FE: Season4 Formula E Powertrain Analysis
As Hong Kong hosted the first two rounds of the fourth ABB FIA formula E season, this season will prove to be a seminal point for the fledgling championship. This will be the last season with the current Spark SRT01e chassis, the Williams Advanced Engineering (WAE) battery and with it, the mid race car swaps.
Equally this will be perhaps the last season where the original independent teams that formed the grid back in 2014s first season will continue to race. As the major automotive manufacturers step up to race and promote the electric formula. Yet this shaping up to be the most competitive season yet, with all the teams all converging on similar design ideas and performance.
Season4 Technical Regulations
Technical rule changes for this year are sparse, the race power limit has been raised by 10kw to 180kw, that’s a 13hp rise, to some 241hp. While qualifying remains at 200kw (270hp) and plans to increase the regenerative braking level have been held back, keeping the 150kw per lap limit.
To aid this hike in race power, the WAE batteries have had refresh of their internals. But otherwise there’s no other technical rule changes for this season. Allowing teams to focus on development on the all new Season5 car.
Snapshot of New Powertrains: Team by Team
Very much the leader on the technology front in FE, Renault already have the definitive powertrain layout, being a single radial flux motor, running a single speed to the differential.As Renault do not have to re-invent their powertrain, they can spend their development time in other areas, to boost their performance. The packaging of the powertrain is impressive, already lightweight and requiring a tiny amount of cooling, the new car still mounts the inverter inside the carbon case, sat down low behind the (what is expected to still be a Zytek) motor.
The silver coloured ballast is evident when looking through the back of the carbon case.With the rear impact structure removed, the open end of the carbon case shows that there is a significant amount of ballast low down in the back of the case. This will further lower the centre of gravity height at the rear of the car.
Rivals noted the rear suspension worked much better in Season4, with the car having great traction in all circumstances. Part of this was down to clever geometry with the rear wishbones and track rod. This is another area where other teams are looking to make gains this year. Again, this year the car runs Sachs dampers and Eibach springs.
For Season4 Audi have stepped up and now headline the team, the WEC LMP1 operation being closed and some (but not all) of the engineers, switched to the FE project. The Season4 motor is all new, bearing no direct relationship to its parent motors. Mentioned by Di Grassi at the car’s launch there is no gearbox, merely a reduction gear to the differential, so from this was can assume the motor is a high torque device.
It’s also clear the motor is transverse mounted and sits with the inverter within a rear carbon casing.As with their LMP1 carbon gearcase, the FE casing is carbon fibre laid around the outside of a male mould for strength.As well as stepping up the motor and casing design, the rear suspension has also been the subject of close attention too, in both its geometry and damper layout.
DS VIRGIN RACING
In the past, there was a single motor and it returned to radial flux layout, driving through a two-speed gearbox with a pneumatic shifting mechanism. This year the layout has not changed much, there’s still a single motor, that now appears to be a single speed transmission.
DSVR's powertrain is long and needs the inverter mounted over the motor and gearbox. The DCDC converter provides 12V power to the car's other low voltage systems. The new DSVR powertrain is a neater package this year, the inner gear casing houses the differential, reduction gears, then the motor and inverter bolt to the case, before sliding into the carbon outer case. The inverter sits over the motor and the DCDC converter sits in the small space left beneath the motor.
The focus in Season4 is to optimise the package, with new Marelli hardware and a weight reduction programme. The new Marelli motor is of the high torque type and thus needs no multi ratio gearbox, while the inverters adopt Silicone Carbide MOSFETs over Silicon IGBTs. This along with a partially painted, rather fully vinyl wrapped livery has saved some 10kg from the car. A new step for Marelli with its six-phase motor, which is effectively two motors running in the same case, is the inverter package. The inverters are packaged within one casing, saving some weight and consolidating the synchronization connections.
ECU and PDM mounted below the radiator duc, tyre temprature or pressure (TPMS) controller mounted on the side. Cooling duct feeds air to the motors electrical connections, helping manage temperatures. The new gearbox does away with the multi ratio gearbox, the size of the casing around the differential suggests that the reduction gearing is largely done with the large final drive gear, rather than a stepped reduction.
For Season4 partner ZF have designed a new gearbox, still with two speeds, as the team feel that’s the best set up to suit the torque and electrical efficiency of the McLaren motor.
A clever piece of work is the rear suspension rocker arrangement. The rules demand the car follows the Season 1 layout with pushrod operated rockers working on coil over dampers. Venturi have maintained this layout with a twist, as the rocker is still pushrod operated, but has the coil over damper slung below it. This lowers the centre of gravity a little aiding handling. Like many teams Sachs dampers and Eibach springs are used.
Nio's season4 layout is a low mounted row of; Inverter, Twin Motors and Differential
In Season2 NextEV were unconventional with its powertrain, however, their Season3 was an improvement. There still being twin pancake motors, again running without multi ratio gears, but in a neater in-house package, Omnigear created a stepped reduction gear train to the differential, MAGELEC creating their own motors and inverter.
In Season 4, again, there’s the MAGELEC twin Axial flux motors, driving the differential ring gear directly without an intermediate reduction gear, this is a shorter and mechanically more efficient set up. Employing Silicon Carbide MOSFETs, the units are much smaller further aiding the packaging of the rear end, so the inverters now sit inside the carbon casing for the first time, mounted low down on the floor of the case.
The semi-conductor switch to SiC and with the inherently better cooling for the pancake motor, means the two radiators are much smaller this year, with them both being angled within the radiator duct to slow the air through the cores for a better heat exchanger effect.
The team’s management were reticent to talk about any of the technology, layout or materials of the new powertrain. This further hampered by the team being very sensitive with photography around the car during the Valencia test, which is unusual in Formula E, as it prides itself on being an open category. With close observation at the test and at the first ePrix double header, we can make some assumptions on the Jaguar technology. It’s clear the team have gone conventional with the powertrain, with a transverse motor packaged with its inverter within carbon case.
With the advent of a full BMW powertrain in Season5, the development to the Season4 set up has been held back. There is the new specification Magnetti Marelli motor and combined SiC inverters, but these sit within the Season3 casings, in the Season1 layout (longitudinal motor, bevel gear, multi speed gearbox, aluminium casing, inverter above the battery). So, while there’s still a three-speed gearbox, but this will superfluous with the high torque motor, so no gears shifts should be required. But weight and mechanical efficiency is penalized by the retention of the gearbox, bevel gear and aluminium case.
Dragon run a modified version of the Mahindra powertrain. The only visible different I have seen is different suspension mounting clevices for the rear wishbones.
2017-18 sees another season for Techeetah as a powertrain customer, again taking the complete Renault rear end package. This is clearly a cheap way of running a cutting edge FE powertrain, certainly comparable in costs to running customer cars in similar series.
Source: Craig Scarborough posted in Everything Technical