New and improved spring design, better than OE Audi parts!
I have learned a great deal more about spring design in the last few weeks than I ever dreamed existed. Apparently, the OE Audi part springs are not ideal for the trunk hinge mod because they are not designed to be installed under tension with a full 25mm of deflection. What is deflection you say? Here's a primer:
- deflection |diˈflekSHən (engineering), the displacement of a structural element under load — in spring language, how far the spring is stretched from it's resting length when under tension.
I won't go into all the other terms. Suffice it to say, the Audi OE springs will eventually lose efficacy because they are deflected 200% of their structural limit in the hinge design as spec'd by the German wizards at PassatPlus.de. Under such a continuous load, the springs stretch and eventually "set" in an elongated, less effective state. Not something they shared in followup to their posting of the design, but probably why their design spec'd the additional Audi buffers to push the lid up with a pop initially when the latch is released. :banghead:
So here's where my spring designer and I have made the breakthrough. I shared with him my design and the deflection requirement, and the actual force requirements of the design. I even added some extra oomph to my lift calculations thanks to SteveInChicago who posited that he has both a Votex spoiler and warning triangle installed on his boot lid, thereby making it heavier.
The end result is that we came up with a spring design that is better suited to the mod, and will not stretch over time due to being installed with a constant 25mm deflection. This means that the springs will be as strong on day one as they will be on day three hundred and one, and for years after that. And it means no one will have to supplement their hinge assists with OE Audi buffers.
How was this done? The new springs are of a slightly
heavier gauge wire, and are wound with a slightly larger
coil diameter with a modest
preload. I promised I wouldn't go into all the other terms, but there I went ahead and used them. In plain English, the wire is thicker and the barrel part of the spring is a little fatter. They will again be made of carbon steel, tempered and finished in black oxide for a tidy look, especially in contrast to the brushed stainless brackets and hardware, and to protect against rust.
OK, so the "tell you like it is" part of me is twisting my arm to finish my lesson in spring design dynamics. Springs strength and performance characteristics are dictated by four factors: 1) wire gauge, 2) type of steel, 3) number and diameter of coils and 4) preload. Safe deflection range of any spring design is a formulaic calculation. The Audi OE springs and the original copies I had produced do not have the needed characteristics to survive under constant deflection of 25mm (stretch applied to springs when trunk lid is closed.) The new ones do, with a little breathing room, just to be sure.
Thanks to the early adopters for helping me test installations other than my own. Your new springs are in production. :thumbup:
:lightsaber: