OVERVIEW: Putting the new GTP hybrid system to the test and the system that produced it

When Porsche tested its new GTP/LMDH car at the Circuit de Catalunya near Barcelona, ​​Spain, it did so in complete secrecy. However, there were a number of very interested parties watching very closely. At the rear of the yet-to-be-named prototype that will be raced in the IMSA WeatherTech SportsCar Championship and World Endurance Championship by Team Penske was the first example of the Energy Recovery System (ERS) unit that will be in all cars of the new formula.

The ERS – essentially the set of components that, added to an internal combustion engine, form a mild hybrid system – consists of a Bosch generator set (MGU), an Xtrac gearbox and batteries supplied by Williams Advanced Engineering, which also produces batteries for Formula E and Extreme E. With the exception of the batteries, which will reside in the cockpit, the entire system fits into the bell housing of the gearbox.

The four manufacturers expected to be on the GTP grid in 2023 each have an engine that they mate to a chassis from their chosen partner, which could be Dallara, Multimatic, ORECA or Ligier. Acura partners with ORECA; BMW and Cadillac use Dallara chassis; and Porsche is a Multimatic. So there is a whole range of possible engine and chassis combinations. The ERS must work transparently with all of them.

“You have quite a variety of combustion engines,” says Martin Frohnmaier, director of customer and product management for Bosch, which coordinates the efforts of the three partner companies. “So we have to be very flexible and it was very difficult to adapt the MGU, an engine, to the gearbox, but we did several iterations with the chassis manufacturers. We found solutions to integrate everything into the bell housing which was tricky but now we have a good connection and it works fine and the first test was pretty good.

The design of the bell housing naturally fell to Xtrac, working with Bosch to fit the components inside, getting the electrics and fluid in and out, and taking into account the different engine and frame configurations. Finding an easily scalable solution for all possible iterations, many of which are not yet known, is a daunting task. On top of that, we try to do it with as few parts – and as few unique parts – as possible so that Xtrac can have all the spare parts it needs for the teams on the track.

“The bell housing designs are going to be quite different,” says Xtrac Assistant Vice President Paul Barton. “So it’s incredibly tight packaging, based on knowing what the rear of the engine will be and where the axle line is. Trying to get an MGU in that space, working hand in hand with Bosch , we’re really proud of this work. On top of that, you start thinking about the power lines, trying to move them out of the bell in a safe way for the crews to maintain. And then he there are things that not everyone considers with the different engines we don’t know who is coming to play long term so the engine could have the water system on the left side or the right side so we have assured that we can adapt the MGU cooling for both in common hybrid case.

To keep everything working together, a hybrid control unit (HCU) interfaces with the batteries, engine control unit, MGU and electronic braking system. The software for this is locked down, as is the case for the other components. But manufacturers and teams will have control over how the MGU’s 40hp is used in conjunction with the internal combustion engine.

“An LMDh manufacturer will control the response of the hybrid system via its ECU, but certain aspects of hybrid operation are limited by the various hybrid control units and/or LMDh technical regulations,” explains Matt Kurdock, technical director of IMSA. “Restrictions on common hybrid hardware and control software are made as a development and operational cost containment measure for manufacturers and LMDh teams. This is critical to the future-proofing of the LMDh platform.

“Manufacturers and LMDh teams will have control over regeneration and deployment strategies, using the control framework described earlier. The management of the state of charge of the ESS is the responsibility of each team. The deployment and regeneration power limits defined in the LMDh Technical Regulations must be respected at all times. There are a variety of system operational parameters, such as temperature and voltage, which must always be observed during operation.

In short, the hybrid system will provide another area of ​​strategy for teams to work with, giving them options on how and when to use the extra power. And while that increase is small compared to the overall combined power limit of 671 hp, the system would be capable of delivering significantly more power if the sanctioning bodies see fit to release it.

Getting the components to work together seamlessly while fitting into a very tight plug-and-play package was a big undertaking that required a lot of coordination between vendors. It also required enormous cooperation between LMDh/GTP makers, an area in which they performed admirably, notes Bill Pearson, senior engineer for performance and simulation at IMSA.

“I think the strength of what the ACO and IMSA have done is they’ve built a framework where manufacturers feel comfortable working together to bring success to everyone,” says -he. “We all know there will be a time when they stop. We all know that there will come a time when they will be racing on the track, but I think they have realized that we all have the best interests of the sport at heart. We want to work together because without all the pieces it doesn’t work. Without all the people, you can’t have a series. Whether it’s ACO, IMSA, all the guys from Bosch, Williams Advanced Engineering and Xtrac, all the manufacturers who built the chassis, all the people who are going to be involved. We all need each other. You can’t win against yourself – that’s what Toyota [in WEC LMH] are proving themselves right now. I think that’s what’s important as we go through this is that we’ve really emphasized at all stages that if we have good governance in the project, right from the top, then people feel comfortable working together to give everything we need to get the show off the ground.

Pearson, along with ACO competition director Thierry Bouvet, was present at the Barcelona test and saw it as a watershed moment in the development of the new GTP class.

“As an engineer, you don’t often get the chance to be at the start of something and see it through to the point where it’s actually going on the right track. It was fantastic to watch the car go, he said. “We imagined where it was going to go, how it was going to fit together, what parts it was going to have, how the system was going to be set up…to see it all go to plan was really, really satisfying.

Porsche has the first leap over other GTP manufacturers; Acura, BMW and Cadillac are expected to begin testing this summer. Other manufacturers are rumored to be joining, such as Lamborghini, which likely won’t be seen in competition until 2024 at the earliest. IMSA will carry out a few tests after the season, one immediately after Petit Le Mans in October, and a compulsory test for all GTP teams in December.

In addition to the ACO/IMSA LMDh platform, Le Mans Hypercars, a category created in collaboration with the ACO and the FIA, are eligible for the GTP. This includes the existing and proven Toyota GR010 HYBRID and future Peugeot 9X8 and Ferrari LMH cars. Kurdock says any LMH manufacturer wishing to participate in GTP in 2023 should notify IMSA by September 1 and undergo wind tunnel testing at a facility in North Carolina that IMSA uses for LMDh certifications, as well as attend. in the December test. .

Irene B. Bowles