4WD EV

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LetsDoIt
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Post by LetsDoIt » Tue, 05 May 2009, 16:53

I have this 5 year old X-Trail which I am considering converting to an EV. My preferred approach would be to power each wheel independently and have a clever computer control to manage slippage, regen, etc. This should mean I can remove motor, transmission, tailshaft, fuel tank, etc to give weight and space for batteries ... what do you reckon? Doug
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Thalass
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Post by Thalass » Tue, 05 May 2009, 17:41

That will be crazy expensive! But also awesome. Unfortunately hub motors are expensive, and perhaps not entirely reliable. And there isn't alot of room for two motors at the front, and two at the back, with driveshafts to each wheel. Though it should be doable.

A good comprimise (which I plan on doing) is to have two motors, one to the rear diff and driveshafts, and the other to the front diff and driveshafts. That way you can use two reasonably priced motors, and still have no real mechanical crap between the motors and wheels.

I've seen it done on one car before - a subaru impreza that is raced in autocross in the usa (if you can call autocross 'racing' >.>). So it ought to work.


Good luck with your project! There needs to be more 4WD EVs out there, proving that EVs aren't all priuses (prii?) and golf carts!
I'll drive an electric vehicle one day.

BaronVonChickenPants
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Post by BaronVonChickenPants » Tue, 05 May 2009, 18:08

I was pondering this myself for potentially converting my Subaru Outback and was thinking about Thalass's Subaru Brumby project, I believe Thalass could be on the right track with his idea of a direct drive motor feeding a differential at each end of the car but for this to work I think you would need something to compensate for front/rear speed variations, otherwise it would be like driving with a locked centre differential and could lead to some interesting cornering experiences.

I have 3 trains of thought in this:

1. Some sort of load/current/speed sensing on each motor with a controller to simulate the centre diff torque split.

2. Using an ABS style metering system for each wheel but this would mean some pretty serious constant on the fly calculations.

3. Using a single larger motor feeding something like a AWD style centre differential/transfer case, or using the centre differential section of someting like a Subaru AWD gearbox, these are fairly simple, can be easily removed from the rear of the gearbox, and being alloy cased are fairly light too.

Looking at this the Xtrail looks to have a very small compact gearbox already, it might be worth investigating how to remove the internals and connect the gearbox input shaft directly to the centre differential input shaft.

The main issue with setup 3 is that you will be dealing with a lot of drive train loss for the sake of a simpler conversion....

As for driving each wheel independantly, I think this would be more in the realm of theory number 2, the question is what motors to use and where/how to mount them. Hub motors may or may not suit, you could probably mount a pair standard style motors more or less in place of the differentials, facing opposing directions and directly connected to the wheel's via CV shafts, fabricating the mounts could be interesting but I think this could work quite well, you wouldn't need much more than 8-10kw motors so they shouldn't be too big to work with.

Ok, I'm done rambling now, food for thought anyway, I hope I haven't confused you too much.

Jordan.

Edit: Sorry for any overlap, takes a while to write a post when you're rambling Image
Last edited by BaronVonChickenPants on Tue, 05 May 2009, 08:11, edited 1 time in total.

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juk
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Post by juk » Tue, 05 May 2009, 20:29

"I think you would need something to compensate for front/rear speed variations"

Dude, if you have front to rear speed variations, then you're either ripping your car apart or compressing it. There are no front to rear speed variations for the rest of us.

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Post by woody » Tue, 05 May 2009, 20:30

Hi Doug & Welcome!

This is the ideal way to do it, the only problem is that motors of the right torque and speed are expensive/unobtainable (US$25K / wheel?).

For one-off conversions it's generally much easier (design / implementation / road registration) to keep the wheels / brakes drivetrain mostly intact and replace just the motor and/or gearbox which is the way most people go.

cheers,
Woody
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Johny
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Post by Johny » Tue, 05 May 2009, 20:40

juk wrote:Dude, if you have front to rear speed variations, then you're either ripping your car apart or compressing it. There are no front to rear speed variations for the rest of us.
Or put another way, unless you are using AC motors or Brushless DC motors and BOTH are running off the SAME controller, you don't really have to consider differences in wheel speed as they will be minor. Good idea if traction control is going to be considered but not necessary (IMO).

Two DC motors and two controllers and some system to feed both controllers with the same accelerator signal would work well.

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Post by BaronVonChickenPants » Tue, 05 May 2009, 20:46

juk wrote:Dude, if you have front to rear speed variations, then you're either ripping your car apart or compressing it. There are no front to rear speed variations for the rest of us.


The variances are minute but if not addressed can produce a lot of understeer, particularly in wet/slippery conditions.

Jordan.

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juk
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Post by juk » Wed, 06 May 2009, 01:50

Before i get carried away with my frustration can you explain how you get sudden and minute variances in torque that are sufficient to either compress or stretch a car or cause it to break traction spontaneously? Can you further describe how the variances are sufficiently large enough in magnitude to do this, but not result in acceleration of the vehicle. And lastly how given the fact that half the motive power is borne through another set of wheels how this effect you claim would not be twice as noticeable in a two wheel drive where the driven wheels conduct twice the motive power.

Cheers.

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Post by BaronVonChickenPants » Wed, 06 May 2009, 02:56

This is really only an issue during cornering but it is due to the length of the various arc's that each wheel takes during the corner, if all wheels travel at the same speed then some wheels will either be pushed or dragged through the corner, on dry tarmac this can cause unfavourable wear and strain on components, in slippery conditions it can get interesting to say the least.

Having actually driven vehicles with locked centre differentials (some due to experimenting, others due to blown viscous couplings) in various conditions, I know what this feels like, and if you expect to be able to drive the car safely let alone anyone else unfamiliar with the car drive it, I recommend that the issue be addressed.

Jordan.

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Johny
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Post by Johny » Wed, 06 May 2009, 03:28

Having 2 electric drive motors, one front and one back, with separate controllers would not handle at all like a locked centre differential where no difference between front to back wheels speeds would be tolerated.

The controllers would be mainly requesting torque from the motors, not an EXACT speed. The few percent of slippage between front and back might be noticed if you were monitoring current on both motors but I seriously doubt that it would be a driving hazard.

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Post by BaronVonChickenPants » Wed, 06 May 2009, 05:45

That's ok then, as long as everyone is safe.

Didn't intend to cause trouble.

Jordan.

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Thalass
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Post by Thalass » Wed, 06 May 2009, 07:51

With DC motors, you are probably right Johny. With AC I'm not sure. Certainly with two controllers it might be minor enough to not cause sliding fun, but I for one would be interested in using a single controller, with two power sections. Mostly for cost reduction, though the IGBTs make up a large chunk of the controller cost anyway, but also I have this idea that you could simulate a variable centre differential for various conditions. Locked for off road, right down to open (or close to it) for tight corners during a race. Whether it works or not... I dunno. heh.

Another issue with using two controllers, DC or AC, is that it is unlikely you will get both motors spinning at exactly the same rate, or producing the exact same torque. Rover (I think) had this issue when they tried to make a 4X4 Mini Moke for the pommy army using a second motor in the back. No doubt it would be easier to do with a pair of electric motors, though. I think some kind of control would be needed ideally.
I'll drive an electric vehicle one day.

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juk
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Post by juk » Wed, 06 May 2009, 09:43

I presume the supposition of different wheel speeds comes from the application of different torques, however whilst the road is connecting the wheels (and the chassis) the only manner in which you can have different wheel speeds is in the case of a loss of traction. The only way in which a loss of traction may occur is through poor suspension, poor road conditions or the application of much too much torque.

There is no problem with having a disproportionate amount of torque to either pair of wheels. You'll notice that a front wheel drive has 100% of the torque directed to the front wheels.

The fact is, that for a given level of performance, having 4WD will only increase the stability of the applied force rather than decrease it. If for instance the applied torque allows the rear wheels to lose traction, you'll still have the front wheels trying to pull the car straight. Since the dynamic friction experienced by the rear wheels is lower than the static force of friction experienced by the front wheels, this will indeed be the case. If in the event that the reverse is true, might i suggest modulating the throttle, transferring more weight to the front wheels and regaining traction. Given that with 4WD the amount of torque per driven wheel is half that of a two wheel drive, you'd have to be either driving on ice with the wrong tyres or driving like a hooligan.

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Post by fuzzy-hair-man » Wed, 06 May 2009, 17:25

Juk you have me confused, 4wds don't drive around (the whole time) with locked centre differentials they are either free/standard (and lockable) centre diffs or limited slip centre diffs, if you lock the centre differential and leave it on you will have either or both of scrubbing tyres or trouble steering (understeer) and wear out the components in the centre diff.

The front wheels take a wider arc when steering through a corner therefore they will need to rotate faster than the rears, limited slip and locking centre differentials don't exist for no reason, which would be the case if they could be locked the whole time. If you aren't arguing this point sorry I thought you were.

The debate to me seems to be, would the controller(s) to AC or DC motors in various configurations provide enough give/slip between the two motors to perform the role of a limited slip differential.

Thalass: They made (4 I think) 4wd moke prototypes here in Australia, but they transfered power rearwards from the front diff. There are also twinni minis though which are the twin engined version of a mini, as the mini and moke motor and front subframe are identical someone probably did the same thing to a moke, but if your looking for info twinni minis will find more info I expect. AFAIK the 2 engined moke wasn't a factory thing but I might be wrong on that. I agree tuning the 2 motors would be problematic some I think just stuck an automatic in the back to handle gear changes and concentrated on setting up the throttle... I'd suspect they dealt with the understeer by fitting a bigger steering wheel and letting the driver fight it same as they did with minis with welded up diffs. Image

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juk
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Post by juk » Wed, 06 May 2009, 18:19

You guys know the relationships between speed and load for an electric motor better than I. You know that when load changes so does the speed for a given input power. You know that given two motors, two controllers and the same duty though through two separate drive mechanisms, that they will adapt and work together. You know that there would never be anything like the mechanical relationship that a locked diff implies.

Fuzzy: many cars with either active or passive rear wheel steering the fronts prescribe a smaller arc.

Also Monster Kojima drove a twin engined suzuki baleno in the race to the sky a couple of times.

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Post by bga » Mon, 11 May 2009, 18:02

Hi LetsDoIt and welcome,

The old Hilux winds the springs transfer case and diffs up horribly if driven in 4WD mode on pavement. You can hear the tyres scrubbing to relieve the stress.

Dual "motor per diff" drive should be no problem:

Locomotives parallel up the DC motors on all of the drive axles, but slip control is a bit of a problem so that tractive effort is reduced somewhat.

AC locos run slip control on each motor(typically 5 or 6 for a heavy haul type), this typically allows about 20% greater tractive effort for the same weight than can be achieved by a DC system, as well as a few percent better efficiency.
[these machines usually have a controller per motor because of the high total power, typically 3-4 MW]

It is common in industrial plant to simply parallel sevral AC Induction Motors on a single controller to achieve roughly synchroinise the motors. [Like having tham all running on the single 50Hz mains supply]

Because ACIMs have a few percent of slip, they can be paralleled with the slip accomodating the slight ratio difference (typically well less than 1%) from front to back. There may be torque variations, but the motors can be sized differently so long as the number of poles is the same. I would expect that this would work just like a really good LSD and only need one controller, making the project cost reasonable.

Cheers

[minor edits]
Last edited by bga on Mon, 11 May 2009, 08:09, edited 1 time in total.

Agoodpaddlin
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Re: 4WD EV - XTRAIL

Post by Agoodpaddlin » Sat, 12 Jan 2019, 16:45

Hey folks. New to the forums and relatively new to EVs.
Hoping to revive this forum and possibly get a new take on it many years later.
What technologies have changed to potentially make this a viable project.

I have had many ideas about why the Xtrail (Old rail chassis version) would make a great EV.
Ive seen many mention the CVT being useful in an EV application.
I also think theres bucketloads of potential battery space in the vehicle. ie: Under rear parcel base, under rear chassis, fuel cell, vacant engine space etc.

You can pick up wrecking Xtrails for under $5k these days with engine failures (perfect) and or minor crash damage. I saw a 2005 model Ti for $1250 with no engine.

Qns to possibly re-address:
With newer AC motor tech, would the drastic modification of the entire drive train be necessary?
Is a dual motor, under bonnet solution possible to increase power to the wheels?
Would utilizing the existing CVT and 4WD setup lose too much power?
If I started with a budget of $40k, would that get a respectable conversion?

Looking fwd to discussing this further for anyone looking to flex their imagination muscles in the DIY realms. I have many ideas that are very ambitious and could be lots of fun.

francisco.shi
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Re: 4WD EV

Post by francisco.shi » Sat, 12 Jan 2019, 19:00

I am converting a Pajero. I think you can have a look at what I have been doing.
The link is https://forums.aeva.asn.au/viewtopic.php?f=33&t=5721
I think for 40k you can get a dual motor and 60kw worth of batteries.
I think the motors I have will probably fit the trail.
The battery modules will probably also fit.

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Re: 4WD EV

Post by Agoodpaddlin » Wed, 23 Jan 2019, 13:03

Heya. Thanks. This looks great.

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