The diesel-electric/hydraulic systems are used in situations where the gearing ratio would have to be absurdly high, they're not used because they're efficient or because they have good torque vectoring capabilities. The electric motor can produce nearly 100% of torque at zero RPM, which helps locomotives get several million pounds of train moving. In your car, truck, or even semi, first gear plus some clutch/torque converter slippage is plenty of mechanical advantage to get going, and once you're underway, a lockup torque converter or a fully engaged clutch is more efficient than the combination of an electric generator and a motor.

There's also the matter of power distribution, if you have four independent electric motors, you can only ever send 25% of available torque to one wheel, if you have front, rear, and center lockers, you can send 100% of torque to one wheel.

> a lockup torque converter or a fully engaged clutch is more efficient than the combination of an electric generator and a motor.

I doubt it, generators and motors operate at 99% efficiency. Do you have any reference?

> if you have four independent electric motors, you can only ever send 25% of available torque to one wheel, if you have front, rear, and center lockers, you can send 100% of torque to one wheel.

That assumes that engines are so small that they operate at 100% under normal conditions. This doesn't have to be the case, electric engines are so small, you can have bigger-sized engines where one single engine can use all the power. The nature of electric engine is such that the loss of efficiency by doing this is minimal. Plus you need to do this only fractions of the time, so the engine doesn't have to be designed to operate in high power mode at full duty cycle.

> I doubt it, generators and motors operate at 99% efficiency. Do you have any reference?

A locked up torque converter or an engaged clutch is basically a solid steel bar. You're the one that is going to need to provide sources that show an electric generator and motor, operating in series, are 99% efficient across a wide operating range. (you won't find that that's true).

>That assumes that engines are so small that they operate at 100% under normal conditions. This doesn't have to be the case, electric engines are so small, you can have bigger-sized engines where one single engine can use all the power. The nature of electric engine is such that the loss of efficiency by doing this is minimal. Plus you need to do this only fractions of the time, so the engine doesn't have to be designed to operate in high power mode at full duty cycle.

Look up the efficiency of electric motors running outside of their optimum power/rpm ranges. Also, you basically just said that you can get around a percentage problem by increasing the coefficient, which kind of misses the point. Also, if you're going to put four motors, you're probably doing that because you want to put them in the hubs, (if you're putting them inboard, you'd just use one or two motors and put a differential in there, like Tesla does), if you're putting motors in your hubs you want the smallest motors you can get away with, because larger motors increase unsprung weight.

Mechanical transmissions are still more efficient, at least for cars, than spinning a generator that then powers an electric motor.

Even hybrids usually have a way to get the engine power directly to the wheel. In the Prius's system, it uses a planetary gear with a pair of electric motor/generators which allow it to split power between the mechanical and electrical paths. In the Volt, there are clutches which allow the car to transition between parallel and serial hybrid modes.

> Mechanical transmissions are still more efficient, at least for cars, than spinning a generator that then powers an electric motor.

Do you have a reference?

Since both electric generators and motors well exceed 99% efficiency at this power level, I don't see how can this be the case.

Do you? I can't dig up anything particularly good, but what I do find indicates in the mid-90% for practical electric motor efficiencies.

This says 85-95% efficiency for the motor in an EV: https://matter2energy.wordpress.com/2013/02/22/wells-to-whee...

This says 93% for a brushless DC motor: http://electronics.stackexchange.com/questions/58236/why-doe...

I found a bunch more of similar quality searching for "ev motor efficiency" and similar.

I'm not particularly satisfied with those, so if you have something better, I'd love to see it!

And don't forget, you have generator efficiency to deal with as well. If you're 90% on both sides, the system is only 81% efficient. Ouch!

The Jaguar C-X75 [1] concept car uses exactly this idea, it uses a tiny and very efficient jet engine that is charging the batteries. Very neat idea.

1: https://en.wikipedia.org/wiki/Jaguar_C-X75

1) That's not a "jet engine". It's a turboshaft. A turboshaft is a gas turbine producing its power mechanically at the shaft. A turbojet is a gas turbine producing its power in the form of reaction thrust out the tailpipe.

2) Gas turbines scaled down to small size (let alone "micro" size) generally have dismal thermal efficiency. All the most efficient gas turbines are gigantic (tens of thousands of hp).

Jet engines are not "efficient". The SFC is worse than piston engines and in fact, the smaller the turbine the worse the efficiency:

https://en.wikipedia.org/wiki/Brake_specific_fuel_consumptio...

I've never heard that jet engines are less efficient. From what I remember piston engines are 33% thermally efficient, diesels 36% and turbine engines are upwards of 60%+. Of course there are many types of jet engines and ways to get power off of them.

You heard wrong. Diesels under optimum conditions can easily exceed 45%, and state of the art is right around 50%. Gasoline engines can reach 40% or better (again, under optimum conditions). Turboshafts are generally around 35-40% efficiency at best-economy conditions, and dismal under low-load conditions. The very largest turboshafts can reach 40-45%, but come nowhere near to diesel efficiency at low load.

In all cases, you can increase efficiency somewhat by going to the complication of compound cycle, where you harness some of the wasted heat in the exhaust by making steam.

Large, high bypass turbofan jet engines are very efficient from an overall propulsive efficiency standpoint, but you aren't measuring the same thing (shaft power times time, divided by energy consumption).

And they burn cheaper fuel

What the f..k. Thanks for that link, a jet engine?! That's crazy. But it's the "awesome" kind of crazy.

And the CO2 values... wow, how is that possible? Burning a defined amount of fuel should always produce the same amount of CO2?

Gas turbines operate efficiently at constant output, which a hybrid-drive system with storage can manage. They only need to kick out enough power, on average, to keep the storage system fully charged. Batteries and eletric motors can handle both high-demand accelleration, and regenerative braking. Since the turbines are running at a very constant range, and can be rated to average out power load inclusive of idle times, they can be designed for optimum efficiency within that range. Or that's the theory.

There've been other gas-turbine automobiles, including some prototypes built in the 1960s. A friend of mine test drove one, claimed it could lay a patch (spin the tires) at highway speeds. Though my understanding is that in direct-drive applications (such as that), turbine lag is an issue.

The exhaust also runs quite hot, and turbines typically emit a lot of NOx (nitrous oxides), what you get when you run atmospheric nitrogen through a high-temperature field.

Much anecdata here, apply salt liberally.

For anyone interested in turbines and cars, there's a delightful episode of Jay Leno's Garage about a Chrysler turbine car:

https://www.youtube.com/watch?v=b2A5ijU3Ivs

He talks extensively about how it works, what it's like to drive, and the various difficulties that resulted in it never entering mass production.

It sounded like a gigantic loud vacuum cleaner even just idling, and gave the impression of straining mightily to achieve even mild acceleration. Fuel consumption was TERRIBLE.

The large volume of very hot exhaust you mention is your clue that the thermal efficiency of small gas turbines is poor to dismal.

I assume the CO2 values factor in the electric only range.

Locomotives are used on railroad tracks. Adding weight does not matter.

Cars generally suffer quite a lot if you add significant weight: both performance and fuel economy will be hit. That is why locomotive solutions are not very suitable for cars.