gearboxes

Technical discussion on converting internal combustion to electric
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chip
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Post by chip » Wed, 17 Aug 2011, 21:33

Why is it gearboxes are not recommended in EV's?

Alot of places i have read seem to think that with the right AC motor and decent controller that gearboxes become irrelevant?
i don't see the logic behind this.

I've been told that gearboxes are heavy, clunky, difficult to couple with the motor ect. ect.

and that's all well and good, but you have the exact same issues in an ICE engine
yes, a gearbox from an ICE motor would probably not be ideal, as their gearing are designed with an ICE torque range in mind

however with the right gearbox you can use smaller motors wich = smaller batteries, which means more space, less charging times, and lower costs

I dont see why more R&D is not put into gearboxes
as Archimedes said: "with enough leverage i could move the world"
smaller more compact and more gears.. like say a Constantly variable box, that could handle the torque??



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Post by Johny » Wed, 17 Aug 2011, 21:53

If a gearbox had no loss, weighed nothing and took up no space - it would be fine.
The advantage of great take-off power is considerable but the disadvantage (at least for me) of a measurable range decrease and lost space ruled it out.

Also don't be too sure that you can get away with a smaller motor. If you want to do highway speeds then the gearbox is of relativley little use unless you have a high RPM motor - even then running an ICE-intentioned gearbox is 2nd or 3rd gear all the time would mean excessive wear.

There have been a few folk who have worked on EV special gear trains (Tritium James for one), but so far it's expensive.

That said. Weigh up the pros and cons and make your own decision. If I had not started with an auto I may have gone the other way....

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Post by gmacd33 » Wed, 17 Aug 2011, 22:35

I'm not sure that gearboxes are not recommended for EVs - in my opinion they certainly are recommended. Also, in my conversion I found it easier to keep the existing gearbox, rather than get rid of it. What would be ideal for EVs would be 2- and 3-stage gearboxes - these are being made by BorgWarner etc specifically for EVs already.

A gearbox will greatly increase acceleration off the line, and the max gradient a vehicle can ascend. Conversely a gearbox can allow for a lower motor current (and hence motor torque) to provide the same torque at the wheels, thus reducing the cooling/max current requirement of the controller.

A gearbox essentially makes the best use of the constant torque part of the (torque vs rpm) curve (of the motor) - allowing for more power to the wheels at low speeds of 0 - x RPM, where x is the RPM at which the motor changes from constant torque to (roughly) constant power. Above x RPM a gearbox is no help, and is a (very slight) hindrance in terms of weight and mechanical efficiency.

Bear in mind that the weight and mechanical efficiency disadvantage of a gearbox will make a difference of a few percent, whereas the torque gains will be a few hundred percent.

If you want good acceleration, or want to go up steep hills, use a gearbox - especially if you have a small motor, and/or low current controller.

If you want maximum efficiency, or have a really huge motor, then I'd say don't use a gearbox.

PS: If your motor is too small (insufficient power) for highway driving, a gearbox can't fix that.
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Post by Canberra32 » Wed, 13 Jun 2012, 14:45

Well you still need a gearbox or at least a clutch for rego perposes. Must be able to mechanically disconnect the drivetrain from the wheels according to the engineer.
Also use the right box.
A 2speed Lenco gearbox holds 1200hp uses planetary gears requires no clutch to shift into neutral and is very small like a rockmellon and only weighs 34kg.
If your car can't handle having an extra 34kg then your running to close to the line of crappy car.
If we want to gain people's interest to switch to electric we need to show them range and power. If we skimp and show them a rangeless slug then that's a huge tick in their box of stay with petrol.

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Post by BigMouse » Wed, 13 Jun 2012, 22:43

Canberra32 wrote: Well you still need a gearbox or at least a clutch for rego perposes. Must be able to mechanically disconnect the drivetrain from the wheels according to the engineer.


This will vary from engineer to engineer and from conversion to conversion. It makes sense for a DC conversion, but for AC, any method of disabling the controller will stop the motor. In DC, if the controller fails, the motor can be connected straight to the battery. If this happens in AC, the motor will freewheel, or at worst, act as a brake.

I don't recall any requirement in NCOP14 to be able to disconnect the motor from the wheels. There are plenty of direct-drive conversions out there all over Australia.

As for gearboxes, I'm keeping mine. I'll be keeping the clutch too. I don't trust the synchros to be able to change the speed of a free-spinning squirrel cage rotor between shifts. They have no problem changing the speed of a comparatively light clutch disk though.

My main decision to stick with a gearbox was the realization that hills exist around here that my car would not be able to climb with direct drive and the tallest final drive available. Whenever I found myself at the bottom of a steep incline (parking garages, driveways, etc), I measured the angle with an app on my phone. I cam across several which were at the calculated limit (12 degrees) for my motor and final drive (250Nm, 4.44:1). I'd rather not risk it. The added acceleration will be nice too ;-)

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Post by PlanB » Thu, 14 Jun 2012, 00:24

Sin 12 = 0.21 so a 12 degree slope adds 21% of the cars weight to the force needed to move it, so an extra ~2100N for a 1 tonne car. Yikes, that is a scary result.

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Post by Canberra32 » Thu, 14 Jun 2012, 01:02

Yes its DC. And even the manufacturer said I'm nuts if I don't have a clutch.
But the engineer did tell me that there must be a mechanical disconnect.
I'm fine with the Lenco, for neutral I just pull the lever out :)
I get the two speeds I want and it shifts clutchless smooth as silk.
They been used in drag cars for years now and proven themselves worthy :)

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Post by antiscab » Thu, 14 Jun 2012, 01:30

in the event of a failed motor controller for a series DC motor, the best solution is to disconnect the power (big contactor, crow bar circuit, etc)

The worst way is to mechanically disconnect the motor, as it just grenades.....

There is no requirement in NCOP14 to mechanically disconnect the motor because you would be crazy to do so....

Keeping a gearbox does mean you can get away with a smaller motor controller and in some circumstances a smaller motor, but your loses increase which lowers your range.

There is a reason production EV's are single ratio

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Post by Canberra32 » Thu, 14 Jun 2012, 01:37

Yes and no.
I would rather the motor grenade than drive me into a tree.
The manufacturer flat out said if it lock full rpm the weight of the stator and copper spinning will have enough push to make trouble.
In their words even my 450mm brakes not going to pull it up.
This made me air on the side of caution anyway as mixed info about you must have mechanical disconnect has come from both RTA and the engineer now.
Perhaps it's because it's an ICV

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Post by gttool » Thu, 14 Jun 2012, 13:38


you could put a clutch in it if they are really persistent, not that difficult
Use a reversing contactor have a switch on the dash for fwd rev and neutral...and then you have a 10 speed gearbox !!and a neutral
this does make the wiring a bit more complex as need to make it start in neutral only
    
the emergency stop is for that instance
Ask the engineer what the emergency stop is for ?

the safety should be put on the starting of the car when it could be turned on accidentally and driven

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Post by Richo » Thu, 14 Jun 2012, 20:33

Canberra32 wrote: Well you still need a gearbox or at least a clutch for rego perposes. Must be able to mechanically disconnect the drivetrain from the wheels according to the engineer.


I bet he was a mechanical engineer.
I'd guess he'd never heard of the Tesla electric car either.

I'm only using a gearbox for convenience on a front wheel drive car conversion.
So the short answer is NO but the long answer is YES.
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Post by BigMouse » Thu, 14 Jun 2012, 21:19

Canberra32 wrote:I'm fine with the Lenco, for neutral I just pull the lever out :)
I get the two speeds I want and it shifts clutchless smooth as silk.
They been used in drag cars for years now and proven themselves worthy :)
Since I'm not finding prices easily online, what does a 2-speed Lenco cost?

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Post by Canberra32 » Thu, 14 Jun 2012, 23:02

2600 landed here.
Check the speedboat parts mags though because they are used a lot in race boats

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Post by BigMouse » Fri, 15 Jun 2012, 03:17

Canberra32 wrote: 2600 landed here.
Check the speedboat parts mags though because they are used a lot in race boats


Yikes. Nearly twice as much as my motor! Image Stock gearbox it is then. Thanks anyway.

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Post by Canberra32 » Fri, 15 Jun 2012, 03:27

Only reason I'm going with it is I will be doubling up the warp11 at some point need it to handle the grunt.
Plus if you ever need another gear you just bolt it on :) it's pricey as hell but next to unbeatable. Plus they have very little mechanical power loss.

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Post by KDRYAN » Fri, 15 Jun 2012, 04:18

Re using a Lenco gerabox module, you will also have to use a reversing module as this gearbox arrangment cannot be reversed. The gearbox uses a sprag clutch bearing, and as I understand it only operates in one direction.

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Post by Canberra32 » Fri, 15 Jun 2012, 12:16

Correct. 2speed with reverse for $2600 landed
Weighing 75pounds not so bad :)
Last edited by Canberra32 on Fri, 15 Jun 2012, 02:17, edited 1 time in total.

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Post by jonescg » Fri, 15 Jun 2012, 18:46

I'm still inclined to use the existing gearbox on the CRX purely out of convenience. I'd leave it in third around town and put it in 4th for the freeway.

So these Lenco gearboxes come with reverse eh? I didn't know this.
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Post by Canberra32 » Sat, 16 Jun 2012, 00:23

No they don't come with it.
They are sections.
I asked how much for a two speed with reverse in the 1200series landed here.
They said 2300-2600 depending on the $$$

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Post by Canberra32 » Sat, 16 Jun 2012, 00:26

Also if it's a front wheel drive a 4wd transfer case works well and holds good power :) but you need the ability to reverse the motor.
A solution controller will do it if your running DC even lets you limit it so you don't go flat out reverse lol

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Post by KDRYAN » Sat, 16 Jun 2012, 04:53

Check with Lenco, they were developing a 2 speed gearbox/differential combination especially for use with electric vehicles. I was looking at this a few years ago and havent followed it up since.

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Post by Canberra32 » Sat, 16 Jun 2012, 05:24

Borgwarner do one.
Lencos are so short they are basically the same if you bolt them straight to a diff.
A Lenco with a 4wd transfer case is a good way to put big power up back with no tunnel needed.
Failing that there are plenty of good transaxles out there.

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Post by KDRYAN » Sat, 16 Jun 2012, 11:39

Do you have the Borgworner link or model/type for there gearbox

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Post by Canberra32 » Sat, 16 Jun 2012, 16:08


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