Dumb question? Cylinder shutdown and fuel shutoff...
 

I have read that when you are coasting the car shuts fuel off to the cylinders and "shuts down" the four cylinders -- an improvement over the HCHI 3-cylinder shut down.

So, my dumb question is: How can they all be shut down and the engine is still turning over? I mean I see RPMs and I hear the engine, but all four cylindars are shut down? What am I missing?

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

The shutting down process refers to the fuel cut-off accompanied by the cylinder valves being left in a closed position. Closing the cylinder valves reduces the mechanical resistance on the spinning crankshaft by eliminating the pumping losses.

Now, in this situation the crankshaft still rotates but with much less friction and we consider the cylinders and their primary function to be de-activated.

Cheers;

MSantos

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

The engine "shut down" actually refers to fuel consumption.


As I understand it, the valves are closed and the fuel injectors turned off but because the wheels are still connected through the transmission to the ICE and the electric motor, they both keep spinning. No fuel is being used, but RPM is still indicated. A neat idea really. The ICE is virtually "coasting", without any drag...or very little anyway.

It's necessary to keep the ICE spinning because when you put your foot back on the accelarator, there will be a smooth transition back to power - either ICE or electric - depending on road speed.

It had me tossed at first too. I asked the same questions.

Hope this helps...or maybe someone else could explain it more eloquently than me.:)

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

Nah, that's pretty much how it works, David :)

Honda Civic Hybrid Engine Video
 

Not sure if you have seen the excellent video ?

http://world.honda.com/news/2005/4050705_b.html

It is well worth saving as a favorite for watching several times over. I think it will answer many of your questions.

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

Another thing to ponder... wouldn't it have made more sense to leave the valves open for this? With them open, there's no air compression / decompression issues. Seems that would offer less resistance per turn of the crankshaft than closing the cylinders.

Another question is just WHEN the valves close... if they close all at one time, then some pistons would likely be at the top of their stroke and (once valves close) this would create a vacuum conditon within that cylinder. Once at BDC, the piston would be sucked back up by the low pressure condition, so overall it balances out. Same on the cylinders where the piston is down when valves close... this would create a compression load as the piston rises in the closed cylinder, but after TDC, the pressure would push the piston back down. I know that overall it will balance out, but it still seems that there would have been less overall resistance with the valves OPEN. Try turning any engine by hand with the spark plugs in... and then with the plugs out... to see what I'm talking about. Much less resistance with no compression!

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

Thanks all for the replies. These are all variations on things I have read before. My question is if there is no fuel going to the engine how can I still hear it running?

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

The thing is...what you are hearing is the engine turning over...mechanically but without power. Because the HCH-II is such a quiet motor, it's hard to tell when it's actually running anyway! Look at the FE guage to confirm.

Re: Dumb question? Cylinder shutdown and fuel shutoff...
 

From what I've read, closing the valves eliminates pumping losses (air having to be pulled in and pumped out of the motor), which in turn gives a ~10% increase to the charging capabilities of the electric motor.