JP5536421B2 - Hydraulic circuit of work machine - Google Patents

Description

  The present invention relates to a hydraulic circuit of a work machine such as a hydraulic excavator.

  FIG. 3 is a diagram illustrating an example of a basic hydraulic circuit in a conventional hydraulic excavator. In the hydraulic circuit 100, the engine 102 and the hydraulic pump 104 are directly connected. Then, the operation lever 108A of the operation lever device 108 is operated to switch the switching valve 106, and pressure oil is supplied from the hydraulic pump 104 to the hydraulic actuator 110 via the center bypass oil passage 112 to drive the hydraulic actuator 110.

  The regulator 114 is connected to the center bypass oil passage 112 via the oil passage 116, and the hydraulic pump 104 decreases the discharge amount as the discharge pressure of the hydraulic pump 104 increases. More specifically, the regulator 114 is a constant horsepower curve (discharge pressure P when the horsepower is constant) in FIG. 4A showing the relationship between the discharge pressure P and the discharge amount Q of the hydraulic pump 104 (pump PQ characteristics). The discharge amount of the hydraulic pump 104 is changed by the load pressure (discharge pressure) so as to follow the curve C1 indicating the relationship between the discharge amount Q and the discharge amount Q.

  As a result, the pump torque of the hydraulic pump 104 (hereinafter sometimes referred to as output torque) is constant (Tmax) and is equal to or less than the rated torque T0 (FIG. 4B) of the engine 102, so that the engine rotation is stable, Actual work using a hydraulic excavator can also be performed in a stable state.

  However, there are various types of work performed by the hydraulic excavator. When the operation lever 108A is suddenly operated, or when the hardness of the excavation target suddenly changes during the excavation work (for example, the bucket becomes rock or tree root during the excavation work). The discharge pressure of the hydraulic pump 104 may suddenly rise (for example, the discharge pressure suddenly rises from P0 to P1 in FIG. 4A).

  At this time, the regulator 114 attempts to lower the discharge amount of the hydraulic pump 104 to Q1, but since the rate of increase in load pressure (discharge pressure) is much faster, the discharge amount decrease curve is shown in FIG. In FIG. 4, a curve C2 indicated by a two-dot chain line is obtained, and a pump torque curve is indicated by a curve C3 indicated by a one-dot chain line in FIG. As a result, since the output torque of the hydraulic pump 104 temporarily rises to T1, the engine 102 tries to suspend the engine torque on the output torque T1 of the hydraulic pump 104, and the rotational speed is increased as shown in FIG. Decrease to N1. As a result, the work speed temporarily decreases. Furthermore, when returning the rotational speed of the engine 102 to the initial rotational speed N0, it is necessary to inject more fuel, which causes a deterioration in fuel consumption.

  On the other hand, for example, Patent Document 1 shows an example in which pump torque is controlled during sudden operation of the operation lever or when the hardness of the object to be excavated is changed to reduce fluctuations in engine rotation speed to improve fuel efficiency. An engine control device for a construction machine is known. As shown in FIG. 5, the engine control device 120 is operated by a main pump 124 driven by the engine 122, an electromagnetic proportional valve (regulator) 126 that controls the torque of the main pump 124, and a remote control valve 130. A control valve 128 for controlling the supply and distribution of pressure oil to the hydraulic actuator, a pressure switch (pressure sensor) 134 provided in a pilot oil passage 132 of the control valve 128, the pressure switch 134, the electromagnetic proportional valve 126 and the engine control And a controller 138 connected to each of the actuators 136. The engine control device 120 sets the main pump 124 to a predetermined low torque when not being operated, and sets the set torque of the main pump 124 to a predetermined time T for a predetermined time T when the start of operation of the hydraulic actuator is detected by the pressure switch 134. By changing from low torque to high torque, a rapid decrease in engine speed at the start of hydraulic actuator operation is prevented, and fuel consumption and exhaust gas deterioration are prevented.

  That is, since the main pump 124 is set to a predetermined low torque t1 at the start of operation of the hydraulic actuator, the rated torque T0 of the engine 122 cannot be reached even if the operating lever 130A is suddenly operated to increase the torque. In addition, the rotational speed of the engine 122 does not decrease, there is no supply of a large amount of fuel in the conventional example, and neither fuel consumption nor exhaust gas deterioration occurs. In addition, after a predetermined time T has elapsed, the current of the electromagnetic proportional valve 126 becomes a predetermined large current i2, thereby setting the main pump 124 at a high torque t2, and thus the operation of the hydraulic actuator can be performed smoothly.

JP 2001-271777 A

  However, when a signal that changes from a predetermined small current i1 to a predetermined large current i2 is input from the controller 138 to the electromagnetic proportional valve 126 at a predetermined time T, the tilt of the main pump 124 is not changed after the signal is input to the electromagnetic proportional valve 126. Since there is a delay in response until the discharge angle and torque are increased or decreased by changing the turning angle, the pump torque may not become the high torque t2 in the predetermined time T, and the current value is changed to a predetermined small current during the predetermined time T. There is a problem in that optimal control cannot be performed because only i1 is changed proportionally to a predetermined large current i2.

  The present invention has been made in view of such a problem, and while maintaining the hydraulic pump at high torque, it is possible to prevent torque over and reduce fluctuations in engine rotation speed to reduce fuel consumption. It is an object to provide a hydraulic circuit for a work machine.

  The present invention includes a variable displacement hydraulic pump driven by an engine, a discharge amount control means for reducing the discharge amount in accordance with an increase in the discharge pressure of the hydraulic pump and maintaining the output torque of the hydraulic pump substantially constant, In the hydraulic circuit of the working machine having the above, a discharge pressure sudden rise advance detection means for detecting in advance a sudden rise in the discharge pressure of the hydraulic pump, and a degree to which the rotational driving force of the engine is transmitted to the engine auxiliary equipment A rotational driving force transmission control means for controlling, and when it is determined in advance that the discharge pressure of the hydraulic pump suddenly increases, the rotational driving force transmitted to the auxiliary devices of the engine is reduced, thereby reducing the problem. It has been solved.

  In the present invention, it is provided with a rotational driving force transmission control means for controlling the degree to which the rotational driving force of the engine is transmitted to the engine accessories, and when it is determined in advance that the discharge pressure of the variable displacement hydraulic pump suddenly rises, Reduces rotational driving force transmitted to engine auxiliary equipment. Therefore, in the present invention, the engine torque (rated torque) that the engine can input to the hydraulic pump increases before the discharge pressure of the variable displacement hydraulic pump suddenly rises, and the output torque of the hydraulic pump exceeds the rated torque of the engine. Thus, torque over is prevented.

  Therefore, in the present invention, even when the hardness of the object to be excavated changes suddenly during excavation work (for example, when the bucket comes into contact with rocks or tree roots during excavation work), the work speed is not reduced. And the engine speed can be maintained at the initial speed, eliminating the need to inject more fuel and return the engine speed to the initial speed. This is also advantageous in terms of fuel consumption. In the present invention, since it is determined in advance whether or not the discharge pressure of the variable displacement hydraulic pump suddenly increases, feedforward control is possible, the rated torque can be increased at an earlier timing, and torque over Can be prevented more reliably.

  The hydraulic circuit further includes a switching valve for switching the direction and flow rate of the pressure oil that drives the hydraulic actuator of the work machine, and an operation lever that operates the switching valve, and the discharge pressure suddenly rising prior detection When the means includes an operation amount detection means for detecting the operation amount of the operation lever, when the operation speed or the operation amount of the operation lever exceeds a predetermined threshold value, the discharge pressure of the hydraulic pump suddenly increases in advance. Can be judged.

  The hydraulic circuit further includes a switching valve for switching the direction and flow rate of the pressure oil that drives the hydraulic actuator of the work machine, and a pilot pressure supply means for supplying a pilot pressure to the switching valve. When the pilot pressure detecting means for detecting the pilot pressure is included in the discharge pressure rapid increase pre-detecting means, when the pilot pressure rising speed or the pilot pressure exceeds a predetermined threshold value, the discharge of the hydraulic pump It can be determined in advance if the pressure rises rapidly.

  Further, when there are a plurality of auxiliary devices of the engine, when it is determined in advance that the discharge pressure of the hydraulic pump suddenly increases, power transmission between at least one of the plurality of auxiliary devices and the engine May be blocked by the rotational driving force transmission control means.

  Another aspect of the present invention is a variable displacement hydraulic pump driven by an engine, and a discharge amount that maintains a substantially constant output torque of the hydraulic pump by decreasing the discharge amount in accordance with an increase in discharge pressure of the hydraulic pump. In a hydraulic circuit of a work machine having a control means, discharge pressure rapid increase detection means for detecting a sudden increase in discharge pressure of the hydraulic pump, and a degree to which the rotational driving force of the engine is transmitted to the engine auxiliary equipment A rotational drive force transmission control means for controlling the hydraulic pump, and when determining that the discharge pressure of the hydraulic pump is rapidly increasing, by reducing the rotational drive force transmitted to the auxiliary equipment of the engine, It solves the problem.

  In the hydraulic circuit, when the discharge pressure rapid increase detection means further includes a discharge pressure detection means for detecting the discharge pressure of the hydraulic pump, an increase rate or a discharge pressure of the discharge pressure of the hydraulic pump is greater than or equal to a predetermined threshold value, respectively. When it becomes, it can be determined that the discharge pressure of the hydraulic pump is rapidly increasing.

  Further, when there are a plurality of auxiliary devices of the engine, when it is determined that the discharge pressure of the hydraulic pump is rapidly increasing, the power of at least one auxiliary device of the plurality of auxiliary devices and the engine Transmission may be interrupted by the rotational driving force transmission control means.

  According to the present invention, while maintaining the hydraulic pump at a high torque, it is possible to prevent a torque over and to reduce fuel consumption by reducing fluctuations in engine rotation speed.

The figure which shows the structure of the hydraulic circuit of the hydraulic shovel which concerns on embodiment of this invention. In the hydraulic circuit of the present embodiment, (A) a graph showing pump PQ characteristics, (B) a graph showing engine torque characteristics The figure which shows an example of the basic hydraulic circuit in the conventional hydraulic excavator In a conventional hydraulic circuit, (A) a graph showing pump PQ characteristics, (B) a graph showing engine torque characteristics The figure which shows the structure of the hydraulic circuit of the hydraulic shovel based on the technique of patent document 1

  Hereinafter, an example of a preferred embodiment of a hydraulic circuit of a hydraulic excavator according to the present invention will be described in detail based on the drawings.

  FIG. 1 is a diagram illustrating a configuration of a hydraulic circuit of a hydraulic excavator according to an embodiment of the present invention.

  The hydraulic circuit 10 includes an engine 12, a variable displacement hydraulic pump 14, a switching valve 16, an operation lever device 18, a hydraulic actuator 20, a center bypass oil passage 22, a regulator (discharge amount control means) 24, A controller 26, a discharge pressure sensor (discharge pressure detection means) 28, and a pilot pressure sensor (pilot pressure detection means) 30 are provided.

  The engine 12 generates a rotational driving force that rotates the main shaft 12A, and drives the variable displacement hydraulic pump 14, the pilot pump 32, and the like directly connected to the main shaft 12A with the rotational driving force. The engine 12 is provided with a cooling fan 50 and a water pump 52 as engine accessories, and although not shown, an alternator and an air conditioner compressor are also provided. The devices are also driven by obtaining a rotational driving force from the main shaft 12A of the engine 12. A rotational driving force is transmitted from the main shaft 12A of the engine 12 to the cooling fan 50 via the electromagnetic clutch 60, and a rotational driving force is transmitted to the water pump 52 from the main shaft 12A of the engine 12 via the belt 64 and the electromagnetic clutch 62. It is comprised so that.

  The variable displacement hydraulic pump 14 is driven by the engine 12, supplies pressure oil to the hydraulic actuator 20 via the center bypass oil passage 22 and the switching valve 16, and drives the hydraulic actuator 20. The direction and flow rate of the pressure oil toward the hydraulic actuator 20 are controlled by the operator operating the operation lever 18A of the operation lever device 18 to switch the switching position of the switching valve 16. The discharge amount of the variable displacement hydraulic pump 14 is controlled by the regulator 24 in accordance with the discharge pressure of the variable displacement hydraulic pump 14.

  The regulator (discharge amount control means) 24 is connected to the center bypass oil passage 22 via an oil passage 24a, and is variable according to an increase in the discharge pressure of the variable displacement hydraulic pump 14, as with the conventional regulator 114. The discharge amount of the displacement hydraulic pump 14 is decreased. Further, the discharge amount of the variable displacement hydraulic pump 14 is increased in accordance with the decrease in the discharge pressure of the variable displacement hydraulic pump 14. More specifically, the regulator 24 has a constant horsepower curve (discharge when the horsepower is constant) in FIG. 2A showing the relationship (pump PQ characteristic) between the discharge pressure P and the discharge amount Q of the variable displacement hydraulic pump 14. The discharge amount of the variable displacement hydraulic pump 14 is changed by the load pressure (discharge pressure) so as to be along the curve C1 (curve showing the relationship between the pressure P and the discharge amount Q).

  As a result, the output torque of the variable displacement hydraulic pump 14 becomes constant (Tmax), and is equal to or less than the rated torque T0 of the engine 12 as shown in FIG. 2B, so that the engine rotation is stable and the actual work by the hydraulic excavator is also stable. Can be done in the state.

  The operating lever device 18 has a role of adjusting the pilot pressure supplied to the pilot ports 16a and 16b of the switching valve 16 according to the operating state of the operating lever 18A, and switching the switching valve 16 according to an instruction from the operator. The operation lever device 18 has a built-in potentiometer (not shown), and an electric signal based on a change in the resistance value is sent to the controller 26 via the electric signal line 18b. Here, the operation lever 18A may be an electric lever. In this case, an electric signal corresponding to the operation amount of the operation lever 18A is transmitted from the operation lever 18A via the electric signal line 18b even if the potentiometer is not incorporated. To the controller 26. If the operation lever 18A is an electric lever, the operation amount of the operation lever 18A can be directly obtained by an electric signal, so that the operation speed of the operation lever 18A can be detected more easily.

  The discharge pressure sensor (discharge pressure detecting means) 28 measures the pressure oil pressure in the center bypass oil passage 22 between the variable displacement hydraulic pump 14 and the switching valve 16 to measure the discharge pressure of the variable displacement hydraulic pump 14. The obtained discharge pressure data is sent to the controller 26 via the electric signal line 28a.

  The pilot pressure sensor (pilot pressure detecting means) 30 is supplied from the pilot pressure (operating lever device 18) supplied to the pilot ports 16a and 16b of the switching valve 16 when the operating lever 18A of the operating lever device 18 is operated. The pilot pressure data obtained is sent to the controller 26 via the electric signal line 30a.

  The controller 26 determines in advance whether or not the discharge pressure of the variable displacement hydraulic pump 14 increases rapidly, and determines whether or not the discharge pressure of the variable displacement hydraulic pump 14 actually increases rapidly. When it is determined in advance that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases, or when it is determined that the discharge pressure of the variable displacement hydraulic pump 14 is actually increasing rapidly, engine auxiliary equipment (cooling fan 50, water A command to turn off the electromagnetic clutches 60 and 62 is issued so that the rotational driving force from the engine 12 is not transmitted to the pump 52 or the like.

  When the electromagnetic clutches 60 and 62 are disengaged, the rotational driving force is not transmitted from the main shaft 12A of the engine 12 to the engine accessories such as the cooling fan 50 and the water pump 52. As a result, the load applied to the auxiliary devices of the engine 12 is reduced, and the amount can be directed to the drive of the variable displacement hydraulic pump 14. As shown by the broken line C4 in FIG. 12 can increase the engine torque that can be input to the variable displacement hydraulic pump 14 (the rated torque is increased from T0 to T01). For this reason, when the operation lever 18A is suddenly operated or when the hardness of the object to be excavated changes suddenly during excavation work (for example, when the bucket comes into contact with rocks or tree roots during excavation work), the hydraulic pump 14 Even if the discharge pressure (load pressure) rises rapidly, the supply of rotational driving force to the engine accessories is stopped or reduced, so that the variable displacement hydraulic pump 14 is sufficient without reducing the rotational speed of the engine 12. Engine torque can be supplied.

  The controller 26 makes a prior determination as to whether or not the discharge pressure of the variable displacement hydraulic pump 14 rapidly increases as follows.

  The controller 26 calculates the operation speed and / or operation amount of the operation lever 18A based on the electric signal sent from the operation lever device 18 via the electric signal line 18b, and the calculated operation speed and / or operation amount is respectively calculated. Is determined in advance that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases.

  Here, the reason why it is determined in advance that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases when the operating speed of the operating lever 18A exceeds a predetermined threshold is that the operating lever 18A is in a direction in which the hydraulic actuator 20 receives an external force. Is suddenly operated, the pilot pressure supplied to the switching valve 16 rapidly rises, the position of the switching valve 16 is rapidly switched, and the discharge pressure (load pressure) of the variable displacement hydraulic pump 14 rapidly increases. This is because it can be determined in advance that the discharge pressure of the hydraulic pump 14 suddenly increases. The reason for determining in advance that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases when the operation amount of the operation lever 18A exceeds a predetermined threshold is that even if the operation of the operation lever 18A is not a sudden operation, In the case of a full operation in which the operation amount is equal to or greater than a predetermined threshold value, the switching valve 16 is switched to the position A or C, and the center bypass oil passage 22 (bleed oil passage) is fully closed. The discharge pressure (load pressure) of the variable displacement hydraulic pump 14 suddenly increases due to slight fluctuations in the external load, so that the output torque of the variable displacement hydraulic pump 14 exceeds the rated torque T0 of the engine 12 due to slight fluctuations in the external load. This is because there is a high possibility that

  As described above, the operation amount of the operation lever 18A can be generated from an electric signal reflecting a change in the resistance value of the potentiometer built in the operation lever device 18 or from the operation lever 18A when the operation lever 18A is an electric lever. Detection based on the electrical signal generated. Therefore, the operation lever device 18 (potentiometer, electric lever) and the controller 26 are “a discharge pressure sudden rise advance detection means for detecting in advance a sudden rise in the discharge pressure of the hydraulic pump”.

  Further, for the same purpose, it is detected in advance that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases depending on the pilot pressure increasing speed and / or pilot pressure value generated in response to the operation of the operating lever 18A. The pilot pressure sensor 30 and the controller 26 are also “a discharge pressure sudden rise advance detection means for detecting in advance a sudden rise in the discharge pressure of the hydraulic pump”.

  Based on the operating speed and operating amount of the operating lever 18A, the increasing speed of the pilot pressure supplied to the switching valve 16, and the pilot pressure, it is determined in advance that the discharge pressure of the variable displacement hydraulic pump 14 will suddenly increase. Control is possible, the rated torque can be increased at an earlier timing, and torque over can be prevented more reliably.

  Further, the controller 26 determines whether or not the discharge pressure of the variable displacement hydraulic pump 14 is actually rapidly increasing as follows.

  The controller 26 calculates the increase rate of the discharge pressure of the variable displacement hydraulic pump 14 based on the discharge pressure data sent from the discharge pressure sensor 28, and when the calculated increase rate of the discharge pressure becomes a predetermined threshold or more, It is determined that the discharge pressure of the variable displacement hydraulic pump 14 is rapidly increasing. Therefore, the discharge pressure sensor 28 and the controller 26 are “a discharge pressure sudden rise detection means for detecting a sudden rise in the discharge pressure of the hydraulic pump”. Further, when the discharge pressure of the variable displacement hydraulic pump 14 is larger than a certain level (for example, when it is greater than or equal to P2 in FIG. 2), the output torque of the variable displacement hydraulic pump 14 is increased by a slight load fluctuation. Therefore, it is determined that the discharge pressure of the variable displacement hydraulic pump 14 is rapidly increasing regardless of the actual increase rate of the discharge pressure.

  In the negative control control type hydraulic circuit, the negative control pressure decreases when the switching amount of the switching valve 16 from the neutral position B to the switching positions A and C is large, and the negative control pressure decreases from the neutral position B to the switching positions A and C. If the switching is performed rapidly, the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases and the negative control pressure rapidly decreases. Therefore, whether the discharge pressure of the variable displacement hydraulic pump 14 increases rapidly based on the decreasing speed of the negative control pressure. It can also be determined whether or not. Therefore, the negative control pressure sensor for detecting the negative control pressure can be a “discharge pressure rapid increase detection means for detecting a rapid increase in the discharge pressure of the hydraulic pump”.

  The electromagnetic clutch 60 is provided between the main shaft 12A of the engine 12 and the rotation shaft 50A of the cooling fan 50, and switches between connection and non-connection between the main shaft 12A of the engine 12 and the rotation shaft 50A. It has a role of switching whether or not the rotational driving force of 12A is transmitted to the rotating shaft 50A of the cooling fan 50. As described above, the electromagnetic clutch 60 is switched between connection and disconnection in response to a command from the controller 26 via the electric signal line 26a. Here, the state where the clutch is “coupled” means a state where the rotational driving force is transmitted via the clutch. Further, the electromagnetic clutch 60 can be used so as to reduce the degree of transmission of the rotational driving force without completely disconnecting the electromagnetic clutch 60.

  The electromagnetic clutch 62 is provided between a pulley shaft (not shown) of the pulley 68 and the rotating shaft 52A of the water pump 52, and has a role of switching connection / disconnection between the pulley shaft of the pulley 68 and the rotating shaft 52A. . As described above, the electromagnetic clutch 62 is switched between connection and disconnection in response to a command from the controller 26 via the electric signal line 26b. Here, a belt 64 is spanned between the pulley 68 and a pulley 66 attached to the main shaft 12 </ b> A of the engine 12, and the rotational driving force of the main shaft 12 </ b> A of the engine 12 passes through the pulley 66 and the belt 64. Thus, the electromagnetic clutch 62 has a role of switching whether or not to transmit the rotational driving force of the main shaft 12A of the engine 12 to the rotational shaft 52A of the water pump 52. Further, the electromagnetic clutch 62 can be used so as not to be completely disconnected and to reduce the degree of transmission of the rotational driving force.

  Therefore, it can be said that the electromagnetic clutches 60 and 62 and the controller 26 are “rotational driving force transmission control means for controlling the degree to which the rotational driving force of the engine is transmitted to the engine auxiliary devices”. Here, “controlling the degree of transmission” includes the case where the rotational driving force of the engine is completely transmitted and the case where it is completely interrupted.

  In the embodiment of the present invention described above, only the switching valve 16, the operating lever device 18, and the hydraulic actuator 20 are taken up as the switching valve, the operating lever device, and the hydraulic actuator. However, the switching valve, the operating lever device, and the hydraulic actuator are The present embodiment can be applied to a plurality of units instead of a single unit.

  In addition, although both the discharge pressure sensor 28 and the pilot pressure sensor 30 are provided in the hydraulic circuit 10, only one of them may be provided. Further, when a potentiometer is built in the operation lever device 18 or the operation lever 18A is an electric lever and an electric signal is sent from the operation lever device 18 via the electric signal line 18b, the discharge pressure sensor 28 and the pilot are transmitted. Both of the pressure sensors 30 may not be provided.

  Next, the operation and action of the hydraulic circuit 10 according to the embodiment configured as described above will be described.

  As described above, there are various types of work performed by the hydraulic excavator. When the operation lever 18A is suddenly operated, or when the hardness of the digging target suddenly changes during the digging work (for example, the bucket is moved during the digging work). The discharge pressure of the hydraulic pump 14 may suddenly rise (for example, in FIG. 2A, the discharge pressure suddenly rises from P0 to P1) when it comes into contact with a rock or tree root.

  At this time, the regulator 24 tries to lower the discharge amount of the hydraulic pump 14 to Q1, but since the rate of increase in the load pressure (discharge pressure) is much faster, the decrease curve of the discharge amount is shown in FIG. In FIG. 2, a curve C2 indicated by a two-dot chain line is obtained, and a pump torque curve is indicated by a curve C3 indicated by a one-dot chain line in FIG. As a result, the output torque of the hydraulic pump 14 temporarily rises to T1.

  On the other hand, in this embodiment, the controller 26 determines that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases, or if the controller 26 determines that the discharge pressure of the variable displacement hydraulic pump 14 rapidly increases, A command to turn off the electromagnetic clutches 60 and 62 is issued so that the rotational driving force from the engine 12 is not transmitted to the auxiliary devices (cooling fan 50, water pump 52, etc.) (alternators such as engine auxiliary devices not shown) An electromagnetic clutch that switches between transmission and non-transmission of the rotational driving force from the engine 12 is also provided to an air conditioner compressor and the like, and the controller 26 issues a command to turn off these electromagnetic clutches). As a result, the engine torque that has been input to the engine auxiliary equipment can be input to the variable displacement hydraulic pump 14, and the engine torque that the engine 12 can input to the variable displacement hydraulic pump 14 is indicated by a broken line in FIG. The engine torque curve C4 shown in FIG. Thereby, even when the output torque of the hydraulic pump 14 rises to T1, the output torque T1 can be prevented from reaching the rated torque (rated torque T01 in the engine torque curve C4), and the rotational speed of the engine 12 can be prevented. Can be maintained at the initial rotational speed N0. In particular, when it is determined in advance that the discharge pressure of the variable displacement hydraulic pump 14 suddenly increases, feedforward control can be performed, the rated torque can be increased at an earlier timing, and torque over can be prevented more reliably. can do.

  Therefore, according to the present embodiment, when the operation lever 18A is suddenly operated, or when the hardness of the excavation target suddenly changes during excavation work (for example, when the bucket comes into contact with rocks or tree roots during excavation work). Even so, the operation can be continued without reducing the operation speed, and the rotation speed of the engine 12 can be maintained at the initial rotation speed N0, so that more fuel is injected and the engine 12 is injected. Therefore, it is not necessary to return the rotational speed to the initial rotational speed N0, which is advantageous in terms of fuel consumption.

  In the embodiment described above, the command to turn off the electromagnetic clutches 60 and 62 issued by the controller 26 is made by an electrical signal, so that the command is transmitted instantaneously, and the operation to turn off the electromagnetic clutches 60 and 62 is performed. , 62 can be achieved instantaneously by separating the power transmission surface as little as possible. For this reason, when the controller 26 determines that the output torque of the variable displacement hydraulic pump 14 is rapidly increasing, the engine torque that can be input to the variable displacement hydraulic pump 14 by the engine 12 immediately disconnecting the electromagnetic clutches 60 and 62 is shown. The engine torque curve C4 of 2 (B) can be immediately increased. Therefore, by using the hydraulic circuit 10 according to the present embodiment, it is possible to sufficiently prevent torque over by using the hydraulic circuit 10 according to the present embodiment as long as the output torque T1 does not exceed the engine torque curve C4. It becomes.

  In the present embodiment, when the controller 26 determines that the discharge pressure of the variable displacement hydraulic pump 14 is rapidly increasing, the electromagnetic clutch is disconnected for all engine accessories, and the rotational driving force of the engine 12 is all However, depending on the work contents, it is not necessary to disengage the electromagnetic clutch for all engine auxiliary equipments. Select the engine auxiliary equipment that cuts the electromagnetic clutch according to the work contents. You may make it do. Further, depending on the engine accessories, the electromagnetic clutch may not be completely disconnected, and the degree of transmission of the rotational driving force may be reduced.

  Further, the disconnection continuation time during which the electromagnetic clutches 60 and 62 of the engine auxiliary devices are disconnected is the time Δt until the output torque of the variable displacement hydraulic pump 14 maintains a constant value (Tmax in FIG. 2). It is a corresponding time (for example, a time until the rate of increase in the discharge pressure of the variable displacement hydraulic pump 14 becomes equal to or less than a predetermined threshold value), which is a short time. Therefore, even if the electromagnetic clutches 60 and 62 of the engine auxiliary devices are disconnected and the engine auxiliary devices 50 and 52 are stopped, there is no adverse effect on the main body of the engine 12.

  For example, it can be suitably used in a hydraulic circuit of a work machine such as a hydraulic excavator.

DESCRIPTION OF SYMBOLS 10 ... Hydraulic circuit 12 ... Engine 12A ... Main shaft 14 ... Variable displacement hydraulic pump 16 ... Switching valve 18 ... Operation lever device 18A ... Operation lever 18b ... Electric signal line 20 ... Hydraulic actuator 22 ... Center bypass oil passage 24 ... Regulator (discharge amount) Control means)
26 ... Controller 28 ... Discharge pressure sensor (Discharge pressure detection means)
30 ... Pilot pressure sensor (pilot pressure detecting means)
32 ... Pilot pump 50 ... Cooling fan 52 ... Water pump 50A, 52A ... Rotary shaft 60, 62 ... Electromagnetic clutch 64 ... Belt 66, 68 ... Pulley

Claims (10)

A variable displacement hydraulic pump driven by an engine, and a discharge amount control means for decreasing the discharge amount according to an increase in the discharge pressure of the hydraulic pump and maintaining the output torque of the hydraulic pump substantially constant In the hydraulic circuit of the machine
A discharge pressure sudden rise advance detection means for detecting in advance a sudden rise in the discharge pressure of the hydraulic pump;
Rotational drive force transmission control means for controlling the degree to which the rotational drive force of the engine is transmitted to the auxiliary equipment of the engine,
A hydraulic circuit for a work machine, characterized in that, when it is determined in advance that the discharge pressure of the hydraulic pump suddenly increases, the rotational driving force transmitted to the auxiliary devices of the engine is reduced. In claim 1, further comprising:
A switching valve for switching the direction and flow rate of the pressure oil that drives the hydraulic actuator of the work machine;
An operation lever for operating the switching valve;
The discharge pressure rapid increase prior detection means includes an operation amount detection means for detecting an operation amount of the operation lever,
A hydraulic circuit for a working machine, wherein when the operation speed of the operation lever becomes equal to or greater than a predetermined threshold, it is determined in advance that the discharge pressure of the hydraulic pump increases rapidly. In claim 1 or 2,
A switching valve for switching the direction and flow rate of the pressure oil that drives the hydraulic actuator of the work machine;
An operation lever for operating the switching valve;
The discharge pressure rapid increase prior detection means includes an operation amount detection means for detecting an operation amount of the operation lever,
A hydraulic circuit for a working machine, wherein when the operation amount of the operation lever becomes equal to or greater than a predetermined threshold, it is determined in advance that the discharge pressure of the hydraulic pump suddenly increases. In any one of Claims 1-3, Furthermore,
A switching valve for switching the direction and flow rate of the pressure oil that drives the hydraulic actuator of the work machine;
Pilot pressure supply means for supplying pilot pressure to the switching valve,
The discharge pressure rapid increase prior detection means includes pilot pressure detection means for detecting the pilot pressure,
A hydraulic circuit for a working machine, wherein when the rate of increase of the pilot pressure exceeds a predetermined threshold value, it is determined in advance that the discharge pressure of the hydraulic pump increases rapidly. In any one of Claims 1-4, Furthermore,
A switching valve for switching the direction and flow rate of the pressure oil that drives the hydraulic actuator of the work machine;
Pilot pressure supply means for supplying pilot pressure to the switching valve,
The discharge pressure rapid increase prior detection means includes pilot pressure detection means for detecting the pilot pressure,
A hydraulic circuit for a working machine, wherein when the pilot pressure is equal to or greater than a predetermined threshold, it is determined in advance that the discharge pressure of the hydraulic pump increases rapidly. In any one of Claims 1-5,
When there are a plurality of auxiliary devices of the engine and it is determined in advance that the discharge pressure of the hydraulic pump suddenly increases, power transmission between at least one auxiliary device of the plurality of auxiliary devices and the engine, A hydraulic circuit for a working machine, wherein the hydraulic circuit is cut off by a rotational driving force transmission control means. A variable displacement hydraulic pump driven by an engine, and a discharge amount control means for decreasing the discharge amount according to an increase in the discharge pressure of the hydraulic pump and maintaining the output torque of the hydraulic pump substantially constant In the hydraulic circuit of the machine
A discharge pressure sudden rise detection means for detecting a sudden rise in the discharge pressure of the hydraulic pump;
Rotational drive force transmission control means for controlling the degree to which the rotational drive force of the engine is transmitted to the auxiliary equipment of the engine,
A hydraulic circuit for a working machine, wherein when it is determined that the discharge pressure of the hydraulic pump is rapidly increasing, the rotational driving force transmitted to the auxiliary devices of the engine is reduced. In claim 7, further:
The discharge pressure rapid increase detection means includes a discharge pressure detection means for detecting the discharge pressure of the hydraulic pump,
A hydraulic circuit for a working machine, wherein when the rate of increase of the discharge pressure of the hydraulic pump becomes equal to or greater than a predetermined threshold, it is determined that the discharge pressure of the hydraulic pump is rapidly increasing. In claim 7 or 8, further
The discharge pressure rapid increase detection means includes a discharge pressure detection means for detecting the discharge pressure of the hydraulic pump,
A hydraulic circuit for a working machine, wherein when the discharge pressure of the hydraulic pump becomes equal to or greater than a predetermined threshold, it is determined that the discharge pressure of the hydraulic pump is rapidly increasing. In any one of Claims 7-9,
When it is determined that there are a plurality of auxiliary devices of the engine and the discharge pressure of the hydraulic pump is rising rapidly, power transmission between at least one auxiliary device of the plurality of auxiliary devices and the engine, A hydraulic circuit of a work machine, wherein the hydraulic circuit is cut off by the rotational driving force transmission control means.

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