Help with a ring and pinion gear problem please 5

[RRiver]

I'm finding some conflicting information about the effects of different ring and pinion gear sizes I'd like some help with. The issue is this, "Does the size of the ring and pinion gear effect the power it can transfer? This is with all things first being equal with acceleration, weight, mass, etc.? Second, comparing ring and pinion sizes, 8.8 and 9.75 for example but with the same ratios, does one size transfer more power than the other?" "Does one size create more power than the other?"

The debate going on described and how it began: Someone said a larger ring and pinion gear creates more power. I disagreed. I said no, power transferred to the wheels is determined by the gear ration and not the size of the gears. The ratio when identical transfers the same amount of power. The gear size has no effect on "creating" power. Furthermore I stated assuming a greater mass from a larger gear set will transfer more power but it doesn't create more power. Additionally I stated since the gear set is rotating mass the amount of power transfer will not be linear (at least in time) due to the conservation of momentum as exampled by a vehicle gaining more acceleration by removing rotating mass than the same amount of static weight.

I'm eager to read any responses.

 

[GregLocock]

"Does the size of the ring and pinion gear effect the power it can transfer? "

All other things being equal the big one will be more durable at high torques. Neither size creates power, in fact diffs are notorious for losing power as friction, that's why they get hot.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[RRiver]

Thank you Greg.

I agree. The ring and pinion is an axle RPM multiplier\divider depending on how it's used. The durability you mention comes from the mass of the larger gears and has nothing to do with physical size. If it were simply size and not mass I suspect machining would be done on the gears to reduce their weight for performance gear sets instead of all things not being equal, using lighter and more expensive materials. Aluminum ring and pinion gear sets are anything but inexpensive to get the strength without the mass.

 

[TugboatEng]

AGMA gear design guidelines emphasize tooth contact pressure and bending stress when designing gears. Mass doesn't factor in. While aluminum can be somewhat strong in bending (7050 has about 1/3 the yield strength of a steel gear) the teeth would have to be absolutely massive to work within the contact pressure limits for aluminum. You'd be better off making the gear out of plastic.

 

[RRiver]

TugboatEng, Aluminum was in error. My mistake.

 

[MintJulep]

As with most things in engineering you need to make compromises.

There are factors that go on the "larger is better" side of the equation.

There are factors that go on the "smaller is better" side of the equation.

Put them all into your optimization function, along with the application factors and you get "best choice for this application."

There is no universal one best answer.

 

[RRiver]

MintJulip, Well said. Unfortunately a lot of time an effort is spent on defeating the realities of balance and equilibrium.

 

[BUGGAR]

I think he meant torque. Yes, everything being equal, a larger ring gear will transmit more torque due to more tooth base circle shear area.

 

[tbuelna]

Many automotive rear end ring and pinion gears use hypoid geometry. Hypoid gears usually have modest tooth bending stress levels due to their curved tooth profiles. Typically they are limited by contact stress levels and/or scuffing/scoring probability. Increasing the pitch dia/pinion offset of a hypoid gearset reduces mesh forces, permits an increase in face width, and provides a higher face contact ratio. While the larger diameter gears offer higher torque capacity, the higher PLV and mesh contact sliding also reduce efficiency.