For the first time in many years, we have three manufacturers competing in the LMP1 class of the World Endurance Championship (WEC). As the current rules dictate, the LMP1-L class is for cars having no Energy Recovery System and is reserved for privateer teams only. The LMP1-H class is for cars with an Energy Recovery System and has strict fuel consumption requirements necessitating the use of a hybrid drive system.
The much-anticipated return of Porsche to the LMP1 class has ensured that everyone has upped their game. All three manufacturers in this class, Audi, Toyota and Porsche all use quite different engine and hybrid drive systems as we outlined in our blog, WEC Season Hots Up, on 4 April 2014. The Audi R18 hybrid system is the most successful of the three hybrid systems, and also the most reliable as it has been developed over several years. The Toyota and Porsche systems are both new this year as even Toyota’s system represents a complete change from their 2013 system in the TS 030 which was a RWD vehicle only. (Video: ACO – Episode 10 – hybrid systems)
As endurance racing offers a more suitable application for energy recovery systems than does Formula 1, the author asked Ralf Jüttner, Managing Director of Joest Racing to explain how this works on the track:
Glen Smale (GS) – Is it possible, from a practical point of view, for the driver to misuse the stored energy and not to have enough hybrid power at the end of a lap?
Ralf Jüttner (RJ) – It is possible. You recuperate more often during the lap wherever you brake hard, and then after that braking point you can then use the energy to accelerate. Based on a lap of Le Mans, we are homologated use 2 MJ per lap, and for Silverstone and other circuits it is calculated down. Nothing prevents you from storing the energy, you can even store more then the 2 MJ but you cannot release more per lap.
GS – So how does the driver make use of the hybrid power?
RJ – There is no push-to-pass button, so it has to be controlled by the driver via the throttle pedal. But it is also up to the engineers to programme how the energy is then sent to the wheels. Just like with a normal combustion engine, there are different mappings where you can underlay different programmes for Le Mans or Silverstone, and this can be changed. The only thing is if something comes as a surprise to the driver, for instance if the hybrid system had a problem or failure, and didn’t work. You have to get the brake balance right, that means the forward and rearward brake bias has to be adjusted. Say the brake system is adjusted and the hybrid system then has a problem, you might be in trouble approaching the next braking point because the brake distribution is unbalanced. So when the hybrid system is not recuperating, then you need a different brake balance and if that happens because of a failure that could be a surprise to the driver. During the practice sessions, the drivers work together with the engineers to let them know where the system has a negative influence when braking, and from which point on would they would like to use the energy when accelerating.
GS – Does the driver know how much power he has used, is there a gauge or a meter?
RJ – No he doesn’t know that, but then again, every lap should be the same anyway because it is programmed, and this ensures that he does not overuse the 2 MJ. So there is no warning, it just doesn’t deliver should he overdo it, but the chance to do that is very small because it is controlled by the car’s computer.
GS – In using this extra power, does the driver have to change his driving style in any way?
RJ – I wouldn’t go so far as to say his driving style has to be changed completely, but they have to get used to what the hybrid system does and what it can do in terms of being a help. This you have to live with, but I wouldn’t say that it is so different from the many other things you do when you try to optimise the car’s set up. Yes, it works in a different way, and although it influences the balance and transient behaviour of the car, many other things do as well and it is just something that you have to sort out between the engineers and the drivers to make it the most efficient and comfortable for them to drive.
GS – What is the next step for hybrid as a technology, what is the next milestone?
RJ – It will be difficult to make bigger hybrid systems. We have seen with both Toyota and Porsche where we all expected them to be in the 8 MJ class, but they both stepped down to 6 MJ because obviously to use 8 MJ they first had to harvest it. Then there is exhaust energy that they can access but this is quite difficult to make, so the majority still comes from braking. You need to have a lot of braking energy to harvest that much and store it to use it for acceleration because you only have so many opportunities around a lap of Le Mans or Silverstone, so there are limits as to what you can do. Looking ahead, I guess a source would obviously be heat because of all the heat that goes out of the car, but that is difficult and I still believe it is small compared to all the kinetic energy that we destroy. I think optimising that and getting the most out of it will be for the next few years the major target. But as I said, I believe that the heat energy that you can get under braking is limited, so it is difficult to say really where it is all going. I think we are still pretty much at the beginning with the systems as they are now, and the process of harvesting energy through the braking system and feeding energy back to the car will undergo a lot of refinement. With much higher G-forces under braking than under acceleration, that is the most powerful [option] that we have in modern race cars.
In closing then, it seems that we are still in for some refinement of the technology that we see currently, with further innovations occurring around these energy recovery systems. Jüttner pointed to the growth of Formula E as the possible way of the future, but he felt that the internal combustion engine as we know it in both petrol and diesel format would be around for quite some time to come. But he added, “As I said, from the beginning, electronics will play a bigger and bigger part.”
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