JPH0435601Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Field of Industrial Application) The present invention relates to a return oil regeneration circuit of a hydraulic cylinder used in construction machines such as hydraulic excavators, various industrial machines, and the like. (Prior Art) To explain a conventional example of a drive circuit in a hydraulic cylinder for driving a boom of a hydraulic excavator, the fifth
As shown in the figure, chambers are provided in both pipes l 2 and l 3 between the variable displacement hydraulic pump 3 having a capacity control section 3a and the tank 10 and both oil chambers _2a and 2b of the hydraulic cylinder 2 for driving the boom ₁ . A pilot pressure supply switching valve 5 that controls the hydraulic pump 3 and the directional switching valve 4 is equipped with a directional switching valve 4 having 4a, 4b, and 4c.
The pilot pressure _supply switching valve 5 is operated in the direction of the arrow _A , and the pressure from the pilot hydraulic pressure source ₆ is Oil is supplied as pilot pressure via the pressure reducing valve 5c and the pilot pipe _l4 ,
The directional control valve 4 is switched from the chamber 4a to the chamber 4c, and the capacity control unit 3a is controlled to increase the capacity (increase the pump discharge flow rate) via the high pressure selection valve 7 and the pilot pipe _l6 , and the discharge of the hydraulic pump 3 is increased. Pressure oil flows from pipe l ₂ to oil chamber (rod side) 2b of hydraulic cylinder 2.
The hydraulic oil in the oil chamber 2a is led from the pipe _l3 to the tank 10, and the hydraulic cylinder 2 is shortened to drive the boom 1 in the direction of the arrow B, and the pilot pressure supply switching valve 5 is activated. When operated in the direction of arrow A′,
The hydraulic cylinder extends and moves the boom in the direction of the arrow.
It has a structure that allows it to be driven to B'. Operation lever 5 of the pilot pressure supply switching valve 5
The operation amount of a is proportional to the pilot pressure, on the other hand, the pilot pressure and the capacity of the hydraulic pump (swash plate control) are proportional, and the pilot pressure and the operation amount of the directional control valve are proportional. A lever controls the operating speed of the hydraulic cylinder. (Problems to be solved by the invention) In the conventional hydraulic cylinder drive circuit, pressure oil must be supplied from the hydraulic pump to the oil chamber of the hydraulic cylinder even when the boom is lowered by the hydraulic cylinder. This results in power loss, and if the boom descends too quickly, negative pressure will occur due to insufficient supply of pressure oil from the hydraulic pump to the oil chamber of the oil chamber cylinder, resulting in abnormal vibrations and noise. There are other problems. (Means for solving the problem) The present invention is a return oil regeneration circuit for a hydraulic cylinder in order to deal with the above-mentioned problems. When the load moves to the load side, the hydraulic cylinder is switched from the heavy load side oil chamber to the negative pressure side oil chamber and the oil regenerates, ensuring pressure oil supply to the negative pressure side oil chamber and operating the cylinder. A regeneration control valve is provided to control the speed, and it is installed at the pilot pressure outlet of the pilot pressure supply switching valve and is switched by the weight load pressure of the weight load side oil chamber to set the directional control valve to neutral and operate the hydraulic pump at a small capacity, and to regenerate. By installing a pilot pressure switching valve that switches the control valve to the regenerative operation side, when the hydraulic cylinder is operated to the same load side due to a heavy load, the return hydraulic oil from the heavy load side oil chamber of the hydraulic cylinder is transferred to the negative pressure side oil chamber. This system secures the supply of pressure oil to the negative pressure side oil chamber and controls the cylinder operating speed to improve the drive performance of the hydraulic cylinder, reduce power consumption, and prevent abnormal vibrations and abnormal noises, as described above. Problems are resolved. (Function) When the hydraulic cylinder is operated to the load side due to a weight load, the pilot pressure switching valve is switched by the weight load pressure in the oil chamber on the weight load side of the hydraulic cylinder, and the pilot pressure switching valve supplies pilot pressure. The pilot pressure is switched and supplied from the switching valve, the directional switching valve becomes neutral, the supply of pressure oil from the hydraulic pump to the hydraulic cylinder is stopped, the hydraulic pump operates at a small capacity, and the regeneration control valve is switched to reduce the weight load on the hydraulic cylinder. The hydraulic oil in the side oil chamber is throttled and supplied to the negative pressure side oil chamber, the pressure oil supply to the negative pressure side oil chamber is ensured, and the hydraulic cylinder is controlled to a predetermined operating speed by regenerative supply of return oil. activated. (Embodiment) Fig. 1 and Fig. 2 show a first embodiment of the present invention, which is a drive circuit for a hydraulic cylinder 2 for driving a boom 1 of a hydraulic excavator, and is a variable displacement type having a displacement control section 3a. Hydraulic pump 3 and tank 10
A directional control valve 4 having chambers 4a, 4b, 4c is interposed in both pipes _l2 , _l3 between the hydraulic pump 3 and both oil chambers 2a, 2b of the hydraulic cylinder 2. Pilot pressure supply switching valve 5 that controls
are connected by pilot pipes l ₄ , l ₅ , l ₆ , l ₇ and a high pressure selection valve 7, and when the pilot pressure supply switching valve 5 is operated in the direction of arrow A, the pilot oil pressure Pressure oil from source 6 is supplied to pressure reducing valve 5
c, the pilot pressure is supplied via the pilot pipes _{l7 and l4} , the directional control valve 4 is switched from chamber 4a to 4c, and the capacity control unit 3a increases the capacity via the high pressure selection valve 7 and the pilot pipe _l6 . The pressure oil discharged from the hydraulic pump 3 is supplied from the pipe l2 to the oil chamber _2b of the hydraulic cylinder 2, and the hydraulic oil in the oil chamber 2a is guided from the pipe _l3 to the tank 10. When the pilot pressure supply switching valve 5 is operated in the direction A', the hydraulic cylinder 2 becomes extended and the boom is moved in the direction indicated by the arrow. The basic configuration is to drive in direction B'. The operating amount of the operating lever 5a of the pilot pressure supply switching valve 5 and the pilot pressure are proportional, the pilot pressure and the capacity of the hydraulic pump are proportional, and the pilot pressure and the operating amount of the directional switching valve are proportional. The structure is such that the operating speed of the cylinder is controlled. Furthermore, in the present invention, the chambers 9a and 9b are provided between the pipes l2 and _l3 between the directional control valve ₄ and the hydraulic cylinder 2.
A regeneration control valve 9 having a regeneration control valve 9 is interposed therein, and a pilot pressure switching valve 8 is provided in one pilot outlet conduit _l7 of the pilot pressure supply switching valve 5. To explain the regeneration control valve 9 in detail, the chamber 9a
When _the hydraulic pump ₃ is switched to A normal drive circuit is formed which is led to the tank 10 that flows through the other pipe l ₃ or l ₂ , and when it is switched to the chamber 9b, it becomes a regenerative operation. By selecting the ratio of the opening area from the oil chamber 2a to 2b of the hydraulic cylinder 2 and the opening area from the chamber 2b to the tank 10, the principle of operation described later can be achieved. Oil chamber 2b (negative pressure side oil chamber)
The lowering speed of the boom 1 is controlled by controlling the operating lever 5a while ensuring a certain appropriate oil pressure without creating a negative pressure in the It has come to be controlled by Furthermore, to explain the pilot pressure switching valve 8 in detail, when the weight load due to the dead weight of the boom 1 increases on the oil chamber 2a (heavy load side oil chamber) side of the hydraulic cylinder 2 and the pressure rises above a predetermined level, Oil room 2
The pressure in a acts as a pilot pressure through the pipe _l3 and the pilot pipe _l9 , and the pilot switching valve 8
is switched to the chamber 8b side, the directional control valve 4 is switched to the neutral chamber 4a, and the displacement control section 3a of the hydraulic pump 3 is switched to the neutral chamber 4a.
is controlled to a small capacity operation, and the regeneration control valve 9
It is configured to switch and control the chamber 9b to the regenerative operation side chamber 9b. The first embodiment of the present invention has the above-mentioned configuration, and when the operating lever 5a of the pilot pressure supply switching valve 5 is operated in the direction of the arrow A, pressure oil from the pilot hydraulic pressure source 6 flows into the pressure reducing valve 5c. , becomes pilot pressure through the pilot pressure outlet pipe _l7 , and when pressure builds up in the chamber 2a of the hydraulic cylinder 2 (heavy load side oil chamber) due to the weight of the boom 1, this pressure passes through the pilot pipe _l9 as pilot pressure. The pressure is then added to the pilot pressure switching valve 8 and switched to the chamber 8b. When the pilot pressure switching valve 8 is switched to the chamber 8b, the pilot pressure in the pilot outlet pipe _l7 is switched to the chamber 9b via the pilot pipe _l8 , and the regeneration control valve 9 is set to regenerative operation. , the pilot line l4 to the directional control valve ₄ , and the pilot line _l6 to the capacity control section 3a of the hydraulic pump 3 are the tank 10a.
The directional control valve 4 is switched to the neutral chamber 4a, and the hydraulic pump 3 is controlled to operate at a small capacity. Therefore, the pressure oil discharged from the hydraulic pump 3 is transferred to the hydraulic cylinder 2.
The hydraulic pump 3 is operated to save power, and the regeneration control valve 9 regenerates the heavy load pressure oil in the chamber 2a (heavy load side oil chamber) of the hydraulic cylinder 2 from the pipe _l3. Due to the throttle opening action of the control valve 9, regenerative supply is supplied to the chamber 2b (load-side oil chamber) through the pipe _l2 , and an appropriate pressure is secured and maintained in the chamber 2b, allowing the hydraulic cylinder 2 to operate smoothly without generating negative pressure. The boom 1 is lowered in the direction of the arrow B, and the operating speed of the hydraulic cylinder 2 and the lowering speed of the boom 1 are controlled by adjusting the aperture area of the regeneration control valve 9 by operating the operating lever 5a. controlled. The regeneration principle of the regeneration control valve 9 will be explained in detail with reference to FIG. 3. The weight applied to the hydraulic cylinder 2 is expressed as W,
The pressure in the chamber 2a of the hydraulic cylinder is Pb, the pressure in the chamber 2b is Pr, the pressure in the tank 10 is Pt, the pressure receiving area on the chamber 2a side of the hydraulic cylinder is Ab, the pressure receiving area on the chamber 2b side is Ar, chamber 2a, pipe l ₃ Let a _b be the aperture opening area from conduit l ₂ to a t , and a _{t be} the aperture area from conduit l ₂ to tank 10.

[Formula] (C: flow coefficient, g: gravitational acceleration, r: specific weight of oil), then depending on the balance of cylinder force, W/Ab+PrAr/Ab=Pb...(1) From chamber 2a, pipe _l3 The flow rate q _b passing through the pipe l ₂ is q _b =ξa _b √− ...(2) The flow rate q _t from the pipe l ₂ to the tank 10 is q _t = ξa _t √− ......(3) On the other hand, from the relationship between the flow rate q _b and the descending speed of the hydraulic cylinder 2 x, q _b = Abx... (4) From the relationship between the flow rate q _t and the descending speed of the hydraulic cylinder 2, x, q _t = (Ab-Ar) x ...(5) If (Ab-Ar)/Ab=K, then q _b = q _t /K ...(6) If Pt≒0 in equation (3), then from equations (6), (2), and (3), a _b √−=a _t /K√ ∴ a _b ² (Pb−Pr)=a _t ² /K ²・Pr ∴ K ² a _b ² +a _t ² /K ²・Pr=a _b ² Pb Pr=K ² a _b ² /a _t ² +K ² a _b ² Pb ...(7) Substituting equation (7) into equation (1), Pb=W/Ab・K ² a _b ² +a _t ² /K ³ a _b ² + a _t ² ...(8) In equation (7), if a _t = Ca _b (however, C is a constant) Pr = K ² /C ² +K ²・Pb ...(9) Similarly Equation (8) is Pb=W/AbK ² +C ² /K ³ +C ² ...(10) From equations (2), (4), and (9) From equations (9), (10), and (11), the opening area from chamber 2a of the hydraulic cylinder and pipe _l3 to pipe _l2 is
By setting a _b and the opening area a _t from pipe l ₂ to tank 10 at a constant ratio, when the weight W applied to the hydraulic cylinder (2) is constant, the pressure Pb in chamber 2a is constant. Therefore, the pressure Pr in chamber 2b will also be constant,
Moreover, the descending speed x of the hydraulic cylinder (2) is also the opening area a _b
Therefore, the operating amount of the operating lever 5a and the descending speed x of the hydraulic cylinder 2 are proportional to each other. On the other hand, when no pressure is built up in the chamber 2a of the hydraulic cylinder 2, that is, when the dead weight of the boom 1 cannot be utilized, the pilot pressure switching valve 8 is switched to the chamber 8a in FIG. The pilot line l ₈ to the chamber 8 of the pilot switching valve 8
Since the regenerative control valve 9 returns to the chamber 9a, the pilot pressure is guided from the chamber 8a of the pilot pressure switching valve 8 to the pilot pipe l4, and the directional switching valve ₄ is transferred to the chamber 4c. and the capacity of hydraulic pump 3 (swash plate) from pilot line l ₆ .
The control unit 3a increases the swash plate angle, that is, the capacity of the hydraulic pump 3, thereby increasing the pump discharge flow rate. (Other Embodiments) FIG. 4 shows a second embodiment of the present invention, which is different from the first embodiment in that a pressure switch 12 is provided in the pilot conduit _l9 , and an electromagnetic switching type pilot pressure switching valve 8 is provided. The second embodiment is characterized by the fact that the second embodiment has the same structure as the first embodiment, and the other configurations are the same as those of the first embodiment, and the same effects can be obtained. In the figure, 11 is a power supply. (Effect of the invention) Since the present invention has the above-mentioned configuration, when the hydraulic cylinder is operated on the load side due to a weight load, the pilot pressure switching valve is switched and the pilot pressure from the pilot pressure supply switching valve is reduced. is switched, the directional control valve is set to neutral, the pressure oil supply to the hydraulic pump is stopped, and the hydraulic pump is operated at a small capacity.The regeneration control valve is switched to regenerate return oil, and the operating speed of the hydraulic cylinder is changed. is controlled, its speed can be freely adjusted, and it has excellent operating performance. Therefore, there are also effects such as a significant reduction in power and the prevention of abnormal vibrations and abnormal noises.

[Brief explanation of drawings]

Fig. 1 is a cylinder drive circuit diagram showing the first embodiment of the present invention, Fig. 2 is a characteristic diagram of the regeneration control valve, Fig. 3 is a diagram explaining the principle of the regeneration control valve, and Fig. 4 is a diagram of the second embodiment. Cylinder Drive Circuit Diagram FIG. 5 is a cylinder drive circuit diagram of a conventional example. 1... Hydraulic cylinder, 2a, 2b... Oil chamber, 3
... Hydraulic pump, 4 ... Direction switching valve, 5 ... Pilot pressure supply switching valve, 8, 8' ... Pilot pressure switching valve, 9 ... Regeneration control valve, 10 ... Tank,
l ₁ , l ₂ ... pipes, l ₃ to _{l 9} ... pilot pipes.

Claims (1)

[Scope of utility model registration request] A variable displacement hydraulic pump and a pilot pressure supply switching system that includes a directional switching valve interposed in both pipelines between a tank and both oil chambers of a hydraulic cylinder, and controls the capacity of the hydraulic pump and the switching of the directional switching valve. In a hydraulic cylinder drive circuit equipped with a valve, a valve is connected between the two pipe lines between the directional control valve and the hydraulic cylinder, and when the hydraulic cylinder is operated to the same load side due to a weight load, the hydraulic cylinder is switched to the weight load side of the hydraulic cylinder. A regeneration control valve is provided that returns from the oil chamber to the negative pressure side oil chamber and enters oil regeneration operation to ensure the supply of pressure oil to the negative pressure side oil chamber and control the cylinder operating speed, and the pilot pressure of the pilot pressure supply switching valve is A pilot pressure switching valve is provided at the outlet and is switched by the weight load pressure of the weight load side oil chamber to set the directional switching valve to neutral, operate the hydraulic pump at a small capacity, and switch the regeneration control valve to the regeneration operating side. A return oil regeneration circuit for a hydraulic cylinder.