I'll show you a project I've been working on for the last few months in my spare time.
The idea came when I got to know about the involute gear feature on the Part Design workbench and I at the same time assembling a real SCCR gearbox in my workshop.
It has become quite complex as you can see from the screenshots. This gear kit used to be available from the Leyland Special Tuning Department in Abingdon-on-Thames when this car manufacturer was still in existance (which it is not any more, I'm afraid). I have got two of these gear kits but I can only remember where I got the one from that is currently fitted beneath an engine. The gear kits are still available from Jack Knight Gears (I think they were the original manufacturers for Leyland ST) and Quaife/Trannex in England and I think from Colotti Trasmissioni in Italy.
- STN0076 SCCR Laygear Assembly 05.jpeg (872.33 KiB) Viewed 6899 times
- STN0076 SCCR Laygear Assembly 06.jpeg (800.76 KiB) Viewed 6899 times
Straight cut gears were contemplated by Leyland because of their lower friction losses, but of course straight cut gears are not as strong as helical gears but that was made up for by better material. So they are much stronger than the standard helical gears.
Of course the close ratio made the first gear a bit higher than standard but as the gear kit was envisaged for competition use where the engines run at higher revolutions nonetheless the RPM drops in the single gears are much less which is in favour of high revving race engines.
The gearbox altogether is a typical three-shaft-gearbox with the input shaft (blue) also called first motion shaft that gets the torque from the crankshaft of the engine via a transfer gear set. The first motion shaft rotates freely on one end of the main shaft, called also third motion shaft. The 1st motion shaft transfers the torque for 1st, 2nd and 3rd gear to the laygear (light blue). For the 4th gear the 1st and 3rd motion shafts are firmly connected by the sychronizer hub, which are missing in the assembly as they are very complex in their own and I will try to model both 1st/2nd and 3rd/4th hubs in the future. While all the gear wheels on the layshaft are one single piece of steel the gears for 1st to 3rd are freely rotating on the main shaft and get fixed by the synchronizer hubs when a gear is switched by the driver. On the other end of the mainshaft the pinion of the final drive is fitted that drives the big toothed wheel where the differential and the driveshafts are fitted (not modelled).
As you can see, the mainshaft is also very complex and modelled in different steps and then fitted together.The gears themselves were of course modelled with the involute gear tool as mentioned, but the synchronizing cones with the teeth that hold the synchonizing hub on were also modelled with involute gear tool but then modified. The bearings of the layshaft were modelled with only four needles in them as I looked at needle bearings that can be downloaded from the appropriate net-pages as step-files which also only have four needles, although in reality they have more of course. Later on I learned how to use polar pattern in the Draft module and fit as many needles as I liked. So the later bearings have the correct numbers of them.
When the assembly of the single parts that you can see on the screenshots was ready the file was very big with 30+ MB of data. If someone wants the complete file, I have put it on my dropbox:
https://www.dropbox.com/s/gzl2j970farey ... FCStd?dl=0
I hope you like the gear assembly.
Kind regards,
Helmut
