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Mazda’s rotary engine in the age of the electric car

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Re: Mazda’s rotary engine in the age of the electric car

#111

Post by 01HNNWZ0MV43FF »

idontwantthis wrote: post #43
ch_sm wrote: post #20

Earlier quoted context omitted.

> It is more efficient to turn gasoline into electricity and then drive the car with that than to directly connect the engine to the wheels I thought so too, but my research suggested that the efficiency is pretty much the same if not worse and power delivery is worse. Do you have some links? I‘d like to be wrong on this one.

I thought the idea is that the battery acts as a buffer and the engine is always either off or at constant rpms in its ideal power band.

Priuses do a power split where the engine drives the wheels and the motor-generators act sort of like an electrical CVT. You would have to be out of the power band a lot to make a series hybrid more efficient than a parallel hybrid. The reason locomotives are series hybrids is just that mechanically switching that amount of power isn't practical. To my surprise, even off-highway mining trucks mostly use mechanical transmissions.

Re: Mazda’s rotary engine in the age of the electric car

#112

Post by ggreer »

eggsboenk wrote: post #106
ggreer wrote: post #60

Earlier quoted context omitted.

Several reasons. First, like most of the Japanese manufacturers, Mazda bet against electric vehicles. They focused R&D on improving engine efficiency and getting their engines to run on hydrogen. If Mazda wants to make electric vehicles now, they have to play catch-up, or license key technologies from other manufacturers. Second, batteries are heavy. For sedans and mid-size crossovers, this isn't much of a problem. E…

The McMurtry Spéirling is claimed to be under 1000kg. A lightweight electric car may not be an oxymoron after all. Just some concessions to make.

The McMurtry Spéirling is not street legal and it costs $1 million.

Re: Mazda’s rotary engine in the age of the electric car

#113

Post by maxerickson »

Tade0 wrote: post #82
mattmaroon wrote: post #15

I have never understood why the Volt Series Hybrid idea never took off. It is more efficient to turn gasoline into electricity and then drive the car with that than to directly connect the engine to the wheels. Is it perhaps that the cost involved is just too much more than a plugin hybrid to make the small extra fuel savings worth it?

Both the Chevy Volt and Toyota's hybrids rely on a planetary gear set to blend power between the gasoline engine and electric motors. Here are the differences explained in more detail: http://roperld.com/science/ChevyVolt.htm

At least one version could run as a series hybrid or as a torque combining hybrid, depending on which clutches were engaged.

Re: Mazda’s rotary engine in the age of the electric car

#114

Post by 01HNNWZ0MV43FF »

Electricniko wrote: post #67
deelowe wrote: post #58

Earlier quoted context omitted.

Still seems like a traditional hybrid would be more efficient. I'm not sure what's gained by removing the mechanical coupling altogether (other than cost/reliability).

Honda has an interesting solution in their latest gen hybrids, where the electric motors power the wheels at lower speeds, the combustion engine runs at its optimum RPMs as a generator while the electric motors are working, and at higher speeds a clutch activates that changes the coupling so that the combustion engine directly drives the wheels.

Whatever the Prius HSD does is great. It'll do 50 MPG city and highway. No clutch at all.

Re: Mazda’s rotary engine in the age of the electric car

#115

Post by knodi123 »

explorigin wrote: post #69
Projectiboga wrote: post #13

I was always impressed by this engine in my childhood, but it never really caught on. Here is a variation I've seen on the internet, i'm not sure how practible it would be. https://arstechnica.com/cars/2023/11/this-inside-out-design-...

https://www.youtube.com/watch?v=X5UOqZn43gY It has longevity-issues due to an internal roller bearing on the main shaft.

wow, thanks. I didn't expect to watch the whole thing, but I did.

Re: Mazda’s rotary engine in the age of the electric car

#116

Post by labcomputer »

callalex wrote: post #78
mattmaroon wrote: post #15

I have never understood why the Volt Series Hybrid idea never took off. It is more efficient to turn gasoline into electricity and then drive the car with that than to directly connect the engine to the wheels. Is it perhaps that the cost involved is just too much more than a plugin hybrid to make the small extra fuel savings worth it?

“It is more efficient to turn gas into electricity” I don’t think that’s correct. It may be true for highly variable/low loads where the pumping losses in the pistons dominates. However the majority of fuel consumption in a car happens at traveling speed (highway miles). That is the area that needs to be optimized for. My 2015 Honda Accord Hybrid takes this approach. At below-freeway speeds the gas motor runs in seri…

> > “It is more efficient to turn gas into electricity”

> I don’t think that’s correct.

You're right, it's not.

In fact, GM wrote an SAE paper about their "2-mode hybrid" transmission (which was used in their 2008-2013 light-duty trucks and SUVs, and then in later modified form in the 2nd gen Volt), where this is plainly explained.

In the paper they describe exactly the tradeoffs made to optimize fuel efficiency in an eCVT... it turns out that you want to set up the planetary gears to minimize the energy transmitted from input to output via electricity and maximize the amount transmitted mechanically because that is most efficient. You especially want to avoid a round trip through the battery in most cases (except when that allows installing a smaller, more efficient ICE).

That has implications for the CVT's mechanical ratio: GM's "2 mode" which has what basically amounts to an auxiliary overdrive integrated in the eCVT so that it can use smaller motor-generators over a wider range of speeds. Smaller motor-generators means more energy is transmitted mechanically, which means higher efficiency.

This is also basically the same reason the 1st gen Volt gets significantly worse highway MPG in range-extender mode than the (contemporary) Prius Hybrid (~35MPG vs ~50MPG): The 1st gen Volt eCVT was envisioned as an EV with a range extender (where energy usually comes from a battery), while the Prius's eCVT was optimized for driving primarily on the ICE, with the battery only supplementing acceleration.

Re: Mazda’s rotary engine in the age of the electric car

#118

Post by labcomputer »

jeremymims wrote: post #27
mattmaroon wrote: post #15

I have never understood why the Volt Series Hybrid idea never took off. It is more efficient to turn gasoline into electricity and then drive the car with that than to directly connect the engine to the wheels. Is it perhaps that the cost involved is just too much more than a plugin hybrid to make the small extra fuel savings worth it?

This was how the BMW i3 worked. It was a rather novel design that included an optional small electric scooter motor in the rear that had a 2.5 gallon gas tank. When the battery was low, it would be charged by running the small generator. This was clearly a wonderful idea but it was hamstrung by a silly California rule requiring the gas range to be less than the electric range to qualify for rebates. With a 6 gallon t…

> it was hamstrung by a silly California rule requiring the gas range to be less than the electric range to qualify for rebates.

The problem is that BMW wanted to get the same amount of credits as a pure-BEV. California anticipated that a car with 300 miles of gas range might spend much of it's life being driven on gas if there was no penalty for doing so... and in fact that is exactly what happened with many European plug-in hybrids sold as company cars.

California never gave BMW the credits, but BMW decided to keep the dinky gas tank anyway, so that's on them.

Re: Mazda’s rotary engine in the age of the electric car

#119

Post by 1970-01-01 »

aunty_helen wrote: post #107
1970-01-01 wrote: post #101

The problem with the Wankel is and has always been apex seals. You need to rebuild it at least once during a vehicle lifetime. I would not say it is safe from this fate, even with modern seals and a hybrid application.

I thought it was the horrible compression and oil burning. Apex seals seem to last if you don’t do silly things to them but you can’t solve inherent issues with the cycle design. For comparison, rotaries get about 100psi of compression, a modern gas car can more than double that. More compression, more efficient burn.

I've read that oil burning (which is directly tied to the apex seals) has been fixed in modern engines. Compression is a somewhat configurable matter, and can be high in a low-torque generator (battery hybrid) application.

Re: Mazda’s rotary engine in the age of the electric car

#120

Post by discreteevent »

ggreer wrote: post #60
skellera wrote: post #8

Earlier quoted context omitted.

I don’t understand why Mazda doesn’t just make a drift-tuned electric car. You could do amazing stuff with software focused on that driving style. A true electric successor to the RX-7 would capture so much attention.

Several reasons. First, like most of the Japanese manufacturers, Mazda bet against electric vehicles. They focused R&D on improving engine efficiency and getting their engines to run on hydrogen. If Mazda wants to make electric vehicles now, they have to play catch-up, or license key technologies from other manufacturers. Second, batteries are heavy. For sedans and mid-size crossovers, this isn't much of a problem. E…

“Adding power makes you faster on the straights. Subtracting weight makes you faster everywhere.” - Colin Chapman (Lotus)
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