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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Inter-office memo from American Bosch Magneto Corporation detailing the computation of governor characteristics.

Identifier  ExFiles\Box 61b\4\  scan0002
Date  12th January 1921
  
X. 4275.

INTER-OFFICE
AMERICAN BOSCH MAGNETO CORPORATION
SPRINGFIELD

American Bosch Magneto Corporation
Building
Refer answer to RHe.
Attention of Mr.Rosenthal.
Dictated by VG:O

SUBJECT COMPUTATION OF GOVERNOR CHARACTERISTIC.
DATE Jan. 12th, 1921.

You will find attached hereto, photostat of the simplified procedure for adapting the ring governor to the advance characteristic curve of the engine as determined from the dynamometer test.

It will be noted that the equation gives us the relation between the unknowns, which are initial torque of spring, torque of spring per degree of ring, known as the scale of the spring, and R, a reduction factor representing degrees advance of the engine shaft per degree movement of ring.

From this factor, it will be noted, there is slight variation with the angularity of the driving crank or "characteristic pin" but by dividing the motion equally on two sides of the center, this variation is reduced to a small matter. These three unknowns are, therefore, easily controlled, initial tension of the spring by the amount of displacement given to the spring in assembly, from its free position, the torque-per-degree by variation in the thickness or number of coils of the spring and the ratio R by variation of eccentricity of the driving pin. It will be noted that one of the quantities in the equation is the initial position of the ring. This, of course, may be varied but it has been deemed advisable to fix this at 50° for the present series.

Using this value of initial angle, and substituting the three sets of values of speed and their corresponding advance angles, equations 1 and 3 are obtained; by subtraction and factoring, the equation 2 is obtained. The equation 2 is most readily solved for practical purposes by a few trials of inserting values of the ratio R, knowing, of course, from considerable experience, the result of slight changes of this value.

The value of the "spring scale" P, is preferably obtained from equation 3, the full advance relation. The values thus obtained are again substituted in the original equation. For convenience in calculation, a curve of the sine of twice the angle-plus-50° has been prepared and is used in calculation. The springs to give the required scale or stiffness are designed according to the blueprint curve (also appended) which shows the relation between the effective free turns of the spring and its stiffness in millimeter ounces per degree distortion, for a considerable range of spring thicknesses, so that the proper spring may readily be selected and the number of turns which should be left free between the points of attachment may be ascertained.

It has been found that governor assemblies made up by this process check the curves of the required spark advance very accurately without any difficulty in the laying out of the parts. It has been even found possible to obtain a curve distinctly concave to the "advance" axis, altho it is doubtful whether any engine has such a speed-advance curve.

S5 6-28-20 25M
  
  


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