Power Steering Cylinders--How Does One Work?

[npalen]

I see some power steering setups with a single cylinder and some with doubles. My question is with regard to a single cylinder of convention design where the displacement on the rod side of the piston is quite a bit less than on the base side. What keeps the steering from being much faster when the cylinder is retracting while it takes much less fluid to move the cylinder a given amount?
I "get" the double rod design where the displacement is equal on either side of the piston or the twin cylinders where the net displacement is the same.

 

[PILOON]

While not sure I'd simply suspect that either the difference is really not noticeable, that or perhaps a restrictor is incorporated on the favored side.

 

[Industrial Toys]

I'm guessing that the flow demanded for steering simply compensates. There is amble in either direction. Who knows? You may notice it works a bit faster one way, but who thinks of that?

I always wondered how power assist steering works.There must be a valve that senses the slightest bit of torque in the steering linkage.

 

[Leejohn]

2 cyls has a crossover valve. One DA cyl you well see the steering wheel doesn't return to the same spot. There is another system that the steering head is the pump and also the wheel well not return to the same spot. I forgot what each system is called.

 

[Industrial Toys]

Yes. Some off road equipment has a manual pump in the steering box, like my Kubota Loader. You have some hard (hydraulic) steering with the motor turned off and then full power steering with motor running.

 

[PILOON]

Yes. Some off road equipment has a manual pump in the steering box, like my Kubota Loader. You have some hard (hydraulic) steering with the motor turned off and then full power steering with motor running.

\

LOL, my l'il Mitsu has no power steering but I always planned on correcting that.
I bought on EBay the proper valve device and have a suitable cylinder.
Just need to make the bracket (and I weld) to anchor the cylinder to the frame and already have the ball joint for the Pittman arm.
Even tho retired I have not found the time to make it happen.
LOL, there is always tomorrow!
Funny how you learn how to work around short comings, and oddly enough 60% of my tractor work involves FEL work, you'd think I'd be motivated.
Even without power assist I can spread and grade a 12 wheel dump truck load of crushed within 1 hour average time so all is not lost.

 

[fatjay]

I added hydraulic steering to my kubota. It's just a hydraulic cylinder bolted to where the arm used to be for the manual steering. I added a steering column from a deere 318.

Steering is effortless now with the blower up on dry asphault. Best thing I did to my tractor.

 

[npalen]

Nice job on the plumbing!

 

[npalen]

Did a bit of calculating on the steering cylinder on my tractor to see how much difference between the rod side and base side of the piston. Using 42mm bore size with a 18mm shaft size, I'm seeing rod side displacement at 81% of the base side which is a lot less difference that I had imagined. Feel free to verify my figures--I did make a mistake one time.
So tend to agree with the comment that it's really not noticeable and will check to verify that the steering wheel does not center at the same place each time the tractor is turned one way or the other.
That stands to reason given the difference in displacement but just never noticed it.
I agree that most folks couldn't care less about trivial details such as this but some of us are just plain gearheads.

 

[TMGT]

You'll notice most factory systems that use a single DA cylinder have very small rod diameters for the cylinder size. As you found out it leads to a neglegable difference in speed.

 

[npalen]

Typical Steering with Orbitrol

A diagram of how the Orbitrol is used for power steering similar to fatjay's setup except twin cylinders.

 

[LD1]

Not only is the difference in the two sides small enough to not be noticeable.....(81% as you calculate)

You are forgetting the most important reason.....

Your steering wheel that is connected to the orbital valve......its like one big flow control device. Meaning you have plenty of flow.......the steering wheel controls how fast the wheels turn by how fast you turn the wheel.

for example....your 18mm rod and 42mm bore cylinder.......probably paired with about 3gpm flow for your steering........that cylinder can extend at ~5.5" per second.....or retract at 6.5" per second.

So unless you are trying to spin the wheels to make the cylinder move much faster than that.......you have ample flow.

The steering wheel controls the speed.

Similar to my front loader......or any controls on my backhoe. By feathering the valve........I can make the cylinders move as fast as the pump will allow.......or as slow as I want. I can make my loader raise (extend the cylinder) FASTER than lowering it simply by feathering the valve (controlling the flow).....which is all the orbital valve is doing.

 

[fatjay]

My steering was a little fast when I first did it, but I quickly got used to it. Just takes a little bit of seat time.

 

[Industrial Toys]

I would still like to know how that orbitrol works. With a hydraulic pump working and not.

 

[PILOON]

While on the subject of cylinders I have one that I can not use for a Kioti DK 40, they use 2 cylinders, bought as new surplus in error. Offers? trade?

 

[npalen]

I would still like to know how that orbitrol works. With a hydraulic pump working and not.

orbitrol - Yahoo Video Search Results

This is a schematic representation of how the orbitrol works. In the video the comment is made that the gerotor (which the steering wheel actuates) acts as a pump or a motor. Lose hydraulic pressure and the steering wheel rotation pumps fluid to the steering cylinders. It's a safety feature in case of loss of pressure while traveling at relatively high speed.

 

[bigdeano]

Automotive power steering gears have a small torsion bar hooked to the input shaft from the steering wheel. As torque is applied to the steering wheel the torsion bar twists, allowing a small amount of relative movement between the two parts of the valve. This opens the ports to allow flow to the cylinder. When the wheel is released the torsion bar centers the valve parts, shutting off the flow.

I suspect the orbitrol valve works the same way, but I've never had one apart.

 

[MHarryE]

The first tractor we bought with hydrostatic power steering was not a balanced double acting cylinder and you needed to keep turning slowly in one direction to keep it going straight. Then I started my engineering career with a combine manufacturer and we had the same problem - too cheap to buy the right cylinder for the job but we were selling everything we could get out the door. With a market downturn, we needed to take customers seriously. 2 single acting cylinders, one for right, one for left, turned out to be cheaper than a single balanced cylinder with the proper capacity and having plenty of room, we went in that direction. A good HMU (hand metering unit) will not give much drift.

 

[nyone]

I added hydraulic steering to my kubota. It's just a hydraulic cylinder bolted to where the arm used to be for the manual steering. I added a steering column from a deere 318.

Steering is effortless now with the blower up on dry asphault. Best thing I did to my tractor.

Its been over a year now. Any updates? How many hours have you put on the unit?

I have ab8200 with a exploded steering box and going full hydro seams to be the best thing. Mine has a loader on it also.

 

[Yooperguy]

Since this old thread has recently be resurrected... I'd just like to say that when I first bought my Mahindra 1626 HST the single DA steering cylinder really messed with my OCD. On at least a couple of occasions I popped the center cap on the steering wheel to "properly" align the logo when the front wheels were straight. It's the only part of the dealer prep I took issue with. LOL! Much to my chagrin... the **** thing would be off center the next time I focused on it's orientation. It made me question whether I had really centered it or not! Finally I said "screw it" and decided not to worry about it... only to see it oriented correctly a day or two later.

I did learn that it was dynamic before finding this thread. But reading this thread really helped me understand it more fully.