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Cat hybrid excavator delivers real-world fuel savings

Caterpillar is recording real-world fuel efficiency gains of up to 68 percent in its 336EH hybrid excavator, according to executives from the US earthmover manufacturer, DAVE BULLARD writes.

The benefits, they say, stem from Cat’s choice of a three-pronged approach to the technology, and from choosing a hydraulic solution over an electric one.

“Caterpillar has looked at a lot of different technologies for a long time, including electric, hydraulic and others,” Caterpillar Hydraulic Excavator Product Application Specialist Kit Kyarsgaard says.

“We had to maintain our reliability and durability, and the return on investment for our customers — they have to make the most money with our machines. We also had to think of sustainability and reducing the carbon footprint,” he adds.

Kyarsgaard gives the definition of hybrid technology as: “Taking energy, storing it and reusing it.” Most people think of electric technology when doing this, he says, but you can also do it with hydraulic energy and pressure.

When designing the 336EH excavator Caterpillar went down both paths and, while it holds a number of patents for electric hybrid technology, the company ultimately decided to go the hydraulic route, combining three technologies to achieve the best results and deliver the same performance as the standard 336E and D models.

Combining hybrid technology

The first tech is the Cat Hydraulic Hybrid Swing System, which uses nitrogen-filled accumulators to capture the excavator’s swing brake energy then reuse that energy during swing acceleration.

“We’re taking the hydraulic flow from the swing motor, which normally would just go back to the tank, and we’re putting it in these accumulators and storing up that energy,” Kyarsgaard says. “Then when you swing back the other way it’s reusing it, and that’s what gets you started.”

Then there’s the Adaptive Control System (ACS) valve, which controls and optimises the motion of the excavator by managing restrictions and flows.

“This is the brains of the machine,” Kyarsgaard says. “It’s a proprietary valve that Caterpillar has been designing for the past decade. Portions of it are being used in multiple different machines out there today.

“What it does is electronically control and share all that hydraulic fluid from all the different functions. So if you’re booming down it’s reusing that fluid and putting it back to the top end of the cylinder — it’s regenerating. But it’s not just boom down, it’s boom up as well.”

Finally, there’s the Electronic Standardized Programmable (ESP) pump, which transitions between the hydraulic hybrid power sources, engine and accumulator. It reduces the engine load as much as possible to save fuel.

Kyarsgaard says it’s an electronic pump that “knows how much to turn on and to turn off to maximise that power and performance”.

“With most hybrid excavators in the marketplace, swinging is the only place where you save fuel. With ours, you save fuel with all these three main components,” he adds.

Cat has also reduced the rpm in this C9.3 ACERT engine to 1650, from 1800 in the E-series, with no loss of power.

Lower fuel consumption

Cat is claiming up to 50 percent greater fuel efficiency in the 336E Hybrid, though some Cat production studies measuring every kilogram of dirt moved and every litre of fuel burned in the field have shown a 68 percent fuel efficiency gain.

“On average, though, we’re saying 50 percent,” Kyarsgaard says. “We’re pretty conservative; we want to make sure we exceed the customers’ expectations.”

A more accessible measurement is fuel consumption, which in the hybrid machine is 25 percent lower than the Cat 336E and 33 percent lower than the 336D (Tier 3).

“With an excavator your biggest expenses are your operator and your fuel bill,” Kyarsgaard says. “If you can reduce that fuel use as much as possible, that puts more money in that customer’s pocket.”

That’s a sentiment borne out by William Adams customer Lima South Quarry near Mansfield in Victoria.

“We had a 336D up on the face of the quarry doing heavy ripping and loading of dump trucks to come down the haul road to the crushers.” LS Quarry Sales & Account Manager Brendan Tipple says. “I spoke to the young operator, who said, ‘It’s the hardest work the machine will ever do.’

“Well, we took the D and sent it out into the field and put the new EH up on the face of the quarry. The fuel it’s burning averages out to about 20.8 litres per hour, whereas it was 30 to 34 before.

“So it’s certainly lived up to the promise of reduced fuel costs,” Tipple says. “It’s only been eight weeks and it’s delivering enormous benefits to the business.”

The quarry operator is operating the 336 EH at maximum revs, Tipple adds, and working for eight to 10 hours a day.

Spot the difference

TradeEarthmovers went out to William Adams’s testing ground to see operator demonstrator John Merlo put the Cat 336E L Hybrid excavator through its paces.

Looking at the machine, you’d be excused for thinking it’s a standard 336E model. Outwardly it is, except for a small ‘Hybrid’ sticker on the rump.

Cat kept things the same, Kyarsgaard says, because using most of the main components from the standard machine means no specialised electricians or mechanics are needed to work on it, and parts are easily available: “We wanted to keep things as simple as possible to make sure the customer can keep the machine running and reduce downtime as much as possible.”

Probably the biggest noticeable difference is this earthmover is a lot quieter than its siblings.

“When you reduce the rpms from 1800, or 1980 on the D-Series, to 1650 rpm you reduce the sound significantly as well,” Kyarsgaard says. “Most of the time we can have a normal conversation while the hybrid works right there, compared to the older versions, which are a lot louder.”

Merlo climbed the 36-tonner up a steep slope and began digging a trench out of the side of the pile of heavy earth. Even when the earthmover was working at top revs it was still remarkably quiet, delivering noise levels more likely to meet increasingly stringent council noise regulations.

On the whole, Merlo was swinging 45 degrees, which Kyarsgaard says is enough to fill the hydraulic accumulators. Even when working without swing, he adds, the machine still saves fuel through the ESP pump, ACS valve and lower revs.

Putting aside the cost savings from reduced fuel use, let’s put things in perspective from a sustainability point of view: In terms of CO2 emissions, a fuel saving of 25 percent on a hard-working excavator of this size is equivalent to taking 12 passenger cars off the road every year.


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