JP2010261340A - Dpf forcible regeneration circuit of construction machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To completely burn and remove PM without causing engine down during low-load/no-load work when DPF is forcibly regenerated. <P>SOLUTION: A DPF forcible regeneration circuit in a construction machine for driving a hydraulic pump by an engine containing a DPF in an exhaust system is provided with: a work load detection means for detecting a work load state of the construction machine; a bleeding-off cut valve interposed in the a most downstream side of a center bypass oil path in the hydraulic pump; and a controller for making switching control of the cut valve in accordance with a result of the work load detection means. The controller controls the cut valve to be gradually switched during low-load or no-load work. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a DPF (Diesel Particulate Filter, also referred to as DPD: Diesel Particulate Defuser) forced regeneration circuit of a construction machine. It relates to the circuit.

  Conventionally, an engine (diesel engine) is mounted on a construction machine such as a hydraulic excavator, and a hydraulic pump is connected to an output shaft of the engine. As shown in FIG. 5, a DPF 28 that functions as a diesel particulate processing device is installed in the exhaust system of the engine (diesel engine) 12. The DPF 28 collects particulate matter (hereinafter referred to as “PM”) contained in the exhaust gas in the exhaust pipe 12 </ b> A of the engine 12, and continuously collects PM by the oxidation catalyst supported by the DPF 28. It is configured so that it can be oxidized and removed.

  However, when the load on the engine 12 is low, the temperature of the exhaust gas does not rise sufficiently, so that PM gradually accumulates inside the DPF 28. When the PM accumulation amount exceeds a predetermined value, the pressure of the exhaust system of the engine 12 increases, leading to deterioration of fuel consumption and the like, and the original performance of the engine 12 cannot be obtained.

In order to prevent this, for example, the pressure on the upstream side of the DPF 28 is sensed by the detector 30, and the load of the engine 12 or the variable displacement type is sent via the airframe controller (hereinafter referred to as “controller”) 46 or the engine controller 52. It is necessary to periodically regenerate the DPF 28 in order to remove the PM by adjusting the load of the hydraulic pump 10 to the pressure.
In the forced regeneration of the DPF 28, fuel is supplied from the exhaust pipe 12A of the engine 12 to the oxidation catalyst in the DPF 28 by post-injecting fuel (post-injection) immediately after the explosion process due to the rise of the engine piston. .

  In this case, the temperature of the oxidation catalyst rises due to heat generated by fuel combustion (oxidation reaction). As a result, the temperature of the PM deposited on the DPF 28 also rises, so that oxidation removal by combustion of the PM is promoted (see, for example, Patent Document 1).

JP 2002-357140 A

  By the way, the progress of the forced regeneration process of the DPF 28 varies greatly depending on the load state during the work of the construction machine. For example, during high-load work, the exhaust gas temperature rises sufficiently according to the magnitude of the engine load, so PM removal and removal proceeds efficiently. However, when the load is low or not (no load), the engine load is lightened and the exhaust gas temperature does not rise sufficiently, making it difficult to completely remove PM.

Therefore, during low-load or no-load work, the engine controller 52 that controls the operation of the engine 12 outputs a request signal for increasing the hydraulic load to the controller 46, thereby forcibly setting the discharge pressure or the discharge flow rate of the hydraulic pump 10. (For example, see Japanese Patent Application No. 2008-249088 by the present applicant).
According to this technique, the engine load increases as the hydraulic load increases, so that the exhaust gas temperature rises and the PM removal and combustion can be promoted. However, when the hydraulic load is increased rapidly during low-load or no-load work, there is a problem that engine down is likely to occur.

  Thus, a technical problem to be solved in order to completely burn and remove PM while preventing engine down during low load or no load work occurs, and the present invention aims to solve this problem. To do.

  The present invention has been proposed to achieve the above object, and the invention according to claim 1 is a DPF forced regeneration circuit of a construction machine in which a hydraulic pump is driven by an engine having a DPF installed in an exhaust system. A work load detecting means for detecting a work load state of the construction machine; a bleed-off cut valve provided on the most downstream side of the center bypass oil passage of the hydraulic pump; and the cut valve of the work load detecting means. A controller for switching control according to a result, and the controller performs control so that the cut valve is gradually switched to a shut-off position during low-load or no-load work. provide.

  According to this configuration, when the construction machine is under low load or no load operation, the controller gradually switches the cut valve to the shut-off position, so that the circuit pressure of the center bypass oil passage gradually increases and the hydraulic load increases rapidly. There is no fear.

  According to a second aspect of the present invention, there is provided the DPF forced regeneration circuit for a construction machine according to the first aspect, wherein the work load detecting means is a rotational speed sensor for detecting the rotational speed of the engine.

  According to this configuration, when the engine speed detected by the speed sensor is equal to or lower than the predetermined value, the controller determines that the construction machine is in a low-load or no-load work state and gradually turns the cut valve. Switch to.

  A third aspect of the present invention provides the DPF forced regeneration circuit for a construction machine according to the first aspect, wherein the work load detecting means is a boost pressure sensor for detecting a boost pressure of the engine.

  According to this configuration, when the engine boost pressure detected by the boost pressure sensor is equal to or lower than the predetermined value, the controller determines that the construction machine is in a low-load or no-load work state and gradually turns the cut valve. Switch to.

  The invention according to claim 4 is characterized in that the controller controls the load of the hydraulic pump so that the exhaust gas temperature becomes a predetermined temperature after the cut valve is switched to the cutoff position. A DPF forced regeneration circuit for construction machinery is provided.

  According to this configuration, after the cut valve is switched to the shut-off position, the hydraulic load is controlled so that the exhaust gas temperature becomes a predetermined temperature, that is, an exhaust gas temperature suitable for burning and removing PM. The combustion removal of PM deposited on the DPF is promoted while maintaining the above.

  According to a fifth aspect of the present invention, the controller receives the forced regeneration start signal and the forced regeneration end signal of the DPF from the engine side, and determines the load of the hydraulic pump at the time of receiving the forced start signal as the forced regeneration signal. 5. A DPF forcible regeneration circuit for a construction machine according to claim 1, wherein control is performed so as to hold until the reception time of.

  According to this configuration, the load of the hydraulic pump at the time of receiving the forced regeneration start signal of the DPF is held until the forced regeneration end signal is received by the controller, so that the forced regeneration of the DPF is performed without the hydraulic load changing. To be implemented.

  According to the first aspect of the present invention, the DPF can be forcibly regenerated without a sudden increase in hydraulic load during low-load or no-load work, so that PM is completely burned and removed while preventing the engine from going down. be able to.

  According to the second aspect of the present invention, the cut valve is switched by accurately determining the low load or no-load operation state based on the engine speed, so that in addition to the effect of the first aspect, the engine speed increases rapidly. Even when the engine fluctuates, the cut valve switching control can be executed more reliably and in a timely manner, and the engine can be prevented more reliably.

  According to the third aspect of the present invention, when forcibly regenerating the DPF, if the boost pressure of the engine is equal to or lower than a predetermined value, it is determined that the engine is in a low-load or no-load operation state and the cut valve is switched. In addition to the effects of the described invention, even when the boost pressure of the engine fluctuates abruptly, the cut valve switching control can be executed more accurately and in a timely manner, and the engine down can be prevented more reliably.

  Since the invention according to claim 4 can promote the combustion removal of PM under a predetermined exhaust gas temperature, in addition to the effect of the invention according to claim 1, efficient forced regeneration of DPF can be stably performed. It can be carried out.

  According to the fifth aspect of the present invention, the forced regeneration of the DPF can be performed in a state where the hydraulic load does not fluctuate. Can be stably obtained.

The side view which shows the hydraulic shovel as an example of the construction machine which concerns on this invention. The hydraulic control circuit diagram which shows Example 1 of this invention and demonstrates DPF forced regeneration of a construction machine. The hydraulic control circuit diagram which shows Example 2 of this invention and demonstrates DPF forced regeneration of a construction machine. The hydraulic control circuit diagram which shows Example 3 of this invention and demonstrates DPF forced regeneration of a construction machine. The block diagram which shows a prior art example and demonstrates the principal part of DPF forced regeneration of a construction machine.

  In the present invention, a DPF is installed in the exhaust system in order to achieve the purpose of completely burning and removing PM without causing an engine down when forced regeneration of the PDF is performed during low-load work or not working. In a DPF forced regeneration circuit of a construction machine that drives a hydraulic pump by an engine, a work load detection means for detecting a work load state of the construction machine, and a bleed provided on the most downstream side of a center bypass oil passage of the hydraulic pump A cut valve that is an on / off switching valve for turning off, and a controller that controls the cut valve according to the result of the work load detection means, and the controller gradually turns the cut valve on during low load or no load work. Realized by controlling to switch to.

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. The same parts as those shown in FIG. 5 are denoted by the same reference numerals, and the description thereof is omitted. Reference numeral 1 denotes a hydraulic excavator as a construction machine, and an upper swing body 4 is rotatably mounted on a lower traveling body 2 via a swing mechanism 3. The lower traveling body 2 is provided with a traveling motor 5, and the crawler 6 is driven by the traveling motor 5. The turning mechanism 3 is driven by a turning motor 7, and the upper turning body 4 is turned by driving the turning motor 7.

  A boom 8 is attached to the front center portion of the upper swing body 4 so as to be able to move up and down, and an arm 9 is attached to the tip of the boom 8 so as to be rotatable up and down. A bucket 10 is attached.

  FIG. 2 shows a DPF forced regeneration circuit in the diesel engine 12 mounted on the upper swing body 4. Note that the DPF forced regeneration circuit according to the present embodiment is configured based on a negative control system.

  In the figure, 52 is an engine controller for controlling the operation of the diesel engine 12, and a DPF 28 is installed on the downstream side of the exhaust pipe 12 </ b> A connected to the diesel engine 12. Further, a swash plate type variable discharge amount hydraulic pump 10 is connected to the output shaft of the diesel engine 12, and a negative control throttle 36 is provided at the most downstream side of the center bypass oil passage 32 connected to the outflow side of the hydraulic pump 10. An oil tank 40 is connected via

The upstream side of the negative control throttle 36 and the hydraulic pump 10 are connected via a negative control circuit 50, and a tilt angle adjusting regulator 14 is provided on the hydraulic pump 10 side in the negative control circuit 50. The discharge amount of the hydraulic pump 10 is controlled by negatively feeding back the negative control pressure by the regulator 14. For example, when the negative control pressure is high, the tilt angle of the hydraulic pump 10 is reduced by the operation of the regulator 14, so that the discharge amount of the hydraulic pump 10 is reduced.

  In the middle of the center bypass oil passage 32, a first directional switching valve 22, a second directional switching valve 24, and a third directional switching valve 26 for controlling the flow of the discharged oil from the hydraulic pump 10 are interposed. The direction switching valve 22, the second direction switching valve 24, and the third direction switching valve 26 are tandemly connected in this order toward the downstream direction.

  A hydraulic actuator is connected to each of the first direction switching valve 22, the second direction switching valve 24, and the third direction switching valve 26. For example, drive cylinders 16 and 20 for work machines such as booms, arms or buckets are connected to the first direction switching valve 22 and the third direction switching valve 26, respectively, and a hydraulic motor is connected to the second direction switching valve 24. 18 is connected.

  A cut valve 34 is interposed on the most downstream side of the center bypass oil passage 32, that is, between the third direction switching valve 26 and the negative control throttle 36, and the cut valve 34 functions as an opening / closing switching valve for bleed-off. is doing. The cut valve 34 is connected to an electromagnetic switching valve 44 via a slow return valve 54, and the solenoid 44 a of the electromagnetic switching valve 44 is connected to a controller 46 via a signal line 56. The cut valve 34 is set to the open position A during normal times, and a part of the pressure oil flowing through the center bypass oil passage 32 is returned to the oil tank 40.

  When a cut valve switching command signal (shutoff signal) is transmitted from the controller 46 to the electromagnetic switching valve 44, the electromagnetic switching valve 44 is switched from the normal position C to the switching position D. As a result, the pressure oil from the hydraulic source 42 is supplied to the pilot port 34 a of the cut valve 34 via the slow return valve 54. As a result, the cut valve 34 switches from the open position A to the cutoff position B, and the hydraulic load in the center bypass oil passage 32 increases.

  In this case, since the moving speed of the pressure oil is delayed when the pressure oil passes through the slow return valve 54, the rising speed of the hydraulic load is delayed by that amount, and a sudden increase in the hydraulic load is prevented.

  The controller 46 includes a microcomputer and includes a CPU, a ROM, a RAM, an input / output interface, and the like. The ROM stores a control program for performing a forced regeneration process in order to incinerate and remove PM deposited on the DPF 28, and various data used when the control program is executed.

  A monitor 48 is connected to the controller 46, and the monitor 48 displays various operation states of the controller 46, for example, a forced regeneration state of the DPF 28 and detection data of various sensors.

  The engine controller 52 according to this embodiment is connected to a rotation speed sensor 61, a boost pressure sensor 62, and a differential pressure sensor 63 that function as a work load detection means. The rotational speed sensor 61 is attached to one end of the diesel engine 12 and detects the rotational speed of the diesel engine 12. The boost pressure sensor 62 is attached to the other end of the diesel engine 12 and detects the boost pressure of the diesel engine 12. Further, the differential pressure sensor 63 is attached to the DPF 28 and detects a pressure difference before and after the DPF 28.

  The detected values of the rotation speed sensor 61, boost pressure sensor 62, and differential pressure sensor 63 are transmitted to the engine controller 52. Then, by comparing the detection result with a preset reference value, it is determined whether or not the work load state of the excavator 1 is a low load or no load work state (engine load state). Is transmitted from the engine controller 52 to the controller 46. Reference numerals 38 and 64 are relief valves.

  In this embodiment, when the controller 46 receives the determination signal of the low load or no load work state from the engine controller 52, it outputs a hydraulic pressure increase command signal to the electromagnetic switching valve 44 and switches the cut valve 34 to the cutoff position B. In this case, since the slow return valve 54 is provided between the output port P3 of the electromagnetic switching valve 44 and the pilot port 34a of the cut valve 34, the cut valve 34 is gradually switched to the cutoff position B. As a result, since the circuit pressure on the output side (load side) of the hydraulic pump 10 gradually increases, the increase in output torque of the hydraulic pump 10 becomes gradual, and engine down is prevented.

  After the switching of the cut valve 34 is completed, a forced regeneration start signal for the DPF 28 is transmitted from the engine controller 52 to the controller 46, and a forced regeneration process for the DPF 28 is started. Thereafter, until the preset time elapses or until the detected pressure of the differential pressure sensor 63 becomes a predetermined value or less and the forced regeneration end signal of the DPF 28 is transmitted from the engine controller 52 to the controller 46. The switching state of the valve 34 is continuously maintained.

  According to the present embodiment, when performing forced regeneration of the DPF 28, the controller 26 performs control so that the cut valve 34 slowly switches to the cutoff position B when the engine load is equal to or less than a predetermined value. Thus, PM can be completely burned and removed while preventing the engine from going down even during low-load / no-load work.

  In the present embodiment, even when the engine speed or boost pressure is below a predetermined value, the cut valve can be gradually switched while monitoring and grasping the low-load / no-load operation state with the monitor 48. Even when the number or the boost pressure is drastically reduced, the forced regeneration process of the DPF 28 can be smoothly executed while preventing an engine strike.

  Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. Unlike the first embodiment, this embodiment is provided with an electromagnetic proportional valve 60 between the cut valve 34 and the controller 46. That is, the output port of the electromagnetic proportional valve 60 is connected to the pilot port 34 a of the cut valve 34, and the signal input part of the electromagnetic proportional valve 60 is connected to the output part of the controller 46. Therefore, the switching operation of the cut valve 34 is controlled via the electromagnetic proportional valve 60 based on the switching command signal from the controller 46.

  In the present embodiment, when the DPF 28 is forcibly regenerated, any one of the following three methods can be adopted as a control method of the cut valve 34 by the electromagnetic proportional valve 60. That is, in the first control method, the cut valve 34 is gradually switched and controlled for a preset time. Further, in the second method, the engine speed is detected by the rotation speed sensor 61 and the change state of the engine speed is grasped by the monitor 48 or the like, and the engine speed is increased so that the engine does not go down. Accordingly, the cut valve 34 is gradually switched and controlled.

  Further, in the third control method, the boost pressure of the diesel engine 12 is detected by the boost pressure sensor 62 and the change in the boost pressure is grasped by the monitor 48 or the like, so that the engine down does not occur. The cut valve 34 is gradually switched and controlled in accordance with the size.

  After switching the cut valve 34 by any of the above three control methods, the electromagnetic proportional valve 60 increases the stroke of the cut valve 34 so that the temperature detected by the exhaust gas temperature sensor (not shown) maintains the set temperature. Adjust to the optimal amount. In this case, when the exhaust gas temperature reaches a predetermined value or more, completely closing the bleed circuit with the cut valve 34 causes wasteful consumption of fuel. Therefore, in order to avoid this, the valve of the cut valve 34 is opened. The degree should be controlled appropriately.

  After the switching of the cut valve 34, a forced regeneration start signal is output from the engine controller 52 to the controller 46 in order to start the forced regeneration of the DPF 28. The output of the current value from the controller 46 to the electromagnetic proportional valve 60 at this time is kept constant until the forced regeneration end signal is transmitted from the engine controller 52 to the controller 46.

  Also in this embodiment, as in the first embodiment, when the forced regeneration of the DPF 28 is performed, the controller 46 gradually switches the cut valve 34 to the cutoff position B when the engine load is equal to or less than a predetermined value. Thus, PM can be completely burned and removed while preventing the engine from going down even during low-load / no-load work.

  Next, Embodiment 3 of the present invention will be described with reference to FIG. Unlike the first and second embodiments based on the negative control system, this embodiment is based on the positive control system. For example, when the circuit pressure of the center bypass oil passage 32 increases, the discharge amount of the hydraulic pump 10 increases via the regulator 14 based on a command signal from the controller 46.

  As shown in FIG. 4, an electromagnetic proportional valve 65 is installed between the regulator 14 and the controller 46. That is, the output port of the electromagnetic proportional valve 65 is connected to the head side oil chamber 14 a of the regulator 14, and the signal input portion of the electromagnetic proportional valve 65 is connected to the output portion of the controller 46. Therefore, the set pressure of the regulator 14 is controlled via the electromagnetic proportional valve 65 based on the command signal from the controller 46.

  A remote control valve 66 is connected to the first direction switching valve 22, and the first direction switching valve 22 is operated by the remote control valve 66. Further, a pilot pressure sensor 67 is installed in the pilot oil passage of the remote control valve 66, and the pilot operating pressure of the remote control valve 66 is detected by the pilot pressure sensor 67. Further, the pilot pressure sensor 67 is connected to the controller 46. Therefore, the pilot operating pressure of the remote control valve 66 is input to the controller 46 via the pilot pressure sensor 67.

  Normally, when the remote control valve 66 is operated, the operation amount is detected by the pilot pressure sensor 67, and the controller 46 controls the electromagnetic proportional valve 65 so as to discharge the pressure oil at a flow rate corresponding to the operation amount of the remote control valve 66. . In the present embodiment, when the hydraulic load increase request signal is output from the engine controller 52 to the controller 46 when the DPF 28 is forcibly regenerated, one of the following three methods can be adopted as the control method of the cut valve 34.

  That is, in the first method, similarly to the second embodiment, the hydraulic valve is increased by gradually switching the cut valve 34 at a preset time by the electromagnetic proportional valve 60. When the hydraulic load is insufficient, the controller 46 gradually increases the discharge amount of the hydraulic pump 10 via the electromagnetic proportional valve 65 to slowly increase the hydraulic load.

  Further, in the second method, the engine speed is detected by the speed sensor 61, and the change state of the engine speed is grasped by the monitor 48 or the like, and the cut valve 34 is electromagnetically operated so that the engine does not go down. The hydraulic load is increased by gradually switching with the proportional valve 60. When the hydraulic load is insufficient, the hydraulic load is slowly increased by the electromagnetic proportional valve 65 while gradually increasing the discharge amount of the hydraulic pump 10 according to the engine speed.

  Further, in the third method, the boost pressure sensor 62 detects the boost pressure of the diesel engine 12 and grasps the change state of the boost pressure, so that the engine down does not occur according to the magnitude of the boost pressure. The hydraulic load is increased by changing the switching control time of the cut valve 34. When the hydraulic load is insufficient, the hydraulic load is slowly increased by the electromagnetic proportional valve 65 while gradually increasing the discharge amount of the hydraulic pump 10 according to the magnitude of the engine speed.

  After the cut valve 34 is switched or the discharge amount of the hydraulic pump 10 is increased by any one of the above three switching control methods, the temperature detected by the exhaust gas temperature sensor (not shown) is maintained at the set temperature. Further, the stroke of the cut valve 34 is adjusted to an optimum amount by the electromagnetic proportional valve 60. The same applies to the pump discharge flow rate, and the discharge flow rate of the hydraulic pump 10 is adjusted by the electromagnetic proportional valve 65 so that the exhaust gas temperature maintains the set temperature.

  Further, when the exhaust gas temperature reaches a predetermined value or more, completely closing the bleed circuit with the cut valve 34 causes wasteful consumption of fuel. Therefore, the valve opening of the cut valve 34 is avoided to avoid this. Shall be controlled appropriately.

  As described above, according to the present invention, when the DPF is forcibly regenerated, the controller gradually switches the cut valve to the shut-off position during low load or no load work of the construction machine, thereby reducing the circuit pressure of the center bypass oil passage. The forced regeneration of the DPF can be performed without causing a rapid rise. In this way, even during low-load or no-load work, the PM deposited on the DPF can be completely burned and removed while preventing the engine from going down.

  In addition, the PM incineration action can be promoted while maintaining the desired exhaust gas temperature by controlling the hydraulic load so that the exhaust gas temperature becomes a predetermined temperature after switching the cut valve to the shut-off position. Can be executed stably.

  Further, the load of the hydraulic pump at the time when the DPF forced regeneration start signal is received is held until the controller receives the forced regeneration end signal. Therefore, the forced regeneration of the DPF can be performed while the hydraulic load is kept constant, and high PM combustion removal can be efficiently performed while preventing the engine from falling down more reliably.

  When the controller controls the load of the hydraulic pump so that the exhaust gas temperature becomes a predetermined temperature after switching the cut valve, the PM combustion removal in the filter is further promoted. As a result, PM accumulation on the filter can be prevented more reliably.

  In particular, the controller receives the forced regeneration start signal and the forced regeneration end signal of the DPF from the engine side, and the load on the hydraulic pump at the time when the forced start signal is received is until the forced regeneration end signal is transmitted to the controller. Controlled to hold. Therefore, while the forced regeneration of the DPF is being performed, the load of the hydraulic pump can be stably adjusted to a predetermined value, so that the PM combustion removal effect can be further enhanced.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

  The present invention is applicable to any DPF forced regeneration circuit of a construction machine (work machine) in which a DPF is installed in an exhaust system of an engine and a hydraulic pump is driven by the engine.

1 Excavator (construction machine)
DESCRIPTION OF SYMBOLS 10 Hydraulic pump 12 Diesel engine 12A Exhaust pipe 14 Regulator 28 DPF (filter)
32 Center bypass oil passage 34 Cut valve 36 Negative control throttle 44 Electromagnetic switching valve 46 Controller 52 Engine controller 54 Slow return valve 60 Proportional solenoid valve 61 Speed sensor (work load detection means)
62 Boost pressure sensor (work load detection means)
63 Differential pressure sensor 65 Proportional solenoid valve 66 Remote control valve 67 Pilot pressure sensor

Claims (5)

In a DPF forced regeneration circuit of a construction machine that drives a hydraulic pump by an engine having a DPF installed in an exhaust system, a work load detection unit that detects a work load state of the construction machine, and a center bypass oil passage of the hydraulic pump. A bleed-off cut valve provided on the downstream side, and a controller for switching and controlling the cut valve according to the detection result of the work load detection means, the controller at the time of low load or no load work A DPF forced regeneration circuit for a construction machine, wherein the cut valve is controlled to be gradually switched to a cutoff position. 2. The DPF forced regeneration circuit for a construction machine according to claim 1, wherein the work load detection means is a rotation speed sensor for detecting the rotation speed of the engine. 2. The DPF forced regeneration circuit for a construction machine according to claim 1, wherein the work load detection means is a boost pressure sensor that detects a boost pressure of the engine. 2. The DPF forced regeneration circuit according to claim 1, wherein the controller controls the hydraulic load of the hydraulic pump so that the exhaust gas temperature of the engine becomes a predetermined temperature after switching the cut valve. The controller receives a forced regeneration start signal and a forced regeneration end signal of the DPF from the engine side, and controls to hold the hydraulic load of the hydraulic pump at the time of receiving the forced start signal until the forced regeneration end signal is received. The DPF forced regeneration circuit for a construction machine according to claim 1 or 4, wherein:

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