JPH03115625A - Hydraulic circuit of hydraulic shovel - Google Patents

Abstract

PURPOSE:To sufficiently supply pressure oil to increase speed of a hydraulic shovel by a method wherein at the time of combined control of a swing motor and a boom cylinder maximum load pressure is functioned to a pressure controlling means of the swing motor and the maximum load pressure is not functioned to a pressure controlling means of the boom cylinder. CONSTITUTION:In combined control of a swing motor 3 and a boom cylinder 13, load pressure of the swing motor 3 is to immediately reach a relief pressure and the load pressure is made present on a maximum load pressure detecting duct 10. On the other hand, maximum load pressure of the maximum load pressure detecting duct 10 is not functioned to a pressure compensating valve 15. A large amount of discharged oil from a hydraulic pump 1 is supplied to the boom cylinder 13 with a lighter load than the swing motor 3 via the pressure compensation valve 15 and a flow rate control valve 14. As a result the discharge pressure of the hydraulic pump 1 is a driving pressure to the boom cylinder 13 while the swing motor 13 is driven by this pressure. Thus the swing motor 3 is gradually accelerated to increase its swing speed thereby reducing its load pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic circuit for a hydraulic excavator equipped with a swing motor, a boom cylinder, and other hydraulic actuators.

[Conventional technology]

A hydraulic excavator has a lower running body for moving it,
an upper rotating body rotatably mounted on the lower traveling body;
It consists of a front mechanism consisting of a boom, arm, and packet. Since various equipment such as a driver's cab, a prime mover, a hydraulic pump, etc. are mounted on the upper rotating body, and a front mechanism is attached thereto, the upper rotating body itself constitutes a load with extremely large inertia.

Incidentally, in recent years, in hydraulic excavators, the driving speed of the hydraulic actuator can be controlled by maintaining a constant pressure difference (differential pressure) between the upstream side and the downstream side of the flow control valve that controls the flow rate of pressure oil supplied to the hydraulic actuator. An excellent speed control system called a load sensing system has been proposed. This load sensing system will be explained with reference to FIG.

FIG. 4 is a hydraulic circuit diagram showing a part of the hydraulic circuit of the hydraulic excavator. In the figure, 1 is a variable displacement hydraulic pump (hereinafter referred to as a hydraulic pump), 1a is a variable displacement mechanism for the hydraulic pump 1 (hereinafter represented by a swash plate), and 2 is a regulator that drives and controls the swash plate 1a. . Regulator 2 is
It is comprised of a hydraulic cylinder 2a that drives the swash plate la, a horsepower control mechanism 2b that is comprised of a discharge capacity switching valve, and a control valve 2c that is driven by the differential pressure. 3 is a swing motor that drives the upper revolving structure, and 4 is a flow control valve that controls the drive of the swing motor 3. 4p+4pt is a pilot line for the flow rate control valve 4, which introduces a pilot pressure corresponding to the amount of operation when a swing lever (not shown) is operated. 5 is a pressure compensation valve interposed between the hydraulic pump 1- and the flow rate control valve 4. 6a and 6b are relief valves provided in the main circuit of the swing motor 3, and define the maximum load pressure of the swing motor 3. Reference numeral 7 designates a detection pipe for guiding the load pressure of the swing motor 3, and reference numeral 8 designates a shuttle valve that selects the higher of the load pressure of the detection pipe and the load pressure of a boom, which will be described later. 9 is a tank. IO is a maximum load pressure detection line that leads to the maximum load pressure selected by the shuttle valve 8.

The maximum load pressure of the maximum load pressure detection pipe 10 and the upstream pressure of the flow control valve 4 are introduced into one side of the pressure compensation valve 5,
Further, the discharge pressure of the hydraulic pump 1 and the load pressure of the swing motor 3 are introduced to the other side of the pressure compensating valve 5. Thereby, the pressure compensating valve 5 has a function of appropriately distributing pressure oil to each hydraulic actuator during a combined operation of a plurality of hydraulic actuators.

12 is a boom of a hydraulic excavator, and 13 is a boom cylinder that drives the boom 12. 14 is the boom cylinder 13
Flow control valve for controlling 14p.

14p2 is its pilot pipe, 15 is a pressure compensation valve, 1
6a, 16b are relief valves, 17 is a boom cylinder 13
This is a detection pipe line that guides the load pressure of the shuttle valve 8 to the shuttle valve 8, and these lines correspond to each element of the hydraulic circuit of the swing motor 3.

Next, the operation of the hydraulic circuit constituting the load sensing system will be explained. When rotating the upper rotating structure of the hydraulic excavator, the operator operates a swing lever (not shown). In response to this, oil pressure is generated in one of the pilot pipes of the flow control valve 4, for example, the pilot pipe 4p+, and the flow control valve 4 is switched to the left position with a throttle corresponding to the operation amount of the swing lever. Therefore, the pressure oil of the hydraulic pump 1 is supplied to the swing motor 3 from the left main pipe of the swing motor 3 through the pressure compensating valve 5 and the throttle of the flow rate control valve 4. As a result, the swing motor 3 begins to swing in one direction. In this case, since the inertia of the upper rotating body is extremely large, most of the oil to be supplied to the rotating motor 3 is discharged to the tank 9 via the relief valve 6a, and the load pressure appearing in the detection pipe 7 is The set pressure is 6a. This load pressure is introduced to one side of the control valve 2C of the regulator 2 via the maximum load pressure detection conduit 10 to increase the amount of tilting of the swash plate 1a. However, since the load pressure of the swing motor 3 is high, the horsepower control mechanism 2b of the regulator 2 suppresses an increase in the amount of tilting of the swash plate 1a, and therefore the discharge flow rate of the hydraulic pump 1 is also suppressed.

As the swing motor 3 is gradually accelerated in this way, the amount of oil relieved from the relief valve 6a also gradually decreases, and the swing motor 3 is gradually accelerated according to the opening area of the flow control valve 4. After reaching around the normal rotational speed, the load pressure rapidly decreases to a value considerably lower than the set pressure of the relief valve 6a. Then, the regulator 2 controls the discharge flow rate of the hydraulic pump 1 according to such a low value of the load pressure.

Now, in the above state, if the load pressure increases due to an external load being applied or the like, the pressure on the downstream side of the flow control valve 4 increases, and therefore the differential pressure across the flow control valve 4 becomes smaller. At the same time, the increased load pressure is applied to one end of the pressure compensating valve 5, so the throttle amount is reduced to increase the upstream pressure of the flow rate control valve 4 to return the differential pressure to the specified value. Further, the increased load pressure is introduced into the regulator 2, which drives the regulator 2 to increase the discharge flow rate of the hydraulic pump 1. Therefore, the upstream pressure of the flow control valve 4 increases, and the differential pressure returns to the default value. That is, even if the load pressure increases due to some reason such as an external load, the differential pressure of the flow control valve 4 is maintained at the specified value, and the swing motor 3 has no control over the swing lever even though the load pressure increases. A flow rate corresponding to the manipulated variable is supplied. When the load pressure decreases, the operation is the opposite of the above operation, and a flow rate corresponding to the operating amount of the swing lever is similarly supplied.

After all, when driving the swing motor 3, a load sensing system that keeps the differential pressure across the flow rate control valve 4 constant acts in a normal state in which the relief valve 6a does not operate, and excellent speed control can be performed.

The driving operation of the boom 12 also follows this.

Furthermore, the operation in the case of a combined operation in which the swing motor 3 and the boom cylinder 13 are driven simultaneously will be explained. Such complex operations are the most frequently performed operations on hydraulic excavators. In other words, the excavated earth and sand are loaded into packets, and then the boom is raised to lift the packets, while at the same time the upper revolving body is rotated to load the earth and sand into waiting trucks. When the swing lever and the boom lever are operated at the same time, the flow control valves 4 and 14 open with throttles corresponding to their operating amounts, and pressure oil is supplied to the swing motor 3 and the boom cylinder 13, and the flow control valves 14 and A predetermined differential pressure is generated between both sides of the flow control valve 4 after the swing motor 3 reaches around the normal rotation speed. These differential pressures are kept constant as in the operation of the swing motor 3 described above.

FIG. 5 is a hydraulic circuit diagram showing a part of another hydraulic circuit of a hydraulic excavator employing a load sensing system. In the figure, parts that are the same as or equivalent to those shown in FIG. 4 are given the same reference numerals and their explanations will be omitted.

Note that illustration of the relief valves 6a, 6b, 16a, and 16b is omitted. 5' and 15' are pressure controllers composed of well-known poppet valves, and the pressure compensating valve 5 shown in FIG.
, 15. 3/, BL is a check valve, 10' is a common detection pipe, and 11 is a throttle. The maximum load pressure among the load pressures of the swing motor 3 and the boom cylinder 13 is selected by each check valve 8', common detection line 10' and throttle 11, and the load pressure is selected by the common detection line 10'.
appears in Note that each load pressure and the pressure of the common detection pipe 10' are introduced to the pressure controllers 5' and 15'. Therefore, when the load pressure is lower than the maximum load pressure, the throttle amount of the pressure controllers 5', 15' increases, similar to the pressure compensating valve 5.15 shown in FIG. The operation of this hydraulic circuit is also substantially the same as the operation of the hydraulic circuit shown in FIG. 4, so a description thereof will be omitted.

[Problem to be solved by the invention]

In a hydraulic circuit using the load sensing system described above, when the swing motor 3, which drives a load with large inertia, and the boom cylinder 13, which drives the boom 12, which has a warmer load with smaller inertia, are operated in combination, the following occurs. A similar problem occurred.

This will be explained with reference to the pressure/flow characteristic diagram shown in FIG. In FIG. 6, the horizontal axis represents the discharge pressure of the hydraulic pump l, and the vertical axis represents the discharge flow rate. When driving the upper rotating body,
Since the inertia at startup is extremely large, the pressure on the downstream side of the flow control valve 4 (the pressure of the swing motor 3) is reduced by the relief valves 6a, 6.
The pressure increases to the relief pressure b, and the discharge flow rate is suppressed by the horsepower control mechanism. This state is shown in Figure 6 as pressure PI.
+Flow it Q I is shown. On the other hand, the inertia of the boom 12 is extremely low compared to the inertia of the upper rotating structure.
Therefore, the load pressure on the boom cylinder 13 is also low (approximately 173 times the load pressure on the swing motor 3).

By the way, as mentioned above, when the swing motor 3 is started, the discharge flow rate of the hydraulic pump 1 is suppressed to a lower amount than normal due to the action of the horsepower control mechanism 2b, and this small discharge flow rate is suppressed by the swing motor 3 and the boom cylinder. 13, and most of the flow rate distributed to the swing motor 3 is relieved via the relief valve 6a. Therefore, the driving speed of the boom cylinder 13 at startup becomes slow, and the energy loss of the prime mover due to relief becomes large. As the acceleration of the swing motor 3 progresses, the speed of the swing motor 3 rapidly increases, its load pressure decreases, and the load pressure of the boom cylinder 13 is detected in the maximum load pressure detection line 10 (common detection line 10'). appears. In this state, load sensing system control is executed, the hydraulic pump 1 supplies pressure oil according to the load pressure of the boom cylinder 13, and the swing motor 3 and boom cylinder 13 are controlled by the opening area of the flow control valve 4°14. is driven at a speed corresponding to

For the above reasons, generally the time it takes for the boom to rise to the required height is longer than the time it takes for the revolving superstructure to rotate the required angle. Therefore, for example, as mentioned above, in the work of loading excavated earth and sand onto a truck, when the upper revolving body rotates and the packet reaches the truck position, the rising speed of the boom 10 is slow, so that the packet reaches the earth and sand discharge height. In extreme cases, there is a risk of collision with the bed of a truck. For this reason, it is often necessary to temporarily stop swinging before the truck position, raise the boom 10 further, and then swing again when the boom 10 has risen sufficiently to position the packet at a predetermined position. However, this has caused problems in that it significantly impedes work efficiency and increases operator fatigue.

In addition, in order to avoid the above-mentioned swing stop, a method is adopted in which the operator adjusts the operating amount of the swing lever, but in the load sensing system, even if the opening area of the flow control valve 4 is reduced by the swing lever, the boom cylinder The supply of pressure oil to 13 does not increase, and not only the efficiency decreases, but also
Operator fatigue due to adjusting the pivot lever cannot be avoided.

Furthermore, the drive of the swing motor 3 is performed by the relief valves 6a and 5b.
Since the drive is performed while relieving pressure oil from the hydraulic pump 1, a large energy loss occurs, and there is also the problem that the load on the prime mover (not shown) that drives the hydraulic pump 1 becomes heavy.

The purpose of the present invention is to solve the problems in the above-mentioned prior art,
During combined operation of the swing motor and boom cylinder in a load sensing system, it is possible to supply sufficient pressure oil to the boom cylinder even during startup to increase its speed, thereby ensuring proper coordination between swing and boom raising operations. It is an object of the present invention to provide a hydraulic circuit for a hydraulic excavator that can provide a high level of performance and further reduce energy loss and load on the prime mover.

[Means to solve the problem]

To achieve the above object, the present invention provides at least two hydraulic actuators, a swing motor and a boom cylinder, a pressure oil supply source for supplying pressure oil to these hydraulic actuators, and a pressure oil supply source for supplying pressure oil to each of the hydraulic actuators. A flow control valve to be controlled, a pressure control means for defining a differential pressure between an upstream side and a downstream side of each of these flow control valves, and a selection means for selecting a maximum load pressure among the load pressures of each of the hydraulic actuators. In a hydraulic circuit of a hydraulic excavator, the hydraulic circuit of a hydraulic excavator is configured to introduce the maximum load pressure of each of the hydraulic actuators into the pressure oil supply source and control the pressure oil supply source so that the differential pressure becomes constant, the swing motor and the boom. During combined operation of the cylinder, the maximum load pressure is applied to the pressure control means of the swing motor, and the maximum load pressure is not applied to the pressure control means of the boom cylinder. .

[Effect]

During combined operation of the swing motor and boom cylinder, the maximum load pressure, which is the load pressure of the swing motor, does not act on the pressure control means of the boom cylinder, so even if the load pressure of the swing motor becomes high at startup, the pressure of the boom cylinder cannot be controlled. The restriction of the means does not increase, the pressure oil to the boom cylinder increases and therefore the drive speed of the boom cylinder also increases. As a result, the discharge pressure of the pressure oil from the pressure oil supply source becomes approximately the load pressure of the boom cylinder, and the swing motor is accelerated by this load pressure. As a result, the activation speed of the boom cylinder during start-up is high and the drive speed of the swing motor is low, so that proper coordination of swing and boom raising movements is achieved. Further, by accelerating the swing motor by the load pressure of the boom cylinder, relief from the relief valve is prevented.

〔Example〕

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a partial circuit diagram of a hydraulic circuit of a hydraulic excavator according to an embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. The configuration of this embodiment is different from the configuration of the hydraulic circuit shown in FIG. hand,
The only difference in the former is that the maximum load pressure is not supplied to the one surface of the pressure compensating valve 15, and the other configurations are the same.

Next, the operation of this embodiment will be explained. In the combined operation of the swing motor 3 and the boom cylinder 13, when the swing motor 3 is started, the load pressure of the swing motor 3 immediately tries to reach the relief pressure.
The load pressure appears in the maximum load pressure detection line 10. on the other hand,
Since the maximum load pressure of the maximum load pressure detection line 10 does not act on the pressure compensation valve 15, the pressure compensation valve I5 is not throttled by the load pressure of the swing motor 3. Therefore, the oil discharged from the hydraulic pump 1 is transferred to the pressure compensation valve 15 and the flow rate control valve 14.
A large amount of the energy is supplied from the swing motor 3 to the boom cylinder 13, which has a lighter load. As a result, hydraulic pump 1
The discharge pressure becomes the driving pressure of the boom cylinder 13, and the swing motor 3 is also driven by this pressure. Therefore, the acceleration force of the swing motor 3 is smaller compared to a conventional hydraulic circuit, and the swing speed at startup is also lower, while a larger amount of pressure oil is supplied to the boom cylinder 13 compared to a conventional hydraulic circuit. As a result, the drive speed at startup increases. After the swing motor 3 is started, it is gradually accelerated and the swing speed increases, and its load pressure decreases, and after a certain point, the load pressure of the boom cylinder 13 appears in the maximum load pressure detection line 10. Load sensing control based on this load pressure will be executed.

FIG. 2 is a characteristic diagram of the amount of rise of the boom. In the figure, the horizontal axis represents the turning angle of the upper revolving structure, and the vertical axis represents the amount of rise of the boom. A shows a characteristic curve in the conventional hydraulic circuit, and B shows a characteristic curve in the hydraulic circuit of this embodiment.

As is clear from the figure, the boom according to the present embodiment can immediately raise a larger amount of boom than the conventional one after startup.

As a result, for example, when a hydraulic excavator performs the work of dumping earth onto a truck from the excavation position at a turning angle θ, the boom rises at the height of the boom at the angle θ in the conventional excavator, whereas the hydraulic excavator in this embodiment A higher height ht can be obtained.

In this way, in this embodiment, the maximum load pressure is not applied to the pressure compensation valve of the boom cylinder, so in the combined operation of the swing motor and the boom cylinder, more pressure is applied to the boom cylinder from the time of activation. Pressurized oil can be supplied, and thus the rotation and boom raising movements can be properly matched. Furthermore, since there is no pressure oil relief from the relief valve, energy loss can be prevented and the load on the prime mover can be reduced.

FIG. 3 is a circuit diagram showing a part of the hydraulic circuit of a hydraulic excavator according to another embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 5 are given the same reference numerals, and explanations thereof will be omitted. The configuration of this embodiment is different from the configuration of the hydraulic circuit shown in FIG. On the other hand, in the former case, the only difference is that the maximum load pressure is not supplied to the one surface of the pressure controller 15', and the other structures are the same.

In this embodiment, as in the previous embodiment, when the swing motor 3 and the boom cylinder 13 are activated in a combined operation, the swing motor 3 that appears in the common detection line 10' is connected to the pressure controller 15'.
The load pressure (maximum load pressure) does not work, and the pressure control device 1
5' is not constricted by this load pressure. Therefore, a large amount of pressure oil is supplied to the boom cylinder 13. The subsequent operations are similar to those of the previous embodiment. Further, the effects of this embodiment are the same as those of the previous embodiment.

〔Effect of the invention〕

As described above, in the present invention, since the maximum load pressure is not applied to the pressure control means of the boom cylinder,
In the combined operation of the swing motor and boom cylinder, it is possible to increase the driving speed of the boom cylinder by supplying a large amount of pressure oil to the boom cylinder from the time of startup, which in turn reduces the amount of swing of the hydraulic excavator and the amount of rise of the boom. Appropriate matching between the two can be obtained. Further, since the swing motor 3 is not accelerated by the relief pressure when it is started, pressure oil is not relieved from the relief valve, and energy loss can be prevented and the load on the prime mover can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a part of the hydraulic circuit of a hydraulic excavator according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of the lift amount of the boom, and FIG.
The figure is a partial circuit diagram of a hydraulic circuit of a hydraulic excavator according to another embodiment of the present invention, FIGS. 4 and 5 are partial circuit diagrams of a hydraulic circuit of a conventional hydraulic excavator, and FIG. It is a pressure/flow characteristic diagram. 1...Hydraulic pump, 2...Regulator, 3...Swivel motor, 4, 14...
Flow rate control valve, 5.15...Pressure compensation valve, 5',
15'...Pressure controller, 13...Boom cylinder Fig. 2'7']

Claims (5)

[Claims] (1) At least two of the swing motor and boom cylinder
a hydraulic actuator, a pressure oil supply source that supplies pressure oil to these hydraulic actuators, a flow control valve that controls the supply of pressure oil to each of the hydraulic actuators, and a link between the upstream and downstream sides of each of these flow control valves. A pressure control means for regulating a differential pressure, and a selection means for selecting a maximum load pressure among the load pressures of each of the hydraulic actuators, and introducing the maximum load pressure of each of the hydraulic actuators into the pressure oil supply source. In a hydraulic circuit of a hydraulic excavator that controls the pressure oil supply source so that the differential pressure is constant, when the swing motor and the boom cylinder are operated in combination, the pressure control means of the swing motor has the maximum load pressure. A hydraulic circuit for a hydraulic excavator, characterized in that the pressure control means of the boom cylinder is configured such that the maximum load pressure does not act on the pressure control means of the boom cylinder. (2) In claim (1), the pressure control means of the swing motor is provided upstream of the flow control valve of the swing motor, and the pressure control means controls the upstream pressure of the flow control valve, the maximum load pressure, and the load. A hydraulic circuit for a hydraulic excavator, characterized in that the hydraulic circuit is a pressure compensating valve controlled by the pressure and the discharge pressure of the pressure oil supply source. (3) In claim (1), the pressure control means of the boom cylinder is provided upstream of the flow control valve of the boom cylinder, and the pressure control means controls the upstream pressure of the flow control valve, the load pressure, and the pressure oil. A hydraulic circuit for a hydraulic excavator characterized by a pressure compensation valve controlled by the discharge pressure of a supply source. (4) In claim (1), the pressure control means of the swing motor is provided on the downstream side of the flow control valve of the swing motor, and the pressure control means of the swing motor is provided on one of two opposing surfaces of the flow control valve of the swing motor. A hydraulic circuit for a hydraulic excavator, characterized in that the output side pressure is a pressure controller into which the maximum load pressure is introduced and which controls the downstream pressure of the flow control valve of the swing motor. (5) In claim (1), the pressure control means of the boom cylinder is provided on the downstream side of the flow control valve of the boom cylinder, and the pressure control means on the output side of the flow control valve is provided on one of two opposing surfaces. is introduced into the hydraulic excavator, and the other is configured such that no hydraulic pressure is introduced, and the hydraulic circuit is a pressure controller that controls the downstream pressure of the flow control valve of the boom cylinder.