Gear whine

[Jack Gifford]

I just read that Honda used "gear pairs" for the primary drive in their 1968 CL350 motorcycle to have the efficiency of straight-cut gears without the usual noise. I need a primer on "gear pair" principles and design details.

 

[BrianPetersen]

Possibly the same concept as "scissor gears", which may be the more modern term for it. Look up that term and see if that is consistent with what you were expecting.

 

[TugboatEng]

Honda still uses it. The primary reduction gear which connects the crankshaft to clutch gear has a thinner gear section that is spring loaded to preload the gear in one direction.

https://drive.google.com/file/d/0B5-lBISTwKZCMDhabklUUXdOcGs/view?usp=drivesdk

You can see a similar apparatus in this Falk marine reversing gear. The astern pinion gets a "detuner" to keep it from banging and rattling when operating in ahead. We removed it because the springs tend to break and destroy the gear set. We were fortunate the broken springs only destroyed our gear pump we used to pump the oil out for the overhaul.

 

[Jack Gifford]

Thanks for the comments.
Wikipedia tells that Opel's "Whisper Diesel" engine uses both scissor gears and LNS (Low Noise Shifting) to quiet its cam drive. LNS appears to be a proprietary tooth grinding process by Reishauer which "prevents the generation of tonal excitations". I need to look into LNS further- anybody here familiar with it?

 

[MikeHalloran]

Wild Ass Guess:

prevents the generation of tonal excitations

... sounds like the sort of thing that's done to quiet highway tires; e.g. shifting the gear faces forward and back, just a tiny bit, within the normal tolerances, in a pseudo-random way, to avoid mutual excitation or resonance.



Mike Halloran
Stratford, CT, USA

 

[Jack Gifford]

Mike- that's also my W.A.G. But I'm wondering if it would be durable enough for thousands of miles of street-driven use in an engine's camshaft gear drive?

 

[GregLocock]

I've never heard before of anybody automotive phasing tooth spacing for gears, but it is SOP for cooling fans. Neat.

Cheers

Greg Locock


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

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

 

[Jack Gifford]

I suppose you could say that my question about durability of LNS has already been answered by Opel's apparent satisfaction with it. I'll see if I can talk with Reishauer about it.

Does the scissor-gear concept always imply spring loading of the paired gears to each other? Would hydraulic loading possibly result in the same quieting?

 

[gruntguru]

I am sure it would, however the hydraulic system would likely have a lower compliance and therefore a reduced ability to cope with any cyclic variation in backlash.

je suis charlie

 

[BrianPetersen]

Why would you want to do this hydraulically instead of just using a plain ordinary set of springs that don't require any active intervention, or reliable pressure supply, or seals (and their associated friction)?

The spring-loading mechanism isn't complicated. I've never seen it done any other way.

And, as noted above, springs are better springs than hydraulic fluid is.

 

[TugboatEng]

As I mentioned in my picture above, that particular case is notorious for breaking the springs and the pieces of spring damage the gears.

 

[Jack Gifford]

I asked about hydraulic gear pair loading because it could be done very compactly in my application, and space is very limited. I would substitute a gear pair for the idler gear of my cam drive which is only 1.970" OD, with no available space around it. Engine oil pressure would be routed through machined passages to cavities in the mating faces of the gear pair. This would avoid any enlargement of my gear system. (Cavities would be offset radially, so that oil pressure would attempt to offset them more).

 

[MikeHalloran]

Engine oil pressure would be routed through machined passages to cavities in the mating faces of the gear pair. This would avoid any enlargement of my gear system. (Cavities would be offset radially, so that oil pressure would attempt to offset them more).

I'm having a hard time picturing how that would work.

BUT, before explaining it further, get a patent on it if you think it has commercial value.



Mike Halloran
Stratford, CT, USA

 

[Jack Gifford]

Mike- No interest in patents or commercial value. Merely entertainment for my retirement years.
Rather than put up with the gear whine, I put a normal timing drive in the engine and it's serving me well. But I'd really like to someday use the variable-cam-phasing on the street. While testing it did an impressive job of "taming" a very lumpy cam, by advancing the cam as little as 9 degrees (crank) at low engine speeds.

It's no wonder you were "having a hard time picturing" since I misspoke. One gear would have a slot for pressurized oil and the other would have a dowel pin "piston" protruding into the slot. Dimensions are very cramped but there's room to allow 60 psi oil pressure to develop about 4 pounds of force. Any idea what magnitude of spring force would be typical for such a gear pair? Idler gear pair is 1.8275" pitch diameter, 22 tooth (between 27 & 54 tooth crank & cam gears) with "piston" at 1.110" pitch diameter. Each gear of pair is .312" thick.

Regarding springs vs. hydraulics: I don't foresee a spring force being better suited to "preventing the generation of tonal excitations" than hydraulic pressure.

Brian- no seals required. All parts would fit with less than .002" clearances, so the hydraulic circuit would function okay with #30 oil. Leakage would drain harmlessly back to the sump.

 

[Jack Gifford]

I'm not getting needed answers nor have I found a gear company offering the LNS grinding, so I'll simply duplicate the gearset with helical gears- and somehow deal with end-thrust of the idler gear.
Thanks for listening.

 

[gruntguru]

The idler gear won't have any net end thrust, just a couple.

je suis charlie

 

[Jack Gifford]

Wrong. Idler gear will have twice the end thrust of the crank gear or cam gear.

 

[gruntguru]

Not on MY FBD it doesn't.

Actually you don't even need a FBD. The gear "driving" the idler applies torque in one direction and therefore applies thrust in a particular direction. The gear "driven by" the idler applies torque in the opposite direction and therefore applies thrust in the opposite direction.

je suis charlie

 

[Jack Gifford]

guru- you are right, no end thrust on idler. I apologize.

 

[chez311]

Interesting note about LNS - a very similar concept is often applied in automotive gear/chain systems where the chain is made up of a series of links with slight differences in the tooth spacing assembled in a specific randomized pattern to shift the phasing of the gear/chain tooth contact.