Machinery News

  • Written by: Farmers Guide
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Agco Challenger Crawler combines performance, economy and comfort

Allowing Fendt engineers to redesign a rubber-tracked crawler series from the ground up meant the result was bound to feature extra comfort and efficiency and especially a CVT transmission. David Williams has been trying it out.


Agco Challenger crawlers are a common sight on UK farms; their ability to stretch work windows and reduce compaction valued by many large arable growers. Sister company Fendt took over the range in late 2017 with first deliveries of green models commencing in early 2018, and while the larger Challenger 800-series remained similar in its new guise as Fendt 1100MT models, the smaller 700-series became 900 Vario MT models and availability stopped for a while concluding 7 years’ research and development as Fendt engineers put final touches to an all-new range.

The larger 1100MT series includes 4 models from 492–646hp, all with the same powershift transmission as their predecessors but Fendt is known for its Vario infinitely-variable transmissions and central to the new 380–431hp, 3-model 900MT series’ design was the inclusion of a new Vario Drive gearbox.

Until quite recently, CVT transmissions were regarded as ideal for tractors working in low draft situations where their operating advantages outweighed the loss in power transmission efficiency. However, design improvements including the ability to ‘lock-up’ the transmission to reduce power losses have made it suitable for larger tractors too, and the small reduction in mechanical efficiency is easily outweighed in most situations by increased flexibility in the field.

Comfort and productivity

Fendt 900 Vario MT models share the company’s own transmission with 1000-series wheeled tractors, available with up to 538hp. “Priority for design engineers was improving operator comfort as much as optimising efficiency and productivity,” explained Fendt tracked tractor product specialist Gergely Olah. “The result was effective chassis and cab suspension and the 900 Vario MT is the only twin-track machine with suspended mid rollers. The whole undercarriage was lengthened by 13cm, all added at the front and much of the weight is carried by coil springs with up to 260mm travel assisted by shock absorbers on each side, and with rubber blocks to cushion in extreme conditions.”

Fendt’s Mobil Trac System has built-in suspension allowing the central carrier to oscillate up to 11 degrees. The three mid wheels are mounted on a Tri Bogie carrier, allowing accurate ground following.
Visibility through the curved rear screen is excellent.

To prove his point, during Farmers Guide’s walk-around, Gergely grabbed the front ballast weight and rocked the front of the 16t tractor up and down.

“Previously the rear mid roller pivots were directly under the seat so when travelling over bumps the shock was felt above. Moving the pivot point forward has reduced the effect of undulations on the driver,” he added.

The new carriage design allows independent movement of each track, and the assemblies oscillate up to 11 degrees for precise ground contour following.

Drive is through the rear wheels by friction and a chevron pattern on the rubber face ensures any debris is quickly cleared. Correct tension is essential and this is provided by hydraulic rams with gas accumulators acting on each front idler wheel allowing a range of movement and keeping the tracks central. “It’s a simple system,” explained Gergely. “In extreme conditions up to 8cm of ram travel is available and to check tension the operator has only to glance at the ram and a visible shiny section means movement is available and no adjustment is needed.”

Three large mid rollers maintain track alignment and maximise ground contact area. Polyurethane snap-in discs on the inner edges where they rub against the tracks’ rubber blocks reduce heat build up. No daily maintenance is needed. Hub oil levels are checked by sightglass and oil is changed at 2,000 hours.

The Tri Bogie suspension system allows any combination of one or more rollers to lift and pivot around objects, and maximises weight distribution and traction.

Gergely explained that for maximum productivity approximately 5 per cent track to ground slippage is ideal, but more than 10 per cent slippage suggests operations should be stopped. “Correct ballasting results in the tractor remaining horizontal under load to maximise track to ground contact, counteracting the natural tendency for the front to lift when pulling hard.”

Engine development

Power is from an Agco Power 7-cyl, 9.8-litre engine with significant updates for this application. Challenger models replaced by the 900 Vario MT-series produced maximum power at 2,100rpm, whereas the new engines achieve maximum power at just 1,700rpm, reducing noise, wear and tear and fuel consumption. “Higher revs were needed for previous models to travel 40kph, but with the Vario the same speed is achieved easily at just 1,500–1,600rpm,” added Gergely.

The main cooling fan is borrowed from 1000 Vario-series wheeled tractors and pushes air through radiator screens from the front, rather than sucking it through from behind the cooling pack. A 1.5mm gap between the fan blade ends and the housing creates a pressurised system, and hydraulic drive precisely regulates fan speed to meet demand.  A reversing fan option is available for high dust environments.

CVT benefits

The Vario transmission is similar to that of the 1000 Vario tractors. Infinite speed control between 20m/h and 40kph can be achieved without manually changing speed ranges.

Two huge 370cm³ hydrostatic motors adjust independently, and at higher operating speeds the second hydro-motor decouples to increase efficiency. Control is fully automatic to maximise efficiency.

Because speed ranges are virtual, target operating speeds can be set and memorised within the Vario terminal for recall at a touch of the screen, and integrated within headland management sequences.

Farmers Guide’s test drive under supervision of Fendt UK tractor product specialist Peter Henson included gentle slopes and wet, slippery ground and the TMS proved extremely efficient adjusting to variable traction conditions and operating speeds. Even with the heavy cultivator at maximum 30cm working depth the CVT transmission was smooth and made easy work of the task, and the only time the change in gear ratios was felt was when mechanical lock-up occurred, providing maximum pulling efficiency.

At a comfortable 11kph operating speed the 431hp engine settled down at approximately 1,550rpm.

Users familiar with the Challenger crawler will know that to maximise work rates and efficiency load requirements must be anticipated in advance and suitable ratios selected, especially when pulling away under load. The new Fendt crawler simply requires the operator to select and adjust the required speed on the joystick by pushing it forward or pulling it back, or to select one of the two cruise control memory buttons through which speeds are achieved without any further operator intervention. Drive take-up is always gentle, although four rates of ‘aggression’ can be selected by a joystick-mounted switch, and this means the tractor is gentler on implements and should result in decreased track wear than direct-drive mechanical systems.

Users interviewed by Farmers Guide who have updated to the new Fendt from the previous model say greater ease of use is a significant benefit and automatic adjustment by the TMS reduces engine revs whenever possible achieving noticeable fuel savings. Although the operator is free to select engine and transmission operating parameters there is little need, as full automatic operation is suitable for most situations including road work where pulling away from junctions is easier without risk of stalling.

Adjustments include engine ‘droop’. This is the amount by which engine revs are allowed to reduce as load increases rather than injecting more fuel to keep them constant. For some PTO operations such as working with pneumatic drills this would be set to minimum variation to keep shaft-driven fan speed constant, while the CVT transmission allows infinitely variable travel speed control, but otherwise most users leave the setting in ‘auto mode’ allowing the TMS system to regulate it.

Operator-friendly

The Fendt 10.4-in Variotronic display monitors and adjusts all operating parameters and is used for GPS guidance. It proved easy to see even with a low sun angle and menus were quick to use and intuitive with quick jump buttons allowing sequences to be by-passed for added convenience.

A criticism of many twin-track crawler auto-steer systems is a twitchy ride caused by the system’s attempts to maintain straight lines through track steering, but there was no evidence of this with the 900 Vario MT.

Programming headland management sequences is straightforward and the novice test user quickly got to grips with setting it up and making changes.

Visibility from the cab, which includes 6.27m2 of glass, is excellent with clear vision down to the front of the tracks. Heavy rain showers on the test day demonstrated the broad sweep of the front wiper, leaving little area obscured. The rear screen is curved, allowing the operator an unobstructed view of wider implements than the 6m Amazone Ceus provided for the test.

Travelling between fields demonstrated the tractor’s impressive ride quality and the visibility. The suspension is effective, soaking up most vibration from the track cleats and comfort levels are close to a wheeled tractor. Use on roads is another situation in which advantages of the CVT have impressed early users, as controlling speed using just the foot pedal without having to select suitable gears allows full attention to other traffic.

Verdict

The new 900 Vario MT is proving popular. Sales so far have been to a mix of customers from first time crawler users to those previously using Challengers and other makes of twin-track machine.

Ease of use is excellent and although there are plenty of automatic settings available to help operators of all levels of experience to achieve impressive economy and work rates; for advanced users there is also potential to make fine adjustments to tweak performance to the maximum.

Comfort is impressive, the cab has plenty of space, clear controls and good visibility and there is plenty of storage for odds and ends.

Noise levels are very low, but first impression is that the Vario transmission is noisier than the Challenger’s powershift. Experienced users of both machines argue that the CVT unit is only heard because of the quieter engine, and overall noise levels are noticeably lower making it easier to spend long days in the seat.

With the 943 Vario MT are Fendt’s tracked tractor product specialist Gergely Olah (left) and UK tractor product specialist Peter Henson.

Future developments

So, with the Fendt brand synonymous with CVT transmissions and the new 900-series crawlers proving popular, how long before we see a Vario transmission offered in the larger 1100MT range? Fendt representatives won’t comment, but for a company offering only CVT systems across its other tractor series, it’s something anticipated by prospective customers and it can’t be too long before its flagship 1100MT tracked tractors have it too.


  • Written by: Farmers Guide
  • Posted:
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