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?
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.
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.
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.
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.
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.
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.
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.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.