Vollintergriertes Kurzhauber Hilfsrahme mit luftfederung

[ChristianJS]

Hallo,

Ich weiß, dass dieses Thema schon tausend Mal diskutiert wurde. Das ist aber etwas anders. Ich hoffe, Sie kommen mit konstruktiver Kritik.
Wie einige von Ihnen wissen, wollte ich die Kabine und die Box integrieren. Ich habe Lösungen studiert und ich glaube, ich hätte meine Hausaufgaben gemacht!
Also versuche ich einen Hilfsrahmen zu entwerfen, der etwas ungewöhnlich ist:

Vorne befinden sich zwei schwere LORD-Kabinenhalterungen, die das Frontgewicht tragen und die Front sowohl vertikal als auch horizontal steuern.
Dadurch bleiben auch der Hilfsrahmen und das Fahrgestell vorne ausgerichtet, sodass die Bedienelemente (Gangschaltung, Gaspedal usw.) nicht durch Bewegungen beeinträchtigt werden.

Ca. Über der Hinterachse befindet sich ein Wattgestänge, das die Rückseite von Seite zu Seite steuert, aber Fahrwerksflex und vertikale Verschiebung ermöglicht.

Hinter der Hinterachse befindet sich auf jeder Seite ein Airbag. Diese tragen das Gewicht des Hilfsrahmens im Heck. Auf der Straße werden diese einzeln aufgeblasen und gesteuert. Im Gelände werden sie miteinander verbunden, damit Luft von einem zum anderen gelangen kann. Auf diese Weise kann sich das Chassis flexen.

Ich glaube, das sollte funktionieren und habe FEA auf dem Hilfsrahmen ausgeführt. Ein Bonus besteht darin, die Box von den Gehäusevibrationen zu isolieren.

Bitte schauen Sie es sich an und geben Sie mir alle Ihre positiven und negativen Gedanken, solange sie konstruktiv sind!

PS: Die gelben Schatten sind ein Interferenzblock, den ich verwendet habe, um sicherzustellen, dass ich nichts entworfen habe, das das Chassis beim Biegen stören würde

[Uwe]

Hallo Christian,

dass Deine Konstruktion keine Rücksicht auf die gängigen Aufbaurichtlinien der Hersteller nimmt, brauchen wir hier denke ich nicht diskutieren

Auf eine Anforderung dieser Richtlinien würde ich trotzdem gerne zurückkommen: punktförmige Lasteinleitungen in den Hauptrahmen sind dort nur in Ausnahmefällen gestattet. Du treibst dieses Thema bei einem relativ leichten Rahmen des Kurzhaubers ins Extrem, indem Du das komplette Aufbaugewicht an nur vier Punkten in den Hauptrahmen einleitest. Hier würde ich zumindest einen kleinen Hilfsrahmen druntersetzen.

Meine generelle Meinung: Kabinenrahmen von hinten bis vor die Hinterachse am Rahmen befestigen und dafür die Pedalerie entkoppeln (Bremsventil in die Kabine, hydraulische Kupplungsbetätigung, Gas per Bowdenzug.

Ansonsten: wenn der TÜV / Bilsyn nichts dagegen hat...

Gruß
Uwe

[ChristianJS]

Danke Uwe!

Meiner Deutch sind immer ein problem...

Verstehe Ich Dich recht, Du würden den Hilfsrahmen umkehren und die Luftbalgen in vorne setzen?

Ich weiß, ich werde die ganze Last auf vier Punkte legen. Aber ich benutze die gleichen Punkte wie das Original, ich benutze nur nicht die mittleren. ich könnte aber ...
Bei einer Registrierung von 7,5 Tonnen ist die Ladung jedoch erheblich geringer als beim Original.

Ich glaube, Bilsyn / Tuv wird kein Problem sein. Mein LKW ist der erste, der in Dänemark als m2 registriert ist. Es hängt alles davon ab, wie gut er gebaut ist.

[Uwe]

Hi Christian,

yes, would be nearer to manufacturer's regulations
Maybe a joint behind the bonnet (like on older integrated Magirus) and the Watt link behind the Gearbox.

Using the original mounting points maybe an option, but keep in mind that especially manufacturers of firetrucks do not care about durability

What do you plan to do with the truck?

Best
Uwe

[felix]

Hi,

you put the fixed brackets close to the front axle, therefore it should be stable on road. But in off-road it will behave as if you drive a tricycle reverse: when you drive one front wheel into a ditch the whole superstructure will follow that front wheel so the vehicle will tip into that direction.

When you put the fixed brackets close to the rear axle it behaves like a tricycle forward: the superstructure will follow the rear axle. This might be the better configuration, because engine and gearbox will follow front axle and rear axle suspension is more stiff so you get more stability.

MlG,
Felix

[hugepanic]

What about taking all that steel and reinforcing the original frame?

That might be critical for the existing load interface points due to higher loads, but also can make your life way easier regarding other topics....

[ChristianJS]

Hi Christian,

yes, would be nearer to manufacturer's regulations
Maybe a joint behind the bonnet (like on older integrated Magirus) and the Watt link behind the Gearbox.

Using the original mounting points maybe an option, but keep in mind that especially manufacturers of firetrucks do not care about durability

What do you plan to do with the truck?

Best
Uwe

Hi Uwe, Thanks for switching to English!

Moving the joint would make it even more complicated!

Think of my solution like a standard 3-point, but with the rear center point being "soft".
The Kurzhaubers have a relatively short wheelbase, and the distance between the point will be no greater than on a lot of truck using 3-points.
The advantage on mine is that the negative rolling effect you can get in turning with a center point in the rear, will be countered by he airbags.

If the Watts Linkage proves to be a problem, it can rather easily be converted to a standard 3-point with the airbags as sideways support.

And true about firetruck manufacturers... The rust - oh the rust!
But I will only use the location, newer, bigger and stronger brackets and mounts will be used.

It will be 90-95% on-road use. Maybe some gravel. So the vibration dampening effect might be a blessing!

Hi,

you put the fixed brackets close to the front axle, therefore it should be stable on road. But in off-road it will behave as if you drive a tricycle reverse: when you drive one front wheel into a ditch the whole superstructure will follow that front wheel so the vehicle will tip into that direction.

When you put the fixed brackets close to the rear axle it behaves like a tricycle forward: the superstructure will follow the rear axle. This might be the better configuration, because engine and gearbox will follow front axle and rear axle suspension is more stiff so you get more stability.

MlG,
Felix

Thanks Felix!

Yes, in the original positions. And you are correct, I really like your picture with the tricycle after I thought about it... But you end up hitting the same potholes, as you say. I don't know which end is the stiffest. it seems the twist in the frame kind of equalizes it.. But you are correct, the whole superstructure will follow the front axle.
But I think it would feel really weird if I reversed everything? And with 20 degrees of frame flex, I would have to completely redesign the front, steering, better clearance for the engine etc.

Some have removed the rear stabilizer on the Kurzhaubers, might be worth trying to counter the stiffer rear axle?

What about taking all that steel and reinforcing the original frame?

That might be critical for the existing load interface points due to higher loads, but also can make your life way easier regarding other topics....

Hi hugepanic, I'm not sure how you mean?

[hugepanic]

Hi hugepanic, I'm not sure how you mean?

You could take your large subframe and bolt it completely to the truck frame. The goal would be to reinforce the complete structure that you have so much stiffness that you can bolt your superstructure to the frame.
You could take the weight from all your bearings, links, airbags and stuff and simply invest in steel/stiffness.

If you "only" plan for gravel roads that might possible, if your TÜV-equivalent agrees to that.

[the_muck]

hehe... this was my idea.

viewtopic.php?p=811917#p811917

but... that is far away from keep it stupid simple

[ChristianJS]

Having thought a bit about it, I am using the original mounting points both front and rear, the airbags are mounted where the box is now, just behind the rear wheels.
So it could be argued that the guidelines are followed, it's just the subframe itself that's a bit unusual, right?

Hi hugepanic, I'm not sure how you mean?

You could take your large subframe and bolt it completely to the truck frame. The goal would be to reinforce the complete structure that you have so much stiffness that you can bolt your superstructure to the frame.
You could take the weight from all your bearings, links, airbags and stuff and simply invest in steel/stiffness.

If you "only" plan for gravel roads that might possible, if your TÜV-equivalent agrees to that.

It is no way near strong enough for that, the frame will twist it.
I have made an FEA (Finite Element Analysis) on it, and with 2.000kg payload it will twist 10mm in extreme conditions:

This exact one is a bit outdated...

hehe... this was my idea.

viewtopic.php?p=811917#p811917

but... that is far away from keep it stupid simple

If I read your diagram right, it's much alike, but yours is a bit more complicated.

[hugepanic]

My idea behind is reinforcing the main frame instead of adding more complications with a second frame.

There are many ways to achieve this.
-Reinforcing the main frame
-adding a secondary frame
-building your box load bearing
-...

To be honest, I don't have a clear understanding of what is the most efficient way to reinforce a frame to be torsional stiff. Converting to a closed box is a solution, but for sure not the solution way for truck frame.

If you do your own FEA, can you do a topology optimisation (e.g. using Optistruct)? If you build your model right, you can get ideas for reinforcement from that. This is what I would do to find ideas....

The simplest solution might be a torsion-box, bolted on top of the main frame. That box can later be used for all your systems, water, baggage...
Downside is that this box will lift your cabin significantly...

[ChristianJS]

My idea behind is reinforcing the main frame instead of adding more complications with a second frame.

There are many ways to achieve this.
-Reinforcing the main frame
-adding a secondary frame
-building your box load bearing
-...

To be honest, I don't have a clear understanding of what is the most efficient way to reinforce a frame to be torsional stiff. Converting to a closed box is a solution, but for sure not the solution way for truck frame.

If you do your own FEA, can you do a topology optimisation (e.g. using Optistruct)? If you build your model right, you can get ideas for reinforcement from that. This is what I would do to find ideas....

The simplest solution might be a torsion-box, bolted on top of the main frame. That box can later be used for all your systems, water, baggage...
Downside is that this box will lift your cabin significantly...

Reinforcing the existing frame is illegal here, and would mean the vehicle would never be MOT/TÜV/Bilsyn again.
I believe the best way to do what I plan, is flexible subframe, the only issue is wether or not what I have drawn will actually work as intended.

A great plus is the vibration dampening. it should make the truck much more comfortable and keep things from rattling apart.

I have tried some optimisation, Fusion360 have that option, but the results does not work with the standard box sections etc I plan on using.