大学生方程式赛车悬架资料(2)

Design Error Four

Well, not really an error in design, rather an error in project management.

This is the famous 2001 WWU 554cc V8. It used Kawasaki cylinder heads on a bespoke block with all internals and systems made by the team.

The engine drove through a carbon fibre cased gearbox housing Honda gears and selectors. The transmission was also designed and built by the students.

The engine made a mockery of the costing formula for engines and raised an enormous amount of interest at the event.

But it all fizzled out to naught. So much effort had gone into the power train that the chassis left much to be desired.

Then the engine could not be started at the event and so did not compete. Under the stresses placed on them by the project, the team had neglected to fit any form of starter! Probably the best example in FSAE history of a team totally forgetting the intent of the competition, still, they will always be remembered for their achievement!

This months Design Error FIVE

More teams are making their own wheels. Usually they make or buy rims and then design and make an aluminiumcentre.

This seems a pretty straightforward task, yet many teams obviously do not understand the loads applied to a wheel on a racecar.

The shear loads across the interface between hub face and wheel is sometimes passed through the root of a thread on the wheel studs. This is particularly common where teams use high tensile bolts or Allen screws as wheel studs.

The wheel should be centered on a spigot on the hub face. Some teams assume that using conical nuts will centre the wheel for them. Conical nuts will introduce stresses in a light alloy wheel centre that may well cause a total failure of the wheel. This is a very public way to have a DNF and might well cause someone to get hurt. People have been injured by wheels coming off cars in competition.

Wheels before and after failure

All the best suspension calculations are useless if wheel flex permits the tyre to assume a positive camber attitude on the track under cornering loads. This picture shows the effect of wheel flex on tyre camber.

So, until next month, good luck with your car and team building exercises.

This months Design Error six

Just to be different, this month I am going to talk about a piece of good design. This is not a Design Error, rather it is a very nice solution to hub and wheel mount design, although it may have one flaw.

The reason for posting this is that I have been very critical of some hub designs. Having thread roots across the shear face between the hub and wheel, no spigot to centre the wheel on the hub and using tapered wheel nuts seating in aluminium wheel centres are all evidence of poor design.

I don’t know where this hub design comes from, but I like it.

As can be seen, the shear load at the hub face is taken through a small shank on the wheel stud. The wheel nuts are sleeve nuts designed to tighten against the steel hub face whilst applying a measured amount of clamping force to the wheels. The flat washer prevents the nuts galling the wheel centre (especially important with magnesium wheels).

The flaw? What about a centering spigot for the wheel? Well, I hope that is machined into the wheel and sits into the recess in the hub face. If the wheels are being centered by the wheel nuts, then this design is not so nice.

Another nice feature is that the tripod recess is machined right through the live hub. This allows the driveshaft length to be as long as possible, therefore reducing angularity losses, whilst at the same time accepting any driveshaft end plunge caused by suspension movement. That is enough for this month. Hopefully teams will be back at work getting ready to build their new car. Good luck to all and I look forward to seeing you all in August.

This Months Design Error Seven

Obviously, my Design error of the month has to relate to a misunderstanding of one of Newton’s Laws, in this case the Third Law.

Look where the bell-crank and spring loads are being reacted! Judges look at a design like this, they can see the load paths and they eliminate the car from the Design Finals!

Now take a look at this load path. Isaac Newton turned in his grave just a couple of minutes before the frame broke.

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