Transmissions - Construction Methods and Materials

[Big Fella From Oz]

Hi People

This is my first post so please forgive if i seem a bit rookie-ish
I've gotta do an engineering assignment and i have found some info on the forum but the main stuff im searching for still elude me
the task sheet we've got has got a basic guideline

Analyse the influence of the main alloying element and its effects in the final alloy - eg the properties that titanium brings to the party when its put into an alloy to form a gearbox housing (like stiffness, brittleness rah rah rah)

The basic materials in the gearbox casting of the actual gears preferably in percentages.

And the construction method - not as important thou

(I can upload the task sheet on request)

Any help would be great

Cheers

[scarbs]

The main requirements for a gearbox casting are

Stiffness, as the case is a structural item

Stiffness under heat, aluminium cases lose stiffness at normal working temperatures 150C

Thermal expansion ratio, to maintain gear alignment and seal the oil within the casing.

Casting - Ability to cast intricate shapes and thin walls with high level of accuracy\repeatability without porosity

Materials
Casing - Investment cast ti is a common method (see the CRPtechnology.com website), also Cast aluminium (zeus part of caparo, Cast a lot of alu cases). Moulded carbon fibre with high temp resins systems and Ti internal bulkheads (see http://www.cytec.com/innovation/pdf/Mar ... ne_CEM.pdf). In the past we've seen cast magnesium and fabricated Ti, as well as hybrid cases with a Ti gear case bolted to a carbon fibre bell housing. Many teams reinforce their cases with Carbon fibre bonded to the outer surfaces, I've seen this on both ti and alu cases. Ferrari simply have a cast Ti skeleton and bond carbon skins to maintain the structural stiffness, this saves making incredibly thin walled castings.

Internals, gears and gear shafts are Steel, bulkheads to mount the bearings for the gear shafts appear to be machined Alu, but equally could be machined MMC. the differential case is commonly Ti, but I have seen some carbon composite\Ti protoypes.

Cheers

Scarbs

PS Welcome to the forum...

[Big Fella From Oz]

Thanks a lot mate appreciate the help

[PlatinumZealot]

I think your lecturer is more interested in the steel that is used to make the gears and the method of hardening of the surface of the gears.

You will get more marks for that. I wish i could post the different alloys but i'm feeling lazy..

[riff_raff]

Oz,

Gearbox housings are usually cast. But the gears and rolling element bearings are made from very high quality wrought materials (billet).

In the old days sand cast aluminum (A356 alloy) or magnesium (AZ91 or ZE41) was used for the transaxle housing. But those materials weren't stiff enough for a modern F1 composite chassis. So the material of choice became titanium (6AL-4V). But it must be cast using a very expensive technique called vacuum investment casting, since it has an adverse reaction with oxygen in a molten state. Recently, some teams have even tried composite housings, but these are difficult since the resin matrix of the composite does not hold up well in contact with hot oil.

The gears are made from a vacuum-melted, Ni-Cr-Mo carburizing grade of alloy steel. In the US it's designation is 9310. The gear blanks are rough machined, the gear teeth are shaped or hobbed, it's then carburized, quenched and tempered, shot peened, and finally the gear teeth and bearing journals are finish ground and/or honed.

The bearings are typically made from a through hardening, double vacuum melted, chromium steel, designated E52100.

If cost is no object, sometimes the bearing rollers or balls are made of silicon nitride ceramic which is much lighter than steel, stiffer and much harder. And the races for those bearings are made from a special tool steel called M50. These types of bearings are usually referred to as "hybrids".

Good luck with the class assignment.