Hybrids Aren't the Only Earthmovers That Can Cut Fuel Costs

While hybrids get all the hype, advanced drivelines and hydraulic system innovations in traditional earthmovers yield major efficiency gains.

The Case D Series excavators use the Case Intelligent Hydraulic System (CIHS), which incorporates Boom Economy Control, Auto Economy Control, Swing Relief Control and Spool Stroke Control.
The Case D Series excavators use the Case Intelligent Hydraulic System (CIHS), which incorporates Boom Economy Control, Auto Economy Control, Swing Relief Control and Spool Stroke Control.

Hybrids have dominated press coverage, but conventional earthmoving equipment has also witnessed advancements that maximize fuel savings.

Fuel efficiency is about more than gallons burned per hour. “The real measure of fuel efficiency is a combination of yards per gallon and yards per hour,” says Brad Stemper, Solutions Marketing Manager, Case Construction Equipment.

Current earthmoving equipment cuts fuel consumption across the board. “Fuel efficiency gains of 5-20% are common and easily obtained,” says Jason Hurdis, Senior Market Professional, Caterpillar Inc..

No single technology is driving these gains. “They all play important and interrelated roles,” says Hurdis. “Load sense hydraulic systems were a big milestone. Advanced powertrains are another game changer. Eco Mode systems providing the same production levels with less fuel burn per production unit are the latest contributors. But other technologies such as grade control and payload control systems are vital for overall fuel efficiency achievement, as well.”

Caterpillar has invested in numerous fuel-saving technologies, including Eco Mode settings, Idle Management systems, payload systems and grade control systems.

Likewise, John Deere implemented many fuel-saving technology advancements. “Some examples are autonomous features such as lock-up torque converters, auto idle, auto shutdown, ECO modes or features that group multiple functions into one, like Driveline Assist on Deere’s articulated dump trucks (ADTs),” says Craig Timmerman, Product Marketing Manager, Engines and Drivetrains, John Deere Construction & Forestry. “The efficiency gains achieved range from just a few percent to as much as 15%.”

Unique powertrains increase efficiency

New driveline technology takes advantage of the strengths and efficiencies of both hydrostatic and mechanical drives.

For instance, Liebherr XPower Tier 4 Final large wheel loaders feature a power-split driveline. It combines a hydrostatic and a mechanical drive into one system. “Hydrostatic drive is the most efficient at going slow into the pile and mechanical drive for going fast uphill,” notes Mark Walcher, Product Manager, Wheel Loaders, Liebherr-Werk Bischofshofen GmBH. “[The power-split driveline] means the power of the engine is going in two paths, so there is less stress on the transmission, which increases its life significantly.”

Power supplied by the diesel engine is split via a planetary gearbox to a hydrostatic branch and a mechanical branch. The two branches are then combined again so that full performance is available. During operation, the ratio between the two branches is variably adjusted.

There is a higher hydrostatic portion when starting and loading, and a higher mechanical portion at higher speeds. Together, the two branches deliver 100% of the power delivered by the diesel engine; only the proportion changes.

The gearbox has two operating ranges. The first goes up to approximately 6 mph and the second up to the final speed of 25 mph. At the top of each range, 100% of the power and torque is transferred through the mechanical branch.

The transmission gearbox manages the interaction of the two drive types, adjusting between drives based on the application. “It is adjustable and continuously adapts the mixing ratio of the two drive paths without noticeable switching and without interrupting traction power,” says Martin Gschwend, Managing Director, Sales, Liebherr-Werk Bischofshofen GmBH. “Liebherr Power Efficiency [software] coordinates the engine and transmission so we are able to get much more fuel efficiency. Our comparative tests have shown that XPower wheel loaders require up to 30% less fuel than conventionally driven wheel loaders.”

Caterpillar recently added a continuously variable transmission (CVT) to the 966 and 972 wheel loaders that combines mechanical and hydrostatic systems. The XE version of the 966K loader with CVT provides up to a 25% improvement in the number of tons of material moved per unit of fuel.

The CVT replaces a traditional driveline’s torque converter with a hydraulic pump and motor (variator), which allows for smooth, continuous ratio changes between engine speed and machine speed. The variator runs cooler under heavy load than a torque converter. That allows the engine to operate in a more efficient range from 1,250-1,600 rpm. “Because a CVT does not have a torque converter, the major source of parasitic losses is removed,” says Hurdis.

Power is transmitted through the CVT in a parallel mechanical path, much like a powershift transmission. It is combined with variator power through a series of planetary gear sets. Transmission operation is automated and transparent to the operator.

Volvo Construction Equipment realized fuel efficiency gains on its wheel loaders with its Opti-Shift system, which consists of a lock-up torque converter and the reverse-by-braking (RBB) system to disengage the driveline and use the brakes to aid in directional change. “Along with enhanced operability and comfort, this system minimizes driveline losses and thus maximizes fuel efficiency, with up to 18% fuel efficiency gains over conventional machines,” says Ray Gallant, Volvo’s Vice President of Sales Support.

Volvo ADTs also use an innovative 6x4 drive mode. “This system engages only the front and mid-axles under normal conditions and will automatically activate lock-up for the third axle as needed,” says Gallant. This saves both fuel and tire wear.

Hydraulic system advancements

Hydraulics play a major role in fuel efficiency. “With hydraulics, you can take advantage of machine momentum and its natural movements to improve its working effort without relying on burning more fuel,” explains Stemper. “Hydraulic system advancements let you leverage the power and force that is already being produced by the machine. Increasing efficiency is about decreasing waste. Turning down hydraulic system output when not in use directly relates to overall machine efficiency.

“Generally speaking, we’ve made hydraulics more efficient by switching from fixed-displacement work pumps to variable displacement,” he notes. “These only put out as much flow as needed.”

Consider the Case Intelligent Hydraulic System (CIHS) on the D Series excavators. “This system relies on four integrated control systems to make the best use of the machine’s hydraulic power and momentum,” says Stemper.

The four systems that make up the CIHS are Boom Economy Control, which reduces rpms during boom down and swing; Auto Economy Control, which lowers rpms during idle and automatically shuts down the engine after a preset idle time; Swing Relief Control, which reduces hydraulic power at the swing start; and Spool Stroke Control, which adjusts hydraulic pressure during digs.

“This system has been matched with a new, electronically controlled pump, larger control valve and multiple sensors,” says Stemper. “Using improvements to the Spool Stroke Control system, D Series excavators also reuse hydraulic fluid whenever possible to automatically increase cycle times and efficiency. The operator experiences a more productive machine without losing the precision of the machine’s controls. Through these and other improvements, we’ve been able to achieve as much as a 14% improvement in fuel efficiency over previous Case excavators.”

Case is also designing equipment with more pumps. “It seems counter intuitive to add pumps as there is a continued focus on becoming more compact. But one pump limits your efficiency,” says Stemper. “By using multiple pumps and separating steering from the work circuit, we were able to match pumps to the pressures needed and reduce throttling losses.”

Liebherr uses an integrated systems approach, in which components are developed and produced in-house to meet the exact application requirements of a specific machine. This approach has been combined with the latest technology in positive control hydraulics and hydraulic flow regeneration for the optimal use of the energy in both individual and combined movements. Operators can actuate three or more overlapping or synchronized functions.

Liebherr wheeled excavators and dozers also use the Liebherr Power Efficiency System. It proactively intervenes in the engine management system, adjusting engine speed and swing angle of the hydraulic pump to provide optimum efficiency of the drive components.

Caterpillar incorporates several fuel-saving hydraulic systems on its machines, as well. “Split-flow hydraulic systems improve fuel efficiency by splitting high pressure (controls) from low pressure paths (torque converter),” says Hurdis. “Load sense hydraulics also improve fuel efficiency with proportional flow or minimum flow during non-working periods. Using larger displacement hydraulic pumps for increased flow at lower engine speeds also helps reduce fuel consumption and improve fuel efficiency. Lastly, implement pump torque limiting automatically balances hydraulic loads with desired machine performance.”

According to Timmerman, there are a number of hydraulic system technologies being incorporated into John Deere machines. “Examples include electronically controlled, variable-displacement pumps, valves designed to minimize pressure drop and variable-displacement motors,” he points out. “In addition to component advancements, there are many examples of system developments that improve efficiency. Grade control is one that is rapidly evolving on dozers, graders and excavators. Our customers are recognizing the value of these systems and making them a normal part of their business.”

Hyundai’s HX Series Tier 4 Final-compliant hydraulic excavators gain fuel efficiency with new engine technologies that combine selective catalytic reduction (SCR) and a diesel oxidation catalyst (DOC); a more efficient vertically stacked cooling design; electronic fan clutch; plus hydraulic system innovations. These features contribute to an overall fuel efficiency improvement of up to 10% compared to the 9A Series models.

Intelligent Power Control (IPC) automatically analyzes operator control patterns and adjusts flow and engine rpm for optimum performance and fuel savings. An 8-in. touchscreen cluster provides access to operator settable functions, including variable power modes and attachment flow and relief pressures. The variable power modes include Power (P), Standard (S) and Efficiency (E) modes for optimum engine to pump output in different applications. The monitor also provides critical machine operating and fuel consumption data.

Systems integration drives efficiency

Systems integration is a key requirement. “Transmissions, hydraulics, controls, axles, electronic technology and work tools must all be designed as a system for optimized efficiency,” says Hurdis. “Fuel efficiency is only as good as the weakest link in the entire machine.”

“Systems integration is the key to providing good fuel efficiency for our customers,” says Volvo’s Gallant. “Systems integration includes not only the balance between peak efficiencies of the machine components, but also the optimal balance with the customer’s applications and the flexibility to change and run efficiently in many applications.”

Opti-shift in Volvo loaders is one example of the dynamic integration of multiple systems. “The brake system, torque converter, transmission and engine are all continually adjusted to deliver optimum performance in any application, ranging from short cycle loading to long distance carry/roading applications,” says Gallant.

As machine designs progress, integration offers the greatest opportunity. “Systems integration plays a very large role in improving fuel efficiency as we continue to deliver more efficient construction machines,” says Timmerman. “For example, eco modes on many of our machines are accomplished by the engine rpm and transmission setting adjusting automatically to provide a more efficient total system. Another example is the Powerwise III system on our excavators, where the engine and hydraulic system work together and can provide the operator adjustable modes to meet the need of the application.

“One of the most significant technology contributors is a machine’s communication network,” he continues. “This enables the systems integration to take place. There is no single solution that will work for all construction machines. Therefore, enabling the different subsystems to work together in a more efficient manner is key to improving efficiency.”

Consider wheel loader design. “Today’s wheel loaders are built with a variety of electronic modules to control functionality,” says Stemper. “Computer Area Network (or CANbus) technology connects the modules and facilitates back and forth communication. With a CANbus, for example, the engine and the transmission are in sync at all times versus working as independent systems. As such, the transmission, related drivetrain components and engine work together to match the demands of a given mode or application."

As with most OEMs, Case is examining the commercial viability of hybrids. However, the immediate focus is on less obvious hybridization.

“This is the wholesale integration between engine, hydraulics and electronics — providing greater connectivity and interrelated operation of these systems to impact overall efficiency and productivity,” Stemper explains. “Incremental gains will continue as engineers fine tune the connections between these systems, learn how to capture and reuse more of the force and power the machine already exerts, and continue to focus on the balance of meeting emissions standards while providing the machine operator greater capabilities.”

“Moving forward, we will continue to see incremental gains in conventional machines as they fill the needs of the dominant market in the near term. Customers in these markets continue to ask for further improvements so they too can lower their cost of operation,” says Timmerman. “As for hybrid technology, the markets for these machines will continue to open up in the future.”

“We believe that hybrid machines are an important step forward, as are the technologies in alternate fuels and alternate power machines (such as electric machines),” says Gallant. “However, I also believe that conventional machines will continue to exist in conjunction with these new technologies and we need to continue to innovate to achieve even greater machine efficiencies.”