So correct me if I'm wrong, but our history to date has seen cars start off as a body on frame design. From there experimental and limited production 'unibody' vehicles started production as early as the 30s, but

Starting, at least as far as I'm aware, in the 60s and 70s, some mainstream vehicles started moving toward a unibody design.

But as I understand it, unibody designs at first were truely supported by the 'skin' of the vehicle and nothing else... most modern day unibody vehicles use several integrated 'sub frames' in their design.

Then there are cars like the Vette that is using a 'space frame' I think I've heard it called - but basically works like a body on frame design where the external body connects to the frame, but it extends to form in internal 'skeleton' of sorts that extends above just the floor of the car to include the roof and so on. I think I've seen/heard of some Audi designs using a similar frame design, and I'm sure others as well.

So I guess I'm just kind of wondering what the future of frame/chassis design entails? Or if it's just going to end up being a bunch of hybrid unibody/spaceframe type designs.

I also was wondering something you engineers might be able to answer - do unibody structures typically lose rigidity over the miles? I'm talking about purely the structure. To me it seems like they definitely would, but how much rigidity? I mean is it to the point that if you measured torsional and bending rigidity in the same vehicle 100,000 miles of normal on-road use later that you'd see a significant reduction in rigidity?

I'm under the impression that a body on frame design doesn't suffer as much from weakening over time? At least I know in terms of towing and off roading it stands up to abuse quite a bit better. Not sure about for normal on-road use if there's any significant difference.

So how does the Corvette's type of frame design stack up compared to unibody and bof?

 

Unibodies definitly get fatigued over time. My 92 has a few groans that I am sure it did not have when it came off the assembly line. Many 3rd and 4th gen owners use sub frame connectors to have give the cars more rigidity. Everytime the cars engine revs it puts a moment on the car over time will start to wear the body out. A lot of third gens had paint cracks on the sail panals right behind the side windows (especially T-top cars).

I am not familiar enough with the vettes design to give an opinion on it.

 

my 1968 bonneville has a 4" by 6" full length frame. if it weren't for that the car would have fallen apart already. for the incredible amount of rust on the body and floorpans the car is still feels solid. I say we go back to body on frame!

 

This is Kappa with its skin off. Basically what you see there is the unibody or space frame. The purely structural hydroformed frame rails are the semi-square structures you can see going from the front to the firewall and bending outwards toward and under the door opening and then back up behind the door to make room for the suspension and running to the rear of the chassis.

The trans tunnel is also a major structural element, adding stiffness to the structure. The rear bulkhead is also VERY important on Kappa.


This is the Aluminum Z06 structure. As you can see it is very similar.


This is a stripped down version of the C6 structure. The front firewall and floor pans are removed.


When we compare the C5/6 space frame to a traditional truck frame, which is what we have here, there are HUGE differences. Number one is that the frame and cross members are the only supports needed. The space frame has much more body structure required than an older truck like frame.


Moving up the scale we have an older space frame design, the first generation Saturn S-series cars. So we go from truck frame with no body needed for strength to C5/6 space frame which requires quite a bit of body structure to complete its space frame with no frame rails at all, which the C5/6 has.



A middle ground between the C5/6 and S-series space frames would be Theta, which uses full frame rails (shown in blue) as well as a stiff body structure (kinda like the Honda Ridgeline).

Where are things going? Well Audi has an aluminum space frame for at least one of its cars, I am thinking the TT or maybe the A8 though I don't recall.
Shown here


Jag is using an aluminum unibody for its XJ, XJ8, and XJR.

So it seems like this is where it is going. But will they be more S-seris like, Theta like, or C5/C6 like? I am thinking that the C5/6 with its tall structurally important trans tunnel just cannot make an effective, usable regular sedan. Also its frame rails are rather bluky and passenger space invading. I think we will see more Theta and S-seris like structures though they are expensive to develop the cost/benefit should be worth it as space and safety take a paramount in cars.

 

^^^

Cool, thanks for the article, very informative and well illustrated.

 

Very cool.

Great explaination.

 

Not an article just something I did while 'studying' for an O.Chem test.

Lets see how well I did on that test.

 

I think this also shows pretty clearly why there won't be a Kappa sedan. Looking at that structure, I really dont see any major piece that could carry over to a sedan at all. I can see maybe a Porsche Carrera-like 4 seater (certainly not 4 passenger).

That said, I'm thinking that the lessons learned in the ways Kappa is made can carry over into making a small, low cost, RWD structure that a sedan can use. Perhaps more of a space frame?

 

That would be pretty interesting.