Less is more in mobile hydraulics

DN Staff

July 24, 1995

11 Min Read
Less is more in mobile hydraulics

For decades, hydraulic systems have done the dirty work all over the globe. From Ankara to Zurich, they've provided the muscle to dig, lift, and push dirt from one place to another. They've propelled, steered, and stopped thousands of off-road vehicles. In construction, they've played critical roles in bulldozers, graders, loaders, and excavators. In agriculture, they've been the backbone of tractors and combines.

Why hydraulics? Because, when it comes to combining sheer muscle with mobility, few other power sources can match it. Hydraulic systems can generate pressures in excess of 5,000 psi, enabling them to supply the force needed for heavy digging. They can stand up to the presence of dirt and moisture. And they can easily serve in rotary or linear applications. "In the mobile arena, many of the loads are linear," notes Raj Oberoi, product sales manager for Vickers' mobile controls. "Unlike electrics, hydraulics can easily move a rotary or linear load."

Those reasons and others are why hydraulics hasn't lost its grip on the mobile market. Every year, manufacturers in construction, agriculture, and material handling spend an estimated $11 billion on hydraulic equipment.

As a result, hydraulic equipment manufacturers continue to innovate. Most are deeply involved in efforts to make hydraulic equipment quieter, more productive, more fuel efficient, more reliable, and cleaner.

Most of all, though, hydraulics manufacturers are integrating more functionality into smaller packages. As a result of their efforts, customers can achieve higher flows and pressures, while eliminating a multitude of hoses, fittings, external valves, and other components.

Following are examples of innovations in mobile fluid power. These examples exemplify the intense efforts by hydraulic system manufacturers to pack more function into smaller packages and greater efficiency into existing systems.

Hydraulic controls stop 'jerky' steering

Large, articulated construction vehicles are notorious for being jerky. No matter how hard a driver tries to steer smoothly, the vehicle's big loads shift, causing it to bounce and shake.

Much of that bouncing and shaking is transmitted through the steering system. For engineers, it's a problem that isn't easily solved. Struggling to minimize the jerkiness, some engineers have added cushioning valves and check valves, but in the process have added cost and complexity.

Now, engineers from Eaton Corp., Eden Prairie, MN, say they've found a better way. The firm's new Char-Lynn 20 Series Steering Control Unit is said to minimize jerkiness without adding cost and complexity.

Key to the system is a new hydraulic design that features a wide deflection angle between the mechanism's spool and sleeve. While conventional steering systems typically employ deflection angles of 10-15 degrees, the Char-Lynn unit offers 30 degrees.

By employing the wider deflection angle, the unit more effectively modulates the flow of pressurized fluid, enabling the system to absorb jerkiness before the operator can feel it. During operation, the operator turns the steering wheel, which is connected through a shaft to the spool. As the wheel turns, the deflection angle increases, thus enabling hydraulic fluid to be metered by a gerotor to the cylinder which moves the tires. When a design uses a shallower deflection angle, says Eaton Senior Design Engineer William J. Novacek, the pump doesn't have as much time to reach full stroke before the operator hits the maximum deflection angle. "By designing it to use a wider angle, we've allowed the operator to turn the wheel a little bit further before he comes to a hard stop," Novacek says. "This gives time for the pump and priority valve to supply the necessary pressure and flow before the operator hits the maximum deflection." The result: The operator doesn't feel as many jerks and "kicks" in the steering.

The Char-Lynn 20 Series is currently rated at 25 gal/min, but certain units will ultimately be rated as high as 33 gal/min as a result of the new feature. By eliminating the need for the cushion valve and/or accumulator, the unit offers more flow in a smaller package, Novacek says. It is said to be well suited for articulated vehicles, such as wheel loaders, log skidders, scrapers, and agricultural tractors.

Integration cuts costs, improves reliability

An engineering partnership between Sauer-Sundstrand and New Holland UK has lowered installation costs, improved reliability, and minimized potential leakage in the design of a new hydraulic system for an agricultural tractor.

Known as the New Holland Series 40, the tractor incorporates a Closed Center Load Sensing System (CCLS) to ensure responsive steering under a variety of conditions. As a result of the new design, steering is unaffected by the demands of the hydraulic system, even at low engine speeds.

More important, the system integrates a multitude of hoses and fittings, thus reducing costs and eliminating leak paths. Designed by engineers at Sauer-Sundstrand's Wiltshire, England facility, the CCLS includes a variable displacement axial piston pump and two fixed displacement gear pumps. The integrated unit supplies pressurized fluid for high and low pressure tractor functions, as well as steering. It also incorporates integral valves for regulation of boost, filter protection, and piston pump load sensing.

Through its integration effort, New Holland experienced cost savings of up to 30% on the hydraulic system. Most of the reductions resulted from elimination of components and lowering of labor costs. Sauer-Sundstrand engineers say that the new integrated design eliminated 11 pipes, 20 fittings, and 80 leak points. In all, it incorporates 21 separate ports.

During operation, the variable speed pump supplies pressure to the tractor's trailer brakes, hydraulic lift system, remote valves, clutches, four-wheel-drive system, and power take-off. One of the fixed displacement pumps supplies oil to the main pump, while the other provides flow to the steering system, cooling, and transmission lubrication circuits.

The compactness of the integrated package enables New Holland to leave maximum space for other components, say engineers. Power losses are minimized due to the reduction of flow passages, fittings, and elbows. Also, all tank returns are located at the pump, requiring no additional piping.

The CCLS unit, which was more than a decade in development, is expected to find applications outside of agriculture. "The concept of integrated systems is appropriate wherever there are multiple hydraulic service requirements," says Sauer-Sundstrand director of engineering, John Hudson. "It's equally applicable to trucks, buses, and construction equipment as it is to agricultural equipment."

Brake valve stops plumbing 'nightmares'

Routing the plumbing for off-road equipment can be a hydraulic nightmare. Plumbing complexities are compounded by the presence of numerous hydraulic systems--braking, steering, and propulsion, among others--on construction equipment. "Experienced users know the pitfalls of complicated hydraulic circuits," notes Ronald P. Middendorf, a designer for MICO Inc., North Mankato, MN, a manufacturer of hydraulic components. "They can be a major installation headache."

By integrating three units into one, however, MICO engineers hope to alleviate some of those headaches. The firm's Pedal-Actuated Integrated Tandem Full Power Brake Valve wraps the brake modulation, accumulator charging, and brake pedal assembly into a single valve package.

Used on an excavator with a load sense priority valve, the new unit eliminates four hydraulic lines. Those include two accumulator lines and two tank lines, both of which would be necessary if the accumulator charging and brake modulation were packaged separately.

Used on split circuit braking systems, the unit charges two accumulators within a predetermined pressure range. The accumulators provide the necessary volume and pressure for actuation of the brakes through a tandem, direct-acting, spool arrangement. This spool arrangement supplies modulated pressure control to both halves of the brake system so that if either half fails, the remaining portion of the valve continues to function.

The new unit will see use on mining, construction, and forestry equipment.

The key to the system, says Middendorf, is the elimination of hydraulic connections. "That's what the industry wants," he says, "to simplify the hydraulic circuits on these machines."

Hydraulics raise pile driver efficiency

Every year, contractors lay out thousands of dollars for specialists to drive piles at construction sites. Problem is, about half of those costs are generated during the transport of pile drivers to the site. On small jobs, transportation can become a significant percentage of overall costs.

Using a new hydraulic design, however, one contractor in Northern Ireland may have solved the problem. James B. Russell, owner of Precast Foundations Piling, Larne, County Antrim, Northern Ireland, replaced conventional pile drivers with a compact, new hydraulic design. Use of a unique hydraulic design enables Russell to mount an assembled piling unit atop the back of a 6 x 4 foot truck chassis, transport it to the site, and use it without set-up time.

Key to the new design is a fast-acting hydraulic valve that dramatically cuts the size of the entire system. Using the technology, a pile driver with a three-ton hammer, for example, weighs less than three-and-a-half tons. In contrast, conventional three-ton piling systems typically weigh five or six tons. Russell's various systems employ hammers ranging in weight from three to ten tons.

Incorporating the fast-acting pilot valve, however, has enabled Russell to dramatically reduce the overall weight of any size system. The key, he says, is greater mechanical efficiency. During operation, a set of two 2-inch-diameter hydraulic cylinders moves the three-ton hammer up within the rig's frame. An adjustable arm atop the hammer trips a pilot valve supplied by Hamworthy Engineering Ltd. This, in turn, opens a "dump" valve, which directs pressurized hydraulic fluid into a balance chamber at the back of the system's tank. As a result, the three-ton hammer falls, imparting the equivalent of about 160 tons of force to the pile.

Power to the system comes from a 240-hp Cummings turbo diesel engine, which drives two 25 gal/min pumps from Dowty Industrial Corp.

Using a hydraulic technique, instead of a gear-and-pulley method, Russell estimates that his system is 90% efficient. Typical winch-type systems, he says, are approximately 50% efficient. The resulting efficiency enables him to cut the hammer's drop distance in half. A three-ton system requires a drop distance of only 18 inches to drive an 80-ton-capacity pile, compared to a three-foot drop distance to achieve the same thing with a winch-style rig. "The efficiency of the hammer is the reason we've been able to make this system so much smaller than the others," Russell says.

Russell is considering other applications for the fast-acting valve technology. He wants to license the technology for use on mechanical punches, guillotines, or to automatically close large fire doors, such as those in power stations. "The advantage of this system," he says, "is that it retains a load and drops it quickly."

How to make mobile hydraulics last longer

When a nine-month-old pump wheezes through its final workday, users often assume that it has lived a full life.

Not so, say engineers from Vickers. Pumps and other hydraulic components should be wearing out after years, rather than months. "Hydraulics are reliable," notes David C. Downs, global business manager for Vickers' Proactive Maintenance program. "The problem is that hydraulic systems are growing more sophisticated. Today's systems offer higher performance and run at higher pressures. As a result, they're more sensitive to contamination."

Between 70% and 90% of all hydraulic system failures are caused by contamination of the fluid, Downs estimates. The problem is compounded in the dusty environments of off-road construction and farming.

That is why Vickers launched their Systemic Contamination and Pro-Active Maintenance Program. The program provides technical solutions and products to solve problems resulting from contamination. Its three steps involve setting target cleanliness levels, selecting the proper filters, and sampling fluid. Products include high efficiency filters and breathers, on-site particle counters, and fluid laboratory services.

The program is critical for design engineers, who can eliminate a large percentage of hydraulic failures with proper design at the outset. Downs recommends that OEM engineers consider the following points while designing hydraulic machinery:

Include an efficient breather to keep out unwanted moisture and particles. In most cases, that means employing a breather that blocks 2-3 micron particles, and water.

  • Ensure that cylinder rods have adequate wiper capability or that they have boots on them.

  • Seal reservoirs to prevent dirt ingression. Reservoir access plates must be sealed and return lines must be sealed or welded.

  • Provide efficient filtration, properly placed throughout the entire system.

  • When adding oil to a new machine, use the best possible filters. During regular operation, oil passes through filters many times. But when it is added initially, it passes through the filter only once.

Many major OEMs test products before shipping to ensure that they contain clean oil and proper filtration before they arrive at the customer site. Some manufacturers also specify fluid cleanliness levels and require periodic reports from customers to prove that the machines are being properly maintained.

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