Hacker News Reader

Comment by malfist | Hacker News Reader

Those 40% numbers, if you actually read how they got that, it's almost always that they were running the engine in a fixed point operation with a constant RPM.

You can make it a bit more efficient by optimizing an engine for a specific singular output, sometimes up to 50% I think is what nissan claims. One automaker, I forget who, was researching doing a hybrid drive train like the volt had, but where the engine could run in that one single speed and charge a battery.

Seems a lot more complicated than just electrifying the system, but I'm not a auto researcher.

Nissan's PR about it: https://www.nissan-global.com/EN/INNOVATION/TECHNOLOGY/ARCHI...

View on HN

> One automaker, I forget who, was researching doing a hybrid drive train like the volt had, but where the engine could run in that one single speed and charge a battery

Not sure if this is what you're thinking of but Honda's eHEV platform drives the wheels with an electric motor and small battery†, with the engine kicking in as needed to generate current and to charge the battery (as well as regen).

†Until you get to high speeds, at which point a clutch engages and the engine drives the wheels directly, via a single fixed gear.

BYD just released such a vehicle with a claimed 2000 km range. Pity we can't buy them in north America. https://www.reuters.com/business/autos-transportation/byd-la...

Sadly, the efficiency gained from being able to run the engine at a fixed RPM is lost in the conversion to electricity and back. This technique has been tried a few times but it never works out in the end. The only time it makes sense is if you have a turbine engine, but since turbines have fairly lousy efficiency to start with this only helps get them back up to the baseline.

audi's dakar car (the rs-q e-tron) proves that it's at least more efficient than petrol based competitors. it doesn't charge overnight so always uses the energy from onboard fuel tanks, which are smaller compared to the other competitors. it doesn't reach peak efficiency of course, but still uses less fuel overall.

Diesel-Locomotives (and apparently submarines?) use that concept a lot in the form of a diesel-electric power train[1]. Mechanical transmissions like in cars were only in use for a very short time. (You didn’t need them for steam locomotives as steam engines can start under load) Of course locomotives are a bit bigger than your average car...

[1] https://en.wikipedia.org/wiki/Diesel–electric_powertrain

> Mechanical transmissions like in cars were only in use for a very short time.

Fortunately.[1][2] British Rail tried in the 1950s. Four 12-cylinder Diesel engines driving the the wheels through three differentials and four hydraulic clutches. The engines were geared such that the speeds added. As speed increased, more engines were turned on. Since startup only used one engine, starting pull was rather low for the engine power installed.

Only one was ever built.

[1] https://en.wikipedia.org/wiki/British_Rail_10100

[2] https://www.youtube.com/watch?v=oYRZIQKMmWo

I guess you can run it in a slightly different engine cycle called the Atkinson cycle, That's one of the tricks that hybrid vehicles used to increase their efficiency

But if you drive like a leadfoot that doesn't really work cuz then usually the hybrid systems fall back on the gasoline engine for additional torque and it goes to the normal gas cycle when it does that and you lose the efficiency

I think this is how some Diesel-electric locomotives are built, with Diesel engines creating electricity for electric motors, running the ICE at constant speed and minimum transmission (not sure a reduction is needed, probably not). Looks like solid engineering for the cases when electrification is not possible for various reasons.

Diesel electrics can be big enough and with long enough expected lifetimes to go 'all out', I think in some ways they can get closer to CCGT as far as efficiency.

Where the challenge comes for smaller vehicles, is the more power you are trying to give, the more you have to build everything up; not just the engine but whatever that engine is inputting into, also trains have somewhat more predictable speed profiles over a trip vs a car.

This is why some manufacturers have vehicles that are PHEVS but really BEVs with an 'oh crap' extender that can struggle to keep up a good grade.

I gotta give TRD/Toyota/Ford credit, the HSD style drive train does work around a lot of this stuff for PHEVS; in lockup mode you have a 1:1 ratio with minimal losses and at that point it's up to the ability of the engine to adjust profile.

Works very well in practice, and far simpler than the setups of others.

Diesel-electric locomotives were the first vehicles to get really good motor control. In what are called "AC" locomotives, the wheel motors are 3 phase variable-frequency AC motors. The power train is Diesel engine -> generator -> really big MOSFETs -> synchronous 3-phase motors. Each motor is separately controlled and they are run as synchronized servomotors, to prevent wheel slip. When multiple locomotives are coupled together, they synchronize at the wheel level. The effect is almost 2x more traction than older technology, which means fewer locomotives per train.

Automotive motor controllers now use similar technology, but the locomotives had it first.

Reply on news.ycombinator.com