4 ms·

I wonder how good their regenerative braking is -- that's a lot of kinetic energy to both have to stop effectively and to take advantage of as, well, energy. M

I wonder how good their regenerative braking is -- that's a lot of kinetic energy to both have to stop effectively and to take advantage of as, well, energy. Most diesel trucks use a jake brake / engine brake because the wheel brakes would otherwise wear out relatively fast, or even overheat and fail on longer downhills. Seems like in-wheel motors are just about perfect for this application, and if they can put a reasonable fraction of that energy back into the batteries, even better.

simondotau 3y ago
There's no theoretical reason why it can't be good. The Tesla Semi is capable of significant regenerative braking capacity over long downhill stretches. Tesla's marketing claim featured a route which included Grapevine Mountain — which has a 4136ft elevation. They assert that it was capable of continuous regenerative braking, though it's not clear how much friction braking was involved. (It's almost certain that some trailer braking was involved for safety and stability.)
- kalleboo 3y ago
  In the interview with Jay Leno they said you can do Grapevine "without ever touching the brake" which I interpreted as 100% regenerative
- martin8412 3y ago
  It's capable of jack shit until they release it and let independent reviewers without NDAs review it.
jasonwatkinspdx 3y ago
In wheel are bad unless you really need the compactness. In general on a vehicle you want to minimize the unsprung mass. Also the geometry of the wheel restricts you to mostly axial geometry, where as radial electric motors can be made as long as you want. These trucks can charge at 160kw, so yeah they can put some pretty serious power back into that battery during regenerative braking.
m463 3y ago
yes regenerative braking is a holy grail. Unfortunately current (haha) car implementations have some corner cases that might be a safety hazard in a truck. EVs nowadays cannot absorb so much electricity with a cold battery or a full battery. Even during ideal battery conditions, I think a fully loaded tractor trailer on a hill could easily overwhelm even a large battery. I think the solution is some sort of hybrid system: https://en.wikipedia.org/wiki/Dynamic_braking https://en.wikipedia.org/wiki/Dynamic_braking like maybe dumping energy into the battery, then overflow into banks of resistors, and then a fallback to friction brakes: https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_braking https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_bra...
- yummypaint 3y ago
  I was thinking about the same issue the other day, but in the context of passenger EVs and tall mountain passes. On the pikes peak descent for example there are many signs imploring drivers to shift down and use engine braking to avoid brake overheating and failure. It would probably be a bad idea to put a charger at the summit.
- benj111 3y ago
  well if youve gone up the hill your battery will be warm and wont be full. if you charge at the top of the hill your battery will be warm you just need to know not to fill it up. you just need to train drivers not to have a break at the top of a hill.
tomohawk 3y ago
Using hydraulic hybrid technology is a better bet for trucks. They recapture 70%-80%, which is a lot better than batteries, and they last a lot longer than batteries. The economics show a savings of $150k per truck over its lifetime (for UPS trucks). The trucks don't have the massive additional battery weight, so less particulates from tire wear and less road repair. https://www.epa.gov/cati/hydraulic-hybrid-vehicles https://www.epa.gov/cati/hydraulic-hybrid-vehicles Garbage trucks can be retrofitted with hydraulic hybrid, for big savings. https://www.powermotiontech.com/hydraulics/accumulators/article/21884076/hydraulic-hybrid-garbage-truck-trashes-energy-waste https://www.powermotiontech.com/hydraulics/accumulators/arti...

simondotau 3y ago

There's no theoretical reason why it can't be good. The Tesla Semi is capable of significant regenerative braking capacity over long downhill stretches. Tesla's marketing claim featured a route which included Grapevine Mountain — which has a 4136ft elevation. They assert that it was capable of continuous regenerative braking, though it's not clear how much friction braking was involved. (It's almost certain that some trailer braking was involved for safety and stability.)

kalleboo 3y ago
In the interview with Jay Leno they said you can do Grapevine "without ever touching the brake" which I interpreted as 100% regenerative
martin8412 3y ago
It's capable of jack shit until they release it and let independent reviewers without NDAs review it.

jasonwatkinspdx 3y ago

In wheel are bad unless you really need the compactness. In general on a vehicle you want to minimize the unsprung mass. Also the geometry of the wheel restricts you to mostly axial geometry, where as radial electric motors can be made as long as you want. These trucks can charge at 160kw, so yeah they can put some pretty serious power back into that battery during regenerative braking.

m463 3y ago

yes regenerative braking is a holy grail. Unfortunately current (haha) car implementations have some corner cases that might be a safety hazard in a truck. EVs nowadays cannot absorb so much electricity with a cold battery or a full battery. Even during ideal battery conditions, I think a fully loaded tractor trailer on a hill could easily overwhelm even a large battery. I think the solution is some sort of hybrid system: https://en.wikipedia.org/wiki/Dynamic_braking https://en.wikipedia.org/wiki/Dynamic_braking like maybe dumping energy into the battery, then overflow into banks of resistors, and then a fallback to friction brakes: https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_braking https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_bra...

yummypaint 3y ago
I was thinking about the same issue the other day, but in the context of passenger EVs and tall mountain passes. On the pikes peak descent for example there are many signs imploring drivers to shift down and use engine braking to avoid brake overheating and failure. It would probably be a bad idea to put a charger at the summit.
benj111 3y ago
well if youve gone up the hill your battery will be warm and wont be full. if you charge at the top of the hill your battery will be warm you just need to know not to fill it up. you just need to train drivers not to have a break at the top of a hill.

tomohawk 3y ago

Using hydraulic hybrid technology is a better bet for trucks. They recapture 70%-80%, which is a lot better than batteries, and they last a lot longer than batteries. The economics show a savings of $150k per truck over its lifetime (for UPS trucks). The trucks don't have the massive additional battery weight, so less particulates from tire wear and less road repair. https://www.epa.gov/cati/hydraulic-hybrid-vehicles https://www.epa.gov/cati/hydraulic-hybrid-vehicles Garbage trucks can be retrofitted with hydraulic hybrid, for big savings. https://www.powermotiontech.com/hydraulics/accumulators/article/21884076/hydraulic-hybrid-garbage-truck-trashes-energy-waste https://www.powermotiontech.com/hydraulics/accumulators/arti...