Significance of Overdrive system in transmission

“It's still magic even if you know how it's done.”
― Terry Pratchett

 

For sustained mobilities, we usually drive a car at top gear (i.e.) a direct-drive arrive at maximum cruising speed. At the time of high-speeds, the engine runs at higher rpm to produce an enormous amount of power. However, some power reductions take place in the transmission unit for shifting speeds. So performance and power output are uncertainly low also lead to wear and tear of the rotating components inside. 

Then how could we execute more power? and rather than that

Would you think, is it probable to increase output more than input?

Obviously yes. This enhanced output will carry out through overdrive, an actualized mechanism adapted in the transmission unit which performs either using mechanical or electrical circuits by activation. 

 

 

Structure-wise, this overdrive comprises an epicyclic gear setup fix up with a sliding cone clutch and free-wheel unit. They are positioned after the transmission using splines in the output shaft. Of course, this setup had installed between the transmission unit and propeller shaft driveline. The sun gear is free to roll around the shaft from the gear-box, if not engaged, and planetary gears mesh with sun gear to send out power to the ring gear (or output shaft). A sliding cone clutch is mounted accompanying by a sun gear with lengthened external splines on the transmission shaft for engaging and disengaging the sun gear accordingly. This clutch had regulated by employing a hydraulic pump with solenoid actuation. The free-wheel unit is placed in the same splined bar behind this gear setup and makes contact with the output shaft permanently.

How does this perplexing mechanism work?

In direct-drive, input power generated by the engine is assuredly equivalent to the output power, which had transmitted to the wheels. When we proceed in a direct-drive (i.e.) top gear, the cone clutch unites with ring gear by spring force generated by a solenoid. This adjustment creates some friction with ring gear and makes the sun gear to roll free. So the power that comes out from the transmission unit is sent to the output shaft via free-wheel. 

 

 

Likewise, in overdrive, output power transfer to the wheels is more than the power produced in the engine. While proceeding in overdrive, a cone clutch separates from the ring gear by hydraulic pressure against spring force and makes the sun gear stationary. So the power flow is handled by the sun gear (i.e.) power from the transmission unit is passed to planetary gears, so the speed gets multiplied, and that speed is transfer to the ring gear (or output shaft). 

 

 

Overall this overdrive is for increasing the power output more than the transmitted output from the transmission unit (i.e.) overdrive can empower more power to wheels further upto 20 percent, even the engine runs at moderate rpm. This mechanism helps in improving better fuel economy in high-speed conditions. Mostly race cars adapt this overdrive mechanism to achieve terrific speeds.

 

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