Off the wall torque convertor setup.

[Mark W]

Here's one that few have had reason to consider. Maybe someone here can save me some pondering and scheming time.


A buddy and I are thinking about undertaking an electric vehicle project. He has just finished up a sports car conversion with his students as a project at the school he runs. We've been talking about building an electric motored minitruck for the trail. Just in the talking pondering stage right now.

Our current thinking is to use no tranny and a pair of Tcases. That will give us four "speed ranges". With basically full torque as soon as the motor is given power and the capability to turn 15 thousand RPM we "should be able to get away with just selecting the appropriate range for the use at the moment and do away with the need to shift gears.

Chances are we can get a motor with plenty of torque to power big tires out of deep mud easily with the lower gears we can select with two Tcases (one at 2.28 and the other at 4.71)

But if we can't it occurs to me that a torque convertor might be more suited to this application than a clutch. A lock up convertor with a manual lockup switch seems like just the ticket for those times when a little more grunt was needed "off the line."

Here's what I'm trying to figure out. Can I set up a convertor without actually having a tranny behind it? Seal it up and leave the fluid inside with no circulation? It will generate some heat when it is slipping, but not when locked up. But how much heat? My gut says that it will have plenty of time to shed the heat once any initial use while the rig is starting from a stop in deep mud is finished up. It would be seldom that it would need to slip anyway, most of the time it would be locked, even during startup.


Anyone with any experience (okay, may be LOTS of experience) that would help answer these ponderings?


Mark...

 

[bustanutley]

electric motors generate their greatest torque at 0 rpm so i'm not really sure what a fluild coupling(torque converter) would net you other than a soft start. If my thinking correctly if it won't pull at idle chances are you will just stall the converter. Max Hp is made at halfway into the motors rpm range, but I don't know if that is where you need to shoot to get it moving?


My thoughts anyway

 

[Mark W]

I'm not sure if there is any reason to consider this either. Still in the pondering stage. My thoughts are that getting the rig started while sitting in deep muck like the shot below is gonna be (momentarily) the highest power demand that the rig would see.

If a fluid coupling would allow us to get away with using a motor that might be marginal for that demand, while satisfying all the other power needs, then It might be worth exploring. That is what I am contemplating at the moment. The addition expense and complexity of this approach over a direct drive may outweigh any potential gains.

But since I'm just thinking things through at the moment, no reason not to look into it.


Mark...

 

[crusier72]

What about a Power glide. It is more to deal with but a small 2speed tranny with a torque converter to a t case is about what you are proposing anyhow. It's just in a little differn't package. You could put a manual valve body in it with the lockup torque converter and you would be circulating fluid through it with a cooler and you could keep it alive longer.
1HP =42.4BTU/min
If you had a 50HP motor spinning a torque converter not locked up for 1 min assuming no speed at max torque you would generate approximately 42.4*50=2120.8 BTU. I think.

 

[Mark W]

Looking to keep it light and compact too. I'm figuring we can put the motor where the tranny would sit and use the area under the hood for a diesel powered generator to recharge the batteries at the end of the day or even while on the trail if need be. I'm expecting that the coupling would only need to slip for a few seconds on startup. Again, if at all. and it wouldn't be turning the motor at full power with no motion of the wheels rig. Nice to have the numbers though. For quick and dirty figuring, speed of motor divided by speed out the backside of the converter should give the amount of power being converted to heat. ???

If we went with a tranny, I'd probably just stick with a manual and a clutch/ Simpler and less parasitic loss than an auto.

And it may make more sense to just do this. Use one of the earlier mini-truck iron case 5 speeds or even 4 speeds to keep it as short as reasonable and just accept that the motor would stick forward a bit more.

Wheels in the back of my head, turnin' and churnin'.

Mark...

 

[FLYINGLOW]

Wouldn't the double tcases take care of the torque better than a tranny? Tcases are made to handle more torque anyway and with the gear reductions you are talking you would have enough gears to choose from. Tranny would be easier to put a clutch on though. What sort of torque are you looking at?

 

[Mark W]

Tcases would handle the torque better. Tranny would allow shifting from one gear range to another with syncro and provide a wider range of gear choices. And the clutch of course. And reverse without having to reverse polarity to the motor to back up.

Not sure what sort of torque we will be looking at yet. Again, just starting to investigate this all. But I expect that it should be pretty significant. With peak torque coming on immediately on motor activation, I may be worrying about nothing when I consider getting the rig moving in the muck. Especially since the high speeds that the electric motor can take will allow me to start in a "crawling" gear and just wind the motor out for wheel speed once moving.


Mark...

 

[FLYINGLOW]

My gut is saying no tranny but WTF do I know? Who needs gear shifting when you have 15000 rpm available? The reverse would be good though. I just think if you are getting peak torque at 0 rpm the torque on the input shaft of a tranny will not take it. I just know from helicopters that the more rpm you have the less torque a shaft sees (rotor speed decreases, torque goes up). And knowing where you will be wheeling a clutch will be a liability, will it not? Just take a higher gear if you need the wheel speed. You may even want a torque indicator (an ammeter would indicate this too) because if the motor doesn't start turning it will just put more torque on things as you give it more power.

 

[Mark W]

Good points all. I'm not too much worried about too much torque on start up. The controller is not just an on-off setup. You moderate the power with the accelerator pedal just like you do in a gasoline engine.

Clutch a liability? No more than in a gas powered rig. But over all, the simpler the better, so yeah, I guess.

Biggest stumbling block I see right off the bat with the project would be waterproofing of the motor. Might have to take some sort of sealed box approach with some of the battery power sacrifices to turn a fan to circulate air through it via a snorkel or such. Maybe just put a fan in the motor shaft.


Mark...

 

[lowtideride]

A green crawler. Very cool.

will be watching this thread.




Not that I have any useful input but I think having a manual transmission would be nice. 1) more gear choices. 2) make it feel more like a normal truck

 

[pjohnson]

I am not certain, but I think that manual lock-up is acheived by fluid pressure into the converter. Without a tranny, there's no way to provide the fluid pressure.

However, an industrial fluid coupling may provide what you want with less design issues than adapting a common torque converter.

One example I found with a quick search: http://www.twindisc.com/IndFC.aspx

Very interesting concept...

Phil

 

[Mark W]

I think that you're right about the lock up mechanism of the torque convertor.

But something like what you linked to would probably be exactly what we needed if we went this route.

Mark...

 

[RHINO]

mark, what about line pressure. your not gonna have it until the motor spools up, seems like you'd need to rig up something where the motor is always "idling".

i really dont think you'll need it, i dont think you'll need the cases either. heck you dont even need the diff gears reduction. the motor size you use will determine the amount of reduction you need, i would start by finding out what size motor you need to turn the size tires you want and the weight of the vehicle, then figure out what size motor you can afford or aquire, then use gearing to meet that. actually use gearing to surpass it just a hair so you can light-em up. i mean what fun is an electric rig if you cant show off?

an electric car junky i met races his early 70's datsun B210,,, he drives to the drags,, blows away any given porsche, corvette what have you thats present, then drives back home.

 

[cruiser boy]

Hmmmm.....great ......now I won't be able to sleep tonight trying to figure out how to build you a converter with a working lock-up....I think it could be done with an electric fluid pump. I work in a tranny shop...dang...now you've got me thinking again...Give me a couple days hehe.....Rod


It's not easy being green.....

 

[CruisinFJ60]

im with Al on this one would get a shifter to make it feel like a truck
other than that i have no useful info but def wanna see it happen or work. would be cool as hell.

 

[nat]

I have designed and built an electric beach wheelchair for a buddy of mine.

I doubt any sort of torque converter would work out well. Shifting using a clutch would be trippy. Maybe something even simpler, a set of gear ranges for your final drive that you can choose from.

 

[Mark W]

I have designed and built an electric beach wheelchair for a buddy of mine.

I doubt any sort of torque converter would work out well. Shifting using a clutch would be trippy. Maybe something even simpler, a set of gear ranges for your final drive that you can choose from.

That's what we discussed the other night. Direct drive, always coupled (solidly), with dual Tcases to give a wide selection of "speed ranges". On initial blush it would seem that this would be all that we would need.

I was just wondering if we've gotten the concept right or if we need to complicate things. But as I think about it some more...

If we work with the 15000 rpm limit that I have been told is not overly optimistic for the type of electric motor we would be using... And it has full torque right from the start...

A 2F works best from about 1000 to 4000. It pulls lower of course, but not with gobs of power. It pulls higher too, but few of us use them much higher except in rare situations. So the electric motor has a working rpm range about 5 times as broad.

So... Roughly anyway... a motor of comparable power to what the 2F has at 1000 rpm couple pull away as strongly as the 2F with any given final gearing... and then turn up to as high a speed as the2F could do in 5th gear OD!?!?

Since it would be rare indeed that you would need this wide coverage speedwise while on the trail, steeper final gearing of the electric motor would allow you to have more bottom end for a given power level (since a 100+HP electric motor will probably be heavier and costlier than we really need), and still let us have a wide enough coverage that we would seldom see any real world handicap from needing to come to a stop and shift into a different speed range while on the trail. (Dual Tcase will give us four speed ranges, but no syncros for shifting on the fly... Looks like that could be handled without it being a big deal.)


Least wise that how it looks right now with the lack of indepth research that I'm working with right now.



Mark...

 

[Trollhole]

I looked into this area a while back. This link is a good place to start with the motors. Your gonna want a fluid cooled motor. That would be the easiest and you would not have to worry about sealing a motor. http://www.metricmind.com/index1.htm

Personally the easiest is to just keep the tranny. I don't think you will have to worry about low speed torque. Most high end 300v motors will give you upwards of 200lbs of torque.

Do you want this to be able to drive on the road as well?

 

[denis]

how about an auto tranny minus t/c just for smooth gear change ?
What max. speed do you need to achieve ? I would not rely on the high torque at low rpms to give the slow speeds, because the electric motor will probably produce more heat than power near stall, so you would need to operate it in a good efficiency island even at low trail speeds.
Take the biggest electric forklift you can find, and drop the drivetrain into the mini, and see how it goes

 

[onesprung60]

Just one of my thoughts. Do you think a tranny or t-case can handle an input shaft speed of 15K? The fastest toyota engine in a truck only goes about 6K, and your double that. If you are planning a speed reduction box between the electric motor and the transmission/t-case, that is going to increase torque even more.

For a lock up clutch to work, you need pressure and a way to get it into the convertor. Additionally most lock up clutches are pretty light duty and not meant for constant engagement. Most fluid couplings are not very efficient, which may be fine off-road, but you will build a lot of heat.

Sounds like a very cool idea, excited to see where it goes.