AirBag (SRS) Deployment Facts....

S

Shipkiller

Veteran
Airbag Triggering

Numerous crash and road tests under extreme conditions have been used to set the BMW
triggering thresholds for all possible types of accidents.
The triggering thresholds are primarily divided into 4 groups according to crash severity:

• CS 0: no crash (parking damage).................CS=Crash Severity
• CS 1: light crash
• CS 2: crash of medium severity
• CS 3: severe crash

The triggering thresholds have been set depending on the crash severity and including
other factors such as direction, overlap on collision, and depending on the evaluation as to
whether the occupant was wearing a seatbelt or not.

This results in the various trigger thresholds for the activation of the various restraint systems.

Triggering in the event of errors

If a fault is detected in the seatbelt buckle detection system, it is assumed that the seatbelt
is not fastened. The triggering threshold is lowered. In spite of the fault recognition, an
attempt is made to activate the seatbelt lock tensioner.

If a fault is detected in the seat occupation detection system, it is assumed that the seat is
occupied. The restraint systems are activated.

If a fault is detected in the airbag switch, it is assumed that a child's seat is fitted. The front
airbag and side airbag on the passenger side are not triggered.

Triggering in the event of a crash

The following examples illustrate the actuators that can be activated:
• Front-end crash
• Side-on collision
• Rear crash

Front-end crash
In the event of a front-end crash, a distinction is made between crash severity "light to
medium collision" or "severe collision" (CS 3).
In the case of crash severity from light to medium collision (CS 1/CS 2), the driver's/front
passenger's airbag are not triggered if it is detected that the occupants are wearing seatbelts.

If the occupants are not wearing seatbelts, the driver's and front passenger's airbag would
be triggered.
The seatbelt tensioners are triggered in all cases.

As of crash severity CS 2, the driver's/front passenger's airbag as well as the seatbelt tensioners
are triggered. The safety battery terminal is activated, the electric fuel pump is
switched off, and an emergency call is placed if a correspondingly prepared telephone is
present in the vehicle.

In the US version, the knee airbags are also triggered.

Side-on collision
In the event of a side-on collision, a crash severity distinction is made between medium and
severe collisions.

As of crash severity of CS 2 (medium collision), the side airbag is triggered on the impact
side. In the event of crash severity CS 3 (severe collision), the safety battery terminal is also
activated, the electric fuel pump is switched off, and an emergency call is placed if a correspondingly
prepared telephone is present in the vehicle.

Rear crash
As of crash severity CS 2 (medium collision), the seatbelt tensioners are triggered.
In the event of crash severity CS 3 (severe collision), the safety battery terminal is also triggered,
the electric fuel pump is switched off, and an emergency call is placed if a correspondingly
prepared telephone is present in the vehicle.

Knee Airbag
In the event of a crash of sufficient severity, the gas generator is ignited. The escaping gas
fills the airbag, which tears open the cover of the knee airbag so that the airbag can
emerge.

The airbag spreads out beneath the steering column and/or in front of the glove compartment
and cushions the lower thighs of the occupant.

The support of the lower thighs initiates a controlled forward shift of the upper body, which
is cushioned by the driver or passenger airbag.

The knee airbags can only be seen by the lettering "AIRBAG" on the cover of the airbag
module as well as on the cable connection for the airbag module.
 
Thanks, very interesting reading.
I saw on your website you have the diagrams for SRS devices integrated into the seats. One of these devices happen to fail somewhat often: the passenger occupancy sensor. It appears the mat under the seat is a little fragile. Some say that happen particularly if you stay with your knees on the seat (e.g. to clean the rear window). I think IMZ4N has this problem and the only solution they gave him is to replace the whole bottom part of the seat for big $$$.
The guys with Z3s developed a device that bypasses the occupancy mat and makes the SRS think there's always someone in the passenger seats. I am not familiar with electronics, but the "box" indicated as X10218-X01009-A113 apper to be the same as the one on the Z3.
The device is based on this circuit. I was wandering if you could take a look and let us know if it would work on the Z4 as well.
 
I have that site archived and converted to a PDF.. Not sure if it works on our Zeds.

I have also heard that just a 4ohm resister will work also..

There IS a part number for just the pressure mat for in the seat. It is just hard to find it.

It is not listed with the seats like it should be. It is listed in 'Audio, Navigation, Electronic Systems' area.

http://bmwfans.info/original/E85/roa/Z4%202.5i-M54/USA/L/N/2002/10/mg-65/ill-65_1221/
 
It took a while but I found the same thing on RealOEM.
Btw, I wanna see with IMZ4N once he gets back from HC. Maybe he can come by my place if he still has the issue and try to get it resolved. Since I have Carsoft now I wanna try a couple things.
1) on my Z3 the problem was solved by spraying some contact cleaner on the plugs.

89400d58.jpg


Before shaking the connectors would cause the Airbag light to come on, after it didn't. Maybe the same trick works on the Z4

2) IMZ4N said he was told he had to replace the whole bottom part of the seat because the mat was integrated into the seat. Looking at RealOEM is says that mat applies to production date up to 01-2006 and I believe his car is older than that.

Just for completeness, here's the link to the thread from Vinci. He makes and sell a nice plugs. Actually a common friend of IMZ4N and I (MC28REPSOL) has the plug installed on his Z3MC. Maybe we can ask him if we can borrow it and see if it works on the Z4 as well. I just wish we could get a technical opinion from someone who understand these schematics ( :roll: ). I just don't wanna fry the SRS module or do more damages than good.

I hope I'm not hijacking your thread.
 
The phone call it makes - is that for the Bluetooth prep, or just with the assist thing you guys have over there?
 
Mattt said:
The phone call it makes - is that for the Bluetooth prep, or just with the assist thing you guys have over there?
Click to expand...


I assume that you have to have the BMW assist installed for the emergency phone call.
 
Interesting definitions. Yesterday I removed my door panels to install some Dynamat on the inside of the door sheet metal and found myself staring face to face with the air bag container and could see how it would deploy of needed.

First off there is a screw holding the rear part of the door panel in place so it won't turn into a large projectile when the bag blows. That is right behind the small plastic trim piece that says Air Bag on it. There is a small panel just in front of the air bag that is designed to burst out if the bag is deployed at which point the whole top trim piece near that plastic screw cover will fly out just in front of the bag and while it will become a small projectile I guess the philosophy is that the resulting cushioning of the air bag will more than offset any bodily harm that will come from the impact and the trim piece bruise on your arm will be a negligible side effect that can be ignored compared to the rest of what probably happened.

Hope I never find out what that experience would be like.....
 
My boss wreaked his 04 Zed last month.

This is the story I have heard from his mouth.

Hit a pothole at speed on the interstate. This threw the car violently left into the jersey barrier, then that impact threw the car into the jersey barrier on the right side of the road, then into a spin and impacted and stopped at the left side jersey barrier agian...

All six airbags deployed. He walked away with out a scratch or a bruise....

Car is totaled.... :(
 
I do nominate Shipkiller for MVP, he has some most informative posts seen in these parts.



What trips me out about Airbags and the corresponding technology, is simply the time limit that the computer decides, ok is this CS1,2, or 3. Damn things gotta be super fast. I'm sure it's probably staged somehow and as whatever meter that monitors impact goes past a certain point the next stage of airbags deploy. But still blows my mind.
 
I recall reading somewhere that the SRS processor has something like 7ms to decide how to react to deploy the side airbags and something like 25ms for the frontal airbags.
 
Shipkiller said:
I recall reading somewhere that the SRS processor has something like 7ms to decide how to react to deploy the side airbags and something like 25ms for the frontal airbags.
Click to expand...

We must of read the same article, I seem to recall those numbers, just couldn't place em enough to say...
 
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