TechnicBrickPower

Gearbox theory application - my attempts towards building an automatic gearbox for a car

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This video applies gearbox, torque, and gearing ratio theory to design a prototype 2 speed automatic gearbox. First I describe the main components of an automatic gearbox, namely a gearing ratio selector and a torque detector. The ideal gear switch over torque point is described in terms of the PF motor torque and speed operating point, as well as the ideal gear switching ratio for the 2nd gear of the automatic gearbox. A technique for creating the 2nd gear is described by either adding to a differential by engaging a gear, or by subtracting by disengaging the gear. Issues around torque friction making it difficult to disengage a gear are mitigated by speeding up the gear switching axle to reduce torque. A torque detection method is shown using a differential for torque detection and driving a rotary catch back to the gear selector to change gears. A strategy is shown to reduce the torque and power loss due to the torque detector by placing it on a secondary path from the main power path. Finally an actual implementation of a 2 speed automatic gearbox is demonstrated and tested using a configurable torque generation mechanism using a series of clutch gears.

 

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Good to see you putting your theory into practice! One thought for how you could make the shifting easier would be to remove the 12T gear driven by the lower 24T differential, and replace it with a 16T gear driven by the 16T output of the same differential, and then add either a pair of 8T gears or some universal joints to transfer the drive back into the same spot. Doing so would double the torque on the shifter, at the cost of some friction.

Of course, I wouldn't be surprised at all if you already have something like that, or better, in the works, seeing how rapidly you are improving your designs!

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