Welcome to Bimmerfest -- The #1 Online Community for BMW related information! Please enjoy the discussion forums below and share your experiences with the 200,000 current, new and past BMW owners. The forums are broken out by car model and into other special interest sections such as BMW European Delivery and a special forum to voice your questions to the many BMW dealers on the site to assist our members!

Please follow the links below to help get you started!

Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E46 (1999 - 2006)

E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

Reply
 
Thread Tools Display Modes
  #1  
Old 10-14-2011, 01:49 AM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 21,620
Mein Auto: 02 BMW 525i M54 auto 130K
Do you know WHY the M54 DISA has BOTH a vacuum accumulator AND a magnetic solenoid?

Over in the E39 threads, we've been discussing the DISA a lot lately.

Specifically, we've been trying to figure out WHY there is BOTH a 13.8 volt DC magnetic solenoid AND a one-way check valve "vacuum accumulator" inside the M54 engine DISA.

If you understand why, please let us know.
- Strange results from a simple test of the M54 DISA valve today


The quote is from this document (with red italics added by me to clarify):
- m54x5[1].pdf

Quote:
The resonance system provides increased engine torque at low RPM, as well as additional power at high RPM. Both of these features are obtained by using a resonance flap (in the intake manifold) controlled by the ECM.

During the low to mid range rpm, the resonance flap is closed (i.e., the flap is actuated by alternator voltage such that it is held vertically against spring tension). This produces a long/single intake tube for velocity, which increases engine torque.

During mid range to high rpm, the resonance flap is open (i.e, the control voltage is reduced to zero which causes the flap to return to the horizontal rest position due to spring tension) . This allows the intake air to pull through both resonance tubes, providing the air volume necessary for additional power at the upper RPM range.

When the flap is closed, this creates another "dynamic" effect. For example, as the intake air is flowing into cylinder #1, the intake valves will close. This creates a "roadblock" for the in rushing air. The air flow will stop and expand back (resonance wave back pulse) with the in rushing air to cylinder #5. The resonance "wave", along with the intake velocity, enhances cylinder filling.

The ECM controls a (magnetic) solenoid valve for resonance flap activation. At speeds below 3750 RPM, the solenoid valve is energized (with alternator voltage at the harness connector) and vacuum supplied from an accumulator closes the resonance flap (where the vacuum accumulator is apparently a one-way flap valve with a 1/16" entrance hole in the side of the DISA) . This channels the intake air through one resonance tube, but increases the intake velocity.

When the engine speed is greater than 4100 RPM (which varies slightly - temperature influenced), the solenoid is de-energized (i.e., the harness control signal goes from ~13.8 volts DC to zero volts DC) The resonance flap is sprung open (by spring tension), allowing flow through both resonance tubes, increasing volume.



Reply With Quote
Advertisement
  #2  
Old 10-14-2011, 11:33 AM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 21,620
Mein Auto: 02 BMW 525i M54 auto 130K
It seems that nobody, to date, has adequately summarized HOW the DISA actually operates.

Putting the scattered tribal knowledge together from these threads:
It appears this (apparent) revelation below gets us another step closer to both understanding the DISA and to figure out how to test it and why it may be the cause of lean conditions (or not):

Quote:
Originally Posted by seemyad View Post
You hit the nail on the head Blubee.

The diaphragm (when vacuum is applied) and the spring are two opposing forces on the flap. The spring is why the flap is open when you hold the DISA in your hand.

From the videos I linked in a previous post (above) I can see the spring tension on the flap when the guy is forcing the flap closed. He then closes the flap by hand and puts his finger over a small hole where the diaphragm is located. The vacuum seal he creates with his finger forces the flap to remain closed against the tension of the spring.

The electrical portion merely creates/completes the path for the vacuum giving the diaphragm enough "suction" to force the flap close (opposing the spring tension). When you exceed X RPM the 12 VDC is removed thereby opening an "escape root" for the vacuum (basically allowing air into the diaphragm). The tension from the spring then forces the flap open.

When the RPM drops back below the threshold, the 12 VDC is reapplied to the solenoid which then closes the path to allow a vacuum to form again which forces the diaphragm to close the flap.

"As soon as the solenoid valve switches (on dropping below the switching speed) the vacuum reservoir and vacuum unit..." (I believe the vacuum unit to be where the spring and diaphragm are located) "...are reconnected and the connecting flap closed." NOTE: As I have not held a DISA in my hand yet I am unsure as to the location of the "vacuum reservoir".

There is much more to the DISA than meets the eye. Although the parts that comprise the DISA are not expensive individually, I can better appreciate the cost. The reality is it is amazing that so many plastic moving parts and the rubber diaphragm hold up as long as they do under such extreme pressure, vibration, and temperature variations (below freezing to above boiling point of H2O).

I no longer view the DISA as an overpriced cheap piece of plastic. It's moving parts appear to last over ten years and over 100,000 miles under extreme; pressure, vibrations, and temperature variation. The DISA alone is engineered better than most American cars (sad fact).

Also, normal rubber would dry up and crack within a year under these conditions yet the diaphragm retains its properties for a decade or more (hot or cold).



Blubee, there IS value in your desire to understand how stuff works. Thank you for always going that extra mile.

You gave me the missing clue when you mentioned the "magnetic switch". I have an extensive electronics background (which paid for my BMW) so that is all I needed to put the rest of the puzzle together. That's what I call "team work".


.
EDIT: The good news is that the DISA group buy is at 100 people so we might get that 1% to autopsy their DISA specifically to prove or disprove the hypothesis above!
- Cheapest OEM DISA group buy on the planet (1)

Last edited by bluebee; 10-14-2011 at 11:54 AM.
Reply With Quote
  #3  
Old 10-14-2011, 12:10 PM
jcourcoul jcourcoul is offline
Supporter of Bimmer Lore
Location: Mexico
 
Join Date: Nov 2008
Posts: 5,192
Mein Auto: 2006 325Ci
Quote:
Originally Posted by bluebee View Post
EDIT: The good news is that the DISA group buy is at 100 people so we might get that 1% to autopsy their DISA specifically to prove or disprove the hypothesis above!
What's the deadline on the Group Buy? When is final delivery expected?
__________________

2006 325Ci
Reply With Quote
Reply

Bookmarks

Tags
disa, disa diy, vacuum connections


Forum Navigation
Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E46 (1999 - 2006)
Today's Posts Search
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On



Forum Jump


All times are GMT -7. The time now is 01:44 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
© 2001-2011 performanceIX, Inc. All Rights Reserved .: guidelines .:. privacy .:. terms