[brian_]

is 2 or 3 motors a lot? the few swaps ive seen for these always have dual motors. and tesla uses dual and tri motor configurations in all vehicles. I just figured i needed that many for this plan.

All AWD production EVs use at least two motors, simply to have at least one at each axle; this avoids a shaft down the length of the vehicle, and avoids a differential between axles. A few EVs (and hybrids) use two motors at one axle - a single motor per wheel - mostly to allow them to independently control the torque applied to each wheel, partially to avoid the axle differential, and perhaps to get twice as much power using available motors and inverters.

Most DIY conversions use a single motor, even for 4WD, because the builders find that easier and probably less expensive.

Tesla has a single motor in 2WD models (assuming that they still sell some of the those), two motors (one per axle) on most AWD models, and three motors (one in front, two at the rear) in the highest-performance models (only the Model S Plaid so far, but planned for the Roadster and whatever else they might eventually build). The Semi - if it is ever produced - will have one motor per rear wheel... with the motors installed right in the beam axles.

In the Cherokee, do you intend to keep the beam axles front and rear, or are you planning (or willing) to replace that with independent suspension at front, or both? If you still have an original beam axle you can only drive it with one motor, so with both original beam axles you have two motors at most. Motors mounted on beam axles are possible, and would certainly work, but are not desirable in car or SUV. A beam axle with two separate inputs (pinion shafts) to connect two frame-mounted motor to one axle would be interesting, but custom, strange, and not worthwhile.

 

[brian_]

...
With the Jeep being a unibody I was going to get a donor frame mounted underneath ...

And so I've just got the body basically that I'm keeping and I'm going to be changing out everything else and upgrading and beefing up.

Ah, so you intended to build a custom truck, and set a Cherokee body on top of it. That's very different from converting a Cherokee, although the Cherokee body limits the truck to a size which is too small to reasonably tow several tons, on the basis of stability.

 

[brian_]

In the UK the 4.0 Auto XJ is rated for 3250kg which is 7165Ib's
Manual's seems to be rated a lot lower at 2500kg = 5511lb's

Jeep Cherokee (1993 - 2001) 4.0 Classic 5d Auto

3250kg​

Obviously we use a different hitch type Euro vs US - but it would be with the same frame/chassis. Don't know if there are axle differences between the man/auto? but if there are it would be simply to fit up-rated axles.

Manual transmissions in light-duty vehicles have lower towing ratings than automatics, because drivers tend to burn out clutches with heavy loads on light vehicles.

European towing ratings are routinely much higher than North American ratings, and it has nothing to do with structure, axles, suspension, brakes, or the hitches (the Euro standard for recreational trailers is a 50 mm ball, that's slightly under 2" diameter). The difference is due to different conditions, including lower speed - in most European countries cars towing trailers are limited to 80 km/h (50 MPH) and wouldn't normally go very far per day, while here people expect to tow at 100 km/h or more all day. Euro trailers are also different, with the mass more concentrated in the middle for better stability so they can get away with less tongue weight, so handling the weight on the hitch is less of a concern.

 

[brian_]

A game changer on modern vehicles in Europe (do you have it in the US?) is TSP (trailer stability program) where vehicle sensors monitor for snaking/yaw while towing and use the ABS/Traction systems to counter act it & correct it.

Yes, electronic trailer stability programs are now common on North American vehicles which are intended for towing; that's not a factor in the difference between Euro and North American ratings. Of course an EV conversion is unlikely to keep any such system functional, and most vehicles being converted (including the Cherokee in this case) never had this capability.

 

[brian_]

Also we have friction hitches (do you have these in the US?) where the caravan hitch has friction pads which clamp a dry tow ball, again to reduce snaking.

The friction-on-ball couplers commonly used in Europe are not used here at all. One reason is that tow balls here are generally stud-mounted, so clamping on the ball risks loosening it in turns. Instead, there are crude sliding bar devices, and various schemes integrated with weight-distributing (WD) hitch systems. WD hitches are generally not used on Europe, but are common here on recreational trailers over a couple of tons. WD is even required above a certain trailer weight for some vehicles, on the assumption that the corresponding hitch weight will be too high; North American trailers run a higher tongue weight (as a fraction of trailer weight) than in Europe.

For the proposed size of trailer, especially with a vehicle as short in wheelbase as the Cherokee, the builder should probably assume that a WD hitch will be used.

By the way, the unstable motion that Europeans call "snaking" is what North Americans call "sway".

 

[brian_]

There's no reason a manual transmission can't be designed with a better towing capacity rating, all manual (proper) Landrovers can tow upto 3500kg - 7700Ibs (which is the maximum allowed for the 50mm euro ball hitch) Can go higher upto 'I think' 4000kg (8800Ib) with coupled brakes and a different hitch but then you start getting into 'commercial' type driving licences.

What would normally result from the lower towing weight limit implied to manuals is if they have reused a transmission/clutch from a lower powered/smaller vehicle - the Landrover Freelander series I for example re-used a car manual transmission and the clutch was no good for HD off roading or towing.

Again, the biggest problem is typically not the transmission itself, it's the clutch. Yes, a very low first gear ratio can be selected to make it easier on the clutch, and in a 13-speed heavy truck transmission that's fine, but in a light vehicle 5-speed that's an undesirable compromise. A high-capacity clutch could be used, but people don't want a heavy and long-travel clutch pedal. And then there's generally incompetent non-commercial driver which the vehicle manufacturer can't control (unlike the automatic transmission that they can), which may be the biggest factor.

The net result is that in a vehicle like a Cherokee, the towing rating will be lower with the manual transmission, regardless of what could be done with a different vehicle under different circumstances. In full-size pickup trucks, when they were still available with manual transmissions, even the manuals had high towing capacity... but almost no one wants to drive those things. The Cherokee is sturdier than a Freelander, but still basically just a car; it's not a commercial vehicle. Some Cherokees have the same transmission as some pickup trucks, so for some of them this isn't the vehicle's towing limitation.

The details don't matter to an EV conversion anyway, except that if a manual transmission is used the lower towing rating rated to the clutch can be ignored - the electric powertrain will become its own limitation, and no one will determine that for the builder. The strongest manual found in a XJ Cherokee is probably the New Venture Gear 3500, but even though it was used in full-sized pickup trucks it would be marginal for the load considered in this conversion... regardless of the clutch.

 

[brian_]

When vehicles are certified for towing in the UK, the trailers used are not caravans - they are usually smaller/lower and more dense - so less effected by cross winds, so while 'legally' you could tow a 3.5 tonne caravan (not even sure if there is a 3.5T caravan for sale in the UK - most max out arround 2T) its probably not recommended - due to cross wind stability.

The caravan (travel trailer) issue applies here, too. While towing rating were determined inconsistently - and often questionably - for many years, an SAE testing standard was developed a couple decades ago and is now is widespread use: SAE J2807. It defines a trailer size (including frontal area) for a given trailer weight, which corresponds to a cargo trailer that is significantly smaller than a typical travel trailer of that weight. The standard even gives specific suitable trailer models for example weights... and they're cargo trailers that are both narrower and lower than travel trailers of that weight.

Trailer weight ratings here are assigned by vehicle manufacturers, and have no legal force.

In addition to the trailer weight limit, many vehicles also have a trailer frontal area limit, which is widely ignored. The purpose of the limit is to reflect the sustained power demand, and therefore load on the powertrain, due to aerodynamic drag. Most travel trailers will exceed the frontal area limit for many vehicles which are used to tow them.

 

[brian_]

Would using a transmission increase or decrease the towing capacity versus not using a transmission in an ev conversation?

You will have a transmission. Most EVs have a fixed-ratio (or "single speed") transmission, because the electric motor works acceptably throughout the vehicle's speed range without changing the gear ratio ("shifting"). Many conversions use the vehicle's original transmission only because that is the easiest method for converting those vehicles, but a multi-ratio (e.g. five-speed) transmission does provide the option to use a lower gear at low speeds and higher gear at high speed, keeping the motor closer to the ideal speed and possibly heating up less under heavy load (which would help reliability when worked hard).