BAKERSFIELD, Calif. — Marrying high horsepower to automatic transmissions is becoming more popular with tractor makers, but a non-articulated 435 h.p. CVT is pushing the boundaries.
A few companies, such as Fendt with its 900 series, have been pairing high power with slicker transmission offerings, but the tendency was limited to sub-300 h.p. machines.
New Holland’s new Genesis T8 435 is the biggest mechanical front-wheel assist tractor in North America. With the company’s new version of its continuously variable transmission, it might also be one of the most efficient and easiest to operate that way.
Managing power efficiently in the field has long been done by shifting up and throttling down. The result allows an engine to be at its most efficient when under load, while not going so far as to dangerously lug the tractor or see it power out or spin out in tough conditions.
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It’s a skill to find that sweet spot between where the machine uses its fuel well and wastes it, while juggling all the other needs of field operations, such as ideal operating speed and ensuring there is adequate hydraulic flow. It’s also a job that is easy to mess up, especially as the horsepower rises.
The new T8 tractors have married New Holland’s nine litre, Fiat Powertrain, selective catalytic reduction engine to a new version of the CVT, which it has used for several years in its T6 and T7 tractors.
“Producers can call for a five m.p.h. speed and get it,” Nathan Graham of New Holland said during a dealer meeting in Bakersfield.
“The Auto Command lets me run the engine at a speed decoupled from the speed of the tractor, and it will allow me to run it at its most efficient or its most aggressive, for heavy, high speed operations, such as transporting from field to field and hauling loads like big grain carts.”
The CVT has four points of complete mechanical efficiency: three for fieldwork and one for transport.
The computer system that manages the tractor can get it to use as much mechanical and as little hydrostatic drive as possible while balancing the machine’s load and engine speed.
“It’s not like you feel the tractor shifting between those four points, but they exist none the less,” Graham said.
The CVT is made up of three major parts: The hydrostatic pump and motor, a four-gear power shift transmission and a compound planetary coupling the first two together.
The engine directly drives the transmission’s planetary sun gear, while a ring gear is run from the hydrostatic motor.
The sun gear and the ring gear jointly drive a four speed, clutched-type, power shift transmission.
The ring gear, driven by the hydrostatic motor, stops turning and powering the machine’s movement when the tractor is in a fully mechanical mode. The hydrostatic motor handles variable amounts of the load at driven speeds that are between the four locked-up phases of the transmission.
The higher the amount of hydrostatic loading that takes place, the less efficient the tractor becomes. However, the machine also has the advantage of running the engine in its most efficient power regions, reducing overall fuel use at any speed.
The components of the Auto Command transmissions found in the T6 and T7 tractors are also in the T8, but the T8’s units are set up and arranged differently, Graham said.
“These are older concepts that farmers understand well,” he said.
“We have had the hydrostatic transmissions since the 1940s and 1950s. This power shift transmission is from the 8970 tractor (model), and the compound planetaries are still found in tractor axles. We just put them together to build something unique.”
From a stop, operators press in the clutch, set the switches on the shuttle control to forward or reverse and release the clutch. The tractor still does not move until the control arm or the floor pedal are pressed.
A thumb wheel on the handgrip sets the target ground speed. Three target speeds can be set into memory and selected. As a result, a target speed becomes the terminal velocity no matter how hard the pedal or arm is pushed.
The computer system will generally try to maximize fuel efficiency while maintaining target speeds.
The units have a manual engine droop control that sets a limit on the lower or upper engine r.p.m. The upper r.p.m. is limited when the droop is being operated normally, and the lower is set when in power take-off mode.
There are four main modes of operation:
- Automatic is the most efficient.
- Cruise mode allows some operator influence over the loading and efficiency.
- Manual mode allows the driver to set both engine and tractor speed.
- P.t.o. mode guarantees a constant p.t.o. output speed.
There is also an aggressiveness setting that lets the operator decide how much power should be applied and how rapidly.
A middle setting is available for baling or other tasks that require smooth, constant speeds.
A slow to speed up, efficient mode allows for heavy draft tillage and seeding tools and where heavy loads need to achieve speed gradually.
The most aggressive setting is used for road transport.
The power shift transmission is still available on the big New Holland, with the CVT being an option.
View a Western Producer video about the T8 CVT at producer.com/section/video.
