## General Mechanical

#### Ananlysis Of Spur Gears

• Shreekara R
Subscriber

Hi,
I am new to ANSYS. I am trying to analyze and optimize a spur gear.
My model basically is a gear train where in two gears are meshed, what are the best constrains and loads that can be applied to achieve best results.

Thank You.

• peteroznewman
Subscriber

Hi Shreekara,

OPTIMIZATION
What are your goals for optimization? Most of the optimization of gear design happens in a spreadsheet or a gear program where things like the number of teeth are selected. Pitch, number of teeth and pitch diameters are interdependent. What is a fixed constraint in the gear design? It is usually the gear ratio. Is the space available for the gear set fixed?  If life is the optimization goal, larger gear diameters are going to have a longer life than smaller gear diameters. But perhaps weight is the optimization goal and larger gears are worse for weight. Gear design programs or spreadsheets will generally deliver a gear design that handles the torque to be transmitted. After that, there is not much left to analyze in ANSYS.

GEOMETRY
Where did the CAD geometry for the spur gear come from? Many CAD systems will illustrate a spur gear with a shape that looks like a spur gear but does not accurately represent the true profile of the gear tooth. This is fine for assembly layout, but is not sufficient for stress analysis. My CAD system (NX) can draw a true involute tooth profile. The design of the root of the tooth is critical for stress analysis so what the gear drawing allows for the shape of the root below the involute surface must be accurately modeled.

TOLERANCES
The center distance between gears is probably the largest tolerance in the gear pair. The stress on the tooth increases as the center distance increases. You may want to construct the model to apply the loads at the largest center distance.

GEOMETRY PREP
Cut a sector out of the gear that has one tooth before and after the tooth in contact. The simplest way to analyze a gear tooth is one gear at a time. Split the face of the tooth at three places, the diameter where the tooth first makes contact, the pitch circle and the diameter where the tooth last makes contact. Then you can apply a fixed support at the center of the gear and apply the force calculated in a spreadsheet to one of the split lines.

A more complicated model is to put the two gears together, with the teeth tangent at one of the diameters, and use contact between the teeth. One gear has a fixed support, the other gear has a revolute joint at the center and a joint load to apply the torque to push the teeth together.

MORE DETAILS
What materials are these gears made from, steel or plastic? Are they lubricated? What is the coefficient of friction between the teeth? What speed do the gears run at? What temperature do the gears run at? What torque and torque profile goes through these gears?  Does the torque reverse? What is the contact ratio? What is the pressure angle? How are the gear axles supported, are they supported on both sides or are they cantilevered?

• Vishal Ganore
Ansys Employee

Super guidance Peter.

Looks like we have tutorials on Workbench & AIM to do such analysis.