Hydraulic directional control valve for the lifting mechanism of an agricultural vehicle

Abstract

Hydraulic directional control valve (10) with a pump port (P), a return port (R) and a first and a second working port (A; B), wherein the first and the second working port (A; B) can be connected to a hydraulic cylinder (30) of a lifting mechanism of a mobile working machine, in particular an agricultural vehicle, wherein the pump port (P) can be connected to a hydraulic pump (40), wherein in a first switching position (11) the pump connection (P), the return connection (R) and the first and second working connections (A; B) are blocked, wherein in a second switching position (12) the pump connection (P) is connected to the first working connection (A) and the return connection (R) is connected to the second working connection (B), wherein in a third switching position (13) the pump connection (P) is connected to the second working connection (B) and the return connection (R) is connected to the first working connection (A), wherein in a fourth switching position (14) the first and second working terminals (A, B) are connected to the return terminal (R), with the pump terminal (P) being blocked, wherein a sixth switching position (60) is provided in which the first working port (A) is connected to the return port (R), wherein the second working port (B) and the pump port (P) are blocked, wherein the third switching position (13) is an end position of the directional control valve (10), wherein the third and the sixth switching positions (13; 60) are arranged immediately adjacent, characterized in that an LS connection (LS) is provided which can be connected to the pressure regulator (44) of the hydraulic pump (40), wherein the LS connection (LS) is connected to the pump connection (P) in the second and third switching positions (12; 13), and wherein it is connected to the return connection (R) in the first, fourth and sixth switching positions (11; 14; 60), wherein the first switching position (11) is arranged immediately adjacent to the sixth switching position (60).

Description

[0001] The invention relates to a hydraulic directional control valve according to the preamble of claim 1.

[0002] US 6,971,453 B2 describes the hydraulic lifting mechanism of an agricultural vehicle. The lifting mechanism comprises two hydraulic cylinders for raising and lowering the lift. These are connected to the first and second working ports of a hydraulic directional control valve. The directional control valve also has a pump port connected to a hydraulic pump, which can deliver hydraulic fluid from a reservoir to the hydraulic cylinders. Furthermore, the directional control valve has a return port connected to the reservoir.

[0003] The hydraulic directional control valve is designed as a proportional valve and has four switching positions. In the first switching position, the pump connection, the return connection, and the first and second working connections are closed, so that the position of the lifting mechanism cannot be changed.

[0004] In the second switching position, the pump connection is connected to the first working connection and the return connection to the second working connection, so that the lifting mechanism is lowered, whereby the attached working device can be pressed against the ground.

[0005] In the third switching position, the pump connection is connected to the second working connection and the return connection to the first working connection, so that the lifting mechanism can be raised.

[0006] Furthermore, a fourth switching position is provided, which is designed as a free-running position; that is, the first and second working ports are connected to the return port, while the pump port is blocked. In this switching position, the lifting mechanism can be freely raised and lowered by external forces. This switching position is used when a working implement is attached to the lifting mechanism that is supported on the ground while the agricultural vehicle is moving, and is intended to follow its movement. The working implement could, for example, be a mower.

[0007] Furthermore, US 6,971,453 B2 features a separate switching valve that enables an additional switching state in which the first working port is connected to the reservoir. This switching valve is closed in the previously described switching positions of the directional control valve. In the aforementioned additional switching state, it is open, with the directional control valve in its second switching position. The hydraulic pump thus delivers fluid to the reservoir without a load, so no pressure builds up in the hydraulic cylinder. In this switching state, the lifting mechanism can only be lowered by the weight of the connected implement. This switching state is used, for example, to lower the lifting mechanism before moving it into the previously mentioned free-running position.

[0008] From DE 40 36 564 A1, a hydraulic device for controlling a working cylinder of a press is known. This device comprises a directional control valve with several switching positions, in particular a sixth switching position as defined in the present invention. A load-dependent pressure supply does not take place, therefore the directional control valve does not have a load-dependent connection to which the load pressure is applied in order to signal this to the pressure regulator of the hydraulic pump.

[0009] From DE 10 2005 005 314 A1, a valve arrangement for controlling a double-acting consumer is known. This includes a directional control valve with several switching positions, which has an LS connection. However, the sixth switching position within the meaning of the present invention is missing.

[0010] The object of the invention is to create a hydraulic directional control valve with which the lifting mechanism can be pressed against the ground with a defined maximum force without requiring pressurized fluid to be pumped. This function is to be implemented with minimal effort, thus keeping costs low. A tractor equipped with such a directional control valve operates particularly energy-efficiently.

[0011] According to the independent claim, a sixth switching position is provided in which the first working port is connected to the return port, while the second working port and the pump port are blocked. The object of the invention is, in particular, to enable load signaling in a particularly simple manner even in the sixth switching position.

[0012] The hydraulic valve is preferably part of a hydraulic drive system with which the lifting mechanism is moved, wherein the second working port is connected to a storage tank via a pressure relief valve.

[0013] As a result, the lift mechanism can be lowered until it rests on the ground. When the tractor is then set in motion, the lift mechanism is forced upwards due to the unevenness of the ground. This creates fluid pressure in the connecting line between the second working port and the lift mechanism's hydraulic cylinder, which is limited to a defined maximum value by the pressure relief valve. The hydraulic pump therefore does not need to circulate pressurized fluid to build up this pressure. The energy for pressure buildup is instead provided by the tractor's drive system. As soon as the lift mechanism moves downwards due to the uneven ground, the pressure in the connecting line drops, ensuring that the lift mechanism rests on the ground at least with its own weight.

[0014] The dependent claims specify advantageous further developments and improvements of the invention.

[0015] According to the invention, the third switching position is an end position of the directional control valve, with the third and sixth switching positions being arranged directly adjacent to each other. This arrangement of the aforementioned switching positions means that only a minimal change of one dimension is required on the known valve to implement the additional function mentioned above. This makes the directional control valve particularly cost-effective.

[0016] The range of motion over which the sixth switching position extends can be between 30% and 100% of the range of motion over which the third switching position extends.

[0017] A fifth switching position can be provided in which the return port is connected to the second working port, while the pump port and the first working port are closed. As a replacement for the separate switching valve, the directional control valve is equipped with a further, fifth switching position. In this fifth switching position, the pump port is closed. In contrast to the solution described above, the pump flow is not diverted to the storage tank via the directional control valve. The first working port is also closed. This design of the directional control valve eliminates the need for an additional switching valve.

[0018] The hydraulic directional control valve can have a linearly movable valve spool, during whose movement the switching positions change in sequence. - third switch position; - sixth gear position; - first switch position; - fifth gear position; - second switch position; and - the fourth switching position is traversed. With this embodiment, the hydraulic directional control valve can be implemented particularly simply. In contrast to the known directional control valve, only the position of a single fine control notch needs to be changed to achieve the sixth or fifth switching position. This is explained with reference to Fig. 3 explained in more detail.

[0019] According to the invention, a load-sensing (LS) port is provided on the hydraulic directional control valve, which can be connected to the pressure regulator of the hydraulic pump. In the second and third switching positions, the LS port is connected to the pump port, and in the first, fourth, and sixth switching positions, it is connected to the return port. Hydraulic lifting mechanism controls that operate according to the load-sensing principle are known from the prior art. In these controls, the load pressure acting on the hydraulic cylinder is fed back to the pressure regulator of the pump in order to regulate the pump pressure. This enables energy-saving operation of the hydraulic pump. The proposed solution also allows the application of the load-sensing principle in the fifth switching position according to the invention.

[0020] The directional control valve can be designed as a proportional valve, in which all fluid connections open and close continuously. This allows for precise control of the lifting mechanism, meaning that slow and fast movement speeds can be set with fine increments according to the operator's requirements.

[0021] The valve spool can pass through a first transition range between the second and fourth switching positions, in which the pump port is connected to the first working port, while the fluid connection from the first working port to the return port is blocked. The transition between the second and fourth switching positions requires several changes to the connection of the directional control valve ports. These connection changes can be implemented particularly easily by introducing the proposed transition range, which is only traversed briefly during operation and is essentially not used for motion control.

[0022] The valve spool can pass through a second transition range between the first transition range and the fourth switching position, in which the fluid connection from the return port to the first working port opens continuously. This measure also enables a simple implementation of the directional control valve.

[0023] The invention is explained in more detail below with reference to the accompanying drawings. It illustrates: Fig. 1 a hydraulic drive system with a hydraulic directional control valve according to a first embodiment according to the invention; Fig. 2 a second embodiment of the hydraulic directional control valve; Fig. 3 a diagram in which the opening cross-sectional area of ​​the different connecting paths of the directional control valve is plotted against the movement path of the valve spool.

[0024] Fig. Figure 1 shows a hydraulic drive system 1 with a hydraulic directional control valve 10 according to a first embodiment of the invention. The hydraulic cylinder 30 is, for example, a component of a (not shown) lifting mechanism of an agricultural vehicle, such as a tractor. By pressurizing the cylinder chamber 32 on the annular surface side, the lifting mechanism is lowered. The annular surface cylinder chamber 32 is connected to the first working port A of the directional control valve 10. By pressurizing the cylinder chamber 31 on the opposite piston base side, the lifting mechanism is raised. The piston base cylinder chamber 31 is connected to the second working port B of the directional control valve 10. The function of the piston base-side and annular surface-side cylinder chambers 31 and 32 can also be reversed.

[0025] The hydraulic cylinder 30 is driven by a hydraulic pump 40, which draws hydraulic fluid from a storage tank 43 and delivers it under pressure to the hydraulic cylinder 30. The hydraulic pump 40 is connected to the pump port P of the directional control valve 10. The corresponding flow is diverted into the storage tank 43. The return port R of the directional control valve 10 is also connected to the storage tank 43.

[0026] The directional control valve 10 is held in the first switching position 11 by the two return springs 20 acting in opposite directions. In the first switching position 11, the pump port P, the return port R, and the first and second working ports A and B are closed. The delivery flow of the hydraulic pump 40 with variable displacement is set to zero.

[0027] To set the third switching state 13, the valve spool is moved to the right by the first electromagnetic actuation 21, so that the pump port P is connected to the second working port B and the first working port A is connected to the return port R. This raises the lifting mechanism.

[0028] Between the first and third switching positions 11; 13, the sixth switching position 60 according to the invention is arranged. In this position, the first working port A is connected to the return port, while the second working port B and the pump port P are closed. The continuously adjustable directional control valve 10 therefore only needs to be switched to this intermediate position to perform its function according to the invention.

[0029] With the second electromagnetic actuation 22, the valve slide is moved to the left, successively entering the fifth 15, the second 12 and the fourth switching position 14.

[0030] In the fifth switching position 15, the pump connection P and the first working port A are closed, while the second working port B is connected to the return port R. The hydraulic fluid in the annular cylinder chamber 32 is pressurized by the weight of the implement attached to the lifting mechanism, and can flow in a controlled manner into the reservoir 43 via the opening cross-sectional area set in the directional control valve 10. The lifting mechanism thus lowers solely due to its own weight.

[0031] If the valve slide is now moved further into the second switching position 12, the pump connection P is connected to the first working connection A, so that the lifting mechanism with the working device can be pushed downwards with hydraulic force in addition to its own weight.

[0032] In the fourth switching position 14, the first and second working ports A and B are connected to the return port R, while the pump port P is blocked. In this switching position, the lifting mechanism can move freely due to external forces.

[0033] Furthermore, an LS port is provided on the directional control valve 10, which is connected to a pressure regulator 44, a hydraulic adjusting device 45, and a hydraulic pump 40 with adjustable displacement. In the second and third switching positions 12 and 13, in which the hydraulic cylinder 30 is to be moved by the fluid flow of the hydraulic pump 40, the pump port P of the directional control valve is connected to the LS port LS. The displacement volume of the hydraulic pump 40 is thus regulated according to the flow rate required at the hydraulic cylinder 30, so that no excess fluid flow needs to be diverted into the reservoir 43.

[0034] In the remaining switching positions one (11), four (14), five (15), and six (60), in which the hydraulic pump 40 does not drive the lifting mechanism, the LS port is connected to the return port R, so that the displacement volume of the hydraulic pump 40 is essentially reduced to zero. The hydraulic pump 40 therefore essentially pumps no hydraulic fluid and consequently requires very little drive power.

[0035] Fig. Figure 2 shows a second embodiment of the hydraulic directional control valve 10. This differs from the first embodiment only in that the LS port has been omitted. It is designed for a so-called open-center system, in which the hydraulic pump has a constant displacement volume, and in switching positions 11, 15, 14, and 60, where the pump port P is closed, the hydraulic pump's delivery flow is routed back to the reservoir 43 via a separate bypass valve. In the second embodiment, the energy losses are higher, but the cost of the hydraulic pump is lower than in the first embodiment.

[0036] Fig. Figure 3 shows a diagram in which the opening cross-sectional area Q of the various connection paths of the directional control valve is plotted against the movement path s of the valve spool. The fluid connections to the LS port are not shown, as only very small volume flows occur here, making the design of the corresponding switching transitions less critical.

[0037] The horizontal plane represents the displacement s of the valve spool. The vertical plane represents the opening cross-sectional area Q of the corresponding fluid connection. The origin of the coordinate system corresponds to the position of the valve spool, which is held in place by the two return springs (No. 20; Fig. 1; Fig. 2) is discontinued.

[0038] The first switching position 11 is located in the region of the origin. In the first switching position 11, all fluid connections are essentially completely closed. Volume flows occur only due to unavoidable leakage.

[0039] When the valve spool is moved towards the third switching position 13, the fluid connection AR from the first working port to the return port opens, while the second working port and the pump port are closed. This is the sixth switching position 60 according to the invention. At the end of the sixth switching position 60, the fluid connection from the PB pump port to the second working port is continuously opened, so that the third switching position 13 is reached. The third switching position 13 is maintained until the valve spool reaches the first end stop 63. The third switching position 13 is therefore an end position of the valve spool. The travel 62 of the valve spool over which the sixth switching position extends is, for example, 50% of the travel 61 of the valve spool over which the third switching position 13 extends. The two travel distances 61 and 62 together amount to, for example, 3 mm.

[0040] The opening cross-sectional area of ​​fluid connection AR is always larger than the opening cross-sectional area of ​​fluid connection PB, so that the hydraulic fluid flowing back into the reservoir is subject to a slight back pressure in the third switching position 13. Even before the valve spool reaches the first end stop 63, fluid connection AR is fully open, while the opening cross-sectional area of ​​fluid connection PB continues to increase steadily until it reaches the first end stop 63.

[0041] The graphs of the two connections PB and AR show a fine control range 51 with a lower slope, which serves for the sensitive movement of the lifting mechanism. The remaining range with a higher slope was introduced to allow large volume flows to be set even with small changes in the valve travel s. Consequently, the total valve travel and thus the size of the directional control valve can be kept small.

[0042] When the valve spool is moved from the first switching position 11 to the fifth switching position 15, the fluid connection BR from the second working port to the return port opens first. This point marks the beginning of the fifth switching position 15. A fine control range 52 with a low slope is also provided here. When the end of the fine control range 52 of the fluid connection BR is reached, the fluid connection PA from the pump port to the first working port also opens. This point marks the beginning of the second switching position 12.

[0043] If the valve spool is moved further towards the second end stop 64, the fluid connection BR reaches its maximum opening cross-sectional area, which remains constantly open until the second end stop 64. Shortly after the fluid connection BR reaches its maximum opening cross-sectional area, the fluid connection PA also reaches its maximum opening cross-sectional area 50, which then decreases back to zero as the valve spool continues to move. The maximum opening cross-sectional area 50 of the fluid connection PA is smaller than the maximum opening cross-sectional area of ​​the fluid connection BR, so that the hydraulic fluid flowing back to the reservoir is also subject to a slight back pressure here.

[0044] The maximum cross-sectional area 50 of the fluid connection PA's opening marks the end of the second switching position 12. Preferably, however, the second switching position 12 ends somewhat earlier. The first transition zone 16, which begins here, extends to the point where the fluid connection PA is completely closed. This is followed by a second transition zone 17, in which the fluid connection AR opens rapidly but continuously from the first working port to the return port to a maximum cross-sectional area. The maximum cross-sectional areas of the fluid connections AR and BR are equal. At this point, the fourth switching position 14 begins, in which the cross-sectional areas of the fluid connections AR and BR remain constant.

[0045] It should be noted that the first and second transition areas 16; 17 are only traversed briefly during operation of the directional control valve. Reference symbol list P Pump connection R return connection A first work connection B second work connection LS LS connection PA fluid connection from pump connection to first working connection PB Fluid connection from pump connection to second working connection AR fluid connection from the first working port to the storage tank BR fluid connection from the second working port to the storage tank Q Opening cross-sectional area s movement path of the valve slide 1 hydraulic drive system 10 hydraulic directional control valve 11 first switching position 12 second switch position 13 third switch position 14 fourth switching position 15 fifth switch position 16 first transition area 17 second transition area 20 Return spring 21 first electromagnetic actuation 22 second electromagnetic actuation 30 hydraulic cylinders 31 piston-side cylinder chamber 32 ring-face-side cylinder space 40 Hydraulic pump 41 Pump line 42 Pressure relief valve 43 Storage tank 44 pressure regulators 45 Adjustment device 50 Maximum of the opening cross-sectional area of ​​the fluid connection PA 51 Fine control range 52 Fine control range 60 sixth shift position 61 Movement path over which the third switching position extends 62 Movement path over which the sixth switching position extends 63 first end stop 64 second end stop

Claims

[1] Hydraulic directional control valve (10) with a pump port (P), a return port (R) and a first and a second working port (A; B), wherein the first and the second working port (A; B) can be connected to a hydraulic cylinder (30) of a lifting mechanism of a mobile working machine, in particular an agricultural vehicle, wherein the pump port (P) can be connected to a hydraulic pump (40), wherein in a first switching position (11) the pump connection (P), the return connection (R) and the first and second working connections (A; B) are blocked, wherein in a second switching position (12) the pump connection (P) is connected to the first working connection (A) and the return connection (R) is connected to the second working connection (B), wherein in a third switching position (13) the pump connection (P) is connected to the second working connection (B) and the return connection (R) is connected to the first working connection (A), wherein in a fourth switching position (14) the first and second working terminals (A, B) are connected to the return terminal (R), with the pump terminal (P) being blocked, wherein a sixth switching position (60) is provided in which the first working port (A) is connected to the return port (R), wherein the second working port (B) and the pump port (P) are blocked, wherein the third switching position (13) is an end position of the directional control valve (10), wherein the third and the sixth switching positions (13; 60) are arranged immediately adjacent, characterized by, that an LS connection (LS) is provided which can be connected to the pressure regulator (44) of the hydraulic pump (40), wherein the LS connection (LS) is connected to the pump connection (P) in the second and third switching positions (12; 13), and wherein it is connected to the return connection (R) in the first, fourth and sixth switching positions (11; 14; 60), wherein the first switching position (11) is located immediately adjacent to the sixth switching position (60). [2] Hydraulic directional control valve according to claim 1, characterized by , that the movement path (62) over which the sixth switching position (60) extends is between 30% and 100% of the movement path (61) over which the third switching position (13) extends. [3] Hydraulic directional control valve according to one of the preceding claims, characterized by, that a fifth switching position (15) is provided in which the return port (R) is connected to the second working port (B), with the pump port (P) and the first working port (A) being blocked. [4] Hydraulic directional control valve according to claim 3, characterized by , that the hydraulic directional control valve (10) has a linearly movable valve spool, during whose movement the switching positions (11-15) in the sequence - third switch position (13); - sixth gear position (60); - first switch position (11); - fifth switch position (15); - second switch position (12); and - fourth switching position (14) will be traversed. [5] Hydraulic directional control valve according to one of the preceding claims, characterized by , that the directional control valve (10) is designed as a proportional valve in which all fluid connections (PA, PB; AR; BR) continuously open and close. [6] Hydraulic directional control valve according to claim 5, characterized by , that the valve slide passes through a first transition area (16) between the second and fourth switching positions (12; 14) in which the pump port (P) is connected to the first working port (A), with the fluid connection (AR) from the first working port (A) to the return port (R) being blocked. [7] Hydraulic drive system with a directional control valve according to one of the preceding claims, characterized by , that the second working port (B) is connected to a storage tank (43) via a pressure relief valve (42). [8] Hydraulic directional control valve according to claim 7, characterized by , that the valve slide passes through a second transition area (17) between the first transition area (16) and the fourth switching position (14), in which the fluid connection (AR) from the return port (R) to the first working port (A) opens continuously.

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