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1. Introduction
The vast majority of manually operated automobile gear boxes use hardened steel gears on shafts supported by ball or
(tapered) roller bearings with a casing cast in a permanent mould. While the majority of designs are 2 shaft layouts,
see diagram below,
one recent design uses a dual clutch, 3 shaft layout and this should be considered (ref 1). This is available
in the 3.2 litre Audi TT and the VW Golf R32.
2. Reverse Engineering
Important areas of the reverse engineering are:
- Gears: sizes, angles, tooth surface roughness (comparator), strength / depth of hardening (Rc and VPN at different loads)
- Shafts: diameters, radii at changes of section, splines
- Casing: strength (hardness tests)
- Bearings: types and dimensions
- Shift mechanism: arrangement
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3. Procedure
It is suggested that you should follow the outline procedure given below, but note that this is an iterative
process and you will probably have to go through the process more than once.
- decide the layout, including that of the shift mechanism
- from the maximum power and speed derive the input torque
- decide on speed ratios
- derive torque on each gear
- size each gear, evaluate shaft and bearing loads
- design the shafts
- select / specify the bearings
- design casing
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