Volvo construction uses an innovative pin-on thumb design that allows the thumb to be used on its extendible dipper with an inner slide design.
Customers always demand more performance out of their backhoe-loaders, particularly on the back end. “In North America, the backhoe end of the machine is used about 70% of the time the machine is operating, so it’s always been an area of focus for our product teams,” says Kevin Hershberger, BHL marketing, Caterpillar.
Several criteria define backhoe performance. “Consider performance specs such as digging depth, forward reach and lift height for truck loading, lift capacity and breakout forces,” says George MacIntyre, global product marketing manager, Case Construction Equipment. “Other important characteristics include machine stability while roading, boom height for transport/working in confined spaces, overall machine dimensions and visibility.”
Other considerations include how much trench you can dig without repositioning the machine, and whether you can see past the boom in the trench or as it’s swinging up and over the side of a truck. “The biggest complaint from the field is the size of the boom, as operators have to look past them into the trench or over them when loading a truck,” says Jim Blower, JCB. The JCB boom is narrow in width and depth to address this issue.
Then there is the issue of strength vs. weight. “The boom has to be able to withstand all of the digging and lifting forces while being as light as possible to get the best performance,” says Blower.
“Strength is a very important attribute when designing the boom,” agrees Jamie Wright, product manager, Terex Construction Americas. “Terex uses an 8mm-thick steel tubular design with its booms, which adds considerable strength and durability to the product. Forged steel at each pivot point reduces wear on pins and bushings.”
A box-style boom design, such as found on Volvo backhoe-loaders, can combine both rigidity and light weight. “The boom is basically a box section with a forging on the bottom and the same forging on the top. It is enclosed,” explains Marcello Bargellini, backhoe product specialist, Volvo Construction Equipment.
Keeping hydraulic lines safe is another priority on any good backhoe design. For instance, many manufacturers route hydraulic lines inside the boom so they are protected, and pay special attention to areas where plumbing has to be exposed. “To the extent that is possible, we always try to use tubes (vs. hoses) for longer life,” says Bargellini.
“Neat routing of hydraulic hoses increases visibility and reduces hose damage,” says Wright. “Visibility to both the loader and backhoe is important for overall efficient operation. A well-dimensioned boom and boom placement give the operator an excellent view into the trench at any position.”
Advantages of over center
Visibility was one of the focal points in development of Case’s N Series backhoes. “Engineering put great emphasis on making sure that any modifications to the boom design to improve performance would not interfere with the operator’s line of sight to the backhoe’s work area,” says MacIntyre. “Case engineering mapped the line-of-site visibility with new boom design concepts to better understand the impact to visibility with any potential changes to the boom design.”
With the N Series, Case unveiled Power Lift technology, which channels hydraulic power directly to the boom with the touch of a button. The company claims this feature can provide lift capabilities comparable to an 8-ton excavator.
To handle the increased capability, Case redesigned the boom, replacing the traditional all-cast backhoe boom with the fabricated S boom. Oversized panels are consistently assembled via robotic welds, adding strength to withstand Power Lift forces. The swing tower, bucket links and internal portion of the extendible dipper stick continue to be cast components.
The new fabricated boom also allows for internal hose routings for improved protection. “Some customers complain that the auxiliary hoses on the boom/dipper get snagged on branches or other obstructions when operating in woods or confined spaces,” says MacIntyre. “The N Series boom design helps to address these concerns. The hydraulic hoses are routed inside the boom for greater protection. Also, Case rerouted hoses and changed the bracket design where the hoses intersect between the boom and dipper to provide less chance of contact with low overhangs. This modification also provides the additional benefit of lower transport height.”
The boom maintains a proven placement on the machine. “One of the mainstays of the Case backhoe design is the over-center boom,” says MacIntyre. The boom is positioned “over center” from vertical and tilts forward, with the boom cylinder pinned more rearward than non-over-center designs.
“Advantages of the over-center design include better balance and ride, lower transport height, steeper downward digging angles and uniform lift performance throughout the boom lifting heights,” says MacIntyre. “For an operator, this means the boom can lift, lower and reposition an object near the hydraulic capacity of the boom without degradation at deep depths.
“All backhoes on the market lift more at full boom raise, but drop off when they are below grade,” he notes. “The Case over-center design allows a very flat curve, meaning the design allows a backhoe to lift almost as much below grade as at full raise.” This is important when excavating below grade or setting pipe in the ground.
Backhoes can utilize a number of attachments, so hydraulic versatility is an important consideration. “If you want to install any attachment, the Volvo machine is equipped with a single- and double-acting circuit,” says Bargellini. “So you can actually convert from single- to double-acting on the same machine. You can also adjust the flow for those circuits.”
Caterpillar offers similar hydraulic system versatility. “Caterpillar offers a combined function hydraulic line kit, which allows use of one-way and two-way flow attachments from the same auxiliary lines,” says Hershberger.
“Machine performance is driven by many variables, including hydraulic systems, pressures, flows, cylinder sizes and pin locations,” he adds. “The shape of the boom factors into performance areas like visibility, truck loading performance and digging over foundation walls and other obstacles. All of these factors and others, such as hydraulic valve tuning, combine to deliver backhoe performance.”
Such capabilities can differentiate one machine from another. Consider the revamped slew system on Terex backhoes. “The TLB840 is designed with a new slew system that provides high torque for easy backfilling and slewing uphill,” says Wright.
Boom shape and geometry
Some manufacturers offer curved boom designs. “This design aids in machine balance, especially when the machine is being driven at speed,” says Blower. “The curved boom aids in throwing the backhoe weight over the tractor and not having it hang out the back of the machine.”
That said, JCB has chosen to stick with a straight boom design. “JCB has elected to stay with the straight boom open box design, as cylinders, hoses, valves, etc., can be located inside the box, thus protected from site damage,” Blower comments. Balance for roading purposes is achieved by moving items on the tractor, such as the engine, transmission, etc.
“The shape of the boom has no reflection on the machine’s performance in terms of digging or lifting,” Blower asserts. “The geometry of the boom and dipper working together along with the hydraulic cylinders and pressure provide the power and productivity within the backhoe, not the shape of the boom.”
However, Wright believes geometry is important when talking about overall backhoe performance. Terex uses a curved boom that, when combined with the large cylinders, increases digging performance. “The curved boom design also offers operators greater clearance to reach over obstacles and the ability to load closer into trucks for greater productivity,” he states.
Several generations of Caterpillar backhoe-loaders have featured an excavator-style boom. “Caterpillar launched the excavator-style curved boom on our 446 in 1989, then carried it over to our B Series machines (416, 426 and 436) in 1992,” says Hershberger. “At that time, and for years following, most competitors maintained a straight boom design. Today, many have added some curvature to their boom design. Since then, we’ve improved versatility through hydraulics and available work tools, such as the Cat hydraulic thumb.”
The excavator-style curved boom design on Caterpillar’s E-Series machines provides additional clearance over obstacles while digging a trench or truck loading. The narrow boom enhances the viewing area to the bucket and trench throughout the entire operating range. It features box section fabrication with thick wear plates for performance and durability.
The Volvo backhoe boom design employs an arched shape that is both narrow and tall. Arch designs are inherently strong, and have traditionally been used in bridge and building construction. The upper and lower end caps on the boom are designed to carry the high stress loads from the pivot pins and distribute them smoothly and evenly throughout the boom.
Another key criterion determined by boom geometry is bucket rotation. “Bucket rotation is very important if you want to scrape or dig,” notes Bargellini. “[Volvo’s] bucket rotates 205°, which is about the maximum industry standard.”
Similarly, a single-pin bucket linkage on the Caterpillar E-Series allows 205° of bucket rotation, while serrated edges on the stick provide improved material clamping.
Another component critical to performance is the backhoe swing casting. The casting on the E-Series features replaceable bushings for durability and service.
Volvo concentrated effort on the swing pivot design. “We are unique in the industry in that we place our swing cylinders on top,” says Bargellini. “We get them away from the dirt, which means longer seal and cylinder life. We also have a yoke on both the upper and lower hinge pivots. We use huge bushings on both pivots.”
Even the design of the boom lock can differentiate the backhoes. “The Volvo boom lock is spring applied and pressure released,” says Bargellini. “It is really easy to actuate by simply pushing the pilot control towers away from the operator. ”
“Safety is always the first concern with Terex,” adds Wright. “The Terex boom and swing locking system offers swing and boom lock at a touch of a button, and all from within the cab.”