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I'm thinking of getting these inflatable spring assisters to help with the heavily loaded journey I'm doing. You can optionally fit a compressor to inflate or deflate the thing from inside the car. Now this got me thinking.
A similar system is an option on a new Passat - apparently it uses level sensors to inflate or deflate as appropriate. I was wondering if I could come up with something similar to fit to the retrofit air spring system.
The question is - how does the OEM system work? Does it wait til you're on flat ground before adjusting, or does it perhaps use some kind of sensor attached to the suspension members to measure the compression?
Not sure which approach would be better to attempt to bodge on. I suppose it could be straightforward to use an accelerometer to see if I'm going up hill or not, and if I'm on the flat then use a level sensor to control the compressor...
(disclaimer - this will almost certainly never get done, but I like to plan stuff in my head 🙂 )
Self levelling Citroens have their sensors reading suspension compression. IIRC the rear sensor is on the anti roll bar, the front is taken from the "shocks". But I could have got that wrong.
Look at the back of TD5 LR Discovery. Some of these have self levelling air on the back end. No idea if they go on the angle of the car or suspension compression, but being a LR of that age it'll probably be fairly agricultural.
A friend of mine used to own a prototype Range Rover that was an old shape Classic used as a development mule for the technology that went into the middle shape (P38). That had air all round, and under the drivers seat were a cluster of Schrader valves that could be used to add or remove air manually.
No idea how it ended up on the market, that car. Interesting bit of kit.
Just go images of your car self adjusting as it goes round corners
Pogo passat !
I see.. hmm.. I wonder if you could have some kind of sensor that just detects how far away the road surface is? Don't they do ultrasound transponders that can do that?
I know that some cars, Volvos for one, use a self-inflating shock absorber that pumps itself up to a specific length using the normal suspension action, via a series of internal valves. They can be easily retrofitted to those cars but not to mine - there's no room apparently.
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Do it properly 
Jack the dog - p38s and discos are horrendous - most folk remove em for springs !
[i]I see.. hmm.. I wonder if you could have some kind of sensor that just detects how far away the road surface is? Don't they do ultrasound transponders that can do that?[/i]
Possibly. As it happens, I've just ordered one of these for measuring road height, but they're about 3K, so probably aren't so applicable.
[url] http://www.micro-epsilon.co.uk/displacement-position-sensors/laser-sensor/optoNCDT_1700_basic/index.html [/url]
Though you could try one of these on a budget.
[url] http://www.sparkfun.com/products/242 [/url]
IanMunro - what's that sensor going on?
EDIT that cheaper one looks excellent though. The range is right within what I need too. Hmmmm... looking like more of a go-er now... 🙂 I wonder how much ambient heat would affect it tho.
Just need to average out the signal over 5-10 seconds or so... Would have to introduce some lag though otherwise it'd be constantly hunting for the right ride height..
I've used the second sensor Ian posted quite a bit in robotics and they work really well. It'll do exactly what you describe, they do digital and analogue ones depending on your control circuit. That said, I'd be measuring the suspension
It's going on a vehicle to measure road height. I can't really say anything more on the specifics, but it's quite an impressive sensor as it can measure 0.05mm height changes 2,500 times a second.
Those cheap sharp ones are pretty good, I've used them in robots for range finding, ambient heat will effect it a little, but I wouldn't have thought enough to worry about, though haven't checked the datasheet. But if you measure the temperature you could then in theory compensate for it.
I suspect (from experience of active suspension on sports cars), that an angular position sensor is fitted to the lower wishbone arm, hence you can tell where each wheel is within its articulation. You would probably have to set the system up with the wheels in the air so you can find the reference point of the wheels being at full re bound.
That said, I'd be measuring the suspension
More complex tho, surely? Unless I just bolt that same sensor to the chassis and have it measure the distance to a swingarm rather than the road...
Bamboo - aye, that's the other thing I was thinking of but getting hold of or fabbing something mechanical would be much harder. Then again, with that IR sensor it could easily get covered in muck.
