Will Electric Vehicles Be Viable? When?

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henry
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Re: Will Electric Vehicles Be Viable? When?

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Is it the diff or the right angle drive that’s the efficiency bottleneck? Do transverse installations suffer from this?
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus

Greg Locock
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Re: Will Electric Vehicles Be Viable? When?

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I suspect a parallel diff would be stiffer, thinking about it, and you are right to imply an EV would use a parallel diff, in fact that explains a lot. I was a RWD /AWD driveline engineer, so never concerned myself with the gruesome details of FWDs.

gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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Greg Locock wrote:
Wed Nov 10, 2021 2:01 am
As the torque is applied the casing flexes, forcing the hypoid gears out of mesh and increasing friction. At high loads this is worse. So, in order to stop the diff oil from boiling the gears are meshed incorrectly at low torques, and then come into alignment at high torques.

This means that at low torques the %efficiency is lousy, but at least in terms of watts into the oil (Torque *(1-efficiency) *rpm*2pi/60) you take the hit where it does the least damage.
Fascinating.
Of course the other reason for lousy efficiency at part load is the viscous drag stays much the same and therefore becomes a higher proportion of the transmitted torque.
je suis charlie

Jolle
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Re: Will Electric Vehicles Be Viable? When?

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I wonder... instead of a diff, would an electric motor with two rotors (both connected to their own axle, wheel) in a single stator?

gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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Not sure what advantages that would have over 2 motors. Packaging?

For the extra cost, I would want to get individual torque control of the two axles.
je suis charlie

Greg Locock
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Re: Will Electric Vehicles Be Viable? When?

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There are very few papers on diff efficiency, and this was all a long time ago. I agree the oil drag would dominate at low torques.

gruntguru
gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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Especially with worm and hypoid gearing where oil experiences a lot of shearing.
je suis charlie

Tommy Cookers
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Re: Will Electric Vehicles Be Viable? When?

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gruntguru wrote:
Thu Nov 11, 2021 12:11 am
... Of course the other reason for lousy efficiency at part load is the viscous drag stays much the same and therefore becomes a higher proportion of the transmitted torque.
yes we can infer this as it's conspicuous in shaft-drive motorcycles on parking and unparking
except when thoroughly hot from a long fast journey
though A.C.B.Chapman in his 750MC racer the Mk 3 Lotus famously used 50/50 Redex and paraffin as axle oil

we might even estimate the final drive losses by looking at the stated oil viscosity requirement
though 'rightangle' CWP oil SAE EP140 grade was measured on a different scale to modern 'parallel-transaxle' oil 50 grade

NL_Fer
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Re: Will Electric Vehicles Be Viable? When?

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Any links how price will develop of Al-Air batteries? Probably pretty expensive, since they are non-rechargeable. But the supporters say aluminium is relatively cheap and I suspect, someone would pay the price once or twice a year, if they take a long power hungry trip.

Like an annual skiing trip, driving a 1000km of autobahn at +160kph or a 2 day trip south towing a caravan.

Greg Locock
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Re: Will Electric Vehicles Be Viable? When?

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Somebody sent me this recently, you can see the load path is much better than in a rear wheel drive diff.

https://files.engineering.com/getfile.a ... earbox.jpg

Image

Tommy Cookers
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Re: Will Electric Vehicles Be Viable? When?

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last night's TV seemed to say that .....

BEV makers tell people to operate the batteries between 80% and 20% capacity
MG even saying don't go below 50% - and others saying don't hold at 100%
for best battery life

on some cars this % is apparent to the user
often the range available figure isn't reliably based on depletion to eg 20% capacity (or replenishment limited to 80%)

and ....
hybrids produce more VOCs than some (diesel) ICE cars - due to more ICE running time without proper warmup
implying that VOCs escape recognition as hydrocarbons
eg aldehydes are VOCs
this from Emission Analytics
(whose Dieselgate tests showed no excess NOx in city driving - the TV then lying about this crucial and central point)

this (from other TV) ignoring the trendy use of unsaturated 'oils' as a general cooking ingredient
eg such use in baking etc giving maybe 10000x the aldehyde dose that fuel burning does ....
caffeine is removed from coffee by dissolving it in formaldehyde .....
(I say) huge amounts of VOCs in wood are mandatorily dumped before wood becomes 'goody-woody' fuel ......
and of course wood-fuel VOCs are similarly unrecognised by regulation

and the financial pages seem to say that ......
EV batteries have for years been sold at below cost - and in the forseeable term costs may increase

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Andres125sx
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Re: Will Electric Vehicles Be Viable? When?

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Tommy Cookers wrote:
Tue Nov 23, 2021 11:34 am
last night's TV seemed to say that .....

BEV makers tell people to operate the batteries between 80% and 20% capacity
MG even saying don't go below 50% - and others saying don't hold at 100%
for best battery life

on some cars this % is apparent to the user
often the range available figure isn't reliably based on depletion to eg 20% capacity (or replenishment limited to 80%)

Range is range, it should not be affected by recommendations to improve battery life, they´re different things.

Same as ICE specs show a maximum bhp, but it´s not recommended to use that max power constantly, or the engine may overheat and cause serious damage to the engine.


That recommendations to stay between 20-80% of battery capacity is the reason I´ve stated several times IMHO lithium batteries are far from a good match to BEV, apart from the high price. I follow that recomendation with my phone batteries since smartphones exist btw, and I´ve never replaced a single battery even when I always keep same phone for 4-5 years. Even at that point battery capacity don´t show any sign of degradation thanks to this. I try to follow this with any lithium battery, from a portable air compressor I carry on my bike, to hand tools

I strongly recommend to follow that advice. As I´ve done several times in this thread for years :wink: