A Real Hybrid XJ

chuckm65

NAXJA Forum User
Location
Orlando, FL
I drive about 50,000 miles a year for my job. It typically involves about 80-90% highway and the rest involves driving back roads in everything from residential subdivisions to logging roads.

In the past, I've used a variety of vehicles (4x4 trucks, cars, vans, etc.) I buy only used vehicles that are known for being reliable, as with four kids, I can't afford that kind of depreciation on a new vehicle. About 6 months ago, I bought a 97 XJ with 88K on it. 4.0, automatic and completely stock. I can only say I wish I had discovered Jeeps a long time ago. This thing does it all. It'll drive over anything, handles fairly well on the highway, gets up and moves when I need it to, and has a TIGHT turning radius. I can take this one vehicle and do any assignment I'm handed.

However, the mileage is not so great. I average a combined mileage of about 18-19 miles per gallon.

With gas going to $4.00 per gallon, I'll be spending about $1,000 per month just to fill this thing up.

I've been doing some research on hybrids, and the bottom line is that I don't feel anything I can buy off the showroom floor will do everything I want it to, and more importantly, I don't think it will hold up under the kind of mileage I demand. And I don't think they make 4WD hybrids yet, nor would I want to scratch up a brand new paint job on an old logging road.

I've decided lo look into the possibilities of building a diesel-electric hybrid XJ. :attom:

The advantages of using an XJ is that the suspension, body and drivetrain (at least the parts that twill remain fairly stock) are durable and when they do wear out, I can either replace them with a plentiful used parts supply, or just buy another used XJ and move over the hybrid components - most of which will outlast several vehicles.

The electric motor I think would be a good replacement for the 4.0 is a 67KW Siemens with a max power output of 150KW (thats about 90HP continuous with a max of 200HP) and the torque is unbelievable - in fact, a limiter of some kind would probably be necessary to prevent breaking stock dirve-line components.

My current need for information relates to sizing the charging generator and matching diesel engine. Depending on the type and quantity of batteries I use, I should be able to get 40-100 miles on the batteries before the diesel has to kick in to provide electricity to keep the car going, or alternately, charge the batteries when I'm stopped in traffic or parked. Essentially, the diesel / generator package should be able to put out just a little more KW/HP than I will use at 70 MPH, which is the top long-haul continuous speed I will need to maintain, even if the batteries are completely drained.

Does anyone know how much horsepower it takes to make an XJ go 70 MPH? or how I can find that out? My current XJ is doing about 2,200-2,300 RPM at that speed with LOTS of pedal left. I know that the 4.0 is rated for around 190 HP at 4,500-ish RPM, and I am hoping I am well under half of that at 70MPH.

Any info would be helpful and appreciated. Also I would love to communicate directly with someone who has experience or knowledge in charging systems. Thanks in advance.
:cheers:
 
Ford offers the Escape in an all wheel drive and Chevy offers the 1500 in a 4WD hybrid. these may be some other options if the hybrid XJ doesnt work out. If you do tackle the hybrid XJ keep us posted on the progress and out come. That would be so awesome to have a XJ that got 50-70 mpg though!!!!
 
droff85 said:
I think that the Chevy 1500 hybrid comes in an extended cab and 4WD.

Well, i didn't know about the Chevy 1500.... but again, the depreciation is a killer, plus anything Detroit builds I would have to go to them for parts when I break it.

I think I can build this thing for between 1.5-2 years worth of fuel at $4.00 for gas. Conservatively, I should triple my mileage when you consider the added efficiency of the diesel, plus the massively more efficent use of my home AC current to charge the batteries at night. The pay back should be just a little over 2.0 years.... and besides, I need a project - could even turn into a new business if I like doing it.
 
I say go for it man! Sorry I don't have any productive info for ya though :dunno:. As far as buying a hybrid escape... I think you're better off with an electric scooter...:nono:
 
paging 5-90, paging 5-90
jon, can you please report to the thread ;)
 
If all this driving is for your job, isn't your employer paying for it?

If you're self employed, obviously a different story. If so I'd go buy a cheap used Civic, and use the Jeep only when your job has you going where you need 4wd.
 
Electric motors in hybrids are not for highways. They're for cities. That's why they get better city mileage than highway mileage.

If you want better mileage, look for a diesel motor to swap in.
 
IslanderOffRoad said:
If all this driving is for your job, isn't your employer paying for it?

If you're self employed, obviously a different story. If so I'd go buy a cheap used Civic, and use the Jeep only when your job has you going where you need 4wd.
I am self-employed. It's very hard to tell sometimes whether or not I will need 4WD - and it's my observation that this XJ seems to do almost as good in 2WD as a an old chevy truck I had a couple of decades ago did in 4WD.

As for a civic - I'm 6'4" and 320 lbs - I don't get in a civic... I put it on... at least that's what it feels like. Also, it's helpfull in my job to sit a little higher than a typical squirrel while driving around off of the highway. Plus it would just be another vehicle I have to insure & maintain.

If I can pull this off, I think the XJ hybrid will be the only vehicle I'll need for several years to come
 
Shavenyak said:
Electric motors in hybrids are not for highways. They're for cities. That's why they get better city mileage than highway mileage.

If you want better mileage, look for a diesel motor to swap in.

My understanding is that the first leg which would be run off of the batteries is what will really increase efficiency. In terms of the cost of the electricity I use to charge the batteries and the distance I go, I've seen cost comparisons that equate to over 100 miles per gallon - that's at $3.00 per gallon. As the cost of gas goes up, that comparison only get's more favorable for battery power since most electricity in this country is coal-fired - ergo its cost does not rise with that of oil. It will rise some, since petroleum fuels are used to some extent in getting the coal out of the ground - but I'm sure there are people here who know more about that than I do.

Now, since the diesel would only be used to drive the generator, it will run at a constant speed. It will only kick on when the batteries reach a certain level of discharge AND will be configured to run flat out at a constant throttle - the most efficient way to run any internal combustion engine. The electricity produced will be consumed by a combination of running the electric drive motor and recharging the batteries.

The efficiency ratios for electrical generation are in the 90+%, as are the conversion back to mechanical power in the drive motor.

Since a diesel, pound for pound, pulls a lot more power out of it's fuel than a gasoline engine and since it will be run in such a way to maximize its efficiency, combined with the low cost of the charge-up I get from home at night, I truly believe that I can get a cost per mile as low the equivalent of 60+ MPG
 
Ok, I found a Brake Horsepower curve for a 4.0 liter.

http://www.wjjeeps.com/misc/curve_40.jpg

It shows about 90 HP at 2,300 RPM, but I assume that is it's maximum horsepower at that speed (i.e. with the throttle wide open).

So does it make sense that at 70 MPH with LOTS of pedal left that I am using something (hopefully considerably) less than 90 HP?
 
chuckm65 said:
I am self-employed. It's very hard to tell sometimes whether or not I will need 4WD - and it's my observation that this XJ seems to do almost as good in 2WD as a an old chevy truck I had a couple of decades ago did in 4WD.

As for a civic - I'm 6'4" and 320 lbs - I don't get in a civic... I put it on... at least that's what it feels like. Also, it's helpfull in my job to sit a little higher than a typical squirrel while driving around off of the highway. Plus it would just be another vehicle I have to insure & maintain.

If I can pull this off, I think the XJ hybrid will be the only vehicle I'll need for several years to come

How much fuel do you think you'll save?

You say you're spending $1000 per month on fuel, thats 12k per year. If you doubled your mileage from this, lets say you're now spending 6k per year.

How much do all these parts cost? How long is it going to take you to get it done? You're self employed, so you know what your hours are worth... plus this means taking your XJ off the road for quite a while to accomplish... now you're buying another vehicle for the interm, which I know, you could sell when you're done, but there's still cost assoicated with it.

If you want to do this project, do it for the coolness factor, not for the MPG.
 
IslanderOffRoad said:
How much fuel do you think you'll save?

You say you're spending $1000 per month on fuel, thats 12k per year. If you doubled your mileage from this, lets say you're now spending 6k per year.

How much do all these parts cost? How long is it going to take you to get it done? You're self employed, so you know what your hours are worth... plus this means taking your XJ off the road for quite a while to accomplish... now you're buying another vehicle for the interm, which I know, you could sell when you're done, but there's still cost assoicated with it.

If you want to do this project, do it for the coolness factor, not for the MPG.
Well, if I triple my mileage (actually the correct term should be "fuel efficiency", since some of my cost will be for diesel and some will be for electricity from the grid), it would cut my cost down to a third, say $350 per month, or a savings of $600-700 each month! That adds up quick.

My reasons for wanting to do it listed by importance to me:

1) this sounds like a fun project
2) the long term pay-off in reducing my fuel costs
3) politics - while I am not Green by any stretch, I hate having no choice other than to pay whatever they demand at the pump
4) the long term savings in learing how to do this stuff myself
5) I've always been intrigued by the idea of cheaper energy - It's just now that I am coming to a point in my life where I can start playing around. I'm also looking into solar panels and/or windmill generator for my home

But I still need to figure out how many horsies it takes to make this brick go 70MPH
hasta
 
The cool thing about electric motors is that they make peak torque at 0 RPM.
 
you realize this is will be a very expensive and difficult project, right? its not just going to be "ok, drop in a diesel gen set and an electric motor with some batteries in a weekend then back to work on monday"

the battery tech is lagging right now, so you will lose a good portion of cargo space to batteries and add 1000 or so lbs, you will need to swap in a 5 speed since the auto is optimized for a gas engine, you'll have to rig some sort of motor to the P/S pump unless you want to armstrong it, vacuum pump for the brake booster, etc, etc, etc

I would be very surprised if you could pull this off for under $20k in a years time (and do a decent job)
 
FoMoCo said:
you realize this is will be a very expensive and difficult project, right? its not just going to be "ok, drop in a diesel gen set and an electric motor with some batteries in a weekend then back to work on monday"

the battery tech is lagging right now, so you will lose a good portion of cargo space to batteries and add 1000 or so lbs, you will need to swap in a 5 speed since the auto is optimized for a gas engine, you'll have to rig some sort of motor to the P/S pump unless you want to armstrong it, vacuum pump for the brake booster, etc, etc, etc

I would be very surprised if you could pull this off for under $20k in a years time (and do a decent job)
You forgot to mention the electrically powered air conditioner, finding space for coolant systems for the diesel and the electric motor (none of the newer ones with good power ratings are air cooled), sensors to monitor temperatures, pressures, amperages (charging & draw) battery status, some sort of computerized control of all of it plus a display so I can monitor things during development, and about 150 other things I haven't yet considered.

BTW, the electric motor will be mounted directly to the input shaft on the transfer case. 3,500 rpm (max rated continuous for the motor) just happens to get me 70MPH with my little 29.5" diameter tires (245-75 tires on 15" rims).

I am completely in research mode at this point - I need to see what options are out there for the major components - I might spend 6 months or more just doing research and picking the brains of whatever experts I can find. Hell, I might even steal my sons bike and electric it up. Could do the same with my daughter's scooter she uses on campus.

And ultimately, once technology and supplies improve, I should think the diesel will be replaced with a fuel cell - now there's some exotic stuff

And I had figured $20-25K plus that much or more in my time. But it's a hell of a lot better than watching TV. Nothing worth doing is either cheap or easy.

I still want to know, short of mapping out my thottle position at 70MPH and then putting it on a rear wheel dyno, how can I get a reasonable guestimate of HP my 4.0 is putting out at that speed?

Any ideas? Thanks
 
Ok, just wanted to make sure you realized the massive scope of this conversion. also I'd strongly recomend some sort of trans, even if its a 2 speed, since you say 90% of your driving is highway. you probably won't get your best efficiency running right at the max 100% duty cycle RPM, and motor life will likely be shortened.

keep us updated for sure, sounds like you're really serious about it and know your stuff
 
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