JP2014163464A - Hydraulic circuit and construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress damage of low-pressure specification equipment without blowing out oil outside a pipeline even in a case where a joint is in a non-connection state.SOLUTION: A return side joint 43 automatically opens in a connection state, and automatically closes in a non-connection state. Setting pressure forced restriction means 70 restricts an initial value of setting pressure of multistep relief valve 61 to low-side setting pressure (P61L). When a predetermined condition is satisfied, the setting pressure forced restriction means 70 releases the setting pressure of the multistep relief valve 61 to high-side setting pressure (P61H). In the predetermined condition, it is included that pressure detection means 81 detects pressure less than a threshold pressure value (Pset).

Description

  The present invention relates to a hydraulic circuit including a joint and a construction machine.

  Conventionally, there is a hydraulic circuit for driving an actuator (for example, Patent Documents 1 and 2). The hydraulic circuits described in Patent Documents 1 and 2 are configured to be split by a joint. This hydraulic circuit is mounted on, for example, a large construction machine that is disassembled and assembled.

  FIG. 6 shows a conventional hydraulic circuit 120. In the hydraulic circuit 120, if the return side joint 143 is forgotten to be connected, the return side oil passage 153 and the port to which the return side oil passage 153 is connected (low pressure specification device 155) may be damaged. The details of this problem are as follows. In a state where the supply side joint 141 is connected (connected state) and a state where the return side joint 143 is not connected (non-connected state), the oil discharged from the pump 125 passes through the neutral control valve 130. After passing, you lose your destination. As a result, the pressure in the return side oil passage 153 increases to the set pressure of the relief valve 161. The set pressure of the relief valve 161 is normally set to a pressure near the maximum specification value of the discharge pressure of the pump 125. On the other hand, the low-pressure specification device 155 normally does not have a strength that can withstand the hydraulic pressure of the set pressure of the relief valve 161. The reason is that when the return side joint 143 is correctly connected, the low-pressure specification device 155 requires only about the hydraulic pressure of the tank 123 (about atmospheric pressure), so it is not necessary to have the strength to withstand the hydraulic pressure. If the hydraulic pressure applied to the low pressure specification device 155 increases to the set pressure of the relief valve 161, the low pressure specification device 155 may be damaged.

  Patent Documents 1 and 2 describe techniques for suppressing problems caused by forgetting to connect a joint. Patent Document 1 (see [Configuration] in the abstract) states that “Only when the pressure in the drain pipe is above a certain level, the drive of the hydraulic motor (14) is forcibly stopped or a warning is given to the outside. It is described. In Patent Document 2 (see abstract), “the hydraulic motor is immediately stopped by the rise of drain pressure” (see [Problem]), “When the drain pressure reaches a predetermined value (P0), the hydraulic switching valve (8 ) Is switched to position a, and the drive of the hydraulic motor (2) is stopped "(see [Solution means]).

  Conventionally, there are joints with a relief function. This relief function is a function that blows out the oil in the pipe from the joint to the outside of the pipe when a predetermined pressure is applied to the pipe when the joint is in a disconnected state.

JP-A-8-282978 Japanese Patent Laid-Open No. 2002-5122

  The techniques described in Patent Documents 1 and 2 detect the pressure in the drain pipe, and stop the hydraulic motor when the pressure reaches a certain value. By applying this technique and configuring a circuit like the hydraulic circuit 220 shown in FIG. 7, it is considered that the low-voltage specification device 155 can be prevented from being damaged. In the hydraulic circuit 220, the pressure of the low-pressure specification device 155 is detected by the pressure detection unit 281. When the pressure reaches a certain value, the pump stop unit 260 stops the pump 125.

  However, the hydraulic circuit 220 has the problem of time lag shown in FIG. The details of this problem are as follows. When the pump 125 is driven when the return side joint 143 shown in FIG. 7 is not connected, the pressure applied to the low-pressure specification device 155 increases as shown in FIG. 8, and this pressure exceeds the threshold value. Is detected by the pressure detection means 281 (see FIG. 7). At the time of this detection, the pump stop means 260 shown in FIG. 7 gives a command for stopping the pump 125. However, as shown in FIG. 8, a time lag occurs between the time of the detection and the actual stop of the pump 125. The discharge pressure of the pump 125 also increases during this time lag. During this time lag, the pressure applied to the low-pressure specification device 155 may exceed the allowable pressure, and thus the low-pressure specification device 155 may be damaged.

  Further, when a joint with a relief function is used for the return side joint 143, oil may blow out of the pipe as described above. Therefore, there is a problem of environmental pollution due to the blown oil, and there is a problem that it is necessary to clean the blown oil. When cleaning is performed, waste of labor, waste of time, waste of materials (waste, cleaning agent, neutralizing agent, etc.), waste of money, and the like occur.

  Therefore, an object of the present invention is to provide a hydraulic circuit and a construction machine that can suppress the breakage of low-pressure specification equipment without oil blowing out of the pipe even when the joint is not connected.

  The hydraulic circuit of the present invention includes a pump that supplies oil to an actuator, a control valve that controls oil flowing from the pump to the actuator, a tank in which oil that has passed through the neutral control valve returns, the pump, A supply side joint provided between the control valve, a return side joint provided between the control valve and the tank, which automatically opens in a connected state and automatically closes in a disconnected state; and A pressure detecting means for detecting a discharge pressure; a multistage relief valve capable of limiting the discharge pressure of the pump to a high side set pressure and a low side set pressure; and a set pressure of the multistage relief valve to the low side set pressure. Set pressure forcing limiting means. A threshold pressure value lower than the low side set pressure is set in the set pressure forcing limit means. The set pressure forced limiting means limits an initial value of the set pressure of the multistage relief valve to the low side set pressure and sets the set pressure of the multistage relief valve to the high side when a predetermined condition is satisfied. Release to pressure. The predetermined condition includes that the pressure detecting means detects a pressure lower than the threshold pressure value.

  With the above configuration, even when the joint is not connected, the oil is not blown out of the pipe, and damage to the low-pressure specification device can be suppressed.

It is the figure which looked at the construction machine from the top. It is a figure which shows the hydraulic circuit 20 with which the construction machine shown in FIG. 1 is provided. FIG. 3 is a block diagram showing a controller 75 and the like of the hydraulic circuit 20 shown in FIG. 2. It is a graph which shows the setting pressure etc. of the multistage relief valve 61 shown in FIG. It is a flowchart of operation | movement of the hydraulic circuit 20 shown in FIG. It is a figure which shows the conventional hydraulic circuit. It is a figure which shows the hydraulic circuit which applied the prior art. It is a graph which shows the time lag etc. in the hydraulic circuit shown in FIG.

  The construction machine 1 will be described with reference to FIGS.

  The construction machine 1 (see FIG. 1) is in a disassembled state during transportation and storage, and is in an assembled state during work. The construction machine 1 is a crane, for example, and is a mobile crane, for example. The construction machine 1 includes a first divided body 11, a second divided body 12, and a hydraulic circuit 20.

  The first divided body 11 is mounted with a hydraulic power source (a pump 25 and the like described later) that is a “part” (described later) of the hydraulic circuit 20.

  A “other part” (described later) different from the “part” of the hydraulic circuit 20 is mounted on the second divided body 12. The second divided body 12 is connected (fixed) to the first divided body 11 when the construction machine 1 is in the assembled state. The second divided body 12 is divided with respect to the first divided body 11 when the construction machine 1 is in a disassembled state. The second divided body 12 is, for example, a main turning frame of the construction machine 1.

  As shown in FIG. 2, the hydraulic circuit 20 is a circuit for driving an actuator 27 (described later). The hydraulic circuit 20 includes an engine 21, a tank 23, a pump 25, an actuator 27, a control valve 30, joints 41 and 43, a supply-side oil passage 51, and a return-side oil passage 53. Furthermore, the hydraulic circuit 20 includes pressure limiting means 61 to 75 and detection means 81 to 87 (see FIG. 3).

  The engine 21 is a drive source for the pump 25.

  The tank 23 is a hydraulic oil tank that supplies oil to the pump 25. The oil that has passed through the actuator 27 and the control valve 30 is returned to the tank 23.

  The pump 25 is a hydraulic pump that supplies oil to the actuator 27.

  The actuator 27 operates the construction machine 1 (see FIG. 1). The actuator 27 is a hydraulic actuator that is driven when oil is supplied from the pump 25. The actuator 27 is, for example, a hydraulic motor, and is, for example, a hydraulic cylinder. The actuator 27 performs, for example, hoisting of a hoisting member (not shown) such as a boom attached to the second divided body 12 shown in FIG. 1, turning of the second divided body 12 with respect to the lower traveling body (not shown), and the like.

  As shown in FIG. 2, the control valve 30 controls the oil flowing from the pump 25 to the actuator 27 (the flow rate and direction of the oil). The control valve 30 is provided between the pump 25 and the actuator 27. Here, “between” means oil passages between the same (hereinafter the same). The control valve 30 includes, for example, a control port 30 a connected to the actuator 27, a return port 30 c and a tank port 30 t respectively connected to the tank 23, and a supply port 30 p connected to the pump 25. The control valve 30 is a three-position direction switching valve having three switching positions, for example. There are two drive positions 31 and a neutral position 33 at the switching position of the control valve 30.

  The drive position 31 is a switching position for supplying oil from the pump 25 to the actuator 27.

  The neutral position 33 is a switching position for returning (passing) oil from the pump 25 to the tank 23 without supplying oil from the pump 25 to the actuator 27. The neutral position 33 allows the supply port 30p and the return port 30c to communicate with each other. The neutral position 33 closes (closes) the control port 30a and the tank port 30t. When the switching position of the control valve 30 is the neutral position 33, it is assumed that the control valve 30 is in the “neutral state”.

  The joints 41 and 43 detachably connect the pipes. The joints 41 and 43 are, for example, quick joints (joints that can be attached and detached without using a special tool, quick couplers), and are, for example, one-touch quick joints (a screw type or the like may be used). The joints 41 and 43 are of an automatic opening / closing type. That is, the joints 41 and 43 automatically open in the connected state and automatically close (close) in the disconnected state. Due to this closure, oil does not flow out of the pipe when the pipes are separated. The joints 41 and 43 include a supply side joint 41 and a return side joint 43. The supply side joint 41 is provided between the pump 25 and the control valve 30. The return side joint 43 is provided between the control valve 30 (return port 30c, tank port 30t) and the tank 23. The joints 41 and 43 may not be quick joints, and the supply-side joint 41 may not be an automatic opening / closing type.

  The supply-side oil passage 51 is an oil passage that connects the pump 25 and the control valve 30. Of the supply side oil passage 51, a portion between the pump 25 and the supply side joint 41 is an oil passage 51 o. Of the supply-side oil passage 51, a portion between the supply-side joint 41 and the control valve 30 is defined as an oil passage 51p.

  The return-side oil passage 53 is an oil passage through which oil that passes through the neutral control valve 30 and returns to the tank 23 flows. The return side oil passage 53 is an oil passage connecting the return port 30 c and the tank port 30 t of the control valve 30 and the tank 23. Of the return side oil passage 53, a portion between the return port 30 c and the return side joint 43 is defined as an oil passage 53 c. Of the return side oil passage 53, a portion between the tank port 30 t and the return side joint 43 is defined as an oil passage 53 t. Of the return side oil passage 53, a portion between the return side joint 43 and the tank 23 is defined as an oil passage 53u.

  The low-voltage specification device 55 will be described. A device that connects the control valve 30 (return port 30c, tank port 30t) and the tank 23 when the control valve 30 is in a neutral state is referred to as a low-pressure specification device 55. The low-pressure specification device 55 includes a return port 30c, a tank port 30t, a return side joint 43, an oil passage 53c, an oil passage 53t, and an oil passage 53u. When the joints 41 and 43 are correctly connected, a pressure of about several tens [kg / square centimeter] acts on the low-pressure specification device 55, for example. In order to reduce the cost and weight of the low-pressure specification device 55, the allowable pressure (strength) of the low-pressure specification device 55 is normally kept to the minimum necessary.

  The pressure limiting means 61 to 75 are means (pressure limiting device, damage preventing device) for suppressing the damage of the low pressure specification device 55. The pressure limiting means 61 to 75 include a multistage relief valve 61, a pilot line 63, and a set pressure forced limiting means 70.

  The multistage relief valve 61 limits the discharge pressure of the pump 25 to a set pressure that will be described later. The multistage relief valve 61 limits the pressure in the supply side oil passage 51. The multistage relief valve 61 limits the pressure in the oil passage 51o. As shown in FIG. 4, the set pressure of the multistage relief valve 61 includes a high side set pressure P61H and a low side set pressure P61L (the set pressure may be 3 or more). FIG. 4 is a graph showing the relationship between the discharge flow rate of the pump 25 and the discharge pressure. FIG. 4 shows the high side set pressure P61H and the low side set pressure P61L as override characteristics (refer to FIG. 4 for the high side set pressure P61H and the low side set pressure P61L hereinafter). The set pressure of the multistage relief valve 61 shown in FIG. 2 changes according to the pilot pressure input to the multistage relief valve 61.

  The high-side set pressure P61H of the multistage relief valve 61 is set so that the capacity of the pump 25 can be fully exhibited (can be used up). The high side set pressure P61H is set, for example, to a pressure close to the maximum specification value of the discharge pressure of the pump 25, and is set to about 300 to 350 [kg / square centimeter], for example. As shown in FIG. 4, the high side set pressure P61H is set higher than the allowable pressure of the low pressure specification device 55.

  The low side set pressure P61L of the multistage relief valve 61 is set lower than the high side set pressure P61H. The low-side set pressure P61L is set lower than the allowable pressure of the low-pressure specification device 55, and is set to several tens [kg / square centimeter], for example.

  The pilot line 63 supplies pilot pressure to the multistage relief valve 61 as shown in FIG. The pilot line 63 connects the pilot port of the multistage relief valve 61 and the tank 23.

  The set pressure forced limiting means 70 is a means for forcibly limiting the set pressure of the multistage relief valve 61 to the low side set pressure P61L (see FIG. 4). The set pressure forced limiting means 70 includes a switching valve 71, a low side set pressure setting valve 73, and a controller 75.

  The switching valve 71 is a valve for switching the set pressure of the multistage relief valve 61 between a low side set pressure P61L and a high side set pressure P61H. The switching valve 71 is provided in the pilot line 63 and switches the pilot pressure acting on the multistage relief valve 61. The switching valve 71 is an electromagnetic switching valve (solenoid valve) that is switched between open and closed by electromagnetic force. The switching valve 71 is closed when in the excited state, and as a result, the set pressure of the multistage relief valve 61 is set to the high side set pressure P61H. When the switching valve 71 is in the non-excited state, the switching valve 71 is opened. As a result, the set pressure of the multistage relief valve 61 is set to the low side set pressure P61L.

  The low side set pressure setting valve 73 is a valve for setting the low side set pressure P61L of the multistage relief valve 61. The low-side set pressure setting valve 73 is a valve for setting a pilot pressure that acts on the multistage relief valve 61 when the switching valve 71 is in the open state. The low side set pressure setting valve 73 is provided in the pilot line 63 on the downstream side (tank 23 side) of the switching valve 71.

  The controller 75 determines whether or not to limit the set pressure of the multistage relief valve 61 to the low side set pressure P61L (described later). The controller 75 switches the setting pressure of the multistage relief valve 61 by switching the switching valve 71. The controller 75 switches the switching valve 71 between an excited state and a non-excited state. In the controller 75, a threshold pressure value Pset shown in FIG. The threshold pressure value Pset is set lower than the low side set pressure P61L. The threshold pressure value Pset is set higher than the maximum neutral pressure Pn. The maximum neutral pressure Pn is a maximum value of pressure loss in the supply side oil passage 51 and the return side oil passage 53 (pressure loss when the discharge flow rate of the pump 25 is, for example, a specification maximum value).

  As shown in FIG. 2, the detection means 81 to 87 include a pressure detection means 81, a discharge state detection means 83, a neutral state detection means 85, and a temperature detection means 87. Each of the detection means 81 to 87 is connected to the controller 75.

  The pressure detector 81 detects the discharge pressure of the pump 25. The pressure detection means 81 detects the pressure of the supply side oil passage 51 (the pressure of the oil passage 53t or the oil passage 53c may be detected). The pressure detection means 81 detects the pressure in the oil passage 51o (the pressure in the oil passage 51p may be detected). The pressure detection means 81 is, for example, a pressure sensor, and may be, for example, a pressure switch.

  The discharge state detection means 83 detects the discharge state of the pump 25 (whether or not oil is being discharged). The discharge state detection means 83 detects the discharge state of the pump 25 indirectly, for example, detects the rotation speed of the engine 21 that is a drive source of the hydraulic pump 25. The discharge state detection unit 83 may directly detect the discharge state of the pump 25, and may be, for example, a flow rate detection unit (not shown) that detects the flow rate of the supply side oil passage 51.

  The neutral state detection means 85 detects the state (which switching position) of the control valve 30 is. The neutral state detection means 85 detects, for example, a signal for switching the switching position of the control valve 30 (such as a pilot pressure or an electric signal (not shown)).

  The temperature detecting means 87 detects the temperature of the oil discharged from the pump 25. The temperature detection means 87 detects the oil temperature of the supply side oil passage 51 (the oil temperature of the oil passage 53t or the oil passage 53c may be detected). The temperature detecting means 87 detects the oil temperature of the oil passage 51o (the oil temperature of the oil passage 51p may be detected).

(Arrangement of each component to the 1st division body 11 and the 2nd division body 12)
As shown in FIG. 1, the hydraulic circuit 20 is mounted on the first divided body 11 and the second divided body 12 (divided). The reason why the hydraulic circuit 20 is divided is that the first divided body 11 and the second divided body 12 in the assembled state exceed the limit values of weight limit and dimensional limit during public road transportation.

  The pump 25 is mounted on the first divided body 11, and the control valve 30 is mounted on the second divided body 12. The reason why the position where the pipe (the supply side oil passage 51 and the return side oil passage 53) is divided is not between the control valve 30 and the actuator 27 but between the pump 25 and the control valve 30 is, for example, Street. In order to prevent the operation delay of the actuator 27 with respect to the operation of the control valve 30, the piping distance between the control valve 30 and the actuator 27 may be shortened as much as possible. In this case, the control valve 30 is mounted on the second divided body 12 on which the actuator 27 is mounted. Then, piping must be divided between the pump 25 mounted on the first divided body 11 and the control valve 30.

  When the first divided body 11 and the second divided body 12 are divided, the components of the hydraulic circuit 20 are arranged so that the electric wires and pipes connecting the components of the hydraulic circuit 20 are not divided as much as possible. Is preferred. Specifically, as shown in FIG. 2, the pressure detection means 81, the multistage relief valve 61, and the set pressure forcible restriction means 70 are only in one of the first divided body 11 and the second divided body 12 (the same (For example, only on the first divided body 11). Furthermore, it is preferable that the discharge state detection means 83 and the temperature detection means 87 (at least one, preferably both) are mounted on the same divided body (for example, the first divided body 11) as the set pressure forced limiting means 70 and the like.

  Specifically, for example, the first divided body 11 includes an engine 21, a tank 23, a pump 25, a multistage relief valve 61, a pilot line 63, a set pressure forcing limit means 70, and a pressure detection means 81. The discharge state detecting means 83 and the temperature detecting means 87 are mounted. For example, the actuator 27, the control valve 30, and the neutral state detection means 85 are mounted on the second divided body 12.

(Operation)
The operation (steps S1 to S8) of the hydraulic circuit 20 (see FIG. 2) will be described with reference to FIG. Hereinafter, each component of the hydraulic circuit 20 described above will be described with reference to FIG.

  In step S1, the set pressure forced limiting means 70 limits the initial value of the set pressure of the multistage relief valve 61 to the low side set pressure P61L (see FIG. 4). The “initial value” is a value at the start of control. The control start time is, for example, when a power switch (such as a key switch (not shown)) of the construction machine 1 (see FIG. 1) is turned on (or just after that). At the start of control, the engine 21 is not started or is in the process of starting the engine 21. Specifically, when the controller 75 puts the switching valve 71 in a non-excited state, the switching valve 71 is opened, and as a result, the set pressure of the multistage relief valve 61 becomes the low side set pressure P61L.

  In step S2, it is determined whether or not the discharge state detecting means 83 detects that the pump 25 is discharging oil. This determination is performed in order to prevent [Error determination 2] described later. This determination is made by the controller 75 (the same applies to the following determinations). Specifically, for example, it is detected whether the rotational speed of the engine 21 is equal to or higher than a predetermined rotational speed. The “predetermined rotational speed” is, for example, the lowest rotational speed among the set values of the rotational speed of the engine 21. When pump 25 is discharging oil (in the case of YES), it progresses to Step S3. When pump 25 is not discharging oil (in the case of NO), it returns to Step S2.

  In step S3, it is determined whether or not the neutral state detecting means 85 detects that the control valve 30 (C / V) is in the neutral state. This determination is performed in order to prevent [Error determination 3] described later. If the control valve 30 is in the neutral position (YES), the process proceeds to step S4. If the control valve 30 is not in the neutral position (NO), the process returns to step S2.

  In step S4, it is determined whether or not the temperature detecting means 87 has detected that the temperature of the oil discharged from the pump 25 (oil temperature) is equal to or higher than a predetermined temperature. This determination is performed in order to prevent [Error Judgment 4] described later, and the “predetermined temperature” is set so as to prevent this [Error Determination 4]. More specifically, the maximum neutral pressure Pn shown in FIG. 4 increases as the oil temperature decreases. For example, the temperature at which the maximum neutral pressure Pn is less than the threshold pressure value Pset is defined as the “predetermined temperature”. As shown in FIG. 5, when the temperature of the discharged oil of the pump 25 is equal to or higher than a predetermined temperature (in the case of YES), the process proceeds to step S5. When the temperature is lower than the predetermined temperature (in the case of NO), the process returns to step S2.

  In step S <b> 5, the discharge pressure of the pump 25 is detected by the pressure detection means 81. The detected discharge pressure is set as a detection pressure P81.

  In step S6, it is determined whether or not the pressure detecting means 81 has detected a pressure lower than the threshold pressure value Pset of the set pressure forcing limiting means 70 (whether or not the detected pressure P81 <the threshold pressure value Pset is determined). ) When the detected pressure P81 ≧ the threshold pressure value Pset (in the case of NO), the controller 75 determines that the return side joint 43 is in a disconnected state, and proceeds to step S7. When the detected pressure P81 <the threshold pressure value Pset (in the case of YES), the controller 75 determines that the return side joint 43 is in the connected state, and proceeds to step S8. The detected pressure P81 used for the determination is, for example, an average value of the detected pressure P81 detected a plurality of times (or for a certain time). This is to prevent the above determination from being made on the basis of an instantaneous surge pressure at which damage to the low-voltage specification device 55 does not become a problem or electrical signal noise.

  In step S7, the controller 75 issues an alarm. For example, the controller 75 outputs a signal for performing an alarm to alarm means (not shown). The alarm is sound, light, text, or a combination of these as appropriate. The content of the alarm informs the operator that the return side joint 43 is not connected (or that there is a possibility). The alarm is, for example, an indication “Please check the connection of piping”. Next, the process returns to step S2.

  In step S8, the set pressure of the multistage relief valve 61 is released to the high side set pressure P61H (see FIG. 4). Specifically, when the controller 75 energizes the switching valve 71, the switching valve 71 is closed, and as a result, the set pressure of the multistage relief valve 61 becomes the high-side set pressure P61H.

(Effect 1)
Next, the effect of the hydraulic circuit 20 shown in FIG. 2 will be described. The hydraulic circuit 20 includes a pump 25 that supplies oil to the actuator 27, a control valve 30 that controls oil flowing from the pump 25 to the actuator 27, a tank 23 that returns the oil that has passed through the neutral control valve 30, and a pump 25. A supply side joint 41 provided between the control valve 30 and the control valve 30; a return side joint 43 provided between the control valve 30 and the tank 23; a pressure detecting means 81 for detecting the discharge pressure of the pump 25; Multi-stage relief valve 61 capable of restricting the discharge pressure of the multi-stage relief valve to the high side set pressure P61H (see FIG. 4) and the low side set pressure P61L (see FIG. 4), and the set pressure of the multistage relief valve 61 to the low side set pressure P61L And a set pressure forcible limiting means 70. As shown in FIG. 4, a threshold pressure value Pset lower than the low-side set pressure P61L is set in the set pressure forcing limit means 70.
[Configuration 1-1] The set pressure forced limiting means 70 shown in FIG. 2 limits the initial value of the set pressure of the multistage relief valve 61 to the low side set pressure P61L (S1 in FIG. 5).
[Configuration 1-2] The set pressure forced limiting means 70 releases the set pressure of the multistage relief valve 61 to the high side set pressure P61H when the “predetermined condition” is satisfied (S8 in FIG. 5).
[Configuration 1-3] The “predetermined condition” includes that the pressure detection means 81 detects a pressure lower than the threshold pressure value Pset (S6 in FIG. 5).
[Configuration 1-4] The return side joint 43 automatically opens in the connected state and automatically closes in the disconnected state.

  By the above [Configuration 1-1] to [Configuration 1-3], the discharge pressure of the pump 25 is limited to the low-side set pressure P61L from the initial state until the condition of the above [Configuration 1-3] is satisfied ( Limit is maintained). Therefore, when the low-side set pressure P61L is set to be smaller than the allowable pressure of the low-pressure specification device 55 (excluding the oil passage 53u; the same applies hereinafter), damage to the low-pressure specification device 55 can be suppressed.

  In the above [Configuration 1-1], the “initial value” of the set pressure of the multistage relief valve 61 is the low-side set pressure P61L. Therefore, the above-described time lag problem (see FIG. 8) does not occur. Therefore, damage to the low-voltage specification device 55 can be suppressed.

  With the above [Configuration 1-4], even when the return side joint 43 is not connected, the oil does not blow out of the pipe.

(Effect 2)
The hydraulic circuit 20 includes discharge state detection means 83 that detects the discharge state of the pump 25.
[Configuration 2] In the “predetermined condition” (see [Configuration 1-2]), the discharge state detection means 83 detects that the pump 25 is discharging oil (YES in S2 of FIG. 5). It is included.

With the above [Configuration 2], the following [Error determination 2] can be prevented.
[Error determination 2] It is assumed that the condition of [Configuration 2] is not included in the “predetermined condition”. When the pump 25 is not discharging oil, the pressure detector 81 may detect a pressure (detected pressure P81) that is less than the threshold pressure value Pset. In this case, the condition of [Configuration 1-3] is satisfied even though the return side joint 43 is not connected (YES in S6 of FIG. 5). That is, it is erroneously determined that the return side joint 43 is in a connected state even though it is in a disconnected state. As a result, the set pressure of the multistage relief valve 61 is released to the high side set pressure P61H (S8 in FIG. 5).

(Effect 3)
The hydraulic circuit 20 includes neutral state detection means 85 that detects the state of the control valve 30.
[Configuration 3] In the “predetermined condition” (see [Configuration 1-2]), the neutral state detection means 85 detects that the control valve 30 is in the neutral state (YES in S3 of FIG. 5). Is included.

With the above [Configuration 3], the following [Error Determination 3] can be prevented.
[Error determination 3] It is assumed that the condition of [Configuration 3] is not included in the “predetermined condition”. When the control valve 30 is not in a neutral state, oil flows from the pump 25 to the actuator 27. When the discharge flow rate of the pump 25 exceeds the flow rate that can be relieved by the multistage relief valve 61, the discharge pressure of the pump 25 increases. As a result, the detected pressure P81 may be equal to or higher than the threshold pressure value Pset (NO in S6 of FIG. 5) even though the return side joint 43 is in the connected state. That is, it is erroneously determined that the return side joint 43 is not connected even though the return side joint 43 is in the connected state.

(Effect 4)
The hydraulic circuit 20 includes temperature detection means 87 that detects the temperature of the oil discharged from the pump 25.
[Configuration 4] In the “predetermined condition” (see [Configuration 1-2]), the temperature detecting means 87 detects that the temperature of the oil discharged from the pump 25 is equal to or higher than the predetermined temperature (S4 in FIG. 5). Yes)

With the above [Configuration 4], the following [Error determination 4] can be prevented.
[Error determination 4] It is assumed that the condition of [Configuration 4] is not included in the “predetermined condition”. The lower the temperature of the discharge oil of the pump 25 (the higher the viscosity of the discharge oil), the higher the pressure loss in the oil passage (supply side oil passage 51 and return side oil passage 53), and the higher the discharge pressure of the pump 25. Become. Therefore, the detected pressure P81 may be equal to or higher than the threshold pressure value Pset (NO in S6 in FIG. 5) even though the return side joint 43 is in the connected state. That is, it is erroneously determined that the return side joint 43 is not connected even though the return side joint 43 is in the connected state.

(Effect 5)
Next, effects of the construction machine 1 shown in FIG. 1 will be described. The construction machine 1 includes a hydraulic circuit 20, a first divided body 11 on which a part of the hydraulic circuit 20 is mounted, and other parts different from the “part” of the hydraulic circuit 20 mounted on the first divided body 11. 2nd division body 12 connected.
[Configuration 5] As shown in FIG. 2, the pressure detecting means 81, the multistage relief valve 61, and the set pressure forcing limiting means 70 are mounted on only one of the first divided body 11 and the second divided body 12. .

  According to the above [Configuration 5], when the first divided body 11 and the second divided body 12 are assembled, the pressure detecting means 81, the multistage relief valve 61, and the set pressure forcing limiting means 70 are connected to each other (the electric wire or the pilot line 63). Connection). Therefore, forgetting this connection can be prevented. In the hydraulic circuit 220 shown in FIG. 7 (application of the prior art), the pressure detection means 281 for detecting the pressure of the low-pressure specification device 155 and the pump stop means 260 are mounted on separate divided bodies. There is a risk of forgetting (refer to the part of reference A).

(Modification)
The above embodiment can be variously modified. For example, in the flowchart shown in FIG. 5, the process proceeds to step S8 only when all the conditions of steps S2, S3, S4, and S6 are satisfied. However, the condition for proceeding to step S8 may include only a part of steps S2, S3, and S4, for example, and may not include any of steps S2, S3, and S4, for example.

DESCRIPTION OF SYMBOLS 1 Construction machine 11 1st division body 12 2nd division body 20 Hydraulic circuit 23 Tank 25 Pump 27 Actuator 30 Control valve 41 Supply side joint 43 Return side joint 61 Multistage relief valve 70 Set pressure forced restriction means 81 Pressure detection means 83 Discharge state Detection means 85 Neutral state detection means 87 Temperature detection means P61H High side set pressure P61L Low side set pressure Pset Threshold pressure value

Claims (5)

A pump that supplies oil to the actuator;
A control valve for controlling oil flowing from the pump to the actuator;
A tank to which the oil that has passed through the neutral control valve returns;
A supply-side joint provided between the pump and the control valve;
A return side joint provided between the control valve and the tank, which automatically opens in a connected state and automatically closes in a disconnected state;
Pressure detecting means for detecting the discharge pressure of the pump;
A multistage relief valve capable of limiting the discharge pressure of the pump to a high-side set pressure and a low-side set pressure;
A set pressure forcing limiting means for limiting the set pressure of the multistage relief valve to the low side set pressure;
With
In the set pressure forced limiting means, a threshold pressure value lower than the low side set pressure is set,
The set pressure forced limiting means limits an initial value of the set pressure of the multistage relief valve to the low side set pressure and sets the set pressure of the multistage relief valve to the high side when a predetermined condition is satisfied. Release to pressure,
The predetermined condition includes that the pressure detecting means detects a pressure less than the threshold pressure value.
Hydraulic circuit. A discharge state detecting means for detecting a discharge state of the pump;
The predetermined condition includes that the discharge state detecting means detects that the pump is discharging oil.
The hydraulic circuit according to claim 1. A neutral state detecting means for detecting the state of the control valve;
The predetermined condition includes that the neutral state detecting means detects that the control valve is in the neutral state.
The hydraulic circuit according to claim 1. Comprising temperature detecting means for detecting the temperature of the oil discharged from the pump;
The predetermined condition includes the temperature detecting means detecting that the temperature of the oil discharged from the pump is equal to or higher than a predetermined temperature.
The hydraulic circuit in any one of Claims 1-3. A hydraulic circuit according to any one of claims 1 to 4;
A first divided body on which a part of the hydraulic circuit is mounted;
A second part that is mounted with another part different from the part of the hydraulic circuit and is connected to the first part;
With
The pressure detection means, the multistage relief valve, and the set pressure forcing limit means are mounted only on one of the first divided body and the second divided body.
Construction machinery.

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