BEVs

[Biospace]

The reason for a large motor isn't acceleration, it's *deceleration*.

Please would you gives us more details on that.

There is enough evidence to suggest that adding gear ratios to BEVs improves efficiencies - ceteris paribus - to allow me to mention it in the first place, you may Google for it. If what's found disagrees with what I suggested, I'd be very happy to discuss.

Not really - if you're making that assertion you need to back it up. I know people who were involved in early Tesla development (the early roadster) and they did try a two speed transmission... it just didn't hold up.
I mean, it clearly does give some benefits in race cars - formula E gearing demonstrates that - but that's a pretty niche problem.
The simplicity of fixed gearing makes a significant difference...

From what I read the two ratio box didn’t hold up mechanically and it inhibited a better 0-60 time. As I explained in an earlier post Tesla does (via two motors) use two ratio transmission.

If you don’t agree with Biospace then please explain why and support your case. IIRC you’re a BEV user and have a physics background so I’d actually be interested to hear your thoughts and to read your references.

Below are some links. My own understanding is based on what I've filtered out for myself down the years, these links do appear to agree although it's clear from their publication dates that the industry chose the simplicity of single ratios, for now, which makes sense for the reasons I give in a previous post. Using two motors with different ratios (and power) is a clever way of improving efficiency and performance but brings may raise stability and balance questions in performance cars which electronics aren't able to reduce sufficiently.

I would guess Porsche is using a two speed transmission because of the need for expected performance at autobahn speeds.

As [XAP] Bob and you mention, Tesla had durability problems with a 2 speed transmission, this was back in 2008 and they found that improvements to both the EM and inverter (33% more current) but with a single ratio more than made up for two ratios with the previous motor setup. Initially they simply locked the cars in 2nd gear before using a new single speed transmission.

The large motor for deceleration comment refers to increasing the regen braking ability, I believe.

https://www.autoblog.com/news/vocis-say ... l-boost-ba
https://www.greencarcongress.com/2010/0 ... 00819.html
https://drivesncontrols.com/two-motor-p ... ies-by-15/
https://newatlas.com/new-multi-speed-el ... nge/11670/
https://newatlas.com/antonov-3-speed-tr ... -ev/19088/

[roubaixtuesday]

Thank you, it’s nice to have a constructive answer …

It's not always clear whether the repeated requests for "evidence" from a very distinct, small group is genuine curiosity or something else. An intelligent conversation on a topic which has broad understanding across those involved generally isn't interrupted by constant calls for data proof, unless someone is making assertions which appear considerably wide of the mark.

I even fielded a call for 'proof' that heavier vehicles with more torque would tend to wear their tyres more rapidly, then pointed out why the academic-penned piece suggesting this isn't the case, cited by the forumite asking for the proof, was misleading.

It's not always clear that repeated assertion of questionable "facts" and subsequent repeated inability to back those up is genuine confusion or something else.

It's also unclear whether trying to create a "very distinct, small group" is a genuine reflection of the discussion or something else.

So much is unclear.

So many questions.

[Biospace]

In terms of efficiency there are losses at both high and low rpm with an electric motor, but they actually relatively small...additional gearing will also have a frictional cost associated, which will be (slightly) higher than a fixed gear train.
...
So the question isn't "would it be marginally more efficient" it's whether the requisite complexity is worth it, and it generally isn't...

Exactly so. The cost element will also feature highly in the decision making within the car industry. To a large extent, multiple ratio gearboxes and the need to change between them while underway are very much associated with the failings of the ICE.

I am guessing it costs less to use a larger electric motor to obtain the same sort of performance of a smaller one with two or more ratios and that the optimum size of EM copes well enough with just the one ratio, unless autobahn performance is required.

Presently we're all in awe of the efficiency of vehicles powered by electric motors (if not their carbon emissions and other pollution when chemical batteries made with carbon dense energy store carbon dense energy) compared with the traditional internal combustion engine car, but it's possible that future economic change may mean more profit comes from having more than one ratio driven by smaller batteries and smaller electric motors.

I'm very happy to have fixed ratio transmission with reversing enabled by simply reversing the flow of electricity.

[[XAP]Bob]

Presently we're all in awe of the efficiency of vehicles powered by electric motors (if not their carbon emissions and other pollution when chemical batteries made with carbon dense energy store carbon dense energy) compared with the traditional internal combustion engine car, but it's possible that future economic change may mean more profit comes from having more than one ratio driven by smaller batteries and smaller electric motors.

And rightly in awe, at least given the starting point of infernal combustion.
I'd quite like to see more city focussed cars, with their drive train more suited to city driving, topping out at 50-60mph - smaller batteries, everything lightweight, but with the mod cons that are basically software in a new car...

The carbon emissions etc of battery manufacture are relatively small - being outpaced by the comparable emissions from the fuel alone of an ICE within a couple of years. And those batteries are lasting well over a decade, and many more miles than many ICE vehicles manage in their lifetimes, and that's before second life and/or recycling (both of which are in their infancy).

[Biospace]

And rightly in awe, at least given the starting point of infernal combustion.
I'd quite like to see more city focussed cars, with their drive train more suited to city driving, topping out at 50-60mph - smaller batteries, everything lightweight, but with the mod cons that are basically software in a new car...

The carbon emissions etc of battery manufacture are relatively small - being outpaced by the comparable emissions from the fuel alone of an ICE within a couple of years. And those batteries are lasting well over a decade, and many more miles than many ICE vehicles manage in their lifetimes, and that's before second life and/or recycling (both of which are in their infancy).

Infernal indeed - as the Great Uncle I mentioned in the first post always called them.

Lifecycle emissions associated with BEVs will be small compared with ICEv, the Chinese are investing heavily in RE and have signed ambitious deals to see peak carbon in 2030, so by 2050 there should be some very good progress. I see there is still hope for Chinese involvement in Northvolt, https://www.ft.com/content/8b447aed-737 ... 94d919c92a

I remember reading this in 2010 - https://www.autocar.co.uk/car-news/new- ... ch-details - with the hope our Government, having invested in this project, might move to incentivise sub-700kg cars.



Here's a link to the vid with corrected aspect ratio, https://file.io/NFtbji9ensQG

[Cowsham]

And rightly in awe, at least given the starting point of infernal combustion.
I'd quite like to see more city focussed cars, with their drive train more suited to city driving, topping out at 50-60mph - smaller batteries, everything lightweight, but with the mod cons that are basically software in a new car...

I just had a thought while reading the first few lines of Bob's post.

What about instead of park and ride you could park and hire a smaller lighter slower electric car to travel around the city in and collect stuff / people with.
No normal cars would be allowed in the city electric trams that could take the goods to the shops from a lorry drop off depo outside the city. A speed limit of 20MPH on all traffic inside the city.

[Jdsk]

What about instead of park and ride you could park and hire a smaller lighter slower electric car to travel around the city in and collect stuff / people with.
No normal cars would be allowed in the city electric trams that could take the goods to the shops from a lorry drop off depo outside the city. A speed limit of 20MPH on all traffic inside the city.

Yes, there's enormous synergy between EVs and autonomous vehicles and niche urban vehicles and not owning your own car.

And electric trams and buses have lots of rôles. But I don't see the advantage of that hand-off of goods with trams over appropriately-sized electric vans....

And there will also continue to be a lot of personally-owned car-like objects meeting other requirements which I don't expect to be met by microcars.

What I'm not expecting is a national transport strategy that tests these options. Local initiatives seem much more likely at present.

Jonathan

[[XAP]Bob]

Below are some links. My own understanding is based on what I've filtered out for myself down the years, these links do appear to agree although it's clear from their publication dates that the industry chose the simplicity of single ratios, for now, which makes sense for the reasons I give in a previous post. Using two motors with different ratios (and power) is a clever way of improving efficiency and performance but brings may raise stability and balance questions in performance cars which electronics aren't able to reduce sufficiently.

...

https://www.autoblog.com/news/vocis-say ... l-boost-ba
https://www.greencarcongress.com/2010/0 ... 00819.html
https://drivesncontrols.com/two-motor-p ... ies-by-15/
https://newatlas.com/new-multi-speed-el ... nge/11670/
https://newatlas.com/antonov-3-speed-tr ... -ev/19088/

Thanks for those...
- So their simulations suggest a 10% increase in efficiency.
- Dual motor option is potentially a 15% increase in efficiency.
- Dual motor each with dual gears might even get 20%.

Two questions occur: What do they mean by an increase in efficiency? Because the numbers there are looking like they're going to go over 100%, so I suspect they actually mean a reduction in inefficiency. How much practical difference has been measured?
Or maybe they're just saying that the efficiency at certain speeds can be increased, but without any analysis on whether that makes a noticeable difference across a representative usage profile.

At the top end there is some benefit in there (and porsche and tesla look to be taking some advantage). But for most vehicles the complexity (and cost) is probably not worth it yet.

[UpWrong]

And rightly in awe, at least given the starting point of infernal combustion.
I'd quite like to see more city focussed cars, with their drive train more suited to city driving, topping out at 50-60mph - smaller batteries, everything lightweight, but with the mod cons that are basically software in a new car...

I just had a thought while reading the first few lines of Bob's post.

What about instead of park and ride you could park and hire a smaller lighter slower electric car to travel around the city in and collect stuff / people with.
No normal cars would be allowed in the city electric trams that could take the goods to the shops from a lorry drop off depo outside the city. A speed limit of 20MPH on all traffic inside the city.

Nissan may be planning something along those lines with their Silence mobility systems dealerships. And Renault might do the same with their Mobilise Duo.

[Carlton green]

Regenerative braking is far preferable to friction brakes.
The rate at which a vehicle can be slowed is therefore directly related to the capability of the motor (and battery).

I’ve only quoted a little from your post and the quote is more of a marker for your attention than anything else.

Thank you for the diagram you supplied, I found it informative and would be glad of additional useful data. Of course - no slight in anyway intended - I’m looking for data (ideally from all who contribute here) that is offered for information far ahead of supporting a particular point of view.

I’d take slight issue with large motors for regeneration, the motor (becomes a generator) needs to be matched to the load pushed into it. To my mind the rate of energy absorption coming down an incline is (pretty much) the same as the rate of (electrical) energy dissipation going up it so the motor should be sized accordingly. Rather than necessarily being appropriately sized generators large motors just give excellent - or should that be excessively fast - 0 - 60 mph times and allow higher starting torque at the wheels, which in turn does away for the need for a costly multi-ratio gearbox.

Some cost effective and pragmatic choices have been made by BEV car suppliers but when it comes to heavy goods vehicles then a different choice has been made, the choice to have multi-ratio gearboxes (my earlier posts supply links to supporting documents/videos).
I’m inclined to think that for BEV car use the higher capital costs of multi-ratio gearboxes and (different to commercial vehicle) duty cycle just make fixed ratio boxes plus slightly oversized motors the better commercial choice. Domestic supplied charge electricity is also relatively cheap (compared to supplied at commercial charging stations), cheap enough to accept a little less than optimum efficiency. Whether relative costs (of fuel and BEV components) will eventually change I don’t know, we’ll have to see what the future brings.

For someone who’s got five minutes to spare this is an informative video about Electric Lorries: https://www.youtube.com/watch?v=29iN39Vhwnc

Whatever, in the meantime, education and informed choice is (I think) all good.

[[XAP]Bob]

Regenerative braking is far preferable to friction brakes.
The rate at which a vehicle can be slowed is therefore directly related to the capability of the motor (and battery).

I’ve only quoted a little from your post and the quote is more of a marker for your attention than anything else.

Thank you for the diagram you supplied, I found it informative and would be glad of additional useful data. Of course - no slight in anyway intended - I’m looking for data (ideally from all who contribute here) that is offered for information far ahead of supporting a particular point of view.

I’d take slight issue with large motors for regeneration, the motor (becomes a generator) needs to be matched to the load pushed into it. To my mind the rate of energy absorption coming down an incline is (pretty much) the same as the rate of (electrical) energy dissipation going up it so the motor should be sized accordingly. Rather than necessarily being appropriately sized generators large motors just give excellent - or should that be excessively fast - 0 - 60 mph times and allow higher starting torque at the wheels, which in turn does away for the need for a costly multi-ratio gearbox.

Do you only ever brake to moderate speed on a descent, or do you brake to stop for traffic lights, or to avoid an incident?
Braking forces are generally *far* higher than accelerating forces - you really do want all the power available for slowing down, and being able to do that without just heating up the environment is a good thing.
If we do start looking at dual motors with different gearing being cost effective... you could have a "low speed" FWD axle, with a "high" speed RWD axle, and have regen braking on all four wheels. That might actually bring more benefit than the dual gearing (though looking ahead on the road would still beat it).

I would welcome graduated licenses, with software limits on acceleration/top speed based on those (actually that would make it even easier for a court to downgrade someone's license of they keep breaking the law). Yes it would mean somehow authenticating with the car to unlock more than base performance, but that's a different problem.

[Carlton green]

Regenerative braking is far preferable to friction brakes.
The rate at which a vehicle can be slowed is therefore directly related to the capability of the motor (and battery).

I’ve only quoted a little from your post and the quote is more of a marker for your attention than anything else.

I’d take slight issue with large motors for regeneration, the motor (becomes a generator) needs to be matched to the load pushed into it. To my mind the rate of energy absorption coming down an incline is (pretty much) the same as the rate of (electrical) energy dissipation going up it so the motor should be sized accordingly. Rather than necessarily being appropriately sized generators large motors just give excellent - or should that be excessively fast - 0 - 60 mph times and allow higher starting torque at the wheels, which in turn does away for the need for a costly multi-ratio gearbox.

Do you only ever brake to moderate speed on a descent, or do you brake to stop for traffic lights, or to avoid an incident?
Braking forces are generally *far* higher than accelerating forces - you really do want all the power available for slowing down, and being able to do that without just heating up the environment is a good thing.

Given that pragmatic stances are being taken about efficiency I’d say that loosing some energy during very hard breaking was, if it actually happened, tolerable. In my journeys it is very rare for me to use all of the power that my small (petrol) engine could deliver and stopping is almost always by light (rather than heavy) use of the brake pedal. Should I break heavily then it will be for but a moment or two and if regenerative energy were absorbed by the motor it would be for a very short duration; the power rating of electrical machines is normally at the continuous load that they can support and they can (typically) withstand short duration overloads. High load braking is short duration.

If you are able to supply it then I’d be interested to see ‘learned’ justification of high powered motors being necessary for energy recovery on braking.

[[XAP]Bob]

I agree - looking forward is always going to get better results than any braking mechanism.
But even relatively gentle brake application deploys much more power than people think.

Not a specifically "learned" analysis, but:
There is a hill near where I live where I see (for some short time) high regen just from maintaining speed, if I wanted to decelerate as well then it would take substantially more - and at the bottom of this hill there is a toucan crossing which is completely hidden (by the hill) until you're already re-genning fairly hard past the speed camera at the top. This is one of those places where a speed limiter and a car that can regen make it much easier to keep eyes on the road, rather than the dials.

There is a pragmatic approach to the energy saving from regen, but that isn't the whole reason you want as much regen capability as you can get. There are other advantages to regen (vs friction braking) in terms of not using consumables, and not putting dust in populated areas. The occasional use of friction brakes is fine, we're going to need them for parking brakes etc anyway. But minimising their use is part of cleaning up the local environments in which we live.

--

I've just been out to drop off a sample to the hospital (yay).
I ran my ODB scanner on the way back down this hill and I was charging the battery at more than 20kW just to maintain speed at 30mph (i.e. not "braking" at all). Now, I'll grant you that my car is larger and heavier than most need - and that has a direct effect on the power required to maintain speed, but that's just to maintain speed. If there had been people crossing at the bottom of the hill I would have needed to do much more than maintain speed, I would have needed to actively decelerate - and that can pull several more tens of kW depending on braking level required (easily 20-30 more).
If that hill was on a 40, 50, or 60mph road, and there was another type of obstruction then the power requirements go up pretty quickly.

[Carlton green]

Not a specifically "learned" analysis, but:
There is a hill near where I live where I see (for some short time) high regen just from maintaining speed, if I wanted to decelerate as well then it would take substantially more - and at the bottom of this hill there is a toucan crossing which is completely hidden (by the hill) until you're already re-genning fairly hard past the speed camera at the top. This is one of those places where a speed limiter and a car that can regen make it much easier to keep eyes on the road, rather than the dials.

There is a pragmatic approach to the energy saving from regen, but that isn't the whole reason you want as much regen capability as you can get. There are other advantages to regen (vs friction braking) in terms of not using consumables, and not putting dust in populated areas. The occasional use of friction brakes is fine, we're going to need them for parking brakes etc anyway. But minimising their use is part of cleaning up the local environments in which we live.

--

I've just been out to drop off a sample to the hospital (yay).
I ran my ODB scanner on the way back down this hill and I was charging the battery at more than 20kW just to maintain speed at 30mph (i.e. not "braking" at all). Now, I'll grant you that my car is larger and heavier than most need - and that has a direct effect on the power required to maintain speed, but that's just to maintain speed. If there had been people crossing at the bottom of the hill I would have needed to do much more than maintain speed, I would have needed to actively decelerate - and that can pull several more tens of kW depending on braking level required (easily 20-30 more).
If that hill was on a 40, 50, or 60mph road, and there was another type of obstruction then the power requirements go up pretty quickly.

That’s interesting and whilst not as rigorous as some here might expect I’m not un-happy with: ‘this was my experience’, etc. Obviously I’d prefer something more analytical but I try not to be a pedant.

I don’t recall what type of car you have but seem to recall it being some form of SUV (IIRC anything smaller being unusable for your wheelchair and the like). Let’s say your car has a 130 Kw motor in it (which seems massive but now isn’t unusual). The regen load of 20 Kw on a 130 Kw motor is under 20% if it’s rated load; you could brake hard down that hill and still only see a peak load of 40Kw or about 30% of the motors rated load.

You being a clever physics type of guy could start plugging in some figures for mass and rate of change of velocity to see what Kw’s are wasted in brakes or (hopefully) reclaimed in regeneration. If you can get at the data in your car then perhaps you might share the peak - if short duration - regeneration rates with us.

[Biospace]

But even relatively gentle brake application deploys much more power than people think.
...
I ran my ODB scanner on the way back down this hill and I was charging the battery at more than 20kW just to maintain speed at 30mph (i.e. not "braking" at all).

20kW sounds a lot, but for how many seconds or minutes?

Travelling for over 1.2km down such a hill while pushing 20kW into the battery would yield 500Wh I think, which after the losses may be closer to 450Wh? Better than an equivalent lardy and over-powerful ICEv of course, but isn't the real route to efficiency to have lighter, less powerful vehicles?