27 replies to this topic

[Malinda]

hi,

Please let me know how the SRS senses a crash to activate airbag? does it through the tensioners in seat belts?

thanks,

Malinda

[kez_19]

All cars with SRS have sensors mounted around the car that sense a crash. When they sense an impact that is greater than a certain g-force (pre determined from the factory) then a signal is sent to the SRS module, (the computer that control's the air bags and seatbelt pre tensioners) when the module receives the signal it know weather it is a front, rear or side impact. It then decides which of the safety features that need to be deployed. It then sends a signal to the air bag / pre-tensioners and fire's them.
The air bag then fires a small explosive charge that allows the air bag to open and fully inflate and immediately start to deflate. The seat belt pre tensioners will activate and another small charge is fired which causes the belt to tighten and pull the person wearing the belt in to the seat to stop them from hitting the windscreen or dash area.

All this is done in less than 1 second

hope this is of some help

michael

[Asphalt]

The MPI's system doesn't sense anything at all, afaik

It's a little (metal) ball held by a feather - if deceleration is over a certain degree (the bespoke g-forces),
it comes loose and triggers the signal for airbag & tensioners. Works only one way (front impact).
(And no, you will not be able to trigger the airbag with hard braking - it needs much more deceleration! )

The Mini's sensor is somewere in the middle of the car, thought, behind the driver & passenger's seat on the floor.

[Ouster]

Yep, I would imagine it would be a ball bearing held by a spring. Significant deceleration causes the ball to extend the spring, which will hit a metal contact, complete a circuit, and set off the airbag.

Airbags contain phosphene gas, which is extremely toxic.

[Dan]

The MPI's system doesn't sense anything at all, afaik

It's a little (metal) ball held by a feather - if deceleration is over a certain degree (the bespoke g-forces),
it comes loose and triggers the signal for airbag & tensioners

Sounds like a sensor to me, in that it detects acceleration and produces a signal. I believe it uses the exact same accelerometer as other SRS systems use, not a ball that breaks loose from anything but a ball or mass that moves and stretches a piezo crystal to generate a signal. There are more basic accelerometers in the innertia switch for the fuel pump (that is a ball that jumps loose and knocks off a switch as it moves) and in the seatbelt innertia reels (balls that tip the pawl into contact with the ratchet when they move). These are accelerometers in that they measure an acceleration, they don't produce a signal as a result but do produce an effect in response to a specific moment. The Mini SRS system only employs one airbag and only in front of the driver who should be wearing a seatbelt so the system only needs to be one dimensional. Intelligent systems are only needed where there are multiple airbags in positions that may do more harm than good if they go off at the wrong time. Many now include proximity circuits that won't fire an airbag if you are too close to it.

[Malinda]

The MPI's system doesn't sense anything at all, afaik

It's a little (metal) ball held by a feather - if deceleration is over a certain degree (the bespoke g-forces),
it comes loose and triggers the signal for airbag & tensioners. Works only one way (front impact).
(And no, you will not be able to trigger the airbag with hard braking - it needs much more deceleration! )

The Mini's sensor is somewere in the middle of the car, thought, behind the driver & passenger's seat on the floor.

Hi,

Is this ball and spring located inside the SRS control box?

Malinda

[s1xpr]

yes, the sensor is built into the srs control box which is under the rear seat in the middle of the floor.

[Twincam]

Sorry to thread jack, but my SRS light is on permeantly - would it still activate if I was involved in a crash? (bought it like that)

[Juju]

Sorry to thread jack, but my SRS light is on permeantly - would it still activate if I was involved in a crash? (bought it like that)

Probably not. If the light stays on, you are supposed to "contact your Rover dealer".
They're supposed to be serviced/reconned after 10 years.

[s1xpr]

twincam, the most likely reason that your airbag light is on is due to the rotary coupler failing. this sits behind the steering wheel and connects the horn/airbag to the wiring loom in the car. easy to change - just make sure you leave the battery disconnected for 30 mins and when you take the wheel off, put it back in the same position!

send me a pm if you need the part or want any guidance fitting it.


thanks


paul

[se7enmvu]

My air bag deployed in an accident in 2010, I have a new air bag and pretensioners can I re-use my existing SRS control box or will it cause my new air bag to deploy when the battery is connected?

 

Cheers

Mark

[FlyingScot]

The sensor is in the SRS box under the rear seat, I would replace this because AFAIK its a one time gig.
Short answer yes

FS

[Joe Nation]

I used to work in a factory that made airbag switches (for Porsche Cayenne/VW Toureg if I remember rightly). The ones I dealt with had a small (5-8mm) tubular magnet that slid up and down on a plastic rod, with a switch inside. As the magnet moved (by inertia in the event of a sudden decceleration) it pulled part of the switch to make or break the circuit. The worst part was that I work in quality assurance, so no pressure!

Edited by Joe Nation, 23 December 2016 - 11:56 AM.

[FlyingScot]

Sorry to thread jack, but my SRS light is on permeantly - would it still activate if I was involved in a crash? (bought it like that)

Probably not. If the light stays on, you are supposed to "contact your Rover dealer".They're supposed to be serviced/reconned after 10 years.

The reason to contact your Rover dealer was to have it plugged into testbook which would read the fault code and determine what was causing the fault.
You can do the same today if you can find a garage with a working testbook or using Sykes Pickavant ACR4 plus Rover pod V4 or later or one of the MAP pods with the later software.

Usually its wiring faults (yellow cables) or as pointed out the rotary coupler

FS

Edited by FlyingScot, 23 December 2016 - 02:45 PM.
Spelling

[FlyingScot]

The sensor is in the SRS box under the rear seat, I would replace this because AFAIK its a one time gig.
Short answer yes
FS

I'm wrong in this post, the ECU stores the fact it's been deployed, but can be reset; apologies I checked once I had researched for another members query. So not a one time event the unit is reset using diagnostic kit which clears the event logged.

FS