Systems, methods, and machines for controlling working machines.

Abstract

In work machines equipped with HMT, high traction force is achieved while suppressing overload on the hydraulic circuit. [Solution] The system according to this disclosure is a system for controlling a work machine including a power transmission device. The system comprises a sensor, an input device, and a controller. The sensor detects the temperature of the hydraulic fluid. The input device is operable to request the operation of a high-power mode, which increases the traction force of the work machine compared to the normal mode. The controller obtains the temperature of the hydraulic fluid. The controller determines whether the permission conditions for the high-power mode are met, including that the hydraulic fluid temperature is below a first threshold. If the permission conditions are met and the input device has requested the operation of the high-power mode, the controller activates the high-power mode to increase the traction force of the work machine by increasing the capacity of the hydraulic pump compared to the normal mode.

Description

Technical Field

[0001] The present disclosure relates to a system, a method for controlling a work machine, and a work machine.

Background Art

[0002] Conventionally, a work machine equipped with a hydraulic mechanical power transmission device (hereinafter, HMT) is known. In an HMT, power from an engine is split and transmitted into mechanically transmitted power (hereinafter, mechanical power) via a plurality of rotating elements of a planetary gear mechanism and hydraulically transmitted power (hereinafter, hydraulic power) via a hydraulic circuit. A hydraulic pump and a hydraulic motor are connected to the hydraulic circuit. The plurality of rotating elements of the planetary gear mechanism include a first rotating element and a second rotating element. The hydraulic pump is connected to the first rotating element. The hydraulic motor is connected to the second rotating element.

[0003] In an HMT, when the rotational speed of the output shaft is low, such as when the work machine stalls, the mechanical power may become small. In this case, since the power that the HMT can transmit is limited by the maximum capacity of the hydraulic motor and the driving hydraulic pressure of the hydraulic circuit, the HMT cannot exert a large traction force. Therefore, there may be a shortage of the traction force that the HMT can exert.

[0004] Therefore, in Patent Document 1, when the maximum output torque that the HMT can exert is insufficient for the target output torque, the control device of the HMT executes torque assist control to increase the output torque of the HMT. In torque assist control, when the maximum output torque that the HMT can exert is insufficient for the target output torque, the control device determines an assist torque based on the difference between the target output torque and the maximum output torque that the HMT can exert. The control device increases the capacity of the hydraulic pump based on the assist torque.

[0005] When the hydraulic pressure of the hydraulic circuit exceeds the relief pressure, hydraulic fluid is discharged from the relief valve. If the capacity of the hydraulic pump is further increased despite the discharge of hydraulic fluid from the relief valve, the torque input from the first rotating element of the planetary gear mechanism to the hydraulic pump increases. In a planetary gear mechanism, an increase in the torque of the first rotating element also increases the torque of the second rotating element. Therefore, the increased mechanical power output from the second rotating element allows for greater traction force in the HMT. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-204351 [Overview of the project] [Problems that the invention aims to solve]

[0007] In the torque assist control described above, an upper limit is set on the assist torque to suppress the occurrence of overload due to excessive relief of the hydraulic fluid. However, in some cases, working machines are required to exert a particularly high traction force compared to normal conditions. For example, when a working machine is transported by trailer, the tires of the working machine are fitted into grooves for wheel chocks provided on the trailer bed. Therefore, when the working machine is unloaded from the trailer, it is difficult to get the tires out of the grooves unless a particularly high traction force is exerted compared to normal conditions. The purpose of this disclosure is to enable working machines equipped with HMT to exert a high traction force while suppressing overload on the hydraulic circuit. [Means for solving the problem]

[0008] A first aspect of this disclosure is a system for controlling a work machine including a power transmission device. The power transmission device includes an input shaft, an output shaft, a planetary gear mechanism, a hydraulic pump, a hydraulic motor, a hydraulic circuit, and a relief valve. The planetary gear mechanism includes a first rotating element connected to the input shaft, a second rotating element connected to the output shaft, and a third rotating element. The hydraulic pump converts the first rotational power of the third rotating element into first hydraulic power. The hydraulic motor converts the first hydraulic power into second rotational power and supplies the second rotational power to the output shaft. The hydraulic circuit connects the hydraulic pump and the hydraulic motor. The relief valve is connected to the hydraulic circuit. The system according to this aspect includes a sensor, an input device, and a controller. The sensor detects the temperature of the hydraulic fluid for driving the hydraulic motor. The input device is operable to request operation in a high-power mode that increases the traction force of the work machine more than in normal mode. The controller obtains the temperature of the hydraulic fluid. The controller determines whether the permission conditions for high-power mode are met, including that the hydraulic fluid temperature is below a first threshold. If the permission conditions are met and the input device requests operation in high-power mode, the controller activates high-power mode to increase the traction force of the work machine by increasing the capacity of the hydraulic pump beyond that of normal mode.

[0009] A second aspect of this disclosure is a method for controlling a work machine including a power transmission device. The power transmission device includes an input shaft, an output shaft, a planetary gear mechanism, a hydraulic pump, a hydraulic motor, a hydraulic circuit, and a relief valve. The planetary gear mechanism includes a first rotating element connected to the input shaft, a second rotating element connected to the output shaft, and a third rotating element. The hydraulic pump converts the first rotational power of the third rotating element into first hydraulic power. The hydraulic motor converts the first hydraulic power into second rotational power and supplies the second rotational power to the output shaft. The hydraulic circuit connects the hydraulic pump and the hydraulic motor. The relief valve is connected to the hydraulic circuit. The method according to this embodiment includes obtaining the temperature of the hydraulic fluid for driving the hydraulic motor, obtaining a request to operate in a high-power mode that increases the traction force of the work machine compared to the normal mode, determining whether the permission conditions for the high-power mode are met, including that the temperature of the hydraulic fluid is below a first threshold, and, if the permission conditions are met and the operation of the high-power mode is requested, activating the high-power mode to increase the capacity of the hydraulic pump compared to the normal mode, thereby increasing the traction force of the work machine.

[0010] A third aspect of this disclosure is a work machine comprising a power transmission device, a sensor, an input device, and a controller. The power transmission device includes an input shaft, an output shaft, a planetary gear mechanism, a hydraulic pump, a hydraulic motor, a hydraulic circuit, and a relief valve. The planetary gear mechanism includes a first rotating element connected to the input shaft, a second rotating element connected to the output shaft, and a third rotating element. The hydraulic pump converts the first rotational power of the third rotating element into first hydraulic power. The hydraulic motor converts the first hydraulic power into second rotational power and supplies the second rotational power to the output shaft. The hydraulic circuit connects the hydraulic pump and the hydraulic motor. A relief valve is connected to the hydraulic circuit. A sensor detects the temperature of the hydraulic fluid for driving the hydraulic motor. The input device is operable to request operation in a high-power mode that increases the traction force of the work machine compared to the normal mode. The controller obtains the temperature of the hydraulic fluid. The controller determines whether the permission conditions for the high-power mode are met, including that the temperature of the hydraulic fluid is below a first threshold. The controller activates high-power mode when the permission conditions are met and the input device requests operation in high-power mode, thereby increasing the traction force of the work machine by increasing the capacity of the hydraulic pump compared to normal mode. [Effects of the Invention]

[0011] In this disclosure, when the conditions for enabling the high-power mode are met, including the hydraulic fluid temperature being below a first threshold, the high-power mode is activated, and the capacity of the hydraulic pump is increased compared to the normal mode. This allows the work machine to exert a high traction force while suppressing overload on the hydraulic circuit. [Brief explanation of the drawing]

[0012] [Figure 1] This is a side view of the work machine according to the embodiment. [Figure 2] This is a block diagram showing the configuration of the drive system for a working machine. [Figure 3] This is a block diagram showing the configuration of a control system for a work machine. [Figure 4]It is a block diagram showing a process for controlling an engine. [Figure 5] It is a block diagram showing a process for controlling an HMT. [Figure 6] It is a diagram showing an example of target capacity data in the normal mode. [Figure 7] It is a diagram showing the configuration of an HMT together with a nomograph. [Figure 8] It is a flowchart showing the process of torque assist control. [Figure 9] It is a block diagram showing the process in the high-output mode. [Figure 10] It is a block diagram showing the process in the high-output mode. [Figure 11] It is a diagram showing an example of target capacity data in the high-output mode. [Figure 12] It is a diagram showing an example of target output torque data in the high-output mode. [Figure 13] It is a diagram showing the vehicle speed - traction characteristics in each of the normal mode and the high-output mode.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a side view of a working machine according to an embodiment of the present disclosure. As shown in FIG. 1, the working machine 1 includes a vehicle body 2 and a working implement 3. The vehicle body 2 includes a front vehicle body 2a, a rear vehicle body 2b, and a cab 4. The rear vehicle body 2b is connected to the front vehicle body 2a so as to be pivotable left and right. A hydraulic cylinder 15 is connected to the front vehicle body 2a and the rear vehicle body 2b. By the expansion and contraction of the hydraulic cylinder 15, the front vehicle body 2a pivots left and right with respect to the rear vehicle body 2b.

[0014] The working implement 3 is used for operations such as excavation. The working implement 3 is attached to the front vehicle body 2a. The working implement 3 includes a boom 11, a bucket 12, and hydraulic cylinders 13 and 14. By the expansion and contraction of the hydraulic cylinders 13 and 14, the boom 11 and the bucket 12 operate.

[0015] Figure 2 is a block diagram showing the configuration of the drive system of the working machine 1. As shown in Figure 2, the drive system of the working machine 1 includes an engine 20, a PTO (Power Take Off) 22, an HMT 23, a traveling device 24, a work machine pump 25, a control valve 26, and a hydraulic oil tank 16.

[0016] The engine 20 is, for example, a diesel engine. The engine 20 is provided with a fuel injection device 21. The fuel injection device 21 controls the output of the engine 20 by adjusting the amount of fuel injected into the cylinder of the engine 20. The PTO 22 distributes the driving force of the engine 20 to the HMT 23 and the work machine pump 25. In Figure 2, only one work machine pump 25 is shown. However, two or more hydraulic pumps may be connected to the engine 20 via the PTO 22.

[0017] The HMT 23 is connected to the engine 20 via the PTO 22. The HMT 23 can change the transmission ratio continuously. The HMT 23 divides the power from the engine 20 into mechanical power by gears and hydraulic power by hydraulics, and transmits it to the traveling device 24. The HMT 23 includes an input shaft 27, an input gear 28, an output shaft 29, a planetary gear mechanism 30, a FR switching mechanism 31, a pump gear 32, and a hydrostatic continuously variable transmission (hereinafter, HST) 33.

[0018] The input shaft 27 is connected to the PTO 22. The input gear 28 is connected to the input shaft 27. The output shaft 29 is connected to the traveling device 24. The transmission ratio of the HMT is the ratio of the rotational speed of the output shaft 29 to the rotational speed of the input shaft 27.

[0019] The planetary gear mechanism 30 is connected to the input shaft 27 and the output shaft 29. The planetary gear mechanism 30 includes a sun gear 34, a plurality of planetary gears 35, a carrier 36, and a ring gear 37. The sun gear 34, the planetary gears 35, the carrier 36, and the ring gear 37 are rotational elements of the planetary gear mechanism 30.

[0020] The sun gear 34 is located at the center of the planetary gear mechanism 30. The sun gear 34 is connected to the output shaft 38 of the planetary gear mechanism 30. The sun gear 34 is mated with the planetary gear 35. The planetary gear 35 is located on the outer circumference of the sun gear 34. The planetary gear 35 is rotatable around the sun gear 34. The carrier 36 supports the multiple planetary gears 35 so that they can rotate around the central axis of each planetary gear 35. The carrier 36 rotates around the sun gear 34 as the planetary gears 35 move. The outer circumference of the carrier 36 is provided with teeth that mate with the input gear 28. The inner circumference of the ring gear 37 is provided with teeth that mate with the multiple planetary gears 35. The outer circumference of the ring gear 37 is provided with teeth that mate with the pump gear 32.

[0021] The HST33 includes a travel pump 40, a hydraulic circuit 41, a travel motor 42, and a relief valve 43. The travel pump 40 is connected to a ring gear 37 via a pump gear 32. The travel pump 40 is a variable displacement hydraulic pump. The travel pump 40 is driven by rotational power from the ring gear 37 to discharge hydraulic fluid into the hydraulic circuit 41. In other words, the travel pump 40 converts the rotational power of the ring gear 37 into hydraulic power. The hydraulic circuit 41 connects the travel pump 40 and the travel motor 42. The hydraulic fluid discharged from the travel pump 40 is supplied to the travel motor 42 via the hydraulic circuit 41.

[0022] The travel motor 42 is connected to the output shaft 38 of the planetary gear mechanism 30. The travel motor 42 is a variable displacement hydraulic motor. The travel motor 42 is driven by the hydraulic fluid supplied from the travel pump 40, which rotates the output shaft 29. In other words, the travel motor 42 converts the hydraulic power from the travel pump 40 into rotational power and supplies it to the output shaft 29. The relief valve 43 is connected to the hydraulic circuit 41. The relief valve 43 opens when the hydraulic pressure in the hydraulic circuit 41 (hereinafter referred to as HST hydraulic pressure) exceeds the set pressure, and discharges the hydraulic fluid. The relief valve 43 is an electromagnetic relief valve, and the set pressure can be changed.

[0023] The FR switching mechanism 31 is connected to the output shaft 38 of the planetary gear mechanism 30 and the output shaft 29 of the HMT 23. The FR switching mechanism 31 can switch the direction of rotation from the planetary gear mechanism 30 between the forward and reverse directions. The FR switching mechanism 31 includes, for example, a forward gear, a reverse gear, and a clutch. The FR switching mechanism 31 transmits power from the planetary gear mechanism 30 to the output shaft 29 of the HMT 23.

[0024] The running gear 24 moves the work machine 1. The running gear 24 includes an axle 44, front wheels 45, and rear wheels 46. The axle 44 is connected to the output shaft 29 of the HMT 23. The front wheels 45 are provided on the front body 2a. The rear wheels 46 are provided on the rear body 2b. Although not shown in the figures, the axle 44 includes an axle for the front wheels 45 and an axle for the rear wheels 46. The axle 44 transmits power from the HMT 23 to the front wheels 45 and the rear wheels 46.

[0025] The work equipment pump 25 is connected to the engine 20 via the PTO 22. The work equipment pump 25 is a variable displacement hydraulic pump. The work equipment pump 25 is driven by the engine 20 and discharges hydraulic fluid. The hydraulic fluid discharged from the work equipment pump 25 is supplied to the hydraulic cylinders 13-15 described above via the control valve 26. This drives the hydraulic cylinders 13-15. The control valve 26 may include multiple valves.

[0026] The drive system of the work machine 1 includes a drain circuit 71, a charge circuit 72, a charge pump 73, and a charge relief valve 74. The drain circuit 71 is connected to the travel motor 42 and the travel pump 40. The hydraulic fluid leaking from the travel motor 42 and the travel pump 40 is discharged into the hydraulic fluid tank 16 via the drain circuit 71.

[0027] The charge circuit 72 is connected to the hydraulic circuit 41 via check valves 75 and 76. The charge pump 73 is connected to the charge circuit 72. The charge pump 73 discharges hydraulic fluid into the charge circuit 72. The charge relief valve 74 is connected to the charge circuit 72. Due to leakage of hydraulic fluid from the travel motor 42 and the travel pump 40, the amount of hydraulic fluid in the hydraulic circuit 41 decreases. Therefore, the amount of hydraulic fluid that has decreased is supplied to the hydraulic circuit 41 via the charge circuit 72 by the charge pump 73.

[0028] The work machine 1 includes an engine sensor 51, a vehicle speed sensor 52, a first hydraulic pressure sensor 53, a second hydraulic pressure sensor 54, a first oil temperature sensor 55, and a second oil temperature sensor 56. The engine sensor 51 detects the engine rotational speed. The engine sensor 51 outputs a detection signal indicating the engine rotational speed.

[0029] The vehicle speed sensor 52 detects the output rotational speed. The output rotational speed is, for example, the rotational speed of the output shaft 29 of the HMT23. However, the output rotational speed may be the rotational speed of other rotating elements located within the HMT23 or downstream of the HMT23. The vehicle speed sensor 52 outputs a detection signal indicating the output rotational speed.

[0030] The first hydraulic sensor 53 detects the discharge pressure of the work equipment pump 25. The first hydraulic sensor 53 outputs a detection signal indicating the discharge pressure of the work equipment pump 25. The second hydraulic sensor 54 detects the HST hydraulic pressure of the HST 33. The second hydraulic sensor 54 outputs a detection signal indicating the HST hydraulic pressure.

[0031] The first oil temperature sensor 55 detects the temperature of the hydraulic fluid in the hydraulic fluid tank 16 (hereinafter referred to as the tank oil temperature). That is, the tank oil temperature is the temperature of the hydraulic fluid supplied from the hydraulic fluid tank 16 to the hydraulic circuit 41 via the charge circuit 72. The first oil temperature sensor 55 outputs a detection signal indicating the tank oil temperature. The second oil temperature sensor 56 detects the temperature of the hydraulic fluid in the hydraulic circuit 41 of the HST 33 (hereinafter referred to as the HST oil temperature). The second oil temperature sensor 56 outputs a detection signal indicating the HST oil temperature. Since the hydraulic fluid in the hydraulic fluid tank 16 is supplied to the hydraulic circuit 41, if the tank oil temperature is high, the HST oil temperature will also be high.

[0032] Figure 3 is a block diagram showing the configuration of the control system for the work machine 1. As shown in Figure 3, the control system for the work machine 1 includes a controller 60. The controller 60 controls the work machine 1. The controller 60 includes a processor 61 and a storage device 62. The processor 61 is, for example, a CPU (Central Processing Unit). Alternatively, the processor 61 may be a different processor from the CPU. The processor 61 performs processing for controlling the work machine 1 according to a program.

[0033] The storage device 62 includes memory such as ROM and RAM. The storage device 62 may also include an auxiliary storage device 62 such as a hard disk or an SSD (Solid State Drive). The storage device 62 is an example of a non-transitory computer-readable recording medium. The storage device 62 stores programs and data for controlling the work machine 1.

[0034] The control system for the work machine 1 includes an accelerator operating member 63, a steering operating member 64, a work machine operating member 65, a shift operating member 66, a gear shift operating member 67, and an input device 68. The accelerator operating member 63 is operable by the operator to control the traction force of the work machine 1. The accelerator operating member 63 is, for example, a pedal. However, the accelerator operating member 63 may be another member such as a lever or a switch.

[0035] The steering operating member 64 is operable by the operator to steer the work machine 1. The steering operating member 64 is, for example, a steering wheel. However, the steering operating member 64 may be other members such as a lever or a switch. The work machine operating member 65 is operable by the operator to control the work machine 3. The work machine operating member 65 is, for example, a lever. However, the work machine operating member 65 may be other members such as a switch.

[0036] The shift operating member 66 is operable by the operator to switch between forward and reverse movement of the work machine 1. The shift operating member 66 can be operated to a forward position, a reverse position, and a neutral position. The shift operating member 66 is, for example, a lever. However, the shift operating member 66 may be other components such as a switch. The speed change operating member 67 is operable by the operator to set the speed range of the work machine 1. The speed change operating member 67 selects one speed range from, for example, 1st to 4th speed. However, the speed range is not limited to 4th speed, and may be lower than 4th speed or higher than 4th speed. The speed change operating member 67 is, for example, a lever. However, the speed change operating member 67 may be other components such as a switch.

[0037] The input device 68 is operable by an operator to select a control mode for the work machine 1. The input device 68 includes, for example, a touch panel. However, the input device 68 may also include other components such as mechanical switches.

[0038] The controller 60 receives an operation signal from the accelerator operating member 63 indicating the amount of operation of the accelerator operating member 63 (hereinafter referred to as the accelerator operation amount). The controller 60 also receives an operation signal from the steering operating member 64 indicating the amount of operation of the steering operating member 64 (hereinafter referred to as the steering operation amount).

[0039] The controller 60 receives an operation signal from the work implement operating member 65 indicating the amount of operation of the work implement operating member 65 (hereinafter referred to as the work implement operating amount). The controller 60 receives an operation signal indicating the position of the shift operating member 66 (hereinafter referred to as the shift position). The controller 60 receives an operation signal indicating the operation of the speed change operating member 67. The controller 60 receives a signal indicating the operation of the input device 68. The controller 60 receives detection signals from each of the sensors 51-56.

[0040] The controller 60 controls the work machine 1 based on operation signals from each operating member 63-67 and input device 68, and detection signals from each sensor 51-56. For example, the controller 60 drives the work machine 1 by controlling the fuel injector 21 and HMT 23 of the engine 20 according to the accelerator operation amount. The controller 60 steers the work machine 1 by operating the hydraulic cylinder 15 by controlling the work machine pump 25 and control valve 26 according to the steering operation amount. The controller 60 operates the hydraulic cylinders 13 and 14 by controlling the work machine pump 25 and control valve 26 according to the work machine operation amount, thereby operating the work machine 3.

[0041] The controller 60 controls the HMT 23 according to the shift position of the shift operating member 66, switching the power transmission in the HMT 23 between forward, reverse, and neutral. The controller 60 controls the speed range of the work machine 1 by controlling the HMT 23 according to the operation of the speed change operating member 67. The controller 60 executes a high-output mode that increases the traction force of the work machine 1 compared to the normal mode, according to the operation of the input device 68. The high-output mode will be described in detail later.

[0042] Next, the process for controlling the engine 20 and HMT23, performed by the controller 60, will be described. Figure 4 is a block diagram showing the process for controlling the engine 20. As shown in Figure 4, in step S101, the controller 60 determines the target output torque. The controller 60 determines the target output torque from the accelerator input and the output rotational speed.

[0043] For example, the controller 60 stores target output torque data D1. The target output torque data D1 defines the relationship between vehicle speed V and target output torque Ft. The target output torque data D1 is changed according to the accelerator pedal input. The target output torque data D1 may also be changed according to a set speed range. The controller 60 calculates the vehicle speed V from the output rotational speed. The controller 60 refers to the target output torque data D1 and determines the target output torque Ft based on the accelerator pedal input and vehicle speed V.

[0044] In step S102, the controller 60 determines the PTO request torque. The controller 60 determines the PTO request torque from the workpiece operating amount and the discharge pressure of the workpiece pump 25. The PTO request torque is the required torque at the equipment connected to the engine 20 via the PTO 22. The PTO request torque includes the required torque at the workpiece pump 25. For example, the controller 60 determines the required flow rate of the hydraulic fluid based on the workpiece operating amount. The controller 60 determines the PTO request torque from the required flow rate and the discharge pressure.

[0045] In step S103, the controller 60 determines the required engine power. The required engine power is the required horsepower for engine 20. The controller 60 determines the required engine power from the PTO required torque and the target output torque. For example, the controller 60 determines the required engine power based on the sum of the PTO required torque and the target output torque.

[0046] In step S104, the controller 60 determines the target engine speed. The controller 60 determines the target engine speed from the requested engine power. For example, the controller 60 stores target engine speed data D2. The target engine speed data D2 defines the relationship between the requested engine power Pe and the target engine speed Nt. The controller 60 refers to the target engine speed data D2 and determines the target engine speed Nt from the requested engine power Pe.

[0047] In step S105, the controller 60 determines the target engine torque according to the target engine speed. The controller 60 determines the target acceleration torque of the engine 20 from the target engine speed and the current engine speed. The controller 60 determines the target engine torque from the PTO request torque, the target output torque and the target acceleration torque.

[0048] In step S106, the controller 60 outputs an engine torque command. The controller 60 outputs an engine torque command indicating a target engine torque. As a result, the output of the engine 20 is controlled so that the target output torque and the PTO request torque are achieved.

[0049] Figure 5 is a block diagram showing the process for controlling the HMT23. As shown in Figure 5, in step S201, the controller 60 determines the output acceleration of the output shaft 29 of the HMT23. The controller 60 determines the output acceleration from the target output torque and the running load. For example, the controller 60 calculates the running load from the output torque of the HMT23, the acceleration of the work machine 1, and the weight of the work machine 1.

[0050] In step S202, the controller 60 determines the target output rotational speed of the output shaft 29 of the HMT23. The target output rotational speed is an estimated value that will be the output rotational speed after a predetermined time. The predetermined time is determined, for example, from the control cycle of the processing performed by the controller 60. The controller 60 determines the target output rotational speed from the current output rotational speed and the output acceleration.

[0051] In step S203, the controller 60 determines the acceleration of the engine 20. The acceleration of the engine 20 is the acceleration of the output shaft of the engine 20. The acceleration of the engine 20 may also be the acceleration of the input shaft 27 of the HMT 23. The controller 60 determines the acceleration of the engine 20 from the target acceleration torque of the engine 20.

[0052] In step S204, the controller 60 determines the target input rotational speed of the input shaft 27 of the HMT 23. The target input rotational speed is an estimated value that will be the input rotational speed after a predetermined time. The controller 60 determines the target input rotational speed from the current engine rotational speed and the acceleration of the engine 20.

[0053] In step S205, the controller 60 determines the target speed ratio. The controller 60 determines the target speed ratio from the target output rotational speed and the target input rotational speed. The target speed ratio is the ratio of the target output rotational speed to the target input rotational speed.

[0054] In step S206, the controller 60 outputs capacity commands for the travel pump 40 and the travel motor 42. The controller 60 determines the target capacities of the travel pump 40 and the travel motor 42 so that the speed ratio of the HMT23 becomes the target speed ratio. The controller 60 stores the target capacity data D3 shown in Figure 6. The target capacity data D3 defines the relationship between the target speed ratio and the target capacity.

[0055] In Figure 6, the solid line L1 represents the target capacity of the travel pump 40. The solid line L2 represents the target capacity of the travel motor 42. The controller 60 refers to the target capacity data D3 and determines the target capacity based on the target speed ratio. The controller 60 outputs a capacity command to the travel pump 40 indicating the target capacity of the travel pump 40. The controller 60 outputs a capacity command to the travel motor 42 indicating the target capacity of the travel motor 42. As a result, the speed ratio of the HMT23 is controlled so that the target output torque and target engine rotational speed are achieved.

[0056] Next, the torque assist control performed by the controller 60 will be described. Torque assist control is a control that increases the output torque of the HMT23 by increasing the capacity of the travel pump 40 when the target output torque of the HMT23 is greater than the maximum output torque of the HMT23 obtained when the hydraulic circuit 41 is not relieved. Torque assist control increases the output torque of the HMT23 by utilizing the output torque increase characteristic of the HMT23 caused by the relief of the hydraulic circuit 41. The output torque increase characteristic of the HMT23 will be described below.

[0057] Figure 7 shows the configuration of the HMT23 along with a collinear diagram. As shown in Figure 7, the output torque T1 from the engine 20 is divided into a first mechanical torque T2 and a second mechanical torque T3 in the carrier 36. The first mechanical torque T2 is transmitted to the travel pump 40 via the carrier 36 and the ring gear 37, where it is converted into hydraulic pressure T4. If the HST hydraulic pressure in the hydraulic circuit 41 exceeds the set pressure of the relief valve 43, a portion of the hydraulic fluid in the hydraulic circuit 41 is discharged to the hydraulic fluid tank 16 via the relief valve 43. As a result, a portion of the hydraulic pressure T4 becomes a loss T5 in the relief valve 43. The remaining hydraulic pressure T6 is converted into a third mechanical torque T7 in the travel motor 42 and output from the travel motor 42. Of the output torque T1 from the engine 20, the second mechanical torque T3 is transmitted to the sun gear 34 via the carrier 36. The second mechanical torque T3 and the third mechanical torque T7 from the travel motor 42 merge in the sun gear 34 and are transmitted to the output shaft 29 as output torque T8.

[0058] Here, when the vehicle speed of the work machine 1 is slow and the rotational speeds of the output shaft 29 and the travel motor 42 are low, the larger the capacity of the travel pump 40, the greater the flow rate of hydraulic fluid discharged from the relief valve 43. The greater the flow rate of hydraulic fluid discharged from the relief valve 43, the greater the torque required to drive the travel pump 40, and the greater the first mechanical torque T2 described above. In the HMT23, as shown in the collinear diagram of Figure 7, the ratio of the rotational speed of the ring gear 37 to the rotational speed of the sun gear 34 when the rotational speed of the carrier 36 is 0 is the same as the ratio of the number of teeth N1 of the sun gear 34 to the number of teeth N2 of the ring gear 37. Therefore, the ratio of the first mechanical torque T2 to the second mechanical torque T3 is the same as the ratio of the number of teeth N2 of the ring gear 37 to the number of teeth N1 of the sun gear 34, regardless of the rotational speed of the carrier 36. As a result, the second mechanical torque T3 increases in accordance with the increase in the first mechanical torque T2. Consequently, the output torque T8 increases.

[0059] Figure 8 is a flowchart showing the torque assist control process. As shown in Figure 8, in step S301, the controller 60 determines whether the target output torque determined in step S101 is greater than the maximum output torque of the HMT23 when it is not in relief, i.e., at the set pressure. If the target output torque is less than or equal to the maximum output torque when it is not in relief, the controller 60 determines not to perform torque assist control. If torque assist control is not performed, in step S309, the controller 60 determines the target speed ratio of the HMT23. Here, the controller 60 determines the target speed ratio based on the target output rotational speed determined in step S202 and the target input rotational speed determined in step S204.

[0060] In step S301, if the target output torque is greater than the maximum output torque, the process proceeds to step S302. In step S302, the controller 60 calculates the torque of the travel motor 42. The controller 60 calculates the torque of the travel motor 42 based on the HST hydraulic pressure of the hydraulic circuit 41 and the capacity command of the travel motor 42.

[0061] In step S303, the controller 60 calculates the estimated output torque of the HMT23. The controller 60 calculates the estimated output torque of the HMT23 based on the torque of the travel motor 42, the output torque of the engine 20, and the gear ratio of the planetary gear mechanism 30. The output torque of the engine 20 is calculated based on the fuel injection amount.

[0062] In step S304, the controller 60 calculates the assist torque. The controller 60 calculates the assist torque based on the difference between the target output torque and the estimated output torque. In step S305, the controller 60 determines whether the assist torque is greater than the first upper limit. If the assist torque is greater than the first upper limit, the process proceeds to step S306.

[0063] In step S306, the controller 60 rewrites the assist torque value to the first upper limit value. That is, the controller 60 limits the assist torque to a value less than or equal to the first upper limit value. The first upper limit value is a value set to suppress the occurrence of overload due to excessive relief in the hydraulic circuit 41.

[0064] In step S307, the controller 60 calculates a correction value for the target output rotational speed. The controller 60 calculates the correction value for the target output rotational speed by multiplying the assist torque by a predetermined gain and integrating it. In step S308, the controller 60 updates the target output rotational speed. The controller 60 updates the target output rotational speed by adding the correction value calculated in step S307 to the target output rotational speed determined in step S202.

[0065] In step S309, the controller 60 determines the target speed ratio of the HMT23. The controller 60 determines the target speed ratio of the HMT23 based on the target output rotational speed updated in step S308 and the target input rotational speed determined in step S204. Similar to step S206, the controller 60 outputs capacity commands for the travel pump 40 and the travel motor 42 based on the target speed ratio.

[0066] As described above, with the torque assist control, the controller 60 corrects the target output rotational speed based on the assist torque when the target output torque of the HMT23 is greater than the maximum output torque of the HMT23, and determines the target speed ratio based on the corrected target output rotational speed. As a result, the capacity of the travel pump 40 increases, and the flow rate of the hydraulic fluid relieved in the hydraulic circuit 41 increases, thereby increasing the output torque of the HMT23.

[0067] Next, the high-power mode will be described. The operator can activate the high-power mode by operating the input device 68. The control of the engine 20 and HMT 23 by the controller 60 described above shows the process in normal mode when the high-power mode is not activated. In high-power mode, the controller 60 temporarily further increases the traction force of the work machine 1 by increasing the capacity of the travel pump 40 compared to normal mode.

[0068] Figures 9 and 10 are block diagrams showing the processing in high-power mode. As shown in Figure 9, when the control system is started, the controller 60 sets the high-power mode permission flag to "0" in state S401. A high-power mode permission flag of "0" means that high-power mode is prohibited.

[0069] With high-power mode disabled, the controller 60 determines whether the permission conditions are met. If the permission conditions are met while high-power mode is disabled, the controller 60 sets the high-power mode permission flag to "1" in state S402. A high-power mode permission flag of "1" means that high-power mode is permitted.

[0070] The conditions for permission are that all of the following conditions A1-A5 are met. (A1) Engine 20 and HST33 are not in the warm-up phase. (A2) The tank oil temperature is below the first temperature threshold. (A3) The HST oil temperature is below the second temperature threshold. (A4) The shift operating member 66 is in the neutral position. (A5) Machine 1 is stopped.

[0071] When high-power mode is permitted, the controller 60 determines whether the prohibition condition is met. If the prohibition condition is met while high-power mode is permitted, the controller 60 sets the high-power mode permission flag to "0" in state S401. The prohibition condition is that at least one of the following conditions B1-B5 is met. (B1) Engine 20 and HST33 are in the warm-up phase. (B2) The tank oil temperature exceeds the first temperature threshold. (B3) The HST oil temperature has exceeded the second temperature threshold. (B4) The shift operating member 66 is located in a position other than the neutral position. (B5) Machine 1 is in motion.

[0072] The controller 60 warms up the engine 20 by increasing its idling speed if the coolant temperature of the engine 20 is below a threshold. The controller 60 also warms up the HST 33 by increasing the idling speed of the engine 20 and activating the warm-up relief circuit in the control valve 26 to quickly raise the tank oil temperature if the HST oil temperature is below a threshold. The controller 60 determines whether the above conditions A1 and B1 are met depending on whether the engine 20 and HST 33 are warming up. The controller 60 determines whether the above conditions A5 and B5 are met based on the vehicle speed of the work machine 1.

[0073] As shown in Figure 10, when the control system is started, the controller 60 sets the operating state of the high-output mode to "stopped" in state S501. When the operating state of the high-output mode is "stopped", the controller 60 does not execute the high-output mode.

[0074] When the operating state of the high-output mode is "stopped", the controller 60 determines whether the operating conditions are met. If the operating conditions are met when the operating state of the high-output mode is "stopped", the controller 60 sets the operating state of the high-output mode to "operated" in state S502. The operating conditions are that all of the following conditions C1-C2 are met. (C1) High power mode enable flag = 1 (enabled) (C2) Receives a request from input device 68 to activate high-power mode. If the operator selects to operate in high-power mode, the input device 68 sends a request to the controller 60 to operate in high-power mode. If the operator selects to stop high-power mode, the input device 68 sends a request to stop high-power mode to the controller 60.

[0075] When the operating state of the high-output mode is set to "operated," the controller 60 activates the high-output mode. When the controller 60 activates the high-output mode, it increases the output torque of the HMT23 by increasing the capacity of the travel pump 40 compared to the normal mode. Specifically, in high-output mode, the controller 60 increases the upper limit of the assist torque described above from the first upper limit to the second upper limit. The second upper limit is greater than the first upper limit. The second upper limit is a fixed value and is stored in the memory device 62. Alternatively, the second upper limit may be changeable.

[0076] Furthermore, the controller 60 changes the target capacity data D3 to the target capacity data D4 for high-output mode. Figure 11 shows an example of the target capacity data D4 for high-output mode. In Figure 11, the solid line L1A shows the target capacity of the travel pump 40 in high-output mode. The solid line L2A shows the target capacity of the travel motor 42 in high-output mode. The dashed line L1 shows the target capacity of the travel pump 40 in normal mode. The dashed line L2 shows the target capacity of the travel motor 42 in normal mode. As shown in Figure 11, the target capacity data D4 for high-output mode is defined so that the target capacity of the travel pump 40 and the target capacity of the travel motor 42 are larger than in normal mode for the same target gear ratio.

[0077] As described above, in high-output mode, the upper limit of the assist torque is increased and the target capacity data is changed, resulting in a larger capacity for the travel pump 40 compared to normal mode.

[0078] In high-power mode, the controller 60 reduces the set pressure of the relief valve 43 compared to normal mode. For example, in normal mode, the controller 60 sets the set pressure of the relief valve 43 to the first set pressure. When the high-power mode is activated, the controller 60 reduces the set pressure of the relief valve 43 from the first set pressure to the second set pressure. The first and second set pressures are fixed values ​​and are stored in the memory device 62. Alternatively, the first and second set pressures may be changeable. In high-power mode, the flow rate of hydraulic fluid relieved in the HST 33 is significantly larger than in normal mode. Therefore, by reducing the set pressure of the relief valve 43, an excessive rise in HST hydraulic pressure due to the override characteristics of the relief valve 43 is suppressed.

[0079] In high-power mode, the controller 60 limits the vehicle speed of the work machine 1 to a predetermined upper speed. For example, the controller 60 limits the vehicle speed of the work machine 1 to the upper speed Vmax by changing the target output torque data D1 to the target output torque data D5 in high-power mode shown in Figure 12. This prevents the work machine 1 from accelerating unintentionally to a high speed.

[0080] As shown in Figure 10, when the high-power mode operating state is "operated", the controller 60 determines whether the conditions for stopping from operation are met. If the conditions for stopping from operation are met when the high-power mode operating state is "operated", the controller 60 sets the high-power mode operating state to "stopped" in state S501. When the high-power mode operating state is set to "stopped", the controller 60 stops the high-power mode and returns to normal mode. The conditions for stopping from operation are that at least one of the following conditions D1-D4 is met. (D1) A request to stop the high-power mode is received from the input device 68. (D2) After the shift operating member 66 is operated to the reverse position, the shift operating member 66 remains in a position other than the reverse position for a predetermined period of time or longer. (D3) After the shift operating member 66 is operated to the forward position, the shift operating member 66 remains in a position other than the forward position for a predetermined period of time or longer. (D4) The vehicle speed is above the specified vehicle speed threshold.

[0081] The predetermined times for conditions D2 and D3 are very short, for example, about 0.1 seconds. Condition D2 is a condition for determining whether the operator has switched the shift operating member 66 from the reverse position to the neutral position or the forward position. Condition D3 is a condition for determining whether the operator has switched the shift operating member 66 from the forward position to the neutral position or the reverse position.

[0082] When the high-power mode is in the "operated" state, the controller 60 determines whether the forced stop condition is met. If the forced stop condition is met while the high-power mode is in the "operated" state, the controller 60 sets the high-power mode to "forced stop" in state S503. When the high-power mode is set to "forced stop", the controller 60 stops the high-power mode and returns to the normal mode. At this time, if the traction force of the work machine 1 suddenly decreases, the vehicle body 2 may oscillate. To avoid this, the controller 60 gradually changes the upper limit of the assist torque to the same value as the normal mode, thereby smoothing the change in traction force. The forced stop condition is that at least one of the following conditions E1 and E2 is met. (E1) The tank oil temperature has exceeded the third temperature threshold. (E2) The usable time for high-power mode has elapsed after the following conditions E2A, E2B, and E2C have been met.

[0083] (E2A) High-power mode operating state = Operated.

[0084] (E2B) The shift operating member 66 is in a position other than the neutral position.

[0085] (E2C) Accelerator input is greater than or equal to the input threshold.

[0086] Under condition E1, the third temperature threshold is higher than the first temperature threshold. Condition E2 is a condition for determining whether usable time has elapsed since the start of operation of the work machine 1 in high-power mode. The elapsed time count begins when conditions E2A, E2B, and E2C are all met simultaneously. Once the elapsed time count begins, the count will not stop even if conditions E2B and E2C are no longer met. However, if condition E2A is no longer met, the controller 60 will stop the count and reset the elapsed time to 0.

[0087] When the high-power mode operating state is "forced stop", the controller 60 determines whether the conditions for stopping from a forced stop are met. If the conditions for stopping from a forced stop are met while the high-power mode operating state is "forced stop", the controller 60 sets the high-power mode operating state to "stopped". The conditions for stopping from a forced stop are that at least one of the following conditions F1-F4 is met. (F1) A request to stop the high-power mode is received from the input device 68. (F2) After the shift operating member 66 is operated to the reverse position, the shift operating member 66 remains in a position other than the reverse position for a predetermined period of time or longer. (F3) After the shift operating member 66 is operated to the forward position, the shift operating member 66 remains in a position other than the forward position for a predetermined period of time or longer. (F4) The vehicle speed is above the specified vehicle speed threshold.

[0088] In the control system of the work machine 1 according to the embodiment described above, when the conditions for enabling the high-power mode are met, including the tank oil temperature being below a first temperature threshold and the HST oil temperature being below a second temperature threshold, the high-power mode is activated and the capacity of the hydraulic pump is increased compared to the normal mode. This prevents the oil temperature in the hydraulic circuit 41 from rising beyond the limits of the equipment of the work machine 1. Therefore, the work machine 1 can exert high traction force while suppressing overload on the hydraulic circuit 41.

[0089] For example, Figure 13 shows the vehicle speed-traction force characteristics for normal mode and high-power mode. In Figure 13, the dashed line F1 shows the vehicle speed-traction force characteristics of the work machine 1 in normal mode. In Figure 13, the solid line F2 shows the vehicle speed-traction force characteristics of the work machine 1 in high-power mode. As shown in Figure 13, in high-power mode, the traction force in the low vehicle speed range is greater than in normal mode. This makes it possible to easily unload the work machine 1 from the trailer. Alternatively, if the work machine 1 gets stuck in a ditch or mud formed in the ground, it can be easily removed from the ditch or mud.

[0090] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. The work machine 1 is not limited to a wheel loader, but may be other machines such as a motor grader.

[0091] The configuration of the work machine 1 is not limited to that of the embodiment described above and may be modified. For example, the work machine 1 may be operable remotely. In that case, the operating members 63-67 and the input device 68 described above may be located outside the work machine 1. The controller 60 may be implemented by multiple controllers. In that case, the processing by the controller 60 described above may be distributed and executed by the multiple controllers.

[0092] The configuration of HMT23 is not limited to that of the embodiment described above and may be modified. The input shaft 27 of HMT23 may be connected to other rotating elements, not just the carrier 36. The travel pump 40 may be connected to other rotating elements, not just the ring gear 37. The travel motor 42 may be connected to other rotating elements, not just the sun gear 34.

[0093] The process for controlling the engine 20 and HMT23 is not limited to the process described above and may be modified. The process for high-power mode is not limited to the process described above and may be modified. For example, the permit conditions or prohibition conditions are not limited to the conditions described above and may be modified. The permit conditions or prohibition conditions are not limited to both the conditions relating to the tank oil temperature and the conditions relating to the HST oil temperature, but may include only one of them. The operating conditions, conditions for stopping from operating, conditions for forced stopping, or conditions for stopping from forced stopping are not limited to the conditions described above and may be modified. In high-power mode, the process for increasing the capacity of the travel pump 40 is not limited to increasing the upper limit of the assist torque, but may be by other means. The data D1-D5 described above are not limited to those described above and may be modified. [Industrial applicability]

[0094] According to this disclosure, a work machine equipped with an HMT can exert high traction force while suppressing overload on the hydraulic circuit. [Explanation of Symbols]

[0095] 1: Working machine, 23: HMT, 27: Input shaft, 29: Output shaft, 30: Planetary gear mechanism, 34: Sun gear, 36: Carrier, 37: Ring gear, 40: Travel pump, 41: Hydraulic circuit, 42: Travel motor, 43: Relief valve, 56: Second oil temperature sensor, 60: Controller, 66: Shift operating member, 68: Input device

Claims

1. A system for controlling a work machine including a power transmission device, The power transmission device is Input axis and, Output shaft and, A planetary gear mechanism including a first rotating element connected to the input shaft, a second rotating element connected to the output shaft, and a third rotating element, A hydraulic pump that converts the first rotational power of the third rotating element into first hydraulic power, A hydraulic motor that converts the first hydraulic power into a second rotational power and supplies the second rotational power to the output shaft, A hydraulic circuit connecting the hydraulic pump and the hydraulic motor, A relief valve connected to the hydraulic circuit, Includes, The aforementioned system, A sensor for detecting the temperature of the hydraulic fluid used to drive the hydraulic motor, An input device that can be operated to request the operation of a high-power mode that increases the traction force of the work machine compared to the normal mode, Controller and Equipped with, The aforementioned controller, The temperature of the hydraulic fluid is obtained, It is determined whether the conditions for enabling the high-power mode, including that the temperature of the hydraulic fluid is below a first threshold, are met. If the aforementioned permission conditions are met and the input device requests the operation of the high-power mode, the high-power mode is activated to increase the capacity of the hydraulic pump compared to the normal mode, thereby increasing the traction force of the work machine. system.

2. The controller stops the high-power mode when the temperature of the hydraulic fluid is greater than a second threshold. The system according to claim 1.

3. The aforementioned permit conditions include the fact that the work machine is stopped. The system according to claim 1.

4. The controller temporarily increases the traction force of the work machine by the high-output mode. The system according to claim 1.

5. The controller stops the high-power mode when the usable time for the high-power mode has elapsed since the start of the operation of the work machine in the high-power mode. The system according to claim 4.

6. When the high-output mode is activated, the controller reduces the set pressure of the relief valve compared to the normal mode. The system according to claim 1.

7. When the high-power mode is activated, the controller limits the vehicle speed of the work machine to a predetermined upper speed. The system according to claim 1.

8. It further includes a shift operating member that can be operated to a forward position, a reverse position, and a neutral position. The permission conditions include the shift operating member being in the neutral position, The system according to claim 1.

9. The controller stops the high-output mode if the shift operating member is operated from the neutral position to the forward position and remains in the neutral position or the reverse position for a predetermined period of time or longer. The system according to claim 8.

10. The controller stops the high-output mode if the shift operating member is operated from the neutral position to the reverse position and remains in the neutral position or the forward position for a predetermined period of time or longer. The system according to claim 8.

11. The aforementioned controller, The vehicle speed of the aforementioned work machine is acquired, If the vehicle speed is equal to or greater than the vehicle speed threshold, the high-power mode is stopped. The system according to claim 1.

12. A method for controlling a working machine including a power transmission device, The power transmission device is Input axis and, Output shaft and, A planetary gear mechanism including a first rotating element connected to the input shaft, a second rotating element connected to the output shaft, and a third rotating element, A hydraulic pump that converts the first rotational power of the third rotating element into first hydraulic power, A hydraulic motor that converts the first hydraulic power into a second rotational power and supplies the second rotational power to the output shaft, A hydraulic circuit connecting the hydraulic pump and the hydraulic motor, A relief valve connected to the hydraulic circuit, Includes, The aforementioned method, To obtain the temperature of the hydraulic fluid used to drive the aforementioned hydraulic motor, To obtain a request for operation in a high-power mode that increases the traction force of the work machine compared to the normal mode, Determining whether the permission conditions for the high-power mode are met, including that the temperature of the hydraulic fluid is below a first threshold, If the aforementioned permission conditions are met and the operation of the high-power mode is required, the high-power mode is activated to increase the capacity of the hydraulic pump compared to the normal mode, thereby increasing the traction force of the work machine. A method for providing this.

13. The system includes a mechanism to stop the high-power mode when the temperature of the hydraulic fluid is greater than a second threshold. The method according to claim 12.

14. The aforementioned permit conditions include the fact that the work machine is stopped. The method according to claim 12.

15. The high-power mode is used to temporarily increase the traction force of the work machine, The method according to claim 12.

16. The system includes a mechanism to stop the high-power mode when the usable time for the high-power mode has elapsed since the start of operation of the work machine in the high-power mode. The system according to claim 15.

17. When the high-output mode is activated, the set pressure of the relief valve is reduced compared to the normal mode. The method according to claim 12.

18. When the high-power mode is activated, the vehicle speed of the work machine is limited to a predetermined upper speed limit. The method according to claim 12.

19. It includes receiving operation signals from a shift operation member that can be operated to a forward position, a reverse position, and a neutral position. The permission conditions include the shift operating member being in the neutral position, The method according to claim 12.

20. It is a work machine, The system includes an input shaft, an output shaft, a planetary gear mechanism, a hydraulic pump, a hydraulic motor, a hydraulic circuit, and a relief valve. The planetary gear mechanism includes a first rotating element connected to the input shaft, a second rotating element connected to the output shaft, and a third rotating element. The hydraulic pump converts the first rotational power of the third rotating element into first hydraulic power. The hydraulic motor converts the first hydraulic power into second rotational power and supplies the second rotational power to the output shaft. The hydraulic circuit connects the hydraulic pump and the hydraulic motor. The relief valve is connected to the hydraulic circuit as a power transmission device. A sensor for detecting the temperature of the hydraulic fluid used to drive the hydraulic motor, An input device that can be operated to request the operation of a high-power mode that increases the traction force of the work machine compared to the normal mode, Controller and Equipped with, The aforementioned controller, The temperature of the hydraulic fluid is obtained, It is determined whether the conditions for enabling the high-power mode, including that the temperature of the hydraulic fluid is below a first threshold, are met. If the aforementioned permission conditions are met and the input device requests the operation of the high-power mode, the high-power mode is activated to increase the capacity of the hydraulic pump compared to the normal mode, thereby increasing the traction force of the work machine. Agricultural machinery.

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