hey
i know thats a big claim but while i was at work this thaught came to me and i knowcked up a rough (by my standards) sketch of it.
http://www.deviantart.com/view/10151681/
during high speed work the airbag in deflated and the subframe rests on bump stops on the chasis using the inderpendent wishbones to soften the ride then when you need articulation the bag is inflated and you get the extra flex of the bag and hight for the flexing not to rub
if you have any questions or are interisted in making or further developing this idear just give us a shout or a post.
Matt
Notice: We request that you don't just set up a new account at this time if you are a previous user.
If you used to be one of our moderators, please feel free to reach out to Chris via the facebook Outerlimits4x4 group and he will get you set back up with access should he need you.
If you used to be one of our moderators, please feel free to reach out to Chris via the facebook Outerlimits4x4 group and he will get you set back up with access should he need you.
Recovery:If you cannot access your old email address and don't remember your password, please click here to log a change of email address so you can do a password reset.
winch chalenge suspention (outback chalenge)
Moderators: toaddog, TWISTY, V8Patrol, Moderators
Hoonz wrote:resting on the bump stops for high speed work?!
what happens when u hit a bit bump/rut?
the centre diff sits on the bumpstops at high speed and just uses the outer wishbones to provide suspension travel, like a normal ifs setup.
then the bag is inflated a little bit to allow the centre diff to 'rotate' like a live axle setup. but like MY45 said, the 4 link setup in that render wouldn't locate the diff centre side to side, and also wouldn't allow much rotational movement without serious binding
it looks like it could work, with attention paid to the centre diff's link arrangement. but i think it'd be hard to package in a normal car as opposed to a custom tube frame.
Camshaft1 wrote:at least your having a go with the thinking ideas scenario, but IFS?..... big letdown.
Hummer's, BAJA Racers, ATV quad bikes... all use IFS/IRS and manage to go flat out accross the desert without too much problem.
Sure if your chasing simple and serious articulation beam axles are the go... but a custom independant job like that could acheive similar wheel travel figures if setup correctly.
Cheers,
Dan.
[i]1996 HDJ80R[/i]
Dan.
[i]1996 HDJ80R[/i]
I have seen pictures of a similiar idea set up before on the rear of a Minitruck in the U.S. Instead of using Airbags as the main suspension to raise and lower, it ran coil over and 4 link on a solid axle. Effectively being a seperate unit from the chassis, it then used Airbags to raise and lower the vehicle from this "suspension unit", but pivoting from a point near the linkages. Athough in this case it was just done more to show off engineering skills, to be different and probably wank factor. But it is a similiar idea to what you have shown here.
Matt,
Sorry if this all sounds negative but here are some thoughts about your idea. I am pretty much just thinking out load to stimulate some discussion.
This setup will have very high unsprung weight, as it will be heavier than both independent and live axle designs, (possibly added together) I think that this very high unsprung weight will lead to dodgy handling when the bag is inflated, even at very low speeds.
The airbag would need to be locked out for travel at speed, as it would want to slap around at speed. heavy solenoids might be possible. If if just rested on the bumpstops, hitting bumps would bounce the chassis away from the subframe as a vacuum was pulled in the bag and lead to a very bouncy ride.
I think another issue is that the central airbag design will have effectively no roll stiffness, so when it is inflated the car will just flop around and the independent system will not travel at all as the roll stiffness of the bag will be many times less than the stiffness of the independent system, unless antisway bars or articulation equalisation etcetc was built in, further adding to the weight/complexity.
The loads being applied to an IFS/IRS system are very high and they are countered by feeding the loads into several points on the chassis. If the subframe was to be supported by only a 3/4 link, the subframe, links and mounting system would need to be VERY strong (read-heavy) in order to handle the punishment.
I suspect that this design might add as much as 250kg per axle in weight over a traditional 4 link/live axle arrangement so any gain would be offset by a substantial increase in weight, not to mention engineering complexity.
IFS systems, in order to work well in high speed situations generally are designed with quite high travel, and VERY precise springing/damping/bumpstop control. Many of these designs will work quite well for low speed work too, their biggest disadvantage being reduced ground clearance under the diff as the suspension cycles, and the shrinking and growing of track width as they cycle.
Live axles can be made to work very well for high speed work too, but generally with much high spring rates then would be used for "recreational" driving in australia
This is where it gets interesting - looking at the design and performance of competition rock buggies in the US evolve over the last couple of years, it seems that some trends are occuring:
travel is being limited. many of these cars now have far less travel than they used to. - generally many of these cars do not run over about 14" at the wheel - well within the range of IFS.
spring rates and especially damper rates are increasing, these cars are pretty stiff now.
They are getting ridiculously light.
What is interesting is that these cars now appear to be pretty handy at speed. they are quite similar in suspension/chassis design to an offroad race car.
There have been a few experiments with IFS rock buggies, but I think that all of these experiments have now been scrapped and live axles rule. however, in "open" desert racing (trohpy truck etc) many of thess car use IFS, but are often 2WD. generally, the 4WD trucks are not competitive due to excessive weight and limited travel compared to the 20-30" travel of the 2WD ifs designs.
I don't think your rendering shows how the Independent system is sprung - is it sprung off the subframe or the chassis? I'm guessing the subframe.
(PS Petersens 4wheel and Offroad ran a suspension design competition a couple of years ago, and an idea similar to yours was entered in that)
PPS - I don't think there is an engineer or competition rule set in australia that would permit this design
Sorry if this all sounds negative but here are some thoughts about your idea. I am pretty much just thinking out load to stimulate some discussion.
This setup will have very high unsprung weight, as it will be heavier than both independent and live axle designs, (possibly added together) I think that this very high unsprung weight will lead to dodgy handling when the bag is inflated, even at very low speeds.
The airbag would need to be locked out for travel at speed, as it would want to slap around at speed. heavy solenoids might be possible. If if just rested on the bumpstops, hitting bumps would bounce the chassis away from the subframe as a vacuum was pulled in the bag and lead to a very bouncy ride.
I think another issue is that the central airbag design will have effectively no roll stiffness, so when it is inflated the car will just flop around and the independent system will not travel at all as the roll stiffness of the bag will be many times less than the stiffness of the independent system, unless antisway bars or articulation equalisation etcetc was built in, further adding to the weight/complexity.
The loads being applied to an IFS/IRS system are very high and they are countered by feeding the loads into several points on the chassis. If the subframe was to be supported by only a 3/4 link, the subframe, links and mounting system would need to be VERY strong (read-heavy) in order to handle the punishment.
I suspect that this design might add as much as 250kg per axle in weight over a traditional 4 link/live axle arrangement so any gain would be offset by a substantial increase in weight, not to mention engineering complexity.
IFS systems, in order to work well in high speed situations generally are designed with quite high travel, and VERY precise springing/damping/bumpstop control. Many of these designs will work quite well for low speed work too, their biggest disadvantage being reduced ground clearance under the diff as the suspension cycles, and the shrinking and growing of track width as they cycle.
Live axles can be made to work very well for high speed work too, but generally with much high spring rates then would be used for "recreational" driving in australia
This is where it gets interesting - looking at the design and performance of competition rock buggies in the US evolve over the last couple of years, it seems that some trends are occuring:
travel is being limited. many of these cars now have far less travel than they used to. - generally many of these cars do not run over about 14" at the wheel - well within the range of IFS.
spring rates and especially damper rates are increasing, these cars are pretty stiff now.
They are getting ridiculously light.
What is interesting is that these cars now appear to be pretty handy at speed. they are quite similar in suspension/chassis design to an offroad race car.
There have been a few experiments with IFS rock buggies, but I think that all of these experiments have now been scrapped and live axles rule. however, in "open" desert racing (trohpy truck etc) many of thess car use IFS, but are often 2WD. generally, the 4WD trucks are not competitive due to excessive weight and limited travel compared to the 20-30" travel of the 2WD ifs designs.
I don't think your rendering shows how the Independent system is sprung - is it sprung off the subframe or the chassis? I'm guessing the subframe.
(PS Petersens 4wheel and Offroad ran a suspension design competition a couple of years ago, and an idea similar to yours was entered in that)
PPS - I don't think there is an engineer or competition rule set in australia that would permit this design
[quote="greg"] some say he is a man without happy dreams, or that he sees silver linings on clouds and wonders why they are not platinum... all we know, is he's called the stevie.[/quote]
Twinnie,
I have given this a bit more thought, and have dreamed up a variation on your plan that might be more realistic.
Instead of a four link, how about pivoting the subframe to allow articulation only rather than any vertical travel? The pivot could more or less be around the input shaft of the diff so no changes in driveshaft angle would be experienced.
Two small hydraulic rams would be used to create "passive" i.e non powered hydraulic forced articulation, as one subframe articulates the other could be forced to articulate in the opposite direction, while for high speed work, the hoses could be blocked with a simple valve and the articulation locked out for high speed stability. The front subframe could be sprung with short hot rod type coilovers to allow some roll stiffness once unlocked, with the rear forced equally to the front, a very balanced feel would result.
This idea doesn't permit the increase in clearance you were planning, but I'm not sure that is such an issue - with high pinion diff centres, and hummer portal boxes, very high clearance at the chassis and diff could be achieved.
I think this idea gets around the weight increase and drivability issues of your first design.
I have given this a bit more thought, and have dreamed up a variation on your plan that might be more realistic.
Instead of a four link, how about pivoting the subframe to allow articulation only rather than any vertical travel? The pivot could more or less be around the input shaft of the diff so no changes in driveshaft angle would be experienced.
Two small hydraulic rams would be used to create "passive" i.e non powered hydraulic forced articulation, as one subframe articulates the other could be forced to articulate in the opposite direction, while for high speed work, the hoses could be blocked with a simple valve and the articulation locked out for high speed stability. The front subframe could be sprung with short hot rod type coilovers to allow some roll stiffness once unlocked, with the rear forced equally to the front, a very balanced feel would result.
This idea doesn't permit the increase in clearance you were planning, but I'm not sure that is such an issue - with high pinion diff centres, and hummer portal boxes, very high clearance at the chassis and diff could be achieved.
I think this idea gets around the weight increase and drivability issues of your first design.
[quote="greg"] some say he is a man without happy dreams, or that he sees silver linings on clouds and wonders why they are not platinum... all we know, is he's called the stevie.[/quote]
sounds good , i'll have a think about it and do a sketch. but that'll be later in the week i'm of to the coast for a bit. i know it sounds weird but if you put the portal boxes inboard the drive shaft angles would not be so great.
if the IS arms are bent and the portal boxes placed conected to the diff then i think a greater clearence could be achived.
if any one has seen the coot aatv then you will know that there lies another solution IS and a pivot in the center of the vehical. this would alow the central pivot to be locked out for high speed.
this alowes a rear tray and even a style side tray, and is a convertion that wouls be hard but posible to do to curent utes it would alow an rti only limited by lenth to with ratio. and high speed stability that would rival a slid state chasis
Matt
if the IS arms are bent and the portal boxes placed conected to the diff then i think a greater clearence could be achived.
if any one has seen the coot aatv then you will know that there lies another solution IS and a pivot in the center of the vehical. this would alow the central pivot to be locked out for high speed.
this alowes a rear tray and even a style side tray, and is a convertion that wouls be hard but posible to do to curent utes it would alow an rti only limited by lenth to with ratio. and high speed stability that would rival a slid state chasis
Matt
I am not a big fan of the centre twisting chassis idea.
About 8 or 9 years ago, a couple of guys in the US built a Chev with a centre pivot chassis. They took it too sierra trek and claimed all sorts of outrageous things for it ( including kits and serious production) but nothing came of it and it looked pretty rough to me.
Last year at TTC (US FourWheeler) there was an old M37 with a centre pivot. I think that this set up might have been hydraulically controlled.
There are a couple of problems with a centre pivot, (apart for massive issues with strength and packaging) Unless it is "forced" via hydraulics or air, it will have almost no roll stiffness, and as a result, the vehicles conventional suspension completely ceases to work while the pivot is unlocked.
as a result, the car will not load compressed wheels properly, and will in fact load them less the more the car articulates, which is A) the opposite of what a "normal" suspension does and B) the opposite of what you want for traction
In the applications I have seen it used, it is usually applied to allow "massive" articulation, which leads to some very awkward drivability problems, as COG still applies, but separately (for lateral COG) to each 1/2. Lets say that the roll over angle for the back 1/2 is 40deg. while the the roll over angle the for the front 1/2 is 50deg. So you are on a 30 degree side angle and cross a rut diagonally or somesuch which pitches the rear 1/2 beyond 40 degrees. the rear 1/2 will now fall over to the extent of the pivot travel (say 40degrees) The front is still stable, but the rear end has now rolled to 80degrees to horizonatal and hit the end of the pivots travel with enough force to roll the car.
If articulation equalisation was fitted, the above example would still occurr. something similar to this happened to the M37 at TTC on a section of track that other vehicles successfully negotiated.
Of course it could be locked out at any time, but I think on a two axled vehicle with decent suspension, it would be better off not engaged at all.
I feel that my design of pivoting IS subframes with articulation equalisation will give the stability of a good stiffly sprung live axle car in difficult terrain and the possible benefits (?)of independent suspension at speed.
I am not sure that the advantage would be of having a drop box at the diff end of the A arm. Set up this way, the drop will be ocurring at the diff where it is likely to encounter obstacles, whereas the point of a portal is to put the drop inside the wheel so the half shaft is above the centre line of the wheel and less likely to encounter damage. Also, the torque multiplication is done at the wheel so the half shafts can be smaller and can take more angle. I agree though that the lower A arms of say a hummer design could be canted to allow more clearance close to the wheel.
Spend some time lying under a hummer, their suspension/dirveline design is quite elegant, moreso than it initially looks.
PS the GAMMA GOAT used an articulated pivot with a drive through with IFS, but is three axle with the power unit ( the front 1/2 having two axles, so the rear 1/2 is pretty much a powered, steering trailer.
Just an observataion, take it as you will, but it seems to me that you are still assuming that very low roll stiffness and very high travel make a better "winch challenge" type of suspension and high roll stiffness and lower travel make a better OBC type of suspension. I am sure that if you asked competitors, they would argue that a similar set up works well for both events. ( they are designed for similar competiitors, and are or were organsied by many of the same faces) Bear in mind that winch challenge is a speed event too.
Perhaps an open trials type of event such as QROCK or similar might be a better example of what you are trying to describe.
In any case, many high travel suspensions actually impede a cars capability even at low speed due to low roll stiffness, poor gemoetry, poor spring and damper control and a thousand other factors generally forgotten when fabricators chase travel.
Steve.
About 8 or 9 years ago, a couple of guys in the US built a Chev with a centre pivot chassis. They took it too sierra trek and claimed all sorts of outrageous things for it ( including kits and serious production) but nothing came of it and it looked pretty rough to me.
Last year at TTC (US FourWheeler) there was an old M37 with a centre pivot. I think that this set up might have been hydraulically controlled.
There are a couple of problems with a centre pivot, (apart for massive issues with strength and packaging) Unless it is "forced" via hydraulics or air, it will have almost no roll stiffness, and as a result, the vehicles conventional suspension completely ceases to work while the pivot is unlocked.
as a result, the car will not load compressed wheels properly, and will in fact load them less the more the car articulates, which is A) the opposite of what a "normal" suspension does and B) the opposite of what you want for traction
In the applications I have seen it used, it is usually applied to allow "massive" articulation, which leads to some very awkward drivability problems, as COG still applies, but separately (for lateral COG) to each 1/2. Lets say that the roll over angle for the back 1/2 is 40deg. while the the roll over angle the for the front 1/2 is 50deg. So you are on a 30 degree side angle and cross a rut diagonally or somesuch which pitches the rear 1/2 beyond 40 degrees. the rear 1/2 will now fall over to the extent of the pivot travel (say 40degrees) The front is still stable, but the rear end has now rolled to 80degrees to horizonatal and hit the end of the pivots travel with enough force to roll the car.
If articulation equalisation was fitted, the above example would still occurr. something similar to this happened to the M37 at TTC on a section of track that other vehicles successfully negotiated.
Of course it could be locked out at any time, but I think on a two axled vehicle with decent suspension, it would be better off not engaged at all.
I feel that my design of pivoting IS subframes with articulation equalisation will give the stability of a good stiffly sprung live axle car in difficult terrain and the possible benefits (?)of independent suspension at speed.
I am not sure that the advantage would be of having a drop box at the diff end of the A arm. Set up this way, the drop will be ocurring at the diff where it is likely to encounter obstacles, whereas the point of a portal is to put the drop inside the wheel so the half shaft is above the centre line of the wheel and less likely to encounter damage. Also, the torque multiplication is done at the wheel so the half shafts can be smaller and can take more angle. I agree though that the lower A arms of say a hummer design could be canted to allow more clearance close to the wheel.
Spend some time lying under a hummer, their suspension/dirveline design is quite elegant, moreso than it initially looks.
PS the GAMMA GOAT used an articulated pivot with a drive through with IFS, but is three axle with the power unit ( the front 1/2 having two axles, so the rear 1/2 is pretty much a powered, steering trailer.
Just an observataion, take it as you will, but it seems to me that you are still assuming that very low roll stiffness and very high travel make a better "winch challenge" type of suspension and high roll stiffness and lower travel make a better OBC type of suspension. I am sure that if you asked competitors, they would argue that a similar set up works well for both events. ( they are designed for similar competiitors, and are or were organsied by many of the same faces) Bear in mind that winch challenge is a speed event too.
Perhaps an open trials type of event such as QROCK or similar might be a better example of what you are trying to describe.
In any case, many high travel suspensions actually impede a cars capability even at low speed due to low roll stiffness, poor gemoetry, poor spring and damper control and a thousand other factors generally forgotten when fabricators chase travel.
Steve.
[quote="greg"] some say he is a man without happy dreams, or that he sees silver linings on clouds and wonders why they are not platinum... all we know, is he's called the stevie.[/quote]
g'day
what i'm realy chasing is a variable suspention that can be atapted at the flick of a switch to adapt to the needs of both high speed stability and low speed stablilty. low cog is a must i agree the center pivot would have lots of strength issues, so i'll scrap that. but after all this thinking i think the new range rover has it right. cross linked air suspention, prehaps a coil and hydrolic set up might work too, this gives you the diff clearance a of IFS and some of the articlulation of a beam axel. there is no point trying to use it for rock crawling because the routes are getting beond the limits of tyre adheasion, therefore keeping the tyres on the rocks isn't going to help only Momentum.
Matt
what i'm realy chasing is a variable suspention that can be atapted at the flick of a switch to adapt to the needs of both high speed stability and low speed stablilty. low cog is a must i agree the center pivot would have lots of strength issues, so i'll scrap that. but after all this thinking i think the new range rover has it right. cross linked air suspention, prehaps a coil and hydrolic set up might work too, this gives you the diff clearance a of IFS and some of the articlulation of a beam axel. there is no point trying to use it for rock crawling because the routes are getting beond the limits of tyre adheasion, therefore keeping the tyres on the rocks isn't going to help only Momentum.
Matt
if you want something that articulates and and can absorb everything why not go king coil over race shocks..
I was down at rangie automotive and saw them fitted to Adrain Cauchi race ute (rangie ute KURMIT)... photos in 4wd monthly ... but coils have just been fitted so he will be competitng with it in the new year...
these are fully kickarse they come through th tray and the remote resevior is massive.
He needs this setup as he needs the travel and articulation and he needs to make sure his shocks wont fail i.e. high speed winch stages..
He used to run OME LTR's but he reckons these shit on everything ............
I was down at rangie automotive and saw them fitted to Adrain Cauchi race ute (rangie ute KURMIT)... photos in 4wd monthly ... but coils have just been fitted so he will be competitng with it in the new year...
these are fully kickarse they come through th tray and the remote resevior is massive.
He needs this setup as he needs the travel and articulation and he needs to make sure his shocks wont fail i.e. high speed winch stages..
He used to run OME LTR's but he reckons these shit on everything ............
---------------------------------------------
04 GU TD6 wagon with some ARB stuff
---------------------------------------------
Morkz Media Web and Graphic Design
Also webhosting and domain registration.
04 GU TD6 wagon with some ARB stuff
---------------------------------------------
Morkz Media Web and Graphic Design
Also webhosting and domain registration.
Who is online
Users browsing this forum: No registered users and 1 guest