Hydraulics at the Heart of Tier 4 Machines
Advanced hydraulics on Tier 4 machines improve productivity and lower fuel consumption but they also require careful maintenance
The day for Tier 4 Final compliance has arrived. And to get here, OEMs faced several interrelated technology challenges. Some machines underwent complete redesigns of their systems, while other OEMs continually refined the engineering of their iterative systems. Regardless of their approach, the changes necessary for Tier 4 compliance impacted the function of machines’ drive and control hydraulics as well as performance, flexibility and reliability.
Most OEMs have taken a holistic approach and developed systems that optimize energy efficiency, yet meet emission standards. Today’s Tier 4 machines have “more brains,” creating synergies among the various systems of the machines.
How hydraulics make a significant improvement to Tier 4 machines
The hydraulic system is one of the main redesigned elements on Tier 4 machines. In many cases, the integration of electronic control with sophisticated new hydraulic components improves performance. With reduced emissions and intelligent integration, control of both diesel engines and hydraulic components can be matched to operate and optimally utilize engine output.
OEMs have increased efficiency by enhancing individual components. For example, variable pumps increase overall efficiency by delivering power to hydraulics systems yet demand less power from diesel systems. The improved functionality of hydraulic components enhances energy efficiency and reduces fuel consumption throughout the system.
The dimensions and placement of hydraulic components have improved machine balance and performance. Some of these modifications accommodate the needs of Tier 4 engines and the necessary aftertreatment hardware.
Cooling-fan speed is electronically controlled and optimized depending on the temperature of the engine coolant, hydraulic oil and ambient air. When cooling is not required, the hydraulically driven fan reduces speed so the power consumed to drive the fan is low. Reducing this parasitic loss maximizes efficiency while reducing overall fuel consumption. Hydraulic fan drives improve fuel economy by keeping engine temperature within a narrow range (since diesel engines exhibit maximum fuel efficiency within a fairly small range).
Hydraulically driven fans also have a reverse function, allowing coolers to be easily blown out, simplifying maintenance.
Enhancements to some hydraulic systems include larger displacement hydraulic pumps, new engine and pump matching control, and reduced hydraulic loss throughout the system.
Many older machines had hydraulic systems that used two variable-displacement piston pumps. The crucial difference in Tier 4 machines is increased pump displacement.
Matching engine to hydraulic pump delivery
The engine-pump matching control allows engine speed to match the hydraulic pump delivery for both high- and low-duty cycles to deliver “variable speed matching.” Tier 4 excavators that employ closed-centre load-sensing hydraulic systems, with variable speed matching, adjust engine speed to match the hydraulic load.
Although closed-centre load-sensing hydraulics have been around for more than 20 years, relief or system maximum pressures have steadily increased over that time. Tier 4 Final machines have added improvements that assist with power balancing and digital communications from the pump controller to the engine. In many instances, OEMs have enlarged pumps to protect flow rates because Tier 4 engines and pumps turn more slowly than their predecessors.
On some older excavators, engines ran at a high speed whether the pumps were delivering a large or small amount of oil. On Tier 4 machines, the machine monitors oil delivery, and in applications where the delivery is small, engine speed adjusts to a lower level to save energy and reduce fuel consumption.
Unlike open-centre hydraulic systems, a closed-centre system ensures that actuator speed is controlled solely by valve spool position. And this works even when loads change or multiple actuators move simultaneously. Bottom line: Less power will be used to move a lighter load – such as a bucket full of low-density soil – and heavy loads are as maneuverable as lighter loads.
On many pre-Tier 4 machines, whether the pump delivery was large or small, engine speed was always high. On Tier 4 machines, if high flow delivery is required, the engine speed will still be high. However, in light-duty applications that require low pump delivery, machines obtain sufficient hydraulic flow at a lower engine speed with variable matching control. Ultimately, the engine speed matches with the pump delivery at the most efficient point to effectively lower fuel consumption in light- and medium-duty applications.
Multiple working modes match engine speed and pump output to load conditions based on the positions of operator controls. This load sensing automatically matches pump output to work conditions. For example, if delicate control is needed when working close to obstacles, controls can be set for low response for the most precise position control. Optimally, work modes can be selected for the best or most precise response to achieve high speed or fine control as the working areas require.
During the digging and hoisting part of an excavator cycle, engine speed and fuel consumption between Tier 4 models and older machines are quite similar because those actions require high flow, and therefore high engine speed.
However, on the dump cycle of an excavator, the engine speed of Tier 4 machines lowers, while predecessor machines remained high.
The same is true when an excavator is returning to the hole. During this part of the cycle, when lower flow is required, Tier 4 machines deliver the greatest fuel savings because they can lower engine speed, while older machines could not.
In fine-grading applications, when the boom begins to raise, engine speed increases, so fuel consumption for Tier 4 machines and older machines is nearly identical. However, when reverse grading begins, the arm moves away from the machine and the boom lowers, causing Tier 4 engine speed to lower while predecessor machine speed remained high.
Other subtle improvements to Tier 4 hydraulic systems have increased efficiency. Increased diameter of some of the piping reduces loss in the system. Additional benefits and features include the arm quick return valve. When an operator goes to dump material from the bucket using an “arm out” function, the quick-return valve reroutes a portion of the oil that would otherwise go back to the main valve. By sending the oil back to the tank and bypassing the main control valve, this speeds up the dump speed, contributing to improved fuel consumption and productivity.
Some Tier 4 machines have added swash-angle sensors on the pumps. These sensors permit the engine to “throttle back’’ 100 to 150 rpm during light or medium work (swash angles are a confirming signal) to save fuel, further reducing emissions and extending the service lives of all components.
Other components, such as the merge/divide valve, are now equipped with full electronic controls, allowing the valve to be employed flexibly. Fuel and hydraulic losses can be cut by automatically shifting partial loads onto a tandem pump assembly, making the working half up to 30 percent more efficient because it pumps at a higher load than with its unloaded twin pump.
Maintenance is now more important
These highly engineered Tier 4 machines feature carefully calibrated systems, which means maintenance is more important than ever. And, while the advanced hydraulic systems on today’s machines ultimately have fewer preventive maintenance needs, Tier 4 machines require extra vigilance because poor maintenance practices can become extremely costly.
Filters and oils
To maintain these gains in productivity, one of the most important things equipment managers should still do is use the filters and oils specified by the OEM. High-efficiency hydraulic oil offers advantages at both low and high temperatures, so some OEMs require its use for their Tier 4 machines. At low temperatures, this high-efficiency oil has lower viscosity than other oils and offers improved operation in cold temperatures as well as improved starting ability. At high temperatures, the dynamic viscosity is higher, and that can reduce hydraulic leaks within the system, increase pump efficiency, and reduce hydraulic drift.
Similarly, the filters for hydraulic systems have vastly improved over the years. Old machines used filters made of pleated paper, but the new systems require spun micro glass. Although the newer filters cost more up front, they are far more efficient per operating hour, in some cases cleaning down to the 8-micron level.
Role of telematics in maintenance
Today, telematics plays an increasingly important role in fleet maintenance. Owners, operators and maintenance managers can monitor machines on the Web – anywhere and anytime. These onboard fleet-monitoring systems send preventive maintenance reminders directly from the machine, and provide equipment managers with pertinent information about machine usage as well as alerts for specific upcoming maintenance for better proactive maintenance planning.
Vigilant oil sampling and analysis
Despite the many advances in machine maintenance, equipment managers must maintain vigilant oil sampling and analysis. Technology today allows equipment managers to follow particle counts as well as advanced wear analysis, such as ferrography or ferrous metals morphology (the study of magnetic and other wear particles) to best predict life cycles of lubricated components.
Complimentary care and maintenance programs
To help off-set the owning and operating costs of Tier 4 machines, some OEMs have also introduced complimentary care and maintenance programs covering factory scheduled maintenance intervals for a given period of time (years or operating hours, whichever occurs first). Under these complimentary care and maintenance programs, services are performed by OEM-certified technicians.
All of these changes have impacted training as well. Some OEMs have shifted training emphasis onto owner and operator training because some of the largest maintenance risks/threats are consumables errors, including wrong fuel, oil or coolants.
In many instances, distributors have become even more instrumental to the training and maintenance education process for Tier 4 hydraulic systems. Some OEMs are now offering “distributor trainer only” classes. The goal in providing this training is to empower the distributor’s trainer to bring the necessary education and training to their area and technicians. In geographic areas that don’t have distributor-based educational training available, OEMs are still providing the necessary training directly to distributor technicians.
The advances on today’s Tier 4 machines offer incredible benefits to owners and operators, but they don’t maintain themselves – equipment managers do.
Doug Morris is director of product marketing, and K.E. “Skip” Kincaid, III, is developer/instructor of technical training for Komatsu America. Reprinted with permission of Equipment Manager, the magazine of the Association of Equipment Management Professionals (AEMP).