Application Analysis
The application of a gear may be the most important consideration during the design process, because of the way that it informs so many decisions from the type of gear to the material of the gear. For example if you are designing gears for a differential in a car those will be very different than the gears that are used for powered surgical hand tools. These will change the various safety factors of the design. The application will determine the cost of manufacture, because if it is a commercial, high volume production the stages of manufacturing will be simpler than prototyping aerospace gears.
In some applications, a specific component of a system is designed to wear faster than others or fail in a particular component. Selecting this component is particular to the application, for instance if you are trying to repair a critical system, you would want it to fail or wear in an easier accessed part of the system. This is also included in the factor of safety, which accounts for uncertainties in the design and environment. One of the major uncertainties is varying applied loads or unknown overloading.
Different types of gears are applied better in some systems over others:
|
Type |
Features |
Applications |
|
Spur |
Parallel shafting. High Precision. High Efficiency. |
Applicable to all types of gear trains and a wide range of velocity ratios. High speeds and loads. |
|
Helical |
Parallel shafting. High speeds. Quiet. |
Most applicable to high speeds and loads; can generally be used wherever spur gears are applied. |
|
Internal Spur |
Parallel shafts. Less space needed than other gears. |
Used for planetary gear sets. |
|
Gear Rack |
Rack is a linear shaped variation of spur gears. |
Used when the need to convert rotational movement to linear movement. |
|
Worm and Worm Wheel |
Worm resembles ACME screw threads. |
Applicable where high reduction ratios are needed and high torque applications. |
After the type of gear needed for a given application, the various geometric components of the involute profile of gear teeth needs to be determined. The application environment would dictate the geometry of the gear. For example if the center distance is critical and the mating gear is already determined then a profile shift may be needed in order for the gears to mesh correctly. Also the application and therefore cost would determine the level of precision in the manufacture of the gears. For help with gear design, contact the staff at Marples Gears for further assistance.
