Hydraulic vs Electric Hybrid Drive
Hydraulic vs Electric Hybrid Drive
(OP)
I just saw on the ASM website that one of the makers of hydraulic motors is working on a hybrid van for UPS that would utilize hydraulic drive instead of electric. This is out of my field, but it strikes me that a hydraulic drive would be more compact, but would fall short on the energy storage aspects compared to electric. What do you guys think?





RE: Hydraulic vs Electric Hybrid Drive
The latter, especially, travels maybe 30m between stops, so it only needs to store enough energy to go that far in order to be effective at reducing fuel consumption, and especially brake consumption.
Mike Halloran
Pembroke Pines, FL, USA
RE: Hydraulic vs Electric Hybrid Drive
Ken
RE: Hydraulic vs Electric Hybrid Drive
A hydraulic hybrid stores energy in compressed gas, which doesn't have the density of chemical storage, so the range on discharge is limited.
Two garbage truck brake jobs, normally needed several weeks apart, will more than pay for a hybrid conversion.
Mike Halloran
Pembroke Pines, FL, USA
RE: Hydraulic vs Electric Hybrid Drive
If so, could one use a cylindrical tank with a spring/piston setup to store additional energy/achieve additional power density?
Just a thought...
RE: Hydraulic vs Electric Hybrid Drive
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Hydraulic vs Electric Hybrid Drive
RE: Hydraulic vs Electric Hybrid Drive
It is also a lot lighter than steel, and has an infinite fatigue life.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Hydraulic vs Electric Hybrid Drive
RE: Hydraulic vs Electric Hybrid Drive
As you say, horses for courses, and one reason we are here is to explore different possibilities.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Hydraulic vs Electric Hybrid Drive
A 3 axle garbage truck weighing 42,000 lbs going 25mph stopping to 0mph in 5 seconds will require 638 hp to stop. This is 18.3 gallons of oil at 5000 psi to store. For an electric vehicle that would be 476 kw for 5 seconds input to batteries or ultra-capacitors.
It is possible to buy accumulators to do this without too much of a weight penalty. I don’t think you can haul enough batteries or ultra-capacitors let alone payload to do this.
What does not exist are hydraulic pump/motors, and valves to do this.
RE: Hydraulic vs Electric Hybrid Drive
There's not much difference between hydraulic pumps and motors. Maybe everything is there but the big accumulator?
RE: Hydraulic vs Electric Hybrid Drive
I saw one where a slim guy could crawl inside the main hydraulic oil line. They had a tanker outside to supply the oil for an oil change.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Hydraulic vs Electric Hybrid Drive
It seem that individual wheel motors will be the best way to collect braking energy, rather than trying to use all wheel drive connected to a large pump motor, or a multi-speed transmission and pump/motor. 600 hp / 6 wheel motors = 100 hp per motor.
Generally speaking pumps have different valve timing and shape than motors for best efficiency.
RE: Hydraulic vs Electric Hybrid Drive
The pumps I was speaking of were both gear and vane types, not much to time. Motors are also often gear or vane types.
Another consideration is the very powerful hydraulic retarders built into the big Allison and ZF transmissions. Why could'nt a similar motor be built in?
RE: Hydraulic vs Electric Hybrid Drive
Hybrids can't afford to.
Mike Halloran
Pembroke Pines, FL, USA
RE: Hydraulic vs Electric Hybrid Drive
Ah, well they don't seem to be alone in that function.
The point was that retarders prove that a large and powerful hydraulic motor could easily exist as an integral component of the input or output section of a typical heavy-duty automatic tranmission. This would also lend itself quite well to re-generative braking and/or energy storage.
Retarders are generally rated at about twice the engine's horsepower. This means that structural, torsional, thermal, size/space/weight, requirements are already in place.
http
RE: Hydraulic vs Electric Hybrid Drive
Mike Halloran
Pembroke Pines, FL, USA
RE: Hydraulic vs Electric Hybrid Drive
MikeHalloran, it would be most helpful if you could take the time to read posts more carefully. None of mine stated anything about a retarder being a hydraulic pump, or using a retarder for anything.
I am quite familiar with the construction of transmission retarders. A proper hydraulic motor/pump unit could easily exist where retarders do now. I would not be at all surprised if the OEMS are already looking into it.
RE: Hydraulic vs Electric Hybrid Drive
The components used in a garbage truck compaction system, or a concrete truck are nothing like what is required for a drive train.
Gear or vane pumps and motors do not operate over a very wide speed range and are not very efficient if operated as both a pump and motor.
Most hydraulic hybrid development is based on axial piston pump motor technology.
The limitation of using a transmission driven regeneration system, electric or hydraulic, are you limit the amount of energy that can be recaptured, increase the complexity of the control system, and create additional wear on the transmission and rear end when decelerating at full load.
Swall,
This link will provide more information about hybrid trucks.
http://www.calstart.org/programs/htuf/?p=programs
RE: Hydraulic vs Electric Hybrid Drive
Unless you have achieved outstanding unquestionable success, you cannot be sure of what is required. The demands of delivery trucks are certainly not the same as rubbish trucks.
I hope Calstart does a better job with hydraulics than they did with electricity or NG. They had a large facility in a Lockheed building right down the street from my work; most unimpressive.
Some concrete trucks use piston pumps and/or piston motors.
While efficiency of a transmission based system may or may not be the highest possible, complications are minimal, and certainly less than a wheel based system. Claiming that the system will cause greatly increased wear on the driveline is not being very realistic as retarders in use now create a very similar reversal of driveline torque with few ill effects. Cooling is usually done separately and driveline shock is non-existent. >>This means a motor/pump unit would operate similarly.
Rubbish trucks do plenty of highway operation. This means efficiency of a wheel based drive system is critical. Added weight would consist of the accumulator, valving, and at least 4 extreme torque motor/pump units. With any system, it's doubtful you will completely shed the brakes anytime soon. Considering the cost of manufacturing and maintaining a wheel based drive system, performance will have to do much better than break even.
Using a motor/pump unit in a place that already exists inside the type of transmission already used on a rubbish truck, is a simple and doable concept for stop-and-go operation. Cost for development, production, and maintenance would be minimal. Added weight would consist of the valving and accumulator.
It is just a simple idea and is not being touted as some ultimate or broad-based answer. And, as always, there is no limit as to how complicated you can get.
As a significant side item, loading and packing trash uses nearly as much fuel as moving the truck from stop to stop. The generated or conserved energy could almost be just as well used to perform only those tasks.
RE: Hydraulic vs Electric Hybrid Drive
Your compaction percentages are way higher than what Ricardo reports in SAE paper 2005-01-1164, at 10%.
Most information I have seen puts garbage trucks at about 2.9 MPG average.
The use of the truck has little to do with optimizing the drive train. The average gross weight, number of stops and travel speed will affect the fuel mileage most. The difficulty is making a cost effective solution. In theory if 100% of the braking energy could be recaptured and reused for starting, the only energy required would be to travel at speed. A highway truck grossing 80,000 lbs traveling 60 mph can get over 5 MPG. This means a city driven vehicle must recapture and reuse most of the braking energy.
Permodrive ( http://www.permodrive.com/ ) , Dana and the EPA are some of the people who have done driveline regeneration. I think putting the pump/motor between the transmission and motor must be more difficult than you think. Currently the DOD is paying Dana and Permodrive to build a hybrid drive for the FMTV.
RE: Hydraulic vs Electric Hybrid Drive
Rubbish trucks are not the same as rubbish trucks.
If you consider how fantastically their service, terrain, and dump distance can vary, and how many there are, it seems fairly absurd to simply average them and develop new technology from that average. For the most part, these trucks are designed, purchased, and assigned according to needs. To whatever extent practical, drive train development should do the same.
The Permodrive is fairly close to what I have been talking about, except external and IMHO, a bit cruder. Keep in mind that only Allison and ZF make traditional automatic transmissions, so changes to them could end up being proprietary, quiet, or absent.
The motor/pump unit I mentioned would more likely be on the output end, not between the engine and transmission, as you mentioned. However, powerful retarders exist in both locations. Conversion of existing systems may lend itself well to re-generation at the rear of the trans and motoring from the front. This could significantly and beneficially affect the size, pressure, flow, and RPM requirements of the fluid motor. As mentioned, existing physical location, torque capacity, and cooling may already be in place.
In addition to pumping and driving with a single unit, the Permodrive has a wide RPM range to deal with. It looks like a good, straight forward beginning.
RE: Hydraulic vs Electric Hybrid Drive
RE: Hydraulic vs Electric Hybrid Drive
Sounds encouraging.
There was something else that was around for a few decades. It was the big electric retarders. Once in a while you would see one on the driveline, mounted very similarly to the unit above. But they were much more often found on rear trailer axles. They were quite effective and reliable, but so far I can't recall who made them.
RE: Hydraulic vs Electric Hybrid Drive
The Eaton system stores sufficient braking energy to launch a refuse truck back up to about 15 mph, and thus gives a huge reduction in brake wear on top of about a 20 - 25% reduction in fuel consumption WHILE COLLECTING REFUSE - not of course while running down the highway.
I believe the power storage is equivalent to about 500 hp-sec., or about the same as the standard diesel engine's output for 2 seconds.
RE: Hydraulic vs Electric Hybrid Drive
I’m very familiar with most current hydraulic and electric hybrid systems and they work over a relatively narrow rpm and power range. I just returned from the SAE Commercial Vehicle Conference. I attended last years HTUF meeting and drove several trucks, and have all the travel plans to be at HTUF November 14-15, 2006.
At the SAE meeting this week the best the Seattle hybrid busses averaged is about 27.8% better than the diesel only busses.
The goal set in the 21st Century truck project was to triple the mileage of transit busses by 2010.
In order to meet the 3X mileage dream, current swash plate driveline systems like Eaton’s, any current electric drives, or any crankshaft engines will be insufficient.
I hope to do some testing next week and present the data at HTUF about garbage truck drive cycles that gives the actual thermal efficiency during at start stop movement to back my position.
So I will be putting my money where my mouth is.