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Ken H.

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I was reading an article this morning on the bus about advancements in fuel efficiency technology, and one of them mentioned was the auto-shutoff and restart of gasoline engines while stopped (at a traffic light or whatever). Well now of course this has been used for awhile in various forms, but I thought Mazda’s latest method of doing it was, uh, “interesting” to say the least. Certainly creative at any rate:

 

When the engine decides it’s appropriate to shut down it ‘parks’ the engine so most of the pistons are at or near mid-stroke. It does by stopping engine rotation at a specific point with the alternator. In effect using it as an electric brake. When the engine is to restart, it fires the sparkplug of the cylinder that is in its up compression stroke. This causes piston to travel down (fuel/air mixture is already present from before shut down) and the crank to rotate the wrong direction. At the same time one of the other cylinders that was (prior to the shut down) in its down power stroke is now moving upward; compressing. So it then injects a bit of fuel into that cylinder and fires its plug at TDC. Which changes the reverse rotation direction to the correct one; and away you go! And because both these firings, first wrong way then correct way, are ‘soft’ partial compression & fuel/air mixture strokes; the pickup is much smoother and seamless that the more traditional way of turning over the engine via the starter or (in the case of a hybrid) with the electric motor to affect a restart.

 

Ingenious!

 

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The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

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The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

:rofl: Been there, done that, with my 1951 Matchless 80 :grin:

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I have hear that Volvo is also squeezing every bit of energy out of a gallon of gas. Electric power-steering, alernators that disengage, etc. I only worry about the maintenance bills.

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The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

 

I was sitting here at work, and a light went off on my desk because someone typed "BSA 441 Victor". Been there done that too, and my knee hurts just thinking about it.

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The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

 

My Bultaco had a similar trait, except that it would actually run backwards.

 

Of course, there was no way to know this before you chucked it into gear & dropped the clutch. :dopeslap:

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Sorry, Ken, for the 100% hijack of your high technology in cars thread, switching it to kick-starting pre-historic motocycles. Not really related. I always wonder how long a gas engine has to be stopped to make it efficient in relation of the energy used to restart it. The old rule with motorcycles was that you have to ride it a half hour just to recharge the battery after a start.

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That's VERY creative, really cool idea.

 

But it makes me wonder... How on earth there is enough O2 left in that cylinder that was stopped on power stroke to still ignite that squirt of gas that gets the engine to run.

Sometimes it seems tough to get engines running even with "fresh" load of air + fuel straight from a carburetor.

 

--

Mikko

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The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

:rofl: Been there, done that, with my 1951 Matchless 80 :grin:

 

I need to remember to empty my oral cavity of all liquids before reading this shite. :P

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Lone_RT_rider
The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

:rofl: Been there, done that, with my 1951 Matchless 80 :grin:

 

My 1973 Harley Sprint did the same thing....my leg still feels the pain.... :eek:

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That's VERY creative, really cool idea.

 

But it makes me wonder... How on earth there is enough O2 left in that cylinder that was stopped on power stroke to still ignite that squirt of gas that gets the engine to run.

Yes, I was kind of pondering that myself. I guess incomplete combustion of that charge still leaves enough O2 in it for another ignition. Plus it's being re-compressed so maybe that helps it light off. Probably why they call that a 'soft power stroke'. Under no load it wouldn't take much to power the upward traveling piston back down again I suppose.

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Joe Frickin' Friday
That's VERY creative, really cool idea.

 

But it makes me wonder... How on earth there is enough O2 left in that cylinder that was stopped on power stroke to still ignite that squirt of gas that gets the engine to run.

 

If the spark never fires, then the engine has coasted into its power stroke without combustion taking place, so you've got a viable unburned mixture in there ready to go. In fact, it's surprising to me that they even need to inject any more fuel.

 

Frankly that would have to be the case; I doubt the alternator could stall the engine in the middle of a real power stroke, since there's a LOT of instantaneous torque right there if combustion has taken place.

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Frankly that would have to be the case; I doubt the alternator could stall the engine in the middle of a real power stroke, since there's a LOT of instantaneous torque right there if combustion has taken place.

But isn't one of the cylinders always going to be in the power stroke when the alternator stalls, parks it?

 

It might be a timing of events sort of a deal... When shutdown is to happen it doesn’t just instantaneously stall. Rather spark (and fuel?) is shut down first then it coast to a near stop (of revolving) then the alternator makes the final stop in the correct position. Speculating mostly…

 

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Joe Frickin' Friday
If the spark never fires, then the engine has coasted into its power stroke without combustion taking place, so you've got a viable unburned mixture in there ready to go. In fact, it's surprising to me that they even need to inject any more fuel.

 

OK, now I understand: this is intended for direct-injection gasoline engines, not port-injected engines:

 

Mazda's Smart Idle Stop System

 

A video is acccessible from that link. The fact that it's direct injection explains why they need to inject fuel just before startup - because the cylinder will be filled with fresh air, rather than unburned mixture, from the previous shutdown.

 

 

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The BSA 441 Victor had a similar system. You would kick down on the lever and it would fire well BTDC, creating a backfire that would catapult you up above the handlebars (to which you must tightly cling). Then, as gravity won the battle and brought you back down to earth, your foot would land on the kickstarter with much greater force, advancing the piston to a TDC or barely BTDC position as ignition would occur, and your bike would start.

 

See, nothing is really new. :grin:

I had a Victor and a Shooting Star (bigger fiberglass plastic tank and more street oriented). I was never afraid that it might be stolen as that person would either be tossed to the ground or have their foot broken. Those bikes convinced me to wear proper footwear.

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If the spark never fires, then the engine has coasted into its power stroke without combustion taking place, so you've got a viable unburned mixture in there ready to go. In fact, it's surprising to me that they even need to inject any more fuel.

 

OK, now I understand: this is intended for direct-injection gasoline engines, not port-injected engines:

 

Mazda's Smart Idle Stop System

 

A video is acccessible from that link. The fact that it's direct injection explains why they need to inject fuel just before startup - because the cylinder will be filled with fresh air, rather than unburned mixture, from the previous shutdown.

 

Exactly (he says as if he already had this figured out. . .uh-huh). Depending on the time from shutdown to restart, in a port-injected engine, that swirling mixture would have stopped swirling and the atomized droplets probably clung to one of the various metal surfaces, rendering it's combustion pretty much impossible. Furthermore, the gassification of the fuel caused by the hot metal surfaces, probably would have succeeded in reducing the amount of O2 down to a level where ignition might not be possible as well. With D/I, the cylinder is clean of all but a whisper of the previous combustion, filled with fresh air, and ready for fuel to be injected prior to a spark sending the crank back the other way.
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I bought a brand new 1968 BSA scrambler upon return from Viet Nam. Best I can recall, I pushed on kickstart till it was on compression and then jumped on it.

 

Does VVT come into play on the Mazda? Has someone already emailed this link to GM, sorry bad joke.

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russell_bynum
If the spark never fires, then the engine has coasted into its power stroke without combustion taking place, so you've got a viable unburned mixture in there ready to go. In fact, it's surprising to me that they even need to inject any more fuel.

 

OK, now I understand: this is intended for direct-injection gasoline engines, not port-injected engines:

 

Mazda's Smart Idle Stop System

 

A video is acccessible from that link. The fact that it's direct injection explains why they need to inject fuel just before startup - because the cylinder will be filled with fresh air, rather than unburned mixture, from the previous shutdown.

 

Exactly (he says as if he already had this figured out. . .uh-huh). Depending on the time from shutdown to restart, in a port-injected engine, that swirling mixture would have stopped swirling and the atomized droplets probably clung to one of the various metal surfaces, rendering it's combustion pretty much impossible. Furthermore, the gassification of the fuel caused by the hot metal surfaces, probably would have succeeded in reducing the amount of O2 down to a level where ignition might not be possible as well. With D/I, the cylinder is clean of all but a whisper of the previous combustion, filled with fresh air, and ready for fuel to be injected prior to a spark sending the crank back the other way.

 

Wouldn't leakdown be a problem, though? I mean...not for really short stops, but how long before enough pressure leaks out past the rings/valves so that it doesn't work?

 

Also, my understanding is that the catalytic converters only work when they're hot. Does the cat cool enough during one of these stops to make a difference in what comes out the tailpipe? What about response time? When the light turns green and you get on the gas, how long before you're making enough power to get the clutch out and get going?

 

I like the idea of saving some $$ on fuel by not running the engine while I'm sitting at a stoplight. But with all three of our current cars, it takes a few seconds for the engine to settle down into a decent idle before you're good to go. Would this be any different?

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Joe Frickin' Friday
Wouldn't leakdown be a problem, though? I mean...not for really short stops, but how long before enough pressure leaks out past the rings/valves so that it doesn't work?

 

At idle, the throttle plate is almost closed, generating a lot of manifold vacuum; the cylinders will be at well below atmospheric pressure for most of the stroke. If stopped and held at mid-stroke, you will end up with fresh air leaking into the cylinders over time, providing plenty of air for a restart.

 

Also, my understanding is that the catalytic converters only work when they're hot. Does the cat cool enough during one of these stops to make a difference in what comes out the tailpipe? What about response time? When the light turns green and you get on the gas, how long before you're making enough power to get the clutch out and get going?

 

Shouldn't be a problem. The cat has quite a bit of mass to it, and if you've just come to a stop from cruise, then it's hotter than it would be if you sat idling for a while (higher exhaust temps under load than at idle), so I expect it can handle a fairly long sitting period without cooling off very much at all. A practical example of this is the Toyota Prius, which shuts itself down all the time, and still meets EPA emissions regs. (To be fair, the Prius gets a head-start on low total city-cycle emissions since it slashes the initial cold-start emissions via a "thermal battery", so it's possible it's spitting out slightly more on these warm-restarts than a continuously-idling vehicle.)

 

But with all three of our current cars, it takes a few seconds for the engine to settle down into a decent idle before you're good to go. Would this be any different?

 

On a port-injected engine, when fuel is injected, some of it remains atomized and suspended in the air of the intake port, and some of it adheres to the walls of the intake port, contributing to the development of a fuel film. The thickness of that fuel film varies depending on load and speed. During the intake event, part of the fuel inducted into the cylinder during the intake stroke comes from the fuel just injected, and part of it comes from that fuel film. One of the challenges of fuel management is dealing with transients: when the operator snaps open the throttle, you have to briefly overfuel to quickly build up that fuel film, and then drop back to the fueling rate required for the new load level; if you don't do this, the engine stumbles. Same thing in the opposite direction when you snap the throttle closed.

 

This is relevant because when you stop a port-injected engine, the fuel film in the intake port boils off (afterall, the port walls are nice and warm). When you try to restart a couple of minutes later, you've got an over-rich mixture in the port that may or may not burn properly (may be too rich), and then it takes a few more cycles before you've built up a decent port film again and achieved a stable idle.

 

Not so with direct-injection, which can handle transients perfectly by delivering the exact right amount of fuel into the combustion chamber to match the amount of air present; every cycle can be given a perfect A/F ratio, regardless of any transient taking place. I'd expect restarts are pretty smooth and quickly stable.

 

Having said that, the Toyota Prius restarts are pretty smooth too, and AFAIK it's a port-injected engine. Maybe restarts on most modern cars aren't so stumbly if the shutdown is only three minutes (as opposed to overnight)...

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Lets_Play_Two
Also, my understanding is that the catalytic converters only work when they're hot. Does the cat cool enough during one of these stops to make a difference in what comes out the tailpipe? What about response time? When the light turns green and you get on the gas, how long before you're making enough power to get the clutch out and get going?

 

I like the idea of saving some $$ on fuel by not running the engine while I'm sitting at a stoplight. But with all three of our current cars, it takes a few seconds for the engine to settle down into a decent idle before you're good to go. Would this be any different?

 

I have a Yukon Hybrid with about 6,000 miles on it. It is referred to as a dual mode which means it uses battery and also at times runs on 4 cylinders. It shuts down the engine at stops and also when driving under about 30 miles per hour and not under any acceleration. Although I do drive differently with it trying to maximize mpg, I have not noticed any problem with start up after sitting at a stoplight. The car switches to batteries before the car comes to a stop (i.e. below 25mph). This is a V8 and uses regular gas and I am averaging 21 mpg. On the longest trip I have taken (400 miles) I was averaging 24 mpg, but I was seldom over 75 mph.

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