576xp being replaced with 572XP . . . Latest generation auto tune

[Derf]

Its the wider torque band, nothing to do with the AV.

Ahh, well then I guess that is just a feature of a strato saw, which in general, regardless of brand, is the general theme I see : more grunt down low.

So now I wonder, in all the threads that I read comparing a 372xp to a 575xp or 576xp, where someone says the 5 series is "smoother", were they comparing pre-xTorq 372 to 575/576 xTorq? It would seem like a 372xp xTorq would be as smooth as the 575xp/576xp xTorq.

Considering you can't even buy non xTorq 372xp saws any more (in the US), the "smoothness" shouldn't be that big of a selling point.




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[KG441c]

There is a member here that said he has a couple buddies that have been on a demo 590 and said it was super smooth? Anyone elsw heard this?

 

[SawTroll]

If you got your hands on one you be realizing that yes, it can be better than the 372. The smoothness of the 576 is attributed to its powerband, and the 576AT really allows that smoothness to shine.

Perhaps the WLC users should be using the 372XPXT as they are available and handle much better and of course are lighter than the 576's.

What the sponsored competitors use likely is a question of marketing policy? At least I can't explain it in any other way....

 

[Franny K]

I'll try to answer the question, even though it is also my own question. Anyone feel free to chime in.

You've got a rotating mass (piston and crank) attached to the crankcase generating vibration, this is isolated from the tank/handles by springs. From my understanding, there are only two things that could contribute to the 5 series feeling smoother than the 3 series.

1) Less mass in the crankshaft. The crankshaft's counterweight lobes contribute greatly to the vibration. I haven't thrown them on the scales to compare, but it could be possible that the 57# series has a lighter weight crankshaft. Less mass would mean less inertia being thrown around which would mean less vibration transmitted to the crankcase.

(there, back on topic)

I think theory 1 above is flawed. The piston and rod create an unbalance as they move. In a single cylinder without a counter balancer this makes shaking in essentially one plane. This shaking isn't really able to be compensate for as if it is offset (say stroke is vertical) then a front back shaking is created. There is a balance factor to basically divide the shaking. It gets more complex because the rod length isn't infinite. I would think more mass in the crank with the same balance factor would score lower vibration. Similar logic as you put farther down.

 

[Derf]

The purpose of the counterweights is to reduce vibration, but they must be matched to the mass of the piston to do that. Arbitrarily increasing or decreasing the size of the counterweights will not improve vibration.

Thanks Chris, I agree that the counterweights are matched to the piston weight and are there to reduce vibration, but I was under the impression that they cannot completely cancel it. I guess what I want to clarify is, a system with a xx weight counterweight on the crankshaft and an similar system with an xx+yy weight counterweight, the latter system would have more vibration than the former. Mentally I'm thinking of the vibration (at similar RPM) to a car engine vs a chainsaw engine. The bigger engine has more vibration. Is this incorrect anybody?

I think theory 1 above is flawed. The piston and rod create an unbalance as they move. In a single cylinder without a counter balancer this makes shaking in essentially one plane. This shaking isn't really able to be compensate for as if it is offset (say stroke is vertical) then a front back shaking is created. There is a balance factor to basically divide the shaking. It gets more complex because the rod length isn't infinite. I would think more mass in the crank with the same balance factor would score lower vibration. Similar logic as you put farther down.

OK, I'll agree that this is a complex system, and I may not understand the theory or math, but I think that we can move on, since Hamish has clarified the "smoother" 576 is a reference to its power band, not its degree of vibration.

 

[spike60]

All these theories are interesting reads; but obviously not all can be correct. Two basic factors though go into what you feel. The effectiveness of the AV system, and the amount of vibration that such system must deal with. So if they get the saw right, then the springs have less vibes to filter out.

If you remember some saws had a choice of rubber or spring mounts, such as the 288, and some had both "soft" and "hard" spring options. Early spring mount saws like the 262 felt real smooth, but we have to admit that the 262 could feel a little flimsy also. With a 262 you often have this nagging feeling that you need to tighten something up. The primary reason is that unlike today's saws, there was no top mount between the handle and the cylinder. (this can be solved somewhat by replacing the 2 rear spring mounts with rubber 288 mounts. Few more vibes, but a much more solid feel to the saw.)

The desire for real smooth, but not to flimsy still exists. One way to compromise is to use softer springs, and add movement limiters so guys don't rip the saw apart when yanking on it. The springs on a 562/2260 are relatively small, and the saw is a smooth as butter. But they could not use small springs like that without movement limiters.

The "new saw" is extremely smooth BTW.

 

[Franny K]

There has got to be some compromise for idle vibration. Or vibration level at idle. I tried out a Husqvarna 390 and couldn't help but think one should figure out where to put the notch bef0re starting the thing.

 

[Husqavarna Guy]

All these theories are interesting reads; but obviously not all can be correct. Two basic factors though go into what you feel. The effectiveness of the AV system, and the amount of vibration that such system must deal with. So if they get the saw right, then the springs have less vibes to filter out.

If you remember some saws had a choice of rubber or spring mounts, such as the 288, and some had both "soft" and "hard" spring options. Early spring mount saws like the 262 felt real smooth, but we have to admit that the 262 could feel a little flimsy also. With a 262 you often have this nagging feeling that you need to tighten something up. The primary reason is that unlike today's saws, there was no top mount between the handle and the cylinder. (this can be solved somewhat by replacing the 2 rear spring mounts with rubber 288 mounts. Few more vibes, but a much more solid feel to the saw.)

The desire for real smooth, but not to flimsy still exists. One way to compromise is to use softer springs, and add movement limiters so guys don't rip the saw apart when yanking on it. The springs on a 562/2260 are relatively small, and the saw is a smooth as butter. But they could not use small springs like that without movement limiters.

The "new saw" is extremely smooth BTW.

Have you heard an approximate release date Spike?

 

[SawTroll]

There is a member here that said he has a couple buddies that have been on a demo 590 and said it was super smooth? Anyone elsw heard this?

I still consider the existense of such a saw a rumor - but I have read things like that a few times....

 

[KG441c]

I still consider the existense of such a saw a rumor - but I have read things like that a few times....

Im 100% this member wouldnt fib

 

[SawTroll]

Im 100% this member wouldnt fib

I don't know/remember who have said it, or what actually was said - so I can't comment on that.

 

[Chris-PA]

First generation Strato saws are the Husky and Stihl ones designed without using the Zenoah patents.

What is the difference? I have not noticed any real difference between the 570/575/576 design and the GZ4000, other than that Husky used longer, angled transfers but I don't see that as fundamentally important. The whole air valve, piston notch and such is the same.

 

[Derf]

I've been doing some reading up on the Zenoah patents, which I hadn't heard mentioned until the other day by SawTroll.

Zenoah, a Japanese company, were the first to create a strato saw back in the late 1990's (1998). If you read up on their patents, many of their core technology patents were filed in early and mid 1990's with more of what I know about strato-saws today (first gen technology?) added in 2001-2004. Husqvarna agreed to buy them in Sept 2006 (finalized in April 2007), and they continue to create patents (I've seen as late as 2013). Most of the patents that I see applied to ownership by Husqvarna exist after 2009.

The most applicable patents to a gen-2 strato engine that I found were filed in late 2012 and 2013. If there is a "gen II" strato engine coming in a 572XP, the patents describing those features have just been filed, which could mean that Husqvarna is close to releasing something.

Does anyone have a theory on how long it will take before Husqvarna makes Autotune ubiquitous and cheaper instead of a premium feature?

 

[SawTroll]

Interesting - I have actually never cared to look into the details, just how the resuling saws are....

 

[Chris-PA]

I've been doing some reading up on the Zenoah patents, which I hadn't heard mentioned until the other day by SawTroll.

Zenoah, a Japanese company, were the first to create a strato saw back in the late 1990's (1998). If you read up on their patents, many of their core technology patents were filed in early and mid 1990's with more of what I know about strato-saws today (first gen technology?) added in 2001-2004. Husqvarna agreed to buy them in Sept 2006 (finalized in April 2007), and they continue to create patents (I've seen as late as 2013). Most of the patents that I see applied to ownership by Husqvarna exist after 2009.

The most applicable patents to a gen-2 strato engine that I found were filed in late 2012 and 2013. If there is a "gen II" strato engine coming in a 572XP, the patents describing those features have just been filed, which could mean that Husqvarna is close to releasing something.

Does anyone have a theory on how long it will take before Husqvarna makes Autotune ubiquitous and cheaper instead of a premium feature?

Thanks for the links! 20130291840 seems to be a means of throttling one branch of the transfers (appears to be the one closest to the intake?) using the lower skirt of the piston:


The wording is hard to follow.

 

[CTYank]

Thanks Chris, I agree that the counterweights are matched to the piston weight and are there to reduce vibration, but I was under the impression that they cannot completely cancel it. I guess what I want to clarify is, a system with a xx weight counterweight on the crankshaft and an similar system with an xx+yy weight counterweight, the latter system would have more vibration than the former. Mentally I'm thinking of the vibration (at similar RPM) to a car engine vs a chainsaw engine. The bigger engine has more vibration. Is this incorrect anybody?


OK, I'll agree that this is a complex system, and I may not understand the theory or math, but I think that we can move on, since Hamish has clarified the "smoother" 576 is a reference to its power band, not its degree of vibration.

What seems to have been overlooked is that we're trying to balance single-cylinder reciprocating mass with rotating one.
Reciprocating: piston assembly and effective mass of rod small-end.
Rotating: crank balance weights & effective mass of rod big-end.
The balancing act has to go on along two perpendicular axes. Neither can be excessive, or the other suffers.
Reducing reciprocating masses helps, but makes things delicate, not such a good idea.

Multi-cylinder engines can enable perfect external engine balance, from opposed-twins and L-4/V-4 up. Ferinstance, as an extreme case, 12-cyl Jaguars are like electric motors or Mazda Wankels.

The same problem plagued steam locomotive design engineers with 2-cylinder machines. Thus all the 3-cyl engines in Europe- huge improvement in mechanical stability of high-specific-output machines. Less of a problem with low specific output machines in US of A.

 

[Derf]

After reading some of the recent patent applications, I think we're going to see
1) simplified carbs appear in next gen strato engines. A lot of patents apply to doing away with dual-barrel carbs, for cost, complexity, size, weight.
2) lighter saws. Simpler carbs mean a little less weight.

Here is a summary of some of the patents I've read.

http://www.freshpatents.com/-dt20090514ptan20090119934.php
May 2009 - Auto chain tensioner.
This sounds a lot like the keyless tensioner found on the 450e series, where the side cover and chain tension are in a single mechanism.

http://www.freshpatents.com/-dt20100408ptan20100083512.php
April 2010 - Chain Saw
Bunch of stuff. Dual-port muffler in case one port is clogged. Partially covering the muffler on small saws with a plastic cover. A pipe coming off the muffler where the hot gases escape, and the pipe has a slit/holes in it to allow a venturi with cool air, so that the ejected gases are not as hot, avoiding discoloration of plastic on the saw.

http://www.freshpatents.com/-dt20100408ptan20100083511.php
April 2010 - Chain Saw
Attempts to overcome reduction in airflow when the openings of the side cover are clogged by i) having windows around the mounting hole of the flywheel, ii) making a larger flywheel (which won't increase the weight since the windows remove some weight), and iii) having cooling veins on the backside of the flywheel to increase airflow.

http://www.freshpatents.com/-dt20100701ptan20100163337.php
July 2010 - Muffler
Smaller lighter saws have smaller mufflers made of thinner metal, that don't last when exposed to hot exhaust gases, so baffles are used, which requires spot welding... But on smaller mufflers welding baffles is difficult and expensive and time consuming, so they propose bending a tab into the path of the exhaust gases inside the muffler so that they can create smaller, cheaper mufflers out of thinner metal.
Note to future self : consider NOT removing this tab if I want my muffler to last.

http://www.freshpatents.com/-dt20101118ptan20100288251.php
November 2010 - Scavenging cover
Since the diameter of the ports in the cylinder affect airflow, optimizing the port size is difficult across different model saws, with a lot of re-casting and trial-and error. Of note, they aren't optimizing for power, they are optimizing to minimize blow-back. So instead they suggest using a replaceable cover between the carb and the cylinder with a window of varying sizes that they can swap in and out to optimize flow for different model saws. Porting gurus rejoice!

http://www.freshpatents.com/-dt20101125ptan20100294249.php
November 2010 - Insulator
Husqvarna is aware of a problem with strato-engines where they run very lean at idle, and off idle they get leaner, can hesitate, choke or die.
A commonly available engine including the stratified scavenging two-cycle engine is typically driven with lean mixture during idling. However, when the stratified scavenging two-cycle engine is suddenly accelerated from an idling state, air from the air passage is initially supplied into the cylinder and therefore mixture having a predetermined fuel ratio, which follows the air, is not sufficiently supplied. Consequently, the lean mixture becomes further lean, which causes acceleration failure or engine stop.
So they propose an accelerator pump to inject fuel and overcome this problem. Accelerator pumps in the carb are not new, so this one is integrated with the heat insulator boot between the cylinder and the carb in the dead space to reduce space used by the accelerator pump.

http://www.freshpatents.com/-dt20120614ptan20120146249.php
June 2012 - Carburetor
In the dual-barrel carb of strato engines, the carb is very large, and the passage is long(er than regular chainsaw carbs). So they suggest using a venturi (a bulge in the airpath) to accelerate the air through the carb in the air-only side, and making a shorter barrel carb.

http://www.freshpatents.com/-dt20120719ptan20120180769.php
July 2012 - Two-Cycle Engine
Offset counterweights on the con.rod to reduce vibration and improve engine efficiency. This one looks juicy, but says very little.

http://www.freshpatents.com/-dt20120920ptan20120234304.php
September 2012 - Stratified-Scavenging Two-cycle Engine
Does away with a dual-barrel carb in strato engines for a simpler single-barrel carb. They suggest that the insulator between the carb and the cylinder has two windows for the air-fuel mixture and the scavenging port, and the jet in the carb is movable. Airflow through the carb through the lower fuel-mixture port creates negative pressure and pulls the jet up and allows fuel to spray into the airstream. Airflow through the carb going through the upper scavenging port doesn't create enough negative pressure around the jet, and it falls down, not spraying fuel into the air stream.

http://www.freshpatents.com/-dt20120927ptan20120240907.php
September 2012 - Stratified-Scavenging Two-cycle Engine and carburetor
Much like the previous patent, just with some wording changes and clarification, and explaining it in conjunction with the strato engine.

http://www.freshpatents.com/-dt20130425ptan20130098325.php
April 2013 - Air Supply Device for 2 Stroke Engine
Blow-back normally causes increased emissions and lower fuel economy by blowing air and fuel back through the carb into the air filter. This solves the problem without preventative plates or reed valves by creating an accumulator that catches the fuel inside the air filter housing, and a passage takes it directly into the crank case body to be used.

http://www.freshpatents.com/-dt20130829ptan20130220260.php
August 2013 - Air Supply Apparatus for Two-Stroke Engine
If using a single-barrel carb with a strata-engine, there may be mixing of fuel in the air-only scavenging airstream. So, they design an air filter housing with two discharge ports to efficiently direct airstreams into the carb.

http://www.freshpatents.com/-dt20130905ptan20130228152.php
September 2013 - Air Supply Device of Stratified Scavenging Two-Cycle Engine
Expounding on the previous patent with pictures and further clarification. Goes on to describe flow rate regulators and their design.

http://www.freshpatents.com/-dt20131107ptan20130291840.php
November 2013 - Stratified Scavenging Two-Stroke Engine
Little confused on this one, not sure if they are talking about the scavenging port, or the transfer ports. In current scavenging engines the amount of air chased through the cylinder is controlled by the port size in the cylinder. The transfer size is defined by a transfer cover, and a partition in the transfer cover. The transfer port is low, close to the case, and to make a cheaper interchangeable lineup of saws, a single crankcase design could mate with the same cylinder and the cylinder would partly determine the port size by using the skirt on the cylinder as a flow restrictor in combination with the different transfer covers.

2014 - no updates
2015 - no updates

 

[Franny K]

Is anyone allowed to state whether these 572 and 590 have crank stuffers and the in board vs outboard clutch on them?

 

[Chris-PA]

http://www.freshpatents.com/-dt20131107ptan20130291840.php
November 2013 - Stratified Scavenging Two-Stroke Engine
Little confused on this one, not sure if they are talking about the scavenging port, or the transfer ports. In current scavenging engines the amount of air chased through the cylinder is controlled by the port size in the cylinder. The transfer size is defined by a transfer cover, and a partition in the transfer cover. The transfer port is low, close to the case, and to make a cheaper interchangeable lineup of saws, a single crankcase design could mate with the same cylinder and the cylinder would partly determine the port size by using the skirt on the cylinder as a flow restrictor in combination with the different transfer covers.

Yeah, I totally misread what this one was about - I though it looked like the piston skirt was was restricting the transfer when it's just the edge of the cylinder.

 

[Derf]

If you got your hands on one you be realizing that yes, it can be better than the 372. The smoothness of the 576 is attributed to its powerband, and the 576AT really allows that smoothness to shine.

Its the wider torque band, nothing to do with the AV.

Hi Hamish,
I found some other posts in another thread that contradict your opinion that the "smoothness" of the 576XP over the 372XP is attributed to the powerband, they seem to suggest the smoothness is due to the AV differences. Just throwing' fuel on the fire here...

I never liked the feel of the 576 over the 372, but they are strong runners. Very smooth/ low vib as you said. Local dealer had one last year he was trying to get rid of for cost, and I missed the boat on it. :msp_ohmy:

The vib difference and faster cuts make up for the 1lb difference.

M&R,

I have a 372 XT/XPW and its vibration dampening is already great and butter smooth. You obviously have both a 372 and 576, so how much better is the vibration dampening on the 576? I get the impression, from what you say, that it is noticeably better.

There's a noticeable difference in them. I've had 2 of each myself. It's just a little less transferred into your hands.

The vib difference isnt anything crazy, but you can tell the 576 is smoother. Dont get me wrong the 372 is more than a great saw and does what i ask of it and it is still a pleasure to run.

As you might recall, M&Rtree owns both the 372XP and 576XP and ran them both, and was attributing the smoothness to better AV.

Of course, the 576XP is an x-torq model, and I've read that in general all x-torq saws are described as having a wider torque band. Many of the original comparisons of the 372XP and 576XP were of the pre-x-torq 372XP. The current 372XP x-torq should also has a wider torque band than the original 372XP, so if you are attributing the smoothness to the torque band, I wonder how the torque band of the 576XP and the 372XP x-torq compare?