Awl --
There was a brief ad campaign in NYC, to the effect that letting your car idle more than **10 secs** wastes gas.
Iow, the "cost" of restarting your car is equivalent to only about 10 secs worth of gas.
NYC has pretty strict idling laws, which, iirc, limit the legal idling to 3 minutes. I guess that could be whittled down to 30 sec!
fwiw.
One of my cars' engine shuts off instead of idling. It will kick back on whenever it is needed. It's pretty slick.
PV & SD:
Well that's interesting. Just playing devils advocate here, but how much gas would you have to save to pay for the labor & parts on a possible early starter motor and/or flywheel ring gear change out? I suppose the smaller the engine the less ring gear wear, but even small engines would have small starter motors.
It's a pretty common feature. I recall a Porsche 924 that did that back around 1980. I suspect the modern systems leave the engine oriented so it injects fuel and fires a plug as soon as the starter tooth contacts the flywheel, making it a low-impact event.
Hybrid I presume? Full of all those toxic chemicals in that there giganto battery? also probably a newer model that cost a whole bunch to produce from recycled materials that could have gone to better use? Maybe a lot of fresh, raw materials too?
I'm no fan of new cars in almost all circumstances as the energy needed to produce a new car is so high that it strips away all savings for a long time to come... An older, efficient smaller car is almost always a better bet financially and environmentally. The inherent issues with hybrids or battery powered vehicles make them even less attractive until the costs come way down and the technology catches up so that other fuels that are much more efficient can be used.
I'll stick with my fuel efficient and reliable 1997 Nissan for now and take the motorcycle when I can. I'm even considering stipping ALL non-essential items off the Sentra to make it super light weight. Ya never know what type of mileage I might be able to get. :)
Just my $0.02
...And almost on-topic considering the manufacturing techniques and materials slant... Sorry for the OT reply but someone has to pull this anti-logic environmental bus over and give it a ticket sooner or later.
Regards, Joe Agro, Jr. (800) 871-5022
01.908.542.0244 Automatic / Pneumatic Drills:
My Honda Civic has a "Brand New" starter motor, ie. it has never been used in the life of the car. The integrated assist motor is used to start the engine directly, as it is part of the flywheel. It is silent and just about instantaneous. The 150 V battery doesn't have to strain to crank the engine, either.
The 12 V cranking motor is only used if it is so cold the hybrid battery would be harmed by cranking the engine (never gets that cold in MO) or if you need to jump-start the car after killing both batteries. It is also a backup if there is a major malfunction in the hybrid drive system.
The Honda Civic Hybrid, once warmed up, generally shuts the engine off while coasting to a stop at about 9 MPH. If you confuse it by pulsing the brakes, it will shut off after idling for 5 seconds. It also cuts off fuel flow and closes all engine valves to allow a minimum-drag coast anytime you take your foot completely off the gas pedal. It coasts remarkably well in that mode.
Jon
I think you mean "opens all engine valves", as closing them would provide maximum compression braking effect.
Yeah, a hybrid. Don't blame me, it was my wife's idea. I'm with you, I usually drive an old camry that gets 30 mpg and cost me a whopping $1200 several years ago.
No, the cars that do that today have flywheel (direct drive) starters that are also Generators and are called Hybrids. Mild hybrid does not do any electric drive - just shut off and restart instead of idle.
No, closing the valves is correct. The cyl compresses the air, which then pushes the piston back down like a spring. VERY efficient.
Can't be that efficient. You'll be lucky if you break even. Laws of thermo. Which are:
But the point is well taken, that valves open or closed should in principle be the same.
However, when they were experimenting with "variable cylinder cars", iirc the trick was to leave the valves open, for non-compression.
While some of the hybrids get very, very little from the electric side, I don't think I've seen any that just use automatic engine stop/start and call it a hybrid drive. Which ones are you thinking of?
I think the Cadillac 8-6-4-0 did that, but the Chrysler 5.7 leaves them closed (is the 5.7 an interference engine? I don't know... if so, you can't leave them open!).
The MOST efficient way to turn an engine when not running.is with all valves closed. Much more efficient than with the valves open as it eliminates virtually all the pumping losses.
Open any one valve and it becomes a brake.
wrote: (clip) Open any one valve and it becomes a brake. ^^^^^^^^^^^^^^^^^^ Yep. That's how the compression release worked on my old Yamaha enduro, and, I believe, on those big trucks you hear decelerating by releasing compression.
That's just downshifting/engine braking. They're not messing with valves, afaik.
As far opening just one valve (presumably the exhaust valve), the piston would just be fanning a little air, no real pumping losses. I can't imagine those losses being greater than spring/friction losses with a closed valve system.
Not to mention the greater wear and tear of a system under pressure.
But they are, PV:
--Winston
That's what I thought, too, but Honda's video explaining the scheme shows that the valves are all made to close and stay that way. With the valves closed, the pistons just go up and down, compressing and expanding the same volume of air. There is a tiny bit of adiabatic loss that way, but less than dragging air in and out of the cylinders. As long as the engine is above 1000 RPM, there's really a VERY minimal braking effect.
Big trucks have engine brakes that change the valve timing to maximize pumping loss. Obviously the valves are open at some part of the stroke to cause that huge trumpeting noise.
Jon
Well, it really does work. First, you can feel the car coasting very well, even coasting pretty good up a slight hill. Also, I get 52 - 56 MPG tooling around town, WITH the air conditioning on.
Jon
The federal highway law of 1986 required all trucks over 12000 Lbs to have a "retarder". Fire trucks use electric retarders (faraday brakes) as they can be disabled by pulling a breaker and it should be totally impossible for a bad electric retarder to disable the truck.
Almost all other large trucks use "pneumatic" retarders. Activating the retarder causes the intake and compression strokes to happen normally, but then the exhaust valves are opened at the peak of compression. One system is the Jacobs brake, sometimes called a "Jake brake" that uses an extra lobe on the camshaft to trip the exhaust valve.
These devices have been built integrally into the engines of large trucks for some years. The federal law was due to a LOT of semi operators disconnecting the front brakes to be sure to have steering control in hard braking, and the rapid wear of brakes (usually replaced every 10K miles!) The retarders don't wear anything out, so the truckers and owners love them.
Jon
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