JP2010242796A - Hydraulic control circuit for construction machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic control circuit for a construction machine, capable of improving fuel consumption, while lowering the discharge quantity of a hydraulic pump when an arm body is lowered by its own weight. <P>SOLUTION: The negative control type hydraulic control circuit 100 includes a boom lowering control valve 56 for opening a recovery oil passage so as to connect a rod chamber and a bottom chamber of a boom cylinder 7 according to the operation of a boom operation lever 50 in a down direction, and a switch valve 55 for returning a first speed boom direction control valve 13R to a neutral position. The switch valve 55 returns the first speed boom direction control valve 13R to the neutral position when the pressure in the bottom chamber of the boom cylinder 7 is a predetermined value or above. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention supplies a hydraulic oil discharged from a hydraulic pump to a hydraulic cylinder, while discharging the hydraulic oil from the hydraulic cylinder to a hydraulic oil tank and expanding and contracting the hydraulic cylinder, and an arm such as a boom, an arm, or a bucket In particular, the hydraulic control circuit used in the construction machine that operates the body reduces the discharge amount of the hydraulic pump when the arm body is lowered by its own weight in the direction of gravity, while against the load for excavation. The present invention relates to a hydraulic control circuit for a construction machine that can improve fuel efficiency by preventing excessive pressure loss from being generated in a pressure oil line when the arm is actively driven in the direction of gravity.

  Conventionally, a negative control type that includes a hydraulic pump that increases or decreases the discharge amount according to the negative control pressure generated by the negative control throttle and a directional control valve that controls the flow of pressure oil circulating in the hydraulic cylinder that operates the arm body. A hydraulic control circuit for construction machinery is known.

  This negative control type hydraulic control circuit for construction machinery operates when the user operates the boom control lever to displace the spool of the boom direction control valve from its neutral position, thereby narrowing the center bypass passage and reducing the negative control pressure. Increase the discharge amount of the hydraulic pump. This is because the boom can be reliably driven with a sufficient amount of pressure oil.

  In addition, the hydraulic pressure control circuit for construction machinery pressurizes the bottom chamber of the boom hydraulic cylinder (the chamber whose volume is reduced when the boom is lowered) and the rod chamber (the chamber whose volume is expanded when the boom is lowered). In some cases, the pressure oil in the bottom chamber communicates with the oil pipe line (regeneration pipe line), and the pressure oil in the bottom chamber is discharged into the pressure oil tank and simultaneously circulated (regenerated) in the rod chamber.

  This construction machine hydraulic control circuit regenerates the pressure oil in the bottom chamber into the rod chamber via the regeneration pipe when the arm body is lowered in the air by its own weight. There is no need to supply oil into the rod chamber.

  Focusing on this point, a variable throttle mechanism that throttles the center bypass passage according to the pressure in the bottom chamber of the boom hydraulic cylinder is provided inside the spool of the boom direction control valve, and the boom is lowered by its own weight (bottom chamber Of the hydraulic pump when the boom is lowered by its own weight by increasing the amount of pressure oil flowing through the center bypass passage and suppressing the negative control pressure from decreasing by using the variable throttle mechanism There is also a circuit that reduces the discharge amount (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-089317

  However, although the circuit described in Patent Document 1 can reduce the discharge amount of the hydraulic pump and improve the fuel consumption while using the regeneration pipeline when the boom is lowered by its own weight, the boom direction control valve P- Since the throttle provided in the C opening (the port on the spool that connects the hydraulic oil line connecting the hydraulic pump and the hydraulic cylinder) cannot be omitted, it is provided as it is. When driving positively in the direction (when the hydraulic oil discharged by the hydraulic pump flows into the hydraulic cylinder for the boom through the PC opening), the pressure loss generated at the throttle cannot be eliminated and the fuel consumption deteriorates Will end up.

  This diaphragm is necessary to smoothly perform the combined operation of the arm body (for example, simultaneous operation of the boom and the bucket). Without this restriction, when the boom is lowered by its own weight during the combined operation and the pressure in the rod chamber (expansion side chamber) of the boom hydraulic cylinder suddenly decreases, the pressure oil from the hydraulic pump flows into the rod chamber intensively. This is because the amount of pressure oil flowing into the bucket hydraulic cylinder is reduced.

  In view of the above points, the present invention provides a hydraulic control circuit for a construction machine that realizes further improvement in fuel efficiency while reducing the discharge amount of the hydraulic pump when the arm body is lowered by its own weight. Objective.

  In order to achieve the above object, a hydraulic control circuit for construction machine according to the present invention includes a hydraulic pump that increases or decreases a discharge amount according to a control pressure generated by a negative control throttle and a pressure that circulates through a hydraulic cylinder that operates a boom. A negative control type hydraulic control circuit for a construction machine including a directional control valve for controlling the flow of oil, comprising a regeneration pipe for connecting an expansion chamber and a reduction chamber of the hydraulic cylinder, the regeneration pipe A boom lowering control valve that opens in response to the boom lowering operation, and a neutral position return means that returns the directional control valve to the neutral position when the pressure in the reduction chamber of the hydraulic cylinder exceeds a predetermined value. And the neutral position return means is configured to return the directional control valve to the neutral position when the boom is lowered by its own weight in response to the boom lowering operation. And butterflies.

  Furthermore, the hydraulic pressure control circuit for a construction machine according to the present invention is a switching valve in which the neutral position return means is disposed in a control pressure line that connects a pilot port of the directional control valve and a control pump that generates pilot pressure. Yes, the switching valve may transmit the pilot pressure to the pilot port in the first state and cancel the pilot pressure in the pilot port in the second state.

  Furthermore, the hydraulic pressure control circuit for a construction machine according to the present invention is such that the neutral position return means returns the neutral valve to the neutral position when the pressure in the expansion chamber of the hydraulic cylinder becomes less than a predetermined value. You may make it prohibit.

  Furthermore, in the hydraulic control circuit for a construction machine according to the present invention, the direction control valve and the boom lowering control valve may be disposed inside a valve unit.

  Furthermore, in the hydraulic control circuit for a construction machine according to the present invention, the boom lowering control valve may be arranged in series with the direction control valve.

  Furthermore, in the hydraulic control circuit for a construction machine according to the present invention, the direction control valve includes a first speed boom direction control valve and a second speed boom direction control valve, and the boom lowering control valve is the second speed boom. You may make it incorporate in a boom direction control valve.

  With the above-described means, the present invention can provide a hydraulic control circuit for a construction machine that realizes further improvement in fuel consumption while reducing the discharge amount of the hydraulic pump when the arm body is lowered by its own weight. .

It is a figure which shows the structural example of the hydraulic excavator by which the hydraulic control circuit for construction machines which concerns on this invention is mounted. It is a hydraulic circuit diagram (the 1) of the hydraulic control circuit mounted in the construction machine which concerns on this invention. It is a figure for demonstrating the difference between the boom direction control valve of a present Example, and the conventional boom direction control valve. FIG. 2 is a diagram (part 1) illustrating a state of a hydraulic control circuit in a standby mode. It is FIG. (1) which shows the state of the hydraulic control circuit when operating a boom in the downward direction against a load for excavation. It is a figure (the 1) which shows the state of the hydraulic control circuit when lowering a boom with dead weight. It is a flowchart which shows the flow of a valve state switching process. It is a hydraulic circuit diagram (the 2) of the hydraulic control circuit mounted in the construction machine which concerns on this invention. FIG. 6 is a diagram (No. 2) illustrating a state of the hydraulic control circuit in the standby mode. FIG. 10 is a diagram (No. 2) illustrating a state of the hydraulic control circuit when the boom is operated in the lowering direction against the load for excavation. It is FIG. (2) which shows the state of the hydraulic control circuit when lowering a boom with dead weight. It is a figure which shows the state of the hydraulic control circuit when raising a boom rapidly.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration example of a hydraulic excavator in which a construction machine hydraulic control circuit according to the present invention is mounted. In FIG. 1, an excavator 1 has an upper swing body 3 mounted on a crawler-type lower traveling body 2 via a swing mechanism so as to be rotatable around the X axis.

  Further, the upper swing body 3 has a excavation attachment composed of a boom 4, an arm 5 and a bucket 6, and a boom cylinder 7, an arm cylinder 8 and a bucket cylinder 9 as hydraulic actuators for driving the boom 4, the arm 5 and the bucket 6 at the front center portion. Prepare.

  FIG. 2 is a hydraulic circuit diagram of a hydraulic control circuit mounted on a construction machine according to the present invention, in which a pressure oil pipeline is indicated by a solid line, a control pressure pipeline is indicated by a broken line, and a control current line is indicated by a hatched line. .

  The hydraulic control circuit 100 includes directional control valves 11L, 12L, 13L, and 15L from two hydraulic pumps 10L and 10R that are driven by an engine or an electric motor and have variable discharge amount (cc / rev) per rotation. The pressure oil is circulated to the pressure oil tank 22 via the center bypass conduit 30L that communicates with the center bypass conduit 30L or the direction control valves 11R, 12R, 13R, 14 and 15R, and the boom lowering control valve 56. .

  The direction control valve 11L is a spool valve (left travel motor direction control valve) that switches the flow of pressure oil in order to circulate the pressure oil discharged from the hydraulic pump 10L in the travel hydraulic motor 42L.

  The direction control valve 11R is a traveling straight valve, and travel hydraulic motors 42L and 42R for driving the lower traveling body 2 and any hydraulic actuator of the upper swing body 3 (for example, boom cylinder 7, arm cylinder 8, bucket). When the cylinder 9 or the turning hydraulic motor 44 is operated at the same time, pressure oil is supplied from the hydraulic pump 10L to both the left and right traveling hydraulic motors 42L and 42R in order to improve the straightness of the lower traveling body 2. This is a spool valve that switches the flow of pressure oil to circulate the oil.

  The direction control valve 12L is a spool valve (swing motor direction control valve) that switches the flow of pressure oil in order to circulate the pressure oil discharged from the hydraulic pump 10L by the swing hydraulic motor 44. The direction control valve 12R This is a spool valve (right travel motor direction control valve) that switches the flow of pressure oil in order to circulate the pressure oil discharged from the pump 10R by the travel hydraulic motor 42R.

  The direction control valves 13L and 13R supply pressure oil discharged from the hydraulic pumps 10L and 10R to the boom cylinder 7 and flow of pressure oil to discharge the pressure oil in the boom cylinder 7 to the pressure oil tank 22, respectively. The direction control valve 13R is a spool valve that operates when the boom operation lever 50 is operated (hereinafter referred to as “first speed boom direction control valve 13R”), and is a direction control valve. 13L is a spool valve (hereinafter referred to as “second speed”) for joining the pressure oil discharged from the hydraulic pump 10L to the bottom chamber of the boom cylinder 7 when the boom operation lever 50 is operated in the upward direction with a predetermined operation amount or more. Boom direction control valve 13L ").

  The direction control valve 14 is a spool valve (bucket direction control valve) for supplying the pressure oil discharged from the hydraulic pump 10R to the bucket cylinder 9 and discharging the pressure oil in the bucket cylinder 9 to the pressure oil tank 22. is there.

  The direction control valves 15L and 15R supply pressure oil discharged from the hydraulic pumps 10L and 10R to the arm cylinder 8 and flow of pressure oil to discharge the pressure oil in the arm cylinder 8 to the pressure oil tank 22, respectively. The direction control valve 15L is a spool valve that operates when the arm operation lever is operated (hereinafter referred to as “first speed arm direction control valve 15L”), and the direction control valve 15R. Is a spool valve (hereinafter referred to as “second speed arm direction control valve 15R”) for joining the pressure oil discharged from the hydraulic pump 10R to the arm cylinder 8 when the arm operation lever is operated at a predetermined operation amount or more. .)

  It is assumed that the direction control valves 11L, 12L, 13L, and 15L and the direction control valves 11R, 12R, 13R, 14 and 15R are collectively stored in the valve unit.

  The center bypass pipes 30L and 30R are respectively provided with negative control throttles 20L and 20R between the directional control valves 15L and 15R and the pressure oil tank 22 located on the most downstream side, and the pressure oil discharged by the hydraulic pumps 10L and 10R. By restricting the flow, upstream of the negative control throttles 20L and 20R, a control pressure (negative control) for controlling each regulator for the hydraulic pumps 10L and 10R (a device that changes the discharge amount of the hydraulic pump). Pressure).

  The control pressure lines 32L and 32R indicated by broken lines are negative control pressure lines for transmitting the negative control pressure generated upstream of the negative control throttles 20L and 20R to the regulators for the hydraulic pumps 10L and 10R.

  When none of the hydraulic actuators in the hydraulic excavator 1 is used (hereinafter referred to as “standby mode”), the pressure oil discharged from the hydraulic pumps 10L and 10R passes through the center bypass pipelines 30L and 30R and is negatively controlled. The negative control pressure generated upstream of the negative control throttles 20L and 20R is increased by reaching the throttles 20L and 20R.

  As a result, the hydraulic pumps 10L and 10R reduce the discharge amount, thereby suppressing the pressure loss (pumping loss) when the discharged pressure oil passes through the center bypass pipelines 30L and 30R.

  On the other hand, when any hydraulic actuator in the hydraulic excavator 1 is used, the pressure oil discharged from the hydraulic pumps 10L and 10R flows into the hydraulic actuator via the directional control valve corresponding to the hydraulic actuator, and the negative control throttle The amount reaching 20L and 20R is reduced or eliminated, and the negative control pressure generated upstream of the negative control throttles 20L and 20R is reduced.

  As a result, the hydraulic pumps 10L and 10R increase the discharge amount, circulate sufficient pressure oil to each hydraulic actuator, and ensure the driving of each actuator.

  With the configuration as described above, in the standby mode, the hydraulic control circuit 100 causes wasteful energy consumption in the hydraulic pumps 10L and 10R (pressure oil discharged from the hydraulic pumps 10L and 10R is generated in the center bypass pipes 30L and 30R. When various hydraulic actuators are operated while suppressing (pumping loss), necessary and sufficient pressure oil can be supplied from the hydraulic pumps 10L and 10R to each hydraulic actuator.

  The boom operation lever 50 uses the pressure oil discharged from the control pump 52 to apply a control pressure corresponding to the lever operation amount to the pilot port of the first speed boom direction control valve 13R and the pilot of the second speed boom direction control valve 13L. It is a device for introducing into a port. Although not shown, other operation levers such as an arm operation lever, a bucket operation lever, or a turning operation lever have the same configuration.

  The control pump 52 is a hydraulic pump for discharging control pressure oil, and is a fixed displacement hydraulic pump that continuously discharges control pressure oil at a predetermined discharge pressure (for example, 4 MPa). .

  The main controller 54 is a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), etc., and stores a program corresponding to the neutral position return means in the ROM while The CPU is caused to execute processing corresponding to the return means.

  Further, the main controller 54 operates the pressure sensor P1 that measures the control pressure generated when the boom operation lever 50 is operated in the up (boom up) direction, and the boom operation lever 50 in the down (boom down) direction. The lever operation direction and lever operation amount of the boom operation lever 50 are detected based on the output of the pressure sensor P2 that measures the control pressure generated in this case. The same applies to the other operation levers.

  Further, the main controller 54 determines whether or not the boom 4 is lowered by its own weight based on the output of the pressure sensor P3 that measures the pressure in the bottom chamber of the boom cylinder 7. This determination is based on the fact that when the boom 4 is lowered by its own weight, the pressure in the bottom chamber of the boom cylinder 7 becomes equal to or higher than a predetermined pressure. When the pressure in the rod chamber of the arm cylinder 8 is measured to determine whether or not the weight of the arm 5 is lowered, or the pressure in the bottom chamber or the rod chamber of the bucket cylinder 9 is measured to determine whether or not the weight of the bucket 6 is lowered. The same applies to the determination.

  Further, the main controller 54 determines the presence or absence of cavitation in the rod chamber of the boom cylinder 7 based on the output of the pressure sensor P4 that measures the pressure in the rod chamber of the boom cylinder 7. This determination is based on the possibility that cavitation may occur when the pressure in the rod chamber of the boom cylinder 7 becomes less than a predetermined pressure. When the pressure in the bottom chamber of the arm cylinder 8 is measured to determine the presence or absence of cavitation in the bottom chamber of the arm cylinder 8, or the pressure in the bottom chamber or rod chamber of the bucket cylinder 9 is measured to measure the bucket cylinder 9 The same applies to the determination of the presence or absence of cavitation in the bottom chamber or rod chamber.

  The neutral position return means is a means for returning the directional control valve that controls the flow of the pressure oil circulating through the hydraulic cylinder to the neutral position. For example, the first pilot port (boom of the first speed boom direction control valve 13R). 4) and a control valve 55 installed on the control pressure line between the control pump 52 and the pilot port of the first speed boom direction control valve 13R. Remove the control pressure (pilot pressure).

  The switching valve 55 is a solenoid valve that switches a state in accordance with a control current output from the main controller 54. For example, a control pressure line between the first pilot port of the first speed boom direction control valve 13R and the control pump 52 is used. The first state in which the pilot pressure is opened and the second state in which the pilot pressure applied to the first pilot port is canceled while the control pressure line is shut off can be switched.

  When the boom operation lever 50 is installed in the control pressure line between the first pilot port of the first speed boom direction control valve 13R and the control pump 52, and the boom operation lever 50 is operated in the downward direction. Then, the control pressure in the control pressure line increases.

  The boom lowering control valve 56 is an additional control pressure line branched from a control pressure line that introduces a control pressure corresponding to the lever operation amount of the boom operation lever 50 to the first pilot port of the first speed boom direction control valve 13R. Is a two-position 6-port spool valve that switches the state in accordance with the control pressure introduced via the control valve (equivalent to the control pressure corresponding to the lever operation amount of the boom operation lever 50). When the control pressure in the control pressure line is operated and becomes a predetermined value or more, the first state for opening the regeneration line that directly connects the bottom chamber of the boom cylinder 7 and the rod chamber, and the control pressure pipe When the control pressure in the path is less than a predetermined value, the second state in which the regeneration pipe is shut off can be switched.

  Further, the boom lowering control valve 56 includes a port for opening the center bypass pipe line 30R in both the first state and the second state, and can always shut off the center bypass pipe line 30R. Absent.

  FIG. 3 is a diagram for explaining the difference between the boom direction control valve of the present embodiment and the conventional boom direction control valve, and FIG. 3 (A) is the first speed boom direction control valve of the present embodiment. FIG. 3B shows a conventional boom direction control valve 130.

  The first speed boom direction control valve 13R of this embodiment and the conventional boom direction control valve 130 are both 3-position 6-port spool valves having three switching positions: a raising operation position, a neutral position, and a lowering operation position. The conventional boom direction control valve 130 has a PC opening (port on a spool for opening a hydraulic oil line connecting the hydraulic pump and the boom cylinder) and a CT opening (boom cylinder and Pipe lines having throttles 131 and 132 in each of the ports on the spool for opening the pressure oil pipe connecting the pressure oil tank, and having a check valve connecting the PC opening and the CT opening It differs from the 1st speed boom direction control valve 13R of a present Example by the point which has 133. FIG.

  The throttle 131 in the conventional boom direction control valve 130 is necessary for smoothly performing the combined operation of the arm body (for example, simultaneous operation of the boom and the bucket). When the boom is lowered by its own weight and the pressure in the rod chamber of the boom cylinder suddenly decreases, the pressure oil from the hydraulic pump flows intensively into the rod chamber, and the amount of pressure oil flowing into the bucket cylinder is significantly reduced. Will end up.

  The hydraulic control circuit 100 according to the present embodiment includes the switching valve 55, thereby eliminating the function of the throttle 131 in the conventional boom direction control valve 130. When the boom 4 is lowered by its own weight, the first speed boom direction control valve 13R is set to the neutral position, and the hydraulic oil line that connects the first speed boom direction control valve 13R and the boom cylinder 7 is shut off, so that the hydraulic pressure is applied during the combined operation. This is because the pressure oil from the pump 10R can be completely prevented from flowing into the rod chamber of the boom cylinder 7.

  Further, the throttle 132 and the pipe 133 in the conventional boom direction control valve 130 are necessary for forming the regeneration pipe, and the flow of the pressure oil flowing from the bottom chamber of the boom cylinder to the pressure oil tank is throttled 132. The flow from the bottom chamber to the rod chamber through the pipe line 133 is generated by squeezing at the bottom.

  The hydraulic control circuit 100 according to the present embodiment includes a structure corresponding to the throttle 132 and the pipe 133 in the conventional boom direction control valve 130 in the boom lowering control valve 56 according to the present embodiment. The structure corresponding to the throttle 132 and the pipe line 133 in the conventional boom direction control valve 130 is removed from the first-speed boom direction control valve 13R.

  Next, the operation of the hydraulic control circuit 100 when the boom 4 is operated in the lowering direction will be described with reference to FIGS.

  4 to 6 are hydraulic circuit diagrams of the hydraulic control circuit 100 in which components related to the operation of the boom 4 are selectively extracted from the hydraulic circuit diagram of FIG. 2, and FIG. 4 shows a state in the standby mode. 5 shows a state when the boom 4 is operated in the downward direction against the load for excavation, and FIG. 6 shows a state when the boom 4 is lowered by its own weight.

  In FIG. 4, the main controller 54 detects that the boom operation lever 50 is not operated based on the outputs of the pressure sensors P <b> 1 and P <b> 2, and does not supply a control current to the switching valve 55.

  Therefore, the switching valve 55 is in the first state in which the control pressure generated when the boom operation lever 50 is operated in the downward direction is transmitted to the first pilot port of the first speed boom direction control valve 13R.

  Further, the boom lowering control valve 56 is in a second state in which the regeneration conduit is shut off because it does not receive the control pressure generated when the boom operation lever 50 is operated in the lowering direction.

  Further, the first speed boom direction control valve 13R is in a neutral position, and the pressure oil discharged from the hydraulic pump 10R through the center bypass conduit 30R reaches the negative control throttle 20R to reduce the discharge amount of the hydraulic pump 10R. .

  On the other hand, in FIG. 5, the main controller 54 detects that the boom operation lever 50 has been operated in the downward direction based on the output of the pressure sensor P2, and the bottom of the boom cylinder 7 based on the output of the pressure sensor P3. When it is detected that the pressure in the chamber is less than a predetermined value, it is determined that the boom 4 is operating in the downward direction against the load for excavation, and the boom operation lever 50 is operated in the downward direction. The control current is not supplied to the switching valve 55 so that the generated control pressure is transmitted to the first pilot port of the first speed boom direction control valve 13R.

  Further, the first speed boom direction control valve 13R receives a control pressure generated when the boom operation lever 50 is operated in the lowering direction at the first pilot port and is in the lowering operation position, and is hydraulically connected via the parallel line 31R. The pressure oil discharged from the pump 10 </ b> R flows into the rod chamber of the boom cylinder 7, and the pressure oil flowing out from the bottom chamber of the boom cylinder 7 is discharged to the pressure oil tank 22.

  The boom lowering control valve 56 receives the control pressure generated when the boom operating lever 50 is operated in the lowering direction and enters the first state in which the regeneration conduit is opened, but the first speed boom direction control valve 13R. Is in the lowering operation position, the pressure in the rod chamber of the boom cylinder 7 is higher than the pressure in the bottom chamber, and the regeneration conduit is blocked by the check valve.

  Further, most of the pressure oil flowing out from the bottom chamber of the boom cylinder 7 is discharged to the pressure oil tank 22 through the C-T opening of the first speed boom direction control valve 13R that does not have resistance due to throttling.

  Thus, when the hydraulic control circuit 100 operates the boom 4 in the downward direction against the load for excavation, the hydraulic oil discharged from the hydraulic pump 10R flows into the boom cylinder 7 without passing through any throttle. In addition, since the pressure oil flowing out from the boom cylinder 7 can be discharged to the pressure oil tank 22 without passing through any throttle, unnecessary pressure loss does not occur.

  Further, in FIG. 6, the main controller 54 detects that the boom operation lever 50 has been operated in the downward direction based on the output of the pressure sensor P2, and the bottom of the boom cylinder 7 based on the output of the pressure sensor P3. When it is detected that the pressure in the chamber is equal to or higher than a predetermined value, it is determined that the boom 4 is operating in the downward direction with its own weight, and the control pressure generated when the boom operating lever 50 is operated in the downward direction is the first control pressure. A control current is supplied to the switching valve 55 so as not to be transmitted to the first pilot port of the first-speed boom direction control valve 13R.

  The switching valve 55 is in a second state in which the pilot pressure applied to the first pilot port is released while blocking the control pressure line between the first pilot port of the first speed boom direction control valve 13R and the control pump 52, If there is pressure oil generating pilot pressure at the first pilot port, the pressure oil is discharged to the pressure oil tank 22.

  As a result, the first speed boom direction control valve 13R is in the neutral position by removing the control pressure at the first pilot port (the control pressure generated when the boom operation lever 50 is operated in the downward direction). While shutting off the exchange of pressure oil with the boom cylinder 7, the pressure oil discharged from the hydraulic pump 10R reaches the negative control throttle 20R through the center bypass conduit 30R to reduce the discharge amount of the hydraulic pump 10R. .

  As in the case of FIG. 5, the boom lowering control valve 56 receives the control pressure generated when the boom operating lever 50 is operated in the lowering direction and enters the first state in which the regeneration conduit is opened. The pressure oil flowing out from the chamber is regenerated in the rod chamber of the boom cylinder 7. This is because the first speed boom direction control valve 13R is in the neutral position and the exchange of pressure oil between the boom cylinder 7 and the first speed boom direction control valve 13R is blocked.

  As a result, when the boom 4 is lowered by its own weight, the hydraulic control circuit 100 can reduce the discharge amount of the hydraulic pump 10R and improve fuel efficiency.

  Even when the main controller 54 lowers the boom 4 by its own weight, when the main controller 54 detects that the pressure in the rod chamber in the boom cylinder 7 is less than a predetermined value based on the output of the pressure sensor P4. It is determined that cavitation may occur, and the supply of the control current to the switching valve 55 is stopped, so that the state shown in FIG. 5 appears. This is because the pressure oil discharged from the hydraulic pump 10R flows into the rod chamber of the boom cylinder 7 so that sufficient pressure oil can be supplied to the rod chamber of the boom cylinder 7.

  Next, a process in which the main controller 54 switches the state of the switching valve 55 (hereinafter referred to as “valve state switching process”) will be described with reference to FIG. FIG. 7 is a flowchart showing the flow of the valve state switching process, and the main controller 54 repeatedly executes this valve state switching process at a predetermined cycle.

  First, the main controller 54 compares the output of the pressure sensor P2 with the threshold value TH1 in order to determine whether or not the boom operation lever 50 has been operated in the downward direction (step S1).

  If it is determined that the output of the pressure sensor P2 is less than the threshold value TH1 and the boom operation lever 50 is not operated in the downward direction (NO in step S1), the main controller 54 does not supply a control current to the switching valve 55. The state switching process is terminated (step S5).

  Thereby, the switching valve 55 opens the control pressure line so that the control pressure corresponding to the lever operation amount of the boom operation lever 50 can be introduced into the first pilot port of the first speed boom direction control valve 13R at any time. The first state is entered.

  On the other hand, if it is determined that the output of the pressure sensor P2 is equal to or greater than the threshold value TH1 and the boom operation lever 50 is operated in the downward direction (YES in step S1), the main controller 54 outputs the output of the pressure sensor P3 (the bottom chamber of the boom cylinder 7 And the threshold TH2 to determine whether the boom 4 is descending by its own weight or is operating against the load, and further, the output of the pressure sensor P4 (the rod chamber of the boom cylinder 7). In the rod chamber of the boom cylinder 7 to determine whether or not there is a risk of cavitation (step S2).

  When it is determined that the boom 4 is lowered by its own weight and there is no risk of cavitation (YES in step S2), the main controller 54 supplies a control current to the switching valve 55.

  Thus, the switching valve 55 prevents the first pilot while blocking the control pressure line so that the control pressure corresponding to the lever operation amount of the boom operation lever 50 is not introduced into the first pilot port of the first speed boom direction control valve 13R. This is a second state in which the pilot pressure applied to the port is eliminated.

  If it is determined that the boom 4 is operating against the load, or if the boom 4 is lowered by its own weight but there is a risk of cavitation (NO in step S2), the main controller 54 The control current is not supplied to the switching valve 55.

  Thus, the switching valve 55 opens the control pressure line so that the control pressure corresponding to the lever operation amount of the boom operation lever 50 is introduced into the first pilot port of the first speed boom direction control valve 13R. Become.

  With the above configuration, when the boom 4 is lowered by its own weight, the hydraulic control circuit 100 uses the regeneration pipeline that does not pass through the first speed boom direction control valve 13R and keeps the first speed boom direction control valve 13R in the neutral position. In this configuration, the discharge amount of the hydraulic pumps 10L and 10R is reduced, but the throttle is not disposed at the P-C opening of the first speed boom direction control valve 13R (with a larger P-C opening diameter than before). Even when the boom 4 is operated against the load as in excavation, the excessive pressure loss is not generated (which is generated at the PC opening in the conventional boom direction control valve 130). Thus, further improvement in fuel consumption can be realized.

  Further, when the boom 4 is lowered by its own weight, the hydraulic control circuit 100 uses a regeneration conduit that does not pass through the first speed boom direction control valve 13R, so that, for example, in the case of combined operation with the bucket 6, the bucket The operation 6 is performed with the pressure oil discharged from the hydraulic pump 10R, and the boom 4 is operated with the pressure oil in the regeneration pipeline, so that the independence of the operation of the bucket 6 can be enhanced.

  Next, another embodiment of the hydraulic control circuit according to the present invention will be described with reference to FIGS.

  The hydraulic control circuit 200 shown in FIGS. 8 to 12 is different from the hydraulic control circuit 100 in that the boom lowering control valve 56 is incorporated in the second speed boom direction control valve 13LA, but is common in other points.

  8 shows an overall view of the hydraulic control circuit 200, and FIGS. 9 to 12 show partial hydraulic pressures of the hydraulic control circuit 200 in which the components related to the operation of the boom 4 are selectively extracted from FIG. A circuit diagram is shown. 9 shows a state in the standby mode, FIG. 10 shows a state when the boom 4 is operated in the downward direction against the load for excavation, and FIG. 11 lowers the boom 4 by its own weight. FIG. 12 shows a state in which the boom 4 is quickly raised using both the first speed boom direction control valve 13R and the second speed boom direction control valve 13LA.

  The second speed boom direction control valve 13LA has a lower operation position for opening a regeneration conduit that directly connects the bottom chamber of the boom cylinder 7 and its rod chamber when the boom operation lever 50 is operated in the lowering direction. A neutral position that blocks the regeneration conduit while opening the center bypass conduit 30L when the boom control lever 50 is not operated or when the boom control lever 50 is operated in the upward direction with less than a predetermined operation amount; A 3-position 6-port switch for switching the position at the time of raising operation for joining the pressure oil discharged from the hydraulic pump 10L to the bottom chamber of the boom cylinder 7 when the boom operating lever 50 is operated in the raising direction with a predetermined operation amount or more. It is a spool valve.

  In FIG. 9, the main controller 54 detects that the boom operation lever 50 is not operated based on the outputs of the pressure sensors P1 and P2, and does not supply a control current to the switching valve 55.

  Therefore, the switching valve 55 is in the first state in which the control pressure generated when the boom operation lever 50 is operated in the downward direction is transmitted to the first pilot port of the first speed boom direction control valve 13R.

  Further, the first speed boom direction control valve 13R is in a neutral position, and the pressure oil discharged from the hydraulic pump 10R through the center bypass pipe line 30R reaches the negative control throttle 20R to reduce the discharge amount of the hydraulic pump 10R. .

  Similarly, the second speed boom direction control valve 13LA is in a neutral position, and the pressure oil discharged from the hydraulic pump 10L reaches the negative control throttle 20L through the center bypass conduit 30L to reduce the discharge amount of the hydraulic pump 10L. Yes.

  On the other hand, in FIG. 10, the main controller 54 detects that the boom operation lever 50 has been operated in the downward direction based on the output of the pressure sensor P2, and the bottom of the boom cylinder 7 based on the output of the pressure sensor P3. When it is detected that the pressure in the chamber is less than a predetermined value, it is determined that the boom 4 is operating in the downward direction against the load for excavation, and the boom operation lever 50 is operated in the downward direction. The control current is not supplied to the switching valve 55 so that the generated control pressure is transmitted to the first pilot port of the first speed boom direction control valve 13R.

  Further, the first speed boom direction control valve 13R receives a control pressure generated when the boom operation lever 50 is operated in the lowering direction at the first pilot port and is in the lowering operation position, and is hydraulically connected via the parallel line 31R. The pressure oil discharged from the pump 10 </ b> R flows into the rod chamber of the boom cylinder 7, and the pressure oil flowing out from the bottom chamber of the boom cylinder 7 is discharged to the pressure oil tank 22.

  The second speed boom direction control valve 13LA is a first pilot port (a pilot port used when the boom 4 is lowered) that generates control pressure when the boom operation lever 50 is operated in the downward direction. The first speed boom direction control valve 13R is in the lowering operation position, so that the pressure in the rod chamber of the boom cylinder 7 is higher than the pressure in its bottom chamber. The regeneration line is blocked by a check valve.

  Further, most of the pressure oil flowing out from the bottom chamber of the boom cylinder 7 is discharged to the pressure oil tank 22 through the C-T opening of the first speed boom direction control valve 13R that does not have resistance due to throttling.

  Thus, when the hydraulic control circuit 200 operates the boom 4 in the downward direction against the load for excavation, the hydraulic oil discharged from the hydraulic pump 10R flows into the boom cylinder 7 without passing through any throttle. In addition, since the pressure oil flowing out from the boom cylinder 7 can be discharged to the pressure oil tank 22 without passing through any throttle, unnecessary pressure loss does not occur.

  Further, in FIG. 11, the main controller 54 detects that the boom operation lever 50 has been operated in the downward direction based on the output of the pressure sensor P2, and the bottom of the boom cylinder 7 based on the output of the pressure sensor P3. When it is detected that the pressure in the chamber is equal to or higher than a predetermined value, it is determined that the boom 4 is operating in the downward direction with its own weight, and the control pressure generated when the boom operating lever 50 is operated in the downward direction is the first control pressure. A control current is supplied to the switching valve 55 so as not to be transmitted to the first pilot port of the first-speed boom direction control valve 13R.

  The switching valve 55 is in a second state in which the pilot pressure applied to the first pilot port is released while blocking the control pressure line between the first pilot port of the first speed boom direction control valve 13R and the control pump 52, If there is pressure oil generating pilot pressure at the first pilot port, the pressure oil is discharged to the pressure oil tank 22.

  As a result, the first speed boom direction control valve 13R is in the neutral position by removing the control pressure at the first pilot port (the control pressure generated when the boom operation lever 50 is operated in the downward direction). While shutting off the exchange of pressure oil with the boom cylinder 7, the pressure oil discharged from the hydraulic pump 10R reaches the negative control throttle 20R through the center bypass conduit 30R to reduce the discharge amount of the hydraulic pump 10R. .

  As in the case of FIG. 10, the second speed boom direction control valve 13LA is in the lowering operation position for receiving the control pressure generated when the boom operating lever 50 is operated in the lowering direction and opening the regeneration conduit. The pressure oil flowing out from the bottom chamber 7 is regenerated in the rod chamber of the boom cylinder 7. This is because the first speed boom direction control valve 13R is in the neutral position and the exchange of pressure oil between the boom cylinder 7 and the first speed boom direction control valve 13R is blocked.

  Thus, when the boom 4 is lowered by its own weight, the hydraulic control circuit 200 can reduce the discharge amount of the hydraulic pump 10R and improve the fuel efficiency.

  Even when the main controller 54 lowers the boom 4 by its own weight, when the main controller 54 detects that the pressure in the rod chamber in the boom cylinder 7 is less than a predetermined value based on the output of the pressure sensor P4. It is determined that cavitation may occur, and the supply of the control current to the switching valve 55 is stopped, so that the state shown in FIG. 10 appears. This is because the pressure oil discharged from the hydraulic pump 10R flows into the rod chamber of the boom cylinder 7 so that sufficient pressure oil can be supplied to the rod chamber of the boom cylinder 7.

  Furthermore, in FIG. 12, when the main controller 54 detects that the boom operation lever 50 is operated in the raising direction based on the output of the pressure sensor P1, it determines that the boom operation lever 50 is not operated in the lowering direction. The control current is not supplied to the switching valve 55 so that the control pressure corresponding to the lever operation amount in the lowering direction of the boom control lever 50 can be introduced to the first pilot port of the first speed boom direction control valve 13R at any time. To.

  Therefore, the switching valve 55 is in the first state in which the control pressure generated when the boom operation lever 50 is operated in the downward direction is transmitted to the first pilot port of the first speed boom direction control valve 13R.

  Further, the first speed boom direction control valve 13R is a second pilot port (a pilot port used when raising the boom 4) that generates control pressure when the boom operation lever 50 is operated in the upward direction. The pressure oil discharged from the hydraulic pump 10 </ b> R flows into the bottom chamber of the boom cylinder 7.

  Similarly, the second speed boom direction control valve 13LA receives the control pressure generated when the boom operation lever 50 is operated in the raising direction at a predetermined operation amount or more at its second pilot port, and is in the raising operation position. The pressure oil discharged from the pump 10L is joined to the bottom chamber of the boom cylinder 7.

  Thus, the hydraulic control circuit 200 quickly raises the boom 4 using the pressure oil discharged from both the hydraulic pumps 10L and 10R when the boom operation lever 50 is operated in the upward direction with a predetermined operation amount or more. Can do.

  Thus, the hydraulic control circuit 200 realizes all advantageous effects in the hydraulic control circuit 100, but incorporates the boom lowering control valve into the second-speed boom direction control valve 13LA, so that it can be compared with the hydraulic control circuit 100. This enables a simpler and space-saving design.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, the main controller 54 determines the operation content of the boom 4 including its own weight drop based on the outputs of the various pressure sensors, and the pressure oil in the hydraulic control circuit according to the operation content of the boom 4. However, instead of or in addition to this, the operation content of the arm 5 or the bucket 6 is determined based on the output of the various pressure sensors, and the hydraulic control circuit according to the operation content of the arm 5 or the bucket 6 The flow of pressure oil inside may be optimized.

DESCRIPTION OF SYMBOLS 1 ... Hydraulic excavator 2 ... Lower traveling body 3 ... Upper turning body 4 ... Boom 5 ... Arm 6 ... Bucket 7 ... Boom cylinder 8 ... Arm cylinder 9 ... Bucket cylinder 10L, 10R ... Hydraulic pump 11L ... Left travel motor direction control valve 11R ... Direct travel valve 12L ... Swivel motor direction control valve 12R ... Right travel motor direction control valve 13L, 13LA ... Second speed boom direction control valve 13R ... First speed boom direction control valve 14 ... Bucket direction control valve 15L ... First speed arm direction control valve 15R ... Second speed arm direction control Valves 20L, 20R ... Negative control throttle 22 ... Pressure oil tank 30L, 30R ... Center bypass pipe 31L, 31R ... Parallel pipe 32L 32R ... Negative control pressure line 42L, 42R ... Traveling hydraulic motor 44 ... Turning hydraulic motor 50 ... Boom operating lever 52 ... Control pump 54 ... Main controller 55 ... Switching Valve 56 ... Control valve for boom lowering 100, 200 ... Hydraulic control circuit P1-P4 ... Pressure sensors TH1-TH3 ... Threshold

Claims (6)

Negative control type hydraulic control for construction machinery including a hydraulic pump that increases or decreases the discharge amount according to the control pressure generated by the negative control throttle and a directional control valve that controls the flow of pressure oil circulating in the hydraulic cylinder that operates the boom A circuit,
A boom lowering control valve that has a regeneration conduit that connects the expansion chamber and the reduction chamber of the hydraulic cylinder, and opens the regeneration conduit in response to the boom lowering operation;
Neutral position return means for returning the directional control valve to a neutral position when the pressure in the reduction chamber of the hydraulic cylinder exceeds a predetermined value,
The neutral position return means returns the directional control valve to a neutral position when the boom is lowered by its own weight in response to the boom lowering operation.
A hydraulic control circuit for a construction machine characterized by the above. The neutral position return means is a switching valve arranged in a control pressure line connecting a pilot port of the directional control valve and a control pump for generating a pilot pressure,
The switching valve transmits the pilot pressure to the pilot port in the first state, and cancels the pilot pressure in the pilot port in the second state.
The hydraulic control circuit for a construction machine according to claim 1. The neutral position return means prohibits the return to the neutral position of the direction control valve when the pressure in the expansion chamber of the hydraulic cylinder becomes less than a predetermined value;
The hydraulic control circuit for construction machine according to claim 1 or 2, characterized in that. The direction control valve and the boom lowering control valve are disposed inside a valve unit,
The hydraulic control circuit for a construction machine according to any one of claims 1 to 3, wherein the hydraulic control circuit is for a construction machine. The boom lowering control valve is arranged in series with the direction control valve.
The hydraulic control circuit for a construction machine according to claim 4. The direction control valve includes a first speed boom direction control valve and a second speed boom direction control valve,
The boom lowering control valve is incorporated in the second speed boom direction control valve,
The hydraulic control circuit for a construction machine according to claim 4.