# Separating Hydraulic / Electric Braking for Performance EV?



## Hollie Maea (Dec 9, 2009)

miscrms said:


> So I had a somewhat wacky idea the other day and am curious what some of you folks that drive EVs fast think.
> 
> On my planned conversion (Leaf Drive Line in '73 Saab Sonett) I'm considering configuring the "gas" pedal to drive both the throttle position sensors when depressed, and the brake position sensors when released. This would effectively give you max throttle when fully down, and max regen when fully up. The brake pedal would then have no electronic sensors, and only a direct connect to the hydraulic brakes through a traditional master cylinder.
> 
> ...


A number of people have done that. The general feedback is that it's great until you get an itch on your foot and lock up your wheels going down the freeway. It depends a little on how aggressive you want your "max regen" to be.


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## dougingraham (Jul 26, 2011)

Unless you integrate traction control you will have a dangerous vehicle under slippery conditions. It is probably ok to have a really light level of regen at off throttle as this is similar to the way an ICE vehicle behaves and people are used to that.

Keep in mind that coasting down is a lot more efficient use of the energy than putting some of it back in the batteries could be. In a good setup you probably lose at least 20% of the energy and probably more like 40% in a typical vehicle. (20% loss when you store it and 20% loss when you take it back out.) And yes you should always gain something from regen vs converting the kinetic energy of motion into heat with friction brakes to slow down.

A number of people have placed a pressure transducer on their hydraulic brake line and mapped in the regen with the application of the brake pedal. They report that with a little tuning it feels completely normal. I would still be concerned if driving under winter weather conditions.


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## miscrms (Sep 25, 2013)

Thanks for the comments! Good points all around. 

Fortunately here in Phoenix wet let alone wintery conditions are a rarity, but still a reasonable concern. 

I'm certain that it takes some adaptation, but I already find it fairly intuitive coasting with partial pedal pressure in order to get a true glide in my Prius. I guess the re-learning curve in this case would be remembering not to lift full off first to get the ICE to shut down  Agreed that routinely slowing with heavy regen rather than coasting would be less efficient, that wouldn't be the intention. 

I can certainly see why some people seem to like running that way in terms of smoothly transitioning from positive drive power to gliding to regen all with one pedal. But I can also see some of the downsides for everyday driving.

Any thoughts on performance driving? I would think controlling regen braking with the right foot into a corner, transitioning to left foot hydraulic while getting back into the throttle with the right could allow for pretty precise vehicle control. Certainly not my area of expertise, but sounds good in theory 

In a way I suppose this is a bit of a work around in this case, as with using components from the Leaf I won't have the ability to alter things like regen response directly.

Thanks again for the input,
Rob


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## mizlplix (May 1, 2011)

I live in the Phoenix East Valley and after 10+ years driving an EV I have tried almost everything. My opinion:

1-One foot driving is neat if you train yourself, but is not intuitive after more years driving an ICE.

2-The formula E open wheel racers tried off pedal regen in the beginning, but most would lose control and spin when pushed into a panic situation.

3-The only fool proof system is a separate control for regen. It can adapt to any road condition without adjustments. 

4-I so seldom use the hydraulic brake that my front rotors get a slight rusty looking haze to them at times. They should never wear out in my lifetime. 

5- In flat territory where there are no real hills, regen braking leads to a more dangerous form of driving. Waiting until the last second to brake. (To get the most from the regen).

6-I like AC systems. But simple regen braking is not the deciding factor and should not be. So little is regained in my circumstance that it is just a "cool factor".

(again, my opinion)

Miz


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## jwiger (Oct 18, 2014)

miscrms said:


> Any thoughts on performance driving? I would think controlling regen braking with the right foot into a corner, transitioning to left foot hydraulic while getting back into the throttle with the right could allow for pretty precise vehicle control. Certainly not my area of expertise, but sounds good in theory
> Rob


Vehicle dynamics play a giant role in this. Are we talking RWD or FWD? If regen horsepower could be precisely dialed in, it could be used during threshold breaking. Track cars usually list a brake proportioning valve, to adjust front/rear bias based on the track. 

In certain hypothetical situations it could be used, however most applications would lean heavier on hydraulic brakes during threshold braking, it is too hard to predict how much braking effort you will get out of regen, not to mention the possibility of suspension bind. 

All that being said, I will experiment with different shifting techniques on my Mustang. One of the first places I will take it is the dragstrip, where I will try different upshifts. I will try some heal-toe downshifts on some back roads, mine will be a DC setup initially, so no regen, just engine (motor) breaking. 

My car is not a conventional street EV setup.


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## miscrms (Sep 25, 2013)

Thanks all, appreciate the experience and comments!

This is for a FWD setup. Natural tendency should be to understeer, so thought with hydraulic LFB would be to neutralize. I can certainly see how excessive regen would tend to bias front and cause problems. I'm no racer, but looking forward to getting back into some more spirited driving and perhaps autocross after a decade of Prius driving 

Host car is '73 Saab Sonett, ~1800 lbs w/CdA of ~4.7 sqft stock. Hopefully sticking close to that finished. Here's a vintage shot of one running "naked" back in the day, to give you an idea what I'm working with.








http://glennbunch.com/car-history/autocross-cars

Donor is '11-12 Nissan Leaf, ~200ftlbs Torque at wheels from roughly 0-20mph, then a little over 100 hp fairly constant to >90mph. Stock single speed gear reduction (~8:1).








Should be entertaining when moved into its new host 

Host vehicle is in hand (currently being driven with old 96V DC system), still waiting for the right donor. Have spent enough time with the Leaf service manuals that I'm gaining confidence on the transplant itself, but still trying to sort out a plan for brakes / tires / suspension.

Was originally thinking of just adapting custom drive shafts from Leaf transaxle to host hubs, but starting to think adapting the Leaf knuckles to the stock a-arms (or having new a-arms made) might make more sense. Oddly the Leaf calipers seem to be two piston units that share much in common with mid-2000s vintage 350z and G35 units. Seems like that creates a lot more pad/rotor options than are available for the old Saab/Lockheed units. Would also probably open up a lot more wheel/tire options.

Thanks again for taking the time to share you thoughts!

Rob


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## jwiger (Oct 18, 2014)

Rockauto.com showes that the US built Leafs used the same caliper as the same year Altimas. Same front pads as Altima and Sentra. Same pistons as almost everything, including the G35/350z. I'm not sure what the difference is between the calipers on the G35 and the Leaf are, but they aren't totally swappable. The good news is you could probably find a master cylinder that would work well from a G or Z car. Read up on master/slave cylinder pressure and volume before you start mixing too many parts though. 

A-arm and spindle geometries gets more critical the harder you drive the car, simply measuring ball-joint distance is not the only thing you need to consider. Let me know if you want to go deeper into that route. As far as using the front knuckles (spindles) from a Leaf. That won't work, the Sonett uses double a arms, the Leafs (and most modern Nissans) are a McPherson strut design.


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## miscrms (Sep 25, 2013)

jwiger, thanks for the feedback! 

I would be very interested in learning if you are willing. I can start a new thread, or just do it here, or I can PM/email you.

This is definitely an area that I'm apprehensive about. I'm an EE by trade, and while I've yet to actually do a conversion I've been reading and designing it in my head for about 10 yrs  I'm feeling pretty good about tackling much of the challenge, but modifying steering / brakes / suspension is all pretty uncharted territory for me.

If it helps, this photo gallery from a pretty extensive restoration has some nice shots on the linked page and the next of the stock sonett front setup.
http://travmattsaabsonettiii.coepercussion.com/categories.php?cat_id=2&page=33

And here's a screen grab from the original parts catalog:









My original plan was just to get some custom drive shafts made to connect the Leaf transaxle to the stock hubs. Then I started having second thoughts. The stock brakes are ok and mine were rebuilt in recent years, but availability of parts is getting limited, particularly for rear drums, and performance parts have pretty much disappeared. The stock wheels are also quite narrow (5") and are an oddball pattern (5x170mm!) which is quite limiting for wheel / tire options. 

That's what originally got me thinking of trying to use the spindles from the Leaf donor. I was hoping the Leaf knuckles could be machined / modified to match up to the sonett's lower ball joint and steering arm, but this may not be feasible. I haven't been able to see them side by side yet, as my leaf arrives next week. Alternatively I thought perhaps the Saab knuckles could be machined to accept the Leaf bearings / hub, which at least might address the tire/wheel challenges, but haven't been able to find dimensions on those yet to gauge feasibility.

Anyway, would be very grateful for any help in this area!

Rob


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## jwiger (Oct 18, 2014)

The basic designs are very different between the two cars, your car uses conventional tapered roller bearings with a 1.5 inch inside diameter. The Leaf uses unit bearings (the inner, outer, and bolt flange for brake rotor and wheel) that bolt on to knuckle using four bolts in a rectangular pattern.

http://www.rockauto.com/catalog/moreinfo.php?pk=4376040&cc=1505865&jnid=530&jpid=0

The knuckle on your car is actually a fairly simple design, and new ones could be machined to accept the more modern unit bearing easily. There is simply the cost involved in that. As far as using the axle shafts, they would have to be made shorter, the Leaf is 153 cm wide at the wheels (track width), the Sonett is 123 cm wide.

As far as sharing educational info I have a lot of sources to site. Enough to fill a few wiki pages, which I will ask the mods about posting. 

For brakes, look for "The Brake Article" by Dean Oshiro. It is 14 pages long and I can guarantee that if you can read the whole thing you will know more about brakes than any "technician" at any of your local repair shops. 

For a good primer in suspension and steering go here: 

http://scandc.com/new/node/674


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## miscrms (Sep 25, 2013)

Awesome, I look forward to reading!
Rob


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