Construction machine

Abstract

To provide a construction machine capable of preventing excessive overshoot of a fluid temperature independently of the state of heat input into fluid as a cooled object.SOLUTION: A hydraulic shovel includes a cooling fan 77, an oil cooler 73 to be cooled by the cooling fan 77, a working oil temperature sensor 73s for detecting the temperature of working oil flowing in the oil cooler 73, and a vehicle body controller 51 for controlling the rotating speed of the cooling fan 77. The vehicle body controller 51 uses proportional-plus integral control for setting the target rotating speed of the cooling fan 77 according to a temperature difference between an actual temperature of the working oil detected by the working oil temperature sensor 73s and a preset target temperature to limit an output value N_I of an integration term to a predetermined integration term lower limit value N_I min or higher in integral control of the proportional-plus integral control.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a construction machine equipped with a cooling fan that cools a heat exchanger, and more particularly to a construction machine in which the rotation speed of the cooling fan can be set regardless of the rotation speed of the engine. [Background technology]

[0002] Cooling fans that are generally used in construction machines such as hydraulic excavators to cool heat exchangers include those that are connected to the engine crankshaft and rotate with the rotation of the engine crankshaft, and those that are disconnected from the engine and driven independently by a hydraulic motor or an electric motor, allowing the rotation speed to be set. The latter control method for cooling fans that are driven independently to set the rotation speed includes a method of monitoring the actual temperature of the fluid flowing through the heat exchanger, setting the target rotation speed of the cooling fan using a proportional-integral controller according to the difference between the detected actual temperature and the target temperature, and variably controlling the target rotation speed of the cooling fan so that the actual temperature becomes the target temperature.

[0003] In construction machinery, the fluid to be cooled includes, for example, engine cooling water and hydraulic oil for driving actuators. Due to a delay in the response of the actual temperature of the fluid to the increase or decrease in the cooling air by the cooling fan, the actual rotation speed of the cooling fan is delayed due to accumulation on the negative side by integral control, and a large overshoot may occur in which the actual temperature of the fluid is excessively high relative to the target temperature. In this case, the target rotation speed of the cooling fan is set excessively high in response to the excessive overshoot, and therefore the actual temperature of the fluid drops too much, resulting in a phenomenon in which a target rotation speed that is too low is set. As a result, the actual rotation speed of the cooling fan may hunt around the target value, which may cause discomfort to the operator and those around due to a deterioration in hearing. In addition, if the fluid becomes excessively hot, it may cause malfunctions in the vehicle body, so it is desirable to avoid excessive overshooting of the fluid temperature.

[0004] As a fan rotation speed control method for suppressing overshooting of fluid temperature, for example, Patent Document 1 describes a method in which the fan target rotation speed is set using only the proportional element of a proportional-integral controller in accordance with the temperature difference between the actual temperature and the target temperature until the fan target rotation speed reaches the minimum fan rotation speed, and when the fan target rotation speed exceeds the minimum fan rotation speed, the fan target rotation speed is set using the proportional and integral elements of the proportional-integral controller in accordance with the temperature difference between the actual temperature and the target temperature, thereby limiting accumulation on the negative side of the integral in the proportional-integral controller. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4206008 Summary of the Invention [Problem to be solved by the invention]

[0006] However, because the heat input conditions to the fluid in construction machinery vary, it is possible that the actual temperature of the fluid will not reach the target temperature for a long period of time after the fan target rotation speed reaches the minimum fan rotation speed. In such a case, even if proportional-integral control is performed according to the difference between the actual temperature and the target temperature, excessive overshoot of the fluid temperature may occur due to accumulation of negative values ​​in the integrator while the actual temperature does not reach the target temperature.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a construction machine that can suppress fluid temperature overshoot regardless of the heat input condition to the fluid to be cooled. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the construction machine of the present invention is equipped with a cooling fan, a heat exchanger cooled by the cooling fan, a temperature detector that detects the temperature of the fluid flowing through the heat exchanger, and a controller that controls the rotation speed of the cooling fan, wherein the controller sets the target rotation speed of the cooling fan by proportional integral control in accordance with the temperature difference between the actual temperature of the fluid detected by the temperature detector and a predetermined target temperature, and limits the output value of the integral term in the integral control of the proportional integral control to a predetermined lower limit value or above. Effect of the Invention

[0009] According to the present invention, it is possible to prevent excessive overshooting of the fluid temperature regardless of the state of heat input to the fluid to be cooled. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a side view showing an example of the overall structure of a hydraulic excavator according to an embodiment of the present invention. [Diagram 2] 2 is a perspective view showing an example of an arrangement of equipment on a rotating body provided in the hydraulic excavator of FIG. 1, as viewed from above the rotating body. FIG. [Diagram 3] FIG. 2 is a block diagram showing an example of a configuration related to control of a cooling fan of a hydraulic excavator. [Figure 4] FIG. 4 is a block diagram showing an example of a control method for a target rotation speed by proportional-integral control based on a hydraulic oil temperature. [Diagram 5] 5 is a flowchart showing an example of a process in an integral term output value determination unit in FIG. 4. [Figure 6] 6 is a block diagram showing an example of a method for determining a lower limit value of an integral term in step S4 of FIG. 5. [Figure 7] 1 is a time chart showing a comparative example in which no limit is imposed on the integral term output value, with the horizontal axis indicating time, and the vertical axis indicating the heat input to the fluid, the actual and target temperatures of the fluid, the proportional and integral term output values, and the actual and target rotation speeds of the cooling fan. [Figure 8]1 is a time chart showing the heat input to the fluid, the actual and target temperatures of the fluid, the proportional and integral term output values, and the actual and target rotation speeds of the cooling fan on the vertical axis and on the horizontal axis, in this embodiment in which the integral term output value is limited. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] <Overall configuration of hydraulic excavator> In this embodiment, a crawler hydraulic excavator will be described as an example of a construction machine. Fig. 1 is a side view showing an example of the overall structure of the hydraulic excavator of this embodiment, and Fig. 2 is a perspective view of the rotating body from above, showing an example of an arrangement of equipment on the rotating body provided in the hydraulic excavator of Fig. 1.

[0013] 1, the hydraulic excavator 1 includes a traveling body 2, a rotating body 3 rotatably provided on the traveling body 2, and a working device 4 attached to the rotating body 3. The working device 4 includes a boom 41 attached to the rotating body 3 so as to be capable of elevation and descent, an arm 42 attached to the tip of the boom 41 so as to be capable of elevation and descent, a bucket 43 attached to the tip of the arm 42 so as to be capable of elevation and descent, a boom cylinder 44 that operates the boom 41, an arm cylinder 45 that operates the arm 42, and a bucket cylinder 46 that operates the bucket 43.

[0014] The rotating body 3 is composed of a main frame 30, a counterweight 31, a cab 32, a building cover 33, etc. The main frame 30 is the base of the rotating body 3, and is made up of a plurality of steel plates and steel materials joined together to form a support structure extending in the front-rear and left-right directions of the vehicle body. A working device 4 is attached to the front of the main frame 30 so that it can be raised and lowered. The counterweight 31 is installed at the rear of the main frame 30 and serves as a weight to balance the weight of the working device 4. The cab 32 is mounted on the front left side of the main frame 30.

[0015] As shown in Fig. 2, the inside of the cab 32 is provided with a driver's seat 50 where an operator sits, and a vehicle controller 51 (an example of a controller). The building cover 33 is a cover that separates devices such as an engine 61 mounted on the main frame 30 and a cooling package 72. The building cover 33 is provided with an engine room 60 located at the rear center of the vehicle body, and a radiator room 70 located at the rear left side of the vehicle body. In the engine room 60, the engine 61 and the hydraulic pump 62 are arranged in a horizontal orientation with the crankshaft extended in the left-right direction. In the radiator room 70, an atmospheric air temperature sensor 71 (see Fig. 3), a cooling package 72, etc. are mounted.

[0016] <Configuration related to cooling fan control> Next, a configuration relating to control of the cooling fan of the hydraulic excavator 1 will be described with reference to Fig. 3. Fig. 3 is a block diagram showing an example of a configuration relating to control of the cooling fan of the hydraulic excavator 1.

[0017] 3, the hydraulic pump 62 is directly connected to the engine 61 and is driven by the output of the engine 61. A pump flow rate / discharge pressure sensor 62s (an example of a vehicle body load detector) is provided near the hydraulic pump 62 and transmits pump flow rate and discharge pressure information (an example of the vehicle body load) to the vehicle body controller 51.

[0018] The cooling package 72 has an oil cooler 73 (an example of a heat exchanger) that cools the hydraulic oil used to drive the working implement 4, a radiator 74 (an example of a heat exchanger) that cools the engine cooling water, an intercooler 75 (an example of a heat exchanger) that cools the intake air supplied to the engine 61 by a turbocharger (not shown), a cooling fan 77, and a fan motor 76 that drives the cooling fan 77. The oil cooler 73, the radiator 74, and the intercooler 75 are cooled by the cooling fan 77.

[0019] A hydraulic oil temperature sensor 73s, an engine cooling water temperature sensor 74s, and an intake air temperature sensor 75s are provided in the flow paths of the hydraulic oil (one example of a fluid) flowing through the oil cooler 73, the engine cooling water (one example of a fluid) flowing through the radiator 74, and the intake air (one example of a fluid) flowing through the intercooler 75. The hydraulic oil temperature sensor 73s (one example of a temperature detector) detects the temperature of the hydraulic oil and transmits the temperature information to the vehicle body controller 51. The engine cooling water temperature sensor 74s (one example of a temperature detector) detects the temperature of the engine cooling water and transmits the temperature information to the vehicle body controller 51. The intake air temperature sensor 75s (one example of a temperature detector) detects the temperature of the intake air and transmits the temperature information to the vehicle body controller 51.

[0020] The fan motor 76 is driven in accordance with a rotation speed command from the vehicle body controller 51. The cooling fan 77 has its rotation speed controlled by the vehicle body controller 51, and blows cooling air to the oil cooler 73, the radiator 74, and the intercooler 75.

[0021] The ambient temperature sensor 71 (an example of an ambient temperature detector) detects the ambient temperature and transmits temperature information to the vehicle body controller 51.

[0022] <How to control the cooling fan> Next, a method for controlling the cooling fan 77 will be described with reference to Figs. 4, 5, and 6, taking hydraulic oil as an example. Fig. 4 is a block diagram showing an example of a method for controlling a target rotation speed by proportional-integral control based on hydraulic oil temperature, Fig. 5 is a flowchart showing an example of processing in the integral term output value determination unit in Fig. 4, and Fig. 6 is a block diagram showing an example of a method for determining an integral term lower limit value in step S4 in Fig. 5. The processing in Figs. 4, 5, and 6 is mainly performed by the vehicle body controller 51. In this embodiment, the processing in Figs. 4, 5, and 6 will be described assuming that the vehicle body controller 51 is the main body of the processing.

[0023] As shown in FIG. 4, the vehicle body controller 51 sets the target rotation speed N_t of the cooling fan 77 by proportional-integral control according to the temperature difference between the actual hydraulic oil temperature Tmo detected by the hydraulic oil temperature sensor 73s and the predetermined hydraulic oil target temperature Tto. Specifically, a deviation Eo obtained by subtracting a preset hydraulic oil target temperature Tto from the actual hydraulic oil temperature Tmo detected by the hydraulic oil temperature sensor 73s is input to a proportional unit S1 and an integrator S2. The proportional unit S1 multiplies the deviation Eo by a proportional gain and outputs the result as a proportional term output value N_P. The integrator S2 multiplies the deviation Eo by an integral gain, and adds the multiplied value to the previous integral term output value N_I to obtain an integral term output candidate value N_It. The integrator S2 inputs the integral term output candidate value N_It to an integral term output value determination unit S3, and determines the integral term output value N_I by a calculation to be described later.

[0024] The vehicle body controller 51 adds together the proportional term output value N_P of the proportional unit S1, the integral term output value N_I of the integrator S2, and a predetermined offset rotation speed N_O to set the target rotation speed N_t of the cooling fan 77. The offset rotation speed N_O is the uncorrected rotation speed of the cooling fan 77 when the actual temperature Tmo and the target temperature Tto match. In other words, the vehicle body controller 51 sets the target rotation speed N_t by correcting the reference offset rotation speed N_O with the proportional term output value N_P and the integral term output value N_I.

[0025] The vehicle body controller 51 executes the process shown in Fig. 5 in the integral term output value determination unit S3 described above. As shown in Fig. 5, in step S4, the vehicle body controller 51 determines an integral term lower limit value N_Imin (an example of a predetermined lower limit value) by a method shown in Fig. 6 described later. After completing the process of step S4, the vehicle body controller 51 proceeds to step S5.

[0026] In step S5, the vehicle body controller 51 determines whether the input integral term output candidate value N_It is below the integral term lower limit value N_Imin determined in step S4. If the integral term output candidate value N_It is below the integral term lower limit value N_Imin, the vehicle body controller 51 proceeds to step S6 (step S5: YES), and if the integral term output candidate value N_It is equal to or greater than the integral term lower limit value N_Imin, the vehicle body controller 51 proceeds to step S7 (step S5: NO).

[0027] In step S6, the vehicle body controller 51 determines the integral term output value N_I to be the integral term lower limit value N_Imin, and ends the processing of the integral term output value determination unit S3. Then, the process returns to the processing shown in FIG. 4. In step S7, the vehicle body controller 51 determines the integral term output value N_I to be the integral term output candidate value N_It, and ends the processing of the integral term output value determination unit S3. Then, the process returns to the processing shown in FIG. 4.

[0028] As described above, the integral term output value N_I is a value obtained by multiplying the previous integral term output value N_I by the current deviation Eo and the integral gain. When the actual temperature Tmo of the hydraulic oil is higher than the target temperature Tto, the deviation Eo is a positive value, so the integral term output value N_I is accumulated on the positive side, and when the actual temperature Tmo of the hydraulic oil is lower than the target temperature Tto, the deviation Eo is a negative value, so the integral term output value N_I is accumulated on the negative side. Then, by the process shown in FIG. 5, the integral term output value N_I is limited so as not to fall below the integral term lower limit value N_Imin.

[0029] The above steps are merely examples, and at least some of the steps may be deleted or changed, or steps other than those described above may be added. Furthermore, the order of at least some of the steps may be changed, or multiple steps may be combined into a single step.

[0030] Next, a method of determining the integral term lower limit value N_Imin executed by the vehicle body controller 51 in the above-mentioned step S4 will be described with reference to Fig. 6. As shown in Fig. 6, the vehicle body controller 51 controls the integral term lower limit value N_Imin in response to the atmospheric temperature and the vehicle body load.

[0031] Specifically, the vehicle body controller 51 determines the integral term lower limit value N_Imint1 according to the atmospheric temperature based on the table T1. The table T1 takes the atmospheric temperature detected by the atmospheric temperature sensor 71 as an input and outputs the integral term lower limit value N_Imint1 according to the atmospheric temperature. The integral term lower limit value N_Imin sets a lower limit value in the proportional-integral control, so that the rotation speed of the cooling fan 77 cannot be reduced to a certain level or more. For this reason, the larger the value of the integral term lower limit value N_Imin, the faster the start-up of the cooling fan 77 becomes and the easier it is to prevent overshooting, but the rotation speed of the cooling fan 77 becomes higher on average, which may worsen fuel efficiency, and when the value is small, the opposite phenomenon is likely to occur. For example, as the atmospheric temperature decreases, the air volume required to establish the heat balance at the target temperature Tto of the hydraulic oil also decreases, but the setting of the integral term lower limit value N_Imin may result in an air volume larger than necessary being output, which may cause overcooling and adversely affect fuel efficiency. Therefore, in order to avoid overcooling, in table T1, the air volume required for each ambient temperature is calculated in advance or confirmed experimentally, and the integral term lower limit value N_Imint1 for each ambient temperature is set so that the rotation speed is the number of revolutions required to establish heat balance at the target temperature Tto of the hydraulic oil at that ambient temperature.

[0032] Further, the vehicle body controller 51 determines the integral term lower limit value N_Imint2 according to the vehicle body load based on the table T2. The table T2 receives the pump output calculated based on the pump flow rate and discharge pressure detected by the pump flow rate / discharge pressure sensor 62s, for example, and outputs the integral term lower limit value N_Imint2 according to the pump output. When the vehicle body load is small, that is, when the heat input to the hydraulic oil is small, the actual temperature Tmo rises slowly, so that a large overshoot does not occur even if the rise in the rotation speed of the cooling fan 77 is delayed compared to when the vehicle body load is large. Therefore, in the table T2, when the pump output is small (when the heat input is small), the integral term lower limit value N_Imint2 is set to be small so that the start of the cooling fan 77 is delayed to prevent deterioration of fuel efficiency.

[0033] In step S8, the vehicle body controller 51 selects the larger of the integral term lower limit value N_Imint1 determined by the atmospheric temperature and the integral term lower limit value N_Imint2 determined by the vehicle body load, and determines the selected lower limit value as the integral term lower limit value N_Imin. This allows the prevention of overshooting that may cause problems in the vehicle body to be given top priority.

[0034] <Effects of the embodiment> The effects obtained by this embodiment will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a time chart of a comparative example in which the integral term output value is not limited, and Fig. 8 is a time chart of this embodiment in which the integral term output value is limited. In each time chart, the horizontal axis indicates time, and the vertical axis indicates the heat input to the fluid, the actual and target temperatures of the fluid, the proportional and integral term output values, the actual and target rotation speeds of cooling fan 77, etc.

[0035] As described above, the integrator S2 adds the previous integral term output value to a value obtained by multiplying the deviation between the actual temperature of the fluid and the target temperature by the integral gain. Therefore, as shown in FIG. 7, the longer the state in which the actual temperature of the fluid does not reach the target temperature continues, the more the accumulation of the integral term output value on the negative side gradually increases. At this time, the actual rotation speed of the cooling fan 77 is maintained at the minimum rotation speed as shown in FIG. 7, since the minimum rotation speed is determined by the hardware and software limitations of the cooling fan itself. From this state, the heat input to the fluid increases and the actual temperature of the fluid starts to rise (time T1), and when the actual temperature exceeds the target temperature (time T2), the integrator S2 starts accumulating the integral term output value on the positive side. When the target rotation speed exceeds the minimum rotation speed, the actual rotation speed of the cooling fan 77 starts to rise (time T3), and thereafter, the rotation speed of the cooling fan 77 is controlled by proportional-integral control so that the actual temperature of the fluid is maintained at the target temperature.

[0036] In the comparative example shown in FIG. 7, due to a large accumulation of the integral term output value on the negative side, the time lag (the time between time T2 and time T3) from when the actual temperature of the fluid exceeds the target temperature to when the actual rotation speed of the cooling fan 77 starts to increase becomes long, resulting in an overshoot phenomenon in which the actual temperature of the fluid rises far beyond the target temperature.

[0037] In contrast, in this embodiment, as shown in FIG. 8, the integral term output value is limited to be equal to or greater than the integral term lower limit value. As a result, even if the state in which the actual temperature of the fluid does not reach the target temperature continues for a long time, the accumulation of the integral term output value on the negative side does not increase. As a result, for example, in the example shown in FIG. 8, the target rotation speed and actual rotation speed of the cooling fan 77 are maintained without falling below the minimum rotation speed. When the heat input to the fluid increases from this state and the actual temperature of the fluid starts to rise (time T1), the target rotation speed and actual rotation speed of the cooling fan 77 also start to rise due to an increase in the proportional term output value. When the actual temperature exceeds the target temperature (time T2), the integrator S2 starts accumulating the integral term output value on the positive side, and the target rotation speed and actual rotation speed of the cooling fan 77 further increase. That is, in a state in which the integral term output value is maintained at the integral term lower limit value due to the limitation of the accumulation of the integral term output value on the negative side, when the actual temperature exceeds the target temperature, the accumulation of the integral term output value on the positive side starts. Thereafter, the rotation speed of the cooling fan 77 is controlled by proportional-integral control so that the actual temperature of the fluid is maintained at the target temperature.

[0038] 8, the actual rotation speed of the cooling fan 77 increases as soon as the actual temperature of the fluid starts to rise, and there is no time lag between when the actual temperature of the fluid exceeds the target temperature and when the actual rotation speed of the cooling fan 77 starts to increase. Therefore, excessive overshooting of the fluid temperature can be suppressed regardless of the heat input condition to the fluid.

[0039] The smaller the limit width of the accumulation of the integral term output value on the negative side (i.e., the larger the integral term lower limit value), the smaller the time lag described above can be. However, the integral term lower limit value is essentially a lower limit value for controlling the rotation speed of the cooling fan 77. For this reason, if the limit width is too small, a phenomenon occurs in which the rotation speed of the cooling fan 77 cannot be reduced to an appropriate rotation speed even in a supercooled state, which may lead to a deterioration in fuel efficiency. Therefore, in this embodiment, as described above, the ambient temperature and the vehicle load are monitored to control the integral term lower limit value, so that the limit width can be set to an appropriate value according to the vehicle environment and state. As a result, it is possible to prevent excessive overshoot while preventing unnecessary deterioration in fuel efficiency.

[0040] In this embodiment, the integral term output value is limited by using the greater of the integral term lower limit determined by the atmospheric temperature and the integral term lower limit determined by the vehicle load, thereby making it possible to give top priority to preventing overshooting that may cause problems to the vehicle body.

[0041] In particular, in this embodiment, in a state where the integral term output value is maintained at the integral term lower limit value due to the limitation on the accumulation of the integral term output value on the negative side, the vehicle body controller 51 starts accumulating the integral term output value on the positive side when the actual temperature exceeds the target temperature. This makes it possible to immediately increase the actual rotation speed of the cooling fan 77 when the actual temperature of the fluid exceeds the target temperature, thereby effectively suppressing excessive overshooting of the fluid temperature.

[0042] <Modification> The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and technical concept of the present invention.

[0043] For example, in the above embodiment, the integral term lower limit value is controlled in response to both the atmospheric temperature and the vehicle load, but the integral term lower limit value may be controlled in response to either the atmospheric temperature or the vehicle load. In this case, the process of step S8 described above is not required.

[0044] In the above embodiment, the target rotation speed of the cooling fan 77 is set based on the actual temperature and the target temperature of the hydraulic oil, but the present invention is not limited to this. The target rotation speed of the cooling fan 77 may be set based on the actual temperature and the target temperature of a fluid other than the hydraulic oil, for example, the engine cooling water or the intake air. In this case, the same method as in the above embodiment can be applied.

[0045] In the above embodiment, an example has been described in which a single cooling fan 77 cools a plurality of heat exchangers (oil cooler 73, radiator 74, and intercooler 75), but the present invention is not limited to this. For example, a method similar to that of the above embodiment can be applied to a case in which a single heat exchanger is cooled by a single cooling fan 77, or a case in which a plurality of heat exchangers are each cooled by a separate cooling fan.

[0046] In the above embodiment, the backward Euler method is used for discretizing the integrator, but other discretization methods such as the forward Euler method may be used.

[0047] In the above embodiment, the construction machine is described taking the crawler type hydraulic excavator 1 as an example, but the application of the present invention is not limited to this. For example, the present invention can be widely applied to other construction machines such as hydraulic cranes and wheel loaders, in which the rotation speed of the cooling fan can be set regardless of the rotation speed of the engine.

[0048] In addition to the above, the above-mentioned embodiments and the methods according to the modifications may be appropriately combined and used. Although not specifically illustrated, the present invention may be implemented with various modifications without departing from the spirit and scope of the present invention.

[0049] Furthermore, the problems to be solved by the invention and the effects of the invention are not limited to those described above. In other words, the present invention may solve problems or achieve effects that are not described above, or may solve only some of the problems or achieve only some of the effects that are described. [Explanation of symbols]

[0050] 1. Hydraulic excavator (an example of construction machinery) 51 Vehicle controller (an example of a controller) 62s Pump flow rate / discharge pressure sensor (an example of a vehicle load detector) 71 Air temperature sensor (an example of an air temperature detector) 73 Oil cooler (an example of a heat exchanger) 73s Hydraulic oil temperature sensor (an example of a temperature detector) 74 Radiator (an example of a heat exchanger) 74s Engine coolant temperature sensor (an example of a temperature detector) 75 Intercooler (an example of a heat exchanger) 75s Intake air temperature sensor (an example of a temperature detector) 77 Cooling Fan N_I Integral term output value N_Imin Integral term lower limit (an example of a specified lower limit) N_Imint1 Integral term lower limit N_Imint2 Integral term lower limit N_t Target RPM S1 proportional regulator S2 integrator Tmo actual temperature Tto target temperature

Claims

1. A cooling fan, a heat exchanger cooled by the cooling fan; a temperature detector for detecting a temperature of a fluid flowing through the heat exchanger; A construction machine equipped with a controller that controls the rotation speed of the cooling fan, the controller sets a target rotation speed of the cooling fan by proportional-integral control in response to a temperature difference between an actual temperature of the fluid detected by the temperature detector and a predetermined target temperature; In the integral control of the proportional-integral control, the output value of the integral term is limited to a predetermined lower limit value or more. A construction machine characterized by:

2. 2. The construction machine according to claim 1, Further comprising an atmospheric temperature detector capable of detecting an atmospheric temperature, The controller controls the lower limit value in response to the atmospheric temperature detected by the atmospheric temperature detector. A construction machine characterized by:

3. 2. The construction machine according to claim 1, Further comprising a vehicle body load detector capable of detecting a vehicle body load, The controller controls the lower limit value in response to the vehicle body load detected by the vehicle body load detector. A construction machine characterized by:

4. The construction machine according to claim 2, Further comprising a vehicle body load detector capable of detecting a vehicle body load, The controller controls the lower limit value in response to the atmospheric temperature detected by the atmospheric temperature detector or the vehicle load detected by the vehicle load detector. A construction machine characterized by:

5. The construction machine according to claim 4, The controller limits the output value of the integral term using a lower limit value determined by the atmospheric temperature or a lower limit value determined by the vehicle load, whichever is larger. A construction machine characterized by:

6. The construction machine according to any one of claims 1 to 5, When a candidate value for the output value of the integral term is smaller than the lower limit value, the controller sets the lower limit value as the output value of the integral term, and when the candidate value is equal to or greater than the lower limit value, sets the candidate value as the output value of the integral term. A construction machine characterized by:

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