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)
With the advent of gasoline direct injection soon most cars will have the means to start without a starter motor. The only additional requirement will be some type of absolute encoder for crank position. You would need a direct injection device capable of operating at electric fuel pump pressures, but that should be possible using electronics. Most EFI cars are already computerized so I am not as worried about that. The system that injects fuel and starts the car would be much lighter than any electric motor/starter/alternator system. you couldn't do regenerative braking though. You could do regenerative braking using a compounding alternator. Turbo-compounding is another way to increase mileage that is already in use by some diesel trucks. That could be used along with the start stop technology. The energy to restart the engine would need to come from somewhere and the battery is the likely victim, but could be designed to handle it. The direct fuel injection method would also be easier on the battery using the energy in the fuel to do the job. coasting also works, but everyone here needs to remember that the highest selling car in america is usually a TRUCK. this makes the need for continuous power steering and brakes a non-removeable item. I don't want to be too antagonistic here but the guy who "doesn't care if people can run their AC all the time" is being silly. the reason that modern cars DEFROST so fast is because the compressor runs and the reciever /dryer of the AC system is used to augment the simple air blown through the ducts. Before putting on your hair shirt you should think about 80 year olds stuck in traffic in Arizona. The system should be seamless or people SHOULDN'T accept it period. We already have way to much government involvement in the car business and don't need more. Soon the only people to have new cars will be government employees driving fleet vehicles because no one else will be able to afford them.
First, auto and battery makers are actively researching using higher voltage batteries. Current draw on a 12V system is severely taxing the electrical systems of current cars; 24, 32 and 48V systems are being evaluated. Second, Mercedes seems (based on observation during a loaner day) to be using start-stop by injecting fuel into a cylinder past top-dead-center, then igniting the spark. No audible starter engagement was evident even with the hood open and the only noticable side-effect was a very slight shudder. Time delay was less than half a second from brake release to power-available. The system did not engage until the engine was fully warmed-up and if frequent starts/stops were necessary in traffic such that the engine cooled-down, the system would disengage. They may have another method but it was inaudible. As far as A/C goes, there shoudl be enough liquid left to evaporate to provide sufficient cooling for up to 5 minutes. I'd guess there must have been an auxilliary electric coolant pump because shutting off an engine after extended highway driving without coolant movement would be destructive. I was unable to notice a change in the cabin air outlet temp in traffic. There was sufficient vacuum available to hold the brakes indefinitely after the car was stopped, though there could have been a hydsraulic motor to assist. Because most new cars have multipoint fuel injection and computer controlled spark, a similar system for start/stop could be used without necessitating a separate starter.
I have always believed that the hybrid was the most innovative and effective improvement on the ICE-based motor vehicle, and past short personal experiences with the Prius (as a rental) were nothing but positive; actually spectacular, iin my view.
The outcome of a recent negative vehicular experience, has me now driving a Ford Escape Hybrid. Just the evolution from 15-16 mpg to 29-31 mpg has been a god-send, and the performance experience has been very admirable. Clearly, there is a start-stop component to the vehicle propulsion system, and I must say it is quite seamless. Watching the tach go from 1000 rpm to zero, either on coast, or stop is quite gratifying. Quite frankly, there is nothing negative I have yet encountered about the vehicle itself or the technology. Clealry , Ford has gotten it right.
I don't understand the discussion about the need to synchronize the starter to restart when a car is at substantial speed. A starter motor is not needed when the momentum of the car can be used (as almost anyone who has driven a standard shift car before steering wheel locks knows). Restaring an engine at speed effiicently is only a matter of reconnecting the engine to the wheels and then knowing the right time to put in fuel and spark. With electronically actually valves it is even easier because rengaging the engine is even more seamless if the valves are held open. Engine managment computers make all of this relatively easy.
For start-stop driving, it would be very easy to have a small hydraulic accumulator to apply full oil pressure before cranking begins. It would take less than a second to bring up the oil presure and about another second to flood all of th bearings. So there would not need to be a lack of oil pressure concern.
One other thing is that with manual control it is easy to get much better than the ten percent reduction in fuel consumption while driving in rush-hour type traffic. Adding the coasting to the stopping does a great job of reducing fuel consumption. At least, that was my experience.
I also agree that improvements to regular gas-powered car engines are not hybrids.
My 2012 Honda Civic turns off the engine when coasting (standard 1.8 litre gasoline). The tires spinning on the road surface, going through the drive-train, keeps the engine spinning. The automatic transmission downshifts when decelerating to keep the engine speed above about 1,200 RPM. The engine automatically turns back on when the gas pedal is used, at speeds below about 10 miles per hour, and when stopped. When coasting, the instantaneous fuel economy gage is pegged at 70 miles per gallon. For best fuel economy, I try to coast as much as possible, especially during city driving.
Of course when stopped, the engine is running and using gas...and that's zero miles per gallon. That's the main advantage of "start-stop", not using gas when stopped. For best fuel economy, I avoid driving around looking for a better parking spot, fast food drive-thru's, and even red lights (when possible).
I will never buy a car with an electric starter - the convenience does not outweigh the cost and the inconvenience of having to repair it when it breaks. And, one crank handle can be used to start many different cars - no need for awkward jumper cables.
This is fascinating but I certainly can see engineering hardware and software challenges with this technology. I am definitely going to follow up with GOOGLE searches to learn more about those automotive companies with systems already in place and being testing. Charles, do you feel this technique would be adaptable to 400 Hp diesel engines--in other words, 18 wheelers? Great post and very informative.
"A study was done years ago that said about 80% of engine wear happens in the first few seconds after starting because of lack of oil pressure."
It is my understanding that the 80% wear referred more to cylinder wall wear as opposed to engine bearing wear. Most wear occurs before cylinders come up to normal operating temperatures and properly mate with pistons and piston rings. It was quite common to see air cooled Volkswagen cylinders with over 100,000 miles that have no wear ridge at the top because they warmed up so fast.
With start-stop technology, certainly oil would not drain off bearings completely. As mentioned, pre-oil systems are already available to combat cold start bearing wear should that prove to be a problem. Study the maintenance history of the U.S. Postal System vehicles if you desire more data, as they are mandated to shut down between stops. Starters and associated systems will definitely be a problem, but one that can be mitigated with a more robust design.
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