Automotive gears can have either positive or negative profile shifts. While the tooth height remains the same, the tooth thickness differs. Gears with increased tooth thickness have positive profile shifts, while those with reduced tooth thickness have negative profile shifts. When the center distance between two gears cannot be changed, a positive profile shift is applied to the pinion (to avoid undercutting) and a negative profile shift to the larger gear, maintaining the same center distance. In this case, the absolute values of the profile shifts are equal. Standard gears mesh with their pitch circles tangent to each other. Gears with profile shifts mesh on the operating pitch circles, where they are tangent. The pressure angle on the operating pitch circle is called the working pressure angle, which differs from the pressure angle on the standard pitch circle (standard pressure angle). The working pressure angle is an important factor in designing gears with profile shifts. Profile shifting can prevent undercutting during manufacturing when the number of teeth is small. It allows achieving the desired center distance and, in cases with a large gear ratio, applying a positive profile shift to the pinion (which is more prone to wear) to increase its tooth thickness. Conversely, a negative profile shift is applied to the larger gear to reduce its tooth thickness, balancing the service life of both gears.
