My first wankel engine 'bits'!

[RP Designs]

Outlines formulas for geometry:
http://www.personal.utulsa.edu/~kenn...n/chapter7.pdf

[johnyswift]

Im looking for an equation which can determine eccentricity ratio. Displacement, rotor width and compression ratio values are known, does anybody know how the eccentricity can be determined from this? Ive been looking at the formula on the chaper 7 article, however im very confused. Any help would be very much appreciated.


thanks.

[RP Designs]

You can solve for the eccentricity ratio directly using equation 7.9. Eqn. 7.9 relates the compression ratio to eccentricity ratio (e/R). Once you have your eccentricity ratio you can use eqn 7.8 along with your displacement to solve for the rotor center to tip distance (R). Once you know the eccentricity ratio and the value for R you can use the definition of the eccentricity ratio to solve for e (eccentricity ratio = (e/R)).

You will most likely then need to go back and iterate a solution using the curved flank equations using your R value to determine the segment volume (eqn 7.14) and then plug the results from eqn 7.14 into eqn 7.16 to recheck your CR. You will most likely need to iterate a few times to determine the geometry.

[Ken McKenzie]

"Im looking for an equation which can determine eccentricity ratio. Displacement, rotor width and compression ratio values are known, does anybody know how the eccentricity can be determined from this? Ive been looking at the formula on the chaper 7 article, however im very confused. Any help would be very much appreciated."

You have to know the diameter of the circle the rotor fits in.

Then divide it by twelve and you have the eccentric radius.

For example the 12A and 13B Mazda rotary engines have a 7.92 diameter rotor and the eccentric is .591 inches

In the alternative first determine the desired eccentric radius and then multiply it times twelve. The compression ratio is always the same. the compression varible results from the amount of cavity you put into the rotor faces.

Ken

[johnyswift]

Ok from using equation (7.9) i have managed to find the eccentricity if using a compression ratio of 14:1 however as the equation is a quadratic there are actually 2 values. One is 0.29 and the other 0.65, does it matter which value is used? and i know these two values are for a flat flanked triangular Rotor.

The second question i have is regarding equation 7.8, the rotor width (w) is reffering to the length of one flank or the actually thickness of the Rotor?

Im just a bit confused in what direction i need to be going in as the e/R ratio cannot be determined for rounded flanks unless the (As) value is known equation (7.16)

All above questions are based on the chapter 7 article, any help would be very much appreciated

thanks.

[RP Designs]

Originally Posted by johnyswift Ok from using equation (7.9) i have managed to find the eccentricity if using a compression ratio of 14:1 however as the equation is a quadratic there are actually 2 values. One is 0.29 and the other 0.65, does it matter which value is used? and i know these two values are for a flat flanked triangular Rotor. The second question i have is regarding equation 7.8, the rotor width (w) is reffering to the length of one flank or the actually thickness of the Rotor? Im just a bit confused in what direction i need to be going in as the e/R ratio cannot be determined for rounded flanks unless the (As) value is known equation (7.16) All above questions are based on the chapter 7 article, any help would be very much appreciated thanks.

I think your best bet is to follow an already established formula, such as the Mazda Wankel. Mazda have spent a great deal of time developing this engine and have probably found a reasonable starting point with dimensions, compression ratios etc. Mazda used an eccentricity ratio of 0.143 for their R26B Le Mans engine. Their generating radius (R in the paper) is 105mm with an eccentricity (e) of 15mm and a width (w) of 80mm. You could scale those to your dimensions, solve for one variable (i.e. R), then use your displacement to determine R. Once you have R you can go back and determine e and w. Once you have determined these basic parameters, plot your epitrichoid and from there you can determine your clearance, flank rounding, compression ratio, segment area, etc.

[johnyswift]

Ok i have managed to calculate all the basic parameters for the design. My values are as follows;

Rotor centre to tip (R) = 57.5mm
Eccentricty = 7mm
e/R ratio = 0.12
Rotor Width = 59.7mm
Segment curvature (theta) = 64.8 degrees

These figures are based on;

Compression Ratio = 14:1
Displacement = 125cc
clearance = 0.26mm

I am now struggling to find any equations to calculate for recesses in the Rotor flanks as i understand the addition of these will lower the compression ratio further. I need some advice in what way to go about calculating how much material needs to be removed from each flank. Any help will be very much appreciated.

thanks.

[RP Designs]

Johnny,
The volumes are additive to both the max and min volumes. So use equation 7.16 using your target CR and add a Volume term to the numerator and denominator. Plug in your values and you can solve for the needed recess volume.

[johnyswift]

Ok thanks for all the help guys, im just getting my final designs modelled up now using solidworks. One quick question though, what are the best type of bearings to use for the Rotor journals??


thanks.

[punktoy]

i need blue prints of a wenkel motor functional

you have some ?