Steering logic.

[BobRip]

Since flow it going back to the tank except when a section is being moved, this would mean that when (for example) the steering is engaged to change steering angle, most of the flow would revert to tilt and lift circuit and there would not be enough pressure to do much steering. Only if both were engaged would there be enough back pressure to do work and then the flow rate would be 1/2. In other words when lift/tilt and steering, are not being changed you would have return flow to tank from both system. When one is engaged to change angle most if not all of the flow would return through the other system and little pressure would be available to do work.

Bob Rip

 

[J_J]

Bob, I tend to disagree for this reason. After modification, if you have a 10 gal pump, and you activate only the steering motor, you will have the full 10 gal available to make your turn at maximum turn rate. The same will occur if you only activate the lift circuit, you would have the full 10 gal available, fast lift. Each system has it's own return line to tank, therefore, they are separate. Now if you turn and lift at the same time, you will have about half going to each circuit. Med turn, and med lift. Neither output will get in the way of the other. You will be using and dumping 5 gal from each circuit. I believe this is correct, but let me know if this logic is not valid.

I just don't like the priority setup as it is now. I can live with it till I get it changed.

 

[Spiffy]

Once again without time to take a closer look at the schematics (I don't recall it showed anyway), I may be typing out of turn:

but it depends whether each is open or closed center. I'll almost bet at least one is; likely steering; maybe both. This would require an auxillary solenoid(s) for your mod to work (to "close" the open center(s) when required); of course, then you need the switch(s) located conveiniently - perhaps a button on the joystick. Could be more trouble than value. /forums/images/graemlins/confused.gif

 

[Highridge]

</font><font color="blue" class="small">( MR: You guessed it; I'm contemplating a rear joystick to make BH life easier. Also would be great if I ever mount a 3pt blower; I think it'd be a snow moving machine with a blower on one end and snow bucket on the other. )</font>

If you ever did that, you would DEFINITELY need to take some pictures! /forums/images/graemlins/cool.gif

 

[J_J]

Open-Center: Typically used with a fixed-displacement pump, allows oil to free-flow back to the tank in neutral position. Shifting the spool redirects oil to the selected work port,
therefore in our situation cutting off, or reducing fluid down stream. If you do a 10 degree turn for instance, you may allow some fluid to slip by. If this steering system had power beyond, I don't believe I would have started this thread.

Closed-Center: Typically used with a variable-displacement pump, oil flow is blocked at the valve until the spool is shifted from neutral.





Open Center is the type valve/motor I believe is used in the PT's.
Therefore the output from the pump is available to either, steering or lift. They must be is series for the steering to affect the lift. In a lift situation, the fluid is going through the steering valve to the lift valve. Each has an output to tank. If you activate the steering, you interrupt the flow to the lift valve, which is exactly what is happening in my situation. Therefore if I separate them, they should work independently.

 

[blackwell]

Its the law.

 

[blackwell]

Not true. The steering meters oil to the steering cllinders at a fixed rate per rev of the steering wheel reguardless of the flow going thru the valve. The only way to increse steering speed is to increase steering valve displacement or decrese cylinder volume. The law requires the steering to take priority. The reason your machine wont lift when the steering is to one side, you are continuing to try to steer when the machine is fully steered, thus opening the relief and not allowing oil to the lift valve. This is the same thing as the little old lady coming out of a parking trying to steer her car more after the steering has hit stops and the belt is squalling due to the steering pump at max pressure.
On Pts the flow goes thru the steering and then to the lift valve, so what is not used steering can be used to lift. Try lifting the arms and steer slowly, you will see the arms slow down, then stop steering and they will speed up.
Try not to squill the belt! /forums/images/graemlins/blush.gif /forums/images/graemlins/cool.gif

 

[BobRip]

J J this is kind of hard to explain in words, but I will try again (and I am not an expert on hydraulics, but I am one on electricity). If the flow is 10 gallons per minute with no change in lift or steering then half will probably go through each of your new parallel circuit. The pressure is very low since these are both free flowing circuits. When you try to turn for example the flow will be restricted through the turning circut and back pressure will try to build up. Since the lift/tilt has not been activated and has little or no back pressure then most (if not all) of the flow will go through this circuit and you will get little or no steering force. Remember, in hydyaulics the flow is greatest when you are not changing the position of a cylinder.

At maximum steering forced to the end of travel the pressure builds up and trips the relief valve because there is no flow. In this situation, since there is no flow through the steering, then the tilt and lift get no pressure in PT plumbing system. In your approach, the pressure would not build since it would flow through the tilt system.

To use an electrical analogy if you have two wires in parallel providing power to a light bulb and the wire lengths and diameters are equal then the currrent (which is actually electron flow) will be the same in each. If you make one of the wires longer then you have more resistance and the current will shift to the wire with less resistance.

If you decide to do this, please make sure you can change it back. Remember if you just stay off the stop then you can still do lift.

Sorry for the long explanations and good luck with what ever you do.

Bob Rip

 

[J_J]

Are you talking about legal law, or laws of hydraulics? If you are talking about legal law, is there a precedent that requires this type of circuit?

 

[BobRip]

J J, I wonder if something is wrong with your particular machine. Please confirm that you do have lift control when you are not at the stops of steering. If you do not then it could be the relief valve is stuck partially open or relieves at too low a pressure.

Bob Rip