Bumper Cars 3

[Dmanley]

Just something I've been thinking about the past while and I can’t seam to find an answer any where.

Why aren't there big springs or shock absorbers in the front of cars to absorb the impact of a crash?
Why isn't there a shock absorber behind the front bumper to help alleviate some of the impact passed onto the passengers?

I've tried all over the net looking for a reason and I don't think I'm asking the right questions!
Is there anybody out there that has seen this and if so could they lead me in the right direction?

Thank you,
Regards,
Derry Manley

 

[patprimmer]

The complete front of virtually all modern cars is a crash shock absorbing device.

You are asking the wrong question.

Try energy absorbing NOT SPRING.



Regards

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[ivymike]

'cause part of the fun of bumper cars is the rough ride?

 

[Dmanley]

Thanks for the replies,
I do understand the difference between springs and energy absorbing, my question is why not add something like two pistons to the front bumper that absorb the impact energy and collapse at a certain pressure?
To me it seams logical, like putting rubber mountings on bull bars, if you actually plan on hitting things with the bull bars!

Thanks again for you comments, I'll keep searching!

P.S. ivymike, I like your thinking!

 

[Hydroformer]

I had an '81 Regal, one of the last bumper cars (as opposed to plastic fascia). The two shock absorbers attached to the frt bumper were quite visible with the hood up. That was pret'near 25 yrs ago.

*Without data, you're just another person with an opinion.*

Hydroformer

 

[patprimmer]

Dmanley

It has been done, but such designs won't pass current crash tests as they cannot allow enough travel to absorb enough energy. The system needs to use the entire front structure of the car to do that and meet current requirements.

Regards

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

 

[Hydroformer]

True Pat...

The shocks in the bumpers are there for the 5mph impacts. They're pretty much useless in a 35mph-40% offset frontal impact.

*Without data, you're just another person with an opinion.*

Hydroformer

 

[Dmanley]

Hydroformer, you seam to know actual details about this kind of stuff, where would be a good source of actual spec's and requirements for the crumble zone of a car?

I'm trying to figure out if an idea I have is good enough for development!?!

Thanks again for all the comments and replies.

Derry

 

[Hydroformer]

With the exception of the 5mph bumper test (repair cost) the specs don't relate so much to 'what happens to the vehicle' as they do 'what happens to the occupants'.

Instruments measure the force of impact to each dummy's head, neck, chest, pelvis, legs and feet. Frontal star ratings indicate the chance of a serious head and chest injury to the driver and right front seat passenger.

NHTSA does a full frontal crash @ 35mph and side impact @ 38.5mph for gov. compliance. IIHS does a 40% frontal offset crash @ 40mph which is a far more brutal test. This closely mirrors a vehicle drifting over the center line and into a head on collision.

Lot's of stuff to absorb here so take your time

http://www.nhtsa.dot.gov/NCAP/info.htm#iq8

http://www.nhtsa.dot.gov/cars/testing/ncap/

Insurance Institute for Highway Safety (IIHS):

http://www.hwysafety.org/vehicle_ratings/ratings.htm

European New Car Assessment Program (Euro NCAP):

http://www.euroncap.com

Australian New Car Assessment Program (ANCAP):

http://www.aaa.asn.au/ancap.htm

New Car Assessment Japan:

http://www.nasva.go.jp/english

My company is a member of

http://www.mira.co.uk/

*Without data, you're just another person with an opinion.*

Hydroformer

 

[Dmanley]

Thank you for all that, I was really expecting one link or look at Google!

[red]This is fabulous information![/red]

 

[Dmanley]

Why do they only test cars up to 64kph(40mph)?
I know that there is a whole range of tests at different speeds, but the highest speed I've come across is 64kph!
I understand that it is a regulatory requirement for them to be tested at this speed but is it that it would be too costly and difficult for higher speed impacts?

To me if two cars travelling at 60 kph hit in a 40% offset condition there would be a relative speed of around 120kph, depending on geometry and what not, with a deformable stationary barrier.

Hydroformer, you stated that the 40% off set models a car drifting across the center line, but wouldn't the on coming car also have a velocity component to play in the impact on the car.
Or is it that 60 kph hit each car?
Do I need to go back to my physics teacher and have him show me relativity again?

Dmanley

 

[patprimmer]

You need to ask him about kinetic energy, newtons laws of motion and vectors.

Regards

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

 

[Hydroformer]

There is SOOO much more to this. "Crash management" is almost an industry of it's own. Huge strides have been made in occupant safety (especially since '96).

"Hydroformer, you stated that the 40% off set models a car drifting across the center line, but wouldn't the on coming car also have a velocity component to play in the impact on the car."

You have to take into account that with the 40% test the vehicle is slammed into a stationary (immovable) barrier. Hitting a brick wall is much different than hitting another car (granted) but you introduce way too many scenarios if you try to model different cars hitting different cars.

The testing is based on crashes that should have a reasonble expectation of being survivable. Start testing @ 120kph and the results will begin to look very similar (everyone's dead).

Long before the NHTSA crashes a car, several rounds of computer crash simulations and improvements have been made by the OEM. The OEM then crashes several vehicles from the pilot build to validate the FEA findings. All of this goes on before a single 'salable' vehicle is made.

Keep reading the links (and links within links), that should keep you swimmin' for a while.

*Without data, you're just another person with an opinion.*

Hydroformer

 

[GregLocock]

If you look at the chassis rails of your reasonably modern passenger car you'll see a whole bunch of darts and corrugations in them. These are to inititiate hinges in the rail. Some older cars used to use telescoping tubes - brilliant in the perfect crash, but they tend to lock up in offset crashes (I guess).

While it would be nice to design cars so that they could be safely crashed at any speed, that is not cost effective. It makes more sense to concentrate on the crash speeds (and relative orientations) that actually cause the most injuries, rather than the alternative. I vaguely remember that in the two years after side airbags were introduced on one car that sold 30000 a year, none were set off. Is that $600 per car well spent? This is not a zero sum game.



Cheers

Greg Locock

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

 

[patprimmer]

Good point Greg

If that $18,000,000 plus all that spent in a similar way on other models, was spent on extra emergency services at hospitals, or safer roads, I think more lives might be saved.

Regards

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

 

[GregLocock]

This is a tricky area. If governments didn't legislate for crash safety at all we pretty much would only do whatever the customer would pay for (not much, at a guess, for the ones most likley to hurt themselves). On the other hand, by defining certain standard tests they may be forcing us to design for less cost effective solutions - for example, it may be that more lives would be saved per dollar by fitting rear vision TVs to SUVs, than by increasing the severity of the frontal impact crash test for passenger cars, again. Unfortunately the market has no sensible way of evaluating this sort of thing, that's why the safety standards need to be set by the manufacturers AND government (and anybody else with a sensible point).

I'd like to see an overall road safety budget, that included expenditure on roads, emergency services, safety devices in cars and any other methods, rather than the current ad hoc approach.

Cheers

Greg Locock

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

 

[jons999]

Not to mention the huge cost to repair new vehicles, since the entire front end of a car is a crumple zone a relatively slow speed crash means that the engine and trans have to be removed to have new frame rails welded in place and the entire front clip needs to be replaced, on an older car you would need a bumper a grill and some headlights.

-Jon

 

[patprimmer]

Extended hospital stays and funerals are expensive compared to car repairs.

Regards

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

 

[Hydroformer]

From the 'human factor' the events to consider are the vehicle making contact with an object, the occupant making contact with the vehicle (interior).

Between these two events, the vehicle's structure needs to absorb as much of the energy as it can in order to lessen the secondary impact. (A tertiary impact is also considered as the occupant's internals contact the rib cage / skull).

Greg's on top of it with the design features incorporated into structural members to manage energy in a crash event. This goes well beyond frame rails and bumpers.
Modern FEA crashes record a multitude of sub-events (ie: radiator contacting a/c compressor @ C+27ms 16.2m/s). I've seen alternator bracketry changes because of a spike in the deceleration curve, or to change the resultant trajectory of an object in crash.

Structural design features are also incorporated to manage secondary crash elements such as strengthening or weakening the instrument panel, knee bolster, toe board, etc. Of course seat belts, airbags and padding also help with the second and third events.

A lot of these efforts don't result in additional cost or weight to components in the vehicle but DO contribute to the over-all engineering cost of the vehicle. I'd still rather buy a well engineered car and never take advantage of the crash management ability than to buy something mediocre and hope for the best.


*Without data, you're just another person with an opinion.*

Hydroformer

 

[Tmoose]

"Extended hospital stays and funerals are expensive compared to car repairs.

extended hospital stays, certainly.

http://www.netcremation.com/

$495 barely buys a basic Maaco paint job