Saving fuel is the obvious benefit of using hydraulic hybrid systems in refuse trucks, along with fewer brake repairs due to regenerating braking energy, but now productivity gains are starting to take the leading position in the value proposition.
There are a lot of issues regarding hybric trucks especially the parts of these vehicles are different from the usual parts. Plus they are very coslty since it is given that parts of an electric car is high, for some unknown reason. Hence, the least people can do is to buy truck parts wholesale and be able to get discounts for their purchases. Well, good luck to the truck owners of our country. :-)
While there are challenges in the passenger vehicle market, I think these can be met. With hybrid electric vehicles and battery electric vehicles there are some costs associated with the batteries that I am not sure are fully appreciated. Anything that can deliver the type of increase in fuel efficiency that hydralic hybrids have shown and do it without some of the side effects is a promising technology in my book. I thinkt the engineering challenges regarding noise can be resolved.
The comment about electric drives and braking is sort of correct, but for the application of stop and go service, such as a garbage truck, it would not last, if batteries were used because a battery just can't accept the charging that fast. Also, a battery has a finite number of charge-discharge cycles, while a bladder accumulator may also have a "cycles limit", it is in the tens of millions of cycles. Besides all of that, the hydraulic system is based on current knowledge, nothing new needs to be invented, it should all be in the catalogs.
The one other thing is that the energy for the short hops that a garbage truck makes is easily withinthe accumulator capacity of a reasonable size device.
One more thing is that regenerative hydraulic braking is good down to zero speed, while electrical regenerative braking must have a minimum speed and use friction brakes to stop.
William K., Re. Hydraulic brakes and quick braking.
The thing is about electric systems, when there is an over-abundance of power available in a circuit, the excess power can easily be stored in capacitors, of varying sizes and duty-cycle design. The circuit then has the storage battery as an additional, and stabilizing, power-storing device.
With hydraulic system design, when an available over-abundance of power is scavenged to be stored, accumulators are the storage device utilized to do the job; accumulators mimic capacitors. There is no "hydraulic- battery" available to mimic the electric storage battery.
Accumulators, by their very nature, are physically large, robust and heavy, in direct relation to the power they are designed to cycle. A large, robust accumulator will not budge nor accommodate a small amount of excess power when it begs to have its quotient contained therein; of course, a smaller one will - both within their design and physical capacity limits.
When comparing electric systems to hydraulic systems, whose designs are engineered to store the same amounts of available power, electric circuits can be BUILT much more easily vis-à-vis power to weight ratio, and space requirements.
A properly laid-out array of capacitors, controlled to temporarily store electric potential energy - and redirect it to battery storage - or - motor needs, can be more efficiently and easily contrived than what would be necessary for the same power and storage re-direction regime in a hydraulic system of the same capacity, in my opinion.
Only an array of differently-sized and rated hydraulic accumulators laid-out to scavenge the varying levels of excess fluid power found available in a hydraulic circuit can realistically store the excess power, ostensibly in parallel application to the MPRV, which is not designed for such a task. An electric circuit does not have this design issue - any amount of electric current can easily be stored, via capacitors, or battery - and as a bonus, there is no "noise" issue of the cycling hydraulic masses being constantly re-routed.
The folks at EPA reference their "patents" in the hydraulic hybrid field but talk as though all this is new to them since around 2006. What about all that money spent between 1994 and 2004 developing these patentable things? They seem to forget that a few of us taxpayers out here in the hinterlands paid attention to that stuff and now wonder where Charles Davis is and the car he developed using our money. It was in the millions, folks. There were more than a few press conferences and news releases beginning back around 1999-2000 announcing this, giving us hope. I know that after 2003 or so Mr. Davis took possession of the car like it was his own. What, did he and his henchmen also abscond with the files on this work? Or is it because his name is also on the patents and he is not allowing the EPA, or more specifically Chrysler to use them? (Fine thing: our money pays for the development and Davis gets his name on the patents, which means essentially that he has a stake in their disposition.) This is a proven technology in the SMALL SIZE (read automotive) that private inventors in the nineteen seventies did a lot with. Google Ernie Parker and Vincent Carman. Oh, and they did it without using a cent of tax money...which was partially their undoing. Due to lack of funding they couldn't get their cutting edge innovations into the consumer market.
It seems that there is a great deal of misunderstanding here. Certainly garbage trucks and such brake as fast as they can in order to minimize cycle time. But that is an extreme use of regenerative hydraulic braking, where a battery could not accept the return of energy at a rate anywhere near that of an accumulator. That is the area where the hydraulic system has no competition. But hydraulics can be as gentle as required. That is old news, not some new development. So the city bus may need a different calibration than the garbage truck, so what? The garbage truck could stop gently, it is a matter of calibration. Even the bus, with it's gentle stops, is still in the realm of returning power faster than a battery could accept it. There indeed will need to be a bit of calibration done so as to have the most possible efficiency, but the hydraulic system can do the job today, not in the future after some new discovery. Of course cost reductions for the hydraulic system will serve to make it much more price competitive, but after all, cost reduction efforts are constant for all types of systems.
This technology seems terrific for Heavy Duty vehicles, except Buses, as I perceive it.
Quick starts and stops are very desirable for lots of work vehicles and performance machines as well; it takes this “quickness” to generate the horsepower necessary to charge the accumulators, unless there is enough Velocity being scrubbed off (and perhaps) geared to do the same job.
In the case of a Transit Bus application, the depletion of the accumulators’ charge during Acceleration can be modulated easily enough - but the generation of a charge for the accumulator through “quick” braking can be very problematic, obviously.
Unless they can devise (or have devised) a roundabout fix, I think that the fuel savings potential through hydraulic regenerative braking will not suit the SAFE daily operations of a Public Transit Bus application. Electric Hybrid Technology makes much more sense for the Public Transit Bus scenario.
The largest gains to be made for delivery trucks was in quick starts and stops with regenerative technology. This doesn't require much energy to be stored, making a hydraulic accumulator a great storage device. Many cycles of small amounts of energy are possible at good efficiencies.
A few years ago after seeing the garbage truck system, I wondered if an all-wheel drive system was possible where the rear wheels might be driven mechanically while the front wheels were hydraulically driven. The hydraulics could be used to take in energy during braking, then re-apply it during acceleration. Wheel speeds and torques would have to be very carefully controlled to prevent dissimilar speeds destabilizing the vehicle. With an engine driven hydraulic pump all-wheel drive could be used continuously for traction needs. It appears that the BMW i8 is using an electric version of this idea.
Al: I'm not very familiar with hydraulic hybrids, but the EPA appears to be saying here that the series hybrid is the way to go. Why series instead of a parallel hybrid (where the pump/motor connects to the driveshaft)? Is that configuration being considered as well?
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