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Drivetrain loses 4wd vs 2wd.


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#51 Tony Matthews

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Posted 05 March 2012 - 16:30

Human beings


cannot


survive speeds


greater than


60 mph - fact.




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#52 24gerrard

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Posted 05 March 2012 - 17:00

Damn Cheapy they should have told you it wasnt an automatic.
Human Beings? in illustration Tony, havnt met any.

#53 cheapracer

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Posted 05 March 2012 - 18:29

Human beings


cannot


survive speeds


greater than


60 mph - fact.


Ray, is that you?


#54 Tony Matthews

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Posted 05 March 2012 - 18:54

Poss


i


bly

#55 saudoso

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Posted 05 March 2012 - 19:09

Posted Image


Ha! The old Passats turned Santanas from Brazil! We flooded China and the Middle East with these beasts.

#56 Greg Locock

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Posted 05 March 2012 - 20:56

Tesla does use a 2 speed box. I've never bothered to find out why.

#57 Lee Nicolle

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Posted 05 March 2012 - 22:29

Tesla does use a 2 speed box. I've never bothered to find out why.

Powerglide reincarnated!

#58 gruntguru

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Posted 05 March 2012 - 22:34

Tesla does use a 2 speed box. I've never bothered to find out why.

One ratio to maximise top speed and economy. Another to maximise acceleration? Guess it depends on the power curve shape.

#59 24gerrard

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Posted 06 March 2012 - 13:45

One ratio to maximise top speed and economy. Another to maximise acceleration? Guess it depends on the power curve shape.


Depends on battery energy density, the lack of any current multi ratio transmissions capable of lasting for usable mileage in an electric vehicle and the head in sand posture of most modern vehicle engineers.

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#60 MatsNorway

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Posted 06 March 2012 - 15:03

Even electric motors have a optimum rpm band.

And when you squeeze it for more it gets less efficient. You can allways add timing and such but i doubt they do that in any other areas than RC car racing. And that again does demand tricky electronics that would add cost and weight.



#61 CaptnMark

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Posted 06 March 2012 - 18:45

Tesla does use a 2 speed box. I've never bothered to find out why.


Huh? I thought they have switched to fixed gear (+differential, obviously) a long time ago?

Edited by CaptnMark, 06 March 2012 - 18:47.


#62 Greg Locock

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Posted 06 March 2012 - 21:25

Huh? I thought they have switched to fixed gear (+differential, obviously) a long time ago?

My appy polly logies, you are right. http://en.wikipedia....er#Transmission Ah well, that makes more sense

#63 24gerrard

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Posted 06 March 2012 - 21:31

Even electric motors have a optimum rpm band.

And when you squeeze it for more it gets less efficient. You can allways add timing and such but i doubt they do that in any other areas than RC car racing. And that again does demand tricky electronics that would add cost and weight.


So a multi speed motor/gearbox that kept things optimum without excess wear and is fully smooth in operation might be useful then?
Hmmm, I seem to have such a unit drawn up somewhere, hang on a minute.

#64 MatsNorway

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Posted 07 March 2012 - 06:54

Looking at the link above it seems like they could have done some fidling with the electronics and gear ratios to compensate. Hence the need for increased cooling.

Im guessing they just push it harder on low rpms to get a better 0-100Km`t time, Simple but less efficient.

Im guessing top speed is the same.



#65 bigleagueslider

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Posted 10 March 2012 - 02:39

So a multi speed motor/gearbox that kept things optimum without excess wear and is fully smooth in operation might be useful then?
Hmmm, I seem to have such a unit drawn up somewhere, hang on a minute.


The Tesla needs a gearbox because the propulsion motor operates at up to 14,000 rpm. A high speed motor and gearbox combination is used because it works out lighter than a low speed direct drive motor.

Tesla had lots of development issues with the transmission. Their current supplier is Borg-Warner. They previously worked with Xtrac and then Magna, but had ongoing quality issues with both suppliers.

I saw a production Tesla roadster a few months back. It looked OK from a distance, but up close the fit, finish and detail were nowhere close to what you would expect in a $110K car.


#66 scolbourne

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Posted 10 March 2012 - 04:06

Back to the thread subject.
I would have thought much of the losses in a 4WD and for that matter FWD would be in the universal joints. Especially when the car is turning.
What is the efficiency of FWD versus RWD whilst doing a tight circle, or when going over a bumpy surface pushing the uj's to the limit.

Using electric motors it would be possible to have the motors inboard but free to pivot (turning with the steering) thus avoiding these losses as well as maintaining minimum un-sprung weight.

I dont think the electronics will end up being a major cost for a mass produced electric car (especially compared with the battery cost).

Having a single speed transmission is Ok but will lead to high maximum amps which can be avoided by using gearing if this is unacceptable. Electric motors do have an efficient rpm range , so it is best to make a compromise based on the requirements as regards weight , cost , complexity and performance over what type of gearbox if any is used.

#67 24gerrard

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Posted 10 March 2012 - 11:21

Back to the thread subject.
I would have thought much of the losses in a 4WD and for that matter FWD would be in the universal joints. Especially when the car is turning.
What is the efficiency of FWD versus RWD whilst doing a tight circle, or when going over a bumpy surface pushing the uj's to the limit.

Using electric motors it would be possible to have the motors inboard but free to pivot (turning with the steering) thus avoiding these losses as well as maintaining minimum un-sprung weight.

I dont think the electronics will end up being a major cost for a mass produced electric car (especially compared with the battery cost).

Having a single speed transmission is Ok but will lead to high maximum amps which can be avoided by using gearing if this is unacceptable. Electric motors do have an efficient rpm range , so it is best to make a compromise based on the requirements as regards weight , cost , complexity and performance over what type of gearbox if any is used.


http://www.ipo.gov.u...r...art=0&epj=y

Will this do?

Edited by 24gerrard, 10 March 2012 - 11:24.


#68 Greg Locock

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Posted 12 March 2012 - 22:44

I would have thought much of the losses in a 4WD and for that matter FWD would be in the universal joints. Especially when the car is turning.
What is the efficiency of FWD versus RWD whilst doing a tight circle, or when going over a bumpy surface pushing the uj's to the limit.


The limits you see in a car are nowhere near the limit a Hookes joint can take. The actual losses in a Hookes joint are very small, essentially because the radius of the joint is so enormous compared with the radius of each roller.

In a Rzeppa joint losses are greater, and are measurable. A tripod joint is measurably more efficient than an Rzeppa. http://www.thompsonc.....cy Report.pdf may answer your question.

The saving grace in all this is that when you are driving over bumps and round corners that there are various massive power drains compared with straight and level running, such as the power to heat the tires, and the power to heat the shock absorbers. So the additional losses in the driveline at high articulation angles pale into insignificance.