Highway Mode - RWD only

[MountainDad]

While driving at highway speed and making few turns, the front motor should be disconnected as a drive motor to enable more efficient highway cruising.

If traction is limited (wheel slip detected with snow/ice/rain) or if acceleration is required (spirited driving or passing maneuvers), then the front motor is automatically engaged.

 

[CarTechGeek]

The way Tesla and some others handle this is too use a front induction motor, and a Permanent Magnet rear motor. The PMM is your main motor.

The front motor is an induction motor, this only engages if you need more power or traction.

Most of the time on the highway, the front induction motor is just freewheeling something induction motors can do without significant drag.

I think that is the preferred way to handle AWD for EVS. So you don't need a mechanical disconnect.

 

[Cranky Canuck]

While driving at highway speed and making few turns, the front motor should be disconnected as a drive motor to enable more efficient highway cruising.

If traction is limited (wheel slip detected with snow/ice/rain) or if acceleration is required (spirited driving or passing maneuvers), then the front motor is automatically engaged.

This is a good idea and how Hyundai does it. There's a clutch on the front motor so the motor is physically disengaged to reduce drag on the powertrain. It works very well in my Ioniq 5 and makes it so that I get almost the exact same highway range as the single-motor version.

The one downside to a clutch is that it's a wear item and takes a moment to re-engage if needed so there's sometime a slight hesitation as the motor reconnects. The Tesla-style induction front motor could be another option but there are downsides to that. I'll be curious to learn what tradeoffs the SM engineers have decided to go with but hopefully they have a way to run the trucks as RWD vehicles for highway driving and efficiency.

 

[Chris27]

How about we don’t have an awd selection where it constantly connects and disconnects. When I think of a truck or true 4WD vehicle, it better have a selector for 2WD (RWD), 4WD high and 4WD low. Whether it’s the Terra or Traveller, this is the way and the ONLY WAY the ‘transfer case’ should be from the factory. It’s not an AWD Bronco sport or Rav 4, it’s a Scout. It’s a rugged off road vehicle or work vehicle.

If you’re going to have the option of locking fronts and rears, you can’t have a generic awd mode.

 

[J Alynn]

How about we don’t have an awd selection where it constantly connects and disconnects. When I think of a truck or true 4WD vehicle, it better have a selector for 2WD (RWD), 4WD high and 4WD low. Whether it’s the Terra or Traveller, this is the way and the ONLY WAY the ‘transfer case’ should be from the factory. It’s not an AWD Bronco sport or Rav 4, it’s a Scout. It’s a rugged off road vehicle or work vehicle.

If you’re going to have the option of locking fronts and rears, you can’t have a generic awd mode.

I agree, but it’s also a daily driver for many buyers and we all need to keep that in mind. The forum is full of enthusiasts but guaranteed when this hits the streets the market will swell and majority of buyers will not off-road. So it needs to be designed solid but also needs to be convenient for daily driving including efficiency. We all tend to forget that here. I still think Bronco Sport is a joke carry the Bronco name but I see tons of them on the road. The new Scouts CAN NOT be on that end of the spectrum but it does need to have solid road manners or sales will not happen

 

[MountainDad]

How about we don’t have an awd selection where it constantly connects and disconnects. When I think of a truck or true 4WD vehicle, it better have a selector for 2WD (RWD), 4WD high and 4WD low. Whether it’s the Terra or Traveller, this is the way and the ONLY WAY the ‘transfer case’ should be from the factory. It’s not an AWD Bronco sport or Rav 4, it’s a Scout. It’s a rugged off road vehicle or work vehicle.

If you’re going to have the option of locking fronts and rears, you can’t have a generic awd mode.

The simple answer: Technology has progressed.

There are a lot of great AWD systems out there that are transparent to the driver. With an EV, you no longer need a mechanical connection between the front and rear axles - you can control locking behavior, torque distribution left/right and front/rear, and traction management behavior more precisely and responsively with sensors and computers that are directly connected to the control logic driving each motor. You also don't need a low range because torque peaks at 0 RPM and is flat until high motor rotational speed, which equates to highway speeds. It's effectively *always* in low range.

Simply having control logic that deactivates the front motor when it makes sense to do so, without the driver having to take action, is now easy to do.

 

[CarTechGeek]

How about we don’t have an awd selection where it constantly connects and disconnects. When I think of a truck or true 4WD vehicle, it better have a selector for 2WD (RWD), 4WD high and 4WD low. Whether it’s the Terra or Traveller, this is the way and the ONLY WAY the ‘transfer case’ should be from the factory. It’s not an AWD Bronco sport or Rav 4, it’s a Scout. It’s a rugged off road vehicle or work vehicle.

If you’re going to have the option of locking fronts and rears, you can’t have a generic awd mode.

Rav4 and BSports don't have the ground clearance, live rear axle, or real diff locks so it's no contest, and dual motor electric AWD/4WD is much better than clutch pack AWD like on the cute utes.

There is no transfer case. There is no physical connection between the front and rear wheels, and it makes no sense to reinstate that connection when you have a batter pack where the drive shaft used to be.

The only place you will see a drive shaft down the center of an EV, is in conversions. It's just poor packaging.

Dual motor AWD/4WD is just better. You can leave it engaged on high traction surfaces, and never have to worry about binding.

The only reason to disconnect the front drive is for efficiency when cruising and that can be done automatically and can be done pure electronically (Induction Motors can freewheel with negligible loss) so you don't even have any mechanical parts to wear out.

There is also no need for 4WD Low, because EV motor have full torque at zero RPM and can crawl.

But, what might actually make sense is to offer:

Offroad Low Mode:

• Change accelerator pedal mapping, to offer slower more nuanced control of power.
• Only enable diff lockers to be engaged in this mode.
• Limit top speed in this mode to 25 MPH (similar to real 4L).
• Attempt to mimic center lock by match the speed of front and rear motors

 

[Logan]

Funny enough, there are a few EV’s out there with two speed transmissions. The Porsche Taycan has a 2 speed transmission for the rear axle, which it uses at highway speeds for more efficiency.

Also, turns out, while EV motors DO have full torque from low speed, the my do pull a lot of amps doing technical off-roading. The Rivian R1S that did the rubicon trail had like 10% battery left after doing a 12 mile segment of the trail.

I actually think there is a potential reason for an off-roading style EV to use a multi-speed transmission, for more efficiency in those lower speed off-roading situations, while also being good at highway speeds.

Also, id assume that there will be a few 4x4 settings.

RWD mode
some sort of an “auto 4x4” setting
Full time 4x4 settings (like when it’s actively snowing)
Low range/off-road tuned 4x4 mode

 

[CarTechGeek]

Funny enough, there are a few EV’s out there with two speed transmissions. The Porsche Taycan has a 2 speed transmission for the rear axle, which it uses at highway speeds for more efficiency.

Taycan doesn't seem faster or more efficient for it's two speed transmission. It just seem like more to go wrong in the future.

What are the others?

I would not buy an EV with a transmission. 4x4 EV with transmission is worse. Because you would either need two transmission one in front and one in the rear, or go back to single motor and drive shafts.

 

[Rampy]

How about we don’t have an awd selection where it constantly connects and disconnects. When I think of a truck or true 4WD vehicle, it better have a selector for 2WD (RWD), 4WD high and 4WD low. Whether it’s the Terra or Traveller, this is the way and the ONLY WAY the ‘transfer case’ should be from the factory. It’s not an AWD Bronco sport or Rav 4, it’s a Scout. It’s a rugged off road vehicle or work vehicle.

If you’re going to have the option of locking fronts and rears, you can’t have a generic awd mode.

The 4A mode Ford has in its F150’s is an excellent feature in heavy rain and even better in snow/ice conditions when its not really appropriate for 4H

 

[Logan]

Taycan doesn't seem faster or more efficient for it's two speed transmission. It just seem like more to go wrong in the future.

What are the others?

I would not buy an EV with a transmission. 4x4 EV with transmission is worse. Because you would either need two transmission one in front and one in the rear, or go back to single motor and drive shafts.

I agree, its hard to compare the Taycan to a version of itself that doesn't have a multi-speed transmission. So its hard to see the difference/benefits. FWIW, from what I've seen, most brands are reporting a 5-15% or so increase in efficiency.

https://insideevs.com/news/511495/two-speed-ev-gearbox-inmotive/

The Taycan only has a 2 speed transmission on the rear axle, the front is still a single speed. Presumably because the rear axle is the one doing the bulk of the load under acceleration, as well as the only one engaged while cruising at highway speeds.

Also, right now, its just two vehicles with it (currently just the Taycan, and its platform partner the Audi Etron-GT ). But the upcoming Mercedes CLA EV, and Dodge Daytona Charger Daytona (This link has a few more details about the Taycan as well) will both have 2 speed transmissions, for the same reasons Porsche/Audi/the transmission companies have stated.

Who knows if it will "stick" as a thing that becomes commonplace though.

However, I do think the best place for a transmission on an EV, is as a "transfer case" sort of range stepdown. Again the R1S that drove the Rubicon apparently used 75% of its packs charge to do 12 miles, and reading somewhere about it afterwards I recall the discussion that while torque was high from 0 RPM of course, the current needed to the motors during those big offroad style moves, was quite high, hence the battery drain. So simply stepping down to a better gear ratio for offroading could help.

Obviously thats all up to the engineers. Just saying, I think there could be a valid use for multi-speed transmissions in EV's, particularly the "transfer case" style low range.

 

[CarTechGeek]

I agree, its hard to compare the Taycan to a version of itself that doesn't have a multi-speed transmission. So its hard to see the difference/benefits. FWIW, from what I've seen, most brands are reporting a 5-15% or so increase in efficiency.

https://insideevs.com/news/511495/two-speed-ev-gearbox-inmotive/

The Taycan only has a 2 speed transmission on the rear axle, the front is still a single speed. Presumably because the rear axle is the one doing the bulk of the load under acceleration, as well as the only one engaged while cruising at highway speeds.

Also, right now, its just two vehicles with it (currently just the Taycan, and its platform partner the Audi Etron-GT ). But the upcoming Mercedes CLA EV, and Dodge Daytona Charger Daytona (This link has a few more details about the Taycan as well) will both have 2 speed transmissions, for the same reasons Porsche/Audi/the transmission companies have stated.

Who knows if it will "stick" as a thing that becomes commonplace though.

However, I do think the best place for a transmission on an EV, is as a "transfer case" sort of range stepdown. Again the R1S that drove the Rubicon apparently used 75% of its packs charge to do 12 miles, and reading somewhere about it afterwards I recall the discussion that while torque was high from 0 RPM of course, the current needed to the motors during those big offroad style moves, was quite high, hence the battery drain. So simply stepping down to a better gear ratio for offroading could help.

Obviously thats all up to the engineers. Just saying, I think there could be a valid use for multi-speed transmissions in EV's, particularly the "transfer case" style low range.

So far just the Audi/Porsche which are the same under the skin.

A transmission company arguing for their product isn't exactly convincing.

I think it will remain a small niche, and stick to what I said before. I'll never buy an EV with a multiple gear box... It's just more to go wrong.

 

[Logan]

So far just the Audi/Porsche which are the same under the skin.

A transmission company arguing for their product isn't exactly convincing.

I think it will remain a small niche, and stick to what I said before. I'll never buy an EV with a multiple gear box... It's just more to go wrong.

Yep, as I said, those two platform-mates are the only ones right now. But the Mercedes CLA and Charger EV will reportedly have them too (pasting the links separately here, as the links aren't very visible in text on this forum for some reason).

https://insideevs.com/news/740071/mercedes-benz-cla-ev-two-speed-transmission/

https://www.topspeed.com/ev-transmission-tech/ (talks about the Taycan, and the Charger in this one).

I'm not really advocating for/against them, nor would I avoid purchasing the scouts if they didn't have them or something like that. Just saying that "IF" there was an application for 2 speed transmissions on EV's, the low range/transfer case style seems like it might make the most sense.

 

[CarTechGeek]

Just saying that "IF" there was an application for 2 speed transmissions on EV's, the low range/transfer case style seems like it might make the most sense.

But as mentioned before, you need two gearboxes for an off road "low range" case, so IMO, that's even worse...

 

[Logan]

But as mentioned before, you need two gearboxes for an off road "low range" case, so IMO, that's even worse...

That is certainly one way to do it, and the only way to do it like it is on a traditional 4x4. But I don't think its the only way to do it.

All of the current/designed 2 speed systems only use it on the rear axle. They use it for performance, but in crawling the rear axle is the one that is doing the brunt of the work to get over obstacles, so you could just do it on the rear. There is no reason they couldn't get the front axle without a transfer case/transmission to rotate at the same speeds as the rear (that did have a transmission/transfer case) with an EV. In fact...

Interestingly, I found while reading the article I linked above, that Tesla sort of does 2 speeds... but they do it very differently. They use different final drive gear ratios in the front and rear axles, and transition between them for acceleration, and cruising (which I guess means that Teslas are primarily FWD at freeway speeds).

Undeterred, Tesla devised a different strategy to incorporate dual gears into their EVs, distinguishing its Dual-Motor Model S, Model X, and Model 3 vehicles. These models feature distinct gear ratios in their front and rear drive units. At lower speeds, over half of the power is directed to the rear drive unit, optimized for efficient lower-speed performance. As the vehicle accelerates to higher speeds, Tesla's advanced computer systems redirect power to the front drive unit, which boasts a superior motorway gear ratio.

I understand you don't want a transmission. I don't even know if I "want" one. Just saying that there are potential use cases for differing gear ratios. And I'm sure the Scout engineers are thinking about any/all options, and will choose what makes the most sense.

 

[CarTechGeek]

Interestingly, I found while reading the article I linked above, that Tesla sort of does 2 speeds... but they do it very differently.

I wouldn't take anything you read at "Topspeed" seriously. I found them to have mostly clickbait and BS articles, and blocked them ages ago.

I've read from multiple sources that Tesla uses a Front Induction Motor (can freewheel with negligible losses), and Rear Permanent Magnet Motor (more efficient). Even the in car display tells you they have those motors:

https://teslamotorsclub.com/tmc/attachments/82438934-5096-47e8-b01e-e6e599e5465a-jpeg.805633/

The strategy that follows from that arrangement, is you only use the front motor when you need more power or traction. When just cruising it only use the more efficient rear motor.

They could be geared different (they are completely different types and power levels so that makes sense), but it isn't to transition between them. The rear motor is the main motor and works from Zero to as fast as you go, so it really isn't switching over from one to the other. The induction is only for intermittent use.

 

[LastDayScout]

How about we don’t have an awd selection where it constantly connects and disconnects. When I think of a truck or true 4WD vehicle, it better have a selector for 2WD (RWD), 4WD high and 4WD low. Whether it’s the Terra or Traveller, this is the way and the ONLY WAY the ‘transfer case’ should be from the factory. It’s not an AWD Bronco sport or Rav 4, it’s a Scout. It’s a rugged off road vehicle or work vehicle.

If you’re going to have the option of locking fronts and rears, you can’t have a generic awd mode.

I do hope that 4 HI or an additional selection like Full Time can be used for wet roads and ponding water on roads. Big issue where I live.

 

[Logan]

I wouldn't take anything you read at "Topspeed" seriously. I found them to have mostly clickbait and BS articles, and blocked them ages ago.

I've read from multiple sources that Tesla uses a Front Induction Motor (can freewheel with negligible losses), and Rear Permanent Magnet Motor (more efficient). Even the in car display tells you they have those motors:

https://teslamotorsclub.com/tmc/attachments/82438934-5096-47e8-b01e-e6e599e5465a-jpeg.805633/

The strategy that follows from that arrangement, is you only use the front motor when you need more power or traction. When just cruising it only use the more efficient rear motor.

They could be geared different (they are completely different types and power levels so that makes sense), but it isn't to transition between them. The rear motor is the main motor and works from Zero to as fast as you go, so it really isn't switching over from one to the other. The induction is only for intermittent use.

Good to know about the source, I just chose a random article on it.

I did some digging just to be sure. The model 3/Y both use the same final drive ratios front and rear (9:1). As do the Model S/X plaid models (7.56:1).

But the standard dual motor versions do feature different final drives front and rear(7.56:1 and 9.04:1).

https://www.tesla.com/ownersmanual/modelx/en_us/GUID-E414862C-CFA1-4A0B-9548-BE21C32CAA58.html

The cybertruck only uses one ratio as well (15.02:1). So it seems maybe they don’t believe it’s necessary/worth the cost anymore?

Anyway, I learned something today.

And back on the thread topic (sorry!) I’m totally on board with multiple drive modes. Rear wheel drive, auto-4wd, 4hi, and 4lo.

 

[CarTechGeek]

I do hope that 4 HI or an additional selection like Full Time can be used for wet roads and ponding water on roads. Big issue where I live.

There is no need for concern. The default mode will be full time AWD better than almost any ICE car out there.

Dual motor has an advantage over ICE based AWD systems in that there is no concern about driveline binding so it can stay engaged all the time. It will likely only disengage for cruising efficiency, and even then if it has an Induction motor in front, it can reengage at any sign of slip faster than any mechanical slip.

 

[LastDayScout]

There is no need for concern. The default mode will be full time AWD better than almost any ICE car out there.

Dual motor has an advantage over ICE based AWD systems in that there is no concern about driveline binding so it can stay engaged all the time. It will likely only disengage for cruising efficiency, and even then if it has an Induction motor in front, it can reengage at any sign of slip faster than any mechanical slip.

My last 3 vehicles have been AWD EVs. The systems have been great for heavy rain and wet road conditions. I was really just reading that so many folks are hoping for old school 4x4 transfer case style systems. I know those are great for off road. I agree with what you said though. I’m sure it’s going to be an excellent all around system.