2nd ICAI 2022

International Conference on Automotive Industry 2022

Mladá Boleslav, Czech Republic

In addition to the above-stated parameters, knowledge of the S-N curve with its characteristic for a given component is essential, or at least we must know the relevant exponent q for this curve’s oblique branch if the gearing is stressed above the fatigue limit. The oblique branch of the S-N curve can be defined using two points, the intersection of fatigue limit σ C and the relevant limit number of cycles until the damage N lim occurs, and some other point defined by the general load amplitude s a and the corresponding

number of cycles until the damage N w,a occurs. For this oblique branch, the following basic relation applies (relationship 1). By rearranging this equation, it is possible to obtain the oblique branch exponent from the well-known S-N curve (relationship 2). As the determination of the curve exponent is costly and time-consuming, the values stated in the literature are used. For the following predication, we start from (ČSN 01 4686) which is used for gears in car gearboxes (structural alloy steel, cemented and hardened, and stainless for structural steel, normalized annealed or heat-treated steel; carbonitrided) the following values are given: • to calculate contact q H,ČSN = 10, • to calculate bending q F,ČSN = 9.

Since the standard (ČSN 01 4686), in Part 2, provides a procedure for calculating the equivalent force from the load spectrum

then following S-N curve exponents were used to calculate the equivalent moments: • for calculation in contact q H = 5, • for calculation in bend q F = 9. Relationships (3) and (4) can be used to calculate the equivalent load for any load parameter – torque, force or tension.

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