery, the decision on where to put the MGU’s is interesting. Since most braking is achieved on the heavily loaded front axle, you can recover far more energy from the front than the back.

Having a pair of hub mounted MGU’s will give you greater recovery, and effectively 4 wheel drive with the hybrid engaged – but this is heavier than a drivetrain system.

The alternative is to put the KERS MGU in the drivetrain (like an F1 car). This is lighter and more compact packaging, but the recovery is limited c.f front because you will lock the rears if you harvest too much.
The decision over front hub mounted MGU, or the MGU integrated into the drivetrain will affect several areas of the cars abilities and dynamics.

Harvesting via the exhaust – MGU-H

An internal combustion engine works because of the expansion of gasses ignited in the combustion chamber. This high pressure expansion initially forces the piston down (making the engine work), and in a non turbo car, these gasses then enter the exhaust and they do no more work – all of that energy is lost as heat (and in the case of a Corvette, the world’s most awesome noise).

A turbocharged car uses a turbine in the exhaust to make use of these (still expanding) gasses – to drive a compressor wheel which in turn forces more air into the engine. In a way, the turbocharger was the first hybrid system, in that it uses energy that would be otherwise wasted to improve the efficiency of the car – the compressor wheel is attached via shaft to an impellor that compresses the inlet charge.

An MGU-H works on the exact same principle as a turbocharger, in that the turbine drives the MGU via a shaft. However, as always there is more than one way to skin a cat, so an MGU-H can be implemented in more than 1 way.

First – a point about how turbos work. In basic “Max Power magazine” terms, more boost = more power. However, too much boost = blown engine – so a turbo has to be done a bit cleverly. In order to maximise efficiency and avoid Saab 900 style throttle lag, the engineers goal is to reach maximum boost as early in the rev range as possible. This is done by using a turbine that gets enough power from the exhaust to reach peak inlet pressure at low revs, then using a valve called a wastegate to bypass the turbine at higher engine speeds in order to not grenade the engine at the top of the rev range. The wastegate operation in effect controls turbine / compressor speed by controlling the amount of exhaust flow is pushed through the turbine.

F1 style MGU-H

In F1, the MGU is attached directly to the single turbo that is being used by the engine. At higher engine speeds, instead of using a wastegate to control turbine speed, the MGU is used – not unlike the KERS brake concept. Once the inlet pressure is at the peak level the engine needs, the MGU slows down the shaft and uses the rotational energy to generate power.

In this implementation, there is another really cool trick that avoids throttle lag – the MGU can actually power the turbo shaft at low engine speeds, meaning that the engine is at peak boost 100% of the time. Mercedes have really used this to good effect in F1.

However, there is also a large downside to this design – if the hybrid system fails, the car will either run very badly, or not at all. If you’ve been following F1 for the last couple of years, you’ll know that the number of cars retiring with ERS failures is quite high. Whilst the 2011 era Red Bull often lost KERS and slowed down a bit, the 2014 Red Bull loses ERS and stops at the side of the track.

Audi originally designed the R18 in 2013 to use this style of MGU-H, but decided against racing it because they felt that the reliability risk outweighed the benefits.

Porsche 919 MGU-H

In the 919, Porsche have taken a very different path to the F1 solution. Instead of bolting the MGU-H to the output shaft of the turbo, they have 2 turbos side by side – one is a conventional turbo driving compressed charge into the engine, and the other is a turbine with a generator on it where you’d expect the wastegate to be. The amount of flow through each of these turbos is directed by how easy / hard it is for the exhaust to flow through them – much like water, exhaust gasses will always take the path of least resistance.

The key to this design is Porsche’s variable vane technology on the ERS turbine. This is effectively a turbine fan where the geometry of the blades can be varied to take more / less power out of the exhaust flow. This in turn gives control over the back pressure of gasses going through the turbine – the geometry of the turbo affects how easy or hard it is for gas to flow through.

At low engine speeds, the MGU-H turbine is moved to “difficult to turn” mode. This means the pressure in that exhaust loop is high, and the exhaust gasses therefore flow through the conventional (primary) turbo, which operates as normal. When the primary turbo is at or near maximum boost, the variable vane MGU turbo is moved to “easier to flow” mode, and so gasses that would normally go via the wastegate instead drive the MGU turbo, and generate power.

There is one last trick in this implementation (which Porsche’s marketeers claim is the most advanced in the world) – which is the effect of a closed throttle on the pair of turbos.

When the throttle is shut, instead of flowing as normal, the compressor side of the primary turbo suddenly sees some really high pressure air. This can cause turbo “stall”, as the compressor suddenly finds spinning rather difficult. In the Porsche biturbo MGU setup, this slower rotation of the primary turbine makes that line of flow really high pressure – meaning the gasses want to go via the MGU turbo. This is why you see the Porsches using “lift and coast” just before the braking zones and looking like they have shite brakes – they’re using that fraction of a second of big exhaust flow and closed throttle to get a big chunk of energy back into the hybrid system ready for the exit of the next corner.

This system is quite a bit heavier than the F1 style one, and also lacks the anti-lag capability of the F1 design. However, if the hybrid system chucks a wobbler, the car can still work at full “normal engine” power rather than parking on the side of the track. The Porsche 919 DOES have a wastegate on the exhaust, but it is only there in case of a hybrid failure – Porsche decided the extra reliability was more important than the extra kilo of weight in the car.


The cars - quick reference guide:

Toyota TS040 Hybrid – 6MJ
MGU built into gearbox
Harvests +deploys via rear axle only.
Energy stored in supercapacator

Porsche 919 – 8MJ

Single MGU-K in nose, connected to wheels via driveshafts.
Harvests via KERS under braking, plus via second, MGU-H specific turbine (which does NOT form part of the intake system).
Deploys via front axle only.
Energy stored in Li-Ion batteries.

Audi R18 E-Tron Quattro – 4MJ

Single MGU-K in nose, connected to wheels via driveshafts.
Harvests via KERS under braking.
Deploys via front axle only.
Energy stored in a flywheel.

Nissan NISMO LMP1 - ??MJ

The final spec of this car is still unknown. It was originally designed to be:
8MJ class
Single MGU-K within the front drivetrain, with separate gearbox / propshaft to drive the rear axle.
Harvests via all wheels under braking.
Deploys via all 4 wheels.
Energy stored in a dual flywheel system.

However, that plan has changed. NISMO have had huge issues with the hybrid system, compounded by car weight. Officially, the rear wheel drive part has been scrapped – so no second gearbox, propshaft, or drop gear system in the hubs (as originally planned). The rear wheels also had to go from small diameter to more conventional size to accommodate bigger rear brakes (more braking needed because of the lack of KERS harvesting). This will have a knock on effect to the cars aero concept at the rear.

What is not yet official is what class of hybrid it will run in. Some reports say that the Torotrak designed and built dual flybrid design is so buggy that they’ve resorted to a single flywheel (which dictates either 2 or 4 MJ class), whilst 1 or 2 photos suggest a dual flywheel is still there. Certainly, if they are running in 2MJ they will be so far off the pace that it won’t be pretty – 4 or more and there is a chance of a raised eyebrow, at last re. top speed.
I’ll be keeping an eye on this best I can, but the first date it becomes public is likely to be when the car is homologated – which is 4 weeks from the start of the race – we should know in a fortnight =)

________________________________________________________

Thanks to anyone who can right me where I'm wrong =)

Graham

Houx Rang 52 2015
BTCC 318d is offline  
Quote
Old 3 May 2015, 22:20 (Ref:3533772)   #2
TF110
Veteran
 
TF110's Avatar
 
Join Date: Sep 2010
United States
Posts: 15,376
TF110 is going for a new world record!TF110 is going for a new world record!TF110 is going for a new world record!TF110 is going for a new world record!TF110 is going for a new world record!TF110 is going for a new world record!TF110 is going for a new world record!
Toyota is 3.7L V8, Mazda dont have an lmp1, so I assume you meant Nissan As for the hybrid, Toyota recover energy on both front and rear axels. Audi and Porsche recover energy only on the front axel for the kers part (on the Porsche), not sure about Nissan if its just the front axel this year.
TF110 is offline  
Quote
Old 3 May 2015, 23:05 (Ref:3533813)   #3
BTCC 318d
Rookie
 
Join Date: May 2015
Posts: 33
BTCC 318d has a lot of promise if they can keep it on the circuit!
Thanks TF - that's the sort of thing I needed!

Daft old me looked at a well out of date (2013??) Toyota website with funky infographic of the original hybrid system - totally failed to spot the update for 2014 =)

Corrected the other bits, including my fictitional return of Mazda to the top flight of LM. Must be some kind of subliminal pining for the 787B =)

PS - any way to edit on this forum?
BTCC 318d is offline  
Quote
Old 3 May 2015, 23:20 (Ref:3533818)   #4
deggis
Veteran
 
deggis's Avatar
 
Join Date: Jan 2008
Finland
Posts: 6,206
deggis is going for a new world record!deggis is going for a new world record!deggis is going for a new world record!deggis is going for a new world record!deggis is going for a new world record!deggis is going for a new world record!deggis is going for a new world record!
Quote:
Originally Posted by BTCC 318d View Post
PS - any way to edit on this forum?
Only for some time right after posting (less than 1 hour or whatever the limit is). Stupid.
deggis is offline  
Quote
Old 4 May 2015, 00:46 (Ref:3533833)   #5
hcl123
Veteran
 
Join Date: Mar 2008
Posts: 889
hcl123 is heading for a stewards' enquiry!
I Think there is 2 relevant incorrections(we don't have to be too neet) related to Toyota in that expose... Toyota engine for 2014 and 2015 is a V8 3.7L (not 3L)... and Toyota hybrid system uses 2 MGU (motors/generatores), 1 at the rear axle integrated in the gear box case, and another at the front axle(the principal) connected by axles to the front wheels.
hcl123 is offline  
Quote
Old 4 May 2015, 01:04 (Ref:3533840)   #6
hcl123
Veteran
 
Join Date: Mar 2008
Posts: 889
hcl123 is heading for a stewards' enquiry!
Also the Porsche 919 MGU-H section is horribly confusing... first of all because the Porsche 919 doesn't have a MGU-H, which means a Motor Generator Unit... ppl use it to describe the system by a license of language... but that system is only a 'generator', and better call it an exhaust alternator in the wastegating routing.

And since all this routing valves can be very precisely controlled electronically, there isn't any danger of turbo stall unless something is very poorly enginered... and i can't see Porsche shite brakes... least of all in this year... and never witness any coasting out of the usual in any Porsche handling (the issue in 2014 was overregen, so braking at full throttle, in the straights, was to avoid (which is seldom the case)... apart from that !... seems like the jump to 8MJ with that system was almost compulsory...).

Quote:
This is why you see the Porsches using “lift and coast” just before the braking zones and looking like they have shite brakes
hcl123 is offline  
Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
How about a LMP1 Pro & LMP1 Privateer class Holt Sportscar & GT Racing 35 6 Jun 2012 13:44
2012 yr of the hybrid in LMP1 for WEC/LeMans? Canada ALMS fan ACO Regulated Series 27 19 Oct 2011 13:25
2006 LMP1/2005(6)Hybrid: The difference? Bentley03 Sportscar & GT Racing 5 14 Jul 2005 00:16


All times are GMT. The time now is 22:16.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Original Website Copyright © 1998-2003 Craig Antil. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2004-2021 Royalridge Computing. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2021-2022 Grant MacDonald. All Rights Reserved.