JPS63265023A - Vibration suppressor for vehicular construction machine - Google Patents

Abstract

PURPOSE:To raise the effect of suppressing vibration by a simple constitution in which an accumulator is connected by outer piping through a mode switching valve to an oil-pressure cylinder for operation. CONSTITUTION:When the boom of a working device is vertically turned during the traveling period, a variation in pressure is produced in the head side oil chamber 8a of a boom cylinder 8. In this case, the chamber 8a is led to an accumulator 18 through pipes 14a and 15, a mode switching valve 16, and a slow-return check valve 17 by switching the valve 16 to the connecting position. Oil in the chamber 8a flows through the valve 17, etc., in or out of the accumulator 18. By spring action resulting from the accumulated pressure of the accumulator 18 and also by damping action resulting from the throttling 17a of the valve 17, the occurrence of vibration can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a vibration suppressing device for a vehicle type construction machine equipped with a working device.

(Prior Art) Conventionally, as a vibration suppressing device for vehicle-based construction machinery, for example, as shown in Japanese Patent Application Laid-Open No. 60-119830M, a vibration suppressing device is used between a boom and an arm cylinder of a hydraulic excavator, or between an arm and a packet cylinder. It is known that a buffer cylinder is provided separately from a working hydraulic cylinder such as an arm cylinder or a packet cylinder. However, this device has the following problems.

(a) The main focus is on suppressing vibrations at the tip of the working device (packet part), and is not aimed at suppressing vibrations on the vehicle body or during driving. Therefore, no vibration suppressing effect on the entire vehicle can be expected.

(b) Oil is sealed in the head-side oil chamber and the rod-side oil chamber of the buffer cylinder, and the two chambers are communicated through a small hole in the piston in the cylinder, with only the throttling action of the small hole! ! ! Since the orifice is inside the cylinder, it is difficult to set the damping coefficient using the orifice.
Vibration reduction efficiency is poor because an accumulator that exerts spring force is not used.

(C) A working hydraulic cylinder was provided separately! ! Since it is supported by the L cylinder, the installation of the M cylinder has a VS difference in its position, which makes manufacturing troublesome.

(d) If the IC machine is subjected to severe shock loads, the am
The mounting and sealing parts of the cylinder are easily damaged and have poor durability.

(Object of the Invention) The present invention has been made to solve the above-mentioned conventional problems, and the first purpose is to reduce costs by making the circuit configuration simple and easy to manufacture. The objective is to have a high vibration suppression effect on the entire vehicle, and to be able to continue to properly exert its vibration suppression effect even when driving for long periods of time, greatly improving riding comfort and reducing operator fatigue. The second purpose is to provide a highly durable vibration suppressor that can prevent damage to the vibration suppressor 5A by preventing high pressure oil from flowing into the vibration suppressor even if the operator makes an incorrect operation. There is a particular thing.

(Structure of the Invention) A first invention is a vehicle-based construction machine in which a working device is supported on a vehicle body having wheels so as to be movable up and down via a working hydraulic cylinder, wherein the hydraulic cylinder is connected to a working device via a directional control valve. Vibration reduction is installed in the middle of the load-holding side pipe between the load-holding side pipe and the load-side pipe that are switchably connected to the hydraulic power source circuit and the tank, and are piped between this directional control valve and the hydraulic cylinder. The accumulator is connected to a communication state and a cutoff state via a mode switching valve so as to be freely switchable between a communication state and a cutoff state, and a first state in which the load-side pipe is always in communication with the tank and a load-side pipe The second part prevents oil from flowing into the tank.
This switching means is operated in conjunction with the mode switching valve, and is in the first state when the mode switching valve is in the communicating state, and in the second state when the mode switching valve is in the disconnected state.
It is configured to be in the following state.

With this configuration, the accumulator can be easily manufactured by connecting the accumulator to the existing working hydraulic cylinder via the mode switching valve with external piping, making it possible to reduce costs.
In addition, it is easy to set the spring constant, damping constant, etc. for vibration reduction, and by switching the mode switching valve to the open position, an appropriate vibration suppression effect can be achieved, especially when driving for a long time. There is no risk of the ura being trapped in the negative side oil chamber of the working hydraulic cylinder, and the vibration suppression effect can continue to be properly exerted, greatly improving riding comfort.

A second invention is based on the first invention, wherein the hydraulic power source circuit includes a high pressure relief valve, a low pressure relief valve, and a low pressure relief valve that operates in conjunction with the mode switching valve and when the mode switching valve is in a communicating state. The high-pressure relief valve is activated when the IC is disconnected.

In this way, even if the operator tries to perform high-pressure work such as excavation with the mode switching valve still in the communication position, the hydraulic power source circuit will be unloaded and high-pressure work will not be possible, causing the high-pressure oil to vibrate. Flow into the accumulator of the suppressor is prevented, protecting the accumulator and improving machine life.

(Example) FIG. 6 shows a wheel loader as an example of a vehicle-based construction machine to which the present invention is applied. This wheel loader is constructed by equipping a front frame 2a of a vehicle body 2 with a plurality of (for example, four) wheels 1 and a work station 3. The working device 3 includes a boom 4 whose base end is rotatably supported by a front frame 2a, a packet 5 rotatably supported at the tip of the boom 4, and a middle portion of the boom 4 and a packet 5. A cross link 6 and a dump link 7 that are bendably connected to one side, a boom cylinder 8 provided between the front frame 2a and the boom 4, and a front frame 2a and the cross link 6 It is constituted by a packet cylinder 9 etc. provided between the

FIG. 1 is a hydraulic circuit diagram of essential parts showing an embodiment of the first invention. In this figure, 10 is a tank, 11 is a hydraulic pump, and both oil chambers 8a of the boom cylinder 8 are connected to the discharge pipe (hydraulic power source circuit) 12 via a boom directional control valve 13 and pipes 14a, 14b. 8b is connected. Further, a packet cylinder 9 shown in FIG. 6 is connected to the discharge pipe 12 via a packet directional control valve (not shown).

A pipe line 15 is branched and connected in the middle of the load holding side pipe line 14a connected to the load holding side part V (head side oil chamber in this embodiment) 8a of the boom cylinder 8, and a mode switching valve is connected to this branch pipe line 15. 16 through the throttle 17a and check valve 17b
A slow return check valve 17 consisting of
An accumulator 18 is connected to this valve 17. As the accumulator 18, a bladder type accumulator is usually used. A vibration suppression circuit 19 consisting of an accumulator 18 and a slow return check valve 17 is connected to pipes 14a and 1 between the oil chamber 8a of the boom cylinder 8 and the direction control valve 13.
Connected by external piping including 5. Therefore, the accumulator 18 and the like are controlled by the rotation of the boom 4 and the boom cylinder 8.
It is installed at any position on the front frame 2a within a range that does not interfere with the telescopic operation of the front frame 2a.

On the other hand, the load side oil chamber (rond side oil chamber) of boom cylinder 8
A bypass pipe line 20 is branched and connected in the middle of the load side pipe line 14b connected to the load side pipe line 14b, and an auxiliary switching valve 21 is provided in this bypass pipe line 20. a first state that communicates with
It is switched to a second state in which it is cut off.

Electromagnetic switching valves are used for each of the switching valves 16 and 21, and are switched between a communicating position (driving mode) and a blocking position (1@cutting mode) in conjunction with each other by a mode changeover switch 22 provided in the driver's cab. . 23 is a power source such as a battery.

Further, 24 is a main relief valve, 25 is a load check valve, 26 is an overload relief valve, and 27 and 28 are check valves for preventing cavity leakage.

In the above configuration, when traveling, the direction control valve 13 is held at the neutral position shown in the figure, the pipes 14a and 14b for supplying and discharging pressure oil to the boom cylinder 8 are blocked, and the mode provided in the driver's cab is With the changeover switch 22 switched to the running mode (ON) and the mode switching valve 16 and the auxiliary switching valve 21 switched to their communication positions, the wheels 1 are driven by the driving force from the engine to drive the vehicle. Note that the switching valves 16 and 21 may be manually operated or hydraulically operated and may be switched in conjunction with each other.

In addition, the mode changeover switch 22 is turned on and off in conjunction with the operation of the travel lever (Ii!l not shown), and the changeover valve 16.
21 may be switched.

During the above-mentioned traveling, the vehicle main body 2 vibrates in response to the undulations of the road surface or during acceleration and deceleration, and the working device 3 vibrates accordingly, causing the boom 4 supporting the working device 3 to move in the vertical direction. As the boom 4 attempts to rotate, a pressure fluctuation occurs in the head-side oil chamber 8a of the boom cylinder 8 that supports the boom 4.

In such a case, the oil chamber 8a is switched to the pipe line 14a by switching the mode switching valve 16 to the communicating position.

15, mode switching valve 16, slow return check valve 1
The oil chamber 8 is connected to the accumulator 18 via the oil chamber 8
The oil in a flows into and out of the accumulator 18 via the slow return check valve 17's. At this time, the vibration is suppressed by the spring action due to the accumulated pressure of the accumulator 18 and the damping action by the throttle 17a of the slow return check valve 17.

In other words, this type of vehicle-based construction machine can be considered as a verb vibration system in which the vehicle main body 2 side is the main vibration system and the working device 3 side, which has a smaller weight (mass) than the vehicle main body 2, is the secondary vibration system. Therefore, the mass of the vehicle body 2, the spring constant of the wheels 1, and the spring constant of the wheels 1 are adjusted so that the natural frequency of the sub-vibration system on the side of the work device 3 is approximately equal to the natural frequency of the main vibration system on the side of the vehicle body 2. Anya L mulator 18 depending on the mass of
By setting the spring constant a3 and the damping coefficient of the diaphragm 17a, the vehicle main body 2 side hardly vibrates while the working device 3 side of the 1i11 vibration system vibrates, and the spring constant on the working device 3 side vibrates. When the force, that is, the accumulated force of the accumulator 18 always acts in the direction opposite to the excitation force received from the road surface side, l1FJJ is suppressed.
7a exhibits a vibration damping effect, thereby suppressing vertical, longitudinal, and lateral vibrations, as well as pitching, rolling, and yawing of the vehicle body 2 during driving, thereby improving ride comfort.

By the way, during the above-mentioned vibration suppression, oil flows into and out of the head-side oil chamber 8a of the boom cylinder 8 from the accumulator 18 in response to vibrations, causing the boom cylinder 8 to expand and contract by a minute.While repeating this slight expansion and contraction, During the stroke in the contraction direction, the aperture 17a and the accumulator 18
The vibration damping effect is exerted by this. However, if we assume that the auxiliary switching valve 21 is not provided or that the auxiliary switching valve 21 is in the ``a-off'' position, when the boom cylinder 8 expands and contracts a small amount to suppress vibration, each time the boom cylinder 8 contracts Since the rod side oil chamber 8b becomes almost negative pressure, the cavitation prevention check valve 2 is removed from the tank 10.
8, oil flows into the rod side oil chamber 8b and is prevented from flowing out from the rod side oil chamber 8b to the tank 10, so the oil is sealed in this rod side oil chamber 8b and the boom cylinder 8 It will be difficult to stroke (extend) the rod side.
While the boom cylinder 8 repeats the above-mentioned slight expansion and contraction, its stroke gradually becomes smaller, and finally it becomes unable to extend and contract, and the above-mentioned vibration suppressing effect cannot be exerted.

However, according to the above configuration, when the mode switching valve 16 is switched to the communicating position by the mode switching switch 22, the auxiliary switching valve 21 is also switched to the communicating position, and the head side pipe line 14b is communicated with the tank 10. Therefore, oil can freely flow in and out from the tank 10 to the rod-side oil chamber 8b of the boom cylinder 8, and the slight expansion and contraction of the boom cylinder 8 is not restricted. Therefore, even when the vehicle is running for a long time, the vibration suppressing effect described above is always properly exerted.

Next, when performing excavation work, the mode changeover switch 22 is switched to the excavation mode (off), and the mode changeover valve 16 and the auxiliary changeover valve 21 are returned to their respective shutoff positions. In this state, by switching the direction control valve 13, the pump 1
The pressure oil from 1 flows into the oil chamber 8a or 8b of the boom cylinder 8.
The cylinder 8 is extended or contracted, the boom 4 is rotated, and the packet 5 is lowered into the stomach. In addition, by switching the packet directional control valve (not shown), pressure oil from the ribbon cylinder 11 is supplied to the packet cylinder 9 shown in FIG. The packet 5 is rotated through. This results in excavation and release of the load.

During this excavation, if the mode selector switch 22 is switched to the excavation mode as described above, the auxiliary selector valve 21 is switched to the cutoff position, so oil flows out into the tank 10 from the middle of the pipe line 14b on the rod side. Without this, the expansion and contraction of the boom cylinder 8 is appropriately controlled by the directional control valve 13.

Also, during this excavation, high-pressure oil is guided to the pipe line 14a, but when the mode selector switch 22 is switched to the excavation mode, the mode selector valve 16 is switched to the cutoff position, so that the high-pressure oil guided to the pipe line 14a is will not flow into the accumulator 18 side, and there is no risk that the accumulator 18 will be damaged.

FIG. 2 shows a second embodiment, in which a cavitation prevention check valve 28 on the rod side of the boom cylinder 8 is shown.
A first state in which a vent relief valve 29 with a low pressure (several tcI/J') setting is provided in parallel with the first state, and the vent pipe line 29a thereof communicates with the tank 10 through an auxiliary switching valve 30;
It is configured to be freely switchable between a second state in which it is cut off.

According to this embodiment, when the auxiliary switching valve 30 is switched to the communication position in the driving mode, the vent relief valve 29
Since the vent pipe line 29a of the boom cylinder 8 is connected to the tank 10, oil can flow from the Orad sub-oil chamber 8b of the boom cylinder 8 to the tank 10 via the vent relief valve 29, and the check valve 28 It is also possible for oil to flow into the rod-side oil chamber 8b through the rod-side oil chamber 8b, thereby preventing the expansion and contraction of the boom cylinder 8b from being restricted during vibration suppression.

As a result, the same effects as the embodiment shown in FIG. 1 (first embodiment) can be obtained. Furthermore, according to the second embodiment, since the auxiliary switching valve 30@ is provided in the vent pipe line 29a, compared to the case where the auxiliary switching valve 21 is provided in the main pipe line 14b as in the first embodiment, it is possible to A small auxiliary switching valve 30 can be used.

FIG. 3 shows a third embodiment, in which a vent unload valve 31 is used in place of the check valve 28 and vent relief valve 29 of the second embodiment, and its vent pipe 31a
is configured to be freely switchable between a first state in which communication with the tank 10 is established and a second state in which communication is interrupted by an auxiliary switching valve 30.

According to this embodiment, by switching the auxiliary switching valve 30 to the communication position in the driving mode, the pent unload valve 3
1 vent pipe line 31a is communicated with the tank 10, and this pent unload valve 31 allows the boom cylinder 8 to be opened.
Oil can freely flow out and flow into the tank 10 from the side oil chamber 8b, and when vibration is suppressed t111, the boom cylinder 8b
The expansion and contraction of is prevented from being restricted. This allows the first
And the same effects as in the second embodiment can be obtained. In particular, in the third embodiment, one pent unload valve 31 can function as both the vent relief valve 29 and the check valve 28 of the second embodiment, so the structure can be simplified by reducing the number of valves.

Incidentally, in each of the above-mentioned embodiments, due to an operator's operational error or the like, there is a case where the operator attempts to perform excavation work with the mode changeover switch 22 switched to the travel mode. In this case, the mode switching valve 16 remains in the communication position and the pipe line 14a
When high pressure oil flows into accumulator 1, the high pressure oil flows into accumulator 1.
8 and may damage the accumulator.

In order to prevent this, the second invention is configured as follows.

FIG. 4 shows an embodiment (fourth embodiment) of the second invention. In the second embodiment, a high pressure is applied to the discharge pipe 12 of the hydraulic pump 11 (for example, 210!). F/cd) l constant main relief valve 24 and low pressure (e.g. 90Kg/
cd) Connect the set vent relief valve 32 in parallel, and connect the vent pipe line 32a of the low pressure vent relief valve 32.
and a first state in which the vent pipe line 29a of the vent relief valve 29 set at a low pressure (several Ng/cj) provided on the 0 side of the boom cylinder 8 is communicated with the tank 10 by the auxiliary switching valve 33; It is configured such that it can be freely switched to a second state in which it is cut off.

According to this fourth example, the same effects as in the second embodiment can be obtained, and at the same time, when the mode switching valve 16 is in the running mode (communication position), the auxiliary switching valve 33 is also in the running mode ( The vent line 29a of the low pressure vent relief valve 29 on the rod side and the vent line 32a of the low pressure vent relief valve 32 on the pump side are both connected to the tank 1.
0, making it possible to perform low-pressure work while preventing damage to the accumulator 18 during travel.

That is, when the directional control valve 13 is switched to the left position in the driving mode, the oil discharged from the pump 11 flows into the pipe 14'a.
k: However, at this point, the main relief valve 24 with a high pressure setting does not work, but the vent relief valve 32 with a low pressure setting works, and the discharge pressure of the pump 11 rises to the set pressure of this vent relief valve 32. , low-pressure oil below the set pressure is guided to the boom cylinder through the pipe 14a, and work is performed at the low pressure of the boom cylinder 8. It is also possible to introduce the low pressure oil to the packet cylinder 9 shown in FIG. 6 and rotate the packet 5 at low pressure.

This makes it possible to operate the boom cylinder 8 or packet cylinder 9 with low-pressure oil while driving.
It is possible to drive while lowering the vehicle, improving work efficiency. Moreover, during this work, the mode switching valve 16 is in the communication position and the accumulator 18 is in communication with the pipe line 14a, but the pipe line 14a1. :34 Since the oil being drained is at low pressure, there is no risk of damage to the accumulator 18.

In addition, since the discharge pressure of the pump 11 is low, excavation work that requires high pressure cannot be performed, and this notifies the operator that it is in travel mode, and prevents damage to the accumulator 18 due to operational errors. Prevented.

In addition, if the mode changeover switch 22 is switched to the excavation mode, the vent pipe line 29a of each vent relief valve 29.32
, 32a are disconnected and each vent relief valve 29.32 is locked, the main relief 920 with high pressure setting is
is activated, the discharge pressure of the pump 11 can rise to the set pressure (high pressure) of the main relief valve 20, and the high pressure oil is supplied to the boom cylinder 8 and packet cylinder 9 to perform high pressure excavation work. , excavation work efficiency is improved.

FIG. 5 shows another embodiment (fifth embodiment) of the second invention. In the fourth embodiment, the hydraulic pump 11
A main relief valve 24 set at high pressure (for example, 210 Kg/cd) and a pent unload valve 34 are installed in the discharge pipe 12 of the
The auxiliary switching valve 33 connects the vent line 34a of the pent unload valve 34 to a low pressure relief valve 35 set to low pressure (for example, 9 (1 g/cd)), and connects the rod side of the boom cylinder 8 in parallel. The vent pipe line 31a of the pent unload valve 31 provided in the tank 10
a first state in which the vent pipes 34a are connected to the vent pipes 34a,
31a is configured to be freely switchable between the second state and the second state in which the power supply 31a is cut off.

In this fifth embodiment, the same effects as in the fourth embodiment can be obtained, and at the same time, the auxiliary switching valve 33 is in the communication position in the running mode, and the vent pipe 31a of the pent unload valve 31 on the rod side is opened. In addition to communicating with the tank 10, the vent pipe line 34a of the pent unload valve 34 on the pump side is connected to a relief valve 35 with a low pressure setting.
5 is activated, and in the excavation mode, the auxiliary switching valve 33 is in the cutoff position, and each vent pipe line 34a, 31a is shut off, and the relief valve 35 with the low pressure setting does not work, but the main relief valve 24 with the high pressure setting is activated. Become. As a result, the same effects as in the fourth embodiment (FIG. 4) can be obtained.

In addition, in the above embodiment, the slow return check valve 17
The accumulator 18 is connected through the aperture 17a.
However, if there is a pressure loss due to the piping, the damping effect may be exerted due to the pressure loss, and in such a case, the orifice 17a
It is also possible to omit.

The present invention is applicable not only to the wheel loader of the above embodiment, but also to power shovels, truck cranes, and other vehicle-based construction machines equipped with other working devices.

(Effects of the Invention) As described above, the first invention can be easily manufactured by connecting an accumulator to an existing working hydraulic cylinder via a mode switching valve with external piping, and can reduce costs. The spring constant, damping constant, etc. for vibration reduction can be set easily and appropriately, and the mode switching valve can be set in the communicating position (
By switching to the driving mode), the optimal photographic suppression effect can be achieved depending on the machine, and the riding comfort can be greatly improved. Moreover, in the running mode, oil can freely flow in and out from the tank to the load-side oil chamber such as the Rondo side of the working cylinder, thereby preventing the cylinder from being restricted in its expansion and contraction operation for vibration suppression. Even when traveling for long periods of time, the above-mentioned vibration suppressing effect can always be properly exhibited.

A second invention is based on the first invention, in which the hydraulic power source circuit is provided with a high pressure relief valve, a low pressure relief valve, and a load switching means, and when in the travel mode, the low pressure relief valve works to prevent excavation. Although high-pressure work cannot be performed, low-pressure work can be performed at will. This prevents high-pressure oil from flowing into the accumulator and protects the accumulator, while making it possible to perform combined work with low-pressure work using hydraulic cylinders for work such as lifting and lowering empty packets, greatly increasing work efficiency. This is something that can be improved.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram of essential parts showing an embodiment (first embodiment) of the first invention, and FIGS. 2 and 3 are hydraulic circuit diagrams of essential parts showing second and third embodiments. Fig. 4 is a hydraulic circuit diagram of a main part showing an embodiment (14th embodiment) of the second invention, and Fig. 5 is a main part showing another embodiment (fifth embodiment) of the second invention. FIG. 6 is a hydraulic circuit diagram of vehicle system 1 to which the present invention is applied.
It is a side view showing an example of 1B construction machine. 1... Wheels, 2... Vehicle body, 3... Work equipment,
4...Boom, 5...Packet, 8...Boom cylinder, 9...Packet cylinder, 11...Hydraulic pump, 12...Discharge pipe line (hydraulic power source circuit), 13...
Directional control valve, 14a...Load holding side pipe line, 14b...
・Load side pipe line, 16...mode switching valve, 17...slow return check valve, 17a...throttle, 18...
・Accumulator, 19... Vibration suppression circuit, 21.3
0.33... Auxiliary switching valve, 22... Mode switching switch, 24... Main relief valve (high pressure relief valve)
, 29... Vent relief valve, 31... Vent unload valve, 32... Vent relief valve (low pressure relief valve), 34... Vent unload valve, 35... Low pressure relief valve. Patent applicant: Kobe Steel, Ltd. Agent
Patent Attorney Etsushi Kotani Patent Attorney Chief 1
) Masamukai Patent Attorney Yasuo Itaya Figure 6

Claims (1)

[Scope of Claims] 1. In a vehicle-based construction machine in which a working device is supported on a vehicle body having wheels so as to be movable up and down via a working hydraulic cylinder, the hydraulic cylinder is connected to a hydraulic power source circuit via a directional control valve. A vibration reduction accumulator is installed in the middle of the load holding side pipe between the load holding side pipe and the load side pipe which are switchably connected to the tank and the directional control valve and the hydraulic cylinder. The connection is switchable between a communication state and a cutoff state via a mode switching valve, and there is a first state in which the load side pipe is constantly connected to the tank, and a first state in which the load side pipe is connected to the tank at all times, and a first state in which the load side pipe is connected to the tank at all times. A switching means is provided for switching to a second state for preventing oil from flowing out, and this switching means is operated in conjunction with the mode switching valve, and when the mode switching valve is in the communication state, the first state is set to the cutoff state. A vibration suppressing device for a vehicle type construction machine, characterized in that it is configured to be in a second state when . 2. In a vehicle type construction machine in which a working device is supported on a vehicle body having wheels so as to be able to rise and fall via a working hydraulic cylinder, the hydraulic cylinder can be freely switched between a hydraulic power source circuit and a tank via a directional control valve. A vibration reduction accumulator is installed in the middle of the load-holding side pipe through a mode switching valve between the load-holding side pipe and the load-side pipe connected to the directional control valve and the hydraulic cylinder. It is connected to be switchable between a communication state and a cutoff state, and is placed in the middle of the load-side pipe in a first state that constantly communicates the load-side pipe with the tank, and in a first state that prevents oil from flowing from the load-side pipe into the tank. A switching means is provided for switching between a second state and a second state, and this switching means is operated in conjunction with the mode switching valve, so that when the mode switching valve is in the communication state, the first state is set and when the mode switching valve is in the disconnected state, the second state is set. The hydraulic pressure source circuit includes a high pressure relief valve, a low pressure relief valve, and a mode switching valve that operates in conjunction with the mode switching valve, and when the mode switching valve is in a communicating state, the low pressure relief valve is operated to shut off the circuit. 1. A vibration suppressing device for a vehicle-based construction machine, characterized in that the device is provided with a switching means for operating a high-pressure relief valve when the condition is met.