Backhoe Bucket
August 9th 2008 03:16 am By Web Development in India
When Curt Maas clamped an immense log — about 18 feet long and 20 inches in diameter — between the backhoe bucket and the hydraulic thumb of a new Cat 420E IT, we had just the fleeting thought that maybe he was kidding. The log seemed to us an impossible load for the machine. But the new Caterpillar made the lift, swung side-to-side with the log in an iron grip, and all the while, as far as we could tell, remained completely stable.
Maas, a test operator at Caterpillar’s Peoria (Ill.) Proving Ground (PPG), spent a couple of days withConstruction Equipmentthis past November, along with fellow operator Norm Miller, demonstrating the capabilities and features of the new 420E IT as representative of the company’s new E-Series backhoe-loader range. The lineup includes the 416E, 420E and 430E — with the latter two models also available with an integrated-tool-carrier (IT) front end. Standard digging depths are, respectively, 14.3, 14.3 and 15.4 feet.
The E-Series models, which replace the D-Series machines launched in late 2000, have quite a long list of design changes, compared with their predecessors and, according to Caterpillar, are also more productive at basic earthmoving tasks. The company put numbers to these stated productivity increases by sharing withCEthe results of a recent PPG comparison between the 420E IT and its 420D IT predecessor.
During our visit to PPG, operators Maas and Miller, along with the PPG backhoe-loader evaluation staff — Brad Holsapple, Gerry Stewart, Nick Krueger and Elizabeth Baldwin — demonstrated the methodology Caterpillar employs in its comparative testing. They arranged for us to observe the machines running side-by-side in trenching and truck-loading operations, while Krueger and Baldwin electronically recorded machine performance.
The electronic test-data-collection system the company uses is a computer-based process that allows every cycle of a test machine to be divided into its primary segments for later analysis. During the trenching comparison, for example, times are recorded for digging, swinging/dumping and returning, as well as for time spent repositioning.
To complement this look at the comparative performance of the new model and its predecessor, senior project engineer Jim Joy, from Caterpillar’s Building Construction Products Division in Clayton, N.C., met us at the Peoria Proving Ground to explain the details of the new E-Series design.
Structures, sticks and thumbs
Structurally, the design enhancements of the E-Series, compared with the D-Series, go right to the very backbone of the new machines — the mainframe, which has been modified significantly in four key areas: loader tower, front and rear axle mounts and swing post. According to Caterpillar, these mainframe changes further complement the already-high-strength design of D-Series models. Structural changes at the loader end of the machine include boom arms with a beefier box-section and a heavier torque tube that provides added rigidity to the assembly.
At the backhoe end, the boom has been modified, says Caterpillar, to reduce stress points in heavy-duty applications. Specific changes include one-piece side plates, versus fabricated side plates, larger mounting pins, and the addition of a replaceable wear pad to protect the boom underside from contact with work tools. Another significant change involves the boom nose, which has been reconfigured and strengthened to accommodate a new extendible stick. The boom lock has been redesigned, too, not only to keep the backhoe tighter during transport, but also to more effectively handle the stress of lifting with the stick when the boom is in its locked position.
The new extendible stick is a significant development for the E-Series, says Joy, and has been designed with an “outside slider” configuration. This means, he says, that the outer structure of the stick extends by sliding over a stationary inner structure. By comparison, the D-Series extendible stick pushed out an inner structure from within a stationary outer structure. And to maintain proper fit between the two sections, the new extendible stick incorporates a redesigned system of greaseless wear pads that can be adjusted in about 30 minutes, according to Caterpillar, compared with two hours on D-Series models.
Two rows of serrated gripping teeth on the bottom surface of the new extendible stick’s sliding section allow the operator to clamp material securely between the bucket and the stick without risking damage to the stick. But as handy as the gripping teeth might be, they can’t match the heavy-duty clamping power and dexterity of an E-Series extendible stick equipped with a hydraulic thumb.
Although the thumb is optional, all E-Series backhoe sticks, whether extendible or standard, are fitted with thumb and thumb-cylinder mounts to allow bolting on the attachment. (The D-Series could use a thumb only with a standard stick.) A thumb-plumbing kit allows quick installation of the attachment, a process facilitated if the machine is equipped with a six-function main valve from the factory.
Stronger hydraulics
In concept, the design of the closed-center, load-sensing, 43-gpm hydraulic system used in the E-Series is essentially the same as that for the D-Series. But, that said, the E-Series incorporates a number of refinements, among them an increase in main-relief pressure to 3,600 psi, up from 3,300 psi in the D-Series.
While the pressure increase results in more available hydraulic horsepower at both the backhoe and loader ends, the new hydraulic system also incorporates features that contribute to easier operation. New thumb wheels near the top of the backhoe joysticks, for example, allow easy control of auxiliary functions — such as the extendible stick and thumb. These controllers replace floor-mounted pedals in D-Series machines and are designed to provide low-effort, precise, proportional control of auxiliary functions — while also providing more foot room for the operator.
Also contributing to ease of operation are the new flow-sharing valves, which automatically proportion hydraulic flow between the boom and stick or between the boom and swing functions to more exactly match the operator’s intentions. In essence, says Joy, the flow-sharing valves make multiple-function operation easier to control, which helps less-experienced operators maintain acceptable production rates, and offers experienced operators more precise control and the prospect of higher production.
Caterpillar backhoe-loaders have long used the company’s “torque-limiter control,” which is basically a system that manages the distribution of engine power between the hydraulic system and the drive train. According to Joy, refinements in this system result not only in enhanced loader performance through a more precise split of engine power between the hydraulic system and drive wheels, but also in a more aggressive backhoe by assuring that maximum engine power is used to develop hydraulic flow.
The operator’s station for E-Series models has been completely redesigned, featuring a new four-post ROPS configuration that provides more interior space than the ROPS configuration for the D-Series. Overall, improvements to fit and finish in the new cab further contribute an automotive-type environment, which was already apparent on D-Series models.
For E-Series models, the front console has been made narrower to provide enhanced visibility to the loader bucket, and a hood that is lower by 3.5 inches at the cowl further improves visibility. The right-side console has been made more compact, further enlarging interior space, and a foot pedal controller for the tilt steering wheel makes the spin from loader to backhoe positions that much easier.
A significant change for E-Series models is the in-cab switch for easily changing the digging pattern between hydraulic-excavator and backhoe-loader configurations. A two-position electrical switch on the left console allows the selection. By contrast, D-series models had a pattern-changer control on the left side of the machine’s frame, behind the rear tire — obviously not as handy as the E-Series design.
Another cab enhancement of note is the increased performance of the optional air-conditioning system. A larger compressor, 20-percent increase in airflow, and repositioned vents go a long way toward increased operator comfort, says Caterpillar. In addition, the air-conditioning system incorporates easier-accessed filter locations, one in the right inner fender and one in the right console. Both can be cleaned with compressed air.
Combine the amenities of the new E-Series cab with Caterpillar’s fresh design for basic structures, hydraulics, power train and utility-enhancing features (like the new extendible stick and hydraulic thumb), and the result is a solid new E-Series platform that should serve the company long and well.
Two very different kinds of backhoe-loader buyers dominate sales of full-sized machines (dig depths of 14 feet and larger), and their very different expectations may have polarized the hydraulic-system designs in this most popular of true earthmovers. The relatively small group of volume buyers from government agencies and large rental fleets are looking for a bombproof machine and tend to be price sensitive. Owner/operators and small-business buyers, while certainly motivated by value, are willing to pay a little extra for proven production-improving features.
In order to take market share in this relatively high-dollar, high-volume machine category, manufacturers must appeal to both groups. They’ve done so admirably with technologies that can be added to machines as standard equipment. For example, the most recent new backhoe designs (from Caterpillar, New Holland and JCB) have replaced foot controls for extending sticks and auxiliary hydraulics with switches mounted on control levers. They employ finger and thumb dexterity to improve control and clear the floor for more comfortable footing.
Pilot hydraulic controls represent another kind of challenge to backhoe OEMs. These circuits are plumbed in between control levers and the valves on the backhoe’s main operating circuits. When you move a joystick in the cab, it activates a pilot hydraulic circuit, which in turn moves a spool on the main-pressure valve. Pilot hydraulics require less lever effort to manipulate the backhoe.
Main pressures in backhoes have climbed to a point where lever effort can influence productivity. Eight of the 35 backhoe models 14-foot and larger have hydraulic-system pressures of 3,500 psi or higher. All eight are available with pilot hydraulic controls, mostly as an option.
Why not make pilot hydraulics standard equipment? One reason is operator preference. Backhoe-loaders have been controlled by levers linked to main valves since their invention, and lots of operators claim they can feel pressure spikes in the hydraulic system when a bucket hits a hard object, like a natural-gas line. Some say pilot hydraulics insulate the control levers to that feedback from the bucket.
Another reason for keeping pilot hydraulics optional is their cost. Nevertheless, most manufacturers (Cat, Deere, JCB, Komatsu, Terex and Volvo) sell at least some of their machines with standard pilot-operated hydraulic controls.
“The inclusion of pilot controls has had the biggest impact on the industry in the last 24 months,” says Bob Tyler, with John Deere. “Operator comfort becomes increasingly more important as businesses try to keep their best operators. With pilot controls, operators are less fatigued at the end of the day, and more productive as a result.”
Deere makes pilot hydraulics standard on the 17-foot 710G, a machine that, by virtue of its size, is clearly targeted at buyers who are willing to pay for backhoe productivity. But pilot hydraulics are optional on the 15-foot 410G and 14-foot 310SG. They’re not offered on the base-model 310G.
Only JCB and Komatsu make pilot hydraulics standard across their full-sized backhoe offering. The other manufacturers retain some models without the feature. Caterpillar, for instance, doesn’t offer pilot controls on the 416E, but makes them standard on the 420E and 430E.
Splitting the product line has become common in recent months. Since the first of this year, Volvo made pilot hydraulics standard equipment on the BL70 but doesn’t offer the option on the lower-spec’d BL60. Terex announced that it would begin installing pilot controls as standard equipment on the TX970 and TX870, leaving the feature as an option on the smaller TX860 and TX760.
If this is indeed an indication of OEMs fielding a price leader for one set of buyers and a full-featured machine for another, it’s also possible that the buyer dichotomy may shape some backhoes’ basic DNA.
There is notable inconsistency in hydraulic-system designs used on today’s full-sized backhoes. Long-time backhoe-loader OEMs such as JCB, Case and New Holland use open-centered hydraulic circuits with fixed-displacement gear pumps. Those who began manufacturing backhoes more recently, such as Caterpillar, Komatsu and Terex, use closed-center hydraulics.
John Deere started a shakeup several years ago by adding machines with closed-center hydraulics to a lineup that had always used open-center designs.
For Deere — one of the venerable names in backhoe-loader manufacture — to design larger backhoe-loaders with closed-center systems and retain 14-foot machines (the 310G and SG) with open-center hydraulics, there must have been convincing market research measuring a significant customer base for both.
The newest entrant to the backhoe market, Volvo, is making similar moves. Volvo first brought the BL70 with a closed-center system, but followed with open-center hydraulics in the BL60. The two machines are nearly identical structurally — same dig depth and basic dimensions — but the BL60 has a little less engine and hydraulic horsepower.
It’s extremely unlikely that an OEM would redesign a system with a higher-cost pump that has even the slightest perception, right or wrong, of shorter life if there was also a strong operator preference for another type of system.
It’s much more likely that a closed-center circuit — technology that drives all full-sized excavators — is a very good choice for production earthmoving. Thanks to Caterpillar bringing it to backhoe-loaders in the 1980s, the challenge to other OEMs competing in the product category has been to either make their open-center systems perform more like closed-center systems, or to build a closed-center system that’s cost effective for these smaller machines.
All of the JCB backhoes, New Holland’s B115, and Volvo’s BL60 use open-center circuits with load-sensing valves that can vary pump flow with oil demand. When flow requirements fall, the valve signals one of these machines’ twin hydraulic pumps to shut down, reducing the amount of energy the machine wastes pushing hydraulic oil over relief. The feature is similar to the interaction between a variable-displacement pump and the main valve in a closed-center system.
There should be lots of new machines to evaluate between now and the end of 2007, when under-100-hp engines will have to comply with EPA’s Tier 3 emissions limits. Real-world issues such as dealer support and operator acceptance should influence those purchase decisions more than pilot hydraulics or closed-center circuits, but it is encouraging to see that sophisticated technologies are shaping the kind of backhoes available. In the end, the industry gets a choice of more-productive backhoes.
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