Are the glory days of hybrid construction equipment finally arriving? It’s hard to argue with a technology that offers reductions in fuel consumption and increased functionality, but most users still focus closely on ROI in evaluating the machines.
Hybrid technology has a long history, depending on how you define it. Rather than struggling with semantics, two technologies are commonly viewed as “hybrid” in the construction equipment arena.
One is the diesel-electric approach, in which a diesel engine running at optimum rpm supplies power to an electric motor that does all the heavy lifting. It’s not a new concept; for example, it has been used in locomotives since the 1920s.
Another concept involves the use of capacitors to capture waste energy from equipment operations such as boom deceleration and supplying it quickly to the machine for reuse.
Considerable development resources were being applied to construction machinery in the
2000s, with machines appearing on the market later in the decade. As most of us recall, 2008 was not the best year to be introducing construction equipment of any kind, let alone new technology that involved a price premium over the other models out there. Despite the recession, hybrids have slowly won interest in the marketplace.
Many equipment OEMs showed interest in the concept. Volvo Construction Equipment, for example, unveiled the prototype of a sophisticated hybrid wheel loader at CONEXPO 2008 that turned a lot of heads. Ultimately, the company decided not to proceed to market with it, citing concerns about payback for the customer.
Caterpillar’s D7E bulldozer was launched in 2008. Energy from a Cat C9.3 diesel engine is converted into AC electrical current to power the final drives as well as DC to power accessories. The electric drive permits a simplified transmission and an engine that runs at optimum conditions.
Since then, Cat has introduced what some would call “true” hybrid equipment with the
308-horsepower 336E H hybrid excavator that uses a hydraulic hybrid system to improve fuel efficiency up to 25 per cent. According to Cat, the 37-ton machine will move up to 50 per cent more material per gallon of fuel than a 336D under a variety of operating conditions.
Three technologies are responsible, says Cat. The Electronic Standardized Programmable pump conserves fuel with engine power management by smoothing transitions between the hydraulic pumps and the accumulator; the Adaptive Control System optimizes performance using restriction management; and a capacitor that enables the machine to reuse brake energy and then release it during swing acceleration.
According to a Cat spokesperson, the company is actively researching ultracapacitors with even higher capabilities.
Komatsu America Corp., too, was an early market leader. In 2008 it launched the PC200-8E0 hybrid excavator. It claims to have sold more than 2,500 hybrid excavators worldwide.
The firm is now up to the third generation of the technology, with the HB215LC-2 excavator. A larger machine, it has an operating weight of 49,383pounds and a bucket capacity of 1.57 cubic yards.
Komatsu’s Hybrid System includes an electric swing motor, a power generator motor, an ultracapacitor and a 139-horsepower SAA-4D107E-2-A diesel engine.
Kinetic energy generated during swing braking is converted to electricity, which goes to an inverter and is then captured by the ultracapacitor. This energy is released quickly for upper structure rotation and to assist the engine as determined by the hybrid controller.
That means the system supplies about 60 additional horsepower to support the engine or the swing power.
Komatsu estimates an approximate 20 per cent reduction in fuel consumption for many users along with commensurate reductions in carbon dioxide emissions compared to an equivalent conventional excavator.
There are actually two sources of energy recovery in this excavator, explains Rob Orlowski, product manager, excavators, at Komatsu America.
The first is energy captured from the swing. “You have a great deal of momentum with the arm carrying a bucket full of dirt. Stopping it takes a tremendous amount of force—force that can be quickly captured and temporarily stored in an ultracapacitor.”
The second source of energy is the engine. “There is a motor generator sandwiched between the engine and the hydraulic pumps that collect energy that would normally be wasted. You can capture that energy when the engine is not being used to capacity,” says Orlowski. “The ultracapacitor in the excavator lets you capture huge amounts of energy very quickly, store it temporarily and release it quickly,” says Orlowski.
While hybrid automobiles tend not to be high-level performers, a hybrid excavator will outperform its conventional counterparts in productivity. Orlowski says some customers have noticed faster swing speeds than those of a comparable conventional excavator.
Fuel savings are posited at 25 per cent, though Orlowski adds that it depends on the application. “You have some applications where you have more swing speed and users claim more than 25 per cent savings.” However, he notes, “If you have an application where you’re not swinging the boom much, you’re not capturing that energy.”
“There’s no magic answer on whether to choose hybrid or conventional technology, but certainly an operation that requires a heavy amount of swing use and long hours lends itself to a hybrid excavator.” Payback depends on the kind of operation you have, how you use your equipment, your cost of operations including the cost of fuel, amount of swing, numbers of hours that the machine is working, etc.
“It’s a performance issue, as well,” says Orlowski. “You’re using two types of energy—hydraulic and the electric swing motor. In the electric swing motor, that energy is separate from the hydraulic pump. We have a lot of hybrid customers who are very pleased with how quick the machine is, just because it has two different sources of energy.”
There are some common misunderstandings about the technology. “Some customers think there’s a battery in the machine. That’s a common misconception,” says Orlowski.
“Another one is the customers think that this is new technology. In fact, we’ve been developing this technology since the 1990s.”
He notes that use of this technology is relatively strong in Eastern Canada, particularly in Quebec. “For one thing, they really seem to care about the environment. There seems to be a greater awareness of that, and customers tend to like that green image.” Another factor is the higher cost of fuel.
“It’s exciting. This technology is certainly scalable. You could potentially use it in different sizes of excavator—who knows what the future might bring?” notes Orlowski.
John Deere very recently introduced its 644K hybrid wheel loader.
This machine comes with a 229-horsepower PowerTech 6.8-litre IT4/Stage IIIB engine that runs at an operator-selected constant speed between 900 and 1,800 rpm. The engine’s constant operating speed maintains continuous hydraulic flow at all times, which delivers crisp hydraulic responsiveness and reduces cycle times. The electric motor smoothly delivers torque resulting in fluid operation and a smoother ride.
According to Deere, the 644K hybrid can reduce fuel consumption up to 25 per cent.
Another benefit is noise reduction, since the engine runs at a constant speed that is continuous and less noticeable, according to John Chesterman, product marketing manager, Four Wheel Drive Loaders, John Deere Construction & Forestry.
Four main components are involved: A brushless generator supplie
s engine energy to an inverter, which in turn delivers electrical energy to the single electric brushless motor. The motor does much the same job as a torque convertor, but also works as a generator to recycle energy back into the system. A water-cooled brake resistor passively consumes excess energy as required.
Deere suggests a figure of 25 per cent fuel savings for many users, with even better numbers depending on the application.
“How many hours are you running the machine?” Chesterman asks. Heavy use has a big impact on payback.
The opportunity goes beyond fuel efficiency, he emphasizes; it’s a question of the longevity of the machine. “Electric motors are extremely durable,” he notes, and transmission wear is significantly reduced. For example, the machine does not have a reverse gear… the electric motor runs backwards to move in reverse. And since the machine runs at constant rpm, it gets fewer stress loads. You won’t be revving the engine.
The user can adjust the engine’s constant operating speed to match his own requirements for productivity versus power, for example.
“As soon as you use the word ‘hybrid,’ some people assume that there’s going to be a sacrifice in performance or efficiency. That is not the case at all,” says Chesterman. While the power specs might resemble those of a conventional machine, the user experience is quite different.
“Highly skilled operators, can make our conventional wheel loader perform similarly to the hybrid. However, the below-average operators have a much easier time operating the hybrid. And even the highly skilled guys find the hybrid very easy to operate, so it’s a question of fatigue as well,” says Chesterman.
Coming soon will be a larger, 944 model. “It will only be available as a hybrid electric. We are very committed to this technology,” says Chesterman.
EMISSIONS TESTS
The California Air Resources Board commissioned the University of California at Riverside’s Center for Environmental Research and technology (CE-CERT) to study emissions from hybrid equipment. The $2-million Hybrid Off-Road Equipment Pilot Project was completed in June 2013.
It examined the emissions benefits of the equipment in real world applications.
The Caterpillar D7E hybrid dozers and Komatsu HB215-LC-1 hybrid excavators were part of the study. Not surprisingly, emissions benefits depend heavily upon the type of work being done.
In the tests performed on the dozers, researchers recorded a two to 28 per cent increase in CO2 emissions, and a NOx increase of between 7 and 21 per cent, with lighter loads providing the greatest efficiencies and fewest NOx.
The excavators provided between a one per cent increase to a 28 per cent decrease in CO2 emissions in the tests, with demolition work providing a 23 per cent decrease and general construction a 13 per cent decrease in CO2 emissions.
The NOx impact of the excavators ranged from an 18 per cent decrease for demolition work to an 11 per cent increase for general construction.
These results are interesting but should not be considered universal and definitive. Kent Johnson, principal investigator, Emissions and Fuels Research at the university, offered some insight.
“After discussing the NOx difference with Cat, it appears the variability can be explained by their engine ratings methods. Thus, I could make the same statements about two conventional machines… This doesn’t mean the difference we measured isn’t real, it just says there can be differences between engine ratings.”
There is a correlation between NOx and fuel efficiency in any construction equipment, so in effect emissions seem to be a bit of a balancing act for the user and OEM.
