The record speaks for itself: third place this year on the Hockenheimring; continuously in the top six of the world rankings since 2009, including the top ranking in the first year; and an impressive acceleration record in 2015. Every year the GreenTeam from the University of Stuttgart works with unflagging determination to build a race car to put to the test in a series of competitions. Once again this year, the up-and-coming engineers of the GreenTeam are waging a successful campaign against the international competition in the Formula Student Electric championship with their self-developed, designed and built electric vehicle.
Formula Student is an international design competition for students with racing events held in locations such as Barcelona, Melbourne and Detroit. For the teams, the objective is to design and build a race car and compete against other teams from around the world. The winner, in the end, is not necessarily the fastest car, but the team with the best overall package consisting of the design, racing performance, financial planning and sales arguments.
There are two classes in which the students can compete: The Formula Student Combustion (FSC) is the class for combustion engines, and the Formula Student Electric (FSE) is for vehicles with electric motors, which are tested for example on the Hockenheimring. Due to the increasing popularity of the competition, prospective entrants must in many cases go through an application phase before they can enter the main competition with teams from other top universities such as Zurich, Delft and Karlsruhe. Only after a strict inspection to ensure that the car complies with the international Formula Student rules are the cars approved for race action.
In two discipline types, a total of 1,000 points are on the line. In the static disciplines, the cars’ costs, mock marketing and engineering performance are evaluated by a jury of experts. In the dynamic disciplines, the cars are submitted to practical tests on various tracks — here the times and energy efficiency are decisive. As the individual categories are weighted differently, the right tactics can be key to victory.
Porsche Engineering is among the main sponsors of the GreenTeam and provides not only financial support, but also material support and the provision of test benches, knowhow and advisory services in the vehicle development process. “The collaboration with Porsche Engineering helps us with the ongoing of our high-voltage components. Without the valuable test bench time, we wouldn’t be able to push the envelope the way we do,” says Alexander Stemmler (25), student of aerospace technology and responsible for aerodynamics and thermodynamics on the GreenTeam, with evident satisfaction.
The long-standing collaboration between students and experts in the engineering services areas is advantageous for both sides. Young prospects come into contact with the company at an early stage and can establish valuable contacts for their later career development. They gain practical experience and learn how to deal with business partners. The companies, too, benefit from direct contact with the young engineering prospects and the associated link to the university and instructors.
The E0711-7 race car
In the current E0711-7 race car, the GreenTeam opted for controlled all-wheel drive with four AC motors installed near the wheels. Each of the electric motors generates up to 35 kilowatts of power and a maximum torque of 36 newtonmeters. The energy is provided by a 6.8 kWh high-voltage battery. To handle the heat generation during high dynamic loads, the accumulator and inverter have an oil-based cooling system. The open-wheel car reaches a top speed of 123 km / h. Most impressive of all is its acceleration: It takes just about 2 seconds for the speedster to accelerate from 0 to 100 km / h. The system electronics required to achieve the feat were also developed by the students.
Sophisticated race car technology is also present in the chassis and aerodynamics. For example, the engineering prospects developed a space-saving and lightweight monospring system with one transverse spring per axle. The generation of downforce and thus high lateral acceleration in competition is achieved by means of a comprehensive aerodynamics package, which enables the race car to achieve a lift coefficient
of cA = –2.8.
From the concept to the race track
The creation process of a GreenTeam race car stretches over a roughly eight-month period and encompasses the four phases of concept, design, production and assembly. In September of the respective year, the overall concept is hashed on the basis of insights from the last competition and knowledge transfer from the previous year’s team. The focal points at this stage are the especially important vehicle development topics such as battery cooling, high-voltage system and aerodynamics. Collaboration with Porsche Engineering begins already at this early stage. The team benefits from early professional feedback and tips for the implementation of the electric race car.
In the concept phase, both the targeted time objectives for the vehicle and the sales strategy to be presented to the Formula Student jury are discussed and defined in detail. At a later stage, the team must explain its vehicle concept, costs and other development details to the Formula Student jury panel. In the following work step, design, which extends from October to mid-December, the future race car is designed on the computer using CAD technology. After that comes the production phase in which the electric vehicle is constructed in collaboration with manufacturing partners. Over a lengthy period within this phase, components of the car are subjected to loads and coordinated with each in successive testing operations. The final step in the process is the assembly of all components to complete the car.
With the rollout at the end of April — the first official presentation of the vehicle to sponsors, supporters, friends and family — the students reach one of their most important intermediate goals. “We learn a lot from the experienced Porsche engineers and are then really excited to show them our own developments,” says Alexander Stemmler. As one of the main sponsors, Porsche Engineering holds a “test design event” in preparation for the presentation of the vehicle to the Formula Student jurors. The race car is presented in a similar manner as in the later contest and discussed and evaluated together with the Porsche engineers. This enables students to acclimate themselves to critical questioning, and they receive an independent estimation of their race car as well as final tips for the competition. Finally, in July and August the electric race cars must ultimately demonstrate how successfully they measure up against the competition from the international university teams in terms of concept and tactics.
The GreenTeam of the University of Stuttgart was formed in 2009 as a non-profit organization and emerged from the Uni Stuttgart e.V. racing team, which develops race cars with combustion engines. The GreenTeam, by contrast, is aiming to occupy one of the top places in the world rankings with a purely electrically powered vehicle in the Formula Student Electric category of the yearly Formula Student competition.
This year, a team of 45 University of Stuttgart bachelor’s and master’s students from the fields of vehicle and engine technology, mechanical engineering, electromobility and environmental protection technology developed an overall concept for an electrically powered race car. Participation in the project, for which some students actually postpone their studies for two semesters, is available to students in their fourth semester or later. For nearly a year, the prospective engineers spend some 60 hours a week tinkering with their electric vehicle — an undertaking that involves comprehensive engagement with topics such as control technology, power electronics and driving dynamics. In addition to responsible handling of the technology, the project also depends on aspects such as time management, teamwork and economic viability.
In recent years, the GreenTeam has scored some successes at the international Formula Student events: In 2015, for example, Stuttgart students set an acceleration record with the E0711-5. With a 0 to 100 km / h time of 1.779 seconds, the electric vehicle was entered in the Guinness Book of World Records.
Text first published in the Porsche Engineering Magazin 2/2016
Text by Peter Weidenhammer // Photos by Felix Bezler and Jörg Eberl