Work machine and method for controlling work machine

Abstract

A work machine includes a drive source, a traveling device, a hydraulic brake, an oil temperature sensor, and a controller. The traveling device is driven by the drive source in order to cause the work machine to travel. The hydraulic brake is driven by hydraulic oil in order to brake the traveling device. The oil temperature sensor detects an oil temperature of the hydraulic oil. The controller acquires the oil temperature of the hydraulic oil, and reduces acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a U.S. National stage application of International Application No. PCT / JP2024 / 008070, filed on Mar. 4, 2024. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2023-054569, filed in Japan on Mar. 30, 2023. The entire contents of Japanese Patent Application No. 2023-054569 is hereby incorporated herein by reference.BACKGROUNDTechnical Field

[0002] The present disclosure relates to a work machine and a method for controlling a work machine.Background Art

[0003] Some work machines include a hydraulic brake. For example, in the work machine of Japanese U.S. Pat. No. 5,412,011 B, hydraulic oil supplied to a hydraulic brake is controlled according to the amount of operation of a brake pedal. Thus, the braking force by the hydraulic brake is controlled.SUMMARY

[0004] The work machine may be used at a harsh site and a heavy burden is placed on the brake. For example, a heavy burden is applied to the brake due to a large number of times the brake is applied per unit time, a long continuous operation time, a heavy weight of the work machine, and the like. Therefore, the hydraulic oil tends to have a high temperature. An object of the present disclosure is to suppress overheating of hydraulic oil of a hydraulic brake in a work machine.

[0005] A work machine according to an aspect of the present disclosure includes a drive source, a traveling device, a hydraulic brake, an oil temperature sensor, and a controller. The traveling device is driven by the drive source and thus causes the work machine to travel. The hydraulic brake is driven by hydraulic oil and thus brakes the traveling device. The oil temperature sensor detects the oil temperature of the hydraulic oil. The controller acquires the oil temperature of the hydraulic oil. The controller reduces the acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

[0006] A method according to another aspect of the present disclosure is a method for controlling a work machine, and the work machine includes a drive source, a traveling device, and a hydraulic brake. The traveling device is driven by the drive source and thus causes the work machine to travel. The hydraulic brake is driven by hydraulic oil and thus brakes the traveling device. The method according to the present aspect includes: acquiring the oil temperature of the hydraulic oil; and reducing the acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

[0007] According to the present disclosure, the acceleration of the work machine is reduced, based on a rise in the oil temperature of the hydraulic oil. Therefore, the time required for the work by the work machine increases. Thus, the number of times the brake is applied per unit time is reduced, and therefore the burden on the hydraulic brake is reduced and overheating of the hydraulic oil is suppressed.BRIEF DESCRIPTION OF DRAWINGS

[0008] Referring now to the attached drawings which form a part of this original disclosure, an illustrative embodiment is shown.

[0009] FIG. 1 is a side view of a work machine according to an embodiment.

[0010] FIG. 2 is a block diagram showing the configuration of the work machine.

[0011] FIG. 3 is a block diagram showing processing for controlling an engine.

[0012] FIG. 4 is a diagram showing an example of driving force data.

[0013] FIG. 5 is a flowchart showing processing of acceleration limiting control.

[0014] FIG. 6 is a diagram showing target matching data according to a modification example.DETAILED DESCRIPTION OF EMBODIMENT(S)

[0015] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. FIG. 2 is a block diagram showing the configuration of the work machine 1. In the present embodiment, the work machine 1 is a wheel loader. As shown in FIG. 1, the work machine 1 includes a vehicle body 2 and a work implement 3.

[0016] The vehicle body 2 includes a front vehicle body 2a and a rear vehicle body 2b. The rear vehicle body 2b is connected to the front vehicle body 2a so as to be able to turn left and right. A hydraulic cylinder 15 is coupled to the front vehicle body 2a and the rear vehicle body 2b. As the hydraulic cylinder 15 expands and contracts, the front vehicle body 2a turns left and right in relation to the rear vehicle body 2b.

[0017] Work implement 3 is used for work such as excavation. The work implement 3 is operably attached to the front vehicle body 2a. The work implement 3 includes a boom 11, a bucket 12, and hydraulic cylinders 13, 14. The boom 11 and the bucket 12 operate as the hydraulic cylinders 13, 14 expand and contract.

[0018] As shown in FIG. 2, the work machine 1 includes an engine 21 as a drive source. The engine 21 is, for example, a diesel engine. The engine 21 is provided with a fuel injection device 30. The fuel injection device 30 adjusts the amount of fuel injected into the cylinder of the engine 21 and thus controls the output of the engine 21. However, the work machine 1 may include an electric motor as a drive source.

[0019] The work machine 1 includes a transmission 24 and a traveling device 25. The transmission 24 is connected to the engine 21. The transmission 24 transfers the driving force from the engine 21 to the traveling device 25. For example, the transmission 24 is a hydraulic mechanical transmission (HMT). The HMT includes a planetary gear mechanism, a hydraulic pump / motor, and a clutch. The HMT can steplessly change the speed ratio by controlling the capacity of the hydraulic pump / motor.

[0020] However, the transmission 24 may be another type of transmission such as an electric mechanical transmission (EMT) or a hydrostatic transmission (HST). Alternatively, the transmission 24 may be a transmission including a torque converter and a plurality of transmission gears.

[0021] The traveling device 25 is installed in the vehicle body 2, and is driven by the driving force from the engine 21 and thus causes the vehicle body 2 to travel. The traveling device 25 includes axles 26, 27, front wheels 28A, 28B, and rear wheels 28C, 28D. The axles 26, 27 are connected to the transmission 24. The front wheels 28A, 28B are provided at the front vehicle body 2a. The rear wheels 28C, 28D are provided at the rear vehicle body 2b. The axle 26 transfers the driving force from the transmission 24 to the front wheels 28A, 28B. The axle 27 transfers the driving force from the transmission 24 to the rear wheels 28C, 28D.

[0022] The work machine 1 includes a power take-off (PTO) 31, a work implement pump 32, and a control valve 33. The PTO 31 distributes the driving force of the engine 21 to the transmission 24 and the work implement pump 32. In FIG. 2, only one work implement pump 32 is illustrated. However, two or more hydraulic pumps may be connected to the engine 21 via the PTO 31.

[0023] The work implement pump 32 is connected to the engine 21 via the PTO 31. The work implement pump 32 is a hydraulic pump. The work implement pump 32 is driven by the engine 21 and discharges hydraulic oil. The hydraulic oil discharged from the work implement pump 32 is supplied to the above-described hydraulic cylinders 13 to 15. The control valve 33 controls the flow rate of the hydraulic oil supplied from the work implement pump 32 to the hydraulic cylinders 13 to 15. The control valve 33 is, for example, an electromagnetic proportional control valve and is controlled according to an input electric signal. Alternatively, the control valve 33 may be a pressure proportional control valve and may be controlled according to an input pilot pressure.

[0024] The work machine 1 includes a brake pump 36 and hydraulic brakes 37A to 37D. The brake pump 36 is driven by the engine 21 and discharges hydraulic oil. The hydraulic oil discharged from the brake pump 36 is supplied to the hydraulic brakes 37A to 37D. The hydraulic brakes 37A to 37D are driven by the hydraulic oil and thus brakes the traveling device 25. The hydraulic brakes 37A to 37D are, for example, wet multi-disc brakes. Specifically, the hydraulic brakes 37A to 37D include front brakes 37A, 37B and rear brakes 37C, 37D. The front brakes 37A, 37B brake the front wheels 28A, 28B. The rear brakes 37C, 37D brake the rear wheels 28C, 28D.

[0025] The work machine 1 includes an engine sensor 34 and a vehicle speed sensor 35. The engine sensor 34 detects an engine rotation speed. The vehicle speed sensor 35 detects a vehicle speed. The vehicle speed sensor 35 detects, for example, an output rotation speed of the traveling device 25 as the vehicle speed. The output rotation speed of the traveling device 25 corresponds to the vehicle speed of the work machine 1. The output rotation speed of the traveling device 25 is, for example, the rotation speed of the output shaft of the transmission 24. However, the output rotation speed may be the rotation speed of another rotary element located in the transmission 24 or downstream of the transmission 24.

[0026] The work machine 1 includes a first oil temperature sensor 39 and a second oil temperature sensor 40. The first oil temperature sensor 39 and the second oil temperature sensor 40 detect the temperature of the hydraulic oil for driving the hydraulic brakes 37A to 37D (hereinafter referred to as brake oil temperature). The first oil temperature sensor 39 detects the brake oil temperature of the front brakes 37A, 37B. The second oil temperature sensor 40 detects the brake oil temperature of the rear brakes 37C, 37D.

[0027] The work machine 1 includes a controller 41. The controller 41 includes a processor such as a central processing unit (CPU) and a storage device such as a RAM and a ROM. The controller 41 may include an auxiliary storage device such as a hard disk or a solid state drive (SSD). The controller 41 stores a program and data for controlling the work machine 1. The controller 41 executes processing for controlling the work machine 1 according to the stored program and data.

[0028] The controller 41 receives a signal indicating the engine rotation speed from the engine sensor 34. The controller 41 receives a signal indicating the vehicle speed from the vehicle speed sensor 35. The controller 41 receives a signal indicating the brake oil temperature of the hydraulic brakes 37A to 37D from the oil temperature sensors 39, 40. The controller 41 receives a signal indicating the brake oil temperature of the front brakes 37A, 37B from the first oil temperature sensor 39. The controller 41 receives a signal indicating the brake oil temperature of the rear brakes 37C, 37D from the second oil temperature sensor 40.

[0029] The controller 41 transmits a command signal to the engine 21 and thus controls the output of the engine 21. The controller 41 transmits a command signal to the transmission 24 and thus controls the speed ratio of the transmission 24. The controller 41 transmits a command signal to the work implement pump 32 and the control valve 33 and thus controls the work implement 3. In the present embodiment, the controller 41 does not limit the output of the work implement 3.

[0030] The work machine 1 includes an accelerator operation member 43, a work implement operation member 44, a brake operation member 45, and an input device 46. The accelerator operation member 43 can be operated by the operator to control the vehicle speed of the work machine 1. The accelerator operation member 43 is, for example, a pedal. However, the accelerator operation member 43 may be another member such as a lever or a switch. The work implement operation member 44 can be operated by the operator to control the work implement 3. The work implement operation member 44 is, for example, a lever. However, the work implement operation member 44 may be another member such as a switch or a pedal.

[0031] The brake operation member 45 can be operated by the operator to drive the hydraulic brakes 37A to 37D. The brake operation member 45 is, for example, a pedal. However, the brake operation member 45 may be another member such as a lever or a switch. The hydraulic pressure of the hydraulic oil supplied to the hydraulic brakes 37A to 37D is controlled according to the operation of the brake operation member 45. Thus, the hydraulic brakes 37A to 37D generate a braking force in accordance with the amount of operation of the brake operation member 45.

[0032] The input device 46 can be operated by the operator to configure settings for the control of the work machine 1. For example, the input device 46 configures settings of the work machine 1 according to an operation by the operator. The input device 46 includes, for example, a touch panel. However, the input device 46 may include other members such as a mechanical switch.

[0033] The controller 41 receives a signal indicating the amount of accelerator operation from the accelerator operation member 43. The amount of accelerator operation is the amount of operation of the accelerator operation member 43. The controller 41 receives a signal indicating the amount of brake operation from the brake operation member 45. The amount of brake operation is the amount of operation of the brake operation member 45. The controller 41 receives a signal indicating the amount of work implement operation from the work implement operation member 44. The amount of work implement operation is the amount of operation of the work implement operation member 44. The controller 41 receives a signal indicating the setting of the work machine 1 from the input device 46.

[0034] Next, processing for controlling the engine 21 executed by the controller 41 will be described. FIG. 3 is a block diagram showing the processing for controlling the engine 21.

[0035] As shown in FIG. 3, in step S101, the controller 41 determines a target driving force. The target driving force is a driving force required for the traveling device 25 to cause the work machine 1 to travel. The controller 41 acquires the amount of accelerator operation and the vehicle speed. The controller 41 determines the target driving force from the amount of accelerator operation and the vehicle speed.

[0036] Specifically, the controller 41 stores driving force data D1. The driving force data D1 defines the relationship of the target driving force (Ft) of the work machine 1 with the vehicle speed (V) and the amount of accelerator operation (A1). The controller 41 refers to the driving force data D1 and determines the target driving force (Ft) from the vehicle speed (V) and the amount of accelerator operation (A1). The driving force data D1 changes such that the target driving force (Ft) in relation to the vehicle speed increases in accordance with the increase in the amount of accelerator operation (A1).

[0037] FIG. 4 is a diagram showing an example of the driving force data D1. FIG. 4 shows the driving force data D1 of when the amount of accelerator operation is 100%. As shown in FIG. 4, the driving force data D1 includes first driving force data L1 and second driving force data L2. The first driving force data L1 indicates driving force data in a high-output mode. The second driving force data L2 indicates driving force data in a low-output mode. The operator can select the high-output mode or the low-output mode by the input device 46.

[0038] When the high-output mode is selected, the controller 41 determines the target driving force (Ft) with reference to the first driving force data L1. When the low-output mode is selected, the controller 41 determines the target driving force (Ft) with reference to the second driving force data L2. The second driving force data L2 in the low-output mode defines a lower target driving force than the first driving force data L1 in the high-output mode. Therefore, when the low-output mode is selected, the target driving force (Ft) is reduced to be lower than when the high-output mode is selected.

[0039] In step S102, the controller 41 determines a target output torque and a target rotation speed of the engine 21. The controller 41 determines a target output torque (T) and a target rotation speed (N) of the engine 21 from the target driving force and the vehicle speed. For example, the controller 41 stores target matching data D2. The target matching data D2 defines the relationship between the target output torque (T) and the target rotation speed (N) of the engine 21. The controller 41 calculates a target output horsepower of the engine 21 from the target driving force and the vehicle speed. The controller 41 determines the target output torque (T) and the target rotation speed (N) of the engine 21 from a point of intersection M1 between a line P1 indicating the target output horsepower and a line indicating the target matching data D2.

[0040] In step S103, the controller 41 determines an engine command. The controller 41 determines a throttle command to the fuel injection device 30 as the engine command in accordance with the target output torque (T) of the engine 21 determined as described above. Thus, the output of the engine 21 is controlled such that the target output torque (T) is achieved.

[0041] In step S104, the controller 41 determines a target speed ratio of the transmission. The controller 41 determines the target speed ratio of the transmission from the target rotation speed (N) of the engine 21 and the vehicle speed. The speed ratio of the transmission indicates the ratio between the output rotation speed and the input rotation speed of the transmission.

[0042] In step S105, the controller 41 determines a transmission command. The controller 41 determines the transmission command such that the target speed ratio is achieved in the transmission. For example, when the transmission is an HMT, the transmission command includes a capacity command to the hydraulic pump / motor and a command to the clutch. As the engine 21 and the transmission 24 are controlled as described above, the target driving force corresponding to the vehicle speed and the amount of accelerator operation is achieved in the work machine 1, as shown in FIG. 4.

[0043] In the work machine 1 according to the present embodiment, the controller 41 executes acceleration limiting control for limiting the acceleration of the traveling of the work machine 1, based on a rise in the brake oil temperature of the hydraulic brakes 37A to 37D. FIG. 5 is a flowchart showing the processing of the acceleration limiting control. As shown in FIG. 5, in step S201, the controller 41 acquires the brake oil temperature (Tm) of the hydraulic brakes 37A to 37D.

[0044] In step S202, the controller 41 determines whether the brake oil temperature (Tm) is equal to or higher than a threshold T1. When at least one of the oil temperature detected by the first oil temperature sensor 39 and the oil temperature detected by the second oil temperature sensor 40 is equal to or higher than the threshold T1, the controller 41 determines that the brake oil temperature (Tm) is equal to or higher than the threshold T1. When the brake oil temperature (Tm) is equal to or higher than the predetermined threshold T1, the processing proceeds to step S203.

[0045] In step S203, the controller 41 reduces the acceleration of the work machine 1. At the same vehicle speed and with the same amount of accelerator operation, when the brake oil temperature is equal to or higher than the threshold T1 (hereinafter referred to as a “high-oil-temperature state”), the controller 41 reduces the acceleration of the work machine 1 to be lower than the acceleration of when the brake oil temperature is lower than the threshold T1 (hereinafter referred to as a “normal state”).

[0046] Specifically, in the high-oil-temperature state, the controller 41 reduces the target driving force to be smaller than in the normal state and thus reduces the acceleration of the vehicle speed of the work machine 1. As shown in FIG. 4, the controller 41 changes the driving force data D1 from the driving force data L1 and L2 in the normal state to driving force data L3 in the high-oil-temperature state. For example, when the high-output mode is selected, the controller 41 changes the driving force data D1 from the first driving force data L1 in the normal state to the driving force data L3 in the high-oil-temperature state. When the low-output mode is selected, the controller 41 changes the driving force data D1 from the second driving force data L2 in the normal state to the driving force data L3 in the high-oil-temperature state.

[0047] In the driving force data L3 in the high-oil-temperature state, the target driving force is smaller than in the first driving force data L1 in the high-output mode. In the driving force data L3 in the high-oil-temperature state, the target driving force is smaller than in the second driving force data L2 in the low-output mode. When the brake oil temperature is equal to or higher than the threshold T1, the controller 41 determines the target driving force with reference to the driving force data L3 in the high-oil-temperature state. Thus, the acceleration of the work machine 1 is reduced.

[0048] However, the driving force data L3 in the high-oil-temperature state has the same maximum vehicle speed Vmax as the driving force data L1 and L2 in the normal state. Therefore, in the high-oil-temperature state, the acceleration is reduced to be lower than in the normal state, but the same maximum vehicle speed as in the normal state is maintained.

[0049] In the work machine 1 according to the present embodiment described above, the acceleration of the work machine 1 is reduced, based on the rise in the brake oil temperature. Therefore, the time required for the work by the work machine 1 increases. Thus, as the number of brakes per unit time decreases, the burden on the hydraulic brakes 37A to 37D is reduced and overheating of the hydraulic oil is suppressed.

[0050] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit and scope of the invention.

[0051] The work machine 1 is not limited to a wheel loader and may be another machine such as a bulldozer or a motor grader. The work machine 1 may be remotely operable. In this case, the accelerator operation member 43, the work implement operation member 44, the brake operation member 45, and the input device 46 may be disposed outside the work machine 1.

[0052] The controller 41 may be configured with a plurality of controllers. The processing of the control of the work machine 1 described above may be distributed to and executed by a plurality of controllers. The control method for the engine 21 is not limited to that of the above-described embodiment and may be changed.

[0053] The processing of the acceleration limiting control is not limited to that of the above-described embodiment and may be changed. For example, in the above embodiment, the target driving force is reduced and thus the acceleration of the work machine 1 is reduced. However, the method for reducing the acceleration of the work machine 1 is not limited to that of the above embodiment and may be changed. For example, the controller 41 may reduce the acceleration of the work machine 1 by reducing the target output torque of the engine 21. FIG. 6 is a diagram showing target matching data according to a modification example.

[0054] As shown in FIG. 6, the controller 41 may change the target matching data from target matching data D2A in the normal state to target matching data D2B in the high-oil-temperature state. The target matching data D2B in the high-oil-temperature state defines a lower target output torque than the target matching data D2A in the normal state. When the brake oil temperature is equal to or higher than the threshold T1, the controller 41 may determine the target output torque of the engine 21, based on the target matching data D2B in the high-oil-temperature state. Thus, the acceleration of the work machine 1 is reduced.Industrial Applicability

[0055] According to the present disclosure, overheating of hydraulic oil of a hydraulic brake is suppressed in a work machine.

Examples

Embodiment Construction

[0015]Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. FIG. 2 is a block diagram showing the configuration of the work machine 1. In the present embodiment, the work machine 1 is a wheel loader. As shown in FIG. 1, the work machine 1 includes a vehicle body 2 and a work implement 3.

[0016]The vehicle body 2 includes a front vehicle body 2a and a rear vehicle body 2b. The rear vehicle body 2b is connected to the front vehicle body 2a so as to be able to turn left and right. A hydraulic cylinder 15 is coupled to the front vehicle body 2a and the rear vehicle body 2b. As the hydraulic cylinder 15 expands and contracts, the front vehicle body 2a turns left and right in relation to the rear vehicle body 2b.

[0017]Work implement 3 is used for work such as excavation. The work implement 3 is operably attached to the front vehicle body 2a. The work implement 3 includes...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a U.S. National stage application of International Application No. PCT / JP2024 / 008070, filed on Mar. 4, 2024. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2023-054569, filed in Japan on Mar. 30, 2023. The entire contents of Japanese Patent Application No. 2023-054569 is hereby incorporated herein by reference.BACKGROUNDTechnical Field

[0002] The present disclosure relates to a work machine and a method for controlling a work machine.Background Art

[0003] Some work machines include a hydraulic brake. For example, in the work machine of Japanese U.S. Pat. No. 5,412,011 B, hydraulic oil supplied to a hydraulic brake is controlled according to the amount of operation of a brake pedal. Thus, the braking force by the hydraulic brake is controlled.SUMMARY

[0004] The work machine may be used at a harsh site and a heavy burden is placed on the brake. For example, a heavy burden is applied to the brake due to a large number of times the brake is applied per unit time, a long continuous operation time, a heavy weight of the work machine, and the like. Therefore, the hydraulic oil tends to have a high temperature. An object of the present disclosure is to suppress overheating of hydraulic oil of a hydraulic brake in a work machine.

[0005] A work machine according to an aspect of the present disclosure includes a drive source, a traveling device, a hydraulic brake, an oil temperature sensor, and a controller. The traveling device is driven by the drive source and thus causes the work machine to travel. The hydraulic brake is driven by hydraulic oil and thus brakes the traveling device. The oil temperature sensor detects the oil temperature of the hydraulic oil. The controller acquires the oil temperature of the hydraulic oil. The controller reduces the acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

[0006] A method according to another aspect of the present disclosure is a method for controlling a work machine, and the work machine includes a drive source, a traveling device, and a hydraulic brake. The traveling device is driven by the drive source and thus causes the work machine to travel. The hydraulic brake is driven by hydraulic oil and thus brakes the traveling device. The method according to the present aspect includes: acquiring the oil temperature of the hydraulic oil; and reducing the acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

[0007] According to the present disclosure, the acceleration of the work machine is reduced, based on a rise in the oil temperature of the hydraulic oil. Therefore, the time required for the work by the work machine increases. Thus, the number of times the brake is applied per unit time is reduced, and therefore the burden on the hydraulic brake is reduced and overheating of the hydraulic oil is suppressed.BRIEF DESCRIPTION OF DRAWINGS

[0008] Referring now to the attached drawings which form a part of this original disclosure, an illustrative embodiment is shown.

[0009] FIG. 1 is a side view of a work machine according to an embodiment.

[0010] FIG. 2 is a block diagram showing the configuration of the work machine.

[0011] FIG. 3 is a block diagram showing processing for controlling an engine.

[0012] FIG. 4 is a diagram showing an example of driving force data.

[0013] FIG. 5 is a flowchart showing processing of acceleration limiting control.

[0014] FIG. 6 is a diagram showing target matching data according to a modification example.DETAILED DESCRIPTION OF EMBODIMENT(S)

[0015] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. FIG. 2 is a block diagram showing the configuration of the work machine 1. In the present embodiment, the work machine 1 is a wheel loader. As shown in FIG. 1, the work machine 1 includes a vehicle body 2 and a work implement 3.

[0016] The vehicle body 2 includes a front vehicle body 2a and a rear vehicle body 2b. The rear vehicle body 2b is connected to the front vehicle body 2a so as to be able to turn left and right. A hydraulic cylinder 15 is coupled to the front vehicle body 2a and the rear vehicle body 2b. As the hydraulic cylinder 15 expands and contracts, the front vehicle body 2a turns left and right in relation to the rear vehicle body 2b.

[0017] Work implement 3 is used for work such as excavation. The work implement 3 is operably attached to the front vehicle body 2a. The work implement 3 includes a boom 11, a bucket 12, and hydraulic cylinders 13, 14. The boom 11 and the bucket 12 operate as the hydraulic cylinders 13, 14 expand and contract.

[0018] As shown in FIG. 2, the work machine 1 includes an engine 21 as a drive source. The engine 21 is, for example, a diesel engine. The engine 21 is provided with a fuel injection device 30. The fuel injection device 30 adjusts the amount of fuel injected into the cylinder of the engine 21 and thus controls the output of the engine 21. However, the work machine 1 may include an electric motor as a drive source.

[0019] The work machine 1 includes a transmission 24 and a traveling device 25. The transmission 24 is connected to the engine 21. The transmission 24 transfers the driving force from the engine 21 to the traveling device 25. For example, the transmission 24 is a hydraulic mechanical transmission (HMT). The HMT includes a planetary gear mechanism, a hydraulic pump / motor, and a clutch. The HMT can steplessly change the speed ratio by controlling the capacity of the hydraulic pump / motor.

[0020] However, the transmission 24 may be another type of transmission such as an electric mechanical transmission (EMT) or a hydrostatic transmission (HST). Alternatively, the transmission 24 may be a transmission including a torque converter and a plurality of transmission gears.

[0021] The traveling device 25 is installed in the vehicle body 2, and is driven by the driving force from the engine 21 and thus causes the vehicle body 2 to travel. The traveling device 25 includes axles 26, 27, front wheels 28A, 28B, and rear wheels 28C, 28D. The axles 26, 27 are connected to the transmission 24. The front wheels 28A, 28B are provided at the front vehicle body 2a. The rear wheels 28C, 28D are provided at the rear vehicle body 2b. The axle 26 transfers the driving force from the transmission 24 to the front wheels 28A, 28B. The axle 27 transfers the driving force from the transmission 24 to the rear wheels 28C, 28D.

[0022] The work machine 1 includes a power take-off (PTO) 31, a work implement pump 32, and a control valve 33. The PTO 31 distributes the driving force of the engine 21 to the transmission 24 and the work implement pump 32. In FIG. 2, only one work implement pump 32 is illustrated. However, two or more hydraulic pumps may be connected to the engine 21 via the PTO 31.

[0023] The work implement pump 32 is connected to the engine 21 via the PTO 31. The work implement pump 32 is a hydraulic pump. The work implement pump 32 is driven by the engine 21 and discharges hydraulic oil. The hydraulic oil discharged from the work implement pump 32 is supplied to the above-described hydraulic cylinders 13 to 15. The control valve 33 controls the flow rate of the hydraulic oil supplied from the work implement pump 32 to the hydraulic cylinders 13 to 15. The control valve 33 is, for example, an electromagnetic proportional control valve and is controlled according to an input electric signal. Alternatively, the control valve 33 may be a pressure proportional control valve and may be controlled according to an input pilot pressure.

[0024] The work machine 1 includes a brake pump 36 and hydraulic brakes 37A to 37D. The brake pump 36 is driven by the engine 21 and discharges hydraulic oil. The hydraulic oil discharged from the brake pump 36 is supplied to the hydraulic brakes 37A to 37D. The hydraulic brakes 37A to 37D are driven by the hydraulic oil and thus brakes the traveling device 25. The hydraulic brakes 37A to 37D are, for example, wet multi-disc brakes. Specifically, the hydraulic brakes 37A to 37D include front brakes 37A, 37B and rear brakes 37C, 37D. The front brakes 37A, 37B brake the front wheels 28A, 28B. The rear brakes 37C, 37D brake the rear wheels 28C, 28D.

[0025] The work machine 1 includes an engine sensor 34 and a vehicle speed sensor 35. The engine sensor 34 detects an engine rotation speed. The vehicle speed sensor 35 detects a vehicle speed. The vehicle speed sensor 35 detects, for example, an output rotation speed of the traveling device 25 as the vehicle speed. The output rotation speed of the traveling device 25 corresponds to the vehicle speed of the work machine 1. The output rotation speed of the traveling device 25 is, for example, the rotation speed of the output shaft of the transmission 24. However, the output rotation speed may be the rotation speed of another rotary element located in the transmission 24 or downstream of the transmission 24.

[0026] The work machine 1 includes a first oil temperature sensor 39 and a second oil temperature sensor 40. The first oil temperature sensor 39 and the second oil temperature sensor 40 detect the temperature of the hydraulic oil for driving the hydraulic brakes 37A to 37D (hereinafter referred to as brake oil temperature). The first oil temperature sensor 39 detects the brake oil temperature of the front brakes 37A, 37B. The second oil temperature sensor 40 detects the brake oil temperature of the rear brakes 37C, 37D.

[0027] The work machine 1 includes a controller 41. The controller 41 includes a processor such as a central processing unit (CPU) and a storage device such as a RAM and a ROM. The controller 41 may include an auxiliary storage device such as a hard disk or a solid state drive (SSD). The controller 41 stores a program and data for controlling the work machine 1. The controller 41 executes processing for controlling the work machine 1 according to the stored program and data.

[0028] The controller 41 receives a signal indicating the engine rotation speed from the engine sensor 34. The controller 41 receives a signal indicating the vehicle speed from the vehicle speed sensor 35. The controller 41 receives a signal indicating the brake oil temperature of the hydraulic brakes 37A to 37D from the oil temperature sensors 39, 40. The controller 41 receives a signal indicating the brake oil temperature of the front brakes 37A, 37B from the first oil temperature sensor 39. The controller 41 receives a signal indicating the brake oil temperature of the rear brakes 37C, 37D from the second oil temperature sensor 40.

[0029] The controller 41 transmits a command signal to the engine 21 and thus controls the output of the engine 21. The controller 41 transmits a command signal to the transmission 24 and thus controls the speed ratio of the transmission 24. The controller 41 transmits a command signal to the work implement pump 32 and the control valve 33 and thus controls the work implement 3. In the present embodiment, the controller 41 does not limit the output of the work implement 3.

[0030] The work machine 1 includes an accelerator operation member 43, a work implement operation member 44, a brake operation member 45, and an input device 46. The accelerator operation member 43 can be operated by the operator to control the vehicle speed of the work machine 1. The accelerator operation member 43 is, for example, a pedal. However, the accelerator operation member 43 may be another member such as a lever or a switch. The work implement operation member 44 can be operated by the operator to control the work implement 3. The work implement operation member 44 is, for example, a lever. However, the work implement operation member 44 may be another member such as a switch or a pedal.

[0031] The brake operation member 45 can be operated by the operator to drive the hydraulic brakes 37A to 37D. The brake operation member 45 is, for example, a pedal. However, the brake operation member 45 may be another member such as a lever or a switch. The hydraulic pressure of the hydraulic oil supplied to the hydraulic brakes 37A to 37D is controlled according to the operation of the brake operation member 45. Thus, the hydraulic brakes 37A to 37D generate a braking force in accordance with the amount of operation of the brake operation member 45.

[0032] The input device 46 can be operated by the operator to configure settings for the control of the work machine 1. For example, the input device 46 configures settings of the work machine 1 according to an operation by the operator. The input device 46 includes, for example, a touch panel. However, the input device 46 may include other members such as a mechanical switch.

[0033] The controller 41 receives a signal indicating the amount of accelerator operation from the accelerator operation member 43. The amount of accelerator operation is the amount of operation of the accelerator operation member 43. The controller 41 receives a signal indicating the amount of brake operation from the brake operation member 45. The amount of brake operation is the amount of operation of the brake operation member 45. The controller 41 receives a signal indicating the amount of work implement operation from the work implement operation member 44. The amount of work implement operation is the amount of operation of the work implement operation member 44. The controller 41 receives a signal indicating the setting of the work machine 1 from the input device 46.

[0034] Next, processing for controlling the engine 21 executed by the controller 41 will be described. FIG. 3 is a block diagram showing the processing for controlling the engine 21.

[0035] As shown in FIG. 3, in step S101, the controller 41 determines a target driving force. The target driving force is a driving force required for the traveling device 25 to cause the work machine 1 to travel. The controller 41 acquires the amount of accelerator operation and the vehicle speed. The controller 41 determines the target driving force from the amount of accelerator operation and the vehicle speed.

[0036] Specifically, the controller 41 stores driving force data D1. The driving force data D1 defines the relationship of the target driving force (Ft) of the work machine 1 with the vehicle speed (V) and the amount of accelerator operation (A1). The controller 41 refers to the driving force data D1 and determines the target driving force (Ft) from the vehicle speed (V) and the amount of accelerator operation (A1). The driving force data D1 changes such that the target driving force (Ft) in relation to the vehicle speed increases in accordance with the increase in the amount of accelerator operation (A1).

[0037] FIG. 4 is a diagram showing an example of the driving force data D1. FIG. 4 shows the driving force data D1 of when the amount of accelerator operation is 100%. As shown in FIG. 4, the driving force data D1 includes first driving force data L1 and second driving force data L2. The first driving force data L1 indicates driving force data in a high-output mode. The second driving force data L2 indicates driving force data in a low-output mode. The operator can select the high-output mode or the low-output mode by the input device 46.

[0038] When the high-output mode is selected, the controller 41 determines the target driving force (Ft) with reference to the first driving force data L1. When the low-output mode is selected, the controller 41 determines the target driving force (Ft) with reference to the second driving force data L2. The second driving force data L2 in the low-output mode defines a lower target driving force than the first driving force data L1 in the high-output mode. Therefore, when the low-output mode is selected, the target driving force (Ft) is reduced to be lower than when the high-output mode is selected.

[0039] In step S102, the controller 41 determines a target output torque and a target rotation speed of the engine 21. The controller 41 determines a target output torque (T) and a target rotation speed (N) of the engine 21 from the target driving force and the vehicle speed. For example, the controller 41 stores target matching data D2. The target matching data D2 defines the relationship between the target output torque (T) and the target rotation speed (N) of the engine 21. The controller 41 calculates a target output horsepower of the engine 21 from the target driving force and the vehicle speed. The controller 41 determines the target output torque (T) and the target rotation speed (N) of the engine 21 from a point of intersection M1 between a line P1 indicating the target output horsepower and a line indicating the target matching data D2.

[0040] In step S103, the controller 41 determines an engine command. The controller 41 determines a throttle command to the fuel injection device 30 as the engine command in accordance with the target output torque (T) of the engine 21 determined as described above. Thus, the output of the engine 21 is controlled such that the target output torque (T) is achieved.

[0041] In step S104, the controller 41 determines a target speed ratio of the transmission. The controller 41 determines the target speed ratio of the transmission from the target rotation speed (N) of the engine 21 and the vehicle speed. The speed ratio of the transmission indicates the ratio between the output rotation speed and the input rotation speed of the transmission.

[0042] In step S105, the controller 41 determines a transmission command. The controller 41 determines the transmission command such that the target speed ratio is achieved in the transmission. For example, when the transmission is an HMT, the transmission command includes a capacity command to the hydraulic pump / motor and a command to the clutch. As the engine 21 and the transmission 24 are controlled as described above, the target driving force corresponding to the vehicle speed and the amount of accelerator operation is achieved in the work machine 1, as shown in FIG. 4.

[0043] In the work machine 1 according to the present embodiment, the controller 41 executes acceleration limiting control for limiting the acceleration of the traveling of the work machine 1, based on a rise in the brake oil temperature of the hydraulic brakes 37A to 37D. FIG. 5 is a flowchart showing the processing of the acceleration limiting control. As shown in FIG. 5, in step S201, the controller 41 acquires the brake oil temperature (Tm) of the hydraulic brakes 37A to 37D.

[0044] In step S202, the controller 41 determines whether the brake oil temperature (Tm) is equal to or higher than a threshold T1. When at least one of the oil temperature detected by the first oil temperature sensor 39 and the oil temperature detected by the second oil temperature sensor 40 is equal to or higher than the threshold T1, the controller 41 determines that the brake oil temperature (Tm) is equal to or higher than the threshold T1. When the brake oil temperature (Tm) is equal to or higher than the predetermined threshold T1, the processing proceeds to step S203.

[0045] In step S203, the controller 41 reduces the acceleration of the work machine 1. At the same vehicle speed and with the same amount of accelerator operation, when the brake oil temperature is equal to or higher than the threshold T1 (hereinafter referred to as a “high-oil-temperature state”), the controller 41 reduces the acceleration of the work machine 1 to be lower than the acceleration of when the brake oil temperature is lower than the threshold T1 (hereinafter referred to as a “normal state”).

[0046] Specifically, in the high-oil-temperature state, the controller 41 reduces the target driving force to be smaller than in the normal state and thus reduces the acceleration of the vehicle speed of the work machine 1. As shown in FIG. 4, the controller 41 changes the driving force data D1 from the driving force data L1 and L2 in the normal state to driving force data L3 in the high-oil-temperature state. For example, when the high-output mode is selected, the controller 41 changes the driving force data D1 from the first driving force data L1 in the normal state to the driving force data L3 in the high-oil-temperature state. When the low-output mode is selected, the controller 41 changes the driving force data D1 from the second driving force data L2 in the normal state to the driving force data L3 in the high-oil-temperature state.

[0047] In the driving force data L3 in the high-oil-temperature state, the target driving force is smaller than in the first driving force data L1 in the high-output mode. In the driving force data L3 in the high-oil-temperature state, the target driving force is smaller than in the second driving force data L2 in the low-output mode. When the brake oil temperature is equal to or higher than the threshold T1, the controller 41 determines the target driving force with reference to the driving force data L3 in the high-oil-temperature state. Thus, the acceleration of the work machine 1 is reduced.

[0048] However, the driving force data L3 in the high-oil-temperature state has the same maximum vehicle speed Vmax as the driving force data L1 and L2 in the normal state. Therefore, in the high-oil-temperature state, the acceleration is reduced to be lower than in the normal state, but the same maximum vehicle speed as in the normal state is maintained.

[0049] In the work machine 1 according to the present embodiment described above, the acceleration of the work machine 1 is reduced, based on the rise in the brake oil temperature. Therefore, the time required for the work by the work machine 1 increases. Thus, as the number of brakes per unit time decreases, the burden on the hydraulic brakes 37A to 37D is reduced and overheating of the hydraulic oil is suppressed.

[0050] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit and scope of the invention.

[0051] The work machine 1 is not limited to a wheel loader and may be another machine such as a bulldozer or a motor grader. The work machine 1 may be remotely operable. In this case, the accelerator operation member 43, the work implement operation member 44, the brake operation member 45, and the input device 46 may be disposed outside the work machine 1.

[0052] The controller 41 may be configured with a plurality of controllers. The processing of the control of the work machine 1 described above may be distributed to and executed by a plurality of controllers. The control method for the engine 21 is not limited to that of the above-described embodiment and may be changed.

[0053] The processing of the acceleration limiting control is not limited to that of the above-described embodiment and may be changed. For example, in the above embodiment, the target driving force is reduced and thus the acceleration of the work machine 1 is reduced. However, the method for reducing the acceleration of the work machine 1 is not limited to that of the above embodiment and may be changed. For example, the controller 41 may reduce the acceleration of the work machine 1 by reducing the target output torque of the engine 21. FIG. 6 is a diagram showing target matching data according to a modification example.

[0054] As shown in FIG. 6, the controller 41 may change the target matching data from target matching data D2A in the normal state to target matching data D2B in the high-oil-temperature state. The target matching data D2B in the high-oil-temperature state defines a lower target output torque than the target matching data D2A in the normal state. When the brake oil temperature is equal to or higher than the threshold T1, the controller 41 may determine the target output torque of the engine 21, based on the target matching data D2B in the high-oil-temperature state. Thus, the acceleration of the work machine 1 is reduced.Industrial Applicability

[0055] According to the present disclosure, overheating of hydraulic oil of a hydraulic brake is suppressed in a work machine.

Examples

Embodiment Construction

[0015]Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. FIG. 2 is a block diagram showing the configuration of the work machine 1. In the present embodiment, the work machine 1 is a wheel loader. As shown in FIG. 1, the work machine 1 includes a vehicle body 2 and a work implement 3.

[0016]The vehicle body 2 includes a front vehicle body 2a and a rear vehicle body 2b. The rear vehicle body 2b is connected to the front vehicle body 2a so as to be able to turn left and right. A hydraulic cylinder 15 is coupled to the front vehicle body 2a and the rear vehicle body 2b. As the hydraulic cylinder 15 expands and contracts, the front vehicle body 2a turns left and right in relation to the rear vehicle body 2b.

[0017]Work implement 3 is used for work such as excavation. The work implement 3 is operably attached to the front vehicle body 2a. The work implement 3 includes...

Claims

1. A work machine comprising:a drive source;a traveling device that is driven by the drive source in order to cause the work machine to travel;a hydraulic brake that is driven by hydraulic oil in order to brake the traveling device;an oil temperature sensor that detects an oil temperature of the hydraulic oil; anda controller, configured toacquire the oil temperature of the hydraulic oil, andreduce acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

2. The work machine according to claim 1, whereinthe controller is configured to reduce the acceleration of the work machine when the oil temperature of the hydraulic oil is equal to or higher than a predetermined threshold.

3. The work machine according to claim 1, whereinthe controller is configured to reduce the acceleration of the work machine while maintaining a maximum vehicle speed of the work machine, based on the rise in the oil temperature of the hydraulic oil.

4. The work machine according to claim 1, further comprising:an accelerator operation member that can be operated by an operator; anda vehicle speed sensor that detects a vehicle speed of the work machine, the controller being configured toacquire an amount of operation of the accelerator operation member, acquire the vehicle speed,determine a target driving force of the work machine in accordance with the amount of operation of the accelerator operation member and the vehicle speed, andreduce the target driving force, based on the rise in the oil temperature of the hydraulic oil, in order to reduce the acceleration of the work machine.

5. The work machine according to claim 4, further comprising:an input device that can be operated by an operator to selecta high-output mode anda low-output mode in which the driving force of the work machine is reduced to be lower than in the high-output mode, whereinthe controller being configured to reduce the target driving force to be lower than in the low-output mode, based on the rise in the oil temperature of the hydraulic oil, in order to reduce the acceleration of the work machine.

6. The work machine according to claim 1, further comprising:an accelerator operation member that can be operated by an operator; anda vehicle speed sensor that detects a vehicle speed of the work machine, the controller being configured toacquire an amount of operation of the accelerator operation member,acquire the vehicle speed,determine a target driving force of the work machine in accordance with the amount of operation of the accelerator operation member and the vehicle speed,determine a target output torque of the drive source in accordance with the target driving force, andreduce the target output torque, based on the rise in the oil temperature of the hydraulic oil, in order to reduce the acceleration of the work machine.

7. The work machine according to claim 1, further comprising:a work implement driven by the hydraulic oil,the controller being configured to not limit an output of the work implement.

8. A method for controlling a work machine including a drive source, a traveling device that is driven by the drive source in order to cause the work machine to travel, and a hydraulic brake that is driven by hydraulic oil in order to brake the traveling device, the method comprising:acquiring an oil temperature of the hydraulic oil; andreducing acceleration of the work machine, based on a rise in the oil temperature of the hydraulic oil.

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