Hydraulic vs Electric Hybrid Drive 1

[swall]

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?

 

[Fabrico]

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.

 

[EdDanzer]

Fabrico,
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.

 

[Fabrico]

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.

 

[swall]

The Eaton/UPS experimental delivery van is reportedly able to operate "several hundred feet" on the accumulator charge. Per the October SAE magazine.

 

[Fabrico]

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.

 

[Rob45]

"What does not exist are hydraulic pump/motors, and valves to do this."

I'm getting a kick out of reading how an hydraulic hybrid can't be done - since we've done extensive testing on them!

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.

 

[EdDanzer]

Rob45,
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.