Tucson, AZ-When a tree falls in the forest, it can do more than make noise. If it lands on a piece of mobile equipment, it can rupture the hydraulic lines that link the machine's cab to its hydraulic actuators. It can also crush the hydraulic valves, spilling gallons of oil onto the ground and necessitating a costly clean-up. Worse, when the clean-up is finished, maintenance personnel must figure out how to repair the equipment on site, without easy access to all the necessary parts.
Up to now, mobile equipment users have considered such mishaps an unfortunate--but almost unavoidable--cost of working on site. Accidents, after all, happen.
|An expandable, two-quart rubber reservoir surrounds the pump, motor, and gearbox.|
Maybe, though, accidents needn't be so catastrophic. At least, that's the thinking behind a pair of revolutionary new hydraulic actuators built by Sargent Controls' CEI Division, Oakhurst, CA. The actuators take a new approach to the protection of hydraulic valves, fittings, reservoirs, and high pressure lines. Instead of asking mobile equipment manufacturers to shield those components behind hunks of sheet metal, the Controls Division engineers have moved the components to a safer location: within the actuator itself.
That's a dramatic departure from the business-as-usual approach of hydraulic parts manufacturers, which have traditionally built cylinders, valves, reservoirs, fittings, and pressure lines as separate components. But by integrating them into a single unit, CEI may have solved a multitude of problems for mobile equipment manufacturers and users. If, for example, a tree now falls on a backhoe, it won't inflict the kind of hydraulic damage that it once would have. Why? Because the hydraulic lines will no longer run the 20 or 30 feet from the machine's cab to its actuators. Instead, they'll be contained inside the actuator's control head, along with the valve, pump, motor, reservoir and fittings.
That means less damage for users and simplicity for manufacturers. "The design engineer no longer has to worry about pumps, pipes, or reservoirs," notes Don Porter, a Sargent Controls consultant and co-inventor of the system. "He doesn't have to worry about installing those parts or protecting them. He doesn't have to worry about space constraints. And the user doesn't have to worry about tightening fittings or maintaining the system. It's all self-contained."
|ORIGINAL SIZE: This is the length of the traditional valve sleeve using O-rings, 6.237 inches long.|
|REDESIGNED SIZE: This is the length of the sleeve without the O-rings, 3.725 inches long.|
Packaging challenge. For engineers at Sargent Controls' CEI Division, the first step in creating such a product was to incorporate the hydraulic valves in the actuator. They included five in all--two pilot-operated check valves, two solenoid-operated pilot valves, and a 40 gallon- per-minute main stage control valve. All five valves, along with their controls, are packed into a control head measuring about 5 x5 x 6 inches. The control head is rigidly attached to the cylinder.
To accomplish all that, engineers overcame numerous packaging challenges. The first was the obvious issue of the main stage control valve. Most such valves would be too long to fit into such a confined area. But the Controls Division engineers solved the problem by employing a control valve with a shrink fit sleeve that uses no O-rings. By doing so, they eliminated as much as 2.5 inches from the length of the valve. That, they say, was just enough to fit the valve inside the head.
Designers of the valve say that the O-ring-less configuration has been used in previous valve designs. But the concept wasn't popularized because users prefer to replace the lap assembly when the valve wears out, and that's a problem for O-ring-less designs. Sargent Controls engineers say they solved the problem, however, through the use of special heat treatments for the lap assembly. The heat treatment enabled them to create a lap assembly that never needs replacement.
Equally important was the design of the hydraulic passages in the control head itself. Because the space was so confined, engineers employed a Pro/ENGINEER CAD system (Parametric Technology Corp., Waltham, MA) to lay out the configuration of hydraulic passages. "We had to make sure we didn't have any intersecting passages," Porter notes. "And the best way to accomplish that was to do it in CAD first, rather than make mistakes in the hardware."
Initially, engineers also hoped to employ off-the-shelf pilot-operated check valves in the control head. They soon found, however, that those, too, were either too long or too fat. Conventional valves, they learned, were about 50% too large in most cases. As a result, the staff used its own servovalve expertise to shorten the fluid passages in the company's pilot-operated check valves. Result: a smaller, easier-to-fit pilot-operated check valve.
To facilitate simplicity of manufacturing, engineers also laid out all the intricate hydraulic passages so that all were perpendicular with a face of the controls head. As a result, none of the passages required angled drilling. "Straight holes are easier to drill," Porter says. "And none of this is any good if the plant can't build it."
|Sargent controls engineers used a direct-acting design to reduce the size of the pilot-operated check valve.|
Step two. The entire system, known as the SMART Cylinder, is the first step in the creation of a nearly-autonomous hydraulic actuator.
The next step, known as the CHAMP cylinder, packs even more functionality into the package. In the CHAMP, engineers have incorporated the valves, lines, reservoir, rotary piston pump, brushless dc motor and planetary gearbox.
In essence, the CHAMP solves a problem that even the SMART cylinder cannot solve. If a tree, or some other heavy object, severs the supply or return lines that lead to the cylinder that's still a problem for the SMART Cylinder because the cylinder is hydraulically linked to the machine's hydraulic pump.
In the CHAMP, however, all hydraulic linkages to the machine's cab are eliminated. Instead of hydraulic links, the CHAMP Cylinder is connected to the joysticks in the cab by electrical wiring. That's possible because each actuator is an autonomous hydraulic system, so it needs only an electrical signal from the cab to activate it.
The CHAMP Cylinder also differs from the SMART Cylinder in size. The cylindrically shaped unit measures about 5 inches in diameter and about 9 inches long, making it considerably larger than its predecessor.
That extra volume is consumed by the rotary piston pump and the system that powers it. A brushless dc motor from BEI/Kimco Magnetics Div., San Marcos, CA, supplies the power for the pump. It operates through a planetary gearbox, which provides 4:1 speed reduction.
Moving the entire hydraulic system inboard also meant that engineers needed to deal with another problem: what to do with the hydraulic oil. As with any system, hydraulic oil from the cylinder must be held in a reservoir when the cylinder's rod retracts. In these cylinders, however, there was little room for a reservoir.
Still, the Controls Division engineers squeezed a two-quart reservoir into the head. The molded rubber reservoir, which is expandable, surrounds the motor, gearbox, and pump. Engineers say that the two-quart volume was sufficiently large because, unlike conventional system reservoirs, it didn't need to hold extra oil in long stretches of tubing.
Mobile system solution. The firm's engineers envision the SMART Cylinder and CHAMP Cylinder being used in a wide variety of applications, including backhoes, wheel loaders, cranes, forklifts, dump trucks, refuse trucks and agricultural machines. In all those applications, they say, the new cylinders offer advantages. "Even if you crush it, there's very little oil loss," notes engineer Wayne Shapiro, Sargent Controls business development manager and a co-inventor of the system. "The only oil you lose is in the reservoir and the cylinder itself. There are no long lines and no remote reservoirs." That's particularly important, they say, because oil clean-ups can be fantastically expensive.
What's more, the new cylinders help address fluid contamination, an issue of growing importance to manufacturers and users alike. Because the system is completely closed, engineers say, there's less potential for adding water and dirt to the oil. "Most reservoirs have a cap for adding oil," Porter says. "But that's also an entranceway for contamination. Here, the water and dirt can't get in, because it's sealed." When oil needs to be replenished, Porter says, users can do it through a tiny charging valve.
The biggest advantages of all, however, may accrue to equipment manufacturers. With the CHAMP Cylinder, OEM engineers no longer need to worry about laying out hundreds of feet of hydraulic tubing, or adding other hydraulic components. "When you first look at it, you might think this cylinder takes up more space," Porter says. "But when you consider that it replaces the entire hydraulic system, you realize that it's smaller, lighter, and uses less oil than conventional designs because you don't have the long lines of tubing."
Traditional main-stage control valves too long. Solution: Shrink-fit sleeve with no O-rings.
Potential for intersecting hydraulic passages because space in the control head so small. Solution: Design passages with CAD software.
Traditional check valves too long or too fat. Solution: Engineers used servovalve expertise to shorten fluid passages.
With hydraulic system moving inboard, what to do with the hydraulic oil. Solution: Molded-rubber reservoir surrounding motor, gearbox, and pump to hold two quarts of oil.