Formula E is a discipline with a high level of engineering not only in the development and management of the cars on the track, but also in their design. However, the frame and the standard aerodynamic design for all the teams, combined with the confidentiality with which the builders work to preserve their trade secrets, outline an impenetrable curtain that makes it particularly difficult to appreciate the design differences in powertrains, real works of engineering. . The recent launch of the M7 Electro, the car with which Mahindra will compete in the championship to come, provided a rare opportunity to observe the powertrain structure realized by ZF. It also provided an opportunity to compare Mahindra’s design choices with those of Audi last season, with the German manufacturer then providing a general overview of their car.
The efficiency of the powetrain, i.e. the ability to deliver useful power to the wheels ensuring minimum dissipation, is strictly influenced by that of the electrical components, on all motors and inverters. Their construction features, however, remain secret as well as being extremely detailed aspects, while the arrangement of the individual components inside the car is more evident. Ian James, Team Principal of the reigning world champion Mercedes, talking with FormulaPassion in the last E-Prix in Rome he described the area in which manufacturers can move in the design of the single-seater: “As for the packaging [la disposizione delle parti a bordo, n.d.r ] we have a perimeter within which we must arrange all the components, but the area where the powertrain is located, which we call CRS, that is Carbon Rear Structure, it is also our responsibility. Once we have defined this and the powertrain with it, then we can develop all the other parts as well ”.
Although the frame is therefore subject to mono-supply for all teams, the design of the carbon structure in the rear, the CRS, is the responsibility of the teams. The arrangement of the powertrain components is crucial as it determines the overall dimensions that affect the shape of the Carbon Rear Structure. Similarly to what happens with the outer shell of the gearbox in Formula 1, the CRS is the structure to which the rear suspension arms are attached. In the photos below, taken from the video made by Mahindra Racing in your workshop during the past season, it is possible to observe the Carbon Rear Structure with the metal supports for the attachment of the suspension arms and its subsequent installation in the rear part of the frame.
Therefore, the smaller the dimensions of the powertrain, the greater the freedom for the design of the CRS and the suspension scheme and therefore the better the management and use of the tires. In the photographs collected in the pit lane at the last Rome E-Prix, it is possible to appreciate how it is there an effective diversification between the teams in the geometries of the rear suspension as regards length and inclination of the arms. Finally, in addition to the aspects listed above, the placement of the powertrain components also affects the distribution of the masses of the car and in particular the height of the center of gravity, a parameter that most of all conditions the dynamics of the vehicle when cornering.
Modular Mahindra, compact Audi
Starting from last season, the Mahindra powertrain is entirely made by ZF, which designs and manufactures the inverter, transmission and MGU, i.e. the motor generator that performs the dual function of electric motor and generator under braking. The videos released by Mahindra Racing on its Twitter profile illustrate the structure of the ZF powertrain, in which the engine coupled to the transmission can be recognized, while the inverter is a mechanically isolated component.
In the last championship Mahindra had released renderings showing the assembly of the powertrain on board the car which, although they may not be fully faithful to reality, seem to be confirmed by the shots taken in the workshop with the cars naked. You can see how the electric motor is mounted in a lowered position, so as to also contain the height of the center of gravity. It is also oriented transversely with respect to the direction of travel, so as to allow the adoption of cylindrical gears for coupling with the transmission. These gears are more efficient than the bevel gears necessary for meshing with a longitudinally mounted motor, as they limit internal friction. Finally, the inverter is the rearmost component and is mounted in a vertical position.
In comparison with the powertrain Audi of last season stands out how the German manufacturer had merged the motor and the inverter into a single assembly, renamed MGU-Inverter unit. Mahindra, on the other hand, has conceived the powertrain with the motor and the inverter separated from each other, a simpler choice, but which in turn requires a different cooling circuit and thermal management of the components than those developed by Audi. The MGU-Inverter unit of the German car was also largely enclosed by a carbon fiber structure, used by Mahindra for the inverter casing alone, while the electric motor is enclosed by a metal case, a more economical choice. but also slightly heavier. However, both teams share the lowered position of the electric motor and its transverse orientation, therefore the adoption of cylindrical gears in coupling with the transmission.
The unknown of double gear
The transmission itself constitutes another point of interest for the new Mahindra single-seater. On the sole basis of the media material released by the team last season, we learn how in the last championship the team used a single gear gearbox. However, during the presentation of the M7 Electro for the 2022 championship, Sascha Ricanek, the Managing Director of ZF Race Engineering, stated that the new car incorporates a two-speed transmission. The multi-gear change on electric cars is not strictly necessary as the electric motor, unlike the thermal engine, allows a wider torque regulation as well as guaranteeing almost constant power. The first generation Formula E single-seaters were equipped with multi-ratio transmissions, but they subsequently disappeared with the development of powertrains and the progression of their efficiency.
Although a gearbox is not strictly necessary on an electric car, adopting a single gear is still a compromise choice that limits performance. In fact, a high transmission ratio guarantees greater torque to the wheels and therefore better acceleration, but also involves higher rotation speeds for the electric motor, increasing losses due to mechanical friction at the expense of efficiency. The engine rotation speed is also limited by regulation to 100,000 rpm. The addition of a second gear therefore allows the adoption of a second higher ratio to improve acceleration performance to then change gear as the engine speed increases, but weighs down the transmission with a greater number of gears whose starting disperses further power.
The choice of the number of gears is therefore also a compromise, but it cannot be overlooked that in recent years the Formula E tracks have progressively accelerated, with the Federation partially eliminating the tightest chicanes and hairpin bends. The design of a single-seater relies on data collection of the conditions faced throughout the entire calendar, which is why the analysis of the trend of racing circuits in recent years may have led Mahindra to reintroduce a second gear. Although less impressive, it is equally plausible that Sacha Ricanek’s statements may have contained a trivial typo, the verification or denial of which will only be possible at the debut of the M7 Electro on the track. The new Mahindra therefore offers some topics of interest from the beginning of the season, inviting you to check whether the adoption of the multi-ratio gearbox is a reality and if this could represent the beginning of a new design trend in Formula E. The hope, however, is that with next season we can also witness another trend, namely a progressive opening of the teams on the characteristics of their powertrains.
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