JP4298674B2 - Hydraulic drive unit for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic cylinder that drives a front work machine, a hydraulic pump that generates pressure oil for driving the hydraulic cylinder, and a direction for switching the flow and flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder. Construction machine comprising a control valve, a variable relief valve for limiting the maximum pressure of the pressure oil supplied to the discharge side pipe of the hydraulic pump, and a relief pressure control means for controlling the relief pressure of the variable relief valve The present invention relates to a hydraulic drive device.

  Construction machines such as hydraulic excavators are a front work machine that performs various operations such as a vehicle body that runs on crawlers and wheels by operating operation means such as operation levers and pedals, and excavation work that is installed on this vehicle body by operating operation means. And is configured. For example, the front working machine includes an arm, a boom, and a bucket as working tools that are driven to rotate in the vertical direction. A hydraulic drive device for a construction machine, which is a device for hydraulically driving such a front work machine, has a hydraulic cylinder as a hydraulic actuator for driving the respective working tools as described above, and drives these hydraulic cylinders. And a directional control valve for controlling the movement of the hydraulic cylinder by switching the flow and flow rate of the pressure oil supplied from the hydraulic pump to each hydraulic cylinder.

  In such a hydraulic drive device for construction machinery, a relief valve is provided in the discharge side pipe line of the hydraulic pump to limit the maximum pressure of the pressure oil in the discharge side pipe line. Designed to withstand. The maximum pressure of the pressure oil in the discharge side pipe stipulates the driving force of the hydraulic cylinder that drives the front work machine, and if the relief pressure of the relief valve is set so as to increase the maximum pressure, the amount of hydraulic cylinder The driving force can be increased. However, when the relief pressure of the relief valve is set, the relief pressure is set to a large value from the viewpoint of economically manufacturing a hydraulic drive device or preventing a decrease in durability of the hydraulic drive device. This is not done, and the force effective for excavation work (hereinafter referred to as “excavation force”) transmitted from the hydraulic cylinder to the work implement of the front working machine (hereinafter referred to as “working force”). .), The relief pressure, that is, the maximum pressure of the pressure oil in the discharge side pipe line, is set so that a working force suitable for performing frequent work can be obtained from the hydraulic cylinder.

  If the maximum pressure of pressure oil in the discharge side pipe is set in this way, most of the work can be performed without any problem. However, if the maximum pressure of the pressure oil is set in this way, the hydraulic cylinder is driven. Depending on the content of the work, there may be cases where power is insufficient. For example, in a hydraulic excavator, this is the case when deep excavation (excavation for digging deep grooves) or lower slope excavation (excavation for excavating from the upper side of the slope to the lower side) is performed. When performing these excavations, the hydraulic cylinder for the arm is contracted and the arm is extended forward to the limit, but the front working machine of the hydraulic excavator contracts as the hydraulic cylinder shrinks and its stroke approaches the minimum value. The force transmitted as excavation force from the hydraulic cylinder to the arm decreases.

  In the excavator, a similar problem occurs when holding excavation for excavating the side wall on the vehicle body side such as a groove (excavation performed by pulling the bucket toward the vehicle body side while operating the standing arm). . That is, when carrying out this excavation, the arm hydraulic cylinder is extended so that its stroke approaches the maximum value, but as the hydraulic cylinder expands and its stroke approaches the maximum value, the hydraulic cylinder moves from the hydraulic cylinder to the arm. The force transmitted as digging force is reduced. As described above, when the stroke of the hydraulic cylinder for the arm is near the minimum value and near the maximum value, the excavation force of the front work machine decreases, and particularly when the stroke is near the minimum value, the excavation force decreases. Remarkably, excavation work cannot be performed smoothly. As described above, as an example, the problem related to the hydraulic cylinder for the arm of the hydraulic excavator has been described. However, the same problem may occur in the hydraulic cylinder for the bucket and the hydraulic cylinder of the construction machine other than the hydraulic excavator depending on the work contents. .

  In response to these problems, the hydraulic drive device for construction machinery includes a variable relief valve that limits the maximum pressure of the pressure oil supplied to the discharge side pipe of the hydraulic pump, and a relief pressure of the variable relief valve. Relief pressure control means to be controlled, and by operating the relief pressure operation means as necessary, the relief pressure of the variable relief valve can be raised from the reference set value through the relief pressure control means There is. By adopting such means, it is possible to increase the hydraulic pressure of the discharge side pipe line of the hydraulic pump and increase the driving force of the hydraulic cylinder as necessary, thereby enhancing the working force of the front working machine. Since these means function temporarily only when necessary, even if the relief pressure is raised above the reference set value, the hydraulic drive device is not substantially damaged. A hydraulic drive device for this type of construction machine is disclosed in Patent Document 1, for example.

The hydraulic drive device for a construction machine described in Patent Document 1 is switched by an electric signal from a relief pressure control means in association with the variable relief valve and the relief pressure control means, and is changed from a pilot hydraulic power source to a variable relief. An electromagnetic valve that adjusts the hydraulic pilot pressure sent to the valve to increase or decrease the relief pressure, and outputs an instruction signal for switching the solenoid valve to the relief pressure control means by an on / off operation to release the relief of the variable relief valve And a pressure increase instruction switch as a relief pressure operating means for increasing or decreasing the pressure. This pressure increase instruction switch is turned off in the standard state, and is manually turned on only when necessary. Since this conventional hydraulic drive device for construction machinery is equipped with such means, a large working force is applied near the minimum or maximum value of the hydraulic cylinder stroke when performing the above-mentioned deep excavation or holding excavation. When it becomes necessary to apply to the machine, the operator can increase the driving force of the hydraulic cylinder and strengthen the work force of the front work machine by turning on the pressure increase instruction switch. .
Japanese Patent Laid-Open No. 2001-330001 (page 2-3, FIG. 7-8)

  However, in the conventional hydraulic drive device for a construction machine described in Patent Document 1, such work that requires applying a large working force to the front work machine near the minimum value or the maximum value of the hydraulic cylinder stroke is appropriately performed. In this case, since it is necessary for the operator to determine whether or not it is necessary to increase the driving force of the hydraulic cylinder and to turn on the pressure increase instruction switch, the operation of the front work machine is extremely complicated. In addition, when it is no longer necessary to increase the driving force of the hydraulic cylinder after the pressure increase instruction switch is turned on, the hydraulic drive device is not burdened with an unnecessary burden so as not to reduce the service life. It is necessary to quickly turn off the pressure indicating switch. Again, at this time, it is necessary for the operator to operate the pressure increase instruction switch, and the operation of the front work machine is troublesome.

  The present invention was created in order to solve such problems of the prior art, and the technical problem is that even if the operator does not operate the relief pressure operating means, the driving force of the hydraulic cylinder is near the minimum value of the stroke. Another object of the present invention is to provide a hydraulic drive device for a construction machine that can be strengthened in the vicinity of the maximum value to enhance the working force applied to the front working machine.

  In order to achieve such a technical problem, the present invention provides a “hydraulic cylinder for driving a front work machine, a hydraulic pump for generating pressure oil for driving the hydraulic cylinder, and a hydraulic pump supplied from the hydraulic pump to the hydraulic cylinder. A directional control valve that switches the flow and flow rate of pressure oil, a variable relief valve that releases the pressure oil supplied to the discharge side pipe of the hydraulic pump and limits the maximum pressure of the pressure oil, and a variable relief valve In the case of configuring a “hydraulic drive device for a construction machine provided with a relief pressure control means for controlling the relief pressure”, the configuration is as follows.

  Stroke detection means for detecting the stroke of the hydraulic cylinder, and stroke storage means for storing a setting range relating to the stroke of the hydraulic cylinder set on at least one of the minimum value side and the maximum value side of the stroke of the hydraulic cylinder. The variable relief valve is provided so as to increase the relief pressure when the detected value of the stroke of the hydraulic cylinder in the stroke detection means is within a setting range related to the stroke of the hydraulic cylinder stored in the stroke storage means. It was comprised so that it might control by a control means.

  The hydraulic drive device of a construction machine has a work force applied from the hydraulic cylinder to the front work machine when performing a work requiring a large work force such as a large excavation force near the minimum value or near the maximum value of the stroke of the hydraulic cylinder. Tends to run out. Since the hydraulic drive device for a construction machine according to the present invention is configured as described above, the stroke of the hydraulic cylinder falls within a set range set on at least one of the minimum value side and the maximum value side of the stroke of the hydraulic cylinder. When there is, the relief pressure control means controls to increase the relief pressure through the variable relief valve. As a result, when the stroke of the hydraulic cylinder is within the set range in the process of driving the hydraulic cylinder, the operator does not operate the relief pressure operating means as in the prior art, but the driving force of the hydraulic cylinder As a result, the working force applied to the front working machine from the hydraulic cylinder also increases.

  Therefore, for the front work machine of the construction machine, the setting range related to the stroke of the hydraulic cylinder to be stored in the stroke storage means while looking at the content of work that requires a large working force near the minimum value or the maximum value of the hydraulic cylinder stroke Can be carried out smoothly near the minimum value or the maximum value of the stroke of the hydraulic cylinder, where the working force applied from the hydraulic cylinder tends to be insufficient. Thus, the driving force of the hydraulic cylinder can be increased by the relief pressure control means. Thus, in the hydraulic drive device of the present construction machine, the driving force of the hydraulic cylinder is increased near the minimum value or the maximum value of the stroke and applied to the front work machine without the operator operating the relief pressure operating means. Work power can be strengthened.

  As will be apparent from the following description, the present invention provides a hydraulic cylinder that drives the front working machine, a hydraulic pump that generates pressure oil for driving the hydraulic cylinder, and a hydraulic pump that is supplied from the hydraulic pump to the hydraulic cylinder. A directional control valve that switches the flow and flow rate of pressure oil, a variable relief valve that releases the pressure oil supplied to the discharge side pipe of the hydraulic pump and limits the maximum pressure of the pressure oil, and this variable relief valve In the case of constructing a “hydraulic drive device for a construction machine having a relief pressure control means for controlling the relief pressure of the construction machine”, it is constructed as described in the above section [Means for Solving the Problems]. According to the hydraulic drive device for a construction machine of the present invention, the driving force of the hydraulic cylinder is increased near the minimum value of the stroke or near the maximum value without the operator operating the relief pressure operating means. It is possible to strengthen the work force to be applied to the door working machine. As a result, when performing work that requires a large work force near the minimum value or the maximum value of the hydraulic cylinder stroke, the operator's work load can be reduced more than before, and the drive force of the hydraulic cylinder can be appropriately increased. Can be performed reliably.

  Hereinafter, how the present invention is actually embodied will be described with reference to FIGS. 1 to 5 to clarify a desirable mode for carrying out the present invention.

  FIG. 1 is a perspective view showing an example of a construction machine for installing a hydraulic drive device for a construction machine according to the present invention, and FIG. 2 is a hydraulic circuit diagram relating to the hydraulic drive device for a construction machine that is embodied by the present invention. FIG. 3 is a conceptual diagram showing the relationship between the stroke of the arm cylinder in the construction machine of FIG. 1 and the excavation force applied from this arm cylinder, and FIG. 4 is the configuration of the control device in the hydraulic drive device of the construction machine of FIG. FIG. 5 is a conceptual diagram showing the relationship between the stroke of the bucket cylinder in the construction machine of FIG. 1 and the excavating force applied from this bucket cylinder. Here, the following description will be given by taking as an example the case where the construction machine is a self-propelled hydraulic excavator.

  The hydraulic drive device for a construction machine according to the present invention includes a hydraulic cylinder that drives a front work machine and a hydraulic pump that generates pressure oil for driving the hydraulic cylinder, as in the conventional hydraulic drive device for a construction machine. And a directional control valve for switching the flow and flow rate of the pressure oil supplied from the hydraulic pump to the hydraulic cylinder, and the pressure oil supplied to the discharge side pipe of the hydraulic pump is released to limit the maximum pressure of the pressure oil. A variable relief valve and a relief pressure control means for controlling the relief pressure of the variable relief valve are provided.

  First, an outline of a self-propelled hydraulic excavator, which is an example of a construction machine for installing a hydraulic drive device for a construction machine according to the present invention, will be described with reference to FIG.

  Reference numeral 1 denotes a lower traveling body that can serve as a base for installing the upper revolving body 2 and can travel on the work site. Reference numeral 2 denotes a revolving frame that is turnably mounted on the lower traveling body 1 and an upper portion of the revolving frame. 2a is a cab installed on the revolving frame for operating a hydraulic excavator, and 3 is a rear end perpendicular to the front of the upper revolving body 2 The boom 4 is pivotally mounted in the direction of rotation, 4 is an arm whose rear end is pivotally mounted to the front end of the boom 3 in the vertical direction, and 5 is at the front end of the arm 4. The bucket is pivotally mounted so as to be rotatable in a vertical direction and detachable. Reference symbol a is a pin for pivotally attaching the rear end portion of the arm 4 to the front end portion of the boom 3, and reference symbol b is the rear end portion of the arm 4 at the front end portion of the arm cylinder 7. Pins for attaching to the shaft, which are particularly provided for convenience of later explanation.

  Self-propelled hydraulic excavators can be broadly classified as a front work machine, hydraulic drive / control equipment such as a hydraulic pump 10 and a control device 50, which will be described later, and a cab 2a for installing the front work machine. The vehicle body includes a lower traveling body 1 and an upper swing body 2. The front work machine is configured by providing a boom 3, an arm 4 and a bucket 5 as work tools, which will be described later for driving these work tools and applying work force such as excavation force to each work tool. A boom cylinder 6, an arm cylinder 7 and a bucket cylinder 8 are attached. This front work machine mainly performs excavation work and loading work of earth and sand with the bucket 5, but instead of the bucket 5, a work tool such as an earth drill or a crusher as an attachment is attached to a hydraulic cylinder such as the bucket cylinder 6. Accordingly, various other operations can be performed.

  6 is a boom cylinder that is driven to extend and retract to rotate (tilt) the boom 3 in the vertical direction, 7 is an arm cylinder that is driven to expand and contract and rotate (swing) the arm 4, and 8 is expanded and contracted. The bucket cylinder 9a that drives the bucket 5 to rotate is pivotally attached at one end to the front end of the bucket cylinder 8 and is pivotally attached to the arm 4 at the other end. One end of the drive link 9b is pivotally attached to the front end of the bucket cylinder 8 so as to be rotatable coaxially with the first drive link 9a, and the other end is pivotally attached to the bucket 5. Reference numeral 41 designates an arm cylinder stroke sensor for detecting the stroke of the arm cylinder 7.

  When grounding with the front work machine, the bucket 5 is cut into the ground by excavating mainly the arm cylinder 7 and the bucket cylinder 8 in the extending direction. In this case, for the arm cylinder 7, the line segment connecting the pin a as the pivoting portion of the arm 4 to the boom 3 and the pin b as the pivoting portion of the arm 4 to the arm cylinder 7, and the thrust of the arm cylinder 7 When the angle α formed with the direction (the axis of the arm cylinder 7) is a right angle, the excavation force of the arm 4 is maximized. As for the bucket cylinder 8, the excavating force of the bucket 5 becomes maximum when the angle β formed by the thrust direction of the bucket cylinder 8 (the axis of the bucket cylinder 8) and the first drive link 9a is a right angle. On the other hand, as will be described later, when the stroke of the arm cylinder 7 is minimum, the excavation force of the arm 4 is minimum, and when the stroke of the bucket cylinder 8 is maximum, the excavation force of the bucket 5 is minimum.

  An example of a hydraulic circuit relating to a hydraulic drive device for a construction machine according to the present invention will be described with reference to FIG. This hydraulic circuit is for explaining an example in which the working force of the arm 4 is increased by increasing the driving force of the arm cylinder 7 near the minimum value or the maximum value of the stroke. The illustration of the directional control valve and the operating device for operating the bucket is omitted.

  Reference numeral 10 denotes a variable displacement hydraulic pump that generates pressure oil for driving the various hydraulic actuators described above of the hydraulic excavator such as the boom cylinder 6 and the arm cylinder 7, and 11 denotes a discharge side pipe 14 of the hydraulic pump 10. A main relief valve as a variable relief valve that releases the supplied pressure oil and limits the maximum pressure of the pressure oil, 12 is a pilot pump as a pilot hydraulic source for generating hydraulic pilot pressure, and 13 is a control device 50 is a proportional solenoid valve that is switched to the upper position or the lower position by 50 to increase or decrease the relief pressure of the main relief valve 11, and 14 is a main line for supplying pressure oil on the discharge side of the hydraulic pump 10 to various hydraulic actuators The discharge side pipe line of the hydraulic pump 10, 15 is a pipe for sending out the hydraulic pilot pressure generated by the pilot pump 12. Tsu DOO pumping Detchi, 16 is a pilot pressure introduction passage for guiding the hydraulic pilot pressure fed to the pilot pumping Detchi 15 to the signal receiving portion of the main relief valve 11.

  The leaf pressure of the main relief valve 11 defines the driving force of the hydraulic cylinder that drives the front working machine, and is set so that a working force suitable for frequent work can be obtained from the driving force of the hydraulic cylinder. Has been. In normal times, the leaf pressure of the main relief valve 11 is set to the reference set value set in this way, and work is performed on the front working machine. The proportional solenoid valve 13 is switched to either the upper position or the lower position by an electric signal from the control device 50, and is normally switched to the lower position shown in FIG. At this time, the proportional solenoid valve 13 blocks communication of the pilot pressure delivery path 15 to the pilot pressure introduction path 16, and the hydraulic pilot pressure of the pilot pump 12 is not sent to the signal receiving portion of the main relief valve 11. First, the leaf pressure of the main relief valve 11 is set to a reference set value.

  Further, as will be described later, the proportional solenoid valve 13 is switched to the upper position by an electric signal from the control device 50 when the stroke of the arm cylinder 7 is in the vicinity of the minimum value or in the set range near the maximum value. At this time, the proportional solenoid valve 13 communicates the pilot pressure delivery path 15 to the pilot pressure introduction path 16 and guides the hydraulic pilot pressure of the pilot pump 12 to the pilot pressure introduction path 16. In that case, the opening amount of the proportional solenoid valve 13 is adjusted according to the output value of the electrical signal from the control device 50, and thereby the output value of the hydraulic pilot pressure guided from the proportional solenoid valve 13 to the pilot pressure introduction path 16. Is adjusted. As a result, the main relief valve 11 is controlled by the output value of the hydraulic pilot pressure adjusted by the proportional solenoid valve 13, and the leaf pressure is controlled. Although not shown, the hydraulic pilot pressure of the pilot pump 12 is also guided to pilot valves 30a and 31a of the operation devices 30 and 31 described later in order to generate a pilot signal for switching the direction control valves 20 and 21. It is like that.

  A boom direction control valve 20 controls the movement of the cylinder 6 by switching the flow and flow rate of pressure oil supplied from the hydraulic pump 10 to the boom cylinder 6, and 21 is supplied from the hydraulic pump 10 to the arm cylinder 7. A direction control valve for an arm that controls the movement of the cylinder 7 by switching the flow and flow rate of pressure oil, and 30 outputs a pilot signal for switching the direction control valve 20 for the boom by operating the operation lever 30b. An operating device for operating the boom, 31 is an operating device for operating the arm that outputs a pilot signal for switching the directional control valve 21 for the arm by operating the operating lever 31b, and 40 is a discharge pressure P of the hydraulic pump 10. A pump discharge pressure sensor for detection, 41 is the arm cylinder stroke sensor described above, and 50 is a relief of the main relief valve 11. A control device 60, which will be described in detail later, as a relief pressure control means for controlling the pressure, outputs an instruction signal for switching the proportional electromagnetic valve 13 to the control device 50 by an operator's operation, thereby relief of the main relief valve 11 It is a pressure instruction switch as a relief pressure operating means for increasing or decreasing the pressure.

  When the boom direction control valve 20 and the arm direction control valve 21 are switched to the left position by the operation of the operation lever, the pressure oil of the hydraulic pump 10 is supplied to the rods of the boom cylinder 6 and the arm cylinder 7, respectively. The pressure oil on each bottom side is discharged to the hydraulic oil tank and the cylinders 6 and 7 can be reduced. Further, when switched to the right position, the pressure oil of the hydraulic pump 10 is supplied to the bottom sides of the boom cylinder 6 and the arm cylinder 7, respectively, and the pressure oil on the rod side is discharged to the hydraulic oil tank, Thereby, both cylinders 6 and 7 can be extended. In that case, the opening amount is adjusted in accordance with the operation amount of the operation lever, whereby the speed at which both the cylinders 6 and 7 expand and contract can be controlled.

  The operating device 31 for arm operation includes a pilot valve 31a (a pair of pressure reducing valves) that outputs a hydraulic pilot pressure, and an operating lever 31b that is tilted and outputs a hydraulic pilot pressure corresponding to the tilting amount from the pilot valve 31a. Configured. The operating device 30 for operation is also provided with a similar pilot valve 30a and a similar operation lever 30b. The discharge pressure P and the arm cylinder stroke of the hydraulic pump 10 detected by the pump discharge pressure sensor 40 and the arm cylinder stroke sensor 41 are input to the control device 50 and used for controlling the main relief valve 11 described later. . The hydraulic drive device of the present construction machine has the greatest feature in the control device 50, and the pressure indicating switch 60 is not indispensable for the present invention. Therefore, the pressure indicating switch 60 can be omitted as appropriate.

  Therefore, the mechanism of the control device 50 will be described with reference to FIGS. 3 and 4.

  First, the basic mechanism of the control device 50 will be described. FIG. 3 schematically shows the relationship between the arm cylinder stroke and the excavating force applied from the arm cylinder 7 to the arm 4. According to FIG. 3, the excavation force of this arm 4 is maximum (excavation force 1) when the arm cylinder stroke is about 60% of its maximum value (100%), and the arm cylinder stroke is 0% (minimum value). At the time of digging force becomes 0.5 (digging force 0.5), and is greatly reduced to about half of the digging force is maximum. Further, when the arm cylinder stroke is 100% (maximum value), the excavation force of the arm 4 is considerably less than 80% of the maximum excavation force.

  When performing the deep excavation or the lower slope excavation as described above, the arm cylinder 7 is contracted and the arm 4 is extended forward to near the limit as shown by the dotted line in FIG. 1. At this time, as shown in FIG. As described above, the excavation force of the arm 4 is greatly reduced, so that the excavation work cannot be performed smoothly and the work efficiency is reduced. Further, when carrying out the excavation as described above, as shown by a solid line in FIG. 1, the arm cylinder 7 is extended so that the arm cylinder stroke is brought close to the maximum value while the arm cylinder 7 is extended and the arm 4 is erected. Excavation is performed while extending the bucket 5 so as to draw the bucket 5 toward the vehicle body. At this time, the excavation force of the arm 4 is considerably reduced as shown in FIG.

  In the hydraulic drive device of the present construction machine, when the relief pressure of the main relief valve 11 is increased to the minimum value side and the maximum value side of the arm cylinder stroke where the excavation force of the arm 4 tends to be insufficient in order to solve such problems. A setting range related to the arm cylinder stroke is set and stored in the stroke storage means of the control device 50. In the control device 50, when the detected value of the arm cylinder stroke by the arm cylinder stroke sensor 41 is within the set range related to the arm cylinder stroke stored in the stroke storage means, the command voltage is set to the proportional solenoid valve 13. The main relief valve 11 is controlled so that a predetermined value of hydraulic pilot pressure is sent to the main relief valve 11 to increase the relief pressure by a set value by switching to the upper position. .

  In the hydraulic drive device of the present construction machine, when the arm cylinder stroke is within the set range as described above, the relief pressure of the main relief valve 11 is increased by the control device 50, so that the arm cylinder 7 is expanded and contracted. In the process, when the arm cylinder stroke is within the set range, the driving force of the arm cylinder 7 is increased, and accordingly, the excavating force applied from the arm cylinder 7 to the arm 4 is also increased. Therefore, the driving force of the arm cylinder 7 is increased near the minimum value and the maximum value of the stroke even if the operator does not operate the relief pressure operating means such as the pressure increase instruction switch as in the prior art. Thus, the excavation force of the arm 4 can be strengthened.

  Next, a specific mechanism of the control device 50 will be described with reference to FIG. In the figure, reference numeral 101 denotes a first stroke storage means for storing an arm cylinder stroke setting range when the relief pressure of the main relief valve 11 is increased and an amount of increase of the relief pressure that is increased within this setting range. A calculating means 102 is a pump discharge pressure storage means for storing a set range of the discharge pressure P of the hydraulic pump 10 when the relief pressure of the main relief valve 11 is increased and an increase amount of the relief pressure that is increased in this set range. A second computing means is provided, 103 is a third computing means provided with a command voltage storage means for storing the command voltage output to the proportional solenoid valve 13 in correspondence with the amount of increase in the relief pressure, and 104 is a first computing means. The first pressure increase amount selecting means 105 for selecting the lower pressure increase amount among the pressure increase amounts output from the calculation means 101 and the second calculation means 102 is the second The second pressure increase amount selection means 106 selects the lower pressure increase amount among the pressure increase amounts output from the calculating means 102 and the pressure designation switch 60, and the first pressure increase amount selection means 104 and the first pressure increase amount selection means 104. This is a third pressure increase amount selection means for selecting a higher pressure increase amount among the pressure increase amounts selected by the second pressure increase amount selection means 105.

  The detection results of the arm cylinder stroke sensor 41 and the pump discharge pressure sensor 40 are input to the first calculation means 101 and the second calculation means 102, respectively. In the stroke storage means in the first calculation means 101 and the pump discharge pressure storage means in the second calculation means 102, the main relief valve 11 set respectively corresponding to the arm cylinder stroke and the discharge pressure P of the hydraulic pump 10 is stored. The increase amount of the relief pressure is stored as a table, and the command voltage output corresponding to the increase amount of the relief pressure of the main relief valve 11 is stored as a table in the command voltage storage means in the third calculation means 103. ing.

  As described above, when the arm cylinder stroke is 0%, the excavation force of the arm 4 is minimized and greatly reduced. Therefore, in the table of the stroke storage means in the first calculation means 101, the arm cylinder stroke is 0. %, The relief pressure of the main relief valve 11 is increased to the maximum pressure increase amount (100% pressure increase amount). On the other hand, when the arm cylinder stroke is 100%, the excavation force of the arm 4 is considerably reduced, but not as much as 0%. Therefore, the relief pressure of the main relief valve 11 is only about half of the maximum pressure increase amount. The pressure is not increased.

  In the table of the pump discharge pressure storage means in the second calculation means 102, unless the discharge pressure P of the hydraulic pump 10 reaches the set value P1, it is not allowed to increase the relief pressure of the main relief valve 11, and the discharge pressure is not allowed. When P reaches the set value P1, the relief pressure is rapidly increased to allow the maximum pressure increase amount to be increased. For example, the set value P1 is set to a value that is about 10% to 20% lower than the normal relief pressure of the main relief valve 11, and when the discharge pressure P of the hydraulic pump 10 does not reach the set value P1, the arm It is assumed that the driving force of the cylinder 7 has a margin. Therefore, the set value P1 is set to a value that serves as a scale for determining whether or not the driving force of the arm cylinder 7 has a margin.

  In the table of the command voltage storage means in the third calculation means 103, a voltage value that is directly proportional to the finally determined relief pressure increase amount of the main relief valve 11 is output to the proportional solenoid valve 13 as a command voltage. ing. The control device 50 is configured to include the above-described calculation means 101, 102, and 103 and pressure increase amount selection means 104, 105, and 106, respectively. In FIG. 4, the pressure indicating switch 60 sets the amount of increase in the relief pressure of the main relief valve 11 to 0% when turned off, and sets the amount of pressure increase to 100% when turned on. It is configured.

  The operation of the control device 50 will be described. When excavation work is started with the front work machine, the detection value related to the arm cylinder stroke is input from the arm cylinder stroke sensor 41 to the first calculation means 101, and the detection related to the discharge pressure P of the hydraulic pump 10 is detected from the pump discharge pressure sensor 40. A value is input to the second calculation means 102. Then, the first calculation means 101 determines whether or not the detection value of the arm cylinder stroke sensor 41 is within the arm cylinder stroke setting range stored in the stroke storage means. As a result, when it is determined that the detected value is within the set range, the value of the pressure increase amount related to the relief pressure of the main relief valve 11 is output according to the table of the stroke storage means, and when it is determined that the detected value is not within the set range, The relief pressure is not increased and a value of 0% is output.

  On the other hand, the second calculation means 102 determines whether or not the detected value of the pump discharge pressure sensor 40 has reached the set value P1 related to the discharge pressure P of the hydraulic pump 10 stored in the pump discharge pressure storage means. . As a result, when it is determined that the detected value has reached the set value P1, the value of the pressure increase amount related to the relief pressure of the main relief valve 11 is output according to the table of the pump discharge pressure storage means, and has reached the set value P1. When it is determined that there is no pressure increase value 0% is output. In the first pressure increase amount selecting means 104, the lower value Pn1 is selected from the values of the pressure increase amounts respectively output from the first calculating means 101 and the second calculating means 102 in this way.

  Such processing performed by the first pressure increase amount selection means 104 is performed by the main relief valve 11 on the minimum value side or the maximum value side of the arm cylinder stroke even though the discharge pressure P of the hydraulic pump 10 has not reached the set value P1. It is prohibited to increase the relief pressure. By performing such a process, the relief pressure is uniformly increased on the minimum value side or the maximum value side of the arm cylinder stroke even though the excavation force that the arm cylinder 7 can apply to the arm 4 is not insufficient. Useless control can be eliminated.

  The second pressure increase amount selection means 105 selects the lower value Pn2 from the values of the pressure increase amounts output from the second calculation means 102 and the pressure designation switch 60, respectively. Therefore, even if the pressure specifying switch 60 is turned on to increase the relief pressure of the main relief valve 11 to 100%, the value of the pressure increase output from the second calculating means 102 is 100%. Unless otherwise, the ON operation of the pressure designation switch 60 does not function. By performing such processing, it is possible to eliminate wasteful control for increasing the relief pressure even though the driving force of the arm cylinder 7 is not insufficient, as in the processing in the first pressure increase amount selecting means 104. . Note that the pressure designation switch 60 is provided as a secondary, and does not need to be operated unless the operator needs it.

  As described above, from the first pressure increase amount selection means 104 and the second pressure increase amount selection means 105, the value of the pressure increase amount actually required for the pressure increase amount related to the relief pressure of the main relief valve 11 is used. Only Pn1 and Pn2 are selected and outputted, and the third pressure increase amount selecting means 106 selects the higher value Px of the pressure increase amount values Pn1 and Pn2 thus output. The pressure increase value Px is input to the third calculation means 103, and the command voltage corresponding to the pressure increase value Px is output from the third calculation means 103 to the proportional solenoid valve 13. Control is performed so that the relief pressure of the main relief valve 11 is increased by a necessary amount. Further, when there is no need to increase the relief pressure, the relief pressure is automatically returned to the normal relief pressure.

  As described above, the example of increasing the driving force of the arm cylinder 7 near the minimum value or the maximum value of the stroke has been described for the hydraulic drive device for a construction machine according to the present invention. An embodiment for enhancing near the maximum value of is outlined.

  FIG. 5 schematically shows the relationship between the bucket cylinder stroke and the excavating force applied from the bucket cylinder 8 to the bucket 5. According to FIG. 5, the excavation force of the bucket 5 is maximum (excavation force 1) when the bucket cylinder stroke is about 30% of the maximum value (100%), and when the bucket cylinder stroke is the maximum value. It becomes the minimum (excavation force of 0.3 or more), and is significantly reduced to about 1/3 of the maximum excavation force. Further, when the bucket cylinder stroke is 0% (minimum value), the excavation force of the bucket 5 is less than 90% at the maximum, and does not decrease so much. Therefore, for the bucket cylinder 8, the excavating force of the bucket 5 is insufficient on the maximum value side of the bucket cylinder stroke depending on the contents of work such as deep excavation.

  In order to solve such a problem for the bucket cylinder 8, a setting range related to the bucket cylinder stroke when the relief pressure of the main relief valve 11 is increased to the maximum value side of the bucket cylinder stroke where the excavation force of the bucket 5 is insufficient. Is stored in the stroke storage means of the control device 50. In the control device 50, when the bucket cylinder stroke is within the setting range related to the bucket cylinder stroke stored in the stroke storage means, the control device 50 controls the main relief valve 11 to increase the relief pressure by a set value. It may be configured to be controlled by. Further, when the hydraulic drive device for such a construction machine is embodied, it may be embodied according to the example of FIG. 4 already described.

  The technical contents described above can be applied to a hydraulic drive device for a construction machine other than a hydraulic excavator as long as it is a construction machine having a hydraulic cylinder for driving a front working machine. The driving force of the hydraulic cylinder can be increased without requiring an operation. That is, with respect to the front working machine of the construction machine, the setting range related to the hydraulic cylinder stroke to be stored in the stroke storage means is set in the vicinity of the minimum value or the maximum value of the hydraulic cylinder stroke while looking at the content of the work that requires a large excavation force. If considering and setting in advance to suit the content of the work, the hydraulic cylinder drive force should be adjusted so that the work can be smoothly performed near the minimum or maximum value of the hydraulic cylinder stroke, where excavation force tends to be insufficient. The control device 50 as a relief pressure control means can automatically increase the pressure appropriately.

  As described above, in the hydraulic drive device for a construction machine according to the present invention, the driving force of the hydraulic cylinder is increased in the vicinity of the minimum value or the maximum value of the stroke without the operator operating the relief pressure operating means. It is possible to reinforce the work force applied to the. As a result, when performing work that requires a large work force near the minimum value or the maximum value of the hydraulic cylinder stroke, the operator's work load can be reduced more than before, and the drive force of the hydraulic cylinder can be appropriately increased. Can be performed reliably.

It is a perspective view which shows an example of the construction machine for installing the hydraulic drive apparatus of the construction machine of this invention. 1 is a hydraulic circuit diagram relating to a hydraulic drive device for a construction machine that is embodied by embodying the present invention. It is a conceptual diagram which shows the relationship between the stroke of the arm cylinder in the construction machine of FIG. 1, and the digging force provided from this arm cylinder. It is a block diagram which shows the component of the control apparatus in the hydraulic drive device of the construction machine of FIG. It is a conceptual diagram which shows the relationship between the stroke of the bucket cylinder in the construction machine of FIG. 1, and the excavation force provided from this bucket cylinder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower traveling body 2 Upper turning body 3 Boom 4 Arm 5 Bucket 6 Boom cylinder 7 Arm cylinder 8 Bucket cylinder 9a 1st drive link 9b 2nd drive link 10 Hydraulic pump 11 Main relief valve 12 Pilot pump 13 Proportional electromagnetic Valve 14 Discharge side pipe 20 Direction control valve for boom 21 Direction control valve for arm 30 Operation device for boom operation 31 Operation device for arm operation 40 Pump discharge pressure sensor 41 Arm cylinder stroke sensor 50 Control device 101 First Calculation means 102 second calculation means 103 third calculation means 104 first pressure increase amount selection means 105 second pressure increase amount selection means 106 third pressure increase amount selection means

Claims (1)

  A hydraulic cylinder that drives the front work machine, a hydraulic pump that generates pressure oil for driving the hydraulic cylinder, a direction control valve that switches a flow and flow rate of the pressure oil supplied from the hydraulic pump to the hydraulic cylinder, A variable relief valve that releases the pressure oil supplied to the discharge side pipe of the hydraulic pump and restricts the maximum pressure of the pressure oil, and a relief pressure control means that controls the relief pressure of the variable relief valve In a hydraulic drive device for a construction machine, stroke detection means for detecting the stroke of the hydraulic cylinder, and a setting range relating to the stroke of the hydraulic cylinder set on at least one of the minimum value side and the maximum value side of the hydraulic cylinder stroke And a stroke storage means for storing the hydraulic cylinder stroke detection value at the stroke detection means. A variable relief valve is configured to be controlled by a relief pressure control means so as to increase a relief pressure when it is within a set range related to a stroke of a hydraulic cylinder stored in a stage. Hydraulic drive device.

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