Accessory Drive Losses

[hayden55]

Here is an interesting video pertaining to what we regularly discuss here.

https://www.youtube.com/watch?v=Hz0ebc6XkFE

[hayden55]

Motor 1
Torq Herspr
406.9 349.0 No Fan
388.8 325.1 Plastic Fan
388.1 318.6 NonFlex Metal Fan
Motor 2
467.5 471.6 Epump (No Fan)
467.1 467.9 Mech Pump (No Fan)
463.5 465.9 Mech + 28%OD pulley + T-stat (Restrictor)
461.0 459.8 Mech + 28%OD pulley + T-stat (Restrictor) +Alternator
453.3 449.7 Above from 136-206F
Motor 3
577.8 614.6 Stock Pan (Crank in oil) (see:windage)
577.1 619.8 1 qt low (Crank out of oil)

[Stubby79]

6hp for the alt. Might barely notice it on a big engine, but explains Metros's 10% FE increase with the alt delete.

And a good 3 for the water pump. That's something to consider.

Do normal/street cars have the oil high enough that the crank drags through it?

The fan bit doesn't apply to most of us.

[serialk11r]

It's not 3 for the water pump, it's more like 6 (without underdrive pulley, with thermostat restriction). With the underdrive pulley, under most driving conditions, the engine rpm will be low enough that the power consumption won't be too crazy. If there were a market for it, a coolant bypass valve to alleviate high rpm pressure would help with that peak loss.

The alternator isn't always pulling that much power either, remember the alternator has a fan built into it, and spinning the fan at 15000rpm uses a lot of power!

[Isaac Zachary]

I wonder if using some sort of thermostatic shutters on anything with a permanent fan (e.g. alternator) would ver worth the effort. From what I understand, if you block air flow a fan will draw less per to turn.

[Ecky]

Useful information, but definitely needs to be taken in context: parasitic losses of components increase exponentially with RPM, and these measurements were taken at engine redline.

I know electric fans cut losses significantly over mechanical fans, or even mechanically clutched fans. I expect the same is probably true of water and oil pumps. Those systems were designed with wide operating bands in mind, and you can be sure that being able to operate at, say, 7000rpm, with no ability to deviate from engine RPM or load, will necessarily have drawbacks.

Honda and Toyota have both gone entirely beltless in their hybrid engines, with accessories electrified as much as possible, so undoubtedly there are gains from it.

One of these days I'll take my car to a load dyno and try to quantify these things under typical cruising conditions.

[cRiPpLe_rOoStEr]

Even though neither the alternator or electric accessory drives would reach a 100% efficiency rate, they're still favored compared to the thermal efficiency of an ICE which hardly surpasses 40%. And nowadays the so-called "intelligent" alternators which are meant to start operating once the battery reaches a low charge or during decelerations as some sort of regenerative braking also tend to increase overall efficiency.

On a sidenote, it's interesting to notice how many trucks still resort to hydraulic power for implements thru PTOs that may be mounted either at the engine or at the transmission, even though some newer ones are now resorting to electric drive for the implements as it doesn't require the engine to be kept at high idle and thus decreasing noise while operating at night.

[serialk11r]

Shutters on a fan aren't great because the pressure drop at the inlet consumes some of the power you just saved. My preferred method for alternator cooling would be an undersized fan (half the flow) with a supplemental electric fan for low speed.

Fans and coolant pumps consume power proportional to the cube of rpm, so those are the biggest gains, and they're big enough to be noticeable even for street driving. Power steering is inefficient because steering assist is not needed most of the time, but the flow control valve built in means parasitic losses are almost linear, proportional to rpm.

My thinking around accessories is underdrive them a bit, and don't think too much about it, with the exception of the cooling system. On a race car that's always running at high speed, you can underdrive everything more and avoid prolonged idling. For a street car that's usually running at low engine speed, the extra hp lost at high rpm isn't usually a concern.

[Ecky]

Originally Posted by serialk11r

Shutters on a fan aren't great because the pressure drop at the inlet consumes some of the power you just saved. My preferred method for alternator cooling would be an undersized fan (half the flow) with a supplemental electric fan for low speed.

Fans and coolant pumps consume power proportional to the cube of rpm, so those are the biggest gains, and they're big enough to be noticeable even for street driving. Power steering is inefficient because steering assist is not needed most of the time, but the flow control valve built in means parasitic losses are almost linear, proportional to rpm.

My thinking around accessories is underdrive them a bit, and don't think too much about it, with the exception of the cooling system. On a race car that's always running at high speed, you can underdrive everything more and avoid prolonged idling. For a street car that's usually running at low engine speed, the extra hp lost at high rpm isn't usually a concern.

This is getting off in the weeds a bit, but I could use an opinion:

Honda's K20 and K24 motors are nearly identical, and share accessories. The K24 block is around 1cm taller, has a longer stroke, and a slightly bigger crank pulley. The K20 is a square engine with a higher redline, and a smaller crank pulley.

I understand these pullies are dampened, which protects all sorts of bits inside the engine. The smaller motor with the higher rev limit has a comparative "underdrive" pulley for accessories. I wonder if the pulley being larger on the bigger motor is only to spin the accessories faster, or if it also serves to provide more dampening. Do you think changing the crank pulley would be safe?

[serialk11r]

Originally Posted by Ecky

I wonder if the pulley being larger on the bigger motor is only to spin the accessories faster, or if it also serves to provide more dampening. Do you think changing the crank pulley would be safe?

Hmmm that's an interesting question. Dampers work at any speed, but the more rotational inertia on the outer ring, the more energy the damper will absorb, so going to the smaller pulley will reduce the damping effect.

There are people running solid aluminum pulleys on a number of engines without snapped cranks, so I want to say on most engines, you're probably fine? Some engines are known for broken crankshafts when running without harmonic damping, so I would be more worried about those.

If the crank pulley is to be avoided, then underdriving accessories would involve switching out each pulley separately which is annoying.