NL2014567B1

NL2014567B1 - Hydraulic balancing of independently loaded suspension cylinders in an implement.

Info

Publication number: NL2014567B1
Application number: NL2014567A
Authority: NL
Inventors: Sieger De Vries Sjoerd; Dale Van Zee Michael
Original assignee: Forage Innovations Bv
Priority date: 2015-02-24
Filing date: 2015-04-01
Publication date: 2017-01-06
Also published as: NL2014567A

Abstract

A movable implement comprises: a frame and a tool suspended from the frame. The tool has a center lengthwise axis that extends through the center of the tool and parallel to a direction of travel of the implement. The center lengthwise axis defines a first side of the tool and a second side of the tool generally opposite the first side. A first hydraulic lift cylinder is attached to the frame and the first side of the tool. A second hydraulic lift cylinder is attached to the frame and the second side of the tool. A hydraulic accumulator is fluidly connected to the first hydraulic lift cylinder. A control system is provided for controlling a first fluid pressure in the first hydraulic lift cylinder to be less than a second fluid pressure in the second hydraulic lift cylinder.

Description

Hydraulic balancing of independently loaded suspension cylinders in an implement FIELD OF THE DISCLOSURE

The field of the disclosure relates to implements having a suspended tool such as a cutter head and, in particular, hydraulic balancing of the suspended tool to account for variations in weight across the tool.

BACKGROUND

Various implements for agricultural, forage or other use involve a tool or “header” suspended from a frame that is supported on wheels or tracks for propulsion through a field or other surface. Examples of such implements include mowers, mower conditioners, road planers, pavers or graders. Such implements may include hydraulic cylinders which are used to suspend the header from the frame. Such conventional suspension systems are poorly adapted to suspend a header that is characterized by an uneven weight distribution across the lateral length of the header, i.e., in which one side of the header weighs more than the other side. Such weight distribution profiles may result from the weight distribution of the header itself or from material (e.g., forage material) that builds up on the header during use. A continuing need exists for implements that compensate for an uneven weight distribution across the length of the header to achieve a more uniform distribution of ground contact force across the header and for methods for using implements in which uneven weight distribution is offset during use of the implement.

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

SUMMARY

One aspect of the present disclosure is directed to a movable implement. The implement includes a frame and a tool suspended from the frame. The tool has a center lengthwise axis that extends through the center of the tool and parallel to a direction of travel of the implement. The center lengthwise axis defines a first side of the tool and a second side of the tool generally opposite the first side. A first hydraulic lift cylinder is attached to the frame and the first side of the tool. A second hydraulic lift cylinder is attached to the frame and the second side of the tool. A hydraulic accumulator is fluidly connected to the first hydraulic lift cylinder. The implement includes a control system for controlling a first fluid pressure in the first hydraulic lift cylinder to be less than a second fluid pressure in the second hydraulic lift cylinder.

Another aspect of the present disclosure is directed to a method for operating a movable implement comprising a frame and a tool suspended from the frame. The tool has a lengthwise axis that extends through the center of the tool and parallel to a direction of travel of the implement. The center lengthwise axis defines a first side of the tool and a second side of the tool generally opposite the first side. The tool has a contact surface with a first end on the first side and a second end on the second side. The first and second sides of the tool each have a weight. The weight of the first side of the tool is less than the second side of the tool. The difference between the first side weight and the second side weight is at least a percentage, X, of the weight of the first side. The implement is propelled over a surface. The tool contacts the surface while the implement is propelled. The first side of the tool exerts a first contact force against the surface at the first end and the second side of the tool exerts a second contact force against the surface at the second end. The difference between the force exerted at the first end and the force exerted at the second end as a percentage of the first force is less than X.

Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present disclosure may be incorporated into any of the above-described aspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic of an implement with a tool supported by balanced hydraulic cylinders;

Figure 2 is a schematic of the implement after contacting a raised portion of the ground surface at the first end of the tool;

Figure 3 is a schematic of the implement after contacting a raised portion of the ground surface at the second end of the tool;

Figure 4 is a schematic of another embodiment of the implement having a second pressure reducing valve;

Figure 5 is a perspective view of an embodiment in which the implement is a mower;

Figure 6 is a perspective view of another embodiment in which the implement is a mower;

Figure 7 is a side view of the mower of Figure 6 with a portion of the frame removed to show components of the mower;

Figure 8 is a schematic of another embodiment of the implement having a second accumulator;

Figure 9 is a schematic of another embodiment of the implement having a pressure reducing valve upstream of the accumulator and having a second accumulator; and

Figure 10 is a schematic of another embodiment of the implement having a pressure reducing valve connected to the air chamber of the accumulator and having a second accumulator.

Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION

Referring now to Figure 1, a movable implement 5 having a tool 8 suspended from a frame 10 is shown. The tool 8 is suspended from the frame 10 by a first hydraulic lift cylinder 16 and a second hydraulic lift cylinder 18. The tool 8 is illustrated to have more volume on the left side than on the right side, to represent an uneven weight distribution. The movable implement 5 may have a variety of functions such as cutting forage material as with mowers or mower conditioners. While the implement 5 and/or tool 8 may be described herein with reference to a mower or mower conditioner having a suspended cutter head, it should be understood that other implements and tools may be used. Other implements having a tool 8 suspended from a frame 10 by use of hydraulic cylinders include, by way of example only, road planers, pavers or graders having a mill drum, screed or blade suspended from a frame, respectively.

Some implements such as various mowers and mower conditioners have tools (e.g. a cutter head) that engage the ground as the implement is propelled forward. Such tools exert a ground contact force against the surface over which the implement 5 is propelled. Hydraulic lift cylinders 16, 18 cause the ground contact force to be less than the weight of the implement 5. The hydraulic lift cylinders 16, 18 act to distribute at least a portion of the weight of the tool 8 to the wheels 23 of the implement 5 that are connected to the frame 10. The contact force is generally the difference between the weight of the header 8 minus the upforce provided by the hydraulic lift cylinders 16, 18. In other embodiments of the present disclosure, the tool 8 is fully carried by the frame 10 and does not contact the ground and the hydraulic lift cylinders 16, 18 act to level the tool for proper use (e.g., cutting). For mowers and mower conditioners it is generally desirable for the ground contact forces to be approximately equal, to assure that the implement is being held at a consistent height off the ground across its width, and to minimize damage to the ground and/or the implement.

In other embodiments, or in other operating conditions of the present disclosure, the tool 8 is fully carried by the frame 10 and does not contact the ground. Further, the hydraulic lift cylinders 16, 18 act to level the tool for proper use. In such a case, it is generally desirable that the implement 5 be kept level while suspended.

The implement 5 may be operated by use of a towing vehicle (e.g., tractor) that propels and directs the implement through the field. The implement 5 may be attached to the pulling vehicle (not shown) by use of a tongue 2 (Fig. 5) by any suitable coupling mechanism. In other embodiments, the implement 5 includes its own propulsion system (e.g., motor) rather than a propulsion system of a towing vehicle (i.e., includes a propulsion system that is integral with the implement). In such embodiments, the implement 5 may be self-guiding through the field. The implement 5 may be supported on wheels 23 or on tracks (not shown) for propulsion through a field or other surface.

While the implement 5 is shown as having two hydraulic lift cylinders 16, 18 to support the tool 8, more cylinders may be used (e.g., 3, 4, 5 or more hydraulic cylinders). In some embodiments, the implement 5 includes separate lift cylinders (not shown) for moving the tool 8 into a transport position for moving the implement 5 to and from a surface upon which the tool works (e.g., to and from a field as with mower conditioners).

The implement 5 includes a vertical axis A. The first hydraulic lift cylinder 16 is mounted to the tool 8 above where the first hydraulic lift cylinder 16 is mounted to the frame 10, with respect to the vertical axis A. Similarly, the second hydraulic lift cylinder 18 is mounted to the tool 8 above where the second hydraulic lift cylinder 18 is mounted to the frame 10, with respect to the vertical axis A. In this mounting position, the tool 8 exerts a compressive force on the first hydraulic lift cylinder 16 and on the second hydraulic lift cylinder 18, with the weight of the tool compressing the cylinders. In such embodiments, the hydraulic supply lines 61, 64, which are fluidly connected to the cylinders 16, 18, may be attached to the extend port of the hydraulic lift cylinders. The extend port is not expressly shown in the Figures, as the drawings are a simplified schematic showing the line as being directly connected to the cylinder with a discrete port. The Figures, as drawn, are intended to illustrate the supply lines being connected to cylinders in any known manner, including by use of a port.

The mechanical arrangement of a frame and linkages could be utilized in a way that the tool 8 would exert an extension force on the lift cylinders, where the weight of the tool 8 extends the cylinders. For example, the first hydraulic lift cylinder 16 may be mounted to the tool 8 below where the cylinder 16 is mounted to the frame 10, with respect to the vertical axis A, and the second lift cylinder 18 may be mounted in a similar arrangement relative to the tool 8 and frame 10. In this mounting position, the tool 8 exerts a tensive force on the first and second hydraulic lift cylinders 16, 18. In this configuration, the hydraulic supply lines 63, 64 would be connected to the retract ports of the cylinders 16, 18.

Generally, the hydraulic lift cylinders 16, 18 are single-acting cylinders but double-acting cylinders which are powered to extend and retract the cylinders may also be used. The implement 5 may also include various pivot linkages between the lift cylinders 16, 18 and the frame 10 and/or the tool 8. The hydraulic circuit (e.g., supply line), hydraulic lift cylinders 16, 18 (including extend and/or retract ports) and any linkages (e.g., pivot linkages) to the frame 10 and/or tool 8 are arranged to provide lift to the tool 8 in a manner such that the contact force of the tool 8 is reduced or the tool is fully suspended by the frame 10, ideally in a manner that the contact force of the tool 8 is equal on both sides.

The implement 5 has a lengthwise axis B (Fig. 5) that extends through the center of the tool 8 and parallel to the direction of travel of the implement 5. As used herein, the center of the tool 8 corresponds to midway between the mounting points of the first and second hydraulic lift cylinders 16, 18 (Fig. 1). The center lengthwise axis B defines a first side 8a of the tool and a second side 8b generally opposite the first side 8a. The first lift cylinder 16 is attached the first side 8a of the tool and the second lift cylinder 18 is attached to the second side 8b of the tool. The tool 8 has a contact surface 21 (e.g., cutter bar) that engages the surface over which the tool travels. The contact surface 21 has a first end 36 on the first side 8a of the tool and a second end 38 on the second end 8b of the tool.

The implement 5 includes a hydraulic accumulator 33 that is fluidly connected to the first hydraulic lift cylinder 16 and to the second hydraulic lift cylinder 18. The hydraulic accumulator 33 exchanges hydraulic fluid with the first hydraulic lift cylinder 16 and the second hydraulic lift cylinder 18 during extension and retraction of the cylinders. In the illustrated embodiment, the accumulator 33 includes a gas chamber 49 and a hydraulic fluid chamber 45 that are separated by a bladder. The gas chamber 49 is typically charged at an initial pressure by use of a gas (e.g., noncombustible gas such as nitrogen).

The implement includes a control system for controlling a first fluid pressure in the first hydraulic lift cylinder 16 to be less than a second fluid pressure in the second hydraulic lift cylinder 18. In the illustrated embodiments, the control system includes a pressure reducing valve 30. The pressure reducing valve 30 is disposed between the accumulator 33 and the first hydraulic lift cylinder 16. The hydraulic accumulator 33, pressure reducing valve 30, and first hydraulic lift cylinder 16 form a first response circuit for adjusting the amount of hydraulic fluid in the accumulator and the cylinder, as the first side 8a of the tool encounters elevation changes to the terrain. The accumulator 33 and second hydraulic lift cylinder 18 form a second response circuit. While the response circuits share an accumulator 33 and may be considered to be parts of a single hydraulic circuit, as referenced herein, the response circuits may be considered to be separate such that the second hydraulic lift cylinder 18 does not form part of the first response circuit and the first hydraulic lift cylinder 16 does not form part of the second response circuit.

The pressure reducing valve 30 acts to reduce downstream pressure in the first response circuit. The valve 30 may be single cartridge valve or a two-cartridge valve which permits back-flow to maintain a constant pressure differential across the valve in instances in which upstream pressure (i.e., in the direction of accumulator 33) is reduced. In some embodiments (e.g., in which a single cartridge valve is used), the valve 30 also acts as a reverse flow check valve that allows reverse flow when the downstream pressure (in the direction of the cylinder 16) exceeds the upstream pressure (in the direction of the accumulator 33) to allow for back flow when the circuit is bled off (e.g., when the tool 8 is moved to a transport position). Suitable valves include the valves disclosed in U.S. Patent No. 7,069,945 and U.S. Patent No. 6,805,155, both of which are incorporated herein by reference for all relevant and consistent purposes.

In the illustrated embodiment, the pressure reducing and reverse check flow functionalities of the valve 30 are combined in a single valve body. In other embodiments, the pressure relief valve and check valve functions are performed in different bodies which may be combined in a manifold arrangement.

Generally, the pressure reducing valve 30 acts to reduce the fluid pressure in the first response circuit fluid downstream of the valve (e.g., fluid pressure in the first hydraulic lift cylinder 16) relative to the pressure of the second hydraulic fluid in the second response circuit (e.g., in the second hydraulic lift cylinder 18). Depending on the type of implement and type of hydraulic system (e.g., open or closed system) and the type of valve 30, the pressure reducing valve 30 may reduce the line pressure by at least about 50 kPa, at least about 1000 kPa, at least about 10,000 kPa or at least about 30,000 kPa or more. The pressure reduction may range up to about 12,500 kPa for systems incorporating tractor hydraulics, up to 20,000 kPa for systems having an independent open loop system and up to 35,000 kPa for an independent closed loop system. It should be noted that the pressure reduction ranges are exemplary and other ranges may be used unless indicated otherwise. A first hydraulic line 61 connects the accumulator 33 to the pressure reducing valve 30, and a second hydraulic line 63 connects the pressure reducing valve 30 to the first hydraulic lift cylinder 16. A third hydraulic line 64 connects the accumulator 33 to the second hydraulic lift cylinder 18.

In some embodiments, the first side 8a of the tool weighs less than the second side 8b of the tool. The pressure reducing valve 30 reduces the pressure downstream of the pressure reducing valve 30 (i.e., in the lift cylinder 16) to offset the reduced weight of the first side 8a of the tool. By independently loading the cylinders 16, 18, the contact force of the tool 8 across its width may be better balanced. In some embodiments, the difference between the first side weight and the second side weight is at least a percentage, X, of the weight of the first side. The percentage difference, X, may be at least about 2.5% or, as in other embodiments, at least about 5%, at least about 10%, at least about 15% or from about 2.5% to about 50%, from about 2.5% to about 35%, from about 2.5% to about 25%, from about 5% to about 50% or from about 5% to about 35%.

While the implement 5 is propelled forward, the contact surface 21 of the tool 8 contacts the surface over which the implement is propelled. The first side 8a of the tool exerts a first contact force against the surface at the first end 36 of the contact surface 21, and the second side 8b of the tool exerts a second contact force against the surface at the second end 38 of the contact surface. The pressure reducing valve 30 acts to offset the reduced weight on the first side 8a of the tool such that the difference between the force exerted at the first end 36 and the force exerted at the second end 38 of the contact surface 21 as a percentage of the first force is less than the percentage difference X between the weights of the two sides 8a, 8b of the apparatus. For example, the difference between the force exerted at the first end 36 and the force exerted at the second end 38 as a percentage of the first force may be less than about 0.75X or less than about 0.5X, less than about 0.25X, less than about 0.1X or even less than 0.05X. In some embodiments, the contact force at the first end 36 is substantially equal to the contact force at the second end 38.

As shown in the illustrated embodiment, the second response circuit does not include a pressure reducing valve. In other embodiments, the implement 5 includes a second pressure reducing valve 66 (Fig. 4) that forms part of the second response circuit. Similar to the first pressure reducing valve 30, the second pressure reducing valve 66 may be disposed between the accumulator 33 and the second hydraulic lift cylinder 18. The first pressure reducing valve 30 and the second pressure reducing valve 66 may be arranged such that the pressure of the first response circuit fluid downstream of the first pressure reducing valve 30 (e.g., in the first lift cylinder 16) is less than the pressure downstream of the second pressure reducing valve 66 (e.g., in the second hydraulic lift cylinder 18). In such embodiments, a pressure reducing line 64 (e.g., third line) connects the accumulator 33 to the second pressure reducing valve 66, and a hydraulic line 74 (e.g., fourth line) connects the second pressure reducing valve 66 to the second hydraulic lift cylinder 18.

As shown in Figure 1, the pressure reducing valve 30 may be set such that the first side 8a of the tool exerts a contact force substantially the same as that exerted by the second side 8b of the tool (or that results in the tool being substantially level when the device is fully suspended), despite the first side 8a having a weight less than that of the second side 8b. In some embodiments, the pressure reducing valve 30 is adjusted by the operator to suitably balance the contact force between the first side 8a of the tool and the second side 8b of the tool. Any suitable method of adjustment may be used, including a spring bias adjustment which is typical for many pressure reducing valves.

During operation of the implement 5, the contact surface 21 of the tool 8 encounters undulations of the surface over which the tool travels. The response of the implement 5 upon the first side 8a of the tool contacting a raised portion of the surface is shown in Figure 2. As the first side 8a contacts the raised portion of the surface, the head of the first lift cylinder 16 lifts, creating additional volume in the cylinder chamber. This reduces the volume of fluid in the accumulator 33 and the overall pressure of the system. As the same pressure differential is maintained across the pressure reducing valve 30, the pressure is lowered in the first lift cylinder 16, allowing the contact forces between both sides 8a, 8b of the tool to be equalized.

As shown in Figure 3, the second side 8b of the tool encounters a raised portion of the surface. As the second side 8b contacts the raised portion of the surface, the head of the second lift cylinder 18 lifts, creating additional volume in the cylinder chamber thereby reducing the system pressure. In this instance, the pressure differential across the valve 30 may be less than the pressure differential before encountering the raised portion, as back flow has not occurred across the valve 30 (e.g., as with single cartridge valves). In other embodiments (e.g., the valve 30 is a two-cartridge valve), the differential pressure is maintained across the valve 30 upon the second side 8b of the tool encountering a raised portion of the surface.

Generally the accumulator 33, pressure reducing valve 30, first lift cylinder 16, second lift cylinder 18 and connecting lines provide suspension (i.e., lift) of the tool during operation. The implement 5 may include additional parts for charging the system and/or for actuating the tool to a travel position. For example, the system may include a take-up cylinder to control the oil volume displaced for lifting and lowering the tool. The system may include an isolation valve (e.g., ball or solenoid) to isolate the hydraulics of the implement 5 from the hydraulic system of the towing vehicle (if any).

The towing vehicle may include hydraulic components for operating the implement, such as a hydraulic fluid reservoir, a hydraulic pump, and/or a spool valve to direct hydraulic fluid back to the reservoir or to one or more of the downstream hydraulic circuits. In such embodiments, the spool valve may include female hydraulic couplers for connecting male hydraulic couplers of the hydraulic system of the implement 5. In other embodiments, the hydraulic pump, spool valve, and reservoir are separate and independent from the towing vehicle and are integrated into the implement 5. Suitable lift systems include the hydraulic lift systems disclosed in U.S. Patent Publication No. 2012/0186216 and U.S. Patent No. 7,596,935, both of which are incorporated herein by reference for all relevant and consistent purposes. Any suitable lift system may be used, and the implement 5 should not be limited to a particular lift system unless stated otherwise.

Another embodiment of the implement 5 is shown in Figure 8. The implement includes a second accumulator 39 connected to the second hydraulic lift cylinder 18. The second accumulator 33 includes a gas chamber 51 and a hydraulic fluid chamber 47 that are separated by a bladder. The first accumulator 33, pressure reducing valve 30, and the first hydraulic lift cylinder 16 form a first response circuit for regulating the contact force on the first side 8a of the tool. The second accumulator 39 and second hydraulic lift cylinder 18 form a second response circuit for regulating the contact force on the second side 8b of the tool. Before use, the first response circuit and the second response circuit may be charged by use of hydraulic pump, spool valve, and isolation valve described above to provide substantially equal system pressures at the accumulators 33, 39. The pressure reducing valve 30 reduces the downstream pressure in the first response circuit such that pressure in the first cylinder 16 is less than the pressure in the second cylinder 18.

Another embodiment of the implement 5 is shown in Figure 9. The implement 5 includes a second accumulator 39 connected to the second hydraulic lift cylinder 18. Rather than being disposed between the first accumulator 33 and the first cylinder 16, the pressure reducing valve 30 is upstream of the first accumulator 33. The pressure reducing valve 30 and first accumulator 33 are connected by a pressure reducing line 72 (e.g., third line).

The first hydraulic accumulator 33 and the first cylinder 16 define a first response circuit and the second hydraulic accumulator 39 and the second cylinder 18 define a second response circuit. The pressure reducing valve 30 is in fluid communication with the first hydraulic accumulator 33 and the first cylinder 16 such that fluid flows from the valve 33 to the first response circuit when charging the first circuit with hydraulic fluid. Positioning the pressure reducing valve 30 upstream of the first accumulator 33 allows the first response circuit to be charged at a pressure less than the second response circuit. After the circuits are isolated, the two circuits operate in a similar manner with the pressure at the first hydraulic lift cylinder 16 being less than the pressure at the second hydraulic lift cylinder 18.

Another embodiment of a two accumulator implement 5 is shown in Figure 10. Rather than being in fluid communication with the hydraulic fluid chamber 45, the pressure reduced valve 30 is fluidly connected to the gas chamber 49 of the accumulator. In such embodiments, after initial charging of the first and second response circuits, the first and second response circuits are isolated from each other. The pressure in the first response circuit (i.e., in the first cylinder 16) is reduced by reducing the pressure on the gas chamber 49 side of the accumulator 33 by use of the pressure reducing valve/check valve 30.

Referring now to Figure 5, the implement is shown as a mower 5. The mower 5 may be coupled to a towing vehicle (not shown) by use of tongue 2. A drive-shaft 70 of the mower 5 may be coupled to a power-take-off (PTO) system of the towing vehicle. The mower 5 includes a cutting head 8 suspended from a frame 10 by hydraulic lift cylinders 16, 18. The frame 10 is fixed in its vertical positon as it is capable of vertical movement or articulation. In other embodiments, the frame or a portion thereof may be moved vertically relative to the ground.

Another embodiment of the mower 5 is shown in Figures 6 and 7 with the hydraulic accumulator 33 (Fig. 6) and second hydraulic lift cylinder 18 (Fig. 7) being shown. The cylinder 18 pushes down on a pivot-arm linkage 78 causing a header support arm 80 to lift the header 8. The mower 5 also includes a separate lift cylinder 74 for moving the cutting head 8 to a transport position. The mower 5 is shown with a number of openings 81, 82 to adjust the attachment point of the lift cylinders to account for variations in the weight of the header. Use of a pressure reducing valve as described above may allow such openings to be eliminated. Other movable implements including other types of mowers or mower conditioners may be used with the principles described above generally applying to such implements.

As used herein, the terms “attached,” “connected” or “fused” herein are not intended to imply direct attachment, connection or fusion of the two respective parts and are intended to also include indirect attachment, connection or fusion such as by intermediary parts unless stated otherwise. Further, the terms “about,” “substantially,” “essentially” and “approximately” when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and/or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation.

When introducing elements of the present disclosure or the embodiments thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," “containing” and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., "top", "bottom", "side", etc.) is for convenience of description and does not require any particular orientation of the item described.

As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

A movable device comprising: - a frame; a tool suspended from the frame, the tool having a central longitudinal axis extending through the center of the tool and parallel to a direction of travel of the device, the central longitudinal axis being a first side of the tool and substantially opposite the defines the first side, second side of the tool; a first hydraulic lifting cylinder attached to the frame and the first side of the tool; a second hydraulic lifting cylinder attached to the frame and the second side of the tool; a hydraulic accumulator that is in fluid communication with the first hydraulic lift cylinder; and a control system for controlling that a first fluid pressure in the first hydraulic lifting cylinder is lower than a second fluid pressure in the second hydraulic lifting cylinder.

Method according to claim 1, wherein the control system is provided with a pressure-limiting valve for controlling that the first fluid pressure in the first hydraulic lifting cylinder is lower than the second fluid pressure in the second hydraulic lifting cylinder.

The movable device of claim 2, wherein the hydraulic accumulator is in fluid communication with the first hydraulic lift cylinder and the second hydraulic lift cylinder, the hydraulic accumulator and the first cylinder defining a first response circuit, the hydraulic accumulator and the second cylinder a second response circuit and wherein the pressure limiting valve is disposed between the accumulator and the first hydraulic lift cylinder in the first response circuit.

The movable device of claim 3, wherein the second response circuit does not include a pressure relief valve.

A movable device according to claim 3 or 4, wherein the pressure-limiting valve is a first pressure-limiting valve, the device comprising a second pressure-limiting valve, wherein the second pressure-limiting valve is arranged between the accumulator and the second hydraulic lifting cylinder in the second response circuit.

A movable device according to claim 5 in combination with a first hydraulic fluid in the first hydraulic lifting cylinder and a second hydraulic fluid in the second hydraulic lifting cylinder, wherein the first pressure-limiting valve and the second pressure-limiting valve are adapted such that the pressure of the first hydraulic fluid is smaller is then the pressure of the second hydraulic fluid.

A movable device according to any of claims 3-6, comprising a first hydraulic line connecting the accumulator to the pressure-limiting valve and a second hydraulic line connecting the pressure-limiting valve to the first hydraulic lifting cylinder.

A movable device as claimed in claim 7, comprising a third hydraulic line connecting the accumulator to the second hydraulic lifting cylinder.

The movable device of claim 2, wherein the hydraulic accumulator is a first hydraulic accumulator, the movable device being provided with a second hydraulic accumulator, the first hydraulic accumulator being in fluid communication with the first hydraulic lifting cylinder, the first hydraulic accumulator, pressure limiting valve, and the first cylinder defining a first response circuit, the pressure limiting valve being arranged between the first accumulator and the first cylinder in the first response circuit, the second hydraulic accumulator being in fluid communication with the second hydraulic lift cylinder, the second hydraulic accumulator and second determine a second response circuit.

The movable device of claim 2, wherein the hydraulic accumulator is a first hydraulic accumulator, wherein the movable device is provided with a second hydraulic accumulator, the first hydraulic accumulator being in fluid communication with the first hydraulic lifting cylinder, the first hydraulic accumulator and the first cylinder determining a first response circuit, wherein the second hydraulic accumulator is in fluid communication with the second hydraulic lift cylinder, the second hydraulic accumulator and second cylinder determining a second response circuit, wherein the pressure limiting valve is in fluid communication with the first hydraulic accumulator and the first cylinder when filling the first circuit with hydraulic fluid.

The movable device of claim 2, wherein the accumulator comprises a gas chamber and a hydraulic fluid chamber, the pressure-limiting valve being in fluid communication with the gas chamber such that the first fluid pressure in the first hydraulic lifting cylinder is reduced to less than a second fluid pressure in the second hydraulic lifting cylinder.

A movable device according to any of claims 1-11, wherein the first and second sides of the tool each have a weight, the weight of the first side of the tool being less than the second side of the tool.

A movable device according to any of claims 1-12, wherein the tool is selected from a cutter head, mill roll, screed or knife.

A movable device according to any of claims 1-13, comprising a tongue for attaching the device to a towing vehicle.

A movable device according to any of claims 1-14 in combination with a first hydraulic fluid in the first hydraulic lifting cylinder and a second hydraulic fluid in the second hydraulic lifting cylinder, wherein the pressure of the first hydraulic fluid is lower than the pressure of the first hydraulic fluid. second hydraulic fluid.

A movable device according to any of claims 1-15, wherein the tool has a vertical axis, wherein the first hydraulic lifting cylinder is mounted on the tool above where the first hydraulic lifting cylinder is mounted on the frame relative to the vertical axis for mounting. applying a compressive force to the first hydraulic lifting cylinder, the second hydraulic lifting cylinder being mounted on the tool above where the first hydraulic lifting cylinder is mounted to the frame relative to the vertical axis for applying a compressive force to the second hydraulic lifting cylinder.

A movable device according to any of claims 1-11 and 13-16, wherein the tool has a vertical axis, the first hydraulic lift cylinder being mounted on the tool below where the first hydraulic lift cylinder is mounted on the frame relative to the vertical axis for exerting a pulling force on the first hydraulic lifting cylinder, the second hydraulic lifting cylinder being mounted on the tool below where the first hydraulic lifting cylinder is mounted on the frame relative to the vertical axis for applying a pulling force on the second hydraulic lifting cylinder hydraulic lifting cylinder.

A movable device according to any of claims 1-17, comprising wheels or tracks attached to the frame.

A method of operating the movable device according to any of claims 1-18, comprising driving the device over a surface, the tool being in contact with the surface while the device is being propelled.

The method of claim 19, wherein the tool is a cutting head, wherein the cutting head cuts off crop material while the movable device is propelled forward.

The method of claim 19 or 20, wherein the difference between the pressure in the first cylinder and the second cylinder is at least about 50 kPa, at least about 1000 kPa, at least about 10,000 kPa or 30,000 kPa or more.

A method of operating a movable device comprising a frame and a tool suspended from the frame, the tool having a longitudinal axis extending through the center of the tool and parallel to a direction of travel of the device, the center longitudinal axis defines a first side of the tool and a second side of the tool substantially opposite the first side, the tool having a contact surface with a first end on the first side and a second end on the second side, the first and second sides of the tool each have a weight, the weight of the first side of the tool being smaller than the second side of the tool, the difference between the weight of the first side and the weight of the second side being at least is a percentage, X, of the weight of the first side, the method comprising: propelling the device over a surface where the tool is in contact with the surface while the device is being propelled, wherein the first side of the tool exerts a first contact force on the surface at the first end and wherein the second side of the tool a second contact force exerts on the surface at the second end, the difference between the force exerted at the first end and the force exerted at the second end as a percentage of the first force being less than X.

The method of claim 22, wherein the difference between the force applied at the first end and the force applied at the second end as a percentage of the first force is less than about 0.75X, less than about 0.5X, less than about 0.25X, less than about 0.1X, or less than 0.05X.

The method of claim 22, wherein the contact force at the first end is substantially equal to the contact force at the second end.

The method of any one of claims 22 to 24 wherein X is at least about 2.5%, at least about 5%, at least about 10%, at least about 15%, from about 2.5% to about 50%, from about 2.5% to about 35%, from about 2.5% to about 25%, from about 5% to about 50%, or from about 5% to about 35%.

A method according to any of claims 22-25, wherein the movable device comprises a first hydraulic lifting cylinder and a second hydraulic lifting cylinder, wherein the first hydraulic lifting cylinder is attached to the frame and the first side of the tool, and wherein the second hydraulic lifting cylinder lifting cylinder is attached to the frame and the second side of the tool, the first cylinder having a hydraulic fluid therein and the second hydraulic lifting cylinder having a second hydraulic fluid therein, the pressure of the first hydraulic fluid being less than the pressure of the second hydraulic fluid.

The method of claim 26, further comprising a pressure limiting valve for controlling that a first fluid pressure in the first hydraulic lift cylinder is less than a second fluid pressure in the second hydraulic lift cylinder.

The method of claim 26 or 27, wherein the difference between the pressure in the first cylinder and the second cylinder is at least about 50 kPa, at least about 1000 kPa, at least about 10,000 kPa or 30,000 kPa or more.

A method according to any of claims 22-28, wherein the tool is a cutting head, wherein the cutting head cuts off crop material while the movable device is moved forward.