Advanced electro-hydraulics makes off-road equipment cleaner, safer, and more productive.
Clean air and oil hydraulics would seem to have little in common. But new emissions requirements for off-road equipment are, surprisingly, driving the need for advanced and innovative mobile-hydraulic controls.
Machine builders are turning to the latest electrohydraulic systems to improve vehicle efficiency and fuel economy, as well as make them safer and more productive. In the process they are meeting user demands for enhanced control, longer service life, easier diagnostics as machines become more complex and, of course, lower operating costs.
A growing trend in mobile equipment is communication between the engine, transmission, and other vehicle subsystems, according to John Treharn, systems engineering manager at Parker Hannifin's Mobile Systems Div., Lincolnshire, Ill. (www.parker.com). The goal, he says, is to optimize performance, cut waste, improve vehicle safety, and provide status feedback to the operators.
Key drivers are new EPA emissions guidelines for mobile equipment, and the new engines that the machines will require. "The Tier 2 and Tier 3 engine-emissions regulations are driving a lot of the need to have implements, cooling systems, and various other subsystems on the machine communicate with the engine," says Treharn.
In these engines, an onboard computer monitors operating information such as speed, boost pressure, and crank position, compares it with ideal conditions, and sends out commands that control fuel-injection quantity, pressure, and timing. Thus, managing engine performance depends on knowing the demands from vehicle propulsion, steering, and other hydraulically powered systems.
"We're taking information from the engine and making decisions to give priority to certain functions if horsepower is limited," says Treharn. The goal is to improve fuel economy, precisely manage available horsepower, and run the engine as close as possible to ideal speed and load conditions, he says. This can reduce emissions and, by matching the available power to the task at hand, result in better overall machine performance.
For instance, several manufacturers have developed cooling systems that interface with the engine controller. Denison Hydraulics, Marysville, Ohio (www.denisonhydraulics.com), offers a digitally controlled hydraulic fan drive that is said to improve fuel efficiency while providing more-precise thermal control.
Today, the radiator must cool engine oil, air-conditioning refrigerant, and transmission, drive train, and hydraulic fluids, says Gary Gotting, the company's fan-drive manager. It also preconditions combustion charge air and even controls the temperature inside the engine compartment.
"Traditional direct-drive fan systems lack the flexibility and controllability to accomplish all of these tasks efficiently," he says, "because their performance is almost entirely determined by engine speed. But engine speed and cooling are not generally well coordinated in these kinds of applications, and the result is a lot of wasted fuel turning the fan at much higher speeds than necessary."
For example, if high ambient temperatures mean more cooling is required at idle, the only way to obtain it with a traditional system is to increase engine speed. "But running the engine faster only adds to the thermal load on the system while increasing fuel consumption and exhaust-gas pollution," says Gotting. At the other end of the spectrum, the fan may not be needed when a vehicle is moving, but direct-drive fans continue to consume engine power and waste fuel, he explains.
By replacing traditional mechanically coupled drives with hydraulic versions, the fan can operate at optimum speed over the entire duty cycle. An electronic controller monitors inputs from various temperature sensors and provides output signals to the valves that regulate fan-motor speed.
The system can noticeably improve fuel economy. "The power absorbed by a rotating fan is much higher than most people believe," says Gotting. The fact is that a direct-drive fan can consume as much as 27 hp at 3,000 rpm, yet this level of cooling is required less than 5% of the time in most applications, he says. Cutting power consumption means better fuel economy and more-efficient operation, directly affecting how much environmental pollution the equipment puts out.
Emissions regulations have also put equipment manufacturers under added pressure to improve fuel economy. "Tier 2 and Tier 3 engines are in the range of 6 to 8% less fuel efficient, and there's no doubt the OEMs want to recover that lost efficiency," says Kells Hall, a senior vice president with Sauer Danfoss, Ames, Iowa (www.sauer-danfoss.com). That makes the efficiencies of propulsion and working systems much more important than even five years ago. "It's always been important in Europe, because of fuel costs," says Hall, "but in America durability, reliability, and cost have been more-pressing issues. Now, efficiency is coming on in a big way."
One way to compensate for lower fuel economy is to optimize performance through highly advanced machine guidance and control. For instance, TSD Integrated Controls, a joint venture between Sauer Danfoss and Topcon, Pleasanton, Calif. (www.tsdcontrols.com), provides OEMs with mobile electrohydraulic controls combined with advanced positioning and tracking systems. For instance, explains Hall, TSD's worksite-management software lets operators precisely determine how many yards of material they need to remove and where to move it to properly grade a site. The software calculates the most efficient method to remove dirt and transport it to another location.
GPS, laser-guidance signals, and on-board sensors provide precise positioning information to the controller on, say, a dozer or motor grader which, in turn, directs sophisticated electrohydraulic valves to move the blade. While the operator drives the machine in a prescribed path, the blade automatically scrapes just the right amount of material to set the proper grade.
The result is that a job can be completed with fewer passes, in fewer hours, in the most efficient way possible. "Even very good operators can't compete with a computer and lasers, it's much more efficient, productivity goes way up, and there's a big improvement in the quality of the site," says Hall.
In fact, he adds, it is now technically possible to eliminate the operator altogether and automate some applications. Given the accuracy of GPS combined with ground-reference signals, an electronic controller can position a machine in a worksite with the accuracy of a human operator. Now it's more a question of robustness, redundancy, and safety before autonomous operation becomes commercially viable, he says.
Another way manufacturers can build more-efficient machines is by eliminating energy losses that were once considered routine. Energy reclamation is a concept in the early stages of development, but quickly gaining momentum, says Parker's John Treharn. Every time a loader empties a bucket of dirt or a truck dumps a load, the raised boom or bed must, in turn, be lowered before the next work cycle begins. Typically that means resisting gravity by metering fluid from the hydraulic cylinders through valves, where the energy dissipates as heat.
With regenerative technology, he explains, the goal is to capture that energy in accumulatorlike devices rather than simply metering it away. The stored energy could then, conceivably, supplement the engine, power auxiliary systems, provide a redundant safety system, or offer a host of other uses.The concept is relatively new, says Treharn, but interest is gaining momentum, again due to emissions regulations. "Look at a garbage truck that lifts and lowers hundreds of times a day, all that is wasted energy," he says. With a properly sized storage system and the necessary controls, it might be possible to lower engine speed, run at idle more often, save fuel, and reduce emissions.
The link that lets machine subsystems communicate with one another and enables more-sophisticated control is CAN-Bus. Well established in automotive and on-highway applications, mobile-hydraulics manufacturers have stepped up development of CAN-Bus compatible subsystems.
For example, Bosch Rexroth, Hoffman Estates, Ill. (www.bosch-rexroth-us.com), recently announced several new additions to its growing family of CAN-compatible products. The RC 2-2 control unit is designed for tasks such as load-limiting control, pump control, and constant speed drives. The M4 load-sensing valve control block distributes flow to several different machine functions that can operate simultaneously. And the DI2 graphical display installs in an operator console and shows operating conditions and error messages, and can be custom programmed for a variety of application-based functions. A CAN-Bus interface allows simple and straightforward integration of these components into a machine's electronic network.
There are several reasons for the move to CAN, according to Terry Hershberger, director of electronic products for the company's Mobile Hydraulics business unit. The first is simplicity and easier installation. Like other fieldbus networks, CAN replaces the many individual wires running from a central controller to every valve and sensor with a single four-wire cable. Thus assembly tends to be quicker and more straightforward, and a missing communications link will quickly identify a miswired connection.
Safety and integrity are other drivers, says Hershberger, because of the fault-checking involved with every message. When the controller sends a message to a valve, for example, the valve, in turn, queries the controller to verify the command. Each device also contains a unique address that virtually eliminates the chances of misguided commands. And the system immediately pinpoints a broken wire, loose connection, or nonfunctioning solenoid. Troubleshooting hard-wired systems, on the other hand, can be extremely time consuming.
Because today's newer engines have CAN interfaces, load-management is another driver, says Hershberger. In addition to emissions issues, "many engines are running at lower speeds because of noise requirements, especially in Europe. With that in mind, we don't have the same power as before, so we have to manage it better."
In a piece of equipment such as a trencher, for instance, the RC 2-2 control unit might receive signals from an operator's joystick and, in turn, command the M4 valves to supply flow to both the cutter head and traction drive. But if the machine encounters particularly heavy soil that taxes the engine, the engine controller can override these commands and automatically direct more power to the cutter and less to the drive, and avoid stalling out. While hardwiring sophisticated sensors and controls into a load-management system is possible, says Hershberger, CAN makes the task much easier.
As CAN is integrated into more products such as sensors, joysticks, controllers, and valves, it opens the door to countless applications, says Hershberger. "The majority of machines being redesigned in the next three to five years will be going to CAN," he says. The old way of running wires to pumps and valves is becoming obsolete.
Though equipment manufacturers are increasingly looking to integrate machine operating systems, one problem is: closing the loop with electronic mobile controllers requires expertise in sophisticated programming languages. Those skills, says Parker Hannifin's John Treharn, are often in short supply, which can hamper product development and customization.
To provide high-level machine control and, at the same time, simplify integration of various vehicle systems, Parker has developed IQAN, a software-based machine-control system that includes a comprehensive family of products and development tools. "IQAN is a high-end solution, with over 80,000 man-hours spent on developing an extremely user-friendly operating system. We have basically empowered the OEM engineers to become software engineers. They don't need to write code, merely assign relationships between the input and output devices," says Treharn.
IQAN lets designers build virtual prototypes, by selecting components from a menu and adding input signals from control levers and sensors. Simulations tools can then evaluate the design and permit quick changes and adjustments to the system, before hardware and software are installed on a vehicle. On a machine, IQAN's electronic mobile controller integrates signals via a CAN-Bus from the engine, transmission, operator controls, and other systems and, in turn, controls electrohydraulic valves and cylinders to help optimize machine performance.
IQAN also addresses operator safety and productivity issues. "In the old days, operators were skilled on a particular type of machine," says Treharn. "Grader operators, for instance, only drove graders." Now, they're expected to operate all types of equipment, and are often expert at none of them.
"They're also expected to be in the equipment longer, operator fatigue becomes an issue. So we have to improve the controllability, responsiveness, and safety of the machine, and build in interlocks to prevent the operator from damaging the machine or endangering himself," he says.
The system's master display module interface permits machine performance characteristics to be altered in a matter of seconds, to adapt to different tasks or operators. Delicate motions, quicker actions, and different setups can be stored and recalled. Safety features include speed control, overload protection, temperature limits, and end-position damping.
Productivity improves by adding functions that improve motions and make the operator's job easier. For instance, the software can calculate the fastest, safest way to lower a load, instead of requiring the operator to control several different parameters. Tasks are completed quicker, with less stress and fatigue.
It also offers diagnostic capabilities. The system's master display module can isolate a nonfunctioning component, saving hours of troubleshooting. Many IQAN components are self-diagnostic, and will alert the operator in case of failure. The result is a compact, operationally reliable, and service-friendly system that increases both productivity and the useful life of equipment.
No threads, lower costs
Off-road machines that offer the latest electronic innovations, top-notch handling, and fuel efficiency are of little use if they are too expensive to afford. Like most OEMs today, mobile-equipment makers are looking to improve manufacturing efficiency and hold the line on costs. That has sparked a growing interest in the Aeroquip Snap-To-Connect (STC) connector, says Scott Campbell, a product manager with Eaton Corp.'s Technical Center, Maumee, Ohio (www.eaton.com).
The threadless connector is an alternative to conventional threaded-type fittings commonly used in fluid-power systems with working pressures up to 6,000 psi. The STC, says Campbell, reduces the time needed to install hydraulic hose and tubing assemblies, and improves machine accessibility. Instead of screwing on the connector and tightening with a wrench, connecting halves simply push together to form a leak-free connection. A latch ring positively engages the male and female halves, without any assembly tools.
Installations with conventional threaded fittings can take several minutes or even hours and are subject to leaks because of torquing inconsistencies and other variables. The STC connector lets even confined, difficult-to-reach connections be completed in minutes.
Japan-based Bunmei, for instance, recently turned to the connectors to streamline assembly of sugar-cane harvesters. "Bunmei was running into production bottlenecks, and the switch to STC let them reduce production time of the harvester and get more product through the door," says Campbell. The company replaced approximately 150 standard, metric screw-on connections with STC and reduced production time from three days to one and a half, he says.
While the primary benefit was faster throughput, the company saw performance benefits as well, explains Campbell. Eliminating leakage resulted in warranty savings. And because the connector rotates freely when not pressurized, installers can adjust the connection to the natural bend of the hose. This eliminates twists that can dramatically reduce hose life. With threaded connectors, on the other hand, a hose can twist when installed and this leads to premature failure. Another space-saving benefit is that STC female ports are machined into Eaton motors, which eliminates the need for an extra adapter between connector and housing. The connectors are available in sizes from 3/8 to 3/4 in.