Understanding Torque Transmission in Engine Clutches

[R Power]

Hi guys
I read somewhere that "the actual torque transmitted from the engine to the clutch is the total engine torque subtacted by the amount of torque required to accelerate the inertia of rotating components of engine.i.e:"

T(c) = T(e) - [ I(e) x $$\alpha$$(e) ]

where T(c)=Torque at clutch
I(e)= inertia of rotating engine parts
$$\alpha$$(e)=angular acceleration of rotating engine parts

Can you explain this?
I mean, I(e) x alpha(e) is the amount of torque produced by engine, then why it is subtracted as inertial loss.

 

[tiny-tim]

Hi R Power!

Total torque in = total torque out.

So torque from engine = torque taken by clutch + torque taken by engine parts.

What's worrying you about that? ​

 

[R Power]

Engine parts are producing torque or I can say engine is producing torque by moving it's parts like crankshaft, how can you write "torque taken by engine parts", it is these engine parts only which carry all the torque to transmitt it further.

 

[Lsos]

What you're saying is true when the parts are accelerating (their rpm is increasing). If it takes 50lb-ft to accelerate the flywheel, then obviously that 50lb-ft is going to have to come from the engine, leaving less to move the wheels. The engine also has inertia, so when revving up it will use up some of its own torque. However, once the parts are up to speed and at constant rpm (such as on a highway at constant speed), then they don't take up that torque anymore, and you have more power to drive the wheels.

The engine is also one of the heaviest parts of the car, and indeed when the car is accelerating, a big chunk of its power goes into accelerating itself...

 

[Ranger Mike]

an engine can in fact produce torque. but...in order to produce this torque, the comonents of the engine must move. to move these parts, energy in the form of torque is required. call it parasitic drag, friction or what ever but resistance to movment is present and the rotaating and reciprocating assemblies suck off a finite amount of power (torque) in the process of producing the resultant useable torque measured at the flywheel. it si a mute point in that this is always the case and by using proper assembly proceedures one ca nmaximize the total torque and minimize the parasitic effects.

 

[sophiecentaur]

Lsos
Are you not confusing the moment of inertia of the rotating parts of the engine with the mass of the engine which is lumped together with the rest of the vehicle? It is only the MI which takes away some of the torque delivered to the wheels, surely.

 

[Lsos]

No, I didn't confuse them. I know they are separate things, that's why I separated them into two paragraphs.

The first paragraph deals with moment of inertia, while the second paragraph deals with just inertia.

They are separate things, but they are, however, very similar concepts. One deals with mass spinning, the other deals with mass moving linearly...but they both deal with accelerating a mass.

The second paragraph was simply meant to show that just as much as an engine wastes power in accelerating itself linearly, it also wastes power in accelerating itself rotationally. I figured this would help make sense of the situation.

 

[sophiecentaur]

OK, I see what you mean.
But the linear aspect of engine acceleration has varying relevance to the discussion - particularly if we are discussing a stationary engine.