Rapid Prototypes: ABT Schaeffler Audi Sport

Current E rapid prototypes 2015-16 ABT Schaeffler Audi Sport powertrain

MGU: Single unit / Schaeffler

Transmission: Three gears / Hewland          

In short: Highly integrated powertrain is fast and light – but not quite enough to match Renault

After showing promising pace throughout summer testing at Donington Park, ABT could be forgiven for being disappointed with the magnitude of the performance gap to Renault once racing begun.

ABT elected to go for a three gears, which was thought to offer more flexibility to cater for both qualifying and race pace laps. It’s believed that both Schaeffler and Audi participated in the development programme, with a Hewland-built gearbox.

It appears that ABT’s powertrain is quite a departure from the others on the grid. What gives it away is the routing of the high voltage cables: a pair of orange DC cables emerge from the battery and, rather than enter an inverter mounted atop the battery box, they loop over and directly into the gearbox. 

There are two possible explanations for this. The first is that the powertrain is using DC motors, which would remove the requirement for an inverter, the primary job of which is to convert between the DC feed from the battery and the three-phase AC feed required by the types of motors in use elsewhere on the grid. Both are complex to achieve with the tight space and weight constraints of the Formula E car.

Although we’ve yet to get a peek at the electrical contents of the bellhousing, we think it’s most likely that the German squad has integrated the motor and inverter into one unit. This configuration greatly reduces installation complexity and, with far less heavy high voltage cabling routed around the back of the car, reduces weight too.

This solution would also lower the centre of gravity of the powertrain, with the inverter being mounted much lower than others in the paddock. While this layout might also result in the weight distribution being shifted unfavourably rearwards, a shorter gearbox which sits within the wheelbase (rather than extending back past the rear axle, as occurs on the first season drivetrain) could offset the disadvantage.

Another issue to be resolved with an integrated design is making it all work within the space available. Thermal management would be trickier with all the electronics trapped inside a hot gearbox case. Here, it’s worth noting that the Schaeffler/Hewland bellhousing features openings in its sides, likely to increase cooling and further reduce weight.  

The Schaeffler-branded gearbox casing is a wholly different design to that of the first generation drivetrains. The differential area in particular takes a different structural route, with mounts through the top of the case rather than through the side. Likely, this results in a much stiffer structure, especially when using regenerative braking, when the bevel gears driving the differential will be trying to push it sideways out of the gearbox.

The team has clearly put a lot of effort into its rear suspension design, installing different rockers and dampers.  The dampers appear to be ZF Sachs units, which would make sense as the company also supplies both Audi and ABT in WEC and DTM series respectively. The units are adjustable for bump and rebound at both high and low shaft speeds. This should allow ABT to better tune the handling of the car for both traction and rear tyre management.

With the integrated inverter, small motor and bespoke gearbox, ABT’s weight targets have been met. Reliability has been good so far and, while Lucas di Grassi hasn’t been able to match the outright performance of the Renaults, he’s been best of the rest so far in the second season and has consistently capitalised when the French squad has had issues.

Scarbs is technical editor at Current E. Follow him: @ScarbsF1

1 Comment

  • David Fraser says:

    Great insight by Scarbs. I do wonder if the gearbox integrated does create thermal issues. More lifting and coasting perhaps?

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