In addition to a heavy-duty starter, start-stop systems require such components as enhanced engine control, battery management, DC/DC converters, and more robust crankshaft sensors.
(Source: Robert Bosch LLC)
Start-stop can be even more efficient and more convenient without the stupid programmed engine controller to make all the wrong decisions. The big challenge is the means to disengage the engine so that the vehicle can coast. The alternator that doubles as a cranking motor is the part that will need some work, mostly to assure a quickly sequenced crand-spark-fuel on sequence at each startup. The regular flywheel engaging starter would wear out way to soon, so it is not a good choice, I don't think.
I have driven a regular car with auto trans in the start-stop mode, manually, and the improvement in economy can be close to 30% with some practice. Just add a hydraulic booster for the brakes, and an accumulator for steering and brakes, and that solves that problem. Auto restart for the engine when the accumulator runs low, and no loss problems. The big deal items are the quick clutch and the direct drive starter. Add a simple sequencer for restarts and manual control is the very best choice ever.
My bus has hydraulic assisted brakes (Hydro-boost), it works off the power steering pump, if the ps hydraulic pressure is low there is an electric pump that provides the boost. It wouldn't be too hard to adapt that to a smaller car.
Interesting story about battery manufacturer pressue, but I'm guessing that today the auto mfgr's will go smaller if possible to save on weight.
I have a 10 year old, first generation Honda Insight, one of the rare manual transmissions, & will address some of the design issues they put in place two generations ago.
The IC engine does not auto-stop until it warms up, and on colder days it stays running more frequently on the in-town portion of my commute. The car does have a 12 v Kettering starter, but it only engages if I run the NiMh battery pack down too low. I think it has engaged twice in 6 years. The motor/generator in the flywheel/clutch pack does the starting: I turn the key and the engine is running.
This first gen design still has traditional HVAC so when the engine stops the HVAC fan stays running but there is no water through the heat exchanger or no AC compressor run. Sometimes I will start the IC engine if it is a long wait, no big deal. I can restart whenever I want, or swtich off the auto-stop if I want.
Electric steering boost doesn't seem to put much load on the storage, and the commonly used vacuum assist brakes are good for about 3-4 stops with the IC engine off. It restarts if the vacuum goes too high. (How many times do you need to start, then stop without the engine?) This first gen does not move on electric motor alone: Honda designed an assist approach, not a parallel one.
Lots more, but in summary: the sytem is pretty flawless, no excessive wear on the Bendix, instant restarts because the egnine is up to speed right away, electric HVAC would be a big plus, as would some power in this case: a 3 cylinder 1 liter engine is not the best choice for SanFran area traffic, although the 5 speed manual helps.
My other car is getting replaced this year, probably will be a diesel or something with a stop/start, even if not a hybrid. In my daily commute I would save idling about 7 to 10 minutes, twice a day.
There is a reason for the torque converter dragging when decelerating as opposed to disengaging and letting the engine idle. Not all Auto companies have adopted it i.e. if you drive certain Chrysler products they coast freewheel style when you take your foot off the gas. If you drive a Honda (and other brands) when you let off the gas you feel the engine braking. Since the 90's Honda has shut off the fuel injectors during deceleration to save fuel, when you hit the gas again the fuel injectors turn back on. The torque converter stays connected to the engine to keep the engine turning--while it's just pumping air.
Non power brakes are not an option with disc brakes - too much pedal force is required, unlike the drum brakes of old. Some manufacturers, Daimler Benz comes to mine, have been experimenting with electric power brakes.
I think the theory on start stop has potential but some recent road tests I have seen have raised questions about the current state of the art.
The Malibu ECO (start/stop: eAssist)has been in two comparison tests against other mid-size sedans (Motor Trend and Edmunds IIRC) and has not demonstrated any mileage advantage in either case. The testers also found the system rather intrusive as I recall. The EPA estimated advantage isn't there apparently.
Over the years I have found that EPA milage ratings provide a rather poor basis for real world comparisons. Features that will do well on the govt treadmill don't always translate to an advantage on the road.
A few years ago... a vendor of mine (I am in the electronics industry) told me of the engineers he was working with at one of big American car test tracks he visits regularly (in our area).
Their focus : reduce size of battery required in cars.. saving costs on battery
The engineers told him they had worked out the details on "instant" start on their engines. These engines had most of the engine management requirements being described for Start/Stop.. but had NO starter required. Because the ECU "knew" the crank position, it could fire up the engine by directly injecting fuel into appropriate cyclinder and fire it - starting the engine from a stop. They demonstrated working units, everything was going fine .. then...
The idea was dropped.
Reason: some of the battery companies got wind of the project and threaten to charge as much for the much smaller batteries as the larger batteries... killing most of the incentive for the change.
Apparently the viewed risks of eliminating the starter (public perception) and the additional costs required of the ECU/additional sensors and valve controls at that time.. were not enough to offset the elimination of the starter.
Maybe this idea is finally seeing it' time "come"?
S/S .... I have every confidence any remaining issues will be resolved. Will it matter (be enought?) is another subject.
However, I have not seen any discussion/mention of the legal issues of implimenting it.
It is eligal in many states (mine included) to allow a car to "coast" on public roads (unless it is unavoidable - as in engine failure).Enforceablity of such a law is questionable (as is many laws).
Basically, a well meaning attempt at improving public safety, because it was viewed as a "un-safe" practice by people that were more concerned with the cost of fuel when cars / trucks had become widespread (1910-1930).. but costs were critical (during depression).
ma and pa kettle.... coming to town, with some quaint ideas on being frugle and causing some "disruption" to the town folk's traffic. Because the law (in this state) was inacted before power steering/power brakes was common place, this was the only explaination given to me that made any sense. (told to me during traffic safety class when asked on the subject - coasting via clutch disengagement)
Every state has some laws on the books - from another era - that should be removed.
I agree with the basic idea of starting and stopping the IC engine when it is not needed in a hybrid but there are is another opportunities right now with conventional vehicles that is being overlooked. In the quest for fewer losses in the automatic tansmission the designer monkeys have tightened up the torque converters so that there is significant "engine braking" everytime one lets up on the foot feed regardless of what 'gear' it is in. Why doesn't the sense all and do all computer controlled engine and transmission controls have the smarts to monitor the foot feed and simply let the car coast? Manually slipping into neutral lets the engine run at idle, with less gasoline consumption, while the car just keeps rolling along. I can always use the brake when I want to slow down or stop and put it back in gear to accelerate. Slipping the car in and out of neutral during my daily commute through stop and go city traffic with gentle rolling hills increases my mileage by several mpg.
The rear window on Ford's Lightweight Concept vehicle, based on the Fusion model, is made with a material combination devised by SABIC that saves 35% of the weight. The car's overall weight is 25% lighter than a standard production 2013 Fusion.
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