Helical Gears Full Chapter URL

Miyachika,. T. Asano, in International Gear Conference 2014: 26th28th August 2014, Lyon, 2014 1 INTRODUCTION Helical gears are used increasingly often as power transmitting gears, since not only can they carry larger loads because of their lower dynamic load but also their noise and vibration levels in operation are lower compared with those of spur gears.

A lot of studies on root stresses of solid spur gears, solid helical gears and thin-rimmed spur gears have been published by many authors in the past ( 1-10 ), but studies on thin-rimmed helical gears are rarely published.

The line of contact of helical gear is diagonal across the tooth trace, while the line of contact of spur gear is parallel to the tooth trace.

Therefore, root stresses of helical gears can be considered to be quite different from those of spur gears ( 3,5 ).

Moreover, the deformation of rim part of thin-rimmed helical gear can be considered to be larger than that of solid helical gear.

In order to estimate the bending strength of the thin-rimmed helical gear more exactly, it is necessary to determine effects of rim and web thickness on the root stress and the bending fatigue strength.

In the previous paper, root stresses and bending fatigue strength of thin-rimmed helical gears with symmetric web arrangement of helix angle 0 20 were published by the authors ( 11-13 ).

In the present paper, the root stress and the bending fatigue strength of thin-rimmed helical gears with symmetric and asymmetric web arrangement of helix angle 0 10 and 30 were investigated.

Root stresses of the thin-rimmed helical gears with symmetric and asymmetric web arrangement of 0 10 and 30 were measured in the meshing process from the beginning of engagement to the end of engagement by means of the strain gage method, and then the changes of the root stresses in the meshing process were obtained.

The maximum root stress and the worst meshing position (the meshing position where the maximum root stress occurs) were determined.

Bending fatigue tests of thin-rimmed helical gears with symmetric web arrangement meshed at the worst meshing position were carried out, and then S-N curves and bending fatigue limits were obtained.

Effects of rim and web thicknesses, web structure and helix angle on the root stress and the bending fatigue strength of the thin-rimmed helical gear with web arrangement were determined.

Helical Gears Full Chapter URL

View chapter Purchase book Read full chapter URL: Gears Neeraj Niijjaawan, Rasshmi Niijjaawan, in Modern Approach to Maintenance in Spinning, 2010 15.3 Helical gears Helical gears are similar to spur gears except that their teeth are cut at an angle to the hole (axis) rather than straight and parallel to the hole like the teeth of a spur gear.

The line of contact between two teeth is not parallel to the teeth but inclined.

This ensures gradual engagement of teeth from one end of tooth to other rather than a sudden engagement as in case of spur gear.

This gradual engagement makes the gears function smoothly without much noise.

Pair of helical gears can be meshed in two ways: with shafts oriented at either the sum or the difference of the helix angles of the gears.

These configurations are referred to as parallel or crossed, respectively.

Types of helical gears.

Helical gears connecting parallel shafts Helical gears connecting parallel shafts will run more smoothly and quietly than spur gears, particularly when the helix angle is great enough to ensure that there is continuous contact from one tooth to the next.

A pair of helical gears used to connect parallel shafts must have the same pitch, pressure angle and helix angle, but they will be opposite hand gears (i.e., one will be a left-hand gear and the other a right-hand gear).

Helical gears connecting non-parallel shafts Helical gears used to connect non-parallel shafts are commonly called spiral gears or crossed axis helical gears.

If the shaft angle is 90 degrees, the gears will be of the same hand and the sum of the helix angles will be equal to the shaft angle (90 degrees).

There is a point of contact between two gears where as there is a line contact in a helical gear.

Because of point of contact which changes during action, there is considerable sliding between the teeth.

Efficiency of spiral gear is very low.

Parallel crossed.

Common terms used in helical gear 1.

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