View Single Post
Old 02-14-2012, 10:22 PM
MJLavelle MJLavelle is offline
Registered User
Location: Charlotte NC
Join Date: Sep 2011
Posts: 30
Mein Auto: 2001 330ci
Originally Posted by gary@germanautosolutions View Post
Thanks, I appreciate all feedback, positive or negative.

1) With regard to bearing pivot point, the stock unit has a steel pin pressed into the flapper valve and the body has a pressed in PTFE or moly coated bearing supporting the pin. The pin rotates within the body, not the flapper valve, and my design does not change that.

2) I agree that the new ass'y will be heavier. That is the reason for going with a much more expensive custom 'titanium' pivot screw (The CAD pictures you referenced here are the Rev 1 not Rev 2 pictures that were posted later). Another point to note is that the stock steel pin is 4mm (.157") in diameter, and the bearing I.D. is 4.37mm (.172"), leaving a pin to bearing clearance of .015". My design reduces that clearance to .002"-.003", which drastically reduces room for vibration between the pivot and bearing. I have checked 2 used (8 years old) and 1 brand new unit and the bearing I.D. is consistent, so I feel comfortable closing up this clearance.

3) The valve spends 90% of it's life in the closed state (low to mid RPM part throttle driving) where the flapper is fully seated against the silicone seal molded into the DISA frame work. In it's closed position all vibrations of the flapper will be damped.

4) The DISA ass'y has a molded in silicone seal around the perimeter of the frame work which dampens vibrations transmitted into it by the valve to the larger mass of the intake manifold.

5) I have a bunch of electronic test equipment here and we plan on testing the ass'y to see if it has any strong resonances that fall within frequencies generated by the motor (2000-6000rpm = 100-300 Hz).

I've spent a considerable amount of time trying to anticipate all failure modes and have had the design reviewed by another engineer. That being said, if anyone sees any other potential problems, please post them for consideration before this goes into production.

Thanks again to everyone who is supporting this project.
In the interest of throwing things out there that could be a problem with this solution, I will ask - what is the weight of the replacement piece, v/s the original piece? This leads directly to my second question - have you performed any testing to see how much force is required to open the flapper? If the weight is greater, then the force required to open it may need to be greater. The same goes for closing the tolerances for the pins. Does this increase the force needed to actuate the valve? I ask, because there are no upgrades to the diaphragm that controls the closing of it, or the actuator that opens it. If it requires more force, it could either not open correctly, and/or cause premature failure to the mechanism needed to open it. It could also cause the valve to snap shut abruptly, if it overpowers the diaphragm, which I am assuming is there to prevent it from snapping closed. I am not sure what would happen if the valve snaps shut abruptly, but I would think it would be noticeable. Are you also looking at the diaphragm, and any possible repair kits or replacements to it as well? Because not all DISA failures are not due to the flapper failing. The diaphragm on the actuator will also fail, mostly with age. It may be another area that needs to be addressed. If the diaphragm or actuator fails, most people will not notice it, and simply write it off as an aging engine. Most of the time, it throws a code for a lean running condition, but not always.
Please don't take this as pi$$ing on the extensive work you have done. I think you are doing a great thing, that many of us admire and appreciate, and also wish we had the resources available to do such things. You could open a skunkworks, taking ideas that people have and making them into workable prototypes (after some review, of course). There are lots of people with good ideas, but absolutely none of the tools needed to actually make those ideas a reality. I just wanted to throw my concerns into the mix, and see if you had considered them (although I am fairly sure these things must have occurred to you). Thanks!

Last edited by MJLavelle; 02-14-2012 at 10:37 PM. Reason: Clarifying some of my points. I blame my iPad autocorrect. :)
Reply With Quote