coyoteboy
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| posted on 2/12/11 at 12:07 PM |
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Stevehubs- thanks for the links, they're looking rather cheap.
I was thinking this over - I'm not sure I'd need an ESP pump arrangement - ABS units include pumps to re-pressurise the wheel-side of the
circuit after the pedal side has been severed with the valve, otherwise the ABS would cause the pedal to travel to the floor as the ABS action
progressed. A two valve system may indeed work in this case - one valve to isolate the pedal input and the other to oscillate between the pump circuit
and the release circuit. Time to dig out some manuals and see if I can find an ABS pump expert!
[Edited on 2/12/11 by coyoteboy]
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v8kid
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| posted on 2/12/11 at 02:20 PM |
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I played around with this idea for ages but gave up and bought a quaiffe unit. Problem was finding a pump with enough capacity to actuate the
brakes.
Cheers
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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alistairolsen
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| posted on 2/12/11 at 03:05 PM |
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Sounds good and is akin to what many oems are doing now as the electronic option si cheaper and easier to fit than a proper diff.
Beware electric calipers, they're not yet mature enough IMO and have some horriffic failure stories, not the mention their frankly insane
relacement cost (£500 ish!)
Following with interest and looking forward to seeing how you get on!
My Build Thread
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coyoteboy
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| posted on 2/12/11 at 03:08 PM |
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quote:
I played around with this idea for ages but gave up and bought a quaiffe unit. Problem was finding a pump with enough capacity to actuate the brakes.
Cheers
That's a pretty big concern actually, if the pump combo can't shift enough to move the pistons (rather than just release and re-apply the
pressure and volume you've shifted by foot as in a normal ABS) . So probably an ABS unit is out of the question again, it would need to be the
unit designed specifically for the task of actively applying brakes when not under pressure from the master cyl.
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mark chandler
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| posted on 2/12/11 at 04:51 PM |
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Range rovers have had this for years, all the way back to very late classic models with air suspension, I had an LSE but it was pretty crude, slightly
better on P38 I had as it clicked in a little more smoothly.
It felt like ABS was rattling the pedal when forcing the car through mud or towing a trailer across a grassy field, I would not want to use it when a
car is on its limit, lightly to throw you off the road IMHO, best left as an agricutural tool.
Regards Mark
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coyoteboy
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| posted on 2/12/11 at 09:22 PM |
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Little bit confused Mark, as this is used now in some very high end performance machines. There's no reason at all that it should be
agricultural or likely to throw you off the road? I also had a classic rangerover LSE, but it didn't have that option I don't think.
I'll look into it. Either way, back in the 80's 90s the processing power and capability was not available that is available now, not even
close. I can hook up a DSP that can make the required measurements at 1MHz and re-calulate the required adjusments a couple of hundred thousand times
a second. Back then you'd be lucky to have electronic ignition that didn't use entirely discrete components 
Add that to the fact that it's on a 4wd system with masses of backlash, horrific driveline wind-up, soggy tyres, compliant suspension etc - no
wonder it wasn't fun. Pushing a RR is never fun
[Edited on 2/12/11 by coyoteboy]
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owelly
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| posted on 2/12/11 at 09:39 PM |
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I've been following this thread and my mechanical head keeps steering me to some sort of vacuum brake or system that puts the brakes on at rest
when there's no fluid pressure. During normal use the brakes work as they do on vacuum brakes on a lorry (did Rollers use a positive pressure
system at some point?) so to apply some brake pressure to the spinning wheel, you would be 'bleeding' pressure away from it. Not knowing
too much about electronics, I'm imagining some sort of wheel speed comparator that would be 'bleeding' pressure away from which ever
wheel was 'gaining' on the other.
I've read through my own post and it makes no sense. Sorry.... 
Anyway, you'll never build a car and it will take you too long to not build it, all your ideas are rubbish and your jumper doesn't suit
you.... Just thought I'd join in.. 
http://www.ppcmag.co.uk
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phelpsa
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| posted on 2/12/11 at 10:06 PM |
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I have been doing a bit of work with electro-hydraulic systems recently and from what I gather you will need....
a) a pump capable of supplying the pressure you require
b) an accumulator capable of holding enough fluid to apply the brake to the pressure you require.
c) a feedback pressure sensor
d) a servo valve to isolate the brake mastercylinder
e) two servoproportional pressure control valves to supply pressure to the brake calipers
f) two servo valves to release the brake pressure back to the LP side of the system
g) your electronic stuff (I dont do that...)
You map your wheel speed differential to the feedback pressure in your computery thing and use it to supply a voltage to the servoproportional valve
to maintain the pressure required.
Then some sort of system to cut the pressure and reconnect the mastercylinder when the brakes are applied.
ITS EASY
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paulf
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| posted on 2/12/11 at 10:49 PM |
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I have just been looking at the spec for Rover 75 traction control and it works by partially using this system coupled with fuel cut as well.I should
imagine most parts are fairly standard mechanical and electrical units that are fitted to many other cars.
http://en.rover-club.net/graphics/manuals/17/r75_technical_brochure.pdf look at the traction control section.
Paul
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coyoteboy
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| posted on 3/12/11 at 01:19 AM |
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quote:
Anyway, you'll never build a car and it will take you too long to not build it, all your ideas are rubbish and your jumper doesn't suit
you.... Just thought I'd join in..
Cheers!  My jumper does look a bit old-man, you're right
quote:
I've been following this thread and my mechanical head keeps steering me to some sort of vacuum brake or system that puts the brakes on at rest
when there's no fluid pressure. During normal use the brakes work as they do on vacuum brakes on a lorry (did Rollers use a positive pressure
system at some point?) so to apply some brake pressure to the spinning wheel, you would be 'bleeding' pressure away from it. Not knowing
too much about electronics, I'm imagining some sort of wheel speed comparator that would be 'bleeding' pressure away from which ever
wheel was 'gaining' on the other. I've read through my own post and it makes no sense. Sorry....
I know exactly where you're coming from, I just wonder if pneumatics have too much lag, but having said that there's plenty of pneumatic
robots that are damn fast and accurate. That's a way of thinking about it that I hadn't thought of - good out of the box thinking
there.
quote:
I have been doing a bit of work with electro-hydraulic systems recently and from what I gather you will need.... a) a pump capable of supplying the
pressure you require b) an accumulator capable of holding enough fluid to apply the brake to the pressure you require. c) a feedback pressure sensor
d) a servo valve to isolate the brake mastercylinder e) two servoproportional pressure control valves to supply pressure to the brake calipers f) two
servo valves to release the brake pressure back to the LP side of the system g) your electronic stuff (I dont do that...) You map your wheel speed
differential to the feedback pressure in your computery thing and use it to supply a voltage to the servoproportional valve to maintain the pressure
required. Then some sort of system to cut the pressure and reconnect the mastercylinder when the brakes are applied. ITS EASY
Looking at it, and I think you're pretty much there but I'll have to draw it all out, almost all of that is housed in an ESP module,
except maybe the proportioning side of it - I think they just use on-off modulation rather than fine control of actual pressure. Are such
proportioning valves available reasonably cheaply?
quote:
I have just been looking at the spec for Rover 75 traction control and it works by partially using this system coupled with fuel cut as well.I should
imagine most parts are fairly standard mechanical and electrical units that are fitted to many other cars.
http://en.rover-club.net/graphics/manuals/17/r75_technical_brochure.pdf look at the traction control section. Paul
Cheers for that pointer, I'm off to read. Rover 75 stuff is cheap as chips.
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