You will have recently read about the incredible Lotus Evija hypercar: road test number 5763. That should be my new PIN number, because I will certainly never forget it.
Never before, not in 15 years in this job, have I felt high-speed acceleration like it. Never have I needed to have a word with myself in order to simply keep my right foot pinned – all the way to infinity and beyond. I’m not sure Dirk Benedict had that problem when launched out of his mothership in Battlestar Galactica. Either way, the experience must have felt fairly similar.
Here, though, I would like to talk about asymmetrical torque vectoring. I’ve lost days of my life dreaming about it, but what would it actually mean?
The Evija has four-wheel independent torque vectoring – and what is, I now appreciate, a pretty well-realised system – but it doesn’t do any of the trick ‘spin on the spot’ stuff. Not that I mind. This car has taught me the size of the notional gap between the dynamic potential of this technology and the reality faced by those who just have to make it work.
The problem is that unless you’re going to fit any car that happens to have four independent electric motors with as many independent accelerator pedals (go on, wiggle that fourth toe), controlling those motors at times when you would rather they weren’t so independent is always going to be a challenge. And that, by the way, is a lot of the time.
Take a conventional car, with normal axles front and rear, going around a corner. It’s moving at a constant 70mph, yet all four wheels need to spin at slightly different speeds, because each is ascribing a path of a slightly different radius. That wheel speed ‘delta’ is what a conventional mechanical differential allows for.
It also delivers something called axle drive equalisation. So now you’re cornering quickly enough to transfer weight onto the outside wheels. If they’re driving forwards, the inside ones may lose grip and start to spin. But as they do that, the open differential driving them will automatically divert torque to the unloaded side of the car, like a blow-off valve letting pressure out of a closed system. The car itself doesn’t suddenly yaw into a slide, as it otherwise might, but stays stable.
Now imagine a much more complex model in which that open diff is constantly correcting for something. Allowing for changes in road camber and steering angle, bump, rebound and surface grip. It’s just doing it; you barely know, because it’s one of the cleverest passive mechanical systems that a car has.
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