Could Tesla and other EV's implement a flat towing mode?

[cruisered]

Flat towing is when a vehicle is towed with all wheels on the ground typically behind an RV. I am full time RVer who stays in many types of parks and needs to flat tow a car. Let's not talk about dollies or trailers.

Most (all) electric cars can not be flat towed because the drive train can not be pulled at high speeds for long periods.

This appears to be because they don't have a tow mode where the vehicle powers the drivetrain sufficiently to drive down the road behind the tow vehicle as opposed to be dragged down the road passively. There needs to be some accomodation for freedom of the steering wheels and braking as well but this seems pretty straight forward.

Self powered trailers are being developed so it seems that devising a control system that will allow a vehicle to be towed and provide assist which establishes some precedence for the technology.

So could Tesla develop basically a software mode that would let the car follow along and keep the drivetrain active and undamaged or would it need hardware as well.

Either way it is such a niche market I'm not hopeful but if hardware is involved then I feel like it will never happen.

 

[Two-rocks]

The rear motor has no coast or free roll ability, it is always powered and just making adjustments for drivability or regen (due to the permanent magnet design).
This doesn't mean it cant be done, but the car would essentially need to be fully energized in operating mode (for motor control, plus the oil is circulated in the gear system with an electric pump)- and like you said, you're a niche market, in a niche market.

 

[Gauss Guzzler]

It certainly could be done in software, but only up to a certain speed. I don't know what the speed limit might be, but clearly the car would have no way of enforcing it.

As @Two-rocks mentioned, the rear motor will always generate power and while the car has a number of ways of dumping excess power into the cooling system, you could certainly imagine a case where the battery is full, the heat and A/C are going full blast, the motor is being field-modified to work inefficiently and has reached maximum operating temperature, the radiator fan and cooling pump are running at max speed, all the legal lights are on, and then the RV driver gooses the throttle.

 

[Twiglett]

it may seem simple to say the words - but its a very, very long way from being straightforward
With such a limited use case its not like to appear anytime before L5 autonomous nationwide taxis

 

[Frank99]

To the best of my knowledge, there is nothing preventing Tesla from putting a line in the owners manual permitting flat towing.
- for Teslas with induction motors, with no permanent magnets in the motor there is zero power generated under tow unless the inverter actively generates the necessary magnetic fields.
- for Teslas with permanent magnet motors, they will generate voltage, but (assumption here) assuming the inverter can disconnect the output of the motor from the electronics, it’s harmless (take a motor from a childs toy and spin the rotor with your fingers; do lightning bolts strike you dead?)
- because the Tesla gearbox has nothing that acts like a clutch, the motor will spin as you go down the highway. That should be a “don’t care”; there will be more mechanical wear than expected based on odometer mileage, but that’s a 300,000 mile concern, not a 30,000 mile concern.
- because everything is spinning, that also implies that the oil pump (in a Model 3, don’t know about Model S) is running and keeping everything lubricated that is moving.

I haven’t heard a good reason why Tesla doesn’t support the RV community with a tow mode, but based on my understanding it’s not an issue with the physical devices.

 

[Two-rocks]

The above are incorrect. Much more than a line item in the manual.

The gear ratio is something like 9:1 (can’t remember) for the rear motor. the oil is circulated (lube and cooling, including inverter cooling) with an electric pump. Then the heat exchanger (multi-plate oil to coolant) using another pump, moves the heat elsewhere with water based coolant. You can’t tow the car wheels down for this reason, even without power regen active.

 

[Gauss Guzzler]

The car is awake anytime it's in neutral so it can certainly run the electric oil and coolant pumps accordingly unlike fossil cars that often can't be towed due to their crankshaft-driven transmission fluid pumps.

@Frank99 It's not always so simple to just open the motor connection and leave it floating but now that I think about it, there's no reason the car couldn't just run the motor at approximately zero torque. This would use a little bit of power to run the computer, oiling, and cooling systems but it could just dip into slight regen every so often to compensate and maintain the battery state of charge.

Perhaps one reason they don't offer this is because the car would be unable to ensure that you stop in the event of a powertrain failure.

 

[Frank99]

Gear ratio is immaterial; towing is no different than coasting, and vastly lower stress on the drivetrain than regen.
The motor is likely driven by a classic H-bridge with numerous paralleled IGBTS/FETs to be able to manage the current. Disconnecting the motor should be no more than NOT driving the base/gate of the igbts/fets. That comes for free when the inverter isn’t powered. The only concern would be whether the open circuit voltage of the motor would exceed the Igbt/fet ratings. I don’t have enough information to know.
I didn’t realize the Model 3 pump was electric; I thought it was mechanically driven. Conceptually, Tesla could run the pump in Tow mode, but that would require the computer to be running. Like you said, apply a little bit of regen to keep the battery level…

 

[Two-rocks]

Easy? Yes.
It should happen 'soon', just after we can adjust the display to our liking. But at least we got waypoints after years and years!
The reality is the market for this is smaller than small. I might even go so far as not the demographic...
Towing behind a fuel guzzling motorhome that are all generally built to a very low price point (exceptions of course, but a Monaco coach will have a proper enclosed trailer.)

 

[Rice&Curry]

I think this is way down the priority list in Tesla's feature requests list, so it is not likely to be implemented anytime soon.

 

[Gauss Guzzler]

I feel like @Rice&Curry did a pretty good job with his/her avatar, and I'm here guzzling Gaussessesss.
TF is with @Two-rocks? Grow some stones man.

 

[Two-rocks]

Added some rocks ;-)

 

[DaveT]

Unfortunate. I had to buy a new ICE this week just to tow behind our RV.

 

[cleverscreenam]

I have flat towed my 2013 Tesla Model S for 2 hours at 65 mph, to a Tesla service center. I've done this on 6 occasions now (and once was for a battery fault, which completely disabled the traction battery). It's much nicer to pay $60 in gas into the pickup truck pulling me, than the $800 that tow trucks were quoting per trip.

As others have already pointed out, every Tesla between 2012 and 2017 has only AC Induction motors, which are essentially disconnected when free-spinning; not generating anything.
Each flat tow has been drama-free and boring, had zero impact on my car, and it still drives like a brand new car.

 

[israndy]

https://twitter.com/x/status/1548742771036459008

 

[S-2000 Roadster]

It seems like there are two parts to the original question.
1) Can a Tesla be safely towed?
2) Can it drive itself behind an RV in such a way that it "pulls its own weight," so to speak.

In the first case, even the original Tesla Roadster has a Tow Mode setting in the vehicle control interface that disables power to (and from) the motor so that a tow truck can pull the car without dragging the wheels or engaging regeneration (which would really make towing a Tesla a drag).

In the second case, engineering a control system that would never push the RV, and never drag, while still actively powered the EV from its motor and power system is a *significant* design challenge. There are so many ways that could go wrong, and would probably require a new protocol to link the RV drive train control to the EV drive train control. I don't see adaptive powered tow mode being anything you'll see. As @Twiglett said, this isn't likely to appear as a feature until the technology has been developed and tested elsewhere.

 

[Mr. Jim]

I have a battery driven air pump I keep in my car and it has proved very usefful and allowed me to avoid towing. I could get to the nearest tire store after a couple of refills.

 

[israndy]

Wasn’t the Semi gonna going to bring Convoy Mode to the Tesla software suite?

 

[Unclepaul]

On the other hand, the new Semi could be developed into an awsome RV.

 

[israndy]

Technically my Airstream motorhome originally went for $239,000, so I guess I could end up with one in that price range again, but I bought my ’05 in ‘15 for $64,000. I got a LONG time to wait and perhaps not that many years of RVing in me.