Optimization of sprockets

How do you get people to hang around and read a full page of text on the Internet. It's probably impossible, but there are few shortcuts to technical subjects, so here we go:

Design of sprockets used to be a question of looking up the classical formulae in your old machine design text books.

That was yesterday. Today, research has opened new opportunities to improve the performance of sprockets far beyond the common rules of dimensioning. Optimization of the tooth shape makes it possible to increase the power transmission of a gear significantly.

Two different failure mechanisms are prevalent in gears:

• wear and pitting of the contact surfaces 
• fatigue failure in the foot of the tooth. 

Both failure mechanisms limit the maximum torque in the transmission and thereby the transmitted power. The first problem can be reduced by using a shape with higher and more slim teeth. This results in a smoother engagement of the teeth and reduces wear as well as noise and vibrations. But the slimmer teeth have more narrow cross sections and are more susceptible to bending fatigue in the foot. So the solution to the first problem may trigger the second.

But only if you use the classical non-optimal shape. A shape-optimized foot carries much more load and represents the solution to both problems.

Initial design.  Textbook shape.	Optimized design.  Stress level reduced by 33%

In the example shown here, the objective has been to minimize the maximum stress in the foot of the teeth. The optimized latter geometry features 33% lower foot stress than the former.

It is characteristic that optimization leads to significant improvements, even of designs that are usually considered to be optimal or near optimal. This is due to the fact that the number of combinations grows exponentially with the number of parameters in the model. The designer may have worked with a specific class of problems for years, and he or she feels on top of the situation and believes the chosen combination of parameters is the best possible, but in reality, the number of combinations is so large that there is virtually no chance of finding the right one per intuition and experience alone.

Sprocket  | Slide gate | Turbine wheel | Electricity Pole | Truck Floor

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Last modified: november 15, 2001