Hi fellow volvo enthusiasts.

Im currently in the *very* early phases of converting a TGB to an electric engine. Still working on if its even feasible to try.

I spotted a pinzgauer that has been converted (project Ecarus https://www.projectecarus.com/ for those interested) and would be very interested in doing the same to a C304 or 306 (depending on which one I can buy and what would be possible. Im worried however about if the car can handle the torque. Ive been trying to find the max torque for the portal axles and transmissions, but cant find it in the documents on tis website, or others.

For the electric conversion you would strip out the gearbox and clutch, but I would be interested in keeping the high/low range transmission and the portal axles stock.

Now some data
The original engine (B30A)

Max power 86 kW
Max torque 206 Nm

Engine im looking at. https://cdn.shopify.com/s/files/1/1820/0269/files/PowerPhase_HD_250.pdf?v=1583493492

Max Power 250 kW with 180 kW Continous
Max RPM 5500
Max Torque 900Nm with 520Nm Continuous

Now this is triple the power with about 2.5-4 times the torque, so this seems like a lot of difference, however with an electric engine you wouldnt need the gearbox anymore.

So torque at wheel
Petrol engine, 1st gear, low range
206 x 3,85 (1st gear) x 2,39 (low range) x 2,91 (axle ratio) x 2,06 (Gear ratio wheel gear) / 6 (all wheels on) = ~1900Nm per wheel

Electric engine, low range
900 x 2,39 (low range) x 2,91 (axle ratio) x 2,06 (Gear ratio wheel gear) / 6 (all wheels on) = 2150Nm per wheel
Continous would be
540 x 2,39 (low range) x 2,91 (axle ratio) x 2,06 (Gear ratio wheel gear) / 6 (all wheels on) = ~1300 Nm per wheel.

I'd assume these values will still fall within safe margins for the transfer case, and the portal axles, but I cant find max torque values. What do you guys think? For electric vehicels however, they will be able to keep torque for a much larger range of RPM then petrol engines can, so the transmission and portal axles would be subject to it for a longer time.

BTW, top speed for this vehicle would be ~130 km/h in high range (with 88cm tall wheels) and ~55 km/h in low range

Don's forget to consider/calculate the necessary/sustainable brake torque.
Otherwise you have a problem, on long downhill sections, at least while also having a full battery (no charge drain)
(IIRC, ordinary gasoline has a 1:10 ratio between power & brake/overrun; diesel 1:5 (but depending on compression, thereby also (factory) turbo mostly being worse than atmospheric).
So, based on your electric motor, you need to 'burn' 40-50kW....either charging or burning off as heat/wind-/water-resistance, or even light, by big incandescent bulbs.....:))

Geartrain-wise, overall, first rule of thumb is the torque multiplication in normal configuration, which is about 50:1, 60:1 and 70:1. (4x4/6x6/TGB20)

Times 206Nm means 10k/12k/14k Nm, at the wheels.
(or 1k/1,2k/1,4k at the T-case)
(based on 5:1 first-gear ratio)

And don't forget to make it waterproof.....;))
(meaning: forced air-cooling ducting, perhaps even watercooling?)

Good points, I think the brake overrun is less of an issue, electric engines can have a lot of regenerative breaking. most of it can likely be backcharged into the batteries, and I only really seem issues if you have a long downhill with a completely full battery.
I plan to set it up as an overlanding vehicle, with camper setup, and worst case scenario I can turn the heaters on full blast for a while. But I think most of it will be taken care of already.

Seems like your rule of thumb for torque came same to my numbers, I just divided it by the 6 wheels.
So I was assuming the c304 gear ratios, which came to 1900Nm per wheel, which with 6 wheels is your 12k Nm from the rule of thumb.

Seeing as the electric engine would have a max of 13k Nm total, less then the 14k the C306 has, the portal axles should be just fine, right?

I feel personally that the not using 1st gear compared to the petrol engine is what makes the torque numbers just fine.

But do you, or anyone else, have the exact max torque allowed figures for the portal axles?

I checked the uploaded service manual again, I would assume its under "General file 5" since that one mentions the power transmission, on page 16, but the document only goes up to page 10
https://www.c303.de/c303-pdf/service/section0general5.pdf

Zitat von: OkkeB am 7.November 2022 18:17:25

Good points, I think the brake overrun is less of an issue, electric engines can have a lot of regenerative breaking. most of it can likely be backcharged into the batteries, and I only really seem issues if you have a long downhill with a completely full battery. I plan to set it up as an overlanding vehicle, with camper setup, and worst case scenario I can turn the heaters on full blast for a while. But I think most of it will be taken care of already.

As a (set of) heater(s), I would put them on the roof....;))
Not your ordinary incarnation of GlowInTheDark....:))

Zitat:

Seems like your rule of thumb for torque came same to my numbers, I just divided it by the 6 wheels. So I was assuming the c304 gear ratios, which came to 1900Nm per wheel, which with 6 wheels is your 12k Nm from the rule of thumb. Seeing as the electric engine would have a max of 13k Nm total, less then the 14k the C306 has, the portal axles should be just fine, right? I feel personally that the not using 1st gear compared to the petrol engine is what makes the torque numbers just fine. But do you, or anyone else, have the exact max torque allowed figures for the portal axles? I checked the uploaded service manual again, I would assume its under "General file 5" since that one mentions the power transmission, on page 16, but the document only goes up to page 10 https://www.c303.de/c303-pdf/service/section0general5.pdf

I should have the full paper version, English or Swedish, somewhere....
(I even remember the days someone put it online for the first time, in USA or SE, nearly 2 decades ago....:))
(at that time, even Tatanka was happy to find/have it in that form)


Btw, I see it also lists the max pulling force at 23250N (4x4, 50:1); by dividing that with the wheel radius (in meter), you get total Nm, at the wheels, all 6 together.

The real fun calculation starts when imagining very steep hill, teethering on 2 wheels, and all that power/torque going through a single (bottom-most) wheel....;))
(with a 6x6 this chance is much less likely, unless also bottoming out on the rear bogie)

Zitat:

I should have the full paper version, English or Swedish, somewhere.... (I even remember the days someone put it online for the first time, in USA or SE, nearly 2 decades ago....:)) (at that time, even Tatanka was happy to find/have it in that form)

If you can find the missing pages that would be great

BTW, I found this website: https://x-engineer.org/calculate-wheel-torque-engine/

If anyone knows the b30a engine torque per RPM chart (first image, but then for the B30A) I can make a fun little chart for the wheel torque per gear (second image)

Zitat:

Zitat von: OkkeB am 6.November 2022 17:40:24

So torque at wheel Petrol engine, 1st gear, low range 206 x 3,85 (1st gear) x 2,39 (low range) x 2,91 (axle ratio) x 2,06 (Gear ratio wheel gear) / 6 (all wheels on) = ~1900Nm per wheel Electric engine, low range 900 x 2,39 (low range) x 2,91 (axle ratio) x 2,06 (Gear ratio wheel gear) / 6 (all wheels on) = 2150Nm per wheel Continous would be 540 x 2,39 (low range) x 2,91 (axle ratio) x 2,06 (Gear ratio wheel gear) / 6 (all wheels on) = ~1300 Nm per wheel.

I don't think this is correct, at least if you retain the original transfer gearbox. The FD51 splits the engine torque in half - 50% goes to the front axle, 50% to the rear two axles. So the front wheel torque should be higher. Also note that most 6WD variants have 7.1:1 final drive (3.44:1 diff ratio) so that will increase the torque at the wheel yet again. However you can't use 4WD/6WD all the time, so you would need to electronically limit the motor output when in RWD mode or use an alternate transfer gearbox that has full time AWD or mount a motor/diff combination sideways to drive the front and rear propshafts directly (preferably with a central torsen diff as in a 6x6 as you don't really want an even split).

This older discussion may be interesting: https://www.c303.de/c303-forum/index.php?board=36;action=display;threadid=14691

Zitat von: OkkeB am 7.November 2022 18:17:25

[W]orst case scenario I can turn the heaters on full blast for a while. But I think most of it will be taken care of already.

I doubt your heaters could drain the battery fast enough to make a difference. Both heaters will take something like 6kWh per hour. That said, it's unlikely that you'll encounter a long, steep downhill section immediately after charging to 100%. Alternately you could just make it a habit to never charge to 100%

Zitat von: OkkeB am 7.November 2022 20:23:40

If anyone knows the b30a engine torque per RPM chart (first image, but then for the B30A) I can make a fun little chart for the wheel torque per gear (second image)

There's a torque curve in the service manual, however I suspect it's for the B30a in the Volvo 164. The Swedish military manual and the English civil version both have the same chart



There's also a different chart in the original brochure



Maurice

Zitat:

I don't think this is correct, at least if you retain the original transfer gearbox. The FD51 splits the engine torque in half - 50% goes to the front axle, 50% to the rear two axles. So the front wheel torque should be higher. Also note that most 6WD variants have 7.1:1 final drive (3.44:1 diff ratio) so that will increase the torque at the wheel yet again. However you can't use 4WD/6WD all the time, so you would need to electronically limit the motor output when in RWD mode or use an alternate transfer gearbox that has full time AWD or mount a motor/diff combination sideways to drive the front and rear propshafts directly (preferably with a central torsen diff as in a 6x6 as you don't really want an even split).

Fair point, and a whole another wheelhouse to look at. but, the values themselves might be off, but how they compare to eachother is another thing

Zitat:

This older discussion may be interesting: https://www.c303.de/c303-forum/index.php?board=36;action=display;threadid=14691

Thanks! definitly interesting

Zitat:

I doubt your heaters could drain the battery fast enough to make a difference. Both heaters will take something like 6kWh per hour. That said, it's unlikely that you'll encounter a long, steep downhill section immediately after charging to 100%. Alternately you could just make it a habit to never charge to 100% wink

In the whole "setting up as overlander" I would add extra heaters for the camper area. A box I would build on the rear frame, which I think I can get some heaters in as well. But indeed just not charging to 100% would already go a long way. I would also keep the original brakes (drum brakes are quite good in combo with electric engines) so its not like I would be completely out of braking power.

Zitat:

There's a torque curve in the service manual, however I suspect it's for the B30a in the Volvo 164. The Swedish military manual and the English civil version both have the same chart rolleyes

assuming this as fact I made some nice diagrams. I used this for the specs https://classicunimogs.com/specs_volvo_c304.html

Main gearbox   
Type name   ZF S4-18
gear ratio 1st gear   3,85:1
gear ratio 2nd gear   2,08:1
gear ratio 3rd gear   1,39:1
gear ratio 4th gear   1:1
gear ratio reverse   4,13:1

Transfer case   
Type name   Volvo FD 51
Gear ratio low range   2,39:1
Gear ratio high range   1:1

These diagrams show Torque in Nm before it gets split between front and rear axles or wheels. so I didnt include the portal axles or the per wheel calculations, but DID include the gearbox (for the petrol) and the high/low range transfer case

First up, Torque curve per RPM (In high range)


Then same, in low range

Some more fun diagrams. This is Torque per speed for different gears

Since im not sure exactly how to split the torque over the wheels,
the Torque is at the end of the transfer case (so including the gearbox and high/low range, not incl the axles)
The speed however uses the values from here:
https://classicunimogs.com/specs_volvo_c304.html

-Important to note that exact speed and torque value while differ depending on what tiresize and gear reduction you are using, *but* the comparison between the values is still the same. (all numbers will be divided or multiplied by the same difference for your exact drivetrain)

If there is interest in it, I can try to make a google spreadsheet where you can fill in your own exact ratios and it will calculate the different diagrams for you

See below images for the list of ratios im using

Including the electric drive im looking at:




Only the B30A for people not interested in the electric engine




Specs used:
Tires   280/85R16 4 ply

Main gearbox   
Type name   ZF S4-18
gear ratio 1st gear   3,85:1
gear ratio 2nd gear   2,08:1
gear ratio 3rd gear   1,39:1
gear ratio 4th gear   1:1
gear ratio reverse   4,13:1

Transfer case   
Type name   Volvo FD 51
Gear ratio low range   2,39:1
Gear ratio high range   1:1
   
Axles   
Gear ratio axle   3,44:1
Gear ratio wheel gear   2,06:1

Zitat von: OkkeB am 8.November 2022 00:12:54

Fair point, and a whole another wheelhouse to look at. but, the values themselves might be off, but how they compare to eachother is another thing

Yes, agreed. My point was that portals and diffs should be able to handle more torque than you estimated. I should also point out that there are third party axle parts available that are supposedly stronger. They're primarily for people using Volvo axles on custom offroad vehicles. See https://custom4x4parts.com/ or https://www.asli4x4.com/. So I'm not convinced you need to worry about the axles, though the inverter will need an appropriate power delivery curve (two curves if you keep the original transfer gearbox).

Zitat:

In the whole "setting up as overlander" I would add extra heaters for the camper area. A box I would build on the rear frame, which I think I can get some heaters in as well. But indeed just not charging to 100% would already go a long way. I would also keep the original brakes (drum brakes are quite good in combo with electric engines) so its not like I would be completely out of braking power.

Yes, no need to change the brakes, that's a whole other can of worms, and a significant expense. Note that if you use the original transfer gearbox your inverter will require different regen settings for 2WD vs 4WD, and the ability to switch between them on the fly, because the front axle is automatically engaged when you brake hard.

Maurice