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Suspension


robhybrid

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You mean like an anti-dive/squat bar? In other words an anti-roll bar following along each chassis rail, then taking a turn and connecting to the outer edge of the axle, thereby inhibiting flex?

yes but only one anti-roll bar connecting roughly over the center of the axle, to allow articulation.

I think the bar would have to be pretty strong as it would be in my case proximately 92" long.with arms 1/2 chassis width so 18" ish.

I was wondering if I could use the suspension rod from a torsion bar suspension vehicle to do this job?

Has anyone ever done this? If so had it got any benefits?

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I think Will is talking about something which allows articulation on opposite directions on the two axles, but resists both leaning in the same direction - stopping it leaning on side slopes but allowing cross-axle.

It could be achieved by connecting a prop shaft to the axle casing such that the prop turns as the axle articulates then joining both props in the middle with a differential. Lock the pinion and it will only allow articulation.

The trouble is, the same as I experienced with my buggy, that diagonal side slopes are if anything more common than regular side slopes on challenge events (and presumably trials). I thus contend that the vehicle needs to be ballanced in it's resistance to side slopes and articulation for good performance in real world situations. Too much freedom of movement is just as limiting as too little.

About the only thing that I think has mileage is forced articulation - using hydraulics (or similar) to limit articulation in some circumstances and force it in others, or more accurately to force the limitation of articulation so when you get in to a situation where it is a problem, you can undo it.

Si

Si, it is similar but completely different. It will literally behave exactly like an anti roll bar but for both axles together rather than one - it would have some give but, at the same time, would have an element of forcing which will promote balanced suspension. Essentially I wouldn't go much softer than would be considered normal but it would give me MUCH more sideslope and high speed stability. I've run a lot of models and scenarios and, so far, it gives no disadvantages in any situations. However, how it behaves in real life is another matter..... If it works I will post up how I did it, but, for the moment I will keep it up my sleeve in case it doesn't.

Rob, I think controlling squat and dive is important but so is controlling roll. Generally speaking you should try designing anti-squat and dive into the suspension geometry and then control anti-roll through anti-roll bars. The problem if you try and control roll and squat/dive via springs and torsion bars is that you end up with a huge restriction to articulation. This is where active suspension comes in but it will be expensive to develop and complex - it took F1 team years to perfect the system but it was seriously effective (and was consequently banned). It could be made to be awesome off road but it would take a lot of development!

One idea I had that I think will makes it's way onto the build is a brake bias adjuster designed to drastically adjust rear bias: set to the rear for hill decents (to give better control and to prevent you locking up the rear brakes and going head over heels and do the opposite for hill climbs). Simple, easy, effective.

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Si, it is similar but completely different. It will literally behave exactly like an anti roll bar but for both axles together rather than one - it would have some give but, at the same time, would have an element of forcing which will promote balanced suspension.

So basically it's a bandaid fix for a poorly balanced suspension. How about creating a balanced suspension in the first place so you don't need this extra contraption underneath.

Essentially I wouldn't go much softer than would be considered normal but it would give me MUCH more sideslope and high speed stability. .

If it works like an anti-roll bar but on the front and rear axle, how is it gonna work on sideslopes? It would be exactly the same like an anti-roll bar on the rear axle, when the rear axle compresses or droops the anti-roll bar doesn't do anything. Same when that anti-roll bar would be connected to the front and rear axle. It would create resistance to articulation but does nothing when one side of the suspension compresses or droops like on a sideslope.

I reckon it's useless. Get a balanced suspension!

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Get a balanced suspension!

I'm inclined to agree - it gives the best all round stability envelope.

If I were building something at the moment (wait a minuite, I am building something at the moment!) I would go for something as balanced as possible front to rear with dual rate springs, dual rate coilovers or Air Shox to allow the rate to increase significantly on compression. Then add a couple of 1000Lb, ATV winches to pull the centre of the axles up towards the chassis. This increases the effective spring rate and stability for side slopes. You can also use it to increase the high side axle weight on hill climbs / desents by pulling up one axle only.

It would also allow you to lower the vehicle for low garages & car parks!

Although it adds a couple more things to control, you wouldn't have to worry about them until stability was proving a problem. At least activating it is (as far as I can see) never going to make you less stable - although it may loose you traction. So I guess you could have it as an "Oh S**T" button on the dash!

Si

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A lot of what is now being discussed in this thread has been done before, in various ways.<div><br></div><div>Toyota have licensed one of the simple systems developed by a company in Aus (their systems go up to much more advanced suspensions as used in world rally cars for example).</div><div><br></div><div>The one Toyota use is a passive (not active) system and basically front and rear anti-roll bars have double acting hydraulic actuators in place of links on one side. The front and rear hydraulic actuators are connected by hydraulic lines in a X manner.</div><div><br></div><div>When the vehicle body rolls to one side (cornering or side slopes) the forces in the actuators are in the same direction so no flow occurs in the X lines so the anti-roll bars act together. When one wheel is pushed up, then flow can occur in the X lines and so the anti-roll bars don't restrict articulation.</div><div><br></div><div>A similar system was on sale in Aus many years ago but it went further by using a hydraulic control valve in the X lines. The control valve was mechanical operated by a pendulum so as to maintain the body level.</div><div><br></div><div>My bushie had (now being re-built but on hold due to moving interstate) coilovers at each corner, each with a pair of strut air springs above a normal coilover spring. My aim was to connect the air lines to the top air springs in an X fashion (front left to rear right and front right to rear left) - they are normally deflated (lower suspension), but when air is added to raise the height the X linking provided forced articulation - note because the air pressure is equalised the weight distribution and size of air springs need to balance. </div>

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... Then add a couple of 1000Lb, ATV winches to pull the centre of the axles up towards the chassis. This increases the effective spring rate ...

Si

Not Only technically correct, unless where progressive rate springs are used, but most will get the idea.

If the springs are linear rate, pulling the down with a winch simply increases the pre-load (not spring rate) and stiffens the suspension (besides changing height).

Edit: Sorry you were specifically speaking of use with air shocks so my first comment doesn't apply so I have crudely edited it.

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A lot of what is now being discussed in this thread has been done before, in various ways.<div><br></div><div>Toyota have licensed one of the simple systems developed by a company in Aus (their systems go up to much more advanced suspensions as used in world rally cars for example).</div><div><br></div><div>The one Toyota use is a passive (not active) system and basically front and rear anti-roll bars have double acting hydraulic actuators in place of links on one side. The front and rear hydraulic actuators are connected by hydraulic lines in a X manner.</div><div><br></div><div>When the vehicle body rolls to one side (cornering or side slopes) the forces in the actuators are in the same direction so no flow occurs in the X lines so the anti-roll bars act together. When one wheel is pushed up, then flow can occur in the X lines and so the anti-roll bars don't restrict articulation.</div><div><br></div><div>A similar system was on sale in Aus many years ago but it went further by using a hydraulic control valve in the X lines. The control valve was mechanical operated by a pendulum so as to maintain the body level.</div><div><br></div><div>My bushie had (now being re-built but on hold due to moving interstate) coilovers at each corner, each with a pair of strut air springs above a normal coilover spring. My aim was to connect the air lines to the top air springs in an X fashion (front left to rear right and front right to rear left) - they are normally deflated (lower suspension), but when air is added to raise the height the X linking provided forced articulation - note because the air pressure is equalised the weight distribution and size of air springs need to balance. </div>

isn't that exactly what the disco td5 has?

Daan

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isn't that exactly what the disco td5 has?

Daan

ACE is similar, but uses electronics whereas the system bought by Toyota is passive.

The Aus company Kinetic Suspension Systems was bought out by Tenneco (who own Ohlins). Kinetic's systems were used by top rally teams until they were banned. Here is a link with some info - scroll down the page.

Some info on the system with pendulum valve here unfortunately not available for several years now!Edit: a link to more info here (pdf format)

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I'm inclined to agree - it gives the best all round stability envelope.

If I were building something at the moment (wait a minuite, I am building something at the moment!) I would go for something as balanced as possible front to rear with dual rate springs, dual rate coilovers or Air Shox to allow the rate to increase significantly on compression. Then add a couple of 1000Lb, ATV winches to pull the centre of the axles up towards the chassis. This increases the effective spring rate and stability for side slopes. You can also use it to increase the high side axle weight on hill climbs / desents by pulling up one axle only.

It would also allow you to lower the vehicle for low garages & car parks!

Although it adds a couple more things to control, you wouldn't have to worry about them until stability was proving a problem. At least activating it is (as far as I can see) never going to make you less stable - although it may loose you traction. So I guess you could have it as an "Oh S**T" button on the dash!

Si

Finally someone is talking sense. That would be how I would do it.

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I personally stick with linear springs. As long as you have enough bump travel, it wont bottom out too soon and you will have a good feel of whats coming when cornering.

I run radius arms front and rear, which add on roll stiffness, but not on normal (flat road) suspension stiffness. I also took particular care to achieve the static deflection of the springs the same front to rear, resulting in totally balanced suspension. This works very well, and despite only 10" travel, lifting a wheel is very uncommon.

Daan

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Pretty sure that's a form of active suspension, with the hill sensing and all.

Not quite - it's a dual rate air spring. The first part of the compression can be set to bee softer than the second. The change over looks as if it's based on pressure rather than displacement.

Like any air springs, the rate will increase as the spring is compressed. What this allows is a dramatic increase in rate after a certain point which will effectively limit roll on side-slopes more than, for example a fox air shock. You could probably achieve something similar using the hydraulic bump stops - so long as they had enough stroke.

I think they are quite interesting! They look expensive though. I rang a couple of their 'dealers' but none were interested in selling me shocks alone - they just want to fabricate whole vehicles, possibly using the shocks.

Si

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Hmm, it's a dual rate where the rate change is defined by a hill being detected - how that's done isn't really important IMO. As far as I've picked up, they'll do their job at whatever position the shaft is in. It's also a bit different from the two and three rate coilovers, where at least one of those rates defines ride height.

Note that I could be very wrong, this is all from memory from what I've read spending way too much time on Pirate :lol:

They are pretty expensive, but they do have hydraulic bumps built in, so you can subtract that.

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Toyrover, did I ever say the system was unbalanced??? In fact it is designed to be as balanced as possible. There will be a slightly differant frequency front and rear but this is necessary for high speed handling.

Bush, my system is very similar. I will explian it briefly.... Assume you have a remote reservoir shock at each corner. Remove the reservoirs and connect the left hand side shocks together via a line with a T piece in it. Do the same on the right hand side. To each T price connect a ram. Make the rams actuate a torsion bar. Result is a passive anti roll system. I've gone through several iterations of the design and I'm rather excited to see how it performs!

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Will, Do you mean the ram twists the torsion bar in such a way as to resist the roll on one axle, or the two rams are connected to one another via the torsion bar.

First thoughts about this, firstly, pressure will be allowed to flow freely between the front & rear on each side without the rams getting involved at all. This will encourage dive & squat as you accelerate & decelerate. It will also encourage or at least not discourage diagonal roll which makes diagonal traverses of slopes unpleasant. Worse than this, as you corner or worse still brake on a corner, the vehicle may be inclined to dive towards the outside front wheel - again not what you need.

Assuming it's the two rams connected via a torsion bar option (it would be simpler to connect them by a simple spring?) then yes it will not restrict the whole vehicle rising & falling with equal movement on all four shocks. It will restrict the lean on static side slopes.

Don't be discouraged though - there probably is still some mileage in entirely passive solutions.

Si

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Si, you are, of course, right about not controlling pure squat and dive. However, I wasn't looking to control squat and dive with my system as it would add extra complexity and I can use the suspension geometry to help control both of these. I also don't think it the system will encourage squat and dive as fluid well flow totally freely so where is the force? If I find squat and dive are a problem I could adapt my system later on to help with this. Although you do get squat and dive on Land Rovers (and similar vehicles) it has never struck me as never being a particularly big issue.

 

What I don't agree with you on is how the vehicle will behave in a cross slope or braking and cornering situation. I did my last post fairly quickly and didn't give much detail. Let me explain the system a little more.... On each corner there will be a primary ram mounted like a shock absorber. The installation ratio will be identical front and rear as the system will only work properly is it is balanced. The primary rams on each side will be connected together and connected to a pair of secondary rams (mounted outside the chassis rails). A torsion bar will be mounted below the fuel cell with a pair of arms running either side of the cell and will connected to one end of the secondary rams. The other end of the secondary rams will be mounted to the chassis. When I first thought about doing something like this I thought about a few ideas - I looked at conventional springs and some of the original ideas were very Heath Robinson. However, I settled on using a torsion bar fairly early on as it is much easier to package and mount. My current design (which may be tweaked before the car's done) is to use a coil over / coil carrier as the primary rams for a few reasons (well made, can take the pressure, hold springs, can run with light valving to help low speed handling). I will also run them with bypass shocks which will deal with most of the damping. Spring rates will be on the softer side of normal for the intended use. The idea is to run the car slightly softer to help traction (but not so soft that it will be undrivable if the system fails) but then gain a lot of extra stability over cars with a more conventional setup. 

 

So, the theory behind the system is that, with pure bump or drop travel, all the primary rams move in the same direction and the torsion bar rotates in its mounts (as a normal anti roll bar). In pure articulation the diagonal wheels move up and down by the same amount meaning there is no imbalance in the secondary rams (the torsion bar will rotate as I will have a higher rate in bump above ride height than droop below ride height) so no restriction to articulation. Now, in pure roll, the primary rams on one side compress and the rams on the other side extend leading meaning the secondary rams move in opposite directions and this is countered by the torsion bar. 

 

Now, let's take your braking and cornering scenario. When you start braking in a straight line the system will have no effect on the car - it will dive and only the springs and geometry will restrict this. As you turn in and part of the dive becomes roll the system will begin to take effect - as soon as there is an imbalance between the left and right hand sides the torsion bar will be twisted and there will resistance to roll. The more you turn the greater the degree of anti roll. The same would also be true with crossing a slope at 45 degrees. I was worried at first that the system may have been unstable at the limit when you have a lot of load on one wheel (the front outside wheel when braking and cornering and the down hill wheel in the slope crossing). I was initially worried that the opposite wheel, which would be unloaded, would prevent the system preventing roll. However, when I thought about it properly, I realised it wouldn't be an issue as the spring on the unloaded side would come into play. Yes, the car may possibly lift a wheel in these situations but that isn't a huge issue as it will only be on an unloaded wheel anyway.

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On each corner there will be a primary ram mounted like a shock absorber. The installation ratio will be identical front and rear as the system will only work properly is it is balanced. The primary rams on each side will be connected together and connected to a pair of secondary rams (mounted outside the chassis rails). A torsion bar will be mounted below the fuel cell with a pair of arms running either side of the cell and will connected to one end of the secondary rams. The other end of the secondary rams will be mounted to the chassis. When I first thought about doing something like this I thought about a few ideas - I looked at conventional springs and some of the original ideas were very Heath Robinson. However, I settled on using a torsion bar fairly early on as it is much easier to package and mount.

This is how we've had a car on hydraulics before (well not connected to others, just by themselves).

Hydraulic ram on each corner, then a hose to it's own ram in the rack. T piece off this hose to the hydraulic pump source.

Pic from google of the spring rack :

142624.jpg

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