Adnectere

Couple of questions on engine mounts.

http://www.corvettemuseum.com/virtua.../crashtest.jpg

Here's a pic of a corvette that was crashed in a study and it's at the NCM. I probably spent 5 minutes just studying it. It's practically a work of art. What I know from crash tests come from tv and I've been interested so it was a good study (anyone have good books on the subject they can recommend?)

My question is that you can see how the crumple zone is working and instead of going straight back the wheels are angling up. Also, instead of going straight back into the passenger compartment, the engine is designed to go under the passenger compartment - you can see it angling up already. How does this occur? Obviously if the car got hit head-on with no crumple zone, the motor would just get pushed wherever the frame metal deformed, straight back, to the side, at an angle, etc. Is the angling and going under a function of the crumple zone or is it a function of the motor mount? Is the motor mount designed in such a way to simply hold the motor and isolate vibrations and torques or is it also designed to act in a crash situation?

Also I have a question on stressed motors. I've read about these being used in racing motors and the c5r block was made as one, but what specifically is this stressed motor concept? I'm presuming it has suspension parts/movements fed into it and also that it acts as a portion of the frame. Is this correct? In that case, do you use less frame with this design and does the suspension basically mount to the motor in some fashion? What are the consequences of getting into a wreck with this design - let's say you tear the engine off the car or the mount moves - if the engine moves on the mount and it is acting as the frame, that would mean the frame is basically being removed and I can't see how that design would be a legitimate design. Many questions and much clarification needed. Please be specific as well. Thank you.

vettedude

You can systematically make certain parts weaker than others, and design parts to fail before others by simply playing with the geometry of a part. Also, you can use methods of analysis such as a multi physics Finite Element code (a code that incorporates dynamics and statics into the model)to simulate what will happen when a crash occurs. It seems and sounds complicated, and it is in a way, but when you have hundreds of engineers working to solve these problems, they can be solved quickly. More or less the engineer would start with a basic model, and setup simulations changing parts or material geometries to cause them to fail in a predictable manner. It's like when you go to break a piece of glass, you score it where you want it to break, and it is pretty easy to make the glass behave how you want it to.

I did not design the motor mount, so, I do not know, but if I had to guess, the motor mount would have been designed to do some of the following.
- Isolate vibrations from the engine
-Support the engine, along with direct forces to and from the engine depending on the load of the engine and the frame
-fail in a specific manner in the event of a crash, the engine mount mos definitely has different properties in different directions, so that it is fine when you are revving or launching, but can still fail in a predictable manner when you are in a serious accident.

Basically the stressed motor design uses the engine to provide structural stability to the suspension frame and passenger compartment of the automobile. Suspension motion would not be fed into the engine, the suspension would ideally feed all load to the dampers and through the suspension components which constrain movement. The engine is designed as a dual purpose structural element and both stresses from the combustion and rotating elements along with the forces from the suspension are taken into account in the design. The way that they compute these stresses are using again FEA, also keep in mind race cars are designed and adhere to quite different standards than an automobile. The engine as a stressed component could still provide impact protection, the stresses and forces of a crash are much greater than just driving, and thus the parts can still be designed to fail in predictable ways.

In an F1 car the suspension would mount to the motor, that is probably not the case in the C5R, but I have not looked at it up close, I believe that like most production to race cars, it uses a space frame type of design, all the space frame terminology means is that it is a three dimensional truss system.

chuntington101

im sure the "enigne under the passanger compartment" is to do with the mounts.

i have seen rally cars smash into solid concreat blocks (designed to stop tacks going off the road) at very high speed (around 100mph). the engine block was some 100yards further down the road than the car. when the enginer got interviewed the answer was "it did just what it was designed to do"!!!

i assume in this case they did it to provent it coming into the cmpartment to. also it gets all the rad hot components away from a posiable ruptured fuel cell!

also i read a report on a car builder (cant rember who) that built a over 2000GB modle of the car and ran countless simulations, not only for crash testing but even down to cliemit controle, so they new just what the car was going to do when it did have to be crash tested!

thansk Chris.

gun5l1ng3r

A 2 Terabyte model of a car! Wow!
I wonder how much we could learn with a 2 TB model of a LSx motor...

chuntington101

i think alot! just think of alll the tests you could put the engine under and the massive numbers of times you could destroy the block and not have to wait to get it rebuilt!

wonder if GM do anything like this when designing blocks???

thnaks Chris.

vettedude

no more than a 5MB model, it all depends on what you want, A 2 TB model of the engine would be pointless, you can only usually simulate a few things at one time, and more than that would be useless.

yes they are

chuntington101

why would a small model be as good as a complex and large one????? suely with a large moddle you cna take everything into acount when you do a test.

Chris.

gun5l1ng3r

I agree with you chuntington101. With more 'space' in the model, you can model everything with a higher resolution.

How big would a model be if you built the engine one molecule at a time?