That is a really good question that goes beyond stalled cars in traffic. I have an Audi Q5 Hybrid - a well engineerd car, but I do worry about the long term efffects of the temperature excursions that must occur within a hot engine, as well as the additional wear that I would think is associated with increased engine rotations without the lubrications system running (i.e, engine lubrication is at its lowest during start cycles since the oil pump is only minimally operating).
The compute power deployed in hybrids seems to be capable of deciding when to implement start-stop, and when not to (which my Audi appears to do). Are all cars using the start-stop technology going to employ the same sophisticated algorithms that the hybrids use?
I don't think that technology is the issue here, it is a matter of whether or not it is cost effective to employ that technology on an "inexpensive" start-stop system. I really love my new hybrid, and have to trust that the engineers at Audi have thought everything through, but it has not withstood the ultimate test of time yet.
As I imagine we have all experienced - engineers don't always have the final say in the design that is ultimately produced. Final designs are usually a compromise involving cost (understandably so).
Engineers need to keep asking the hard questions so that we end up with the best products possible for the dollar.
Another bunch of good questions here. In particular, I wonder about the software algorithms. My guess would be that the engine control algorithms can be tweaked to help deal with wear issues, especially by the automakers who are also building hybrids and already have the intellectual property. To be sure, we'll talk to the suppliers.
This is a good question. I don't believe there would be a problem with traffic stalls, Rob, since the engine is warmed up and the starters are designed for 250,000 to 500,000 starts. It's not as if the engine is being started cold every time, but this is a question that I need to discuss with some of the suppliers.
As mentioned in previous comments, there are a lot of complexities behin the correct and longterm handling of Start-Stop technologies. Beside a reliable starter and sophisticated algorithms, the lubrication is critcal.
Hot engine (hot spots are not dissipate properly when the oil is not circulating) and lack of lubrication during start-stop transient phase have an impact on engine wear and have to be taken into account when developing engines.
For exemple, we are working extensively on turbochargers by measuring in real-time the shaft and bearings wear but also oil consumption of the turbocharger only. At the same time, we are simulating Start-Stop conditions and we have interessant results.
I am very confused. This is standard technology on all modern diesel and petrol cars in Europe. In the pub my friends boast about mpg when they used to talk about horsepower. BMW 3 series will do 67mpg on a long run and average 47 around town. The stop/start is a bit weird at first but not a problem. I just don't understand the fuss.
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.
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.
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.
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.
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....
There's one more step to add to your concept, R. An integrated alternator/starter could easily be used to add regenerative braking (to use those famous last words, "It's only software")! That would likely be even more of a contributor to overall efficiency than the "start-stop" function. Obviously, that would work best combined with a "mild hybrid" configuration, but even in a pure ICE vehicle, putting the vehicle momentum "back into the battery" would provide most if not all of the energy needed to restart.
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.
Gas-powered golf carts have been using this technology for decades. Step on the gas pedal and the engine immediately starts to drive you to the next hole. Let up on it and the engine stops. I always wondered why this never propogated to cars.
I used to laugh at the thought of a car starting and stoping with each traffic stop. I laughed until I was in a car that did that. I thought it was fascinating! It got me thinking of all the considerations for such a thing- airconditioning, lights, radio, and restarting, to name a few. Someone has been thinking! I am sold.
I hope it was an engineer that came up with this and not a high school student... Vanity rules!
I just drove a start-stop Focus all over western Germany and Belgium for 2 weeks. I'm not the type who sits in city traffic waiting for lights to change; I drive in the country and stop for a few seconds at a roundabout or stop sign. I found myself keeping the clutch down just to keep it from "stalling". Since it was a diesel, I'm not sure if the potential savings were worth the annoyance or wear on the engine. (Diesels idle with less fuel, and take more power to start.) If I drove city traffic all the time, I'd get an electric.
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.
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.
I'm sure the engineers considering design concepts relative to start-stop have on their "to-do" list testing for MTBF (mean time between failure) and MTTF (mean time to failure). It is probably obvious to everyone that there will be considerable stress added to components as a result of the technology. I do not see how existing equipment can survive without redesign. The concept is certainly viable but the execution might be significantly tricky. In the appliance business the "bean - counters" run the show and cost reduction rules the day and frequently trumps sound engineering. Let's hope the automakers see things differently.
I don't understand the thinking behind start-stop. I did a Mythbusters study a few years ago for our local ASME chapter. We used the onboard fuel usage indicator to get an idea of the amount of fuel used by an idling engine compared to stopping it and starting it.
The study results used to be on line through our local chapter web site but got lost during the last update. It was published in ASME magazine.
The results indicated that an idling car, even with A/C going full blast on a hot day, did not use that much fuel. Even with 25 stoplights of 30 seconds or more, the change in fuel mileage would be less than 1 mpg. Compared to the savings of hybrid storing braking energy and applying it to acceleration or going up hill, it just didn't seem like it was worth the extra strain on the starter and lack of AC at idle.
If you don't believe me, try shutting the engine down, shifting to neutral, and restarting at each stoplight on your way home for a week and comparing your mileage with a normal week. You probably won't be able to discern any difference.
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