Helical Gears vs Spur Gears
Helical Gears vs Spur Gears
(OP)
Does Helical Gears provide better motion quality vs Spur Gears? If so, how does one calculate the difference?
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Helical Gears vs Spur Gears
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Helical Gears vs Spur GearsHelical Gears vs Spur Gears(OP)
Does Helical Gears provide better motion quality vs Spur Gears? If so, how does one calculate the difference?
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RE: Helical Gears vs Spur Gears
RE: Helical Gears vs Spur Gears
RE: Helical Gears vs Spur Gears
israelkk,
Are you implying the losses that occur from the thrust load which has to be accounted for the lost energy in the effiency?
Thanks,
ME7
RE: Helical Gears vs Spur Gears
It is important to be very carefuly when manufacturing helical gears because little differences on angles can be very dangerous for the correct working of the engagement.
RE: Helical Gears vs Spur Gears
Regards,
ME7
RE: Helical Gears vs Spur Gears
If you have high pitch line velocities, then a helical mesh is preferrable over a spur mesh. Since the dynamic tooth loads are much lower. You can also use a wider face width with helicals than you can with spurs, since they are less affected by torsional wind-up. The practical L/D for spurs is about 1.0. With helicals, the L/D can be closer to 2.0.
If you use a double helical mesh, then there is no net axial force produced by the mesh.
As for efficiency, a well designed helical (equalised sliding or recess action) is virtually as good as a spur mesh.
RE: Helical Gears vs Spur Gears
RE: Helical Gears vs Spur Gears
RE: Helical Gears vs Spur Gears
The key is use helical, extended addendum, composite materials, and materials with high internal damping such as aluminum, brass.
RE: Helical Gears vs Spur Gears
A key example of helical noise versus spur gear noise is in an automotive transmission. Usually the reverse gear is a spur to you get that noisy whine as apposed to forward gears when you don't hear a gear meshing whine.
RE: Helical Gears vs Spur Gears
As others said, helical gears are mandatory if noise is an issue. At very high pitch line velocities, helical gears are better in that they are less likely to trap oil in mesh.
Tooth deflection is an issue. Spur gear teeth come into contact all at once, and the best tooth modification for max torque is not the best modification for part torque. Helical gears, whose tooth contact starts as a point and gradually puts load across a tooth, can have a corner modification - or just an end easing, and still have unmodified profile that is optimum for all torque loads.
RE: Helical Gears vs Spur Gears
To make a spur gear less noisy, you can decrease the gear tooth's pressure angle. The gear tooth's bending strength will be reduced, but the contact ratio of the mesh will be greater. So the release of strain energy will be less pronounced as each tooth comes out of mesh contact.
As an example, high capacity gears are designed with pressure angles as high as 25 deg., if noise is no concern. On the other hand, where noise is a concern, but not so much bending strength, a pressure angle of 14 deg. or less may be used.
RE: Helical Gears vs Spur Gears
RE: Helical Gears vs Spur Gears
I assisted in design of a gearbox that had two helical gears on a shaft, both same hand so the axial loads offset each other. Helix angle of one of the gears was 15 degrees, the other was larger. Both had face contact ratio 1.0. This helical gearbox replaced a spur gearbox, and there was an order of magnitude reduction in vibration levels. I am convinced of the superiority of helical gears, in applications where noise or vibration are an issue.