[srini1785]

Originally Posted by Kosfactor

I have not seen air suspensions of cars up close, but the big buses use only the rubber bellows and a normal suspension damper especially in the rear, usually called as 'Air Bus'.

As i said, I'm not a suspension expert. All air suspensions still use a hydraulic or a mechanical spring to maintain the structural integrity. Its not possible to just float a 20-30 ton bus on just air springs. These bellows are basically made of rubber and due to the uneven weight distribution in vehicles, they front and rear bellows would be distorted differently. I pulled these images from the net for air bus suspension and as you can see they all have either a leaf spring or a hydraulic (closed loop) shocks for attaching to the chassis. These springs/shocks take the main load while the air spring only damps the vibrations.

Such air bellows are also used in military vehicles for Radar vibration damping too. Normal suspension would damage the radar so while the vehicle in moving the bellows are inflated and when vehicle is stationary and when the radar is working, these bellows are deflated. Even in these vehicles the bellow only inflates a guided platform on which the radars are placed. I've also attached the data sheet of Parker bellows. From page 7 you can see the limits of radial and axial mismatch depending on how many bulges there are in the bellows.

If the vehicle is only attached to air bellows, a simple dynamic braking would make the bellow go beyond its maximum misalignment limits.






Air Bellows.pdf

[Kosfactor]

^ They are just the usual suspension dampers , they cannot carry any weight. The links are usual 3 link or 4 link set up with Anti toll bars, which is adequate for that task to keep the suspension located within the requirements for the bellows to function.

After riding in Volvo 8400 for many years , when I got into a normal high floor bus elsewhere I felt the springiness , continuous movement in those buses especially when nearly empty, they had leaf springs of course.

So clearly air suspension has a superior ride but why in cars do they have both metal springs and air ride? Does it have something to do with high speed handling ?

[Motard_Blr]

My understanding of air suspension is that its main purpose is to behave like an adjustable rate spring so that the ride height is maintained at a set level irrespective of the load.

So when there are more passengers, the vehicle height reduces due to the additional weight. This is sensed by the controller and commands the air valve to add air to increase the pressure in the suspension to increase ride height.

When there are fewer passengers, the load reduces and increases the ride height beyond the set limit. Then controller then open the air valve to exhaust air and reduce the pressure. The vehicle then lowers the ride height.

Mechanical springs generally aren't adjustable for preload (in cars, buses etc.). So they are sized to maybe 70% to 90% of max payload. This means that at part load, the springs are too stiff for a good ride. Like all things in engineering, everything is a compromise between different requirements, each pulling in different directions.

In the case of Jeroen's Jaguar, I think (I'm not sure) the air suspension may be acting as a supplement to the mechanical suspension to control ride height. The adaptive dampers complement this by adjusting for a perfect ride in all conditions. Jaguars are known to favour great ride quality over hard sports car suspension.

Motorcycles have had preload adjustable suspension for a long time. But they aren't meant to be frequently adjusted - it's impractical to change preload every time a passenger gets on or off the bike. But BMW now has optional electronically adjustable suspension on their big bikes.

https://www.bmw-motorrad.co.uk/en/en...sa-esatwo.html

Incidentally, some bikes (motorcycles and bicycles) come with air suspension.

BMW HP2
https://www.press.bmwgroup.com/globa...sion-system-04

Aftermarket
https://www.arnottcycles.com/

Bicycle
https://airbike.uk/collections/mtb-f...ack-gold-120mm

[Jeroen]

Originally Posted by Motard_Blr

My understanding of air suspension is that its main purpose is to behave like an adjustable rate spring so that the ride height is maintained at a set level irrespective of the load.
]

On premium cars where you will have these air suspension systems, the main purpose is to provide a more comfortable ride. The fact that is able to maintain a certain ride hide, or adjust it based on speed, is more about performance and comfort too.

Jeroen

[Motard_Blr]

Originally Posted by Jeroen

On premium cars where you will have these air suspension systems, the main purpose is to provide a more comfortable ride. The fact that is able to maintain a certain ride hide, or adjust it based on speed, is more about performance and comfort too.

Jeroen

I agree. Comfort is greatly affected by the spring stiffness, although damping also a major role. Generally a softer spring provides more comfort but it also allows the suspension to sag more, which affects handling.

[Akshay1234]

Great thread, and a very interesting topic. I am a fan of air suspensions for the comfort and refinement they offer, and in spite of the probably of failure at some point, I wouldn't think twice about buying a vehicle with air suspension.

I think though this may be more Jaguar focused in some aspects. The air suspension systems in the BMWs, Mercs, Audis etc don't have any mechanical spring inside. They are just the damper with an air spring fitted on top. Of course the rest of the system is pretty much similar.

By and large they have become a lot more robust and reliable, than what they were even 15 years ago. Few Mercs like the W164 and W220 and even some W221s gave air suspensions a bad name here. In the newer ones the failure rate is a lot less, and will almost never leave one stranded with the vehicle dropped low.

The only suspensions which I feel are even better than air suspension, are the hydraulic set ups, what Mercedes called ABC, and later on Magic Body control, and Audi launched something similar with the A8 a few years ago (as an option), and even the new Panamera revealed yesterday has this.

[Turbanator]

There’s also Hydraulic suspension that we find on Toyota Land Cruisers/ LX. Pretty reliable, just an oil change at 100K mark.

Also, some of the newer cars like i7 have independent 4 wheel suspension that appears to be controlled by air and electricity(electronic dampers?). Though all articles talk about the same being Air suspension, it’s definitely different than before as the time it takes to rise up is fraction of what it used to be earlier.

[Akshay1234]

Originally Posted by Turbanator

There’s also Hydraulic suspension that we find on Toyota Land Cruisers/ LX. Pretty reliable, just an oil change at 100K mark.

Also, some of the newer cars like i7 have independent 4 wheel suspension that appears to be controlled by air and electricity(electronic dampers?). Though all articles talk about the same being Air suspension, it’s definitely different than before as the time it takes to rise up is fraction of what it used to be earlier.

Those are air suspensions too. Some other cars like Porsche, Land Rover etc use a larger resevoir with the systems running at a higher pressure. Its pretty much a closed loop system, with the compressor just being an aid. Hence the raise and drop is a lot faster. The open loop systems like what Merc uses take much longer to raise and lower.

[Jeroen]

Originally Posted by Turbanator

There’s also Hydraulic suspension that we find on Toyota Land Cruisers/ LX. Pretty reliable, just an oil change at the 100K mark.

You know what they say:

They say if you want to go into the outback, take a Land Rover - if you want to get back, take a Landcruiser

Having said these days Landcruisers pack a lot of very complicated systems too. Likely still far superior to Landrover of course.

I am not sure if this is the latest, but I came across this Toyota Land Cruiser suspension article.

https://mag.toyota.co.uk/how-does-ki...n-system-work/

Originally Posted by Turbanator

Also, some of the newer cars like i7 have independent 4 wheel suspension that appears to be controlled by air and electricity(electronic dampers?). Though all articles talk about the same being Air suspension, it’s definitely different than before as the time it takes to rise up is fraction of what it used to be earlier.

Could be, all the electronic dampers I am familiar with, work on the same principle. The dampening characters are electronically controlled. Either by metallic fillings that when in a magnetic field alter viscosity in the damper and or throttling the restriction in the damper through which the fluid needs to pass.

On the Jaguar X350 series the air and electronic damper work together. However as far I can tell the air suspension is basically a more sophisticated version of the springs, or adjusts the springs to be felt more comfortable.

One interesting thing I did not mention. According to Raymond on the X350, the dampers do affect vehicle height a little bit. On most suspension systems it will be the springs (and bellows of course, when fitted) that determine the vehicle height.

I have fitted dampers that had to be tensioned somewhat in order to be installed, so it's likely they have some effect. But I always presumed it was marginal at best. But apparently, not always. Live and learn as they say.

Jeroen

[podher]

Hi, friends. I need some help. My BMW X5 30D MSport is giving a suspension problem. The rear suspension has sunk and giving a rough ride. Is it because of a software problem (this is an air suspension car) or is it a hardware problem? Would appreciate your guidance. Furthermore, do you know of any reliable garage in Pune that would repair this problem. The official BMW service centre says repair is not possible. The whole unit will have to be replaced. However some friends informed me that some private garages do repair these vehicles.

[adasisthefuture]

Originally Posted by Jeroen

The fact that is able to maintain a certain ride hide, or adjust it based on speed, is more about performance and comfort too.

Jeroen

I have ordered 245/35R21 wheels for my soon to be delivered Volvo S90. The stock wheels are 245/45R18.

I have ordered this upgrade as with stock wheels, the Ground Clearance is 152mm however, with 245/35R21 (biggest size approved by Volvo), the GC would increase to 165mm. This is desirable because many S90 owners in cities like Ahmedabad and Bangalore have reported belly scraping even in the cities. Link to the calculator relied upon by me to arrive at the GC is given below for your kind reference:

https://net-comber.com/tirecalc.html

My question is as under :

The car comes with rear Air Suspension. Would the car's electronics bring the GC increased to 165mm (due to installation of 21inch wheels) down again to 152mm when the Air Suspension is switched on (there is an option to switch Air Suspension on or off in the car) ?

If that is the case then upgrading the Wheels would not make any sense. Please advise.

Thank you.

[Jeroen]

Originally Posted by adasisthefuture

The car comes with rear Air Suspension. Would the car's electronics bring the GC increased to 165mm (due to installation of 21inch wheels) down again to 152mm when the Air Suspension is switched on (there is an option to switch Air Suspension on or off in the car) ?

No, it won’t I would think. You air suspension has no clue what wheels you fitted. It does not measure ground clearance. There are usually a couple of sensors that look at the position of the suspension relative to the chassis. Usually a pretty simple electromechanical device that measure change in angle.

However, on modern cars sometimes there are parameters that can be set. Either by the owner/driver or authorised dealer. There might be something about different wheel sizes. It is likely to correct the speedo accordingly. Not sure what it would do with ride height..

Jeroen

[adasisthefuture]

Originally Posted by Jeroen

However, on modern cars sometimes there are parameters that can be set. Either by the owner/driver or authorised dealer. There might be something about different wheel sizes. It is likely to correct the speedo accordingly. Not sure what it would do with ride height..

Jeroen

Thank you for a prompt response. The dealer informed me that the system will have to be updated which I suppose would be with regard to the correction of speedometer. However, he has no clue about the ride height.

The dealership tells me that the Rear Air Suspension in the S90 keeps the ride height at 152mm when the car is loaded with four Passengers which would mean that with Passengers seated at the back, the Suspension would compress however the same would be taken care of by the Air Suspension.

Is there a way to measure the GC without employing complex tools?

What would be the effect if Air Suspension is switched off ?

Please advise.

Thank you in advance.

[Jeroen]

Originally Posted by adasisthefuture

Thank you for a prompt response. The dealer informed me that the system will have to be updated which I suppose would be with regard to the correction of speedometer. However, he has no clue about the ride height.

The dealership tells me that the Rear Air Suspension in the S90 keeps the ride height at 152mm when the car is loaded with four Passengers which would mean that with Passengers seated at the back, the Suspension would compress however the same would be taken care of by the Air Suspension.

Is there a way to measure the GC without employing complex tools?

What would be the effect if Air Suspension is switched off ?
.

The system can only keep the ride height at 152mm for a given wheel circumference.

If it does adjust for the circumference, it also means you ride will become a little bit harsher. Because in order for it to maintain that 152mm it needs to adjust the suspension upwards. Which means it has a bit less height to compress. I am not sure if that is an issue, probably not.

I am not familiar with the Volvo system, but usually switching off the air suspension means the car starts to ride lower eventually as air leaks out of the bellows. Also, it will be a noticeable harsher ride.

Jeroen

[adasisthefuture]

Originally Posted by Jeroen

. Because in order for it to maintain that 152mm it needs to adjust the suspension upwards. Which means it has a bit less height to compress.

Jeroen

With upgrade of Alloys to 21 inches, GC increases by 13mm i.e from 152 mm to 165 mm. In such a scenario, the suspension has to compress more, not less in my limited understanding as the GC is more than 152mm (165 mm to be precise) with 21 inch alloys and the system has to adjust the suspension downwards, not upwards if I have understood it correctly.

Thank you once again.