Wednesday 8 May 2013

Manual Transmission - Part 2

I continue with calculating the gear ratio on day 2 for gear 1 to 5 as well as the reverse gear. The formula applied is driven over driver:

                       driven gear teeth
Gear ratio =                                
                       driver gear teeth

For example:


Gear ratio = 30 / 60
                 = 0.5 : 1

And for reverse gear, I have ignored the reverse idler gear and used just the gears on the input and output shafts for the calculation of gear ratio because of a couple of reasons:

a) The purpose of reverse idler gear is only to change the direction of the driven gear.
b) For multiple gear calculations, the result will be the same if the following formula is applied:

       

                       driven gear teeth            driven gear teeth
Gear ratio =                                    x                                   
                       driver gear teeth             driver gear teeth



I then moved on to measure the thrust clearance of the gears. Well, this is when the feeler gauge comes in place. I pushed the gear to the most upward and downward on the shaft and measure the biggest and the smallest gap it has by inserting the different thickness of steels of the feeler gauge into the gap. Then added up all the numbers in millimetre (mm) that marked on the steels for both the biggest and smallest gap, subtracted them to get the answer for thrust clearance for each gear to ensure there meet with the manufacturer specifications.

I have just learnt about thrust clearance today and I would like to talk a little bit more about it because it is essential in most of the mechanical parts assembly. Thrust clearance is a gap or distance in between two or more moving objects, it's purposes are to provide space for lubricating oil, thermal expansion, manufacturing tolerances and objects distortion to minimise wears or damages from the engagement of moving objects in long run.


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