Regeneration specs?

I haven't seen specs for Leaf regenerative braking, but I expect that it should be quite effective on the Leaf.

Electric motors, by their very nature, are also generators. Toyota emphasizes their dual nature by calling them MGs, but the Leaf's electric motor should do as well. On the Leaf though, it only acts like a generator for regerative braking.

I think the Leaf will have an advantage with regenerative braking because of its large battery capacity. On long downgrades in the Prius, the battery fills within minutes. The Leaf's battery capacity should have more room to recover regerative energy.

 

I suspect the Leaf's superior power ratings will allow better regen than the Prius.

 

I'm less concerned with kilowatt ratings than with how the regenerative braking is engaged: Is it like the Prius, where stepping on the brake pedal engages it and ALL braking is regen except for very hard (emergency) braking and braking at very slow speed; or is it like the Tesla, where you get SOME regen when you take your foot off the accelerator but the brake pedal engages friction brakes?

 

It would be great if it were like the AC eBox, where there was a dial inside the car for adjusting regen. Dialed up all the way, you never had to touch the brake pedal. Dialed down, you got some regen without it slowing the car by much.

 

I disagree. I'd like to see the brake pedal operate like the Prius: All regen and no friction braking unless the demand for braking was more than the regen could supply or the speed was too slow; and the accelerator pedal like my Xebra (and some other EVs) where taking your foot off the accelerator results in pure coasting.

The idea of putting regen on the accelerator pedal is an atavistic attempt to make an EV (or a Prius) "feel" like a car with an automatic transmission, which slows the car down when you take your foot off the pedal.

Putting a lot of regen on the accelerator pedal would make it more difficult to control the braking. The accelerator pedal should be for accelerating, and the brake pedal should be for slowing.

Prius drivers have to find exactly the right pedal pressure to coast. With my Xebra, I take my foot off the pedal and I coast. This is much nicer, and is a more relaxed way to drive. An EV is not an automatic and should not pretend to be an automatic.

Just my opinion.

 

Exactly. That's how I'd want it to work on the Leaf.

Even if it normally regens with foot off, I'd like a mode that lets it coast. My foot gets tired of keeping the pedal at the "sweet spot" on the Prius.

 

The battery temp management is WAY simpler than the Prius, so it may be safe to assume the regen will be equally simple. Even so, it'd be WAY impressive if regen was adjustable as it is with the RAV4-ev.
http://avt.inel.gov/pdf/fsev/sce_rpt/rav4_ind_report.pdf

But you don't get a cheep price if you have tons of fancy stuff.

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Any software engineer will tell you it's a lot more successful to engineer the system to match the human than to try to engineer the human to match the system, even if it's much harder.

The Prius has one brake pedal that operates two different systems and one power pedal that operates two different systems. It would have been so easy to engineer it with a regen brake pedal, a friction brake pedal, an ICE power pedal and an electric motor power pedal. You wouldn't have sold any. It's much more successful imitating what the owners were used to.

Should we also get rid of creep, since that's faking an automatic car function? Actually, those of us who came from manual transmissions would quite like that!

 

YES!!! Absolutely!

 

I bet there would be sales in massive numbers to the organist community!

 

This is one reason. I highly suspect that Toyota's user testing showed that it was a good way to ensure some regeneration of the traction battery, even with heavy footed drivers not adequately using the regenerative brake system while braking.

 

Regen braking does nearly nothing useful. The battery is largely charged simply by the engine running. The car will run the engine harder - consuming more fuel - the further it gets away from the optimal charge point (six bars out of eight).

You get useful energy from regen when descending a hill but you had to put more energy than that into it to climb the hill in the first place. (Or, you'll use more getting back up there, assuming a round trip.)

It's better than throwing the energy away as heat (friction braking) but ultimately most of the drive force comes from the petrol/gasoline (hybrid) or from the plug (EV).

 

Agreed. I was simply saying that some drivers who brake late and hard may not get an interesting charge back from regen and that the simulated drag on the transmission may help.

 

In cars with an ICE, engine braking is a useful way to dissipate energy as heat without heating the brake pads. There is no analogous system in a pure EV. Regen captures energy, but once the battery is full the only way to dissipate that heat would be to have a large resistor (in effect a resistive heater) to dissipate the heat.

Since an EV has a larger battery than the Prius, there is more room for energy capture. But there will be times when the battery is full. Perhaps EVs will have the ability to use the car's heater to dissipate "motor braking" energy by directing unwanted heat to the outside.

 

Those times would be very rare. Leaving fully charged and going down a long long hill right away is the only one I can think of. Most of the time going down a large hill is preceded by going up a long hill. As the car is not 100% efficient there should almost always be room in the battery for dumping power.

 

I agree that it would be rare. However if you live on a higher spot than the surroundings, and there is a long steep downhill, and you charge fully before leaving home, you will encounter the situation of having no other way to slow your descent than your friction brakes, which will then be subject to overheating.

Rare as it may be, a well-designed car should have some system analogous to engine compression braking to protect the friction brakes.

Shunting regen power to the resistive heater and blowing that heat to the outside would accomplish this.

 

This reminds me of the Hydro-Québec's Pierre Couture serial hybrid (some info in French here or do a Google search on "moteur-roue couture hydro-québec"): four linear "motor-wheels" with integrated DC-AC converters (97% efficiency, 70 kw each, 1200 N-m/885 lb-ft each, at the wheel), no drive train, shafts or transmission of any kind, no friction brakes, internally developed 200 kg battery pack, planned 25 kw gas generator.

When the 4 motors stopped the car with their 4800 N-m total torque, energy that could not be "absorbed" by the battery was pushed to a big resistor to dissipate it as heat. So much motor torque was required to ensure adequate braking power (up to the limit the tires).

Sadly, this research was ended by Hydro-Québec as they didn't feel they could easily go against the big three alone (neither wanted it as it would have meaned a revolution nobody was yet ready to deal with).

All is left is TM4. Tata, Peugeot and Citroën are using the technology currently, but with a conventional hybrid design, with a central, unique motor. Any way, we still have lost 20 years.