Camber Dave
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| posted on 14/12/15 at 12:56 PM |
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Power Brakes
Hi Guys
A group of friends in the West Country are building a Haynes 7 to be used by wheelchair users for track days.
We have formed the charity Go Inspire Now for the purpose.
The website is being revised so try Facebook /Ben Conolly Chairwarrior or Facebook/Go Inspire Now for more info.
I would like to use some form of power brakes.
This is so drivers can apply the brakes from a ‘squeeze’ lever behind (and moving with) the steering wheel and so trail brake into the corners with
both hands on the wheel. The effective movement of this lever would be about 40mm.
Fly by wire throttle control would seem to be easy enough to set up but the brakes are giving us concept / design problems.
My initial thoughts were to have a pump on the engine pressurizing an accumulator but the actuation of the master cylinder needs a length of motion
in excess of that that can be delivered by the squeeze lever idea.
Another way could be an electrical solenoid powering the M/C actuated by the squeeze lever actuating a controller on the wheel.
Any thoughts or experience gratefully received.
Thanks
The Go Inspire team
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rodgling
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| posted on 14/12/15 at 01:15 PM |
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That's a tough one, leg effort for hard braking on track can easily be 40 - 50 kg - whereas I'd think you probably want maybe 100th of
this effort if using your fingers while steering. So you need a mechanism that can multiply the input 100x.
If it's just mechanical, then obviously travel will increase 100x - which is a non-starter, as you need travel to remain about the same.
Increasing braking torque via big discs and grippy pads will not get you anywhere near this. Brake boosters appear to give around 2.5x boost - again
not even close.
http://www.classicperform.com/PDFs/BoosterBrakePressureChart.pdf
You could certainly use a sensor and some electronics to drive an electric motor or pump to pressurise the brake lines, you'd have to be very
very confident in the electronics and software to implement your own BBW though.
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coyoteboy
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| posted on 14/12/15 at 01:17 PM |
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Not thought it through with great vigour, and safety would be a major concern with any solution like this, but hows about a power steering pump and a
spool valve?
That said, electronic throttle will require equal amounts of thought to remain safe. There's a reason most student competitions don't
allow electronic throttles - most people can't do it safely.
[Edited on 14/12/15 by coyoteboy]
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obfripper
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| posted on 14/12/15 at 01:56 PM |
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In the spool valve vein, you could borrow the whole system from an old citroen bx/cx/xm/xantia, for a tried and tested system, you might need to use
the calipers from the donor to ensure compatibility with lhm fluid.
Another idea may be to try eddy current braking, which would require an electromagnetic caliper over the disc, and a variable control for the
electromagnet.
This would need to be combined with normal brakes though, as they become less efficient as the speed reduces.
I'm not too sure how you would go about proportioning the mechanical and electronic braking though.
Dave
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redturner
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| posted on 14/12/15 at 02:13 PM |
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Maybe I am missing something but what could be a more simple way of slowing/stopping the car by fitting a conventional brake survo unit and using a
lever from the column to the brake pedal' For years, a friend had to use the old Feeney and Johnson vacuum brakes and cable throttle set up on
his Land Rover, however, when he bought the big Audi he discovers that they cant use vac brakes anymore, apparently they had pipe failures or
something. He could bring the car and a big trailer to a stop with very little effort. I drove the car a few times and did it with out using my legs,
though I found it uncomfortably scarey.....
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Sam_68
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| posted on 14/12/15 at 02:19 PM |
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In the interests of KISS could you not model the system (ie. hydraulic ratios) on that used on a heavy motorcycle, then add a servo to further reduce
the effort?
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Camber Dave
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| posted on 14/12/15 at 02:26 PM |
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Quote
'In the interests of KISS could you not model the system (ie. hydraulic ratios) on that used on a heavy motorcycle,
then add a servo to further reduce the effort?'
Now that I like
Any more?
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owelly
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| posted on 14/12/15 at 04:36 PM |
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I was thinking along the lines of a set of handle-bars, quick-rack and motorcycle levers. I'm sure that would be the way forward (pardon the
pun).
http://www.ppcmag.co.uk
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adithorp
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| posted on 14/12/15 at 04:58 PM |
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Might be worth a u2u to raptor700. He built an MK BEC with hand controls and is part way through building another.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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froggy
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| posted on 14/12/15 at 09:53 PM |
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I've swapped a couple of hand systems from motability cars and maybe a conventional servo set up with a hand bar but extend the bar to form a
semi circle under the wheel . A big enough servo would make it very or possibly too easy to pull though . A Chrysler voyager I did needed very little
effort to stand it on its nose
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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02GF74
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| posted on 14/12/15 at 11:05 PM |
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My 2p worth.
Brake servo.
Solenoid to operate master push rod.
Pressure transducer on steering wheel to vary power to solenoid.
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britishtrident
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| posted on 15/12/15 at 06:33 PM |
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All that is needed is a big servo and enough mechanical and hydraulic advantage. A vacuum booster pump might also be a good idea.
The problem being finding a location for a Jag XJ sized servo which might require some out of the box thinking.
If you could get away with part of the system being single circuit ie not to MSA or IVA standards you could have the servo and tandem master
cylinder located anywhere on the car activated hydraulically.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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rusty nuts
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| posted on 15/12/15 at 06:49 PM |
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The Citroen system is fairly easy to understand, doesn't need any servos , no long levers and doesn't take up a lot of space . The pump
supplies all of the effort needed , the brake pedal just opens a valve supplying pressure to the callipers, no reason the valve cannot be operated by
hand . Should be easy enough to do away with the suspension pipes etc. The biggest problem I can see is the need for a Citroen type pipe flaring tool
as Citroen pipes are a fair bit sammel than normal although Rolls Royce use a variation of the Citroen system with normal brake pipes, it might be
easier to use a RR pedal valve from something like a Shadow 2?
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froggy
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| posted on 15/12/15 at 07:24 PM |
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Bmw e30 pedal box has a bell crank to mount the servo and mc vertically on the n/s .ive used this set up on my car as I can't have anything in
the engine bay and turned the servo mount 90 dry to get it vertical . A servo and master from a Saab 9000 is what I used and well up to the job
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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britishtrident
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| posted on 16/12/15 at 07:13 AM |
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quote:
Originally posted by froggy
Bmw e30 pedal box has a bell crank to mount the servo and mc vertically on the n/s .ive used this set up on my car as I can't have anything in
the engine bay and turned the servo mount 90 dry to get it vertical . A servo and master from a Saab 9000 is what I used and well up to the job
Rover 75 has the same arrangement another alternative is the system used on the Metro/Rover 100 but that limits the size of the servo.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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