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Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 03:19
by acmotor
Hemonster,
Yes, simulating engine braking as you take your foot off accelerator is the way I operate (setting a regen torque limit on controller). It is quite natural and requires far less moving the foot from accelerator to brake since for a lot of driving you don't need to use the brake. (regen torque is constant all the way to zero speed unlike ICE where it diminishes)
There is a lot of foot on pedal swapping on DC conversions without regen(those with low rolling resistance that is) and does not make for relaxed driving.

The point is that there is a lot more regen available and using the top of the brake pedal travel or a 'clutch' pedal to control extra regen is worth looking at. Braking distribution needs to be considered though if the regen is on rear wheels.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 03:27
by woody
Goombi's right you can get almost as much braking as accelleration from AC.
Another nice usability thing is to have a "dead zone" in the accellerator travel between accelleration and braking to enable easy freewheeling.
Maybe with your setup a "Pro" switch for yourself which would double/triple the regen for drivers who wanted that.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 03:47
by Tritium_James
The porsche has a slider in the dash which controls how much regen you get when you fully lift off your foot. Works really well, and people can start with it just set to a bit, and turn it up as they get used to it.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 04:05
by Johny
I hadn't considered a gearbox with regen braking so the clutch disengaging regen would be a very smart move. I can't see the point in a switch on the accelerator though. I'm with woody on the "dead zone".

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 04:10
by Goombi
I like to stipulate that doing HARD regen will defeat the regulated battery charge . By going hard you will pump 10-14 amp to batteries andy will stop too fast --at speed or Regen to compare to ICE will offer the charge at 4-8 amp and it will still recharge even when you use brakes.. One must not forget the gentleness of regen and gentle braking.. to try to go extreme will not work like slider or more switches.. huge cotrasts are not recommended or desierable..regen will only work up to 7% charge with normal travel... you will not get more with sliders or booster switches. or miracles

One more point.. The controller will supply x amount of amps to propel the ev. same with regen   only so much will be offered from controller.
If there was no control you will lock the motor and brake the gearbox or diff or the motor shaft itself and burn the lot

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 04:38
by woody
... or batteries which like fast charging.

I think for my car the limit will be the rear wheel traction (Light RWD) despite an extra 150kg behind the rear axle (batteries + controller)

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 05:00
by acmotor
'dead zone' well not quite.
I run a sine response with slip compensation at -400%. This means there is an exponentially reducing effort to hold speed over about a 400RPM band around a cruising speed. OK, a bit like a rounded edge dead zone if you like.

Goombi, it (regen) is all very smooth, controlled and limits are settable in current and torque. In fact it is very driveable.
But yes you are right. There is a lot of regen available depending on settings. I can put 60A at 600V back to battery pack and almost lock the back wheels, but I don't (not as standard practice) as, because you correctly say, the batteries are not up to it.

I didn't quite get your point re 7% ? did you mean the energy recovery from regen ?

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 05:23
by Goombi
Perhaps I should have said it is estimated 7% to be the most dsirable Regen charge. If you were to tow the car in a gear it will take 10 hours plus to regen charge the batteries. One advantage is that Controller will cut off the regen if the batteries are fully charged or reaching maximum voltage.( voltage in Regen only) not in Motor controller
There is a lot more to REGEN but that later...

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 05:55
by Squiggles
Hmm, here is a thought, would regen braking in its extreme form not work like ABS. Don't you need movement of the rotor to create the resistive torque? If there is no rotation there would be no resistance....just pondering...anyone out there actually know what would happen?

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 06:11
by Goombi
Definitely.Regen is in fact a dynamo without it rotating, so disingaging a clutch will also disingage the regen. There will be no result. The resistance is created through controller. Once you pass the ZERO zone (+0-) the controller engages the motor to change its character and become another animal. One has to have the motor connected to gear when direcly coupled (without a clutch)

If reverse tension is in progress can it be called " Torque" or brake horse power??

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 06:22
by acmotor
Well the most desirable regen charge is only limited by
1) What your batteries (or one day ultracaps) can accept
2) How hard you wish to brake
7.13526% has got nothing to do with it !! Image For some actual recorded data see the viewtopic.php?p=7619&t=615#p7619.

Squiggles, ABS sort of, partly by way of the slip operation of the induction motor but moreso by the controller setup.
Eventually, as I keep saying, mechanical brakes will end up being used for parking only. Regen on hub motors (when they come of age) will give the ultimate in braking.

The way regen is set up on red suzi, if the drive wheels tend to lock up then the regen torque immediately reduces as the new slower speed is instantly less than the rampdown time. It is not refined and not independent side to side but the basic operation is ABS like and I can see it being very much part of future drive, traction and stability systems.
The rampdown time is automatically extended by the controller one a regen or motoring torque limit is reached.


Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 13:35
by Tritium_James
Your motor controller will only overcharge your batteries on regen if it's a crap one. Sorry to be blunt but if you have a controller that can't limit on max (or min, when driving) battery voltage, that's the way it is.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 17:03
by fuzzy-hair-man
Hemonster wrote: Wanted to run this past the forum, see what you'll thought. What if I set regen to be equivalent to my car's current engine braking force (by experiment), but this level of regen can be reduced down to zero by pressing the clutch pedal in.

The clutch itself will not be connected to the gearbox as the motor is driving direct into the gear box. The result of this is that when the clutch pedal is fully depressed the motor will freewheel and you can change gears - effectively you have an electrical clutch system.

If you wanted to glide either push the clutch in or shift to neutral, otherwise the car will slow down at the max regen rate allowed (also set to be within acceptable limits for the battery pack).

This I believe would mimic how a standard manual car works, and you can independantly control the regen force and resistive braking force just as before, and have your gliding ability as before.

A micro switch on the accelerator pedal would disengage regen all together so that you can't accelerate and regen at the same time.

Thoughts?
I had similar thoughts, I haven't been convinced they won't work yet, I'd be interested how much extra load / wear is going to go onto the synchros and how easy it would be to change gears, would it be similar to changing gears using the clutch? or would you have to carefully pick revs and time the gear change perfectly. It might be harder picking up what revs a E motor is doing too (no noise), and I want to look at the road not the tacho.

I figure the synchros are only spinning up a couple of kgs of gear box gears and the clutch plate in an ICE the only thing we have gotten rid of is the clutch plate but they also need to spin up the E motors rotor, how much weight is this likely to be?

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 17:54
by Tritium_James
The rotor in my 132 frame size induction motor is about 20kg. Types with copper squirrel cage bars are up around 25-30kg.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 18:35
by fuzzy-hair-man
Tritium_James wrote: The rotor in my 132 frame size induction motor is about 20kg. Types with copper squirrel cage bars are up around 25-30kg.
Is the motor all up about 70 -80kg? (the ABB catalogue has 11kW 132 frame high output motors at 76kg) so rotor ~= 1/4 motor weight?
So we've increased by about a factor of 10 the weight (clutch plate is 2 -3 kg) that the synchros are going to have to spin up/down to speed. Image if that means the synchros are going to wear out something like 10 times as fast then I think that's a deal breaker, it's relatively involved/expensive AFAIK to rebuild gearboxes. Image

Mind you are probably going to be doing a lot less gear changes too... so perhaps half as many? and we would probably have more time to do them so lets say 1/3rd the wear? that still means the synchros might wear out 3 times as fast?

Problem is I really like changing gears whilst driving, what am I going to do with myself if I only have to do them 1/3 as much? Image Image I figure I'll have to make regen steps so they can behave like gears to change the engine braking, still it won't be any fun accelerating. Image

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 18:38
by Johny
Keep the clutch. Makes regen easier etc. Regen can slow the motor down really quickly for fast changes - better than ICE.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 19:02
by acmotor
Tritium_James wrote: Your motor controller will only overcharge your batteries on regen if it's a crap one. Sorry to be blunt but if you have a controller that can't limit on max (or min, when driving) battery voltage, that's the way it is.


Totally agree. To think otherwise would be to underestimate the intellegence of a AC VFD ! or a BLDC controller. (at least as they should be)

Gears to change ??? clutch ??? is this a history lesson ??? Image Image

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 20:14
by Tritium_James
Is the motor all up about 70 -80kg? (the ABB catalogue has 11kW 132 frame high output motors at 76kg) so rotor ~= 1/4 motor weight?
It's a Western Electric 'high efficiency' type and it's about 63kg.

I'm keeping the gearbox in my conversion, no clutch. If it looks like the synchros are wearing out then it's time to add some switches around the gearshift lever and start doing rev-matching with the motor controller. Will be a bit of software effort though...
Problem is I really like changing gears whilst driving, what am I going to do with myself if I only have to do them 1/3 as much? I figure I'll have to make regen steps so they can behave like gears to change the engine braking, still it won't be any fun accelerating.
Speaking from experience driving the Porsche (150kW, fixed reduction, ie no changing) not having to change gears is great - it's ALWAYS in the perfect gear for maximum acceleration :)

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 20:19
by Goombi
Who threw the spanner in the works about Synchro in gear wear?? Please get some information and ask what goes first in Gearbox and what last the life of a gearbox.. I say no more
The subject runs well and everyone following the thread.. Then some plurry I---..

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 20:41
by Mr. Mik
zeva wrote: As a corollary to my earlier post, I also believe we are hugely under-playing the importance of vehicle efficiency, which can have a far greater impact on your range than regenerative braking. Factors in particular are aerodynamic drag, rolling resistance, vehicle mass, and frontal area. Your average vehicle in a normal driving cycle will lose around the same energy to rolling resistance as aerodynamic drag.

Let's say regenerative braking would offer most of us about 10% more range. A good start. What else might help us get longer range?

Reducing aerodynamic drag: A Prius has a Cd of 0.26. My MX5 has a Cd of 0.39 - much worse! Assuming equal frontal area, the Prius loses 33% less energy to aero drag (at any speed). At 100km/h, this is about 3.5kW less power needed! (Any my MX5 is far from the worst example of vehicle aerodynamics..)

Reducing rolling resistance: Modern low rolling resistance (LRR) tires have a coefficient of rolling resistance (Crr) around 0.008 (reference). Normal car tires are around 0.02, i.e you can better than HALVE your rolling resistance with the right tires. This alone will offer you around 20% more range in a normal driving cycle.

Vehicle mass: Rolling resistance is proportional to vehicle mass, so for a given set of tires, a 2-tonne vehicle will lose TWICE as much energy to rolling resistance as a 1-tonne vehicle. At 60km/h, this alone would shorten your range by about 25%. (Yet another good argument for choosing lithium batteries?)

Frontal area: Vehicle drag is proportional to frontal area, so a vehicle with 20% smaller frontal area will lose 20% less energy to drag.. and gain about 10% more range.

And transmission losses: Simply going without a gearbox can gain you 10% more range due to lower transmission losses.. (all other things being equal)

So in conclusion: If you need long range, the most important factor may be a wise choice of donor vehicle. If it has just a few of the above working in its favour, you can stand to more than double your range from a given battery pack. There are also a whole lot of things you can do to your existing vehicle to gain additional range, such as LRR tires and aerodynamic improvements (under-body panelling is one example).


The various friction losses you mention are only a greater factor than regen breaking because they are greater....that sound silly, but it's true.

Here is why:

Once the losses due to air turbulence, rolling resistance etc. are much reduced, then regen breaking will have a much bigger impact on range than before.

Currently the combined friction losses are so great that regen fades in comparison.

To make this clearer: If we were able to reduce the wind resistance, rolling resistance etc. to zero, then regen breaking would extend BEV range massively, because deliberate breaking would be the only energy loss encountered. Of course this is impossible, but if you reduce the other losses by 90%, you would probably get something like a 10-fold increase in the range extending effect of regen breaking.

And that would mean doubling the range, rather than adding 10% range to a typical contemporary BEV car.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 22:00
by acmotor
Thanks Mr Nik for bringing us back on topic ! Image

The range and regen question also depends on the use of the vehicle.

If your commute is at 100kmph on a freeway with one start and stop then regen does little for you and all those other frictional losses matter most. Aerodynamic drag is #1 power eater.

But if you are start stop driving in city traffic with 30kmph average speed and a stop ever 500m then regen can be your #1 range extender and probably the simplest to implement in AC and will save your mechanical brakes as well. Note here, the better the regen overall efficiency, the less the vehicle mass is a problem as acceleration energy is recovered.

Image

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 22:12
by Taffy
The thing is what will be easier to implement.

Regen
Smaller front area (remove roof racks, new mirrors, etc)
Better areo (close up grills, body pans, etc)
New tires
Remove transmission.
Reduce powered devices on the car (windows, lower powered heater, lights etc).

In terms of time spent/difficulty/$spent per km increased in range will vary greatly.

Im my case (as thats all i have to use with offending anyone) i have a custom built car.

Reduce areo - installing a sealed underside, reducing/closing all intakes.
Reduce front area - not an easy one unless i take the windscreen off but that should make a big difference. I wont need dinner after eating all the bugs. I am making the ride hieght fairly low so that should help abit.
Change tires - buying new ones anyway so a real option. Anyone have a $value for a set of these?
Transmission - its gone.
Regen - not at the moment but i am thinking about trying something stupid with an alternator just to measure its effect.
Lights - use LEDS were possible.

And then to wreck it all:
Install 10 tons of lead acids - nearly. Should end up with a 750kg sled.
Install a set of subs and some full sick neons (joking! - the subs wont fit and i would break off the neons on first speed hump)

RE: Weight - True AC but you must get that up to speed in the first place which costs more energy then is gained by regen. Maybe electric cars will be the cure of our overweight population?


Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 22:27
by fuzzy-hair-man
Goombi wrote: Who threw the spanner in the works about Synchro in gear wear?? Please get some information and ask what goes first in Gearbox and what last the life of a gearbox.. I say no more
The subject runs well and everyone following the thread.. Then some plurry I---..
Well, I did but I have a reason for that if you change gears without the clutch in an ICE you are putting the load of synching revs onto the synchromesh a friend mentioned you can change gears without the clutch and for a while I tried it my father (a mechanic of some 30 - 40 years) when I told him nearly blew a gasket!! We've already replaced the synchos in my gearbox once and taking a gearbox out and to pieces is not the quickest and easiest task IMO.

We also have other cars that are starting to grind gears and need synchros, often enough to suggest that synchros are subject to wear and one of the wear components.

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 22:35
by acmotor
Taffy wrote:

RE: Weight - True AC but you must get that up to speed in the first place which costs more energy then is gained by regen. Maybe electric cars will be the cure of our overweight population?


Are yes, but that is the point. Efficient regen (that does not include a hotwired alternator) recovers as much of the energy used to accelerate the mass as possible. Simple physics with a target of 99% Image (optomistically in practice at this stage maybe 60% i.e. battery to controller to motor to wheels and back again. e.g. motor and controller in motor or regen mode >90% eff. diff 90%, battery discharge/recharge 90% so .9 x .9 x .9 x.9 x.9 =59% This would be considering AC and lithium. You can argue the percentages but you get the drift.) Image

Soapbox on regenerative braking

Posted: Fri, 29 May 2009, 22:39
by acmotor
What's more, when we have hub motors and ultracaps this might jump to 90% overall regen. That will put a smile on the dial ! Image