Posted on 09/09/2008 5:21:03 PM PDT by decimon
Fuel-saving designs improve efficiency of hydraulic systems
WEST LAFAYETTE, Ind. - Researchers at Purdue University have shown how to reduce fuel consumption and dramatically improve the efficiency of hydraulic pumps and motors in heavy construction equipment.
The new designs incorporate two innovations: They eliminate valves now needed to direct the flow of hydraulic fluid in heavy equipment, and they also might incorporate textured "microstructured" surfaces inside pumps to improve performance.
Research has shown the "valveless" design alone could reduce fuel consumption by 40 percent. Further savings could be realized by combining the valveless design with the advanced microstructured surface concept, said Monika Ivantysynova, Maha Fluid Power Systems Professor in Purdue's School of Mechanical Engineering.
The microstructured surfaces have been shown to dramatically reduce power losses due to friction caused by hydraulic fluid, said Ivantysynova, director of Purdue's Maha Fluid Power Research Center.
Findings were detailed in several technical papers presented by her research group earlier this summer at the Fifth Fluid Power Net International Ph.D. Symposium in Krakow, Poland.
"Currently, the best pumps and motors may have a top efficiency of 92 percent, but this efficiency level is only in a certain range of operation," Ivantysynova said. "These hydraulic pumps don't always run at this maximum level. Sometimes you only need them to provide a small amount of pressure or flow, for example, to simply hold a tool in place. Then you aren't running the pump under its highest loads, and the efficiency goes way down."
Findings have shown the microstructured surfaces reduce losses due to friction by up to 57 percent when the pump is operating at low levels and about 10 percent when operating under heavy loads. One of the research papers about the microstructured surfaces was cited as a "best paper" during the conference and was written by graduate student Jonathan Baker and Ivantysynova.
Engineers in the center are working on ways to design pumps and motors that are more efficient in their entire range of operation.
Hydraulic systems use a central "variable displacement pump" that pressurizes fluid, and valves direct the flow of fluid to "actuators," which move tools such as shovels and buckets in excavation equipment. In the new valveless design, each actuator has its own pump, eliminating the need for valves.
An excavator has been equipped with the new valveless technology in the Purdue center.
These microstructured surfaces are located in narrow gaps at several locations inside a pump that are filled with hydraulic fluid. The fluid-filled gaps, which both seal the high-pressure chamber and also work as a bearing that allows parts to move freely, are a major source of power losses.
"We are working on those gaps by using computer simulations to understand all the physical effects and to reduce efficiency losses due to friction caused by the viscosity of hydraulic fluid," she said. "We know our simulations are very close to the real physics, and we are currently working to manufacture the surfaces and will do measurements."
Conventional wisdom states that the surfaces should be polished smooth, but Ivantysynova discovered that having a surface containing features one micron high improves efficiency. The gaps are located between the pump's piston and cylinder walls and between the cylinder block and a part called the valve plate, which connects to the cylinder along with the pump ports.
Ivantysynova made the microstructured surface discovery while studying the effects of improperly machined surfaces.
"We learned that it actually improved performance to have surfaces that were not completely smooth, which was unexpected," she said.
Purdue has filed a patent for the innovation, called an "advanced gap surface design."
The innovations might be applied to a new "hydraulic hybrid" concept for cars that would use a hydraulic motor to save energy in hybrid cars.
While hydraulic pumps work by compressing a fluid, which is then used to drive tools, hydraulic motors operate in the reverse manner: high-pressure fluid is pushed into a chamber, which is used to drive a shaft and provide torque.
The hydraulic hybrids would store energy while a car is braking by compressing hydraulic fluid in a tanklike "accumulator." Then the high-pressure fluid in the accumulator would be used to drive a hydraulic motor, providing torque to the wheels and saving fuel.
In conventional electric hybrids, energy is stored by charging a battery while the car is braking.
"With batteries, however, only a portion of the braking energy can be stored because it takes much longer to charge the battery than it does to charge the accumulator with high-pressure hydraulic fluid," she said.
Engineers in the center are building a test rig of the hydraulic hybrid design, and Purdue has filed a patent on the concept.
The Maha Fluid Power Research Center is part of the Engineering Research Center for Compact and Efficient Fluid Power, funded by the National Science Foundation, participating companies and universities.
Writer: Emil Venere, (765) 494-4709, venere@purdue.edu
Source: Monika Ivantysynova: 765 49-66578, mivantys@purdue.edu
Ping.
They get to automobiles in the last paragraphs.
Boiler Bump!
Interesting but the part where they talk about compressing hydraulic fluid raises questions about the authors understanding of the subject.
This would be a very welcome improvement in hydraulics in a large variety of ag and construction equipment.
Just think of the run-of-the-mill skid steer. Hydraulic drive, hydraulic attachments. Hydraulic everything, in fact. Easily 25 to 35% of the power from the engine is frittered away in heating the hydraulic fluid.
My pet application would be rotary mowers for hay. These invariably (today) use hydraulics to drive the disc cutterbar as well as drive the motors that propel the machine. Many of them have 5.9L Cummins engine in them, tuned to about 180 to 190HP. I can take the same header in a pull-behind mower powered by a PTO shaft off a 140HP tractor and lap the hydraulic-powered machine around a field - because so much power is frittered away in the hydraulics.
Hydraulic systems are very versatile ways to transmit power... but until now, they’ve been so wasteful of power, creating a lot of heat. Create enough heat, the oil breaks down and expensive things start to happen...
Well, to be fair to the author (who doesn’t write like an engineer), an accumulator is a high pressure tank where the fluid compresses a trapped gas, usually nitrogen. Think of a pressure tank on a domestic well - only the gas in the bladder is held at about 3000psi, and you get an idea of what these accumulators are like.
Hey, hey. I was expecting the usual, this will be commercialized in ten years statement, which really means our discovery is crap and we aren't disclosing what's really wrong with it.
I was wondering about that too, but NVDave seems to have explained it.
Why didn't this knowledge get transferred to the hydraulics engineers decades ago?
Why didn't this knowledge get transferred to the hydraulics engineers decades ago?
Maybe they don't have golfs.
Hydraulic systems aren’t flying through the air.
Let’s back up: A golf ball is flying through the air. To a fluids engineer, this is a small, regular object (a nice, spherical object at that), flying through a very large fluid body (air - you can model gases as fluids).
In hydraulic systems, you have irregular voids and spaces that contain fluid of medium to high(er) viscosity, at great pressures (2500+ PSI) moving this way and that. The fluid is moving, the bodies are mostly at rest.
Modeling how this fluid flows at the “macro” level is a challenge. Modeling how such minute changes in the surfaces inside an irregularly-shaped chamber change how the fluid flows in a macro sense is a much harder job yet.
Just modeling how hydraulic fluid flows past an irregularity in the line (say, a connector, a valve, a 90 degree bend) in detail was a neat piece of work only 10 to 12 years ago.
Unfortunately, if hydraulic engineers are no different than aerospace engineers like me, then every time they came in contact with golf balls they were most likely conducting hydraulic experiments involving their throats and large quantities of beer. ;-)
Well, I suppose so. But... until this whole hydraulic hybrid thing has come along, there’s not been a terrific amount of interest in wringing the last possible bit of efficiency out of hydraulic power transmission systems. A lot of people knew that if you wanted the highest possible efficiency in power transmission, you simply chose some other transmission method than hydraulics. eg, in farm equipment, you found a way to use shafts or belts rather than hydraulics.
A related question. Would this new knowledge have any application to pipeline pipe construction? I know wear inside the pipeline is a serious issue and i’m thinking anything that would make the fluid flow more easily would have other applications than the one discussed in the article.
Dunno. I’d have to see the engineering paper on the matter to see what their results really are.
Most liquid pipelines run at pretty low pressures (less than 200psi) due to friction losses over the long run. The higher the pressure, the higher the friction losses at irregularities.
For water pipelines, PVC has less friction than aluminum, which has less friction than steel. The differences are enough that they show up quite readily in irrigation pipelines coming off of wellheads where you’re paying an electric bill to pump the water.
Thanks for the reply. The following sentence was the one that caused me to ask the question and your comment that oil pipelines run at about 200 psi would qualify I think as low levels when they’re talking about pressures of around 3000 psi in hydraulic lines which I’m assuming is what they’re referring to as heavy loads.
Findings have shown the microstructured surfaces reduce losses due to friction by up to 57 percent when the pump is operating at low levels and about 10 percent when operating under heavy loads.
Since 1955 the Citroen ID & DS models ran a little 7 piston swash-plate pump @ 2750 psi for suspension/brakes/transmission shifting etc.
All with steel lines.
It was a pretty cool system, especially for the 50's , hydraulic suspension, inboard disc brakes(you could change the brake shoes yourself by lifting the hood and a clip on the tranny).
I remember reading an article in the chiropractors office waiting room about a Ford truck they called the Tonka that was a “hydraulic” hybrid as they describe here. Never saw anything else about it though...
Duh, I just googled it: http://www.fordmuscle.com/blog/ford-to-build-60-mpg-f150/112114
Yeah, that includes links to articles about the Ford 150 hydraulic hybrid that was announced to never be heard of again. I hope they succeed and come out with that.
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