Variable Intake w/ VVT 1

[Greg5OH]

Hello, as a final school project i would like to design a system that uses both constant variable valve timing along with constantly variable intake. This would be for a race engine setup. Basically telescoping intake runners, that are synced to the cam variation as well. Change in both is based on engine load and throttle position.
1) is factoring engine load necessery for this to work effectively, or is throttle position enough?
2) What kind of setup would be best for the motorization of the telescoping intact tracts?
3) Im thinking electro magnetic magnets for the VVT system, (unless the project scope allows me to use a current manufactureres VVT system, and then i just integrate the variable intake..)

 

[patprimmer]

Why would you base either on load or throttle position as the only variable of interest is rpm.

Regards
Pat
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[Greg5OH]

my reason for throttle position or engine load, is say you are coming out of a corner and you need some TORQUE, so you roll onto the gas pretty quickly out of the corner, the runners extend, favouring torque, then retract at a specified rate (relative to rpms i guess) and at the same time retarding the camshaft to maximize low rpm air intake, gradually advancing the cam and shortening the intake based on RPM-as you mentioned.

Or would it be easier to simply have both controlled exclusively by RPM?

 

[patprimmer]

If you are at part throttle as all you need to do to increase power is to open the throttle. That's kinda what it's for.

If you want more power available at wide open throttle, you adjust inlet manifold runner length and camshaft timing to optimum for that rpm and have it automatically adjust to changing rpm. It can be by a simple bob weight system.

Cam timing is relatively easy re indexing. Changing duration and lift seamlessly is a whole other ball game. Computer controlled pneumatics, electrical/magnetic or a 3D camshaft are all I can think of as possible. I doubt it can be done to be durable with existing technology at a budget a mere mortal could contemplate.

On the fly seamless adjustment to intake runner length also has issues, mainly re friction air leaks and speed of change required.

The air leaks could be resolved by placing it in a box or by placing it upstream of the throttles.

Regards
Pat
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[SomptingGuy]

Back when it was still legal, the F1 teams used stepper motors to adjust the lengths of their intake runners. About 10mm-30mm in discrete 2mm steps. As a function of only engine speed. During a run-up transient, the runners could cycle their range 3 or 4 times.

- Steve

 

[AllAngles]

The new 6.4L HEMI from Dodge features both VVT and an "active" intake design. One good place to start might be exploring how existing systems function and why. Then you can idenfity where concessions had to be made for packaging, reliability, cost, etc. and see which of those concessions you can ignore for your project.

Mikah B.

http://www.allanglesdesign.com

 

[Lou Scannon]

Was it BMW that introduced the rotating scroll a few years ago? That was one of the more elegant implementations that I've seen.

I forgot what I was going to say

 

[patprimmer]

I think it was VW or Nissan. Both had it quite a few years ago, but that is only a 2 step system and only truly matches 2 rpm points.

Regards
Pat
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[HRHtex]

Greg50H - I am not quite sure what you are doing but it sounds interesting.
You may be also interested to see the following:

http://www.helicalcamshaft.com/

http://en.wikipedia.org/wiki/Helical_camshaft

This is one of the very few (maybe the only?) mechanical varible duration system that exists. Note that the website shows a short video showing a basic control and actuation arrangement by centrifugal means.

 

[Greg5OH]

Patprimmer-can you elaborate on the bobweight system you are speaking of? How would that be affected by rapid direction changes as seen on tight race tracks? I was almost thinking a pneumatic system, or maybe hydraulic. In any case-i would like the runners to respond as quickly as possible (ideally at an allowable rate close to that of throttle position change.

thinking back, you are right in that length only needs to be influenced by RPM, no matter what the engine load is, is you need 100% power at 2000 rpom or 7000 rpm (coming out of a corner-lifftle throttle, then roll onto it quick)-engine will still produce its best torque when the intake is at its helmholtz resonance.

Now, will the intake adjustment process have to be synced in time with the constantly variable cam adjustment to work to its fullest capacity? (i will be sticking with a conventional camshaft-3d and helicals are cool-but that is a project to deal with on its own accord), as in-will the length of the runner have to compensate for the advancement/ratardation of the cam?

 

[patprimmer]

Pull any old mechanical advance distributor apart for a real world example.

Regards
Pat
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[thruthefence]

I'm dating myself here, but back in the 60's there was a device called the "Vari cam",for small block chevys, that used flyweights to advance or retard cam timing. No experience with it, just remember seeing the adverts.

 

[HRHtex]

The centrifugal advance mechanism on a diesel injector pump camshaft may give you a few ideas.

I have read that the "Varicam" (or whatever it was called) did operate OK but had little or no measureable effect on the engine output.

I think if you are going to work with conventional camshafts you are not going to get any real results that could be applied to a racing engine. A lot (maybe most) of manufacturers already have continuously variable valve phasing - BMW's Vanos being a notable example.

To get worthwhile improvements in performance I think you need to work with variable duration. Honda's variable duration VTEC (although stepped and not continuous) demonstrates how effective variable duration can be.

 

[patprimmer]

Simply varying cam timing without changing lift or duration works better on a twin cam engine because you can change lobe centres as well as overall advance or retard cam timing.

BMW also had a variable lift system by simply moving the fulcrum on the rocker arm thereby changing rocker ratio.

Regards
Pat
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[Greg5OH]

im more concerned with the variable intake, not really the VVT, more interested in making the variable intake work WITH the vvt to further exploit both mechanisms benefits.

 

[HRHtex]

PP - BMW's Valvetronic (if that is the system you are referring to) is not just variable fulcrum but an "oscillating cam" system of linked variable duration and variable lift.

Greg - Just what do you mean by "variable intake"? variable lift, duration or length of the intake tracts?

 

[moon161]

This guy does lots of neat variable timing things:

http://www.pattakon.com

 

[patprimmer]

moon.

Nice find.

Regards
Pat
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[dicer]

Isn't it part of engineering to figure this stuff out? Especially a school project?

 

[Rob821]

You may need to add intake cam position into your runner length equation as it will affect your optimal runner length since the vavle is open or closing at a different point.

You could however just set the cam phasing first and then adjust your runer length based on rpm only.

I always looked at this project to - and I just looked at using a DC motor controlled ball and screw setup.