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Torque Multiplication?

Riventures

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Hello All,

I am not sure if this belongs in this thread group, but I though I should try.

As I understand, there isn’t a transfer case as in a traditional off-road vehicle. Without a transfer case, how would Rivian provide proper torque multiplication, or do they?

Thank you.
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Zoidz

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Hello All,

I am not sure if this belongs in this thread group, but I though I should try.

As I understand, there isn’t a transfer case as in a traditional off-road vehicle. Without a transfer case, how would Rivian provide proper torque multiplication, or do they?

Thank you.
A couple of things to consider:
1. Torque conversion, compared to an ICE, is not needed nearly as much. Electric motors (and the well designed inverter/controller powering it) in EVs produce very high torque at starting speed, and torque tapers off only at higher speed. IC engines produce low torque and low speed, and it increases as engine speed increases. That's why a multispeed transmission is needed for ICE.

2. Rivian does have a "single speed gearbox" so there is some torque conversion taking place. Read this lengthy comment from the VP of propulsion design at Rivian:

Charged: You said that there are symmetrical drive units, so you have four identical sets of motors and drives?


Richard Farquhar:
That’s correct – we have four identical motors, left and right, front and rear. Every wheel has the exact same amount of torque and power available to it to maximize performance. We achieve over 14,000 Newton-meters of grounded torque at the wheels combined and 125 miles per hour maximum speed. With the fixed-ratio single-speed gearbox there is no need to change gears, no need for twin speeds. This maximizes efficiency in terms of losses from gear meshing while achieving all of our performance targets.


The inverters are one of the jewels in the crown of this propulsion system, and are fully designed in-house. We designed a dual power inverter device integrated into the drive unit assembly, which allows very efficient control of two electric motors from one inverter assembly. We focused a lot on electrical efficiency from the battery to the inverters to the motors and on to the wheels. Having one dual combined inverter per axle allows us to maximize that electrical efficiency and therefore use the energy to maximize the vehicle’s range.
 

ajdelange

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Rivian has PM motors so torque is controlled by controlling stator current and field angle. But the important fact is that the torque vs speed curve is essentially flat (torque limited region) to the point (60 mph) where the motor's power limit is reached beyond which point it tapers linearly with speed so that torque*speed does not exceed the max power rating (speed limited region). Thus maximum torque is available at any speed below the speed at which the power limit is reached including 0 mph.

At maximum road speed the motors are most probably turning well over 10,000 rpm so that there has to be reduction gearing between rotor and wheel. This multiplies torque by the same ratio by which it reduces shaft speed but there is only one ratio. Thus the motors must be designed to be able to produce sufficient torque to meet the needs of the vehicle at any speed within the torque limited region.
 

electruck

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With the question focused around the lack of a transfer case, I am assuming the concern is around the lack of low-range gearing. The guys above have done a great job explaining why this isn't an issue with electric motors so I won't repeat any of that. I will, however, share this quote from Emme Hall regarding her first hand experience driving the R1T in the Rebelle Rally:

Rivian R1T R1S Torque Multiplication? eh_quote
 

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Riventures

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With the question focused around the lack of a transfer case, I am assuming the concern is around the lack of low-range gearing. The guys above have done a great job explaining why this isn't an issue with electric motors so I won't repeat any of that. I will, however, share this quote from Emme Hall regarding her first hand experience driving the R1T in the Rebelle Rally:

eh_quote.png
You are correct. I would not put the issue into the "concern" category :) however, I am trying to understanding how things work since I am totally green on EVs.

As you correctly interpreted, with traditional mechanical drivetrains, a transfer case using low-range gearing is invaluable off-road. I was not aware of the 14K Nm number, which is roughly 11K ft-lbs. Those are astonishing numbers. The wording is a bit confusing to me, manufacturers tend to use various words that I don't always relate to. Either way, since there aren't any gears on this vehicle, anything that is available to a single wheel as a fraction of 11 ft-lbs of torque should ease any "concerns." :)

Thank you all for your clarifications and input.
 

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redhilllabs

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You are correct. I would not put the issue into the "concern" category :) however, I am trying to understanding how things work since I am totally green on EVs.

As you correctly interpreted, with traditional mechanical drivetrains, a transfer case using low-range gearing is invaluable off-road. I was not aware of the 14K Nm number, which is roughly 11K ft-lbs. Those are astonishing numbers. The wording is a bit confusing to me, manufacturers tend to use various words that I don't always relate to. Either way, since there aren't any gears on this vehicle, anything that is available to a single wheel as a fraction of 11 ft-lbs of torque should ease any "concerns." :)

Thank you all for your clarifications and input.
The graph below depicts torque at lower gear settings and crawl speeds for a custom built Jeep and the stock factory Jeep Rubicon along with an EV curve in red. This is explained in depth in the following video (torque starts at 4:31):



Rivian R1T R1S Torque Multiplication? 1635542867688
 

electruck

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okey dokey then
 

White Shadow

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I know this is an older thread, but I wanted to revive it because I think this illustrates perfectly why Rivian should in fact have at least a 2-speed gearbox that incorporates low gearing for those who like to offroad in difficult situations like hill climbs or rock crawling.

It's this quote that has me wondering what they were thinking:

"Richard Farquhar: That’s correct – we have four identical motors, left and right, front and rear. Every wheel has the exact same amount of torque and power available to it to maximize performance. We achieve over 14,000 Newton-meters of grounded torque at the wheels combined and 125 miles per hour maximum speed. "

14,000 Nm is about 10,300 lb.ft. of torque. That really isn't all that much for an offroad machine. For example, even a basic V6 Grand Cherokee can put more torque to the wheels than that. All of these ICE vehicles have a big advantage when it comes to torque multiplication between their transmissions, transfer cases, and differentials. A V8 Grand Cherokee puts down more than 17,000 lb.ft. The Wrangler 392 puts down over 22,000 lb.ft.

The one big advantage of electric motors in that they pretty much make maximum torque as soon as they start spinning. But without the proper toque multiplication, it's not going to help much for steep hill climbs and the kind of toque necessary for rock crawling. The weight of these Rivians also doesn't help, so those motors really have their work cut out for them. That said, who thinks we'll see Rivian eventually offer low range gearing on their vehicles? At least for the vehicles they want to market as off-road capable?
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