Page 18 - Gear Technology Solutions

multiplied with the pinion torque in inch-lbs. In the metric system when the Q-
factor is multiplied by the pinion torque in Nm the result has to be multiplied by
0.61 in order to obtain a result in N/mm². The conversion of Nm in inch-lbs
requires a factor of 8.85075. This factor multiplied by the Q-factor results in
PSI, which has to be converted with the factor 0.0068947 into N/mm²:

Torque [Nm] * 8.85075 * Q * 0.0068947 = Surface Stress [N/mm²]

or: Q * 0.6102327 * Torque [Nm] = Surface Stress [N/mm²]

Figure 2: Special Methods Dimension-Sheet
part 2, strength factors

The calculation of the gear torque is done similarly by multiplying the Q-factor
first with 0.61 and then with the torque in Nm. The J-factor is used to calculate
the Q-factor. Because some gear engineers use it for additional calculations it
is shown separately. The geometry factor I is the basis of a rather complex
surface stress calculation in connection with coefficients for elastic
deformation, surface conditions, size etc. This calculation procedure is
explained in detail in the Gleason manual “Surface Durability - Pitting Formulas
for Bevel Gear Teeth” [3].

1.5 Back Driving Factor

Back driving is the condition when, for example a vehicle drives with a certain
speed on a highway with a downhill slope and the driver releases the

3