The FIA Formula E Championship has always been aimed improving the breed of electric vehicles. To do this the rules and the category’s road map are carefully set up to allow the manufacturers to focus on the electrical powertrain and not aerodynamics, chassis or battery technology. Last season the manufacturers produced their first of a new generation of electric racing powertrains. Now we are in the second cycle of powertrain development, with the eight manufacturers producing all new powertrains for Season 3. Showing that variety adds spice, each of these powertrains is unique and different, both to each other and to the Season 2 installations. Progress is rapid within Formula E and the level of technology on show in the back of the cars is at seriously high standard.
SEASON 1 POWERTRAIN
The championship started with a fixed specification powertrain supplied by Spark with sub systems provided by specialists in each area. The set-up is based around a single eMotor supplied by McLaren Applied Technologies and mounted longitudinally within a cast aluminium bellhousing. Transferring the electrical energy between the battery and eMotor is an inverter, again supplied by McLaren Applied Technologies and this is mounted above the battery behind the chassis’ roll hoop. This placement was due to a lack of space inside the casing around the eMotor, but equally in this position the inverter was accessible and easy to cool. Attached to the eMotor’s housing is a Hewland five-speed gearbox, this selected gears via a pneumatic paddle shift system. As with now, the powertrain is a fixed specification and each of a driver’s two cars had a dedicated powertrain, which had to last the full season.
Powering all of this is the Traction battery, supplied by Williams Advanced Engineering. This unit was effectively a sealed black box for the teams, no access or maintenance was allowed by the teams and again each unit is required to last a full season.
As part of the Formula E roadmap to allow the manufacturers to develop new technologies, Season 2 opened the regulations to allow them to design and build their own powertrains. With this, the Traction battery remains a fixed specification and teams are only able to develop the powertrain parts downstream of this, namely the eMotor, gearbox, differential and casings.
With the initial powertrain specification built to a cost and within tight timescales, there remain greater efficiencies to be gained from developing each element of the set up. Some teams opted to follow this route, either by keeping the actual Season 1 hardware, or by using the existing partners to further develop the hardware. More attractive for some, was the option to develop a wholly new powertrain, taking all new hardware from new partners and starting to map-out the future of electric racing with second generation powertrains.
The freedom to develop the powertrain remains for Season 3, there are few new regulations to affect the powertrain design, but the additional development time has allowed every manufacturer to develop a powertrain unrelated to the Season 1 package. Thus this Season 1 set up will no longer be raced, although several of the new powertrains are relatives of its basic design.
It’s refreshing that each manufacture has chosen to follow its own development path, no two powertrains are alike and this shows the diverse technical possibilities for electric racing. So we now have eight different powertrains with two teams opting to take a customer supply of a manufacturer’s solution.
The aims for each manufacture is to make the most efficient powertrain, making the most of the fixed energy and power available. This way the electricity leaving the battery is maximized in making the car go forwards quicker. With efficiencies in the high 90 per cent’s everything the manufacturer can do to reduce losses, friction and weight will help the car’s performance on track, both in qualifying and in the race.
Season 2 (1 Transverse Motor – 2 Gears)
Winning both championships Renault’s Season2 powertrain was a new generation of powertrain compared to the Season 1 package. It is also a model from which many teams will learn from when designing their season 3 set ups.
Designed by RenaultSport in Paris, the set up placed the eMotor transversely across the car behind the battery. This drove through a two-speed gearbox to the differential. In this orientation there was not the 90-degree turn in the transmission that would otherwise create frictional losses and loads in the gearbox. Also with this set up the length of the drivetrain from eMotor to differential is shorter and lower, allowing the Inverter that transforms the DC power of the battery into the AC power for the eMotor, to be fitted inside the gearbox casing. This further reducing the Centre of Gravity height of the powertrain for better handling. Further aiding weight loss was a carbon fibre gear casing that houses the eMotor, Inverter and Differential, all these parts bolting through the side of the casing.
Renault opted for a two-speed gearbox to allow the eMotor to work in in its most efficient range at both high and low speeds. With the first gear used only for starts and a few low-speed hairpins, the driver then shifting up and completing the lap without need for gear shifts. Unlike the pneumatic paddle shift of the Season 1 powertrain, the shift was via vestigial gear lever fitted in the right side of the cockpit and connected to the gearbox via a cable. A set up lighter and simpler than the hardware and electronics associated with paddle shifts.
Season 3 (1 Transverse eMotor – No Gears)
With so much proven so right in Season 2, the work for RenaultSport over the winter was largely to refine the set up. So again continuing with Zytek for the eMotor and Inverter. The basic layout has been carried over, but the powertrain now runs without a multi-speed gearbox, so the motor drives the differential directly via a reduction gear. This reduces the weight and losses of what was already a small gearbox and simplifies the job of the driver, with no gearshifts required at all. The simplification of the powertrain has allowed the gear casing to be even slimmer and lower, with the overall effect of reducing the weight and Centre of Gravity height of the entire powertrain, Renault must require ballast to reach the minimum weight limit further aiding set up to improve handling.
With the Aguri team having run the Season 1 powertrain in Season 2, what is now called the Techeetah team have elected to have a customer supply of the Season 3 Renault set up.
ABT SCHAEFFLER AUDI SPORT
Season2 (1 Longitudinal eMotor – 3 Gears)
Abt’s investment into a bespoke powertrain for Season 2 paid off with a package that ran consistently well at most tracks. Its approach to the layout was unique with an eMotor, produced by partner Schaeffler, along with its Inverter mounted longitudinally inside a bellhousing which then drove a transverse gearbox and the differential. This set up being a halfway house between the Season 1 powertrain and the Renault set up. Having the gearbox transversely mounted allowed more space for the eMotor and reduced the loadings passed into the gearcase from the bevel drive ahead of the differential. This gearbox being three-speed unit that allowed the motor to keep in its most efficient RPM range at both slow turns and the longer straights, especially with qualifying power. No doubt the gears and layout aided the Abt car suit the variety of tracks in both race and qualifying modes. This consistency nearly paying off over the course of the championship.
Season 3 (1 Longitudinal eMotor – 3 Gears)
Unlike many of its rivals the winter’s work has not been a wholesale revision of the SeasOn 2 package, rather refinement. So the Audi Abt still retains the same basic layout, with the individual elements, eMotor, Inverter, gearbox and casings, are optimised from the learnings of Season 2. This refinement is likely to help again in consistency over the course of the year.
DS VIRGIN RACING
Season 2 (2 Pancake Motors – No Gears)
With an eye on the future direction of the regulations, DS Virgin made the bold step for a very different powertrain lead by an equally very different eMotor technology. Running Axial flux eMotors, better known as pancake motors due to their large flat shape, with two of them transversely mounted to a common final drive set up. These eMotors produce more torque and run at lower RPM than conventional radial flux eMotors, thus they can be run without the need for a multi-speed gearbox. So the Season 2 layout simply geared the motors direct to the differential, the assembly being mounted inside aluminium casings. With the number and size of the eMotors, there needed to be two Inverters, one per eMotor and these were mounted over the top of the battery. This twin motor set up worked well, but the added weight of the set up hindered handling throughout the year.
Season 3 (1 Transverse eMotor – 2 Gears)
Wanting to run a lighter set up, DS Virgin have dropped the pancake eMotors this season and now run a single conventional eMotor. This being mounted transversely ala Renault and driving the differential through a two-speed gearbox. The change in eMotor is detectable from the higher pitched engine note, when the car is running down the pit lane. Although a two-speed gearbox has added weight, the single eMotor and the carbon fibre outer case have greatly reduced the overall weight of the package. Also helping weight and packaging is the Inverter which now sits inside the carbon casing to keep weight low.
Season 2 (1 longitudinal eMotor – 3 Gears)
Given the short timescales in which to prepare a new powertrain, Mahindra opted to keep the basics of the Season 1 set up and employ McLaren Applied Technologies and Hewland to further optimise the package for lower weight and better efficiency. Thus the eMotor and inverter were updated by McLaren Applied Technologies and Hewland made a four-speed version of the five-speed season 1 gearbox. But visually the set up appeared the same as the original specification installation.
Season 3 (1 Transverse eMotor – 2 Gears)
With a desire to progress and with a longer lead time, Mahindra opted for a full second generation powertrain, which has taken cues from the Renault’s Season 2 package. Partnering with Italian electrical experts Magnetti Marelli, Mahindra run a six-phase motor, effectively two three-phase units within one casing. Outwardly this appears like any radial flux eMotor, but the double internal set up reduces electrical losses from the shorter cable windings within.
This eMotor is mounted transversely and drives the differential through a two-speed gearbox with a pneumatic paddle shift. Despite the double eMotors requiring two Inverters, the Mahindra package is still able to place these inside the carbon casing, aided by Marelli’s F1 Silicon-Carbide switch know-how to create a smaller more efficient inverter.
Another team to run a refined Season 1 powertrain developed by Venturi in Season 2. Dragon worked closely with Mahindra to develop the Season 3 powertrain, complete with the Magnetti Marelli eMotors
Season 2 (1 longitudinal eMotor – 3 Gears)
As with Mahindra, Venturi developed a new version of the Season 1 powertrain, branded as their own and developed by McLaren Applied Technologies and Hewland.
Season 3 (1 longitudinal eMotor – 3 Gears)
For Season 3 it appears the same powertrain is now in its third iteration. So the Venturi runs a longitudinal eMotor developed by McLaren along with an all new Inverter, this adopts some interesting new material technology for its inner workings, with Silicone-Carbide switches doing the work of converting the electrical phases. While different in detail, it still sits above the battery. Now the eMotor drives through a two-speed gearbox, within lightweight casings.
A full Season 2 powertrain was developed by Andretti with its technical partners, but troubles in testing prevented the car completing hardly any running. With the clock ticking to the upcoming season, Andretti had little choice but to revert to the Season 1 package, rather than risk an untested and unreliable new set up.
With the passing of another full year and a change in technical partners, Andretti has now completed the development of its own powertrain. This takes technology from Magnetti Marelli for the eMotor and Inverters, these are mounted Season 1 style with the eMotor in-line with the car and the Inverter above the battery. Similarly, the set up drives a gearbox now with just three speeds, again all this hardware residing in lightweight casings.
Season 3 (1 longitudinal eMotor – 2 Gears)
As this season is its first entry into FIA Formula E, Jaguar has no experience with the Season 1 powertrain. The timing of its announcement to join the championship in Season 3 back in December left little time to reinvent the wheel and still meet the deadlines for crash testing, track testing and FIA inspections. With the assistance of its partners Williams Advanced Engineering, a consultative offshoot from the F1 team, Jaguar has produced its own powertrain. This follows the Season 1 layout with a longitudinal motor, driving a two-speed gearbox, all contained within a single aluminium casing. In this layout as with Season 1, there is not the space to mount the inverter low down, so its placed above the battery in its traditional location.
Season 2 (2 Longitudinal Pancake eMotors – No Gears)
With Partner Omnigear NextEV went on from its success with the drivers’ championship in Season 1, to develop a unique powertrain. This also adopted the pancake style eMotors like DS Virgin, albeit from a different manufacturer. These were mounted to the back of the battery, in-line with the car and the common shaft they ran on connected directly to the differential with no multi-speed gearbox. All of this was packaged inside a racecar style steel tubular spaceframe. The twin eMotors required twin Inverters and their size forced the installation above the battery.
This set up was not a racing success, the car was heavy with the twin eMotors and then made even heavier when the steel spaceframe required reinforcing to prevent flexing. This specification was frozen at the start of the season and left the team without a powertrain performance to match its rivals.
Season 3 (2 Transverse Pancake eMotors – No Gears)
No surprise the lessons were learnt from Season 2 and the NIO NextEV team now have an all new powertrain, albeit one not so different in layout, but far improved in execution. Omnigear took on the development of the eMotors, still based on the pancake concept, and the Inverter design. These twin pancake eMotors are now mounted transversely and a spur gear between them drives the differential without a multi-speed gearbox. Further saving weight and increasing stiffness is a new carbon fibre casing that encloses the eMotors and differential. Packaging of the inverters is tidier, with the two units combined into one, although these are still mounted above the battery.
Published on 8th October 2016