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Filler cap and rear inner and outer panels

Filler cap and rear inner and outer panels

Filler cap and rear inner and outer panels

During a barrier test the outer and inner body panels shear apart thus causing the filler cap to fall off. After the barrier test a roll over test is performed and of course without the filler cap the petrol flows out. Rather than havin a spring loaded flap to prevent the flow of petrol from leaking im looking at trying to keep the distance between the 2 panels. could you please give me any ideas.

RE: Filler cap and rear inner and outer panels

Hi Marc,

Rollover if a fuel system is quite a tricky subject to design for - normally the fuel system supplier will ask that the body is 'no worse than the previous' - and then get left between a rock and a hard place when costs for altering the body are compared to the cap if things go wrong !!!

Most design alternatives for fuel cap system components centre on creating a shear plane around the periphery of the cap so that when the inner and outer panels seperate - the'plug' part of the cap is left in the filler neck.  Usually the force to achieve this is approximately 280 -400 N prefereably lower !!! The problem is that this force has to be balanced against other physical tests - particularly  things like 'overtorque'.   Physical testing of the sub-assembly (fuel cap)  is usually quite simple and inexpensive - however - testing of the system via the barrier test (I'm presuming this is a rear impact barrier ?) is normally quite expensive and normally requires FEA techniques beforehand - just to minimise the chance of an unexpected/undesireable result !!!

'Capless' systems however are a lot more difficult to design for, since they require the lock for the filler flap being located on a non-moving part of the body.  These systems tend to require a lot more design analysis work (ie F.E.A.) so that the energy dissapation throughout the body can be understood fully.

best wishes


RE: Filler cap and rear inner and outer panels

hi sean

Thankyou very much for your help.
i also was thinking of a  of a plug type mechanism to prevent flow of petrol. However this already happens but instead of a plug it is a breather and the petrol flows out of the breather. it is only the top of the cap falls off, the rest of the cap remains in the filler neck. Therefor if i exchange the breather for a plug i will need to reposition the breather as this is vital. Do you have any suggestions where to.

I was also thinking of getting rid of the inner panel and attaching the filler cap/neck arrangement to the outer panel. Thus causing wherever the outer panel moves, everything moves with it. What do you think.
Thnx again


RE: Filler cap and rear inner and outer panels

Hi Mark,

Thanks for your feedback and additional info !

I presume by 'breather' you are referring to a component intended to vent fuel vapour to atmosphere as a result of thermal cycling ?  If this is right - the fuel caps I designed always had the component associated with this function (normally a combination of non-return valve for rollover and low pressure valve for vapour escape) inside the cap - there was only one exception to this which was a 'capless' system, but this was abandoned recently by the OEM that was using it because its development was putting the project delivery at risk.

If you need to position the breather somewhere - the most obvious position is on somewhere that doesn't move - normally on something that goes across the car.  I've personally seen some breathers mounted on subframes, wishbones - even one on the same reinforcer that the fuel filler pipe is bolted on.  One position I have thought about trying though is somewhere on the wheelarch - the only reason I can think of not doing it would be that the fixing for the anchorage (if its a screw) could encroach on the package for tyre movement.  One way round this might be a self adhesive fastening though ?

Doing away with the inner panel sounds a novel idea - cetainly would improve the performance of the fuel filler system but before you pursue it with effort - in my experience this mounting tends to be on a reinforcing panel for the rear quarter.  Without this reinforcer - the cars I have worked on would always fail crash - either rear or side !!!

best wishes


RE: Filler cap and rear inner and outer panels

Hi Sean

Tanx again for more feedback
I have considered my possibilities and i think ill either go for the "plug" system and place the breather on the same panel which the filler neck is connected to which i think vauxhall do. My other alternative is getting rid of the outer panel. I have thought about what you said but it seems fail safe, i have quite a high budget so i think trial and error is the way to go. I have looked at capless systems but i dont fully understand the concept so i must research that before i have my design review.

thanks again

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