S-gears: From Metal to Polymer Solution

Comparison of Selected Parameters of a Planetary Gearbox with Involute and Convex–Concave Teeth Flank Profiles

“…The shape of the tooth surface of the S-gear also provides higher comparative reduced-curvature radii. Therefore, the contact load is lower [31].Tests were performed, which led to the confirmation of the assumption that the theoretical tooth flank geometry of S-gears provides more rolling and less sliding between the matching flanks compared to involute gears. The convex-concave contact leads to lower contact stress, which in combination with less sliding, means lower losses due to sliding friction, and consequently, less heat generated [32].The S-gears were also used by the design of the planocentric gear boxes and devices for large transmission ratios, primarily applied in automation and mechatronic industry, which decrease rotational movement and increase torque to the largest possible extent in the smallest available space [33].In all applications where the reduction gear must be as small as possible, a planetary gearset is preferred as it has the additional advantage of the input and output shafts being coaxial.…”

“…The full mechanical properties of the polymer and functionality of the gear is then realized via subsequent cooling, solidification, and ejection from the die and final trimming, if required [43]. The POM-C and PA66 materials are often used in plastic gear manufacturing because of the good dynamic friction coefficient values and the price criterion [31]. As an example of a typical plastic material used for gears, BASF Ultramid A3K (PA66) provides an easy flowing injection molding grade for fast processing and is commonly used in highly stressed technical parts, such as bearings and gear wheels.…”

“…The shape of the tooth surface of the S-gear also provides higher comparative reduced-curvature radii. Therefore, the contact load is lower [31].…”

The effect of the teeth profile shape on polymer gear pair properties

“…However, involute gears also have their shortcomings, i.e., a convex/convex contact along the path of the contact, resulting in higher stress at the contact [13]. If the case of less than a marginal number of teeth, undercutting of the tooth root occurs, thereby weakening the root.…”

“…The tooth roots of S-teeth are much wider, compared to the involute teeth, which increases the root strength, while at the same time it means that gears can be created with a much smaller number of teeth, compared to involute gears. The shape of the S-gear's tooth flank is defined using an analytical equation [13,14,15]. A mathematical model allows the shape of the tooth flank and the corresponding counterflank to be defined [14].…”