JP2660267B2 - Lifting position control device for lifting body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Industrial Field of the Invention The present invention relates to a hydraulic cylinder for lifting and lowering which is connected to a lifting and lowering body in order to raise and lower the lifting and lowering body in response to the supply of hydraulic pressure. A hydraulic supply position for connecting the hydraulic supply source and the hydraulic cylinder for raising and lowering and a hydraulic supply stop position for connecting the hydraulic supply source to the oil tank and stopping the supply of hydraulic pressure to the hydraulic cylinder for raising and lowering. And a control valve having a spool valve body slidably fitted in the casing so as to be slidable between the control valve and the spool valve body. The spool valve body is moved to a hydraulic supply position side for raising the elevating body to a predetermined position. The present invention relates to a lifting / lowering position control device of a lifting / lowering body to which a driving member is interlocked and connected so as to switch between the operation of (1) and the operation to a hydraulic supply stop position for stopping the lifting / lowering body.

(2) Conventional technology Conventionally, in such a device, a control valve is interposed between an oil tank and a middle of an oil passage connecting a hydraulic supply source and a hydraulic cylinder for raising and lowering, and a spool valve body of the control valve is hydraulically operated. The elevator is moved to the supply position, and when the elevator reaches the desired position, it is returned to the hydraulic supply stop position to stop the operation of the hydraulic cylinder for lifting, and the switching operation of the control valve causes the hydraulic cylinder for lifting to move to the hydraulic cylinder for lifting. Between the supply of hydraulic pressure and the stop of the supply of hydraulic pressure.

(3) Problems to be Solved by the Invention In the conventional control valve, the casing is provided with an inlet port communicating with the oil passage between the hydraulic supply source and the hydraulic cylinder for raising and lowering, and an outlet port communicating with the oil tank. An annular groove is provided on the outer surface of the spool valve body to allow communication between the two ports. A hydraulic supply stop position for communicating between the two ports via the annular groove, and a hydraulic supply for shutting off between the two ports are provided. The spool valve element is driven between the positions. However, when the hydraulic pressure is supplied by driving the spool valve body to a hydraulic supply position that shuts off between the two ports and the lifting hydraulic cylinder operates by a desired amount, the spool valve body is driven to the hydraulic supply stop position. When moving to the hydraulic supply stop position, the hydraulic pressure at the inlet port, i.e., the hydraulic pressure between the hydraulic supply source and the hydraulic cylinder for elevating and lowering the hydraulic pressure at the inlet port is increased with the annular groove communicating with the inlet port slightly communicating with the outlet port. In some cases, the value becomes lower than a value at which the lifting hydraulic cylinder can be operated, and the operation of the lifting hydraulic cylinder stops. When such a state occurs, the hydraulic oil from the hydraulic pressure supply source is throttled between the annular groove and the outlet port and escapes to the oil tank. As a result, the hydraulic pressure in the oil passage between the hydraulic supply source and the hydraulic cylinder for raising and lowering is not high enough to supply hydraulic pressure to the hydraulic cylinder for raising and lowering, but remains relatively high. Load remains relatively high, causing unnecessary energy consumption and an increase in oil temperature.

The present invention has been made in view of such circumstances,
When stopping the operation of the lifting hydraulic cylinder, the spool valve body of the control valve is reliably operated to the hydraulic supply stop position to avoid unnecessary energy consumption at the hydraulic supply source,
It is an object of the present invention to provide a lifting position control device for a lifting body which can prevent an increase in oil temperature.

B. Configuration of the Invention (1) Means for Solving the Problems According to the present invention, the driving member rotatably disposed includes:
The base end of the leaf spring is fixed so that the base end can be brought into contact with the end of the spool valve body. The base end has an axis parallel to the spool valve body and the outer end can abut on the free end of the leaf spring. The regulating piston is slidably fitted to a cylinder body that is immovable with respect to the casing, and the cylinder body is provided with a regulating hydraulic chamber communicating with a hydraulic supply source and facing the inner end of the regulating piston, A return spring that biases the restricting piston toward the restricting hydraulic chamber contacts the restricting piston.

(2) Action According to the above configuration, when the spool valve element moves to the hydraulic pressure supply position by the rotation of the driving member, the hydraulic pressure is supplied to the hydraulic cylinder for lifting and lowering, and the lifting and lowering body is raised. The regulation piston is in a state where the outer end protrudes against the return spring force due to the action of the oil pressure of the oil pressure supply source. on the other hand,
When the driving member is rotated in the opposite direction to that described above, the spool valve body is pressed toward the hydraulic pressure supply stop position by the portion near the base end of the leaf spring. In addition, the free end of the leaf spring is in contact with the outer end of the regulating piston, and the leaf spring presses the spool valve body while its free end position is regulated by the regulating piston. Will be done. When the spool valve element moves to a position where the oil passage between the hydraulic supply source and the hydraulic cylinder for raising and lowering slightly communicates with the oil tank, the hydraulic pressure in the oil passage slightly decreases, and the hydraulic pressure for the hydraulic cylinder for raising and lowering increases. When the supply is stopped, the hydraulic pressure in the restriction hydraulic chamber slightly decreases, and the reduction in the hydraulic pressure causes the restriction piston to be pressed inward in the axial direction of the return spring. As a result, the regulation by the regulation piston at the free end of the leaf spring is released, and the spool valve element is resiliently moved to the hydraulic supply stop position side by the accumulated spring force, and the hydraulic supply source and the hydraulic cylinder for elevating and lowering. It is possible to communicate with the oil tank without narrowing the oil passage between them.

(3) Embodiment Hereinafter, an embodiment in which the present invention is applied to a working machine of a riding type tractor will be described with reference to the drawings.
In the figure, a transmission unit 2 is attached to a rear part of a vehicle body 1a of a riding type tractor 1, and a pair of left and right rear wheels W, W are steerably suspended below the transmission unit 2. The transmission unit 2 includes a clutch, a transmission, a rear differential, and a front wheel drive shaft so that the rear wheels W, W and the front wheels (not shown) can be driven by receiving the power of an engine (not shown). Things. A work sheet 3 is provided above the transmission unit 2.

A lift cylinder 4 as a hydraulic cylinder for elevating and lowering is installed on the transmission unit 2 below the work sheet 3, and a working machine 5 such as a rotary cultivator as an elevating body which is raised and lowered by the lift cylinder 4 is linked. It is connected to the rear end of the transmission unit 2 via the mechanism 6.

The link mechanism 6 includes a single top link 7 pivotally supported by the transmission unit 2 so as to be vertically swingable, and a pair of lower left and right pivotally supported by the transmission unit 2 below the top link 7 so as to be vertically swingable. A pair of left and right lift arms 9, 9 connected to the lift cylinder 4 and individually connected to intermediate portions of the lower links 8, 8, respectively.
One lift arm 9 is connected to an intermediate portion of one lower link 8 via a telescopic cylinder 10, and the other lift arm 9 is connected to an intermediate portion of the other lower link 8 via a lift rod 11.

According to the link mechanism 6, the work machine 5 can be raised by swinging the lift arms 9, 9 upward by supplying pressure oil to the lift cylinder 4, and the work machine can be lifted by releasing the hydraulic pressure of the lift cylinder 4. 5 can be lowered by its own weight. In addition, the work machine 5 can be tilted left and right with respect to the riding tractor 1 by the expansion and contraction operation of the expansion and contraction cylinder 10 to maintain a horizontal state.

2 and 3, on the transmission unit 2, a cylinder body 12 of the lift cylinder 4 and a bracket
A housing 14 integrally fixed to the housing 13 is fixed. The lift cylinder 4 has a piston 15 slidably fitted in the cylinder body 12, and a hydraulic chamber 16 is defined between the front end wall 12 a of the cylinder body 12 and the piston 15.
Further, a piston rod 17 extending to a side opposite to the hydraulic chamber 16 is connected to the piston 15. On the other hand, an elevating drive shaft 18 having an axis orthogonal to the axis of the piston 15 is rotatably supported on the bracket 13, and a swing arm 19 having a base end fixed to an intermediate portion of the elevating drive shaft 18 and the aforementioned The piston rod 17 is connected. Moreover, the lifting drive shaft 18 protrudes from the bracket 13 on both sides, and both protruding ends of the lifting drive shaft 18 are attached to both lift arms 9 and 9 of the link mechanism 6.
Nine bases are fixed.

In FIG. 4, a hydraulic control device 21 for controlling the supply of pressure oil to the hydraulic chamber 16 in the lift cylinder 4 is shown.
Is provided on one side surface of the housing 14. The hydraulic control device 21 includes a relief valve 23, a one-way valve 25, a descending valve 26,
An ascending control valve 27, a descending control valve 28, and a regulating piston 24 as control valves are provided.

An oil passage 32 is connected to an outlet of a hydraulic pump 31 as a hydraulic supply source connected to an oil tank 30 via a filter 29, and a relief valve 23 is connected to the oil passage 32. Therefore, the oilway
The pressure oil regulated by the relief valve 23 is supplied to the relief valve 32, and the oil passage 32 is connected to the one-way valve 25. In addition, the lift control valve 27 is provided between the intermediate portion of the oil passage 32 and the oil tank 30.
Is interposed.

The one-way valve 25 has an inlet port 42 connected to the oil passage 32.
Is opened only when the pressure becomes higher than the outlet port 43. The outlet port 43 communicates with the inlet port 44 of the descending valve 26 and is connected to the hydraulic chamber 16 of the lift cylinder 4 via the oil passage 45. Further, the descending valve 26 includes a valve body 47 that opens and closes between the inlet port 44 and the outlet port 46, and a back pressure chamber 48 for generating an oil pressure that urges the valve body 47 to the closing side. The chamber 48 communicates with the inlet port 44 via an orifice 49 provided in the valve body 47. The outlet port 46 is opened to the oil tank 30, and the oil passage 50 communicating with the back pressure chamber 48 communicates with the inlet port 51 of the descending control valve 28.

2, the front end wall 12a of the cylinder body 12 of the lift cylinder 4 has an outlet port 4 of the one-way valve 25.
An oil passage 45 communicating with the inlet port 44 of the lower valve 3 and the lowering valve 44 is provided. Further, a gentle lowering valve 52 is disposed on the front end wall 12a so as to be interposed between the oil passage 45 and the hydraulic chamber 16. The gentle downward pressure 52 allows a flow of oil from the passage 53 leading to the oil passage 45 to the hydraulic chamber 16 but restricts the flow in the opposite direction, and adjusts the minimum opening of the check valve 54. And an adjustment bolt 55. In addition, an overload relief valve 56 is provided at the front end 12a so as to be interposed between the hydraulic chamber 16 and the oil tank 30.
Is arranged. The overload relief valve 56 opens when the hydraulic pressure in the hydraulic chamber 16 rises excessively, and releases the excess pressure to the oil tank 30.

5A to 5C, the lift control valve 27
The communication between the inlet port 34 communicating with the oil passage 32 and the outlet port 41 communicating with the oil tank 30 is switched by the axial movement of the spool valve body 58. A portion near the base end of the leaf spring 61 abuts on a contact pin 59 provided coaxially at one end, and the spool pin 59 is fixed to the leaf spring by a spring 62 provided between the spool valve body 58 and the casing 22. The spring is urged in the direction of contact with 61. In addition, the base end of the leaf spring 61 is fixed to a control shaft 66 as a driving member supported on the casing 22 so as to be rotatable around an axis orthogonal to the axis of the spool valve element 58. The spool valve element 58 moves in the axial direction in response to the rotation of the leaf spring 61.

The inlet port 34 and the outlet port 41 are disposed on the casing 22 with the inlet port 34 disposed on the leaf spring 61 side. The spool valve element 58 is slidably fitted to the casing 22 so as to switch between communication and blocking between the ports 34 and 41, and the outer surface of the spool valve element 58 connects between the ports 34 and 41. An annular groove 58a that can communicate is provided.

The control shaft 66 has a neutral position in which the leaf spring 61 is at a position substantially orthogonal to the axis of the spool valve element 58 as shown in FIG.
As shown in FIG. 5A, it is rotatable between a raised position that is rotated upward and a lowered position that is slightly rotated downward from the neutral position. Thus, when the control shaft 66 is at the neutral position, the spool valve element 58 of the ascending control valve 27 is at a hydraulic pressure supply stop position in which the two ports 34, 41 communicate with each other via the annular groove 58a, and from the neutral position. When the control shaft 66 is rotated to the raised position as shown in FIG. 5A, the spool valve element 58 of the raised control valve 27 is in the hydraulic pressure supply position in which the ports 34 and 41 are shut off. Moreover, when the control shaft 66 is rotated from the neutral position to the lowered position,
The spool valve element 58 of the ascending control valve 27 keeps the oil pressure supply stopped state in which the ports 34 and 41 communicate with each other.

The lowering control valve 28 includes a poppet valve body 64 that can open and close between an outlet port 63 and an inlet port 51 communicating with the oil tank 30, and a spring 65 that urges the valve body 64 in a valve closing direction. It is arranged coaxially with the lift control valve 27. That is, the poppet valve body 64 can coaxially contact the other end of the spool valve body 58 in the ascending control valve 27, and the spool when the control shaft 66 is in the neutral position with the poppet valve body 64 in the closed position. The other end of the valve element 58 contacts the poppet valve element 64. Thus, when the control shaft 66 moves from the neutral position shown in FIG. 4 to the lowered position, the poppet valve 64 is opened by being pressed by the spool valve 58. When the spool valve element 58 is at the hydraulic pressure supply position, the poppet valve element 64 is not in contact with the spool valve element 58, and the closed state of the descending control valve 28 is maintained by the spring 65.

The regulating piston 24 is slidably fitted to a cylinder body 33 fixedly arranged in the casing 22.
And a second piston 36 substantially integrated with the first piston 35 and arranged coaxially with the first piston 35,
This regulating piston 24 has an outer end, that is, a second piston.
The outer end of 36 is arranged in parallel with the spool valve body 58 of the elevation control valve 27 so that the outer end of the 36 can contact the free end of the leaf spring 61.

The first piston 35 is slidably fitted to the cylinder body 33 while defining a regulated hydraulic chamber 38 through an inlet port 34 of the elevation control valve 27 between the inner end thereof and the cylinder body 33. A guide hole 39 for fitting and fixing the cylinder body 33 is formed in the casing 22 so as to have an inner diameter corresponding to the outer diameter of the cylinder body 33. Tsuba
A second piston 36 having an inner end 36a is slidably penetrated through the outer end wall of the guide hole 39, and the second piston 36 is provided at the outer end of the first piston 35 projecting from the cylinder body 33. The ends are abutted coaxially. Moreover, a first return spring 37a is contracted between the outer end wall of the guide hole 39 and the guide flange 36a of the second piston 36, and the second piston 36 is connected to the first piston 35 by the spring force of the first return spring 37a. The pistons 35, 36 are substantially united by being biased to abut. Moreover, the inner end of a second return spring 37b, whose outer end can contact the outer end wall of the guide hole 39, is in contact with the guide flange 36a. When the oil pressure is low, that is, when the regulating piston 24 is returned to the maximum inward by the spring force of the first return spring 37a, it is in a free state and does not exert a spring force. As a result, the restricting piston 33 is contracted between the outer end wall of the guide hole 39 and the guide flange 36a in response to being pressed outward, thereby exerting a spring force.

In the hydraulic control device 21, the control shaft 66 and the leaf spring 61
Is in the neutral position as shown in FIG.
27 is in a state of communicating between the inlet port 34 and the outlet port 41, and the descending control valve 28 is kept closed.
, The lift cylinder 4 is inactive.

Next, when the control shaft 66 and the leaf spring 61 are rotated to the raised position as shown in FIG.
The spool valve body 58 is moved by the spring force of the spring 62 toward the hydraulic supply device that has cut off between the outlet port 41 and the outlet port 41, whereby the pressure oil from the hydraulic pump 31 is lifted by the lift control valve 27, the one-way valve
25, the air is supplied to the hydraulic chamber 16 of the lift cylinder 4 via the gentle lowering valve 52, and the lift cylinder 4 is extended. The extension operation of the lift cylinder 4 is transmitted to the link mechanism 16 via the lifting drive shaft 18, whereby the working machine 5 is driven to rise. At this time, the hydraulic pump 31 is also
High hydraulic pressure from the control piston 24
Move the outer end in the direction to project from the casing 22,
In this state, the first and second return springs 37a, 37b are contracted, and the spring force of both return springs 37a, 37b is reduced by the regulating piston 24.
Acts in the direction of returning to the original.

Further, during the rotation of the control shaft 66 and the leaf spring 61 from the raised position to the neutral position side as shown by 5B, the free end of the leaf spring 61 abuts on the outer end of the regulating piston 24 in the protruding state,
The leaf spring 61 presses the spool valve body 58 toward the proximal end while curving while the rotation of the free end portion thereof is regulated by the regulating piston 24, and the spool valve body 58 is pressed toward the hydraulic pressure supply stop position side. Is done. Therefore, the leaf spring 61 accumulates the spring force while bending.

When the control shaft 66 and the leaf spring 61 are further rotated to the neutral position side so that the spool valve element 58 is pressed to a state where the spool valve element 58 slightly communicates between the inlet port 34 and the outlet port 41, the hydraulic pressure of the inlet port 34 is reduced. That is, the oil pressure of the oil passage 32 is
The pressure drops below the pressure at which the pressure oil can be supplied to the hydraulic chamber 16 of the lift cylinder 4, and the extension operation of the lift cylinder 4 stops.
In addition, the hydraulic pressure in the regulating hydraulic chamber 38 also decreases in accordance with the decrease in the oil pressure in the inlet port 34, and as shown in FIG. 5C, the regulating piston 24 returns to the original state by the spring forces of the first and second return springs 37a and 37b. Returning to the position, the regulation of the free end of the leaf spring 61 by the regulation piston 24 is released. For this reason, the leaf spring 61 exerts the spring force stored up to that point, and the spool valve element 58 reliably presses the oil pressure supply stop position to reliably communicate the annular groove 58a communicating with the inlet port 34 with the outlet port 41. Will be done.

When the control shaft 66 and the leaf spring 61 rotate to the lowering position, the lowering control valve 28 opens, and the pressure in the back pressure chamber 48 decreases at the lowering valve 26. On the other hand, since the weight of the working machine 5 acts on the hydraulic chamber 16 of the lift cylinder 4, the hydraulic pressure at the inlet port 44 of the descending valve 26 is high, and therefore the descending valve 26
Is opened, and the hydraulic pressure in the hydraulic chamber 16 is released. In addition, at this time, the discharge of the pressure oil from the hydraulic chamber 16 is restricted by the function of the slow down valve 52, the contraction operation of the lift cylinder 4 is slow, and the working machine 5 also descends slowly.

With reference to FIGS. 6, 7, 8, 9, and 10, a control shaft 67 for operating the ascending control valve 27 and the descending control valve 28 is provided with an operation lever 67 for position control. And a feedback control link mechanism 69 is connected via the position control link mechanism 68.

On the outer surface of the casing 22 of the hydraulic control device 21,
An approximately U-shaped support bracket 70 is fixedly mounted, and the operation lever 67 is supported by the support bracket 70 so as to be rotatable and maintain its operation position by frictional force. That is, the base end of the operation lever 67 is fixed to the rocking plate 71, and the pivot 72 is implanted on the rocking plate 71. On the other hand, the support bracket 70 is provided with a through hole 73 through which the pivot 72 penetrates, and a support cylinder 74 connected to the through hole 73 is fixed to the outer surface of the support bracket 70. The oscillating plate 71 supports a friction plate 75 made of a material having a large friction coefficient with a support bracket 70.
The pivot 72 is inserted into the through hole 73 and the support cylinder 74. Moreover, the pivot 72 and the support cylinder
Between the 74, a cylindrical liner 76 is interposed.

In FIG. 11, the outer periphery of the support cylinder 74 is formed in a substantially oval shape having a pair of flat surfaces 74a, 74a parallel to each other, and allows the support cylinder 74 to move along the axial direction. A first receiving plate 77 is fitted on the outer periphery of the support cylinder 74 to prevent rotation about the axis. The first receiving plate 77 and the support bracket 70
A disc spring 78 is interposed therebetween, and the first receiving plate 77 is urged outward in the axial direction of the support cylinder 74 by the spring force of the disc spring 78.

The pivot 72 has a threaded shaft protruding outward from the support cylinder 74.
A second receiving plate 79 is provided coaxially with the first receiving plate 77. The second receiving plate 79 has a hole 79a for projecting the screw shaft portion 72a outward and covers the open end of the support cylinder 74. . Moreover, a pin 81 parallel to the axis of the support cylinder 74 is inserted through the first and second receiving plates 77 and 79, and the two receiving plates 77 and 79 are substantially integrated.

A washer 82 made of a material having a small friction coefficient such as an oil-impregnated resin is provided on the screw shaft portion 72a protruding from the second receiving plate 79.
A nut 83 is screwed in between the outer surface of the receiving plate 79 and a lock nut 84 is screwed into the screw shaft portion 72a protruding from the nut 83.

In this manner, the swing plate 71, that is, the operation lever 67 is supported by the support bracket 70, but the swing plate 71 is pressed against the support bracket 70 via the friction plate 75 by the spring force of the disc spring 78, The operation rotation position of the operation lever 67 is held by the frictional force between the swing plate 71 and the friction plate 75 unless an external force is applied.

By the way, the rotation range of the operation lever 67 and the swing plate 71 is restricted to a range in which the swing plate 71 comes into contact with the stopper 93 provided on the support bracket 70 and the support bracket 70 itself. That is, the operating lever 67 is moved between the maximum ascending side operation position indicated by the chain line in FIG. 9 (solid line in FIG. 10) and the maximum descending side operation position as indicated by the solid line in FIG. 9 (dashed line in FIG. 10). It is pivotable.

The position control link mechanism 68 includes a rotation bar 86 having one end connected to the swing plate 71 via a connection pin 85 parallel to the pivot 72.
A lever 88 having one end fixed to the control shaft 66 protruding from the casing 22 and the other end rotatably supported by a roller 87 as a contact member slidable on the side surface of the rotary bar 86; And a coil spring 89 contracted between the support bracket 70 and the lever 88 so as to exert a spring force in a direction to slide the rotation bar 86 on the side surface thereof. The link mechanism 69 is connected via a connecting pin 90.

When the connecting pin 90 at the other end is in the fixed position, the operation bar 67 and the swinging plate 71 are rotated from the maximum descending operation position to the maximum ascending operation position as shown by an arrow 91 with the pivot bar 86 in the fixed position. When the roller 87 is rotated in the same direction as the swinging plate 71, the lever 88 that follows the rotating bar 86 as the roller 87 slides on the rotating bar 86, The control shaft 66 is arranged to rotate in the direction indicated by the arrow 92 in accordance with the rotation.

Referring again to FIGS. 2 and 3, in order to detect the vertical position of the work machine 5, that is, the rotational position of the lifting drive shaft 18,
A rotation shaft 94 having an axis parallel to the lifting drive shaft 18 is rotatably supported on a bracket 13 integral with the cylinder body 12 of the lift cylinder 4. One end of a link plate 95 is fixed to the inner end of the rotation shaft 94, and one end of a link plate 97 is connected to the other end of the link plate 95 via a pin 96 parallel to the rotation shaft 94. The other end of the plate 97 is connected to the swing arm 19. As a result, the amount of rotation of the lifting drive shaft 18, that is, the work implement 5
The rotation shaft 94 is rotated by an amount of angular displacement corresponding to the vertical position.

The rotation shaft 94 protrudes from the bracket 13, and the outer end of the rotation shaft 94 and the other end of the rotation bar 86 in the position control link mechanism 68 are connected to a feedback control link mechanism.
Connected via 69.

The link mechanism 69 for feedback control includes a link 100 having one end connected to an outer end of the rotating shaft 94 via a bolt 98,
A link 101 having one end connected to the other end of the rotating bar 86 via the connecting pin 90, and a connecting means 102 for connecting the other ends of the links 100 and 101 so that their connecting positions are adjustable.

Referring to FIG. 12 together, the connecting means 102 includes a link 101
The other end of the link 101 has a long hole 103 formed long along the longitudinal direction of the link 101, and the other end of the link 101 has an adjustment bolt 104 fixed to the other end of the link 101 with an axis extending along the longitudinal direction of the link 101.
And an adjustment bolt having an annular engagement groove 105a
An adjusting nut 105 screwed into and out of the engaging groove 104;
A connecting plate 106 having a locking portion 106a at one end to be engaged with 5a
A connecting shaft 107 fixed to the other end of the connecting plate 106 so as to pass through the other end of the link 100 and slide through the long hole 103 while sliding on one surface of the link 101; A lock bolt 109 screwed to the connecting shaft 107 via a washer 108 between the fixed link 103 and the fixed link 101.

A circular hole 110 is formed at the other end of the link 100. The connecting shaft 107 has a cylindrical portion 107a inserted into the circular hole 110 via the cylindrical liner 110, and a rectangular prism portion 107b movable in the elongated hole 103. The cylindrical portion 107a has a length that allows the link 100 to swing around the axis of the connecting shaft 107 between the connecting plate 106 and the link 101. The length of the prism 107b is set so that the tip of the prism 107b does not protrude from the elongated hole 103 when the step 107c is in sliding contact with one surface of the link 101. Further, the connecting shaft 107 is provided with a screw hole 115 over the entire length thereof, and a lock bolt 109 is screwed into the screw hole 115.

According to the connecting means 102, the position in the elongated hole 103 of the connecting shaft 107, that is, the connecting position of the two links 100 and 101 can be adjusted by loosening the lock bolt 109 and rotating the adjusting nut 105. By tightening the bolt 109, its position can be fixed.

According to such a feedback control link mechanism 69, when the work implement 5 is raised, the operation shown in FIGS.
The link 101 moves in the direction indicated by the arrow 112 in the figure, and when the link 101 moves downward, the link 101 moves in the direction opposite to the direction indicated by the arrow 112.

Moreover, the operation lever 67 and the position control link mechanism 68
When the operation lever 67 is operated on the ascending side (the state shown by the solid line in FIG. 10), the control shaft 66 is rotated in the direction of the arrow 92, and the feedback control link mechanism according to the ascending operation of the work machine 5. The operation of 69 causes the control shaft 66 to rotate to the neutral position, and when the operation lever 67 is operated to move down (the state shown by the solid line in FIG. 9), the control shaft 66 is moved from the center position to the arrow 92.
And the control shaft 66 is rotated to the neutral position by the operation of the feedback control link mechanism 69 in accordance with the self-weight lowering operation of the work machine 5, but the self-weight lowering of the work machine 5 is suppressed by the ground resistance. Then, the control shaft 66 is connected to the rotation bar 86 so as to separate the rotation bar 86 from the roller 87 as shown in FIG. 9 in order to rotate the control shaft 66 to the hydraulic pressure release position.

Next, the operation of this embodiment will be described. To raise the working machine 5 in the lowered state, the operation lever 67 is rotated in the direction shown by the arrow 91, and the hand is released from the operation lever 67 at an arbitrary position. Since the swing plate 71 integrated with the operation lever 67 is pressed toward the support bracket 70 via the friction plate 75 by the spring force of the disc spring 78, the friction between the friction plate 75 and the swing plate 71 The position of the swing plate 71, that is, the operation lever 67 is held by the force. Moreover, since the spring force of the disc spring 78 can be adjusted by the nut 83 and the lock nut 84,
The adjustment of the frictional force can be easily performed.

Assuming that the operation lever 67 is rotated to the maximum ascending position, for example, as shown by the solid line in FIG. 10, the rotation bar 86 of the position control link mechanism 68 is
, The lever 88 and the control shaft 66 rotate in the direction shown by the arrow 92 in accordance with the rotation of the rotation bar 86, and the control shaft 66 and the leaf spring 61 move as shown in FIG. 5A. It becomes the ascending position. As a result, the inlet port 34 and the outlet port 41 of the lift control valve 27 are shut off, and the pressure oil from the hydraulic pump 31 is supplied to the hydraulic chamber 16 of the lift cylinder 4. Accordingly, the lift cylinder 4 is extended, and the work implement 5 is raised via the link mechanism 6.

The rotating shaft 94 also rotates according to the lifting operation of the work machine 5,
In the feedback control link mechanism 69, the link 101 moves in the direction indicated by the arrow 112, and the rotating bar 86 also moves the connecting pin 85.
Can be rotated around the fulcrum. This allows the rotation bar 86
The control shaft 66 and the lever 88 provided with the roller 87 that slides in the opposite direction rotate in the direction opposite to the arrow 92. Therefore, the leaf spring 61 rotates to the descending side, and immediately before the work machine 5 rises to the desired position, the leaf spring 61 is at the position shown in FIG. 5B.

In this state, the free end of the leaf spring 61 is
The rotation of the leaf spring 61 is restricted by contact with the outer end of the ascending control valve 27 and the spool valve body of the ascending control valve 27 near the base end while bending.
58 is pressed toward the hydraulic pressure stop position, and the spring force is accumulated in the leaf spring 61.

Next, the inlet port 34 and the outlet port of the lift control valve 27
When the control shaft 66 further rotates toward the neutral position side until the communication between the control cylinder 41 and the control cylinder 41 is slight, the supply of the hydraulic pressure to the hydraulic chamber 16 of the lift cylinder 4 is stopped, and the restricting piston 24 is moved as shown in FIGS. To the inward side, thereby causing the leaf spring 61
In accordance with the release of the rotation restriction of the free end of the leaf spring 61.
Exerts the spring force accumulated so far at once,
The spool valve element 58 is pushed to a hydraulic supply stop position that completely communicates between the inlet port 34 and the outlet port 41.
Accordingly, the flow resistance between the oil passage 32 and the oil tank 30 is reduced, so that an unnecessary load is not applied to the hydraulic pump 31 and the oil temperature is prevented from rising.

When lowering the work machine 5 at the ascending position, the operation lever 67 may be rotated in the direction opposite to the arrow 91. Then, the lever 88 follows the rotation of the rotation bar 85.
Also rotates in the direction opposite to the arrow 92, and when the control shaft 66 and the leaf spring 61 are at the lowered position, the lowering control valve 28 is opened, and the pressure is controlled from the hydraulic chamber 16 of the lift cylinder 4 by the gentle lowering valve 52 while being restricted. The oil is discharged, the lift cylinder 4 contracts slowly, and the work implement 5 descends slowly. At this time, in the feedback control link mechanism 69, the link 101 moves to the side opposite to the arrow 112, and the rotation bar 86 of the position control link mechanism 68
Rotates about the connection pin 85 as a fulcrum. Therefore, a lever 88 having a roller 87 that slides on a rotating bar 86 and a control shaft
When the control shaft 66 is in the neutral position as shown in FIG. 4, the lower control valve 28 shuts off the inlet port 51 and the outlet port 63. The discharge of pressurized oil from the chamber 16 is stopped, and the work equipment 5
Reaches a desired position corresponding to the operation of the operation lever 67.

Next, it is assumed that the operating lever 67 is operated to the maximum down position as shown by the solid line in FIG. In this case, the lever 88 follows the rotation of the rotation bar 86.
Also rotates in the direction opposite to the arrow 92, and the leaf spring 61 is at the lowered position. In addition, the amount of rotation of the leaf spring 61 from the neutral position to the lower side is limited, and the rotation of the rotation bar
The control shaft 66 rotates only within a limited range even if the amount of rotation of the 86 to the descending side is large, and the roller 87 separates from the side surface of the rotating bar 86 as shown in FIG.

On the other hand, when the work machine 5 descends until it touches the ground, the rotating bar 86
Is the position shown by the chain line in FIG. 9, and in this state, the lever
88 cannot be rotated in the direction indicated by the arrow 92, and the control shaft 66 does not rotate.
And the leaf spring 61 remains in the lowered position, and the hydraulic chamber 16 of the lift cylinder 4 remains released. Therefore, even if the ground resistance of the working machine 5 acts on the lift cylinder 4 via the link mechanism 6, the lifting drive shaft 18, and the swing arm 19,
Since the hydraulic chamber 16 of the lift cylinder 4 is in a hydraulic release state, no overload acts on the lift cylinder 4.

By the way, the feedback control link mechanism 69 feeds back the operation amount of the work implement 5 to the position control link mechanism 68. In order to accurately transmit the operation amount, it is necessary to adjust the connection point of the links 100 and 101. is there. In the adjustment, when the lock nut 109 is loosened and the adjusting nut 105 is rotated in the connecting means 102 for connecting the links 100 and 101, the connecting shaft 107 moves along the elongated hole 103. Therefore, when the position of the connecting shaft 107 in the elongated hole 103, that is, the connecting position of the two links 100, 101 becomes a desired position, the connecting position can be fixed by tightening the lock bolt 109. Therefore, the adjustment of the connection point can be performed extremely easily, and the adjustment operation is easy, so that the adjustment accuracy is also increased.

C. Effects of the Invention As described above, according to the present invention, the base end of the leaf spring is fixed to the rotatable driving member so that the base end of the spool valve body can be abutted. A regulating piston having an axis parallel to the spool valve body and having an outer end abuttable on the free end of the leaf spring is slidably fitted to a cylinder body immovable with respect to the casing. The cylinder body is provided with a regulating hydraulic chamber communicating with the hydraulic supply source and facing the inner end of the regulating piston, and a return spring for urging the regulating piston toward the regulating hydraulic chamber is in contact with the regulating piston. Therefore, when the drive member moves the spool valve element from the hydraulic supply position to the hydraulic supply stop position, the regulating piston restricts the rotation of the free end of the leaf spring, accumulates spring force in the leaf spring, and supplies hydraulic pressure. The oil passage between the source and the hydraulic cylinder Release the restriction of rotation of the leaf spring by the restricting piston in a state where it is slightly connected to the spool spring, and make the spring force accumulated by the leaf spring at a stroke to move the spool valve body to the hydraulic supply stop position without fail. Can avoid unnecessary energy consumption and prevent an increase in oil temperature.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a rear perspective view of a riding tractor to which the present invention is applied, FIG. 2 is an enlarged vertical sectional view of a lift cylinder, and FIG. III-III
FIG. 4 is a hydraulic control circuit, FIG. 5A is a cross-sectional view showing the operation of the ascending control valve, descending control valve, and regulating piston when the control shaft is at the ascending position, and FIG. 5B is a control shaft. Is a cross-sectional view showing the operation mode of the ascending control valve, the descending control valve and the regulating piston during the rotation from the ascending position to the neutral position side, FIG.5C is an ascending control valve when the control shaft returns to the neutral position, FIG. 6 is a sectional view showing an operation mode of the lowering control valve and the regulating piston, FIG. 6 is a plan view showing an operation unit for operating the work machine, FIG. 7 is a sectional view taken along line VII-VII of FIG.
Fig. 6 is a sectional view taken along the line VIII-VIII in Fig. 6, Fig. 9 is a sectional view taken along the line IX-IX in Fig. 6, showing a state in which the operating lever is operated to the lowered position, and Fig. 9 is a cross-sectional view corresponding to FIG. 9, FIG. 11 is a cross-sectional view taken along line XI-XI of FIG. 6, and FIG. 12 is an enlarged cross-sectional view taken along line XII-XII of FIG. 4. Lift cylinder as hydraulic cylinder for lifting and lowering, 5
…… Working machine as elevating body, 22 …… Casing, 24 ……
Restriction piston, 27 ... Lift control valve as control valve, 30 ...
... oil tank, 31 ... hydraulic pump as hydraulic supply source, 33
…… Cylinder body, 37a, 37b …… Return spring, 38 …… Regulatory hydraulic chamber, 58 …… Spool valve body, 61 …… Leaf spring, 66 …… Control shaft as drive member

Claims (1)

(57) [Claims] An elevation hydraulic cylinder (4) is connected to the elevating body (5) for raising and lowering the elevating body (5) according to the hydraulic pressure supply, and a hydraulic supply source (31) and an elevating hydraulic cylinder ( Between 4), a hydraulic supply device that communicates the hydraulic supply source (31) and the hydraulic cylinder (4) for elevating and lowering, and a hydraulic cylinder (4) that communicates the hydraulic supply source (31) to the oil tank (30). A control valve (27), which is slidably fitted to a casing (22) so as to be movable to and from a hydraulic supply stop position for stopping the supply of hydraulic pressure to the casing, The spool valve element (58) switches between operation to a hydraulic supply position side for raising the elevating body (5) to a desired position and operation to a hydraulic supply stop position for stopping the elevating body (5). The drive member (66) is interlocked and connected to the elevating body There are, to a drive member which is pivotably arranged (66), the spool valve body (58) the leaf spring so as to a proximally possible contact with the end portion (61)
A regulating piston (24) having an axis parallel to the spool valve body (58) and having an outer end abuttable on the free end of the leaf spring (61) is fixed to the casing ( The cylinder body (33) slidably fitted to the cylinder body (33), which is fixed to the cylinder body (22). The cylinder body (33) communicates with the hydraulic supply source (31) and faces the inner end of the regulating piston (24). A regulating hydraulic chamber (38) is provided, and a return spring (37b) for biasing the regulating piston (24) is brought into contact with the regulating piston (24) toward the regulating hydraulic chamber (38). , Lifting position control device of the lifting body.