JP4176275B2 - Hydraulic switching valve / PTO interlocking device for raising and lowering the dump truck's cargo box - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic switching valve / PTO interlocking device for raising and lowering a cargo box of a dump truck, in particular, a power take-off device that is interposed between a power unit and a hydraulic pump and can be connected and disconnected, and a hydraulic pressure for raising and lowering the cargo box. A hydraulic switching valve interposed between the hydraulic cylinder and the hydraulic pump / oil tank, and the hydraulic switching valve supplies hydraulic oil from the hydraulic pump to the hydraulic cylinder to raise the cargo box. A lifting position, a neutral position where the hydraulic oil is prevented from returning from the hydraulic cylinder to the oil tank and the cargo box is stopped at an arbitrary tilting position, and the hydraulic oil is allowed to return from the hydraulic cylinder to the oil tank. A movable valve element that can be selectively moved between a lowered position for lowering the box and the power take-off device has a switching operation member that switches between a connected state and a shut-off state. Movable valve The and is operatively connected to a hydraulic switching valve · PTO interlock device having a structure as a power take-off is placed in a connected state when it is in its movable valve body is raised position.
[0002]
[Prior art]
The hydraulic switching valve for raising / lowering the packing box / PTO interlocking device having the above structure is conventionally known (see, for example, Japanese Utility Model Publication No. 2-41362).
[0003]
In the conventional apparatus, as illustrated in FIG. 5, the switching timing a ′ when the power take-out device PTO switches from the shut-off state to the connected state, i. The meshing start time at which the teeth start to mesh with each other is set so as to come in the course of the switching movement from the lowered position D of the movable valve body of the hydraulic switching valve to the neutral position N.
[0004]
[Problems to be solved by the invention]
However, in the configuration in which the movable valve body is switched from the lowered position to the neutral position (that is, the intermediate position between the lowered position and the neutral position) as in the conventional device, the power take-off device is switched from the shut-off state to the connected state. There are the following problems when attempting to make an emergency stop by switching the movable valve element from the lowered position to the neutral position during the lowering operation of the packing box.
[0005]
For example, in the high-speed rotation state of the power unit, the relative rotation speeds of the drive teeth and the driven teeth of the power take-out device are too high to engage with each other, so that the power take-off device cannot be smoothly switched from the disconnected state to the connected state. . Therefore, even if it is attempted to switch the movable valve body of the hydraulic switching valve that is linked to the switching operation member of the power take-off device during the high-speed rotation of the power unit from the lowered position to the neutral position, the power take-off device is caused by the above switching malfunction. Thus, the movable valve body stops in the middle of the stroke (that is, between the lowered position and the neutral position), and it becomes difficult to completely switch to the normal neutral position. In such a case, once the clutch in the power unit is disengaged, the power take-off device can be switched to the connected state and the movable valve body can be switched, but this series of operations is complicated and quick. , Lack of certainty. Therefore, there is a possibility that a quick and accurate response cannot be taken in an emergency where the lowering operation of the packing box should be stopped immediately.
[0006]
Further, when the power unit is stopped, the power take-out device may not be switched to the connected state because the drive teeth and the driven teeth of the power take-out device cannot be meshed with each other depending on their stop positions. At this time, even if the movable valve body of the hydraulic switching valve that is linked to the switching operation member of the power take-out device is to be switched from the lowered position to the neutral position, the movable valve body is caused by the above switching malfunction of the power take-out device. Stops in the middle of the stroke, making it difficult to completely switch to the normal neutral position. Therefore, in this case as well, it is necessary to switch the movable valve body by switching the power take-off device to the connected state by disengaging the clutch or starting the power unit. There is.
[0007]
The present invention has been made in view of such circumstances, and provides a hydraulic switching valve / PTO interlocking device for lifting and lowering a cargo box of a dump truck that can solve the problems of the conventional device with a simple structure. It is aimed.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a power take-off device that is interposed between a power unit and a hydraulic pump and that can be connected / disconnected between the power unit, a hydraulic cylinder for raising and lowering a cargo box, and the hydraulic cylinder and hydraulic pressure A hydraulic switching valve interposed between the pump and the oil tank. The hydraulic switching valve supplies a hydraulic oil from the hydraulic pump to the hydraulic cylinder to raise the cargo box, and from the hydraulic cylinder. A neutral position that prevents the return of hydraulic oil to the oil tank and stops the cargo box at an arbitrary tilting position, and a lowered position that allows the hydraulic oil to return from the hydraulic cylinder to the oil tank and lowers the cargo box. The power take-off device has a switching operation member that switches between a connected state and a shut-off state, and a movable valve body is linked to the switching operation member. It is possible In the dump truck's hydraulic valve for lifting / lowering the cargo box / PTO interlocking device, the power take-off device switches from the shut-off state to the connected state so that the power take-out device is placed in the connected state when the valve body is in the raised position. The timing is set so as not to overlap with the switching movement timing of the movable valve body from the lowered position to the neutral position.
[0009]
According to the above feature, since the power take-off device is not switched from the shut-off state to the connected state during the switching movement of the movable valve body from the lowered position to the neutral position, the movable valve body of the hydraulic switching valve is powered off. Even when mechanically linked to the switching operation member of the device, the movable valve body can be switched from the lowered position to the neutral position at a stroke without being affected by the switching failure of the power take-off device. For this reason, even when an emergency stop is attempted during the lowering operation of the cargo box, the movable valve body is quickly and reliably switched from the lowered position to the neutral position without being affected by the power take-off device, and the lowering operation of the cargo box is immediately performed. Can be stopped.
[0010]
According to a second aspect of the invention, in addition to the feature of the first aspect of the invention, the movable valve body can be moved to a standby position set on the opposite side of the neutral position with the lowered position interposed therebetween. , And is configured to allow the return of the hydraulic oil from the hydraulic cylinder to the oil tank over the entire section of the standby position or the lowered position so that the cargo box can be lowered. The power take-off device is placed in a shut-off state when in the position, and the switching time is set so that the valve body moves from the standby position toward the lowered position.
[0011]
According to this feature, while the movable valve body is switched between the three positions of the lowered position, the neutral position, and the raised position, the power take-off device is not switched, and the device is changed from the shut-off state to the connected state. Since it is not necessary to perform any troublesome clutch operation for switching, the dumping operation of the packing box becomes easier.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below based on the embodiments of the present invention illustrated in the accompanying drawings.
[0013]
In the accompanying drawings, FIGS. 1 to 3 show a first embodiment of the device of the present invention. In particular, FIG. 1 is an overall longitudinal sectional view, and FIG. 2 is a power take-out device and hydraulic pressure at each operation position. FIG. 3 is an enlarged cross-sectional view showing a related configuration of the switching valve, and FIG. 3 is an explanatory diagram of the relationship between the stroke of the movable valve body and each switching mode of the power take-out device / hydraulic switching valve. FIG. 4 is an explanatory diagram showing the relationship between the stroke of the movable valve body and each switching mode of the power take-out device / hydraulic switching valve in the second embodiment, and FIG. 5 shows the stroke and power of the movable valve body in the conventional example. It is a relation explanatory view with each change mode of an extraction device and a hydraulic change valve.
[0014]
First, in FIG. 1, a cargo box 1 mounted on a vehicle body F of a dump truck is pivotally supported 2 so as to be tiltable to the vehicle body F. Between the cargo box 1 and the vehicle body F, a cargo box 1 A hydraulic cylinder Cy that raises and lowers is interposed. Thus, the packing box 1 swings upward as the hydraulic cylinder Cy extends, and swings downward as the contraction.
[0015]
The traveling power unit PU mounted on the vehicle body F includes an engine and a transmission that is linked to the engine via a clutch, as is well known in the art, and is connected to drive wheels on the output side of the transmission. The transmission system is connected. Further, the power unit P is provided with a power take-out device PTO for taking out the power of the engine at any time and driving the hydraulic pump P on the output side of the clutch.
[0016]
The hydraulic pump P has a suction side connected to the oil tank T, and a discharge side connected to the base oil chamber Ca on the piston side of the hydraulic cylinder Cy via the output oil passage 3. The front oil chamber Cb on the piston rod side of the hydraulic cylinder Cy is connected to the oil tank T via the return oil passage 4.
[0017]
A spool valve V as a hydraulic switching valve is interposed in an oil passage connecting the hydraulic cylinder Cy and the hydraulic pump P / oil tank T. The spool valve V is configured by fitting a spool valve body S as a movable valve body into a valve hole 5v formed in the housing 5 so as to be slidable in the axial direction. Is supplied to the base oil chamber Ca of the hydraulic cylinder Cy to raise the cargo box 1 (see FIG. 2 (d)), and oil is supplied from the base oil chamber Ca of the hydraulic cylinder Cy. The neutral position N (see FIG. 2 (c)), which prevents the return of hydraulic oil to the tank T and stops the cargo box 1 at an arbitrary tilting position, and oil from the base oil chamber Ca of the hydraulic cylinder Cy. When shown in a lowered position D (see FIG. 2B) that allows the return of the hydraulic oil to the tank T and lowers the cargo box 1, the base oil chamber Ca of the hydraulic cylinder Cy to the oil tank T is also shown. Waiting position D ′ for allowing the hydraulic oil to return and lowering the packing box 1 (see FIG. Is selectively movable operate between the reference) to.
[0018]
The hydraulic pump P is constituted by a conventionally known gear pump or the like and is built in the housing 5. The housing 5 is formed with a suction port 6 and a discharge port 7 respectively connected to the suction side and the discharge side of the hydraulic pump P. The suction port 6 communicates with the oil tank T, and the discharge port 7 has a valve hole. It opens to an annular groove 8 formed on the inner peripheral surface of 5v. Further, the housing 5 has an output port 9 that is always in communication with the suction port 6 via the annular groove 8 (that is, irrespective of the sliding position of the spool valve body S), and one side and the other side of the annular groove 8. A discharge port 10 and a return port 11 that directly open to the valve hole 5v are formed at positions displaced to the sides.
[0019]
The output port 9 communicates with a base oil chamber Ca of the hydraulic cylinder Cy via a check valve Vc built in the housing 5, and the discharge port 10 bypasses the check valve Vc and a base oil chamber of the hydraulic cylinder Cy. The return port 11 is always in communication with the oil tank T. Thus, the suction port 6, the annular groove 8 and the output port 9 constitute a part of the discharge oil passage 3. The check valve Vc allows only one-way oil flow from the output port 9 to the hydraulic cylinder Cy, and blocks the reverse flow.
[0020]
The spool valve body S is adjacent to the outer peripheral surface in the axial direction with a wide and annular oil passage groove g straddling the discharge port 10, the output port 9 and the return port 11, with the oil passage groove g interposed therebetween. The first and second land portions L1 and L2 are in sliding contact with the valve hole 5v. Thus, when the spool valve body S is in the lowered position D shown in FIG. 2B, the return port 11 communicates with the suction port 6 and the discharge port 10 through the oil passage groove g. While the discharged oil is short-circuited to the oil tank T side, the hydraulic oil in the base oil chamber Ca of the hydraulic cylinder Cy returns to the oil tank T side based on the weight of the cargo box 1 and the load, and the cylinder contracts.
[0021]
When the spool valve body S is in the neutral position N shown in FIG. 2 (c), the first land portion L1 passes through the annular groove 8 (therefore, the output port 9 and the discharge port 7), and the groove 8 and the return port. 11 is disconnected from the discharge port 10 while maintaining the communication state with the port 11. Accordingly, the discharge oil of the hydraulic pump P is short-circuited to the oil tank T side, while the return of hydraulic oil from the base oil chamber Ca of the hydraulic cylinder Cy to the oil tank T side is prevented, and the operation of the cylinder is kept stopped. It is.
[0022]
Further, when the spool valve body S is in the raised position U shown in FIG. 2 (d), the first land portion L1 passes through the annular groove 8 (and hence the output port 9 and the discharge port 7), and the return port 11 and the discharge port 10 And the return port 11 and the discharge port 10 are also blocked. Accordingly, the oil discharged from the hydraulic pump P is not short-circuited to the oil tank T side, but is pumped to the base oil chamber Ca of the hydraulic cylinder Cy to extend the cylinder.
[0023]
The pump shaft Pj of the hydraulic pump P and the power take-off shaft 15 as the driven-side element of the power take-out device PTO are arranged on the same axis line and are connected to each other so that they rotate integrally. The housing 5 is rotatably fitted and supported. A cylindrical slider 16 is spline-fitted 17 on the outer periphery of the power take-off shaft 15 so as to be slidable in the axial direction and not relatively rotatable. A driven gear as a driven tooth is provided on the outer periphery of one end of the slider 16. 18 is provided integrally. A drive gear 19 as a drive tooth that can mesh with the driven gear 18 is provided integrally with a drive shaft 20 as a drive-side element that is rotatably supported by the housing 5. The drive unit 19 is linked to the transmission input shaft or output shaft of the power unit PU via the drive gear 19. Therefore, when the engine of the power unit PU is in the operating state and the clutch is in the connected state, the drive shaft 20 receives the engine output and rotates.
[0024]
Thus, the slider 16 has a blocking position where the driven gear 18 is not meshed with the drive gear 19 (see FIG. 1), and a connecting position where the both gears 18 and 19 are sufficiently meshed by sliding for a predetermined stroke from the blocking position. 2 (see FIGS. 2C and 2D). An annular engagement groove 16a is formed on the outer periphery of the slider 16, and a fork-like tip portion 21a of a shift fork 21 for driving and controlling the slider 16 is engaged with the engagement groove 16a. .
[0025]
The shift fork 21 constitutes a switching operation member of the power take-out device PTO, and its base portion 21b is formed in a cylindrical shape. The outer peripheral portion of the cylindrical base 21 b is slidably fitted into a support hole 5 a formed in the housing 5, and the inner peripheral portion of the shift shaft 22 slidably fitted to the housing 5 is supported. The outer periphery is slidably fitted.
[0026]
The shift shaft 22 is coaxially and integrally connected to one end of the spool valve body S in the illustrated example. An interlocking mechanism I that mechanically interlocks the shift shaft 22 and the shift fork 21 is interposed between the shift shaft 22 and the shift fork 21. In the illustrated example, the interlocking mechanism I includes an annular first engagement groove 22a formed on the outer periphery of the shift shaft 22, and an engagement hole 23 formed in the base 21b of the shift fork 21 corresponding to the engagement groove 22a. And an annular second engagement groove 25 formed in the support hole 5a, and can be selectively engaged with the first engagement groove 22a or the second engagement groove 25 by being fitted into the engagement hole 23. The ball 24 is configured. This ball 24 is a shift fork in the first engagement state in which the ball 24 is engaged across the first engagement groove 22a and the engagement hole 23 as shown in FIGS. The axial relative movement of the shift shaft 21 and the shift fork 21 is restricted while allowing the axial movement of the housing 21 with respect to the housing 5, and the second engagement groove 25 as shown in FIGS. 2 (c) and 2 (d). In the second engagement state where the engagement is performed across the engagement hole 23, the axial movement of the shift fork 21 relative to the housing 5 is restricted while allowing the shift shaft 21 and the shift fork 21 to move relative to each other in the axial direction. The slider 16 is held at the connection position.
[0027]
An operating device Co for selectively switching the switching position of the spool valve body S is connected to the outer end of the spool valve body S via an interlocking rod 27. The operating device Co includes an operating lever L having four operating positions d ′, d, n, u corresponding to the standby position D ′, lowered position D, neutral position N and raised position U of the spool valve body S, respectively. The operating lever L is connected to a holding mechanism (not shown) that can selectively hold it at the four switching positions d ′, d, n, u.
[0028]
Next, the operation of the embodiment will be described with reference to FIG.
[0029]
While the vehicle is traveling, the operation lever L is placed at the first operation position d ′. Thus, when the operating lever L is in the first operating position d ′ and the spool valve body S is in the standby position D ′, the slider 16 has the driven gear 18 separated from the driving gear 19 as shown in FIG. In the shut-off position, the engine output is not transmitted to the hydraulic pump P, and the pump P is stopped. In this state, the ball 24 is in a first engagement state where the ball 24 is engaged across the first engagement groove 22 a and the engagement hole 23, and the shift fork 21 moves in the axial direction relative to the housing 5. The relative movement in the axial direction between the shift shaft 21 and the shift fork 21 is restricted while allowing
[0030]
From this state, the operation lever L is operated toward the second operation position d, and the spool valve body S slides by a predetermined stroke s, and the first switching position X before the lowered position D (see (a) of FIG. 2). ), The driven gear 18 starts to mesh with the drive gear 19. This meshing start timing corresponds to the switching timing a from the shut-off state to the connected state of the power take-out device PTO. Thereafter, the amount of meshing of the driven gear 18 with the drive gear 19 gradually increases as it moves to the right. The device PTO approaches the fully connected state from the incompletely connected state.
[0031]
When the operating lever L is operated past the first switching position X to the second operating position d, the spool valve body S reaches the lowered position D shown in FIG. 1 lowering operation is performed. After this position, as the spool valve body S approaches the neutral position N, the opening degree of the discharge port 10 gradually decreases, and this state is an incompletely lowered state.
[0032]
Further, when the operation lever L is operated toward the third operation position n and the spool valve body S slides by the stroke A from the standby position D ′ and reaches the second switching position Y before the neutral position N, The driven gear 18 and the drive gear 19 are sufficiently engaged, and the power take-out device PTO is completely connected. At this time, since the ball 24 is detached from the first engagement groove 22a and engaged with the second engagement groove 25 and the engagement hole 23, the shift shaft 21 is engaged. In addition, the axial movement of the shift fork 21 relative to the housing 5 is restricted while allowing the relative movement of the shift forks 21 in the axial direction. Therefore, thereafter, only the shift shaft 22 and the spool valve body S slide to the neutral position N side while the shift fork 21 is left behind and the power take-out device PTO is kept in a completely connected state.
[0033]
When the operation lever L is operated to the third operation position n, the spool valve body S has slid by the stroke B from the standby position D ′ and reaches the neutral position N shown in FIG. At this position, the cargo box 1 is held in a lift stop state. After this position, the effective cross-sectional area of the communication portion between the annular groove 8 and the return port 11 gradually decreases as the spool valve body S approaches the raised position U, and this state is an incompletely raised state.
[0034]
Further, when the operating lever L is operated to the fourth operating position u, the spool valve body S has slid by the stroke C from the neutral position N and reaches the raised position U shown in FIG. At this position, the normal lifting operation of the packing box 1 is performed.
[0035]
Thus, the switching timing a for switching from the power take-off device PTO cutoff state to the connected state (incompletely connected state in the illustrated example) is the switching movement timing of the spool valve body S as the movable valve body from the lowered position D to the neutral position N. In other words, the power take-out device PTO is not switched from the shut-off state to the incompletely connected state during the switching movement from the lowered position D to the neutral position N of the valve body S. Even if the spool valve body S of the hydraulic switching valve V is mechanically coupled to the shift fork 21 which is a switching operation member of the power take-out device PTO, the power take-out from the lowered position D to the neutral position N is performed. Switching operation can be performed at a time without being affected by the switching failure of the device PTO. Therefore, even when an emergency stop is attempted during the lowering operation of the cargo box 1, the spool valve body S is quickly and reliably switched from the lowered position D to the neutral position N without being affected by the power take-out device PTO. 1 descent operation can be stopped immediately.
[0036]
Particularly in this embodiment, the spool valve element S can be moved to a standby position D ′ specially set on the opposite side of the neutral position N with the lowered position D in between, and the standby position D ′ or Over the entire section of the lowered position D, the return of the hydraulic oil from the hydraulic cylinder Cy to the oil tank T is allowed and the cargo box 1 can be lowered. Then, when the spool valve body S is at the standby position D ′, the power take-out device PTO is placed in the shut-off state, and while the valve body S is moving from the standby position D ′ toward the lowered position D, the power take-out device The switching time a from the PTO shut-off state to the connected state (incompletely connected state in the illustrated example) is set. Therefore, while the spool valve body S is switched between the lowered position D, neutral position N and raised position U, the power take-off device PTO is not switched, and the device is connected from the shut-off state. Since it is not necessary to perform any troublesome clutch operation for switching to the state, the dumping operation of the packing box 1 is simplified accordingly.
[0037]
Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the switching timing a when the power take-out device PTO is switched from the shut-off state to the connected state (incompletely connected state in the illustrated example) is the switching movement timing of the spool valve body S from the lowered position D to the neutral position N. In order not to overlap, the switching timing a shifts to an intermediate position between the neutral position N and the raised position U of the spool valve body S (in the illustrated example, a position immediately after the neutral position N, that is, an incompletely raised state). Position).
[0038]
Accordingly, in this embodiment, when the spool valve body S is switched from the neutral position N to the raised position U, if the switching cannot be performed smoothly, the power take-out device PTO is turned off by temporarily disengaging the clutch of the power unit PU. After switching from the cut-off state to the cut-off state, the spool valve body S is switched to the raised position U.
[0039]
Thus, in this embodiment, basically the same effect as that of the first embodiment can be achieved.
[0040]
Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various embodiments are possible within the scope of the present invention. For example, in the above-described embodiment, the pump shaft Pj of the hydraulic pump P and the power take-off shaft 15 are integrally formed. However, in the present invention, they may be formed separately and linked together. In the above embodiment, the spool valve body S as the movable valve body and the shift shaft are integrally formed. However, in the present invention, they may be separately formed and interlocked.
[0041]
【The invention's effect】
As described above, according to the first aspect of the present invention, the switching timing when the power take-off device switches from the shut-off state to the connected state does not overlap with the switching movement timing of the movable valve body of the hydraulic switching valve from the lowered position to the neutral position. As a result, even if the movable valve body is mechanically coupled to the switching operation member of the power take-out device, the movable valve body is not affected by the switching failure of the power take-out device from the lowered position to the neutral position. Therefore, even if an attempt is made to make an emergency stop during the lowering operation of the cargo box, the movable valve body is quickly and reliably switched from the lowered position to the neutral position without being affected by the power take-off device. The box can be stopped immediately, improving work safety. In addition, since the above-described effect can be obtained with a simple configuration by simply setting the connection / disconnection switching timing of the power take-off device as described above, the manufacturing cost can be reduced.
[0042]
According to the invention of claim 2, the movable valve element can be moved to a standby position set on the opposite side of the neutral position with the lowered position in between, and the movable valve body can be operated in all sections of the standby position or the lowered position. It is configured to allow the hydraulic oil to return from the hydraulic cylinder to the oil tank and to lower the cargo box, and when the movable valve body is in the standby position, the power take-off device is in a shut-off state. In addition, the switching timing comes in the middle of moving the valve body from the standby position toward the lowered position, so that the movable valve body is switched between the lowered position, neutral position and raised position. While being operated, the power take-off device is kept connected, and it is not necessary to perform a troublesome clutch operation for switching the device from the disconnected state to the connected state. Work efficiency .
[Brief description of the drawings]
FIG. 1 is an overall longitudinal sectional view showing a first embodiment of the apparatus of the present invention. FIG. 2 is an enlarged cross-sectional view showing a related configuration of a power take-off device and a hydraulic switching valve at each operation position in the first embodiment. 3 is an explanatory diagram of the relationship between the stroke of the movable valve body and each switching mode of the power take-out device / hydraulic switching valve in the first embodiment. FIG. 4 shows the stroke of the movable valve body and the power take-out device / hydraulic switching in the second embodiment. FIG. 5 is a diagram illustrating the relationship between each switching mode of the valve. FIG. 5 is a diagram illustrating the relationship between the stroke of the movable valve body and each switching mode of the power take-out device / hydraulic switching valve in the conventional example.
1 .... Packing box 21 ... Shift fork (switching operation member)
a ... Transmission start timing Cy ... Hydraulic cylinder D ... Lowering position D '... Standby position I ... Interlocking mechanism N ... Neutral position P ... Hydraulic pump PTO .... Power take-off device PU ... Power unit S ... Spool valve element (movable valve element)
T ... Oil tank U ... Raised position V ... Spool valve (hydraulic selector valve)

Claims (2)

A power take-off device (PTO) that is interposed between the power unit (PU) and the hydraulic pump (P) and can be connected / disconnected therebetween, a hydraulic cylinder (Cy) for raising and lowering the cargo box (1), A hydraulic switching valve (V) interposed between the hydraulic cylinder (Cy) and the hydraulic pump (P) / oil tank (T);
The hydraulic switching valve (V) supplies hydraulic oil from the hydraulic pump (P) to the hydraulic cylinder (Cy) to raise the cargo box (1) and oil pressure from the hydraulic cylinder (Cy). The neutral position (N) that prevents the hydraulic oil from returning to the tank (T) and stops the packing box (1) at an arbitrary tilting position, and the hydraulic oil from the hydraulic cylinder (Cy) to the oil tank (T) A movable valve body (S) capable of selectively moving between a lowered position (D) for allowing the return and lowering the packing box (1);
The power take-off device (PTO) has a switching operation member (21) for switching between a connected state and a disconnected state, and a movable valve body (S) is linked to the switching operation member (21). In a hydraulic switching valve / PTO interlocking device for lifting and lowering a cargo box of a dump truck, the power take-off device (PTO) is placed in a connected state when the movable valve body (S) is at least in the raised position (U).
The switching timing (a) when the power take-off device (PTO) switches from the shut-off state to the connected state does not overlap with the switching movement timing of the movable valve body (S) from the lowered position (D) to the neutral position (N). A hydraulic switching valve and PTO interlocking device for raising and lowering the dump truck's cargo box, characterized by being set. The movable valve element (S) can be moved to a standby position (D ') set on the opposite side of the neutral position (N) with the lowered position (D) in between, and the standby position (D' ) Or the lowering position (D) is configured to allow the hydraulic oil to return from the hydraulic cylinder (Cy) to the oil tank (T) and to lower the cargo box (1) over the entire section. And
When the movable valve body (S) is in the standby position (D ′), the power take-off device (PTO) is placed in a shut-off state, and the valve body (S) is lowered from the standby position (D ′). The hydraulic switching valve / PTO interlocking device for lifting / lowering a cargo box of a dump truck according to claim 1, wherein the switching timing (a) is set in the middle of moving toward (D).

Images