Another Position and Draft Control Thread

[onymous]

I would greatly appreciate help and comments from members in looking at this a conceptual model of Position and Draft Control. As will be painfully evident, I'm a retired pencil-pusher who has acquired a tractor and I know less than nothing about hydraulics (yes, it can be less than nothing because my head is full of negative, or false, information). I'm sure the attached diagram bears absolutely no relation to how things actually work, but is just a toy model that would help me to think about things.

Please ignore the top of the diagram (draft control, sensor, and top link) for the moment.

So, there is some black-box valve/controller/magic at C that sends oil to the cylinder's piston and raises it to level B. It now continues to ensure that level B is maintained. This is straightforward as the oil has nowhere to go because C has locked all exit paths. The piston can, however, bounce above the oil level and it is only the implement's weight that holds it in place with a downward force. In some other tractors oil was actually maintained around the piston's rod to create a downward force as shown with the light grey color. However, modern tractors seldom do this.

The distance B is established by receiving a signal from the Position Control Lever. I have no idea whether this signal is hydraulic, mechanical or electrical. I don't think it really matters for the purpose of this toy model.

Returning now to the top of the diagram (and assuming Kubota uses top-link draft sensing), the black-box/magic Sensor shown senses the amount of strain that the tractor is being subjected to from the implement. If this strain exceeds a level controlled by the Draft Control lever (from Sensitive to Insensitive), the Sensor sends a signal to C that will inject more oil into the cylinder and thereby raise the implement just enough to reduce the strain on the tractor to an acceptable level. When the strain decreases to acceptable levels, the Sensor sends another signal to C, which will then allow the oil in the cylinder to exit just enough to return to level B (as defined by Position Control). B will/can never get below the level defined by the Position Control lever.

Is any of this even remotely accurate?

If so, the next mystery to me is the U (Up) setting on the Draft Control lever. It is beyond the most Sensitive setting so I'm guessing it simply means 途aise the lower links up now!? If true, I have no idea how this differs from raising with the Position Control lever. Does it respond faster? Or, by raising the 3pt this way, one doesn't lose the exact setting of Position Control?

Lastly, my manual says "place both Draft Control lever and Position Control lever in the F (float) position to make the lower links move freely along with the ground conditions". In terms of this toy model, does it mean "turn off strain sensing" and "reduce level B to a minimum level"?

Help please.

 

[EE_Bota]

You are probably being modest when you claim to know less than nothing about hydraulics, but if you are not, your question is quite open-ended to explain to a person hydraulics challenged. This may explain why you have not got too many takers yet.

If you can tell us WHY you want to know, it may offer a bit of guidance as to precisely WHAT you what to know. (It's touch and go, but people at work have gotten less sensitive to me asking "Why do you want to know?" They know my question is aimed at telling them precisely what they want to know, instead of boring them to death and wasting their time.)

If this link goes through, it should help you quite a lot:
http://www.fofh.co.uk/tech/draught.htm

and this one as well
Yesterday's Tractors - Ferguson System Principal and Theory of Operation

If they fell you, search for other links on Google about
What is draught control?
The Ferguson system.
Hope this helps a bit, and maybe it will more carefully target your thinking.

As you can see, most of these systems are strictly hydraulic/linkage/mechanical in nature, no real sensors per se. This has been quite robust over the years. You specific tractor MAY be different, but probably not hugely different.

 

[Yankee Clipper]

Onymous,

Kubota uses position control on all it's tractors from BX to the L40. Position and draft are found only on the M series, with the large chassis MX (not 5100) using electronic draft control. Top link sensing is used on all M series.

Postion control - you have one lever in the quadrant - you pull it back and the postion control valve ports fluid to a one way cylinder under the cover. The hitch will continue to raise until the follow up lilnkage neutralizes the position control valve. To lower the hitch, you let the fluid out that is trapped in the cylinder by opening a port to tank.

Draft control - this valve is parallel to the position control valve and the depth / amount of travel is set by the PC and the rate of change or sensing is set by the draft handle. You lower the tool into the ground by pushing both handles forward (depth set with PC) and then pull back on the draft until the tool starts to raise. The amount of draft / resistance will be constant assuming the soil in uniform in composition and type of ground cover is uniform.

When you come to a tough spot / compacted soil, the resistance increases and this is sensed back from the tool via the top link. The draft valve will port fluid to the lift cyllinder to raise the hitch and the load will decrease. This change is sensed via the linkage so the hitch will now return to it's prior depth setting assuming the conditions are no longer creating a high draft.

The electronics work the same way but sense 5 times a second and get their feed back from potentiometers and switches attached to the rockshaft and the control levers. The signals are sent to a processor (computer) that will then fire the raise or lower solenoid to port fluid to or away from the lift cylinder(s).

All teh various manufacturere's systems work in a similar fashion - some use lower link sensing on larger machines.

Good luck!

 

[kthompson]

I have a M Kubota and Yankee Clipper seems to have done a good job. I know when I purchased the owner of the dealership did not like the Kubota system as well as what he called true farm tractors. Based upon my experience agree with him. Some systems do a good job keeping a plow level in the dirt as you travel across such as rows or unleveled ground. The system my Kubota uses works as YC has said the resistance the plow has which could be due to going deeper or as he said harder dirt. To me when using such as a subsoiler I don't want it picking up due to hitting harding dirt as long as the tractor can pull it. If you have the manual there is a section in it on how to set it but think again Yankee Clipper has it covered.

 

[dcondo]

Just for the record, the Grand L-series has optional draft control.

 

[onymous]

Yankee Clipper:

Thank you very much for the explanation. It's finally beginning to make sense to me. The point I missed was cleared up by you saying "You lower the tool into the ground by PUSHING BOTH HANDLES FORWARD forward (depth set with PC) and THEN PULL BACK ON THE DRAFT until the tool starts to raise". I somehow missed the point about pushing both handles forward in unison.

Does the same apply to the FLOAT and UP positions -- is one supposed to push/pull BOTH handles? What is the consequence of ONLY putting the POSITION handle in the FLOAT or UP position (as I've been doing)?

Thanks again for the explanation.

 

[onymous]

EE_Bota:

Thanks for the links. I'm still reading them. The Ferguson history is especially interesting.

 

[art]

The position valve should be lowered to the bottom and your depth set with the draft lever! They don't have to be dropped in unison to achieve your depth or performance. That way at the end of the row you only use your depth lever for your up and down.

The draft systems can vary and in soils that change from hard to soft the draft will need to be adjusted to maintain your depth. Different systems do work differently. Some draft systems will take 20% load change just to register and to adjust. Some will do it with less then a 7% load change.

 

[onymous]

Actually, on the Kubota the Draft lever is used to set the Sensitivity of Draft Control. The Position lever is used to set depth. That is why Yankee Clipper's explanation makes a lot of sense to me: by moving the two levers in unison, one is lowering the links and and setting Draft control to insensitive -- then one gradually increases draft sensitivity until the implement just raises.

"Some draft systems will take 20% load change just to register and to adjust. Some will do it with less then a 7% load change" -- draft control allows one to adjust this load change sensitivity.