Variable length intake

[sion_williams]

As you may remember a few moths back i was enquiring about variable length intakes (vli) this is why....

http://img.photobucket.com/albums/v243/ ... _00024.jpg

http://img.photobucket.com/albums/v243/ ... _00023.jpg

These have been made as a university project for a formula student car. As they are variable length i need something to control their height, it has to be fast response!

look forward to you replies

[sion_williams]

Anyone?

[guest]

try a dc motor. the mazda 787b had variable intake trumpets arraged very similarly to your set up. they used a simple dc motor with a cable attached to the intake trumpets. it was a simple solution and worked beautifully. do a search on r26b and you'll see the dc motor on top of the engine conected to the trumpets. if it'll work for the lemans it should suit your purposes.

[manchild]

I'd go for intake vacuum operated cylinder with piston and lever moving the VLI, more vacuum length +, less vacuum less length –

That way VLI would work automatically without need for additional system to control it. Even if you choose DC motor you'll have to use vacuum sensors unless you're basing input on rpm.

For first option (DC motor controlled by vacuum sensor) I suggest you too look at Turbo water injection kits that also use vacuum sensors and DC motors, only in their case DC motor drives the water pump.

http://www.dawesdevices.com/water.html

Basically, you need a hose connected on one end to one cylinder intake (since you have separate inlets not common inlet manifold), other end connected to vacuum sensor. Vacuum sensor breaks the circuit between the DC motor and the one line of the power source.

So, when rpm are down or when engine is accelerating (those are situations when VLI is most welcomed) vacuum sensor closes the circuit which powers the DC engine and engine will move the VLI using some gears, semi-gears and levers etc.

When engine picks up the revs and starts running smoothly vacuum drops and vacuum sensor breaks the circuit turning of DC motor and the weight of VLI should be enough to lower the trumpets and turn the DC motor and transmission as mush as necessary.

Simplest way than this would be if instead of DC motor you'd use electric magnet which would have better response but also require more power and less smooth operating.


BTW, it would be better to reduce size of those pics you posted or to just link them because they are stretching the post content (text).

[sion_williams]

Thanks guys, would it be possible to use a linear actuator?

[tt]

We looked at a similar set up for our FS car last year. We came up with a simple stepper motor and control set up based upon RPM (5 length settings). Its hard to get a fully progressive system and implemment it neatly but im sure it can be done.

Good luck.

MrT

[guest]

the 787b varied length based on rpm. as the rpm signal increased so did the signal to the dc motor. i think this or the stepper motor idea would be the simplest/cheapest solution. besides, if your competing in fsae, you'd be better off using your budget toward other areas of car design. althought the fsae gives students an opportunity to pursue new or extreme ideas in intelligent automotive design, most often, the team that ends up winning is the team with the most reliability, which in turn translates to simplicity. ask yourself if the gains from the variable length intake can be found in some other area of car design. then ask youself if the gains from the variable lenght intake are worth the amount of resources you are allocating to its design.

[sion_williams]

Some really good ideas but i still have a problem. The ideal situation is that at high RPM the length needs to be at its shortest, at low RPM the length has to be at its highest.

The problem: If we say we can get a signal voltage relative to RPM from the rev counter. And use it to control a stepper motor. It will lower the Intakes as rpm rises(great), but as RPM lowers again it will still be turning in the same direction, maybe at a slower rate but it will still be pushing it down! try and picture it and you will see my problem.

What i really need is a system where height is set relative to voltage. For example, at 0V its at its higest at 2.5v its in the middle and at 5v its at its lowest!

Please help

[Guest]

I disagree you can have the stepper motor position govenrned by a basic voltage produced from a pulse to voltage converted IC (i used one to create a rev indicator for my electronics a level). Im sure you can get stepper motors whose position relates to the voltage.

Mr T

[manchild]

What i really need is a system where height is set relative to voltage. For example, at 0V its at its higest at 2.5v its in the middle and at 5v its at its lowest!

Please help

Relative on voltage? I think that rev counter works by number of ingintions. The voltage is the same only frequency of ignition changes, right?

[ginsu]

For a linear movement wouldn't it be technically best to use a linear actuator?
Those are probably pretty expensive though.

Some of the cheapest solutions are usually mechanical. It's amazing what you can do with cables and levers. You could have a return spring that somehow returned the trumpets to the long configuration, and have a cable hooked to the transmission, much the way the speedometer is hooked up (you'd want the cable hooked to the flywheel gear teeth or something. then at idle the trumpets would be longest, and 10,000rpm it would be shortest). It sounds crude, but I bet you could make such a simple mechanical device to perform this task.

[manchild]

... and 10,000rpm it would be shortest). It sounds crude, but I bet you could make such a simple mechanical device to perform this task.

VLI is not only rpm dependable but most of all vacuum dependable. On identical rpm engine can have different need for VLI depending on if it is running with low vacuum or high vacuum (engine accelerating or running on desired rpm).

RPM dependability is simpler and it says - longest intake on idle and shortest on max rpm but the tricky part is to make VLI be useful in that zone from idle to max rpm. Elasticity of engine should be VLI’s main concern.

[Guest]

That intake looks just like the one at my uni, does SIHE mean anything to you?!

MrT

[sion_williams]

Yeh ive been helping danny and his buddy with the making. Im now trying to help him with a solution to controlling the movement!

[ginsu]

VLI is not only rpm dependable but most of all vacuum dependable. On identical rpm engine can have different need for VLI depending on if it is running with low vacuum or high vacuum (engine accelerating or running on desired rpm).

I'm pretty sure intake manifold flow is most dependent on the engine speed, that is what's driving the flow after all.

But, it might not matter because you shouldn't be going full throttle until you're over 4,000-5,000rpm. So, wouldn't this be easier to do by hooking it to the throttle cable? If it's vacuum dependent or engine speed dependent, then this would be the simplest solution.