[Deanwvu]

And, does the brake pedal have to be depressed to use it?


For example, if the driver is simply coasting down a hill, is the battery charging? Or, must the brakes be depressed to engage the regenerative brakes?


And, here is another question regarding efficiency:

In a real-world test, let's say we are cruising along at 55MPH. We approach a hill that is an average 3% grade and is 1200 linear feet long. We roll over the top of that hill, and as we do, let off the accelerator, rolling down the other side of the hill, which is also an average -3% grade and 1200 linear feet, until we are level again.

Approximately how much charge to we regenerate on the downhill, compared to the charge we used on the uphill?

 

[Tom]

Volt Motor Regen Simulation

“What is efficiency of regenerative braking?”
Refer to post http://gm-volt.com/forum/showthread.php?t=719 which shows the estimated efficiency vs. deceleration curve. I attached the model curve below for convenience.

“And, does the brake pedal have to be depressed to use it?”
All EVs with regen use a four-quadrant motor controller system. The quadrants are defined by +- Torque and +- speed –(relative to the motor synchronous speed). Refer to the attached plot for a hypothetical Volt Motor/Controller Plot. Assume the motor is outputting 100 lbf ft of [email protected] RPM at the commanded motor drive frequency f1, as shown by the black curve. The break is applied, and the system controller’s algorithm tells the motor to go to the slower frequency f2 (blue dotted curve). The speed (2500 RPM) cannot instantaneously change, so the torque characteristic drops to -100 lbf ft at the commanded f2, which is deceleration, and the motor controller then chops and stores this energy to the battery. The breaking/regen continues as long as there is kinetic energy to convert, torque < 0, the driver applies the break, and the system controller’s algorithm commands it.

“Approximately how much charge to we regenerate on the downhill, compared to the charge we used on the uphill?”
This depends on the kinetic energy, speed/wind drag, road grade, deceleration, and system controller’s algorithm. Again, refer to the above post to get some sense of the effects of these variables. Given a profile, e.g. Highway Driving with road grade, we could use the Volt Simlulation to plot the resulting regen response during commanded deceleration.

 

[Jason M. Hendler]

I could be wrong, but I thought I remembered reading on the Tesla Motors website that regenerative braking in the Tesla Roadster actually starts at some level when you lift your foot off the "accelerator" pedal, to recreate the engine braking sensation we now experience in our ICE vehicles. Stepping on the brake just increases the amount of regenerative braking beyond engine braking levels.

 

[Joshua Bretz]

I've posted this before, but I think it's important, so I'll post it again.

Regen efficiency is similar to drive efficiency. It's the same electronics, afterall, with current just running the other direction. Maybe 70-90% depending on acceleration magnitude.

Some people say that it should have regen when you let off the pedal.
(The question in this case is how much?)

Others say that it should coast down a hill for maximum efficiency.
(This gives a lot of people an uneasy feeling beyond their desired speed)

I say coast until the driver taps the brake pedal, which they'll do when they have reached their desired speed.

Then use regen to keep a constant speed down the hill.

 

[Tom]

Hair pulling

Jason,

I have a similar recollection about the Tesla site. I imagine the Volt designer’s are pulling out their hair in attempting to resolve all the regen algorithm tradeoffs (maximizing AER/mpg, minimizing stopping distance, motor/battery thermal overload, matching familiar ICE-like response, specifying maximum allowed motor current ripple, predicting the driving profile to optimize, accommodating preferences from Bob Lutz and company). I would hope that they would offer the driver the option of choosing different regen strategies.

 

[DaV8or]

I'm hoping for user adjustable regen braking system with a button on the steering wheel to activate a preset (by the user) amount resistance that you can elect to use as "engine braking" when you let off the gas. If you don't activate the button the car freewheels. If the brake pedal is depressed, both the braking button and freewheeling is over ridden.

I think this type of system would give the driver more control during decents or entering corners much like a manual transmission does now, give the driver the option of charging the battery if it really needs it and allow freewheeling where possible for hypermiling if the driver so chooses. As you all might be able to tell by now, I'm not a big fan of automatic driving, I like to actually drive the car, not just ride in it.

 

[Jason M. Hendler]

Considering that vehicle response, as resulting from pedal position, is also a safety issue, I doubt they would allow options. I imagine that if you want to coast, you only need to step on the "accelerator" pedal slightly.

 

[Jackson]

The ability to set a desired "engine braking level" really opens up another can of worms:

There must surely be a great many things which could, in theory, have customizable settings. But I suspect you could very quickly get away from a "Mass Market" vehicle to more of an imposing "Techie" vehicle; to satisfy only a few, and perhaps repel many.

A more characterstic-tunable model can be explored AFTER the proving out of a Volt which "just works," even for Grandma. Not as exciting if you're a techie, but much more marketing-sound IMHO.

 

[DaV8or]

The ability to set a desired "engine braking level" really opens up another can of worms:

There must surely be a great many things which could, in theory, have customizable settings. But I suspect you could very quickly get away from a "Mass Market" vehicle to more of an imposing "Techie" vehicle; to satisfy only a few, and perhaps repel many.

A more characterstic-tunable model can be explored AFTER the proving out of a Volt which "just works," even for Grandma. Not as exciting if you're a techie, but much more marketing-sound IMHO.

That's the beauty of the system I discribed above, you don't have to use it. Kind of like cruise control, it's on the car and if you want to learn how to use it, it can be of great benifit, however Grandma can leave it turned off and the car drives just fine. If people just want to "plug and play" there could be factory presets so people could start using it right away without reading the manual. If the system has significant costs associated with it, it could be offered as an extra cost option, just like cruise control is now. I believe it would be a very simple system to engineer without a lot of extra equipment required.

 

[cosmo88]

Seems like brake regen might also go well with cruise control. In that case the pedal wouldn't be depressed(if it is we'd need to prescribe zoloft) but the car would still be braking when going down hill.

I'm not a big fan of engine braking but if it's an option I'm all for it. I doubt it would be worth the development effort though when only a few would use it. My girlfriend still doesn't know how to change the clock on her car radio. Evrey time there's a daylight savings shift.. well nevermind that's a bit off topic...

 

[nlh_90210]

keep it simple

I want to coast when I take my foot off of the accelerator and only have the regen kick in when I depress the brake pedal. I figure the counter-torque can grow linearly as a function of how far I depress the brake pedal (with a dead zone at the top), and then once I reach a certain point the mechanical brake kicks in.

The exception to the this could be for cruise control going down hill, where the control system will provide counter-torque to keep the speed down.

 

[BigRedFed]

I want to coast when I take my foot off of the accelerator and only have the regen kick in when I depress the brake pedal. I figure the counter-torque can grow linearly as a function of how far I depress the brake pedal (with a dead zone at the top), and then once I reach a certain point the mechanical brake kicks in.

The exception to the this could be for cruise control going down hill, where the control system will provide counter-torque to keep the speed down.

I agree. The one thing I hate about my Honda Civic Hybrid is the algorithms that they created to determine when to turn the engine on/off, initiate recharge of the battery and have the Integrated Motor Assist (IMA) kick in. They are too complicated, it seems to me. They try to be smart, but they scenario base that they are programmed is so small, they are actually pretty stupid.

The engine doesn't always shut off when you expect it would, based off the information in the owners manual.

The IMA kicks in too late in my opinion and if you are going more than 65mph and it kicks in, it actually slows down the car.

If the battery depletes below 50%, the regen kicks in at odd times that cause the vehicle to have difficulty maintaining a constant speed, which of course actually uses more fuel.

The algorithms for the volt need to maintain simplicity and through that simplicity people will learn how to best drive the vehicle and work with the algorithms instead of them being at odds.

 

[Joshua Bretz]

I want to coast when I take my foot off of the accelerator and only have the regen kick in when I depress the brake pedal. I figure the counter-torque can grow linearly as a function of how far I depress the brake pedal (with a dead zone at the top), and then once I reach a certain point the mechanical brake kicks in.

The exception to the this could be for cruise control going down hill, where the control system will provide counter-torque to keep the speed down.

What he said.

 

[Dr Mark]

Controlling Regen

I want to coast when I take my foot off of the accelerator and only have the regen kick in when I depress the brake pedal. I figure the counter-torque can grow linearly as a function of how far I depress the brake pedal (with a dead zone at the top), and then once I reach a certain point the mechanical brake kicks in.

The exception to the this could be for cruise control going down hill, where the control system will provide counter-torque to keep the speed down.

I have an Electric Toyota MR2, which I converted using an AC induction motor and controller from Azure Dynamics. I thought I would prefer the regen to be controlled by the first 1/4 of the brake pedal travel, but they put it into the accelerator pedal; i.e. when you let off on the pedal the regen kicks in and it feels like an ICE decelerating in a low gear (i.e. engine braking), so it is actually more natural feeling than if the car just free-wheels, which I can also do by holding the "Regen Disable" switch.

The control for how hard the regen operates is in a set of parameters you set thru a PC serial port; but it would be much nicer to have that on a slider switch so you could change it (say to avoid using your brakes going down a mountain or long hill). I don't have this, but a big resistor could be necessary to dump charge if the batteries are full, otherwise you have no "engine braking" going down a steep hill. Diesel-electric locomotives have this and those resistors take up most of the central tunnel and have huge fans to dissipate the heat from a train decending a mountain; too bad they don't have a MegaWatt-hour battery pack to soak up all that energy!

 

[nlh_90210]

I don't think you are in serious danger of topping off the additional 3.2 kWh between the 80% charging limit and 100% saturation. If I did the math right, assuming even with no energy loss due to drag/heat/etc. (which is a horrible assumption) you would have to drop a 3000 lb car something like 1/2 mile to get 3.2 kWh. So even if you lived at the top of a mountain, you are in little danger of overcharging the battery.

I really hope this technology make it out to the transportation industry. Both trucking and trains could benefit from the low end torque of an electric motor. Adding electric storage could do nothing but improve the cost of transportation.

I'm not sure that I would want too much regen drag when I pulled my foot off the accelerator. Maybe if GM provided an on the fly switch that allowed me to chose different settings that would be nice. Or maybe a "regen disable" button, is, in practice, what really fits my needs. I dunno, but, Dr. Mark, your experience is certainly invaluable in this forum.

 

[DaV8or]

I don't think you are in serious danger of topping off the additional 3.2 kWh between the 80% charging limit and 100% saturation. If I did the math right, assuming even with no energy loss due to drag/heat/etc. (which is a horrible assumption) you would have to drop a 3000 lb car something like 1/2 mile to get 3.2 kWh. So even if you lived at the top of a mountain, you are in little danger of overcharging the battery.

The problem is the rate of charge. For long battery life, they need to be charged much slower than they are discharged, so on a long decent in regen mode, the rate of charge may exceed the optimal rate and so the excess needs to be diverted to some sort of resistor.

I'm not sure that I would want too much regen drag when I pulled my foot off the accelerator. Maybe if GM provided an on the fly switch that allowed me to chose different settings that would be nice. Or maybe a "regen disable" button, is, in practice, what really fits my needs.

Isn't this almost exactly what I have been advocating and people have been telling me "No, No, keep it simple. What if Grandma can't figure it out? All we need is the brake pedal." What I have been proposing as a user adjustable preset regen braking would not need to be anymore complicated than cruise control or intermittent windshield wipers. I wasn't talking about scrolling through drop down menus in some God awful software program. Tactile things like buttons knobs and switches is what I'm thinking just like current car systems have, all of it easily adjustable on the fly by the driver. I feel confident that when they start seriously racing EVs on road courses, those race cars will have a system similar to what I'm talking about.

 

[nlh_90210]

The problem is the rate of charge. For long battery life, they need to be charged much slower than they are discharged, so on a long decent in regen mode, the rate of charge may exceed the optimal rate and so the excess needs to be diverted to some sort of resistor.

I wouldn't advocate the use of regeneration beyond what is safe, and there is always going to be mechanical brakes (I hope). I don't know enough about regeneration to know if the peak allowable rate is much greater than the steady state allowable rate. But, I certainly won't want the "coasting" regeneration near the steady state rate anyway.

Isn't this almost exactly what I have been advocating and people have been telling me "No, No, keep it simple. What if Grandma can't figure it out? All we need is the brake pedal." What I have been proposing as a user adjustable preset regen braking would not need to be anymore complicated than cruise control or intermittent windshield wipers. I wasn't talking about scrolling through drop down menus in some God awful software program. Tactile things like buttons knobs and switches is what I'm thinking just like current car systems have, all of it easily adjustable on the fly by the driver. I feel confident that when they start seriously racing EVs on road courses, those race cars will have a system similar to what I'm talking about.

You won't find me advocating the "K.I.S.S" principle, at least in the name dropping way that most have. Keeping a design simple does not require that you lose versatility. Also, I think you'd find that a manual transmission is "simpler" than an automatic. If Granny can't figure it out then Granny can take the bus. Besides there will be a default setting that I am sure is compatible with all but 3-sigma Grannies. Heaven forbid anyone has to think.

And I will say this. The more flexibility you design into the initial architecture the more versatile and capable the end result will be.

 

[Dr Mark]

I have an Azure Dynamics AC24 motor and DMOC445 controller in my Toyota MR2. The Azure setup puts the regen control in the accelerator which I thought I wouldn't like, but it actually works great. There is a regen disable switch, which I now have learned when to use and when not to use. Believe me it is disconcerting to let off the accelerator and experience absolutely no deceleration. The reverse torque generated can be controlled by not releasing the accelerator all the way, but if you really want to coast (like when you see cars stopped at a redlight 1/4 mile ahead of you) it's hard to control the accelerator right at the zero torque point, so throwing the regen disable is easier.

One feature I don't have and would like is a slide or roller pot to set the max regen (i.e. what you get when you let the accelerator all the way up). You could use this to control your speed coasting downhill and not have to try to control it by finding the right point on the accelerator pedal. I can set this parameter in EEPROM via my laptop but would really like to control it in real-time.

I don't think GM will struggle with these issues though since they had 850 EV1's running around California for four years, and from what I hear, the EV1 was a dream to drive. I hope they didn't destroy the engineering drawings, flowcharts, test data etc, since there is apparently only one real EV1 to look at and even that one I don't think is operational. Bizarre behavior, it makes me tear-up over what we all lost every time I think of it.

 

[willdryden]

I really hope this technology make it out to the transportation industry. Both trucking and trains could benefit from the low end torque of an electric motor. Adding electric storage could do nothing but improve the cost of transportation.

Trains have been made like this since 1928. They did not bother with batteries because diesel fuel was so cheap. Now they are adding the batteries to the trains to save some of that energy from braking.

 

[willdryden]

One feature I don't have and would like is a slide or roller pot to set the max regen (i.e. what you get when you let the accelerator all the way up). You could use this to control your speed coasting downhill and not have to try to control it by finding the right point on the accelerator pedal. I can set this parameter in EEPROM via my laptop but would really like to control it in real-time.

I don't think GM will struggle with these issues though since they had 850 EV1's running around California for four years, and from what I hear, the EV1 was a dream to drive. I hope they didn't destroy the engineering drawings, flowcharts, test data etc, since there is apparently only one real EV1 to look at and even that one I don't think is operational. Bizarre behavior, it makes me tear-up over what we all lost every time I think of it.

Adjustable regen is standard on the Ebox conversion of the Scion. It is done with a slider like a volume control on expensive audio equipment and is mounted in the console.

There were never more than 800 EV-1s on lease at any one time. They actually ran around California and Arizona. GM gutted and donated about 40 of them, split roughly between colleges and museums. Stan Ovshinsky kept one operational EV1 for himself, though, I've heard, so add that to the dozen or so that GM has on the research lab in
MI. oh, and this one..

http://www.youtube.com/watch?v=YCBc8pL1SGc