How does a HYD self leveling bucket work?

[bx24]

I understand how you can mechnically keep a set of forks or your bucket on your FEL level as the arms are raised or lowered, but on some tractors (ie Kubota B26) it seems like you can hydraulicly "turn on or off" a self leveling circuit ....

Anyone have any insight into how this system works?

Thanks

Paul

 

[IceStationZebra]

Hydraulic self leveling systems are basically flow dividers/combiners. Check out the attached link, it has pretty pictures and all.

http://hydraulics.eaton.com/products/pdfs/11-503.pdf

Advantages - easier to implement than mechanical linkage, cheaper, can be retrofit.

Disadvantage - because you are splitting XX% of the flow (a linear function) but the boom works on a radius you will have some error and the bucket will not remain completely level throughout the lift/lower cycle. The amount of error depends on how close the flow split matches the boom/bucket cylinder area ratio, and where in the cycle you start (since the cylinder geometries are always changing). Mechanical systems are typically better in this regard.

Note: some valves only work in one direction, usually lifting.

ISZ

 

[Rocwin]

In the aerial industry keeping our buckets level is vital, since there is a man in them, the function is similar to a loader though.

Two systems are used, one is mechanical and as mentioned they tend to be expensive. They use gears, chains, pulleys and rods/cables to adjust the bucket as the lower arm raises. Repair costs on these can get pricey is you break a chain or something gets out of adjustment.
The hydraulic method is cheaper; generally a closed circuit is put into the system, one cylinder will be at your base which senses the position of the lower arm and the cylinder at the bucket responds to the lower cylinder's movement, they can be manually adjusted with hydraulic controls too. The only real disadvantages of this system is cylinder maintance (you can't slap any cylinder on there or they go out of synch) and problems occuring when air gets into the system, generally this can be bleed out in a few seconds on start up though.

 

[MossRoad]

In the aerial industry keeping our buckets level is vital, since there is a man in them, the function is similar to a loader though.

Two systems are used, one is mechanical and as mentioned they tend to be expensive. They use gears, chains, pulleys and rods/cables to adjust the bucket as the lower arm raises. Repair costs on these can get pricey is you break a chain or something gets out of adjustment.
The hydraulic method is cheaper; generally a closed circuit is put into the system, one cylinder will be at your base which senses the position of the lower arm and the cylinder at the bucket responds to the lower cylinder's movement, they can be manually adjusted with hydraulic controls too. The only real disadvantages of this system is cylinder maintance (you can't slap any cylinder on there or they go out of synch) and problems occuring when air gets into the system, generally this can be bleed out in a few seconds on start up though.

That is a lot more complicated than a bucket on a tractor. A simple mechanical parallel link will keep a bucket level on a front end loader. I say simple, because there are few parts. Figuring out where exactly to mount everything and the link lengths, etc... are not so simple. :laughing:

 

[bx24]

In the aerial industry keeping our buckets level is vital, since there is a man in them, the function is similar to a loader though.

I am familiar with the leveling systems on bucket trucks, but I could not think about how to bridge that technology with the one on a FEL

Hydraulic self leveling systems are basically flow dividers/combiners. Check out the attached link, it has pretty pictures and all.

http://hydraulics.eaton.com/products/pdfs/11-503.pdf

ISZ

ISZ - Thanks for the link, those diagrams are worth a thousand words!

 

[J_J]

Here is an article about self leveling.

Bidirectional Self-Leveling Hydraulic Valves For Off-Road Use | Diesel Progress North American Edition | Find Articles at BNET

 

[Rocwin]

A bucket is definitely more complicated than a tractor leveling. You have large distances through a boom to run (40 ft+) along with a 180° elbow and usually one or two insulated boom sections, which can't have steel running through them. Many systems use a turnbuckle so a cable or thread can be adjusted and 100% accuracy isn't required for assembly.

 

[KWentling]

Hydraulic self leveling systems are basically flow dividers/combiners. Check out the attached link, it has pretty pictures and all.

http://hydraulics.eaton.com/products/pdfs/11-503.pdf

Advantages - easier to implement than mechanical linkage, cheaper, can be retrofit.

Disadvantage - because you are splitting XX% of the flow (a linear function) but the boom works on a radius you will have some error and the bucket will not remain completely level throughout the lift/lower cycle. The amount of error depends on how close the flow split matches the boom/bucket cylinder area ratio, and where in the cycle you start (since the cylinder geometries are always changing). Mechanical systems are typically better in this regard.

Note: some valves only work in one direction, usually lifting.

ISZ

Any idea how much one of these Eaton valves cost? Sure would be nice to have when using the pallet forks.

Kim

 

[IceStationZebra]

................The hydraulic method is cheaper; generally a closed circuit is put into the system, one cylinder will be at your base which senses the position of the lower arm and the cylinder at the bucket responds to the lower cylinder's movement, they can be manually adjusted with hydraulic controls too. The only real disadvantages of this system is cylinder maintenance (you can't slap any cylinder on there or they go out of sync) and problems occurring when air gets into the system, generally this can be bleed out in a few seconds on start up though.

I think what you are describing is the same way telescopic handlers work. They have a slave cylinder at the main boom pivot that sends oil to the fork tilt cylinder. Since both work on an arc the volume is always in the correct proportion. Similar to a boom truck, they need to keep the forks level so they don't drop the load and they can not use mechanical linkage because the boom can change length constantly.

When I worked for Lull/Sky Trak I measured the error on two different prototype telehandlers and as I recall the error was less than a couple degrees. (It can be tough to get the ideal geometries due to packaging constraints.) In contrast, when I worked for CaseIH I tested a flow divider set-up on a FEL and the error was probably 10 to 15 degrees, but with oil temps below ~32 deg-F it didn't work at all!

ISZ