Necessity of Throttle Valve

[gluaisdan]

I've been lately doing some research as to whether or not the throttle valve will be a component in future generations of direct injection petrol engines. Theoretically in the fully variable valve drive motor systems (BMW's Valvetronic motor for instance) it is not really necessary, yet to my knowledge it is still being incorporated.
Could this be because the throttle valve must fulfill secondary functions, (vacuum for brake cylinder, carbon filter regeneration for the fuel tank, exhaust gas recycling)?

 

[ivymike]

I think it's mostly because they can't quite run as lean as they'd like to yet, so for the low end of part load operation they need to restrict airflow.

 

[patprimmer]

If they can reduce inlet valve lift and duration enough, they should not need a throttle plate to control engine speed.

Maybe there is a problem controlling the valve train to the required degree of accuracy.

Maybe there is more mass to move to control the valve train, therefore maybe the response rate is to slow to maintain a stable idle under various loads from ancillaries.

Maybe it is as you say, to provide a vacuum source.

Regards
pat

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[enginesrus]

If so it would need direct injection. Intake manifold velocity would be slow at low rpms. It is like what happens above the throttle plate in a carb at idle speeds. Difference is you would be throttling with the intake
valve(s) instead. Just something else to cost a motorist more money to fix when something goes wrong. Kinda like the set prices on O2 sensers. $90.00 everyplace you go.

 

[gluaisdan]

Thanks for your help guys.

A motor without a throttle valve must of course have direct injection.

I thought that one of the main benefits of variable valve motor systems was the absence of throttling at the low end part of the load cycle, thereby avoiding the resulting pressure and efficiency loses. It would seem that the motor manufacturers for whatever reason have not achieved this goal yet. If this is the reason I would assume that they are working on a solution. And then the days of the throttle valve are numbered.

As far as generating vacuum is concerned, it seems to me that the throttling of the engine for this purpose is a pretty inefficient way to go about it. A vacuum pump would seem like an better solution, unless you would need a number of them, in which case it may not be cost effective.

Regards

 

[obanion]

Direct injection isn't required for throttleless operation. It certainly helps, and MOST throttless engines use some form of direct injection, but not all.

http://carambola.usc.edu/Research/TPCE/TPCE.html

Intake air heating + lean burn + CNG or LPG fuel

 

[patprimmer]

I imagine if you can get the fuel to hit directly on the back of the inlet valve very close to the seat just as it starts to open, it will have the same effect as the fuel being drawn out of the idle ports in a carby, i.e. being introduced to a very localised high air speed area. This should result in good dispersion and vapourisation. The trick will be in metering, timing and accuracy of aim and control of pattern with very small shots.

To maintain accuracy and patern, very small injectors might prove necessary. This might make secondary (large) injectors necessary for full power and/or high speed.

To help minimise cost increases, less than one injector per cyl could be used if placed in the plenumb area, with cyl to cyl trimming done by the idle injectors, or with one secondary injector per cyl, and only half the cylinders operating at idle. This would double the air and fuel requirements on the few cylinders being used at idle.

Sorry for the ramble.

Regards
pat

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