positive engagment clutch advantages

[greycloud]

Why don't we see much use of positive engagment clutches in automobiles or other equipment?

They can eliminate the wear issue commonly occuring with friction clutches which in my experience is behind most tranmission failures.

They don't release alot of heat as well.

 

[TugboatEng]

We do, manual transmissions use positive engagement clutches between the gears to transfer power from the shafts. This type of clutch requires synchronization which is usually achieved directly by the operator or through friction clutches.

 

[BrianPetersen]

Dual-clutch automatics also use them. When a combustion engine is involved, there has to be slippage somewhere to start off from a stop, and to cushion gear changes. Thd dual clutch transmissions just move it elsewhere in the driveline.

A few automated manual transmissions have made it to production. They have interesting driveability quirks because of the power interruptions to change gear.

 

[MC6]

A lot of work goes into optimizing friction materials and fluids (tribology) to manage the shift quality. Unfortunately fuel economy takes precedence over everything else. But, even though most of these 8 and 10 speeds even 6 speeds have shift quality issues, there is a lot of dedication to cushioning shifts. Fluid, and paper clutches are a consumable. Gears and shafts are not. There can be significant drivetrain ring if shifts are too "positive."

Furthermore, most late model automatics run a transmission fluid specifically designed to have a negative friction curve (dynamic to static). This is again, to help soften shifts. Yes at the cost of excess heat. But if it means customers are happier, and drivetrain hard parts experience a softer engagement that will improve durability, it's a no brainer.

 

[BrianPetersen]

Motorcycles use positive dog-engagement clutches, but with a (slippable) friction clutch for starting off from a stop, and these days, the premium models have electronic engine management to quickly synchronise engine speed through clutchless upshifts or downshifts.

They're not immune to wearing out or breaking shift forks or engagement dogs, and the friction clutch is a necessary wear component. Generally, in that application, the friction clutch plates are pretty easy to swap out.

 

[greycloud]

thanks for your answers guys.you are actually right; I guess so far there is no positive engagment clutch that has ability to slip built into it.