How about a mild hybrid version of the RX8?
 

I think that a true hybrid electric rotary engine would kinda defeat the purpose of a small, light weight engine, but, what if mazda did what GM did for there trucks in a smaller form?..that is have a small set of batteries that run the alternator, AC, water pump, steering and any other function normally run off of the belts? I wonder how much of a gas mileage improvement that would add as well as power? I'm sure this could be done for less than 60-70lbs. GM gets a good 10-13% increase in fuel economy, so for us, that be another 1.8-2.5mpg city wise....not to mention the AC wouldn't rob power...just a thought.

On another note, is is possible to shut our engines down when coasting, but be able to start back up quickly enough to not really be noticed by the driver?

i don't think the rotary is the best engine for that, and hybrid engine systems are really best suited for cars which do not have any duty other than grocery getting or commuting (basically, boring mom and dad cars, SUVs included).

all the weight, and all the fuss, and all the cost just couldn't be justified for a sports car. but does mazda need some sort of hybrid or alternative fuel offering in the very near future to stay competitive?? yes.

Check out this thread on Honda IMA with the RX-8

Honda IMA with RX-8

Personally I this is a way to get more low end torque without going FI. I think of it more as a performance improvement than a gas mileage improvement. Gas mileage improvement is a bonus.

Eventually all cars and even trucks will have some sort of a hybrid, especially if they switch to the 42V system.
Currently all cars have a starter and an alternator, which is a real waste, since you're carrying a 5kW or so motor around that you only use to start the car. It would be much smarter if starter and alternator would be the same entity and some of the brake energy would be regenerated as well as the 'starter' could be used to help accelerating the car.

This hybrid has only a 14kW electric motor and still seems to be quite effective:
theautochannel.com/N/F/news/2004/09/17/229317.html?%7BLF%7D&

I think its pretty clear that the next rotary engine is going to have to have some major improvements in efficiencies if it is to be a realistic option in the future. To me the biggest reason for the rotary is its size and weight, which allow for car designs that no other vehicle can have as a result. That said, this is not a compelling enough reason to have one if its gets ½ the gas mileage or less than a slightly larger and heavier 4banger. A hybrid or IMA would seem to be the answer, but in doing so you might lose any weight and size advantages, which calls the whole idea into question.

A mild hybrid would offer some of the advantages of a full one without the major weight gain of having to haul around enough batteries to truly power the car. With gas prices where they are in the U.S. (and especially Europe), you run the risk that people just simply won’t want a vehicle with such a mileage to power ratio. If this were a 500 HP Ferrari, things might be different.

I’m just trying to think ahead and kick around ways to get the city mileage into the low to mid 20’s, which I think would be an almost certain requirement by 2010.

Adding some sort of electric boost motor could definitely help with the low-end torque issues inherent to the engine.

From the cartoons (meaning just "not to scale" or "reference" drawings/cutaways in engineering slang) I've seen of the Honda system, it looks like they have some sort of a system where the flywheel doubles as an armature for an electric motor, which gets energized when it's needed as a "boost" motor (and could presumably function as a starter and/or alternator depending on the state of the vehicle).

I'm not sure if there's any way in such a setup to aviod the power drain in "alternator" mode from potentially limiting/reducing top speed, as it would presumably be in such a mode during cruising, and engaged as a motor when the throttle gets goosed.


A couple comments directly responding to brillo:

1) The engine can, in some cases do OK restarting on the fly. I had an experience coming down El Cajon pass on the way back from Vegas once where my engine stalled while freewheeling on the downhill side of the pass (I didn't see the need to keep the engine spinning at full revs when I was holding 90 MPH in neutral with the grade). It restarted OK, but doing so regularly can be an unneccesary distraction for the driver, and also leaves you a couple seconds from having acceleration available when you might need it in less than 1 second. All told, I'm going to avoid having such a thing happen again in the future, and wouldn't reccomend doing it deliberately.

2) (this is a bit of a nit-pick) Are you sure that GM uses batteries to drive the alternator? While I wouldn't put it beyond GM to do such a thing, it sounds like a system that is ultimately doomed to not start up someday, as it basically relies on the energy left in the batteries to replace the energy consumed from the batteries....

I went back and tried to find the write-up on that Silverado, while it does not haul around a bunch of batteries, it must have some extra ones for it to need the regenerative braking technology. Some really good comments and insite thus far.

To bgreenes point, I think that the car would still need a normal battery for startup, and even those if left to sit for months would die, so I don't think that starting the vehicle would be a issue....as you would have a normal battery and then a small battery pack to power all the other equipment.

I'll take a 42V RX8. I don't even need a IMA or hybrid. Think about the horsepower you can save by eliminate the need to run things like the water pump, oil pump, A/C off the engine! The weight distribution will also be advantageous since these items don't need to be "connected" to the engine. Not to mention that I can run a true electric supercharger of the 42V system.

Actually the use of batteries has also some advantages since they can lower the center of gravity.
I think Mazda added a flywheel/motor/alternator on its hydrogen RX-8 as well as an electric turbo. Both concepts would increase mileage and low end torque on a gasoline RX-8.