Mazda bringing back rotary engines as EV extenders

[Andrew]

Interesting, but I thought they were fundamentally inefficient compared to reciprocating engines ?

[Colin Bignell]

They can, however, rev at very high speeds. If that means they don't need to use gears to drive the alternator that charges the battery, that would be quite a saving in weight.

[John Rumm]

From what I read elsewhere, they are a bit less efficient, but have a number of advantages in this particular application - particularly very compact size and can be installed in places you could not stick a conventional reciprocating engine.

Running them at fixed or limited rev ranges since they are only in effect coupled to a generator (they never drive they car directly) lets them get round some of the better known problems.

[The Natural Philosopher]

just not for very long. the main cause of failure was worn rotor seals.

If that means they don't

Possibly.

[Andrew]

Hmm, bit of a grey area if your EV is taxed as an EV and allowed to access areas where IC cars are not allowed (though this applies to the BMW i3 with the optional motorbike range extender too).

[Joe]

I've seen a picture of a Tesla towing a generator...

[Joe]

I can recall a magazine article from about fifty years ago about replacing a rotary engine with a V4 Transit engine. I can't recall which car was involved, and Google doesn't seem to know.

[Theo]

It shouldn't count as an EV for tax purposes, it's a plugin hybrid. With an

17.8kWh battery you only get 53 miles of EV range - that makes it likely any longer journey will be using the range extender.

I think the i3 REX was similarly classified.

If you could get one in a suitcase sized box you could plug in aftermarket, that would be quite interesting - leave the ICE at home when you don't need it. But that's not on offer here.

Theo

[Brian]

Possibly the RX7, although I’m not sure it was Transit engine. I thought it was a V4 from one of the older Ford saloons.

[mm0fmf]

Fifty years ago... it will have been for an NSU Ro80 engine.

[SteveW]

But can modern materials and modern accurate machining overcome that?

[Paul]

The rotary will be running at a constant speed, which is supposed to be good for it.

Just as another serial hybrid, uses the Atkinson cycle.

Running a generator, is a different design task.

And they're doing it this way, because they are running out of rich people to sell to. You'll notice the design has a lack of superlatives, in all dimensions :-) You won't be burning donuts in the drive with it. Or drag racing on Friday nights. You won't be driving on the Autobahn with it (likely to be gutless for such purpose, no torque near top speed). Will you be towing things to the skip ? You probably could, but the rotary would be running the whole time to keep up.

It's not a golf cart. You can't carry the battery pack into the house.

Paul

[The Natural Philosopher]

IIRC that *was* the transit engine. Might have had a different cam tho. Ah different compression ratio..

"The Essex V4 is a 60° V4 engine with a cast iron cylinder block and heads. The engine block was just 20 in (510 mm) long.[3]: 60, 61  The heads are crossflows with 2 overhead valves per cylinder operated through pushrods and rocker arms by a single camshaft in the block. Inlet valves had a diameter of 41 mm (1.6 in), while exhaust valves were

37 mm (1.5 in).

All Essex V4s had the same 93.66 mm (3.69 in) bore diameter, but the 1.7 L version had a stroke length of 60.35 mm (2.38 in) and the 2.0 L version had a stroke length of 72.42 mm (2.85 in). Connecting rod lengths were the same, so the different displacements were achieved by changing the crankshaft throw lengths and the piston heights. The cylinder firing order was 1-3-2-4.

The 1.7 L and 2.0 L engines in the Transit van had a standard compression ratio of 7.7:1. A ratio of 9.1:1 was standard for 1.7 L engines in passenger cars, while 8.9:1 was standard for 2.0 L engines in passenger cars and was optional for the 2.0 L in the Transit. Power output varied from 73 hp (54.4 kW) for the low-compression 1.7 L engine to 93 hp (69.4 kW) for the high-compression 2.0 L engine, while torque ranged from 100 lb⋅ft (136 N⋅m) to 123.5 lb⋅ft (167.4 N⋅m). With the Essex V4 engine's Heron cylinder head design and bowl-in-crown pistons, different compression ratios were achieved with different cylinder heads. Low-compression cylinder heads such as the ones fitted to Ford Transits had shallow combustion chambers in them while high-compression heads were completely flat"

[The Natural Philosopher]

You cannot overcome the problem that the gap between the rotor and the combustion chamber walls is not quite constant. So the seals have to slide in and out. And it is pretty much impossible to have oil control seals there as well. And the rotor ends don't seal so well either. So these motors are big oil burners.

I used to see them being raced a lot at Kyalami in the early 1980s. Power they had, but they rebuilt the engines pretty frequently.

[Tim+]

It was indeed. Short engine bay made the V4 the easiest swap at the time.

Tim

[mm0fmf]

To a large degree it can. The later Mazda rotary engines had a lifespan around 150000miles before needing major work. The early ones much less so. They were also very intolerant of poor maintenance.

[fred]

BMW I3 is regarded as a hybrid

[Robert]

Mounting kits were readily available and buying an Ro80 with a knackered engine and doing a transplant could be a cheap way of getting an interesting car

[Brian Gaff]

Not sure about that. The rotary engine has been around for a long time, but it seems that the wear in them is the big problem. I'm assuming you do mean the Wankel type with the central gear drive? All the ones I remember used oil a lot. Brian

[Brian Gaff]

Maybe you need a radial engine then, like they used to use on Aircraft, where the cylinders were arranged around the drive shaft on the basis that it was supposed to be smoother, but they are hard to keep cool if use for land transport as you would need to mount them at degrees, and then you would tend to try to turn the car in the opposite direction.

Brian