By Peter Cleaveland, Technical EditorHydraulic technology has been used in industrial and mobile applications for many years, and has been reliable for all that time. But, hydraulics are facing challenges from multiple directions. They face competition from electrical systems and resistance from users who worry about energy efficiency, leakage, and noise.
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| In this mobile application from Bosch Rexroth Mobile Hydraulics, one axial piston pump drives the engine cooling fan, and can also be used to power a secondary circuit such as a compressor or a generator. |
Hydraulics can do what nothing else can. It would be difficult to find an electrical actuator with the combination of force, stroke, and rapidity of movement available with a hydraulic cylinder with a big pump behind it. It’s not difficult to get five horsepower from a hydraulic motor the size of a beer can. Yet, electrical actuators are making increasing inroads. Why? Dr. Joseph A. Kovach, vice president of technology and innovation for the Hydraulics Products Group at Parker Hannifin cites five main reasons: energy efficiency, leakage, noise, difficulty in control, and weight. Considering each of these areas, it’s possible to take a look at where hydraulics is likely to go in the future.
Energy Efficiency
Traditionally, hydraulic systems are designed to attack space constraints, according to Kovach. “Where can I get a lot of force in a little bit of area,” he asks.
In the past, efficiency took a back seat to space considerations. Efficient components were available, but at a premium price. When it came time to choose between a load-compensating pump and a plain one, or between an open-center valve or a closed-center one, many manufacturers opted for the lowest cost choice.
Keeping Clean
Leaking hydraulic systems win no popularity contests. They’re messy, they’re wasteful, they create environmental problems, and they can be a fire hazard. What can be done? Kovach says that his company is working on leak-free hydraulics, but that technology is still in the future, and at this point no one has found a way to banish all leaks. Equipment wears, it’s not always maintained properly, and it drips, sprays, or gushes.
If you can’t keep things from leaking, what about making the leaks less of a problem? The obvious choice from an environmental and fire safety standpoint would be water. Water-based hydraulic fluids are available, as are pumps and other components. Freezing can be prevented by adding non-toxic propylene glycol. Yet, water has not taken over. One reason for this, suggests Jeff Klingberg, president and CEO of Fluid Power Technologies International, is it doesn’t get much publicity. “How many articles have you seen in trade publications about water hydraulics?” he asks. “Very few, if any.”
Another path to environmental friendliness is vegetable oil, which is biodegradable and produced from domestic sources. It offers performance equivalent to petroleum-based fluids, with the exception of possible instability at high temperatures. “But once again this is an education thing,” says Klingberg.
Quiet, Please
While the power steering in a passenger car is quiet enough, many hydraulic systems are noisy. Anyone who has been near a small skid-steer loader may wonder how something so small can make so much noise. Driven by hydrostatic transmissions and powered by high-rpm diesel engines, some of these units have been measured at 82 dB in the (open) cab when idling and 90 to 100 dB when operational.
“I could come up to a machine almost any time and tell you if there’s a hystat on it,” says Terry Hershberger, director of electronic products at Bosch Rexroth Mobile Hydraulics. “When you swivel a variable motor towards minimum displacement you’re going to have the higher-pitch noise.”
Ever-tighter OSHA and ISO noise regulations will affect designs and manufacturing costs. In the meantime, suggests Hershberger, reducing internal windage in pumps can help, as can going to the smallest engine that can do the job. Modern electronic controls can manage energy needs to help reduce required horsepower as well as both noise and fuel consumption.
Electrohydraulics and Electronics
Hydraulics have been losing out to electrical systems in recent years, notes Klingberg, and increasing use of servo pneumatics threatens to further erode industrial hydraulics. In the future, he asserts, electronics and hydraulics will become more and more integrated. “Electric actuators and electronics and servo pneumatics and servo hydraulics or proportional hydraulics are certainly going to have to be integrated into one package, ideally,” he says.
The trend, says Hershberger, will be “specifically towards more of intelligent-type control or providing system expertise through the electronics as opposed to relying only on the operator.” At the same time, these new-found electronic capabilities will provide much-needed diagnostic capabilities to hydraulic systems. “Saying do I have a wire break or do I have a solenoid fault, or monitoring of systems while saying, this is the pressure in the system and this is what’s going on at this point in time,” Hershberger says.
Electronics capability will have other benefits as well, Hershberger continues. Adding intelligence to hydraulic systems will make it possible, he suggests, to more accurately match loads in real-time. That could allow for smaller engines to be used and provide savings in both noise and cost. On top of that, he suggests, it may even help improve operator performance.“If I went and rented an excavator today, I could be dangerous,” he says. “Somebody jumping into it who’s just a novice as opposed to an expert being able to change modes [is possible].” Embedded intelligence can also enable a system to compensate for changes in fluid viscosity with temperature, for better control, adds Kovach.
People Problem
One threat to hydraulics comes from a lack of trained people. Many of the best engineers in the industry are approaching retirement or have been pushed out of the workforce for cost reasons, says Klingberg, and schools are not graduating enough to replace them. One result of this, he continues, is that OEMs will come to depend more on manufacturers and distributors to help them design circuitry and systems.
A Look Ahead
Where will hydraulics hold market share, and where will it lose it? In low-end, low power density applications, suggests Kovach, electrical systems may come to dominate, while in some areas now served by transmissions with discrete gear changes we’re likely to see more infinitely-variable transmissions that integrate mechanical gear and hydraulics.
In mobile applications, Klingberg predicts, hydraulics will continue to do well. “Electric motors are coming a long way,” he says, “but I really don’t believe they’re ever going to replace hydraulics in mobile applications.”
Finally, says Klingberg, hydraulics will become smarter. Valves, cylinders, pumps, and other components will come with built in sensors that will monitor operating conditions and allow not only better control, but also more predictive maintenance.
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