Rear Drive Unit Continuous Rating?

[Scrappyjoe]

Hello,

I need to decide whether to use my Outlander rear drive unit as a primary traction motor or a secondary one (in a parallel hybrid configuration). A key issue here is the continuous rating of the motor.

My research into the continuous rating of the Outlander rear motor (pre 2022) is that it is rated for 85kw peak, but there's little on the ground on the continuous rating. My math suggests that 30kw will be too little for highway driving, 35kw might work, and 40kw will be fine.

Has anyone done any empirical research into the subject? What are your findings?

[johu]

Continuous rating is pretty much irrelevant in road use that's why you never find anything on it. Think of it, 85 kW will suck dry any reasonably sized battery pack in about 30 minutes.
The Leaf motor in Touran can't sustain 180 kph for very long but is perfectly happy at 140 kph. Same goes for the battery as well

[Scrappyjoe]

If it is irrelevant, how do I reason about motor sizing? My vehicle is about 2000kg. Stock motor puts out 81kw. Aerodynamics are really poor. Actually, you can probably think of a Touran with 5 heavy adults plus luggage. Highway speed will not exceed 100km continuously.

[johu]

You can stick your cars aerodynamic data (width x height x Cw) into into an aerodynamic drag calculator and it will spit out the power needed at 100 kph and no incline. It will be surprisingly low. Don't know your vehicle but I'm guessing in the 20-30 kW ballpark.

Now you can say "but there can be inclines". Yes, but they don't go on for very long unless you're planning for pikes peak.

[arber333]

If it is irrelevant, how do I reason about motor sizing? My vehicle is about 2000kg. Stock motor puts out 81kw. Aerodynamics are really poor. Actually, you can probably think of a Touran with 5 heavy adults plus luggage. Highway speed will not exceed 100km continuously.

Outlander rear motor is appropriate for 1t cars 35kw cont. 100kw max power. 2t vehicle are better off with Leaf motor 80kw cont. and 200kW max... if your inverter will cope thatis...

[Scrappyjoe]

That’s the thing I am trying to square, arber.

My math suggests that 35kw cont, 85kw peak should be sufficient for a 2t vehicle with performance characteristics of a microbus from 1989 - that is, slow, but able to keep going at 100km/h continuously.

After all, the T2 buses could go 100km/h and had 45kw peak engines.

But the EV common sense suggests this is not appropriate. Now I don’t know whether I should trust my math, or common sense.

[arber333]

That’s the thing I am trying to square, arber.

My math suggests that 35kw cont, 85kw peak should be sufficient for a 2t vehicle with performance characteristics of a microbus from 1989 - that is, slow, but able to keep going at 100km/h continuously.

After all, the T2 buses could go 100km/h and had 45kw peak engines.

But the EV common sense suggests this is not appropriate. Now I don’t know whether I should trust my math, or common sense.

Well it will work because it is liquid cooled. But it wont be very quick. If you have space you could use 2x outlander motor inverter combos...
I know a guy who converted Audi A6 quattro in such a way in Poland. Not finished yet though...

[Scrappyjoe]

Ok, here is the math, for the benefit for anyone who searched for ‘VW T3 Syncro energy efficiency’

I’m running quite large 15 inch tyres, diameter 28.5 inches, diff ratio for a syncro is 5.43

Continuous expected speed 100km/h

Wheel revolutions per km 743

Vehicle weight 1900kg

Frontal area 3.06m2

Drag coefficient 0.45

Ecomodder energy requirement tool gives me 26kw/35hp on the flat at 105km/h


Acceleration calcs -

0-100km/h OEM 2.1l WBX engine is 17 seconds. This translates to 28m/s2

To replicate that acceleration we would need 43.8kw for 17 seconds.

so: 26kw continuous + 43kw accel gives 69kw peak.

Some miscellaneous torque calcs:

Continuous torque is 35hpx5252/743rpm which equals 247 (Nm? Lb/ft? I forget) at the wheel.

Peak torque is 69kwx1.34x5252/744 which equals 652 at the wheel.

To get torque at the motor, divide by your diff ratio. With an outlander stock diff with a 7.06 diff ratio that is 652/7.06 which is 92(Nm? Lb/ft?).

If you choose to stick with the stock transaxle, 3rd gear for the syncro is about about equivalent when passed through the 5.32 diff.

At any rate, the 185Nm of this motor is sufficient.

[tom91]

Math does not lie. so if you say I need 35Kw continuous because my vehicle is a big heavy barge so it is. As soon as you drop the speed to 100km/h the required power drops drastically compared to lets say 120kmh.

As for the outlander rear motor reliably doing 35Kw continuous, no hard facts and as you said information online currently suggests it is a bit below that.

the issue you need to be careful of there is no torque curve available for the outlander motor so no idea where the "knee" point live. This means you will have the full 195Nm upto a certain point and then it declines due to field weakening.

If you are using the stock gearbox and the Outlander motor can produce around or above the "OE" torque you will be fine in replicating the original performance.

[arber333]

Math does not lie. so if you say I need 35Kw continuous because my vehicle is a big heavy barge so it is. As soon as you drop the speed to 100km/h the required power drops drastically compared to lets say 120kmh.
.....

True, back in the day i measured (watt meter) required power for my mazda mx3 at 100km/h at 110km/h at 120km/h and 130km/h...up to 180km/h.
Where it would draw 18kW cont. at 100km/h it would draw 42kW at 130km/h and full 85kW available to keep the car at 180km/h! That was with air cooled motor of 30kW nominal...
Besides getting the motor to overheat i managed to nearly sieze both rear wheel bearings or at least that was what i heared at that speed...

[Scrappyjoe]

Thanks tom91, yup, I've thought about the knee point, my understanding is it's about 4000rpm, and I'll be safe at that speed in 4th.

[Scrappyjoe]

FWIW it looks to me like the Outlander rear drive unit and Netgain Hyper9 are really close to each other in terms of power output - about 35Kw continuous, 85Kw peak. So if you’ve seen a vehicle with a Hyper9 installed, there’s a good chance the Outlander unit will be able to move it as well.

[arber333]

My math suggests that 35kw cont, 85kw peak should be sufficient for a 2t vehicle with performance characteristics of a microbus from 1989 - that is, slow, but able to keep going at 100km/h continuously.

Well i can say i could get 11s to 100km/h for 1.2T car. I can see max 230A with 320Vdc battery = 73kW and some spare for 100Hp!
I will try to get more power still and inverter seems to be able to oblige. I dont see any obstacle short of OEM hard limit.
My plan is to increase voltage to 360Vdc (96S) and see if i can get to 300A. It certainly feels it has enough OOMPH.

For now motor temp did not reach more than 60deg. I am more concerned about inverter as its thermal mass is low.
I still have one other Mitsu rear inverter here and will try to get it to run my Kia HSG motor just for fun. Its resolver seems the same and motor has the same pole count. Should be fun .