EV towing and trailer brakes

[Dennis C]

Originally Posted by richard5933

That's good to know, and sounds like for the most part the regen can be depended on for help is maintaining speed on a downhill run. I'd still probably have my foot hovering over the brake anyhow, at least for the first few trips down a long/steep descent.

I agree. That said, in max regen mode the car will slow enough to come to a stop even on a steep grade. On a 7% grade, I usually apply a light amount of throttle to keep the regen from stopping the car or at least slowing it more than I’d like. With the added weight of a trailer, this may be different.

[Life is a Highway]

The new Airsteam Wirth push pull and stop your toaster on wheels

[DrivingDan]

Originally Posted by richard5933

Interesting concepts to ponder, for sure. Any chance there is an early copy of the owners' manual out there?

I wish

Originally Posted by Dennis C

My EV activates the brake lights during regen in some scenarios, but not all … The algorithm is pretty sophisticated.

The Bolt that I’ve been driving was a learning for Ultium, and I can see a lot is getting ported directly to the new platform. On the Bolt I think the brake lights do come on according to an algorithm, I suspect the idea is since EV’s regen so much in responding to the road and driver that the lights only come on in response to significant slowdowns.

But the brake light is probably a red herring, I think the key is that the car knows when your trying to lose significant speed, when that occurs I’ll bet the trailer brakes kick on too.

Originally Posted by DMT

I think you will like the Silverado. I have a reservation on one but just recently purchased the new Tundra. The charging infrastructure in my area needs to build out more before the EV truck would work for me towing my International.

In addition to the significant existing infrastructure the first 1.5B has been released for NEVI buildout, you can see detailed plans and the corridors here

https://driveelectric.gov/state-plans/

Click on anything in the “EV Charging Corridors” column and you’ll get to a map where you can see the buildout plan, which is DCFC every 50 miles.

By the time this truck is available infrastructure will be everywhere except a patchwork of off the main routes locations which will get addressed with private funding probably (if it isn’t already, there’s charging all over the place already)

[Vitaver]

Another component of the convoy is the hitch: will it help you keep the TT straight with the TV when slowing down/braking with the engine alone? If we can agree that a 5th wheel assembly is more effective in preventing sway with just engine brakes, then you may consider the PP3 (Pro Pride 3) that projects the pivoting point from the traditional ball on a traditional hitch, to the center of the rear TV axel, emulating a 5th wheel. I use such hitch and notice on downhill runs, with the engine controlling the speed (with driver assist engaged and sat at a constant speed), the TT stays right behind me, no sway. Even on turns.

[cedonly]

This is not an EV question but a physics I question. Braking with just the TV generates a flex back to the ball. The trailer has momentum, and the ball is a pin joint free to rotate. So you just created a Jack - knife scenario. Ideally when braking both the tv and trailer brake their own momentum and you impart no additional forces on the ball. QUOTE=DrivingDan;2632478]Disclaimer: before people get worked up about safety and start lecturing about EV this or that, this thread is meant to be a theoretical and practical discussion of trailer braking in the era of EV’s, and what may or may not make sense. Let’s keep it on topic and focus on the discussion point

As discussed elsewhere I’m planning on stepping up my EV driving to towing with (we’ve decided) and Airstream using a Silverado EV truck. This lead me to think about trailer brakes. Now the Silverado EV comes with a trailer brake controller built in and the seven pin socket so that is available. However using the trailer brake is robbing the regenerative braking from all that potential energy. In an ideal world you would have no trailer brakes as the regen can certainly handle it (the battery can charge at 350kW and I’d estimate max regen with trailer would be < 200 kW)

So I’m wondering what the best approach is? For example, you’re going down a long constant grade as is common on the Interstates, would it be safe and reasonable to back the brakes off to maximize the regeneration on the tow vehicle? If the trailer and hitch have no issues with it, are you safe with going to zero trailer braking? What is the ultimate point of trailer braking, to give your tow brakes some help (which regen doesn’t need), or to help the hitch, or to prevent control issues with the trailer, or a combination of the above?

For reference EV’s generally treat regenerative cycles as braking and turn on the brake lights, presumably the same applies for the seven pin connector when in regen. OTOH maybe GM is programming it to only activate the trailer brakes when the car brakes - not regen - are activated. I’d guess they act normally no matter what.[/QUOTE]

[richard5933]

Originally Posted by cedonly

This is not an EV question but a physics I question. Braking with just the TV generates a flex back to the ball. The trailer has momentum, and the ball is a pin joint free to rotate. So you just created a Jack - knife scenario. Ideally when braking both the tv and trailer brake their own momentum and you impart no additional forces on the ball. QUOTE=DrivingDan;2632478]Disclaimer: before people get worked up about safety and start lecturing about EV this or that, this thread is meant to be a theoretical and practical discussion of trailer braking in the era of EV’s, and what may or may not make sense. Let’s keep it on topic and focus on the discussion point

As discussed elsewhere I’m planning on stepping up my EV driving to towing with (we’ve decided) and Airstream using a Silverado EV truck. This lead me to think about trailer brakes. Now the Silverado EV comes with a trailer brake controller built in and the seven pin socket so that is available. However using the trailer brake is robbing the regenerative braking from all that potential energy. In an ideal world you would have no trailer brakes as the regen can certainly handle it (the battery can charge at 350kW and I’d estimate max regen with trailer would be < 200 kW)

So I’m wondering what the best approach is? For example, you’re going down a long constant grade as is common on the Interstates, would it be safe and reasonable to back the brakes off to maximize the regeneration on the tow vehicle? If the trailer and hitch have no issues with it, are you safe with going to zero trailer braking? What is the ultimate point of trailer braking, to give your tow brakes some help (which regen doesn’t need), or to help the hitch, or to prevent control issues with the trailer, or a combination of the above?

For reference EV’s generally treat regenerative cycles as braking and turn on the brake lights, presumably the same applies for the seven pin connector when in regen. OTOH maybe GM is programming it to only activate the trailer brakes when the car brakes - not regen - are activated. I’d guess they act normally no matter what.

[/QUOTE]

I understand what you're saying about the trailer brakes reducing the effectiveness of the regenerative braking. The more important issue is that the basic physics of pulling a trailer don't change at all. Many tow vehicles have more than enough braking power to stop both the TV and the trailer, but that's not the point. The point is that having trailer brakes increases the safety of the rig, reduces the likelihood of jackknifing, and reduces the likelihood of a sway event.

This was covered quite a bit in the earlier part of the thread.

Let's take your example - you're going down a long constant grade. Downhill runs are more prone to sway events than uphill runs. That stays the same whether your TV is powered by dinos or electrons. If you have your brakes backed off to maximize the regenerative braking, you're leaving yourself at risk in either a panic stop situation or a reduced traction situation.

Both of these (panic stops & reduced traction) happen as often in an EV tow vehicle as they do in an ICE tow vehicle. Slam on the brakes in a panic stop without trailer brakes, especially on a downhill run, and that trailer is going to want to keep on going - even if it means passing up the tow vehicle. To be clear on this - the reduced traction I'm referring to is for the trailer. If the regenerative braking kicks in when the trailer has weaker/no brakes and less traction it's prone to moving sideways as it tries to maintain the same speed.

Other than the additional regenerative braking, do you see another positive of backing off the trailer brakes?

[AlbertF]

This has me thinking about trailer brake controllers. The prodigy P2 has an adjustable boost function that sends a spike of current to the trailer brakes when the brake pedal is applied. I believe this happens because of a connection to the brake light circuit. Does this mean the trailer brakes would be activated when backing off the accelerator on an EV?

It seems to me that a trailer brake controller optimized for EVs would provide an initial boost in response to brake pedal movement rather than brake light activation. In this way a light touch of the brake pedal could be used to deal with instability of the trailer, with battery regeneration used to meet most slowing and stopping needs.

Of course having a battery pack on the trailer with regeneration from the trailer axles would be ideal.

[richard5933]

I believe that most of the newer brake controllers operate with a number of inputs. Mine starts the process when the brake lights are activated, and how forcefully it applies the trailer brakes is determined by an accelerometer that measures how quickly the tow vehicle is slowing. Nit sure why it would function any differently in an EV towing.

In an earlier post someone mentioned that the brake lights in their EV could be activated by the regen braking, and since braking can occur in an EV by a single pedal I'm not sure that the brake pedal itself needs to be involved. As long as the trailer brake controller knows that the TV is braking, and knows how quickly it's slowing, it can apply the trailer brakes appropriately.

[CR-Rylie]

Originally Posted by DrivingDan

Disclaimer: before people get worked up about safety and start lecturing about EV this or that, this thread is meant to be a theoretical and practical discussion of trailer braking in the era of EV’s, and what may or may not make sense. Let’s keep it on topic and focus on the discussion point

As discussed elsewhere I’m planning on stepping up my EV driving to towing with (we’ve decided) and Airstream using a Silverado EV truck. This lead me to think about trailer brakes. Now the Silverado EV comes with a trailer brake controller built in and the seven pin socket so that is available. However using the trailer brake is robbing the regenerative braking from all that potential energy. In an ideal world you would have no trailer brakes as the regen can certainly handle it (the battery can charge at 350kW and I’d estimate max regen with trailer would be < 200 kW)

So I’m wondering what the best approach is? For example, you’re going down a long constant grade as is common on the Interstates, would it be safe and reasonable to back the brakes off to maximize the regeneration on the tow vehicle? If the trailer and hitch have no issues with it, are you safe with going to zero trailer braking? What is the ultimate point of trailer braking, to give your tow brakes some help (which regen doesn’t need), or to help the hitch, or to prevent control issues with the trailer, or a combination of the above?

For reference EV’s generally treat regenerative cycles as braking and turn on the brake lights, presumably the same applies for the seven pin connector when in regen. OTOH maybe GM is programming it to only activate the trailer brakes when the car brakes - not regen - are activated. I’d guess they act normally no matter what.

Is your manual available yet? I have attached the relevant section from my Rivian R1T manual. While it may not be relevant to your vehicle, you might want to look at some of the towing related posts on https://www.rivianforums.com/forum/f...ific-topics.2/ Lots of folks towing Airstreams (and others) with their R1T EV.

[DrivingDan]

Originally Posted by CR-Rylie

Is your manual available yet? I have attached the relevant section from my Rivian R1T manual. While it may not be relevant to your vehicle

No I’m pretty sure the manual hasn’t been released.

Otherwise I’m not expecting much similarity between Rivian and GM. This is GM’s third EV architecture, they learned a lot from the Bolt (architecture #2) and I’m seeing that they are keeping many good elements and stepping up others. For example now they’re offering towing adaptive cruise control and towing Super Cruise (autonomous freeway). The Rivian - being a newcomer, is likely more conservative. For example from the manual it downgrades to manual cruise control when towing. I wouldn’t expect the Rivian to do anything but vanilla ICE traditional towing response.

The EV 1 (BEV1 arch) was groundbreaking. The Bolt (BEV2) was pretty conservative. But Ultium (BEV3) they are getting aggressive on pushing new capabilities. The Hummer pushes everything while the Silverado pushes range which was the #1 goal from the beginning and why they have a 400 mi range (and GM is always conservative with range, real world will be probably 430-450 mi depending on how you drive. They’re really focused on towing here, for example the 20k tow capacity they’ll be offering. Given all the tricks they’ve done to pull this off is what led to me thinking about how they might goose the towing regen.

I sound like a fanboy but as an engineer I am impressed with their architecture.

[AlbertF]

Originally Posted by richard5933

I believe that most of the newer brake controllers operate with a number of inputs. Mine starts the process when the brake lights are activated, and how forcefully it applies the trailer brakes is determined by an accelerometer that measures how quickly the tow vehicle is slowing. Nit sure why it would function any differently in an EV towing.

In an earlier post someone mentioned that the brake lights in their EV could be activated by the regen braking, and since braking can occur in an EV by a single pedal I'm not sure that the brake pedal itself needs to be involved. As long as the trailer brake controller knows that the TV is braking, and knows how quickly it's slowing, it can apply the trailer brakes appropriately.

I think I didn’t clearly articulate where I’m coming from. I would want to minimize trailer braking where possible and maximize regenerative braking - but not at the expense of downhill stability or accident avoidance.

[CR-Rylie]

Originally Posted by DrivingDan

No I’m pretty sure the manual hasn’t been released.

Otherwise I’m not expecting much similarity between Rivian and GM. This is GM’s third EV architecture, they learned a lot from the Bolt (architecture #2) and I’m seeing that they are keeping many good elements and stepping up others. For example now they’re offering towing adaptive cruise control and towing Super Cruise (autonomous freeway). The Rivian - being a newcomer, is likely more conservative. For example from the manual it downgrades to manual cruise control when towing. I wouldn’t expect the Rivian to do anything but vanilla ICE traditional towing response.

The EV 1 (BEV1 arch) was groundbreaking. The Bolt (BEV2) was pretty conservative. But Ultium (BEV3) they are getting aggressive on pushing new capabilities. The Hummer pushes everything while the Silverado pushes range which was the #1 goal from the beginning and why they have a 400 mi range (and GM is always conservative with range, real world will be probably 430-450 mi depending on how you drive. They’re really focused on towing here, for example the 20k tow capacity they’ll be offering. Given all the tricks they’ve done to pull this off is what led to me thinking about how they might goose the towing regen.

I sound like a fanboy but as an engineer I am impressed with their architecture.

The interesting thing about the R1T is (likely true of GM/Ford, certainly Tesla) that they can be conservative and then up the game through OTA updates...so far 4 majors since April when I got mine adding snow mode, sand mode, camp mode, and a bunch else. Upgrade to towing/cruise is on the list...

[richard5933]

Originally Posted by AlbertF

I think I didn’t clearly articulate where I’m coming from. I would want to minimize trailer braking where possible and maximize regenerative braking - but not at the expense of downhill stability or accident avoidance.

Are you planning to be constantly tinkering with the brake adjustment as you drive, turning it up & down depending on the road contours and grade on hills?

To me, this is a recipe for disaster, as it only increases the likelihood of having inadequate trailer brakes at the moment you need them most. We have no control over what's going to be happening at every moment we're driving, and counting on having a free hand every time you need to crank up the trailer brakes just doesn't seem wise to me.

I guess in the end you're going to have to weigh the increase in regen you'll get against the increase in risk you'll get by driving at times with inadequate trailer brakes. You might be able to predict the road contour and how steep the grades are, but you cannot predict the moment you'll need to do a panic stop. Hopefully when that happens it's when your trailer brakes happen to be set correctly.

Not sure it's possible to accomplish your goal of maximizing regen braking on the TV while at the same time not reducing downhill stability or accident avoidance. Everything is a compromise, and in this one I'd vote for compromising on the side of safety.

[AlbertF]

Originally Posted by richard5933

Are you planning to be constantly tinkering with the brake adjustment as you drive, turning it up & down depending on the road contours and grade on hills?



To me, this is a recipe for disaster, as it only increases the likelihood of having inadequate trailer brakes at the moment you need them most. We have no control over what's going to be happening at every moment we're driving, and counting on having a free hand every time you need to crank up the trailer brakes just doesn't seem wise to me.



I guess in the end you're going to have to weigh the increase in regen you'll get against the increase in risk you'll get by driving at times with inadequate trailer brakes. You might be able to predict the road contour and how steep the grades are, but you cannot predict the moment you'll need to do a panic stop. Hopefully when that happens it's when your trailer brakes happen to be set correctly.



Not sure it's possible to accomplish your goal of maximizing regen braking on the TV while at the same time not reducing downhill stability or accident avoidance. Everything is a compromise, and in this one I'd vote for compromising on the side of safety.

The first to brake controller I ever had was the Jordan Ultima. It had no accelerometer; rather there was a cable connected to the brake pedal arm and the amount of braking force you got from trailer was entirely correlated with how far you were pushing the brake pedal. In theory you would still have trailer brakes even with complete failure on the tow vehicle. It worked extremely well but unfortunately the owner sold the company and the new owner never continued production, and I’d guess that the market has moved way beyond that analog approach.

You should be able to have a system that gives you the best of both worlds without continuously adjusting the amount of braking force on the trailer. The idea that I was suggesting was to only have the trailer brakes actually work if the brake pedal is being used, and to use something like the Prodigy boost system to provide a pulse of current to the trailer brakes when the pedal is first depressed.

Some kind of trailer stability sensing system to provide inputs to the brake controller might be helpful. If trailer yaw is detected the brake controller could send current to the trailer brakes even without brake pedal activation. This would also be helpful with an exhaust brake equipped tow vehicle when towing in slippery conditions.

These are ideas that would need to be tested and proven by those who produce the equipment. However given the sheer amount of technology built into electric vehicles I don’t think any of this is beyond the realm of possibility.

[richard5933]

Originally Posted by AlbertF

... You should be able to have a system that gives you the best of both worlds without continuously adjusting the amount of braking force on the trailer. The idea that I was suggesting was to only have the trailer brakes actually work if the brake pedal is being used, and to use something like the Prodigy boost system to provide a pulse of current to the trailer brakes when the pedal is first depressed.

Some kind of trailer stability sensing system to provide inputs to the brake controller might be helpful. If trailer yaw is detected the brake controller could send current to the trailer brakes even without brake pedal activation. This would also be helpful with an exhaust brake equipped tow vehicle when towing in slippery conditions.

These are ideas that would need to be tested and proven by those who produce the equipment. However given the sheer amount of technology built into electric vehicles I don’t think any of this is beyond the realm of possibility.

Seems to me that some have talked about their regen braking system being able to stop the vehicle, negating the need to use the service brakes or touch the brake pedal. There'd have to be more to the system than applying the trailer brakes when the brake pedal is mashed.

Not sure how if it would be possible to detect the trailer moving sideways. How would the system know the difference between a trailer moving sideways because it's about to jack knife vs. it moving sideways because of a curve in the road? Detecting a lock-up on a trailer tire is much easier, but that wouldn't be the issue if the trailer is under-braking and sliding sideways due to a panic stop in the tow vehicle.

The type of smart system you're describing where the TV and the trailer communicate and coordinate braking is likely on the horizon, but my guess is it won't reach the RV market for at least a few more years. The eStream and similar types of trailers will likely be the first to see this type of technology.

I think it's important to keep in mind that many (most??) people who will be using an EV as a tow vehicle will be towing traditional trailers with electric brakes that only do what they're told to do - no 2-way communication or anything fancy. Because of this, the brake controllers in the EV have to be able to accommodate them.

[CR-Rylie]

If you are charged to 100% for a longer trip, regen won't work few a few miles. Don't worry, that's normal.

[RedSHED]

Originally Posted by richard5933

...
Not sure how if it would be possible to detect the trailer moving sideways. How would the system know the difference between a trailer moving sideways because it's about to jack knife vs. it moving sideways because of a curve in the road? ...

Good question. However, it's a pretty straightforward controls problem. The actual approach would vary with what sensors a specific vehicle had, but something to detect steering angle, accel pedal position, brake pedal position, and what you typically have for ABS is likely plenty for a rudimentary system. If you have a 3 axis accelerometer (and lots do, partially to govern airbag deployment), that helps too.

Originally Posted by richard5933

.The type of smart system you're describing where the TV and the trailer communicate and coordinate braking is likely on the horizon, but my guess is it won't reach the RV market for at least a few more years. The eStream and similar types of trailers will likely be the first to see this type of technology.

I think it's important to keep in mind that many (most??) people who will be using an EV as a tow vehicle will be towing traditional trailers with electric brakes that only do what they're told to do - no 2-way communication or anything fancy. Because of this, the brake controllers in the EV have to be able to accommodate them.

That sounds right. Well, about right. The brake signal itself is an analog communication link to the trailer's brake system. If we can think of comm kind of like human voices, it's more like a baby's scream than a master's thesis, but it's still a communication "standard" basic as it is.


The weird stuff starts happening when the trailer's engineers have to guess what the truck's engineers are intending with any combination of signals. Until there's something like an SAE standard, it's going to be kind of expensive (proprietary) and possibly a little dicey.



We all have a general idea of these things working together like a perfectly drawn circle - seamless, smooth. But the first couple of generations are more likely to resemble a stop sign: a bunch of straight lines and some pretty sharp corners, but if you look at it in the right light and from a distance, it'll seem sorta round.

[richard5933]

Guess I was asking more about how a tow vehicle would know that the trailer it was pulling was starting to slide sideways. The tow vehicle could have the steering wheel pointed straight ahead, jam on the brakes in a panic stop situation, and have the trailer start sliding sideways due to a number of factors including the trailer not having adequate brakes.

Since an EV tow vehicle will typically be towing a trailer with a traditional electric braking system and without any fancy electronic sensors on the wheels, the only thing an EV can monitor with its onboard systems will be the reaction of the EV to the trailer. This puts any possible corrective action behind the curve from the start. Using the onboard sensors in the EV to monitor the trailer likely means it's reactive rather than proactive and not able to apply the trailer brakes to prevent the problem to begin with.

The brake controllers I've seen on the market today can send a variable signal to the trailer brakes. They can vary the amount of braking force sent. But they cannot receive any data directly from the trailer. They must wait until there is something felt inside the tow vehicle before reacting.

My main point is that not having the trailer brakes set properly in order to maximize regen braking puts the combination rig at a disadvantage when it comes time for emergency braking or driving in less-than-ideal road conditions.

[cedonly]

This has nothing to do with EVs.. regen braking is a benefit of hybrid + systems to recoup energy NOT to stop your vehicle.. reference EVs with disc brakes.. regen is not strong enough to be a braking system and existing batteries are worse for the environment that classical cars.. they are good at displacing emissions from city centers and that is it… batteries need to get to solid state. The rest of this discussion is about not allowing the travel trailer to put a forward load onto the TV since it is a pinned connection. ANd systems exist today with accelerometers to stop trailer away with trailer brakes but you need to hack the trailer brake system to separate left and right brakes.

Originally Posted by DrivingDan

Disclaimer: before people get worked up about safety and start lecturing about EV this or that, this thread is meant to be a theoretical and practical discussion of trailer braking in the era of EV’s, and what may or may not make sense. Let’s keep it on topic and focus on the discussion point

As discussed elsewhere I’m planning on stepping up my EV driving to towing with (we’ve decided) and Airstream using a Silverado EV truck. This lead me to think about trailer brakes. Now the Silverado EV comes with a trailer brake controller built in and the seven pin socket so that is available. However using the trailer brake is robbing the regenerative braking from all that potential energy. In an ideal world you would have no trailer brakes as the regen can certainly handle it (the battery can charge at 350kW and I’d estimate max regen with trailer would be < 200 kW)

So I’m wondering what the best approach is? For example, you’re going down a long constant grade as is common on the Interstates, would it be safe and reasonable to back the brakes off to maximize the regeneration on the tow vehicle? If the trailer and hitch have no issues with it, are you safe with going to zero trailer braking? What is the ultimate point of trailer braking, to give your tow brakes some help (which regen doesn’t need), or to help the hitch, or to prevent control issues with the trailer, or a combination of the above?

For reference EV’s generally treat regenerative cycles as braking and turn on the brake lights, presumably the same applies for the seven pin connector when in regen. OTOH maybe GM is programming it to only activate the trailer brakes when the car brakes - not regen - are activated. I’d guess they act normally no matter what.

[richard5933]

Originally Posted by cedonly

This has nothing to do with EVs.. regen braking is a benefit of hybrid + systems to recoup energy NOT to stop your vehicle.. reference EVs with disc brakes.. regen is not strong enough to be a braking system and existing batteries are worse for the environment that classical cars.. they are good at displacing emissions from city centers and that is it… batteries need to get to solid state. The rest of this discussion is about not allowing the travel trailer to put a forward load onto the TV since it is a pinned connection. ANd systems exist today with accelerometers to stop trailer away with trailer brakes but you need to hack the trailer brake system to separate left and right brakes.

Not sure where you're going here...

The thread is a theoretical discussion of EV tow vehicles and trailer braking. The initial question revolved around lowering the trailer braking so that the kinetic energy of the trailer could be used to increase the amount of regen on the EV's batteries.

We're also not discussing any comparison between EVs and classical cars regarding emissions. While an important conversation, it's not the subject of this one.

My comments about trailer brakes not being set up to prevent trailer sway was based on the current state of trailer brakes which are installed on nearly all current-day trailers. Perhaps there will be a system developed that incorporates accelerometers and wheel speed sensors, but as of today that's not the kind of trailer most will be pulling with an EV tow vehicle.