US 12,312,764 B2
Self-leveling lift arm assembly for power machines
Daniel J. Krieger, Bismarck, ND (US); and David Glasser, Bismarck, ND (US)
Assigned to Doosan Bobcat North America, Inc., West Fargo, ND (US)
Filed by Doosan Bobcat North America, Inc., West Fargo, ND (US)
Filed on May 20, 2022, as Appl. No. 17/750,080.
Claims priority of provisional application 63/191,416, filed on May 21, 2021.
Prior Publication US 2022/0372726 A1, Nov. 24, 2022
Int. Cl. E02F 3/38 (2006.01); E02F 3/28 (2006.01); E02F 3/42 (2006.01); E02F 9/22 (2006.01); F15B 13/02 (2006.01)
CPC E02F 3/38 (2013.01) [E02F 3/283 (2013.01); E02F 3/422 (2013.01); E02F 9/2203 (2013.01); E02F 9/2267 (2013.01); E02F 9/2271 (2013.01); F15B 13/024 (2013.01); E02F 9/2292 (2013.01)] 27 Claims
OG exemplary drawing
 
1. A lift arm assembly comprising:
a lift arm that is pivotally secured at a first end to a main frame of a power machine;
an implement carrier that is pivotally secured to a second end of the lift arm;
a lift cylinder that is pivotally secured at a first end to the lift arm and pivotally secured at a second end to the main frame, so that extending or retracting the lift cylinder raises or lowers the lift arm;
a leveling link that is pivotally secured at a first end to the lift arm;
a tilt cylinder that is pivotally secured at a first end to the implement carrier and pivotally secured at a second end to the leveling link, so that operation of the tilt cylinder causes the implement carrier to pivot relative to the lift arm; and
an isolated hydraulic circuit that includes:
a follower cylinder that is pivotally secured at a first end to the lift arm and pivotally secured at a second end to the main frame, so that the follower cylinder is mechanically synchronized with the lift cylinder;
a leveling cylinder that is pivotally secured at a first end to the lift arm and pivotally secured at a second end to the leveling link;
a first conduit providing hydraulic flow between a base end of the follower cylinder and a base end of the leveling cylinder; and
a second conduit providing hydraulic flow between a rod end of the follower cylinder and a rod end of the leveling cylinder, wherein movement of the follower and leveling cylinders is hydraulically synchronized by flow through the first and second conduits.