Tesla Semi Aims to Put an End to Dangerous Jackknifing

If a truck pulling a trailer skids, the trailer can push the truck from behind until it spins the vehicle around and faces backwards. Caused by equipment failure, improper braking, or adverse road conditions, this precarious situation is known as a jackknife.

The Tesla Semi aims to end this dangerous, decades old problem on roadways. The truck uses independent motors for each of the wheels and can sense distribution of weight across those wheels. This allows the truck to engage the motors or brake as needed to maintain control of the vehicle. The system can also correct an oversteer in the event of a significant weight shift.

All of this happens automatically. It requires no advanced driving skills from the person in the cab. And, maybe that’s the point – the company does not hide its intentions to make the Tesla Semi fully autonomous.

But, while humans are still behind the wheel, Tesla is being thoughtful about creating a safer experience for drivers.

“Jackknifing is impossible,” Musk said at the Tesla Semi unveiling.

 

[jr4488]

Then Tesla does not understand jackknifing. It is caused by the trailer, not the tractor. It happens on icy roads, windy conditions, or under emergency braking. The trailer simply gets past the tractor, due to length and weight of the trailers. The trailer only has eight wheels near the back and a higher COG. The tractor has 10 evenly spaced at all four corners. The trailer cannot stop as fast as the tractor so any evasive maneuver can swing the trailer around the tractor.

You are absolutely right. When the trailer gets sideways, your best chance is to accelerate and pull the trailer straight. An experienced driver allows leaves enough room and keeps the speed low enough to pull the trailer straight in an emergency...

 

[Farmertom]

I think the jackknifing issue might be the unintended benefit of a freaking heavy truck...

Trucks are designed to put as mush weight as possible on the steering axle (hence the engine, fuel tanks etc. moved as far forward as possible and set back front axles). This makes the rear of the tractor relatively light in an unladen condition and very susceptible to jackknifing.

Tesla mounting the batteries midship tells me they are achieving maximum weight on the steering axle with virtually nothing in there and must transfer the rest to drive axles thus making this truck much better balanced and controllable.

 

[EvanLin]

Then Tesla does not understand jackknifing. It is caused by the trailer, not the tractor. It happens on icy roads, windy conditions, or under emergency braking. The trailer simply gets past the tractor, due to length and weight of the trailers.

It's not about how it happens. It's about why it happens.

If the tractor can keep the truck absolutely straight (via one-side motor and its instant response), how would the trailer "pass" it?
It's only a problem that "can't slow down enough and hit front obstacles".

 

[mongo]

It's not about how it happens. It's about why it happens.

If the tractor can keep the truck absolutely straight (via one-side motor and its instant response), how would the trailer "pass" it?
It's only a problem that "can't slow down enough and hit front obstacles".

Sure, which is how SpaceX lands rockets.
I don't understand your why vs how statement. Situations cause the trailer cg to not be in line with tractor and kingpin. There are the when to your why which create a how.
Most scenarios involve also needing to decelerate, if there is no need to slow, the tractor can drift the trailer.
Once there is the need to slow and stay in lane, other effects can remove stability.
If the semi is on a curve, inertial vector does not line up with centerline.
Or if the 300 sqft sail gets pushed sidways.
Or if there is an evasive maneuver (really looking forward to radar and traffic feedback to prevent pileups in whiteouts)

If the world shifts the trailer and the tires don't hold when the tractor needs to slow in a straight line/ one traffic lane, there is no recovery mechanism since the force vector of the trailer's CG does not line up with the point at which the tractor imparts force to the trailer (creating a rotational vector with no counter). And the tractor can't get them to line up again.

 

[EvanLin]

I am just saying op listed a bunch of situations, but not discussing how to solve it.

Maybe I shouldn't use the word "straight". I should use "zero-torque."
Even on a curve, if motor-control can achieve a zero-torque environment, there is no jackknifing.

You can balance a broom upside down while standing still -> like preventing jackknifing on a straight
You can also balance a broom upside down while moving forward -> like preventing jackknifing on a curve

 

[mongo]

You can balance a broom upside down while standing still -> like preventing jackknifing on a straight
You can also balance a broom upside down while moving forward -> like preventing jackknifing on a curve

I had originally written in that analogy (with a pencil, not broom). Either the trailer need to grip, or the tractor need to get in line with the front vector. The problem is the tractor can't more sideways (at least for long). So once there is torque/ lack of alignemnt, the system can't be stabilized (depending on constraints).

 

[Saxxon]

It may reduce the incidence of jack knifed rigs, but there are times you can't stop it. I was driving south out of Cheyenne, WY one morning with an inch plus of ice on the road, and gusting winds slamming the truck in the side. It was like driving thru a corridor with all the rigs laying on their sides off the road.

A gust of 50+ mph hit the truck, put me in an immediate 30 degree jackknife. The only reason I didn't wreck was I had an empty trailer, and a lot of experience screwing around in a raid yard skidding intermodal chassis in a dirt lot in deliberate skids (you get it whipped sideways and dust the guy parking in the lot). The truck went thru 4 cycles of left to right jack knife as I fought to get it under control sliding down the slight grade. Finally got it centered thru the oscillations and almost stopped - I'd only been doing 25-30mph when it started.

Now the automatic steering and power controls might have made it easier, or it might have made it worse because of the confluence of factors. My driving background certainly gave me an edge, but the maintenance crew searched in vain for the missing seat cushion when I got back to Denver.

 

[RamgeRover]

I provided some physical explanation on how this would work in my post of last May on this topic:

Tesla Semi

There is actually nothing useful you can change to the trailer to prevent jackknifing. So you might as well leave it standard and let the semi handle it.

 

[Sunshine State]

Although I don’t drive a tractor trailer frequently anymore l do have a Class A CDL with lots of miles of experience with oversize and heavy loads plus I own a heavy equipment company. One of the last things a truck driver with any experience has on his mind is jack knifing and if Tesla did any research they know this also. Not that jack knifing can’t happen, but it isn’t the problem they try to make it sound like(claiming driver nightmares). Maby Tesla can also address over the road driver wife infidelity too. That leads me to believe that Tesla is talking about Jack knifing for PR with car drivers that have no truck experience. Another disorienting feature of the Tesla design is the center driving position which puts the driver further away from the driver side mirror which an experienced CDL driver relies on. I recently drove a 40’ high end motor home, while being a significantly smaller and lighter vehicle than what I have great experience driving, it felt very odd because it had a sightly further distance to the drivers mirror, no where near the center position of the Tesla truck. If Tesla was serious about building a truck that would be accepted rather than a PR exercise or distraction they would build a truck with the refined design of today’s trucks that works and use the electric drivetrain if they think that the EV drivetrain could be a serious improvement. Already some big fleets that buy trucks by the 10’s of thousands have committed to a handful of Teslas to get the virtually free PR (by comparison to what they buy).

 

[electracity]

LCD screens can provide images far superior to mirrors. Cameras can do light amplification. Vehicles around the truck can be tagged. The exact location of vehicle relative to the end of the trailer can be displayed.

There is no aspect of situational awareness that can't be made better with the tech Tesla is using. The only problem will be that experience drivers will have to change well established driving behaviors.

 

[Sunshine State]

LCD screens can provide images far superior to mirrors. Cameras can do light amplification. Vehicles around the truck can be tagged. The exact location of vehicle relative to the end of the trailer can be displayed.

There is no aspect of situational awareness that can't be made better with the tech Tesla is using. The only problem will be that experience drivers will have to change well established driving behaviors.

I’ve seen mirrors crack but not fail, I think that’s why DOT doesn’t allow trucks to be driven without them. (Cameras are not allowed as a replacement) Its a bit like bureaucrats getting involved with something they know nothing about because they think they know better

 

[electracity]

I am just saying op listed a bunch of situations, but not discussing how to solve it.

Maybe I shouldn't use the word "straight". I should use "zero-torque."
Even on a curve, if motor-control can achieve a zero-torque environment, there is no jackknifing.

You can balance a broom upside down while standing still -> like preventing jackknifing on a straight
You can also balance a broom upside down while moving forward -> like preventing jackknifing on a curve

Perhaps you could keep the tractor parallel to the trailer, but that doesn't prevent the whole rig from sliding sideways. This trades a jacknife for a roll over. The bigger problem isn't jackknifing. It's keeping truck and trailer parallel to the direction of travel.

 

[electracity]

’ve seen mirrors crack but not fail, I think that’s why DOT doesn’t allow trucks to be driven without them. (Cameras are not allowed as a replacement) Its a bit like bureaucrats getting involved with something they know nothing about because they think they know better

I've seen heated mirrors stop working and become unusable.
Tesla will probably design a vision system that will have some redundancy. For example, camera images can be displayed on either LED screen. A truck with a broken camera will still have ultrasonic sensors.

A good aspect is that Tesla has to make all sensing and display ultra reliable for all vehicles. None of these issues apply to only the semi.

 

[Sunshine State]

I've seen heated mirrors stop working and become unusable.
Tesla will probably design a vision system that will have some redundancy. For example, camera images can be displayed on either LED screen. A truck with a broken camera will still have ultrasonic sensors.

A good aspect is that Tesla has to make all sensing and display ultra reliable for all vehicles. None of these issues apply to only the semi.

You may be missing my point that actual physical mirrors are required by law, because they are so simple and reliable. I love technology. I drink water and could stop that and go on an IV drip but the water works really well for me and is simple

 

[mongo]

Text from : 49 CFR 571.111 - Standard No. 111; Rear visibility.

Mirrors are required by law for the following stated reason: " S2. Purpose. The purpose of this standard is to reduce the number of deaths and injuries that occur when the driver of a motor vehicle does not have a clear and reasonably unobstructed view to the rear."

And the law was written before camera and display tech was were it is now.

Mirrors are also wasteful or energy at highway speed.

For trucks, the requirement is
"S8.1 Each multipurpose passenger vehicle and truck with a GVWR of 11,340 kg or more shall have outside mirrors of unit magnification, each with not less than 323 cm 2 of reflective surface, installed with stable supports on both sides of the vehicle. The mirrors shall be located so as to provide the driver a view to the rear along both sides of the vehicle and shall be adjustable both in the horizontal and vertical directions to view the rearward scene."

Interestingly, although trucks don't reference the backing event, there is no requirement I see in the testing that says you can't auto fold the mirrors when moving forward. So until regulation change, both could be used to achieve legality and efficiency.

"
Backing event means an amount of time which starts when the vehicle's direction selector is placed in reverse, and ends at the manufacturer's choosing, when the vehicle forward motion reaches:

(a) a speed of 10 mph,

(b) a distance of 10 meters traveled, or

(c) a continuous duration of 10 seconds.
"

 

[boki]

I agree with
etna,
evanlin: "It's only a problem that "can't slow down enough and hit front obstacles",
jr4488 "An experienced driver allows leaves enough room and keeps the speed low enough to pull the trailer straight in an emergency."

My full comments on this are here (Tesla Semi suggestions? | Tesla).

"
I would say 'impossible jacknifing' is- detecting onset and then automatically correcting it properly/optimally: steer into the skid (prevent driver's over steering), release tractor brakes (max brake but not lock up, abs), use independent traction control of each drive wheel to help straighten the tractor. The reason I think they can't (yet) prevent the onset is because they don't know exact traction (varies 10x from dry to icy road). If driver brakes and locks brakes on a slippery road, and trailer is at an angle, the onset will happen. Corrective action will help if jackinfing is the only problem and there is enough room ahead. And I think it would be useful to perfect this, if possible.

Sometimes truckers will jacknife their truck on purpose if their brakes fail in order to stop, or if there is a greater hazard ahead. So I don't think it is good idea to make it 'impossible' for those reasons.

If you go too fast on a black ice and you don't jacknife, it can take you forever to come to a stop. But you also don't want jacknife and to go off-road.

So my thought was that only proper way is prevention. And if we had exact knowledge of traction, along with other easily obtainable data, it is possible. So I think it would boil down to R&D of traction. The perfect solution could be: for a given vehicle (dims, weight, load, known tire/road friction), given the speed of travel, determine maximum safe stopping (following) distance without jacknifing onset. Or for a given stopping (following) distance, give maximum safe speed without onset of jacknifing. That is how I would formulate the task. I am open for any inputs.
"

 

[beachbum77]

Text from : 49 CFR 571.111 - Standard No. 111; Rear visibility.

Mirrors are required by law for the following stated reason: " S2. Purpose. The purpose of this standard is to reduce the number of deaths and injuries that occur when the driver of a motor vehicle does not have a clear and reasonably unobstructed view to the rear."

And the law was written before camera and display tech was were it is now.

Mirrors are also wasteful or energy at highway speed.

For trucks, the requirement is
"S8.1 Each multipurpose passenger vehicle and truck with a GVWR of 11,340 kg or more shall have outside mirrors of unit magnification, each with not less than 323 cm 2 of reflective surface, installed with stable supports on both sides of the vehicle. The mirrors shall be located so as to provide the driver a view to the rear along both sides of the vehicle and shall be adjustable both in the horizontal and vertical directions to view the rearward scene."

Interestingly, although trucks don't reference the backing event, there is no requirement I see in the testing that says you can't auto fold the mirrors when moving forward. So until regulation change, both could be used to achieve legality and efficiency.

"
Backing event means an amount of time which starts when the vehicle's direction selector is placed in reverse, and ends at the manufacturer's choosing, when the vehicle forward motion reaches:

(a) a speed of 10 mph,

(b) a distance of 10 meters traveled, or

(c) a continuous duration of 10 seconds.
"

Mongo

No matter what the Tesla Semi is equipped with you will notice on the recent photos and videos that the big Silver rig now has side mirrors that were not installed at the unveiling. Laws trump technology every time. Until all trucks have cameras, etc. you can expect the mirrors to be required.

 

[mongo]

Mongo

No matter what the Tesla Semi is equipped with you will notice on the recent photos and videos that the big Silver rig now has side mirrors that were not installed at the unveiling. Laws trump technology every time. Until all trucks have cameras, etc. you can expect the mirrors to be required.

Yah, I was providing the law that requires the mirrors for reference. Until FMVSS is updated to allow cameras, the mirrors will be required equipment.