Doesn't the engine just inject some fuel and spark into the cylinder that is in that stroke, causing the engine to rotate, putting other cylinders in that position and starting the engine without the starter?
Doesn't the engine just inject some fuel and spark into the cylinder that is in that stroke, causing the engine to rotate, putting other cylinders in that position and starting the engine without the starter?
Kramer wrote: Doesn't the engine just inject some fuel and spark into the cylinder that is in that stroke, causing the engine to rotate, putting other cylinders in that position and starting the engine without the starter?
Not yet. Still uses a motor to turn the engine over.
Kramer wrote: Doesn't the engine just inject some fuel and spark into the cylinder that is in that stroke, causing the engine to rotate, putting other cylinders in that position and starting the engine without the starter?
Mazda had a system to do that, but I dunno if they ever shipped it.
Hmmm. Just wondering what happens on a 100* day in stop and go traffic. No engine - no a/c. Maybe it's the luddite in me - I don't like the thought of my car deciding when it should run or not.
In reply to oldtin:
It will still start-stop. But it uses the input from the a/c system to see if the compressor needs to pump or not. There's enough stored energy in the system to give you nice cool air without the pump for a while.
oldtin wrote: Hmmm. Just wondering what happens on a 100* day in stop and go traffic. No engine - no a/c. Maybe it's the luddite in me - I don't like the thought of my car deciding when it should run or not.
Yeah, like I said in my post, it will keep the engine running if the A/C or the heat is engaged or needs to run.
Its really very seemless thanks to modern ECU tuning and direct injection. Push the clutch and by the time I've got it in 1st, its already running and ready to go.
I'm not a fan of the system on my company car, a '15 Chevy Malibu. It works okay, but it's definitely not seamless. Stops and starts vary, from smooth to abrupt and jarring. I've gotten used to it, but it surprises passengers. Some even thought that a car bumped us. The system most definitely affects the A/C. Not only does the air heat up quickly, but the fan speed automatically drops significantly when the engine turns off. It then turns on shortly thereafter, almost why bother. Fiddling with the fan or temp knobs will kick the engine back on. It's downright stupid when parking. Pull into a spot, stop the car, and the engine stops. E36 M3 to park, and the engine starts as the shifter passes through reverse.
I can't see much benefit with this system on this car. It has a huge battery, plus another smaller one in the trunk. The time actually spent off is very short, it mostly just turns off and on over and over again. I'd bet the real world benefit is small, a least for my use, and it's more of a trick to lower emissions and raise fuel economy test scores.
In reply to Boost_Crazy:
That was my take-away after renting a Chevy Impala…there’s got to be a threshold of stop time below which cycling the engine is counterproductive. Of course, the definition of counterproductive could be limited to only considering the environmental impact or it could be expanded to include operational cost, user experience, safety, etc..
Even if we only consider the environmental impact, I really can’t imagine a net benefit being achieved for stops of less than a couple of seconds and as I indicated in my original post, the Impala seemed to shut off pretty much the instant I stopped.
Question for the Hive…what percent power does an engine draw during idle???
I’m going to guess it’s ~3.0%. If so, a 250 Hp. engine requires ~7.5 Hp. to sustain itself at idle. I think typical modern automotive engines have BSFC’s (Best Specific Fuel Consumption) of around 0.47 as measured by pounds of fuel consumed per hour per horse power so that’s ~3.525 pounds per hour or ~.588 gallons per hour.
Anecdotally, I did a business trip to Atlanta recently and one of my co-workers mentioned that he had gotten so distracted unloading stuff from his rental car that he wound up leaving it running the entire day. Nine+ hours later when he returned to his rental car and discovered his mistake, he noticed that the fuel gage still showed ¾ full.
Anyway, if my idle consumption estimate is reasonably accurate, and assuming no energy is lost getting the engine back up to speed or that any additional parts ever need to be replaced (both ridiculous assumptions IMHO) increasing the shut off wait time from zero seconds to two seconds would get you ~3,060 avoided shut-offs per gallon.
Come on, nobody in their right mind would be willing to cycle their engine 3,000 times in exchange for a gallon of gas and yet that’s essentially what we’re talking about in the case of systems that immediately shut off.
In reply to RX Reven':
I find it amusing you think minnesota weather is 'harsh' for 10.5 months. Alaska might have been a better comparison.
1kris06 wrote: In reply to RX Reven': I find it amusing you think minnesota weather is 'harsh' for 10.5 months. Alaska might have been a better comparison.
It was a playful little jab…I’m a California lifer but I’ve made at least 30 trips to the fine state of Minnesota resulting in about 4.5 months of evenly distributed experience with their weather.
In reply to RX Reven':
So you know, 7.5hp is WAY high for idle. Technically, it's zero brake HP... 
And 7.5 hp will probably propel that Chevy ~50mph.
On the other hand, your idle time is too short. Lots of people live near lights, where the nominal red light is about 30 seconds. And your brake spec fuel consumption is generous. It's quite a bit worse than that at idle. For some reason, the "base spark of 10 deg" is still going strong, even when MBT is closer to 40-50deg BTDC- so there's a HUGE loss of thermal efficiency. Kinda dumb that the solution isn't to run the engine more efficiently, but to just turn it off.... (probably because controlling air to that low amount is really hard)
While I can't give you numbers, the benefit is measureable, pretty clearly.
(again, I'm no fan of it, either)
it's not even fuel economy. It's the carbon "footprint", yes you may only use a gallon of fuel on a 4 banger idling all day, but it is still breathing in all that air and putting out pollution.
In reply to alfadriver:
Having recently experimented with my Insight (with a smaller frontal area) there is no way 7.5hp is pushing you through the air at 50mph. Air is thick and heavy and hard to move.
As to the start stop, they're clearly built with the test cycles in mind, and they clearly work in that environment. You're likely to see more systems that shut the car off completely as it coasts and uses a bigger battery than usual to pick up the slack when acceleration resumes. Cars are heavy, you can build the starter into the transmission like Honda's IMA system, add some extra battery, and nobody will even notice, but you can gain a couple extra MPG which is a big deal.
In reply to alfadriver:
Good point on the BSFC being far worse at idle…that occurred to me but I had no clue what its value was so I just plugged in the number I had. So, if we aggressively try to make the best case for the system by assuming the BSFC is twice an engine’s optimal value at idle (0.94), we’ll still have to cycle the engine 1,500 times to save one gallon of gas; horrible deal.
In terms of your comment about 30 second stop lights, I’m far more receptive to that situation creating a net positive…I’m not suggesting the system has no merit, I’m only saying they should provide a wait time of a few seconds to avoid shutting down when you’re just doing a touch-n-go at a stop sign, transitioning between forward and reverse, stuff like that.
I don’t want to get all tinfoil hatie but I can’t help but suspect there’s more to the system’s design than straight, honest engineering...the math is screaming “horrible deal” so loudly than even if my initial assumptions are off by an entire order of magnitude, it still doesn’t make sense to not wait a couple of seconds.
In reply to mazdeuce:
50mph on a flat road isn't much. Really.
In reply to alfadriver:
My real world experience with my Chevy, I don't think I've ever seen it stop for 30 seconds. Even when stopped at a red light, the car restarts well before it turns green. Either due to the A/C, heater, or traffic creep, real world stops are very short for me. I'll pay more attention tomorrow. I'll compare normal driving with trying to get it to stay stopped.
In reply to RX Reven':
I had to pretty much turn off my mechanical empathy with this car. It helps that it is a leased company car appliance. If it were mine, I would have found a way to defeat the system. There are times when the car turns off and on so suddenly- it's restarting before the engine has even fully stopped, and it doesn't feel conducive to a long life. The auto stop also functions well before the car is fully warmed up. I'm also in CA, but it gets pretty cold for a few days in the winter. Maybe engines, or at least newer engines, are a lot more tolerant than I thought. Or maybe GM doesn't care as long as it meets CAFE standards and makes it through warranty. Or maybe both.
I'm kind of curious how they respond to a stall or a money shift.
Until this thread, I had no idea this stuff was in manual transmission vehicles. I just thought it was something in the penalty box cars that might help average company emissions for the big power vehicles they produce.
It still seems somewhat pointless and possibly problematic in long term maintenance to me though. Like the cars that "shutdown" cylinders during certain driving conditions.
In reply to mazdeuce:
My understanding is that newer cars already shut off fuel under certain conditions when coasting. Rather than shut down the engine they let the cars momumentum keep it spinning and just turn the fuel back on when needed.
RX Reven' wrote:1kris06 wrote: In reply to RX Reven': I find it amusing you think minnesota weather is 'harsh' for 10.5 months. Alaska might have been a better comparison.It was a playful little jab…I’m a California lifer but I’ve made at least 30 trips to the fine state of Minnesota resulting in about 4.5 months of evenly distributed experience with their weather.
Yeah, 10.5 months is a bit of an exaggeration. The last winter I lived in MN, it snowed three different times in May, so it was only like 7.5 months of freezing. I am here for work this week and it is in the 30's, but at least the ice is gone and the grass is green.
mad_machine wrote: I like it. I personally do it manually at some of the longer lights around here. I do not see the need to sit at a light for two minutes with the engine running
You like to live dangerously shutting of a River in traffic.
jstand wrote: In reply to mazdeuce: My understanding is that newer cars already shut off fuel under certain conditions when coasting. Rather than shut down the engine they let the cars momumentum keep it spinning and just turn the fuel back on when needed.
Megasquirt calls that "Overrun", and can cut fuel when you're off the throttle over a certain RPM, but I don't know how people who do it for a living actually do it. I do know that in the Ford van I had, if you were in regular old "Drive", it would continue to feed the engine when coasting. If you had O/D turned off, it would cut fuel. I presume that it was because they assumed you were towing and would want the extra engine braking effect going down a hill.
Boost_Crazy wrote: In reply to alfadriver: My real world experience with my Chevy, I don't think I've ever seen it stop for 30 seconds. Even when stopped at a red light, the car restarts well before it turns green. Either due to the A/C, heater, or traffic creep, real world stops are very short for me. I'll pay more attention tomorrow. I'll compare normal driving with trying to get it to stay stopped.
Traffic lights do tend to be about 30 seconds. If someone decides to creep at that point, well, can't do anything about that. And many times in the country, AC isn't needed- for instance, now in Michigan. So just yesterday, I was able to have a solid 30 seconds of off time waiting patiently at a light. YMMV, but there's a good instance of being able to take advantage of it.
jstand wrote: In reply to mazdeuce: My understanding is that newer cars already shut off fuel under certain conditions when coasting. Rather than shut down the engine they let the cars momumentum keep it spinning and just turn the fuel back on when needed.
That's been going on for decades. Heck, my '73 GTV had that feature on the mechanical injection.
It is more aggressive, now.
T.J. wrote:RX Reven' wrote:Yeah, 10.5 months is a bit of an exaggeration. The last winter I lived in MN, it snowed three different times in May, so it was only like 7.5 months of freezing. I am here for work this week and it is in the 30's, but at least the ice is gone and the grass is green.1kris06 wrote: In reply to RX Reven': I find it amusing you think minnesota weather is 'harsh' for 10.5 months. Alaska might have been a better comparison.It was a playful little jab…I’m a California lifer but I’ve made at least 30 trips to the fine state of Minnesota resulting in about 4.5 months of evenly distributed experience with their weather.
Hell, it flurried last night and it's 'supposed' to snow today and monday.
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