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X-Deflex Anti Sway Bar - Pressure or Vac operated?


simonr
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X-Deflex Pressure or Vacuum  

34 members have voted

  1. 1. Pressure / Vacuum

    • Pressure from compressor
    • Brake Vacuum
  2. 2. Default state if pressure / vac is lost

    • Locked (Articulation reduced)
    • Unlocked (Free to Articulate)


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As you probably know, X-Eng currently sells an unlockable anti roll / anti sway bar called X-Deflex. Many people have asked for an in-cab remote control to select between locked and unlocked.

The only sensible way to achieve this is using air pressure or vacuum - but which to choose seems to be causing some controversy! Also, if the system fails through loss of pressure / vacuum, in what state should it default to?

Vacuum

Pro:

Every car has a vacuum supply built in for the brake servo assist

Con:

Potentially compromising braking system / safety issues

Pressure

Pro

Bigger difference to air pressure so actuator can be smaller for a given force

Con

Expense - you may need to buy a compressor / on board air system.

The prototype I've built is vacuum operated and fails locked. It seems to work pretty well - but now I've made it, I'm not convinced it's the right way to go! If you wouldn't mind giving me your opinion - I'd appreciate it!

Si

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Which is the safer condition? That's the one it should fail to. I think it's the one which gives greater stability and less articulation. For anything except a dedicated off-roader, surely the on-road performance should take precedence over the off-road performance? AFAIK, that's what the VCA will tell you, anyway.

As a principle, safety related controls should be spring applied, pressure released. In other words, failure of the power supply should result in the system coming to rest in the safer condition. But you knew that already, didn't you!

This sort of analysis is what my company does for a living. It's not difficult so long as you are methodical about how you do it. This advice is worth exactly what you paid for it!

Nick.

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pressure switching, failing in a locked mode.

Perhaps you could have a kit option with a compressor with all fittings to do a complete install. My take on your kit, is it would mostly benefit over-landers, people who tow or carry a lot of weight. Adding a tire inflation ability would go hand in hand with your rollbar.

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If it fails, is it possible it fails in a very flexed mode? I.e. like when an ARB flips? Only ask as I understand it works on a spline.

That's one problem with failing engaged! A nother risk is driving on the road with it unlocked, it failing and locking while the user is cornering - leaving the vehicle leaning significantly.

But you knew that already, didn't you!

Yup! ;)

Si

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I'd say vacuum because, as you say, every car has it. Budgets are tight at the mo, and not having to buy a compressor setup might turn some people towards this solution. Locked or unlocked I'm not sure. It's not like a land rover is downright dangerous without swaybar, and if you had a light telling you it isn't engaged you'd be aware and drive accordingly (Like a brake light switch or pressure/vacuum switch and a light in the breaker in the cab, like the airlocker) For overlanders it might be catastrophic loosing that much travel? whereas swaying can be limited by driving style.

But all be said a manual engagement/disengagement option ALONGSIDE the pressure/vacuum would get you as close to faultproof as possible.

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That's one problem with failing engaged! Another risk is driving on the road with it unlocked, it failing and locking while the user is cornering - leaving the vehicle leaning significantly.

I'm persuaded that failing to the stiff position is the best result.

Thus the control system operates to leave the bar 'unlocked', at which point the system is at it's most flexible.

So in an ideal world you would want 'failure locking' to occur only while the vehicle was close to it's level stance.

The control system might fail while under significant flex, but some sort of limit switch would leave the system operated (unlocked and flexible) until the suspension load became more or less equal, then the locking would come into effect.

More or less equal could be measured via spring pressure on each end of the bar (but how would you allow for static unbalanced corner weights?),

OR equality would be via some sort of electrical potentiometer, similar to those used on air suspended Range Rovers, Discos, etc, to establish ride height. I'm not sure your customer base is ready for that!!

OR the potentiometer could be some sort of pneumatic switch, which only 'conducts' when the pressure each side of a diaphragm is more or less equal.

Come to think of it, do you want a control system that allows the bar to become more flexible when there is a significant imbalance across the ends of the anti-roll bar?

I'm thinking of a user forgetting to switch to flexible until traction is lost through a twisted axle. Then realising the mistake, switching from stiff to flexible, when the vehicle suddenly twists in response to the change in roll stiffness, with the movement being enough to throw the vehicle down a slope.

Thus your limit switch could serve two purposes.

HTH, but I have no idea of the details :-)

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I'd say vacuum because, as you say, every car has it.

Do they? How many Land Rover models have pressurised braking systems, apart from the 38A?

Aren't pressurised systems more or less common now in high end cars with ABS and Traction Control? I thought it was the only way to get the required performance.

Of course, if the target market excludes any such vehicles then fine, vacuum remains an option, although I'm persuaded that people who go for the X-Deflex won't be averse to installing on-board air as well.

Regards.

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Simon, how about making the splines keyed, so it won't lock immediately, only once the vehicle is level. Should just be a case of filling in one spline and fettling the freewheel hub....?

RRC is a boosted circuit too, but as most have proper engines (V8) a vacuum take off shouldn't be a problem.

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Erh.. What are you talking about exactly? do you think there's a little air compressor that pumps pressure into the ABS module?? Cars with ABS do NOT have an air compressor (unless it's for the suspension, but this has nothing to do with ABS) And a defender with ABS STILL has a vacuum operated brake servo. As do many other cars with ABS. So can't really see where you are going?

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I think you'd have to "fail" into the locked mode as that would give the safest on-road handling. Losing a bit of articulation is not a big deal, having your car suddenly go all floppy whilst going round a roundabout at 40mph could be a bit more serious!

If there is a way to frig the mechanism so it locks itself in the home position automatically, and the actuator just holds the "latch" open when the user wants it to be unlocked that would be groovy.

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The other thing with pressurize it and needing a compressor is a more basic question: who will buy it? I think it is going to be people who use their landrovers mainly on the road. These are people who usually dont have a compressor. Hence, a vacuum system will be better, because it is cheaper, as you say vacuum is already there.

Daan

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Isn't there a history of problems with the vacuum capsule on the LT95 central diff lock failing, I think through the diaphragm rupturing or corroding? Not saying that you couldn't make a better capsule than 1970's BL though! ;)

FWIW it's an interesting idea and my feeling is to go with a pressure operated, fail to locked design. Fail to locked for the obvious reasons and pressure operated would be fine as anyone who's interested in fitting such a device would either have, or be amenable to fitting, on-board air. As mentioned above, do a kit with a little compressor, receiver, maybe an air-line take-off for tyres and (importantly) a well thought-out way of wiring it into a Landy's electrics.

Cheers,

AndyC.

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Isn't there a history of problems with the vacuum capsule on the LT95 central diff lock failing, I think through the diaphragm rupturing or corroding? Not saying that you couldn't make a better capsule than 1970's BL though! ;)

Lots of stuff on cars uses vacuum actuation - cruise control, heater vents, EGR valves... the difflocks on my Volvo axles are vacuum operated as standard and work fine.

You do have to be a bit savvy about how and where to tap the system - a misfire can blow back up the system and damage things, and a leak could suck in water/mud or cause loss of braking assistance. Nothing that's hard to overcome, you just need to think about failure modes when designing it.

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