Hydraulic system and grass cutter

Abstract

To provide a hydraulic system which can easily prevent oil leakage from a hydraulic motor used in an operation mode of two-way rotation with switching of normal rotation and reverse rotation, and to provide a grass cutter including the hydraulic system.SOLUTION: A hydraulic system is divided into a primary side and a secondary side and has, at the secondary side, a hydraulic motor 16 including a motor internal oil seal 14, two main duct lines 17, 18, and motor drain duct lines with check valves which connect the uppermost stream side of the main duct lines with the interior of the motor, and a coupling 4 serving as a shaft joint for the hydraulic motor 16. The hydraulic system further has, at the primary side, a directional control valve which switches flow directions of the main duct lines 17, 18. The hydraulic system includes: a housing 1 which incorporates the coupling 4 and is circumscribed with the hydraulic motor 16; a housing internal oil seal 13 which achieves higher pressure-resistance than the motor internal oil seal 14 as a function for preventing oil leakage around an output shaft 5 connected to the coupling 4; and a coupling drain duct line 20 which allows the inside of the housing 1 between the motor internal oil seal 14 and the housing internal oil seal 13 to communicate with the outside.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hydraulic device and a grass mower, and more particularly to a hydraulic device that easily prevents oil leakage from a hydraulic motor that repeatedly rotates forward and backward, and a grass mower equipped with the same. [Background technology]

[0002] Generally, hydraulic equipment having a hydraulic motor is often used for heavy machinery. The hydraulic circuit of a hydraulic equipment having a hydraulic motor is divided into a primary side and a secondary side. The secondary side has a hydraulic motor, two main lines for feeding and discharging oil to and from the hydraulic motor, and a secondary side motor drain line for discharging oil from the hydraulic motor. The two main lines may be equipped with a pressure or flow control unit. On the other hand, the primary side has a tank, a hydraulic pump for pressurizing and sending out oil from the tank, a pressurized line for passing oil from the hydraulic pump, a return line for passing oil returning to the tank, and a primary side motor drain line. The primary side further has a directional control valve for switching the connection paths between the pressurized line and the return line and each of the two main lines, making one of the two main lines the pressurized side and the other the return side. Typically, the primary side is installed on the main body of the heavy equipment, and the secondary side is installed on the heavy equipment's ancillary equipment. In order to make it easier to separate and connect the two when transporting the heavy equipment, the secondary side pipeline and the corresponding primary side pipeline are connected detachably with a quick coupler-type connecting fitting with a check valve.

[0003] In such a hydraulic device, Patent Document 1 focuses on the fact that an accidental connection failure between the secondary motor drain line and the primary motor drain line causes the pressure of the discharged oil trapped on the secondary side to rise during operation of the heavy equipment, leading to malfunction of the hydraulic motor. As a countermeasure to this, Patent Document 1 proposes providing a line for releasing a portion of the discharged oil from the secondary motor drain line. Patent Documents 2 and 3 also propose providing a line for releasing a portion of the discharged oil in a similar manner.

[0004] In contrast, there are known hydraulic systems that do not have a primary motor drain line. An example of such a system is shown in Figure 3.

[0005] As shown in FIG. 3, the secondary side includes a hydraulic motor 16, two main lines 17 and 18 for feeding hydraulic oil to and from the hydraulic motor 16, and a motor drain line 19 for draining oil from the hydraulic motor 16. The two main lines 17 and 18 are provided with, as pressure or flow control units, for example, a counterbalance valve 22, a brake valve 23, and a pressure-compensated flow control valve 24, in this order from the hydraulic motor 16, which is the most downstream side, to the upstream side. The motor drain line 19 branches into two motor drain lines 19A and 19B on the outlet side of the hydraulic motor 16, and these two motor drain lines 19A and 19B are connected to the two main lines 17 and 18 via check valves 19a and 19b, respectively. In a hydraulic device that does not have a primary motor drain line, the primary motor drain lines 19A and 19B are not directly connected to the secondary side in this way.

[0006] On the other hand, the primary side has a tank 27, a hydraulic pump 26 for pressurizing and sending out oil in the tank 27, a pressurized line 10 for passing oil from the hydraulic pump 26, and a return line 11 for passing oil returning to the tank 27. The primary side further has a directional control valve 25 for switching the connection paths between the pressurized line 10 and the return line 11 and the two main lines 17, 18, respectively, so that one of the two main lines 17, 18 is the pressurized side and the other is the return side. In other words, the directional control valve 25 switches the flow direction of the main lines 17, 18. Thus, in a hydraulic device without a primary side motor drain line, there is no primary side motor drain line directly connected to the secondary side motor drain lines 19A, 19B on the primary side.

[0007] Normally, the primary side is installed on the main body of the heavy equipment, and the secondary side is installed on the auxiliary equipment of the heavy equipment. To facilitate the separation and connection of the two when transporting the heavy equipment, the two main lines on the secondary side and the corresponding lines on the primary side (pressurized line and return line) are sometimes detachably connected with quick coupler-type connecting fittings (not shown) with check valves. If there is a connection problem with the connecting fittings of these main lines, the hydraulic motor will not operate, so the hydraulic motor will not be damaged.

[0008] In the hydraulic system described above that does not have a primary motor drain line, a pressure increase in the discharged oil does not occur during operation of the heavy equipment due to a connection failure between the primary and secondary motor drain lines. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Utility Model Application Publication No. 64-014901 [Patent Document 2] Japanese Patent Application Publication No. 08-105375 [Patent Document 3] JP 2001-289201 A Summary of the Invention [Problem to be solved by the invention]

[0010] The above-mentioned hydraulic device without a primary motor drain line is often applied to, for example, a lawnmower and used in a bidirectional rotation operation mode including forward and reverse rotation switching, which is an operation mode advantageous in terms of work efficiency. However, at this time, the load on the hydraulic motor may become excessive, causing oil leakage around the shaft of the hydraulic motor. When such oil leakage occurs, the hydraulic motor is used in a unidirectional rotation operation mode that does not include forward and reverse rotation switching to prevent the load on the hydraulic motor from becoming excessive and avoid oil leakage, which causes a problem of reduced work efficiency. One possible measure to prevent such oil leakage is to increase the pressure resistance of the oil seal built into the hydraulic motor, but this requires significant modification of the hydraulic motor, which increases the equipment costs.

[0011] In view of the above problems, the present invention aims to provide a hydraulic device that can easily prevent oil leakage from a hydraulic motor used in a bidirectional rotation operation mode including switching between forward and reverse rotation, for a hydraulic device that does not have a primary motor drain line. Another object of the present invention is to provide a grass mower equipped with this hydraulic device. [Means for solving the problem]

[0012] The inventors conducted intensive research to solve the above problems, and as a result, they came up with the idea of ​​providing an oil reservoir in a coupling (shaft joint) for a hydraulic motor and providing a pipeline to drain the oil in this oil reservoir. After further research, they developed the present invention.

[0013] That is, the present invention is as follows. [1] A hydraulic system having a primary side and a secondary side, the secondary side including a hydraulic motor (16) having an in-motor oil seal (14), two main lines (17, 18), and motor drain lines (19A, 19B) with check valves (19a, 19b) connecting the most upstream sides of the main lines (17, 18) to the inside of the motor, and a coupling (4) which is a shaft joint for the hydraulic motor (16), and the primary side including a directional control valve (25) for switching the flow direction of the main lines (17, 18), a housing (1) incorporating the coupling (4) and externally contacting the hydraulic motor (16); a housing oil seal (13) having a higher pressure resistance than the motor oil seal (14) for preventing oil leakage around an output shaft (5) connected to the coupling (4); a coupling drain line (20) for connecting the inside of the housing (1) between the motor oil seal (14) and the housing oil seal (13) with the outside. [2] The hydraulic device according to [1], further comprising two coupling drain lines (20A, 20B) branching off from the coupling drain line (20) and connecting to the most upstream sides of the main lines (17, 18) via check valves (20a, 20b), respectively. [3] A grass mower comprising the hydraulic device described in [1] or [2] above. [4] The grass mower according to [3] above, characterized in that the grass mower is detachably attached to the tip of the arm of a power shovel. Effect of the Invention

[0014] According to the present invention, in a hydraulic device that does not have a motor drain line on the primary side, oil leakage can be easily prevented without modifying a ready-made hydraulic motor used in a bidirectional rotation operation mode including switching between forward and reverse rotation. Therefore, it is possible to achieve the excellent effect of improving work efficiency by using the bidirectional rotation operation mode while preventing environmental pollution. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing a main part of an example of a hydraulic device according to the present invention; [Diagram 2] 1 is a hydraulic circuit diagram showing an example of a hydraulic device of the present invention. [Diagram 3] FIG. 1 is a hydraulic circuit diagram showing an example of a hydraulic device in which a primary side motor drain line is not present. [Figure 4] 1 is a schematic overall view showing an example of a power shovel equipped with a grass mower according to the present invention. [Diagram 5] FIG. 5 is an enlarged view of the mower of FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the hydraulic device of the present invention (hereinafter also referred to as "the device of the present invention") and a grass cutter will be described with reference to the drawings. Figures 1 and 2 show an example of the device of the present invention. As shown in these figures, the device of the present invention is divided into a primary side and a secondary side (Figure 2).

[0017] The secondary side has a hydraulic motor 16 (Figs. 1 and 2) and a coupling 4 (Fig. 1) which is a shaft joint of the hydraulic motor 16. The hydraulic motor 16 is equipped with an internal motor oil seal 14 (Fig. 1) that prevents oil leakage from around the motor shaft 3, and two main lines 17 and 18 (Figs. 1 and 2). The hydraulic motor 16 further has motor drain lines 19A and 19B (Figs. 1 and 2) equipped with check valves 19a and 19b that connect the most upstream sides of the main lines 17 and 18 to the inside of the motor.

[0018] The primary side has a directional control valve 25 (FIG. 2) that switches the flow direction of the main lines 17, 18. In the drawings, the same reference symbols indicate the same members.

[0019] The primary side directional control valve 25 (the two pipes downstream of it) and the secondary side main lines 17, 18 are connected by connecting members (connecting fittings, hydraulic piping, hydraulic hoses, or a combination of these (not shown)).

[0020] The device of the present invention further comprises a housing 1 incorporating the coupling 4 and circumscribing the hydraulic motor 16, and an in-housing oil seal 13 (Fig. 1) having a higher pressure resistance than the in-motor oil seal 14 for preventing oil leakage around the output shaft 5 connected to the coupling 4. The device of the present invention further comprises a coupling drain pipe 20 (Figs. 1 and 2) which connects the inside of the housing 1 between the in-motor oil seal 14 and the in-housing oil seal 13 with the outside.

[0021] The counterbalance valve 22, the brake valve 23 and the pressure compensated flow rate control valve 24 (FIG. 2) are incorporated in a valve unit 30 (FIG. 1).

[0022] As a result, oil leaking from the motor oil seal 14 remains inside the housing 1 between the motor oil seal 14 and the housing oil seal 13, and will not leak out to the outside unless the housing 1 is filled with oil and overflows.

[0023] Here, the housing 1 is provided with a bearing and a bearing retainer on its inside, and is in contact with the hydraulic motor 16 via a flange. The area inside the housing 1 and on the inner surface side of the flange, excluding the overlapping parts of the coupling 4, the bearing, the bearing retainer, and the motor shaft 3, becomes an oil reservoir for retaining the leaked oil. Note that in Figure 1, hatching indicating a cross section is applied to the periphery of the oil reservoir, and is omitted in other parts. FIG. 1 shows an example in which a pulley for rotating a grass cutting blade (see FIG. 5) is attached to the tip of the output shaft 5.

[0024] [Pressure resistance of oil seal inside housing, etc.] Here, if the pressure resistance of the oil seal in the housing 13 is equal to or lower than the pressure resistance of the oil seal in the motor 14, oil will leak from the oil seal in the housing 13 when a pressure rise occurs inside the housing 1 to the same extent as inside the motor. To prevent this, the pressure resistance of the oil seal in the housing 13 must be greater than the pressure resistance of the oil seal in the motor 14. Usually, the pressure resistance of the oil seal in the motor 14 is set to 0.03 MPa, which is within a range in which leakage does not occur in the operation mode of unidirectional rotation. On the other hand, in the operation mode of bidirectional rotation, the pressure inside the motor rises rapidly to nearly 10 times the steady state before and after switching between forward and reverse rotation during the non-steady state. For this reason, it is preferable that the pressure resistance of the oil seal in the housing 13 is 0.3 MPa or more. Since the pressure inside the motor during the non-steady state does not rise to more than 2.0 MPa, the pressure resistance of the oil seal in the housing 13 is more preferably 0.3 to 2.0 MPa. The oil seal has a hollow shape, and the material therefor is not particularly limited, but in terms of strength and elasticity, an elastomer is preferable.

[0025] In addition, with regard to the oil seal 13 inside the housing, from the standpoint of sealing performance and durability, it is preferable that the outer circumferential side of the seal be held in place by metal so that the outer circumferential side of the seal is the fixed side with the inner circumferential surface of the housing 1 and the inner circumferential side of the seal is the sliding side with the outer circumferential surface of the output shaft 5.

[0026] [Coupling drain line] If the inside of the housing 1 is closed, oil leaking from inside the motor will gradually be added to the oil filled inside the housing 1, resulting in excess oil, which may result in excessive pressure inside the housing 1 and lead to damage to the housing 1. Therefore, it is necessary to provide a coupling drain pipe 20 that connects the inside of the housing 1 to the outside in order to release the excess oil to the outside. In the example of Figure 1, the coupling drain pipe 20 is a through hole that connects the inner side and outer side of the flange.

[0027] Here, the following method can be given as an example of a method for recovering the excess oil spilling out of the coupling drain pipe 20 without leaking it. That is, a cock (not shown) is fixed to the open end (see FIG. 1) of the coupling drain pipe 20, and a transparent container (not shown) for recovering oil is detachably attached to the cock. Then, the cock is opened to store the excess oil in the container, and when the amount of stored oil is visually nearly full, the cock is closed and the container containing the oil is replaced with an empty container.

[0028] [Connection between coupling drain line and main line] The above-mentioned method using a transparent container for oil recovery involves manual work such as replacing the container and recovering the oil from the container. In contrast, in the device of the present invention, as shown in FIG. 2, it is preferable to provide two coupling drain lines 20A and 20B that branch off from the coupling drain line 20 and connect to the most upstream sides of the main lines 17 and 18 via check valves 20a and 20b, respectively. According to this, when the main line 17 is the pressurized side and the main line 18 is the return side in the directional control valve 25, the excess oil in the coupling drain line 20A is at a lower pressure than the internal pressure of the main line 17, so that it is prevented from entering the main line 17. However, the excess oil in the coupling drain line 20B is at a pressure higher than the internal pressure of the main line 18, so it enters the main line 18 and returns to the tank 27 via the return line 11. Conversely, when the directional control valve 25 sets the main line 17 as the return side and the main line 18 as the pressurized side, the excess oil in the coupling drain 20B has a lower pressure than the internal pressure of the main line 18 and is therefore prevented from entering the main line 18. However, the excess oil in the coupling drain 20A has a pressure higher than the internal pressure of the main line 17 and enters the main line 17, and returns to the tank 27 via the return line 11.

[0029] In this way, by providing two coupling drain pipes 20A, 20B, excess oil in the coupling drain pipe 20 can be automatically collected in the tank 27 without leakage and can be reused.

[0030] [Grass mower equipped with the device of the present invention] A mower equipped with the device of the present invention (hereinafter also referred to as the "mower of the present invention") is driven by a hydraulic motor, and is therefore preferably detachably attached to the tip of the arm of a hydraulic construction machine, such as a power shovel. An example is shown in Figs. 4 and 5. Fig. 4 is an overall view of the power shovel, and Fig. 5 is an enlarged view of the mower. As shown in Fig. 4, the mower is attached to the tip of the arm of the power shovel and is detachable. Part A on the crawler side indicates the location where the primary components (tank, etc.) of the device of the present invention are installed. Part B in the mower shown in Fig. 5 indicates the location where the secondary components (hydraulic motor, etc.) of the device of the present invention are installed. The primary side (part A) and secondary side (part B) of the device of the present invention are connected by a connecting member (not shown) arranged along the arm.

[0031] According to the grass cutter of the present invention, the operation mode of bidirectional rotation, including switching between forward and reverse rotation of the grass cutter blade, allows for efficient grass cutting work without environmental pollution due to oil leakage.

[0032] Here, the reason why the bidirectional rotation operation mode can perform grass cutting work more efficiently than the unidirectional rotation operation mode will be qualitatively explained below.

[0033] Conventional grass cutters are driven by a hydraulic device as shown in FIG. 3. As mentioned above, the hydraulic device as shown in FIG. 3 is forced to be used in a one-way rotation operation mode because oil leakage occurs when switching between forward and reverse rotation. In the one-way rotation operation mode, if a long and thin object such as ivy or a string gets tangled in the grass cutter blade (hereinafter also simply referred to as the "blade"), the worker has no choice but to get off the driver's seat and remove it by hand, which causes a time loss by stopping the heavy equipment (and the grass cutter). Also, in the one-way rotation operation mode, the direction in which the cut grass flies is determined by the rotation direction of the blade. Therefore, if there is a road or a house in the direction in which the grass flies, the only way to prevent the grass from flying in that direction is to stop the grass cutter and change the direction of the heavy equipment, which causes a time loss.

[0034] In contrast, the mower of the present invention can automatically untangle long grass that has become tangled in the blades by switching between forward and reverse rotation in the bidirectional rotation operation mode. It can also change the direction in which the cut grass flies on the spot. Therefore, there is no time loss caused by stopping heavy machinery or changing its direction as in the past. EXAMPLES

[0035] The hydraulic system shown in Figures 1 and 2 was applied to the grass cutter shown in Figures 4 and 5 as an example of the present invention. The oil seal 14 inside the motor was made of an elastomer with a pressure resistance of 0.03 MPa. The oil seal 13 inside the housing was made of an elastomer with a pressure resistance of 1 MPa, and was held in place by metal so that the outer periphery of the seal was the fixing side with the inner periphery of the housing 1 and the inner periphery of the seal was the sliding side with the outer periphery of the output shaft 5. The hydraulic system shown in FIG. 3 was applied to a grass cutter having the same specifications as the example of the present invention, which served as a comparative example.

[0036] Oil leakage was visually confirmed during mowing work in bidirectional rotation mode using the mower of the comparative example. In a similar working environment (condition of overgrowth of grass to be cut, working area, etc.) to that at the time, mowing work was performed using the mower of the present invention in bidirectional rotation mode at the same rotation speed as in the comparative example. As a result, oil leakage was not visually confirmed, and no time loss as described above occurred.

[0037] In addition, when the comparative example mower was used in a similar working environment as described above to perform mowing work in a unidirectional rotation operating mode at the same rotation speed as in the bidirectional rotation mode, no oil leakage was visible, but the time loss described above occurred. [Explanation of symbols]

[0038] 1. Housing 3 Motor shaft 4 Couplings (shaft joints) 5 Output shaft 10 Pressurized Pipeline 11 Return pipe 13 Housing oil seal 14 Motor oil seal 16 Hydraulic motor 17, 18 Main pipeline 19, 19A, 19B Motor drain line 19a, 19b Check valves for motor drain lines 19A, 19B 20, 20A, 20B Coupling drain line 20a, 20b Check valves for coupling drain lines 20A, 20B 22 Counterbalance valve 23 Brake valve 24 Pressure compensated flow control valve 25 Directional control valve 30 Valve unit

Claims

1. A hydraulic system having a primary side and a secondary side, the secondary side including a hydraulic motor (16) having an in-motor oil seal (14), two main lines (17, 18), and motor drain lines (19A, 19B) with check valves (19a, 19b) connecting the most upstream sides of the main lines (17, 18) to the inside of the motor, and a coupling (4) which is a shaft joint for the hydraulic motor (16), and the primary side including a directional control valve (25) which switches the flow direction of the main lines (17, 18), a housing (1) incorporating the coupling (4) and externally contacting the hydraulic motor (16); an oil seal (13) in the housing having a higher pressure resistance than the oil seal (14) in the motor for preventing oil leakage around the output shaft (5) connected to the coupling (4); a coupling drain line (20) for connecting the inside of the housing (1) between the motor oil seal (14) and the housing oil seal (13) with the outside.

2. The hydraulic device according to claim 1, further comprising two coupling drain lines (20A, 20B) branching off from the coupling drain line (20) and connecting to the most upstream sides of the main lines (17, 18) via check valves (20a, 20b), respectively.

3. A grass mower comprising the hydraulic device according to claim 1 or 2.

4. 4. The grass mower according to claim 3, wherein the grass mower is detachably attached to the tip of an arm of a power shovel.

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