Engine Balance Shaft?

I'm having a hard time figuring out what you have, what you want, and what in the heck you are trying to do.

Are you trying to engine swap an M20A into your 2013PiP? Or are you getting a gen5 and want to swap something different into it?



As was guessed at earlier in the thread, Toyota probably decided whether or not to add the balancer depending on cost, space, and the purpose of the car it's going into. In a regular Prius, don't put it in to get maximum mpg. On a Lexus UX 250h, put it in because the buyer likely wants max comfort. Maybe there's a case or two where they would've normally added it, but there wasn't space for it(it makes the oil pan and crankcase stiffener a little bigger in one direction). Whatever the case, the choice to add or not add the balancer is not directly linked to the car being a hybrid or not.


If I had complete access to the American version of the MicroCat parts software, I could probably find out some more details about where the balancer is used and where it isn't, but that access doesn't come with a US Toyota TIS subscription like it does with the European TIS.

 

In general, most associated with relatively large-displacement in-line Fours in applications where refinement is a priority.

They increased the stroke vs. the 4th-generation engine. Any time you increase the ratio of stroke to connecting rod length, motion of the pistons deviates farther from purely sinusoidal, thereby increasing vibration at twice crankshaft frequency. Balance shafts counteract that shake----at increased cost, friction. and complication.

 

Confirmed that the regular Prius does not have the engine balancer. I just got to look at my oil pan while it was on the lift for an oil change.

 

Well, it looks like your UX250h engine has it, so I'd call it a win unless the very slightly larger crankcase stiffener causes clearance issues anywhere.

 

Well, why do balance shafts exist?
What do people expect of a luxury car?

 

I would guess they build a car, have someone test it, and if they come back saying "I feel a lot of vibration in the car" then they add a ballancing shaft. There are other things that also reduce the vibrations coming into the car. The motor mounts are one of them.

Ballancing shafts are usually used on smaller engines. Large crossplane V8's and I6's don't need ballancing shafts.

 

And people expect a smoother experience from a luxury brand like a Lexus. Thus why such might have the balance shaft when other models don't.

 

Yes, while it still depends.

Like I said earlier, the newest Corvette has a secondary imballance, the same as in the 4-cylinder Lexus. Yet the Corvette doesn't have ballancing shafts.

But yes, generally the more expensive the car the more likely it will have ballancing shafts, assuming it's a type of engine that would benefit from ballancing shafts, as ride comfort becomes more important than fuel mileage.

 

Okay, I think this is the complete list for the 2023 model year excluding the Chinese market. Make of it what you will.

M20A-FKS
Yes:
Camry(Europe)
RAV4(all markets)
Harrier(Japan)
Lexus ES 200(Europe)
Lexus NX 200(Europe)
No:
Corolla(Japan, Mexico)
Corolla Sport(Japan)
Corolla Hatch(USA)
Corolla SED(USA)
Corolla Cross(USA, Europe)
Noah/Voxy(Japan)
Lexus UX series(all markets)

M20A-FXS
Yes:
Corolla Hybrid(Europe)
Prius Prime(all markets)
C-HR Hybrid(USA, Europe)
Lexus UX h series(all markets)
No:
Prius(all markets)
Corolla Cross(USA, Europe)
Innova Hybrid(Europe)

 

From other comments, drivers of sports cars with manuals use the vibrations of that imbalance to time shifts.

 

Just a little over my head, so here's a read for those that have more experience with all the moving parts.
Balancing Science 101 — Battling Primary Rotational Imbalance

 

Uh... Ya...

That's somewhat the basic idea, but that article is talking about the crossplane V8, which is an entirely different animal.

An inline 4 cylinder engine has perfect primary ballance. As the two outer pistons come down the two center pistons go up, and vice versa. So they cancel each other out. Perfectly ballanced right? Well no.

As the pistons go up and down the connecting rod angles which makes them travel faster in the top of the cylinders and slower in the bottom of the cylinders. This creates an upward force at top and bottom dead center and a downward force when the crank is at a 90° angle. Since all the pistons are at TDC or BDC at the same time and are at 90° from either TDC or BDC at the same time they all cause the whole enigne to experience a force that moves up and down. Hence, why inline 4 cylinder engines benefit from a pair of balancing shafts that create a force that is opposite of the force of the imballance.

 

Umm, what? ... Try 90° from TDC..

 

Haha! I think I've been doing too much framing. Two 45° angles make a 90° angle. I think that got stuck in my head for some reason.

 

Balance shaft adds weight. It also reduces response to throttle input (additional mass to rotate, friction…etc.). Nothing is for free. Interested in knowing how much a balance shaft takes in terms of reduced HP or MPG.

 

All Dynamic Force engines use Atkinson cycle, afaik. The non-hybrid ones (K) have the same 13:1 ratio as the original Prius's 1NZ-FXE. The hybrid Dynamic Force engines (X) are just more Atkinson at 14:1.