He adds, "Our experience tells us that the lock-up torque converter and auto-idle/auto-shutdown have the potential to make the largest impact on fuel economy."
Volvo has increased the fuel efficiency of its wheel loaders by designing them to run at lower engine speeds. "The operation... is much more efficient at 1,100 to 1,500 rpm, where the torque curve is best. The loader is designed with plenty of hydraulic flow at low rpm to save fuel," says Tullo. "New re-handling buckets that enter the pile more easily also help. Couple these with TP link, which keeps 70% of breakout force through the lifting cycle, and we do not have to run the engine at high rpm to load our buckets."
This technology does necessitate operator training. "If they have run competitive machines, they must be completely retrained to realize the fuel savings by low rpm loading cycles," Tullo notes. He advises working at between 1,200 and 1,700 rpm when digging or loading material.
Save with on-demand hydraulics
"The design of the hydraulic system is critical to machine fuel economy," says Hindman. "The load-sensing hydraulic system utilized in today's John Deere wheel loaders provides only the necessary flow required by the operator for the task at hand. Special attention was paid to minimizing hydraulic losses (pressure drop) in the hydraulic system design for our new K-Series wheel loaders."
Of course, the role of the hydraulic system in potential fuel savings requires some perspective. "The hydraulic system plays a smaller role in fuel efficiency on a wheel loader than, say, an excavator," says Ellis. "But you try to maximize fuel efficiency in every aspect of machine design. Doosan has implemented on-demand pumps in its larger wheel loaders to maximize fuel efficiency."
It is all about eliminating unnecessary waste of energy. "Volvo has a load-sensing hydraulic system that improves fuel efficiency - the parasitic load on the engine activates the hydraulic pumps only when the machine is working," says Tullo. The engine and hydraulic system are also optimized for maximum efficiency. "Volvo designs the pumps around the engine curve so they can achieve full flow at low rpm. There is no need to run the engine up to the red line."
Get a grip
Wheel slippage is another energy waster. "Both wheel spin and slippage reduce fuel efficiency and increase operating costs," says Tullo.
Spin or slip control can be beneficial, depending on the operator skill level. "If a new operator is frequently spinning the tires while loading, this feature can have a significant impact on operating costs by improving fuel economy and minimizing tire wear," Hindman explains.
It is also beneficial in less than ideal ground conditions. "In poor underfoot conditions, spin/slip control features can impact fuel economy and production significantly by keeping the loader more mobile and producing," says Sameer Marathe, performance controls engineer for large wheel loaders, Caterpillar. "Without a spin/slip control feature, the operator can waste a lot of fuel maneuvering the machine... because he must deliver power to all the wheels and try positioning the machine to gain traction.
"Smart spin/slip control features can automatically divert power to wheels with good traction and get the machine mobile faster," he adds.
Of the spin/slip control features typically used on wheel loaders, those using brakes are the least efficient, Marathe asserts, because they waste energy across the brakes. "Features using lock-up differentials are more efficient," he states, "and features using independent wheel power control are most efficient - such as four-wheel hystat or electric drive."
Don't work up a sweat
Cooling systems have been designed to further reduce parasitic losses. "Auto-reversing cooling fans only run when cooling is required," notes Tullo, "and the speed is variable based on the temperature of the component."
The fuel savings from a hydraulically driven fan will vary. "The fuel savings is in direct relation to the environment and temperature the machine is working in," says Tullo. "The fan helps reduce burn up to 30% over conventional belt-driven systems. This is due to the automatic adjustability of fan speed, instead of running at high rpm constantly like belt-driven fans."