# Contact stiffness (Cɣ) in gear.

• k.udhay
In summary, the conversation discusses the concept of contact stiffness in gears and its influence on gear vibration behavior. The mean value and fluctuation limit of stiffness vary throughout the meshing process and can be adjusted by changing gear parameters such as contact angle, tooth size, gear width, base circle to pitch circle ratio, using helical gears, increasing contact ratio, and changing material selection. The range of stiffness for automobile transmissions is not mentioned.
k.udhay
Hi,

When I discuss about gears NVH, the term contact stiffness(Cɣ) comes across very often. It is given with a nominal mean value with its upper and lower fluctuation. I can thus understand that the stiffness varies from the start of mesh till end of mesh reaching the mean value at it's pitch point.

Now my doubt is how do the mean value of stiffness and fluctuation limit influence in gear vibration behavior. Generally what is the range kept for an automobile transmission? If I want to increase / decrease the mean value and fluctuation of stiffness what are the main gear parameters that I should play with?

Thanks.

I have no idea about gear vibration dependency on stiffness, or the stiffness range expected...

To increase gear tooth stiffness I would consider the following;

1. Increase the contact angle so teeth are more stubby.
2. Use less but bigger teeth.
3. Widen the gear.
4. Adjust base circle to pitch circle ratio.
5. Use helical gear to average the stiffness over contacts.
6. Increase contact ratio. Consider an internal gear.
7. Change material selection. Use steel, cast iron, or carbide.

1 person
Thanks, Baluncore.

## 1. What is contact stiffness (Cɣ) in gear?

Contact stiffness (Cɣ) in gear refers to the ability of a gear to resist deformation and maintain its shape when under load. It is a measure of the gear's stiffness or rigidity, and it is an important factor in determining the gear's performance and durability.

## 2. How is contact stiffness (Cɣ) in gear calculated?

Contact stiffness (Cɣ) in gear is calculated by dividing the contact force between two mating gears by the amount of displacement or deflection that occurs at the contact point. This calculation is typically done using specialized software or through experimental testing.

## 3. What factors can affect contact stiffness (Cɣ) in gear?

Contact stiffness (Cɣ) in gear can be affected by several factors, including the material properties of the gears, the gear geometry, the lubrication used, and the operating conditions such as load and speed. Changes in any of these factors can impact the gear's contact stiffness and overall performance.

## 4. Why is contact stiffness (Cɣ) in gear important?

Contact stiffness (Cɣ) in gear is important because it directly affects the gear's ability to transmit power and torque efficiently. A higher contact stiffness means less energy loss and better performance of the gear system. It also helps to reduce wear and noise, thus increasing the gear's lifespan.

## 5. How can contact stiffness (Cɣ) in gear be improved?

Contact stiffness (Cɣ) in gear can be improved by using high-quality materials with good stiffness properties, optimizing the gear geometry to distribute the load evenly, and using proper lubrication to reduce friction and wear. Additionally, proper maintenance and regular inspection can help to identify and address any issues that may affect the gear's contact stiffness.

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