I have an OC (open center) hydraulic steering system on my tractor. And looking for solution to make AOG steering via hydraulics.
Whats valves do I need for autosteering?
Unfortunately I cannot create hydraulic schemes, so I’ll try to enumerate what is required as I’ve observed so far and you please correct me if I’m wrong.
Directonal valve 3/2 (Pressure to Orbitrol by default and switched to Autosteer when needed). Turn it off and Autosteer is completely disabled.
Proportional valve, 4/3, closed center (Here we make an actual steering left/right)
Relief valve (when we are on Autosteer and actually not steering, pressure is going upper, as our proportional valve is normally closed.
That should work fine for OC system and would cost around 300-400 Eur (roughly)
What I’m worried about is that this scheme would result in an oil heating when Autosteer is ON and system is not steering actually and idling, hence oil is going back to Tank via Relief valve (as Relief Valve’s working pressure has to be set a bit over normally working pressure for each particular tractor). How to solve that heating problem?
Tractor make and model could be useful.
How does your oil flow?
Om my Hürlimann both (6135 year 1996 and 913 year 2003) oil flows like this: Oil pump to orbitrol (which has relief valve at around 160 bar inside) from orbitrol to cooler in front of tractor, cooler to gearbox where oil is used for shift between H-M and Low. In gearbox (and therefore in cooler) pressure is set around 25 bar.
Mine is MTZ. It has separate oil pump used for steering only. Oil flows from an oil pump to Orbitrol and then to L/R steering cylinders. Very simple configuration. And I think many of us farmers here have similar hydraulic steering configuration irrelevant of the tractor make and model.
All you need is one 2-way valve. To cut off the orbitrola proposes a so-called lock, otherwise a check valve controlled by oil pressure. Just like in the diagram.
I think you should stick to your original thoughts. If you use an extra piloted relief valve, then the heating will not be so much, and only when autosteer is on.
And if your relief valve is after the 3/2 valve you can set the relief pressure much lower (50 bar and it will still steer)
Using a OC valve of Cetop type to autosteer, gives slow reaction because the spool has to move almost to end before oil pressure rises enough to move the wheels. I bet Danfoss does it better but also another price tag!
Could you describe it a bit more detailed please?
Shouldn’t hydraulic scheme avoid using relief valve for depressurizing 90% of the working time?
If we use 4/3 open center valve, then Yes, there is no heating problem as oil flows freely to the Tank. We only have pressure spikes on actual Steering, that’s the case when Relief Valve may be in action (depends on what tractor/pump is it).
But with opened valve we have slowed down reaction, as you mentioned it as well. That’s because we have valve is fully opened and moving the spool a bit wouldn’t make any impact on L/R steering line, until pressure restance between T and L/R become equal.
CC 4/3 valve doesn’t have this slow reaction problem and would steer right away which is very important and that’s the reason to use hydraulics instead of steering on the wheel.
So I would stick to CC valve for this good reaction feature. What to do with extra pressure being dissipated via P Relief valve is still a question…
Pressure relief valve work on Max allowed steering pressure for the tractor plus a bit more, hence our system will use Tractor resources at max as if it was steering hardly all the time.
With the OC valve, the delay can be eliminated by setting the initial control voltage exactly at the point of beginning of the piston movement. If I understood correctly, it is possible to set a minimum PWM in AG, so if I think correctly there should be no problems with the speed of response.
And like in the Fluid system scheme, pressure relief valve to the LS line too.
What comes after steering valve and/or orbitrol (steering lines), totally depends how you want to build manual steering interruption: with magnets on steering column and reed switch there is no need of extra valves OR with pressure switch when extra valves is needed. OR maybe pressure switch with low pressure settings between priority valve EF and orbitrol P could work? Would be an easy solution if works.
BUT, since I’m not hydraulics expert, I can’t guarantee this works.
Thoughts anyone?
Would be lovely with an automatic priority valve like the one in fluid system, to do the shift job that the 3/2 valve do, but can´t find any at a reasonable price.
Most hits gives me flow dividers with a fixed amount of oil to orbitrol.
What’s wrong with simple 3/2 directional valve and steering encoder on the wheel to turn it off? Overhead installation process of an encoder?
Yes, the best and more convenient way is to buy a universal autosteer hydraulic system that fits oc and cc, but is 3-4 times more expensive. That’s why I’ve crated this thread
All I meant to say, is that Fluid system has thought this through and made a working solution. It’s providing hydraulic schematic which can be used. I didn’t mean you should buy that valve.
I’ve installed steering wheel encoder (magnets + reed switch) in 2 tractors. First was quite easy, and the second was not. It really can be tricky job to do. If there is a possibility to put hydraulic pressure switch somewhere, I recommend to do so instead of a steering wheel encoder.
I looked at this steering Valve diagram, it is built of proportional valves with LS type control and something like a pressure relief valve controlled by an auxiliary stream from proportional valves. In addition, there is a switch solenoid valve between the orbitrol and the proportional valve.
If you don’t have proportional valves with an additional LS control line, you probably can’t think of a strain relief, the only thing I can think of is the solenoid valve closing the circuit during the operation of the proportional valves and opening in the phase when they are not controlled.
Yes the fluid system block has a 6/2 valve at the top, it shall be powered when you turn on autosteer, it only moves when powered, and returns when not powered.
The spring at the right side of the bottom valve, makes the valve sending oil to P on proportional valve. If proportional valve is not using oil, then pressure vill rise and move bottom valve to the right, and therefore relieve oil through orbitrol to tank
You are correct the ls oil from proportional valve passes through the 0.8 hole and helps the spring to move the bottom valve to the left. (if too high pressure in ls line oil will pass the internal relief valve to tank)
So if steering wheels are hard to move, there will be higher pressure also in ls line when proportional valve is activated left or right.
If autosteer keeps turning to one side and the internal relieve valve is set higher than external relieve valve, then oil will get away through relieve valve at the pump.
I believe the P/I sign on port M is fluid systems symbol for pressure indicator or pressure switch
I don´t think you can tie the 6/2 valve together with the encoder. But I accept that the encoder must be fine counting, because of the short movement of steering wheel, when output from orbitrol is blocked of 6/2 valve.
You are correct that the 6/2 valve is not needed in the system d187 have, when using either a non reacting orbitrol or reacting orbitrol with piloted check/cut off valves.
Fluid system has the 6/2 valve in the block so they can tell that the block works both on reacting and non reacting systems.
And it is also a security item as it adds one more valve that must be on, before any automatic action can happen.
