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Tractor hydraulic systems

Most of the world doesn't think tractor hydraulics is very exciting. But engineer Rich Job thinks it is. For instance, Job will tell you how, when he was a boy, it saved his back by lifting implements on the farm.

Job and experts like him also will tell you how hydraulics has advanced from simple lifting to powering implements, taking the place of the tractor PTO. The science has advanced so far that in some cases you don't even have to move a lever or touch a switch to get the fluids moving in a direction you need them to go. All that's taken over by tiny computer processors on valves and pumps that can shout out commands faster than our minds can even process them.

“Today's hydraulic systems are sophisticated engineering systems,” Job says. “They allow the machine operator to perform many functions so that farmers can produce food and fiber at a competitive price. Without that, the cost of that food and fiber would be dramatically higher.”

Hydraulics is so interwoven into our mechanical systems that we don't even think about it anymore. But that's a mistake, experts say. The science is advancing so rapidly that if we don't stay up on the topic we could miss out on all the benefits enabled by fluid dynamics.

“Overall, it is important for tractor buyers to understand about hydraulic systems so they can properly and safely operate them,” says Kevin Watts, John Deere service instructor. “They also won't be able to take advantage of new features if they are not informed about current hydraulic systems.”

We've gathered a panel of experts to tell you what you need to know about this fast-changing science.

FIN: What is the purpose of tractor hydraulic systems?

RICHARD JOB: Basically, hydraulics allows the tractor operator to do tasks that require high effort with a simple push of a lever or flip of an electrical switch, which actuates the hydraulic circuit. In its simplest form, hydraulic pressure and flow can be converted to forces and motion that allow the tractor to perform tasks that an operator cannot do physically.

SCOTT SCHELLHORN AND KEVIN WATTS: The basic purpose of tractor hydraulic systems is to use fluid dynamics [fluids don't compress, while air does] to perform work both on and off the tractor. Typical uses on the tractor are braking and steering. Implements are the typical use of hydraulics off the tractor, and selective control valves (SCVs) control the volume of flow. Implements use hydraulic oil to perform a variety of functions such as raising and lowering parts as well as providing power to motors and other devices for mechanical movement.

How has the purpose changed over the years?

JOHN INMAN: When I got started farming as a kid in the '50s, the hydraulic system consisted of something to raise and lower the 3-pt. hitch and maybe one remote cylinder to raise a hay rake or plow. Now you are running sophisticated air planters that have the ability to put down fertilizer at the same time as seed. This is all done through utilizing the tractor hydraulic system, whereas in the past you might have driven those things with a PTO shaft.

SS/KW: Modern farming equipment uses hydraulics for functions that were previously controlled by purely mechanical means. Today's hydraulic systems use electronics to vary pressure and flow. As a result, hydraulic systems have become more precise and can now be used to control devices such as variable-rate planter seed drives or hydrostatic drive systems and transmissions.

ROGER LEWNO: Implements are getting larger, so hydraulics are being used not only to raise and fold the unit but also to steer and brake the unit. Our Case IH Early Riser 1260 planter uses hydraulics to steer the rear like a fire truck trying to get around in the city, and we are offering hydraulic brakes tied into the tractor system to aid in stopping.

What's different about hydraulics now versus 10 or 15 years ago? How has the technology changed?

RL: We are now using pressure flow systems that produce pressure and flow only on demand and to the amount required to perform the operation. Instead of the system being at a “set” pressure and flow, the pressure and flow are controlled. Fluid is directed by valves that are controlled electronically.

RJ: The difference in hydraulics today versus 10 to 15 years ago is in the control capability of today's systems, the volume of fluid available and the number of circuits available on the tractors. Today electronic controls allow many more types of functions to be done by hydraulics, such as trailer braking and hydraulic motor operation. The rated flow on some large tractors is now 80 to 90 gpm with up to nine remote circuits available.

JI: Manufacturers have increased the hydraulic capacity in the tractor, adding more remote valves. This has opened the opportunity for implement designers to utilize that hydraulic capability. Again, in the old days we ran a lot of things through the PTO shaft, which meant you had to use chains and have a drive shaft on the implement. Now all you need are a few hydraulic pipes and hoses and you drive the implement directly with the hydraulic motor. So the operation becomes a lot simpler and you reduce the number of parts involved. And you can control it electronically, which gives you a lot better control.

SS/KW: One big change is the use of load sensing to control a variable pump in a pressure- and flow-compensated system. This new system allows control of hydraulic flow and power to specific systems upon demand while also saving fuel when no hydraulic functions are in use. Also, as previously mentioned, another big change has been the advent of computer-controlled hydraulic systems coupled with precise-machined hydraulic components that allow the electronics to monitor and control all hydraulic systems. These system advances are particularly useful for real-time, minute mechanical movements such as infinitely variable transmissions, GPS steering controls, and suspension systems [cab and seat].

What has enabled these advancements?

JI: It is the ability to use electronic control systems to control the hydraulics. When we are able to integrate all the nice things in the hydraulics — like the superior motors and control valves — with electronic controls, then we've just put together an awesome system.

RL: We moved away from mechanical hydraulics, where you as an operator moved a handle and pulled a lever on a spool to activate the system. From there we started using solenoids, which activated the spool, and from the solenoids we started to regulate the time limits that the solenoid can work. So instead of a manual operation, hydraulics is now tied to other functions on the machine so that the machine itself tells the hydraulics what it needs.

What are some examples that show just how far the technology has taken us?

SS/KW: Examples include: 1) continued increases in hydraulic capacity to meet customer demand for larger, more complex implements; 2) SCVs that have more precise controls at higher pressure and flow volumes while giving the customer more adjustability for their specific applications; 3) infinitely variable transmissions that use electronically controlled hydraulic systems to vary speed and direction of drive train gearing; and 4) cab, seat and chassis suspension systems to provide greater comfort, performance and adjustability for specific applications.

RJ: Electronic headland management is one example of the many system capabilities available in hydraulics today.

RL: Look at what we've done with just the transmission on tractors. On our Magnums, for example, we have linked together a basic powershift transmission with an electronically fueled engine and enabled the operator to select the desired speed. Then the tractor engine rpm will go up and down, and the transmission will upshift and downshift to find the most efficient place to operate. We call this our Diesel Saver Auto Productivity Management system. This is all done through electrohydraulic interaction.

Where is the industry headed? Where is hydraulics going to take us?

RL: I think both interfaces — electric and hydraulic — will continue to be used. So in an electrical over hydraulic portion, you'd have hydraulics to do the work and the electrical to direct when and how the hydraulics will do the work. Take a planter for instance. Maybe the planter is being driven hydraulically, and electrically we can shut off individual rows. The two interfaces are working together to make things happen.

What's the next phase?

RL: The next phase might come in where you do more work electrically than mechanically with hydraulics. Like with drive mechanisms, maybe we'll go to an electric drive versus a hydraulic drive and/or a mechanical drive. Today we are using transmissions, like a continuously variable transmission or powershift. But if you look at big commercial dirt-hauling trucks, the engine drives a generator, and the generator drives electric motors that propel the vehicle. I don't know where that technology is today, but it could come.

RL: The use of hydraulics in the future is only limited to what the operators want the tractor to do. With new developments in electromechanical systems, we will probably see some traditional hydraulic functions done by electromechanical systems where they are more cost effective and efficient. Other new uses will come along that will continue the need for hydraulics on tractors.


is an engineering consultant (retired from AGCO) who keeps close tabs on emerging technologies

is an agricultural engineer and farm advisor emeritus with the University of California Cooperative Extension Service

are service instructors with John Deere Waterloo Works

is a large-tractor marketing specialist with Case IH

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