helical(?) vs straight cut gears

[Reed]

im assuming that the gears in street cars that are cut at angles are called helical cut. i have read a few times about straight cut gears. What are the differences between these two (advantages and disadvantages). I tried to write what i thaught they were but it sounded stupid when i read it back so i deleted it.

[RandomTask]

Helical Gears
www.gearmotions.com/ helical.htm

Straight Cut
www.cbperformance.com/ catalog.asp?ProductID=64

For the scientific proof:
http://www-2.cs.cmu.edu/People/rapid...sms/chpt7.html

In short, helical gears operate quieter than straight cut. Straight cut will 'whine' the faster they go but offer both A. More directional application of force allowing for less power loss. and B. Higher acceptable loads until failure. Basically making the transmission stronger and more efficient. However though, like noted before, car manufacturers don't use straight cut due to the imense noise the transmission will produce.

Joe

[beyondloadedSE]

Not to mention, straight cut gears are a buttload of money! If only I could afford a quaife gearset for my car , but its $5,000 for the gearset alone.

[MagicRat]

To get an idea of a straight cut gear noise, many manual transmissions (especially the older ones) use straight cut gears for reverse only. Therefore, going in reverse produces a whine, but forward will not.

[Reed]

I love that noise.

I like any noise that a car makes besides the exhaust (not that i dont like that noise too).

[beyondloadedSE]

and btw, if youve heard an F1 indy car...thats not the engine thats so noisy, thats the transmission your hearing.

[bronxblaza117]

yea i always wondered wat that noise was wen goin in reverse

[The Dude]

Helical cut gears are stronger because they make more tooth contact with each other Like your differential assembly, Ring and Pinion. There is one problem with Helical Cut gears is that when you have alot of torque say like an 18 wheeler the gears not only push away from each other, they also have Thrust loads. This is where the gears moves laterally away from each other. To stop this we need strong Large tapered roller bearings or some sort of thrust washerat the ends of the shafts.But if the engine is making 1800 ft lbs of torque you can easily wipe out the bearings. This is why Heavy duty trucks have spur cut gear trannies with roller ball bearings like Road Ranger 9 speeds and 13 speeds.

[Evil Result]

If we put the cost of this to the side... how would the Herringbone gear do with noise, strength, and application of loading forces?

[TRD2000]

EVERYTHING I'VE READ SAYS STRAIGHT CUT ARE STRONGER. while helical cut gears do have a longer tooth to contact over, not all of it is in contact at any one time. helical gears transfer force over multiple teeth at any one time and the transfer in a lot smoother and quieter but because of "thrust loads" and unequal stress concentrations along the tooth they are not as strong as straight cut.

another key difference is gear changing. generally synchro is used on helical gears and dog engagement on straight cut. synchro's are nice and easy for everyone, dog engagement is not. you CAN get mixed gearsets... say helical first and 5th so its easy to engage first and quiet when cruising in top but mean in between...

[Reed]

Mixed gearsets sounds like fun. Do you have to double clutch when you dont have syncros? Do trannys with straight cut gears always have dog engagement without syncros? How do sports cars shift so fast with SMTs if they have straight cut gears with dog engagement?

[curtis73]

One of the weakest points of a manual tranny is the case. The helical cut gears place huge side loads on the tranny and can just blow the shafts right out of the case. As far as the actual gears themselves being stronger I don't know.

I've heard of manual trannys using straight cut gears for 1-3 during the hard acceleration, but 4 used helical gears for quiet cruising. Not sure how they did it since many gears are shared, but it would be a nice thing.