A hydraulic system, a closed-loop piston pump, and a bidirectional electro-proportional displacement control device.

Abstract

This invention discloses a hydraulic system, a closed-loop piston pump, and a bidirectional electro-proportional displacement control device. The bidirectional electro-proportional displacement control device includes a valve body containing an A-side electro-proportional control valve core and an A-side electro-proportional start-point adjusting spring, as well as a B-side electro-proportional control valve core and a B-side electro-proportional start-point adjusting spring. An A-side electromagnet and a B-side electromagnet are located outside the valve body. The outlet of the A-side electro-proportional control valve core is connected to the first side of the variable piston, and the inlet of the A-side electro-proportional control valve core is selectively connected to either the inlet or return oil flow. The outlet of the B-side electro-proportional control valve core is connected to the second side of the variable piston, and the inlet of the B-side electro-proportional control valve core is selectively connected to either the inlet or return oil flow. This bidirectional electro-proportional displacement control device ensures absolute reliability of the hydraulic neutral position in the closed-loop piston pump under conditions of component machining, wear, or slight jamming, solving the problem of hydraulic neutral position misalignment in the closed-loop piston pump causing self-propelled or automatic rotation of the main engine system.

Description

Technical Field

[0001] This invention relates to the field of piston pump technology, and particularly to a bidirectional electro-proportional displacement control device. It also relates to a closed-loop piston pump and a hydraulic system. Background Technology

[0002] With the electrification and intelligentization of the host control system, electro-proportional displacement control is a widely used variable control method for closed-loop piston pumps.

[0003] When the main unit is operating, the system program automatically adjusts the control current of the closed-loop piston pump according to the load pressure, thereby changing the output flow and controlling the movement speed of the main unit's travel, slewing, and other actions. When the closed-loop piston pump has no output flow requirement, the proportional control valve receives no control current input, and the closed-loop piston pump must be completely in a zero-displacement state, known as the hydraulic neutral position. Currently, the bidirectional electro-proportional displacement control of the closed-loop piston pump involves the integrated linkage of the proportional control valve core, feedback device, and variable displacement mechanism, which places very high demands on the machining of parts. The reliability of the hydraulic neutral position depends entirely on the level of parts machining, and during later use, wear, jamming, and other reasons may cause the hydraulic neutral position to shift, posing a significant safety hazard.

[0004] Therefore, how to provide a bidirectional electro-proportional displacement control device that can ensure the absolute reliability of the hydraulic neutral position of the bidirectional electro-proportional displacement control valve is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a bidirectional electro-proportional displacement control device that ensures absolute reliability of the hydraulic neutral position in a closed-loop piston pump under conditions of component machining, wear, or slight jamming, thus solving the problem of hydraulic neutral position misalignment in closed-loop piston pumps causing self-propelled or automatic rotation of the main unit system. Another purpose of this invention is to provide a closed-loop piston pump. A further purpose of this invention is to provide a hydraulic system.

[0006] To achieve the above objectives, the present invention provides a bidirectional electro-proportional displacement control device, comprising a valve body, wherein an A-side electro-proportional control valve core and a B-side electro-proportional control valve core are slidably disposed in the valve body, an A-side electromagnet and a B-side electromagnet are disposed outside the valve body, and an A-side electro-proportional starting point adjusting spring and a B-side electro-proportional starting point adjusting spring are respectively disposed on the outer side of the A-side electro-proportional control valve core and the B-side electro-proportional control valve core, respectively; the outlet of the A-side electro-proportional control valve core is connected to a first side of the variable piston, and the inlet of the A-side electro-proportional control valve core is used to selectively connect with oil inlet or oil return; the outlet of the B-side electro-proportional control valve core is connected to a second side of the variable piston, and the inlet of the B-side electro-proportional control valve core is used to selectively connect with oil inlet or oil return.

[0007] When the electromagnet on side A is energized, the proportional control valve core on side A moves and supplies oil to the variable piston. The variable piston moves in the closed piston pump to achieve a positive increase in the displacement of the closed piston pump.

[0008] When the electromagnet on side B is energized, the proportional control valve core on side B moves and supplies oil to the variable piston. The variable piston moves in the closed-loop piston pump to achieve a reverse increase in the displacement of the closed-loop piston pump.

[0009] Preferably, the inner sides of the A-side electro-proportional control valve core and the B-side electro-proportional control valve core are respectively provided with an A-side feedback spring and a B-side feedback spring, and a feedback rod is provided between the A-side feedback spring and the B-side feedback spring. The feedback rod is connected to the variable piston and is used to move with the variable piston and apply force to the A-side feedback spring or the B-side feedback spring.

[0010] Preferably, the A-side proportional starting point adjusting spring and the B-side proportional starting point adjusting spring are respectively installed in the A-side proportional starting point adjusting spring seat and the B-side proportional starting point adjusting spring seat used to adjust the initial elastic force.

[0011] Preferably, the A-side proportional starting point adjusting spring seat and the B-side proportional starting point adjusting spring seat are provided with conical surfaces, and the valve body is provided with A-side adjusting screw and B-side adjusting screw for adjusting the initial elastic force through the conical surfaces.

[0012] The present invention also provides a closed-loop piston pump, including the bidirectional electro-proportional displacement control device described above.

[0013] The present invention also provides a hydraulic system including the closed-loop piston pump described above.

[0014] Compared to the aforementioned background technology, the bidirectional electro-proportional displacement control device provided by this invention includes a valve body, in which an A-side electro-proportional control valve core and an electro-proportional control valve core are slidably disposed. The valve body also includes an A-side electro-proportional starting point adjusting spring and a B-side electro-proportional starting point adjusting spring, which are respectively located outside the A-side and B-side electro-proportional control valve cores. An A-side electromagnet and a B-side electromagnet are disposed outside the valve body. The outlet of the A-side electro-proportional control valve core is connected to the first side of the variable piston, and the inlet of the A-side electro-proportional control valve core is selectively connected to either the oil inlet or the oil return. The outlet of the B-side electro-proportional control valve core is connected to the second side of the variable piston, and the inlet of the B-side electro-proportional control valve core is selectively connected to either the oil inlet or the oil return. In specific operation, if neither the A-side nor the B-side electromagnet is energized, the electro-proportional control valve core does not move. The variable piston moves under the action of the spring, providing a stable effect. At this time, the electro-proportional control valve core is connected to the return oil, so that both sides of the variable piston are connected to the return oil, and the pressure on both sides is equal. The closed piston pump is in the hydraulic neutral position with zero displacement. If the electromagnet on side A or side B is energized, the electro-proportional control valve core is subjected to magnetic force and overcomes the elastic force of the spring. The electro-proportional control valve core moves and is connected to the inlet oil. At this time, the electro-proportional control valve core supplies oil to the variable piston. The variable piston moves due to the force of the pressure oil, which links the variable mechanism of the closed piston pump, thereby realizing the displacement of the closed piston pump gradually increasing from zero. This bidirectional electro-proportional displacement control device can ensure that the hydraulic neutral position of the closed piston pump is absolutely reliable under the conditions of part processing, wear, and slight jamming. It solves the problem of hydraulic neutral position deviation that often occurs in closed piston pumps, which causes the main system to move or rotate automatically. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the bidirectional electric proportional displacement control device provided in an embodiment of the present invention;

[0017] Figure 2 for Figure 1 Hydraulic schematic diagram of a bidirectional electro-proportional displacement control device;

[0018] Figure 3 The current-displacement curve is provided for an embodiment of the present invention.

[0019] in:

[0020] 1-Closed-loop piston pump; 2-Variable displacement piston; 3-A-side electromagnet; 4-A-side electro-proportional control valve core; 5-A-side electro-proportional start-up adjusting spring; 6-A-side feedback spring; 7-B-side feedback spring; 8-B-side electro-proportional start-up adjusting spring; 9-B-side electro-proportional control valve core; 10-B-side electromagnet; 11-Feedback rod; 12-A-side electro-proportional start-up adjusting spring seat; 13-A-side sealing lock nut; 14-A-side adjusting screw; 15-A-side feedback spring seat; 16-Valve body; 17-B-side feedback spring seat; 18-B-side electro-proportional start-up adjusting spring seat; 19-B-side sealing lock nut; 20-B-side adjusting screw. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Please refer to Figures 1 to 3 ,in, Figure 1 This is a schematic diagram of the bidirectional electric proportional displacement control device provided in an embodiment of the present invention. Figure 2 for Figure 1 Hydraulic schematic diagram of the bidirectional electro-proportional displacement control device. Figure 3 This is a current-displacement curve provided in an embodiment of the present invention; side A and side B in the figure are two opposing sides, X1 and X2 are the two sides of the variable piston 2, respectively, P S For oil inlet, the remaining undescribed markings are not improvements to this invention or affect the core content of this invention.

[0024] In a first specific embodiment, the bidirectional electro-proportional displacement control device provided by the present invention is a control valve structure, including a valve body 16. A pair of electro-proportional control valve cores and a pair of electro-proportional starting adjustment springs are installed in the valve body 16. The electro-proportional starting adjustment springs are connected to the electro-proportional control valve cores. The electro-proportional control valve cores can slide in the valve body 16. A pair of electromagnets are provided outside the valve body 16. Before energization, the electro-proportional control valve cores remain fixed to control the hydraulic neutral position absolutely reliably. After energization, the electro-proportional control valve cores move to control the increase of oil discharge.

[0025] Specifically, the two opposing sides of the valve body 16 are side A and side B, which are described in detail with side A and side B as the left and right directions of the valve body 16. The pair of electromagnets includes side A electromagnet 3 and side B electromagnet 10 respectively located on side A and side B. The pair of electro-proportional control valve cores includes side A electro-proportional control valve core 4 and side B electro-proportional control valve core 9 respectively located on side A and side B. The pair of electro-proportional start-up adjusting springs includes side A electro-proportional start-up adjusting spring 5 and side B electro-proportional start-up adjusting spring 8 respectively located on side A and side B.

[0026] In addition, the A-side electro-proportional control valve core 4 has two adjustment positions: left and right. In the right position, the outlet of the A-side electro-proportional control valve core 4 is connected to the first side of the variable piston 2 (e.g., X1), and the inlet of the A-side electro-proportional control valve core 4 is connected to the return oil. In the left position, the outlet of the A-side electro-proportional control valve core 4 is connected to the first side of the variable piston 2, and the inlet of the A-side electro-proportional control valve core 4 is connected to the inlet oil (e.g., P). S Similarly, the B-side electro-proportional control valve core 9 also has two adjustment positions: left and right. In the left position, the outlet of the B-side electro-proportional control valve core 9 is connected to the second side of the variable piston 2 (e.g., X2), and the inlet of the B-side electro-proportional control valve core 9 is connected to the return oil. In the right position, the outlet of the B-side electro-proportional control valve core 9 is connected to the second side of the variable piston 2, and the inlet of the B-side electro-proportional control valve core 9 is connected to the inlet oil (e.g., P). S Connected.

[0027] When electromagnet 3 on side A is energized, the input current is slowly increased. The proportional control valve core 4 on side A experiences a rightward thrust from electromagnet 3 and a leftward elastic force from the proportional control starting spring 5 on side A. When the thrust exceeds the leftward elastic force, the proportional control valve core 4 on side A moves to the right. When the current is sufficiently large, the proportional control valve core 4 on side A switches from the right position to the left position, connecting P... S When the pressure oil is supplied to the X1 side of the variable piston 2, the variable piston 2 is compressed by the pressure oil, causing it to move to the left. This triggers the variable mechanism of the closed-loop piston pump 1, and the displacement gradually increases from zero. Throughout the entire variable control process, the B-side electro-proportional control valve core 9 remains in the left position due to the action of the B-side electro-proportional starting point adjusting spring 8, and the X2 side of the variable piston 2 is always in communication with the return oil.

[0028] When electromagnet 10 on side B is energized, the proportional control valve core 9 on side B moves and connects the X2 side of variable piston 2 with P. S The pressure oil is supplied to the inlet, while the X1 side of the variable piston 2 is always connected to the return oil. Similar to the above process, the difference is that the increase in displacement of the closed piston pump 1 is a reverse increase, which will not be elaborated here.

[0029] In this embodiment, when neither the electromagnet 3 on side A nor the electromagnet 10 on side B is energized, the electro-proportional starting point adjusting spring 5 on side A ensures that the electro-proportional control valve core 4 on side A is in the right position, and the electro-proportional starting point adjusting spring 8 on side B ensures that the electro-proportional control valve core 9 on side B is in the left position. The pressure on both sides of the variable piston 2 is equal, and the closed-loop piston pump 1 is in the zero displacement position with no flow output. This ensures that the hydraulic neutral position of the closed-loop piston pump 1 is absolutely reliable even if there is wear or slight jamming due to parts processing, wear, or slight jamming. This solves the problem of hydraulic neutral position deviation of the closed-loop piston pump 1 causing the main system to self-walk or automatically rotate.

[0030] Furthermore, the elastic coefficients of the A-side proportional starting adjustment spring 5 and the B-side proportional starting adjustment spring 8 are relatively large, which can effectively prevent the A-side proportional control valve core 4 and the B-side proportional control valve core 9 from jamming. In the variable process, it can also significantly reduce the overshoot and shorten the response time.

[0031] Based on this, a feedback spring is also provided inside the electro-proportional control valve core. One side of the feedback spring is connected to the electro-proportional control valve core, and the other side is connected to the feedback rod 11. The feedback rod 11 is connected to the variable piston 2 and moves together with the variable piston 2.

[0032] Specifically, the feedback spring includes an A-side feedback spring 6 and a B-side feedback spring 7, which are respectively located inside the A-side electro-proportional control valve core 4 and the B-side electro-proportional control valve core 9. The feedback rod 11 is located between the A-side feedback spring 6 and the B-side feedback spring 7. The feedback rod 11 moves with the variable piston 2 and applies force to the A-side feedback spring 6 or the B-side feedback spring 7.

[0033] In this embodiment, the feedback spring 6 on side A and the electro-proportional starting point adjusting spring 5 on side A are located on both sides of the electro-proportional control valve core 4 on side A, respectively. The feedback spring 6 and the electro-proportional starting point adjusting spring 5 on side A together provide the holding force to maintain the position when no power is applied, ensuring that the hydraulic neutral position is absolutely reliable; they also provide the elastic force when power is applied. Similarly, the situation on side B is similar to that on side A, and will not be described again here.

[0034] When either side A or side B is energized, the proportional control valve core on the corresponding side needs to overcome the combined force of the proportional starting adjustment spring and the feedback spring simultaneously. For example, when the electromagnet 3 on side A is energized, the proportional control valve core 4 on side A is subjected to the rightward thrust of the electromagnet 3 on side A, the leftward elastic force of the proportional starting adjustment spring 5 on side A, and the leftward elastic force of the feedback spring 6 on side A. When the rightward thrust F3 of the electromagnet 3 on side A is greater than the resultant force of the leftward elastic force F5 of the proportional starting adjustment spring 5 on side A and the leftward elastic force F6 of the feedback spring 6 on side A, the proportional control valve core 4 on side A moves to the right until the current is large enough, at which point the proportional control valve core 4 on side A switches from the right position to the left position.

[0035] In this embodiment, communication PS Pressure oil is supplied to the X1 side of the variable piston 2. The variable piston 2 is subjected to the force of the pressure oil, which compresses the spring in the variable piston 2 and moves to the left. This links the variable mechanism of the closed-loop piston pump 1, and the displacement gradually increases from zero. When the variable piston 2 moves to the left, it drives the feedback rod 11 to move to the left. The feedback spring 6 on the A side is compressed under the action of the feedback rod 11, and the elastic force of the feedback spring 6 on the A side increases until the force on the electro-proportional control valve core 4 on the A side is balanced. The electro-proportional control valve core 4 on the A side switches back and forth between the left and right positions to ensure that the electromagnet 3 on the A side has a fixed rightward thrust when there is a certain input current. The displacement of the feedback rod 11 provides the elastic force of the feedback spring 6 on the A side to the left, ensuring the linear change of current I and displacement Vg. During the entire variable control process, the electro-proportional control valve core 9 on the B side is always in the left position due to the action of the electro-proportional starting adjustment spring 8 on the B side and the feedback spring 7 on the B side. The X2 side of the variable piston 2 is always in communication with the return oil.

[0036] Similarly, when the electromagnet 10 on side B is energized, the corresponding electro-proportional control valve core 9 on side B, the electro-proportional starting point adjusting spring 8 on side B, the feedback spring 7 on side B, and the feedback rod 11 will perform the opposite action to that when the electromagnet 3 on side A is energized, so as to ensure that when the electromagnet 10 on side B is energized, the closed plunger pump 1 has a reverse variable, and the current I is linearly related to the displacement Vg.

[0037] In addition, the A-side proportional starting point adjustment spring 5 and the B-side proportional starting point adjustment spring 8 are respectively installed on the A-side proportional starting point adjustment spring seat 12 and the B-side proportional starting point adjustment spring seat 18 used to adjust the initial elastic force.

[0038] In this embodiment, the variable piston 2 is assembled inside the closed-loop piston pump 1. Since oil needs to be sealed at both ends of the variable piston 2, the sealing parts have a certain damping effect on the reciprocating motion of the variable piston 2. Moreover, the damping is different when the reciprocating motion of the variable piston 2 is used for bidirectional displacement control. Different damping corresponds to different variable pressures. The variable pressure is directly related to the displacement of the electro-proportional control valve core. The displacement of the electro-proportional control valve core directly depends on the input current of the electromagnet. Therefore, the current required for the left and right electro-proportional displacement control corresponding to the same displacement output is different, which will cause interference to the electrical parameter calibration during the debugging of the host system and fail to meet the current requirements of the host system for the bidirectional electro-proportional displacement control of the closed-loop piston pump 1.

[0039] For better technical performance, the A-side proportional starting point adjusting spring seat 12 and the B-side proportional starting point adjusting spring seat 18 are provided with conical surfaces. The valve body 16 is provided with an A-side adjusting screw 14 and a B-side adjusting screw 20 for adjusting the initial elastic force through the conical surfaces. The A-side adjusting screw 14 is locked and fixed by the A-side sealing lock nut 13, and the B-side adjusting screw 20 is locked and fixed by the B-side sealing lock nut 19.

[0040] In this embodiment, the initial spring force of the electric proportional displacement control start point on side A or side B can be adjusted to make the electric proportional displacement control start points on side A or side B close to or even completely consistent.

[0041] When the measured current of the A-side proportional displacement control starting point is lower than the current value required by the host system, the A-side adjusting screw 14 can be adjusted downwards. Through the conical surface of the adjusting screw 14, the A-side proportional starting point adjusting spring seat 12 is pushed to the left, compressing the A-side proportional starting point adjusting spring 5 and increasing the initial elastic force of the A-side proportional starting point adjusting spring 5, thereby increasing the A-side proportional control starting current to the same current value required by the host system.

[0042] When the measured current at the starting point of the proportional displacement control on side A is higher than the current value required by the host system, the adjusting screw 14 on side A can be adjusted upwards. The adjusting spring 5 on side A pushes the adjusting spring seat 12 on side A to move to the right until it contacts the adjusting screw 14 on side A. The adjusting spring 5 on side A extends, reducing the initial elastic force of the adjusting spring 5 on side A, thereby reducing the starting current of the proportional control on side A to the same current value required by the host system.

[0043] Similarly, the method for adjusting the starting current of the proportional control on side B is exactly the same as that on side A, and will not be repeated here.

[0044] In addition, the A-side feedback spring 6 is installed on the A-side feedback spring seat 15, and the B-side feedback spring 7 is installed on the B-side feedback spring seat 17.

[0045] In existing technologies, if the starting current of bidirectional proportional displacement control is not adjustable, and the starting currents on side A and side B are inconsistent, the host system can only resolve this through hardware adjustments and differences in program programming, which is very difficult for the host system. In this embodiment, such as Figure 3 As shown, the measured starting current of the proportional displacement control on side A or side B is within the starting adjustment range, but the starting currents are different and cannot meet the requirements of the host. The host actually requires the starting currents on both sides A and B to be consistent, as shown in the figure. Through the above adjustment process, the starting currents of the proportional displacement control on side A or side B can be made completely consistent, thus better meeting the requirements of the host.

[0046] The present invention also provides a closed-loop piston pump 1, including the above-mentioned bidirectional electro-proportional displacement control device, which not only ensures the hydraulic neutral position safety and reliability of the closed-loop piston pump 1, but also has an adjustable starting current for bidirectional electro-proportional displacement control. It should have all the beneficial effects of the above-mentioned bidirectional electro-proportional displacement control device, which will not be elaborated here.

[0047] The present invention also provides a hydraulic system including the above-mentioned closed-loop piston pump 1, which should have all the beneficial effects of the above-mentioned closed-loop piston pump 1 and the bidirectional electro-proportional displacement control device, which will not be described in detail here.

[0048] It should be noted that in this specification, relational terms such as first and second are used only to distinguish one entity from several other entities, and do not necessarily require or imply any such actual relationship or order between these entities.

[0049] The hydraulic system, closed-loop piston pump, and bidirectional electro-proportional displacement control device provided by this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A bidirectional electric proportional displacement control device, characterized in that, The valve body (16) includes an A-side electro-proportional control valve core (4) and a B-side electro-proportional control valve core (9) which are slidably disposed in the valve body (16). An A-side electromagnet (3) and a B-side electromagnet (10) are disposed outside the valve body (16). An A-side electro-proportional starting point adjusting spring (5) and a B-side electro-proportional starting point adjusting spring (8) are respectively disposed on the outer side of the A-side electro-proportional control valve core (4) and the B-side electro-proportional control valve core (9). The outlet of the A-side electro-proportional control valve core (4) is connected to the first side of the variable piston (2). The inlet of the A-side electro-proportional control valve core (4) is used to selectively connect with the oil inlet or the oil return. The outlet of the B-side electro-proportional control valve core (9) is connected to the second side of the variable piston (2). The inlet of the B-side electro-proportional control valve core (9) is used to selectively connect with the oil inlet or the oil return. When the electromagnet (3) on side A is energized, the proportional control valve core (4) on side A moves and supplies oil to the variable piston (2). The variable piston (2) is used to move in the closed piston pump (1) to achieve a positive increase in the displacement of the closed piston pump (1). When the electromagnet (10) on side B is energized, the proportional control valve core (9) on side B moves and supplies oil to the variable piston (2). The variable piston (2) is used to move in the closed piston pump (1) to achieve a reverse increase in the displacement of the closed piston pump (1). The inner sides of the A-side electro-proportional control valve core (4) and the B-side electro-proportional control valve core (9) are respectively provided with an A-side feedback spring (6) and a B-side feedback spring (7). A feedback rod (11) is provided between the A-side feedback spring (6) and the B-side feedback spring (7). The feedback rod (11) is connected to the variable piston (2). The feedback rod (11) is used to move with the variable piston (2) and apply force to the A-side feedback spring (6) or the B-side feedback spring (7). The A-side proportional starting point adjustment spring (5) and the B-side proportional starting point adjustment spring (8) are respectively installed on the A-side proportional starting point adjustment spring seat (12) and the B-side proportional starting point adjustment spring seat (18) for adjusting the initial elastic force. The A-side proportional starting point adjusting spring seat (12) and the B-side proportional starting point adjusting spring seat (18) are provided with conical surfaces, and the valve body (16) is provided with an A-side adjusting screw (14) and a B-side adjusting screw (20) for adjusting the initial elastic force through the conical surfaces.

2. A closed-loop piston pump (1), characterized in that, Includes the bidirectional electric proportional displacement control device as described in claim 1.

3. A hydraulic system, characterized in that, Including the closed-loop piston pump (1) as described in claim 2.

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