Basic proving ground for not suspended vehicle

[pietro82]

Hi all,

for our customer we need to develop a basic and cheap proving ground to test its vehicles. Their are a not suspended with a top speed of 40km/h. The proving ground would not be used for durability purposes just for reliability ones. Our idea was to use a composition of speed bumps, humps. Do you think it will be a good idea? Any suggestion is appreciated.

Thanks

 

[IRstuff]

There are commercial facilities already configured for this:

http://natc-ht.com/Test_Course_Descriptions.htm

Somewhere on their site used to be descriptions of the various test, but you can probably get them directly from NATC

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[IRstuff]

here's a link to a description of the Aberdeen Proving Ground test facility:

http://quicksearch.dla.mil/basic_profile.cfm?ident_number=278849&method=basic

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[MikeHalloran]

My first thought was to just buy a defunct kart track.
... but they're usually pretty smooth.

Who gets to drive a nonsuspended vehicle over a bumpy track for however long it takes to assess its reliability? That has to get old pretty fast.



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

I don't understand the difference you make between reliability and durability. What aspects of the car are you testing?

At least one company I have worked at just used pave, aka Belgian Block, but we were primarily interested in the durability of the sprung body, especially welds.

You have to be careful that the loads you are applying are somewhat related to the real world application, for eample if the real world doesn't include driving over speed humps at 40 kph then the failures you get from doing so on the track may not be representative.



Cheers

Greg Locock


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[pietro82]

Hi all,

thanks for your reply.

our clients already have a kind of track with harsh bumps placed in a circle and they make the tractor travelling on in whithout the driver. Our idea was to use the same system but with smoother bumps.

Our customer doesn't want to reproduce the vehicle life, but just checking small failures in the early time of its life.

@Greg: you're rigth, but that vehicle is driven on-road and off-road and especially in winter it's not possible to test the vehicle due to the mud. So he needs something different.

 

[GregLocock]

OK, what you need to do is log a real vehicle for pseudo damage loads in real life and then correlate that to your PG.

That is not a trivial exercise.

Cheers

Greg Locock


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[pietro82]

Hi Greg,

Oh thanks, I got it, I have already done something similar. Do you know any wave humps?

 

[IRstuff]

The document I cited describes a variety of washboard road surfaces.

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[sbozy25]

Just run the Perryman 3 profile. If it doesn't break there, I doubt it will break elsewhere!

Definition of irony: A Ford Focus driver with ADD...

 

[IRstuff]

"Our customer doesn't want to reproduce the vehicle life, but just checking small failures in the early time of its life. "

That's basically Environmental Stress Screening (ESS), so it typically needs to be more stressful than normal operation

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[pietro82]

Hi IRstuff,

you got it! I didn't know that was the right translation.
Yes in the document you cited before there are the surface description but for our customer it's probably too expensive. Anyway thanks a lot for your help

 

[pietro82]

Hi all,

I have just got further information from our customer. They have built a new cab for that vehicle and they need to know if there are some design mistakes that can bring any "stupid" failure such as parts come unscrewed. My idea is: installing accelerometers at each wheel hub and one at the cab. Perform some measurements during service usage and some measurments during speed humps travelling and then compute the SRS or the something similar and compare it. Since the vehicle travels mostly on soil so the excitation of speed humps is quite different than during the service and checking which speed humps composition better reproduce the service spectra can be problematic. So I thought to develop a multibody model and simulate the vehicle while travelling on different speed humps and select which speed humps better reproduce the accelerations.
Is it a good idea? It's a not suspended vehicle, so there are just tires and rubber mounts between the cab and frame and the vehicle top speed on service is mostly slower than 10km/h. I'm not very expert in multibody dynamics so I would use an easy model. Do a linear model reproduce quite well the vehicle vertical dynamics for such vehicle and at that speed? I would use this simulation to getting a rough result and to avoid to buy many useless speed humps.
any suggestion is appreciated.

Thanks

 

[IRstuff]

"Is it a good idea? It's a not suspended vehicle, so there are just tires and rubber mounts between the cab and frame and the vehicle top speed on service is mostly slower than 10km/h."

Not unless you are going to do the testing over thousands of hours and thousands of miles of road. If the sole intent is to determine whether there is enough vibration to shake loose or fatigue, then using something like MIL-STD-810 vehicle vibration profiles might be the simplest thing. Conversely, you could possibly outfit a real vehicle with sensors and then apply an envelope along with safety factors for use in your simulations.

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[GregLocock]

Some car factories do have a short length of road, say 200m long, fitted with a variety of potholes and speedhumps, which are designed to allow the driver to determine if there are squeaks and rattles. I have seen amusing pictures of things they find by the side of that road, handfuls of screws and so on.

Your basic idea is good but it will need much more fidelity than just one acc on the cab, and deriving the equivalence between in service loads and test road profiles is a big job.

Cheers

Greg Locock


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[pietro82]

Thanks for your reply.

Greg you're right, but our customer produces a special off-road vehicle and the market is pretty small, at least in Europe. He had been sold the mostly the same vehicle for more than 20 years, so he doesn't use to test anything. Now he is about to release a new vehicle so before to release it he wants to do a little test. So we need to do something quite good and cheap.

IRStuff: I'll take a look at the mil standard.

Thanks