Why regenerative braking belongs on the brake pedal

[JeffC]

On a thread about the Leaf, there was a complaint that Nissan got it wrong then they had the default regen setting when coming off the throttle to be very light regen. Actually that is the correct way to do things for several reasons. Reasons which non-automotive engineers and non-racing drivers generally would not be aware of. Most of the regen is done on the brake pedal on the Leaf, Volt, EV1, Toyota RAV4 EV (the original one made by Toyota, not Tesla), Prius, VW e-Golf and many other EVs and hybrids. Read some of the history in my link below.

Tesla got it wrong when they put heavy regen on the throttle. It's one of several things they got wrong, but probably the most serious one. It's not stopping me for buying a Tesla or two, but worth pointing out. When I test drove a Model S, I liked it much better with Low Regen. I realize I'm probably in the minority on that, but I also realize most people are very likely ignorant about the reasons why.

Please read and learn: Why Regenerative Braking Belongs... On The Brake Pedal

Also be aware that Tesla itself is not monolithic on the issue. There are engineers inside Tesla who agree that regen belongs on the brake pedal, not the throttle.

Please educate yourself first before commenting.

Flames to /dev/null

 

[zenmaster]

My BMW starts regen off throttle, but I don't notice any slow down during coast. It'd be annoying otherwise.. On cruise control it will of course know to increase regen when going downhill.

 

[JeffC]

I test drove the i3 and found it regened heavily off throttle. Which BMW are you referring to? How do you coast it?

Regen downhill with cruise control on sounds correct.

 

[JeffK]

My prius regens off throttle too.

 

[JeffC]

My prius regens off throttle too.

Only really mildly though. Nothing like Teslas on Standard Regen.

Very slight regen on off throttle is useful since it imitates the drag on automatic transmission cars that most people are accustomed to. It's also useful for slowing at intersections, etc.

 

[Fluke]

One man's opinion, with the linked backup being...one man's opinion.

 

[JeffK]

on automatic transmission cars that most people are accustomed to.

Most Americans you mean... You're forgetting the rest of the world where manual transmission is still king. There are many who say that Americans can't drive.

 

[JeffC]

One man's opinion, with the linked backup being...one man's opinion.

It's human factors engineering and science, and understanding non-racing-trained driver psychology. It's ergonomics, which is absolutely a science.

 

[jerry33]

Regen does not belong on the brake pedal, it adds unneeded complexity and poor brake feel. Tesla got it right.

 

[JeffC]

Most Americans you mean... You're forgetting the rest of the world where manual transmission is still king. There are many who say that Americans can't drive.

Definitely most Americans.

 

[JeffC]

Regen does not belong on the brake pedal, it adds unneeded complexity and poor brake feel. Tesla got it right.

It's a little added complexity for engineering a car to properly integrate regenerative braking with the brake pedal, but it's a great simplification for the driver to have all of the braking in one place, smoothly integrated into a single control that does one thing: braking.

It is hard to integrate regen with friction brakes well, but lots of other manufacturers have done it, some better than others. It can be done.

GM did it very well 20 years ago in the EV1; Toyota a little later with the second generation Prius.

 

[zenmaster]

I test drove the i3 and found it regened heavily off throttle. Which BMW are you referring to? How do you coast it?

Regen downhill with cruise control on sounds correct.

Their hybrid. Coasting, as in whenever the throttle is let up fully.

 

[JeffC]

Their hybrid. Coasting, as in whenever the throttle is let up fully.

Good to hear. Coasting is the most efficient. Regen should only be used when slowing down is actually needed, since it has efficiency losses.

The i3 definitely did not coast. It regened heavily when lifting off the throttle. (Not sure what settings it was in, or whether it was adjustable.)

 

[jerry33]

Toyota a little later with the second generation Prius.

Unless you drove over an expansion joint or pavement irregularity while braking, then it felt as if the car lurched ahead--really poor brake feel. And the third generation was so bad they had to recall the cars to fix it. The only way in which regen on the brake pedal can be done smoothly is to have the friction brakes do a lot of the braking so that the transition isn't felt. It's a bad idea.

 

[tpoltron]

We have a Fiat 500e as well as a Model S and I have to admit I like the blended (regen+friction) brakes on the 500e better. Its nice to easily be able to coast. When the Model S first came out Tesla may not have had the time/skill to perfect blended brakes but now they easily could and I wish it was a user option.

 

[Ciaopec]

It's a little added complexity for engineering a car to properly integrate regenerative braking with the brake pedal, but it's a great simplification for the driver to have all of the braking in one place, smoothly integrated into a single control that does one thing: braking.

It is hard to integrate regen with friction brakes well, but lots of other manufacturers have done it, some better than others. It can be done.

GM did it very well 20 years ago in the EV1; Toyota a little later with the second generation Prius.

Lexus performance hybrid, GS450h, begins regen after throttle release but it is very gentle. Most regen comes from brake application. Computer determines speed, brake pedal angle (how hard you are mashing it) and determines how much regen to apply. Calipers only clamp at very low speeds or if computer determine you have reached the speed/ oh *sugar* brake pedal angle for immediate friction brakes.
I like the system. Letting up on throttle is a bit like the lowest setting on the MS. JMHO

 

[JeffC]

Unless you drove over an expansion joint or pavement irregularity while braking, then it felt as if the car lurched ahead--really poor brake feel. And the third generation was so bad they had to recall the cars to fix it. The only way in which regen on the brake pedal can be done smoothly is to have the friction brakes do a lot of the braking so that the transition isn't felt. It's a bad idea.

Not the only way, but using a very small amount of friction brakes can help. In cars with regen integrated with the brakes, full regen is activated very early in the braking, so most of the energy that can be recovered, is.

A low powered EV like a Leaf can regen at say 80 kW. It can friction brake at about 1000 kW. The regen gets used fully long before the friction brakes reach any of their potential.

 

[zenmaster]

Good to hear. Coasting is the most efficient. Regen should only be used when slowing down is actually needed, since it has efficiency losses.

The i3 definitely did not coast. It regened heavily when lifting off the throttle. (Not sure what settings it was in, or whether it was adjustable.)

I don't understand why they would not do the most efficient thing. Seems trivial to test.

 

[JeffC]

We have a Fiat 500e as well as a Model S and I have to admit I like the blended (regen+friction) brakes on the 500e better. Its nice to easily be able to coast. When the Model S first came out Tesla may not have had the time/skill to perfect blended brakes but now they easily could and I wish it was a user option.

Same here.

Coasting is always more efficient because regen has losses both in taking the energy back into the battery pack and taking from the battery pack back into motion.

 

[EdA]

I'm not buying the original post after 56k miles on my car and probably 5k on my wife's.
Where are the excessive accidents from people crossing lanes and skidding out of control
due to regen?

I really don't recall any unsafe situation even in emergency braking, dry, rain, snow,
dry with snow tires, etc. Tesla can tweak the algorithm for regen to (hopefully)
prevent unsafe situations.

But I've never driven another type of EV. I'm also not a car geek, I tend to try
and drive safely and under control.