How Does Regeneration Work

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Johny
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How Does Regeneration Work

Post by Johny »

Jeepers. Not only does it have to make a noise like George Jetson's car when it's accelerating or cruising, it has to make a noise like a Mac truck under exhaust brakes as well! I was trying to avoid needing the subwoofer - extra weight.

Edit: Apostrophe
Last edited by Johny on Thu, 05 Mar 2009, 08:25, edited 1 time in total.

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How Does Regeneration Work

Post by fuzzy-hair-man »

HeadsUp wrote: i think my personal choice would be the steering column fitted, fingertip , pressure sensitive regen lever fitted with a return spring

( it complies with the KISS principle )
I don't know that I'd like that because I figure it would be too easy to have to take you hand off the lever to do something else like go round a corner, indicate, dip the headlights, etc and if there was considerable regen you don't want it to disappear all of a sudden.

I think I'd go for a sliding pot on the dash or gearstick which lets you adjust the default or throttle off regen.

Again not sure I get this turning regen off because you hit the brakes thing, I mean I don't put my car in neutral as soon as I touch the brakes in an ICE and I only put the clutch in to change gears or stop it stalling. Image

OK so I don't drive an ABS car but they have no way of disabling engine braking because you hit the brakes they just have to work around it.

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How Does Regeneration Work

Post by HeadsUp »


ultracaps is it.

takes the spike off regen and delivers it past a zener or other voltage limiting device

maxwells and others have claimed for a while that ultracaps will replace batteries one day.... bring it on i say.

http://www.ultracapacitors.org/forum/56.html

just found a new product link http://www.eestorbatteries.com , which is "supposed to" already be a viable replacement for lithium

i like the sound effect options

i heard of an EV in the UK that had the sound of a trotting horse while driving , but i like the jetsons option ... hahahaha !
Last edited by HeadsUp on Thu, 05 Mar 2009, 09:09, edited 1 time in total.

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How Does Regeneration Work

Post by HeadsUp »

fuzzy hair man

if you dont like the stalk on steering column , how about a ferrari style paddle on the steering wheel that you press with your thumb ?


i accept that you dont need regen turned off just because you started pushing the brake pedal harder

as long as regen doesnt kick in when you are coasting on the highway and take your foot slightly off the throttle then i would be happy



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Post by Johny »

I have posted this before but can't find it. It's an extract from a AWD VERY expensive conversion. His regen was obviously more "robust" than necessary.
----------------------

"First, I noticed I have to freeze my foot in strictly one position as I drive, no stretches, no movements. I had to take something from behind my seat while cruising on a freeway, and to reach far corner I had to stretch my body body took my foot off the accelerator pedal for 2-3 seconds - action I never think about as it would not be noticeable for "normal" setup. Well, it was equivalent to slamming brakes 100% while in the middle of freeway and no one in front of me, so no one behind would expect such a stunt. And, I wasn't consciously braking, the effect was as if some one slams on the brakes for you without any warning. The rear of the car breaks loose, I'm thrown toward wind shield and intuitively as in any emergency situation, before my brain assess the situation, my right foot goes from already 100% braking accelerator to real brake pedal, compounding effect. Now the car really grips the road, scarring me out of my pants! Mind you, I had about 450kg (1,000 lb) of lead in the car at that time (I think around 2002). It would take thinking twice to realize that to rectify situation I had to slam on "gas". Anyway, I'm coming to a complete sketching stop in the middle lane of I84 freeway. I was LUCKY - no one was following me on my lane, and I noticed couple of by-passers looked at me as if I was total moron (and I probably was!). This was first and last time I tried off-throttle regen. You may like it, but it would take a lot of money to make me do it again..."

-------------
The whole article is good reading but the bit we are discussing is covered in "Speed Selector Modifications" (left side of page).
Here is the link to the whole thing

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How Does Regeneration Work

Post by fuzzy-hair-man »

HeadsUp wrote: fuzzy hair man

if you dont like the stalk on steering column , how about a ferrari style paddle on the steering wheel that you press with your thumb ?
Hmmm, yes and no I want to be able to have regen on no matter what I'm doing with my hands so if I'm turning sharply, think a 2nd gear turn down a steep hill where I have to turn hand over hand and therefore I have to take both hands off the wheel (at differing times of course Image ).

getting wires in through the steering wheel is a little difficult (unless wireless I guess) some? horn contacts are a little weird and wear out to avoid wrapping wires around the steering column. How do those push button gear changes do it out of interest?
HeadsUp wrote: i accept that you dont need regen turned off just because you started pushing the brake pedal harder

as long as regen doesnt kick in when you are coasting on the highway and take your foot slightly off the throttle then i would be happy
I'd be happy for regen to kick in just so long as I knew and was aware it was going to kick in and could control it.
Agreed, wheel locking regen on throttle off at 100km/hr would be scary!!!

There's the problem, how do you select an appropriate level of regen for the speed? and that the driver expects?
In an ICE they select the engine braking by which gear they are in and need to change gears as they accelerate again but a direct drive EV they wouldn't. Because ICE's have to change it on acceleration, they are aware of the gear they are in and how much engine braking to expect.

Is regen selected by kWs or braking torque? if it's kW then it seems it will be OKish? because power = revs x torque so at high revs (high speed) you will get more gentle (low torque) braking but at low revs (low speed) you will get more severe (high torque) braking.

I figure an ICE has to be constant torque, as there would be a fixed force per revolution to pump air through the engine, the driver changes down gears to increase the engine braking effort by increasing RPMs.

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Post by Johny »

The Lenze VFD has 2 current limit settings. Maximum current as a motor, and maximum current as a Generator. Regen is normally controlled as a current (or torque) setting.

Assuming AC systems here, regen braking would correspond to how much you released the accelerator - up to maximum regen current/torque.
So you control it with the accelerator.

A manual control would allow increasing the maximum (and thereby slope) of this accelerator release regen.

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Post by acmotor »

Ditto for Danfoss control i.e. current and torque limits for motor and generator. These are probably the same for most VFDs.

If you are in speed mode and you reach a preset torque limit in say regen of say 60% then the ramp is simply automatically extended by the controller. No drama at all. Not hard walls or edges, and I speak from real life experience here.

I must say the metric mind audi guy as mentioned in the post above needs to do a bit more setup before he goes on the road. Regen is actually quite smooth, seemless and requires not special driver input. Nothing happens 'suddenly' and grossly unless you have it badly set up.
Imagine badly setup ABS, you'll get the picture !

If you are at 80kmph and remove your foot completely from the pedal then there is just 'engine' braking as with an ICE. (probably a bit more is my preference). No wheel lockups (unless you program them in !)

Danfoss (and others) have an analogue input for dynamic torque control (even when in speed mode) that would suit the jake brake level as described earlier. I've not used this yet as I get on OK with the accelerator pedal controlled 'engine braking' quite well.

This fits Johny's comment above.
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Post by Johny »

BTW I currently drive around in my daughters Honda Jazz CVT.

It has a "manual mode" which is 7 preset points in the CVT. These are controlled with steering wheel paddles - one on each side.

They are DREADFUL. When you are halfway around a corner and want to change gears you have to guess where the paddles are going to be...

Not recommended by me.

Also.
The Jazz also has higher-than-normal engine braking due to it's "Grade Logic" which changes ratios all the way down to 5k/h.
When driving quietly, I find that I only use the brake pedal to actually pull up that last 5k/h - or an unexpected stop.

I tend to think you will adapt your driving based on the amount of regen you have. (Wife hates the Jazz for this reason - it wants to stop before she's ready). It does take time to get used to it, but you do.


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How Does Regeneration Work

Post by fuzzy-hair-man »

acmotor wrote: Ditto for Danfoss control i.e. current and torque limits for motor and generator. These are probably the same for most VFDs.

If you are in speed mode and you reach a preset torque limit in say regen of say 60% then the ramp is simply automatically extended by the controller. No drama at all. Not hard walls or edges, and I speak from real life experience here.
OK still a little confused, regen is set at 60% of what? the motors peak power? maximum regen? so presumably these current settings are at or near a constant voltage, as you don't want to send too much back to your battery pack and blow it up? so the current with voltage constant is analogous to power.

Does this percentage regen give smooth deceleration from any speed?
acmotor wrote: I must say the metric mind audi guy as mentioned in the post above needs to do a bit more setup before he goes on the road. Regen is actually quite smooth, seemless and requires not special driver input. Nothing happens 'suddenly' and grossly unless you have it badly set up.
Imagine badly setup ABS, you'll get the picture !

If you are at 80kmph and remove your foot completely from the pedal then there is just 'engine' braking as with an ICE. (probably a bit more is my preference). No wheel lockups (unless you program them in !)
This was with metric mind's previous CRX, and he was experimenting with different ways of controlling regen and in this case was using the top (idle) half? or third? of accelerator travel to control regen, when he accidentally took his foot off the accelerator he had all of a sudden all available regen hence the skidding down the road.

At the moment my thoughts would be you have a potbox to control default or throttle lift/engine braking regen (say 0 -15%) and if you touch the brakes (brake lights are on) another say 5% is added (numbers are entirely made up) if you need more braking than that well use the mechanical brakes. I think that could give a reasonably intuitive control especially if you are used to covering your brakes coming into a turn.

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Post by acmotor »

"regen is set to 60%" yes, means 60% of motor nominal torque (72Nm in the case of red suzi).

It can be set from 0 466% on red suzi. At around 400% the back wheels lock up (if you have selected a short ramp time faster than the vehicle can actually stop that is) so don't go there.

Regen based on torque is best as the pull up is smooth and constant at all speeds down to zero rpm. Obviously more kW are recovered at higher speeds so a kW based regen would not be much good around town IMHO.

As mentioned already, the torque limit is a dynamic setting that can come from a 'potbox' for that extra bit of regen if 'engine braking' simulation is not enough.

The future of braking systems is all about regen.
Mechanical brakes will end up being only for parking.
The full electronic/emotor system will incorporate traction control, ABS EBD ESB and of course optimal regeneration. Some of this will only become of age with individual hub motors, however single emotor gives you a real feel for the concept.
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Post by juk »

"When you are halfway around a corner and want to change gears you have to guess where the paddles are going to be... "

I find it incredible that one would want to change gears whilst cornering. It upsets the balance of the car and one should already be in the right gear prior to going into the corner.

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Post by Johny »

Ouch. OK, I'll reword it and/or I'm a crappy driver (probably the latter). If the steering wheel isn't straight you have to guess. Since my road car isn't Grand Prix and the steering wheel goes around a full turn...

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Post by coulomb »

fuzzy-hair-man wrote:I'm not quite with you here coulomb my impression was as your pads wear down the pads are pushed further out towards the disks so even if your pads are worn down they still require the same pedal pressure and travel to move the pads out onto the disks...

So AFAIK the brake pedal free play should remain roughly constant regardless of wear...
Well, I'm happy to learn that I'm wrong, then.
ABS normally plays nicely with the engine braking developed by ICE vehicles right? doesn't it monitor how much the wheel turns relative to the other wheels to detect the wheel that locks?
My suggestion of removing regen with heavy mechanical braking was from someone else; perhaps Weber. I can imagine that in a skidding or slipping situation (e.g. ice, water, or oil on the road) and the ABS is doing it's thing to keep the humans alive, it needs at time to reduce the torque applied by a wheel to zero or near zero. If that wheel happens to be a driven wheel, and it is getting a large torque from regen, then regardless of how well the ABS has decided which wheel has lost traction, it can't reduce the torque to zero (possibly momentarily) to do its job. ICE engine braking is fairly mild, so I assume that ABS plays nicely with that. It's heavy regen that could badly affect ABS operation, and I assume that it's usually at heavy mechanical braking that ABS would be needed.

The diff may interact with this, but if two driven wheels lose traction, the diff will make no difference and the problem stands.

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Post by Electrocycle »

under hard mechanical braking there is not much IC engine braking as the car will slow down faster than, or at least close to, the time is takes for the engine to slow down due to its inertia.

Even very mild engine braking can cause stability problems (even a reduction of power without any braking is enough to upset a car in low grip cornering situation)

I think the only way to really maximise regen capability is to have a separate control for it, and a driver who knows what they're doing.

Failing that, using the first bit of the brake pedal travel (between brake lights on and actual mechanical braking) to control the regen is the best bet.

I don't like the idea of using large amounts of throttle off regen (controller running in speed feedback mode) because it would be very easy to lose control with only a small slip of the foot while cornering.

The tricky part is using as much regen as possible without making it easy to upset the car's balance or complicate "normal" braking.
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Post by Richo »

Johny wrote:I was trying to avoid needing the subwoofer - extra weight.


I looked at it from the point of view that I'm only putting in a small pack of lithium.
The lithium is up the front in the engine bay.
So the back now is too light.
No exhaust system no fuel tank.

I figured 2 x 15" subs should even it out Image
Got to keep those Inpectors happy with weight distribution Image

I was reading up on those CVT's a few nights ago.
Would be interesting to see how much power they consume to keep ratios correct.
Ditch the ICE, clutch and CVT ECU.
Replace with ACIM and new ECU.
Now ACIM sits at peak torque/power.
Do they handle 100kW+? Image
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So the short answer is NO but the long answer is YES.
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Post by Tritium_James »

The ACP motor controller we've got in the Porsche has the regen set up on the accelerator pedal. Fully lifted off is 'full' regen. There's a slider pot on the dash that controls what 'full' is. With it set to about 1/4 of the way, it feels like strong engine braking and is quite natural. With it wound up to 100% is comes close to locking up the rear end and gets pretty severe.

Pros:
- completely unmodified/unmolested brake pedal, keeps inspectors happy
- you can normally drive the car with one pedal
- smooth transition from drive to regen

Cons:
- If you need to jump on the (hydraulic) brakes, you also get 'full' regen at the same time by the fact that you've lifted off the accelerator pedal to put your foot on the brakes. With the regen wound up, this pretty much sucks.
- It's hard to coast, small pedal movements means you're constantly transitioning from small amounts of drive to regen and back again = less efficient than rolling.
- The car now drives 'weird' and this potentially means if some random person is driving it, things are not 'normal'. Normal = brake pedal, not accelerator pedal, slows you down.

With a decent motor controller you'll be controlling the motor torque anyway, both in drive and regen, so it's all smooth and well controlled. It's the user interface that presents all the issues.

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Post by Tritium_James »

Richo wrote: Do they handle 100kW+? Image


Yes, but your small lithium pack probably won't! :)

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Post by acmotor »

TJ, you describe very much the behaviour of my AC EV red suzi

I have found 60% regen to be a good number (~40Nm).
The response to operation of accelerator pedal I have found to be acceptable if the slip compensation / speed control gain are reduced so the controller does not try too hard to hold a speed.
Torque mode is quite scary to drive in that with the extremely free coasting of a direct drive induction motor, taking your foot off lacks any engine braking and you get that runaway feeling !

From a safety point of view, the critical half a second or so it takes to remove the foot from the accel and apply to the brake is lost time without regen starting as soon as the foot starts to back off.
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Post by Tritium_James »

acmotor wrote: TJ, you describe very much the behaviour of my AC EV red suzi

I have found 60% regen to be a good number (~40Nm).
The response to operation of accelerator pedal I have found to be acceptable if the slip compensation / speed control gain are reduced so the controller does not try too hard to hold a speed.
Torque mode is quite scary to drive in that with the extremely free coasting of a direct drive induction motor, taking your foot off lacks any engine braking and you get that runaway feeling !

From a safety point of view, the critical half a second or so it takes to remove the foot from the accel and apply to the brake is lost time without regen starting as soon as the foot starts to back off.


I agree with all this. The Porsche pedal controls torque, not speed, but it's hard to actually have it at zero torque, you need finer control over the pedal than is humanly possible. So I haven't experienced what you're talking about with the free 'runaway' effect, but yes I can imagine it might feel weird.

Agreed on the time delay - this is why having regen control on the accel pedal is nice. Like I mentioned, you can drive to work and not have to move your foot off the one pedal.

FYI, in the Porsche, 60% regen is 132Nm at the motor, ~1390Nm at the wheels. :)

The thing we're going to try in the Civic conversion we're working on at the moment is to have mild regen on the accel pedal (similar to engine braking) and have the proper regen controlled by the initial brake pedal travel. This should feel 'normal'.

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Post by juk »

Surely this must upset the brake balance. Is there any adjustment made in the brake bias? How legal is it?


We're lucky we don't get snow here.

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Post by Tritium_James »

Yeah it probably does upset it a little, but the weight distribution in a porsche is already screwed up! The ACP controller is also capable of doing it's own ABS if necessary (although it's not hooked up in this particular car). The donor vehicle does not have ABS, it's an old model vehicle.

Yes, it's legal, and has been tested when it was first registered (in NSW). I don't know what the test involved though.

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