Digital valves raise machine performance, not cost

Christopher Kolbe
Husco International
Waukesha,Wis.

Today's mobile-equipment users increasingly demand machines that are highly productive, efficient, and reliable, offer exacting control, and are safe to operate. At the same time OEMs are under pressure to hold the line on costs. Electronic control of hydraulic systems has been touted as one way to improve vehicle performance. But conventional electrohydraulics typically increase vehicle costs, have difficulty controlling systems that contain load-holding valves, and sacrifice efficiency for performance. A new electrohydraulic control technology, called Incova ( Intelligent control valve), overcomes such limitations.

Instead of controlling flow with spool-and-sleeve valves, the Incova distributed valve uses four independently controlled electrohydraulic poppet valves configured in a Wheatstone-bridge arrangement. An electronic controller mounts on the unit and built-in transducers measure cylinder-workport pressures. This lets Incova provide electronic load sensing and pressure compensation, quickly opening and closing valves as the load varies to maintain a constant velocity. Independent meter-in/meter-out capabilities provide the opportunity to develop proprietary software to customize performance and control.

The valve mounts at the machine's hydraulic cylinders and provides precise bidirectional metering, zero-leak load holding, as well as functions not possible with conventional spool valves. It also eliminates the need for counterbalance valves or pilotoperated checks and significantly reduces hose and fittings. An operator runs the system using electronic joysticks, and a controller on the pump coordinates actions of other control units over an SAE J1939 (CAN) communication network.

PERFORMANCE UPGRADE
One benefit is that the Incova system can cut off-road vehicle cycle times in half by facilitating regenerative flows. The Wheatstonebridge arrangement permits multiple metering configurations, including gravity-lower regeneration and high-side regeneration. On a telescopic material handler, for example, gravity-lower regeneration routes oil from the cylinder's piston side to the rod side. Gravity provides the force to retract the lift cylinder and lower the boom without pump flow. Lowering speed is not limited by hydraulic pump size and full flow can be devoted to retracting the telescopic cylinder. Thus, cycle time to lower and retract a telescopic arm can be half that of a conventional system.

Relying on gravity also improves efficiency. Traditionally, pump pressure is metered across the valve, which consumes unnecessary power and generates heat. Take for example, a telehandler that simultaneously lowers and retracts a load. Retracting requires 120 bar and 75 lpm, and lowering (because of gravity) requires 75 lpm and 0 bar. In a traditional system, on the other hand, the spool valve meters the pump's 120 bar to the required 0 bar. Tests show the traditional system requires 31 kW of power and generates 24 kW of heat, whereas the Incova system needs only 15 kW of power and generates 13 kW of heat — a 50% reduction in parasitic losses and energy requirements. Incova also eliminates the need for load-holding valves and their inherent power losses, and permits flow regeneration at the cylinder to reduce line losses.

When cylinder forces are small, such as extending a light load, highside regeneration reduces cycle times by up to 50%. Here, the cylinder's rod-end and cap-end ports connect and pump flow need only match the rod volume. The cylinder extends faster and requires less pump flow. Because integrated sensors continuously measure load pressures, the intelligent system automatically shifts from low-side to high-side regeneration to standard metering based on load conditions, much like a car's automatic transmission.

Electronic load-sensing and pressure-compensation features also let multiple functions operate simultaneously, regardless of load conditions. Multifunctioning is critical on equipment because operators routinely move more than one actuator at a time. Hydraulic systems with load-holding valves often encounter "cross talk" between control and load-holding valves that results in a chattering cylinder. The Incova valve performs both control and load-holding functions, eliminating this problem.

Precise control and stability permits coordinated X-Y movements. For instance, telehandler-joystick movements can simultaneously lift, extend, and tilt the fork and automatically keep the load parallel or perpendicular to the ground. In the past, only an expert operator could accomplish this feat. Now, even rental operators can move loads with great precision.

SAFE AND RELIABLE
The number-one safety and warranty issue for most equipment OEMs is plumbing failures and oil leaks. The best way to minimize this problem is to use fewer fittings and less hose and tubing. Incova relies on a hydraulic bus similar to an electrical communication bus, with a single pressure and return line routed to each function.

This can significantly cut the amount of hose and fittings in a hydraulic system. For example, it can reduce plumbing on a telehandler by 50% and the number of fittings by 30%. This means fewer potential leak points and lower hardware costs. Having only two hoses also means more flexibility in configuring a vehicle. For instance, adding an auxiliary valve to the end of a boom means simply mounting the valve and connecting to the existing supply and return lines.

Integrated pressure transducers can also improve vehicle safety by letting the system control load acceleration and deceleration. This can be used, for instance, to prevent a telehandler from inertial tip-over when stopping a load too quickly. The system also improves diagnostic capabilities, with the ability to sense pressure abnormalities across a valve, sticking poppets, or coil failures. And the system can provide feedback on various load conditions, such as the approximate weight of a load.

The Incova valve can be actuated without pump pressure, provided it has electrical power. This lets a vehicle lower a load without engine power. Husco's electronic E406 joystick also incorporates redundant sensing to prevent a sensor failure from causing unwanted motion. Adding a seat switch can also stop hydraulic movements when the driver is not in an acceptable operating position.

In the past, many OEMs have shied away from electrohydraulic control systems because users felt additional features were not worth a higher price. Husco aims to price Incova systems on par with or less than pilot-operated hydraulic systems. Significant savings come from eliminating many components found in a traditional hydraulic system. For example, a telehandler eliminates four counterbalance valves, a compensation cylinder, the pilot-operated joystick and associated plumbing, main control valve, 65% of the plumbing, and the installation labor associated with all those components. Thus, costs compare favorably to traditional hydraulics on a total system basis, as well as providing value-added features not possible with standard electrohydraulic-control systems.

The technology is suited for a range of construction vehicles, including telehandlers, backhoes, excavators, forestry machines, and material-handling equipment.

For more information:
Husco International,
(262) 513-4200,
www.huscointl.com