So the Miata has regenerative braking now...

"slipperysallylikespenguins" (slipperysally) 01/08/2020 at 13:28 • Filed to: None

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Only in Europe for now, and only to power the car’s electronics. They claim a 5% gain in efficiency.

I’m curious though to how much weight it will add, specifically unsprung weight. Also curious how it might complicate the use of aftermarket brake components.(edit: seems like not much effect at all)

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farscythe - makin da cawfee! > slipperysallylikespenguins 01/08/2020 at 13:37

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hehe mazda i-elope

bet its a nissan.... i wouldnt want my parents finding out either

Longtime Lurker > slipperysallylikespenguins 01/08/2020 at 13:38

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Shouldn't be any noticable amount. If I understand Mazda's system. The use a lightweight capacitor to store the excess power. The alternator has a clutched pulley active when the vehicle is decelerating. So there should be no change to the brakes system.

slipperysallylikespenguins > Longtime Lurker 01/08/2020 at 13:44

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So its really not linked to the brakes at all, it just happens when the vehicle is decelerating though.

Longtime Lurker > slipperysallylikespenguins 01/08/2020 at 13:46

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That's how I understand it at least.

Tekamul > slipperysallylikespenguins 01/08/2020 at 13:52

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J ust so we’re clear, hybrid regen brakes also don't involve the actual brakes. It's done with the electric motor that's used for propulsion.

slipperysallylikespenguins > Tekamul 01/08/2020 at 13:58

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For some reason I was thinking it was like the hub based KERS systems.

Tekamul > slipperysallylikespenguins 01/08/2020 at 14:02

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That would be complicated as hell. Maybe fun to tinker with in the garage though.

Ram_Riot_6 > slipperysallylikespenguins 01/08/2020 at 14:27

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I have this system in my Mazda 6. Brakes are no different than the other models. T he alternator is what charges the capacitor. I dont know how much fuel, if any, it saves me but it has a fun screen to watch showing it charge and dissipate in the menu as you drive along. One downside is it takes a unique battery vs the standard models and last I checked it is double or triple the typical battery cost.

bhtooefr > slipperysallylikespenguins 01/08/2020 at 19:13

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So “hub based KERS systems” just means a vehicle with hub motors that are used for regenerative braking - so, it’s still the electric motor that’s used for propulsion, it’s just that the motor is mounted in the wheels, rather than to the subframe and with axles to the wheels.

...that isn’t done in production cars, though, because the unsprung weight of a powerful electric hub motor is incredibly high, and that causes all sorts of problems for acceleration, braking, and suspension. So, even when there’s per-wheel motors, most cars have them mounted to the subframe with CV axles to the hubs.

In any case, the traditional problem with regenerative braking is how to make it feel natural.

Some cars put all or most of it on the brake pedal. This means that you need a system that switches between regenerative braking and friction braking automatically, and provides consistent brake feel... and this is easier said than done. (The brake feel on my Prius is dreadful .)

Other cars (famously, Teslas) put all of it on the accelerator pedal. This means that the brake pedal just does the brakes and therefore feels better , but it also means you can’t just lift off and coast easily, you have to balance the accelerator at the zero power point (or shift into “neutral”, which doesn’t actually exist on most EVs or some hybrids, but it does force a zero power state ). And, when you have 75 kW or so of regen, lifting off suddenly gets you quite significant braking...

Looks like Mazda’s solution here was to map it to the accelerator. And, I’m finding claims that the i-ELOOP system has about 5 kW maximum regen, not exactly a lot.

Also, this system has been on the ND in some countries all along to help meet CO2 emissions targets , apparently it’s about 9.3 kg added weight above the standard alternator setup.