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• # Helical & Spur Gear Combination

Discussion in 'The main mechanical design forum' started by Mekanimo, Mar 30, 2012.

1. ### MekanimoMember

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Hello all,

I've been given an assignment to analyze a patent consisting of a helical drive train , here's the link to the patent : http://www.google.com/patents?id=SgA6AAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false

It claims that this set won't need thrust bearings and that the axial forces developed by the helical pair will be contained by the spur gears.

What I need first is to know HOW is that , I did the force analysis and there is no force equivalent to the axial force of the helical gear ... Second , if so , will it be valuable to use such a patent or not? .. third , the helical gear face width is almost 4 times larger than the spur gear face width , what's the significance of that?

I hope you reply as soon as possible because I'm really desperate and can't even refer to any solution ..

2.
3. ### ErichWell-Known Member

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That is proof that an idea does not have to work to get a patent.

4. ### MekanimoMember

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he just paid his dues to register the patent so why not

Do you have any idea about the equilibrium forces or the 3 questions that I mentioned?

5. ### MekanimoMember

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guys I must deliver this on monday so if anyone has an idea please do reply (knowing that the professor told us it satisfies the principle it claims and it won't need thrust bearings but it's not valuable)

6. ### vic.blackallWell-Known Member

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As the pair of helical gears rotate, an axial parting force is exerted trying to separate the two gears along each axis, in opposing directions. The drive gear is fixed to the drive shaft, the driven gear arrangement is allowed to slide on its support shaft by means of a keyway. Because of the gear helix angles, as the gears do actually move apart the driven gear rotates along the helix angle relative to the other gear. Without the spur gears the driven helical gear would continue to rotationaly advance while moving axially along the shaft.
As the helical driven gear rotates relative to the drive gear it's rotation is stopped because of the rotation taking up the tooth clearance between the two spur gears.
Because of these spur gears, the advancing helical gear also advances the attached spur gear, the spur gear can only advance to the extent of the clearance between the spur gear mesh. This takes the load off of the helical gear and prevents further axial movement and therefor any further axial force.

I don't believe this is a very practical design by virtual of the spur gear taking more drive loading off of the helical gearing and the possible fretting of the driven gear cluster on the driven shafting.

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