Accessory Drive Losses

[Isaac Zachary]

Originally Posted by Ecky

I want to say Honda didn't install them on their D15 engines, but the slightly longer stroke D16 (and every engine of larger displacement) got one.

I had to check, and the Insight's 1.0L 3 cylinder has a harmonic damper. That surprised me a bit as I imagine it's probably an accessory loss, turning some crank motion into heat.

Maybe all timing chain motors have one? I could see a belt as providing some damping.

I'll have to check my Prius and Avalon hybrids. They have a lone pulley sticking out of the front but I don't think they have a harmonic dampener, and they are timing chain driven.

[cRiPpLe_rOoStEr]

Originally Posted by Ecky

I could see a belt as providing some damping.

That's a good point. AFAIK those Ford 3-cyls inherently unbalanced are all fitted with that oil-bathed timing belt layout.

[serialk11r]

Originally Posted by Ecky

I had to check, and the Insight's 1.0L 3 cylinder has a harmonic damper. That surprised me a bit as I imagine it's probably an accessory loss, turning some crank motion into heat.

I think the way to think about crank harmonics is that they are the residual \angular vibrations in the crank. Most of that energy isn't going to make it into moving the car if it's connected directly to the wheels, since it'll just rock things back and forth in a perfectly rigid drivetrain. In real life, it just goes through the sprung hub, dual mass flywheel springs (if applicable), gear lash, etc.

The downside apart from the crank being under more stress is that ignition timing goes off. I think it's pretty normal to observe more power from a damped engine on a dyno because the ignition timing variance is reduced.

[hayden55]

Originally Posted by serialk11r

I think the way to think about crank harmonics is that they are the residual \angular vibrations in the crank. Most of that energy isn't going to make it into moving the car if it's connected directly to the wheels, since it'll just rock things back and forth in a perfectly rigid drivetrain. In real life, it just goes through the sprung hub, dual mass flywheel springs (if applicable), gear lash, etc.

The downside apart from the crank being under more stress is that ignition timing goes off. I think it's pretty normal to observe more power from a damped engine on a dyno because the ignition timing variance is reduced.

I remember the Honda/JDM guys losing horses on the dyno going to their lightweight all aluminum pulley kits. Makes sense. Steeda (OEM contractor with Ford) uses a harmonic balancer for their underdrive pulley kits for the mustang.

[cRiPpLe_rOoStEr]

Originally Posted by serialk11r

dual mass flywheel

Makes me wonder how effective would it be to resort to a pair of flywheels, with one connected to the transmission as usual and the other to an accessory drive which could be either a gearbox or a starter-generator.

[Isaac Zachary]

Originally Posted by cRiPpLe_rOoStEr

Makes me wonder how effective would it be to resort to a pair of flywheels, with one connected to the transmission as usual and the other to an accessory drive which could be either a gearbox or a starter-generator.

If it reduces vibration without causing more friction, perhaps. But another variable we have to contend with is rotating mass. Rotating mass can help fuel efficiency in only certain rare cases, like when going uno and down a series of small hills. But in most other areas it hurts efficiency.

I think once vibration is near zero then there becomes a point of diminishing returns.

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

If it reduces vibration without causing more friction, perhaps. But another variable we have to contend with is rotating mass. Rotating mass can help fuel efficiency in only certain rare cases, like when going uno and down a series of small hills. But in most other areas it hurts efficiency.

I was mostly considering any counterbalancing effect leading to an improved smoothness, instead of an actual impact on thermal efficiency.

I think once vibration is near zero then there becomes a point of diminishing returns.

The only engine I remember seeing with a near-zero vibration was Chrysler's flathead-six. Sure it might not be so efficient at all, but its smoothness really impressed me.