BMW's throttle-less engines 3

[ufe777]

Why does it get bandied about that these engines don't have pumping losses? As far as I'm concerned a restriction is a restriction. The only advantage in terms of pumping loss I can imagine is a possible reduction in turbulence of the incoming charge which at part-load might not be an advantage at all because of charge mixing.

 

[globi5]

I'm not familiar with the details of this valve train. But if it is able to close the exhaust valve early, it could reduce or even get rid of pumping losses. (Basically an integrated EGR).

 

[schmidtj86]

Also if you close the intake very early, there is no pumping losses when the piston goes down, because that same force that resists it going down, helps it come up (neglecting heat transfer, and friction). It can get the charge into the cylinder nearer to atmospheric pressure, but closes before it displaces a lot - to regulate power.
I don't really know if that's how BMW does it, but that's what popped into my head when thinking about it.

 

[SomptingGuy]

They don't have throttle-related pumping losses because they don't have throttles.

 

[patprimmer]

If they deliberately constrict the inlet flow path, it is throttled, whether done by a butterfly valve or a poppet valve

Regards

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[crysta1c1ear]

Intake Valve Throttling

schmidtj86 (Mechanical) said:
Also if you close the intake very early, there is no pumping losses when the piston goes down, because that same force that resists it going down, helps it come up (neglecting heat transfer, and friction).

Crystalclear:
Okay. But that's not what they are doing, is it? They are not closing it earlier if they want to partially fill a cylinder, they are closing it later. Normally you are sucking air past a restriction to run at low load. If you want to half fill a cylinder with air you could create a (throttle) restriction in the air flow, causing a pressure drop, and completely fill a cylinder with air at 1/2 an atmosphere pressure. Alternatively, you could close the intake valve when the piston was half way up and have half a cylinder of air at normal atmospheric pressure.

Now let's forget about the cylinder in both cases, as somebody will argue that (in the throttled case) the partial vacuum will help suck the piston up at the start of the compression stoke. But the work done to create a partial vacuum between the throttle and intake valve is lost.

Pumping losses is a generic term. You have to (1) suck air past a throttle. You have to (2) suck air past an intake valve and exhaust gas energy or a piston has to (3) push air past an exhaust valve.

Intake valve throttling is about reducing (1) the losses sucking air past the throttle, particularly at part load, by not having the throttle. I don't see how intake valve throttling can fail to recover the energy cost of creating the partical vaccuum between throttle and intake valve: energy lost when the intake valve closes and air seeps past the partially operated throttle ready to fill the cylinder when the intake valve opens next time.

 

[tbuelna]

BMW Valvetronic Intake:

 

[SomptingGuy]

Less of the handwaving. Does anyone have PV diagrams for the valvetronic system? Or PMEP figures?

 

[crysta1c1ear]

More handwaving below!

http://www.erc.wisc.edu/Symosium_and_meetings/2005_Symposium/June 8 PM/Whitaker_Ricardo.pdf

has some figures for PMEPs on the last page, showing what is possible eliminating the throttle and controlling the valves. Unfortunately they show dual variable cam phasing (rather than intake only) and don't show the base figures for comparison.

From Mitsubishi Motors Technical Review 2005 No. 17.

http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2005/17e.pdf

MMC’s GDI technology was hailed
inside and outside Japan as the ultimate means of overcoming
the inherent shortcomings of gasoline engines.
The higher thermal efficiency yielded by GDI technology
prompted some observers to comment that there
was no longer any need for passenger-car diesel
engines; it triggered the subsequent advance from indirect-
injection diesel engines (the type of engine that had
been prevalent in diesel passenger cars) to direct-injection
diesel engines. Diesel engines have since shown
great advances in power, thermal efficiency, and emissions
performance owing to high-pressure direct injection
(made possible by electronically controlled common-
rail fuel-injection technology) and to high boost
pressure (made possible by advanced turbochargers).
In fact, the most important advantage of gasoline
engines, namely the ease with which load control can
be effected using throttle valves, has come to be seen
as less of an advantage since the pumping losses
caused by throttle valves are hindering improvements
in gasoline engines’ thermal efficiency. To remedy this
situation, it is urgently important to eliminate the factor
that is hindering improvements in gasoline engines’
thermal efficiency. In other words, gasoline-engine
developers are likely to pursue higher thermal efficien-
cy using throttle-valve-less designs while seeking further
improvements in gasoline engines’ inherently high
power density.

(My highlighting.)

 

[cleverlever]

In the 1980's I designed 7 intake valve throttled engines for Gm,Ford and Chrysler.

My conclusion was its a great thing in a laboratory but isn't practical in mainstream cars. 1st its dificult to have all valve events the same at all operating conditions.

Secondly IVT is great for light load but it imposes lots of detonation problems at heavy load because you can't get rid of the fast burn.

After 10 years and 500 thousand dollars of research I concluded the best implementation of variable valve timing was via patent 4,961,406.

In my opinion the engine of the future is basically using an early close atkinson cycle at heavy load and a late close atkinson cycle at light load.

The big advantage of the early close atkinson engine at heavy load is it has a cooler intake charge which alows a higher bmep without incurring detonation.

The cost to implement this control strategy is minimal considering most new engines have VVT technology

 

[rdd48856]

Fiat is developing a new throttless engine with the intake valves electronically controlled. It will begin its production next year. Something changed between 1980 and 2006: electronics.

 

[dgallup]

Valeo has camless engines with electro-magnetic actuators running around in Peugeot 406 cars. They claim 20% reduction in fuel consumption & emissions along with 20% increase in low end torque. The system allows for infinitely variable valve timing along with independant cylinder deactivation. They have reportedly made great progress in quieting the electromagnets and providing a soft landing for the valves in their seats. Optimistically, production is 3 years away.

 

[Hybridinstructor]

In response to the idea that the atkinson engine is the solution for anything is, with all due respect, a stretch. Inherit problems with engine life with units larger than 2000cc have plagued the design. The best way to increase volumetic efficiency, in a practical way was done with Honda's IMA (I do not work for nor ever have worked for Honda). Honda changed the valve angles in the cylinders, created a vortex intake with the use of a computer designed "bump" in the intake port to allow for an extremely lean mixture that would cause backfiring in any other design. The engine runs cool, lean and meets SULEV standards, something that the atkinson miller engine, thus far, has not. Is it any wonder that Toyota is moving away from that engine as it builds its Lexus hybrid?

 

[globi5]

The atkinson engine reduces maximum power output. It's a compromise between power and efficiency. Apparently Toyota didn't want to make a power compromise with the Lexus hybrid.
The 2007 Camry hybrid again has an atkinson cycle engine:

http://www.greencarcongress.com/2006/01/toyota_rolls_ou.html

Also I don't see why lean mixture and atkinson cycle can't be combined.
Once they start to introduce electric superchargers such as these:

http://www.turbos.bwauto.com/en/products/ebooster.asp

atkinson/miller cycle engines might become more popular, since there will be less of a power reduction.

 

[Marquis]

A restriction is NOT just a restriction, the closer you retrict to the engine you end up cutting your pumping work on the PV diagram on the bottom loop. This isn't connected to the Atkinson cycle. Even a port throttled engine has a part load fuel economy benefit relative to a normal butterfly throttled engine- obviously the more throttled the typical condition you run at the more saving you can have. Hence bigger engines have the potential to save the most.
Restricting performance via valve timing rather than throttling is even better.

For the doubters, short of running an engine with czyl pressure tapping, simply utilise a simulation package such as GT power or Ricardo Wave and do a comparison