sharkmeister85

Is that because all the oil leaks out?
Glenn

6.0-928S

Where do you keep coming off with the undamped spring? Maybe you should read the previous posts before you put yer chops in gear. Read my lips........THERE IS AN OIL FILLED DAMPER TUBE IN THE CENTER OF THE SPRING ASSEMBLY!

6.0-928S

As I said earlier, to know what I was working with, the first thing I did was buy a brand new tensioner assembly & cross section it (cut it open) to see what the theory of operation was. I'm going to see if I can find it this weekend & post the pics.
Hammer

Daniel Dudley

I think that there is a possibility that this hybrid unit might have qualities that would be useful during those episodes when unexplained belt failures happen. I don't think it has to be a problem if the belt can compress the spring, as long as it is well damped and can readjust to normal spec in a timely fashion. The spring only gives the tension. It is the damper that supplies resistance to compression, presumably in direct opposition to the force/speed applied to it. The question is, what happens when the belt wants that compensation and can't get it ? That is the situation with the current tensioner.

I think this could be a good system, in an as good as or better than way. It will have to be tested. I would like to point out that many of Porsche's hypothetically superior designs were proven ineffective by their customers. In this case the designer is putting his money where his mouth is.

Nice work. I'm impressed. Next round's on me.

blown 87

Any one that has ever tried to compress a hydraulic tensioner knows that is a job for a vice, the spring just sets the tension and the tension is kept by the hydraulic unit.

PorKen

I want one of these!

blown 87

Need more information on that. Is that some kind of IR belt tension checking device?

Garth S

Ah ... so many people ... so many opinions: I would be remiss if I didn't add one too ..

Firstly, Hammer - I admire your approach and due diligence in presenting this development: I particularly like the retention of the low tension alarm system - for that is a concern area for me, having seen more TB's fail due to water pump issues than tensioners.
I would be interested in your dissection of the Volvo units oil filled chamber ... for I suspect that may address the concerns some express. To tame a resonant spring, a 50:50 valved 'shock absorber' with a chamber to address oil expansion when heated comes to mind .... but I wasn't the guy with $70 and a hacksaw in hand ... to find out.
If this particular spring is sufficiently compressed when it reaches the correct static belt tension, then it will retain tension as flopping belt harmonics require it to extend ever so slightly ( an overly strong spring would be my only concern, for there would be insufficient travel on the extension mode - compression is always available) . That is unlikely an issue, so all looks good.

As to the factory tensioner, I've always thought of the series/parallel configuration of the Belleville ( bimetallic) washers as a rather sophisticated high rate spring with temperature compensation. That spring is allowed somewhat less than 4mm of compression in the newer tensioners ( with oil bleed ports) as evidenced by the fit of the washer centering rod into the bottom piston. That the bottom piston has both an o-ring and a check valve indicates its role in managing oil flow: further, a concentric cylinder within the housing open to the back side of the bottom piston traces the oil circulation path in a loop within the tensioner, bathing the washers as it helps damp spring oscillations .... and these oscillations/compressions from the TB harmonics make the bottom piston the driving oil pump.
As deceptively complex as the OE tensioner is, it is an intriguing design; however, three cheers for efforts to improve upon it!

PorKen

Greg - just click on the pic.

Natch, it's for static testing, not while running.

Larry928GTS

I think what would concern most people more than that is what happens when the belt wants that compensation and CAN get it.

blown 87

Ok, I want one also.
When you consider the price of the three belt tensioning measuring devices I have now, it looks cheap.

How in the world did you run across something like that?

Charley B

Remember Hammer, no good deed ever goes unpunished.

mark kibort

thats like saying a shock that is blown out is a doing something! there is oil yes, but it aint doing any measureable damping, not unless there is a pressure rise in the fluid somewhere, which in a suspension shock, there is, its a valve. you make the orifice larger and smaller to change its damping charateristics. a spring osliating at high frequencies just exposed to fluid is not going to do anything (measureable) so read my lips: " springs submerged in oil dont have any measureable damping charaterisitcs vs dry". now,if there was a pin hole between the washers and the fluid was forced through them upon movement, then you might have something. [

NOW, i just measured the "movement" "springrate" of a stock tensioner. 200lbs, and no movement, measureable with some calipers. it just plain doesnt move. now, im willing to bet that little spring set up we are talking about will move a WHOLE bunch if i stood on it! why, because it is a spring, in our application of the tensioner, the washers, and more like wavy washers than belville washers, dont show any movement upon pressure.

why are you fighting this? go out and test your own tensioner and see if it moves with 200lbs of force. then, think about in spec and out of spec tension for the belt being .75mm of the tensioner. if it can move this much under some kind of resonance, then you could be in trouble. thats my only point! the stock set up will not move. the little spring at the end is not part of the compliance equation. it only does something if the contact is broken under a loose belt condition.
MK

QUOTE=6.0-928S]Where do you keep coming off with the undamped spring? Maybe you should read the previous posts before you put yer chops in gear. Read my lips........THERE IS AN OIL FILLED DAMPER TUBE IN THE CENTER OF THE SPRING ASSEMBLY![/QUOTE]

Mike Simard

But Mark, there's a seperate damper in the Volvo unit. It sounds like you see the picture on page 1 and believe the shaft inside the spring is dormant. Hammer said that it's a damper with it's own internal oil supply. Hammer is that correct?

mark kibort

Unless he has one heck of a valving setup to dampen this type of spring, yes.
the "Damper" would be a "Shock" like set up that is claimed to be apart of our systems. however, in measureing the movement (there is very little with serious pressure) i would think any "valving" may have other purposes. again, i see absolutely no movement with 200lbs of force applied to a stock tensioner.

If you understand resonance, you can see that if the natural frequency of the spring is equaled by some harmonic of the engines natural vibrations at all the different rpm ranges, then you can see at some point, this could be a serious issue on the spring shown in the proposed design.

again, the roller and tensioner is to be set to keep tension. if this setting can vary, because its a spring design, i would be concerned, thats all.

I would spend more time developing some type of analog or digital sensor that can give you a read out of timing belt tension! the Sunx pressure sensors could be a great fit here. very very accurate. Then, you would get a read out continously and be able to address the belt when the tension goes below set values.

MK