Renesis tech tidbits from engineering-process magazine
 

I just received a 3 page article from an engineering magazine (AEI Jan ’04) that may be of interest. The article is entitled, “Mazda Overhauls Rotary Engine Plant.”
Here are a the relevant items:

“Now Mazda is gearing up to produce 60,000 units of the new RX-8 every year. The rotary plant has been completely overhauled, renovated, and largely ditigized…. // the remaining article deals w the up-rated manufacturing processes re the Renesis… Digitally modeled based on Mazda’s veteran rotary craftsmen’s skills and know-how, the manufacturing facilities have been updates and rebuilt to incorporate the latest numerical control technology. …
many of the major components of the new Renesis engine in-house. The engine, which inherits the 13B 2 rotor engine family’s internal dimensions and geometry, is a new design with few carry-over parts. Mazda casts, machines, heat-treats, plates, and finishes the engine’s major components, including die cast aluminum rotor housings, cast-iron side and intermediate housings, and cast-iron rotors. The steel eccentric shaft forging, equivalent to the conventional crankshaft, is supplied by an outside specialist, with Mazda machining and finishing it…….. The peritrochoid profile must be precisely shaped. Previously, a mechanical machine tool (!!!!!!!!!!!!!!!!!!) using the copying-grinder principle was employed. For the new Renesis engine, Mazda designed a CNC five-axis grinding machine that improves machining precision by 60% contributing to the engine’s gas-tightness
For Renesis rotors molten metal is poured centrally versus the previous 13B-REW’s pouring from the corner. Uniform metal distribution and more precise rotor balance are achieved. The cast-iron rotor is one of the 2 heaviest rotating components of the rotary engine. The other is the eccentric shaft, whose motion is nicely balanced compared with the rotor’s planetary motion. The Renesis rotor has shed 5% of it’s mass versus the previous 13-B-REW, and now has a mass of 8.6 pounds. That is still a hefty mass, but the rotor revolves at a third of the eccentric shaft rpm… Molten metal previously was poured into a mold between apices of six rotors, three stacked in 2 pairs. In this casting method, molten metal cooling temperature is not even, causing irregular density in the casting. For the Renesis rotor, molten metal is poured into the center of the mold of the 3 rotors, delivering a more even weight balance and casting density.
Each apex-seal groove corner is induction-hardened. A “pin-point” induction-hardening device was developed by a Mazda heat-treatment expert, winning the government sponsored Award of Excellence in 2002. The new system allows full automation of the process and ensures stable hardening.
For the rotary engine, gas sealing has been by far the most crucial technological challenge in design, development, material and manufacturing….. Mazda relies on it’s former subsidiary, Micro-Techno, now spun off and renamed Koldenschmidt KK, to supply the apex and corner seals.
The rotary engine’s gas seals consist of apex and corner seals in the 3 apices of the rotor, and the side seals and a newly added blow-by cut-off ring seal on each side of the rotor. Previously the side seal was arched and rectangular-sectioned piece w a thickness of .03 in. The new engine’s side port configuration allowed significant enlargement of both intake and exhaust port opening areas. Earlier in the development stage, Mazda engineers experienced frequent breakage and “swallowing” of side seals when they traversed over the ports. A new keystone seal, .05 in thick at the top is adopted to solve this problem.
The keystone seal has a trapezoidal section, thicker at the top and tapering down at 4.5 degrees in its .14 in height. Machining 3 trapezoidal-sectioned grooves on each rotor side was another challenge to the manufacturing team. The cutting tool is subjected to lateral force in addition to vertical because of the tapered groove. A new CNC machining system was developed in-house with improved cutting tool rigidity. The tool cuts .002 in in each of it’s 78 travels (it moves arched sideways in a reciprocating movement) delivering a groove .18 in deep to accommodate the seal.
The whole rotor and eccentric shaft assembly is balanced. The rotors sides must be gas tight; therefore, the previous method of balancing by milling is no longer possible.”

follow-up comments re the article:

while there are lots of interesting details engineering-wise in the above article the figure that jumps out at me is 60,000 per year. i have no idea as to how many rx8s mazda is hoping to sell yearly but i doubt if the number is 60,000. obviously you can add in some rx7 sales eventually too if the car comes out. i am hoping that mazda will go back to what initially made it's reputation.

Ressurect The RX3.

can you imagine how many rear drive small sedan Renesis powered RX3s mazda could sell? imagine the tuner market for such a vehicle. i realize that's a subject for another part of the forum. i just can't stop drooling over the idea.

howard coleman

I dont know, they might sell close to that world wide, plus they are going to have to keep stock for warrenty issues and such.

Interesting article, thanks for posting it
STEPHEN

That's the stuff I like to read about. Thanks.

Nothing like a little engineer-speak in the morning to wake you up.

Thanks for the outtakes.

They have already sold more than planned in the US. Looks like sales are going well. We're having lots of fun discovering the new technologies used. Things like four separate ignition coils, with spark timing varying between L and T and between the two rotors as well! If you want to go to a "better" aftermarket ignition system, it's going to be expensive! Electric power steering. The DSC (dynamic stability control) system is amazing. The car is such a "control freak" it's hard to dyno as it tends to go into a "safe mode" if it sees non-standard wheel motion. We had to pull the rear ABS sensors out of the hubs, and even then, only had 20 sec. to dyno before the car's systems reacted.
There appears to be lots of "head room" in the fuel system anyway. WOT we only see injector duty cycles of around 40%.
It's got a system bus to ensure everything is working correctly. Very cool. The PCM (we've been calling it an ECU but PCM is the correct ANSI term) controls everything on the car, though the fuel pump system is the same design as previous RXs with no PCM intervention.

Very interesting car to work with.

Great post Howard. Now if they would only start turbo'ing them...

Thats what I am talking about, something not so "sophisticated" as the RX8, just a small\medium size RWD 13B renesis :)

maybe even a rensises 12a for it to help gas milage a little

i have heard rumors of a fourth gen rx7 to be released in 2006 does anyone anything about that

13B's generally get better mileage than 12A's because the 13B has a lower internal surface:volume ratio, meaning less heat escapes to the cooling system proportional to how much is generated.

The best mileage I ever got with a 12A was ~26 highway. GSL-SE guys, running a richer fuel mixture (I run lean of stoich on highway), get as high as the lower 30's.

A 15A would probably get better mileage than a 13B, however the eccentric shaft would probably start to be a bit ropey for the sky-high RPM that the side port engines need.

thx for the info

and a nice middle bearing would help with that alot