EP4660381A1

EP4660381A1 - Improved work machine and control method thereof

Info

Publication number: EP4660381A1
Application number: EP25180322.7A
Authority: EP
Inventors: Francesco CHIOCCOLA
Original assignee: CNH Industrial Italia SpA
Current assignee: CNH Industrial Italia SpA
Priority date: 2024-06-05
Filing date: 2025-06-03
Publication date: 2025-12-10

Abstract

A work machine (1) comprising a body (2), a dozer blade (20) movably carried by the body (2), a hydraulic actuator (22) interposed between the body (2) and the dozer blade (20), a hydraulic arrangement (24) configured to provide pressurized hydraulic fluid towards the hydraulic actuator (22) and comprising: a source of pressurized hydraulic fluid (25), at least one main control valve (30), which is fluidly interposed between the source of pressurized hydraulic fluid (25) and the hydraulic actuator (22), and is configured to control the flow of pressurized hydraulic fluid fed towards the first inlet and/or the second inlet of the hydraulic actuator (22), two hydraulic lines (32, 33) fluidly connecting the main control valve (30) with the two inlets of the hydraulic actuator (22), at least one check valve (35) arranged along the first hydraulic line (32) or the second hydraulic line (33), a pilot circuit (37) configured to actuate said main control valve (30), and comprising a floating control stage (45) configured to realize a floating function of the dozer blade of the hydraulic actuator (22) with the tank (28), and is configured to open the check valve (35).

Description

TECHNICAL FIELD

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.
More in detail, the present invention relates to a hydraulic arrangement to control operation of a dozer blade 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

As is known, work machines such as excavators, diggers and the like are provided with a hydraulically actuated work implement, which is carried by a 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.
Such work machines generally comprise a body movable on the ground via ground resting wheels or tracks.
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.
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.
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.
In addition, such work machines further comprise a dozer blade, which is movably carried by the undercarriage, in particular by a front portion of the undercarriage, and is configured to be arranged abutting against the ground to perform levelling operations and/or to push loose material present on the ground, such as gravel, rocks, sand, earth or the like.
The work machine further comprises a hydraulic actuator, configured to control the position of the dozer blade with respect to the ground.
In some cases, the need is felt to let the dozer blade 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.
In other cases, the need is felt to offer an anti-drift or anti-sink function, i.e. to maintain the dozed blade lifted above the ground and to avoid that it may inadvertently lower until it comes into contact with the ground. In particular, this allows to prevent the dozer blade from getting stuck on the ground while the work machine is travelling, potentially causing the latter to overturn.
In addition, the need is felt also to offer a stabilizer function, i.e. to maintain the dozer blade lowered on the ground and to avoid that it may inadvertently lift due to weight of machine. In particular, this allows to prevent the machine from getting down on the ground while the work machine is digging or lifted for maintenance, potentially causing the latter to overturn.
In view of the above, the need is felt to provide a work machine able to improve the control of the dozer blade.
Aim of the present invention is to satisfy the above-mentioned need in an optimized and cost-effective manner.

SUMMARY OF THE INVENTION

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

BRIEF DESCRIPTION OF DRAWINGS

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, and
Figures 2, 3, 4 and 5 are four schematic representations of hydraulic arrangements of the work machine illustrated in Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figure 1, number 1 denotes, as a whole, a work machine, in particular an earth-moving machine such as an excavator, a digger, a mechanical shovel or the like.
Work machine 1 comprises a body 2 movable on the ground by means of ground resting wheels or tracks 3.
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 orthogonal to the advancing plane of work machine 1, i.e. orthogonal to the ground.
As known, a swivel joint (not visible) is interposed between upper frame 6 and lower frame 5.
In addition, work machine 1 comprises a hydraulically actuated work implement 8, 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.
In addition, work machine 1 comprises a hydraulic actuator assembly 10, which is configured to actuate body 2 and/or hydraulically actuated work implement 8.
More in detail, hydraulic actuator assembly 10 preferably comprise at least a first hydraulic motor (not visible in Figure 1), 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.
In addition, hydraulic actuator assembly 10 preferably further comprise at least one, and preferably a pair of hydraulic motors (not visible in Figure 1), 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.
With reference to Figure 1, hydraulically actuated work implement 8 preferably comprises: a boom 12 rotatably carried the body 2, in particular by the upper frame 6; a stick or arm or dipper 13 rotatably carried by boom 12; and a bucket 14 and/or other similar tools rotatably carried by arm 13.
Hydraulic actuator assembly 10 preferably comprise a plurality of hydraulic cylinders, in particular double-acting hydraulic cylinders, configured to actuate hydraulically actuated work implement 8.
More in detail, hydraulic actuator assembly 10 preferably comprise at least one boom actuator 16, which is operatively interposed between body 2 and boom 12 and is configured to rotate boom 12 with respect to body 2.
In addition, hydraulic actuator assembly 10 preferably further comprise at least one arm actuator 17, which is operatively interposed between boom 12 and arm 13 and is configured to rotate arm 13 with respect to boom 12.
Preferably, hydraulic actuator assembly 10 further comprise at least one bucket actuator 18, which is operatively interposed between arm 13 and bucket 14 and is configured to rotate bucket 14 with respect to arm 13.
With reference to the exemplary embodiment illustrated in Figure 1, work machine 1 further comprises a dozer blade 20 carried in a movable manner by body 2, preferably by undercarriage 5.
More in detail, dozer blade 20 is preferably carried in a rotatable manner by body 2 so as to be rotatable about a rotation axis R₁. Rotation axis R₁ is preferably transversal, in particular orthogonal, to the advancing direction of work machine 1.
Hydraulic actuator assembly 10, in addition, comprises a further hydraulic actuator 22, for example a double effect hydraulic cylinder, which is operatively interposed between body 2, in particular undercarriage 5, and dozer blade 20 and is configured to move dozer blade 20 with respect to body 2, in order to control the distance of the same dozer blade 20 from the ground.
Preferably, hydraulic actuator 22 is provided with a first inlet 22a configured to receive pressurized hydraulic fluid in order to move the dozer blade 20 in a first direction, for instance upwards, and with a second inlet 22b configured to receive pressurized hydraulic fluid in order to the dozer blade 20 in a second direction opposite to the first direction, for instance downwards.
As per se known, hydraulic actuator 22 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.
With reference to the preferred embodiment illustrated in Figure 2, work machine 1 further comprises a hydraulic arrangement 24, which is configured to provide pressurized hydraulic fluid towards hydraulic actuator assembly 10, in other to operate/actuate the latter.
More in detail, hydraulic arrangement 24 preferably comprises a source of pressurized hydraulic fluid 25, which is configured to provide at outlet a flow of pressurized hydraulic fluid.
In particular, the source of pressurized hydraulic fluid 25 preferably comprises pumping means 27, in particular a hydraulic pump, which may be carried by an internal combustion engine of work machine 1, and are configured to suck hydraulic fluid from a tank 28 and to provide at outlet a pressurized flow of such hydraulic fluid.
More in detail, pumping means 27 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.
In addition, hydraulic arrangement 24 preferably comprises a plurality of main control valves or distributors fluidly interposed between the source of pressurized hydraulic fluid 25 and hydraulic actuator assembly 10.
In particular, main control valves are preferably hydraulically controlled valves.
With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 24 comprises a main control valve 30 fluidly interposed between the outlet of source of pressurized hydraulic fluid 25 and hydraulic actuator 22 of dozer blade 20.
Main control valve 30 is configured to selectively route/throttle the pressurized hydraulic fluid provided by source 25 to one of the two ends of hydraulic actuator 22, in order to operate/actuate the latter and raise or lower dozer blade 20 accordingly.
With reference to the exemplary embodiment illustrated in Figure 2, main control valve 30 preferably comprises a threeposition hydraulic valve.
The two inlets of main control valve 30 are preferably fluidly connected respectively to the source 25 and to tank 28.
The two outlets of main control valve 30 are preferably fluidly connected respectively to hydraulic actuator 22, in particular to the two chambers of hydraulic actuator 22 via a correspondent hydraulic supply line 32 and 33.
Preferably, in a first or neutral operative position 30a, also called float position, valve 30 is preferably configured to fluidly isolate source 25 from hydraulic actuator 22 and put both chambers of hydraulic actuator 22 in fluid communication with tank 28.
In a second position 30b, main control valve 30 is preferably configured to put source 25 in fluid communication with a first chamber of hydraulic actuator 22 via supply line 32 and tank 28 in fluid communication with a second chamber of hydraulic actuator 22 via supply line 33.
In a third position 30c, on the other hand, main control valve 30 is preferably configured to put source 25 in fluid communication with the second chamber of hydraulic actuator 22 via supply line 33 and tank 28 in fluid communication with the first chamber of hydraulic actuator 22 via supply line 32.
With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 24 further comprises a first check valve or non-return valve or anti-drift valve 35 arranged along supply line 32, and a second check valve 36 arranged along supply line 33.
In use, when main control valve 30 is arranged in its first position 30a, check valves 35 and 36 are adapted to avoid the hydraulic fluid to flow from hydraulic actuator 22 towards main control valve 30, to avoid lowering or lifting of dozer blade 30.
In other words, in use check valves 35 and 36 are adapted to perform a so-called anti-drift or anti-sink function and/or a stabilizer function of dozer blade 20.
Preferably, check valves 35 and 36 are mounted directly on hydraulic actuator 22. In particular, check valves 35 and 36 are fixed directly on the housing of hydraulic actuator 22 and are each fluidly connected to a respective chamber of hydraulic actuator 22.
Preferably, check valve 35 and/or check valve 36 are pilot operated check valves.
More in detail, check valves 35 and 36 are preferably provided with a pilot port, which is adapted to receive a pilot pressure that is adapted to open the corresponding check valve 35 or 36, and to allow hydraulic fluid to flow from hydraulic actuator 22 towards main control valve 30.
Check valves 35 and 36 are preferably configured to normally allow pressurized hydraulic fluid to flow from main control valve 30 towards hydraulic actuator 22, while preventing fluid to flow from hydraulic actuator 22 to main control valve 30.
As explained more in detail after, check valves 35 and 36 are further configured to be selectively opened by means of a hydraulic pilot signal, in order to allow fluid to flow from hydraulic actuator 22 to main control valve 30.
With reference to the exemplary embodiment illustrated in Figure 2, hydraulic arrangement 24 further comprises a pilot circuit 37, which is operatively connected at least to main control valve 30 and is configured to actuate the latter, in order to control the pressurized hydraulic fluid provided to hydraulic actuator 22.
In other words, pilot circuit 37 is fluidly connected to main control valve 30 and is configured to provide a hydraulic pilot signal to the same main control valve 30, in order to operate this latter.
With reference to the exemplary embodiment illustrated in Figure 2, source of pressurized hydraulic fluid 25 preferably comprises further pumping means 38, 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 28 and to provide at outlet a pressurized flow of such hydraulic fluid.
Preferably, pumping means 38 are separate and distinct from pumping means 27.
Pilot circuit 37 is preferably fluidly connected to the outlet of pumping means 38, in order to receive pressurized hydraulic fluid therefrom.
Preferably, pumping means 38 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.
More in detail, pumping means 38 are preferably provided with a pressure relief valve or pressure reducing valve 39 fluidly connected downstream the outlet of pumping means 38 and configured to set the pressure of the pressurized hydraulic fluid fed within pilot circuit 37.
For example, pressure relief valve 39 may be configured to set the pressure of the pressurized hydraulic fluid fed within pilot circuit 37 to approximately 40 bar.
With reference to the exemplary embodiment illustrated in Figure 2, pilot circuit 37 preferably comprises two hydraulic pilot lines 40 and 41, each of which fluidly connects the outlet of pumping means 38 with a corresponding end of main control valve 30.
Hydraulic pilot lines 40 and 41 are preferably configured to carry a pressure signal to a respective end of main control valve 30, in order to exert on the latter forces adapted to move the movable spool of main control valve 30 in a corresponding direction.
In other words, the hydraulic fluid flowing within hydraulic pilot lines 40 and 41 is adapted to exert a respective pressure on main control valve 30 adapted to arrange this latter respectively in its second position 30b or in its third position 30c.
In addition, pilot circuit 37 further comprises a pair of pressure reducing valves 42 and 43, each arranged along a corresponding pilot line 40 and 41 and configured to reduce the pressure of the hydraulic pilot signal within the latter.
With reference to the exemplary embodiment illustrated in Figure 2, pressure reducing valves 42 and 43 are preferably electronically controlled pressure reducing valve, i.e. solenoid-controlled pressure reducing valves.
In particular, pressure reducing valves 42 and 43 may comprise respective solenoids 42a and 43a configured to control the operation of the same valves 42 and 43.
More in detail, pressure reducing valves 42 and 43 are preferably two-ways two-positions valves operable between a closed position and an open position.
Solenoids 42a and 43a are preferably configured to arrange the respective pressure reducing valve 42 and 43 towards its open position.
In addition, pressure reducing valves 42 and 43 preferably comprises each a biasing means 42b and 43b adapted to arrange the same pressure reducing valve 42 and 43 towards its closed position.
With reference to the exemplary embodiment illustrated in Figure 2, work vehicle 1 preferably further comprises manually actuated commands input means 44, 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 hydraulic actuator 22.
More in detail, manually actuated commands input means 44 are preferably electronically connected to pressure reducing valves 42 and 43 and are preferably configured to output signals adapted to control operation of these latter.
In addition, work vehicle 1 preferably comprises an electronic control unit 70, which is preferably connected to commands input means 44 and to pressure reducing valves 42 and 43, and is provided with elaboration means configured to control the operation of the same valves 42 and 43 as function of the signals provided by command input means 44.
With reference to the exemplary embodiment illustrated in Figure 2, pilot circuit 37 is further provided with a floating control stage 45 fluidly connected to check valves 35 and 36.
In addition, floating control stage 45 is preferably fluidly connected to the outlet of pumping means 38.
Floating control stage 45 is configured to selectively open check valves 35 and 36, in order to allow free flowing of hydraulic fluid from hydraulic actuator 22 to main control valve 30 and vice-versa and to fluidly connect the two chambers of hydraulic actuator 22 to tank 28, so as to allow to dozer blade 20 to free float resting on the ground due to its own weight.
In other words, floating control stage 45 is configured to selectively activate a floating function of dozer-blade 20, in which none of chambers of hydraulic actuator 22 is pressurized and the dozer blade 20 may rest on the ground due to its own weight and may to move up during traveling of work machine 1 following the contour of the ground.
More in detail, floating control stage 45 preferably comprises a hydraulic pilot line 46, which is fluidly connected to check valves 35 and 36, and is adapted to selectively open these latter.
With reference to the example illustrated in Figure 2, hydraulic pilot line 46 preferably fluidly connects the outlet of pumping means 38 with the pilot port of check valve 35 and check valve 36, in order to be able to open these latter, to allow hydraulic fluid to flow from hydraulic actuator 22 towards main control valve 30.
In other words, the hydraulic fluid flowing within hydraulic pilot line 46 is configured to exert a pressure adapted to open check valves 35 and 36.
More in detail, hydraulic pilot line 46 preferably branches off from hydraulic pilot line 40, preferably downstream pressure reducing valve 42.
With reference to the exemplary embodiment illustrated in Figure 2, floating control stage 45 preferably further comprises a shuttle valve assembly 53, which is interposed between supply lines 32 and 33, pilot line 46 and check valves 35 and 36.
Shuttle valve assembly 53 is preferably configured to open selectively check valve 36 when main control valve 30 is in its second position 30b and to open selectively check valve 35 when main control valve 30 is in its third position 30c.
More in detail, floating control stage 45 preferably comprises a first shuttle valve 54 interposed between supply line 32, pilot line 46 and the pilot port of check valve 36.
In particular, preferably a first inlet of shuttle valve 54 is fluidly connected to supply line 32 and a second inlet of shuttle valve 54 is fluidly connected to pilot line 46.
The outlet of shuttle valve 54 is preferably fluidly connected to the pilot port of check valve 36 via a hydraulic line 58.
In use, the hydraulic fluid flowing within hydraulic line 58 is configured to open check valve 36.
Shuttle valve 54 is preferably configured to fluidly connects its outlet with its highest-pressure inlet.
In other words, shuttle valve 54 is preferably configured to fluidly connect the pilot port of check valve 36 via hydraulic line 58 with the highest-pressure between supply line 32 and pilot line 46.
In addition, shuttle valve 54 is preferably provided with biasing means, for example a spring, configured to maintain the same shuttle valve 54 in its closed position, in which it fluidly separates its inlets from its outlet.
Preferably, shuttle valve 54 is preferably configured to open when the pressure at one of its inlet exceeds a predetermined threshold, for instance approximately 30 bar.
In other words, the set pressure or opening pressure of shuttle valve 54 is set to approximately 30 bar.
With reference to the exemplary embodiment illustrated in Figure 2, floating control stage 45 preferably comprises a second shuttle valve 56 interposed between line 33, pilot line 46 and the pilot port of check valve 35.
In particular, preferably a first inlet of shuttle valve 56 is fluidly connected to supply line 33 and a second inlet of shuttle valve 56 is fluidly connected to pilot line 46.
The outlet of shuttle valve 56 is preferably fluidly connected to the pilot port of check valve 35 via a hydraulic line 60.
In use, the hydraulic fluid flowing within hydraulic line 60 is configured to open check valve 35.
Shuttle valve 56 is preferably configured to fluidly connects its outlet with its highest-pressure inlet.
In other words, shuttle valve 56 is preferably configured to fluidly connect the pilot port of check valve 35 via hydraulic line 60 with the highest-pressure between supply line 33 and pilot line 46.
In addition, shuttle valve 56 is preferably provided with biasing means, for example a spring, configured to maintain the same shuttle valve 56 in its closed position, in which it fluidly separates its inlets from its outlet.
Preferably, shuttle valve 56 is preferably configured to open when the pressure at one of its inlet exceeds a predetermined threshold, for instance approximately 30 bar.
In other words, the set pressure or opening pressure of shuttle valve 56 is set to approximately 30 bar.
With reference to the exemplary embodiment illustrated in Figure 1, work machine 1 preferably further comprises manually actuated commands input means 72, such as a button, a knob or portions of a touch-sensitive display, which are adapted to be actuated by the work machine user and are adapted to output commands/signals for controlling the operation of floating control stage 45.
More in detail, commands input means 72 are configured to be actuated by the work machine user to impart commands adapted to arrange main control valve 30 in its float position 30a and at the same time to open check valves 35 and 36.
Preferably, commands input means 72 are electrically connected to electronic control unit 70.
Electronic control unit 70, in turn, is preferably configured to control operation of pressure reducing valves 42 and 43 according to the signals received from commands input means 72.
More in detail, electronic control unit 70 is preferably configured to control operation of pressure reducing valves 42 and 43 in order to arrange main control valve 30 in its float position 30a and to open check valves 35 and 36 upon receipt of commands from commands input means 72.
According to the preferred embodiment of the present invention, in particular, when work machine user operates commands input means 72, electronic control unit 70 is preferably configured to control pressure reducing valves 42 and 43 in order to pressurize both pilot lines 40 and 41 with a pilot signal having a pressure greater than said predetermined threshold (for instance greater than 30 bar), in order to arrange main control valve 30 in its float position 30a and to open check valves 35 and 36.
On the other hand, when work machine user does not operate commands input means 72, electronic control unit 70 is preferably configured to control pressure reducing valves 42 and 43 according to the signals received from command input means 44 and in such a way that the pressure within pilot line 40 or pilot line 41 does not exceed said predetermined threshold (for instance lower than 30 bar), in order to prevent pilot line 46 from opening check valves 35 and 36.
The operation of the above-described work machine 1 is the following.
In general, the pressurized hydraulic fluid provided by pumping means 27 is throttled by main control valve 30 to hydraulic actuator 22 in order to actuate this latter accordingly.
The operative position of main control valve 30 is controlled by pilot circuit 37 and depends on the operation of pressure reducing valves 42 and 43, which in turn depends on the actuation of commands input means 44 (i.e. the joystick).
In particular, when work machine user actuates commands input means 44, electronic control unit 70 controls pressure reducing valves 42 and 43 to output a hydraulic pressure signal adapted to control the position of main control valve 30 and having a pressure lower than 30 bar. This, in particular, avoids that hydraulic pilot line 46 may open shuttle valves 35 and 36.
More in detail, when main control valve 30 is arranged in its second position 30b, the pressurized hydraulic fluid provided by pumping means 27 is fed towards a first chamber of hydraulic actuator 22 via supply line 32, while the second chamber of the same hydraulic actuator 22 is fluidly connected to tank 28.
In addition, shuttle valve 54 fluidly connects supply line 32 with the pilot port of check valve 36, via hydraulic line 58, in order to open check valve 36 and allow fluid to flow from second chamber of hydraulic actuator 22 towards main control valve 30 and tank 28.
Similarly, when main control valve 30 is arranged in its third position 30c, the pressurized hydraulic fluid provided by pumping means 27 is fed towards the second chamber of hydraulic actuator 22 via supply line 33, while the first chamber of the same hydraulic actuator 22 is fluidly connected to tank 28.
In addition, shuttle valve 56 fluidly connects hydraulic line 33 with check valve 35, via hydraulic line 60, in order to open check valve 35 and allow fluid to flow from first chamber of hydraulic actuator 22 towards main control valve 30 and tank 28.
With reference to the exemplary embodiment illustrated in Figure 2, when the work machine user actuates user input means 72, electronic control unit 70 controls pressure reducing valves 42 and 43, in order to arrange main control valve 30 in its float position 30a.
More in detail, when the work machine user actuates user input means 72, electronic control unit 70 open both pressure reducing valves 42 and 43 in order to pressurize pilot lines 40 and 41 with a pilot pressure greater than 30 bar, in particular equal to about 40 bar, in order to maintain main control valve 30 in its float position 30a and open both check valves 35 and 36.
In particular, in such operative condition, pilot line 46 is pressurized with a pilot pressure of about 40 bar, shuttle valves 54 and 56 are open and as a consequence check valves 35 and 36 are open by the pressure signal provided respectively by shuttle valve 54 via line 58 and shuttle valve 56 via line 60.
In such operating conditions, dozer blade 20 is not lifted by hydraulic actuator 22 and is able to move up and down in contact with the ground.
In view of the above, the present invention if further directed to a method for controlling the above described work vehicle 1, wherein the method comprises the following steps:

a) Receiving a command from user input means 72 to arrange main control valve 30 in its float position 30a and open check valves 35 and 36, and
b) Controlling pressure reducing valve 42 and 43 in order to pressurize the corresponding pilot lines 40 and 41 with a pilot signal having a pressure greater than said predetermined threshold.

In view of the foregoing, the advantages of the work machine 1 according to the invention are apparent.
In particular, thanks to the proposed hydraulic arrangement 24, it is possible to provide at the same time both the anti-drift or anti-sink function, the stabilizer function and the floating function of the dozer blade without however impacting on the complexity of the hydraulic arrangement 24 and without using non-standard, i.e. using only off-the-shelf components, with the obvious advantages that this entails.
In addition, the use of a main control valve 30 in which, in the first or neutral position, both outlets are in communication with tank 28 removes the risks that pressurized hydraulic fluid may remain trapped in the flexible hoses 32 and 33 fluidly connecting the main control valve 30 with the check valves 35 and 36 preventing these latter from closing.
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.
For instance, the source of pressurized hydraulic fluid 25 may comprise only one hydraulic pump fluidly connected to main control valve 30 and to pilot stage 37.
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.
According to the exemplary embodiment illustrated in Figure 3, hydraulic pilot line 46 may be arranged in parallel to pilot lines 40 and 41.
In addition, floating control stage 45 may further comprise a valve 48, in particular an on off valve 48, which is arranged along hydraulic pilot line 46, is normally closed and is configured to open in order to put the outlet of pumping means 38 in fluid communication with the pilot port of check valves 35 and 36. For example, valve 48 may be a solenoid-controlled valve.
More in detail, valve 48 may be a two-position valve and may be operable between a closed position 48a and an open position 48b.
In the closed position 48a, valve 48 may prevent fluid communication between the outlet of pumping means 38 and the pilot port of check valves 35 and 36.
In the open position 48b, valve 48 may put the outlet of pumping means 38 in fluid communication with the pilot port of check valves 35 and check valve 36.
In addition, valve 48 may comprise biasing means 48c, such as a spring, adapted to maintain valve 48 in its closed position 48a, and a solenoid 48d adapted to arrange valve 48 in its open position 48b.
In addition, electronic control unit 70 may be connected to valve 48 and may be configured to be actuated by the work machine user to impart commands adapted to arrange valve 48 its open position 48b, to pressurize hydraulic pilot line 46 and open check valves 35 and 36 upon receipt of commands from commands input means 72. More in detail, electronic control unit 70 may be configured to arrange valve 48 in its open position 48b in response to actuation of commands input means 72.
In addition, Figure 4 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.
The hydraulic arrangement 24 according to the embodiment of Figure 4 differs from the one illustrated in Figure 2 in that the main control valve 30 is substituted by a fourpositions hydraulic valve 130.
In a first or neutral position 130a, main control valve 130 may be configured to prevent fluid communication between source 6, tank 28 and the corresponding hydraulic actuator 3.
In a second position 130b, main control valve 130 may be configured to put source 25 in fluid communication with a first chamber of hydraulic actuator 22 via line 32 and tank 28 in fluid communication with a second chamber of hydraulic actuator 22 via line 33.
In a third position 130c, on the other hand, main control valve 130 may be configured to put source 25 in fluid communication with the second chamber of hydraulic actuator 22 via line 33 and tank 28 in fluid communication with the first chamber of hydraulic actuator 22 via line 32.
In addition, in a fourth position 130d, also called float position, valve 130 may be configured to fluidly isolate source 25 from hydraulic actuator 22 and put both chambers of hydraulic actuator 22 in fluid communication with tank 28.
Depending on the actuation of commands input means 44, electronic control unit 70 may be configured to control pressure reducing valves 42 and 43 in order to arrange main control valve 130 in its first 130a, second 130b or third position 130c.
In addition, in response to the actuation of commands input means 72, electronic control unit 70 may be configured to control pressure reducing valves 42 and 43 in order arrange main control valve 130 in its float position 130d.
Figure 5 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.
The hydraulic arrangement 24 according to the embodiment of Figure 5 differs from the one illustrated in Figure 2 in that main control valve 30 is replaced with a main control valve 130 similar to the one of the embodiment of Figure 4, not described again for brevity.
In addition, the hydraulic arrangement 24 according to the embodiment of Figure 5 differs from the one illustrated in Figure 2 in that the solenoid-controlled pressure reducing valves 42 are 43 replaced by hydraulically controlled pressure reducing valves 242 and 243.
With reference to the example illustrated in Figure 5, in addition, work machine 1 may comprise manually actuated commands input means 244, such as joysticks, levers, buttons, or portions of a touch-sensitive display, which are mechanically and/or hydraulically connected to pressure reducing valves 242 and 243, and are adapted to be handled/actuated by a work machine user to control operation of the same pressure reducing valves 242 and 243.
In particular, pressure reducing valves 242 and 243 are preferably normally closed and are adapted to open according to the actuation of commands input means 244, in order to provide to main control valve 130 a corresponding hydraulic pilot signal.
In addition, with reference to the embodiment illustrated in Figure 5, pilot line 46 preferably merges with hydraulic pilot line 40 upstream main control valve 130, at a merging point 47, and is operatively connected to main control valve 130.
Hydraulic pilot line 46 is preferably configured to carry a pressure signal to main control valve 130 adapted to arrange this latter in its fourth position 130d.
In other words, the hydraulic fluid flowing within hydraulic pilot line 46 is adapted to exert a pressure on main control valve 130 adapted to arrange this latter in its fourth position 130d.
With reference to the exemplary embodiment illustrated in Figure 5, pilot stage 37 is further provided with at least one valve 250 arranged along pilot line 40, downstream the corresponding pressure reducing valve 242.
Valve 250 is preferably a hydraulically controlled on off valve.
More in detail, valve 250 is a two-ports two-position valve and is operable between an open position 250a and a closed position 250b.
Pilot stage 37 preferably further comprises a pilot line 251, which branches off pilot line 46 and is connected to valve 250, in order to arrange this latter in its open position 50b.
In other words, the hydraulic fluid flowing within hydraulic pilot line 251 is adapted to exert a pressure on valve 250 adapted to arrange this latter in its closed position 250b.
In addition, valve 250 preferably further comprises biasing means 250c, such as a spring, adapted to maintain valve 250 in its open position 250a.

Claims

A work machine (1) comprising:
• a body (2) movable on the ground by means of ground resting means (3),

• a dozer blade (20) movably carried by the body (2),

• a hydraulic actuator (22), which is operatively interposed between the body (2) and the dozer blade (20), and is provided with a first inlet (22a) configured to receive pressurized hydraulic fluid in order to move the dozer blade (20) in a first direction and with a second inlet (22b) configured to receive pressurized hydraulic fluid in order to the dozer blade (20) in a second direction opposite to said first direction,

• a hydraulic arrangement (24) configured to provide pressurized hydraulic fluid towards the hydraulic actuator (22),
the hydraulic arrangement (24) comprising:
• a source of pressurized hydraulic fluid (25), which is configured to suck hydraulic fluid from a tank (28) and to provide at outlet a pressurized flow of the hydraulic fluid,

• at least one main control valve (30, 130), which is fluidly interposed between the source of pressurized hydraulic fluid (25) and the hydraulic actuator (22), and is configured to control the flow of pressurized hydraulic fluid fed towards the first inlet and/or the second inlet of the hydraulic actuator (22),

• a first supply line (32) fluidly connecting a first outlet of the main control valve (30, 130) with the first inlet (22a) of the hydraulic actuator (22),

• a second supply line (33) fluidly connecting a second outlet of the main control valve (30, 130) with the second inlet (22b) of the hydraulic actuator (22),

• a first check valve (35) arranged along said first supply line (32),

• a second check valve (36) arranged along said second supply line (33), and

• a pilot circuit (37), which is operatively connected to the main control valve (30) and is configured to actuate said main control valve (30),
said pilot circuit (37) further comprising a floating control stage (45), which is operatively connected to the main control valve (30, 130), to the first check valve (35) and to the second check valve (36), is configured to selectively arrange the main control valve (30, 130) in an operative position (30a, 130d) in which the main control valve (30, 130) fluidly isolates the source of pressurized hydraulic fluid (25) from the hydraulic actuator (22) and fluidly connects the first inlet (22a) and the second inlet (22b) of the hydraulic actuator (22) with the tank (28), and is configured to open the first check valve (35) and the second check valve (36).
Work machine according to claim 1, wherein the pilot circuit (37) comprises:
a first hydraulic pilot line (40) fluidly connecting the source of pressurized hydraulic fluid (25) with a first end of the main control valve (30, 130),

a second hydraulic pilot line (41) fluidly connecting the source of pressurized hydraulic fluid (25) with a second end of the main control valve (30, 130),

a first pressure reducing valve (42) arranged along the first hydraulic pilot line (40), and

a second pressure reducing valve (43) arranged along the second hydraulic pilot line (41).
Work machine according to claim 2, wherein the first check valve (35) and the second check valve (36) are pilot operated check valves,
the floating control stage (45) comprising a third hydraulic pilot line (46), which is fluidly connected to the source of pressurized hydraulic fluid (25) and to the pilot ports of the first check valve (35) and of the second check valve (36), and is adapted to selectively open the first check valve (35) and the second check valve (36).
Work machine according to claim 3, wherein the first hydraulic pilot line (46) branches off from the first hydraulic pilot line (40), downstream the first pressure reducing valve (42).
Work machine according to claim 3 or 4, wherein the floating control stage (45) comprises:
a first shuttle valve (54) provided with a first inlet fluidly connected to the first supply line (32), a second inlet fluidly connected to the third hydraulic pilot line (46) and with an outlet fluidly connected to the pilot port of the second check valve (36), and

a second shuttle valve (56) provided with a first inlet fluidly connected to the second supply line (33), a second inlet fluidly connected to the third hydraulic pilot line (46) and with an outlet fluidly connected to the pilot port of the first check valve (35).
Work machine according to claim 5, wherein:
the first shuttle valve (54) is configured to fluidly connect the pilot port of the second check valve (36) with the highest pressure between the third hydraulic pilot line (46) and the first supply line (32), and

the second shuttle valve (56) is configured to fluidly connect the pilot port of the first check valve (35) with the highest pressure between the third hydraulic pilot line (46) and the second supply line (33).
Work machine according to claim 5 or 6, wherein said first check valve (35) and said second check valve (36) comprise biasing means configured to maintain respectively the first check valve (35) and said second check valve (36) closed when the pressure of the hydraulic fluid at their inlets does not exceed a predetermined threshold.
Work machine according to any of claims 7, further an electronic control unit (70), which is electrically connected to said first pressure reducing valve (42) and to said second pressure reducing valve (43), and comprises elaboration means configured to control said first pressure reducing valve (42) and said second pressure reducing valve (43) in order to arrange said main control valve (30) in said operative position (30a) and to open said first check valve (35) and said second check valve (36).
Work machine according to claim 8, wherein said electronic control unit (70) is configured to selectively open said first pressure reducing valve (42) and said second pressure reducing valve (43) in order to pressurize said first hydraulic pilot line (40), said second hydraulic pilot line (41) and said third hydraulic pilot line (46) with a pilot pressure greater than said predetermined threshold, so as to arrange said main control valve (30, 130) in said operative position (30a, 130d) and to open said first check valve (35) and said second check valve (36).
A method for controlling a work vehicle realized according to claim 8 or 9, the method comprising the following steps:
a) receiving a command to arrange the main control valve (30, 130) in said operative position (30a, 130d) and to open the first check valve (35) and the second check valve (36), and

b) opening the first pressure reducing valve (42) and the second pressure reducing valve (43) in order to pressurize said first hydraulic pilot line (40), said second hydraulic pilot line (41) and said third hydraulic pilot line (46) with a pilot pressure greater than said predetermined threshold, so as to arrange said main control valve (30, 130) in said operative position (30a, 130d) and to open said first check valve (35) and said second check valve (36).