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Re: Tesla Model 3

Posted: Feb 05 2019 10:28pm
by cricketo
billvon wrote:
Feb 05 2019 11:37am
I'm not sure how codes would address that. "You have to have a mostly planar roof?"
For starters, code could say at least 30% of the roof surface has to be South-facing. Then indeed, they could require that South facing part of the roof doesn't have any of these features :

Image

Re: Tesla Model 3

Posted: Feb 06 2019 3:52am
by Punx0r
billvon wrote:
Feb 05 2019 6:00pm
Probably. Compare that to ~40% for the charge-discharge cycle loss.

In general, the fewer conversion steps, the better. An ICE used only at highway speeds - with electric taking care of city driving - is pretty hard to beat.
40% Round trip efficiency on a li-ion battery seems high?

Agree on the latter, this constant load/speed centred around an efficient operating point for the ICE is exactly what the series hybrid system would aim to achieve but with the additional conversion steps & losses. I was thinking more of mixed or urban driving where thermal efficiency of the ICE drops from ~30% to 10-20%, but I suppose that kind of driving is not what the ICE range extender is typically used for...

Re: Tesla Model 3

Posted: Feb 06 2019 10:28am
by neptronix
cricketo wrote:
Feb 05 2019 10:14pm
neptronix wrote:
Feb 05 2019 8:34pm
ICE mechanical energy > transmission ( ~7% loss )
What does this 7% represent ? Increased friction due to gear box ? Oil pumps ? Sub-optimal engine performance due to variance in RPM ? Friction losses in the transmission ? Any difference between 2wd, 4wd, FWD, RWD ?

Also don't tell these guys :)

https://en.wikipedia.org/wiki/Workhorse_SureFly
That ~7% is friction losses in the transmission. There are multiple gears that the engine power must go through before it hits the wheels. This is the same reason that mid drive efficiency is significantly lower than what we see in hub motors ( until you go and climb a 15% grade and your hub motor falls out of it's efficiency curve in a dramatic way - in that case, the mid drive obviously wins the efficiency challenge ).

AWD and RWD significantly increases this friction figure. There is a big difference in the reported fuel economy for a FWD version of a car versus an AWD version. A couple mpg, usually - due to the fact that you have an additional a pair of 90 degree angled gear engagements.

One thing of note is that Honda's newer hybrids use a single ratio, single gear reduction from the gasoline engine to the wheels, and the electric motor provides the startup torque needed. This reduces the friction of the gasoline engine to the bare minimum and is the reason why these vehicles have fantastic fuel economy, despite their lack of the aerodynamic gifts that the Priuses have. The downside is that if the hybrid system fails, the car cannot get going from a stop.

Re: Tesla Model 3

Posted: Feb 06 2019 10:40am
by cricketo
neptronix wrote:
Feb 06 2019 10:28am
That ~7% is friction losses in the transmission. There are multiple gears that the engine power must go through before it hits the wheels.
Understood. So for comparing against an ICE vehicle we still need to account for drop in engine efficiency due to variance in RPMs. That may be lower for a hybrid like you're describing, but even there engine won't run at steady RPMs at its peak performance.

Re: Tesla Model 3

Posted: Feb 06 2019 11:39am
by billvon
Punx0r wrote:
Feb 06 2019 3:52am
40% Round trip efficiency on a li-ion battery seems high?
That's not just lithium ion charge/discharge efficiency. It's also generator efficiency, power conversion efficiency, controller efficiency and motor efficiency. Let's ballpark those numbers:

Generator efficiency 90%
Power conversion efficiency 93% (generator AC voltage to battery charge DC voltage)
Battery POWER (not coulombic) efficiency 90%
Motor controller efficiency 95%
Motor efficiency 90%
Powertrain efficiency 95%

Overall 61% efficiency (39% loss.)

Now, you can do a lot to get around those numbers. For example, you can throttle the engine up and down to closely match the power requirements at the wheels - that way the battery isn't being charged or discharged much so you gain that 10% back. But that's what you have to do for direct-to-wheels anyway.

Re: Tesla Model 3

Posted: Feb 06 2019 11:41am
by billvon
cricketo wrote:
Feb 06 2019 10:40am
Understood. So for comparing against an ICE vehicle we still need to account for drop in engine efficiency due to variance in RPMs. That may be lower for a hybrid like you're describing, but even there engine won't run at steady RPMs at its peak performance.
I would note that since most hybrids don't use standard transmissions, the engine RPM is largely uncoupled from the wheel RPM. So you can run at a more efficient speed, rather than a ratio to vehicle speed.

Re: Tesla Model 3

Posted: Feb 07 2019 4:19am
by Punx0r
Are those efficiency values typical? I would have expected ~95% for alternator & motor and 98-99% for battery charger and motor controller based on industrial equipment, but appreciate a vehicle may be different - especially for the motor operating over a wide range of speeds.

Re: Tesla Model 3

Posted: Feb 07 2019 11:30am
by billvon
Punx0r wrote:
Feb 07 2019 4:19am
Are those efficiency values typical? I would have expected ~95% for alternator & motor and 98-99% for battery charger and motor controller based on industrial equipment . . .
It depends what you are quoting and how. For example, a lithium ion battery might well have a 99% coulombic efficiency (amp-hours in to amp-hours out) but a 90% power efficiency (watts in to watts out) since you have to charge at a higher voltage than you discharge. If you are charging at 4 volts and discharging at 3.6 volts, that's 90% right there. (Lower charge rates result in greater efficiencies.)

Re: Tesla Model 3

Posted: Feb 08 2019 4:12am
by Punx0r
Good point :thumb:

Re: Tesla Model 3

Posted: Feb 08 2019 4:47am
by Ianhill
Temperature makes a big difference with ice engines too, Cold air is more dense and needs more fuel to reach it's stochmetric value of 15-1 so the Injectors have to work harder and throw more fuel in. This then means you get more power per stroke but your efficiency drops with worse thermal loss in the block.

Like climbing pikes peak ice engines struggle and very rarely are in ideal conditions to make max power it's a juggling game that's just not there with electric motors but batterys they are more sensitive to heat but less so altitude but from my understanding alitiutue does affect range due to pressure within the cell but by how much or little to compare I'm unsure.

Re: Tesla Model 3

Posted: Feb 08 2019 12:08pm
by billvon
Ianhill wrote:
Feb 08 2019 4:47am
Temperature makes a big difference with ice engines too, Cold air is more dense and needs more fuel to reach it's stochmetric value of 15-1 so the Injectors have to work harder and throw more fuel in. This then means you get more power per stroke but your efficiency drops with worse thermal loss in the block.
Mostly agreed. But the primary efficiency loss isn't due to "thermal loss" - it's due to pumping losses. When it's cold out, air is denser, so the throttle plate has to remain more closed for the same mixture - and it is harder to pump air past the narrower opening.

Re: Tesla Model 3

Posted: Feb 08 2019 1:33pm
by Ianhill
billvon wrote:
Feb 08 2019 12:08pm
Ianhill wrote:
Feb 08 2019 4:47am
Temperature makes a big difference with ice engines too, Cold air is more dense and needs more fuel to reach it's stochmetric value of 15-1 so the Injectors have to work harder and throw more fuel in. This then means you get more power per stroke but your efficiency drops with worse thermal loss in the block.
Mostly agreed. But the primary efficiency loss isn't due to "thermal loss" - it's due to pumping losses. When it's cold out, air is denser, so the throttle plate has to remain more closed for the same mixture - and it is harder to pump air past the narrower opening.
If you dont mind me asking bill how you learnt all this random information ?

Re: Tesla Model 3

Posted: Feb 08 2019 2:06pm
by billvon
Ianhill wrote:
Feb 08 2019 1:33pm
If you dont mind me asking bill how you learnt all this random information ?
That particular tidbit came from working with Ford on their VCC110 program. I was working for a subcontractor but worked with their engineers quite a bit - and they were looking at both EV's and hybrids, and looking at ways to optimize both. Understanding where ICE engines were most efficient was critical for optimizing hybrids.

Re: Tesla Model 3

Posted: Feb 08 2019 2:50pm
by Ianhill
billvon wrote:
Feb 08 2019 2:06pm
Ianhill wrote:
Feb 08 2019 1:33pm
If you dont mind me asking bill how you learnt all this random information ?
That particular tidbit came from working with Ford on their VCC110 program. I was working for a subcontractor but worked with their engineers quite a bit - and they were looking at both EV's and hybrids, and looking at ways to optimize both. Understanding where ICE engines were most efficient was critical for optimizing hybrids.
That gives good reasoning to all this juicy info I read of yours then, all my ev knowledge comes from potching about with stand on scooters or the ice side ive only learnt from reading and building a basic turbo track car, my main college was for electrical installation so I knew a bit of the language and a bit about older type motors, I've learnt more outside of college than in and I'm only 33. It's costs to much for me to further my education.

Re: Tesla Model 3

Posted: Feb 09 2019 5:35am
by Punx0r
The avoidance of pumping losses is one of the reasons diesel engines are generally more efficient than spark-ignition ones like petrol/gasoline. Although a solution to this is valve-throttled engines that use variable valve lift instead of a throttle plate are supposed to give up to a 10% efficiency gain. The Fiat 500 multi-air is probably the most common car with this system.

Re: Tesla Model 3

Posted: Feb 09 2019 7:55am
by Ianhill
Punx0r wrote:
Feb 09 2019 5:35am
The avoidance of pumping losses is one of the reasons diesel engines are generally more efficient than spark-ignition ones like petrol/gasoline. Although a solution to this is valve-throttled engines that use variable valve lift instead of a throttle plate are supposed to give up to a 10% efficiency gain. The Fiat 500 multi-air is probably the most common car with this system.
Like the freevalve system used in the agera, I looked into the past of rover uk and they had a patent for a electrically controlled hydraulic actuated valvetrain back in the 90's and developed it over a few years then flopped.

They never had direct injection so im guessing they struggled obtaining the air fuel ratios with fuel coming out of suspension in the runners and limiting them getting higher compression ratios with knock happening and having issues with emissions to the funding dried up they were just a little to early shame.

Re: Tesla Model 3

Posted: Feb 09 2019 8:24am
by Punx0r
That was the "VVC" variant of the Rover K-series engine. It allowed infinitely variable timing and duration (when the valve opens and for how long) but could not vary lift (how much the valve opens), which is what makes valve throttling possible. If you're interested there's more information on how it works here: http://www.sandsmuseum.com/cars/elise/t ... e/vvc2.pdf

Gasoline Direct Injection is another thing entirely that allows spark ignition engines to run high compression ratios than would otherwise be possible by removing the opportunity for detonation (knock) to occur. Greater compression ratio is the other factor that makes diesels more efficient and also gives a nice boost to power. It's a big win for the format of low-capacity, high-boost turbocharged petrol engines that are increasingly popular both for powering pure-ICE cars and for hybrid vehicles due to their small size, low weight and greater efficiency.

I think we're getting off topic now though as the Model 3 is a pure BEV 8)

Re: Tesla Model 3

Posted: Feb 09 2019 9:07am
by Ianhill
I had a k series vvc in a 825kg metro then the later 1.8 turbo unit at 200bhp in same car thing was a rocket 13 second quarters and economic 40mpg.
This patent was from camcon and powertrain limited working for mg rover with a camless engine back in 2001 it was developed before that but they took it Detroit that year for investment and failed.

I just like it as a hobbie and learning a few new things outside of my education, I'd like to do a few extra course really can never know to much or get bored of learning.

Back on electric check out thunderfoots battery video what a condescending tosser most of his past videos make sense but seems he got an elon chip lately and making himself look a fool.

Re: Tesla Model 3

Posted: Feb 09 2019 12:20pm
by billvon
Punx0r wrote:
Feb 09 2019 8:24am
That was the "VVC" variant of the Rover K-series engine. It allowed infinitely variable timing and duration (when the valve opens and for how long) but could not vary lift (how much the valve opens), which is what makes valve throttling possible.
I would add that the Prius uses an Atkinson cycle engine. It is not a "true" Atkinson in that the piston always moves the same distance regardless of position in the four-stroke cycle. Instead, Atkinson operation is obtained by leaving the intake valve open for too long; some of the charge is ejected before the intake valve closes, resulting in a small volume of mixture compressed followed by a large expansion during the power phase. Variable valve timing allows operation in both Atkinson mode (most of the time) and conventional 4-stroke operation during wide open throttle operation (for maximum power.)

Since Atkinson cycle engines are more thermodynamically efficient but less powerful, the throttle plate has to be open wider at moderate power settings - thus reducing pumping losses.