JPS61103004A - Control circuit of hydraulic cylinder - Google Patents

Abstract

PURPOSE:To quickly contract a selected hydraulic cylinder by connecting a shuttle valve between pipelines connecting control valves and flow dividers, and connecting the outlet of the shuttle valve to a tank through the main shuttle valve and switch valve. CONSTITUTION:The second and third shuttle valves 22, 23 are connected between pipelines 14a, 14b, 14c, 14d connecting the first and second control valves 15a, 15b and the second flow dividers 12, and the third and fourth control valves 15c, 15d and the third flow divider 13. Outlet of the second and third shuttle valves 22, 23 are connected to a tank 19 through the first shuttle valve 21 and a switch valve 27. In this arrangement, hydraulic cylinders can be individually or a selected pair of cylinders can be simultaneously contracted quickly.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control circuit for a hydraulic cylinder, and in particular to a control circuit for an outrigger jack cylinder (hereinafter referred to as a jack cylinder) used during disassembly and assembly of a large crawler crane. The present invention relates to a control circuit for a hydraulic cylinder suitable for control.

[Conventional technology]

When transporting a large crawler crane or the like on a road, there are legal restrictions on weight, height, and width, so a jack cylinder is used to separate the upper revolving structure, truck frame, and side frame.

Figures 2 and 3 show the disassembly work of a large crawler crane.

As shown in FIG. 2, the four jack cylinders 4a to 4d attached to the upper revolving structure 1 are extended, and then the two rear jack cylinders 4a, 4b'i are simultaneously extended. and -10,000 side frames 3 to the ground G, L
Then, using an auxiliary crane or the like, separate the side frame 3 lifted from the ground G, L from the truck frame, and then lift the rear jack cylinders 4a, 4b. Next, 2 pieces 1
Operate the front jack cylinders 4c and 4di of the set, and separate the other side frame 3 in the same manner as described above.

Next, as shown in FIG. 3, the truck frame 2 and the upper revolving body 1 are mounted on the trailer 100, and the four jack cylinders 4&~4d are simultaneously extended to remove the upper revolving body 1t- from the truck frame 2. Separate, upper revolving body 1, track frame 2 and side, )"7L/-"°'
″'t-, 81J & K Mゞ1゜Therefore, in the jack cylinders 4a to 4d used for disassembly and assembly of large crawler cranes, the rear jack cylinder 4m,
There is a mounting mechanism that allows the group 4b and the front group of jack cylinders 4c and 4d to be expanded and contracted separately, and the loads applied to each jack cylinder 41 to 4d are different. Since there is a difference in the amount of expansion and contraction, in order to correct this difference, each of the jack cylinders 4a to 4d is individually expanded 1.
It is necessary to reduce m.

Next, in the fourth column, a conventional technology of a control circuit for a jack cylinder disclosed in Japanese Patent Application Laid-Open No. 109904/1988 will be shown.

The control circuit shown in this figure includes a hydraulic pump 5, a main control valve 6, an extension side pipe 7 and a contraction side pipe 8 connected thereto, and the contraction side pipe 8 and the cylinders 4a to 4d. Branch pipe 8a ~ connecting with the rod side oil chamber of
8d, a first flow divider 9 as a main flow divider connected to the extension side pipe line 7, and two pieces 1
One of the first flow dividers 9 is provided for each set of cylinders 4a, 4b and 4c, 4d.
A second. The third flow divider 12.13 and each jack cylinder 4a~
4d and connected to the second.4d via conduits 14a to 14d. 1st to 4th control valves connected to the third 70-Zoibida 12.13 breath ~ 1
5 d and the first to fourth control valves 151
15 d and the cylinder head side oil chamber (hereinafter referred to as head side oil chamber) of the relevant jack cylinder 41 to 4 d, a pipe 15 m = 16 d, and this pipe 16 a
Bypass branch pipes 17 a to 17 connected to 16 d
d, a fifth control valve 18 connected to the bypass line 17, and an oil tank 19.

The control circuit is then operated as follows.

■ When extending all jack cylinders 4 &~4di at the same time, main control valve 6f: (→ position) -1st~4th control valves 15a~15
d - Switch the fifth control valve 18 to the (C) position, which is the production position, and to the (E) position, which is the neutral position.

As a result, the pressure oil discharged from the hydraulic pump 5 changes from the main control valve 6 to the extension side pipe 7 to the first flow divider 9 to the pipe 10.11 to the second pipe. Third 70-Zoibida 12.13 → Pipe line 14 a to 14 d → First to
Fourth control valve 15 a ~ 15 d - + pipe line 16 a ~ 16 d t - is supplied to the head side oil chamber of the jack cylinders 4 a - 4 d. Rod of the jack cylinders 41 - 4 d The pressure oil in the side oil chambers is returned to the oil tank 19 through branch pipes 8a to 8d-+reduction side W route 8→main control pallet flow t-.

Therefore, each of the jack cylinders 4a to 4d simultaneously extends.

■ When extending the jack cylinders 4a'jz individually among the jack cylinders 4a to 4d, only the first control valve 15m corresponding to this jack cylinder 4a is turned to the operating position (c). and the other second to fourth control valves 15 b to 15 d.
to the neutral position).

As a result, pressure oil is supplied to the head side oil chamber of the jack cylinder 4a through the same route as when all the jack cylinders 4a to 4di are extended simultaneously. Further, the second to fourth control valves 15 b to 15 d
The pressure oil that has flowed into is dropped into the oil tank 19.

Therefore, only the jack cylinder 4a is extended, and the other jack cylinders 4b to 4d are not extended.

When extending the other jack cylinders 4b to 4d1 individually, when extending the set of rear jack cylinders 4m and 4b or the set of front jack cylinders 4c and 4d, or when extending the three jack cylinders individually, A similar operation can be performed when expanding at the same time.

■ When reducing all the cylinders 41 to 4d at the same time, set all main control valves 6 to the (a) position, and set the first to fourth control valves 15&~15df:
The fifth control valve 18 is switched to the 09 position, which is the operating position, and to the (E) position, which is the neutral position under normal conditions.

As a result, the pressure oil discharged from the hydraulic cylinder 15 changes from the main control valve 6 to the contraction side pipe 8 to the branch pipe 8I.
The oil passes through L to 8d and is supplied to the rod side oil chambers of the jack cylinders 4a to 4d.

At this time, the pressure oil in the head side oil chambers of the jack cylinders 4a to 4d is transferred from pipes 16a to 16d→first to fourth control pulses 7''15a to 15d→pipelines 14a to 14
d→Second. Third 70-Zobider 12, 13 → Pipe lines 10, 11 → First flow divider 9 → Extension side pipe line 8
→It passes through the main control valve 6 and is returned to the oil tank 19.

Therefore, each of the jack cylinders 4a to 4d performs the contraction operation at the same time.

■ If a synchronization error occurs during the small movement of the jack cylinders 4a to 4d and one of the jack cylinders 4a to 4d does not contract to the stroke end, the fifth control valve 18 is moved to the operating position. (off) change.

As a result, 1. For example, when the jack cylinder 4a does not reach the stroke end, the pressure oil in the head side oil chamber is transferred from the pipe 16a to the bypass branch pipe 171L to the bypass pipe 17 to the fifth control valve 18. It passes through and escapes to the oil tank 19.

As a result, the jack cylinder 4a whose contraction operation has been delayed also reaches its stroke end. Other jack cylinder 4b~
The same applies to the case of 4d.

However, in the conventional control circuit, the jack cylinders 4a to 4d are controlled individually or in sets of two, and preselected sets of two jack cylinders from among a plurality of sets of jack cylinders are controlled simultaneously. It is practically impossible to reduce the size.

That is, for example, when attempting to contract the jack cylinders 4a individually, the main control valve 6 is placed in the (a) position, the first control valve 151 corresponding to the jack cylinder 4& is placed in the (c) position, and the other positions are set. 2nd to 4th
Switch the control valves 15b to 15d to the () position.

As a result, the pressure oil discharged from the hydraulic cylinder 15 is transferred from the main control valve 6 to the reduction side pipe line 8 to the branch pipe line 13.
a'i and flows into the rod side oil chamber of the jack cylinder 4a.

10,000, since the pressure oil in the head side oil chamber of the jack cylinder 4a is switched to the position of the first control valve 151L, the circuit moves from the pipe line 16a to the first control valve 7. ” 15 a → tube K 14 a −+
Second flow divider 12 → conduit 10 → first 7-
The oil appears to flow from the low-zoobider 9 to the extension side pipe 7 to the main control valve 6 to the oil tank 19.

However, the second to fourth control valves 15 b to 1
The pipe line 16 is switched to the 5d position and is connected to the head side oil chamber of the jack cylinders 4b to 4d.
b to 16 d are the second to fourth control pulses 7''
15b to 15d, so the conduit 14
b~14 d to 2nd. Third flow divider 12
, Pressure oil does not flow to the 13 side. As a result, the second floativizer 12 functionally limits the branch port to which the conduit 14a is connected to the maximum extent.

Therefore, the flow rate of the pressure oil that flows through the head side oil chamber of the shirtkin cylinder 4m → pipe u ts a → first control valve 15 a → pipe line 141L to the second flow divider 12 becomes extremely small, so that the Since the contraction operation of the cylinder 4m is extremely slow, the individual contraction operation of the cylinder 4a becomes practically impossible.

The same goes for the other jack cylinders 4b to 4d. When it is desired to individually reduce the set of rear and rear jack cylinders 4m and 4b, the first flow divider 9 functions to divide the pressure oil inflow side. Since all the ports are compressed, it is practically impossible to reduce the size of the cylinders 41 to 4d individually, as described above.

However, when disassembling and assembling a large crawler crane, the loads acting on the four jack cylinders 4 and ~4d tend to be unbalanced, and there is a difference in the amount of expansion and contraction of the jet cylinders 4a to 4d. In order to correct this, there are cases where it is necessary to reduce the size of the jack cylinders 4a to 4dt individually.In order to reduce the total working time, for example, there is a case where it is necessary to reduce the size of the rear side jack cylinders 4a and 4b at the same time. be.

On the other hand, there is a problem that cannot be addressed by the conventional control circuit.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the problems of the prior art and to solve the problems of the prior art.
Hydraulic cylinders without a set or in multiple sets are individually
Another object of the present invention is to provide a control circuit for hydraulic cylinders that can quickly compress/J- a set of two preselected hydraulic cylinders at the same time.

[Means to resolve the problem]

The present invention is characterized in that a shuttle valve is connected between pipes connecting two control valves provided corresponding to each hydraulic cylinder and one flow divider, and that one outlet of the two shuttle valves is connected to one flow divider. The outlet of the main shuttle valve is connected to the inlets on both sides of the main shuttle valve, and the outlet of the main shuttle valve is connected to an oil tank, and a switching valve is provided between the oil tank and the main shuttle valve. The present invention is characterized in that a plurality of pipelines are connected to a flow divider provided for one set of selected two hydraulic cylinders, and the switching valve is connected to the flow divider in a plurality of pipelines.

[Effect]

In the present invention, when contracting the hydraulic cylinders individually,
Set the main control valve to the contraction side ((a) in Figure 1)
position) and the control valve corresponding to the hydraulic cylinder to be contracted to the operating position (position (c) in Figure 1).
Then, the other control valves are switched to the neutral position (FIG. 1, position &), and the switching valve is switched to the first position (FIG. 1, position (g)) K.

As a result, pressure oil is supplied to the rond side oil chamber of the hydraulic cylinder to be contracted through the main control valve→reduction side conduit. In addition, the pressure oil in the head side oil chamber of the hydraulic cylinder to be reduced is transferred from the control valve switched to the above (c) position to the pipe connecting the control pal 7' and the flow divider a. Path → Shuttle valve → The shuttle valve and main shuttle pal 7
” To k It passes through the connecting pipe → main shuttle valve → selector valve and is dropped into the oil tank.

In this way, the pressure oil in the head-side oil chamber of the hydraulic cylinder to be reduced passes through the 70-tabider and main flow divider, passes through the lath, shuttle valve, main shuttle valve, and switching valve, and drops into the oil tank. The hydraulic cylinders to be contracted can be individually and quickly contracted, regardless of the throttling action of the flow divider or the main flow divider.

In addition, when contracting a set of two preselected hydraulic cylinders at the same time, close the main control valve to 0).
The control valve corresponding to the hydraulic cylinder to be reduced by 1 is placed in the (c) position, all other control valves are placed in the (a) position, and the switching valve 't - the second position (first position) is set.
In the figure, switch to (g) position).

As a result, pressure oil is supplied to the rond side oil chamber of the hydraulic cylinder to be contracted through the main control valve collar contraction side conduit. On the other hand, the pressure oil in the head side oil chamber of the hydraulic cylinder to be reduced is cut to the position (c).
Control valve being replaced → Pipe line connecting the control valve and the flow divider → Flow divider corresponding to the hydraulic cylinder to be reduced →
The pipe connecting this divider and the main flow divider → the pipe connected to this → the flow passes through the switching valve and drops into the oil tank.

Therefore, irrespective of the action of the throttle 9 of the main flow divider, a set of two preselected hydraulic cylinders can be contracted at the same operating speed as when all the hydraulic cylinders are contracted at the same time.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

The first factor shows an embodiment of the present invention, in which a main shuttle: a first shuttle valve 21 as a valve is installed in a control circuit for two sets of four hydraulic cylinders 4a to 4d. has been done.

Also, a second flow divider 12 is arranged for a set of two jack cylinders 4m, 4b, and a first flow piper 12 is arranged corresponding to the jack cylinders 4m, 4b. Second control valve 15a.

A second shuttle valve 4 is connected between the pipes 14a and 14b connecting the pipes 15b. Furthermore, a third flow tie piper 13 arranged for a set of two jack cylinders 4e and 4d, and the above-mentioned jack cylinder 4e,
A third shuttle valve n is connected between conduits 14c and 14d that connect the third and fourth control valves 15e and 15d provided corresponding to the control valves 15e and 15d.

The outlet of the second shuttle valve n passes through a conduit 24 to one inlet of the first shuttle valve 21, and the outlet of the third shuttle valve N passes through a conduit 25 to one of the inlets of the second shuttle valve 21. Each is connected to the other entrance.

The outlet of the first shuttle valve 21 is communicated with the oil tank 19 through a conduit section.

Between the first shuttle valve 21 and the oil tank 19,
A switching valve is provided, and this switching valve is a 4-port, 3-position, solenoid valve.

A conduit lO connecting the first flow divider 9 and the second flow divider 12 via a conduit 28 is connected to the switching valve n. This switching valve part is switched to the first position (g) when the cylinders 4a to 4dt are contracted individually, and the cylinders 4m and 4b'i on the rear side are simultaneously compressed. When letting
It is possible to switch to the ←) position as the second position, and in other cases to the neutral position.

The other configurations of the embodiment shown in FIG. 1 are the same as those shown in FIG. 2, and the same members are designated by the same reference numerals and further explanation will be omitted.

The control circuit of the embodiment shown in FIG. 1 is operated and functions as follows.

(1) When extending all jack cylinders 4a to 4d=i, main control valve 6 is fully extended.
lK, first to fourth control valves 15 a to 15
The switching valve 27 is switched to the d'i (c) position and the switching valve 27 is switched to the neutral position.

In this case, the pressure oil discharged from the hydraulic pump 5 is transferred from the main control valve 6 to the extension side pipe 7 to the first 70-
Diviter "9→Pipe line 10.11→Second and third flow divider 12.13→Pipe lines 14 a to 14 d→First
~Fourth control valve 15a~15d→Jacket cylinder 4&~4 through pipe line 16a~16d
On the other hand, the pressurized oil in the rond side oil chambers of the engine cylinders 4a to 4d is supplied to the head side oil chamber of the engine cylinder 4d through branch pipes 83 to 8d-+reduction side pipe 8→main control valve 6. The oil is returned to the oil tank 19.

Therefore, all the jack cylinders 4a to 4d are
They can be stretched at the same time.

(2) When extending the jack cylinder 4at individually among the jack cylinders 4a to 4d, for example, the first control valve 15 is switched to the &only (c) position, and the other second to fourth controls are extended. Valve 15b~1
5 Switch d to position.

As a result, in the head side oil chamber of the jack cylinder 4a,
Pressure oil is supplied through the same route as in case (1) above,
And the pressure oil in the rod side oil chamber of the jack cylinder 4a is
The oil is returned to the oil tank 19 through the same route as in case (1) above.

On the other hand, the second to fourth control pals 7-15b to 15
The pressure oil that has entered d is dropped into the oil tank 19. Therefore, the jack cylinders 4at can be extended individually at the same operating speed as when all the jack cylinders 4 and 4d are extended simultaneously.

(3) In FIG. 1, when extending three or less jack cylinders, the same as in the case of (2) above is used. (4) When all the jack cylinders 4a to 4dt are contracted at the same time, Main control valve 61
The first to fourth control valves 1 are in the eeo position.
5. Switch a to 15 d to the e→ position, and switch the switching valve 2'7 to the neutral position.

As a result, the pressure oil discharged from the hydraulic pump 5 changes from the main control valve 6 to the contraction side pipe 8 to the branch pipe 8.
&~8d and is supplied to the rod side oil chambers of the jack cylinders 4a~4d.

- 10,000, the pressure oil in the head side oil chambers of the Schatzkin cylinders 4a to 4d is transmitted through pipes 161L to 16d-+first to fourth control valves 1511 to 15d→pipe 14a to 14
d-+ 2nd. 3rd flow tabider 12.13 → pipe line 10.11- + first 70 - taper pipe 9 → extension side pipe line 7 → oil tank 19 through main control valve 6
Returned to 0 Therefore, all jack cylinders 4&~4di can be simultaneously reduced.

(5) For example, a set of two 4m jack cylinders as rear jack cylinders for large crawler clay.
, 4b at the same time, the main control valve 6t? (A) position, the 1st degree second control valve 15a, 15b k'=<j position, and the other 3rd degree. Fourth control valve 15C215d'i
) position and the switching valve 27t position.

As a result, the pressure oil discharged from the hydraulic pump 5, main control valve 6→reduction side pipe 8→branch pipe 8a,
The oil is supplied to the rod-side oil chambers of the jack cylinders 4a and 4b through the cylinder 8b.

- 10,000, the pressure oil in the head side oil chambers of the cylinders 4m and 4b is transmitted through pipes 16 &..., 16b → 1st. Second control valve 15m, 15b→pipeline 14a.

14 b-Th second flow divider 12 → pipe line 10
→ Pipe A → Passes through the switching valve 27 and drops into the oil tank 19. At this time, the third Fourth control valve 15c, 15
d is switched to position 1), and the conduits 14c, 14
dX Since pressure oil does not flow from the third flow divider 13 and pipe line 11 to the first flow divider 9, the diversion port to which the pipe line 10 of this first flow divider 9 is connected is It is narrowed down to 1. The pressure oil flowing out from the second flow divider 12 through the second control valves 15m, 15b-+pipe lines 14m, 14bt passes through the switching valve 27 and drops into the oil tank 19 as described above. Due to the squeezing action of the floaty vider 9 of 1,
Even if the branch boat on the pipe line 10 side is narrowed to the maximum, the jack cylinders 4a and 4bi can be reduced at the same operating speed as when all the jack cylinders 4a to 4d are reduced at the same time.

(6) When shrinking the jack cylinders 4at individually among the jack cylinders 4a to 4d, for example,
The main control valve 6k is in the () position, the first control valve 15ai is in the (c) position, the other second to fourth control valves 15b to 15d are in the () position, and the switching valve 27t is in the (g) position. Switch to .

As a result, the pressure oil discharged from the hydraulic pump 5 is transferred from the main control valve 6 to the contraction side pipe 8 to the branch pipe 8a.
The oil is supplied to the rod-side oil chamber of the jack cylinder 4a through the oil chamber.

- 10,000, the pressure oil in the head side oil chamber of the jack cylinder 4a is connected to the pipe line 16a- + the first control puff 15a
→Pipeline 14a-+Second shuttle valve 22→Pipeline →
The oil passes through the first shuttle valve 21 → pipe 26 → switching valve 27 and is dropped into the oil tank 19.

At this time, the second control valve 15b di)
7 m from the conduit 14 m.
Since no pressure oil flows into the 0-tavider 12, the diversion boat to which the pipe line 14a of the second flowtabider 12 is connected is throttled to the maximum, but the pressure flowing out from the first control valve 15m As mentioned above, the oil passes through the second shuttle valve ρ, the first shuttle valve 21 and the switching valve 27 and drops into the oil tank 19. Therefore, due to the throttling action of the second flow divider 12, υ Conduit 141
Even if the side branch boats are narrowed to the maximum, all of the jack cylinders 41 can be individually reduced at the same operating speed as when all the jack cylinders 43 to 4di are simultaneously reduced.

Also, compress the jacket cylinder 4b individually! The switching can also be performed through the actions of the second shuttle valve n1, the first shuttle valve 21, and the switching valve n.

When the cylinders 4c and 4dt are contracted individually, this can be done through the actions of the third shuttle valve n1, the first shuttle valve 21, and the switching valve n.

It should be noted that the present invention can be applied to control circuits for three or more sets of hydraulic cylinders, and furthermore, it can be applied to control circuits for hydraulic cylinders in general, in which two or more sets of hydraulic cylinders are arranged. can.

〔Effect of the invention〕

According to the present invention described above, a shuttle valve is connected between the pipes connecting two control valves provided corresponding to each hydraulic cylinder and one flow divider, and the outlet of the two shuttle valves is are connected to the inlets on both sides of the main shuttle valve, and the outlet of the main shuttle valve is communicated with an oil tank, and a switching valve is provided between the oil tank and the main shuttle valve, and the main flow piper and the main shuttle valve are connected in advance to each other. By connecting a pipe line connecting each set of two hydraulic cylinders with a flow pipe provided for one hydraulic cylinder and the switching valve to the pipe line, it is possible to connect a set of two hydraulic cylinders and a plurality of sets of hydraulic cylinders. It has the effect of being able to reduce the hydraulic cylinders individually and moreover at the same operating speed as when all the hydraulic cylinders are reduced at the same time. Therefore, for example, this control circuit for a jack cylinder for disassembling and assembling a large crawler crane, etc. When applied to a machine, when a difference occurs in the amount of expansion and contraction of the jack cylinder due to unbalanced loads, it can be quickly corrected and the work can be carried out safely.

Further, according to the present invention, there is an effect that a set of two preselected hydraulic cylinders can be reduced by ml'1 at the same time and at the same operating speed as when all the hydraulic cylinders are reduced at the same time. For example, when completely disassembling the side frame from the truck frame of a large crawler crane, 2
Since all the rear hydraulic cylinders as a set of individual hydraulic cylinders can be simultaneously reduced, there is an advantage that the setup time for removing the side frame can be shortened.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the control circuit of the present invention, and Figs. 2 and 3 show disassembly work of a large crawler crane using a set of two hydraulic cylinders (T-2) as hydraulic cylinders. FIG. 4 is a side view showing the control circuit of the jack cylinder according to the prior art. 41-4d...Jax cylinder as a hydraulic cylinder, 5...Hydraulic pump, 6...Main control valve, 7.8...Extension and contraction side pipe line, 9...Main flow tabider The first floataypaida as,
10.11...1st 70-Teibida and 2nd゜3rd
12.13 . . . 2nd. Third 70-Teibaidah, 14a-14d...
Pipe lines connecting the second and third flow pipers and the first to fourth control valves, 15a to 15d...first
~Fourth Control Pal'', 16a~16d...
Pipe line connecting the head side oil chambers of the first to fourth control valve cylinders, 19... Oil tank, 21
. . . the first shuttle valve as the main shuttle valve, 22.23 . . . the second shuttle valve. a third shuttle valve;
Sae, 25...2nd. Pipe line connecting the outlet of the third shuttle valve and the inlet of the first shuttle valve, 26...Pipe line connecting the outlet of the first shuttle valve and the oil tank, n
...Switching valve, ah... A pipe line that connects the first flow divider and the second flow divider and the switch valve.

Claims (1)

[Claims] Hydraulic cylinders arranged in a plurality of sets of two;
A main control valve, an extension-side pipe line and a contraction-side pipe line connecting the main control valve and each hydraulic cylinder, a main flow divider provided in the extension-side pipe line, and a set of the two hydraulic cylinders. In the hydraulic cylinder control circuit, the hydraulic cylinder control circuit includes a flow divider arranged in the main flow divider and connected to the main flow divider, and a control valve provided between the flow divider and each hydraulic cylinder. A shuttle valve is connected between the pipes connecting two control valves provided correspondingly to one flow divider, and the outlets of the two shuttle valves are connected to the inlets on both sides of the main shuttle valve. At the same time, the outlet of the main shuttle valve is communicated with an oil tank, and a switching valve is provided between the oil tank and the main shuttle valve, and one switching valve is provided between the main flow divider and a set of two preselected hydraulic cylinders. A control circuit for a hydraulic cylinder, characterized in that a conduit connecting a flow divider provided at the destination and the switching valve is connected by a conduit.