Hydraulic leveling circuit for power machines

A hydraulic assembly for controlling position of portions of a lift arm assembly, the lift arm assembly including a main lift arm portion, an extendable lift arm portion configured to be extended relative to the main lift arm portion, and an implement interface for supporting an implement, the hydraulic assembly comprising:

• a leveling cylinder configured to adjust an attitude of the implement relative to the extendable lift arm portion, causing one of a tensile load or a compression load on the leveling cylinder depending on a load introduced by an implement attached to the implement interface;
• an extension cylinder configured to move the extendable lift arm portion relative to the main lift arm portion;
• a main control valve configured to control commanded movement of the extension and leveling cylinders by selectively directing flow along a first hydraulic flow path to rod ends of the extension and leveling cylinders or along a second hydraulic flow path to base ends of the leveling and extension cylinders;
• a flow combiner/divider along one of the first or second hydraulic flow paths, the flow combiner/divider configured to divide hydraulic flow to, respectively, one of (i) the rod ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during extension of the extension and leveling cylinders, and to combine hydraulic flow from, respectively, one of (i) the rod ends of the extension and leveling cylinders during extension of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders, including for synchronized operation of the leveling and extension cylinders when the extension cylinder is under tension;
• and
• a lock valve arranged along one of the first hydraulic flow path and the second hydraulic flow path;
• the lock valve being configured to be moved to a first configuration during commanded movement of the extension and leveling cylinders and to a second configuration when there is no commanded movement of the extension and leveling cylinders;
• the first configuration of the lock valve permitting hydraulic flow between the rod ends of the extension and leveling cylinders;
• and
• the second configuration of the lock valve blocking hydraulic flow between the rod ends of the extension and leveling cylinders.

A hydraulic assembly for controlling position of portions of a lift arm assembly, the lift arm assembly including a main lift arm portion, an extendable lift arm portion configured to be extended relative to the main lift arm portion, and an implement interface for supporting an implement, the hydraulic assembly comprising:

• a leveling cylinder configured to adjust an attitude of the implement relative to the extendable lift arm portion, causing one of a tensile load or a compression load on the leveling cylinder depending on a load introduced by an implement attached to the implement interface;
• an extension cylinder configured to move the extendable lift arm portion relative to the main lift arm portion, the extension cylinder being under a compression load;
• a main control valve configured to control commanded movement of the leveling and extension cylinders by selectively directing flow along a first hydraulic flow path to rod ends of the extension and leveling cylinders or along a second hydraulic flow path to base ends of the leveling and extension cylinders;
• a first flow divider along the first hydraulic flow path configured to divide hydraulic flow to the rod ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders, for synchronized operation of the extension and leveling cylinders;
• a second flow divider along the second hydraulic flow path configured to divide hydraulic flow to the base ends of the extension and leveling cylinders during extension of the extension and leveling cylinders, for synchronized operation of the extension and leveling cylinders;
• a first flow-blocking arrangement along the first hydraulic flow path configured to restrict flow from the rod end of the leveling cylinder, during movement of the extension and leveling cylinders;
• and
• a second flow-blocking arrangement along the second hydraulic flow path configured to restrict flow from the base end of the extension cylinder, during movement of the extension and leveling cylinders,
• wherein the first flow divider includes a directional bypass to allow flow from the first flow-blocking arrangement to bypass the flow divider.

A hydraulic assembly for controlling position of portions of a lift arm assembly, the lift arm assembly including a main lift arm portion, an extendable lift arm portion configured to be extended relative to the main lift arm portion and an implement interface for supporting an implement, the hydraulic assembly comprising:

• a leveling cylinder configured to adjust an attitude of the implement supported by the implement interface relative to the extendable lift arm portion, causing one of a tensile load or a compression load on the leveling cylinder depending on a load introduced by an implement attached to the implement interface;
• an extension cylinder configured to move the extendable lift arm portion relative to the main lift arm portion, the extension cylinder;
• a main control valve configured to control commanded movement of the leveling and extension cylinders by selectively directing flow along a first hydraulic flow path to rod ends of the extension and leveling cylinders or along a second hydraulic flow path to base ends of the leveling and extension cylinders;
• a flow combiner/divider along one of the first or second hydraulic flow paths, the flow combiner/divider configured to divide hydraulic flow to, respectively, one of (i) the rod ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during extension of the extension and leveling cylinders, and to combine hydraulic flow from, respectively, one of (i) the rod ends of the extension and leveling cylinders during extension of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders, for synchronized operation of the leveling and extension cylinders;
• and
• a first flow-blocking arrangement positioned along the first hydraulic flow path, a second flow-blocking arrangement positioned along the second hydraulic flow path, and a third flow-blocking arrangement positioned along the second hydraulic flow path;
• the first flow-blocking arrangement configured to restrict flow from the rod end of the leveling cylinder during extension of the leveling and extension cylinders when the leveling cylinder is under tension and the extension cylinder is under compression;
• the second flow-blocking arrangement configured to restrict flow from the base end of the extension cylinder during retraction of the leveling and extension cylinders when the leveling cylinder is under tension and the extension cylinder is under compression;
• and
• the third flow-blocking arrangement configured to restrict flow from the base end of the leveling cylinder during retraction of the leveling and extension cylinders when the leveling cylinder is under compression,
• wherein a plurality of the first, second, and third flow-blocking arrangements include a restriction orifice in parallel with a check valve.

A hydraulic assembly for controlling position of portions of a lift arm assembly, the lift arm assembly including a main lift arm portion, an extendable lift arm portion configured to be extended relative to the main lift arm portion and an implement interface for supporting an implement, the hydraulic assembly comprising:

• a leveling cylinder configured to adjust an attitude of the implement supported by the implement interface relative to the extendable lift arm portion;
• an extension cylinder configured to move the extendable lift arm portion relative to the main lift arm portion;
• a main control valve configured to control commanded movement of the leveling and extension cylinders by selectively directing flow along a first hydraulic flow path to rod ends of the extension and leveling cylinders or along a second hydraulic flow path to base ends of the leveling and extension cylinders;
• a flow combiner/divider along one of the first or second hydraulic flow paths, the flow combiner/divider configured to divide hydraulic flow to, respectively, one of (i) the rod ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during extension of the extension and leveling cylinders, and to combine hydraulic flow from, respectively, one of (i) the rod ends of the extension and leveling cylinders during extension of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders, for synchronized operation of the leveling and extension cylinders;
• and
• a first flow-blocking arrangement positioned along the first hydraulic flow path and a second flow-blocking arrangement positioned along the second hydraulic flow path, the first flow-blocking arrangement configured to restrict flow from the rod end of the leveling cylinder and the second flow-blocking arrangement configured to restrict flow from the base end of the extension cylinder during movement of the leveling and extension cylinders, the second flow-blocking arrangement including a counterbalance valve having:
• a first position with a check valve configured to permit flow through the check valve to the base end of the extension cylinder during extension of the leveling and extension cylinders;
• and
• a second position with a flow orifice configured to restrict flow from the base end of the extension cylinder during retraction of the leveling and extension cylinders.

A hydraulic assembly for controlling position of portions of a lift arm assembly, the lift arm assembly including a main lift arm portion, an extendable lift arm portion configured to be extended relative to the main lift arm portion and an implement interface for supporting an implement, the hydraulic assembly comprising:

• a leveling cylinder configured to adjust an attitude of the implement supported by the implement interface relative to the extendable lift arm portion;
• an extension cylinder configured to move the extendable lift arm portion relative to the main lift arm portion;
• a main control valve configured to control commanded movement of the leveling and extension cylinders by selectively directing flow along a first hydraulic flow path to rod ends of the extension and leveling cylinders or along a second hydraulic flow path to base ends of the leveling and extension cylinders;
• a flow combiner/divider along one of the first or second hydraulic flow paths, the flow combiner/divider configured to divide hydraulic flow to, respectively, one of (i) the rod ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during extension of the extension and leveling cylinders, and to combine hydraulic flow from, respectively, one of (i) the rod ends of the extension and leveling cylinders during extension of the extension and leveling cylinders or (ii) the base ends of the extension and leveling cylinders during retraction of the extension and leveling cylinders, for synchronized operation of the leveling and extension cylinders;
• a first flow-blocking arrangement positioned along the first hydraulic flow path and configured to restrict flow from the rod end of the leveling cylinder;
• a second flow-blocking arrangement positioned along the second hydraulic flow path and configured to restrict flow from the base end of the extension cylinder during movement of the leveling and extension cylinders;
• and
• a third flow-blocking arrangement positioned along the second hydraulic flow path and configured to restrict flow from the base end of the leveling cylinder during retraction of the leveling and extension cylinders when the leveling cylinder is under compression, the third flow-blocking arrangement including a restriction orifice in parallel with a pilot-operated check valve that is configured to block flow from the base end of the leveling cylinder in a default state and to be:
• opened by pressurization of the first hydraulic flow path, during retraction of the leveling and extension cylinders, to permit flow through the pilot-operated check valve from the base end of the leveling cylinder;
• and
• closed, during retraction of the leveling and extension cylinders, upon compression loading of the leveling cylinder.