Working machinery

Abstract

To provide a technique for preventing an overheat of a work machine having a common cool air flow path through which cool air generated by a plurality of cooling fans passes.SOLUTION: A work machine executes a fan control process which calculates a first target rotational speed such that the machine works faster as the first temperature is higher; and calculates (S12) a second target rotational speed such that the machine works faster as the second temperature is higher. When the difference value in which the second target rotational speed is deducted from the first target rotational speed is less than the threshold value (S13: Yes), the first cooling fan is rotated at the first target rotational speed (S14), and the second cooling fan is rotated at the second target rotational speed (S15). When the difference value is the threshold value or more (S13: No), the first cooling fan is rotated at the first target rotational speed (S17), and the second cooling fan is rotated at the modified second target rotational speed in which the threshold value is deducted from the first target rotational speed (S18).SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a work machine including a plurality of heat exchangers and a plurality of cooling fans.

Background Art

[0002] Conventionally, work machines such as hydraulic excavators have been equipped with a plurality of heat exchangers, such as a radiator for cooling the engine coolant, an oil cooler for cooling the hydraulic oil of the hydraulic system, and an intercooler for cooling the air compressed by the supercharger.

[0003] For example, Patent Document 1 discloses a work machine including a plurality of heat exchangers and a plurality of cooling fans arranged facing each of the plurality of heat exchangers. Further, in Patent Document 1, the flow path of the cooling air generated by each cooling fan is divided for each heat exchanger. And this work machine individually controls the rotational speed of each of the plurality of cooling fans according to the temperature of the fluid in the corresponding heat exchanger.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] FIG. 15 is a schematic view of a heat exchanger unit 90 according to a conventional example. FIG. 16 is a diagram showing the transition of the heat exchanger temperature (A) and the cooling fan rotational speed (B) of the heat exchanger unit 90 in FIG. 15. As shown in FIG. 15, in the heat exchanger unit 90 according to another conventional example, the flow paths of the cooling air from the heat exchangers 91a and 91b to the cooling fans 92a and 92b are shared. Hereinafter, consider the case where the above-described individual control is applied to the heat exchanger unit 90 shown in FIG. 15. Note that the thickness of the arrows in FIG. 15 represents the air volume of the cooling air.

[0006] First, as shown in Figure 15(A), when the rotational speeds of cooling fans 92a and 92b are approximately the same, the airflow volume of cooling air passing through heat exchangers 91a and 91b will also be approximately the same. If the temperature of the fluid inside heat exchanger 91b rises from this state, the rotational speed of cooling fan 92b will increase through individual control in order to increase the airflow volume of cooling air passing through heat exchanger 91b.

[0007] However, as shown in Figure 15(B), when the difference in rotational speed between cooling fans 92a and 92b becomes large, cooling fan 92b draws in not only the cooling air that has passed through the heat exchanger 91b opposite it, but also the cooling air that has passed through the adjacent heat exchanger 91a. In other words, even if the rotational speed of cooling fan 92b is increased by individual control in the heat exchanger unit 90 shown in Figure 15, the amount of cooling air passing through the heat exchanger 91b does not increase enough to suppress the temperature rise inside the heat exchanger 91b.

[0008] As a result, as shown in Figure 16, the heat exchanger temperature of heat exchanger 91b rises further, and the rotation speed of cooling fan 92b also increases further. This leads to a vicious cycle where the difference in rotation speed between cooling fans 92a and 92b becomes even larger, causing the heat exchanger temperature of heat exchanger 91b to reach its upper limit (i.e., overheat).

[0009] This invention has been made in view of the above-described circumstances, and its purpose is to provide a technology for preventing overheating in a work machine having a common cooling air passage through which cooling air generated by multiple cooling fans passes. [Means for solving the problem]

[0010] To achieve the above objective, the present invention provides a first cooling fan and a second cooling fan for generating cooling air, a flow path member for defining a common cooling air passage through which the cooling air generated by the first cooling fan and the second cooling fan passes, a first heat exchanger positioned facing the first cooling fan and exchanging heat between the cooling air passing through the cooling air passage and a first fluid, a second heat exchanger positioned facing the second cooling fan and exchanging heat between the cooling air passing through the cooling air passage and a second fluid, a first temperature sensor for detecting a first temperature which is the temperature of the first fluid, a second temperature sensor for detecting a second temperature which is the temperature of the second fluid, and based on the detection results of the first temperature sensor and the second temperature sensor, the first cooling fan In a work machine comprising a fan and a controller for controlling the rotation speed of the second cooling fan, the controller is characterized in that it performs fan control processing such that it calculates a first target rotation speed such that the speed increases as the first temperature increases, calculates a second target rotation speed such that the speed increases as the second temperature increases, rotates the first cooling fan at the first target rotation speed and rotates the second cooling fan at the second target rotation speed if the difference value obtained by subtracting the second target rotation speed from the first target rotation speed is less than a threshold, and rotates the first cooling fan at the first target rotation speed and rotates the second cooling fan at a modified second target rotation speed obtained by subtracting the threshold from the first target rotation speed if the difference value is greater than or equal to the threshold. [Effects of the Invention]

[0011] According to the present invention, overheating can be prevented in a work machine having a common cooling air passage through which cooling air generated by multiple cooling fans passes. Other problems, configurations, and effects will be clarified by the following description of embodiments. [Brief explanation of the drawing]

[0012] [Figure 1] This is a side view of a hydraulic excavator. [Figure 2] This is a plan view of the upper rotating body. [Figure 3] This is a control block diagram for a hydraulic excavator. [Figure 4] It is a flowchart of fan control processing. [Figure 5] It is a diagram showing an example of a table indicating the correspondence between the heat exchanger temperature and the target rotation speed. [Figure 6] It is a diagram showing the transition of the heat exchanger temperature (A) and the cooling fan rotation speed (B) during the fan control process shown in FIG. 4. [Figure 7] It is a flowchart of the warm-up control process according to the present embodiment. [Figure 8] It is a diagram showing an example of a table indicating the correspondence between the heat exchanger temperature and the warm-up rotation speed according to the present embodiment. [Figure 9] It is a diagram showing the transition of the heat exchanger temperature (A) and the cooling fan rotation speed (B) during the warm-up control process shown in FIG. 7. [Figure 10] It is a flowchart of the warm-up control process according to Modification 1. [Figure 11] It is a diagram showing an example of a table indicating the correspondence between the heat exchanger temperature and the warm-up rotation speed according to Modification 1. [Figure 12] It is a flowchart of the warm-up control process according to Modification 2. [Figure 13] It is a diagram showing the transition of the heat exchanger temperature (A) and the cooling fan rotation speed (B) during the warm-up control process shown in FIG. 12. [Figure 14] It is a flowchart of the warm-up control process according to Modification 3. [Figure 15] It is a schematic diagram of a heat exchanger unit according to a conventional example. [Figure 16] It is a diagram showing the transition of the heat exchanger temperature (A) and the cooling fan rotation speed (B) of the heat exchanger unit in FIG. 15.

Mode for Carrying Out the Invention

[0013] An embodiment of a hydraulic excavator 1 (working machine) according to the present invention will be described with reference to the drawings. Note that the specific example of the working machine is not limited to the hydraulic excavator 1, and may be a wheel loader, a crane, a dump truck, or the like. In addition, the front, rear, left, and right in this specification are based on the perspective of an operator who rides on and operates the hydraulic excavator 1 unless otherwise specified.

[0014] FIG. 1 is a side view of the hydraulic excavator 1. As shown in FIG. 1, the hydraulic excavator 1 includes a lower traveling body 2 and an upper revolving body 3 supported by the lower traveling body 2. The lower traveling body 2 and the upper revolving body 3 are an example of a vehicle body. The lower traveling body 2 includes a pair of left and right crawlers 4 that are endless track belts. Then, by driving the traveling motor 5, the pair of left and right crawlers 4 rotate independently. As a result, the hydraulic excavator 1 travels. However, the lower traveling body 2 may be wheel-mounted instead of the crawlers 4.

[0015] The upper revolving body 3 is supported by the lower traveling body 2 so as to be rotatable by a slewing motor 6. The upper revolving body 3 mainly includes a revolving frame 7 as a base, a cab (driver's seat) 8 disposed on the front left side of the revolving frame 7, a counterweight 9 disposed at the rear of the revolving frame 7, and a front working machine 10 (working device) attached to the front center of the revolving frame 7 so as to be rotatable in the vertical direction.

[0016] A space for an operator to ride and operate the hydraulic excavator 1 is formed in the cab 8. Inside the cab 8, a seat on which the operator sits and an operating device operated by the operator sitting on the seat are arranged.

[0017] The control device receives operator input for operating the hydraulic excavator 1. When the operator operates the control device, the lower traveling body 2 moves, the upper rotating body 3 rotates, and the front work implement 10 operates. Specific examples of the control device include levers, steering wheels, pedals, switches, etc. The control device includes, for example, a warm-up switch 8a (see Figure 3) that instructs the execution of the warm-up control process described later, and an adjustment button 8b (see Figure 3) that instructs the adjustment of the warm-up target temperature Tb_h.

[0018] Furthermore, a display 8c (see Figure 2) is installed in cab 8. Display 8c is an example of a notification device that informs the operator in cab 8 of information. Note that the specific example of a notification device is not limited to display 8c, but may also be an LED lamp, a speaker, or a combination thereof.

[0019] The front work implement 10 includes a boom 11 supported on the upper slewing body 3 so as to be able to be raised and lowered, an arm 12 rotatably supported at the tip of the boom 11, a bucket 13 rotatably supported at the tip of the arm 12, a boom cylinder 14 for driving the boom 11, an arm cylinder 15 for driving the arm 12, and a bucket cylinder 16 for driving the bucket 13. The counterweight 9 is for balancing the weight with the front work implement 10 and is a heavy object that forms an arc shape when viewed from above.

[0020] Furthermore, the upper slewing body 3 supports the engine building 20 (building). The engine building 20 is supported by the slewing frame 7 behind the cab 8 and front work implement 10, and in front of the counterweight 9. The engine building 20 has a space for housing components for operating the hydraulic excavator 1.

[0021] Figure 2 is a plan view of the upper rotating body 3. As shown in Figure 2, the engine building 20 houses components for operating the hydraulic excavator 1, such as the engine 21, hydraulic pump 22, and heat exchanger unit 23.

[0022] The engine 21 is located to the right of the heat exchanger unit 23 and to the left of the hydraulic pump 22. The engine 21 generates the driving force to operate the hydraulic excavator 1 by burning a mixture of fossil fuel and air.

[0023] The hydraulic pump 22 is located to the right of the engine 21 and the heat exchanger unit 23. The hydraulic pump 22 is connected to the output shaft of the engine 21 and rotates to pump the hydraulic fluid stored in the hydraulic fluid tank (not shown) to the hydraulic actuators (travel motor 5, slewing motor 6, boom cylinder 14, arm cylinder 15, and bucket cylinder 16).

[0024] The heat exchanger unit 23 is a unit for cooling multiple fluids. The heat exchanger unit 23 according to this embodiment comprises multiple heat exchangers 24a, 24b and multiple cooling fans 25a, 25b.

[0025] Heat exchanger 24a is a radiator that exchanges heat between the coolant (fluid) that cools the engine 21 and cooling air. Heat exchanger 24b is an oil cooler that exchanges heat between the hydraulic fluid (fluid) that operates the hydraulic actuator and cooling air. The heat exchanger unit 23 may also include an intercooler that cools the air (fluid) compressed by the supercharger mounted on the engine 21.

[0026] The cooling fans 25a and 25b generate a cooling airflow that flows from left to right within the engine building 20. The cooling fans 25a and 25b are rotated by the driving force of their corresponding fan motors 26a and 26b (see Figure 3). The fan motors 26a and 26b may be electric motors that rotate in response to an electric power supply, or hydraulic motors that rotate in response to a hydraulic fluid supply.

[0027] The cooling fans 25a and 25b are configured to have their rotational speeds independently changed according to the control of the controller 30 (see Figure 3). More specifically, the rotational speeds of the cooling fans 25a and 25b are increased or decreased by increasing or decreasing the power or hydraulic fluid supplied to the fan motors 26a and 26b.

[0028] As shown in Figure 2, the heat exchanger unit 23 includes a housing 23a. The housing 23a houses the heat exchangers 24a and 24b and the cooling fans 25a and 25b. However, the upstream side of the cooling airflow (i.e., the left side) and the downstream side of the cooling airflow (i.e., the right side) are open. That is, the cooling air generated by the cooling fans 25a and 25b flows into the heat exchanger unit 23 from the left side and flows out from the right side. The housing 23a constitutes an example of a flow path member that defines a common cooling airflow path 27 through which the cooling air generated by the cooling fans 25a and 25b passes.

[0029] The heat exchangers 24a, 24b and cooling fans 25a, 25b are arranged in the internal space of the housing 23a. The heat exchangers 24a, 24b are arranged in a direction perpendicular to the direction of cooling airflow (front-to-back direction). The cooling fans 25a, 25b are arranged downstream of the heat exchangers 24a, 24b in the direction of cooling airflow, and are also arranged in a direction perpendicular to the direction of cooling airflow (front-to-back direction). Furthermore, the cooling fans 25a, 25b are positioned facing the corresponding heat exchangers 24a, 24b in the direction of cooling airflow.

[0030] Therefore, heat exchanger 24a is supplied mainly with cooling air generated by cooling fan 25a, but also with a portion of the cooling air generated by cooling fan 25b. Similarly, heat exchanger 24b is supplied mainly with cooling air generated by cooling fan 25b, but also with a portion of the cooling air generated by cooling fan 25a. In other words, heat exchangers 24a and 24b exchange heat between the cooling air passing through the common cooling air passage 27 and the fluid (coolant, air).

[0031] In this embodiment, heat exchanger 24a is an example of a first heat exchanger, heat exchanger 24b is an example of a second heat exchanger, cooling fan 25a is an example of a first cooling fan, cooling fan 25b is an example of a second cooling fan, the coolant of the engine 21 is an example of a first fluid, and the hydraulic fluid that operates the hydraulic actuator is an example of a second fluid. However, heat exchanger 24b may be used as the first heat exchanger and heat exchanger 24a as the second heat exchanger.

[0032] As shown in Figure 1, an air intake port 28 is formed on the left side of the engine building 20. Furthermore, an exhaust port (not shown) is formed on the right side of the engine building 20. When the cooling fans 25a and 25b rotate, the air (cooling air) that flows into the engine building 20 from the air intake port 28 passes through the heat exchanger unit 23 and is discharged to the outside of the engine building 20 from the exhaust port.

[0033] The direction of the cooling airflow generated by the cooling fans 25a and 25b is not limited to left to right. As another example, if the cooling airflow direction is right to left, the arrangement of the heat exchangers 24a and 24b and the cooling fans 25a and 25b within the heat exchanger unit 23 is reversed left to right. That is, the cooling fans 25a and 25b only need to be positioned downstream of the heat exchangers 24a and 24b in the direction of the cooling airflow.

[0034] Figure 3 is a control block diagram of the hydraulic excavator 1. As shown in Figure 3, the hydraulic excavator 1 includes a controller 30 having a CPU 31 (Central Processing Unit) and memory 32. The memory 32 is composed of, for example, ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), or a combination thereof. The controller 30 performs the processing described later by having the CPU 31 read and execute the program code stored in the memory 32.

[0035] However, the specific configuration of the controller 30 is not limited to this and may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array).

[0036] The controller 30 is connected to temperature sensors 33a and 33b, a warm-up switch 8a, and an adjustment button 8b. On the other hand, although an outside temperature sensor 34 is also shown in Figure 3, the outside temperature sensor 34 can be omitted in this embodiment.

[0037] The temperature sensors 33a and 33b detect the temperature of the fluid (coolant, hydraulic oil) in the corresponding heat exchangers 24a and 24b (hereinafter referred to as "heat exchanger temperature") and output a temperature signal indicating the detected heat exchanger temperature to the controller 30. Temperature sensor 33a is an example of a first temperature sensor, temperature sensor 33b is an example of a second temperature sensor, the heat exchanger temperature Ta detected by temperature sensor 33a is an example of a first temperature, and the heat exchanger temperature Tb detected by temperature sensor 33b is an example of a second temperature.

[0038] Furthermore, the controller 30 controls the operation of the fan motors 26a and 26b and the display 8c. More specifically, the controller 30 controls the rotation speed of the fan motors 26a and 26b based on the detection results of the temperature sensors 33a and 33b. In addition, the controller 30 informs the operator in the cab 8 of information via the display 8c.

[0039] Next, the fan control process will be explained with reference to Figures 4 to 6. Figure 4 is a flowchart of the fan control process. Figure 5 is an example of a table showing the correspondence between heat exchanger temperatures Ta and Tb and target rotational speeds Na and Nb. Figure 6 is a diagram showing the changes in heat exchanger temperature (A) and cooling fan rotational speed (B) during the fan control process shown in Figure 4. The controller 30 repeatedly executes the fan control process at predetermined time intervals, for example, after the warm-up process described later is completed and until the engine 21 stops.

[0040] First, the controller 30 acquires the heat exchanger temperatures Ta and Tb detected by the temperature sensors 33a and 33b (S11). Next, the controller 30 calculates the target rotational speeds Na and Nb corresponding to the acquired heat exchanger temperatures Ta and Tb (S12). Target rotational speed Na is an example of the first target rotational speed of the cooling fan 25a corresponding to the heat exchanger temperature Ta. Target rotational speed Nb is an example of the second target rotational speed of the cooling fan 25b corresponding to the heat exchanger temperature Tb.

[0041] As shown in Figure 5(A), the memory 32 stores the correspondence between the heat exchanger temperature Ta of the heat exchanger 24a and the target rotational speed Na of the cooling fan 25a. When the heat exchanger temperature Ta is below the specified temperature Ta_low, the target rotational speed Na remains constant at the specified rotational speed Na_low. When the heat exchanger temperature Ta is equal to or greater than the specified temperature Ta_low, the target rotational speed Na increases as the heat exchanger temperature Ta increases.

[0042] Furthermore, as shown in Figure 5(B), the memory 32 stores the correspondence between the heat exchanger temperature Tb of the heat exchanger 24b and the target rotational speed Nb of the cooling fan 25b. When the heat exchanger temperature Tb is less than the specified temperature Tb_low, the target rotational speed Nb remains constant at the specified rotational speed Nb_low. Also, when the heat exchanger temperature Tb is equal to or greater than the specified temperature Tb_low, the target rotational speed Nb increases as the heat exchanger temperature Tb increases.

[0043] The controller 30 then calculates the target rotational speed Na based on the correspondence shown in Figure 5(A) and the target rotational speed Nb based on the correspondence shown in Figure 5(B). In other words, the controller 30 calculates the target rotational speeds Na and Nb so that they increase as the heat exchanger temperatures Ta and Tb increase. Note that the relationship between the heat exchanger temperatures Ta and Tb and the target rotational speeds Na and Nb is not limited to the linear relationship shown in Figure 5, but may also be a nonlinear relationship.

[0044] Next, the controller 30 compares the difference value (= Na - Nb) obtained by subtracting the target rotation speed Nb from the target rotation speed Na with the threshold value ΔN stored in the memory 32 (S13). The threshold value ΔN may be a predetermined fixed value or a variable value that becomes larger as the heat exchanger temperature Ta is lower.

[0045] Then, when the difference value (Na - Nb) is less than the threshold value ΔN (S13: Yes), the controller 30 rotates the cooling fan 25a at the target rotation speed Na calculated in step S12 (S14) and rotates the cooling fan 25b at the target rotation speed Nb calculated in step S12 (S15). That is, when the difference between the target rotation speeds Na and Nb is small, the rotation speeds of the cooling fans 25a and 25b are individually controlled based on the heat exchanger temperatures Ta and Tb.

[0046] On the other hand, when the difference value (Na - Nb) is greater than or equal to the threshold value ΔN (S13: No), the controller 30 subtracts the threshold value ΔN from the target rotation speed Na calculated in step S12 to calculate a corrected target rotation speed Nb' (S16). The corrected target rotation speed Nb' becomes a value larger than the target rotation speed Nb calculated in step S12. The corrected target rotation speed Nb' is an example of a corrected second target rotation speed.

[0047] Then, the controller 30 rotates the cooling fan 25a at the target rotation speed Na calculated in step S12 (S17) and rotates the cooling fan 25b at the corrected target rotation speed Nb' calculated in step S16 (S18). That is, when the difference between the target rotation speeds Na and Nb is large, while allowing the heat exchanger 24b to be overcooled as shown in FIG. 6(A), the difference in the rotation speeds of the cooling fans 25a and 25b is controlled to be constant (= threshold value ΔN) as shown in FIG. 6(B).

[0048] In addition, in FIG. 5, the process assuming Na > Nb is illustrated. On the other hand, when Na < Nb, the cooling fan 25a is rotated at the corrected target rotation speed Na' (= Nb - ΔN), and the cooling fan 25b is rotated at the target rotation speed Nb.

[0049] Next, the warm-up control process according to this embodiment will be described with reference to Figures 7 to 9. Figure 7 is a flowchart of the warm-up control process according to this embodiment. Figure 8 is a diagram showing an example of a table that shows the correspondence between the heat exchanger temperatures Ta and Tb and the warm-up rotation speeds Na_h1 and Nb_h1 according to this embodiment. Figure 9 is a diagram showing the changes in the heat exchanger temperature (A) and cooling fan rotation speed (B) during the warm-up control process shown in Figure 7.

[0050] The controller 30 executes the warm-up control process shown in Figure 7 when, for example, it is instructed to perform the warm-up process via the warm-up switch 8a (i.e., the warm-up switch 8a is turned ON). The operator can, for example, start the operation of the hydraulic excavator 1 in a cold region by turning the warm-up switch 8a ON.

[0051] Warm-up is the process of raising the temperature of the coolant and hydraulic oil to a temperature range in which the hydraulic excavator 1 can operate stably. To this end, the controller 30 rotates the engine 21 to raise the temperature of the coolant and pumps the hydraulic oil to the hydraulic pump 22 to raise the temperature of the hydraulic oil. In this embodiment, the target temperature of the coolant is set to the warm-up target temperature Ta_h, and the target temperature of the hydraulic oil is set to the warm-up target temperature Tb_h. However, the controller 30 does not need to continue the warm-up process until both the coolant and hydraulic oil reach the target temperature. In other words, warm-up is the process of bringing the coolant and hydraulic oil, respectively, closer to the target temperature. In this embodiment, the warm-up process continues until either the coolant or the hydraulic oil reaches the target temperature.

[0052] In this embodiment, it is assumed that the temperature of the fluid (hydraulic oil) in heat exchanger 24b does not rise as easily as the temperature of the fluid (coolant) in heat exchanger 24a. Therefore, if the rotation speeds of the cooling fans 25a and 25b are controlled individually based on the heat exchanger temperatures Ta and Tb, the heat exchanger temperature Ta will reach the target warm-up temperature Ta_h before the heat exchanger temperature Tb is much lower, and the warm-up process will end. Therefore, in the warm-up control process according to this embodiment, the following control is performed.

[0053] First, the controller 30 obtains the target warm-up temperatures Ta_h and Tb_h for the heat exchangers 24a and 24b (S21). The target warm-up temperature Ta_h (first target warm-up temperature) for heat exchanger 24a is a fixed value stored in memory 32, for example. On the other hand, the target warm-up temperature Tb_h (second target warm-up temperature) for heat exchanger 24b is a variable value that can be set by the operator via adjustment button 8b, for example. However, specific examples of the target warm-up temperatures Ta_h and Tb_h are not limited to the examples given above.

[0054] Next, the controller 30 acquires the heat exchanger temperatures Ta and Tb detected by the temperature sensors 33a and 33b (S22). Next, the controller 30 compares the target warm-up temperature Ta_h acquired in step S21 with the heat exchanger temperature Ta acquired in step S22 (S23). The controller 30 also compares the target warm-up temperature Tb_h acquired in step S21 with the heat exchanger temperature Tb acquired in step S22 (S24).

[0055] Then, if the heat exchanger temperature Ta is less than the warm-up target temperature Ta_h and the heat exchanger temperature Tb is less than the warm-up target temperature Tb_h (S23:Yes & S24:Yes), the controller rotates the cooling fan 25a at a warm-up rotation speed Na_h1 (an example of the first warm-up rotation speed) calculated based on the correspondence shown in Figure 8(A) (S25), and rotates the cooling fan 25b at a warm-up rotation speed Nb_h1 (an example of the first warm-up rotation speed) calculated based on the correspondence shown in Figure 8(B) (S26).

[0056] As shown in Figure 8(A), the memory 32 stores the correspondence between the heat exchanger temperature Ta of the heat exchanger 24a and the warm-up speed Na_h1 of the cooling fan 25a. When the heat exchanger temperature Ta is below the minimum temperature Ta_min, the warm-up speed Na_h1 remains constant at the minimum speed Na_min. When the heat exchanger temperature Ta is above the minimum temperature Ta_min, the warm-up speed Na_h1 increases as the heat exchanger temperature Ta increases. Furthermore, when the heat exchanger temperature Ta reaches the warm-up target temperature Ta_h, the warm-up speed Na_h1 reaches the maximum speed Na_max. Note that the relationship between the heat exchanger temperature Ta and the warm-up speed Na_h1 is not limited to the linear relationship shown in Figure 8(A), but may also be nonlinear.

[0057] Furthermore, as shown in Figure 8(B), the memory 32 stores the correspondence between the heat exchanger temperature Tb of the heat exchanger 24b and the warm-up speed Nb_h1 of the cooling fan 25b. The warm-up speed Nb_h1 is a fixed value that remains constant regardless of the heat exchanger temperature Tb.

[0058] In other words, the controller 30 rotates the cooling fan 25a at a warm-up speed Na_h1 calculated to be faster as the heat exchanger temperature Ta increases (S25), and rotates the cooling fan 25b at a warm-up speed Nb_h1 which is set to a fixed value in advance (S26).

[0059] The controller 30 then repeatedly executes the processes in steps S22 to S26 while the engine 21 is running (S27: No). On the other hand, during the process of repeatedly executing the processes in steps S22 to S26, the controller 30 terminates the processes in steps S22 to S26 if the heat exchanger temperature Ta becomes equal to or above the warm-up target temperature Ta_h, or if the heat exchanger temperature Tb becomes equal to or above the warm-up target temperature Tb_h (S23: No / S24: No). The processes in steps S22 to S26 are an example of a warm-up process. After terminating the warm-up process, the controller 30 turns off the warm-up switch 8a (S28) and starts the fan control process shown in Figure 4 (S29).

[0060] According to the warm-up process (S22-S26) shown in Figure 7, as shown in Figure 9(B), the rotation speed of cooling fan 25a increases as the heat exchanger temperature Ta rises, while the rotation speed of cooling fan 25b remains constant. As a result, as shown in Figure 9(A), the rise in heat exchanger temperature Ta is suppressed, and the rise in heat exchanger temperature Tb is promoted. Consequently, at the end of the warm-up process, the heat exchanger temperature Tb can be brought close to the warm-up target temperature Tb_h1. Note that in Figure 9, the warm-up target temperatures Ta_h1 and Tb_h1 are shown as the same value, but they may be different values.

[0061] According to the above embodiment, for example, the following effects are achieved.

[0062] According to the fan control process of the above embodiment, if the difference between the target rotational speeds Na and Nb, which are individually calculated based on the heat exchanger temperatures Ta and Tb, exceeds a threshold ΔN, the cooling fan 25b is rotated at a modified target rotational speed Nb' (=Na-ΔN) instead of the target rotational speed Nb. As a result, the difference in rotational speed between the cooling fans 25a and 25b does not become too large, and the proportion of cooling air that has passed through the heat exchanger 24b and is drawn in by the cooling fan 25a is reduced compared to the individual control described with reference to Figure 15(B). As a result, the temperature rise of the heat exchanger 24a can be suppressed, and overheating of the engine 21, which is cooled by the fluid (coolant) of the heat exchanger 24a, is prevented.

[0063] Furthermore, according to the above embodiment, the threshold ΔN is increased as the heat exchanger temperature Ta decreases, and the threshold ΔN is decreased as the heat exchanger temperature Ta increases. As a result, when the risk of engine 21 overheating is low (i.e., the heat exchanger temperature Ta is low), a large difference between the target rotational speeds Na and Nb is allowed, and the cooling fans 25a and 25b are made to generate the minimum necessary cooling air. On the other hand, when the risk of engine 21 overheating is high (i.e., the heat exchanger temperature Ta is high), a large difference between the target rotational speeds Na and Nb is prevented, and the heat exchanger 24a is appropriately cooled while allowing the heat exchanger 24b to become overcooled.

[0064] Furthermore, according to the warm-up control process of the above embodiment, the cooling fan 25a is rotated at a warm-up rotation speed Na_h1 corresponding to the heat exchanger temperature Ta, and the cooling fan 25b is rotated at a warm-up rotation speed Nb_h1 which is set to a fixed value in advance. As a result, the temperature rise of the heat exchanger temperature Ta is suppressed, and the temperature rise of the heat exchanger temperature Tb is promoted. As a result, in the warm-up process, the temperature of the fluid that is relatively difficult to raise in temperature (in this case, the hydraulic oil) can be raised to a temperature close to the warm-up target temperature Tb_h.

[0065] [Example 1] Next, the warm-up control process according to Modification 1 will be explained with reference to Figures 10 and 11. Figure 10 is a flowchart of the warm-up control process according to Modification 1. Figure 11 is a diagram showing an example of a table that shows the correspondence between heat exchanger temperatures Ta and Tb and warm-up rotation speeds Na_h1 and Nb_h2 according to Modification 1. Note that a detailed explanation of the common points with the above embodiment will be omitted, and the explanation will focus on the differences.

[0066] As shown in Figure 3, the hydraulic excavator 1 according to Modification 1 is equipped with an ambient temperature sensor 34. The ambient temperature sensor 34 detects the ambient temperature To, which is the temperature around the hydraulic excavator 1, and outputs a temperature signal indicating the detected ambient temperature To to the controller 30.

[0067] Furthermore, in the warm-up control process according to Modification 1, the rotation speed control of the cooling fan 25b (S30) differs from that of the above embodiment (S26 in Figure 7). Specifically, in step S30, the controller 30 according to Modification 1 rotates the cooling fan 25b at a warm-up rotation speed Nb_h2 (an example of a second warm-up rotation speed) corresponding to the ambient temperature To detected by the ambient temperature sensor 34. More specifically, the controller 30 according to Modification 1 rotates the cooling fan 25b at a warm-up rotation speed Nb_h2 calculated according to the correspondence shown in Figure 11(B), such that the rotation speed increases as the ambient temperature To increases.

[0068] As shown in Figure 11(B), the memory 32 stores the correspondence between the ambient temperature To and the warm-up speed Nb_h2 of the cooling fan 25b. When the ambient temperature To is less than the minimum temperature To_min, the warm-up speed Nb_h2 remains constant at the minimum speed Nb_min. When the ambient temperature To is equal to or greater than the minimum temperature To_min, the warm-up speed Nb_h2 increases as the ambient temperature To increases. Note that the relationship between ambient temperature To and warm-up speed Nb_h2 is not limited to the linear relationship shown in Figure 11(B), but may also be nonlinear. Furthermore, the correspondence between the heat exchanger temperature Ta and the warm-up speed Na_h1 shown in Figure 11(A) is the same as that in Figure 8(A).

[0069] If the temperature of the fluid (i.e., hydraulic oil) in the heat exchanger 24b rises too quickly, sticking is more likely to occur in the components of the hydraulic equipment. Furthermore, the higher the ambient temperature To, the easier it is for the heat exchanger 24b to warm up. Therefore, according to Modification 1, the higher the ambient temperature To, the faster the warm-up rotation speed Nb_h2 of the cooling fan 25b becomes, making it possible to warm up the fluid in the heat exchanger 24b at an appropriate speed.

[0070] [Differentiation 2] Next, the warm-up control process according to Modification 2 will be explained with reference to Figures 12 and 13. Figure 12 is a flowchart of the warm-up control process according to Modification 2. Figure 13 is a diagram showing the changes in heat exchanger temperature (A) and cooling fan rotation speed (B) during the warm-up control process shown in Figure 12. Detailed explanations of the common points with the above embodiment will be omitted, and the explanation will focus on the differences.

[0071] In the modified example 2, the controller 30 rotates the cooling fan 25b in step S31 at a warm-up rotation speed Nb_h3 (an example of a second warm-up rotation speed) corresponding to the time change dTb of the heat exchanger temperature Tb during the warm-up process. More specifically, the controller 30 in the modified example 2 rotates the cooling fan 25b at a warm-up rotation speed Nb_h3 that becomes faster the larger the time change dTb of the heat exchanger temperature Tb during the warm-up process is.

[0072] In other words, during the warm-up process which is repeatedly performed, the controller 30 stores the heat exchanger temperature Tb acquired in step S22 in the memory 32. Next, the controller 30 calculates the time change dTb of the multiple heat exchanger temperatures Tb stored in the memory 32. The time change dTb is calculated, for example, by dividing the time difference between two temporally adjacent heat exchanger temperatures Tb by the interval between acquiring the heat exchanger temperatures Tb (the execution interval of step S22).

[0073] The controller 30 then determines the warm-up rotation speed Nb_h3 according to a predetermined correspondence between the time change dTb of the heat exchanger temperature Tb and the warm-up rotation speed Nb_h3. The correspondence between the time change dTb of the heat exchanger temperature Tb and the warm-up rotation speed Nb_h3 has a positive correlation, for example, as shown in Figure 11(B).

[0074] According to Modification 2, for example, as shown in Figure 13, when the rate of increase of the heat exchanger temperature Tb slows down, the warm-up speed Tb_h3 of the cooling fan 25b slows down, making it possible to warm up the fluid in the heat exchanger 24b at an appropriate rate. That is, by suppressing the warm-up speed Tb_h3 of the cooling fan 25b during the warm-up process (Figure 13(B)), the rise in the heat exchanger temperature Tb is promoted (Figure 13(A)). Furthermore, by releasing the suppression of the warm-up speed Tb_h3 after the warm-up process is completed (Figure 13(B)), the rate of increase in the heat exchanger temperature Tb becomes gentler compared to during the warm-up process (Figure 13(A)).

[0075] [Difference 3] Next, with reference to Figure 14, the warm-up control process according to Modified Example 3 will be explained. Figure 14 is a flowchart of the warm-up control process according to Modified Example 3. Note that a detailed explanation of the similarities with the above embodiment will be omitted, and the explanation will focus on the differences.

[0076] In the modified example 3, when the warm-up process (S22-S27) is completed, that is, when the heat exchanger temperature Ta becomes equal to or above the warm-up target temperature Ta_h, or when the heat exchanger temperature Tb becomes equal to or above the warm-up target temperature Tb_h (S23:No / S24:No), the controller 30 reduces the speed of the cooling fan 25a to a specified rotational speed Na_low (S32). After that, the controller 30 executes the processes in steps S28 and S29.

[0077] Here, the specified rotational speed Na_low is set to a value smaller than the warm-up rotational speed Na_h1 at the end of the warm-up process. The specified rotational speed Na_low may be, for example, a predetermined fixed value, or it may be the same value as the warm-up rotational speed Nb_h1 at the end of the warm-up process. In other words, by adding step S32, the difference in rotational speeds of the cooling fans 25a and 25b at the start of the fan control process (S29) becomes smaller.

[0078] If the fan control process (S29) is started when there is a large difference in the rotational speeds of cooling fans 25a and 25b, backflow will occur in cooling fan 25b. If the process in step S16 of Figure 4 (i.e., the process of increasing the rotational speed of cooling fan 25b) is executed in this state, a large torque will be required for the fan motor 26b. Therefore, as shown in Modification 3, by reducing the difference in rotational speeds of cooling fans 25a and 25b prior to starting the fan control process (S29), the fan control process can be executed smoothly.

[0079] The embodiments described above are illustrative for explaining the present invention and are not intended to limit the scope of the invention to those embodiments only. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the invention. [Explanation of symbols]

[0080] 1. Hydraulic excavator (working machine) 2 Lower running body 3. Upper rotating body 4 Crawler 5. Driving motor 6. Swivel motor 7. Swivel Frame 8 Cab 8a Warm-up switch 8b Adjustment button 8c display 9 Counterweight 10 Front work equipment 11 Boom 12 arms 13 buckets 14 Boom Cylinder 15 Arm Cylinder 16 Bucket Cylinder 20 Engine building 21 Engine 22 Hydraulic pumps 23.90 Heat exchanger unit 23a Enclosure 24a,24b,91a,91b Heat exchanger 25a, 25b, 92a, 92b Cooling Fan 26a, 26b Fan motor 27 Cooling air flow path 28 Air supply port 30 controllers 31 CPU 32 memory 33a, 33b Temperature Sensor 34. Outdoor temperature sensor

Claims

1. A first cooling fan and a second cooling fan that generate cooling air, A flow path member that defines a common cooling air passage through which the cooling air generated by the first cooling fan and the second cooling fan passes, A first heat exchanger is positioned opposite the first cooling fan and exchanges heat between the cooling air passing through the cooling air passage and the first fluid, A second heat exchanger is positioned opposite the second cooling fan and exchanges heat between the cooling air passing through the cooling air passage and the second fluid, A first temperature sensor for detecting a first temperature, which is the temperature of the first fluid, A second temperature sensor for detecting the second temperature, which is the temperature of the second fluid, A work machine comprising a controller that controls the rotation speed of the first cooling fan and the second cooling fan based on the detection results of the first temperature sensor and the second temperature sensor, The aforementioned controller, The first target rotational speed is calculated such that it increases as the first temperature increases. The second target rotational speed is calculated such that it increases as the second temperature increases. A work machine characterized by performing a fan control process in which, if the difference value obtained by subtracting the second target rotation speed from the first target rotation speed is less than a threshold, the first cooling fan is rotated at the first target rotation speed and the second cooling fan is rotated at the second target rotation speed, and if the difference value is greater than or equal to the threshold, the first cooling fan is rotated at the first target rotation speed and the second cooling fan is rotated at a modified second target rotation speed obtained by subtracting the threshold from the first target rotation speed.

2. In the work machine described in claim 1, The controller is characterized in that it increases the threshold as the first temperature decreases.

3. In the work machine described in claim 1, The system includes a warm-up switch that initiates a warm-up process to bring the first fluid and the second fluid closer to a target temperature. The controller, when instructed to start the warm-up process by the warm-up switch, rotates the first cooling fan at a first warm-up rotation speed calculated to increase as the first temperature increases, and rotates the second cooling fan at a second warm-up rotation speed set to a fixed value in advance, and continues the warm-up process until the first temperature reaches or exceeds the first warm-up target temperature, or the second temperature reaches or exceeds the second warm-up target temperature.

4. In the work machine described in claim 1, A warm-up switch that initiates a warm-up process to bring the first fluid and the second fluid closer to the target temperature, The machine is equipped with an ambient temperature sensor that detects the ambient temperature, which is the temperature of the surrounding air. The controller, when instructed to start the warm-up process by the warm-up switch, rotates the first cooling fan at a first warm-up rotation speed calculated to increase as the first temperature increases, and rotates the second cooling fan at a second warm-up rotation speed calculated to increase as the ambient temperature increases, and continues the warm-up process until the first temperature reaches or exceeds the first warm-up target temperature, or the second temperature reaches or exceeds the second warm-up target temperature.

5. In the work machine described in claim 1, The system includes a warm-up switch that initiates a warm-up process to bring the first fluid and the second fluid closer to a target temperature. The controller, when instructed by the warm-up switch to start the warm-up process, rotates the first cooling fan at a first warm-up rotation speed calculated to increase as the first temperature increases, and rotates the second cooling fan at a second warm-up rotation speed calculated to increase as the time change of the second temperature increases, and continues the warm-up process until the first temperature reaches or exceeds the first warm-up target temperature, or until the second temperature reaches or exceeds the second warm-up target temperature.

6. In the work machine described in claim 3, The controller is characterized in that, when the warm-up process is completed, it decelerates the first cooling fan to a specified rotational speed before starting the fan control process.

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