Spiroid Gears for Hypoid???

[MrGear]

I am going through some papers, according to some russian dr., spiroid gears could be used more efficiently instead of hypoid gears. I am trying to get things to gether if it is doable and what are the disadvantages and advantages. could it be manufactured with the same equipment, cost etc.,
I will really appreciate if someone has any idea i'll be more then happy to discuss further.

Thanks

 

[Metalguy]

Hypoids have more sliding friction. They are used when car makers wanted to lower the floors of the cars.

 

[patprimmer]

Why do they use them in trucks then, as floor height is not normally limited by tailshaft position

Regards
pat

 

[Metalguy]

Because truckers haven't figured ut the loss in efficiency? If eff. mattered, most truck cargo would be on trains instead.

 

[PJGD]

Metalguy;
I think Pat is talking about pick-up trucks, which are essentially light-duty oriented. That is to say the technology comes from the LD direction.

Efficiency is very important for the Heavy-Duty truck operators since fuel costs are such a major percentage of their operating costs. Heavy trucks typically use worm reduction, or on-center hypoid reduction gears. Yes, the rolling friction of straight bevels would be more efficient than the sliding friction of worm and hypoid, but the very high torque loadings require that the load be shared across multiple teeth at any one time.

PJGD

 

[Metalguy]

Worm gear reducers have about the worst efficiency of all. The correct way to design big truck gear trains is to get most of the reduction in the trans. using helical gears, a larger dia. driveshaft, and a spiral bevel gearset in the diff.

If the diff. doesn't have to have a large reduction, it can be stronger.

 

[JayMaechtlen]

As soon as you put more of the reduction in the trans, you get much higher torque loads on the engine/trans mounting system, higher tooth loading in the final reduction stages of the trans requiring much heavier construction, much heavier U-joints in the driveshaft, etc., etc.
Optimizing the system may lead to more reduction in the final drive and less in the transmission!

Truckers, believe it or not, are weight-sensitive, too!
The whole vehicle is limited to a max GVW. The less the vehicle weighs, the more payload they can haul!

cheers
Jay



Jay Maechtlen

 

[Metalguy]

Let us assume for the moment that the determining factor in the rear is the dia. of the ring gear. That ring gear will deliver the same torque to the axles regardless of where the previous reduction is done.

So, since the ring gear will have the same no. of teeth, it is better to deliver the input torque to more of them via a larger drive pinion.

 

[JayMaechtlen]

If the diameter of the ring gear is critical, that approach may be a reasonable tradeoff. Alternatively, I believe that some axle packages have more than one stage of reduction?
Also, I thought we were really referring to heavy over-the-road transport, where ground clearance is generally not in question?

Jay Maechtlen

 

[Metalguy]

I don't really know what is used in big truck rears, but *if* they are using hypoids or worm drives they are wasting money.

How much money is open to question-perhaps 1% or even less. Gear designers obviously know all about this, but knowledge doesn't always result is a well designed whatever.

 

[JayMaechtlen]

well, here's a site-
Eaton / Dana/Spicer

http://www.roadranger.com/products/axle/axle.htm

Jay Maechtlen

 

[Metalguy]

Took a quick look at their heavy-duty axles. They all seem to use spiral-bevel gearing, not hypoid or worm drives.