JPS6334304A - Hydraulic circuit for hydraulic shovel - Google Patents

Abstract

PURPOSE:To prevent the remarkable reduction in operating speed of an actuator, by providing a restriction for decreasing an opening according to a selected position, in an upstream selector valve connected to a first pump. CONSTITUTION:A pair of selector valves 7 and 8 are connected to a first pump 1. The upstream selector valve 7 is provided with restrictions 4a and 4b for communicating a supply passage 16 of the upstream selector valve 7 with a supply passage 17 of the downstream selector valve 8 at a neutral position 7a of the upstream selector valve 7, while decreasing an opening according to a selected position. In a simultaneous operation wherein the upstream selector valve 7 is maintained in the neutral position, and a load of the downstream selector valve 8 is in a loaded condition, a pressure oil may be supplied to the downstream selector valve 8 not through the restrictions 4a and 4b. Accordingly, the operating speed of an actuator to be controlled by the downstream selector valve may be prevented from being remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic circuit for civil engineering construction machines such as hydraulic excavators.

[Prior Art] Fig. 3 is a diagram showing a hydraulic circuit of a conventional hydraulic excavator. is the boom cylinder, 5.6.37 and 8 are the first pump l
The switching valves 5.6 and 37 are connected in parallel to control the bias motor, the speed increase of the boom cylinder, the swing motor and the arm cylinder, respectively. 16.17 is a supply passage for the switching valves 37 and 8, and the switching valve 8 is connected in tandem with the switching valve, and
They are connected in parallel via an aperture 4. 9 to 12 are connected to the second pump 2, and the other side travel motor,
The switching valves 9 to 11 are connected in parallel, and the switching valve r12 is connected in tandem with the switching valves. In addition, the arm switching valve 8 and the arm speed increasing switching valve 12 and the boom switching valve 10 and the boom speed increasing switching valve 6 can be operated in conjunction with each other.Next, in the hydraulic circuit of a conventional hydraulic excavator, the arm switching valve 8 , swing switching valve 3
The effect when 7 is operated singly or in combination will be explained.

When the arm switching valve 8 is operated independently to the 8a side, most of the pressure oil of the pump 1 flows through the center bypass path, and the remainder passes through the parallel passage 18 and the throttle 4, joins the supply path 17, passes through the switching valve 8, and is transferred to the arm cylinder. It is supplied to the head end side of No. 14 to extend the arm cylinder and cloud the arm. The pressure oil discharged from the rod end side of the arm cylinder returns to the tank 3 via the arm switching valve 8. When the operating field (not shown) is further operated, the arm speed increase switching valve 12 is switched to the position 12a, and the pressure oil in the ribbon pump 2 is switched to the position 12a. is the arm speed increase switching valve 12
It joins the pressure oil of the pump L and is supplied to the head end side of the arm cylinder 14, so the cylinder expands at high speed, and the pressure oil on the rod end side flows into the arm switching valve 8 and the arm speed increasing switching valve 12. Reflux to tank 3 via dispersion.

When the arm switching valve 8 is switched to the 8b side and the arm speed increasing switching valve 12 is switched to the 12b side, the positions 8b and 12b are the same as above except that the supply and discharge passages to the cylinder connection port are opposite to those of 8a and 12a, respectively. Because there is arm cylinder 14
is contracted, and the contraction speed is increased by operating the speed increase switching valve 12.

When the arm switching valve 8 is switched to the 8a side and the swing switching valve 37 is simultaneously switched to any switching position, for example, 37a, the swing switching valve 37 blocks the center bypass passage, so only the pressure oil that has passed through the throttle 4 flows into the arm cylinder. Supplied. Since the load pressure in the extension direction of the arm cylinder is low and the starting pressure of the swing motor is high, most of the pressure oil is initially supplied to the arm cylinder, and at that time, the loss pressure generated in the throttle 4 and the load pressure of the arm cylinder are The flow rate to both is distributed so that the sum is balanced with the starting pressure of the swing motor. As the swing motor accelerates after startup, the load pressure decreases, so the flow rate is distributed less to the arm cylinder and more to the swing motor so that both pressures are balanced by reducing the loss pressure of the throttle. . By manipulating the operating field to a greater extent to the arm cylinder, the arm speed increase switching valve 12 can also supply the discharge oil of the second pump 2, allowing for balanced swing and arm operation.

In addition, the arm switching valve 8 is moved to the 8b side, and the swing switching valve 37 is moved to the 37 side.
When simultaneously switched to the a side, the arm cylinder 14 contracts and the swing motor starts rotating.

The load pressure when the arm cylinder is contracted is higher than when it is extended, so in this state, the flow distribution to the arm cylinder is less than when it is extended.However, as above, by operating the arm speed increase switching valve, the discharge oil of the second pump is increased. Since it can be used, there will be no noticeable problems with the balance of rotation and simultaneous arm operation.

[Problems to be solved by the invention] However, at the same time, the boom switching valve 10 is switched to 10a, the boom speed increasing switching valve 6 is switched to 6a, and the boom cylinder is extended, and at the same time, the arm switching valve 8 is switched to 8b. When the arm cylinder 14 is contracted, all the flow distributed to the arm cylinder passes through the throttle 4. Since the load pressure of the arm cylinder is high when the cylinder is contracted, the loss pressure of the throttle 4, which is added to the load pressure of the arm cylinder, is kept low in order to balance out the load pressure of the boom cylinder.
The flow rate that can pass through at that loss pressure is significantly lower, so that the boom cylinder is supplied with the entire output of the second pump 2 and most of the output oil of the first pump l, whereas the arm is supplied with the first oil. Only a small amount of the oil discharged from the pump 1 is supplied. As described above, the conventional technology has the problem of not being able to balance simultaneous operations of boom raising and arm dumping.

[Means for Solving the Problems] The present invention solves the above-mentioned problems, and the details thereof will be explained below using FIG. 1.

The first and second pumps 1 and 2, a plurality of actuators 13 to 15, etc. driven by pressure oil from these hydraulic pumps, and the direction and flow of the pressure oil supplied from the hydraulic pumps to the actuators are controlled. A circuit is configured with a plurality of directional control valves 5 to 8 and 9 to 12 to be controlled,
A pair of switching valves 7 and 8 connected to the first pump l
Of these, the supply passage 16 of the upstream switching valve 7 and the downstream switching valve 8
The upstream switching valve 7 is provided with throttles 4a and 4b that communicate with the supply passage 17 at the neutral position 7C of the upstream switching valve 7 and reduce the openings that communicate with each other in accordance with the switching positions 7a and 7b.

[Operation] When the arm switching valve 8 is switched to the switching position i8a or 8b, the pressure oil of the pump 1 is supplied to the supply passage of the arm switching valve 8 through the supply passage 16 of the swing switching valve 7 on the upstream side, and the arm switching valve 8 is switched to the switching position i8a or 8b. The cylinder 14 is expanded and contracted. When the arm operation stick is further operated, the arm speed increase switching valve 12 changes to 12a or 12b.
The pressure oil of the second pump 2 joins the pressure oil of the first pump 1, causing the arm cylinder 14 to expand and contract at high speed.

When the arm switching valve 8 is switched to switching position 8a or 8b and the swing switching valve 7 is switched to 7a or 7b, all of the pressure oil of the first pump l is supplied to the supply passage 17 of the arm switching valve 8. It passes through the throttle 4a or 4b, and the sum of the loss pressure generated at that time and the load pressure of the arm cylinder reaches the starting pressure of the swing motor 13, and simultaneous, balanced operation of the swing and arm is possible in the same way as in the circuit according to the prior art. It is.

The boom switching valve lO is set to 10a, and the boom speed increasing switching valve 6 is set to 6. When the arm switching valve 8 is switched to 8b to contract the arm cylinder 14 while switching to 8b to extend the boom cylinder, the swing switching valve 7 is in the neutral position, so the pressure oil discharged by the first pump l is It is supplied to the arm cylinder 14 through a path that does not involve the throttle of the swing switching valve 7. Since the load pressure of the arm cylinder during retraction is somewhat lower than the load pressure of the boom cylinder extension, the arm cylinder receives most of the pressure oil discharged by the first pump, and the boom cylinder receives the remainder of the discharge oil of the first pump. It is driven by the sum of the oil discharged from the pump and the second pump, and the simultaneous operation of arm dumping and boom raising can be controlled in a well-balanced manner.

[Embodiment] A composite control valve in which a plurality of switching valves constituting the main part of the circuit of the present invention are integrated will be described below as illustrated in FIG.

Spools 45 to 48 communicate the center bypass path 21 at the neutral position with a valve body 42 provided in the center with the center bypass path 21 that communicates from the pump connection port 49 to the tank connection port 43 and block it at the left/right reswitching position. are slidably inserted to form a composite control valve 41 in which the switching valves 5 to 8 are integrally integrated. Supply passages 16 are arranged symmetrically on both sides of the center bypass passage 21 of the valve body 42 and extend from the pump connection port to the switching valve 7. Supply passage 1 for switching valve 8
7 are also provided on both sides of the center bypass passage 21 and communicate with each other by passages provided three-dimensionally with respect to the plane of the drawing, and the supply passage on the right side of the figure is extended to be adjacent to the supply passage 16 of the switching valve 7. The supply passage 16 and the supply passage 17 communicate with each other through a narrow diameter section provided on the spool 47 of the swing switching valve 7 when in neutral mode, and when switching to the right or left, throttles provided near both ends of the narrow diameter section remain open. to shut it off. In FIG. 2, the apertures 44a and 44b have a shape in which the outer circumferential surfaces on both sides of the narrow diameter portion are partially shaved off on a plane descending to the spool axis, but the apertures 44a and 44b are not limited to this type. You can choose a flat surface or a conical surface depending on the application.Furthermore, cylinder ports 23 to 30 are provided on both sides of the supply passage to connect the actuators, and cylinder ports 23 to 30 are provided on both sides to connect to the respective hydraulic motors and cylinders. A return passage 20 is provided and connected to the tank 3.

When the spool 48 of the arm switching valve 8 is switched to the right, the first
Since the center bypass passage, which was a path for the pressurized oil discharged from the pump 1 to flow back to the tank 3, is blocked, the horizontal hole 31 and the axial hole of the sleeve 48 exposed to the supply passages 16 and 17 and the supply passage 17 are cut off. 35, the horizontal hole 32, and the cylinder port 29 to the arm cylinder 14, and the pressure oil on the other side of the cylinder is supplied to the cylinder port 30 and the spool 48.
It is discharged to the tank through the horizontal hole 33, the axial hole 36, the horizontal hole 34, and the return passage 20. As a result, the arm cylinder contracts. When the arm switching valve is switched to the left in the opposite direction, the arm cylinder 14 is extended because the switching valve 8 is symmetrically constructed. The boom speed increasing switching valve 6 is configured to function in the same manner as described above, but as shown in FIG. It is generally used by restricting the cylinder head side from its position so that it can only move towards the side connected to the pump l. Similarly to the arm switching valve, the swing switching valve 7 also supplies and discharges pressure oil to the cylinder port in response to switching the spool 47 to the right or left to turn the swing motor to the right or left, and also to the downstream switching valve 8. The amount of oil supplied is limited by the throttle 44a or 44b.

The above is a concrete configuration of the circuit diagram shown in FIG. 1, and the operation of the individual and combined operation of each switching valve is the same as the explanation regarding FIG. 1 above.

[Effects of the Invention] As described above, the present invention provides the supply passage 16 of the upstream switching valve 7 and the supply passage of the downstream switching valve 8 of the pair of switching valves 7 and 8 connected to the first pump l. 17 is communicated with the upstream switching valve 7 at the neutral position 7C, and since the ha side switching valve 7 is provided with a throttle that reduces the communication opening according to the switching position B, the upstream switching valve 7 is kept in the neutral position. During simultaneous operation when the load on the downstream switching valve is close to the upstream switching valve on the inner ring, pressure oil can be supplied to the downstream switching valve without going through a restriction, so the actuator controlled by the downstream switching valve can be This has the effect of preventing a significant drop in operating speed, and by supplying the pressure oil of the second pump to the actuator controlled by the switching valve further upstream, well-balanced simultaneous operation can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a hydraulic circuit according to the present invention, FIG. 2 is a sectional view showing an embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional hydraulic circuit. l...first pump, 2...second pump, 4a. 4b... Throttle, 5-12... Directional switching valve, 13-1
5... Actuator, 16.17... Supply passage.

Claims (1)

[Claims] (1) A plurality of hydraulic pumps, a plurality of actuators driven by pressure oil from these hydraulic pumps, and a plurality of directional switching valves that control the direction and flow rate of the pressure oil supplied from the hydraulic pumps to the actuators. In a hydraulic circuit of a civil engineering/construction machine equipped with A hydraulic circuit for a hydraulic excavator in which an upstream switching valve is provided with a throttle that communicates at the neutral position and reduces the opening that communicates depending on the switching position.