Suitable Rubber mounts for Axle attachment to chassis

[morris9791]

Dear Experts,

What products are normally used for mounting the axle housings onto the chassis?
We use trelleborg anti vibration cab mounts.

What is the normal way of sizing these mounts? My method: An FEA analysis on the housing which contains the reaction bearing loads due to applied torques at the gears. A typical load case would be stall torque etc. From this, I can obtain the reaction loads at the axle mounts and use this as a basis for sizing the components.

What are ye guys opinion on this method? Is this an overly conservative approach?

Thanks
Ed

 

[morris9791]

Hi Guys,

I forgot to add:

Is just the total weight of the axle the normal way to size the mountings?

The load case I used was stall torque; however this is an instantaneous application that will happen rarely. So I feel this approach may be overkill since the reaction forces I get from model are way bigger that that of axle weight alone.

Any comments welcomed.

Thanks
Ed

 

[MikeHalloran]

It sounds underly conservative to me.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

What kind of vehicle are we talking about here.

In my (automotive/motorcycle) world, axles are never bolted directly to the chassis ... they're separated by suspension links, springs, dampers (shocks), etc.

 

[GregLocock]

FEA?

real men use free body diagrams.

I think you are talking about mounting the differential in an independent suspension to the chassis.

If so you can ignore the static mass of the diff, but suspect(that is i know damn well) that the shock loads in the driveline will be more than the stall torque of the converter.

Howver the rubber mount manufacturers are not idiots and usually spec their components to handle a bit of unintentional overload.

So I think yuor basic approach is OK, but you are relying on the manufacturer's credibility rather than being conservative as such.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[morris9791]

Brian, Greg, Mike.

It is a military vehicle and the axles are mounted to the chassis via rubber anti vibration mounts.

I choose FEA because I needed to do a stress analysis on the axle housings anyway. In addition, the problem is statically indeterminate to solve by hand.

So Greg, even though a shock load would only be instantaneous, it still should be considered?


Regards
Eddie

 

[MikeHalloran]

Uh-oh.


Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

Shock load should certainly be considered unless you want your axle to break off the first time the vehicle hits a bump.

P.S. this is one of the functions of "suspension".

 

[patprimmer]

Axles are rarely mounted directly to the chassis.

The question was already asked by Greg but not answered.
To offer useful information, we need useful input. If you choose to ignore valid questions, you won't get useful answers.

Regards
Pat
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[LionelHutz]

An any road condition military vehicle will likely see a lot of abuse shich will mean high levels of shock loads.

Besides accounting for large shock loads I would also make sure that you could destroy or pound apart this rubber bushing/mount without the axle falling off. I think you'd call this a captive bushing or captive bushing mount.

 

[morris9791]

Hi Guys,

First of all I want to apologise for my poor choice of words in describing the problem initially. I will rephrase for clarity:

The axle I was referring to is a housing which contains the pinion/crown wheel and cross diff which are connected to the half shafts. These shafts extend externally from the housing into the hubs which are mounted on independent suspension which is then mounted to the chassis.
I was not referring to rigid beam live axles etc.

Regards
Ed

 

[patprimmer]

So are you asking about the differential housing mounting or the suspension link mountings or pivot points.

Regards
Pat
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[morris9791]

Hi Pat,

I am asking about the differential housing mounting. This housing contains both a cross and interaxle diff and weighs about 180kg.
My FEA is reading 100kN at one of the mounts due to this high stall torque. My intuition is telling this is reasonable because bearing forces which have to be reacted by the mounts are high like 160kN.
I’m just wondering are these forces possible wrt axle mounts based on peoples experience.

I’m just 2 years in on this mechanical engineering job so I’m on a big learning curve Thanks for you patience and help.


Best regards
Ed

 

[patprimmer]

OK

In my opinion your worst case scenario will be a loss of traction at full throttle somewhere near maximum torque in low gear allowing the rpm to flare up to rev limit, then a sudden regain a lot of traction pulling the engine suddenly back to somewhere near maximum torque. You will be subject to the torque and the inertia of the drive line. If you have the polar moment and the speed change and time taken, you should be able to calculate the influence of the inertia.

Regards
Pat
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[rmw]

And, while Pat has adequately described a worst case scenario, every application of torque through the diff will cause it to want to react so you are looking at torque reaction forces each time power is applied, however that might be and in which ever direction that might be.

rmw

 

[morris9791]

rmw,

Yes, since I know what the gear forces are, I can apply the resulting bearing forces to the housing due to the transmission of this high torque via the gear train.

Cheers Ed