JPH0336194A - Displacement control mechanism for movable crane - Google Patents

Abstract

PURPOSE:To eliminate the danger of sudden lowering of a boom by constituting such that a mode switching mechanism is made to running mode when the running mode is selected with a mode selection switch and when the pressure detected with accumulated pressure detection means is above a suitable running pressure. CONSTITUTION:When a vehicle is to be run, a boom in working mode is made to a most retracted position, the boom is brought to an appropriate running height with a hydraulic cylinder 50 for elevating/depressing the boom, and made to the running mode. Here, a mode switching mechanism 40 is made to the running mode when the accumulated pressure in an accumulator 53 is above a preset value, and a closed circuit is formed with switching valves 41, 42 switched respectively to positions (d) and (f), and with both oil chambers 51, 52 of the cylinder 50 connected to each other. Although the boom moves up and down and the cylinder 50 is forced to be elevated and depressed with the oscillation of the vehicle body due to the irregularities of the road surface when the vehicle is run, the pressure variance is restricted with the accumulator 53 and the pressure loss in the closed circuit described above.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a displacement suppressing mechanism for suppressing vibrations during traveling in a mobile crane such as a rough terrain crane.

[Prior Art] Generally, as shown in FIG. 5, a mobile crane has a vehicle body 2 supported by wheels 1, and a boom 3 that is rotatable around a horizontal axis 5 via a hydraulic cylinder 4 for raising and lowering the boom. It is supported by In this mobile crane,
When the vehicle body 2 vibrates due to undulations on the road surface, sudden acceleration and deceleration, etc. while driving, the boom 3 etc. swing in the vertical direction, further increasing the vibration of the vehicle body 2, resulting in poor ride comfort. .

As a device for suppressing vibrations during running, a device disclosed in, for example, Japanese Unexamined Patent Publication No. 18295/1982 is known. As shown in FIG. 6, this device is constructed by providing a dump mechanism 19 inside a boom elevation hydraulic cylinder 18, and an oil chamber 181 that holds the load of this cylinder 18.
A counterbalance valve 12 is provided in an oil passage 13 connected to the oil passage 13 and an oil passage 17 connected to the other oil chamber 182 and an oil passage 14 connected to the directional control valve 11. An electromagnetic switching valve 6 and a shuttle valve 15 are provided.

According to this device, during crane work, when the switching valve 16 is in the A position and the direction control valve 11 is switched to the boom up position or the boom down position, the oil discharged from the pump 10 is transferred to the oil chamber 181 or the oil chamber 182 of the cylinder 8. into the cylinder 8
is extended and contracted, and the boom is raised and lowered. When driving, the cylinder 18 is expanded and contracted while the switching valve 16 is kept in the A position, and the height from the ground to the boom tip is slightly raised from the lower limit height HQ. Proper running height Hl below the legal limit height H2
After setting (Ho < Hl < H2), the switching valve 16
Switch to the mouth position. As a result, the oil passage 13 is connected to the switching valve 16.
and communicates with the oil passage 17 via the shuttle valve 15, and the oil chamber 1
81, oil chamber 182, and dump mechanism 191 are communicated with each other to form a closed circuit. By driving the vehicle in this state, a displacement suppressing effect on the vehicle body 1 is exerted.

[Problem to be solved by the invention]

In the above conventional device, during the initial setting during driving, the switching valve 1
6 to the A position, switch the directional control valve 11 to extend and retract the cylinder 8, raise and lower the boom 3, and set the appropriate running height Hl.
After setting the switching valve 16 to the open position, a closed circuit is formed. As a result, the load pressure acting on the oil chamber 181 of the cylinder 8 is guided to the oil chamber 191 of the dump mechanism 19 and is accumulated, thereby exerting a displacement suppressing effect. but,
The dump mechanism 1 dumps the load pressure acting on the oil chamber 181.
9 to the oil chamber 191 to accumulate pressure,
During the pressure accumulation, the cylinder 8 rapidly contracts by the compression volume of the oil chamber 191 of the dump mechanism 19 due to the load of the gym 3, etc., and the boom 3 suddenly descends. In addition,
Even if the amount of sudden descent of the boom 3 is small, the sudden descent of the boom 3 gives a great sense of anxiety to the driver, which is not preferable.

Further, due to the sudden descent of the boom 3, the boom height becomes lower than the initially set appropriate running height Hl, and the displacement suppressing effect is no longer exerted. Therefore, it is necessary to readjust the boom 3 to the appropriate travel height Hl, and this adjustment work is troublesome.

The present invention solves these problems, and after crane work,
This eliminates the risk of the boom dropping suddenly when switching to travel mode for driving, allowing the driver to use it safely without causing a sense of anxiety.It also maintains the boom at the appropriate height for travel and suppresses displacement. It is an object of the present invention to provide a displacement suppressing mechanism for a mobile crane that can reliably exhibit its effect.

[Means to solve the problem]

In order to achieve the above object, the present invention utilizes a boom elevating hydraulic cylinder connected between the vehicle body and the boom of a mobile crane, a main hydraulic pump, and a main pressure pump to reduce the load on the cylinder by discharging oil from the main hydraulic pump. The first oil chamber to hold the oil chamber and the second oil chamber on the opposite side.
a directional control valve for switchably supplying and discharging the oil to and from the oil chamber; a displacement suppressing accumulator connected between the cylinder and the directional control valve; and communicating the first oil chamber, the second oil chamber, and the accumulator with each other. a mode switching valve mechanism that can be freely switched between a running mode in which a closed circuit is formed, and a working mode in which the communication is released and pressurized oil is supplied and discharged independently to the first oil chamber and the second oil chamber; a selection switch, an accumulator accumulated pressure detection means, and when the pressure detected by the accumulated pressure detection means is equal to or higher than the appropriate running pressure and the moto selection switch selects a running mode, the mode switching valve mechanism is set to a running mode;
Control means for setting the mode switching valve mechanism to the working mode at other times is provided.

In this configuration, when the auxiliary hydraulic pressure source and the mode selection switch are in the driving mode and the pressure detected by the accumulated pressure detection means is less than the appropriate driving pressure, the auxiliary hydraulic source is in the replenishment position to replenish the accumulator with pressure oil from the auxiliary hydraulic source, and at other times. A configuration may also be provided in which a replenishment switching valve is provided at a cutoff position to cut off the replenishment.

Further, in the above configuration, the present invention uses pressure detection means in the first oil chamber of the cylinder instead of the accumulated pressure detection means of the accumulator, and the mode selection switch is set to the first pressure detected by the pressure detection means in the traveling mode. The present invention includes a control means that sets the mode switching valve mechanism to the traveling mode when the pressure in the oil chamber is substantially zero, and sets the mode switching means to the working mode at other times.

In this configuration, when the auxiliary hydraulic power source, the mode selection switch, and the mode selector valve mechanism are in the travel mode, pressure oil from the auxiliary hydraulic power source is supplied to the accumulator and the closed circuit, and a replenishment switch is configured to cut off the supply at other times. It is also possible to have a configuration including a valve.

[For production]

With the above configuration, unless the accumulated pressure in the accumulator exceeds the appropriate driving pressure, that is, the pressure is substantially equivalent to the pressure in the first oil chamber of the cylinder, the switching valve mechanism will not switch to the driving mode. Become. Therefore, when switching to the driving mode, the accumulated pressure in the accumulator and the first
Since the accumulated pressure with the oil chamber is substantially the same, rapid contraction of the cylinder and sudden descent of the boom can be reliably prevented, and the driver will not feel uneasy. In addition, by using the replenishment switching valve mentioned above, when switching from work mode to travel mode, switch the directional control valve in work mode to extend and retract the cylinder, adjust the boom to the appropriate travel height, and then press the mode selection switch. When the driving mode is set, the replenishment switching valve is switched to the replenishing position, pressure oil from the auxiliary hydraulic pressure source is accumulated in the accumulator, and when the accumulated pressure exceeds the above-mentioned appropriate driving pressure, the mode switching valve mechanism switches to the driving mode. The system automatically stores pressure in the accumulator and switches to driving mode.

On the other hand, when the pressure detection means of the first oil chamber of the cylinder is used instead of the accumulated pressure detection means of the accumulator, the pressure of the first oil chamber is substantially zero, that is, the cylinder is forged and the boom is at the lower limit height. Otherwise, the mode switching means cannot be switched to the traveling mode. Since the cylinder is in the line state at the time of switching to the traveling mode, sudden descent of the boom can be more reliably prevented. In addition, by using the replenishment selector valve, with the cylinder forged and the boom set to the lower limit height, the mode selection switch is set to travel mode, and then the replenishment selector valve is switched to the replenishment position to control the auxiliary hydraulic pressure. The height of the boom can be easily adjusted by accumulating pressure oil from the source in the accumulator and supplying it to the first oil chamber of the cylinder to extend the cylinder.

〔Example〕

FIG. 1 shows an embodiment of the invention. In FIG. 1, a check valve 22 is installed in the discharge side oil passage 21 of the main hydraulic pump 20.
and the main relief valve 23 are connected, and furthermore, a directional control valve 30, a counterbalance valve 33, a mode switching valve mechanism 4
A boom elevation hydraulic cylinder 50 (corresponding to cylinder 4 in FIG. 6) is connected through 0.

The mode switching valve mechanism 40 includes the following valves 41, 42°43.4
Consists of 4.45. The first switching valve 41 is connected between the oil passage 34 communicating with the first oil chamber 51 of the cylinder 50 and the oil passage 35 communicating with the second oil chamber 52.
It is provided so as to be freely switchable between a C position in which the inflow into the pipe is blocked and a reverse flow thereof is allowed, and a D position in which both the passages 34 and 35 are communicated with each other. The first switching valve 41 is a pilot type,
The accumulated pressure of the accumulator 53 is
, this switching valve 41 via the throttle 55 and the pilot oil passage 56.
When the accumulated pressure is less than the set pressure, it is held at the C position, and when it exceeds the set pressure, it is switched to the D position.

The second switching valve 42 is an oil passage 5 communicating with an accumulator 53.
4 into the oil passage 35 and blocking the reverse flow, and position d, which allows both passages 35 and 54 to communicate with each other. The main pilot check valve 43 is oriented to allow inflow from the oil passage 32 to the oil passage 35 and block reverse flow, and the auxiliary pilot check valve 44 is oriented to block outflow from the oil passage 54 to the drain oil passage 57. It is oriented in a direction that allows the opposite inflow.

Pilot oil passages 58, 59 for opening each pilot check valve 43, 44 are communicated via a throttle 65 and an oil passage 64 with a discharge side oil passage 62 of 6 auxiliary hydraulic pumps (auxiliary oil pressure sources). The third switching valve 45 is connected to the oil passages 58 and 5.
The oil passage 66 and the oil passage 57 are provided in a position that can be freely switched between a position g, which blocks outflow from the oil passage 66 communicating with the oil passage 57 and allows an inflow in the opposite direction, and a position h, where both passages 66 and 57 are communicated with each other.

Is the supply switching valve 46 connected to the accumulator 53? lt12 For replenishment, it is provided between the oil passage 62 and the oil passage 67, and is provided so as to be freely switchable between a j position where communication between both passages 62 and 67 is cut off, and a position where they are communicated with each other. The oil passage 67 is communicated with the oil passage 54 via a check valve 68. A pressure switch 69 is connected to the oil passage 54 as a means for detecting the accumulated pressure of the accumulator 53 . This pressure switch 6
9 is turned off when the accumulated pressure of the accumulator 53 is less than the proper running pressure (the pressure necessary to exert a vibration suppressing effect during running), and is turned on when the accumulated pressure is equal to or higher than the proper running pressure.

Each of the above switching valves 42, 45, and 46 is an electromagnetic switching valve,
Switching is controlled by the electric circuit shown in FIG.

In FIG. 2, 70 is a damper switch (mode selection switch), and when turned on, the driving mode is set, and when turned off, the working mode is set. R1 is a relay with a delay function, RSl is its contact, PSa is the A contact of the pressure switch 69 in Fig. 1,
PSb is the same B contact, 421, . Reference numerals 451 and 461 indicate the solenoids of the switching valves 42, 43 and 5.46 in FIG.

When performing crane work in the above 11 to S configurations,
If the damper switch 70 is turned off (work mode), the relay R1 is not activated and its contact RS1 is opened, so each solenoid 421.451461 is demagnetized and each switching valve 42, 45, 4.6 is are held at e, g, and j positions. Therefore, the pressure oil discharged from the auxiliary hydraulic pump 61 and regulated by the auxiliary relief valve 63 flows through the oil passage 62,
64 and throttle 65 into the pilot oil passages 58, 59, and each pilot check valve 43, 44 is opened. Further, the accumulated pressure in the accumulator 53 is drained to the tank 25 through the throttle 55 and the pilot check valve 44. Therefore, pressure switch 69 is not activated.

When the directional control valve 30 is switched to the boom-up position a in this state, the oil discharged from the main hydraulic pump 20 flows into the first oil chamber 51 of the cylinder 50 via the counterbalance valve 33, the cylinder 50 is extended, and the boom is raised. will be held. At this time, the main pilot check valve 43 is open, so oil discharged from the second oil chamber 52 as the cylinder 50 expands passes through the pilot check valve 43, passes through the directional control valve 30, and enters the tank. It will be returned to 26. Furthermore, when the directional control valve 30 is switched to the boom lower position, the oil discharged from the pump 22 flows into the second/rIF chamber 52 via the main pilot check valve 43, contrary to the above, and the inflow pressure at this time causes a counterbalance. Valve 3
3 is opened, the cylinder 50 is contracted while the oil in the first oil chamber 51 is returned to the tank 25, and the boom is lowered.

Next, when running the vehicle, first, in the above-mentioned work mode, the boom 3 is brought into a substantially linear state by the boom extension/retraction hydraulic cylinder (not shown), and the boom 3 is moved to the appropriate running height Hl by the boom elevation hydraulic cylinder 50. Adjust to Further, the suspended load is removed, and a crane hook (not shown) is latched to the vehicle body 2 with appropriate flexibility.

Thereafter, when the damper switch 70 is turned on (driving mode), the relay R1 is energized and its contacts 5 R31 are closed. Note that at the initial stage of switching to this driving mode, the accumulated pressure in the accumulator 53 is the tank pressure, which is lower than the set pressure, and the six pressure switches are not operating, so the A contact PSa is opened and the B contact PSb is closed. It is known. Therefore, the solenoids 451 and 461 are energized, and the switching valve 45 is switched to the h position and the switching valve 46 is switched to the k position, respectively. On the other hand, the solenoid 421 is demagnetized and the switching valve 42 remains in position e.

When the switching valve 45 is switched to the h position, the pilot oil passages 58 and 59 are communicated with the drain oil passage 57, and both pilot check valves 43 and 44 are closed. Further, when the changeover valve 46 is switched to the one position, the oil discharged from the auxiliary hydraulic pump 61 passes through the check valve 68 to the accumulator 53.
and gradually accumulates pressure. Further, the accumulated pressure of the accumulator 53 is guided to the pilot oil passage 56 via the throttle 55.

When the accumulated pressure in the accumulator 53 exceeds the set pressure, the switching valve 41 is switched to the d6 position by the pressure, and the oil passages 34 and 35 are communicated with each other to form a closed circuit. Further, when the accumulated pressure is equal to or higher than the set pressure, the pressure switch 69 is operated, its A contact PSa is closed, the solenoid 421 is energized, and the switching valve 42 is set to f.
At the same time, the B contact PSb is opened, the solenoid 461 is demagnetized, and the switching valve 46 is returned to the j position.

By thus switching the switching valve 42 to the f position, the oil passages 5435 are communicated with each other, and the accumulator 53
is communicated with the closed circuit. At this time, accumulator 5
Since the accumulated pressure of No. 3 is equivalent to the load pressure of the first oil chamber 51 of the cylinder 50, the switching valves 41 and 42 are
There is no risk that the cylinder 50 will contract even if it is switched to the and f positions. Moreover, since the replenishment of pressure oil to the accumulator 53 side is stopped by returning the switching valve 46 to the j position, there is no fear that the cylinder 50 will extend. Therefore, cylinder 50 remains stopped and boom 3
While the oil chambers 51 and 52 of the cylinder 50 and the accumulator 53 are communicated with each other while the cylinder 50 remains stopped at the proper running height Hl, a closed circuit is formed.

Next, the vehicle is driven by a traveling drive device (not shown) to travel. During this driving, unevenness of the road surface, sudden acceleration of driving,
When the vehicle body 2 vibrates due to deceleration or the like, the boom 2 swings up and down, and the cylinder 50 tends to expand and contract. At this time, both oil chambers 51 of the cylinder 50. , 52 and the accumulator 53 are in communication with each other, so that the cylinder 5
Pressure fluctuations caused by the expansion and contraction of zero are suppressed by the pressure loss of the accumulator 53 and the oil passage of the closed circuit, a damping effect is exerted, and riding comfort is improved.

When performing crane work after traveling as described above, by turning off the damper switch 70 (work mode), the relay R
1 is demagnetized and its contact R8i is opened, so that the solenoids 421, 451 . ．． 461 are all demagnetized and each switching valve 42, 45, 46 is returned to the e+g+J position shown. Therefore, the pilot check valves 43 and 44 are opened by the oil discharged from the auxiliary hydraulic pump 61, and the pilot oil passage 5 is opened.
68 The pilot pressure led to pilot check valve 4
4 to the tank 26, the switching valve 41 is returned to the C position, and the oil passages 34 and 35 are connected, that is, both oil chambers 5
1 and 52 are cut off.

Also, the accumulated pressure in the accumulator 53 is drained through the throttle 55 and the pilot check valve 44, and the pressure switch 6
9 no longer works. Thereafter, the crane work is performed by the above-described action.

Next, another example will be described.

FIG. 3 shows an embodiment in which the pressure in the first oil chamber 51 of the cylinder 50 is detected and controlled. Pressure switch 71
is connected to an oil passage 34 communicating with the first oil chamber 51.

In this case, the electrical circuit of FIG. 4 is used to control each solenoid 421, 451, 461. In FIG. 4, psbl is a contact point of the pressure switch 71 in FIG. 3, which is closed when the pressure in the first oil chamber 51 is substantially zero (the cylinder 50 is in the line state) and is opened when the pressure increases.

R2 and R3 are relays R32 and R83 are their contacts, 72
73 indicates a raise switch and a lower switch.

9. The other configurations are substantially the same as those in FIGS. 1 and 2.

3 and 4, when performing crane work, the damper switch 70 is off (work mode) and the solenoids 421, 451. ．． 461 is demagnetized, and each switching valve 42,
45.46 are e and g shown.

The boom is held at position j, and crane operations such as raising and lowering the boom are performed in the same manner as in the embodiment described above. In this case, during crane work, the load pressure is acting on the first oil chamber 51 of the cylinder 50, the pressure switch 71 is activated, and its contact PSbj is opened, so the operator accidentally switches off the damper switch 70. Even if you turn on solenoid 42
1,451.461 is not energized and each switching valve 42, 45, 46 and switching valve 41 remains in working mode.

Next, when the vehicle is run, first, in the above work mode, the cylinder 50 is set to the height line, and the boom 3 is set to the lower limit height HQ. This activates the pressure switch 71, after which point PSbi is closed. After that, when damper switch 70 is turned on (driving mode), relay R2 is activated, contact R32 is closed, and relay R
3 operates, contact R83 closes, and solenoids 421, 4
51 is energized, and the switching valves 42 and 45 are switched to the e+g position. As a result, the oil passages 54 and 35 are communicated with each other, the accumulator 53 is communicated with the second chamber, and the pilot oil passages 58 and 59 are communicated with the drain oil passages 5 and 7.
Each pilot check valve 43,44 is closed. However, since the raise switch 72 has not yet been operated and the switching valve 46 remains at the J position, no pressure is accumulated in the accumulator 53, and the accumulator 53 remains at low pressure, so the switching valve 41 remains at the C position. It remains as it is.

Next, when the raise switch 72 is turned on, the solenoid 46
1 is energized and the switching valve 46 is switched to the OFF position. Then, the oil discharged from the auxiliary hydraulic pump 61 flows into the accumulator 5.
3 and gradually accumulates pressure. At this time? The oil discharged from the iD auxiliary hydraulic pump 61 also flows into the oil passage 35 through the F position of the switching valve 42, 1 and then through the C position of the switching valve 41 into the oil passage 34 and the first oil chamber 5.
It also flows into the first side. Further, the accumulated pressure of the accumulator 53 is also guided to the pilot oil passage 56 via the throttle 55. When the accumulated pressure in the accumulator 535 exceeds the set pressure, the switching valve 41 is switched to the d position, and the oil passages 34, 3
5 are communicated with each other to form a closed circuit. Further, when the raise switch 72 is continuously turned on, the oil discharged from the auxiliary extraction pump 53 flows into the accumulator 53 and the closed circuit, that is, the first oil chamber 51, and accordingly the cylinder 50 is moved into the ram cylinder. The boom 3 is gradually extended in the same manner as described above, and the boom 3 is raised. Thereafter, when the boom 3 has risen to the proper running height Hl, the solenoid 461 is demagnetized by turning off the raise switch 72, and the switching valve 46 is demagnetized.
is returned to the j position, and the supply of oil to the accumulator 53 and the closed circuit is stopped.

In addition, when the boom 3 is raised too much, by turning the lowering switch 73 to Jff1 (off), the solenoid 451
The pilot check valve 43 is demagnetized and the oil discharged from the auxiliary extraction 2 pressure pump 61 is demagnetized by the action described above.
is opened and the oil in the closed circuit flows out into the tank 26,
The cylinder 50 is retracted and the boom 3 is lowered.

In this way, the cylinder 50 is at the height line, and the boom 3 is at the lower limit height H.
At Q, turn on the damper switch 70 and turn on the accumulator 5.
3 is communicated with the second oil chamber 52, and then the up switch 7
2 is turned on to accumulate pressure in the accumulator 53,
By extending the cylinder 50 and adjusting the boom 3 to the appropriate running height Hl, there is no possibility that the boom 3 will suddenly descend at the initial stage of switching to the running mode. Further, by running the vehicle in this state, a vibration suppressing effect is exerted in the same manner as in the above-described embodiment, and riding comfort is improved.

〔Effect of the invention〕

As described above, in the present invention, when switching from work mode to driving mode, unless the accumulated pressure in the accumulator becomes substantially equal to the pressure in the first oil chamber of the cylinder, the mode cannot be changed to driving mode. Therefore, when switching to travel mode, the accumulated pressure in the accumulator and the accumulated pressure in the first oil chamber are substantially the same, so that the cylinder does not contract rapidly and the boom It is possible to reliably prevent the vehicle from descending suddenly, and it can be used with peace of mind without causing any anxiety to the driver.

As in claim 2, by using the replenishment switching valve,
When switching from work mode to travel mode, after adjusting the boom to the appropriate travel height and setting the mode selection switch to travel mode, the replenishment selector valve will automatically switch to the replenishment position and pressurized oil from the auxiliary hydraulic source will be switched to the replenishment position. is stored in the accumulator,
When the accumulated pressure exceeds the above-mentioned appropriate driving pressure, the mode switching valve mechanism is automatically switched to driving mode, and the accumulation of pressure in the accumulator and switching to driving/mode can be performed automatically, improving operability. can.

In addition, as in claim 3, if the cylinder is at the height line and the boom is not at the lower limit height, it is not possible to switch to the travel mode, it is further ensured that the boom suddenly descends at the initial stage of switching to the travel mode. 4 can be prevented.

Furthermore, as in claim 4, by using the replenishment switching valve, after switching to the travel mode, the oil discharged from the auxiliary hydraulic pressure source is used to accumulate pressure in the accumulator and adjust the boom to the appropriate height for travel. can be done relatively easily,
Operability can be improved.

[Brief explanation of drawings]

Fig. 1 is a hydraulic circuit diagram showing an embodiment of the present invention, Fig. 2 is an electrical circuit diagram thereof, Fig. 3 is a hydraulic circuit diagram showing another embodiment, Fig. 4 is an electrical circuit diagram thereof, and Fig. 5 is a hydraulic circuit diagram showing an embodiment of the present invention. is a side view of a mobile crane, and FIG. 6 is a conventional hydraulic circuit diagram. 22... Main hydraulic pump, 30... Directional control valve, 40
...Mode switching valve mechanism, 41...First switching valve, 42
...Second switching valve, 43...Main pilot check valve, 44...Auxiliary pilot check valve, 45...Third switching valve, 46...Replenishment switching valve, 50...Boom elevation hydraulic cylinder, 51...first oil chamber, 52...
2nd oil chamber, 53...accumulator, 61...auxiliary hydraulic pump (auxiliary hydraulic pressure source), 6...pressure switch,
70... Damper switch (mode selection switch), R1... Relay, R51... Contact, PSa, PSb... Contact of pressure switch 69, 71... Pressure switch, PSbl.
...Contact point of pressure switch 71.

Claims (1)

[Claims] 1. A boom elevating hydraulic cylinder connected between the vehicle body and the boom of a mobile crane, a main hydraulic pump, and a main hydraulic pump that maintains the load of the cylinder by discharging oil from the main hydraulic pump. a directional control valve that can switchably supply and discharge the first oil chamber and the second oil chamber on the opposite side; a displacement suppressing accumulator connected between the cylinder and the directional control valve; and the first oil chamber and the second oil chamber on the opposite side thereof. There is a running mode in which the second oil chamber and the accumulator are communicated with each other to form a closed circuit, and a working mode in which the communication is released and pressure oil is supplied and discharged independently to the first oil chamber and the second oil chamber. A freely switchable mode switching valve mechanism, a mode selection switch, an accumulator accumulated pressure detection means, and when the pressure detected by this accumulated pressure detection means is equal to or higher than the appropriate running pressure and the driving mode is selected by the mode selection switch, the above mode is selected. A displacement suppressing mechanism for a mobile crane, comprising a control means that sets a mode switching valve mechanism to a traveling mode, and sets the mode switching valve mechanism to a working mode at other times. 2. When the auxiliary hydraulic pressure source and the mode selection switch are in driving mode and the pressure detected by the accumulated pressure detection means is less than the appropriate driving pressure, the auxiliary hydraulic pressure source is in the replenishment position to replenish the accumulator with pressure oil, and at other times, the above replenishment is performed. 2. The displacement suppressing mechanism for a mobile crane according to claim 1, further comprising a replenishment switching valve that is in a cutoff position to cut off the supply. 3. A boom elevating hydraulic cylinder connected between the vehicle body and the boom of the mobile crane, a main hydraulic pump, a first oil chamber that holds the load of the cylinder for the oil discharged from the main hydraulic pump, and its opposite. a directional control valve that can switchably supply and discharge to and from a second oil chamber on the side; a displacement suppressing accumulator connected between the cylinder and the directional control valve; and the first oil chamber, the second oil chamber, and the accumulator. A mode switching valve that can be freely switched between a running mode in which a closed circuit is formed in which the two are communicated with each other, and a working mode in which the communication is released and pressurized oil is supplied and discharged independently to the first oil chamber and the second oil chamber. a mechanism, a mode selection switch, a pressure detection means in the first oil chamber of the cylinder, and a mode selection switch when the mode selection switch is in the traveling mode and the pressure in the first oil chamber detected by the pressure detection means is substantially zero; A displacement suppressing mechanism for a mobile crane, comprising a control means that sets a valve mechanism to a traveling mode and, at other times, sets a mode switching means to a working mode. 4. A replenishment switching valve that replenishes pressure oil from the auxiliary hydraulic power source to the accumulator and the closed circuit when the auxiliary hydraulic power source, mode selection switch, and mode selector valve mechanism are in the travel mode, and cuts off replenishment at other times. The displacement suppressing mechanism for a mobile crane according to claim 3, further comprising: a displacement suppressing mechanism for a mobile crane according to claim 3.