JPH0228725B2 - FUKUGOYUATSUKAIRO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a complex hydraulic circuit for a lifting and lowering cargo handling machine that performs lifting and lowering operations using two double-acting cylinders. When a bucket or fork at the tip of a lift arm or other work equipment is operated by a moving cylinder, the above two double-acting cylinders are operated simultaneously or each is operated independently. The object of the present invention is to provide a composite hydraulic circuit that improves the operating characteristics when two double-acting cylinders are operated simultaneously, and that can smoothly operate each cylinder independently.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described below with reference to embodiments shown in the drawings.

In the figure, reference numeral 1 denotes a first double-acting cylinder for raising and lowering the lift arm in an undulating manner, and when the cylinder extends, the arm stands up, and when it contracts, the arm falls down. Reference numeral 2 denotes a second double-acting cylinder for discharging or scooping the bucket.When the cylinder is extended, the bucket is discharged, and when it is contracted, the bucket is scooped. Reference numeral 3 indicates a directional switching valve for the first double-acting cylinder, 4 indicates a directional switching valve for the second double-acting cylinder, 5 indicates a hydraulic pump, and 6 indicates a tank.

The first double-acting cylinder directional switching valve 3 is a switching valve with 9 ports and 3 positions: extension, neutral, and contraction, and has a neutral port N ₁ , a pressure oil port P 1 , and a pressure oil port P ₁ on the pump side.
It has 5 ports: 1st series port S ₁ , 2nd series port S ₂ and tank port T ₁ , neutral port N ₂ on the cylinder side, 1st and 2nd cylinder ports A, B and return port R _1. It has 4 ports. In addition, the directional control valve 4 for the second double-acting cylinder
is a 3-position, 7-port switching valve for contraction, neutral, and extension, and has 4 ports on the pump side: neutral port N ₃ , hydraulic port P ₂ , return port R ₂ , and tank port T ₂ , and has 4 ports on the cylinder side. It has three ports: a neutral port _N4 and first and second cylinder ports C and D.

The neutral port _N1 on the pump side of the first double-acting cylinder directional control valve 3 is connected to the hydraulic pump 5 through an oil passage 7, and an oil passage 8 branched from this oil passage 7.
is connected to the pressure oil port _P1 via the first check valve 9. The first series port S ₁ is connected to the neutral port N 3 on the pump side of the second double-acting cylinder directional control valve 4 via the first connecting oil passage 10 and the oil passage 16, and is further connected to the neutral port N ₃ on the pump side of the second double-acting cylinder directional control valve 4. It is connected to the pressure oil port P ₂ via an oil passage 17 having a passage 10 and a third check valve 18 . Also 2nd series port
S ₂ is connected to the first connecting oil passage 10 via a second connecting oil passage 11, and a second check valve 12 is provided in the middle of this second connecting oil passage 11. A branch oil passage 13 is connected to the tank 6 from upstream of the second check valve 12, and a throttle mechanism 14 is provided in the middle of this branch oil passage 13. Furthermore, the tank port _T1 is connected to the tank 6 via the oil passage 15.
It is connected to. Also, the neutral port on the cylinder side
_N2 is connected to the neutral port _N3 on the pump side of the second double-acting cylinder directional control valve 4 via an oil passage 16, and the first connecting oil passage 10 is connected in the middle of this oil passage 16. It has been done. One first cylinder port A of the first double-acting cylinder directional control valve 3 is connected to the oil passage 19.
via the piston rear chamber 1 of the first double-acting cylinder 1
a, and the other second cylinder port B
is connected to the piston front chamber 1b via an oil passage 20. Further, the return port R ₁ of the first double-acting cylinder directional control valve 3 is connected to the return port R ₂ of the second double-acting cylinder directional control valve 4 via an oil passage 21 . On the other hand, the tank port T ₂ of the second double-acting cylinder directional control valve 4 is connected to the tank 6 via an oil passage 22 . The neutral port _N4 on the cylinder side is connected to a tank (not shown) through an oil passage 23, forming a neutral circuit. Further, one first cylinder port C of the second double-acting cylinder directional control valve 4 is connected to the piston front chamber 2a of the second double-acting cylinder 2 via an oil passage 24, and the other second
The cylinder port D is connected to the piston rear chamber 2b via an oil passage 25.

In the first double-acting cylinder directional control valve 3, in the neutral position, the neutral ports N ₁ and N ₂ communicate with each other, and the pressure oil port P ₁ , the first and second series ports S ₁ and S ₂ , and the cylinder port communicate with each other. A and B are blocked, and tank port _T1 and return port _R1 are in communication.
Furthermore, when the switching valve 3 is switched to the extended position, the neutral ports N ₁ , N ₂ and the second series port S ₂ are blocked, and the pressure oil port P ₁ , one first cylinder port A, and the other second cylinder port are blocked. B and the first series port S ₁ and the return port R ₁ and the tank port T ₁ communicate with each other. In this case, a flow rate control mechanism 26 having the function of a brake valve or a counterbalance valve is provided in the communication section between the return port R ₁ and the tank port T ₁ , and this flow rate control mechanism 26 is provided with a flow rate control mechanism 26 that functions as a brake valve or a counterbalance valve. The pilot pressure from the communication part with the 1 series port _S1 is applied, and when this pilot pressure exceeds a predetermined value, the flow rate control mechanism 26 is activated and the return port _R1 and the tank port _T1 are connected. communicate. Also, when the switching valve 3 is switched to the retracted position, the neutral ports N ₁ , N ₂ and the first series port
S ₁ is blocked and the pressure oil port P ₁ and the other
Cylinder port B, one first cylinder port A
and the second series port S ₂ , as well as the return port
R ₁ and tank port T ₁ communicate with each other.

On the other hand, in the neutral position of the second double-acting cylinder directional control valve 4, the neutral ports N ₃ and N ₄ communicate with each other, and the other pressure oil ports P ₂ , return port R ₂ , and tank port communicate with each other.
_T2 and the first and second cylinder ports C and D are blocked, respectively. When the switching valve 4 is switched to the retracted position, the neutral ports _N3 , _N4 and return port _R2 are blocked, and the pressure oil port _P2 , one first cylinder port C, and the other second cylinder port are blocked. D and tank port _T2 communicate with each other. Also, when the switching valve 4 is switched to the extended position, neutral ports N ₃ and N ₄ and tank port T ₂
The ports are blocked, and the pressure oil port _P2 and the other second cylinder port D communicate with each other, and the one first cylinder port C and the return port _R2 communicate with each other.

Next, to explain the operation, the state shown in Fig. 1 is as follows.
Both the first double-acting cylinder directional control valve 3 and the second double-acting cylinder directional control valve 4 are in the neutral position,
The hydraulic oil from the hydraulic pump 5 is routed through oil path 7 → neutral port N ₁ → neutral port N ₂ → oil path 16 → neutral port N ₃
→ Neutral port N ₄ → Return to tank via oil path 23,
It is in a no-load neutral state.

Next, to explain the case where the first double-acting cylinder directional switching valve 3 is operated independently, when the switching valve 3 is switched to the extended position, the hydraulic fluid from the hydraulic pump 5 is
The oil is supplied to the piston rear chamber 1a of the first double-acting cylinder 1 through the oil passage 8 → check valve 9 → pressure oil port P ₁ → cylinder port A → oil passage 19, and then to the piston front chamber 1.
The return oil from b is oil path 20 → cylinder port B →
First series port S ₁ → first connecting oil passage 10 → neutral port N ₃ → neutral port N ₄ → returns to the tank via oil passage 23, and only the first double-acting cylinder 1 is extended. That is, the lift arm operates to stand up. Also, when the switching valve 3 is switched to the retracted position, the hydraulic pump 5
Hydraulic oil flows from oil line 8 → check valve 9 → pressure oil port
P ₁ → Cylinder port B → Supplied to the piston front chamber 1b of the first double-acting cylinder 1 via the oil passage 20,
The return oil from the piston rear chamber 1a flows through the oil passage 19→
Cylinder port A → 2nd series port S ₂ flows, whereby some of the return oil returns to tank 6 via branch oil path 13 → throttling mechanism 14, and the rest returns to check valve 12 → 2nd communication oil path 11 → The first communication oil passage 10 → neutral port N ₃ → neutral port N ₄ → returns to the tank via the oil passage 23, and the first double-acting cylinder 1 contracts.
The lift arm moves downward. In this case, a part of the return oil returns to the tank 6 through the branch oil passage 13 having the throttling mechanism 14, so that all of the return oil does not take a long path through the first communication oil passage 10. As a result, pressure loss can be reduced and the contraction speed can be increased.

Next, to explain the case where the second double-acting cylinder directional switching valve 4 is operated independently, when the switching valve 4 is switched to the retracted position, the hydraulic fluid from the hydraulic pump 5 is
Oil path 7 → Neutral port N ₁ → Neutral port N ₂ → Oil path 1
6 → Branch oil path 17 → Check valve 18 → Pressure oil port P ₂
→ Cylinder port C → Oil is supplied to the piston front chamber 2a of the second double-acting cylinder 2 via oil passage 24, and return oil from the piston rear chamber 2b is supplied to oil passage 25 → Cylinder port D → Tank port T ₂ → Oil Returning to the tank 6 via channel 22, only the second double-acting cylinder 2 is retracted at normal speed. That is, the packet is scooped. Furthermore, when the switching valve 4 is switched to the extended position, the hydraulic oil from the hydraulic pump 5 flows through the oil path 7 → neutral port N ₁ → neutral port N ₂ → oil path 16 → branch oil path 17 → check valve 18 → pressure Oil is supplied to the piston rear chamber 2b of the second double-acting cylinder 2 via oil port P ₂ → cylinder port D → oil passage 25, and return oil from the piston front chamber 2a is supplied to oil passage 24 → cylinder port C → return port R. ₂ → oil path 21 → return port R ₁ → tank port T ₁ → returns to tank 6 via oil path 15, and second double-acting cylinder 2 is extended at normal speed. That is, the bucket performs a discharge operation.

In this way, by independently operating the first double-acting cylinder directional control valve 3 or the second double-acting cylinder directional control valve 4, the corresponding first double-acting cylinder 1 or second double-acting cylinder
Only the double-acting cylinder 2 can be independently extended or contracted.

Next, the operation when the switching valves 3 and 4 are operated simultaneously will be explained with reference to FIGS. 2 to 5. First, put the first double-acting cylinder directional control valve 3 in the extended position,
When the second double-acting cylinder directional control valve 4 is in the retracted position, as shown in _FIG .
The oil is supplied to the piston rear chamber 1a of the first double-acting cylinder 1 through the cylinder port A → oil passage 19, and the return oil from the piston front chamber 1b is supplied through the oil passage 20 → cylinder port B → first series port S ₁ → 1 Connecting oil line 10 → Branch oil line 17 → Check valve 18 → Pressure oil port
Hydraulic oil is supplied to the piston front chamber 2a of the second double-acting cylinder 2 via P ₂ → cylinder port C → oil passage 24, and return oil from the piston rear chamber 2b goes through oil passage 25 → cylinder port D → tank port T. ₂ → Returns to the tank 6 via the oil path 22, and the extension operation of the first double-acting cylinder 1 (raising operation of the lift arm) and the contraction operation of the second double-acting cylinder 2 (squeezing operation of the bucket) are performed at normal speed. are carried out simultaneously and in conjunction.
In this case, if the cylinder inner diameters and piston rod shapes of both cylinders 1 and 2 are made equal, the operating strokes of both cylinders 1 and 2 can be made equal.

Next, when the first double-acting cylinder directional control valve 3 is set to the extended position and the second double-acting cylinder directional control valve 4 is set to the extended position, the hydraulic pump 5
Hydraulic oil flows from oil line 8 → check valve 9 → pressure oil port
P ₁ → Cylinder port A → Supplied to the piston rear chamber 1a of the first double-acting cylinder 1 via the oil passage 19,
The return oil from the piston front chamber 1b flows through the oil passage 20→
Cylinder port B → 1st series port S ₁ → 1st
It is supplied as hydraulic oil to the piston rear chamber 2b of the second double-acting cylinder 2 via the connecting oil passage 10 → branch oil passage 17 → check valve 18 → pressure oil port P ₂ → cylinder port D → oil passage 25, and The return oil from the chamber 2a returns to the tank 6 via the oil path 24 → cylinder port C → return port R ₂ → oil path 21 → return port R ₁ → flow rate control mechanism 26 → tank port T ₁ → oil path 15. A circuit is formed, but in this case, the flow rate control mechanism 26 is initially off and not in communication, so the return oil in the piston front chamber 2a of the second double-acting cylinder 2 does not return to the tank 6, and each oil Since the oil in the passage does not flow, the first and second double acting cylinders 1,
2 do not operate together, but the pressure in each oil passage increases, and the pilot pressure that acts on the flow rate control mechanism 26,
That is, when the pressure of the oil sent from the piston front chamber 1b of the first double-acting cylinder 1 to the piston front chamber 2b of the second double-acting cylinder 2 exceeds a predetermined pressure, the flow rate control mechanism 26 is turned on and communicated, and the return oil is returns to the tank 6, so the first and second double-acting cylinders 1 and 2 operate simultaneously. In this way, only when the first double-acting cylinder 1 is extended at a pressure higher than a predetermined pressure, the second double-acting cylinder 2 is also extended, and both cylinders 1, 2
The extension actuation of is a completely related actuation. Therefore, even when a load is applied in the direction of extension of the second double-acting cylinder 2, the extension operation of the first double-acting cylinder 1 is restricted, and rapid extension due to an increase in load is prevented.
That is, when the second double-acting cylinder 2 suddenly expands due to a load, its piston rear chamber 2b becomes a vacuum state, and the feed oil from the piston front chamber 1b of the first double-acting cylinder 1 rapidly flows, causing the oil pressure to increase. This will result in a decline. Therefore, the pilot pressure also decreases, the passage of the flow rate control mechanism 26 is blocked, and the return oil from the piston front chamber 2a of the second double-acting cylinder 2 does not flow, so that no extension operation occurs. Similarly, when a load in the contraction direction is applied to the first double-acting cylinder 1 and the extension is stopped, the passage of the flow rate control mechanism 26 is blocked, and the second double-acting cylinder 2 does not extend.

Next, when the first double-acting cylinder directional control valve 3 is set to the retracted position and the second double-acting cylinder directional control valve 4 is set to the retracted position, as shown in FIG. , oil passage 8 → check valve 9 → pressure oil port P ₁ → cylinder port B → oil passage 20 to the first
Oil is supplied to the piston front chamber 1b of the double-acting cylinder 1 and returned from the piston rear chamber 1a through the oil path 1.
9→cylinder port A→second series port _S2 , some of the return oil returns to tank 6 via branch oil path 13→throttle mechanism 14, and the rest flows through check valve 12→second connecting oil path 11 → First connecting oil passage 10 → Branch oil passage 17 → Check valve 18 → Pressure oil port P ₂ → Cylinder port C → Supplied as hydraulic oil to the piston front chamber 2a of the second double-acting cylinder 2 via oil passage 24 The return oil from the piston rear chamber 2b flows through the oil passage 2.
5→cylinder port D→tank port T ₂ →returns to tank 6 via oil path 22, and both the first and second double-acting cylinders 1 and 2 contract. In this case, the first
Since a part of the return oil from the piston rear chamber 1a of the double-acting cylinder 1 is returned to the tank 6 via the branch oil passage 13 having the throttling mechanism 14, the second double-acting cylinder 2 is contracted to the maximum in the middle or from the beginning. Even if the first double-acting cylinder 1 is in the state of When maximum contraction is reached,
Even when the load increases, the throttle mechanism 14 of the branch oil passage 13 acts as a bleed-off hole, preventing the generation of surge pressure. And the branch oil passage 13
Due to the presence of , the pressure loss during simultaneous contraction is reduced,
Moreover, the contraction speed of the first double-acting cylinder 1 can be increased.

Finally, when the first double-acting cylinder directional control valve 3 is set to the retracted position and the second double-acting cylinder directional control valve 4 is set to the extended position, the hydraulic pump 5 operates as shown in FIG. Oil is supplied to the piston front chamber 1b of the first double-acting cylinder 1 via the oil passage 8 → check valve 9 → pressure oil port P ₁ → cylinder port B → oil passage 20, and the oil is returned from the piston rear chamber 1a. is oil path 19 → cylinder port A → 2nd series port
S ₂ , and some of the return oil flows through branch oil path 1.
3 → returns to the tank 6 via the throttle mechanism 14, and the remaining return oil is returned to the tank 6 through the check valve 12 → second connecting oil path 11 → first
It is supplied as hydraulic oil to the piston rear chamber 2b of the second double-acting cylinder 2 via the connecting oil passage 10 → branch oil passage 17 → check valve 18 → pressure oil port P ₂ → cylinder port D → oil passage 25, and Return oil from the chamber 2a returns to the tank 6 via oil path 24 → cylinder port C → return port R ₂ → oil path 21 → return port R ₁ → tank port T ₁ → oil path 15,
The first double-acting cylinder 1 contracts and the second double-acting cylinder 2 extends. In this case, since a part of the return oil from the rear chamber 1a of the first double-acting cylinder 1 is returned to the tank 6 via the branch oil passage 13 having the throttling mechanism 14, the second double-acting cylinder 2 is Even if the first double-acting cylinder 1 is moved to the maximum extension state midway through, the aperture mechanism 14 becomes a bleed-off hole, and the first double-acting cylinder 1 can be retracted without any trouble. Moreover, due to the presence of the branch oil passage, the pressure loss during the contraction operation of the first double-acting cylinder 1 can be reduced, and the contraction speed can be increased.

As explained above, the present invention includes a first neutral port N ₁ connected to the hydraulic pump 5 via the oil passage 7 on the pump side for controlling the first double-acting cylinder 1;
a hydraulic port P ₁ connecting an oil passage 8 having a check valve 9 branched from the oil passage 7; a first series port S ₁ ;
2nd series boat S ₂ , with tank port T ₁ ,
On the cylinder side, a second neutral port N ₂ , a first cylinder port A connected to the piston rear chamber 1a of the first double-acting cylinder 1, a second cylinder port B connected to the piston front chamber 1b of the first double-acting cylinder 1, and a return A 3-position, 9-port directional control valve 3 for the first double-acting cylinder, which has port _R1 and takes three positions: extended, neutral, and retracted, and a pump side for controlling the second double-acting cylinder 2. It has a third neutral port N ₃ , a hydraulic port P ₂ , a return port R ₂ , and a tank port T ₂ , and a fourth neutral port N ₄ and a second
It has a first cylinder port C connected to the piston front chamber 2a of the double-acting cylinder 2, and a second cylinder port D connected to the piston rear chamber 2b of the second double-acting cylinder 2, and has three positions: contraction, neutral, and extension. It consists of a 7-port second double-acting cylinder directional control valve 4, and the piping connection between the first double-acting cylinder directional control valve 3 and second double-acting cylinder directional control valve 4 is connected to the first double-acting cylinder directional control valve 4. The second neutral port N 2 on the cylinder side of the directional control valve ₃ for use is connected with the third neutral port N 3 on the pump side of the directional control valve ₄ for the second double-acting cylinder by an oil passage 16, The other end of the first connecting oil passage 10, one end of which is connected to the first series port S ₁ on the pump side of the directional control valve 3, is connected to the oil passage 16.
The first connection oil passage 10 is connected to the pump side hydraulic port _P2 of the second double-acting cylinder directional control valve 4 by an oil passage 17 having a check valve 18. Return port R ₁ of directional control valve 3 for double-acting cylinder and directional control valve 4 for second double-acting cylinder
The return port R ₂ of the above is connected by an oil passage 21, and the second connecting oil passage 11, which is branched from the middle of the first connecting oil passage 10 and has a second check valve 12 in the middle, is connected in the direction for the first double-acting cylinder. Connected to the second series port _S2 on the pump side of the switching valve 3, and connected to the second connecting oil passage 11.
and the upstream side of the second check valve 12 and the tank 6 are connected by an oil passage 13 having a throttle mechanism 14, and the return port on the cylinder side in the extended position of the first double-acting cylinder directional control valve 3 is connected. A flow rate control mechanism 26 that opens and closes based on pilot pressure is provided in the communication section between R ₁ and the tank port T ₁ on the pump side, and the pilot pressure that opens and closes the flow rate control mechanism 26 is connected to the second cylinder port B on the cylinder side. , from the middle of the connection part of the first series port S ₁ on the pump side, and the first double-acting cylinder directional control valve 3 is in the extended position, the first neutral port N ₁ on the pump side, the second series port S 1 on the pump side.
The series port S ₂ and the second neutral port N ₂ on the cylinder side are respectively blocked, and in the neutral position, the hydraulic port P ₁ on the pump side, the first series port S ₁ and the second
The series port S ₂ is blocked, the first cylinder port A and the second cylinder port B on the cylinder side are respectively blocked, and in the retracted position, the first neutral port N ₁ on the pump side is blocked.
The first series port _S1 and the second neutral port _N2 on the cylinder side are respectively blocked, and the second double-acting cylinder directional control valve 4 is in the retracted position and the third series port on the pump side is blocked.
The neutral port N ₃ and return port R ₂ are blocked, and the fourth neutral port N ₄ on the cylinder side is blocked respectively, and in the neutral position, the hydraulic port P ₂ , return port R ₂ and tank port T ₂ on the pump side are blocked. Block the first cylinder port C and second cylinder port D on the side, and block the third neutral port N ₃ and tank port T ₂ on the pump side and the fourth neutral port N ₄ on the cylinder side in the extended position, respectively. Therefore, when the first and second double-acting cylinders are extended simultaneously, the second
Even if a large load is applied in the direction of extension of the double-acting cylinder, the piston front chamber 1b of the first double-acting cylinder 1
Unless a certain pilot pressure is generated between the piston rear chamber 2b of the second double-acting cylinder 2, the flow rate control mechanism 26 will not open and both double-acting cylinders 1 and 2 will not extend. Therefore, it is possible to prevent the rapid extension operation accompanying the increase in the second double-acting cylinder, to prevent the piston rear chamber of the second double-acting cylinder from becoming a vacuum, and to reduce the expansion rate of the first double-acting cylinder.
It is possible to perform multiple simultaneous operations in which the expansion rate of the second double-acting cylinder theoretically matches. Further, when both the double-acting cylinders are simultaneously retracted, even if the second double-acting cylinder reaches its maximum contraction state from the beginning or halfway, the first double-acting cylinder can be retracted without any problem. When the contraction operation of the first double-acting cylinder and the extension or contraction operation of the second double-acting cylinder are performed at the same time, pressure loss can be reduced;
The contraction operation speed of the double-acting cylinder can be increased. In addition, it is possible to operate the first double-acting cylinder and the second double-acting cylinder not only independently but also simultaneously, and the second double-acting cylinder can be operated with the return oil of the first double-acting cylinder. ,
Both double-acting cylinders can be operated simultaneously and in parallel. Furthermore, since the second double-acting cylinder does not pass through the throttling mechanism when it operates independently, the expansion speed can be increased.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the overall configuration of a composite hydraulic circuit according to the present invention. Figures 2 to 5 are
FIG. 6 is an explanatory diagram showing the piping connection state in each simultaneous operation state of the second double-acting cylinder directional switching valve. DESCRIPTION OF SYMBOLS 1...First double-acting cylinder, 2...Second double-acting cylinder, 3...Directional switching valve for first double-acting cylinder, 4
... Second double-acting cylinder directional control valve, 5 ... Hydraulic pump, 6 ... Tank, 10 ... First connecting oil path,
11...Second connection oilway, 13...Branch oilway, 26
...Flow control mechanism.

Claims (1)

[Claims] 1. A first neutral port N ₁ connected to the hydraulic pump 5 via an oil path 7 on the pump side and a reverse port branched from the oil path 7 for controlling the first double-acting cylinder 1. a hydraulic port P ₁ connecting an oil passage 8 having a stop valve 9;
1st series port S ₁ , 2nd series port S ₂ ,
It has a tank port _T1 , a second neutral port _N2 on the cylinder side, a first cylinder port A connected to the piston rear chamber 1a of the first double-acting cylinder 1, and a piston front chamber 1b of the first double-acting cylinder 1. The second in a row
Has cylinder port B and return port R ₁ ,
A 3-position, 9-port directional switching valve 3 for the first double-acting cylinder that takes three positions: extension, neutral, and contraction; and a third neutral port N ₃ on the pump side for controlling the second double-acting cylinder 2; It has a hydraulic port P ₂ , a return port R ₂ , and a tank port T ₂ , and on the cylinder side, a fourth neutral port N ₄ , a first cylinder port C connected to the piston front chamber 2a of the second double-acting cylinder 2, and a second cylinder port. Piston rear chamber 2 of double acting cylinder 2
a 3-position, 7-port directional control valve 4 for the first double-acting cylinder, which has a second cylinder port D connected to the cylinder port D, and has three positions: contraction, neutral, and extension; 3 and the second double-acting cylinder directional control valve 4, and the second neutral port N2 on the cylinder side of the first double-acting cylinder directional control valve ₃ and the second double-acting cylinder directional control valve 4. A first connecting oil passage 10 is connected to the third neutral port _N3 on the pump side by an oil passage 16, and one end is connected to the first series port _S1 on the pump side of the first double-acting cylinder directional control valve 3. The other end is connected to the middle of the oil passage 16, and the oil passage has a check valve 18 between the middle of the first connecting oil passage 10 and the pump side hydraulic port _P2 of the second double-acting cylinder directional control valve 4. 17, the return port R1 of the first double-acting cylinder directional control valve ₃ and the return port R2 of the second double-acting cylinder directional control valve ₄ are connected by an oil passage 21, and the first connecting oil passage A second connecting oil passage 11 having a second check valve 12 in the middle, which branches off from the middle of the first double-acting cylinder directional control valve 3, is connected to the second series port S2 on the pump side of the first double-acting cylinder directional control valve ₃ . 2 connecting oil passages 11, and the second check valve 1
2 and the tank 6 are connected by an oil passage 13 having a throttle mechanism 14, and the return port _R1 on the cylinder side and the tank port T on the pump side in the extended position of the first double-acting cylinder directional control valve 3 are connected. ₁ is provided with a flow rate control mechanism 26 that opens and closes based on pilot pressure, and the pilot pressure that opens and closes the flow rate control mechanism 26 is connected to the second cylinder port B on the cylinder side.
The first double-acting cylinder directional control valve 3 is connected to the first neutral port N ₁ and the second series port S ₂ on the pump side in the extended _position . , the second neutral port on the cylinder side
N ₂ respectively, and at the neutral position, connect the hydraulic port P ₁ , 1st series port S ₁ , and 2nd series port S ₂ on the pump side, and the 1st cylinder port A and 2nd cylinder port B on the cylinder side, respectively. in the blocked and retracted position, the first neutral port N ₁ on the pump side;
The first series port S ₁ and the second neutral port N ₂ on the cylinder side are respectively blocked, and the second double-acting cylinder directional control valve 4 is in the retracted position, and the third neutral port N ₃ on the pump side and the return port are blocked. R ₂ and the fourth neutral port N ₄ on the cylinder side are respectively blocked, and in the neutral position, the hydraulic port P ₂ , return port R ₂ and tank port T ₂ on the pump side are blocked.
The first cylinder port C and the second cylinder port D on the cylinder side are respectively blocked, and in the extended position, the third neutral port N ₃ and the tank port T ₂ on the pump side are blocked.
A composite hydraulic circuit characterized in that the fourth neutral port _N4 on the cylinder side is respectively blocked.