JP5944293B2 - Working machine hydraulic circuit - Google Patents

Description

  The present invention relates to a hydraulic circuit of a work machine such as a front loader that is mounted on a tractor or the like and lifts a heavy object, and a work machine including the hydraulic circuit.

  The work machine is an attachment device that is detachably attached to a tractor or the like, and the one that is attached to the front side of the tractor 10 as shown in FIG. The front loader 20 has a lift arm 22 that is moved up and down by a lift cylinder 21, and various tip attachments such as a bucket 23, a fork, a grader, a roll grab, a container bucket, and a loading hook at the tip of the lift arm 22. Is attached according to the work content. Hereinafter, it is assumed that the attachment is the bucket 23. A dump cylinder 24 is disposed at the upper end of the lift arm 22, and the dump cylinder 24 is configured to tilt the bucket 23 forward (dump operation) or backward (squeeze operation).

  The lifting and lowering operation of the lift arm 22 and the dumping and squeezing operation of the bucket 23 are performed by operating, for example, a joystick type operation lever 25 provided in the driver's seat of the tractor 10 in the front, rear, left and right directions as shown in FIG. . The operation lever 25 can perform combined operations such as raising and lowering the lift arm 22, dumping the bucket 23, and squeezing each single operation, as well as dumping or squeezing the bucket 23 while raising or lowering the lift arm 22. It has become.

  By the way, as for the hydraulic circuit of the front loader 20, for example, as disclosed in Patent Document 1 (Patent No. 3096992), a load circuit equipped with a leveling mechanism is known in order to prevent the load from falling or collapse (see FIG. 9). By this leveling mechanism, the bucket 23 is dumped or squeezed simultaneously with the lifting and lowering operation of the lift arm 22, and the angle of the bucket 23 with respect to the ground is maintained substantially constant.

  That is, a parallel control cylinder 27 is provided in parallel with the lift cylinder 21, and the parallelism of the bucket 23 (levelness with respect to the ground) is maintained by the parallel control cylinder 27. The working chamber of the parallel control cylinder 27 is connected to the squeeze working chamber of the dump cylinder 24. When the lift arm 22 is raised and lowered, pressure oil is taken in and out of the squeeze working chamber of the dump cylinder 24 according to the height of the lift arm 22. The bucket 23 is leveled.

  Further, as a leveling mechanism that does not use the parallel control cylinder 27, for example, a hydraulic circuit as in Patent Document 2 (Japanese Patent No. 3542373) is also known. As shown in FIG. 10, this hydraulic circuit introduces pressure oil from the head side of the lift cylinder 21 into the dump operation chamber of the dump cylinder 24 when the lift cylinder 21 is operated to raise the lift arm 22. Further, when the lift arm 22 is lowered, the pressure oil coming out from the cap side of the lift cylinder 21 is introduced into the squeeze operation chamber of the dump cylinder 24 through the diversion control valve 56. In this way, the bucket 23 is leveled.

Japanese Patent No. 3096922 Japanese Patent No. 3542373

  The maximum lifting force and the maximum lifting height of the front loader 20 are determined by the strength and balance of the tractor 10 to which the front loader 20 is mounted, the capacity of the lift cylinder 21 and the hydraulic pump, and the like. However, as the bucket 23 moves away from the pivot point of the lift arm 22 in the horizontal direction, there is a structural restriction that the liftable weight decreases. In addition, there are various types of attachments, and a large attachment has a considerable weight in itself. For this reason, depending on the usage state of the front loader, the maximum lifting force may not be fully exhibited.

  In the front loader disclosed in Patent Document 1 (Patent No. 3096922) described above, the parallel control cylinder 27 is arranged in parallel with the lift cylinder. It has become. However, the parallel control cylinder 27 is for leveling control of the dump cylinder 24, and the cylinder cross-sectional area of the parallel control cylinder 27 and the head-side cross-sectional area of the dump cylinder 24 must be set to a constant ratio. There are restrictions.

  The front loader of Patent Document 2 (Japanese Patent No. 3542373) relies only on the lift cylinder 21 for the lifting force of the lift arm 22. For this reason, when the lift arm 22 is lifted or the heavy load is lifted with the lift arm 22 and the attachment bucket 23 extended in the horizontal direction, the force of the lift cylinder 21 may be insufficient. is there.

  An object of the present invention is to provide a lift arm using a load force acting on a tip attachment of a lift arm without changing the specifications of a hydraulic pump or a lift cylinder as a hydraulic supply source in a working machine having a leveling mechanism. It is to increase the lifting force of the necessary amount. Further, in optimizing the leveling mechanism, it is to avoid being restricted by the design due to the available cylinder diameter of the lift cylinder and the dump cylinder.

The present invention solves the above problems by the following means.
That is, the hydraulic circuit of the working machine according to the present invention includes a lift arm having an attachment rotatably attached to a distal end portion and a base end portion rotatably supported by a support base, and the attachment in the vertical direction. For a working machine having a first cylinder for rotationally driving, a second cylinder for driving the lift arm 22 up and down, and an auxiliary cylinder arranged in parallel to the second cylinder and assisting the second cylinder The hydraulic circuit is connected to a hydraulic pressure source, and has a first switching valve and a second switching valve having a first position, a second position, and a neutral N position as switching positions, respectively, 1 switching valve and the first cylinder are connected, the attachment is squeezed at the first position of the first switching valve, and the attachment is dumped at the second position of the first switching valve. A first hydraulic pipe that is piped to be operated, the second switching valve, and the second cylinder are connected, the lift arm 22 is lifted up at a first position of the second switching valve, and the second switching is performed. A second hydraulic pipe piped to lift down the lift arm 22 at a second position of the valve; a third hydraulic pipe connecting a squeeze working chamber of the first cylinder and a lift up working chamber of the auxiliary cylinder; And a diversion control means for adjusting the amount of oil flowing from the second cylinder to the first cylinder so as to make the angle of the attachment relative to the ground constant, corresponding to the elevation height of the lift arm 22. When the second switching valve is switched to the first position with the first switching valve in the N position, the pressure oil that has flowed out of the lift-down working chamber of the second cylinder is attached. At the same time, a part or all of the pressure oil flowing out from the squeeze operation chamber of the first cylinder is supplied to the lift-up operation chamber of the auxiliary cylinder. When the remaining pressure oil is returned to the hydraulic pressure source and the second switching valve is switched to the second position, the pressure oil flowing out from the lift-up working chamber of the second cylinder squeezes the attachment. At the same time as being supplied to the squeeze operation chamber of the first cylinder so as to be operated, the pressure oil that has flowed out of the dump operation chamber of the first cylinder is returned to the hydraulic power source and flows out of the lift-up operation chamber of the auxiliary cylinder The first to third hydraulic pipes are configured so that the pressurized oil is returned to the squeeze working chamber of the first cylinder.

  According to the present invention, the auxiliary cylinder is juxtaposed with the second cylinder that drives the lift arm up and down, and the squeeze operation chamber of the first cylinder that drives the attachment in the vertical direction and the lift-up operation chamber of the auxiliary cylinder are provided in the first cylinder. Since the three hydraulic pipes are connected, the pressure oil generated in the squeeze working chamber by the load force of the load acting on the attachment can be taken out by the third hydraulic pipe and used as the lifting force of the auxiliary cylinder. For this reason, in a usage state where a heavy load is lifted or lifted up and down with the lift arm extended in the horizontal direction, the lifting force of the lift cylinder is insufficient with a conventional hydraulic circuit. However, since the load force of the load can be utilized as a lifting force by the auxiliary cylinder, it can be lifted and lowered stably even with a heavy load. Further, since the leveling mechanism can be optimized by adjusting the amount of oil flowing from the second cylinder to the first cylinder by the diversion control means, the volume of the auxiliary cylinder is limited in accordance with the volume of the first cylinder that performs leveling. The degree of freedom in design between the cylinder sizes and link dimensions of the first, second, and auxiliary cylinders is increased, and as a result, the lifting force of the lift arm can be increased to a necessary size.

It is the side view of the front loader which concerns on embodiment of this invention, and its hydraulic circuit (at the time of neutral). It is the side view of the front loader which concerns on embodiment of this invention, and its hydraulic circuit (at the time of lift-up). It is a side view of the front loader concerning the embodiment of the present invention, and its hydraulic circuit (at the time of lift down). It is the side view of the front loader which concerns on embodiment of this invention, and its hydraulic circuit (at the time of a squeeze). It is a side view of the front loader concerning the embodiment of the present invention, and its hydraulic circuit (at the time of dumping). It is the side view of the front loader which concerns on embodiment of this invention, and its hydraulic circuit (at the time of turbo dumping). It is a side view of the tractor equipped with the conventional front loader. It is a perspective view which shows the operation direction of the operation lever of the conventional tractor. It is the side view of the conventional front loader, and its hydraulic circuit (at the time of lift-up). It is a side view of another conventional front loader and its hydraulic circuit (at the time of lift-up).

Hereinafter, a front loader as a working machine according to an embodiment of the present invention and its hydraulic circuit will be described with reference to the drawings.
(Front loader and its hydraulic circuit)
As shown in FIG. 1, a bucket 23 as an attachment is rotatably attached to a tip end portion of a lift arm 22 constituting a main body of the front loader 20 by a support pin 26. A base end portion of the lift arm 22 is attached to a support bracket 29 as a support base fixedly provided on the tractor 10 of FIG. That is, the support pin 30 is provided on the upper part of the support bracket 29, and the base end portion of the lift arm 22 is rotatably supported by the support pin 30. Further, a support pin 33 is provided on a bracket 32 provided below the middle portion in the longitudinal direction of the lift arm 22, and a lift is provided between the support pin 33 and a support pin 31 provided below the support bracket 29. A cylinder 21 is provided.

  The lift cylinder 21 is a single rod double acting hydraulic cylinder, the cap side of which is connected to the support bracket 29 via the support pin 31, and the head side to the bracket 32 of the lift arm 22 via the support pin 33. It is connected. The feature of the present invention is that the auxiliary cylinder 60 is arranged in parallel with the lift cylinder 21 and the lift-up operation chamber 60a of the auxiliary cylinder 60 is connected to the squeeze operation chamber 24a of the dump cylinder 24 described later by the third hydraulic pipe 63. It is to have done. The details of the auxiliary cylinder 60 will be described after the basic operation of the hydraulic circuit is described.

  A bracket 34 is disposed on the upper side in the longitudinal direction of the lift arm 22, and a support pin 35 is provided on the bracket 34. Further, a first link 40 connected to the back surface of the bucket 23 by a support pin 39 and a second link 42 connected to a tip portion of the lift arm 22 by a support pin 41 are disposed on the tip side of the lift arm 22. Has been. The first link 40 and the second link 42 are connected to each other by a connecting pin 43, and the dump cylinder 24 is disposed between the connecting pin 43 and the support pin 35 of the bracket 34. Like the lift cylinder 21, the dump cylinder 24 is a single-rod double-acting hydraulic cylinder, the cap side of which is supported by the bracket 34 by the support pin 35, and the head side by the connecting pin 43 and the first link 40 and the second link cylinder. It is connected to the link 42.

  A hydraulic pump 50 as a hydraulic source is mounted on the tractor 10, and the hydraulic pump 50 and the front loader 20 are detachably connected via a hydraulic coupler (not shown). As shown in the figure, a first switching valve 51 and a second switching valve 52 are connected to the hydraulic pump 50 in parallel. Accordingly, the first switching valve 51 and the second switching valve 52 can be operated alone or simultaneously. The operation of the first switching valve 51 and the second switching valve 52 can be performed by the operation lever 25 of FIG. 8 described above.

  A relief valve 49 is connected to the outlet side of the hydraulic pump 50, and pressure oil of a predetermined pressure or more is allowed to escape to the hydraulic tank 55 through the relief valve 49. The first switching valve 51 has a first position I, a second position II, and a neutral N position as switching positions, and is connected to the dump cylinder 24 via a first hydraulic pipe 53. The second switching valve 52 has a first position I, a second position II, and a neutral N position as switching positions, and is connected to the lift cylinder 21 via a second hydraulic pipe 54. In addition, a diversion control valve 56 is connected to the second switching valve 52, and this diversion control valve 56 is connected to the squeeze side 53 a of the first hydraulic pipe 53 via a fourth hydraulic pipe 57.

A brake valve 58 is connected to the fourth hydraulic pipe 57. The brake valve 58 is for controlling the dump cylinder 24 by controlling the flow of pressure oil discharged from the squeeze operation chamber 24a of the dump cylinder 24 and returning to the hydraulic tank 55 during the lift-up operation. For this purpose, pilot pressure from the pressure oil discharged from the lift-down working chamber 21b of the lift cylinder 21 and passing through the second switching valve 52 toward the dump working chamber 24b of the dump cylinder 24 is introduced into the brake valve 58 through the pipe 44, The brake valve 58 is opened only after a predetermined pressure (for example, 294 kPa = about 3 kgf / cm ² ) stands on the dump side 53 b of the first hydraulic pipe 53 following the dump working chamber 24 b.

  A check valve 59 is provided between the second switching valve 52 and the dump side 53 b of the first hydraulic pipe 53. Pilot pressure is introduced into the check valve 59 through the pipe 45 from the downstream side of the flow dividing control valve 56, that is, from the pipe line passing through the fourth hydraulic pipe 57 toward the squeeze side 53 a of the first hydraulic pipe 53. Yes. Thus, when pressure is applied to the pressure oil flowing from the flow dividing control valve 56 to the squeeze working chamber 24a, that is, when the pressure rises in the squeeze working chamber 24a, the check valve 59 is opened. Relief valves 46 to 48 are provided in the first hydraulic pipe 53, the second hydraulic pipe 54, and the fourth hydraulic pipe 57, respectively.

(Front loader operation)
The front loader 20 described above operates as follows. In FIG. 1 to FIG. 6, a hydraulic line in which pressure oil is generated or flows is shown by a thick line for easy understanding.
FIG. 1 shows a state where both the first switching valve 51 and the second switching valve 52 are switched to the N position. In the state of the N position, the pressure oil of the hydraulic pump 50 is not supplied to either the lift cylinder 21 or the dump cylinder 24. For this reason, the lift arm 22 maintains a stop state.

  Next, when the lift arm 22 is lifted up, the second switching valve 52 is switched to the first position I while keeping the first switching valve 51 at the N position as shown in FIG. As a result, the pressure oil of the hydraulic pump 50 is introduced into the lift-up chamber of the lift cylinder 21, and the lift arm 22 rises in the direction of the arrow about the support pin. Further, the pressure oil in the lift-down working chamber of the lift cylinder 21 passes through the lift-down side 54 b of the second hydraulic pipe 54 and the second switching valve 52 and is introduced into the dump working chamber of the dump cylinder 24. Then, as the lift arm 22 is raised, the dump cylinder 24 is extended, and the bucket 23 is dumped, so that a so-called leveling operation is performed in which the angle of the bucket 23 with respect to the ground is maintained constant.

  Next, when the lift arm 22 is lowered, as shown in FIG. 3, the second switching valve 52 is switched to the second position II while the first switching valve 51 is kept at the N position. Thereby, the pressure oil of the hydraulic pump 50 is introduced into the lift-down operation chamber 21 b of the lift cylinder 21 through the second switching valve 52 and the second hydraulic pipe 54. Further, the pressure oil in the lift-up working chamber 21 a of the lift cylinder 21 is supplied to the lift-up side 54 a of the second hydraulic pipe 54, the second switching valve 52, the flow control valve 56, the fourth hydraulic pipe 57, and the first hydraulic pipe 53. It passes through the squeeze side 53 a and is introduced into the squeeze operation chamber 24 a of the dump cylinder 24. Then, the lift arm 22 is lifted down and the bucket 23 is squeezed to keep the angle of the bucket 23 with respect to the ground constant. The pressure oil in the dump working chamber 24 b of the dump cylinder 24 is returned to the hydraulic tank 55 through the dump side 53 b of the first hydraulic pipe 53, the check valve 59, and the second switching valve 52.

  When the lift arm 22 is lowered and the bucket 23 is attached to the ground and the lift arm 22 is further lowered, the bucket 23 tends to rotate to the squeeze side due to the reaction force received from the ground (at this time, the pressure in the squeeze working chamber 24a). Suddenly decreases). If this rotation is allowed, the operation of floating the front wheel of the tractor 10 by pressing the bucket 23 against the ground cannot be performed. The check valve 59 prevents rotation of the bucket 23 to the squeeze side in such a case. When the squeeze operation chamber 24a becomes negative pressure, the check valve 59 is automatically closed by the negative pressure to lock the dump cylinder 24. To do. Thereby, the front wheel floating operation of the tractor 10 by the lift-down of the lift arm 22 becomes possible.

  Next, when the bucket 23 performs a squeeze operation, the second switching valve is set to the N position and the first switching valve 51 is switched to the first switching position as shown in FIG. Thereby, the pressure oil of the hydraulic pump 50 is introduced into the squeeze operation chamber 24a of the dump cylinder 24 through the first switching valve 51 and the squeeze side 53a of the first hydraulic pipe 53, and thereby the bucket 23 is squeezed. The pressure oil in the dump working chamber 24 b of the dump cylinder 24 is returned to the hydraulic tank 55 through the dump side 53 b of the first hydraulic pipe 53 and the first switching valve 51.

  Next, when the bucket 23 is dumped, as shown in FIG. 5, the second switching valve is switched to the N position, and the first switching valve 51 is switched to the second switching position II. Thereby, the pressure oil of the hydraulic pump 50 is introduced into the dump working chamber 24 b of the dump cylinder 24 through the first switching valve 51 and the dump side 53 b of the first hydraulic pipe 53. Then, the dump cylinder 24 is extended and the bucket 23 is dumped. The pressure oil in the squeeze working chamber 24 a of the dump cylinder 24 is returned to the hydraulic tank 55 through the squeeze side 53 a of the first hydraulic pipe 53 and the first switching valve 51.

  Next, turbo dumping will be described. In order to perform the turbo dump, a turbo dump switching position T is added to the first switching valve 51 as shown in FIG. With this turbo dump switching position T, the pressure oil discharged from the squeeze working chamber 24a during the dump operation passes through the squeeze side 53a of the first hydraulic piping 53, and further passes through the turbo dump switching position T of the first switching valve 51, It is again introduced into the dump working chamber 24b of the dump cylinder 24. Thereby, the pressure oil discharged from the squeeze operation chamber 24a can be used for the dump operation of the dump cylinder 24, and the dump operation can be accelerated.

(Auxiliary cylinder and its operation)
The auxiliary cylinder 60 is disposed between a support pin 61 provided at an intermediate height position of the support bracket 29 and a support pin 62 provided on the lift arm 22. The auxiliary cylinder 60 is a single-rod single-acting hydraulic cylinder, and the volume increase (push-in amount) of the auxiliary cylinder during ascending leveling is less than the volume decrease (discharge amount) of the dump cylinder squeeze chamber at that time. Design to be

  The lift-up operation chamber 60 a of the auxiliary cylinder 60 and the squeeze operation chamber 24 a of the dump cylinder 24 are directly connected by a third hydraulic pipe 63. And the mutual movement of the pressure oil via the 3rd hydraulic piping 63 is enabled between the lift-up operation chamber 60a of the auxiliary cylinder 60 and the squeeze operation chamber 24a of the dump cylinder 24. As a result, the pressure in the squeeze working chamber 24 a of the dump cylinder 24 is introduced into the lift-up working chamber 60 a of the auxiliary cylinder 60, and the pressure acts in the direction of pushing up the lift arm 22.

  In the present invention, since the squeeze operation chamber 24a of the dump cylinder 24 is directly connected to the lift-up operation chamber 60a of the auxiliary cylinder 60 as described above, the pressure oil in the squeeze operation chamber 24a is effectively used as the lifting force of the lift arm. Thus, the load on the hydraulic pump 50 can be reduced, and energy saving operation can be performed.

  More specifically, as shown in FIG. 2 showing the lift-up operation, the bucket 23 is substantially horizontal, and the lift arm 22 is also substantially horizontal, and the distance from the fulcrum pin 30 to the center of gravity G including the load of the bucket 23. Is R1, the moment M1 around the support pin 30 acting on the lift arm 22 is M1 = R1 × W. Further, the rotational moment M2 around the support pin 26 of the bucket 23 is M2 = R2 × W, where R2 is the distance from the support pin 26 to the center of gravity G. Due to this rotational moment M2, the piston rod of the dump cylinder 24 is strongly pulled, and a large hydraulic pressure is generated in the squeeze working chamber 24a.

  In the hydraulic circuit of the present invention, a large hydraulic pressure increase generated in the squeeze working chamber 24 a can be introduced into the lift-up working chamber 60 a of the auxiliary cylinder 60 and effectively used as a lifting assist force for the lift arm 22. When the lift moment of the lift arm 22 by the lift cylinder 21 is ML and the lift moment of the lift arm 22 by the auxiliary cylinder is MA, M1 = R1 × W = ML + MA. Therefore, W = (ML + MA) / R1, and the maximum load that can be lifted increases. Thereby, even when a heavy load is mounted on the bucket 23 and the lift arm 22 is supported in a state of being extended in the horizontal direction, the load in the bucket 23 can be stably moved up and down.

  As described above, the lift arm 22 is supported by the two cylinders of the lift cylinder 21 and the auxiliary cylinder 60, and the lift-up operation chamber 60 a of the auxiliary cylinder 60 is connected to the squeeze operation chamber 24 a of the dump cylinder 24. The angle is ensured as before (invention of Patent Document 2).

  That is, when the lift arm 22 is raised as shown in FIG. 2, as described above, the lift arm 22 is raised, the dump cylinder 24 is extended, the bucket 23 is dumped, and the angle of the bucket 23 with respect to the ground is constant. Maintained. At this time, the pressure oil flows from the squeeze operation chamber 24a to the lift-up operation chamber 60a of the auxiliary cylinder 60. In the lift-up operation, the pressure oil discharged from the squeeze operation chamber 24a to the squeeze side 53a of the first hydraulic pipe 53 is the first. 1 Since one side of the hydraulic pipe 53 is released from the brake valve 58 according to the pressure on the dump side 53b, even if a part or all of it flows into the lift-up operation chamber 60a of the auxiliary cylinder 60, the leveling operation of the bucket 23 is completely affected. There is no.

  When the lift arm 22 is lowered as shown in FIG. 3, the pressure oil discharged from the lift-up working chamber 21 a of the lift cylinder 21 is diverted by the diversion control valve 56 and introduced into the squeeze working chamber 24 a of the dump cylinder 24. Is done. The diversion control valve 56 diverts the pressure oil according to the ratio of the hole diameters of the two throttle portions 56a and 56b (diversion ratio), introduces the pressure oil that has passed through one throttle portion 56a into the squeeze operation chamber 24a, and the remaining pressure. The oil is returned to the hydraulic tank 55. The diversion ratio is based on the ratio of the volumes of the lift-up operation chamber 21a of the lift cylinder 21, the squeeze operation chamber 24a of the dump cylinder 24, and the lift-up operation chamber 60a of the auxiliary cylinder 60 so that the bucket 23 operates correctly. Can be set. By appropriately setting the flow dividing ratio, the amount of oil necessary for leveling is introduced from the throttle portion 56a of the flow dividing control valve 56 into the squeeze operation chamber 24a of the dump cylinder 24, and the leveling operation of the bucket 23 is performed correctly even in the lift down operation. Is called.

  The mechanism of the diversion of the diversion control valve 56 is as follows. That is, the internal spool moves in the axial direction to one side or the opposite side depending on the balance of the amount of pressure oil passing through the two throttle portions 56a and 56b. When the amount of pressure oil passing through one throttle part 56a (56b) increases, the pressure loss at the throttle part 56a (56b) increases, and the force that moves the spool to the opposite side works, and the spool moves to the opposite side. Moving. In this case, the amount of pressure oil passing through one throttle portion 56a (56b) is reduced, and the amount of pressure oil passing through the opposite throttle portion 56b (56a) is increased, and the pressure oil returned to the tank. The amount of increases.

  When the spool of the diversion control valve 56 repeats the left and right movements as described above, the pressure oil discharged from the lift-up operation chamber 21a of the lift cylinder 21 during the lift-down operation is given to the squeeze operation chamber 24a of the dump cylinder 24 at a constant rate. So that the angle of the bucket 23 relative to the ground is maintained constant.

  The flow dividing control valve 56 has a third throttle portion 56c in addition to the throttle portions 56a and 56b. The third throttle 56c is pressurized oil discharged from the lift-up working chamber 21a of the lift cylinder 21 when the lift arm 22 is to be lifted down with the dump cylinder 24 fully squeezed to the limit. Is gradually released to the hydraulic tank 55. Without the third throttle 56c, the lift-down operation may not be possible depending on the squeeze angle of the bucket 23. The throttle portion 56c can be disposed on the upstream side or the downstream side of the flow dividing control valve 56.

  The diversion control valve 56 is configured as described above. The shunt control valve 56 facilitates optimization of the leveling mechanism and increases the degree of freedom in designing the work implement. That is, in the conventional leveling mechanism using the parallel control cylinder 27 as in Patent Document 1, in order to optimize the leveling mechanism, the mounting position of the lift cylinder 21 and the dump cylinder 24 and the link mechanism are made to correspond to the leveling. There was a need to design. Since the types of commercially available cylinder diameters (cylinder volumes) that can be used for the lift cylinder 21 and the dump cylinder 24 are gradual, when the working machine is designed, the mounting position and link mechanism are set according to the available cylinder diameter. This is because it is necessary to design. However, in the present invention, since the leveling mechanism can be optimized by the ratio of the hole diameters of the throttle portions 56a and 56b of the flow dividing control valve 56, the working machine can be freely separated from the design restrictions due to the available cylinder diameter. It becomes possible to design.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, the flow dividing control valve 56 that performs the flow dividing action with the amount of oil passing through the two throttle portions 56a and 56b is used as the flow dividing control means. Instead of the flow dividing control valve 56, the inclination angle of the tip attachment is used. Alternatively, the angle of inclination of the lift arm 22 may be detected by an angle sensor, and the flow dividing valve may be replaced with a type that adjusts the nozzle opening area of the variable nozzle based on the detection result. The directions of the lift cylinder 21 and the dump cylinder 24 may be reversed on the cap side and the head side. Further, not only one auxiliary cylinder but also two, for example, can be arranged in parallel if there is enough space. Further, the lift arm 22 is not limited to an integral type, and can be changed to a form that can be bent at a middle portion in the longitudinal direction. The tip attachment is not limited to the bucket 23, and various tip attachments such as a fork, a grader, a roll grab, a container bucket, and a loading hook can be attached. The present invention can also be applied to various working machines other than the front loader.

10: Tractor 20: Front loader 21: Lift cylinder 22: Lift arm 23: Bucket 24: Dump cylinders 46 to 49: Relief valve 50: Hydraulic pump 51: First switching valve 52: Second switching valve 53: First hydraulic piping 54: Second hydraulic piping 56: Split flow control valves 56a to 56c: Restriction portion 57: Fourth hydraulic piping 58: Brake valve 60: Auxiliary cylinder 63: Third hydraulic piping

Claims (4)

A lift arm 22 having an attachment rotatably attached to the distal end and a base end rotatably supported by a support base, a first cylinder for rotationally driving the attachment in the vertical direction, and the lift A hydraulic circuit for a working machine having a second cylinder for driving the arm 22 up and down, and an auxiliary cylinder arranged in parallel to the second cylinder and assisting the second cylinder, the hydraulic circuit comprising:
A first switching valve and a second switching valve which are connected to a hydraulic pressure source and have a first position, a second position and a neutral N position as switching positions;
A pipe that connects the first switching valve and the first cylinder, squeezes the attachment at a first position of the first switching valve, and dumps the attachment at a second position of the first switching valve. First hydraulic piping
The second switching valve and the second cylinder are connected, the lift arm 22 is lifted up at a first position of the second switching valve, and the lift arm 22 is lifted down at a second position of the second switching valve. A second hydraulic pipe that is piped to allow
A third hydraulic pipe connecting the squeeze working chamber of the first cylinder and the lift-up working chamber of the auxiliary cylinder;
A diversion control means for adjusting the amount of oil flowing from the second cylinder to the first cylinder so as to make the angle of the attachment relative to the ground constant, corresponding to the lifting height of the lift arm 22;
With the first switching valve in the N position,
When the second switching valve is switched to the first position, the pressure oil flowing out from the lift-down working chamber of the second cylinder is supplied to the dump working chamber of the first cylinder so as to dump the attachment. At the same time, part or all of the pressure oil flowing out from the squeeze operation chamber of the first cylinder is supplied to the lift-up operation chamber of the auxiliary cylinder, and the remaining pressure oil is returned to the hydraulic source, and
When the second switching valve is switched to the second position, the pressure oil flowing out from the lift-up working chamber of the second cylinder is supplied to the squeezing working chamber of the first cylinder so as to squeeze the attachment. At the same time, the pressure oil that has flowed out from the dumping operation chamber of the first cylinder is returned to the hydraulic pressure source, and the pressure oil that has flowed out from the lift-up operation chamber of the auxiliary cylinder is returned to the squeeze operation chamber of the first cylinder. A hydraulic circuit for a working machine comprising the first to third hydraulic pipes.   The branch flow control means is constituted by a branch flow control valve having two throttle portions for restricting the amount of oil passing therethrough, and pressure oil is supplied to the first cylinder through one throttle portion according to the opening ratio of the two throttle portions. The hydraulic circuit for a working machine according to claim 1, wherein the remaining pressure oil is returned to the hydraulic pressure source through the other throttle portion.   A third position as a switching position is added to the first switching valve, and the second switching valve is set to the N position, and the squeeze operation chamber of the first cylinder is changed to the dump operation chamber at the third position. The hydraulic circuit for a working machine according to claim 1, wherein the first hydraulic pipe is configured to be connected.   A working machine comprising the hydraulic circuit according to any one of claims 1 to 3.