Go Back   EcoModder Forum > EcoModding > General Efficiency Discussion
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 04-03-2018, 07:33 AM   #1 (permalink)
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: Vermont
Posts: 2,541

Gaptooth - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 68.85 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Velomobile - '13 Sun Seeker EZ-TAD SX
Last 3: 2142.86 mpg (US)
Thanks: 854
Thanked 970 Times in 618 Posts
Limited slip differential efficiency?

I've been reading about transmissions a lot lately, and I realize I don't fully understand limited slip differentials.

My reading has lead me to believe there are a few types, at least that apply to FWD vehicles:

-Viscous
-Clutch-type - Either electric or mechanical
-Helical

My understanding is that the viscous types behave much like torque converters in automatic transmissions. Clutched seem relatively straightforward. Helical I can vaguely conceptualize.

What isn't clear to me is what sort of effect each of these would have on efficiency, and what their disadvantages are.

Clutched, my reading suggests that they're wear parts and require both frequent oil changes and occasional service. Also, when engaged, there's a 1:1 between wheels and would greatly increase wear on tires. I can see this being useful off-road, but it sounds very inappropriate for road cars.

I could see viscous torque converters eating power, but I'm unsure if this applies all the time, or just when there's a difference in wheel speed? Can someone tell me more about these?

As far as helical, my reading suggests that if one wheel is free-spinning, it won't send power to the other wheel - both must have some traction. Is this correct? What would be the point of a helical LSD in that case? Also, do the extra frictional losses apply all the time, or only when there's a difference in wheel speed?

~

What got me thinking about these was parking on icy slopes this last winter. I can think of a few times I had to have my neighbor pull me out, because I couldn't get traction to both wheels. Perhaps in the future when we have a motor for each wheel, this won't be an issue, but for now I'm interested in educating myself on the various engineering solutions to this.

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 04-03-2018, 09:12 AM   #2 (permalink)
Master EcoModder
 
Stubby79's Avatar
 
Join Date: Sep 2012
Location: Victoria, BC
Posts: 1,062

'91 Miata - '91 Mazda Miata
90 day: 27.11 mpg (US)

'86 Fiero GT - '86 Pontiac Fiero GT

Purple Penny Pincher - '95 Pontiac Firefly Base
90 day: 43.68 mpg (US)

Jett-Black - '01 Volkswagen Jetta
90 day: 39.32 mpg (US)

Firefly EV - '98 Pontiac Firefly EV
90 day: 107.65 mpg (US)

Little Boy Blue - '05 Toyota Echo
90 day: 32.25 mpg (US)
Thanks: 39
Thanked 302 Times in 226 Posts
Ahh...er...I understand how each works and can make plenty of assumptions, but I think it would be better for an expert to try ans answer your question.

For the most part, I don't see them throwing away efficiency, beyond the additional rotating mass, except for when they're engaged...and 99% of the time they aren't. There may be a slight efficiency hit for the viscous, but I doubt it would be noticeable.

As to the helical....yes, it needs traction to engage, otherwise there's not enough torque to spread the gears/clutches/whathaveyou apart and cause them to lock up. If you're on ice or with a wheel off the ground, you aren't going to be able to apply any torque because said wheel will spin freely.

The point of them is on the street or track, you will almost always have some traction, so they still do their job. Even if one breaks loose, it still takes torque to keep spinning a tire on pavement, and chances are the diff will have already locked up before you do.
__________________

  Reply With Quote
Old 04-03-2018, 09:20 AM   #3 (permalink)
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: Vermont
Posts: 2,541

Gaptooth - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 68.85 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Velomobile - '13 Sun Seeker EZ-TAD SX
Last 3: 2142.86 mpg (US)
Thanks: 854
Thanked 970 Times in 618 Posts
Sometimes ice and streets are synonymous here.
  Reply With Quote
Old 04-03-2018, 09:46 AM   #4 (permalink)
Master EcoModder
 
Stubby79's Avatar
 
Join Date: Sep 2012
Location: Victoria, BC
Posts: 1,062

'91 Miata - '91 Mazda Miata
90 day: 27.11 mpg (US)

'86 Fiero GT - '86 Pontiac Fiero GT

Purple Penny Pincher - '95 Pontiac Firefly Base
90 day: 43.68 mpg (US)

Jett-Black - '01 Volkswagen Jetta
90 day: 39.32 mpg (US)

Firefly EV - '98 Pontiac Firefly EV
90 day: 107.65 mpg (US)

Little Boy Blue - '05 Toyota Echo
90 day: 32.25 mpg (US)
Thanks: 39
Thanked 302 Times in 226 Posts
Traction control is probably better for the average joe driving in winter.
__________________

  Reply With Quote
Old 04-03-2018, 09:51 AM   #5 (permalink)
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: Vermont
Posts: 2,541

Gaptooth - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 68.85 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Velomobile - '13 Sun Seeker EZ-TAD SX
Last 3: 2142.86 mpg (US)
Thanks: 854
Thanked 970 Times in 618 Posts
Quote:
Originally Posted by Stubby79 View Post
Traction control is probably better for the average joe driving in winter.
Makes sense. I know you can add a LSD to many manual transmissions though, but haven't the faintest idea about how one would retrofit traction control.
  Reply With Quote
Old 04-05-2018, 04:00 AM   #6 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 6,458
Thanks: 0
Thanked 634 Times in 562 Posts
I see no reason for an LSD to decrease fuel-efficiency, but a handful of extra pieces in the differential might increase internal frictions. Well, nowadays that most cars are fitted with ABS brakes (even in my country it's now mandatory), it's easier for automakers to resort to traction control.
  Reply With Quote
Old 04-05-2018, 04:43 AM   #7 (permalink)
Furry Furfag
 
Baltothewolf's Avatar
 
Join Date: Nov 2013
Location: Apple Valley
Posts: 2,070

Winsight - '00 Honda Insight
90 day: 56.86 mpg (US)

Miaderp - '95 Mazda Miata
90 day: 28.53 mpg (US)
Thanks: 67
Thanked 382 Times in 293 Posts
Even vicious wouldn't have an efficieny hit, at least not enough to notice. It's not that much weight, or rotational mass. Maybe a pound difference, but again, I would guess not even enough to notice. Also vicious is absolutely trash. I don't think anyone uses that technology anymore. Most Miatas (90-93) that had it, no longer had it beyond about 50k miles. Just a bad design.
__________________

  Reply With Quote
Old 04-05-2018, 04:58 AM   #8 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 6,458
Thanks: 0
Thanked 634 Times in 562 Posts
Quote:
Originally Posted by Baltothewolf View Post
I don't think anyone uses that technology anymore.
It's still used at least in trucks, but the modern crossover SUVs mostly replaced it for the ASR.
  Reply With Quote
Old 04-05-2018, 05:02 AM   #9 (permalink)
Master EcoModder
 
Join Date: May 2012
Location: Indiana
Posts: 1,323

Traverse 2LT FWD - '12 Chevrolet Traverse 2LT
90 day: 21.2 mpg (US)

Volt, gas only - '12 Chevrolet Volt Premium
90 day: 41.42 mpg (US)

Volt, electric only - '12 Chevrolet Volt Premium
90 day: 132.59 mpg (US)
Thanks: 119
Thanked 276 Times in 183 Posts
I can't imagine a FE reduction from an lsd. They only engage under moderate to heavy torque situations.

I had one in my cts and I can attest, it is very beneficial when paired with traction control. In rwd vehicles it can cause understeer when cornering and accelerating(NOT eco friendly )
__________________




  Reply With Quote
Old 04-05-2018, 05:16 AM   #10 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 6,458
Thanks: 0
Thanked 634 Times in 562 Posts
Well, I'm sure it may actually benefit the efficiency in slippy terrain conditions, such as driving uphill in a rainy morning in Porto Alegre...

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com