Featured Wankle Range Extender

Regulations limit the range of the extender though. Refueling every 70 miles on a long trip must get tiring. The additional stops extend travel time too.

 

That's not the first time Mazda's done a serial hybrid with a Wankel, FWIW - they've done a dual-fuel (hydrogen and gasoline) Wankel in the Mazda5 before.

I'd expect efficiency to be quite dire in range extending operation, Wankels aren't known for their thermal efficiency. However, in an i3 REx-like situation, where the engine literally just needs to be there to sell the car, it won't actually get used by most buyers, the lighter weight and smaller size for a given power output will help the Wankel.

There's only one regulation that I'm aware of that limits extender range, and that's the California ZEV regulations (which nine other states also follow), and then only if you want maximum ZEV credits (that is, if you want to be counted as a Type I.5x or a Type IIx vehicle, which gets the same credits as a Type I.5 (2.5 credits) or II (3 credits) vehicle). That regulation requires the extender to not start under driver control (no Hold mode, no Charge/Mountain mode), to only start after all electric range is depleted, and for extender range to be less than or equal to all electric range on the UDDS cycle (so, effectively, city range).

The trick is, the rules are biased pretty strongly against conventional PHEVs - they get a lot fewer credits, and their credits are worth less due to being limited in application (TZEV credits are a smaller portion of the allowable ZEV credits, although I.5x/IIx vehicles are also their own pool separate from other ZEVs).

 

The extender range must be less than or at most equal to the electric range. @bwilson4web would be more knowledgeable than I. I believe he needs to refill every 70 miles on long trips with his BMW.

The Electric BMW i3: BMW i3 REx Lawsuit: How'd This Happen & Who's Really at Fault

 

Yes, but what I'm saying is, that range is a California rule. Outside of the 10 ZEV states (California and those that follow the California ZEV rules), that rule does not exist anywhere in the world.

 

Car manufacturers now view the US as one market when designing vehicles due to economies of c=scale. They do not tend to have CARB-only designs any more. All US is somewhat bound by CARB regulations.

 

Except there are plenty of cars built to non-CARB regulations still - even the Volt has an AT-PZEV package that's only sold in CARB states.

And, when you consider that something like the i3 REx's prohibitions on hold mode and (on the small battery model) using all of the fuel are purely software, if BMW thought they could sell enough volume outside of CARB states, they could certify them separately.

Oh, and there's also Europe, Japan, and the other countries that follow European, Japanese, or their own standards. I'll note that the i3 REx in Europe has hold mode and uses all of its fuel, it's not built to CARB standards.

 

The A1 E-tron Audi was working on used a Wankel for a range extender. It was only 250cc in displacement, and the whole unit with generator sat between the rear wheels. This A1 PHEV lost no cargo or passenger space in comparison to the ICE model. So while a rotorary engine is less fuel efficiency, their packaging can trump that when grid energy is going to be the car's main energy source.

California and those ten states are a huge market though. The days of a car manufacturer offering a physical CARB and federal version is pretty much gone. So California rules are effectively rules for the US.

The Volt is the only exception that I know of, and it exists for the HOV sticker.

Other countries also have their own vehicle codes and safety standards. The car makers would be extremely happy if they could simply make a car to one set of standards for all markets

In the case of the i3, it is a mere half gallon of fuel that is unavailable in the US. As for the rest of the CARB's REx rule, I hold it up there with their hydrogen support. With the reports of underpower, and potential lawsuits, BMW probably no wishes they hadn't bowed to CARB.

 

AFAIK, Subaru's entire model line is sold in PZEV and non-PZEV models, too - non-PZEV for 38 states (I think that's the current count, some states have reverted to federal standards), PZEV for the 12 CARB emissions states and DC.

 

A while back I read about the rotary range extender .... they are talking (I believe) about a grapefruit size rotary running at a constant speed.

 

Same with the Prius. Yet this doesn't mean the cars are physically different; the engine codes need to be compared.
Compare Side-by-Side


This is a sample of Subaru models with different engines. Only the 2.5L Legacy comes equipped with two different engines. The others are sold with the same engine and emission system, no matter the state. Subaru and maybe all the others will certify an engine of a car sold in federal states to a lower standard in order to save money on emission warranty costs. It also saves development costs to design just one, cleaner engine.

That was likely was the A1 E-tron; 250cc is just a quarter liter. It was conceived to run the genset at one speed, but drivers found the one constant hum when the ICE was on unappealing. Audi switched to three engine speeds to allow the rev noise to better match vehicle speed. The test fleet might of had a dozen or so cars before the program was axed as a victim of the 2008 recession.

The EV range was 31 miles, but the gas tank size would be copied by BMW for the i3REx. Around 100 miles or so, the hybrid mode was seen mostly as a way for getting between European cities.
Audi A1 e-tron: First Drive Of Range-Extended Electric Car Prototype
Audi A1 E-Tron Concept – Review – Car and Driver

 

No need for the GPS behavior changes - and that would violate CARB specs anyway for the BEVx class.

Simply configure the ZEV state cars with a no-cost mandatory option for BEVx parameters (equal UDDS range on gasoline as on electric, no hold mode), and everything else without those parameters. Owners can figure out how to disable the BEVx parameters after the fact if they want to and bought a BEVx-spec car meant for a ZEV state.

But if you can simply leave off some things like advanced evaporative emissions hardware...

 

It would have a different engine code from my understanding.

 

They really need to let the Rotary engine go. They suffer from poor efficiency, poor emissions and poor reliability.

Let. It. Go. Mazda.

 

The number is referred to as the engine family or test group, and it includes emission systems.

Mazda has filed new patents in regard to the rotary. One is just using it as a range extender as mentioned in the OP. The other is in relation to a start/stop system.

Mazda's piston engine start/stop system is novel in that it doesn't make use of the starter. Simplified, the ECU keeps precise track of piston position, injects fuel and fires the spark in the ideal one to get the whole crank spinning. They've adopted this for their Wankel. Part of the start stop process has the rotor always stopping at the point where it seals the intake port. This cuts down on emissions going out the front end of the engine.

So Mazda is improving the emissions and possibly the efficiency of the rotary. I don't see this as enough to challenge their SkyActiv piston engines, but if they do bring the Wankel back, it most likely be as a range extender in a plug in. In that application the rotary's advantages could trump its disadvantages in regards to the piston.

• They have higher power to weight/size output than a piston engine. The one in the A1 Etron was 250cc in displacement, Mazda's in the Mazda2 PHEV concept is 330cc. This makes it easier to package them in a PHEV.
• Without pieces violently moving back and forth, but just spinning, they make less noise and vibrations. This could result in less weight from sound deadening, or make the ICE on transition less noticable.
• Lower efficiency becomes less of a con as grid energy and EV efficiency make up more of the car's daily use. The Volt and i3 REx have lower hybrid efficiency than the Prime, but can result in less gasoline use over time for many.

Mazda patents show rotary engine for range-extended EV - Autoblog
Mazda Patent Reveals Rotary Engine for Use in Hybrids - The Drive

 

If we don't look at price the ford 3 banger (1L turbo) is quite small and efficient. A wankel would be cheaper to produce, but won't be nearly as efficient. The iron block of the ford allows it to be smaller and gives less of a warm up penalty than aluminum, but adds weight. In a PHEV application though I don't even think the prius engine weight (100 kg) matters, but you would like to take up less room.

Only reason for a wankel is for press. From an engineering point of view if we look at efficiency and reliability it is a non-starter. Remember if you only use the ice occasionally that reliability is even more important. Drop the turbo and go atkinson on that ford design and costs would get quite low, perhaps even close to the wankles (but hp would drop considerably and may be require a bigger battery for headroom.