Improved work machine and control method thereof

Abstract

A work machine (1) comprising a body (2), a hydraulically actuated work implement (10), one hydraulic actuator (20) connected to the hydraulically actuated work implement (10), and a hydraulic arrangement (30) configured to control the hydraulic actuator (22). The hydraulic arrangement (30) comprises source (31) of pressurized hydraulic fluid, at least one main control valve (36), a first supply line (38) fluidly connecting a first outlet (36c) of the main control valve (36) with the first inlet (20a) of the hydraulic actuator (20), a second supply line (39) fluidly connecting a second outlet (36d) of the main control valve (36) with the second inlet (20b) of the hydraulic actuator (20), a pilot-operated non-return valve (40) arranged along the first supply line (38), and an electronically controlled pilot circuit (42) configured to control the operation of the main control valve (36) and of the non-return valve (40) and comprising a floating control stage (71) configured to put the first supply line (38) and the second supply line (39) in fluid communication with the tank (34).

Description

TECHNICAL FIELD

[0001] The present invention relates to a work machine, in particular to an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like, and to the related control method.

[0002] More in detail, the present invention relates to a hydraulic arrangement configured to control a floating function of the hydraulically actuated work implement of the work machine. Reference will be made to this application by way of the example below, without however losing in generality.BACKGROUND OF THE INVENTION

[0003] As is known, work machines such as excavators, diggers and the like are provided with a hydraulically actuated work implement, which is movably carried by the body of the work machine and is configured to perform multiple earth-moving operations, such as digging, handling earth or gravel, loading trucks and / or similar operations.

[0004] Such work machines generally comprise a body movable on the ground via ground resting wheels or tracks.

[0005] More in detail, the body comprises: an undercarriage, which carries the ground resting wheels or tracks to allow motion of the body with respect to the ground; and a superstructure, which is carried in a rotatable manner by the undercarriage.

[0006] The aforementioned work machines usually further comprise a hydraulic motor configured to rotate the superstructure with respect to the undercarriage and a pair of further hydraulic motors configured to drive the ground resting wheels or tracks in rotation to allow motion of the body with respect to the ground.

[0007] As per se known, the aforementioned hydraulically actuated work implement comprises: a boom rotatably carried by the superstructure; a boom actuator configured to rotate the boom with respect to the superstructure; a stick or arm or dipper rotatably carried by the boom; an arm hydraulic actuator configured to rotate the arm with respect to the boom; a bucket and / or other similar tools rotatably carried by the arm; and a bucket hydraulic actuator configured to rotate the bucket with respect to the arm.

[0008] As known, such work machines comprise a hydraulic system configured to control the pressurized hydraulic provided the aforementioned hydraulic actuators, in order to control the operation and the position of the members of the hydraulically actuated work implement.

[0009] For safety reasons, such hydraulic system comprises also the so called "hose burst check valve" according to the standard ISO 8643 - Earth-Moving Machinery - Hydraulic Excavator and Backhoe Loader Boom-Lowering Control Device, which is fluidly connected to the boom actuator. Such valve comprises a check valve configured to maintain the boom actuator pressurized should the flexible hose fluidly connecting the high-pressure hydraulic pump with the same boom actuator break. This allows to prevent the boom from falling downward out of control and thus posing serious hazards to nearby operators.

[0010] However, in some cases, the need is felt to let the tool carried by the hydraulically actuated work implement to free float in contact with the ground due to its own weight, so that it can follow the profile of the ground, for instance to perform levelling operations.

[0011] Such operation condition, also call "floating function", may be performed by shortcutting both ends of the boom and / or the arm actuator to tank, so that the hydraulically actuated work implement may float freely following the profile of the ground.

[0012] However, the hydraulic systems currently available to perform the boom free floating function are rather complex and expensive, and their development and production impacts in a not negligible manner on the overall costs of the work machine.

[0013] In view of the above, the need is felt to provide a work machine able to improve the free-floating function of the hydraulically actuated work implement of the work machine.

[0014] Aim of the present invention is to satisfy the above-mentioned need in an optimized and cost-effective manner.SUMMARY OF THE INVENTION

[0015] The aforementioned aims are reached by a work machine and by a method as claimed in the appended set of claims.

[0016] The claims describe preferred forms of embodiment of the present invention and forms an integral part of this description.BRIEF DESCRIPTION OF DRAWINGS

[0017] For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example, with reference to the attached drawings, wherein: Figure 1 is an illustration of an example of a work machine according to the present invention, with parts removed for clarity and Figures 2 and 3 are two schematic representations of hydraulic arrangements of the work machine illustrated in Figure 1, with parts removed for clarity. DETAILED DESCRIPTION OF THE INVENTION

[0018] With reference to Figure 1, number 1 denotes, as a whole, a work machine / vehicle, in particular an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like.

[0019] Work machine 1 comprises a body 2 movable on the ground by means of ground resting wheels or tracks 3.

[0020] In particular, said body preferably comprises: a lower frame or undercarriage 5, which carries the ground resting wheels or tracks 3 to allow motion of the body with respect to the ground; and an upper frame 6 or superstructure, which is carried in a rotatable manner by lower frame 5 preferably about a rotation axis R 1 orthogonal to the advancing plane of work machine 1, i.e. orthogonal to the ground.

[0021] As known, a swivel joint 8 may be interposed between upper frame 6 and lower frame 5.

[0022] In addition, work machine 1 comprises a hydraulically actuated work implement 10, which is carried by body 2 and is configured to perform multiple earth moving operations, such as digging, handling earth or gravel, loading trucks and / or similar operations. In particular, work implement 8 is rotatably carried by upper frame 6.

[0023] In addition, work machine 1 comprises a hydraulic actuator assembly 12, which is configured to actuate body 2 and / or hydraulically actuated work implement 10.

[0024] Preferably, hydraulic actuator assembly 12 comprises at least one hydraulic actuator, which is coupled to a movable member of work machine 1 and is configured to control the movement / position of this latter.

[0025] More in detail, hydraulic actuator assembly 12 preferably comprise at least a first hydraulic motor (not visible), in the following referred also to as "swing motor", which is operatively interposed between lower frame 5 and upper frame 6 and is configured to rotate upper frame 6 with respect lower frame 5.

[0026] In addition, hydraulic actuator assembly 12 preferably further comprise at least one, and preferably a pair of hydraulic motors (not visible), in particular reversible hydraulic motors, in the following referred also to as "drive motors", each configured to drive a corresponding ground resting wheel or track 3 in rotation to allow motion of body 2 with respect to the ground.

[0027] With reference to Figure 1, hydraulically actuated work implement 10 preferably comprises: a boom 14 rotatably carried the body 2, in particular by the upper frame 6; a stick or arm or dipper 16 rotatably carried by boom 14; and a bucket 18 and / or other similar tools, such as an asphalt cutter, a grapple, a ripper or the like, rotatably carried by arm 16.

[0028] Hydraulic actuator assembly 12 preferably comprise a plurality of hydraulic cylinders, in particular double-acting hydraulic cylinders, configured to actuate hydraulically actuated work implement 10.

[0029] More in detail, hydraulic actuator assembly 12 preferably comprise at least one boom actuator 20, which is operatively interposed between body 2 and boom 14 and is configured to rotate boom 14 with respect to body 2.

[0030] In addition, hydraulic actuator assembly 12 preferably further comprise at least one arm actuator 22, which is operatively interposed between boom 14 and arm 16 and is configured to rotate arm 16 with respect to boom 14.

[0031] Preferably, hydraulic actuator assembly 12 further comprise at least one bucket actuator 24, which is operatively interposed between arm 16 and bucket 18 and is configured to rotate bucket 18 with respect to arm 16.

[0032] With reference to the exemplary embodiment illustrated in Figure 1, work machine 1 further comprises a dozer blade 26 carried in a movable manner by body 2, preferably by undercarriage 5, in a manner per se known and therefore not further described.

[0033] With reference to the preferred embodiment illustrated in Figure 2, work machine 1 further comprises a hydraulic arrangement 30, which is fluidly connected to the aforementioned hydraulic actuator assembly 12 and is configured to provide pressurized hydraulic fluid towards the same hydraulic actuator assembly 12, in other to operate / actuate the latter.

[0034] More in detail, hydraulic arrangement 30 is fluidly connected at least to one of the hydraulic actuators of the hydraulic actuator assembly 12. Preferably, hydraulic arrangement 30 is fluidly connected at least to boom actuator 20, in the following referred to only as "actuator 20" for brevity.

[0035] It is understood that the hydraulic arrangement 30 may be fluidly connected other / addition hydraulic actuators of hydraulic actuator assembly 12, such as to arm actuator 22 and / or to bucket actuator 24.

[0036] Preferably, actuator 20 is provided with a first inlet 20a configured to receive pressurized hydraulic fluid in order to move the related member, in particular boom 14, in a first direction, for instance upwards. In addition, actuator 20 is preferably provided with a second inlet 20b configured to receive pressurized hydraulic fluid in order to move the related member, in particular boom 14, in a second direction opposite to the first direction, for instance downwards.

[0037] As per se known, actuator 20 preferably comprises a housing accommodating in a fluid tight and slidable manner a piston, so as to define within the same housing two hydraulic chambers opposite to each other.

[0038] With reference to the example illustrated in Figure 2, hydraulic arrangement 30 preferably comprises a source of pressurized hydraulic fluid 31, which is configured to provide at outlet a flow of pressurized hydraulic fluid.

[0039] In particular, the source of pressurized hydraulic fluid 31 preferably comprises pumping means 32, in particular a hydraulic pump, carried by an internal combustion engine of work machine 1. Pumping means 32 may be configured to suck hydraulic fluid from a tank 34 and to provide at outlet a pressurized flow of such hydraulic fluid.

[0040] More in detail, pumping means 32 preferably comprises a high-pressure hydraulic pump configured to deliver at outlet a pressurized hydraulic fluid with a pressure greater than 100 bar, more preferably up to or greater than 350 bar.

[0041] In addition, hydraulic arrangement 30 preferably comprises one or more main control valves or distributors or spool valves 36 fluidly interposed between the source of pressurized hydraulic fluid 31 and hydraulic actuator assembly 12.

[0042] In particular, main control valves 36 are preferably hydraulically controlled valves.

[0043] With reference to the exemplary and non-limitative embodiment illustrated in Figure 2, control valves 36 may comprise load-sensing control valves.

[0044] Preferably, hydraulic arrangement 30 comprises a main control valve 36 fluidly interposed between the outlet of source of pressurized hydraulic fluid 31 and actuator 20.

[0045] Main control valve 36 is configured to selectively route / throttle the pressurized hydraulic fluid provided by source 31 to one of the two ends of actuator 20, in order to operate / actuate the latter and raise or lower the associated member, in particular boom 14, accordingly.

[0046] With reference to the exemplary embodiment illustrated in Figure 2, main control valve 36 preferably comprises a three-position valve.

[0047] Preferably, valve 36 is a hydraulically actuated valve.

[0048] Two ports 36a and 36b of main control valve 36 are preferably fluidly connected respectively to source 31 and to tank 34, respectively via a suction line 33 and a tank line 35.

[0049] Two ports 36c and 36d of main control valve 36 are preferably fluidly connected respectively to actuator 20, in particular to the two chambers of hydraulic actuator 20 via a correspondent hydraulic supply line 38 and 39.

[0050] Preferably, in a first or closed operative position 36', valve 36 is preferably configured to fluidly isolate its ports / openings.

[0051] More in detail, in the closed position 36', valve 36 is preferably configured to fluidly isolate tank 34 and source 31 from hydraulic supply lines 38 and 39.

[0052] In other words, in the closed position 36', valve 36 is preferably configured to fluidly isolate its ports 36a, 36b, 36c and 36d to each other.

[0053] In addition, in a second position 36'', valve 36 is preferably configured to fluidly connect its port 36a with its port 36d, to fluidly connect source 31 with supply line 39.

[0054] In the second position 36'', in addition, valve 36 is preferably further configured to fluidly connect its port 36d with port 36b, to fluidly connect supply line 39 with tank 34.

[0055] Therefore, in the second position 36'', valve 36 is preferably configured to put the first chamber of actuator 20 in fluid communication with source 31 and put the other chamber of actuator 20 in fluid communication with tank 34, in order to move boom 14 in the first direction.

[0056] In addition, in a third position 36‴, valve 36 is preferably configured to fluidly connect its port 36a with its port 36d, to fluidly connect source 31 with supply line 39.

[0057] In the third position 36''', in addition, valve 36 is preferably further configured to fluidly connect its port 36d with port 36a, to fluidly connect supply line 38 with tank 34.

[0058] Therefore, in the third position 36‴, valve 36 is preferably configured to put the second chamber of actuator 20 in fluid communication with source 31 and put the other chamber of actuator 20 in fluid communication with tank 34, in order to move boom 14 in the second direction.

[0059] With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 30 further comprises a first check valve or non-return valve, also called "hose burst valve" 40 arranged along supply line 38.

[0060] Non-return valve 40 is configured to selectively prevent the hydraulic fluid to flow out of the first chamber of hydraulic actuator 20 and port 20a.

[0061] This in use allows to maintain pressurized the first chamber of hydraulic actuator 20 should the flexible hose (part of supply line 38) fluidly connecting port 20a of hydraulic actuator 20 with control valve 36 break, to avoid unwanted lowering of boom 14.

[0062] More in detail, non-return valve 40 is preferably a two-position valve.

[0063] In a first position 40', non-return valve 40 preferably allows hydraulic fluid to flow only from valve 36 toward actuator 20, preventing hydraulic fluid flow in the opposite direction.

[0064] In a second position 40", non-return valve 40 preferably allows hydraulic fluid to flow from actuator 20 towards valve 36.

[0065] With reference to Figure 2, non-return valve 40 preferably comprises biasing means 40a, such as a spring, configured to exert forces on the same non-return valve 40 adapted to bias this latter in its first position 40'.

[0066] Preferably, non-return valve 40 is a pilot operated check valve.

[0067] More in detail, non-return valve 40 is preferably provided with a pilot port, which is adapted to receive a pilot pressure that is adapted to open the same valve, i.e. to arrange it in its second position 40", in order to allow hydraulic fluid to flow back from actuator 20 towards main control valve 36.

[0068] In addition, hydraulic arrangement 30 preferably further comprises a pressure-relief or safety valve 41 associated to non-return valve 40.

[0069] More in detail, pressure-relief valve 41 is preferably arranged in parallel to non-return valve 40 and is preferably configured to open should the pressure at the first opening 20a of hydraulic actuator 20 exceed a predetermined safety threshold.

[0070] With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 30 further comprises an electronically controlled pilot circuit 42, which is operatively connected at least to main control valve 36 and is configured to actuate the latter, in order to control the pressurized hydraulic fluid provided to hydraulic actuator 22.

[0071] In other words, pilot circuit 42 is fluidly connected to main control valve 36 and is configured to provide a hydraulic pilot signal to the same main control valve 36, in order to operate this latter.

[0072] With reference to the exemplary embodiment illustrated in Figure 2, source of pressurized hydraulic fluid 31 preferably comprises further pumping means 43, in particular a further hydraulic pump, which may be carried by an internal combustion engine of work machine 1, and are configured to suck hydraulic fluid from tank 34 and to provide at outlet a pressurized flow of such hydraulic fluid.

[0073] Preferably, pumping means 43 are separate and distinct from pumping means 32.

[0074] Pilot circuit 42 is preferably fluidly connected to the outlet of pumping means 43, in order to receive pressurized hydraulic fluid therefrom.

[0075] Preferably, pumping means 43 comprises a low-pressure hydraulic pump configured to deliver at outlet a pressurized hydraulic fluid with a pressure lower than 60 bar, for instance equal to about 40 bar.

[0076] As per se known, pumping means 43 may be provided with a pressure relief valve or pressure reducing valve (not illustrated) fluidly connected downstream the outlet of pumping means 43 and configured to set the pressure of the pressurized hydraulic fluid fed within pilot circuit 42.

[0077] For example, such pressure relief valve may be configured to set the pressure of the pressurized hydraulic fluid fed within pilot circuit 42 to approximately 40 bar.

[0078] According to the preferred embodiment of the present invention, pilot circuit 42 is configured to selectively control main control valve 36 and non-return valve 40 in order to prevent fluid flow from the source 31 toward the actuator 20 and at the same time to open non-return valve 40.

[0079] With reference to the exemplary embodiment illustrated in Figure 2, pilot circuit 42 preferably comprises two hydraulic pilot lines 44 and 45, each of which fluidly connects the outlet of pumping means 43 with a corresponding end of main control valve 36.

[0080] Hydraulic pilot lines 44 and 45 are preferably configured to carry a pressure signal to a respective end of main control valve 36, in order to exert on the latter forces adapted to move the movable spool of main control valve 30 in a corresponding direction.

[0081] In other words, the hydraulic fluid flowing within hydraulic pilot lines 44 and 45 is adapted to exert a respective pressure on main control valve 36 adapted to arrange this latter respectively in its second position 36" or in its third position 36‴.

[0082] With reference the exemplary embodiment illustrated in Figure 2, pilot circuit 42 preferably comprises an additional hydraulic pilot line 40b, which is fluidly connected to pilot line 45. Hydraulic pilot line 40b is preferably operatively connected to non-return valve 40 and is preferably configured to exert on this latter a pressure adapted to bias the same non-return valve 40 in its second or open position 40".

[0083] Hydraulic pilot line 40b preferably branches off hydraulic pilot line 45.

[0084] Therefore, in use, when hydraulic pilot line 45 is pressurized in order to arrange control valve 36 in its third position 36‴, also hydraulic pilot line 40b is pressurized in order to arrange non-return valve 40 in its second or open position 40".

[0085] In addition, pilot circuit 42 further comprises a pair of pressure reducing valves 48 and 50, each fluidly connected to a corresponding pilot line 44 and 45 and configured to reduce the pressure of the hydraulic pilot signal within the latter.

[0086] With reference to the exemplary embodiment illustrated in Figure 2, pressure reducing valves 48 and 50 are preferably electronically controlled pressure reducing valve, i.e. solenoid-controlled pressure reducing valves.

[0087] In particular, pressure reducing valves 48 and 50 may comprise respective solenoids 48a and 50a configured to control the operation of the same valves 48 and 50.

[0088] With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement preferably further comprises pressure-relief or safety valves 54 and 55 fluidly connected respectively to supply line 38 and to supply line 39. More in detail, pressure-relief valves 54 and 55 are fluidly interposed between the corresponding supply line 38 and 39 and tank 34.

[0089] As per se known, and therefore not described in detail, pressure-relief valves 54 and 55 are normally closed and are configured to open should the pressure of the hydraulic fluid within the corresponding supply line 38 or 39 exceed a predetermined safety threshold, to reduce the pressure of the hydraulic fluid within the same.

[0090] With reference to the exemplary embodiment illustrated in Figure 2, work machine 1 preferably further comprises manually actuated commands input means 60, such as joysticks, levers, buttons, or portions of a touch-sensitive display, which are adapted to be manually actuated / handled by the work machine user to impart commands for controlling the operation of actuator 20.

[0091] More in detail, manually actuated commands input means 60 are preferably electronically connected at least to pressure reducing valves 48 and 50 and are preferably configured to output signals adapted to control operation of these latter.

[0092] In addition, work machine 1 preferably comprises an electronic control unit 70, which is preferably operatively connected at least to commands input means 60 and to pressure reducing valves 48 and 50, and is provided with elaboration means configured to control the operation of the same valves 48 and 50 as function of the signals provided by command input means 60.

[0093] With reference to the exemplary embodiment illustrated in Figure 2, pilot circuit 42 is further provided with a floating control stage 71.

[0094] Preferably, floating control stage is fluidly connected to supply lines 38 and 39.

[0095] Floating control stage 71 is preferably configured to selectively fluidly connect both supply lines 38 and 39 to tank 34, in order to discharge the pressure at actuator 20 and allow free flowing of hydraulic fluid from hydraulic actuator 20 to main control valve 36 and vice-versa. This in use allows boom 14 (or any other member of hydraulically actuated work implement 10 coupled to actuator 20) to free float resting on the ground due to its own weight.

[0096] In other words, floating control stage 71 is configured to selectively activate a floating function of hydraulically actuated work implement 10 (in particular of boom 14), in which none of chambers of actuator 20 is pressurized and the hydraulically actuated work implement 10 may rest on the ground due to its own weight and may to move up during traveling of work machine 1 following the profile of the ground.

[0097] More in detail, floating control stage 71 preferably comprises a pair of on / off valves 72 and 74 fluidly connected respectively to supply line 38 and to supply line 39.

[0098] More in detail, each on / off valves 72 and 74 is fluidly interposed respectively between supply line 38 or to supply line 39 and tank 34, and is configured to selectively fluidly connect the corresponding supply line 38 or 39 to tank.

[0099] Preferably, pressure on / off 72 and 74 are electronically controlled on / off valve, i.e. solenoid-controlled on / off valves.

[0100] In addition, on / off valves 72 and 74 preferably comprises two-position valves.

[0101] In a first position 72' and 74', on / off valves 72 and 74 are preferably configured to prevent fluid communication between supply lines 38 and 39 and tank 34.

[0102] In a second position 72'' and 74", pressure reducing valves 72 and 74 are preferably configured to fluidly connect supply lines 38 and 39 with tank 34.

[0103] In addition, on / off valves 72 and 74 preferably comprises biasing means 72a and 74a, in particular springs, configured to bias the same on / off valves 72 and 74 towards their first position 72' and 74'.

[0104] Moreover, on / off valves 72 and 74 preferably comprises solenoids 72b and 74b configured to arrange the same on / off valves 72 and 74 in their second position 72" and 74".

[0105] With reference to the exemplary embodiment illustrated in Figure 2, work machine 1 preferably further comprises manually actuated commands input means 75, such as a button, a knob or portions of a touch-sensitive display, which are operatively connected to electronic control unit 70 and are adapted to be actuated by the work machine user to activate the floating function of hydraulically actuated work implement 10.

[0106] More in detail, manually actuated commands input means 75 are preferably adapted to output commands / signals for controlling the operation of floating control stage 71.

[0107] In particular, commands input means 75 are configured to be actuated by the work machine user to impart commands suited to control electronic control unit 70 in order to arrange main control valve 36 in its first position 36' and at the same time to arrange non-return valve 40 in its second position 40" and to arrange on / off valves 72 and 74 in their second position 72'' and 74".

[0108] In particular, electronic control unit 70 may be configured to control operation of pressure reducing valves 48 and 50 according to the signals received from commands input means 75.

[0109] More in detail, electronic control unit 70 may be configured to control operation of pressure reducing valves 48 and 50 in order to pressurize both pilot lines 44 and 45, in order to arrange main control valve 36 in its first position 36' and at the same time to pressurize pilot line 40b, in order to arrange non-return valve 40 in its second or open position 40', advantageously upon receipt of commands from commands input means 75.

[0110] In addition, electronic control unit 70 may be configured to control on / off valves 72 and 74 to fluidly connect both supply lines 38 and 39 to tank 34, advantageously upon receipt of commands from commands input means 75.

[0111] According to the preferred embodiment of the present invention, in particular, when work machine user operates commands input means 75, electronic control unit 70 is preferably configured to control pressure reducing valves 48 and 50 in order to pressurize both pilot lines 44 and 45 with two respective pilot signals having substantially the same pressure, in order to maintain main control valve 36 in its first position 36'.

[0112] The general operation of the above-described work machine 1 is the following.

[0113] In general, the pressurized hydraulic fluid provided by pumping means 31 is throttled by main control valve 36 to hydraulic actuator 20 in order to actuate this latter accordingly.

[0114] The operative position of main control valve 36 is controlled by pilot circuit 42 and depends on the operation of pressure reducing valves 48 and 50, which in turn depends on the actuation of commands input means 60 (i.e. the joystick) .

[0115] In particular, when the work machine 1 user actuates commands input means 60, electronic control unit 70 controls pressure reducing valves 48 and 50 to output a hydraulic pressure signal adapted to control the position of main control valve 36 according to the input of the commands input means 60.

[0116] More in detail, when main control valve 36 is arranged in its second position 36'', the pressurized hydraulic fluid provided by pumping means 31 is fed towards the first inlet 20a of actuator 20 via supply line 38, while the second inlet 20b of the same actuator 30 is fluidly connected to tank 34.

[0117] Similarly, when main control valve 36 is arranged in its third position 36‴, the pressurized hydraulic fluid provided by pumping means 31 is fed towards the second inlet 20b of actuator 20 via supply line 39, while the first inlet 20a of the same actuator 30 is fluidly connected to tank 34. At the same time, pilot line 40b is pressurized in order to arrange non-return valve 40 in its second or open position 40", and allow the hydraulic fluid to flow from actuator 20 back towards control valve 36 along supply line 38.

[0118] With reference to the exemplary embodiment illustrated in Figure 2, when the work machine user actuates user input means 75, electronic control unit 70 controls pressure reducing valves 48 and 50, in order to pressurize both pilot lines 44 and 45 and arrange main control valve 36 in its first position 36'. At the same time pilot line 40b is pressurized in order to arrange non-return valve 40 in its second or open position 40".

[0119] In addition, when the work machine user actuates user input means 75, electronic control unit 70 arranges both on / off valves 72 and 74 in their second position, in order to fluidly connect both supply lines 38 and 39 with tank 34.

[0120] In such operating conditions, both chambers of actuator 20 are fluidly connected to tank 20 and hydraulically actuated work implement 10, in particular boom 14, is not lifted by actuator 20 and is able to move up and down in contact with the ground.

[0121] In view of the above, the present invention if further directed to a method for controlling the above described work machine 1, wherein the method comprises the following steps: a) Receiving a command from user input means 75 suited to activate a floating function of hydraulic arrangement 30, and b) Arranging main control valve 36 in its first position 36' , c) Opening non-return valve 40, and d) Fluidly connecting both ends 20a and 20b of hydraulic actuator 20 to tank 34.

[0122] More in detail, said steps b) and c) comprises the step of controlling pressure reducing valves 48 and 50 in order to pressurize pilot lines 44 and 45 to arrange control valves 36 in its first position 36'' and at the same time to pressurize pilot line 40b, to arrange non-return valve 40 in its second or open position 40".

[0123] In addition, said step d) comprises the step of arranging pressure reducing valves 72 and 74 in their second position 72" and 74'', to fluidly connect supply lines 38 and 39 with tank 34.

[0124] In view of the foregoing, the advantages of the work machine 1 and of the related control method according to the invention are apparent.

[0125] In particular, thanks to the proposed hydraulic arrangement 30, it is possible to provide a floating function of the hydraulically actuated work implement 10 in a simple and economic manner, since the modification required to the standard hydraulic arrangement are minimal. In particular, no modification to main control valve 36, to non-return valve 40 and / or to pressure reducing valves 48 and 50 are required.

[0126] Further no additional valves are required to arrange non-return valve 40 in its second or open position 40".

[0127] In addition, the electronic control of pressure reducing valves 48 and 50 allows to pressurize at the same time both pilot lines 44 and 45, to maintain control valve 36 in its first position 36' while opening non return valve 40. Conversely, with the traditional hydraulically controlled joysticks, it is not possible to pressure at the same time both pilot lines 44 and 45, because it is physically impossible to move joysticks in both opposite directions.

[0128] In addition, the proposed arrangement allows to realize a floating function of the hydraulically actuated work implement 10 without impacting on the complexity of the hydraulic arrangement 30 and without using non-standard, i.e. using only off-the-shelf components, with the obvious advantages that this entails.

[0129] It is clear that modifications can be made to the work machine 1, which do not extend beyond the scope of protection defined by the claims.

[0130] For instance, the source of pressurized hydraulic fluid 31 may comprise only one hydraulic pump fluidly connected to main control valve 36 and to pilot stage 42.

[0131] In addition, Figure 3 illustrates an alternative embodiment, in which is similar to the embodiment illustrated in Figure 2 and in which the common components will be denoted with the same reference number.

[0132] According to the exemplary embodiment illustrated in Figure 3, floating control stage 71 may not on / off valve 72 and 74.

[0133] In addition, pressure-relief valves 54 and 55 may be electronically controlled valves, i.e. solenoid-controlled valves, and electronic control unit 70 may be configured to selectively open both pressure-relief valves 54 and 55 on the basis of the commands received from input means 75, to perform the floating function of hydraulically actuated work implement 10.

Examples

Embodiment Construction

[0018]With reference to Figure 1, number 1 denotes, as a whole, a work machine / vehicle, in particular an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like.

[0019]Work machine 1 comprises a body 2 movable on the ground by means of ground resting wheels or tracks 3.

[0020]In particular, said body preferably comprises: a lower frame or undercarriage 5, which carries the ground resting wheels or tracks 3 to allow motion of the body with respect to the ground; and an upper frame 6 or superstructure, which is carried in a rotatable manner by lower frame 5 preferably about a rotation axis R 1 orthogonal to the advancing plane of work machine 1, i.e. orthogonal to the ground.

[0021]As known, a swivel joint 8 may be interposed between upper frame 6 and lower frame 5.

[0022]In addition, work machine 1 comprises a hydraulically actuated work implement 10, which is carried by body 2 and is configured to perform multiple earth moving operations, such as digging, h...

TECHNICAL FIELD

[0001] The present invention relates to a work machine, in particular to an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like, and to the related control method.

[0002] More in detail, the present invention relates to a hydraulic arrangement configured to control a floating function of the hydraulically actuated work implement of the work machine. Reference will be made to this application by way of the example below, without however losing in generality.BACKGROUND OF THE INVENTION

[0003] As is known, work machines such as excavators, diggers and the like are provided with a hydraulically actuated work implement, which is movably carried by the body of the work machine and is configured to perform multiple earth-moving operations, such as digging, handling earth or gravel, loading trucks and / or similar operations.

[0004] Such work machines generally comprise a body movable on the ground via ground resting wheels or tracks.

[0005] More in detail, the body comprises: an undercarriage, which carries the ground resting wheels or tracks to allow motion of the body with respect to the ground; and a superstructure, which is carried in a rotatable manner by the undercarriage.

[0006] The aforementioned work machines usually further comprise a hydraulic motor configured to rotate the superstructure with respect to the undercarriage and a pair of further hydraulic motors configured to drive the ground resting wheels or tracks in rotation to allow motion of the body with respect to the ground.

[0007] As per se known, the aforementioned hydraulically actuated work implement comprises: a boom rotatably carried by the superstructure; a boom actuator configured to rotate the boom with respect to the superstructure; a stick or arm or dipper rotatably carried by the boom; an arm hydraulic actuator configured to rotate the arm with respect to the boom; a bucket and / or other similar tools rotatably carried by the arm; and a bucket hydraulic actuator configured to rotate the bucket with respect to the arm.

[0008] As known, such work machines comprise a hydraulic system configured to control the pressurized hydraulic provided the aforementioned hydraulic actuators, in order to control the operation and the position of the members of the hydraulically actuated work implement.

[0009] For safety reasons, such hydraulic system comprises also the so called "hose burst check valve" according to the standard ISO 8643 - Earth-Moving Machinery - Hydraulic Excavator and Backhoe Loader Boom-Lowering Control Device, which is fluidly connected to the boom actuator. Such valve comprises a check valve configured to maintain the boom actuator pressurized should the flexible hose fluidly connecting the high-pressure hydraulic pump with the same boom actuator break. This allows to prevent the boom from falling downward out of control and thus posing serious hazards to nearby operators.

[0010] However, in some cases, the need is felt to let the tool carried by the hydraulically actuated work implement to free float in contact with the ground due to its own weight, so that it can follow the profile of the ground, for instance to perform levelling operations.

[0011] Such operation condition, also call "floating function", may be performed by shortcutting both ends of the boom and / or the arm actuator to tank, so that the hydraulically actuated work implement may float freely following the profile of the ground.

[0012] However, the hydraulic systems currently available to perform the boom free floating function are rather complex and expensive, and their development and production impacts in a not negligible manner on the overall costs of the work machine.

[0013] In view of the above, the need is felt to provide a work machine able to improve the free-floating function of the hydraulically actuated work implement of the work machine.

[0014] Aim of the present invention is to satisfy the above-mentioned need in an optimized and cost-effective manner.SUMMARY OF THE INVENTION

[0015] The aforementioned aims are reached by a work machine and by a method as claimed in the appended set of claims.

[0016] The claims describe preferred forms of embodiment of the present invention and forms an integral part of this description.BRIEF DESCRIPTION OF DRAWINGS

[0017] For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example, with reference to the attached drawings, wherein: Figure 1 is an illustration of an example of a work machine according to the present invention, with parts removed for clarity and Figures 2 and 3 are two schematic representations of hydraulic arrangements of the work machine illustrated in Figure 1, with parts removed for clarity. DETAILED DESCRIPTION OF THE INVENTION

[0018] With reference to Figure 1, number 1 denotes, as a whole, a work machine / vehicle, in particular an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like.

[0019] Work machine 1 comprises a body 2 movable on the ground by means of ground resting wheels or tracks 3.

[0020] In particular, said body preferably comprises: a lower frame or undercarriage 5, which carries the ground resting wheels or tracks 3 to allow motion of the body with respect to the ground; and an upper frame 6 or superstructure, which is carried in a rotatable manner by lower frame 5 preferably about a rotation axis R 1 orthogonal to the advancing plane of work machine 1, i.e. orthogonal to the ground.

[0021] As known, a swivel joint 8 may be interposed between upper frame 6 and lower frame 5.

[0022] In addition, work machine 1 comprises a hydraulically actuated work implement 10, which is carried by body 2 and is configured to perform multiple earth moving operations, such as digging, handling earth or gravel, loading trucks and / or similar operations. In particular, work implement 8 is rotatably carried by upper frame 6.

[0023] In addition, work machine 1 comprises a hydraulic actuator assembly 12, which is configured to actuate body 2 and / or hydraulically actuated work implement 10.

[0024] Preferably, hydraulic actuator assembly 12 comprises at least one hydraulic actuator, which is coupled to a movable member of work machine 1 and is configured to control the movement / position of this latter.

[0025] More in detail, hydraulic actuator assembly 12 preferably comprise at least a first hydraulic motor (not visible), in the following referred also to as "swing motor", which is operatively interposed between lower frame 5 and upper frame 6 and is configured to rotate upper frame 6 with respect lower frame 5.

[0026] In addition, hydraulic actuator assembly 12 preferably further comprise at least one, and preferably a pair of hydraulic motors (not visible), in particular reversible hydraulic motors, in the following referred also to as "drive motors", each configured to drive a corresponding ground resting wheel or track 3 in rotation to allow motion of body 2 with respect to the ground.

[0027] With reference to Figure 1, hydraulically actuated work implement 10 preferably comprises: a boom 14 rotatably carried the body 2, in particular by the upper frame 6; a stick or arm or dipper 16 rotatably carried by boom 14; and a bucket 18 and / or other similar tools, such as an asphalt cutter, a grapple, a ripper or the like, rotatably carried by arm 16.

[0028] Hydraulic actuator assembly 12 preferably comprise a plurality of hydraulic cylinders, in particular double-acting hydraulic cylinders, configured to actuate hydraulically actuated work implement 10.

[0029] More in detail, hydraulic actuator assembly 12 preferably comprise at least one boom actuator 20, which is operatively interposed between body 2 and boom 14 and is configured to rotate boom 14 with respect to body 2.

[0030] In addition, hydraulic actuator assembly 12 preferably further comprise at least one arm actuator 22, which is operatively interposed between boom 14 and arm 16 and is configured to rotate arm 16 with respect to boom 14.

[0031] Preferably, hydraulic actuator assembly 12 further comprise at least one bucket actuator 24, which is operatively interposed between arm 16 and bucket 18 and is configured to rotate bucket 18 with respect to arm 16.

[0032] With reference to the exemplary embodiment illustrated in Figure 1, work machine 1 further comprises a dozer blade 26 carried in a movable manner by body 2, preferably by undercarriage 5, in a manner per se known and therefore not further described.

[0033] With reference to the preferred embodiment illustrated in Figure 2, work machine 1 further comprises a hydraulic arrangement 30, which is fluidly connected to the aforementioned hydraulic actuator assembly 12 and is configured to provide pressurized hydraulic fluid towards the same hydraulic actuator assembly 12, in other to operate / actuate the latter.

[0034] More in detail, hydraulic arrangement 30 is fluidly connected at least to one of the hydraulic actuators of the hydraulic actuator assembly 12. Preferably, hydraulic arrangement 30 is fluidly connected at least to boom actuator 20, in the following referred to only as "actuator 20" for brevity.

[0035] It is understood that the hydraulic arrangement 30 may be fluidly connected other / addition hydraulic actuators of hydraulic actuator assembly 12, such as to arm actuator 22 and / or to bucket actuator 24.

[0036] Preferably, actuator 20 is provided with a first inlet 20a configured to receive pressurized hydraulic fluid in order to move the related member, in particular boom 14, in a first direction, for instance upwards. In addition, actuator 20 is preferably provided with a second inlet 20b configured to receive pressurized hydraulic fluid in order to move the related member, in particular boom 14, in a second direction opposite to the first direction, for instance downwards.

[0037] As per se known, actuator 20 preferably comprises a housing accommodating in a fluid tight and slidable manner a piston, so as to define within the same housing two hydraulic chambers opposite to each other.

[0038] With reference to the example illustrated in Figure 2, hydraulic arrangement 30 preferably comprises a source of pressurized hydraulic fluid 31, which is configured to provide at outlet a flow of pressurized hydraulic fluid.

[0039] In particular, the source of pressurized hydraulic fluid 31 preferably comprises pumping means 32, in particular a hydraulic pump, carried by an internal combustion engine of work machine 1. Pumping means 32 may be configured to suck hydraulic fluid from a tank 34 and to provide at outlet a pressurized flow of such hydraulic fluid.

[0040] More in detail, pumping means 32 preferably comprises a high-pressure hydraulic pump configured to deliver at outlet a pressurized hydraulic fluid with a pressure greater than 100 bar, more preferably up to or greater than 350 bar.

[0041] In addition, hydraulic arrangement 30 preferably comprises one or more main control valves or distributors or spool valves 36 fluidly interposed between the source of pressurized hydraulic fluid 31 and hydraulic actuator assembly 12.

[0042] In particular, main control valves 36 are preferably hydraulically controlled valves.

[0043] With reference to the exemplary and non-limitative embodiment illustrated in Figure 2, control valves 36 may comprise load-sensing control valves.

[0044] Preferably, hydraulic arrangement 30 comprises a main control valve 36 fluidly interposed between the outlet of source of pressurized hydraulic fluid 31 and actuator 20.

[0045] Main control valve 36 is configured to selectively route / throttle the pressurized hydraulic fluid provided by source 31 to one of the two ends of actuator 20, in order to operate / actuate the latter and raise or lower the associated member, in particular boom 14, accordingly.

[0046] With reference to the exemplary embodiment illustrated in Figure 2, main control valve 36 preferably comprises a three-position valve.

[0047] Preferably, valve 36 is a hydraulically actuated valve.

[0048] Two ports 36a and 36b of main control valve 36 are preferably fluidly connected respectively to source 31 and to tank 34, respectively via a suction line 33 and a tank line 35.

[0049] Two ports 36c and 36d of main control valve 36 are preferably fluidly connected respectively to actuator 20, in particular to the two chambers of hydraulic actuator 20 via a correspondent hydraulic supply line 38 and 39.

[0050] Preferably, in a first or closed operative position 36', valve 36 is preferably configured to fluidly isolate its ports / openings.

[0051] More in detail, in the closed position 36', valve 36 is preferably configured to fluidly isolate tank 34 and source 31 from hydraulic supply lines 38 and 39.

[0052] In other words, in the closed position 36', valve 36 is preferably configured to fluidly isolate its ports 36a, 36b, 36c and 36d to each other.

[0053] In addition, in a second position 36'', valve 36 is preferably configured to fluidly connect its port 36a with its port 36d, to fluidly connect source 31 with supply line 39.

[0054] In the second position 36'', in addition, valve 36 is preferably further configured to fluidly connect its port 36d with port 36b, to fluidly connect supply line 39 with tank 34.

[0055] Therefore, in the second position 36'', valve 36 is preferably configured to put the first chamber of actuator 20 in fluid communication with source 31 and put the other chamber of actuator 20 in fluid communication with tank 34, in order to move boom 14 in the first direction.

[0056] In addition, in a third position 36‴, valve 36 is preferably configured to fluidly connect its port 36a with its port 36d, to fluidly connect source 31 with supply line 39.

[0057] In the third position 36''', in addition, valve 36 is preferably further configured to fluidly connect its port 36d with port 36a, to fluidly connect supply line 38 with tank 34.

[0058] Therefore, in the third position 36‴, valve 36 is preferably configured to put the second chamber of actuator 20 in fluid communication with source 31 and put the other chamber of actuator 20 in fluid communication with tank 34, in order to move boom 14 in the second direction.

[0059] With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 30 further comprises a first check valve or non-return valve, also called "hose burst valve" 40 arranged along supply line 38.

[0060] Non-return valve 40 is configured to selectively prevent the hydraulic fluid to flow out of the first chamber of hydraulic actuator 20 and port 20a.

[0061] This in use allows to maintain pressurized the first chamber of hydraulic actuator 20 should the flexible hose (part of supply line 38) fluidly connecting port 20a of hydraulic actuator 20 with control valve 36 break, to avoid unwanted lowering of boom 14.

[0062] More in detail, non-return valve 40 is preferably a two-position valve.

[0063] In a first position 40', non-return valve 40 preferably allows hydraulic fluid to flow only from valve 36 toward actuator 20, preventing hydraulic fluid flow in the opposite direction.

[0064] In a second position 40", non-return valve 40 preferably allows hydraulic fluid to flow from actuator 20 towards valve 36.

[0065] With reference to Figure 2, non-return valve 40 preferably comprises biasing means 40a, such as a spring, configured to exert forces on the same non-return valve 40 adapted to bias this latter in its first position 40'.

[0066] Preferably, non-return valve 40 is a pilot operated check valve.

[0067] More in detail, non-return valve 40 is preferably provided with a pilot port, which is adapted to receive a pilot pressure that is adapted to open the same valve, i.e. to arrange it in its second position 40", in order to allow hydraulic fluid to flow back from actuator 20 towards main control valve 36.

[0068] In addition, hydraulic arrangement 30 preferably further comprises a pressure-relief or safety valve 41 associated to non-return valve 40.

[0069] More in detail, pressure-relief valve 41 is preferably arranged in parallel to non-return valve 40 and is preferably configured to open should the pressure at the first opening 20a of hydraulic actuator 20 exceed a predetermined safety threshold.

[0070] With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 30 further comprises an electronically controlled pilot circuit 42, which is operatively connected at least to main control valve 36 and is configured to actuate the latter, in order to control the pressurized hydraulic fluid provided to hydraulic actuator 22.

[0071] In other words, pilot circuit 42 is fluidly connected to main control valve 36 and is configured to provide a hydraulic pilot signal to the same main control valve 36, in order to operate this latter.

[0072] With reference to the exemplary embodiment illustrated in Figure 2, source of pressurized hydraulic fluid 31 preferably comprises further pumping means 43, in particular a further hydraulic pump, which may be carried by an internal combustion engine of work machine 1, and are configured to suck hydraulic fluid from tank 34 and to provide at outlet a pressurized flow of such hydraulic fluid.

[0073] Preferably, pumping means 43 are separate and distinct from pumping means 32.

[0074] Pilot circuit 42 is preferably fluidly connected to the outlet of pumping means 43, in order to receive pressurized hydraulic fluid therefrom.

[0075] Preferably, pumping means 43 comprises a low-pressure hydraulic pump configured to deliver at outlet a pressurized hydraulic fluid with a pressure lower than 60 bar, for instance equal to about 40 bar.

[0076] As per se known, pumping means 43 may be provided with a pressure relief valve or pressure reducing valve (not illustrated) fluidly connected downstream the outlet of pumping means 43 and configured to set the pressure of the pressurized hydraulic fluid fed within pilot circuit 42.

[0077] For example, such pressure relief valve may be configured to set the pressure of the pressurized hydraulic fluid fed within pilot circuit 42 to approximately 40 bar.

[0078] According to the preferred embodiment of the present invention, pilot circuit 42 is configured to selectively control main control valve 36 and non-return valve 40 in order to prevent fluid flow from the source 31 toward the actuator 20 and at the same time to open non-return valve 40.

[0079] With reference to the exemplary embodiment illustrated in Figure 2, pilot circuit 42 preferably comprises two hydraulic pilot lines 44 and 45, each of which fluidly connects the outlet of pumping means 43 with a corresponding end of main control valve 36.

[0080] Hydraulic pilot lines 44 and 45 are preferably configured to carry a pressure signal to a respective end of main control valve 36, in order to exert on the latter forces adapted to move the movable spool of main control valve 30 in a corresponding direction.

[0081] In other words, the hydraulic fluid flowing within hydraulic pilot lines 44 and 45 is adapted to exert a respective pressure on main control valve 36 adapted to arrange this latter respectively in its second position 36" or in its third position 36‴.

[0082] With reference the exemplary embodiment illustrated in Figure 2, pilot circuit 42 preferably comprises an additional hydraulic pilot line 40b, which is fluidly connected to pilot line 45. Hydraulic pilot line 40b is preferably operatively connected to non-return valve 40 and is preferably configured to exert on this latter a pressure adapted to bias the same non-return valve 40 in its second or open position 40".

[0083] Hydraulic pilot line 40b preferably branches off hydraulic pilot line 45.

[0084] Therefore, in use, when hydraulic pilot line 45 is pressurized in order to arrange control valve 36 in its third position 36‴, also hydraulic pilot line 40b is pressurized in order to arrange non-return valve 40 in its second or open position 40".

[0085] In addition, pilot circuit 42 further comprises a pair of pressure reducing valves 48 and 50, each fluidly connected to a corresponding pilot line 44 and 45 and configured to reduce the pressure of the hydraulic pilot signal within the latter.

[0086] With reference to the exemplary embodiment illustrated in Figure 2, pressure reducing valves 48 and 50 are preferably electronically controlled pressure reducing valve, i.e. solenoid-controlled pressure reducing valves.

[0087] In particular, pressure reducing valves 48 and 50 may comprise respective solenoids 48a and 50a configured to control the operation of the same valves 48 and 50.

[0088] With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement preferably further comprises pressure-relief or safety valves 54 and 55 fluidly connected respectively to supply line 38 and to supply line 39. More in detail, pressure-relief valves 54 and 55 are fluidly interposed between the corresponding supply line 38 and 39 and tank 34.

[0089] As per se known, and therefore not described in detail, pressure-relief valves 54 and 55 are normally closed and are configured to open should the pressure of the hydraulic fluid within the corresponding supply line 38 or 39 exceed a predetermined safety threshold, to reduce the pressure of the hydraulic fluid within the same.

[0090] With reference to the exemplary embodiment illustrated in Figure 2, work machine 1 preferably further comprises manually actuated commands input means 60, such as joysticks, levers, buttons, or portions of a touch-sensitive display, which are adapted to be manually actuated / handled by the work machine user to impart commands for controlling the operation of actuator 20.

[0091] More in detail, manually actuated commands input means 60 are preferably electronically connected at least to pressure reducing valves 48 and 50 and are preferably configured to output signals adapted to control operation of these latter.

[0092] In addition, work machine 1 preferably comprises an electronic control unit 70, which is preferably operatively connected at least to commands input means 60 and to pressure reducing valves 48 and 50, and is provided with elaboration means configured to control the operation of the same valves 48 and 50 as function of the signals provided by command input means 60.

[0093] With reference to the exemplary embodiment illustrated in Figure 2, pilot circuit 42 is further provided with a floating control stage 71.

[0094] Preferably, floating control stage is fluidly connected to supply lines 38 and 39.

[0095] Floating control stage 71 is preferably configured to selectively fluidly connect both supply lines 38 and 39 to tank 34, in order to discharge the pressure at actuator 20 and allow free flowing of hydraulic fluid from hydraulic actuator 20 to main control valve 36 and vice-versa. This in use allows boom 14 (or any other member of hydraulically actuated work implement 10 coupled to actuator 20) to free float resting on the ground due to its own weight.

[0096] In other words, floating control stage 71 is configured to selectively activate a floating function of hydraulically actuated work implement 10 (in particular of boom 14), in which none of chambers of actuator 20 is pressurized and the hydraulically actuated work implement 10 may rest on the ground due to its own weight and may to move up during traveling of work machine 1 following the profile of the ground.

[0097] More in detail, floating control stage 71 preferably comprises a pair of on / off valves 72 and 74 fluidly connected respectively to supply line 38 and to supply line 39.

[0098] More in detail, each on / off valves 72 and 74 is fluidly interposed respectively between supply line 38 or to supply line 39 and tank 34, and is configured to selectively fluidly connect the corresponding supply line 38 or 39 to tank.

[0099] Preferably, pressure on / off 72 and 74 are electronically controlled on / off valve, i.e. solenoid-controlled on / off valves.

[0100] In addition, on / off valves 72 and 74 preferably comprises two-position valves.

[0101] In a first position 72' and 74', on / off valves 72 and 74 are preferably configured to prevent fluid communication between supply lines 38 and 39 and tank 34.

[0102] In a second position 72'' and 74", pressure reducing valves 72 and 74 are preferably configured to fluidly connect supply lines 38 and 39 with tank 34.

[0103] In addition, on / off valves 72 and 74 preferably comprises biasing means 72a and 74a, in particular springs, configured to bias the same on / off valves 72 and 74 towards their first position 72' and 74'.

[0104] Moreover, on / off valves 72 and 74 preferably comprises solenoids 72b and 74b configured to arrange the same on / off valves 72 and 74 in their second position 72" and 74".

[0105] With reference to the exemplary embodiment illustrated in Figure 2, work machine 1 preferably further comprises manually actuated commands input means 75, such as a button, a knob or portions of a touch-sensitive display, which are operatively connected to electronic control unit 70 and are adapted to be actuated by the work machine user to activate the floating function of hydraulically actuated work implement 10.

[0106] More in detail, manually actuated commands input means 75 are preferably adapted to output commands / signals for controlling the operation of floating control stage 71.

[0107] In particular, commands input means 75 are configured to be actuated by the work machine user to impart commands suited to control electronic control unit 70 in order to arrange main control valve 36 in its first position 36' and at the same time to arrange non-return valve 40 in its second position 40" and to arrange on / off valves 72 and 74 in their second position 72'' and 74".

[0108] In particular, electronic control unit 70 may be configured to control operation of pressure reducing valves 48 and 50 according to the signals received from commands input means 75.

[0109] More in detail, electronic control unit 70 may be configured to control operation of pressure reducing valves 48 and 50 in order to pressurize both pilot lines 44 and 45, in order to arrange main control valve 36 in its first position 36' and at the same time to pressurize pilot line 40b, in order to arrange non-return valve 40 in its second or open position 40', advantageously upon receipt of commands from commands input means 75.

[0110] In addition, electronic control unit 70 may be configured to control on / off valves 72 and 74 to fluidly connect both supply lines 38 and 39 to tank 34, advantageously upon receipt of commands from commands input means 75.

[0111] According to the preferred embodiment of the present invention, in particular, when work machine user operates commands input means 75, electronic control unit 70 is preferably configured to control pressure reducing valves 48 and 50 in order to pressurize both pilot lines 44 and 45 with two respective pilot signals having substantially the same pressure, in order to maintain main control valve 36 in its first position 36'.

[0112] The general operation of the above-described work machine 1 is the following.

[0113] In general, the pressurized hydraulic fluid provided by pumping means 31 is throttled by main control valve 36 to hydraulic actuator 20 in order to actuate this latter accordingly.

[0114] The operative position of main control valve 36 is controlled by pilot circuit 42 and depends on the operation of pressure reducing valves 48 and 50, which in turn depends on the actuation of commands input means 60 (i.e. the joystick) .

[0115] In particular, when the work machine 1 user actuates commands input means 60, electronic control unit 70 controls pressure reducing valves 48 and 50 to output a hydraulic pressure signal adapted to control the position of main control valve 36 according to the input of the commands input means 60.

[0116] More in detail, when main control valve 36 is arranged in its second position 36'', the pressurized hydraulic fluid provided by pumping means 31 is fed towards the first inlet 20a of actuator 20 via supply line 38, while the second inlet 20b of the same actuator 30 is fluidly connected to tank 34.

[0117] Similarly, when main control valve 36 is arranged in its third position 36‴, the pressurized hydraulic fluid provided by pumping means 31 is fed towards the second inlet 20b of actuator 20 via supply line 39, while the first inlet 20a of the same actuator 30 is fluidly connected to tank 34. At the same time, pilot line 40b is pressurized in order to arrange non-return valve 40 in its second or open position 40", and allow the hydraulic fluid to flow from actuator 20 back towards control valve 36 along supply line 38.

[0118] With reference to the exemplary embodiment illustrated in Figure 2, when the work machine user actuates user input means 75, electronic control unit 70 controls pressure reducing valves 48 and 50, in order to pressurize both pilot lines 44 and 45 and arrange main control valve 36 in its first position 36'. At the same time pilot line 40b is pressurized in order to arrange non-return valve 40 in its second or open position 40".

[0119] In addition, when the work machine user actuates user input means 75, electronic control unit 70 arranges both on / off valves 72 and 74 in their second position, in order to fluidly connect both supply lines 38 and 39 with tank 34.

[0120] In such operating conditions, both chambers of actuator 20 are fluidly connected to tank 20 and hydraulically actuated work implement 10, in particular boom 14, is not lifted by actuator 20 and is able to move up and down in contact with the ground.

[0121] In view of the above, the present invention if further directed to a method for controlling the above described work machine 1, wherein the method comprises the following steps: a) Receiving a command from user input means 75 suited to activate a floating function of hydraulic arrangement 30, and b) Arranging main control valve 36 in its first position 36' , c) Opening non-return valve 40, and d) Fluidly connecting both ends 20a and 20b of hydraulic actuator 20 to tank 34.

[0122] More in detail, said steps b) and c) comprises the step of controlling pressure reducing valves 48 and 50 in order to pressurize pilot lines 44 and 45 to arrange control valves 36 in its first position 36'' and at the same time to pressurize pilot line 40b, to arrange non-return valve 40 in its second or open position 40".

[0123] In addition, said step d) comprises the step of arranging pressure reducing valves 72 and 74 in their second position 72" and 74'', to fluidly connect supply lines 38 and 39 with tank 34.

[0124] In view of the foregoing, the advantages of the work machine 1 and of the related control method according to the invention are apparent.

[0125] In particular, thanks to the proposed hydraulic arrangement 30, it is possible to provide a floating function of the hydraulically actuated work implement 10 in a simple and economic manner, since the modification required to the standard hydraulic arrangement are minimal. In particular, no modification to main control valve 36, to non-return valve 40 and / or to pressure reducing valves 48 and 50 are required.

[0126] Further no additional valves are required to arrange non-return valve 40 in its second or open position 40".

[0127] In addition, the electronic control of pressure reducing valves 48 and 50 allows to pressurize at the same time both pilot lines 44 and 45, to maintain control valve 36 in its first position 36' while opening non return valve 40. Conversely, with the traditional hydraulically controlled joysticks, it is not possible to pressure at the same time both pilot lines 44 and 45, because it is physically impossible to move joysticks in both opposite directions.

[0128] In addition, the proposed arrangement allows to realize a floating function of the hydraulically actuated work implement 10 without impacting on the complexity of the hydraulic arrangement 30 and without using non-standard, i.e. using only off-the-shelf components, with the obvious advantages that this entails.

[0129] It is clear that modifications can be made to the work machine 1, which do not extend beyond the scope of protection defined by the claims.

[0130] For instance, the source of pressurized hydraulic fluid 31 may comprise only one hydraulic pump fluidly connected to main control valve 36 and to pilot stage 42.

[0131] In addition, Figure 3 illustrates an alternative embodiment, in which is similar to the embodiment illustrated in Figure 2 and in which the common components will be denoted with the same reference number.

[0132] According to the exemplary embodiment illustrated in Figure 3, floating control stage 71 may not on / off valve 72 and 74.

[0133] In addition, pressure-relief valves 54 and 55 may be electronically controlled valves, i.e. solenoid-controlled valves, and electronic control unit 70 may be configured to selectively open both pressure-relief valves 54 and 55 on the basis of the commands received from input means 75, to perform the floating function of hydraulically actuated work implement 10.

Examples

Embodiment Construction

[0018]With reference to Figure 1, number 1 denotes, as a whole, a work machine / vehicle, in particular an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like.

[0019]Work machine 1 comprises a body 2 movable on the ground by means of ground resting wheels or tracks 3.

[0020]In particular, said body preferably comprises: a lower frame or undercarriage 5, which carries the ground resting wheels or tracks 3 to allow motion of the body with respect to the ground; and an upper frame 6 or superstructure, which is carried in a rotatable manner by lower frame 5 preferably about a rotation axis R 1 orthogonal to the advancing plane of work machine 1, i.e. orthogonal to the ground.

[0021]As known, a swivel joint 8 may be interposed between upper frame 6 and lower frame 5.

[0022]In addition, work machine 1 comprises a hydraulically actuated work implement 10, which is carried by body 2 and is configured to perform multiple earth moving operations, such as digging, h...

Claims

1. A work machine (1) comprising: • a body (2) movable on the ground by means of ground resting means (3), • a hydraulically actuated work implement (10) movably carried by the body (2) and configured to perform earth moving operations, • at least one hydraulic actuator (20) operatively connected to the hydraulically actuated work implement (10) and configured to control the movement and / or the position of the same hydraulically actuated work implement (10), and • a hydraulic arrangement (30) configured to provide pressurized hydraulic fluid towards the hydraulic actuator (22), wherein the hydraulic actuator (20) comprises a first inlet (20a) configured to receive pressurized hydraulic fluid in order to move the hydraulically actuated work implement (10) in a first direction, and a second inlet (20b) configured to receive pressurized hydraulic fluid in order to the hydraulically actuated work implement (10) in a second direction opposite to said first direction, the hydraulic arrangement (30) comprising: • a source (31) of pressurized hydraulic fluid, which is configured to suck hydraulic fluid from a tank (34) and to provide at outlet a pressurized flow of the hydraulic fluid, • at least one main control valve (36), which is fluidly interposed between the source of pressurized hydraulic fluid (31) and the hydraulic actuator (20), and is configured to control the flow of pressurized hydraulic fluid fed towards the first inlet (20a) and / or the second inlet (20b) of the hydraulic actuator (20), • a first supply line (38) fluidly connecting a first outlet(36c) of the main control valve (36) with the first inlet (20a) of the hydraulic actuator (20), • a second supply line (39), which is arranged in parallel to the first supply line (39) and fluidly connects a second outlet(36d) of the main control valve (36) with the second inlet (20b) of the hydraulic actuator (20), • a pilot-operated non-return valve (40) arranged along the first supply line (38), upstream the first inlet (20a) of the hydraulic actuator (20), and • an electronically controlled pilot circuit (42), which is operatively connected to the main control valve (36) and to the non-return valve (40), is configured to control the operation of the main control valve (36) and of the non-return valve (40), wherein the electronically controlled pilot circuit (42) is configured to selectively control main control valve (36) and non-return valve (40) in order to prevent fluid flow from the source (31) toward the hydraulic actuator (20) and at the same time to open non-return valve (40), and wherein the electronically-controlled pilot circuit (42) further comprises a floating control stage (71) configured to put the first supply line (38) and the second supply line (39) in fluid communication with the tank (34).

2. Work machine according to claim 1, wherein the floating control stage (71) comprises a first on / off valve (72) fluidly connected to the first supply line (38) and configured to selectively put the first supply line (38) in fluid communication with the tank (34), and / or a second on / off valve (74) fluidly connected to the first supply line (39) and configured to selectively put the first supply line (39) in fluid communication with the tank (34).

3. Work machine according to claim 1 or 2, wherein the main control valve is operable alternatively in three different operating positions (36', 36'', 36‴), in a first operative positions (36'), the main control valve (36) is configured to prevent fluid communication between the source (31), the tank (34) and the hydraulic actuator (20), in a second operative position (36"), the main control valve (36) is configured to fluidly connect the first opening (20a) of hydraulic actuator (20) with the source (31) and the second opening (20b) of the hydraulic actuator (20) with the tank (34), and in a third operative position (36'''), the main control valve (36) is configured to fluidly connect the second opening (20b) of hydraulic actuator (20) with the source (31) and the first opening (20a) of the hydraulic actuator (20) with the tank (34).

4. Work machine according to claim 3, wherein the electronically controlled pilot circuit (42) comprises: a first pilot line (44) fluidly connected to a first end of the main control valve (36) and configured to exert a pressure on the main control valve (36) adapted to arrange the same main control valve (36) in the second position (36"), and a second pilot line (45) fluidly connected to a second end of the main control valve (36) and configured to exert a pressure on the main control valve (36) adapted to arrange the same main control valve (36) in the second position (36").

5. Work machine according to claim 4, wherein the electronically controlled pilot circuit (42) comprises a first electronically controlled pressure reducing valve (48) arranged along the first pilot line (44) and a second electronically controlled pressure reducing valve (50) arranged along the second pilot line (45).

6. Work machine according to claim 4 or 5, wherein the electronically controlled pilot circuit (42) comprises a third pilot line (40b), which is fluidly connected to the second pilot line (45), is operatively connected to the pilot-operated non-return valve (40) and is configured to exert a pressure on the same pilot-operated non-return valve (40) adapted to open the same pilot-operated non-return valve (40).

7. Work machine according to claim 5, wherein the third hydraulic pilot line (40b) branches off from the second hydraulic pilot line (45), downstream the second pressure reducing valve (50).

8. Work machine according to claim 4, 5 or 6, further comprising an electronic control unit (70) electronically connected to the floating control stage (71), to the first electronically controlled pressure reducing valve (48) and to the second electronically controlled pressure reducing valve (50), and comprises elaboration means configured to control the operation of the floating control stage (71) and of the first electronically controlled pressure reducing valve (48) and to the second electronically controlled pressure reducing valve (50) in order to: • put the first supply line (48) and the second supply line (50) in fluid communication with the tank (34), and at the same time, • pressurize the first pilot line (44) and the second pilot line (45) in order to arrange the main control valve (36) in the first position (36') and open the pilot-operated non-return valve (40).

9. Work machine according to claim 8, further comprising command input means (60, 75), which are electrically connected to the electronic control unit (70) and are adapted to be operated by a work machine driver in order to impart commands / signals to control operation of the hydraulic arrangement (30).

10. A method for controlling a work machine realized according to any of the preceding claims, the method comprising the following steps: a) Receiving a command suited to activate a floating function of said hydraulically actuated work implement (12), b) Controlling the floating control stage (71) in order to put the first supply line (38) and the second supply line (39) in fluid communication with the tank (34), c) Controlling the main control valve (36) in order to prevent fluid communication between the source (31), the tank (34) and the hydraulic actuator (20), and d) Opening the pilot-operated non-return valve (40).

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