Start-stop technology is at the low end of the electrification scheme, which begins with the start-stop micro-hybrid, and moves up through hybrids, plug-in hybrids, and pure electric cars. With each step in the electrification curve, CO2 emissions are reduced. (Source: Continental Automotive)
A warm engine probably starts up in half a rotation. A computer could detect the duty cycle and keep the engine running occasionally to keep things charged up during short "stuck in traffic" cycles. The AC could be electric driven to keep things constantly cool in the cabin. I think this would save a lot of gas, especially at long traffic light cycles. I don't know how a trasmission would react to a free-wheeling engine going downhill, unless, of course, it is designed for that.
The stop/start requirement is, in my humble opinion, a complete misallocation of scarce resources. (time, money, manpower)
The cost-benefit of stop/start is not clear, and it does not solve a fundamental engineering problem. ( it does help to passify meddlesome legislator busybodies who have somehow come to believe that they have the rightful power to regulate fuel economy in privately-owned vehicles...but I digress ) Were it not for CAFE standards, would there be a real market-driven demand for stop start?
As if $1200 up-front cost vs $300 per year fuel savings (or $220 over five years in the case of the Fusion) weren't paltry and underwhelming enough, I'm not sure that all of the associated costs have been accounted for.
In addition to the improved/enhanced systems necessary to directly support the stop/start functionality, there are also peripherial costs in otherwise unrelated sub-systems. The electrical profile (rapid dips below the nominal operating voltage range) during a stop/start cycle imposes even more strict performance requirements on subsystems (especially subsystems related to safety). The existing range of input voltages is already wide, imposing much additional system cost that would not be otherwise necessary, but the stop/start profile demands far-and-above more sophisticated power regulation on each sub-system level. (i.e. ICs requiring memory to function properly cannot lose that memory... brake lights cannot be allowed to flicker, air-bag control units must remain fully operational...etc) Beyond safety, many other subsystems (radio, GPS, IP cluster...etc) will be desired to not skip any beats during the stop/start cycle. All of these subsystems need more sophistry (or reduced nominal electrical efficiency) to function normally during the stop/start cycle, and these "improvements" act like a hot poker straight up into the backside of Mr. System Cost. (i.e. system cost jumps)
In addition to the actual systems costs, there is a developmental cost associated with this whole task, up and down the food-chain, where legions of engineerrs are spending their precious time addressing a problem that isn't really a problem. Of course, there are also opportunity costs....what real and market-driven improvements could have been made if the engineering community were not focused on solving an artificial and politically driven "problem"?
But, it's good for the starter and battery makers, eh? Surely, the leading European adoption rate should tell the tale, given that the ECE mandate is to promote economic activity of Europe. (Contrast with NHTSA where the madate is to promote public safety)
Sadly, I don't see it going away though, and as a matter of practicality, I see redundant battery systems (like the Johnson Controls 48V system concept) as a real means to mitigate much of the sub-system costs associated with stop/start power cycle....
Chuck, this is a good incremental product change. It helps at a significant level while not requiring a whole new infrastructure. Considering that about 10% of cars are replaced each year, it is not necessary to do a wholesale change, unless a new technology comes along that really fits the bill.
I actually know people who do this manually in a bid to save gas and cut CO2.
First, it's not just the customers driving the fuel economy drive in an era of $4.00/gal. (US) gasoline, but the government. Much of this work is required to meet the 2016 CAFE standard of 34.5 mpg and the 2025 standard of 50 mpg. So economy is a requirement if you don't want the government to put you out of business.
Second, I have had several starters fail during my driving life, when the Bendix drive failed to engage the ring gear, leaving me stranded waiting for a tow truck. The reliability has probably improved since then, but I would think that electronic components are more reliable than their mechanical counterparts in most cases (EFI vs. Carburetors, or Electronic Ignition vs. Breaker Points). I will concede however, that the mechanical components offer more ways to jerry-rig a solution to get you home (whack the starter with a hammer to unstick the Bendix drive). When an electronic component does fail, however, you are often really stuck, with no choice but to to tow it to the garage for replacement.
Finally, using your example of $1200 purchase price increase vs. $300/year fuel savings, that's a four (4) year payback, so if you keep the car longer than four years , you're ahead of the game. Of course, if you don't keep the car for four years, or can't afford the upfront cost, then the payback is meaningless.
If you save 400$ a year on fuel and increase the cost of the vehicle by $1200 do not expect a round of applause from your customers. If you acheive the same saving using off-the-shelf production components you can thumb your nose at your competitors. Remember, car manufacturers earn their living by selling cars, not by saving fuel, and they fully understand that when it comes to purchase price increase versus fuel cost saving, a lot of their customers can't do the math.
By the way, I wouldn't call the Bendix drive "failure prone". It's probably less failure prone than an electric water pump.
One concern mentioned in this forum has been reliability, but I have the opposite concern, in that all of the sytems shown don't go far enough to advance the energy saving potential of this technology. All of these systems are conventional in the sense that they employ a separate gear-driven starter (Bendix Drive) with a conventional belt-driven alternator. This retains the weight of two separate components, with the failure mode of the mechanical starter drive still present. Switching to a crankshaft-driven Integrated Starter-Alternator (ISA) with electronic commutation eliminates the weight of the redundant components and the failure prone Bendix drive, while increasing alternator output. It could also interface with the engine management computer and crank position sensor to use spark ignition to restart the engine so the starter would only be used to ensure that the engine doesn't spin backwards on the re-start, reducing the load on the starter. Combined with the electric air conditioning compressor already shown, electric power steering and an electrically driven water pump, you could completely eliminate accessory drives on the front of the engine, improving underhood packaging options, increasing reliability (no more drive belts) and further reducing weight. The electric A/C compressor could also be driven in reverse to act as a heat pump, allowing you to pre-heat the interior on a cold day, without starting the engine, further reducing fuel consumption.
Why not combine this concept with GPS & mapping technology - after all, we should be able to reasonable anticipate when a driver is letting up "gas" pedal because of an upcoming intersection versus simply slowing a bit. Also, I have found by experimenting in my car that simply bumping the transmission into neutral and while coming to stops can save a bit of gas as well.
You are going to have a lot of high-current starting cycles during the day if you drive in traffic, and not a great deal of time to recharge. SO battery lifetime will be shorter compared to the 3-7 years we know now, and you will need a higher capacity (more expensive) battery to handle the starting cycles.
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