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10.3 BEVEL GEARS
À pThese gears are like normal spur gears, except that they have a conical form.
Their applications are characterized by,
Bevel gears are meshed so that the points of their cones are coincident.
As we move towards the point of the cones, the number of teeth remains the same, but the diameter reduces towards zero. This changes the size of the teeth, and the pitch diameter.
The form of the gears is like that of spur gears, but each has a cone angle, and when added together this gives the angle between the shafts.
We can apply some of the basic ratios to bevel gears,
10.3.1 Design of Bevel Gears
(|To determine the pitch angles for the gears we can write the following expressions,
An approximate methods for creating bevel gears is called `Tredgold's approximation'
Tredgold's technique requires that a cone on the bottom of the bear be found. This cone is then flattened out, and normal gear design is done. Finally the cone is mapped back onto the bottom of the gear. The profiles are then projected up to the point of the cone.
Typical design parameters include,
- deflections mean that the wider base tends to take most of the load, so the teeth are designed with a short length (commonly less tan 1/3 of the total cone length)
10.3.2 Other Bevelled Gears
(|Crown and Face Gear - this gear is much like a rack for spur gears. To get this, one of the gears is given a pitch angle of 90°.
Spiral Bevel Gears - to reduce noise in beveled gears, a spiral can be added to the teeth.
Hypoid gears - the centers of the bevelled gears are not coincident - the shaft is offset.
10.3.3 Practice Problems
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