JP2012172687A - Drain circuit protection device in tractor removable type working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent any further hydraulic pressure rise of a tank circuit and a drain circuit, and to protect the drain circuit of a hydraulic motor by automatically closing (shutting off) a hydraulic pressure feed circuit.SOLUTION: A shutoff valve 31 is disposed in a hydraulic pressure supply circuit 22 from a tractor to hydraulic motors 16a, 16b via a coupler P. A hydraulic pressure sensitive shutoff spool 31a to be operated by the hydraulic pressure when the hydraulic pressure of the tank circuit 24b exceeds the predetermined value is disposed in that tank circuit 24b returning from the hydraulic motor to the tractor via a coupler T. The shutoff valve 31 is closed by the operation of the shutoff spool 31a having a hydraulic pressure sensitive member.

Description

  The present invention relates to a drain circuit protection device in a tractor detachable work machine, and more particularly to a protection circuit that prevents an abnormal increase in drain circuit pressure of a work machine equipped with a hydraulic motor.

  In general, a hitch for detachably connecting a work machine is provided as standard equipment at the rear of the tractor. A dedicated work machine or general-purpose work machine specialized for various kinds of work such as mowing work, harvesting work, and fertilization work is detachably connected to the hitch as necessary. FIG. 8 shows a state in which the mower 10 that is a dedicated work machine is connected to the tractor 11, and the mower 10 is connected to the tractor 11 via the first work arm 12 and the second work arm 13. Connected to the rear hitch 14. A base portion of the first work arm 12 is pin-coupled to a connecting portion 15 detachably connected to the rear hitch 14 so as to be able to swing horizontally and swing up and down. Two work arms 13 are pin-coupled. The mower 10 is swingably supported at the tip of the second work arm 13. The mower 10 is of a tandem type and is equipped with two hydraulic motors 16a and 16b, and a pair of mowing blades are rotated by the operation of the hydraulic motors 16a and 16b (in a single type mower, One motor and one mowing blade). The first work arm 12 can be fixed at a desired horizontal turning position by inserting and removing a fixing pin provided in the connecting portion 15. In addition, the above working machines are well-known, For example, it is disclosed by patent document 1. FIG.

  A first cylinder 17 and a second cylinder 18 are respectively attached to the first work arm 12 and the second work arm 13. The first working arm 12 and the second working arm 13 are swung by the expansion and contraction operation of the first and second cylinders 17 and 18. The first cylinder 17, the second cylinder 18 and the hydraulic motors 16 a and 16 b are operated by a common hydraulic pressure from a hydraulic pump mounted on the tractor 11. This is performed by the arranged valve unit 21.

  As shown in FIG. 11, the valve unit 21 includes an on-off valve 21a that supplies and stops hydraulic pressure to the hydraulic motors 16a and 16b, and first and second valves that supply and stop hydraulic pressure to the first and second cylinders 17 and 18. It comprises an operation valve 21b, 21c and a unit housing 21d that houses these three valves 21a, 21b, 21c. FIG. 11 is a hydraulic circuit diagram in which the on-off valve 21a and the operation valves 21b and 21c are in a neutral state. All the valves 21a, 21b, and 21c are unified with a 6-port 3-position direction control valve (electromagnetic operation, spring return type) for cost reduction. The open / close valve 21a is used as a two-position switching valve, and one electromagnetic solenoid is turned on to switch from the neutral stop position to the supply position. In addition, the first and second operation valves 21b and 21c turn on only one of the electromagnetic solenoids to extend the first and second cylinders 17 and 18 and turn on only the opposite electromagnetic solenoid. By doing so, the first and second cylinders 17 and 18 are shortened.

  In order to prevent unexpected expansion and contraction of the first and second cylinders 17 and 18 due to hydraulic circuit disconnection, etc., the two ports on the rod side and head side of the first and second cylinders 17 and 18 Pilot pressure introduction type check valves 17a and 18a are attached. When hydraulic pressure is supplied to one of the ports of the first and second cylinders 17 and 18, the hydraulic pressure is used as a pilot pressure to open the check valve of the other port, and supply hydraulic oil to the one port. Corresponding to the amount of expansion / contraction of the first and second cylinders 17 and 18, hydraulic oil is discharged from the other port to the tank circuit side.

JP-A-11-9008

  The valve unit 21 includes three couplers P, T, and N connected to a hydraulic hose. The coupler P is arranged at the most upstream end of the hydraulic pressure supply circuit 22 of the valve unit 21, and the coupler N is arranged at the most downstream end of the neutral hydraulic oil return circuit 23 of the on-off valve 21a. A coupler T is disposed at the most downstream end of the tank circuit 24b of the hydraulic motors 16a and 16b, the opening / closing valve 21a, and the operation valves 21b and 21c. In FIG. 11, the portion where the hydraulic pressure of the hydraulic pressure supply circuit 22 following the coupler P is continuous is given “light ink” for easy understanding.

  When the mower 10 is connected to the tractor 11, the connecting portion 15 is connected to, for example, the rear hitch 14, and the three couplers P, T, and N are connected to the corresponding three couplers on the tractor 11 side. At this time, the two couplers P and N are connected, but forgetting to connect the coupler T, or even if the coupler T is intended to be connected, the connection is poor, and the hydraulic motors 16a and 16b are operated in that state. The opening / closing valve 21a may be opened.

  When the open / close valve 21a is opened when the coupler T is not connected or poorly connected, the hydraulic pressure supplied from the coupler P through the hydraulic pressure supply circuit 22 is supplied to the hydraulic motors 16a and 16b via the open / close valve 21a. But then you lose your destination.

  That is, because the coupler T is not connected or is poorly connected, the hydraulic oil that leaves the hydraulic motors 16a and 16b and returns to the oil tank on the tractor 11 side through the tank circuit 24b cannot return to normal.

  For this reason, the hydraulic pressure of the tank circuit 24b increases abnormally, and the pressure of the drain circuit 24a of the hydraulic motors 16a and 16b also increases simultaneously. This increased drain circuit pressure may damage the shaft seals of the hydraulic motors 16a, 16b. If the shaft seal is damaged, hydraulic oil leaks from the shaft seal on the mower 10 side.

  The purpose of the present invention is to switch the open / close valve to the open side in an attempt to operate the hydraulic motor with the tank circuit side coupler disconnected or incompletely connected, and even if the hydraulic circuit drain circuit hydraulic pressure rises abnormally, The hydraulic pressure is detected, and the hydraulic pressure supply circuit is automatically closed (shut off) to prevent further increase in the hydraulic pressure of the tank circuit and the drain circuit and to protect the drain circuit of the hydraulic motor.

The above-described problems are solved by the following inventions 1 to 3.
1. A drain circuit protection device for a work machine that is equipped with a hydraulic motor that operates with hydraulic pressure supplied from a tractor, and that can be attached to and detached from the tractor,
A hydraulic pressure supply circuit from the tractor via the first coupler to the hydraulic motor;
A shut-off valve disposed in the hydraulic pressure supply circuit;
A tank circuit returning from the hydraulic motor to the tractor via a second coupler;
A hydraulic pressure sensitive member disposed in the tank circuit and actuated by the hydraulic pressure when the hydraulic pressure of the tank circuit exceeds a predetermined pressure;
A drain circuit protection device for a work machine, wherein the shut-off valve is closed by an operation of the hydraulic pressure sensitive member.
2. When the hydraulic motor is not operated, the hydraulic oil of the hydraulic pressure supply circuit is returned to the tractor via the hydraulic oil return circuit and the third coupler, and the tank circuit is closed when the shutoff valve is closed. The drain circuit protection device for a work machine according to claim 1, wherein a bypass circuit for bypassing the hydraulic pressure exceeding the pressure to the hydraulic oil return circuit is provided.
3. The drain circuit protection device for a work machine according to claim 2, wherein the bypass circuit is opened and closed by an opening / closing member integral with the shut-off valve.

4). By operating the shut-off valve in the direction opposite to the closing operation direction, the opening and closing member of the bypass circuit is opened, and the hydraulic pressure exceeding the predetermined pressure of the tank circuit is returned to the hydraulic oil through the bypass circuit. The drain circuit protection device for a work machine according to the third aspect, which is bypassed to the circuit.
5. The drain circuit protection device for a work machine according to claim 1, wherein an opening / closing valve for supplying / stopping hydraulic pressure to the hydraulic motor is disposed in the hydraulic pressure supply circuit between the hydraulic motor and the first coupler.
6). The drain circuit protection device for a work machine according to 5, wherein the open / close valve is disposed downstream of the shut-off valve.

7). The working machine is movably attached to the tractor by a working arm with a cylinder, and the working arm is swung by operating the cylinder to extend and contract by hydraulic pressure from the hydraulic pressure supply circuit,
An operation valve for supplying / stopping hydraulic pressure to the cylinder is disposed in the hydraulic pressure supply circuit, and
The drain circuit protection device for a work machine according to 5 or 6, wherein the shut-off valve, the operation valve, and the opening / closing valve are housed in one housing.
8). The drain circuit protection device for a working machine according to the seventh aspect, wherein the shut-off valve is disposed on the most upstream side of the hydraulic pressure supply circuit in the housing.
The term “tank circuit” is used as a concept including a drain circuit of a hydraulic motor. Therefore, in the present invention, “tank circuit hydraulic pressure” and “drain circuit hydraulic pressure” are synonymous.

  In the present invention, as described above, the shutoff valve is closed by the operation of the hydraulic pressure sensitive member, so that the hydraulic pressure of the tank circuit that returns from the hydraulic motor to the tractor via the second coupler rises to a predetermined pressure or higher. It is possible to prevent the shaft seal of the hydraulic motor from being damaged at a high pressure.

  Also, the increased hydraulic pressure of the tank circuit is bypassed to the hydraulic oil return circuit through the bypass circuit, so that the increased hydraulic pressure of the tank circuit can be reduced and the second coupler of the tank circuit can be easily connected. In addition, oil leakage at the time of connection can be prevented.

FIG. 3 is a hydraulic circuit diagram of the drain circuit protection device according to the present invention in which all couplers are normally connected, the on-off valve and the operation valve are in a neutral state, and the shut-off valve is in an open state. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 1A. FIG. 2 is a hydraulic circuit diagram of the drain circuit protection device according to the present invention in which only the second coupler is not connected and the other is the same as FIG. 1A. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 2A. FIG. 2 is a hydraulic circuit diagram of the drain circuit protection device according to the present invention in which only the second coupler is not connected, the open / close valve of the hydraulic motor is in an open state, and the others are the same as in FIG. 1A. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 3A. FIG. 4 is a hydraulic circuit diagram of the drain circuit protection device according to the present invention in which the shut-off valve is in a closed state and the other states are the same as those in FIG. 3A. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 4A. It is a hydraulic circuit diagram of a drain circuit protection device according to a modification of the present invention corresponding to FIG. 1A. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 5A. FIG. 4B is a hydraulic circuit diagram of a drain circuit protection device according to a modification of the present invention corresponding to FIG. 4A. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 6A. FIG. 6 is a hydraulic circuit diagram of a drain circuit protection device according to a modification of the present invention when the hydraulic pressure of the tank circuit is bypassed to the hydraulic oil return circuit. It is sectional drawing of the valve unit which comprises the drain circuit protection apparatus of FIG. 7A. It is a side view of the tractor which connected the mower as a working machine. It is a top view of the tractor which connected the mower as a working machine. It is a rear view of the tractor which connected the mower as a working machine. It is a hydraulic circuit diagram of the valve unit of the conventional working machine.

  Embodiments of a drain circuit protection device according to the present invention will be described below with reference to the drawings. 1A, FIG. 2A, FIG. 3A, and FIG. 4A show hydraulic circuit diagrams of a valve unit 21 having a drain circuit protection device according to the present invention. The basic configuration is the same as that of the conventional valve unit 21 of FIG. The same. That is, the valve unit 21 includes an open / close valve 21a that supplies and stops hydraulic pressure to the hydraulic motors 16a and 16b of the mower 10 of FIG. 8, and the first and second working arms 12 and 13 of FIG. The first and second operation valves 21b and 21c supply and stop the hydraulic pressure to the two cylinders 17 and 18, and a unit housing 21d that houses these three valves 21a, 21b, and 21c.

  The drain circuit protection device of the present invention is characterized in that a shut-off valve 31 is provided in the hydraulic pressure supply circuit 22 on the upstream side of the operation valve 21c. The shut-off valve 31 is closed by the hydraulic pressure when the hydraulic pressure of the drain circuit 24a and the tank circuit 24b of the hydraulic motors 16a and 16b exceeds a predetermined pressure. When the hydraulic pressure drops below the predetermined pressure, the shut-off valve 31 is opened again. To do.

  In both FIG. 1A and FIG. 2A, the three valves 21a to 21c are in a neutral state, and the shut-off valve 31 is in an open state. In FIG. 1A, all the couplers P, N and T are normally connected, and in FIG. 2A, FIG. 3A and FIG. 4A, only one coupler T is not connected. In both FIG. 3A and FIG. 4A, the two operation valves 21b and 21c are in the neutral state, and the open / close valve 21a is in the open state. FIG. 3A shows the shut-off valve in an open state, and FIG. 4A shows the shut-off valve in a closed state.

  The mechanical structure of the valve unit 21 is as shown in FIGS. 1B, 2B, 3B, and 4B. The states of the valves 21a to 21c and the couplers P, N, and T correspond to FIGS. 1A, 2A, 3A, and 4A, respectively. In FIG. 1B, FIG. 2B, FIG. 3B, and FIG. 4B, although only the AA cross section is shown about the opening-and-closing valve 21a, this cross-sectional structure is the same also in the two operation valves 21b and 21c. In FIG. 1A to FIG. 4B, the portion where the hydraulic pressure of the hydraulic pressure supply circuit 22 following the coupler P is continuous is given “light ink” for easy understanding.

  When one solenoid of each valve 21a to 21c is excited, the spool S of each valve 21a to 21c shifts to the solenoid side, and the port A (or B) on the shifted side becomes the hydraulic pressure supply side, and the opposite The port B (or A) on the side is the drain side. However, the opening / closing valve 21 a has a port A dedicated to supplying hydraulic pressure and a port B closed by a plug 28.

  The shut-off valve 31 has a shut-off spool 31a that is slidably disposed with respect to the unit housing 21d. The shut-off spool 31a is disposed so as to cross the hydraulic pressure supply circuit 22 and the tank circuit 24b. A center bolt 31b as a hydraulic pressure sensitive member is screwed and fixed coaxially to one end of the shut-off spool 31a. The center bolt 31b is disposed inside an end cap 33 fixed to the side surface of the unit housing 21d by a plurality of mounting bolts 32. A drain hydraulic pressure introduction chamber 34 is formed in the inner space of the end cap 33. A communication hole 35 for communicating the tank circuit 24b and the drain hydraulic pressure introduction chamber 34 is formed in the shut-off spool 31a in the axial direction. A pair of left and right spring seats 36, 37 are mounted on the shut-off spool 31a on the side where the center bolt 31b is fixed, and a spool spring 38 compressed with a predetermined set pressure is disposed between the spring seats 36, 37. Has been. The spring seats 36 and 37 function as spacers that form a slight gap between the center bolt 31 b and the end cap 33.

  In the middle portion in the longitudinal direction of the shut-off spool 31a, a first small diameter portion d1 that guides the oil in the tank circuit 24b to the communication hole 35 that continues to the drain hydraulic pressure introduction chamber 34, and the hydraulic pressure supply circuit 22 and the tank at the neutral position in FIG. A first large-diameter portion d2 that always fluid-tightly partitions the circuit 24b, and a second small-diameter portion d3 that communicates the hydraulic pressure supply circuit 22 on the coupler P side and the downstream side of the shut-off spool 31a during normal operation at the same neutral position. When the shut-off spool 31a moves to the left as shown in FIGS. 1B to 4B when the drain circuit pressure abnormally rises, the second small-diameter portion d3 A second large-diameter portion d4 that closes the hydraulic pressure supply circuit 22 in the communication state is continuously formed from the left side to the right side in FIG. 1B.

  An extension rod 39 is connected to the end of the shut-off spool 31a opposite to the center bolt 31b. A shut-off release knob 40 is fixed to the tip of the extension rod 39. The knob 40 is housed in a hole 42 of a side plate 41 that is fixedly provided near the connection portion 15 of the work arm. Normally, the end surface of the knob 40 can be seen from the outside. It is almost hidden in the hole 42 so that it cannot be seen. The peripheral surface of the knob 40 is painted in a conspicuous color such as red or fluorescent color. When the knob 40 protrudes from the hole 42 of the side plate 41 as shown in FIG. 4B, the peripheral surface of the knob 40 can be easily visually recognized from the outside.

  The drain circuit protection device is constructed as described above and operates as described below. In FIGS. 1A and 1B, all couplers P, N, and T are normally connected. Therefore, when the three valves 21a to 21c are in a neutral state, the couplers P (first coupler) and the hydraulic pressure supply circuit 22 are used from the tractor side. The hydraulic oil supplied to the valve unit 21 returns to the tractor side through the hydraulic oil return circuit 23 and the coupler N (third coupler). The hydraulic oil return circuit 23 functions as a so-called power beyond circuit, and the hydraulic oil returned to the tractor side is used by another hydraulic device on the tractor side.

  As shown in FIGS. 2A and 2B, when the two couplers P and N are connected but the remaining one coupler T (second coupler) is not connected, the positions of the valves 21a to 21c are as shown in FIGS. 1A and 1B. If neutral, the hydraulic fluid returns to the tractor side through the hydraulic fluid return circuit 23 and the coupler N in the same manner as in FIGS. 1A and 1B, so that no particular problem occurs.

  However, as shown in FIGS. 3A and 3B, when the open / close valve 21a is opened while the coupler T is not connected, the hydraulic oil pressure acts on the hydraulic motors 16a and 16b through the hydraulic pressure supply circuit 22, and the hydraulic pressure is increased. The motors 16a and 16b are about to operate. However, since the coupler T is not connected, the hydraulic oil discharged from the hydraulic motors 16a and 16b loses its place, the hydraulic pressure of the tank circuit 24b increases, and the drain circuit pressure of the hydraulic motor also increases. If this state continues, the shaft seals of the hydraulic motors 16a, 16b will lose the hydraulic pressure and jump out, deform, or be damaged. As a result, hydraulic oil may leak to the outside from the shaft seals of the hydraulic motors 16a and 16b.

  Therefore, in such a case, in the present invention, the shutoff valve 31 is operated to automatically prevent further increase in the hydraulic pressure of the tank circuit. 3A and 3B, when the hydraulic pressure of the tank circuit 24b is introduced into the drain hydraulic pressure introduction chamber 34 through the communication hole 35 of the shut-off spool 31a, this hydraulic pressure acts on the end face of the center bolt 31b. As a result, as shown in FIGS. 4A and 4B, the shut-off spool 31a moves to the extension rod 39 side (left direction in the figure) against the set pressure of the spool spring 38 and causes the knob 40 to protrude from the side plate 41. . The hydraulic pressure in the drain hydraulic pressure introduction chamber 34 when the shut-off spool 31a starts to move can be adjusted by changing the set pressure of the spool spring 38. The tractor operator visually recognizes that the peripheral surface of the knob 40 painted in red or fluorescent color is exposed from the hole 42 of the side plate 41 and exposed to the outside, so that the tank circuit 24b (and the drain circuit 24a) is exposed. Know the oil pressure rise. Simultaneously with the protrusion of the knob 40, the second large diameter portion d4 of the shut-off spool 31a closes the small diameter portion 22a of the hydraulic pressure supply circuit 22, and stops further hydraulic pressure supply to the hydraulic motors 16a and 16b. As a result, further increase in the hydraulic pressure of the tank circuit 24b and the drain circuit 24a is prevented, and the shaft seals of the hydraulic motors 16a and 16b are protected from popping out, deformation and damage, and leakage of hydraulic oil from the shaft seal is prevented. Note that the hydraulic pressure supply circuit 22 on the downstream side of the shut-off spool 31a is lightly colored because the hydraulic pressure is applied in FIGS. 1B, 2B, and 3B, but in FIG. 4B, the hydraulic pressure is supplied after the shut-off valve 31 is closed. Has not been lightly inked as a natural loss.

  As described above, in FIGS. 4A and 4B, the hydraulic motors 16 a and 16 b do not rotate and the knob 40 of the shut-off valve 31 protrudes from the side plate 41 even though the opening and closing valve 21 a is opened. Thus, the tractor operator notices that the coupler T is not connected. When the tractor operator returns the open / close valve 21a to the neutral position and tries to connect the unconnected coupler T, if the hydraulic pressure of the tank circuit 24b remains high, the coupler T is moved toward the tractor with a strong force to overcome this hydraulic pressure. Without pressing, the coupler T cannot be connected. Further, if the hydraulic pressure of the tank circuit 24b remains high, there is a risk that the hydraulic oil will be ejected to the outside vigorously or the coupler seal may be broken at the moment when the coupler T is connected.

  Therefore, as shown in FIGS. 5A to 7B, in another embodiment of the present invention, the hydraulic pressure of the tank circuit 24 b is returned to the hydraulic fluid by operating the shut-off spool 51 a before connecting the unconnected coupler T. The circuit 23 can be bypassed. In this embodiment, the shut-off valve 51 is constituted by a 6-port 3-position direction control valve. The two symbols on the center and right side of the shut-off valve 51 shown in FIGS. 5A to 7A correspond to the two symbols on the shut-off valve 31 in FIG. 1A. A left side symbol of the shut-off valve 51 shown in FIGS. 5A to 7A indicates a switching state when bypassing from the tank circuit 24 b to the hydraulic oil return circuit 23. As in FIGS. 1A to 4B, in FIGS. 5A to 7B, the portion where the hydraulic pressure of the hydraulic pressure supply circuit 22 following the coupler P is continuous is given “light ink” for easy understanding. .

  Specifically, as shown in FIGS. 5B to 7B, the shut-off valve 51 has the head of the center bolt 51b changed to be thinner than that of FIG. 1B. It is the same. Then, as shown in FIG. 5B, in the neutral state of the shut-off spool 51a, the hydraulic pressure supply circuit 22 is brought into the normal hydraulic pressure supply state by the second small diameter portion d3, and in the left-handed state of FIG. The supply circuit 22 is closed by the second large diameter portion d4. In order to bypass the tank circuit 24 b to the hydraulic oil return circuit 23 from this closed state, the knob 40 is manually pushed toward the side plate 41 against the hydraulic pressure in the drain hydraulic pressure introduction chamber 34 and the spool spring 38. As a result, the shut-off spool 51a moves to the right as shown in FIG. 7B, the first large-diameter portion d2 closes the small-diameter portion 22a of the hydraulic-supply circuit 22, and the hydraulic-supply circuit 22 on the downstream side of the shut-off valve 51. And the tank circuit 24b are communicated by the first small diameter portion d1 of the shutoff valve 51. Thereby, the hydraulic pressure exceeding the predetermined pressure in the tank circuit 24 b can be released to the hydraulic oil return circuit 23 via the hydraulic pressure supply circuit 22. In this case, the hydraulic pressure supply circuit 22 constitutes a bypass circuit. Also, the hydraulic pressure exceeding the predetermined pressure in the drain hydraulic pressure introduction chamber 34 is released to the hydraulic oil return circuit 23 through the hydraulic pressure supply circuit 22. Therefore, the connecting operation of the coupler T can be performed smoothly, the leakage of the hydraulic oil from the coupler T is minimized, and there is no fear of seal breakage or protrusion. Thereafter, when the hand is released from the knob 40, the shut-off spool 51a returns to the neutral position in FIG.

  As described above, the embodiment of the present invention has been described by taking the mower as the working machine as an example. However, the present invention can be applied to all working machines that are equipped with a hydraulic motor and can be attached to and detached from the tractor. Further, the shut-off valves 31 and 51 are electromagnetically operated valves, the pressure sensor detects that the hydraulic pressure of the tank circuit (or the drain circuit of the hydraulic motor) has exceeded a predetermined pressure, and the electromagnetically operated valve is closed by this detection signal. You may make it operate. Further, a bypass circuit that bypasses the hydraulic pressure exceeding the predetermined pressure in the tank circuit to the hydraulic oil return circuit may be provided in another path that does not pass through the shutoff valves 31 and 51. However, the structure via the shut-off valve 31 as in the above-described embodiment is advantageous for downsizing and cost reduction of the apparatus because the shut-off spools 31a and 51a can be used as opening / closing members of the bypass circuit. Further, in order to notify the operator of the tractor that the coupler T is not connected, an alarm may be issued by sound or light in conjunction with the protruding operation of the knob 40.

DESCRIPTION OF SYMBOLS 10 Mower 11 Tractor 12 1st work arm 13 2nd work arm 14 Rear hitch 15 Connection part 16a, 16b Hydraulic motor 17 1st cylinder 18 2nd cylinder 21 Valve unit 21a Open / close valve 21b, 21c Operation valve 21d Unit housing 22 Hydraulic pressure Supply circuit 22a Small diameter portion 23 Hydraulic oil return circuit 24b Tank circuit 31, 51 Shutoff valve 31a Shutoff spool d1 First small diameter portion of shutoff spool d2 First large diameter portion of shutoff spool d3 Second small diameter of shutoff spool Portion d4 Second large diameter portion 31b of the shut-off spool Center bolt 32 Mounting bolt 33 End cap 34 Drain hydraulic pressure introduction chamber 35 Communication hole 36, 37 Spring seat 38 Spool spring 39 Extension rod 40 Knob 51a Shut-off spool 51b Center bolt P, N, T coupler

Claims (8)

A drain circuit protection device for a work machine that is equipped with a hydraulic motor that operates with hydraulic pressure supplied from a tractor, and that can be attached to and detached from the tractor,
A hydraulic pressure supply circuit from the tractor via the first coupler to the hydraulic motor;
A shut-off valve disposed in the hydraulic pressure supply circuit;
A tank circuit returning from the hydraulic motor to the tractor via a second coupler;
A hydraulic pressure sensitive member disposed in the tank circuit and actuated by the hydraulic pressure when the hydraulic pressure of the tank circuit exceeds a predetermined pressure;
A drain circuit protection device for a work machine, wherein the shut-off valve is closed by an operation of the hydraulic pressure sensitive member.   When the hydraulic motor is not operated, the hydraulic oil of the hydraulic pressure supply circuit is returned to the tractor via the hydraulic oil return circuit and the third coupler, and the tank circuit is closed when the shutoff valve is closed. The drain circuit protection device for a working machine according to claim 1, further comprising a bypass circuit that bypasses the hydraulic pressure exceeding the pressure to the hydraulic oil return circuit.   The drain circuit protection device for a working machine according to claim 2, wherein the bypass circuit is opened and closed by an opening / closing member integral with the shut-off valve.   By operating the shut-off valve in the direction opposite to the closing operation direction, the opening and closing member of the bypass circuit is opened, and the hydraulic pressure exceeding the predetermined pressure of the tank circuit is returned to the hydraulic oil through the bypass circuit. The drain circuit protection device for a working machine according to claim 3, wherein the drain circuit protection device is bypassed to the circuit.   The drain circuit protection device for a working machine according to claim 1, wherein an opening / closing valve for supplying / stopping hydraulic pressure to the hydraulic motor is disposed in the hydraulic pressure supply circuit between the hydraulic motor and the first coupler.   The drain circuit protection device for a working machine according to claim 5, wherein the opening / closing valve is disposed downstream of the shut-off valve. The working machine is movably attached to the tractor by a working arm with a cylinder, and the working arm is swung by operating the cylinder to extend and contract by hydraulic pressure from the hydraulic pressure supply circuit,
An operation valve for supplying / stopping hydraulic pressure to the cylinder is disposed in the hydraulic pressure supply circuit, and
The drain circuit protection device for a working machine according to claim 5 or 6, wherein the shut-off valve, the operation valve, and the opening / closing valve are housed in one housing.   The drain circuit protection device for a work machine according to claim 7, wherein the shut-off valve is disposed on the most upstream side of the hydraulic pressure supply circuit in the housing.

Images