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Comment by chem83 | Hacker News Reader

I always thought the problem with hybrids was the complexity of the drive train, but this video is challenging that notion. It argues that the hybrid pack (minus the battery, perhaps?) is more compact and simpler than a manual gearbox, even. It consists of two electric motors and a planetary gear set, which is seemingly simpler than clutch packs, gear sets and belts of regular transmissions, including CVTs.

Time codes 3:06, 37:07, 43:57, 43:36 (note on the eCVT naming), and 44:17.

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>> It argues that the hybrid pack (minus the battery, perhaps?) is more compact and simpler than a manual gearbox, even.

Having worked in the field I've been of that opinion for 15 years or more. Two motors and a planetary gear are simpler than a regular transmission. More efficient also, and more reliable. The inverter and small battery may add some cost, but the MPG improvement is more than worth it.

Hybrids are an awesome improvement over plain old ICE, but they tend to get an unnecessary price premium due to their advantages.

Well for quite a while, this has been a Toyota specific design, per their patents, but they ceded all royalties to those a few years ago [0], and to me, this seems like such a fundementally elegant design.

[0] https://global.toyota/en/newsroom/corporate/27512455.html

On a completely tangential note, has anyone ever tried a hybrid that was like a diesel-electric train? The engine just charges the battery. IIRC it can be much simpler, no need for gearing at all, the engine just runs at a constant speed and the battery handles delivering variable amounts of power.

one of the primary arguments of the video is that ecvt is a strictly superior solution. (and that diesel electric exists for massive torque conversion in trains, but loses efficiency)

Called a series hybrid, and it has been done. However gears are more efficient than a generator -> motor, and charging a battery adds even more losses. Thus if the engine is running anyway you are better off just mechanically connecting it to the wheels.

Trains don't do the above in large parts because the gears needed either wouldn't fit in the allowed space. (we may not be able to make them large enough either - that problem is solvable but may not be worth it)

I wonder if fuel efficiency just doesn't matter enough for trains, since they're already so efficient at turning motive energy into motion. Other costs may dominate.

Cost matter, but the dominate costs are important. The steam engine was more efficient than diesel when they scraped all the steam engines for diesel - steam engines need a lot more labor and so were more expensive despite using less fuel.

At that scale I think ICE engines preferably run at the same RPM continuously, and a gearbox and a clutch would be massive and require a lot of maintenance. The electric motor gives you the huge amount of torque you need to get a train going from stand-still. Not sure what actually tips the scale though.

This is correct or close too. The small steel on steel contact surface has so much less friction, that some conversion losses are fine in exchange for massive torque, and less moving parts (The diesel electrics replaced steam locomotives over maintenance cost/operation not pulling power).

The main thing for them is torque. Need a whole buttload of that to get it going. The efficiency of the train then comes from steel wheels on steel rails really. Electric motors is for the torque.

I have understood that idea as with some ships using similar systems is that this allows generators to run at optimal speed for efficiency which is rather tight band when you are looking for few of the last percentage.

With cars the speed range is much larger.

Series hybrids, where only electric motors drive the wheels, are becoming more common: Nissan now sells many models under their e-POWER brand.

Efficiency seems to match or exceed conventional hybrids in city driving, and only slightly less efficient for highway driving. And people like the instant torque and the smooth “EV like” driving feel.

I've got a Nissan Epower Kicks. I bought it exactly because the technology was different than standard Hybrid cars.

Here in Mexico there's no infra for fully electric cars, and they are still way too expensive.

The Nissan setup is pretty cool in that the generator is quite small, and the car doesn't need all the mechanical parts of an ICE car. It also gives us the range of a standard ICE car. So far it has been pretty good.

Series hybrids do have efficiency advantages in some situations -- for example, they can run in EV mode at any speed, and they can also have more freedom to run the engine at speeds independent of the vehicle speed, which can enable it to be programmed to prefer running it at speeds dictated by efficiency rather than by the drive wheel speed.

The place where they fall behind is at steady state on the highway -- but all of the series hybrid systems on the road have a solution for this problem too! They typically have clutch that engages a one-speed direct drive from the engine to the wheels. This skips the double-conversion losses at highway cruising. Then if you give it some gas to accelerate, the clutch disengages and you go back to full double-conversion again.

These are range extenders, and were used with the Fisker Karma, BMW i3 (as an option) and, most recently, the Mazda CX-30 with a Wankel engine.

The latter was sold in the UK/EU and was on the market for two years only.

That's called a series hybrid: https://en.wikipedia.org/wiki/Hybrid_vehicle_drivetrain#Seri...

Rumor mill, but the Mazda RX9 may have their rotary engine powering the battery, which then delivers energy to the drivetrain.

"In that concept, the rotary engine functions as a generator to produce electricity for the battery and electric motor, rather than mechanically driving the wheels."

Excited to see if this becomes a reality

more: https://uscarcover.com/blog/2026-mazda-rx9-review-rotary-is-...

Related: Honda's 2 Motor Hybrid System Explained. https://www.youtube.com/watch?v=-P_VChtMGK8

That is a series hybrid.

The Chevy Volt was one and the current Honda CRV is another. Both of them work mainly by the gas engine driving one of the electric motors as a generator while the other motor drives the vehicle. They have a simple eCVT transmission. However, both vehicles have a mode where they directly engage the engine to the transmission at highway speed cruising because that is more efficient.

Nissan has a series hybrid system that they have used in the Note that is only the series hybrid without the direct connect mode. That saves some money.

The Chevrolet Volt and Honda’s recent hybrids work this way. They are mechanically even more simple than Toyota’s drivetrain.

The engine doesn’t run at a constant speed though, it responds to the amount of electrical power needed.

And the BMW i3. It had a 2-stroke engine that allowed you to charge the battery.

However, in the USA, in order to get EV status, it was nerfed where it was only allowed to use its engine to charge the battery once you went below a 30% state of charge, and next to that, the fuel capacity was electronically limited.

A neighbor of mine had one, and the engine couldn't keep up with charging the battery to move the car on the freeway + running the AC, because it wasn't powerful enough.

In the EU version, this wasn't a problem, because you could set up the motor to run to maintain a charge (instead of only allowing it to run below 30%).

Edit: 30% state of charge, not 10%.

RAM and Ford are about to launch range extended EV pickups with 609 miles of Range and 14,000lbs of towing

https://expeditionportal.com/the-extended-range-ev-influx-is...

This was addressed explicitly in the video. It's far less efficient end-to-end, even though the gearing is theoretically simpler. Trains do it because diesel engines just can't produce the torque you need to move a train (at least, in the form factor of a locomotive), so they need to use electric motors.

He makes that argument but IMO it's not particularly well founded. He talks about his old Chevy Volt and guesses about the new Nissan series hybrids while ignoring Honda's current lineup of series hybrids. The Civic hybrid* meets or beats the EPA ratings on both the Corolla and Camry hybrids when on the same size wheels (18").

I agree in principal that there's efficiency to be gained by minimizing conversion losses, but Honda may be clawing that back with larger and more efficient motor-generators that only package well because no planetary gear set is required to connect everything.

* Honda hybrids do have either one or two clutches to mechanically connect the engine to the wheels at fixed ratios for highway cruising, but their city EPA numbers are still very competitive.

Ford is replacing their Lightning EV with an “EREV” gas generator.

There's so much variety in hybrids that's hard to discuss as a single category.

I think the most important question is whether the system requires a regular automatic/manual transmission or forgoes one entirely. The Toyota planetary gear system forgoes one, as does the modern Honda and Nissan approaches. Not having a transmission in the traditional sense saves so much complexity that the overall system is net simpler imo even with the additional complexity from having a motor and engine.

Then there are systems that have a full automatic drivetrain and some extra clutches to couple to a motor-generator. And there's even systems with an electronically controlled manual transmission instead. Those systems are going to be incredibly complex and fragile.

This is why there have been Prius taxis that were in service for 1 million km.

Yes, but specifically about the Toyota's hybrid system. Other systems are more complex, they have a traditional engine and transmission and an electrical system on top.

Ford has been making very similar hybrids for 20+ years. The old Escape, the Fusion, CMax, Maverick. These are all the same general layout as the Prius.

I probably should have said Toyota-like hybrid system, to include manufacturers that either licensed Toyota's system or developed something similar themselves.

There are other, more focused (also arguably better at explaining) videos on explaining how it works. Here is one: https://youtu.be/dxmxIsoV_Xo

It took a while and several explanations for it to completely click for me. The e-cvt mechanism does seem to be quite clever and simpler (at least mechanically).

There's a lot of memes about how dumb it is to have all of the ICE moving parts, but they're just memes. We know how to make engines and they are cheap to mass produce. The complexity argument is aesthetic.

I don't know much about cars, but I have to assume that fewer moving parts means less wear and repairs.

That's a fair assumption that doesn't prove itself in practice. In practice, a Prius engine lasts forever. Someone will jump in to complain about some anecdotal failure but the fleet statistics are strong. They even outlast other non-hybrid Toyotas. There are a lot of reasons for this but a significant one is the lack of belt-driven accessories, lack of friction clutches, and ability to avoid high-stress operation because of the electric side of the power train.

This is exactly correct, and I can't count how many times I've had to have this argument, thank you for pointing it out.

My hybrid (not a Prius, actually) doesn't have a dedicated starter motor, the traction motor starts the ICE engine. The climate control is electric and powered by the hybrid battery (with the added benefit of being able to run the A/C while the ICE engine is off). The power steering is electric so there's no hydraulic power steering pump to fail. I'm sure there's more I'm forgetting. Mechanically, it's just simpler than an ICE engine alone.

> ability to avoid high-stress operation because of the electric side of the power train.

This one is huge, also, and people always forget about it, so thank you for raising it. ICE hate being heavily loaded at low RPMs (also known as "lugging"), and the electric motors alleviate a lot of that low-end workload. It's a big win not just for efficiency, but also drivability, as almost all non-diesel engines make terrible torque low in their RPM range.

I could go on and on about the enhanced reliability features of my hybrid. One reason why it will last forever is that when the engine needs to start, the ECU grabs the crankshaft with the MGU and spins it up to 1000 RPM, and doesn't deliver fuel until oil pressure is verified. The cam phaser also keeps the valves wide open so there's little compression while starting. And, unlike other ICE engines that are forced to operate at certain speeds depending on what the car is doing, the ECU in my hybrid can detect oil dilution and simply fix it.

Yeah, there’s just so much you can do (or not do, depending on how you look at it) when you have a well-integrated ~50hp electric motor and decent sized battery.

It may be aesthetic now but it will become economic soon enough. There is just no way a complicated hybrid system stays price competitive with a dumb simple electric motors and some batteries. Hybrids will end up more expensive as batteries drop rapidly in price - the gas engine and system costs are mature and thus fixed and will not decline. Batteries get substantially cheaper and better every year. Hybrids have a short economically viable window whose days are numbered (I personally think 2026 is the last year they’ll compete in many markets)

Interestingly, iForceMax drivetrains in Toyotas seen in Tundras and derivatives are the “other” kind with conventional transmissions.

This does not appear to be a packaging issue, as the late 2000s LS 600h had a V8 with rear-wheel drive (and then AWD) with an “eCVT” in a “conventional” longitudinal package.

It might be simpler than a regular gearbox, but so what? That tech is already commoditised, and generally very reliable. The engine - not the transmission - is the biggest pain point with ICE vehicles. It’s what needs constant maintenance and fluid changes.

> The engine [...] neds constant maintenance and fluid changes.

I drive my ICE to the dealership once a year, and one hour later the above is all done (in the meantime I drink coffee and read a book nearby). Once a year. I wouldn't call that "constant maintenance and fluid changes". It's "yearly", as in "once a year".

I will be getting an EV in the future (we're setting up our house with solar and a V2H system - Vehicle To House), but that's not because an ICE needs constant engine maintenance. It doesn't.

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