# Managing Braking Bias With Regen



## BHall (Aug 1, 2007)

I too have wondered about this. Hopefully someone with regen experience will chime in. 

I wonder if a regen braking system could actually replace the rear brakes (on a rear driven car).

Brian


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## major (Apr 4, 2008)

toddshotrods said:


> How is brake bias managed when using regen?


Hi todd,

I have used aggressive regen on a competition EV. Brake bias was adjusted heavily to the nonpowered axel. It worked great.

And BHall,

I doubt that regen would allow the elimination of the friction brake on any wheel or axel. Unless a lot of validation and redundancy is done, the safety consideration will require the service brakes on all fours.

Regards,

major


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## toddshotrods (Feb 10, 2009)

major said:


> Hi todd,
> I have used aggressive regen on a competition EV. Brake bias was adjusted heavily to the nonpowered axel. It worked great...


Cool, thanks Major! Can't beat experience. I was expecting a discussion based on theory, but hearing that it was used successfully is great.


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## Usher (Feb 4, 2009)

I have a few thoughts on how you could do this:
1) If you want to get rid of the mechanical rear brakes, you could put a pressure sensor on the front brake hydraulic system and apply regen proportional to the pressure you measure. This of course assumes that your regen can provide as much braking force as the mechanical rear brakes would have.

2) Some cars run a lot of rear bias in their brakes normally, and use the ABS system to prevent problems. If you implemented ABS in your motor controller, you could do all initial braking with the motor, then add mechanical brakes as necessary. For example, add a potentiometer to the brake pedal which engages the regen in the first few centimeters of travel and adjust the pedal so engagement of the mechanical brakes requires more pedal travel.

3) The way I would do it in my own car would be to use the (former) clutch pedal to control regen and leave the mechanical brakes as is.


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## rillip3 (Jun 19, 2009)

From what I have heard, regen typically does not work like a break, but rather, like weak engine breaking. there's just a push against the inertia, like downshifting too soon, not a full on break. Unless you have a lot more resistance generated than I have heard of in the past, I wouldn't think it would require a complete rebalancing of the breaks. Toddshotrods (EDIT: major said it, sorry major!) indicates his was "agressive" for a competition vehicle. The amount of regen you'll get from typical regen on a street vehicle is probably not worth considering as a breaking factor in and of itself. But YMMV, no personal experience with regen.


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## toddshotrods (Feb 10, 2009)

rillip3 said:


> ...Toddshotrods indicates his was "agressive" for a competition vehicle...


Actually that was Major, but he hit the nail on the head because aggressive competition usage is what I am aiming for.




rillip3 said:


> From what I have heard, regen typically does not work like a break, but rather, like weak engine breaking. there's just a push against the inertia, like downshifting too soon, not a full on break...


That's what I've heard as well.



rillip3 said:


> ...Unless you have a lot more resistance generated than I have heard of in the past, I wouldn't think it would require a complete rebalancing of the breaks... The amount of regen you'll get from typical regen on a street vehicle is probably not worth considering as a breaking factor in and of itself...


It has to be taken into consideration. In an extreme competition setting, it doesn't take much to get bent out of shape.


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## rillip3 (Jun 19, 2009)

toddshotrods said:


> Actually that was Major, but he hit the nail on the head because aggressive competition usage is what I am aiming for.
> 
> 
> 
> ...


Edited the last post to correct that, thanks. Was reading too fast I guess.  

If you're going for agressive competition then yeah, I have to agree with you and major. But for a normal street car I'm sure it wouldn't really be an issue. Unless you drive like a crazy person. In which case, simple driving changes will reach the goal.


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## Usher (Feb 4, 2009)

With an AC motor, you should be able generate as much power during braking as you can dump into the motor while accelerating. My post was assuming you actually designed your controller to brake the vehicle, instead of using a little bit of regen when off throttle to simulate engine braking.


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## toddshotrods (Feb 10, 2009)

Usher said:


> With an AC motor, you should be able generate as much power during braking as you can dump into the motor while accelerating. My post was assuming you actually designed your controller to brake the vehicle, instead of using a little bit of regen when off throttle to simulate engine braking.


I'm running a big SepEx. I would prefer the regen to be more like engine braking, but I'm more inclined towards "on-the-brakes" activation. I don't think I want it to be there, in any capacity, every time I lift off the throttle. How was yours set up Major?

Edit - On second thought, maybe I do want it to be there off throttle. That would make teh vehicle perform more like a typical manual-trans ICE vehicle.


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## Usher (Feb 4, 2009)

I didn't realize you were talking about SepEx. I just assumed AC, since I've been looking exclusively at AC systems for my project.


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## major (Apr 4, 2008)

Usher said:


> add a potentiometer to the brake pedal which engages the regen in the first few centimeters of travel and adjust the pedal so engagement of the mechanical brakes requires more pedal travel.


Yep, that is how to do it. Works great.

The regeneration set up on motor/controller and vehicle packages vary. Some are as mentioned, set up to simulate the engine or transmission retardation you typically expect from a gas car. I call it a coast down mild regen. I don't like this set up personally. I rather have the vehicle coast free and have the regen control on the brake pedal where it belongs and have it provide a variable torque to decelerate the vehicle as I want it to.

If you have the means to get into the controls, you can make regeneration as strong as the energy storage system will allow. It has been my experience that when using AC systems and certain energy storage systems, regeneration power can exceed motoring power. I have recorded regen events exceeding 160 kW. That was on a 20,000 lb bus.

Regards,

major


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## toddshotrods (Feb 10, 2009)

Great information here, thanks guys! I shouldn't have second-guessed myself - I'll stick with on-the-brakes regen.


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## DavidDymaxion (Dec 1, 2008)

You can buy brake bias controls. Some racers even mount them within the driver's reach, so the brake bias can be adjusted during the race. You could set up some level of regen, and then various brake bias settings to tune the system.

If your system regens the same amount of current, regardless of the gear you were in (in other words, over a wide range of rpm), that would be neat.


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## toddshotrods (Feb 10, 2009)

DavidDymaxion said:


> You can buy brake bias controls. Some racers even mount them within the driver's reach, so the brake bias can be adjusted during the race. You could set up some level of regen, and then various brake bias settings to tune the system...


Yeah, I definitely plan to have an adjustable bias valve. That's pretty much standard equipment for the type of project I'm doing. It'll be driver's seat accessible as well. I was just wondering about the effects of regen at various speeds and conditions. In other words, once I wag the tail enough to find the ultimate setting for extreme conditions, with regen, how it will affect the car's balance in less extreme situations.


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