Techwatch: Lightning fast flow

|  March 25, 2009 |

Where operators once needed to exert strength by manually pulling and pushing levers, newer electro-hydraulic controls rely on joysticks and the push of a button.

While complex in structure, electro-hydraulics simplify operation by handling many functions at a time. “Electronic controls allow us to do a lot more with hydraulics and create a system more in tune with engine operations,” says Richard Kimpel, senior engineering manager, Parker Hannifin.

Electro-hydraulics currently cost around $2,000 extra as an option on select machines, but most OEMs plan to eventually incorporate these systems as standard equipment.

Inner workings
Machines equipped with electro-hydraulics generally use one of two systems, each involving a microprocessor-based controller (or a computer) to monitor electro-hydraulic functions.

One system uses in-cab joysticks attached to a wire harness that runs an electric current to the motor. The motor powers the hydraulic pump and proportional valve responsible for regulating hydraulic flow. The other system uses joysticks and a wire harness or sensors to communicate with a solenoid-powered actuator (or valve). On both, the computer/control module will determine how much pressure is being exerted on the joystick to gauge speed and actuation of the blade or bucket.

Both systems also eliminate the need for in-cab hydraulic lines and levers, saving space and reducing the amount of heat and noise associated with typical hydraulics.

“Most early mobile electronic control components were actually designed for stationary industrial applications and they didn’t survive well in the rugged world of mobile equipment,” notes Clyde Thomas, senior manager, marketing and technical services, Eaton.

Suppliers worked to come up with more robust components to not only combat the elements, but also handle vibration better than early systems. Many now use ingress protection (IP) 67-rated housings to resist dust and temporary water immersion, according to Thomas.

Availability is also becoming less of an issue, as more OEMs equip a variety of machines with electro-hydraulics. Currently, electro-hydraulic equipped machines include backhoes, skid-steer loaders, compact track loaders, motor graders and excavators, with wheel loaders joining the ranks in the near future.

All the extras
As with any new technology, operator acceptance of electro-hydraulic controls began slowly, with interest building in the last few years, says Hank Schillmoeller, product development group, Case Construction Equipment. “Newer operators, or those acquainted with video games and computers, will become easily accustomed to using these,” he says.

Any operator can appreciate electro-hydraulics optimizing hydraulic flow, however. “In most cases, electro-hydraulics lead to greater accuracy, so operators accomplish the same job they once did in less time,” says Les Scott, crawler dozer product manager, Komatsu America.

The benefits don’t end there
Operators or OEMs can program in specific application parameters to be used again and again, or a combination of functions. “Differences in user skills and preferences resulted in a need for mobile equipment that can be configured to accommodate a variety of individuals. Software-programmable electronic controls offer a solution by adjusting machine capabilities at the flick of a switch,” Thomas says.

For instance, if a new operator always moves an excavator’s bucket too fast when digging, changing certain electro-hydraulic parameters on the machine’s computer can slow down a cylinder as it reaches its stroke for smoother movement. When you modify parameters, electrical impulses send a signal to the hydraulic valve to control how fast it actuates.
“Other functions include ‘return to dig’ to automatically reposition implements to begin a loading cycle,” says Gerald Graf, manager, hydraulic systems, Caterpillar. “More advanced yet is automatic dozer control to cut-to-contour using a grade control system, such as Cat’s AccuGrade technology.”

A dealer service person should set parameters originally, but in the future (and in some cases now) operators will be able to program different modes for themselves, says Stefan Salmonsson, wheel loader product specialist, Volvo Construction Equipment North America.

Electro-hydraulic controls are more ergonomic, leading to increased productivity. Pilot hydraulics can lead to lower productivity because hot hydraulic lines run into the operator station and connect directly to the pilot joystick controls. The added heat makes it harder for some operators to work comfortably. With electro-hydraulic joysticks, heat is not an issue. Operators can set bucket angles and boom position from the cab by simply moving the joystick controls, which are connected to wires. Popular joystick configurations include the ISO-pattern (or controlling the machine with the left hand, and using the right hand to control the boom/bucket) or the H-pattern (or SAE pattern), according to Gregg Zupancic, product marketing manager for skid steers and compact track loaders, John Deere Construction and Forestry.

Lower fuel usage, fewer emissions lead to lower operating costs. Electronic controls interface with the engine and transmission, making sure the engine runs in its sweet spot.

As a result, electro-hydraulics deliver power to the actuators more efficiently than prior hydraulics and prevent throttling losses by providing the correct flow without excess power. “You can set your pump to provide only the flow required as you speed up and slow down an actuator, so the total operation of the machine is smoother,” Kimpel explains. “You’re limiting power losses and controlling the engine more effectively, which leads to less fuel usage and lower machine emissions.”

Electro-hydraulic controls require little maintenance. These systems are relatively self-sufficient and require mainly routine maintenance similar to conventional hydraulics. “While they may be more technologically complex, they allow simplification by reducing the number of pilot lines,” Graf says. “This in turn reduces leak points and improves accessibility.”
Most electro-hydraulic components can also be tied into the machine’s electronic control module to monitor for problems, or you can identify and diagnose issues with diagnostic equipment. If you do encounter a problem you’re not familiar with, go to your dealer.

Electro-hydraulics are compatible with other technology. While it may be challenging to incorporate technology on a standard hydraulic machine, electro-hydraulically controlled machines have an advantage. “It’s easier to install additional machine controls, such as a laser leveling system on a dozer, because machines equipped with electro-hydraulics offer plug-and-play capability,” Schillmoeller says.

Future possibilities
Electro-hydraulics display a big advantage by managing the same amount of pressure as standard hydraulics through fingertip control, but they could provide even greater benefits in the future.

Eventually, manufacturers will offer electro-hydraulics on their standard machines and it will be even easier to change or add application parameters to suit a variety of operators. But for now, ask your dealer about computer software upgrades – which are available for certain machines – if you’re interested in managing multiple machine functions.