Question - car technology

On a modern car there are many controls on the steering wheel (radio, cruise, phone) as well as airbag controls - how are the connections made between the rotating shaft and the fixed part of the car? Is it by using remote control type of technology?

Reply to
John
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Rodders

Reply to
Pat Crouch

Normally a bit of flexible cable that winds up, you can only rotate the wheel so far.

Reply to
Duncan Wood

Yes. More intriguing is how tyre pressure sensors work and connects?

Reply to
johannes

They're wireless. Airbags are often on a "clockspring" & horns tend to be on sliprings.

Reply to
Duncan Wood

My air bag is on a clock spring link between wheel and column. The horn is on a slip ring arrangement, a fixed metal ring with a sprung contact on the moving part. I suspect the other buttons on the wheel are on a multi-core cable wound around the column and/or the buttons use multi-plex control.

Reply to
Harry Bloomfield

Yes. I had to change the flexible coupler on my Rover because the SRS lamp kept coming on. This is apparently the most common cause after seat belt connectors.

Andy

Reply to
Andy Cap

johannes wrote: [...]

Various methods are used.

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Reply to
Chris Whelan

I don't know for sure if this is how they do work, but I heard a plausible theory once.

If the tyre's a bit flat, the wheel's radius is effectively reduced, so it does more revolutions for a given vehicle speed.

You can work out what the wheel rpm should be by knowing the engine rpm, what gear you're in, the final drive ratio, and the wheel radius at the proper pressure. If the wheels are turning faster than they should be, then the tyres are probably going soft.

Many cars already have sensors for measuring that kind of thing for the traction control. Possibly for ABS too.

You can also just look at any difference in revolution rate between tyres to detect a puncture. That will change a bit when you go round corners, but unless you're either driving through Milton Keynes or round and round a race circuit, it should average out over a few miles. Same goes for wheelspin-- you wouldn't get that continuously for several miles.

Reply to
Ben C

It's quite simple, the flexible cable is as long as the manufacturer expects the system to last. The cables they fit to some marques wind round the wheels more than others.

Reply to
Douglas Payne

The cheap solutions do it that way using the ABS sensors & comparing between tyres as well. Snag is they're not very good if all your tyres are going down & you need to lose a lot of air before they notice.

Reply to
Duncan Wood

Close, the posh ones do actually have a battery.

Reply to
Duncan Wood

Duncan Wood ("Duncan Wood" ) gurgled happily, sounding much like they were saying:

Or if you have a different brand of tyre (or a newer tyre) on one side than the other.

Reply to
Adrian

WEll they maight just be making a point.

Reply to
Duncan Wood

No it doesn't. Unless somebody's taken a slice of rubber out of it which would probably negate the need for a pressure sensor.

John

Reply to
John Greystrong

If you're going to be pedantic it's the tyres rolling radius that is reduced, & if it's dropped by more than 25% it's detectable.

Reply to
Duncan Wood

Duncan Wood ("Duncan Wood" ) gurgled happily, sounding much like they were saying:

If you're relying on pressure sensors - or, indeed, any other technology

- to tell you when the rolling radius of a tyre's reduced by ONE WHOLE QUARTER, then I'd suggest you shouldn't be driving.

Reply to
Adrian

HOist by my own petard. But you know I meant the pressure.

Reply to
Duncan Wood

Duncan Wood ("Duncan Wood" ) gurgled happily, sounding much like they were saying:

Very much depends on the car, and even which tyre it is.

I checked the pressures on the Saab t'other day, because I thought I'd gained a slow puncture in one front. It was barely 5psi down, but looked and felt very soft. One rear, on the other hand, was down 17psi, but looked and felt fine.

Reply to
Adrian

You don't need much change in diameter to be detectable though. The US has a national requirement coming in for all cars to have tyre pressure monitoring & everybodies happy that you can detect 30% pressure drop indirectly. Not everybodies happy that that's accurate enough though.

Reply to
Duncan Wood

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