Apps-e

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Hydraulics for Full Tree Harvesting Machines

RE 00 207/10.00

Hydraulics for Full Tree HarvestingMachines

S. AppsBasic Technologies, CanadaPhone +1 905 735-05 10Fax +1 905 788-35 84E-mail [email protected]

Full Tree Harvesting - What is it?

Full tree harvesting (FTH) is primarily a NorthAmerican tree-harvesting principle where by thetree is handled throughout the harvesting processin its full-length form. The steps within the proc-ess include: felling (cutting); transporting (withinthe forest); processing (preparing for transport tomill) and; loading. There are several variations ofthis process, and consequently several differenttypes of machines, due to terrain conditions and/or tree size. For the purpose of this presentationthe most common method and types of machineswill be discussed.

Types of Full Tree HarvestingMachines

Feller BunchersThe feller buncher is used to cut (fell) and thenbunch or pile the trees on the ground. The originsof the feller buncher come from the excavator, thusits appearance. However, this is where the similari-ties end. The hydraulic system, the machine struc-ture, the tractive effort and boom attachment areall significantly different. For example, the empha-sis, or priority, is not on the slewing function as itis with an excavator. A feller buncher may be re-quired to perform as many as six or seven move-ments simultaneously with each movement beingequally as important as the other. Due to the se-vere terrain conditions in which this machine mustoperate, as well as heavier loads it must lift, themachines structure is significantly stronger thena typical excavator. The steep slopes, commonlyfound in North American forests, require the ma-chines tractive effort to weight ratio to be one to

Disc Saw felling Head

Feller Buncher

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one or greater where as in an excavator it is less.Finally, a high-speed disc saw felling headmounted on the boom is perhaps the most con-trasting visual difference between a feller buncherand an excavator.

Disc Saw felling HeadThe disc saw felling head is perhaps the most im-portant element of a feller buncher. The head is thepart which does the cutting of the tree as well asholds or bunches cut trees before they are laiddown on the ground. The cutting is done using afly wheel or inertial type disc with carbide tippedsaw teeth fastened on the perimeter of the disc.The disc is driven by a hydraulic motor while thegrab arms are controlled via cylinders.

SkiddersTo remove a felled tree from the forest, a machinecalled a skidder is used. By the nature of the name,the machine literally skids trees through theforest and then out to a processing site. Althougha simple process, the demands put on this machineare unparalleled in the mobile field. Typically thesemachines are 4 wheel driven, with some designsgoing to six and eight wheels (bogey systems) anduntil recently were almost exclusively mechanicallypowered using power shift gearboxes and driveaxles. The trend over the last couple of years how-ever, is to move towards hydrostatic transmissionswith more and more manufacturers exploring thisavenue.

DelimbersOnce a tree has been brought out of the woods toa processing site, the next step in the full tree har-vesting process is to prepare it for road transport.When the tree arrives at the site it is still full lengthwith branches and limbs still attached. Dependingon the final destination, and intended use of thelumber, the tree may or may not have to be cut toa predetermined length. However, in all cases thebranches and limbs must be removed. To accom-plish this a machine called a delimber is used. Adelimber is a stand-alone piece of equipment,which is then fitted to a carrier. Typically the car-rier is a tracked excavator which has had the boom

Skidder

DelimberLog Loaders

removed. The carriers hydraulic system then pro-vides the power to the delimber.

The basic operation of a delimber is to grasp thetree, then via drive rolls or a winch system, pull thetree through a set of stationary knives whichthen literally shear or delimb the branches fromthe tree. As stated, it may be required that the treesbe cut into predetermined lengths thus providingfixed lengths of logs for the buyer of the wood.Electronic measuring systems in conjunction withproportional control of the rolls or winch motorsprovide this function.

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Log LoadersThe last step in the full tree harvesting process isto load the fully processed tree or log onto a haul-ing truck. A log loader accomplishes this function.Much like the feller buncher, a log loaders originscome from the excavator. Many of the differencesbetween a feller buncher and an excavator alsoapply with a log loader. However, the difference isthat a log loader has a hydraulically powered grap-ple mounted on the end of the boom. In addition,depending on customer requirements, sometimesthe operators cab is elevated in order to providebetter visibility.

A4VG

Hydraulic Systems and Compo-nents for FTH MachinesHydraulics plays a significant role in todays forestrymachines and is perfectly suited where high loadsand precision movements are required. High powerto weight ratio and fine metering capabilities, areonly two of the reasons why. As a result of todaysever increasing demands on efficiency, productiv-ity, reliability and state of the art technology,Rexroth Hydraulics, Brueninghaus Hydromatik andLohmann & Stolterfoht have developed productfamilies which meet and often surpass those needsof forestry machine manufacturers.

Hydraulics found in todays FTH machines cover thecomplete spectrum of system concepts and prin-ciples as well as types of components. Componentssuch as open and closed loop pumps, motors in-tegrated with gear drives, standard throttling, loadsensing or LUDV distribution valves, machine con-trol concepts from simple power regulation to fullmicroprocessor controlled systems, can all be foundoperating in forests throughout North America.Electronics can also be found on some machineshowever, it should be pointed out that this is morethe exception than the norm. With the increase inreliability and user friendliness of such systems,this technology is slowly gaining acceptance andis surely a harbinger of things to come in the evo-lution of FTH machines.

Rexroth Product Offering forFTH MachinesThe vast range of the Rexroth product offering issecond to none in the global hydraulics industry.Products from all three business units, RexrothHydraulics, Brueninghaus Hydromatik andLohmann & Stolterfoht lend themselves perfectlyto FTH applications. The following are those com-ponents or component families most commonlyused today:

A11VO and A10VOThe A11VO and A10VO pumps from BHY offer thecomplete size and pressure range, along with awide variety of control options, needed to powerthe open loop hydraulic systems on FTH machines.Power regulated, with load sensing and cross sens-ing controlled A11VO pumps are commonly usedfor the carrier functions on feller bunchers and logloaders. A11VO and A10VO pumps, with load sens-ing controls, fit the need for the working hydrau-lics on skidders while the disc saw felling head for

Closed loop transmission A4VG + A6VM

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feller bunchers rely on an A10VO or A11VO pumpwith a pressure compensated control.

A4VGThe closed loop drive line requirement for skiddersis perfectly suited for the A4VG from BHY. This lat-est trend for more efficient power transfer, duringall portions of the skidders operation, as well asimproved driver comfort (no manual shifting ofgears), has provided the perfect opportunity for thispump. The initial machine control concept useshydraulic displacement controls with hydraulicpower regulation via the DA option. With the ad-dition of integrated filtration, cold start function-ality, and the high-pressure capabilities, the A4VGsfuture in FTH machines looks bright.

Normal closed loop A4VG + A6VMTo round out the drive requirements for a skidderhydrostatic transmission, the BHY A6VM motorwith hydraulic displacement control and integratedpressure cut off is most often selected. Mountedto a single input drop box with drive shafts to frontand rear axles, the pressure and speed capabili-ties of this family of motors is the perfect counter,versus a mechanical system. Integrated flushingand speed measuring options add versatility andflexibility, which further enhance the A6VM as themotor of choice.

A6VE with integrated brake valveA6V motors are also found in other FTH propelsystems. An A6V motor, in a plug-in design orthe E version, powers the tracks on both fellerbunchers and log loaders. Mounted in a gear drive,and almost exclusively utilizing the automatic pres-sure control type HA, BHYs design with integratedbrake valve (counter balance valve), and an auto-matic brake release signal for propel gear drivebrakes, have established a bench mark which hasyet to be surpassed. BHY A6VE motors are liter-ally the tallest tree in the hydraulic motor forest!

A6VMA6VM motors can also be found in non-drive func-tions in FTH machines. The disc saw felling head,used on almost 98% of every feller buncher manu-factured, owes a significant amount of its success

to A6VM motors. The A6VM with an HA controlhas been used in this application since its incep-tion and is still as reliable now as it was then. The

A6VE with integrated brake valve

A6VM saw motor

integration of a free flow check in the motor portplate has strengthened this motors position to thepoint where it is almost exclusively used.

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A2FE mounted into an L&S GFB

The newest development in delimber drives alsouses an A6VM motor. When combined with a geardrive, this combination yields very positive resultsas compared to a traditional low speed high torquemotor. An increased performance and a projectedincrease in life expectancy are two major reasonswhy the population of A6VM motors on delimbersis expected to increase.

GFT + A6VEAs previously mentioned, BHY A6VE motors arevery popular and successful for the propel appli-cation on tracked feller bunchers and log loaders.When combined with Lohmann & Stolterfoht GFTtwo and three stage planetary track drives, withan internal brake release port, this self containedand compact package is difficult to match. Reli-ability and a proven history in the North Ameri-can forest industry have made L&S the #1 propeldrive supplier to feller buncher and log loadermanufacturers in North America.

GFB + A2FELohmanns success in FTH machines does not liesolely with propel drives. The same high quality andproven planetary gears are also found in similarlyreliable and successful GFB slew drives for fellerbunchers and log loaders. Matched with a BHYA2FE, the fixed version of the popular A6VE, theGFB/A2FE package has complimented the GFT/A6VE package and has made the system con-cept easy to implement where planetary gear/motor drives are required.

A6VE with integrated counterbalance valve mounted into an L&S GFT

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MP-18Where pumps, motors and gear drives provide thebrute force, distribution valves provide the preci-sion control and effective use of oil for many of thedemanding applications in full tree harvesting. Theload sense MP18 and MP22 valves from theRexroth Corporations Wooster facility have estab-lished themselves firmly in this field. The carrierfunctions for small to medium sized feller bunchersand log loaders is one area in particular as well asfor auxiliary working hydraulics for skidders.

M4-15When flow and pressure limit the application ofthe MP valve, Rexroth Hydraulics M4-15 can ef-fectively pick up where the MP valve left off. Withpressures up to 350 bar and section flows up to200 l/min, the M4-15 is slowly making its presencefelt. Working hydraulics for skidders is a perfectplace for this valve as is the disc saw felling headcylinder functions. The modular design of the M4-15 also makes system changes, as result of cus-tomer demands, a much easier task.

M7-20

M7-20For large flows, such as the carrier functions onlarge feller bunchers and log loaders, the M7 se-ries 2X LUDV valve from Rexroth Hydraulics meetsthe requirements and then some. The LUDV con-

M4-15MP-18

cept is already accepted in the North American FTHmachines, primarily in feller bunchers, which hasmade the integration of this valve into new designsan easy process.

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2TH6R

4TH6E & 2TH6RAs mentioned earlier, electronic proportional con-trol is not totally accepted yet and is slowly mak-ing in-roads into FTH machines. Black and whiteor electric on-off controls are common place whereapplicable. However, for fine control of MP, M4 orM7 distribution valves as well as pumps and mo-tors, all with hydraulic pilots, the Rexroth Hydrau-lics TH pilot controller family is the perfect solu-tion. For working hydraulics on skidders, and forboom functions on feller bunchers or log loaders,the ergonomic hand grip 4TH6E pilot controllermeets the requirements and is a popular choice.For the propel function on feller bunchers and logloaders, the foot pedal type 2TH6R is equally aspopular. For both types of controllers, the abilityto precisely match the output pilot pressure curveto the required spool movement, provides the finemetering control needed for small incrementalmovements and high controlled flows for high pro-duction rates.

4TH6E

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What Does the Future Holdfor FTH Machine HydraulicSystemsThe future for FTH hydraulic systems can be lookedat from two different angles, from the componentangle and from the systems angle. From the com-ponent angle, the trend will be for higher pressures,faster speeds in smaller packages. From the sys-tem angle, the trend will be towards electronicsystems using BUS technology for integration ofall machine components and functions. The endresult with these trends will be next generation FTHmachines with improved operator comfort, im-proved user friendliness, a more efficient use ofavailable power and the preservation of the envi-ronment.

The challenges that lie ahead for the FTH machinedesigner and hydraulic suppliers will require closeco-operation in a partnership format. This will in-sure the continued success and secure the placeof full tree harvesting equipment in the NorthAmerican wood harvesting market.

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