82 replies to this topic

[Spider]

Martin, sorry but I beg to differ on your theory that Helicals are less efficient and have higher losses.

 

Gear for gear, helicals do have a longer tooth and a high contact ratio, therefore the Spot Pressures of Helical Gears is lower, so the tooth frictional load (wiping effect as you put it earlier) is lower. This is widely known. I may still even have some back to back test data on this. As a further result, Helical Gearboxes run cooler, but not by bucket loads, usually more like by academic numbers.

 

I was able to lay my hands on a couple of slides ('Spur Gears' being Straight Cuts);-

 

 

 

This is also why Helicals are popular in Industrial type gearboxes where noise is not a consideration, but high strength, low losses and a small footprint  are a higher consideration.

 

BUT, I will stress, if the gearbox is not well made or shaftings are out of alignment, Straight Cuts are much more forgiving than Helicals under these less than ideal conditions. I'm guessing here that the 10 - 15% improvement you mentioned may have come from this?

 

A very close and dear friend of mine (David Rosenthal) did make a Herring Bone set of drop gears a few years back. I have no photos I'm sorry, I'll see if Dave has any. There was an issue he had with them, but it wasn't related to the gears themselves. If I recall, he made these by the double helical method.

 

Warwick Augustin made a chain drive for the drop gears on one of his race minis. I have no details, but I am aware it did take him a very long time to get it to work right and be issue free. He then ran with it for many years (and may still), so I draw from that he found it was better than gears here.

Edited by Moke Spider, 30 June 2016 - 09:38 AM.

[Squares]

Great thread, I have found it interesting reading so far.

 

Can I please pose a question, sort of the other way around to the OP's but hopefully still on topic. Ratio's aside for one moment, is it possible to run helical gearbox on a high powered engine? In this day in age when there are many options for getting, say 120+bhp from an a-series, with 7 or 8 port heads, or 16v head conversions, is there any type of option to run such an engine with a gearbox that doesn't have the noise of a straight cut box.

Or are the drop gears part of the problem, both with how loud they are in straight cut form, and the issues that they are under a lot of load and fairly small.

 

Many thanks in advance.

 

Richard.

[Guess-Works.com]

Great thread, I have found it interesting reading so far.

 

Can I please pose a question, sort of the other way around to the OP's but hopefully still on topic. Ratio's aside for one moment, is it possible to run helical gearbox on a high powered engine? In this day in age when there are many options for getting, say 120+bhp from an a-series, with 7 or 8 port heads, or 16v head conversions, is there any type of option to run such an engine with a gearbox that doesn't have the noise of a straight cut box.

Or are the drop gears part of the problem, both with how loud they are in straight cut form, and the issues that they are under a lot of load and fairly small.

 

Many thanks in advance.

 

Richard.

 

Yes.

If you drive it like you stole it, expect it to break, whatever shape the teeth are...

If you drive sensibly and with consideration then I've heard of reasonably large turbo motors running standard transmissions...

PS..

It's not power which kills gearboxes, it's torque.

[Ethel]

The choice will be at least as much down to how the power is made. Forced induction excepted, high HP needs high revs to consume enough air. That leads to closer gear ratios being preferable* and the production costs would be prohibitive to make them helical in such small quantities.

 

 

*The gear ratios give simple multiplication of the rpm, but the power to car speed relationship is exponential - wind drag would stop you before you got the rpm high enough to see all that power. At the other end you'd struggle to get enough traction to put that extra power in to the road (if you just changed the final drive for a shorter one) - the speed range hasn't increased as much as the power so the spread of gear ratios required is narrower.

 

 

It's not torque that kills gearboxes as much as fatigue from the constant hammering of applying that torque. Helicals transfer loads from tooth to tooth more gradually.

[MRA]

Martin, sorry but I beg to differ on your theory that Helicals are less efficient and have higher losses.

 

Gear for gear, helicals do have a longer tooth and a high contact ratio, therefore the Spot Pressures of Helical Gears is lower, so the tooth frictional load (wiping effect as you put it earlier) is lower. This is widely known. I may still even have some back to back test data on this. As a further result, Helical Gearboxes run cooler, but not by bucket loads, usually more like by academic numbers.

 

I was able to lay my hands on a couple of slides ('Spur Gears' being Straight Cuts);-

 

 

 

This is also why Helicals are popular in Industrial type gearboxes where noise is not a consideration, but high strength, low losses and a small footprint  are a higher consideration.

 

BUT, I will stress, if the gearbox is not well made or shaftings are out of alignment, Straight Cuts are much more forgiving than Helicals under these less than ideal conditions. I'm guessing here that the 10 - 15% improvement you mentioned may have come from this?

 

A very close and dear friend of mine (David Rosenthal) did make a Herring Bone set of drop gears a few years back. I have no photos I'm sorry, I'll see if Dave has any. There was an issue he had with them, but it wasn't related to the gears themselves. If I recall, he made these by the double helical method.

 

Warwick Augustin made a chain drive for the drop gears on one of his race minis. I have no details, but I am aware it did take him a very long time to get it to work right and be issue free. He then ran with it for many years (and may still), so I draw from that he found it was better than gears here.

 

I upload an engineering report and you upload a mickey mouse picture, we are not talking about efficiencies in the same way, for us as in those who use straight cut gears we are looking at power transmission, ie as much as possible and we are not concerned with accuracy of mesh, smoothness to a certain degree and certainly not noise, the point is you are putting incorrect information on here....

 

1) which is stronger helical or spur ?   if everything is equal then helical, however the production gears are not made using any special materials, this makes them weaker

2) The surface finish on BMC production gears is not that great so higher  loads are registered

3) The lower spec materials also allow for more tooth bending.

4) with straight cut gears you can run higher clearances thus less frictional loss, whether you like it or not is immaterial, it is proven that straight cut gears use less energy to rotate them, that is irrefutable fact not science fiction based on what somebody thinks.

 

Your mate did not make a set of herringbone drops, he might have made a set of double helical drops but that would give no benefits over standards, due to all of the above issue when making this type of gear.

 

Only a herringbone gear set offers more strength as it has no gap between the gear "pairs" (ie the left and right side of the gear

 

The wipe, of mesh of helical's is in fact higher than spur gears as they are in contact for longer.

 

Thousands of Mini owners who have broken helical gears change to straight cut and go on for years without an issue....

 

Finally if helical gears are so good, why do 95+% of racers use them then ?

[Orange-Phantom]

As Martin has said, why are all racing gearboxes straight cut? Performance being the main factor. Look at all of the performance gearboxes out there, they are all straight cut.

[nicklouse]

As Martin has said, why are all racing gearboxes straight cut? Performance being the main factor. Look at all of the performance gearboxes out there, they are all straight cut.

Cheaper to produce is the main reason.

The quantities are small and it is easier to do small batches of different sets.

[Spider]

As Martin has said, why are all racing gearboxes straight cut? Performance being the main factor. Look at all of the performance gearboxes out there, they are all straight cut.

 

While the gears themselves are less efficient, overall - including side thrust - there are less losses, so overall, there are gains. I was only looking at and referring to the gears themselves in isolation.

 

I think I already mentioned that earlier on in this thread and now while it's all fine detail, it is getting a little twisted and distorted.