Spiral and Straight Bevel Gears for machine designers

hypoid gear
The standard definition of a Bevel Gear is a cone-shaped gear which transmits power between 2 intersecting axels.

Looking at bevel gears from the differences in helix angles, they can be generally classified into straight bevel gears, which do not have helix angles, and spiral bevel gears (including zerol bevel gears), which do have helix angles. However, because of the fact that manufacture facilities for straight bevel gears are becoming rare and the fact that straight bevel gears teeth cannot be polished, making spiral bevel gears which can be polished superior in terms of noise reduction, spiral bevel gears are likely to become more common in the future.

Bevel gears can be generally classified by their manufacturing methods, namely the Gleason method and Klingelnberg method, which each have differing teeth shapes, and presently most gears use the Gleason method. Incidentally, all gears manufactured by KHK use the Gleason method.

Furthermore, there are also variations in gears in terms of teeth pitch (modules, etc.), whether polished or not, and materials used. For example in the case of materials, S45C of machine structural carbon steel, SCM415 of machine structual alloy steel and MC901 of engineering plastic, etc. are often used, and duracon, etc. are used for plastic molded parts.

Related links :
Miter Gears – Main page of miter gears
Zerol Bevel Gears – Main page of zerol bevel gears
Hypoid Gears – Main page of hypoid gears
Equivalent tables of each standard relating to raw materials and precision grades of gears
The ABC’s of Gears / Basic Guide – B
Introduction to Gears
Gear Technical Reference
锥齿轮 – 中文页

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Introduction

The bevel gear is a gear that transmits rotation between two axes that mesh in the same plane and has the teeth on the conical surface, and has a shape of an opened umbrella. The bevel gears are roughly divided into “the straight bevel gear” that has straight teeth and “the spiral bevel gear” that has spiral teeth. In spiral bevel gears, the one with two axes in the different plane is called the hypoid gear.

What are Bevel Gears ?

We will re-confirm the characteristics of bevel gears here.

Kinds of bevel gears :

Bevel gears are the generic terms for gears with cone shaped pitch surface and cone shaped outer surface. Teeth are cut on the cone surface and gears are able to transmit power between two intersecting shafts. When the gears are sorted by the orientation of the shafts, most bevel gears belong to intersecting shaft gears. Bevel gears can be roughly divided into the following kinds.

  • Straight bevel gears
  • Helical bevel gears
  • Spiral bevel gears
  • Hypoid gears
  • Miter gears
  • Zerol bevel gears
  • Oblique angle bevel gears
  • Crown gears

 

Characteristics :

Used in applications in which the shaft directions are changed. The manufacturing of straight bevel gears are somewhat easier and they are often used in differential gears. Spiral bevel gears are suitable for high load, high speed applications but production is more difficult and they have the disadvantage of creating thrust forces. Miter gears are often used when there is no need to change speed.

Efficiency :

Because most bevel gears belong to intersecting shaft gears, meshing is almost always a rolling contact and the general efficiency of bevel gears is high around 98-99%.

Tips in using the bevel gear :

Though designing the bevel gear is complicated due to the angle compared to the spur gear, you may decide the numbers as you work on the drawing. Also you may use a design supporting software from gear manufacturers.

Attentions in using the bevel gear :

When using the bevel gear, axial thrust forces are produced due to its shape. It is necessary to design the thrust bearing around the bearing at the stage of drawing.

Recommended usage location of the bevel gear :

The spur gear has two axes horizontally, however the bevel gear is used with two axes orthogonally. As an example, it is used for the axial end of a drive shaft of vehicles.

Conclusion :

In bevel gears, the one that has the same pitch cone diameter and the number of teeth in a pair is called miter. The miter gear has each cone point corresponded. If you are not familiar with using the bevel gear, you may use this one.

About Straight Bevel Gears

Bevel gears are cone shaped gears which transmit motion between two intersecting shafts. Straight bevel gears are the simplest of these bevel gears with their teeth being straight and pointing toward the apex of the cone. They are easier than spiral bevel gears to make and do not produce inward thrust (in the minus direction), simplifying bearing construction. On the other hand, they have the disadvantage of not being able to grind teeth after heat treatment.

Straight bevel gears are divided into two groups: profile shifted Gleason type and non-profile shifted ones called standard type or Klingelnberg type. Over all, the Gleason system is presently the most widely used. In addition, the Gleason Company’s adoption of the tooth crowning method called Coniflex gears produces gears that tolerate slight assembly errors or shifting due to load and increases safety by eliminating stress concentration on the edges of the teeth.

Straight bevel gears are generally used in relatively slow speed applications (less than 2m/s circumferential speed). They are often not used when it is necessary to transmit large forces. Generally they are utilized in machine tool equipment, printing machines and differentials.

Types of KHK Straight Bevel Gears :
SB, SBY, SUB, PB, DB

About Spiral Bevel Gears

Bevel gears are cone shaped gears which transmit motion between two intersecting shafts. Spiral bevel gears are one type in which the teeth are curved spirally. Unlike straight bevel gears, these teeth contact each other gradually and smoothly from one end to the other. The meshing of teeth are, as in straight bevel gears, rolling contacts on the pitch cone surface.

With regard to design and gear cutting, just as in straight bevel gears, the Gleason type is most widely used in spiral bevel gears. However, in Germany, the Klingelnberg type with equal toe and heel tooth depth is still deeply rooted in use.

Spiral bevel gears have the advantage of being able to grind teeth after heat treatment, making it possible to produce high precision gears. Also, because the teeth contact ratio is higher than with straight bevel gears, noise and vibration are reduced and they are better suited for high speed applications. For example, noise and vibration are markedly reduced at high operating speed (more than 10m/s). They are also stronger and more durable than straight bevel gears allowing for higher load operations. On the other hand, it is more difficult to manufacture
spiral bevel gears and needs attention regarding change in thrust directions depending on the rotation and twist angle. These are some of the disadvantages.

In use, the right-hand spiral is mated with the left-hand spiral. As for their applications, they are frequently used in automotive speed reducers and machine tools.

Spiral Bevel Gears Supplied by KHK :
MBSG, SBSG, MBSA/MBSB, SBS, SBZG, KSP