# 1999 Jeep TJ - Design Stage



## prdufresne (Sep 3, 2009)

Hi guys, I'm just in the design stage of my project, and I'm hoping to get some feedback on the best approach for my project.

My 199 Jeep TJ comes standard with an 4.0L I6 engine. I'm running 33" tires on my otherwise stock drivetrain. This is a trail truck, so it rarely comes out of the garage unless we're heading for the trail.

On that basis, here are a few design criteria:


Should deliver excellent torque at low speed
Should be capable of attaining highway speeds
Regenerative braking is a must to control the vehicle when going down obstacles.
Range is a consideration, but I'm pretty sure I won't achieve the necessary range to drive it from home to the trail, so I will likely tow it to the trail. The trails are usually relatively short, less than 30 miles round trip.
My preference is to go all-electric, but to avoid towing, I'm willing to consider a hybrid configuration, but I'm not sure where to start.
Okay, so the first, and most important decision to make is WRT the drivetrain. My initial plan was to dispose of the transmission and transfer case along with the engine. Since I want regen braking, I'm already going to AC motors. The question is, can I get the necessary power band. So my options are (in order of preference)"


*Two motors mounted where the transfer case sits today*. One connected to the rear drive shaft, the other to the front. This configuration allows me to easily control whether I'm running in 2 or 4 wheel drive by simply switching off the front motor. It also allows me to do interesting things like lock the rear while spinning the front or vice versa. The question is can I generate the required torque without burning out motors and controllers.
*Two motors on a common shaft attached to the transfer case input shaft.* This will allow me to switch my gear ratios for on and off road driving. My transfer case is effectively direct drive in High gear, and 2.72:1 in low gear (although this could be upgraded to 4:1).
*One motor attached to the transmission.* This allows me a greater range of gear ratios for on-road and off-road use, adds weight and reduces the space available for batteries under the hood. This approach does allow me to eliminate one gear and use it as a parking gear.
Thoughts, comments, critiques and questions welcomed!


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## dragster (Sep 3, 2008)

HI
Just remove the engine no need to reinvent the wheel.


http://www.htcracing.com/electriccar.htm


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## racunniff (Jan 14, 2009)

prdufresne said:


> *One motor attached to the transmission.* This allows me a greater range of gear ratios for on-road and off-road use, adds weight and reduces the space available for batteries under the hood. This approach does allow me to eliminate one gear and use it as a parking gear.


That gets my vote, partly because it was the choice that I made - http://electrojeep.blogspot.com

Although I have not (yet?) gone the "eliminate one gear and use it as a parking gear" route. Any suggestions on how to do that?


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## prdufresne (Sep 3, 2009)

racunniff said:


> That gets my vote, partly because it was the choice that I made - http://electrojeep.blogspot.com
> 
> Although I have not (yet?) gone the "eliminate one gear and use it as a parking gear" route. Any suggestions on how to do that?


I've read your blog, and I've learned a great deal from it, so thank you for that.

I'm not an expert on transmissions, in fact I'm not even a mechanic. Assume, though, that you want to convert 5th gear into a parking gear. I believe you would have to remove the 5th gear cog from the layshaft (which is rotated by the input shaft) and weld or find some means to prevent the 5th gear output gear from spinning when it's engaged.










That's probably an over-simplification, but essentially, you don't want the output shaft to spin when engaged in 5th gear or first gear. I think with moth transmissions, first gear is easier to convert because it's usually next to a surface that it can be welded to.


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## prdufresne (Sep 3, 2009)

dragster said:


> HI
> Just remove the engine no need to reinvent the wheel.


I understand the benefits of that approach, but I also lose the benefit of controlling front and rear separately.

I have been able to do all the speed calculations without any trouble, but I haven't figured out how to calculate the torque numbers, or figure out if running at a higher voltage can compensate for the gear ratio.

I would really prefer to get rid of the transmission and transfer case.


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## gte718p (Jul 30, 2009)

I like option 1. It depends on the type of wheeling you do, and what other work you have or want.

I know rock crawling and trail running. I don't do mud and snow. Option one woud give you front and rear dig which would be cool. However unless you have some aftermarket axles I doubt you would have enough gearing to spin the tires. Shove some rockwells under it and that would just be cool.

Thats just something I thought would be notionally cool. You left out way to many details for me to really make any usefull comments.
Well start with
Experiance?
Budget?
expectations?
type of wheeling?


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## Woodsmith (Jun 5, 2008)

If you are determined to loose the transmission and go with two axles then it may be worth looking at having the motors geared right down before joining onto the propshafts. Top speed won't matter if you are towing the truck out to play but not having a clutch will. With direct drive you may want to have a method of disconnecting the drive to save the wheels overspeeding the motor and generating lots of random currents.
Though you could put the truck on a trailer.

I was wondering if wheel motors from a forklift complete with gear reduction may be a way to go? Could be heavy though.
You could change to portal axles for rock hopping, that would give you double reduction and dropped hubs for extra ground clearance. Axles off the Unimog or Volvo trucks might be an option. I would think you would still need to gear down the motors though.

If you know a good tranmissions place you could try taking the epicyclic gears from an autobox and having it fixed in a low gear. Chuck out eveerything that is not needed. Bolt or weld up any parts that are clutched or braked and put the whole lot inside a steel or aluminum pipe on the end of the motor. That would give you a simple and strong set of fixed reduction gears for each motor.

The more I think about this, if you are not using on the road then, I would be tempted to say build a rock hopper from scratch using the best axles, best drive system to the motors and a space frame for strength and light weight. Invest your weight in the motors and batteries.


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## prdufresne (Sep 3, 2009)

gte718p said:


> I like option 1. It depends on the type of wheeling you do, and what other work you have or want.
> 
> I know rock crawling and trail running. I don't do mud and snow. Option one woud give you front and rear dig which would be cool. However unless you have some aftermarket axles I doubt you would have enough gearing to spin the tires. Shove some rockwells under it and that would just be cool.


Snow is less of a concern, but mud is a reality. I'd be concerned about the extra weight the Rockwell's would add to the truck, but then I could attach the motor directly to the axle and dispose of the driveshafts. Could be a future consideration.



> Thats just something I thought would be notionally cool. You left out way to many details for me to really make any usefull comments.
> Well start with
> 
> Experiance?


In EV, none. I have experience working on my Jeep, and am pretty handy with electrical circuits, but I'm not an EE. That said, I had no mechanical experience when I swapped out my clutch, installed an SYE kit in my transfer case and installed all the upgrades to my Jeep.



> Budget?


TBD. I was planning for the conversion to cost around $10,000 and I was hoping to source the motors through someone I know that works for Yale Forklifts or another guy repairs motors for Siemens to save some bucks.



> expectations?


A Jeep that can, at a minimum, perform the same as my current ICE Jeep with it's 4.0L I6 on the trail. Street performance is less of a concern, I can tow it out if necessary, but ideally it should do both.




> type of wheeling?


I'm in Eastern Canada, so our wheeling is a mixture of muddy trails and rock climbing. I'm not going to Moab on a regular basis, but my preference is rock. Here though, you often have to cross the mud to get to the good rocks.


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## NickRummy (Aug 17, 2009)

I'm still fresh to the EV world but I have been reading on this site A LOT about an offroad setup I've been trying to develop. So take my input with a grain of salt 

From my research if you want your truck to perform as well as it did with the ICE in it then you need to replace it with a motor of equal performance. That's going to be quite a task if you ask me? 

Gear reduction IS YOUR FRIEND. In my project I'm trying to eliminate the transmission just for the sake of weight and space. The problem is that throws out a lot of gear reduction that is needed to amplify your motor's performance to the wheels. What I'm planning on doing is running (2) transfer cases in line since the truck I'm working with has REALLY small transfer cases. The first will be modded to 4:1 reduction and the second will be a stock 2.268:1 reduction giving me 9.072:1 overall reduction through the (2) t-cases. Stock reduction with the transmission in first gear after the stock tcase is 8.28:1 so I'll actually have more reduction than the stock setup in low range 1st gear. I'll also still be able to go back to high range in each transfer case giving me a few other gear ratios to use for cruising on open trails. 

I think you're going to have to have a really big wallet to get your jeep to perform like it does with the ICE especially if you want to go offroad. I found this thread a while back which was interesting.

http://www.diyelectriccar.com/forum...limited-conversion-34217.html?&highlight=jeep

Here is a great post from that thread just to give you an idea of what you're in for

http://www.diyelectriccar.com/forums/showpost.php?p=130109&postcount=3


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## prdufresne (Sep 3, 2009)

NickRummy said:


> I think you're going to have to have a really big wallet to get your jeep to perform like it does with the ICE especially if you want to go offroad. I found this thread a while back which was interesting.
> 
> http://www.diyelectriccar.com/forum...limited-conversion-34217.html?&highlight=jeep
> 
> ...


ThanX for the feedback. I've read through those threads. I think though, there are a couple of things that are being overlooked:

If I build the Jeep with two motors, one fore each axle, I'll be doubling the torque available when in 4 wheel drive. With the ICE, when I'm running in 4WD, I'm dividing the engine power between the two axles, effectively cutting my output power in two. With two motors, I'm not doing that, so the numbers have to be adjusted accordingly.

I've looked at my current gear ratios, and I think by adjusting them, I can gain some performance. I don't mind the idea of a dual transfer case, but I was hoping to avoid it. If I need the gear reduction then, I may have to go that route. I can pick-up another NV231 or a Dana T-casse fairly cheap and re-gear it to provide 4:1.

My current gear ratios are:

Axle: 3.73
Transfer Case: High: 1, Low: 2.72
Transmission (1st to 5th): 3.83, 2.33, 1.44, 1, 0.79

Doing the math, that gives me a 39:1 in 1st gear in 4L, but since I'm running two axles, I have to divide the engine torque in two.

So, I can do a few things like re-gear my axles, but I think the best I can get for my axles is 5.13.

Great feedback. Keep it coming.


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## gte718p (Jul 30, 2009)

Based on your reply I would have to go with swap the motor for and electric, keep the drive train, and buy the largest lithium pack your budget will allow.

There are a couple of reasons. First mixing rock crawling and mud is not fun or easy. Mud you need high wheel speeds to clear the tread, rocks you need very very slow wheel speed with tons of torque. Its very hard to do that with a fixed gear ratio. Depending on the RPM range of your motor it could be possiblem but its a lot of engineering to make it work, and I suspect you'll end up with some compromise that fails at both.

If you are absolutely set on eleminating the trans. You could take the reduction section out of two toyota cases with the 4.7 reduction gears and mount that directly to the motor face, run that to the axles. http://www.marlincrawler.com/transf...drive-unit-right-hand-output-gear-drive-tcase You'll still need at least 1 ton axles inorder to be able to get enough gearing in the axles. The lowest I've seen for a Dana 44 is 5.88. I don't think thats going to cut it. Something like the 7.17 available for the Dana 60 may be closer, but I haven't run the numbers. Thats still a lot of custom design and machining. If your up for it it would be very cool.


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## Woodsmith (Jun 5, 2008)

prdufresne said:


> If I build the Jeep with two motors, one fore each axle, I'll be doubling the torque available when in 4 wheel drive.


You would only get that doubling of torque when all the wheels are equally loaded. When rock hopping you would only get the torque of one motor at an axle. 

If you have a locked transfer box and lockers in the axles on an ICE then when you are waving wheels or axles in the air all of the engine torque will go to the wheel with the most grip.
If you have a front and rear motors then you will only get the torque from one motor at the wheel with the most grip. All the torque available in the other motor will be lost to the axle waving in the air. Essentially you have lost half your available torque.

You could have a transfer box in the middle driven from two motors, one in the front of the box and one in the back of the box. Then you will have all your torque at whichever wheel has the most grip.

I don't know your transfer box but I do know Land Rover ones. 
So for example:
The input to the Land Rover transfer box could be adapted to one motor. That will drive the vehicle. The PTO output could be installed on the back of the transfer box and a second motor connected to it. The PTO selector will then allow a second motor to be connected to add to the power and torque available when needed off road and disconneted when on the road.

The gear ratios would still be too high though.


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## NickRummy (Aug 17, 2009)

prdufresne said:


> ThanX for the feedback. I've read through those threads. I think though, there are a couple of things that are being overlooked:
> 
> If I build the Jeep with two motors, one fore each axle, I'll be doubling the torque available when in 4 wheel drive. With the ICE, when I'm running in 4WD, I'm dividing the engine power between the two axles, effectively cutting my output power in two. With two motors, I'm not doing that, so the numbers have to be adjusted accordingly.
> 
> ...


What is the stock power output of the 4L ICE?

I'm not sure how these big electric motors work in these trucks (so correct me if I'm wrong here) but in the RC world I've built a few RC trucks that have two motors. One for each axle. One of the biggest problems (which can be turned into an advantage) was motor stall. When you're climbing a hill there will obviously be a great load on the motor powering the rear axle and the load on the front axle is a lot less. Power will travel to least resistance so you'll end up getting more power to the front motor slipping the tires while the rear wheels struggle to turn over. 

I think that no matter which way you go you're going to have to have the same drive shaft rpm regardless. Whether it be direct drive with a gear reduction unit and a motor for each shaft or one motor through a t-case. 

31" tire has a roll out of about 97.34". So technically speaking with a drive shaft speed of 200rpm and 3:73 diff gears you're wheel is spinning at 53.6rpm. That's 217.4 feet per minute or 4.94mph. 

Only reason I'm mentioning this is because going direct drive from a motor to spin a shaft at 200rpm is going to be a lot of reduction!


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## prdufresne (Sep 3, 2009)

gte718p said:


> There are a couple of reasons. First mixing rock crawling and mud is not fun or easy. Mud you need high wheel speeds to clear the tread, rocks you need very very slow wheel speed with tons of torque. Its very hard to do that with a fixed gear ratio. Depending on the RPM range of your motor it could be possiblem but its a lot of engineering to make it work, and I suspect you'll end up with some compromise that fails at both.


I agree, yet I tend to tackle both mud and rock in 1st gear, in 4L. So I wasn't expecting to need a huge difference in gearing to handle both. 

Here's a small photo album of photos to give you an idea of the terrain we're working with.

http://flickr.com/gp/[email protected]/4o82dv



Woodsmith said:


> You would only get that doubling of torque when all the wheels are equally loaded. When rock hopping you would only get the torque of one motor at an axle.
> 
> If you have a locked transfer box and lockers in the axles on an ICE then when you are waving wheels or axles in the air all of the engine torque will go to the wheel with the most grip.
> If you have a front and rear motors then you will only get the torque from one motor at the wheel with the most grip. All the torque available in the other motor will be lost to the axle waving in the air. Essentially you have lost half your available torque.


Understood. I'm running open differentials at the moment, but the NP231 is chain driven so that the front and rear drive shafts always spin at the same speed. I intend to install some selectable diff lockers in the future. I do typically try to keep all 4 wheels on the ground though, 3 usually and 2 at a minimum... Most of our trail activity doesn't even register on the speedometer, it's so slow.

Hmmm....

I ws really hoping to do "dig". I'll have to start looking at motor specs and do the math...


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## prdufresne (Sep 3, 2009)

NickRummy said:


> What is the stock power output of the 4L ICE?


I've been struggling to find this information. This was the best I could find:










So on average, I guess I'm getting about 225lbft.

Also, so more complete calculations. I was using 3500 RPM as a max. motor speed in these assumptions.


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## NickRummy (Aug 17, 2009)

225ft-lb is going to be a tough motor to find  Even if you divide that into two as you're thinking for doing direct drive you're at 113ft-lb per motor. Max RPM looks to be similar to an electric motor.


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## Woodsmith (Jun 5, 2008)

Just a thought....

I wonder if there is a standard industrial worm drive gear box that you could find in a breakers yard like these:








You could mount a motor on it and use the worm drive reduction to your transfer box.
Advantages are a very low gear ratio and non reversing drive so the best possible 'engine braking' when dropping down a rock.

It does mean that your motor is sideways, maybe under a seat and direct coupled to the box shaft or you could mount the motor next to the box and couple it with a chain or toothed belt.


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## PartsMan (Aug 20, 2009)

prdufresne said:


> Doing the math, that gives me a 39:1 in 1st gear in 4L, but since I'm running two axles, I have to divide the engine torque in two.


Yes but a Jeep 4.0 makes a couple hundred foot pounds of torque.

Multiply that by 39 and all you need is two motors that make 3900 foot pounds at low rpm without getting hot. 

I keep the transmission\transfer and be able to climb strait up at a low amperage.


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## prdufresne (Sep 3, 2009)

NickRummy said:


> 225ft-lb is going to be a tough motor to find  Even if you divide that into two as you're thinking for doing direct drive you're at 113ft-lb per motor. Max RPM looks to be similar to an electric motor.


The problem is I'm not sure if that graph was measuring torque at the engine's output shaft or at the wheel, which would make a big difference.

This is where I'm struggling. As I understand it, electric motors provide more torque at low RPM then gas engines do. I should, in theory, be able to get equal power to the ground with less gearing. Or so I thought. I expected to have issues with highway speeds in a direct drive system, not with rock crawling.


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## Woodsmith (Jun 5, 2008)

prdufresne said:


> Here's a small photo album of photos to give you an idea of the terrain we're working with.
> 
> http://flickr.com/gp/[email protected]/4o82dv


Nice photos.
This is what I built to play with 19 years ago when straight forward Land Rover off roading became boring.

It started off as one of these:

















Then I converted it to this:

























This is the insides of the 3 speed remote mount transfer box I designed and built using standard LR gear wheels. It had 3 axle outputs and a PTO.


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## Woodsmith (Jun 5, 2008)

prdufresne said:


> This is where I'm struggling. As I understand it, electric motors provide more torque at low RPM then gas engines do. I should, in theory, be able to get equal power to the ground with less gearing. Or so I thought. I expected to have issues with highway speeds in a direct drive system, not with rock crawling.


You will be able to get a motor to do that 'massive torque at near zero rpm' thing but the motor will be working really hard, drawing lots of amps and being very inefficient. It would be better for the motor and your battery pack if your motor was doing the hard work while running at its nominal rpm.


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## NickRummy (Aug 17, 2009)

prdufresne said:


> As I understand it, electric motors provide more torque at low RPM then gas engines do.


Electric motors can produce their max amount of torque at 1 rpm which an ICE can not do. However, the size of the electric motor is what determines the amount of torque it can produce. A motor able to produce 225ft-lb is going to be massive and have a massive current draw.


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## PartsMan (Aug 20, 2009)

PartsMan said:


> Yes but a Jeep 4.0 makes a couple hundred foot pounds of torque.
> 
> Multiply that by 39 and all you need is two motors that make 3900 foot pounds at low rpm without getting hot.
> 
> I keep the transmission\transfer and be able to climb strait up at a low amperage.


Wait. My bad. You would "only" need 2100 foot pounds if you kept the axle gears. 1500 ft lb if you switch to 5.13:1 gears.

Keep the tranny, throw a 4:1 transfer case kit and some 5.13:1 gears in it and you only need a 100 ft lb motor.


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## prdufresne (Sep 3, 2009)

PartsMan said:


> Wait. My bad. You would "only" need 2100 foot pounds if you kept the axle gears. 1500 ft lb if you switch to 5.13:1 gears.
> 
> Keep the tranny, throw a 4:1 transfer case kit and some 5.13:1 gears in it and you only need a 100 ft lb motor.


That's my question though, when I look at that power curve, if that's measured at the axles, then I need much less then that don't I. I'm just not sure whether those numbers are measured at the engine or at the wheels.

*Nevermind, answered my own question. Engine specs indicated 235 lb-ft @ 3200 RPM*. I guess I should appreciate the engine I have, as it appears to have excellent torque even at low RPM.


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