Three-pump hydraulic circuit powers forest harvester



The new Komatsu 931XC harvester has a double-bogie 8WD system designed to tackle steep, rough and soft terrain.

The new 8-wheel-drive 931XC (Xtreme Conditions) forestry harvester from Komatsu America, Chattanooga, Tenn., is reportedly built to deliver high performance, particularly on steep, rough or soft terrain.

One notable feature, according to the company, is the 3PS three-pump hydraulic system. It provides significantly higher hydraulic working flow at low engine speeds than comparable machines—which combines greater productivity with lower fuel consumption.

One hydraulic pump and circuit is dedicated solely to the transmission for maneuvering the machine. The other two variable-piston pumps supply the work hydraulic in a dual-circuit, load-sensing system. Working flow is split into two circuits that can operate separately or together, at different pressures, depending on actuator demands and speed requirements. Pressure and flow optimization lets operators work significantly faster without losing power when using multiple functions. For example, the operator can actuate several crane and head functions simultaneously with maximum hydraulic power, such as slewing the crane, feeding a log and maneuvering the machine, while limiting fuel consumption. The hydraulic system is controlled by Komatsu’s MaxiXplorer control system.


The cab offers excellent visibility and 360° cab/crane rotation.

Flow rating is 528 lpm (139 gpm) at 1,600 rpm and system pressure is 280 bar (4,061 psi). The system includes pressure filtration for the hydrostatic circuit, and return filters for hydrostatic and working hydraulics. Environmentally friendly hydraulic oil is an option.

The 931XC drive system also differs from those used on similar 8WD harvesters, according to the company. It includes a proven articulated frame joint, rear swing axle, and Komatsu’s high oscillation Comfort Bogie front axle. The new design adds a second Comfort Bogie axle to the rear swing axle, which reportedly provides excellent uphill/downhill and left/right oscillation. This “double Comfort Bogie” drive system is said to give the 931XC superior handling characteristics as the machine follows the terrain more closely than 8WD machines with a fixed rear-axle design.

The hydrostatic-mechanical transmission, controlled by MaxiXplorer, includes a two-position transfer gearbox, disengageable front-wheel drive, and front and rear-axle differential locks. The steering system includes a hydraulic articulation joint with two dual-acting hydraulic cylinders, and a steering angle of ±40°. The hydrostatic transmission in the 931XC can use full engine power, an advantage when navigating gradients and difficult terrain. There are also several pre-set and task-specific driving modes. Top speed is 7.6 km/hr (4.7 mph) off-road and 23 km/hr (14 mph) on road.


Hydraulic cab-levelling keeps the operator upright and comfortably seated.

Compared to the previous 931-6WD model, the new 8WD system generates 11% more tractive force and reduces rear ground pressure 54% with tracks and by 23% with tires. It also increases ground clearance. Combined with the new 8WD system, this improves harvesting capabilities on challenging terrain.

The machine also offers 360° cab/crane rotation and cab/crane leveling systems. Cab-levelling keeps the operator seated comfortably and gives a clear and unobstructed view to the harvesting head.

A 251-hp Tier 4f engine powers the machine. A standard cold-weather package heats the batteries, diesel exhaust fluid (DEF), engine coolant and hydraulic oil to facilitate easy starting in sub-zero conditions.

The MaxiXplorer control and information system has many software options for controlling, monitoring and reporting vehicle conditions. Daily maintenance checks can be performed at ground level or from inside the cab. The machine includes a one-piece hood that opens rearward to fully expose the entire engine compartment for easy service access. Well-placed front, rear, cab and hydraulic tank service platforms further simplify serviceability. All filters are vertically mounted to ease replacement and minimize the potential for spills.

Komatsu America

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