The heat flow path from combustion chamber to the rotor
bearing and then on to the e-shaft is very short in Wankel
engines. See the attached jpg.s. The rotor combustion
chamber surface runs up to 500 F. This heat transfer
path must be blocked or the rotor cooled to prevent
the rotor bearing and e-shaft from over heating.
The rotor bearing integrity is key to the maximum RPM
of any Wankel engine. Since HP is a direct function of RPM
the power to weight ratio of a rotary is also a function
of the maximum RPM the engine can achieve.
The current oil cooled rotor Mazda engine is limited to about
11,000 RPM in racing and about 9,000 RPM street.
It seems to me this problem or feature needs to be addressed
in future rotary engine designs. SAE paper 900035 addresses this issue
for charged cooled (CCR) rotaries but it may be applicably to
oil cooled (OCR) rotor Wankel engines such as the Mazda as well.
http://www.rotaryeng.net/
"Down load tech paper on charged cooled Rotamax type rotary engines."
What this SAE paper suggest is making the e-shaft hollow and cooling
the rotor bearing area from within the e-shaft by oil or glycol/water
coolant. How this is achieved is through relatively new technology
called hydro-forming. The frame rails on a Corvette are hydro-formed.
It has the potential for cutting the cost of the e-shaft as well.
A length of 4340 steel tube is placed in a very strong female mold
and super high pressure is applied. A hardenable steel alloy is chosen
as the hardness of the rotor bearing e-shaft surface is critical.
The wall thickness of the tube could be pre-machined to better control
the wall thickness of the final product. FEA or Finite Element Analysis
would be used to determine the wall stresses so local wall thickness can
be tailored to equalize the stress and minimize the weight
and maximize the heat transfer to the coolant.
http://en.wikipedia.org/wiki/Hydroforming-
Something as simple as a glorified fire cracker placed in the tube
could also do the job. US coins are made by explosively bonding
dissimilar metals.
Paul Lamar ...No rotor no motor.
Paul,
Cooling the inside of a hydroformed e-shaft with cooling would
necessitate a different oil path for the rotor bearings along with the
stationary gear "squirters". Do you think this would require roller
bearings in the rotors in order to work or do you have some idea
different than that. Just a little insight on what timkin is up to these
days. Crossover with rollerized rotor bearings for a mazda. I know that
one company that already does it but a split would be intersting.
http://wardsautoworld.com/ar/auto_timken_bearings_boost/
http://engineeringtv.com/blogs/etv/archive/2007/05/31/episode-42-rollerized-engines.aspx
Rob
I don't think so. The complete shaft could be pressurized to what it is now.
No difference. Keep the plain journal bearings. More internal surface
area to transfer the heat from the metal to the oil. Roller bearings
don't work well as rotor bearings. The inertia forces on the rollers
are complex.
Paul Lamar ...No rotor no motor.
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