ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

was a crucial requirement Everrati had of all the partners it worked with, something that was of major importance when choosing the suspension. “We have an adjustable suspension on the Signature version of the car, which was made by a company called TracTive,” Kerr says. “That really allows us to modify the damping – the yaw stiffness, roll stiffness and each of the damping rates in the corner of the vehicle – to make the car quite flexible and adaptable for driving on country roads, track driving and so on. The adjustability on those dampers has been really helpful in trying to establish the set-up of the car.” Drivingmodes and technologies On the driving experience, Williams says Everrati’s most important reviews are those reporting that the car ‘still sounds and feels like an original Porsche 911’.” Kerr says, “As far as driving is concerned, we’ve always kept a core focus on maintaining the analogue feel, feedback and driver engagement in the vehicle controls. We really wanted to make it the most analogue EV ever.” To preserve that feel, the power- assisted steering pump, brake pump and other control parts (both interior and exterior) have been kept in place but have been changed to electrically powered units. The motor controller delivers the power and signals for regeneration, as this takes place in the motor independently of the mechanical brakes. The company is also developing a dedicated vehicle control unit (VCU), which will process and distribute the driver’s inputs to the BMS, inverter, steering pump and brakes, as well as toggling the volume and crescendos of the sound generation system, known as the augmented sound generator (ASG). This sits in the back of the car and recreates the original motor sounds of the classic 911; it is built around a 105 dB subwoofer. Initially this was installed just for fun for an electric car show in London, where every other car was bound to be deathly silent. “We soon realised though that the ASG actually restored a lot of the original car’s feel in NVH terms,” Williams remarks. “The speakers get the steering wheel and seat vibrating almost exactly as if you had a 3.3 litre M30/69 turbo flat-six in the back.” The bespoke sound track is modulated in real time, and it tracks linearly with the power delivery. However, Kerr is currently programming the sound system to account for torque interruptions as well, for example owing to emulated gear changes. These will be mapped from the motor controller to ensure the correct ‘blips’ of power reduction to emulate the output ripples of shifting gear. “We’re looking to implement a virtual geared system,” Kerr says. “Although we currently have just one physical, mechanical gear, we will have simulated gear change points based on throttle demand, vehicle speed and motor speed. We’ll also keep the original gear lever for ergonomics’ sake though; either way we want those shifts to be reflected audibly.” Williams adds that since the speakers are simply playing sound files to provide a feeling of familiarity to reluctant adopters of EV resto-mods, future updates might include the sounds of other car engines – or even aircraft or fictional spacecraft. “There’s also a striking presence the car creates if you whizz past someone while completely silent,” he muses. “I honestly think even the biggest petrolheads will turn off the ASG in the long run.” liquid-cooling circuit thermally manages the drive unit. As Kerr notes, the iconic behaviour and performance of the 911 comes not just from its powerplant but how it puts its power onto the road. That is managed by a single final-drive gear reduction, which is fitted with a torque biasing differential from Quaife to help keep the car planted during sharp cornering. “There are some flexible features of that differential that we can set up accordingly, such as the preload across the differential or the torque biasing ratio, to suit the user’s application or driving conditions,” Kerr adds. A bespoke control board has also been fitted to the inverter, using the same original OEM function control strategy, while also allowing wireless logging, diagnosis and control of the drive unit’s operating parameters. “We’ve had quite a bit of help from Tim Harvey [British motorsport driver and 1992 British Touring Car Champion] in iterating the control responses in our software – in fact a fair amount of the rest of the engineering, given his extensive experience with Porsche cars,” Kerr explains. Williams adds, “If you ever owned a Porsche 911 Turbo, you’d remember that its power delivery was brutal. It would wait for the boost to come on, then all hell would break loose in the back. It was worlds of fun to drive but very, very tricky to manage. “When you have an electric motor controlled via an inverter and ECU, you can achieve such a linear power delivery: it engages the second you touch the accelerator but holds power so well without any spikes. So this powertrain means all the petrolheads who test-drive our car, with initially dubious looks on their faces, still get all the fun of a 911 – 0 to 60 in 4 seconds, and relentless power, without the performance drawbacks of the old IC engines.” As mentioned though, maintaining the analogue feel of the original 911 >Oere tOe oriNinal fuel filler bowl used to be, there is now a CCS2 charging input 54 Winter 2021 | E-Mobility Engineering