Driving an EV in slow moving traffic?

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HuffnPuff
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Driving an EV in slow moving traffic?

Post by HuffnPuff » Sat, 30 Dec 2017, 19:31

I don't actually have an EV yet as I'm still in the early planning phase for a vintage vehicle conversion and my mind wanders while waiting for traffic to move ahead of me. When in heavy traffic how do you manage the throttle in an EV. In a manual ICE vehicle you can creep along in 1st or sometimes 2nd and if your vehicle has suitable torque just keep moving/stopping using the clutch. In an auto ICE simply releasing the brake pedal is enough to keep moving in traffic. My morning commute can have a couple of sections where this creep motion is kinda handy.

My understanding is that no throttle = no motion in an EV and I'd guess that feathering the pedal to idle along could be annoying/difficult. How do you actual EV owners manage it?

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Re: Driving an EV in slow moving traffic?

Post by Johny » Sat, 30 Dec 2017, 20:18

Mine does not have creep mode and I find it no concern at all. With Regen braking it's pretty much single pedal with just moving to the brake pedal to hold still. On hills I two foot it. I don't miss creep mode and find driving normal autos a bit annoying now.

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Re: Driving an EV in slow moving traffic?

Post by mikedufty » Sat, 30 Dec 2017, 22:42

i-mievs creep with no throttle, but I don't think it is that important. They are very nice to drive in traffic compared to ICE, range is very good in slow traffic too.

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Re: Driving an EV in slow moving traffic?

Post by antiscab » Sun, 31 Dec 2017, 00:24

My previous dc car would roll for ages. You take your foot off the pedal and you just stop accelerating. It takes ages to actually slow down without using the brakes, especially at low speed.

My current ac car does Regen a 0 throttle (which I absolutely hate BTW). So you have to hold a specific throttle position to coast without power going in either direction.

In both cases, it's far better than driving a manual ice car.
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Re: Driving an EV in slow moving traffic?

Post by weber » Sun, 31 Dec 2017, 09:52

Hi HuffnPuff. Driving an EV at a crawl is not a problem at all, with or without creep. I'm not even sure I understand why you think it might be difficult.

Regarding creep, I have it set for just enough positive torque when stationary with zero pedal, to take the backlash out of the drivetrain so it doesn't go clunk when I take off. But it isn't enough to overcome the static rolling resistance on a level road. So it doesn't actually creep.

Pedal mapping is tricky because you want to control both torque and rpm with one pedal. The trick is to map pedal position directly to requested speed, but map it only indirectly to the torque that the drive is allowed to use to try to achieve that speed. The torque should be proportional to the difference between the requested speed and the actual speed, with a carefully chosen (e.g. by trial and error) constant of proportionality.

Also, you want a progressive mapping from pedal motion to both torque and rpm. This is what makes it easy to crawl in slow traffic. In other words, near zero pedal, a small movement has a much smaller effect than the same degree of movement near maximum pedal. In mine, when stationary, half pedal gives a quarter of the torque.

Antiscab, it sounds like the pedal mapping in your AC car is not well designed. Mine does regen at zero pedal, with the strength of the regen depending on how close the actual speed is to zero. i.e. the regen torque reduces gradually to zero (or rather the tiny anti-backlash "creep" value) as the speed goes to zero. And yes, strictly speaking, to coast with absolutely no power going in either direction I would have to hold a specific pedal position, but because the torque only increases gradually with deviation from the ideal pedal position, there is a wide enough region where the power either way is negligible.

It's all explained here: viewtopic.php?p=30613#p30613 and on the following page.
I note that by trial and error Coulomb and I gradually increased the torque proportionality constant ("k" in the formulae) to 0.6 and that's where it has stayed for many years now. It is an absolute joy to be able to drive the MX-5 on winding mountain roads using only the accelerator pedal.

This scheme also provides a kind of traction control in regen, because if the wheels lock up due to excessive regen torque, due to me having yanked my foot off the accelerator at max rpm (e.g. at 100 km/h in 2nd gear), the difference between actual and requested rpm goes to zero (because both are zero), and so the regen torque goes to zero and frees it up again. The calculation is done at 25 Hz, so there is a 40 ms delay and you typically get a single loud (but brief) chirp from the tyres.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

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Re: Driving an EV in slow moving traffic?

Post by HuffnPuff » Mon, 01 Jan 2018, 05:02

Thanks all. I guess, I was just curious as to the differences between ICE and EV. Shows I have a lot to learn!

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Re: Driving an EV in slow moving traffic?

Post by Johny » Mon, 01 Jan 2018, 08:30

Didn't (don't) we all. It was a good question and I congratulate you on remembering to ask. My driving musings get forgotten 30 seconds out of the car.

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Re: Driving an EV in slow moving traffic?

Post by 4Springs » Mon, 01 Jan 2018, 16:46

I go between our DC conversion (Brumby) and our Outlander.

The Brumby has no creep and no regenerative braking. It has a 'clunk' as described by weber, where if you start out from a standstill the motor gets up a bit of movement before all the play in the drivetrain is taken up. I can stop this clunk by touching the accelerator pedal while the handbrake is on, or more recently I've been experimenting with using my left foot on the brake. This takes up the slack before the car actually moves, so when the brake is released the car moves forward smoothly. Because of this clunk the Brumby is slightly irritating in slow moving stop/start traffic. But not as irritating as an ICE.

The Outlander has creep and works just like an ICE automatic. The creep means that in slow stop/start traffic you drive with your foot on the brake, releasing it slightly to move slowly. It also means that the Outlander uses electricity when stopped - one of the differences often cited between ICE and EV. I've been sitting motionless in traffic with my foot on the brake and had the petrol engine start up!
Creep is annoying when coming to a stop. Our garage is at the top of a slight slope, so when parking we come in with the foot on the accelerator (just slightly). Then we get to the flat garage floor and have to quickly switch from accelerator to brake. This always seems to result in a jerky stop for me, although the wife is better at it. In the Brumby it is smooth as silk, going from slight accelerator to none, then the foot moves to the brake.

Of the two I prefer to have no creep. weber's set-up sounds ideal, but unfortunately my controller isn't as configurable as his. The Outlander also is not able to be changed. I hear that in a Tesla you can turn the creep off.

Writing this has made me realise that both our cars are more suited to using the right foot for accelerator and left for brake. I'm not sure I want to go down that path though, there is potential for bad things to happen if my brain mixes things up...

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Re: Driving an EV in slow moving traffic?

Post by MDK » Mon, 01 Jan 2018, 17:48

4Springs wrote:
Mon, 01 Jan 2018, 16:46
I hear that in a Tesla you can turn the creep off.
Yes in a Tesla "creep" is optional. I've always driven manual cars & find creep annoying in automatics, so I've never turned it on.

And the mapping on the accelerator pedal is awesome. It's easy to crawl along at very slow speeds, which is useful because my driveway also slopes upwards.

And in slow moving traffic I use the adaptive cruise control (or autopilot) to perfectly follow the cars in front...

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Re: Driving an EV in slow moving traffic?

Post by Peter C in Canberra » Sat, 27 Jan 2018, 12:38

No problem at all having fine control while going slowly, both in my converted car and commercial cars, iMiEV and Volt. The converted car has a Kelly controller that can plug into a PC to use an application to set the motor controller parameters, including various aspects of throttle response.
Daihatsu charade conversion 2009-18, demo iMiEV 2013-present, used Holden Volt 2018-present, on the ACT's 100%-renewable-by-2020 electricity.

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Re: Driving an EV in slow moving traffic?

Post by offgridQLD » Fri, 11 May 2018, 07:56

One advantage that the Imiev has is there is very little if driveline backlash. The electric motor is a gear on gear drive and a single reduction out to two very short drive shafts. That said you can induce a thump on rare accessions loading and unloading the drive but its more of a rubber (suspended) drive frame thump than a backlash issue.

My ICE car on the other hand is terrible for backlash being a very long front engine/ rear drive Ute with lots of tail shaft/gearbox and multiple joints, gears and so on to contend with before finally turning the wheels. I always find my self playing mediator preloading tricks iron out the clunk.

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Re: Driving an EV in slow moving traffic?

Post by doggy » Tue, 24 Jul 2018, 13:28

My Zoe is fine to drive very slowly.

It has a built-in gentle "creep".

The other thing of interest is that they have split the regen between the accelerator and the brake. You take your foot off the accelerator and as long as the vehicle is not fully charged, the regen is similar to a diesel ICE or maybe halfway between petrol and diesel. When you gently press the brake, it is all regen until a certain point (43kW of total regen if fast enough or down hill) when the friction brakes start being used as well.

Overall, makes for a pleasant and economical driving experience if you do not pound either pedal. As with most EVs you do not use the friction brakes much at all in normal driving.

Regds,
Dave

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Re: Driving an EV in slow moving traffic?

Post by rhills » Tue, 24 Jul 2018, 13:43

Hi Dave,

I'm guessing you can't "dial up" the amount of regenerative braking in a Zoe?

This is a feature of the Outlander PHEV that I really love. I can adjust the level of regen with the steering wheel paddles, rather like changing down gears in a manual (or Auto for that matter). I tweak regen up and down all the time when coasting up to lights etc.
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Re: Driving an EV in slow moving traffic?

Post by doggy » Tue, 24 Jul 2018, 15:40

Hi Rob,
It behaves exactly like that if you choose to use or not use the "brake" pedal which is really a regen+brake pedal. So you get to play with up to half (approx) of the regen with the throttle pedal and the other half (approx) with the "brake" pedal.
But no, there are no paddles or other adjustments per se.
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Re: Driving an EV in slow moving traffic?

Post by bladecar » Wed, 25 Jul 2018, 04:39

Hi
This is what I understand the Prius is doing. It regens on light brake application and then moves on to mechanical braking beyond that.

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Re: Driving an EV in slow moving traffic?

Post by doggy » Wed, 25 Jul 2018, 07:29

I like this arrangement rather than having the full regen on the accelerator (which is, I think, the "ePedal" on the new Leaf). I am sure either system has proponents and detractors. In our case, as we also have a turbo diesel car, driving either of them is extremely similar which is particularly important for my wife. Her first two Zoe drives (which exceeded 30km each), she achieved an "Eco-rating" of 90% and 91% without using the Eco button and with air-conditioning working. The Zoe computer continuously evaluates your driving style and gives you a rating (if you ask for it). These are pretty good numbers for a first or indeed any drive and she very quickly fell in love with little Zoe.

Regards,
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Re: Driving an EV in slow moving traffic?

Post by T1 Terry » Thu, 26 Jul 2018, 13:38

bladecar wrote:
Wed, 25 Jul 2018, 04:39
Hi
This is what I understand the Prius is doing. It regens on light brake application and then moves on to mechanical braking beyond that.
The 2008 ex taxi Prius we have is kinda strange when it comes to regen braking and creep. At low speed crawling sometimes simply touching the brake pedal will stop the creep drive and just let the car roll, sometimes the creep mode doesn't seem to be there at all. The selection of the B for added regen braking is quite effective up to around 60km/h, sometimes 80km/h, but the cruise control doesn't work while the added regen "B" is selected which is a bit of a bugga cause the cruise control is great for avoiding speeding in 50km/h zones but the standard regen braking isn't particularly startling, well not near as good as the "B" mode anyway. When in "B" mode and lightly applying the brake so some friction braking is happening, the regen is excellent and will have the battery back in the green bar graph fairly quickly.
The whole thing has become a bit of a competition between the wife and I as to how many cars and skip bins (half a car) we can accumulate in the width of the bargraph display over a known section of road we travel regularly, something to do in a car that requires next to zero input from the driver besides aiming it in the right direction

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