EP3786461A1

EP3786461A1 - Directional valve for a work vehicle and related hydraulic arrangement

Info

Publication number: EP3786461A1
Application number: EP20193827.1A
Authority: EP
Inventors: Peter Arbeithuber; Franz Haider
Original assignee: CNH Industrial Italia SpA
Current assignee: CNH Industrial Italia SpA
Priority date: 2019-09-02
Filing date: 2020-09-01
Publication date: 2021-03-03
Also published as: IT201900015363A1

Abstract

Directional valve (12) for a hydraulic arrangement (1) of a work vehicle for controlling the operation of a double acting cylinder (2) comprising a piston chamber (6a) and a rod chamber (6b), such directional valve (12) comprising a first port (12a) fluidly connectable to an output of a load sensing hydraulic supply system (10), a second port (12b) fluidly connectable to a reservoir (11), a third port (12c) fluidly connectable to said hydraulic supply system (10) to carry a load sensing signal configured to control the operation of this latter, a fourth and fifth ports (12d, 12e) fluidly connectable to respectively piston and rod chambers (6a, 6b), such valve (12) being configured to allow the generation of an appropriate load sensing signal in both a lowering and lifting operational condition of the cylinder (2).

Description

TECHNICAL FIELD

The present invention concerns a directional valve, in particular a directional valve for a hydraulic cylinder of a work vehicle.

BACKGROUND OF THE INVENTION

Work vehicles are usually provided with implements actuated by hydraulic cylinders; an example may be found in a front loader that carries a bucket lifted by a boom that is actuated by a hydraulic cylinder.
Figure 1 discloses a known hydraulic arrangement 1' for managing the lifting or lowering of a double acting cylinder 2' .
Briefly, such known hydraulic arrangement 1' comprises a load sensing pump 3' and a directional valve 4', fluidly interposed between the load sensing pump 3', the hydraulic cylinder 2' and a discharge 5'.
In synthesis, directional valve 4' is configured to assume different position to allow a lowering, a lifting or a neutral stationary condition of the hydraulic cylinder 2'. Such positions may be assumed in function of a mechanical or electronic input given by the user of the work vehicle which needs to use the implement actuated by cylinder 2'.
In lifting condition, pump 3' is configured to pump pressurized fluid towards piston chamber of cylinder 2' thereby lifting a load carried by the housing of the cylinder 2'and, at the same time, generating a load sensing signal x' which is proportional to the fluid sent to cylinder 2'. Such load sensing signal x' is fluidly connected to pump 3', thereby controlling its operation.
In neutral condition, pump 3', discharge 5' and cylinder 2' are isolated one with respect to the other. Accordingly, the position of cylinder 2' is fixed as also the pressure of the fluid in both rod and piston chambers of this latter, thereby guarantee a correct support and stiffness of the cylinder 2'.
In lowering condition, valve 4' make communicate fluidly discharge 5' with piston chamber from which, thanks to the action on the load on cylinder 2', fluid flow out. Also in this case pump 3' can supply with pressurized fluid rod chamber of cylinder 2', however load sensing signal x" is very low and accordingly pump 3' is not controlled to supply fluid; therefore the movement of cylinder 2' is passive and actuated only by gravity acting on load M.
In view of the above, cavitation may arise in rod chamber of cylinder 2' thereby decreasing quality of cylinder 2' and, during use, filling rod chamber with air. Furthermore, such passive movement is low and cannot be actively hydraulically controlled.
Therefore, the need is felt to provide a directional valve and a related hydraulic arrangement comprising such directional valve for controlling a hydraulic cylinder of a work vehicle that solve the above problems.
An aim of the present invention is to satisfy the above mentioned needs in an economic and optimized way.

SUMMARY OF THE INVENTION

The aforementioned aim is reached by a directional valve and a related hydraulic circuit 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 a schematic representation of a hydraulic circuit as known in the prior art;
Figure 2 is a schematic representation of a hydraulic circuit comprising a directional valve according to the invention; and
Figure 3 is an enlarged schematic representation of the directional valve according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 2 shows a hydraulic arrangement 1 for controlling the operation of an active cylinder 2 suitable for handling of a load M.
In particular, cylinder 2 is a standard double acting differential hydraulic cylinder comprising a body 3 defining a volume suitable for housing a piston 4 configured to slide in tight manner inside such volume and connected to a rod 5 configured to pass through body 3 in tight manner.
According to the exemplarily disclosed embodiment, an extremity of rod 5 with respect to piston 4 is fixed to a portion of a work vehicle (not shown) while piston 4 subdivides the volume defined by body 3 in a piston chamber 6a and a rod chamber 6b. Piston chamber 6a if fluidly connectable via a conduit 7a and a related hose 8 to a piston conduit 9a of hydraulic arrangement 1 and, similarly, rod chamber 6b is fluidly connectable to this latter via a conduit 7b and a related hose 8 to a rod conduit 9b.
According to the above-defined arrangement, when a fluid enters into piston chamber 6a, body 3 is pushed against mass M in order to lift said mass while when a fluid enters into rod chamber 6b, body 3 is pushed concordantly with gravity of mass M, lowering this latter.
Hydraulic arrangement 1 further comprises a pump 10 preferably a load sensing pump configured to suck fluid, e.g. oil, from a reservoir 11, increase its pressure and provide a pressurized fluid as output. Such pump 10 is connectable to both piston and rod conduits 9a, 9b mentioned above as defined in the following.
Hydraulic arrangement 1 further comprises a directional valve 12 according to the present invention fluidly interposed between cylinder 2 and pump 10. In particular, hydraulic cylinder 2 comprises a send conduit 13 fluidly connecting an output of pump 10 with a first port 12a of directional valve 12 and a return conduit 14 fluidly connecting directional a second port 12b of valve 12 with reservoir 11. Moreover, a directional third port 12c of valve 12 is fluidly connect to pump 10 via a conduit 15 carrying a load sensing signal configured to control pump 10. Furthermore, a fourth and fifth ports 12d, 12e of directional valve 12 is fluidly connected to piston and rod conduits 9a, 9b mentioned above.
Directional valve 12 is configured to allow a lifting, a lowering, a neutral and a closed operational configuration by connecting in different manners piston and rod conduits 9a, 9b with send and return conduits 13, 14. In particular, the above mentioned operational conditions may be set thanks to actuators means 16 configured to move directional valve 12. In the described embodiment, such actuator means 16 are mechanical means and preferably acts against elastic means 17 configured to maintain directional valve in the neutral operational configuration. Accordingly, directional valve is a five ways - four positions valve.
Hydraulic arrangement may further comprise a non return valve 18 fluidly interposed on send conduit 13 upstream with respect to directional valve 11, so as to allow passage only from pump 10 towards cylinder 2 and not vice versa.
Always preferably and optionally, hydraulic arrangement 1 may comprise a pressure compensator module 20, provided with a narrowing 21 and proportional ON-OFF valve 22 fluidly interposed in series upstream with the non-return valve 18. Such pressure compensation module is per se known and therefore is not described for sake of brevity.
Making reference to enlarged view of directional valve 12 of figure 3, said valve may assume a first position I, i.e. rest neutral position wherein load signal conduit 15 is connected to return conduit 14, i.e. to reservoir 11. Accordingly, pump 10 does not provide any pressurized flow to cylinder 2 and piston and rod chambers 6a, 6b and pump 2 output are isolated. Accordingly, load M is maintained at a pre-set position since body 3 cannot be moved with respect to work vehicle. Indeed, pressure in piston and rod chambers 6a, 6b defines a stiffness of support given by cylinder 2 to mass M.
In a second position II, send conduit 13 is fluidly connected to piston conduit 9a and a portion X' of such fluid is spilled to load sensing conduit 15, while rod conduit 9b is fluidly connected to return conduit 14. Accordingly, pump 10 can provide pressurized fluid to piston chamber 6a thereby moving body 3 and decreasing volume of rod chamber 6b. Fluid from such chamber may flow out via conduits 9b, 14. In parallel, the load sensing signal given by portion X' is collected by conduit 15 and sent to pump 10 which is controlled consequently.
In a third position III, which is according to the present invention, send conduit 13 is fluidly connected to rod conduit 9b, while return conduit 14 is fluidly connected to piston conduit 9a; according to the invention, respective fluid portions X", X''' are spilled from both the fluid connection between conduits 9b and 13 and the fluid connection between conduits 9a, 14. Such fluid portions are fluidly directed to a selection module 25, for example comprising a shuttle valve, configured to allow the passage of fluid to load sensing signal conduit 15 only to the portion X", X''' having the greater pressure.
In a fourth position IV, send conduit 13 is open while both piston and rod conduits 9a, 9b and load sensing conduit 15 are fluidly connected to return conduit 14. Accordingly, pump 10 cannot provide pressurized fluid to cylinder 2, which is totally vent out to reservoir 11.
The operation of the above described directional valve 12 and related hydraulic arrangement 1 is the following.
As said, in first position IV of directional valve 12 send conduit 13 is open and all other conduits 9a, 9b, 15 are connected to return conduit 14 to reservoir and cylinder 2 is empty.
In neutral condition, i.e. first position I, all conduits 9a, 9b and 15 are isolated while load sensing signal 15 is sent via conduit 14 to reservoir 11 and accordingly level of cylinder 2 is maintained with the stiffness defined by the pressure ratio between piston and road chambers 6a, 6b.
In a lifting condition, i.e. second position II, fluid will flow from send conduit 13 towards piston conduit 9a to piston chamber 6a, thereby lifting body 3 and mass M accordingly. Operation of valve 10 is controlled by load sensing signal x' spilled to conduit 15 from the fluid flowing between conduits 9a and 13.
In a lowering condition, i.e. third position III, fluid will flow from piston conduit 9a, i.e. flowing out from piston chamber 9a under load acted by mass M, towards return conduit 14 and, in parallel, pump 10 may send pressurized fluid to rod chamber 6b via fluid connection between send conduit 13 and rod conduit 9b. Fluid is spilled from both fluid connection between rod conduits 9b and send conduit 13 (X") and connection between piston conduit 9a and return conduit 14 (X'''). Such spilled fluid portions X", X''' then pass to selection module 25, e.g. to a shuttle valve, in which the one with greatest pressure will pass to pump 10 as loading sensing signal. In this way, a sufficient load sensing signal is always sent to pump 10 which can provide pressurized flow to rod chamber 6b, thereby avoiding cavitation and assuring a fast lowering of load M.
In view of the foregoing, the advantages of a directional valve 12 and a related hydraulic arrangement 1 according to the invention are apparent.
The proposed directional valve 12 allows to provide always a sufficient load sensing signal to control pump 10 thereby pressurizing road chamber 6b and avoiding cavitation.
Accordingly, the work quality of cylinder 2 is improved and the formation of air inside the volume of this latter is decreased.
Moreover, the proposed solution of a selection module as shuttle valve is economic and compact thereby allowing the use of the directional valve 12 according to the present invention in already existing hydraulic arrangements.
It is clear that modifications can be made to the described a directional valve 12 and a related hydraulic arrangement 1 which do not extend beyond the scope of protection defined by the claims.
For example, pressure compensation module 20 may be optional, such as the non-return valve 18. Furthermore, the pump 10 may be substituted by a hydraulic supply system of any known typology.
Moreover, neutral position is optional and, accordingly, the present invention may apply to 5/3 way valves as known in the art.
In addition, fixation of cylinder 2 elements to work vehicle may be realized in specular or different way.
Again, selection module 25 may comprise elements having the same function of the described shuttle valve.

Claims

Directional valve (12) for a hydraulic arrangement (1) of a work vehicle for controlling the operation of a double acting cylinder (2) comprising a piston chamber (6a) and a rod chamber (6b), such directional valve (12) comprising a first port (12a) fluidly connectable to an output of a load sensing hydraulic supply system (10), a second port (12b) fluidly connectable to a reservoir (11), a third port (12c) fluidly connectable to said hydraulic supply system (10) to carry a load sensing signal configured to control the operation of said supply system (10), a fourth and fifth ports (12d, 12e) fluidly connectable to respectively said piston and rod chambers (6a, 6b), said valve being configured to assume at least:
- a first operational position (II) in which said first port (12a) is fluidly connected to said fourth port (12d) and said fifth (12e) port is fluidly connected to said second port (12b), in parallel, a portion (X') of fluid passing through said first and fourth ports (12a, 12d) is spilled to generate a load sensing signal sent through said third port (12c) to said hydraulic supply system (10); and

- a second operational position (III) in which said first port (12a) is fluidly connected to said fifth port (12e) and said fourth port (12d) is fluidly connected to said second port (12b), in parallel, a portion (X") of fluid passing through said first and fifth ports (12a, 12e) is spilled and a portion (X''') of fluid passing through said second and fourth ports (12b, 12d) is spilled, such fluid spilled portions (X", X''') being fluidly connected to a selection module (25) configured to allow the passage towards said third port (12c) to the greatest between such spilled portions (X", X"') as load sensing signal for said hydraulic supply system (10) .
Directional valve according to claim 1, wherein said selection module (25) comprising a shuttle valve.
Directional valve according to claim 1 or 2, further comprising a third operational position (I) in which said first, fourth and fifth ports (12a, 12d, 12e) are not connected to any other among said ports of said valve (12) and in which said second and third ports (12b, 12c) are fluidly connected to each other.
Directional valve according to any of the preceding claims, further comprising a fourth operational position (IV) in which said second, third, fourth and fifth ports (12b, 12c, 12d, 12e) are fluidly connected to each other and in which said first port (12a) is not connected to any other among said ports.
Directional valve according to any of the preceding claims, comprising actuator means (16) configured to move said valve (12) to select one between said operational positions (I, II, III, IV).
Directional valve according to claim 5, wherein said actuator means (16) comprise mechanical actuator means.
Directional valve according to claim 5 or 6, further comprising elastic means (17) configured to impart a force to said valve (12) opposed to the action of said actuator means (16) and configured to maintain said valve (12) in a pre-set operational position.
Hydraulic arrangement (1) for controlling the operation of a double acting cylinder (2) comprising a piston chamber (6a) and a rod chamber (6b), said arrangement (1) further comprising a reservoir (11) and a load sensing hydraulic supply system (10) configured to suck fluid from said reservoir (11), pressurize and send this latter towards said cylinder (2), said hydraulic arrangement (1) further comprising a directional valve (12) according to any of the preceding claims fluidly interposed between said hydraulic supply system (10), said reservoir (11) and said piston and rod chambers (6a, 6b).
Hydraulic arrangement according to claim 8, further comprising a non-return valve (18) fluidly interposed between the output of said hydraulic supply system (10) and said directional valve (12).
Hydraulic arrangement according to claim 9, further comprising a pressure compensator module (20) fluidly interposed between the output of said hydraulic supply system (10) and said directional valve (12), upstream with respect to said non-return valve (18).
Hydraulic arrangement according to claim 10, wherein said pressure compensator module (20) comprises a narrowing (21) and a proportional valve (22) fluidly in series one with respect to the other.
Hydraulic arrangement according to any of claims 8 to 11, wherein said cylinder (2) comprises a body (3) defining a volume housing a piston (4) carried by a rod (5) passing through said body (3), said piston (4) subdividing such volume into said piston and rod chambers (6a, 6b), said rod (5) being fixed to a portion of a work vehicle.