JPH04292399A - Boom drive device for boom-equipped working vehicle - Google Patents

Abstract

PURPOSE:To restrain large swing of a boom that is apt to occur at start and stop in a boom-equipped working vehicle. CONSTITUTION:At start and stop, a bypass valve 15 is opened to be operated prior to operation of a change-over valve 13. As a result, since a part of fluid supplied to an actuator 10 at start or stop is bypassed through a throttle valve 17 and the bypass valve 15, the turn of a boom 1 is started or stopped moderately. Therefore any large swing of the boom that is apt to occur at start and stop can be restrained.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a boom drive device for a work vehicle with a boom, such as an aerial work vehicle, a concrete pump vehicle with a boom, or a truck crane vehicle, which can suppress large swings of the boom that tend to occur when starting or stopping. .

0002

[Prior Art] Conventionally, as shown in FIG. 6, a boom-equipped work vehicle (
In the aerial work vehicle) 2, the boom 1 may be rotated or raised and lowered (moved up and down) in a fully extended state.

0003

[Problems to be Solved by the Invention] However, when the boom 1 starts swinging or when the boom 1 starts raising and lowering, the boom 1 and the bucket 3 shake greatly, causing a shock so large that the worker is thrown out from inside the bucket 3. receive. In addition, a large impact is applied to the swinging fluid actuator and the undulating fluid actuator of the boom 1. The cause of this is that the directional control valve of each fluid actuator is electromagnetic, so when the boom drive switch is turned on or off, the directional control valve spool suddenly switches to the fully open or fully closed position, causing the fluid to flow from the pump. This is because fluid is suddenly supplied to the actuator. In other words, if the entire amount of fluid is suddenly supplied to each fluid actuator when the boom 1 starts turning or luffing, the jerk/acceleration at the start will suddenly increase as the boom 1 will suddenly start turning or luffing. As a result, the boom 1 and bucket 3 swing significantly in the left-right direction or up-down direction. Furthermore, when the boom 1 stops turning or undulating, the supply of fluid to each fluid actuator suddenly stops, causing the boom 1 and the bucket 3 to swing significantly in the left-right direction or the up-down direction.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a boom drive device for a work vehicle with a boom that can suppress the large swings of the boom that tend to occur when starting or stopping.

[0005]

[Means for Solving the Problems] In order to achieve the above object, a boom drive device of a first invention includes an actuator for driving a boom mounted on a work vehicle, a pump for supplying fluid to this actuator, and a boom drive device for driving a boom mounted on a work vehicle. An electromagnetic direction switching valve is provided in the fluid supply passage between the pump and the actuator to switch the driving direction of the actuator, and an electromagnetic direction switching valve is provided in the fluid supply passage to bypass a portion of the fluid supplied to the actuator. a bypass valve that allows
A throttle valve provided in the bypass passage in which this bypass valve is provided opens the bypass valve prior to the opening operation of the directional switching valve when the boom is started, and from the time the switching valve starts opening. The present invention is characterized by comprising a control means for closing and operating the bypass valve after a predetermined period of time.

[0006] Furthermore, the boom drive device of the second invention includes an actuator for driving a boom mounted on a work vehicle;
a pump that supplies fluid to the actuator; an electromagnetic direction switching valve that is provided in a fluid supply passage between the pump and the actuator and switches the drive direction of the actuator; A bypass valve that bypasses a part of the fluid supplied to the actuator, a throttle valve provided in the bypass passage where this bypass valve is provided, and when the boom is stopped, the bypass valve is closed prior to the closing operation of the directional switching valve. The present invention is characterized by comprising control means for opening the valve and closing the directional switching valve after a predetermined period of time from the start of the opening operation of the bypass valve.

[0007]

In the first invention, when the boom is started, the bypass valve is opened by the control means prior to the opening operation of the directional control valve. Therefore, fluid is supplied from the pump to the actuator, but some of this supplied fluid is bypassed through the throttle valve and bypass valve, so the actuator suddenly receives the entire amount of fluid from the pump. is not supplied. Therefore, since the boom starts to rotate or rise slowly, the jerk/acceleration at the time of startup does not suddenly increase, and large shaking of the boom at the time of startup is suppressed. Then, when a predetermined period of time has elapsed from the start of the opening operation of the switching valve, the bypass valve is closed by the control means, so that the entire amount of fluid is supplied to the actuator, and the boom continues to swing or undulate at the normal speed. .

In the second invention, before the boom is stopped, the bypass valve is first opened by the control means prior to the closing operation of the directional switching valve. Therefore, a portion of the fluid supplied from the pump toward the actuator is bypassed through the throttle valve and the bypass valve, and the swinging or hoisting speed of the boom is reduced. That is, before the boom stops, the turning or hoisting speed of the boom is first reduced, so that large shaking when the boom stops is suppressed. Then, when a predetermined period of time has elapsed from the start of the opening operation of the bypass valve, the direction switching valve is closed by the control means.
The fluid supply to the actuator is stopped and the boom stops pivoting or luffing.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to illustrated embodiments.

First, an embodiment of the first invention will be described. FIG. 1 is a hydraulic circuit diagram of a hydraulic motor 10 for turning, but if a hydraulic cylinder 11 is used in place of the hydraulic motor 10, it becomes a hydraulic circuit diagram for luffing. FIG. 6 is a perspective view of a work vehicle with a boom. The boom 1 mounted on the work vehicle 2 is raised and lowered by a hydraulic cylinder 11 for raising and lowering as an actuator.
The hydraulic motor 10 and the hydraulic cylinder 11 are rotated by a hydraulic motor 10 via a swivel table (not shown).
Oil is supplied from the hydraulic pump 12. Note that 19 is a relief valve.

A hydraulic circuit 14 between the hydraulic pump 12 and the hydraulic motor 10 is provided with an electromagnetic direction switching valve 13 for switching the drive direction of the hydraulic motor 10. The direction switching valve 13 for this hydraulic motor is a solenoid A.
When excited, the supply stop position is switched to the supply position a, and oil is supplied to the hydraulic motor 10 in the normal rotation direction. Also,
When the solenoid B is energized, it is switched from the supply stop position to the supply position b, and oil is supplied to the hydraulic motor 10 in the reverse direction.

A bypass passage 16 is formed in the hydraulic circuit 14 between the hydraulic motor 10 and the switching valve 13, and the bypass passage 16 includes an electromagnetic type that bypasses a portion of the oil supplied to the hydraulic motor 10. A bypass valve 15 and a variable throttle valve 17 are provided. This bypass valve 15 is operated to the open position when the solenoid C is demagnetized, and is switched to the closed position c when the solenoid C is energized. Note that the bypass passage 16 may be formed in the hydraulic circuit 14 between the hydraulic pump 12 and the switching valve 13.

FIG. 2 is an electrical circuit. A movable contact 21d of the boom rotation switch 21 is connected to the power line DC of this electric circuit, and this movable contact 21d moves from the neutral OFF position to the forward rotation position where it contacts the forward rotation fixed contact 21a and the reverse rotation fixed contact 21b. manually switched to the reverse position and in contact with the

From the fixed contact 21a for normal rotation to the ground G
Solenoid A of the switching valve 13 is connected to the circuit connected to ND.
is provided, and the ground G is connected from the fixed contact 21b for reverse rotation.
Solenoid B of the switching valve 13 is connected to the circuit connected to ND.
is provided. Further, a solenoid C of the switching valve 13 is provided in a circuit between the power line DC and the ground GND.

On the other hand, each circuit connected to the forward rotation fixed contact 21a and the reverse rotation fixed contact 21b includes a diode 2.
A circuit having a coil 23 of relay R is connected via 2a and 22b. In addition, the contact 23a of the relay R
an on-delay circuit 24 that turns on the contact 24a of the circuit connected to the solenoid C after a predetermined time t1 has elapsed since the turn-on of the solenoid A; , an off-delay circuit 2 that turns off the contacts 25a and 25b of the circuit of B.
5 is provided.

Note that the relay R and each delay circuit 24, 2
5, a timer relay may be used.

FIG. 3 shows the operation of the boom drive device configured as described above.
This will be explained with reference to the time chart of FIG. 4 and the time-velocity diagram of FIG.

When the movable contact 21d of the switch 21 is in the neutral off position, the coil 23 of the relay R is demagnetized and the relay contacts 23a and 23b are off. Also,
Each contact 24a, 25a, 2 of each delay circuit 24, 25
5b is also off, and each solenoid A to C is also demagnetized. Therefore, the bypass valve 15 is operated to open and the switching valve 13 is in the supply stop position.

In this state, when the switch 21 is turned on to the normal rotation side, the coil 23 of the relay R is energized and the relay contacts 23a and 23b are turned on. As a result, the contacts 25a and 25b of the off-delay circuit 25 are turned on immediately, but the contact 24a of the on-delay circuit 24 is turned on after a predetermined time t1 has elapsed since the turn-on.

When the contact 25a is turned on, the solenoid A of the switching valve 13 is energized and switched from the supply stop position to the supply position a. Although the contact 25b is also turned on, the solenoid B is not excited because the switch 21 is turned off on the reverse rotation side. The switching valve 13 is in the supply position a
When the pump 12 is switched to and operated, oil is supplied from the pump 12 toward the hydraulic motor 10, but a part of this supplied oil is bypassed via the throttle valve 17 and the bypass valve 15, so that the hydraulic motor 10 is not suddenly supplied with the entire amount of oil from pump 12.

[0021] Therefore, the normal rotation of the boom 1 is gradually started (see stop (1) and low speed rotation (2) in Fig. 4). As a result, the jerk/acceleration at the time of starting does not suddenly increase, so that large shaking of the boom 1 at the time of starting is suppressed.

A predetermined time t1 after the switch 21 is turned on
When , the contact 24a of the on-delay circuit 24 is turned on, the solenoid C is energized, and the bypass valve 15 is closed and operated. As a result, the entire amount of oil from the hydraulic pump 12 is supplied to the hydraulic motor 10, and the normal rotation of the boom 1 becomes the normal high speed, and the rotation continues.

Note that the speed of the low speed turning (2) can be adjusted by the variable throttle valve 17.

When the switch 21 is turned on to the reverse direction, the boom 1 is rotated in the reverse direction under the same control.

Although the above operation was explained only for the hydraulic motor 10 for swinging the boom 1, the hydraulic cylinder 11 for hoisting the boom 1 is also controlled in a similar manner to allow the boom 1 to rise (upward movement) or fall down (downward movement). verb) to be done.

Next, a first embodiment of the second invention will be described. In this embodiment, only the electric circuit shown in FIG.
Since this embodiment differs from the embodiment of the invention described in FIG. 7, the electric circuit shown in FIG. 7 will be mainly explained.

FIG. 7 shows the electrical circuit of this embodiment. A movable contact 71d of a boom rotation switch 71 is connected to the power line DC of this electric circuit, and this movable contact 71d
is manually switched from a neutral off position to a forward rotation position in which it contacts the forward rotation fixed contact 71a and a reverse rotation position in which it contacts the reverse rotation fixed contact 71b.

The circuit connected to the forward rotation fixed contact 71a and the reverse rotation fixed contact 71b includes diodes 72a and 72.
An on-delay timer 75 is provided via b. The on-delay timer 75 turns on the contact 75a of the circuit connected to the solenoid C after a predetermined time t1 has elapsed since the movable contact 71d was turned on by contacting the forward rotation fixed contact 71a or the reverse rotation fixed contact 71b.

On the other hand, a circuit having a coil 73 of a relay R1 is connected to a circuit connected from the normal rotation fixed contact 71a to the ground GND. An off-delay timer 76 is provided that turns off the contact 76a of the solenoid A circuit after a predetermined time t2 has elapsed since the contact 73a of the relay R1 was turned off. In addition, a relay R is connected to the circuit connected from the fixed contact 71b for reverse rotation to the ground GND.
A circuit having two coils 74 is connected. and,
An off-delay timer 77 is provided that turns off the contact 77a of the solenoid B circuit after a predetermined time t2 has elapsed since the contact 74a of the relay R2 was turned off.

FIG. 3 shows the operation of the boom drive device having the above configuration.
This will be explained with reference to the time chart of FIG. 4 and the time-velocity diagram of FIG.

When the movable contact 71d of the switch 71 is in the neutral off position, the coil 73 of the relay R1 and the coil 74 of the relay R2 are demagnetized and the relay contact 73
a, 74a is off. In addition, each delay timer 75
, 76, 77 are also off, and the solenoids A to C are also demagnetized. Therefore, the bypass valve 15 is operated to open and the switching valve 13 is in the supply stop position.

In this state, when the switch 71 is turned on to the normal rotation side, the coil 73 of the relay R1 is energized and the relay contact 73a is turned on. As a result, the contact 76a of the off-delay timer 76 is turned on immediately, but the contact 75a of the on-delay timer 75 is turned on for a predetermined time t1.
It is turned on after .

When the contact 76a is turned on, the solenoid A of the switching valve 13 is energized and switched from the supply stop position to the supply position a. Note that since the switch 71 is off in the reverse direction, the solenoid B is not excited. When the switching valve 13 is switched to the supply position a and operated, oil is supplied from the pump 12 toward the hydraulic motor 10, but a part of the supplied oil is passed through the throttle valve 17 and the bypass valve 15. Since it is bypassed, the hydraulic motor 10 is not suddenly supplied with the entire amount of oil from the pump 12.

[0034] Therefore, the normal rotation of the boom 1 is gradually started (see stop (1) and low speed rotation (2) in Fig. 4). As a result, the jerk/acceleration at the time of starting does not suddenly increase, so that large shaking of the boom 1 at the time of starting is suppressed.

A predetermined time t1 after the switch 71 is turned on
lapses, the contact 75a of the on-delay timer 75
is turned on, solenoid C is energized, and bypass valve 15 is activated.
is closed and activated. As a result, the entire amount of oil from the hydraulic pump 12 is supplied to the hydraulic motor 10.
The normal rotation of the boom 1 becomes the normal high speed and continues the rotation.

On the other hand, when the switch 71 is turned off after the boom 1 has been rotated in the normal direction to the required position, the relay R1 is turned off.
The coil 73 is demagnetized and the relay contact 73a is turned off. By turning off the switch 71, the on-delay timer 7
The contact 75a of the off-delay timer 76 is turned off immediately, but the contact 76a of the off-delay timer 76 is turned off after a predetermined time t2 has elapsed since it was turned off.

Then, by turning off the contact 75a, the solenoid C of the bypass valve 15 is demagnetized, and the bypass valve 15 is turned off.
is opened and activated. As a result, part of the hydraulic pressure being supplied from the hydraulic pump 12 to the hydraulic motor 10 is transferred to the throttle valve 17.
Since the hydraulic motor 10 is bypassed via the bypass valve 15, the hydraulic motor 10 has a low speed. Then, when a predetermined time t2 has elapsed since the switch 71 was turned off, the off delay timer 7
The contact 76a of the boom 1 is turned off, the solenoid A is demagnetized, and the switching valve 13 is operated to switch from the supply position a to the supply stop position. The forward rotation of the vehicle stops.

In this way, the normal rotation of the boom 1 is gradually stopped (see low speed rotation (3) and stop (4) in FIG. 4). As a result, the jerk/acceleration at the time of stopping does not suddenly increase, so that large shaking of the boom 1 at the time of stopping is suppressed.

Note that the speeds of low-speed turns (2) and (3) are as follows:
It can be adjusted by a variable throttle valve 17.

When the switch 71 is turned on to the reverse direction,
By similar control, the boom 1 is rotated in the opposite direction.

Although the above operation was explained only for the hydraulic motor 10 for swinging the boom 1, the hydraulic cylinder 11 for hoisting the boom 1 is also controlled in a similar manner to allow the boom 1 to rise (upward movement) or fall down (downward movement). verb) to be done.

Next, a second embodiment of the second invention will be described. In this embodiment, only the electric circuit shown in FIG.
Since this embodiment is different from the embodiment of the present invention, the electric circuit shown in FIG. 8 will be mainly explained.

FIG. 8 is an electrical circuit diagram of this embodiment. A movable contact 81d of a boom rotation switch 81 is connected to the power line DC of this electric circuit, and this movable contact 81
d is manually switched from a neutral off position to a forward rotation position in which it contacts the forward rotation fixed contact 81a and a reverse rotation position in which it contacts the reverse rotation fixed contact 81b.

A circuit having a coil 83 of relay R and an on-delay timer 85 are connected in parallel to the circuit connected to the fixed contact 81a for forward rotation and the fixed contact 81b for reverse rotation via a diode. An on-delay timer 86 is provided that turns off the contact 86a after a predetermined time t2 has elapsed since the contact 83a of the relay R was turned off. This contact 86a is connected to the circuit of solenoid A and solenoid B via a diode. In addition, the above on/off
The delay timer 85 turns on the contact 85a of the circuit connected to the solenoid C after a predetermined time t1 has elapsed since the movable contact 81d was turned on by contacting the forward rotation fixed contact 81a.

Further, the fixed contact 81a for normal rotation and the fixed contact 81b for reverse rotation are connected to a set/reset circuit 84. This set/reset circuit 84 includes a movable contact 8
When 1d is brought into contact with the fixed contact 81a for normal rotation, the contact 84a of the circuit of solenoid A is held on, and the contact 84b of the circuit of solenoid B is held off. Further, when the movable contact 81d contacts the fixed reverse rotation contact 81b, the set/reset circuit 84 holds the contact 84a of the solenoid A circuit OFF and the contact 84b of the solenoid B circuit ON.

FIG. 3 shows the operation of the boom drive device configured as described above.
This will be explained with reference to the time chart of FIG. 4 and the time-velocity diagram of FIG.

When the movable contact 81d of the switch 81 is in the neutral off position, the coil 83 of the relay R is demagnetized and the relay contact 83a is off. Further, each contact 86a, 85a of each delay timer 86, 85 is also off,
Each solenoid A to C is also demagnetized. Therefore, the bypass valve 15 is operated to open and the switching valve 13 is in the supply stop position.

In this state, when the switch 81 is turned on to the normal rotation side, the set/reset circuit 84 is activated to hold the contact 84a of the solenoid A circuit on and turn off the contact 84b of the solenoid B circuit. to hold. Further, at this time, the coil 83 of the relay R is excited and the relay contact 83a is turned on. As a result, the contact 86a of the off-delay timer 86 is turned on immediately, but the contact 85a of the on-delay timer 85 is turned on for a predetermined time t1.
It is turned on after .

When the contact 86a is turned on, the solenoid A of the switching valve 13 is energized and switched from the supply stop position to the supply position a. When the switching valve 13 is switched to the supply position a and operated, oil is supplied from the pump 12 toward the hydraulic motor 10, but a part of the supplied oil is passed through the throttle valve 17 and the bypass valve 15. Since it is bypassed, the hydraulic motor 10 is not suddenly supplied with the entire amount of oil from the pump 12.

[0050] Therefore, the normal rotation of the boom 1 is gradually started (see stop (1) and low speed rotation (2) in Fig. 4). As a result, the jerk/acceleration at the time of starting does not suddenly increase, so that large shaking of the boom 1 at the time of starting is suppressed.

A predetermined time t1 after the switch 81 is turned on
lapses, the contact 85a of the on-delay timer 85
is turned on, solenoid C is energized, and bypass valve 15 is activated.
is closed and activated. As a result, the entire amount of oil from the hydraulic pump 12 is supplied to the hydraulic motor 10.
The normal rotation of the boom 1 becomes the normal high speed and continues the rotation.

On the other hand, when the switch 81 is turned off after the boom 1 has been rotated in the normal direction to the required position, the relay R1 is turned off.
The coil 83 is demagnetized and the relay contact 83a is turned off. Then, the contact 85a of the on-delay timer 85 is immediately turned off, but the contact 85a of the off-delay timer 86 is turned off.
6a is turned off after a predetermined time t2 has elapsed since it was turned off.

Then, by turning off the contact 85a, the solenoid C of the bypass valve 15 is demagnetized, and the bypass valve 15 is turned off.
is opened and activated. As a result, part of the hydraulic pressure being supplied from the hydraulic pump 12 to the hydraulic motor 10 is transferred to the throttle valve 17.
Since the hydraulic motor 10 is bypassed via the bypass valve 15, the hydraulic motor 10 has a low speed. Then, when a predetermined time t2 has elapsed since the switch 81 was turned off, the off delay timer 8
6 contact 86a is turned off, solenoid A is demagnetized,
Since the switching valve 13 is switched from the supply position a to the supply stop position, the supply of oil to the hydraulic motor 10 is completely stopped, and normal rotation of the boom 1 is stopped.

In this way, the normal rotation of the boom 1 is gradually stopped (see low speed rotation (3) and stop (4) in FIG. 4). As a result, the jerk/acceleration at the time of stopping does not suddenly increase, so that large shaking of the boom 1 at the time of stopping is suppressed.

[0055] The speeds of low-speed turns (2) and (3) are as follows:
It can be adjusted by a variable throttle valve 17.

When the switch 21 is turned on to the reverse side,
The set/reset circuit 84 holds the contact 84a of the solenoid A circuit OFF and the contact 84b of the solenoid B circuit ON, and the boom 1 is rotated reversely by the same control as described above.

Although the above operation was explained only for the hydraulic motor 10 for swinging the boom 1, the hydraulic cylinder 11 for hoisting the boom 1 is also controlled in a similar manner to allow the boom 1 to rise (upward movement) or fall down (downward movement). verb) to be done.

Next, measurement data of the jerk/acceleration on the bucket 3 when the boom 1 of the working vehicle 2 of the embodiments of the first and second inventions is extended to its maximum length (10 m) and horizontally rotated will be explained. do.

FIG. 5 shows data when the drive device of the above embodiment is started and stopped. The upper row of Figure 5 shows the acceleration of the boom versus time, and the lower curves (1) and (4) represent the current applied to the switching valve.
The curve represents the current applied to the bypass valve. According to the data in Fig. 5, the jerk/acceleration from stop at startup to low-speed turning shown in (1) is as shown in the following equation 1,
The jerk/acceleration shown in (2) from low-speed turning to normal turning is as shown in Equation 2 below. In addition, the acceleration/acceleration from normal turning to low-speed turning when stopping shown in (3) is as shown in equation 3 below, and the acceleration/acceleration from low-speed turning to stopping shown in (4)
The acceleration is as shown in equation 4 below.

[0060]

[Math 1] 0.065×9.8/0.5=1.24 m
/s3

[0061]

[Math 2] 0.069×9.8/0.3=2.25 m
/s3

[0062]

[Math 3] 0.073×9.8/0.5=1.43 m
/s3

[0063]

[Math. 4] 0.027×9.8/0.2=1.32 m
/s3

It has been found that the jerk/acceleration data of the above embodiment is 1/2 to 1/4 lower than the conventional jerk/acceleration.

[0065]

[Effects of the Invention] As is clear from the above description, the boom drive device for a work vehicle with a boom according to the first invention bypasses the fluid supplied toward the actuator using the bypass valve when starting the boom. This is controlled by a control means. Therefore, at the time of startup, the boom starts to rotate or rise gently, so that the jerk and acceleration are reduced, and the shaking of the boom at the time of startup can be suppressed. Furthermore, since the entire amount of fluid from the pump is not suddenly supplied to the actuator, a large impact is not applied to the actuator, and the durability of the actuator is also improved.

[0066] The boom drive device for a work vehicle with a boom according to the second invention is configured such that, before the boom is stopped, the control means controls the fluid supplied to the actuator to be bypassed by a bypass valve. It is. therefore,
Since the turning or hoisting speed of the boom is reduced before the boom stops, jerk/acceleration is reduced, and shaking when the boom is stopped can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram of an embodiment of the first invention.

FIG. 2 is an electrical circuit diagram of the above embodiment.

FIG. 3 is a time chart illustrating embodiments of the first and second inventions.

FIG. 4 is a time-velocity diagram illustrating the embodiments of the first and second inventions.

FIG. 5 is a diagram showing the current and acceleration applied to the direction switching valve and the bypass valve in the embodiments of the first and second inventions.

FIG. 6 is a perspective view of a work vehicle with a boom.

FIG. 7 is an electrical circuit diagram of the first embodiment of the second invention.

FIG. 8 is an electrical circuit diagram of a second embodiment of the second invention.

[Explanation of symbols]

1 Boom 2 Work vehicle 3 Bucket 10 Hydraulic motor 11 Hydraulic cylinder 12
Hydraulic pump 13 Directional switching valve 14
Hydraulic circuit 15 Bypass valve 16 Bypass passage 17
variable throttle valve

Claims (2)

[Claims] 1. An actuator for driving a boom mounted on a work vehicle, a pump for supplying fluid to the actuator, and a fluid supply passage provided between the pump and the actuator to direct the driving direction of the actuator. an electromagnetic directional switching valve to be switched; a bypass valve provided in the fluid supply passage to bypass a part of the fluid supplied to the actuator; and a throttle valve provided in the bypass passage in which the bypass valve is provided. and control means for opening the bypass valve prior to the opening operation of the directional switching valve when starting the boom, and closing the bypass valve after a predetermined time from the start of the opening operation of the switching valve. A boom drive device for a work vehicle with a boom. 2. An actuator for driving a boom mounted on a work vehicle, a pump for supplying fluid to the actuator, and a fluid supply passage provided between the pump and the actuator to direct the driving direction of the actuator. an electromagnetic directional switching valve to be switched; a bypass valve provided in the fluid supply passage to bypass a part of the fluid supplied to the actuator; and a throttle valve provided in the bypass passage in which the bypass valve is provided. , control means for opening the bypass valve prior to the closing operation of the directional switching valve when the boom is stopped, and closing the directional switching valve after a predetermined time from the start of the opening operation of the bypass valve. A boom drive device for a work vehicle with a boom, characterized by: