JP4969541B2 - Hydraulic control device for work machine - Google Patents

Description

  The present invention relates to a hydraulic control device for a work machine such as a hydraulic excavator.

  Conventionally, a hydraulic control device HCo as shown in FIG. 7 is known. The hydraulic control device HCo includes first and second hydraulic pumps 5 and 6.

  On the first hydraulic pump 5 side, a bucket cylinder switching valve 11 that controls the bucket cylinder 10 in the center bypass oil passage 52, a boom cylinder switching valve 21 that controls the boom cylinder 20, and an arm cylinder switching valve 31 that controls the arm cylinder 30 are provided. Connected to tandem. Each cylinder switching valve 11, 21, 31 is also connected to a parallel circuit 64.

  On the second hydraulic pump 6 side, the second boom cylinder switching valve 22 and the second arm cylinder switching valve 32 for controlling the arm cylinder 30 are connected to the center bypass oil passage 54 in tandem. Each cylinder switching valve 22, 32 is also connected to a parallel circuit 66.

  However, in this method, for example, when excavation work is performed, if the three operations of “bucket closing”, “arm pulling”, and “boom raising” are performed at the same time, the boom raising operation cannot be performed satisfactorily. There was a problem that. This defect will be briefly described with reference to FIG.

  When the above three operations are performed simultaneously, the “bucket closing” pilot pressure Pp1 of the bucket operating lever 13 acts on the pilot port 11P1 of the bucket cylinder switching valve 10. The pilot pressure Pp <b> 2 for “boom raising” of the boom operation lever 23 acts on the pilot ports 21 </ b> P <b> 1 and 22 </ b> P <b> 1 of the boom cylinder switching valves 21 and 22. The pilot pressure Pp3 for “arm pull” of the arm operation lever 33 acts on the pilot ports 31P1 and 32P1 of the arm cylinder switching valves 31 and 32. As a result, the bucket cylinder switching valve 10, the boom cylinder switching valves 21 and 22, and the arm cylinder switching valves 31 and 32 are all switched to their A positions.

  However, in this state, the arm is falling under its own weight, the bucket is falling under its own weight (or low load), and the boom is subjected to the load of the entire work machine, so the load pressure is highest. In this hydraulic control device HCo, a large amount of pressure oil from the second hydraulic pump 6 is supplied to the low load arm cylinder 34 via the parallel oil passage 66. Therefore, the pressure oil is hardly supplied from the second boom cylinder switching valve 22 side to the boom cylinder 20. On the other hand, the pressure oil on the first pump 5 side is also supplied in a large amount to the bucket cylinder 10 having a lower load than the boom cylinder 20 through the parallel oil passage 64. Therefore, in spite of performing the “boom raising” operation, the boom does not rise after all.

  Therefore, as a means for increasing the bucket load pressure to avoid this problem, the bucket spool opening characteristic of the bucket cylinder switching valve 11 (opening characteristic of the port 11P3) is changed to a characteristic as shown by a solid line in FIG. Even if the spool 14 of the bucket cylinder switching valve 11 is fully stroked to the A position, it is conceivable to set so that the opening of the port 11P3 remains deeply squeezed. However, if such a setting is always made, not only the excavation force is reduced when the bucket is operated alone, but also there is a risk of deteriorating heat balance and fuel consumption due to heat generation near the port 11P3.

  Patent Document 1 proposes an example of a technique for solving such a problem. In this technique, a variable throttle valve 56 (as shown by a broken line) that restricts the supply flow rate of the feeder oil passage 54 is interposed in the feeder oil passage 54 that branches from the parallel oil passage 64 to the bucket cylinder switching valve 11 in FIG. It is what I did. Thereby, only when the boom raising operation is detected, the supply flow rate of the feeder oil passage 54 can be narrowed down to increase the bucket load pressure.

Japanese Patent No. 2892939

  However, since the technique according to Patent Document 1 performs the operation of reducing the flow rate of the feeder oil passage 54 to the bucket cylinder switching valve 11 when the operation of “boom raising” is detected, for example, the boom Even when the bucket load pressure is higher than the load pressure, the feeder oil passage 54 remains in a throttled state as long as the boom raising operation is performed. For this reason, problems such as an inadvertent increase in circuit pressure, deterioration in heat balance characteristics, reduction in bucket working speed, or deterioration in fuel consumption due to an increase in engine output have been caused.

  The present invention has been made in order to solve such a conventional problem. In particular, the intended work can be reliably and quickly performed on the boom and the bucket, and the heat balance can be improved. The challenge is to improve fuel efficiency.

  The present invention provides at least a bucket cylinder and a boom cylinder for driving a bucket and a boom of a work machine, and each of the cylinders is controlled by a bucket cylinder switching valve and a boom cylinder switching valve. Bucket closing operation detecting means for detecting that the closing operation of the boom has been performed, boom raising operation detecting means for detecting that the boom raising operation has been performed, and bucket cylinder load for detecting the load pressure of the bucket cylinder Pressure detecting means, and flow rate adjusting means capable of adjusting the flow rate of return oil from the rod side of the bucket cylinder to the tank, the bucket closing operation and the boom raising operation being performed simultaneously, and the bucket When it is detected that the load pressure of the cylinder is below a predetermined value, the flow rate adjusting means , By constructing the rod side of the bucket cylinder to regulate the flow rate of oil returning to the tank is obtained by solving the above problems.

  In the present invention, when the bucket closing operation is performed simultaneously with the boom raising operation, special control is performed with respect to the bucket closing operation. That is, when the load pressure of the bucket cylinder at that time is detected and it is determined that the load pressure of the bucket cylinder is not more than a predetermined value, the flow rate of the return oil on the rod side of the bucket cylinder is regulated. For this reason, the load pressure of the bucket cylinder is increased, and the pump discharge oil can be prevented from concentrating and flowing into the bucket cylinder, and can be smoothly guided and supplied to the boom cylinder.

  Here, in the present invention, the flow rate restriction of the return oil from the bucket cylinder rod side to the tank is performed when the load pressure of the bucket cylinder is a predetermined value or less. In other words, when the load pressure exceeds a predetermined value, this flow rate regulation is not performed. Further, in the present invention, there is no restriction that particularly impedes the flow rate of the feeder oil passage of the bucket cylinder. As a result, the driving of the bucket is not adversely affected. Further, since the feeder oil passage is not restricted unnecessarily, the heat balance performance can be improved, and it is not necessary to maintain the engine output at a high level, so that the fuel efficiency is also improved.

  A preferred embodiment of the present invention includes, for example, a stroke restricting mechanism for restricting a stroke of the bucket cylinder switching valve toward a closing operation side of the spool as the flow rate adjusting means, and the closing operation of the bucket and the raising operation of the boom Are simultaneously performed, and when the load pressure of the bucket cylinder is detected to be equal to or less than a predetermined value, the stroke regulating mechanism causes the spool of the bucket cylinder switching valve to stroke closer to the bucket than the predetermined stroke position. Is configured to regulate.

  Thereby, the said subject can be solved by only a slight design change of the bucket cylinder switching valve. In addition, since a component with electrical wiring is not required and it can be realized only by control on the hydraulic circuit, the operation reliability is high.

  Further, a preferred embodiment of the present invention includes, for example, an electromagnetic proportional valve capable of applying an arbitrary pilot pressure to the pilot port on the open side of the bucket cylinder as the flow rate adjusting means, And when the load pressure of the bucket cylinder is detected to be equal to or lower than a predetermined value, the spool of the bucket cylinder switching valve is closed on the bucket closing side by the pilot pressure regulated by the electromagnetic proportional valve. It is configured to be maintained at a predetermined stroke position other than the stroke end.

  Thereby, the setting of the predetermined stroke position itself can be set more finely in consideration of not only the load pressure of the bucket cylinder but also other situations such as the load pressure of the boom cylinder if necessary. .

  In this way, particularly when the flow rate is adjusted by adjusting the spool stroke of the bucket cylinder switching valve, for example, the bucket cylinder when the bucket cylinder switching valve strokes from the closed side to the open side. The opening characteristic of the return port from the cylinder to the tank may be set such that the degree of enlargement is small from the bucket closing side to the predetermined stroke position, and the degree of enlargement is set larger on the opening side than the stroke position.

  As a result, when the load pressure of the bucket cylinder is less than or equal to a predetermined value, the discharged oil is well guided to the boom cylinder side, while for the original bucket driving operation where the load pressure of the bucket cylinder exceeds the predetermined value, this is performed more quickly. Can be made to do.

  Still another preferred embodiment of the present invention includes, for example, an electromagnetic proportional flow rate adjustment valve capable of adjusting the flow rate of return oil from the rod side of the bucket cylinder to the tank as the flow rate adjusting means, The boom raising operation is performed simultaneously, and the flow rate of return oil from the rod side of the bucket cylinder to the tank is regulated by the electromagnetic proportional flow rate adjustment valve depending on the load pressure of the bucket cylinder. That is.

  This configuration does not require any particular design changes for the bucket cylinder switching valve, and is optional in consideration of other conditions such as the load pressure of the boom cylinder as well as the load pressure of the bucket cylinder (if necessary). With this characteristic, only the flow rate of the return oil on the rod side of the bucket cylinder can be controlled very finely, and boom driving and bucket driving can be realized more satisfactorily.

  According to the present invention, it is possible to reliably and quickly perform the intended work particularly on the boom and the bucket, and it is possible to improve the heat balance and the fuel efficiency.

  Hereinafter, examples of embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 3 shows an outline of the main part of a hydraulic excavator (work machine) SC1 to which an example of the embodiment of the present invention is applied, and FIG. 2 shows the main part near the bucket cylinder switching valve of the hydraulic control device HC1. In order to facilitate understanding, parts having the same or similar functions as those of the hydraulic control apparatus HCo already described are denoted by the same reference numerals.

  As shown in FIG. 3, the excavator SC <b> 1 includes a boom 1, an arm 2, and a bucket 3. The boom 1 is driven by the boom cylinder 20, the arm 2 is driven by the arm cylinder 30, and the bucket 3 is driven by the bucket cylinder 10.

  As shown in FIG. 2, the hydraulic control device HC1 includes first and second hydraulic pumps 5 and 6. On the first hydraulic pump 5 side, a bucket cylinder switching valve 11 that controls the bucket cylinder 10 in the center bypass oil passage 52, a boom cylinder switching valve 21 that controls the boom cylinder 20, and an arm cylinder switching valve 31 that controls the arm cylinder 30 are provided. Connected to tandem. Each cylinder switching valve 11, 21, 31 is also connected to a parallel circuit 64.

  On the second hydraulic pump 6 side, the second boom cylinder switching valve 22 and the second arm cylinder switching valve 32 for controlling the arm cylinder 30 are connected to the center bypass oil passage 54 in tandem. Each cylinder switching valve 22, 32 is also connected to a parallel circuit 66.

  Throttle valves 56 and 58 are arranged on the most downstream side of the respective center bypass oil passages 52 and 54, and the negative control pressure generated thereby is applied to the pump regulators 60 and 62 to control the discharge flow rate of the hydraulic pumps 5 and 6. is doing. This control method is called a two-pump type negative control method (so-called negative control), and is widely used as a method that can satisfactorily realize various composite controls of the boom 1, arm 2, and bucket 3.

  In the following, each configuration will be described in detail, including a description of the action as appropriate for convenience.

  The bucket cylinder 10 is actuated and controlled by a bucket cylinder switching valve 11. The bucket cylinder switching valve 11 is a 6-port 3-position switching valve in this example. When the bucket operating lever 13 operated by the operator is closed, the bucket closing pilot pressure Pp1 from a well-known pilot pressure generating means (not shown) is connected to the pilot port 11P1. That is, in this embodiment, the pilot pressure Pp1 of the pilot port 11P1 also serves as a closing signal for the bucket closing operation detection means. When the bucket closing signal of the bucket operating lever 13 is applied to the pilot port 11P1, the bucket spool 14 of the bucket cylinder switching valve 11 is switched to the position A in FIG. As a result, the pressure oil from the first pump 5 is supplied to the bottom side 10 </ b> B of the bucket cylinder 10 via the parallel oil passage 64 and the feeder oil passage 54, and the return oil on the rod side 10 </ b> R is drained via the drain line 69. . Further, when the bucket opening pilot pressure Pp4 from the operation lever 13 is applied to the pilot port 11P2, the bucket spool 11A of the bucket cylinder switching valve 11 is switched to the position C in FIG. As a result, the pressure oil from the first pump 5 is supplied to the rod side 10 </ b> R of the bucket cylinder 10 via the parallel oil passage 64 and the feeder oil passage 54, and the bottom side 10 </ b> B is drained from the drain line 69.

  Here, the opening of the return port 11P3 from the rod side 10R of the bucket cylinder 10 to the tank T when the bucket spool 14 of the bucket cylinder switching valve 11 strokes from the bucket closing side to the opening side of the bucket cylinder switching valve 11. The characteristics are different from the conventional design. That is, as shown in FIG. 4, the opening characteristic of the return port 11P3 at this time is small from the bucket fully closed position to the vicinity of the “predetermined stroke position” Sp, but is smaller than the stroke position Sp. On the side, the degree of enlargement is set to be larger (in this example, as shown by a broken line, it expands rapidly). The bucket cylinder switching valve 11 is provided with a stroke regulating mechanism 74 that defines the predetermined stroke position Sp. The configuration of the stroke restriction mechanism 74 will be described in detail later.

  The boom cylinder 20 is actuated and controlled by a boom cylinder switching valve 21 and a second boom cylinder switching valve 22. The boom cylinder switching valve 21 is a 6-port 3-position switching valve in this example. When the boom operating lever 23 operated by the operator is brought into the boom raising state, the boom raising pilot pressure Pp2 from a well-known pilot pressure generating means (not shown) is connected to the pilot port 21P1. That is, in this embodiment, the pilot pressure Pp2 of the pilot port 21P1 also serves as the raising signal of the boom raising operation detecting means. When the pilot pressure Pp2 for raising the boom from the boom operation lever 23 is applied to the pilot port 21P1, the boom spool 24 of the boom cylinder switching valve 21 is switched to the position A in FIG. As a result, the pressure oil from the first pump 5 is supplied to the bottom side 20B of the boom cylinder 20 via the parallel oil passage 64 and the feeder oil passage 55, and the rod side 20R is drained. Further, when a boom lowering signal from the operation lever 23 is applied to the pilot port 21P2 via a pilot line (not shown), the boom spool 24 of the boom cylinder switching valve 21 is switched to the position C in FIG. As a result, the pressure oil from the first pump 5 is supplied to the rod side 20 </ b> R of the boom cylinder 20 via the parallel oil passage 64 and the feeder oil passage 55, and the rod side 20 </ b> R is drained via the drain line 71.

  The second boom cylinder switching valve 22 is a 6-port 2-position switching valve. When a boom raising signal from the operation lever 23 is applied to the pilot port 22P1, the boom spool 26 of the boom cylinder switching valve 22 is switched to the position A in FIG. Is supplied via the parallel oil passage 66 and the feeder oil passage 73, and the rod side 20R is drained. When the boom raising signal is not applied to the pilot port 22P1, the boom spool 26 of the boom cylinder switching valve 22 is switched to the position C in FIG. As a result, the boom cylinder 20 is shut off at both the bottom side 20B and the rod side 20R, and the center bypass oil passage 54 is communicated to the second arm cylinder switching valve 32 side.

  The arm cylinder 30 is operated and controlled by an arm cylinder switching valve 31 and a second arm cylinder switching valve 32. The arm cylinder switching valve 31 and the second arm cylinder switching valve 32 supply pressure oil to the bottom side 30B of the arm cylinder 30 when the arm is pulled, but the other operations are basically the same as those of the boom cylinder 21. To do.

  That is, the arm cylinder switching valve 31 is a 6-port 3-position switching valve similar to the boom cylinder 21 in this example. When the arm operating lever 33 operated by the operator is brought into the arm pulling state, the arm pulling pilot pressure Pp5 from a well-known pilot pressure generating means (not shown) is changed to the pilot port 31P1 (and the second arm cylinder switching valve 32). The pilot port 32P1) is connected so as to be given. That is, in this embodiment, the pilot pressure Pp5 of the pilot port 31P1 (32P1) is also used as the arm pulling signal of the arm pulling operation detecting means. When the arm pulling pilot pressure Pp5 from the arm operating lever 33 is applied to the pilot port 31P1, the spool 31A of the arm cylinder switching valve 31 is switched to the position A in FIG. As a result, the pressure oil from the first pump 5 is supplied to the bottom side 30 </ b> B of the arm cylinder 30 through the parallel oil passage 64 feeder oil passage 57, and the rod side 30 </ b> R is drained through the drain line 75. Further, when the arm raising signal from the arm operation lever 33 is applied to the pilot port 31P2, the spool 34 of the arm cylinder switching valve 31 is switched to the position C in FIG. As a result, the pressure oil from the first pump 5 is supplied to the rod side 30 </ b> R of the arm cylinder 30 via the parallel oil passage 64 and the feeder 57, and the bottom side 30 </ b> B is drained via the drain line 75.

  The second arm cylinder switching valve 32 is a 6-port 2-position switching valve. When the arm pulling pilot pressure Pp5 from the arm operating lever 33 is applied to the pilot port 32P1, the arm spool 36 of the arm cylinder switching valve 32 is switched to the position A in FIG. As a result, the pressure oil from the second pump 6 is supplied to the bottom side 30B of the arm cylinder 30 via the parallel oil passage 66, and the rod side 30R is drained. When the arm raising signal from the arm operation lever 33 is applied to the pilot port 32P2, the spool 36 of the arm cylinder switching valve 32 is switched to the position C in FIG. As a result, the pressure oil from the second pump 6 is supplied to the rod side 30R of the arm cylinder 30 via the parallel oil passage 66, and the bottom side 30B is drained.

  In connection with the supply of pressure oil to the bottom side 30B of the arm cylinder 30, the throttle valve 70 (see FIG. 7) provided in the feeder oil passage 57 of the conventional first hydraulic pump 5 is the present embodiment. It is omitted. In this embodiment, the pressure oil is supplied to the bottom side 30B of the arm cylinder 30 mainly from the parallel oil passage 66 of the second pump 6, and the arm cylinder 14 in this portion due to the effect of the present invention. This is based on the reason that the pressure oil supply to the boom cylinder 20 can be sufficiently expected even if the supply to the boom cylinder 20 is not particularly limited.

  Here, the configuration of the flow rate adjusting means FR1 attached to the bucket cylinder switching valve 11 will be described in detail with reference to FIG. At the bucket opening side end portion of the bucket cylinder switching valve 11, a stroke restricting mechanism 74 that acts during the bucket closing operation is provided. The stroke regulating mechanism 74 is the core of the flow rate adjusting means FR1, and the closing operation of the bucket 3 and the raising operation of the boom 1 are performed at the same time, and the load pressure P1 of the bucket cylinder 10 is detected to be less than a predetermined value. The bucket spool 14 of the bucket cylinder switching valve 11 is restricted from moving toward the bucket closing side (arrow X1 side) from the predetermined stroke position Sp. In FIG. 1, in order to describe each oil chamber described later, the regulating piston 78 is depicted at a position slightly pulled from a predetermined stroke position Sp.

  Specifically, the stroke restricting mechanism 74 includes a restricting cylinder 76 having two step surfaces 76A and 76B, and a restricting piston 78 having two step surfaces 78A and 78B corresponding to the step surfaces 76A and 76B, respectively. It is mainly composed of. The small diameter portion 78C of the regulating piston 78 faces the oil chamber 15 of the pilot port 11P2 on the open side of the bucket cylinder switching valve 11. The oil chamber 15 of the pilot port 11P2 is a space in which the pilot pressure Pp4 generated when the bucket 3 is being opened is reflected. When the tip 14A of the bucket spool 14 of the bucket cylinder switching valve 11 moves toward the bucket closing side (X1 direction), the bucket cylinder switching valve 11 is configured to come into contact with the end surface 78D of the regulating piston 78.

  The oil chamber 81A formed on the stepped surface 78A of the intermediate diameter portion 78E of the regulating piston 78 is a space in which the load pressure P1 on the bottom side 10B of the bucket cylinder 10 is reflected via the line 77, and the bucket cylinder load pressure detection is performed. It functions as a means.

  The oil chamber 81B formed in the bottom surface 78G of the large diameter portion 78F of the regulating piston 78 is a space in which the boom raising pilot hydraulic pressure Pp2 of the boom operating lever 23 is reflected via the line 79, and the boom raising operation detecting means. Is functioning.

  As described above, the pilot hydraulic pressure Pp1 for closing the bucket is applied to the pilot port 11P1 (the oil chamber 16), and the oil chamber 16 functions as a bucket closing operation detecting means.

  Note that an oil chamber 81 </ b> C formed on the distal end side of the large diameter portion 78 </ b> F of the regulating piston 78 communicates with the tank T. Reference numerals 17A and 17B in the figure are springs for returning the bucket spool 14 to the neutral position B.

  Next, the operation of this embodiment will be described by paying attention to the flow of pressure oil and return oil particularly in a situation that is a problem in the present invention.

  For example, a case will be described in which three operations of “bucket closing”, “arm pulling”, and “boom raising” are performed simultaneously in the case of performing an operation of scooping up accumulated sand as shown in FIG. In this situation, it has already been described that “boom raising” cannot be performed well according to the conventional hydraulic control device (FIG. 7). In this embodiment, in this situation, the boom 1 can be driven in the raising direction without any problem.

  Referring to FIG. 1, when bucket operating lever 13 is in a “bucket closed” state, pilot pressure Pp <b> 1 is applied to pilot port 11 </ b> P <b> 1 of bucket cylinder switching valve 11. For this reason, the bucket spool 14 overcomes the urging force of the spring 17 </ b> B and moves in the left direction (arrow X <b> 1 direction) in FIG. 1, and comes into contact with the end surface 78 </ b> D of the restriction piston 78 of the stroke restriction mechanism 74. At the same time, the load pressure (bottom side pressure) P1 of the bucket cylinder 10 is applied to the oil chamber 81A, and the boom raising pilot pressure Pp2 is applied to the oil chamber 81B.

  Since the bucket is in the “closed bucket” state, no pilot pressure is applied to the pilot port 11P2 (the oil chamber 15) on the open side of the bucket cylinder switching valve 11. Also, since the oil chamber 81C is connected to the tank T, no hydraulic pressure is applied thereto.

  As a result, a biasing force obtained by multiplying the restriction piston 78 by the load pressure P1 of the bucket cylinder 10 and the area S1 of the step surface 78A exposed to the oil chamber 81A acts in the direction of the arrow X1. Further, an urging force obtained by multiplying the pilot pressure Pp2 of “boom raising” by the area S2 of the bottom surface 78G facing the oil chamber 81B acts in the direction of the arrow X2. Therefore, unless the load pressure P1 of the bucket cylinder 10 is increased to some extent, the urging force of the piston 78 of the stroke restricting mechanism 74 is superior to the right side (X2 direction) in the drawing, and the restricting piston 78 is restricted by its stepped surface 78B. The cylinder 76 cannot move while remaining in contact with the stepped surface 76B of the cylinder 76. That is, as a result, the bucket spool 14 cannot move from the specific stroke position Sp to the bucket closing side until the load pressure P1 of the bucket cylinder 10 rises to some extent.

  Thereby, the flow rate of the return oil from the rod side 10R of the bucket cylinder 10 to the tank T is restricted, and the pressure oil is prevented from flowing into the bottom side 10B of the bucket cylinder 10 rapidly. Accordingly, the pressure oil of the first pump 5 can be effectively utilized for driving the boom cylinder 20.

  Further, as shown in FIG. 4, in this embodiment, when the bucket spool 14 of the bucket cylinder switching valve 11 strokes from the bucket closing side to the opening side, the bucket cylinder 10 returns from the rod side to the tank. In the opening characteristic of the port 11P3, the degree of enlargement is small from the fully closed position of the bucket to the vicinity of the “predetermined stroke position Sp”, but the degree of enlargement is larger on the opening side than the stroke position Sp (in this example, a broken line) Set to “expand” (as shown). The fact that the bucket spool 14 starts to move in the opening direction from the predetermined stroke position Sp is nothing but that the load pressure P1 of the bucket cylinder 10 has risen to some extent. In this state, the situation in which pressure oil cannot be supplied to the boom cylinder 20 is almost eliminated. Therefore, in this embodiment, when the bucket spool 14 starts to move in the opening direction from the “predetermined stroke position Sp”, the opening of the return oil is rapidly expanded. Thereby, the load of the pressure oil on the rod side 10R of the bucket cylinder 10 is drastically reduced, the pressure oil can be smoothly flowed into the bottom side 10B of the bucket cylinder 10, and the workability of the bucket 3 can be further improved. .

  The flow rate regulation using the stroke regulation mechanism 74 can be realized only by a slight design change of the bucket cylinder switching valve 11 and can be realized only by control on the hydraulic circuit without requiring a component with electrical wiring. Therefore, there is an advantage that operation reliability is high.

  In this embodiment, the flow rate restriction is not performed when the load pressure P1 of the bucket cylinder 10 exceeds a predetermined value. Further, there is no restriction on the feeder oil passage 54 of the bucket cylinder 10 that hinders its flow rate. As a result, the driving of the bucket 3 is not adversely affected. Further, since the feeder oil passage 54 is not unnecessarily restricted, the heat balance performance can be improved, and it is not necessary to maintain the engine output at a high level.

  By the way, in the present invention, the specific configuration of the flow rate adjusting means is not particularly limited to the above example. For example, an embodiment as shown in FIG. 5 may be used.

  In the embodiment shown in FIG. 5, a pilot that strokes the bucket spool 14 of the bucket cylinder switching valve 11 to the open side as the flow rate adjusting means FR2 that can adjust the flow rate of the return oil from the rod side 10R of the bucket cylinder 10 to the tank T. The port 11P2 includes an electromagnetic proportional valve 82 that can apply an arbitrary pilot pressure PpS. The bucket cylinder switching valve 11 is obtained by removing the stroke restricting mechanism 74 from the bucket cylinder switching valve 11 in the above-described embodiment, and the opening characteristics of the port 11P3 of the bucket cylinder switching valve 11 are the bucket cylinder switching valve in the previous embodiment. 11 (abrupt increase from the vicinity of a predetermined stroke position Sp as indicated by a broken line in FIG. 4).

  In this embodiment, the bucket closing operation detecting means for detecting that the closing operation of the bucket 3 has been performed is the pressure switch 84. The boom raising operation detecting means for detecting that the raising operation of the boom 1 has been performed is a pressure switch 86. The bucket cylinder load pressure detecting means for detecting the load pressure P 1 of the bucket cylinder 11 is a pressure sensor 88.

  When the closing operation of the bucket 3 and the raising operation of the boom 1 are performed at the same time and the load pressure P1 of the bucket cylinder 11 is detected to be equal to or lower than a predetermined value, these pieces of information are input to the controller 90 and a corresponding electric signal is generated. It is output to the electromagnetic proportional valve 82. The electromagnetic proportional valve 82 outputs a pilot pressure PpS corresponding to the electric signal, and this pilot hydraulic pressure PpS is input to a pilot port 11P2 that strokes the bucket spool 14 of the bucket cylinder 11 to the open side. This electric signal corresponds to a pilot pressure that positions the bucket spool 14 at a “predetermined stroke position Ps” other than the stroke end on the bucket closing side.

  Also with this configuration, substantially the same effect as the previous embodiment using the previous stroke restriction mechanism 74 can be obtained. Further, although not shown, according to this configuration, for example, other elements such as the load pressure of the boom cylinder 20 or the load pressure of the arm cylinder 30 (or information that can infer the situation at that time in more detail). In consideration of this, the output from the electromagnetic proportional valve 82 can be determined, and finer inflow regulation can be performed as necessary.

  In this embodiment as well as the previous embodiment, the opening characteristic of the return port 11P3 from the rod side 10R of the bucket cylinder 10 to the tank T is changed from the vicinity of the “predetermined stroke position Sp”. In particular, the workability of the bucket can be further improved.

  FIG. 6 shows an example of still another embodiment of the present invention.

  In this embodiment, the flow rate of the return oil from the rod side 10R of the bucket cylinder 10 to the tank T is regulated as the flow rate adjusting means FR3 capable of adjusting the flow rate of the return oil from the rod side 10R of the bucket cylinder 10 to the tank T. The electromagnetic proportional flow rate adjusting valve 92 is arranged directly on the drain line 69 for returning oil from the rod side 10R of the bucket cylinder 10 to the tank T. As in the above embodiment, the pressure switch 84 as a bucket closing operation detecting means for detecting that the bucket 3 has been closed, and the boom raising operation detecting means for detecting that the boom 1 has been raised. Pressure switch 86, and a pressure sensor 88 as a bucket cylinder load pressure detecting means for detecting the load pressure P1 of the bucket cylinder 10. When the closing operation of the bucket 3 and the raising operation of the boom 1 are performed at the same time and the load pressure P1 of the bucket cylinder 10 is detected to be equal to or less than a predetermined value, the tank 90 starts from the rod side 10R of the bucket cylinder 10 according to a command from the controller 90. The flow rate of the return oil to T is directly regulated by the electromagnetic proportional flow control valve 92.

  Since this embodiment does not regulate the movement of the bucket spool 14, there is no influence on the supply of pressure oil to the bottom side 10 </ b> B of the bucket cylinder 10. Only the degree of pressure oil load on the rod side 10R can be independently controlled to an arbitrary value. Therefore, the bucket cylinder switching valve 11 does not require any design change (from the conventional bucket spool) including the above-mentioned “opening characteristics” of the bucket spool 14A, and substantially considers the opening characteristics. Can be implemented in a centralized manner.

  In addition, this control configuration directly controls the flow rate of the return oil from the rod side R of the bucket cylinder 10 to the tank T by the electromagnetic proportional flow rate adjusting valve 92. In addition to the information on the presence / absence of the lifting operation and the load pressure of the bucket cylinder, if necessary, the load pressure of the boom cylinder 20 and the load pressure of the arm cylinder 30 are also taken into consideration, for example. It is also possible to control the flow rate of return oil from the tank to the tank T. Therefore, it is possible to carry out more comprehensive control that is more balanced.

  In the above-described embodiment, the negative control type hydraulic control device has been exemplified. However, the present invention can achieve the same effect even in the positive control type hydraulic control device.

  The present invention can be applied to a hydraulic control device for a working machine in which each cylinder switching valve of the work machine is connected in tandem and the cylinder switching valve is also connected in a parallel circuit.

1 is a schematic hydraulic circuit diagram showing a configuration in the vicinity of a bucket cylinder switching valve of a hydraulic control device for a work machine to which an example of an embodiment of the present invention is applied. Hydraulic circuit diagram showing the main part of the overall configuration of the hydraulic control device The front view which shows schematic structure of the boom of the said working machine, an arm, and a bucket. Graph showing opening characteristics of bucket cylinder switching valve Schematic hydraulic circuit diagram showing the vicinity of a bucket cylinder switching valve showing an example of another embodiment of the present invention Schematic hydraulic circuit diagram showing the vicinity of a bucket cylinder switching valve showing an example of still another embodiment of the present invention FIG. 2 is a hydraulic circuit diagram showing a schematic configuration of a conventional hydraulic control device for a work machine

Explanation of symbols

5, 6 ... 1st, 2nd hydraulic pump
DESCRIPTION OF SYMBOLS 10 ... Bucket cylinder 11 ... Bucket cylinder switching valve 11P1 ... Pilot port 13 ... Bucket operation lever 14 ... Stroke control mechanism 20 ... Boom cylinder 20P1 ... Pilot port 21 ... Boom cylinder switching valve 23 ... Boom operation lever 30 ... Arm cylinder 31 ... Arm Cylinder switching valve 33 ... Arm operation lever 52, 54 ... Center bypass oil passage 64, 66 ... Parallel oil passage 82 ... Electromagnetic proportional valve 92 ... Electromagnetic proportional flow control valve

Claims (5)

Work having at least a bucket cylinder and a boom cylinder for driving a bucket and a boom of a work machine, and connecting a bucket cylinder switching valve and a boom cylinder switching valve for switching each cylinder in tandem, and also connecting the cylinder switching valve with a parallel circuit In the machine hydraulic control device,
Bucket closing operation detection means for detecting that the bucket closing operation has been performed;
Boom raising operation detecting means for detecting that the boom raising operation has been performed;
Bucket cylinder load pressure detecting means for detecting the load pressure of the bucket cylinder;
Flow rate adjusting means capable of adjusting the flow rate of return oil from the rod side of the bucket cylinder to the tank, and
When the bucket closing operation and the boom raising operation are performed at the same time and it is detected that the load pressure of the bucket cylinder is equal to or lower than a predetermined value, the flow rate adjusting means causes the tank from the rod side of the bucket cylinder to A hydraulic control device for a work machine, characterized in that the flow rate of return oil to the engine is regulated. In claim 1,
As the flow rate adjusting means, provided with a stroke regulating mechanism for regulating the stroke of the bucket cylinder switching valve toward the closing operation side of the spool,
When the bucket closing operation and the boom raising operation are performed at the same time, and the load pressure of the bucket cylinder is detected to be equal to or less than a predetermined value, the stroke restriction mechanism causes the bucket cylinder switching valve to have a predetermined spool. A hydraulic control device for a work machine, characterized by regulating a stroke closer to a bucket closing side than a stroke position. In claim 1,
As the flow rate adjusting means, an electromagnetic proportional valve capable of applying an arbitrary pilot pressure to a pilot port that strokes the spool of the bucket cylinder to the open side,
When the bucket closing operation and the boom raising operation are performed at the same time and the load pressure of the bucket cylinder is detected to be a predetermined value or less, the electromagnetic proportional valve strokes the bucket cylinder spool to the open side. A hydraulic pressure control device for a work machine, characterized in that a pilot pressure is applied to a pilot port that causes the spool to be positioned at a predetermined stroke position other than a stroke end on a bucket closing side. In any one of Claims 1-3,
The opening characteristic of the return port from the bucket cylinder rod side to the tank when the spool of the bucket cylinder switching valve strokes from the closed side to the open side is from the bucket fully closed position to the predetermined stroke position. A hydraulic control device for a working machine, characterized in that the degree of expansion is small and the degree of expansion is set larger on the opening side than the stroke position. In claim 1,
As the flow rate adjusting means, an electromagnetic proportional flow rate adjustment valve capable of adjusting the flow rate of return oil from the rod side of the bucket cylinder to the tank is provided,
When the bucket closing operation and the boom raising operation are performed at the same time, and the load pressure of the bucket cylinder is detected to be equal to or lower than a predetermined value, the electromagnetic proportional flow rate adjusting valve controls the tank from the rod side of the bucket cylinder. A hydraulic control device for a work machine, characterized in that the flow rate of return oil to the engine is regulated.

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