New Electric Class 8 Truck and a physics question

[dmarbell]

Apparently this new truck concept has created the youngest billionaire in the US. The truck touts a 1,000 mile range and an all-electric range of 25 miles - the latter with no decrease in performance fully loaded to 80,000 lbs.

The truck has an all electric drive train powered by batteries that are recharged by an onboard engine running on renewable natural gas, and features regenerative braking.

See the "How it Works" section of this website.

https://www.hyliion.com/erx-page/#/find/nearest?fuel=CNG

Now to the physics question. If the truck has a 1,000 mile range, with a 25 mile all electric component, and the batteries are recharged to be able to go 975 miles (1,000-25, in theory) by the onboard engine, wouldn't the onboard engine have to be powerful enough to propel the truck 975 miles? I left out the positive effects of regenerative braking, so there is some gain there. But the overall energy needed to travel 1,000 miles is the same regardless of the method of power generation.

So is all this effort just to get the gain from regenerative braking plus the feel-good effects of a 25 mile all electric range? I haven't seen the estimated cost of a truck like this, but I would guess it would be about double the cost of a conventional diesel truck.

 

[LeeMajors]

Apparently this new truck concept has created the youngest billionaire in the US. The truck touts a 1,000 mile range and an all-electric range of 25 miles - the latter with no decrease in performance fully loaded to 80,000 lbs.

The truck has an all electric drive train powered by batteries that are recharged by an onboard engine running on renewable natural gas, and features regenerative braking.

See the "How it Works" section of this website.

https://www.hyliion.com/erx-page/#/find/nearest?fuel=CNG

Now to the physics question. If the truck has a 1,000 mile range, with a 25 mile all electric component, and the batteries are recharged to be able to go 975 miles (1,000-25, in theory) by the onboard engine, wouldn't the onboard engine have to be powerful enough to propel the truck 975 miles? I left out the positive effects of regenerative braking, so there is some gain there. But the overall energy needed to travel 1,000 miles is the same regardless of the method of power generation.

So is all this effort just to get the gain from regenerative braking plus the feel-good effects of a 25 mile all electric range? I haven't seen the estimated cost of a truck like this, but I would guess it would be about double the cost of a conventional diesel truck.

Do we know the size of the engine powering the generator. Thats a big factor in answering your question.

But I highly doubt it takes a 450hp engine to drive the generator

 

[Get Off My Lawn]

Regen braking adds some, not a lot. The technology has been used in forklifts for ~15-20 years, along with regen lowering. It works by applying the rotational torque the motors, making them a generator.

 

[mj1angier]

So is all this effort just to get the gain from regenerative braking plus the feel-good effects of a 25 mile all electric range?

I know nothing about the power thoughts but I think we are quickly coming to the point that there will be some cities (to start, then states) that will require all cars/ trucks that enter be electric. Kind of like some lakes only allow boats with electric motors. So with that in mind, this truck could use non electric power to get between towns and use the 25 miles of power around town. I am sure it will start in CA but will spread from there.

 

[DCGallim]

Republic Waste is getting ready to test all electric garbage trucks. I’m predicting failure, trash trucks leak and those batteries are going to be coated in juice. Probably over the next 10 years they will become the norm.

 

[mj1angier]

Says 0-60 in 20 seconds. Fully loaded. That's great, but how fast can it stop, lol

 

[chiefjason]

Says 0-60 in 20 seconds. Fully loaded. That's great, but how fast can it stop, lol

That system is pretty well established. And it's faster than you might expect IF the driver is paying attention. The problem with rear end accidents isn't always stopping distance. It's the driver not realizing they should be stopping. And around 75% of truck/car accidents are the cars fault. Sometimes by getting inside that stopping distance when they should not. Give them plenty of room. Because panic braking is hard on everything and now it gets you a phone call from the boss.

 

[noway2]

Sounds like they borrowed the concept of the diesel-electric transmission, where an engine drives a dynamo that produces (DC) electricity to drive the motors. Often times rechargeable batteries are placed in the system as a buffer. The DC motors have maximum torque at low speeds which gives them good acceleration, especially under load.

 

[dmarbell]

Do we know the size of the engine powering the generator. Thats a big factor in answering your question.

But I highly doubt it takes a 450hp engine to drive the generator

We don't know the size of the engine. But the engine would have to be powerful enough to generate enough electricity to propel the truck 975 miles, less of course the power generated by fully charging the batteries with plug in electricity to start with. This initial charge is 25 miles worth of power. And I believe there would be power loss in the generation of electricity to storage batteries and then transfer of that electricity to the drivetrain. Once the initial charge of the batteries is exhausted the engine would need to generate the power to propel the truck. So if it takes 450 hp to propel the truck at accepted performance standards, then yes it would take a 450 hp engine to power the generator of sufficient size to power the drivetrain.

I know it doesn't seem reasonable on it's face but it has to be true.

 

[GymB]

I suspect that the electric motor is far more efficient than the internal combustion engine would be for getting up to speed, so a smaller diesel motor continuously running at an optimal level to feed the electric motor will turn out to be more efficient overall.

I believe that railroad locomotives are powered this way.

 

[noway2]

But the engine would have to be powerful enough to generate enough electricity to propel the truck

Yes, the engine has to be big enough to power the truck. Per the link in the OP, it is using a natural gas engine to run a generator which produces enough electricity to drive the motors. The batteries act as a buffer. It isn't all that different than a Prius or other hybrid.

So if it takes 450 hp to propel the truck at accepted performance standards, then yes it would take a 450 hp engine to power the generator of sufficient size to power the drivetrain.

Maybe, it depends upon relative efficiencies and losses. It is difficult comparison to make. A diesel engine is roughly 45-50% efficient in terms of thermal / mechanical energy and then if you're using this for a drive with a transmission you have all the losses from the gears, etc. What's the efficiency of the (natural) gas engine, generator, and motors? Per NEMA standards for larger motors the efficiency is going to be somewhere up around 92-94% and I imagine the generator is somewhere in this vicinity (>80%). Hence you can deliver the same brake (output) power with a smaller generator. Plus the batteries can supplement high current draw at very low loss during acceleration which is made up more slowly by the smaller engine, whereas a combustion engine would loses a lot of efficiency during acceleration.

 

[spittinfire]

Trains do this and have been for years. A diesel generator powers batteries that supply electric motors to drive the train.

The engine powering the generator can be made more efficient as it has one single task, at one speed, all the time. Current truck engines can’t do that because they have varying demands.


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[Scsmith42]

Trains do this and have been for years. A diesel generator powers batteries that supply electric motors to drive the train.

The engine powering the generator can be made more efficient as it has one single task, at one speed, all the time. Current truck engines can’t do that because they have varying demands.


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I actually hold a locomotive Engineers license and the locomotives that I've operated are not battery powered.

The DC generator operated by the diesel engine provides power directly to the DC traction motors. Batteries are only used to start the diesel.

Dmarbel, I dont think that a 450 hp generator would be required because the only time that 450 hp is required is accelerating from a standstill undera heavy load, or climbing a hill.

With a hybrid system, you could get by with say a 300 hp generator and have the batteries supply the extra power when needed.

This is why a hybrid Prius can get 50 mpg versus the same non hybrid would be much lower. The battery makes up the difference and then is recharged during light loading times and via regenerative braking.

 

[dmarbell]

I actually hold a locomotive Engineers license and the locomotives that I've operated are not battery powered.

The DC generator operated by the diesel engine provides power directly to the DC traction motors. Batteries are only used to start the diesel.

Dmarbel, I dont think that a 450 hp generator would be required because the only time that 450 hp is required is accelerating from a standstill undera heavy load, or climbing a hill.

With a hybrid system, you could get by with say a 300 hp generator and have the batteries supply the extra power when needed.

This is why a hybrid Prius can get 50 mpg versus the same non hybrid would be much lower. The battery makes up the difference and then is recharged during light loading times and via regenerative braking.

That's a great analysis. But, does a Prius get better mileage than a non hybrid model of the same weight and power if you take the initial electric charge of the batteries out of the equation? This is a valid question.

 

[Scsmith42]

That's a great analysis. But, does a Prius get better mileage than a non hybrid model of the same weight and power if you take the initial electric charge of the batteries out of the equation? This is a valid question.

I believe that the answer is yes, primarily due to regenerative braking. One interesting little tidbit is that the original Prius models had a more powerful battery than the newer ones. Honda refined the design to reduce the weight / power of the battery because they found that a lighter battery that only provided additional power for acceleration provided overall better mileage versus a heavier battery that had more capacity.

The change was good for another mile or two per gallon, which makes sense when you consider that most of the fuel is used to accelerate the engine. Using the batteries to provide the acceleration power and the generator for providing the cruising and recharging power is a good compromise.

 

[GymB]

I thought that when you stomped the accelerator on a Prius that it went to gas and that when you cruised it used electric. Have I got it backwards?

 

[noway2]

I thought that when you stomped the accelerator on a Prius that it went to gas and that when you cruised it used electric. Have I got it backwards?

Don’t know about stomping on it, but I believe it uses battery for stop and go traffic and switches over to gas for steady state cruising.

 

[spittinfire]

I thought that when you stomped the accelerator on a Prius that it went to gas and that when you cruised it used electric. Have I got it backwards?

Yes, you're backwards. Most hybrids use electric power to get up to speed because it takes more energy to accelerate than it does to maintain speed. At low speeds or stopped in traffic it will actually use the battery for things like radio, heat & a/c, power windows, until the battery had reached a low level and then it starts the gas engine to recharge the battery.

 

[Scsmith42]

I thought that when you stomped the accelerator on a Prius that it went to gas and that when you cruised it used electric. Have I got it backwards?

Somewhat . Spitinfire explained it well. The basic hybrid design uses the battery as a substitute for a mid fuel demand scenario, such as accelerating. But if the demand is too great, ie stomping the accelerator, it will go immediately to gas. If you light foot it, it will use battery power from 0 to around 25 mph, and then the gasoline engine kicks in.

 

[RedneckFur]

I think this could make for a more efficient truck, since the engine only has one job, and that's drive a generator. It can be tuned specifically for optimum performance for that, instead of having to rev up and down constantly.

At cruising speed, excess power can be used to charge the battery, and battery power used for additional torque when starting and accelerating a heavy load.

 

[VA_GENTLEMAN]

Meanwhile.. my brain is fried trying to figure this out....

 

[RetiredUSNChief]

Maybe, it depends upon relative efficiencies and losses. It is difficult comparison to make. A diesel engine is roughly 45-50% efficient in terms of thermal / mechanical energy and then if you're using this for a drive with a transmission you have all the losses from the gears, etc. What's the efficiency of the (natural) gas engine, generator, and motors? Per NEMA standards for larger motors the efficiency is going to be somewhere up around 92-94% and I imagine the generator is somewhere in this vicinity (>80%). Hence you can deliver the same brake (output) power with a smaller generator. Plus the batteries can supplement high current draw at very low loss during acceleration which is made up more slowly by the smaller engine, whereas a combustion engine would loses a lot of efficiency during acceleration.

This.

There's more to this than just what's powering everything. It's overall efficiency of the entire propulsion train that's the driving factor for the bottom line.

At face value, converting hydrocarbons to electricity to kinetic energy (motion) would seem to be less efficient than converting hydrocarbons to kinetic energy, because you take out the middleman, right?

Well, it turns out that the efficiency of all that stuff between the internal combustion engine and the wheels is significantly improved when going electric. This includes the computer controls for everything, too.

And that's where the gains come from.

 

[Scsmith42]

I think this could make for a more efficient truck, since the engine only has one job, and that's drive a generator. It can be tuned specifically for optimum performance for that, instead of having to rev up and down constantly.

At cruising speed, excess power can be used to charge the battery, and battery power used for additional torque when starting and accelerating a heavy load.

Keep in mind that typical DC generators produce constant voltage but more current at higher rpm’s, versus most ac generators that require a fixed rpm in order to generate the correct cycles. Inverter ac generators produce DC and then invert it to AC, so they can have different operating RPM's (such as the Honda with the "economy" low RPM mode inverter generator).

On a diesel electric locomotive, speed is directly correlated to the generator rpm/current output.